publicationDate,title,abstract,id
2016-12-18,Heusler 4.0: Tunable Materials,"Heusler compounds are a large family of binary, ternary and quaternary
compounds that exhibit a wide range of properties of both fundamental and
potential technological interest. The extensive tunability of the Heusler
compounds through chemical substitutions and structural motifs makes the family
especially interesting. In this article we highlight recent major developments
in the field of Heusler compounds and put these in the historical context. The
evolution of the Heusler compounds can be described by four major periods of
research. In the latest period, Heusler 4.0 has led to the observation of a
variety of properties derived from topology that includes: topological metals
with Weyl and Dirac points; a variety of non-collinear spin textures including
the very recent observation of skyrmions at room temperature; and giant
anomalous Hall effects in antiferromagnetic Heuslers with triangular magnetic
structures. Here we give a comprehensive overview of these major achievements
and set research into Heusler materials within the context of recent emerging
trends in condensed matter physics.",1612.05947v2
2014-09-23,Guidelines for understanding cubic manganese-rich Heusler compounds,"Manganese-rich Heusler compounds are attracting much interest in the context
of spin transfer torque and rare-earth free hard magnets. Here we give a
comprehensive overview of the magnetic properties of non-centrosymmetric cubic
Mn$_2$-based Heusler materials, which are characterized by an antiparallel
coupling of magnetic moments on Mn atoms. Such a ferrimagnetic order leads to
the emergence of new properties that are absent in ferromagnetic
centrosymmetric Heusler structures. In terms of the band structure
calculations, we explain the formation of this magnetic order and the Curie
temperatures. This overview is intended to establish guidelines for a basic
understanding of magnetism in Mn2 -based Heusler compounds.",1409.6532v1
2018-12-18,Atomistic study of an ideal metal/thermoelectric contact: the full-Heusler/half-Heusler interface,"Half-Heusler alloys such as the (Zr,Hf)NiSn intermetallic compounds are
important thermoelectric materials for converting waste heat into electricity.
Reduced electrical resistivity at the hot interface between the half-Heusler
material and a metal contact is critical for device performance, however this
has yet to be achieved in practice. Recent experimental work suggests that a
coherent interface between half-Heusler and full-Heusler compounds can form due
to diffusion of transition metal atoms into the vacant sublattice of the
half-Heusler lattice. We study theoretically the structural and electronic
properties of such an interface using a first-principles based approach that
combines {\it ab initio} calculations with macroscopic modeling. We find that
the prototypical interface HfNi$_2$Sn/HfNiSn provides very low contact
resistivity and almost ohmic behavior over a wide range of temperatures and
doping levels. Given the potential of these interfaces to remain stable over a
wide range of temperatures, our study suggests that full-Heuslers might provide
nearly ideal electrical contacts to half-Heuslers that can be harnessed for
efficient thermoelectric generator devices.",1812.07189v1
2013-01-12,Effect of Co-Fe substitutions on the room-temperature spin polarization in Co_3-xFe_xSi Heusler-compound films,"Using low-temperature molecular beam epitaxy, we study substitutions of Fe
atoms for Co ones in Co_3-xFe_xSi Heusler-compound films grown on Si and Ge.
Even for the low-temperature grown Heusler-compound films, the Co-Fe atomic
substitution at A and C sites can be confirmed by the conversion electron
M""ossbauer spectroscopy measurements. As a result, the magnetic moment and
room-temperature spin polarization estimated by nonlocal spin-valve
measurements are systematically changed with the Co-Fe substitutions. This
study experimentally verified that the Co-Fe substitution in Co_3-xFe_xSi
Heusler compounds can directly affect the room-temperature spin polarization.",1301.2645v1
2002-11-14,"Preparation and structural properties of thin films and multilayers of the Heusler compounds Cu2MnAl, Co2MnSn, Co2MnSi and Co2MnGe","We report on the preparation of thin films and multilayers of the
intermetallic Heusler compound CuMnAl, Co2MnSn, Co2MnSi and Co2MnGe by
rf-sputtering on MgO and Al2O3 substrates. Cu2MnAl can be grown epitaxially
with (100)-orientation on MgO (100) and in (110)-orientation on Al2O3 a-plane.
The Co based Heusler alloys need metallic seedlayers to induce high quality
textured growth. We also have prepared multilayers with smooth interfaces by
combining the Heusler compounds with Au and V. An analysis of the ferromagnetic
saturation magnetization of the films indicates that the Cu2MnAl-compound tends
to grow in the disordered B2-type structure whereas the Co-based Heusler alloy
thin films grow in the ordered L21 structure. All multilayers with thin layers
of the Heusler compounds exhibit a definitely reduced ferromagnetic
magnetization indicating substantial disorder and intermixing at the
interfaces.",0211271v1
2019-05-09,Half-Heusler Compounds: Promising Materials For Mid-To-High Temperature Thermoelectric Conversion,"Half-Heusler compounds (space group Fm3m) has garnered increasing attention
in recent years in the thermoelectric community. Three decades ago, refractory
RNiSn half-Heusler compounds (R represents refractory metals such as Hf, Zr,
Ti) were found to be narrow-gap semiconductors with large Seebeck coefficients
in 100s of micro-volt per Kelvin. Today, half-Heusler (HH) compounds have
emerged as promising thermoelectric materials in the intermediate temperature
range (400-800oC). HH materials are endowed with good thermal stability and
scalability. Thermoelectric n-p modules based on HH materials demonstrate
conversion efficiency near 10% and power density output near 9 W/cm2. The
objective of this article is to present a historical account of the research
and development of thermoelectric half-Heusler compounds. Particularly, there
have been notable achievements since 2012 thanks to the emergence of new
approaches. As a result, ZT has risen from ~1 to 1.5. The various advances made
since the early 1990s to the present are recounted by categorizing half-Heusler
materials into three generations (Gen): Gen-1 Gen-2, and Gen-3 HH materials.",1905.03845v1
2007-05-25,Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys,"Half-metallic Heusler alloys are among the most promising materials for
future applications in spintronic devices. Although most Heusler alloys are
ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated
ferrimagnetic) alloys would be more desirable for applications due to the lower
external fields. Ferrimagnetism can be either found in perfect Heusler
compounds or achieved through the creation of defects in ferromagnetic Heusler
alloys.",0705.3731v1
2018-12-04,Recent Advances in Thermoelectric Performance of Half-Heusler Compounds,"Half-Heusler phases (space group F43m, C1b) have recently captured much
attention as promising thermoelectric materials for heat-to-electric power
conversion in the mid-to-high temperature range. The most studied ones are the
RNiSn-type half-Heusler compounds, where R represents refractory metals Hf, Zr,
and Ti. These compounds have shown a high-power factor and high-power density,
as well as good material stability and scalability. Due to their high thermal
conductivity, however, the dimensionless figure of merit (zT) of these
materials has stagnated near 1 for a long time. Since 2013, the verifiable ZT
of half-Heusler compounds has risen from 1 to near 1.5 for both n- and p-type
compounds in the temperature range of 500 to 900 degrees C. In this brief
review, we summarize recent advances as well as approaches in achieving the
high ZT reported. In particular, we discuss the less-exploited strain-relief
effect and dopant resonant state effect studied by the author and his
collaborators in more detail. Finally, we point out directions for further
development.
  Keywords: half-Heusler compounds; figure of merit; power density; lattice
disorder; dopant resonant states",1812.01709v1
2005-10-11,Introduction to half-metallic Heusler alloys: Electronic Structure and Magnetic Properties,"Intermetallic Heusler alloys are amongst the most attractive half-metallic
systems due to the high Curie temperatures and the structural similarity to the
binary semiconductors. In this review we present an overview of the basic
electronic and magnetic properties of both Heusler families: the so-called
half-Heusler alloys like NiMnSb and the the full-Heusler alloys like
Co$_2$MnGe. \textit{Ab-initio} results suggest that both the electronic and
magnetic properties in these compounds are intrinsically related to the
appearance of the minority-spin gap. The total spin magnetic moment $M_t$
scales linearly with the number of the valence electrons $Z_t$, such that
$M_t=Z_t-24$ for the full-Heusler and $M_t=Z_t-18$ for the half-Heusler alloys,
thus opening the way to engineer new half-metallic alloys with the desired
magnetic properties.",0510276v1
2005-11-18,Investigation of Co$_2$FeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment,"This work reports on structural and magnetic investigations of the Heusler
compound Co$_2$FeSi. X-Ray diffraction and M\""o\ss bauer spectrometry indicate
an ordered $L2_1$ structure. Magnetic measurements by means of X-ray magnetic
circular dichroism and magnetometry revealed that this compound is, currently,
the material with the highest magnetic moment ($6 \mu_B$) and Curie-temperature
(1100K) in the classes of Heusler compounds as well as half-metallic
ferromagnets.",0511462v1
2019-01-28,An Enormous Class of Double Half-Heusler Compounds with Low Thermal Conductivity,"Since their discovery around a century ago, the structure and chemistry of
the multi-functional half-Heusler semiconductors have been studied extensively
as three component systems. The elemental groups constituting these ternary
compounds with the nominal formula XYZ are well established. From the very same
set of well-known elements we explore a phase space of quaternary double
($X'X''Y_2Z_2$, $X_2Y'Y''Z_2$, and $X_2Y_2Z'Z''$), triple ($X_2'X''Y_3Z_3$) and
quadruple ($X_3'X''Y_4Z_4$) half-Heusler compositions which 10 times larger in
size. Using a reliable, first-principles thermodynamics methodology on a
selection of 347 novel compositions, we predict 127 new stable quaternary
compounds, already more than the 89 reported almost exhaustively for ternary
systems. Thermoelectric performance of the state-of-the-art ternary
half-Heusler compounds are limited by their intrinsically high lattice thermal
conductivity ($\kappa_{L}$). In comparison to ternary half-Heuslers, thermal
transport in double half-Heuslers is dominated by low frequency phonon modes
with smaller group velocities and limited by disorder scattering. The double
half-Heusler composition Ti$_2$FeNiSb$_2$ was synthesized and confirmed to have
a significantly lower lattice thermal conductivity (factor of 3 at room
temperature) than TiCoSb, thereby providing a better starting point for
thermoelectric efficiency optimization. We demonstrate a dependable strategy to
assist the search for low thermal conductivity half-Heuslers and point towards
a huge composition space for implementing it. Our findings can be extended for
systematic discovery of other large families of multi-component intermetallic
semiconductors.",1901.09800v1
2023-06-29,High-throughput design of all-d-metal Heusler alloys for magnetocaloric applications,"Due to their versatile composition and customizable properties, A$_2$BC
Heusler alloys have found applications in magnetic refrigeration, magnetic
shape memory effects, permanent magnets, and spintronic devices. The discovery
of all-$d$-metal Heusler alloys with improved mechanical properties compared to
those containing main group elements, presents an opportunity to engineer
Heuslers alloys for energy-related applications. Using high-throughput density
functional theory calculations, we screened magnetic all-$d$-metal Heusler
compounds and identified 686 (meta)stable compounds. Our detailed analysis
revealed that the inverse Heusler structure is preferred when the
electronegativity difference between the A and B/C atoms is small, contrary to
conventional Heusler alloys. Additionally, our calculations of Pugh ratios and
Cauchy pressures demonstrated that ductile and metallic bonding are widespread
in all-$d$-metal Heuslers, supporting their enhanced mechanical behaviour. We
identified 49 compounds with a double-well energy surface based on Bain path
calculations and magnetic ground states, indicating their potential as
candidates for magnetocaloric and shape memory applications. Furthermore, by
calculating the free energies, we propose that 11 compounds exhibit structural
phase transitions, and propose isostructural substitution to enhance the
magnetocaloric effect.",2306.17092v1
2018-02-13,Designing and discovering a new family of semiconducting quaternary Heusler compounds based on the 18-electron rule,"Intermetallic compounds with sizable band gaps are attractive for their
unusual properties but rare. Here, we present a new family of stable
semiconducting quaternary Heusler compounds, designed and discovered by means
of high-throughput \textit{ab initio} calculations based on the 18-electron
rule. The 99 new semiconductors reported here adopt the ordered quaternary
Heusler structure with the prototype of LiMgSnPd (F$\bar{\mathbf{4}}$3m,
No.\,216) and contain 18 valence electrons per formula unit. They are realized
by filling the void in the half Heusler structure with a small and
electropositive atom, i.e., lithium. These new stable quaternary Heusler
semiconductors possess a range of band gaps from 0.3 to 2.5\,eV, and exhibit
some unusual properties different from conventional semiconductors, such as
strong optical absorption, giant dielectric screening, and high Seebeck
coefficient, which suggest these semiconductors have potential applications as
photovoltaic and thermoelectric materials. While this study opens up avenues
for further exploration of this novel class of semiconducting quaternary
Heuslers, the design strategy used herein is broadly applicable across a
potentially wide array of chemistries to discover new stable materials.",1802.04875v1
2005-09-18,Covalent bonding and the nature of band gaps in some half-Heusler compounds,"Half-Heusler compounds \textit{XYZ}, also called semi-Heusler compounds,
crystallize in the MgAgAs structure, in the space group $F\bar43m$. We report a
systematic examination of band gaps and the nature (covalent or ionic) of
bonding in semiconducting 8- and 18- electron half-Heusler compounds through
first-principles density functional calculations. We find the most appropriate
description of these compounds from the viewpoint of electronic structures is
one of a \textit{YZ} zinc blende lattice stuffed by the \textit{X} ion. Simple
valence rules are obeyed for bonding in the 8-electron compound. For example,
LiMgN can be written Li$^+$ + (MgN)$^-$, and (MgN)$^-$, which is isoelectronic
with (SiSi), forms a zinc blende lattice. The 18-electron compounds can
similarly be considered as obeying valence rules. A semiconductor such as
TiCoSb can be written Ti$^{4+}$ + (CoSb)$^{4-}$; the latter unit is
isoelectronic and isostructural with zinc-blende GaSb. For both the 8- and
18-electron compounds, when \textit{X} is fixed as some electropositive cation,
the computed band gap varies approximately as the difference in Pauling
electronegativities of \textit{Y} and \textit{Z}. What is particularly exciting
is that this simple idea of a covalently bonded \textit{YZ} lattice can also be
extended to the very important \textit{magnetic} half-Heusler phases; we
describe these as valence compounds \textit{ie.} possessing a band gap at the
Fermi energy albeit only in one spin direction. The \textit{local} moment in
these magnetic compounds resides on the \textit{X} site.",0509472v1
2005-10-08,Slater-Pauling Rule and Curie-Temperature of Co$_2$-based Heusler compounds,"A concept is presented serving to guide in the search for new materials with
high spin polarization. It is shown that the magnetic moment of half-metallic
ferromagnets can be calculated from the generalized Slater-Pauling rule.
Further, it was found empirically that the Curie temperature of Co$_2$ based
Heusler compounds can be estimated from a seemingly linear dependence on the
magnetic moment. As a successful application of these simple rules, it was
found that Co$_2$FeSi is, actually, the half-metallic ferromagnet exhibiting
the highest magnetic moment and the highest Curie temperature measured for a
Heusler compound.",0510210v1
2011-09-26,Anomalous Hall effect in the Co-based Heusler compounds Co$_{2}$FeSi and Co$_{2}$FeAl,"The anomalous Hall effect (AHE) in the Heusler compounds Co$_{2}$FeSi and
Co$_{2}$FeAl is studied in dependence of the annealing temperature to achieve a
general comprehension of its origin. We have demonstrated that the crystal
quality affected by annealing processes is a significant control parameter to
tune the electrical resistivity $\rho_{xx}$ as well as the anomalous Hall
resistivity $\rho_{ahe}$. Analyzing the scaling behavior of $\rho_{ahe}$ in
terms of $\rho_{xx}$ points to a temperature-dependent skew scattering as the
dominant mechanism in both Heusler compounds.",1109.5498v1
2012-11-01,Prediction of topological insulating behavior in Hg2CuTi-type Heusler compounds from first principles,"The topological band structures of the X2YZ Heusler compounds with the
Hg2CuTi structure are investigated by using first-principles calculations
within density functional theory. Our results clearly show that a large number
of the Hg2CuTi type Heusler compounds naturally exhibit distinct band-inversion
feature, which is mainly controlled by the Y-Z zinc blende sublattice. Similar
to the half-Heusler family, the topological band order in Hg2CuTi type Heusler
compounds is sensitive to the variation of lattice constant, and most of them
possess a negative formation energy, which makes them more suitable in material
growth and could easily achieve the topological insulating behavior by alloying
or proper strain.",1211.0190v1
2013-09-27,A first-principles investigation of the thermodynamic and mechanical properties of Ni-Ti-Sn Heusler and half-Heusler materials,"First principles calculations of the vibrational, thermodynamic and
mechanical properties of the Ni-Ti-Sn Heusler and half-Heusler compounds have
been performed. First, we have calculated the Raman and infrared spectra of
NiTiSn, providing benchmark theoretical data directly useful for the
assignments of its experimental spectra and clarifying the debate reported in
the literature on the assignment of its modes. Then, we have discussed the
significant vibrational density-of-states of Ni2TiSn at low-frequencies. These
states are at the origin of (i) its smaller free energy, (ii) its higher
entropy, and (iii) its lower Debye temperature, with respect to NiTiSn.
Finally, we have reported the mechanical properties of the two compounds. In
particular, we have found that the half-Heusler compound has the largest
stiffness. Paradoxically, its bulk modulus is also the smallest. This unusual
behavior has been related to the Ni-vacancies that weaken the structure under
isostatic compression. Both compounds show a ductile behavior.",1309.7195v1
2015-04-13,Evidence for Localized Moment Picture in Mn-based Heusler Compounds,"X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism
(XMCD) were used to probe the oxidation state and element specific magnetic
moments of Mn in Heusler compounds with different crystallographic structure.
The results were compared with theoretical calculations, and it was found that
in full Heusler alloys, Mn is metallic (oxidation state near 0) on both
sublattices. The magnetic moment is large and localized when octahedrally
coordinated by the main group element, consistent with previous theoretical
work, and reduced when the main group coordination is tetrahedral. By contrast,
in the half Heusler compounds the magnetic moment of the Mn atoms is large and
the oxidation state is +1 or +2. The magnetic and electronic properties of Mn
in full and half Heusler compounds are strongly dependent on the structure and
sublattice, a fact that can be exploited to design new materials.",1504.03088v1
2021-09-03,"Magnetic Properties of the Heusler Ru$_2$Mn$_X$ ($X$ = Nb, Ta or V) Compounds: Monte Carlo Simulations","In this paper, we have focused on a comparison of the different magnetic
properties of the three nano-Heusler Ru$_2$Mn$_X$ (X = Nb, Ta or V) compounds
using the Blume-Capel Ising model. The Heusler structures are composed by
different mixed spins. In fact, the Ru and Mn atoms are modeled by spin-5/2 and
spin-1/2, respectively. While, the X atoms ($X$ = Nb, Ta and V) are represented
by the spin-7/2, spin-3/2 and spin-5/2, respectively. This study is carried out
by using the Monte Carlo simulations under the Metropolis algorithm. The
magnetic behaviors of the three nano-Heusler compounds have been studied and
discussed. It is found that Ferrimagnetic to superparamagnetic transitions were
observed corresponding to different blocking temperatures. Besides, the effect
of the crystal field, the exchange coupling interactions and the external
magnetic field have been inspected on the magnetization of each nano-Heusler
compound Ru$_2$Mn$_X$ ($X$ = Nb, Ta or V).",2109.01708v1
2022-06-23,A general rule for predicting the magnetic moment of Cobalt-based Heusler compounds using compressed sensing and density functional theory,"We propose a general rule for estimating the magnetic moments of Co$
2$(cobalt)-based Heusler alloys, especially when doped with late transition
metals. We come up with a descriptor that can characterise both pure Co$_2$YZ
compounds and the doped ones with the chemical formula Co$_2$Y$_{1-x}$M$_x$Z (M
is the dopant) using online data for magnetic moments of Heusler alloys with
Co$_2$YZ structure and compressive sensing approach. The newly proposed
descriptor not only depends on the number of valence electrons of the compound
also it depends on the number of unoccupied d-electrons in the doping site. A
comparison of the performance of the proposed descriptor and the Slater-Pauling
rule is made. Unlike the Slater-Pauling rule, which is only effective for
half-metallic Heusler compounds, our machine-learning approach is more generic
since it applies to any Co$_2$YZ Heusler compounds, regardless of whether they
are half-metals or not. We use this new rule to estimate the magnetic moments
of a few yet-to-be-discovered Heusler compounds and compare the results to
density functional theory (DFT) based calculations. Finally, we use DFT and
machine learning investigations to prove their stability.",2206.11635v3
2018-02-11,"Heusler, Weyl, and Berry","Heusler materials, initially discovered by Fritz Heusler more than a century
ago, have grown into a family of more than 1000 compounds, synthesized from
combinations of more than 40 elements. These materials show a wide range of
properties, but new properties are constantly being found. Most recently, by
incorporating heavy elements that can give rise to strong spin-orbit coupling
(SOC), non-trivial topological phases of matter, such as topological insulators
(TIs), have been discovered in Heusler materials. Moreover, the interplay of
symmetry, SOC and magnetic structure allows for the realization of a wide
variety of topological phases through Berry curvature design. Weyl points and
nodal lines can be manipulated by various external perturbations, which results
in exotic properties such as the chiral anomaly, and large anomalous spin and
topological Hall effects. The combination of a non-collinear magnetic structure
and Berry curvature gives rise a non-zero anomalous Hall effect, which was
first observed in the antiferromagnets Mn3Sn and Mn3Ge. Besides this k-space
Berry curvature, Heusler compounds with non-collinear magnetic structures also
possess real-space topological states in the form of magnetic antiskyrmions,
which have not yet been observed in other materials. The possibility of
directly manipulating the Berry curvature shows the importance of understanding
both the electronic and magnetic structures of Heusler compounds. Together,
with the new topological viewpoint and the high tunability, novel physical
properties and phenomena await discovery in Heusler compounds.",1802.03771v1
2020-10-23,Machine-Learning-based Prediction of Lattice Thermal Conductivity for Half-Heusler Compounds using Atomic Information,"The half-Heusler compound has drawn attention in a variety of fields as a
candidate material for thermoelectric energy conversion and spintronics
technology. This is because it has various electronic structures, such as
semi-metals, semiconductors, and a topological insulator. When the half-Heusler
compound is incorporated into the device, the control of high lattice thermal
conductivity owing to high crystal symmetry is a challenge for the thermal
manager of the device. The calculation for the prediction of lattice thermal
conductivity, which is an important physical parameter for controlling the
thermal management of the device, requires a calculation cost of several 100
times as much as the usual density functional theory calculation. Therefore, we
examined whether lattice thermal conductivity prediction by machine learning
was possible on the basis of only the atomic information of constituent
elements for thermal conductivity calculated by the density functional theory
calculation in various half-Heusler compounds. Consequently, we constructed a
machine learning model, which can predict the lattice thermal conductivity with
high accuracy from the information of only atomic radius and atomic mass of
each site in the half-Heusler type crystal structure. Applying our results, the
lattice thermal conductivity for an unknown half-Heusler compound can be
immediately predicted. In the future, low-cost and short-time development of
new functional materials can be realized, leading to breakthroughs in the
search of novel functional materials.",2010.12467v1
2023-05-04,Experimental observation of spin glass state in highly disordered quaternary Heusler alloy FeRuMnGa,"The realization of spin-glass (S-G) state in Heusler alloys is very rare
despite the presence of inherent structural and elemental disorder in those
compounds. Although a few half and full Heusler alloys are known to exhibit S-G
state, there is hardly any manifestation of the same in cases of quaternary
Heusler compounds. Here we report the observation of S-G state in a highly
disordered equiatomic quaternary Heusler compound: FeRuMnGa, where the S-G
state is in between of canonical S-G and cluster glass. Different intricate
features of S-G state including non-equilibrium magnetic dynamics at low
temperature in the compound are unveiled through our comprehensive magnetic,
heat capacity and neutron diffraction studies. The structural disorder in the
sample is neither conventional \textit{A2}- nor \textit{B2}-type while those
two types are commonly observed for Heusler compounds. The presence of disorder
also plays a significant role in electron transport properties of the alloy,
which is reflected in its exhibition of semi-metallic behavior and anomalous
Hall effect at low temperature.",2305.03093v1
2002-05-07,Slater-Pauling Behavior of the Half-Ferromagnetic Full-Heusler Alloys,"Using the full-potential screened Korringa-Kohn-Rostoker method we study the
full-Heusler alloys based on Co, Fe, Rh and Ru. We show that many of these
compounds show a half-metallic behavior, however in contrast to the
half-Heusler alloys the energy gap in the minority band is extremely small.
These full-Heusler compounds show a Slater-Pauling behavior and the total
spin-magnetic moment per unit cell (M_t) scales with the total number of
valence electrons (Z_t) following the rule: M_t=Z_t-24. We explain why the
spin-down band contains exactly 12 electrons using arguments based on the group
theory and show that this rule holds also for compounds with less than 24
valence electrons. Finally we discuss the deviations from this rule and the
differences compared to the half-Heusler alloys.",0205129v2
2013-04-01,First-principles investigation of half-metallic ferromagnetism of half-Heusler compounds XYZ,"We investigate the electronic structure and magnetism of half-Heusler
compounds XYZ (X, Y=V, Cr, Mn, Fe, Co and Ni; Z=Al, Ga, In, Si, Ge, Sn, P, As,
and Sb) using the ab initio density functional theory calculations. Nine
half-metals with half-Heusler structure have been predicted with the
half-metallic gap of 0.07-0.67 eV. The calculations show that the formation
energies for these nine half-Heusler compounds range from -1.32 to -0.12
eV/f.u., and for CoCrSi, CoCrGe, CoFeGe, CoMnSi, CoMnGe, FeMnGe and FeMnAs, the
total energy differences between the half-Heusler structure and the
corresponding ground-state structure are small (0.07-0.76 eV/f.u.), thus it is
expected that they would be realized in the form of thin films under metastable
conditions for spintronic applications. The stability of the half-metallicity
of CoCrGe and FeMnAs to the lattice distortion is also investigated in detail.",1304.0344v2
2017-04-06,A critical study of the elastic properties and stability of Heusler compounds: Phase change and tetragonal $X_{2}YZ$ compounds,"In the present work, the elastic constants and derived properties of
tetragonal and cubic Heusler compounds were calculated using the high accuracy
of the full-potential linearized augmented plane wave (FPLAPW). To find the
criteria required for an accurate calculation, the consequences of increasing
the numbers of $k$-points and plane waves on the convergence of the calculated
elastic constants were explored. Once accurate elastic constants were
calculated, elastic anisotropies, sound velocities, Debye temperatures,
malleability, and other measurable physical properties were determined for the
studied systems. The elastic properties suggested metallic bonding with
intermediate malleability, between brittle and ductile, for the studied Heusler
compounds. To address the effect of off-stoichiometry on the mechanical
properties, the virtual crystal approximation (VCA) was used to calculate the
elastic constants. The results indicated that an extreme correlation exists
between the anisotropy ratio and the stoichiometry of the Heusler compounds,
especially in the case of Ni$_{2}$MnGa.",1704.01741v1
2022-08-04,"Ab-initio study of stable 3d, 4d and 5d transition metal based Quaternary Heusler compounds","The realization of the stable structure of Heusler compounds and the study of
different properties is an important step for their potential application in
spintronics and magnetoelectronic devices. In this paper, using the plane-wave
pseudopotential method within the framework of density functional theory (DFT),
we investigate 25 Quaternary Heusler compounds for their electronic, magnetic,
and mechanical properties. The Open Quantum Materials Database (OQMD) is used
to screen a large number of compounds to narrow down the possible synthesizable
materials. The convex-hull distance and elastic constants are exploited to
confirm the thermodynamic and mechanical stability of the compounds. The
careful study of the different structures suggests that 5 of the compounds
crystallize in type-1 structure whereas 20 compounds adopt type-3 structure.
The possible explanation for the observed behavior is made by invoking
electronegativity arguments and through the study of individual spin magnetic
moments in different structures. The compounds with diverse electronic and
magnetic properties such as half-metallicity, spin gapless semiconducting
behavior, and non-magnetic semi-conducting property have been identified.",2208.02401v2
2010-10-11,Half-Heusler Topological Insulators: A First-Principle Study with the Tran-Blaha Modified Becke-Johnson Density Functional,"We systematically investigate the topological band structures of half-Heusler
compounds using first-principles calculations. The modified Becke-Johnson
exchange potential together with local density approximation for the
correlation potential (MBJLDA) has been used here to obtain accurate band
inversion strength and band order. Our results show that a large number of
half-Heusler compounds are candidates for three-dimensional topological
insulators. The difference between band structures obtained using the local
density approximation (LDA) and MBJLDA potential is also discussed.",1010.2179v1
2014-01-24,Performance Analysis of Spin Transfer Torque Random Access Memory with cross shaped free layer using Heusler Alloys by using micromagnetic studies,"We investigated the performance of spin transfer torque random access memory
(STT-RAM) cell with cross shaped Heusler compound based free layer using
micromagnetic simulations. We designed the free layer using Cobalt based
Heusler compounds. Here in this paper, simulation results predict that
switching time from one state to other state is reduced. Also it is examined
that critical switching current density to switch the magnetization of free
layer of STT RAM cell is reduced.",1401.6971v1
2018-12-07,Systematic understanding of half-metallicity of ternary compounds in Heusler and Inverse Heusler structures with 3$d$ and 4$d$ elements,"Employing {\it ab initio} electronic structure calculations we extensively
study ternary Heusler compounds having the chemical formula X$_2$X$^\prime$Z,
where X = Mn, Fe or Co; Z = Al or Si; and X$^\prime$ changes along the row of
4$d$ transition metals. A comprehensive overview of these compounds, addressing
the trends in structural, electronic, magnetic properties and Curie temperature
is presented here along with the search for new materials for spintronics
applications. A simple picture of hybridization of the $d$ orbitals of the
neighboring atoms is used to explain the origin of the half-metallic gap in
these compounds. We show that arrangements of the magnetic atoms in different
Heusler lattices are largely responsible for the interatomic exchange
interactions that are correlated with the features in their electronic
structures as well as possibility of half-metallicity. We find seven
half-metallic magnets with 100\% spin polarization. We identify few other
compounds with high spin polarisation as ""near half-metals"" which could be of
potential use in applications as well. We find that the major features in the
electronic structures remain intact if a 3$d$ X$^{\prime}$ constituent is
replaced with an isoelectronic 4$d$, implying that the total number of valence
electrons can be used as a predictor of half-metallic nature in compounds from
Heusler family.",1812.02856v1
2020-03-25,Tetragonal superstructure of the antiskyrmion hosting Heusler compound Mn1.4PtSn,"Skyrmions in non-centrosymmetric magnets are vortex-like spin arrangements,
viewed as potential candidates for information storage devices. The crystal
structure and non-collinear magnetic structure together with magnetic and
spin-orbit interactions define the symmetry of the Skyrmion structure. We
outline the importance of these parameters in the Heusler compound Mn1.4PtSn
which hosts antiskyrmions, a vortex-like spin texture related to skyrmions.1 We
overcome the challenge of growing large micro-twin-free single crystals of
Mn1.4PtSn which has proved to be the bottleneck for realizing bulk
skyrmionic/antiskyrmionic states in a compound. The use of 5d-transition metal,
platinum, together with manganese as constituents in the Heusler compound such
as Mn1.4PtSn is a precondition for the non-collinear magnetic structure. Due to
the tetragonal inverse Heusler structure, Mn1.4PtSn exhibits large
magneto-crystalline anisotropy and D2d symmetry, which are necessary for
antiskyrmions. The superstructure in Mn1.4PtSn is induced by Mn-vacancies which
enables a ferromagnetic exchange interaction to occur. Mn1.4PtSn, the first
known tetragonal Heusler superstructure compound, opens up a new research
direction for properties related to the superstructure in a family containing
thousands of compounds.",2003.11344v1
2021-01-26,Co$_2$FeAl full Heusler compound based spintronic terahertz emitter,"To achieve a large terahertz (THz) amplitude from a spintronic THz emitter
(STE), materials with 100\% spin polarisation such as Co-based Heusler
compounds as the ferromagnetic layer are required. However, these compounds are
known to loose their half-metallicity in the ultrathin film regime, as it is
difficult to achieve L2$_1$ ordering, which has become a bottleneck for the
film growth. Here, the successful deposition using room temperature DC
sputtering of the L2$_1$ and B2 ordered phases of the Co$_2$FeAl full Heusler
compound is reported. Co$_2$FeAl is used as ferromagnetic layer together with
highly orientated Pt as non-ferromagnetic layer in the Co$_2$FeAl/Pt STE, where
an MgO(10 nm) seed layer plays an important role to achieve the L2$_1$ and B2
ordering of Co$_2$FeAl. The generation of THz radiation in the CFA/Pt STE is
presented, which has a bandwidth in the range of 0.1-4 THz. The THz electric
field amplitude is optimized with respect to thickness, orientation, and growth
parameters using a thickness dependent model considering the optically induced
spin current, superdiffusive spin current, inverse spin Hall effect and the
attenuation of THz radiation in the layers. This study, based on the full
Heusler Co$_2$FeAl compound opens up a plethora possibilities in STE research
involving full Heusler compounds.",2101.10911v1
2013-01-31,A New Spin Gapless Semiconductors Family: Quaternary Heusler Compounds,"Using first-principles calculations, we investigate the band structures of a
series of quaternary LiMgPdSn-type Heusler compounds. Our calculation results
show that five compounds CoFeMnSi, CoFeCrAl, CoMnCrSi, CoFeVSi and FeMnCrSb
possess unique electronic structures characterized by a half-metallic gap in
one spin direction while a zero-width gap in the other spin direction showing
spin gapless semiconducting behavior. We further analysis the electronic and
magnetic properties of all quaternary Heusler alloys involved, and reveal a
semi-empirical general rule (total valence electrons number being 26 or 28) for
indentifying spin gapless semiconductors in Heusler compounds. The influences
of lattice distortion and main-group element change have also been discussed.",1301.7488v1
2016-02-18,"Observation of Unusual Topological Surface States in Half-Heusler Compounds LnPtBi (Ln=Lu, Y)","Topological quantum materials represent a new class of matter with both
exotic physical phenomena and novel application potentials. Many Heusler
compounds, which exhibit rich emergent properties such as unusual magnetism,
superconductivity and heavy fermion behaviour, have been predicted to host
non-trivial topological electronic structures. The coexistence of topological
order and other unusual properties makes Heusler materials ideal platform to
search for new topological quantum phases (such as quantum anomalous Hall
insulator and topological superconductor). By carrying out angle-resolved
photoemission spectroscopy (ARPES) and ab initio calculations on rare-earth
half-Heusler compounds LnPtBi (Ln=Lu, Y), we directly observed the unusual
topological surface states on these materials, establishing them as first
members with non-trivial topological electronic structure in this class of
materials. Moreover, as LnPtBi compounds are non-centrosymmetric
superconductors, our discovery further highlights them as promising candidates
of topological superconductors.",1602.05633v2
2020-01-06,Giant anomalous Hall and Nernst effect in magnetic cubic Heusler compounds,"The interplay of magnetism and topology opens up the possibility for exotic
linear response effects, such as the anomalous Hall effect and the anomalous
Nernst effect, which can be strongly enhanced by designing a strong Berry
curvature in the electronic structure. It is even possible to utilize this to
create a quantum anomalous Hall state at high temperatures by reducing the
dimensionality. Magnetic Heusler compounds are a promising class of materials
for this purpose because they grow in thin films, have a high Curie
temperature, and their electronic structure hosts strong topological features.
Here, we provide a comprehensive study of the intrinsic anomalous transport for
magnetic cubic full Heusler compounds and we illustrate that several Heusler
compounds outperform the best so far reported materials. The results reveal the
importance of symmetries, especially mirror planes, in combination with
magnetism for giant anomalous Hall and Nernst effects, which should be valid in
general for linear responses (spin Hall effect, spin orbital torque, etc.)
dominated by intrinsic contributions.",2001.01698v3
2017-10-03,Search for Thermoelectrics with High Figure of Merit in half-Heusler compounds with multinary substitution,"In order to improve the thermoelectric performance of TiCoSb we have
substituted 50% of Ti equally with Zr and Hf at Ti site and Sb with Sn and Se
equally at Sb site. The electronic structure of Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5
is investigated using the full potential linearized augmented plane wave method
and the thermoelectric transport properties are calculated on the basis of
semi-classical Boltzmann transport theory. Our band structure calculations show
that Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has semiconducting behavior with indirect
band gap value of 0.98 eV which follow the empirical rule of 18
valence-electron content to bring semiconductivity in half Heusler compounds,
indicating that one can have semiconducting behavior in multinary phase of half
Heusler compounds if they full fill the 18 VEC rule and this open-up the
possibility of designing thermoelectrics with high figure of merit in half
Heusler compounds. We show that at high temperature of around 700K
Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has high thermoelectric figure of merit of ZT =
1.05 which is higher than that of TiCoSb (~ 0.95) suggesting that by going from
ternary to multinary phase system one can enhance the thermoelectric figure of
merit at higher temperatures.",1710.01012v1
2021-02-03,First principles design of Ohmic spin diodes based on quaternary Heusler compounds,"The Ohmic spin diode (OSD) is a recent concept in spintronics, which is based
on half-metallic magnets (HMMs) and spin-gapless semiconductors (SGSs).
Quaternary Heusler compounds offer a unique platform to realize the OSD for
room temperature applications as these materials possess very high Curie
temperatures as well as half-metallic and spin-gapless semiconducting behavior
within the same family. Using state-of-the-art first-principles calculations
combined with the non-equilibrium Green's function method we design four
different OSDs based on half-metallic and spin-gapless semiconducting
quaternary Heusler compounds. All four OSDs exhibit linear current-voltage
($I-V$) characteristics with zero threshold voltage $V_T$. We show that these
OSDs possess a small leakage current, which stems from the overlap of the
conduction and valence band edges of opposite spin channels around the Fermi
level in the SGS electrodes. The obtained on/off current ratios vary between
$30$ and $10^5$. Our results can pave the way for the experimental fabrication
of the OSDs within the family of ordered quaternary Heusler compounds.",2102.01919v1
2021-10-20,Anomalous Hall effect from gapped nodal line in Co2FeGe Heusler compound,"Full Heusler compounds with Cobalt as a primary element show anomalous
transport properties owing to the Weyl fermions and broken time-reversal
symmetry. We present here the study of anomalous Hall effect (AHE) in Co2FeGe
Heusler compound. The experiment reveals anomalous Hall conductivity (AHC) 100
S/cm at room temperature with an intrinsic contribution of 78 S/cm . The
analysis of anomalous Hall resistivity suggests the scattering independent
intrinsic mechanism dominates the overall behaviour of anomalous Hall
resistivity. The first principles calculation reveals that the Berry curvature
originated by gapped nodal line near EF is the main source of AHE in Co2FeGe
Heusler compound. The theoretically calculated AHC is in agreement with the
experiment.",2110.10677v1
2012-10-19,Search for spin gapless semiconductors: The case of inverse Heusler compounds,"We employ ab-initio electronic structure calculations to search for spin
gapless semiconductors, a recently identified new class of materials, among the
inverse Heusler compounds. The occurrence of this property is not accompanied
by a general rule and results are materials specific. The six compounds
identified show semiconducting behavior concerning the spin-down band structure
and in the spin-up band structure the valence and conduction bands touch each
other leading to 100% spin-polarized carriers. Moreover these six compounds
should exhibit also high Curie temperatures and thus are suitable for
spintronics applications.",1210.5355v1
2013-09-25,Half metallic state and magnetic properties versus the lattice constant in Ti\raisebox{-.2ex}{\scriptsize 2}CoSn Heusler compound: an ab initio study,"The half metallic properties of Ti\raisebox{-.2ex}{\scriptsize 2}CoSn
full-Heusler compound is studied within the framework of the density functional
theory with the Perdew Burke Ernzerhof generalized gradient approximation
(GGA). Structural optimization was performed and the calculated equilibrium
lattice constant is 6.340 A. The spin up band of compound has metallic
character and spin down band is semiconducting with an indirect gap of 0.598 eV
at equilibrium lattice constant. For the lattice parameter, ranging from 6.193
to 6.884 A the compound presents 100% spin polarization and a total magnetic
moment of 3$\mu_{B}$.",1309.6437v1
2013-01-09,New iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties,"The present work reports on the new soft ferromagnetic Heusler phases
Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been
predicted to exist in a tetragonal regular Heusler structure. Together with the
known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and
characterized by powder XRD, 57 Fe M\""ossbauer spectroscopy, SQUID and EDX
measurements. In particular M\""ossbauer spectroscopy was used to monitor the
degree of local atomic order/disorder and to estimate magnetic moments at the
Fe sites from the hyperfine fields. It is shown that in contrast to the
previous predictions all the materials except Fe2NiGa basically adopt the
inverse cubic Heusler (X-) structure with differing degrees of disorder. The
disorder is more enhanced in case of Fe2NiGa, which was predicted as an inverse
Heusler phase. The experimental data are compared with results from ab-inito
electronic structure calculations on LDA level incorporating the effects of
atomic disorder by using the coherent potential approximation (CPA). A good
agreement between calculated and experimental magnetic moments is found for the
cubic inverse Heusler phases. Model calculations on various atomic
configurations demonstrate that antisite disorder tends to enhance the
stability of the X-structure. Given the fundamental scientific and
technological importance of tetragonal Heusler phases the present results call
for further investigations to unravel the factors stabilizing tetragonal
Heusler materials.",1301.1988v1
2014-10-26,Half-Heusler topological insulators,"Ternary semiconducting or metallic half-Heusler compounds with an atomic
composition 1:1:1 are widely studied for their flexible electronic properties
and functionalities. Recently, a new material property of half-Heusler
compounds was predicted based on electronic structure calculations: the
topological insulator. In topological insulators, the metallic surface states
are protected from impurity backscattering due to spin-momentum locking. This
opens up new perspectives in engineering multifunctional materials. In this
article, we introduce half Heusler materials from the crystallographic and
electronic structure point of view. We present an effective model Hamiltonian
from which the topological state can be derived, notably from a non-trivial
inverted band structure. We discuss general implications of the inverted band
structure with a focus on the detection of the topological surface states in
experiments by reviewing several exemplary materials. Special attention is
given to superconducting half-Heusler materials, which have attracted ample
attention as a platform for non-centrosymmetric and topological
superconductivity.",1410.7011v1
2015-11-30,Band structure and transport studies of half Heusler compound DyPdBi: An efficient thermoelectric material,"The discovery of Heusler alloys has revolutionized the research field of
intermetallics due to the ease with which one can derive potential candidates
for multifunctional applications. During recent years, many half Heusler alloys
have been investigated for their thermoelectric properties. The f electron
based rare earth ternary half Heusler compound DyPdBi has its f energy levels
located close to the Fermi energy level. Other research efforts have emphasized
that such materials have good thermoelectric capabilities. We have explored
using first principles the electronic band structure of DyPdBi by use of
different exchange correlation potentials in the density functional theoretical
framework. Transport coefficients that arise in the study of thermoelectric
properties of DyPdBi have been calculated and illustrate its potential as an
efficient thermoelectric material. Both the theoretically estimated Seebeck
coefficient and the power factor agree well with the available experimental
results. Our calculations illustrate that it is essential to include spin-orbit
coupling in these models of f electron half Heusler materials.",1511.09187v1
2015-11-15,Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films,"The discovery of topological insulators (TIs), materials with bulk band gaps
and protected cross-gap surface states, in compounds such as Bi2Se3 has
generated much interest in identifying topological surface states (TSSs) in
other classes of materials. In particular, recent theory calculations suggest
that TSSs may be found in half-Heusler ternary compounds. If experimentally
realizable, this would provide a materials platform for entirely new
heterostructure spintronic devices that make use of the structurally-identical
but electronically-varied nature of Heusler compounds. Here, we show the
presence of a TSS in epitaxially grown thin films of the half-Heusler compound
PtLuSb. Spin and angle-resolved photoemission spectroscopy (ARPES),
complemented by theoretical calculations, reveals a surface state with linear
dispersion and a helical tangential spin texture consistent with previous
predictions. This experimental verification of TI behavior is a significant
step forward in establishing half-Heusler compounds as a viable material system
for future spintronics devices.",1511.04778v3
2006-11-07,"Calculated electronic and magnetic properties of the half-metallic, transition metal based Heusler compounds","In this work, results of {\it ab-initio} band structure calculations for
$A_2BC$ Heusler compounds that have $A$ and $B$ sites occupied by transition
metals and $C$ by a main group element are presented. This class of materials
includes some interesting half-metallic and ferromagnetic properties. The
calculations have been performed in order to understand the properties of the
minority band gap and the peculiar magnetic behavior found in these materials.
Among the interesting aspects of the electronic structure of the materials are
the contributions from both $A$ and $B$ atoms to states near the Fermi energy
and to the total magnetic moment. The magnitude of the total magnetic moment,
which depends as well on the kind of $C$ atoms, shows a trend consistent with
the Slater-Pauling type behavior in several classes of these compounds. The
localized moment in these magnetic compounds resides at the $B$ site. Other
than in the classical Cu$_2$-based Heusler compounds, the $A$ atoms in Co$_2$,
Fe$_2$, and Mn$_2$ based compounds may contribute pronounced to the total
magnetic moment.",0611179v1
2016-04-18,"Itinerant G-type antiferromagnetism in D0$_3$-type V$_3$Z (Z=Al, Ga, In) compounds: A first-principles study","Heusler compounds are widely studied due to their variety of magnetic
properties making them ideal candidates for spintronic and magnetoelectronic
applications. V$_3$Al in its metastable D0$_3$-type Heusler structure is a
prototype for a rare antiferromagnetic gapless behavior. We provide an
extensive study on the electronic and magnetic properties of V$_3$Al, V$_3$Ga
and V$_3$In compounds based on state-of-the-art electronic structure
calculations. We show that the ground state for all three is a G-type itinerant
antiferromagnetic gapless semiconductor. The large antiferromagnetic exchange
interactions lead to very high N\'eel temperatures, which are predicted to be
around 1000 K. The coexistence of the gapless and antiferromagnetic behaviors
in these compounds can be explained considering the simultaneous presence of
three V atoms at the unit cell using arguments which have been employed for
usual inverse Heusler compounds. We expect that our study on these compounds to
enhance further the interest on them towards the optimization of their growth
conditions and their eventual incorporation in devices.",1604.05137v1
2020-08-31,Giant magnetocaloric effect driven by first-order magneto-structural transition in cosubstituted Ni-Mn-Sb Heusler compounds: predictions from \textit{Ab initio} and Monte Carlo calculations,"Using Density Functional Theory and a thermodynamic model [Physical Review B
86, 134418 (2012)], in this paper, we provide an approach to systematically
screen compounds of a given Heusler family to predict ones that can yield giant
magnetocaloric effect driven by a first-order magneto-structural transition. We
apply this approach to two Heusler series
Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and
Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at
Ni and Mn sites. We predict four new compounds with potentials to achieve the
target properties. Our computations of the thermodynamic parameters, relevant
for magnetocaloric applications, show that the improvement in the parameters in
the predicted cosubstituted compounds can be as large as four times in
comparison to the off-stoichiometric Ni-Mn-Sb and a compound derived by single
substitution at the Ni site, where magnetocaloric effects have been observed
experimentally. This work establishes a protocol to select new compounds that
can exhibit large magnetocaloric effects and demonstrate cosubstitution as a
route for more flexible tuneability to achieve outcomes, better than the
existing ones.",2008.13479v1
2018-12-11,Half-metallicity in quaternary Heusler alloys with 3$d$ and 4$d$ elements: observations and insights from DFT calculations,"In this work, we provide important insights into the evolution of
half-metallicity in quaternary Heusler alloys. Employing {\it ab initio}
electronic structure methods we study 18 quaternary Heusler compounds having
the chemical formula CoX$^\prime$Y$^\prime$Al, where Y$^\prime$ = Mn, Fe; and
X$^\prime$ a 4$d$ element. Along with the search for new materials for
spintronics applications, the trends in structural, electronic, magnetic
properties and Curie temperature were investigated. We have made comparative
studies with the compounds in the quaternary series
CoX$^{\prime}$Y$^{\prime}$Si with X$^{\prime}$ materials from 3$d$ and 4$d$
transition metal series in the periodic table. We observe that the
half-metallic behaviour depends primarily on the crystal structure type based
on atomic arrangements and the number of valence electrons. As long as these
two are identical, the electronic structures and the magnetic exchange
interactions bear close resemblances. Consequently, the materials exhibit
identical electronic properties, by and large. We analysed the roles of
different transition metal atoms in affecting hybridisations and correlated
them with the above observations. This work, therefore, provides important
perspectives regarding the underlying physics of half-metallic behaviour in
quaternary Heusler compounds which goes beyond specifics of a given material.
This, thus, paves way for smart prediction of new half-metals. This work also
figures out an open problem of understanding how different ternary Heuslers
with different electronic behaviour may lead to half-metallic behaviour in
quaternary Heuslers with 4$d$ transition metal elements.",1812.04477v1
2017-04-06,A critical study of the elastic properties and stability of Heusler compounds: Cubic Co$_{2}YZ$ compounds with $L2_{1}$ structure,"Elastic constants and their derived properties of various cubic Heusler
compounds were calculated using first-principles density functional theory. To
begin with, Cu$_2$MnAl is used as a case study to explain the interpretation of
the basic quantities and compare them with experiments. The main part of the
work focuses on Co$_2$-based compounds that are Co$_2$Mn$M$ with the main group
elements $M=$~Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, and Co$_2TM$ with the main
group elements Si or Ge, and the $3d$ transition metals $T=$~Sc, Ti, V, Cr, Mn,
and Fe. It is found that many properties of Heusler compounds correlate to the
mass or nuclear charge $Z$ of the main group element.
  Blackman's and Every's diagrams are used to compare the elastic properties of
the materials, whereas Pugh's and Poisson's ratios are used to analyze the
relationship between interatomic bonding and physical properties. It is found
that the {\it Pugh's criterion} on brittleness needs to be revised whereas {\it
Christensen's criterion} describes the ductile--brittle transition of Heusler
compounds very well. The calculated elastic properties give hint on a metallic
bonding with an intermediate brittleness for the studied Heusler compounds.
  The universal anisotropy of the stable compounds has values in the range of
$0.57 <A_U <2.73$. The compounds with higher $A_U$ values are found close to
the middle of the transition metal series. In particular, Co$_2$ScAl with
$A_U=0.01$ is predicted to be an isotropic material that comes closest to an
ideal Cauchy solid as compared to the remaining Co$_2$-based compounds. Apart
from the elastic constants and moduli, the sound velocities, Debye
temperatures, and hardness are predicted and discussed for the studied systems.
The calculated slowness surfaces for sound waves reflect the degree of
anisotropy of the compounds.",1704.01752v1
2002-04-03,Surface Properties of the Half- and Full-Heusler Alloys,"Using a full-potential \textit{ab-initio} technique I study the electronic
and magnetic properties of the (001) surfaces of the half-Heusler alloys,
NiMnSb, CoMnSb and PtMnSb and of the full-Heusler alloys Co$_2$MnGe, Co$_2$MnSi
and Co$_2$CrAl. The MnSb terminated surfaces of the half-Heusler compounds
present properties similar to the bulk compounds and, although the
half-metallicity is lost, an important spin-polarisation at the Fermi level. In
contrast to this the Ni terminated surface shows an almost zero net
spin-polarisation. While the bulk Co$_2$MnGe and Co$_2$MnSi are almost
half-ferromagnetic, their surfaces lose the half-metallic character and the net
spin-polarisation at the Fermi level is close to zero. Contrary to these
compounds the CrAl terminated (001) surface of Co$_2$CrAl shows a spin
polarisation of about 84%.",0204083v1
2005-06-29,Anomalous vibrational effects in non-magnetic and magnetic Heusler alloys,"First-principles calculations are used in order to investigate phonon
anomalies in non-magnetic and magnetic Heusler alloys. Phonon dispersions for
several systems in their cubic L2$\mathrm{_1}$ structure were obtained along
the [110] direction. We consider compounds which exhibit phonon instabilities
and compare them with their stable counterparts. The analysis of the electronic
structure allows us to identify the characteristic features leading to
structural instabilities. The phonon dispersions of the unstable compounds show
that, while the acoustic modes tend to soften, the optical modes disperse in a
way which is significantly different from that of the stable structures. The
optical modes that appear to disperse at anomalously low frequencies are Raman
active, which is considered an indication of a stronger polarizability of the
unstable systems. We show that phonon instability of the TA$_{2}$ mode in
Heusler alloys is driven by interaction(repulsion) with the low energy optical
vibrations. The optical modes show their unusual behavior due to covalent
interactions which are additional bonding features incommensurate with the
dominating metallicity in Heusler compounds.",0506774v1
2007-02-19,Defects-driven appearance of half-metallic ferrimagnetism in Co-Mn--based Heusler alloys,"Half-metallic ferromagnetic full-Heusler alloys containing Co and Mn, having
the formula Co$_2$MnZ where Z a sp element, are among the most studied Heusler
alloys due to their stable ferromagnetism and the high Curie temperatures which
they present. Using state-of-the-art electronic structure calculations we show
that when Mn atoms migrate to sites occupied in the perfect alloys by Co, these
Mn atoms have spin moments antiparallel to the other transition metal atoms.
The ferrimagnetic compounds, which result from this procedure, keep the
half-metallic character of the parent compounds and the large
exchange-splitting of the Mn impurities atoms only marginally affects the width
of the gap in the minority-spin band. The case of [Co$_{1-x}$Mn$_x$]$_2$MnSi is
of particular interest since Mn$_3$Si is known to crystallize in the Heusler
$L2_1$ lattice structure of Co$_2$MnZ compounds. Robust half-metallic
ferrimagnets are highly desirable for realistic applications since they lead to
smaller energy losses due to the lower external magnetic fields created with
respect to their ferromagnetic counterparts.",0702437v1
2008-01-15,Fundamentals of half-metallic Full-Heusler alloys,"Intermetallic Heusler alloys are amongst the most attractive half-metallic
systems due to the high Curie temperatures and the structural similarity to the
binary semiconductors. In this review we present an overview of the basic
electronic and magnetic properties of the half-metallic full-Heusler alloys
like Co$_2$MnGe. Ab-initio results suggest that the electronic and magnetic
properties in these compounds are intrinsically related to the appearance of
the minority-spin gap. The total spin magnetic moment in the unit cell, $M_t$,
scales linearly with the number of the valence electrons, $Z_t$, such that
$M_t=Z_t-24$ for the full-Heusler alloys opening the way to engineer new
half-metallic alloys with the desired magnetic properties. Moreover we present
analytical results on the disorder in Co$_2$Cr(Mn)Al(Si) alloys, which is
susceptible to destroy the perfect half-metallicity of the bulk compounds and
thus degrade the performance of devices. Finally we discuss the appearance of
the half-metallic ferrimagnetism due to the creation of Cr(Mn) antisites in
these compounds and the Co-doping in Mn$_2$VAl(Si) alloys which leads to the
fully-compensated half-metallic ferrimagnetism.",0801.2252v1
2012-10-22,Generalized Slater-Pauling rule for the inverse Heusler compounds,"We present extensive first-principles calculations on the inverse
full-Heusler compounds having the chemical formula X$_2$YZ where (X = Sc, Ti,
V, Cr or Mn), (Z = Al, Si or As) and the Y ranges from Ti to Zn. Several of
these alloys are identified to be half-metallic magnets. We show that the
appearance of half-metallicity is associated in all cases to a Slater-Pauling
behavior of the total spin-magnetic moment. There are three different variants
of this rule for the inverse Heusler alloys depending on the chemical type of
the constituent transition-metal atoms. Simple arguments regarding the
hybridization of the d-orbitals of neighboring atoms can explain these rules.
We expect our results to trigger further experimental interest on this type of
half-metallic Heusler compounds.",1210.5816v1
2018-08-14,Screening potential topological insulators in half-Heusler compounds via compressed-sensing,"Ternary half-Heusler compounds with widely tunable electronic structures,
present a new platform to discover topological insulators. Due to
time-consuming computations and synthesis procedures, the identification of new
topological insulators is however a rough task. Here, we adopt a
compressed-sensing approach to rapidly screen potential topological insulators
in half-Heusler family, which is realized via a two-dimensional descriptor that
only depends on the fundamental properties of the constituent atoms. Beyond the
finite training data, the proposed descriptor is employed to screen many new
half-Heusler compounds, including those with integer and fractional
stoichiometry, and a larger number of possible topological insulators are
predicted.",1808.04748v5
2022-10-24,Ab-initio calculation of the Hubbard $U$ and Hund exchange $J$ in local moment magnets: The case of Mn-based full Heusler compounds,"Mn-based full Heusler compounds possess well-defined local atomic Mn moments,
and thus the correlation effects between localized d electrons are expected to
play an important role in determining the electronic and magnetic properties of
these materials. Employing ab-initio calculations in conjunction with the
constrained random-phase approximation (cRPA) method, we calculate the strength
of the effective on-site Coulomb interaction parameters (Hubbard U and Hund
exchange J) in the case of X2MnZ full Heusler compounds with X being one of Ni,
Pd or Cu, and Z being one of In, Sn, Sb or Te. We show that the Z element (or
sp element) in Heusler compounds significantly reduces the strength of the
Hubbard U parameter for Mn 3d electrons compared to the elementary bulk Mn. On
the contrary, the effect of the sp-atom on the strength of the U parameter of
Ni, Cu or Pd valence d electrons is not so substantial with respect to the
elementary bulk values. The U values for all transition metal atoms decrease
with increasing sp electron number in the In-Sn-Sb-Te sequence. Our cRPA
calculations reveal that despite their well-defined local magnetic moments, the
Mn-based full Heusler alloys fall into the category of the weakly correlated
materials.",2210.13061v1
2006-10-17,Surface and bulk properties of the Heusler compound Co2Cr0.6Fe0.4Al: a Moessbauer study,"To explore its structural and magnetic properties, the Heusler compound
Co2Cr0.6Fe0.4Al was investigated using Moessbauer spectroscopy. The results of
both transmission and conversion electron Moessbauer spectroscopy (CEMS) are
analyzed to obtain insight into both the disorder effects as well as the
differences between bulk and surface properties. It was found that mechanical
treatment of the surfaces of bulk samples causes disorder and phase
segregation, effects that should be taken into consideration when performing
studies using surface-informative techniques. Results from bulk sample CEMS
measurements of Co2Cr0.6Fe0.4Al are used to interpret the thin film Moessbauer
spectra of this compound.",0610480v1
2009-04-27,Exchange stiffness in Co$_{2}$-based Heusler compounds,"We determine the spin wave exchange stiffness $D$ and the exchange constant
$A$ for the full Heusler compound \CFS using Brillouin light scattering
spectroscopy. We find an extraordinarily large value of $D=715\pm20$ meV
\AA$^2$ ($A=31.5\pm1.0$ pJ/m) which is, to the best of our knowledge, only
surpassed by the intermetallic compound Fe$_{53}$Co$_{47}$ (J. Appl. Phys.
\textbf{75}, 7021 (1994)). Furthermore, we provide a systematization of the
exchange stiffnesses determined for a variety of Co$_2$-based Heusler
compounds. We find that for the investigated compounds, the exchange stiffness
is a function of the valence electron concentration and the crystallographic
ordering. The exchange stiffness increases when the valence electron
concentration and/or the amount of the L2$_1$ ordering increase. A qualitative
explanation for the dependence on the valence electron concentration is
provided.",0904.4194v1
2010-04-07,Single-Dirac-cone Z2 topological insulator phases in distorted Li2AgSb-class and related quantum critical Li-based spin-orbit compounds,"We have extended our new materials class search for the experimental
realization of Z2 topological insulators from binary [Bi2Se3-class, Xia et.al.,
Nature Phys. 5, 398 (2009)] and the ternary [Half-Heusler class, Lin et.al.,
arXiv:1003.0155v1 (2010); arXiv:1003.2615v1 (2010)] series to non-Heusler
Li-based ternary intermetallic series Li2M'X ($M'$=Cu, Ag, and Au, $X$=Sb and
Bi) with CuHg2Ti-type structure. We discovered that the distorted-Li2AgSb is a
lightweight compound harboring a 3D topological insulator state with Z2=-1
although the groundstate lies near a critical point, whereas the related
Li2CuSb-type compounds are topologically trivial. Non-Heusler ternary Li2M'X
series (with a number of variant compounds) we identified here is a new
platform for deriving novel stoichiometric compounds, artificial
quantum-well/heterostructures, nano-wires, nano-ribbons and nanocrystals. We
have grown some of these bulk materials (experimental results will be reported
separately).",1004.0999v1
2013-09-24,"Electronic structure and magnetism of new scandium-based full Heusler compounds: Sc2CoZ (Z=Si, Ge, Sn)","First principles FPLAPWcalculations were performed in the framework of
Density Functional Theory (DFT), to study the electronic structures and
magnetic properties for the new full-Heusler compounds: Sc2CoZ (Z=Si, Ge, Sn).
The investigated materials are stable against decomposition, in ferromagnetic
configuration and crystallize in the inverse Heusler structures. The
half-metallic properties as function of the variation of unit cell volumes are
analysed regarding the fourth main group constituent elements. The electronic
structure calculations for Sc2CoSi and Sc2CoSn show half-metallic characters,
with indirect band gaps of 0.544 eV and 0.408 eV at optimized lattice
parameters of 6.28 A and 6.62 A, respectively. For Sc2CoGe compound, the Fermi
energy is not pinned inside the energy band gap from minority density of
states, neither for unit cell contraction or for enlargement. The calculated
total magnetic moments are 1muB/f.u., for all compounds, in agreement with
Slater-Pauling rule.",1309.6256v3
2015-02-06,Long-term stability of phase-separated Half-Heusler compounds,"Half-Heusler (HH) compounds have shown high Figure of merits up to 1.5. The
key to these high thermoelectric efficiencies is an intrinsic phase separation,
which occurs in multicomponent Half-Heusler compounds and leads to an
significantly reduction of the thermal conductivity. For commercial
applications, compatible n- and p-type materials are essential and their
thermal stability under operating conditions, e.g. for an automotive up to 873
K, needs to be guaranteed. For the first time, the long-term stability of n-
and p-type HH materials is proved. We investigated HH materials based on the
Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both
compounds exhibit a maximum Seebeck coefficient of S around 210 muV/K and an
intrinsic phase separation into two HH phases. The dendritic microstructure is
temperature resistant and maintained the low thermal conductivity values (kappa
less than 4 W/Km). Our results emphasize that phase-separated HH compounds are
suitable low cost materials and can lead to enhanced thermoelectric
efficiencies beyond the set benchmark for industrial applications.",1502.01828v1
2018-01-31,Unconventional superconductivity and Surface pairing symmetry in Half-Heusler Compounds,"Signatures of nodal line/point superconductivity have been observed in
half-Heusler compounds, such as LnPtBi (Ln = Y, Lu). Topologically non-trivial
band structures, as well as topological surface states, has also been confirmed
by angular-resolved photoemission spectroscopy in these compounds. In this
work, we present a systematical classification of possible gap functions of
bulk states and surface states in half-Heusler compounds and the corresponding
topological properties based on the representations of crystalline symmetry
group. Different from all the previous studies based on four band Luttinger
model, our study starts with the six-band Kane model, which involves both four
p-orbital type of {\Gamma}8 bands and two s-orbital type of {\Gamma}6 bands.
Although the {\Gamma}6 bands are away from the Fermi energy, our results reveal
the importance of topological surface states, which originate from the band
inversion between {\Gamma}6 and {\Gamma}8 bands, in determining surface
properties of these compounds in the superconducting regime by combining
topological bulk state picture and non-trivial surface state picture.",1801.10286v1
2012-05-02,Superconductivity in the Heusler Family of Intermetallics,"Several physical properties of the superconducting Heusler compounds,
focusing on two systems (Y, Lu, Sc)Pd2Sn and APd2M, where A=Hf, Zr and M=Al,
In, are summarized and compared. The analysis of the data shows the importance
of the electron-phonon coupling for superconductivity in this family. We report
the superconducting parameters of YPd2Sn, which has the highest Tc among all
known Heusler superconductors.",1205.0433v1
2013-02-04,Disorder-induced cubic phase in Fe$_2$-based Heusler alloys,"Based on first-principles electronic structure calculations, we analyze the
chemical and magnetic mechanisms stabilizing the cubic phase in Fe$_2$-based
Heusler materials, which were previously predicted to be tetragonal when being
chemically ordered. In agreement with recent experimental data, we found that
these compounds crystallize within the so-called ""inverted"" cubic Heusler
structure perturbed by a certain portion of the intrinsic chemical disorder.
Understanding these mechanisms is a necessary step to guide towards the
successful future synthesis of the stable Fe$_2$-based tetragonal phases, which
are very promising candidates for the fabrication of rare-earth-free permanent
magnets.",1302.0713v1
2018-02-20,Ultrafast magnetization dynamics in pure and doped Heusler and inverse Heusler alloys,"By using a multiscale approach based on first-principles density functional
theory combined with atomistic spin dynamics, we investigate the electronic
structure and magnetization dynamics of an inverse Heusler and a Heusler
compound and their alloys, i. e. Mn$_{2-x}Z_x$CoAl and Mn$_{2-x}Z_x$VAl, where
$Z$ = Mo, W, Os and Ru, respectively. A signature of the ferrimagnetic ordering
of Mn$_{2}$CoAl and Mn$_{2}$VAl Heusler alloys is reflected in the calculated
Heisenberg exchange constants. They decay very rapidly with the interatomic
distance and have short range, which is a consequence of the existence of the
finite gap in the minority spin band. The calculated Gilbert damping parameter
of both Mn$_2$CoAl and Mn$_2$VAl is high compared to other half-metals, but
interestingly in the particular case of the inverse Mn$_{2}$CoAl alloys and due
to the spin-gapless semiconducting property, the damping parameters decrease
with the doping concentration in clear contradiction to the general trend.
Atomistic spin dynamics simulations predict ultrafast magnetisation switching
in Mn$_{2}$CoAl and Mn$_{2}$VAl under the influence of an external magnetic
field, starting from a threshold field of $2\text{T}$. Our overall finding
extends with Heusler and inverse Heusler alloys, the class of materials that
exhibits laser induced magnetic switching.",1802.07195v1
2017-02-27,Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: a systematic study,"With a view to the design of hard magnets without rare earths we explore the
possibility of large magnetocrystalline anisotropy energies in Heusler
compounds that are unstable with respect to a tetragonal distortion. We
consider the Heusler compounds Fe$_2$YZ with Y = (Ni, Co, Pt), and Co$_2$YZ
with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find
that for the Co$_2$NiZ, Co$_2$PtZ, and Fe$_2$PtZ families the cubic phase is
always, at $T=0$, unstable with respect to a tetragonal distortion, while, in
contrast, for the Fe$_2$NiZ and Fe$_2$CoZ families this is the case for only 2
compounds -- Fe$_2$CoGe and Fe$_2$CoSn. For all compounds in which a tetragonal
distortion occurs we calculate the MAE finding remarkably large values for the
Pt containing Heuslers, but also large values for a number of the other
compounds (e.g. Co$_2$NiGa has an MAE of -2.11~MJ/m$^3$). The tendency to a
tetragonal distortion we find to be strongly correlated with a high density of
states at the Fermi level in the cubic phase. As a corollary to this fact we
observe that upon doping compounds for which the cubic structure is stable such
that the Fermi level enters a region of high DOS, a tetragonal distortion is
induced and a correspondingly large value of the MAE is then observed.",1702.08150v1
2020-11-16,A high throughput search of efficient thermoelectric half-Heusler compounds,"Half-Heusler compounds have emerged as promising thermoelectric materials
that offer huge compositional space to tune their thermoelectric performance. A
class of stable half Heusler compounds formed from elements of three specific
groups in the periodic table viz.
X$_{p}$X$'_{1-p}$Y$_{q}$Y$'_{1-q}$Z$_{r}$Z$'_{1-r}$ (with X, X$'$= Ti, Zr, Hf,
Y, Y$'$ = Ni, Pd, Pt and Z, Z$'$ = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and
1) via various stoichiometric isoelectronic elemental substitution at the X, Y
and Z sites respectively is investigated. Intelligent filters are employed at
each step of our high throughput density functional theory calculations to
filter compounds with improved figure of merit. While confirming several known
results, the calculations also reveal unknown pathways to improve the
thermoelectric performance of the compound class. The 50% X as well as Z site
substitution of the parent Heusler individually are found to marginally enhance
the power factor for both the $p$- and $n$-type doping, while leading to
considerable enhancement in the figure of merit (by $\sim$24 %) specifically
due to lowering of the lattice thermal conductivity because of increase in
lattice disorder in approximately the same cell volume. Furthermore, the
present study confirms the experimental scenario that Y site substitution does
not lead to enhancement of the powerfactor because of the breaking of band
degeneracies at the high symmetry points. This work will serve as a
consolidated cost effective guideline for experimentalist working with this
compound class on enhancing the powerfactor and figure of merit of the
compositions.",2011.08134v1
2013-12-10,Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in Half-Heusler and Heusler limits,"Half-Heusler and Heusler compounds have been of great interest for several
decades for thermoelectric, magnetic, half-metallic and many other interesting
properties. Among these systems, Zr-Ni-Sn compounds are interesting
thermoelectrics which can go from semiconducting half-Heusler (HH) limit,
ZrNiSn, to metallic Heusler (FH) limit, ZrNi$_2$Sn. Recently Makogo et al. [J.
Am. Chem. Soc. 133, 18843 (2011)] found that dramatic improvement in the
thermoelectric power factor of HH can be achieved by putting excess Ni into the
system. This was attributed to an energy filtering mechanism due to the
formation of FH nanostructures in the HH matrix. Using density functional
theory we have investigated clustering and nanostructure formation in
HH$_{1-x}$FH$_x$ systems near the HH and FH ends and found that excess Ni atoms
in HH tend to stay close to each other and form nanoclusters of FH. On the
other hand, there is competing interaction between Ni-vacancies in FH which
prevent them from forming HH nano clusters. Effects of nano inclusions on the
electronic structure at both HH and FH ends will be discussed.",1312.2985v2
2022-05-05,Electronic band structure screening for Dirac points in Heuslers,"The Heusler compounds have provided a playground of material candidates for
various technological applications based on their highly diverse and tunable
properties, controlled by chemical composition and crystal structure. However,
physical exploration of the Heusler chemical space en masse is impossible in
practice, hindering the exploration of the chemical composition vs. proprieties
relationship. Many of these applications are related to the Heuslers electron
transport characteristics, which are embedded in their electronic band
structure (EBS). Here we we created a Heuslers dataset using the Materials
Project (MP) database -- retrieving both chemical composition and their EBSs.
We then used machine learning to develop a model correlating the composition
vs. number of Dirac points in the EBS for Heuslers and also other Cubic
compounds by identifying said Dirac points using an automated algorithm as well
as generating chemical composition and global crystal structure features. Our
ML model captures the overall trend, as well as identifies significant
electronic and global crystal structure features, however, the ML model
suffered from significant variance due to the lack of site specific features.
Future work on a methodology for handling atomic site specific features will
allow ML models to better match the underlying quantum mechanics governing the
properties (also based on site specific properties) and capture the electronic
properties in a more generalized approach.",2205.02547v1
2019-07-31,Perspective: Heusler interfaces -- opportunities beyond spintronics?,"Heusler compounds, in both cubic and hexagonal polymorphs, exhibit a
remarkable range of electronic, magnetic, elastic, and topological properties,
rivaling that of the transition metal oxides. To date, research on these
quantum materials has focused primarily on bulk magnetic and thermoelectric
properties or on applications in spintronics. More broadly, however, Heuslers
provide a platform for discovery and manipulation of emergent properties at
well-defined crystalline interfaces. Here, motivated by advances in the
epitaxial growth of layered Heusler heterostructures, I present a vision for
Heusler interfaces, focusing on the frontiers and challenges that lie beyond
spintronics. The ability to grow these materials epitaxially on technologically
important semiconductor substrates, such as GaAs, Ge, and Si, provides a direct
path for their integration with modern electronics. Further advances will
require new methods to control the stoichiometry and defects to ""electronic
grade"" quality, and to control the interface abruptness and ordering at the
atomic scale.",1908.00101v1
2005-05-25,Semimetalic antiferromagnetism in the half-Heusler compound CuMnSb,"The half-Heusler compound CuMnSb, the first antiferromagnet (AFM) in the
Mn-based class of Heuslers and half-Heuslers that contains several conventional
and half metallic ferromagnets, shows a peculiar stability of its magnetic
order in high magnetic fields. Density functional based studies reveal an
unusual nature of its unstable (and therefore unseen) paramagnetic state, which
for one electron less (CuMnSn, for example) would be a zero gap semiconductor
(accidentally so) between two sets of very narrow, topologically separate bands
of Mn 3d character. The extremely flat Mn 3d bands result from the environment:
Mn has four tetrahedrally coordinated Cu atoms whose 3d states lie well below
the Fermi level, and the other four tetrahedrally coordinated sites are empty,
leaving chemically isolated Mn 3d states. The AFM phase can be pictured
heuristically as a self-doped Cu$^{1+}$Mn$^{2+}$Sb$^{3-}$ compensated semimetal
with heavy mass electrons and light mass holes, with magnetic coupling
proceeding through Kondo and/or antiKondo coupling separately through the two
carrier types. The ratio of the linear specific heat coefficient and the
calculated Fermi level density of states indicates a large mass enhancement
$m^*/m \sim 5$, or larger if a correlated band structure is taken as the
reference.",0505624v1
2008-08-18,A Ni-based Superconductor: the Heusler Compound ZrNi$_2$Ga,"This work reports on the novel Heusler superconductor ZrNi2Ga. Compared to
other nickel-based superconductors with Heusler structure, ZrNi2Ga exhibits a
relatively high superconducting transition temperature of Tc=2.9 K and an upper
critical field of 1.5 T. Electronic structure calculations show that this
relatively high transition temperature is caused by a van Hove singularity,
which leads to an enhanced density of states at the Fermi energy. The van Hove
singularity originates from a higher order valence instability at the L-point
in the electronic structure. The enhanced density of states at the Fermi level
was confirmed by specific heat and susceptibility measurements. Although many
Heusler compounds are ferromagnetic, our measurements of ZrNi2Ga indicate a
paramagnetic state above Tc and could not reveal any traces of magnetic order
down to temperatures of at least 0.35 K. We investigated in detail the
superconducting state with specific heat, magnetization, and resistivity
measurements. The resulting data show the typical behavior of a conventional,
weakly coupled BCS (s-wave) superconductor.",0808.2356v1
2013-01-23,Data Storage: Review of Heusler Compounds,"In the recent decade, the family of Heusler compounds has attracted
tremendous scientific and technological interest in the field of spintronics.
This is essentially due to their exceptional magnetic properties, which qualify
them as promising functional materials in various data-storage devices, such as
giant-magnetoresistance spin valves, magnetic tunnel junctions, and
spin-transfer torque devices. In this article, we provide a comprehensive
review on the applications of the Heusler family in magnetic data storage. In
addition to their important roles in the performance improvement of these
devices, we also try to point out the challenges as well as possible solutions,
of the current Heusler-based devices. We hope that this review would spark
further investigation efforts into efficient incorporation of this eminent
family of materials into data storage applications by fully arousing their
intrinsic potential.",1301.5455v2
2014-12-01,Quality of Heusler Single Crystals Examined by Depth Dependent Positron Annihilation Techniques,"Heusler compounds exhibit a wide range of different electronic ground states
and are hence expected to be applicable as functional materials in novel
electronic and spintronic devices. Since the growth of large and defect-free
Heusler crystals is still challenging, single crystals of Fe2TiSn and Cu2MnAl
were grown by the optical floating zone technique. Two positron annihilation
techniques -Angular Correlation of Annihilation Radiation (ACAR) and Doppler
Broadening Spectroscopy (DBS)- were applied in order to study both, the
electronic structure and lattice defects. Recently, we succeeded to observe
clearly the anisotropy of the Fermi surface of Cu2MnAl, whereas the spectra of
Fe2TiSn were disturbed by foreign phases. In order to estimate the defect
concentration in different samples of Heusler compounds the positron diffusion
length was determined by DBS using a monoenergetic positron beam.",1412.0435v1
2015-02-11,High thermoelectric figure of merit in p-type Half-Heuslers by intrinsic phase separation,"Improvements in the thermoelectric properties of Half-Heusler materials have
been achieved by means of a micrometer-scale phase separation that increases
the phonon scattering and reduces the lattice thermal conductivity. A detailed
study of the p-type Half-Heusler compounds Ti(1-x)Hf(x)CoSb0.85Sn0.15 using
high-resolution synchrotron powder X-ray diffraction and element mapping
electron microscopy evidences the outstanding thermoelectric properties of this
system. A combination of intrinsic phase separation and adjustment of the
carrier concentration via Sn substitution is used to realize a record
thermoelectric figure of merit for p-type Half-Heusler compounds of ZT around
1.15 at 710C in Ti0.25Hf0.75CoSb0.85Sn0.15. The phase separation approach can
form a significant alternative to nanostructuring processing time, energy
consumption and increasing the thermoelectric efficiency.",1502.03336v1
2018-05-07,"Electronic, Elastic and X-ray spectroscopic properties of direct and inverse full Heusler compounds: DFT+U study","Half-metallicity, low magnetic damping and high curie temperature (TC) are
crucial for application in spintronics and full Heusler alloys in this regard
exhibit remarkable properties. Herein, we have considered Co2FeAl (CFA) and
Fe2CoAl (FCA) as a representative of direct and indirect full Heusler compounds
which crystallises in L21 and C1b phases, respectively. The theory of L21 type
Heusler alloys has been well established, however the fundamental understanding
of Fe2CoAl is still under developed. In this paper, we have employed density
functional theory (DFT) to study the electronic, elastic and X-ray
spectroscopic properties of Co2FeAl and Fe2CoAl. The electron exchange
correlation were treated within a generalized gradient approximation (GGA) as
PBE-scheme. In order to include the impact of valence electrons an onsite
Coulomb potential is added to GGA as GGA+U. Within both GGA and GGA+U, CFA
shows a half-metallic behaviour but FCA is metallic. The calculated values of
magnetic moment and TC are in close agreement with the experimental data.",1805.02618v1
2019-01-27,Correlation effects on ground-state properties of ternary Heusler alloys: first-principles study,"The strongly constrained and appropriately normed (SCAN) semi-local
functional for exchange-correlation is deployed to study the ground-state
properties of ternary Heusler alloys transforming martensitically. The
calculations are performed for ferromagnetic, ferrimagnetic, and
antiferromagnetic phases. Comparisons between SCAN and generalized gradient
approximation (GGA) are discussed. We find that SCAN yields smaller lattice
parameters and higher magnetic moments compared to the GGA corresponding values
for both austenite and martensite phases. Furthermore, in the case of
ferromagnetic and non-magnetic Heusler compounds, GGA and SCAN display similar
trends in the total energy as a function of lattice constant and tetragonal
ratio. However, for some ferrimagnetic Mn-rich Heusler compounds, different
magnetic ground states are found within GGA and SCAN.",1901.09460v1
2016-03-17,Ultrafast Local Magnetization and Demagnetization in Heusler Alloys,"With the goal of pushing Spintronic devices towards faster and faster
timescales, we demonstrate, using ab-intio time-dependent density functional
theory simulations of bulk Heusler compounds subject to ultrashort intense
laser pulses, that the local magnetic moment can increase or decrease in a few
femtoseconds. This speed is due to the all optical nature of the process, which
transfers spin moment from one sublattice to another. This transfer depends on
easily tunable laser parameters. By comparing the spin dynamics of a variety of
Heusler (or half-Heusler) compounds, we demonstrate that the density of states
explains the observed moment transfer; most the physics of inter sublattice
moment transfer is due to the flow of spin current which is governed by
availability of states above the Fermi level.",1603.05603v1
2021-06-02,MgPd$_2$Sb -- the first Mg-based Heusler-type superconductor,"We report the synthesis and physical properties of a full Heusler compound,
MgPd$_2$Sb, which we found to show superconductivity below $T_c$ = 2.2 K.
MgPd$_2$Sb was obtained by a two-step solid-state reaction method and its
purity and cubic crystal structure (Fm-3m, a=6.4523(1) \r{A}) were confirmed by
powder x-ray diffraction. Normal and superconducting states were studied by
electrical resistivity, magnetic susceptibility, and heat capacity
measurements. The results show that MgPd$_2$Sb is a type-II, weak coupling
superconductor ($\lambda_{e-p}$ = 0.53). The observed pressure dependence of
$T_c$ ($\Delta T_c / p \approx $ -0.23 K/GPa) is one of the strongest reported
for a superconducting Heusler compound. The electronic structure, phonons, and
electron-phonon coupling in MgPd$_2$Sb were theoretically investigated. The
obtained results are in agreement with the experiment, confirming the
electron-phonon coupling mechanism of superconductivity. We compare the
superconducting parameters tothose of all reported Heusler-type
superconductors.",2106.01133v2
2021-08-11,DFT and Monte Carlo simulations of the equiatomic quaternary Heusler Alloy CoFeCrP,"In this work, we study the equiatomic quaternary Heusler Alloy CoFeCrP using
two methods: DFT and Monte Carlo simulations. The DFT method allowed us to
illustrate the structural, electronic and magnetic properties of this alloy.
The ground state phase diagrams have been presented to show the stable
configurations in different physical parameter planes. On the other hand, the
Monte Carlo simulations, performed under the Metropolis algorithm, permitted to
deduce the critical the behavior of the equiatomic quaternary Heusler alloy
CoFeCrP. The structural properties results show that the phase of type I, of
this alloy is the most stable configuration. In addition, the band structures,
and density of states calculations results show that this compound exhibits a
half-metallic character with a 100 % of spin polarization (SP) at the
Fermi-level. The total magnetic moment of the Heusler compound is found to be
4.00 mu_B. Moreover, it is found that the Slater-Pauling is well described for
this alloy. Our results show that this material is a potential candidate for
the spintronic applications. This is due to its half-metallicity, its high spin
moments, its complete SP polarization and its high Curie temperature.",2108.05160v1
2020-01-20,Ab initio design of quaternary Heusler compounds for reconfigurable magnetic tunnel diodes and transistors,"Reconfigurable magnetic tunnel diodes and transistors are a new concept in
spintronics. The realization of such a device requires the use of materials
with unique spin-dependent electronic properties such as half-metallic magnets
(HMMs) and spin-gapless semiconductors (SGSs). Quaternary Heusler compounds
offer a unique platform to design within the same family of compounds HMMs and
SGSs with similar lattice constants to make coherent growth of the consecutive
spacers of the device possible. Employing state-of-the-art first-principles
calculations, we scan the quaternary Heusler compounds and identify suitable
candidates for these spintronic devices combining the desirable properties: (i)
HMMs with sizable energy gap or SGSs with spin gaps both below and above the
Fermi level, (ii) high Curie temperature, (iii) convex hull energy distance
less than 0.20 eV, and (iv) negative formation energies. Our results pave the
way for the experimental realization of the proposed magnetic tunnel diodes and
transistors.",2001.07029v1
2018-10-11,Unconventional transport behavior in the Quaternary Heusler compounds CoFeTiSn and CoFeVGa,"We report here the electrical transport and magnetic properties of the newly
synthesized quaternary Heusler compound CoFeTiSn and CoFeVGa. We observe a
striking change in the electronic transport properties of CoFeTiSn as the
system undergoes the paramagnetic to ferromagnetic transition. While the sample
shows an activated semiconducting behaviour in the paramagnetic phase, it turns
abruptly to a metallic phase with the onset of ferromagnetic transition. We
have compared the system with other Hesuler compounds showing similar anomaly
in transport, and it appears that CoFeTiSn has much similarities with the
Fe$_2$VAl compound having pseudogap in the paramagnetic phase. In sharp
contrast, CoFeVGa shows a predominantly semiconducting behaviour down to 90 K,
below which it shows a window of metallic region. Both the compositions show
negative Seebeck coefficient varying linearly with temperature. The value of
the Seebeck coefficient of CoFeTiSn is comparable to that of many Heusler
alloys identified as potential thermoelectric materials.",1810.04865v1
2020-08-11,"Anomalous Hall effect in half-metallic Heusler compound Co$_{2}$Ti$X$ ($X$=Si, Ge)","Though Weyl fermions have recently been observed in several materials with
broken inversion symmetry, there are very few examples of such systems with
broken time reversal symmetry. Various Co$_{2}$-based half-metallic
ferromagnetic Heusler compounds are lately predicted to host Weyl type
excitations in their band structure. These magnetic Heusler compounds with
broken time reversal symmetry are expected to show a large momentum space Berry
curvature, which introduces several exotic magneto-transport properties. In
this report, we present systematic analysis of experimental results on
anomalous Hall effect (AHE) in Co$_2$Ti$X$ ($X$=Si and Ge). This study is an
attempt to understand the role of Berry curvature on AHE in Co$_2$Ti$X$ family
of materials. The anomalous Hall resistivity is observed to scale quadratically
with the longitudinal resistivity for both the compounds. The detailed analysis
indicates that in anomalous Hall conductivity, the intrinsic Karplus-Luttinger
Berry phase mechanism dominates over the extrinsic skew scattering and
side-jump mechanism.",2008.04837v1
2020-11-12,Anomalous Hall effect and negative longitudinal magnetoresistance in half-Heusler topological semimetal candidates TbPtBi and HoPtBi,"Half-Heusler compounds have attracted significant attention because of their
topologically non-trivial electronic structure, which leads to unusual electron
transport properties. We thoroughly investigated the magnetotransport
properties of high-quality single crystals of two half-Heusler phases, TbPtBi
and HoPtBi, in pursuit of the characteristic features of topologically
non-trivial electronic states. Both studied compounds are characterized by the
giant values of transverse magnetoresistance with no sign of saturation in
magnetic field up to 14 T. HoPtBi demonstrates the Shubnikov-de Haas effect
with two principal frequencies, indicating a complex Fermi surface; the
extracted values of carrier effective masses are rather small, $0.18\,m_e$ and
$0.27\,m_e$. The investigated compounds exhibit negative longitudinal
magnetoresistance and anomalous Hall effect, which likely arise from a nonzero
Berry curvature. Both compounds show strongly anisotropic magnetoresistance,
that in HoPtBi exhibits a butterfly-like behavior.",2011.06290v1
2022-01-08,Atomic disorder and Berry phase driven anomalous Hall effect in Co2FeAl Heusler compound,"Co2-based Heusler compounds are the promising materials for the spintronics
application due to their high Curie temperature, large spin-polarization, large
magnetization density, and exotic transport properties. In the present
manuscript, we report the anomalous Hall effect (AHE) in a polycrystalline
Co2FeAl Heusler compound using combined experimental and theoretical studies.
The Rietveld analysis of high-resolution synchrotron x-ray diffraction data
reveals a large degree (~50 %) of antisite disorder between Fe and Al atoms.
The analysis of anomalous transport data provides the experimental anomalous
Hall conductivity (AHC) about 227 S/cm at 2 K with an intrinsic contribution of
155 S/cm, which has nearly constant variation with temperature. The detailed
scaling analysis of anomalous Hall resistivity suggests that the AHE in Co2FeAl
is governed by the Berry phase driven intrinsic mechanism. Our theoretical
calculations reveal that the disorder present in Co2FeAl compound enhances the
Berry curvature induced intrinsic AHC.",2201.02864v1
2018-01-11,"Structural, elastic, electronic, magnetic and thermoelectric properties of new quaternary Heusler compounds CoZrMnX (X=Al, Ga, Ge, In)","We have performed a comprehensive set of first principles calculations to
study the structural, elastic, electronic, magnetic and transport properties of
new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In). The results
showed that all the quaternary Heusler compounds were stable in Type(I)
structure. CoZrMnX are elastically stable and relatively hard materials.
CoZrMnAl, CoZrMnGa, and CoZrMnIn are found to be ductile and CoZrMnGe is
brittle in nature. The calculated Debye temperatures of all compounds are
relatively high. The electronic structure calculations reveal that CoZrMnAl is
nearly half metallic, CoZrMnGa and CoZrMnIn are metallic, and CoZrMnGe is a
narrow indirect bandgap semiconductor. The calculated magnetic properties
implies that CoZrMnAl, CoZrMnGa, and CoZrMnIn are ferromagnetic while CoZrMnGe
is non-magnetic material. The CoZrMnAl is highly spin-polarized (96%) and
CoZrMnGe is non-spin-polarized. Seebeck coefficent (S) in CoZrMnGe is
relatively high (-106 {\mu}V/K at 650K) due to its semiconducting nature. The
calculated thermoelectric figure of merit CoZrMnGe is 0.1 at 600K and for
CoZrMnIn it is also 0.1 at 900 K. We hope our interesting results will inspire
experimentalist to synthesis the new quaternary Heusler compounds CoZrMnX (X
=Al, Ga, Ge, In).",1801.03719v1
2023-09-14,Chemical-substitution-driven giant anomalous Hall and Nernst effects in magnetic cubic Heusler compounds,"Chemical substitution efficiently optimizes the physical properties of
Heusler compounds, especially their anomalous transport properties, including
anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC). This
study systematically investigates the effect of chemical substitution on AHC
and ANC in 1493 magnetic cubic Heusler compounds using high-throughput
first-principles calculations. Notable trends emerge in Co- and Rh-based
compounds, where chemical substitution effectively enhances the AHC and ANC.
Intriguingly, certain chemically substituted candidates exhibit outstanding
enhancement in AHCs and ANCs, such as (Co$_{0.8}$Ni$_{0.2}$)$_2$FeSn with
considerable AHC and ANC values of $-2567.78$ S cm$^{-1}$ and $8.27$ A
m$^{-1}$K$^{-1}$, respectively, and (Rh$_{0.8}$Ru$_{0.2}$)$_2$MnIn with an AHC
of $1950.49$ S cm$^{-1}$. In particular, an extraordinary ANC of $8.57$ A
m$^{-1}$K$^{-1}$ is identified exclusively in Rh$_2$Co$_{0.7}$Fe$_{0.3}$In,
nearly double the maximum value of $4.36$ A m$^{-1}$K$^{-1}$ observed in the
stoichiometric Rh$_2$CoIn. A comprehensive band structure analysis underscores
that the notable enhancement in ANC arises from the creation and modification
of the energy-dependent nodal lines through chemical substitution. This
mechanism generates a robust Berry curvature, resulting in significant ANCs.
These findings emphasize the pivotal role of chemical substitution in
engineering high-performance materials, thereby expanding the horizons of
transport property optimization within Heusler compounds.",2309.07722v3
2016-10-07,Computational Investigation of Half-Heusler Compounds for Spintronics Applications,"We present first-principles density functional calculations of the electronic
structure, magnetism, and structural stability of 378 $\textit{XYZ}$
half-Heusler compounds (with $X=$ Cr, Mn, Fe, Co, Ni, Ru, Rh, $Y=$ Ti, V, Cr,
Mn, Fe, Ni, $Z=$ Al, Ga, In, Si, Ge, Sn, P, As, Sb). We find that a
""Slater-Pauling density of states"" with a gap or pseudogap at three states per
atom below the gap in at least one spin channel is a common feature in
half-Heusler compounds. We find that the presence of such a gap at the Fermi
energy in one or both spin channels contributes greatly to the stability of a
half-Heusler compound. We calculate the formation energy of each compound and
systematically investigate its stability against all other phases in the Open
Quantum Materials Database (OQMD). We represent the thermodynamic phase
stability of each compound as its distance from the convex hull of stable
phases in the respective chemical space and show that the hull distance of a
compound is a good measure of the likelihood of its experimental synthesis. We
identify 26 18-electron semiconductors, 45 half-metals, and 34 near half-metals
with negative formation energy, that follow the Slater-Pauling rule of three
electrons per atom. Our calculations predict new thermodynamically stable
semiconducting phases NiScAs, RhTiP, and RuVAs, which merit further
experimental exploration. Further, two interesting zero-moment half-metals,
CrMnAs and MnCrAs, are calculated to have negative formation energy. In
addition, our calculations predict a number of new, hitherto unreported,
semiconducting (e.g., CoVGe, FeVAs), half-metallic (e.g., RhVSb), near
half-metallic (e.g., CoFeSb, CoVP) half-Heusler compounds to lie close to the
respective convex hull of stable phases, and thus may be experimentally
realized under suitable synthesis conditions, resulting in potential candidates
for various spintronics applications.",1610.02444v2
2006-05-29,Epitaxy of thin films of the Heusler compound Co2Cr0.6Fe0.4Al,"Epitaxial thin films of the highly spin polarized Heusler compound
Co2Cr0.6Fe0.4Al are deposited by dc magnetron sputtering. It is shown by XRD
and TEM investigations how the use of an Fe buffer layer on MgO(100) substrates
supports the growth of highly ordered Co2Cr0.6Fe0.4Al at low deposition
temperatures. The as grown samples show a relatively large ordered magnetic
moment of mu = 3.0mu_B/f.u. providing evidence for a low level of disorder.",0605698v2
2006-09-02,A new diluted magnetic semiconductor: The half-metallic ferromagnet CoTi(1-x)FexSb,"Half-Heusler compounds with 18 valence electrons are semi-conducting. It will
be shown that doping with electrons results in half-metallic ferromagnets,
similar to the case of diluted semi-conductors. CoTiSb is known to be a
semi-conducting Half-Heusler compound. Doping by Fe is expected to result in
ferromagnetic order. It was found that Ti can be replaced by up to about 10% Fe
while its crystal structure still remains C1b, which was proved by X-ray powder
diffraction. SQUID magnetometry revealed a magnetic moment of 0.32 mB per unit
cell at 5K.",0609042v1
2011-10-13,Berry-curvatures and anomalous Hall effect in Heusler compounds,"Berry curvatures are computed for a set of Heusler compounds using density
functional (DF) calculations and the wave functions that DF provide. The
anomalous Hall conductivity is obtained from the Berry curvatures. It is
compared with experimental values in the case of Co$_2$CrAl and Co$_2$MnAl. A
notable trend cannot be seen but the range of values is quite enormous. The
results for the anomalous Hall conductivities and their large variations can be
qualitatively understood by means of the band structure and the Fermi-surface
topology.",1110.2878v1
2013-09-25,Prediction of half metallic properties in Ti\raisebox{-.2ex}{\scriptsize 2}CoSi Heusler alloy based on density functional theory,"The electronic and magnetic properties of Ti\raisebox{-.2ex}{\scriptsize
2}CoSi Heusler compound are investigated using density functional calculations.
The optimized lattice constant is found to be 6.030 A. The compound is a
half-metallic ferromagnet with an energy gap in minority spin channel of 0.652
eV at equilibrium lattice constant, which leads to a 100% spin-polarization.
The obtained total magnetic moment from spin-polarized calculations is 3.0
$\mu_{B}$ for values of lattice constants higher than 5.941 A. The
half-metallicity is spoiled for a compressed volume of 4%, suggesting a
possible application as pressure sensitive material.",1309.6427v1
2013-12-20,Multiple phases in sputtered Cr2CoGa films,"By magnetron co-sputtering, thin films of a nominal Cr2CoGa compound were
deposited on MgO and MgAl2O4. To achieve crystallisation in the inverse Heusler
structure, different heat treatments were tested. Instead of the inverse
Heusler structure, we observed phase separation and precipitate formation in
dependence on the heat treatment. The main precipitate is Cr3Ga in A15
structure. The remainder forms Co-rich CoGa in the B2 structure and possibly
Cr-rich CoCr in the sigma-phase.",1312.6014v2
2014-11-26,Theoretical investigations of electronic structure and magnetism in Zr2CoSn full-Heusler compound,"The half-metallic properties of a new and promising full-Heusler compound,
Zr2CoSn, are investigated by means of ab initio calculations within the Density
Functional Theory framework. The ferromagnetic ordered Hg2CuTi-type crystal
structure is energetically favorable and the optimized lattice parameter is
6.76 A. The total magnetic moment calculated is 3 uB/f.u. and follows a typical
Slater-Pauling dependence. The half metallicity disappears if the unit cell
volume is contracted by 5 %.",1411.7154v1
2018-04-01,"First-principles study on thermoelectric properties of half-Heusler compounds CoMSb(M=Sc, Ti, V, Cr, and Mn)","We have performed systematic density functional calculations and evaluated
thermoelectric properties, See- beck coefficient and anomalous Nernst
coefficient of half-Heusler comounds CoMSb(M=Sc, Ti, V, Cr, and Mn). The
carrier concentration dependence of Seebeck coefficients in nonmagnetic
compounds are in good agreement with experimental values. We found that the
half-metallic ferromagnetic CoMnSb show large anomalous Nernst effect
originating from Berry curvature at the Brillouin zone boundary. These results
help to understanding for the mechanism of large anomalous Nernst coefficient
and give us a clue to design high performance magnetic thermoelectric
materials.",1804.00297v1
2007-10-30,Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds,"The XYZ half-Heusler crystal structure can conveniently be described as a
tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X
species. This description is well suited to understand the electronic structure
of semiconducting 8-electron compounds such as LiAlSi (formulated
Li$^+$[AlSi]$^-$) or semiconducting 18-electron compounds such as TiCoSb
(formulated Ti$^{4+}$[CoSb]$^{4-}$). The basis for this is that [AlSi]$^-$
(with the same electron count as Si$_2$) and [CoSb]$^{4-}$ (the same electron
count as GaSb), are both structurally and electronically, zinc-blende
semiconductors. The electronic structure of half-metallic ferromagnets in this
structure type can then be described as semiconductors with stuffing magnetic
ions which have a local moment: For example, 22 electron MnNiSb can be written
Mn$^{3+}$[NiSb]$^{3-}$. The tendency in the 18 electron compound for a
semiconducting gap -- believed to arise from strong covalency -- is carried
over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly
propose the systematic examination of 18-electron hexagonal compounds for
semiconducting gaps; these would be the ""stuffed wurtzite"" analogues of the
""stuffed zinc blende"" half-Heusler compounds. These semiconductors could then
serve as the basis for possibly new families of half-metallic compounds,
attained through appropriate replacement of non-magnetic ions by magnetic ones.
These semiconductors and semimetals with tunable charge carrier concentrations
could also be interesting in the context of magnetoresistive and thermoelectric
materials.",0710.5769v1
2006-11-22,Magnetism and structure of magnetic multilayers based on the fully spin polarized Heusler alloys Co2MnGe and Co2MnSn,"Our Introduction starts with a short general review of the magnetic and
structural properties of the Heusler compounds which are under discussion in
this book. Then, more specifically, we come to the discussion of our
experimental results on multilayers composed of the Heusler alloys Co2MnGe and
Co2MnSn with V or Au as interlayers. The experimental methods we apply combine
magnetization and magneto-resistivity measurements, x-ray diffraction and
reflectivity, soft x-ray magnetic circular dichroism and spin polarized neutron
reflectivity. We find that below a critical thickness of the Heusler layers at
typically dcr = 1.5 nm the ferromagnetic order is lost and spin glass order
occurs instead. For very thin ferromagnetic Heusler layers there are
peculiarities in the magnetic order which are unusual when compared to
conventional ferromagnetic transition metal multilayer systems. In [Co2MnGe/Au]
multilayers there is an exchange bias shift at the ferromagnetic hysteresis
loops at low temperatures caused by spin glass ordering at the interface. In
[Co2MnGe/V] multilayers we observe an antiferromagnetic interlayer long range
ordering below a well defined Neel temperature originating from the dipolar
stray fields at the magnetically rough Heusler layer interfaces.",0611590v1
2010-02-28,Tunable Multifunctional Topological Insulators in Ternary Heusler Compounds,"Recently the Quantum Spin Hall effect (QSH) was theoretically predicted and
experimentally realized in a quantum wells based on binary semiconductor
HgTe[1-3]. QSH state and topological insulators are the new states of quantum
matter interesting both for fundamental condensed matter physics and material
science[1-11]. Many of Heusler compounds with C1b structure are ternary
semiconductors which are structurally and electronically related to the binary
semiconductors. The diversity of Heusler materials opens wide possibilities for
tuning the band gap and setting the desired band inversion by choosing
compounds with appropriate hybridization strength (by lattice parameter) and
the magnitude of spin-orbit coupling (by the atomic charge). Based on the
first-principle calculations we demonstrate that around fifty Heusler compounds
show the band inversion similar to HgTe. The topological state in these
zero-gap semiconductors can be created by applying strain or by designing an
appropriate quantum well structure, similar to the case of HgTe. Many of these
ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the
rare earth element Ln which can realize additional properties ranging from
superconductivity (e. g. LaPtBi[12]) to magnetism (e. g. GdPtBi[13]) and
heavy-fermion behavior (e. g. YbPtBi[14]). These properties can open new
research directions in realizing the quantized anomalous Hall effect and
topological superconductors.",1003.0193v1
2021-06-27,Ferromagnetic Cr4PtGa17: A Novel Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice,"We describe the crystal structure and elementary magnetic properties of a
previously unreported ternary intermetallic compound, Cr4PtGa17, which
crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group
R3m. The crystal structure is closely related to those of XYZ half-Heusler
compounds, where X, Y and Z are reported to be single elements only, occupying
three different face-centered cubic sublattices. The new material, Cr4PtGa17,
can be most straightforwardly illustrated by writing the formula as
(PtGa2)(Cr4Ga14)Ga (X=PtGa2, Y = Cr4Ga14, Z = Ga), that is, the X and Y sites
are occupied by clusters instead of single elements. The magnetic Cr occupies a
breathing pyrochlore lattice. Ferromagnetic ordering is found below TC ~61 K,
by both neutron diffraction and magnetometer studies, with a small, saturated
moment of ~0.25 muB/Cr observed at 2 K, making Cr4PtGa17 the first
ferromagnetically ordered material with a breathing pyrochlore lattice. A
magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that
the material has a nearly-half-metallic electronic structure. The new material,
Cr4PtGa17, the first realization of both a half-Heusler-type structure and a
breathing pyrochlore lattice, might pave a new way to achieve novel types of
half-Heusler compounds.",2106.14296v2
2023-01-02,Double Half-Heusler Alloys X$_2$Ni$_2$InSb (X= Zr/Hf) with promising Thermoelectric Performance: Role of varying structural phases,"Double half-heusler alloys are the new class of compounds which can be seen
as transmuted version of two single half-heusler with higher flexibility of
tuning their properties. Here, we report a detailed study of thermoelectric
(TE) properties of two double half-heusler (HH) alloys X$_2$Ni$_2$InSb
(X=Hf/Zr), using first-principles calculation. These alloys exhibit a rich
phase diagram with the possibility of tetragonal, cubic and solid solution
phase at different temperature range. As such, a comparative study of TE
properties of all these phases is performed. The ordered phases show quite
favorable electronic transport as compared to the disordered ones in both
compounds. Lattice thermal conductivity of double HH alloys is lower than their
ternary counter-part, making them most promising for TE application. Simulated
band gap, obtained using hybrid functional, of ordered phases of
Hf$_2$Ni$_2$InSb and Zr$_2$Ni$_2$InSb lie in the range 0.24-0.4 eV and
0.17-0.59 eV respectively, while for disordered phase, it is 0.05- 0.06 eV.
Hf$_2$Ni$_2$InSb shows a reasonably high ZT value of $\sim$ 2.19, while
Zr$_2$Ni$_2$InSb yields 2.46 at high temperature for n-type conduction in
tetragonal phase. The ZT value for p-type conduction is also quite promising
($\sim$ 1.35 and $\sim$ 2.19 for Hf- and Zr-based compounds). In both the
compounds, electronic transport (Seebeck and electrical conductivity) plays the
dominant role for the high ZT-value. Keeping in mind the promising TE
performance, we propose immediate attention from experimentalists to synthesize
and cross validate our findings for these new candidate materials.",2301.00598v1
2023-02-07,Colossal anomalous Hall and Nernst effect from the breaking of nodal-line symmetry in Cu2CoSn Weyl semimetal: A first-principles study,"The presence of topological band crossings near the Fermi energy is essential
for the realization of large anomalous transport properties in the materials.
The topological semimetals (TSMs) host such properties owing to their unique
topological band structure such as Weyl points or nodal lines (NLs), that is
protected by certain symmetries of the crystal. When the NLs break out in the
system due to perturbation in Hamiltonian, a large Berry curvature arises in
the surrounding area of the gapped NL. In the present work, we studied
anomalous transport properties of Cu2CoSn compound, which has a cubic Heusler
crystal structure (space group: Fm-3m). The Cu2CoSn full Heusler compound
possesses three NLs in the absence of spin-orbit coupling close to the Fermi
level. These NLs gap out with the consideration of the SOC and a large Berry
curvature observed along the gapped NLs. The integral of Berry curvature gives
the intrinsic anomalous Hall conductivity (AHC) about 1003 S/cm and the
anomalous Nernst conductivity (ANC) of about 3.98 A/m-K at the Fermi level.
These values of AHC and ANC are comparable to the largest reported values for
the Co2MnGa Heusler compound. Therefore, Cu2CoSn becomes a newborn member of
the family of full Heusler compounds, which possesses giant AHC and ANC that
can be useful for the spintronics application.",2302.03279v1
2023-02-09,Spin-polarized two-dimensional electron/hole gas at the interface of non-magnetic semiconducting half-Heusler compounds: Modified Slater-Pauling rule for half-metallicity at the interface,"Half-Heusler compounds with 18 valence electrons per unit cell are well-known
non-magnetic semiconductors. Employing first-principles electronic band
structure calculations, we study the interface properties of the half-Heusler
heterojunctions based on FeVSb, CoTiSb, CoVSn, and NiTiSn compounds, which
belong to this category of materials. Our results show that several of these
heterojunction interfaces become not only metallic but also magnetic. The
emergence of spin-polarization is accompanied by the formation of
two-dimensional electron gas (2DEG) or hole gas (2DHG) at the interface. We
qualitatively discuss the origin of the spin polarization at the interfaces on
the basis of the Stoner model. For the cases of magnetic interfaces where
half-metallicity is also present, we propose a modified Slater-Pauling rule
similar to the one for bulk half-metallic half-Heusler compounds. Additionally,
we calculate exchange parameters, Curie temperatures and magnetic anisotropy
energies for magnetic interfaces. Our study, combined with the recent
experimental evidence for the presence of 2DEG at CoTiSb/NiTiSn heterojunctions
might motivate future efforts and studies toward the experimental realization
of devices using the proposed heterojunctions.",2302.04563v1
2023-06-07,Searching for ductile superconducting Heusler X2YZ compounds,"Heusler compounds have always attracted a great deal of attention from
researchers thanks to a wealth of interesting properties for technological
applications. They are intermetallic ductile compounds, and some of them have
been found to be superconducting. With this in mind, we perform an extensive
study of the superconducting and elastic properties of the cubic (full-)Heusler
family. Starting from thermodynamically stable compounds, we use ab initio
methods for the calculation of the phonon spectra, electron-phonon couplings,
superconducting critical temperatures and elastic tensors. By analyzing the
statistical distributions of these properties and comparing them to
anti-perovskites we recognize universal behaviors that should be common to all
conventional superconductors while others turn out to be specific to the
material family. The resulting data is used to train interpretable and
predictive machine learning models, that are used to extend our knowledge of
superconductivity in Heuslers and to provide an interpretation of our results.
In total, we discover a total of 8 hypothetical materials with critical
temperatures above 10 K, to be compared with the current record of Tc = 4.7 K
in this family. Furthermore, we expect most of these materials to be highly
ductile, making them potential candidates for the manufacture of wires and
tapes for superconducting magnets.",2306.04439v1
2019-10-07,Accurate high-throughput screening of I-II-V 8-electron Half-Heusler compounds for renewable-energy applications,"Renewable energy resources have emerged as the best alternatives to fossil
fuel energy which are rapidly declining with time. Here, eight valence-electron
count Half-Heusler(HH) alloys have been studied using reliable first principles
calculations in the search of potential candidates for renewable energy
applications like thermoelectric (TE), solar harvesting, topological insulator
(TI) and transparent conductor (TC) applications. The initial screening
parameters used for our study are chemical and thermal stability, band gap,
nature of bandgap and band inversion strength. We have performed quasistatic
G0W0 calculation starting from HSE groundstate wavefunction to predict the most
accurate estimation of bandgap for these class of compounds. A total of 960
compounds were simulated. 121 out of 960 compounds were found to be thermally
and chemically stable. 31 compounds with bandgap less than 1.5 eV were studied
for thermoelectric application out of which 13 compounds were found to show
thermoelectric figure of merit ZT > 0.7 for both p-type and n-type conduction.
30 compounds with band gap 1-1.8 eV were studied for optoelectronic application
out of which 13 compounds were found to show Spectroscopic Limited Maximum
Efficiency (SLME) more than 20%, comparable to existing state of the art
materials. 21 compounds were found to show band inversion at ambient conditions
which is a necessary condition for topological insulators. The surface band
structure calculations for one of the promising candidate was done to check
robustness of the topological behaviour. 29 compounds were found to have
bandgap more than 2 eV which are promoted for transparent conductor
applications with further band engineering. We strongly believe that our
calculations will give useful insights to experimentalists for synthesizing and
investigating proposed compounds for different energy applications.",1910.02984v1
2023-03-04,Giant anomalous Hall and Nernst conductivities in magnetic all-$d$ metal Heusler alloys,"All-$d$ Heuslers are a category of novel compounds combining versatile
functionalities such as caloric responses and spintronics with enhanced
mechanical properties. Despite the promising transport properties (anomalous
Hall (AHC) and anomalous Nernst (ANC) conductivities) shown in the conventional
Co$_2$XY Heuslers with $p$-$d$ hybridization, the all-$d$ Heuslers with only
$d$-$d$ hybridization open a new horizon to search for new candidates with
outstanding transport properties. In this work, we evaluate the AHC and ANC for
thermodynamically stable ferro/ferri-magnetic all-$d$-metal regular Heusler
compounds based on high-throughput first-principles calculations. It is
observed that quite a few materials exhibit giant AHCs and ANCs, such as cubic
Re$_2$TaMn with an AHC of 2011 S/cm, and tetragonal Pt$_2$CrRh with an AHC of
1966 S/cm and an ANC of 7.50 A/mK. Comprehensive analysis on the electronic
structure reveals that the high AHC can be attributed to the occurrence of the
Weyl nodes or gapped nodal lines in the neighbourhood of the Fermi level. The
correlations between such transport properties and the number of valence
electrons are also thoroughly investigated, which provides a practical guidance
to tailor AHC and ANC via chemical doping for transverse thermoelectric
applications.",2303.02351v1
2007-09-26,Role of defects and disorder in the half-metallic full-Heusler compounds,"Half-metallic ferromagnets and especially the full-Heusler alloys containing
Co are at the center of scientific research due to their potential applications
in spintronics. For realistic devices it is important to control accurately the
creation of defects in these alloys. We review some of our late results on the
role of defects and impurities in these compounds. More precisely we present
results for the following cases (i) doping and disorder in Co$_2$Cr(Mn)Al(Si)
alloys, (ii) half-metallic ferrimagnetism appeared due to the creation of
Cr(Mn) antisites in these alloys, (iii) Co-doping in Mn$_2$VAl(Si) alloys
leading to half-metallic antiferromagnetism, and finally (iv) the occurrence of
vacancies in the full-Heusler alloys containing Co and Mn. These results are
susceptible of encouraging further theoretical and experimental research in the
properties of these compounds.",0709.4183v2
2010-07-31,Half-Heusler Compounds as a New Class of Three-Dimensional Topological Insulators,"Using first-principles calculations within density functional theory, we
explore the feasibility of converting ternary half-Heusler compounds into a new
class of three-dimensional topological insulators (3DTI). We demonstrate that
the electronic structure of unstrained LaPtBi as a prototype system exhibits
distinct band-inversion feature. The 3DTI phase is realized by applying a
uniaxial strain along the [001] direction, which opens a bandgap while
preserving the inverted band order. A definitive proof of the strained LaPtBi
as a 3DTI is provided by directly calculating the topological Z2 invariants in
systems without inversion symmetry. We discuss the implications of the present
study to other half-Heusler compounds as 3DTI, which, together with the
magnetic and superconducting properties of these materials, may provide a rich
platform for novel quantum phenomena.",1008.0057v1
2010-11-05,Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films,"We correlate simultaneously recorded magnetotransport and spatially resolved
magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films
micropatterned into Hall bars. Room temperature MOKE images reveal the
nucleation and propagation of domains in an externally applied magnetic field
and are used to extract a macrospin corresponding to the mean magnetization
direction in the Hall bar. The anisotropic magnetoresistance calculated using
this macrospin is in excellent agreement with magnetoresistance measurements.
This suggests that the magnetotransport in Heusler compounds can be adequately
simulated using simple macrospin models, while the magnetoresistance
contribution due to domain walls is of negligible importance.",1011.1417v1
2011-07-31,Room-temperature generation of giant pure spin currents using Co$_2$FeSi spin injectors,"Generation, manipulation, and detection of a pure spin current, i.e., the
flow of spin angular momentum without a charge current, are prospective
approaches for realizing next-generation spintronic devices with ultra low
electric power consumptions. Conventional ferromagnetic electrodes such as Co
and NiFe have so far been utilized as a spin injector for generating the pure
spin currents in nonmagnetic channels. However, the generation efficiency of
the pure spin currents is extremely low at room temperature, giving rise to a
serious obstacle for device applications. Here, we demonstrate the generation
of giant pure spin currents at room temperature in lateral spin valve devices
with a highly ordered Heusler-compound Co$_2$FeSi spin injector. The generation
efficiency of the pure spin currents for the Co$_2$FeSi spin injectors reaches
approximately one hundred times as large as that for NiFe ones, indicating that
Heusler-compound spin injectors enable us to materialize a high-performance
lateral spin device. The present study is a technological jump in spintronics
and indicates the great potential of ferromagnetic Heusler compounds with half
metallicity for generating pure spin currents.",1108.0156v2
2011-11-03,Estimation of the spin polarization for Heusler-compound thin films by means of nonlocal spin-valve measurements: Comparison of Co$_{2}$FeSi and Fe$_{3}$Si,"We study room-temperature generation and detection of pure spin currents
using lateral spin-valve devices with Heusler-compound electrodes, Co$_{2}$FeSi
(CFS) or Fe$_{3}$Si (FS). The magnitude of the nonlocal spin-valve (NLSV)
signals is seriously affected by the dispersion of the resistivity peculiarly
observed in the low-temperature grown Heusler compounds with ordered
structures. From the analysis based on the one-dimensional spin diffusion
model, we find that the spin polarization monotonically increases with
decreasing the resistivity, which depends on the structural ordering, for both
CFS and FS electrodes, and verify that CFS has relatively large spin
polarization compared with FS.",1111.0742v2
2012-10-17,GW study of the half-metallic Heusler compounds Co2MnSi and Co2FeSi,"Quasiparticle spectra of potentially half-metallic Co2MnSi and Co2FeSi
Heusler compounds have been calculated within the one-shot GW approximation in
an all-electron framework without adjustable parameters. For Co2FeSi the
many-body corrections are crucial: a pseudogap opens and good agreement of the
magnetic moment with experiment is obtained. Otherwise, however, the changes
with respect to the density-functional-theory starting point are moderate. For
both cases we find that photoemission and x-ray absorption spectra are well
described by the calculations. By comparison with the GW density of states, we
conclude that the Kohn-Sham eigenvalue spectrum provides a reasonable
approximation for the quasiparticle spectrum of the Heusler compounds
considered in this work.",1210.4776v1
2012-10-29,Modified Becke-Johnson potential investigation of half-metallic Heusler compounds,"We have investigated the electronic structures of various potentially
half-metallic Heusler compounds with the Tran-Blaha modified Becke-Johnson
(TB-mBJLDA) potential within the density functional theory. The half-metallic
gaps are considerably enhanced with respect to values from the
Perdew-Burke-Ernzerhof (PBE) functional. In particular the unoccupied densities
of states are modified by mBJLDA, and agreement with experiment is considerably
worse than for PBE. The agreement of the densities of states can be improved by
reducing the Tran-Blaha parameter c. However, ground state properties such as
the hyperfine fields are more accurately described by PBE than by mBJLDA.
Despite its success for ionic and covalent semiconductors and insulators, we
conclude that mBJLDA is not a suitable approximation for half-metallic Heusler
compounds.",1210.7738v1
2013-03-03,High spin polarization of the anomalous Hall current in Co-based Heusler compounds,"Based on first principles density functional calculations of the intrinsic
anomalous and spin Hall conductivities, we predict that the charge Hall current
in Co-based full Heusler compounds Co$_2$XZ (X = Cr and Mn; Z = Al, Si, Ga, Ge,
In and Sn) except Co$_2$CrGa would be almost fully spin-polarized even although
Co$_2$MnAl, Co$_2$MnGa, Co$_2$MnIn and Co$_2$MnSn do not have a half-metallic
band structure. Furthermore, the ratio of the associated spin current to the
charge Hall current is slightly larger than 1.0. This suggests that these
Co-based Heusler compounds, especially Co$_2$MnAl, Co$_2$MnGa and Co$_2$MnIn
which are found to have large anomalous and spin Hall conductivities, might be
called anomalous Hall half-metals and could have valuable applications in
spintronics such as spin valves as well as magnetoresistive and spin-torque
driven nanodevices. These interesting findings are discussed in terms of the
calculated electronic band structures, magnetic moments and also anomalous and
spin Hall conductivities as a function of the Fermi level.",1303.0509v1
2013-07-25,Plasmon dispersions in simple metals and Heusler compounds,"We present a comprehensive study of plasmon dispersions in simple metals and
Heusler compounds based on an accurate ab-initio evaluation of the momentum and
frequency dependent dielectric function in the random-phase approximation.
Using a momentum-dependent tetrahedron method for the computation of the
dielectric function, we extract and analyze ""full"" and ""intraband"" plasmon
dispersions: The ""full"" plasma dispersion is obtained by including all bands,
the intraband plasma dispersion by including only intraband transitions. For
the simple metals silver and alu- minum, we show that the intraband plasmon
dispersion has an unexpected downward slope and is therefore markedly different
from the results of an effective-mass electron-gas model and the full plasmon
dispersion. For the two Heusler compounds Co2FeSi and Co2MnSi, we present
spectra for the dielectric function, their loss functions and plasmon
dispersions. The latter exhibit the same negative intraband plasmon dispersion
as found in the simple metals. We also discuss the influence of spin-mixing on
the plasmon dispersion.",1307.6844v1
2014-08-25,Nanograined half-Heusler semiconductors as advanced thermoelectrics: an ab-initio high-throughput statistical study,"Nanostructuring has spurred a revival in the field of direct thermoelectric
energy conversion. Nanograined materials can now be synthesized with higher
figures of merit (ZT) than the bulk counterparts. This leads to increased
conversion efficiencies. Despite considerable effort in optimizing the known
and discovering the unknown, technology still relies upon a few limited
solutions. Here we perform ab-initio modeling of ZT for 75 nanograined
compounds obtained by filtering down the 79,057 half-Heusler entries available
in the AFLOWLIB.org repository according to electronic and thermodynamic
criteria. For many of the compounds the $ZT$s are markedly above those
attainable with nanograined IV and III-V semiconductors. About 15% of them may
even outperform ZT~2 at high temperatures. Our analysis elucidates the origin
of the advantageous thermoelectric properties found within this broad material
class. We use machine learning techniques to unveil simple rules determining if
a nanograined half-Heusler compound is likely to be a good thermoelectric given
its chemical composition.",1408.5859v1
2015-06-11,Magnetism in tetragonal manganese-rich Heusler compounds,"A comprehensive study of the total energy of manganese-rich Heusler compounds
using density functional theory is presented. Starting from a large set of
cubic parent systems, the response to tetragonal distortions is studied in
detail. We single out the systems that remain cubic from those that most likely
become tetragonal. The driving force of the tetragonal distortion and its
effect on the magnetic properties, especially where they deviate from the
Slater--Pauling rule, as well as the trends in the Curie temperatures, are
highlighted. By means of partial densities of states, the electronic structural
changes reveal the microscopic origin of the observed trends. We focus our
attention on the magnetocrystalline anisotropy and find astonishingly high
values for tetragonal Heusler compounds containing heavy transition metals
accompanied by low magnetic moments, which indicates that these materials are
promising candidates for spin-transfer torque magnetization-switching
applications.",1506.03735v1
2015-07-30,"First principle investigations of the structural, electronic and magnetic properties of the new zirconium based full-Heusler compounds, Zr2MnZ (Z = Al, Ga and In)","The crystal structure, electronic and magnetic properties of the new
full-Heusler compounds Zr2MnZ (Z=Al, Ga, In), were studied within the Density
Functional Theory (DFT) framework. The materials exhibit unique properties that
connect the spin gapless semiconducting character with the completely
compensated ferrimagnetism. In magnetic configurations, Zr2MnZ (Z=Al, Ga, In)
crystallize in inverse Heusler structure, are stable against decomposition and
have zero magnetic moment per formula unit properties, in agreement with
Slater-Pauling rule. The Zr2MnAl compound presents spin gapless semiconducting
properties with a energy band gap of 0.41 eV in the majority spin channel and a
zero band gap in the minority spin channel. By substituting Ga or In elements,
for Al in Zr2MnAl, semiconducting pseudo band gaps are formed in the majority
spin channels due to the different neighborhood around the manganese atoms,
which decreases the energy of Mn's triple degenerated anti-bonding states.",1507.08605v2
2016-01-28,LaPtSb: a half-Heusler compound with high thermoelectric performance,"The electronic and transport properties of the half-Heusler compound LaPtSb
are investigated by performing first-principles calculations combined with
semi-classical Boltzmann theory and deformation potential theory. Compared with
many typical half-Heusler compounds, the LaPtSb exhibits obviously larger power
factor at room temperature, especially for the n-type system. Together with the
very low lattice thermal conductivity, the thermoelectric figure of merit (ZT)
of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the
carrier concentration.",1601.07690v4
2016-04-13,Ultralow Thermal Conductivity in Full-Heusler Semiconductors,"Semiconducting half- and, to a lesser extent, full-Heusler compounds are
promising thermoelectric materials due to their compelling electronic
properties with large power factors. However, intrinsically high thermal
conductivity resulting in a limited thermoelectric efficiency has so far
impeded their widespread use in practical applications. Here, we report the
computational discovery of a class of hitherto unknown stable semiconducting
full-Heusler compounds with ten valence electrons ($X_2YZ$, $X$=Ca, Sr, and Ba;
$Y$= Au and Hg; $Z$=Sn, Pb, As, Sb, and Bi) through high-throughput $ab-initio$
screening. These new compounds exhibit ultralow lattice thermal conductivity
$\kappa_{\text{L}}$ close to the theoretical minimum due to strong anharmonic
rattling of the heavy noble metals, while preserving high power factors, thus
resulting in excellent phonon-glass electron-crystal materials.",1604.03827v2
2020-06-09,Detection of antiskyrmions by topological Hall effect in Heusler compounds,"Heusler compounds having $\textit{D}$${}_{2d}$ crystal symmetry gained much
attention recently due to the stabilization of a vortex-like spin texture
called antiskyrmions in thin lamellae of Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn
as reported in the work of Nayak $\textit{et al.}$ [Nature (London) 548, 561
(2017)]. Here we show that bulk Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn
undergoes a spin-reorientation transition from a collinear ferromagnetic to a
noncollinear configuration of Mn moments below 135 K, which is accompanied by
the emergence of a topological Hall effect. We tune the topological Hall effect
in Pd and Rh substituted Mn${}_{1.4}$PtSn Heusler compounds by changing the
intrinsic magnetic properties and spin textures. A unique feature of the
present system is the observation of a zero-field topological Hall resistivity
with a sign change which indicates the robust formation of antiskyrmions.",2006.05190v1
2022-07-15,Band splitting induced Berry flux and intrinsic anomalous Hall conductivity in NiCoMnGa quaternary Heusler compound,"The anomalous transport properties of Heusler compounds become a hotspot of
research in recent years due to their unique band structure and possible
application in spintronics. In this paper, we report the anomalous Hall effect
in polycrystalline NiCoMnGa quaternary Heusler compound by experimental means
and theoretical calculations. The experimental anomalous Hall conductivity
(AHC) was found at about 256 S/cm at 10K with an intrinsic contribution of ~
121 S/cm. The analysis of Hall data reveals the presence of both extrinsic and
intrinsic contributions in AHE. Our theoretical calculations show that a pair
of spin-orbit coupled band formed by the band splitting due to spin-orbit
interaction (SOI) at the Fermi level produces a finite Berry flux in the system
that provides the intrinsic AHC about 100 S/cm, which is in good agreement with
the experiment.",2207.07313v1
2022-08-31,Unusual kinetic properties of usual Heusler alloys,"The review considers various groups of Heusler compounds, which can have the
properties of a semiconductor, a half-metallic ferromagnet, a spin gapless
semiconductor, a topological semimetal, and a noncollinear antiferromagnet. In
these Heusler compounds, ""conventional"" from the point of view of the crystal
structure, unusual kinetic and magnetic properties can be observed, which are
caused by the features of their electronic structure (e.g., presence of an
energy gap for one spin projection) and magnetic state (e.g., strong
ferromagnetism, compensated ferrimagnetism, etc.). Their magnetic and kinetic
characteristics are very sensitive to external influences. Depending on the
alloy composition and external parameters, transitions between the considered
states can be realized. All this opens up further prospects for controlling the
electronic and magnetic characteristics of such compounds and their practical
application.",2208.14868v1
2024-03-01,Spin-gapped metals: A novel class of materials -- the case of semi-Heusler compounds,"Gapped metals, a recently discovered new class of materials, possess a band
gap slightly above or below the Fermi level. These materials are intrinsic p-
or n-type semiconductors eliminating the need for extrinsic doping. Inspired by
this concept, we propose the so-called ""spin-gapped metals"" exhibiting
intrinsic p- or n-type behavior for each spin channel independently. Their
properties would be similar to the dilute magnetic semiconductors eliminating
the requirement for transition metal doping. Here, we demonstrate this novel
concept in semi-Heusler compounds using first principles electronic band
structure calculations. We comprehensively analyze their electronic and
magnetic properties, paving the way for novel technological applications of
Heusler compounds.",2403.00936v1
2019-12-17,"Type-II Dirac states in full Heusler compounds XInPd2 (X = Ti, Zr and Hf)","We predict three full Heusler compounds XInPd2 (X = Zr, Hf and Ti) to be
potential candidates for type-II Dirac semimetals. The crystal symmetry of
these compounds have appropriate chemical environment with a unique interplay
of inversion, time reversal and mirror symmetry. These symmetries help to give
six pairs of type-II Dirac nodes on the C_4 rotation axis, closely located
at/near the Fermi level. Using first principle calculations, symmetry arguments
and crystal field splitting analysis, we illustrate the occurrence of such
Dirac nodes in these compounds. Bulk Fermi surfaces have been studied to
understand the Lorentz symmetry breaking and Lifshitz transition (LT) of Fermi
surfaces. Bulk nodes are projected on the (001) and (111) surfaces which form
the surface Fermi arcs, that can further be detected by probes such as angle
resolved photo-emission and scanning tunneling spectroscopy. By analyzing the
evolution of arcs with changing chemical potential, we prove the fragile nature
and the absence of topological protection of the Dirac arcs. Our predicted
compounds overcome the limitations of the previously reported PtTe2 class of
compounds.",1912.07807v1
2018-07-12,Synthesis and structural characterization of Sb-doped TiFe2Sn Heusler compounds,"Heusler compounds form a numerous class of intermetallics, which include two
families of compositions ABC and AB2C, usually referred to as half- and
full-Heusler compounds, respectively. Given their tunable electronic
properties, made possible by adjusting the chemical composition, these
materials are currently considered for the possible use in sustainable
technologies such as solar energy and thermoelectric conversion. According to
theoretical predictions, Sb substitution in the TiFe2Sn full-Heusler compound
is thought to yield band structure modifications that should enhance the
thermoelectric power factor. In this work we tested the phase stability and the
structural and microstructural properties of such heavily-doped compounds. We
synthesized polycrystalline TiFe2Sn1-xSbx samples (x=0,0.1,0.2 and 1.0) by arc
melting, followed annealing. The structural characterization, performed by
x-ray powder diffraction and microscopy analyses, confirmed the formation of
the Heusler AB2C structure (cF16, Fm-3m, prototype: MnCu2Al) in all samples,
with only few percent amounts of secondary phases and only slight deviations
from nominal stoichiometry. With increasing Sb substitution we found a steady
decrease of the lattice parameter, confirming that the replacement takes place
at the Sn site. Quite unusually, the as cast samples exhibited a higher lattice
contraction than the annealed ones. The fully substituted x=1.0 compound, again
adopting the MnCu2Al structure, does not form as stoichiometric phase and
turned out to be strongly Fe deficient.The physical behavior at room
temperature indicated that annealing with increasing temperature is beneficial
for electrical and thermoelectrical transport. Moreover, we measured a slight
improvement of electrical and thermoelectrical properties in the x=0.1 sample
and a suppression in the x=0.2 sample, as compared to the undoped x=0 sample.",1807.04545v2
2005-07-28,Exchange interactions and temperature dependence of the magnetization in half--metallic Heusler alloys,"We study the exchange interactions in half-metallic Heusler alloys using
first-principles calculations in conjunction with the frozen-magnon
approximation. The Curie temperature is estimated within both mean-field (MF)
and random-phase-approximation (RPA) approaches. For the half-Heusler alloys
NiMnSb and CoMnSb the dominant interaction is between the nearest Mn atoms. In
this case the MF and RPA estimations differ strongly. The RPA approach provides
better agreement with experiment. The exchange interactions are more complex in
the case of full-Heusler alloys Co$_2$MnSi and Co$_2$CrAl where the dominant
effects are the inter-sublattice interactions between the Mn(Cr) and Co atoms
and between Co atoms at different sublattices. For these compounds we find that
both MF and RPA give very close values of the Curie temperature slightly
underestimating experimental quantities. We study the influence of the lattice
compression on the magnetic properties. The temperature dependence of the
magnetization is calculated using the RPA method within both quantum mechanical
and classical approaches.",0507697v2
2006-03-24,Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films,"We investigate the structure and magneto-transport properties of thin films
of the Co_2Cr_xFe_(1-x)Al full-Heusler compound, which is predicted to be a
half-metal by first-principles theoretical calculations. Thin films are
deposited by magnetron sputtering at room temperature on various substrates in
order to tune the growth from polycrystalline on thermally oxidized Si
substrates to highly textured and even epitaxial on MgO(001) substrates,
respectively. Our Heusler films are magnetically very soft and ferromagnetic
with Curie temperatures up to 630 K. The total magnetic moment is reduced
compared to the theoretical bulk value, but still comparable to values reported
for films grown at elevated temperature. Polycrystalline Heusler films combined
with MgO barriers are incorporated into magnetic tunnel junctions and yield 37%
magnetoresistance at room temperature.",0603649v1
2010-03-10,Evidence for triplet superconductivity in Josephson junctions with ferromagnetic Cu$_{2}$MnAl-Heusler barriers,"We have studied Josephson junctions with barriers prepared from the Heusler
compound Cu$_2$MnAl. In the as-prepared state the Cu$_2$MnAl layers are non
ferromagnetic and the critical Josephson current density $j_{c}$ decreases
exponentially with the thickness of the Heusler layers $d_{F}$. On annealing
the junctions at 240\degree C the Heusler layers develop ferromagnetic order
and we observe a dependence $j_{c}(d_{F}$) with $j_{c}$ strongly enhanced and
weakly thickness dependent in the thickness range 7.0 nm < $d_{F}$ < 10.6 nm.
We attribute this feature to a triplet component in the superconducting pairing
function generated by the specific magnetization profile inside thin Cu$_2$MnAl
layers.",1003.2082v1
2014-05-06,Theoretical search for half-Heusler topological insulators,"We have performed ab-initio band structure calculations on more than two
thousand half-Heusler compounds in order to search for new candidates for
topological insulators. Herein, LiAuS and NaAuS are found to be the strongest
topological insulators with the bulk band gap of 0.20 and 0.19 eV,
respectively, different from the zero band gap feature reported in other
Heusler topological insulators. Due to the inversion asymmetry of the Heusler
structure, their topological surface states on the top and bottom surfaces
exhibit p-type and n-type carriers, respectively. Thus, these materials may
serve as an ideal platform for the realization of topological magneto-electric
effects as polar topological insulators. Moreover, these topological surface
states exhibit the right-hand spin-texture in the upper Dirac cone, which
distinguish them from currently known topological insulator materials. Their
topological nontrivial character remains robust against in-plane strains, which
makes them suitable for epitaxial growth of films.",1405.1305v1
2015-06-04,Low-moment ferrimagnetic phase of the Heusler compound Cr2CoAl,"Synthesizing half-metallic fully-compensated ferrimagnets that form in the
inverse Heusler phase could lead to superior spintronic devices. These
materials would have high spin polarization at room temperature with very
little fringing magnetic fields. Previous theoretical studies indicated that
Cr2CoAl should form in a stable inverse Heusler lattice due to its low
activation energy. Here, stoichiometric Cr2CoAl samples were arc-melted and
annealed at varying temperatures, followed by studies of their structural and
magnetic properties. High-resolution synchrotron X-ray diffraction revealed a
chemically ordered Heusler phase in addition to CoAl and Cr phases. Soft X-ray
magnetic circular dichroism revealed that the Cr and Co magnetic moments are
antiferromagnetically oriented leading to the observed low magnetic moment in
Cr2CoAl.",1506.01738v1
2023-06-26,Origin of magnetic ordering in half-Heusler RuMnGa,"The half-Heusler alloy RuMnGa having valence electron count (VEC) 18 has
recently been theoretically proposed to exhibit compensated ferrimagnetic
(CFiM) character instead of the expected nonmagnetic ground state. On the other
hand, a preliminary experimental study proposed ferromagnetic (FM) ordering. As
no half-Heusler system with VEC 18 is known to exhibit magnetic ordering, we
have investigated the details of crystal structure and magnetic properties of
RuMnGa using a combination of experimental tools, viz., x-ray and neutron
diffraction techniques, dc and ac susceptibility, isothermal magnetisation,
heat capacity, resistivity and neutron depolarisation measurements. Rietveld
refinements of x-ray and neutron diffraction data suggest single phase nature
of the compound with elemental composition RuMn$_{0.86}$Ga$_{1.14}$. We have
shown that the system exhibits FM-type ordering owing to the inherent presence
of this minor off-stoichiometry, showing very low magnetic moment. The system
also exhibits reentrant canonical spin-glass behaviour, which is rarely
observed in half-Heusler alloys. The temperature coefficient of resistivity
changes its sign from negative to positive and further to negative as the
temperature decreases.",2306.14836v1
2015-04-07,Thermal Expansion of Ni-Ti-Sn Heusler and Half-Heusler Materials from First Principles Calculations and Experiments,"We coupled first principles calculations and the quasiharmonic approximation
combined with experiments (X-Ray diffraction and dilatometry measurements) to
determine the thermal properties of NiTiSn (half-Heusler) and Ni2TiSn (Heusler)
compounds. These properties are important especially if they are to be used in
thermoelectric applications. First, the calculation of their mode Gruneisen
parameter shows that it is positive throughout the first Brillouin zone. This
suggests that these compounds undergo a regular thermal expansion. Then, the
calculation of the Ni2TiSn thermal expansion shows an excellent agreement, even
in the high temperature range, with our high energy powder X-Ray diffraction
measurements (ESRF) and dilatometry experiments. In the case of NiTiSn, this
agreement is less impressive. This could be due to stronger phonon-phonon
interactions that are not considered within the quasiharmonic approximation,
but also to the difficulty of making high-quality NiTiSn samples. Finally, the
constant-pressure and constant-volume heat capacities have been calculated for
both compounds and compared with the experimental data reported in the
literature. In particular, we have decomposed the constant-volume heat capacity
of Ni2TiSn into a purely electronic and a phonon-mediated contribution, and we
discuss each of them.",1504.01606v1
2015-05-14,"First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors","Employing first principles electronic structure calculations in conjunction
with the frozen-magnon method we calculate exchange interactions, spin-wave
dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin
gapless semiconductor (SGS) compounds Mn$_2$CoAl, Ti$_2$MnAl, Cr$_2$ZnSi,
Ti$_2$CoSi and Ti$_2$VAs. We find that their magnetic behavior is similar to
the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice
exchange interactions play an essential role in the formation of the magnetic
ground state and in determining the Curie temperature, $T_\mathrm{c}$. All
compounds, except Ti$_2$CoSi possess a ferrimagnetic ground state. Due to the
finite energy gap in one spin channel, the exchange interactions decay sharply
with the distance, and hence magnetism of these SGSs can be described
considering only nearest and next-nearest neighbor exchange interactions. The
calculated spin-wave dispersion curves are typical for ferrimagnets and
ferromagnets. The spin-wave stiffness constants turn out to be larger than
those of the elementary 3$d$-ferromagnets. Calculated exchange parameters are
used as input to determine the temperature dependence of the magnetization and
$T_\mathrm{c}$ of the SGSs. We find that the $T_\mathrm{c}$ of all compounds is
much above the room temperature. The calculated magnetization curve for
Mn$_2$CoAl as well as the Curie temperature are in very good agreement with
available experimental data. The present study is expected to pave the way for
a deeper understanding of the magnetic properties of the inverse-Heusler-based
SGSs and enhance the interest in these materials for application in spintronic
and magnetoelectronic devices.",1505.03632v1
2016-04-06,Anomalous Hall effect in Weyl semimetal half Heusler compounds RPtBi (R = Gd and Nd),"Topological materials ranging from topological insulators to Weyl and Dirac
semimetals form one of the most exciting current fields in condensed-matter
research. Many half-Heusler compounds, RPtBi (R= rare earth) have been
theoretically predicted to be topological semimetals. Among various topological
attributes envisaged in RPtBi, topological surface states, chiral anomaly and
planar Hall effect have been observed experimentally. Here, we report on an
unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler
Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide
temperature range. In particular, GdPtBi exhibits an anomalous Hall
conductivity of up to 60 ohm-1cm-1 and an anomalous Hall angle as large as 23%.
Muon spin resonance (mu-SR) studies of GdPtBi indicate a sharp
antiferromagnetic transition (T_N) at 9 K without any noticeable magnetic
correlations above T_N. Our studies indicate that Weyl points in these
half-Heuslers are induced by a magnetic field via exchange-splitting of the
electronic bands at or near to the Fermi energy which is the source of the
chiral anomaly and the AHE.",1604.01641v2
2018-03-01,Observation of Dirac state in half-Heusler material YPtBi,"The prediction of non-trivial topological electronic states hosted by
half-Heusler compounds makes them prime candidates for discovering new physics
and devices as they harbor a variety of electronic ground states including
superconductivity, magnetism, and heavy fermion behavior. Here we report normal
state electronic properties of a superconducting half-Heusler compound YPtBi
using angle-resolved photoemission spectroscopy (ARPES). Our data reveal the
presence of a Dirac state at the zone center of the Brillouin zone at 500 meV
below the chemical potential. We observe the presence of multiple Fermi surface
pockets including two concentric hexagonal and six half oval shaped pockets at
the gamma and K points of the Brillouin zone, respectively. Furthermore, our
measurements show Rashba-split bands and multiple surface states crossing the
chemical potential which are supported by the first-principles calculations.
Our finding of a Dirac state in YPtBi plays a significant role in establishing
half-Heusler compounds as a new potential platform for novel topological phases
and explore their connection with superconductivity.",1803.00589v1
2023-05-04,4d-element induced improvement of structural disorder and development of weakly re-entrant spin-glass behaviour in NiRuMnSn,"The pursuit of efficient spin-polarization in quaternary Heusler alloys with
the general formula $XX'YZ$ (where X, $X'$, and Y are transition metals and Z
is a p-block element), has been a subject of significant scientific interest.
While previous studies shows that isoelectronic substitution of 4d element in
place of 3d element in quaternary Heusler alloy, improves the half-metallic
ferromagnetic characteristics, our research on the quaternary Heusler alloy
NiRuMnSn reveals a strikingly different scenario. In this study, we present a
detailed structural analysis of the material using X-ray absorption fine
structure (EXAFS) and neutron diffraction (ND) techniques, which confirms the
formation of a single-phase compound with 50:50 site disorder between Ni/Ru
atoms at 4c/4d sites. Contrary to expectations, our DFT calculations suggests a
considerable decrease in spin-polarization even in the ordered structure.
Additionally, we report on the compound's exceptional behavior, displaying a
rare re-entrant spin glass property below $\sim$60 K, a unique and intriguing
feature for quaternary Heusler-type compounds.",2305.03087v1
2017-12-06,Computational Investigation of Inverse-Heusler compounds for Spintronics Applications,"First-principles calculations of the electronic structure, magnetism and
structural stability of inverse-Heusler compounds with the chemical formula
\textit{X$_2$YZ} are presented and discussed with a goal of identifying
compounds of interest for spintronics. Compounds for which the number of
electrons per atom for \textit{Y} exceed that for \textit{X} and for which
\textit{X} is one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu; \textit{Y} is one of
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn; and \textit{Z} is one of Al, Ga, In, Si,
Ge, Sn, P, As or Sb were considered. The formation energy per atom of each
compound was calculated. By comparing our calculated formation energies to
those calculated for phases in the Inorganic Crystal Structure Database (ICSD)
of observed phases, we estimate that inverse-Heuslers with formation energies
within 0.052 eV/atom of the calculated convex hull are reasonably likely to be
synthesizable in equilibrium. The observed trends in the formation energy and
relative structural stability as the \textit{X}, \textit{Y} and \textit{Z}
elements vary are described. In addition to the Slater-Pauling gap after 12
states per formula unit in one of the spin channels, inverse-Heusler phases
often have gaps after 9 states or 14 states. We describe the origin and
occurrence of these gaps. We identify 14 inverse-Heusler semiconductors, 51
half-metals and 50 near half-metals with negative formation energy. In
addition, our calculations predict 4 half-metals and 6 near half-metals to lie
close to the respective convex hull of stable phases, and thus may be
experimentally realized under suitable synthesis conditions, resulting in
potential candidates for future spintronics applications.",1712.02278v1
2014-06-13,"Investigation of the electronic and thermoelectric properties of Fe2 ScX (X = P, As and Sb) full Heusler alloys by using first principles calculations","By using ab initio electronic structure calculations here we report the three
new full Heusler alloys which are possessing very good thermoelectric behavior
and expected to be synthesized in the laboratories. These are Fe2 ScP, Fe2 ScAs
and Fe2 ScSb compound. First two compounds are indirect band gap semiconductors
and the last one shows semimetallic ground state. The value of band gap of Fe2
ScP and Fe2 ScAs is 0.3 and 0.09 eV, respectively. These compounds show the
presence of flat conduction bands along {\Gamma} - X-direction suggesting for
the large electron like effective mass and promising for very good
thermoelectric behavior of the compounds. At 200 K, the Seebeck coefficients of
Fe2 ScP, Fe2 ScAs and Fe2 ScSb compounds are -770, -386 and -192{\mu}V/K,
respectively. The maximum power factor (P F ) is expected for the n-type doping
in these materials. The heavily doped Fe2 ScP and Fe2 ScAs have P F >60 for a
wide temperature range, which is comparable to the PF of Bi2 Te3 - a well known
and one of the best commercially used thermoelectric material. Present work
suggests the possible thermoelectric applicability of these materials in a wide
temperature range.",1406.3425v1
2022-04-28,Observation of Griffiths-like phase in the quaternary Heusler compound NiFeTiSn,"The quaternary Heusler compound NiFeTiSn can be considered to be derived from
the exotic pseudogap-compound Fe2TiSn by the replacement of one Fe atom by Ni.
In contrast to Fe2TiSn, which shows a disorder-induced ferromagnetic phase, the
ground state of NiFeTiSn is antiferromagnetic with the signature of spin
canting. Interestingly, NiFeTiSn shows a Griffiths-like phase characterized by
isolated ferromagnetic clusters before attaining the antiferromagnetic state.
The Griffiths-like phase is possibly associated with the antisite disorder
between Fe and Ti sites as evident from our powder X-ray diffraction study. The
compound also shows rather an unusual temperature dependence of resistivity,
which can be accounted for by the prevailing structural disorder in the system.
NiFeTiSn turned out to be a rare example where a Griffiths-like phase is
observed in a semiconducting 3d transition metal-based intermetallic compound
with an antiferromagnetic ground state.",2204.13462v1
2006-01-30,Correlation in the transition metal based Heusler compounds Co$_2$MnSi and Co$_2$FeSi,"Half-metallic ferromagnets like the full Heusler compounds with formula
X$_2$YZ are supposed to show an integer value of the spin magnetic moment.
Calculations reveal in certain cases of X = Co based compounds non-integer
values, in contrast to experiments. In order to explain deviations of the
magnetic moment calculated for such compounds, the dependency of the electronic
structure on the lattice parameter was studied theoretically. In local density
approximation (LDA), the minimum total energy of Co$_2$FeSi is found for the
experimental lattice parameter, but the calculated magnetic moment is about 12%
too low. Half-metallic ferromagnetism and a magnetic moment equal to the
experimental value of $6\mu_B$ are found, however, only after increasing the
lattice parameter by more than 6%.
  To overcome this discrepancy, the LDA$+U$ scheme was used to respect on-site
electron correlation in the calculations. Those calculations revealed for
Co$_2$FeSi that an effective Coulomb-exchange interaction $U_{eff}=U-J$ in the
range of about 2eV to 5eV leads to half-metallic ferromagnetism and the
measured, integer magnetic moment at the measured lattice parameter. Finally,
it is shown in the case of Co$_2$MnSi that correlation may also serve to
destroy the half-metallic behavior if it becomes too strong (for Co$_2$MnSi
above 2eV and for Co$_2$FeSi above 5eV). These findings indicate that on-site
correlation may play an important role in the description of Heusler compounds
with localized moments.",0601671v1
2005-05-11,"Above-room-temperature ferromagnetism in half-metallic Heusler compounds NiCrP, NiCrSe, NiCrTe and NiVAs: A first-principles study","We study the interatomic exchange interactions and Curie temperatures in
half-metallic semi Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study
is performed within the framework of density functional theory. The calculation
of exchange parameters is based on the frozen-magnon approach. It is shown that
the exchange interactions in NiCrZ vary strongly depending on the Z
constituent. The Curie temperature, Tc, is calculated within the mean field and
random phase approximations. The difference between two estimations is related
to the properties of the exchange interactions. The predicted Curie
temperatures of all four systems are considerably higher than room temperature.
The relation between the half-metallicity and the value of the Curie
temperature is discussed. The combination of a high spin-polarization of charge
carriers and a high Curie temperature makes these Heusler alloys interesting
candidates for spintronics applications.",0505299v1
2006-07-25,Doping and disorder in the Co$_2$MnAl and Co$_2$MnGa half-metallic Heusler alloys,"We expand our study on the full-Heusler compounds [I. Galanakis \textit{et
al.}, Appl. Phys. Lett. \textbf{89}, 042502 (2006)] to cover also the case of
doping and disorder in the case of Co$_2$MnAl and Co$_2$MnGa half-metallic
Heusler alloys. These alloys present a region of very small minority density of
states instead of a real gap. Electronic structure calculations reveal that
doping with Fe and Cr in the case of Co$_2$MnAl retains the half-metallicity
contrary to the Co$_2$MnGa compound. Cr impurities present an unusual behavior
and the spin moment of the Cr impurity scales almost linearly with the
concentration of Cr atoms contrary to the Co$_2$MnZ (Z= Si, Ge, Sn) where it
was almost constant. Half-metallicity is no more preserved for both Co$_2$MnAl
and Co$_2$MnGa alloys when disorder occurs and there is either excess of Mn or
$sp$ atoms.",0607652v1
2011-10-25,"Half-metallic properties for the Ti2YZ (Y=Fe,Co,Ni,Z=Al,Ga,In) Hesuler alloys: A first-principles study","Using the full-potential local orbital minimum-basis method,the Ti2-based
full-Heusler alloys are studied. The results show that these compounds exhibit
a half-metallic behavior, however, in contrast to the conventional full-Heusler
alloys,the full-Heusler alloys show a Slater-Pauling behavior and the total
spin magnetic moment per unit cell(Mt) following the rule Mt=Zt-18. The origin
of the gap in these half-metallic alloys are well understood. It is found that
the half-metallic properties of Ti2-based compounds are insensitive to the
lattice distortion and a fully spin polarization can be obtained within a wide
range of lattice parameters. This is favorable in practical application.",1110.5411v1
2013-04-16,Kinetic arrest related to a first-order ferrimagnetic to antiferromagnetic transition in the Heusler compound Mn2PtGa,"We report a magnetization study of the Heusler compound Mn2PtGa that shows
the existence of a magnetic-glass state. Mn2PtGa shows a first-order
ferromagnetic (FM)/ferrimagnetic (FI) to antiferromagnetic (AFM) transition in
contrast to the martensitic structural transition observed in several Heusler
alloys. The kinetic arrest of this first-order FM (FI) to AFM transition leads
to the observed magnetic-glass behavior. We show that the strength of the
applied magnetic field, which is the primary parameter to induce the
magnetic-glass state, is also responsible for the stability of the supercooled
FM (FI) phase in time.",1304.4459v1
2013-10-17,A new class of topological insulators from I-III-IV half-Heusler compounds with strong band inversion strength,"In this paper, by first principle calculations, we investigate systematically
the band topology of a new half-Heusler family with composition of
I(A)-III(A)-IV(A). The results clearly show that many of the I-III-IV
half-Heusler compounds are in fact promising to be topological insulator
candidates. The characteristic feature of these new topological insulators is
the naturally strong band inversion strength (up to -2eV) without containing
heavy elements. Moreover, we found that both the band inversion strength and
the topological insulating gap can be tailored through strain engineering, and
therefore would be grown epitaxially in the form of films, and useful in
spintronics and other applications.",1310.4696v1
2015-11-10,Large low-field positive magnetoresistance in nonmagnetic half-Heusler ScPtBi single crystal,"High-quality nonmagnetic half-Heusler ScPtBi single crystals were synthesized
by a Bi self-flux method. This compound was revealed to be a hole-dominated
semimetal with a large low-field magnetoresistance up to 240% at 2K in a
magnetic field of 1T. Magneto-transport measurements demonstrated that the
large low-field magnetoresistance effect resulted from the coexistence of
field-induced metal-semiconductor transition and weak-antilocalization effect.
Moreover, Hall measurements indicated that ScPtBi single crystal showed a high
mobility over a wide temperature region even up to room temperature (4050
cm2V-1s-1 at 2K - 2016 cm2V-1s-1 at 300K). These findings not only suggest the
nonmagnetic ScPtBi semimetal a potential material candidate for applications in
high-sensitivity magnetic sensors, but also are of great significance to
comprehensively understand the rare-earth based half-Heusler compounds.",1511.03017v1
2017-07-10,Inflated nodes and surface states in superconducting half-Heusler compounds,"Two topics of high current interest in the field of unconventional
superconductivity are non-centrosymmetric superconductors and multiband
superconductivity. Half-Heusler superconductors such as YPtBi exemplify both.
In this paper, we study bulk and surface states in nodal superconducting phases
of the half-Heusler compounds, belonging to the $A_1$ ($s+p$-like) and $T_2$
($k_zk_x+ik_zk_y$-like) irreducible representations of the point group. These
two phases preserve and break time-reversal symmetry, respectively. For the
$A_1$ case, we find that flat surface bands persist in the multiband system. In
addition, the system has dispersive surface bands with zero-energy crossings
forming Fermi arcs, which are protected by mirror symmetries. For the $T_2$
case, there is an interesting coexistence of point and line nodes, known from
the single-band case, with Bogoliubov Fermi surfaces (two-dimensional nodes).
There are no flat-band surface states, as expected, but dispersive surface
bands with Fermi arcs exist. If these arcs do not lie in high-symmetry planes,
they are split by the antisymmetric spin-orbit coupling so that their number is
doubled compared to the inversion-symmetric case.",1707.02739v2
2020-04-26,High thermoelectric performance of half-Heusler compound BiBaK with intrinsically low lattice thermal conductivity,"Half-Heusler compounds usually exhibit relatively higher lattice thermal
conductivity that is undesirable for thermoelectric applications. Here we
demonstrate by first-principles calculations and Boltzmann transport theory
that the BiBaK system is an exception, which has rather low thermal
conductivity as evidenced by very small phonon group velocity and relaxation
time. Detailed analysis indicates that the heavy Bi and Ba atoms form a
cage-like structure, inside which the light K atom rattles with larger atomic
displacement parameters. In combination with its good electronic transport
properties, the BiBaK shows a maximum n-type ZT value of 1.9 at 900 K, which
outperforms most half-Heusler thermoelectric materials.",2004.12324v1
2016-12-19,Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compound Mn1.5FeV0.5Al,"The Slater-Pauling rule states that L21 Heusler compounds with 24 valence
electrons do never exhibit a total spin magnetic moment. In case of strongly
localized magnetic moments at one of the atoms (here Mn) they will exhibit a
fully compensated half-metallic ferrimagnetic state instead, in particular,
when symmetry does not allow for antiferromagnetic order. With aid of magnetic
and anomalous Hall effect measurements it is experimentally demonstrated that
Mn1.5V0.5FeAl follows such a scenario. The ferrimagnetic state is tuned by the
composition. A small residual magnetization, that arises due to a slight
mismatch of the magnetic moments in the different sublattices results in a
pronounced change of the temperature dependence of the ferrimagnet. A
compensation point is confirmed by observation of magnetic reversal and sign
change of the anomalous Hall effect. Theoretical models are presented that
correlate the electronic structure and the compensation mechanisms of the
different half-metallic ferrimagnetic states in the Mn-V-Fe-Al Heusler system.",1612.06300v1
2016-12-29,Magnetovolume Effects in Heusler Compounds via First-Principles Calculations,"Heusler alloys are promising for several applications, including magnetic
refrigeration, due to high magnetocaloric and magnetovolume effects. One way to
optimize this potential is by increasing the magnetovolume effect. Using
density functional theory with the Korringa-Kohn-Rostoker method, we calculate
the effective exchange interaction energies and corresponding mean field Curie
temperature as a function of the volume (hydrostatic pressure) in several L2 1
-type Co 2 YZ Heusler alloys. Different qualitative trends and signs of the
pressure derivatives of the Curie temperature and moments are found among these
compounds, discussed and compared with previous calculations and experiments.",1612.09133v1
2020-10-22,Anomalous Quantum Oscillations in Spin-3/2 Topological Semimetal YPtBi,"The proposed high-spin superconductivity in the half-Heusler compounds
changes the landscape of superconductivity research. While superconducting
instability is possible only in systems with quantum mechanically coherent
quasiparticles, it has not been verified for any proposed high-spin Fermi
surfaces. Here we report an observation of anomalous Shubnikov-de Haas effect
in half-Heusler YPtBi, which is compatible with a coherent $j=3/2$ Fermi
surface. The quantum oscillation (QO) signal in cubic YPtBi manifests extreme
anisotropy upon rotation of the magnetic field from [100] to [110]
crystallographic direction where the QO signal drastically vanishes near [110].
This radical anisotropy for a cubic system cannot be explained by trivial
scenarios for QO involving effective mass or impurity scattering, but it is
naturally explained by the warping feature of the $j=3/2$ Fermi surface YPtBi.
Our results prove the high-spin nature of the quasiparticle in the half-Heusler
compounds, which makes the realization of the unprecedented high-spin
superconductivity more plausible.",2010.12085v2
2017-10-27,"Near total magnetic moment compensation without reduction in T_C of Mn_2 V_0.5 Co_0.5 Z (Z=Ga,Al) Heusler compounds","Mn_2V_1-xCo_xZ (Z=Ga,Al and x=0, 0.25, 0.5, 0.75, 1) Heusler compounds have
been synthesized to investigate the effect of Co substitution at the V site on
the magnetic moment and Curie temperatures of half-metallic ferrimagnets
Mn_2VGa and Mn_2VAl. The Co substituted compounds show a non linear decrease in
lattice parameter without altering the crystal structure of the parent
compounds. The end members Mn_2VGa and Mn_2CoGa have the saturation
magnetization of 1.80 {\mu}_B/f.u and 2.05 {\mu}_B/f.u respectively whereas for
the Mn_2V_0.5Co_0.5Ga compound, a near total magnetic moment compensation (0.10
{\mu}_B/f.u) was observed due to the ferrimagnetic coupling of Mn with
parallelly aligned V and Co. The Co substituted Mn_2VAl has also shown the
similar trend with compensated magnetic moment value of 0.06 {\mu}_B/f.u for
x=0.5. The Curie temperatures of the compounds including the x=0.5 composition
are well above the room temperature (more than 700 K) which is in sharp
contrast to the earlier reported values of 171 K for the (MnCo)VGa and 105 K
for the (MnCo)VAl compounds (substitution at the Mn site). The magnetic moment
compensation without significant reduction in T_C indicates that the V site
substitution of Co does not weaken the magnetic interaction in Mn_2VZ (Z=Ga,
Al) compounds which is in contrary to the earlier experimental reports on Mn
site substitution.",1710.09971v1
2004-07-01,Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al,"The Heusler alloy is used as an electrode of magnetic tunneling junctions.
The junctions are deposited by magnetron dc sputtering using shadow mask
techniques with AlO_{x} as a barrier and cobalt as counter electrode.
Measurements of the magnetoresistive differential conductivity in a temperature
range between 4K and 300K are shown. An analysis of the barrier properties
applying the Simmons model to the bias dependent junction conductivity is
performed. VSM measurements were carried out to examine the magnetic properties
of the samples.",0407034v1
2007-03-28,Crystalline electric fields and the magnetic ground state of the novel Heusler intermetallic YbRh$_{2}$Pb,"We have synthesized a new intermetallic compound with a distorted Heusler
structure, YbRh$_{2}$Pb. We present a study of the magnetic, thermal, and
transport properties. Heat capacity measurements revealed that YbRh$_{2}$Pb
orders magnetically below T$_{N}$=0.57 K from a paramagnetic state with
substantial crystal electric field splitting. Magnetic field further splits the
ground state, which leads to the suppression of magnetic order in YbRh$_{2}$Pb.",0703765v2
2007-01-25,Doping of Mn$_2$VAl and Mn$_2$VSi Heusler alloys as a route to half-metallic antiferromagnetism,"Half-metallic antiferromagnets are the ideal materials for spintronic
applications since their zero magnetization leads to lower stray fields and
thus tiny energy losses. Starting from the Mn$_2$VAl and Mn$_2$VSi alloys we
substitute Co or Fe for Mn and we show by means of first-principle electronic
structure calculations that the resulting compounds are ferrimagnets. When the
total number of valence electrons reaches the magic number of 24 the Fe-doped
compounds are semi-metals and thus non-magnetic while the Co-doped ones show
the desirable half-metallic antiferromagnetic character. The compounds are very
likely to be synthesized experimentally since the parent compounds, Mn$_2$VAl
and Co$_2$VAl, have been already grown in the Heusler $L2_1$ lattice structure.",0701611v1
2010-02-28,A new platform for topological quantum phenomena : Topological Insulator states in thermoelectric Heusler-related ternary compounds,"Topological insulators (TI) realize a novel state of quantum matter that are
distinguished by topological invariants of bulk band structure rather than
spontaneously broken symmetries. A number of exotic quantum phenomena have been
predicted to exist in multiply-connected geometries which require an enormous
amount of materials flexibility. We have extended our previous search for TI
materials from binary (Bi2X3 series) to the thermoelectric ternary compounds.
We discover that the distorted LuPtSb is the first ternary compound harboring a
3D topological insulator state. We also show that the half-Heusler LuPtSb-type
series is a natural platform that hosts a range of candidate compounds, alloys
and artificial heterostructures (quantum-wells). We also discovered several
different paradigms of trivial and non-trivial topological ordering in this
class, including a metallic nontrivial topological state in YAuPb. Some of
these materials are grown (results will be reported separately).",1003.0155v1
2017-05-11,Pursuit of thermoelectric properties in a novel Half Heusler compound: HfPtPb,"We explore the structural, electronic, mechanical and thermoelectric
properties of a new half Heusler compound, HfPtPb which is all metallic heavy
element and has been recently been proposed to be stable [Nature Chem 7 (2015)
308]. In the present work, we employ density functional theory and
semiclassical Boltzmann transport equations with constant relaxation time
approximation. The mechanical properties such as Shear modulus, Young modulus,
elastic constants, Poisson ratio, and shear anisotropy factor are investigated.
The elastic and phonon properties reveal that this compound is mechanically and
dynamically stable. Pugh and Frantsevich ratio demonstrates the ductile
behavior and Shear anisotropic factor reflects the anisotropic nature of
HfPtPb. The calculation of band structure predicts that this compound is
semiconductor in nature with band gap 0.86 eV. The thermoelectric transport
parameters such as Seebeck coefficient, electrical conductivity, and electronic
thermal conductivity and lattice thermal conductivity have been calculated as a
function of temperature. The highest value of Seebeck coefficient is obtained
for n-type doping at optimal carrier concentration. We predict the maximum
value of the figure of merit 0.25 at 1000 K. Our investigation suggests that
this material is n-type semiconductor.",1705.04015v1
2019-09-24,"Understanding the origin of the magneto-caloric effects in substitutional Ni-Mn-Sb-Z (Z=Fe, Co, Cu) compounds: insights from first-principles calculations","Ni-Mn based ternary Heusler compounds have drawn attentions lately as
significant magneto-caloric effects in some of them have been observed.
Substitution of Ni and Mn by other $3d$ transition metals in controlled
quantity have turned out to be successful in enhancing the effect and bring the
operational temperatures closer to the room temperature. Using density
functional theory calculations, in this work, we have systematically explored
the roles of various factors such as site occupancies, magnetic interactions,
and compositions associated with the constituents of Mn-excess Ni$_{2}$MnSb
Heusler compounds upon substitution of Ni and/or Mn by $3d$ transition metals
Fe, Co and Cu. Our calculations unveiled the physics behind the variations of
physical properties associated with the magneto-caloric effects, and thus
interpreted the available experimental results successfully. The work also
provided important information on the compounds and the composition ranges
where significant magneto-caloric effects may be realised and further
experimental investigations need to be done.",1909.10667v1
2021-06-06,Prediction of half-metallicity and spin-gapless semiconducting behavior in the new series of FeCr-based quaternary Heusler alloys: an ab initio study,"This paper presents a detailed investigation of FeCr-based quaternary Heusler
alloys. By using ultrasoft pseudopotential, electronic and magnetic properties
of the compounds are studied within the framework of Density Functional Theory
(DFT) by using the Quantum Espresso package. The thermodynamic, mechanical, and
dynamical stability of the compounds is established through the comprehensive
study of different mechanical parameters and phonon dispersion curves. The
meticulous study of elastic parameters such as bulk, Young's, shear moduli,
etc. is done to understand different mechanical properties. The FeCr-based
compounds containing also Yttrium are studied to redress the contradictory
electronic and magnetic properties observed in the literature. The interesting
properties like half-metallicity and spin-gapless semiconducting (SGS) behavior
are realized in the compounds under study.",2106.03026v1
2021-06-24,"A first-principles investigation of band inversion in topologically nontrivial Na2AgX (X= As, Sb and Bi) full Heusler compounds","Topological nontrivial nature are the latest phases to be discovered in
condensed matter physics with insulating bulk band gaps and topologically
protected metallic surface states; they are one of the current hot topics
because of their unique properties and potential applications. In this paper,
we have highlighted a first-principles study of the structural stability and
electronic behavior of the Na${}_{2}$AgX (X= As, Sb and Bi) full Heusler
compounds, using the Full-Potential Linear Muffin-Tin Orbital (FP-LMTO) method.
We have originated that the Hg${}_{2}$CuTi structure is appropriate in all
studied materials. The negative values of the calculated formation energies
mean that these compounds are energetically stable. The band structure is
studied for the two cases relating the existence and the absence of
spin-orbital couplings, where all materials are shown to be topologically
non-trivial compounds. Spin orbital couplings were noticed to have no
significant effect on the electronic properties such as the topological order.",2106.13184v1
2023-12-06,First-principles prediction of energy band gaps in 18-valence electron semiconducting half-Heusler compounds: Exploring the role of exchange and correlation,"The choice of exchange functional is a critical factor in determining the
energy bandgap of semiconductors. Ab initio calculations using different
exchange functionals, including the conventional generalized-gradient
approximation (GGA) functionals, meta-GGA functionals, and hybrid functionals,
show significant differences in the calculated energy bandgap for
semiconducting half-Heusler compounds. These compounds, which have 18 valence
electrons per unit cell, are of great interest due to their thermoelectric
properties, making them suitable for energy conversion applications. In
addition, accounting for electronic correlations using the GW method also
affects the calculated energy bandgaps compared to standard GGA calculations.
The variations in calculated energy bandgaps are specific to each material when
using different functionals. Hence, a detailed investigation of the electronic
properties of each compound is necessary to determine the most appropriate
functional for an accurate description of the electronic properties. Our
results indicate that no general rules can be established and a comparison with
experimental results is required to determine the most appropriate functional.",2312.03321v2
2013-07-08,"Significant ZT Enhancement in p-type Ti(Co,Fe)Sb-InSb Nanocomposites via a Synergistic High Mobility Electron Injection Energy filtering and Boundary Scattering Approach","It has been demonstrated that InSb nanoinclusions, which are formed in situ,
can simultaneously improve all three individual thermoelectric properties of
the n-type half Heusler compound (Ti,Zr,Hf)(Co,Ni)Sb [Xie et al., Acta Mater.
58, 4795 (2010)]. In the work presented herein, we have adopted the same
approach to the p-type half Heusler compound Ti(Co,Fe)Sb. The results of
resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient
measurements indicate that the combined high mobility electron injection, low
energy electron filtering, and boundary scattering, again, lead to a
simultaneous improvement of all three individual thermoelectric properties:
enhanced Seebeck coefficient and electrical conductivity as well as reduced
lattice thermal conductivity. A figure of merit of ZT=0.33 was attained at 900
K for the sample containing 1 atomic percent InSb nanoinclusions, a 450 percent
improvement over the nanoinclusion-free sample. This represents a rare case
that the same nanostructuring approach successfully works for both p-type and
n-type thermoelectric materials of the same class, hence pointing to a
promising materials design route for higher performance half-Heusler materials
in the future and hopefully will realize similar improvement in TE devices
based on such half Heusler alloys.",1307.2160v1
2018-03-05,Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds,"Newly emerged materials from the family of Heuslers and complex oxides
exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much
higher than even room temperature. In this work, using the semiclassical
top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that
utilizes such ferromagnetic semiconductors as channel materials, in addition to
ferromagnetic source/drain contacts. Such a device could retain the spin
polarization of injected electrons in the channel, the loss of which limits the
operation of traditional spin transistors with non-ferromagnetic channels. We
examine the operation of four material systems that are currently considered
some of the most prominent known ferromagnetic semiconductors, three
Heusler-type alloys (Mn2CoAl, CrVZrAl, CoVZrAl) and one from the oxide family
(NiFe2O4). We describe their bandstructures by using data from DFT
calculations. We investigate under which conditions high spin polarization and
significant ION/IOFF ratio, two essential requirements for the spin-MOSFET
operation, are both achieved. We show that these particular Heusler channels,
in their bulk form, do not have adequate bandgap to provide high ION/IOFF
ratios, and have small magnetoconductance compared to state-of-the-art devices.
However, with confinement into ultra-narrow sizes down to a few nanometers, and
by engineering their spin dependent contact resistances, they could prove
promising channel materials for the realization of spin-MOSFET transistor
devices that offer combined logic and memory functionalities. Although the main
compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4
alone, we expect that the insight we provide is relevant to other classes of
such materials as well.",1803.01789v1
2019-09-27,Surface Reconstructions of Heusler Compounds in the Ni-Ti-Sn (001) System,"As progress is made on thin-film synthesis of Heusler compounds, a more
complete understanding of the surface will be required to control their
properties, especially as functional heterostructures are explored. Here, the
surface reconstructions of semiconducting half-Heusler NiTiSn(001), and
Ni1+xTiSn(001) (x=0.0-1.0) are explored as a way to optimize growth conditions
during molecular beam epitaxy. Density functional theory (DFT) calculations
were carried out to guide the interpretation of the experimental results. For
NiTiSn(001) a c(2x2) surface reconstruction was observed for Sn rich samples,
while a (1x1) unreconstructed surface was observed for Ti-rich samples. A
narrow range around 1:1:1 stoichiometry exhibited a (2x1) surface
reconstruction. Electrical transport is used to relate the observed reflection
high energy electron diffraction (RHEED) pattern during and after growth with
carrier concentration and stoichiometry. Scanning tunneling microscopy and
RHEED were used to examine surface reconstructions, the results of which are in
good agreement with density functional calculations. X-ray photoelectron
spectroscopy was used to determine surface termination and stoichiometry.
Atomic surface models are proposed, which suggest Sn-dimers form in
reconstructed Ni1+xTiSn(001) half-Heusler surfaces (x<0.25) with a transition
to Ni terminated surfaces for x > 0.25.",1909.12487v1
2023-11-10,Strong-coupling superconductivity of the Heusler-type compound ScAu2Al: Ab-initio studies,"The ScAu$_2$Al superconducting Heusler-type compound was recently
characterized to have the highest critical temperature of $T_c = 5.12$ K and
the strongest electron-phonon coupling among the Heusler family. In this work,
the electronic structure, phonons, electron-phonon coupling, and
superconductivity of ScAu$_2$Al are studied using \textit{ab initio}
calculations. The spin-orbit coupling significantly changes the electronic
structure removing the van Hove singularity from the vicinity of the Fermi
level. In the phonon spectrum, low frequency acoustic modes, additionally
softened by the spin-orbit interaction, strongly couple with electrons, leading
to the electron-phonon coupling constant $\lambda=1.25$, a record high among
Heuslers. The density functional theory for superconductors is then used to
analyze superconducting {state in this two-band superconductor}. The effect of
spin fluctuations (SF) on superconductivity is also analyzed. The calculated
critical temperatures of $T_c = 5.16$ K (4.79 K with SF) agree very well with
the experiment, confirming the electron-phonon mechanism of superconductivity
and showing a weak spin-fluctuations effect. The superconducting gaps formed on
two Fermi surface sheets exhibit moderate anisotropy. Their magnitudes confirm
the strong coupling regime, as the reduced average values are $2\Delta_1/k_BT_c
\simeq 4.1$ and $2\Delta_2/k_BT_c \simeq 4.3$. Anisotropy of the gaps and large
spread in their values significantly affect the calculated quasiparticle
density of states.",2311.06075v3
2015-12-24,"Importance of spin-orbit coupling in power factor calculations for half-Heusler ANiB (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi)","We investigate the spin-orbit coupling (SOC) effects on the electronic
structures and semi-classic transport coefficients of half-Heusler
$\mathrm{ANiB}$ (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi) by using generalized gradient
approximation (GGA). Calculated results show that SOC splits the valence bands
at high symmetry $\Gamma$ point, and modifies the outline of $\Gamma$-centered
valence bands, which has remarkable effects on the electron transport
properties. Thermoelectric properties are performed through solving Boltzmann
transport equations within the constant scattering time approximation. It is
found that the compounds containing Sn atom have larger power factor in p-type
doping than ones in n-type doping, and it is just the opposite for compounds
containing Sb and Bi elements. The SOC has obvious detrimental influence on
power factor in p-type doping, while has a negligible effect in n-type doping.
These can be understood by considering the effects of SOC on the valence bands
and conduction bands. The maximum power factors (MPF) are extracted in n-type
and p-type doping with GGA and GGA+SOC, and the MPF at 300 K with SOC is
predicted to be about 4.25\%$\sim$44.13\% smaller than that without SOC in the
case of p-type doping for $\mathrm{ANiB}$ (A=Ti, Hf, Sc, Y; B=Sn, Sb, Bi).
Therefore, it is crucial to consider SOC effects for theoretical analysis in
the case of p-type doping in half-Heusler compounds composed of heavy elements.",1512.07710v1
2017-08-03,"A comparative study of different exchange-correlation functionals in understanding structural, electronic and thermoelectric properties of Fe$_{2}$VAl and Fe$_{2}$TiSn compounds","Fe$_{2}$VAl and Fe$_{2}$TiSn are full Heusler compounds with non-magnetic
ground state. The two compouds are good thermoelectric materials. PBE and
LDA(PW92) are the two most commonly used density functionals to study the
Heusler compounds. Along with these two well studied exchange-correlation
functionals, recently developed PBEsol, mBJ and SCAN functionals are employed
to study the two compounds. Using the five functionals equilibrium lattice
parameter and bulk modulus are calculated. Obtained values are compared with
experimental reports wherever available. Electronic structure properties are
studied by calculating dispersion curves, total and partial density of states.
For Fe$_{2}$VAl, band gap of 0.22 eV is obtained from the mBJ potential which
is in reasonable agreement with experimental value while, for Fe$_{2}$TiSn band
gap of 0.68 eV is obtained. Fe$_{2}$VAl is predicted to be semimetallic with
different values of negative gaps from LDA,PBEsol,PBE and SCAN functionals.
Whereas, Fe$_{2}$TiSn is found to be semimetallic(semiconducting) from
LDA,PBEsol(PBE,SCAN) functionals employed calculations. From the dispersion
curve effective mass values are also computed to see the contribution to the
Seebeck coefficient. In Fe$_{2}$TiSn, a flat band is present along the
$\Gamma$-X direction with calculated value of effective mass $\sim$36 more than
the mass of electron. The improvements or inadequacies among the functionals in
explaining the properties of full Heusler alloys for thermoelectric application
are thus observed through this study.",1708.01180v1
2023-07-26,Giant spin-charge conversion in ultrathin films of the MnPtSb half-Heusler compound,"Half-metallic half-Heusler compounds with strong spin-orbit-coupling and
broken inversion symmetry in their crystal structure are promising materials
for generating and absorbing spin-currents, thus enabling the electric
manipulation of magnetization in energy-efficient spintronic devices. In this
work, we report the spin-to-charge conversion in sputtered ultrathin films of
the half-Heusler compound MnPtSb with thickness (t) in the range from 1 to 6
nm. A combination of X-ray and transmission electron microscopy measurements
evidence the epitaxial nature of these ultrathin non-centrosymmetric MnPtSb
films, with a clear (111)-orientation obtained on top of (0001) single-crystal
sapphire substrates. The study of the thickness (t)-dependent magnetization
dynamics of the MnPtSb(t)/Co(5nm)/Au(5nm) heterostructure revealed that the
MnPtSb compound can be used as an efficient spin current generator, even at
film thicknesses as low as 1 nm. By making use of spin pumping FMR, we measure
a remarkable t-dependent spin-charge conversion in the MnPtSb layers, which
clearly demonstrate the interfacial origin of the conversion. When interpreted
as arising from the inverse Edelstein effect (IEE), the spin-charge conversion
efficiency extracted at room temperature for the thinnest MnPtSb layer reaches
{\lambda}IEE~3 nm, representing an extremely high spin-charge conversion
efficiency at room temperature. The still never explored ultrathin regime of
the MnPtSb films studied in this work and the discover of their outstanding
functionality are two ingredients which demonstrate the potentiality of such
materials for future applications in spintronics.",2307.14516v1
2005-10-08,Design of magnetic materials: Co$_2$Cr$_{1-x}$Fe$_{x}$Al,"Doped Heusler compounds Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe
ratio $x$ were investigated experimentally and theoretically. The electronic
structure of the ordered, doped Heusler compound Co$_2$Cr$_{1-x}$Fe$_{x}$Al
($x=n/4, n=0,1,2,3,4)$ was calculated using different types of band structure
calculations. The ordered compounds turned out to be ferromagnetic with small
Al magnetic moment being aligned anti-parallel to the 3d transition metal
moments. All compounds show a gap around the Fermi-energy in the minority
bands. The pure compounds exhibit an indirect minority gap, whereas the
ordered, doped compounds exhibit a direct gap. Magnetic circular dichroism
(MCD) in X-ray absorption spectra was measured at the $L_{2,3}$ edges of Co,
Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to determine
element specific magnetic moments. Calculations and measurements show an
increase of the magnetic moments with increasing iron content. The
experimentally observed reduction of the magnetic moment of Cr can be explained
by Co-Cr site-disorder. The presence of the gap in the minority bands of
Co$_2$CrAl can be attributed to the occurrence of pure Co$_2$ and mixed CrAl
(001)-planes in the $L2_1$ structure. It is retained in structures with
different order of the CrAl planes but vanishes in the $X$-structure with
alternating CoCr and CoAl planes.",0510203v1
2013-09-25,Band structure calculations of Ti\raisebox{-.2ex}{\scriptsize 2}FeSn: a new half-metallic compound,"Within the framework of density functional theory, the electronic structure
and magnetic properties have been studied for the
Ti\raisebox{-.2ex}{\scriptsize 2}FeSn full-Heusler compound. The ferromagnetic
state is found to be energetically more favorable than paramagnetic and
antiferromagnetic states. The spin-polarized results show that
Ti\raisebox{-.2ex}{\scriptsize 2}FeSn compound has half-metallic ferromagnetic
character with a total spin moment of $2 \mu_{B}$ and a band gap in the
minority spin channel of 0.489 eV, at the equilibrium lattice constant a=6.342
A.",1309.6442v1
2015-11-09,NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds,"Spin-orbit coupling (SOC) is expected to partly determine the topologically
nontrivial electronic structure of heavy half-Heusler ternary compounds.
However, to date, attempts to experimentally observe either the strength of SOC
or how it modifies the bulk band structure have been unsuccessful. By using
bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with
first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale
with relativity in terms of the strength of SOC and average atomic numbers,
indicating strong relativistic effects on NMR parameters. According to
first-principles calculations, we further claim that nuclear magnetic
shieldings from relativistic p1/2 states and paramagnetic contributions from
low-lying unoccupied p3/2 states are both sensitive to the details of band
structures tuned by relativity, which explains why the hidden relativistic
effects on band structure can be revealed by 209Bi NMR isotropic shifts in
topologically nontrivial half-Heusler compounds. Used in complement to
surface-sensitive methods, such as angle resolved photon electron spectroscopy
and scanning tunneling spectroscopy, NMR can provide valuable information on
bulk electronic states.",1511.02706v2
2020-02-07,"Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization","Engineering of magnetic materials for developing better spintronic
applications relies on the control of two key parameters: the spin polarization
and the Gilbert damping responsible for the spin angular momentum dissipation.
Both of them are expected to affect the ultrafast magnetization dynamics
occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x
Heusler compounds to adjust the degree of spin polarization P from 60 to 100%
and investigate how it correlates with the damping. We demonstrate
experimentally that the damping decreases when increasing the spin polarization
from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of
4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the
relation between these two parameters and the ultrafast demagnetization time
characterizing the loss of magnetization occurring after femtosecond laser
pulse excitation. The demagnetization time is observed to be inversely
proportional to 1-P and as a consequence to the magnetic damping, which can be
attributed to the similarity of the spin angular momentum dissipation processes
responsible for these two effects. Altogether, our high quality Heusler
compounds allow controlling the band structure and therefore the channel for
spin angular momentum dissipation.",2002.02686v1
2020-03-21,Scaling of quadratic and linear magnetooptic Kerr effect spectra with L2$_1$ ordering of Co$_2$MnSi Heusler compound,"The Heusler compound Co$_2$MnSi provides a crystallographic transition from
B2 to L2$_1$ structure with increasing annealing temperature $T_a$, being a
model system for investigating the influence of crystallographic ordering on
structural, magnetic, optic, and magnetooptic (MO) properties. Here, we present
quadratic magnetooptic Kerr effect (QMOKE) spectra depending on $M^2$ in
addition to the linear magnetooptic Kerr effect (LinMOKE) spectra being
proportional to $M$, both in the extended visible spectral range of light from
0.8\,eV to 5.5\,eV. We investigated a set of Co$_2$MnSi thin films deposited on
MgO(001) substrates and annealed from 300$^\circ$C to 500$^\circ$C. The
amplitude of LinMOKE and QMOKE spectra scales linearly with $T_a$, and this
effect is well pronounced at the resonant peaks below 2.0\,eV of the QMOKE
spectra. Furthermore, the spectra of the MO parameters, which fully describe
the MO response of Co$_2$MnSi up to the second order in $M$, are obtained
dependend on $T_a$. Finally, the spectra are compared to ab-initio calculations
of a purely L2$_1$ ordered Co$_2$MnSi Heusler compound.",2003.09728v2
2023-07-18,Effect of Spin Orbit Coupling in non-centrosymmetric half-Heusler alloys,"Spin-orbit coupled electronic structure of two representative non-polar
half-Heusler alloys, namely 18 electron compound CoZrBi and 8 electron compound
SiLiIn have been studied in details. An excursion through the Brillouin zone of
these alloys from one high symmetry point to the other revealed rich local
symmetry of the associated wave vectors resulting in non-trivial spin splitting
of the bands and consequent diverse spin textures in the presence of spin-orbit
coupling. Our first principles calculations supplemented with low energy
$\boldsymbol{k.p}$ model Hamiltonian revealed the presence of linear
Dresselhaus effect at the X point having $D_{2d}$ symmetry and Rashba effect
with both linear and non-linear terms at the L point with $C_{3v}$ point group
symmetry. Interestingly we have also identified non-trivial Zeeman spin
splitting at the non-time reversal invariant W point and a pair of
non-degenerate bands along the path $\Gamma$ to L displaying vanishing spin
polarization due to the non-pseudo polar point group symmetry of the wave
vectors. Further a comparative study of CoZrBi and SiLiIn suggest, in addition,
to the local symmetry of the wave vectors, important role of the participating
orbitals in deciding the nature and strength of spin splitting. Our
calculations identify half-Heusler compounds with heavy elements displaying
diverse spin textures may be ideal candidate for spin valleytronics where spin
textures can be controlled by accessing different valleys around the high
symmetry k-points.",2308.03760v2
2021-07-08,Lattice thermal conductivity of half-Heuslers with density functional theory and machine learning: Enhancing predictivity by active sampling with principal component analysis,"Low lattice thermal conductivity is essential for high thermoelectric
performance of a material. Lattice thermal conductivity is often computed using
density functional theory (DFT), typically at a high computational cost.
Training machine learning models to predict lattice thermal conductivity could
offer an effective procedure to identify low lattice thermal conductivity
compounds. However, in doing so, we must face the fact that such compounds can
be quite rare and distinct from those in a typical training set. This
distinctness can be problematic as standard machine learning methods are
inaccurate when predicting properties of compounds with features differing
significantly from those in the training set. By computing the lattice thermal
conductivity of 122 half-Heusler compounds, using the temperature-dependent
effective potential method, we generate a data set to explore this issue. We
first show how random forest regression can fail to identify low lattice
thermal conductivity compounds with random selection of training data. Next, we
show how active selection of training data using feature and principal
component analysis can be used to improve model performance and the ability to
identify low lattice thermal conductivity compounds. Lastly, we find that
active learning without the use of DFT-based features can be viable as a
quicker way of selecting samples.",2107.03735v2
2020-08-09,"Ab initio study of the half-metallic full-Heusler compounds Co$_2$ZAl [Z = Sc, Ti, V, Cr, Mn, Fe]; the role of electronic correlations","We study the structural, electronic, and magnetic properties of Co$_2$ZAl
compounds employing a pseudopotential electronic bandstructure method. The
stability of the compounds is established through the formation and cohesive
energy calculations. The effect of the lattice parameter variation on the
electronic and magnetic properties of the compounds is investigated and
meticulous explanation is provided for the observed behavior. The variation of
the individual spin magnetic moments and the stability of the total spin
magnetic moment during the expansion and contraction of the lattice parameter
is observed and an attempt is made to understand the obtained behavior.
Finally, we implement DFT+U to examine its consequences on the electronic and
magnetic properties of the Co$_2$ZAl compounds. We find that the use of DFT+U
is not justified for these compounds and in some cases like Co$_2$MnAl it
produces unrealistic properties. The exception is Co2FeAl where the desired
half-metallicity is restored after the inclusion of on-site correlations. We
explain why the on-site correlations might be important for Co$_2$FeAl by
comparing it with other Heusler alloys where the correlation was found to be
meaningful to explain the observed magnetic moments.",2008.03732v1
2002-03-04,X-ray spectra of 3d metals of Heusler alloys and La$_{1-x}$Sm$_x$Mn$_2$Si$_2$ compounds,"The Mn x-ray emission spectra and x-ray photoemission spectra of Mn-based
Heusler alloys Co$_2$MnAl, Co$_2$MnSb and La$_{1-x}$Sm$_x$Mn$_2$Si$_2$
compounds (x=0, 0.8) have been measured and discussed in connection with a
value local magnetic moment at Mn site. The spectra peculiarities reflect also
the localization degree of 3d valence electrons of 3d metals in considered
compounds.",0203069v3
2006-11-17,"Ab initio prediction of half-metallic properties for the ferromagnetic Heusler alloys Co$_2$MSi (M=Ti, V, Cr)","By means of density functional calculations the magnetic and electronic
properties and phase stabilities of the Heusler compounds Co$_2$MSi (with M=Ti,
V, Cr, Mn, Fe, Co, Ni) were investigated. Based on the calculated results we
predict the ferromagnetic phases of the compounds Co$_2$TiSi, Co$_2$VSi and
Co$_2$CrSi to be half-metals. Of particular interest is Co$_2$CrSi because of
its high density of majority spin states at Fermi energy in combination with a
reasonably high estimated Curie temperature of 747K. The compounds Co$_2$TiSi
and Co$_2$VSi are thermodynamically stable, whereas Co$_2$CrSi is a metastable
phase which might be stabilized by suitable experimental techniques.",0611466v1
2008-10-05,Determination of exchange constants of Heusler compounds by Brillouin light scattering spectroscopy: application to Co$_2$MnSi,"Brillouin light scattering spectroscopy from so-called standing spin waves in
thin magnetic films is often used to determine the magnetic exchange constant.
The data analysis of the experimentally determined spin-wave modes requires an
unambiguous assignment to the correct spin wave mode orders. Often additional
investigations are needed to guarantee correct assignment. This is particularly
important in the case of Heusler compounds where values of the exchange
constant vary substantially between different compounds. As a showcase, we
report on the determination of the exchange constant (exchange stiffness
constant) in Co$_2$MnSi, which is found to be $A=2.35\pm0.1$ $\mu$erg/cm
($D=575\pm20$ meV \AA$^2$), a value comparable to the value of the exchange
constant of Co.",0810.0834v3
2008-11-27,Electron correlations in Co$_2$Mn$_{1-x}$Fe$_x$Si Heusler compounds,"This study presents the effect of local electronic correlations on the
Heusler compounds Co$_2$Mn$_{1-x}$Fe$_x$Si as a function of the concentration
$x$. The analysis has been performed by means of first-principles
band-structure calculations based on the local approximation to spin-density
functional theory (LSDA). Correlation effects are treated in terms of the
Dynamical Mean-Field Theory (DMFT) and the LSDA+U approach. The formalism is
implemented within the Korringa-Kohn-Rostoker (KKR) Green's function method.
  In good agreement with the available experimental data the magnetic and
spectroscopic properties of the compound are explained in terms of strong
electronic correlations. In addition the correlation effects have been analysed
separately with respect to their static or dynamical origin. To achieve a
quantitative description of the electronic structure of
Co$_2$Mn$_{1-x}$Fe$_x$Si both static and dynamic correlations must be treated
on equal footing.",0811.4625v1
2010-11-10,"Ab initio prediction of ferrimagnetism, exchange interactions and Curie temperatures in Mn2TiZ Heusler compounds","The Heusler compounds Mn$_2$TiZ (Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb) are
of large interest due to their potential ferrimagnetic properties and high spin
polarization. Here, we present calculations of the structural and magnetic
properties of these materials. Their magnetic moment follows the Slater-Pauling
rule $m = N_V - 24$. None of them is actually a perfect half-metallic
ferrimagnet, but some exhibit more than 90% spin polarization and Curie
temperatures well above room temperature. The exchange interactions are
complex, direct and indirect exchange contributions are identified. The Curie
temperature scales with the total magnetic moment, and it has a positive
pressure dependence. The role of the Z element is investigated: it influences
the properties of the compounds mainly via its valence electron number and its
atomic radius, which determines the lattice parameter. Based on these results,
Mn$_2$TiSi, Mn$_2$TiGe, and Mn$_2$TiSn are proposed as candidates for
spintronic applications.",1011.2486v1
2011-07-04,Influence of tetragonal distortion on the topological electronic structure of the half-Heusler compound LaPtBi from first principles,"The electronic structures of tetragonally distorted half-Heuselr compound
LaPtBi in the C1b structure are investigated in the framework of density
functional theory using the full potential linearized augmented plane with
local spin density approximation method. The calculation results show that both
the band structures and the Fermi level can be tuned by using either
compressive or tensile in-plane strain. A large bulk band gap of 0.3 eV can be
induced through the application of a compressive in-pane strain in LaPtBi with
the assumption of a relaxed volume of the unit cell. Our results could serve as
a guidance to realize topological insulators in half-Heusler compounds by
strain engineering.",1107.0531v1
2012-09-29,Realization of spin gapless semiconductors: the Heusler compound Mn2CoAl,"Recent studies have reported an interesting class of semiconductor materials
that bridge the gap between semiconductors and halfmetallic ferromagnets. These
materials, called spin gapless semiconductors, exhibit a bandgap in one of the
spin channels and a zero bandgap in the other and thus allow for tunable spin
transport. Here, a theoretical and experimental study of the spin gapless
Heusler compound Mn2CoAl is presented. It turns out that Mn2CoAl is a very
peculiar ferrimagnetic semiconductor with a magnetic moment of 2 {\mu}B and a
high Curie temperature of 720 K. Below 300 K, the compound exhibits nearly
temperature-independent conductivity, very low, temperature-independent carrier
concentration, and a vanishing Seebeck coefficient. The magnetoresistance
changes sign with temperature. In high fields, it is positive and
non-saturating at low temperatures, but negative and saturating at high
temperatures. The anomalous Hall effect is comparatively low, which is
explained by the close antisymmetry of the Berry curvature for kz of opposite
sign.",1210.0148v1
2012-12-13,"First-principles study of the structural stability of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds","We investigate the structural stability and magnetic properties of cubic,
tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds
using first-principles density-functional theory. We propose that the cubic
phase plays an important role as an intermediate state in the phase transition
from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge
behave differently from Mn3Sn, because the relative energies of the cubic and
hexagonal phases are different. This result agrees with experimental
observations from these three compounds. The weak ferromagnetism of the
hexagonal phase and the perpendicular magnetocrystalline anisotropy of the
tetragonal phase obtained in our calculations are also consistent with
experiment.",1212.3144v1
2014-02-24,Experimental realization of a semiconducting full Heusler compound: Fe2TiSi,"Single-phase films of the full Heusler compound Fe2TiSi have been prepared by
magnetron sputtering. The compound is found to be a semiconductor with a gap of
0.4eV. The electrical resistivity has a logarithmic temperature dependence up
to room temperature due to Kondo scattering of a dilute free electron gas off
superparamagnetic impurities. The origin of the electron gas is extrinsic due
to disorder or off-stoichiometry. Density functional theory calculations of the
electronic structure are in excellent agreement with electron energy loss,
optical, and x-ray absorption experiments. Fe2TiSi may find applications as a
thermoelectric material.",1402.5755v1
2016-04-21,Magnetic properties and Curie temperatures of disordered Heusler compounds: Co(1+x)Fe(2-x)Si,"The local atomic environments and magnetic properties were investigated for a
series of Co(1+x)Fe(2-x)Si (0<x<1) Heusler compounds. While the total magnetic
moment in these compounds increases with the number of valance electrons, the
highest Curie temperature (Tc) in this series was found for Co1.5Fe1.5Si, with
a Tc of 1069 K (24 K higher than the well known Co2FeSi). 57Fe M\""ossbauer
spectroscopy was used to characterize the local atomic order and to estimate
the Co and Fe magnetic moments. Consideration of the local magnetic moments and
the exchange integrals is necessary to understand the trend in Tc.",1604.06235v1
2016-11-24,Design of L2_1-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT+GW study,"Antiferromagnetic spintronics is an on-going growing field of research.
Employing both standard density functional theory and the $GW$ approximation
within the framework of the FLAPW method, we study the electronic and magnetic
properties of seven potential antiferromagnetic semiconducting Heusler
compounds with 18 (or 28 when Zn is present) valence electrons per unit cell.
We show that in these compounds G-type antiferromagnetism is the ground state
and that they are all either emiconductors (Cr$_2$ScP, Cr$_2$TiZn, V$_2$ScP,
V$_2$TiSi, and V$_3$Al) or semimetals (Mn$_2$MgZn and Mn$_2$NaAl). The
many-body corrections have a minimal effect on the electronic band structure
with respect to the standard electronic structure calculations.",1611.08080v2
2018-01-25,Heusler compounds -- how to tune the magnetocrystalline anisotropy,"Tailoring and controlling magnetic properties is an important factor for
materials design. Here, we present a case study for Ni-based Heusler compounds
of the type Ni$_2$YZ with Y = Mn, Fe, Co and Z = B, Al, Ga, In, Si, Ge, Sn
based on first principles electronic structure calculations. These compounds
are interesting since the materials properties can be quite easily tuned by
composition and many of them possess a non-cubic ground state being a
prerequisite for a finite magnetocrystalline anisotropy (MAE). We discuss
systematically the influence of doping at the Y and Z sublattice as well of
lattice deformation on the MAE. We show that in case of Ni$_2$CoZ the phase
stability and the MAE can be improved using quaternary systems with elements
from group 13 and 14 on the Z sublattice whereas changing the Y sublattice
occupation by adding Fe does not lead to an increase of the MAE. Furthermore,
we studied the influence of the lattice ratio on the MAE. Showing that small
deviations can lead to a doubling of the MAE as in case of Ni$_2$FeGe. Even
though we demonstrate this for a limited set of systems the findings may carry
over to other related systems.",1801.08511v1
2018-06-14,Superconductivity in half-Heusler compound TbPdBi,"We have studied the half-Heusler compound TbPdBi through resistivity,
magnetization, Hall effect and heat capacity measurements. A semimetal behavior
is observed in its normal state transport properties, which is characterized by
a large negative magnetoresistance below 100 K. Notably, we find the
coexistence of superconductivity and antiferromagnetism in this compound. The
superconducting transition appears at 1.7 K, while the antiferromagnetic phase
transition takes place at 5.5 K. The upper critical field $H_{c2}$ shows an
unusual linear temperature dependence, implying unconventional
superconductivity. Moreover, when the superconductivity is suppressed by
magnetic field, its resistivity shows plateau behavior, a signature often seen
in topological insulators/semimetals. These findings establish TbPdBi as a
platform for study of the interplay between superconductivity, magnetism and
non-trivial band topology.",1806.05314v1
2018-11-12,Interface spin polarization of the Heusler compound Co2MnSi probed by unidirectional spin Hall magnetoresistance,"Many Heusler compounds are predicted to be ferromagnetic half metals in the
bulk, which makes them promising compounds for spintronics. However, for
devices the transport spin polarization at specific interfaces requires
optimization. We show that investigations of the unidirectional
magnetoresistance provide an alternative approach to access this quantity.
Based on a Wheatstone-bridge design we probed the unidirectional
magnetoresistance of Co2MnSi/(Ag, Cu, or Cr)(0.5 nm)/Pt (or Ta) multilayers and
separate the spin-dependent unidirectional spin Hall magnetoresistance from
other contributions. We demonstrated that by the insertion of a thin epitaxial
Ag layer the spin-dependent contribution is doubled corresponding to a
significant increase of the transport spin polarization, which is discussed in
the framework of highly spin polarized interface states.",1811.04592v2
2020-08-11,Effect of doping on SGS and weak half-metallic properties of inverse Heusler Alloys,"Heusler alloys with Mn and Co have been found to exhibit interesting
electronic and magnetic properties. Mn$_2$CoAl is well known SGS compound while
Mn$_2$CoGa has weak half metallic character. By using plane wave
pseudo-potential method, we studied the effect of Fe and Cr doping on
half-metalicity and magnetism of these compounds. The doping destroys the SGS
nature of Mn$_2$CoAl while the small-scale doping enhance the half-metallicity
of Mn$_2$CoGa making it perfect half-metal. In case of Mn$_2$CoAl, the doping
decrease the band gap while increase in band width is noticed for Mn$_2$CoGa.
The half-metallicity is destroyed in both cases when the doping level is beyond
certain degree. Moreover, we have also computed magnetic behavior of Mn$_2$CoZ
alloys and we found that total magnetic moments of dopped samples have higher
values than that of pristine compounds.",2008.04536v1
2019-03-28,Anisotropic Topological Hall Effect with Real and Momentum Space Berry Curvature in the Antiskrymion Hosting Heusler Compound Mn$_{1.4}$PtSn,"The topological Hall effect (THE) is one of the key signatures of
topologically non-trivial magnetic spin textures, wherein electrons feel an
additional transverse voltage to the applied current. The magnitude of THE is
often small compared to the anomalous Hall effect. Here, we find a large THE of
0.9 $\mu\Omega$cm that is of the same order of the anomalous Hall effect in the
single crystalline antiskyrmion hosting Heusler compound Mn$_{1.4}$PtSn, a
non-centrosymmetric tetragonal compound. The THE is highly anisotropic and
survives in the whole temperature range where the spin structure is noncoplanar
(<170 K). The THE is zero above the spin reorientation transition temperature
of 170 K, where the magnetization will have a collinear and ferromagnetic
alignment. The large value of the THE entails a significant contribution from
the momentum space Berry curvature along with real space Berry curvature, which
has never been observed earlier.",1903.12037v1
2019-05-23,"Thermodynamic and Thermoelectric Properties of CoFeYGe (Y= Ti, Cr) Quaternary Heusler Alloys: First Principle Calculations","Utilizing a material in thermoelectric applications requires a mechanical,
thermal, and lattice stability as well a high figure of merit (ZT). In this
work, we present the structural, electronic, magnetic, mechanical,
thermodynamic, dynamic, and thermoelectric properties of CoFeYGe (Y = Ti, Cr)
quaternary Heusler compounds using the density functional theory (DFT). The
calculated mechanical properties and phonon dispersions reveal that the
structures of these compounds are stable. Both CoFeCrGe and CoFeTiGe compounds
show a ferromagnetic and ferrimagnetic half-metallic behavior with band gaps of
0.41 and 0.38 eV, respectively. The lattice thermal conductivity (\k{appa}L)
exhibits low values that reach 3.01 W/(m.K) (3.47 W/(m.K)) for CoFeCrGe
(CoFeTiGe) at 1100 K. The optical phonon modes have a large contribution of
60.2% (70.9 %) to \k{appa}L value for CoFeCrGe (CoFeTiGe). High ZT values of
0.71 and 0.65 were obtained for CoFeCrGe and CoFeTiGe, respectively. Based on
our calculations, CoFeCrGe and CoFeTiGe combine both good spintronic and
thermoelectric behaviors that may be used in spin injection applications.",1905.09854v1
2020-03-06,Unexpected band gap increase in the Fe2VAl Heusler compound,"Knowing the electronic structure of a material is essential in energy
applications to rationalize its performance and propose alternatives. Materials
for thermoelectric applications are generally small-gap semiconductors and
should have a high figure of merit ZT. Even if the Fe2VAl Heusler compound has
a decent ZT, its conductive nature (semi-metal or semiconductor) is not yet
clarified especially at low temperature. In this paper, we focus our DFT
calculations on the effect of temperature on the bandgap of Fe2VAl. In contrast
to what is usually observed, we show that both the temperature increase and the
formation of thermally-activated Al/V inversion defects (observed
experimentally), open the bandgap. Such an unusual behavior is the key for
reconciling all bandgap measurements performed on the Fe2VAl compound using a
standard GGA functional and could be an efficient way for improving the
thermoelectric properties of this family of materials.",2003.03166v1
2020-12-08,Importance of Electronic Correlation in the Intermetallic Half-Heusler Compounds,"Low temperature scanning tunneling spectroscopy of HfNiSn shows a V^m(m < 1)
zero bias anomaly around the Fermi level. This local density of states with a
fractional power law shape is well known to be a consequence of electronic
correlations. For comparison, we have also measured the tunneling conductances
of other half-Heusler compounds with 18 valence electrons. ZrNiPb shows a
metal-like local density of states, whereas ZrCoSb and NbFeSb show a linear and
V^2 anomaly. One interpretation of these anomalies is that a correlation gap is
opening in these compounds. By analyzing the magnetoresistance of HfNiSn, we
demonstrate that at low temperatures, electron-electron scattering dominates.
The T^m(m < 1) temperature dependence of the conductivity confirms that the
electronic correlations are a bulk rather than a surface property.",2012.04184v1
2021-12-18,"Structural, elastic, electronic and optical properties of the half-Heusler ScPtSb and YPtSb compounds under pressure","First-principles calculations using the plane-wave pseudopotential method
within the generalized gradient approximation method were performed to study
the pressure dependence of the structural, elastic, electronic and optical
properties for the half-Heusler compounds ScPtSb and YPtSb in a cubic
MgAgAs-type structure. The calculations were performed with the inclusion of
spin-orbit coupling. The calculated equilibrium lattice parameters are in good
agreement with the available experimental and theoretical values. The crystal
rigidity and mechanical stability were discussed using the elastic constants
and related parameters, namely bulk modulus, shear modulus, Debye temperature,
Poisson's coefficient, Young's modulus and isotropic sound velocities. The
calculated electronic band structures show that ScPtSb has an indirect gap of
$\Gamma-X $ type, whereas YPtSb has a direct band gap of $\Gamma -\Gamma $
type. Furthermore, the effect of pressure on the optical properties, namely the
dielectric function, absorption spectrum, refractive index, extinction
coefficient, reflectivity and energy-loss spectrum is investigated for both
compounds ScPtSb and YPtSb.",2112.09940v1
2003-05-07,Appearance of Half-Metallicity in the Quaternary Heusler Alloys,"I report systematic first-principle calculations of the quaternary Heusler
alloys like Co$_2$[Cr$_{1-x}$Mn$_x$]Al, Co$_2$Mn[Al$_{1-x}$Sn$_x$] and
[Fe$_{1-x}$Co$_x$]$_2$MnAl. I show that when the two limiting cases (x=0 or 1)
correspond to a half-metallic compound, so do the intermediate cases. Moreover
the total spin moment $M_t$ in $\mu_B$ scales linearly with the total number of
valence electrons $Z_t$ (and thus with the concentration $x$) following the
relation $M_t=Z_t-24$, independently of the origin of the extra valence
electrons, confirming the Slater-Pauling behavior of the normal Heusler alloys.
Finally I discuss in all cases the trends in the atomic projected DOSs and in
the atomic spin moments.",0305134v1
2006-10-30,Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first-principles,"Half-metallic Heusler alloys are amongst the most promising materials for
future magnetoelectronic applications. We review some recent results on the
electronic properties of these compounds. The origin of the gap in these
half-metallic alloys and its connection to the magnetic properties are well
understood. Changing the lattice parameter shifts slightly the Fermi level.
Spin-orbit coupling induces states within the gap but the alloys keep a very
high degree of spin-polarization at the Fermi level. Small degrees of doping
and disorder as well as defects with low formation energy have little effect on
the properties of the gap, while temperature effects can lead to a quick loss
of half-metallicity. Finally we discuss two special issues; the case of
quaternary Heusler alloys and the half-metallic ferrimagnets.",0610827v1
2013-04-12,Crossover of magnetoresistance in the zerogap half-metallic Heusler alloy Fe2CoSi,"This work reports on the band structure and magneto-transport investigations
of the inverse Heusler compound Fe2CoSi. The first-principles calculations
reveal that Fe2CoSi has a very peculiar band structure with a conducting
property in the majority spin channel and a nearly zero bandgap in the minority
spin channel. The synthesized Fe2CoSi sample shows a high-ordered inverse
Heusler structure with a magnetic moment of 4.88 {\mu}B at 5 K and a high Curie
temperature of 1038 K. With increasing temperature, a crossover from positive
to negative magnetoresistance (MR) is observed. Complemented with the Hall
effect measurements, we suggest the intriguing crossover of MR can be ascribed
to the dominant spin carriers changing from the gapless minority spin channel
to the majority spin channel at Fermi level.",1304.3517v1
2018-03-27,Subamorphous thermal conductivity of crystalline half-Heusler superlattices,"The quest to improve the thermoelectric figure of merit has mainly followed
the roadmap of lowering the thermal conductivity while keeping unaltered the
power factor of the material. Ideally an electron-crystal phonon-glass system
is desired. In this work, we report an extraordinary reduction of the
cross-plane thermal conductivity in crystalline (TiNiSn):(HfNiSn) half-Heusler
superlattices. We create SLs with thermal conductivities below the effective
amorphous limit, which is kept in a large temperature range (120-300 K). We
measured thermal conductivity at room temperature values as low as 0.75 W/(m
K), the lowest thermal conductivity value reported so far for half-Heusler
compounds. By changing the deposition conditions, we also demonstrate that the
thermal conductivity is highly impacted by the way the single segments of the
superlattice grow. These findings show a huge potential for thermoelectric
generators where an extraordinary reduction of the thermal conductivity is
required but without losing the crystal quality of the system.",1803.09920v2
2018-09-19,Quaternary Heusler Alloy: An Ideal Platform to Realize Triple Point Fermion,"The existence of three fold rotational, mirror and time reversal symmetries
often give rise to the triply degenerate nodal point (TP) in the band structure
of a material. Based on point group symmetry analysis and first principle
electronic structure, we predict, in this article, a series of quaternary
Heusler alloys host an ideal platform for the occurrence of TP. We simulated,
the projection of these TPs onto the (111) and (100) surfaces lead to form
topological Fermi arcs, which may further be detected by scanning tunneling
spectroscopy and angle resolved photoemission spectroscopy. These Fermi arcs
arise due to the symmetry protected band degeneracies, which are robust and can
not be avoided due to the non-trivial band topology. Interestingly the TPs, in
these class of Heusler alloys are far away from the $\Gamma$ point along C$_3$
axes, which allow to overcome the experimental difficulties over previously
studied hexagonal and HgTe-type compounds.",1809.07026v1
2017-04-03,Half-Heusler alloy LiBaBi: A new topological semimetal with five-fold band degeneracy,"Based on first-principles study, we report the finding of a new topological
semimetal LiBaBi in half-Heusler phase. The remarkable feature of this
nonmagnetic, inversion-symmetry-breaking material is that it consists of only
simple $s$- and $p$-block elements. Interestingly, the material is ordinary
insulator in the absence of spin-orbit coupling (SOC) and becomes nodal-surface
topological semimetal showing drumhead states when SOC is included. This is in
stark contrast to other nodal-line and nodal-surface semimetals, where the
extended nodal structure is destroyed once SOC is included. Importantly, the
linear band crossings host three-, four-, five- and six-fold degeneracies near
the Fermi level, making this compound very attractive for the study of
`unconventional' fermions. The band crossing points form a three-dimensional
nodal structure around the zone center at the Fermi level. We identify the
surface states responsible for the appearance of the drumhead states. The alloy
also shows a phase transition from topological semimetal to a trivial insulator
on application of pressure. In addition to revealing an intriguing effect of
SOC on the nodal structure, our findings introduce a new half-Heusler alloy in
the family of topological semimetals, thus creating more avenues for
experimental exploration.",1704.00697v1
2019-01-28,Magnetotransport properties and giant anomalous Hall angle in half-Heusler compound TbPtBi,"Magnetic lanthanide half-Heuslers ($R$PtBi; $R$ being the lanthanide)
represent an attractive subgroup of the Heusler family and have been identified
as ideal candidates for time reversal symmetry breaking topological Weyl
semimetals. In this paper, we present the detailed analysis of the
magnetotransport properties of frustrated antiferromagnet TbPtBi. This material
shows large, non-saturating magnetoresistance (MR) with unusual magnetic field
dependence. The MR of TbPtBi is significantly anisotropic with respect to the
magnetic field, applied along different crystallographic directions and
indicates the anisotropic nature of the Fermi surface. The chiral anomaly
induced negative longitudinal magnetoresistance confirms the presence of Weyl
fermions. At low temperature, Berry phase driven large anomalous Hall
conductivity has been observed. The calculated anomalous Hall angle is the
largest reported so far.",1901.09534v1
2012-09-27,Fabrication and characterization of semiconducting half Heusler YPtSb thin films,"The semiconducting half Heusler compound YPtSb was predicted theoretically to
be capable of changing into topological insulator under proper strain. In this
work, p type semiconducting half-Heusler YPtSb thin films were prepared by
magnetron co-sputtering method from a specially designed target for the first
time. Textured structure with (111) plane paralleling with (001) of MgO
substrate was observed when YPtSb thin films were grown on MgO (100) substrate
at 600{\deg}C.Electrical measurements show that the resistivity of YPtSb films
decreases with increasing temperature, indicating a semiconductor-like
behavior. The carrier density is as high as 1.15 X 10^21 cm-3 at 300 K. The
band gap of YPtSb thin films obtained by infrared spectroscopy is around 0.1 -
0.15 eV, which is well in agreement with the theoretical prediction and the
value measured in bulk YPtSb.",1209.6288v2
2018-02-07,"Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy","Future spintronics requires the realization of thin film of half-metallic
ferromagnets having high Curie temperature and 100\% spin polarization at the
Fermi level for potential spintronics applications. In this paper, we report
the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO
(001) substrate using pulsed laser deposition system, along with the study of
structural, magnetic and transport properties. The magnetic property
measurements of the thin film suggest a soft ferromagnetic state at room
temperature with an in-plane magnetic anisotropy and a Curie temperature well
above the room temperature. Anisotropic magnetoresistance (AMR) ratio and
temperature dependent electrical resistivity measurements of the thin film
indicate the compound to be half-metallic in nature and therefore suitable for
the fabrications of spintronics devices.",1802.02413v1
2017-06-01,Prediction of triple point fermions in simple half-Heusler topological insulators,"We predict the existence of triple point fermions in the band structure of
several half-Heusler topological insulators by $ab~initio$ calculations and the
Kane model. We find that many half-Heusler compounds exhibit multiple triple
points along four independent $C_3$ axes, through which the doubly degenerate
conduction bands and the nondegenerate valence band cross each other linearly
nearby the Fermi energy. When projected from the bulk to the (111) surface,
most of these triple points are located far away from the surface
$\bar{\Gamma}$ point, as distinct from previously reported triple point fermion
candidates. These isolated triple points give rise to Fermi arcs on the
surface, that can be readily detected by photoemission spectroscopy or scanning
tunneling spectroscopy.",1706.00200v1
2020-09-09,"Structural, Elastic, Electronic and Magnetic Properties of MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) Semi-Heusler Alloys","The study of structural, electronic, magnetic, and elastic properties of new
series of semi-Heusler alloys MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) has been
performed by density functional theory. The magnetic phase and hence the
structural stability of the alloys were considered wherein ferromagnetic state
is found to stable. The half-metallic states are observed from the density of
states and band structure calculations. The total magnetic moments found for
all studied compounds are 1 $\mu_B$/f.u., which obey Slating-Pauling rule for
semi-Heusler with ferromagnetic behavior. The calculated elastic constant
C$_{ij}$, cohesive energy, and formation energy confirmed that these materials
are mechanically stable. Among the four system, MnNbAs is found to have the
highest ductility while the remaining systems are found to be brittle in
nature. These properties confirmed that among others, MnNbAs is one of the
novel candidate for spintronic devices applications.",2009.04123v1
2021-04-29,Nonlinear Hall Effect in Antiferromagnetic Half-Heusler Materials,"It has recently been demonstrated that various topological states, including
Dirac, Weyl, nodal-line, and triple-point semimetal phases, can emerge in
antiferromagnetic (AFM) half-Heusler compounds. However, how to determine the
AFM structure and to distinguish different topological phases from transport
behaviors remains unknown. We show that, due to the presence of combined
time-reversal and fractional translation symmetry, the recently proposed
second-order nonlinear Hall effect can be used to characterize different
topological phases with various AFM configurations. Guided by the symmetry
analysis, we obtain the expressions of the Berry curvature dipole for different
AFM configurations. Based on the effective model, we explicitly calculate the
Berry curvature dipole, which is found to be vanishingly small for the
triple-point semimetal phase, and large in the Weyl semimetal phase. Our
results not only put forward an effective method for the identification of
magnetic orders and topological phases in AFM half-Heusler materials, but also
suggest these materials as a versatile platform for engineering the non-linear
Hall effect.",2104.14127v1
2024-03-13,Study of Physical Characteristics of the New Half-Heusler Alloy BaHgSn by DFT Analysis,"To investigate the physical characteristics of the half-Heusler BaHgSn
molecule, we used theoretical calculations within the Density Functional Theory
(DFT) framework utilizing the LSDA+mBJ technique in this study. Using the
optimal lattice parameters, we discover that half-Heusler BaHgSn exhibits a
Dirac semimetal behavior with a band gap of 0.1 eV. Thomas Charpin's numerical
first-principles calculation approach was applied to determine the elastic
constants of hexagonal BaHgSn alloys. The material's optical characteristics
verified its prospective use in infrared-visible devices. According to a
thermo-electric properties analysis, at 20x10^18 {\Omega}-1.m-1.s-1, the
electrical conductivity reaches its maximum after increasing gradually up to
500 K. Compared to other compounds, these results indicate that BaHgSn has
potential for use in opto-electronic and thermo-electric devices.",2403.08483v1
2014-12-07,Prediction and accelerated laboratory discovery of previously unknown 18-electron ABX compounds,"Chemists and material scientists have often focused on the properties of
previously reported compounds, leaving out numerous unreported but chemically
plausible compounds that could have interesting properties. For example, the
18-valence electron ABX family of compounds includes the half-Heusler subgroup,
and features examples of topological insulators, thermoelectrics and
superconductors, but only 83 out of 483 of these possible compounds have been
made. Using first-principles thermodynamics we have examined the theoretical
stability of 400 unreported members and predict that 54 should be stable. 15
previously missing materials, now predicted stable, were grown in this study;
X-ray studies agreed with the predicted crystal structure in all 15 cases.
Among the characterized properties of the missing compounds are potential
transparent conductors, thermoelectric materials and topological semimetals.
This integrated process-prediction of functionality in unreported compounds
followed by laboratory synthesis and characterization-could be a route to the
systematic discovery of hitherto missing, realizable functional materials.",1412.2398v1
2017-06-01,Materials Screening for the Discovery of New Half-Heuslers: Machine Learning versus Ab Initio Methods,"Machine learning (ML) is increasingly becoming a helpful tool in the search
for novel functional compounds. Here we use classification via random forests
to predict the stability of half-Heusler (HH) compounds, using only
experimentally reported compounds as a training set. Cross-validation yields an
excellent agreement between the fraction of compounds classified as stable and
the actual fraction of truly stable compounds in the ICSD. The ML model is then
employed to screen 71,178 different 1:1:1 compositions, yielding 481 likely
stable candidates. The predicted stability of HH compounds from three previous
high throughput ab initio studies is critically analyzed from the perspective
of the alternative ML approach. The incomplete consistency among the three
separate ab initio studies and between them and the ML predictions suggests
that additional factors beyond those considered by ab initio phase stability
calculations might be determinant to the stability of the compounds. Such
factors can include configurational entropies and quasiharmonic contributions.",1706.00192v1
2011-05-02,Design scheme of new multifunctional Heusler compounds for spin-transfer torque applications,This paper has been withdrawn.,1105.0337v2
2022-02-14,$Ab$ $Initio$ Study of Magnetic Tunnel Junctions Based on Half-Metallic and Spin-Gapless Semiconducting Heusler Compounds: Reconfigurable Diode and Inverse Tunnel-Magnetoresistance Effect,"Magnetic tunnel junctions (MTJs) have attracted strong research interest
within the last decades due to their potential use as nonvolatile memory such
as MRAM as well as for magnetic logic applications. Half-metallic magnets
(HMMs) have been suggested as ideal electrode materials for MTJs to achieve an
extremely large tunnel-magnetoresistance (TMR) effect. Despite their high TMR
ratios, MTJs based on HMMs do not exhibit current rectification, i.e., a diode
effect, which was achieved in a magnetic tunnel junction concept based on HMMs
and type-II spin-gapless semiconductors (SGSs). The proposed concept has
recently been experimentally demonstrated using Heusler compounds. In the
present work, we investigate from first-principles MTJs based on type-II SGS
and HMM quaternary Heusler compounds FeVTaAl, FeVTiSi, MnVTiAl, and CoVTiSb.
Our $ab$ $initio$ quantum transport calculations based on a nonequilibrium
Green's function method have demonstrated that the MTJs under consideration
exhibit current rectification with relatively high on:off ratios. We show that,
in contrast to conventional semiconductor diodes, the rectification bias
voltage window (or breakdown voltage) of the MTJs is limited by the spin gap of
the HMM and SGS Heusler compounds. A unique feature of the present MTJs is that
the diode effect can be configured dynamically, i.e., depending on the relative
orientation of the magnetization of the electrodes, the MTJ allows the
electrical current to pass either in one or the other direction, which leads to
an inverse TMR effect. The combination of nonvolatility, reconfigurable diode
functionality, tunable rectification voltage window, and high Curie temperature
of the electrode materials makes the proposed MTJs very promising for
room-temperature spintronic applications and opens ways to magnetic memory and
logic concepts as well as logic-in-memory computing.",2202.06752v2
2006-06-05,Properties of the quaternary half-metal-type Heusler alloy Co$_2$Mn$_{1-x}$Fe$_x$Si,"This work reports on the bulk properties of the quaternary Heusler alloy
Co$_2$Mn$_{1-x}$Fe$_x$Si with the Fe concentration $x=$. All samples, which
were prepared by arc melting, exhibit $L2_1$ long range order over the complete
range of Fe concentration. Structural and magnetic properties of
Co$_2$Mn$_{1-x}$Fe$_x$Si Heusler alloys were investigated by means of X-ray
diffraction, high and low temperature magnetometry, M{\""o\ss}bauer
spectroscopy, and differential scanning calorimetry. The electronic structure
was explored by means of high energy photo emission spectroscopy at about 8 keV
photon energy. This ensures true bulk sensitivity of the measurements. The
magnetization of the Fe doped Heusler alloys is in agreement with the values of
the magnetic moments expected for a Slater-Pauling like behavior of
half-metallic ferromagnets. The experimental findings are discussed on the hand
of self-consistent calculations of the electronic and magnetic structure. To
achieve good agreement with experiment, the calculations indicate that on-site
electron-electron correlation must be taken into account, even at low Fe
concentration. The present investigation focuses on searching for the
quaternary compound where the half-metallic behavior is stable against outside
influences. Overall, the results suggest that the best candidate may be found
at an iron concentration of about 50%.",0606108v2
2015-12-15,"Half-metallic, Co-based quaternary Heuslers for spintronics: defect- and pressure-induced transitions and properties","Heusler compounds offer potential as spintronic devices due to their
spin-polarization and half-metallicity properties, where electron spin-majority
(minority) manifold exhibits states (band gap) at the electronic chemical
potential, yielding full spin-polarization in a single manifold. Yet, Heuslers
often exhibit intrinsic disorder that degrades its half-metallicity and
spin-polarization. Using density-functional theory, we analyze the electronic
and magnetic properties of equiatomic Heusler ($L$2$_{1}$) CoMnCrAl and
CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder
(thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl
undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained
for a limited range. Antisite disorder between Co-Al pairs in CoMnCrAl and
Co-Ge pairs in CoFeCrGe is energetically the most favored, and retain
half-metallic character in Co-excess samples. However, Co-deficient samples
undergo a transition from half-metallic to metallic, with a discontinuity in
the saturation magnetization. For binary swaps, configurations that compete
with the ground state are identified and show no loss of half-metallicity;
however, the minority-spin bandgap and magnetic moments vary depending on the
atoms swapped. For single binary swaps, there is a significant energy cost in
CoMnCrAl but with no loss of half metallicity. Although a few configurations in
CoFeCrGe energetically compete with the ground statei, however the
minority-spin bandgap and magnetic moments vary depending on the atoms swapped.
These informations should help in controlling these potential spintronic
materials.",1512.04805v2
2022-08-29,Substantial enhancement in thermoelectric figure-of-merit of half Heusler ZrNiPb alloys,"Ternary half Heusler alloys are under intense investigations recently towards
achieving high thermoelectric figure-of-merit (ZT). Of particular interest is
the ZrNiPb based half Heusler (HH) alloy where an optimal value of ZT = 0.7 at
773 K has been achieved by co-doping Sn and Bi at Pb site. In this work, we
identify an excellent ZT of 1.3 in ZrNi1+xPb0.38Sn0.6Bi0.02 (x= 0.03, at 773 K)
composite alloy. This is achieved by synergistic modulation of electronic as
well as thermal properties via introduction of minor phase of full Heusler (FH)
in the HH matrix through compositional tuning approach. These Ni-rich
ZrNi1+xPb0.38Sn0.6Bi0.02 alloys were synthesized via Arc melting followed by
consolidation via Spark Plasma Sintering (SPS). These alloys were characterized
by XRD and SEM that shows formation of nanocomposites comprising of HH matrix
phase and FH secondary minor phases. Enhancement in ZT is mainly attributed to
a synchronized increase in power factor and about 25% decrease in its thermal
conductivity. The thermoelectric compatibility factor (S) is also calculated
for all samples. The theoretically calculated thermoelectric device efficiency
of best performing sample ZrNi1.03Pb0.38Sn0.6Bi0.02 is estimated to be 13.6%.
Our results imply that controlled fine tuning in HH compounds through
compositional tuning approach would lead to novel off-stoichiometric HH phases
with enhanced ZT value for efficient thermoelectric device fabrication.",2208.13563v1
2022-09-28,First Principles Study of the Electronic Structure of the Ni$_2$MnIn/InAs and Ti$_2$MnIn/InSb interfaces,"We present a first-principles study of the electronic and magnetic properties
of epitaxial interfaces between the Heusler compounds Ti$_2$MnIn and Ni$_2$MnIn
and the III-V semiconductors, InSb and InAs, respectively. We use density
functional theory (DFT) with a machine-learned Hubbard $U$ correction
determined by Bayesian optimization. We evaluate these interfaces for
prospective applications in Majorana-based quantum computing and spintronics.
In both interfaces, states from the Heusler penetrate into the gap of the
semiconductor, decaying within a few atomic layers. The magnetic interactions
at the interface are weak and local in space and energy. Magnetic moments of
less than 0.1 $\mu_B$ are induced in the two atomic layers closest to the
interface. The induced spin polarization around the Fermi level of the
semiconductor also decays within a few atomic layers. The decisive factor for
the induced spin polarization around the Fermi level of the semiconductor is
the spin polarization around the Fermi level in the Heusler, rather than the
overall magnetic moment. As a result, the ferrimagnetic narrow-gap
semiconductor Ti$_2$MnIn induces a more significant spin polarization in the
InSb than the ferromagnetic metal Ni$_2$MnIn induces in the InAs. This is
explained by the position of the transition metal $d$ states in the Heusler
with respect to the Fermi level. Based on our results, these interfaces are
unlikely to be useful for Majorana devices but could be of interest for
spintronics.",2209.14101v3
2022-12-15,Exploration of all-3d Heusler alloys for permanent magnets: an ab initio based high-throughput study,"Heusler alloys have attracted interest in various fields of functional
materials since their properties can quite easily be tuned by composition.
Here, we have investigated the relatively new class of all-3d Heusler alloys in
view of its potential as permanent magnets. To identify suitable candidates, we
performed a high-throughput study using an electronic structure database to
search for X$_2$YZ-type Heusler systems with tetragonal symmetry and high
magnetization. For the alloys which passed our selection filters, we have used
a combination of density functional theory calculations and spin dynamics
modelling to investigate their magnetic properties including the
magnetocrystalline anisotropy energy and exchange interactions. The candidates
which fulfilled all the search criteria served as input for the investigation
of the temperature dependence of the magnetization and determination of Curie
temperature. Based on our results, we suggest that Fe$_2$NiZn, Fe$_2$NiTi and
Ni$_2$CoFe are potential candidates for permanent magnets with large
out-of-plane magnetic anisotropy (1.23, 0.97 and 0.82 MJ/m$^3$ respectively)
and high Curie temperatures lying more than 200 K above the room temperature.
We further show that the magnitude and direction of anisotropy is very
sensitive to the strain by calculating the values of anisotropy energy for
several tetragonal phases. Thus, application of strain can be used to tune the
anisotropy in these compounds.",2212.07845v3
2016-10-19,Bismuth based Half Heusler Alloys with giant thermoelectric figure of merit,"Half Heusler (HH) thermoelectric alloys provide a wide platform to choose
materials with non-toxic and earth abundant elements. This article presents an
ab-initio theoretical evaluation of electrical and thermal transport properties
of three Bismuth-based most promising thermoelectric alloys, selected out of 54
stable HH compounds. These are brand new compounds which are recently proposed
to be stable (Nature Chem. 7, 308 (2015)) and may have interesting properties.
The calculated band structure of the three compounds, namely HfRhBi, ZrIrBi and
ZrRhBi, served as a hint for their promising thermoelectric properties. To gain
confidence on the theoretical predictions of these unreported systems, we first
checked our calculated results for a well studied similar compound, ZrNiSn, and
showed reasonable agreement with the measured ones. HfRhBi and ZrIrBi turn out
to be narrow band gap while ZrRhBi is a moderate band gap semiconductor. A
detailed study of the carrier concentration and temperature dependance of the
Seebeck coefficient (S), Power factor (S$^2 \sigma$), lattice ($\kappa_L$) and
electronic ($\kappa_e$) thermal conductivity and hence the figure of merit (ZT)
is carried out. In contrast to most promising known thermoelectric materials,
we found high power factor for these materials (highest S$^2 \sigma\sim$17.36
mWm$^{-1}$K$^{-2}$ for p-type ZrIrBi). All the three systems (specially p-type)
show high figure of merit, with ZT value as high as 0.45 for ideal crystal.
Maximum ZT and the corresponding optimal n- and p-type doping concentrations
($n_c$) are calculated for all the three compounds, which shall certainly pave
guidance to future experimental work.",1610.06038v2
2018-11-12,Evidence for unconventional superconductivity in Half-Heusler YPdBi and TbPdBi compounds revealed by London penetration depth measurements,"The half-Heusler compounds YPdBi and TbPdBi, while having similar band
structure, exhibit different magnetic properties. YPdBi is a diamagnet, while
TbPdBi shows antiferromagnetic order below 5.5 K. Both are superconductors with
T${_c}\approx$1 K for YPdBi and T${_c}\approx$1.75 K for TbPdBi. Such a
contrast in properties between these two compounds opens a question about the
effects of band structure or magnetic correlations on superconductivity. Using
the combination of a tunnel diode oscillator (TDO) and a commercial dilution
refrigerator, we measured temperature dependent magnetic penetration depth
$\Delta\lambda(T)$ in single crystals of YPdBi and TbPdBi, down to temperatures
as low as 0.1K. We found that penetration depths of both compounds do not show
exponential temperature dependence and saturation at low temperatures, as
expected for conventional BCS superconductors. Instead, in both compounds, the
penetration depth can be described by a power law $\Delta\lambda(T) = A\times
T^{n}$. The coefficient A was found to be about 50$\%$ smaller in TbPdBi, but
the exponents are very similar, $n = 2.76\pm 0.04$ in YPdBi and $n = 2.6\pm
0.3$ in TbPdBi, respectively. Our results suggest unconventional
superconductivity in both YPdBi and TbPdBi.",1811.05045v1
2023-03-15,Rare observation of spin-gapless semiconducting characteristics and related band topology of quaternary Heusler alloy CoFeMnSn,"In this paper, we report the theoretical investigation and experimental
realization of a new spin-gapless semiconductor (SGSs) compound CoFeMnSn
belonging to the family of quaternary Heusler alloys. Through the use of
several ground-state energy calculations, the most stable structure has been
identified. Calculations of the spin-polarized band structure in optimized
structure's reveals the SGS nature of the compound. The compound form in an
ordered crystal structure and exhibit a high ferromagnetic transition
temperature (T$_{\rm C}$ = 560 K), making the material excellent for room
temperature applications. Adherence of saturation magnetization to the
Slater-Pauling rule, together with the nearly temperature-independent
resistivity, conductivity, and carrier concentration of the compound in the
temperature regime 5$-$300 K along with the low value of anomalous Hall
conductivity (AHC) further confirms the SGS nature. Theoretical calculations
also reveal the robustness of the SGS state due to lattice contraction and one
can obtain a high value of intrinsic AHC using hole doping. Combined SGS and
topological properties of the compound make CoFeMnSn suitable for spintronics
and magneto-electronics devices.",2303.08589v2
2023-09-09,Accelerating Discovery of Vacancy Ordered 18-Valence Electron Half-Heusler Compounds: A Synergistic Approach of Machine Learning and Density Functional Theory,"In this study, we attempted to model vacancy ordered half Heusler compounds
with 18 valence electron count (VHH) derived from 19 VEC compounds such as
TiNiSb such that the compositions will be Ti0.75NiSb, Zr0.75NiSb and Hf0.75NiSb
with semiconducting behavior. The main motivation is that such a
vacancy-ordered phase not only introduces semi conductivity but also it
disrupts the phonon conducting path in HH alloys and thus reduces the thermal
conductivity and as a consequence enhances the thermoelectric figure of merit.
In order to predict the formation energy ({\Delta}Hf) from composition and
crystal structure we have used 4684 compounds for their {\Delta}Hf values are
available in the material project database and trained a machine learning model
with R2 value of 0.943. Using this trained model, we have predicted the
{\Delta}Hf of a list of VHH. From the predicted database of VHH we have
selected Zr0.75NiSb and Hf0.75NiSb to validate the machine learning prediction
using accurate DFT calculation. The calculated {\Delta}Hf for these two
compounds from DFT calculation are found to be comparable with our ML
prediction. The calculated electronic and lattice dynamics properties show that
these materials are narrow band gap semiconductors and are dynamically stable
as their all-phonon dispersion curves are having positive frequencies. The
calculated Seebeck coefficient, electrical conductivity as well as thermal
conductivity, power factor and thermoelectric figure of merit are analyzed.",2309.04692v1
2011-08-18,Comparison of two structures for transition-metal-based half Heusler alloys exhibiting fully compensated half metallicity,"We search for new fully compensated half metals, in which only one electronic
spin channel is conducting and there exists no net magnetic moment. We focus on
half Heusler alloys and we examine the physical consequence of different
crystal structures found in the literature for these compounds, XMnZ, with a
transition metal element, such as Cr, Mn, and Fe for X and a nonmetallic
element, such as P, Sb and Si for Z. The structures differ in the placement of
voids in the L2$_1$ structure of the full Heulser alloy. One structure has the
void at (1/4, 3/4, 1/4)a and the other places the void at (0.0, 0.0, 1/2)a. The
first structure is expected to have greater d-p hybridization between Mn and
the Z atom. The other exhibits strong d-d hybridization between the nearest
neighboring transition metal elements. Five XMnZ compounds are considered along
with the previously studied CrMnSb in the second structure, which serves as a
reference. Besides the CrMnSb, only one other alloy, MnMnSi, shows fully
compensated half metallic properties in both structures. Both these alloys obey
the Slater-Pauling electron counting rule for half Hesuler alloys. The
differences between CrMnSb and MnMnSi in the two structures are discussed based
on their atomic properties. In the search for fully compensated half metals in
transition metal-based half Heusler alloys, we suggest using the counting rule
as a guide.",1108.3651v1
2017-07-03,Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes,"Spin caloritronics studies the interplay between charge-, heat- and
spin-currents, which are initiated by temperature gradients in magnetic
nanostructures. A plethora of new phenomena has been discovered that promises,
e.g., to make wasted heat in electronic devices useable or to provide new
read-out mechanisms for information. However, only few materials have been
studied so far with Seebeck voltages of only some {\mu}V, which hampers
applications. Here, we demonstrate that half-metallic Heusler compounds are hot
candidates for enhancing spin-dependent thermoelectric effects. This becomes
evident when considering the asymmetry of the spin-split density of electronic
states around the Fermi level that determines the spin-dependent thermoelectric
transport in magnetic tunnel junctions. We identify Co$_2$FeAl and Co$_2$FeSi
Heusler compounds as ideal due to their energy gaps in the minority density of
states, and demonstrate devices with substantially larger Seebeck voltages and
tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B based
junctions.",1707.00505v2
2019-05-22,Ultra-low magnetic damping in Co 2 Mn-based Heusler compounds: promising materials for spintronic,"The prediction of ultra-low magnetic damping in Co 2 MnZ Heusler half-metal
thin-film magnets is explored in this study and the damping response is shown
to be linked to the underlying electronic properties. By substituting the Z
elements in high crystalline quality films (Co 2 MnZ with Z=Si, Ge, Sn, Al, Ga,
Sb), electronic properties such as the minority spin band gap, Fermi energy
position in the gap and spin polarization can be tuned and the consequence on
magnetization dynamics analyzed. The experimental results allow us to directly
explore the interplay of spin polarization, spin gap, Fermi energy position and
the magnetic damping obtained in these films, together with ab initio
calculation predictions. The ultra-low magnetic damping coefficients measured
in the range 4.1 10-4-9 10-4 for Co 2 MnSi, Ge, Sn, Sb are the lowest values
obtained on a conductive layer and offers a clear experimental demonstration of
theoretical predictions on Half-Metal Magnetic Heusler compounds and a pathway
for future materials design.",1905.08987v1
2020-06-17,"Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes","Single-crystalline membranes of functional materials enable the tuning of
properties via extreme strain states; however, conventional routes for
producing membranes require the use of sacrificial layers and chemical
etchants, which can both damage the membrane and limit the ability to make them
ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler
compound GdPtSb on graphene-terminated Al$_2$O$_3$ substrates. Despite the
presence of the graphene interlayer, the Heusler films have epitaxial registry
to the underlying sapphire, as revealed by x-ray diffraction, reflection high
energy electron diffraction, and transmission electron microscopy. The weak Van
der Waals interactions of graphene enable mechanical exfoliation to yield
free-standing GdPtSb membranes, which form ripples when transferred to a
flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic,
measurements on rippled membranes show a spontaneous magnetic moment at room
temperature, with a saturation magnetization of 5.2 bohr magneton per Gd.
First-principles calculations show that the coupling to homogeneous strain is
too small to induce ferromagnetism, suggesting a dominant role for strain
gradients. Our membranes provide a novel platform for tuning the magnetic
properties of intermetallic compounds via strain (piezomagnetixm and
magnetostriction) and strain gradients (flexomagnetism).",2006.10100v3
2020-07-15,Experimentally correlating thermal hysteresis and phase compatibility in multifunctional Heusler alloys,"Thermal hysteresis is recognized as one of the main drawbacks for cyclical
applications of magnetocaloric and ferromagnetic shape memory materials with
first order transformations. As such, the challenge is to develop strategies
that improve the compatibility between the phases involved in the transitions
and study its influence on thermal hysteresis. With this purpose, we explore
the thermal, structural and magnetic properties of the Ni2Mn1-xCuxGa0.84Al0.16
Heusler alloys. The alloys present a thermal hysteresis reduction of ~60% when
the Cu content in the compound varies from x = 0.10 to x = 0.25, with a minimum
hysteresis width of 6 K being achieved. We applied the geometric non-linear
theory of martensite to address the phase compatibility, quantified by the
parameter lambda2, the middle eigenvalue of the transformation stretch tensor,
and found that the minimum of hysteresis is associated with a better
crystallographic compatibility (lambda2 closer to 1) between the austenite and
martensite phases. In addition, we show that the valley-like properties of
hysteresis found in the Ni2Mn1-xCuxGa0.84Al0.16 compounds is present in several
other alloys in the literature. These results provide new pathways to
understand as well as to masters the phase compatibility and ultimately achieve
a low thermal hysteresis in multifunctional Heusler alloys.",2007.07485v1
2022-04-07,"First Principles Study of the Structural, Mechanical, Electronic, and Lattice Dynamical Properties of the Half-Heusler Alloys ZrCoY (Y=Sb, Bi )","First-principles calculation has led to significant discoveries in materials
science. Half heusler (HH) alloys, which are potential thermoelectric materials
have demonstrated significant improvements in thermoelectric performance owing
to their thermal stability, mechanical strength, and moderate ZT. Using Density
Functional Theory (DFT), the structural, mechanical, electronic, and lattice
dynamical properties of cubic Half Heusler alloys ZrCoY (Y=Sb, Bi) have been
investigated. The unknown exchange-correlation functional is approximated using
the generalized gradient approximation (GGA) pseudopotential plane-wave
approach. The structural parameters, that is, equilibrium lattice constant,
elastic constants, and their derivatives are consistent with reported
experimental and theoretical studies where available. Mechanical properties
such as anisotropy factor A, shear modulus G, bulk modulus B, Youngs modulus E,
and Poisons ratio n, are calculated using the Voigt-Reuss-Hill average approach
based on elastic constants. The Debyes temperature, as well as longitudinal and
transverse sound velocities, are predicted from elastic constants at GGA-PBE
and GW approximations. The study of elastic constants showed that the compounds
are mechanically stable, and the phonon dispersion study showed that they are
dynamically stable as well. The ductility and anisotropic nature of the
compounds are confirmed by the elastic constants and mechanical properties.",2204.03759v1
2022-10-14,Anti-site disorder and Berry curvature driven anomalous Hall effect in spin gapless semiconducting Mn2CoAl Heusler compound,"Spin gapless semiconductors exhibit a finite band gap for one spin channel
and closed gap for other spin channel, emerged as a new state of magnetic
materials with a great potential for spintronic applications. The first
experimental evidence for the spin gapless semiconducting behavior was observed
in an inverse Heusler compound Mn2CoAl. Here, we report a detailed
investigation of the crystal structure and anomalous Hall effect in the Mn2CoAl
using experimental and theoretical studies. The analysis of the high-resolution
synchrotron x-ray diffraction data shows anti-site disorder between Mn and Al
atoms within the inverse Heusler structure. The temperature-dependent
resistivity shows semiconducting behavior and follows Mooijs criteria for
disordered metal. Scaling behavior of the anomalous Hall resistivity suggests
that the anomalous Hall effect in the Mn2CoAl is primarily governed by
intrinsic mechanism due to the Berry curvature in momentum space. The
experimental intrinsic anomalous Hall conductivity (AHC) is found to be 35
S/cm, which is considerably larger than the theoretically predicted value for
ordered Mn2CoAl. Our first-principle calculations conclude that the anti-site
disorder between Mn and Al atoms enhances the Berry curvature and hence the
value of intrinsic AHC, which is in a very well agreement with the experiment.",2210.07668v1
2002-09-11,"Exchange bias in [Co2MnGe/Au],[Co2MnGe/Cr] and [Co2MnGe/Cu2MnAl] multilayers","We report structural and magnetic properties of multilayers composed of thin
layers of the half metallic ferromagnetic Heusler compound Co2MnGe and layers
of Au, Cr and the Heusler compound Cu2MnAl. The hysteresis loops measured at
low temperatures reveal the existence of an exchange bias field HEB in all of
these multilayers. For the [Co2MnGe/Au] multilayer system HEB is largest
reaching up to 1 kOe at a temperature of 2 K. We characterize the exchange bias
phenomenon in detail and show that it originates from a spin glass type of
magnetic order for a thin interlayer at the interfaces. We discuss the results
in the light of different models proposed for the explanation of the exchange
bias effect.",0209259v1
2006-06-21,Magnetic anisotropies and magnetization reversal of the Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al Heusler compound,"Magnetic anisotropies and magnetization reversal properties of the epitaxial
Heusler compound Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al (CCFA) deposited on Fe and Cr
buffer layers are studied. Both samples exhibit a growth-induced fourfold
anisotropy, and magnetization reversal occurs through the formation of stripy
domains or 90 degree domains. During rotational magnetometric scans the sample
deposited on Cr exhibits about 2 degree sharp peaks in the angular dependence
of the coercive field, which are oriented along the hard axis directions. These
peaks are a consequence of the specific domain structure appearing in this
particular measurement geometry. A corresponding feature in the sample
deposited on Fe is not observed.",0606542v1
2006-12-10,Substituting the main group element in cobalt - iron based Heusler alloys: Co$_2$FeAl$_{1-x}$Si$_x$,"This work reports about electronic structure calculations for the Heusler
compound Co$_2$FeAl$_{1-x}$Si$_x$. Particular emphasis was put on the role of
the main group element in this compound. The substitution of Al by Si leads to
an increase of the number of valence electrons with increasing Si content and
may be seen as electron-doping. Self-consistent electronic structure
calculations were performed to investigate the consequences of the electron
doping for the magnetic properties. The series Co$_2$FeAl$_{1-x}$Si$_x$ is
found to exhibit half-metallic ferromagnetism and the magnetic moment follows
the Slater-Pauling rule. It is shown that the electron-doping stabilises the
gap in the minority states for $x=0.5$.",0612241v1
2008-09-29,"Hall effect in laser ablated Co_2(Mn,Fe)Si thin films","Pulsed laser deposition was employed to grow thin films of the Heusler
compounds Co_2MnSi and Co_2FeSi. Epitaxial growth was realized both directly on
MgO (100) and on a Cr or Fe buffer layer. Structural analysis by x-ray and
electron diffraction shows for both materials the ordered L2_1 structure. Bulk
magnetization was determined with a SQUID magnetometer. The values agree with
the Slater-Pauling rule for half-metallic Heusler compounds. On the films grown
directly on the substrate measurements of the Hall effect have been performed.
The normal Hall effect is nearly temperature independent and points towards a
compensated Fermi surface. The anomalous contribution is found to be dominated
by skew scattering. A remarkable sign change of both normal and anomalous Hall
coefficients is observed on changing the valence electron count from 29 (Mn) to
30 (Fe).",0809.4978v1
2009-05-24,Density functional study of elastic and vibrational properties of the Heusler-type alloys Fe$_2$VAl and Fe$_2$VGa,"The structural and elastic properties as well as phonon-dispersion relations
of the Heusler-type alloys Fe$_2$VAl and Fe$_2$VGa are computed using
density-functional and density-functional perturbation theory within the
generalized-gradient approximation. The calculated equilibrium lattice
constants agree well with the experimental values. The elastic constants of
Fe$_2$VAl and Fe$_2$VGa are predicted for the first time. From the elastic
constants the shear modulus, Young's modulus, Poisson's ratio, sound velocities
and Debye temperatures are obtained. By analyzing the ratio between the bulk
and shear modulii, we conclude that both Fe$_2$VAl and Fe$_2$VGa are brittle in
nature. The computed phonon-dispersion relation shows that both compounds are
dynamically stable in the L1$_2$ structure without any imaginary phonon
frequencies. The isomer shifts of Fe in the two compounds are discussed in
terms of the Fe s partial density of states, which reveal larger ionicity/less
hybridization in Fe$_2$VGa than in Fe$_2$VAl. For the same reason the Cauchy
pressure is negative in Fe$_2$VAl but positive in Fe$_2$VGa",0905.3909v1
2012-07-27,"Half-Metallic Ferromagnetism in the Heusler Compound Co$_2$FeSi revealed by Resistivity, Magnetoresistance, and Anomalous Hall Effect measurements","We present electrical transport data for single-crystalline Co$_2$FeSi which
provide clear-cut evidence that this Heusler compound is truly a half-metallic
ferromagnet, i.e. it possesses perfect spin-polarization. More specifically,
the temperature dependence of $\rho$ is governed by electron scattering off
magnons which are thermally excited over a sizeable gap $\Delta\approx 100 K$
($\sim 9 meV$) separating the electronic majority states at the Fermi level
from the unoccupied minority states. As a consequence, electron-magnon
scattering is only relevant at $T\gtrsim\Delta$ but freezes out at lower
temperatures, i.e., the spin-polarization of the electrons at the Fermi level
remains practically perfect for $T\lesssim\Delta$. The gapped magnon population
has a decisive influence on the magnetoresistance and the anomalous Hall effect
(AHE): i) The magnetoresistance changes its sign at $T\sim 100 K$, ii) the
anomalous Hall coefficient is strongly temperature dependent at $T\gtrsim 100
K$ and compatible with Berry phase related and/or side-jump electronic
deflection, whereas it is practically temperature-independent at lower
temperatures.",1207.6611v1
2013-02-08,Superconductivity in the noncentrosymmetric half-Heusler compound LuPtBi : A possible topological superconductor,"We report superconductivity in the ternary half-Heusler compound LuPtBi, with
Tc = 1.0 K and Hc2 = 1.6 T. The crystal structure of LuPtBi lacks inversion
symmetry, hence the material is a noncentrosymmetric superconductor.
Magnetotransport data show semimetallic behavior in the normal state, which is
evidence for the importance of spin-orbit interaction. Theoretical calculations
indicate that the strong spin-orbit interaction in LuPtBi should cause strong
band inversion, making this material a promising candidate for 3D topological
superconductivity.",1302.1943v2
2013-02-11,Phase stability of chromium based compensated ferrimagnets with inverse Heusler structure,"Chromium based inverse Heusler compounds of the type Cr2YZ (Y=Co, Fe; Z=Al,
Ga, In, Si, Ge, Sn) have been proposed as fully compensated half-metallic
ferrimagnets. Such materials are of large interest for spintronics because they
combine small magnetic moment with high spin polarization over a wide
temperature range. We assess their thermodynamic stability by their formation
enthalpies obtained from density functional theory calculations. All compounds
under investigation are unstable. Cr2FeSi and Cr2CoAl are stable with respect
to the elemental constituents, but decompose into binary phases. Cr2FeGe,
Cr2CoGa, Cr2FeSn and Cr2CoIn are found to be unstable with respect to their
elemental constituents. We identify possible binary decompositions.",1302.2487v2
2013-10-17,Superconductivity and magnetic order in the non-centrosymmetric Half Heusler compound ErPdBi,"We report superconductivity at $T_c = 1.22$ K and magnetic order at $T_N =
1.06$ K in the semi-metallic noncentrosymmetric Half Heusler compound ErPdBi.
The upper critical field, $B_{c2}$, has an unusual quasi-linear temperature
variation and reaches a value of 1.6 T for $T \rightarrow 0$. Magnetic order is
found below $T_c$ and is suppressed at $B{_M} \sim 2.5$ T for $T \rightarrow
0$. Since $T_c \simeq T_N$, the interaction of superconductivity and magnetism
is expected to give rise to a complex ground state. Moreover, electronic
structure calculations show ErPdBi has a topologically nontrivial band
inversion and thus may serve as a new platform to study the interplay of
topological states, superconductivity and magnetic order.",1310.4592v1
2014-03-11,Spin Dependent Lifetimes and Spin-orbit Hybridization Points in Heusler Compounds,"We present an ab initio calculation of the k and spin-resolved electronic
lifetimes in the half-metallic Heusler compounds Co(2)MnSi and Co(2)FeSi. We
determine the spin-flip and spin-conserving contributions to the lifetimes and
study in detail the behavior of the lifetimes around states that are strongly
spin-mixed by spin-orbit coupling. We find that, for non-degenerate bands, the
spin mixing alone does not determine the energy dependence of the (spin-flip)
lifetimes. Qualitatively, the lifetimes reflect the lineup of electron and hole
bands. We predict that different excitation conditions lead to drastically
different spin-flip dynamics of excited electrons and may even give rise to an
enhancement of the non-equilibrium spin polarization.",1403.2590v2
2015-03-15,Magnetic structure of the antiferromagnetic half-Heusler compound NdBiPt,"We present results of single crystal neutron diffraction experiments on the
rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits
an AFM phase transition at $T_{\mathrm N}=2.18$~K with an ordered moment of
$1.78(9)$~$\mu_{\mathrm B}$ per Nd atom. The magnetic moments are aligned along
the $[001]$-direction, arranged in a type-I AFM structure with ferromagnetic
planes, alternating antiferromagnetically along a propagation vector $\tau$ of
$(100)$. The $R$BiPt ($R$= Ce-Lu) family of materials has been proposed as
candidates of a new family of antiferromagnetic topological insulators (AFTI)
with magnetic space group that corresponds to a type-II AFM structure where
ferromagnetic sheets are stacked along the space diagonal. The resolved
structure makes it unlikely, that NdBiPt qualifies as an AFTI.",1503.04487v3
2015-10-21,Titanium Nitride as a Seed Layer for Heusler Compounds,"Titanium nitride (TiN) shows low resistivity at room temperature, high
thermal stability and thus has the potential to serve as seed layer in magnetic
tunnel junctions. High quality TiN thin films with regard to the
crystallographic and electrical properties were grown and characterized by
X-ray diffraction and 4-terminal transport measurements. Element specific X-ray
absorption spectroscopy revealed pure TiN in the bulk. To investigate the
influence of a TiN seed layer on a ferro(i)magnetic bottom electrode, an
out-of-plane magnetized Mn2.45Ga as well as in- and out-of-plane magnetized
Co2FeAl thin films were deposited on a TiN buffer, respectively. The magnetic
properties were investigated using a superconducting quantum interference
device (SQUID) and anomalous Hall effect (AHE) for Mn2.45Ga. Magneto optical
Kerr effect (MOKE) measurements were carried out to investigate the magnetic
properties of Co2FeAl. TiN buffered Mn2.45Ga thin films showed higher
coercivity and squareness ratio compared to unbuffered samples. The Heusler
compound Co2FeAl showed already good crystallinity when grown at room
temperature.",1510.06256v3
2015-10-27,Spin-resolved Fermi surface of the localized ferromagnetic Heusler compound Cu$_2$MnAl measured with spin-polarized positron annihilation,"We determined the bulk electronic structure in the prototypical Heusler
compound Cu$_2$MnAl by measuring the Angular Correlation of Annihilation
Radiation (2D-ACAR) using spin-polarized positrons. To this end, a new
algorithm for reconstructing 3D densities from projections is introduced that
allows us to corroborate the excellent agreement between our electronic
structure calculations and the experimental data. The contribution of each
individual Fermi surface sheet to the magnetization was identified, and summed
to a total spin magnetic moment of $3.6\,\pm\,0.5\,\mu_B/\mathrm{f.u.}$.",1510.07808v1
2015-11-26,Symmetry-protected ideal Weyl semimetal in HgTe-class materials,"Ideal Weyl semimetals with all Weyl nodes exactly at the Fermi level and no
coexisting trivial Fermi surfaces in the bulk, similar to graphene, could
feature deep physics such as exotic transport phenomena induced by the chiral
anomaly. Here, we show that HgTe and half-Heusler compounds, under a broad
range of in-plane compressive strain, could be materials in nature realizing
ideal Weyl semimetals with four pairs of Weyl nodes and topological surface
Fermi arcs. Generically, we find that the HgTe-class materials with nontrivial
band inversion and noncentrosymmetry provide a promising arena to realize ideal
Weyl semimetals. Such ideal Weyl semimetals could further provide a unique
platform to study emergent phenomena such as the interplay between ideal Weyl
fermions and superconductivity in the half-Heusler compound LaPtBi.",1511.08284v2
2016-10-18,Magnetic properties of low-moment ferrimagnetic Heusler Cr2CoGa thin films grown by molecular beam epitaxy,"Recently, theorists have predicted many materials with a low magnetic moment
and large spin-polarization for spintronic applications. These compounds are
predicted to form in the inverse Heusler structure, however, many of these
compounds have been found to phase segregate. In this study, ordered Cr2CoGa
thin films were synthesized without phase segregation using molecular beam
epitaxy. The present as-grown films exhibit a low magnetic moment from
antiferromagnetically coupled Cr and Co atoms as measured with SQUID
magnetometry and soft X-ray magnetic circular dichroism. Electrical
measurements demonstrated a thermally-activated semiconductor-like resistivity
with an activation energy of 87 meV. These results confirm spin gapless
semiconducting behavior, which makes these thin films well positioned for
future devices.",1610.05808v1
2017-03-06,A first-principles DFT+GW study of spin-filter and spin-gapless semiconducting Heusler compounds,"Among Heusler compounds, the ones being magnetic semiconductors (also known
as spin-filter materials) are widely studied as they offer novel
functionalities in spintronic/magnetoelectronic devices. The spin-gapless
semiconductors are a special case. They possess a zero or almost-zero energy
gap in one of the two spin channels. We employ the $GW$ approximation, which
allows an elaborate treatment of the electronic correlations, to simulate the
electronic band structure of these materials. Our results suggest that in most
cases the use of $GW$ self energy instead of the usual density functionals is
important to accurately determine the electronic properties of magnetic
semiconductors.",1703.02142v2
2018-06-11,Positron annihilation spectroscopy for the pure and Niobium doped ZrCo$_2$Sn Heusler compound,"We perform spin-polarized two-dimensional angular correlation of annihilation
radiation (2D-ACAR) calculations for the recently predicted ZrCo$_2$Sn-Weyl
Heusler compound within the density functional theory using the generalized
gradient approximation (GGA) and its extension GGA+U. We confirm that within
the GGA+U method, a pair of Weyl-points are revealed, and that by doping with
Niobium, for the composition Nb$_{0.3}$Zr$_{0.7}$Co$_2$Sn, the Weyl points are
reaching the Fermi level. Our 2D-ACAR results indicate the existence of the
Weyl points, however, within the present calculation, it is uncertain if the
smearing at the Fermi level can be attributed to the positron wave function.",1806.04093v1
2018-11-15,"LnPd$_{2}$Sn (Ln=Sc, Y, Lu) class of Heusler alloys for topological superconductivity","Based on the first-principles electronic structure calculations and the
symmetry analysis, we predict that the topological superconductivity may occur
on the surface of the LnPd$_{2}$Sn (Ln=Sc, Y, Lu) class of Heusler alloys. The
calculated electronic band structure and topological invariant demonstrate that
the LnPd$_{2}$Sn family is topologically nontrivial. The further slab
calculations show that the nontrivial topological surface states of
LnPd$_{2}$Sn exist within the bulk band gap and meanwhile they cross the Fermi
level. Considering that the LnPd$_{2}$Sn class of compounds were all found
experimentally to be superconducting at low temperature, the surface
topological superconductivity is likely to be generated via the proximity
effect. Thus the LnPd$_{2}$Sn class of compounds shall be a promising platform
for exploring novel topological superconductivity and handling Majorana zero
modes.",1811.06401v1
2020-01-22,Characterization of rattling in relation to thermal conductivity: ordered half-Heusler semiconductors,"The factors that affect the thermal conductivity of semiconductors is a topic
of great scientific interest, especially in relation to thermoelectrics. Key
developments have been the concept of the phonon-glass-electron-crystal (PGEC)
and the related idea of rattling to achieve this. We use first principles
phonon and thermal conductivity calculations in order to explore the concept of
rattling for stoichiometric ordered half-Heusler compounds. These compounds can
be regarded as filled zinc blende materials, and the filling atom could be
viewed as a rattler if it is weakly bound. We use two simple metrics, one
related to the frequency and the other to bond frustration and anharmonicity.
We find that both measures correlate with thermal conductivity. This suggests
that both may be useful in screening materials for low thermal conductivity.",2001.08029v1
2021-07-15,Microstructure manipulation by laser-surface remelting of a full-Heusler compound to enhance thermoelectric properties,"There is an increasing reckoning that the thermoelectric performance of a
material is dependent on its microstructure. However, the
microstructure-properties relationship often remains elusive, in part due to
the complexity of the hierarchy and scales of features that influence transport
properties. Here, we focus on the promising Heusler-Fe2VAl compound. We
directly correlate microstructure and local properties, using advanced scanning
electron microscopy methods including in-situ four-point-probe technique for
electron transport measurements. The local thermal conductivity is investigated
by scanning thermal microscopy. Finally, atom probe tomography provides
near-atomic scale compositional analysis. To locally manipulate the
microstructure, we use laser surface remelting. The rapid quenching creates a
complex microstructure with a high density of dislocations and small, elongated
grains. We hence showcase that laser surface remelting can be employed to
manipulate the microstructure to reduce the thermal conductivity and electrical
resistivity, leading to a demonstrated enhancement of the thermoelectric
performance at room temperature.",2107.07327v1
2017-05-23,Integration of antiferromagnetic Heusler compound Ru$_2$MnGe into spintronic devices,"We report on the first integration of an antiferromagnetic Heusler compound
acting as a pinning layer into magnetic tunneling junctions. The
antiferromagnet Ru$_2$MnGe is used to pin the magnetization direction of a
ferromagnetic Fe layer in MgO based thin film tunnelling magnetoresistance
stacks. The samples were prepared using magnetron co-sputtering. We investigate
the structural properties by X-ray diffraction and reflection, as well as
atomic force and high-resolution transmission electron microscopy. We find an
excellent crystal growth quality with low interface roughnesses of 1-3 \r{A},
which is crucial for the preparation of working tunnelling barriers. Using Fe
as a ferromagnetic electrode material we prepared magnetic tunneling junctions
and measured the magnetoresistance. We find a sizeable maximum
magnetoresistance value of 135%, which is comparable to other common Fe based
MTJ systems.",1705.08420v1
2019-07-09,Magnetic instabilities in doped Fe$_2YZ$ full-Heusler thermoelectric compounds,"Thermoelectricity is a promising avenue for harvesting energy but large-scale
applications are still hampered by the lack of highly-efficient low-cost
materials. Recently, Fe$_2YZ$ Heusler compounds were predicted theoretically to
be interesting candidates with large thermoelectric power factor. Here, we show
that under doping conditions compatible with thermoelectric applications, these
materials are prone to an unexpected magnetic instability detrimental to their
thermoelectric performance. We rationalize the physics at the origin of this
instability, provide guidelines for avoiding it and discuss its impact on the
thermoelectric power factor. Doing so, we also point out the shortcomings of
the rigid band approximation commonly used in high-throughput theoretical
searches of new thermoelectrics.",1907.04267v2
2018-08-08,High throughput screening for spin-gapless semiconductors in quaternary Heusler compounds,"Based on high throughput density functional theory calculations, we performed
systematic screening for spin-gapless semiconductors (SGSs) in quaternary
Heusler alloys XX 0 YZ (X, X 0 , and Y are transition metal elements without
Tc, and Z is one of B, Al, Ga, In, Si, Ge, Sn, Pb, P, As, Sb, and Bi).
Following the empirical rule, we focused on compounds with 21, 26, or 28
valence electrons, resulting in 12, 000 possible chemical compositions. After
systematically evaluating the thermodynamic, mechanical, and dynamical
stabilities, we successfully identified 70 stable SGSs, confirmed by explicit
electronic structure calculations with proper magnetic ground states. It is
demonstrated that all four types of SGSs can be realized, defined based on the
spin characters of the bands around the Fermi energy, and the type-II SGSs show
promising transport properties for spintronic applications. The effect of
spin-orbit coupling is investigated, resulting in large anisotropic
magnetoresistance and anomalous Nernst effects.",1808.02684v1
2018-12-20,"Theoretical study of the structural stability, electronic and magnetic properties of XVSb (X $=$ Fe, Ni, and Co) half-Heusler compounds","The structural, electronic and magnetic properties of half-Heusler compounds
XVSb (X $=$ Fe, Co and Ni) are investigated by using the density functional
theory with generalized gradient approximation (GGA), and Tran-Blaha modified
Becke-Johnson (TB-mBJ) exchange potential approximation. It is found that the
half-metallic gaps are generally reasonably widened by mBJ as compared to the
GGA approximation. The magnetic proprieties of XVSb (X $=$ Fe, Co and Ni) are
well defined within mBJ with an exact integer value of magnetic moment. The
band gaps given by TB-mBJ are in good agreement with the available theoretical
data. The FeVSb exhibits a semiconductor nature. The CoVSb and NiVSb present
half-metallic behaviour with total magnetic moment of $1\mu_\text{B}$ and
$2\mu_\text{B}$ in good agreement with Slater-Pauling rule. These alloys seem
to be a potential candidate of spintronic devices.",1812.08559v1
2020-08-07,Magnetoelastic and Magnetostrictive Properties of Co$_2$XAl Heusler Compounds,"We present a comprehensive first principles electronic structure study of the
magnetoelastic and magnetostrictive properties in the Co-based Co$_2$XAl (X =
V, Ti, Cr, Mn, Fe) full Heusler compounds. In addition to the commonly used
total energy approach, we employ torque method to calculate the magnetoelastic
tensor elements. We show that the torque based methods are in general
computationally more efficient, and allow to unveil the atomic- and
orbital-contributions to the magnetoelastic constants in an exact manner, as
opposed to the conventional approaches based on second order perturbation with
respect to the spin-orbit coupling. The magnetostriction constants are in good
agreement with available experimental data. The results reveal that the main
contribution to the magnetostriction constants, $\lambda_{100}$ and
$\lambda_{111}$, arises primarily from the strained-induced modulation of the
$\langle d_{x^2-y^2}|\hat{L}_z|d_{xy}\rangle$ and $\langle
d_{z^2}|\hat{L}_x|d_{yz}\rangle$ spin orbit coupling matrix elements,
respectively, of the Co atoms.",2008.03005v1
2022-03-22,"Lattice Dynamics, Mechanical Properties, Electronic Structure and Magnetic Properties of Equiatomic Quaternary Heusler Alloys CrTiCoZ (Z =Al,Si) using first principles calculations","First principles calculations are performed to investigate the
thermodynamical stability, dynamical, mechanical, electronic and magnetic
properties of CrTiCoZ (Z= Al/Si) novel quaternary Heusler alloys. Y-type III
atomic configuration is found to be the most stable structure for both
compounds. The melting temperatures of both compounds are as high as 2142 K and
2420 K for CrTiCoAl and CrTiCoSi, respectively. The electronic structure
calculations using GGA-PBE approach show a half metallic behavior of CrTiCoAl.
The spin-down channel exhibits a direct band gap of 0.15 eV, whereas the
spin-up channel is metallic making CrTiCoAl a half metallic ferromagnet with
100% spin polarization and an appreciable magnetic moment of -2 Bohr Magnetons.
The Curie temperature of CrTiCoAl is well above the room temperature (385K),
whereas that of CrTiCoSi is below the room temperature (203K).",2203.11858v1
2017-02-15,Stability of Weyl points in magnetic half-metallic Heusler compounds,"We employ {\it ab-initio} fully-relativistic electronic structure
calculations to study the stability of the Weyl points in the momentum space
within the class of the half-metallic ferromagnetic full Heusler materials, by
focusing on Co$_2$TiAl as a well-established prototype compound. Here we show
that both the number of the Weyl points together with their $k$-space
coordinates can be controlled by the orientation of the magnetization. This
alternative degree of freedom, which is absent in other topological materials
(e.g. in Weyl semimetals), introduces novel functionalities, specific for the
class of half-metallic ferromagnets. Of special interest are Weyl points which
are preserved irrespectively of any arbitrary rotation of the magnetization
axis.",1702.04558v1
2019-03-28,Inducing half metallicity with alloying in Heusler Compound CoFeMnSb,"First principles studies were performed in order to find out the possibility
of inducing half-metallicity in Heusler Compound CoFeMnSb, by means of alloying
it with 3d-transition metal elements. Proper alloying element is selected
through the calculations of formation energies. These calculations were tested
with different concentrations of alloying elements at different atomic sites.
Among the selected transition metal elements Sc and Ti are proposed to be
excellent alloying elements particularly at Mn site. By using these alloying
elements complete half metallic behaviour is obtained in CoFeMn0.25Sc0.75Sb,
CoFeMn0.75Ti0.25Sb, CoFeMn0.625Ti0.375Sb, CoFeMn0.50Ti0.50Sb,
CoFeMn0.25Ti0.75Sb and CoFeTiSb alloys. Shifting of Co-Fe d-states towards
lower energy region leads to zero density of states at Fermi level for the spin
minority channel. Alloying effects on the electronic structure and
magnetization are discussed in details. Thermodynamical stability of these new
alloys are major part of this study. The Curie temperatures of
CoFeMn0.25Sc0.75Sb and CoFeMn0.75Ti0.25Sb were found to be 324.5 K and 682 K;
respectively, showing good candidature for spintronics applications. For
understanding the bonding nature of constituent atom of CoFeMnSb, crystal
orbital Hamiltonian populations have been analysed.",1903.11799v1
2019-12-09,Intrinsically high thermoelectric figure of merit of half-Heusler ZrRuTe,"The electronic structure and thermoelectric properties of ZrRuTe-based
Half-Heusler compounds are studied using density functional theory (DFT) and
Boltzmann transport formalism. Based on rigorous computations of electron
relaxation time $\tau$ considering electron-phonon interactions and lattice
thermal conductivity $\kappa_l$ considering phonon-phonon interactions, we find
ZrRuTe to be an intrinsically good thermoelectric material. It has a high power
factor of $\sim 2\times 10^{-3}$ W/m-K$^{2}$ and low $\kappa_l\sim 10$ W/m-K at
800 K. The thermoelectric figure of merit $ZT \sim 0.13$ at 800 K is higher
than similar other compounds. We have also studied the properties of the
material as a function of doping and find the thermoelectric properties to be
substantially enhanced for $p$-doped ZrRuTe with the $ZT$ value raised to $\sim
0.2$ at this temperature. The electronic, thermodynamic, and transport
properties of the material are thoroughly studied and discussed",1912.03883v3
2020-03-14,Exceptionally large anomalous Hall effect due to anticrossing of spin-split bands in the antiferromagnetic half-Heusler compound TbPtBi,"We have investigated magnetotransport properties and the topological
electronic structure of the half-Heusler compound TbPtBi. Our experiments
reveal an exceptionally large anomalous Hall effect (AHE) in the canted
antiferromagnetic state of TbPtBi with the anomalous Hall angle (AHA) reaching
~0.68-0.76, which is a few times larger than the previously reported record in
GdPtBi. First-principles electronic structure and the associated anomalous Hall
conductivity were computed in order to interpret the experimental results. Our
analysis shows that the AHE in TbPtBi does not originate from the Weyl points
but that it is driven by the large net Berry curvature produced by the
anticrossing of spin-split bands near the Fermi level in TbPtBi.",2003.06688v1
2020-07-12,"Magnetocaloric effect in Ni2(Mn,Cu)Ga0.84Al0.16 Heusler alloys","Polycrystalline Heusler compounds Ni2Mn0.75Cu0.25Ga0.84Al0.16 with a
martensitic transition between ferromagnetic phases and
Ni2Mn0.70Cu0.30Ga0.84Al0.16 with a magnetostructural transformation were
investigated by magnetization and thermal measurements, both as a function of
temperature and magnetic field. The compound Ni2Mn0.75Cu0.25Ga0.84Al0.16
presents a large magnetocaloric effect among magnetically aligned structures
and its causes are explored. In addition, Ni2Mn0.70Cu0.30Ga0.84Al0.16 shows
very high, although irreversible, entropy and adiabatic temperature change at
room temperature under a magnetic field change 0-1 T. Improved refrigerant
capacity is also a highlight of the 30% Cu material when compared to similar
Ni2MnGa-based alloys.",2007.05899v2
2020-09-02,"Phase transition in the magnetocrystalline anisotropy of tetragonal Heusler alloys: Rh$_2T$Sb, $T=$ Fe, Co","This work reports on first principles calculations of the electronic and
magnetic structure of tetragonal Heusler compounds with the composition
Rh$_2$Fe$_{x}$Co$_{1-x}$Sb ($0\leq x\leq1$). It is found that the magnetic
moments increase from 2 to 3.4~$\mu_B$ and the Curie temperature decreases from
500 to 464~K with increasing Fe content $x$. The $3d$ transition metals make
the main contribution to the magnetic moments, whereas Rh contributes only
approximately 0.2~$\mu_B$ per atom, independent of the composition. The paper
focuses on the magnetocrystalline anisotropy of the borderline compounds
Rh$_2$FeSb, Rh$_2$Fe$_{0.5}$Co$_{0.5}$Sb, and Rh$_2$CoSb. A transition from
easy-axis to easy-plane anisotropy is observed when the composition changes
from Rh$_2$CoSb to Rh$_2$FeSb. The transition occurs at an iron concentration
of approximately 40\%.",2009.00920v1
2020-09-07,Strain driven emergence of topological non-triviality in YPdBi thin films,"Half-Heusler compounds exhibit a remarkable variety of emergent properties
such as heavy-fermion behaviour, unconventional superconductivity and
magnetism. Several of these compounds have been predicted to host topologically
non-trivial electronic structures. Remarkably, recent theoretical studies have
indicated the possibility to induce non-trivial topological surface states in
an otherwise trivial half-Heusler system by strain engineering. Here, using
magneto-transport measurements and first principles DFT-based simulations, we
demonstrate topological surface states on strained [110] oriented thin films of
YPdBi grown on (100) MgO. These topological surface states arise in an
otherwise trivial semi-metal purely driven by strain. Furthermore, we observe
the onset of superconductivity in these strained films highlighting the
possibility of engineering a topological superconducting state. Our results
demonstrate the critical role played by strain in engineering novel topological
states in thin film systems for developing next-generation spintronic devices.",2009.03018v3
2021-12-16,Spin Hall Conductivity and Anomalous Hall Conductivity in Full Heusler compounds,"The spin Hall conductivity (SHC) and anomalous Hall conductivity (AHC) in
more than 120 full Heusler compounds are calculated using density functional
theory in a high-throughtput way. The electronic structures are mapped to the
Wannier basis and the linear response theory is used to get the conductivity.
Our results show that the mechanism under the SHC or AHC cannot be simply
related to the valence electron numbers or atomic weights, is related to the
very details of the electronic structure, which can only be obtained by
calculations. A high throughput calculation is efficient to screen out the
desired materials. According to our present results, Cu2CoSn, as well as
Co2MnAl and Co2MnGa are candidates in spintronic materials regarding to their
high SHC and AHC values, which can benefit the spin-torque-driven nanodevices.",2112.08630v1
2022-09-21,Effect of Co Substitution on Ferrimagnetic Heusler compound Mn3Ga,"Effect of Co substitution on Mn$_3$Ga is investigated using first-principles
study for structural and magnetic properties. Without Co, ferrimagnetic Heusler
compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co
concentration (x) Mn$_3$Ga prefers tetragonal (cubic) phase when x \leq 0.5 (x
\geq 0.5). Ferrimagnetism is robust regardless of x in both phases. While
magnetic moments of two Mn do not vary significantly with x, Co magnetic moment
in two phases exhibit different behaviors, leading to distinct features in
total magnetic moment (M_{tot}). When x \leq 0.5, in tetragonal phase, Co
magnetic moment is vanishingly small, resulting in a decrease of M_{tot} with
x. In contrast, when x \geq 0.5, in cubic phase, Co magnetic moment is roughly
1$\mu_B$, which is responsible for an increase of Mtot. Electronic structure is
analyzed with partial density of states for various x. To elucidate the
counterintuitively small Co moment, the magnetic exchange interaction is
investigated where exchange coefficient between Co and Mn is much smaller in x
\leq 0.5 case than x \geq 0.5 one.",2209.10216v1
2024-03-24,"Ideal spin-polarized Weyl-half-semimetal with a single pair of Weyl points in half-Heusler compounds XCrTe (X=K, Rb)","Realizing ideal Weyl semimetal state with a single pair of Weyl points has
been a long-sought goal in the field of topological semimetals. Here, we reveal
such a state in the Cr-based half-Heusler compounds XCrTe (X=K, Rb). We show
that these materials have a half metal ground state, with Fermi level crossing
only one spin channel. Importantly, the Fermi surface is clean, consisting of
the minimal number (i.e., a single pair) of spin-polarized Weyl points, so the
state represents an ideal Weyl half semimetal. We show that the locations of
the two Weyl points and the associated Chern vector can be flexibly tuned by
rotating the magnetization vector. The minimal surface Fermi arc pattern and
its contribution to anomalous Hall transport are discussed. Our finding offers
an ideal material platform for exploring magnetic Weyl fermions, which will
also facilitate the interplay between Weyl physics and spintronics.",2403.16195v1
2002-09-24,Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni2.19Mn0.81Ga Heusler alloy,"In this paper we report the existence of a giant magnetocaloric effect (MCE)
in a intermetallic compound non-containing rare-earth. This effect is
associated with the concomitant occurrence of a structural and a magnetic
transition. The result has been compared with that obtained in a parent
compound in which magnetic and structural transition occur separately.",0209564v2
2009-06-04,Giant diamagnetism in half-metallic Co$_{2}$CrAl Heusler alloy,"A giant diamagnetism in the Co$_{2}$CrAl compounds, in both bulk and thin
film, below a certain temperature ($T_z$) was observed. Above $T_z$, the
compound behaves as an ordinary ferromagnet. The diamagnetic alignment might be
initiated by the Landau diamagnetism because of the half-metallic properties
and the pinning of the diamagnetism is preserved by the peculiar electronic
structures.",0906.0824v1
2015-09-18,Electron-phonon-averaged approximation for first-principles computations of electron relaxation times and transport properties in semiconductor materials,"We present a simple and efficient approximation to the electron-phonon
scattering rate suitable for high-throughput screening of candidate materials
for thermoelectric devices, based on electronic transport. The method is
applied to calculate the electronic transport coefficients of half-Heusler
compounds, showing agreement with experimental data. By directly computing
electrical and the electronic part of the thermal conductivities, we find
deviations from the Wiedemann-Franz law in these compounds at high temperatures
and low carrier concentrations.",1509.05800v2
2016-02-01,Anti-sites disordering suppression of the possible phase transition in Mn2CrGa,"Theoretical and experimental characterizations of Mn2CrGa compound in regard
to the possibility of phase transformation have been carried out in this work.
Under a high ordering L21 structure, this compound has the potential to be a
martensite phase transition material. However, experimental results show a
severe disordering took place in this system, which forbids the occurring of
the phase transition. This work provides important reference for the design of
new phase transition materials in Heusler alloys.",1602.00397v1
2016-07-13,Unraveling the dominant phonon scattering mechanism in thermoelectric compound ZrNiSn,"Determining defect types and concentrations remains a big challenge of
semiconductor materials science. By using ab-initio thermal conductivity
calculations we reveal that Ni/vacancy antisites, and not the previously
claimed Sn/Zr antisites, are the dominant defects affecting thermal transport
in half-Heusler compound ZrNiSn. Our calculations correctly predict the thermal
conductivity dependence with temperature and concentration, in quantitative
agreement with published experimental results. Furthermore, we find a
characteristic proportionality between phonon-antisite scattering rates and the
sixth power of phonon frequency, for which we provide an analytic derivation.
These results suggest that thermal conductivity measurements in combination
with ab-initio calculations can be used to quantitatively assess defect types
and concentrations in semiconductors.",1607.03624v1
2017-07-26,Magnetism from intermetallics and perovskite oxides,"This work has been presented by RJCV to obtain his PhD degree at Fluminense
Federal University, in March of 2017. We focused on the synthesis of compounds
and then on their magneto-strucutral characterization; mainly due to the
interplay of these physical properties. We have prepared intermetallic alloys
(including Heusler alloys) and perovskite oxides (manganites and cobaltites);
in bulk and nanoparticles. A thorough analysis of the influence of the
morphology and crystal structure on the magnetic properties of these compounds
is addressed.",1707.09868v2
2005-06-28,"Geometric, electronic, and magnetic structure of Co$_2$FeSi: Curie temperature and magnetic moment measurements and calculations","In this work a simple concept was used for a systematic search for new
materials with high spin polarization. It is based on two semi-empirical
models. Firstly, the Slater-Pauling rule was used for estimation of the
magnetic moment. This model is well supported by electronic structure
calculations. The second model was found particularly for Co$_2$ based Heusler
compounds when comparing their magnetic properties. It turned out that these
compounds exhibit seemingly a linear dependence of the Curie temperature as
function of the magnetic moment. Stimulated by these models, Co$_2$FeSi was
revisited. The compound was investigated in detail concerning its geometrical
and magnetic structure by means of X-ray diffraction, X-ray absorption and
M\""o\ss bauer spectroscopies as well as high and low temperature magnetometry.
The measurements revealed that it is, currently, the material with the highest
magnetic moment ($6\mu_B$) and Curie-temperature (1100K) in the classes of
Heusler compounds as well as half-metallic ferromagnets. The experimental
findings are supported by detailed electronic structure calculations.",0506729v4
2006-09-22,"Electronic structure, magnetism, and disorder in the Heusler compound Co$_2$TiSn","Polycrystalline samples of the half-metallic ferromagnet Heusler compound
Co$_2$TiSn have been prepared and studied using bulk techniques (X-ray
diffraction and magnetization) as well as local probes ($^{119}$Sn M\""ossbauer
spectroscopy and $^{59}$Co nuclear magnetic resonance spectroscopy) in order to
determine how disorder affects half-metallic behavior and also, to establish
the joint use of M\""ossbauer and NMR spectroscopies as a quantitative probe of
local ion ordering in these compounds. Additionally, density functional
electronic structure calculations on ordered and partially disordered
Co$_2$TiSn compounds have been carried out at a number of different levels of
theory in order to simultaneously understand how the particular choice of DFT
scheme as well as disorder affect the computed magnetization. Our studies
suggest that a sample which seems well-ordered by X-ray diffraction and
magnetization measurements can possess up to 10% of antisite (Co/Ti)
disordering. Computations similarly suggest that even 12.5% antisite Co/Ti
disorder does not destroy the half-metallic character of this material.
However, the use of an appropriate level of non-local DFT is crucial.",0609578v2
2014-01-10,Finding unprecedentedly low-thermal-conductivity half-Heusler semiconductors via high-throughput materials modeling,"The lattice thermal conductivity ({\kappa}{\omega}) is a key property for
many potential applications of compounds. Discovery of materials with very low
or high {\kappa}{\omega} remains an experimental challenge due to high costs
and time-consuming synthesis procedures. High-throughput computational
pre-screening is a valuable approach for significantly reducing the set of
candidate compounds. In this article, we introduce efficient methods for
reliably estimating the bulk {\kappa}{\omega} for a large number of compounds.
The algorithms are based on a combination of machine-learning algorithms,
physical insights, and automatic ab-initio calculations. We scanned
approximately 79,000 half-Heusler entries in the AFLOWLIB.org database. Among
the 450 mechanically stable ordered semiconductors identified, we find that
{\kappa}{\omega} spans more than two orders of magnitude- a much larger range
than that previously thought. {\kappa}{\omega} is lowest for compounds whose
elements in equivalent positions have large atomic radii. We then perform a
thorough screening of thermodynamical stability that allows to reduce the list
to 77 systems. We can then provide a quantitative estimate of {\kappa}{\omega}
for this selected range of systems. Three semiconductors having
{\kappa}{\omega} < 5 W /(m K) are proposed for further experimental study.",1401.2439v2
2016-02-03,"Robust tunability of magnetorestance in Half-Heusler RPtBi (R = Gd, Dy, Tm, and Lu) compounds","We present the magnetic field dependencies of transport properties for
$R$PtBi ($R$ = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature and
field dependent resistivity measurements of high quality $R$PtBi single
crystals reveal an unusually large, non-saturating magnetoresistance (MR) up to
300 K under a moderate magnetic field of $H$ = 140 kOe. At 300 K, the large MR
effect decreases as the rare-earth is traversed from Gd to Lu and the magnetic
field dependence of MR shows a deviation from the conventional $H^{2}$
behavior. The Hall coefficient ($R_{H}$) for $R$ = Gd indicates a sign change
around 120 K, whereas $R_{H}$ curves for $R$ = Dy, Tm, and Lu remain positive
for all measured temperatures. At 300 K, the Hall resistivity reveals a
deviation from the linear field dependence for all compounds. Thermoelectric
power measurements on this family show strong temperature and magnetic field
dependencies which are consistent with resistivity measurements. A highly
enhanced thermoelectric power under applied magnetic field is observed as high
as $\sim$100 $\mu$V/K at 140 kOe. Analysis of the transport data in this series
reveals that the rare-earth-based Half-Husler compounds provide opportunities
to tune MR effect through lanthanide contraction and to elucidate the mechanism
of non-trivial MR.",1602.01194v1
2019-12-21,Non-collinear antiferromagnetic states in Ru-based Heusler compounds induced by biquadratic coupling,"We investigate the magnetic properties of Ru$_{2}$Mn$Z$ ($Z$ = Sn, Sb, Ge,
Si) chemically ordered full Heusler compounds for zero as well as finite
temperatures. Based on first principles calculations we derive the interatomic
isotropic bilinear and biquadratic couplings between Mn atoms from the
paramagnetic state. We find frustrated isotropic couplings for all compounds
and in case of $Z$ = Si and Sb a nearest-neighbor biquadratic coupling that
favors perpendicular alignment between the Mn spins. By using an extended
classical Heisenberg model in combination with spin dynamics simulations we
obtain the magnetic equilibrium states. From these simulations we conclude that
the biquadratic coupling, in combination with the frustrated isotropic
interactions, leads to non-collinear magnetic ground states in the Ru$_{2}$MnSi
and Ru$_{2}$MnSb compounds. In particular, for these alloys we find two
distinct, non-collinear ground states which are energetically equivalent and
can be identified as $3-q$ and $4-q$ states on a frustrated fcc lattice.
Investigating the thermal stability of the non-collinear phase we find that in
case of Ru$_{2}$MnSi the multiple$-q$ phase undergoes a transition to the
single$-q$ phase, while in case of Ru$_{2}$MnSb the corresponding transition is
not obtained due to the larger magnitude of the nearest-neighbor biquadratic
coupling.",1912.10299v1
2020-11-20,"Mechanical, optoelectronic and thermoelectric properties of half-Heusler p-type semiconductor BaAgP: A DFT investigation","We have explored the mechanical, electronic, optical and thermoelectric
properties of p-type half-Heusler compound BaAgP for the first time using
density functional theory based calculations. The mechanical and dynamical
stability of this compound is confirmed by studying the Born stability criteria
and phonon dispersion curve, respectively. It is soft, ductile and elastically
anisotropic. The atomic bonding along a-axis is stronger than that along
c-axis. The calculated electronic structure reveals that the studied compound
is an indirect band gap semiconductor. The analysis of charge density
distribution map and Mulliken population reveals that the bonding in BaAgP is a
mixture of covalent and ionic. The optical features confirm that BaAgP is
optically anisotropic. The high absorption coefficient and low reflectivity in
the visible to ultraviolet region make this compound a possible candidate for
solar cell and optoelectronic device applications. The thermoelectric
properties have been evaluated by solving the Boltzmann semi-classical
transport equations. The calculated power factor at 1000K along a-axis is 35.2
micro-W/cmK2 (with tau=10-14 s) which is ~3.5 times larger than that of SnSe, a
promising layered thermoelectric materials. The thermoelectric figure of merit,
ZT of BaAgP is 0.44 which is small due to high thermal conductivity. So the
reduction of thermal conductivity is essential to enhance thermoelectric
performance of BaAgP in device applications.",2011.10506v1
2021-10-30,Self Doping for Synergistically Tuning the Electronic and Thermal Transport Coefficients in n-type Half-Heuslers,"Ternary intermetallic half-Heusler (HH) compounds (XYZ) with 18 valence
electron count viz. ZrCoSb, ZrNiSn, and ZrPdSn, have revealed promising
thermoelectric properties. Exemplarily, it has been experimentally observed
that a slight change in the content of Y-site atoms (by ~3-12.5% i.e., m =0.03,
0.125 in ZrY(1+m)Z) leads to drastic lowering in the lattice thermal
conductivity (kL) by more than 65-80% in many of these compounds. The present
work aims at exploring the possibility of maximizing the electronic transport
scenario after achieving the low kL limit in these compounds. By taking into
account the full anharmonicity of the lattice dynamics, Boltzmann transport
calculations are performed under the framework of density functional theory.
Our results show that these excess atoms present in the vacant lattice site
induce scattering by acting either as a rattling mode or by hybridizing with
the acoustic modes of the host depending upon their mass and bonding chemistry,
respectively. Furthermore, the introduction of these scattering centers may
lead to the formation of a defect mid-gap state in the electronic band
structure (detrimental for electronic transport) or lead to light doping of the
host compound. The latter is found to be particularly conducive for attaining
synergy in both thermal as well as electronic transport.",2111.00186v1
2022-07-20,Tunable phase transitions in half-Heusler TbPtBi compound,"We report various phase transitions in half-Heusler TbPtBi compound using
Density Functional Theory (DFT). Specifically, inclusion of spin-orbit coupling
(SOC) leads to band inversion resulting in transition from the metallic to the
topological semimetallic phase. However, in presence of SOC, there is a phase
transition from the topological semimetal to the trivial semimetal when the
material is subjected to compressive strain ($\lt -7\%$). Subsequently, under
further increase of compressive strain ($\ge -7\%$), we find an opening of a
direct band gap at the $\Gamma$ point, driving the system from the trivial
semimetallic to the semiconducting state with changes in the sequence of bands.
In the absence of SOC, only transition from the metallic to the semiconducting
phase is noticed. Under tensile strain, the TbPtBi compound maintains its phase
as in the unstrained condition but with an increase in the hole pocket at the
Fermi level, both in the absence and presence of SOC. These tunable phase
transitions (especially as a fraction of strain) make this compound very
promising for application in various quantum devices such as highly sensitive
strain gauges.",2207.09704v4
2009-11-03,Seebeck coefficients of half-metallic ferromagnets,"In this report the Co2 based Heusler compounds are discussed as potential
materials for spin voltage generation. The compounds were synthesized by
arcmelting and consequent annealing. Band structure calculations were performed
and revealed the compounds to be half-metallic ferromagnets. Magnetometry was
performed on the samples and the Curie temperatures and the magnetic moments
were determined. The Seebeck coefficients were measured from low to ambient
temperatures for all compounds. For selected compounds high temperature
measurements up to 900 K were performed.",0911.0553v1
2023-06-26,Large saturation moment and high ferromagnetic transition temperature in a structurally disordered inverse Heusler alloy Fe2RuGe,"We report the successful synthesis of a new 4$d$ based polycrystalline
inverse Heusler alloy Fe$_2$RuGe by an arc melting process and have studied in
detail its structural, magnetic and transport properties complemented with
first principle calculations. X-ray and neutron diffraction, Extended X-ray
Absorption Fine Structure and $^{57}$Fe M\""{o}ssbauer spectroscopic studies
confirm the single phase nature of the system where the Fe and Ru atoms are
randomly distributed in the 4$c$ and 4$d$ Wyckoff positions in a ratio close to
50:50. The formation of the disordered structure is also confirmed by the
theoretical energy minimization calculation. Despite the random cross-site
disorder of Fe and Ru atoms, magnetic measurements suggest not only a high
Curie temperature of $\sim$860\,K, but also a large saturation magnetic moment
$\sim$4.9\,$\mu_B$ per formula unit at 5\,K, considerably exceeding the
theoretical limit (4\,$\mu_B$ per formula unit) predicted by the Slater-Pauling
rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high
Curie temperatures. Neutron diffraction analysis coupled with the isothermal
magnetization value indicates that the magnetic moments in Fe$_2$RuGe are
associated with Fe-atoms only, which is also confirmed by M\""ossbauer
spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of
the parent compound, Fe$_3$Ge, the Curie temperature of Fe$_2$RuGe has
increased significantly despite the substitution of the nonmagnetic, yet
isoelectronic element Ru in this structurally disordered compound. Our
theoretical calculation reveals that the large Fe moment ($\sim2.8\mu_B$/Fe) on
the 4$b$ site can be attributed to a charge transfer from this Fe site towards
its Ru neighbours. Such a substantial increase in magnetic moment due to
electron charge transfer has not previously been reported in a Heusler alloy
system.",2306.14831v1
2016-03-03,"Predicted superconductivity of Ni2VAl and pressure dependence of superconductivity in Ni2NbX (X = Al, Ga and Sn) and Ni2VAl","A first-principles study of the electronic and superconducting properties of
the Ni$_2$VAl Heusler compound is presented. The electron-phonon coupling
constant of $\lambda_{ep}$ = 0.68 is obtained, which leads to a superconducting
transition temperature of T$_c$ = $\sim$4 $K$ (assuming a Coulomb
pseudopotential $\mu^*$ = 0.13), which is a relatively high transition
temperature for Ni based Heusler alloys. The electronic density of states
reveals a significant hybridization between Ni-$eg$ and V-$t_{2g}$ states
around the Fermi level. The Fermi surface, consisting of two electron pockets
around the X-points of the Brillouin zone, exhibits nesting and leads to a Kohn
anomaly of the phonon dispersion relation for the transverse acoustic mode TA2
along the (1,1,0) direction, which is furthermore found to soften with
pressure. As a consequence, T$_c$ and $\lambda_{ep}$ vary non-monotonically
under pressure. The calculations are compared to similar calculations performed
for the Ni$_2$NbX (X = Al, Ga and Sn) Heusler alloys, which experimentally have
been identified as superconductors. The experimental trend in T$_c$ is well
reproduced, and reasonable quantitative agreement is obtained. The calculated
T$_c$ of Ni$_2$VAl is larger than either calculated and observed T$_c$s of any
of the Nb compounds. The Fermi surfaces of Ni$_2$NbAl and Ni$_2$NbGa consist of
only a single electron pocket around the X point, however under compression
second electron pocket similar to that of Ni2VAl emerges only in Ni2NbAl and
the Tc increases non monotonically in all the compounds. Fermi surface nesting
and associated Kohn anomalies are a common feature of all four compounds,
albeit weakest in Ni$_2$VAl.",1603.01104v1
2020-03-11,High Thermoelectric Performance and Defect Energetics of Multi-pocketed Full-Heusler Compounds,"We report first-principles density-functional study of electron-phonon
interactions and thermoelectric transport properties of full-Heusler compounds
Sr$_{2}$BiAu and Sr$_{2}$SbAu. Our results show that ultrahigh intrinsic bulk
thermoelectric performance across a wide range of temperatures is physically
possible and point to the presence of multiply degenerate and highly dispersive
carrier pockets as the key factor for achieving it. Sr$_{2}$BiAu, which
features ten energy-aligned low effective mass pockets (six along $\Gamma-X$
and four at $L$), is predicted to deliver $n$-type $zT=0.4-4.9$ at
$T=100-700$~K. Comparison with the previously investigated Ba$_{2}$BiAu
compound shows that the additional $L$-pockets in Sr$_{2}$BiAu significantly
increase its low-temperature power factor to a maximum value of
$12$~mW~m$^{-1}$~K$^{-2}$ near $T=300$~K. However, at high temperatures the
power factor of Sr$_{2}$BiAu drops below that of Ba$_{2}$BiAu because the $L$
states are heavier and subject to strong scattering by phonon deformation as
opposed to the lighter $\Gamma-X$ states that are limited by polar-optical
scattering. Sr$_{2}$SbAu is predicted to deliver lower $n$-type of $zT=3.4$ at
$T=750$~K due to appreciable misalignment between the $L$ and $\Gamma-X$
carrier pockets, generally heavier scattering, and slightly higher lattice
thermal conductivity. Soft acoustic modes, responsible for low lattice thermal
conductivity, also increase vibrational entropies and high-temperature
stability of the Heusler compounds, suggesting that their experimental
synthesis may be feasible. The dominant intrinsic defects are found to be Au
vacancies, which drive the Fermi level towards the conduction band and work in
favor of $n$-doping.",2003.05506v3
2006-11-17,Electronic structure and magnetism in doped semiconducting half-Heusler compounds,"We have studied in details the electronic structure and magnetism in M (Mn
and Cr) doped semiconducting half-Heusler compounds FeVSb, CoTiSb and NiTiSn
(XM$_{x}$Y$_{1-x}$Z) in a wide concentration range using local-spin density
functional method in the framework of tight-binding linearized muffin tin
orbital method(TB-LMTO) and supercell approach. Our calculations indicate that
some of these compounds are not only ferromagnetic but also half-metallic and
may be useful for spintronics applications. The electronic structure of the
doped systems is analyzed with the aid of a simple model where we have
considered the interaction between the dopant transition metal (M) and the
valence band X-Z hybrid. We have shown that the strong X-d - M-d interaction
places the M-d states close to the Fermi level with the M-t$_{2g}$ states lying
higher in energy in comparison to the M-e$_{g}$ states. Depending on the number
of available d-electrons, ferromagnetism is realized provided the d-manifold is
partially occupied. The tendencies toward ferromagnetic(FM) or
antiferromagnetic(AFM) behavior are discussed within Anderson-Hasegawa models
of super-exchange and double-exchange. In our calculations for Mn doped NiTiSn,
the strong preference for FM over AFM ordering suggests a possible high Curie
temperature for these systems.",0611478v1
2013-07-24,μSR and NMR study of the superconducting Heusler compound YPd2Sn,"We report on muon spin rotation/relaxation and $^{119}$Sn nuclear magnetic
resonance (NMR) measurements to study the microscopic superconducting and
magnetic properties of the Heusler compound with the highest superconducting
transition temperature, \ypd\ ($T_c=5.4$ K). Measurements in the vortex state
provide the temperature dependence of the effective magnetic penetration depth
$\lambda(T)$ and the field dependence of the superconducting gap $\Delta(0)$.
The results are consistent with a very dirty s-wave BCS superconductor with a
gap $\Delta(0)=0.85(3)$ meV, $\lambda(0)= 212(1)$ nm, and a Ginzburg-Landau
coherence length $\xi_{\mathrm{GL}}(0)\cong 23$ nm. In spite of its very dirty
character, the effective density of condensed charge carriers is high compared
to the normal state. The \mSR data in a broad range of applied fields are well
reproduced by taking into account a field-related reduction of the effective
superconducting gap. Zero-field \mSR measurements, sensitive to the possible
presence of very small magnetic moments, do not show any indications of
magnetism in this compound.",1307.6386v2
2017-07-13,"The role of grain boundary scattering in reducing the thermal conductivity of polycrystalline XNiSn (X = Hf, Zr, Ti) half-Heusler alloys","Thermoelectric application of half-Heusler compounds suffers from their
fairly high thermal conductivities. Insight into how effective various
scattering mechanisms are in reducing the thermal conductivity of fabricated
XNiSn compounds (X = Hf, Zr, Ti, and mixtures thereof) is therefore crucial.
Here, we show that such insight can be obtained through a concerted
theory-experiment comparison of how the lattice thermal conductivity kLat(T)
depends on temperature and crystallite size. Comparing theory and experiment
for a range of Hf0.5Zr0.5NiSn and ZrNiSn samples reported in the literature and
in the present paper revealed that grain boundary scattering plays the most
important role in bringing down kLat, in particular so for unmixed compounds.
Our concerted analysis approach was corroborated by a good qualitative
agreement between the measured and calculated kLat of polycrystalline samples,
where the experimental average crystallite size was used as an input parameter
for the calculations. The calculations were based on the Boltzmann transport
equation and ab initio density functional theory. Our analysis explains the
significant variation of reported kLat of nominally identical XNiSn samples and
is expected to provide valuable insights into the dominant scattering
mechanisms even for other materials.",1707.04302v2
2020-11-03,Fully-Compensated Ferrimagnetic Spin Filter Materials within the Cr$\textit{M}\textit{N}$Al Equiatomic Quaternary Heusler Alloys,"XX'YZ equiatomic quaternary Heusler alloys (EQHA's) containing Cr, Al, and
select Group IVB elements ($\textit{M}$ = Ti, Zr, Hf) and Group VB elements
($\textit{N}$ = V, Nb, Ta) were studied using state-of-the-art density
functional theory to determine their effectiveness in spintronic applications.
Each alloy is classified based on their spin-dependent electronic structure as
a half-metal, a spin gapless semiconductor, or a spin filter material. We
predict several new fully-compensated ferrimagnetic spin filter materials with
small electronic gaps and large exchange splitting allowing for robust spin
polarization with small resistance. CrVZrAl, CrVHfAl, CrTiNbAl, and CrTiTaAl
are identified as particularly robust spin filter candidates with an exchange
splitting of $\sim 0.20$ eV. In particular, CrTiNbAl and CrTiTaAl have
exceptionally small band gaps of $\sim 0.10$ eV. Moreover, in these compounds,
a spin asymmetric electronic band gap is maintained in 2 of 3 possible atomic
arrangements they can take, making the electronic properties less susceptible
to random site disorder. In addition, hydrostatic stress is applied to a subset
of the studied compounds in order to determine the stability and tunability of
the various electronic phases. Specifically, we find the CrAlV$\textit{M}$
subfamily of compounds to be exceptionally sensitive to hydrostatic stress,
yielding transitions between all spin-dependent electronic phases.",2011.01389v1
2021-01-04,Influence of the martensitic transformation kinetics on the magnetocaloric effect in Ni-Mn-In,"The inverse magnetocaloric effect (MCE) in Ni-Mn-based Heusler compounds
occurs during the magnetostructural transition between low-temperature,
low-magnetization martensite and high-temperature, high-magnetization
austenite. In this study, we analyze the metamagnetic transformation of a
$Ni_{49.8}Mn_{35}In_{15.2}$ compound by simultaneous adiabatic temperature
change and strain measurements in pulsed magnetic fields up to 10 T. We observe
an adiabatic temperature change of -10 K and a strain of -0.22 % when the
reverse martensitic transition is fully induced at a starting temperature of
285 K. By a variation of the magnetic field-sweep rates between 316 Ts$^{-1}$,
865 Ts$^{-1}$ and 1850 Ts$^{-1}$, the transitional dynamics of the reverse
martensitic transformation have been investigated. Our experiments reveal an
apparent delay upon the end of the reverse martensitic transformation at field
rates exceeding 865 Ts$^{-1}$ which is related to the annihilation of retained
martensite. As a consequence, the field hysteresis increases and higher fields
are required to saturate the transition. In contrast, no time-dependent effects
on the onset of the reverse martensitic transformation were observed in the
studied field-sweep range. Our results demonstrate that kinetic effects in
Heusler compounds strongly affect the magnetic cooling cycle, especially when
utilising a multicaloric ""exploiting-hysteresis cycle"" where high magnetic
field-sweep rates are employed.",2101.00840v1
2013-11-20,Nuclear magnetic resonance study of thin Co$_2$FeAl$_{0.5}$Si$_{0.5}$ Heusler films with varying thickness,"Type, degree and evolution of structural order are important aspects for
understanding and controlling the properties of highly spin polarized Heusler
compounds, in particular with respect to the optimal film growth procedure. In
this work, we compare the structural order and the local magnetic properties
revealed by nuclear magnetic resonance (NMR) spectroscopy with the macroscopic
properties of thin Co$_2$FeAl$_{0.5}$Si$_{0.5}$ Heusler films with varying
thickness. A detailed analysis of the measured NMR spectra presented in this
paper enables us to find a very high degree of $L2_1$ type ordering up to 81%
concomitantly with excess Fe of 8 to 13% at the expense of Al and Si. We show,
that the formation of certain types of order do not only depend on the
thermodynamic phase diagrams as in bulk samples, but that the kinetic control
may contribute to the phase formation in thin films. It is an exciting finding
that Co$_2$FeAl$_{0.5}$Si$_{0.5}$ can form an almost ideal $L2_1$ structure in
films though with a considerable amount of Fe-Al/Si off-stoichiometry.
Moreover, the very good quality of the films as demonstrated by our NMR study
suggests that the novel technique of off-axis sputtering technique used to grow
the films sets stage for the optimized performance of
Co$_2$FeAl$_{0.5}$Si$_{0.5}$ in spintronic devices.",1311.5070v2
2014-08-19,Phase formation characteristics and magnetic properties of bulk Ni2MnGe Heusler alloy,"We have systemically studied the effects of annealing temperature and alloy
composition on the structural and magnetic properties of bulk Ni$_{2}$MnGe and
Ni$_{2.1}$Mn$_{0.9}$Ge Heusler alloys. We have observed that both annealing
temperature and the alloy composition drastically alter the phases found in the
samples due to the presence of competing ternary phases. Annealing at 900 and
950 $^{\circ}$C for both alloy compositions facilitate the formation of
L2$_{1}$ Heusler phase. Nevertheless, formation of Ni$_{5}$Mn$_{4}$Ge$_{3}$ and
Ni$_{16}$Mn$_{6}$Ge$_{7}$ phases cannot be prevented for Ni$_{2}$MnGe and
Ni$_{2.1}$Mn$_{0.9}$Ge alloys, respectively. In order to estimate the magnetic
contribution of the Ni$_{5}$Mn$_{4}$Ge$_{3}$ impurity phase to that of the
parent Ni$_{2}$MnGe, we have also synthesized pure Ni$_{5}$Mn$_{4}$Ge$_{3}$
alloy. Antiferromagnetic nature of Ni$_{5}$Mn$_{4}$Ge$_{3}$ with low
magnetization response allows us to reveal the magnetic response of the
stoichiometric bulk Ni$_{2}$MnGe. Bulk Ni$_{2}$MnGe shows simple ferromagnetic
behavior with a Curie temperature of 300 K, in agreement with the previous
results on thin films. Despite the divergence of magnetization curves between
field cooled (FC) and field heated (FH) modes, stoichiometric Ni$_{2}$MnGe
alloy does not undergo a martensitic phase transition based on our variable
temperature x-ray diffraction experiments.",1408.4241v1
2015-06-23,Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias,"The discovery of materials with improved functionality can be accelerated by
rational material design. Heusler compounds with tunable magnetic sublattices
allow to implement this concept to achieve novel magnetic properties. Here, we
have designed a family of Heusler alloys with a compensated ferrimagnetic
state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant
exchange bias (EB) of more than 3 T and a similarly large coercivity are
established. The large exchange anisotropy originates from the exchange
interaction between the compensated host and ferrimagnetic clusters that arise
from intrinsic anti-site disorder. We demonstrate the applicability of our
design concept on a second material, Mn-Fe-Ga, with a magnetic transition above
room temperature, exemplifying the universality of the concept and the
feasibility of room-temperature applications. Our study points to a new
direction for novel magneto-electronic devices. At the same time it suggests a
new route for realizing rare-earth free exchange-biased hard magnets, where the
second quadrant magnetization can be stabilized by the exchange bias.",1506.07028v1
2021-07-10,Anisotropic exchange and non-collinear antiferromagnets on a noncentrosymmetric fcc structure as in the half-Heuslers,"One of the signatures of the face-centered cubic (fcc) antiferromagnet as a
typical example of a geometrically frustrated system is the large ground state
degeneracy of the classical nearest neighbor and next-nearest neighbor
Heisenberg (isotropic) model on this lattice. In particular, collinear states
are degenerate with non-collinear and non-coplanar ones: this degeneracy is
accidental and is expected to be lifted by anisotropic exchange interactions.
In this work, we derive the most general nearest and next-nearest neighbor
exchange model allowed by the space-group symmetry of the noncentrosymmetric
half-Heusler compounds, which includes three anisotropic terms: the so-called
Kitaev, Gamma and Dzyaloshinskii-Moriya interactions -- most notably, the
latter is allowed by the breaking of inversion symmetry in these materials and
has not been previously been studied in the context of the fcc lattice. We
compute the resulting phase diagram and show how the different terms lift the
ground state degeneracy of the isotropic model, and lay emphasis on finding
regimes where multi-q (non-collinear/non-coplanar) states are selected by
anisotropy. We then discuss the role of quantum fluctuations and the coupling
to a magnetic field in the ground state selection, and show that these effects
can stabilize non-coplanar (triple-q) states. These results suggest that some
half-Heusler antiferromagnets might host rare non-collinear/non-coplanar
orders, which may in turn explain the unusual transport properties detected in
these semimetals.",2107.04906v2
2019-07-05,Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy,"Materials suitable for magnonic crystals demand low magnetic damping and long
spin wave (SW) propagation distance. In this context Co based Heusler compounds
are ideal candidates for magnonic based applications. In this work, antidot
arrays (with different shapes) of epitaxial
$\mathrm{Co}_2\mathrm{Fe}_{0.4}\mathrm{Mn}_{0.6}\mathrm{Si}$ (CFMS) Heusler
alloy thin films have been prepared using e-beam lithography and sputtering
technique. Magneto-optic Kerr effect and ferromagnetic resonance analysis have
confirmed the presence of dominant cubic and moderate uniaxial magnetic
anisotropies in the thin films. Domain imaging via x-ray photoemission electron
microscopy on the antidot arrays reveals chain like switching or correlated
bigger domains for different shape of the antidots. Time-resolved MOKE
microscopy has been performed to study the precessional dynamics and magnonic
modes of the antidots with different shapes. We show that the optically induced
spin-wave spectra in such antidot arrays can be tuned by changing the shape of
the holes. The variation in internal field profiles, pinning energy barrier,
and anisotropy modifies the spin-wave spectra dramatically within the antidot
arrays with different shapes. We further show that by combining the
magnetocrystalline anisotropy with the shape anisotropy, an extra degree of
freedom can be achieved to control the magnonic modes in such antidot lattices.",1907.02746v1
2020-08-31,Robust topological Hall effect driven by tunable noncoplanar magnetic state in Mn-Pt-In inverse tetragonal Heusler alloys,"Manipulation of magnetic ground states by effective control of competing
magnetic interactions has led to the finding of many exotic magnetic states. In
this direction, the tetragonal Heusler compounds consisting of multiple
magnetic sublattices and crystal symmetry favoring chiral Dzyaloshinskii-Moriya
interaction (DMI) provide an ideal base to realize non-trivial magnetic
structures. Here, we present the observation of a large robust topological Hall
effect (THE) in the multi-sublattice Mn$_{2-x}$PtIn Heusler magnets. The
topological Hall resistivity, which originates from the non-vanishing real
space Berry curvature in the presence of non-zero scalar spin chirality,
systematically decreases with decreasing the magnitude of the canting angle of
the magnetic moments at different sublattices. With help of first principle
calculations, magnetic and neutron diffraction measurements, we establish that
the presence of a tunable non-coplanar magnetic structure arising from the
competing Heisenberg exchanges and chiral DMI from the D$_{2d}$ symmetry
structure is responsible for the observed THE. The robustness of the THE with
respect to the degree of non-collinearity adds up a new degree of freedom for
designing THE based spintronic devices.",2008.13505v1
2017-06-11,First principles study of the structural phase stability and magnetic order in various structural phases of Mn$_2$FeGa,"We investigate the structural and magnetic properties of Mn$_{2}$FeGa for
different phases(cubic, hexagonal and tetragonal) reported experimentally using
density functional theory. The relative structural stabilities, and the
possible phase transformation mechanisms are discussed using results for total
energy, electronic structure and elastic constants. We find that the phase
transformation form hexagonal to ground state tetragonal structure would take
place through a Heusler-like phase which has a pronounced electronic
instability. The electronic structures, the elastic constants and the
supplementary phonon dispersions indicate that the transition from the
Heusler-like to the tetragonal phase is of pure Jahn-Teller origin. We also
describe the ground state magentic structures in each phase by computations of
the exchange interactions. For Heusler-like and tetragonal phases, the
ferromagnetic exchange interactions associated with the Fe atoms balance the
dominating antiferromagnetic interactions between the Mn atoms leading to
collinear magnetic structures. In the hexagonal phase, the direction of atomic
moment are completely in the planes with a collinear like structure, in stark
contrast to the well known non-collinear magnetic structure in the hexagonal
phase of Mn$_{3}$Ga, another material with similar structural properties. The
overwhelmingly large exchange interactions of Fe with other magnetic atoms
destroy the possibility of magnetic frustration in the hexagonal phase of
Mn$_{2}$FeGa. This comprehensive study provides significant insights into the
microscopic physics associated with the structural and magnetic orders in this
compound.",1706.03425v1
2017-10-05,"First-principles investigation of competing magnetic interactions in (Mn,Fe)Ru$_2$Sn Heusler solid solutions","Many Heusler compounds possess magnetic properties well-suited for
applications as spintronic materials. The pseudo-binary
Mn$_{0.5}$Fe$_{0.5}$Ru$_2$Sn, formed as a solid solution of two full Heuslers,
has recently been shown to exhibit exchange hardening suggestive of two
magnetic phases, despite existing as a \textit{single} chemical phase. We have
performed a first-principles study of the chemical and magnetic degrees of
freedom in the Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn pseudo-binary to determine the origin
of the unique magnetic behavior responsible for exchange hardening within a
single phase. We find a transition from antiferromagnetic (AFM) to
ferromagnetic (FM) behavior upon replacement of Mn with Fe, consistent with
experimental results. The lowest energy orderings in Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn
consist of chemically- and magnetically-uniform (111) planes, with Fe-rich
regions preferring FM ordering and Mn-rich regions preferring AFM ordering,
independent of the overall composition. Analysis of the electronic structure
suggests that the magnetic behavior of this alloy arises from a competition
between AFM-favoring Sn-mediated superexchange and FM-favoring RKKY exchange
mediated by spin-polarized conduction electrons. Changes in valency upon
replacement of Mn with Fe shifts the balance from superexchange-dominated
interactions to RKKY-dominated interactions.",1710.02089v1
2020-03-12,Semi-adsorption-controlled growth window for half Heusler FeVSb epitaxial films,"The electronic, magnetic, thermoelectric, and topological properties of
Heusler compounds (composition $XYZ$ or $X_2 YZ$) are highly sensitive to
stoichiometry and defects. Here we establish the existence and experimentally
map the bounds of a \textit{semi} adsorption-controlled growth window for
semiconducting half Heusler FeVSb films, grown by molecular beam epitaxy (MBE).
We show that due to the high volatility of Sb, the Sb stoichiometry is
self-limiting for a finite range of growth temperatures and Sb fluxes, similar
to the growth of III-V semiconductors such as GaSb and GaAs. Films grown within
this window are nearly structurally indistinguishable by X-ray diffraction
(XRD) and reflection high energy electron diffraction (RHEED). The highest
electron mobility and lowest background carrier density are obtained towards
the Sb-rich bound of the window, suggesting that Sb-vacancies may be a common
defect. Similar \textit{semi} adsorption-controlled bounds are expected for
other ternary intermetallics that contain a volatile species $Z=$\{Sb, As,
Bi\}, e.g., CoTiSb, LuPtSb, GdPtBi, and NiMnSb. However, outstanding challenges
remain in controlling the remaining Fe/V ($X/Y$) transition metal
stoichiometry.",2003.05971v2
2022-08-11,"Controlling the balance between remote, pinhole, and van der Waals epitaxy of Heusler films on graphene/sapphire","Remote epitaxy on monolayer graphene is promising for synthesis of highly
lattice mismatched materials, exfoliation of free-standing membranes, and
re-use of expensive substrates. However, clear experimental evidence of a
remote mechanism remains elusive. In many cases, due to contaminants at the
transferred graphene/substrate interface, alternative mechanisms such as
pinhole-seeded lateral epitaxy or van der Waals epitaxy can explain the
resulting exfoliatable single-crystalline films. Here, we find that growth of
the Heusler compound GdPtSb on clean graphene on sapphire substrates produces a
30 degree rotated epitaxial superstructure that cannot be explained by pinhole
or van der Waals epitaxy. With decreasing growth temperature the volume
fraction of this 30 degree domain increases compared to the direct epitaxial 0
degree domain, which we attribute to slower surface diffusion at low
temperature that favors remote epitaxy, compared to faster surface diffusion at
high temperature that favors pinhole epitaxy. We further show that careful
graphene/substrate annealing ($T\sim 700 ^\circ C$) and consideration of the
film/substrate vs film/graphene lattice mismatch are required to obtain epitaxy
to the underlying substrate for a variety of other Heusler films, including
LaPtSb and GdAuGe. The 30 degree rotated superstructure provides a possible
experimental fingerprint of remote epitaxy since it is inconsistent with the
leading alternative mechanisms.",2208.05927v1
2023-11-03,Giant tunneling magnetoresistance in Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi magnetic tunnel junction,"We propose a theoretical model for an all-Heusler magnetic tunnel junction
that uses two Heusler compounds: Fe$_2$CrSi and Fe$_2$TiSi, both of which can
be experimentally synthesized. Fe$_2$CrSi is a half-metallic ferromagnet,
making it a promising material for efficient spin injection in magnetic random
access memories and other spin-dependent devices. While, Fe$_2$TiSi is a
nonmagnetic semiconductor that has the same lattice structure and comparable
lattice constant with Fe$_2$CrSi, as it can be obtained by substituting the
$Y$-site atoms in Fe$_2$CrSi. By using Fe$_2$TiSi as a tunneling barrier
sandwiched by two pieces of semi-infinite Fe$_2$CrSi to construct an
all-Heusler magnetic tunnel junction, the interface disorder is naturally
reduced. Our calculations demonstrate that this magnetic tunnel junction can
exhibit a giant tunneling magnetoresistance of up to 10$^{9}$\% and remains
robust under finite bias voltage. These characteristics suggest that
Fe$_2$CrSi/Fe$_2$TiSi/Fe$_2$CrSi MTJ will be an ideal candidate for future
spintronic applications. More importantly, such a device model can keep such a
giant tunneling magnetoresistance at and beyond room temperature due to the
high Curie temperature of Fe$_2$CrSi.",2311.01772v1
2020-04-02,$d$ band filling and magnetic phase separation in transition metal-doped Mn$_3$SnC,"The structural and magnetic properties of transition metal-doped Mn$_3$SnC
are studied with an aim to understand the effect of transition metal atom on
magnetostructural properties of the antiperovskite compound. The doped
Mn$_{2.8}$T$_{0.2}$SnC (T = Cr, Fe, Co, Ni and Cu) compounds show a distinctly
different magnetic behavior which can be related to electronic filling of the
$d$ band of the transition metal atom. While Cr and Fe doped Mn$_3$SnC show
properties similar to that of Mn$_3$SnC, the Co, Ni and Cu doped compounds
exhibit nucleation of secondary phases which are devoid of carbon and having
Heusler and DO19 type hexagonal structure. A strong magnetic interaction is
observed between the impurity phases and the major antiperovskite phase leading
to a sharp decrease in magnetostructural transition temperature of the
antiperovskite phase and a cluster glassy ground state.",2004.00804v1
2015-03-01,"Anomalous Hall effect and current spin polarization in Co$_2$FeX (X = Al, Ga, In, Si, Ge, and Sn) Heusler compounds: A systematic {\it ab initio} study","In this paper, we perform a systematic {\it ab initio} study of two principal
spin-related phenomena, namely, anomalous Hall effect and current spin
polarization, in Co$_2$Fe-based Heusler compounds Co$_2$FeX (X = Al, Ga, In,
Si, Ge, Sn) within the generalized gradient approximation (GGA). The accurate
full-potential linearized augmented plane-wave method is used. We find that the
spin-polarization of the longitudinal current ($P^L$) in Co$_2$FeX (X = Al, Ga,
In, Al$_{0.5}$Si$_{0.5}$ and Sn) is $\sim$100 \% even though that of the
electronic states at the Fermi level ($P^D$) is not. Further, the other
compounds also have a high current spin polarization with $P^L > 85$ \%. This
indicates that all the Co$_2$FeX compounds considered are promising for
spin-transport devices. Interestingly, $P^D$ is negative in Co$_2$FeX (X = Si,
Ge and Sn), differing in sign from the $P^L$ as well as that from the transport
experiments. Secondly, the calculated anomalous Hall conductivities (AHCs) are
moderate, being within 200 S/cm, and agree well with the available experiments
on highly L2$_1$ ordered Co$_2$FeSi specimen although they differ significantly
from the reported experiments on other compounds where the B2 antisite
disorders were present. Surprisingly, the AHC in Co$_2$FeSi decreases and then
changes sign when Si is replaced by Ge and finally by Sn. Third, the calculated
total magnetic moments agree well with the corresponding experimental ones in
all the studied compounds except Co$_2$FeSi where a difference of 0.3
$\mu_B$/f.u. exists. We also perform the GGA plus on-site Coulomb interaction
$U$ calculations in the GGA+$U$ scheme. We find that including the $U$ affects
the calculated total magnetic moment, spin polarization and AHC significantly,
and in most cases, results in a disagreement with the available experimental
results.",1503.00204v1
2019-04-08,"Two functionals approach in DFT for the prediction of thermoelectric properties of Fe$_{2}$ScX (X = P, As, Sb) full Heusler compounds","In the quest of new thermoelectric (TE) materials with high power factors,
full-Heusler compounds having flat band are found to be promising candidates.
In this direction, Fe$_{2}$ScX (X=P,As,Sb) compounds are investigated using mBJ
for the band gap and SCAN to describe the electronic bands and phonon
properties for TE applications. The band gaps obtained from mBJ are 0.81 eV,
0.69 eV and 0.60 eV for Fe$_{2}$ScX compounds, respectively. The phonon
dispersion, phonon density of states (DOS) and partial DOS are calculated. The
phonon contributions to specific heat are obtained as a function of temperature
under harmonic approximation. The electronic band structutre calculated from
mBJ and SCAN functionals are qualitatively compared. The TE parameters are
calculated for both hole and electron dopings under semiclassical theory. We
use simple, but reasonable method to estimate phonon relaxation time
($\tau_{ph}$). Using the specific heat, estimated $\tau_{ph}$ and slopes (phase
velocity) of acoustic branches in the linear region, lattice thermal
conductivity ($\kappa_{ph}$) at 300 K is calculated for three compounds. The
obtained values of $\kappa_{ph}$ with constant $\tau_{ph}$ are 18.2, 13.6 and
10.3 $Wm^{-1}K^{-1}$, respectively. Finally, the temperature dependent figure
of merit $ZT$ values are calculated for optimal carrier concentrations in the
doping range considered, to evaluate the materials for TE application. The $ZT$
values for n-type Fe$_{2}$ScX, in 900-1200 K, are 0.34-0.43, 0.40-0.48 and
0.45-0.52, respectively. While, the p-type Fe$_{2}$ScX have $ZT$ of 0.25-0.34,
0.20-0.28 and 0.18-0.26, respectively in the same temperature range. The $ZT$
values suggest that, Fe$_{2}$ScX compounds can be promising materials in high
temperature power generation application on successful synthesis and further
$\kappa_{ph}$ reduction by methods like nanostructuring.",1904.04322v1
2002-03-26,Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys,"We study the origin of the gap and the role of chemical composition in the
half-ferromagnetic Heusler alloys using the full-potential screened KKR method.
In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap.
Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are
semiconductors, but when Z_t > 18 antibonding states are also populated, thus
the paramagnetic phase becomes unstable and the half-ferromagnetic one is
stabilized. The minority occupied bands accommodate a total of nine electrons
and the total magnetic moment per unit cell in mu_B is just the difference
between Z_t and $2 \times 9$. While the substitution of the transition metal
atoms may preserve the half-ferromagnetic character, substituting the $sp$ atom
results in a practically rigid shift of the bands and the loss of
half-metallicity. Finally we show that expanding or contracting the lattice
parameter by 2% preserves the minority-spin gap.",0203534v3
2005-04-26,"First-principles study of exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge)","We report the parameter-free, density functional theory calculations of
interatomic exchange interactions and Curie temperatures of half-metallic
ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge). To calculate the
interatomic exchange interactions we employ the frozen-magnon approach. The
Curie temperatures are calculated within the mean-field approximation to the
classical Heisenberg Hamiltonian by solving a matrix equation for a
multi-sublattice system. Our calculations show that, although a large magnetic
moment is carried by Mn atoms, competing ferromagnetic (inter sublattice) and
antiferromagnetic (intra sublattice) Mn-Mn interactions in Mn2VAl almost cancel
each other in the mean-field experienced by the Mn atoms. In Mn2VGe the leading
Mn-Mn exchange interaction is antiferromagnetic. In both compounds the
ferromagnetism of the Mn subsystem is favored by strong antiferromagnetic Mn-V
interactions. The obtained value of the Curie temperature of Mn2VAl is in good
agrement with experiment. For Mn2VGe there is no experimental information
available and our calculation is a prediction.",0504679v1
2005-12-15,"Search for half-metallic ferrimagnetism in V-based Heusler alloys Mn$_2$VZ (Z$=$Al, Ga, In, Si, Ge, Sn)","Using a state-of-the-art full-potential electronic structure method within
the local spin density approximation, we study the electronic and magnetic
structure of Mn$_2$V-based full Heusler alloys: Mn$_2$VZ (Z=Al, Ga, In, Si, Ge,
and Sn). We show that small expansion of the calculated theoretical equilibrium
lattice constants restores the half-metallic ferrimagnetism in these compounds.
Moreover a small degree of disorder between the V and Z atoms, although iduces
some states within the gap, it preserves the Slater-Pauling behaviour of the
spin magnetic moments and the alloys keep a high degree of spin-polarisation at
the Fermi level opening the way for a half-metallic compensated ferrimagnet.",0512361v1
2006-01-17,Electron Correlations and the Minority-Spin Band Gap in Half-Metallic Heusler Alloys,"Electron-electron correlations affect the band gap of half-metallic
ferromagnets by introducing non-quasiparticle states just above the Fermi
level. In contrast to the spin-orbit coupling, a large asymmetric
non-quasiparticle spectral weight is present in the minority-spin channel,
leading to a peculiar finite-temperature spin depolarization effects. Using
recently developed first-principle dynamical mean field theory, we investigate
these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We
discuss depolarization effects in terms of strength of local Coulomb
interaction $U$ and temperature in FeMnSb. We propose Ni$_{1-x}$Fe$_{x}$MnSb
alloys as a perspective materials to be used in spin-valve structures and for
experimental search of non-quasiparticle states in half-metallic materials.",0601376v1
2006-12-01,Epitaxial Co2Cr0.6Fe0.4Al thin films and magnetic tunneling junctions,"Epitaxial thin films of the theoretically predicted half metal
Co2Cr0.6Fe0.4Al were deposited by dc magnetron sputtering on different
substrates and buffer layers. The samples were characterized by x-ray and
electron beam diffraction (RHEED) demonstrating the B2 order of the Heusler
compound with only a small partition of disorder on the Co sites. Magnetic
tunneling junctions with Co2Cr0.6Fe0.4Al electrode, AlOx barrier and Co counter
electrode were prepared. From the Julliere model a spin polarisation of
Co2Cr0.6Fe0.4Al of 54% at T=4K is deduced. The relation between the annealing
temperature of the Heusler electrodes and the magnitude of the tunneling
magnetoresistance effect was investigated and the results are discussed in the
framework of morphology and surface order based of in situ STM and RHEED
investigations.",0612022v1
2007-06-25,Optical and magneto-optical properties of ferromagnetic full-Heusler films: experiments and first-principles calculations,"We report a joint theoretical and experimental study focused on understanding
the optical and magneto-optical properties of Co-based full-Heusler compounds.
We show that magneto-optical spectra calculated within ab-initio density
functional theory are able to uniquely identify the features of the
experimental spectra in terms of spin resolved electronic transitions. As
expected for 3d-based magnets, we find that the largest Kerr rotation for these
alloys is of the order of 0.3o in polar geometry. In addition, we demonstrate
that (i) multilayered structures have to be carefully handled in the
theoretical calculations in order to improve the agreement with experiments,
and (ii) combined theoretical and experimental investigations constitute a
powerful approach to designing new materials for magneto-optical and
spin-related applications",0706.3613v1
2010-06-01,Giant inverse magnetocaloric effect near room temperature in Co substituted NiMnSb Heusler alloys,"The effect of Co on the structural, magnetic and magnetocaloric effect (MCE)
of Ni50-xCoxMn38Sb12 (x=0,2,3,4,5) Heusler alloys was studied. Using x-ray
diffraction, we show the evolution of the martensitic phase from the austenite
phase. The martensitic transition temperature is found to decrease
monotonically with Co concentration. Remarkable enhancement of MCE is observed
near room temperature upon Co substitution. The maximum magnetic entropy change
of 34 Jkg-1K-1 was achieved in x=5 at 262 K in a field of 50 kOe and a value of
29 Jkg-1K-1 found near room temperature. The significant increase in the
magnetization associated with the reverse martensitic transition is responsible
for the giant MCE in these compounds.",1006.0072v1
2010-11-26,Weak itinerant ferromagnetism in Heusler type Fe2VAl0.95,"We report measurements of the magnetic, transport and thermal properties of
the Heusler type compound Fe2VAl0.95. We show that while stoichiometric Fe2VAl
is a non-magnetic semi-metal a 5% substitution on the Al-site with the 3d
elements Fe and V atoms leads to a ferromagnetic ground state with a Curie
temperature TC = 33+-3 K and a small ordered moment ms = 0.12 mB/Fe in
Fe2VAl0.95. The reduced value of the ratio ms/mp = 0.08, where mp = 1.4 mB/Fe
is the effective Curie-Weiss moment, together with the analysis of the
magnetization data M(H,T), show magnetism is of itinerant nature. The specific
heat shows an unusual temperature variation at low temperatures with an
enhanced Sommerfeld coefficient, g = 12 mJK-2mol-1. The resistivity, r(T), is
metallic and follows a power law behavior r(T) = r0+AT^n with n = 1.5 below TC.
With applying pressure, TC decreases with the rate of (1/TC)(dTC /dP) = -0.061
GPa-1. We conclude substitution on the Al-site with Fe and V atoms results in
itinerant ferromagnetism with a low carrier density.",1011.5704v1
2011-02-25,CuMn-V compounds: a transition from semimetal low-temperature to semiconductor high-temperature antiferromagnets,"We report on a theoretical and experimental study of CuMn-V antiferromagnets.
Previous works showed low-temperature antiferomagnetism and semimetal
electronic structure of the semi-Heusler CuMnSb. In this paper we present
theoretical predictions of high-temperature antiferromagnetism in the stable
orthorhombic phases of CuMnAs and CuMnP. The electronic structure of CuMnAs is
at the transition from a semimetal to a semiconductor and we predict that CuMnP
is a semiconductor. We show that the transition to a semiconductor-like band
structure upon introducing the lighter group-V elements is present in both the
metastable semi-Heusler and the stable orthorhombic crystal structures. On the
other hand, the orthorhombic phase is crucial for the high N\'eel temperature.
Results of X-ray diffraction, magnetization, transport, and neutron diffraction
measurements we performed on chemically synthesized CuMnAs are consistent with
the theory predictions.",1102.5373v1
2011-07-25,Half-Heusler semiconductors as piezoelectrics,"One of the central challenges in materials science is the design of
functional and multifunctional materials, in which large responses are produced
by applied fields and stresses. A rapidly developing paradigm for the rational
design of such materials is based on the first-principles study of a large
materials family, the perovskite oxides being the prototypical case.
Specifically, first-principles calculations of structure and properties are
used to explore the microscopic origins of the functional properties of
interest and to search a large space of equilibrium and metastable phases to
identify promising candidate systems. In this paper, we use a first-principles
rational-design approach to demonstrate semiconducting half-Heusler compounds
as a previously-unrecognized class of piezoelectric materials, and to provide
guidance for the experimental realization and further investigation of
high-performance materials suitable for practical applications.",1107.5078v2
2013-07-08,Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds,"Half-Heusler (HH) alloys have attracted considerable interest as promising
thermoelectric (TE) materials in the temperature range around 700 K and above,
which is close to the temperature range of most industrial waste heat sources.
The past few years have seen nanostructuing play an important role in
significantly enhancing the TE performance of several HH alloys. In this
article, we briefly review the recent progress and advances in these HH
nanocomposites. We begin by presenting the structure of HH alloys and the
different strategies that have been utilized for improving the TE properties of
HH alloys. Next, we review the details of HH nanocomposites as obtained by
different techniques. Finally, the review closes by highlighting several
promising strategies for further research directions in these very promising TE
materials.",1307.2156v1
2013-11-28,Local magnetism and structural properties of Heusler Ni$_2$MnGa alloys,"We present a detailed experimental study of bulk and powder samples of the
Heusler shape memory alloy Ni$_2$MnGa, including zero-field static and dynamic
$^{55}$Mn NMR experiments, X-ray powder diffraction and magnetization
experiments. The NMR spectra give direct access to the sequence of structural
phase transitions in this compound, from the high-T austenitic phase down to
the low-T martensitic phase. In addition, a detailed investigation of the
so-called rf-enhancement factor provides local information for the magnetic
stiffness and restoring fields for each separate coordination, structural,
crystallographic environment, thus differentiating signals coming from
austenitic and martensitic components. The temperature evolution of the NMR
spectra and the rf-enhancement factors shows strong dependence on sample
preparation. In particular, we find that sample powderization gives rise to a
significant portion of martensitic traces inside the high-T austenitic region,
and that these traces can be subsequently removed by annealing.",1311.7414v1
2015-09-20,"Electronic structure, magnetism and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys","We present a combined theoretical and experimental study of two quaternary
Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for
spintronics applications. Magnetization measurement shows the saturation
magnetization and transition temperature to be $3\; \mu_B$, $866$ K and $0.9 \;
\mu_B$, $358$ K for CFCG and CMCA respectively. The magnetization values agree
fairly well with our theoretical results and also obey the Slater-Pauling rule,
a prerequisite for half metallicity. A striking difference between the two
systems is their structure; CFCG crystallizes in fully ordered Y-type structure
while CMCA has L2$_1$ disordered structure. The antisite disorder adds a
somewhat unique property to the second compound, which arises due to the
probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is
possibly expected due to comparable electronegativities of Al and Cr/Mn. {\it
Ab-initio} simulation predicted a unique transition from half metallic
ferromagnet to metallic antiferromagnet beyond a critical excess amount of Al
in the alloy.",1509.05971v2
2016-04-05,Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl,"We report the magnetism and transport properties of the Heusler compound
Fe2+xV1-xAl at -0.10 < x < 0.10 under pressure and a magnetic field. A
metal-insulator quantum phase transition occurred at x = -0.05. Application of
pressure or a magnetic field facilitated the emergence of finite
zero-temperature conductivity around the critical point, which scaled
approximately according to the power law. At x < -0.05, a localized
paramagnetic spin appeared, whereas above the ferromagnetic quantum critical
point at x = 0.05, itinerant ferromagnetism was established. At the quantum
critical points at x = -0.05 and 0.05, the resistivity and specific heat
exhibited singularities characteristic of a Griffiths phase appearing as an
inhomogeneous electronic state.",1604.01114v2
2016-07-19,Lattice Thermal Conductivity of NiTiSn Half-Heusler Thermoelectric Materials from First-Principles Calculations,"The microscopic physics behind the lattice thermal conductivity of NiTiSn is
investigated using first-principles-based anharmonic lattice dynamics. The
calcu lated lattice thermal conductivity of bulk materials (5.3 W/m.K) is in
good agreement with the experimental value at the optimal working temper ature
(700 K), but is overestimated below this temperature. The calculated values can
be strongly affected by the size of the crystalline grains. We show tha t the
lattice thermal conductivity is dominated by the acoustic (transverse and
mostly longitudinal) modes with no contribution from the optical modes. The a
coustic phonons are located below 150 cm-1 and involve mainly the tin atoms.
The calculated mean free path of the most heat carrying phonons is around f
ifty nanometers with a maximum life time of approx. 100 ps. These theoretical
results are a step forward in developing the experimental design of low thermal
conductivity NiTiSn Heusler based materials.",1607.05558v1
2017-03-03,Discovery of Magnetic Antiskyrmions Beyond Room Temperature in Tetragonal Heusler Materials,"Skyrmions, topologically stable spin textures, are of great interest for new
generations of spintronic devices. In general, the stabilization of skyrmions
has been achieved in systems with broken inversion symmetry, where the
asymmetric Dzyaloshinskii-Moriya interaction (DMI) modifies the uniform
magnetic state to a swirling state. Depending on the crystal symmetries, two
distinct types of skyrmions, Bloch and N\'eel types, have been observed
experimentally. Here, we present, the experimental manifestation of a special
type of spin-swirling, namely antiskyrmions, in a family of acentric tetragonal
Heusler compounds with D2d crystal symmetry. A spiral magnetic ground-state,
which propagates in the tetragonal basal plane, is transformed into a skyrmion
lattice-state under magnetic fields applied along the tetragonal axis over a
wide temperature interval. Direct imaging by Lorentz Transmission Electron
Microscopy (LTEM) shows field stabilized antiskyrmion lattices and isolated
antiskyrmions between 100 K and 400 K, and zero-field metastable antiskyrmions
at low temperatures.",1703.01017v1
2018-06-04,"Atomistic Study of the Electronic Contact Resistivity Between the Half-Heusler Alloys (HfCoSb, HfZrCoSb, HfZrNiSn) and the Metal Ag","Half-Heusler(HH) alloys have shown promising thermoelectric properties in the
medium and high temperature range. To harness these material properties for
thermoelectric applications, it is important to realize electrical contacts
with low electrical contact resistivity. However, little is known about the
detailed structural and electronic properties of such contacts, and the
expected values of contact resistivity. Here, we employ atomistic ab initio
calculations to study electrical contacts in a subclass of HH alloys consisting
of the compounds HfCoSb, HfZrCoSb, and HfZrNiSn. By using Ag as a prototypical
metal, we show that the termination of the HH material critically determines
the presence or absence of strong deformations at the interface. Our study
includes contacts to doped materials, and the results indicate that the p-type
materials generally form ohmic contacts while the n-type materials have a small
Schottky barrier. We calculate the temperature dependence of the contact
resistivity in the low to medium temperature range and provide quantitative
values that set lower limits for these systems.",1806.01375v1
2019-04-04,\textit{Ab initio} study of Bi-based half Heusler alloys as potential thermoelectric prospects,"We investigated six heavy element bismuth-based 18-VEC half-Heusler alloys
CoTiBi, CoZrBi, CoHfBi, FeVBi, FeNbBi, and FeTaBi by first principles approach,
in search of better thermoelectric prospects. The motivation is driven by
expected lower thermal conductivity and the recent discovery of CoZrBi-based
materials. Significantly, our calculated power factor values of all the systems
show an increment of $\sim$40\% in comparison to the reported \textit{p}-type
CoTiSb. We propose that doping at Bi-site, on account of electronic features,
will be helpful in achieving the proposed power factor values. Interestingly,
the thermal conductivity of CoTiBi and CoZrBi was found to be lower and that of
CoHfBi was almost parallel, in comparison to the reported CoTiSb. We also
provide conservative estimates of the figure of merit, exceeding the reported
CoTiSb and comparable to FeNbSb. Overall, our results suggest potential new
candidates of bismuth-based ternary compounds for high thermoelectric
performance.",1904.02488v1
2018-02-01,Stability of Room Temperature Compensated Half-Metallicity in Cr-based Inverse-Heusler Compounds,"Using three correlated band approaches, namely the conventional band approach
plus on-site Coulomb repulsion $U$, the modified Becke-Johnson functional, and
hybrid functional, we have investigated inverse-Heusler ferrimagnets
Cr$_2$Co${\cal Z}$ (${\cal Z}$=Al, Ga, In). These approaches commonly indicate
that the Cr$_2$CoAl synthesized recently is a precise compensated half-metal
(CHM), whereas Cr$_2$CoGa and Cr$_2$CoIn are ferrimagnets with a small moment.
This is also confirmed by the fixed spin moment approach. Analysis of the Bader
charge decomposition and the radial charge densities indicates that this
contrast is due to chemical differences among the ${\cal Z}$ ions.
Additionally, in Cr$_2$CoAl, changing the volume by $\pm$ 5% or the ratio of
$c/a$ by $\pm$ 2% does not alter the CHM state, suggesting that this state is
robust even under application of moderate pressure or strain. Considering the
observed high Curie temperature of 750 K, our results suggest that Cr$_2$CoAl
is a promising candidate for robust high $T_C$ CHMs. Furthermore, the
electronic structure of the CHM Cr$_2$CoAl is discussed.",1802.00125v2
2018-02-28,Magnetocaloric effect in some magnetic materials in alternating magnetic fields up to 22 Hz,"Direct measurements of the magnetocaloric effect (MCE) in different materials
(Gd, Fe48Rh52, Ni43Mn37.9In12.1Co7 and Ni2.07Co0.09Mn0.84Ga) in alternating
magnetic fields with frequencies f < 22 Hz and an amplitude deltaH = 6.2 kOe
are carried out. The MCE in Gd shows inconsiderable changes with field
frequency. Near paramagnetic-ferromagnetic phase transition in
Ni43Mn37.9In12.1Co7 Heusler alloy a slight reduction of MCE with frequency is
observed. In weak alternating fields in materials with AFM-FM
magneto-structural phase transitions (Fe48Rh52, Ni43Mn37.9In12.1Co7) it is not
possible to get a structural contribution to overall MCE because of
irreversibility of the transitions in these fields. Near magneto-structural
phase transitions the MCE in these alloys has only magnetic contribution, and
does not show a significant dependence on the magnetic field frequency. In
Ni2.07Co0.09Mn0.84Ga Heusler alloy the MCE vanishes at frequencies about 20 Hz.
The obtained results show the increase of frequencies of operating cycles is
one of the powerful methods to improve the efficiency of magnetic refrigerators
in case of Gd as a refrigerant.",1802.10391v1
2018-08-21,Negative longitudinal magnetoresistance as a sign of a possible chiral magnetic anomaly in the half-Heusler antiferromagnet DyPdBi,"Magnetotransport investigation of a half-Heusler antiferromagnet DyPdBi
revealed hallmark features of Weyl semimetal: huge negative longitudinal
magnetoresistance and planar Hall effect. Both effects have recently been
linked to chiral magnetic anomaly - axial charge pumping between Weyl nodes.
Magnetoresistance (MR) of single crystals of DyPdBi is very pronounced. In
magnetic field longitudinal to electrical current direction it reaches -80% and
its relative difference with respect to that measured in transverse field
(expressed as anisotropic magnetoresistance) is extremely strong: -60% at 10K
and 14 T. The planar Hall effect in DyPdBi depends on temperature and magnetic
field in non-monotonous way, which has not been previously reported. We compare
magnetoresistance measured with voltage contacts on mid-line of the sample with
that measured with contacts on its edge, and show that the role of
current-jetting, an extrinsic source of anisotropic negative magnetoresistance,
is marginal. We discuss that nature of the compound and sample quality exclude
intrinsic sources of negative and anisotropic magnetoresistance other than weak
localization and the chiral magnetic anomaly.",1808.06856v2
2021-03-29,"Prediction of electronic and half metallic properties of Mn$_2$YSn (Y = Mo, Nb, Zr) Heusler alloys","We investigate the structural, electronic and magnetic properties of the full
Heusler compounds Mn$_2$YSn (Y = Mo, Nb, Zr) by first-principles density
functional theory using the generalized gradient approximation. It is found
that the calculated lattice constants are in good agreement with the
theoretical values. We observe that the Cu$_2$MnAl-type structure is more
stable than the Hg$_2$CuTi type. The calculated total magnetic moments of
Mn$_2$NbSn and Mn$_2$ZrSn are 1 $\mu_{\text{B}}$ and 2 $\mu_{\text{B}}$ at the
equilibrium lattice constant of 6.18 \AA and 6.31 \AA, respectively, for the
Cu$_2$MnAl-type structure. Mn$_2$MoSn have a metallic character in both
Hg$_2$CuTi and Cu$_2$MnAl type structures. The total spin magnetic moment obeys
the Slater-Pauling rule. Half-metal exhibits 100% spin polarization at the
Fermi level. Thus, these alloys are promising magnetic candidates in spintronic
devices.",2103.15542v1
2016-03-15,Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors,"Transition-metal-based Heusler semiconductors are promising materials for a
variety of applications ranging from spintronics to thermoelectricity.
Employing the $GW$ approximation within the framework of the FLAPW method, we
study the quasi-particle band structure of a number of such compounds being
almost gapless semiconductors. We find that in contrast to the
\textit{sp}-electron based semiconductors such as Si and GaAs, in these systems
the many-body corrections have a minimal effect on the electronic band
structure and the energy band gap increases by less than 0.2~eV, which makes
the starting point density functional theory (DFT) a good approximation for the
description of electronic and optical properties of these materials.
Furthermore, the band gap can be tuned either by the variation of the lattice
parameter or by the substitution of the \emph{sp}-chemical element.",1603.04677v1
2017-10-07,Effect of multinary substitution on electronic and transport properties of TiCoSb based half-Heusler alloys,"The electronic structures of TixZrx/2CoPbxTex, TixZrx/2Hfx/2CoPbxTex (x =
0.5), and the parent compound TiCoSb were investigated using the full potential
linearized augmented plane wave method. The thermoelectric transport properties
of these alloys are calculated on the basis of semi-classical Boltzmann
transport theory. From the band structure calculations we show that the
substitution of Zr,Hf in the Ti site and Pb and Te in the Sb site lower the
band gap value and also change the indirect band (IB) gap of TiCoSb to the
direct band (DB) gap. The calculated band gap of TiCoSb, TixZrx/2CoPbxTex, and
TixZrx/2Hfx/2CoPbxTex are 1.04 eV (IB), 0.92 eV (DB), and 0.93 eV (DB),
respectively. All these alloys follow the empirical rule of 18 valence-electron
content which is essential for bringing semiconductivity in half Heusler
alloys. It is shown that the substitution of Hf at the Ti site improve the ZT
value (~1.05) at room temperature, whereas there is no significant difference
in ZT is found at higher temperature. Based on the calculated thermoelectric
transport properties, we conclude that the appropriate concentration of Hf
substitution can further improve the thermoelectric performance of
TixZrx/2Hfx/2CoPbxTex.",1710.02639v1
2018-04-23,"Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations","Structural, electronic, and transport properties of ScNiSb, ScPdSb, and
ScPtSb were investigated from first principles. Electronic band structures
derived within the fully relativistic MBJLDA approach were compared with those
obtained from the standard GGA calculations. All the compounds studied exhibit
indirect narrow band gaps (0.24-0.63 eV). The effective masses of hole-like
carriers are relatively small (0.27-0.36), and decrease with an increasing
atomic number of the transition metal component. The carrier relaxation time,
required for realistic calculations of the electrical conductivity, was
approximated within the deformation potential theory. The GGA approach yielded
overestimated transport characteristics with respect to those derived within
the MBJLDA analysis. The largest power factor of 4-6 mWK^-2m^-1 ) at high
temperatures was obtained for ScPtSb. This value is comparable with those
observed experimentally for Fe-Nb-Sb half-Heusler alloys, and hence makes
ScPtSb a very good candidate material for thermoelectric applications.",1804.08423v1
2019-03-28,Surface resonance of the Heusler half metal Co2MnSi probed by SX-ARPES,"Heusler compounds are promising materials for spintronics with adjustable
electronic properties including 100% spin polarization at the Fermi energy. We
investigate the electronic states of AlOx capped epitaxial thin films of the
ferromagnetic half metal Co2MnSi ex-situ by soft X-ray angular resolved
photoemission spectroscopy (SX-ARPES). Good agreement between the experimental
SX- ARPES results and photoemission calculations including surface effects was
obtained. In particular, we observed in line with our calculations a large
photoemission intensity at the center of the Brillouin zone, which does not
originate from bulk states, but from a surface resonance. This provides strong
evidence for the validity of the previously proposed model based on this
resonance, which was applied to explain the huge spin polarization of Co2MnSi
observed by angular-integrating UV-photoemission spectroscopy.",1903.11840v1
2019-05-25,Magnetic 2D electron liquid at the surface of Heusler semiconductors,"Conducting and magnetic properties of a material often change in some
confined geometries. However, a situation where a non-magnetic semiconductor
becomes both metallic and magnetic at the surface is quite rare, and to the
best of our knowledge has never been observed in experiment. In this work, we
employ first-principles electronic structure theory to predict that such a
peculiar magnetic state emerges in a family of quaternary Heusler compounds. We
investigate magnetic and electronic properties of CoCrTiP, FeMnTiP and CoMnVAl.
For the latter material, we also analyse the magnetic exchange interactions and
use them for parametrizing an effective spin Hamiltonian. According to our
results, magnetism in this material should persist at temperatures at least as
high as 155 K.",1905.10541v1
2021-08-11,Critical Magnetic Behavior of the Half Heusler Alloy RhCrSi: Monte Carlo Study,"In this paper, we study the critical magnetic properties of the Half Heusler
alloy RhCrSi, using Monte Carlo simulations (MCS) under the Metropolis
algorithm. In fact, to study this alloy, we apply an Ising model using the MCS
simulations, we concentrate only on the magnetic atoms: Rh and Cr. For this
purpose, these magnetic atoms are modeled by the spin moments S=5/2 for Rh
atoms and sigma=2 for Cr atoms, respectively. In addition, we discuss the
ground state phase diagrams in different planes corresponding to different
physical parameters. On the other hand, for non-null temperature values, we
perform the Monte Carlo simulations (MCS) to study the critical behavior of the
compound RhCrSi, in the Ising approximation. Indeed, we present a detailed
discussion of the obtained results for the magnetizations as a function of the
temperature, the crystal field and the exchange coupling interactions.
Additionally, we give the reliance of the basic temperature as an element of
precious crystal field when fixing the exchange coupling interactions. To
finish this work, we built up and examined the magnetic hysteresis cycles and
the relating coercive fields as a part of the external magnetic field.",2108.05162v1
2021-09-02,A first-principles investigation of pressure induced topological phase transition in Half-Heusler AgSrBi,"Topological Insulators (TI) are materials with novel quantum states which
exhibit a bulk insulating gap while the edge/surface is conducting. This has
been extensively explored in several Half-Heusler (HH) compounds hosting the
exotic TI behaviour. In the present work we employ, first-principles based
Density Functional Theory to perform thorough investigations of pressure
induced topological phase transition (TPT) in HH AgSrBi which belongs to the
F-43m space group. AgSrBi is intrinsically semi-metallic in nature which, under
isotropic pressure exhibits semi-metal to trivial insulator transition
retaining the cubic symmetry whereas, on breaking the cubic symmetry we observe
the much sought after non-trivial semi-metal to TI phase transition. We also
explore the effect of lowering crystal symmetry in realizing TI nature.
Following this we perform qualitative analysis of the electronic properties to
understand the origin of this non-trivial behavior followed by the quantitative
analysis of the Z$_2$ classification which indicates that AgSrBi is a strong TI
(i.e., Z$_2$ = (1, 101)). We thus, propose AgSrBi as a dynamically stable TI
which can be used as ultra-thin films thermoelectric and nanoelectronic
applications.",2109.01108v1
2021-11-28,"Electronic properties of the Weyl semimetals Co$_2$MnX (X=Si, Ge, Sn)","Using first-principles electronic structure calculations, we show that
ferromagnetic Heusler compounds Co$_2$MnX (X= Si, Ge, Sn) present non-trivial
topological characteristics and belong to the category of Weyl semimetals.
These materials exhibit two topologically interesting band crossings near the
Fermi level. These band crossings have complex 3D geometries in the Brillouin
zone and are characterized by non-trivial topology as Hopf links and chain-like
nodal lines, that are protected by the perpendicular mirror planes. The
spin-orbit interaction split these nodal lines into several zero-dimensional
Weyl band crossings. Unlike previously known topologically non-trivial Heusler
materials, these majority-spin band crossings lie in the band gap of minority
spin bands, potentially facilitating its experimental realization.",2111.14135v1
2022-05-07,First-principle calculations on Li2CuSb: A novel material for lithium-ion batteries,"We investigate the Li2CuSb full-Heusler alloy using the first-principles
electronic structure calculations and propose the electrochemical lithiation in
this alloy. Band structure calculations suggest the presence of metallic nature
in this alloy contrary to half-metallic nature as predicted for most of the
members of the full-Heusler alloy family. This alloy is found to be a promising
anode material for high-capacity rechargeable batteries based on lithium-ion.
We found a removal voltage of 2.48 V for lithium ions in the Li2CuSb/Cu cell,
which is in good agreement with the experimentally obtained result for a
similar kind of material Cu3Sb. During charge and discharge cycles of the
Li2CuSb/Cu cell, the formation of a non-stoichiometric compound Li2-yCu1+xSb
having a similar structure as Li2CuSb suggests a better performance as well as
stabilitty of this cell.",2205.03631v1
2022-11-23,Molecular Beam Epitaxy of a Half-Heusler Topological Superconductor Candidate YPtBi,"The search for topological superconductivity has motivated investigations
into materials that combine topological and superconducting properties. The
half-Heusler compound YPtBi appears to be such a material, however experiments
have thus far been limited to bulk single crystals, drastically limiting the
scope of available experiments. This has made it impossible to investigate the
potential topological nature of the superconductivity in this material.
Experiments to access details about the superconducting state require
sophisticated lithographic structures, typically based on thin films. Here we
report on the establishment of high crystalline quality epitaxial thin films of
YPtBi(111), grown using molecular beam epitaxy on Al2O3(0001) substrates. A
robust superconducting state is observed, with both critical temperature and
critical field consistent with that previously reported for bulk crystals.
Moreover we find that AlOx capping sufficiently protects the sample surface
from degradation to allow for proper lithography. Our results pave a path
towards the development of advanced lithographic structures, that will allow
the exploration of the potentially topological nature of superconductivity in
YPtBi.",2211.13106v1
2023-02-15,"Magnetic phase diagram of the austenitic Mn-rich Ni-Mn-(In,Sn) Heusler alloys","Heusler compounds have been intensively studied owing to the important
technological advancements that they provide in the field of shape memory,
thermomagnetic energy conversion and spintronics. Many of their intriguing
properties are ultimately governed by their magnetic states and understanding
and possibly tuning them is evidently of utmost importance. In this work we
examine the \alloys alloys with Density Functional Theory simulations and
$^{55}$Mn Nuclear Magnetic Resonance and combine these two methods to carefully
describe their ground state magnetic order. In addition, we compare the results
obtained with the conventional generalized gradient approximation with the ones
of strongly constrained and appropriately normed (SCAN) semilocal functionals
for exchange and correlation. Experimental results eventually allow to
discriminate between two different scenarios identified by ab initio
simulations.",2302.07550v1
2023-11-26,Machine Learning-based estimation and explainable artificial intelligence-supported interpretation of the critical temperature from magnetic ab initio Heusler alloys data,"Machine Learning (ML) has impacted numerous areas of materials science, most
prominently improving molecular simulations, where force fields were trained on
previously relaxed structures. One natural next step is to predict material
properties beyond structure. In this work, we investigate the applicability and
explainability of ML methods in the use case of estimating the critical
temperature for magnetic Heusler alloys calculated using ab initio methods
determined materials-specific magnetic interactions and a subsequent Monte
Carlo (MC) approach. We compare the performance of regression and
classification models to predict the range of the critical temperature of given
compounds without performing the MC calculations. Since the MC calculation
requires computational resources in the same order of magnitude as the
density-functional theory (DFT) calculation, it would be advantageous to
replace either step with a less computationally intensive method such as ML. We
discuss the necessity to generate the magnetic ab initio results to make a
quantitative prediction of the critical temperature. We used state-of-the-art
explainable artificial intelligence (XAI) methods to extract physical relations
and deepen our understanding of patterns learned by our models from the
examined data.",2311.15423v1
2018-01-10,Prediction of a magnetic Weyl semimetal without spin-orbit coupling and strong anomalous Hall effect in the Heusler compensated ferrimagnet Ti2MnAl,"We predict a magnetic Weyl semimetal in the inverse Heusler Ti2MnAl, a
compensated ferrimagnet with a vanishing net magnetic moment and a Curie
temperature of over 650 K. Despite the vanishing net magnetic moment, we
calculate a large intrinsic anomalous Hall effect (AHE) of about 300 S/cm. It
derives from the Berry curvature distribution of the Weyl points, which are
only 14 meV away from the Fermi level and isolated from trivial bands.
Different from antiferromagnets Mn3X (X= Ge, Sn, Ga, Ir, Rh, and Pt), where the
AHE originates from the non-collinear magnetic structure, the AHE in Ti2MnAl
stems directly from the Weyl points and is topologically protected. The large
anomalous Hall conductivity (AHC) together with a low charge carrier
concentration should give rise to a large anomalous Hall angle. In contrast to
the Co-based ferromagnetic Heusler compounds, the Weyl nodes in Ti2MnAl do not
derive from nodal lines due to the lack of mirror symmetries in the inverse
Heusler structure. Since the magnetic structure breaks spin-rotation symmetry,
the Weyl nodes are stable without SOC. Moreover, because of the large
separation between Weyl points of opposite topological charge, the Fermi arcs
extent up to 75% of the reciprocal lattice vectors in length. This makes
Ti2MnAl an excellent candidate for the comprehensive study of magnetic Weyl
semimetals. It is the first example of a material with Weyl points, large
anomalous Hall effect and angle despite a vanishing net magnetic moment.",1801.03273v3
1994-10-27,"Band gap and stability in the ternary intermetallic compounds NiSnM (M = Ti, Zr, Hf): A first principles study","The structural stability and electronic properties of the ternary
intermetallic compounds NiSnM (M = Ti, Zr, Hf) and the closely related Heusler
compounds Ni$_2$SnM are discussed using the results of ab initio
pseudopotential total energy and band-structure calculations performed with a
plane wave basis set using the conjugate gradients algorithm. The results
characterize the lowest energy phase of NiSnM compounds, with a SnM rocksalt
structure sublattice, as narrow gap semiconductors with indirect gaps near 0.5
eV. Two other atomic arrangements for NiSnM in the MgAgAs structure result in
energetically unfavorable compounds that are metallic. The gap formation in the
lowest energy structure of NiSnZr and relative stability of the three atomic
arrangements are investigated within a tight-binding framework and by
considering the decompositions of each ternary compound into a binary
substructure plus a third element sublattice. The stabilization of the lowest
energy phase of NiSnZr is found to be mainly due to the relative stability of
the SnZr rocksalt substructure, while the opening of the gap induced by the
addition of the symmetry-breaking Ni sublattice makes a relatively minor
contribution. From analysis of structural and chemical trends, CoVSn is
predicted to be a new semiconducting intermetallic in the MgAgAs structure with
a 0.8 eV indirect gap.",9411001v2
2009-02-18,Majority-spin non-quasiparticle states in half-metallic ferrimagnet Mn$_2$VAl,"The density of non-quasiparticle states in the ferrimagnetic full-Heuslers
Mn$_2$VAl alloy is calculated from first principles upon appropriate inclusion
of correlations. In contrast to most half-metallic compounds, this material
displays an energy gap in the majority-spin spectrum. For this situation,
non-quasiparticle states are located below the Fermi level, and should be
detectable by spin-polarized photoemission. This opens a new way to study
many-body effects in spintronic-related materials.",0902.3109v1
2009-08-21,Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures,"Combining density-functional theory calculations with many-body
Green's-function technique, we reveal that the macroscopic magnetization in
half-metallic antiferromagnets does not vanish at finite temperature as for the
T=0 limit. This anomalous behavior stems from the inequivalent magnetic
sublattices which lead to different intrasublattice exchange interactions. As a
consequence, the spin fluctuations suppress the magnetic order of the
sublattices in a different way leading to a ferrimagnetic state at finite
temperatures. Computational results are presented for the half-metallic
antiferromagnetic CrMnZ (Z=P,As,Sb) semi-Heusler compounds.",0908.3044v1
2011-12-09,Spin polarized tunneling in MgO-based tunnel junctions with superconducting electrodes,"We prepared magnetic tunnel junctions with one ferromagnetic and one
superconducting Al-Si electrode. Pure cobalt electrodes were compared with a
Co-Fe-B alloy and the Heusler compound Co2FeAl. The polarization of the
tunneling electrons was determined using the Maki-Fulde-model and is discussed
along with the spin-orbit scattering and the total pair-breaking parameters.
The junctions were post-annealed at different temperatures to investigate the
symmetry filtering mechanism responsible for the giant tunneling
magnetoresistance ratios in Co-Fe-B/ MgO/ Co-Fe-B junctions.",1112.2110v1
2019-10-29,Possible martensitic transformation in Pd2MnTi and Pt2MnTi: First-principles investigation,"The martensitic transformation in new-type all-d-metal Heusler alloys Pd2MnTi
and Pt2MnTi have been investigated based on first-principles investigations.
The calculated results indicate that the martenstic transformation have great
possibility to occur in both Pd2MnTi and Pt2MnTi. The energy differences
between the cubic and tetragonal phases are 215.12 meV and 329.45 meV for
Pd2MnTi and Pt2MnTi, respectively. The analysis of the electronic structure of
cubic and tetragonal phases also support this conclusion. The magnetic
properties are also investigated for the two compounds.",1910.13075v1
2019-10-11,Band structure tuning of Heusler compounds revisited: Spin- and momentum-resolved electronic structure analysis of compounds with different band filling,"Spin-filtered time-of-flight photoelectron momentum microscopy reveals a
systematic variation of the band structure within a series of highly
spin-polarized ferromagnetic Heusler compounds with increasing number of
valence electrons (Co2MnGa, Co2MnSi and Co2Fe0.4Mn0.6Si). The positions of the
Fermi energy for minority and majority electrons deviate strongly from a simple
band-filling model. Photoexcitation at h$\nu$=6.05 eV (4th harmonic of a
Ti:sapphire laser) gives access to the spin-polarization texture P(EB,kx,ky) of
the bulk bands in a (kx,ky)-range with diameter 1.4{\AA}$^{-1}$ and energies
from the Fermi energy EF to a binding energy of EB=2 eV. The minority bands of
Co2MnGa cross the Fermi level, inhibiting half-metallicity; the crossing points
allow a precise adjustment of experimental and theoretical majority and
minority bands, requiring shifts in opposite directions. The top of the
minority band lies only 0.15 eV above EF, i.e. Co2MnGa is much closer to being
half-metallic than predicted by calculations. For half-metallic Co2MnSi and
Co2Fe0.4Mn0.6Si clear minority band gaps are visible, the topmost occupied
minority bands lie 0.5 and 0.35 eV below EF, in reasonable agreement with
theory; the exchange splitting is significantly smaller than in theory. The
comparison of all three compounds uncovers the surprising fact that with
increasing number of valence electrons the frontier majority bands (close to
EF) exhibit an increasing deficiency in filling, in comparison with the
prediction of a DFT calculation. The same trend is visible in comparison with a
DMFT calculation. For s-polarized excitation both half-metallic compounds
exhibit nearly complete positive spin polarization close to EF, consistent with
previous work in literature.",1910.05205v1
2023-03-15,High spin-polarization in a disordered novel quaternary Heusler alloy FeMnVGa,"In this work, we report the successful synthesis of a Fe-based novel
half-metallic quaternary Heusler alloy FeMnVGa and its structural, magnetic and
transport properties probed through different experimental methods and
theoretical technique. Density functional theory (DFT) calculations performed
on different types of structure reveal that Type-2 ordered structure (space
group: F-43m, Ga at 4a, V at 4b, Mn at 4c and Fe at 4d) possess minimum energy
among all the ordered variants. Ab-initio simulations in Type 2 ordered
structure further reveal that the compound is half-metallic ferromagnet (HMF)
having a large spin-polarization (89.9 %). Neutron diffraction reveal that the
compound crystalizes in disordered Type-2 structure (space group: Fm-3m) in
which Ga occupy at 4a, V at 4b and Fe/Mn occupy 4c/4d sites with 50:50
proportions. The structural disorder is further confirmed by X-ray diffraction
(XRD), extended X-ray absorption fine structure (EXAFS),57Fe Mossbauer
spectrometry results and DFT calculations. Magnetisation studies suggest that
the compound orders ferromagnetically below TC ~ 293 K and the saturation
magnetization follows Slater-Pauling rule. Mossbauer spectrometry, along with
neutron diffraction suggest that Mn is the major contributor to the total
magnetism in the compound consistent with the theoretical calculations. First
principle calculations indicate that spin-polarization remain high (81.3 %)
even in the presence of such large atomic disorder. The robustness of the HMF
property in presence of disorder is a quite unique characteristic over other
reported HMF in literature and make this compound quiet promising for
spintronics applications.",2303.08579v1
2018-06-18,Anomalous Nernst effect beyond the magnetization scaling relation in the ferromagnetic Heusler compound Co$_2$MnGa,"Applying a temperature gradient in a magnetic material generates a voltage
that is perpendicular to both the heat flow and the magnetization. This is the
anomalous Nernst effect (ANE) which was thought to be proportional to the value
of the magnetization for a long time. However, more generally, the ANE has been
predicted to originate from a net Berry curvature of all bands near the Fermi
level. Subsequently, a large anomalous Nernst thermopower has recently been
observed in topological materials with no net magnetization but large net Berry
curvature around E$_F$. These experiments clearly fall outside the scope of the
conventional magnetization-model of the ANE, but a significant question
remains: Can the value of the ANE in topological ferromagnets exceed the
highest values observed in conventional ferromagnets? Here, we report a
remarkably high anomalous Nernst thermopower value of ~6.0 \mu V/K at 1 T in
the ferromagnetic topological Heusler compound Co$_2$MnGa at room temperature,
which is around 7-times larger than any anomalous Nernst thermopower value ever
reported for a conventional ferromagnet. Combined electrical, thermoelectric
and first-principles calculations reveal that this high value of the ANE arises
from a large net Berry curvature near the Fermi level associated with nodal
lines and Weyl points.",1806.06753v1
2018-09-13,High-Throughput Calculations of Thermal Conductivity in Nanoporous Materials: The Case of Half-Heusler Compounds,"Achieving low thermal conductivity and good electrical properties is a
crucial condition for thermal energy harvesting materials. Nanostructuring
offers a very powerful tool to address both requirements: in nanostructured
materials, boundaries preferentially scatter phonons compared to electrons. The
search for low-thermal-conductivity nanostructures is typically limited to
materials with simple crystal structures, such as silicon, because of the
complexity arising from modeling branch- and wave vector- dependent nanoscale
heat transport. Using the phonon mean-free-path (MFP) dependent Boltzmann
transport equation, a model that overcomes this limitation, we compute thermal
transport in 75 nanoporous half-Heusler compounds for different pore sizes. We
demonstrate that the optimization of thermal transport in nanostructures should
take into account both bulk thermal properties and geometry-dependent phonon
suppression, two aspects that are typically engineered separately. In fact, our
work predicts that, given a set of bulk materials and a system geometry, the
ordering of the thermal conductivity of the nanostructure does not necessarily
align with that of the bulk: We show that what dictates thermal transport is
the interplay between the bulk MFP distribution and the nanostructuring length
scale of the material. Finally, we derive a thermal transport model that
enables fast systems screening within large bulk material repositories and a
given geometry. Our study motivates the need for a holistic approach to
engineering thermal transport and provides a method for high-throughput
materials discovery.",1809.04751v1
2017-04-01,"Native defects in the Co$_2$Ti$Z$ ($Z=$ Si, Ge, Sn) full Heusler alloys: formation and influence on the thermoelectric properties","We have performed first-principles investigations on the native defects in
the full Heusler alloys Co$_2$Ti$Z$ ($Z$ one of the group IV elements Si, Ge,
Sn), determining their formation energies and how they influence the transport
properties. We find that Co vacancies (Vc) in all compounds and the
Ti$_\text{Sn}$ anti-site exhibit negative formation energies. The smallest
positive values occur for Co in excess on anti-sites (Co$_Z$ or Co$_\text{Ti}$)
and for Ti$_Z$. The most abundant native defects were modeled as dilute alloys,
treated with the coherent potential approximation in combination with the
multiple-scattering theory Green function approach. The self-consistent
potentials determined this way were used to calculate the residual resistivity
via the Kubo-Greenwood formula and, based on its energy dependence, the Seebeck
coefficient of the systems. The latter is shown to depend significantly on the
type of defect, leading to variations that are related to subtle, spin-orbit
coupling induced, changes in the electronic structure above the half-metallic
gap. Two of the systems, Vc$_\text{Co}$ and Co$_Z$, are found to exhibit a
negative Seebeck coefficient. This observation, together with their low
formation energy, offers an explanation for the experimentally observed
negative Seebeck coefficient of the Co$_2$Ti$Z$ compounds as being due to
unintentionally created native defects.",1704.00149v2
2019-10-17,High electrical conductivity in the epitaxial polar metals LaAuGe and LaPtSb,"Polar metals are an intriguing class of materials that simultaneously host
free carriers and polar structural distortions. Despite the name ""polar metal,""
however, most well-studied polar metals are poor electrical conductors. Here,
we demonstrate the molecular beam epitaxial (MBE) growth of LaPtSb and LaAuGe,
two polar metal compounds whose electrical resistivity is an order of magnitude
lower than the well studied oxide polar metals. These materials belong to a
broad family of $ABC$ intermetallics adopting the stuffed wurtzite structure,
also known as hexagonal Heusler compounds. Scanning transmission electron
microscopy (STEM) reveals a polar structure with unidirectionally buckled $BC$
(PtSb, AuGe) planes. Magnetotransport measurements demonstrate good metallic
behavior with low residual resistivity ($\rho_{LaAuGe}=59.05$
$\mu\Omega\cdot$cm and $\rho_{LaAPtSb}=27.81$ $\mu\Omega\cdot$cm at 2K) and
high carrier density ($n_h\sim 10^{21}$ cm$^{-3}$). Photoemission spectroscopy
measurements confirm the band metallicity and are in quantitative agreement
with density functional theory (DFT) calculations. Through DFT-Chemical
Pressure and Crystal Orbital Hamilton Population analyses, the atomic packing
factor is found to support the polar buckling of the structure, though the
degree of direct interlayer $B-C$ bonding is limited by repulsion at the $A-C$
contacts. When combined with insulating hexagonal Heuslers, these materials
provide a new platform for fully epitaxial, multiferroic heterostructures.",1910.07685v1
2018-12-12,First-principles prediction of half-Heusler half-metals above room temperature,"Half-metallicity (HM) offers great potential for engineering spintronic
applications, yet only few magnetic materials present metallicity in just one
spin channel. In addition, most HM systems become magnetically disordered at
temperatures well below ambient conditions, which further hinders the
development of spin-based electronic devices. Here, we use first-principles
methods based on density functional theory (DFT) to investigate the electronic,
magnetic, structural, mixing, and vibrational properties of $90$ $XYZ$
half-Heusler (HH) alloys ($X =$ Li, Na, K, Rb, Cs; $Y =$ V,Nb, Ta; $Z =$ Si,
Ge, Sn, S, Se, Te). We disclose a total of $28$ new HH compounds that are
ferromagnetic, vibrationally stable, and HM, with semiconductor band gaps in
the range of $1$-$4$ eV and HM band gaps of $0.2$-$0.8$ eV. By performing Monte
Carlo simulations of a spin Heisenberg model fitted to DFT energies, we
estimate the Curie temperature, $T_{\rm C}$, of each HM compound. We find that
$17$ HH HM remain magnetically ordered at and above room temperature, namely,
$300 \le T_{\rm C} \le 450$ K, with total magnetic moments of $2$ and $4$
$\mu_{\rm B}$. A further materials sieve based on zero-temperature mixing
energies let us to conclude $5$ overall promising ferromagnetic HH HM at and
above room temperature: NaVSi, RbVTe, CsVS, CsVSe, and RbNbTe. We also predict
$2$ ferromagnetic materials that are semiconductor and magnetically ordered at
ambient conditions: LiVSi and LiVGe.",1812.04813v1
2020-09-24,Electronic correlations in the semiconducting half-Heusler compound FeVSb,"Electronic correlations are crucial to the low energy physics of metallic
systems with localized $d$ and $f$ states; however, their effect on band
insulators and semiconductors is typically negligible. Here, we measure the
electronic structure of the half-Heusler compound FeVSb, a band insulator with
filled shell configuration of 18 valence electrons per formula unit ($s^2 p^6
d^{10}$). Angle-resolved photoemission spectroscopy (ARPES) reveals a mass
renormalization of $m^{*}/m_{bare}= 1.4$, where $m^{*}$ is the measured
effective mass and $m_{bare}$ is the mass from density functional theory (DFT)
calculations with no added on-site Coulomb repulsion. Our measurements are in
quantitative agreement with dynamical mean field theory (DMFT) calculations,
highlighting the many-body origin of the mass renormalization. This mass
renormalization lies in dramatic contrast to other filled shell intermetallics,
including the thermoelectric materials CoTiSb and NiTiSn; and has a similar
origin to that in FeSi, where Hund's coupling induced fluctuations across the
gap can explain a dynamical self-energy and correlations. Our work calls for a
re-thinking of the role of correlations and Hund's coupling in intermetallic
band insulators.",2009.11489v2
2022-07-11,Hybrid Bloch-Néel spiral states in Mn$_{1.4}$PtSn probed by resonant soft x-ray scattering,"Multiple intriguing phenomena have recently been discovered in tetragonal
Heusler compounds, where $D_{2d}$ symmetry sets a unique interplay between
Dzyaloshinskii-Moriya (DM) and magnetic dipolar interactions. In the prototype
$D_{2d}$ compound Mn$_{1.4}$PtSn, this has allowed the stabilization of exotic
spin textures such as first-reported anti-skyrmions or elliptic Bloch-type
skyrmions. While less attention has so far been given to the low-field spiral
state, this remains extremely interesting as a simplest phase scenario on which
to investigate the complex hierarchy of magnetic interactions in this materials
family. Here, via resonant small-angle soft x-ray scattering experiments on
high-quality single crystals of Mn$_{1.4}$PtSn at low temperatures, we evidence
how the underlying $D_{2d}$ symmetry of the DMI in this material is reflected
in its magnetic texture. Our studies reveal the existence of a novel and
complex metastable phase, which possibly has a mixed character of both the
N\'{e}el-type cycloid and the Bloch-type helix, that forms at low temperature
in zero fields upon the in-plane field training. This hybrid spin-spiral
structure has a remarkable tunability, allowing to tilt its orientation beyond
high-symmetry crystallographic directions and control its spiral period. These
results broaden the reachness of Heusler $D_{2d}$ materials exotic magnetic
phase diagram and extend its tunability, thus enhancing a relevant playground
for further fundamental explorations and potential applications in energy
saving technologies.",2207.04968v1
2023-01-24,"Ab initio Prediction of Mechanical, Electronic, Magnetic and Transport Properties of Bulk and Heterostructure of a Novel Fe-Cr based Full Heusler Chalcogenide","Using electronic structure calculations based on density functional theory,
we predict and study the structural, mechanical, electronic, magnetic and
transport properties of a new full Heusler chalcogenide, namely, Fe$_2$CrTe,
both in bulk and heterostructure form. The system shows a ferromagnetic and
half-metallic(HM) like behavior, with a very high (about 95%) spin polarization
at the Fermi level, in its cubic phase. Interestingly, under tetragonal
distortion, a clear minimum (with almost the same energy as the cubic phase)
has also been found, at a c/a value of 1.26, which, however, shows a
ferrimagnetic and fully metallic nature. The compound has been found to be
dynamically stable in both the phases against the lattice vibration. The
elastic properties indicate that the compound is mechanically stable in both
the phases, following the stability criteria of the cubic and tetragonal
phases. The elastic parameters unveil the mechanically anisotropic and ductile
nature of the alloy system. Due to the HM-like behavior of the cubic phase and
keeping in mind the practical aspects, we probe the effect of strain as well as
substrate on various physical properties of this alloy. Transmission profile of
the Fe$_2$CrTe/MgO/Fe$_2$CrTe heterojunction has been calculated to probe it as
a magnetic tunneling junction (MTJ) material in both the cubic and tetragonal
phases. Considerably large tunneling magnetoresistance ratio (TMR) of 1000% is
observed for the tetragonal phase, which is found to be one order of magnitude
larger than that of the cubic phase.",2301.09843v1
1998-01-28,"Electronic Structure, Local Moments and Transport in Fe_2VAl","Local spin density approximation calculations are used to elucidate
electronic and magnetic properties of Heusler structure Fe_2VAl. The compound
is found to be a low carrier density semimetal. The Fermi surface has small
hole pockets derived from a triply degenerate Fe derived state at Gamma
compensated by an V derived electron pocket at the X point. The ideal compound
is found to be stable against ferromagnetism. Fe impurities on V sites,
however, behave as local moments. Because of the separation of the hole and
electron pockets the RKKY interaction between such local moments should be
rapidly oscillating on the scale of its decay, leading to the likelihood of
spin-glass behavior for moderate concentrations of Fe on V sites. These
features are discussed in relation to experimental observations of an unusual
insulating state in this compound.",9801302v1
2011-01-31,Ferrimagnetism and disorder in epitaxial Mn(2-x)Co(x)VAl thin films,"The quaternary full Heusler compound Mn(2-x)Co(x)VAl with x = 1 is predicted
to be a half-metallic antiferromagnet. Thin films of the quaternary compounds
with x = 0...2 were prepared by DC and RF magnetron co-sputtering on heated MgO
(001) substrates. The magnetic structure was examined by x-ray magnetic
circular dichroism and the chemical disorder was characterized by x-ray
diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn2VAl (x = 0).
For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to
Mn. The observed reduced magnetic moments are interpreted with the help of band
structure calculations in the coherent potential approximation. Mn2VAl is very
sensitive to disorder involving Mn, because nearest-neighbor Mn atoms couple
anti-ferromagnetically. Co2VAl has B2 order and has reduced magnetization. In
the cases with x >= 0.9 conventional ferromagnetism was observed, closely
related to the atomic disorder in these compounds.",1101.5994v1
2016-07-01,Ultra-high vacuum compatible induction-heated rod casting furnace,"We report the design of a radio-frequency induction-heated rod casting
furnace that permits the preparation of polycrystalline ingots of intermetallic
compounds under ultra-high vacuum compatible conditions. The central part of
the system is a bespoke water-cooled Hukin crucible supporting a casting mold.
Depending on the choice of mold, typical rods have a diameter between 6 mm and
10 mm and a length up to 90 mm, suitable for single-crystal growth by means of
float-zoning. The setup is all-metal sealed and may be baked out. We find that
the resulting ultra-high vacuum represents an important precondition for
processing compounds with high vapor pressures under a high-purity argon
atmosphere up to 3 bar. Using the rod casting furnace, we succeeded to prepare
large high-quality single crystals of two half-Heusler compounds, namely the
itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb.",1607.00821v1
2018-08-17,Magnetic and structural properties of Co$_2$MnSi based Heusler compound,"The influence of antisite disorder occupancies on the magnetic properties of
the half-metallic Co$_2$MnSi compound was studied by experimental techniques
and first-principles calculations. The neutron diffraction studies show almost
identical amount of Mn and Co disorders of 6.5\% and 7.6\%, which was found to
be in good agreement with density functional theory (DFT) calculations of the
stable Co$_2$MnSi system with the corresponding disorders. DFT studies reveal
that antiferromagnetic interactions introduced by Mn disorder lead to a
reduction of the net magnetic moment. The results are discussed in conjunction
with neutron diffraction and magnetization measurements. Transport property
measurement under magnetic field up to 9 Tesla revealed a positive
magnetoresistance for bulk Co$_2$MnSi that persists up to room temperature. A
Curie temperature of $\sim$1014 K was determined for the compound by high
temperature electrical resistivity and dilatometry measurements.",1808.05743v3
2020-02-06,Thermal dependence of the mechanical properties of NiTiSn using first-principles calculations and high-pressure X-ray diffraction,"In this work we aim to study the effect of temperature on the mechanical
properties of a solid. For this, we have introduced a new first-principles
based methodology to obtain the thermal variation of the elastic constants of
NiTiSn, a multifunctional Heusler compound. In parallel using X-ray
diffraction, we have measured the isothermal bulk modulus at 300~K. The
agreement between the calculations and the experiments is within the
experimental error bars showing the accuracy of the calculations. Using two
other numerical methods, which give all coherent results, we have shown that
NiTiSn conserves its very good mechanical properties up to 1500~K. In
particular at 700~K (the best working temperature for thermoelectric
applications), NiTiSn remains a ductile and robust material making it a
compound of choice for applications in which large temperature fluctuations are
present.",2002.02161v1
2018-01-22,Effect of density functionals on the vibrational and thermodynamic properties of Fe$_{2}$VAl and Fe$_{2}$TiSn compounds,"First-principles phonon calculations along with Kohn-Sham density functional
theory (DFT) is an essential tool to study the lattice dynamics,
thermodynamical properties and phase-transitions of materials. The two
full-Heusler compounds Fe$_{2}$VAl and Fe$_{2}$TiSn are studied for lattice
vibration dependent properties using finite displacement method and supercell
approach. For the investigation, four density functionals viz., LDA, PBE,
PBEsol and meta-GGA SCAN are employed. Using these functionals, phonon
dispersion, phonon density of states (DOS), partial density of states (PDOS)
thermal propertis and zero-point energy are calculated at equilibrum lattice
parameters under harmonic approximation. For the two compounds the Debye
temperatures are calculated from the obtained phonon DOS which are $\sim$660 K
and $\sim$540 K, respectively. The obtained results from different functionals
are compared among each other. The overall phonon energy in the dispersion is
found to be $\sim$15 meV higher in Fe$_{2}$VAl than the Fe$_{2}$TiSn compounds.
For the two compounds PBE is yielding the lowest phonon frequencies while LDA
or SCAN functional is giving the highest. The same pattern is observed in
phonon DOS plots of two compounds. The zero-point energy calculated is the
highest from SCAN (21.04 and 16.95 J) and the lowest from PBE functionals
(20.09 and 16.02 J) obeying the same trend as frequency for both compounds. A
general prediction of nature of lattice thermal conductivity is made based on
the velocities of acoustic phonons which is in agreement with the qualitative
behavior of reported experimental thermal conductivity of two compounds. Phonon
spectra obtained from PBE and SCAN have similar general features while those
from LDA and PBEsol have resembling features for Fe$_{2}$VAl, while this trend
is not observed for the compound Fe$_{2}$TiSn.",1801.06980v2
2006-12-07,"Influence of mixing the low-valent transition metal atoms (Y,Y$^*$=Cr,Mn,Fe) on the properties of the quaternary Co$_2$[Y$_{1-x}$Y$^*_x$]Z (Z=Al,Ga,Si,Ge,Sn) Heusler compounds","We complement our study on the doping and disorder in Co$_2$MnZ compounds [I.
Galanakis \textit{et al.}, Appl. Phys. Lett. \textbf{89}, 042502 (2006) and K.
\""Ozdo\~gan \textit{et al.}, Phys. Rev. B \textbf{74}, (2006)] to cover also
the quaterarny Co$_2$[Y$_{1-x}$Y$^*_x$]Z compounds with the lower-valent
transition metals Y,Y$^*$ being Cr, Mn or Fe and the sp atom Z being one of Al,
Ga, Si, Ge, Sn. This study gives a global overview of the magnetic and
electronic properties of these compounds since we vary both Y and Z elements.
Our results suggest that for realistic applications the most appropriate
compounds are the ones belonging to the families Co$_2$[Mn$_{1-x}$Cr$_x$]Z with
$x>0.5$ irrespectively of the nature of the $sp$ atoms since they combine high
values of majority DOS at the Fermi level due to the presence of Cr, and
half-metallicity with large band-gaps. On the other hand the presence of Fe
lowers considerably the majority density of states at the Fermi level and when
combined with an element belonging to the Si-column, it even can destroy
half-metallicity.",0612194v1
2014-06-03,Design and discovery of a novel Half-Heusler transparent hole conductor made of all-metallic heavy elements,"Metallic conductors that are optically transparent represent a rare breed of
generally contraindicated physical properties that are nevertheless critically
needed for application where both functionalities are crucial. Such rare
materials have traditionally been searched in the general chemical neighborhood
of compounds containing metal oxides, expected to be wide gap insulators that
might be doped to induce conductivity.Focusing on the family of 18 valence
electron ABX compounds we have searched theoretically for the ability of the
compound's electronic structure to simultaneously lead to optical transparency,
in parallel with the ability of its intrinsic defect structures to produce
uncompensated free holes.This led to the prediction of a stable, never before
synthesized TaIrGe compound made of all-metal heavy atom compound as the ""best
of class"" from the V-IX-IV group. Laboratory synthesis then found it to be
stable in the predicted crystal structure and p-type transparent conductor with
measured strong direct absorption of 3.36 eV and remarkably high (albeit not
predicted) hole mobility of 2730 cm2/Vs at room temperature. This methodology
opens the way to future searches of transparent conductors in unexpected
chemical groups.",1406.0872v2
2019-10-30,Magnon spectrum of the Weyl semimetal half-Heusler compound GdPtBi,"The compound GdPtBi is known as a material where the non-trivial topology of
electronic bands interplays with an antiferromagnetic order, which leads to the
emergence of many interesting magnetotransport phenomena. Although the magnetic
structure of the compound has previously been reliably determined, the magnetic
interactions responsible for this type of order remained controversial. In the
present study, we employed time-of-flight inelastic neutron scattering to map
out the low-temperature spectrum of spin excitations in single-crystalline
GdPtBi. The observed spectra reveal two spectrally sharp dispersive spin-wave
modes, which reflects the multi-domain state of the $\mathbf{k} =
(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ face-centred cubic antiferromagnet in the
absence of a symmetry-breaking magnetic field. The magnon dispersion reaches an
energy of $\sim 1.1$~meV and features a gap of $\sim 0.15$~meV. Using linear
spin-wave theory, we determined the main magnetic microscopic parameters of the
compound that provide good agreement between the simulated spectra and the
experimental data. We show that GdPtBi is well within the
($\frac{1}{2}\frac{1}{2}\frac{1}{2}$) phase and is dominated by second-neighbor
interactions, thus featuring low frustration.",1910.13845v2
2014-06-26,Unusual weak magnetic exchange in two different structure types: YbPt$_2$Sn and YbPt$_2$In,"We present the structural, magnetic, thermodynamic, and transport properties
of the two new compounds YbPt$_2$Sn and YbPt$_2$In. X-ray powder diffraction
shows that they crystallize in different structure types, the hexagonal
ZrPt$_2$Al and the cubic Heusler type, respectively. Despite quite different
lattice types, both compounds present very similar magnetic properties: a
stable trivalent Yb$^{3+}$, no evidence for a sizeable Kondo interaction, and
very weak exchange interactions with a strength below 1K as deduced from
specific heat $C(T)$. Broad anomalies in $C(T)$ suggest short range magnetic
ordering at about 250mK and 180mK for YbPt$_2$Sn and YbPt$_2$In, respectively.
The weak exchange and the low ordering temperature result in a large
magnetocaloric effect as deduced from the magnetic field dependence of $C(T)$,
making these compounds interesting candidates for magnetic cooling. In addition
we found in YbPt$_2$In evidences for a charge density wave transition at about
290K. The occurrence of such transitions within several RET$_2$X compound
series (RE = rare earth, T = noble metal, X = In, Sn) is analyzed.",1406.6800v2
2020-10-06,Tailoring magnetocaloric effect in all-d-metal Ni-Co-Mn-Ti Heusler alloys: a combined experimental and theoretical study,"Novel Ni-Co-Mn-Ti all-d-metal Heusler alloys are exciting due to large
multicaloric effects combined with enhanced mechanical properties. An optimized
heat treatment for a series of these compounds leads to very sharp phase
transitions in bulk alloys with isothermal entropy changes of up to 38 J
kg$^{-1}$ K$^{-1}$ for a magnetic field change of 2 T. The differences of
as-cast and annealed samples are analyzed by investigating microstructure and
phase transitions in detail by optical microscopy. We identify different grain
structures as well as stoichiometric (in)homogenieties as reasons for
differently sharp martensitic transitions after ideal and non-ideal annealing.
We develop alloy design rules for tuning the magnetostructural phase transition
and evaluate specifically the sensitivity of the transition temperature towards
the externally applied magnetic fields ($\frac{dT_t}{\mu_0dH}$) by analyzing
the different stoichiometries. We then set up a phase diagram including
martensitic transition temperatures and austenite Curie temperatures depending
on the e/a ratio for varying Co and Ti content. The evolution of the Curie
temperature with changing stoichiometry is compared to other Heusler systems.
Density Functional Theory calculations reveal a correlation of T$_C$ with the
stoichiometry as well as with the order state of the austenite. This combined
approach of experiment and theory allows for an efficient development of new
systems towards promising magnetocaloric properties. Direct adiabatic
temperature change measurements show here the largest change of -4 K in a
magnetic field change of 1.93 T for Ni$_{35}$Co$_{15}$Mn$_{37}$Ti$_{13}$.",2010.02620v2
2008-10-10,Anomalous Magnetic Properties in Ni50Mn35In15,"We present here a comprehensive investigation of the magnetic ordering in
Ni50Mn35In15 composition. A concomitant first order martensitic transition and
the magnetic ordering occurring in this off-stoichiometric Heusler compound at
room temperature signifies the multifunctional character of this magnetic shape
memory alloy. Unusual features are observed in the dependence of the
magnetization on temperature that can be ascribed to a frustrated magnetic
order. It is compelling to ascribe these features to the cluster type
description that may arise due to inhomogeneity in the distribution of magnetic
atoms. However, evidences are presented from our ac susceptibility, electrical
resistivity and dc magnetization studies that there exists a competing
ferromagnetic and antiferromagnetic order within crystal structure of this
system. We show that excess Mn atoms that substitute the In atoms have a
crucial bearing on the magnetic order of this compound. These excess Mn atoms
are antiferromagnetically aligned to the other Mn, which explains the peculiar
dependence of magnetization on temperature.",0810.1850v1
2010-12-15,Exchange interactions and Curie temperatures in Mn2CoZ compounds,"The generalized Heusler compounds Mn2CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb)
with the Hg2CuTi structure are of large interest due to their half-metallic
ferrimagnetism. The complex magnetic interactions between the constituents are
studied by first principles calculations of the Heisenberg exchange coupling
parameters, and Curie temperatures are calculated from those. Due to the direct
Mn-Mn exchange interaction in Mn2CoZ, the Curie temperature decreases, while
the total moment increases when changing Z from one group to another. The
exchange interactions are dominated by a strong direct exchange between Co and
its nearest neighbor Mn on the B site, which is nearly constant. The coupling
between the nearest-neighbor Mn atoms scales with the magnetic moment of the Mn
atom on the C site. Calculations with different lattice parameters suggest a
negative pressure dependence of the Curie temperature, which follows from
decreasing magnetic moments. Curie temperatures of more than 800 K are
predicted for Mn2CoAl (890 K), Mn2CoGa (886 K), and Mn2CoIn (845 K).",1012.3261v1
2014-01-25,Investigation of thermoelectric properties of half-metallic Co2 MnGe by using first principles calculations,"By combining the electronic structures obtained from first principles
calculations with Boltzmann transport theory we have investigated the
electronic, magnetic and transport properties of Co$_{2}$MnGe Heusler compound.
The density of states plots, dispersion curves and total energy of paramagnetic
and ferromagnetic (FM) phases clearly show the half-metallic FM ground state
for the compound with an indirect band gap of about 400 meV in the minority
spin channel. It has integer value of the magnetic moment equal to 5 $\mu_{B}$.
In the FM phase a very large value ($\sim$550 $\mu$V/K) of Seebeck coefficient
(S) is obtained for down-spin electrons due to the existence of almost flat
conduction band along X to $\Gamma$ direction. The two current model has been
used to find the total S and the obtained value is about 10 $\mu$V/K. The
calculated values of Seebeck coefficient, resistivity and electronic thermal
conductivity show nice agreement with the experimental results.",1401.6511v2
2014-11-03,Importance of two current model in understanding the electronic transport behavior of inverse Heusler alloy: Fe 2 CoSi,"Here we explore the applicability of the two current model in understanding
the transport behavior of Fe 2 CoSi compound by using the first principles
calculations in combination with the Boltzmann transport theory. The
spin-unpolarized calculation shows large density of states (DOS) at Fermi level
(E F) and is unable to provide the correct temperature dependence of transport
coefficients. The spin-polarised calculation shows reduced DOS at the E F in
the spin-up channel, whereas spin-dn channel have almost zero DOS at the E F .
The absolute value of Seebeck coefficient in the spin-up channel shows linear
increment with the temperature and in the spin-dn channel it varies
non-linearly. The electrical conductivity also shows non-linear temperature
dependence in both the spin channels whereas, the electronic thermal
conductivity shows linear temperature dependence. The values of transport
coefficients and their temperature dependence obtained by using the two current
model are found to be in fairly good agreement with the experimental data.
Present work clearly suggests the importance of two current model in
understanding the transport properties of the compound.",1411.0367v1
2015-02-02,Large linear magnetoresistance and weak anti-localization in Y(Lu)PtBi topological insulators,"Topological insulators are new kind of Dirac materials that possess bulk
insulating and surface conducting behavior. They are basically known for their
unique electronic properties at the surface. Here we present the
magneto-transport properties of our high quality single crystalline Y(Lu)PtBi
Heusler topological insulators, which belong to a group of noncentrosymmetric
superconductor with Tc = 0:8 K. Both the compounds show semi-metallic behavior
with low charge carrier of 6 x1018 cm^-3 for YPtBi and 8 x1019 cm^-3 for LuPtBi
at 2 K. Magneto-conductivity measurements in the tilted field indicate that the
charge carriers transport through quantum interference. This provide a direct
evidence of weak anti-localization below 50 K, giving a strong signature of
surface transport. Most importantly, these compounds show very high unsaturated
linear magnetoresistance of approximately 2000% at 10 K in a magnetic field of
60 T.",1502.00604v2
2015-06-29,Magnetization and magneto-transport studies on Fe$_2$VAl$_{1-x}$Si$_x$,"We report on magnetoresistance, Hall and magnetization measurements of
Fe2VAl1-xSix Heusler compounds for x= 0.005, 0.015, 0.02. There is a systematic
change in the temperature coefficient of resistance (TCR) from negative to
positive as the Si composition is increased. The Hall co-efficient shows that
the carriers are electron like and the carrier density increases with Si
concentration. Resistance measurements under magnetic field indicate a
decreasing behavior under the application of magnetic field at low temperature
region (T< 60 K), suggesting the suppression of scattering by magnetic field.
Temperature and field dependent magnetization measurements did not show any
significant change apart from the fact that the presence of super paramagnetic
(SPM) cluster and its ordering at low temperatures. Arrott plot analysis of
magnetization versus field also indicates the magnetic ordering with applied
field below 60 K.",1506.08516v1
2016-09-22,Quantum-Many-Body Intermetallics: Phase Stability of Fe$_3$Al and Small-Gap Formation in Fe$_2$VAl,"Various intermetallic compounds harbor subtle electronic correlation effects.
To elucidate this fact for the Fe-Al system, we perform a realistic many-body
investigation based on the combination of density functional theory with
dynamical mean-field theory in a charge self-consistent manner. A better
characterization and understanding of the phase stability of bcc-based
D0$_3$-Fe$_3$Al through an improved description of the correlated charge
density and the magnetic-energy is achevied. Upon replacement of one Fe
sublattice by V, the Heusler compound Fe$_2$VAl is realized, known to display
bad-metal behavior and increased specific heat. We here document a charge-gap
opening at low temperatures in line with previous experimental work. The gap
structure does not match conventional band theory and is reminiscent of
(pseudo)gap charateristics in correlated oxides.",1609.06928v2
2016-11-13,Topological Materials: Weyl Semimetals,"Topological insulators and topological semimetals are both new classes of
quantum materials, which are characterized by surface states induced by the
topology of the bulk band structure. Topological Dirac or Weyl semimetals show
linear dispersion round nodes, termed the Dirac or Weyl points, as the
three-dimensional analogue of graphene. We review the basic concepts and
compare these topological states of matter from the materials perspective with
a special focus on Weyl semimetals. The TaAs family is the ideal materials
class to introduce the signatures of Weyl points in a pedagogical way, from
Fermi arcs to the chiral magneto-transport properties, followed by the hunting
for the type-II Weyl semimetals in WTe2, MoTe2 and related compounds. Many
materials are members of big families and topological properties can be tuned.
As one example, we introduce the multifuntional topological materials, Heusler
compounds, in which both topological insulators and magnetic Weyl semimetals
can be found. Instead of a comprehensive review, this article is expected to
serve as a helpful introduction and summary by taking a snapshot of the quickly
expanding field.",1611.04182v2
2017-11-07,YbPd$_2$In: a promising candidate to strong entropy accumulation at very low temperature,"We report on synthesis, crystal structure, magnetic, thermodynamic and
transport properties of the new compound YbPd$_2$In, crystallizing as a Heusler
structure type. A trivalent state of the rare earth was determined by fitting
the magnetic susceptibility with a Curie-Weiss law. This compound is
characterized by showing very weak magnetic interactions and a negligible Kondo
effect. A specific heat jump was observed at $T\approx 250$ mK, followed at
higher temperature by a power law decrease of $C_P(T)/T$. The resulting large
electronic entropy increase at very low temperature is rapidly shifted to
higher temperature by the application of magnetic field. This magnetocaloric
effect places YbPd$_2$In as a very good candidate for adiabatic demagnetization
cooling processes.",1711.02335v3
2019-01-24,Effect of secondary LuNiSn phase on thermoelectric properties of half-Heusler alloy LuNiSb,"We report on the high-temperature (350 K <T< 1000 K) thermoelectric
properties of the ternary compounds LuNiSb (cubic) and LuNiSn (orthorhombic)
and a composite material (LuNiSb)$_{0.5}$(LuNiSn)$_{0.5}$. The electrical
conductivity in LuNiSn is metallic, while it is semiconducting-like in LuNiSb.
The Seebeck coefficient reaches -5.5 $\mu$V/K at 700 K for the former compound
and 66 $\mu$V/K at 607 K for the latter one. The composite sample
(LuNiSb)$_{0.5}$(LuNiSn)$_{0.5}$ constructed from orthorhombic matrix with
cubic inclusions combines the electrical conductivity of LuNiSn with the
thermoelectric properties of LuNiSb. Nonetheless, no enhancement of the
thermoelectric performance occurs for this material.",1901.08399v1
2020-12-11,Absence of superconductivity in topological metal ScInAu$_2$,"The Heusler compound ScInAu$_2$ was previously reported to have a
superconducting ground state with a critical temperature of 3.0 K. Recent high
throughput calculations have also predicted that the material harbors a
topologically non-trivial band structure similar to that reported for
beta-PdBi$_2$. In an effort to explore the interplay between the
superconducting and topological properties properties, electrical resistance,
magnetization, and x-ray diffraction measurements were performed on
polycrystalline ScInAu$_2$. The data reveal that high-quality polycrystalline
samples lack the super-conducting transition present samples that have not been
annealed. These results indicate the earlier reported superconductivity is
non-intrinsic. Several compounds in the Au-In-Sc ternary phase space (ScAu$_2$,
ScIn$_3$, and ScInAu$_2$) were explored in an attempt to identify the secondary
phase responsible for the non-intrinsic superconductivity. The results suggest
that elemental In is responsible for the reported superconductivity in
ScInAu$_2$.",2012.06501v1
2006-01-30,Electronic structure and spectroscopy of the quaternary Heusler alloy Co$_2$Cr$_{1-x}$Fe$_{x}$Al,"Quaternary Heusler alloys Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe
ratio $x$ were investigated experimentally and theoretically. The electronic
structure and spectroscopic properties were calculated using the full
relativistic Korringa-Kohn-Rostocker method with coherent potential
approximation to account for the random distribution of Cr and Fe atoms as well
as random disorder. Magnetic effects are included by the use of spin dependent
potentials in the local spin density approximation.
  Magnetic circular dichroism in X-ray absorption was measured at the $L_{2,3}$
edges of Co, Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to
determine element specific magnetic moments. Calculations and measurements show
an increase of the magnetic moments with increasing iron content. Resonant
(560eV - 800eV) soft X-ray as well as high resolution - high energy ($\geq
3.5$keV) hard X-ray photo emission was used to probe the density of the
occupied states in Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al.",0601670v1
2007-07-05,"Engineering the electronic, magnetic and gap-related properties of the quinternary half-metallic Heusler alloys","We review the electronic and magnetic properties of the quinternary full
Heusler alloys of the type Co$_2$[Cr$_{1-x}$Mn$_x$][Al$_{1-y}$Si$_y$] employing
three different approaches : (i) the coherent potential approximation (CPA),
(ii) the virtual crystal approximation (VCA), and (iii) supercell calculations
(SC). All three methods give similar results and the local environment
manifested itself only for small details of the density of states. All alloys
under study are shown to be half-metals and their total spin moments follow the
so-called Slater-Pauling behavior of the ideal half-metallic systems. We
especially concentrate on the properties related to the minority-spin band-gap.
We present the possibility to engineer the properties of these alloys by
changing the relative concentrations of the low-valent transition metal and
$sp$ atoms in a continuous way. Our results show that for realistic
applications, ideal are the compounds rich in Si and Cr since they combine
large energy gaps (around 0.6 eV), robust half-metallicity with respect to
defects (the Fermi level is located near the middle of the gap) and high values
of the majority-spin density of states around the Fermi level which are needed
for large values of the perfectly spin-polarized current in spintronic devices
like spin-valves or magnetic tunnel junctions.",0707.0728v1
2008-02-18,Ab-initio determined electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys; the role of interfaces and defects,"Using state-of-the-art first-principles calculations we study the properties
of the ferromagnetic Heusler compounds NiYSi where Y stands for V, Cr or Mn.
NiCrSi and NiMnSi contrary to NiVSi are half-metallic at their equilibrium
lattice constant exhibiting integer values of the total spin magnetic moment
and thus we concentrate on these two alloys. The minority-spin gap has the same
characteristics as for the well-known NiMnSb alloy being around $\sim$1 eV.
Upon tetragonalization the gap is present in the density of states even for
expansion or contraction of the out-of-plane lattice parameter by 5%. The Cr-Cr
and Mn-Mn interactions make ferromagnetism extremely stable and the Curie
temperature exceeds 1000 K for NiMnSi. Surface and interfaces with GaP, ZnS and
Si semiconductors are not half-metallic but in the case of NiCrSi the Ni-based
contacts present spin-polarization at the Fermi level over 90%. Finally, we
show that there are two cases of defects and atomic-swaps. The first-ones which
involve the Cr(Mn) and Si atoms induce states at the edges of the gap which
persists for a moderate-concentration of defects. Defects involving Ni atoms
induce states localized within the gap completely destroying the
half-metallicity. Based on single-impurity calculations we associate these
states to the symmetry of the crystal.",0802.2531v1
2014-08-07,Weak Antilocalization Effect and Noncentrosymmetric Superconductivity in a Topologically Nontrivial Semimetal LuPdBi,"A large number of half-Heusler compounds have been recently proposed as
three-dimensional (3D) topological insulators (TIs) with tunable physical
properties.However, no transport measurements associated with the topological
surface states have been observed in these half-Heusler candidates due to the
dominating contribution from bulk electrical conductance. Here we show that, by
reducing the mobility of bulk carriers, a two-dimensional (2D) weak
antilocalization (WAL) effect, one of the hallmarks of topological surface
states, was experimentally revealed from the tilted magnetic field dependence
of magnetoconductance in a topologically nontrivial semimetal LuPdBi. Besides
the observation of a 2D WAL effect, a superconducting transition was revealed
at Tc~1.7 K in the same bulk LuPdBi. Quantitative analysis within the framework
of a generalized BCS theory leads to the conclusion that the noncentrosymmetric
superconductivity of LuPdBi is fully gapped with a possibly unconventional
pairing character. The co-existence of superconductivity and the transport
signature of topological surface states in the same bulk alloy suggests that
LuPdBi represents a very promising candidate as a topological superconductor.",1408.1543v1
2015-01-16,Topological $R$PdBi half-Heusler semimetals: a new family of non-centrosymmetric magnetic superconductors,"We report superconductivity and magnetism in a new family of topological
semimetals, the ternary half Heusler compounds $R$PdBi ($R$ : rare earth). In
this series, tuning of the rare earth $f$-electron component allows for
simultaneous control of both lattice density via lanthanide contraction, as
well as the strength of magnetic interaction via de Gennes scaling, allowing
for a unique tuning of both the normal state band inversion strength,
superconducting pairing and magnetically ordered ground states.
Antiferromagnetism with ordering vector (0.5,0.5,0.5) occurs below a Ne\'eel
temperature that scales with de Gennes factor $dG$, while a superconducting
transition is simultaneously linearly suppressed. With superconductivity
appearing in a system with non-centrosymmetric crystallographic symmetry, the
possibility of spin-triplet Cooper pairing with non-trivial topology analogous
to that predicted for the normal state electronic structure provides a unique
and rich opportunity to realize both predicted and new exotic excitations in
topological materials.",1501.04096v3
2015-03-05,Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy,"The magnitude of the spin polarization at the Fermi level of ferromagnetic
materials at room temperature is a key property for spintronics. Investigating
the Heusler compound Co$_2$MnSi a value of 93$\%$ for the spin polarization has
been observed at room temperature, where the high spin polarization is related
to a stable surface resonance in the majority band extending deep into the
bulk. In particular, we identified in our spectroscopical analysis that this
surface resonance is embedded in the bulk continuum with a strong coupling to
the majority bulk states. The resonance behaves very bulk-like, as it extends
over the first six atomic layers of the corresponding (001)-surface. Our study
includes experimental investigations, where the bulk electronic structure as
well as surface-related features have been investigated using spin-resolved
photoelectron spectroscopy (SR-UPS) and for a larger probing depth
spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The
results are interpreted in comparison with first-principles band structure and
photoemission calculations which consider all relativistic, surface and
high-energy effects properly.",1503.01573v1
2017-12-29,From colossal to zero: Controlling the Anomalous Hall Effect in Magnetic Heusler Compounds via Berry Curvature Design,"Since the discovery of the anomalous Hall effect (AHE), the anomalous Hall
conductivity (AHC) has been thought to be zero when there is no net
magnetization. However, the recently found relation between the intrinsic AHE
and the Berry curvature predicts other possibilities, such as a large AHC in
non-colinear antiferromagnets with no net magnetization but net Berry
curvature. Vice versa, the AHE in principle could be tuned to zero,
irrespective of a finite magnetization. Here, we experimentally investigate
this possibility and demonstrate that, the symmetry elements of Heusler magnets
can be changed such that the Berry curvature and all the associated properties
are switched while leaving the magnetization unaffected. This enables us to
tune the AHC from 0 {\Omega}-1cm-1 up to 1600 {\Omega}-1cm-1 with an
exceptionally high anomalous Hall angle up to 12 %, while keeping the
magnetization same. Our study shows that the AHC can be controlled by
selectively changing the Berry curvature distribution, independent of the
magnetization.",1712.10174v3
2017-04-26,Ordering tendencies and electronic properties in quaternary Heusler derivatives,"The phase stabilities and ordering tendencies in the quaternary full-Heusler
alloys NiCoMnAl and NiCoMnGa have been investigated by in-situ neutron
diffraction, calorimetry and magnetization measurements. NiCoMnGa was found to
adopt the L2$_1$ structure, with distinct Mn and Ga sublattices but a common
Ni-Co sublattice. A second-order phase transition to the B2 phase with disorder
also between Mn and Ga was observed at 1160 K. In contrast, in NiCoMnAl slow
cooling or low-temperature annealing treatments are required to induce
incipient L2$_1$ ordering, otherwise the system displays only B2 order. Linked
to this L2$_1$ ordering, a drastic increase in the magnetic transition
temperature was observed in NiCoMnAl, while annealing affected the magnetic
behavior of NiCoMnGa only weakly due to the low degree of quenched-in disorder.
First principles calculations were employed to study the thermodynamics as well
as order-dependent electronic properties of both compounds. It was found that a
near half-metallic pseudo-gap emerges in the minority spin channel only for the
completely ordered Y structure, which however is energetically unstable
compared to the predicted ground state of a tetragonal structure with
alternating layers of Ni and Co. The experimental inaccessibility of the
totally ordered structures is explained by kinetic limitations due to the low
ordering energies.",1704.08100v1
2018-08-07,Theoretical Investigation on the Effect of multinary Isoelectronic Substitution on TiCoSb based half-Heusler alloys,"To understand the effect of isoelectronic substitution on thermoelectric
properties of TiCoSb based half - Heusler (HH) alloys, we have systematically
studied the transport properties with substitution of Zr at Ti and Bi at Sb
sites. The electronic structure of TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) and
parent TiCoSb are investigated using the full potential linearized augmented
plane wave method and the thermoelectric transport properties are calculated on
the basis of semiclassical Boltzmann transport theory. The band analysis of the
calculated band structures reveal that TixZr1-xCoSbxBi1-x has semiconducting
behavior with indirect band gap at x = 0.25, 0.5 concentration and direct band
gap behavior at x = 0.75 concentration. The TixZr1-xCoSbxBi1-x (x = 0.25, 0.5,
0.75) compounds show smaller band gap values as compared to the pure TiCoSb.
The d electrons of Ti/Zr and Co dominate the electronic transport properties of
TixZr1-xCoSbxBi1-x system. All these systems follow the empirical rule of 18
valence-electron content to bring semiconductivity in HH alloys. The
isoelectronic substitution in TiCoSb can tune the band structure by shifting
the Fermi level. This provides us lot of possibilities to get the desired band
gap values for designing thermoelectrics with high efficiency. In this study we
have showed that the isoelectronic substitution at both Ti and Sb site of
TiCoSb has very small effect for increasing the ZT values and one should go for
isoelectronic substitution at any one sites of TiCoSb HH alloys alone to
improve ZT.",1808.02514v1
2020-08-28,Effect of Bi-substitution on Structural Stability and Improved Thermoelectric Performance of p-type Half-Heusler TaSbRu: A First-principles Study,"Recently, Fang et al. have predicted a high ZT of 1.54 in TaSbRu alloys at
1200 K from first-principles without considering spin-orbit interaction,
accurate electronic structure, details of phonon scattering, and
energy-dependent holes relaxation time. Here, we report the details of
structural stability and thermoelectric performance of Bi-Substituted p-type
TaSbRu from first-principles calculations considering theses important
parameters. This indirect bandgap semiconductor (Eg=0.8 eV by TB-mBJ+SOC) has
highly dispersive and degenerate valence bands, which lead to a maximum power
factor, 3.8 mWm-1K-2 at 300K. As Sb-5p has a small contribution to the bandgap
formation, the substitution of Bi on the Sb site does not cause significant
change to the electronic structure. Although the Seebeck coefficient increases
by Bi due to slight changes in the bandgap, electrical conductivity, and hence,
the power factor reduces to ~3 mW m-1K-2 at 300K (50% Bi). On the other side,
lattice thermal conductivity drops effectively to 5 from 20 W/m K as Bi
introduces a significant contribution in the acoustic phonon region and
intensify phonon scattering. Thus, ZT value is improved through
Bi-substitution, reaching 1.1 (50% Bi) at 1200 K from 0.45 (pure TaSbRu) only.
Therefore, the present study suggests how to improve the TE performance of
Sb-based half-Heusler compounds and TaSbRu (with 50% Bi) is a promising
material for high-temperature applications.",2008.12564v1
2016-12-22,Co-sputtered PtMnSb thin films and PtMnSb/Pt bilayers for spin-orbit torque investigations,"The manipulation of the magnetization by spin-orbit torques (SOTs) has
recently been extensively studied due to its potential for efficiently writing
information in magnetic memories. Particular attention is paid to
non-centrosymmetric systems with space inversion asymmetry, where SOTs emerge
even in single-layer materials. The half-metallic half-Heusler PtMnSb is an
interesting candidate for studies of this intrinsic SOT. Here, we report on the
growth and epitaxial properties of PtMnSb thin films and PtMnSb/Pt bilayers
deposited on MgO(001) substrates by dc magnetron co-sputtering at high
temperature in ultra-high vacuum. The film properties were investigated by
x-ray diffraction, x-ray reflectivity, atomic force microscopy, and electron
microscopy. Thin PtMnSb films present a monocrystalline C1b phase with (001)
orientation, coexisting at increasing thickness with a polycrystalline phase
with (111) texture. Films thinner than about 5 nm grow in islands, whereas
thicker films grow layer-by-layer, forming a perfect MgO/PtMnSb interface. The
thin PtMnSb/Pt bilayers also show island growth and a defective transition
zone, while thicker films grow layer-by-layer and Pt grows epitaxially on the
half-Heusler compound without significant interdiffusion.",1612.07614v1
2017-10-06,Relative Cooling Power Enhancement by Tuning Magneto-structural Stability in Ni-Mn-In Heusler Alloys,"Off-stoichiometric Ni$_2$MnIn Heusler alloys have drawn recent attention due
to their large magnetocaloric entropy change associated with the first-order
magneto-structural transition. Here we present crystal structural, calorimetric
and magnetic studies of three compositions. Temperature-dependent X-ray
diffraction shows clear structural transition from a 6M modulated monoclinic to
a L2$_1$ cubic. A significant enhancement of relative cooling power (RCP) was
achieved by tuning the magnetic and structural stability through minor
compositional changes, with the measured results quantitatively close to the
prediction as a function of the ratio between the martensitic transition
($T_m$) temperature and austenite Curie temperature ($T_C$) although the
maximal magnetic induced entropy change ($\Delta S_{max}$) reduction is
observed in the same time. The results provided an evaluation guideline of RCPs
as well as magnetic-induced entropy change in designing practical active
materials.",1710.02522v6
2017-10-12,Manifestation of the Berry curvature in Co2TiSn Heusler films,"Various Co2 based Heusler compounds are predicted to be Weyl materials. These
systems with broken symmetry possess a large Berry curvature, and introduce
exotic transport properties. The present study on epitaxially grown Co2TiSn
films is an initial approach to understand and explore this possibility. The
anomalous Hall effect in the well-ordered Co2TiSn films has been investigated
both experimentally and theoretically. The measured Hall conductivity is in
good agreement to the calculated Berry curvature. Small deviations between them
are due to the influence of skew scattering on the Hall effect. From
theoretical point of view, the main contribution to the anomalous Hall effect
originates from slightly gapped nodal lines, due to a symmetry reduction
induced by the magnetization. It has been found that only part of the nodal
lines contributed near to the anomalous Hall conductivity at a fixed Fermi
energy which can be explained from a magnetic symmetry analysis. Furthermore,
from hard x-ray photoelectron spectroscopy measurements, we establish the
electronic structure in the film that is comparable to the theoretical density
of states calculations. The present results provide deeper insight into the
spintronics from the prospect of topology.",1710.04393v1
2018-04-15,$\mathrm{Co_2Fe_{1-x}Cr_xSi}$ Heusler Alloys : A promising material for spintronics application,"In this article, we investigated the effect of Cr substitution in place of Fe
on the structural, magnetic and transport properties of $\mathrm{Co_2FeSi}$
alloy. A comprehensive structural analysis is done using X-ray diffraction
(XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
Quaternary Heusler compounds $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ with Cr content (x =
0.1, 0.3, 0.5) were found to crystallize in cubic structure. The synchrotron
based EXAFS studies reveal that the anti-site disorder increases with the
increase in Cr concentration. The saturation magnetization values in all the
alloys are found to be less than those expected from the Slater-Pauling rule,
which may be due to the some inherent disorder. A detailed resistivity analysis
in the temperature range of 5-300 K is done, taking into account different
scattering mechanisms. The residual resistivity ratio is found to decrease with
increasing Cr concentration. A disorder induced resistivity minimum due to weak
localization effect is seen for x = 0.5. The resistivity measurements also
indicate that the half-metallic character survives upto 100 K for x = 0.1,
whereas the alloys with x= 0.3 and 0.5 show signature of half- metallic nature
even at higher temperatures. First principles calculation done with a more
robust exchange correlation functional (namely HSE-06) confirms the half
metallicity in the entire concentration range. Theoretically simulated band gap
and magnetic moments compliment the experimental findings and are compared
wherever possible. All these properties make $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ a
promising material for spintronics application.",1804.05321v1
2019-03-26,Complex exchange mechanism driven ferromagnetism in half-metallic Heusler Co$_{2}$TiGe: Evidence from critical behavior,"We have investigated the critical phenomenon associated with the magnetic
phase transition in the half-metallic full-Heusler Co$_2$TiGe. The compound
undergoes a continuous ferromagnetic to paramagnetic phase transition at the
Curie temperature $T_{C}$=371.5 K. The analysis of magnetization isotherms in
the vicinity of $T_{c}$, following modified Arrott plot method, Kouvel-Fisher
technique, and critical isotherm plot, yields the asymptotic critical exponents
$\beta$=0.495, $\gamma$=1.324, and $\delta$=3.67. The self-consistency and
reliability of the obtained exponents are further verified by the Widom scaling
relation and scaling equation of states. The mean-field-like value of the
critical exponent $\beta$ suggests long-range nature of the exchange
interactions, whereas the values of the critical exponents $\gamma$ and
$\delta$, imply sizeable critical spin fluctuations. The half-metallic
itinerant character of Co$_{2}$TiGe in the presence of magnetic inhomogeneity
may result in such a strong deviation from the three-dimensional Heisenberg
values ($\beta$=0.369, $\gamma$=1.38 and $\delta$=4.8) of the critical
exponents towards the mean field values ($\beta$=0.5, $\gamma$=1 and
$\delta$=3). The results suggest complex nature of exchange couplings that
stabilize the long-range ferromagnetic ordering in the system and are
consistent with the earlier theoretical studies on the exchange mechanism in
Co$_2$TiGe.",1903.10987v1
2020-10-16,THz range Faraday rotation in the Weyl Semimetal Candidate $\mathrm{Co_2TiGe}$,"The $\mathrm{Co_2}$ family of ferromagnetic Heusler alloys have attracted
interest due to their fully spin-polarized nature, making them ideal for
applications in spintronic devices. More recently, the existence of room
temperature time-reversal-breaking Weyl nodes near the Fermi level was
predicted and confirmed in these systems. As a result of the presence of these
Weyl nodes, these systems possess a non-zero momentum space Berry curvature
that can dramatically influence transport properties such as the anomalous Hall
effect. One of these candidate compounds is $\mathrm{Co_2 Ti Ge}$. Recently,
high quality molecular beam epitaxy-grown thin films of $\mathrm{Co_2 Ti Ge}$
have become available. In this work, we present THz-range measurement of
MBE-grown $\mathrm{Co_2 Ti Ge}$ films. We measure the THz-range Faraday
rotation, which can be understood as a measure of the anomalous Hall effect. We
supplement this work with electronic band structure calculations showing that
the principal contribution to the anomalous Hall effect in the this material
stems from the Berry curvature of the material. Our work shows that this class
of Heusler materials shows promise for Weyl semimetal based spintronics.",2010.08589v2
2020-10-22,Multicaloric effects in Metamagnetic Heusler Ni-Mn-In under uniaxial stress and magnetic field,"The world's growing hunger for artificial cold on the one hand, and the ever
more stringent climate targets on the other, pose an enormous challenge to
mankind. Novel, efficient and environmentally friendly refrigeration
technologies based on solid-state refrigerants can offer a way out of the
problems arising from climate-damaging substances used in conventional
vapor-compressors. Multicaloric materials stand out because of their large
temperature changes which can be induced by the application of different
external stimuli such as a magnetic, electric, or a mechanical field. Despite
the high potential for applications and the interesting physics of this group
of materials, only few studies focus on their investigation by direct methods.
In this paper, we report on the advanced characterization of all relevant
physical quantities that determine the multicaloric effect of a Ni-Mn-In
Heusler compound. We have used a purpose-designed calorimeter to determine the
isothermal entropy and adiabatic temperature changes resulting from the
combined action of magnetic field and uniaxial stress on this metamagnetic
shape-memory alloy. From these results, we can conclude that the multicaloric
response of this alloy by appropriate changes of uniaxial stress and magnetic
field largely outperforms the caloric response of the alloy when subjected to
only a single stimulus. We anticipate that our findings can be applied to other
multicaloric materials, thus inspiring the development of refrigeration devices
based on the multicaloric effect.",2010.11511v1
2021-08-15,An ab-initio study of topological and transport properties of YAuPb,"In the last few decades, the study of topological materials has been carried
out on an extensive scale. Half-Heusler alloys are well known for their
topological behaviours. In this work, we present a detailed study of
topological properties of a ternary Half-Heusler alloy, YAuPb, using the
tight-binding approach. We have calculated some important topological
properties which includes$-$ finding nodes and their chiralities, Berry
curvature ($\boldsymbol\Omega$) and the surface-states. Based on the study of
these properties, we categorise the material as non-trivial topological
semimetal. Besides the topological behaviours, we present a comparative study
of temperature dependent transport properties corresponding to the chemical
potential ($\mu$) of the Fermi level and the node points. The results obtained
from the calculations of electrical conductivity per unit relaxation time
($\boldsymbol\sigma/\tau$) and the electronic part of thermal conductivity per
unit relaxation time ($\boldsymbol\kappa_0$) indicates the conducting nature of
the material to both the heat and electricity. Furthermore, the negative value
of $S$ obtained, indicates the n-type behaviour of the compound. The calculated
value of electronic specific heat (Pauli magnetic susceptibility) corresponding
to Fermi level is $\sim 0.03 \hspace{1mm}(0.18) \times 10^{-2}$ $
Jmol^{-1}K^{-1}$ ($\sim 1.21 \hspace{1mm}(1.14) \times 10^{-10}$ $
m^{3}mol^{-1}$) at 50 (300) K. This work suggests that YAuPb is a promising
candidate of non-trivial topological semimetals which can be employed in
transmission of heat and electricity, and as n-type material within the
temperature range of 50-300 K.",2108.06678v1
2023-03-06,"Structural phase transitions and superconductivity in the Heusler intermetallics $X$Pd$_2$Sn ($X$ = Ti, Zr, Hf)","We report the discovery of structural phase transitions and superconductivity
in the full Heusler compounds $X$Pd$_2$Sn ($X$ = Ti, Zr, Hf), by means of
electrical transport, magnetic susceptibility, specific heat and x-ray
diffraction measurements. TiPd$_2$Sn, ZrPd$_2$Sn and HfPd$_2$Sn undergo
structural phase transitions from the room-temperature cubic MnCu$_2$Al-type
structure (space group $Fm\bar{3}m$) to a low-temperature tetragonal structure
at around 160 K, 110 K and 90 K, respectively, which are likely related charge
density wave (CDW) instabilities. Low temperature single crystal x-ray
diffraction measurements of ZrPd$_2$Sn demonstrate the emergence of a
superstructure with multiple commensurate modulations below $T_s$. ZrPd$_2$Sn
and HfPd$_2$Sn have bulk superconductivity (SC) with transition temperatures
$T_c$ $\sim$ 1.2 K and 1.3 K, respectively. Density functional theory (DFT)
calculations reveal evidence for structural and electronic instabilities which
can give rise to CDW formation, suggesting that these $X$Pd$_2$Sn systems are
good candidates for examining the interplay between CDW and SC.",2303.02908v1
2023-05-25,Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100 fs timescales,"The direct manipulation of spins via light may provide a path toward
ultrafast energy-efficient devices. However, distinguishing the microscopic
processes that can occur during ultrafast laser excitation in magnetic alloys
is challenging. Here, we study the Heusler compound Co2MnGa, a material that
exhibits very strong light-induced spin transfers across the entire M-edge. By
combining the element-specificity of extreme ultraviolet high harmonic probes
with time-dependent density functional theory, we disentangle the competition
between three ultrafast light-induced processes that occur in Co2MnGa:
same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast
spin-flips mediated by spin-orbit coupling. By measuring the dynamic magnetic
asymmetry across the entire M-edges of the two magnetic sublattices involved,
we uncover the relative dominance of these processes at different probe energy
regions and times during the laser pulse. Our combined approach enables a
comprehensive microscopic interpretation of laser-induced magnetization
dynamics on timescales shorter than 100 fs.",2305.16455v2
2023-07-11,Microstructure of a spark-plasma-sintered Fe2VAl-type Heusler alloy for thermoelectric application,"The influence of microstructure on thermoelectricity is increasingly
recognized. Approaches for microstructural engineering can hence be exploited
to enhance thermoelectric performance, particularly through manipulating
crystalline defects, their structure, and composition. Here, we focus on a
full-Heusler Fe2VAl-based compound that is one of the most promising
thermoelectric materials containing only Earth-abundant, non-toxic elements. A
Fe2VTa0.05Al0.95 cast alloy was atomized under a nitrogen-rich atmosphere to
induce nitride precipitation. Nanometer- to micrometer-scale microstructural
investigations by advanced scanning electron microscopy and atom probe
tomography (APT) are performed on the powder first and then on the material
consolidated by spark-plasma sintering for an increasing time. APT reveals an
unexpected pick-up of additional impurities from atomization, namely W and Mo.
The microstructure is then correlated with local and global measurements of the
thermoelectric properties. At grain boundaries, segregation and precipitation
locally reduce the electrical resistivity, as evidenced by in-situ four-point
probe measurements. The final microstructure contains a hierarchy of structural
defects, including individual point defects, dislocations, grain boundaries,
and precipitates, that allow for a strong decrease in thermal conductivity. In
combination, these effects provide an appreciable increase in thermoelectric
performance.",2307.05051v1
2024-01-22,Off-stoichiometric effect on magnetic and electron transport properties of Fe$_2$VAl$_{1.35}$ in respect to Ni$_2$VAl; Comparative study,"Density functional theory (DFT) calculations confirm that the structurally
ordered Fe$_2$VAl Heusler alloy is nonmagnetic narrow-gap semiconductor. This
compound is apt to form various disordered modifications with high
concentration of antisite defects. We study the effect of structural disorder
on the electronic structure, magnetic, and electronic transport properties of
the full Heusler alloy Fe$_2$VAl and its off-stoichiometric equivalent
Fe$_2$VAl$_{1.35}$. Data analysis in relation to {\it ab initio} calculations
indicates an appearance of antisite disorder mainly due to Fe--V and Fe--Al
stoichiometric variations. The data for weakly magnetic Fe$_2$VAl$_{1.35}$ are
discussed in respect to Ni$_2$VAl. Fe$_2$VAl$_{1.35}$ can be classified as a
nearly ferromagnetic metal with a pronounced spin glassy contribution, which,
however, does not give a predominant effect on its thermoelectric properties.
The figure of merit $ZT$ is at 300 K about 0.05 for the Fe sample and 0.02 for
Ni one, respectively. However, it is documented that the narrow $d$ band
resulting from Fe/V site exchange can be responsible for the unusual
temperature dependencies of the physical properties of the Fe2TiAl$_{1.35}$
alloy, characteristic of strongly correlated electron systems. As an example,
the magnetic susceptibility of Fe$_2$VAl$_{1.35}$ exhibits singularity
characteristic of a Griffiths phase, appearing as an inhomogeneous electronic
state below $T_G\sim 200$ K. We also performed numerical analysis which
supports the Griffiths phase scenario.",2401.12218v1
2017-07-26,Studying the effect of different exchange correlation functionals on the structural and electronic properties of a half-Heusler NaAuS compound,"Theoretically, NaAuS is predicted as topological insulator, while no detail
electronic structure study has been done for this compound. Here, we report the
structural and electronic properties of NaAuS by using LDA, PBEsol, PBE and
revPBE exchange correlation functionals. The calculated values of equilibrium
lattice constant for LDA, PBEsol, PBE and revPBE exchange correlation
functionals are found to be $\sim$6.128 {\AA}, $\sim$6.219 {\AA}, $\sim$6.353
{\AA} and $\sim$6.442 {\AA}, respectively. The bulk modulus predicted by LDA,
PBEsol, PBE and revPBE exchange correlation functionals is $\sim$66.6,
$\sim$56.4, $\sim$46.5 and $\sim$39.3 GPa, respectively. Hence, the order of
calculated values of bulk modulus is consistent with the order of calculated
values of equilibrium lattice parameters for these exchange correlation
functionals. The spread of total density of states below the Fermi level
decreases as the exchange correlation functional changes from LDA to PBEsol to
PBE to revPBE, which is also found to be consistent with the order of bulk
modulus for these exchange correlation functionals. In presence of spin-orbit
coupling, a direct band gap is observed in NaAuS compound, which is found to be
$\sim$0.26, $\sim$0.25, $\sim$0.24 and $\sim$0.23 eV for LDA, PBEsol, PBE and
revPBE exchange correlation functionals, respectively. Here, NaAuS is found to
be topological insulator as it shows band inversion at $\Gamma$ point. The
calculated values of band inversion strength for LDA (PBEsol) and PBE (revPBE)
exchange correlation functionals are $\sim$1.58 eV ($\sim$1.57 eV) and
$\sim$1.50 eV ($\sim$1.47 eV), respectively.",1707.08457v1
2016-11-06,Lattice thermal conductivity of Ti$_x$Zr$_y$Hf$_{1-x-y}$NiSn half-Heusler alloys calculated from first principles: Key role of nature of phonon modes,"In spite of their relatively high lattice thermal conductivity
$\kappa_{\ell}$, the XNiSn (X=Ti, Zr or Hf) half-Heusler compounds are good
thermoelectric materials. Previous studies have shown that $\kappa_{\ell}$ can
be reduced by sublattice-alloying on the X-site. To cast light on how the alloy
composition affects $\kappa_\ell$, we study this system using the phonon
Boltzmann-transport equation within the relaxation time approximation in
conjunction with density functional theory.The effect of alloying through
mass-disorder scattering is explored using the virtual crystal approximation to
screen the entire ternary Ti$_x$Zr$_{y}$Hf$_{1-x-y}$NiSn phase diagram. The
lowest lattice thermal conductivity is found for the Ti$_x$Hf$_{1-x}$NiSn
compositions; in particular, there is a shallow minimum centered at
Ti$_{0.5}$Hf$_{0.5}$NiSn with $\kappa_l$ taking values between 3.2 and 4.1 W/mK
when the Ti content varies between 20 and 80\%. Interestingly, the overall
behavior of mass-disorder scattering in this system can only be understood from
a combination of the nature of the phonon modes and the magnitude of the mass
variance. Mass-disorder scattering is not effective at scattering acoustic
phonons of low energy. By using a simple model of grain boundary scattering, we
find that nanostructuring these compounds can scatter such phonons effectively
and thus further reduce the lattice thermal conductivity; for instance,
Ti$_{0.5}$Hf$_{0.5}$NiSn with a grain size of $L= 100$ nm experiences a 42\%
reduction of $\kappa_{\ell}$ compared to that of the single crystal.",1611.01757v2
2020-12-23,Identifying the fingerprints of topological states by tuning magnetoresistance in a semimetal: the case of topological half-Heusler Pt1-xAuxLuSb,"Topological materials often exhibit remarkably linear, non-saturating
magnetoresistance (LMR), which is both of scientific and technological
importance. However, the role of topologically non-trivial states in the
emergence of such a behaviour has eluded clear demonstration in experiments.
Here, by reducing the coupling between the topological surface states (TSS) and
the bulk carriers we controllably tune the LMR behavior in Pt1-xAuxLuSb into
distinct plateaus in Hall resistance, which we show arise from a quantum Hall
phase. This allowed us to reveal how smearing of the Landau levels, which
otherwise give rise to a quantum Hall phase, results in an LMR behavior due to
strong interaction between the TSS with a positive g-factor and the bulk
carriers. We establish that controlling the coupling strength between the
surface and the bulk carriers in topological materials can bring about dramatic
changes in their magnetotransport behavior. In addition, our work outlines a
strategy to reveal macroscopic physical observables of TSS in compounds with a
semi-metallic bulk band structure, as is the case in multi-functional Heusler
compounds, thereby opening up opportunities for their utilization in hybrid
quantum structures.",2012.12633v5
2003-10-16,Magnetotransport in Single Crystal Half-Heusler Compounds,"We present the results of electrical resistivity and Hall effect measurements
on single crystals of HfNiSn, TiPtSn, and TiNiSn. Semiconducting behavior is
observed in each case, involving the transport of a small number of highly
compensated carriers. Magnetization measurements suggest that impurities and
site disorder create both localized magnetic moments and extended paramagnetic
states, with the susceptibility of the latter increasing strongly with reduced
temperature. The magnetoresistance is sublinear or linear in fields ranging
from 0.01 - 9 Tesla at the lowest temperatures. As the temperature increases,
the normal quadratic magnetoresistance is regained, initially at low fields,
and at the highest temperatures extending over the complete range of fields.
The origin of the vanishingly small field scale implied by these measurements
remains unknown, presenting a challenge to existing classical and quantum
mechanical theories of magnetoresistance.",0310369v2
2005-11-18,Half-metallic ferromagnetism with high magnetic moment and high Curie temperature in Co$_2$FeSi,"Co$_2$FeSi crystallizes in the ordered L2$_1$ structure as proved by X-ray
diffraction and M\""o\ss bauer spectroscopy. The magnetic moment of Co$_2$FeSi
was measured to be about $6\mu_B$ at 5K. Magnetic circular dichroism spectra
excited by soft X-rays (XMCD) were taken to determine the element specific
magnetic moments of Co and Fe. The Curie temperature was measured with
different methods to be ($1100\pm20$)K. Co$_2$FeSi was found to be the Heusler
compound as well as the half-metallic ferromagnet with the highest magnetic
moment and Curie temperature.",0511463v1
2006-06-26,Epitaxial film growth and magnetic properties of Co_2FeSi,"We have grown thin films of the Heusler compound Co_2FeSi by RF magnetron
sputtering. On (100)-oriented MgO substrates we find fully epitaxial
(100)-oriented and L2_1 ordered growth. On Al_2O_3 (11-20) substrates, the film
growth is (110)-oriented, and several in-plane epitaxial domains are observed.
The temperature dependence of the electrical resistivity shows a power law with
an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic
properties reveals an extrapolated saturation magnetization of 5.0 mu_B/fu at 0
K. The films on Al_2O_3 show an in-plane uniaxial anisotropy, while the
epitaxial films are magnetically isotropic in the plane. Measurements of the
X-ray magnetic circular dichroism of the films allowed us to determine element
specific magnetic moments. Finally we have measured the spin polarization at
the surface region by spin-resolved near-threshold photoemission and found it
strongly reduced in contrast to the expected bulk value of 100%. Possible
reasons for the reduced magnetization are discussed.",0606666v2
2006-09-25,Ion beam induced modification of exchange interaction and spin-orbit coupling in the Co$_2$FeSi Heusler compound,"A Co$_2$FeSi (CFS) film with L2$_1$ structure was irradiated with different
fluences of 30 keV Ga$^+$ ions. Structural modifications were subsequently
studied using the longitudinal (LMOKE) and quadratic (QMOKE) magneto-optical
Kerr effect. Both the coercivity and the LMOKE amplitude were found to show a
similar behavior upon irradiation: they are nearly constant up to ion fluences
of $\approx6\times10^{15}$ ion/cm$^2$, while they decrease with further
increasing fluences and finally vanish at a fluence of $\approx9\times10^{16}$
ion/cm$^2$, when the sample becomes paramagnetic. However, contrary to this
behavior, the QMOKE signal nearly vanishes even for the smallest applied
fluence of $3\times10^{14}$ ion/cm$^2$. We attribute this reduction of the
QMOKE signal to an irradiation-induced degeneration of second or higher order
spin-orbit coupling, which already happens at small fluences of 30 keV Ga$^+$
ions. On the other hand, the reduction of coercivity and LMOKE signal with high
ion fluences is probably caused by a reduction of the exchange interaction
within the film material.",0609633v2
2006-09-27,Huge quadratic magneto-optical Kerr effect and magnetization reversal in the Co$_2$FeSi Heusler compound,"Co$_2$FeSi(100) films with L2$_1$ structure deposited onto MgO(100) were
studied exploiting both longitudinal (LMOKE) and quadratic (QMOKE)
magneto-optical Kerr effect. The films exhibit a huge QMOKE signal with a
maximum contribution of up to 30 mdeg, which is the largest QMOKE signal in
reflection that has been measured thus far. This large value is a fingerprint
of an exceptionally large spin-orbit coupling of second or higher order. The
Co$_2$FeSi(100) films exhibit a rather large coercivity of 350 and 70 Oe for
film thicknesses of 22 and 98 nm, respectively. Despite the fact that the films
are epitaxial, they do not provide an angular dependence of the anisotropy and
the remanence in excess of 1% and 2%, respectively.",0609688v2
2007-11-06,Half-metallic ferromagnets: From band structure to many-body effects,"A review of new developments in theoretical and experimental electronic
structure investigations of half-metallic ferromagnets (HMF) is presented.
Being semiconductors for one spin projection and metals for another ones, these
substances are promising magnetic materials for applications in spintronics
(i.e., spin-dependent electronics). Classification of HMF by the peculiarities
of their electronic structure and chemical bonding is discussed. Effects of
electron-magnon interaction in HMF and their manifestations in magnetic,
spectral, thermodynamic, and transport properties are considered. Especial
attention is paid to appearance of non-quasiparticle states in the energy gap,
which provide an instructive example of essentially many-body features in the
electronic structure. State-of-art electronic calculations for correlated
$d$-systems is discussed, and results for specific HMF (Heusler alloys,
zinc-blende structure compounds, CrO$_{2},$ Fe$_{3}$O$_{4}$) are reviewed.",0711.0872v1
2008-04-17,Electronic Structures of Fe$_{3-x}V$_x$Si Probed by Photoemission Spectroscopy,"The electronic structures of the Heusler type compounds Fe$_{3-x}V$_x$Si in
the concentration range between x = 0 and x = 1 have been probed by
photoemission spectroscopy (PES). The observed shift of Si 2p core- level and
the main valence band structres indicate a chemical potential shift to higher
energy with increasing x. It is also clarified that the density of state at
Fermi edge is owing to the collaboration of V 3d and Fe 3d derived states.
Besides the decrease of the spectral intensity near Fermi edge with increasing
x suggests the formation of pseudo gap at large x.",0804.2712v1
2008-09-18,"Improvement of structural, electronic, and magnetic properties of Co$_2$MnSi thin films by He$^+$-irradiation","The influence of 30 keV He$^+$ ion irradiation on structural, electronic and
magnetic properties of Co$_2$MnSi thin films with B2 order was investigated. It
was found, that irradiation with light ions can improve the local chemical
order. This provokes changes of the electronic structure and element-specific
magnetization towards the bulk properties of the well-ordered Co$_2$MnSi
Heusler compound with L2$_1$ structure.",0809.3192v1
2008-10-05,Brillouin light scattering study of Co$_{2}$Cr$_{0.6}$Fe$_{0.4}$Al and Co$_{2}$FeAl Heusler compounds,"The thermal magnonic spectra of Co$_{2}$Cr$_{0.6}$Fe$_{0.4}$Al (CCFA) and
Co$_2$FeAl were investigated using Brillouin light scattering spectroscopy
(BLS). For CCFA, the exchange constant A (exchange stiffness D) is found to be
0.48 $\mu$erg/cm (203 meV A$^2$), while for Co$_2$FeAl the corresponding values
of 1.55 $\mu$erg/cm (370 meV A$^2$) were found. The observed asymmetry in the
BLS spectra between the Stokes and anti-Stokes frequencies was assigned to an
interplay between the asymmetrical profiles of hybridized Damon-Esbach and
perpendicular standing spin-wave modes, combined with the optical sensitivity
of the BLS signal to the upper side of the CCFA or Co$_2$FeAl film.",0810.0838v2
2010-10-27,Electronic structure of fully epitaxial Co2TiSn thin films,"In this article we report on the properties of thin films of the full Heusler
compound Co2TiSn prepared by DC magnetron co-sputtering. Fully epitaxial,
stoichiometric films were obtained by deposition on MgO (001) substrates at
substrate temperatures above 600{\deg}C. The films are well ordered in the L21
structure, and the Curie temperature exceeds slightly the bulk value. They show
a significant, isotropic magnetoresistance and the resistivity becomes strongly
anomalous in the paramagnetic state. The films are weakly ferrimagnetic, with
nearly 1 \mu_B on the Co atoms, and a small antiparallel Ti moment, in
agreement with theoretical expectations. From comparison of x-ray absorption
spectra on the Co L3/L2 edges, including circular and linear magnetic
dichroism, with ab initio calculations of the x-ray absorption and circular
dichroism spectra we infer that the electronic structure of Co2TiSn has
essentially non-localized character. Spectral features that have not been
explained in detail before, are explained here in terms of the final state band
structure.",1010.5754v1
2010-11-11,Influence of tetragonal distortion on the magnetic and electronic properties of the Heusler compound Co2TiSn from first principles,"Using the full potential linearized augmented plane wave plus local orbitals
method we determine ab-initio the lattice parameters of tetragonally distorted
Co2TiSn in the L21 structure. The tetragonal lattice parameter c is determined
as a function of the lattice parameter a by energy minimization. The change in
total energy is found to be only a few $k_B T$ with respect to room
temperature. The spin polarizations as well as the magnetizations are stable
against small lattice distortions. It is shown, that the volume is not constant
upon distortion and that the volume change is related with significant changes
in the magnetization and the gap energy.",1011.2657v1
2010-12-14,Scaling behavior of the spin pumping effect in ferromagnet/platinum bilayers,"We systematically measured the DC voltage V_ISH induced by spin pumping
together with the inverse spin Hall effect in ferromagnet/platinum bilayer
films. In all our samples, comprising ferromagnetic 3d transition metals,
Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V_ISH
invariably has the same polarity. V_ISH furthermore scales with the
magnetization precession cone angle with a universal prefactor, irrespective of
the magnetic properties, the charge carrier transport mechanism or type. These
findings quantitatively corroborate the present theoretical understanding of
spin pumping in combination with the inverse spin Hall effect.",1012.3017v2
2011-01-06,"Metallic surface electronic state in half-Heusler compounds RPtBi (R = Lu, Dy, Gd)","Rare-earth platinum bismuth (RPtBi) has been recently proposed to be a
potential topological insulator. In this paper we present measurements of the
metallic surface electronic structure in three members of this family, using
angle resolved photoemission spectroscopy (ARPES). Our data shows clear
spin-orbit splitting of the surface bands and the Kramers' degeneracy of spins
at the Gamma and M points, which is nicely reproduced with our full-potential
augmented plane wave calculation for a surface electronic state. No direct
indication of topologically non-trivial behavior is detected, except for a weak
Fermi crossing detected in close vicinity to the Gamma point, making the total
number of Fermi crossings odd. In the surface band calculation, however, this
crossing is explained by another Kramers' pair where the two splitting bands
are very close to each other. The classification of this family of materials as
topological insulators remains an open question.",1101.1261v1
2011-06-19,Magnetic and transport properties of rare-earth-based half-Heusler phases RPdBi: prospective systems for topological quantum phenomena,"RPdBi (R = Er, Ho, Gd, Dy, Y, Nd) compounds were studied by means of x-ray
diffraction, magnetic susceptibility, electrical resistivity,
magnetoresistivity, thermoelectric power and Hall effect measurements,
performed in the temperature range 1.5-300 K and in magnetic fields up to 12 T.
These ternaries, except diamagnetic YPdBi, exhibit localized magnetism of
$R^{3+}$ ions, and order antiferromagnetically at low temperatures ($T_{N}$ =
2-13 K). The transport measurements revealed behavior characteristic of
semimetals or narrow-band semiconductors. Both, electrons and holes contribute
to the conductivity with dominant role of p-type carriers. The Hall effect of
ErPdBi is strongly temperature and magnetic field dependent, reflecting complex
character of the underlying electronic structures with multiple electron and
hole bands. RPdBi, and especially DyPdBi, exhibit very good thermoelectric
properties with a power factor coefficient $PF$ ranging from 6 to 20
$\mu$Wcm$^{-1}$K$^{-2}$.",1106.3763v1
2011-09-05,Superconductivity in the topological semimetal YPtBi,"The noncentrosymmetric Half Heusler compound YPtBi exhibits superconductivity
below a critical temperature T_c = 0.77 K with a zero-temperature upper
critical field H_c2(0) = 1.5 T. Magnetoresistance and Hall measurements support
theoretical predictions that this material is a topologically nontrivial
semimetal having a surprisingly low positive charge carrier density of 2 x
10^18 cm^-3. Unconventional linear magnetoresistance and beating in
Shubnikov-de Haas oscillations point to spin-orbit split Fermi surfaces. The
sensitivity of magnetoresistance to surface roughness suggests a possible
contribution from surface states. The combination of noncentrosymmetry and
strong spin-orbit coupling in YPtBi presents a promising platform for the
investigation of topological superconductivity.",1109.0979v2
2011-09-16,Magnetic order in GdBiPt studied by x-ray resonant magnetic scattering,"Rare earth (R) half-Heusler compounds, RBiPt, exhibit a wide spectrum of
novel ground states. Recently, GdBiPt has been proposed as a potential
antiferromagnetic topological insulator (AFTI). We have employed x-ray resonant
magnetic scattering to elucidate the microscopic details of the magnetic
structure in GdBiPt below T_N = 8.5 K. Experiments at the Gd L_2 absorption
edge show that the Gd moments order in an antiferromagnetic stacking along the
cubic diagonal [1 1 1] direction satisfying the requirement for an AFTI, where
both time-reversal symmetry and lattice translational symmetry are broken, but
their product is conserved.",1109.3521v1
2011-10-25,Surface spin polarization of the non-stoichiometric Heusler compound Co2Mn(alpha)Si,"Using a combined approach of spin-resolved photoemission spectroscopy, band
structure and photoemission calculations we investigate the influence of bulk
defects and surface states on the spin polarization of Co2Mn(alpha)Si thin
films with bulk L21 order. We find that for Mn-poor alloys the spin
polarization at EF is negative due to the presence of Co_Mn antisite and
minority surface state contributions. In Mn-rich alloys, the suppression of
Co(Mn) antisites leads to a positive spin polarization at the Fermi energy, and
the influence of minority surface states on the photoelectron spin polarization
is reduced.",1110.5451v2
2011-11-04,Electronic structure and symmetry of valence states of epitaxial NiTiSn and NiZr$_{0.5}$Hf$_{0.5}$Sn thin films by hard x-ray photoelectron spectroscopy,"The electronic band structure of thin films and superlattices made of Heusler
compounds with NiTiSn and NiZr$_{0.5}$Hf$_{0.5}$Sn composition was studied by
means of polarization dependent hard x-ray photoelectron spectroscopy. The
linear dichroism allowed to distinguish the symmetry of the valence states of
the different types of layered structures. The films exhibit a larger amount of
{\it ""in-gap""} states compared to bulk samples. It is shown that the films and
superlattices grown with NiTiSn as starting layer exhibit an electronic
structure close to bulk materials.",1111.1031v1
2012-07-11,Optical floating zone growth of high-quality Cu2MnAl single crystals,"We report the growth of large single-crystals of Cu2MnAl, a ferromagnetic
Heusler compound suitable for polarizing neutron monochromators, by means of
optical floating zone under ultra-high vacuum compatible conditions. Unlike
Bridgman or Czochralsky grown Cu2MnAl, our floating zone grown single-crystals
show highly reproducible magnetic properties and an excellent crystal quality
with a narrow and homogeneous mosaic spread as examined by neutron diffraction.
An investigation of the polarizing properties in neutron scattering suggests a
high polarization efficiency, limited by the relatively small sample dimensions
studied. Our study identifies optical floating zone under ultra-high vacuum
compatible conditions as a highly reproducible method to grow high-quality
single-crystals of Cu2MnAl.",1207.2803v1
2012-10-10,Negative spin polarization of Mn2VGa probed by tunnel magnetoresistance,"The ferrimagnetic Heusler compound Mn2VGa is predicted to have a pseudogap in
the majority spin channel, which should lead to a negative tunnel
magnetoresistance. We synthesized epitaxial Mn2VGa thin films on MgO(001)
substrates by dc and rf magnetron co-sputtering, resulting in nearly
stoichiometric films. XRD analysis revealed a mostly B2-ordered structure for
the films deposited at substrate temperatures of 350{\deg}C, 450{\deg}C, and
550{\deg}C. Magnetic tunnel junctions with MgO barrier and CoFe
counter-electrodes were fabricated. After post-annealing at up to
T_a=425{\deg}C negative TMR was obtained around zero bias, providing evidence
for the inverted spin-polarization. Band structures of both electrodes were
computed within the coherent potential approximation and used to calculate the
TMR(V) characteristics, which are in good agreement with our experimental
findings.",1210.2966v1
2013-02-21,Large zero-field cooled exchange-bias in bulk Mn2PtGa,"We report a large exchange-bias (EB) effect after zero-field cooling the new
tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The
first-principle calculation and the magnetic measurements reveal that Mn2PtGa
orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that
ferrimagnetic (FI) ordering is essential to isothermally induce the exchange
anisotropy needed for the zero-field cooled (ZFC) EB during the virgin
magnetization process. The complex magnetic behavior at low temperatures is
characterized by the coexistence of a field induced irreversible magnetic
behavior and a spin-glass-like phase. The field induced irreversibility
originates from an unusual first-order FI to antiferromagnetic transition,
whereas, the spin-glass like state forms due to the existence of anti-site
disorder intrinsic to the material.",1302.5229v1
2013-09-25,Ab-initio calculation of the effective on-site Coulomb interaction parameters for half-metallic magnets,"Correlation effects play an important role in the electronic structure of
half-metallic (HM) magnets. In particular, they give rise to non-quasiparticle
states above (or below) the Fermi energy at finite temperatures that reduce the
spin polarization and, as a consequence, the efficiency of spintronics devices.
Employing the constrained random-phase approximation (cRPA) within the
full-potential linearized augmented-plane-wave (FLAPW) method using maximally
localized Wannier functions, we calculate the strength of the effective on-site
Coulomb interaction (Hubbard $U$ and Hund exchange $J$) between localized
electrons in different classes of HM magnets considering: (i)
\emph{sp}-electron ferromagnets in rock-salt structure, (ii) zincblende
3\emph{d} binary ferromagnets, as well as (iii) ferromagnetic and ferrimagnetic
semi- and full-Heusler compounds.",1309.6657v1
2013-11-26,Large enhancement in the generation efficiency of pure spin currents in Ge using Heusler-compound Co_2FeSi electrodes,"We show nonlocal spin transport in n-Ge based lateral spin-valve devices with
highly ordered Co_2FeSi/n^+-Ge Schottky tunnel contacts. Clear spin-valve
signals and Hanle-effect curves are demonstrated at low temperatures,
indicating generation, manipulation, and detection of pure spin currents in
n-Ge. The obtained spin generation efficiency of ~ 0.12 is about two orders of
magnitude larger than that for a device with Fe/MgO tunnel-barrier contacts
reported previously. Taking the spin related behavior with temperature
evolution into account, we infer that it is necessary to simultaneously
demonstrate the high spin generation efficiency and improve the quality of the
transport channel for achieving Ge based spintronic devices.",1311.6601v1
2014-03-14,Investigation on Mn$_{3-δ}$Ga/MgO interface for magnetic tunneling junctions,"The Mn$_3$Ga Heusler compound and related alloys are the most promising
materials for the realization of spin-transfer-torque switching in magneto
tunneling junctions. Improved performance can be achieved by high quality
interfaces in these multilayered structured devices. In this context, the
interface between Mn$_{1.63}$Ga and MgO is of particular interest because of
its spin polarization properties in tunneling junctions. We performed a
chemical characterization of the MgO/Mn$_{1.63}$Ga junction by hard x-ray
photoelectron spectroscopy (HAXPES). The experiment indicated the formation of
Ga-O bonds at the interface and evidenced changes in the local environment of
Mn atoms in the proximity of the MgO film. In addition, we show that the
insertion of a metallic Mg-layer interfacing the MgO and Mn--Ga film strongly
suppresses the oxidation of gallium.",1403.3556v4
2014-10-02,Investigation of the temperature-dependence of ferromagnetic resonance and spin waves in Co2FeAl0.5Si0.5,"Co2FeAl0.5Si0.5 (CFAS) is a Heusler compound that is of interest for
spintronics applications, due to its high spin polarization and relatively low
Gilbert damping constant. In this study, the behavior of ferromagnetic
resonance as a function of temperature was investigated in CFAS, yielding a
decreasing trend of damping constant as the temperature was increased from 13
to 300 K. Furthermore, we studied spin waves in CFAS using both frequency
domain and time domain techniques, obtaining group velocities and attenuation
lengths as high as 26 km/s and 23.3 um, respectively, at room temperature.",1410.0439v1
2014-12-23,Pressure effects on the superconductivity of HfPd2Al Heusler compound: Experimental and theoretical study,"Polycrystalline HfPd2Al has been synthesized using the arc-melting method and
studied under ambient pressure conditions by x-ray diffraction from room
temperature up to 450^oC. High pressure x-ray diffraction up to 23 GPa was also
performed using Diacell-type membrane diamond anvil cells. The estimated linear
thermal expansion coefficient was found to be {\alpha} = 1.40(3)x10^{-5}
K^{-1}, and the bulk modulus derived from the fit to the 3rd order
Birch-Murnaghan EOS (BMEOS) is B0 = 97(2) GPa. Resistivity studies under
applied pressure (p < 7.49 GPa) showed a linear decrease of superconducting
critical temperature with increasing pressure and the slope dTc/dp = -0.13(1) K
GPa^{-1}. The same behavior is observed for the electron-phonon coupling
constant {\lambda_{ep}}(p) that changes from 0.67 to 0.6, estimated for p =
0.05 GPa and 7.49 GPa, respectively. First principles electronic structure and
phonon calculation results are presented and used to estimate the magnitude of
electron-phonon interaction {\lambda_{ep}} and its evolution with pressure.
Theoretical results explain the experimentally observed decrease in Tc due to
considerable lattice stiffening.",1412.7362v2
2015-03-12,"Shubnikov-de Haas oscillations, weak antilocalization effect and large linear magnetoresistance in the putative topological superconductor LuPdBi","We present electronic transport and magnetic properties of single crystals of
semimetallic half-Heusler phase LuPdBi, having theoretically predicted band
inversion requisite for nontrivial topological properties. The compound
exhibits superconductivity below a critical temperature $T_{\rm c}=1.8\,$K,
with a zero-temperature upper critical field $B_{\rm c2}\approx2.3\,$T.
Although superconducting state is clearly reflected in the electrical
resistivity and magnetic susceptibility data, no corresponding anomaly can be
seen in the specific heat. Temperature dependence of the electrical resistivity
suggests existence of two parallel conduction channels: metallic and
semiconducting, with the latter making negligible contribution at low
temperatures. The magnetoresistance is huge and clearly shows a weak
antilocalization effect in small magnetic fields. Above about 1.5 T, the
magnetoresistance becomes linear and does not saturate in fields up to 9 T. The
linear magnetoresistance is observed up to room temperature. Below 10 K, it is
accompanied by Shubnikov-de Haas oscillations. Their analysis reveals charge
carriers with effective mass of $0.06\,m_e$ and a Berry phase very close to
$\pi$, expected for Dirac-fermion surface states, thus corroborating
topological nature of the material.",1503.03697v1
2015-06-07,Experimental observation of the interaction of propagating spin waves with Néel domain walls in a Landau domain structure,"The interaction of propagating dipolar spin waves with magnetic domain walls
is investigated in square-shaped microstructures patterned from the Heusler
compound Co$_2$Mn$_{0.6}$Fe$_{0.4}$Si. Using magnetic force microscopy, the
reversible preparation of a Landau state with four magnetic domains separated
by N\'eel domain walls is confirmed. A local spin-wave excitation using a
microstructured antenna is realized in one of the domains. It is shown by
Brillouin light scattering microscopy (BLS) that the domain structure in the
remanence state has a strong influence on the spin-wave excitation and
propagation. The domain walls strongly reflect the spin waves and can be used
as spin-wave reflectors. A comparison with micromagnetic simulations shows that
the strong reflection is due to the long-range dipolar interaction which has
important implications for the use of these spin waves for exerting an
all-magnonic spin-transfer torque.",1506.02303v1
2015-12-18,Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi,"We observed the coexistence of superconductivity and antiferromagnetic order
in the single-crystalline ternary pnictide HoPdBi, a plausible topological
semimetal. The compound orders antiferromagnetically at $T_N =$1.9 K and
exhibits superconductivity below $T_c =$0.7 K, which was confirmed by magnetic,
electrical transport and specific heat measurements. The specific heat shows
anomalies corresponding to antiferromagnetic ordering transition and
crystalline field effect, but not to superconducting transition. Single-crystal
neutron diffraction indicates that the antiferromagnetic structure is
characterized by the (1/2, 1/2, 1/2) propagation vector. Temperature variation
of the electrical resistivity reveals two parallel conducting channels of
semiconducting and metallic character. In weak magnetic fields, the
magnetoresistance exhibits weak antilocalization effect, while in strong fields
and temperatures below 50 K it is large and negative. At temperatures below 7 K
Shubnikov-de Haas oscillations with two frequencies appear in the resistivity.
These oscillations have non-trivial Berry phase, which is a distinguished
feature of Dirac fermions.",1512.05972v1
2016-04-25,Room temperature tetragonal noncollinear antiferromagnet Pt$_2$MnGa,"Here we present the tetragonal stoichiometric Heusler compound Pt$_2$MnGa
with the noncollinear AFM order stable up to 350 K. It is resolved by the
neutron diffraction as a helical spiral propagating along the tetragonal axis.
Ab-initio calculations suggest a pure exchange origin of the spiral and explain
its helical character being stabilized by a large basal plane
magnetocrystalline anisotropy (MCA). Together with the inversion-symmetric
crystal structure, this provides a bi-stability of a spiral with respect to the
right- and left-handed magnetic helices. Despite the large MCA, the long period
of a helix might greatly facilitate the switch of the helicity by the
precessional reorientation, suggesting Pt$_2$MnGa as a potential candidate for
the vector-helicity based non-volatile magnetic memory.",1604.07137v1
2016-07-01,Generation of Spin Currents by Magnetic Field in $\mathcal{T}$- and $\mathcal{P}$-Broken Materials,"Pure spin currents carry information in quantum spintronics and could play an
essential role in the next generation low-energy-consumption electronics. Here
we theoretically predict that the magnetic field can induce a quantum spin
current without a concomitant charge current in metals without time reversal
symmetry $\mathcal{T}$ and inversion symmetry $\mathcal{P}$ but respect the
combined $\mathcal{PT}$ symmetry. It is governed by the magnetic moment of the
Bloch states on the Fermi surface, and can be regarded as a spinful
generalization of the gyrotropic magnetic effect in $\mathcal{P}$-broken
metals. The effect is explicitly studied for a minimal model of an
antiferromagnetic Dirac semimetal, where the experimental signature is
proposed. We further propose candidate materials, including topological
antiferromagnetic Dirac semimetals, Weyl semimetals, and tenary Heusler
compounds.",1607.00116v1
2016-10-21,Giant Positive Magnetoresistance and field-induced metal insulator transition in Cr2NiGa,"We report here the magneto-transport properties of the newly synthesized
Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure
belonging to Pm-3m space group. The sample is found to be paramagnetic down to
2 K with metallic character. On application of magnetic field, a significantly
large increase in resistivity is observed which corresponds to
magnetoresistance as high as 112% at 150 kOe of field at the lowest
temperature. Most remarkably, the sample shows negative temperature coefficient
of resistivity below about 50 K under the application of field gretare than or
equal to 80 kOe, signifying a field-induced metal to `insulating' transition.
The observed magnetoresistance follows Kohler's rule below 20 K indicating the
validity of the semiclassical model of electronic transport in metal with a
single relaxation time. A multi-band model for electronic transport, originally
proposed for semimetals, is found to be appropriate to describe the
magneto-transport behavior of the sample.",1610.06771v1
2016-11-08,Geometry of Adaptive Martensite in Ni-Mn-based Heusler alloys,"Modulated martensites play an important role in magnetic shape memory alloys,
because all functional properties are closely connected to the twin
microstructure and the phase boundary. The nature of the modulated martensites
is still unclear. One approach is the concept of adaptive martensite, which
regards all modulated phases as nanotwinned microstructures. In this article,
we use the Ni-Mn-based shape memory alloys as an example to show the geometric
rationale behind this concept using analytic equations based on the
phenomenological theory of martensite. This could enhance discussions about the
implications of the adaptive martensite by showing the exact relations between
the various unit cells used to describe the structure. We use the concept to
discuss the compatibility at the habit plane, the nature of high-order twin
boundaries and the dependence of the lattice constants on the different types
of modulation.",1611.02535v2
2017-01-06,Generic coexistence of Fermi arcs and Dirac cones on the surface of time-reversal invariant Weyl semimetals,"The hallmark of Weyl semimetals is the existence of open constant-energy
contours on their surface -- the so-called Fermi arcs -- connecting Weyl
points. Here, we show that for time-reversal symmetric realizations of Weyl
semimetals these Fermi arcs in many cases coexist with closed Fermi pockets
originating from surface Dirac cones pinned to time-reversal invariant momenta.
The existence of Fermi pockets is required for certain Fermi-arc connectivities
due to additional restrictions imposed by the six $\mathbb{Z}_2$ topological
invariants characterizing a generic time-reversal invariant Weyl semimetal. We
show that a change of the Fermi-arc connectivity generally leads to a different
topology of the surface Fermi surface, and identify the half-Heusler compound
LaPtBi under in-plane compressive strain as a material that realizes this
surface Lifshitz transition. We also discuss universal features of this
coexistence in quasi-particle interference spectra.",1701.01660v3
2017-03-15,Two-channel conduction in YbPtBi,"We investigated transport, magnetotransport, and broadband optical properties
of the half-Heusler compound YbPtBi. Hall measurements evidence two types of
charge carriers: highly mobile electrons with a temperature-dependent
concentration and low-mobile holes; their concentration stays almost constant
within the investigated temperature range from 2.5 to 300 K. The optical
spectra (10 meV - 2.7 eV) can be naturally decomposed into contributions from
intra- and interband absorption processes, the former manifesting themselves as
two Drude bands with very different scattering rates, corresponding to the
charges with different mobilities. These results of the optical measurements
allow us to separate the contributions from electrons and holes to the total
conductivity and to implement a two-channel-conduction model for description of
the magnetotransport data. In this approach, the electron and hole mobilities
are found to be around 50000 and 10 cm$^{2}$/Vs at the lowest temperatures (2.5
K), respectively.",1703.05202v1
2017-07-23,Majorana surface modes of nodal topological pairings in spin-$\frac{3}{2}$ semi-metals,"Multi-component electronic systems can appear in solid state systems with
active orbital band structures. They exhibit richer structures of topological
superconductivity beyond the conventional scenarios of spin singlet and triplet
pairings in spin-$\frac{1}{2}$ systems. Examples include the half-Heusler
compounds RPtBi series (R for a rare earth element), whose electronic
structures are described by the effective Luttinger-Kohn model with
spin-$\frac{3}{2}$ fermions exhibiting strong spin-orbit coupling and band
conversion. Recent experiments provide evidence to unconventional
superconductivity in the YPtBi material with nodal spin-septet pairing. We
systematically study topological pairing structures in spin-$\frac{3}{2}$
systems with cubic group symmetries and calculate surface Majorana spectra,
which exhibit both the zero energy flat band and the cubic dispersion. The
signatures of these surface states in the quasi-particle interference patterns
are studied, which can be tested in future tunneling experiments.",1707.07261v3
2017-09-19,Effect of Co substitution on Ni$_{2}$MnGe Heusler alloy: ab initio study,"Ab initio calculations shown that the Co substitution instead of Ni in
Ni$_{2}$MnGe with the L2$_{1}$ crystallographic structure leads to a decrease
of the lattice constant and an increase of the total magnetic moment of the
Ni$_{2-x}$Co$_{x}$MnGe compounds. The Mn(B) has the largest local moment above
$3~\mu_{B}$ coupled parallel to moments on the Ni(A,C) and Co(A,C), which are
found in the ranges of $0.19\div0.26~\mu_{B}$ for Ni(A,C) and
$1.03\div0.97~\mu_{B}$ for Co(A,C) for studied range of $x$. Using the results
stemming from the total energy calculations, the values of bulk modulus and its
pressure derivatives are estimated according to the Murnaghan EOS.",1709.06490v1
2017-11-11,Planar Hall effect in the Weyl semimetal GdPtBi,"Observation of Weyl and Dirac Fermions in condensed matter systems is one of
the most important discoveries. Among the very few available tools to
characterize Weyl semimetals through electrical transport, negative
magnetoresistance is most commonly used. Considering shortcomings of this
method, new tools to characterize chiral anomaly in Weyl semimetals are
desirable. We employ planar Hall effect as an effective technique in half
Heusler Weyl semimetal GdPtBi to study chiral anomaly. This compound exhibits a
large value of 1.5 mohm cm planar Hall resistivity at 2 K and in 9 T. Our
analysis reveals that the observed amplitude is dominated by Berry curvature
and chiral anomaly contributions. Through the angle dependent transport studies
we establish that GdPtBi with relatively small orbital magnetoresistance is an
ideal candidate to observe large planar Hall effect .",1711.04133v2
2017-12-30,Singlet-Quintet Mixing in Spin-Orbit Coupled Superconductors with j=3/2 Fermions,"In non-centrosymmetric superconductors, spin-orbit coupling can induce an
unconventional superconducting state with a mixture of s-wave spin-singlet and
p-wave spin-triplet channels, which leads to a variety of exotic phenomena,
including anisotropic upper critical field, magnetoelectric effect, topological
superconductivity, et al. It is commonly thought that inversion symmetry
breaking is substantial for pairing-mixed superconducting states. In this work,
we theoretically propose that a new type of pairing-mixed state, namely the
mixture of s-wave spin-singlet and d-wave spin-quintet channels, can be induced
by spin-orbit coupling even in the presence of inversion symmetry when
electrons effectively carry ""spin-3/2"" in superconductors. As a physical
consequence of the singlet-quintet pairing mixing, topological nodal-line
superconductivity is found in such system and gives rise to flat surface
Majorana bands. Our work provides a possible explanation of unconventional
superconducting behaviors observed in superconducting half-Heusler compounds.",1801.00083v2
2018-01-17,Multiple Triple-Point Fermions in Heusler Compounds,"Using the density functional theoretical calculations, we report a new set of
topological semimetals X$_{2}$YZ (X = \{Cu, Rh, Pd, Ag, Au, Hg\}, Y = \{Li, Na,
Sc, Zn, Y, Zr, Hf, La, Pr, Pm, Sm, Tb, Dy, Ho, Tm\} and Z =\{Mg, Al, Zn, Ga, Y,
Ag, Cd, In, Sn, Ta, Sm\}), which show the existence of multiple topological
triple point fermions along four independent $C_{3}$ axes. These fermionic
quasiparticles have no analogues elementary particle in the standard model. The
angle-resolved photoemission spectroscopy is simulated to obtain the exotic
topological surface states and the characteristic Fermi arcs. The inclusion of
spin-orbit coupling splits the triple-point into two Dirac points. The
triple-point fermions are exhibited on the easily cleavable (111) surface and
are well separated from the surface $\bar{\Gamma}$ point, allowing them to be
resolved in the surface spectroscopic techniques. This intermediate linearly
dispersive degeneracy between Weyl and Dirac points may offer prospective
candidates for quantum transport applications.",1801.05699v1
2018-03-02,Linear-in-frequency optical conductivity in GdPtBi due to transitions near the triple points,"The complex optical conductivity of the half-Heusler compound GdPtBi is
measured in a frequency range from 20 to 22 000 cm$^{-1}$ (2.5 meV - 2.73 eV)
at temperatures down to 10 K in zero magnetic field. We find the real part of
the conductivity, $\sigma_{1}(\omega)$, to be almost perfectly linear in
frequency over a broad range from 50 to 800 cm$^{-1}$ ($\sim$ 6 - 100 meV) for
$T \leq 50$ K. This linearity strongly suggests the presence of
three-dimensional linear electronic bands with band crossings (nodes) near the
chemical potential. Band-structure calculations show the presence of triple
points, where one doubly degenerate and one nondegenerate band cross each other
in close vicinity of the chemical potential. From a comparison of our data with
the optical conductivity computed from the band structure, we conclude that the
observed nearly linear $\sigma_{1}(\omega)$ originates as a cumulative effect
from all the transitions near the triple points.",1803.00840v2
2018-03-09,Strong anomalous Nernst effect in collinear magnetic Weyl semimetals without net magnetic moments,"We predict a large anomalous Nernst effect in the inverse Heusler compensated
ferrimagnets Ti$_2$Mn$X$ ($X$=Al,Ga,In) with vanishing net magnetic moments.
Though the net magnetic moment is zero, the Weyl points in these systems lead
to a large anomalous Nernst conductivity (ANC) due to the lack of a magnetic
sublattice that inverses the sign of the Berry curvature. In comparison to the
noncollinear antiferromagnets Mn$_3$Sn and Mn$_3$Ge, the high ANC stems almost
entirely from the Weyl points in this class of compounds, and thus, it is
topologically protected. This work shows for the first time a large ANC with
zero net magnetic moments in collinear systems, which is helpful for
comprehensive understanding of the thermoelectric effect in zero-moment
magnetic materials and its further applications.",1803.03439v3
2018-06-03,"Chiral Magnetic Skyrmions with Arbitrary Topological Charge (""skyrmionic sacks"")","We show that continuous and spin-lattice models of chiral ferro- and
antiferromagnets provide the existence of an infinite number of stable soliton
solutions of any integer topological charge. A detailed description of the
morphology of new skyrmions and the corresponding energy dependencies are
provided. The considered model is general, and is expected to predict a
plethora of particle-like states which may occur in various chiral magnets
including atomic layers, e.g., PdFe/Ir(111), rhombohedral GaV$_4$S$_8$
semiconductor, B20-type alloys as Mn$_{1-x}$Fe$_x$Ge, Mn$_{1-x}$Fe$_x$Si,
Fe$_{1-x}$Co$_x$Si, Cu$_2$OSeO$_3$, acentric tetragonal Heusler compounds.",1806.00782v2
2019-04-04,First-principles investigations of orthorhombic-cubic phase transition and its effect on thermoelectric properties in cobalt-based ternary alloys,"We screened six cobalt-based 18-VEC systems CoVSi, CoNbSi, CoTaSi (Si-group)
and CoVGe, CoNbGe, CoTaGe (Ge-group) by the first-principles approach, with the
motivation of stabilizing these orthorhombic phases into the cubic symmetry --
favorable for thermoelectrics. Remarkably, it was found that the Ge-group is
energetically more favorable in the cubic symmetry than the hitherto
orthorhombic phase. We account the cubic ground state of the Si-group to the
interplay of internal pressure and covalent interactions. The principle of
covalent interactions will provide an insight and could be vital in speeding
the search of missing cubic half-Heusler alloys. Meanwhile, the calculated
transport properties of all the systems on \textit{p}-type doping, except
CoVSi, are more promising than the well-known CoTiSb. We also provide
conservative estimates of the figure of merit, exceeding the CoTiSb. Based on
our findings, we suggest possible new phases of ternary compounds for
thermoelectric applications.",1904.02485v1
2019-07-29,Strain engineered higher order topological phases for spin-3/2 Luttinger fermions,"Recently, the notion of topological phases of matter has been extended to
higher-order incarnations, supporting gapless modes on even lower dimensional
boundaries, such as corners and hinges. We here identify a collection of cubic
spin-3/2 fermions with biquadratic touching of Kramers degenerate valence and
conduction bands as a platform to strain-engineer higher-order topological
(HOT) phases: external uniaxial strain gives birth to a HOT Dirac semimetal or
an insulator, depending on its sign, featuring topological \emph{hinge} modes
in the strain direction. The insulator in fact exhibits \emph{mixed} topology,
and in addition supports edge modes on orthogonal planes. These outcomes are
germane when the external strain is applied along one of the $C_{4v}$ or
coordinate axes, as well as $C_{3v}$ or body-diagonal, directions. Our findings
place HgTe, gray-Sn, 227 pyrochlore iridates and half-Heusler compounds at the
frontier of strain-engineered electronic HOT phases.",1907.12568v2
2012-09-19,Revealing the spin and symmetry properties of the buried Co2MnSi/MgO interface by low energy spin-resolved photoemission,"We present a novel approach to study the spin and symmetry electronic
properties of buried interfaces using low-energy spin-resolved photoemission
spectroscopy. We show that this method is sensitive to interfaces buried below
more than 20ML (~4nm) MgO, providing a powerful tool for the non-destructive
characterization of spintronics interfaces. As a demonstration, we apply this
technique to characterize the Co2MnSi/MgO interface, a fundamental building
block of state-of-the-art magnetic tunnel junctions based on Heusler compounds.
We find that a surface state with {\Delta}1 symmetry and minority spin
character dominating the electronic structure of the bare Co2MnSi(100) surface
is quenched at the Co2MnSi(100)/MgO interface. As a result, the interface
spin-dependent electronic structure resembles the theoretically expected
Co2MnSi bulk band structure, with majority spin electronic states of both
{\Delta}1 and {\Delta}5 symmetry. Furthermore we find an additional
thermally-induced contribution in the minority channel, mirroring the
{\Delta}1/{\Delta}5 asymmetry of the majority channel.",1209.4368v1
2012-09-25,"A p-type Heusler compound: Growth, structure, and properties of epitaxial thin NiYBi films on MgO(100)","Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100)
substrates by magnetron sputtering. The intensity ratio of the (200) and (400)
diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value
(3.03). The electronic structure of NiYBi was calculated using WIEN2k and a
narrow indirect band gap of width 210 meV was found. The valence band spectra
of the films obtained by linear dichroism in hard X-ray photoelectron
spectroscopy exhibit clear structures that are in good agreement with the
calculated band structure of NiYBi.",1209.5707v1
2012-09-25,Electronic and crystalline structures of zero band-gap PdLuBi thin films grown epitaxially on MgO(100),"Thin films of the proposed topological insulator PdLuBi - a Heusler compound
with the C1b structure - were prepared on Ta-Mo-buffered MgO(100) substrates by
co-sputtering from PdBi2 and Lu targets. Epitaxial growth of high-quality
PdLuBi films was confirmed by X-ray spectrometry and reflection high-energy
electron diffraction. The root-mean-square roughness of the films was as low as
1.45 nm, although the films were deposited at high temperature. The film
composition is close to the ideal stoichiometric ratio. The valence band
spectra of the PdLuBi films, observed by hard X-ray photoelectron spectroscopy,
correspond perfectly to the ab-initio-calculated density of states.",1209.5710v1
2018-02-20,Thermoelectricity in correlated narrow-gap semiconductors,"We review many-body effects, their microscopic origin, as well as their
impact onto thermoelectricity in correlated narrow-gap semiconductors. Members
of this class---such as FeSi and FeSb$_2$---display an unusual temperature
dependence in various observables: insulating with large thermopowers at low
temperatures, they turn bad metals at temperatures much smaller than the size
of their gaps. This insulator-to-metal crossover is accompanied by spectral
weight-transfers over large energies in the optical conductivity and by a
gradual transition from activated to Curie-Weiss-like behaviour in the magnetic
susceptibility. We show a retrospective of the understanding of these
phenomena, discuss the relation to heavy-fermion Kondo insulators---such as
Ce$_3$Bi$_4$Pt$_3$ for which we present new results---and propose a general
classification of paramagnetic insulators. From the latter FeSi emerges as an
orbital-selective Kondo insulator. Focussing on intermetallics such as
silicides, antimonides, skutterudites, and Heusler compounds we showcase
successes and challenges for the realistic simulation of transport properties
in the presence of electronic correlations. Further, we advert to new avenues
in which electronic correlations may contribute to the improvement of
thermoelectric performance.",1802.07220v1
2018-08-06,Formation of Spatial Patterns by Spin-selective Excitations of Interacting Fermions,"We describe the formation of charge- and spin-density patterns induced by
spin-selective photoexcitations of interacting fermionic systems in the
presence of a microstructure. As an example, we consider a one-dimensional
Hubbard-like system with a periodic magnetic microstructure, which has a
uniform charge distribution in its ground state, and in which a long-lived
charge-density pattern is induced by the spin-selective photoexcitation. Using
tensor-network methods, we study the full quantum dynamics in the presence of
electron-electron interactions and identify doublons as the main decay channel
for the induced charge pattern. Our setup is compared to the OISTR mechanism,
in which ultrafast optically induced spin transfer in Heusler and magnetic
compounds is associated to the difference of the local density of states of the
different elements in the alloys. We find that applying a spin-selective
excitation there induces spatially periodic patterns in local observables.
Implications for pump-probe experiments on correlated materials and experiments
with ultracold gases on optical lattices are discussed.",1808.02138v3
2018-12-29,Magnetization flip in Fe-Cr-Ga system,"A systematic investigation about the structure and magnetism of Fe75-xCr25Gax
(11<x<33) and Fe50Cr50-yGay (0<y<33) series has been carried out in this work.
It shows that the parent Fe50Cr25Ga25 phase has higher tolerance for Ga
replacing Cr than replacing Fe atoms. An abrupt flip of Curie temperature and
magnetization in the Fe50Cr50-yGay (0<y<33) series was observed at the
composition of Fe50Cr25Ga25. We proposed an explanation concerning anti-sites
occupation and magnetic structure transition in this series. The induced
structure is proved energetically favorable from first-principles calculations.
This work can help us to understand the dependences between the crystal
structure and magnetism in Fe-based Heusler compounds, and provides a method to
deduce the atomic configurations based on the evolution of magnetism.",1812.11304v1
2020-04-01,Importance of site occupancy and absence of strain glassy phase in Ni$_{2-x}$Fe$_{x}$Mn$_{1.5}$In$_{0.5}$,"Martensitic transition temperature steadily decreases in
Ni$_{2-x}$Fe$_{x}$Mn$_{1.5}$In$_{0.5}$ and is completely suppressed at $x$ =
0.2. Despite suppression of martensitic transition,
Ni$_{1.8}$Fe$_{0.2}$Mn$_{1.5}$In$_{0.5}$ does not display the expected strain
glassy phase. Instead, a ground state with dominant ferromagnetic interactions
is observed. A study of structural and magnetic properties of $x$ = 0.2 reveal
that the alloy consists of a major Fe rich cubic phase and a minor Fe deficient
monoclinic phase favoring a ferromagnetic ground state. This is exactly
opposite of that observed in Ni$_2$Mn$_{1-y}$Fe$_{y}$In$_{0.5}$ wherein a
strain glassy phase is observed for $y$ = 0.1. The change in site symmetry of
Fe when doped for Ni in contrast to Mn in the Heusler composition seems to
support the growth of the ferromagnetic phase.",2004.00256v1
2020-05-07,Exchange-correlation corrections for electronic properties of half-metallic Co$_2$FeSi and nonmagnetic semiconductor CoFeTiAl,"We consider two cobalt-based full-Heusler compounds CoFeTiAl and Co$_2$FeSi,
for which Coulomb correlation effects play an important role. Since the
standard GGA scheme does not provide a precise description of the electronic
properties near the Fermi level, we use a meta-GGA functional capable to
improve the description of the electronic properties of CoFeTiAl and
Co$_2$FeSi. In particular, we find a better agreement with the experiment for
the magnetic moment and the energy-band gap. Moreover, our calculations show
that pressure enhances the insulating properties of Co$_2$FeSi and CoTiFeAl.",2005.03383v1
2020-05-29,Superconducting and Antiferromagnetic Properties of Dual-Phase V$_3$Ga,"The binary compound V$_3$Ga can exhibit two near-equilibrium phases,
consisting of the A15 structure that is superconducting, and the Heusler D0$_3$
structure that is semiconducting and antiferromagnetic. Density functional
theory calculations show that the two phases are closely degenerate, being
separated by only ~10 meV/atom. Magnetization measurements on bulk-grown
samples show superconducting behavior below 14 K. These results indicate the
possibility of using V$_3$Ga for quantum technology devices utilizing both
superconductivity and antiferromagnetism at the same temperature.",2005.14348v1
2018-04-09,Canted antiferromagnetism in phase-pure CuMnSb,"We report the low-temperature properties of phase-pure single crystals of the
half-Heusler compound CuMnSb grown by means of optical float-zoning. The
magnetization, specific heat, electrical resistivity, and Hall effect of our
single crystals exhibit an antiferromagnetic transition at $T_{\mathrm{N}} =
55~\mathrm{K}$ and a second anomaly at a temperature $T^{*} \approx
34~\mathrm{K}$. Powder and single-crystal neutron diffraction establish an
ordered magnetic moment of $(3.9\pm0.1)~\mu_{\mathrm{B}}/\mathrm{f.u.}$,
consistent with the effective moment inferred from the Curie-Weiss dependence
of the susceptibility. Below $T_{\mathrm{N}}$, the Mn sublattice displays
commensurate type-II antiferromagnetic order with propagation vectors and
magnetic moments along $\langle111\rangle$ (magnetic space group $R[I]3c$).
Surprisingly, below $T^{*}$, the moments tilt away from $\langle111\rangle$ by
a finite angle $\delta \approx 11^{\circ}$, forming a canted antiferromagnetic
structure without uniform magnetization consistent with magnetic space group
$C[B]c$. Our results establish that type-II antiferromagnetism is not the
zero-temperature magnetic ground state of CuMnSb as may be expected of the
face-centered cubic Mn sublattice.",1804.03223v1
2018-04-25,High $n$-type thermoelectric power factor and efficiency in Ba$_{2}$BiAu from a highly dispersive band,"Using first-principles density-functional theory calculations, we predict the
potential for unprecedented thermoelectric efficiency $zT=5$ at 800 K in
$n$-type Ba$_{2}$BiAu full-Heusler compound. Such a high efficiency arises from
an intrinsically ultralow lattice thermal conductivity coupled with a very high
power factor reaching 7 mW m$^{-1}$ K$^{-2}$ at 500 K. The high power factor
originates from a light, sixfold degenerate conduction band pocket along the
$\Gamma$-X direction. Weak acoustic phonon scattering and sixfold multiplicity
combine to yield high mobility and high Seebeck coefficient. In contrast, the
flat-and-dispersive (a.k.a. low-dimensional) valence band of Ba$_{2}$BiAu fail
to generate a high power factor due to strong acoustic phonon scattering. The
Lorenz numbers at optimal doping are smaller than the Wiedemann-Franz value, an
integral feature for $zT$ enhancement as electrons are the majority heat
carriers.",1804.09392v2
2019-12-08,Investigation of Thermoelectric properties of Magnetic Insulator FeRuTiSi Using First Principle Calculation,"In this work, we have investigated the electronic structure and
thermoelectric properties of quaternary heusler alloy, FeRuTiSi, using first
principle DFT tools implemented in WIEN2k and BoltzTraP code. Electronic
structure calculations using TB-mBJ potential shows appearance of flat band at
the conduction band edge, thus electron in conduction band have the large
effective mass (me*), and therefore mainly contribute for negatively large
value of Seebeck coefficient (S). This alloy has indirect band gap of 0.59 eV,
and shows the n-type transport behavior. Under the constant relaxation time
approximation (tau = 10 -14 s), temperature dependent Seebeck coefficient,
electrical conductivity (sigma), and electronic thermal conductivity (ke) were
also estimated. The maximum figure-of-merit (ZT), for the FeRuTiSi compound is
found to be ~0.86 at 840 K, with n-type doping, which suggests that this
quaternary alloy can be a good candidate among the n-type material for
thermoelectric applications in high-temperature reg",1912.03708v1
2019-12-11,Chirality-induced linear response properties in non-coplanar Mn$_3$Ge,"Taking the non-collinear antiferromagnetic hexagonal Heusler compound
Mn$_3$Ge as a reference system, the contributions to linear response phenomena
arising solely from the chiral coplanar and non-coplanar spin configurations
are investigated. Orbital moments, X-ray absorption, anomalous and spin Hall
effects, as well as corresponding spin-orbit torques and Edelstein
polarizations are studied depending on a continuous variation of the polar
angle relative to the Kagome planes of corner-sharing triangles between the
non-collinear antiferromagnetic and the ferromagnetic limits. By scaling the
speed of light from the relativistic Dirac case to the non-relativistic limit
the chirality-induced or topological contributions can be identified by
suppressing the spin-orbit coupling.",1912.05211v1
2020-03-04,"Theoretical study of phase stability, electronic and magnetic properties of Rh$_2$CrGe$_{1-x}$Al$_x$ ($x = 0$, $0.25$, $0.50$, $0.75$ and $1$) Heusler alloys by FP-LAPW method","First-principle calculations were performed within the framework of the
density functional theory (DFT) using FP-LAPW method as implemented in WIEN2k
code to determine the structural stability, electronic and magnetic properties
of Rh$_2$CrGe$_{1-x}$Al$_x $($x = 0$, $0.25$, $0.50$, $0.75$ and $1$). The
results showed that for Rh$_2$CrAl and Rh$_2$CrGe, the Cu$_2$MnAl-type
structure is energetically more stable than Hg$_2$CuTi-type structure at the
equilibrium volume. The calculated densities of states for Rh$_2$CrAl and
Rh$_2$CrGe show half-metallic and nearly half-metallic behavior, respectively.
Rh$_2$CrGe$_{1-x}$Al$_x$ ($x = 0.25$, $0.50$, $0.75$) these alloys show a
half-metallic character, and these compounds are predicted to be good
candidates for spintronic applications.",2003.02067v1
2020-03-25,Crystal and magnetic structure of antiferromagnetic Mn$_{2}$PtPd,"We have investigated the crystal and magnetic structure of Mn${}_{2}$PtPd
alloy using powder x-ray and neutron diffraction experiments. This compound is
believed to belong to the Heusler family having crystal symmetry
$\mathit{I}$4/$\mathit{mmm}$ (TiAl${}_{3}$-type). However, in this work we
found that the Pd and Pt atoms are disordered and thus Mn${}_{2}$PtPd
crystallizes in the $\mathit{L}$1${}_{0}$ structure having
$\mathit{P}$4/$\mathit{mmm}$ symmetry (CuAu-I type) like MnPt and MnPd binary
alloys. The lattice constants are $\mathit{a}$ = 2.86 \r{A} and $\mathit{c}$ =
3.62 \r{A} at room temperature. Mn${}_{2}$PtPd has a collinear
antiferromagnetic spin structure below the N\'{e}el temperature
$\mathit{T}$${}_{N}$ = 866 K, where Mn moments of $\mathrm{\sim}$4
$\mu$${}_{B}$ lie in the $\mathit{ab}$-plane. We observed a strong change in
the lattice parameters near $\mathit{T}$${}_{N}$. The sample exhibits metallic
behaviour, where electrical resistivity and carrier concentration are of the
order of 10${}^{-5}$ $\Omega$ cm and 10${}^{21}$ cm${}^{-3}$, respectively.",2003.11569v1
2020-12-01,Nanocontact vortex oscillators based on Co$_2$MnGe pseudo-spin valves,"We present an experimental study of vortex dynamics in magnetic nanocontacts
based on pseudo spin valves comprising the Co$_2$MnGe Heusler compound. The
films were grown by molecular beam epitaxy, where precise stoichiometry control
and tailored stacking order allowed us to define the bottom ferromagnetic layer
as the reference layer, with minimal coupling between the free and reference
layers. 20-nm diameter nanocontacts were fabricated using a nano-indentation
technique, leading to self-sustained gyration of the vortex generated by
spin-transfer torques above a certain current threshold. By combining
frequency- and time-domain measurements, we show that different types of
spin-transfer induced dynamics related to different modes associated to the
magnetic vortex configuration can be observed, such as mode hopping, mode
coexistence and mode extinction appear in addition to the usual gyration mode.",2012.00522v3
2022-05-17,Cubic magneto-optic Kerr effect in Ni(111) thin films with and without twinning,"In most studies utilizing the magneto-optic Kerr effect (MOKE), the detected
change of polarized light upon reflection from a magnetized sample is supposed
to be proportional to the magnetization $\boldsymbol{M}$. However, MOKE
signatures quadratic in $\boldsymbol{M}$ have also been identified and
utilized, e.g., to sense the structural order in Heusler compounds, to detect
spin-orbit torques or to image antiferromagnetic domains. In our study, we
observe a strong anisotropic MOKE contribution of third order in
$\boldsymbol{M}$ in Ni(111) thin films, attributed to a cubic magneto-optic
tensor $\propto $ $\boldsymbol{M}^3$. We further show that the angular
dependence of cubic MOKE (CMOKE) is affected by the amount of structural domain
twinning in the sample. Our detailed study on CMOKE for two selected photon
energies will open up new opportunities for CMOKE applications with sensitivity
to twinning properties of thin films, e.g. CMOKE spectroscopy and microscopy or
time-resolved CMOKE.",2205.08298v2
2022-10-10,Numerical stability and efficiency of response property calculations in density functional theory,"Response calculations in density functional theory aim at computing the
change in ground-state density induced by an external perturbation. At finite
temperature these are usually performed by computing variations of orbitals,
which involve the iterative solution of potentially badly-conditioned linear
systems, the Sternheimer equations. Since many sets of variations of orbitals
yield the same variation of density matrix this involves a choice of gauge.
Taking a numerical analysis point of view we present the various gauge choices
proposed in the literature in a common framework and study their stability.
Beyond existing methods we propose a new approach, based on a Schur complement
using extra orbitals from the self-consistent-field calculations, to improve
the stability and efficiency of the iterative solution of Sternheimer
equations. We show the success of this strategy on nontrivial examples of
practical interest, such as Heusler transition metal alloy compounds, where
savings of around 40% in the number of required cost-determining Hamiltonian
applications have been achieved.",2210.04512v2
2023-01-24,Ru$_{2-x}$Mn$_{1+x}$Al thin films,"The cubic Heusler alloy Ru$_{2-x}$Mn$_{1+x}$Al is grown in thin film form on
MgO and MgAl$_2$O$_4$ substrates. It is a highly spin-polarised ferrimagnetic
metal, with weak magnetocrystalline anisotropy. Although structurally and
chemically similar to $\text{Mn}_2\text{Ru}_x\text{Ga}$, it does not exhibit
ferrimagnetic compensation, or large magneto galvanic effects. The differences
are attributed to a combination of atomic order and the hybridisation with the
group 13 element Al or Ga. The spin polarisation is around 50 to 60 %. There is
a gap in the density of states just above the Fermi level in fully ordered
compounds.",2301.10148v2
2023-02-14,Perspective: strain and strain gradient engineering in membranes of quantum materials,"Strain is powerful for discovery and manipulation of new phases of matter;
however, the elastic strains accessible to epitaxial films and bulk crystals
are typically limited to small ($<2\%$), uniform, and often discrete values.
This Perspective highlights new directions for strain and strain gradient
engineering in free-standing single crystalline membranes of quantum materials.
Membranes enable large ($\sim 10\%$), continuously tunable strains and strain
gradients via bending and rippling. Moreover, strain gradients break inversion
symmetry to activate polar distortions, ferroelectricity, chiral spin textures,
novel superconductivity, and topological states. Recent advances in membrane
synthesis by remote epitaxy and sacrificial etch layers enable extreme strains
in new materials, including transition metal oxides and Heusler compounds,
compared to natively van der Waals (vdW) materials like graphene. We highlight
new opportunities and challenges for strain and strain gradient engineering in
membranes of non-vdW materials.",2302.07390v1
2023-05-15,Magnetic order and electronic transport properties in the Mn$_3$Al compound: the role of the structural state,"Electronic transport and magnetic properties of bulk and rapid melt quenched
samples of the Mn$_3$Al Heusler alloy were studied. A correlation between the
magnetic and structural states was established. For a cast sample, there is no
ferromagnetic moment, and the behavior of the magnetic susceptibility (break at
low temperatures and the Curie-Weiss law with high values of the paramagnetic
Curie temperature) indicates a frustrated antiferromagnetic state. At the same
time, for a rapid melt quenched sample, a ferrimagnetic state is observed with
a moment close to compensation. The results of measurements of the electrical
resistivity and the Hall effect evidence as well in favor of the implementation
of these magnetic states.",2305.08646v1
2024-02-28,Symmetry-breaking normal state response and surface superconductivity in topological semimetal YPtBi,"Most of the half-Heusler RPtBi compounds (R=rare earth) host various surface
states due to spin-orbit coupling driven topological band structure. While
recent ARPES measurements ubiquitously reported the existence of surface states
in RPtBi, their evidence by other experimental techniques remains elusive. Here
we report the angle-dependent magnetic field response of electrical transport
properties of YPtBi in both the normal and superconducting states. The angle
dependence of both magnetoresistance and the superconducting upper critical
field breaks the rotational symmetry of the cubic crystal structure, and the
angle between the applied magnetic field and the measurement plane of a
plate-like sample prevails. Furthermore, the measured upper critical field is
notably higher than the bulk response for an in-plane magnetic field
configuration, suggesting the presence of quasi-2D superconductivity. Our work
suggests the transport properties cannot be explained solely by the bulk
carrier response, requiring robust normal and superconducting surface states to
flourish in YPtBi.",2402.18735v1
2011-10-10,"Ab-initio calculation of effective exchange interactions, spin waves, and Curie temperature in L2_1- and L1_2-type local moment ferromagnets","Employing first-principles electronic structure calculations in conjunction
with the frozen-magnon method we study the effective exchange interactions and
spin waves in local moment ferromagnets. As prototypes we have chosen three
L2$_1$-type full Heusler alloys Cu$_2$MnAl, Ni$_2$MnSn and Pd$_2$MnSn, and the
L1$_2$-type XPt$_3$ compounds with X= V, Cr and Mn. We have also included
CoPt$_3$ which is a usual ferromagnet. In all compounds due to the large
spatial separation ($\sim 4$ \AA) of the magnetic transition metal atoms, the
3\textit{d} states belonging to different atoms overlap weakly and as a
consequence the exchange coupling is indirect, mediated by the \textit{sp}
electrons. Calculated effective exchange parameters are long range and show
RKKY-type oscillations. The spin-wave dispersion curves are in reasonable
agreement with available experimental data. Using the calculated exchange
parameters we have estimated the Curie temperatures within both the mean-field
and the random-phase approximations. In local moment ferromagents deviations of
the estimated Curie temperature with respect to the available experimental data
occur when the ground-state electronic structure calculations overestimate the
values of the spin magnetic moments as in VPt$_3$.",1110.2156v1
2014-05-19,Low-Dimensional Transport and Large Thermoelectric Power Factors in Bulk Semiconductors by Band Engineering of Highly Directional Electronic States,"Thermoelectrics are promising to address energy issues but their exploitation
is still hampered by low efficiencies. So far, much improvement has been
achieved by reducing the thermal conductivity but less by maximizing the power
factor. The latter imposes apparently conflicting requirements on the band
structure: a narrow energy distribution and a low effective mass. Quantum
confinement in nanostructures or the introduction of resonant states were
suggested as possible solutions to this paradox but with limited success. Here,
we propose an original approach to fulfill both requirements in bulk
semiconductors. It exploits the highly-directional character of some orbitals
to engineer the band-structure and produce a type of low-dimensional transport
similar to that targeted in nanostructures, while retaining isotropic
properties. Using first-principles calculations, the theoretical concept is
demonstrated in Fe$_2$YZ Heusler compounds, yielding power factors 4-5 times
larger than in classical thermoelectrics at room temperature. Our findings are
totally generic and rationalize the search of alternative compounds with a
similar behavior. Beyond thermoelectricity, these might be relevant also in the
context of electronic, superconducting or photovoltaic applications.",1405.4685v3
2015-06-29,Giant magnetocaloric effect from reverse martensitic transformation in Ni-Mn-Ga-Cu ferromagnetic shape memory alloys,"In an effort to produce Giant Magnetocaloric effect (GMCE) near room
temperature, in a first ever such study, the austenite transformation
temperature (As) was fine tuned to ferromagnetic Curie temperature (TC) in
Ferromagnetic Shape Memory Alloys (FSMA) and a large GMCE of delta-SM = - 81.75
J/Kg-K was achieved in Ni50Mn18.5Cu6.5Ga25 alloy during reverse martensitic
transformation (heating cycle) for a magnetic field change of 9 T at 302.5 K.
Fine tuning of As with TC was achieved by Cu substitution in Ni50Mn25-xCuxGa25
(0< x < 7.0)-based FSMAs. Characterizations of these alloys were carried out
using Optical and Scanning Electron Microscopy, X-ray Diffraction (XRD),
Differential Scanning Calorimetry (DSC) and DC magnetization measurements.
Addition of Cu to stoichiometric Heusler type Ni2MnGa increases the martensitic
transformation temperatures and decreases TC. Concurrently, DSM increases with
Cu addition and peaks at 6.5 at. % Cu for which there is a virtual overlap
between TC and As. Maximum Refrigerant Capacity (RCP) of 327.01 J/Kg was also
achieved in the heating cycle for 9 T field change at 302.5 K. Corresponding
values for the cooling cycle measurements (measured during forward
transformation) were 30.4 J/Kg-K and 123.52 J/Kg respectively for the same 6.5
at. % Cu sample and same thermo-magnetic conditions.",1506.08709v2
2018-05-16,Thermoelectric Alchemy: Designing A Chemical Analog to PbTe with Intrinsic High Band Degeneracy and Low Lattice Thermal Conductivity,"Improving the figure of merit $zT$ of thermoelectric materials requires
simultaneously a high power factor and low thermal conductivity. An effective
approach for increasing the power factor is to align the band extremum and
achieve high band degeneracy ($\geq$ 12) near the Fermi level as realized in
PbTe [\textcolor{blue}{Pei et. al. \textit{Nature} 473, 66 (2010)}], which
usually relies on band structure engineering, e.g., chemical doping and strain.
However, very few materials could achieve such a high band degeneracy without
heavy doping or suffering impractical strain. By employing state-of-the-art
first-principles methods with direct computation of phonon and carrier
lifetime, we demonstrate that two new full-Heusler compounds Li$_2$TlBi and
Li$_2$InBi, possessing a PbTe-like electronic structure, show exceptionally
high power factors ($\sim$ 20 mWm$^{-1}$K$^{-2}$ at 300 K) and low lattice
thermal conductivities (2.36 and 1.55 Wm$^{-1}$K$^{-1}$) at room temperature.
The Tl$^{+}$Bi$^{3-}$ (In$^{+}$Bi$^{3-}$) sublattice forms a rock-salt
structure, and the additional two valence electrons from Li atoms essentially
make these compounds isovalent with Pb$^{2+}$Te$^{2-}$. The larger rock-salt
sublattice of TlBi (InBi) shifts the valence band maximum from L point to the
middle of the $\Sigma$ line, increasing the band degeneracy from fourfold to
twelvefold. On the other hand, resonance bond in the PbTe-like sublattice and
soft Tl-Bi (In-Bi) bonding interaction is responsible for intrinsic low lattice
thermal conductivities. Our results present a novel strategy of designing
high-performance thermoelectric materials.",1805.06433v1
2018-06-18,AFLOW-CHULL: Cloud-oriented platform for autonomous phase stability analysis,"$\textit{A priori}$ prediction of phase stability of materials is a
challenging practice, requiring knowledge of all energetically-competing
structures at formation conditions. Large materials repositories
$\unicode{x2014}$ housing properties of both experimental and hypothetical
compounds $\unicode{x2014}$ offer a path to prediction through the construction
of informatics-based, $\textit{ab-initio}$ phase diagrams. However, limited
access to relevant data and software infrastructure has rendered thermodynamic
characterizations largely peripheral, despite their continued success in
dictating synthesizability. Herein, a new module is presented for autonomous
thermodynamic stability analysis implemented within the open-source,
$\textit{ab-initio}$ framework AFLOW. Powered by the AFLUX Search-API,
AFLOW-CHULL leverages data of more than 1.8 million compounds currently
characterized in the AFLOW.org repository and can be employed locally from any
UNIX-like computer. The module integrates a range of functionality: the
identification of stable phases and equivalent structures, phase coexistence,
measures for robust stability, and determination of decomposition reactions. As
a proof-of-concept, thorough thermodynamic characterizations have been
performed for more than 1,300 binary and ternary systems, enabling the
identification of several candidate phases for synthesis based on their
relative stability criterion $\unicode{x2014}$ including 18 promising
$C15_{b}$-type structures and two half-Heuslers. In addition to a full report
included herein, an interactive, online web application has been developed
showcasing the results of the analysis, and is located at
aflow.org/aflow-chull.",1806.06901v1
2018-09-19,Exploring the best scenario for understanding the high temperature thermoelectric behaviour of Fe2VAl,"Heusler-type Fe2VAl compound is a promising thermoelectric candidate with
non-magnetic ground state. The present work investigates the Seebeck
coefficient (S) of Fe2VAl in the temperature region 300 to 620 K with the help
of experimental and theoretical tools. The experimental value of S is observed
-130 {\mu}V/K at 300 K. Afterthat, the magnitude of S decreases gradually as
the temperature increases. At T = 620 K, the value of S is found to be -26
{\mu}V/K. In order to understand the behaviour of the experimentally observed S
value, the band-structure and density of states calculations are performed by
using LDA, PBE, PBEsol, mBJ and SCAN within density functional theory. All the
above mentioned exchange-correlation (XC) functionals (except mBJ) predict the
semi-metal like behaviour of the compound, whereas the mBJ gives the indirect
band gap of 0.22 eV having the well agreement with experimentally observed
value. The temperature dependence of S for Fe2VAl is also calculated with the
help of all the five mentioned functionals individually. The best XC functional
is investigated for searching the new thermoelectric materials by taking Fe2VAl
as a case example through this study. The best matching between experimental
and calculated values of S as a function of temperature is observed by setting
the mBJ band gap with the band-structure of PBEsol or SCAN. Therefore, the
present study suggests that the band-structure of PBEsol or SCAN with mBJ band
gap can be used for searching the new thermoelectric materials.",1809.07015v1
2019-04-10,Non-trivial topological valence bands of common diamond and zinc-blende semiconductors,"The diamond and zinc-blende semiconductors are well-known and have been
widely studied for decades. Yet, their electronic structure still surprises
with unexpected topological properties of the valence bands. In this joint
theoretical and experimental investigation we demonstrate for the benchmark
compounds InSb and GaAs that the electronic structure features topological
surface states below the Fermi energy. Our parity analysis shows that the
spin-orbit split-off band near the valence band maximum exhibits a strong
topologically non-trivial behavior characterized by the $\mathcal{Z}_2$
invariants $(1;000)$. The non-trivial character emerges instantaneously with
non-zero spin-orbit coupling, in contrast to the conventional topological phase
transition mechanism. \textit{Ab initio}-based tight-binding calculations
resolve topological surface states in the occupied electronic structure of InSb
and GaAs, further confirmed experimentally by soft X-ray angle-resolved
photoemission from both materials. Our findings are valid for all other
materials whose valence bands are adiabatically linked to those of InSb, i.e.,
many diamond and zinc-blende semiconductors, as well as other related
materials, such as half-Heusler compounds.",1904.05063v1
2016-03-03,"Room-temperature magnetic topological semimetal state in half-metallic Heusler Co$_2$TiX (X=Si, Ge, or Sn)","Topological semimetals (TSMs) including Weyl semimetals and nodal-line
semimetals are expected to open the next frontier of condensed matter and
materials science. Although the first inversion breaking Weyl semimetal was
recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal
breaking Weyl and nodal line semimetals, remain elusive. They are predicted to
exhibit exotic properties distinct from the inversion breaking TSMs including
TaAs. In this paper, we identify the magnetic topological semimetal state in
the ferromagnetic half-metal compounds Co$_2$TiX (X=Si, Ge, or Sn) with Curie
temperatures higher than 350 K. Our first-principles band structure
calculations show that, in the absence of spin-orbit coupling, Co$_2$TiX
features three topological nodal lines. The inclusion of spin-orbit coupling
gives rise to Weyl nodes, whose momentum space locations can be controlled as a
function of the magnetization direction. Our results not only open the door for
the experimental realization of topological semimetal states in magnetic
materials at room temperatures, but also suggest potential applications such as
unusual anomalous Hall effects in engineered monolayers of the Co$_2$TiX
compounds at high temperatures.",1603.01255v3
2020-07-27,Role of magnetic exchange interactions in chiral-type Hall effects of epitaxial Mn$_{x}$PtSn films,"Tetragonal Mn-based Heusler compounds feature rich exchange interactions and
exotic topological magnetic textures, such as antiskyrmions, complimented by
the chiral-type Hall effects. This makes the material class interesting for
device applications. We report the relation of the magnetic exchange
interactions to the thickness and Mn concentration of Mn$_{x}$PtSn films, grown
by magnetron sputtering. The competition of the magnetic exchange interactions
determines the finite temperature magnetic texture and thereby the chiral-type
Hall effects in external magnetic fields. We investigate the magnetic and
transport properties as a function of magnetic field and temperature. We focus
on the anomalous and chiral-type Hall effects and the behavior of the
dc-magnetization, in relation to chiral spin textures. We further determine the
stable crystal phase for a relative Mn concentration between 1.5 and 1.85 in
the $I\overline{4}2d$ structure. We observe a spin-reorientation transition in
all compounds studied, which is due to the competition of exchange interactions
on different Mn sublattices. We discuss our results in terms of exchange
interactions and compare them with theoretical atomistic spin calculations.",2007.13412v1
2022-04-19,Thermoelectric properties of Fe$_{2}$VAl at high temperature region: A combined experimental and theoretical study,"Heusler type compounds have long been recognized as potential thermoelectric
(TE) materials. Here, the experimentally observed TE properties of Fe$_{2}$VAl
are understood through electronic structure calculations in the temperature
range of $300-800$ K. The observed value of $S$ is $\sim-$138 $\mu$V/K at 300
K. Then, the $|S|$ decreases with increase in temperature up to the highest
temperature with the value of $\sim-$18 $\mu$V/K at 800 K. The negative sign of
$S$ in the full temperature window signifies the dominating $n$-type character
of the compound. The temperature dependent of electrical conductivity, $\sigma$
(thermal conductivity, $\kappa$) exhibits the increasing (decreasing) trend
with the values of $\sim$1.2 $\times$ 10$^{5}$ $\Omega^{-1}$m$^{-1}$
($\sim$23.7 W/m-K) and $\sim$2.2 $\times$ 10$^{5}$ $\Omega^{-1}$m$^{-1}$
($\sim$15.3 W/m-K) at 300 K and 800 K, respectively. In order to understand
these transport properties, the DFT based semi-classical Boltzmann theory is
used. The contributions of multi-band electron and hole pockets are found to be
mainly responsible for the temperature dependent trend of these properties. The
decrement of $|S|$ and increment of $\sigma/\tau$ $\&$ $\kappa_{e}/\tau$
($\tau$ is relaxation time) with temperature is directly related with the
contribution of multiple hole pockets. Present study suggests that DFT based
electronic calculations provide reasonably good explanations of experimental TE
properties of Fe$_{2}$VAl in the high temperature range of $300-800$ K.",2204.08654v1
2005-04-20,First-principles study of thin magnetic transition-metal silicide films on Si(001),"In order to combine silicon technology with the functionality of magnetic
systems, a number of ferromagnetic (FM) materials have been suggested for the
fabrication of metal/semiconductor heterojunctions. In this work, we present a
systematic study of several candidate materials in contact with the Si surface.
We employ density-functional theory calculations to address the thermodynamic
stability and magnetism of both pseudomorphic CsCl-like $M$Si ($M$=Mn, Fe, Co,
Ni) thin films and Heusler alloy $M_2$MnSi ($M$=Fe, Co, Ni) films on Si(001).
Our calculations show that Si-termination of the $M$Si films is energetically
preferable during epitaxy since it minimizes the energetic cost of broken bonds
at the surface. Moreover, we can explain the calculated trends in thermodynamic
stability of the $M$Si thin films in terms of the $M$-Si bond-strength and the
$M$ 3d orbital occupation. From our calculations, we predict that ultrathin
MnSi films are FM with sizable spin magnetic moments at the Mn atoms, while
FeSi and NiSi films are nonmagnetic. However, CoSi films display itinerant
ferromagnetism. For the $M_2$MnSi films with Heusler-type structure, the MnSi
termination is found to have the highest thermodynamic stability. In the FM
ground state, the calculated strength of the effective coupling between the
magnetic moments of Mn atoms within the same layer approximately scales with
the measured Curie temperatures of the bulk $M_2$MnSi compounds. In particular,
the Co$_2$MnSi/Si(001) thin film has a robust FM ground state as in the bulk,
and is found to be stable against a phase separation into CoSi/Si(001) and
MnSi/Si(001) films. Hence this material is of possible use in FM-Si
heterojunctions and deserves further experimental investigations.",0504515v2
2017-08-25,Topological superconductivity of spin-3/2 carriers in a three-dimensional doped Luttinger semimetal,"We investigate topological Cooper pairing, including gapless Weyl and fully
gapped class DIII superconductivity, in a three-dimensional doped Luttinger
semimetal. The latter describes effective spin-3/2 carriers near a quadratic
band touching and captures the normal-state properties of the 227 pyrochlore
iridates and half-Heusler alloys. Electron-electron interactions may favor
non-$s$-wave pairing in such systems, including even-parity $d$-wave pairing.
We argue that the lowest energy $d$-wave pairings are always of complex (e.g.,
$d + i d$) type, with nodal Weyl quasiparticles. This implies $\varrho(E) \sim
|E|^2$ scaling of the density of states (DoS) at low energies in the clean
limit, or $\varrho(E) \sim |E|$ over a wide critical region in the presence of
disorder. The latter is consistent with the $T$-dependence of the penetration
depth in the half-Heusler compound YPtBi. We enumerate routes for experimental
verification, including specific heat, thermal conductivity, NMR relaxation
time, and topological Fermi arcs. Nucleation of any $d$-wave pairing also
causes a small lattice distortion and induces an $s$-wave component; this gives
a route to strain-engineer exotic $s+d$ pairings. We also consider odd-parity,
fully gapped $p$-wave superconductivity. For hole doping, a gapless Majorana
fluid with cubic dispersion appears at the surface. We invent a generalized
surface model with $\nu$-fold dispersion to simulate a bulk with winding number
$\nu$. Using exact diagonalization, we show that disorder drives the surface
into a critically delocalized phase, with universal DoS and multifractal
scaling consistent with the conformal field theory (CFT) SO($n$)${}_\nu$, where
$n \rightarrow 0$ counts replicas. This is contrary to the naive expectation of
a surface thermal metal, and implies that the topology tunes the surface
renormalization group to the CFT in the presence of disorder.",1708.07825v2
2019-07-05,Thermoelectric transport trends in group 4 half-Heusler alloys,"The thermoelectric properties of 54 different group 4 half-Heusler (HH)
alloys have been studied from first principles. Electronic transport was
studied with density functional theory using hybrid functionals facilitated by
the $\mathbf{k} \cdot \mathbf{p}$ method, while the temperature dependent
effective potential method was used for the phonon contributions to the figure
of merit $ZT$. The phonon thermal conductivity was calculated including
anharmonic phonon-phonon, isotope, alloy and grain-boundary scattering. HH
alloys have an ${\it XYZ}$ composition and those studied here are in the group
4-9-15 (Ti,Zr,Hf)(Co,Rh,Ir)(As,Sb,Bi) and group 4-10-14
(Ti,Zr,Hf)(Ni,Pd,Pt)(Ge,Sn,Pb). The electronic part of the thermal conductivity
was found to significantly impact $ZT$ and thus the optimal doping level.
Furthermore, the choice of functional was found to significantly affect
thermoelectric properties, particularly for structures exhibiting band
alignment features. The intrinsic thermal conductivity was significantly
reduced when alloy and grain boundary scattering were accounted for, which also
reduced the spread in thermal conductivity. It was found that sub-lattice
disorder on the ${\it Z}$-site, i.e. the site occupied by group 14 or 15
elements, was more effective than ${\it X}$-site substitution, occupied by
group 4 elements. The calculations confirmed that ZrNiSn, ZrCoSb and ZrCoBi
based alloys display promising thermoelectric properties. A few other n-type
and p-type compounds were also predicted to be potentially excellent
thermoelectric materials, given that sufficiently high charge carrier
concentrations can be achieved. This study provides insight into the
thermoelectric potential of HH alloys and casts light on strategies to optimize
thermoelectric performance of multicomponent alloys.",1907.02845v1
2021-11-02,Microstructure engineering of metamagnetic Ni-Mn-based Heusler compounds by Fe-doping: A roadmap towards excellent cyclic stability combined with large elastocaloric and magnetocaloric effects,"Ni-Mn-based metamagnetic shape-memory alloys exhibit a giant thermal response
to magnetic fields and uniaxial stress which can be utilized in single caloric
or multicaloric cooling concepts for energy-efficient and sustainable
refrigeration. However, during cyclic operation these alloys suffer from
structural and functional fatigue as a result of their high intrinsic
brittleness. Here, we present based on Fe-doping of Ni-Mn-In a microstructure
design strategy which simultaneously improves cyclic stability and maintains
the excellent magnetocaloric and elastocaloric properties. Our results reveal
that precipitation of a strongly Fe-enriched and In-depleted coherent secondary
gamma-phase at grain boundaries can ensure excellent mechanical stability by
hindering intergranular fracture during cyclic loading. In this way, a large
elastocaloric effect of -4.5 K was achieved for more than 16000 cycles without
structural or functional degradation, which corresponds to an increase of the
cyclic stability by more than three orders of magnitude as compared to
single-phase Ni-Mn-In-(Fe). In addition, we demonstrate that the large
magnetocaloric effect of single-phase Ni-Mn-In-(Fe) can be preserved in the
dual-phase material when the secondary gamma-phase is exclusively formed at
grain boundaries as the martensitic transformation within the Heusler matrix is
barely affected. This way, an adiabatic temperature change of -3 K and an
isothermal entropy change of 15 $Jkg^{-1}K^{-1}$ was obtained in 2 T for
dual-phase Ni-Mn-In-Fe. We expect that this concept can be applied to other
single caloric and mutlicaloric materials, therewith paving the way for
solid-state caloric cooling applications.",2111.01621v2
2022-06-22,Non-trivial topological phases in transition metal rich half-Heusler Oxides,"Topological Insulators with gapless surface states and insulating bulk in
non-centrosymmetric cubic systems have been extensively explored following the
discovery of two-dimensional quantum spin hall effect in zincblende HgTe. In
such systems the negative band inversion strength E$_{BIS}$ ($=$ E$_{\Gamma_6}
-$ E$_{\Gamma_8} <$ 0) governs the robustness of the non-trivial topological
states at ambient conditions. Hence, realizing large negative values of
E$_{BIS}$ has been a guiding motivation of several investigations reported in
literature. Here, we present a material design approach which can be employed
to realize large negative values of E$_{BIS}$ in cubic materials such as
half-Heusler (HH) oxides with 18 valence electron configurations. We explore 27
HH oxides of the form ABO (A = Li, K, Rb; B = Cu, Ag, Au) in $\alpha$-,
$\beta$-, and $\gamma$-phase (by placing transition metal atom at different
Wyckoff positions) for their non-trivial topological phase. Off these three
phases, we found that, the $\alpha$-phase of nine HH oxides (wherein the
transition metal atoms occupy 4a Wyckoff positions in the crystal structure) is
the most promising with non-trivial topological phase which is governed by the
mass-darwin relativistic effects enhancing E$_{BIS}$. Whereas the other phases
were found to be either trivial semiconductors or semimetals or metals and most
of them being dynamically unstable. We focus on RbAuO in $\alpha$-phase with
E$_{BIS}$ of $-$ 1.29 eV and the effect of strain fields on the topological
surface states of this compound. We conclude that the $\alpha$-phase of HH
oxide presented here can be synthesized experimentally for diverse room
temperature applications in spintronics and nanoelectronics.",2206.10976v2
2023-09-14,Composition and Structure Based GGA Bandgap Prediction Using Machine Learning Approach,"This study focuses on developing precise machine learning (ML) regression
models for predicting energy bandgap values based on chemical compositions and
crystal structures. The primary aim is to match the accuracy of predictions
derived from GGA-PBE calculations and validate them through density functional
theory (DFT)-based band structure calculations. We assessed eight standalone ML
regression models, including AdaBoost, Bagging, CatBoost, LGBM, RF, DT, GB, and
XGB. These models were analyzed for their ability to predict GGA-PBE bandgap
values across diverse material structures and compositions, using a dataset
containing bandgap values for 106,113 compounds. Additionally, we constructed
four ensemble models using the stacking method and seven using the bagging
method. These ensemble models incorporated RidgeCV and LassoCV to explore if
ensemble techniques could enhance prediction accuracy. The dataset was divided
into subsets of varying sizes: 10,000, 25,000, 50,000, and 100,000 entries. We
determined feature importance through permutation techniques and established a
correlation coefficient matrix using the Pearson correlation method. The Random
Forest (RF) model emerged as the top performer among standalone models,
achieving an R2 value of 0.943 and an RMSE value of 0.504 eV. Bagging
regression demonstrated improved performance across different dataset sizes
with streamlined feature selection. Ensemble models, particularly bagging,
consistently outperformed standalone models, achieving the best R2 value of
0.948 and an RMSE value of 0.479 eV in the test dataset. Using the
best-performing model, we predicted bandgap values for new half-Heusler
compounds with 18 valence electron counts. These predictions were successfully
validated using accurate DFT calculations. DFT calculations indicated that the
newly predicted compounds are narrow bandgap semiconductors with dynamic
stability.",2309.07424v1
2011-06-24,Magnetic dichroism in angular-resolved hard X-ray photoelectron spectroscopy from buried layers,"This work reports the measurement of magnetic dichroism in angular-resolved
photoemission from in-plane magnetized buried thin films. The high bulk
sensitivity of hard X-ray photoelectron spectroscopy (HAXPES) in combination
with circularly polarized radiation enables the investigation of the magnetic
properties of buried layers. HAXPES experiments with an excitation energy of 8
keV were performed on exchange-biased magnetic layers covered by thin oxide
films. Two types of structures were investigated with the IrMn exchange-biasing
layer either above or below the ferromagnetic layer: one with a CoFe layer on
top and another with a Co$_2$FeAl layer buried beneath the IrMn layer. A
pronounced magnetic dichroism is found in the Co and Fe $2p$ states of both
materials. The localization of the magnetic moments at the Fe site conditioning
the peculiar characteristics of the Co$_2$FeAl Heusler compound, predicted to
be a half-metallic ferromagnet, is revealed from the magnetic dichroism
detected in the Fe $2p$ states.",1106.4976v1
2012-01-30,Insights into the electronic structure of Co2FeSi from x-ray magnetic linear dichroism,"Experimental evidence both for and against a half-metallic ground-state of
the Heusler compound Co2FeSi has been published. Density functional theory
based calculations suggest a non half-metallic ground state. It has been
argued, that on-site Coulomb interaction of the d electrons has to be taken
into account via the LDA+U method, which predicts a half-metallic ground-state
for U = 2.5...4.5 eV. X-ray magnetic linear dichroism (XMLD) can be used as a
tool to assess the appropriateness of the LDA+U approach: the calculated
spectra within the LDA+U or GGA+U schemes are different from those within the
LDA or GGA. Due to its ability to separate different orbital symmetries, XMLD
allows us to distinguish between different models of the electronic structure
of Co2FeSi. In this article we discuss experimental XMLD spectra and compare
them with detailed first principles calculations. Our findings give evidence
for the inadequacy of the LDA+U or GGA+U band structures, whereas constrained
calculations with the GGA and a fixed spin moment of 6 \mu_B give better
overall agreement between experiment and theory.",1201.6263v2
2012-03-13,Stabilization of Majorana modes in vortices in the superconducting phase of topological insulators using topologically trivial bands,"If superconductivity is induced in the metallic surface states of topological
insulators via proximity, Majorana modes will be trapped on the vortex cores.
The same effects hold for doped topological insulators which become bulk s-wave
superconductors as long as the doping does not exceed a critical values $
\mu^{\pm}_c.$ It is this critical chemical potential at which the material
forgets it arose from a band-inverted topological insulator; it loses its
topological \emph{imprint.} For the most common classes of topological
insulators, which can be modeled with a minimal 4-band Dirac model the values
of $\mu^{\pm}_c$ can be easily calculated, but for materials with more
complicated electronic structures such as HgTe or ScPtBi the result is unknown.
We show that due to the hybridization with an additional Kramers' pair of
topologically trivial bands the topological imprint of HgTe-like electronic
structures (which includes the ternary Heusler compounds) can be widely
extended for p-doping. As a practical consequence we consider the effects of
such hybridization on the range of doping over which Majorana modes will be
bound to vortices in superconducting topological insulators and show that the
range is strongly extended for p-doping, and reduced for n-doping. This leaves
open the possibility that other topological phenomena may be stabilized over a
wider range of doping.",1203.2958v2
2013-11-21,Effect of annealing on spinodally decomposed Co2CrAl grown via floating zone technique,"Among the large class of Heusler compounds, Co2CrAl is predicted to be 100 %
spin polarized and is hence, a potential candidate for application in
spintronics. So far, the predicted properties have not been experimentally
realized which may be attributed to the phase segregated nature of samples.
This phase segregation is avoided using floating zone growth. However, the
grown sample was found to have undergone phase transformation via spinodal
decomposition at low temperatures. In the present work, thermal annealing has
been done on the spinodally decomposed samples and its effect on
microstructure, crystallographic structure and magnetic properties has been
studied. Annealing experiments were done and analyzed in order to understand
the extent of the solid state miscibility gap. With regards to the phase
diagram, the two-phase regime was found to extend till 1000 {\deg}C. Even at
1250 {\deg}C, we are still inside the immiscibility region. The thermodynamic
miscibility gap was thus found to exist until high temperatures and alternate
routes might be required to obtain a single phase sample with the desired high
spin polarization and Curie temperature in the Co-Cr-Al system.",1311.5453v1
2015-01-16,State of Co and Mn in half-metallic ferromagnet Co$_2$MnSi explored by magnetic circular dichroism in hard X-ray photoelectron emission and soft X-ray absorption spectroscopies,"The half-metallic Heusler compound Co$_2$MnSi is a very attractive material
for spintronic devices because it exhibits very high tunnelling
magnetoresistance ratios. This work reports on a spectroscopic investigation of
thin Co$_2$MnSi films as they are used as electrodes in magnetic tunnel
junctions. The investigated films exhibit a remanent in-plane magnetisation
with a magnetic moment of about 5~$\mu_B$ when saturated, as expected. The low
coercive field of only 4~mT indicates soft magnetic behaviour. Magnetic
dichroism in emission and absorption was measured at the Co and Mn $2p$ core
levels. The photoelectron spectra were excited by circularly polarised hard
X-rays with an energy of of 6~keV and taken from the remanently magnetised
film. The soft X-ray absorption spectra were taken in an induction field of
4~T. Both methods yielded large dichroism effects. An analysis reveals the
localised character of the electrons and magnetic moments attributed to the Mn
atoms, whereas the electrons related to the Co atoms contribute an itinerant
part to the total magnetic moment.",1501.03966v1
2016-11-28,Synthesis of low-moment CrVTiAl: a potential room temperature spin filter,"The efficient production of spin-polarized currents at room temperature is
fundamental to the advancement of spintronics. Spin-filter materials ---
semiconductors with unequal band gaps for each spin channel --- can generate
spin-polarized current without the need for spin-polarized contacts. In
addition, a spin-filter material with zero magnetic moment would have the
advantage of not producing strong fringing fields that would interfere with
neighboring electronic components and limit the volume density of devices. The
quaternary Heusler compound CrVTiAl has been predicted to be a zero-moment
spin-filter material with a Curie temperature in excess of 1000 K. In this
work, CrVTiAl has been synthesized with a lattice constant of $a = 6.15 \AA$.
Magnetization measurements reveal an exceptionally low moment of $\mu = 2.3
\times 10^{-3} \mu_B/f.u.$ at a field of $\mu_0 H = 2 T$, that is independent
of temperature between T = 10 K and 400 K, consistent with the predicted
zero-moment ferrimagnetism. Transport measurements reveal a combination of
metallic and semiconducting components to the resistivity. Combining a
zero-moment spin-filter material with nonmagnetic electrodes would lead to an
essentially nonmagnetic spin injector. These results suggest that CrVTiAl is a
promising candidate for further research in the field of spintronics.",1611.09307v3
2017-07-11,Unconventional Superconductivity in Luttinger Semimetals: Theory of Complex Tensor Order and the Emergence of the Uniaxial Nematic State,"We investigate unconventional superconductivity in three-dimensional
electronic systems with the chemical potential close to a quadratic band
touching point in the band dispersion. Short-range interactions can lead to
d-wave superconductivity, described by a complex tensor order parameter. We
elucidate the general structure of the corresponding Ginzburg--Landau free
energy and apply these concepts to the case of an isotropic band touching
point. For vanishing chemical potential, the ground state of the system is
given by the superconductor analogue of the uniaxial nematic state, which
features line nodes in the excitation spectrum of quasiparticles. In contrast
to the theory of real tensor order in liquid crystals, however, the ground
state is selected here by the sextic terms in the free energy. At finite
chemical potential, the nematic state has an additional instability at weak
coupling and low temperatures. In particular, the one-loop coefficients in the
free energy indicate that at weak coupling genuinely complex orders, which
break time-reversal symmetry, are energetically favored. We relate our analysis
to recent measurements in the half-Heusler compound YPtBi and discuss the role
of the cubic crystal symmetry.",1707.03444v2
2017-11-30,Topological Hopf and chain link semimetal states and their application to Co2MnGa (Theory and Materials Prediction),"Topological semimetals can be classified by the connectivity and
dimensionality of the band cross- ing in momentum space. The band crossings of
a Dirac, Weyl, or an unconventional fermion semimet- al are 0D points, whereas
the band crossings of a nodal-line semimetal are 1D closed loops. Here we
propose that the presence of perpendicular crystalline mirror planes can
protect 3D band crossings characterized by nontrivial links such as a Hopf link
or a coupled-chain, giving rise to a variety of new types of topological
semimetals. We show that the nontrivial winding number protects topolog- ical
surface states distinct from those in previously known topological semimetals
with a vanishing spin-orbit interaction. We also show that these nontrivial
links can be engineered by tuning the mirror eigenvalues associated with the
perpendicular mirror planes. Using first-principles band structure
calculations, we predict the ferromagnetic full Heusler compound Co2MnGa as a
candidate. Both Hopf link and chain-like bulk band crossings and unconventional
topological surface states are identified.",1712.00055v1
2018-11-09,Topological d+s wave superconductors in a multi-orbital quadratic band touching system,"Realization of topological superconductors is one of the most important goals
in studies of topological phases in quantum materials. In this work, we
theoretically propose a novel way to attain topological superconductors with
non-trivial Fermi surfaces of Bogoliubov quasiparticles. Considering the
interacting Luttinger model with $j\!=\!3/2$ electrons, we investigate the
dominant superconducting channels for a multi-orbital quadratic band-touching
system with finite chemical potential, which breaks the particle-hole symmetry
in the normal state. Notably, while the system generally favors d-wave pairing,
the absence of the particle-hole symmetry necessarily induces parasitic s-wave
pairing. Based on the Landau theory with $SO(3)$ symmetry, we demonstrate that
two kinds of topological superconductors are energetically favored; uniaxial
nematic phase with parasitic $s$ wave pairing ($d_{(3z^2-r^2)}\!+\!s$) and
time-reversal-symmetry broken phase with parasitic $s$ wave pairing
($d_{(3z^2-r^2,xy)}\!+\!id_{x^2-y^2}\!+\!s$). These superconductors contain
either nodal lines or Fermi pockets of gapless Bogoliubov quasiparticles and
moreover exhibit topological winding numbers $\pm2$, leading to non-trivial
surface states such as drumhead-like surface states or Fermi arcs. We discuss
applications of our theory to relevant families of materials, especially
half-heusler compound YPtBi, and suggest possible future experiments.",1811.04046v1
2018-11-10,Magnetic Order and Lattice Instabilities in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ Heusler based Magnetic Shape-Memory Alloys,"The magnetic correlations in the austenite phase and the consequent
martensitic transition in inverse magnetocaloric alloys,
Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$, have been a matter of debate for decades. We
conclusively establish using {\it ab initio} phonon calculations that the spin
alignment of excess Mn at the Sn site (Mn$_{Sn}$) with the existing Mn in the
unit cell in the high temperature cubic phase of Ni-Mn-Sn alloy is
ferromagnetic (FM), and not ferrimagnetic (FI), resolving a long lasting
controversy. Using first principles density functional perturbation theory
(DFPT), we observe an instability of the TA$_{2}$ mode along the $\Gamma$-M
direction in the FM phase, very similar to that observed in the prototypical
ferromagnetic shape memory alloy (FSMA) Ni$_{2}$MnGa. This specific instability
is not observed in the FI phase. Further finite temperature first principles
lattice dynamics calculations reveal that at 300 K the FM phase becomes
mechanically stable, while the FI phase continue to remain unstable providing
credence to the fact that the high-temperature phase has FM order. These
results will be primordial to understand the magneto-structural properties of
this class of compounds.",1811.04221v1
2018-11-12,"Large anomalous Hall and Nernst effect from nodal line symmetry breaking in Fe$_2$MnX (X=P,As,Sb)","A large Berry curvature in the vicinity of the Fermi energy is required in
order to obtain a large anomalous Hall and Nernst effect. This Berry curvature
can be induced by Weyl points and gapped nodal lines. One of the possible
mechanisms takes place in systems with a symmetry group where mirror planes
lead to protected nodal line structures. When these mirror symmetries are
broken, e. g. via fixing a magnetization direction, a gap in the former nodal
line can create Weyl points and a large Berry curvature along the gapped lines.
In this work we study this effect in a minimal effective model and relate the
results to the real regular Heusler compounds Fe$_2$MnX (X=P,As,Sb). These
materials have three mirror planes in the non-magnetic case, leading to three
nodal lines near the Fermi level. However, dependent on the orientation of the
magnetization, some of the mirror planes are broken and the respective lines
are gapped, creating large Berry curvature. Because the Fermi level is located
in vicinity of the gapped lines, this leads to a large anomalous Hall and
Nernst effect, which can be tuned to even higher values with a little bit of
doping in the system.",1811.04680v1
2018-07-06,Strategic enhancement of anomalous Nernst effect in Co2MnAl1-xSix Heusler compounds,"The anomalous Nernst effect (ANE), a thermoelectric phenomenon in magnetic
materials, has potential for novel energy harvesting applications because its
orthogonal relationship between the temperature gradient and the electric field
enables us to utilize the large area of non-flat heat sources. In this study,
the required thermopower of ANE for practical energy harvesting applications is
evaluated in simulations of electric power obtainable from ANE using a
low-temperature heat source. A strategy for finding magnetic materials having
large ANEs is proposed, which suggests that a large ANE originates from the
constructive relationship between large Seebeck, anomalous Hall, and transverse
Peltier effects. This strategy leads us to investigate the electric and
thermoelectric properties in Co2MnAl1-xSix. As a result, it is found that
Co2MnAl0.63Si0.37 has the largest ANE thermopower ever reported, 6.2 uV/K. A
first principles calculation of the anomalous Hall conductivity and transverse
Peltier coefficient in B2 and L21-ordered Co2MnAl0.63Si0.37 shows close
agreement with the experimental results, indicating that the observed large ANE
arises from the intrinsic Berry phase curvature of Co2MnAl1-xSix. This study
can be a guide for developing materials for new thermoelectric applications
using ANE.",1807.02209v3
2018-07-17,Large anomalous Nernst effect in thin films of the Weyl semimetal Co2MnGa,"The magneto-thermoelectric properties of Heusler compound thin films are very
diverse. Here, we discuss the anomalous Nernst response of Co$_2$MnGa thin
films. We systematically study the anomalous Nernst coefficient as a function
of temperature, and we show that unlike the anomalous Hall effect, the
anomalous Nernst effect in Co$_2$MnGa strongly varies with temperature. We
exploit the on-chip thermometry technique to quantify the thermal gradient,
which enables us to directly evaluate the anomalous Nernst coefficient. We
compare these results to a reference CoFeB thin film. We show that the
50-nm-thick Co$_2$MnGa films exhibit a large anomalous Nernst effect of
-2$\mu$V/K at 300 K, whereas the 10-nm-thick Co$_2$MnGa film exhibits a
significantly smaller anomalous Nernst coefficient despite having similar
volume magnetizations. These findings suggest that the microscopic origin of
the anomalous Nernst effect in Co$_2$MnGa is complex and may contain
contributions from skew-scattering, side-jump or intrinsic Berry phase. In any
case, the large anomalous Nernst coefficent of Co$_2$MnGa thin films at room
temperature makes this material system a very promising candidate for efficient
spin-caloritronic devices.",1807.06487v1
2018-07-20,Characterization of topological band structures away from the Fermi level by anomalous Nernst measurements,"Resolving the structure of energy bands in transport experiments is a major
challenge in condensed matter physics and material science. Sometimes, however,
traditional electrical conductance or resistance measurements only provide very
small signals, and thus limit the ability to obtain direct band structure
information. In this case, it has been proven beneficial to employ
thermoelectric measurements which are sensitive to the first derivative of the
density of states with respect to energy, rather than to its value itself. Due
to the large interest in topological effects these days, it is important to
identify a similar concept for detecting the Berry curvature in a band
structure. Nowadays, the common way to access the Berry curvature directly via
measurements is the anomalous Hall effect, but the corresponding signal can be
too small to be detected when the topological features of the band structure
lie too far off the Fermi level. In this work we propose to investigate
topological band structure features utilizing the anomalous Nernst effect which
is tied to the derivative of the anomalous Hall effect with respect to energy.
Thereby, also signatures become resolvable, which are elusive in anomalous Hall
measurements. We demonstrate the underlying mechanisms for a minimal effective
four-band model and exemplary for the real Heusler compounds Co$_2$Fe$X$
($X$=Ge,Sn), which host topological nodal lines about 100 meV above the Fermi
level. This work demonstrates that anomalous Nernst measurements can be an
effective tool for the characterization of topological band structures, both at
room temperature and in the quantum transport regime at cryogenic temperatures.",1807.07843v1
2019-04-02,Spin pumping and spin torque in interfacial tailored Co2FeAl/\b{eta}-Ta layers,"The Heusler ferromagnetic (FM) compound Co2FeAl interfaced with a high-spin
orbit coupling non-magnetic (NM) layer is a promising candidate for energy
efficient spin logic circuits. The circuit potential depends on the strength of
angular momentum transfer across the FM/NM interface; hence, requiring low spin
memory loss and high spin-mixing conductance. To highlight this issue, spin
pumping and spin-transfer torque ferromagnetic resonance measurements have been
performed on Co_2FeAl/\beta-Ta heterostructures tailored with Cu interfacial
layers. The interface tailored structure yields an enhancement of the effective
spin-mixing conductance. The interface transparency and spin memory loss
corrected values of the spin-mixing conductance, spin Hall angle and spin
diffusion length are found to be 3.40 \pm 0.01 \times 10^{19} m^{-2}, 0.029 \pm
0.003, and 2.3 \pm 0.5 nm, respectively. Furthermore, a high current modulation
of the effective damping of around 2.1 % has been achieved at an applied
current density of 1 \times 10^9 A/m^2 , which clearly indicates the potential
of using this heterostructure for energy efficient control in spin devices",1904.01506v3
2022-03-04,In-situ nitriding of Fe2VAl during laser surface remelting to manipulate microstructure and crystalline defects,"Tailoring the physical properties of complex materials for targeted
applications requires optimizing the microstructure and crystalline defects
that influence electrical and thermal transport, and mechanical properties.
Laser surface remelting can be used to modify the sub-surface microstructure of
bulk materials and hence manipulate their properties locally. Here, we
introduce an approach to perform remelting in a reactive nitrogen atmosphere,
in order to form nitrides and induce segregation of nitrogen to structural
defects. These defects arise from the fast solidification of the full-Heusler
Fe2VAl compound that is a promising thermoelectric material. Advanced scanning
electron microscopy, including electron channelling contrast imaging and
three-dimensional electron backscatter diffraction, is complemented by atom
probe tomography to study the distribution of crystalline defects and their
local chemical composition. We reveal a high density of dislocations, which are
stable due to their character as geometrically necessary dislocations. At these
dislocations and low-angle grain boundaries, we observe segregation of nitrogen
and vanadium, which can be enhanced by repeated remelting in nitrogen
atmosphere. We propose that this approach can be generalized to other additive
manufacturing processes to promote local segregation and precipitation states,
thereby manipulating physical properties.",2203.02209v1
2019-05-24,A first-principles investigation of Topological Phase Transition in face-centred cubic LiMgBi,"Topological Insulators (TI) exhibit robust spin-locked dissipationless
Fermion transport along the surface states. In the current study, we use
\textit{first-principles} calculations to investigate a Topological Phase
Transition (TPT) in a Half-Heusler (HH) compound LiMgBi driven by a Volume
Expansive Pressure (VEP) which is attributed to the presence of, intrinsic
voids, thermal perturbations and/or due to a phenomena known as cavity nuclei.
We find that, the dynamically stable \textit{face-centred cubic} (FCC)
structure of LiMgBi (which belongs to the F$\overline{4}$3m[216] space group),
undergoes TPT beyond a critical VEP at 4.0\%. The continuous application of VEP
from 0.0\% to 8.0\% results in a phase transition from a, band insulator to a
Dirac semi-metal nature. Qualitatively, the Dirac cone formation and band
inversion along the high symmetry point $\mathbf{\Gamma}$ in the Brillouin Zone
(BZ) are analysed in terms of Electronic Band Structure (EBS) and Projected
Local Density of States (LDOS). The TPT is further characterised by the
$\mathbb{Z}_2$ invariant, ($\nu_0$, $\nu_1$ $\nu_2$ $\nu_3$) $\equiv$ (1, 0 0
0) along the (0001) surface which indicates quantitatively that, HH LiMgBi is a
strong TI. We hence propose, HH LiMgBi (known for its piezoelectric,
thermo-electric and semi-conducting applications) as a strong TI with potential
multipurpose application in the field of electronics, spintronics and quantum
computation.",1905.10103v2
2019-09-04,Exploring Disorder in the Spin Gapless Semiconductor Mn$_2$CoAl,"Since the prediction of spin-gapless semiconducting behaviour in the Heusler
compound Mn$_2$CoAl, evidence of spin-gapless behaviour in thin films has
typically been inferred from magnetotransport measurements. The spin gapless
state is however fragile, and further, band structure calculations indicate
that even a small amount of atomic disorder may destroy it. To explore the
impact of disorder on the properties of Mn$_2$CoAl, we have undertaken an
experimental study of the structural, magnetotransport and optical properties
from the far infrared to the UV, on DC magnetron sputtered Mn$_2$CoAl thin
films. A very short mean free path, of the order of a lattice spacing, is
extracted from the DC transport data. A room temperature resistivity of 200
$\mu$$\Omega$cm along with a small and negative temperature coefficient of
resistance between 4 and 400 K was measured. We note that parameters of this
magnitude are often observed in disordered metals. We find this behaviour is
well described by a weak localisation model, a result that is supported by a
large Drude contribution to the optical response, where a high scattering rate
is derived, which is equal to the value derived from the DC conductivity and
Hall effect data. We also note the strong similarities between the
magnetotransport behaviour reported for Mn$_2$CoAl films in the literature,
including ours. We conclude that, based on comparisons between the experimental
data, and recent band structure calculations that explicitly include disorder,
as-prepared Mn$_2$CoAl films are best described as a disordered metal, rather
than a spin gapless semiconductor.",1909.02153v1
2019-12-13,Shallow impurity band in ZrNiSn,"ZrNiSn and related half Heusler compounds are candidate materials for
efficient thermoelectric energy conversion with a reported thermoelectric
figure-of-merit of n-type ZrNiSn exceeding unity. Progress on p-type materials
has been more limited, which has been attributed to the presence of an impurity
band, possibly related to the presence of Ni interstitials in nominally vacant
4d position. The specific energetic position of this band, however, has not
been resolved. Here, we report results of a concerted theory-experiment
investigation for a nominally undoped ZrNiSn, based on measurements of
electrical resistivity, Hall coefficient, Seebeck coefficient and Nernst
coefficient, measured in a temperature range from 80 to 420 K. The results are
analyzed with a semi-analytical model combining a density functional theory
(DFT) description for ideal ZrNiSn, with a simple analytical correction for the
impurity band. The model provides a good quantitative agreement with
experiment, describing all salient features in the full temperature span for
the Hall, conductivity, and Seebeck measurements, while also reproducing key
trends in the Nernst results. This comparison pinpoints the impurity band edge
to 40 meV below the conduction band edge, which agrees well with a separate DFT
study of a supercell containing Ni interstitials. Moreover, we corroborate our
result with a separate study of ZrNiSn0.9Pb0.1 sample showing similar agreement
with an impurity band edge shifted to 32 meV below the conduction band.",1912.06539v1
2020-06-04,Material Descriptors for the Discovery of Efficient Thermoelectrics,"The predictive performance screening of novel compounds can significantly
promote the discovery of efficient, cheap, and non-toxic thermoelectric
materials. Large efforts to implement machine-learning techniques coupled to
materials databases are currently being undertaken, but the adopted
computational methods can dramatically affect the outcome. With regards to
electronic transport and power factor calculations, the most widely adopted and
computationally efficient method, is the constant relaxation time approximation
(CRT). This work goes beyond the CRT and adopts the proper, full energy and
momentum dependencies of electron-phonon and ionized impurity scattering, to
compute the electronic transport and perform power factor optimization for a
group of half-Heusler alloys. Then the material parameters that determine the
optimal power factor based on this more advanced treatment are identified. This
enables the development of a set of significantly improved descriptors that can
be used in materials screening studies, and which offer deeper insights into
the underlying nature of high performance thermoelectric materials. We have
identified $n_v$$\epsilon_r$ / $D_o^2m_{cond}$ as the most useful and generic
descriptor, a combination of the number of valleys, the dielectric constant,
the conductivity effective mass, and the deformation potential for the dominant
electron-phonon process. The proposed descriptors can accelerate the discovery
of new efficient and environment friendly thermoelectric materials in a much
more accurate and reliable manner, and some predictions for very high
performance materials are presented.",2006.02789v2
2021-01-29,Room-temperature antiskyrmions and sawtooth surface textures in a noncentrosymmetric magnet with $S_4$ symmetry,"Topological spin textures have attracted much attention both for fundamental
physics and spintronics applications. Among them, antiskyrmions possess a
unique spin configuration with Bloch-type and N\'eel-type domain walls due to
anisotropic Dzyaloshinskii-Moriya interaction (DMI) in the noncentrosymmetric
crystal structure. However, antiskyrmions have thus far only been observed in a
few Heusler compounds with $D_{2\mathrm{d}}$ symmetry. Here, we report a new
material Fe$_{1.9}$Ni$_{0.9}$Pd$_{0.2}$P in a different symmetry class ($S_4$
symmetry), where antiskyrmions exist over a wide temperature region including
room temperature, and transform to skyrmions upon changing magnetic field and
lamella thickness. The periodicity of magnetic textures greatly depends on
crystal thickness, and domains with anisotropic sawtooth fractals are observed
at the surface of thick crystals, which are attributed to the interplay between
dipolar interaction and DMI as governed by crystal symmetry. Our findings
provide a new arena to study antiskyrmions, and should stimulate further
research on topological spin textures and their applications.",2101.12359v1
2021-10-11,Absolute calibration of the latent heat of transition using differential thermal analysis,"We describe a simple and accurate differential thermal analysis set up to
measure the latent heat of solid state materials undergoing abrupt phase
transitions in the temperature range from 77 K to above room temperature. We
report a numerical technique for the absolute calibration of the latent heat of
the transition, without the need of a reference sample. The technique is
applied to three different samples -- vanadium sesquioxide undergoing the Mott
transition, bismuth barium ruthenate undergoing a magnetoelastic transition,
and an intermetallic Heusler compound. In each case, the inferred latent heat
value agrees with the literature value to within its error margins. To further
demonstrate the importance of absolute calibration, we show that the changes in
the latent heat of the Mott transition in vanadium sesquioxide (V$_2$O$_3$)
stays constant to within 2% even as the depth of supersaturation changes by
about 10 K, in non-equilibrium dynamic hysteresis measurements. We also apply
this technique for the measurement of the temperature-dependent specific heat.",2110.05046v1
2021-11-20,Skyrmionics in correlated oxides,"While chiral magnets, metal-based magnetic multilayers, or Heusler compounds
have been considered as the material workhorses in the field of skyrmionics,
oxides are now emerging as promising alternatives, as they host special
correlations between the spin-orbital-charge-lattice degrees of freedom and/or
coupled ferroic order parameters. These interactions open new possibilities for
practically exploiting skyrmionics. In this article, we review the recent
advances in the observation and control of topological spin textures in various
oxide systems. We start with the discovery of skyrmions and related
quasiparticles in bulk and heterostructure ferromagnetic oxides. Next, we
emphasize the shortcomings of implementing ferromagnetic textures, which have
led to the recent explorations of ferrimagnetic and antiferromagnetic oxide
counterparts, with higher Curie temperatures, stray-field immunity, low Gilbert
damping, ultrafast magnetic dynamics, and/or absence of skyrmion deflection.
Then, we highlight the development of novel pathways to control the stability,
motion, and detection of topological textures using electric fields and
currents. Finally, we present the outstanding challenges that need to be
overcome to achieve all-electrical, nonvolatile, low-power oxide skyrmionic
devices.",2111.10562v2
2021-11-28,CoFeVSb: A Promising Candidate for Spin Valve and Thermoelectric Applications,"We report a combined theoretical and experimental study of a novel quaternary
Heusler system CoFeVSb from the view point of room temperature spintronics and
thermoelectric applications. It crystallizes in cubic structure with small
DO$_3$-type disorder. The presence of disorder is confirmed by room temperature
synchrotron X-ray diffraction(XRD) and extended X-ray absorption fine structure
(EXAFS) measurements. Magnetization data reveal high ordering temperature with
a saturation magnetization of 2.2 $\mu_B$/f.u. Resistivity measurements reflect
half-metallic nature. Double hysteresis loop along with asymmetry in the
magnetoresistance(MR) data reveals room temperature spin-valve feature, which
remains stable even at 300 K. Hall measurements show anomalous behavior with
significant contribution from intrinsic Berry phase. This compound also large
room temperature power factor ($\sim0.62$ mWatt/m/K$^{2}$) and ultra low
lattice thermal conductivity ($\sim0.4$ W/m/K), making it a promising candidate
for thermoelectric application. Ab-initio calculations suggest weak
half-metallic behavior and reduced magnetization (in agreement with experiment)
in presence of DO$_3$ disorder. We have also found an energetically competing
ferromagnetic FM)/antiferromagnetic (AFM) interface structure within an
otherwise FM matrix: one of the prerequisites for spin valve behavior.
Coexistence of so many promising features in a single system is rare, and hence
CoFeVSb gives a fertile platform to explore numerous applications in future.",2111.14081v1
2022-06-06,Quantitative theory of magnetic interactions in solids,"In this report we review the method of explicit calculations of interatomic
exchange interactions of magnetic materials. This involves exchange mechanisms
normally referred to as Heisenberg exchange, Dzyaloshinskii-Moriya interaction
and anisotropic symmetric exchange. The connection between microscopic theories
of the electronic structure, such as density functional theory or dynamical
mean field theory, and interatomic exchange, is given in detail. The different
aspects of extracting information for an effective spin Hamiltonian that
involves thousands of atoms, from electronic structure calculations considering
significantly fewer atoms (1-50) is highlighted. Examples of exchange
interactions of a large group of materials is presented, which involves heavy
elements of the 3d period, alloys between transition metals, Heusler compounds,
multilayer systems as well as overlayers and adatoms on a substrate, transition
metal oxides, 4f elements, magnetic materials in two dimensions and molecular
magnets. Where possible, a comparison to experimental data is made, that
naturally becomes focused on the magnon dispersion. The influence of relativity
is reviewed for a few cases, as is the importance of dynamical correlations.
Development to theories that handle out of equilibrium conditions is also
described here. The review ends with a short description of extensions of the
theories behind explicit calculations of interatomic exchange, to non-magnetic
situations, e.g. that describe chemical (charge) order and superconductivity.",2206.02415v2
2022-08-24,The type-I antiferromagnetic Weyl semimetal InMnTi$_2$,"Topological materials have been a main focus of studies in the past decade
due to their protected properties that can be exploited for the fabrication of
new devices. Among them, Weyl semimetals are a class of topological semimetals
with non-trivial linear band crossing close to the Fermi level. The existence
of such crossings requires the breaking of either time-reversal or inversion
symmetry and is responsible for the exotic physical properties. In this work we
identify the full-Heusler compound InMnTi$_2$, as a promising, easy to
synthesize, $T$- and $I$-breaking Weyl semimetal. To correctly capture the
nature of the magnetic state, we employed a novel $\mathrm{DFT}+U$
computational setup where all the Hubbard parameters are evaluated from
first-principles; thus preserving a genuinely predictive \textit{ab initio}
character of the theory. We demonstrate that this material exhibits several
features that are comparatively more intriguing with respect to other known
Weyl semimetals: the distance between two neighboring nodes is large enough to
observe a wide range of linear dispersions in the bands, and only one kind of
such node's pairs is present in the Brillouin zone. We also show the presence
of Fermi arcs stable across a wide range of chemical potentials. Finally, the
lack of contributions from trivial points to the low-energy properties makes
the materials a promising candidate for practical devices.",2208.11412v3
2022-12-05,Quantifying nonadiabaticity in major families of superconductors,"The classical Bardeen-Cooper-Schrieffer and Eliashberg theories of the
electron-phonon-mediated superconductivity are based on the Migdal theorem,
which is an assumption that the energy of charge carriers, $k{_B}T{_F}$,
significantly exceeds the phononic energy, $\hbar{\omega{_D}} $, of the
crystalline lattice. This assumption, which is also known as adiabatic
approximation, implies that the superconductor exhibits fast charge carriers
and slow phonons. This picture is valid for pure metals and metallic alloys
because these superconductors exhibit $\hbar{\omega{_D}}$/$k{_B}T{_F}<0.01$.
However, n-type doped semiconducting $SrTiO_3$ was the first superconductor
which beyond this adiabatic approximation, because this material exhibits
$\hbar{\omega{_D}}$/$k{_B}T{_F} $~$ 50$. There is growing number of newly
discovered superconductors which also beyond the adiabatic approximation. Here,
leaving apart pure theoretical aspects of nonadiabatic superconductors, we
classified major classes of superconductors (including, elements, A-15 and
Heusler alloys, Laves phases, intermetallics, noncentrosymmetric compounds,
cuprates, pnictides, highly-compressed hydrides and oxygen, and magic-angle
twisted bilayer graphene) by the strength of nonadiabaticity (for which the
ratio of the Debye temperature to the Fermi temperature, $T{_\theta}/T{_F}$, is
used as a criterion for the nonadiabaticity) versus the superconducting
transition temperature, $T{_c}$. The discussion of this classification scheme
and its relation to other known classification counterparts is given.",2212.02396v3
2023-01-13,Spin and current transport in the robust half-metallic magnet $c$-CoFeGe,"Spintronics is an emerging form of electronics based on the electrons' spin
degree of freedom for which materials with robust half-metallic ferromagnet
(HMF) character are very attractive. Here we determine the structural
stability, electronic, magnetic, and mechanical properties of the half-Heusler
(hH) compound CoFeGe, in particular also in its cubic form. The
first-principles calculations suggest that the electronic structure is robust
with 100 \% spin polarization at the Fermi level under hydrostatic pressure and
uni-axial strain. Both the longitudinal and Hall current polarization are
calculated and the longitudinal current polarization ($P_{L}$) is found to be
$>99\%$ and extremely robust under uniform pressure and uni-axial strain. The
anomalous Hall conductivity (AHC) and Spin Hall conductivity (SHC) of hH cubic
CoFeGe (\textit{c}-CoFeGe) are found to be $\sim -100$ S/cm and $\sim
39~\hbar/e$ S/cm, respectively. Moreover, the Curie temperature of the alloy is
calculated to be $\sim$524 K with a 3 $\mu_{B}$ magnetic moment. Lastly, the
calculated mechanical properties indicate that \textit{c}-CoFeGe is ductile and
mechanically stable with a bulk modulus of $\approx$ 154 GPa. Overall, this
analysis reveals that cubic CoFeGe is a robust half-metallic ferromagnet and an
interesting material for spintronic applications.",2301.05493v1
2022-08-07,A machine learning approach to predict the structural and magnetic properties of Heusler alloy families,"Random forest (RF) regression model is used to predict the lattice constant,
magnetic moment and formation energies of full Heusler alloys, half Heusler
alloys, inverse Heusler alloys and quaternary Heusler alloys based on existing
as well as indigenously prepared databases. Prior analysis was carried out to
check the distribution of the data points of the response variables and found
that in most of the cases, the data is not normally distributed. The outcome of
the RF model performance is sufficiently accurate to predict the response
variables on the test data and also shows its robustness against overfitting,
outliers, multicollinearity and distribution of data points. The parity plots
between the machine learning predicted values against the computed values using
density functional theory (DFT) shows linear behavior with adjusted R2 values
lying in the range of 0.80 to 0.94 for all the predicted properties for
different types of Heusler alloys. Feature importance analysis shows that the
valence electron numbers plays an important feature role in the prediction for
most of the predicted outcomes. Case studies with one full Heusler alloy and
one quaternary Heusler alloy were also mentioned comparing the machine learning
predicted results with our earlier theoretical calculated values and
experimentally measured results, suggesting high accuracy of the model
predicted results.",2208.12705v1
2007-11-15,Characterization of half-metallic L2_1-phase Co_2FeSi full-Heusler alloy films formed by rapid thermal annealing,"The authors developed a preparation technique of Co_2FeSi full-Heusler alloy
films with the L2_1-ordered structure on silicon-on-insulator (SOI) substrates,
employing rapid thermal annealing (RTA). The Co_2FeSi full-Heusler alloy films
were successfully formed by RTA-induced silicidation reaction between an
ultrathin SOI (001) layer and Fe/Co layers deposited on it. The highly
(110)-oriented L2_1-phase polycrystalline full-Heusler alloy films were
obtained at the RTA temperature of 700 C. Crystallographic and magnetic
properties of the RTA-formed full-Heusler alloy films were qualitatively the
same as those of bulk full-Heusler alloy. This technique is compatible with
metal source/drain formation process in advanced CMOS technology and would be
applicable to the fabrication of the half-metallic source/drain of MOSFET type
of spin transistors.",0711.2404v1
2013-01-25,All-Heusler giant-magnetoresistance junctions with matched energy bands and Fermi surfaces,"We present an all-Heusler architecture which could be used as a rational
design scheme for achieving high spin-filtering efficiency in the
current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A
Co2MnSi/Ni2NiSi/Co2MnSi trilayer stack is chosen as the prototype of such an
architecture, of which the electronic structure and magnetotransport properties
are systematically investigated by first principles approaches. Almost
perfectly matched energy bands and Fermi surfaces between the all-Heusler
electrode-spacer pair are found, indicating large interfacial spin-asymmetry,
high spin-injection efficiency, and consequently high GMR ratio. Transport
calculations further confirms the superiority of the all-Heusler architecture
over the conventional Heusler/transition-metal(TM) structure by comparing their
transmission coefficients and interfacial resistances of parallel conduction
electrons, as well as the macroscopic current-voltage (I-V) characteristics. We
suggest future theoretical and experimental efforts in developing novel
all-Heusler GMR junctions for the read heads of the next generation
high-density hard disk drives (HDDs).",1301.6106v1
2017-04-05,"Structure, site-specific magnetism and magneto-transport properties of epitaxial D0$_{22}$ Mn$_2$Fe$_x$Ga thin films","Ferrimagnetic Mn$_2$Fe$_x$Ga $(0.26 \leq x \leq 1.12)$ thin films have been
characterised by X-ray diffraction, SQUID magnetometry, X-ray absorption
spectroscopy, X-ray magnetic circular dichroism and M\""{o}ssbauer spectroscopy
with the aim of determining the structure and site-specific magnetism of this
tetragonal, D0$_{22}$-structure Heusler compound. High-quality epitaxial films
with low RMS surface roughness ($\sim 0.6$ nm) are grown by magnetron
co-sputtering. The tetragonal distortion induces strong perpendicular magnetic
anisotropy along the $c$-axis with a typical coercive field $\mu_0 H\sim 0.8$ T
and an anisotropy field ranging from $6$ to $8$ T. Upon increasing the Fe
content $x$, substantial uniaxial anisotropy, $K_\mathrm{u} \geq 1.0$ MJ/m$^3$
can be maintained over the full $x$ range, while the magnetisation of the
compound is reduced from $400$ to $280$ kA/m. The total magnetisation is almost
entirely given by the sum of the spin moments originating from the
ferrimagnetic Mn and Fe sublattices, with the latter being coupled
ferromagnetically to one of the former. The orbital magnetic moments are
practically quenched, and have negligible contributions to the magnetisation.
The films with $x=0.73$ exhibit a high anomalous Hall angle of $2.5$ % and a
high Fermi-level spin polarisation, above $51$ %, as measured by point contact
Andreev reflection. The Fe-substituted Mn$_2$Ga films are highly tunable with a
unique combination of high anisotropy, low magnetisation, appreciable spin
polarisation and low surface roughness, making them very strong candidates for
thermally-stable spin-transfer-torque switching nanomagnets with lateral
dimensions down to $10$ nm.",1704.01326v1
2021-06-22,"Superconductivity in spin-$3/2$ systems: symmetry classification, odd-frequency pairs, and Bogoliubov Fermi surfaces","The possible symmetries of the superconducting pair amplitude is a
consequence of the fermionic nature of the Cooper pairs. For spin-$1/2$ systems
this leads to the $\mathcal{SPOT}=-1$ classification of superconductivity,
where $\mathcal{S}$, $\mathcal{P}$, $\mathcal{O}$, and $\mathcal{T}$ refer to
the exchange operators for spin, parity, orbital, and time between the paired
electrons. However, this classification no longer holds for higher spin
fermions, where each electron also possesses a finite orbital angular momentum
strongly coupled with the spin degree of freedom, giving instead a conserved
total angular moment. For such systems, we here instead introduce the
$\mathcal{JPT}=-1$ classification, where $\mathcal{J}$ is the exchange operator
for the $z$-component of the total angular momentum quantum numbers. We then
specifically focus on spin-$3/2$ fermion systems and several superconducting
cubic half-Heusler compounds that have recently been proposed to be spin-$3/2$
superconductors. By using a generic Hamiltonian suitable for these compounds we
calculate the superconducting pair amplitudes and find finite pair amplitudes
for all possible symmetries obeying the $\mathcal{JPT}=-1$ classification,
including all possible odd-frequency (odd-$\omega$) combinations. Moreover, one
of the very interesting properties of spin-$3/2$ superconductors is the
possibility of them hosting a Bogoliubov Fermi surface (BFS), where the
superconducting energy gap is closed across a finite area. We show that a
spin-$3/2$ superconductor with a pair potential satisfying an odd-gap
time-reversal product and being non-commuting with the normal-state Hamiltonian
hosts both a BFS and has finite odd-$\omega$ pair amplitudes. We then reduce
the full spin-$3/2$ Hamiltonian to an effective two-band model and show that
odd-$\omega$ pairing is inevitably present in superconductors with a BFS and
vice versa.",2106.11983v2
2021-10-26,Spin- and time-resolved photoelectron spectroscopy and diffraction studies using time-of-flight momentum microscopes,"Momentum microscopy (MM) is a novel way of performing angular-resolved
photoelectron spectroscopy (ARPES). Combined with time-of-flight (ToF) energy
recording, its high degree of parallelization is advantageous for photon-hungry
experiments like ARPES at X-ray energies and spin-resolved ARPES. This article
introduces into the spin-resolved variant of ToF-MM and illustrates its
performance by selected examples obtained in different spectral ranges. In a
multidimensional view of the photoemission process, spectral density function
$\rho(k,E_B)$, spin polarization $P(k,E_B)$ and related quantities of circular
dichroism in the angular distribution (CDAD) are part of the complete
experiment, a concept adopted from atomic photoemission. We show examples of
spin-resolved valence-band mapping in the UV, VUV, soft- and hard-X-ray range.
Spin mapping of the Heusler compounds Co$_2$MnGa and
Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si at $h\nu=6$~eV prove that the second compound is a
half-metallic ferromagnet. Analysis of the Tamm state on Re(0001) using
VUV-excitation reveals a Rashba-type spin texture. Bulk band structure
including Fermi surface, Fermi velocity distribution $v_F(k,E_F)$, full CDAD
texture and spin signature of W(110) have been derived via tomographic mapping
with soft X-rays. Hard X-rays enable accessing large k$_{par}$-regions so that
the final-state sphere crosses many Brillouin zones in $k$-space with different
$k_z$. At $h\nu=5.3$~keV this fast 4D mapping mode (at fixed $h\nu$) revealed
the temperature dependence of the Fermi surface of the Kondo system
YbRh$_2$Si$_2$. Probing the true bulk spin polarization of Fe$_3$O$_4$ at
$h\nu=5$~keV proved its half-metallic nature. The emerging method of ToF-MM
with fs X-ray pulses from a free-electron laser enables simultaneous valence,
core-level and photoelectron diffraction measurements in the ultrafast regime.",2110.13832v2
2022-11-25,Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi,"The present work aims to address the electronic and magnetic properties of
the intermetallic compound GdPd$_2$Bi through a comprehensive study of the
structural, magnetic, electrical and thermal transport on a polycrystalline
sample, followed by theoretical calculations. Our findings indicate that the
magnetic ground state is antiferromagnetic in nature. Magnetotransport data
present prominent hysteresis loop hinting a structural transition with further
support from specific heat and thermopower measurements, but no such signature
is observed in the magnetization study. Temperature dependent powder x-ray
diffraction measurements confirm martensitic transition from the
high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature
(LT) orthorhombic $Pmma$ structure similar to many previously reported shape
memory alloys. The HT to LT phase transition is characterized by a sharp
increase in resistivity associated with prominent thermal hysteresis. Further,
we observe robust Bain distortion between cubic and orthorhombic lattice
parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and
$c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and
elongation along $a$-axis respectively. The sample shows an unusual
`non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field
as high as 150 kOe. In addition, non-linear field dependence of Hall
resistivity is observed below about 30 K, which coincides with the sign change
of the Seebeck coefficient. The electronic structure calculations confirm
robust metallic states both in the LT and HT phases. It indicates complex
nature of the Fermi surface along with the existence of both electron and hole
charge carriers. The anomalous transport behaviors can be related to the
presence of both electron and hole pockets.",2211.13982v1
2019-10-29,Perpendicular magnetic anisotropy in Pt/Co-based full Heusler alloy/MgO thin films structures,"Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a
key ingredient for the development of electrically controlled spintronic
devices. Due to their relatively large spin-polarization, high Curie
temperature and low Gilbert damping the Co-based full Heusler alloys are of
special importance from a scientific and applications point of view. Here, we
study the mechanisms responsible for the PMA in Pt/Co-based full Heusler
alloy/MgO thin films structures. We show that the ultrathin Heusler films
exhibit strong PMA even in the absence of magnetic annealing. By means of
ferromagnetic resonance experiments, we demonstrate that the effective
magnetization shows a two-regime behavior depending on the thickness of the
Heusler layers. Using Auger spectroscopy measurements, we evidence
interdiffusion at the underlayer/Heusler interface and the formation of an
interfacial CoFe-rich layer which causes the two-regime behavior. In the case
of the ultrathin films, the interfacial CoFe-rich layer promotes the strong PMA
through the electronic hybridization of the metal alloy and oxygen orbitals
across the ferromagnet/MgO interface. In addition, the interfacial CoFe-rich
layer it is also generating an increase of the Gilbert damping for the
ultrathin films beyond the spin-pumping effect. Our results illustrate that the
strong PMA is not an intrinsic property of the Heusler/MgO interface but it is
actively influenced by the interdiffusion, which can be tuned by a proper
choice of the underlayer material, as we show for the case of the Pt, Ta and Cr
underlayers.",1910.13107v1
2009-01-12,Screening and Fabrication of Half-Heusler phases for thermoelectric applications,"Half-Heusler phases have gained recently much interest as thermoelectric
materials. Screening of possible systems was performed by ab-initio simulation
using VASP-software. The energy-versus-Volume (E(V)) curves were calculated and
calibrated. For TiCoSb, NbNiSn, FeMoSb the stability of Half-Heusler phase
against concurrent crystal structures like TiNiSi, ZrCoAl, ZrBeSi, FeSiV, ZrNiP
and Full Heusler was confirmed. However, the thermo-dynamical driving force as
calculated from the difference in lattice energies is less than 0.1eV/atom.
Hence, the fabrication of Half Heusler phases is a challenge and requires three
steps, surface activation of the raw material by ball milling, arc-melting of
pressed pellets and finally long-term annealing treatment in a vacuum furnace.
On doped TiCoSb specimens, Seebeck coefficients up to 0.1 mV/K, on NiNbSn 0.16
mV/K were measured, although the microstructure was not yet optimized.",0901.1491v3
2015-07-21,Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases,"Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of
transition-group d-metals and main-group p-elements. Here, we report the
realization of FSMAs in Heusler phases that completely consist of d metals. By
introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is
obtained and the martensitic transformation temperature is decreased
efficiently. Strong ferromagnetism is established by further doping Co atoms
into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the
magnetic-field-induced martensitic transformations, collective multifunctional
properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only
facilitate the formation of B2-type Heusler phases, but also establish strong
ferromagnetic coupling and offer the possibility to tune the martensitic
transformation.",1507.05907v1
2016-08-10,Equiatomic quaternary Heusler alloys: a material perspective for spintronic applications,"Half-metallic ferromagnetic (HMF) materials show high spin polarization and
are therefore interesting to researchers due to their possible applications in
spintronic devices. In these materials, while one spin sub band has a finite
density of states at the Fermi level, the other sub band has a gap. Because of
their high Curie temperature and tunable electronic structure, HMF Heusler
alloys have a special importance among the HMF materials. Full Heusler alloys
with the stoichiometric composition X2YZ (where X and Y are the transition
metals and Z is a sp element) have the cubic structure with four
interpenetrating fcc sublattices. When each of these four fcc sublattices is
occupied by different atoms, a quaternary Heusler structure with different
structural symmetry is obtained. Recently, these equiatomic quaternary Heusler
alloys (EQHAs) with 1:1:1:1 stoichiometry have attracted a lot of attention due
to their superior magnetic and transport properties.",1608.03088v1
2002-09-24,On Order-Disorder ($L2_1 \to B2^\prime$) Phase Transition in Ni$_{2+x}Mn_{1-x}$Ga Heusler Alloys,"Order-disorder phase transition in Ni$_{2+x}Mn_{1-x}$Ga Heusler alloys has
been studied. It was found that the $L2_1 \to B2^{\prime}$ phase transition in
Ni2+xMn1-xGa (x = 0.16 - 0.20) Heusler alloys is of second order and the
temperature of this transition decreases with Ni excess.",0209547v1
2011-03-30,The efficient spin injector scheme based on Heusler materials,"We present the rational design scheme intended to provide the stable high
spin-polarization at the interfaces of the magneto-resistive junctions by
fulfilling the criteria of structural and chemical compatibilities at the
interface. This can be realized by joining the semiconducting and half-metallic
Heusler materials with similar structures. The present first-principal
calculations verify that interface remains half-metallic if the nearest
interface layers effectively form a stable Heusler material with the properties
intermediate between the surrounding bulk parts. This leads to a simple rule
for selecting the proper combinations.",1103.5928v1
2015-01-16,A first-principle study on some quanternary Heusler alloys with 4d and 3d transition metal elements,"In this letter, we investigate the magnetic properties, electronic
structures, Slater-Pauling behaviours of some quanternary Heusler alloys with
4d and 3d transition metal elements. The energy levels of the minority-spin
electronic band structures for all our calculated alloys are discussed. We have
summaried 21 quanternary Heusler alloys. Our calculations indicate that the
half metals ZrCoCrSi, ZrCoCrIn, ZrCoFeSi, ZrFeVAl, ZrFeVGa and NbFeCrAl have
large spin-flip gaps.",1501.03871v1
2017-03-24,Probing the degree of spin polarization of a ferromagnet with ferromagnet/superconductor proximity effect,"Superconductor/ferromagnet proximity effect has been studied for
Pb/Co$_2$Cr$_{1-x}$Fe$_x$Al bilayers. Different substrate temperatures allowed
us to prepare the Heusler alloy Co$_2$Cr$_{1-x}$Fe$_x$Al films with different
degree of spin polarization of conduction band of the Heusler layer. We obtain
a strong correlation between the dependence of the superconducting transition
temperature on the Pb-layer thickness at fixed thickness of the Heusler layer
and the degree of spin polarization in the ferromagnetic layer.",1703.08422v1
2012-02-17,Insights into ultrafast demagnetization in pseudo-gap half metals,"Interest in femtosecond demagnetization experiments was sparked by Bigot's
discovery in 1995. These experiments unveil the elementary mechanisms coupling
the electrons' temperature to their spin order. Even though first quantitative
models describing ultrafast demagnetization have just been published within the
past year, new calculations also suggest alternative mechanisms.
Simultaneously, the application of fast demagnetization experiments has been
demonstrated to provide key insight into technologically important systems such
as high spin polarization metals, and consequently there is broad interest in
further understanding the physics of these phenomena. To gain new and relevant
insights, we perform ultrafast optical pump-probe experiments to characterize
the demagnetization processes of highly spin-polarized magnetic thin films on a
femtosecond time scale. Previous studies have suggested shifting the Fermi
energy into the center of the gap by tuning the number of electrons and thereby
to study its influence on spin-flip processes. Here we show that choosing
isoelectronic Heusler compounds (Co2MnSi, Co2MnGe and Co2FeAl) allows us to
vary the degree of spin polarization between 60% and 86%. We explain this
behavior by considering the robustness of the gap against structural disorder.
Moreover, we observe that Co-Fe-based pseudo gap materials, such as partially
ordered Co-Fe-Ge alloys and also the well-known Co-Fe-B alloys, can reach
similar values of the spin polarization. By using the unique features of these
metals we vary the number of possible spin-flip channels, which allows us to
pinpoint and control the half metals electronic structure and its influence
onto the elementary mechanisms of ultrafast demagnetization.",1202.3874v1
2015-10-12,Room-temperature spin-orbit torque in NiMnSb,"Materials that crystalize in diamond-related lattices, with Si and GaAs as
their prime examples, are at the foundation of modern electronics.
Simultaneoulsy, the two atomic sites in the unit cell of these crystals form
inversion partners which gives rise to relativistic non-equilibrium spin
phenomena highly relevant for magnetic memories and other spintronic devices.
When the inversion-partner sites are occupied by the same atomic species,
electrical current can generate local spin polarization with the same magnitude
and opposite sign on the two inversion-partner sites. In CuMnAs, which shares
this specific crystal symmetry of the Si lattice, the effect led to the
demonstration of electrical switching in an antiferromagnetic memory at room
temperature. When the inversion-partner sites are occupied by different atoms,
a non-zero global spin-polarization is generated by the applied current which
can switch a ferromagnet, as reported at low temperatures in the diluted
magnetic semiconductor (Ga,Mn)As. Here we demonstrate the effect of the global
current-induced spin polarization in a counterpart crystal-symmetry material
NiMnSb which is a member of the broad family of magnetic Heusler compounds. It
is an ordered high-temperature ferromagnetic metal whose other favorable
characteristics include high spin-polarization and low damping of magnetization
dynamics. Our experiments are performed on strained single-crystal epilayers of
NiMnSb grown on InGaAs. By performing all-electrical ferromagnetic resonance
measurements in microbars patterned along different crystal axes we detect
room-temperature spin-orbit torques generated by effective fields of the
Dresselhaus symmetry. The measured magnitude and symmetry of the
current-induced torques are consistent with our relativistic density-functional
theory calculations.",1510.03356v1
2016-11-14,"Phase diagram of electronic systems with quadratic Fermi nodes in $2<d<4$: $2+ε$ expansion, $4-ε$ expansion, and functional renormalization group","Several materials in the regime of strong spin-orbit interaction such as
HgTe, the pyrochlore iridate Pr$_2$Ir$_2$O$_7$, and the half-Heusler compound
LaPtBi, as well as various systems related to these three prototype materials,
are believed to host a quadratic band touching point at the Fermi level.
Recently, it has been proposed that such a three-dimensional gapless state is
unstable to a Mott-insulating ground state at low temperatures when the number
of band touching points $N$ at the Fermi level is smaller than a certain
critical number $N_c$. We further substantiate and quantify this scenario by
various approaches. Using $\epsilon$ expansion near two spatial dimensions, we
show that $N_c = 64/(25 \epsilon^2) + O(1/\epsilon)$ and demonstrate that the
instability for $N < N_c$ is towards a nematic ground state that can be
understood as if the system were under (dynamically generated) uniaxial strain.
We also propose a truncation of the functional renormalization group equations
in the dynamical bosonization scheme which we show to agree to one-loop order
with the results from $\epsilon$ expansion both near two as well as near four
dimensions, and which smoothly interpolates between these two perturbatively
accessible limits for general $2<d<4$. Directly in $d=3$ we therewith find $N_c
= 1.86$, and thus again above the physical $N=1$. All these results are
consistent with the prediction that the interacting ground state of pure,
unstrained HgTe, and possibly also Pr$_2$Ir$_2$O$_7$, is a strong topological
insulator with a dynamically-generated gap -- a topological Mott insulator.",1611.04594v2
2017-07-12,Superconductivity in three-dimensional spin-orbit coupled semimetals,"Motivated by the experimental detection of superconductivity in the
low-carrier density half-Heusler compound YPtBi, we study the pairing
instabilities of three-dimensional strongly spin-orbit coupled semimetals with
a quadratic band touching point. In these semimetals the electronic structure
at the Fermi energy is described by spin j=3/2 quasiparticles, which are
fundamentally different from those in ordinary metals with spin j=1/2. We
develop a general approach to analyzing pairing instabilities in j=3/2
materials by decomposing the pair scattering interaction into irreducible
channels, projecting them to the Fermi surface and deriving the corresponding
Eliashberg theory. Applying our method to a generic density-density interaction
in YPtBi we establish the following results: (i) The pairing strength in each
channel uniquely encodes the j=3/2 nature of the Fermi surface band
structure--a manifestation of the fundamental difference with ordinary metals.
In particular, this implies that Anderson's theorem, which addresses the effect
of spin-orbit coupling and disorder on pairing states of spin-1/2 electrons,
cannot be applied in this case. (ii) The leading pairing instabilities are
different for electron and hole doping. This implies that superconductivity
depends on carrier type. (iii) In the case of hole doping--relevant to YPtBi,
we find two odd-parity channels in close competition with s-wave pairing. One
of these two channels is a multicomponent pairing channel, allowing for the
possibility of time-reversal symmetry breaking. (iv) In the case of Coulomb
interactions mediated by the long-ranged electric polarization of optical
phonon modes, a significant coupling strength is generated in spite of the
extremely low density of carriers. Furthermore, non-linear response and Fermi
liquid corrections can favor non-s-wave pairing and potentially account for the
experimentally-observed Tc.",1707.03831v2
2018-01-06,Development of half metallicity within mixed magnetic phase of Cu$_{1-x}$Co$_x$MnSb alloy,"Cubic Half-Heusler Cu$_{1-x}$Co$_x$MnSb (0 $\leq$ $x$ $\leq$ 0.1) compounds
have been investigated both experimentally and theoretically for their
magnetic, transport and electronic properties in search of possible half
metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest
as the end member alloys CuMnSb and CoMnSb are semi metallic (SM)
antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM),
respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in
the carrier concentration at the Fermi level that may lead to half-metallic
ground state but there remains a persistent controversy whether the AFM to FM
transition occurs simultaneously. Our experimental results reveal that the AFM
to FM magnetic transition occurs through a percolation mechanism where
Co-substitution gradually suppresses the AFM phase and forces FM polarization
around every dopant cobalt. As a result a mixed magnetic phase is realized
within this composition range while a nearly HM band structure is developed
already at the 10% Co-doping. Absence of T$^2$ dependence in the resistivity
variation at low T-region serves as an indirect proof of opening up an energy
gap at the Fermi surface in one of the spin channels. This is further
corroborated by the ab-initio electronic structure calculations that suggests a
nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes
produced upon Co doping.",1801.02035v1
2020-09-02,New highly-anisotropic Rh-based Heusler compound for magnetic recording,"The development of high-density magnetic recording media is limited by the
superparamagnetism in very small ferromagnetic crystals. Hard magnetic
materials with strong perpendicular anisotropy offer stability and high
recording density. To overcome the difficulty of writing media with a large
coercivity, heat assisted magnetic recording (HAMR) has been developed, rapidly
heating the media to the Curie temperature Tc before writing, followed by rapid
cooling. Requirements are a suitable Tc, coupled with anisotropic thermal
conductivity and hard magnetic properties. Here we introduce Rh2CoSb as a new
hard magnet with potential for thin film magnetic recording. A
magnetocrystalline anisotropy of 3.6 MJm-3 is combined with a saturation
magnetization of {\mu}0Ms = 0.52 T at 2 K (2.2 MJm-3 and 0.44 T at
room-temperature). The magnetic hardness parameter of 3.7 at room temperature
is the highest observed for any rare-earth free hard magnet. The anisotropy is
related to an unquenched orbital moment of 0.42 {\mu}B on Co, which is
hybridized with neighbouring Rh atoms with a large spin-orbit interaction.
Moreover, the pronounced temperature-dependence of the anisotropy that follows
from its Tc of 450 K, together with a high thermal conductivity of 20 Wm-1K-1,
makes Rh2CoSb a candidate for development for heat assisted writing with a
recording density in excess of 10 Tb/in2.",2009.01034v1
2021-11-04,Influence of microstructure on the application of Ni-Mn-In Heusler compounds for multicaloric cooling using magnetic field and uniaxial stress,"Novel multicaloric cooling utilizing the giant caloric response of
Ni-Mn-based metamagnetic shape-memory alloys to different external stimuli such
as magnetic field, uniaxial stress and hydrostatic pressure is a promising
candidate for energy-efficient and environmentally-friendly refrigeration.
However, the role of microstructure when several external fields are applied
simultaneously or sequentially has been scarcely discussed in literature. Here,
we synthesized ternary Ni-Mn-In alloys by suction casting and arc melting and
analyzed the microstructural influence on the response to magnetic fields and
uniaxial stress. By combining SEM-EBSD and stress-strain data, a significant
effect of texture on the stress-induced martensitic transformation is revealed.
It is shown that a <001> texture can strongly reduce the critical
transformation stresses. The effect of grain size on the material failure is
demonstrated and its influence on the magnetic-field-induced transformation
dynamics is investigated. Temperature-stress and temperature-magnetic field
phase diagrams are established and single caloric performances are
characterized in terms of ${\Delta}{s_T}$ and ${\Delta}{T_{ad}}$. The cyclic
${\Delta}{T_{ad}}$ values are compared to the ones achieved in the multicaloric
exploiting-hysteresis cycle. It turns out that a suction-cast microstructure
and the combination of both stimuli enables outstanding caloric effects in
moderate external fields which can significantly exceed the single caloric
performances. In particular for Ni-Mn-In, the maximum cyclic effect in magnetic
fields of 1.9 T is increased by more than 200 % to -4.1 K when a moderate
sequential stress of 55 MPa is applied. Our results illustrate the crucial role
of microstructure for multicaloric cooling using Ni-Mn-based metamagnetic
shape-memory alloys.",2111.03092v2
2022-07-12,First-principles study of optoelectronic and thermoelectronic properties of the ScAgC half-Heusler compound,"This work presents a theoretical study regarding photovoltaic (PV) &
thermoelectric (TE) applications of ScAgC. The electronic, optical and
thermoelectric properties are investigated using DFT and semi-classical
Boltzmann transport theory. DFT calculates a direct band-gap of $\sim$$0.47$
eV, while $G_{0}W_{0}$ method estimates a band-gap of $\sim1.01$ eV. We used
parabola fitting to estimate effective mass ($m^{*}$) values for bands B1-B4 at
$\Gamma$-point, which are $\sim$ -0.087 (-0.075), $\sim$ -0.17 (-0.27), $\sim$
-0.17 (-0.27), and $\sim$ 0.049 (0.058) along the $\Gamma-X$ ($\Gamma-L$)
direction, respectively. We also examine phonon dispersion and thermal
properties. Furthermore, optoelectronics' properties are calculated within the
energy range of 0 to 10 eV. The optical conductivity $\sigma (\omega)$,
refractive index $\tilde{n}(\omega)$, and dielectric function $\epsilon
(\omega)$ show strong optical transitions in the visible region. The lowest
calculated value of reflectivity r($\omega$) is $\sim$0.24 at $\sim$4.7 eV, and
the highest calculated value of absorption coefficient $\alpha (\omega )$ is
$\sim1.7\times 10^{6} cm^{-1}$ at $\sim$ 8.5 eV. At 300 K, we expect a maximum
solar efficiency (SLME) of $\sim$33% at $\sim$1 $\mu m$. The lattice thermal
conductivity $\kappa_{ph}$ shows maximum value of $\sim$3.8 W$m^{-1}K^{-1}$ at
1200 K. At 1200 K, for electron doping of $\sim$3.9$\times$$10^{21}$$cm^{-3}$,
the maximum value of $S^{2}\sigma /\tau$ is $\sim$145 $\times 10^{14}$ $\mu
WK^{-2}cm^{-1}s^{-1}$, while for hole doping of
$\sim$1.5$\times$$10^{21}$$cm^{-3}$, it is $\sim$123 $\times 10^{14}$ $\mu
WK^{-2}cm^{-1}s^{-1}$. The highest $ZT$ at 1200 K is expected to be $\sim$0.53,
whereas the optimal \%efficiency is predicted as $\sim$8.5% for cold (hot)
temperatures of 300 (1200) K. The results suggest that ScAgC can be a potential
candidate for solar cell and TE applications.",2207.05661v2
2022-09-30,Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl,"Half-metallic ferromagnets (HMF) are on one of the most promising materials
in the field of spintronics due to their unique band structure consisting of
one spin sub-band having metallic characteristics along with another sub-band
with semiconductor-like behavior. In this work, we report the synthesis of a
novel quaternary Heusler alloy FeMnVAl and have studied the structural,
magnetic, transport, and electronic properties complemented with
first-principles calculations. Among different possible structurally ordered
arrangements, the optimal structure is identified by theoretical energy
minimization. The corresponding spin-polarized band structure calculations
indicates the presence of a half-metallic ferromagnetic ground state. A
detailed and careful investigation of the x-ray diffraction data, M\""{o}ssbauer
and nuclear magnetic resonance spectra suggest the presence of site-disorder
between the Fe and Mn atoms in the stable ordered structure of the system. The
magnetic susceptibility measurement clearly establishes a ferromagnetic-like
transition below $\sim$213 K. The ${^{57}}$Fe M\""{o}ssbauer spectrometry
measurements suggest only the Mn-spins could be responsible for the magnetic
order, which is consistent with our theoretical calculation. Surprisingly, the
density-functional-theory calculations reveal that the spin-polarization value
is almost immunized (92.4\% ${\rightarrow}$ 90.4\%) from the Mn-Fe structural
disorder, even when nonmagnetic Fe and moment carrying Mn sites are entangled
inseparably. Robustness of spin polarization and half metallicity in the
studied FeMnVAl compound comprising structural disorder is thus quite
interesting and could provide a new direction to investigate and understand the
exact role of disorders on spin polarization in these class of materials, over
the available knowledge.",2209.15243v1
2022-10-09,High-performance non-Fermi-liquid metallic thermoelectric materials,"Searching for high-performance thermoelectric (TE) materials in the paradigm
of narrow-bandgap semiconductors has lasted for nearly 70 years and is
obviously hampered by a bottleneck of research now. Here we report on the
discovery of a few metallic compounds, TiFexCu2x-1Sb and TiFe1.33Sb, showing
the thermopower exceeding many TE semiconductors and the dimensionless figure
of merits comparable with the state-of-the-art TE materials. A quasi-linear
temperature (T) dependence of electrical resistivity in 2 K - 700 K and the
logarithmic T-dependent electronic specific heat at low temperature are also
observed to coexist with the high thermopower, highlighting the strong
intercoupling of the non-Fermi-liquid (NFL) quantum critical behavior of
electrons with TE transports. Electronic structure analysis reveals the
existence of fluctuating Fe-eg-related local magnetic moments, Fe-Fe
antiferromagnetic (AFM) interaction at the nearest 4c-4d sites, and two-fold
degenerate eg orbitals antiferromagnetically coupled with the dual-type
itinerant electrons close to the Fermi level, all of which infer to a
competition between the AFM ordering and Kondo-like spin compensation as well
as a parallel two-channel Kondo effect. These effects are both strongly
meditated by the structural disorder due to the random filling of Fe/Cu at the
equivalent 4c/4d sites of the Heusler crystal lattice. The magnetic
susceptibility deviates from ideal antiferromagnetism but can be fitted well by
x(T) = 1/({\theta} + BT{\alpha}), seemingly being consistent with the quantum
critical scenario of strong local correlation as discussed before. Our work not
only breaks the dilemma that the promising TE materials should be heavily-doped
semiconductors, but also demonstrates the correlation among high TE
performance, NFL quantum criticality, and magnetic fluctuation, which opens up
new directions for future research.",2210.04201v1
2023-01-03,Surprisingly large anomalous Hall effect and giant negative magnetoresistance in half-topological semimetals,"Large intrinsic anomalous Hall effect (AHE) due to the Berry curvature in
magnetic topological semimetals is attracting enormous interest due to its
fundamental importance and technological relevance. Mechanisms resulting in
large intrinsic AHE include diverging Berry curvature in Weyl semimetals,
anticrossing nodal rings or points of non-trivial bands, and noncollinear spin
structures. Here we show that a half-topological semimetal (HTS) state near a
topological critical point can provide a new mechanism for driving an
exceptionally large AHE. We reveal this through a systematic experimental and
theoretical study of the antiferromagnetic (AFM) half-Heusler compound TbPdBi.
We not only observed an unusual AHE with a surprisingly large anomalous Hall
angle {\Theta}H (tan {\Theta}H ~ 2, the largest among the antiferromagnets) in
its field-driven ferromagnetic (FM) phase, but also found a distinct Hall
resistivity peak in the canted AFM phase within a low field range, where its
isothermal magnetization is nearly linearly dependent on the field. Moreover,
we observed a nearly isotropic, giant negative magnetoresistance with a
magnitude of ~98%. Our in-depth theoretical modelling demonstrates that these
exotic transport properties originate from the HTS state. A minimal Berry
curvature cancellation between the trivial spin-up and nontrivial spin-down
bands results not only in an extremely large AHE, but it also enhances the spin
polarization of the spin-down bands substantially and thus leads to a giant
negative magnetoresistance. Our study advances the understanding of the
interplay between band topology and magnetism and offers new clues for
materials design for spintronics and other applications.",2301.01074v1
2020-10-09,Structural and magnetic properties of epitaxial films of CoIrMnAl equiatomic quaternary Heusler alloy designed from first-principles calculation,"MgO-barrier magnetic tunnel junctions with half-metallic Heusler alloy
electrodes attracted much attentions for spintronics applications. However, a
couples of issues related to materials still remain to be resolved for
practical uses. Recently, quarterly equiatomic Heusler alloys attracted
attentions as advanced Heusler alloys. CoIrMnZ (Z = Al, Si, Ga, and Ge)
half-metallic Heusler alloys were designed and predicted to have moderate Curie
temperatures and to be a lattice-matched with the MgO barrier, being
advantageous to traditional Co2 Heusler alloys [T. Roy et al., J. Magn. Magn.
Mater. 498, 166092 (2020)]. Here we experimentally investigated structure and
magnetic properties for thin films of one of those alloys, CoIrMnAl with a
sputtering deposition. We successfully obtained the films with the B2 chemical
ordering even with no post-annealing process. The lattice constant for the
films annealed at 500-600$^\circ$C approximates the predicted values. The
magnetization at 10 K was near 500 kA/m and the Curie temperature was
approximately 400 K were observed, which were about 70% of the values predicted
for the fully ordered structure. The magnetic properties observed in those B2
ordered films were well explained by ferrimagnetism appeared in B2 ordered
CoIrMnAl with full-swap disorders of Co-Ir and Mn-Al and almost full-swap
disorder of Co-Mn, predicted from the first-principles calculations.",2010.04369v1
2021-02-22,High T$_C$ ferromagnetic inverse Heusler alloys: A comparative study of Fe$_2$RhSi and Fe$_2$RhGe,"We report the results of experimental investigations on structural, magnetic,
resistivity, caloric properties of Fe$_2$RhZ (Z=Si,Ge) along with
\textit{ab-initio} band structure calculations using first principle
simulations. Both these alloys are found to crystallize in inverse Heusler
structure but with disorder in tetrahedral sites between Fe and Rh. Fe$_2$RhSi
has saturation moment of 5.00 $\mu_B$ and while its counterpart has 5.19
$\mu_B$. Resistivity measurement reveals metallic nature in both of them.
Theoretical simulations using generalized gradient approximation(GGA) predict
inverse Heusler structure with ferromagnetic ordering as ground state for both
the alloys. However it underestimates the experimentally observed moments.
GGA+$U$ approach, with Hubbard $U$ values estimated from density functional
perturbation theory helps to improve the comparison of the experimental
results. Fe$_2$RhSi is found to be half metallic ferromagnet while Fe$_2$RhGe
is not. Varying $U$ values on Fe and Rh sites does not change the net moment
much in Fe$_2$RhSi, unlike in Fe$_2$RhGe. Relatively small exchange splitting
of orbitals in Fe$_2$RhGe compared to that of Fe$_2$RhSi is the reason for not
opening the band gap in the minority spin channel in the former. High ordering
temperature and moment make Fe$_2$RhSi useful for spintronics applications.",2102.10967v1
2004-07-21,Orbital magnetism in the half-metallic Heusler alloys,"Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study
the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are
almost completely quenched and they are negligible with respect to the spin
moments. The change in the atomic-resolved orbital moments can be easily
explained in terms of the spin-orbit strength and hybridization effects.
Finally I discuss the orbital and spin moments derived from X-ray magnetic
circular dichroism experiments.",0407560v1
1996-07-01,On the Uniqueness of the Papapetrou--Majumdar Metric,"We establish the equality of the ADM mass and the total electric charge for
asymptotically flat, static electrovac black hole spacetimes with completely
degenerate, not necessarily connected horizon.",9607001v1
2013-01-03,Enhanced thermoelectric performance in TiNiSn-based half-Heuslers,"Thermoelectric figures of merit, ZT > 0.5, have been obtained in arc-melted
TiNiSn-based ingots. This promising conversion efficiency is due to a low
lattice thermal conductivity, which is attributed to excess nickel in the
half-Heusler structure.",1301.0419v1
2014-09-23,The shifts X-Ray Mn Kα and 2p spectra of Mn-Heusler alloys,"X-ray emission K{\alpha}1,2 spectra of Mn in Heusler alloys Co2MnMe (Me = Al,
Ga, Sb), Ni2MnIn, Cu2MnAl were studied. Shifts of Mn K{\alpha}1,2 lines
relatively pure Mn in high-energy region and low-energy shifts of binding
energy Mn 2p XPS is detected. X-ray emission and XPS shifts are in qualitative
agreement.",1409.6375v1
2014-10-08,Direct Measurement of Magnetocaloric Effect in Metamagnetic Ni43Mn37.9In12.1Co7 Heusler Alloy,"The magnetocaloric effect in the metamagnetic Ni43Mn37.9In12.1Co7 Heusler
alloy is directly studied experimentally under the adiabatic and
quasi-isothermal conditions in a magnetic field with induction of up to 14 T.",1410.2139v1
2023-02-13,"Structural, magnetic and elastic properties on stoichometric $Ni-Mn-Cu$ Heusler alloys","Heusler alloys with $Ni-Mn-Cu$ (all d-transition metal) composition have been
studied; equilibrium structures for different magnetic configurations are
found. Elastic constants and tetragonal distortion are analyzed. Distortion
effect on densities of electronic state peaks are characterized. For this
ternary family of alloys, we find that the one with the most interesting
properties and mechanical stability is $Ni_2MnCu$.",2302.06472v2
2009-08-09,Synthetic antiferromagnet with Heusler alloy Co2FeAl ferromagnetic layers,"Heusler alloy Co2FeAl was employed as ferromagnetic layers in
Co2FeAl/Ru/Co2FeAl synthetic antiferromagnet structures. The experimental
results show that the structure with a Ru thickness of 0.45 nm takes on
strongly antiferromagnetic coupling, which maintains up to 150 oC annealing for
1 hour. The structure has a very low saturation magnetization Ms of 425 emu/cc,
a low switching field Hsw of 4.3 Oe and a high saturation field Hs of 5257 Oe
at room temperature, which are favorable for application in ultrahigh density
magnetic read heads or other magnetic memory devices. XRD study testifies that
the as-deposited Co2FeAl film is in B2 phase. Therefore Heusler alloys can be
used to fabricate SyAF and it is possible to make ""all-Heusler"" spin-valves or
magnetic tunneling junctions with better magnetic switching properties and high
magnetoresistance.",0908.1215v1
2010-02-08,Quantitative analysis of atomic disorders in full-Heusler Co2FeSi alloy thin films using x-ray diffraction with Co-Ka and Cu-Ka sources,"The authors developed a new analysis technique for atomic disorder structures
in full-Heusler alloys using x-ray diffraction (XRD) with Co-Ka and Cu-Ka
sources. The developed technique can quantitatively evaluate all the atomic
disorders for the exchanges between X, Y, and Z atoms in full-Heusler X2YZ
alloys. In particular, the technique can treat the DO3 disorder that cannot be
analyzed by ordinary Cu-Ka XRD. By applying this technique to full-Heusler
Co2FeSi alloy thin films formed by rapid thermal annealing (RTA),
RTA-temperature (TA) dependence of the atomic disorders was revealed. The site
occupancies of Co, Fe, and Si atoms on their original sites were 98 %, 90 %,
and 93 %, respectively, for the film formed at TA = 800 degree C, indicating
that the RTA-formed Co2FeSi film had the L21 structure with the extremely high
degree of ordering.",1002.1564v1
2013-11-08,"Electronic, magnetic and transport properties of full and half-metallic thin film Heusler alloys","The electronic and magnetic bulk properties of half-metallic Heusler alloys
such as Co$_{2}$FeSi, Co$_{2}$FeAl, Co$_{2}$MnSi and Co$_{2}$MnAl are
investigated by means of {\em ab initio} calculations in combination with Monte
Carlo simulations. The electronic structure is analyzed using the plane wave
code Quantum Espresso and magnetic exchange interactions are determined using
the KKR method. From the magnetic exchange interactions the Curie temperature
is obtained via Monte Carlo simulations. In addition, electronic transport
properties of the trilayer systems consisting of two semi-infinite platinum
leads and a Heusler layer in between are obtained from the fully relativistic
KKR method by employing the Kubo-Greenwood formalism. The focus is on
thermoelectric properties, namely the Seebeck effect and its spin dependence.
It turns out that already thin Heusler layers provide highly polarized currents
within the systems. This is attributed to the recovery of half-metallicity with
increasing thickness. The absence of electronic states of the spin down
electrons around the Fermi level suppresses the contribution of this spin
channel to the total conductivity. This strongly influences the thermoelectric
properties of such systems and results in polarized thermoelectric currents.",1311.1950v1
2014-04-17,Large Noncollinearity and Spin Reorientation in the Novel Mn2RhSn Heusler Magnet,"Noncollinear magnets provide essential ingredients for the next generation
memory technology. It is a new prospect for the Heusler materials, already well
known due to the diverse range of other fundamental characteristics. Here, we
present a combined experimental and theoretical study of novel noncollinear
tetragonal Mn2RhSn Heusler material exhibiting unusually strong canting of its
magnetic sublattices. It undergoes a spin-reorientation transition, induced by
a temperature change and suppressed by an external magnetic field. Because of
the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn2RhSn
is suggested to be a promising candidate for realizing the Skyrmion state in
the Heusler family.",1404.4581v2
2015-03-10,Vanadium sacrificial layers as a novel approach for the fabrication of freestanding Heusler Shape Memory Alloys,"In this study we report a method for the preparation of freestanding
magnetocaloric thin films. Non-stoichiometric Heusler alloys Ni-Mn-Sn,
Ni-Co-Mn-Sn and Ni-Co-Mn-Al are prepared via sputter deposition. A sacrificial
vanadium layer is added between the substrate and the Heusler film. By means of
selective wet-chemical etching the vanadium layer can be removed. Conditions
for the crystallization of Vanadium layers and epitaxial growth of the Heusler
films are indicated. Magnetic and structural properties of freestanding and
as-prepared films are compared in detail. The main focus of this study is on
the influence of substrate constraints on the Martensitic transistion.",1503.02987v1
2015-05-28,"Uncovering High Thermoelectric Figure of Merit in (Hf,Zr)NiSn Half-Heusler Alloys","Half-Heusler alloys (MgAgSb structure) are promising thermoelectric
materials. RNiSn half-Heusler phases (R=Hf, Zr, Ti) are the most studied in
view of their thermal stability. The highest dimensionless figure of merit (ZT)
obtained is ~1 in the temperature range ~450-900oC, primarily achieved in
nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a
previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an
appreciable increase in the power factor, decrease in charge carrier density,
and increase in carrier mobility. The findings are attributed to the
improvement of structural order. Present approach may be applied to optimize
the functional properties of Heusler-type alloys.",1505.07773v2
2017-11-01,Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering,"We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature",1711.00406v1
2018-06-13,Minimizing hysteresis in martensite phase transforming magnetocaloric Heusler alloys,"The large magnetocaloric effect in Heusler alloys showing martensite phase
transformation puts them forward as efficient materials for magnetic
refrigeration. However, irreversibility of the magnetocaloric cooling cycle is
a major challenge for real applications. This irreversibility is directly
linked to the thermal hysteresis at the first-order martensite phase
transition. Therefore, minimizing the hysteresis is essential in order to
achieve reversibility. Here we show a large reduction in the thermal hysteresis
at the martensite transition in the Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and
Ni$_{1.8}$Co$_{0.2}$Mn$_{1.4}$In$_{0.6}$ Heusler alloys upon the application of
hydrostatic pressure. Our pressure dependent X-ray diffraction study on
Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ reveals that with increasing pressure the lattice
parameters of the two crystallographic phases (austenite and martensite) change
in such a way that they increasingly satisfy the geometric compatibility
(co-factor) condition. These results provide an opportunity to overcome the
hysteresis problem and hence the irreversible behavior in Heusler materials
using pressure as an external parameter.",1806.05075v1
2018-09-04,Increasing the performance of the superconducting spin valve using a Heusler alloy,"We have studied superconducting properties of the spin-valve thin layer
heterostructures CoO$_x$/F1/Cu/F2/Cu/Pb where the ferromagnetic F1 layer was
standardly made of Permalloy whereas for the F2 layer we have taken a specially
prepared film of the Heusler alloy Co$_2$Cr$_{1-x}$Fe$_x$Al with a small degree
of spin polarization of the conduction band. The heterostructures demonstrate a
significant superconducting spin-valve effect, i.e. a complete switching on and
off of the superconducting current flowing through the system by manipulating
the mutual orientations of the magnetization of the F1 and F2 layers. The
magnitude of the effect is doubled in comparison with the previously studied
analogous multilayers with the F2 layer made of the strong ferromagnet Fe.
Theoretical analysis shows that a drastic enhancement of the switching effect
is due to a smaller exchange field in the heterostructure coming from the
Heusler film as compared to Fe. This enables to approach almost ideal
theoretical magnitude of the switching in the Heusler-based multilayer with the
F2 layer thickness of $\sim 1$\,nm.",1809.00876v1
2018-12-14,Formation of two-dimensional electron and hole gases at the interface of half-Heusler semiconductors,"Heuslers are a prominent family of multi-functional materials that includes
semiconductors, half metals, topological semimetals, and magnetic
superconductors. Owing to their same crystalline structure, yet quite different
electronic properties and flexibility in chemical composition, Heusler-based
heterostructures can be designed to show intriguing properties at the
interface. Using electronic structure calculations, we show that two
dimensional electron or hole gases (2DEG or 2DHG) form at the interface of
half-Heusler (HH) semiconductors without any chemical doping. We use
CoTiSb/NiTiSn as an example, and show that the 2DEG at the TiSb/Ni(001)
termination and the 2DHG at the Co/TiSn(001) termination are intrinsic to the
interface, and hold rather high charge densities of 3x10^14 carriers/cm^2.
These excess charge carriers are tightly bound to the interface plane and are
fully accommodated in transition-metal d sub-bands. The formation of 2DEG and
2DHG are not specific to the CoTiSb/NiTiSn system; a list of combinations of HH
semiconductors that are predicted to form 2DEG or 2DHG is provided based on
band alignment, interface termination, and lattice mismatch.",1812.05991v1
2020-04-02,Reversible adiabatic temperature change in the shape memory Heusler alloy Ni2.2Mn0.8Ga: An effect of structural compatibility,"The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory
Heusler alloys put them forward to use in magnetic refrigeration technology. It
is associated with a first-order magnetostructural (martensitic) phase
transition. We conducted a comprehensive study of the MCE for the
off-stoichiometric Heusler alloy Ni$_{2.2}$Mn$_{0.8}$Ga in the vicinity of its
first-order magnetostructural phase transition. We found a reversible MCE under
repeated magnetic field cycles. The reversible behavior can be attributed to
the small thermal hysteresis of the martensitic phase transition. Based on the
analysis of our detailed temperature dependent X-ray diffraction data, we
demonstrate the geometric compatibility of the cubic austenite and tetragonal
martensite phases. This finding directly relates the reversible MCE behavior to
an improved geometric compatibility condition between cubic austenite and
tetragonal martensite phases. The approach will help to design shape-memory
Heusler alloys with a large reversible MCE taking advantage of the first-order
martensitic phase transition.",2004.00949v1
2020-05-07,Structural and magnetic behavior of Cr$_2$Co$_{(1-x)}$Cr$_x$Al inverse Heusler alloys,"We report the structural and magnetic behavior of single phase inverse
Heusler alloys Cr$_2$Co$_{(1-x)}$Cr$_x$Al ($x = $ 0, 0.2, 0.4) using x-ray
diffraction (XRD), Raman spectroscopy, isothermal magnetization, and magnetic
susceptibility measurements. Interestingly, the Rietveld refinement of XRD data
with the space group I$\bar{4}m2$ reveal a tetragonal distortion with c/a ratio
around 1.38 in these inverse Heusler structures. The bulk compositions have
been confirmed by energy dispersive x-ray spectroscopy measurements. The active
Raman mode F$_{2g}$ is observed at 320~cm$^{-1}$, which confirms the X-type
Heusler structure as the A2 and B2 type structures are known to be not Raman
active. The area of F$_{2g}$ mode decreases with Cr concentration, which
indicate the origin of this mode due to Co vibrations. The isothermal
magnetization data confirm the magnetic moment close to zero ($\le$0.02
$\mu_B/f.u.$) at $\approx$70~kOe and negligible coercive field suggest the
fully compensated ferrimagnetic nature of these samples. The susceptibility
behavior indicates irreversibility between zero-field and field-cooled curves
and complex magnetic interactions at low temperatures.",2005.03528v1
2016-12-19,How to enable bulk-like martensitic transformation in epitaxial films,"The present study is dedicated to the influence of different substrate and
buffer layer materials on the martensitic transformation in sputter deposited
epitaxial shape memory Heusler alloys. For this, the magnetocaloric Heusler
alloy Ni-Co-Mn-Al \cite{Teichert2015b} is grown on MgO(001),
MgAl$_{2}$O$_{4}$(001), and MgO(001)/V substrates, which exhibit a lattice
misfit to the Ni-Co-Mn-Al between $-1.2\%$ and $3.6\%$. By temperature
dependent X-ray diffraction measurements it is shown that the optimum buffer
layer for shape memory Heusler films is not one with minimum lattice misfit,
but one with minimum Young's modulus and moderate misfit because an elastic
buffer layer can deform during the martensitic transformation of the Heusler
layer. Furthermore, epitaxial strain caused by a moderate lattice misfit does
not significantly change the martensitic transformation temperatures.",1612.06077v1
2017-06-14,Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order,"Half-metallicity and low magnetic damping are perpetually sought for in
spintronics materials and full Heusler alloys in this respect provide
outstanding properties. However, it is challenging to obtain the well-ordered
half-metallic phase in as-deposited full Heusler alloys thin films and theory
has struggled to establish a fundamentals understanding of the temperature
dependent Gilbert damping in these systems. Here we present a study of the
temperature dependent Gilbert damping of differently ordered as-deposited
Co2FeAl full Heusler alloy thin films. The sum of inter- and intraband electron
scattering in conjunction with the finite electron lifetime in Bloch states
govern the Gilbert damping for the well-ordered phase in contrast to the
damping of partially-ordered and disordered phases which is governed by
interband electronic scattering alone. These results, especially the ultralow
room temperature intrinsic damping observed for the well-ordered phase provide
new fundamental insights to the physical origin of the Gilbert damping in full
Heusler alloy thin films.",1706.04670v2
2021-08-04,Theory of Huge Thermoelectric Effect Based on Magnon Drag Mechanism: Application to Thin-Film Heusler Alloy,"To understand the unexpectedly high thermoelectric performance observed in
the thin-film Heusler alloy Fe$_2$V$_{0.8}$W$_{0.2}$Al, we study the magnon
drag effect, generated by the tungsten based impurity band, as a possible
source of this enhancement, in analogy to the phonon drag observed in FeSb$_2$.
Assuming that the thin-film Heusler alloy has a conduction band integrating
with the impurity band, originated by the tungsten substitution, we derive the
electrical conductivity $L_{11}$ based on the self-consistent t-matrix
approximation and the thermoelectric conductivity $L_{12}$ due to magnon drag,
based on the linear response theory, and estimate the temperature dependent
electrical resistivity, Seebeck coefficient and power factor. Finally, we
compare the theoretical results with the experimental results of the thin-film
Heusler alloy to show that the origin of the exceptional thermoelectric
properties is likely to be due to the magnon drag related with the
tungsten-based impurity band.",2108.01880v1
2022-04-13,Influence of Co and Mn on Electronic and Magnetic properties of Ni2MnGa Heusler alloy,"The ferromagnetic Heusler alloy $Ni_2MnGa$ had been of major interest in the
past few years because of its magnetic properties which can be easily tuned.
The $Ni_2MnGa$ Heusler alloys are intermetallic alloy with $L2_1$ structure.
Here we report a detailed investigation of the effect of doping of Co and Mn in
Ni2MnGa. Magnetic properties and electronic structure of
$Ni_{2-x}Co_xMnGa_{1-y}Mn_y$ Heusler alloys have been studied by using Green's
function-based KKR-CPA method based DFT calculations. We will show the
magnetization can be tuned depending on the Co and Mn occumencies. We will also
discuss the critical temperature, magnetic interactions and magnetic stability
of the systems.",2204.06140v4
2023-06-25,"First-principles study of disordered half-Heusler alloys \textit{X}Fe$_{0.5}$Ni$_{0.5}$Sn (\textit{X} = Nb, Ta) as thermoelectric prospects","High lattice thermal conductivity in half-Heusler alloys has been the major
bottleneck in thermoelectric applications. Disordered half-Heusler alloys could
be a plausible alternative to this predicament. In this paper, utilizing
first-principles simulations, we have demonstrated the low lattice thermal
conductivity in two such phases, NbFe$_{0.5}$Ni$_{0.5}$Sn and
TaFe$_{0.5}$Ni$_{0.5}$Sn, in comparison to well-known half-Heusler alloy
TiCoSb. We trace the low thermal conductivity to their short phonon lifetime,
originating from the interaction among acoustic and low-lying optical phonons.
We recommend nanostructuring as an effective route in further diminishing the
lattice thermal conductivity. We further predict that these alloys can be best
used in the temperature range 400-600~K and carrier concentration of less than
10$^{21}$ carriers cm$^{-3}$. We found $\sim$35\% and $\sim$17\% enhancement in
$ZT$ for NbFe$_{0.5}$Ni$_{0.5}$Sn and TaFe$_{0.5}$Ni$_{0.5}$Sn, respectively,
as compared to TiCoSb. We are optimistic of the findings and believe these
materials would attract experimental investigations.",2306.14234v1
2021-11-09,"Effect of substitutional doping and disorder on the phase stability, magnetism, and half-metallicity of Heusler alloys","Spintronics is the fast growing field that will play a key role in optimizing
power consumption, memory, and processing capabilities of nanoelectronic
devices. Heusler alloys are potential candidates for application in spintronics
due to their room temperature (RT) half-metallicity, high Curie temperature,
low lattice mismatch with most substrates, and strong control on electronic
density of states at Fermi level. In this work, we investigate the effect of
{substitutional doping and disorder} on the half-metallicity, phase stability,
and magnetism of Heusler alloys using density functional theory methods. Our
study shows that electronic and magnetic properties of half/full-Heusler alloys
can be tuned by changing electron-count through controlled variation of
chemical compositions of alloying elements. We provide a detailed discussion on
the effect of substitutional doping and disorder on the tunability of
half-metallic nature of Co$_{2}$MnX and NiMnX based Heusler alloys, where X
represents group 13\textendash 16 and period 3\textendash 6 elements of the
periodic table. {Based on the idea of electron count and disorder, we predicted
a possible existence of thermodynamically stable half-metallic multicomponent
bismuthides, for example, (CuNi$_{3}$)Mn$_{4}$Bi$_{4}$ and
(ZnNi$_{7}$)Mn$_{8}$Bi$_{8}$, through substitution doping at Ni site by
specific Cu and Zn composition in half-Heusler NiMnBi.} We believe that the
design guide {based on electron-counts} presented for half-metals will play a
key role in electronic-structure engineering of novel Heusler alloys for
spintronic application, which will accelerate the development and synthesis of
novel materials.",2111.05179v1
2010-10-14,Pressure dependence of Curie temperature and resistivity in complex Heusler alloys,"Using first-principles electronic structure calculations, we have studied the
dependence of the Curie temperature on external hydrostatic pressure for random
Ni2MnSn Heusler alloys doped with Cu and Pd atoms, over the entire range of
dopant concentrations. The Curie temperatures are calculated by applying
random-phase approximation to the Heisenberg Hamiltonian whose parameters are
determined using the linear response and multiple scattering methods, based on
density-functional theory. In (Ni1-x,Pdx)2MnSn alloys, the Curie temperature is
found to increase with applied pressure over the whole concentration range. The
crossover from the increase to the decrease of the Curie temperature with
pressure takes place for Cu concentrations larger than about 70% in
(Ni1-x,Cux)2MnSn Heusler alloys. The results for the reference Ni2MnSn Heusler
alloy agree well with a previous theoretical study of E. Sasioglu, L. M.
Sandratskii and P. Bruno Phys. Rev. B 71 214412 (2005) and also reasonably well
with available experimental data. Results for the spin-disorder-induced part of
the resistivity in (Ni1-x,Pdx)2MnSn Heusler alloys, calculated by using the
disordered local moment model, are also presented. Finally, a qualitative
understanding of the results, based on Anderson's superexchange interaction and
Stearn's model of the indirect exchange interaction between localized and
itinerant d electrons, is provided.",1010.3025v2
2017-06-06,Designing magnetism in Fe-based Heusler alloys: a machine learning approach,"Combining material informatics and high-throughput electronic structure
calculations offers the possibility of a rapid characterization of complex
magnetic materials. Here we demonstrate that datasets of electronic properties
calculated at the ab initio level can be effectively used to identify and
understand physical trends in magnetic materials, thus opening new avenues for
accelerated materials discovery. Following a data-centric approach, we utilize
a database of Heusler alloys calculated at the density functional theory level
to identify the ideal ions neighbouring Fe in the $X_2$Fe$Z$ Heusler prototype.
The hybridization of Fe with the nearest neighbour $X$ ion is found to cause
redistribution of the on-site Fe charge and a net increase of its magnetic
moment proportional to the valence of $X$. Thus, late transition metals are
ideal Fe neighbours for producing high-moment Fe-based Heusler magnets. At the
same time a thermodynamic stability analysis is found to restrict $Z$ to main
group elements. Machine learning regressors, trained to predict magnetic moment
and volume of Heusler alloys, are used to determine the magnetization for all
materials belonging to the proposed prototype. We find that Co$_2$Fe$Z$ alloys,
and in particular Co$_2$FeSi, maximize the magnetization, which reaches values
up to 1.2T. This is in good agreement with both ab initio and experimental
data. Furthermore, we identify the Cu$_2$Fe$Z$ family to be a cost-effective
materials class, offering a magnetization of approximately 0.65T.",1706.01840v1
2019-05-20,Band alignment and scattering considerations for enhancing the thermoelectric power factor of complex materials: The case of Co-based half-Heuslers,"Half-Heuslers, an emerging thermoelectric material group, has complex
bandstructures with multiple bands that can be aligned through band engineering
approaches, giving us an opportunity to improve their power factor. In this
work, going beyond the constant relaxation time approximation, we perform an
investigation of the benefits of band alignment in improving the thermoelectric
power factor under different density of states dependent scattering scenarios.
As a test case we consider the Co-based p-type half-Heuslers TiCoSb, NbCoSn and
ZrCoSb. First, using simplified effective mass models combined with Boltzmann
transport, we investigate the conditions of band alignment that are beneficial
to the thermoelectric power factor under three different carrier scattering
scenarios: i) the usual constant relaxation time approximation, ii) intra-band
scattering restricted to the current valley with the scattering rates
proportional to the density of states as dictated by Fermi's Golden Rule, and
iii) both intra- and inter-band scattering across all available valleys, with
the rates determined by the total density of states at the relevant energies.
We demonstrate that the band-alignment outcome differs significantly depending
on the scattering details. Next, using the density functional theory calculated
bandstructures of the half-Heuslers we study their power factor behavior under
strain induced band alignment. We show that strain can improve the power factor
of half-Heuslers, but the outcome heavily depends on the curvatures of the
bands involved, the specifics of the carrier scattering mechanisms, and the
initial band separation. Importantly, we also demonstrate that band alignment
is not always beneficial to the power factor.",1905.07951v1
2002-03-07,Resonant x-ray emission spectra of Mn based Heusler alloys,"The Mn L_2,L_3 x-ray spectra of the Cu_2MnAl and Co_2MnZ (Z=Al,Ga, Sn, Sb)
Heusler alloys have been investigated by the Resonant X-ray Emission
Spectroscopy (RXES) using linearly polarized monochromatic synchrotron
radiation for. The interplay between the half-metallic character of the Mn 3d
electronic structure in connection with the local magnetic moment $\mu_{Mn}$
and Mn $2p\to 3d$ x-ray emission spectra is discussed.",0203169v1
2002-09-25,Magnetic properties of Ni2.18Mn0.82Ga Heusler alloys with a coupled magnetostructural transition,"Polycrystalline Ni2.18Mn0.82Ga Heusler alloys with a coupled
magnetostructural transition are studied by differential scanning calorimetry,
magnetic and resistivity measurements. Coupling of the magnetic and structural
subsystems results in unusual magnetic features of the alloy. These uncommon
magnetic properties of Ni2.18Mn0.82Ga are attributed to the first-order
structural transition from a tetragonal ferromagnetic to a cubic paramagnetic
phase.",0209574v1
2004-06-24,Electronic Structure and Magnetic Exchange Coupling in Ferromagnetic Full Heusler Alloys,"Density-functional studies of the electronic structures and exchange
interaction parameters have been performed for a series of ferromagnetic full
Heusler alloys of general formula Co$_2$MnZ (Z = Ga, Si, Ge, Sn), Rh$_2$MnZ (Z
= Ge, Sn, Pb), Ni$_2$MnSn, Cu$_2$MnSn and Pd$_2$MnSn, and the connection
between the electronic spectra and the magnetic interactions have been studied.
Different mechanisms contributing to the exchange coupling are revealed. The
band dependence of the exchange parameters, their dependence on volume and
valence electron concentration have been thoroughly analyzed within the Green
function technique.",0406588v1
2004-08-03,Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys,"Introductory chapter for the book ""Halfmetallic Alloys - Fundamentals and
Applications"" to be published in the series Springer Lecture Notes on Physics,
P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical
work on the half-metallic Heusler alloys.",0408068v1
2006-03-23,Inverted spin polarization of Heusler alloys for new spintronic devices,"A new magnetic logic overcomes the major limitations of field programmable
gate arrays while having a 50% smaller unit cell than conventional designs
utilizing magnetic tunnel junctions with one Heusler alloy electrode. These
show positive and negative TMR values at different bias voltages at room
temperature which generally adds an additional degree of freedom to all
spintronic devices.",0603616v1
2006-03-30,Effect of doping and disorder on the half-metallicity of full Heusler alloy,"Heusler alloys containing Co and Mn are amongst the most heavily studied
half-metallic ferromagnets for future applications in spintronics. Using
state-of-the-art electronic structure calculations, we investigate the effect
of doping and disorder on their electronic and magnetic properties. Small
degrees of doping by substituting Fe or Cr for Mn scarcely affect the
half-metallicity. A similar effect is also achieved by mixing the sublattices
occupied by the Mn and sp atoms. Thus the half-metallicity is a robust property
of these alloys.",0603811v1
2006-09-20,Towards a full Heusler alloy showing room temperature half-metallicity at the surface,"In this article we investigate the surface spin polarization in a 100 nm
Co2Cr0.6Fe0.4Al (CCFA) film grown ex situ epitaxially on MgO(100) with a 10 nm
Fe buffer layer by means of spin resolved photoemission. We show that a careful
in situ preparation of the sample surface leads to values for the room
temperature spin polarization up to 45% at the Fermi level. To our knowledge,
this is the highest value measured so far at the surface region of a full
Heusler alloy at room temperature.",0609504v1
1995-03-28,THE UNIQUENESS THEOREM FOR ROTATING BLACK HOLE SOLUTIONS OF SELF-GRAVITATING HARMONIC MAPPINGS,"We consider rotating black hole configurations of self-gravitating maps from
spacetime into arbitrary Riemannian manifolds. We first establish the
integrability conditions for the Killing fields generating the stationary and
the axisymmetric isometry (circularity theorem). Restricting ourselves to
mappings with harmonic action, we subsequently prove that the only stationary
and axisymmetric, asymptotically flat black hole solution with regular event
horizon is the Kerr metric. Together with the uniqueness result for
non-rotating configurations and the strong rigidity theorem, this establishes
the uniqueness of the Kerr family amongst all stationary black hole solutions
of self-gravitating harmonic mappings.",9503053v1
1995-06-15,Pulsation of Spherically Symmetric Systems in General Relativity,"The pulsation equations for spherically symmetric black hole and soliton
solutions are brought into a standard form. The formulae apply to a large class
of field theoretical matter models and can easily be worked out for specific
examples. The close relation to the energy principle in terms of the second
variation of the Schwarzschild mass is also established. The use of the general
expressions is illustrated for the Einstein-Yang-Mills and the Einstein-Skyrme
system.",9506027v1
1996-10-11,No-Hair Theorems and Black Holes with Hair,"The critical steps leading to the uniqueness theorem for the Kerr-Newman
metric are reexamined in the light of the new black hole solutions with
Yang-Mills and scalar hair. Various methods -- including scaling techniques,
arguments based on energy conditions, conformal transformations and divergence
identities -- are reviewed, and their range of application to selfgravitating
scalar and non-Abelian gauge fields is discussed. In particular, the no-hair
theorem is extended to harmonic mappings with arbitrary Riemannian target
manifolds. (This paper is an extended version of an invited lecture held at the
Journ\'ees Relativistes 96.)",9610019v1
1997-03-06,Mass formulae for a class of nonrotating black holes,"In the presence of a Killing symmetry, various self-gravitating field
theories with massless scalars (moduli) and vector fields reduce to
sigma-models, effectively coupled to 3-dimensional gravity. We argue that this
particular structure of the Einstein-matter equations gives rise to quadratic
relations between the asymptotic flux integrals and the area and surface
gravity (Hawking temperature) of the horizon. The method is first illustrated
for the Einstein-Maxwell system. A derivation of the quadratic formula is then
also presented for the Einstein-Maxwell-axion-dilaton model, which is relevant
to the bosonic sector of heterotic string theory.",9703015v1
1998-05-15,On rotational excitations and axial deformations of BPS monopoles and Julia-Zee dyons,"It is shown that Julia-Zee dyons do not admit slowly rotating excitations.
This is achieved by investigating the complete set of stationary excitations
which can give rise to non-vanishing angular momentum. The relevant zero modes
are parametrized in a gauge invariant way and analyzed by means of a harmonic
decomposition. Since general arguments show that the solutions to the
linearized Bogomol'nyi equations cannot contribute to the angular momentum, the
relevant modes are governed by a set of electric and a set of non self-dual
magnetic perturbation equations. The absence of axial dipole deformations is
also established.",9805061v1
2001-05-22,Semiclassical evidence for the BGS-conjecture,"Recently, M. Sieber and K. Richter achieved a breakthrough towards a proof of
the BGS-conjecture by calculating semiclassically a first correction to the
diagonal approximation of the orthogonal form factor for geodesic flow on a
Riemann surface of constant negative curvature. In this note, we try to
generalize the arguments. However, the solution proposed is not yet correct,
because also other geometries must be taken into account.",0105052v3
2001-06-22,Near action degeneracy of periodic orbits in systems with non-conventional time reversal,"Recently, Sieber and Richter calculated semiclassically a first off-diagonal
contribution to the orthogonal form factor for a billiard on a surface of
constant negative curvature by considering orbit pairs having almost the same
action. For a generalization of this derivation to systems invariant under
non-conventional time reversal symmetry, which also belong to the orthogonal
symmetry class, we show in this paper that it is necessary to redefine the
configuration space in an appropriate way.",0106035v1
2007-11-05,Magnetization easy-axis in martensitic Heusler alloys estimated by strain measurements under magnetic-field,"We study the temperature dependence of strain under constant magnetic-fields
in Ni-Mn based ferromagnetic Heusler alloys in the form Ni-Mn-$X$ ($X$: Ga, In,
Sn, Sb) which undergo a martensitic transformation. We discuss the influence of
the applied magnetic-field on the nucleation of ferromagnetic martensite and
extract information on the easy-axis of magnetization in the martensitic state.",0711.0639v1
2011-02-18,Perpendicular magnetic anisotropy of full-Heusler films in Pt/Co2FeAl/MgO trilayers,"We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO
sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is
thermally stable that the anisotropy energy density Ku is 1.3{\times}106
erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 oC. The
thicknesses of Co2FeAl and MgO layers greatly affect the PMA. Our results
provide an effective way to realize relative thick perpendicularly magnetized
Heusler alloy films.",1102.3802v1
2012-06-06,Probing the superconducting state of the Heusler supercoductor: ZrNi$_2$Ga,"Using both muon spin rotation and muon spin relaxation, the superconducting
ground state of the Heusler superconductor {ZrNi$_2$Ga} has been studied. The
temperature dependence of the magnetic penetration depth of {ZrNi$_2$Ga} is
consistent with a single isotropic gap s-wave BCS superconductor. The gap
energy is \Delta(0)=0.44(1) meV and the magnetic penetration depth, \lambda(0),
is 310(5) nm. Furthermore, we show evidence of a possible cross-over from an
square flux line lattice to a hexagonal lattice at low temperatures. No
evidence of time reversal symmetry breaking has been observed as might be
expected for a half metal superconductor.",1206.1182v1
2015-01-03,"First-principles study of four quaternary Heusler alloys ZrMnVZ and ZrCoFeZ (Z=Si, Ge)","We investigate the electronic structure and magnetic properties of four
quaternary Heusler alloys ZrMnVZ and ZrCoFeZ (Z=Si, Ge) by using
first-principle calculations. It is shown that ZrMnVSi, ZrMnVGe and ZrCoFeSi
are half-metallic ferromagnets with considerable half-metallic gaps of 0.14,
0.18 and 0.22 eV, respectively. ZrCoFeGe is a nearly half-metallic, the changes
of properties for this alloy under pressure is investigated, the spin
polarization of this alloy is 98.99\% at equilibrium lattice constant.",1501.00542v1
2018-03-30,Boosting Material Modeling Using Game Tree Search,"We demonstrate a heuristic optimization algorithm based on the game tree
search for multi-component materials design. The algorithm searches for the
largest spin polarization of seven-component Heusler alloys. The algorithm can
find the peaks quickly and is more robust against local optima than Bayesian
optimization approaches using the expected improvement or upper confidence
bound approaches. We also investigate Heusler alloys including anti-site
disorder and show that
[Fe$_{0.9}$Co$_{0.1}$]$_{2}$Cr$_{0.95}$Mn$_{0.05}$Si$_{0.3}$Ge$_{0.7}$ has the
potential to be a high spin polarized material with robustness against
anti-site disorder.",1803.11338v2
2018-06-18,Large anomalous Nernst effect across the magneto-structural transition in bulk Ni-Co-Mn-Sn full Heusler alloy,"We report on the observation of temperature and field dependent anomalous
Nernst effect (ANE) in Ni-rich bulk Ni-Co-Mn-Sn full Heusler alloy. A large
change in the transverse Nernst coefficient (N) is obtained across the first
order magnetostructural transition from a tetragonal martensite to a cubic
austenite phase. The saturation of ANE and magnetic data appear to depend
largely on the magnetic anisotropy of the device. Such change in the Nernst
co-efficient may prove to be useful for switching applications controlled by
temperature and magnetic field changes.",1806.06675v1
2018-11-09,Anomaly in anomalous Nernst effect at low temperature for C1b-type NiMnSb half-Heusler alloy thin film,"The anomaly in the anomalous Nernst effect (ANE) was observed for a C1b-type
NiMnSb half-Heusler alloy thin film deposited on a MgO (001) substrate. The
Nernst angle ({\theta}ANE) showed maximum peak with decreasing temperature and
reached 0.15 at 80 K, which is considered to be brought by the cross-over from
half-metal to normal ferromagnet in NiMnSb at low temperature. This anomaly was
also observed for the transport properties, that is, both the resistivity and
the anomalous Hall resistivity in the same temperature range.",1811.03791v1
2020-01-17,Fermi Level Controlled Ultrafast Demagnetization Mechanism in Half-Metallic Heusler Alloy,"The electronic band structure-controlled ultrafast demagnetization mechanism
in Co2FexMn1-xSi Heusler alloy is underpinned by systematic variation of
composition. We find the spin-flip scattering rate controlled by spin density
of states at Fermi level is responsible for non-monotonic variation of
ultrafast demagnetization time ({\tau}M) with x with a maximum at x = 0.4.
Furthermore, Gilbert damping constant exhibits an inverse relationship with
{\tau}M due to the dominance of inter-band scattering mechanism. This
establishes a unified mechanism of ultrafast spin dynamics based on Fermi level
position.",2001.06217v1
2022-01-14,Antisite disorder and phase segregation in Mn$_{2}$NiSn,"A systematic study of crystal structure, local structure, magnetic and
transport properties in quenched and temper annealed Ni$_{2-x}$Mn$_{1+x}$Sn
alloys indicate the formation of Mn$_3$Sn type structural defects caused by an
antisite disorder between Mn and Sn occupying the Y and Z sublattices of
X$_2$YZ Heusler structure. The antisite disorder is caused by the substitution
of Ni by Mn at the X sites. On temper annealing, these defects segregate and
phase separate into $L2_1$ Heusler and $D0_{19}$ Mn$_3$Sn type phases.",2201.05283v1
2022-12-19,Chiral surface superconductivity in half-Heusler semimetals,"We propose the metallic and weakly dispersive surface states of half-Heusler
semimetals as a possible domain for the onset of unconventional surface
superconductivity ahead of the bulk transition. Using density functional theory
(DFT) calculations and the random phase approximation (RPA), we analyse the
surface band structure of LuPtBi and its propensity towards Cooper pair
formation induced by screened electron-electron interactions in the presence of
strong spin-orbit coupling. Over a wide range of model parameters, we find an
energetically favoured chiral superconducting condensate featuring Majorana
edge modes, while low-dimensional order parameter fluctuations trigger
time-reversal symmetry breaking to precede the superconducting transition.",2212.09786v1
2023-02-13,"Half-metallicity in $Ni_2XMn$ Heusler alloys ($X=Fe,Co,Cr$): ab-initio calculations","Lattice parameter, bulk modulus, formation energy and magnetism equilibrium
structure in all-d transition metals $Ni_2XMn$ (X=Co,Cr,Fe) for Full and
Inverse Heusler structure are studied by first-principles calculations.
Tetragonal distortion is calculated for the equilibrium volume of each alloy
and possible new equilibrium structures are reported. Density of electronic
states are analyzed and the results lead to half-metallicity for this type of
alloys.",2302.06450v1
2007-12-02,Role of the conduction electrons in mediating exchange interactions in Heusler alloys,"Because of large spatial separation of the Mn atoms in Heusler alloys the Mn
3d states belonging to different atoms do not overlap considerably. Therefore
an indirect exchange interaction between Mn atoms should play a crucial role in
the ferromagnetism of the systems. To study the nature of the ferromagnetism of
various Mn-based semi- and full-Heusler alloys we perform a systematic
first-principles calculation of the exchange interactions in these materials.
The calculation of the exchange parameters is based on the frozen-magnon
approach. The calculations show that the magnetism of the Mn-based Heusler
alloys depends strongly on the number of conduction electrons, their spin
polarization and the position of the unoccupied Mn 3d states with respect to
the Fermi level. Various magnetic phases are obtained depending on the
combination of these characteristics. The Anderson's s-d model is used to
perform a qualitative analysis of the obtained results. The conditions leading
to diverse magnetic behavior are identified. If the spin polarization of the
conduction electrons at the Fermi energy is large and the unoccupied Mn 3d
states lie well above the Fermi level, an RKKY-type ferromagnetic interaction
is dominating. On the other hand, the contribution of the antiferromagnetic
superexchange becomes important if unoccupied Mn 3d states lie close to the
Fermi energy. The resulting magnetic behavior depends on the competition of
these two exchange mechanisms. The calculational results are in good
correlation with the conclusions made on the basis of the Anderson s-d model
which provides useful framework for the analysis of the results of
first-principles calculations and helps to formulate the conditions for high
Curie temperature.",0712.0158v1
2012-12-01,On the half-metallicity of Co2FeSi Heusler alloy: an experimental and ab initio study,"Co2FeSi, a Heusler alloy with the highest magnetic moment per unit cell and
the highest Curie temperature, has largely been described theoretically as a
half-metal. This conclusion, however, disagrees with Point Contact Andreev
Reflection (PCAR) spectroscopy measurements, which give much lower values of
spin polarization, P. Here, we present the spin polarization measurements of
Co2FeSi by the PCAR technique, along with a thorough computational exploration,
within the DFT and a GGA+U approach, of the Coulomb exchange U-parameters for
Co and Fe atoms, taking into account spin-orbit coupling. We find that the
orbital contribution (mo) to the total magnetic moment (mT) is significant,
since it is at least 3 times greater than the experimental uncertainty of mT.
Account of mo radically affects the acceptable values of U. Specifically, we
find no values of U that would simultaneously satisfy the experimental values
of the magnetic moment and result in the half-metallicity of Co2FeSi. On the
other hand, the ranges of U that we report as acceptable are compatible with
spin polarization measurements (ours and the ones found in the literature),
which all are within approximately 40-60% range. Thus, based on reconciling
experimental and computational results, we conclude that: a) spin-orbit
coupling cannot be neglected in calculating Co2FeSi magnetic properties, and b)
Co2FeSi Heusler alloy is not half-metallic. We believe that our approach can be
applied to other Heusler alloys such as Co2FeAl.",1212.0168v1
2013-01-27,"Spintronic properties and stability of the half-Heusler alloys LiMnZ (Z=N, P, Si)","Li-based half-Heusler alloys have attracted much attention due to their
potential applications in optoelectronics and because they carry the
possibility of exhibiting large magnetic moments for spintronic applications.
Due to their similarities to metastable zinc blende half-metals, the
half-Heusler alloys $\beta$-LiMnZ (Z = N, P and Si) were systematically
examined for their electric, magnetic and stability properties at optimized
lattice constants and strained lattice constants that exhibit half-metallic
properties. Other phases of the half-Heusler structure ($\alpha$ and $\gamma$)
are also reported here, but they are unlikely to be grown. The magnetic moments
of these stable Li-based alloys are expected to reach as high as 4
$\mu_{\mathrm{B}}$ per unit cell when Z = Si and 5 $\mu_{\mathrm{B}}$ per unit
cell when Z = N and P, however the antiferromagnetic spin configuration is
energetically favored when Z is a pnictogen. $\beta$-LiMnSi at a lattice
constant 14\% larger than its equilibrium lattice constant is a promising
half-metal for spintronic applications due to its large magnetic moment and
vibrational stability. The modified Slater--Pauling rule for these alloys is
determined. Finally, a plausible method for developing half-metallic Li$_x$MnZ
at equilibrium, by tuning $x$, is investigated, but, unlike tetragonalization,
this type of alloying introduces local structural changes that destroy the
half-metallicity.",1301.6367v3
2016-04-26,First principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys,"Heusler alloys have been intensively studied due to the wide variety of
properties that they exhibit. One of these properties is of particular interest
for technological applications, i.e. the fact that some Heusler alloys are
half-metallic. In the following, a systematic study of the magnetic properties
of three different Heusler families $\textrm{Co}_2\textrm{Mn}\textrm{Z}$,
$\text{Co}_2\text{Fe}\text{Z}$ and $\textrm{Mn}_2\textrm{V}\textrm{Z}$ with
$\text{Z}=\left(\text{Al, Si, Ga, Ge}\right)$ is performed. A key aspect is the
determination of the Gilbert damping from first principles calculations, with
special focus on the role played by different approximations, the effect that
substitutional disorder and temperature effects. Heisenberg exchange
interactions and critical temperature for the alloys are also calculated as
well as magnon dispersion relations for representative systems, the
ferromagnetic $\textrm{Co}_2\textrm{Fe}\textrm{Si}$ and the ferrimagnetic
$\textrm{Mn}_2\textrm{V}\textrm{Al}$. Correlations effects beyond standard
density-functional theory are treated using both the local spin density
approximation including the Hubbard $U$ and the local spin density
approximation plus dynamical mean field theory approximation, which allows to
determine if dynamical self-energy corrections can remedy some of the
inconsistencies which were previously reported for these alloys.",1604.07552v1
2018-01-09,Epitaxial Heusler Superlattice Co2MnAl/Fe2MnAl with Perpendicular Magnetic Anisotropy and Termination-Dependent Half-Metallicity,"Single-crystal Heusler atomic-scale superlattices that have been predicted to
exhibit perpendicular magnetic anisotropy and half-metallicity have been
successfully grown by molecular beam epitaxy. Superlattices consisting of
full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity
were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy
loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers
with high cobalt or high iron concentrations for samples grown near room
temperature on GaAs (001). Superlattice structures grown with an excess of
aluminum had significantly lower thin film shape anisotropy and resulted in an
out-of-plane spin reorientation transition at temperatures below 200 K for
samples grown on GaAs (001). Synchrotron-based spin resolved photoemission
spectroscopy found that the superlattice structure improves the Fermi level
spin polarization near the X point in the bulk Brillouin zone. Stoichiometric
Co$_2$MnAl terminated superlattice grown on MgO (001) had a spin polarization
of 95%, while a pure Co$_2$MnAl film had a spin polarization of only 65%.",1801.02787v1
2019-02-20,Spin-charge conversion in NiMnSb Heusler alloy films,"Half-metallic Heusler alloys are attracting considerable attention because of
their unique half-metallic band structures which exhibit high spin polarization
and yield huge magnetoresistance ratios. Besides serving as ferromagnetic
electrodes, Heusler alloys also have the potential to host spin-charge
conversion which has been recently demonstrated in other ferromagnetic metals.
Here, we report on the spin-charge conversion effect in the prototypical
Heusler alloy NiMnSb. Spin currents were injected from Y3Fe5O12 into NiMnSb
films by spin pumping, and then the spin currents were converted to charge
currents via spin-orbit interactions. Interestingly, an unusual charge signal
was observed with a sign change at low temperature, which can be manipulated by
film thickness and ordering structure. It is found that the spin-charge
conversion has two contributions. First, the interfacial contribution causes a
negative voltage signal, which is almost constant versus temperature. The
second contribution is temperature dependent because it is dominated by
minority states due to thermally excited magnons in the bulk part of the film.
This work provides a pathway for the manipulation of spin-charge conversion in
ferromagnetic metals by interface-bulk engineering for spintronic devices.",1902.07406v1
2020-02-11,A simple model for vacancy order and disorder in defective half-Heusler systems,"Defective half-Heusler systems X(1-x)YZ with large amounts of intrinsic
vacancies, such as Nb(1-x)CoSb, Ti(1-x)NiSb and V(1-x)CoSb, are a group of
promising thermoelectric materials. Even with high vacancy concentrations they
maintain the average half-Heusler crystal structure. These systems show high
electrical conductivity but low thermal conductivity arising from an ordered YZ
lattice, which conducts electrons, while the large amounts of vacancies on the
X sublattice effectively scatters phonons. Using electron scattering it was
recently observed that in addition to Bragg diffraction from the average cubic
half-Heusler structure, some of these samples show broad diffuse scattering
indicating short-range vacancy order while other samples show sharp additional
peaks, indicating long-range vacancy ordering. Here we show that both the short
and long-range ordering can be explained using the same simple model, which
assumes that vacancies on the X-sublattice avoid each other. The samples
showing long-range vacancy order are in agreement with the predicted
ground-state of the model, while short-range order samples are quenched
high-temperature states of the system. A previous study showed that changes in
sample stoichiometry affect whether the short or long-range vacancy structure
is obtained, but the present model suggests that thermal treatment of samples
should allow controlling the degree of vacancy order, and thereby the thermal
conductivity, without changes in composition. This is important as the
composition also dictates the amount of electrical carriers. Independent
control of electrical carrier concentration and degree of vacancy order should
allow further improvements in the thermoelectric properties of these systems.",2002.04281v2
2021-02-22,"Structural, magnetic, and magnetocaloric properties of Fe2CoAl Heusler nanoalloy","Spherical nanoparticles (NPs) of size 14 nm, made of intermetallic Fe2CoAl
(FCA) Heusler alloy, are synthesized via the co-precipitation and thermal
deoxidization method. X-ray diffraction (XRD) and selected area electron
diffraction (SAED) patterns confirm that the present nanoalloy is crystallized
in A2-disordered cubic Heusler structure. Magnetic field (H) and temperature
(T) dependent magnetization (M) results reveal that the NPs are soft
ferromagnetic (FM) with high saturation magnetization (Ms) and Curie
temperature (Tc). Fe2CoAl nanoalloy does not follow the Slater Pauling (SP)
rule, possibly because of the disorder present in the system. We also
investigate its magnetic phase transition (MPT) and magnetocaloric (MC)
properties. The peak value of the magnetic entropy change vs T curve at a
magnetic field change of 20 kOe corresponds to about 2.65 J/kg-K, and the
observed value of refrigeration capacity (RCP) is as large as 44 J/kg,
suggesting a large heat conversion in magnetic refrigeration cycle. The Arrott
plot and the nature of the universal curve accomplish that the FM to
paramagnetic (PM) phase transition in Fe2CoAl nanoalloy is of second-order. The
present study suggests that the Fe2CoAl nanoscale system is proficient, useful
and a good candidate for the spintronics application and opens up a window for
further research on full-Heusler based magnetic refrigerants.",2102.11195v2
2022-12-02,FeRhCrSi: A new spin semimetal with room temperature spin-valve behavior,"Spin semimetals are a recently discovered new class of spintronic materials,
which exhibit a band gap in one spin channel while a semimetallic feature in
the other and thus allows for tunable spin transport. Here, we present
experimental verification of spin semimetallic behavior in FeRhCrSi, a
quaternary Heusler alloy with saturation moment 2 $\mu_B$ and Curie temperature
$>$ 400 K. It crystallises in the L2$_1$ structure with 50$\%$ antisite
disorder between Fe and Rh. Below 300 K, it shows a weakly temperature
dependent electrical resistivity with negative temperature coefficient,
indicating the normal semimetal or spin semimetal behavior. Anomalous
magnetoresistance data reveals dominant contribution from asymmetric part, a
clear signature of spin-valve nature, which is retained even at room
temperature. \textcolor{black}{The asymmetric part of magneto-resistance shows
an unusual increase with increasing temperature.} Hall measurements confirm the
anomalous nature of conductivity originating from the intrinsic Berry
curvature, with holes being the majority carriers. Ab-initio simulation
confirms a unique long-range ferrimagnetic ordering to be the ground state,
explaining the origin behind the unexpected low saturation moment. The
ferrimagnetic disordered structure confirms the spin semimetallic feature of
FeRhCrSi, as observed experimentally.",2212.00924v2
2023-03-17,Intrinsic and extrinsic anomalous transport properties of Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl from first principles,"Recently, Heusler ferromagnets have been found to exhibit unconventional
anomalous electric, thermal, and thermoelectric transport properties. In this
study, we employed first-principles density functional theory calculations to
systematically investigate both intrinsic and extrinsic contributions to the
anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and anomalous
thermal Hall effect (ATHE) in two Heusler ferromagnets: Fe$_2$CoAl and
Fe$_2$NiAl. Our analysis reveals that the extrinsic mechanism originating from
disorder dominates the AHE and ATHE in Fe$_2$CoAl , primarily due to the steep
band dispersions across the Fermi energy and corresponding high longitudinal
electronic conductivity. Conversely, the intrinsic Berry phase mechanism,
physically linked to nearly flat bands around the Fermi energy and gapped by
spin-orbit interaction band crossings, governs the AHE and ATHE in Fe$_2$NiAl.
With respect to ANE, both intrinsic and extrinsic mechanisms are competing in
Fe$_2$CoAl as well as in Fe$_2$NiAl. Furthermore, Fe$_2$CoAl and Fe$_2$NiAl
exhibit tunable and remarkably pronounced anomalous transport properties. For
instance, the anomalous Nernst and anomalous thermal Hall conductivities in
Fe$_2$NiAl attain giant values of 8.29 A/Km and 1.19 W/Km, respectively, at
room temperature. To provide a useful comparison, we also thoroughly
investigated the anomalous transport properties of Co$_2$MnGa. Our findings
suggest that Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl are promising
candidates for spintronics and spin-caloritronics applications.",2303.09812v2
2023-10-24,"Tuning the topological character of half-Heusler systems: A comparative study on Y$T$Bi ($T$ = Pd, Pt)","Half-Heusler systems host a plethora of different ground states, especially
with non-trivial topology. However, there is still a lack of spectroscopic
insight into the corresponding band inversion in this family. In this work, we
locally explore the half-Heuslers Y$T$Bi ($T =$ Pt and Pd) by means of scanning
tunneling microscopy/spectroscopy. From our analysis of the (120) surface
plane, we infer that the increase of the spin--orbit coupling upon going from
Pd to Pt is the main player in tuning the surface states from trivial to
topologically non-trivial. Our measurements unveil a ($2 \times 1$)
reconstruction of the (120) surface of both systems. Using density functional
theory calculations, we show that the observed different behavior of the local
density of states near the Fermi level in these two materials is directly
related to the presence of metallic surface states. Our work sheds new light on
a well known tunable family of materials and opens new routes to explore the
presence of topological states of matter in half-Heusler systems and its
microscopic observation.",2310.15708v1
2006-11-17,Electronic structure of half-metallic magnets,"We have analyzed the electronic structure of half-metallic magnets based on
first principles electronic structure calculations of a series of semi-Heusler
alloys. The characteristic feature of the electronic structure of semi-Heusler
systems is a d-d gap in the density of states lying at/close to the Fermi level
depending on the number of valence electrons. We have employed various
indicators of chemical bonding to understand the origin of the gap in these
systems, which is crucial for their half-metallic property. The density of
states of other half-metallic magnets also supports a gap and it is a generic
feature of these systems. We have discussed in some details the origin of
magnetism, in particular, how the presence of the gap is crucial to stabilize
half-metallic ferro and ferri magnetism in these systems. Finally, we have
studied the role of magnetic impurities in semiconducting semi-Heusler systems.
We show with the aid of model supercell calculations that these systems are not
only ferromagnetic but also half-metallic with possibly high Curie temperature.",0611476v1
2008-11-10,Tuning the magnetic properties of half-metallic semi-Heusler alloys by sp-electron substitution: The case of AuMnSn$_{1-x}$Sb$_x$ quaternary alloys,"We study the electronic and magnetic properties of the quaternary
AuMnSn$_{1-x}$Sb$_{x}$ Heusler alloys using first principles calculations. We
determine their magnetic phase diagram and we show that they present a phase
transition from a ferromagnetic to an antiferromagnetic state with increasing
Sb concentration. For large Sb concentrations the antiferromagnetic
superexchange coupling dominates over the ferromagnetic RKKY-like exchange
mechanism. This behavior is similar to the one demonstrated by the isovalent
Ni$_{1-x}$Cu$_x$MnSb alloy studied recently by the authors [I. Galanakis et al,
Phys. Rev. B. \textbf{77}, 214417 (2008)]. Thus the variation of the
concentration of the \textit{sp}-electrons (Sn and Sb atoms) and the variation
of the concentration of the non-magnetic \textit{3d} atoms (Cu) lead to a
similar tuning of the the magnetic properties of the Heusler alloys. We show
that the inclusion of correlation effects does not alter the phase diagram.
Calculated results are in good agreement with the available experimental data.",0811.1408v1
2009-02-09,Analysis of L21-ordering in full-Heusler Co2FeSi alloy thin films formed by rapid thermal annealing,"The authors developed a new analysis approach for evaluation of atomic
ordering in full-Heusler alloys, which is extension of the commonly used
Webster model. Our model can give accurate physical formalism for the degree of
atomic ordering in the L21 structure, including correction with respect to the
fully disordered A2 structure, i.e., the model can directly evaluate the degree
of L21-ordering under a lower ordering structure than the complete B2-ordering
structure. The proposed model was applied to full-Heusler Co2FeSi alloy thin
films formed by rapid thermal annealing. The film formed at TA = 800 C showed a
relatively high degree of L21-ordering of 83 % under a high degree of
B2-ordering of 97 %.",0902.1438v1
2009-06-16,Epitaxial Growth of a Full-Heusler Alloy Co$_{2}$FeSi on Silicon by Low-Temperature Molecular Beam Epitaxy,"For electrical spin injection and detection of spin-polarized electrons in
silicon, we explore highly epitaxial growth of ferromagnetic full-Heusler-alloy
Co2FeSi thin films on silicon substrates using low-temperature molecular beam
epitaxy (LTMBE). Although in-situ reflection high energy electron diffraction
images clearly show two-dimensional epitaxial growth for growth temperatures
T_G of 60, 130, and 200 C, cross-sectional transmission electron microscopy
experiments reveal that there are single-crystal phases other than Heusler
alloys near the interface between Co_2FeSi and Si for T_G = 130 and 200 C. On
the other hand, almost perfect heterointerfaces are achieved for T_G = 60 C.
These results and magnetic measurements indicate that highly epitaxial growth
of Co_2FeSi thin films on Si is demonstrated only for T_G = 60 C.",0906.2840v1
2009-10-26,Direct determination of the surface termination in full Heusler alloys by means of low energy electron diffraction,"The performance of Heusler based magnetoresistive multilayer devices depends
crucially on the spin polarization and thus on the structural details of the
involved surfaces. Using low energy electron diffraction (LEED), one can
non-destructively distinguish between important surface terminations of Co2XY
full-Heusler alloys. We present an analysis of the LEED patterns of the Y-Z
,the vacancy-Z, the Co and the disordered B2 and A2 terminations. As an
example, we show that the surface geometries of bulk L21 ordered Co2MnSi and
bulk B2 disordered Co2Cr0.6Fe0.4Al can be determined by comparing the
experimental LEED patterns with the presented reference patterns.",0910.4909v2
2010-06-01,Observation of enhanced exchange bias behavior in NiCoMnSb Heusler alloys,"We report the observation of large exchange bias in Ni50-xCoxMn38Sb12 Heusler
alloys with x=0, 2, 3, 4, 5, which is attributed to the coexistence of
ferromagnetic and antiferromagnetic phases in the martensitic phase. The phase
coexistence is possibly due to the supercooling of the high temperature
ferromagnetic phase and the predominant antiferromagnetic component in the
martensitic phase. The presence of exchange bias is well supported by the
observation of training effect. The exchange bias field increases with Co
concentration. The maximum value of 480 Oe at T=3K is observed in x=5 after
field cooling in 50 kOe, which is almost double the highest value reported so
far in any Heusler alloy system. Increase in the antiferromagnetic coupling
after Co substitution is found to be responsible for the increase in the
exchange bias.",1006.0071v1
2012-06-11,Crossover from antiferromagnetic to ferromagnetic ordering in semi-Heusler alloys Cu1-xNixMnSb with increasing Ni concentration,"The magnetic properties and transition from an antiferromagnetic (AFM) to a
ferromagnetic (FM) state in semi Heusler alloys Cu1-xNixMnSb, with x < 0.3 have
been investigated in details by dc magnetization, neutron diffraction, and
neutron depolarization. We observe that for x < 0.05, the system Cu1-xNixMnSb
is mainly in the AFM state. In the region 0.05 \leq x \leq 0.2, with decrease
in temperature, there is a transition from a paramagnetic to a FM state and
below ~50 K both AFM and FM phases coexist. With an increase in Ni
substitution, the FM phase grows at the expense of the AFM phase and for x >
0.2, the system fully transforms to the FM phase. Based on the results
obtained, we have performed a quantitative analysis of both magnetic phases and
propose a magnetic phase diagram for the Cu1-xNixMnSb series in the region x <
0.3. Our study gives a microscopic understanding of the observed crossover from
the AFM to FM ordering in the studied semi Heusler alloys Cu1-xNixMnSb.",1206.2243v1
2012-11-02,Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers,"All-Heusler multilayer structures have been investigated by means of high
kinetic x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism,
aiming to address the amount of disorder and interface diffusion induced by
annealing of the multilayer structure. The studied multilayers consist of
ferromagnetic Co$_2$MnGe and non-magnetic Rh$_2$CuSn layers with varying
thicknesses. We find that diffusion begins already at comparably low
temperatures between 200 $^{\circ}$C and 250 $^{\circ}$C, where Mn appears to
be most prone to diffusion. We also find evidence for a 4 {\AA} thick
magnetically dead layer that, together with the identified interlayer
diffusion, are likely reasons for the small magnetoresistance found for
current-perpendicular-to-plane giant magneto-resistance devices based on this
all-Heusler system.",1211.0489v2
2013-04-09,Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi,"In this paper, we investigate the half-metallicity of Heusler alloys
Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance
measurements. It is found that, with the increase of Cr content x, the Fermi
level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of
conduction band, and a large half-metallic band gap of 0.75 eV is obtained for
x=0.75. We then successfully synthesized a series Heusler Fe2Co1-xCrxSi
polycrystalline ribbon samples. The results of X-ray diffraction indicate that
the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order
and the saturation magnetic moment follows half-metallic Slater-Pauling rule.
Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic
magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, 0.75) show a negative value
suggesting they are stable half-metallic ferromagnets.",1304.2602v1
2013-07-11,Large Linear Magnetoresistance and Shubnikov-de Hass Oscillations in Single Crystals of YPdBi Heusler Topological Insulators,"We report the observation of a large linear magnetoresistance (MR) and
Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi
Heusler topological insulators. Owning to the successfully obtained the
high-quality YPdBi single crystals, large non-saturating linear MR of as high
as 350% at 5K and over 120% at 300 K under a moderate magnetic field of 7 T is
observed. In addition to the large, field-linear MR, the samples exhibit
pronounced SdH quantum oscillations at low temperature. Analysis of the SdH
data manifests that the high-mobility bulk electron carriers dominate the
magnetotransport and are responsible for the observed large linear MR in YPdBi
crystals. These findings imply that the Heusler-based topological insulators
have superiorities for investigating the novel quantum transport properties and
developing the potential applications.",1307.3022v1
2013-11-22,Full-Heusler Co2FeSi alloy thin films with perpendicular magnetic anisotropy induced by MgO-interface,"The authors demonstrated that L21-ordered full-Heusler Co2FeSi (CFS) alloy
film with thickness of 100 nm were formed by facing targets sputtering (FTS)
method at a substrate temperature TS = 300 deg C. Degrees of L21- and B2- order
for the film were 0.37, and 0.96, respectively. Furthermore, full-Heusler CFS
alloy thin films with perpendicular magnetic anisotropy (PMA) induced by
MgO-interface magnetic anisotropy were successfully formed by the FTS method.
The CFS/MgO stacking layers showed PMA when dCFS was 0.6 nm <= dCFS <= 1.0 nm.
The PMA in these structures resulted from the CFS/MgO interfacial perpendicular
magnetic anisotropy.",1311.5670v2
2014-02-18,Interplay of growth mode and thermally induced spin accumulation in epitaxial Al/Co$_2$TiSi/Al and Al/Co$_2$TiGe/Al contacts,"The feasibility of thermally driven spin injectors built from half-metallic
Heusler alloys inserted between aluminum leads was investigated by means of
{\em ab initio} calculations of the thermodynamic equilibrium and electronic
transport. We have focused on two main issues and found that: (i) the interface
between Al and the closely lattice-matched Heusler alloys of type Co$_2$Ti$Z$
($Z=$ Si or Ge) is stable under various growth conditions; and (ii) the
conventional and spin-dependent Seebeck coefficients in such heterojunctions
exhibit a strong dependence on both the spacer and the atomic composition of
the Al/Heusler interface. The latter quantity gives a measure of the spin
accumulation and varies between $+8$~$\mu$V/K and $-3$~$\mu$V/K near $300$~K,
depending on whether a Ti-Ge or a Co-Co plane makes the contact between Al and
Co$_2$TiGe in the trilayer. Our results show that it is in principle possible
to tailor the spin-caloric effects by a targeted growth control of the samples.",1402.4396v2
2014-10-07,"Anti-site disorder and improved functionality of Mn$_{2}$Ni{\it X} ({\it X}= Al, Ga, In, Sn) inverse Heusler alloys","Recent first-principles calculations have predicted Mn$_{2}$Ni{\it X} ({\it
X}=Al, Ga, In, Sn) alloys to be magnetic shape memory alloys. Moreover,
experiments on Mn$_{2}$NiGa and Mn$_{2}$NiSn suggest that the alloys deviate
from the perfect inverse Heusler arrangement and that there is chemical
disorder at the sublattices with tetrahedral symmetry. In this work, we
investigate the effects of such chemical disorder on phase stabilities and
magnetic properties using first-principles electronic structure methods. We
find that except Mn$_{2}$NiAl, all other alloys show signatures of martensitic
transformations in presence of anti-site disorder at the sublattices with
tetrahedral symmetry. This improves the possibilities of realizing martensitic
transformations at relatively low fields and the possibilities of obtaining
significantly large inverse magneto-caloric effects, in comparison to perfect
inverse Heusler arrangement of atoms. We analyze the origin of such
improvements in functional properties by investigating electronic structures
and magnetic exchange interactions.",1410.1690v1
2014-11-27,$Ab$ $intito$ study on some new spin-gapless semiconductors: The Zr-based quanternary Heusler alloys,"Employing $ab$ $intito$ electronic structure calculations, we have
investigated electronic and magnetic properties of the Zr-based quanternary
Heusler alloys: ZrCoVIn, ZrFeVGe, ZrCoFeP, ZrCoCrBe and ZrFeCrZ (Z=In and Ga).
Our $ab$ $intito$ calculation results show that all the alloys are (or nearly)
spin-gapless semiconductors. All the alloys have large band gaps, indicating
the stability of them at room temperature. The Slater-Pauling behaviours of
these alloys are discussed as well. The values of Curie temperature of all the
alloys are estimated. And it is found that the values of the Curie temperature
for all our calculated quanternary Heusler alloys are higher than that of room
temperature.",1411.7570v2
2015-06-22,Two successive magneto-structural transformations and their relation to enhanced magnetocaloric effect for Ni55.3Mn19.7Ga25 Heusler alloy,"In the present work, two successive magneto-structural transformations (MSTs)
consisting of martensitic and intermartensitic transitions have been reported
in polycrystalline Ni55.8Mn18.1Ga26.1 Heusler alloy. Benefiting from the
additional latent heat contributed from intermediate phase, this alloy exhibits
a large transition entropy change {\Delta}Str with the value of ~28 J/kg K.
Moreover, the magnetocaloric effect (MCE) has been also evaluated in terms of
Maxwell relation. For the magnetic field change of 3 T, it is found that the
calculated value of refrigeration capacity for Ni55.8Mn18.1Ga26.1 attains to
~72 J/kg around room temperature, which significantly surpasses those obtained
in many Ni-Mn based Heusler alloys. The mechanism underlying the enhanced MCE
is believed to be responsible for these multiple transformations, which can
sustain the pronounced isothermal entropy change {\Delta}ST over a relatively
wide temperature interval.",1506.06517v2
2015-08-07,Multifunctional Heusler alloy: experimental evidences of enhanced magnetocaloric properties at room temperature and half-metallicity,"Heusler alloys are widely studied due to their interesting structural and
magnetic properties, like magnetic memory shape ability, coupled
magneto-structural phase transitions and half-metallicity; ruled, for many
cases, by the valence electrons number ($N_v$). The present work focuses on the
magnetocaloric potentials of half-metals, exploring the effect of $N_v$ on the
magnetic entropy change, preserving half-metallicity. The test bench is the
Si-rich side of the half-metallic series Fe$_2$MnSi$_{1-x}$Ga$_x$. From the
obtained experimental results it was possible to obtain $|\Delta
S|_{max}=\Delta H^{0.8}(\alpha+\beta N_v)$, i.e., the maximum magnetic entropy
change depends in a linear fashion on $N_v$, weighted by a power law on the
magnetic field change $\Delta H$ ($\alpha$ and $\beta$ are constants
experimentally determined). In addition, it was also possible to predict a new
multifunctional Heusler alloy, with enhanced magnetocaloric effect, Curie
temperature close to 300 K and half-metallicity.",1508.01828v1
2016-04-19,Half Heusler Alloys for Efficient Thermoelectric Power Conversion,"Half-Heusler (HH) phases (space group F43m, Clb) are increasingly gaining
attention as promising thermoelectric materials in view of their thermal
stability, scalability, and environmental benignity as well as efficient power
output. Until recently, the verifiable dimensionless figure of merit (ZT) of HH
phases has remained moderate near 1, which limits the power conversion
efficiency of these materials. We report herein ZT~1.3 in n-type (Hf,Zr)NiSn
alloys near 850 K developed through elemental substitution and simultaneously
embedment of nanoparticles in the HH matrix, obtained by annealing the samples
close to their melting temperatures. Introduction of mass fluctuation and
scattering centers play a key role in the high ZT measured, as shown by the
reduction of thermal conductivity and increase of thermopower. Based on
computation, the power conversion efficiency of a n-p couple module based on
the new n-type (Hf,Zr,Ti)NiSn particles-in-matrix composite and recently
reported high-ZT p-type HH phases is expected to reach 13%, comparable to that
of state-of-the-art materials, but with the mentioned additional materials and
environmental attributes. Since the high efficiency is obtained without tuning
the microstructure of the Half-Heusler phases, it leaves room for further
optimization.",1604.05397v2
2019-11-22,Superconducting spin-valve effect in heterostructures with ferromagnetic Heusler alloy layers,"We report a comparative analysis and theoretical description of the
superconducting properties of two spin-valve-valve structures containing the
Heusler alloy Co$_2$Cr$_{1-x}$Fe$_x$Al$_{y}$ as one of two ferromagnetic (F1 or
F2) layers of the F1/F2/S structure, where S stands for the superconducting Pb
layer. In our experiments we used the Heusler alloy layer in two roles: as a
weak ferromagnet on the place of the F2 layer and as a half-metal on the place
of the F1 layer. In the first case, we obtained a large ordinary
superconducting spin-valve effect $\Delta T_c$ assisted by the triplet
superconducting spin-valve effect $\Delta T_c^{trip}$. In the second case, we
observed a giant magnitude of $\Delta T_c^{trip}$ reaching 0.5 K. An underlying
theory based on the solution of the Usadel equations using Kupriyanov-Lukichev
boundary conditions with arbitrary material parameters for all layers and
arbitrary boundary parameters for all interfaces is presented in Appendix. We
find a good agreement between our experimental data and theoretical results.",1911.09984v1
2017-04-04,Model Hamiltonian and Time Reversal Breaking Topological Phases of Anti-ferromagnetic Half-Heusler Materials,"In this work, we construct a generalized Kane model with a new coupling term
between itinerant electron spins and local magnetic moments of
anti-ferromagnetic ordering in order to describe the low energy effective
physics in a large family of anti-ferromagnetic half-Heusler materials.
Topological properties of this generalized Kane model is studied and a large
variety of topological phases, including Dirac semimetal phase, Weyl semimetal
phase, nodal line semimetal phase, type-B triple point semimetal phase,
topological mirror (or glide) insulating phase and anti-ferromagnetic
topological insulating phase, are identified in different parameter regions of
our effective models. In particular, we find that the system is always driven
into the anti-ferromagnetic topological insulator phase once a bulk band gap is
open, irrespective of the magnetic moment direction, thus providing a robust
realization of anti-ferromagentic topological insulators. Furthermore, we
discuss the possible realization of these topological phases in realistic
anti-ferromagnetic half-Heusler materials. Our effective model provides a basis
for the future study of physical phenomena in this class of materials.",1704.01138v1
2017-05-17,High Thermoelectric Figure of Merit by Resonant Dopant in Half-Heusler Alloys,"Half-Heusler alloys have been one of the benchmark high temperature
thermoelectric materials owing to their thermal stability and promising figure
of merit ZT. Simonson et al. early showed that small amounts of vanadium doped
in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change
with the increased density of states near the Fermi level. We herein report a
systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta)
as prospective resonant dopants in enhancing the ZT of n-type half-Heusler
alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase
the Seebeck coefficient in the temperature range 300-1000 K, consistent with a
resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as
evident by the systematic decrease in electrical resistivity and Seebeck
coefficient. The combination of enhanced Seebeck coefficient due to the
presence of V resonant states and the reduced thermal conductivity has led to a
state-of-the-art ZT of 1.3 near 850 K in n-type
(Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.",1705.06100v1
2018-07-17,Ferromagnetically correlated clusters in semi-metallic Ru2NbAl Heusler alloy,"In this work, we report the structural, magnetic and electrical and thermal
transport properties of the Heusler-type alloy Ru2NbAl. From the detailed
analysis of magnetization data, we infer the presence of superparamagnetically
interacting clusters with a Pauli paramagnetic background, while short-range
ferromagnetic interaction is developed among the clusters below 5 K. The
presence of this ferromagnetic interaction is confirmed through heat capacity
measurements. The relatively small value of electronic contribution to specific
heat, gamma (~2.7 mJ/mol-K2), as well as the linear nature of temperature
dependence of Seebeck coefficient indicate a semi-metallic ground state with a
pseudo-gap that is also supported by our electronic structure calculations. The
activated nature of resistivity is reflected in the observed negative
temperature coefficient and has its origin in the charge carrier localization
due to antisite defects, inferred from magnetic measurements as well as
structural analysis. Although the absolute value of thermoelectric figure of
merit is rather low (ZT = 5.2*10-3) in Ru2NbAl, it is the largest among all the
reported non-doped full Heusler alloys.",1807.06608v1
2019-01-27,Computational search for ultrasmall and fast skyrmions in the Inverse Heusler family,"Skyrmions are magnetic excitations that are potentially ultrasmall and
topologically protected, making them interesting for high-density
all-electronic ultrafast storage applications. While recent experiments have
confirmed the existence of various types of skyrmions, their typical sizes are
much larger than traditional domain walls, except at very low temperature. In
this work, we explore the optimal material parameters for hosting ultra-small,
fast, and room temperature stable skyrmions. As concrete examples, we explore
potential candidates from the inverse Heusler family. Using first-principles
calculations of structural and magnetic properties, we identify several
promising ferrimagnetic inverse Heusler half-metal/near half-metals and analyze
their phase space for size and metastability.",1901.09446v1
2019-04-03,Observation of Topological Hall Effect and Signature of Room Temperature Antiskyrmions in Mn-Ni-Ga D2d Heusler magnets,"Topologically stable nontrivial spin structures, such as skyrmions and
antiskyrmions, display a large topological Hall effect owing to their quantized
topological charge. Here, we present the finding of a large topological Hall
effect beyond room temperature in the tetragonal phase of a Mn-Ni-Ga based
ferrimagnetic Heusler shape memory alloy system. The origin of the field
induced topological phase, which is also evidenced by the appearance of dips in
the ac-susceptibility measurements, is attributed to the presence of magnetic
antiskyrmions driven by D2d symmetry of the inverse Heusler tetragonal phase.
Detailed micromagnetic simulations asserts that the antiskyrmionic phase is
stabilized as a result of interplay among inhomogeneous Dzyaloshinskii-Moriya
interaction, the Heisenberg exchange, and the magnetic anisotropy energy. The
robustness of the present result is demonstrated by stabilizing the
antiskyrmion hosting tetragonal phase up to a temperature as high as 550 K by
marginally varying the chemical composition, thereby driving us a step closer
to the realization of ferrimagnetic antiskyrmion based racetrack memory.",1904.01894v1
2019-04-25,Low damping magnetic properties and perpendicular magnetic anisotropy with strong volume contribution in the Heusler alloy Fe1.5CoGe,"We present a study of the dynamic magnetic properties of TiN-buffered
epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series
annealed at different temperatures are prepared and the magnetic damping is
measured, a lowest value of $\alpha=2.18\times 10^{-3}$ is obtained. The
perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also
characterized. The evolution of the interfacial perpendicular anisotropy
constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and
compared with the widely used CoFeB/MgO interface. A large volume contribution
to the perpendicular anisotropy of $(4.3\pm0.5)\times 10^{5}$ $\rm J/m^3$ is
also found, in contrast with vanishing bulk contribution in common Co- and
Fe-based Heusler alloys.",1904.11247v1
2018-02-17,FeTaSb and FeMnTiSb as promising thermoelectric materials: An ab initio approach,"Thermoelectricity in principle provides a pathway to put waste heat to good
use. Motivated by this we investigate thermal and electrical transport
properties of two new Fe-based Heusler alloys, FeTaSb and FeMnTiSb, by a first
principles approach and semiclassical Boltzmann transport theory within the
constant relaxation-time approximation. We find a high power factor of
\textit{p}-doped FeTaSb, competitive with best performing Heusler alloy FeNbSb
at 1100 K. The obtained power factor of \textit{n}-doped FeMnTiSb at room
temperature is higher than that of both FeNbSb and FeTaSb. Remarkably, FeMnTiSb
can be used for both \textit{n}-type and \textit{p}-type legs in a
thermoelectric module. The Seebeck coefficients of the two proposed systems are
in line with those of earlier reported Heusler alloys. We also provide
conservative estimates of the figure of merit for the two systems. Overall, our
findings suggest a high temperature thermoelectric potential of FeTaSb while
the low cost FeMnTiSb is a viable room temperature thermoelectric candidate
material.",1802.06254v1
2018-12-13,Current-induced nucleation and dynamics of skyrmions in a Co-based Heusler alloy,"We demonstrate room-temperature stabilization of dipolar magnetic skyrmions
with diameters in the range of $100$ nm in a single ultrathin layer of the
Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced
skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy
magnetometer operating in the photoluminescence quenching mode. We first
demonstrate skyrmion nucleation by spin-orbit torque and show that its
efficiency can be significantly improved using tilted magnetic fields, an
effect which is not specific to Heusler alloys and could be advantageous for
future skyrmion-based devices. We then show that current-induced skyrmion
motion remains limited by strong pinning effects, even though CFA is a magnetic
material with a low magnetic damping parameter.",1812.05345v1
2020-04-03,Improved magnetostructural and magnetocaloric reversibility in magnetic Ni-Mn-In shape-memory Heusler alloy by optimizing the geometric compatibility condition,"We report an improved reversibility of magnetostriction and inverse
magnetocaloric effect (MCE) for the magnetic shape-memory Heusler alloy
Ni$_{1.8}$Mn$_{1.8}$In$_{0.4}$. We show that the magnetostriction and MCE
crucially depends on the geometrical compatibility of the austenite and
martensite phases. Detailed information on the compatibility of both phases has
been obtained from the transformation matrix calculated from x-ray diffraction
data. The uniqueness of the lattice parameters results in an improved
reversibility of the magnetostriction and the MCE. In the thermal hysteresis
region of the martensitic transformation, the maximum relative length change is
0.3% and the adiabatic temperature change $\Delta T_{ad}\approx -10$ K in
pulsed magnetic fields. Our results reveal that the approach of geometric
compatibility will allow one to design materials with reversible
magnetostriction and reversible inverse MCE at a first-order magnetostructural
phase transition in shape-memory Heusler alloys.",2004.01527v1
2020-08-17,Interaction between skyrmions and antiskyrmions in a coexisting phase of a Heusler material,"Coexisting phases of magnetic skyrmions and antiskyrmions have proposed to
exhibit a variety of fascinating properties, owing to interactions between
them. The recent discovery of the coexisting phase in a Heusler material could
offer a platform for skyrmion-antiskyrmion-based spintronics. Here we report
Lorentz electron microscopy experiments and micromagnetic simulations in a
similar Heusler material, Mn$_{1.3}$Pt$_{1.0}$Pd$_{0.1}$Sn. Around $B_c \sim$
420$\,$mT, we find a stochastic reversible transformation and a room
temperature coexisting phase of elliptical skyrmions and square-shaped
antiskyrmions. The closeness of the energy competition is sensitive to the
exchange stiffness constants and sample thickness. Furthermore, we reveal
isotropic long-range repulsive interaction between the skyrmions and
antiskyrmions regardless of their shapes and the skyrmion helicities, in stark
contrast to conventional thought of angle- and helicity-dependent short-range
pairwise interactions. The observed interaction possibly results from the
topological protection against the intrusion of magnetic flux density coming
from skyrmions (antiskyrmions) into antiskyrmions (skyrmions). Our results
provide new insight into interacting skyrmions and antiskyrmions and a guide
for developing skyrmion-antiskyrmion-based spintronics.",2008.07272v2
2016-03-10,Pairing of j=3/2 fermions in half-Heusler superconductors,"We theoretically consider the superconductivity of the topological
half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between
j=3/2 fermion states, which leads to qualitative differences from the
conventional theory of pairing between j=1/2 states. In particular, this
permits Cooper pairs with quintet or septet total angular momentum, in addition
to the usual singlet and triplet states. Purely on-site interactions can
generate s-wave quintet time-reversal symmetry-breaking states with
topologically nontrivial point or line nodes. These local s-wave quintet pairs
reveal themselves as d-wave states in momentum space. Furthermore, due to the
broken inversion symmetry in these materials, the s-wave singlet state can mix
with a p-wave septet state, again with topologically-stable line nodes. Our
analysis lays the foundation for understanding the unconventional
superconductivity of the half-Heuslers.",1603.03376v3
2016-03-27,Thermoelectric properties of half-Heusler $\mathrm{ZrNiPb}$ by using first principles calculations,"We investigate electronic structures and thermoelectric properties of recent
synthetic half-Heusler $\mathrm{ZrNiPb}$ by using generalized gradient
approximation (GGA) and GGA plus spin-orbit coupling (GGA+SOC). Calculated
results show that $\mathrm{ZrNiPb}$ is a indirect-gap semiconductor. Within the
constant scattering time approximation, semi-classic transport coefficients are
performed through solving Boltzmann transport equations. It is found that the
SOC has more obvious influence on power factor in p-type doping than in n-type
doping, leading to a detrimental effect in p-type doping. These can be
explained by considering the SOC influences on the valence bands and conduction
bands near the Fermi level. The lattice thermal conductivity as a function of
temperature is calculated, and the corresponding lattice thermal conductivity
is 14.5 $\mathrm{W m^{-1} K^{-1}}$ at room temperature. By comparing the
experimental transport coefficients with calculated ones, the scattering time
is attained for 0.333 $\times$ $10^{-14}$ s. Finally, the thermoelectric figure
of merit $ZT$ can be attained, and the $ZT$ value can be as high as 0.30 at
high temperature by choosing appropriate doping level. It is possible to reduce
lattice thermal conductivity by point defects and boundaries, and make
half-Heusler $\mathrm{ZrNiPb}$ become potential candidate for efficient
thermoelectricity.",1603.08203v1
2016-03-28,"Ab initio Studies on Electronic and Magnetic Properties of X$_{2}$PtGa (X = Cr, Mn, Fe, Co) Heusler Alloys","Using first-principles calculations based on density functional theory, we
probe the electronic and magnetic properties of X$_{2}$PtGa (X being Cr, Mn,
Fe, Co) Heusler alloys. Our calculations predict that all these systems possess
inverse Heusler alloy structure in their respective ground states. Application
of tetragonal distortion leads to lowering of energy with respect to the cubic
phase for all the materials. The equilibrium volumes of both the phases are
nearly the same. These results of our calculations indicate that all these
materials are prone to undergo martensite transition, as has been recently
shown theoretically for Mn$_{2}$PtGa in the literature. Ground state with a
tetragonal symmetry of these materials is supported by the observation of soft
tetragonal shear constants in their cubic phase. By comparing the energies of
various types of magnetic configurations of these alloys we predict that
Cr$_{2}$PtGa and Mn$_{2}$PtGa possess ferrimagnetic configuration whereas
Fe$_{2}$PtGa and Co$_{2}$PtGa possess ferromagneic configuration in their
respective ground states.",1603.08350v2
2019-08-20,Coexistence of spin frustration and spin unfrustration induced spontaneous exchange bias in Heusler alloys,"The mechanism of spontaneous exchange bias (SEB) and the dominant factor of
its blocking temperature are still unclear in Heusler alloys. Here, the related
investigations are performed in Mn2Ni1.5Al0.5 Heusler alloys with SEB. The
results of both magnetic measurements and first-principles calculations
confirmed that spin frustrated and unfrustrated antiferromagnetic (AFM) states
coexist there and they have different magnetic anisotropies, which are
essential for SEB. Based on a series of measurement strategies, we demonstrate
that the frustrated AFM state undergoes a first-order magnetic transition to
the superferromagnet (SFM) state with the help of an external magnetic field,
and SFM is retained due to the first-order property of the magnetic transition.
SEB originates from the interface coupling of multiple sublattices between the
unfrustrated AFM state and SFM state. By analyzing the Arrott plot using the
Landau model, we found that the internal field of the system dominates the
blocking temperature of SEB, which paves the way for improving the blocking
temperature.",1908.07149v1
2019-12-23,Peculiarities of electronic transport and magnetic state in half-metallic ferromagnetic and spin gapless semiconducting Heusler alloys,"A brief survey of experimental and theoretical studies of half-metallic
ferromagnets (HMFs) and spin gapless semiconductors is given, the possible
candidates being the X$_2$YZ (X = Mn, Fe, Co; Y = Ti, V, Cr, Mn, Fe, Co, Ni; Z
= Al, Si, Ga, Ge, In, Sn, Sb) Heusler alloys. The data on the electrical
resistivity, normal and anomalous Hall Effect, and magnetic properties are
presented. It is shown that the Co$_2$FeZ alloys demonstrate properties of
conventional ferromagnets, the HMF properties being also manifested at the
variation of the Z-component. The Fe$_2$YAl and Mn$_2$YAl alloys show at the
variation of the Y-component both metallic and semiconducting electronic
characteristics, the magnetic properties, changing from the ferromagnetic to
compensated ferrimagnetic state. The HMF and spin gapless semiconductor states
are supposed to exist in these Heusler alloys systems.",1912.10771v1
2020-03-20,A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculations,"In the present work, the aspects of magnetic and structural properties of
Ni-Mn-Ga alloys are described in the framework of fist-principles approach and
mapped into ternary composition diagrams. The stable atomic arrangement and
magnetic alignment for compositions with cubic austenite and tetragonal
martensite structures across phase diagrams are predicted. It is shown that Ni-
and Ga-rich compositions possess the regular Heusler structure in contrast to
Mn-rich compositions with inverse Heusler structure as favorable one.
Compositions with unstable austenite structure are concentrated in the left and
right sides of diagram whereas compositions with unstable martensite structure
are located in the low-middle part of diagram. The magnetic phase diagrams
showing regions with the ferromagnetic order and the complex ferrimagnetic
order for austenitic and martensitic compositions are obtained. The results of
calculations are in a good agreement with available experimental data.",2003.09128v1
2020-06-05,Anomalous dependence of thermoelectric parameters on carrier concentration and electronic structure in Mn-substituted Fe2CrAl Heusler alloy,"We investigate the high temperature thermoelectric properties of Heusler
alloys Fe2-xMnxCrAl (0<x<1). Substitution of 12.5% Mn at Fe-site (x = 0.25)
causes a significant increase in high temperature resistivity (\r{ho}) and an
enhancement in the Seebeck coefficient (S), as compared to the parent alloy.
However, as the concentration of Mn is increased above 0.25, a systematic
decrement in the magnitude of both parameters is noted. These observations have
been ascribed (from theoretical analysis) to a change in band gap and
electronic structure of Fe2CrAl with Mn-substitution. Due to absence of mass
fluctuations and lattice strain, no significant change in thermal conductivity
is seen across this series of Heusler alloys. Additionally, S drastically
changes its magnitude along with a crossover from negative to positive above
900 K, which has been ascribed to the dominance of holes over electrons in high
temperature regime. In this series of alloys, S and \r{ho} shows a strong
dependence on the carrier concentration and strength of d-d hybridization
between Fe/Mn and Cr atoms.",2006.03234v2
2020-09-24,Electronic Structure and Thermoelectric Properties of Half-Heusler Alloys NiTZ,"We have investigated the electronic and thermoelectric properties of
half-Heusler alloys NiTZ (T = Sc, and Ti; Z = P, As, Sn, and Sb) having 18
valence electron. Calculations are performed by means of density functional
theory and Boltzmann transport equation with constant relaxation time
approximation, validated by NiTiSn. The chosen half-Heuslers are found to be an
indirect band gap semiconductor, and the lattice thermal conductivity is
comparable with the state-of-the-art thermoelectric materials. The estimated
power factor for NiScP, NiScAs, and NiScSb reveals that their thermoelectric
performance can be enhanced by appropriate doping rate. The value of ZT found
for NiScP, NiScAs, and NiScSb are 0.46, 0.35, and 0.29, respectively at 1200 K.",2009.11916v4
2020-12-22,"Structural insight using anomalous XRD into Mn2CoAl Heusler alloy films grown by magnetron sputtering, IBAS and MBE techniques","Inverse Heusler alloy Mn2CoAl thin films, known as a spin-gapless
semiconductor (SGS), grown by three different methods: ultra-high vacuum
magnetron spattering, Ar-ion beam assisted sputtering, and molecular beam
epitaxy, are investigated by comparing their electric transport properties,
microstructures and atomic-level structures. Of the samples, the Mn2CoAl thin
film grown by MBE consists of Mn- and Co-rich phases, the structures of which
are determined to be the L21B-type and disordered L21-type, respectively,
according to anomalous XRD analysis. None of them forms the XA-type structure
expected for SGS Heusler alloy, although they all show SGS characteristics. We
suggest, to validate SGS characteristics, it is necessary to extract not only
magnetic and electric transport properties but also information about
microstructures and atomic-scale structures of the films including defects such
as atomic swap.",2012.12282v1
2021-02-01,"Electronic, magnetic and galvanomagnetic properties of Co-based Heusler alloys: possible states of a half-metallic ferromagnet and spin gapless semiconductor","Parameters of the energy gap and, consequently, electronic, magnetic and
galvanomagnetic properties in different X$_2$YZ Heusler alloys can vary quite
strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless
semiconductors (SGSs) with almost 100% spin polarization of charge carriers are
promising materials for spintronics. The changes in the electrical, magnetic
and galvanomagnetic properties of the Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and
Co$_2$MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF and/or SGS states
were followed and their interconnection was established. Significant changes in
the values of the magnetization and residual resistivity were found. At the
same time, the correlations between the changes in these electronic and
magnetic characteristics depending on the number of valence electrons and spin
polarization are observed.",2102.00952v1
2021-04-22,Chemical bonding origin of the thermoelectric power factor in Half-Heusler semiconductors,"Intermetallic semiconductors with the cubic Half-Heusler structure (XYZ) have
excellent thermoelectric properties. This has been attributed to the high
degeneracy of the carrier pockets in the band structure, but large differences
are found between different material compositions. Half-Heuslers are often
interpreted within Zintl chemistry, making a clear distinction between an
electropositive cation ($X^{n+}$) and an extended polyanion ($YZ^{n-}$). Based
on quantitative real space chemical bonding analysis, we unravel large degrees
of covalent bonding between the formal cation and anion, making the Zintl
distinction clearly invalid. This covalence is shown to strongly affect the
band structure, thermoelectric properties and response properties in the
materials, with improved thermoelectric properties observed for those materials
that least follow the Zintl concept. This expands our knowledge of the chemical
bonding motifs governing physical properties, and gives a critical view on the
simplistic chemical concepts too often applied for design of complex materials.",2104.11281v1
2021-05-11,First-principles calculations and experimental studies on Co2FeGe Heusler alloy nanoparticles for spintronics applications,"Here, we report the synthesis and physical properties of Co2FeGe (CFG)
Heusler alloy (HA) nanoparticles (NPs). The NPs of size 23 nm are prepared
using the co-precipitation method. X-ray and selected area electron diffraction
patterns have confirmed the cubic Heusler phase of the NPs with the
A2-disorder. These NPs are soft ferromagnetic, and exhibit a high saturation
magnetization (Ms) along with a very high Curie temperature (Tc) of 1060 K. The
observed Tc value matches closely with the theoretically calculated one
following a model provided by Wurmehl et al. [1]. The high Ms and Tc make the
present system a potential candidate for magnetically activated nano-devices
working at high temperatures. The near-integral value 5.9 mehoB/f.u. of Ms at
low temperatures indicates that the half-metallic ferromagnetism is preserved
even in the particles even on the 20 nm length scale. Additionally, we have
facilitated the existing HA-NP preparation method, which can be used in
synthesizing other HA-NPs. The first-principles density functional theory
computations complement the experimental results.",2105.05200v1
2021-09-23,Tuning magnetic antiskyrmion stability in tetragonal inverse Heusler alloys,"The identification of materials supporting complex, tunable magnetic order at
ambient temperatures is foundational to the development of new magnetic device
architectures. We report the design of Mn2XY tetragonal inverse Heusler alloys
that are capable of hosting magnetic antiskyrmions whose stability is sensitive
to elastic strain. We first construct a universal magnetic Hamiltonian
capturing the short- and long- range magnetic order which can be expected in
these materials. This model reveals critical combinations of magnetic
interactions that are necessary to approach a magnetic phase boundary, where
the magnetic structure is highly susceptible to small perturbations such as
elastic strain. We then computationally search for quaternary Mn2(X1,X2)Y
alloys where these critical interactions may be realized and which are likely
to be synthesizable in the inverse Heusler structure. We identify the
Mn2Pt(1-z)X(z)Ga family of materials with X=Au, Ir, Ni as an ideal system for
accessing all possible magnetic phases, with several critical compositions
where magnetic phase transitions may be actuated mechanically.",2109.11423v1
2021-09-24,Impact of local arrangement of Fe and Ni on the phase stability and magnetocrystalline anisotropy in Fe-Ni-Al Heusler alloys,"On the basis of density functional calculations, we report on a comprehensive
study of the influences of atomic arrangement and Ni substitution for Al on the
ground state structural and magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$
Heusler alloys. We discuss systematically the competition between five
Heusler-type structures formed by shuffles of Fe and Ni atoms and their
thermodynamic stability. All~Ni-rich Fe$_2$Ni$_{1+x}$Al$_{1-x}$ tend to
decompose into a dual-phase mixture consisting of Fe$_2$NiAl and~FeNi.
The~successive replacement of Ni by Al leads to a change of ground state
structure and eventually an increase in magnetocrystalline anisotropy
energy~(MAE). We predict for stoichiometric Fe$_2$NiAl a ground state structure
with nearly cubic lattice parameters but alternating layers of Fe and Ni
possessing an uniaxial MAE which is even larger than tetragonal L1$_0$-FeNi.
This opens an alternative route for improving the phase stability and magnetic
properties in FeNi-based permanent magnets.",2109.12005v2
2023-09-06,Development of a self-consistent thermodynamically optimized database along with phase transition experiments in Ni-Mn-Ga system for magnetocaloric applications,"Magnetocaloric materials have received significant attention of research
community as they can minimize the use of harmful gases (CFCs, HFCs) and render
eco-friendly refrigeration. Heusler alloys (Ni2MnGa) are known for their
magnetocaloric effects, which make them useful as energy efficient and
eco-friendly refrigerating materials. Magnetocaloric properties significantly
depend on the composition of these alloys. Ni-Mn-Ga is one of the interesting
Heusler systems, which exhibits magnetocaloric properties. In the present
study, we performed the thermodynamic optimization of two sub binaries of the
Ni-Mn-Ga system: Mn-Ga and Ni-Ga, using CALPHAD approach. A Modified
Quasichemical Model (MQM) was used to describe the thermodynamic properties of
the liquid solutions in both the binaries. Both the binaries were combined with
Mn-Ni to develop a self-consistent thermodynamic database for Ni-Mn-Ga. In
order to resolve the existing experimental discrepancies in the Mn-Ga and Ni-Ga
system, few alloy compositions were prepared and analyzed using differential
thermal analysis. Finally, the developed thermodynamic database was used to
calculate the ternary isothermal section of the Ni-Mn-Ga (Heusler alloy) system
at 1073 K with a proposed phase region for magnetocaloric applications.",2309.02694v1
2024-03-12,Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization,"Magnetic random access memory that uses magnetic tunnel junction memory cells
is a high performance, non-volatile memory technology that goes beyond
traditional charge-based memories. Today its speed is limited by the high
magnetization of the memory storage layer. Here we show that fast and highly
reliable switching is possible using a very low magnetization ferrimagnetic
Heusler alloy, Mn3Ge. Moreover, the tunneling magnetoresistance is the highest
yet achieved for a ferrimagnetic material at ambient temperature. Furthermore,
the devices were prepared on technologically relevant amorphous substrates
using a novel combination of a nitride seed layer and a chemical templating
layer. These results show a clear path to the lowering of switching currents
using ferrimagnetic Heusler materials and, therefore, to the scaling of high
performance magnetic random access memories beyond those nodes possible with
ferromagnetic devices.",2403.08112v1
2023-02-22,"Influence of Gd-rich precipitates on the martensitic transformation, magnetocaloric effect and mechanical properties of Ni-Mn-In Heusler alloys -- A comparative study","A multi-stimuli cooling cycle can be used to increase the cyclic caloric
performance of multicaloric materials like Ni-Mn-In Heusler alloys. However,
the use of a uniaxial compressive stress as an additional external stimulus to
a magnetic field requires good mechanical stability. Improvement of mechanical
stability and strength by doping has been shown in several studies. However,
doping is always accompanied by grain refinement and a change in transition
temperature. This raises the question of the extent to which mechanical
strength is related to grain refinement, transition temperature, or
precipitates. This study shows a direct comparison between a single-phase
Ni-Mn-Sn and a two-phase Gd-doped Ni-Mn-In alloy with the same transition
temperature and grain size. It is shown that the excellent magnetocaloric
properties of the Ni-Mn-In matrix are maintained with doping. The isothermal
entropy change and adiabatic temperature change are reduced by only 15% in the
two-phase Ni-Mn-In-Heusler alloy compared to the single-phase alloy, which is
resulting from a slight increase in thermal hysteresis and the width of the
transition. Due to the same grain size and transition temperature, this effect
can be directly related to the precipitates. The introduction of Gd
precipitates leads to a 100% improvement in mechanical strength, which is
significantly lower than the improvement observed for Ni-Mn-In alloys with
grain refinement and Gd precipitates. This reveals that a significant
contribution to the improved mechanical stability in Gd-doped Heusler alloys is
related to grain refinement.",2302.11439v1
2008-10-29,Thermodynamics of the Heusler alloy Co_2-xMn_1+xSi: a combined density functional theory and cluster expansion study,"Previous studies indicated that intrinsic point defects play a crucial role
for the density of states of ferromagnetic half-metals in the band gap region:
At large concentrations, defect-derived bands might close the gap at the Fermi
energy in the minority spin channel. In this work, structural disorder in the
Co- and Mn-sublattices of the full Heusler alloy Co_2-xMn_1+xSi (-1 < x < 2) is
investigated with a cluster expansion approach, parametrized using all-electron
density functional theory calculations. By establishing two separate cluster
expansions, one for the formation energy and one for the total spin moment, we
are in position to determine the stability of different configurations, to
predict new (also half-metallic) ground states and to extend the known
Slater-Pauling rule for ideally stoichiometric Heusler alloys to
non-stoichiometric, Mn-rich compositions. This enables us to identify
potentially half-metallic structures in the Mn-rich region. With the help of
Monte Carlo simulations based on the cluster expansion, we establish
theoretically that Co_2-xMn_1+xSi close to the stoichiometric composition ought
to show a high degree of structural order in thermodynamic equilibrium. Hence,
samples prepared with the correct stoichiometry should indeed be half-metallic
after thermal annealing. Moreover, we predict that adding a small amount of Mn
to stoichiometric Co_2MnSi allows to suppress the thermally activated formation
of detrimental Co antisites. At Mn-rich compositions (x>1), the ordered ground
state structures predicted for zero temperature are found to be thermally
unstable and to decompose into Co2MnSi and Mn3Si above room temperature.",0810.5354v2
2014-10-01,Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy,"Spin gapless semiconductors (SGS) form a new class of magnetic
semiconductors, which has a band gap for one spin sub band and zero band gap
for the other, and thus are useful for tunable spin transport based
applications. In this paper, we report the first experimental evidence for spin
gapless semiconducting behavior in CoFeMnSi Heusler alloy. Such a behavior is
also confirmed by first principles band structure calculations. The most stable
configuration obtained by the theoretical calculation is verified by
experiment. The alloy is found to crystallize in the cubic Heusler structure
(LiMgPdSn type) with some amount of disorder and has a saturation magnetization
of 3.7 Bohr's magneton/f.u.. and Curie temperature of 620 K. The saturation
magnetization is found to follow the Slater-Pauling behavior, one of the
prerequisites for SGS. Nearly temperature-independent carrier concentration and
electrical conductivity is observed from 5 to 300 K. An anomalous Hall
coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection
data has yielded the current spin polarization value of 0.64, which is found to
be robust against the structural disorder. All these properties are quite
promising for the spintronic applications such as spin injection and can bridge
a gap between the contrasting behavior of half-metallic ferromagnets and
semiconductors.",1410.0177v1
2016-08-09,Compensated ferrimagnetic tetragonal Heusler thin films for antiferromagnetic spintronics,"In recent years, antiferromagnetic spintronics has received much attention
since ideal antiferromagnets do not produce stray fields and are much more
stable to external magnetic fields compared to materials with net
magnetization. Akin to antiferromagnets, compensated ferrimagnets have zero net
magnetization but have the potential for large spin-polarization and strong out
of plane magnetic anisotropy, and, hence, are ideal candidates for high density
memory applications. Here, we demonstrate that a fully compensated magnetic
state with a tunable magnetic anisotropy is realized in Mn-Pt-Ga based
tetragonal Heusler thin films. Furthermore, we show that a bilayer formed from
a fully compensated and a partially compensated Mn-Pt-Ga layer, exhibits a
large interfacial exchange bias up to room temperature. The present work
establishes a novel design principle for spintronic devices that are formed
from materials with similar elemental compositions and nearly identical crystal
and electronic structures. Such devices are of significant practical value due
to their improved properties such as thermal stability. The flexible nature of
Heusler materials to achieve tunable magnetizations, and anisotropies within
closely matched materials provides a new direction to the growing field of
antiferromagnetic spintronics.",1608.02887v1
2018-09-20,Surface Majorana Flat Bands in $j=\frac{3}{2}$ Superconductors with Singlet-Quintet Mixing,"Recent experiments have revealed the evidence of nodal-line superconductivity
in half-Heusler superconductors, e.g. YPtBi. Theories have suggested the
topological nature of such nodal-line superconductivity and proposed the
existence of surface Majorana flat bands on the (111) surface of half-Heusler
superconductors. Due to the divergent density of states of the surface Majorana
flat bands, the surface order parameter and the surface impurity play essential
roles in determining the surface properties. In this work, we studied the
effect of the surface order parameter and the surface impurity on the surface
Majorana flat bands of half-Heusler superconductors based on the Luttinger
model. To be specific, we consider the topological nodal-line superconducting
phase induced by the singlet-quintet pairing mixing, classify all the possible
translationally invariant order parameters for the surface states according to
irreducible representations of $C_{3v}$ point group, and demonstrate that any
energetically favorable order parameter needs to break time-reversal symmetry.
We further discuss the energy splitting in the energy spectrum of surface
Majorana flat bands induced by different order parameters and non-magnetic or
magnetic impurities. We proposed that the splitting in the energy spectrum can
serve as the fingerprint of the pairing symmetry and mean-field order
parameters. Our theoretical prediction can be examined in the future scanning
tunneling microscopy experiments.",1809.07455v2
2019-11-12,"Formation and magnetic properties of spark plasma sintered Mn$_{3-δ}$ ($δ$ = 0, 1) alloys","We present the synthesis of D0$_{22}$ Mn$_{3 - \delta}$Ga ($\delta$ = 0, 1)
Heusler alloys by Spark Plasma Sintering method. The single phase Mn$_3$Ga
(T$_\mathrm{c}$ $\simeq$ 780 K) is synthesized, while Mn$_2$Ga (T$_\mathrm{c}$
$\simeq$ 710 K) is found to coexist with a near-stoichiometric room temperature
paramagnetic Mn$_9$Ga$_5$~($\approx$ 15 \%) phase due to its lower formation
energy, as confirmed from our density functional theory (DFT) calculations. The
alloys show hard magnetic behavior with large room temperature spontaneous
magnetization m$_s$(80 kOe) = 1.63 (0.83) $\mu_\mathrm{B}$/f.u. and coercivity
H$_\mathrm{c}$ = 4.28 (3.35) kOe for Mn$_3$Ga (Mn$_2$Ga). The magnetic
properties are further investigated till T$_\mathrm{c}$ and the H$_\mathrm{c}$
(T) analysis by Stoner-Wohlfarth model shows the nucleation mechanism for the
magnetization reversal. The experimental results are well supported by DFT
calculations, which reveal that the ground state of D0$_{22}$ Mn$_2$Ga is
achieved by the removal of Mn-atoms from full Heusler Mn$_3$Ga structure in
accordance with half Heusler alloy picture.",1911.05040v1
2021-07-19,Impact of local arrangement of Fe and Ni in Fe-Ni-Al Heusler alloys on the phase stability and magnetocrystalline anisotropy,"On the basis of the density functional calculations in combination with the
supercell approach, we report on a complete study of the influences of atomic
arrangement and Ni substitution for Al on the ground state structural and
magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss
systematically the competition between five cubic Heusler-type structures
formed by shuffles of Fe and Ni atoms to reveal routes for improving the phase
stability and magnetic properties, in particular magnetocrystalline
anisotropy~(MAE). We predict that in case of Fe$_2$NiAl the ground state cubic
structure with alternated layers of Fe and Ni possesses the highest uniaxial
MAE which twice larger than that for the tetragonal L1$_0$ FeNi. The successive
Ni doping at Al sublattice leads to a change of ground state structure and to
reduce of the MAE. In addition, the phase stability against the decomposition
into the stable systems at finite-temperatures is discussed. All~Ni-rich
Fe$_2$Ni$_{1+x}$Al$_{1-x}$ are turned to be decomposed into a dual-phase
consisting of Fe$_2$NiAl and FeNi.",2107.08804v2
2019-03-11,Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys,"Shell ferromagnetism is a new functional property of certain Heusler alloys
which has been recently observed in
$\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$. We report the results of a
comparative study of the magnetic microstructure of bulk
$\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys using
magnetometry, synchrotron x-ray diffraction, and magnetic small-angle neutron
scattering (SANS). By combining unpolarized and spin-polarized SANS (POLARIS)
we demonstrate that a number of important conclusions regarding the mesoscopic
spin structure can be made. In particular, the analysis of the magnetic neutron
data suggests that nanoprecipitates with an effective ferromagnetic component
form in an antiferromagnetic matrix on field annealing at $700 \, \mathrm{K}$.
These particles represent sources of perturbation, which seem to give rise to
magnetically disordered regions in the vicinity of the particle-matrix
interface. Analysis of the spin-flip SANS cross section via the computation of
the correlation function yields a value of $\sim 55 \, \mathrm{nm}$ for the
particle size and $\sim 20 \, \mathrm{nm}$ for the size of the spin-canted
region.",1903.04183v1
2020-03-25,Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materials,"Chemical doping is one of the most important strategies for tuning electrical
properties of semiconductors, particularly thermoelectric materials. Generally,
the main role of chemical doping lies in optimizing the carrier concentration,
but there can potentially be other important effects. Here, we show that
chemical doping plays multiple roles for both electron and phonon transport
properties in half-Heusler thermoelectric materials. With ZrNiSn-based
half-Heusler materials as an example, we use high-quality single and
polycrystalline crystals, various probes, including electrical transport
measurements, inelastic neutron scattering measurement, and first-principles
calculations, to investigate the underlying electron-phonon interaction. We
find that chemical doping brings strong screening effects to ionized
impurities, grain boundary, and polar optical phonon scattering, but has
negligible influence on lattice thermal conductivity. Furthermore, it is
possible to establish a carrier scattering phase diagram, which can be used to
select reasonable strategies for optimization of the thermoelectric
performance.",2003.11222v3
2020-06-03,Half-Heusler thermoelectric materials: NMR studies,"We report $^{59}$Co, $^{93}$Nb, and $^{121}$Sb nuclear magnetic resonance
(NMR) measurements combined with density functional theory (DFT) calculations
on a series of half-Heusler semiconductors, including NbCoSn, ZrCoSb, TaFeSb
and NbFeSb, to better understand their electronic properties and general
composition-dependent trends. These materials are of interest as potentially
high efficiency thermoelectric materials. Compared to the other materials, we
find that ZrCoSb tends to have a relatively large amount of local disorder,
apparently antisite defects. This contributes to a small excitation gap
corresponding to an impurity band near the band edge. In NbCoSn and TaFeSb,
Curie-Weiss-type behavior is revealed, which indicates a small density of
interacting paramagnetic defects. Very large paramagnetic chemical shifts are
observed associated with a Van Vleck mechanism due to closely spaced $d$ bands
splitting between the conduction and valence bands. Meanwhile, DFT methods were
generally successful in reproducing the chemical shift trend for these
half-Heusler materials, and we identify an enhancement of the larger-magnitude
shifts, which we connect to electron interaction effects. The general trend is
connected to changes in $d$-electron hybridization across the series.",2006.02013v1
2020-11-06,Thermoelectric power factor under strain-induced band-alignment in the half-Heuslers NbCoSn and TiCoSb,"Band convergence is an effective strategy to improve the thermoelectric
performance of complex bandstructure thermoelectric materials. Half-Heuslers
are good candidates for band convergence studies because they have multiple
bands near the valence bad edge that can be converged through various band
engineering approaches providing power factor improvement opportunities.
Theoretical calculations to identify the outcome of band convergence employ
various approximations for the carrier scattering relaxation times (the most
common being the constant relaxation time approximation) due to the high
computational complexity involved in extracting them accurately. Here, we
compare the outcome of strain-induced band convergence under two such
scattering scenarios: i) the most commonly used constant relaxation time
approximation and ii) energy dependent inter- and intra-valley scattering
considerations for the half-Heuslers NbCoSn and TiCoSb. We show that the
outcome of band convergence on the power factor depends on the carrier
scattering assumptions, as well as the temperature. For both materials
examined, band convergence improves the power factor. For NbCoSn, however, band
convergence becomes more beneficial as temperature increases, under both
scattering relaxation time assumptions. In the case of TiCoSb, on the other
hand, constant relaxation time considerations also indicate that the relative
power factor improvement increases with temperature, but under the energy
dependent scattering time considerations, the relative improvement weakens with
temperature. This indicates that the scattering details need to be accurately
considered in band convergence studies to predict more accurate trends.",2011.04288v1
2021-05-05,Rhodium based half-Heusler alloys as possible optoelectronic and thermoelectric materials,"On the basis of density functional theory and semi-classical Boltzmann
theory, we have investigated the structural, elastic, electronic, optical and
thermoelectric properties of 18--valence electron count rhodium based
half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The absence
of imaginary frequencies in the phonon dispersion curve for these system
verifies that they are structurally stable. RhTiP is ductile in nature, while
others are brittle. The alloys are found to be semiconducting with indirect
band gaps ranging from 0.94 to 1.01 eV. Our calculations suggest these
materials to have high absorption coefficient and optical conductivity in the
ultraviolet as well as visible region. While considering thermoelectricity, we
found that $p$--type doping is more favorable in improving the thermoelectric
properties. The calculated values of power factor with $p$-type doping are
comparable to some of the reported half-Heusler materials. The optimum figure
of merit \zt\ is $\sim1$ for RhTiBi suggesting it as a promising candidate for
thermoelectric applications while RhTiP, RhTiAs, and RhTiSb with optimum \zt \
values between 0.38 to 0.67 are possible candidates for use in thermoelectric
devices.",2105.02177v1
2021-10-05,Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor,"In superconductors, electrons with spin ${s=1/2}$ form Cooper pairs whose
spin structure is usually singlet (${S=0}$) or triplet (${S=1}$). When the
electronic structure near the Fermi level is characterized by fermions with
angular momentum ${j=3/2}$ due to strong spin-orbit interactions, novel pairing
states such as even-parity quintet (${J=2}$) and odd-parity septet (${J=3}$)
states become allowed. Prime candidates for such exotic states are half-Heusler
superconductors, which exhibit unconventional superconducting properties, but
their pairing nature remains unsettled. Here we show that the superconductivity
in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by
the admixture of isotropic even-parity singlet and anisotropic odd-parity
septet pairing, whose ratio can be tuned by electron irradiation. From
magnetotransport and penetration depth measurements, we find that carrier
concentrations and impurity scattering both increase with irradiation,
resulting in a nonmonotonic change of the superconducting gap structure. Our
findings shed new light on our fundamental understanding of unconventional
superconducting states in topological materials.",2110.01819v2
2022-08-10,Defect engineering and Fermi-level tuning in half-Heusler topological semimetals,"Three-dimensional topological semimetals host a range of interesting quantum
phenomena related to band crossing that give rise to Dirac or Weyl fermions,
and can be potentially engineered into novel quantum devices. Harvesting the
full potential of these materials will depend on our ability to position the
Fermi level near the symmetry-protected band crossings so that their exotic
spin and charge transport properties become prominent in the devices. Recent
experiments on bulk and thin films of topological half-Heuslers show that the
Fermi level is far from the symmetry-protected crossings, leading to strong
interference from bulk bands in the observation of topologically protected
surface states. Using density functional theory calculations we explore how
intrinsic defects can be used to tune the Fermi level in the two representative
half-Heusler topological semimetals PtLuSb and PtLuBi. Our results explain
recent results of Hall and angle-resolved photoemission measurements. The
calculations show that Pt vacancies are the most abundant intrinsic defects in
these materials grown under typical growth conditions, and that these defects
lead to excess hole densities that place the Fermi level significantly below
the expected position in the pristine material. Directions for tuning the Fermi
level by tuning chemical potentials are addressed.",2208.05415v2
2023-03-08,Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa,"Spin semimetals are amongst the most recently discovered new class of
spintronic materials, which exhibit a band gap in one spin channel and
semimetallic feature in the other, thus facilitating tunable spin transport.
Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along
with giant coercivity and spin-valve characteristics using a combined
experimental and theoretical study. The alloy crystallizes in an inverse
Heusler structure (without any martensitic transition) with a para- to
ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant
coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient,
relatively low magnitude and weak temperture dependance of electrical
resistivity suggest the semimetallic character of the alloy. This is further
supported by our specific heat measurement. Magnetoresistance (MR) confirms an
irreversible nature (with its magnitude $\sim$1\%) along with a change of sign
across the magnetic transition indicating the potentiality of Mn$_2$IrGa in
magnetic switching applications. In addition, asymmetric nature of MR in the
positive and negative field cycles is indicative of spin-valve characteristics.
Our ab-initio calculations confirm the inverse Heusler structure with
ferrimagnetic ordering to be the lowest energy state, with a saturation
magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic
axis with considerable magneto-crystalline anisotropy energy. A large positive
Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall
conductivity ($\sim$-180 S/cm).",2303.04649v2
2017-01-28,"Half-metallicity versus Symmetry in Pt, Ni and Co-based Half Heusler Alloys: A First-principles Calculation","Using first principles calculations based on density functional theory, we
study the geometric, electronic, and magnetic properties of Pt, Ni and Co-based
half Heusler alloys, namely, Pt$BC$, Ni$BC$ and Co$BC$ ($B$ = Cr, Mn and Fe;
$C$ = Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te). We calculate the
formation energy of these alloys in various crystal symmetries, which include,
the (face-centered) cubic $C1_{b}$ ($F\bar{4}$3m), orthorhombic ($Pnma$), as
well as hexagonal ($P\bar{6}2m$ and $P6_{3}/mmc$) structures. It has been
observed that out of all the 108 structures, studied here, energetically stable
cubic structure is observed for only 18 materials. These alloys are primarily
having either a $C$ atom or an $A$ atom with a high atomic number. We also
observe that along with the alloys with $C$ atoms from group IIIA, IVA and VA
-- alloys with $C$ atoms from group VIA are also found to be, by and large,
energetically stable. To examine the relative stabilities of different
symmetries in order to search for the respective lowest energy state for each
of the above-mentioned systems, as well as to find whether a material in the
ground state is half-metallic or not, we analyze the formation energy, and the
electronic density of states, in detail. Based on these analyses, the
possibility of existence of any {\it one-to-one relationship} between the {\it
cubic symmetry} and the {\it half-metallicity} in these half Heusler alloys is
probed. Subsequently, we predict about the existence of a few new {\it
non-cubic} half Heusler alloys with substantially low density of states at one
of the spin channels and reasonably {\it high spin polarization at the Fermi
level}",1701.08282v2
2014-06-03,Phase coexistence and interrupted 1st order transition in magnetic shape memory alloys,"Current theoretical studies on structural and magnetic properties of
functional Ni-Mn-Z (Z = Ga, In, Sn) Heusler alloys address the origin of the
structural transition from the austenite to martensite, and also address the
dominant contribution to the latent heat associated with this
magneto-structural transition. This should help understand the origin of
kinetic arrest of 1st order magnetic transitions.",1406.0627v1
2022-10-25,Conventional Half-Heusler Alloys Advance State-of-the-Art Thermoelectric Properties,"Half-Heusler (HH) phases have garnered much attention as thermally stable and
non-toxic thermoelectric materials for power conversion. The most studied
alloys to date utilize Hf, Zr, and Ti as the base components. These alloys can
achieve a moderate dimensionless figure of merit, ZT, near 1. Recent studies
have advanced the thermoelectric performance of HH alloys by employing
nanostructures and novel compositions to achieve larger ZT, reaching as high as
1.5. Herein, we report that traditional alloying techniques applied to the
conventional HfZr-based half-Heusler alloys can also lead to exceptional ZT.
Specifically, we present the well-studied p-type Hf0.3Zr0.7CoSn0.3Sb0.7,
previously reported to have a ZT~0.8, resonantly doped with less than 1 at. %
metallic Al on the Sn/Sb site, touting a remarkable ZT near 1.5 at 980 K. This
is achieved through a significant increase in power factor, by ~65%, and a
notable but smaller decrease in thermal conductivity, by ~13%, at high
temperatures. These favorable thermoelectric properties are discussed in terms
of a local anomaly in the density of states near the Fermi energy designed to
enhance the Seebeck coefficient, as revealed by first-principles calculations,
as well as the emergence of a highly heterogeneous grain structure that can
scatter phonons across different length scales, effectively suppressing the
thermal conductivity. Consequently, the effective mass is significantly
enhanced from ~ 7 to 10me within a single parabolic band model, consistent with
the result from first-principles calculations. The discovery of high ZT in a
commonly studied half-Heusler alloy through a conventional and non-complex
approach opens a new path for further discoveries in similar types of alloys.
Furthermore, it is reasonable to believe that the study will reinvigorate
effort in exploring high thermoelectric performance in conventional alloy
systems.",2210.13949v1
2024-02-08,Inflation and Isotropization in Quintom Cosmology,"This paper studies inflation and isotropization in the quintom model in the
Bianchi I, Bianchi III, and Kantowski-Sachs backgrounds. First, we investigate
inherent properties and generalize Heusler's proposition. Then by the use of
the dynamical system approach, we consider the system in multiplicative and
collective modes of potentials. The conclusions of Collins and Hawking and also
Burd and Barrow are discussed.",2402.05454v1
2015-07-05,k-bitransitive and compound operators on Banach spaces,"In this this paper, we introduce new classes of operators in complex Banach
spaces, which we call k-bitransitive operators and compound operators to study
the direct sum of diskcyclic operators. We create a set of sufficient
conditions for k-bitransitivity and compound. We show the relation between
topologically mixing operators and compound operators. Also, we extend the
Godefroy-Shapiro Criterion for topologically mixing operators to compound
operators.",1507.01166v1
2020-07-07,A Natural Discrete One Parameter Polynomial Exponential Distribution,"In this paper, a new natural discrete version of the one parameter polynomial
exponential family of distributions have been proposed and studied. The
distribution is named as Natural Discrete One Parameter Polynomial Exponential
(NDOPPE) distribution. Structural and reliability properties have been studied.
Estimation procedure of the parameter of the distribution have been mentioned.
Compound NDOPPE distribution in the context of collective risk model have been
obtained in closed form. The new compound distribution has been compared with
the classical compound Poisson, compound Negative binomial, compound discrete
Lindley, compound xgamma-I and compound xgamma-II distributions regarding
suitability of modelling extreme data with the help of some automobile claim.",2007.03571v1
2021-05-07,Compound Arbitrarily Varying Channels,"We propose a communication model, that we call compound arbitrarily varying
channels (CAVC), which unifies and generalizes compound channels and
arbitrarily varying channels (AVC). A CAVC can be viewed as a noisy channel
with a fixed, but unknown, compound-state and an AVC-state which may vary with
every channel use. The AVC-state is controlled by an adversary who is aware of
the compound-state. We study three problems in this setting: 'communication',
'communication and compound-state identification', and 'communication or
compound-state identification'. For these problems, we study conditions for
feasibility and capacity under deterministic coding and random coding.",2105.03420v1
1999-11-25,Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation,"The results of fluorescence measurements of magnetic circular dichroism (MCD)
in Mn L_2,L_3 X-ray emission and absorption for Heusler alloys NiMnSb and
Co2MnSb are presented. Very intense resonance Mn L_3 emission is found at the
Mn 2p_3/2 threshold and is attributed to a peculiarity of the threshold
excitation in materials with the half-metallic character of the electronic
structure. A theoretical model for the description of resonance scattering of
polarized x-rays is suggested.",9911415v1
2003-04-15,First-principles study of lattice instabilities in the ferromagnetic martensite Ni$_2$MnGa,"The phonon dispersion relations and elastic constants for ferromagnetic
Ni$_2$MnGa in the cubic and tetragonally distorted Heusler structures are
computed using density-functional and density-functional perturbation theory
within the spin-polarized generalized-gradient approximation. For
$0.9<c/a<1.06$, the TA$_2$ tranverse acoustic branch along $[110]$ and
symmetry-related directions displays a dynamical instability at a wavevector
that depends on $c/a$. Through examination of the Fermi-surface nesting and
electron-phonon coupling, this is identified as a Kohn anomaly. In the parent
cubic phase the computed tetragonal shear elastic constant,
C$^\prime$=(C$_{11}-$C$_{12}$)/2, is close to zero, indicating a marginal
elastic instability towards a uniform tetragonal distortion. We conclude that
the cubic Heusler structure is unstable against a family of energy-lowering
distortions produced by the coupling between a uniform tetragonal distortion
and the corresponding $[110]$ modulation. The computed relation between the
$c/a$ ratio and the modulation wavevector is in excellent agreement with
structural data on the premartensitic ($c/a$ = 1) and martensitic ($c/a$ =
0.94) phases of Ni$_2$MnGa.",0304349v1
2004-04-07,"First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb)","The interatomic exchange interactions and Curie temperatures in Ni-based full
Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework
of the density-functional theory. The calculation of the exchange parameters is
based on the frozen-magnon approach. Despite closeness of the experimental
Curie temperatures for all four systems their magnetism appeared to differ
strongly. This difference involves both the Mn-Mn and Mn-Ni exchange
interactions. The Curie temperatures, Tc, are calculated within the mean-field
approximation by solving a matrix equation for a multi-sublattice system. Good
agreement with experiment for all four systems is obtained. The role of
different exchange interactions in the formation of Tc of the systems is
discussed.",0404162v1
2004-10-28,Spin injection from the Heusler alloy Co_2MnGe into Al_0.1Ga_0.9As/GaAs heterostructures,"Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n
Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum
steady-state spin polarization of approximately 13% at 2 K is measured in two
types of heterostructures. The injected spin polarization at 2 K is calculated
to be 27% based on a calibration of the spin detector using Hanle effect
measurements. Although the dependence on electrical bias conditions is
qualitatively similar to Fe-based spin injection devices of the same design,
the spin polarization injected from Co_2MnGe decays more rapidly with
increasing temperature.",0410751v1
2005-04-26,Pressure dependence of the Curie temperature in Ni2MnSn Heusler alloy: A first-principles study,"The pressure dependence of electronic structure, exchange interactions and
Curie temperature in ferromagnetic Heusler alloy Ni2MnSn has been studied
theoretically within the framework of the density-functional theory. The
calculation of the exchange parameters is based on the frozen--magnon approach.
The Curie temperature, Tc, is calculated within the mean-field approximation by
solving the matrix equation for a multi-sublattice system. In agrement with
experiment the Curie temperature increased from 362K at ambient pressure to 396
at 12 GPa. Extending the variation of the lattice parameter beyond the range
studied experimentally we obtained non-monotonous pressure dependence of the
Curie temperature and metamagnetic transition. We relate the theoretical
dependence of Tc on the lattice constant to the corresponding dependence
predicted by the empirical interaction curve. The Mn-Ni atomic interchange
observed experimentally is simulated to study its influence on the Curie
temperature.",0504644v1
2005-06-06,Unusual transport properties of ferromagnetic Heusler alloy Co$_2$TiSn,"We report results of magnetization, zero field resistivity and
magnetoresistance measurements in ferromagnetic Heusler alloy Co$_2$TiSn. There
is a striking change in the character of electron transport as the system
undergoes the paramagnetic to ferromagnetic transition. In the paramagnetic
state the nature of the electron transport is like that of a semiconductor and
this changes abruptly to metallic behaviour at the onset of ferromagnetic
ordering. Application of external magnetic field tends to suppress this
semiconducting like transport leading to a negative magnetoresistance which
reaches a peak in the vicinity of Curie temperature. Comparison is made with
the similar unusual behaviour observed in other systems including UNiSn and
manganites.",0506126v1
2006-01-24,Lattice dynamics and phonon softening in Ni-Mn-Al Heusler alloys,"Inelastic and elastic neutron scattering have been used to study a single
crystal of the Ni$_{54}$Mn$_{23}$Al$_{23}$ Heusler alloy over a broad
temperature range. The paper reports the first experimental determination of
the low-lying phonon dispersion curves for this alloy system. We find that the
frequencies of the TA$_2$ modes are relatively low. This branch exhibits an
anomaly (dip) at a wave number $\xi_{0} ={1/3}\approx 0.33$, which softens with
decreasing temperature. Associated with this anomalous dip at $\xi_{0}$, an
elastic central peak scattering is also present. We have also observed
satellites due to the magnetic ordering.",0601546v1
2006-05-31,Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films,"We have studied the possibly half metallic Co2FeSi full Heusler alloy by
means of spin- and time-resolved photoemission spectroscopy. For excitation,
the second and fourth harmonic of femtosecond Ti:sapphire lasers were used,
with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the
dependence of the measured surface spin polarization on the particular
photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon
photoemission (2PPE). The observed differences in the spin polarization can be
explained by a spin-dependent lifetime effect occurring in the 2-photon
absorption process. The difference in escape depth of the two methods in this
context suggests that the observed reduction of spin polarization (compared to
the bulk) cannot be attributed just to the outermost surface layer but takes
place at least 4-6 nm away from the surface.",0606006v1
2006-06-02,Temperature and magnetic field dependences of the elastic constants of Ni-Mn-Al magnetic Heusler alloys,"We report on measurements of the adiabatic second order elastic constants of
the off-stoichiometric Ni$_{54}$Mn$_{23}$Al$_{23}$ single crystalline Heusler
alloy. The variation in the temperature dependence of the elastic constants has
been investigated across the magnetic transition and over a broad temperature
range. Anomalies in the temperature behaviour of the elastic constants have
been found in the vicinity of the magnetic phase transition. Measurements under
applied magnetic field, both isothermal and variable temperature, show that the
value of the elastic constants depends on magnetic order, thus giving evidence
for magnetoelastic coupling in this alloy system.",0606065v1
2006-06-28,The study of electronic and magnetic properties of the partially disordered pseudo-Heusler alloy Co2Fe0.4Cr0.6Al : an augmented space approach,"In this communication we present a study of the electronic structure of
partially disordered bulk and (100) thin film of quaternary pseudo-Heusler
alloy Co$_2$Fe$_{0.4}$Cr$_{0.6}$Al in the L2$_1$ phase using the Augmented
Space recursion (ASR) in a scalar-relativistic tight binding linear muffin-tin
orbitals (TB-LMTO) basis. We study the orbital resolved magnetic moment
contributions of the constituents of the alloy. Our theoretical predictions
match well with the available experimental observations for the magnetic
moments of Fe and Co but they overestimate that of Cr. For a (100) thin film,
layer as well as orbital resolved properties have been studied.",0606737v2
2006-08-31,Magnetic phase diagram of the semi-Heusler alloys from first-principles,"The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined
at T=0 using first-principles calculations in conjunction with the
frozen-magnon approximation. We show that the magnetism in these systems
strongly depends on the number of conduction electrons, their spin polarization
and the position of the unoccupied Mn 3d states with respect to Fermi energy.
Various magnetic phases are obtained depending on these characteristics. The
conditions leading to diverse magnetic behavior are identified. We find that in
the case of a large conduction electron spin polarization and the unoccupied Mn
3d states lying far above the Fermi level, an RKKY-like ferromagnetic
interaction is dominating. On the other hand, the antiferromagnetic
superexchange becomes important in the presence of large peaks of the
unoccupied Mn 3d states lying close to the Fermi energy. The overall magnetic
behavior depends on the competition of these two exchange mechanisms. The
obtained results are in very good agreement with the available experimental
data.",0609001v1
1994-11-21,A Mass Bound for Spherically Symmetric Black Hole Spacetimes,"Requiring that the matter fields are subject to the dominant energy
condition, we establish the lower bound $(4\pi)^{-1} \kappa {\cal A}$ for the
total mass $M$ of a static, spherically symmetric black hole spacetime. (${\cal
A}$ and $\kappa$ denote the area and the surface gravity of the horizon,
respectively.) Together with the fact that the Komar integral provides a simple
relation between $M - (4\pi)^{-1} \kappa A$ and the strong energy condition,
this enables us to prove that the Schwarzschild metric represents the only
static, spherically symmetric black hole solution of a selfgravitating matter
model satisfying the dominant, but violating the strong energy condition for
the timelike Killing field $K$ at every point, that is, $R(K,K) \leq 0$.
Applying this result to scalar fields, we recover the fact that the only black
hole configuration of the spherically symmetric Einstein-Higgs model with
arbitrary non-negative potential is the Schwarzschild spacetime with constant
Higgs field. In the presence of electromagnetic fields, we also derive a
stronger bound for the total mass, involving the electromagnetic potentials and
charges. Again, this estimate provides a simple tool to prove a ``no-hair''
theorem for matter fields violating the strong energy condition.",9411054v1
1997-06-20,Stationary perturbations and infinitesimal rotations of static Einstein-Yang-Mills configurations with bosonic matter,"Using the Kaluza-Klein structure of stationary spacetimes, a framework for
analyzing stationary perturbations of static Einstein-Yang-Mills configurations
with bosonic matter fields is presented. It is shown that the perturbations
giving rise to non-vanishing ADM angular momentum are governed by a
self-adjoint system of equations for a set of gauge invariant scalar
amplitudes. The method is illustrated for SU(2) gauge fields, coupled to a
Higgs doublet or a Higgs triplet. It is argued that slowly rotating black holes
arise generically in self-gravitating non-Abelian gauge theories with bosonic
matter, whereas, in general, soliton solutions do not have rotating
counterparts.",9706064v1
1999-06-22,The generalization of the Regge-Wheeler equation for self-gravitating matter fields,"It is shown that the dynamical evolution of perturbations on a static
spacetime is governed by a standard pulsation equation for the extrinsic
curvature tensor. The centerpiece of the pulsation equation is a wave operator
whose spatial part is manifestly self-adjoint. In contrast to metric
formulations, the curvature-based approach to gravitational perturbation theory
generalizes in a natural way to self-gravitating matter fields. For a certain
relevant subspace of perturbations the pulsation operator is symmetric with
respect to a positive inner product and therefore allows spectral theory to be
applied. In particular, this is the case for odd-parity perturbations of
spherically symmetric background configurations. As an example, the pulsation
equations for self-gravitating, non-Abelian gauge fields are explicitly shown
to be symmetric in the gravitational, the Yang Mills, and the off-diagonal
sector.",9906090v1
1999-10-18,Perturbation theory for self-gravitating gauge fields I: The odd-parity sector,"A gauge and coordinate invariant perturbation theory for self-gravitating
non-Abelian gauge fields is developed and used to analyze local uniqueness and
linear stability properties of non-Abelian equilibrium configurations. It is
shown that all admissible stationary odd-parity excitations of the static and
spherically symmetric Einstein-Yang-Mills soliton and black hole solutions have
total angular momentum number $\ell = 1$, and are characterized by
non-vanishing asymptotic flux integrals. Local uniqueness results with respect
to non-Abelian perturbations are also established for the Schwarzschild and the
Reissner-Nordstr\""om solutions, which, in addition, are shown to be linearly
stable under dynamical Einstein-Yang-Mills perturbations. Finally, unstable
modes with $\ell = 1$ are also excluded for the static and spherically
symmetric non-Abelian solitons and black holes.",9910059v1
2001-03-09,The topology of the off-diagonal terms of the semiclassical form factor,"The semiclassical origin of the logarithmic singularity at the Heisenberg
time of the symplectic form factor is deduced by combining the result of M.
Sieber and K. Richter for the first term of the loop-expansion in the
orthogonal case with the contribution that arises due to the spin.
  We are able to make a quantitative statement about the topology of all
non-diagonal contributions in terms of integrals over SU(2) leading to the
conclusion that the same perturbative loop expansion is responsible for the
form factor in the region $0 < \tau < 2$ in the orthogonal and symplectic case
taking into account Kramers' degeneracy; the only difference being a phase
factor arising due to the spin.",0103007v4
2006-01-11,The i11/2 f5/2 and i11/2 p3/2 neutron particle-hole multiplets in 208Pb,"Inelastic proton scattering via isobaric analog resonances allows to derive
rather complete information about neutron particle-hole states. We applied this
method to the doubly-magic nucleus 208Pb by measuring angular distributions of
208Pb(p, p') on top of the isobaric analog resonances in 209Bi with the Q3D
magnetic spectrograph at M\""unchen. We identify the six states of the i11/2
f5/2 multiplet and the four states of the i11/2 p3/2 multiplet in the energy
range 4.6 MeV < Ex < 5.3 MeV. Firm spin assignments for the ten states are
given, some of them new. Additional measurements of the reaction 207Pb(d, p)
confirm the fragmented i11/2 p1/2 multiplet.",0601016v1
2006-11-10,On the mixing strength in the two lowest 0- states in 208Pb,"With a resolution of 3 keV, the two lowest 0- states in 208Pb are identified
by measurements of the reaction 207Pb(d, p) with the Muenchen Q3D magnetic
spectrograph in a region where the average level spacing is 6 keV. Precise
relative spectroscopic factors are determined. Matrix elements of the residual
interaction among one-particle one-hole configurations in a two-level scheme
are derived for the two lowest 0- states in 208Pb. The off-diagonal mixing
strength is determined as 105 +-10(experimental) +-40(systematic) keV.
Measurements of the reaction 208Pb(p,p') via isobaric analog resonances in
209Bi support the structure information obtained.",0611013v1
2007-06-29,"Role of the exchange and correlation potential into calculating the x-ray absorption spectra of half-metallic alloys: the case of Mn and Cu K-edge XANES in Cu$_2$MnM (M = Al, Sn, In) Heusler alloys","This work reports a theoretical study of the x-ray absorption near-edge
structure spectra at both the Cu and the Mn K-edge in several Cu$_2$MnM (M= Al,
Sn and In) Heusler alloys. Our results show that {\it ab-initio} single-channel
multiple-scattering calculations are able of reproducing the experimental
spectra. Moreover, an extensive discussion is presented concerning the role of
the final state potential needed to reproduce the experimental data of these
half-metallic alloys. In particular, the effects of the cluster-size and of the
exchange and correlation potential needed in reproducing all the experimental
XANES features are discussed.",0706.4370v3
2007-07-03,Effect of Co and Fe on the inverse magnetocaloric properties of Ni-Mn-Sn,"At certain compositions Ni-Mn-$X$ Heusler alloys ($X$: group IIIA-VA
elements) undergo martensitic transformations, and many of them exhibit inverse
magnetocaloric effects. In alloys where $X$ is Sn, the isothermal entropy
change is largest among the Heusler alloys, particularly in
Ni$_{50}$Mn$_{37}$Sn$_{13}$ where it reaches a value of 20 Jkg$^{-1}$K$^{-1}$
for a field of 5T. We substitute Ni with Fe and Co in this alloy, each in
amounts of 1 at% and 3 at% to perturb the electronic concentration and examine
the resulting changes in the magnetocaloric properties. Increasing both Fe and
Co concentrations causes the martensitic transition temperature to decrease,
whereby the substitution by Co at both compositions or substituting 1 at% Fe
leads to a decrease in the magnetocaloric effect. On the other hand, the
magnetocaloric effect in the alloy with 3 at% Fe leads to an increase in the
value of the entropy change to about 30 Jkg$^{-1}$K$^{-1}$ at 5T.",0707.0360v1
2007-08-24,Influence of the L21 ordering degree on the magnetic properties in Co2MnSi Heusler films,"We report on the influence of the improved L21 ordering degree on the
magnetic properties of Co2MnSi Heusler films. Different fractions of the L21
phase are obtained by different post-growth annealing temperatures ranging from
350 degC to 500 degC. Room temperature magneto-optical Kerr effect measurements
reveal an increase of the coercivity at an intermediate annealing temperature
of 425 degC, which is a fingerprint of an increased number of pinning centers
at this temperature. Furthermore, Brillouin light scattering studies show that
the improvement of the L21 order in the Co2MnSi films is correlated with a
decrease of the saturation magnetization by about 9%. The exchange stiffness
constant of Co2MnSi, however, increases by about 8% when the L21 order is
improved. Moreover, we observe a drop of the cubic anisotropy constant K1 by a
factor of 10 for an increasing amount of the L21 phase.",0708.3303v1
2008-01-13,3d-electron induced magnetic phase transition in half-metallic semi-Heusler alloys,"We study the effect of the non-magnetic 3\textit{d} atoms on the magnetic
properties of the half-metallic (HM) semi-Heusler alloys Co$_{1-x}$Cu$_{x}$MnSb
and Ni$_{1-x}$Cu$_{x}$MnSb ($0 \leq x \leq 1$) using first-principles
calculations. We determine the magnetic phase diagram of both systems at zero
temperature and obtain a phase transition from a ferromagnetic to an
antiferromagnetic state. For low Cu concentrations the ferromagnetic RKKY-like
exchange mechanism is dominating, while the antiferromagnetic superexchange
coupling becomes important for larger Cu content leading to the observed
magnetic phase transition. A strong dependence of the magnetism in both systems
on the position of the Fermi level within the HM gap is obtained. Obtained
results are in good agreement with the available experimental data.",0801.1968v1
2008-01-15,"Structural and magnetic properties of half-heusler alloys NiCrZ (Z = Si, P, Ge, As, Te): First principle study","We present a first principle study of new class of high-$T_c$ half-heusler
ferromagnets NiCrZ (Z = Si, P, Ge, As, Te). The structure and magnetic
properties are investigated through the calculation of the electronic
structure, equilibrium lattice constant, magnetic exchange interaction $J_{ij}$
and Curie temperature $T_c$. The role of $sp$-elements and the influence of
lattice expansion/compression are also studied. In alloys having 20 valence
electrons, a pseudo-gap of the majority band can be formed at Fermi level.
Otherwise, the half-metallicity and ferromagnetism at temperatures much higher
than room temperature are found to be stable in a wide range of lattice
expansion. Based on these results, NiCrZ can be expected to be promising
materials for spintronics.",0801.2222v1
2008-01-15,"New High-$T_c$ Half-Heusler Ferromagnets NiMnZ (Z = Si, P, Ge, As)","Based on the first principle calculation, we propose a new class of
high-$T_c$ half-heusler ferromagnets NiMnZ (Z = Si, P, Ge, As). The structural
and magnetic properties are investigated through the calculation of the
electronic structure, phase stability, equilibrium lattice constant, magnetic
exchange interaction $J_{ij}$ and Curie temperature $T_c$. It is found that all
alloys show half-metallicity and ferromagnetism at temperatures much higher
than room temperature in a wide range of lattice expansion (compression). At
the equilibrium lattice constant, $T_c$ of 715K, 840K, 875K and 1050K are
predicted by Monte Carlo simulation for NiMnP, NiMnAs, NiMnGe and NiMnSi,
respectively. Following these results, these alloys are strongly expected to be
promising candidates for spintronic applications.",0801.2225v1
2008-11-20,Current-perpendicular-to-plane giant magnetoresistance of a spin valve using Co2MnSi Heusler alloy electrodes,"We report the current-perpendicular-to-plane giant magnetoresistance of a
spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A
multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a
MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown
on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after
annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu
spacer layer despite the large lattice mismatch between Cu and CMS. The highest
MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room temperature and 6
K, respectively. The high spin polarization of the epitaxial CMS layers is the
most likely origin of the high MR ratio.",0811.3282v1
2009-03-29,The semiclassical origin of curvature effects in universal spectral statistics,"We consider the energy averaged two-point correlator of spectral determinants
and calculate contributions beyond the diagonal approximation using
semiclassical methods. Evaluating the contributions originating from
pseudo-orbit correlations in the same way as in [S. Heusler {\textit {et al.}}\
2007 Phys. Rev. Lett. {\textbf{98}}, 044103] we find a discrepancy between the
semiclassical and the random matrix theory result. A complementary analysis
based on a field-theoretical approach shows that the additional terms occurring
in semiclassics are cancelled in field theory by so-called curvature effects.
We give the semiclassical interpretation of the curvature effects in terms of
contributions from multiple transversals of periodic orbits around shorter
periodic orbits and discuss the consistency of our results with previous
approaches.",0903.5091v1
2009-04-17,Ferromagnetism and Electronic Structures of Nonstoichiometric Heusler-Alloy Fe_3-xMn_xSi Epilayers Grown on Ge(111),"For the study of ferromagnetic materials which are compatible with group-IV
semiconductor spintronics, we demonstrate control of the ferromagnetic
properties of Heusler-alloys Fe_3-xMn_xSi epitaxially grown on Ge(111) by
tuning the Mn composition x. Interestingly, we obtain L2_1-ordered structures
even for nonstoichiometric atomic compositions. The Curie temperature of the
epilayers with x ~ 0.6 exceeds 300 K. Theoretical calculations indicate that
the electronic structures of the nonstoichiometric Fe_3-xMn_xSi alloys become
half-metallic for 0.75 < x < 1.5. We discuss the possibility of
room-temperature ferromagnetic Fe_3-xMn_xSi/Ge epilayers with high spin
polarization.",0904.2610v1
2010-06-01,Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy,"The effect of pressure on the magnetic and the magnetocaloric properties
around the martensitic transformation temperature in NiCoMnSb Heusler alloy has
been studied. The martensitic transition temperature has significantly shifted
to higher temperatures with pressure, whereas the trend is opposite with the
application of applied magnetic field. The maximum magnetic entropy change
around the martensitic transition temperature for Ni45Co5Mn38Sb12 is 41.4 J/kg
K at the ambient pressure, whereas it is 33 J/kg K at 8.5 kbar. We find that by
adjusting the Co concentration and applying suitable pressure, NiCoMnSb system
can be tuned to achieve giant magnetocaloric effect spread over a large
temperature span around the room temperature, thereby making it a potential
magnetic refrigerant material for applications.",1006.0067v1
2010-08-24,"Magnetism of mixed quaternary Heusler alloys: (Ni,T)$_{2}$MnSn (T=Cu,Pd) as a case study","The electronic properties, exchange interactions, finite-temperature
magnetism, and transport properties of random quaternary Heusler Ni$_{2}$MnSn
alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it
ab initio} calculations over the entire range of dopant concentrations. While
the magnetic moments are only weakly dependent on the alloy composition, the
Curie temperatures exhibit strongly non-linear behavior with respect to
Cu-doping in contrast with an almost linear concentration dependence in the
case of Pd-doping. The present parameter-free theory agrees qualitatively and
also reasonably well quantitatively with the available experimental results. An
analysis of exchange interactions is provided for a deeper understanding of the
problem. The dopant atoms perturb electronic structure close to the Fermi
energy only weakly and the residual resistivity thus obeys a simple Nordheim
rule. The dominating contribution to the temperature-dependent resistivity is
due to thermodynamical fluctuations originating from the spin-disorder, which,
according to our calculations, can be described successfully via the disordered
local moments model. Results based on this model agree fairly well with the
measured values of spin-disorder induced resistivity.",1008.4060v1
2010-10-15,"Direct measurements of the magnetocaloric effect in ribbon samples of Heusler alloys Ni - Mn - M (M = In, Sn)","Direct measurements of the magnetocaloric effect in samples of rapidly
quenched ribbons of Mn50Ni40In10 and Ni50Mn37Sn13 Heusler alloys, with
potential applications in magnetic refrigeration technology, are carried out.
The measurements were made by a precise method based on the measurement of the
oscillation amplitude of the temperature in the sample while is subjected to a
modulated magnetic field. In the studied compositions both direct and inverse
magnetocaloric effects associated with magnetic (paramagnet - ferromagnet -
antiferromagnet) and structural (austenite - martensite) phase transitions are
found. Additional inverse magnetocaloric effects of small value are observed
around the ferromagnetic transitions.",1010.3135v1
2010-12-09,Epitaxial germanidation of full-Heusler Co2FeGe alloy thin films formed by rapid thermal annealing,"The authors demonstrated that a full-Heusler Co2FeGe (CFG) alloy thin film
was epitaxially grown by rapid-thermal-annealing-induced germanidation of an
Fe/Co/pseudo-Ge(001)-on-insulator (GOI) multilayer formed on a Si-on-insulator
(SOI) substrate. X-ray diffraction (XRD) measurements with the out-of-plane and
in-plane configurations revealed that the CFG film was epitaxially grown along
the [001] direction with the in-plane epitaxial relation of CFG[100]||GOI[100],
although the film slightly contained a texture component. The strong (111) and
(200) superlattice diffraction intensities indicated that the CFG film had a
high degree of order for the L21 structure. Cross-sectional high-resolution
transmission electron microscopy images of the film implied that the film had
the dominant epitaxial and slight texture components, which was consistent with
the XRD measurements. The epitaxial component was grown directly on the BOX
layer of the SOI substrate without the formation of any interfacial layer.",1012.1917v1
2010-12-13,Effect of Si and Ga substitutions on the magnetocaloric properties of NiCoMnSb quaternary Heusler alloys,"The effect of Si and Ga substitutions on the magnetic and the magnetocaloric
properties in Heusler based system Ni46Co4Mn38Sb12-xZx (Z=Si and Ga) has been
studied. From the M(T) plots it is found that Si substitution stabilizes the
austenite phase, whereas, Ga substitution stabilizes the martensite phase.
Strong metamagnetic behaviour is observed in the M(H) isotherms for Si=0.75 and
1, whereas, such a behaviour is absent in the Ga substituted alloys. Associated
with magneto-structural transition, large MCE of 58 J/kg K and 70 J/kg K is
observed for x=0.75 and 1, respectively in the case of Si. Though the MCE
observed in x=0.5 and 1 in the case of Ga is much lower, the MCE peak is found
to be quite broad.",1012.2684v1
2011-04-21,"Effect of Fe substitution on the magnetic, transport, thermal and magnetocaloric properties in Ni50Mn38-xFexSb12 Heusler alloys","The structural, magnetic, transport, thermal and magnetothermal properties of
quaternary Heusler alloys Ni50Mn38-xFexSb12 have been studied. Powder x-ray
diffraction and temperature dependence of magnetization studies reveal that
with addition of Fe in Mn site, the martensitic transition shifts to lower
temperatures. It is also found that the martensitic transition becomes broader
for the higher Fe concentrations. The metamagnetic transition in M(H) isotherms
becomes very prominent in x=2 and vanishes for x=3 and 4. A maximum positive
magnetic entropy change of 14.2 J/kg K is observed for x=2 at 288 K for 50 kOe.
Resistivity shows an abrupt decrease across the martensitic transition in all
the alloys, except x=6, which does not have the martensitic transition. Maximum
negative magnetoresistance of 21% has been obtained for x=2 at 50 kOe. The same
alloy also shows an exchange bias field of 288 Oe.",1104.4214v1
2011-08-19,Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films,"This paper shows the correlation between chemical order, lattice strains and
magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A
detailed magnetic characterization has been performed using vector field
magnetometery combined with numerical Stoner-Wohlfarth analysis. We demonstrate
the presence of three types of in-plane anisotropies: one biaxial, as expected
for the cubic symmetry, and other two uniaxial ones. The three anisotropies
show different behavior with the annealing temperature. The biaxial anisotropy
shows a monotonous increase. The uniaxial anisotropy, parallel with the hard
biaxial axes, related to the chemical homogeneity, decreases, while the other,
supposed to have magnetostatic origin, remains constant.",1108.4043v2
2011-11-19,Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars,"We have studied microwave emission from a current-perpendicular-to-plane
pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes.
Large emission amplitude exceeding 150 nV/Hz^0.5, partly owing to the large
magnetoresistance, and narrow generation linewidth below 10 MHz are observed.
We also find that the linewidth shows significant dependence on the applied
field magnitude and its angle within the film plane. A minimum in the linewidth
is observed when the slope of the frequency versus current becomes near zero.
This agrees with theoretical prediction that takes into account non-linear
phase noise as a source for linewidth broadening.",1111.4539v1
2012-02-08,Evolution of microstructural and mechanical properties of nanocrystalline Co2FeAl Heusler alloy prepared by mechanical alloying,"Mechanical alloying (MA) has been used to fabricate the Co2FeAl Heusler alloy
with a nanocrystalline structure. The formation mechanism of the alloy has been
investigated. Rietveld analysis showed that all samples that were milled for
more than 15 hours had an L21 structure with a space group of Fm3m. The
crystallite size and internal strain of the samples were calculated using the
Williamson-Hall equation. With mechanical alloying of up to 20 hours the
crystallite size of Co2FeAl increased, after which the crystallite size started
to decrease. In contrast, internal strain first decreased during the process
and then increased with the increase of milling time. The powder obtained after
20 hours of MA was split into three parts and separately annealed at 300, 500
and 700 oC for 5 hours. A considerable increase was observed in the hardness
value of powder particles with the increase of annealing temperature up to 500
oC. However, the hardness value of the sample annealed at 700 oC decreased. It
seems that this feature is related to parameters such as increase of
crystallite size, enhancement of lattice ordering, change in density of defects
and impurities and nonstoichiometric effects.",1202.1754v1
2012-05-28,Stationary Black Holes: Uniqueness and Beyond,"The spectrum of known black-hole solutions to the stationary Einstein
equations has been steadily increasing, sometimes in unexpected ways. In
particular, it has turned out that not all black-hole-equilibrium
configurations are characterized by their mass, angular momentum and global
charges. Moreover, the high degree of symmetry displayed by vacuum and
electro-vacuum black-hole spacetimes ceases to exist in self-gravitating
non-linear field theories. This text aims to review some developments in the
subject and to discuss them in light of the uniqueness theorem for the
Einstein-Maxwell system.",1205.6112v1
2012-08-10,"Electronic structure, optical and magnetic properties of Co$_{2}$FeGe Heusler alloy films","Optical properties of ferromagnetic half-metallic full-Heusler Co$_{2}$FeGe
alloy are investigated experimentally and theoretically. Co$_{2}$FeGe thin
films were obtained by DC magnetron sputtering and show the saturation
magnetization at $T$=10 K of $m\approx$5.6 $\mu_{B}$/f.u., close to the value
predicted by the Slater-Pauling rule. First-principles calculations of the
electronic structure and the dielectric tensor are performed using the
full-potential linearized-augmented-plane-wave method in the generalized
gradient (GGA) and GGA+U approximations. The measured interband optical
conductivity spectrum for the alloy exhibits a strong absorption band in the 1
- 4 eV energy range with pronounced fine structure, which agrees well with the
calculated half-metallic spectrum of the system, suggesting a near perfect
spin-polarization in the material.",1208.2193v1
2012-10-22,"Thickness-dependent structural, magnetic and transport properties of epitaxial Co2FeAl Heusler alloy thin films","We report on a systematic study of the structural, magnetic properties and
the anomalous Hall effect, in the Heusler alloy Co2FeAl (CFA) epitaxial films
on MgO(001), as a function of film thickness. It was found that the epitaxial
CFA films show a highly ordered B2 structure with an in-plane uniaxial magnetic
anisotropy. An analysis of the electrical transport properties reveals that the
lattice and magnon scattering contributions to the longitudinal resistivity.
Independent on the thickness of films, the anomalous Hall resistivity of CFA
films is found to be dominated by skew scattering only. Moreover, the anomalous
Hall resistivity shows weakly temperature dependent behavior, and its absolute
value increases as the thickness decreases. We attribute this temperature
insensitivity in the anomalous Hall resistivity to the weak temperature
dependent of tunneling spin-polarization in the CFA films, while the thickness
dependence behavior is likely due to the increasing significance of interface
or free surface electronic states.",1210.5807v1
2012-10-22,Fabrication and characterization of the gapless half-Heusler YPtSb thin films,"Half-Heusler YPtSb thin films were fabricated by magnetron co-sputtering
method on MgO-buffered SiO2/Si(001) substrates. X-ray diffraction pattern and
Energy dispersive X-ray spectroscopy confirmed the high-quality growth and
stoichiometry. The temperature dependence of the resistivity shows a
semiconducting-type behavior down to low temperature. The Hall mobility was
determined to be 450 cm2/Vs at 300K, which is much higher than the bulk value
(300 cm2/Vs). In-plane magnetoresistance (MR) measurements with fields applied
along and perpendicular to the current direction show opposite MR signs, which
suggests the possible existence of the topological surface states.",1210.5808v1
2012-12-08,$Ab~initio$ studies of Co$_2$FeAl$_{1-x}$Si$_x$ Heusler alloys,"We present results of extensive theoretical studies of
Co$_2$FeAl$_{1-x}$Si$_x$ Heusler alloys, which have been performed in the
framework of density functional theory employing the all-electron
full-potential linearized augmented plane-wave scheme. It is shown that the
Si-rich alloys are more resistive to structural disorder and as a consequence
Si stabilizes the $L2_1$ structure. Si alloying changes position of the Fermi
level, pushing it into the gap of the minority spin-band. It is also shown that
the hyperfine field on Co nuclei increases with the Si concentration, and this
increase originates mostly from the changes in the electronic density of the
valence electrons.",1212.1781v2
2013-01-31,"Structure and magnetic properties of Heusler alloy Fe2NiZ (Z=Al, Ga, Si and Ge)","The Heusler alloys Fe2NiZ (Z=Al, Ga, Si and Ge) have been synthesized and
investigated focusing on the phase stability and the magnetic properties. The
experimental and theoretical results reveal the covalent bonding originated
from p-d hybridization takes an important role in these alloys, which dominates
the stability of ordered structure but leads to the decline of the band
splitting. The electronic structure shows the IV group main group element (Si
and Ge) provides stronger covalent effect than that of the III group element
(Al and Ga). It has been found that the variations of the physical parameters,
lattice constants, critical ordering temperature, magnetic moments and Curie
temperature, precisely follow these covalent characters.",1301.7489v1
2013-04-20,Antiferromagnetic Exchange Interactions in Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ ferromagnetic Heusler alloy,"Magnetism in Ni-Mn-Z (Z = Ga,In,Sn,Sb) Heusler alloys has so far been
predominantly attributed to Rudermann-Kittel-Kasuya-Yoshida type interactions
between Mn atoms. We investigate magnetic interactions in one such alloy,
Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and attempt to explain the origin of
antiferromagnetic (AFM) interactions that coexist with ferromagnetic ones.
Through the combination of x-ray absorption spectroscopy and x-ray magnetic
circular dichroism (XMCD), we find that Ni plays an important role along with
Mn in the overall magnetism. A significant hybridization that develops between
Mn and Ni orbitals results in a small antiferromagnetic moment at Ni sites. The
shift in the XMCD hysteresis loops in the martensitic phase suggests that
antiferromagnetism results from superexchange like interactions between Mn
atoms mediated by Ni.",1304.5580v1
2013-06-26,Effective Scattering Cross-section in Lattice Thermal Conductivity Calculation with Differential Effective Medium Method,"To further reduce the lattice thermal conductivity of thermoelectric
materials, the technique of embedding nano-inclusions into bulk matrix
materials, in addition to point defect scattering via alloying, was widely
applied. Differential Effective Medium (DEM) method was employed to calculate
two-phase heterogeneous systems. However, in most effective medium treatment,
the interface scattering of matrix phonons by embedded nanoparticle was
underestimated by adopting particle's projected area as scattering
cross-section. Herein, modified cross-section calculations, as well as grain
sizes dispersions, are applied in DEM, with the calculations then validated by
comparing with Monte-Carlo simulations and existing experimental data.
Predictions of lattice thermal conductivity reduction on in-situ formed Full
Heusler(FH)/Half Heusler(HH) nano/matrix system are discussed.",1306.6274v1
2014-04-22,First principles investigation of magnetocrystalline anisotropy at the L2$_1$ Full Heusler|MgO interfaces and tunnel junctions,"Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been
studied using first principles calculations. It is found that Co terminated
Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31
mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic
anisotropy. Atomic layer resolved analysis indicates that the origin of
perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be
attributed to the out-of-plane orbital contributions of interfacial Co atoms.
At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to
favor in-plane magnetic anisotropy for all terminations.",1404.5646v2
2014-05-26,Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa,"Magnetic shape memory Heusler alloys are multiferroics stabilized by the
correlations between electronic, magnetic and structural order. To study these
correlations we use time resolved x-ray diffraction and magneto-optical Kerr
effect experiments to measure the laser induced dynamics in a Heusler alloy
Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We
observe a coherent phonon which we identify as the amplitudon of the modulated
structure and an ultrafast phase transition leading to a quenching of the
incommensurate modulation within 300~fs with a recovery time of a few ps. The
thermally driven martensitic transition to the high temperature cubic phase
proceeds via nucleation within a few ps and domain growth limited by the speed
of sound. The demagnetization time is 320~fs, which is comparable to the
quenching of the structural modulation.",1405.6534v1
2014-08-01,NMR evidence for enhanced orbital diamagnetism in topologically nontrivial half-Heusler semimetals,"209Bi nuclear magnetic resonance (NMR) spectroscopy was employed to probe
potential spin-orbit effects on orbital diamagnetism in YPtBi and YPdBi
crystals. The observed opposite sign and temperature dependent magnitude of
209Bi NMR shifts of both crystals reveal experimental signatures of enhanced
orbital diamagnetism induced by spin-orbit interactions. This investigation
indicates that NMR isotropic shifts might be beneficial in search of
interesting spin-electronic phases among a vast number of topological
nontrivial half-Heusler semimetals.",1408.0078v2
2014-08-02,Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on Kapton,"Bending effect on the magnetic anisotropy in 20 nm Co$_{2}$FeAl Heusler thin
film grown on Kapton\textregistered{} has been studied by ferromagnetic
resonance and glued on curved sample carrier with various radii. The results
reported in this letter show that the magnetic anisotropy is drastically
changed in this system by bending the thin films. This effect is attributed to
the interfacial strain transmission from the substrate to the film and to the
magnetoelastic behavior of the Co$_{2}$FeAl film. Moreover two approaches to
determine the in-plane magnetostriction coefficient of the film, leading to a
value that is close to $\lambda^{CFA}=14\times10^{-6}$, have been proposed.",1408.0379v1
2014-08-11,High spin polarization in CoFeMnGe quaternary Heusler alloy,"We report the structure, magnetic property and spin polarization of CoFeMnGe
equiatomic quaternary Heusler alloy. The alloy was found to exist in the L21
structure with considerable amount of DO3 disorder. Thermal analysis result
indicated the Curie temperature is about 711K without any other phase
transformation up to melting temperature. The magnetization value was close to
that predicted by the Slater-Pauling curve. Current spin polarization of P =
0.70 {plus/minus}0.1 was deduced using point contact Andreev reflection (PCAR)
measurements. Half-metallic trend in the resistivity has also been observed in
the temperature range of 5 K to 300 K. Considering the high spin polarization
and Curie temperature, this material appears to be promising for spintronic
applications.",1408.2408v2
2014-11-13,Electrical Control of Carriers Spin Orientation in FeVTiSi Heusler Alloy,"The direct control of carriers spin by electric field under room temperature
is one of the most important challenges in the field of spintronics. For this
purpose, we here propose a quaternary Heusler alloy FeVTiSi. Based on first
principles calculations, FeVTiSi alloy is found to be an intrinsic bipolar
magnetic semiconductor in which the valence band and conduction band approach
the Fermi level through opposite spin channels. Thus FeVTiSi alloy can conduct
completely spin-polarized currents with tunable spin-polarization direction
simply by applying a gate voltage. Furthermore, by Monte Carlo simulations
based on the classical Heisenberg Hamiltonian, the Curie temperature of FeVTiSi
alloy is predicted to be as high as 1293 K, far above the room temperature. The
bipolar magnetic semiconducting character and the high Curie temperature endow
the FeVTiSi alloy great potentials in developing electrically controllable
spintronic devices working at room temperature.",1411.3426v1
2014-12-10,Chemical disorder as engineering tool for spin-polarizationin Mn3Ga-based Heusler systems,"Our study highlights spin-polarization mechanisms in metals, by focusing on
the mobilities of conducting electrons with different spins instead of their
quantities. Here, we engineer electron mobility by applying chemical disorder
induced by non-stoichiometric variations. As a practical example, we discuss
the scheme that establishes such variations in tetragonal Mn3Ga Heusler
material. We justify this approach using first-principles calculations of the
spin-projected conductivity components based on the Kubo-Greenwood formalism.
It follows that, in majority of the cases, even a small substitution of some
other transition element instead of Mn may lead to a substantial increase in
spin-polarization along the tetragonal axis.",1412.3394v2
2015-01-19,Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$,"We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ by direct measurements in pulsed magnetic
fields up to 6 and 20 T. The results in 6 T are compared with data obtained
from heat-capacity experiments. We find a saturation of the inverse MCE,
related to the first-order martensitic transition, with a maximum adiabatic
temperature change of $\Delta T_{ad} = -7$ K at 250 K and a conventional
field-dependent MCE near the second-order ferromagnetic transition in the
austenitic phase. The pulsed magnetic field data allow for an analysis of the
temperature response of the sample to the magnetic field on a time scale of
$\sim 10$ to 100 ms which is on the order of typical operation frequencies (10
to 100 Hz) of magnetocaloric cooling devices. Our results disclose that in
shape-memory alloys the different contributions to the MCE and hysteresis
effects around the martensitic transition have to be carefully considered for
future cooling applications.",1501.04430v1
2015-01-21,"Antiferromagnetism in Ru2MnZ (Z=Sn, Sb, Ge, Si) full Heusler alloys: effects of magnetic frustration and chemical disorder","We present systematic theoretical investigations to explore the microscopic
mechanisms leading to the formation of antiferromagnetism in Ru2MnZ (Z=
Sn,Sb,Ge,Si) full Heusler alloys. Our study is based on first-principles
calculations of inter-atomic Mn-Mn exchange interactions to set up a suitable
Heisenberg spin-model and on subsequent Monte-Carlo simulations of the magnetic
properties at finite temperature. The exchange interactions are derived from
the paramagnetic state, while a realistic account of long-range chemical
disorder is made in the framework of the Coherent Potential Approximation. We
find that in case of the highly ordered alloys (Z=Sn and Sb) the exchange
interactions derived from the perfectly ordered L21 structure lead to N\'eel
temperatures in excellent agreement with the experiments, whereas, in
particular, in case of Si the consideration of chemical disorder is essential
to reproduce the experimental N\'eel temperatures. Our numerical results
suggest that improving a heat treatment of the samples to suppress the
intermixing between the Mn and Si atoms, the N\'eel temperature of the Si-based
alloys can potentially be increased by more than 30%. Furthermore, we show that
in strongly disordered Ru2MnSi alloys a distinct change in the
antiferromagnetic ordering occurs.",1501.05116v1
2015-04-13,Magnetic and superconducting phase diagram of the half-Heusler topological semimetal HoPdBi,"We report a study of the magnetic and electronic properties of the
non-centrosymmetric half-Heusler antiferromagnet HoPdBi ($T_N = 2.0$ K).
Magnetotransport measurements show HoPdBi has a semimetallic behaviour with a
carrier concentration $n=3.7 \times 10^{18}$ cm$^{-3}$ extracted from the
Shubnikov-de Haas effect. The magnetic phase diagram in the field-temperature
plane has been determined by transport, magnetization and thermal expansion
measurements: magnetic order is suppressed at $B_M\sim 3.6$ T for $T
\rightarrow 0$. Superconductivity with $T_c \sim 1.9$ K is found in the
antiferromagnetic phase. Ac-susceptibility measurements provide solid evidence
for bulk superconductivity below $T_c = 0.75$ K with a screening signal close
to a volume fraction of 100 %. The upper critical field shows an unusual linear
temperature variation with $B_{c2}(T \rightarrow 0) = 1.1$ T. We also report
electronic structure calculations that classify HoPdBi as a new topological
semimetal, with a non-trivial band inversion of 0.25 eV.",1504.03181v1
2015-04-14,Effect of ball milling and post annealing on structural and magnetic properties in Ni50Mn36Fe2Sb12 Heusler alloy,"The effect of ball milling on the structural, magnetic and exchange bias
properties of Ni50Mn36Fe2Sb12 Heusler alloys was studied. The ball milled
samples exhibited coexisting austenite and martensite phases at room
temperature, while annealing supresses the austenite phase completely. Ball
milling was found to reduce the grain size, which resulted in the weakening of
the ferromagnetic properties. An exchange bias field of 111 Oe and coercivity
of 826 Oe were observed at 5 K in the as-milled sample, in contrast to the bulk
alloy values of 288 Oe and 292 Oe, respectively. Annealing causes an increase
in the ferromagnetic ordering and a decrease in the interfacial exchange
coupling, resulting in a decrease of both exchange bias and coercivity.",1504.03460v1
2015-05-12,Examining the thermal conductivity of half-Heusler alloy TiNiSn by first-principles calculations,"The thermoelectric properties of half-Heusler alloy TiNiSn have been studied
for decade, however, theoretical report on its thermal conductivity is still
little known, because it is difficult to estimate effectively the lattice
thermal conductivity. In this work, we use the ShengBTE code developed recently
to examine the lattice thermal conductivity of TiNiSn. The calculated lattice
thermal conductivity at room temperature is 7.6 W/mK, which is close to the
experimental value of 8 W/mK. We also find that the total and lattice thermal
conductivities dependent temperature are in good agreement with available
experiments, and the total thermal conductivity is dominated by the lattice
contribution. The present work is useful for the theoretical prediction of
lattice thermal conductivity and the optimization of thermoelectric
performance.",1505.02845v1
2015-05-28,Large ground state magnetic moment and magnetocaloric effect in Ni2Mn1.4In0.6,"A large conventional magnetocaloric effect at the second order magnetic
transition in cubic Ni2Mn1.4In0.6 Heusler alloy is reported. The isothermal
magnetization at 2K shows a huge ground state magnetic moment of about 6.17
{\mu}B/f.u. The theoretical calculations show that the origin of the large
magnetic moment in cubic Ni2Mn1.4In0.6 results from the strong ferromagnetic
interaction between Mn- Ni and Mn-Mn sublattices. The experimental magnetic
moment is in excellent agreement with the moment calculated from the theory.
The large magnetic moment gives rise to considerably high adiabatic temperature
and entropy changes at the magnetic transition. The present study opens up the
possibility to explore cubic Heusler alloys for magnetocaloric applications.",1505.07677v2
2015-06-10,A first-principle study of half-Heusler alloys CKMg and SiKMg,"The structural, electronic, and magnetic properties of half-Heusler alloys
CKMg and SiKMg are studied by using first-principle density functional theory.
The calculations reveal the SiKMg alloy is a half-metallic ferromagnet with the
magnetic moment of 1 $\mu_B$ per formula unit at equilibrium lattice constant.
The magnetic moment mainly originates from the strong spin-polarization of $p$
electrons of Si atom and partial involvement of $d$ electrons of K atom. The
half-metallic gap is 0.105 eV. The robustness of half-metallic against the
lattice constants for SiKMg is also calculated. CKMg alloy is nearly
half-metallic with a spin polarization of 99.99 \%\ at equilibrium lattice
constant, but it is a good half-metallic alloy when a low pressure is applied.
This shows CKMg is a very promising spintronic functional material.",1506.03297v1
2015-06-23,Spin polarization studies in half-metallic Co2TiX (X = Ge and Sn) Heusler alloys,"In this paper, we investigated the Co2TiX (X = Ge, Sn) Heusler alloys by
structural, magnetic and spin polarization measurements to probe the
half-metallic nature. Alloys are synthesized using the arc melting technique,
and found to exist in L21 crystal structure with Fm-3m space group. Curie
temperature (TC) is found to be 384 and 371 K for Co2TiGe and Co2TiSn
respectively. The saturation magnetization (MS) value of 1.8 and 2.0 Bohr
magneton/f.u. are obtained at 5 K for for Co2TiGe and Co2TiSn respectively,
compared to 2.0 Bohr magneton/f.u. calculated by Slater-Pauling rule. To obtain
the spin polarization value, differential conductance curves are recorded at
the ferromagnetic/superconducting point contact at 4.2 K. The current spin
polarization (P) value of 0.63 and 0.64 are deduced for Co2TiGe and Co2TiSn
respectively. Considering the high current spin polarization and TC, these
materials appear to be promising for spintronic devices.",1506.07109v1
2015-09-16,Structural and magnetic properties of a new and ordered quaternary alloy MnNiCuSb (SG: F-43m),"We have synthesized a new crystallographically ordered quaternary Heusler
alloy, MnNiCuSb. The crystal structure of the alloy has been determined by
Rietveld refinement of the powder x-ray diffraction data. This alloy
crystallizes in the LiMgPdSb type structure with F-43m space group. MnNiCuSb is
a ferromagnet with a high TC ~ 690K and magnetic moment of 3.85MuB/f.u. Besides
this we have also studied two other off-stoichiometric compositions; one Cu
rich and the other Ni rich (MnNi0.9Cu1.1Sb and MnNi1.1Cu0.9Sb) which are also
ferromagnets. It must be stressed that MnNiCuSb is one of the very few known,
non-Fe containing quaternary Heusler alloys with 1: 1: 1: 1 composition.",1509.04833v1
2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for
applications in spintronic devices due to its low magnetic damping and its rich
anisotropies. Here we use ferromagnetic resonance (FMR) measurements and
calculations from first principles to investigate how the composition of the
epitaxially grown NiMnSb influences the magnetodynamic properties of saturation
magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$.
$M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while
the Gilbert damping is minimum. We find excellent quantitative agreement
between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows
the same trend as the experimental data, but has a larger magnitude.
Additionally to the unique in-plane anisotropy of the material, these
tunabilities of the magnetodynamic properties can be taken advantage of when
employing NiMnSb films in magnonic devices.",1510.01894v1
2015-10-17,Direct evidence for minority spin gap in the Co2MnSi Heusler alloy,"Half Metal Magnets are of great interest in the field of spintronics because
of their potential full spin-polarization at the Fermi level and low
magnetization damping. The high Curie temperature and predicted 0.7eV minority
spin gap make the Heusler alloy Co2MnSi very promising for applications.We
investigated the half-metallic magnetic character of this alloy using
spin-resolved photoemission, ab initio calculation and ferromagnetic resonance.
At the surface of Co2MnSi, a gap in the minority spin channel is observed,
leading to 100% spin polarization. However, this gap is 0.3 eV below the Fermi
level and a minority spin state is observed at the Fermi level. We show that a
minority spin gap at the Fermi energy can nevertheless be recovered either by
changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi
or MgO. This results in extremely small damping coefficients reaching values as
low as 7x 10-4.",1510.05085v1
2015-10-23,Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet,"Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.",1510.06793v1
2015-10-23,Resonant impurity states in chemically disordered half-Heusler Dirac semimetals,"We address the electron transport characteristics in bulk half-Heusler alloys
with their compositions tuned to the borderline between topologically
nontrivial semi-metallic and trivial semiconducting phases. The precise
first-principles calculations based on the coherent potential approximation
(CPA) reveal that all the studied systems exhibit sets of dispersionless
impurity-like resonant levels, with one of them being located right at the
Dirac point. By means of the Kubo formalism we reveal that the residual
conductivity of these alloys is strongly suppressed by impurity scattering,
whereas the spin Hall conductivity exhibits a large value which is comparable
to that of Pt, thereby leading to divergent spin Hall angles.",1510.06935v1
2015-12-04,Suppression of the ferromagnetic order in the Heusler alloy Ni50Mn35In15 by hydrostatic pressure,"We report the effect of hydrostatic pressure on the magnetic and structural
properties of the shape-memory Heusler alloy Ni50Mn35In15. Magnetization and
x-ray diffraction experiments were performed at hydrostatic pressures up to 5
GPa using diamond anvil cells. Pressure stabilizes the martensitic phase,
shifting the martensitic transition to higher temperatures and suppresses the
ferromagnetic austenitic phase. Above ~3 GPa, where the martensitic-transition
temperature approaches the Curie temperature in the austenite, the
magnetization shows no indication of ferromagnetic ordering anymore. We further
find an extremely large temperatureregion with a mixture of martensite and
austenite phases, which directly relates to the magnetic properties.",1512.01407v1
2016-06-14,Defect-induced magnetic structure of CuMnSb,"Ab initio total energy calculations show that the antiferromagnetic (111)
order is not the ground state for the ideal CuMnSb Heusler alloy in contrast to
the results of neutron diffraction experiments. It is known, that Heusler
alloys usually contain various defects depending on the sample preparation. We
have therefore investigated magnetic phases of CuMnSb assuming the most common
defects which exist in real experimental conditions. The full-potential
supercell approach and a Heisenberg model approach using the coherent potential
approximation are adopted. The results of the total energy supercell
calculations indicate that defects that bring Mn atoms close together promote
the antiferromagnetic (111) structure already for a low critical defect
concentrations ($\approx$ 3%). A detailed study of exchange interactions
between Mn-moments further supports the above stabilization mechanism. Finally,
the stability of the antiferromagnetic (111) order is enhanced by inclusion of
electron correlations in narrow Mn-bands. The present refinement structure
analysis of neutron scattering experiment supports theoretical conclusions.",1606.04238v1
2016-08-22,Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys,"The all-d-metal Mn2-based Heusler ferromagnetic shape memory alloys
Mn50Ni40-xCoxTi10 (x = 8 and 9.5) are realized. With a generic comparison
between d-metal Ti and main-group elements in lowering the transformation
temperature, the magnetostructural martensitic transformations are established
by further introducing Co to produce local ferromagnetic Mn-Co-Mn
configurations. A 5-fold modulation and (3, -2) stacking of [00 10] of
martensite are determined by XRD and HRTEM analysis. Based on the
transformation, a large magneto-strain of 6900 ppm and a large volume change of
-2.54% are observed in polycrystalline samples, which makes the all-d-metal
magnetic martensitic alloys of interest for magnetic/pressure multi-field
driven applications.",1608.06301v1
2016-09-29,"On the rich magnetic phase diagram of (Ni, Co)-Mn-Sn Heusler alloys","We put a spotlight on the exceptional magnetic properties of the metamagnetic
Heusler alloy (Ni,Co)-Mn-Sn by means of first principles simulations.
  In the energy landscape we find a multitude of local minima, which belong to
different ferrimagnetic states and are close in total magnetization and energy.
All these magnetic states correspond to the local high spin state of the Mn
atoms with different spin alignments and are related to the magnetic properties
of Mn. Compared to pure Mn, the magneto-volume coupling is reduced by Ni, Co,
and Sn atoms in the lattice and no local low-spin Mn states appear. For the
cubic phase we find a ferromagnetic ground state whereas the global energy
minimum is a tetragonal state with complicated spin structure and vanishing
magnetization which so far has been overlooked in simulations.",1609.09399v1
2016-10-09,Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure,"The thermoelectric properties of n type semiconductor, TiNiSn is optimized by
partial substitution with metallic, MnNiSb in the half Heusler structure.
Herein, we study the transport properties and intrinsic phase separation in the
system. The Ti1-xMnxNiSn1-xSbx alloys were prepared by arc-melting and were
annealed at temperatures obtained from differential thermal analysis and
differential scanning calorimetry results. The phases were characterized using
powder X-ray diffraction patterns, energy dispersive X-ray spectroscopy, and
differential scanning calorimetry. After annealing the majority phase was
TiNiSn with some Ni rich sites and the minority phases was majorly Ti6Sn5, Sn,
and MnSn2. Ni rich sites were caused by Frenkel defects, this led to a
metal-like behavior of the semiconducting specimens at low temperature. For x
up to 0.05 the samples showed an activated conduction, whereas for x>0.05 they
showed metallic character. The figure of merit for x=0.05 was increased by 61%
(ZT=0.45) in comparison to the pure TiNiSn.",1610.02657v1
2017-01-06,Modulations in martensitic Heusler alloys originate from nanotwin ordering,"Heusler alloys exhibiting magnetic and martensitic transitions enable
applications like magnetocaloric refrigeration and actuation based on the
magnetic shape memory effect. Their outstanding functional properties depend on
low hysteresis losses and low actuation fields. These are only achieved if the
atomic positions deviate from a tetragonal lattice by periodic displacements.
The origin of the so-called modulated structures is the subject of much
controversy: They are either explained by phonon softening or adaptive
nanotwinning. Here we used large-scale density functional theory calculations
on the Ni2MnGa prototype system to demonstrate interaction energy between twin
boundaries. Minimizing the interaction energy resulted in the experimentally
observed ordered modulations at the atomic scale, it explained that a/b twin
boundaries are stacking faults at the mesoscale, and contributed substantially
to the macroscopic hysteresis losses. Furthermore, we found that phonon
softening paves the transformation path towards the nanotwinned martensite
state. This unified both opposing concepts to explain modulated martensite.",1701.01562v2
2017-01-29,$d^0$-$d$ half-Heusler alloys: A class of future spintronic materials,"It is shown by rigorous ab initio calculations that half-Heusler alloys of
transition metals and $d^0$ metals, defined by the valence electronic
configuration $ns^{1,2},(n-1)d^0$, can produce all kinds of half-metallic
behavior including the elusive Dirac half-semimetallicity that is reported for
the first time in the real 3D material CoKSb. Together with the predicted
magnetic and chemical stability, this paves the way for massless and
dissipationless spintronics of the future. Furthermore, the introduction of
$d^0$ atoms is shown to stabilize the otherwise instable chemical structure of
zinc-blende transition metal pnictides and chalcogeneides without altering the
$p$-$d$ exchange that is mainly responsible for their half-metallicity,
therefore, making their application in spintronic devices feasible.",1701.08397v3
2017-07-17,Possible spin gapless semiconductor type behaviour in CoFeMnSi epitaxial thin films,"Spin-gapless semiconductors with their unique band structures have recently
attracted much attention due to their interesting transport properties that can
be utilized in spintronics applications. We have successfully deposited the
thin films of quaternary spin-gapless semiconductor CoFeMnSi Heusler alloy on
MgO (001) substrates using a pulsed laser deposition system. These films show
epitaxial growth along (001) direction and display uniform and smooth
crystalline surface. The magnetic properties reveal that the film is
ferromagnetically soft along the in-plane direction and its Curie temperature
is well above 400 K. The electrical conductivity of the film is low and
exhibits a nearly temperature independent semiconducting behaviour. The
estimated temperature coefficient of resistivity for the film is -7x10^-10
Ohm.m/K, which is comparable to the values reported for spin-gapless
semiconductors.",1707.05078v2
2017-07-21,Mn$_2$VAl Heusler alloy thin films: Appearance of antiferromagnetism and an exchange bias in a layered structure with Fe,"Mn$_2$VAl Heusler alloy films were epitaxially grown on MgO(100) single
crystal substrates by means of ultra-high-vacuum magnetron sputtering. A2 and
L2$_1$ type Mn$_2$VAl order was controlled by the deposition temperatures.
A2-type Mn$_2$VAl films showed no spontaneous magnetization and L2$_1$-type
Mn$_2$VAl films showed ferrimagnetic behavior with a maximum saturation
magnetization of 220 emu/cm$^3$ at room temperature. An antiferromagnetic
reflection was observed with neutron diffraction at room temperature for an
A2-type Mn$_2$VAl film deposited at 400$^\circ$C. A bilayer sample of the
antiferromagnetic A2 Mn$_2$VAl and Fe showed an exchange bias of 120 Oe at 10
K.",1707.06731v1
2017-08-15,Electronic fitness function for screening semiconductors as thermoelectric materials,"We introduce a simple but efficient electronic fitness function (EFF) that
describes the electronic aspect of the thermoelectric performance. This EFF
finds materials that overcome the inverse relationship between $\sigma$ and $S$
based on the complexity of the electronic structures regardless of specific
origin (e.g., isosurface corrugation, valley degeneracy, heavy-light bands
mixture, valley anisotropy or reduced dimensionality). This function is well
suited for application in high throughput screening. We applied this function
to 75 different thermoelectric and potential thermoelectric materials including
full- and half-Heuslers, binary semiconductors and Zintl phases. We find an
efficient screening using this transport function. The EFF identifies known
high performance $p$- and $n$-type Zintl phases and half-Heuslers. In addition,
we find some previously unstudied phases with superior EFF.",1708.04499v2
2017-08-16,Ab-initio design of new Heusler materials for thermoelectric applications,"In search of new prospects for thermoelectric materials, using ab-initio
calculations and semi-classical Boltzmann theory, we have systematically
investigated the electronic structure and transport properties of 18-valence
electron count cobalt based half-Heusler alloys with prime focus on CoVSn,
CoNbSn, CoTaSn, CoMoIn, and CoWIn. The effect of doping on transport properties
has been studied under the rigid band approximation. The maximum power factor,
S$^2\sigma$, for all systems is obtained on hole doping and is comparable to
the existing thermoelectric material CoTiSb. The stability of all the systems
is verified by phonon calculations. Based on our calculations, we suggest that
CoVSn, CoNbSn, CoTaSn, CoMoIn and CoWIn could be potential candidates for high
temperature thermoelectric materials.",1708.04768v1
2017-08-28,"Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond","We present our recent results on temperature behaviour of magnetization
observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished
in the M-T diagram: (I) low temperature martensitic phase (with the Curie
temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical
temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM
and T_MS) and (III) high temperature austenitic phase (with the Curie
temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS
and T_CA). By arguing that powerful structural transformations, causing drastic
modifications of the domain structure in alloys, would also trigger strong
fluctuations of the order parameters throughout the entire M-T diagram, we were
able to successfully fit all the data by incorporating Gaussian fluctuations
(both above and below the above three critical temperatures) into the
Ginzburg-Landau scenario.",1708.08368v1
2017-09-13,Hole-doped cobalt-based Heusler phases as prospective high-performance high-temperature thermoelectrics,"Materials design based on first-principles electronic calculations has proven
a fruitful strategy to identify new thermoelectric materials with a favorable
figure of merit. Recent electronic structure calculations predict that in
cobalt-based half-Heusler systems a power factor higher than in CoTiSb can be
achieved upon p-type doping of CoVSn, CoNbSn, CoTaSn, CoMoIn, and CoWIn. Here,
using a first-principles approach and semi-classical Boltzmann transport
theory, we investigate the electrical and thermal transport properties of these
materials. The calculated thermal conductivity at room temperature of all the
systems is lower than that of CoTiSb, with CoMoIn and CoWIn having an almost
3-fold lower thermal conductivity than CoTiSb. We also provide conservative
estimates of the figure of merit for these systems which all turn out to be
higher than in CoTiSb and to have a maximum value for CoWIn.",1709.04243v1
2018-01-24,Origin of efficient thermoelectric performance in half-Heusler FeNb$_{0.8}$Ti$_{0.2}$Sb,"A half-Heusler material FeNb$_{0.8}$Ti$_{0.2}$Sb has been identified as a
promising thermoelectric material due to its excellent thermoelectric
performance at high temperatures. The origins of the efficient thermoelectric
performance are investigated through a series of low-temperature (2 - 400 K)
measurements. The high data coherence of the low and high temperatures is
observed. An optimal and nearly temperature-independent carrier concentration
is identified, which is ideal for the power factor. The obtained single type of
hole carrier is also beneficial to the large Seebeck coefficient. The
electronic thermal conductivity is found to be comparable to the lattice
thermal conductivity and becomes the dominant component above 200 K. These
findings again indicate that electron scattering plays a key role in the
electrical and thermal transport properties. The dimensionless figure of merit
is thus mainly governed by the electronic properties. These effects obtained at
low temperatures with the avoidance of possible thermal fluctuations together
offer the physical origin for the excellent thermoelectric performance in this
material.",1801.07935v1
2018-01-26,Stoichiometric and off-stoichiometric full Heusler $\mathbf {Fe_2V_{1-x}W_xAl} $ thermoelectric systems,"A series of full-Heusler alloys, $\rm Fe_2V_{1-x}W_xAl$, $0 \leq x \leq 0.2$,
was prepared, characterized and relevant physical properties to account for the
thermoelectric performance were studied in a wide temperature range.
Additionally, off-stoichiometric samples with similar compositions have been
included, and a 10~\% improvement of the thermoelectric figure of merit was
obtained. The V/W substitution causes i) a change of the main carrier type,
from holes to electrons as evidenced from Seebeck and Hall measurements and ii)
a substantial reduction of the lattice thermal conductivity due to a creation
of lattice disorder by means of a distinct different mass and metallic radius
upon the V/W substitution. Moreover $ZT$ values above 0.2 have been obtained. A
microscopic understanding of the experimental data observed is revealed from
ab-initio calculations of the electronic and phononic structure.",1801.08966v2
2018-03-05,Measurement independent magnetocaloric effect in Mn-rich Mn-Fe-Ni-Sn(Sb/In) Heusler alloys,"We report a systematic study on the magneto-structural transition in Mn-rich
Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence
electron concentration (e/a ratio) fixed. The martensitic transition (MT)
temperature is found to shift by following a proportional relationship with the
e/a ratio of the magnetic elements alone. The magnetic entropy change across MT
for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different
measurement methods (isofield magnetization (M) vs temperature (T), isothermal
M vs field (H) and heat capacity (HC) vs T). We observed that though the peak
value of magnetic entropy change changes with the measurement methods, the
broadened shape of the magnetic entropy change vs T curves and the
corresponding cooling power (~140 Jkg-1) remains invariant. The equivalent
adiabatic temperature change ~ -2.6 K has been obtained from indirect
measurements of temperature change. Moreover, an exchange bias field ~ 783 Oe
at 5 K and a magnetoresistance of -30% are also obtained in one of these
materials.",1803.01566v3
2018-05-07,High-temperature thermoelectric properties of half-Heusler phases Er$_{1-x}$Ho$_x$NiSb,"Polycrystalline samples of Er$_{1-x}$Ho$_x$NiSb ($x$ = 0, 0.2, 0.3, 0.5, 0.7,
0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning
electron microscopy (SEM), and optical metallography. The results proved the
formation of half-Heusler alloys in the entire composition range. Their
electrical transport properties (resistivity, thermoelectric power) were
studied in the temperature interval 350-1000 K. The measured electrical
resistivity spanned between 5 and 25 $\mu \Omega$m. The maximum thermopower of
50-65 $\mu$V/K was observed at temperatures 500-650 K. Replacing Ho for Er
resulted in a non-monotonous variation of the thermoelectric power factor ($PF
= S^2/\rho$). The largest $PF$ of 4.6 $\mu$WcmK$^{-2}$ was found at 660 K for
Er$_{0.5}$Ho$_{0.5}$NiSb. This value is distinctly larger than PF determined
for the terminal phases ErNiSb and HoNiSb.",1805.02435v1
2019-11-06,High spin mixing conductance and spin interface transparency at $Co_2Fe_{0.4}Mn_{0.6}Si$ Heusler alloy and Pt interface,"Ferromagnetic materials exhibiting low magnetic damping ($\alpha$) and
moderately high saturation magnetization are required from the viewpoints of
generation, transmission and detection of spin wave. Since spin-to-charge
conversion efficiency is another important parameter, high spin mixing
conductance ($g_{r}^{\uparrow \downarrow}$) is the key for efficient
spin-to-charge conversion. Full Heusler alloys e.g. $Co_2Fe_{0.4}Mn_{0.6}Si$
(CFMS), which are predicted to be 100$\%$ spin polarized, possess low $\alpha$.
However, the $g_{r}^{\uparrow \downarrow}$ at the interface between CFMS and a
paramagnet has not fully been understood. Here, we report the investigations of
spin pumping and inverse spin Hall effect in $CFMS/Pt$ bilayers. Damping
analysis indicates the presence of significant spin pumping at the interface of
CFMS and Pt, which is also confirmed by the detection of inverse spin Hall
voltage. We show that in CFMS/Pt the $g_{r}^{\uparrow \downarrow}$
(1.77$\times$10$^{20}$m$^{-2}$) and interface transparency (84$\%$) are higher
compared to values reported for other ferromagnet/heavy metal systems.",1911.02230v1
2020-01-03,Neutron diffraction and ab initio studies on the fully compensated ferrimagnetic characteristics of Mn2V1-xCoxGa Heusler alloys,"Neutron diffraction and ab initio studies were carried out on Mn2V1-xCoxGa
(x=0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high TC fully
compensated ferrimagnetic characteristic for x=0.5. A combined analysis of
neutron diffraction and ab initio calculations revealed the crystal structure
and magnetic configuration which could not be determined from the X-ray
diffraction and magnetic measurements. As reported earlier, Rietveld refinement
of neutron diffraction data confirmed L21 structure for Mn2VGa and Xa structure
for Mn2CoGa. The alloys with x=0.25 and 0.5 possess L21 structure with Mn(C)-Co
disorder. As the Co concentration reaches 0.75, a structural transition has
been observed from disordered L21 to disordered Xa. Detailed ab initio studies
also confirmed this structural transition. The reason for the magnetic moment
compensation in Mn2(V1-xCox)Ga was identified to be different from that of the
earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of
neutron diffraction and ab initio studies, it is identified that the disordered
L21 structure with antiparallel coupling between the ferromagnetically aligned
magnetic moments of (Mn(A)-Mn(C)) and (V-Co) atom pairs enables the
compensation in Mn2V1-xCoxGa.",2001.00707v1
2017-05-30,Heteroepitaxial growth of tetragonal Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ (0 $\leqslant$ x $\leqslant$ 1.2) Heusler films with perpendicular magnetic anisotropy,"This work reports on the structural and magnetic properties of
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ Heusler films with different Fe content x (0
$\leqslant$ x $\leqslant$ 1.2). The films were deposited heteroepitaxially on
MgO single crystal substrates, by magnetron sputtering.
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films with the thickness of 35 nm were
crystallized in tetragonal D0$_{22}$ structure with (001) preferred
orientation. Tunable magnetic properties were achieved by changing the Fe
content x. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ thins films exhibit high uniaxial
anisotropy Ku $\geqslant$ 1.4 MJ/m3, coercivity from 0.95 to 0.3 T and
saturation magnetization from 290 to 570 kA/m. The film with
Mn$_{1.6}$Fe$_{1.1}$Ga$_{1.3}$ composition shows high Ku of 1.47 MJ/m3 and
energy product ${(BH)_{max}}$ of 37 kJ/m3, at room temperature. These findings
demonstrate that Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films have promising properties
for mid-range permanent magnet and spintronic applications.",1705.10668v1
2012-09-12,Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements,"We determine experimentally the spin structure of half-metallic
Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following
magnetic saturation, the dominant magnetic states consist of quasi-uniform
configurations, where a strong influence from the magnetocrystalline anisotropy
is visible. Heating experiments show the stability of the spin configuration of
domain walls in confined geometries up to 800 K. The switching temperature for
the transition from transverse to vortex walls in ring elements is found to
increase with ring width, an effect attributed to structural changes and
consequent changes in magnetic anisotropy, which start to occur in the narrower
elements at lower temperatures.",1209.2702v1
2012-09-17,Nonlinear emission of spin-wave caustics from an edge mode of a micro-structured Co2Mn0.6Fe0.4Si waveguide,"Magnetic Heusler materials with very low Gilbert damping are expected to show
novel magnonic transport phenomena. We report nonlinear generation of higher
harmonics leading to the emission of caustic spin-wave beams in a low-damping,
micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide. The source for the higher
harmonic generation is a localized edge mode formed by the strongly
inhomogeneous field distribution at the edges of the spin-wave waveguide. The
radiation characteristics of the propagating caustic waves observed at twice
and three times the excitation frequency are described by an analytical
calculation based on the anisotropic dispersion of spin waves in a magnetic
thin film.",1209.3669v2
2018-02-20,Signature of a highly spin polarized resonance state at Co2MnSi(001)/Ag(001) interfaces,"We investigated interfaces of halfmetallic Co2MnSi(100) Heusler thin films
with Ag(100), Cr(100), Cu and Al layers relevant for spin valves by high energy
x-ray photoemission spectroscopy (HAXPES). Experiments on Co2MnSi samples with
an Ag(100) interface showed a characteristic spectral shoulder feature close to
the Fermi edge, which is strongly diminished or suppressed at Co2MnSi (100)
interfaces with the other metallic layers. This feature is found to be directly
related to the Co2MnSi(100) layer, as reflected by control experiments with
reference non-magnetic films, i.e. without Heusler layer. By comparison with
HAXPES calculations, the shoulder feature is identified as originating from an
interface state related to a highly spin polarized surface resonance of Co2MnSi
(100).",1802.07005v1
2019-02-05,Co-existence of spin semi-metallic and Weyl semi-metallic behavior in FeRhCrGe,"In this letter, we report the discovery of a new class of spintronic
materials, namely spin semi-metals (SSM), employing both theoretical and
experimental tools. The band structure of this class of materials is such that
one of the spin bands resembles that of a semi-metal, while the other is
similar to that of an insulator/semiconductor. This report is the experimental
verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a
magnetic moment 3 $\mu_B$ and a Curie temperature of 550 K. The measurement
below 300 K shows nearly temperature independent conductivity and a relatively
moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous
first principles calculations. Band structure calculations also reveal that the
spin up (semi metallic) band has combined features of type II Weyl and nodal
line semimetal. As such, this study opens up the possibility of a new class of
material with combined spintronic and topological properties, which is
important both from fundamental and applied point of view.",1902.01593v2
2020-04-13,Half-metallic compositional ranges for selected Heusler alloys,"For a material that is a half-metal, there should exist a range of
compositions for half-metallicity. This compositional range can be expressed in
terms of electron count and computed. We investigate electronic and magnetic
properties of doped full- and half-Heusler alloys (stoichiometry XYZ2 and XYZ,
respectively) with elements X from groups 13-16 and periods 3-6 of the Periodic
Table, Y={Mn, Fe}, and Z={Co, Ni}. Using spin density functional theory, we
predict shifts of the Fermi energy in the doped and solid-solution alloys.
These predictions can be used for band-gap engineering of multicomponent
half-metals and provide the viable range of compositions, such as for a range
of n=x+y+z in (Co$_{2-z}Ni_z)$(Mn$_{1-y}$Fe$_{y}$)(Sn$_{1-x}$Sb$_{x}$). This
methodology for doped and chemically disordered half-metallic alloys offers a
design approach to electronic-structure engineering that can accelerate
development of half-metals for novel electronic and spintronic applications.",2004.06233v1
2020-04-15,Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys,"Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large
thermal hysteresis at their first-order martensitic phase transition which
hinder a technological application in magnetic refrigeration. By optimizing the
Cu content in Ni$_2$Cu$_x$Mn$_{1.4-x}$In$_{0.6}$, we obtained a thermal
hysteresis of the martensitic phase transition in
Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ of only 6 K. We can explain this very
small hysteresis by an almost perfect habit plane at the interface of
martensite and austenite phases. Application of hydrostatic pressure does not
reduce the hysteresis further, but shifts the martensitic transition close to
room temperature. The isothermal entropy change does not depend on warming or
cooling protocols and is pressure independent. Experiments in pulsed-magnetic
fields on Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ find a reversible
magnetocaloric effect with a maximum adiabatic temperature change of -13 K.",2004.07145v1
2022-03-22,A strategic high throughput search for identifying stable Li based half Heusler alloys for spintronics applications,"In this work, high throughput DFT calculations are performed on the alkali
metal-based half Heusler alloys; LiY$_p$Y$^\prime_{1-p}$S (Y, Y$^\prime$ = V,
Cr, Mn, Fe, Co, Ni and $\mathit{p}$ = 0, 0.25, 0.5, 0.75, 1). Starting with 243
structural replica, systematic filters are designed to select the energetically
and vibrationally favorable compositions by considering the contributions
stemming from the magnetic alignments of the ions. Thereby, 26 dynamically
stable magnetic compositions are identified, of which 10 are found to be
ferromagnetic (FM), 4 antiferromagnetic (AFM) and 12 ferrimagnetic (FiM). 4 FM
and 8 FiM ones are found to show 100 $\%$ spin polarization. Further,
tetragonal distortion is found to be present in 4 FM, 3 FiM and 4 AFM
compositions, which indicates the possibility of easy-axis magnetocrystalline
anisotropy. The ferromagnetic LiFe$_{0.5}$Mn$_{0.5}$S and antiferromagnetic
LiFeS are found to have the most prominent easy-axis magnetocrystalline
anisotropy.",2203.11794v1
2022-03-23,Effective decoupling of ferromagnetic sublattices by frustration in Heusler alloys,"Magnetic frustration in ferromagnetic metallic systems is unusual due to the
long-range and symmetric nature of the exchange interactions. In this work we
prove that it is possible to obtain a highly frustrated ferromagnetic phase in
a multi-sublattices cubic structure through a fine tuning of the magnetic
interactions. This peculiar state is achieved in Ni-Mn-(In, Sn) Heusler alloys
and results in the effective decoupling of their two intertwined ferromagnetic
sublattices. One sublattice is ferromagnetic long range ordered below the
macroscopic Curie temperature (TC ) whereas the second one remains disordered
until a crossover to a polarized state occurs at T << TC . This result points
out that a fine engineering of the magnetic interactions in metallic systems
can lead to interesting novel and emergent phenomena.",2203.12498v2
2016-03-29,Revealing the nature of magnetic phases in the semi-Heusler alloy Cu0.85Ni0.15MnSb,"We report the magnetic, magnetocaloric, and magnetotransport properties of
the semi-Heusler alloy Cu0.85Ni0.15MnSb, which exhibits coexistence of
antiferromagnetic (AFM) and ferromagnetic (FM) phases. A broad magnetic phase
transition is evident from the temperature variations of magnetization, heat
capacity, and isothermal magnetic entropy change. This is due to the presence
of both AFM and FM phases at low temperatures. The variation of electrical
resistivity with temperature shows three distinct regions of magnetic phases.
The magnetoresistance (MR) results also show the presence of AFM and FM phases
at temperatures below 45 K, and a FM phase at temperature above 45K. Though
there is no signature of a spin-glass state at low temperatures, various
results point towards the presence of short-range magnetic correlations at low
temperatures.",1603.08618v1
2016-12-21,Volume dependence of magnetic properties in Co2Cr1-xYxGa (Y=Ti-Ni) Heusler alloys: a first-principles study,"The magnetic properties tuning and volume dependence in the series of
quaternary full Heusler alloys with formula Co2Cr1-xYGa (Y = Ti, V, Mn, Fe, Co,
Ni) were studied with a detailed first-principles exploration. We employ the
density functional KKR method with the coherent potential approximation,
estimating effective Heisenberg exchange constants via the magnetic force
theorem together with mean-field Curie temperature (TC) and magnetic moment for
compositions in the whole concentration range. The volumetric dependency of
these magnetic properties is studied, particularly the pressure derivatives of
TC at equilibrium. Our ternary alloy calculations show good agreement with
local-density and generalized gradient approximations in the literature. The
quaternary alloys show a wide range of tunable magnetic properties, where
magnetic moments range from 0.8 to 4.9 mu_B, TC from 130 K to 1250 K, and
dTC/dV values range from -7 to +6.3 K A-3.",1612.07071v1
2017-02-03,Field dependent neutron diffraction study in Ni50Mn38Sb12 Heusler alloy,"In this paper, we present temperature and field dependent neutron diffraction
(ND) study to unravel the structural and the magnetic properties in
Ni50Mn38Sb12 Heusler system. This alloy shows martensitic transition from high
temperature austenite cubic phase to low temperature martensite orthorhombic
phase on cooling. At 3 K, the lattice parameters and magnetic moments are found
to be almost insensitive to field. Just below the martensitic transition
temperature, the martensite phase fraction is found to be 85%. Upon applying
the field, the austenite phase becomes dominant, and the field induced reverse
martensitic transition is clearly observed in the ND data. Therefore, the
present study gives an estimate of the strength of the martensite phase or the
sharpness of the martensitic transition. Variation of individual moments and
the change in the phase fraction obtained from the analysis of the ND data
vividly show the change in the magneto-structural state of the material across
the transition.",1702.00940v1
2019-05-21,Competition of L21 and XA Ordering in Fe2CoAl Heusler Alloy: A First-Principles Study,"The physical properties of Fe2CoAl (FCA) Heusler alloy are systematically
investigated using the first-principles calculations within generalized
gradient approximation (GGA) and GGA+U. The influence of atomic ordering with
respect to the Wyckoff sites on the phase stability, magnetism and half
metallicity in both the conventional L21 and XA phases of FCA is focused in
this study. Various possible hypothetical structures viz., L21, XA-I, and XA-II
are prepared by altering atomic occupancies at their Wyckoff sites. At first,
we have determined the stable phase of FCA considering various non-magnetic (or
paramagnetic), ferromagnetic (FM) and antiferromagnetic (AFM) configurations.
Out of these, the ferromagnetic (FM) XA-I structure is found to be
energetically most stable. The total magnetic moments per cell are not in
agreement with the Slater-Pauling (SP) rule in any phases; therefore, the
half-metallicity is not observed in any configurations. However, FM ordered
XA-I type FCA shows 78% spin polarization at EF. Interestingly, the results of
XA-I type FCA are closely matched with the experimental results.",1905.08476v2
2019-08-16,Scaling Analysis of Anomalous Hall Resistivity in the Co$_{2}$TiAl Heusler Alloy,"A comprehensive magnetotransport study including resistivity ($\rho_{xx}$) at
various fields, isothermal magnetoresistance and Hall resistivity ($\rho_{xy}$)
has been carried out at different temperatures on the Co$_{2}$TiAl Heusler
alloy. Co$_{2}$TiAl alloy shows a paramagnetic (PM) to ferromagnetic (FM)
transition below the curie temperature (T$_{C}$) $\sim$ 125 K. In the FM
region, resistivity and magnetoresistance reveals a spin flip electron-magnon
scattering and the Hall resistivity unveils the anomalous Hall resistivity
($\rho_{xy}^{AH}$). Scaling of anomalous Hall resistivity with resistivity
establishes the extrinsic scattering process responsible for the anomalous hall
resistivity; however Skew scattering is the dominant mechanism compared to the
side-jump contribution. A one to one correspondence between magnetoresistance
and side-jump contribution to anomalous Hall resistivity verifies the
electron-magnon scattering being the source of side-jump contribution to the
anomalous hall resistivity.",1908.05974v1
2019-09-06,The interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films,"We report on broadband ferromagnetic resonance linewidth measurements
performed on epitaxial Heusler thin films. A large and anisotropic two-magnon
scattering linewidth broadening is observed for measurements with the
magnetization lying in the film plane, while linewidth measurements with the
magnetization saturated perpendicular to the sample plane reveal low Gilbert
damping constants of $(1.5\pm0.1)\times 10^{-3}$, $(1.8\pm0.2)\times 10^{-3}$,
and $<8\times 10^{-4}$ for Co$_2$MnSi/MgO, Co$_2$MnAl/MgO, and Co$_2$FeAl/MgO,
respectively. The in-plane measurements are fit to a model combining Gilbert
and two-magnon scattering contributions to the linewidth, revealing a
characteristic disorder lengthscale of 10-100 nm.",1909.02738v2
2019-09-07,Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping,"Based on high-throughput density functional theory calculations, we
investigated the effects of light interstitial H, B, C, and N atoms on the
magnetic properties of cubic Heusler alloys, with the aim to design new
rare-earth free permanent magnets. It is observed that the interstitial atoms
induce significant tetragonal distortions, leading to 32 candidates with large
($>$ 0.4 MJ/m$^3$) uniaxial magneto-crystalline anisotropy energies (MAEs) and
10 cases with large in-plane MAEs. Detailed analysis following the the
perturbation theory and chemical bonding reveals the strong MAE originates from
the local crystalline distortions and thus the changes of the chemical bonding
around the interstitials. This provides a valuable way to tailor the MAEs to
obtain competitive permanent magnets, filling the gap between high performance
Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.",1909.03275v1
2019-09-23,Giant magnetocaloric effect in Co2FeAl Heusler alloy nanoparticles,"A giant magnetocaloric effect across the ferromagnetic (FM) to paramagnetic
(PM) phase transition was observed in chemically synthesized Co2FeAl Heusler
alloy nanoparticles with a mean diameter of 16 nm. In our previous report, we
have observed a significant enhancement in its saturation magnetization (Ms)
and Curie temperature (Tc) as compared with the bulk counterpart. Motivated
from those results, here, we aim to explore its magnetocaloric properties near
the Tc. The magnetic entropy change shows a positive anomaly at 1252 K.
Magnetic entropy change increases linearly with the magnetic field, and a large
value of ~15 J/Kg-K is detected under a moderate field of 14 kOe. It leads to a
net relative cooling power of 89 J/Kg for the magnetic field change of 14 kOe.
To confirm the nature of magnetic phase transition, a detailed study of its
magnetization is performed. The Arrott plot and nature of the universal curve
conclude that FM to PM phase transition in the present system is of
second-order.",1909.10201v4
2020-02-27,Ultrafast magnetization dynamics in half-metallic Co$_2$FeAl Heusler alloy,"We report on optically induced, ultrafast magnetization dynamics in the
Heusler alloy $\mathrm{Co_{2}FeAl}$, probed by time-resolved magneto-optical
Kerr effect. Experimental results are compared to results from electronic
structure theory and atomistic spin-dynamics simulations. Experimentally, we
find that the demagnetization time ($\tau_{M}$) in films of
$\mathrm{Co_{2}FeAl}$ is almost independent of varying structural order, and
that it is similar to that in elemental 3d ferromagnets. In contrast, the
slower process of magnetization recovery, specified by $\tau_{R}$, is found to
occur on picosecond time scales, and is demonstrated to correlate strongly with
the Gilbert damping parameter ($\alpha$). Our results show that
$\mathrm{Co_{2}FeAl}$ is unique, in that it is the first material that clearly
demonstrates the importance of the damping parameter in the remagnetization
process. Based on these results we argue that for $\mathrm{Co_{2}FeAl}$ the
remagnetization process is dominated by magnon dynamics, something which might
have general applicability.",2002.12255v1
2020-10-16,Visualizing half-metallic bulk band structure with multiple Weyl cones of the Heusler ferromagnet,"Using a well-focused soft X-ray synchrotron radiation beam, angle-resolved
photoelectron spectroscopy was applied to a full-Heusler-type Co$_2$MnGe alloy
to elucidate its bulk band structure. A large parabolic band at the Brillouin
zone center and several bands that cross the Fermi level near the Brillouin
zone boundary were identified in line with the results from first-principles
calculations. These Fermi level crossings are ascribed to majority spin bands
that are responsible for electron transport with extremely high spin
polarization especially along the direction being perpendicular to the
interface of magneto-resistive devices. The spectroscopy confirms there is no
contribution of the minority spin bands to the Fermi surface, signifying
half-metallicity for the alloy. Furthermore, two topological Weyl cones with
band crossing points were identified around the $X$ point, yielding the
conclusion that Co$_2$MnGe could exhibit topologically meaningful behavior such
as large anomalous Hall and Nernst effects driven by the Berry flux in its
half-metallic band structure.",2010.08415v1
2020-10-19,"Investigation on structural, electronic and magnetic properties of Co2FeGe Heusler alloy: experiment and theory","Experimental and computational studies were performed on Co2FeGe Heusler
alloy. It was found that the alloy has very high experimental magnetic moment
of 6.1 muB/f.u., curie temperature of 1073K and very high spin-wave stiffness
constant of 10.4 nm2-meV, which indicates that the magnetic moment is very high
and do not vary with change in temperature in the range 0-300K. The alloy
strictly follows Slater-Pauling (SP) rule and the minor experimental deviation
from its SP value is justified by doing full-potential density functional
calculations which gives more accurate result when electron-electron
correlation parameter (U) is taken into account with conventional GGA method.
Effect of lattice strain and electron correlation on individual atomic moments,
total magnetic moment and spin-polarization is studied in detail and can be
concluded that they have a role in the deviation of the experimental results
from the expected theoretical values.",2010.09590v1
2021-02-15,Prediction of a Heusler alloy with switchable metal-to-half-metal behavior,"We propose a ferromagnetic Heusler alloy that can switch between a metal and
a half-metal. Thiseffect can provide tunable spintronics properties. Using the
density functional theory (DFT) withreliable implementations of the electron
correlation effects, we find Mn2ScSi total energy curvesconsisting of distinct
branches with a very small energy difference. The phase at low lattice
crystalvolume is a low magnetic half-metallic state while the phase at high
lattice crystal volume is a highmagnetic metallic state. We suggest that the
transition between half-metallic and metallic statescan be triggered by a
triaxial contraction/expansion of the crystal lattice or by an external
magneticfield if we assume that the lattice is cubic and remains cubic under
expansion/contraction. However,the phase at high volume can also undergo an
austenite-martensite phase transition because of thepresence of Jahn-Teller
active3delectrons on the Mn atoms.",2102.07447v1
2021-02-23,Strain glass versus antisite disorder induced ferromagnetic state in Fe doped Ni-Mn-In Heusler martensites,"Fe doping in Ni$_2$Mn$_{1.5}$In$_{0.5}$ results in suppression of the
martensitic phase via two contrasting routes. In
Ni$_2$Mn$_{1.5-x}$Fe$_{x}$In$_{0.5}$, the martensitic phase is converted to a
strain glassy phase, while in Ni$_{2-y}$Fe$_y$Mn$_{1.5}$In$_{0.5}$, a cubic
ferromagnetic phase results at the expense of the martensite. Careful studies
of magnetic and structural properties reveal the presence of the impurity
$\gamma -$(Fe,Ni) phase as the reason for the emergence of non-ergodic strain
glassy phase when Fe is sought to be doped at Y/Z (Mn) sites of X$_2$YZ Heusler
alloy. Whereas attempts to dope Fe in the X (Ni) sublattice result in an A2
type antisite disorder that promotes a ferromagnetic ground state.",2102.11611v1
2021-06-18,Atomistic spin model of single pulse toggle switching in Mn$_2$Ru$_x$Ga Heusler alloys,"Single femtosecond pulse toggle switching of ferrimagnetic alloys is an
essential building block for ultrafast spintronics. Very different
element-specific demagnetization dynamics is believed to be a hard limit for
switching in ferrimagnets. This suggests that ferrimagnets composed of two ions
of different nature, such as rare earth transition metal alloys, are necessary
for switching. However, experimental observation of toggle switching in
Mn$_2$Ru$_x$Ga Heusler alloys, has contested this limit since Mn ions are of
the same nature. To shed some light into this question, we present an atomistic
spin model for the simulation of single pulse toggle switching of
Mn$_2$Ru$_x$Ga. The magnetic parameters entering in our model are extracted
from previous experimental observations. We show that our model is able to
quantitatively reproduce measured magnetization dynamics of single pulse toggle
switching. We demonstrate that differently to previous understanding toggle
switching in Mn$_2$Ru$_x$Ga is possible even when both Mn sublattices
demagnetization at very similar rate.",2106.10111v2
2021-06-25,"First-principles investigation of half-metallic ferromagnetism of Fe$_2$YSn (Y = Mn, Ti and V) Heusler alloys","In this paper, we use the first-principles calculations based on the density
functional theory to investigate structural, electronic and magnetic properties
of Fe$_{2}$YSn with (Y = Mn, Ti and V). The generalized gradient approximation
(GGA) method is used for calculations. The Cu$_{2}$MnAl type structure is
energetically more stable than the Hg$_{2}$CuTi type structure. The negative
formation energy is shown as the evidence of thermodynamic stability of the
alloy. The calculated total spin moment is found as 3$\mu_\text{B}$ and
0$\mu_\text{B}$ at the equilibrium lattice constant for Fe$_{2}$MnSn and
Fe$_{2}$TiSn respectively, which agrees with the Slater-Pauling rule of $M_t=
Z_t-24$. The study of electronic and magnetic properties proves that
Fe$_{2}$MnSn and Fe$_{2}$TiSn full-Heusler alloys are complete half-metallic
ferromagnetic materials.",2106.13604v1
2021-11-29,"Half-metallic Ferromagnets, Spin Gapless Semiconductors, and Topological Semimetals Based on Heusler Alloys","A review of theoretical and experimental studies of the electronic structure,
electronic and magnetic properties of various systems of Heusler alloys in the
states of a half-metallic ferromagnet, a spin gapless semiconductor, and a
topological semimetal is presented. These substances have unusual, highly
sensitive to external influences, magnetic and electronic characteristics,
which is associated with the presence of energy gaps and exotic excitations in
them. The features of the behavior and evolution of the electronic structure
and properties in each of these states, as well as during the transition
between them, are considered. The possibility to purposefully control the
properties of such materials is prospective for their practical application.",2111.14537v1
2022-08-06,Giant spin Hall effect in half-Heusler alloy topological semimetal YPtBi grown at low temperature,"Half-Heusler alloy topological semimetal YPtBi is a promising candidate for
an efficient spin source material having both large spin Hall angle
${\theta}$$_{SH}$ and high thermal stability. However, high-quality YPtBi thin
films with low bulk carrier density are usually grown at 600${\deg}$C, which
exceeds the limitation of 400${\deg}$C for back end of line (BEOL) process.
Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films
grown at lower growth temperature down to 300${\deg}$C. Although
${\theta}$$_{SH}$ degraded with lowering the growth temperature to 300${\deg}$C
due to degradation of the crystallinity, it was recovered by reducing the
sputtering Ar gas pressure. We achieved a giant ${\theta}$$_{SH}$ up to 8.2 and
demonstrated efficient spin-orbit torque magnetization switching by ultralow
current density of ~10$^5$ A/cm$^2$ in YPtBi grown at 300${\deg}$C with the Ar
gas pressure of 1 Pa. Our results provide the recipe to achieve giant
${\theta}$$_{SH}$ in YPtBi grown at lower growth temperature suitable for BEOL
process.",2208.03413v1
2022-09-18,Superparamagnetic and metal-like Ru2TiGe: a propitious thermoelectric material,"We report a study of structural, magnetic, heat capacity and thermoelectric
properties of a Rubased Heusler alloy, Ru2TiGe. The magnetic measurements
reveal that at higher temperatures, diamagnetic and Pauli paramagnetic
contributions dominate the magnetic behaviour whereas, at lower temperatures
(T<= 20 K), superparamagnetic interaction among clusters is observed. Effect of
such magnetic defects is also evident in the electrical resistivity behaviour
at lower temperatures. Though the temperature dependence of resistivity
exhibits a metal-like nature, the large value of Seebeck coefficient leads to
an appreciable power factor of the order of 1 mW/mK2 at 300 K. Large power
factor as well as low thermal conductivity results in a value of ZT = 0.025 at
390 K for Ru2TiGe that is orders of magnitude higher than that of the other
pure Heusler alloys and point towards its high potential for practical
thermoelectric applications.",2209.08474v1
2022-11-22,Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl,"Heusler alloys based magnetic tunnel junctions can potentially provide high
magnetoresistance, small damping and fast switching. Here junctions with
Co2FeAl as a ferromagnetic electrode are fabricated by room temperature
sputtering on Si/SiO2 substrates. The doping of Boron in Co2FeAl is found to
have a large positive impact on the structural, magnetic and transport
properties of the junctions, with a reduced interfacial roughness and
substantial improved tunneling magnetoresistance. A two-level magnetoresistance
is also observed in samples annealed at low temperature, which is believed to
be related to the memristive effect of the tunnel barrier with impurities.",2211.12448v1
2023-04-06,Formation of Core-Shell Precipitates in off-stochiometric Ni-Mn-Sn Heusler alloys probed through the induced Sn-moment,"The Shell-ferromagnetic effect originates from the segregation process in
off-stochiometric Ni-Mn-based Heusler. In this work, we investigate the
precipitation process of L2$_1$-ordered Ni$_2$MnSn and L1$_0$-ordered NiMn in
off-stochiometric Ni$_{50}$Mn$_{45}$Sn$_{5}$ during temper annealing, by X-ray
diffraction (XRD) and $^{119}$Sn M\""ossbauer spectroscopy. While XRD probes
long-range ordering of the lattice structure, M\""ossbauer spectroscopy probes
nearest-neighbour interactions, reflected in the induced Sn magnetic moment. As
shown in this work, the induced magnetic Sn moment can be used as a detector
for microscopic structural changes and is, therefore, a powerful tool for
investigating the formation of nano-precipitates. Similar research can be
performed in the future, for example, on different pinning type magnets like
Sm-Co or Nd-Fe-B.",2304.03033v1
2023-04-12,"Large Violation of the Wiedemann Franz Law in Heusler, Ferromagnetic, Weyl Semimetal Co$_2$MnAl","The Wiedemann-Franz (WF) law relates the electronic component of the thermal
conductivity to the electrical conductivity in metals through the Lorenz
number. The WF law has proven to be remarkably robust, however violations have
been observed in many topological materials. In this work, we report
thermoelectric measurements conducted on Heusler, ferromagnetic, Weyl semimetal
Co$_2$MnAl which shows a drastic, temperature dependent violation of the WF law
below 300 K. We then discuss our result in the context of known physical
explanations for WF law violation. Both the magnitude and temperature
dependence of the violation in Co2MnAl are extreme, indicating that there may
be more than one effect contributing to the violation in this system.",2304.05595v1
2023-09-11,Experimental realization of a high Curie temperature CoFeRuSn quaternary Heusler alloy for spintronic applications,"We synthesize CoFeRuSn equiatomic quaternary Heusler alloy using arc-melt
technique and investigate its structural, magnetic and transport properties.
The room temperature powder X-ray diffraction analysis reveals that CoFeRuSn
crystallizes in cubic crystal structure with small amount of DO3 - disorder.
The field dependence of magnetization shows non-zero but small hysteresis and
saturation behavior up to room temperature, indicating soft ferromagnetic
nature of CoFeRuSn. The magnetic moment estimated from the magnetization data
is found to be 4.15 {\mu}B / f.u., which is slightly less than the expected
Slater-Pauling rule. The deviation in the value of experimentally observed
moment from the theoretical value might be due to small disorder in the
crystal. The low temperature fit to electrical resistivity data show absence of
quadratic temperature dependence of resistivity, suggesting half-metallic
behavior of CoFeRuSn. The high Curie temperature and possible half-metallic
behavior of CoFeRuSn make it a highly promising candidate for room temperature
spintronic applications.",2309.05493v1
2023-12-28,Possible Unconventional Surface Superconductivity in the Half-Heusler YPtBi,"We report an extensive extensive study of the noncentrosymmetric half-Heusler
topological superconductor YPtBi, revealing unusual relation between bulk
superconductivity and the appearance of surface superconductivity at
temperatures up to 3 times the bulk transition temperature. Transport
measurements confirmed the low carrier density of the material and its bulk
superconducting transition, which was also observed in ac susceptibility
through mutual inductance (MI) measurements. However, a weak signature of
superconductivity in the MI measurements appeared much above the bulk
transition temperature, which was further observed in scanning tunneling
spectroscopy. Polar Kerr effect measurements suggest that while the bulk
superconductor may exhibit an unusual nodal superconducting state, only the
surface state breaks time reversal symmetry. Complementary tunneling
measurements on LuPtBi are used to establish the observations on YPtBi, while
density-functional theory (DFT) calculations may shed light on the origin of
this unusual surface state.",2312.17213v1
2024-03-27,THz probing of non-trivial topological states in Co2MnGe Heusler alloy thin films,"Co2MnGe (CMG) has been demonstrated recently as a half-metallic ferromagnetic
Heusler alloy which possesses a topologically non-trivial band structure. This
behavior is unique to such systems and hence warrants extensive experimental
exploration for potential spintronic and chirality sensitive optoelectonic
applications. Here, we demonstrate that an epitaxial thin film of CMG acts as a
source of THz radiation upon photoexcitation by optical femtosecond laser
pulses. Detailed experiments have revealed that a large contribution to THz
emission occurs due to nonmagnetic or spin-independent origin, however,
significant contribution in the THz generation is evidenced through excitation
light helicity dependent circular photogalvanic effect (CPGE) confirming the
presence of topologically non-trivial carriers. Furthermore, we show that not
only the topological contribution is easily suppressed but also the overall THz
generation efficiency is also affected adversely for the epitaxial films grown
at high substrate temperatures.",2403.18332v1
2022-07-12,"CompoundE: Knowledge Graph Embedding with Translation, Rotation and Scaling Compound Operations","Translation, rotation, and scaling are three commonly used geometric
manipulation operations in image processing. Besides, some of them are
successfully used in developing effective knowledge graph embedding (KGE)
models such as TransE and RotatE. Inspired by the synergy, we propose a new KGE
model by leveraging all three operations in this work. Since translation,
rotation, and scaling operations are cascaded to form a compound one, the new
model is named CompoundE. By casting CompoundE in the framework of group
theory, we show that quite a few scoring-function-based KGE models are special
cases of CompoundE. CompoundE extends the simple distance-based relation to
relation-dependent compound operations on head and/or tail entities. To
demonstrate the effectiveness of CompoundE, we conduct experiments on three
popular KG completion datasets. Experimental results show that CompoundE
consistently achieves the state of-the-art performance.",2207.05324v1
2023-09-26,Model for compound nucleus formation in various heavy-ion systems,"The statistical model for the calculation of the compound nucleus formation
cross section and the probability of compound nucleus formation in heavy-ion
collisions is discussed in detail. The light, heavy, and super-heavy
nucleus-nucleus systems are considered in this model in the framework of one
approach. It is shown that the compound nucleus is formed in competition
between passing through the compound-nucleus formation barrier and the
quasi-elastic barrier. The compound-nucleus formation barrier is the barrier
separating the system of contacting incident nuclei and the spherical or
near-spherical ground state of the compound nucleus. The quasi-elastic barrier
is the barrier between the contacting and well-separated deformed ions. It is
shown that the compound nucleus formation cross-section is suppressed when the
quasi-elastic barrier is lower than the compound nucleus formation barrier. The
critical value of angular momentum, which limits the compound nucleus formation
cross-section values for light and medium ion-ion systems at over-barrier
collision energies, is discussed in the model. The suppression of the compound
nucleus formation cross-section even at small partial waves for very heavy
ion-ion systems is obtained in the model. The values of the capture and
compound nucleus formation cross-sections calculated for various light, heavy,
and super-heavy nucleus-nucleus systems as well as the probability of the
compound nucleus formation for super-heavy nuclei are well agreed with the
available experimental data.",2309.14995v1
2006-05-29,"High pressure high temperature (HPHT) synthesis and magnetism of MSr2Y1.5Ce0.5Cu2O10 compounds with M = Ru, Mn, and Cr","The M-1222 compounds are synthesized in near single phase form. These
compounds crystallise in I4/mmm Tetragonal structure. None of the studied
compound is superconducting but they asre weakly magnetic. This is first report
on synthesis of Cr and Mn -1222 compounds. These compounds are synthesized at
ultra conditions of HPHT that is the 6 Gpa and 1400 C.",0605693v1
2006-07-03,Magnetic excitation in a new spin gap compound Cu$_2$Sc$_2$Ge$_4$O$_{13}$: Comparison to Cu$_2$Fe$_2$Ge$_4$O$_{13}$,"The compound \CuScGeO is presented as a new member of the family of weakly
coupled spin chain and dimer compounds \CuMGeO. Magnetic susceptibility, heat
capacity, and neutron inelastic scattering measurements reveal that the
compound has the same spin dimer component as \CuFeGeO. The observed narrow
band excitation in bulk measurements is consistent with spin gap behavior. The
energy scale of the weakly coupled dimers in the Sc compound is perfectly
coincident with that in the Fe compound.",0607029v1
2010-10-13,"Generation of Single, Monodisperse Compound Droplets","The generation of single, monodisperse compound droplets is shown in these
fluid dynamics videos. In an apparatus designed to produce single compound
droplets, a piezoelectric diaphragm generates a pressure pulse from a voltage
waveform input to eject a droplet. In the method presented, oil is allowed to
flow into the water nozzle with the pressure pulse ejecting both fluids as a
compound droplet. Experiments were performed to demonstrate how changes in
water pressure affect compound droplet compositions. It was found that
increasing the water pressure decreased the thickness of the compound droplet's
oil layer.",1010.2687v1
2011-12-15,Ab initio derivation of electronic low-energy models for C60 and aromatic compounds,"We present a systematic study for understanding the relation between
electronic correlation and superconductivity in C60 and aromatic compounds. We
derived, from first principles, extended Hubbard models for twelve compounds;
fcc K3C60, Rb3C60, Cs3C60 (with three different lattice constants), A15 Cs3C60
(with four different lattice constants), doped solid picene, coronene, and
phenanthrene. We show that these compounds are strongly correlated and have a
similar energy scale of the bandwidth and interaction parameters. However, they
have a different trend in the relation between the strength of electronic
correlation and superconducting transition temperature; while the C60 compounds
have a positive correlation, the aromatic compounds exhibit negative
correlation.",1112.3483v1
2021-03-01,Compound Lucas Magic Squares,"We review a general parameterization of an order-3 magic square derived by
Lucas and we compound it to produce a parameterized order-9 magic square.
Sequential compounding to higher order also is treated. Expressions are found
for the matrices in the Jordan canonical form and the singular value
decomposition of the compound Lucas magic square matrices. We develop a
procedure for determining if an order-n magic square may be natural. This
enables determination of numerical values for parameters in natural compound
Lucas magic squares. Also, we find commuting pairs of compound Lucas matrices
and formulas for matrix powers of order-3 and order-9 Lucas matrices. A
parameterization due to Frierson is related to Lucas' parameterization and our
results specialize to it, complementing previous results.",2103.04774v1
2024-01-04,Multiplicative and additive compounds via Kronecker products and Kronecker sums,"Compound matrices play an important role in many fields of mathematics and
have recently found new applications in systems and control theory. However,
the explicit formulas for these compounds are non-trivial and not always easy
to use. Here, we derive new formulas for the multiplicative and additive
compounds of a matrix using Kronecker products and sums. This provides a new
approach to matrix compounds based on the well-known and powerful theory of
Kronecker products and sums. We demonstrate several applications of these new
formulas, including deriving a new expression for the additive compound of the
product of two matrices.",2401.02100v1
2009-07-19,The Compound Capacity of Polar Codes,"We consider the compound capacity of polar codes under successive
cancellation decoding for a collection of binary-input memoryless
output-symmetric channels. By deriving a sequence of upper and lower bounds, we
show that in general the compound capacity under successive decoding is
strictly smaller than the unrestricted compound capacity.",0907.3291v1
2012-02-03,Capacities of classical compound quantum wiretap and classical quantum compound wiretap channels,"We determine the capacity of the classical compound quantum wiretapper
channel with channel state information at the transmitter. Moreover we derive a
lower bound on the capacity of this channel without channel state information
and determine the capacity of the classical quantum compound wiretap channel
with channel state information at the transmitter.",1202.0773v1
2015-10-01,#Bieber + #Blast = #BieberBlast: Early Prediction of Popular Hashtag Compounds,"Compounding of natural language units is a very common phenomena. In this
paper, we show, for the first time, that Twitter hashtags which, could be
considered as correlates of such linguistic units, undergo compounding. We
identify reasons for this compounding and propose a prediction model that can
identify with 77.07% accuracy if a pair of hashtags compounding in the near
future (i.e., 2 months after compounding) shall become popular. At longer times
T = 6, 10 months the accuracies are 77.52% and 79.13% respectively. This
technique has strong implications to trending hashtag recommendation since
newly formed hashtag compounds can be recommended early, even before the
compounding has taken place. Further, humans can predict compounds with an
overall accuracy of only 48.7% (treated as baseline). Notably, while humans can
discriminate the relatively easier cases, the automatic framework is successful
in classifying the relatively harder cases.",1510.00249v1
2016-04-05,A General Formula for Compound Channel Capacity,"A general formula for the capacity of arbitrary compound channels with the
receiver channel state information is obtained using the information density
approach. No assumptions of ergodicity, stationarity or information stability
are made and the channel state set is arbitrary. A direct (constructive) proof
is given. To prove achievability, we generalize Feinstein Lemma to the compound
channel setting, and to prove converse, we generalize Verdu-Han Lemma to the
same compound setting. A notion of a uniform compound channel is introduced and
the general formula is shown to reduce to the familiar $\sup-\inf$ expression
for such channels. As a by-product, the arbitrary varying channel capacity is
established under maximum error probability and deterministic coding.
Conditions are established under which the worst-case and compound channel
capacities are equal so that the full channel state information at the
transmitter brings in no advantage.
  The compound inf-information rate plays a prominent role in the general
formula. Its properties are studied and a link between information-unstable and
information-stable regimes of a compound channel is established. The results
are extended to include $\varepsilon$-capacity of compound channels. Sufficient
and necessary conditions for the strong converse to hold are given.",1604.01434v1
2019-10-16,A Coupling Proof of Convex Ordering for Compound Distributions,"In this paper, we give an alternative proof of the fact that, when
compounding a nonnegative probability distribution, convex ordering between the
distributions of the number of summands implies convex ordering between the
resulting compound distributions. Although this is a classical textbook result
in risk theory, our proof exhibits a concrete coupling between the compound
distributions being compared, using the representation of one-period discrete
martingale laws as a mixture of the corresponding extremal measures.",1910.07218v1
2021-03-28,Compound matrices in systems and control theory,"The multiplicative and additive compounds of a matrix play an important role
in several fields of mathematics including geometry, multi-linear algebra,
combinatorics, and the analysis of nonlinear time-varying dynamical systems.
There is a growing interest in applications of these compounds, and their
generalizations, in systems and control theory. This tutorial paper provides a
gentle introduction to these topics with an emphasis on the geometric
interpretation of the compounds, and surveys some of their recent applications.",2103.15097v1
2023-12-24,Deformation and breakup of compound droplets in airflow,"Hypothesis: Immiscible liquids are commonly used to achieve unique functions
in many applications, where the breakup of compound droplets in airflow is an
important process. Due to the existence of the liquid-liquid interface,
compound droplets are expected to form different deformation and breakup
morphologies compared with single-component droplets. Experiments: We
investigate experimentally the deformation and breakup of compound droplets in
airflow. The deformation characteristics of compound droplets are
quantitatively analyzed and compared with single-component droplets.
Theoretical models are proposed to analyze the transition between breakup
morphologies. Findings: The breakup modes of compound droplets are classified
into shell retraction, shell breakup, and core-shell breakup based on the
location where the breakup occurs. The comparison with single-component
droplets reveals that the compound droplet is stretched more in the flow
direction and expands less in the cross-flow direction, and these differences
occur when the core of the compound droplet protrudes into the airflow. The
transition conditions between different breakup modes are obtained
theoretically. In addition, the eccentricity of the compound droplet can lead
to the formation of the thick ligament or the two stamens in the droplet
middle.",2312.15498v1
2016-11-21,Adaptive modulation in Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy,"The origin of incommensurate structural modulation in Ni-Mn based Heusler
type magnetic shape memory alloys (MSMAs) is still an unresolved issue inspite
of intense focus on this due to its role in the magnetic field induced
ultra-high strains. In the archetypal MSMA Ni2MnGa, the observation of
non-uniform displacement of atoms from their mean positions in the modulated
martensite phase, premartensite phase and charge density wave as well as the
presence of phason broadening of satellite peaks have been taken in support of
the electronic instability model linked with a soft acoustic phonon. We present
here results of a combined high resolution synchrotron x-ray powder diffraction
(SXRPD) and neutron powder diffraction (NPD) study on Ni2Mn1.4In0.6 using
(3+1)D superspace group approach, which reveal not only uniform atomic
displacements in the modulated structure of the martensite phase with
physically acceptable ordered magnetic moments in the antiferromagnetic phase
at low temperatures but also the absence of any premartensite phase and phason
broadening of the satellite peaks. Our HRTEM studies and first principles
calculations of the ground state also support uniform atomic displacements
predicted by powder diffraction studies. All these observations suggest that
the structural modulation in the martensite phase of Ni2Mn1.4In0.6 MSMA can be
explained in terms of the adaptive phase model. The present study underlines
the importance of superspace group analysis using complimentary SXRPD and NPD
in understanding the physics of the origin of modulation as well as the
magnetic and the modulated ground states of the Heusler type MSMAs. Our work
also highlights the fact that the mechanism responsible for the origin of
modulated structure in different Ni-Mn based MSMAs may not be universal and it
must be investigated thoroughly in different alloy compositions.",1611.06688v2
2016-03-30,Probing the possibility of coexistence of martensite transition and half-metallicity in Ni and Co-based full Heusler Alloys : An ab initio Calculation,"Using first-principles calculations based on density functional theory, we
have studied the mechanical, electronic, and magnetic properties of Heusler
alloys, namely, Ni$_{2}BC$ and Co$_{2}BC$ ($B$ = Sc, Ti, V, Cr and Mn as well
as Y, Zr, Nb, Mo and Tc; $C$ = Ga and Sn). On the basis of electronic structure
(density of states) and mechanical properties (tetragonal shear constant), as
well as magnetic interactions (Heisenberg exchange coupling parameters), we
probe the properties of these materials in detail. We calculate the formation
energy of these alloys in the (face-centered) cubic austenite structure to
probe the stability of all these materials. From the energetic point of view,
we have studied the possibility of the electronically stable alloys having a
tetragonal phase lower in energy compared to the respective cubic phase. A
large number of the magnetic alloys is found to have the cubic phase as their
ground state. On the other hand, for another class of alloys, the tetragonal
phase has been found to have lower energy compared to the cubic phase. Further,
we find that the values of tetragonal shear constant show a consistent trend :
a high positive value for materials not prone to tetragonal transition and low
or negative for others. In the literature, materials, which have been seen to
undergo the martensite transition, are found to be metallic in nature. We probe
here if there is any Heusler alloy which has a tendency to undergo a tetragonal
transition and at the same time possesses a high spin polarization at the Fermi
level. From our study, it is found that out of the four materials, which
exhibit a martensite phase as their ground state, three of these, namely,
Ni$_{2}$MnGa, Ni$_{2}$MoGa and Co$_{2}$NbSn have a metallic nature; on the
contrary, Co$_{2}$MoGa exhibits a high spin polarization.",1603.09112v1
2020-02-18,Anisotropic RKKY interactions mediated by $j=3/2$ quasiparticles in half-Heusler topological semimetal,"We theoretically explore the RKKY interaction mediated by spin-3/2
quasiparticles in half-Heusler topological semimetals in quasi-two-dimensional
geometries. We find that while the Kohn-Luttinger terms gives rise to
generalized Heisenberg coupling of the form ${\cal H}_{\rm RKKY} \propto
{\sigma}_{1,i} {\cal I}_{ij} {\sigma}_{2,j}$ with a symmetric matrix ${\cal
I}_{ij}$, addition of small antisymmetric linear spin-orbit coupling term leads
to Dzyaloshinskii-Moriya (DM) coupling with an antisymmetric matrix ${\cal
I}'_{ij}$. We demonstrate that besides the oscillatory dependence on the
distance, all coupling strengths strongly depend on the relative orientation of
the two impurities with respect to the lattice. This yields a strongly
anisotropic behavior for ${\cal I}_{ij}$ such that by only rotating one
impurity around another at a constant distance, we can see further oscillations
of the RKKY couplings. This unprecedented effect is unique to our system which
combines spin-orbit coupling with strongly anisotropic Fermi surfaces. We
further find that all of the RKKY terms have two common features: a tetragonal
warping in their map of spatial variations, and a complex beating pattern.
Intriguingly, all these features survive in all dopings and we see them in both
electron- and hole-doped cases. In addition, due to the lower dimensionality
combined with the effects of different spin-orbit couplings, we see that only
one symmetric off-diagonal term, ${\cal I}_{xy}$ and two DM components ${\cal
I}'_{xz}$ and ${\cal I}'_{yz}$ are nonvanishing, while the remaining three
off-diagonal components are identically zero. This manifests another drastic
difference of RKKY interaction in half-Heusler topological semimetals compared
to the electronic systems with spin-1/2 effective description.",2002.07736v1
2021-05-14,"Understanding Magnetic Phase Coexistence in Ru$_2$Mn$_{1-x}$Fe$_x$Sn Heusler Alloys: A Neutron Scattering, Thermodynamic, and Phenomenological Analysis","The random substitutional solid solution between the antiferromagnetic (AFM)
full-Heusler alloy Ru$_2$MnSn and the ferromagnetic (FM) full-Heusler alloy
Ru$_2$FeSn provides a rare opportunity to study FM-AFM phase competition in a
near-lattice-matched, cubic system, with full solubility. At intermediate $x$
in Ru$_2$Mn$_{1-x}$Fe$_x$Sn this system displays suppressed magnetic ordering
temperatures, spatially coexisting FM and AFM order, and strong coercivity
enhancement, despite rigorous chemical homogeneity. Here, we construct the most
detailed temperature- and $x$-dependent understanding of the magnetic phase
competition and coexistence in this system to date, combining
wide-temperature-range neutron diffraction and small-angle neutron scattering
with magnetometry and specific heat measurements on thoroughly characterized
polycrystals. A complete magnetic phase diagram is generated, showing FM-AFM
coexistence between $x \approx 0.30$ and $x \approx 0.70$. Important new
insight is gained from the extracted length scales for magnetic phase
coexistence (25-100 nm), the relative magnetic volume fractions and ordering
temperatures, in addition to remarkable $x$-dependent trends in magnetic and
electronic contributions to specific heat. An unusual feature in the magnetic
phase diagram (an intermediate FM phase) is also shown to arise from an
extrinsic effect related to a minor Ru-rich secondary phase. The established
magnetic phase diagram is then discussed with the aid of phenomenological
modeling, clarifying the nature of the mesoscale phase coexistence with respect
to the understanding of disordered Heisenberg models.",2105.06629v1
2021-08-26,Magnetoelastic anisotropy in Heusler-type Mn$_{2-δ}$CoGa$_{1+δ}$ films,"Perpendicular magnetization is essential for high-density memory application
using magnetic materials. High-spin polarization of conduction electrons is
also required for realizing large electric signals from spin-dependent
transport phenomena. Heusler alloy is a well-known material class showing the
half-metallic electronic structure. However, its cubic lattice nature favors
in-plane magnetization and thus minimizes the perpendicular magnetic anisotropy
(PMA), in general. This study focuses on an inverse-type Heusler alloy,
Mn$_{2-\delta}$CoGa$_{1+\delta}$ (MCG) with a small off-stoichiometry
($\delta$) , which is expected to be a half-metallic material. We observed
relatively large uniaxial magnetocrystalline anisotropy constant
($K_\mathrm{u}$) of the order of 10$^5$ J/m$^3$ at room temperature in MCG
films with a small tetragonal distortion of a few percent. A positive
correlation was confirmed between the $c/a$ ratio of lattice constants and
$K_\mathrm{u}$. Imaging of magnetic domains using Kerr microscopy clearly
demonstrated a change in the domain patterns along with $K_\mathrm{u}$. X-ray
magnetic circular dichroism (XMCD) was employed using synchrotron radiation
soft x-ray beam to get insight into the origin for PMA. Negligible angular
variation of orbital magnetic moment ($\Delta m_\mathrm{orb}$) evaluated using
the XMCD spectra suggested a minor role of the so-called Bruno's term to
$K_\mathrm{u}$. Our first principles calculation reasonably explained the small
$\Delta m_\mathrm{orb}$ and the positive correlation between the $c/a$ ratio
and $K_\mathrm{u}$. The origin of the magnetocrystalline anisotropy was
discussed based on the second-order perturbation theory in terms of the
spin--orbit coupling, claiming that the mixing of the occupied $\uparrow$- and
the unoccupied $\downarrow$-spin states is responsible for the PMA of the MCG
films.",2108.11547v2
2023-08-18,Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films,"Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high
Curie temperature (TC) and sizeable spin polarization have emerged as potential
candidates for tunable spintronic applications. We report comprehensive
investigation of the temperature dependent ANE and intrinsic longitudinal spin
Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our
findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm)
film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders
of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (=
0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa
thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our
MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $\mu$V/K/$\Omega$ at
room temperature which is twice larger than that of the half-metallic
ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5
$\mu$V/K/$\Omega$). We show that both ANE and LSSE coefficients follow
identical temperature dependences and exhibit a maximum at $\cong$ 225 K which
is understood as the combined effects of inelastic magnon scatterings and
reduced magnon population at low temperatures. Our analyses not only indicate
that the extrinsic skew scattering is the dominating mechanism for ANE in these
films but also provide critical insights into the functional form of the
observed temperature dependent LSSE at low temperatures. Furthermore, by
employing radio frequency transverse susceptibility and broadband ferromagnetic
resonance in combination with the LSSE measurements, we establish a correlation
among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the
CoFeCrGa thin films, which will be beneficial for fabricating tunable and
highly efficient Heusler alloys based spincaloritronic nanodevices.",2308.09843v1
2019-11-23,Using the Web as an Implicit Training Set: Application to Noun Compound Syntax and Semantics,"An important characteristic of English written text is the abundance of noun
compounds - sequences of nouns acting as a single noun, e.g., colon cancer
tumor suppressor protein. While eventually mastered by domain experts, their
interpretation poses a major challenge for automated analysis. Understanding
noun compounds' syntax and semantics is important for many natural language
applications, including question answering, machine translation, information
retrieval, and information extraction. I address the problem of noun compounds
syntax by means of novel, highly accurate unsupervised and lightly supervised
algorithms using the Web as a corpus and search engines as interfaces to that
corpus. Traditionally the Web has been viewed as a source of page hit counts,
used as an estimate for n-gram word frequencies. I extend this approach by
introducing novel surface features and paraphrases, which yield
state-of-the-art results for the task of noun compound bracketing. I also show
how these kinds of features can be applied to other structural ambiguity
problems, like prepositional phrase attachment and noun phrase coordination. I
address noun compound semantics by automatically generating paraphrasing verbs
and prepositions that make explicit the hidden semantic relations between the
nouns in a noun compound. I also demonstrate how these paraphrasing verbs can
be used to solve various relational similarity problems, and how paraphrasing
noun compounds can improve machine translation.",1912.01113v1
1999-10-15,"Electronic structure and magnetism of Fe$_{3-x}$V$_{x}$X (X = Si, Ga and Al) alloys by the KKR-CPA method","We present first principles charge- and spin-selfconsistent electronic
structure computations on the Heusler-type disordered alloys Fe$_{3-x}$V$_{x}$X
for three different metalloids X=(Si, Ga and Al). In these calculations we use
the methodology based on the Korringa-Kohn- Rostoker formalism and the
coherent-potential approximation (KKR-CPA), generalized to treat disorder in
multi-component complex alloys.",9910249v1
2001-03-23,Premartensitic Transition in Ni2+xMn1-xGa Heusler Alloys,"The temperature dependencies of the resistivity and magnetization of a series
of Ni2+XMn1-XGa (X = 0 - 0.09) alloys were investigated. Along with the
anomalies associated with ferromagnetic and martensitic transitions,
well-defined anomalies were observed at the temperature of premartensitic
transformation. The premartensitic phase existing in a temperature range 200 -
260 K in the stoichiometric Ni2MnGa is suppressed by the martensitic phase with
increasing Ni content and vanishes in Ni2.09Mn0.91Ga composition.",0103483v1
2002-02-27,Electronic Structure and Charge Dynamics of Huesler Alloy Fe2TiSn Probed by Infrared and Optical Spectroscopy,"We report on the electrodynamics of a Heusler alloy Fe2TiSn probed over four
decades in energy: from the far infrared to the ultraviolet. Our results do not
support the suggestion of Kondo-lattice behavior inferred from specific heat
measurements. Instead, we find a conventional Drude-like response of free
carriers, with two additional absorption bands centered at around 0.1 and 0.87
eV. The latter feature can be interpreted as excitations across a pseudogap, in
accord with band structure calculations.",0202512v2
2003-08-07,The effect of the spin-orbit interaction on the band gap of half-metals,"The spin-orbit interaction can cause a nonvanishing density of states (DOS)
within the minority-spin band gap of half-metals around the Fermi level. We
examine the magnitude of the effect in Heusler alloys, zinc-blende half metals
and diluted magnetic semiconductors, using first-principles calculations. We
find that the ratio of spin-down to spin-up DOS at the Fermi level can range
from below 1% (e.g. 0.5% for NiMnSb) over several percents (4.2% for (Ga,Mn)As)
to 13% for MnBi.",0308146v1
2003-09-11,An efficient control of Curie temperature $T_C$ in Ni-Mn-Ga alloys,"We have studied the influence of alloying with a fourth element on the
temperature of ferromagnetic ordering $T_C$ in Ni-Mn-Ga Heusler alloys. It is
found that $T_C$ increases or decreases, depending on the substitution. The
increase of $T_C$ is observed when Ni is substituted by either Fe or Co. On the
contrary, the substitution of Mn for V or Ga for In strongly reduces $T_C$.",0309271v1
2004-07-07,"A critical discussion of calculated modulated structures, Fermi surface nesting and phonon softening in magnetic shape memory alloys Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge)","A series of first principles calculations have been carried out in order to
discuss electronic structure, phonon dynamics, structural instabilities and the
nature of martensitic transformations of the Heusler alloys Ni$_2$Mn(Ga, Ge,
Al) and Co$_2$Mn(Ga, Ge). The calculations show that besides electronic
pecularities like Fermi--surface nesting, hybridizing optical and acoustic
phonon modes are important for the stabilization of the modulated martensitic
structures.",0407157v1
2005-09-23,Semiclassical Theory of Chaotic Conductors,"We calculate the Landauer conductance through chaotic ballistic devices in
the semiclassical limit, to all orders in the inverse number of scattering
channels without and with a magnetic field. Families of pairs of
entrance-to-exit trajectories contribute, similarly to the pairs of periodic
orbits making up the small-time expansion of the spectral form factor of
chaotic dynamics. As a clue to the exact result we find that close
self-encounters slightly hinder the escape of trajectories into leads.",0509598v1
2005-11-11,Semiclassical Prediction for Shot Noise in Chaotic Cavities,"We show that in clean chaotic cavities the power of shot noise takes a
universal form. Our predictions go beyond previous results from random-matrix
theory, in covering the experimentally relevant case of few channels. Following
a semiclassical approach we evaluate the contributions of quadruplets of
classical trajectories to shot noise. Our approach can be extended to a variety
of transport phenomena as illustrated for the crossover between symmetry
classes in the presence of a weak magnetic field.",0511292v1
2006-03-10,Model Hamiltonian parameters for half-metallic ferromagnets NiMnSb and CrO2,"Using the recently developed Nth-order muffin-tin-orbital (NMTO) based
downfolding technique we revisit the electronic properties of half-metallic
ferromagnets, the semi-Heusler NiMnSb and rutile CrO2. The NMTO Wannier
orbitals for the Mn-d and Cr-t2g manifolds are constructed and the mechanism of
chemical bonding is discussed. The effective hopping Hamiltonian parameters are
calculated using a NMTO downfolded basis set. We propose model Hamiltonian
parameters with possibly minimal basis sets for both half-metallic
ferromagnetic alloys.",0603305v2
2006-10-20,Semiclassical Approach to Chaotic Quantum Transport,"We describe a semiclassical method to calculate universal transport
properties of chaotic cavities. While the energy-averaged conductance turns out
governed by pairs of entrance-to-exit trajectories, the conductance variance,
shot noise and other related quantities require trajectory quadruplets; simple
diagrammatic rules allow to find the contributions of these pairs and
quadruplets. Both pure symmetry classes and the crossover due to an external
magnetic field are considered.",0610560v1
1997-02-05,"Matters of Gravity, the newsletter of the APS TG on gravitation","Contents:
  News:
  April 1997 Joint APS/AAPT Meeting, by Beverly Berger
  TGG News, by Jim Isenberg
  Report from NSF, by David Berley
  We hear that..., by Jorge Pullin
  Research briefs:
  GR in GPS, by Neil Ashby
  What happens near the innermost stable circular orbit? by Doug Eardley
  Conference reports:
  Journees Relativistes 96, by D. Brill, M. Heusler, G. Lavrelashvili
  TAMA Workshop, by Peter Saulson
  Midwest gravity meeting, by Comer Duncan
  OMNI-1 Workshop by N.S. Magalhaes, W. F. Velloso Jr and O.D. Aguiar
  Chandra Symposium, by Robert Wald
  Penn State Meeting, by Lee Smolin
  Aspen Winter Conference, by Syd Meshkov",9702010v1
1997-07-29,"Rotating solitons and non-rotating, non-static black holes","It is shown that the non-Abelian black hole solutions have stationary
generalizations which are parameterized by their angular momentum and electric
Yang-Mills charge. In particular, there exists a non-static class of stationary
black holes with vanishing angular momentum. It is also argued that the
particle-like Bartnik-McKinnon solutions admit slowly rotating, globally
regular excitations. In agreement with the non-Abelian version of the staticity
theorem, these non-static soliton excitations carry electric charge, although
their non-rotating limit is neutral.",9707057v1
2000-10-19,Self-adjoint wave equations for dynamical perturbations of self-gravitating fields,"It is shown that the dynamical evolution of linear perturbations on a static
space-time is governed by a constrained wave equation for the extrinsic
curvature tensor. The spatial part of the wave operator is manifestly elliptic
and self-adjoint. In contrast to metric formulations, the curvature-based
approach to gravitational perturbation theory generalizes in a natural way to
self-gravitating matter fields. It is also demonstrated how to obtain symmetric
pulsation equations for self-gravitating non-Abelian gauge fields, Higgs fields
and perfect fluids. For vacuum fluctuations on a vacuum space-time, the
Regge-Wheeler and Zerilli equations are rederived.",0010067v1
2006-07-30,Semiclassical Theory for Parametric Correlation of Energy Levels,"Parametric energy-level correlation describes the response of the
energy-level statistics to an external parameter such as the magnetic field.
Using semiclassical periodic-orbit theory for a chaotic system, we evaluate the
parametric energy-level correlation depending on the magnetic field difference.
The small-time expansion of the spectral form factor $K(\tau)$ is shown to be
in agreement with the prediction of parameter dependent random-matrix theory to
all orders in $\tau$.",0607070v1
2006-10-20,Periodic-Orbit Theory of Level Correlations,"We present a semiclassical explanation of the so-called
Bohigas-Giannoni-Schmit conjecture which asserts universality of spectral
fluctuations in chaotic dynamics. We work with a generating function whose
semiclassical limit is determined by quadruplets of sets of periodic orbits.
The asymptotic expansions of both the non-oscillatory and the oscillatory part
of the universal spectral correlator are obtained. Borel summation of the
series reproduces the exact correlator of random-matrix theory.",0610053v1
2007-07-11,Interface effects at a half-metal/ferroelectric junction,"Magnetoelectric effects are investigated ab-initio at the interface between
half-metallic and ferroelectric prototypes: Heusler Co$_2$MnSi and perovskite
BaTiO$_3$. For the Co-termination ferroelectricity develops in BaTiO$_3$ down
to nanometer thicknesses, whereas for the MnSi-termination a paraelectric and a
ferroelectric state energetically compete, calling for a full experimental
control over the junction atomic configuration whenever a ferroelectric barrier
is needed. Switch of the electric polarization largely affects magnetism in
Co$_2$MnSi, with magnetoelectric coupling due to electronic hybridization at
the MnSi termination and to structural effects at the Co-termination.
Half-metallicity is lost at the interface, but recovered already in the
subsurface layer.",0707.1665v1
2007-11-15,Non-quasiparticle states in Co$_2$MnSi evidenced through magnetic tunnel junction spectroscopy measurements,"We investigate the effects of electronic correlations in the full-Heusler
Co$_2$MnSi, by combining a theoretical analysis of the spin-resolved density of
states with tunneling-conductance spectroscopy measurements using Co$_2$MnSi as
electrode. Both experimental and theoretical results confirm the existence of
so-called non-quasiparticle states and their crucial contribution to the
finite-temperature spin polarisation in this material.",0711.2476v2
2007-11-19,Room Temperature Magnetocaloric Effect in Ni-Mn-In,"We have studied the effect of magnetic field on a non-stoichiometric Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ that undergoes a martensitic as well as a
magnetic transition near room temperature. Temperature dependent magnetization
measurements demonstrate the influence of magnetic field on the structural
phase transition temperature. From the study of magnetization as a function of
applied field, we show the occurrence of inverse-magnetocaloric effect
associated with this magneto-structural transition. The magnetic entropy change
attains a value as high as 25 J/kg-K (at 5 T field) at room temperature as the
alloy transforms from the austenitic to martensitic phase with a concomitant
magnetic ordering.",0711.2896v1
2007-11-28,Tailoring magnetic and magnetocaloric properties of martensitic transitions in ferromagnetic Heusler alloys,"Ni$_{50}$Mn$_{34}$In$_{16}$ undergoes a martensitic transformation around 250
K and exhibits a field induced reverse martensitic transformation and
substantial magnetocaloric effects. We substitute small amounts Ga for In,
which are isoelectronic, to carry these technically important properties to
close to room temperature by shifting the martensitic transformation
temperature.",0711.4506v1
2010-01-04,Rare-earth impurities in Co$_2$MnSi: an opportunity to improve Half-Metallicity at finite temperatures,"We analyse the effects of doping Holmium impurities into the full-Heusler
ferromagnetic alloy Co$_2$MnSi. Experimental results, as well as theoretical
calculations within Density Functional Theory in the ""Local Density
Approximation plus Hubbard U"" framework show that the holmium moment is aligned
antiparallely to that of the transition metal atoms. According to the
electronic structure calculations, substituting Ho on Co sites introduces a
finite density of states in the minority spin gap, while substitution on the Mn
sites preserves the half-metallic character.",1001.0480v1
2010-04-28,Triplet supercurrent due to spin-active zones in a Josephson junction,"Motivated by a recent experiment evidencing triplet superconductivity in a
ferromagnetic Josephson junction with a Cu$_2$MnAl-Heusler barrier, we
construct a theoretical model accounting for this observation. The key
ingredients in our model which generate the triplet supercurrent are
\textit{spin-active zones}, characterised by an effective canted interface
magnetic moment. Using a numerical solution of the quasiclassical equations of
superconductivity with spin-active boundary conditions, we find qualitatively
very good agreement with the experimentally observed supercurrent. Further
experimental implications of the spin-active zones are discussed.",1004.5124v2
2012-10-27,"Structural, magnetic, magnetocaloric and magneto-transport properties in Ge doped Ni-Mn-Sb Heusler Alloys","The effect of Ge substitution on the magnetic, magnetocaloric and transport
properties of Ni45Co5Mn38Sb12-xGex (x=0-3) has been investigated. The decrease
in the exchange interaction brought by Ge substitution can be seen from the
reduction in the magnetization of austenite phase and the increase in the
martensitic transition temperature. Large magnetocaloric effect and
magnetoresistance have been observed at room temperature, making it a potential
material system for various applications.",1210.7297v2
2013-09-25,Magnetic and transport properties of Mn2CoAl oriented thin films,"The structure, magnetic and transport properties of thin films of the Heusler
ferrimagnet Mn_{2}CoAl have been investigated for properties related to spin
gapless semiconductors. Oriented films were grown by molecular beam epitaxy on
GaAs substrates and the structure was found to transform from tetragonal to
cubic for increasing annealing temperature. The anomalous Hall resistivity is
found to be proportional to the square of the longitudinal resistivity and
magnetization expected for a topological Berry curvature origin. A delicate
balance of the spin-polarized carrier type when coupled with voltage
gate-tuning could significantly impact advanced electronic devices.",1309.6660v1
2013-12-05,What we can learn about quantum physics from a single qubit,"We present an approach for teaching quantum physics at high school level
based on the simplest quantum system - the single quantum bit (qubit). We show
that many central concepts of quantum mechanics, including the superposition
principle, the stochastic behavior and state change under measurements as well
as the Heisenberg uncertainty principle can be understood using simple
mathematics, and can be illustrated using catchy visualizations. We discuss
abstract features of a qubit in general, and consider possible physical
realizations as well as various applications, e.g. in quantum cryptography.",1312.1463v1
2014-01-08,Tri-Dirac Surface Modes in Topological Superconductors,"We propose a new type of topological surface modes having cubic dispersion in
three-dimensional topological superconductors. Lower order dispersions are
prohibited by the threefold rotational symmetry and time-reversal symmetry.
Cooper pairing in the bulk changes sign under improper rotations, akin
to$^{3}$He-B. The surface manifestations are a divergent surface density of
states at the Fermi level and isospins that rotate three times as they circle
the origin in momentum space. We propose that Heusler alloys with band
inversion are candidate materials to harbor the novel topological
superconductivity.",1401.1823v1
2014-09-24,Direct magnetocaloric effect measurement technique in alternating magnetic fields,"A method for direct measurement of the magnetocaloric effect (MCE) in
alternating magnetic fields is offered. Main advantages of the method compared
to a classical direct one are the high temperature sensitivity (better than
10-3 K); the ability of measuring of MCE in weak magnetic fields (by several
tens oersteds and higher); the ability of measuring of MCE on small-sized
samples (1x1x 0.01 mm3 and larger); the ability of measuring of MCE in
alternating magnetic fields up to 50 Hz of frequency. The results on
measurement of MCE on Gd and Ni-Mn-In Heusler alloy are reported.",1409.6898v1
2016-11-16,Perpendicular magnetic anisotropy in Co$_2$MnGa,"We report perpendicular magnetic anisotropy in the ferromagnetic Heusler
alloy Co$_2$MnGa in a MgO/Co$_2$MnGa/Pd trilayer stack for Co$_2$MnGa
thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin
reorientation transition from perpendicular to in-plane magnetic anisotropy
which we study through the anomalous Hall effect. From the temperature
dependence of the anomalous Hall effect, we observe the expected scaling of
$\rho_{xy}^{AHE}$ with $\rho_{xx}$, suggesting the intrinsic and side-jump
mechanisms are largely responsible for the anomalous Hall effect in this
material.",1611.05110v1
2017-07-26,Interfacial exchange interactions and magnetism of Ni2MnAl/Fe bilayers,"Based on a multi-scale calculations, combining ab-initio methods with spin
dynamics simulations, we perform a detailed study of the magnetic behavior of
Ni2MnAl/Fe bilayers. Our simulations show that such a bilayer exhibits a small
exchange bias effect when the Ni2MnAl Heusler alloy is in a disordered B2
phase. Additionally, we present an effective way to control the magnetic
structure of the Ni2MnAl antiferromagnet, in the pseudo-ordered B2-I as well as
the disordered B2 phases, via a spin-flop coupling to the Fe layer.",1707.08651v1
2020-04-25,Mechanical and thermodynamical properties of $β-Cu-Al-Mn$ alloys along the $Cu_3Al \to Cu_2AlMn$ compositional line,"The elastic properties of $Cu-Al-Mn$ alloys with compositions along the
$Cu_3Al \to Cu_2AlMn$ line and $bcc$-based structures, are studied by means of
first-principles calculations. From the calculated elastic constants, the
Zener's anisotropy, sound velocities and Debye temperature are determined. The
theoretical results compare well with the available experimental data. The
influence of vibrations is introduced through the quasi-harmonic Debye model,
and different properties are studied as functions of temperature and
composition.",2004.12253v1
2016-03-13,Perpendicular magnetic anisotropy in Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si,"We report perpendicular magnetic anisotropy (PMA) in the half-metallic
ferromagnetic Heusler alloy Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS) in a
MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2
nm, with a magnetic anisotropy energy density of $K_U = 1.5\times 10^6$
erg/cm$^3$ for t$_{\tiny \textrm{CFMS}} = 1.5$ nm. Both the MgO and Pd layer
are necessary to induce the PMA. We measure a tunable anomalous Hall effect,
where its sign and magnitude vary with both the CFMS and Pd thickness.",1603.04072v1
2016-12-22,Ab initio Study of Effect of Co Substitution on the Magnetic Properties of Ni and Pt-based Heusler Alloys,"Using density functional theory based calculations, we have carried out
in-depth studies of effect of Co substitution on the magnetic properties of Ni
and Pt-based shape memory alloys. We show the systematic variation of the total
magnetic moment, as a function of Co doping. A detailed analysis of evolution
of Heisenberg exchange coupling parameters as a function of Co doping has been
presented here. The strength of RKKY type of exchange interaction is found to
decay with the increase of Co doping.",1612.07518v1
2019-03-26,Quantum topological transitions and spinons in metallic ferro- and antiferromagnets,"An effective Hamiltonian describing fluctuation effects in the magnetic
phases of the Hubbard model in terms of spinon excitations is derived. A
comparison of spin-rotational Kotliar-Ruckenstein slave boson and Ribeiro-Wen
dopon representations is performed. The quantum transition into the
half-metallic ferromagnetic state with vanishing of spin-down Fermi surface is
treated as the topological Lifshitz transition in the quasimomentum space. The
itinerant-localized magnetism transitions and Mott transition in
antiferromagnetic state are considered in the topological context. Related
metal-insulator transitions in Heusler alloys are discussed.",1903.11003v1
2022-12-15,Griffiths' phase behavior of the Weyl semimetal CrFeVGa,"We report a combined theoretical and experimental study of a new topological
semimetal CrFeVGa with an emphasis on the role of atomic disorder on the
magnetoelectronic properties and its applications.CrFeVGa belongs to the
quaternary Heusler alloy family and crystallizes in the cubic structure.
Synchrotron XRD measurement confirms B2 disorder, which plays a crucial role in
dictating the electronic and magnetic properties of the system.",2212.07576v1
2023-04-27,Effective Tight-Binding Model of Compensated Ferrimagnetic Weyl Semimetal with Spontaneous Orbital Magnetization,"The effective tight-binding model with compensated ferrimagnetic
inverse-Heusler lattice Ti$_{2}$MnAl, candidate material of magnetic Weyl
semimetal, is proposed. The energy spectrum near the Fermi level, the
configurations of the Weyl points, and the anomalous Hall conductivity are
calculated. We found that the orbital magnetization is finite, while the total
spin magnetization vanishes, at the energy of the Weyl points. The magnetic
moments at each site are correlated with the orbital magnetization, and can be
controlled by the external magnetic field.",2304.14009v1
2023-09-29,Micromagnetics of ferromagnetic/antiferromagnetic nanocomposite materials. Part I: Towards the mesoscopic approach,"In the first of two articles, we present here a novel mesoscopic
micromagnetic approach for simulating materials composed of ferromagnetic and
antiferromagnetic phases. Starting with the atomistic modeling of quasi
one-dimensional systems, we explicitly show how the material parameters for the
mesoscopic model of an antiferromagnet can be derived. The comparison between
magnetization profiles obtained in atomistic and mesoscopic calculations (using
a Heusler alloy as an example) proves the validity of our method. This approach
opens up the possibility to recover the details of the magnetization
distribution in ferromagnetic/antiferromagnetic materials with the resolution
of a few nanometers covering length scales up to several hundreds of
nanometers.",2309.17131v1
2012-05-17,Effect of electron doping on the magnetic correlations in the bilayered brownmillerite compound Ca_{2.5-x}La_{x}Sr_{0.5}GaMn_{2}O_{8}: a neutron diffraction study,"The effect of electron doping on the magnetic properties of the
Brownmillerite-type bilayered compounds has been investigated by neutron powder
diffraction in La substituted Ca2.5-xLaxSr0.5GaMn2O8 compounds (x = 0.05 and
0.1), in comparison with the undoped compound (x = 0). In all compounds, a
long-range three dimensional collinear antiferromagnetic (AFM) structure is
found below the N\'eel temperature TN of respective compound, whereas, well
above TN, three dimensional short-range magnetic ordering is observed. In the
intermediate temperature range just above TN, a strong effect of electron
doping (La substitution) on the magnetic correlations has been observed. Here,
a short-range AFM correlation with possible dimensionality of three has been
found for substituted compounds (x = 0.05 and 0.1) as compared to the reported
two dimensional long-range AFM ordering in the parent compound. With increasing
the electron doping, a decrease in TN is also observed. The short-range
magnetic correlations set in over a large temperature range above TN. A
magnetic phase diagram in the x-T plane is proposed from these results.",1205.3872v1
2014-11-13,"Preparation, structure evolution, and magnetocaloric effects of MnFe(PGe) compounds","As one of magnetic refrigerants with giant magnetocaloric effect (GMCE),
MnFePGe-based compounds had drawn tremendous attention due to their many
advantages for practical applications. In this paper, correlations among
preparation conditions, magnetic and crystal structures, and magnetocaloric
effects (MCE) of the MnFePGe-based compounds are reviewed. Structure evolution
and phase transformation in the compounds as a function of temperature,
pressure, and magnetic field were reported. Influences of preparation
conditions to the chemical composition and microstructure homogeneity of the
compounds, which play key role to the MCE and thermal hysteresis of the
compounds, were introduced. Based upon these experimental results, a new method
to evaluate MCE of the compounds via DSC measurements was proposed. Moreover,
the origin of virgin effect of the MnFePGe-based compounds was discussed.",1411.3460v1
2016-06-03,Automatic Separation of Compound Figures in Scientific Articles,"Content-based analysis and retrieval of digital images found in scientific
articles is often hindered by images consisting of multiple subfigures
(compound figures). We address this problem by proposing a method to
automatically classify and separate compound figures, which consists of two
main steps: (i) a supervised compound figure classifier (CFC) discriminates
between compound and non-compound figures using task-specific image features;
and (ii) an image processing algorithm is applied to predicted compound images
to perform compound figure separation (CFS). Our CFC approach is shown to
achieve state-of-the-art classification performance on a published dataset. Our
CFS algorithm shows superior separation accuracy on two different datasets
compared to other known automatic approaches. Finally, we propose a method to
evaluate the effectiveness of the CFC-CFS process chain and use it to optimize
the misclassification loss of CFC for maximal effectiveness in the process
chain.",1606.01021v2
2018-05-23,Uncovering anisotropic magnetic phases via fast dimensionality analysis,"A quantitative geometric predictor for the dimensionality of magnetic
interactions is presented. This predictor is based on networks of superexchange
interactions and can be quickly calculated for crystalline compounds of
arbitrary chemistry, occupancy, or symmetry. The resulting data is useful for
classifying structural families of magnetic compounds. Starting with 42,520
compounds, we have classified and quantified compounds with $3d$ transition
metal cations. The predictor reveals trends in magnetic interactions that are
often not apparent from the space group of the compounds, such as triclinic or
monoclinic compounds that are strongly 2D. We present specific cases where the
predictor identifies compounds that should exhibit competition between 1D and
2D interactions, and how the predictor can be used to identify
sparsely-populated regions of chemical space with as-yet-unexplored topologies
of specific $3d$ magnetic cations. The predictor can be accessed for the full
list of compounds using a searchable web form, and further information on the
connectivity, symmetry, and valence of cation-anion and cation-cation
coordination can be freely exported.",1805.09433v1
2018-06-04,Compound Bi-free Poisson Distributions,"In this paper, we study compound bi-free Poisson distributions for {\sl
two-faced families of random variables}. We prove a Poisson limit theorem for
compound bi-free Poisson distributions. Furthermore, a bi-free infinitely
divisible distribution for a two-faced family of self-adjoint random variables
can be realized as the limit of a sequence of compound bi-free Poisson
distributions of two-faced families of self-adjoint random variables. If a
compound bi-free Poisson distribution is determined by a positive number and
the distribution of a two faced family of finitely many random variables, which
has an almost sure random matrix model, and the left random variables commute
with the right random variables in the two-faced family, then we can construct
a random bi-matrix model for the compound bi-free Poisson distribution. If a
compound bi-free Poisson distribution is determined by a positive number and
the distribution of a commutative pair of random variables, we can construct an
asymptotic bi-matrix model with entries of creation and annihilation operators
for the compound bi-free Poisson distribution.",1806.01007v2
2020-05-24,Protein-ligand interaction study to identify potential dietary compounds binding at the active site of therapeutic target proteins of SARS-CoV-2,"Objective: Total 186 biologically important phenylpropanoids and polyketides
compounds from different Indian medicinal plants and dietary sources were
screened to filter potential compounds that bind at the active site of the
therapeutic target proteins of SARS-CoV-2. Method: The molecular docking
studies were carried out by using the Autodock Vina. The in silico ADMET and
drug-likeness properties of the compounds were predicted from SwissADME server.
Result: The molecular docking study of the 186 compounds with the therapeutic
target proteins (Mpro, PLpro, RdRp, SGp and ACE2) of SARS-CoV-2 resulted 40
compounds that bind at the active site with dock score above -8.0 kcal/mol.
Conclusion: Based on the in silico ADMET study and drug-likeness prediction of
40 compounds, we proposed petunidin, baicalein, cyanidin,
7-hydroxy-3',4'-methylenedioxyflavan, quercetin and ellagic acid among the 186
biologically important phenylpropanoids and polyketides as potential lead
compounds, which can further be investigated pharmacologically and clinically
to formulate therapeutic approaches for the COVID-19.",2005.11767v1
2020-03-21,A Joint Approach to Compound Splitting and Idiomatic Compound Detection,"Applications such as machine translation, speech recognition, and information
retrieval require efficient handling of noun compounds as they are one of the
possible sources for out-of-vocabulary (OOV) words. In-depth processing of noun
compounds requires not only splitting them into smaller components (or even
roots) but also the identification of instances that should remain unsplitted
as they are of idiomatic nature. We develop a two-fold deep learning-based
approach of noun compound splitting and idiomatic compound detection for the
German language that we train using a newly collected corpus of annotated
German compounds. Our neural noun compound splitter operates on a sub-word
level and outperforms the current state of the art by about 5%.",2003.09606v1
2021-02-02,Superconductivity in HEA-type compounds,"Since the discovery of superconductivity in a high-entropy alloy (HEA)
Ti-Zr-Nb-Hf-Ta in 2014, the community of superconductor science has explored
new HEA superconductors to find the merit of the HEA states on superconducting
properties. Since 2018, we have developed HEA-type compounds as superconductors
or thermoelectric materials. As well known, compounds like intermetallic
compounds or layered compounds are composed of multi crystallographic sites. In
a HEA-type compounds, one or more sites are alloyed and total mixing entropy
satisfies with the criterion of HEA. Herein, we summarize the synthesis
methods, the crystal structural variation and superconducting properties of the
HEA-type compounds, which include NaCl-type metal tellurides, CuAl2-type
transition metal zirconides, high-Tc cuprates, and BiS2-based layered
superconductors. The effects of the introduction of a HEA site in various kinds
of complicated compounds are discussed from the structural-dimensionality
viewpoint.",2102.01321v1
2022-10-17,A Transformer-based Generative Model for De Novo Molecular Design,"In the scope of drug discovery, the molecular design aims to identify novel
compounds from the chemical space where the potential drug-like molecules are
estimated to be in the order of 10^60 - 10^100. Since this search task is
computationally intractable due to the unbounded search space, deep learning
draws a lot of attention as a new way of generating unseen molecules. As we
seek compounds with specific target proteins, we propose a Transformer-based
deep model for de novo target-specific molecular design. The proposed method is
capable of generating both drug-like compounds (without specified targets) and
target-specific compounds. The latter are generated by enforcing different keys
and values of the multi-head attention for each target. In this way, we allow
the generation of SMILES strings to be conditional on the specified target.
Experimental results demonstrate that our method is capable of generating both
valid drug-like compounds and target-specific compounds. Moreover, the sampled
compounds from conditional model largely occupy the real target-specific
molecules' chemical space and also cover a significant fraction of novel
compounds.",2210.08749v2
2023-10-09,Prediction of Gaussian Volterra Processes with Compound Poisson Jumps,"We consider a Gaussian Volterra process with compound Poisson jumps and
derive its prediction law.",2310.05675v1
2023-11-27,Target-Free Compound Activity Prediction via Few-Shot Learning,"Predicting the activities of compounds against protein-based or phenotypic
assays using only a few known compounds and their activities is a common task
in target-free drug discovery. Existing few-shot learning approaches are
limited to predicting binary labels (active/inactive). However, in real-world
drug discovery, degrees of compound activity are highly relevant. We study
Few-Shot Compound Activity Prediction (FS-CAP) and design a novel neural
architecture to meta-learn continuous compound activities across large
bioactivity datasets. Our model aggregates encodings generated from the known
compounds and their activities to capture assay information. We also introduce
a separate encoder for the unknown compound. We show that FS-CAP surpasses
traditional similarity-based techniques as well as other state of the art
few-shot learning methods on a variety of target-free drug discovery settings
and datasets.",2311.16328v1
2012-09-29,"Hard X-ray photoelectron spectroscopy on buried, off-stoichiometric CoxMnyGez (x : z = 2 : 0.38) Heusler thin films","Fully epitaxial magnetic tunnel junctions (MTJs) with off-stoichiometric
Co2-based Heusler alloy shows a intense dependency of the tunnel
magnetoresistance (TMR) on the Mn composition, demonstrating giant TMR ratios
of up to 1995% at 4.2 K for 1. This work reports on the electronic structure of
non-stoichiometric CoxMnyGez thin films with a fixed Co/Ge ratio of x : z = 2 :
0.38. The electronic structure was investigated by high energy, hard X-ray
photoelectron spectroscopy combined with first-principles calculations. The
high-resolution measurements of the valence band of the non-stoichiometric
CoxMnyGez films close to the Fermi energy indicate a shift of the spectral
weight compared to bulk Co2MnGe. This is in agreement with the changes in the
density of states predicted by the calculations. Furthermore it is shown that
the co-sputtering of Co2MnGe together with additional Mn is an appropriate
technique to adjust the stoichiometry of the CoxMnyGez film composition. The
resulting changes of the electronic structure within the valence band will
allow to tune the magnetoresistive characteristics of CoxMnyGez based tunnel
junctions as verified by the calculations and photoemission experiments.",1210.0146v1
2012-10-22,"Structure, magnetism and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys","The structure, magnetism, magnetic compensation behavior, exchange
interaction and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25
(x=0-25) alloys have been systematically investigated by both experiments and
first-principles calculations. We found that all the samples exhibited body
centered cubic structures with a high degree of atomic ordering. With
increasing Ga content, the composition dependence of lattice parameters shows a
kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be
attributed to the enhanced covalent effect between the Ga and the transition
metals. Furthermore, a complicated magnetic competition has been revealed in
Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically
decrease and results in a magnetic moment compensation behavior. In
Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional
ferrimagnetic configuration was established in the native ferromagnetic matrix,
which causes the molecular moment monotonously decreases and the exchange
interaction enhances gradually. The electronic structure calculations indicate
that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the
itinerant and localized magnetism. Our study will be helpful to understand the
nature of magnetic ordering as well as to tune magnetic compensation and
electronic properties of Heusler alloys.",1210.5810v1
2013-05-15,"Structural ordering driven anisotropic magnetoresistance, anomalous Hall resistance and its topological overtones in full-Heusler Co2MnSi thin films","We report the evolution of crystallographic structure, magnetic ordering and
electronic transport in thin films of full-Heusler alloy Co$_2$MnSi deposited
on (001) MgO with annealing temperatures ($T_A$). By increasing the $T_A$ from
300$^\circ$C to 600$^\circ$C, the film goes from a disordered nanocrystalline
phase to $B2$ ordered and finally to the $L2_1$ ordered alloy. The saturation
magnetic moment improves with structural ordering and approaches the
Slater-Pauling value of $\approx 5.0 \mu_B$ per formula unit for $T_A$ =
600$^\circ$C. At this stage the films are soft magnets with coercive and
saturation fields as low as $\approx$ 7 mT and 350 mT, respectively. Remarkable
effects of improved structural order are also seen in longitudinal resistivity
($\rho_{xx}$) and residual resistivity ratio. A model based upon electronic
transparency of grain boundaries illucidates the transition from a state of
negative $d\rho/dT$ to positive $d\rho/dT$ with improved structural order. The
Hall resistivity ($\rho_{xy}$) derives contribution from the normal scattering
of charge carriers in external magnetic field, the anomalous effect originating
from built-in magnetization and a small but distinct topological Hall effect in
the disordered phase. The carrier concentration ($n$) and mobility ($\mu$) have
been extracted from the high field $\rho_{xy}$ data. The highly ordered films
are characterized by $n$ and $\mu$ of 1.19$\times$ 10$^{29}$ m$^{-3}$ and 0.4
cm$^2V^{-1}s^{-1}$ at room temperature. The dependence of $\rho_{xy}$ on
$\rho_{xx}$ indicates the dominance of skew scattering in our films, which
shows a monotonic drop on raising the $T_A$. The topological Hall effect is
analyzed for the films annealed at 300$^\circ$C. ......",1305.3453v1
2014-08-02,Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates,"We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based
magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate.
Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a
flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance
(TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on
a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching
was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a
switching layer. Using a thermal activation model, the intrinsic critical
current density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lower
than 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett.
100, 182403 (2012)]. We found that the Gilbert damping constant evaluated using
ferromagnetic resonance measurements for the polycrystalline CFA film was
~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0
for the polycrystalline MTJ was mainly attributed to the low damping of the CFA
layer compared with the value in the epitaxial one (~0.04).",1408.0341v1
2014-11-21,A new spin gapless semiconductor: quaternary Heusler CoFeCrGa alloy,"Despite a plethora of materials suggested for spintronic applications, a new
class of materials has emerged, namely spin gapless semiconductors (SGS), that
offers potentially more advantageous properties than existing ones. These
magnetic semiconductors exhibit a finite band gap for one spin channel and a
closed gap for the other. Here, supported by the first-principles,
electronic-structure calculations, we report the first experimental evidence of
SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (L21)
structure but exhibiting chemical disorder (DO3 structure). CoFeCrGa is found
to transform from SGS to half-metallic phase under pressure, which is
attributed to unique electronic-structure features. The saturation
magnetization (MS) obtained at 8 K agrees with the Slater-Pauling rule and the
Curie temperature (TC) is found to exceed 400 K. Carrier concentration (up to
250 K) and electrical conductivity are observed to be nearly temperature
independent, prerequisites for SGS. The anomalous Hall coefficient is estimated
to be 185 S/cm at 5 K. Considering the SGS properties and high TC, this
material appears to be promising for spintronic applications.",1411.5772v2
2015-01-22,High spin polarization and large spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy,"In this paper, we investigate CoFeCrAl alloy by means of various experimental
techniques and ab-initio calculations to look for half-metallic nature. The
alloy is found to exist in the cubic Heusler structure, with presence of B2
ordering. Saturation magnetization (MS) value of about 2 Bohr magneton/f.u. is
observed at 8 K under ambient pressure, which is in good agreement with the
Slater-Pauling rule. MS values are found to be independent of pressure, which
is a prerequisite for half-metals. The ab-initio electronic structure
calculations predict half-metallic nature for the alloy with a spin slitting
energy of 0.31 eV. Importantly, this system shows a high current spin
polarization value of 0.67 [with error of 0.02], as deduced from the point
contact Andreev reflection (PCAR) measurements. Linear dependence of electrical
resistivity with temperature indicates the possibility of reasonably high spin
polarization at elevated temperatures (~150 K) as well. All these suggest that
CoFeCrAl is a promising material for the spintronic devices.",1501.05599v1
2015-02-12,High Electron Mobility and Large Magnetoresistance in the Half-Heusler Semimetal LuPtBi,"Materials with high carrier mobility showing large magnetoresistance (MR)
have recently received much attention because of potential applications in
future high-performance magneto-electric devices. Here, we report on the
discovery of an electron-hole-compensated half-Heusler semimetal LuPtBi that
exhibits an extremely high electron mobility of up to 79000 cm2/Vs with a
non-saturating positive MR as large as 3200% at 2 K. Remarkably, the mobility
at 300 K is found to exceed 10500 cm2/Vs, which is among the highest values
reported in three-dimensional bulk materials thus far. The clean Shubnikov-de
Haas quantum oscillation observed at low temperatures and the first-principles
calculations together indicate that the high electron mobility is due to a
rather small effective carrier mass caused by the distinctive band structure of
the crystal. Our finding provide a new approach for finding large,
high-mobility MR materials by designing an appropriate Fermi surface topology
starting from simple electron-hole-compensated semimetals.",1502.03523v5
2016-02-23,The chiral anomaly and thermopower of Weyl fermions in the half-Heusler GdPtBi,"The Dirac and Weyl semimetals are unusual materials in which the nodes of the
bulk states are protected against gap formation by crystalline symmetry. The
chiral anomaly~\cite{Adler,Bell}, predicted to occur in both systems, was
recently observed as a negative longitudinal magnetoresistance (LMR) in
Na$_3$Bi and in TaAs. An important issue is whether Weyl physics appears in a
broader class of materials. We report evidence for the chiral anomaly in the
half-Heusler GdPtBi. In zero field, GdPtBi is a zero-gap semiconductor with
quadratic bands. In a magnetic field, the Zeeman energy leads to Weyl nodes. We
have observed a large negative LMR with the field-steering properties specific
to the chiral anomaly. The chiral anomaly also induces strong suppression of
the thermopower. We report a detailed study of the thermoelectric response
function $\alpha_{xx}$ of Weyl fermions. The scheme of creating Weyl nodes from
quadratic bands suggests that the chiral anomaly may be observable in a broad
class of semimetals.",1602.07219v2
2016-11-24,Thermophysical and magnetic properties of p- and n-type Ti-Ni-Sn based half-Heusler alloys,"A total of 5 different half-Heusler alloys, two p-type and two n-type with
the fifth a charge compensated alloy have been designed and synthesized. The
thermophysical properties of these alloys have been investigated in the range
10 K to 1000 K while the magnetic behavior has been studied up to 300 K. The
electrical resistivity of all the alloys varies within the range 0.06 to 5
m{\Omega} cm indicating that they are in the degenerate semiconductor limits.
The temperature dependence of p-type alloys exhibits a transition from metallic
to semiconducting behavior, typical of topological insulators. The transition
is found to occur in the range 300 K to 500 K. The n-type and compensated
alloys exhibit a weak metallic behavior in the complete temperature range. The
Seebeck coefficient in the p-type alloys increases with temperature reaching a
maximum value of 50 microV K-1 while that of the n-type alloys increases
continuously reaching a value of 45 microV K-1 at ~ 800 K. The corresponding
power factor of the n-type alloy reaches 900 microW m-1 K-2 at ~ 900 K compared
to a maximum of ~ 250 microW m-1 K-2 at 700 K for the p-type alloy.
Magnetically the p-type and n-type alloys are found to be paramagnetic while
the compensated alloy exhibits a ferromagnetic behavior.",1611.08148v1
2017-01-09,Spin-Wave versus Joule Heating in Spin-Hall-Effect/Spin-Transfer-Torque Driven Cr/Heusler/Pt Waveguides,"We present a time-resolved study of the DC-current driven magnetization
dynamics in a microstructured Cr/Heusler/Pt waveguide by means of Brillouin
light scattering. A reduction of the effective spin-wave damping via the
spin-transfer-torque effect leads to a strong increase in the magnon density.
This is accompanied by a decrease of the spin-wave frequencies. By evaluating
the time scales of these effects, the origin of this frequency shift can be
identified. However, recently, we found that the experimental setup partially
influences the decay of the spin-wave intensity after the current pulse is
switched off. Thus, further investigations on the presented effect are needed
to allow for a more detailed analysis. For this reason, we need to withdraw the
manuscript at this point and might publish an updated version later.",1701.02094v2
2017-11-29,Methods to induce perpendicular magnetic anisotropy in full-Heusler Co2FeSi thin layers in a magnetic tunnel junction structure,"In this study, to obtain perpendicular magnetic tunnel junctions (p-MTJs)
using half-metallic ferromagnets (HMFs), several methods were developed to
induce perpendicular magnetic anisotropy (PMA) in full-Heusler Co2FeSi (CFS)
alloy thin layers in an MTJ multilayer composed of a layered CFS/MgO/CFS
structure. Oxygen exposure at 2.0 Pa for 10 min after deposition of the bottom
CFS layer was effective for obtaining PMA in the CFS layer. One of the reasons
for the PMA is the formation of nearly ideal CFS/MgO interfaces due to oxygen
exposure before the deposition of the MgO layer. The annealing process was
effective for obtaining PMA in the top CFS layer capped with a Pd layer. PMA
was clearly observed in the top CFS layer of a Cr(40 nm)/Pd(50 nm)/bottom
CFS(0.6 nm)/MgO(2.0 nm)/top CFS(0.6 nm)/Pd(10 nm) multilayer, where the top CFS
and Pd thin films were deposited at RT and subsequently annealed at 300{\deg}C.
In addition to the continuous layer growth of the films, the crystalline
orientation alignment at the top CFS/Pd interface probably attributes to the
origin of PMA at the top CFS layer.",1711.10722v3
2017-12-05,Peculiarities of the electronic transport in half-metallic Co-based Heusler alloys,"Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler
alloys of Co$_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn,
Sb) were studied in the temperature range 4.2--900 K and in magnetic fields of
up to 100 kOe. It was found that varying Y in affects strongly the electric
resistivity and its temperature dependence $\rho(T)$, while this effect is not
observed upon changing Z. When Y is varied, extrema (maximum or minimum) are
observed in $\rho(T)$ near the Curie temperature $T_C$. At $T < T_C$, the
$\rho(T)$ behavior can be ascribed to a change in electronic energy spectrum
near the Fermi level. The coefficients of the normal and anomalous Hall effect
were determined. It was shown that the latter coefficient, $R_S$, is related to
the residual resistivity $\rho_0$ by a power law $R_S \sim \rho_0^k/M_S$ with
$M_S$ the spontaneous magnetization. The exponent $k$ was found to be 1.8 for
Co$_2$FeZ alloys, which is typical for asymmetric scattering mechanisms, and
2.9 for Co$_2$YAl alloys, which indicates an additional contribution to the
anomalous Hall effect. The temperature dependence of resistivity at low
temperatures is analyzed and discussed in the framework of the two-magnon
scattering theory.",1712.01584v1
2018-05-18,Reentrant cluster glass and stability of ferromagnetism in Ga2MnCo Heusler alloy,"We present here a detailed investigation into the magnetic ordering of full
Heusler alloy Ga$_2$MnCo using dc, ac magnetization measurements, neutron
diffraction and neutron depolarization experiments. Crystal structure at room
temperature was first confirmed to be L2$_1$ using the highly intense
synchrotron X-ray diffraction (XRD) technique. Temperature dependent
magnetization reveals that Ga$_2$MnCo enters a ferromagnetic (FM) state at $T_C
= $154 K, characterized by a sharp increase in magnetization and a plateau-like
region hereafter. As the temperature is decreased further, a sharp drop in
magnetization is observed at $T_f$ = 50 K, hinting towards an antiferromagnetic
(AFM) phase change. Neutron diffraction (ND) recorded over the range of
temperature from 6 to 300 K, provides combined information regarding crystal as
well as magnetic structure. Accordingly, an increase in the intensity of the ND
pattern is seen at 150 K, signaling onset of long range FM order. However,
there is no sign of appearance of superlattice reflections corresponding to the
AFM phase, in the patterns recorded below 50 K. An unusual discontinuity in the
unit cell volume is seen around $T_f$ indicating a coupling of this second
transition with the contraction of the lattice. Attempts to unravel this
interesting magnetic behaviour using ac susceptibility measurements lead to the
existence of glassy magnetism below $T_f$. Systematic analysis of the
susceptibility results along with neutron depolarization measurement,
identifies the low temperature phase as a reentrant cluster glass.",1805.07320v1
2019-11-15,Fermi level tuning and atomic ordering induced giant anomalous Nernst effect in Co2MnAl1-xSix Heusler alloy,"Co2MnAl has been predicted to have Weyl points near Fermi level which is
expected to give rise to exotic transverse transport properties such as large
anomalous Hall(AHE) and Nernst effects(ANE) due to large Berry curvature. In
this study, the effect of Fermi level position and atomic ordering on AHE and
ANE in Co2MnAl1-xSix were studied systematically. The Co2MnAl film keeps
B2-disordred structure regardless of annealing temperature, which results in
much smaller anomalous Hall conductivity sigma_xy and transverse Peltier
coefficient sigma_xy than those calculated for L21-ordered Co2MnAl. Our newly
performed calculation of sigma_xy with taking B2 disordering into account well
reproduces experimental result, thus it was concluded that Berry curvature
originating from Weyl points is largely reduced by B2 disordering. It was also
revealed Al substitution with Si shifts the position of Fermi level and
improves the L21-atomic ordering largely, leading to strong enhancement of
sigma_xy, which also agreed with our theoretical calculation. The highest
thermopower of ANE of 6.1uV, which is comparable to the recent reports for
Co2MnGa, was observed for Co2MnAl0.63Si0.37 because of dominant contribution of
sigma_xy. This study clearly shows the importance of both Fermi level tuning
and high atomic ordering for obtaining the effect of topological feature in
Co-based Heusler alloys on transverse transport properties.",1911.07741v1
2021-07-01,Dopant-segregation to grain boundaries controls electrical conductivity of n-type NbCo(Pt)Sn half-Heusler alloy mediating thermoelectric performance,"Science-driven design of future thermoelectric materials requires a deep
understanding of the fundamental relationships between microstructure and
transport properties. Grain boundaries in polycrystalline materials influence
the thermoelectric performance through the scattering of phonons or the
trapping of electrons due to space-charge effects. Yet, the current lack of
careful investigations on grain boundary-associated features hinders further
optimization of properties. Here, we study n-type NbCo1-xPtxSn half-Heusler
alloys, which were synthesized by ball milling and spark plasma sintering
(SPS). Post-SPS annealing was performed on one sample, leading to improved
low-temperature electrical conductivity. The microstructure of both samples was
examined by electron microscopy and atom probe tomography. The grain size
increases from ~230 nm to ~2.38 {\mu}m upon annealing. Pt is found within
grains and at grain boundaries, where it locally reduces the resistivity, as
assessed by in situ four-point-probe electrical conductivity measurement. Our
work showcases the correlation between microstructure and electrical
conductivity, providing opportunities for future microstructural optimization
by tuning the chemical composition at grain boundaries.",2107.00326v1
2021-07-24,"Unravelling the phonon scattering mechanism in Half-Heusler alloys ZrCo1-xIrxSb (x = 0, 0.1, and 0.25)","Insight about the scattering mechanisms responsible for reduction in the
lattice thermal conductivity (\k{appa}L) in Half-Heusler alloys (HHA) is
imperative. In this context, we have thoroughly investigated the temperature
response of thermal conductivity of ZrCo1-xIrxSb (x = 0, 0.1 and 0.25). For
ZrCoSb, \k{appa}L is found to be ~15.13 W/m-K at 300 K, which is drastically
reduced to ~4.37 W/m-K in ZrCo0.9Ir0.1Sb. This observed reduction is ascribed
to softening of acoustic phonon modes and point defect scattering, on
substitution of heavier mass. However, no further reduction in \k{appa}L is
observed in ZrCo0.75Ir0.25Sb, because of identical scattering parameter. This
has been elucidated based on the Klemens Callaway model. Also, in the parent
alloy, phonon-phonon scattering mechanism plays a significant role in heat
conduction process, whereas in Ir substituted alloys, point defect scattering
(below 500 K) and phonon-phonon scattering (above 750 K) are the dominant
scattering mechanisms. The minimum \k{appa}L is found to be ~1.73 W/m-K (at 950
K) in ZrCo0.9Ir0.1Sb, which is the lowest reported value till now, for n-type
Zr based HHA. Our studies indicate that partial substitution of heavier mass
element Ir at Co-site effectively reduces the \k{appa}L of n-type ZrCoSb,
without modifying the nature of charge carriers.",2107.11567v1
2018-10-17,"Investigation of the structural, electronic, transport and magnetic properties of Co$_2$FeGa Heusler alloy nanoparticles","We report the structural, transport, electronic, and magnetic properties of
Co$_2$FeGa Heusler alloy nanoparticles. The Rietveld refinements of x-ray
diffraction (XRD) data with the space group Fm$\bar {3}$m clearly demonstrates
that the nanoparticles are of single phase. The particle size (D) decreases
with increasing the SiO$_2$ concentration. The Bragg peak positions and the
inter-planer spacing extracted from high-resolution transmission electron
microscopy image and selected area electron diffraction are in well agreement
with data obtained from XRD. The coercivity initially increases from 127~Oe to
208~Oe between D = 8.5~nm and 12.5~nm, following the D$^{-3/2}$ dependence and
then decreases with further increasing D up to 21.5~nm with a D$^{-1}$
dependence, indicating the transition from single domain to multidomain regime.
The effective magnetic anisotropic constant behaves similarly as coercivity,
which confirms this transition. A complex scattering mechanisms have been
fitted to explain the electronic transport properties of these nanoparticles.
In addition we have studied core-level and valence band spectra using
photoemission spectroscopy, which confirm the hybridization between $d$ states
of Co/Fe. Further nanoparticle samples synthesized by co-precipitation method
show higher saturation magnetization. The presence of Raman active modes can be
associated with the high chemical ordering, which motivates for detailed
temperature dependent structural investigation using synchrotron radiation and
neutron sources.",1810.07660v1
2019-04-24,Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe2-xMnxCrAl,"We present a detailed study of structural, magnetic and thermodynamic
properties of a series of Heusler alloys Fe2-xMnxCrAl (x=0, 0.25, 0.5, 0.75 and
1). Structural investigation of this series is carried out using high
resolution synchrotron X-ray diffraction. Results suggest that with increasing
Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC
magnetization results show a decrement in paramagnetic (PM) to ferromagnetic
(FM) phase transition temperature (TC) with increasing Mn concentration. From
the systematic analysis of magnetic memory effect, heat capacity, time
dependent magnetization, and DC field dependent AC susceptibility studies it is
observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately
at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double
CG-like transitions near Tf1~22 K, Tf2~4.2 K and Tf1~30.4 K, Tf2~9.5 K
respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is
noted at Tf2~11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long
ranged magnetic ordering and this alloy undergoes three CG-like transitions at
~ 22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed
analysis of temperature response of inverse DC susceptibility clearly reveals
the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this
phase persists with Mn concentration with a decrement in T*.",1904.10648v2
2019-07-13,Magnetocaloric properties and critical behavior of Co$_2$Cr$_{1-x}$Mn$_x$Al Heusler alloys,"We study the magnetocaloric effect and critical behavior of
Co$_2$Cr$_{1-x}$Mn$_x$Al ($x=$ 0.25, 0.5, 0.75) Heusler alloys across the
ferromagnetic (FM) transition (T$_{\rm C}$). The Rietveld refinement of x-ray
diffraction patterns exhibit single phase cubic structure for all the samples.
The temperature dependent magnetic susceptibility $\chi$(T) data show a
systematic enhancement in the Curie temperature and effective magnetic moment
with Mn concentration, which is consistent with the Slater-Pauling behavior.
The M(H) isotherms also exhibit the FM ordering and the analysis of $\chi$(T)
data indicates the nature of the phase transition to be a second order, which
is further supported by scaling of the entropy curves and Arrott plot.
Interestingly, the Mn substitution causes an increase in the magnetic entropy
change and hence large relative cooling power for multi-stage magnetic
refrigerator applications. In order to understand the nature of the magnetic
phase transition we examine the critical exponents $\beta$, $\gamma$, $\delta$
for the $x=$ 0.75 sample by the modified Arrott plot and the critical isotherm
analysis, which is further confirmed by Kouvel-Fisher method and Widom scaling
relation, respectively. The estimated values of $\beta=$ 0.507, $\gamma=$
1.056, $\delta=$ 3.084 are found to be close to the mean field theoretical
values. The renormalized isotherms (m vs h) corresponding to these exponent
values collapse into two branches, above and below T$_{\rm C}$ that validates
our analysis. Our results suggest for the existence of long-range FM
interactions, which decays slower than power law as $J(r)\sim r^{-4.5}$ for a 3
dimensional mean field theory.",1907.06114v1
2019-10-15,Impact of the scattering physics on the power factor of complex thermoelectric materials,"We assess the impact of the scattering physics assumptions on the
thermoelectric properties of five Co-based p-type half-Heusler alloys by
considering full energy-dependent scattering times, versus the commonly
employed constant scattering time. For this, we employ DFT bandstructures and a
full numerical scheme that uses Fermi's Golden Rule to extract the momentum
relaxation times of each state at every energy, momentum, and band. We consider
electron-phonon scattering (acoustic and optical), as well as ionized impurity
scattering, and evaluate the qualitative and quantitative differences in the
power factors of the materials compared to the case where the constant
scattering time is employed. We show that the thermoelectric power factors
extracted from the two different methods differ in terms of i) their ranking
between materials, ii) the carrier density where the peak power factor appears,
and iii) their trends with temperature. We further show that the constant
relaxation time approximation smoothens out the richness in the bandstructure
features, thus limiting the possibilities of exploring this richness for
material design and optimization. These details are more properly captured
under full energy/momentum-dependent scattering time considerations. Finally,
by mapping the conductivities extracted within the two schemes, we provide
appropriate density-dependent constant relaxation times that could be employed
as a fast first order approximation for extracting charge transport properties
in the half-Heuslers we consider.",1910.06628v3
2019-10-16,Modeling magnetic evolution and exchange hardening in disordered magnets: The example of Mn$_{1-x}$Fe$_x$Ru$_2$Sn Heusler alloys,"We demonstrate how exchange hardening can arise in a chemically-disordered
solid solution from a first-principles statistical mechanics approach. A
general mixed-basis chemical and magnetic cluster expansion has been developed,
and applied to the Mn$_{1-x}$Fe$_x$Ru$_2$Sn Heusler alloy system; single-phase
solid solutions between antiferromagnetic \ch{MnRu2Sn} and ferromagnetic
\ch{FeRu2Sn} with disorder on the Mn/Fe sublattice that exhibit unexpected
exchange hardening. Monte Carlo simulations applied to the cluster expansion
are able to reproduce the experimentally measured magnetic transition
temperatures and the bulk magnetization as a function of composition. The
magnetic ordering around a site is shown to be dependent not only on bulk
composition, but also on the identity of the site and the local composition
around that site. The simulations predict that local antiferromagnetic
orderings form inside a bulk ferromagnetic region at intermediate compositions
that drives the exchange hardening. Furthermore, the antiferromagnetic regions
disorder at a lower temperature than the ferromagnetic regions, providing an
atomistic explanation for the experimentally-observed decrease in exchange
hardening with increasing temperature. These effects occur on a length scale
too small to be resolved with previously-used characterization techniques.",1910.07543v1
2018-12-13,"Noncentrosymmetric compensated half-metal hosting pure spin Weyl nodes, triple nodal points, nodal loops, and nexus fermions","Materials containing multiple topological characteristics become more exotic
when combined with noncentrosymmetric crystal structures and unusual magnetic
phases such as the compensated half-metal state, which is gapped in one spin
direction and conducting in the other. First principles calculations reveal
these multiple topological features in the compensated half-metal Cr$_2$CoAl
having neither time-reversal nor inversion symmetries. In the absence of
(minor) spin-orbit coupling (SOC), there are (1) a total of twelve pairs of
magnetic Weyl points, (2) three distinct sets of triple nodal points near the
Fermi level that are (3) interconnected with six symmetry related nodal lines.
This combination gives rise to fully spin polarized nexus fermions, in a system
with broken time-reversal symmetry but negligible macroscopic magnetic field.
The observed high Curie temperature of 750 K and calculated SOC hybridization
mixing of several meV should make these nexus fermions readily measurable.
Unlike topological features discussed for other Heuslers which emphasize their
strong ferromagnetism, this compensated half-metal is impervious to typical
magnetic fields, thus providing a complementary set of experimental phenomena.
Making use of the soft calculated magnetic state, large magnetic fields can be
used to rotate the direction of magnetism, during which certain topological
features will evolve. Our results suggest that these features may be common in
inverse-Heusler systems, particularly the isostructural and isovalent Ga and In
analogs.",1812.05273v2
2019-02-20,Effect of the temperature and magnetic field induced martensitic transformation in bulk Fe$_{45}$Mn$_{26}$Ga$_{29}$ alloy on its electronic structure and physical properties,"Effect of the temperature and magnetic field induced martensitic
transformation (MT) on the electronic structure and some physical properties of
bulk Fe$_{45.2}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy has been investigated.
{According to the experimental results of DSC, magnetic and transport
measurements direct and reverse martensitic transformation without external
magnetic field takes place within 194 $\leq T \leq$ 328 K temperature range
with a hysteresis up to $\Delta T \approx$ 100 K defined as $\Delta T$ =
$A_{f,s}$ - $M_{s,f}$, where $A_{f,s}$ and $M_{s,f}$ are the critical
temperatures of direct and reverse martensitic transformation. External
magnetic field of $\mu_{0}H$ = 5 T causes a high-temperature shift of MT
temperatures.} MT from parent austenite L2$_{1}$ phase to martensitic
tetragonally distorted L2$_{1}$ one (i. e. to L1$_{0}$) causes significant
changes in the electronic structure of alloy, a drastic increase in alloy
magnetization, a decrease in the alloy resistivity, and a reversal of the sign
of the temperature coefficient of resistivity from negative to positive. At the
same time experimentally determined optical properties of
Fe$_{45.6}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy in austenitic and martensitic
states look visually rather similar being noticeable different in microscopic
nature as can be concluded from first-principle calculations. Experimentally
observed changes in the physical properties of the alloy are discussed in terms
of the electronic structures of an austenite and martensite phases.",1902.07462v1
2019-06-15,"Effect of L21 and XA ordering on phase stability, half-metallicity and magnetism of Co2FeAl Heusler Alloy: GGA and GGA+U approach","The generalized gradient approximation (GGA) scheme in the first-principles
calculations are used to study the effect of L21 and XA ordering on the phase
stability, half-metallicity and magnetism of Co2FeAl (CFA) Heusler alloy.
Various possible hypothetical structures: L21-I, L21-II, XA-I, and XA-II were
prepared under the conventional L21 and inverse XA phases by altering the
atomic occupancies at their Wyckoff sites. It is found that the XA-II phase of
CFA is the most stable phase energetically among all the structures. The
electronic structure calculations without U show the presence of half-metallic
(HM) ground state only in L21-1 structure and the other structures are found to
be metallic. However, the electronic structures of CFA are significantly
modified in the presence of U, although the total magnetic moments per cell
remained the same and consistent with the Slater-Pauling (SP) rule. The
metallic ground states of CFA in L21-II and XA-II structures are converted into
the half-metallic ground states in presence of U but remained the same
(metallic) in XA-I structure. The results indicate that the electronic
structures are not only dependent on the L21 and XA ordering of the atoms but
also depend on the choice of U values. So experiments may only verify the
superiority of GGA+U to GGA.",1906.06516v2
2020-04-04,Improved crystallographic compatibility and magnetocaloric reversibility in Pt substituted Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy,"We present here the improved crystallographic/geometric compatibility and
magnetocaloric reversibility by measurement of magnetic entropy change using
different protocols in 10% Pt substituted Ni2Mn1.4In0.6 magnetic shape memory
alloy. The substitution of Pt reduces the thermal hysteresis about 50% to the
Ni2Mn1.4In0.6. The origin of the reduced thermal hysteresis is investigated by
the crystallographic compatibility of the austenite and martensite phases. The
calculated middle eigenvalue of the transformation matrix turned out to be
0.9982, which is very close to 1 (deviation is only 0.18%) suggests for the
crystallographic compatibility between the austenite and martensite phases in
Ni1.9Pt0.1Mn1.4In0.6. A very small thermal hysteresis and crystallographic
compatibility between two phases in this alloy system indicate a stress-free
transition layer (i.e. perfect habit plane) between the austenite and
martensite phase, which is expected to give reversible martensite phase
transition and therefore reversible magnetocaloric effect (MCE) as well. The
calculated value of the isothermal entropy change ({\Delta}Siso) using the
magnetization curve under three different measurement protocols (i.e.
isothermal, loop, and isofield measurement protocol) is found to be nearly same
indicating a reversible MCE in the present alloy system. Our work provides a
path to design new magnetic shape memory Heusler alloys for magnetic
refrigeration and also suggest that any of the above measurement protocol can
be used for the calculation of {\Delta}Siso for materials satisfying
geometrical compatibility condition.",2004.01854v1
2021-03-06,Observation of inverse magnetocaloric effect in magnetic-field-induced austenite phase of Heusler Alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7),"Magnetocaloric effect (MCE), magnetization, specific heat, and
magnetostriction measurements were performed in both pulsed and steady high
magnetic fields to investigate the magnetocaloric properties of Heusler alloys
Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7). From direct MCE measurements for
Ni41Co9Mn31.5Ga18.5 up to 56 T, a steep temperature drop was observed for
magnetic-field-induced martensitic transformation (MFIMT), designated as
inverse MCE. Remarkably, this inverse MCE is apparent not only with MFIMT, but
also in the magnetic-field-induced austenite phase. Specific heat measurements
under steady high magnetic fields revealed that the magnetic field variation of
the electronic entropy plays a dominant role in the unconventional
magnetocaloric properties of these materials. First-principles based
calculations performed for Ni41Co9Mn31.5Ga18.5 and Ni45Co5Mn36.7In13.3 revealed
that the magnetic-field-induced austenite phase of Ni41Co9Mn31.5Ga18.5 is more
unstable than that of Ni45Co5Mn36.7In13.3 and that it is sensitive to slight
tetragonal distortion. We conclude that the inverse MCE in the
magnetic-field-induced austenite phase is realized by marked change in the
electronic entropy through tetragonal distortion induced by the externally
applied magnetic field.",2103.04143v1
2021-03-18,Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co$_2$MnGa,"Weyl semimetals are playing a major role in condensed matter physics due to
exotic topological properties, and their coexistence with ferromagnetism may
lead to enhanced spin-related phenomena. Here, the inverse spin Hall effect
(ISHE) in the ferromagnetic Weyl-semimetal Heusler alloy Co$_2$MnGa was
investigated at room temperature by means of electrical spin injection in
lateral spin valve structures. Spin transport properties such as spin
polarization and spin diffusion length in this material were precisely
extracted in order to estimate the spin Hall angle $\theta_{\textrm{SH}}$,
which was found to be $-0.19\pm0.04$ and is among the highest reported for a
ferromagnet. Although this value is on the same order of magnitude of known
heavy metals, the significantly higher resistivity of Co$_2$MnGa implies an
improvement on the magnitude of detection voltages, while its ferromagnetic
nature allows controlling the intensity of SHE through the magnetization
direction. It was also shown that Onsager's reciprocity does not hold for this
system, which is in part attributable to a different spin-dependent Hall
conductivity for spin-up and spin-down carriers.",2103.10188v1
2022-03-20,Deposition temperature dependence of thermo-spin and magneto-thermoelectric conversion in Co$_2$MnGa films on Y$_3$Fe$_5$O$_{12}$ and Gd$_3$Ga$_5$O$_{12}$,"We have characterized Co$_2$MnGa (CMG) Heusler alloy films grown on
Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates at
different deposition temperatures and investigated thermo-spin and
magneto-thermoelectric conversion properties by means of a lock-in thermography
technique. X-ray diffraction, magnetization, and electrical transport
measurements show that the deposition at high substrate temperatures induces
the crystallized structures of CMG while the resistivity of the CMG films on
YIG (GGG) prepared at and above 500 {\deg}C (550 {\deg}C) becomes too high to
measure the thermo-spin and magneto-thermoelectric effects due to large
roughness, highlighting the difficulty of fabricating highly ordered continuous
CMG films on garnet structures. Our lock-in thermography measurements show that
the deposition at high substrate temperatures results in an increase in the
current-induced temperature change for CMG/GGG and a decrease in that for
CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen
effect in CMG through crystallization. The latter can be explained by the
superposition of the anomalous Ettingshausen effect and the spin Peltier effect
induced by the positive (negative) charge-to-spin conversion for the amorphous
(crystallized) CMG films. These results provide a hint to construct
spin-caloritronic devices based on Heusler alloys.",2203.10566v2
2016-03-01,Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys,"Weyl fermions have recently been observed in several time-reversal-invariant
semimetals and photonics materials with broken inversion symmetry. These
systems are expected to have exotic transport properties such as the chiral
anomaly. However, most discovered Weyl materials possess a substantial number
of Weyl nodes close to the Fermi level that give rise to complicated transport
properties. Here we predict, for the first time, a new family of Weyl systems
defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler
materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions
in the centrosymmetric magnetic systems, we recall an easy and practical
inversion invariant, which has been calculated to be -1, guaranteeing the
existence of an odd number of pairs of Weyl fermions. These materials exhibit,
when alloyed, only two Weyl nodes at the Fermi level - the minimum number
possible in a condensed matter system. The Weyl nodes are protected by the
rotational symmetry along the magnetic axis and separated by a large distance
(of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been
calculated as well. This discovery provides a realistic and promising platform
for manipulating and studying the magnetic Weyl physics in experiments.",1603.00479v2
2017-06-06,"Structural, electronic, magnetic and transport properties of equiatomic quaternary Heusler Alloy CoRhMnGe: Theory and Experiment","In this work, we present structural, electronic, magnetic, mechanical and
transport properties of equiatomic quaternary Heusler alloy, CoRhMnGe using
both theoretical and experimental techniques. A detailed structural analysis is
performed using X-ray diffraction(XRD) and extended X-ray absorption fine
structure(EXAFS) spectroscopy. The alloy is found to crystallize in Y-type
structure having space group $F\bar{4}3m$ (\# 216). The ab-initio simulation
pedict half-metallic ferromagnetic characteristics leading to large spin
polarization. The calculated magnetization is found to be in fair agreement
with experiment as well as those predicted by the Slater-Pauling rule, which is
a prerequisite for half-metallicity. The magnetic transition
temperature($\mathrm{T_{C}}$) is found to be $\sim 760$ K. Measured electrical
resistivity in the temperature range 2-400 K also gives an indication of
half-metallic behavior. Simulated resistivity matches fairly well with those
measured, with the temperature dependant carrier relaxation time lying in the
range $1-2$ fs. Effect of hydrostatic pressure on electronic structure,
magnetic and mechanical properties are investigated in detail. The alloy is
found to preserve half-metallic characteristics upto 30.27 GPa beyond which it
transit to metallic phase. No magnetic phase transition is found to occur in
the whole range of pressure. The system also satisfies the Born-Huang criteria
for mechanical stability upto a limited range of pressure. All these properties
make CoRhMnGe alloy promising for spintronics devices.",1706.01624v1
2018-04-17,Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy,"Resonant ultrasound spectroscopy and magnetic susceptibility experiments have
been used to characterize strain coupling phenomena associated with structural
and magnetic properties of the shape-memory Heusler alloy series
Ni$_{50+x}$Mn$_{25-x}$Ga$_{25}$ ($x=0$, 2.5, 5.0, and 7.5). All samples exhibit
a martensitic transformation at temperature $T_M$ and ferromagnetic ordering at
temperature $T_C$, while the pure end member ($x=0$) also has a premartensitic
transition at $T_{PM}$, giving four different scenarios: $T_C>T_{PM}>T_M$,
$T_C>T_M$ without premartensitic transition, $T_C\approx T_M$, and $T_C<T_M$.
Fundamental differences in elastic properties i.e., stiffening versus
softening, are explained in terms of coupling of shear strains with three
discrete order parameters relating to magnetic ordering, a soft mode and the
electronic instability responsible for the large strains typical of martensitic
transitions. Linear-quadratic or biquadratic coupling between these order
parameters, either directly or indirectly via the common strains, is then used
to explain the stabilities of the different structures. Acoustic losses are
attributed to critical slowing down at the premartensite transition, to the
mobility of interphases between coexisting phases at the martensitic transition
and to mobility of some aspect of the twin walls under applied stress down to
the lowest temperatures at which measurements were made.",1804.06183v1
2018-04-20,Presence of atomic disorder and its effect on magnetic and electronic properties of NiCrGa half Heusler alloy,"In this work, polycrystalline NiCrGa half Heusler alloy, which is predicted
to be half-metallic ferromagnet from first principles calculations, has been
synthesized by arc meting technique and its structural, magnetic as well as the
electronic properties have been studied. The measured x-ray diffraction (XRD)
pattern shows the signature of a disordered structure. From the magnetization
measurements, there is no evidence of ferromagnetic ordering observed in this
system down to the lowest temperature studied. Instead, the system shows the
signature of an antiferromagnetic ordering at very low temperature. The
experimentally observed structural and magnetic properties are found to be
significantly different from the theoretically predicted properties of the
ordered cubic C1b structure. To probe the possible disorder present in the
system and its effect on the magnetic properties, we have carried out first
principles calculations using the spin-polarized-relativistic
Korringa-Kohn-Rostoker method (SPR-KKR). Using a combination of XRD,
photoelectron spectroscopy, magnetization measurements and first principles
calculations, we conclude that NiCrGa has significant amount of atomic
disorder. Although, the ordered structure is energetically more stable than the
disordered structures, we find that after synthesis, the system tends to
stabilize in a disordered structure. With this atomic disorder present in the
sample, the ferromagnetic ordering is disturbed and the calculated spin
polarization is consequently reduced.",1804.07613v1
2019-03-01,Linear-response-based DFT+U method for exploring half-metallic Co-based full Heusler alloys,"The density functional theory (DFT)+U method based on the linear response
(LR) theory was applied to investigate the electronic structures of Co-based
ternary full Heusler alloy Co$_2Y$Si for exploring half-metallic (HM)
ferromagnets with a wide HM gap. The LR-based DFT+U calculations tend to obtain
a reasonable correlation parameter for $Y$ site, while the correlation of Co
site misleads to the unphysical ground state due to the overestimated parameter
value that arises from the delocalized electronic structure of Co. Furthermore,
we found that the HM gap of Co$_2$MnSi originates from Co $e_u$ orbital in the
conduction state and Co-Mn hybridizing $t_{2g}$ orbital in the valence state
around the Fermi energy. This means that the HM gap is a tunable property by
selecting the $Y$ element and/or mixing several elements into the $Y$ site
through $t_{2g}$ atomic-orbital coupling. Our LR-based DFT+U method was
extended to other ternary Co$_2Y$Si and quaternary Co$_2$($Y$,Mn)Si. We found
that Co$_2$(Ti$_{0.25}$,Mn$_{0.75}$)Si and Co$_2$(Fe$_{0.25}$,Mn$_{0.75}$)Si
show HM nature, with the Fermi energy being at almost the center of the
minority band gap, which leads to high thermal stability.",1903.00180v2
2019-05-10,Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy,"The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for
spin-gapless semiconductors (SGSs). However, to date, there have been no
experimental attempts at fabricating a junction device. This paper reports a
fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with
CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction
measurements show that the (001) CoFeCrAl electrode films with atomically flat
surfaces have a $B2$-ordered phase. The saturation magnetization is 380
emu/cm$^3$, almost the same as the value given by the Slater--Pauling--like
rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87%
and 165%, respectively. Cross-sectional electron diffraction analysis shows
that the MTJs have MgO interfaces with fewer dislocations. The temperature- and
bias-voltage-dependence of the transport measurements indicates magnon-induced
inelastic electron tunneling overlapping with the coherent electron tunneling.
X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic
arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in
contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state
possessing SGS characteristics. Ab-initio calculations taking account of the
Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect
of the Cr-Fe swap disorder on the ability for electronic states to allow
coherent electron tunneling is discussed.",1905.04070v1
2019-08-21,Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi,"We report a combined theoretical and experimental investigation of
half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi.
Room temperature XRD analysis reveals that the alloy crystallizes in L21
disorder instead of pristine Y-type structure due to 50% swap disorder between
the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal
a net magnetization of 4 $\mu_B$ with Curie temperature of ~780 K. Resistivity
measurement reveals the presence of localization effect below 35 K while above
100 K, a linear dependence is observed. Resistivity behavior indicates the
absence of single magnon scattering, which indirectly supports the
half-metallic nature. The majority spin band near the Fermi level clearly
indicates the overlap of flat eg bands with sharply varying conduction bands
that are responsible for the localization. In-depth analysis of the projected
atomic d-orbital character of band structure reveals unusual bonding, giving
rise to the flat eg bands purely arising out of Ru ions. Co-Ru swap disorder
calculations indicate the robustness of half-metallic nature, even when the
structure changes from Y-type to L21-type, with no major change in the net
magnetization of the system. Thus, robust half-metallic nature, stable
structure, and high Curie temperature make this alloy quite a promising
candidate to be used as a source of highly spin-polarized currents in
spintronic applications.",1908.07804v1
2020-11-20,An ac-susceptibility study of magnetic relaxation phenomena in the antiskyrmion hosting tetragonal Mn-Pt(Pd)-Sn system,"Here, we report an exhaustive study of the frequency-dependent ac-magnetic
susceptibility of the $D_{2d}$ symmetric Heusler system Mn-Pt(Pd)-Sn that hosts
antiskyrmions over a wide temperature range. Magnetic relaxation studies using
Cole-Cole formalism reveal a Debye-type relaxation with a nearly negligible
distribution in relaxation times. In contrast to the archetypical skyrmion
hosts, the high Curie temperature ($ T_C $) of the present system ensures
shorter switching times, and, correspondingly, higher frequencies are required
to probe the relaxation dynamics. We find a non-monotonic variation in the
characteristic relaxation time with distinct maxima at the phase boundaries
\textit{via} helical $\longrightarrow$ antiskyrmion $\longrightarrow$
field-polarized states, indicating slower magnetization dynamics over the
region of phase coexistence. The temperature-dependent relaxation time across
different phases is of the order of $ 10^{-5} - 10^{-4} $ s and follows the
well-known Arrhenius law with reasonable values of the energy barriers. The
present study concerning the magnetization dynamics in the antiskyrmion host
tetragonal Heusler system is an important contribution towards the basic
understanding of the dynamical aspects of antiskyrmions for their potential
applications.",2011.10229v1
2020-12-03,When Band Convergence is Not Beneficial for Thermoelectrics,"Band convergence is considered a clear benefit to thermoelectric performance
because it increases the charge carrier concentration for a given Fermi level,
which typically enhances charge conductivity while preserving the Seebeck
coefficient. However, this advantage hinges on the assumption that interband
scattering of carriers is weak or insignificant. With first-principles
treatment of electron-phonon scattering in
CaMg$_{2}$Sb$_{2}$-CaZn$_{2}$Sb$_{2}$ Zintl system and full Heusler
Sr$_{2}$SbAu, we demonstrate that the benefit of band convergence can be
intrinsically negated by interband scattering depending on the manner in which
bands converge. In the Zintl alloy, band convergence does not improve weighted
mobility or the density-of-states effective mass. We trace the underlying
reason to the fact that the bands converge at one k-point, which induces strong
interband scattering of both the deformation-potential and the polar-optical
kinds. The case contrasts with band convergence at distant k-points (as in the
full Heusler), which better preserves the single-band scattering behavior
thereby successfully leading to improved performance. Therefore, we suggest
that band convergence as thermoelectric design principle is best suited to
cases in which it occurs at distant k-points.",2012.02272v2
2021-02-21,Experimental method to determine specific heat and transition enthalpy at a first order phase transition: fundamentals and application to a NiMnIn Heusler alloy,"A new method that characterizes thermal properties during a first-order phase
transition is described. The technique consists in exciting the sample by a
series of constant frequency thermal pulses which one in every N pulses (N is a
small number like four) being exceedingly large in amplitude. This pulse
induces phase transformation which is inhibited during the following smaller
pulses due to thermal hysteresis. That way the specific heat for a given
mixture of phases can be determined. The results obtained are independent of
experimental parameters like the rate and the amplitude of the pulses, unlike
what happens in other calorimetric techniques. The method also provides the
enthalpy excess by analyzing the energy balance between the dissipated heat and
the heat flowing during each pulse of measurement.
  The protocol is tested to analyze the phase transitions of a Heusler alloy Ni
50.54 Mn 33.65 In 15.82 . The paramagnetic-ferromagnetic transition for the
austenite phase is continuous and the specific heat shows a lambda anomaly. The
martensitic phase transition shows a first-order character and the specific
heat follows a step-like behaviour in contrast with previously reported
large-peak anomalies.",2102.10653v2
2021-07-31,Optical phonon modes assisted thermal conductivity in p-type ZrIrSb Half-Heusler alloy: A combined experimental and computational study,"Half Heusler (HH) alloys with 18 valence electron count have attracted
significant interest in the area of research related to thermoelectrics.
Understanding the novel transport properties exhibited by these systems with
semiconducting ground state is an important focus area in this field. Large
thermal conductivity shown by most of the HH alloy possesses a major hurdle in
improving the figure of merit (ZT). Additionally, understanding the mechanism
of thermal conduction in heavy constituents HH alloys is an interesting aspect.
Here, we have investigated the high temperature thermoelectric properties of
ZrIrSb through experimental studies, phonon dispersion and electronic band
structure calculations. ZrIrSb is found to exhibit substantially lower
magnitude of resistivity and Seebeck coefficient near room temperature, owing
to existence of anti-site disorder between Ir/Sb and vacant sites.
Interestingly, in ZrIrSb, lattice thermal conductivity is governed by coupling
between the acoustic and low frequency optical phonon modes, which originates
due to heavier Ir/Sb atoms. This coupling leads to an enhancement in the
Umklapp processes due to the optical phonon excitations near zone boundary,
resulting in a lower magnitude of \k{appa}L. Our studies point to the fact that
the simultaneous existence of two heavy mass elements within a simple unit cell
can substantially decrease the lattice degrees of freedom.",2108.00210v1
2021-10-29,Stability and magnetic properties of grain boundaries in the inverse Heusler phase Fe$_2$CoGa and in bcc Fe,"We investigate grain boundaries (GBs) in the cubic inverse Heusler phase
Fe$_2$CoGa by means of first principles calculations based on density
functional theory. Besides the energetic stability, the analysis focuses on the
magnetic properties of a set of 16 GB structures in this intermetallic phase.
We determine the integrated excess magnetization across the GB and analyze it
in terms of the projected local magnetic moments of the atoms and their local
Voronoi volumes. The results are systematically compared to those of
corresponding GBs in body-centered cubic (bcc) Fe. The studied GBs in
Fe$_2$CoGa may have a considerably increased magnetization at the GB, up to
more than twice as much as in bcc Fe, depending on the GB type, while
geometrical quantities like GB widening or local GB excess volume distributions
are similar for both phases. We explain this difference by the higher
flexibility of the ternary Fe$_2$CoGa phase in compensating the disturbance of
a crystal defect by structural relaxation. The GB structures therefore have a
lower energy accompanied with increased local magnetic moments of the Co and
half of the Fe atoms within a distance of a few angstrom around the GB plane.",2110.15896v1
2021-11-25,Efficient spin current source using a half-Heusler alloy topological semimetal with Back-End-of-Line compatibility,"Topological materials, such as topological insulators (TIs), have great
potential for ultralow power spintronic devices, thanks to their giant spin
Hall effect. However, the giant spin Hall angle (${\theta}_{SH}$ > 1) is
limited to a few chalcogenide TIs with toxic elements and low melting points,
making them challenging for device integration during the silicon
Back-End-of-Line (BEOL) process. Here, we show that by using a half-Heusler
alloy topological semi-metal (HHA-TSM), YPtBi, it is possible to achieve both a
giant ${\theta}_{SH}$ up to 1.6 and a high thermal budget up to 600${\deg}$C.
We demonstrate magnetization switching of a CoPt thin film using the giant spin
Hall effect of YPtBi by current densities lower than those of heavy metals by
one order of magnitude. Since HHA-TSM includes a group of three-element
topological materials with great flexibility, our work opens the door to the
third-generation spin Hall materials with both high ${\theta}_{SH}$ and high
compatibility with the BEOL process that would be easily adopted by the
industry.",2111.12889v1
2022-07-21,First-principles insights into all-optical spin switching in the half-metallic Heusler ferrimagnet Mn$_2$RuGa,"All-optical spin switching (AOS) represents a new frontier in magnetic
storage technology -- spin manipulation without a magnetic field, -- but its
underlying working principle is not well understood. Many AOS ferrimagnets such
as GdFeCo are amorphous and renders the high-level first-principles study
unfeasible. The crystalline half-metallic Heusler Mn$_2$RuGa presents an
opportunity. Here we carry out hitherto the comprehensive density functional
investigation into the material properties of Mn$_2$RuGa, and introduce two
concepts - the spin anchor site and the optical active site - as two pillars
for AOS in ferrimagnets. In Mn$_2$RuGa, Mn$(4a)$ serves as the spin anchor
site, whose band structure is below the Fermi level and has a strong spin
moment, while Mn$(4c)$ is the optical active site whose band crosses the Fermi
level. Our magneto-optical Kerr spectrum and band structure calculation jointly
reveal that the delicate competition between the Ru-$4d$ and Ga-$4p$ states is
responsible for the creation of these two sites. These two sites found here not
only present a unified picture for both Mn$_2$RuGa and GdFeCo, but also open
the door for the future applications. Specifically, we propose a
Mn$_2$Ru$_x$Ga-based magnetic tunnel junction where a single laser pulse can
control magnetoresistance.",2207.10443v1
2022-12-01,Extrinsic to intrinsic mechanism crossover of anomalous Hall effect in the Ir-doped MnPtSn Heusler system,"Recent findings of large anomalous Hall signal in nonferromagnetic and
nonferrimagnetic materials suggest that the magnetization of the system is not
a critical component for the realization of the anomalous Hall effect (AHE).
Here, we present a combined theoretical and experimental study demonstrating
the evolution of different mechanisms of AHE in a cubic Heusler system
MnPt$_{1-x}$Ir$_x$Sn. With the help of magnetization and neutron diffraction
studies, we show that the substitution of nonmagnetic Ir in place of Pt
significantly reduces the net magnetic moment from 4.17 $ \mu _B$/f.u. in
MnPtSn to 2.78 $ \mu _B$/f.u. for MnPt$_{0.5}$Ir$_{0.5}$Sn. In contrast, the
anomalous Hall resistivity is enhanced by nearly three times from 1.6 $ \mu
\Omega $ cm in MnPtSn to about 5 $ \mu \Omega $ cm for
MnPt$_{0.5}$Ir$_{0.5}$Sn. The power law analysis of the Hall resistivity data
suggests that the extrinsic contribution of AHE that dominates in the case of
the parent MnPtSn almost vanishes for MnPt$_{0.5}$Ir$_{0.5}$Sn, where the
intrinsic mechanism plays the major role. The experimental results are well
supported by our theoretical study, which shows a considerable enhancement of
the spin-orbit coupling when Ir is introduced into the system. Our finding of a
crossover of the anomalous Hall effect with chemical engineering is a major
contribution toward the recent interest in controlling the band topology of
topological materials, both in bulk and thin-film forms.",2212.00360v1
2023-04-11,Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy -- Microstructure and magnetic properties from powder to printed parts,"Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as
magnetocaloric effect during the magneto-structural phase transition, making
this material interesting for solid-state cooling application. Material
processing by additive manufacturing can overcome difficulties related to
machinability of the alloys, caused by their intrinsic brittleness. Since the
magnetic properties and transition temperature are highly sensitive to the
chemical composition, it is essential to understand and monitoring these
properties over the entire processing chain. In the present work the
microstructural and magnetic properties from gas-atomized powder to
post-processed Ni-Mn-Sn alloy are investigated. Direct energy deposition was
used for processing, promoting the evolution of a polycrystalline
microstructure being characterized by elongated grains along the building
direction. A complete and sharp martensitic transformation can be achieved
after applying a subsequent heat treatment at 1173 K for 24 h. The
Mn-evaporation of 1.3 at. % and the formation of Mn-oxide during DED-processing
lead to an increase of the transition temperature of 45 K and a decrease of
magnetization, clearly pointing at the necessity of controlling the
composition, oxygen partial pressure and magnetic properties over the entire
processing chain.",2304.05383v1
2023-07-31,Ballistic spin-transport properties of magnetic tunnel junctions with MnCr-based ferrimagnetic quaternary Heusler alloys,"We investigate the suitability of nearly half-metallic ferrimagnetic
quaternary Heusler alloys, CoCrMnZ (Z=Al, Ga, Si, Ge) to assess the feasibility
as electrode materials of MgO-based magnetic tunnel junctions (MTJ). Low
magnetic moments of these alloys originated from the anti-ferromagnetic
coupling between Mn and Cr spins ensure a negligible stray field in spintronics
devices as well as a lower switching current required to flip their spin
direction. We confirmed mechanical stability of these materials from the
evaluated values of elastic constants, and the absence of any imaginary
frequency in their phonon dispersion curves. The influence of swapping
disorders on the electronic structures and their relative stability are also
discussed. A high spin polarization of the conduction electrons are observed in
case of CoCrMnZ/MgO hetrojunctions, independent of terminations at the
interface. Based on our ballistic transport calculations, a large coherent
tunnelling of the majority-spin $s$-like $\Delta_1$ states can be expected
through MgO-barrier. The calculated tunnelling magnetoresistance (TMR) ratios
are in the order of 1000\%. A very high Curie temperatures specifically for
CoCrMnAl and CoCrMnGa, which are comparable to $bcc$ Co, could also yield a
weaker temperature dependece of TMR ratios for CoCrMnAl/MgO/CoCrMnAl (001) and
CoCrMnGa/MgO/CoCrMnGa (001) MTJ.",2307.16442v1
2023-09-18,Coherent Tunneling and Strain Sensitivity of an All Heusler Alloy Magnetic Tunneling Junction: A First-Principles Study,"Half-metallic Co-based full Heusler alloys have captured considerable
attention of the researchers in the realm of spintronic applications, owing to
their remarkable characteristics such as exceptionally high spin polarization
at Fermi level, ultra-low Gilbert damping, and high Curie temperature. In this
comprehensive study, employing density functional theory, we delve into the
stability and electron transport properties of a magnetic tunneling junction
(MTJ) comprising a Co$_2$MnSb/HfIrSb interface. Utilizing a standard model
given by Julliere, we estimate the tunnel magnetoresistance (TMR) ratio of this
heterojunction under external electric field, revealing a significantly high
TMR ratio (500%) that remains almost unaltered for electric field magnitudes up
to 0.5 V/A. In-depth investigation of K-dependent majority spin transmissions
uncovers the occurrence of coherent tunneling for the Mn-Mn/Ir interface,
particularly when a spacer layer beyond a certain thickness is employed.
Additionally, we explore the impact of bi-axial strain on the MTJ by varying
the in-plane lattice constants between -4% and +4%. Our spin-dependent
transmission calculations demonstrate that the Mn-Mn/Ir interface manifests
strain-sensitive transmission properties under both compressive and tensile
strain, and yields a remarkable three-fold increase in majority spin
transmission under tensile strain conditions. These compelling outcomes place
the Co2MnSb/HfIrSb junction among the highly promising candidates for nanoscale
spintronic devices, emphasizing the potential significance of the system in the
advancement of the field.",2309.09755v1
2023-09-20,Effects of disorder on the magnetic properties of the Heusler alloy V$_{2}$FeAl,"Magnetic properties of multicomponent alloys depend sensitively on the degree
of atomic order on the different crystallographic sites. In this work we
demonstrate the magnetic contrast between bulk and thin-film samples of the
Heusler alloy V$_{2}$FeAl. Arc-melted bulk ingots show practically no site
preference of the elements (A2 structure), whereas magnetron-sputtered
thin-film samples display a higher degree of atomic ordering with a tendency
towards XA-type order. Electronic structure calculations favour ferrimagnetic
XA-type ordering, and the effect of different pairwise atomic disorder on the
element specific and net magnetic moments are evaluated to reproduce
experimental observations. XA-type thin-films with iron moment of 1.24
$\mu_{\mathrm{B}}$ determined by X-ray magnetic circular dichroism are in
agreement with calculation, but the measured net moment of 1.0
$\mu_{\mathrm{B}}$ per formula unit and average vanadium moment are smaller
than expected from calculations. The measured Curie temperature is
approximately 500 K. Films with a higher degree of disorder have a
T$_{\mathrm{C}}$ close to 300 K with a net moment of 0.1 $\mu_{\mathrm{B}}$ at
low temperature. The large calculated vanadium moments are destroyed by partial
disorder on $4d$ vanadium sites. By contrast, the arc-melted and annealed bulk
alloy with a fully-disordered A2 structure shows no spontaneous magnetization;
it is a Pauli paramagnet with dimensionless susceptibility
$\chi_{\mathrm{v}}=-2.95\times10^{-4}$.",2309.11480v1
2023-09-29,Micromagnetics of ferromagnetic/antiferromagnetic nanocomposite materials. Part II: Mesoscopic modeling,"In the second part of this publication, we present simulation results for two
three-dimensional models of Heusler-type alloys obtained by the mesoscopic
micromagnetic approach. In the first model, we simulate the magnetization
reversal of a single ferromagnetic (FM) inclusion within a monocrystalline
antiferromagnetic (AFM) matrix, revealing the evolution of the complex
magnetization distribution within this inclusion when the external field is
changed. The main result of this ``monocrystalline'' model is the absence of
any hysteretic behavior by the magnetization reversal of the FM inclusion.
Hence, this model is unable to reproduce the basic experimental result for the
corresponding nanocomposite -- hysteresis in the magnetization reversal of FM
inclusions with a vertical shift of the corresponding loops. To explain this
latter feature, in the second model we introduce a polycrystalline AFM matrix,
with exchange interactions between AFM crystallites and between the FM
inclusion and these crystallites. We show that within this model we can not
only reproduce the hysteretic character of the remagnetization process, but
also achieve a semi-quantitative agreement with the experimentally observed
hysteresis loop assuming that the concentration of FM inclusions strongly
fluctuates. These findings demonstrate the reliability of our enhanced
micromagnetic model and set the basis for its applications in future studies of
Heusler alloys and FM/AFM nanocomposites.",2309.17129v1
2023-10-03,Complex magnetic interactions and critical behavior analysis in quaternary CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy,"We investigate the magnetic behavior and critical exponents of quaternary
CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy to understand the interactions across
the Curie temperature ($T_{\rm C}$). The Rietveld refinement of the x-ray
diffraction pattern with the space group F$\bar{4}$3m confirms a single-phase
cubic Y-type crystal structure. The magnetic susceptibility $\chi (T)$ data
show a ferromagnetic nature with a second-order phase transition from
paramagnetic to ferromagnetic at $446\pm1$~K. The saturation magnetization at
5~K is determined to be 2.2~$\mu_B$/f.u., which found to be close to the
Slater--Pauling rule and indicates its half-metallic nature. The values of
asymptotic critical exponents ($\beta$, $\gamma$, and $\delta$) and the $T_{\rm
C}$ are extracted through detailed analytical analysis including the Modified
Arrott plot, the Kouvel-Fisher (K--F) method, and the Widom scaling relation.
Interestingly, the estimated values of $\beta$ = 0.369 and $\gamma$ = 1.445
closely approximate the theoretical values of the 3D Heisenberg model and
second-order thermodynamic phase transition across the $T_{\rm C}$. The
obtained exponents lead to the collapse of renormalized isotherms, represented
by the relationship between the magnetization (m) and the applied magnetic
field (h), into two distinct branches above and below the $T_{\rm C}$, which
validates the reliability of the analysis. Furthermore, these exponents suggest
that the spin interaction follows a decay pattern of $J(r) \sim r^{-4.99}$,
indicating a short-range magnetic ordering, akin to the itinerant-electron 3D
Heisenberg model.",2310.01790v1
2010-11-26,Compound Poisson and signed compound Poisson approximations to the Markov binomial law,"Compound Poisson distributions and signed compound Poisson measures are used
for approximation of the Markov binomial distribution. The upper and lower
bound estimates are obtained for the total variation, local and Wasserstein
norms. In a special case, asymptotically sharp constants are calculated. For
the upper bounds, the smoothing properties of compound Poisson distributions
are applied. For the lower bound estimates, the characteristic function method
is used.",1011.5734v1
2014-09-10,On some compound distributions with Borel summands,"The generalized Poisson distribution is well known to be a compound Poisson
distribution with Borel summands. As a generalization we present closed
formulas for compound Bartlett and Delaporte distributions with Borel summands
and a recursive structure for certain compound shifted Delaporte mixtures with
Borel summands. Our models are introduced in an actuarial context as claim
number distributions and are derived only with probabilistic arguments and
elementary combinatorial identities. In the actuarial context related compound
distributions are of importance as models for the total size of insurance
claims for which we present simple recursion formulas of Panjer type.",1409.3113v1
2018-05-07,Paraphrase to Explicate: Revealing Implicit Noun-Compound Relations,"Revealing the implicit semantic relation between the constituents of a
noun-compound is important for many NLP applications. It has been addressed in
the literature either as a classification task to a set of pre-defined
relations or by producing free text paraphrases explicating the relations. Most
existing paraphrasing methods lack the ability to generalize, and have a hard
time interpreting infrequent or new noun-compounds. We propose a neural model
that generalizes better by representing paraphrases in a continuous space,
generalizing for both unseen noun-compounds and rare paraphrases. Our model
helps improving performance on both the noun-compound paraphrasing and
classification tasks.",1805.02442v1
2020-09-08,Commuting Magic Square Matrices,"We review a known method of compounding two magic square matrices of order m
and n with the all-ones matrix to form two magic square matrices of order mn.
We show that these compounded matrices commute. Simple formulas are derived for
their Jordan form and singular value decomposition. We verify that regular
(associative) and pandiagonal commuting magic squares can be constructed by
compounding. In a special case the compounded matrices are similar.
Generalization of compounding to a wider class of commuting magic squares is
considered. Three numerical examples illustrate our theoretical results.",2009.03499v1
2021-10-30,Stability of B2 compounds: Role of the $M$ point phonons,"Although many binary compounds have the B2 (CsCl-type) structure in the
thermodynamic phase diagram, an origin of the structural stability is not
understood well. Here, we focus on 416 compounds in the B2 structure extracted
from the Materials Project, and study the dynamical stability of those
compounds from first principles. We demonstrate that the B2 phase stability
lies in whether the lowest frequency phonon at the $M$ point in the Brillouin
zone is endowed with a positive frequency. We show that the interatomic
interactions up to the fourth nearest neighbor atoms are necessary for
stabilizing such phonon modes, which should determine the minimum cutoff radius
for constructing the interatomic potentials of binary compounds with guaranteed
accuracy.",2111.00183v1
2023-05-04,Compound WKI-SP hierarchy and multiloop soliton solutions,"The generalized hierarchies of compound WKI-SP (Wadati-Konno-Ichikawa and
short pulse) equations are presented. The proposed integrable nonlinear
equations include the WKI-type equations, the SP-type equations and the
compound generalized WKI-SP equations. A chain of hodograph transformations are
established to relate the compound WKI-SP equations with the MKdV-SG (modified
Korteweg-de Vries and sine-Gordon) equations. As applications, the multiloop
soliton solutions of one compound WKI-SP equation are obtained. We emphasize on
showing abundant solitonic behaviors of two loop solitons. The role of each
parameter plays in the movement of two-loop solion are shown detailedly in a
table.",2305.02532v1
2011-03-21,The Periodic Table as a Part of the Periodic Table of Chemical Compounds,"The numbers of natural chemical elements, minerals, inorganic and organic
chemical compounds are determined by 1, 2, 3 and 4-combinations of a set 95 and
are respectively equal to 95, 4,465, 138,415 and 3,183,545. To explain these
relations it is suggested the concept of information coefficient of
proportionality as mathematical generalization of the proportionality
coefficient for any set of positive numbers. It is suggested a hypothesis that
the unimodal distributions of the sets of information coefficients of
proportionality for atomic weights of chemical elements of minerals and
chemical compounds correspond to unimodal distributions of the above sets for
combination of 2, 3 and 4 atomic weights of 95 natural chemical elements. The
expected values of symmetrized distributions of information coefficients of
proportionality sets for atomic weights of minerals and chemical compounds are
proposed to be used to define chemical compounds, like atomic weights define
chemical elements. Variational series of the expected values can be represented
as a sequence of packets of 95 values. The Periodic Table should be extended to
the Periodic Table of Chemical Elements and Chemical Compounds consisting of a
short period with 95 chemical elements and 4,465 minerals, and 24 periods with
138,415 compounds each. All naturally occurred chemical elements, minerals and
chemical compounds should be packed in 95 to compose the suggested Table. The
first long period comprises the packets of inorganic compounds, the rest of the
periods include the packets of organic compounds.",1103.3972v1
2015-09-07,The Secrecy Capacity of Compound Gaussian MIMO Wiretap Channels,"Strong secrecy capacity of compound wiretap channels is studied. The known
lower bounds for the secrecy capacity of compound finite-state memoryless
channels under discrete alphabets are extended to arbitrary uncertainty sets
and continuous alphabets under the strong secrecy criterion. The conditions
under which these bounds are tight are given. Under the saddle-point condition,
the compound secrecy capacity is shown to be equal to that of the worst-case
channel. Based on this, the compound Gaussian MIMO wiretap channel is studied
under the spectral norm constraint and without the degradedness assumption.
First, it is assumed that only the eavesdropper channel is unknown, but is
known to have a bounded spectral norm (maximum channel gain). The compound
secrecy capacity is established in a closed form and the optimal signaling is
identified: the compound capacity equals the worst-case channel capacity thus
establishing the saddle-point property; the optimal signaling is Gaussian and
on the eigenvectors of the legitimate channel and the worst-case eavesdropper
is isotropic. The eigenmode power allocation somewhat resembles the standard
water-filling but is not identical to it. More general uncertainty sets are
considered and the existence of a maximum element is shown to be sufficient for
a saddle-point to exist, so that signaling on the worst-case channel achieves
the compound capacity of the whole class of channels. The case of
rank-constrained eavesdropper is considered and the respective compound secrecy
capacity is established. Subsequently, the case of additive uncertainty in the
legitimate channel, in addition to the unknown eavesdropper channel, is
studied. Its compound secrecy capacity and the optimal signaling are
established in a closed-form as well, revealing the same saddle-point property.",1509.02182v1
2018-01-15,Flow structure of compound droplets moving in microchannels,"Compound droplets can be used in substance encapsulation and material
compartmentalization to achieve a precise control over the relevant processes
in many applications, such as bioanalysis, pharmaceutical manufacturing, and
material synthesis. The flow fields in compound droplets directly affect the
performance of these applications, but it is challenging to measure them
experimentally. In this study, the flow in compound droplets in axisymmetric
microchannels is simulated using the Finite Volume Method, and the interface is
captured using the Level Set Method with surface tension accounted for via the
Ghost Fluid Method. The combination of the Level Set Method and the Ghost Fluid
Method reduces spurious currents that are produced unphysically near the
interface, and achieves a precise simulation of the complex flow field within
compound droplets. The shape of compound droplets, the vortical patterns, the
velocity fields, and the eccentricity are investigated and the effects of the
key dimensionless parameters, including the size of the compound droplet, the
size of the core droplet, the capillary number, and the viscosity ratio, are
analyzed. The flow structures in multi-layered compound droplets are also
studied. This study not only unveils the complex flow structure within compound
droplets moving in microchannels, but can also be used to achieve a precise
control over the relevant processes in a wide range of applications of compound
droplets.",1801.04646v1
2020-04-14,Hydrodynamics of a Compound Drop in Plane Poiseuille Flow,"We numerically investigate the hydrodynamics of a compound drop in a plane
Poiseuille flow under Stokes regime. A neutrally buoyant, initially concentric
compound drop is released into a fully developed flow, where it migrates to its
equilibrium position. Based on the results, we find that the core-shell
interaction affects the dynamics of both the core and the compound drop. During
the initial transient period, the core revolves about the center of the
compound drop due to the internal circulation inside the shell. At equilibrium,
depending upon the nature of the flow field inside the shell, we identify two
distinct core behaviors: stable state and limit-cycle state. In the stable
state, the core stops revolving and moves outward very slowly. The core in the
limit-cycle state continues to revolve in a nearly fixed orbit with no further
inward motion. We also find that the migration of the compound drop affects the
eccentricity of the core significantly. A comparison with the simple drop
reveals that the core enhances the deformation of the compound drop. The
outward moving core in stable state pushes the compound drop towards the walls,
and the revolving core in limit-cycle state makes the compound drop to
oscillate at its equilibrium position. From the parametric study, we find that
the core affects the compound drop dynamics only at intermediate sizes, and
increase in any parameter sufficiently causes a transition from limit-cycle
state to stable state.",2004.06428v2
2022-01-20,Stabilization of CeGe$_3$ with Ti and O featuring tetravalent Ce ions: (Ce$_{0.85}$Ti$_{0.15}$)Ge$_3$O$_{0.5}$,"Sub-oxides with the anti-perovskite structure constitute a large part of the
interstitial stabilized compounds with novel chemical and physical properties,
especially in the systems containing rare earth elements and/or early
transition metal elements. A new sub-oxide compound,
(Ce$_{0.85}$Ti$_{0.15}$)Ge$_3$O$_{0.5}$, is synthesized by flux growth. The
compound crystallizes in a cubic structure which can be considered as an
ordered vacancy variant of anti-perovskite-structure or an ordered interstitial
variant of the Cu$_3$Au type, with a space group of Fm-3m (225). The structure
is refined from X-ray single crystal methods. The compound may be considered as
a compound stabilized by chemical pressure generated by the substitution and
the interstitials atoms. The stability of the compounds in RTr$_3$ systems (R =
rare earth elements except Pm and Sc, Tr = tetrel elements such as Si, Ge, Sn,
Pb) seem to be highly correlated to the ratio of the rare earth elements' radii
to the main group elements' atomic radii. The magnetic property of the compound
confirms the 4$^+$ valence of the Ce atoms. The resistivity measurement of the
compound shows that it is metallic.",2201.08449v1
2004-04-29,Strongly-correlated crystal-field approach to 3d oxides - the orbital magnetism in 3d-ion compounds,"We have developed the crystal-field approach with strong electron
correlations, extended to the Quantum Atomistic Solid-State theory (QUASST), as
a physically relevant theoretical model for the description of electronic and
magnetic properties of 3d-atom compounds. Its applicability has been
illustrated for LaCoO3, FeBr2 and Na2V3O7. According to the QUASST theory in
compounds containing open 3d-/4f-/5f-shell atoms the discrete atomic-like
low-energy electronic structure survives also when the 3d atom becomes the full
part of a solid matter. This low-energy atomic-like electronic structure, being
determined by local crystal-field interactions and the intra-atomic spin-orbit
coupling, predominantly determines electronic and magnetic properties of the
whole compound.
  We understand our theoretical research as a continuation of the Van Vleck's
studies on the localized magnetism. We point out, however, the importance of
the orbital magnetism and the intra-atomic spin-orbit coupling for the
physically adequate description of real 3d-ion compounds and 3d magnetism. Our
studies clearly indicate that it is the highest time to ''unquench'' the
orbital moment in solid-state physics in description of 3d-atom containing
compounds.
  PACS No: 75.10.D; 71.70.E
  Keywords: magnetism, transition-metal compounds, 3d magnetism, crystal field,
spin-orbit coupling, orbital magnetism",0404713v1
2004-06-24,"Magneto-transport studies on (Pr1/3Sm2/3)2/3A1/3MnO3 (A = Ca, Sr and Ba) compounds","Magnetic and transport properties of (Pr1/3Sm2/3)2/3A1/3MnO3 (A = Ca, Sr and
Ba) compounds, prepared by the citrate gel route, have been investigated. These
compounds are found to crystallize in the orthorhombic structure. Charge
ordering transport behavior is indicated only in Ca-substituted compound. The
Sr- and Ba-substituted compounds show metal-insulator transition and
semiconducting-like behavior, respectively. The magnetoresistance is highest in
the Ba substituted compound. All the three samples show irreversibility in
magnetization as a function of temperature in zero-field cooled (ZFC) and field
cooled (FC) plots. The non-saturating magnetization, even at 5K and 4 Tesla
field, are observed in Ca as well Ba-substituted compounds.",0406599v1
2006-08-08,Measurement of pressure effects on the magnetic and the magnetocaloric properties of the intermetallic compounds R(Co1-xSix)2 [R=Dy and Er],"The effect of external pressure on the magnetic properties and magnetocaloric
effect of R(Co1-xSix)2 [R= Er, Dy and x=0, 0.025 and 0.05] compounds has been
studied. The ordering temperatures of both the parent as well as the Si
substituted compounds are found to decrease with pressure. In all the
compounds, the critical field for metamagnetic transition increases with
pressure. It is seen that the magnetocaloric effect in the parent compounds is
almost insensitive to pressure, while there is considerable enhancement in the
case of Si substituted compounds. Spin fluctuations arising due to the
magnetovolume effect play a crucial role in determining the pressure dependence
of magnetocaloric effect in these compounds. Analysis of the magnetization data
using the Landau theory has shown that the magnitude of the Landau coefficient
(C3) decreases with Si concentration whereas it is found to increase with
pressure. The isothermal magnetic entropy change is found to behave in the same
manner as C3, both with Si concentration (at ambient pressure) as well as with
the applied pressure.",0608191v1
2005-02-04,Compound and quasi-compound states in low-energy scattering of nucleons from 12C,"A multi-channel algebraic scattering theory has been used to study the
properties of nucleon scattering from 12C and of the sub-threshold compound
nuclear states, accounting for properties in the compound nuclei to ~10 MeV.
All compound and quasi-compound resonances observed in total cross-section data
are matched, and on seeking solutions of the method at negative energies, all
sub-threshold states in 13C and 13N are predicted with the correct
spin-parities and with reasonable values for their energies. A collective-model
prescription has been used to define the initiating nucleon-12C interactions
and via use of orthogonalizing pseudo-potentials, account is made of the Pauli
principle. Information is extracted on the underlying structure of each state
in the compound systems by investigating the zero-deformation limit of the
results.",0502016v1
2007-05-15,"Magnetic, magneto-thermal and magneto-transport properties in SmMn2Si2-xGex compounds","The effect of Ge substitution for Si in SmMMn2Si2-xGex compounds has been
studied. The Sm ordering temperature is found to be much larger in the compound
with x=2, as compared to the compounds with x=0 and 1. The increase in the
intra layer Mn-Mn distance is found to be responsible for this increase. Among
these three compounds, SmMn2Ge2 is found to show re-entrant ferromagnetism at
low temperatures. The magnetic contribution to the heat capacity has been found
in all the three compounds. The splitting of the ground state multiplet has
been estimated by fitting the magnetic part of the heat capacity data using the
Schottky formula. The isothermal magnetic entropy change is found to remain the
same for x=0 and 1, but decrease in the compound with x=2, though the nature of
magnetic transition changes from second order to first order, as x is increased
from 0 to 2. The electrical resistivity increases with Ge concentration. The
excess resistivity in the antiferromagnetic region has been calculated.",0705.2237v1
2011-03-03,A class of CTRWs: Compound fractional Poisson processes,"This chapter is an attempt to present a mathematical theory of compound
fractional Poisson processes. The chapter begins with the characterization of a
well-known L\'evy process: The compound Poisson process. The semi-Markov
extension of the compound Poisson process naturally leads to the compound
fractional Poisson process, where the Poisson counting process is replaced by
the Mittag-Leffler counting process also known as fractional Poisson process.
This process is no longer Markovian and L\'evy. However, several analytical
results are available and some of them are discussed here. The functional limit
of the compound Poisson process is an $\alpha$-stable L\'evy process, whereas
in the case of the compound fractional Poisson process, one gets an
$\alpha$-stable L\'evy process subordinated to the fractional Poisson process.",1103.0647v1
2011-11-03,Physical properties of Thallium-Tellurium based thermoelectric compounds using first-principles simulations,"We present a study of the thermodynamic and physical properties of Tl5Te3,
BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based
calculations. The optimized lattice constants of the compounds are in good
agreement with the experimental data. The electronic density of states and band
structures are calculated to understand the bonding mechanism in the three
compounds. The indirect band gap of BiTl9Te6 and SbTl9Te6 compounds are found
to be equal to 0.256 eV and 0.374 eV, respectively. The spin-orbit coupling has
important effects on the electronic structure of the two semiconducting
compounds and should therefore be included for a good numerical description of
these materials. The elastic constants of the three compounds have been
calculated, and the bulk modulus, shear modulus, and young's modulus have been
determined. The change from ductile to brittle behavior after Sb or Bi alloying
is related to the change of the electronic properties. Finally, the Debye
temperature, longitudinal, transverse and average sound velocities have been
obtained.",1111.0793v1
2012-07-30,Thermoelectric properties of Pr3Rh4Sn13-type Yb3Co4Ge13 and Yb3Co4Sn13 compounds,"Crystallographic data and thermoelectric properties (from 240 K up to 380 K)
of Yb3Co4Ge13, Yb3Co4Sn13 compounds and Yb2CeCo4Ge13 and Yb2.3La0.7Co4Ge13
solid solutions are reported. The Seebeck coefficients, electric resistance and
thermal conductivity increase monotonically with increasing temperature from
240 to 380 K for all the compounds. The Seebeck coefficient is S = 14 - 27 \mu
V//K for Yb3Co4Sn13, and S = -21 -- -12 \mu V/K for Yb3Co4Ge13. The
substitution of Yb for cerium or lanthanum in Yb3Co4Ge13 shifts the Seeebeck
coefficient to positive values. The Yb3Co4Sn13 has a maximal ZT parameter from
available Pr3Rh4Sn13-type compounds. The ZT parameter of Yb3Co4Sn13 compound
increases from 0.006 up to 0.017 with increasing temperature from 240 K to 380
K.",1207.6875v2
2014-12-16,"Magnetic correlations of the quasi-one-dimensional half-integer spin-chain antiferromagnets Sr$M_2$V$_2$O$_8$ ($M$ = Co, Mn)","Magnetic correlations of two iso-structural quasi-one-dimensional (1D)
antiferromagnetic spin-chain compounds Sr$M_2$V$_2$O$_8$ ($M$ = Co, Mn) have
been investigated by magnetization and powder neutron diffraction. Two
different collinear antiferromagnetic (AFM) structures, characterized by the
propagation vectors, $k$ = (0 0 1) and $k$ = (0 0 0), have been found below
$\sim$ 5.2 K and $\sim$ 42.2 K for the Co- and Mn-compounds, respectively. For
the Mn-compound, AFM chains (along the $c$ axis) order ferromagnetically within
the $ab$ plane, whereas, for the Co-compound, AFM chains order
ferro-/antiferromagnetically along the $a/b$ direction. The critical exponent
study confirms that the Co- and Mn-compounds belong to the Ising and Heisenberg
universality classes, respectively. For both compounds, short-range spin-spin
correlations are present over a wide temperature range above $T_N$. The reduced
ordered moments at base temperature (1.5 K) indicate the presence of quantum
fluctuations in both compounds due to the quasi-1D magnetic interactions.",1412.5009v1
2015-09-15,Splitting Compounds by Semantic Analogy,"Compounding is a highly productive word-formation process in some languages
that is often problematic for natural language processing applications. In this
paper, we investigate whether distributional semantics in the form of word
embeddings can enable a deeper, i.e., more knowledge-rich, processing of
compounds than the standard string-based methods. We present an unsupervised
approach that exploits regularities in the semantic vector space (based on
analogies such as ""bookshop is to shop as bookshelf is to shelf"") to produce
compound analyses of high quality. A subsequent compound splitting algorithm
based on these analyses is highly effective, particularly for ambiguous
compounds. German to English machine translation experiments show that this
semantic analogy-based compound splitter leads to better translations than a
commonly used frequency-based method.",1509.04473v1
2015-10-13,"Review paper: Magnetocaloric effects in RTX intermetallic compounds (R = Gd~Tm, T = Fe~Cu and Pd, X = Al and Si)","The ternary intermetallic RTX compounds (R = rare earth, T = transitional
metal, X = p-block metal) have been investigated extensively in the past few
decades due to their interesting physical properties. Recently, much attention
has been paid to the magnetocaloric effect (MCE) of these RTX compounds,
especially the ones with heavy rare-earth, for their potential application in
low temperature magnetic refrigeration. In this paper, we review the MCE of
RTSi and RTAl systems with R = Gd~Tm, T = Fe~Cu and Pd, which are widely
investigated in recent years. It is found that these RTX compounds exhibit
various crystal structures and magnetic properties, which then result in
different MCE. Large MCE has been observed not only in the typical
ferromagnetic materials but also in the antiferromagnetic materials. The
magnetic properties have been studied in detail to discuss the physical
mechanism of large MCE in RTX compounds. Particularly, some RTX compounds, such
as ErFeSi, HoCuSi, HoCuAl, etc, exhibit large reversible MCE under low magnetic
field change, which suggests that these compounds could be promising materials
for magnetic refrigeration in low temperature range.",1510.03503v1
2016-05-13,Ferromagnetism in orthorhombic RAgAl3 (R = Ce and Pr) compounds,"We present a detailed study on magnetic, thermodynamic and transport
properties of polycrystalline RAgAl3(R = Ce and Pr) compounds. Both compounds
crystallize in orthorhombic structure, which is distorted from the tetragonal
BaAl4 structure with the space group Cmcm. Heat capacity measurement indicates
the bulk magnetic ordering of the compounds. CeAgAl3 and PrAgAl3 order
ferromagnetically at TC = 3.8 K and 5.8 K, respectively as it was confirmed
from magnetic measurements. CeAgAl3 exhibits heavy Fermion behaviour. The
Schottky behaviour in heat capacity data was observed in both compounds. The
crystalline electric field (CEF) analysis of the magnetic parts of heat
capacity of CeAgAl3 and PrAgAl3 yielded to a CEF level scheme with three
doublets and nine singlets and with an overall splitting of 51 K and 180 K,
respectively. Fit yielded a magnetic doublet state for CeAgAl3, whereas for
PrAgAl3 a pseudo-doublet ground-state with an energy difference of 15 K has
been obtained. The resistivity measurements display a low temperature drop at
the magnetic ordering temperature of the compounds. Negative magnetoresistance
(MR) due to the ferromagnetic ordering has been observed for both Ce and Pr
compounds.",1605.04261v3
2016-06-06,Enhanced spin reorientation temperature and origin of magnetocapacitance in HoFeO3,"We report on the increase in the spin reorientation temperature in
HoFe0.5Cr0.5O3 compound by isovalent substitution Cr3+ at the Fe-site and the
magnetocapacitance in the HoFeO3 compound. Spin reorientation transition is
evident around 50 K and 150 K for the x = 0 and x = 0.5 compounds respectively.
The increase in the spin reorientation transition temperature in case of x =
0.5 compound can be attributed to the domination of the Ho3+ to Fe3+
interaction over the Fe3+ to Fe3+ interaction. Decrease in Neel temperature
from 643 K (x = 0) to 273 K (x = 0.5) can be ascribed to the decrease in the
interaction between antiferromagnetically aligned Fe3+ moments as a result of
the dilution of the Fe3+ moments with the Cr3+ addition. From the magnetization
M vs magnetic field H variation it is evident that the coercivity, HC decreases
for x = 0.5 compound, hinting the magnetic softening of the HoFeO3 compound.
Observed magnetocapacitance could be due to lossy dielectric mechanism in the
present compound. Indeed, present results would be helpful in understanding the
physics behind rare- earth orthoferrites.",1606.01703v1
2016-09-14,Investigation of supramolecular architectures of bent-shaped pyridine derivatives: from a three-ring crystalline compound towards five-ring mesogens,"In searching for novel photoactive liquid crystals, we have synthesized a
series of five-ring pyridine-based bent-core compounds bearing different
substituents at the peripheral phenyl rings (CH3O, Cl and NO2). Their
mesomorphic behaviour has been investigated by polarizing optical microscopy,
differential scanning calorimetry and X-ray scattering, and then compared with
the unsubstituted parent compound. The introduction of the methoxy groups at
the peripheral phenyl rings of the bent core results in a non-mesomorphic
compound, whereas the chloro- and nitro-substituted compounds form
enantiotropic B1-like phases. Significant changes of the textures and
transition temperatures of the mesophase have been observed under UV light. The
presented investigation of the mesomorphic properties of the synthesized
compounds, coupled with analysis of the molecular packing of the related
three-ring compounds, will help to design self-organized molecules suitable for
UV indicators.",1609.04215v1
2017-07-21,Synthesis of Xenon and Iron/Nickel intermetallic compounds at Earth's core thermodynamic conditions,"Although Xe is known to form stable compounds with strong electronegative
elements, evidence on the formation of stable compounds with electropositive
elements, such as Fe and Ni, was missing until very recently. In addition to
the significance of the emerging field of noble gas elements chemistry, the
possible formation of Xe-Fe/Ni compounds has been proposed as a plausible
explanation of the so-called ""missing Xe paradox"". Here we explore the possible
formation of stable compounds in the Xe-Fe/Ni systems at thermodynamic
conditions representative of Earth's core. Using in situ synchrotron X-ray
diffraction and Raman spectroscopy in concert with first principles
calculations we demonstrate the synthesis of stable Xe(Fe,Fe/Ni)$_3$ and
XeNi$_3$ compounds. The results indicate the changing chemical properties of
elements under extreme conditions where noble gas elements can form stable
compounds with elements which are electropositive at ambient conditions but
become slightly electronegative at high pressures.",1707.07541v1
2017-09-28,Bayesian Multi Plate High Throughput Screening of Compounds,"High throughput screening of compounds (chemicals) is an essential part of
drug discovery [7], involving thousands to millions of compounds, with the
purpose of identifying candidate hits. Most statistical tools, including the
industry standard B-score method, work on individual compound plates and do not
exploit cross-plate correlation or statistical strength among plates. We
present a new statistical framework for high throughput screening of compounds
based on Bayesian nonparametric modeling. The proposed approach is able to
identify candidate hits from multiple plates simultaneously, sharing
statistical strength among plates and providing more robust estimates of
compound activity. It can flexibly accommodate arbitrary distributions of
compound activities and is applicable to any plate geometry. The algorithm
provides a principled statistical approach for hit identification and false
discovery rate control. Experiments demonstrate significant improvements in hit
identification sensitivity and specificity over the B-score method, which is
highly sensitive to threshold choice. The framework is implemented as an
efficient R extension package BHTSpack and is suitable for large scale data
sets.",1709.10041v1
2019-11-27,Optimization of criteria for an efficient screening of new thermoelectric compounds: the TiNiSi structure type as a case-study,"High-throughput calculations are a very promising tool for screening a large
number of compounds in order to discover new useful materials. Ternary
intermetallic are thus investigated in the present work to find new compounds
potentially interesting for thermoelectric applications. The screening of the
stable non-metallic compounds required for such applications is obtained by
calculating their electronic structure by DFT methods. In a first part, the
study of the density of states at the Fermi level of well-known chemical
elements and binary compounds allows to empirically optimize the selection
criteria between metals and non-metals. In a second part, the TiNiSi
structure-type is used as a case-study through the investigation of 570
possible compositions. This screening method leads to the selection of 12
possible semiconductors. For these selected compounds, their Seebeck
coefficient and their lattice thermal conductivity are calculated in order to
identify the most interesting one. TiNiSi, TaNiP or HfCoP could thus be
compounds worth an experimental investigation.",1911.12027v1
2019-07-18,High-pressure hybrid materials that can store hydrogen in table salt,"We demonstrate in this paper that high pressure can promote the reactions
between the ionic compounds and H2 molecules and form thermodynamically stable
hybrid compounds. Using crystal structure search method based on first
principles calculations and particle swarm optimization algorithm, we show that
many alkali halides XY (X=Na, K, Rb, Cs; Y=Cl, Br, I) can form stable hybrid
compounds with various H2 compositions under different pressures that could be
as low as 0.8 GPa (KIH2). Especially, the commonly known table salt, NaCl, can
form stable NaClH2 and NaCl(H2)4 hybrid compounds under pressures of 19.7 and
37.9 GPa, respectively. Our results demonstrate that pressure can promote the
formation of solid-molecule hybrid compounds, which reveals a new unique way of
discovering novel materials that can combine the advantages of inorganic
compounds and small molecules. A direct application of our work is the proof of
turning the common table salt and other similar ionic compounds into hydrogen
storage materials under moderate pressures.",1907.08295v2
2018-12-18,Observation of field induced anomalous quantum criticality in Ce0.6Y0.4NiGe2 compound,"We report the results of our investigation of magnetization and heat capacity
on a series of compounds Ce1-xYxNiGe2 (x = 0.1, 0.2 and 0.4) under the
influence of external magnetic field. Our studies of the thermodynamic quantity
-dM/dT on these compounds indicate that magnetic frustration persists in
Ce0.9Y0.1NiGe2, as also reported for the parent compound CeNiGe2. The weak
signature of this frustration is also noted in Ce0.8Y0.2NiGe2, whereas, it is
suppressed in Ce0.6Y0.4NiGe2. Heat capacity studies on Ce0.9Y0.1NiGe2 and
Ce0.8Y0.2NiGe2 indicate the presence of a new magnetic anomaly at high field
which indicates that quantum criticality is absent in these compounds. However,
for Ce0.6Y0.4NiGe2 such an anomaly is not noted. For this later compound, the
magnetic field (H) and temperature (T) dependence of heat capacity and
magnetization obey H/T scaling above critical fields. However, the obtained
scaling critical parameter ({\delta}) is 1.6, which is away from mean field
value of 3. This deviation suggests the presence of unusual fluctuations and
anomalous quantum criticality in these compounds. This unusual fluctuation may
arise from disorderness induced by Y-substitution.",1812.07171v1
2020-12-08,High-throughput computational search for two-dimensional binary compounds: Energetic stability versus synthesizability of three-dimensional counterparts,"Using first principles calculations, the energetic stability of
two-dimensional (2D) binary compounds $XY$ is investigated, where $X$ and $Y$
indicate the metallic element from Li to Pb in the periodic table. Here, 1081
compounds in the buckled honeycomb (BHC), buckled square, B2, L1$_0$, and B$_h$
structures are studied. For the compounds that have negative formation energy
in the BHC structure or the compounds that can have the B$_h$ structure, the
phonon dispersions of the 2D structures are also calculated. We demonstrate
that (i) a negative formation energy is neither a sufficient nor necessary
condition for yielding the dynamical stability of 2D compounds; and (ii) if a
compound in the B$_h$ structure has been synthesized experimentally, that in
the BHC structure is dynamically stable.",2012.04790v2
2021-01-06,Classification of chemical compounds based on the correlation between \textit{in vitro} gene expression profiles,"Toxicity evaluation of chemical compounds has traditionally relied on animal
experiments;however, the demand for non-animal-based prediction methods for
toxicology of compounds is increasing worldwide. Our aim was to provide a
classification method for compounds based on \textit{in vitro} gene expression
profiles. The \textit{in vitro} gene expression data analyzed in the present
study was obtained from our previous study. The data concerned nine compounds
typically employed in chemical management.We used agglomerative hierarchical
clustering to classify the compounds;however, there was a statistical
difficulty to be overcome.We needed to properly extract RNAs for clustering
from more than 30,000 RNAs. In order to overcome this difficulty, we introduced
a combinatorial optimization problem with respect to both gene expression
levels and the correlation between gene expression profiles. Then, the
simulated annealing algorithm was used to obtain a good solution for the
problem. As a result, the nine compounds were divided into two groups using
1,000 extracted RNAs. Our proposed methodology enables read-across, one of the
frameworks for predicting toxicology, based on \textit{in vitro} gene
expression profiles.",2101.01837v1
2022-11-25,Application of Molecular Topology to the Prediction of Antioxidant Activity in a Group of Phenolic Compounds,"The study of compounds with antioxidant capabilities is of great interest to
the scientific community, as it has implications in several areas, from
Agricultural Sciences to Biological Sciences, including Food Engineering,
Medicine and Pharmacy. In applications related to human health, it is known
that antioxidant activity can delay or inhibit oxidative damage to cells,
reducing damage caused by free radicals, helping in the treatment, or even
preventing or postponing the onset of various diseases. Among the compounds
that have antioxidant properties, there are several classes of Phenolic
Compounds, which include several compounds with different chemical structures.
In this work, based on the molecular branching of compounds and their
intramolecular charge distributions, and using Molecular Topology, we propose a
significant topological-mathematical model to evaluate the potential of
candidate compounds to have an antioxidant function.",2211.14373v1
2022-12-02,Compound Tokens: Channel Fusion for Vision-Language Representation Learning,"We present an effective method for fusing visual-and-language representations
for several question answering tasks including visual question answering and
visual entailment. In contrast to prior works that concatenate unimodal
representations or use only cross-attention, we compose multimodal
representations via channel fusion. By fusing on the channels, the model is
able to more effectively align the tokens compared to standard methods. These
multimodal representations, which we call compound tokens are generated with
cross-attention transformer layers. First, vision tokens are used as queries to
retrieve compatible text tokens through cross-attention. We then chain the
vision tokens and the queried text tokens along the channel dimension. We call
the resulting representations compound tokens. A second group of compound
tokens are generated using an analogous process where the text tokens serve as
queries to the cross-attention layer. We concatenate all the compound tokens
for further processing with multimodal encoder. We demonstrate the
effectiveness of compound tokens using an encoder-decoder vision-language model
trained end-to-end in the open-vocabulary setting. Compound Tokens achieve
highly competitive performance across a range of question answering tasks
including GQA, VQA2.0, and SNLI-VE.",2212.01447v1
2023-02-14,A Psycholinguistic Analysis of BERT's Representations of Compounds,"This work studies the semantic representations learned by BERT for compounds,
that is, expressions such as sunlight or bodyguard. We build on recent studies
that explore semantic information in Transformers at the word level and test
whether BERT aligns with human semantic intuitions when dealing with
expressions (e.g., sunlight) whose overall meaning depends -- to a various
extent -- on the semantics of the constituent words (sun, light). We leverage a
dataset that includes human judgments on two psycholinguistic measures of
compound semantic analysis: lexeme meaning dominance (LMD; quantifying the
weight of each constituent toward the compound meaning) and semantic
transparency (ST; evaluating the extent to which the compound meaning is
recoverable from the constituents' semantics). We show that BERT-based measures
moderately align with human intuitions, especially when using contextualized
representations, and that LMD is overall more predictable than ST. Contrary to
the results reported for 'standard' words, higher, more contextualized layers
are the best at representing compound meaning. These findings shed new light on
the abilities of BERT in dealing with fine-grained semantic phenomena.
Moreover, they can provide insights into how speakers represent compounds.",2302.07232v1
2023-05-18,DrugChat: Towards Enabling ChatGPT-Like Capabilities on Drug Molecule Graphs,"A ChatGPT-like system for drug compounds could be a game-changer in
pharmaceutical research, accelerating drug discovery, enhancing our
understanding of structure-activity relationships, guiding lead optimization,
aiding drug repurposing, reducing the failure rate, and streamlining clinical
trials. In this work, we make an initial attempt towards enabling ChatGPT-like
capabilities on drug molecule graphs, by developing a prototype system
DrugChat. DrugChat works in a similar way as ChatGPT. Users upload a compound
molecule graph and ask various questions about this compound. DrugChat will
answer these questions in a multi-turn, interactive manner. The DrugChat system
consists of a graph neural network (GNN), a large language model (LLM), and an
adaptor. The GNN takes a compound molecule graph as input and learns a
representation for this graph. The adaptor transforms the graph representation
produced by the GNN into another representation that is acceptable to the LLM.
The LLM takes the compound representation transformed by the adaptor and users'
questions about this compound as inputs and generates answers. All these
components are trained end-to-end. To train DrugChat, we collected instruction
tuning datasets which contain 10,834 drug compounds and 143,517 question-answer
pairs. The code and data is available at
\url{https://github.com/UCSD-AI4H/drugchat}",2309.03907v1
2024-02-19,Network topology mapping of Chemical Compounds Space,"We define bipartite and monopartite relational networks of chemical elements
and compounds using two different datasets of inorganic chemical and material
compounds, as well as study their topology. We discover that the connectivity
between elements and compounds is distributed exponentially for materials, and
with a fat tail for chemicals. Compounds networks show similar distribution of
degrees, and feature a highly-connected club due to oxygen. Chemical compounds
networks appear more modular than material ones, while the communities detected
reveal different dominant elements specific to the topology. We successfully
reproduce the connectivity of the empirical chemicals and materials networks by
using a family of fitness models, where the fitness values are derived from the
abundances of the elements in the aggregate compound data. Our results pave the
way towards a relational network-based understanding of the inherent complexity
of the vast chemical knowledge atlas, and our methodology can be applied to
other systems with the ingredient-composite structure.",2402.11774v1
2011-01-20,Heavy Fermion scaling: Uranium versus Cerium and Ytterbium compounds,"In an effort to explore the differences between rare-earth-based and
uranium-based heavy Fermion (HF) compounds that reflect the underlying
difference between local 4$f$ moments and itinerant 5$f$ moments we analyze
scaling laws that relate the low temperature neutron spectra of the primary
(""Kondo-esque"") spin fluctuation to the specific heat and susceptibility. While
the scaling appears to work very well for the rare earth intermediate valence
compounds, for a number of key uranium compounds the scaling laws fail badly.
There are two main reasons for this failure. First, the presence of
antiferromagnetic (AF) fluctuations, which contribute significantly to the
specific heat, alters the scaling ratios. Second, the scaling laws require
knowledge of the high temperature moment degeneracy, which is often
undetermined for itinerant 5$f$ electrons. By making plausible corrections for
both effects, better scaling ratios are obtained for some uranium compounds. We
point out that while both the uranium HF compounds and the rare earth
intermediate valence (IV) compounds have spin fluctuation characteristic
energies of order 5 - 25 meV, they differ in that the AF fluctuations that are
usually seen in the U compounds are never seen in the rare earth IV compounds.
This suggests that the 5f itineracy increases the f-f exchange relative to the
rare earth case.",1101.3992v1
2018-04-01,Evidence of large magnetic cooling power and double glass transition in Tb5Pd2,"We report a detailed dc magnetization, ac susceptibility and magnetocaloric
properties of a binary intermetallic compound Tb5Pd2. Our dc magnetization and
heat capacity results reveal absence of long range ordering in this compound.
Two distinct frequency dependent peaks (Tf1~60 K and Tf2~21 K) had been
observed in the ac-susceptibility. Analysis of these frequency dependent peaks
by Mydosh parameter, power and Vogel-Fulcher law reveals that around Tf1 the
compound is at the boundary of spin glass (SG) like-cluster glass (CG) like
state and it undergoes a cluster glass-like freezing below Tf2. Zero field
cooled memory effect and non-linear dc susceptibility also confirmed the
presence of two glassy transitions in this compound. The transformation from
SG/CG boundary to CG phase was also confirmed by the magnetic relaxation
measurement and Arrott plots study. Remarkably, a significant magnetic entropy
change was also observed in the temperature range of 60-120 K. Additionally a
large relative cooling power also observed in this compound. The observed value
is comparable to those of promising refrigerant material in this temperature
range and is quite notable as in this compound magnetic hysteresis was absent
in this temperature range. It was noted that in this compound short-range
interactions persist up to a higher temperature above Tf1 and this is
responsible for the observation of significant MCE over a wide temperature
range. Our studies suggest that this compound is an example of a glassy
magnetic compound which shows large magnetocaloric effect.",1804.00255v1
2023-10-14,DepNeCTI: Dependency-based Nested Compound Type Identification for Sanskrit,"Multi-component compounding is a prevalent phenomenon in Sanskrit, and
understanding the implicit structure of a compound's components is crucial for
deciphering its meaning. Earlier approaches in Sanskrit have focused on binary
compounds and neglected the multi-component compound setting. This work
introduces the novel task of nested compound type identification (NeCTI), which
aims to identify nested spans of a multi-component compound and decode the
implicit semantic relations between them. To the best of our knowledge, this is
the first attempt in the field of lexical semantics to propose this task.
  We present 2 newly annotated datasets including an out-of-domain dataset for
this task. We also benchmark these datasets by exploring the efficacy of the
standard problem formulations such as nested named entity recognition,
constituency parsing and seq2seq, etc. We present a novel framework named
DepNeCTI: Dependency-based Nested Compound Type Identifier that surpasses the
performance of the best baseline with an average absolute improvement of 13.1
points F1-score in terms of Labeled Span Score (LSS) and a 5-fold enhancement
in inference efficiency. In line with the previous findings in the binary
Sanskrit compound identification task, context provides benefits for the NeCTI
task. The codebase and datasets are publicly available at:
https://github.com/yaswanth-iitkgp/DepNeCTI",2310.09501v1
2023-12-09,Bachelorthesis: Calculation of the magnetic properties of quarternary ThMn$_{12}$-type compounds with Zr as a substitution for Nd,"This research aims to identify an alternative solution for the
Nd$_2$Fe$_{14}$B magnet in light of the scarcity of rare earth (RE) resources.
The investigation uses density functional theory (DFT) calculations to assess
the effect of partial substitution of Nd with the transition metal (TM) Zr
within the ThMn$_{12}$ structure, focusing specifically on the
(Zr$_{0.5}$Nd$_{0.5}$)Fe$_{11}$Ti compound. In order to gain a comprehensive
understanding, an investigation of intrinsic and magnetic properties, including
saturation magnetisation ($M_S$), Curie temperature ($T_C$) and magnetic
anisotropy energy (MAE), is carried out on binary to quinary compounds
RFe$_{11-y}$Ti$_{y}$ (R: Nd, Zr and Zr$_{0.5}$Nd$_{0.5}$, y: $0 \leq y \leq 1$)
and (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{10}$CoTi. The substitution of Ti at different
concentrations for thermodynamic stabilisation is studied in ternary and
quaternary compounds RFe$_{12-y}$Ti$_y$ ($0 \leq y \leq 1$). In addition, the
influence of Co on phase stability and intrinsic magnetic properties is studied
in the quinary compound (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{10}$CoTi. Special attention
is given to the treatment of the 4$f$-electrons of Nd and their interaction
with the 3$d$-electrons. Theoretical results are compared with available
experimental data, although the limited availability of data, especially for
Zr-containing compounds, limits the scope of such comparisons. Based on the
literature and the calculations of binary and ternary compounds, the
calculations of quaternary and quinary compounds are encouraged. Promising
magnetic properties of an Nd-lean quaternary compound suitable for engineering
applications have been identified.",2312.14951v1
2001-08-22,Shubnikov-de Haas effect in quasi-two-dimensional compounds,"The Shubnikov - de Haas effect in quasi-two-dimensional compounds is studied.
The conductivity is calculated from the Kubo formula. Two effects -- the
field-dependent phase shift of the beats and the slow oscillations of the
conductivity are explained and calculated. The results are applicable to the
strongly anisotropic organic metals and other layered compounds.",0108352v1
2001-10-04,General elements in anticanonical systems of threefolds with divisorial contractions and applications to classification,"We treat threefolds with divisorial contractions whose exceptional divisors
contract to compound Du Val points. We prove that general elements in their
anticanonical systems around the exceptional divisors have at worst Du Val
singularities. As applications to classification, we describe divisorial
contractions to compound A_n points, and moreover we conclude that
discrepancies of divisorial contractions to compound D_n or E_n points are at
most four.",0110050v1
2008-08-16,Higher Order Moments Generation by Mellin Transform for Compound Models of Clutter,"The compound models of clutter statistics are found suitable to describe the
nonstationary nature of radar backscattering from high-resolution observations.
In this letter, we show that the properties of Mellin transform can be utilized
to generate higher order moments of simple and compound models of clutter
statistics in a compact manner.",0808.2227v1
2008-09-28,Estimation of Higher Order Moments for Compound Models of Clutter by Mellin Transform,"The compound models of clutter statistics are found suitable to describe the
nonstationary nature of radar backscattering from high-resolution observations.
In this letter, we show that the properties of Mellin transform can be utilized
to generate higher order moments of simple and compound models of clutter
statistics in a compact manner",0809.4846v1
2009-03-16,Compound and scale mixture of vector and spherical matrix variate elliptical distributions,"Several matrix variate hypergeometric type distributions are derived. The
compound distributions of left-spherical matrix variate elliptical
distributions and inverted hypergeometric type distributions with matrix
arguments are then proposed. The scale mixture of left-spherical matrix variate
elliptical distributions and univariate inverted hypergeometric type
distributions is also derived as a particular case of the compound distribution
approach.",0903.2875v1
2010-03-09,MAGNETIC ANOMALY IN SUPERCONDUCTING FeSe,"Synthesis, electrical and magnetic characterization of superconducting
FeSe0.85 compound is reported. An anomaly in the magnetization against
temperature around 90K is observed. Magnetic characterization of a commercial
compound with nominal FeSe stoichiometry is also presented. The overall
magnetic behaviors as well as the magnetic anomaly in both compounds are
discussed in terms of magnetic impurities and secondary phases. Keyword: A.
Superconductors",1003.1966v1
2014-02-23,Error Bound for Compound Wishart Matrices,"In this paper we consider non-asymptotic behavior of the real compound
Wishart matrices that generalize the classical real Wishart distribution. In
particular, we consider matrices of the form 1/nXBX', where X consists of real
centered Gaussian elements and B is an arbitrary real matrix and sequences of
such matrices for varying n. We show how the expectation of deviations from the
mean can be bounded for compound Wishart matrices.",1402.5581v2
2016-05-04,Compound chondrule formation via collision of supercooled droplets,"We present a novel model showing that compound chondrules are formed by
collisions of supercooled droplets. This model reproduces two prominent
observed features of compound chondrules: the nonporphyritic texture and the
size ratio between two components.",1605.01437v1
2017-08-16,Pricing compound and extendible options under mixed fractional Brownian motion with jumps,"This study deals with the problem of pricing compound options when the
underlying asset follows a mixed fractional Brownian motion with jumps. An
analytic formula for compound options is derived under the risk neutral
measure. Then, these results are applied to value extendible options. Moreover,
some special cases of the formula are discussed and numerical results are
provided.",1708.04829v1
2017-09-06,Descriptors for Machine Learning of Materials Data,"Descriptors, which are representations of compounds, play an essential role
in machine learning of materials data. Although many representations of
elements and structures of compounds are known, these representations are
difficult to use as descriptors in their unchanged forms. This chapter shows
how compounds in a dataset can be represented as descriptors and applied to
machine-learning models for materials datasets.",1709.01666v1
2014-06-04,Mutual Rényi information for two disjoint compound systems,"The leading term for the mutual R\'enyi information is studied for two widely
separated identical compound systems for free scalar fields in $(d+1)$
Euclidean space. The compound system consists of two identical spheres in
contact, with a result consistent with a universal form for the leading term
for the mutual R\'enyi information.",1406.1161v3
2020-03-21,Compound Poisson approximations in $\ell_p$-norm for sums of weakly dependent vectors,"The distribution of the sum of 1-dependent lattice vectors with supports on
coordinate axes is approximated by a multivariate compound Poisson distribution
and by signed compound Poisson measure. The local and $\ell_\alpha$-norms are
used to obtain the error bounds. The Heinrich method is used for the proofs.",2003.09650v2
2021-09-16,Malliavin-Stein method for the multivariate compound Hawkes process,"In this paper, we provide upper bounds on the d2 distance between a large
class of functionals of a multivariate compound Hawkes process and a given
Gaussian vector. This is proven using Malliavin's calculus defined on an
underlying Poisson embedding. The upper bound is then used to infer the speed
of convergence of Central Limit Theorems for the multivariate compound Hawkes
process with exponential kernels as the observation time T goes to infinity.",2109.07749v1
2022-04-05,"Angle-resolved polarized Raman spectroscopy for distinguishing stage-I graphite intercalation compounds with Thorium, Uranium and Plutonium","Graphite intercalation compounds (GICs) with the geometrical anisotropy and
strong electron-phonon coupling are in full swing and have shown their great
potential for applications in nanodevices. I selected representative three
elements in actinide group with valence electron arrangement: Thorium (Th)
([Rn]6d27s2), Uranium (U) ([Rn]5f36d17s2), Plutonium (Pu) ([Rn]5f67s2). I
calculated their phonon spectra and demonstrated the atomic-scale
microstructure identification of actinide graphite intercalation compounds by
angle-resolved polarized Raman spectroscopy.",2204.01967v1
2023-03-15,Asymptotic results for compound sums in separable Banach spaces,"We prove large and moderate deviation results for sequences of compound sums,
where the summands are i.i.d. random variables taking values on a separable
Banach space. We establish that the results hold by proving that we are dealing
with exponentially tight sequences. We present two moderate deviation results:
in the first one the summands are centered, in the second one the compound sums
are centered.",2303.08788v2
1994-12-25,Analysis of Japanese Compound Nouns using Collocational Information,"Analyzing compound nouns is one of the crucial issues for natural language
processing systems, in particular for those systems that aim at a wide coverage
of domains. In this paper, we propose a method to analyze structures of
Japanese compound nouns by using both word collocations statistics and a
thesaurus. An experiment is conducted with 160,000 word collocations to analyze
compound nouns of with an average length of 4.9 characters. The accuracy of
this method is about 80%.",9412008v1
1995-10-27,Lattice Dynamics of II-VI materials using adiabatic bond charge model,"We extend the adiabatic bond charge model, originally developed for group IV
semiconductors and III-V compounds, to study phonons in more ionic II-VI
compounds with a zincblende structure. Phonon spectra, density of states and
specific heats are calculated for six II-VI compounds and compared with both
experimental data and the results of other models. We show that the 6-parameter
bond charge model gives a good description of the lattice dynamics of these
materials. We also discuss trends in the parameters with respect to the
ionicity and metallicity of these compounds.",9510155v1
2000-04-14,The electronic structure of CuSiO3 - a possible candidate for a new inorganic spin-Peierls compound ?,"Electronic structure calculations are presented for the well-known CuGeO3 and
the recently discovered isostructural CuSiO3 compounds. The magnitude of the
dispersion in chain direction is considerably smaller for CuSiO3, whereas the
main interchain couplings are rather similar in both compounds. Starting from
extended one-band tight-binding models fitted to the bandstructures, the
exchange integrals were estimated for both compounds in terms of a spatially
anisotropic Heisenberg model. Remarkable frustrating second neighbor couplings
are found both for intra- and inter-chain interactions. A magnetic moment of
about 0.35 Bohr-magneton is predicted for CuSiO3 in the Neel state.",0004239v1
2003-07-23,A novel approach to the crystal-field theory - the orbital magnetism in 3d-ion compounds,"We point out that the orbital magnetism has to be taken into account in the
description of real 3d-ion compounds. According to the developed by us the
Quantum-Atomistic Solid-State (QUASST) theory in compounds containing open
3d-/4f-/5f-shell atoms there exists a discrete atomic-like low-energy
electronic structure that predominantly determines electronic and magnetic
properties of the whole compound. The relatively weak intra-atomic spin-orbit
coupling is fundamentally important as it governs the low-energy discrete
electronic structure.",0307575v1
2003-09-30,"Spin glass anomalies in stoichiometric spin-chain oxides, Ca3CoXO6 (X = Rh, Ir and Co)","The results of ac susceptibility (chi) measurements for Ca3CoXO6 (X = Rh, Ir
and Co) compounds, containing spin-chains separated by Ca ions, are presented.
All these compounds exhibit an unusually large frequency dependence of ac chi,
in the vicinity of respective magnetic ordering temperatures, which is normally
not encountered in conventional spin-glasses. The frequency dependence of ac
chi, peak temperature is however found to obey Vogel-Fulcher relationship. The
results thus establish that these compounds are unusual spin-glasses, that too
among stoichiometric compounds presumably due to geometrical frustration.",0309702v1
2004-02-26,"Zinc-blende CaP, CaAs and CaSb as half-metals: A new route to magnetism in calcium compounds","Existence of ferromagnetism in bulk calcium compounds is discovered
theoretically. First-principles calculations of calcium phosphide, calcium
arsenide and calcium antimonide in the zinc-blende structure have been
performed to show the half-metallic ground state in each optimized stable
structure. Magnetism comes from spin-polarization of electrons in
  $p$-orbitals of P, As or Sb and $d$-orbitals of calcium atoms. The
half-metallicity is analogous to the half-metallic zinc-blende compounds, {\it
e.g.} CrAs or CrSb, but the predicted compounds become ferromagnetic without
transition metals. In (In$_{1-x}$Ca$_x$)Sb, the magnetism remains to be stable
in a range of the doping rate ($x>0.8$).",0402641v1
2004-12-15,"Magnetic behavior of the spin-chain compounds,Ca3CuIrO6 and Ca3CuRhO6","The spin-chain compounds, Ca3CuIrO6 and Ca3CuRhO6, crystallizing in a
K4CdCl6-derived monoclinic structure, are investigated by ac and dc
magnetization, isothermal remnant magnetization as well as heat capacity
measurements. The results reveal the existence of a magnetic ordering in the
vicinity of 15 K for both the compounds, but the transition appears to be of a
complex nature. The existence of a spin-glass component is strongly indicated
by the results. We propose that topological effects play a role on magnetism of
these compounds. The magnetic properties for these two compounds are
interestingly similar as though isoelectronic chemical substitution at the
octahedral coordination site does not significantly interfere in the magnetic
exchange process.",0412386v1
2005-06-01,"Crystal field states in conducting magnetic materials: NdAl2, UPd2Al3 and YbRh2Si2","The existence of CEF states and the magnetism in conducting compounds NdAl2,
UPd2Al3 and YbRh2Si2 is discussed. We point out that in metallic compounds
localized crystal-field states coexist with conduction electrons. These
compounds are physical realization of an anisotropic spin liquid, which in case
of the atomic-like configuration with an odd number of f electrons, is unstable
with respect to spin fluctuations for T->0K. YbRh2Si2 is discussed as a
compound with the Kramers doublet ground state with a very low magnetic
ordering temperature being a reason for the quantum critical point phenomena at
low T.",0506021v1
2007-03-09,"Crystal structure, magnetism, and bonding of the hexagonal compounds Pd$_{1.63}$Mn$_{0.37}$Si and Pd$_{1.82}$Mn$_{0.18}$Ge related to the Fe$_2$P structure","We have used single crystal X-ray diffraction methods to establish the
crystal structures of a compound in the Pd-Mn-Si system and in the Pd-Mn-Ge
system. The title compounds have structures related to the Fe$_2$P structure
type and are ferromagnetic with Curie temperatures above the room temperature.
Density functional electronic structure calculations help to understand the
nature of the local moment ferromagnetism in these compounds. However neither
the electronic structure calculations nor the magnetic measurements provide any
evidence of half-metallic behavior.",0703240v1
1996-08-26,Evaluation of the mean intensity of the P-odd mixing of nuclear compound states,"A temperature version of the shell-optical-model approach for describing the
low-energy compound-to-compound transitions induced by external single-particle
fields is given. The approach is applied to evaluate the mean intensity of the
P-odd mixing of nuclear compound states. Unified description for the mixing and
electromagnetic transitions allows one to evaluate the mean intensity without
the use of free parameters. The valence-mechanism contribution to the mentioned
intensity is also evaluated. Calculation results are compared with the data
deduced from cross sections of relevant neutron-induced reactions.",9608055v1
2007-06-02,Thermodynamic Properties of Ferromagnetic Mott- Insulators GaV4S8,"We present the results of the magnetic and specific heat measurements on V4
tetrahedral-cluster compound GaV4S8 between 2 to 300K. We find two transitions
related to a structural change at 42K followed by ferromagnetic order at 12K on
cooling. Remarkably similar properties were previously reported for the cluster
compounds of Mo4. These compounds show an extremely high density of low energy
excitations in their electronic properties. We explain this behavior in a
cluster compound as due to the reduction of coulomb repulsion among electrons
that occupy highly degenerate orbits of different clusters.",0706.0265v1
2007-08-10,Multi-channel algebraic scattering theory and the structure of exotic compound nuclei,"A Multi-Channel Algebraic Scattering (MCAS) theory is presented with which
the properties of a compound nucleus are found from a coupled-channel problem.
The method defines both the bound states and resonances of the compound
nucleus, even if the compound nucleus is particle unstable. All resonances of
the system are found no matter how weak and/or narrow. Spectra of mass-7 nuclei
and of {}^{15}F, and MCAS results for a radiative capture cross section are
presented.",0708.1354v1
2007-12-07,"Magnetocaloric effect in R2Ti3Ge4 (R = Gd, Tb and Er) Compounds","Heat capacity of polycrystalline R2Ti3Ge4 (R = Gd, Tb and Er) compounds
(Orthorhombic, Sm5Ge4-type, Space group Pnma) has been studied in the
temperature range of 1.8 K to 300 K in various applied magnetic fields. The
compounds with magnetic lanthanide elements show interesting low field
magnetism intrigued by possible presence of competing antiferromagnetic and
ferromagnetic interactions. The magnetocaloric effect in these compounds is
estimated from the field dependent heat capacity data. The magnetic entropy
change and the adiabatic temperature change in the vicinity of the magnetic
transition are found to be significant.",0712.1095v1
2008-07-11,Breakdown of half-metallic ferromagnetism in zinc-blende II-V compounds,"We investigated the electronic and magnetic properties of a series of
zinc-blend II-V compounds by carrying out density-functional-theory
calculations including spin-orbit couplings. Contrary to the case of CaN and
CaP, the half-metallic characteristics of the II-V compounds such as CaSb and
CaBi were found to be destroyed. Our analysis of the valence band structures of
CaAs, CaSb, and CaBi revealed a critical role of the spin-orbit coupling
interactions on the exchange-split band structure, thereby leading to breakdown
of the half-metallic ferromagnetism for the systems with heavier group V
elements in the zinc-blend II-V compounds.",0807.1778v1
2008-09-26,{Spin polarization tuning in Mn$_{x}$Fe$_{1-x}$Ge$_{3}$,"Experimentally, the intermetallic compound Mn$_{4}$FeGe$_{3}$ has been
recently shown to exhibit enhanced magnetic properties and spin polarization
compared to the Mn$_{5}$Ge$_{3}$ parent compound. The present {\em ab-initio}
study focusses on the effect of Fe substitution on the electronic and magnetic
properties of the compound. Our calculations reveal that the changes on the
Fermi surface of the doped compound are remarkable and provide explanations for
the enhanced spin-polarization observed. Finally, we show that it is indeed
possible to tune the degree of spin-polarization upon Fe doping, thus making
the Mn$_{1-x}$Fe$_{x}$Ge$_{3}$ intermetallic alloy very promising for future
spintronic applications.",0809.4680v1
2008-12-03,Relationship between the magnetic hyperfine field and the magnetic moment,"Based on experimental data it is shown, for some chosen alloys and compounds
of iron, that there is no one unique relationship between the 57Fe-site
magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead,
the Bhf-m plot consists of several branches, each of them being characteristic
of a given alloy or compound. Consequently, the effective proportionality
constant (hyperfine coupling constant) depends on the alloy system or compound,
and for a given alloy system or compound it depends on the composition or even
on the lattice site. Consequently, the scaling of Bhf into the underlying m
cannot be done a priopri.",0812.0671v1
2009-02-16,Phenomena of Time Resonances Explosions for the Compound-Clot Decays in High-Energy Nuclear Reactions,"The phenomenon of time resonances (or explosions) can explain the exponential
reduction of the energy, which is accompanied for the certain degree by slight
fluctuations under some conditions in the range of the energy strongly
overlapped compound-resonances. These resonant explosions correspond to
formation of several highly-exited non-exponentially decaying nuclear clots
(partial compound nuclei consisting of several small groups of projectile
nucleons and targets). This paper is a continuation and expansion of
theoretical authors' work, which is a more general self-consistent version of
the time-evolution approach in comparison with the traditional Izumo-Araseki
time compound-nucleus model.",0902.2665v1
2013-01-04,Romancing Mathematics with Chemistry - How Mathematical Trees Can Be Used to Synthesize Molecular Structures,"Structures of chemical compounds can be synthesized and categorized through
mathematical means. Organic compounds are suitable targets because of their
simple valences. Acyclic organic compounds made of hydrogen and second-row
elements C, N, O, and F are presented as an example. In five categories of
organic compounds, chemical structures can be generated exclusively and
exhaustively using ab initio methods. It is shown that mathematical variables
can serve as chemical symbols and mathematical equations are chemical structure
generators.",1301.0833v1
2013-03-14,Characteristics of Compound Multiplicity in 84^Kr_36 with various light and heavy targets at 1 GeV per nucleon,"Present article focuses on the interactions of 84 Kr 36 having kinetic energy
around 1 GeV per nucleon with NIKFI BR2 nuclear emulsion detectors targets,
that can reveal important features of some compound multiplicity. The
observation showed that the width of the compound multiplicity distributions
and value of the mean compound multiplicity have linear relation with the mass
number of the projectile as well as colliding system.",1303.3362v1
2013-07-11,Tuning the giant inverse magnetocaloric effect in Mn2-xCrxSb compounds,"Structural, magnetic and magnetocaloric properties of Mn2-xCrxSb compounds
have been studied. In these compounds a first order magnetic phase transition
from the ferrimagnetic to the antiferromagnetic state occurs with decreasing
temperature, giving rise to giant inverse magnetocaloric effects that can be
tuned over a wide temperature interval through changes in substitution
concentration. Entropy changes as high as 7.5 J/kgK have been observed, and a
composition independent entropy change is obtained for several different
concentrations/working temperatures, making these compounds suitable candidates
for a composite working material.",1307.3194v1
2013-08-02,Phonon-induced topological insulating phases in group IV-VI semiconductors,"Development of topological insulating phases in IV-VI compounds under dynamic
lattice deformations is studied using first-principles methods. Unlike the
static state of topological phases at equilibrium conditions, we show that
non-trivial topological phases are induced in the compounds by the dynamic
lattice deformations from selective phonon modes. Calculations of the
time-reversal polarization show that the Z2 invariant of the compounds is
flipped by the atomic displacements of selective phonon modes and that the
compounds exhibit oscillating topological phases upon dynamic lattice
deformations. Our results indicate that the elementary excitations in solids
can trigger topological phases in trivial band insulators.",1308.0434v1
2013-09-14,High Throughput Screening of Natural Phenolic Compounds Against Migration of Metastatic Triple-Negative Breast Cancer (TNBC) Cells,"In this report, we hypothesize that natural phenolic compounds may present a
new class of chemotherapeutics against migration of metastatic triple-negative
breast cancers (TNBC). In this project we will screen a small library of
phenolic compounds to test this hypothesis, identify compounds that show
efficacy against TNBC cell migration, and elucidate underlying molecular
mechanisms.",1309.3626v2
2013-10-15,MBE grown microcavities based on selenium and tellurium compounds,"In this work, we present three groups of microcavities: based on selenium
compounds only, based on tellurium compounds only, and structures based on
mixed selenium and tellurium compounds. We focus on their possible applications
in the field of optoelectronic devices and fundamental physics (VCSELs, narrow
range light sources, studies of cavity-polariton electrodynamics) in a range of
wavelength from 540 to 760 nm.",1310.4015v1
2015-12-14,Superconductivity in the Niobium-rich compound Nb5Se4,"The niobium rich selenide compound Nb5Se4 was synthesized at ambient pressure
by high-temperature solid-state reaction in a sealed Ta tube. Resistivity and
heat capacity measurements reveal that this compound is superconducting, with a
T_c = 1.85K. The electronic contribution to the specific heat {\gamma} and the
Debye temperature are found to be 18.1 mJ/mol/K^2 and 298 K respectively. The
calculated electron-phonon coupling constant {\lambda}_ep = 0.5 and the
{\Delta}C_p/{\gamma}Tc = 1.42 ratio imply that Nb5Se4 is a weak coupling BCS
superconductor. The upper critical field and coherence length are found to be
1.44 T and 15.1 nm, respectively.",1512.04144v1
2016-08-02,Modelling and computation using NCoRM mixtures for density regression,"Normalized compound random measures are flexible nonparametric priors for
related distributions. We consider building general nonparametric regression
models using normalized compound random measure mixture models. Posterior
inference is made using a novel pseudo-marginal Metropolis-Hastings sampler for
normalized compound random measure mixture models. The algorithm makes use of a
new general approach to the unbiased estimation of Laplace functionals of
compound random measures (which includes completely random measures as a
special case). The approach is illustrated on problems of density regression.",1608.00874v3
2017-01-19,On Approximating Ruin Probability of Double Stochastic Compound Poisson Processes,"Consider a surplus process which both of collected premium and payed claim
size are two independent compound Poisson processes. This article derives two
approximated formulas for the ruin probability of such surplus process, say
double stochastic compound poisson process. More precisely, it provides two
mixture exponential approximations for ruin probability of such double
stochastic compound poisson process. Applications to long_term Bonus_Malus
systems and a heavy-tiled claim size distribution have been given. Improvement
of our findings compared to the Cramer- Lundberg upper bound has been given",1701.05536v1
2018-01-09,Quadrature Compound: An approximating family of distributions,"Compound distributions allow construction of a rich set of distributions.
Typically they involve an intractable integral. Here we use a quadrature
approximation to that integral to define the quadrature compound family.
Special care is taken that this approximation is suitable for computation of
gradients with respect to distribution parameters. This technique is applied to
discrete (Poisson LogNormal) and continuous distributions. In the continuous
case, quadrature compound family naturally makes use of parameterized
transformations of unparameterized distributions (a.k.a ""reparameterization""),
allowing for gradients of expectations to be estimated as the gradient of a
sample mean. This is demonstrated in a novel distribution, the diffeomixture,
which is is a reparameterizable approximation to a mixture distribution.",1801.03080v1
2018-06-08,Helium-iron compounds at terapascal pressures,"We investigate the binary phase diagram of helium and iron using
first-principles calculations. We find that helium, which is a noble gas and
inert at ambient conditions, forms stable crystalline compounds with iron at
terapascal pressures. A FeHe compound becomes stable above 4 TPa, and a
FeHe$_2$ compound above 12 TPa. Melting is investigated using molecular
dynamics simulations, and a superionic phase with sublattice melting of the
helium atoms is predicted. We discuss the implications of our predicted
helium-iron phase diagram for interiors of giant (exo)planets and white dwarf
stars.",1806.03017v1
2019-11-18,Universal superposition codes: capacity regions of compound quantum broadcast channel with confidential messages,"We derive universal codes for transmission of broadcast and confidential
messages over classical-quantum-quantum and fully quantum channels. These codes
are robust to channel uncertainties considered in the compound model. To
construct these codes we generalize random codes for transmission of public
messages, to derive a universal superposition coding for the compound quantum
broadcast channel. As an application, we give a multi-letter characterization
of regions corresponding to the capacity of the compound quantum broadcast
channel for transmitting broadcast and confidential messages simultaneously.
This is done for two types of broadcast messages, one called public and the
other common.",1911.07753v2
2019-11-27,Large-Scale Noun Compound Interpretation Using Bootstrapping and the Web as a Corpus,"Responding to the need for semantic lexical resources in natural language
processing applications, we examine methods to acquire noun compounds (NCs),
e.g., ""orange juice"", together with suitable fine-grained semantic
interpretations, e.g., ""squeezed from"", which are directly usable as
paraphrases. We employ bootstrapping and web statistics, and utilize the
relationship between NCs and paraphrasing patterns to jointly extract NCs and
such patterns in multiple alternating iterations. In evaluation, we found that
having one compound noun fixed yields both a higher number of semantically
interpreted NCs and improved accuracy due to stronger semantic restrictions.",1911.12085v1
2019-06-11,A Systematic Comparison of English Noun Compound Representations,"Building meaningful representations of noun compounds is not trivial since
many of them scarcely appear in the corpus. To that end, composition functions
approximate the distributional representation of a noun compound by combining
its constituent distributional vectors. In the more general case, phrase
embeddings have been trained by minimizing the distance between the vectors
representing paraphrases. We compare various types of noun compound
representations, including distributional, compositional, and paraphrase-based
representations, through a series of tasks and analyses, and with an extensive
number of underlying word embeddings. We find that indeed, in most cases,
composition functions produce higher quality representations than
distributional ones, and they improve with computational power. No single
function performs best in all scenarios, suggesting that a joint training
objective may produce improved representations.",1906.04772v1
2022-04-01,Compound matrices in systems and control theory: a tutorial,"The multiplicative and additive compounds of a matrix play an important role
in several fields of mathematics including geometry, multi-linear algebra,
combinatorics, and the analysis of nonlinear time-varying dynamical systems.
There is a growing interest in applications of these compounds, and their
generalizations, in systems and control theory. The goal of this tutorial paper
is to provide a gentle and self-contained introduction to these topics with an
emphasis on the geometric interpretation of the compounds, and to describe some
of their recent applications including several non-trivial generalizations of
positive systems, cooperative systems, contracting systems, and more.",2204.00676v1
2022-11-01,Two-color pulse compounds in waveguides with a zero-nonlinearity point,"We study incoherently coupled two-frequency pulse compounds in waveguides
with single zero-dispersion and zero-nonlinearity points. In such waveguides,
supported by a negative nonlinearity, soliton dynamics can be obtained even in
domains of normal dispersion. We demonstrate trapping of weak pulses by
solitary-wave wells, forming nonlinear-photonics meta-atoms, and molecule-like
bound-states of pulses. We study the impact of Raman effect on these pulse
compounds, finding that, depending on the precise subpulse configuration, they
decelerate, accelerate, or are completely unaffected. Our results extend the
range of systems in which two-frequency pulse compounds can be expected to
exist and demonstrate further unique and unexpected behavior.",2211.00530v1
2023-03-11,Semi-Tensor Product of Hypermatrices with Application to Compound Hypermatrices,"The semi-tensor product (STP) of matrices is extended to the STP of
hypermatrices. Some basic properties of the STP of matrices are extended to the
STP of hypermatrices. The hyperdeterminant of hypersquares is introduced. Some
algebraic and geometric structures of matrices are extended to hypermatrices.
Then the compound hypermatrix is proposed. The STP of hypermatrix is used to
compound hypermatrix. Basic properties are proved to be available for compound
hypermatrix.",2303.06295v1
2014-07-08,Effect of divalent Ba cation substitution with Sr on coupled multiglass state in the magnetoelectric multiferroic compound Ba3NbFe3Si2O14,"(Ba/Sr)3NbFe3Si2O14 is a magnetoelectric multiferroic with an incommensurate
antiferromagnetic spiral magnetic structure which induces electric polarization
at 26 K. The structure, as revealed by x-rays and neutrons, as well as static
and dynamic magnetic and dielectric properties of these compounds have been
studied down to 6 K under different conditions. Both the compounds have similar
crystal structure but with different lattice constants down to 6 K. The Ba-and
Sr-compounds exhibit a transition at 26 K and 25 K respectively, as indicated
by the specific heat capacity and dc specific magnetization, into an
antiferromagnetic state. Although Ba and Sr are isovalent, they exhibit very
different static and dynamic magnetic behavior. The Ba-compound exhibits both
thermal and magnetic field hysteresis with the thermal hysteresis decreasing
with increasing magnetic field, a behavior typical of glasses. The glassy
behavior is also clearly seen in the ac susceptibility studies which show a
dispersive peak in the range 40 K to 90 K in the frequency range 10^1 Hz to
10^4 Hz. The dispersive behavior follows a cluster glass critical slowing
dynamics with a freezing temperature of 35 K and a critical exponent of 3.9, a
value close to the 3-D Ising model. The Sr-compound however does not exhibit
any dispersive behavior except for the invariant transition at 25 K in ac
susceptibility with no magnetic field hysteresis at all temperatures. The
dielectric constant studied in the frequency range 10^1 Hz to 10^6 Hz also
reflects the magnetic behavior of the two compounds. The Ba-compound has two
distinct dispersive peaks near TN and in the range 40 K to 125 K while the
Sr-compound has a single dispersive peak in the range 40 K to 80 K. The
activation energy of the high temperature dispersive peak in both compounds
however is found to be similar, 71 meV and 65 meV respectively for Ba- and
Sr-compounds.",1407.2049v1
2022-09-08,Pathfinder -- Navigating and Analyzing Chemical Reaction Networks with an Efficient Graph-based Approach,"While the field of first-principles explorations into chemical reaction space
has been continuously growing, the development of strategies for analyzing
resulting chemical reaction networks (CRNs) is lagging behind. A CRN consists
of compounds linked by reactions. Analyzing how these compounds are transformed
into one another based on kinetic modeling is a nontrivial task. Here, we
present the graph-optimization-driven algorithm and program Pathfinder to allow
for such an analysis of a CRN. The CRN for this work has been obtained with our
open-source Chemoton reaction network exploration software. Chemoton probes
reactive combinations of compounds for elementary steps and sorts them into
reactions. By encoding these reactions of the CRN as a graph consisting of
compound and reaction vertices and adding information about activation barriers
as well as required reagents to the edges of the graph yields a complete
graph-theoretical representation of the CRN. Since the probabilities of the
formation of compounds depend on the starting conditions, the consumption of
any compound during a reaction must be accounted for to reflect the
availability of reagents. To account for this, we introduce compound costs to
reflect compound availability. Simultaneously, the determined compound costs
rank the compounds in the CRN in terms of their probability to be formed. This
ranking then allows us to probe easily accessible compounds in the CRN first
for further explorations into yet unexplored terrain. We first illustrate the
working principle on an abstract small CRN. Afterward, Pathfinder is
demonstrated in the example of the disproportionation of iodine with water and
the comproportionation of iodic acid and hydrogen iodide. Both processes are
analyzed within the same CRN which we construct with our autonomous
first-principles CRN exploration software Chemoton guided by Pathfinder.",2209.04039v2
2000-01-05,Study of Ce intermetallic compounds: an LDA classification and hybridization effects,"Spin-polarized calculations within the LDA approximation have been done with
the goal of characterizing Ce intermetallic compounds. Symmetry and chemical
environment effects on 4f hybridization and, thereafter, on magnetization
effects have been studied.",0001054v1
2006-07-26,"A Note On 3Solitary Wave Solutions of the Compound Burgers-Korteweg-de Vries Equation""","The goal of this note is to construct a class of traveling solitary wave
solutions for the compound Burgers-Korteweg-de Vries equation by means of a
hyperbolic ansatz.",0607680v1
2007-12-18,Chiral d-wave superconductivity in the heavy-fermion compound CeIrIn_5,"Recent thermal conductivity measurements in the heavy-fermion compound
CeIrIn_5 indicate that its superconducting order parameter is very different
from CeCoIn_5. Here we show that these experiments are consistent with chiral
d-wave symmetry.",0712.3058v1
2008-01-27,A note on the Compound Burgers-Korteweg-de Vries Equation with higher-order nonlinearities and its traveling solitary waves,"In this paper, we study a compound Korteweg-de Vries-Burgers equation with a
higher-order nonlinearity. A class of solitary wave solutions is obtained by
means of a series expansion.",0801.4121v1
2011-06-15,A Compound Determinant Identity for Rectangular Matrices,"A compound determinant identity for minors of rectangular matrices is
established. As an application, we derive Vandermonde type determinant formulae
for classical group characters.",1106.2915v1
2014-09-04,"Formation of Compound Flux Rope by The Merging of Two Filament Channels, Associated Dynamics and its Stability","We present the observations of compound flux rope formation via merging of
two nearby filament channels, associated dynamics and its stability that
occurred on 2014 January 1 using multiwavelength data. We have also discussed
the dynamics of cool and hot plasma moving along the newly formed compound flux
rope. The merging started after the interaction between the southern leg of
northward filament and the northern leg of the southward filament at around
01:21 UT and continue until a compound flux rope formed at around 01:33 UT.
During the merging the cool filaments plasma heated up and started to move
along the both side of the compound flux rope i.e., toward north (approx 265
km/s) and south (approx 118 km/s) from the point of merging. After travelling a
distance of approx 150 Mm towards north the plasma become cool and started to
returns back towards south ( approx 14 km/s) after 02:00 UT. The observations
provide an clear example of compound flux rope formation via merging of two
different flux ropes and occurrence of flare through tether cutting
reconnection. However, the compound flux rope remained stable in the corona and
made an confined eruption. The coronal magnetic field decay index measurements
revealed that both the filaments and the compound flux rope axis lies within
the stability domain (decay index less than 1.5), which may be the possible
cause for their stability. The present study also deals with the relationship
between the filaments chirality (sinistral) and the helicity (positive) of the
surrounding flux rope.",1409.1359v1
2015-01-29,Magnetocaloric effect in Gd3Ir compound,"Here we report magneto-thermal properties of Gd3Ir compounds using magnetic
and heat capacity data. We observed large isothermal entropy change, adiabatic
temperature change and relative cooling power are 4.1J/Kg, 4K and 437J/Kg on
50KOe respectively.",1501.07426v1
2015-09-17,The oldest example of compound interest in Sumer: Seventh power of four-thirds,"In the present paper I shall clarify that the origin of compound interest
goes back 4400 years to Sumer by showing the Sumerian scribe of Enmetena
Foundation Cone calculated seventh power of four-thirds.",1510.00330v1
2015-10-31,Limit distributions of sample covariance matrices are compound free Poisson,"We show that the empirical distribution of the eigenvalues of the sample
covariance matrix of certain random vectors (not necessarily independent
entries) with bounded marginal $L^{4}$ norms converges weakly to a compound
free Poisson distribution.",1511.00049v1
2015-12-09,Structural and antiferromagnetic properties of Ba(Fe$_{1-x-y}$Co$_x$Rh$_y$)$_2$As$_2$ compounds,"We present a systematic investigation of the electrical, structural, and
antiferromagnetic properties for the series of
Ba(Fe$_{1-x-y}$Co$_{x}$Rh$_{y}$)$_{2}$As$_{2}$ compounds with fixed $x \approx$
0.027 and $ 0 \leq y \leq 0.035$. We compare our results for the Co-Rh doped
Ba(Fe$_{1-x-y}$Co$_{x}$Rh$_{y}$)$_{2}$As$_{2}$ compounds with the Co doped
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ compounds. We demonstrate that the
electrical, structural, antiferromangetic, and superconducting properties of
the Co-Rh doped compounds are similar to the properties of the Co doped
compounds. We find that the overall behaviors of
Ba(Fe$_{1-x-y}$Co$_{x}$Rh$_{y}$)$_{2}$As$_{2}$ and
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ compounds are very similar when the total
number of extra electrons per Fe/$TM$ ($TM$ = transition metal) site is
considered, which is consistent with the rigid band model. Despite the
similarity, we find that the details of the transitions, for example, the
temperature difference between the structural and antiferromagnetic transition
temperatures and the incommensurability of the antiferromangetic peaks, are
different between Ba(Fe$_{1-x-y}$Co$_{x}$Rh$_{y}$)$_{2}$As$_{2}$ and
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ compounds.",1512.02974v1
2016-08-09,Strongly correlated Fermi systems as a new state of matter,"The aim of this review paper is to expose a new state of matter exhibited by
strongly correlated Fermi systems represented by various heavy-fermion (HF)
metals, two-dimensional liquids like $\rm ^3He$, compounds with quantum spin
liquids, quasicrystals, and systems with one-dimensional quantum spin liquid.
We name these various systems HF compounds, since they exhibit the behavior
typical of HF metals. In HF compounds at zero temperature the unique phase
transition, dubbed throughout as the fermion condensation quantum phase
transition (FCQPT) can occur; this FCQPT creates flat bands which in turn lead
to the specific state, known as the fermion condensate. Unlimited increase of
the effective mass of quasiparticles signifies FCQPT; these quasiparticles
determine the thermodynamic, transport and relaxation properties of HF
compounds. Our discussion of numerous salient experimental data within the
framework of FCQPT resolves the mystery of the new state of matter. Thus, FCQPT
and the fermion condensation can be considered as the universal reason for the
non-Fermi liquid behavior observed in various HF compounds. We show
analytically and using arguments based completely on the experimental grounds
that these systems exhibit universal scaling behavior of their thermodynamic,
transport and relaxation properties. Therefore, the quantum physics of
different HF compounds is universal, and emerges regardless of the microscopic
structure of the compounds. This uniform behavior allows us to view it as the
main characteristic of a new state of matter exhibited by HF compounds.",1608.02754v2
2017-04-27,"Crystal Growth of Cu6(Ge,Si)6O18.6H2O and Assignment of UV-VIS Spectra in Comparison to Dehydrated Dioptase and Selected Cu(II) Oxo-Compounds Including Cuprates","It is reported on growth of mm-sized single-crystals of the low-dimensional S
= 1/2 spin compound Cu6(Ge,Si)6O18.6H2O by a diffusion technique in aqueous
solution. A route to form Si-rich crystals down to possibly dioptase, the pure
silicate, is discussed. Further, the assignment of dd excitations from UV-VIS
spectra of the hexahydrate and the fully dehydrated compound is proposed in
comparison to dioptase and selected Cu(II) oxo-compounds using bond strength
considerations. Non-doped cuprates as layer compounds show higher excitation
energies than the title compound. However, when the antiferromagnetic
interaction energy as Jzln(2) is taken into account for cuprates, a single
linear relationship between the Dqe excitation energy and equatorial Cu(II)-O
bond strength is confirmed for all compounds. A linear representation is also
confirmed between 2A1g energies and a function of axial and equatorial Cu-O
bond distances, when auxiliary axial bonds are used for four-coordinated
compounds. The quotient Dt/Ds of experimental orbital energies deviating from
the general trend to smaller values indicates the existence of H2O respectively
Cl1- axial ligands in comparison to oxo-ligands, whereas larger Dt/Dqe values
indicate missing axial bonds. The quotient of the excitation energy 2A1g by
2x2Eg-2B2g allows to check for correctness of the assignment and to distinguish
between axial oxo-ligands and others like H2O or Cl1-. Some assignments
previously reported were corrected.",1705.00526v1
2018-10-18,The role of decomposition reactions in assessing first-principles predictions of solid stability,"The performance of density functional theory (DFT) approximations for
predicting materials thermodynamics is typically assessed by comparing
calculated and experimentally determined enthalpies of formation from elemental
phases, {\Delta}Hf. However, a compound competes thermodynamically with both
other compounds and their constituent elemental forms, and thus, the enthalpies
of the decomposition reactions to these competing phases, {\Delta}Hd,
determines thermodynamic stability. We evaluated the phase diagrams for 56,791
compounds to classify decomposition reactions into three types: 1. those that
produce elemental phases, 2. those that produce compounds, and 3. those that
produce both. This analysis shows that the decomposition into elemental forms
is rarely the competing reaction that determines compound stability and that
approximately two-thirds of decomposition reactions involve no elemental
phases. Using experimentally reported formation enthalpies for 1,012 solid
compounds, we assess the accuracy of the generalized gradient approximation
(GGA) (PBE) and meta-GGA (SCAN) density functionals for predicting compound
stability. For 646 decomposition reactions that are not trivially the formation
reaction, PBE (MAD = 70 meV/atom) and SCAN (MAD = 59 meV/atom) perform
similarly, and commonly employed correction schemes using fitted elemental
reference energies make only a negligible improvement (~2 meV/atom).
Furthermore, for 231 reactions involving only compounds (Type 2), the agreement
between SCAN, PBE, and experiment is within ~35 meV/atom and is thus comparable
to the magnitude of experimental uncertainty.",1810.08248v2
2017-06-11,"Structural, elastic, electronic, and bonding properties of intermetallic Nb3Pt and Nb3Os compounds: a DFT study","Theoretical investigation of structural, elastic, electronic and bonding
properties of A-15 Nb-based intermetallic compounds Nb3B (B = Pt, Os) have been
performed using first principles calculations based on the density functional
theory (DFT). Optimized cell parameters are found to be in good agreement with
available experimental and theoretical results. The elastic constants at zero
pressure and temperature are calculated and the anisotropic behaviors of the
compounds are studied. Both the compounds are mechanically stable and ductile
in nature. Other elastic properties such as Pugh's ratio, Cauchy pressure,
machinability index are derived for the first time. Nb3Os is expected to have
good lubricating properties compared to Nb3Pt. The electronic band structure
and energy density of states (DOS) have been studied with and without
spin-orbit coupling (SOC). The band structures of both the compounds are spin
symmetric. Electronic band structure and DOS reveal that both the compounds are
metallic and the conductivity mainly arise from the Nb 4d states. The Fermi
surface features have been studied for the first time. The Fermi surfaces of
Nb3B contain both hole- and electron-like sheets which change as one replaces
Pt with Os. The electronic charge density distribution shows that Nb3Pt and
Nb3Os both have a mixture of ionic and covalent bonding. The charge transfer
between atomic species in these compounds has been explained by the Mulliken
bond population analysis.",1706.03314v1
2019-08-22,Dynamics and stability of a compound particle -- a theoretical study,"Particles confined in droplets are called compound particles. They are
encountered in various biological and soft matter systems. Hydrodynamics can
play a decisive role in determining the configuration and stability of these
multiphase structures during their preparation and use. Therefore, we
investigate the dynamics and stability of a concentric compound particle under
external forces and imposed flows. Governing equations are solved analytically
in the inertia-less limit using the standard technique of superposition of
vector harmonics and the solutions obtained are reported in terms of steady
state flow fields, viscous drag on the particle and the time evolution of the
confining drop shape. The limiting form of compound particle as a thin film
coated rigid particle is analyzed in each case. We find that concentric
configuration of a rotating compound particle is a steady state solution, and
we calculate the extra force required to stabilize the concentric configuration
of a translating compound particle. A comprehensive comparison of drop
deformations in various linear ambient flows is also provided. Based on the
findings, we propose pulsatile flow as a reliable method to transport compound
particles without breakup of the confining drop. Thus, our analysis provides
useful guidelines in preparation and transportation of stable compound
particles in the context of nucleated cells, aerosols, droplet-based
encapsulation of motile organisms and polymer microcapsules.",1908.08202v1
2020-07-31,Product systems associated to compound Poisson Processes,"In this paper, we consider a simple test case of multiparameter product
systems that arise out of random measures. We associate a product system to a
stationary Poisson process and a stationary compound Poisson process. We show
that the resulting $E_0$-semigroups are CCR flows.",2007.15844v1
2021-09-30,Synthesis and structure of carbon doped H3S compounds at high pressure,"Understanding of recently reported putative close-to-room-temperature
superconductivity in C-S-H compounds at 267 GPa demands reproducible synthesis
protocol as well as knowledge of its structure and composition. We synthesized
C-S-H compounds with various carbon composition at high pressures from
elemental C and methane CH4, sulfur S, and molecular hydrogen H2. Here we focus
on compounds synthesized using methane as these allow a straightforward
determination of their structure and composition by combining single-crystal
X-ray diffraction (XRD) and Raman spectroscopy. We applied a two-stage
synthesis of ((CH4)x(H2S)(1-x))2H2 compounds by first reacting sulfur and mixed
methane-hydrogen fluids and forming CH4 doped H2S crystals at 0.5-3 GPa, and
then by growing single crystals of the desired hydrogen rich compound. Raman
spectroscopy applied to this material shows the presence of the CH4 molecules
incorporated into the lattice and allows to determine the CH4 content, while
single-crystal X-ray diffraction results suggest that the methane molecules
substitute H2S ones. The structural behavior of these compounds is very similar
to the previously investigated methane free compounds demonstrating a
transition from Al2Cu type I4/mcm structure to a modulated structure at 20-30
GPa and back to the same basic structure in an extended modification with
greatly modified Raman spectra. This latter phase demonstrates a distortion
into Pnma structure at 132-159 GPa and then transforms into a common Im-3m H3S
phase at higher pressures, however, no structural anomaly is detected near 220
GPa, where a sharp upturn in Tc has been reported.",2110.00038v1
2022-11-07,ToDD: Topological Compound Fingerprinting in Computer-Aided Drug Discovery,"In computer-aided drug discovery (CADD), virtual screening (VS) is used for
identifying the drug candidates that are most likely to bind to a molecular
target in a large library of compounds. Most VS methods to date have focused on
using canonical compound representations (e.g., SMILES strings, Morgan
fingerprints) or generating alternative fingerprints of the compounds by
training progressively more complex variational autoencoders (VAEs) and graph
neural networks (GNNs). Although VAEs and GNNs led to significant improvements
in VS performance, these methods suffer from reduced performance when scaling
to large virtual compound datasets. The performance of these methods has shown
only incremental improvements in the past few years. To address this problem,
we developed a novel method using multiparameter persistence (MP) homology that
produces topological fingerprints of the compounds as multidimensional vectors.
Our primary contribution is framing the VS process as a new topology-based
graph ranking problem by partitioning a compound into chemical substructures
informed by the periodic properties of its atoms and extracting their
persistent homology features at multiple resolution levels. We show that the
margin loss fine-tuning of pretrained Triplet networks attains highly
competitive results in differentiating between compounds in the embedding space
and ranking their likelihood of becoming effective drug candidates. We further
establish theoretical guarantees for the stability properties of our proposed
MP signatures, and demonstrate that our models, enhanced by the MP signatures,
outperform state-of-the-art methods on benchmark datasets by a wide and highly
statistically significant margin (e.g., 93% gain for Cleves-Jain and 54% gain
for DUD-E Diverse dataset).",2211.03808v1
2023-02-08,Orbitally driven spin reorientation in Mn doped YBaCuFeO$_{5}$,"Oxygen-deficient layered perovskite YBaCuFeO$_{5}$ (YBCFO) is one rare
type-II multiferroic material where ferroelectricity, driven by incommensurate
spiral magnetic order, is believed to be achievable up to temperatures higher
than room temperature. A cycloidal spiral rather than helical spiral order is
essential ingredient for the existence of ferroelectricity in this material.
Motivated by a recent experimental work on Mn-doped YBCFO where the spiral
plane is observed to cant more towards the crystallographic $c$ axis upon Mn
doping at Fe sites compared to that in the parent compound, we performed a
detailed theoretical investigation using the density functional theory
calculations to understand the mechanism behind such spin reorientation. Our
total energy calculations, within GGA+U+SO approximation, reveal that Fe/Cu
spin moments indeed align more towards $c$ axis in the Mn-doped compounds than
they were in parent compound YBCFO. Largest exchange interaction (Cu-Cu in the
$ab$-plane) is observed to decrease systematically with Mn doping concentration
reflecting the lowering of transition temperature seen in experiment. Further,
the inter-bilayer Cu-Mn exchange interaction becomes ferromagnetic in the doped
compound whereas the corresponding Cu-Fe exchange was antiferromagnetic in the
parent compound giving rise to frustration in the commensurate magnetic order.
Most importantly, our electronic structure calculations reveal that in the
doped compounds because of hybridization with the d$_{z^2}$ orbital of Mn, the
highest occupied Cu orbital becomes d$_{z^2}$ as opposed to the parent compound
where the highest occupied Cu orbital is d$_{x^2-y^2}$. Therefore, we believe
that the occupancy of out of plane oriented Cu d$_{z^2}$ orbital in place of
planar d$_{x^2-y^2}$ orbital along with the frustrating exchange interaction
drive the spins to align along $c$ in doped compound.",2302.04072v1
2023-05-23,CompoundPiece: Evaluating and Improving Decompounding Performance of Language Models,"While many languages possess processes of joining two or more words to create
compound words, previous studies have been typically limited only to languages
with excessively productive compound formation (e.g., German, Dutch) and there
is no public dataset containing compound and non-compound words across a large
number of languages. In this work, we systematically study decompounding, the
task of splitting compound words into their constituents, at a wide scale. We
first address the data gap by introducing a dataset of 255k compound and
non-compound words across 56 diverse languages obtained from Wiktionary. We
then use this dataset to evaluate an array of Large Language Models (LLMs) on
the decompounding task. We find that LLMs perform poorly, especially on words
which are tokenized unfavorably by subword tokenization. We thus introduce a
novel methodology to train dedicated models for decompounding. The proposed
two-stage procedure relies on a fully self-supervised objective in the first
stage, while the second, supervised learning stage optionally fine-tunes the
model on the annotated Wiktionary data. Our self-supervised models outperform
the prior best unsupervised decompounding models by 13.9% accuracy on average.
Our fine-tuned models outperform all prior (language-specific) decompounding
tools. Furthermore, we use our models to leverage decompounding during the
creation of a subword tokenizer, which we refer to as CompoundPiece.
CompoundPiece tokenizes compound words more favorably on average, leading to
improved performance on decompounding over an otherwise equivalent model using
SentencePiece tokenization.",2305.14214v2
2023-10-13,Study of the Physical Properties of the EuCoA$_2$As$_2$ Compound: A DFT approach,"In this study, we carried out an investigation of the EuCoA$_2$As$_2$
compound, focusing on its various physical properties. Our analysis covered the
structural, magnetic, electronic, optical, thermodynamic and thermoelectric
characteristics of this compound. To carry out this study, we used density
functional theory (DFT) implemented in the Wien2k software package. To
determine the exchange-correlation potential, we used the GGA-PBE (Perdew,
Burke and Ernzerhof) approach, taking spin-orbit coupling (SOC) into account.
Our results indicate that the EuCoA$_2$As$_2$ compound exhibits metallic
behavior. In addition, we have determined that the compound's stable ground
state is the ferromagnetic (FM) phase. We have also calculated the Debye
temperature and the Gr\""uneisen parameter. In addition, we evaluated various
optical properties, including electron energy loss, absorption coefficient,
real and imaginary dielectric tensors, and real and imaginary optical
conductivity. We found that the compound has excellent absorption
characteristics in the low and mid ultraviolet (UV) spectra. In addition, we
investigated the electrical conductivity, Seebeck coefficient, electronic
conductivity and thermal conductivity of the lattice. The results revealed that
the compound exhibits n-type behavior, with negative values for the Seebeck
coefficient. These results are analyzed in detail and provide valuable
information on the properties of the EuCoA$_2$As$_2$ compound. Additionally,
the computed parameters were compared to those found in the literature. A good
deals have been revealed with the existing results.",2310.09007v1
2006-09-15,"Large magnetoresistance in intermetallic compounds R2Mn3Si5 (R = Tb, Dy and Ho)","Magnetization (M) and magnetoresistance (MR) measurements on polycrystalline
R2Mn3Si5 (R = Tb, Dy and Ho) compounds (tetragonal, space group P4/mnc) have
been carried out in the temperature range of 2 K-300 K, in various applied
fields. Both, the rare earth and the Mn, are found to carry magnetic moments in
these compounds. Mn has two sub-lattices (Mn1 and Mn2) that order magnetically
at two different temperatures. Rare earth and Mn1 moments order
ferromagnetically at TC1 whereas Mn2 is found to magnetically order at TC2 (TC1
= 89 K, 86 K, 78 K and TC2 = 18 K, 34 K, 16 K for R = Tb, Dy and Ho compounds,
respectively). Magnetoresistance measurements reveal large negative MR values
of about 50 % near TC2 at 9 T in all these compounds. This giant
magnetoresistance is attributed to the spin-dependent scattering effects,
competing exchange interactions and the layered structure of these compounds",0609358v1
2006-05-18,Second quantization method in the presence of bound states of particles,"We develop an approximate second quantization method for describing the
many-particle systems in the presence of bound states of particles at low
energies (the kinetic energy of particles is small in comparison to the binding
energy of compound particles). In this approximation the compound and
elementary particles are considered on an equal basis. This means that creation
and annihilation operators of compound particles can be introduced. The
Hamiltonians, which specify the interactions between compound and elementary
particles and between compound particles themselves are found in terms of the
interaction amplitudes for elementary particles. The nonrelativistic quantum
electrodynamics is developed for systems containing both elementary and
compound particles. Some applications of this theory are considered.",0605159v1
2008-05-23,Magnetism in Gallium doped CeFe_2: The martensitic scenario,"Ce(Fe_{1-x}Ga_x)_2 compounds with x = 0, 0.01, 0.025 and 0.05 have been
investigated to unravel the effect of Ga on the magnetic state of CeFe_2. For
the first time, we find that the dynamic antiferromagnetic phase present in
CeFe_2 gets stabilized with Ga substitution. The hysteresis loops show that
while the compounds with x = 0 and 0.01 show normal behavior, the other two
show multiple magnetization steps across the antiferromagnetic-ferromagnetic
transition region. The virgin curve is found to lie outside the envelope curve
in these two compounds, similar to the observations made in Ru and Re
substituted CeFe_2 compounds. Temperature, sweep rate and time dependences of
the magnetization show that the compounds with x >=0.025 possess glassy
behavior at low temperatures. Various results obtained reveal that these two
compounds belong to the martensite family.",0805.3589v1
2008-08-07,On Quantum Capacity of Compound Channels,"In this paper we address the issue of universal or robust communication over
quantum channels. Specifically, we consider memoryless communication scenario
with channel uncertainty which is an analog of compound channel in classical
information theory. We determine the quantum capacity of finite compound
channels and arbitrary compound channels with informed decoder. Our approach in
the finite case is based on the observation that perfect channel knowledge at
the decoder does not increase the capacity of finite quantum compound channels.
As a consequence we obtain coding theorem for finite quantum averaged channels,
the simplest class of channels with long-term memory. The extension of these
results to quantum compound channels with uninformed encoder and decoder, and
infinitely many constituents remains an open problem.",0808.1007v1
2009-03-09,"Thermal and Transport Behavior of Single Crystalline R2CoGa8 (R = Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) Compounds","The anisotropy in electrical transport and thermal behavior of single
crystalline R$_{2}$CoGa$_{8}$ series of compounds is presented. These compounds
crystallize in a tetragonal structure with space gropup P4/mmm. The nonmagnetic
counterparts of the series namely Y$_{2}$CoGa$_{8}$ and Lu$_{2}$CoGa$_{8}$show
a behavior consistent with the low density of states at the fermi level. In
Y$_{2}$CoGa$_{8}$, a possibility of charge density wave transition is observed
at $\approx$ 30 K. Gd$_{2}$CoGa$_{8}$ and Er$_{2}$CoGa$_{8}$ show a presence of
short range correlation above the magnetic ordering temperature of the
compound. In case of Gd$_{2}$CoGa$_{8}$, the magnetoresistance exhibits a
significant anisotropy for current parallel to {[}100{]} and {[}001{]}
directions. Compounds with other magnetic rare earths (R = Tb, Dy, Ho and Tm)
show the normal expected magnetic behavior whereas Dy$_{2}$CoGa$_{8}$ exhibits
the possibility of charge density wave (CDW) transition at approximately same
temperature as that of Y$_{2}$CoGa$_{8}$. The thermal property of these
compounds is analysed on the basis of crystalline electric field (CEF)
calculations.",0903.1607v1
2010-09-03,"Structural, Elastic, Electronic and Optical Properties of a New Layered-Ternary Ta4SiC3 Compound","We propose a new layered-ternary Ta4SiC3 with two different stacking
sequences ({\alpha}- and {\beta}-phases) of the metal atoms along c axis and
study their structural stability. The mechanical, electronic and optical
properties are then calculated and compared with those of other compounds M4AX3
(M = V, Nb, Ta; A = Al, Si and X = C). The predicted compound in the
{\alpha}-phase is found to possess higher hardness than any of these compounds.
The independent elastic constants of the two phases are also evaluated and the
results discussed. The electronic band structures for {\alpha}- and
{\beta}-Ta4SiC3 show metallic conductivity. Ta 5d electrons are mainly
contributing to the total density of states (DOS). We see that the
hybridization peak of Ta 5d and C 2p lies lower in energy and the Ta 5d-C 2p
bond is stronger than Ta 5d-Si 3p bond. Further an analysis of the different
optical properties shows the compound to possess improved behavior compared to
similar types of compounds.",1009.0595v1
2011-08-24,Compound p-Value Statistics for Multiple Testing Procedures,"Many multiple testing procedures make use of the p-values from the individual
pairs of hypothesis tests, and are valid if the p-value statistics are
independent and uniformly distributed under the null hypotheses. However, it
has recently been shown that these types of multiple testing procedures are
inefficient since such p-values do not depend upon all of the available data.
This paper provides tools for constructing compound p-value statistics, which
are those that depend upon all of the available data, but still satisfy the
conditions of independence and uniformity under the null hypotheses. As an
example, a class of compound p-value statistics for testing for location shifts
is developed. It is demonstrated, both analytically and through simulations,
that multiple testing procedures tend to reject more false null hypotheses when
applied to these compound p-values rather than the usual p-values, and at the
same time still guarantee the desired type I error rate control. The compound
p-values, in conjunction with two different multiple testing methods, are used
to analyze a real microarray data set. Applying either multiple testing method
to the compound p-values, instead of the usual p-values, enhances their powers.",1108.4848v1
2014-10-02,Compound random measures and their use in Bayesian nonparametrics,"A new class of dependent random measures which we call {\it compound random
measures} are proposed and the use of normalized versions of these random
measures as priors in Bayesian nonparametric mixture models is considered.
Their tractability allows the properties of both compound random measures and
normalized compound random measures to be derived. In particular, we show how
compound random measures can be constructed with gamma, $\sigma$-stable and
generalized gamma process marginals. We also derive several forms of the
Laplace exponent and characterize dependence through both the L\'evy copula and
correlation function. A slice sampler and an augmented P\'olya urn scheme
sampler are described for posterior inference when a normalized compound random
measure is used as the mixing measure in a nonparametric mixture model and a
data example is discussed.",1410.0611v3
2014-11-02,Capacity Region Continuity of the Compound Broadcast Channel with Confidential Messages,"The compound broadcast channel with confidential messages (BCC) generalizes
the BCC by modeling the uncertainty of the channel. For the compound BCC, it is
only known that the actual channel realization belongs to a pre-specified
uncertainty set of channels and that it is constant during the whole
transmission. For reliable and secure communication is necessary to operate at
a rate pair within the compound BCC capacity region. Therefore, the question
whether small variations of the uncertainty set lead to large losses of the
compound BCC capacity region is studied. It is shown that the compound BCC
model is robust, i.e., the capacity region depends continuously on the
uncertainty set.",1411.0294v2
2014-11-17,"RRhGe (R=Tb, Dy, Er, Tm): An experimental and theoretical study","RRhGe (R=Tb, Dy, Er, Tm) compounds have been studied by a number of
experimental probes and theoretical ab initio calculations. These compounds
show very interesting magnetic and electrical properties. All the compounds are
antiferromagnetic with some of them showing spin-reorientation transition at
low temperatures. The magnetocaloric effect (MCE) estimated from magnetization
data shows very good value in all these compounds. The electrical resistivity
shows metallic behavior of these compounds. MR shows negative sign near
ordering temperatures and positive at low temperatures. The electronic
structure calculations accounting for electronic correlations in the 4f
rare-earth shell reveal the closeness of the antiferromagnetic ground state and
other types of magnetic orderings in the rare-earth sublattice.",1411.4432v1
2015-04-29,Half-metallic ferromagnetism in the RbSe and CsTe compounds with CsCl structure: A first-principles study,"We investigate the electronic structures and magnetic properties of RbSe and
CsTe compounds in CsCl, RS and ZB structures by using first-principles
calculation. It is shown that these two compounds exhibit half-metallic
ferromagnetism with an integer magnetic moment of 1.00 $\mu_B$ per formula in
all the three structures. Total energy calculations indicate the CsCl phase is
more stable than the other two phases. We investigate these two compounds with
CsCl structure in detail. The ferromagnetism results mainly from the
spin-polarization of p states of anion Se (Te) for the two compounds. The
half-metallicities of RbSe and CsTe compounds can be preserved up to 2.5\% and
0.8\% compression of lattice constants with respect to their equilibrium
lattices, respectively.",1504.07705v1
2015-06-09,Poisson Processes in Free Probability,"We prove a multidimensional Poisson limit theorem in free probability, and
define joint free Poisson distributions in a non-commutative probability space.
We define (compound) free Poisson process explicitly, similar to the
definitions of (compound) Poisson processes in classical probability. We proved
that the sum of finitely many freely independent compound free Poisson
processes is a compound free Poisson processes. We give a step by step
procedure for constructing a (compound) free Poisson process. A Karhunen-Loeve
expansion theorem for centered free Poisson processes is proved. We generalize
free Poisson processes to a notion of free Poisson random measures (which is
slightly different from the previously defined ones in free probability, but
more like an analogue of classical Poisson random measures). Then we develop
the integration theory of real-valued functions with respect to a free Poisson
random measure, generalizing the classical integration theory to the free
probability case. We find that the integral of a function (in certain spaces of
functions) with respect to a free Poisson random measure has a compound free
Poisson distribution. For centered free Poisson random measures, we can get a
simpler and more beautiful integration theory.",1506.03130v2
2015-09-07,Compound surface-plasmon-polariton waves guided by a thin metal layer sandwiched between a homogeneous isotropic dielectric material and a structurally chiral material,"Multiple compound surface plasmon-polariton (SPP) waves can be guided by a
structure consisting of a sufficiently thick layer of metal sandwiched between
a homogeneous isotropic dielectric (HID) material and a dielectric structurally
chiral material (SCM). The compound SPP waves are strongly bound to both
metal/dielectric interfaces when the thickness of the metal layer is comparable
to the skin depth but just to one of the two interfaces when the thickness is
much larger. The compound SPP waves differ in phase speed, attenuation rate,
and field profile, even though all are excitable at the same frequency. Some
compound SPP waves are not greatly affected by the choice of the direction of
propagation in the transverse plane but others are, depending on metal
thickness. For fixed metal thickness, the number of compound SPP waves depends
on the relative permittivity of the HID material, which can be useful for
sensing applications.",1509.02079v2
2016-01-27,Secret-Key Generation Using Compound Sources and One-Way Public Communication,"In the classical Secret-Key generation model, Common Randomness is generated
by two terminals based on the observation of correlated components of a common
source, while keeping it secret from a non-legitimate observer. It is assumed
that the statistics of the source are known to all participants. In this work,
the Secret-Key generation based on a compound source is studied where the
realization of the source statistic is unknown. The protocol should guarantee
the security and reliability of the generated Secret-Key, simultaneously for
all possible realizations of the compound source. A single-letter lower-bound
of the Secret-Key capacity for a finite compound source is derived as a
function of the public communication rate constraint. A multi-letter capacity
formula is further computed for a finite compound source for the case in which
the public communication is unconstrained. Finally a single-letter capacity
formula is derived for a degraded compound source with an arbitrary set of
source states and a finite set of marginal states.",1601.07513v1
2016-05-18,Structural evolution of MnTi0.8Ru0.2O3,"Here We present the structural studies on MnTi1-xRuxO3(x=0, 0.2) compounds.
The role of Ti ions in the magnetism of MnTiO3 was unclear so here this issue
has been tried to address in this manuscript. The magnetic susceptibility data
shows that the 3-dimensional magnetic character has been improved in the doped
MnTiO3. The x=0 compound goes paramagnetic to antiferromagnetic phase at a
temperature 64K followed by a broad peak at a temperature 100K . But in x=0.2
compound the antiferromagnetic transition temperature has been shifted towards
the lower temperature to 47.5K with a broad peak at temperature 79K. On the
doping of Ru at Ti site a sharp anomaly is observed 47.5K in the case of x=0.2
compound. This sharp anomaly attributes to the improved 3D character of
magnetism in this compound which is weak in x=0 compound.",1605.05636v1
2017-11-09,Predicted bulk photovoltaic effect in hydrogenated Zintl compounds,"The bulk photovoltaic effect (BPVE) is a phenomenon which creates a net
electrical current from sunlight in a polar noncentrosymmetric material
possessing a moderate band gap. This effect is being explored as an alternative
to traditional pn-junction solar cells to convert solar energy into
electricity. This paper assesses the possibility that hydrogenated Zintl-phase
compounds consisting only of metal, metalloid, and hydrogen atoms, may be able
to provide a BPVE response. Towards this end, the magnitude of the BPVE shift
current is calculated for each of the compounds AeTrTtH (Ae = Ca, Sr, and Ba;
Tr = Al and Ga; and Tt = Si, Ge, and Sn). For this family of hydogenated Zintl
compounds, maximum shift current responses are predicted that are up to eight
times greater than that calculated for BiFeO3, and have a significant response
down to much lower photon energies than BiFeO3 as well. With band gaps below 1
eV, and with some members of this family of compounds exhibiting stability in
air up to 770 K, some of these compounds may find use in photovoltaic devices.",1711.04647v1
2018-09-27,Competing rhombohedral and monoclinic crystal structures in Mn$Pn_2Ch_4$ compounds: an {\em ab-initio} study,"Based on the relativistic spin-polarized density functional theory
calculations we investigate the crystal structure, electronic and magnetic
properties of a family MnPn2Ch4 compounds, where pnictogen metal atoms (Pn) are
Sb and Bi; chalcogens (Ch) are Se, Te. We show that in the series the compounds
of this family with heavier elements prefer to adopt rhombohedral crystal
structure composed of weakly bonded septuple monoatomic layers while those with
lighter elements tend to be in the monoclinic structure. Irrespective of the
crystal structure all compounds of the MnPn2Ch4 series demonstrate a weak
energy gain (of a few meV per formula unit or even smaller than meV) for
antiferromagnetic (AFM) coupling for magnetic moments on Mn atoms with respect
to their ferromagnetic (FM) state. For rhombohedral structures the interlayer
AFM coupling is preferable while in monoclinic phases intralayer AFM
configuration with ferromagnetic ordering along the Mn chain and
antiferromagnetic ordering between the chains has a minimum energy. Over the
series the monoclinic compounds are characterized by substantially wider
bandgap than compounds with rhombohedral structure.",1809.10343v1
2019-11-20,Paraphrasing Verbs for Noun Compound Interpretation,"An important challenge for the automatic analysis of English written text is
the abundance of noun compounds: sequences of nouns acting as a single noun. In
our view, their semantics is best characterized by the set of all possible
paraphrasing verbs, with associated weights, e.g., malaria mosquito is carry
(23), spread (16), cause (12), transmit (9), etc. Using Amazon's Mechanical
Turk, we collect paraphrasing verbs for 250 noun-noun compounds previously
proposed in the linguistic literature, thus creating a valuable resource for
noun compound interpretation. Using these verbs, we further construct a dataset
of pairs of sentences representing a special kind of textual entailment task,
where a binary decision is to be made about whether an expression involving a
verb and two nouns can be transformed into a noun compound, while preserving
the sentence meaning.",1911.08762v1
2020-01-07,A semi-supervised learning framework for quantitative structure-activity regression modelling,"Supervised learning models, also known as quantitative structure-activity
regression (QSAR) models, are increasingly used in assisting the process of
preclinical, small molecule drug discovery. The models are trained on data
consisting of a finite dimensional representation of molecular structures and
their corresponding target specific activities. These models can then be used
to predict the activity of previously unmeasured novel compounds. In this work
we address two problems related to this approach. The first is to estimate the
extent to which the quality of the model predictions degrades for compounds
very different from the compounds in the training data. The second is to adjust
for the screening dependent selection bias inherent in many training data sets.
In the most extreme cases, only compounds which pass an activity-dependent
screening are reported. By using a semi-supervised learning framework, we show
that it is possible to make predictions which take into account the similarity
of the testing compounds to those in the training data and adjust for the
reporting selection bias. We illustrate this approach using publicly available
structure-activity data on a large set of compounds reported by GlaxoSmithKline
(the Tres Cantos AntiMalarial Set) to inhibit in vitro P. falciparum growth.",2001.01924v1
2018-10-02,Topological insulators vs. topological Dirac semimetals in honeycomb compounds,"Intriguing physical property of materials stems from their chemical
constituent whereas the connection between them is often not clear. Here, we
uncover a general chemical classification for the two quantum phases in the
honeycomb ABX structure--topological insulator (TI) and topological Dirac
semimetal (TDSM). First, we find among the 816 (existing as well as
hypothetical) calculated compounds, 160 TI's (none were noted before), 96
TDSM's, 282 normal insulators (NI's), and 278 metals. Second, based on this
classification, we have distilled a simple chemical regularity based on
compound formulae for the selectivity between TI and TDSM: The ABX compounds
that are TDSM have B atoms (part of the BX honeycomb layers) that come from the
Periodic Table columns XI (Cu, Ag, Au) or XII (Zn, Cd, Hg), or Mg (group II),
whereas the ABX compounds whose B atoms come from columns I (Li, Na, K, Rb, Cs)
or II (Ca, Sr, Ba) are TI's. Third, focusing on the ABX Bismide compounds that
are thermodynamically stable, we find a structural motif that delivers
topological insulation and stability at the same time. This study opens the way
to simultaneously design new topological materials based on the compositional
rules indicated here.",1810.01044v1
2020-04-16,Kvistur 2.0: a BiLSTM Compound Splitter for Icelandic,"In this paper, we present a character-based BiLSTM model for splitting
Icelandic compound words, and show how varying amounts of training data affects
the performance of the model. Compounding is highly productive in Icelandic,
and new compounds are constantly being created. This results in a large number
of out-of-vocabulary (OOV) words, negatively impacting the performance of many
NLP tools. Our model is trained on a dataset of 2.9 million unique word forms
and their constituent structures from the Database of Icelandic Morphology. The
model learns how to split compound words into two parts and can be used to
derive the constituent structure of any word form. Knowing the constituent
structure of a word form makes it possible to generate the optimal split for a
given task, e.g., a full split for subword tokenization, or, in the case of
part-of-speech tagging, splitting an OOV word until the largest known
morphological head is found. The model outperforms other previously published
methods when evaluated on a corpus of manually split word forms. This method
has been integrated into Kvistur, an Icelandic compound word analyzer.",2004.07776v1
2016-03-21,Optical spectroscopy and ultrafast pump-probe studies on the heavy fermion compound CePt$_2$In$_7$,"We report optical spectroscopy and ultrafast pump-probe measurements on the
antiferromagnetic heavy fermion compound CePt$_2$In$_7$, a member showing
stronger two dimensionality than other compounds in CeIn$_3$-derived
heavy-fermion family. We identify clear and typical hybridization spectral
structures at low temperature from the two different spectroscopy probes.
However, the strength and related energy scale of the hybridization are much
weaker and smaller than that in the superconducting compounds CeCoIn$_5$ and
CeIrIn$_5$. The features are more similar to observations on the
antiferromagnetic compounds CeIn$_3$ and CeRhIn$_5$ in the same family. The
results clearly indicate that the Kondo interaction and hybridizations exist in
the antiferromagnetic compounds but with weaker strength.",1603.06325v1
2019-03-08,Prediction of fundamental properties of Be-B-Ta based novel ternary compounds from first-principles calculations,"Be-B/B-Ta based compounds are very attractive to researchers because of their
high density and ultra-hardness. But ternary Be-B-Ta compounds are neither
synthesized nor predicted. In this paper, variable composition evolutionary
crystal structure prediction calculations based on first-principles method have
been performed to find the stable crystal structure containing Be-B-Ta at
ambient condition. The predicted five compounds BeB$_2$Ta, BeB$_3$Ta$_2$
(high-pressure phase), BeBTa, BeBTa$_2$, and Be$_2$B$_2$Ta have been found to
be highly dense and very hard materials. All these compounds are metallic and
spin-orbit coupling (SOC) effect is significant in them. Only two of them
(BeB$_2$Ta and Be$_2$B$_2$Ta) have been found to be superconductors within
Migdal-Eliashberg theory. The calculated critical temperature including SOC
effect is 8 and 9 K for BeB$_2$Ta and Be$_2$B$_2$Ta, respectively. Because of
their energetic and dynamic stability, these compounds might be favorable to
synthesize in the laboratory.",1903.03271v1
2019-12-16,Semantic Segmentation for Compound figures,"Scientific literature contains large volumes of unstructured data,with over
30\% of figures constructed as a combination of multiple images, these compound
figures cannot be analyzed directly with existing information retrieval tools.
In this paper, we propose a semantic segmentation approach for compound figure
separation, decomposing the compound figures into ""master images"". Each master
image is one part of a compound figure governed by a subfigure label (typically
""(a), (b), (c), etc""). In this way, the separated subfigures can be easily
associated with the description information in the caption. In particular, we
propose an anchor-based master image detection algorithm, which leverages the
correlation between master images and subfigure labels and locates the master
images in a two-step manner. First, a subfigure label detector is built to
extract the global layout information of the compound figure. Second, the
layout information is combined with local features to locate the master images.
We validate the effectiveness of proposed method on our labeled testing dataset
both quantitatively and qualitatively.",1912.07142v3
2020-11-27,d0 Ferromagnetism in Ag-doped Monoclinic ZrO2 Compounds,"Recently d0 or intrinsic ferromagnetism was believed to provide an
alternative pathway to transition metal induced ferromagnetism in oxide. In
pursuit of augmenting the area of d0 ferromagnetism; we have undertaken to
study the crystal structure and magnetic properties of Ag-doped ZrO2 compounds.
Polycrystalline samples of Zr1-xAgxO2 (with x=0, 0.02, 0.04, 0.06 and 0.08)
were prepared by solid-state reaction route. All the prepared compounds are
found to crystallize in monoclinic symmetry of ZrO2. In our study, pure ZrO2
compound exhibits paramagnetic behavior. However, the Ag-doped ZrO2 compounds
exhibit ferromagnetic to paramagnetic transition. The Curie temperature was
found to increase from 28.7 K for x=0.02 to 173.2 K for x= 0.08 doped ZrO2.
Thus, the introduction of Ag in ZrO2 induces ferromagnetism with a large
ThetaC. The measurements of hysteresis curves indicate that Ag doped ZrO2
compounds exhibit hysteresis loops with a coercivity of around 1350 Oe.
Moreover, increase in Ag concentration resulted increase in the value of
saturation magnetization (MS); the maximum value of MS was recorded as 0.01
{\mu}B/Ag ion for x= 0.06 sample. The sintering of sample at high temperature
(13500C) diminishes the ferromagnetism and it leads to paramagnetic behaviour.",2011.13727v1
2021-01-25,A Two-stage Framework for Compound Figure Separation,"Scientific literature contains large volumes of complex, unstructured figures
that are compound in nature (i.e. composed of multiple images, graphs, and
drawings). Separation of these compound figures is critical for information
retrieval from these figures. In this paper, we propose a new strategy for
compound figure separation, which decomposes the compound figures into
constituent subfigures while preserving the association between the subfigures
and their respective caption components. We propose a two-stage framework to
address the proposed compound figure separation problem. In particular, the
subfigure label detection module detects all subfigure labels in the first
stage. Then, in the subfigure detection module, the detected subfigure labels
help to detect the subfigures by optimizing the feature selection process and
providing the global layout information as extra features. Extensive
experiments are conducted to validate the effectiveness and superiority of the
proposed framework, which improves the detection precision by 9%.",2101.09903v2
2021-05-10,Compound Channel Capacities under Energy Constraints and Application,"Compound channel models offer a simple and straightforward way of analyzing
the stability of decoder design under model variations. With this work we
provide a coding theorem for a large class of practically relevant compound
channel models. We give explicit formulas for the cases of the Gaussian
classical-quantum compound channels with unknown noise, unknown phase and
unknown attenuation. We show analytically how the classical compound channel
capacity formula motivates nontrivial choices of the displacement parameter of
the Kennedy receiver. Our work demonstrates the value of the compound channel
model as a method for the design of receivers in quantum communication.",2105.04274v1
2021-09-08,Scale-invariant Machine-learning Model Accelerates the Discovery of Quaternary Chalcogenides with Ultralow Lattice Thermal Conductivity,"Intrinsically low lattice thermal conductivity ($\kappa_l$) is a desired
requirement in many crystalline solids such as thermal barrier coatings and
thermoelectrics. Here, we design an advanced machine-learning (ML) model based
on crystal graph convolutional neural network that is insensitive to volumes
(i.e., scale) of the input crystal structures to discover novel quaternary
chalcogenides, AMM'Q$_3$ (A/M/M'=alkali, alkaline-earth, post-transition
metals, lanthanides, Q=chalcogens). Upon screening the thermodynamic stability
of $\sim$ 1 million compounds using the ML model iteratively and performing
density functional theory (DFT) calculations for a small fraction of compounds,
we discover 99 compounds that are validated to be stable in DFT. Taking several
DFT-stable compounds, we calculate their $\kappa_l$ using phonon-Boltzmann
transport equation, which reveals ultralow-$\kappa_l$ ($<$ 2 Wm$^{-1}$K$^{-1}$
at room-temperature) due to their soft elasticity and strong phonon
anharmonicity. Our work demonstrates the high-efficiency of scale-invariant ML
model in predicting novel compounds and presents experimental research
opportunities with these new compounds.",2109.03751v1
2021-11-04,A compound Poisson perspective of Ewens-Pitman sampling model,"The Ewens-Pitman sampling model (EP-SM) is a distribution for random
partitions of the set $\{1,\ldots,n\}$, with $n\in\mathbb{N}$, which is index
by real parameters $\alpha$ and $\theta$ such that either $\alpha\in[0,1)$ and
$\theta>-\alpha$, or $\alpha<0$ and $\theta=-m\alpha$ for some
$m\in\mathbb{N}$. For $\alpha=0$ the EP-SM reduces to the celebrated Ewens
sampling model (E-SM), which admits a well-known compound Poisson perspective
in terms of the log-series compound Poisson sampling model (LS-CPSM). In this
paper, we consider a generalization of the LS-CPSM, which is referred to as the
negative Binomial compound Poisson sampling model (NB-CPSM), and we show that
it leads to extend the compound Poisson perspective of the E-SM to the more
general EP-SM for either $\alpha\in(0,1)$, or $\alpha<0$. The interplay between
the NB-CPSM and the EP-SM is then applied to the study of the large $n$
asymptotic behaviour of the number of blocks in the corresponding random
partitions, leading to a new proof of Pitman's $\alpha$ diversity. We discuss
the proposed results, and conjecture that analogous compound Poisson
representations may hold for the class of $\alpha$-stable Poisson-Kingman
sampling models, of which the EP-SM is a noteworthy special case.",2111.02731v1
2022-04-01,Sense disambiguation of compound constituents,"In distributional semantic accounts of the meaning of noun-noun compounds
(e.g. starfish, bank account, houseboat) the important role of constituent
polysemy remains largely unaddressed(cf. the meaning of star in starfish vs.
star cluster vs. star athlete). Instead of semantic vectors that average over
the different meanings of a constituent, disambiguated vectors of the
constituents would be needed in order to see what these more specific
constituent meanings contribute to the meaning of the compound as a whole. This
paper presents a novel approach to this specific problem of word sense
disambiguation: set expansion. We build on the approach developed by Mahabal et
al. (2018) which was originally designed to solve the analogy problem. We
modified their method in such a way that it can address the problem of sense
disambiguation of compound constituents. The results of experiments with a data
set of almost 9000 compounds (LADEC, Gagn\'e et al. 2019) suggest that this
approach is successful, yet the success is sensitive to the frequency with
which the compounds are attested.",2204.00429v1
2022-07-16,Learn-to-Decompose: Cascaded Decomposition Network for Cross-Domain Few-Shot Facial Expression Recognition,"Most existing compound facial expression recognition (FER) methods rely on
large-scale labeled compound expression data for training. However, collecting
such data is labor-intensive and time-consuming. In this paper, we address the
compound FER task in the cross-domain few-shot learning (FSL) setting, which
requires only a few samples of compound expressions in the target domain.
Specifically, we propose a novel cascaded decomposition network (CDNet), which
cascades several learn-to-decompose modules with shared parameters based on a
sequential decomposition mechanism, to obtain a transferable feature space. To
alleviate the overfitting problem caused by limited base classes in our task, a
partial regularization strategy is designed to effectively exploit the best of
both episodic training and batch training. By training across similar tasks on
multiple basic expression datasets, CDNet learns the ability of
learn-to-decompose that can be easily adapted to identify unseen compound
expressions. Extensive experiments on both in-the-lab and in-the-wild compound
expression datasets demonstrate the superiority of our proposed CDNet against
several state-of-the-art FSL methods. Code is available at:
https://github.com/zouxinyi0625/CDNet.",2207.07973v1
2022-09-07,Compound Defects in Halide Perovskites: A First-Principles Study of CsPbI$_3$,"Lattice defects affect the long-term stability of halide perovskite solar
cells. Whereas simple point defects, i.e., atomic interstitials and vacancies,
have been studied in great detail, here we focus on compound defects that are
more likely to form under crystal growth conditions, such as compound vacancies
or interstitials, and antisites. We identify the most prominent defects in the
archetype inorganic perovskite CsPbI$_3$, through first-principles density
functional theory (DFT) calculations. We find that under equilibrium conditions
at room temperature, the antisite of Pb substituting Cs forms in a
concentration comparable to those of the most prominent point defects, whereas
the other compound defects are negligible. However, under nonequilibrium
thermal and operating conditions, other complexes also become as important as
the point defects. Those are the Cs substituting Pb antisite, and, to a lesser
extent, the compound vacancies of PbI$_2$ or CsPbI$_3$ units, and the I
substituting Cs antisite. These compound defects only lead to shallow or
inactive charge carrier traps, which testifies to the electronic stability of
the halide perovskites. Under operating conditions with a quasi Fermi level
very close to the valence band, deeper traps can develop.",2209.03484v1
2023-04-16,"A comprehensive ab-initio insights into the pressure dependent mechanical, phonon, bonding, electronic, optical, and thermal properties of CsV3Sb5 Kagome compound","In this paper, we have presented a comprehensive study of the physical
properties of Kagome superconductor CsV3Sb5 using the density functional theory
(DFT). The structural, mechanical, electronic, atomic bonding, hardness,
thermodynamic, and optical properties, and their pressure dependences have been
investigated for the first time. The calculated ground state lattice parameters
and volume are in excellent agreement with available experimental results. The
estimated single-crystal elastic constants ensured the mechanical stability of
the compound, whereas phonon spectra endorse dynamical stability at zero
pressure. The electronic band structure, energy density of states, optical
properties confirmed the metallic features. The Pugh ratio, Poisson's ratio of
the compound revealed softness and ductility. The hardness, estimated from
several formulae, is quite low while the machinability index predicted good
machinability with excellent dry lubricating properties. The compound shows
tendency towards structural instability at a pressure around 18 GPa. The
optical constants have also been studied to correlate those with electronic
properties and to predict possible applications of this compound. Both
mechanical and optical properties show anisotropy.CsV3Sb5 is predicted to be an
efficient absorber of ultraviolet radiation. The compound is also an efficient
reflector of visible light.",2304.07669v1
2023-05-17,From chocolate bunny to chocolate crocodile: Do Language Models Understand Noun Compounds?,"Noun compound interpretation is the task of expressing a noun compound (e.g.
chocolate bunny) in a free-text paraphrase that makes the relationship between
the constituent nouns explicit (e.g. bunny-shaped chocolate). We propose
modifications to the data and evaluation setup of the standard task (Hendrickx
et al., 2013), and show that GPT-3 solves it almost perfectly. We then
investigate the task of noun compound conceptualization, i.e. paraphrasing a
novel or rare noun compound. E.g., chocolate crocodile is a crocodile-shaped
chocolate. This task requires creativity, commonsense, and the ability to
generalize knowledge about similar concepts. While GPT-3's performance is not
perfect, it is better than that of humans -- likely thanks to its access to
vast amounts of knowledge, and because conceptual processing is effortful for
people (Connell and Lynott, 2012). Finally, we estimate the extent to which
GPT-3 is reasoning about the world vs. parroting its training data. We find
that the outputs from GPT-3 often have significant overlap with a large web
corpus, but that the parroting strategy is less beneficial for novel noun
compounds.",2305.10568v2
2023-08-10,"First-principles calculation on the electronic structures, phonon dynamics, and electrical conductivities of Pb$_{10}$(PO$_4$)$_6$O and Pb$_9$Cu(PO$_4$)$_6$O compounds","Superconducting materials with high critical temperature have the potential
to revolutionize many fields, including military, electronic communications,
and power energy. Therefore, Scientists around the world have been tirelessly
working with the ultimate goal of achieving high temperature superconductivity.
In 2023, a preprint by S. Lee et al in South Korea claimed the discovery of
ultra-high-temperature superconductivity with a critical temperature of up to
423 K in Cu-doped lead-apatite (LK-99) (arXiv:2307.12008, arXiv:2307.12037),
which caused a worldwide sensation and attention. Herein, the electronic
structures, phonon dynamics, and electrical conductivities of LK-99 and its
parent compound lead-apatite have been calculated using first-principles
methods. The results show that the lead-apatite compound and the LK-99 compound
are insulator and half-metal respectively. The flat band characteristic is
consistent with previous calculations. The electrical conductivity of LK-99
compound shows two extreme point, and the electrical conductivity along the
C-axis increases significantly after 400 K. The phonon dispersion spectra of
the compounds were investigated, demonstrating their dynamic instability.",2308.05618v1
2017-11-14,"Growth, electrical, structural, and magnetic properties of half-Heusler CoTi$_{1-x}$Fe$_x$Sb","Epitaxial thin films of the substitutionally alloyed half-Heusler series
CoTi$_{1-x}$Fe$_x$Sb were grown by molecular beam epitaxy on InAlAs/InP(001)
substrates for concentrations 0.0$\leq$x$\leq$1.0. The influence of Fe on the
structural, electronic, and magnetic properties was studied and compared to
that expected from density functional theory. The films are epitaxial and
single crystalline, as measured by reflection high-energy electron diffraction
and X-ray diffraction. Using in-situ X-ray photoelectron spectroscopy, only
small changes in the valence band are detected for x$\leq$0.5. For films with
x$\geq$0.05, ferromagnetism is observed in SQUID magnetometry with a saturation
magnetization that scales linearly with Fe content. A dramatic decrease in the
magnetic moment per formula unit occurs when the Fe is substitutionally alloyed
on the Co site indicating a strong dependence on the magnetic moment with site
occupancy. A crossover from both in-plane and out-of-plane magnetic moments to
only in-plane moment occurs for higher concentrations of Fe. Ferromagnetic
resonance indicates a transition from weak to strong interaction with a
reduction in inhomogeneous broadening as Fe content is increased.
Temperature-dependent transport reveals a semiconductor to metal transition
with thermally activated behavior for x$\leq$0.5. Anomalous Hall effect and
large negative magnetoresistance (up to -18.5% at 100 kOe for x=0.3) are
observed for higher Fe content films. Evidence of superparamagnetism for x=0.3
and x=0.2 suggests for moderate levels of Fe, demixing of the
CoTi$_{1-x}$Fe$_x$Sb films into Fe rich and Fe deficient regions may be
present. Atom probe tomography is used to examine the Fe distribution in a
x=0.3 film. Statistical analysis reveals a nonhomogeneous distribution of Fe
atoms throughout the film, which is used to explain the observed magnetic and
electrical behavior.",1711.05320v1
2020-08-26,"First-principles electronic structure, phonon properties, lattice thermal conductivity and prediction of figure of merit of FeVSb half-Heusler","In this work, we have studied the electronic structure of a promising
thermoelectric half-Heusler FeVSb using FP-LAPW method and SCAN meta-GGA
including spin-orbit coupling. Using the obtained electronic structure and
transport calculations we try to address the experimental Seebeck coefficient
$S$ of FeVSb samples. The good agreement between the experimental and
calculated $S$ suggests the band gap could be $\sim$0.7 eV. This is supported
by the obtained mBJ band gap of $\sim$0.7 eV. Further, we study and report the
phonon dispersion, density of states and thermodynamic properties. The effect
of long range Coulomb interactions on phonon frequencies are also included by
non-analytical term correction. Under quasi-harmonic approximation, the thermal
expansion behaviour upto 1200 K is calculated. Using the first-principles
anharmonic phonon calculations, the lattice thermal conductivity $\kappa_{ph}$
of FeVSb is obtained under single-mode relaxation time approximation
considering the phonon-phonon interaction. At 300 K, the calculated
$\kappa_{ph}$ is $\sim$18.6 W$m^{-1}K^{-1}$ which is higher compared to
experimental value. But, above 500 K the calculated $\kappa_{ph}$ is in good
agreement with experiment. A prediction of figure of merit $ZT$ and efficiency
for p-type and n-type FeVSb is made by finding out optimal carrier
concentration. At 1200 K, a maximum $ZT$ of $\sim$0.66 and $\sim$0.44 is
expected for p-type and n-type FeVSb, respectively. For p-type and n-type
materials, maximum efficiency of $\sim$12.2 \% and $\sim$6.0 \% are estimated
for hot and cold temperature of 1200 K and 300 K, respectively. A possibility
of achieving n-type and p-type FeVSb by various elemental doping/vacancy is
also discussed. Our study is expected to help in further exploring the
thermoelectric material FeVSb.",2008.11693v1
2019-03-07,"Uniaxial anisotropy, intrinsic and extrinsic damping in Co$_{2}$FeSi Heusler alloy thin films","Ferromagnetic resonance (FMR) technique has been used to study the
magnetization relaxation processes and magnetic anisotropy in two different
series of the Co2FeSi (CFS) Heusler alloy thin films, deposited on the Si(111)
substrate by UHV sputtering. While the CFS films of fixed (50 nm) thickness,
deposited at different substrate temperatures (TS) ranging from room
temperature (RT) to 600^C, constitute the series-I, the CFS films with
thickness t varying from 12 nm to 100 nm and deposited at 550^C make up the
series-II. In series-I, the CFS films deposited at TS = RT and 200^C are
completely amorphous, the one at TS = 300^C is partially crystalline, and those
at TS equal 450^C, 550^C and 600^C are completely crystalline with B2 order. By
contrast, all the CFS films in series-II are in the fully-developed B2
crystalline state. Irrespective of the strength of disorder and film thickness,
angular variation of the resonance field in the film plane unambiguously
establishes the presence of global in-plane uniaxial anisotropy. Angular
variation of the linewidth in the film plane reveals that, in the CFS thin
films of varying thickness, a crossover from the in-plane local four-fold
symmetry (cubic anisotropy) to local two-fold symmetry (uniaxial anisotropy)
occurs as t exceeds 50 nm. Gilbert damping parameter {\alpha} decreases
monotonously from 0.047 to 0.0078 with decreasing disorder strength (increasing
TS) and jumps from 0.008 for the CFS film with t = 50 nm to 0.024 for the film
with t equal 75 nm. Such variations of {\alpha} with TS and t are understood in
terms of the changes in the total (spin-up and spin-down) density of states at
the Fermi level caused by the disorder and film thickness.",1903.02976v1
2019-03-18,"Experimental and Theoretical Investigation on the Possible Half-metallic Behaviour of Equiatomic Quaternary Heusler Alloys: CoRuMnGe and CoRuVZ (Z = Al, Ga)","In this report, structural, electronic, magnetic and transport properties of
quaternary Heusler alloys CoRuMnGe and CoRuVZ (Z = Al, Ga) are investigated.
All the three alloys are found to crystallize in cubic structure. CoRuMnGe
exhibits L2$_1$ structure whereas, the other two alloys have B2-type disorder.
For CoRuMnGe and CoRuVGa, the experimental magnetic moments are in close
agreement with the theory as well as those predicted by the Slater-Pauling
rule, while for CoRuVAl, a relatively large deviation is seen. The reduction in
the moment in case of CoRuVAl possibly arises due to the anti-site disorder
between Co and Ru sites as well as V and Al sites. Among these alloys, CoRuMnGe
has the highest T$\mathrm{_C}$ of 560 K. Resistivity variation with temperature
reflects the half-metallic nature in CoRuMnGe alloy. CoRuVAl shows metallic
character in both paramagnetic and ferromagnetic states, whereas the
temperature dependence of resistivity for CoRuVGa is quite unusual. In the last
system, $\rho$ vs. T curve shows an anomaly in the form of a maximum and a
region of negative temperature coefficient of resistivity (TCR) in the
magnetically ordered state. The ab initio calculations predict nearly
half-metallic ferromagnetic state with high spin polarization of 91, 89 and 93
\% for CoRuMnGe, CoRuVAl and CoRuVGa respectively. To investigate the
electronic properties of the experimentally observed structure, the Co-Ru swap
disordered structures of CoRuMnGe alloy are also simulated and it is found that
the disordered structures retain half-metallic nature, high spin polarization
with almost same magnetic moment as in the ideal structure. Nearly
half-metallic character, high T$\mathrm{_C}$ and high spin polarization make
CoRuMnGe alloy promising for room temperature spintronic applications.",1903.07265v2
2019-09-18,Neutron diffraction and magnetic properties of Co$_2$Cr$_{1-x}$Ti$_x$Al Heusler alloys,"We report the structural, magnetic, and magnetocaloric properties of
Co$_2$Cr$_{1-x}$Ti$_x$Al ($x=$ 0--0.5) Heusler alloys for spintronic and
magnetic refrigerator applications. Room temperature X-ray diffraction and
neutron diffraction patterns along with Rietveld refinements confirm that the
samples are of single phase and possess a cubic structure. Interestingly,
magnetic susceptibly measurements indicate a second order phase transition from
paramagnetic to ferromagnetic where the Curie temperature (T$_{\rm C}$) of
Co$_2$CrAl increases from 330~K to 445~K with Ti substitution. Neutron powder
diffraction data of the $x=$ 0 sample across the magnetic phase transition
taken in a large temperature range confirm the structural stability and exclude
the possibility of antiferromagnetic ordering. The saturation magnetization of
the $x=$ 0 sample is found to be 8000~emu/mol (1.45~$\mu_{\rm B}$/{\it f.u.})
at 5~K, which is in good agreement with the value (1.35$\pm$0.05~$\mu_{\rm
B}$/{\it f.u.}) obtained from the Rietveld analysis of the neutron powder
diffraction pattern measured at temperature of 4~K. By analysing the
temperature dependence of the neutron data of the $x=$ 0 sample, we find that
the change in the intensity of the most intense Bragg peak (220) is consistent
with the magnetization behavior with temperature. Furthermore, an enhancement
of change in the magnetic entropy and relative cooling power values has been
observed for the $x=$ 0.25 sample. Interestingly, the critical behavior
analysis across the second order magnetic phase transition and extracted
exponents ($\beta\approx$ 0.496, $\gamma\approx$ 1.348, and $\delta\approx$
3.71 for the $x=$ 0.25 sample) suggest the presence of long-range ordering,
which deviates towards 3D Heisenberg type interactions above T$_{\rm C}$,
consistent with the interaction range value $\sigma$.",1909.08292v1
2021-01-23,Studying the lifetime of charge and heat carriers due to intrinsic scattering mechanisms in FeVSb half-Heusler thermoelectric,"This work, presents a study of lifetime of carriers due to intrinsic
scattering mechanisms $viz.$ electron-electron (EEI), electron-phonon (EPI) and
phonon-phonon interactions (PPI) in a promising half-Heusler thermoelectric
FeVSb. Using the full-$GW$ method, the effect of EEI and temperature on the
valence and conduction band extrema and band gap are studied. The lifetime of
carriers with temperature are estimated at these band extrema. At 300 K,
estimated value of lifetime at VBM (CBM) is $\sim$1.91 x10$^{-14}s$ ($\sim$2.05
x10$^{-14}s$). The estimated ground state band gap considering EEI is $\sim$378
meV. Next, the effect of EPI on the lifetime of electrons and phonons with
temperature are discussed. The comparison of two electron lifetimes suggests
that EEI should be considered in transport calculations along with EPI. The
average acoustic, optical and overall phonon lifetimes due to EPI are studied
with temperature. Further, the effect of PPI is studied by computing average
phonon lifetime for acoustic and optical phonon branches. The lifetime of the
acoustic phonons are higher compared to optical phonons which indicates
acoustic phonons contribute more to lattice thermal conductivity
($\kappa_{ph}$). The comparison of phonon lifetime due to EPI and PPI suggests
that, above 500 K EPI is the dominant phonon scattering mechanism and cannot be
ignored in $\kappa_{ph}$ calculations. Lastly, a prediction of the power factor
and figure of merit of n-type and p-type FeVSb is made by considering the
temperature dependent carrier lifetime for the electronic transport terms. This
study shows the importance of considering EEI in electronic transport
calculations and EPI in phonon transport calculations. Our study is expected to
provide results to further explore the thermoelectric transport in this
material.",2101.09555v1
2023-01-10,Dissipation losses limiting first-order phase transition materials in cryogenic caloric cooling: A case study on all-d-metal Ni(-Co)-Mn-Ti Heusler alloys,"Ni-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are
highly promising materials for energy-efficient solid-state refrigeration as
large multicaloric effects can be achieved across their magnetostructural
martensitic transformation. However, no comprehensive study on the crucially
important transition entropy change $\Delta s_t$ exists so far for
Ni(-Co)-Mn-Ti. Here, we present a systematic study analyzing the composition
and temperature dependence of $\Delta s_t$. Our results reveal a substantial
structural entropy change contribution of approximately 65 J(kgK)$^{-1}$, which
is compensated at lower temperatures by an increasingly negative entropy change
associated with the magnetic subsystem. This leads to compensation temperatures
$T_{comp}$ of 75 K and 300 K in Ni$_{35}$Co$_{15}$Mn$_{50-y}$Ti$_{y}$ and
Ni$_{33}$Co$_{17}$Mn$_{50-y}$Ti$_{y}$, respectively, below which the
martensitic transformations are arrested. In addition, we simultaneously
measured the responses of the magnetic, structural and electronic subsystems to
the temperature- and field-induced martensitic transformation near $T_{comp}$,
showing an abnormal increase of hysteresis and consequently dissipation energy
at cryogenic temperatures. Simultaneous measurements of magnetization and
adiabatic temperature change $\Delta T_{ad}$ in pulsed magnetic fields reveal a
change in sign of $\Delta T_{ad}$ and a substantial positive and irreversible
$\Delta T_{ad}$ up to 15 K at 15 K as a consequence of increased dissipation
losses and decreased heat capacity. Most importantly, this phenomenon is
universal, it applies to any first-order material with non-negligible
hysteresis and any stimulus, effectively limiting the utilization of their
caloric effects for gas liquefaction at cryogenic temperatures.",2301.03934v1
2009-04-22,"Effects of magnetic doping and temperature dependence on phonon dynamics in CaFe\_{1-x}Co\_{x}AsF compounds (x = 0, 0.06, 0.12)","We report detailed measurements of composition as well as temperature
dependence of the phonon density-of-states in a new series of FeAs compounds
with composition CaFe1\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12). The composition as
well as temperature dependence of phonon spectra for CaFe\_{1-x}Co\_{x}AsF (x =
0, 0.06, 0.12) compounds have been measured using time of flight IN4C and IN6
spectrometers at ILL, France. The comparison of phonon spectra at 300 K in
these compounds shows that acoustic phonon modes up to 12 meV harden in the
doped compounds in comparison to the parent CaFeAsF. While intermediate energy
phonon modes from 15 meV to 25 meV are also found to shift towards high
energies only in the 12 % Co doped CaFeAsF compound. The experimental results
for CaFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) are quite different from our
previous phonon studies on parent and superconducting MFe2As2 (M=Ba, Ca, Sr)
where low-energy acoustic phonon modes do not react with doping, while the
phonon spectra in the intermediate range from 15 to 25 K are found to soften in
these compounds. We argue that stronger spin phonon interaction play an
important role for the emergence of superconductivity in these compounds. The
lattice dynamics of CaFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) compounds is also
investigated using the ab-initio as well as shell model phonon calculations. We
show that the nature of the interaction between the Ca and the Fe-As layers in
CaFeAsF compounds is quite different compared with our previous studies on
CaFe2As2.",0904.3464v1
2002-09-26,"Cation intermixing and ordering phenomenon in MO layer of MSr2YCu2Oz (M1212) compounds with M = Fe, Co, Al, and Ga: A neutron powder diffraction study","Various MSr2YCu2Oz (M1212 with M = Fe, Co, Al and Ga) compounds have been
synthesized through a solid state reaction route. All these compounds are
derived from the basic CuBa2YCu2O7 structure. Rietveld structural refinement of
the room-temperature neutron diffraction data for Fe-1212 reveals that nearly
half of Fe remains at the M site, while the other half goes to the Cu site in
the CuO2 plane. For the M = Co, Al and Ga compounds, the basic unit cell gets
doubled due to two distinct M sites in the M-O layer and the space group Ima2,
without any cation intermixing is found more appropriate. For the M = Fe
sample, magnetic ordering of Fe spins is seen from magnetization data below 70
K. In the case of the M = Co compound, a shallow down-turn in magnetic
susceptibility is seen below 150 K, indicating low dimensional magnetic
characteristics of the CoO layer. The compounds with M = Al and Ga show
paramagnetic behaviour in their magnetization data down to 5 K. The oxygen
content, established for each compound based on oxygen occupancies, refined
from the neutron diffraction data comes close to 7.0 for each.",0209605v1
2003-11-19,"Magnetic Ordering and Superconductivity in the RE$_2$Ir$_3$Ge$_5$ (RE = Y, La-Tm, Lu) System","We find that the compounds for RE = Y, La-Dy, crystallize in the tetragonal
Ibam (U$_2$Co$_3$Si$_5$ type) structure whereas the compounds for RE = Er-Lu,
crystallize in a new orthorhombic structure with a space group Pmmn. Samples of
Ho$_2$Ir$_3$Ge$_5$ were always found to be multiphase. The compounds for RE = Y
to Dy which adopt the Ibam type structure show a metallic resistivity whereas
the compounds with RE = Er, Tm and Lu show an anomalous behavior in the
resistivity with a semiconducting increase in $\rho$ as we go down in
temperature from 300K. Interestingly we had earlier found a positive
temperature coefficient of resistivity for the Yb sample in the same
temperature range. We will compare this behavior with similar observations in
the compounds RE$_3$Ru$_4$Ge$_{13}$ and REBiPt. La$_2$Ir$_3$Ge$_5$ and
Y$_2$Ir$_3$Ge$_5$ show bulk superconductivity below 1.8K and 2.5K respectively.
Our results confirm that Ce$_2$Ir$_3$Ge$_5$ shows a Kondo lattice behavior and
undergoes antiferromagnetic ordering below 8.5K. Most of the other compounds
containing magnetic rare-earth elements undergo a single antiferromagnetic
transition at low temperatures (T$\leq$12K) while Gd$_2$Ir$_3$Ge$_5$,
Dy$_2$Ir$_3$Ge$_5$ and Nd$_2$Ir$_3$Ge$_5$ show multiple transitions. The
T$_N$'s for most of the compounds roughly scale with the de Gennes factor.
which suggests that the chief mechanism of interaction leading to the magnetic
ordering of the magnetic moments may be the RKKY interaction.",0311441v1
2004-03-16,Calculated spin-orbit splitting of all diamond-like and zinc-blende semiconductors: Effects of p1/2 local orbitals and chemical trends,"e have calculated the spin-orbit (SO) splitting $\Delta_{SO}=\epsilon
(\Gamma_{8v}) - \epsilon (\Gamma_{7v})$ for all diamond-like group IV and
zinc-blende group III-V, II-VI, and I-VII semiconductors using the full
potential linearized augmented plane wave method within the local density
approximation. The SO coupling is included using the second variation
procedure, including the $p_{1/2}$ local orbitals. The calculated SO splittings
are in very good agreement with available experimental data. The corrections
due to the inclusion of the $p_{1/2}$ local orbital are negligible for lighter
atoms, but can be as large as $\sim$250 meV for 6$p$ anions. We find that (i)
the SO splittings increase monotonically when anion atomic number increases;
(ii) the SO splittings increase with the cation atomic number when the compound
is more covalent such as in most III-V compounds; (iii) the SO splittings
decrease with the cation atomic number when the compound is more ionic, such as
in II-VI and the III-nitride compounds; (iv) the common-anion rule, which
states that the variation of $\Delta_{SO}$ is small for common-anion systems,
is usually obeyed, especially for ionic systems, but can break down if the
compounds contain second-row elements such as BSb;(v) for IB-VII compounds, the
$\Delta_{SO}$ is small and in many cases negative and it does not follow the
rules discussed above. These trends are explained in terms of atomic SO
splitting, volume deformation-induced charge renormalization, and cation-anion
$p$--$d$ couplings.",0403409v2
2006-09-16,Correlation between magnetism and magnetocaloric effect in RCo2-based Laves phase compounds,"By virtue of the itinerant electron metamagnetism (IEM), the RCo2 compounds
with R=Er, Ho and Dy are found to show first order magnetic transition at their
ordering temperatures. The inherent instability of Co sublattice magnetism is
responsible for the occurrence of IEM, which leads to interesting magnetic and
related properties. The systematic studies of the variations in the magnetic
and magnetocaloric properties of the RCo2-based compounds show that the
magnetovolume effect plays a decisive role in determining the nature of
magnetic transitions and hence the magnetocaloric effect (MCE) in these
compound. It is found that the spin fluctuations arising due to the
magnetovolume effect reduce the strength of IEM in these compounds, which
subsequently lead to a reduction in the MCE. Most of the substitutions at the
Co site are found to result in a positive magnetovolume effect, leading to an
initial increase in the ordering temperature. Application of pressure, on the
other hand, causes a reduction in the ordering temperature due to the negative
magnetovolume effect. A comparative study of the magnetic and magnetocaloric
properties of RCo2 compounds under various substitutions and applied pressure
is presented. Analysis of the magnetization data using the Landau theory has
shown that there is a strong correlation between the Landau coefficient (B) and
the MCE. The variations seen in the order of magnetic transition and the MCE
values seem to support the recent model proposed by Khmelevskyi and Mohn for
the occurrence of IEM in RCo2 compounds.",0609401v1
2007-08-28,Fractionally Quantized Hall Effect: Liquid-Crystal Ground-State and it Excitations,"It is shown that the ground-state and the lowest excited-states of
two-dimensional electron system (2DES), with ion jellium background, correspond
to partial crystal-like (with the period $L_{x}^{\square}=\sqrt{2 m \pi}
\ell_{0}$) correlation order among $N$ electrons of the main region (MR; $L_{x}
\times L_{y}$). Many-body variational ground-state wave function of 2DES is
presented at the fractional and the integral filling factors $\nu=1/m$;
$m=2\ell+1$ and $\ell=0, 1, 2,...$. The ground-state manifests the broken
symmetry liquid-crystal state with 2DES density that is periodic along the $y-$
direction, with the period $L_{x}^{\square}/m$, and independent of $x$. At
$m=3, 5$, the ground-state has essentially lower energy per electron than the
Laughlin, uniform liquid, ground-state; the same holds at $m=1$. At $m \geq 3$,
the compound form of the many-body ground-state wave function leads to the
compound structure of each electron within the main strip (MS; $L_{x}^{\square}
\times L_{y}$). Obtained compound exciton and compound spin-exciton states show
finite excitation gaps. The excited compound electron (hole) is composed,
within MS, from $m$ strongly correlated quasielectrons (quasiholes) of the
total charge $e/m$ ($-e/m$) each. The activation gap is obtained: it is given
by the excitation gap of relevant compound exciton, at $m \geq 3$, and by the
gap of pertinent compound spin-exciton, at $m=1$. Quantized Hall conductance
$\sigma_{H}=e^{2}/(2 m \pi \hbar)$ is obtained. The theory is in good agreement
with experiments.",0708.3817v2
2008-01-29,"Anisotropic magnetization studies of $R_2 Co Ga_8$ (R = Gd, Tb, Dy, Ho, Er, Tm, Y and Lu) single crystals","Single crystals of R$_2$CoGa$_8$ series of compounds were grown, for the
first time, by high temperature solution growth (flux) method. These compounds
crystallize in a tetragonal crystal structure with the space group $P4/mmm$. It
has been found that R$_2$CoGa$_8$ phase forms only with the heavier rare
earths, starting from Gd with a relatively large $c/a$ ratio of $\approx$ 2.6.
The resultant anisotropic magnetic properties of the compounds were
investigated along the two principal crystallographic directions of the crystal
viz., along [100] and [001]. The nonmagnetic compounds Y$_2$CoGa$_8$ and
Lu$_2$CoGa$_8$ show diamagnetic behavior down to the lowest temperature (1.8 K)
pointing out the non-magnetic nature of Co in these compounds and a relatively
low density of electronic states at the Fermi level. Compounds with the
magnetic rare earths order antiferromagnetically at temperatures lower than 30
K. The easy axis of magnetization for R$_2$CoGa$_8$ (R = Tb, Dy and Ho) is
found to be along the [001] direction and it changes to [100] direction for
Er$_2$CoGa$_8$ and Tm$_2$CoGa$_8$. The magnetization behavior is analyzed on
the basis of crystalline electric field (CEF) model. The estimated crystal
field parameters explains the magnetocrystalline anisotropy in this series of
compounds.",0801.4518v1
2011-04-27,Density Functional Study of Ternary Topological Insulator Thin Films,"Using an ab-initio density functional theory based electronic structure
method with a semi-local density approximation, we study thin-film electronic
properties of two topological insulators based on ternary compounds of Tl
(Thallium) and Bi (Bismuth). We consider TlBiX$_2$ (X=Se, Te) and Bi$_2$$X$_2$Y
(X,Y= Se,Te) compounds which provide better Dirac cones, compared to the model
binary compounds Bi$_2$X$_3$ (X=Se, Te). With this property in combination with
a structurally perfect bulk crystal, the latter ternary compound has been found
to have improved surface electronic transport in recent experiments. In this
article, we discuss the nature of surface states, their locations in the
Brillouin zone and their interactions within the bulk region. Our calculations
suggest a critical thin film thickness to maintain the Dirac cone which is
significantly smaller than that in binary Bi-based compounds. Atomic
relaxations or rearrangements are found to affect the Dirac cone in some of
these compounds. And with the help of layer-projected surface charge densities,
we discuss the penetration depth of the surface states into the bulk region.
The electronic spectrum of these ternary compounds agrees very well with the
available experimental results.",1104.5204v1
2014-02-24,Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory,"Type-I clathrate compounds have attracted a great deal of interest in
connection with the search for efficient thermoelectric materials. These
compounds constitute networked cages consisting of nano-scale
tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the
group 1 or 2 elements in the periodic table are encaged as the so-called
rattling guest atom. It is remarkable that, though these compounds have
crystalline cubic-structure, they exhibit glass-like phonon thermal
conductivity over the whole temperature range depending on the states of
rattling guest atoms in the tetrakaidecahedron. In addition, these compounds
show unusual glass-like specific heats and THz-frequency phonon dynamics,
providing a remarkable broad peak almost identical to those observed in
topologically disordered amorphous materials or structural glasses, the
so-called Boson peak. An efficient thermoelectric effect is realized in
compounds showing these glass-like characteristics. This decade, a number of
experimental works dealing with type-I clathrate compounds have been published.
These are diffraction experiments, thermal and spectroscopic experiments in
addition to those based on heat and electronic transport. These form the raw
materials for this article based on advances this decade. The subject of this
article involves interesting phenomena from the viewpoint of not only physics
but also from the view point of the practical problem of elaborating efficient
thermoelectric materials. This review presents a survey of a wide range of
experimental investigations of type-I clathrate compounds, together with a
review of theoretical interpretations of the peculiar thermal and dynamic
properties observed in these materials.",1402.5756v1
2017-07-19,Pharmacokinetics and Molecular Docking studies of Plant-Derived Natural Compounds to Exploring Potential Anti-Alzheimer Activity,"Alzheimer disease (AD) is the leading cause of dementia, accounts for 60 to
80 percent cases. Two main factors called beta amyloid plaques and tangles are
prime suspects in damaging and killing nerve cells. However, oxidative stress,
the process which produces free radicals in cells, is believed to promote its
progression to the extent that it may responsible for the cognitive and
functional decline observed in AD. As of today there are few FDA approved drugs
in the market for treatment, but their cholinergic adverse effect, potentially
distressing toxicity and limited targets in AD pathology limits their use.
Therefore, it is crucial to find an effective compounds to combat AD. We choose
45 plant derived natural compounds that have antioxidant properties to slow
down disease progression by quenching free redicals or promoting endogenous
antioxidant capacity. However, we performed molecular docking studies to
investigate the binding interactions between natural compounds and 13 various
anti Alzheimer drug targets. Three known Cholinesterase inhibitors (Donepezil,
Galantamine and Rivastigmine) were taken as reference drugs over natural
compounds for comparison and drug likeness studies. Few of these compounds
showed good inhibitory activity besides anti oxidant activity. Most of these
compounds followed pharmacokinetics properties that make them potentially
promising drug candidates for the treatment of Alzheimer disease.",1709.10374v1
2018-06-13,Eu valence transition behavior in the nano form of EuPd2Si2,"The compound EuPd2Si2 is a well-known valence-fluctuating compound with a
largest variation of Eu valence in a narrow temperature interval (around 150
K). The ball-milled form of this compound was investigated to understand the Eu
valence behavior in the nanoform. The compound is found to retain the
ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in
particle size, typically falling in the range 10 - 100 nm. We find that there
is a qualitative change in the temperature dependence of magnetic
susceptibility for such small particles, with respect to that known for bulk
form. To understand this microscopically, Mossbauer spectra as a function of
temperature were taken. The Mossbauer spectrum of the nanocrystalline compound
is essentially divalent-like at room temperature, but becomes distinctly
bimodal at all temperatures below 300 K, unlike that of the bulk form. That is,
there is a progressive transfer of intensity from divalent position to
trivalent position with a gradual decrease of temperature. We attribute it to a
first-order valence transition, with extreme broadening by defects in the nano
specimen. Thus, there is a qualitative change in the valence behavior in this
compound as the particle size is reduced by ball-milling. Such a particle size
study is reported for the first time for a Eu-based mixed-valent compound.",1806.04985v1
2018-09-10,"Nature of glassy magnetic state in magnetocaloric materials Dy5Pd2-xNix (x = 0 and 1) and universal scaling analysis of R5Pd2 (R = Tb, Dy and Er)","We report a systematic investigation of the magnetic and magnetocaloric
properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence
that they exhibit complex magnetic behaviour along with the presence of
glass-like magnetic phase. Furthermore, in these compounds both second order
and first order phase transitions were present, which were validated through
Arrott plots and Landau parameter analysis. AC susceptibility along with time
dependent magnetisation study has confirmed the presence of double cluster
glass-like freezing in both Dy5Pd2 and Dy5PdNi. These compounds show
significant value of isothermal entropy change and relative cooling power and
these values increased with Ni substitution. Beside conventional magnetocaloric
effect, inverse magnetocaloric effect was noted in these compounds, which might
arise due to the presence of complex non-equilibrium magnetic state. Along with
these compounds a universal characteristic curve involving two other members of
R5Pd2 family i.e. Er5Pd2 and Tb5Pd2 was constructed. The master curve
reaffirmed the presence of both second and first order magnetic phase
transition in such compounds which were in analogy to our results of Arrott
plots and Landau parameter analysis. Additionally, magnetic entropy change
followed the power law and the obtained exponent values indicated the presence
of mixed magnetic interactions in these compounds.",1809.03249v1
2018-07-03,Predicting Diamond-like Co-based Chalcogenides as Unconventional High Temperature Superconductors,"We predict Co-based chalcogenides with a diamond-like structure can host
unconventional high temperature superconductivity (high-$T_c$). The essential
electronic physics in these materials stems from the Co layers with each layer
being formed by vertex-shared CoA$_4$ (A=S,Se,Te) tetrahedra complexes, a
material genome proposed recently by us to host potential unconventional
high-$T_c$ close to a $d^7$ filling configuration in 3d transition metal
compounds. We calculate the magnetic ground states of different transition
metal compounds with this structure. It is found that (Mn,Fe,Co)-based
compounds all have a G-type antiferromagnetic(AFM) insulating ground state
while Ni-based compounds are paramagnetic metal. The AFM interaction is the
largest in the Co-based compounds as the three $t_{2g}$ orbitals all strongly
participate in AFM superexchange interactions. The abrupt quenching of the
magnetism from the Co to Ni-based compounds is very similar to those from Fe to
Co-based pnictides in which a C-type AFM state appears in the Fe-based ones but
vanishes in the Co-based ones. This behavior can be considered as an electronic
signature of the high-$T_c$ gene. Upon doping, as we predicted before, this
family of Co-based compounds favor a strong d-wave pairing superconducting
state.",1807.00934v1
2019-07-12,Electronic and Optical Properties of Zinc based Hybrid Organic-Inorganic Compounds for Ultraviolet Applications,"Hybrid organic-inorganic (HOI) compounds are excellent candidates for a wide
spectrum of applications in diverse fields such as optics, electronics, energy
and biotechnology. Their broad range of versatility is achieved by combining
the functionalities of organic and inorganic materials to generate unique
properties. Current research has mostly focused on perovskite HOIs due to their
wide range of uses in solar cells, photo detectors and memory devices. However,
drawbacks such as instability and lead toxicity limit further implementation
into other new areas. Thus, there is a need to develop stable and non-toxic HOI
perovskite materials. Zinc is an attractive substitute for Pb in HOIs. Here, we
apply a functionality based materials selection approach to screen for Zn-based
HOI compounds from two crystallographic repositories; Inorganic Crystal
Structure Database and American Mineralogist Crystal Structure Database. We
successfully identify thirteen Zn-based HOI compounds. The electronic structure
and optical properties of these compounds are investigated using density
functional theory. The calculated optical absorbance fall within the far
ultra-violet (FUV) region of 200-112 nm wavelength. We selected four of these
compounds and calculated their band gaps; they were found to range between
4.9-5.7 eV. Considering that the UV absorbance is three times larger than
average tissue absorbance and the refractive index (> 1.49) is greater than
typical tissue materials, one could consider these Zn-based HOI compounds for
selective photothermolysis treatment and UV protectant coating for electronic
devices.",1907.05865v1
2019-10-31,Generative network complex (GNC) for drug discovery,"It remains a challenging task to generate a vast variety of novel compounds
with desirable pharmacological properties. In this work, a generative network
complex (GNC) is proposed as a new platform for designing novel compounds,
predicting their physical and chemical properties, and selecting potential drug
candidates that fulfill various druggable criteria such as binding affinity,
solubility, partition coefficient, etc. We combine a SMILES string generator,
which consists of an encoder, a drug-property controlled or regulated latent
space, and a decoder, with verification deep neural networks, a target-specific
three-dimensional (3D) pose generator, and mathematical deep learning networks
to generate new compounds, predict their drug properties, construct 3D poses
associated with target proteins, and reevaluate druggability, respectively. New
compounds were generated in the latent space by either randomized output,
controlled output, or optimized output. In our demonstration, 2.08 million and
2.8 million novel compounds are generated respectively for Cathepsin S and BACE
targets. These new compounds are very different from the seeds and cover a
larger chemical space. For potentially active compounds, their 3D poses are
generated using a state-of-the-art method. The resulting 3D complexes are
further evaluated for druggability by a championing deep learning algorithm
based on algebraic topology, differential geometry, and algebraic graph
theories. Performed on supercomputers, the whole process took less than one
week. Therefore, our GNC is an efficient new paradigm for discovering new drug
candidates.",1910.14650v1
2020-04-27,"Ab-initio calculations of magnetic and optical properties of 3x3 supercell of TiX$_2$ (X = S, Se and Te) compounds under the effect of externally applied electric field and strain","The magnetic and optical properties of titanium dichalcogenide compounds,
TiX$_2$ (X = S, Se and Te) have been calculated by first principles
calculations using density functional theory (DFT) as implemented in SIESTA
code. A 3x3 supercell of the compounds is taken in this study to be able to
tune the properties obtained from the unit cell of these compounds. With
magnetic states (ferromagnetic nature) as the attained ground state, spin
polarized calculations are performed to obtain the mentioned properties.
Further, with spin polarization into effect, external electric field (along
z-direction) and biaxial strain (along x and y-directions) is employed to study
their effect on these properties. The effect of biaxial strain on the geometry
of the compounds is also studied. It is observed that the pristine supercell of
the compounds possess a good amount of magnetic moment and this can be
modulated using the applied field and strain. For the optical properties,
polarized light along the z-direction (c axis) is used. These properties
include the calculation of real & imaginary parts of dielectric function,
absorption coefficient, reflectance, optical conductivity and refractive index
in 0-25 eV energy range. Various modulations of these properties are observed
including the blue-shifts and red-shifts of energies with highest peaks in the
visible region and also shifting of energies to other regions of the
electromagnetic spectrum. Hence, with the tunable magnetic and diverse optical
properties, the compounds can be useful in the field of spintronics and in
making various optical devices.",2004.12632v1
2019-05-08,Compound redistribution due to droplet evaporation on a thin polymeric film: theory,"A thin polymeric film in contact with a fluid body may leach
low-molecular-weight compounds into the fluid. If this fluid is a small
droplet, the compound concentration within the liquid increases due to ongoing
leaching in combination with the evaporation of the droplet. This may
eventually lead to an inversion of the transport process and a redistribution
of the compounds within the thin film. In order to gain an understanding of the
compound redistribution, we apply a macroscopic model for the evaporation of a
droplet and combine that with a diffusion model for the compound transport. In
the model, material deposition and the resulting contact line pinning are
associated with the precipitation of a fraction of the dissolved material. We
find three power law regimes for the size of the deposit area as a function of
the initial droplet size, dictated by the competition between evaporation,
diffusion and the initial compound concentrations in the droplet and the thin
film. The strength of the contact line pinning determines the deposition
profile of the precipitate, characterised by a pronounced edge and a linearly
decaying profile towards the centre of the stain. Our predictions for the
concentration profile within the solid substrate resemble patterns found
experimentally.",1905.02983v1
2021-08-31,Virtual screening of Microalgal compounds as potential inhibitors of Type 2 Human Transmembrane serine protease (TMPRSS2),"More than 198 million cases of severe acute respiratory syndrome coronavirus
2 (SARS-CoV-2) has been reported that result in no fewer than 4.2 million
deaths globally. The rapid spread of the disease coupled with the lack of
specific registered drugs for its treatment pose a great challenge that
necessitate the development of therapeutic agents from a variety of sources. In
this study, we employed an in-silico method to screen natural compounds with a
view to identify inhibitors of the human transmembrane protease serine type 2
(TMPRSS2). The activity of this enzyme is essential for viral access into the
host cells via angiotensin-converting enzyme 2 (ACE-2). Inhibiting the activity
of this enzyme is therefore highly crucial for preventing viral fusion with
ACE-2 thus shielding SARS-CoV-2 infectivity. 3D model of TMPRSS2 was
constructed using I-TASSER, refined by GalaxyRefine, validated by Ramachandran
plot server and overall model quality was checked by ProSA. 95 natural
compounds from microalgae were virtually screened against the modeled protein
that led to the identification 17 best leads capable of binding to TMPRSS2 with
a good binding score comparable, greater or a bit lower than that of the
standard inhibitor (camostat). Physicochemical properties, ADME (absorption,
distribution, metabolism, excretion) and toxicity analysis revealed top 4
compounds including the reference drug with good pharmacokinetic and
pharmacodynamic profiles. These compounds bind to the same pocket of the
protein with a binding energy of -7.8 kcal/mol, -7.6 kcal/mol, -7.4 kcal/mol
and -7.4 kcal/mol each for camostat, apigenin, catechin and epicatechin
respectively. This study shed light on the potential of microalgal compounds
against SARS-CoV-2. In vivo and invitro studies are required to developed
SARS-CoV-2 drugs based on the structures of the compounds identified in this
study.",2108.13764v1
2022-01-18,When Facial Expression Recognition Meets Few-Shot Learning: A Joint and Alternate Learning Framework,"Human emotions involve basic and compound facial expressions. However,
current research on facial expression recognition (FER) mainly focuses on basic
expressions, and thus fails to address the diversity of human emotions in
practical scenarios. Meanwhile, existing work on compound FER relies heavily on
abundant labeled compound expression training data, which are often laboriously
collected under the professional instruction of psychology. In this paper, we
study compound FER in the cross-domain few-shot learning setting, where only a
few images of novel classes from the target domain are required as a reference.
In particular, we aim to identify unseen compound expressions with the model
trained on easily accessible basic expression datasets. To alleviate the
problem of limited base classes in our FER task, we propose a novel Emotion
Guided Similarity Network (EGS-Net), consisting of an emotion branch and a
similarity branch, based on a two-stage learning framework. Specifically, in
the first stage, the similarity branch is jointly trained with the emotion
branch in a multi-task fashion. With the regularization of the emotion branch,
we prevent the similarity branch from overfitting to sampled base classes that
are highly overlapped across different episodes. In the second stage, the
emotion branch and the similarity branch play a ""two-student game"" to
alternately learn from each other, thereby further improving the inference
ability of the similarity branch on unseen compound expressions. Experimental
results on both in-the-lab and in-the-wild compound expression datasets
demonstrate the superiority of our proposed method against several
state-of-the-art methods.",2201.06781v1
2002-05-29,Magnetic fluctuations and superconductivity in YbPd$_2$Sn,"We report muon spin relaxation and inelastic neutron measurements on the
Heusler system YbPd$_2$Sn. Localised anisotropic and quasi-elastic Yb magnetic
fluctuations are observed below $T = 150$K. Both $\mu$SR and neutron data
indicate a slowing-down of the spin-fluctuations, upon lowering the
temperature, similar to that observed in Kondo lattices. The temperature
dependence of the quasi-elastic neutron signal is compatible with a
crystal-electric field scheme having a $\Gamma_7^{\rm CEF}$ ground state. The
muon depolarization rate exhibits an additional contribution upon decreasing
the temperature below $T_{\rm c}$ suggesting a close interplay between magnetic
fluctuations and the superconducting state.",0205617v2
2002-07-10,Martensitic transition and magnetoresistance in a Cu-Al-Mn shape memory alloy. Influence of aging,"We have studied the effect of ageing within the miscibility gap on the
electric, magnetic and thermodynamic properties of a non-stoichiometric Heusler
Cu-Al-Mn shape-memory alloy, which undergoes a martensitic transition from a
$bcc$-based ($\beta$-phase) towards a close-packed structure ($M$-phase).
Negative magnetoresistance which shows an almost linear dependence on the
square of magnetization with different slopes in the $M$- and $\beta$-phases,
was observed. This magnetoresistive effect has been associated with the
existence of Mn-rich clusters with the Cu$_2$AlMn-structure. The effect of an
applied magnetic field on the martensitic transition has also been studied. The
entropy change between the $\beta$- and $M$-phases shows negligible dependence
on the magnetic field but it decreases significantly with annealing time within
the miscibility gap. Such a decrease is due to the increasing amount of
Cu$_2$MnAl-rich domains that do not transform martensitically.",0207254v1
2002-10-22,First-principles calculations of spin spirals in Ni2MnGa and Ni2MnAl,"We report here non-collinear magnetic configurations in the Heusler alloys
Ni2MnGa and Ni2MnAl which are interesting in the context of the magnetic shape
memory effect. The total energies for different spin spirals are calculated and
the ground state magnetic structures are identified. The calculated dispersion
curves are used to estimate the Curie temperature which is found to be in good
agreement with experiments. In addition, the variation of the magnetic moment
as a function of the spiral structure is studied. Most of the variation is
associated with Ni, and symmetry constraints relevant for the magnetization are
identified. Based on the calculated results, the effect of the constituent
atoms in determining the Curie temperature is discussed.",0210482v1
2003-07-04,Detection of weak-order phase transitions in ferromagnets by ac resistometry,"It is shown that ac resistometry can serve as an effective tool for the
detection of phase transitions, such as spin reorientation or premartensitic
phase transitions, which generally are not disclosed by dc resistivity
measurement. Measurement of temperature dependence of impedance, $Z(T)$, allows
one to unmask the anomaly, corresponding to a weak-order phase transition. The
appearance of such an anomaly is accounted for by a change in the effective
permeability $\mu$ of a sample upon the phase transition. Moreover, frequency
dependence of $\mu$ makes it possible to use the frequency of the applied ac
current as an adjusting parameter in order to make this anomaly more
pronounced. The applicability of this method is tested for the rare earth Gd
and Heusler alloy Ni$_2$MnGa.",0307096v1
2003-11-13,"Structural, magnetic and transport properties of thin films of the Heusler alloy Co2MnSi","Thin films of Co2MnSi have been grown on a-plane sapphire substrates from
three elemental targets by dc magnetron co-sputtering. These films are single
phase, have a strong (110) texture and a saturation magnetization of 4.95
uB/formula unit at 10 K. Films grown at the highest substrate temperature of
715 K showed the lowest resistivity (47 uOhm cm at 4.2 K) and the lowest
coercivity (18 Oe). The spin polarization of the transport current was found to
be of the order of 54% as determined by point contact Andreev reflection
spectroscopy. A decrease in saturation magnetization with decreasing film
thickness and different transport behaviour in thinner films indicate a graded
disorder in these films grown on non-lattice matched substrates.",0311316v1
2003-11-19,Shape memory ferromagnets,"In ferromagnetic alloys with shape memory large reversible strains can be
obtained by rearranging the martensitic domain structure by a magnetic field.
Magnetization through displacement of domain walls is possible in the presence
of high magnetocrystalline anisotropy, when martensitic structure rearrangement
is energetically favorable compared to the reorientation of magnetic moments.
In ferromagnetic Heusler alloys Ni$_{2+x}$Mn$_{1-x}$Ga the Curie temperature
exceeds the martensitic transformation temperature. The fact that these two
temperatures are close to room temperature offers the possibility of
magnetically controlling the shape and size of ferromagnets in the martensitic
state. In Ni$_{2+x}$Mn$_{1-x}$Ga single crystals, a reversible strain of $\sim
6$% is obtained in fields of $\sim 1$ T.",0311433v1
2003-12-04,Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition,"The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with
coupled magnetic and structural (martensitic) phase transitions were studied
experimentally and theoretically. The magnetocaloric effect was measured by a
direct method in magnetic fields 0-26 kOe at temperatures close to the
magnetostructural transition temperature. For theoretical description of the
alloy properties near the magnetostructural transition a statistical model is
suggested, that takes into account the coexistence of martensite and austenite
domains in the vicinity of martensite transformation point.",0312110v1
2004-03-09,Resistivity and Thermopower of Ni2.19Mn0.81Ga,"In this paper, we report results of the first studies on the thermoelectric
power (TEP) of the magnetic heusler alloy Ni$_{2.19}$Mn$_{0.81}$Ga. We explain
the observed temperature dependence of the TEP in terms of the crystal field
(CF) splitting and compare the observed behavior to that of the stoichiometric
system Ni$_2$MnGa. The resistivity as a function of temperature of the two
systems serves to define the structural transition temperature, T$_M$, which is
the transition from the high temperature austenitic phase to low temperatures
the martensitic phase. Occurrence of magnetic (Curie-Weiss) and the martensitic
transition at almost the same temperature in Ni$_{2.19}$Mn$_{0.81}$Ga has been
explained from TEP to be due to changes in the density of states (DOS) at the
Fermi level.",0403232v2
2004-05-07,Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys,"A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.",0405134v1
2004-08-10,Towards half-metallic interfaces: the Co$_2$CrAl/InP contacts,"Although the interest on half-metallic Heusler alloys, susceptible to be used
in spintronic applications, has considerably grown, their interfaces with
semiconductors show very low spin-polarization. I identify mechanisms which can
keep the high spin-polarization at the interface (more than 80% of the
electrons at the Fermi level are of majority spin) although the
half-metallicity is lost. The large enhancement of the Cr moment at the
interface between a CrAl terminated Co$_2$CrAl(001) spacer and the InP(001)
semiconductor weakens the effect of the interface states resulting in this high
spin-polarization. On the other hand the Co$_2$CrAl/InP interfaces made up by a
Co layer and either an In or a P one show a severe decrease of the Co spin
moment but Cr in the subinterface layer is bulklike and the resulting
spin-polarization is similar to the CrAl-based interfaces.",0408204v3
2004-09-13,Interface properties of the NiMnSb/InP and NiMnSb/GaAs contacts,"We study the electronic and magnetic properties of the interfaces between the
half-metallic Heusler alloy NiMnSb and the binary semiconductors InP and GaAs
using two different state-of-the-art full-potential \textit{ab-initio}
electronic structure methods. Although in the case of most NiMnSb/InP(001)
contacts the half-metallicity is lost, it is possible to keep a high degree of
spin-polarization when the interface is made up by Ni and P layers. In the case
of the GaAs semiconductor the larger hybridization between the Ni-$d$ and
As-$p$ orbitals with respect to the hybridization between the Ni-$d$ and P-$p$
orbitals destroys this polarization. The (111) interfaces present strong
interface states but also in this case there are few interfaces presenting a
high spin-polarization at the Fermi level which can reach values up to 74%.",0409333v1
2004-12-22,Investigation of the growth and magnetic properties of highly oriented films of the Heusler alloy Co2MnSi on GaAs(001),"Highly (001) oriented thin films of Co2MnSi have been grown on lattice
matched GaAs(001) without a buffer layer. Stoichiometric films exhibited a
saturation magnetization slightly reduced from the bulk value and films grown
at the highest substrate temperature of 689 K showed the lowest resistivity (33
micro.ohm.cm at 4.2 K) and the lowest coercivity (14 Oe). The spin polarization
of the transport current was found to be of the order of 55% as determined by
point contact Andreev reflection spectroscopy. The reduced magnetization
obtained was attributed to the antiferromagnetic Mn2As phase. Twofold in-plane
magnetic anisotropy was observed due to the inequivalence of the <110>
directions, and this was attributed to the nature of the bonding at the
reconstructed GaAs surface.",0412636v1
2005-02-24,Structural and magnetic properties of the (001) and (111) surfaces of the half-metal NiMnSb,"Using the full potential linearised augmented planewave method we study the
electronic and magnetic properties of the (001) and (111) surfaces of the
half-metallic Heusler alloy NiMnSb from first-principles. We take into account
all possible surface terminations including relaxations of these surfaces.
Special attention is paid to the spin-polarization at the Fermi level which
governs the spin-injection from such a metal into a semiconductor. In general,
these surfaces lose the half-metallic character of the bulk NiMnSb, but for the
(111) surfaces this loss is more pronounced. Although structural optimization
does not change these features qualitatively, specifically for the (111)
surfaces relaxations can compensate much of the spin-polarization at the Fermi
surface that has been lost upon formation of the surface.",0502597v1
2006-05-15,Vortex fluctuations and freezing of dipolar-coupled granular moments in thin ferromagnetic films,"Below the Curie temperature T_c of a Heusler-alloy film, consisting of
densely packed, but exchange-decoupled nanograins, the spontaneous
magnetization M_s(T) and static in-plane susceptibility \chi_{||}(T) increase
very slowly signalizing a suppression of magnetization fluctuations. The
unpredicted variation \chi_{||}(T) ~ G_d^2(T), where G_d ~ M_s^2 is the
intergranular dipolar coupling, and also the magnetic freezing observed in the
dynamic susceptibility at lower temperatures is quantitatively reproduced by
Monte Carlo (MC) simulations with 10^4 dipolar-coupled moments on a disordered
triangular lattice. At high temperatures, the MC spin configurations clearly
reveal a dense gas of local vortex structures, which at low temperatures
condense in regions with stronger disorder. This vortex depletion upon
decreasing temperature seems to be responsible for the observed
\textit{increase} of the magnetic relaxation time. For weak disorder, the
temperature dependence of the MC vorticity and a singularity of the specific
heat at T_v=1/2 G_d(T_v)/k_B indicate a thermal transition from a vortex gas to
a state with a single vortex center plus linear vortex structures.",0605377v1
2006-12-04,"Structural, magnetic, and transport properties of Co$_2$FeSi Heusler films","We report the deposition of thin Co$_2$FeSi films by RF magnetron sputtering.
Epitaxial (100)-oriented and L2$_1$ ordered growth is observed for films grown
on MgO(100) substrates. (110)-oriented films on Al$_2$O$_3$(110) show several
epitaxial domains in the film plane. Investigation of the magnetic properties
reveals a saturation magnetization of 5.0 $mu_B/f.u.$ at low temperatures. The
temperature dependence of the resistivity $rho_{xx}(T)$ exhibits a crossover
from a T^3.5 law at T<50K to a T^1.65 behaviour at elevated temperatures.
$rho_{xx}(H)$ shows a small anisotropic magnetoresistive effect. A weak
dependence of the normal Hall effect on the external magnetic field indicates
the compensation of electron and hole like contributions at the Fermi surface.",0612073v1
1998-10-07,Towards a classification of static electro-vacuum space-times containing an asymptotically flat spacelike hypersurface with compact interior,"We show that static electro-vacuum black hole space-times containing an
asymptotically flat spacelike hypersurface with compact interior and with both
degenerate and non-degenerate components of the event horizon do not exist,
under the supplementary hypothesis that all degenerate components of the event
horizon have charges of the same sign. This extends previous uniqueness
theorems of Simon and Masood-ul-Alam (where only non-degenerate horizons were
allowed) and Heusler (where only degenerate horizons were allowed).",9810022v3
2002-10-08,"On ""time-periodic"" black-hole solutions to certain spherically symmetric Einstein-matter systems","This paper explores ``black hole'' solutions of various Einstein-wave matter
systems admitting an isometry of their domain of outer communications taking
every point to its future. In the first two parts, it is shown that such
solutions, assuming in addition that they are spherically symmetric and the
matter has a certain structure, must be Schwarzschild or Reissner-Nordstrom.
Non-trivial examples of matter for which the result applies are a wave map and
a massive charged scalar field interacting with an electromagnetic field. The
results thus generalize work of Bekenstein [1] and Heusler [12] from the static
to the periodic case. In the third part, which is independent of the first two,
it is shown that Dirac fields preserved by an isometry of a spherically
symmetric domain of outer communications of the type described above must
vanish. It can be applied in particular to the Einstein-Dirac-Maxwell equations
or the Einstein-Dirac-Yang/Mills equations, generalizing work of Finster,
Smoller, and Yau [9], [7], [8], and also [6].",0210025v1
1996-05-13,Cosmological Analogues of the Bartnik--McKinnon Solutions,"We present a numerical classification of the spherically symmetric, static
solutions to the Einstein--Yang--Mills equations with cosmological constant
$\Lambda$. We find three qualitatively different classes of configurations,
where the solutions in each class are characterized by the value of $\Lambda$
and the number of nodes, $n$, of the Yang--Mills amplitude. For sufficiently
small, positive values of the cosmological constant, $\Lambda < \Llow(n)$, the
solutions generalize the Bartnik--McKinnon solitons, which are now surrounded
by a cosmological horizon and approach the deSitter geometry in the asymptotic
region. For a discrete set of values $\Lambda_{\rm reg}(n) > \Lambda_{\rm
crit}(n)$, the solutions are topologically $3$--spheres, the ground state
$(n=1)$ being the Einstein Universe. In the intermediate region, that is for
$\Llow(n) < \Lambda < \Lhig(n)$, there exists a discrete family of global
solutions with horizon and ``finite size''.",9605089v1
1996-05-22,Stability Analysis of New Solutions of the EYM system with Cosmological Constant,"We analyze the stability properties of the purely magnetic, static solutions
to the Einstein--Yang--Mills equations with cosmological constant. It is shown
that all three classes of solutions found in a recent study are unstable under
spherical perturbations. Specifically, we argue that the configurations have
$n$ unstable modes in each parity sector, where $n$ is the number of nodes of
the magnetic Yang--Mills amplitude of the background solution. The
``sphaleron--like'' instabilities (odd parity modes) decouple from the
gravitational perturbations. They are obtained from a regular Schr\""odinger
equation after a supersymmetric transformation. The body of the work is devoted
to the fluctuations with even parity. The main difficulty arises because the
Schwarzschild gauge -- which is usually imposed to eliminate the gravitational
perturbations from the Yang--Mills equation -- is not regular for solutions
with compact spatial topology. In order to overcome this problem, we derive a
gauge invariant formalism by virtue of which the unphysical (gauge) modes can
be isolated.",9605166v1
2002-06-14,Statistics of Self-Crossings and Avoided Crossings of Periodic Orbits in the Hadamard-Gutzwiller Model,"Employing symbolic dynamics for geodesic motion on the tesselated
pseudosphere, the so-called Hadamard-Gutzwiller model, we construct extremely
long periodic orbits without compromising accuracy. We establish criteria for
such long orbits to behave ergodically and to yield reliable statistics for
self-crossings and avoided crossings. Self-encounters of periodic orbits are
reflected in certain patterns within symbol sequences, and these allow for
analytic treatment of the crossing statistics. In particular, the distributions
of crossing angles and avoided-crossing widths thus come out as related by
analytic continuation. Moreover, the action difference for Sieber-Richter pairs
of orbits (one orbit has a self-crossing which the other narrowly avoids and
otherwise the orbits look very nearly the same) results to all orders in the
crossing angle. These findings may be helpful for extending the work of Sieber
and Richter towards a fuller understanding of the classical basis of quantum
spectral fluctuations.",0206023v1
2003-09-05,Universal spectral form factor for chaotic dynamics,"We consider the semiclassical limit of the spectral form factor $K(\tau)$ of
fully chaotic dynamics. Starting from the Gutzwiller type double sum over
classical periodic orbits we set out to recover the universal behavior
predicted by random-matrix theory, both for dynamics with and without time
reversal invariance. For times smaller than half the Heisenberg time
$T_H\propto \hbar^{-f+1}$, we extend the previously known $\tau$-expansion to
include the cubic term. Beyond confirming random-matrix behavior of individual
spectra, the virtue of that extension is that the ``diagrammatic rules'' come
in sight which determine the families of orbit pairs responsible for all orders
of the $\tau$-expansion.",0309022v1
2004-01-15,Semiclassical Foundation of Universality in Quantum Chaos,"We sketch the semiclassical core of a proof of the so-called
Bohigas-Giannoni-Schmit conjecture: A dynamical system with full classical
chaos has a quantum energy spectrum with universal fluctuations on the scale of
the mean level spacing. We show how in the semiclassical limit all system
specific properties fade away, leaving only ergodicity, hyperbolicity, and
combinatorics as agents determining the contributions of pairs of classical
periodic orbits to the quantum spectral form factor. The small-time form factor
is thus reproduced semiclassically. Bridges between classical orbits and (the
non-linear sigma model of) quantum field theory are built by revealing the
contributing orbit pairs as topologically equivalent to Feynman diagrams.",0401021v2
2005-03-23,Periodic-Orbit Theory of Universality in Quantum Chaos,"We argue semiclassically, on the basis of Gutzwiller's periodic-orbit theory,
that full classical chaos is paralleled by quantum energy spectra with
universal spectral statistics, in agreement with random-matrix theory. For
dynamics from all three Wigner-Dyson symmetry classes, we calculate the
small-time spectral form factor $K(\tau)$ as power series in the time $\tau$.
Each term $\tau^n$ of that series is provided by specific families of pairs of
periodic orbits. The contributing pairs are classified in terms of close
self-encounters in phase space. The frequency of occurrence of self-encounters
is calculated by invoking ergodicity. Combinatorial rules for building pairs
involve non-trivial properties of permutations. We show our series to be
equivalent to perturbative implementations of the non-linear sigma models for
the Wigner-Dyson ensembles of random matrices and for disordered systems; our
families of orbit pairs are one-to-one with Feynman diagrams known from the
sigma model.",0503052v1
2007-07-06,"Effect of surfaces and interfaces on the electronic, magnetic and gap-related properties of the half-metal Co$_2$MnSn","We present state-of-the-art electronic structure calculations for the
Co$_2$MnSn full-Heusler alloy. We show that in its bulk form it is a
half-metallic ferromagnet with the Fermi level being located within a tiny gap
of the minority-spin density of states. Moreover the alloy shows the
Slater-Pauling behavior with a total spin magnetic moment in the unit cell of 5
$\mu_B$. In the case of the (001) surfaces, the broken bonds at the surface
form a minority band pinned exactly at the Fermi level destroying the
half-metallicity. Our calculations reveal that both the interfaces with the
non-magnetic metal V and the semiconductor InAs are no more half-metallic due
to the different environment of the atoms of the half-metal at the interface.
These interface states although localized only at the first few interface
layers can become conducting when coupled to defect states and kill the
spin-polarization of the current injected from the half-metal into the
semiconductor or the non-magnetic metallic spacer.",0707.0941v1
2007-09-01,Local atomic arrangement and martensitic transformation in Ni$_{50}$Mn$_{35}$In$_{15}$: An EXAFS Study,"Heusler alloys that undergo martensitic transformation in ferromagnetic state
are of increasing scientific and technological interest. These alloys show
large magnetic field induced strains upon martensitic phase change thus making
it a potential candidate for magneto-mechanical actuation. The crystal
structure of martensite is an important factor that affects both the magnetic
anisotropy and mechanical properties of such materials. Moreover, the local
chemical arrangement of constituent atoms is vital in determining the overall
physical properties. Ni$_{50}$Mn$_{35}$In$_{15}$ is one such ferromagnetic
shape memory alloy that displays exotic properties like large magnetoresistance
at moderate field values. In this work, we present the extended x-ray
absorption fine-structure measurements (EXAFS) on the bulk
Ni$_{50}$Mn$_{35}$In$_{15}$ which reveal the local structural change that
occurs upon phase transformation. The change in the bond lengths between
different atomic species helps in understanding the type of hybridization which
is an important factor in driving such Ni-Mn based systems towards martensitic
transformation.",0709.0030v1
2008-04-23,Hybridization Effects in Ni-Mn based Shape Memory Alloys: XAFS Study,"Martensitic and magnetic properties of ferromagnetic shape memory alloys are
known to depend up on structural modulations and associated changes in the
Fermi surface. These modulations although periodic and spanning over multiple
unit cells, involve movement of atoms typically of the order of 0.01A.
Therefore X-ray Absorption Fine Structure (XAFS) is an ideal tool to map both,
local atomic movements and changes in density of states (DOS) due to changing
hybridization as the system transforms from austenitic to martensitic phase.
This paper presents a compilation of our XAFS studies on the Ni-Mn based shape
memory alloys. A complete description of the changes in local structure around
the constituent metal ions in the following alloy compositions: Ni2+xMn1-xGa,
Ni2Mn1.4Sn0.6 and Ni2Mn1.4In0.6 in the austenitic and martensitic phases have
been obtained. The results give the new experimental evidence for the crucial
hybridization component that influences and leads to structural transition in
these Ni-Mn based Heusler alloys.",0804.3663v1
2008-11-14,Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study,"The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with
unique properties for future applications. Band structure calculations predict
exclusively majority bands at the Fermi level, thus indicating {100%} spin
polarization there. As one thinks about applications and the design of
functional materials, the influence of chemical disorder in these materials
must be considered. The magnetization, spin polarization, and electronic
structure are expected to be sensitive to structural and stoichiometric
changes. In this contribution, we report on an investigation of the
spin-dependent electronic structure of NiMnSb. We studied the influence of
chemical disorder on the unoccupied electronic density of states by use of the
ab-initio Coherent Potential Approximation method. The theoretical analysis is
discussed along with corresponding spin-resolved Appearance Potential
Spectroscopy measurements. Our theoretical approach describes the spectra as
the fully-relativistic self-convolution of the matrix-element weighted,
orbitally resolved density of states.",0811.2300v1
2009-01-21,Ruderman-Kittel-Kasuya-Yosida spin density oscillations: impact of the finite radius of the exchange interaction,"A non-interacting electron gas on a one-dimensional ring is considered at
finite temperatures. The localized spin is embedded at some point on the ring
and it is assumed that the interaction between this spin and the electrons is
the exchange interaction being the basis of the Ruderman-Kittel-Kasuya-Yosida
indirect exchange effect. When the number of electrons is large enough, it
turns out that any small but finite interaction radius value can always produce
an essential change of the spin density oscillations in comparison with the
zero interaction radius traditionally used to model the
Ruderman-Kittel-Kasuya-Yosida effect.",0901.3339v2
2009-06-10,Periodic-orbit theory of universal level correlations in quantum chaos,"Using Gutzwiller's semiclassical periodic-orbit theory we demonstrate
universal behaviour of the two-point correlator of the density of levels for
quantum systems whose classical limit is fully chaotic. We go beyond previous
work in establishing the full correlator such that its Fourier transform, the
spectral form factor, is determined for all times, below and above the
Heisenberg time. We cover dynamics with and without time reversal invariance
(from the orthogonal and unitary symmetry classes). A key step in our reasoning
is to sum the periodic-orbit expansion in terms of a matrix integral, like the
one known from the sigma model of random-matrix theory.",0906.1960v2
2009-06-19,Lattice dynamics in magnetic superelastic Ni-Mn-In alloys. Neutron scattering and ultrasonic experiments,"Neutron scattering and ultrasonic methods have been used to study the lattice
dynamics of two single crystals of Ni-Mn-In Heusler alloys close to
Ni$_{50}$Mn$_{34}$In$_{16}$ magnetic superelastic composition. The paper
reports the experimental determination of the low-lying phonon dispersion
curves and the elastic constants for this alloy system. We found that the
frequencies of the TA$_{2}$ branch are relatively low and it exhibits a small
dip anomaly at a wave number $\xi_{0} \approx 1/3$, which softens with
decreasing temperature. Associated with the softening of this phonon, we also
observed the softening of the shear elastic constant $C'=(C_{11}-C_{12})/2$.
Both temperature softenings are typical for bcc based solids which undergo
martensitic transformations and reflect the dynamical instability of the cubic
lattice against shearing of $\{110\}$ planes along $<1\bar{1}0>$ directions.
Additionally, we measured low-lying phonon dispersion branches and elastic
constants in applied magnetic fields aimed to characterize the magnetoelastic
coupling.",0906.3622v1
2009-06-26,Near action-degenerate periodic-orbit bunches: A skeleton of chaos,"Long periodic orbits of hyperbolic dynamics do not exist as independent
individuals but rather come in closely packed bunches. Under weak resolution a
bunch looks like a single orbit in configuration space, but close inspection
reveals topological orbit-to-orbit differences. The construction principle of
bunches involves close self-""encounters"" of an orbit wherein two or more
stretches stay close. A certain duality of encounters and the intervening
""links"" reveals an infinite hierarchical structure of orbit bunches. -- The
orbit-to-orbit action differences $\Delta S$ within a bunch can be arbitrarily
small. Bunches with $\Delta S$ of the order of Planck's constant have
constructively interfering Feynman amplitudes for quantum observables, and this
is why the classical bunching phenomenon could yield the semiclassical
explanation of universal fluctuations in quantum spectra and transport.",0906.4930v1
2009-12-04,A new spin-functional MOSFET based on magnetic tunnel junction technology: pseudo-spin-MOSFET,"We fabricated and characterized a new spin-functional MOSFET referred to as a
pseudo-spin-MOSFET (PS-MOSFET). The PS-MOSFET is a circuit using an ordinary
MOSFET and magnetic tunnel junction (MTJ) for reproducing functions of
spin-transistors. Device integration techniques for a bottom gate MOSFET using
a silicon-on-insulator (SOI) substrate and for an MTJ with a full-Heusler alloy
electrode and MgO tunnel barrier were developed. The fabricated PS-MOSFET
exhibited high and low transconductance controlled by the magnetization
configurations of the MTJ at room temperature. This is the first observation of
spin-transistor operations for spin-functional MOSFETs.",0912.0835v1
2010-02-19,Interplay of magnetic order and Jahn-Teller distortion in a model with strongly correlated electron system,"The Hubbard model has been employed successfully to understand many aspects
of correlation driven physical properties, in particular, the magnetic order in
itenerant electron systems. In some systems such as Heusler alloys, manganites
etc., it is known that, in addition to magnetic order, distortion induced by
Jahn-Teller(J-T) effect also exists. In this paper, based on two-fold
degenerate Hubbard model, the influence of magnetic order on J-T distortion is
investigated. The electron correlation is treated using a spectral density
approach and J-T interaction is added to the model. We find that magnetic order
and structural distortion coexist at low temperature $T$ for a certain range of
electron correlation strength $U$, J-T coupling strength $G$ and band
occupation $n$. At T=0, for a given $n$ and $U$, magnetic order is present but
distortion appears only for a $G$ larger than a critical value. We also studied
the temperature dependence of lattice strain and magnetization choosing a $G$
close to the critical value.",1002.3718v2
2010-02-28,A Frequency-Controlled Magnetic Vortex Memory,"Using the ultra low damping NiMnSb half-Heusler alloy patterned into
vortex-state magnetic nano-dots, we demonstrate a new concept of non-volatile
memory controlled by the frequency. A perpendicular bias magnetic field is used
to split the frequency of the vortex core gyrotropic rotation into two distinct
frequencies, depending on the sign of the vortex core polarity $p=\pm1$ inside
the dot. A magnetic resonance force microscope and microwave pulses applied at
one of these two resonant frequencies allow for local and deterministic
addressing of binary information (core polarity).",1003.0158v1
2010-03-26,Tunnel effect in ferromagnetic half-metal Co$_2$CrAl-superconductor heterostructures,"Ferromagnetic half-metal Co$_2$CrAl films and tunnel contacts Co$_2$CrAl -
insulator (I) - Pb are fabricated and investigated. It is found that the
normalized differential conductivity $\sigma ^{\rm FS} $ of such tunnel
junctions with low resistance is larger than the normalized differential
conductivity $\sigma ^{\rm NS} $ of known normal metal - I - superconductor
type tunnel junctions. It is shown that the observed increase in $\sigma ^{\rm
FS} $ is caused by the accumulation of spin polarized electrons in a
superconductor and can be used for estimating the spin polarization degree $P$
in ferromagnets. This method shows that $P$ of L2$_1$-type ordered Co$_2$CrAl
Heusler alloy films at $T = 4.2{\rm K}$ is close to 1.",1003.5093v1
2010-05-26,Correlation between Local Structure Distortions and Martensitic Transformation in Ni-Mn-In alloys,"The local structural distortions arising as a consequence of increasing Mn
content in Ni_2Mn_1+xIn_1-x (x=0, 0.3, 0.4, 0.5 and 0.6) and its effect on
martensitic transformation have been studied using Extended X-ray Absorption
Fine Structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni
and Mn K-edges in the above compositions, the changes associated with respect
to the local structure of these absorbing atoms are compared. It is seen that
in the alloys exhibiting martensitic transformation ($x \ge 0.4$) there is a
significant difference between the Ni-In and Ni-Mn bond lengths even in the
austenitic phase indicating atomic volume to be the main factor in inducing
martensitic transformation in Ni-Mn-In Heusler alloys.",1005.4873v1
2012-04-03,Effect of interfacial strain on spin injection and spin polarization of Co2CrAl/NaNbO3/Co2CrAl magnetic tunneling junction,"First-principles calculations were carried out to investigate interfacial
strain effects on spin injection and spin polarization of a magnetic tunnel
junction consisting of half-metallic full-Heusler alloy Co2CrAl and
ferroelectric perovskite NaNbO3. Spin-dependent coherent tunneling was
calculated within the framework of non-equilibrium Green's function technique.
Both spin polarization and tunnel magnetoresistance (TMR) are affected by the
interfacial strain but their responses to compressive and tensile strains are
different. Spin polarization across the interface is fully preserved under a
compressive strain due to stronger coupling between interfacial atoms, whereas
a tensile strain significantly enhances interface states and lead to
substantial drops in spin polarization and TMR.",1204.0611v1
2012-06-11,Residual disorder and diffusion in thin Heusler alloy films,"Co2FeSi/GaAs(110) and Co2FeSi/GaAs(111)B hybrid structures were grown by
molecular-beam epitaxy and characterized by transmission electron microscopy
(TEM) and X-ray diffraction. The films contained inhomogeneous distributions of
ordered L2_1 and B2 phases. The average stoichiometry was controlled by lattice
parameter measurements, however diffusion processes lead to inhomogeneities of
the atomic concentrations and the degradation of the interface, influencing
long-range order. An average long-range order of 30-60% was measured by
grazing-incidence X-ray diffraction, i.e. the as-grown Co2FeSi films were
highly but not fully ordered. Lateral inhomogeneities of the spatial
distribution of long-range order in Co2FeSi were found using dark-field TEM
images taken with superlattice reflections.",1206.2242v1
2012-08-15,Two-dimensional electron-gas-like charge transport at magnetic Heusler alloy-SrTiO$_3$ interface,"We report remarkably low residual resistivity, giant residual resistivity
ratio, free-electron-like Hall resistivity and high mobility ($\approx$ 10$^4$
cm$^2$V$^{-1}$s$^{-1}$) charge transport in epitaxial films of Co$_2$MnSi and
Co$_2$FeSi grown on (001) SrTiO$_3$. This unusual behavior is not observed in
films deposited on other cubic oxide substrates of comparable lattice
parameters. The scaling of the resistivity with thickness of the films allow
extraction of interface conductance, which can be attributed to a layer of
oxygen vacancies confined within 1.9 nm of the interface as revealed by
atomically resolved electron microscopy and spectroscopy. The high mobility
transport observed here at the interface of a fully spin polarized metal is
potentially important for spintronics applications.",1208.3099v2
2012-11-12,Magnetic and transport properties of tetragonal- or cubic-Heusler-type Co-substituted Mn-Ga epitaxial thin films,"The composition dependence of the structural, magnetic, and transport
properties of epitaxially grown Mn-Co-Ga films were investigated. The crystal
structure was observed to change from tetragonal to cubic as the Co content was
increased. In terms of the dependence of saturation magnetization on the Co
content, relatively small value was obtained for the
Mn$_{2.3}$Co$_{0.4}$Ga$_{1.3}$ film at a large {\it K}$_\textrm u$ value of 9.2
Merg/cm$^3$. Electrical resistivity of Mn-Co-Ga films was larger than that of
pure Mn-Ga film. The maximum value of the resistivity was 490 $\mu\Omega$cm for
Mn$_{2.2}$Co$_{0.6}$Ga$_{1.2}$ film. The high resistivity of Mn-Co-Ga might be
due to the presence of localized electron states in the films due to chemical
disordering caused by the Co substitution.",1211.2524v1
2012-12-03,Role of covalent hybridization in martensitic structure and magnetic properties of shape memory alloys: the case of Ni50Mn5+xGa35-xCu10,"We have investigated the impact of covalent hybridization on martensitic
structure and magnetic properties of Ni50Mn5+xGa35-xCu10 shape memory alloys.
We found that the lattice distortion ((c-a)/a) of L10 martensite monotonously
changes with the substitution of Mn for Ga atoms and shows a kink behavior at
Ga(at.%)= 25 due to the weakened covalent effect between main-group and
transition-metal atoms. Moreover, owing to the competition between covalence
hybridization and magnetic ordering of introduced Mn atoms, the molecular
magnetic moment and Curie temperature coincidently show maximums at Ga(at.%)=25
as well. These behaviors are closely associated with corresponding changes of
the strength of covalent hybridization. The results therefore suggest that
careful control of the concentration of main-group atoms in Heusler alloys can
serve as an additional general tuning parameter for searching new
multifunctional materials.",1212.0302v1
2013-03-14,Thermal Stability and Electrical Control of Magnetization of Heusler/Oxide Interface and Non-collinear Spin Transport of Its Junction,"Towards next-generation spintronics devices, such as computer memories and
logic chips, it is necessary to satisfy high thermal stability, low-power
consumption and high spin-polarization simultaneously. Here, from
first-principles, we investigate thermal stability (both structure and
magnetization) and the electric field control of magnetic anisotropy on Co2FeAl
(CFA)/MgO. A phase diagram of structural thermal stability of the CFA/MgO
interface is illustrated. An interfacial perpendicular-anisotropy, coming from
the Fe-O orbital hybridization, provides high magnetic thermal stability and a
low stray field. We find an electric-field-induced giant modification of such
perpendicular-anisotropy via a great magnetoelectric effect (the anisotropy
energy coefficient beta~10-7 erg/V cm). Our spin electronic-structure and
non-collinear transport calculations indicate high spin-polarized interfacial
states and good magnetoresistance properties of CFA/MgO/CFA perpendicular
magnetic tunnel junctions.",1303.3473v2
2013-03-29,Formation of double ring patterns on Co2MnSi Heusler alloy thin film by anodic oxidation under scanning probe microscope,"Double ring formation on Co2MnSi (CMS) films is observed at electrical
breakdown voltage during local anodic oxidation (LAO) using atomic force
microscope (AFM). Corona effect and segregation of cobalt in the vicinity of
the rings is studied using magnetic force microscopy and energy dispersive
spectroscopy. Double ring forma-tion is attributed to the interaction of
ablated material with the induced magnetic field during LAO. Steepness of
forward bias transport characteristics from the unperturbed region of the CMS
film suggest a non equilibrium spin contribution. Such mesoscopic textures in
magnetic films by AFM tip can be potentially used for memory storage
applications.",1303.7470v2
2013-04-22,Giant enhancement of spin pumping efficiency using Fe3Si ferromagnet,"Spincurrentronics, which involves the generation, propagation and control of
spin currents, has attracted a great deal of attention because of the
possibility of realizing dissipation-free information propagation. Whereas
electrical generation of spin currents originally made the field of
spincurrentronics possible, and significant advances in spin-current devices
has been made, novel spin-current-generation approaches such as dynamical
methods have also been vigorously investigated. However, the low spin-current
generation efficiency associated with dynamical methods has impeded further
progress towards practical spin devices. Here we show that by introducing a
Heusler-type ferromagnetic material, Fe3Si, pure spin currents can be generated
about twenty times more efficiently using a dynamical method. This achievement
paves the way to the development of novel spin-based devices.",1304.5890v1
2013-05-30,Evolution of ferromagnetic and spin-wave resonances with crystalline order in thin films of full-Heusler alloy Co2MnSi,"We report the evolution of magnetic moment as well as magnetic anisotropy
with crystalline order in Co$_2$MnSi thin films grown on $(100)$ MgO by pulsed
laser deposition. The films become more ordered as the annealing temperature
($T_A$) increases from 400 to 600 $^0$C. The extent of \emph{L}$2_1$ ordering
in the films annealed at 600 $^0$C is $\approx 96%$. The static magnetization
measurements by vibrating sample magnetometry shows a maximum moment of 4.95
$\mu_B$ per formula unit with low coercivity ($H_C$ $\approx$ 65 Oe) in the
films annealed at 600 $^0$C. A rigorous analysis of the azimuthal and polar
angle dependent ferromagnetic resonance (FMR) measured at several temperatures
allows determination of various anisotropy fields relevant to our system as a
function of $T_A$. Finally, we have evaluated the exchange stiffness constant
down to 100 K using spin wave modes in FMR spectra. We have also estimated the
exchange energies as well as stiffness constant by varying the lattice
parameter \emph{ab-initio} using the Korringa-Kohn-Rostoker method.",1305.7048v1
2013-07-14,"Effect of annealing on the magnetic, magnetocaloric and magnetoresistance properties of Ni-Co-Mn-Sb melt spun ribbons","The structural, magnetic, magnetocaloric and magnetotransport properties of
Ni46Co4Mn38Sb12 melt spun ribbons have been systematically investigated. The
partially ordered B2 phase of the as-spun ribbon transforms to fully ordered
L21 phase upon annealing, which signifies a considerable change of the atomic
ordering in the system. The presence of atomic disorder in the as-spun ribbon
gives rise to a higher martensitic transition temperature and a lower
magnetization as compared to the bulk sample. However, annealing the ribbons
helps in regaining the bulk properties to a large extent. Significant changes
in magnetocaloric effect, exchange bias and magnetoresistance have been
observed between the as-spun and the annealed ribbons, indicating the role of
atomic ordering on the functional as well as fundamental properties in the
Heusler system. Importantly, the study shows that one can reduce the hysteresis
loss by preparing melt spun alloys and subjecting them to appropriate annealing
conditions, which enable them to become practical magnetic refrigerants.",1307.3776v1
2013-07-14,In-plane and out of plane magnetic properties in Ni46Co4Mn38Sb12 Heusler alloys ribbons,"Magnetic, magnetocaloric and exchange bias properties have been
systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic
field along (IP) and perpendicular (OP) to the ribbon plane. From the
thermo-magnetization curves, the sharpness of the martensitic transition is
observed to be nearly the same for both IP and OP ribbons. The thermomagnetic
irreversibility region is found to be larger in the OP ribbon at 500 Oe,
indicating that the magnetic anisotropy is larger in this case. The OP ribbon
shows the Hopkinson maximum at 500 Oe, both for the FCC and ZFC modes. The
magnetization curve for IP ribbon shows a faster approach to saturation,
compared to the OP ribbon. Isothermal magnetic entropy change at 50 kOe has
been found to be nearly same for both the ribbons. At 5 K the coercivity and
exchange bias values are larger for the OP ribbon. Crystallographic texturing
of the ribbons and its effect in the easy magnetization direction are found to
be the reason behind the differences between the two ribbons.",1307.3778v1
2013-11-04,Magnetic interactions in the Martensitic phase of Mn rich Ni-Mn-In shape memory alloys,"The magnetic properties of Mn$_{2}$Ni$_{(1+x)}$In$_{(1-x)}$ ($x$ = 0.5, 0.6,
0.7) and Mn$_{(2-y)}$Ni$_{(1.6+y)}$In$_{0.4}$ ($y$ = -0.08, -0.04, 0.04, 0.08)
shape memory alloys have been studied. Magnetic interactions in the martensitic
phase of these alloys are found to be quite similar to those in
Ni$_2$Mn$_{(1+x)}$In$_{(1-x)}$ type alloys. Doping of Ni for In not only
induces martensitic instability in Mn$_2$NiIn type alloys but also affects
magnetic properties due to a site occupancy disorder. Excess Ni preferentially
occupies X sites forcing Mn to the Z sites of X$_2$YZ Heusler composition
resulting in a transition from ferromagnetic ground state to a state dominated
by ferromagnetic Mn(Y) - Mn(Y) and antiferromagnetic Mn(Y)-Mn(Z) interactions.
These changes in magnetic ground state manifest themselves in observation of
exchange bias effect even in zero field cooled condition and virgin
magnetization curve lying outside the hysteresis loop.",1311.0579v1
2014-01-31,First-principles calculation of the instability leading to giant inverse magnetocaloric efects,"The structural and magnetic properties of functional Ni-Mn-Z (Z = Ga, In, Sn)
Heusler alloys are studied by first-principles and Monte Carlo methods. The
\textit{ab initio} calculations give a basic understanding of the underlying
physics which is associated with the strong competition of ferro- and
antiferromagnetic interactions with increasing chemical disorder. The resulting
$d$-electron orbital dependent magnetic ordering is the driving mechanism of
magnetostructural instability which is accompanied by a drop of magnetization
governing the size of the magnetocaloric effect. The thermodynamic properties
are calculated by using the \textit{ab initio} magnetic exchange coupling
constants in finite-temperature Monte Carlo simulations, which are used to
accurately reproduce the experimental entropy and adiabatic temperature changes
across the magnetostructural transition.",1401.8148v1
2014-02-07,Fermi sea term in the relativistic linear muffin-tin-orbital transport theory for random alloys,"We present a formulation of the so-called Fermi sea contribution to the
conductivity tensor of spin-polarized random alloys within the fully
relativistic tight-binding linear muffin-tin-orbital (TB-LMTO) method and the
coherent potential approximation (CPA). We show that the configuration
averaging of this contribution leads to the CPA-vertex corrections that are
solely due to the energy dependence of the average single-particle propagators.
Moreover, we prove that this contribution is indispensable for the invariance
of the anomalous Hall conductivities with respect to the particular LMTO
representation used in numerical implementation. Ab initio calculations for
cubic ferromagnetic 3d transition metals (Fe, Co, Ni) and their random binary
alloys (Ni-Fe, Fe-Si) indicate that the Fermi sea term is small against the
dominating Fermi surface term. However, for more complicated structures and
systems, such as hexagonal cobalt and selected ordered and disordered Co-based
Heusler alloys, the Fermi sea term plays a significant role in the quantitative
theory of the anomalous Hall effect.",1402.1643v1
2014-02-28,The fate of half-metallicity near interfaces: the case of NiMnSb/MgO and NiMnSi/MgO,"The electronic and magnetic properties of the interfaces between the
half-metallic Heusler alloys NiMnSb, NiMnSi and MgO have been investigated
using first-principles density-functional calculations with projector augmented
wave potentials generated in the generalized gradient approximation. In the
case of the NiMnSb/MgO (100) interface the half-metallicity is lost, whereas
the MnSb/MgO contact in the NiMnSb/MgO (100) interface maintains a substantial
degree of spin polarization at the Fermi level ($\sim 60$%). Remarkably, the
NiMnSi/MgO (111) interface shows 100% spin polarization at the Fermi level,
despite considerable distortions at the interface, as well as rather short Si/O
bonds after full structural optimization. This behavior markedly distinguishes
NiMnSi/MgO (111) from the corresponding NiMnSb/CdS and NiMnSb/InP interfaces.",1403.0889v1
2014-03-28,First-principle prediction of Martensitic transformation and magnetic properties of Heusler-type Pt2-xMn1+xGa alloys,"The electronic structure, magnetism and phase stability of Pt2-xMn1+xGa(x=0,
0.25, 0.5, 0.75, 1) alloys are studied by first-principle calculations. The
calculations reveal that a potential magnetic martensitic transformation can be
expected in all the series. In addition, a large magnetic-field-induced strain
is likely to appear in Pt2-xMn1+xGa(x=0, 0.25, 0.75, 1) alloys. The electronic
structure calculations indicate that the tetragonal phase is stabilized upon
the distortion because of the pseudogap formation at the Fermi Level. The
magnetic structure is also investigated and the total magnetic moment of the
tetragonal phase is a little larger than that of the cubic austenite phase in
all the series.",1403.7318v3
2014-04-27,Magnetic shape memory microactuator,"Bimetallic composite nanotweezers based on Ti2NiCu alloy with shape memory
effect (SME) have recently demonstrated the ability to manipulate real
nano-objects, such as nanotubes, and bionanoparticles when heated to 40-60 C by
laser radiation. The possibility of developing nanotweezers operating at
constant temperature is of particular importance mainly for the manipulation of
biological objects. In this work, a microactuator was produced using a
composite bilayer made of a layer of rapidly quenched Ni53Mn24Ga23
ferromagnetic shape memory Heusler alloy and an elastic layer of Pt. The size
of the microactuator is 25x2.3x1.7 micro-meters3. A controlled bending
deformation of the actuator of 1.2 %, with a deflection of the end of the
actuator higher than 2 micro-meter was obtained by applying a magnetic field of
8 T at T = 62 C. The possibility of the development of new technologies for
magnetic-field-controlled nanotools operating at a constant temperature using
the new multifunction magnetic shape memory alloys will be discussed.",1404.6762v1
2014-07-11,A 4-fold-symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy and tunnel magnetoresistance,"An unusual crystallographic orientation of hexagonal Ru with a 4-fold
symmetry emerging in epitaxial MgO/Ru/Co2FeAl/MgO heterostructures is reported,
in which an approximately Ru(02-23) growth attributes to the lattice matching
among MgO, Ru, and Co2FeAl. Perpendicular magnetic anisotropy of the
Co2FeAl/MgO interface is substantially enhanced as compared with those with a
Cr(001) layer. The MTJs incorporating this structure gave rise to the largest
tunnel magnetoresistance for perpendicular MTJs using low damping Heusler
alloys. The 4-fold-symmetry hexagonal Ru arises from an epitaxial growth with
an unprecedentedly high crystal index, opening a unique pathway for the
development of perpendicular anisotropy films of cubic and tetragonal
ferromagnetic alloys.",1407.3160v2
2015-01-27,Transition from semiconducting to metallic-like conducting and weak antilocalization effect in single crystals of LuPtSb,"High quality half-Heusler single crystals of LuPtSb have been synthesized by
a Pb flux method. The temperature dependent resistivity and Hall effects
indicate that the LuPtSb crystal is a p-type gapless semiconductor showing a
transition from semiconducting to metallic conducting at 150 K. Moreover, a
weakly temperature-dependent positive magnetoresistance (MR) as large as 109 %
and high carrier mobility up to 2950 cm2/Vs are experimentally observed at
temperatures below 150 K. The low-field MR data shows evidence for weak
antilocalization (WAL) effect at temperatures even up to 150 K. Analysis of the
temperature and angle dependent magnetoconductance manifests that the WAL
effect originates from the bulk contribution owing to the strong spin-orbital
coupling.",1501.06714v1
2015-04-14,Reduced thermal conductivity of TiNiSn/HfNiSn superlattices,"Diminution of the thermal conductivity is a crucial aspect in thermoelectric
research. We report a systematic and significant reduction of the cross-plane
thermal conductivity in a model system consisting of DC sputtered TiNiSn and
HfNiSn half-Heusler superlattices. The reduction of $\kappa$ is measured by the
3$\omega$ method and originates from phonon scattering at the internal
interfaces. Heat transport in the superlattices is calculated based on
Boltzmann transport theory, including a diffusive mismatch model for the
phonons at the internal interfaces. Down to superlattice periodicity of 3 nm
the phonon spectrum mismatch between the superlattice components quantitatively
explains the reduction of $\kappa$. For very thin individual layers the
interface model breaks down and the artificial crystal shows an enhanced
$\kappa$. We also present an enhanced ZT value for all investigated
superlattices compared to the single TiNiSn and HfNiSn films.",1504.03468v2
2015-05-01,"Half-metallic state and magnetic properties versus the lattice constant in Zr2RhZ (Z = Al, Ga, In) Heusler alloys","The half metallic and magnetic properties of Zr2RhZ (Z = Al, Ga, In) alloys
with an Hg2CuTi-type structure were systematically investigated using the
first-principle calculations. Zr2RhZ (Z = Al, Ga, In) alloys are predicted to
be half-metallic ferrimagnets at their equilibrium lattice constants. The
Zr2Rh-based alloys have Mt (the total magnetic moment per unit cell) and Zt
(the valence concentration) values that in agreement with Slater-Pauling rule
Mt = Zt -18. The half-metallic properties and the magnetic properties at
different lattice constants are discussed in detail. We expect that our results
may trigger Zr2RhZ (Z = Al, Ga, In) applying in the future spintronics field.",1505.00203v1
2015-05-29,Strain behavior and lattice dynamics in Ni50Mn35In15,"The lattice dynamics in the polycrystalline shape-memory Heusler alloy
Ni$_{50}$Mn$_{35}$In$_{15}$ has been studied by means of resonant ultrasound
spectroscopy (RUS). RUS spectra were collected in a frequency range $100-1200$
kHz between 10 and 350 K. Ni$_{50}$Mn$_{35}$In$_{15}$ exhibits a ferromagnetic
transition at 313 K in the austenite and a martensitic transition at 248 K
accompanied by a change of the magnetic state. Furthermore it displays a
antiferromagnetic to ferromagnetic transition within the martensitic phase. We
determined the temperature dependence of the shear modulus and the acoustic
attenuation of Ni$_{50}$Mn$_{35}$In$_{15}$ and compared it with magnetization
data. Following the structural softening, which accompanies the martensitic
transition as a pretransitional phenomenon, a strong stiffening of the lattice
is observed at the martensitic magneto-structural transition. Only a weak
magnetoelastic coupling is evidenced at the Curie temperatures both in
austenite and martensite phase. The large acoustic damping in the martensitic
phase compared with the austenitic phase reflects the motion of the twin walls,
which freezes out in the low temperature region.",1505.08090v1
2015-06-28,Calorimetric and magnetic study for Ni$_{50}$Mn$_{36}$In$_{14}$ and relative cooling power in paramagnetic inverse magnetocaloric systems,"The non-stoichiometric Heusler alloy Ni$_{50}$Mn$_{36}$In$_{14}$ undergoes a
martensitic phase transformation in the vicinity of 345 K, with the high
temperature austenite phase exhibiting paramagnetic rather than ferromagnetic
behavior, as shown in similar alloys with lower-temperature transformations.
Suitably prepared samples are shown to exhibit a sharp transformation, a
relatively small thermal hysteresis, and a large field-induced entropy change.
We analyzed the magnetocaloric behavior both through magnetization and direct
field-dependent calorimetry measurements. For measurements passing through the
first-order transformation, an improved method for heat-pulse relaxation
calorimetry was designed. The results provide a firm basis for the analytic
evaluation of field-induced entropy changes in related materials. An analysis
of the relative cooling power (RCP), based on the integrated field-induced
entropy change and magnetizing behavior of the Mn spin system with
ferromagnetic correlations, shows that a significant RCP may be obtained in
these materials by tuning the magnetic and structural transformation
temperatures through minor compositional changes or local order changes.",1506.08351v1
2015-07-22,An indirect magnetic approach for determining entropy change in first-order magnetocaloric materials,"Taking into account the phase fraction during transition for the first-order
magnetocaloric materials, an improved isothermal entropy change determination
has been put forward based on the Clausius-Clapeyron (CC) equation. It was
found that the isothermal entropy change value evaluated by our method is in
excellent agreement with those determined from the Maxwell-relation (MR) for
Ni-Mn-Sn Heusler alloys, which usually presents a weak field-induced phase
transforming behavior. In comparison with MR, this method could give rise to a
favorable result derived from few thermomagnetic measurements. More
importantly, we can eliminate the isothermal entropy change overestimation
derived from MR, which always exists in the cases of Ni-Co-Mn-In and MnAs
systems with a prominent field-induced transition. These results confirmed that
such a CC-equation-based method is quite practical and superior to the MR-based
ones in eliminating the spurious spike and reducing measuring cost.",1507.06133v2
2015-10-09,Better Band Gaps with Asymptotically Corrected Local Exchange Potentials,"We formulate a spin-polarized van Leeuwen and Baerends (vLB) correction to
the local density approximation (LDA) exchange potential [Phys. Rev. A 49, 2421
(1994)] that enforces the ionization potential (IP) theorem following Stein et
al. [Phys. Rev. Lett. 105, 266802 (2010)]. For electronic-structure problems,
the vLB-correction replicates the behavior of exact-exchange potentials, with
improved scaling and well-behaved asymptotics, but with the computational cost
of semi-local functionals. The vLB+IP corrections produces large improvement in
the eigenvalues over that from LDA due to correct asympotic behavior and atomic
shell structures, as shown on rare-gas, alkaline-earth, zinc-based oxides,
alkali-halides, sulphides, and nitrides. In half-Heusler alloys, this
asymptotically-corrected LDA reproduces the spin-polarized properties
correctly, including magnetism and half-metallicity. We also considered
finite-sized systems [e.g., ringed boron-nitirde (B$_{12}$N$_{12}$) and
graphene (C$_{24}$)] to emphasize the wide applicability of the method.",1510.02688v3
2015-10-21,Unconventional superconductivity in YPtBi and related topological semimetals,"YPtBi, a topological semimetal with very low carrier density, was recently
found to be superconducting below $T_\mathrm{c} = 0.77$\,K. In the conventional
theory, the nearly vanishing density of states around the Fermi level would
imply a vanishing electron-phonon coupling and would therefore not allow for
superconductivity. Based on relativistic density functional theory calculations
of the electron-phonon coupling in YPtBi it is found that carrier
concentrations of more than $10^{21}$\,cm$^{-3}$ are required to explain the
observed critical temperature with the conventional pairing mechanism, which is
several orders of magnitude larger than experimentally observed. It is very
likely that an unconventional pairing mechanism is responsible for the
superconductivity in YPtBi and related topological semimetals with the
Half-Heusler structure.",1510.06209v2
2016-05-01,First clear evidence of quantum chaos in the bound states of an atomic nucleus,"We study the spectral fluctuations of the $^{208}$Pb nucleus using the
complete experimental spectrum of 151 states up to excitation energies of
$6.20$ MeV recently identified at the Maier-Leibnitz-Laboratorium at Garching,
Germany. For natural parity states the results are very close to the
predictions of Random Matrix Theory (RMT) for the nearest-neighbor spacing
distribution. A quantitative estimate of the agreement is given by the Brody
parameter $\omega$, which takes the value $\omega=0$ for regular systems and
$\omega \simeq 1$ for chaotic systems. We obtain $\omega=0.85 \pm 0.02$ which
is, to our knowledge, the closest value to chaos ever observed in experimental
bound states of nuclei. By contrast, the results for unnatural parity states
are far from RMT behavior. We interpret these results as a consequence of the
strength of the residual interaction in $^{208}$Pb, which, according to
experimental data, is much stronger for natural than for unnatural parity
states. In addition our results show that chaotic and non-chaotic nuclear
states coexist in the same energy region of the spectrum.",1605.00210v1
2016-05-13,Spin injection into multilayer graphene from highly spin-polarized Co2FeSi Heusler alloy,"We demonstrate electrical spin injection into multilayer graphene (MLG) in a
lateral spin valve device from a highly spin-polarized Co2FeSi (CFS) Huesler
electrode. Exfoliated MLG was transferred onto pre-patterned epitaxial CFS
wires grown on an Si(111) substrate by a polymer-based transfer method. This
method enabled us to fabricate multiple single-crystal CFS electrodes in
contact with MLG. Electrical spin injection from CFS to MLG was detected
through non-local magnetoresistance (MR) measurement. A non-local spin signal
of 430 ohm was observed; this is the largest value among all reported non-local
MR values in graphene-based devices.",1605.04213v1
2016-08-31,Spin polarization ratios of resistivity and density of states estimated from anisotropic magnetoresistance ratio for nearly half-metallic ferromagnets,"We derive a simple relational expression between the spin polarization ratio
of resistivity, $P_\rho$, and the anisotropic magnetoresistance ratio $\Delta
\rho/\rho$, and that between the spin polarization ratio of the density of
states at the Fermi energy, $P_{\rm DOS}$, and $\Delta \rho/\rho$ for nearly
half-metallic ferromagnets. We find that $P_\rho$ and $P_{\rm DOS}$ increase
with increasing $|\Delta \rho/\rho|$ from 0 to a maximum value. In addition, we
roughly estimate $P_\rho$ and $P_{\rm DOS}$ for a Co$_2$FeGa$_{0.5}$Ge$_{0.5}$
Heusler alloy by substituting its experimentally observed $\Delta \rho/\rho$
into the respective expressions.",1608.08888v1
2016-10-12,Spin injection and detection up to room temperature in Heusler~alloy/$n$-GaAs spin valves,"We have measured the spin injection efficiency and spin lifetime in
Co$_2$FeSi/$n$-GaAs lateral nonlocal spin valves from 20 to 300 K. We observe
large ($\sim$40 $\mu$V) spin valve signals at room temperature and injector
currents of $10^3~$A/cm$^2$, facilitated by fabricating spin valve separations
smaller than the 1 $\mu$m spin diffusion length and applying a forward bias to
the detector contact. The spin transport parameters are measured by comparing
the injector-detector contact separation dependence of the spin valve signal
with a numerical model accounting for spin drift and diffusion. The apparent
suppression of the spin injection efficiency at the lowest temperatures
reflects a breakdown of the ordinary drift-diffusion model in the regime of
large spin accumulation. A theoretical calculation of the D'yakonov-Perel spin
lifetime agrees well with the measured $n$-GaAs spin lifetime over the entire
temperature range.",1610.03797v1
2016-10-17,Designing compensated magnetic states in tetragonal Mn3Ge-based alloys,"Magnetic compensated state attracted much interests due to the observed large
exchange bias and large coercivity, and its potential applications in the
antiferromagnetic spintronics with merit of no stray field. In this work, by ab
initio calculations with KKR-CPA for the treatment of random substitution, we
obtain the complete compensated states in the Ni (Pd, Pt) doped Mn3Ge-based
D022-type tetragonal Heusler alloys. We find the total moment change is
asymmetric across the compensation point (at ~ x = 0.3) in Mn3-xYxGe (Y = Ni,
Pd, Pt), which is highly conforming to that experimentally observed in Mn3Ga.
In addition, an uncommon discontinuous jump is observed across the critical
zero-moment point, indicating that some non-trivial properties can emerge at
this point. Further electronic analysis for the three compensation compositions
reveals large spin polarizations, together with the high Curie temperature of
the host Mn3Ge, making them promising candidates for spin transfer torque
applications.",1610.04971v1
2017-01-30,Effect of site occupancy disorder on Martensitic properties of Mn$_{2}$NiIn type alloys: x-ray absorption fine structure study,"We have carried out \textit{ab-initio} calculations of local structure of Mn
and Ni in Mn$_{2}$Ni$_{1.5}$In$_{0.5}$ alloy with different site occupancies in
order to understand the similarities in martensitic and magnetic properties of
Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ and Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Our results
show that in Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ alloys there is a strong possibility
of Mn atoms occupying all the three, X, Y and Z sites of X$_2$YZ Heusler
structure while Ni atoms preferentially occupy the X sites. Such a site
occupancy disorder of Mn atoms is in addition to a local structural disorder
due to size differences between Mn and In atoms which is also present in
Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Further, a comparison of the calculations
with experimental XAFS at the Mn and Ni K edges in
Mn$_{2-y}$Ni$_{1.6+y}$In$_{0.4}$ ($-0.08 \le y \le 0.08$) indicate a strong
connection between martensitic transformation and occupancy of Z sites by Mn
atoms.",1701.08561v1
2017-03-04,Impact of Anisotropy on Antiferromagnet Rotation in Heusler-type Ferromagnet/Antiferromagnet Epitaxial Bilayers,"We report the magnetotransport properties of ferromagnet (FM)/antiferromagnet
(AFM) Fe$_2$CrSi/Ru$_2$MnGe epitaxial bilayers using current-in-plane
configurations. Above the critical thickness of the Ru$_2$MnGe layer to induce
exchange bias, symmetric and asymmetric curves were observed in response to the
direction of FM magnetocrystalline anisotropy. Because each magnetoresistance
curve showed full and partial AFM rotation, the magnetoresistance curves imply
the impact of the Fe$_2$CrSi magnetocrystalline anisotropy to govern the AFM
rotation. The maximum magnitude of the angular-dependent resistance-change
ratio of the bilayers is more than an order of magnitude larger than that of
single-layer Fe$_2$CrSi films, resulting from the reorientation of AFM spins
via the FM rotation. These results highlight the essential role of controlling
the AFM rotation and reveal a facile approach to detect the AFM moment even in
current-in-plane configurations in FM/AFM bilayers.",1703.01406v2
2017-03-20,Topological phase transitions in multi-component superconductors,"We study the phase transition between a trivial and a time-reversal-invariant
topological superconductor in a single-band system. By analyzing the interplay
of symmetry, topology and energetics, we show that for a generic normal state
band structure, the phase transition occurs via extended intermediate phases in
which even- and odd-parity pairing components coexist. For inversion-symmetric
systems, the coexistence phase spontaneously breaks time-reversal symmetry. For
noncentrosymmetric superconductors, the low-temperature intermediate phase is
time-reversal breaking, while the high-temperature phase preserves
time-reversal symmetry and has topologically protected line nodes. Furthermore,
with approximate rotational invariance, the system has an emergent $U(1) \times
U(1)$ symmetry, and novel topological defects, such as half vortex lines
binding Majorana fermions, can exist. We analytically solve for the dispersion
of the Majorana fermion and show that it exhibit small and large velocities at
low and high energies. Relevance of our theory to superconducting pyrochlore
oxide Cd$_2$Re$_2$O$_7$ and half-Heusler materials is discussed.",1703.06880v2
2017-03-29,Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Films,"Magnetic skyrmions are topological spin structures having immense potential
for energy efficient spintronic devices. However, observations of skyrmions at
room temperature are limited to patterned nanostructures. Here, we report the
observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film
heterostructures at room temperature and in zero external magnetic field
employing magnetic force microscopy. The skyrmions are observed in a trilayer
structure comprised of heavy metal (HM)/ferromagnet (FM)/Oxide interfaces which
result in strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as
evidenced by Brillouin light scattering measurements, in agreement with the
results of micromagnetic simulations. We also emphasize on room temperature
observation of multiple skyrmions which can be stabilized for suitable choices
of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These
results open up a new paradigm for designing room temperature spintronic
devices based on skyrmions in FM continuous thin films.",1703.10224v1
2017-07-27,Reversible tuning of magnetocaloric Ni-Mn-Ga-Co films on ferroelectric PMN-PT substrates,"Tuning functional properties of thin caloric films by mechanical stress is
currently of high interest. In particular, a controllable magnetisation or
transition temperature is desired for improved usability in magnetocaloric
devices. Here, we present results of epitaxial magnetocaloric Ni-Mn-Ga-Co thin
films on ferroelectric Pb(Mg$_{1/3}$Nb$_{2/3}$)$_{0.72}$Ti$_{0.28}$O$_3$
(PMN-PT) substrates. Utilizing X-ray diffraction measurements, we demonstrate
that the strain induced in the substrate by application of an electric field
can be transferred to the thin film, resulting in a change of the lattice
parameters. We examined the consequences of this strain on the magnetic
properties of the thin film by temperature and electric field dependent
measurements. We did not observe a change of martensitic transformation
temperature but a reversible change of magnetisation within the austenitic
state, which we attribute to the intrinsic magnetic instability of this
metamagnetic Heusler alloy.",1707.08839v1
2017-08-03,Room-temperature spin transport in n-Ge probed by four-terminal nonlocal measurements,"We demonsrtate electrical spin injection and detection in $n$-type Ge
($n$-Ge) at room temperature using four-terminal nonlocal spin-valve and
Hanle-effect measurements in lateral spin-valve (LSV) devices with
Heusler-alloy Schottky tunnel contacts. The spin diffusion length
($\lambda$$_{\rm Ge}$) of the Ge layer used ($n \sim$ 1 $\times$ 10$^{19}$
cm$^{-3}$) at 296 K is estimated to be $\sim$ 0.44 $\pm$ 0.02 $\mu$m.
Room-temperature spin signals can be observed reproducibly at the low bias
voltage range ($\le$ 0.7 V) for LSVs with relatively low resistance-area
product ($RA$) values ($\le$ 1 k$\Omega$$\mu$m$^{2}$). This means that the
Schottky tunnel contacts used here are more suitable than ferromagnet/MgO
tunnel contacts ($RA \ge$ 100 k$\Omega$$\mu$m$^{2}$) for developing Ge
spintronic applications.",1708.00962v1
2017-11-16,Using the Callaway model to deduce relevant phonon scattering processes: The importance of phonon dispersion,"The thermal conductivity $\kappa$ of a material is an important parameter in
many different applications. Optimization strategies of $\kappa$ often require
insight into the dominant phonon scattering processes of the material under
study. The Callaway model is widely used as an experimentalist's tool to
analyze the lattice part of the thermal conductivity, $\kappa_l$. Here, we
investigate how deviations from the implicitly assumed linear phonon dispersion
relation affect $\kappa_l$ and in turn conclusions regarding the relevant
phonon scattering processes. As an example, we show for the half-Heusler system
(Hf,Zr,Ti)NiSn, that relying on the Callaway model in its simplest form has
earlier resulted in a misinterpretation of experimental values by assigning the
low measured $\kappa_l$ with unphysically strong phonon scattering in these
materials. Instead, we propose an implementation of more realistic phonon
dispersion curves, combined with empirical expressions for typical phonon
scattering processes, which leads to far better quantitative agreement with
both theoretical and experimental values. This method can easily be extended to
other materials with known phonon dispersion relations.",1711.06153v3
2017-11-27,Characterization of Spin-Transfer-Torque effect induced magnetization dynamics driven by short current pulses,"We present a time-resolved study of the magnetization dynamics in a
microstructured Cr$|$Heusler$|$Pt waveguide driven by the Spin-Hall-Effect and
the Spin-Transfer-Torque effect via short current pulses. In particular, we
focus on the determination of the threshold current at which the spin-wave
damping is compensated. We have developed a novel method based on the temporal
evolution of the magnon density at the beginning of an applied current pulse at
which the magnon density deviates from the thermal level. Since this method
does not depend on the signal-to-noise ratio, it allows for a robust and
reliable determination of the threshold current which is important for the
characterization of any future application based on the Spin-Transfer-Torque
effect.",1711.09647v1
2017-12-06,First-principles investigation of magnetocrystalline anisotropy oscillations in Co$_{2}$FeAl/Ta heterostructures,"We report first-principles investigations of magnetocrystalline anisotropy
energy (MCAE) oscillations as a function of capping layer thickness in Heusler
alloy Co\textsubscript{2}FeAl/Ta heterostructures. Substantial oscillation is
observed in FeAl-interface structure. According to $k$-space and
band-decomposed charge density analyses, this oscillation is mainly attributed
to the Fermi-energy-vicinal quantum well states (QWS) which are confined
between Co\textsubscript{2}FeAl/Ta interface and Ta/vacuum surface. The smaller
oscillation magnitude in the Co-interface structure can be explained by the
smooth potential transition at the interface. These findings clarify that MCAE
in Co\textsubscript{2}FeAl/Ta is not a local property of the interface and that
the quantum well effect plays a dominant role in MCAE oscillations of the
heterostructures. This work presents the possibility of tuning MCAE by QWS in
capping layers, and paves the way for artificially controlling magnetic
anisotropy energy in magnetic tunnel junctions.",1712.02139v2
2017-12-13,Co$_{2}$PtGa: A promising magnetic shape memory alloy with high martensite transition temperature,"In the present work, a combined theoretical and experimental study on
Co$_{2}$PtGa Heusler alloy shows that it exhibits a martensite transition
around 1320 K with a small thermal hysteresis (10 K). Dynamical stability of
Co$_2$PtGa in the tetragonal phase has been established by the theoretically
calculated phonon dispersion curves. Magnetization measurements suggest that
this alloy is a ferromagnetic material with a saturation magnetic moment of
2.83 $\mu_B$/f.u. at 2 K, which is in excellent agreement with the value
obtained from \textit{ab-initio} calculations (2.87 $\mu_B$/f.u.). Our present
study demonstrates that Co$_{2}$PtGa is a promising material for high
temperature magnetic shape memory application.",1712.04765v4
2018-01-12,Irradiated three-dimensional Luttinger semimetal: A factory for engineering Weyl semimetals,"We study the interaction between elliptically polarized light and a
three-dimensional Luttinger semimetal with quadratic band touching using
Floquet theory. In the absence of light, the touching bands can have the same
or the opposite signs of the curvature; in each case, we show that simply
tuning the light parameters allows us to create a zoo of Weyl semimetallic
phases. In particular, we find that double and single Weyl points can coexist
at different energies, and they can be tuned to be type I or type II. We also
find an unusual phase transition, in which a pair of Weyl nodes form at finite
momentum and disappear off to infinity. Considering the broad tunability of
light and abundance of materials described by the Luttinger Hamiltonian, such
as certain pyrochlore iridates, half-Heuslers and zinc-blende semiconductors,
we believe this work can lay the foundation for creating Weyl semimetals in the
lab and dynamically tuning between them.",1801.04287v1
2018-03-07,Edge currents as a probe of the strongly spin-polarized topological noncentrosymmetric superconductors,"Recently the influence of antisymmetric spin-orbit coupling has been studied
in novel topological superconductors such as half-Heuslers and artificial
hetero-structures. We investigate the effect of Rashba and/or Dresselhaus
spin-orbit couplings on the band structure and topological properties of a
two-dimensional noncentrosymetric superconductor. For this goal, the
topological helical edge modes are analyzed for different spin-orbit couplings
as well as for several superconducting pairing symmetries. To explore the
transport properties, we examine the response of the spin-polarized edge states
to an exchange field in a superconductor-ferromagnet heterostructure. The
broken chiral symmetry causes the uni-directional currents at opposite edges.",1803.02591v1
2018-05-15,Spincaloric properties of epitaxial Co$_2$MnSi/MgO/Co$_2$MnSi magnetic tunnel junctions,"The electronic transport and spincaloric properties of epitaxial magnetic
tunnel junctions with half-metallic Co$_2$MnSi Heusler electrodes, MgO
tunneling barriers, and different interface terminations are investigated by
using first-principles calculations. A new approach to spincaloric properties
is presented that circumvents the linear response approximation inherent in the
Seebeck coefficient and compared to the method of Sivan and Imry. This approach
supports two different temperatures in the two electrodes and provides the
exact current and/or voltage response of the system. Moreover, it accounts for
temperature-dependent chemical potentials in the electrodes and finite-bias
effects. We find that especially the former are important for obtaining
qualitatively correct results, even if the variations of the chemical
potentials are small. It is shown how the spincaloric properties can be
tailored by the choice of the growth conditions. We find a large effective and
spin-dependent Seebeck coefficient of $-65$ $\mu$V/K at room temperature for
the purely Co-terminated interface. We suggest to use such interfaces in
thermally operated magnetoresistive random access memory modules, which exploit
the magneto-Seebeck effect, to maximize the thermally induced readout voltage.",1805.05805v1
2018-05-18,Search for alternative magnetic tunnel junctions based on all-Heusler stacks,"By imposing the constraints of structural compatibility, stability and a
large tunneling magneto-resistance, we have identified the
Fe$_3$Al/BiF$_3$/Fe$_3$Al stack as a possible alternative to the
well-established FeCoB/MgO/FeCoB in the search for a novel materials platform
for high-performance magnetic tunnel junctions. Various geometries of the
Fe$_3$Al/BiF$_3$/Fe$_3$Al structure have been analyzed, demonstrating that a
barrier of less than 2~nm yields a tunneling magneto-resistance in excess of
25,000~\% at low bias, without the need for the electrodes to be half-metallic.
Importantly, the presence of a significant spin gap in Fe$_3$Al for states with
$\Delta_1$ symmetry along the stack direction makes the TMR very resilient to
high voltages.",1805.08603v1
2018-09-19,Structure-property relationship of Co$_2$MnSi thin films in response to He$^+$ -irradiation,"We investigated the structure-property relationship of Co$_2$MnSi Heusler
thin films upon the irradiation with He$^+$ ions. The variation of the crystal
structure with increasing ion fluence has been probed using nuclear magnetic
resonance (NMR) and transmission electron microscopy (TEM), and associated with
the corresponding changes of the magnetic behavior. A decrease of both the
structural order and the moment in saturation is observed. Specifically, we
detect a direct transition from a highly $L2_1$-ordered to a fully
$A2$-disordered structure type and quantify the evolution of the $A2$
structural contribution as a function of ion fluence. Complementary TEM
analysis reveals a spatially-resolved distribution of the $L2_1$ and $A2$
phases showing that the $A2$ disorder starts at the upper part of the films.
The structural degradation in turn leads to a decreasing magnetic moment in
saturation in response to the increasing fluence.",1809.07097v1
2019-11-09,Multi-Principal-Element Approach to High-Performance Thermoelectric Materials,"High-entropy alloys are characterized by high configurational entropy. Since
the discovery of high-entropy alloys (HEA) in 2004, entropy engineering has
provided a promising direction for exploiting composition, lattice disorder,
band structure, and microstructure effects to advance thermoelectric
performance. This review discusses the impact of entropy on thermoelectric
properties and looks back at the role of multi-principal-element alloys, a
weaker version of HEA, on the development of compositionally complex
thermoelectric alloys in achieving high thermoelectric performance. The
experimental and theoretical efforts in a wide range of material systems such
as TAGS, LAST, half-Heusler, liquid-like copper chalcogenides, SnTe, and
CuInTe2 chalcopyrites provide insights into the entropy engineering approach
and also promise an emerging paradigm of high-entropy thermoelectrics.",1911.03797v1
2021-07-02,Investigating 3D printed Cartesian Divers,"Despite the difficult circumstances due to the COVID-19 pandemics, physics
students can tackle interesting questions that are part of physics competitions
as the German Physicists' Tournament (GPT) 2020. Due to the COVID-19 pandemics
in 2020, many competitions such as the GPT are held online. Furthermore, the
usual options of equipment offered by the supervising university institutions
could not be used by the students. The problems of the GPT 2020 therefore had
to be chosen in such a way that they could be examined at home using simple
means. One of these supposedly simple but profound experiments - the Cartesian
divers - is described in this article. By using 3D printing, the relevant
variables could be varied in a controlled manner and the theoretical model for
Cartesian divers could be examined experimentally.",2107.00950v1
2021-07-24,Randomly packed Ni$_2$MnIn and NiMn structural units in off stoichiometric Ni$_2$Mn$_{2-y}$In$_y$ alloys,"Ni$_2$Mn$_{2-y}$In$_y$ alloys transform from the martensitic $L1_0$
antiferromagnetic ground state near $y = 0$ to austenitic ferromagnetic $L2_1$
Heusler phase near $y = 1$ due to doping of In impurity for Mn. The off
stoichiometric alloys prepared by rapid quenching are structurally metastable
and dissociate into a mixture of $L2_1$ (Ni$_2$MnIn) and $L1_0$ (NiMn) phases
upon temper annealing. Despite this structural disintegration, the martensitic
transformation temperature remains invariant in the temper annealed alloys.
Investigations of the local structure of the constituent atoms reveal the
presence of strongly coupled Ni$_2$MnIn and NiMn structural units in the temper
annealed as well as the rapidly quenched off stoichiometric
Ni$_2$Mn$_{2-y}$In$_y$ alloys irrespective of their crystal structure. This
random packing of the $L2_1$ and $L1_0$ structural units seems to be
responsible for invariance of martensitic transition temperature in the temper
annealed alloys as well as the absence of strain glass transition in rapidly
quenched alloys.",2107.11551v1
2018-10-08,Porosity-mediated High-performance Thermoelectric Materials,"Whether porosity can effectively improve thermoelectric performance is still
an open question. Herein we report that thermoelectric performance can be
significantly enhanced by creating porosity in n-type
Mg3.225Mn0.025Sb1.5Bi0.49Te0.01, with a ZT of ~0.9 at 323 K and ~1.6 at 723 K,
making the average ZT much higher for better performance. The large improvement
at room temperature is significant considering that such a ZT value is
comparable to the best ZT at this temperature in n-type Bi2Te3. The enhancement
was mainly from the improved electrical mobility and multi-scale phonon
scattering, particularly from the well-dispersed bismuth nano-precipitates in
the porous structure. We further extend this approach to other thermoelectric
materials such as half-Heuslers Nb0.56V0.24Ti0.2FeSb and
Hf0.25Zr0.75NiSn0.99Sb0.01 and Bi0.5Sb1.5Te3 showing similar improvements,
further advancing thermoelectric materials for applications.",1810.03356v2
2019-10-09,Superconductivity from Coulomb repulsion in three-dimensional quadratic band touching Luttinger semimetals,"We study superconductivity driven by screened Coulomb repulsion in
three-dimensional Luttinger semimetals with a quadratic band touching and
strong spin-orbit coupling. In these semimetals, the Cooper pairs are formed by
spin-3/2 fermions with non-trivial wavefunctions. We numerically solve the
linear Eliashberg equation to obtain the critical temperature of a singlet
s-wave gap function as a function of doping, with account of spin-orbit and
self-energy corrections. In order to understand the underlying mechanism of
superconductivity, we compute the sensitivity of the critical temperature to
changes in the dielectric function $\epsilon(i\Omega_n,q)$. We relate our
results to the plasmon and Kohn-Luttinger mechanisms. Finally, we discuss the
validity of our approach and compare our results to the litterature. We find
good agreement with some bismuth-based half-Heuslers, such as YPtBi, and
speculate on superconductivity in the iridate Pr2Ir2O7.",1910.04189v2
2014-06-25,Magnetic structure of GdBiPt: A candidate antiferromagnetic topological insulator,"A topological insulator is a state of matter which does not break any
symmetry and is characterized by topological invariants, the integer
expectation values of non-local operators. Antiferromagnetism on the other hand
is a broken symmetry state in which the translation symmetry is reduced and
time reversal symmetry is broken. Can these two phenomena coexist in the same
material? A proposal by Mong {\it et al.}\cite{Mong2010} asserts that the
answer is yes. Moreover, it is theoretically possible that the onset of
antiferromagnetism enables the non-trivial topology since it may create
spin-orbit coupling effects which are absent in the non-magnetic phase. The
current work examines a real system, half-Heusler GdBiPt, as a candidate for
topological anti ferromagnetism. We find that the magnetic moments of the
gadolinium atoms form ferromagnetic sheets which are stacked
antiferromagnetically along the body diagonal. This magnetic structure may
induce spin orbit coupling on band electrons as they hop perpendicular to the
ferromagnetic sheets.",1406.6663v1
2018-12-03,"Mn2V0.5Co0.5Z (Z= Ga, Al) Heusler alloys: Fully compensated ferrimagnets with high Tc and compensation temperature","High TC fully compensated ferrimagnets are potential candidates for spin
transfer torque based spintronic devices. We report the structural and magnetic
properties of high TC fully compensated ferrimagnets Mn2V0.5Co0.5Z where Z is
Ga, Al, in the melt spun ribbon and arc melted bulk form. While the parent
alloys Mn2YZ where Y is V, Co and Z is Ga, Al exhibits a magnetic moment value
around 2 muB per f.u, the Mn2V0.5Co0.5Ga alloy exhibits room temperature nearly
fully compensated moment value of 0.09 and 0.13 muB per f.u. in the bulk and
ribbon form respectively. For Mn2V0.5Co0.5Al this turned out to be 0.04 and
0.08 muB per f.u. In Contrast to the bulk sample's Neel P type ferrimagnetic
behaviour, ribbon samples exhibit Neel N type ferrimagnetic characteristic with
a high compensation temperature of 420 K for Ga alloy and 275 K for Al alloy.
The observed TC values are more than 640 K for all samples. The differences in
the magnetic properties of arc melted and melt spun alloys indicates that even
a slight variation in stoichiometry and sample preparation method can influence
the physical properties of a compensated system.",1812.00714v1
2018-12-05,Majorana multipole response of topological superconductors,"In contrast to elementary Majorana particles, emergent Majorana fermions
(MFs) in condensed-matter systems may have electromagnetic multipoles. We
developed a general theory of magnetic multipoles for surface helical MFs on
time-reversal-invariant superconductors. The results show that the multipole
response is governed by crystal symmetry, and that a one-to-one correspondence
exists between the symmetry of Cooper pairs and the representation of magnetic
multipoles under crystal symmetry. The latter property provides a way to
identify nonconventional pairing symmetry via the magnetic response of surface
MFs. We also find that most helical MFs exhibit a magnetic-dipole response, but
those on superconductors with spin-3/2 electrons may display a
magnetic-octupole response in leading order, which uniquely characterizes
high-spin superconductors. Detection of such an octupole response provides
direct evidence of high-spin superconductivity, such as in half-Heusler
superconductors.",1812.01857v1
2018-12-18,Optical response of Luttinger semimetals in the normal and superconducting states,"We investigate the optical response properties of three-dimensional Luttinger
semimetals with the Fermi energy close to a quadratic band touching point. In
particular, in order to address recent experiments on the spectroscopy of
Pyrochlore Iridates and half-Heusler superconductors, we derive expressions for
the optical conductivity in both the normal and general superconducting states
in the linear response regime within the random phase approximation. The
response functions can be decomposed into contributions from intraband and
interband transitions, the latter comprising a genuine signature of the
quadratic band touching point. We demonstrate the importance of interband
transitions in the optical response in the normal state both in the homogeneous
and quasi-static limit. Our analysis reveals a factorization property of the
homogeneous conductivity in the spatially anisotropic case and the divergence
of the conductivity for strong spatial anisotropy. In the quasi-static limit,
the response is dominated by interband transitions and significantly different
from systems with a single parabolic band. As an applications of the formalism
in the superconducting state we compute the optical conductivity and superfluid
density for the s-wave singlet superconducting case for both finite and
vanishing chemical potential.",1812.07555v2
2020-04-21,Building hierarchical martensite,"Martensitic materials show a complex, hierarchical microstructure containing
structural domains separated by various types of twin boundaries. Several
concepts exist to describe this microstructure on each length scale, however,
there is no comprehensive approach bridging the whole range from the nano- up
to the macroscopic scale. Here, we describe for a Ni-Mn-based Heusler alloy how
this hierarchical microstructure is built from scratch with just one key
parameter: the tetragonal distortion of the basic building block at the atomic
level. Based on this initial block, we introduce five successive levels of
nested building blocks. At each level, a larger building block is formed by
twinning the preceding one to minimise the relevant energy contributions
locally. This naturally explains the occurrence of different types of twin
boundaries. We compare this scale-bridging approach of nested building blocks
with experiments in real and reciprocal space. Our approach of nested building
blocks is versatile as it can be applied to the broad class of functional
materials exhibiting diffusionless transformations.",2004.09768v1
2020-05-07,Ultrafast All Optical Magnetization Control for Broadband Terahertz Spin Wave Generation,"Terahertz spin waves could be generated on-demand via all-optical
manipulation of magnetization by femtosecond laser pulse. Here, we present an
energy balance model, which explains the energy transfer rates from laser pulse
to electron bath coupled with phonon, spin, and magnetization of five different
magnetic metallic thin films: Iron, Cobalt, Nickel, Gadolinium and Ni$_{2}$MnSn
Heusler alloy. Two types of transient magnetization dynamics emerge in metallic
magnetic thin films based on their Curie temperatures (T$_{C}$): type I (Fe,
Co, and Ni with T$_{C}$ > room temperature, RT) and type II films (Gd and
Ni$_{2}$MnSn with T$_{C}$ $\approx$ RT). We study the effect of laser fluence
and pulse width for single Gaussian laser pulses and the effect of metal film
thickness on magnetization dynamics. Spectral dynamics show that broadband spin
waves up to 24 THz could be generated by all-optical manipulation of
magnetization in these nanofilms.",2005.03493v1
2020-08-04,Ultra-High Thermoelectric Power Factors in Narrow Gap Materials with Asymmetric Bands,"We theoretically unveil the unconventional possibility to achieve extremely
high thermoelectric power factors in lightly doped narrow gap semiconductors
with asymmetric conduction/valence bands operated in the bipolar transport
regime. Specifically, using Boltzmann transport simulations, we show that
narrow bandgap materials, rather than suffering from performance degradation
due to bipolar conduction, if they possess highly asymmetric conduction and
valence bands in terms of either effective masses, density of states, or phonon
scattering rates, then they can deliver very high power factors. We show that
this is reached because, under these conditions, electronic transport becomes
phonon scattering limited, rather than ionized impurity scattering limited,
which allows large conductivities. We explain why this effect has not been
observed so far in the known narrow-gap semiconductors, interpret some recent
related experimental findings, and propose a few examples from the half-Heusler
materials family for which this effect can be observed and power factors even
up to 50 mW/m$K^2$ can be reached.",2008.01359v1
2020-08-26,Field-induced magnetic phase transitions and the resultant giant anomalous Hall effect in antiferromagnetic half-Heusler DyPtBi,"We report field-induced magnetic phase transitions and transport properties
of antiferromagnetic DyPtBi. We show that DyPtBi hosts a delicate balance
between two different magnetic ground states, which can be controlled by a
moderate magnetic field. Furthermore, it exhibits giant anomalous Hall effect
(\sigma_A=1540 (ohm cm)^{-1},\theta_{AHE} = 24%) in a field-induced Type-I spin
structure, presumably attributed to the enhanced Berry curvature associated
with avoided band-crossings near the Fermi energy and / or non-zero spin
chirality. The latter mechanism points DyPtBi towards a rare potential
realization of anomalous Hall effect in an antiferromagnet with
face-center-cubic lattice that was proposed in [Physical Review Letters 87,
116801 (2001)].",2008.11345v1
2020-08-27,Lattice strain accommodation and absence of pre-transition phases in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$,"The stoichiometric Ni$_{50}$Mn$_{25}$In$_{25}$ Heusler alloy transforms from
a stable ferromagnetic austenitic ground state to an incommensurate modulated
martensitic ground state with a progressive replacement of In with Mn without
any pre-transition phases. The absence of pre-transition phases like strain
glass in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$ alloys is explained to be the ability
of the ferromagnetic cubic structure to accommodate the lattice strain caused
by atomic size differences of In and Mn atoms. Beyond the critical value of $x$
= 8.75, the alloys undergo martensitic transformation despite the formation of
ferromagnetic and antiferromagnetic clusters and the appearance of a super spin
glass state.",2008.11982v1
2021-03-15,Tuneable local order in thermoelectric crystals,"Although crystalline solids are characterized by their periodic structures,
some are only periodic on average and deviate on a local scale. Distinct local
orderings can exist with identical periodic structures making their differences
hidden to normal diffraction methods. Using x-ray scattering we investigate the
thermoelectric half-Heusler, Nb1-xCoSb, with high vacancy concentrations, where
signs of local order have been attributed to differences in stoichiometry. We
show that the composition is actually always very close to x = 1/6 irrespective
of nominal sample composition, and that the synthesis method controls the local
order. The vacancy distribution is shown to follow a vacancy repulsion model,
and local structural relaxations around the vacancies are characterized.
Control over the local structure provides a new frontier for tuning material
properties.",2103.08543v1
2016-03-30,Magnetic Interactions and Electronic Structure of Pt$_{2}$Mn$_{1-x}$Y$_{x}$Ga (Y = Cr and Fe) system : An ab-initio calculation,"First principles density functional theory based calculations have been
carried out to predict the effects of Mn replacement by Fe and Cr on electronic
as well as magnetic properties of Pt$_{2}$MnGa as well as Ni$_{2}$MnGa. All the
materials studied here are predicted to have conventional Heusler alloy
structure in their ground state and they are found to be electronically stable
on the basis of their respective formation energy. The replacement of Mn by Fe
leads to a ferromagnetic ground state whereas in case of Mn replacement by Cr
an {\it intra-sublattice} anti-ferromagnetic configuration has been observed to
have lower energy. We study the magnetic exchange interaction between the atoms
for the materials with ferromagnetic and anti-ferromagnetic configurations to
show the effects of Fe and Cr substitution at Mn site on the magnetic
interactions of these systems. Detailed analysis of electronic structure in
terms of density of states has been carried out to study the effect of
substitution.",1603.09139v1
2016-12-22,Type-II Dirac semimetals in the YPd$_2$Sn class,"The Lorentz-invariance-violating Weyl and Dirac fermions have recently
attracted intensive interests as new types of particles beyond high-energy
physics, and they demonstrate novel physical phenomena such as angle-dependent
chiral anomaly and topological Lifshitz transition. Here we predict the
existence of Lorentz-invariance-violating Dirac fermions in the YPd$_2$Sn class
of Heusler alloys that emerge at the boundary between the electron-like and
hole-like pockets in the Brillouin zone, based on the first-principles
electronic structure calculations. In combination with the fact that this class
of materials was all reported to be superconductors, the YPd$_2$Sn class
provides an appropriate platform for studying exotic physical properties
distinguished from conventional Dirac fermions, especially for realizing
possible topological superconductivity.",1612.07456v1
2017-06-06,Coupling between a charge density wave and magnetism in an Heusler material,"The Prototypical magnetic memory shape alloy Ni$_2$MnGa undergoes various
phase transitions as a function of temperature, pressure, and doping. In the
low-temperature phases below 260 K, an incommensurate structural modulation
occurs along the [110] direction which is thought to arise from softening of a
phonon mode. It is not at present clear how this phenomenon is related, if at
all, to the magnetic memory effect. Here we report time-resolved measurements
which track both the structural and magnetic components of the phase transition
from the modulated cubic phase as it is brought into the high-symmetry phase.
The results suggest that the photoinduced demagnetization modifies the Fermi
surface in regions that couple strongly to the periodicity of the structural
modulation through the nesting vector. The amplitude of the periodic lattice
distortion, however, appears to be less affected by the demagnetizaton.",1706.01685v1
2017-10-25,"Site occupancy, composition and magnetic structure dependencies of martensitic transformation in Mn$_{2}$Ni$_{1+x}$Sn$_{1-x}$","A delicate balance between various factors such as site occupancy,
composition and magnetic ordering seems to affect the stability of the
martensitic phase in Mn$_{2}$Ni$_{1+x}$Sn$_{1-x}$. Using first-principles DFT
calculations, we explore the impacts of each one of these factors on the
martensitic stability of this system. Our results on total energies, magnetic
moments and electronic structures upon changes in the composition, the magnetic
configurations and the site occupancies show that the occupancies at the 4d
sites in the Inverse Heusler crystal structure play the most crucial role. The
presence of Mn at the 4d sites originally occupied by Sn and it's interaction
with the Mn atoms at other sites decide the stability of the martensitic
phases. This explains the discrepancy between the experiments and earlier DFT
calculations regarding phase stability in Mn$_{2}$NiSn. Our results
qualitatively explain the trends observed experimentally with regard to
martensitic phase stability and the magnetisations in Ni-excess, Sn-deficient
Mn$_{2}$NiSn system.",1710.09093v1
2019-09-12,Single pulse all-optical toggle switching of magnetization without Gd: The example of Mn2RuxGa,"Energy-efficient control of magnetization without the help of a magnetic
field is a key goal of spintronics. Purely heat-induced single-pulse
all-optical toggle switching has been demonstrated, but so far only in Gd based
amorphous ferrimagnet films. In this work, we demonstrate toggle switching in
the half-metallic compensated ferrimagnetic Heusler alloys Mn2RuxGa, which have
two crystallographically-inequivalent Mn sublattices. Moreover, we observe the
switching at room temperature in samples that are immune to external magnetic
fields in excess of 1 T, provided they exhibit compensation above room
temperature. Observations of the effect in compensated ferrimagnets without Gd
challenges our understanding of all-optical switching. The dynamic behavior
indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis
for fast optical switching of magnetization and break new ground for engineered
materials that can be used for nonvolatile ultrafast switches using ultrashort
pulses of light.",1909.05809v2
2019-09-26,The study of magnetic topological semimetals by first principles calculations,"Magnetic topological semimetals (TSMs) are topological quantum materials with
broken time-reversal symmetry (TRS) and isolated nodal points or lines near the
Fermi level. Their topological properties would typically reveal from the
bulk-edge correspondence principle as nontrivial surface states such as Fermi
arcs or drumhead states, etc. Depending on the degeneracies and distribution of
the nodes in the crystal momentum space, TSMs are usually classified into Weyl
semimetals (WSMs), Dirac semimetals (DSMs), nodal-line semimetals (NLSMs),
triple-point semimetals (TPSMs), etc. In this review article, we present the
recent advances of magnetic TSMs from a computational perspective. We first
review the early predicted magnetic WSMs such as pyrochlore iridates and
HgCr2Se4, as well as the recently proposed Heusler, Kagome layers, and
honeycomb lattice WSMs. Then we discuss the recent developments of magnetic
DSMs, especially CuMnAs in Type-III and EuCd2As2 in Type-IV magnetic space
groups (MSGs). Then we introduce some magnetic NLSMs that are robust against
spin-orbit coupling (SOC), namely Fe3GeTe2 and LaCl (LaBr). Finally, we discuss
the prospects of magnetic TSMs and the interesting directions for future
research.",1909.11999v1
2019-09-28,Size-Dependent Structural and Magnetic Properties of Disordered Co2FeAl Heusler Alloy Nanoparticles,"Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by
chemical route. The effect of the size of NPs upon the structure and
magnetization compared to its bulk counterpart was investigated. The structure
and composition were determined from X-ray diffraction (XRD) and electron
microscopy. XRD analysis shows that the samples are having single (A2-type)
disordered phase. Magnetization measurements suggest that the samples are soft
ferromagnetic in nature with very low coercivity. Enhanced magnetic properties
like saturation magnetization, coercive force, retentivity, and
Curie-temperature are observed with a decrease in particle size. The effect of
particle size on hysteresis losses is also discussed. The smallest particles of
size 16 nm exhibited the highest saturation magnetization and transition
temperature of 180.73 emu/g and 1261 K, respectively. The origin of enhancement
in the magnetization of Co2FeAl nano-alloy is attributed to the strong Co-Co
exchange interaction due to disorder present in the systems.",1909.13088v1
2020-06-29,Spin-polarized Weyl cones and gigantic anomalous Nernst effect in ferromagnetic Heusler films,"Weyl semimetals are characterized by the presence of massless band dispersion
in momentum space. When a Weyl semimetal meets magnetism, large anomalous
transport properties emerge as a consequence of its topological nature. Here,
using $in-situ$ spin- and angle-resolved photoelectron spectroscopy combined
with $ab\ initio$ calculations, we visualize the spin-polarized Weyl cone and
flat-band surface states of ferromagnetic Co$_2$MnGa films with full remanent
magnetization. We demonstrate that the anomalous Hall and Nernst conductivities
systematically grow when the magnetization-induced massive Weyl cone at a
Lifshitz quantum critical point approaches the Fermi energy, until a high
anomalous Nernst thermopower of $\sim 6.2$ $\rm \mu V K^{-1}$ is realized at
room temperature. Given this topological quantum state and full remanent
magnetization, Co$_2$MnGa films are promising for realizing high efficiency
heat flux and magnetic field sensing devices operable at room temperature and
zero-field.",2006.15769v2
2020-07-04,Impurities in 3D quadratic band-touching Luttinger semimetals : Friedel and RKKY oscillations,"We investigate the response of 3D Luttinger semimetals to localized charge
and spin impurities as a function of doping. The strong spin-orbit coupling of
these materials strongly influences the Friedel oscillations and RKKY
interactions. This can be seen at short distances with an $1/r^4$ divergence of
the responses, and anisotropic behavior. Certain of the spin-orbital signatures
are robust to temperature, even if the charge and spin oscillations are smeared
out, and give an unusual diamagnetic Pauli susceptibility. We compare our
results to the experimental literature on the bismuth-based half-Heuslers such
as YPtBi and on the pyrochlore iridate Pr$_2$Ir$_2$O$_7$.",2007.02046v2
2020-09-01,Molecular beam epitaxy of the half-Heusler antiferromagnet CuMnSb,"We report growth of CuMnSb thin films by molecular beam epitaxy on InAs(001)
substrates. The CuMnSb layers are compressively strained ($0.6~\text{%}$) due
to lattice mismatch. The thin films have a $\omega$ full width half max of
$7.7^{''}$ according to high resolution X-ray diffraction, and a root mean
square roughness of $0.14~\text{nm}$ as determined by atomic force microscopy.
Magnetic and electrical properties are found to be consistent with reported
values from bulk samples. We find a N\'eel temperature of $62~\text{K}$, a
Curie-Weiss temperature of $-65~\text{K}$ and an effective moment of
$5.9~\mu_{\text{B}}/\text{f.u.}$. Transport measurements confirm the
antiferromagetic transition and show a residual resistivity at $4~\text{K}$ of
$35~\mu\Omega\cdot \text{cm}$.",2009.00342v1
2020-09-02,Accessing the Single-Particle Structure of the Pygmy Dipole Resonance in $^{208}$Pb,"New experimental data on the neutron single-particle character of the Pygmy
Dipole Resonance (PDR) in $^{208}$Pb are presented. They were obtained from
$(d,p)$ and resonant proton scattering experiments performed at the Q3D
spectrograph of the Maier-Leibnitz Laboratory in Garching, Germany. The new
data are compared to the large suite of complementary, experimental data
available for $^{208}$Pb and establish $(d,p)$ as an additional, valuable,
experimental probe to study the PDR and its collectivity. Besides the
single-particle character of the states, different features of the strength
distributions are discussed and compared to Large-Scale-Shell-Model (LSSM) and
energy-density functional (EDF) plus Quasiparticle-Phonon Model (QPM)
theoretical approaches to elucidate the microscopic structure of the PDR in
$^{208}$Pb.",2009.01151v1
2020-10-14,"Ab-initio study of electronic and magnetic properties of Mn$_2$RuZ/MgO (001) heterojunctions (Z= Al, Ga, Si, Ge)","Using first-principles calculations, we studied Mn$_2$RuZ (Z=Al, Ga, Si, Ge)
and their heterojunctions with MgO along (001) direction. All these alloys
possess Hg$_2$CuTi-type inverse Heusler alloy structure and ferrimagnetic
ground state. Our study reveals the half-metallic electronic structure with
highly spin-polarized $\Delta_1$ band, which is robust against atomic disorder.
Next we studied the electronic structure of Mn$_2$RuAl/MgO and Mn$_2$RuGe/MgO
heterojunctions. We found that the MnAl- or MnGe-terminated interface is
energetically more favorable compared to the MnRu-terminated interface.
Interfacial states appear at the Fermi level in the minority-spin gap for the
Mn$_2$RuGe/MgO junction. We discuss the origin of these interfacial states in
terms of local environment around each constituent atom. On the other hand, in
the Mn$_2$RuAl/MgO junction, high spin polarization of bulk Mn$_2$RuAl is
preserved independent of its termination.",2010.06761v1
2020-11-13,Large anomalous Hall angle in a topological semimetal candidate TbPtBi,"The magnetotransport properties in antiferromagnetic half-Heusler single
crystals of TbPtBi, a magnetic-field-induced topological semimetal with simple
band structure, are investigated. We found that a nonmonotonic magnetic field
dependence of the anomalous Hall resistivity in a high magnetic field (B>7T),
which come from the change of band structure induced by the Zeeman-like
splitting when applying the external magnetic field. The experiment results
show that credible anomalous Hall resistivity and conductivity reach up to
0.6798m{\Omega}cm and 125{\Omega}-1cm-1, respectively. A large AHA up to 33% is
obtained in TbPtBi, which is comparable to typical ferromagnetic Weyl
semimetal. The analysis of results show it should be attributed to topological
band around EF and low carrier density.",2011.06864v1
2020-12-04,"Growth, strain and spin orbit torques in epitaxial NiMnSb films sputtered on GaAs","We report current-induced spin torques in epitaxial NiMnSb films on a
commercially available epi-ready GaAs substrate. The NiMnSb was grown by
co-sputtering from three targets using optimised parameter. The films were
processed into micro-scale bars to perform current-induced spin-torque
measurements. Magnetic dynamics were excited by microwave currents and electric
voltages along the bars were measured to analyse the symmetry of the
current-induced torques. We found that the extracted symmetry of the spin
torques matches those expected from spin-orbit interaction in a tetragonally
distorted half-Heusler crystal. Both field-like and damping-like torques are
observed in all the samples characterised, and the efficiency of the
current-induced torques is comparable to that of ferromagnetic metal/heavy
metal bilayers.",2012.02568v4
2020-12-12,Ultra-fast Double Pulse All-Optical Re-switching of a Ferrimagnet,"All-optical re-switching has been investigated in the half-metallic Heusler
ferrimagnet Mn2Ru0.9Ga, where Mn atoms occupy two inequivalent sites in the
XA-type structure. The effect of a second 200 fs 800 nm pump pulse that follows
a first pulse, when both are above the threshold for switching, is studied as a
function of t12, the time between them. The aims are to identify the physical
mechanisms involved and to determine the minimum time needed for re-switching.
The time trajectory of the switching process on a plot of sublattice angular
momentum, S4a vs S4c, is in three stages; When t < 0.1 ps, the sublattice
moments are rapidly disordered, but not destroyed, while conserving net angular
momentum via optical spin-wave excitations. This leads to transient parallel
alignment of the residual Mn spins in the first quadrant. The net angular
momentum associated with the majority sublattice then flips in about 2 ps, and
a fully-reversed ferrimagnetic state is then established via the spin-lattice
interaction, which allows re-switching provided t12 > 10 ps.",2012.06823v1
2020-12-29,Magnetotransport signatures of chiral magnetic anomaly in the half-Heusler phase ScPtBi,"Study of magnetotransport properties of ScPtBi revealed simultaneously: a
negative contribution to the longitudinal magnetoresistance, the planar Hall
effect, and distinct angular narrowing of the longitudinal magnetoresistance {
three hallmarks of chiral magnetic anomaly (pumping of axial charge between
Weyl nodes), a distinct property of topological semimetals. Electronic
structure calculations show that structural defects, such as antisites and
vacancies, bring substantial density of states at the Fermi level of ScPtBi,
indicating that it is a semimetal, not a zero-gap semiconductor, as predicted
earlier. This is in accord with electrical resistivity in ScPtBi, showing no
characteristics of semiconductor. Moreover, below 0.7K we observed an onset of
a superconducting transition, with the resistivity disappearing completely
below 0.23 K.",2012.14819v2
2021-02-22,Suppression of spinodal instability by disorder in an athermal system,"We observed asymmetric critical slowing down and asymmetric dynamical scaling
exponent in the superheating and supercooling kinetic processes during the
thermally-induced metal-insulator transition of MnNiSn based heusler alloy.
During the transition to the insulator phase, the critical-like features get
enhanced compared to the transition back to the metal phase. These experimental
findings suggest that the metastable phase in the cooling branch of hysteresis
has approached close to the spinodal instability. On the other hand, the
extended disorder, generated over and above the intrinsic crystal defects
during heating, triggers the excess heterogeneous nucleation before reaching
the spinodal point. Zero temperature random field Ising model (ZTRFIM)
simulation, inscribed for the athermal martensitic transitions, support the
argument that the disorder smears the spinodal instabilities as the correlation
length is bounded by the average distance between the disorder points.",2102.11347v2
2021-06-03,Quaternary-digital data storage based on magnetic bubbles in anisotropic materials,"The topologically non-trivial nano-whirls, called magnetic skyrmions, are
often considered attractive for spintronic applications like the racetrack data
storage device. However, skyrmions do not move parallel to applied currents and
typically do not coexist with other nano-objects, making the realization of
such storage concepts difficult. Herein we consider materials with an
anisotropic DMI, like tetragonal Heusler materials, and show that four distinct
types of topologically trivial bubbles can coexist. We show that each of them
can be written by spin torques and that they can be distinguished using a
single magnetic tunneling junction. Due to their trivial topology, the four
types of bubbles move parallel to applied electrical currents and remain
equidistant under motion. Still, the bubbles have a small size and high
stability comparable to topologically non-trivial spin textures. This allows to
construct a quaternary-digit-based racetrack storage device that overcomes the
two mentioned drawbacks of skyrmion-based racetracks.",2106.01747v2
2021-06-24,Structure and magnetism in Fe-doped FeVSb and epitaxial Fe/FeVSb nanocomposite films,"The combination of ferromagnetism and semiconducting behavior offers an
avenue for realizing novel spintronics and spin-enhanced thermoelectrics. Here
we demonstrate the synthesis of doped and nanocomposite half Heusler
Fe$_{1+x}$VSb films by molecular beam epitaxy. For dilute excess Fe ($x <
0.1$), we observe a decrease in the Hall electron concentration and no
secondary phases in X-ray diffraction, consistent with Fe doping into FeVSb.
Magnetotransport measurements suggest weak ferromagnetism that onsets at a
temperature of $T_{c} \approx$ 5K. For higher Fe content ($x > 0.1$),
ferromagnetic Fe nanostructures precipitate from the semiconducting FeVSb
matrix. The Fe/FeVSb interfaces are epitaxial, as observed by transmission
electron microscopy and X-ray diffraction. Magnetotransport measurements
suggest proximity-induced magnetism in the FeVSb, from the Fe/FeVSb interfaces,
at an onset temperature of $T_{c} \approx$ 20K.",2106.13165v1
2021-08-19,"IrCrMnZ (Z=Al, Ga, Si, Ge) Heusler alloys as electrode materials for MgO-based magnetic tunneling junctions: A first-principles study","We study IrCrMnZ (Z=Al, Ga, Si, Ge) systems using first-principles
calculations from the perspective of their application as the electrode
materials of MgO-based MTJs. These materials have highly spin-polarized
conduction electrons with partially occupied $\Delta_1$ band, which is
important for coherent tunneling in parallel magnetization configuration. The
Curie temperatures of IrCrMnAl and IrCrMnGa are very high (above 1300 K) as
predicted from mean-field-approximation. The stability of ordered phase against
various antisite disorders has been investigated. We discuss here the effect of
""spin-orbit-coupling"" on the electronic structure around Fermi level. Further,
we investigate the electronic structure of IrCrMnZ/MgO heterojunction along
(001) direction. IrCrMnAl/MgO and IrCrMnGa/MgO maintain half-metallicity even
at the MgO interface, with no interfacial states at/around Fermi level in the
minority-spin channel. Large majority-spin conductance of IrCrMnAl/MgO/IrCrMnAl
and IrCrMnGa/MgO/IrCrMnGa is reported from the calculation of ballistic
spin-transport property for parallel magnetization configuration. We propose
IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa as promising MTJs with a weaker
temperature dependence of tunneling magnetoresistance ratio, owing to their
very high Curie temperatures.",2108.08501v1
2021-10-26,Giant quadratic magneto-optical response of thin YIG films for sensitive magnetometric experiments,"We report on observation of a magneto-optical effect quadratic in
magnetization (Cotton-Mouton effect) in 50 nm thick layer of Yttrium-Iron
Garnet (YIG). By a combined theoretical and experimental approach, we managed
to quantify both linear and quadratic magneto-optical effects. We show that the
quadratic magneto-optical signal in the thin YIG film can exceed the linear
magneto-optical response, reaching values of 450 urad that are comparable with
Heusler alloys or ferromagnetic semiconductors. Furthermore, we demonstrate
that a proper choice of experimental conditions, particularly with respect to
the wavelength, is crucial for optimization of the quadratic magneto-optical
effect for magnetometry measurement.",2110.13679v1
2021-11-12,"First-principles investigations of the electronic, magnetic and thermoelectric properties of VTiRhZ (Z= Al, Ga, In) Quaternary Heusler Alloys","Calculations using density functional theory (DFT) were performed to
investigate the structural, dynamical, mechanical, electronic, magnetic, and
thermoelectric properties of VTiRhZ (Z = Al, Ga, In) alloys. The most stable
structure of these alloys was found to be the type-I configuration. Using
GGA-PBE functional, VTiRhGa, and VTiRhIn alloys are predicted as half-metallic
ferromagnets with a 100% spin-polarization and a total magnetic moment of
3{\mu}B, which is promising for spintronic applications. The thermoelectric
properties and lattice thermal conductivity of VTiRhZ alloys were obtained
using the Boltzmann transport theory within the constant relaxation time and
Slack equation, respectively. The figure-of-merit (ZT) values of VTiRhAl,
VTiRhGa, and VTiRhIn alloys were found to be 0.96, 0.88 and 0.64, respectively,
which are promising for future thermoelectric applications.",2111.06915v1
2022-01-31,Disorder-mediated quenching of magnetization in NbVTiAl: Theory and Experiment,"In this paper, we present the structural, electronic, magnetic and transport
properties of a equiatomic quaternary alloy NbVTiAl. The absence of (111) and
(200) peaks in X-ray diffraction (XRD) data confirms the A2-type structure.
Magnetization measurements indicate a high Curie temperature and a negligibly
small magnetic moment ($\sim 10^{-3} \mu_B/f.u.$) These observations are
indicative of fully compensated ferrimagnetism in the alloy.
Temperature-dependent resistivity indicates metallic nature. Ab-initio
calculation of fully ordered NbVTiAl structure confirms a nearly half metallic
behavior with a high spin polarization ($\sim$ 90 \%) and a net magnetic moment
of 0.8 $\mu_B/f.u.$ (in complete contrast to the experimental observation). One
of the main objective of the present paper is to resolve and explain the
long-standing discrepancy between theoretical prediction and experimental
observation of magnetization for V-based quaternary Heusler alloys, in general.
To gain an in-depth understanding, we modelled various disordered states and
its subsequent effect on the magnetic and electronic properties. The
discrepancy is attributed to the A2 disorder present in the system, as
confirmed by our XRD data. The presence of disorder also causes the emergence
of finite states at the Fermi level, which impacts the spin polarization of the
system.",2201.13037v1
2022-04-04,Phase-field modeling of paramagnetic austenite-ferromagnetic martensite transformation coupled with mechanics and micromagnetics,"A three-dimensional phase-field model is proposed for simulating the magnetic
martensitic phase transformation. The model considers a paramagnetic cubic
austenite to ferromagnetic tetragonal martensite transition, as it occurs in
magnetic Heusler alloys like Ni2 MnGa, and is based on a Landau 2-3-4
polynomial with temperature dependent coefficients. The
paramagnetic-ferromagnetic transition is recaptured by interpolating the
micromagnetic energy as a function of the order parameter for the ferroelastic
domains. The model is numerically implemented in real space by finite element
(FE) method. FE simulations in the martensitic state show that the model is
capable to correctly recapture the ferroelastic and -magnetic microstructures,
as well as the influence of external stimuli. Simulation results indicate that
the paramagnetic austenite to ferromagnetic martensite transition shifts
towards higher temperatures when a magnetic field or compressive stress is
applied. The dependence of the phase transition temperature shift on the
strength of the external stimulus is uncovered as well. Simulation of the phase
transition in magnetocaloric materials is of high interest for the development
of energy-efficient magnetocaloric cooling devices.",2204.01308v1
2022-09-10,First-principles analysis of intravalley and intervalley electron-phonon scattering in thermoelectric materials,"Intervalley collisions, which scatter electrons from one valley or band to
another, can be detrimental to thermoelectric performance in materials with
multiple valleys/bands. In this study, density functional theory is used to
investigate the electron-phonon scattering characteristics of three lead
chalcogenides (PbS, PbSe, PbTe) and three half-Heuslers (ScNiBi, ScPdSb,
ZrNiSn), which all possess multiple equivalent conduction valleys, in order to
characterize and analyze their intravalley/intervalley components. To elucidate
what controls the degree of intravalley and intervalley transitions, the
scattering rates are decomposed into the product of the phase space (a measure
of how much scattering is possible) and the average electron-phonon coupling.
To help guide the search for improved thermoelectric and high-conductivity
materials, simple and approximate approaches are demonstrated that can be
adopted to identify materials with reduced intervalley scattering, which
circumvent the need for computationally-demanding electron-phonon scattering
calculations. In addition, the benefits of selecting materials with
large-energy zone-edge phonons are explored in the limit $\hbar\omega \gg
k_BT$, and found to potentially suppress intervalley processes by up to an
order of magnitude, leading to a 70% and 100% increase in conductivity and
power factor, respectively.",2209.04659v1
2022-11-14,Coactive-Staggered Feature in Weyl Materials for Enhancing the Anomalous Nernst Conductivity,"Power generation through the anomalous Nernst effect in topological Weyl
materials has several advantages over conventional thermoelectrics due to the
transverse geometry. However, the magnitude of the anomalous Nernst
conductivity (ANC) in most known materials is too small to be of practical use,
and there exist few guiding principles for finding materials with optimal
thermoelectric properties. This work shows that the ANC is maximal when there
is a ``coactive-staggered"" feature in the anomalous Hall conductivity (AHC). It
is shown that a minimal arrangement of two Weyl pairs leads to such a feature,
and tuning the separations between the pairs controls the temperature at which
the ANC is maximal. Several methods are proposed for creating such arrangements
of Weyl points starting from Dirac semimetal materials. It is also demonstrated
how an existing coactive-staggered AHC in a Heusler material can be exploited,
by collectively tuning the positions of the Weyl points through strain to
further enhance the ANC. A modest 20% amplification of the ANC is achieved,
even with relatively minor changes in Weyl point positions.",2211.07773v1
2022-12-09,Modelling assisted tunneling on the Bloch sphere using the Quantum Composer,"The Bloch sphere representation is a geometric model for all possible quantum
states of a two-level system that can be used to describe the time dynamics of
a qubit. As explicit application, we consider the time dynamics of a particle
in a double-well potential. In particular, we adopt a recent method for
off-resonant excitations, the so-called SUPER principle (Swing-UP of the
quantum emitter population) driven by periodic electromagnetic fields, to the
context of quantum tunnelling. We show that the tunnelling probability can be
enhanced significantly when an appropriate oscillation of the potential height
is introduced. Driven by a collaborative approach we call educator-developer
dialogue, an updated version of the software Quantum Composer is presented. For
educational purposes, we map the two lowest energy states of the
1D-Schr\""odinger equation to the Bloch sphere representation, leading to a
rather clear and intuitive physical picture for the pertinent time dynamics.",2212.04845v3
2022-12-15,Resonant and off-resonant magnetoacoustic waves in epitaxial Fe$_3$Si/GaAs hybrid structures,"Surface acoustic waves (SAWs) provide an efficient dynamical coupling between
strain and magnetization in micro/nano-metric devices. Using a hybrid device
composed of a piezoelectric, GaAs, and a ferromagnetic Heusler alloy thin film,
Fe$_3$Si, we are able to quantify the amplitude of magnetoacoustic waves
generated with SAWs via magnetic imaging in an X-ray photoelectron microscope.
The cubic anisotropy of the sample together with a low damping coefficient
allows for the observation of resonant and non-resonant magnetoelastic
coupling. Additionally, via micromagnetic simulation, we verify the
experimental behavior and quantify the magnetoelastic shear strain component in
Fe$_3$Si that appears to be very large ($b_2=14\times 10^6$ J/m$^3$), much
larger than the one found in Nickel.",2212.07994v1
2022-12-21,"Electronic and phonon contributions to the Thermoelectric properties of newly discovered half-Heusler alloys XHfPb (X= Ni, Pd, and Pt)","In this work we calculate the thermoelectric figure of merit of XHfPb (X= Ni,
Pd, and Pt) by computing the both the power factor and the lattice thermal
conductivity by first principles. We make reasonable approximations: we use the
Constant Relaxation Time Approximation (CRTA) to compute the electron transport
contribution and the modified Debye-Callaway model to calculate the thermal
lattice conductivity. We also report the dielectric properties of these
semiconductors and the mode Gr\""uneisen parameters. Not surprisingly we find
that the average Gr\""uneisen coefficient correlates with the tehrmal
conductivity. Next, we consider a realistic relaxation time $\tau$ and carrier
concentration $n$ from experimental data on ZrHfPb and obtain the figure of
merit $ZT$ as a function of temperature. Our main finding is that despite the
Pt is isoelectronic with Ni and Pd, the $ZT$ of PtHfPb is larger and behaves
differently from the other two materials, suggesting that PtHfPb is better
suited for high temperature thermoelectric generators.",2212.10848v1
2022-12-31,An implementation of the density functional perturbation theory in the PAW framework,"Quantifying materials' dynamical responses to external electromagnetic fields
is central to understanding their physical properties. Here we present an
implementation of the density functional perturbation theory for the
computation of linear susceptibilities using the projector augmented-wave
method. The Sternheimer equations are solved self-consistently through a nested
iterative procedure to compute the first-order wavefunctions, from which the
linear susceptibilities are obtained. As a demonstration, we compute the spin
wave spectral functions of two magnetic metals. The computed magnon spectra for
half-metallic CrO$_2$ and a Heusler intermetallic Cu$_2$MnAl show gapless
Goldstone modes when spin rotation symmetry is preserved and display reasonable
agreement with available experimental data. The Landau damping is computed to
be small in CrO$_2$, but significant in Cu$_2$MnAl producing an asymmetric
Lorentzian spectral lineshape. The access to linear susceptibilities as well as
first-order wavefunctions offers a range of novel possibilities in quantitative
understanding of materials' electronic properties from \textit{ab initio}
methods.",2301.00143v1
2023-03-21,Unveiling the magnetic structure and phase transition of Cr$_2$CoAl using neutron diffraction,"We report the detailed analysis of temperature dependent neutron diffraction
pattern of the Cr$_2$CoAl inverse Heusler alloy and unveil the magnetic
structure up to the phase transition as well as its fully compensated
ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using
the space group I$\bar4${\it m}2 confirm the inverse tetragonal structure over
the large temperature range from 100~K to 900~K. The refinement of the magnetic
phase considering the wave vector $k=$ (0, 0, 0) reveals the ferrimagnetic
nature of the sample below 730$\pm$5~K. This transition temperature is obtained
from empirical power law fitting of the variation in the ordered net magnetic
moment and intensity of (110) peak as a function of temperature. The spin
configuration of the microscopic magnetic structure suggests the nearly fully
compensated ferrimagnetic behavior where the magnetic moments of Cr2 are
antiparallel with respect to the Cr1, and Co moments. Moreover, the observed
anomaly in the thermal expansion and lattice parameters at 730$\pm$5~K suggest
that the distortion in crystal structure may play an important role in the
magnetic phase transition.",2303.11869v1
2023-12-14,"Defect formation energy, electronic structure and phonon dispersion study of half-Heusler TiSnX (X = Pd, Pt and Ni): an ab initio approach","In order to obtain reliable and close to the experimental transport
properties, it is necessary to have a good description of the structural,
electronic and vibrational properties of the materials. In this regard, the
defect formation plays a crucial hole, specially when it has a small formation
energy. In this study we have calculated, under the Density Functional Theory
(DFT) formalism, the formation energy for five different models of defects,
where one of them is interstitial and the other four substitutional. The
interstitial Pd defect presented a very low formation energy, while the other
defects have shown higher energies and, therefore they are less likely to
emerge in the synthesis of the material.",2312.09186v1
2024-03-20,Record-high Anomalous Ettingshausen effect in a micron-sized magnetic Weyl semimetal on-chip cooler,"Solid-state cooling devices offer compact, quiet, reliable and
environmentally friendly solutions that currently rely primarily on the
thermoelectric (TE) effect. Despite more than two centuries of research,
classical thermoelectric coolers suffer from low efficiency which hampers wider
application. In this study, the less researched Anomalous Ettingshausen effect
(AEE), a transverse thermoelectric phenomenon, is presented as a new approach
for on-chip cooling. This effect can be boosted in materials with non-trivial
band topologies as demonstrated in the Heusler alloy $\text{Co}_2\text{MnGa}$.
Enabled by the high quality of our material, in situ scanning thermal
microscopy experiments reveal a record-breaking anomalous Ettingshausen
coefficient of $-2.1$~mV in $\mu$m-sized on-chip cooling devices at room
temperature. A significant 44\% of the effect is contributed by the intrinsic
topological properties, in particular the Berry curvature of
$\text{Co}_2\text{MnGa}$, emphasising the unique potential of magnetic Weyl
semimetals for high-performance spot cooling in nanostructures.",2403.13598v1
2011-10-31,Electronic Structure of Heavy Fermion Uranium Compounds Studied by Core-Level Photoelectron Spectroscopy,"High-energy-resolution core-level and valence-band photoelectron
spectroscopic studies were performed for the heavy Fermion uranium compounds
UGe2, UCoGe, URhGe, URu2Si2, UNi2Al3, UPd2Al3, and UPt3 as well as typical
localized and itinerant uranium compounds to understand the relationship
between the uranium valence state and their core-level spectral line shapes. In
addition to the main line and high-binding energy satellite structure
recognized in the core-level spectra of uranium compounds, a shoulder structure
on the lower binding energy side of the main lines of localized and nearly
localized uranium compounds was also found. The spectral line shapes show a
systematic variation depending on the U 5f electronic structure. The core-level
spectra of UGe2, UCoGe, URhGe, URu2Si2, and UNi2Al3 are rather similar to those
of itinerant compounds, suggesting that U 5f electrons in these compounds are
well hybridized with ligand states. On the other hand, the core-level spectra
of UPd2Al3 and UPt3 show considerably different spectral line shapes from those
of the itinerant compounds, suggesting that U 5f electrons in UPd2Al3 and UPt3
are less hybridized with ligand states, leading to the correlated nature of U
5f electrons in these compounds. The dominant final state characters in their
core-level spectra suggest that the numbers of 5f electrons in UGe2, UCoGe,
URhGe, URu2Si2, UNi2Al3, and UPd2Al3 are close to but less than three, while
that of UPt3 is close to two rather than to three.",1110.6689v1
2019-01-11,Superconductivity in an organometallic compound,"Organometallic compounds constitute a very large group of substances that
contain at least one metal-to-carbon bond in which the carbon is part of an
organic group. They have played a major role in the development of the science
of chemistry. These compounds are used to a large extent as catalysts
(substances that increase the rate of reactions without themselves being
consumed) and as intermediates in the laboratory and in industry. Recently,
novel quantum phenormena such as topological insulators and superconductors
were also suggested in these materials. However, there has been no report on
the experimental exploration for the topological state. Evidence for
superconductivity from the zero-resistivity state in any organometallic
compound has not been achieved yet, though much efforts have been devoted. Here
we report the experimental realization of superconductivity with the critical
temperature of 3.6 K in a potassium-doped organometallic compound, $ i.e.$
tri-$o$-tolylbismuthine with the evidence of both the Meissner effect and the
zero-resistivity state through the $dc$ and $ac$ magnetic susceptibility and
resistivity measurements. The obtained superconducting parameters classify this
compound as a type-II superconductor. The benzene ring is identified to be the
essential superconducting unit in such a phenyl organometallic compound. The
superconducting phase and its composition are determined by the combined
studies of the X-ray diffraction and theoretical calculations as well as the
Raman spectroscopy measurements. These findings enrich the applications of
organometallic compounds in superconductivity and add a new electron-acceptor
family for organic superconductors. This work also points to a large pool for
finding superconductors from organometallic compounds.",1901.03572v1
2020-04-29,MatriVasha: A Multipurpose Comprehensive Database for Bangla Handwritten Compound Characters,"At present, recognition of the Bangla handwriting compound character has been
an essential issue for many years. In recent years there have been
application-based researches in machine learning, and deep learning, which is
gained interest, and most notably is handwriting recognition because it has a
tremendous application such as Bangla OCR. MatrriVasha, the project which can
recognize Bangla, handwritten several compound characters. Currently, compound
character recognition is an important topic due to its variant application, and
helps to create old forms, and information digitization with reliability. But
unfortunately, there is a lack of a comprehensive dataset that can categorize
all types of Bangla compound characters. MatrriVasha is an attempt to align
compound character, and it's challenging because each person has a unique style
of writing shapes. After all, MatrriVasha has proposed a dataset that intends
to recognize Bangla 120(one hundred twenty) compound characters that consist of
2552(two thousand five hundred fifty-two) isolated handwritten characters
written unique writers which were collected from within Bangladesh. This
dataset faced problems in terms of the district, age, and gender-based written
related research because the samples were collected that includes a verity of
the district, age group, and the equal number of males, and females. As of now,
our proposed dataset is so far the most extensive dataset for Bangla compound
characters. It is intended to frame the acknowledgment technique for
handwritten Bangla compound character. In the future, this dataset will be made
publicly available to help to widen the research.",2005.02155v2
2022-01-28,AI for Chemical Space Gap Filling and Novel Compound Generation,"When considering large sets of molecules, it is helpful to place them in the
context of a ""chemical space"" - a multidimensional space defined by a set of
descriptors that can be used to visualize and analyze compound grouping as well
as identify regions that might be void of valid structures. The chemical space
of all possible molecules in a given biological or environmental sample can be
vast and largely unexplored, mainly due to current limitations in processing of
'big data' by brute force methods (e.g., enumeration of all possible compounds
in a space). Recent advances in artificial intelligence (AI) have led to
multiple new cheminformatics tools that incorporate AI techniques to
characterize and learn the structure and properties of molecules in order to
generate plausible compounds, thereby contributing to more accessible and
explorable regions of chemical space without the need for brute force methods.
We have used one such tool, a deep-learning software called DarkChem, which
learns a representation of the molecular structure of compounds by compressing
them into a latent space. With DarkChem's design, distance in this latent space
is often associated with compound similarity, making sparse regions interesting
targets for compound generation due to the possibility of generating novel
compounds. In this study, we used 1 million small molecules (less than 1000 Da)
to create a representative chemical space (defined by calculated molecular
properties) of all small molecules. We identified regions with few or no
compounds and investigated their location in DarkChem's latent space. From
these spaces, we generated 694,645 valid molecules, all of which represent
molecules not found in any chemical database to date. These molecules filled
50.8% of the probed empty spaces in molecular property space. Generated
molecules are provided in the supporting information.",2201.12398v1
2024-03-28,A Comprehensive Review of Coastal Compound Flooding Literature,"Compound flooding, where the combination or successive occurrence of two or
more flood drivers leads to an extreme impact, can greatly exacerbate the
adverse consequences associated with flooding in coastal regions. This paper
reviews the practices and trends in coastal compound flood research
methodologies and applications, as well as synthesizes key findings at regional
and global scales. Systematic review is employed to construct a literature
database of 271 studies relevant to compound flood hazards in a coastal
context. This review explores the types of compound flood events, their
mechanistic processes, and synthesizes the definitions and terms exhibited
throughout the literature. Considered in the review are six flood drivers
(fluvial, pluvial, coastal, groundwater, damming/dam failure, and tsunami) and
five precursor events and environmental conditions (soil moisture, snow,
temp/heat, fire, and drought). Furthermore, this review summarizes the trends
in research methodology, examines the wide range of study applications, and
considers the influences of climate change and urban environments. Finally,
this review highlights the knowledge gaps in compound flood research and
discusses the implications of review findings on future practices. Our five
recommendations for future compound flood research are to: 1) adopt consistent
definitions, terminology, and approaches; 2) expand the geographic coverage of
research; 3) pursue more inter-comparison projects; 4) develop modelling
frameworks that better couple dynamic earth systems; and 5) design urban and
coastal infrastructure with compound flooding in mind. We hope this review will
help to enhance understanding of compound flooding, guide areas for future
research focus, and close knowledge gaps.",2404.01321v1
1994-09-06,A Probabilistic Model of Compound Nouns,"Compound nouns such as example noun compound are becoming more common in
natural language and pose a number of difficult problems for NLP systems,
notably increasing the complexity of parsing. In this paper we develop a
probabilistic model for syntactically analysing such compounds. The model
predicts compound noun structures based on knowledge of affinities between
nouns, which can be acquired from a corpus. Problems inherent in this
corpus-based approach are addressed: data sparseness is overcome by the use of
semantically motivated word classes and sense ambiguity is explicitly handled
in the model. An implementation based on this model is described in Lauer
(1994) and correctly parses 77% of the test set.",9409003v1
2002-11-18,"Synthesis of RuSr2(Ln3/4Ce1/4)2Cu2O10 magneto-superconducting compounds with Ln = Ho, Y and Dy by high-pressure high-temperature (HPHT) technique","The samples of composition RuSr2(Ln3/4Ce1/4)2Cu2O10 with Ln = Ho, Y and Dy.
being synthesized by high pressure high temperature (6Gpa, 1200 0C) solid state
synthesis route do crystallize in space group I4/mmm. These samples exhibit
magnetic transitions at ~150 K with significant branching of zfc
(zero-field-cooled) and fc (field-cooled) magnetization and a sharp cusp in zfc
at ~ 100 K, followed by a superconducting transition at lower temperatures. All
the compounds show typical ferromagnetic hysteresis loops in magnetic moment
(M) versus field (H) magnetization at 5 K. Near saturation of the moments at 5
K is achieved in above 5 T (Tesla) applied fields with a value of ~ 0.80 muB.
At low temperatures (5 K) these compounds exhibit both superconductivity and
ferromagnetism. To our knowledge these are first successfully synthesized
Ru-1222 compounds with various lanthanides including Y, Dy, and Ho. The results
are compared with widely reported Gd/Ru-1222 compound.",0211359v1
2003-04-23,"Magnetic frustration in a stoichiometric spin-chain compound, Ca$_3$CoIrO$_6$","The temperature dependent ac and dc magnetization and heat capacity data of
Ca$_3$CoIrO$_6$, a spin-chain compound crystallizing in a K$_4$CdCl$_6$-derived
rhombohedral structure, show the features due to magnetic ordering of a
frustrated-type below about 30 K, however without exhibiting the signatures of
the so-called ""partially disordered antiferromagnetic structure"" encountered in
the isostructural compounds, Ca$_3$Co$_2$O$_6$ and Ca$_3$CoRhO$_6$. This class
of compounds thus provides a variety for probing the consequences of magnetic
frustration due to topological reasons in stoichiometric spin-chain materials,
presumably arising from subtle differences in the interchain and intrachain
magnetic coupling strengths. This compound presents additional interesting
situations in the sense that, ac susceptibility exhibits a large frequency
dependence in the vicinity of 30 K uncharacteristic of conventional
spin-glasses, with this frustrated magnetic state being robust to the
application of external magnetic fields.",0304518v1
2003-08-01,A Structural Parameter for High Tc Superconductivity from an Octahedral Moebius Strip in RBaCuO:123 type Perovskites,"An index for the characterisation of the Perovskite type Superconductors is
introduced. The index, denominated as Structural Parameter of High Tc
Superconductivity (PESATc from its name in Spanish), is calculated using a
Moebius Orbital defined as the length of an Octahedral Moebius Strip overlaying
the octahedra created by the CuO planes and the apical Oxygen atoms, O(4).
Results for structures of YBCO:123 type compounds are presented; their atomic
positions were measured by neutron diffraction and x-ray diffraction techniques
as reported in the literature. It has been found that critical temperature
depends on the value of the measured structural parameter; furthermore, for a
set of RBCO compounds there is a lineal response between Tc and PESATc. In the
former case, a specific range for the superconducting behaviour is established
by PESATc values, and a well-defined point for the maximum Tc is found. In the
latter one, a slope of 4.515 with correlation coefficient of 0.9402 was found
when seven Rare Earth compounds were considered. The only compound that goes
out from this trend, is the La based compound.",0308019v1
2003-09-02,Low temperature irreversibility induced by thermal cycles on two prototypical phase separated manganites,"We have studied the effect of irreversibility induced by repeated thermal
cycles on the electric transport and magnetization of polycrystalline samples
of La0.5Ca0.5MnO3 and La0.325Pr0.3Ca0.375MnO3. An increase of the resistivity
and a decrease of the magnetization at different temperature ranges after
cycling is obtained in the temperature range between 300 K and 30 K. Both
compounds are known to exhibit intrinsic submicrometric coexistence of phases
and undergo a sequence of phase transitions related to structural changes.
Changes induced by thermal cycling can be partially inhibited by applying
magnetic field and hydrostatic pressure.
  Our results suggest that the growth and coexistence of phases with different
structures gives rise to microstructural tracks and strain accommodation,
producing the observed irreversibility. Irrespective of the actual ground state
of each compound, the effect of thermal cycling is towards an increase of the
amount of the insulating phase in both compounds.",0309073v2
2003-10-01,Spin and orbital structure of uranium compounds on the basis of a j-j coupling scheme,"Key role of orbital degree of freedom to understand the magnetic structure of
uranium compounds is discussed from a microscopic viewpoint by focusing on
typical examples such as UMGa$_5$ (M=Ni and Pt) and the mother compound
UGa$_3$. By analyzing an orbital degenerate Hubbard model constructed from the
$j$-$j$ coupling scheme in the cubic system, we obtain the phase diagram
including several kinds of magnetic states. Especially, in the parameter region
corresponding to actual uranium compounds, the phase diagram suggests
successive transitions among paramagnetic, magnetic metallic, and insulating
N\'eel states, consistent with the experimental results for AuCu$_3$-type
uranium compounds. Furthermore, taking account of tetragonal effects such as
level splitting and reduction of hopping amplitude along the z-axis, an
orbital-based scenario is proposed to understand the change in the magnetic
structure from G- to A-type antiferromagnetic phases, experimentally observed
in UNiGa$_5$ and UPtGa$_5$.",0310008v2
2004-06-04,Superconductivity in the intermetallic compound YRhAl,"The intermetallic compound, YRhAl, has been prepared and is found to be
isomorphic with RRhAl (R=Pr, Nd, Gd, Ho and Tm) compounds crystallizing in the
orthorhombic TiNiSi-type structure (Space group Pnma). Heat capacity and
electrical resistivity measurements in the He-3 temperature range reveal that
this compound is superconducting with a transition temperature, Tc, of 0.9 K.
The electronic specific heat coefficient, gamma, and the Debye temperature are
found to be 6.1 mJ/mole K and 197 K, respectively. The specific heat jump at
the superconducting transition temperature is found to be consistent with the
BCS weak-coupling limit. This combined with the earlier observation of
superconductivity in LaRhAl (Tc = 2.4 K) having a different structure than that
of YRhAl, suggests that the underlying structure is not very crucial for the
occurrence of superconductivity in RRhAl series of compounds.",0406109v1
2004-11-13,Large magnetoresistance anomalies in Dy7Rh3,"The compound Dy7Rh3 ordering antiferromagnetically below (TN=) 59 K has been
known to exhibit a temperature (T) dependent electrical resistivity (rho)
behavior in the paramagnetic state unusual for intermetallic compounds in the
sense that there is a broad peak in rho(T) in the paramagnetic state (around
130 K) as though there is a semi-conductor to metal transition. In addition,
there is an upturn below T_N due to magnetic super-zone gap effects. Here we
report the influence of external magnetic field (H) on the rho(T) behavior of
this compound below 300 K. The rise of rho(T) found below TN could be
suppressed at very high fields (>> 60 kOe), thus resulting in a very large
magnetoresistance (MR) in the magnetically ordered state. The most notable
finding is that the magnitude of MR is large for moderate applications of H
(say 80 kOe) in a temperature range far above T_N as well, which is untypical
of intermetallic compounds. Thus, this compound is characterized by large MR
anomalies in the entire T range of investigation.",0411360v1
2005-03-23,Superconductivity in the Intercalated Graphite Compounds C6Yb and C6Ca,"In this letter we report the discovery of superconductivity in the
isostructural graphite intercalation compounds C6Yb and C6Ca, with transition
temperatures of 6.5K and 11.5K respectively. A structural characterisation of
these compounds shows them to be hexagonal layered systems in the same class as
other graphite intercalates. If we assume that all the outer s-electrons are
transferred from the intercalant to the graphite sheets, then the charge
transfer in these compounds is comparable to other superconducting graphite
intercalants such as C8K 1,2 . However, the superconducting transition
temperatures of C6Yb and C6Ca are up to two orders of magnitude greater.
Interestingly, superconducting upper critical field studies and resistivity
measurements suggest that these compounds are significantly more isotropic than
pure graphite. This is unexpected as the effect of introducing the intercalant
is to move the graphite layer further apart.",0503570v1
2005-03-30,Stability of ferromagnetism in the half-metallic pnictides and similar compounds: A first-principles study,"Based on first-principles electron structure calculations and employing the
frozen-magnon approximation we study the exchange interactions in a series of
transition-metal binary alloys crystallizing in the zinc-blende structure and
calculate the Curie temperature within both the mean-field approximation (MFA)
and random-phase approximation (RPA). We study two Cr compounds, CrAs and CrSe,
and four Mn compounds: MnSi, MnGe, MnAs and MnC. MnC, MnSi and MnGe are
isovalent to CrAs and MnAs is isoelectronic with CrSe. Ferromagnetism is
particular stable for CrAs, MnSi and MnGe: All three compounds show Curie
temperatures around 1000 K. On the other hand, CrSe and MnAs show a tendency to
antiferromagnetism when compressing the lattice. In MnC the half-metallic gap
is located in the majority-spin channel contrary to the other five compounds.
The large half-metallic gaps, very high Curie temperatures, the stability of
the ferromagnetism with respect to the variation of the lattice parameter and a
coherent growth on semiconductors make MnSi and CrAs most promising candidates
for the use in spintronics devises.",0503713v1
2005-10-21,Low temperature properties of a new Kondo Lattice compound Yb$_2$Ir$_3$Sn$_5$,"We report the preparation and results of our magnetic and transport
measurements on a new Yb-based ternary compound Yb$_2$Ir$_3$Sn$_5$. This
compound forms in the orthorhombic Cmc21 structure. DC magnetic susceptibility
between 1.8 K and 300 K reveal that Yb is in its magnetic trivalent state in
this compound. Electrical resistivity measurements down to 1. 5K show a
behavior typical of Kondo lattice compounds with a minimum in resistivity
around 8K and a coherence peak near 3K. AC magnetic susceptibility down to
100mK reveals an anti-ferromagnetic transition below 1.35 K.",0510583v1
2005-11-14,Magnetic Properties of Ternary Gallides of type RNi4Ga (R = Rare earths),"The magnetic properties of RNi4Ga (R = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm
and Lu) compounds have been investigated. These compounds form in a hexagonal
CaCu5 type structure with a space group P6/mmm. Compounds with the magnetic
rare earths, R = Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm, undergo a ferromagnetic
transition at 5 K, 17 K, 20 K, 19 K, 12 K, 3.5 K, 8 K and 6.5 K, respectively.
The transition temperatures are smaller compared to their respective parent
compounds RNi5. PrNi4Ga is paramagnetic down to 2 K. LaNi4Ga and LuNi4Ga are
Pauli paramagnets. All the compounds show thermomagnetic irreversibility in the
magnetically ordered state except GdNi4Ga.",0511335v1
2005-12-20,Theory of Knight Shift and Spin-Lattice Relaxation Rates of Pu-115,"We calculated the Knight shift and spin-lattice relaxation rates of Pu-115
compounds assuming d-wave superconductivity in the presence of strong impurity
scattering. We discuss the implications for recent measurements of the
spin-lattice relaxation rate in the Pu-115 compound PuRhGa5 by Sakai and
coworkers [J. Phys. Soc. Jpn. 74, 1710 (2005)] and present a prediction for the
corresponding Knight shift. In addition, we noticed a significant round-off of
the spin-lattice relaxation rate 1/T1 just above the superconducting transition
temperature that is not observed in the sister compound PuCoGa5. It appears
that in PuRhGa5 superconductivity is mediated by spin fluctuations, too. This
provides additional support to the scenario of superconducting pairing mediated
by spin fluctuations in the Pu-115 compounds similar to the Ce-115 compounds
and the high-temperature copper-oxide superconductors.",0512509v1
2006-04-27,Universal scaling in the dynamical conductivity of heavy fermion Ce and Yb compounds,"Dynamical conductivity spectra s(w) have been measured for a diverse range of
heavy-fermion (HF) Ce and Yb compounds. A characteristic excitation peak has
been observed in the mid-infrared region of s(w) for all the compounds, and has
been analyzed in terms of a simple model based on conduction (c)-f electron
hybridized band. A universal scaling is found between the observed peak
energies and the estimated c-f hybridization strengths of these HF compounds.
This scaling demonstrates that the model of c-f hybridized band can generally
and quantitatively describe the charge excitation spectra of a wide range of HF
compounds.",0604612v4
2006-09-08,Electronic structure and optical properties of lightweight metal hydrides,"We study the electronic structures and dielectric functions of the simple
hydrides LiH, NaH, MgH2 and AlH3, and the complex hydrides Li3AlH6, Na3AlH6,
LiAlH4, NaAlH4 and Mg(AlH4)2, using first principles density functional theory
and GW calculations. All these compounds are large gap insulators with GW
single particle band gaps varying from 3.5 eV in AlH3 to 6.5 eV in the MAlH4
compounds. The valence bands are dominated by the hydrogen atoms, whereas the
conduction bands have mixed contributions from the hydrogens and the metal
cations. The electronic structure of the aluminium compounds is determined
mainly by aluminium hydride complexes and their mutual interactions. Despite
considerable differences between the band structures and the band gaps of the
various compounds, their optical responses are qualitatively similar. In most
of the spectra the optical absorption rises sharply above 6 eV and has a strong
peak around 8 eV. The quantitative differences in the optical spectra are
interpreted in terms of the structure and the electronic structure of the
compounds.",0609189v1
2006-09-15,Effect of Ge substitution for Si on the anomalous magnetocaloric and magnetoresistance properties of GdMn2Si2 compounds,"The effect of Ge substitution on the magnetization, heat capacity,
magnetocaloric effect and magnetoresistance of GdMn2Si2-xGex (x=0, 1, and 2)
compounds has been studied. The magnetic transition associated with the Gd
ordering is found to change from second order to first order on Ge
substitution. Magnetic contributions to the total heat capacity and the entropy
have been estimated. Magnetocaloric effect has been calculated in terms of
adiabatic temperature change (deltaTad) as well as isothermal magnetic entropy
change (deltaSM) using the heat capacity data. The temperature dependence of
the magnetocaloric effect in all the three compounds have shown broad peaks.
The maximum values of deltaSM and deltaTad for GdMn2Ge2 are found to be 5.9
J/kgK and 1.2 K, respectively. The magnetoresistance is found to be very large
and positive with a maximum value of about 22% in the case of GdMn2Ge2. In the
other two compounds also, the magnetoresistance is predominantly positive,
except in the vicinity of the Gd ordering temperature. The anomalous nature of
the magnetocaloric effect and the magnetoresistance has been attributed to the
canted magnetic structure of these compounds.",0609382v1
2006-09-16,Role of Fe substitution on the anomalous magnetocaloric and magnetoresistance behavior in Tb(Ni1-xFex)2 compounds,"We report the magnetic, magnetocaloric and magnetoresistance results obtained
in Tb(Ni1-xFex)2 compounds with x=0, 0.025 and 0.05. Fe substitution leads to
an increase in the ordering temperature from 36 K for x=0 to 124 K for x=0.05.
Contrary to a single sharp MCE peak seen in TbNi2, the MCE peaks of the Fe
substituted compounds are quite broad. We attribute the anomalous MCE behavior
to the randomization of the Tb moments brought about by the Fe substitution.
Magnetic and magnetoresistance results seem to corroborate this proposition.
The present study also shows that the anomalous magnetocaloric and
magnetoresistance behavior seen in the present compounds is similar to that of
Ho(Ni,Fe)2 compounds.",0609400v1
2006-10-30,"Crystal-field splittings in CeX (X= N, P, As, Sb, Bi) compounds","The unusual and interesting physical properties of rare earth intemetallic
compounds have their origin in the combination of strongly correlated 4f states
and their hybridization with the conduction electron sea, which gives rise to
their complex low temperature Kondo behavior. In particular, Ce compounds are
very sensitive to the crystalline and chemical environment, as compared to
other rare earth systems. The interaction of the 4f state with the conduction
band plays an important role in the determination of the different magnetic,
structural and transport properties of these systems. Among the cerium
compounds, those of the type CeX, which crystallize in the rock salt structure,
exhibit extremely unusual magnetic properties. By making use of the mixed
LDA-NCA calculation technique we analyse the crystal-field splittings of CeX
compounds (X=N, P, As, Sb, Bi). The obtained ab-initio hybridization functions
are taken as imputs to calculate the crystal-field splittings within NCA (non
crossing approximation) and the tendencies are contrasted with experiments. KEY
WORDS: Highly correlated systems, crystal fields, p-electron.",0610845v1
2006-12-21,"Search of low-dimensional magnetics on the basis of structural data: spin-1/2 antiferromagnetic zigzag chain compounds In2VO5, beta-Sr(VOAsO4)2,(NH4,K)2VOF4 and alpha-ZnV3O8","A new technique for searching low-dimensional compounds on the basis of
structural data is presented. The sign and strength of all magnetic couplings
at distances up to 12 A in five predicted new antiferromagnetic zigzag spin-1/2
chain compounds In2VO5, beta-Sr(VOAsO4)2, (NH4)2VOF4, K2VOF4 and alpha-ZnV3O8
were calculated. It was stated that in the compound In2VO5 zigzag spin chains
are frustrated, since the ratio (J2/J1) of competing antiferromagnetic (AF)
nearest- (J1) and AF next-to-nearest-neighbour (J2) couplings is equal to 1.68
that exceeds the Majumdar-Ghosh point by 1/2. In other compounds the zigzag
spin chains are AF magnetically ordered single chains as value of ratios J2/J1
is close to zero. The interchain couplings were analyzed in detail.",0612543v2
1999-08-13,Differential Geometry on Compound Poisson Space,"In this paper we carry out analysis and geometry for a class of infinite
dimensional manifolds, namely, compound configuration spaces as a natural
generalization of the work \cite{AKR97}. More precisely a differential geometry
is constructed on the compound configuration space $\Omega_{X}$ over a
Riemannian manifold $X$. This geometry is obtained as a natural lifting of the
Riemannian structure on $X$. In particular, the intrinsic gradient, divergence,
and Laplace-Beltrami operator are constructed. Therefore the corresponding
Dirichlet forms on $L^{2}(\Omega_{X})$ can be defined. Each is shown to be
associated with a diffusion process on $\Omega_{X}$ (so called equilibrium
process) which is nothing but the diffusion process on the simple configuration
space $\Gamma_{X}$ together with corresponding marks. As another consequence of
our results we obtain a representation of the Lie-algebra of compactly
supported vector fields on $X$ on compound Poisson space. Finally
generalizations to the case when the compound Poisson measure is replaced by a
marked Poisson measure easily follow from this construction.",9908059v1
2007-04-11,Fan-shaped and toric textures of mesomorphic oxadiazoles,"When a family of non symmetrical heterocycled compounds is investigated, a
variety of mesophases can be observed with rather different features. Here we
report the behaviour of seven different members among a family of such
materials, that consists of mesomorphic oxadiazole compounds. In two of these
compounds, the optical microscope investigation shows very interesting
behaviours. In their smectic phases, fan-shaped and toric textures, sometimes
with periodic instability, are observed. Moreover, the nematic phase displays a
texture transition. Texture transitions have been previously observed only
inside the nematic phase of some compounds belonging to the families of the
oxybenzoic and cyclohexane acids. In these two oxadiazole compounds we can
observe what we define as a ""toric nematic phase"", heating the samples from the
smectic phase. The toric nematic texture disappears as the sample is further
heated, changing into a smooth texture.",0704.1474v1
2007-06-13,"Magnetic excitations in the spin-trimer compounds Ca3Cu3-xNix(PO4)4 (x=0,1,2)","Inelastic neutron scattering experiments were performed for the spin-trimer
compounds Ca3Cu3-xNix(PO4)4 (x=0,1,2) in order to study the dynamic magnetic
properties. The observed excitations can be associated with transitions between
the low-lying electronic states of linear Cu-Cu-Cu, Cu-Cu-Ni, and Ni-Cu-Ni
trimers which are the basic constituents of the title compounds. The exchange
interactions within the trimers are well described by the Heisenberg model with
dominant antiferromagnetic nearest-neighbor interactions J. For x=0 we find
JCu-Cu=-4.74(2) meV which is enhanced for x=1 to JCu-Cu=-4.92(6) meV. For x=1
and x=2 we find JCu-Ni=-0.85(10) meV and an axial single-ion anisotropy
parameter DNi=-0.7(1) meV. While the x=0 and x=1 compounds do not exhibit
long-range magnetic ordering down to 1 K, the x=2 compound shows
antiferromagnetic ordering below TN=20 K, which is compatible with the
molecular-field parameter 0.63(12) meV derived by neutron spectroscopy.",0706.1881v1
2007-11-03,Fragment-collision model for compound chondrule formation: Estimation of collision probability,"We propose a new scenario for compound chondrule formation named as
""fragment-collision model,"" in the framework of the shock-wave heating model. A
molten cm-sized dust particle (parent) is disrupted in the high-velocity gas
flow. The extracted fragments (ejectors) are scattered behind the parent and
the mutual collisions between them will occur. We modeled the disruption event
by analytic considerations in order to estimate the probability of the mutual
collisions assuming that all ejectors have the same radius. We found that the
estimated collision probability, which is the probability of collisions
experienced by an ejector in one disruption event, can account for the observed
fraction of compound chondrules. In addition, the model predictions are
qualitatively consistent with other observational data (oxygen isotopic
composition, textural types, and size ratios of constituents). Based on these
results, we concluded that this new model can be one of the strongest
candidates for the compound chondrule formation.
  It should be noted that all collisions do not necessarily lead to the
compound chondrule formation. The formation efficiency and the future works
which should be investigated in the forthcoming paper are also discussed.",0711.0427v1
2007-11-05,Feedback Capacity of the Compound Channel,"In this work we find the capacity of a compound finite-state channel with
time-invariant deterministic feedback. The model we consider involves the use
of fixed length block codes. Our achievability result includes a proof of the
existence of a universal decoder for the family of finite-state channels with
feedback. As a consequence of our capacity result, we show that feedback does
not increase the capacity of the compound Gilbert-Elliot channel. Additionally,
we show that for a stationary and uniformly ergodic Markovian channel, if the
compound channel capacity is zero without feedback then it is zero with
feedback. Finally, we use our result on the finite-state channel to show that
the feedback capacity of the memoryless compound channel is given by
$\inf_{\theta} \max_{Q_X} I(X;Y|\theta)$.",0711.0705v1
2008-05-27,On the entropy and log-concavity of compound Poisson measures,"Motivated, in part, by the desire to develop an information-theoretic
foundation for compound Poisson approximation limit theorems (analogous to the
corresponding developments for the central limit theorem and for simple Poisson
approximation), this work examines sufficient conditions under which the
compound Poisson distribution has maximal entropy within a natural class of
probability measures on the nonnegative integers. We show that the natural
analog of the Poisson maximum entropy property remains valid if the measures
under consideration are log-concave, but that it fails in general. A parallel
maximum entropy result is established for the family of compound binomial
measures. The proofs are largely based on ideas related to the semigroup
approach introduced in recent work by Johnson for the Poisson family.
Sufficient conditions are given for compound distributions to be log-concave,
and specific examples are presented illustrating all the above results.",0805.4112v1
2008-09-16,La-dilution effects in TbRhIn5 antiferromagnet,"We report measurements of temperature dependent magnetic susceptibility,
resonant x-ray magnetic scattering (XRMS) and heat capacity on single crystals
of Tb1-xLaxRhIn5 for nominal concentrations in the range 0.0 < x < 1.0. TbRhIn5
is an antiferromagnetic (AFM) compound with TN ~ 46 K, which is the highest TN
values along the RRhIn5 series. We explore the suppression of the
antiferromagnetic (AFM) state as a function of La-doping considering the
effects of La-induced dilution and perturbations to the tetragonal crystalline
electrical field (CEF) on the long range magnetic interaction between the
Tb$^{3+}$ ions. Additionally, we also discuss the role of disorder. Our results
and analysis are compared to the properties of the undoped compound and of
other members of the RRhIn5 family and structurally related compounds (R2RhIn8
and RIn3). The XRMS measurements reveal that the commensurate magnetic
structure with the magnetic wave-vector (0,1/2,1/2) observed for the undoped
compound is robust against doping perturbations in Tb0.6La0.4RhIn5 compound.",0809.2765v1
2009-02-21,Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics in Iron Arsenide Compounds,"Neutrons have played an important role in advancing our understanding of the
pairing mechanism and the symmetry of the superconducting energy gap in the
iron arsenide compounds. Neutron measurements of the phonon density-of-state
are in good agreement with ab initio calculations, provided the magnetism of
the iron atoms is taken into account. However, the predicted superconducting
transition temperatures are less than 1 K, making a conventional phononic
mechanism for superconductivity highly unlikely. Measurements of the spin
dynamics within the spin density wave phase of the parent compounds show
evidence of strongly dispersive spin waves with exchange interactions
consistent with the observed magnetic order. Antiferromagnetic fluctuations
persist in the normal phase of the superconducting compounds, but they are more
diffuse. Below Tc, there is evidence compounds that these fluctuations condense
into a resonant spin excitation at the antiferromagnetic wavevector with an
energy that scales with Tc, consistent with unconventional superconductivity of
extended-s+/- wave symmetry.",0902.3760v1
2009-07-21,"Anomalous transport properties of the halfmetallic ferromagnets Co2TiSi, Co2TiGe, and Co2TiSn","In this work the theoretical and experimental investigations of Co2TiZ (Z =
Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is
predicted for all three compounds with only two bands crossing the Fermi energy
in the majority channel. The magnetic moments fulfill the Slater-Pauling rule
and the Curie temperatures are well above room temperature. All compounds show
a metallic like resistivity for low temperatures up to their Curie temperature,
above the resistivity changes to semiconducting like behavior. A large negative
magnetoresistance of 55% is observed for Co2TiSn at room temperature in an
applied magnetic field of 4T which is comparable to the large negative
magnetoresistances of the manganites. The Seebeck coefficients are negative for
all three compounds and reach their maximum values at their respective Curie
temperatures and stay almost constant up to 950 K. The highest value achieved
is -52muV/K m for Co2TiSn which is large for a metal. The combination of
half-metallicity and the constant large Seebeck coefficient over a wide
temperature range makes these compounds interesting materials for
thermoelectric applications and further spincaloric investigations.",0907.3562v1
2009-09-02,"Magnetic Behavior in RRhX (R = rare earths; X=B, C) Compounds","We report on the magnetic behavior of RRhB (R = La, Ce, Pr, Nd, Gd, Tb and
Tm) and RRhC (R = La, Ce, Pr and Gd) compounds crystallizing in the cubic
perovskite type structure with space group Pm3m. The heat capacity data on
Pauli-paramagnetic LaRhB and LaRhC indicate a high frequency vibrating motion
of boron and carbon atoms in the unit cell. Ce is in -like nonmagnetic state in
both the compounds. Pr compounds show a dominant crystal field effect with a
nonmagnetic singlet ground state in PrRhB and a nonmagnetic quadrupolar doublet
in PrRhC. Compounds with other rare earths order ferromagnetically at low
temperatures except TmRhB in which the zero field evolution of magnetic
interactions is relatively more complicated. The electrical resistivity of
GdRhB decreases with increasing temperature in the paramagnetic state in the
vicinity of T, which is rarely seen in ferromagnets. The behavior is discussed
to be arising due to the short range spin fluctuation and a possible
contribution from Fermi surface geometry.",0909.0460v2
2009-11-10,Opportunistic capacity and error exponent regions for compound channel with feedback,"Variable length communication over a compound channel with feedback is
considered. Traditionally, capacity of a compound channel without feedback is
defined as the maximum rate that is determined before the start of
communication such that communication is reliable. This traditional definition
is pessimistic. In the presence of feedback, an opportunistic definition is
given. Capacity is defined as the maximum rate that is determined at the end of
communication such that communication is reliable. Thus, the transmission rate
can adapt to the channel chosen by nature. Under this definition, feedback
communication over a compound channel is conceptually similar to multi-terminal
communication. Transmission rate is a vector rather than a scalar; channel
capacity is a region rather than a scalar; error exponent is a region rather
than a scalar. In this paper, variable length communication over a compound
channel with feedback is formulated, its opportunistic capacity region is
characterized, and lower bounds for its error exponent region are provided..",0911.2023v3
2010-03-13,Ferromagnetic Clusters in the Brownmillerite Bilayered Compounds Ca2.5-xLaxSr0.5GaMn2O8: An Approach to Achieve Layered Spintronics Materials,"We report the effect of La-substitution on the magnetic and magnetotransport
properties of Brownmillerite-like bilayered compounds Ca2.5-xLaxSr0.5GaMn2O8 (x
= 0, 0.05, 0.075, and 0.1) by using dc-magnetization, resistivity and
magnetoresistance techniques. The Rietveld analysis of the room temperature
x-ray diffraction patterns confirms no observable change of average crystal
structure with the La-substitution. Both magnetic and magnetotransport
properties are found to be very sensitive to the La-substitution.
Interestingly, the La-substituted compounds show ferromagnetic-like behavior
(due to the occurrence of a double exchange mechanism) whereas, the parent
compound is an antiferromagnet (TN 150 K). All compounds show an insulating
behavior, in the measured temperature range of 100 - 300 K, with an overall
decrease in the resistivity with the substitution. A higher value of
magnetoresistance has been successfully achieved by the La-substitution. We
have proposed an electronic phase separation model, considering the formation
of ferromagnetic clusters in the antiferromagnetic matrix, to interpret the
observed magnetization and magnetotransport results for the La-substituted
samples. The present study demonstrates an approach to achieve new functional
materials, based on naturally occurring layered system like
Ca2.5-xLaxSr0.5GaMn2O8, for possible spintronics applications.",1003.2685v1
2010-07-23,Observation of re-entrant spin glass behavior in (Ce1-xErx)Fe2 compounds,"Clear experimental evidence of re-entrant spin glass state has been revealed
in Er doped CeFe2 compounds. The zero field cooled - field cooled bifurcation
in dc magnetization, frequency dependence of freezing temperature, relaxation
in zero field cooled magnetization and presence of large remanence confirm the
spin glass state in these compounds. Frequency dependence is found to follow
the critical slowing down mechanism. The random substitution of Er and the
change in the valence state of Ce along with an enhancement of the
ferromagnetic component in the Fe sublattice seem to be responsible for the
spin glass state. Using detailed experimental protocols, we also prove that the
low temperature state in these compounds is not a magnetic glass. The absence
of exchange bias gives an indication that there is no coexistence of
ferromagnetism and spin glass state in these compounds. The RSG state is found
to be associated with the randomly magnetized clusters instead of atomic level
randomness.",1007.4103v1
2010-09-22,"Pressure effects in PrT2B2C (T = Co, Ni, Pt): Applied and chemical pressure","High-pressure electrical resistivity, r(T), measurements on intermetallic
Pr(Co, Ni, Pt)2B2C compounds were performed down to 2K. At room pressure the
r(T) in a-b direction curves for the non superconducting Pr(Co, Ni)2B2C
compounds exhibit magnetic correlations at about 10 and 4 K, respectively. At
low temperatures, PrCo2B2C shows a large spin-dependent electron scattering in
comparison to PrNi2B2C. Under applied pressure the magnetic scattering tends to
be suppressed more effectively in PrCo2B2C than in PrNi2 B2C. The low
temperature behavior of r(T,P) for PrNi2B2C and PrCo2B2C suggests a spin
fluctuations mechanism. In the other hand PrPt2B2C compound shows
superconductivity at about 6 K and under pressure its superconducting
transition temperature tends to be degraded at a rate dTc/dP = -0.34 K/GPa, as
expected in compounds with transition metals. The experimental results in Co,
Ni and Pt based compounds are analyzed from the point of view of the external
and chemical internal pressure effects.",1009.4437v1
2011-04-01,Topological insulators in filled skutterudites,"We propose new topological insulators in cerium filled skutterudite (FS)
compounds based on ab initio calculations. We find that two compounds CeOs4As12
and CeOs4Sb12 are zero gap materials with band inversion between Os-d and Ce-f
orbitals, which are thus parent compounds of two and three-dimensional
topological insulators just like bulk HgTe. At low temperature, both compounds
become topological Kondo insulators, which are Kondo insulators in the bulk,
but have robust Dirac surface states on the boundary. This new family of
topological insulators has two advantages compared to previous ones. First,
they can have good proximity effect with other superconducting FS compounds to
realize Majarona fermions. Second, the antiferromagnetism of CeOs4Sb12 at low
temperature provides a way to realize the massive Dirac fermion with novel
topological phenomena.",1104.0641v1
2011-06-16,Topological insulators in the quaternary chalcogenide compounds and ternary famatinite compounds,"We present first-principles calculations to predict several three dimensional
(3D) topological insulators in quaternary chalcogenide compounds which are made
of I$_2$-II-IV-VI$_4$ compositions and in ternary compositions of
I$_3$-V-VI$_4$ famatinite compounds. Among the large members of these two
families, we give examples of naturally occurring compounds which are mainly
Cu-based chalcogenides. We show that these materials are candidates of 3D
topological insulators or can be tuned to obtain topological phase transition
by manipulating the atomic number of the other cation and anion elements. A
band inversion can occur at a single point $\Gamma$ with considerably large
inversion strength, in addition to the opening of a bulk band gap throughout
the Brillouin zone. We also demonstrate that both of these families are related
to each other by cross-substitutions of cations in the underlying tetragonal
structure and that one can suitably tune their topological properties in a
desired manner.",1106.3316v1
2011-07-29,Superconductivity at 38 K in Iron-Based Compound with Platinum-Arsenide Layers Ca10(Pt4As8)(Fe2-xPtxAs2)5,"We report superconductivity in novel iron-based compounds
Ca10(PtnAs8)(Fe2-xPtxAs2)5 with n = 3 and 4. Both compounds crystallize in
triclinic structures (space group P-1), in which Fe2As2 layers alternate with
PtnAs8 spacer layers. Superconductivity with a transition temperature of 38 K
is observed in the n = 4 compound with a Pt content of x ~ 0.36 in the Fe2As2
layers. The compound with n = 3 exhibits superconductivity at 13 K.",1108.0029v2
2011-09-07,Predicting Two-Dimensional Boron-Carbon Compounds by the Global Optimization Method,"We adopt a global optimization method to predict two-dimensional (2D)
nanostructures through the particle-swarm optimization (PSO) algorithm. By
performing PSO simulations, we predict new stable structures of 2D boron-carbon
(B-C) compounds for a wide range of boron concentrations. Our calculations show
that: (1) All 2D B-C compounds are metallic except for BC3 which is a magic
case where the isolation of carbon six-membered ring by boron atoms results in
a semiconducting behavior. (2) For C-rich B-C compounds, the most stable 2D
structures can be viewed as boron doped graphene structures, where boron atoms
typically form 1D zigzag chains except for BC3 in which boron atoms are
uniformly distributed. (3) The most stable 2D structure of BC has alternative
carbon and boron ribbons with strong in-between B-C bonds, which possesses a
high thermal stability above 2000K. (4) For B-rich 2D B-C compounds, there is a
novel planar-tetracoordinate carbon motif with an approximate C2v symmetry.",1109.1594v1
2011-09-27,Impurity-induced quasiparticle interference in the parent compounds of iron-pnictide superconductors,"The impurity-induced quasiparticle interference(QPI) in the parent compounds
of iron-pnictide superconductors is investigated based on a phenomenological
two-orbital four-band model and T-matrix method. We find the QPI is sensitive
to the value of the magnetic order which may vary from one compound to another.
For small value of the magnetic order, the pattern of oscillation in the local
density of states (LDOS) induced by the QPI exhibits two-dimensional
characteristics, consistent with the standing wave state observed in the 1111
compound. For larger value of the magnetic order, the main feature of the
spatial modulation of the LDOS is the existence of one-dimensional stripe
structure which is in agreement with the nematic structure in the parent
compound of the 122 system. In both cases the system shows $C_2$ symmetry and
only in the larger magnetic order case, there exist in-gap bound states. The
corresponding QPI in $q$-space is also presented. The patterns of modulation in
the LDOS at nonzero energies are attributed to the interplay between the
underlying band structure and Fermi surfaces.",1109.5928v1
2011-11-02,Effect of doping on the thermoelectric properties of thallium tellurides using first principles calculations,"We present a study of the electronic properties of Tl5Te3, BiTl9Te6 and
SbTl9Te6 compounds by means of density functional theory based calculations.
The optimized lattice constants of the compounds are in good agreement with the
experimental data. The band gap of BiTl9Te6 and SbTl9Te6 compounds are found to
be equal to 0.589 eV and 0.538 eV, respectively and are in agreement with the
available experimental data. To compare the thermoelectric properties of the
different compounds we calculate their thermopower using Mott's law and show,
as expected experimentally, that the substituted tellurides have much better
thermoelectric properties compared to the pure compound.",1111.0534v1
2011-11-29,Medicinal Plants Database and Three Dimensional Structure of the Chemical Compounds from Medicinal Plants in Indonesia,"During this era of new drug designing, medicinal plants had become a very
interesting object of further research. Pharmacology screening of active
compound of medicinal plants would be time consuming and costly. Molecular
docking is one of the in silico method which is more efficient compare to in
vitro or in vivo method for its capability of finding the active compound in
medicinal plants. In this method, three-dimensional structure becomes very
important in the molecular docking methods, so we need a database that provides
information on three-dimensional structures of chemical compounds from
medicinal plants in Indonesia. Therefore, this study will prepare a database
which provides information of the three dimensional structures of chemical
compounds of medicinal plants. The database will be prepared by using MySQL
format and is designed to be placed in http://herbaldb.farmasi.ui.ac.id website
so that eventually this database can be accessed quickly and easily by users
via the Internet.",1111.7183v1
2012-05-30,Spin-Orbit Coupling in Iridium-Based 5d Compounds Probed by X-ray Absorption Spectroscopy,"We have performed x-ray absorption spectroscopy (XAS) measurements on a
series of Ir-based 5d transition metal compounds, including Ir, IrCl3, IrO2,
Na2IrO3, Sr2IrO4, and Y2Ir2O7. By comparing the intensity of the ""white-line""
features observed at the Ir L2 and L3 absorption edges, it is possible to
extract valuable information about the strength of the spin-orbit coupling in
these systems. We observe remarkably large, non-statistical branching ratios in
all Ir compounds studied, with little or no dependence on chemical composition,
crystal structure, or electronic state. This result confirms the presence of
strong spin-orbit coupling effects in novel iridates such as Sr2IrO4, Na2IrO3,
and Y2Ir2O7, and suggests that even simple Ir-based compounds such as IrO2 and
IrCl3 may warrant further study. In contrast, XAS measurements on Re-based 5d
compounds, such as Re, ReO2, ReO3, and Ba2FeReO6, reveal statistical branching
ratios and negligible spin-orbit coupling effects.",1205.6540v1
2012-06-07,Observation of different spin behavior with temperature variation and Cr substitution in a multiferroic compound YMn$_2$O$_5$,"In this article, the collective response of the spins is explored through low
field bulk magnetic measurement for the series YMn$_{2-x}$Cr$_x$O$_5$ (x= 0.0,
0.05). Low field ac susceptibility and dc magnetization of YMn$_2$O$_5$ shows
multiple transition in analogy to those observed in electrical measurement of
the compound. Using various time dependent magnetization protocols it has been
observed that the behavior of spins in commensurate and incommensurate phase
are drastically different. YMn$_{1.95}$Cr$_{0.05}$O$_5$ undergoes a
ferrimagnetic ordering with an enhanced magnetic ordering temperature as
compared to the parent, which undergoes an antiferromagnetic ordering.
Appearance of spontaneous magnetization without any major change in the atomic
structure is rather significant since the parent compound is an important
multiferroic material. In addition, magnetic memory effect is observed in the
Cr substituted compound whereas it is absent in the parent compound.",1206.1446v1
2012-07-20,"Magnetic, magnetocaloric and magnetotransport properties of RSn_{1+x}Ge_{1-x} compounds (R=Gd, Tb, Er; x=0.1)","We have studied the magnetic, magnetocaloric and magnetotransport properties
of RSn1+xGe1-x(R=Gd, Tb, Er; x=0.1) series by means of magnetization, heat
capacity and resistivity measurements. It has been found that all the compounds
crystallize in the orthorhombic crystal structure described by the
centrosymmetric space group Cmcm (No. 63). The magnetic susceptibility and heat
capacity data suggest that all the compounds are antiferromagnetic. Large
negative values of {\theta}p in case of GdSn1.1Ge0.9 and TbSn1.1Ge0.9 indicate
that strong antiferromagnetic interactions are involved, which is also
reflected in the magnetization isotherms. On the other hand ErSn1.1Ge0.9 shows
weak antiferromagnetic interaction. The heat capacity data have been analyzed
by fitting the temperature dependence and the values of {\theta}D and {\gamma}
have been estimated. Among these three compounds, ErSn1.1Ge0.9 shows
considerable magnetic entropy change of 9.5 J/kg K and an adiabatic temperature
change of 3.2 K for a field of 50 kOe. The resistivity data in different
temperature regimes have been analyzed and the dominant contributions have been
identified. All the compounds show small but positive magnetoresistance.",1207.4971v1
2012-08-31,Statistical inference in compound functional models,"We consider a general nonparametric regression model called the compound
model. It includes, as special cases, sparse additive regression and
nonparametric (or linear) regression with many covariates but possibly a small
number of relevant covariates. The compound model is characterized by three
main parameters: the structure parameter describing the ""macroscopic"" form of
the compound function, the ""microscopic"" sparsity parameter indicating the
maximal number of relevant covariates in each component and the usual
smoothness parameter corresponding to the complexity of the members of the
compound. We find non-asymptotic minimax rate of convergence of estimators in
such a model as a function of these three parameters. We also show that this
rate can be attained in an adaptive way.",1208.6402v3
2012-11-07,Synthesis of ReN3 thin films by magnetron sputtering,"Recently was reported a novel compound between rhenium and nitrogen,
announced with ReN2 composition. This compound was synthesized by the high
temperature and high pressure method. We found that the diffraction peaks of
this compound are in agreement with the x-ray pattern of a rhenium-nitrogen
film, under the assumption that the film is oriented on the substrate. The film
was prepared by reactive magnetron sputtering, at room temperature, and
deposited on a silicon wafer. From the analysis of the diffractograms it could
be concluded that both materials share the same structure. By density
functional calculation was found that the composition could be ReN3, instead of
ReN2, as stated before. The ReN3 fits in the Ama2 (40) orthorhombic space
group, and by the existence of N3 anions it should be categorized as an azide;
that is, a nitrogen-rich compound. To reach high nitrogen concentrations by
sputtering a crucial step is the target-poisoning. Under this regime of
deposition is ensured that the compound is formed simultaneously on the
substrate and the target. The poisoned target is rarely used because of a
reduced sputtering yield, but as shall see, it can be used as a novel synthetic
technique.",1211.1698v1
2012-12-14,Compound Multiple Access Channel with Common Message and Intersymbol Interference,"In this paper, we characterize the capacity region for the two-user linear
Gaussian compound Multiple Access Channel with common message (MACC) and with
intersymbol interference (ISI) under an input power constraint. The region is
obtained by converting the channel to its equivalent memoryless one by defining
an n-block memoryless circular Gaussian compound MACC model and applying the
discrete Fourier transform (DFT) to decompose the n-block channel into a set of
independent parallel channels whose capacities can be found easily. Indeed, the
capacity region of the original Gaussian compound MACC equals that of the
n-block circular Gaussian compound MACC in the limit of infinite block length.
Then by using the obtained capacity region, we derive the capacity region of
the strong interference channel with common message and ISI.",1212.3557v2
2013-01-16,"Superconductivity of F-substituted LnOBiS2 (Ln = La, Ce, Pr, Nd, Yb) compounds","Polycrystalline samples of F-substituted LnOBiS2 (Ln = La, Ce, Pr, Nd, Yb)
compounds were synthesized by solid-state reaction. The samples were
characterized by x-ray diffraction measurements and found to have the ZrCuSiAs
crystal structure. Electrical resistivity and magnetic susceptibility
measurements were performed on all of the samples and specific heat
measurements were made on those with Ln = La, Ce, and Yb. All of these
compounds exhibit superconductivity in the range 1.9 K - 5.4 K, which has not
previously been reported for the compounds based on Ce, Pr, and Yb. The
YbO0.5F0.5BiS2 compounds was also found to exhibit magnetic order at ~2.7 K
that apparently coexists with superconductivity below 5.4 K.",1301.3932v1
2013-02-14,Secrecy capacities of compound quantum wiretap channels and applications,"We determine the secrecy capacity of the compound channel with quantum
wiretapper and channel state information at the transmitter. Moreover, we
derive a lower bound on the secrecy capacity of this channel without channel
state information and determine the secrecy capacity of the compound
classical-quantum wiretap channel with channel state information at the
transmitter. We use this result to derive a new proof for a lower bound on the
entanglement generating capacity of compound quantum channel. We also derive a
new proof for the entanglement generating capacity of compound quantum channel
with channel state information at the encoder.",1302.3412v5
2013-03-20,Three Packets of Minerals of the Periodic Table of Chemical Elements and Chemical Compounds,"The concepts of alpha- and beta-packets of the periodic table of chemical
elements and chemical compounds are defined. The first of the 47 minerals
alpha-packets is composed. In it all minerals are arranged in increasing Iav
index of proportionality of atomic weights of composing chemical elements, the
same way as chemical elements are located in increasing atomic weights in the
Periodic table. The packet includes 93 known minerals and two compounds - N2O5
and CO2 - being actually minerals. Beta-packet of oxides and hydroxides
minerals includes 88 known minerals and five chemical compounds - N2O5, CO2,
CO, SO3 and SO2. Two minerals of the packet have not been determined yet.
Besides, beta-packet of minerals with sulfur, selenium or arsenic is composed,
with one mineral not defined yet. The results of the calculations can be used
for further development of the Periodic Table of Chemical Elements and Chemical
Compounds and their properties investigation.",1304.1280v1
2013-05-27,"On the isotope effects of ZrX2 (X = H, D and T): A First-principles study","Zirconium hydride is an important material for storage of hydrogen isotopes.
Here we report the structural, electronic, vibrational and thermodynamic
properties of ZrH2, ZrD2 and ZrT2 using density functional theory (DFT). The
structural optimization was carried out by the plane-wave based
pseudo-potential method under the generalized gradient approximation (GGA)
scheme. The electronic structure of the ZrH2 compound was illustrated in terms
of the electronic density of states, charge density distribution and the
electron localization function. The phonon dispersion curves, phonon density of
states and thermodynamic properties of ZrX2 (X= H, D, T) compounds were
evaluated based on frozen phonon method. Both the Raman and infrared active
vibrational modes of ZrX2 at {\Gamma}-point were analyzed which showed
significant isotopic effect on ZrX2 compounds. For example, the energy gap
between optical and acoustic modes reduces for ZrT2 than ZrD2 and ZrH2. The
formation energies of ZrX2 compounds, including the ZPE contributions, were
-113.97, -126.50 and -132.04 kJ/(mole of compound) for X = H, D and T,
respectively.",1305.6109v1
2013-08-20,A high-throughput ab initio review of platinum-group alloy systems,"We report a comprehensive study of the binary systems of the platinum group
metals with the transition metals, using high-throughput first-principles
calculations. These computations predict stability of new compounds in 38
binary systems where no compounds have been reported in the literature
experimentally, and a few dozen of as yet unreported compounds in additional
systems. Our calculations also identify stable structures at compound
compositions that have been previously reported without detailed structural
data and indicate that some experimentally reported compounds may actually be
unstable at low temperatures. With these results we construct enhanced
structure maps for the binary alloys of platinum group metals. These are much
more complete, systematic and predictive than those based on empirical results
alone.",1308.4357v4
2013-11-05,Mixed valency and site-preference chemistry for Cerium and its compounds: A predictive DFT study,"Cerium and its technologically relevant compounds are examples of anomalous
mixed valency, originating from two competing oxidation states -- itinerant
Ce$^{3+}$ and localized Ce$^{4+}$. Under applied stress, anomalous transitions
are observed but not well understood. Here we treat mixed valency as an ""alloy""
involving two valences with competing and numerous site-occupancy
configurations, and we use density functional theory with Hubbard U ($i.e.$,
DFT+U) to evaluate the effective valence and predict properties, including
controlling valence by pseudo-ternary alloying. For Ce and its compounds, such
as (Ce-La)$_2$(Fe-Co)$_{14}$B permanent magnets, we find a stable mixed-valent
$\alpha$-state near the spectroscopic value of $\nu_s=3.53$. Ce valency in
compounds depends on its steric volume and local chemistry; for La doping,
Ce-valency shifts towards $\gamma$-like Ce$^{3+}$, as expected from steric
volume; for Co doping, valency depends on local Ce-site chemistry and steric
volume. Our approach captures the key origins of anomalous valency and
site-preference chemistry in complex compounds.",1311.0962v1
2014-01-25,A Machine Learning Approach for the Identification of Bengali Noun-Noun Compound Multiword Expressions,"This paper presents a machine learning approach for identification of Bengali
multiword expressions (MWE) which are bigram nominal compounds. Our proposed
approach has two steps: (1) candidate extraction using chunk information and
various heuristic rules and (2) training the machine learning algorithm called
Random Forest to classify the candidates into two groups: bigram nominal
compound MWE or not bigram nominal compound MWE. A variety of association
measures, syntactic and linguistic clues and a set of WordNet-based similarity
features have been used for our MWE identification task. The approach presented
in this paper can be used to identify bigram nominal compound MWE in Bengali
running text.",1401.6567v1
2014-02-24,Compound Multiple Access Channel with Confidential Messages,"In this paper, we study the problem of secret communication over a Compound
Multiple Access Channel (MAC). In this channel, we assume that one of the
transmitted messages is confidential that is only decoded by its corresponding
receiver and kept secret from the other receiver. For this proposed setting
(compound MAC with confidential messages), we derive general inner and outer
bounds on the secrecy capacity region. Also, as examples, we investigate 'Less
noisy' and 'Gaussian' versions of this channel, and extend the results of the
discrete memoryless version to these cases. Moreover, providing numerical
examples for the Gaussian case, we illustrate the comparison between achievable
rate regions of compound MAC and compound MAC with confidential messages.",1402.5869v1
2014-04-07,Co-existence of ferromagnetic and antiferromagnetic interactions in Mn$_3$Ga$ _{(1-x)} $Sn$_x$C,"The magnetic properties of the Mn$_3$Ga$_{(1-x)}$Sn$_x$C, 0 $\le$ x $\le$ 1
antiperovskite compounds have been investigated in detail. Though all compounds
of this series crystallize in a cubic structure, the Ga rich (x $\le$ 0.2)
compounds transform, via a first order transformation, to an antiferromagnetic
ground state and the Sn rich (x $\ge$ 0.8) compounds exhibit dominant
ferromagnetic interactions at low temperature. In the intermediate range (0.4
$\le$ x $\le$ 0.7) co-existence of ferromagnetic and antiferromagnetic
interactions can be seen. The results have been explained to be due to growth
of ferromagnetic sub-lattice at the expense of antiferromagnetic sub-lattice
with increasing Sn concentration in Mn$_3$Ga$_{(1-x)}$Sn$_x$C. This growth
occurs to a point where the first-order transition is altered from a
ferromagnetic - antiferromagnetic type in Ga rich compounds to a paramagnetic -
ferrimagnetic type in Mn$_3$SnC.",1404.1753v1
2014-05-03,Numerical Investigation of Effects of Compound Angle and Length to Diameter Ratio on Adiabatic Film Cooling Effectiveness,"A modification has been done in the normal injection hole of 35 degree, by
injecting the cold fluid at different angles(compound angle) in lateral
direction, providing a significant change in the shape of holes which later we
found in our numerical investigation giving good quality of effectiveness in
cooling. Different L/D ratios are also studied for each compound angle. The
numerical simulation is performed based on Reynolds Averaged
Navier-Stokes(RANS) equations with k-epsilon turbulence model by using
Fluent(Commercial Software). Adiabatic Film Cooling Effectiveness has been
studied for compound angles of (0, 30, 45 and 60 degrees) and L/D ratios of (1,
2, 3 and 4) on a hole of 6mm diameter with blowing ratio 0.5. The findings are
obtained from the results, concludes that the trend of laterally averaged
adiabatic effectiveness is the function of L/D ratio and compound angle.",1405.0560v1
2014-05-09,"Layered Compounds BaM2Ge4Ch6 (M = Rh, Ir and Ch = S, Se) with Pyrite-Type Building Blocks and Ge-Ch Heteromolecule-Like Anions","Structure and chemical features of layered compounds BaM2Ge4Ch6 (M = Rh, Ir;
Ch = S, Se) synthesized under high-pressure and high-temperature method are
systematically studied. These compounds crystallize in an orthorhombic phase
with space group Pbca (No. 61). The remarkable structural feature is to have
the M-Ge-Ch pyrite-type building units, stacking with Ba-Ch layers
alternatively along c axis. It is very rare and novel that pyrite-type subunits
as the building blocks in the layered compounds. Theoretical calculations and
experimental results indicate that there are strongly polarized covalent bonds
between Ge and Ch atoms, forming heteromolecule-like anions in these compounds.
Moreover, Ge atoms in this structure exhibit unusual valence state (~ +1) due
to the tetrahedral coordination environment of Ge atoms along with M and Ch
atoms simultaneously.",1405.2231v1
2014-07-11,"Appearance of bulk Superconductivity under Hydrostatic Pressure in Sr0.5RE0.5FBiS2 (RE = Ce, Nd, Pr and Sm) compounds","We report the appearance of superconductivity under hydrostatic pressure
(0.35 to 2.5GPa) in Sr0.5RE0.5FBiS2 with RE = Ce, Nd, Pr and Sm. The studied
compounds, synthesized by solid state reaction route, are crystallized in
tetragonal P4/nmm space group. At ambient pressure though the RE = Ce exhibit
the onset of superconductivity below 2.5K, the Nd, Pr and Sm samples are not
superconducting down to 2K. With application of hydrostatic pressure (up to
2.5GPa), superconducting transition temperature is increased to around 10K for
all the studied samples. The magneto-transport measurements are carried out on
all the samples with maximum Tc i.e., at under 2.5GPa pressure and their upper
critical fields are determined. The new superconducting compounds appear to be
quite robust against magnetic field but within Pauli paramagnetic limit. The
new superconducting compounds with various RE (Ce, Nd, Pr and Sm) belonging to
Sr0.5La0.5FBiS2 family are successfully synthesized for the first time and
superconductivity is induced in them under hydrostatic pressure.",1407.3105v3
2014-08-24,Formation of Stoichiometric CsF$_n$ Compounds,"Alkali halides $MX$, have been viewed as typical ionic compounds,
characterized by 1:1 ratio necessary for charge balance between M$^+$ and
X$^-$. It was proposed that group I elements like Cs can be oxidized further
under high pressure. Here we perform a comprehensive study for the CsF-F system
at pressures up to 100 GPa, and find extremely versatile chemistry. A series of
CsF$_n$ ($n$ $\geq$ 1) compounds are predicted to be stable already at ambient
pressure. Under pressure, 5$p$ electrons in Cs atoms become active, with
growing tendency to form Cs$^{3+}$ and Cs$^{5+}$ valence states at
fluorine-rich conditions. Although Cs$^{2+}$ and Cs$^{4+}$ are not
energetically favoured, the interplay between two mechanisms (polyfluoride
anions and polyvalent Cs cations) allows CsF$_2$ and CsF$_4$ compounds to be
stable under pressure. The estimated defluorination temperatures of CsF$_n$
(n=2,3,5) compounds at atmospheric pressure (218 $^\circ$C, 150 $^\circ$C, -15
$^\circ$C, respectively), are attractive for fluorine storage applications.",1408.5551v1
2014-10-21,Li intercalation in graphite: a van der Waals density-functional study,"Modeling layered intercalation compounds from first principles poses a
problem, as many of their properties are determined by a subtle balance between
van der Waals interactions and chemical or Madelung terms, and a good
description of van der Waals interactions is often lacking. Using van der Waals
density functionals we study the structures, phonons and energetics of the
archetype layered intercalation compound Li-graphite. Intercalation of Li in
graphite leads to stable systems with calculated intercalation energies of
$-0.2$ to $-0.3$~eV/Li atom, (referred to bulk graphite and Li metal). The
fully loaded stage 1 and stage 2 compounds LiC$_6$ and Li$_{1/2}$C$_6$ are
stable, corresponding to two-dimensional $\sqrt3\times\sqrt3$ lattices of Li
atoms intercalated between two graphene planes. Stage $N>2$ structures are
unstable compared to dilute stage 2 compounds with the same concentration. At
elevated temperatures dilute stage 2 compounds easily become disordered, but
the structure of Li$_{3/16}$C$_6$ is relatively stable, corresponding to a
$\sqrt7\times\sqrt7$ in-plane packing of Li atoms. First-principles
calculations, along with a Bethe-Peierls model of finite temperature effects,
allow for a microscopic description of the observed voltage profiles.",1410.5632v1
2014-12-15,Superconductivity at 4.4K in PdTe2-chains of a Ta Based Compound,"Superconductivity in PdTe2 heavy transition metal based compounds is rapidly
developing field in condensed matter physics community. Here, we report
superconductivity in a nominal ternary telluride Ta2Pd0.97Te6 compound, which
is synthesized in sealed evacuated quartz ampoule. The resultant compound is
crystallized in layered monoclinic Ta4Pd3Te16 phase with space group C2/m,
having lattice parameters a=21.304(6)A, b=3.7365(7)A, and c=17.7330A with Beta
=120.65(1)degree. Both transport and magnetic measurements demonstrated bulk
superconductivity at 4.4K in studied polycrystalline sample. The metallic
normal state conductivity can be well ascribed to Fermi-liquid behaviour. The
superconducting upper critical field of the compound is determined to be
5.5Tesla based on magneto-restively measurements.",1412.4462v3
2015-04-06,Decomposition of solid hydrogen bromide at high pressure,"The stability of different stoichiometric H$_n$Br ($n$=1-7) compounds under
pressure are extensively studied using density functional theory calculations.
Five new energetically stable stoichiometries of H$_2$Br, H$_3$Br, H$_4$Br,
H$_5$Br, and H$_7$Br were uncovered at high pressure. The results show that HBr
is stable below 64 GPa, then decomposes into new compound H$_2$Br and Br$_2$
molecular crystal. For H$_2$Br and H$_3$Br compounds, they were found to become
stable above 30 GPa and 8 GPa, respectively. In addition, we accidentally
discovered the triangular H$_3^+$ species in H$_5$Br compounds at 100 GPa.
Further electron-phonon coupling calculations predicted that hydrogen-rich
H$_2$Br and H$_4$Br compounds are superconductors with critical temperature of
superconductivity $T_c$ of 12.1 K and 2.4 K at 240 GPa, respectively.",1504.01196v1
2015-10-16,"Magnetic Property of Rutile Ti0.94A0.06O2 (A=Li, Mg, K) Compounds","Our purpose is to study role of ionic radii of non-magnetic dopants; Li+
(0.68 {\AA}), Mg2+ (0.72 {\AA}) and K+ (1.38 {\AA}) on the magnetic property of
rutile TiO2 compound. The Ti0.94A0.06O2 (A=Li, Mg, K) compounds have been
synthesized via solid state route method at equilibrium. The structural
analyses of X-ray diffraction pattern reveals that the doping of Li and Mg lead
to Ti site substitution and K doping lead to core shell kind of structure. The
magnetic property measurement by SQUID magnetometer indicate that all compounds
exhibit weak paramagnetism with highest paramagnetic moment of ~ 0.3 MuB / ion
for K doped compound but no long-range ferromagnetic ordering. We have
discussed the observed magnetism in correlation with the nature of
substitution.",1510.04782v1
2015-10-29,"Lattice Dynamics and Thermal Expansion Behavior in Metal Cyanides, MCN (M=Cu, Ag, Au): Neutron Inelastic Scattering and First Principles Calculations","We report measurement of temperature dependence of phonon spectra in quasi
one-dimensional metal cyanides MCN (M=Cu, Ag and Au). Ab initio lattice
dynamics calculations have been performed to interpret the phonon-spectra as
well as to understand the anamolous thermal expansion behavior in these
compounds. We bring out the differences in the phonon mode behavior to explain
the differences in the thermal expansion behavior among the three compounds.
The chain-sliding modes are found to contribute maximum to the negative thermal
expansion along c axis in the Cu and Ag compounds, while the same modes
contribute to positive thermal expansion in the Au compound. Several low energy
transverse modes lead to positive thermal expansion along a and b axis in all
the compounds. The calculated elastic constants and Born effective charges are
correlated with the difference in nature of bonding among these metal cyanides.",1510.08639v1
2015-12-01,Highly Scalable Tensor Factorization for Prediction of Drug-Protein Interaction Type,"The understanding of the type of inhibitory interaction plays an important
role in drug design. Therefore, researchers are interested to know whether a
drug has competitive or non-competitive interaction to particular protein
targets.
  Method: to analyze the interaction types we propose factorization method
Macau which allows us to combine different measurement types into a single
tensor together with proteins and compounds. The compounds are characterized by
high dimensional 2D ECFP fingerprints. The novelty of the proposed method is
that using a specially designed noise injection MCMC sampler it can incorporate
high dimensional side information, i.e., millions of unique 2D ECFP compound
features, even for large scale datasets of millions of compounds. Without the
side information, in this case, the tensor factorization would be practically
futile.
  Results: using public IC50 and Ki data from ChEMBL we trained a model from
where we can identify the latent subspace separating the two measurement types
(IC50 and Ki). The results suggest the proposed method can detect the
competitive inhibitory activity between compounds and proteins.",1512.00315v1
2015-12-29,Violation of Kohler rule in Ta2PdTe6 and absence of same in Nb2PdS5- A high field magneto transport study,"Here, we present the comparative study of magnetotransport properties of
recently discovered Ta2PdTe6 and Nb2PdS5 superconductors. The XRD and
magnetotransport measurements are performed on these samples to investigate
structure and superconducting properties as well as normal state transport
properties of these compounds. Both the compounds are crystallized in
monoclinic structure within space group C2m. Here, we observe superconductivity
in both the compounds Ta2PdTe6 (Tc =4.4 K) and Nb2PdS5 (Tc =6.6 K). We see a
linear magnetoresistance in Ta2PdTe6 as well as violation of Kohler rule in
same compound. On the other hand, we find the absence of same in Nb2PdS5
compound.",1512.09316v1
2016-01-26,Chemical Substitution and High Pressure Effects on Superconductors in the $Ln$OBiS$_{2}$ ($Ln$ = La-Nd) System,"A large number of compounds which contain BiS$_{2}$ layers exhibit enhanced
superconductivity upon electron doping. Much interest and research effort has
been focused on BiS$_{2}$-based compounds which provide new opportunities for
exploring the nature of superconductivity. Important to the study of
BiS$_{2}$-based superconductors is the relation between structure and
superconductivity. By modifying either the superconducting BiS$_2$ layers or
the blocking layers in these layered compounds, one can effectively tune the
lattice parameters, local atomic environment, electronic structure, and other
physical properties of these materials. In this article, we will review some of
the recent progress on research of the effects of chemical substitution in
BiS$_{2}$-based compounds, with special attention given to the compounds in the
$Ln$OBiS$_{2}$ ($Ln$ = La-Nd) system. Strategies which are reported to be
essential in optimizing superconductivity of these materials will also be
discussed.",1601.07128v1
2016-05-31,Thermoelectric properties of iron-based superconductors and parent compounds,"Herewith, we review the available experimental data of thermoelectric
transport properties of iron-based superconductors and parent compounds. We
discuss possible physical mechanisms into play in determining the Seebeck
effect, from whence one can extract information about Fermi surface
reconstruction and Lifshitz transitions, multiband character, coupling of
charge carriers with spin excitations and its relevance in the unconventional
superconducting pairing mechanism, nematicity, quantum critical fluctuations
close to the optimal doping for superconductivity, correlation. Additional
information is obtained from the analysis of the Nernst effect, whose
enhancement in parent compounds must be related partially to multiband
transport and low Fermi level, but mainly to the presence of Dirac cone bands
at the Fermi level. In the superconducting compounds, large Nernst effect in
the normal state is explained in terms of fluctuating precursors of the spin
density wave state, while in the superconducting state it mirrors the usual
vortex liquid dissipative regime. A comparison between the phenomenology of
thermoelectric behavior of different families of iron-based superconductors and
parent compounds allows to evidence the key differences and analogies, thus
providing clues on the rich and complex physics of these fascinating
unconventional superconductors.",1605.09577v1
2016-03-07,"Electronic topological transitions in Nb$_3$X (X = Al, Ga, In, Ge and Sn) under compression investigated by first principles calculations","First principles electronic structure calculations of A-15 type Nb$_3$X (X =
Al, Ga, In, Ge and Sn) compounds are performed at ambient and high pressures.
Mechanical stability is confirmed in all the compounds both at ambient as well
as under compression from the calculated elastic constants. We have observed
four holes and two electron Fermi surfaces (FS) for all the compounds studied
and FS nesting feature is observed at M and along X - $\Gamma$ in all the
compounds. A continuous change in the FS topology is observed under pressure in
all the compounds which is also reflected in the calculated elastic constants
and density of states under pressure indicating the Electronic topological
transitions (ETT). The ETT observed at around 21.5 GPa, 17.5 GPa in Nb$_3$Al
and Nb$_3$Ga are in good agreement with the anomalies observed by the
experiments.",1606.00460v1
2016-06-13,Electronic and magnetic structures and bonding properties of Ce2CrN3 and U2CrN3 from first principles,"The electronic and magnetic structures of A2CrN3 (A = Ce, U) ternary
compounds calculated based on band magnetism within DFT exhibit different
behaviors of the nf elements (n = 4, 5 resp.). Charge analysis allows to
formally express the two compounds as A2Cr 5+ N3 5- thus classifying them as
covalent nitrides, i.e. far from formal exchange of +- 9 electrons. From
establishing the energy-volume equations of state, the two compounds are found
with hardness magnitudes: B0(A=Ce) =192 GPa and B0(A=U) = 243 GPa, within range
of oxides due to covalent metal-nitrogen bonding shown as based on overlap
matrix analysis. The uranium compound is harder due to a smaller volume and
less compressible U versus Ce metals. Ce2CrN3 exhibits large magnetization on
Cr (1.94BM) and a very small moment develops on cerium (0.14 BM) pointing out
to an intermediate valence state while in U2CrN3, M(Cr) = 0.49 BM and M(U) =
0.97BM. These results are stressed by broad band-like density of states (DOS)
behavior for A=U and localized DOS for A=Ce. Both compounds are found
ferromagnetic in the ground state",1606.04066v1
2016-09-28,ThCr2Si2-type Ru-based superconductors LaRu2M2 (M = P and As): An ab-initio investigation,"ThCr2Si2-type Ru-based superconductors LaRu2P2 and LaRu2As2 with Tc ~ 4 K and
7.8 K respectively have been reported very recently. Using the first principles
method we investigate the details physical and superconducting properties
including the structural properties, electronic properties, elastic properties
and Thermodynamic properties of these newly discovered superconductors. Our
investigated lattice parameters accord well with the experimental result. The
analysis of the electronic band structure and density of states (DOS) indicates
the metallic nature of both the compounds emerges from the La and Ru and the
study of chemical bonding implies that a mixture of covalent, ionic and
metallic bonds exist in both the compounds. The study of the mechanical
properties revels that LaRu2P2 is brittle in nature while LaRu2As2 demonstrates
the ductile nature and both the compounds show anisotropic characteristics.
Finally we determine the Debye temperature and details superconducting
parameters indicating that both the compounds under study are phonon-mediated
medium coupled BCS superconductors.",1609.08856v2
2016-10-04,Effects of Pb doping on the Thermoelectric Properties of Tl8.67PbxSb1.33-xTe6 Materials,"We present the effects of lead doping on the thermoelectric properties of
Tellurium Telluride, prepared by solid state reactions in an evacuated sealed
silica tubes. Structurally, all these compounds were found to be phase pure as
confirmed by the x-rays and energy dispersive spectroscopy analysis. The
Seebeck co-efficient S was measured for all these compounds which show that S
increases with increasing temperature from 295 to 550 K. The Seebeck
coefficient is positive for the whole temperature range, showing p-type
semiconductor characteristics. Complex behavior of Seebeck coefficient for lead
doped compounds has been observed that at room temperature, the values of S for
these compounds have complex behavior, first S decreasing with increase in lead
concentration, and then S increases with increase in lead contents up to
Similarly the electrical conductivity and the power factors have also complex
behavior with lead concentrations. The power factor observed for these
compounds are increases with increase in the whole temperature range studied
here.",1610.00849v1
2016-11-10,Ultra-high vacuum compatible preparation chain for intermetallic compounds,"We report the development of a versatile material preparation chain for
intermetallic compounds that focuses on the realization of a high-purity growth
environment. The preparation chain comprises of an argon glovebox, an
inductively heated horizontal cold boat furnace, an arc melting furnace, an
inductively heated rod casting furnace, an optically heated floating-zone
furnace, a resistively heated annealing furnace, and an inductively heated
annealing furnace. The cold boat furnace and the arc melting furnace may be
loaded from the glovebox by means of a load-lock permitting to synthesize
compounds starting with air-sensitive elements while handling the constituents
exclusively in an inert gas atmosphere. All furnaces are all-metal sealed,
bakeable, and may be pumped to ultra-high vacuum. We find that the latter
represents an important prerequisite for handling compounds with high vapor
pressure under high-purity argon atmosphere. We illustrate operational aspects
of the preparation chain in terms of the single-crystal growth of the
heavy-fermion compound CeNi2Ge2.",1611.03392v1
2016-11-26,Representation of compounds for machine-learning prediction of physical properties,"The representations of a compound, called ""descriptors"" or ""features"", play
an essential role in constructing a machine-learning model of its physical
properties. In this study, we adopt a procedure for generating a systematic set
of descriptors from simple elemental and structural representations. First it
is applied to a large dataset composed of the cohesive energy for about 18000
compounds computed by density functional theory (DFT) calculation. As a result,
we obtain a kernel ridge prediction model with a prediction error of 0.041
eV/atom, which is close to the ""chemical accuracy"" of 1 kcal/mol (0.043
eV/atom). The procedure is also applied to two smaller datasets, i.e., a
dataset of the lattice thermal conductivity (LTC) for 110 compounds computed by
DFT calculation and a dataset of the experimental melting temperature for 248
compounds. We examine the performance of the descriptor sets on the efficiency
of Bayesian optimization in addition to the accuracy of the kernel ridge
regression models. They exhibit good predictive performances.",1611.08645v2
2017-03-13,The structure and composition statistics of 6A binary and ternary crystalline materials,"The fundamental principles underlying the arrangement of elements into solid
compounds with an enormous variety of crystal structures are still largely
unknown. This study presents a general overview of the structure types
appearing in an important subset of the solid compounds, i.e., binary and
ternary compounds of the 6A column oxides, sulfides and selenides. It contains
an analysis of these compounds, including the prevalence of various structure
types, their symmetry properties, compositions, stoichiometries and unit cell
sizes. It is found that these compound families include preferred
stoichiometries and structure types that may reflect both their specific
chemistry and research bias in the available empirical data. Identification of
non-overlapping gaps and missing stoichiometries in these structure populations
may be used as guidance in the search for new materials.",1703.04497v3
2017-03-15,A Data Driven Approach for Compound Figure Separation Using Convolutional Neural Networks,"A key problem in automatic analysis and understanding of scientific papers is
to extract semantic information from non-textual paper components like figures,
diagrams, tables, etc. Much of this work requires a very first preprocessing
step: decomposing compound multi-part figures into individual subfigures.
Previous work in compound figure separation has been based on manually designed
features and separation rules, which often fail for less common figure types
and layouts. Moreover, few implementations for compound figure decomposition
are publicly available.
  This paper proposes a data driven approach to separate compound figures using
modern deep Convolutional Neural Networks (CNNs) to train the separator in an
end-to-end manner. CNNs eliminate the need for manually designing features and
separation rules, but require a large amount of annotated training data. We
overcome this challenge using transfer learning as well as automatically
synthesizing training exemplars. We evaluate our technique on the ImageCLEF
Medical dataset, achieving 85.9% accuracy and outperforming previous
techniques. We have released our implementation as an easy-to-use Python
library, aiming to promote further research in scientific figure mining.",1703.05105v2
2017-11-17,Compositional descriptor-based recommender system accelerating the materials discovery,"Structures and properties of many inorganic compounds have been collected
historically. However, it only covers a very small portion of possible
inorganic crystals, which implies the presence of numerous currently unknown
compounds. A powerful machine-learning strategy is mandatory to discover new
inorganic compounds from all chemical combinations. Herein we propose a
descriptor-based recommender-system approach to estimate the relevance of
chemical compositions where stable crystals can be formed [i.e., chemically
relevant compositions (CRCs)]. As well as data-driven compositional similarity
used in the literature, the use of compositional descriptors as a prior
knowledge can accelerate the discovery of new compounds. We validate our
recommender systems in two ways. Firstly, one database is used to construct a
model, while another is used for the validation. Secondly, we estimate the
phase stability for compounds at expected CRCs using density functional theory
calculations.",1711.06387v1
2017-11-29,Compounding Doubly Affine Matrices,"Weighted sums of left and right hand Kronecker products of Integer Sequence
Doubly Affine (ISDA) as well as Generalized Arithmetic Progression Doubly
Affine (GAPDA) arrays are used to generate larger ISDA arrays of multiplicative
order (compound squares) from pairs of smaller ones.
  In two dimensions we find general expressions for the eigenvalues (EVs) and
singular values (SVs) of the larger arrays in terms of the EVs and SVs of their
constituent matrices, leading to a simple result for the rank of these highly
singular compound matrices. Since the critical property of the smaller
constituent matrices involves only identical row and column sums (often called
semi-magic), the eigenvalue and singular value results can be applied to both
magic squares and Latin squares. Additionally, the compounding process works in
arbitrary dimensions due to the generality of the Kronecker product, providing
a simple method to generate large order ISDA cubes and hypercubes.
  The first examples of compound magic squares are found in manuscripts that
date back to the 10th century CE, and other representative applications are
outlined through judicious examples.",1711.11084v1
2017-12-18,Complex magnetic behaviour and evidence of superspin glass state in a binary intermetallic compound Er5Pd2,"A binary intermetallic compound Er5Pd2 has been investigated using dc and ac
magnetic susceptibilities, magnetic memory effect, isothermal magnetization,
non-linear dc susceptibility, heat capacity and magnetocaloric effect studies.
Interestingly, even though the compound does not show geometrical frustration
it undergoes glassy magnetic phase transition below 17.2 K. Investigation of dc
magnetisation and heat capacity data divulged absence of long-ranged magnetic
ordering. Through magnetic memory effect, time dependent magnetization and ac
susceptibility studies it was revealed that the compound undergoes glass-like
freezing below 17.2 K. Analysis of frequency dependence of this transition
temperature through scaling and Arrhenius law; along with Mydosh parameter
indicate, that the dynamics in Er5Pd2 is due to the presence of strongly
interacting superspins rather than individual spins. This phase transition was
further investigated by non-linear dc susceptibility and was characterized by
static critical exponents {\gamma} and {\delta}. Our results indicate that this
compound show signature of superspin glass at low temperature. Additionally,
both conventional and inverse magnetocaloric effect was observed with large
value of magnetic entropy change and relative cooling power. Our results
suggest that Er5Pd2 can be classified as a superspin glass system with large
magnetocaloric effect.",1712.06388v1
2018-05-13,An attention-based Bi-GRU-CapsNet model for hypernymy detection between compound entities,"Named entities are usually composable and extensible. Typical examples are
names of symptoms and diseases in medical areas. To distinguish these entities
from general entities, we name them \textit{compound entities}. In this paper,
we present an attention-based Bi-GRU-CapsNet model to detect hypernymy
relationship between compound entities. Our model consists of several important
components. To avoid the out-of-vocabulary problem, English words or Chinese
characters in compound entities are fed into the bidirectional gated recurrent
units. An attention mechanism is designed to focus on the differences between
the two compound entities. Since there are some different cases in hypernymy
relationship between compound entities, capsule network is finally employed to
decide whether the hypernymy relationship exists or not. Experimental results
demonstrate",1805.04827v3
2018-06-09,"Multiferroicity in a spin-chain compound, Tb2BaCoO5, with exceptionally large magnetodielectric coupling in polycrystalline form","We report the results of detailed investigations of magnetization,
heat-capacity, dielectric, pyrocurrent, and magneto(di)electric measurements on
Tb2BaCoO5, belonging to a hither-to-unexplored spin-chain cobaltates family,
R2BaCoO5 (R= Rare-earths). The magnetic measurements reveal that this compound
exhibits an antiferromagnetic transition at (T_N=) 18.8 K and there is a
spin-reorientation beyond 40 kOe below T_N. Dielectric and pyrocurrent data
measured as a function of temperature and magnetic-field establish that this
compound is a type-II multiferroic material. The most fascinating finding which
we would like to emphasize is that the observed value of the magnetodielectric
effect beyond the metamagnetic transition field is the largest (close to 55%,
below 10 K, for H= 100 kOe) ever reported for polycrystals of a compound in
bulk form, thereby offering a hope to find a single-phase polycrystalline
compound at room temperature to enable ease of applications.",1806.03502v1
2018-11-16,${\it Ab\ initio}$ thermodynamic properties of certain compounds in Nd-Fe-B system,"In this work, we report the results of \emph{ab initio} calculations of
thermochemical properties of several compounds in the Fe-Nd, B-Nd and B-Fe-Nd
systems. We have performed DFT+U calculations to compute the enthalpy of
formation of the compounds NdB$_6$, NdB$_4$, Nd$_2$B$_5$, Nd$_2$Fe$_{17}$ and
Nd$_5$Fe$_2$B$_6$. It was found that the values obtained with an effective
Hubbard $U$ correction have better agreement with the experimental data. We
have also computed the vibrational contribution to the heat capacity ($C_p$) of
the compounds as a function of temperature was computed using the quasharmonic
approximation. For most of the compounds these properties have not been
experimentally determined until now. Hence, the computed \emph{ab initio}
thermodynamic properties will serve as useful input for the Gibbs energy model
parameter assessment using the CALPHAD method.",1811.06744v5
2018-11-22,"Mössbauer and X-ray Photoelectron Spectroscopy Studies of Fe2BiMO7 (M = Sb, Ta) pyrochlore compounds synthesized by molten salts method","Polycrystalline samples of Fe2BiMO7 (M = Sb, Ta) compounds with
pyrochlore-type structure were synthesized for the first time by the molten
salts method. The compounds were obtained in one hour at 950 C. The structures
were determined by Rietveld refinement. Through M\""ossbauer spectroscopy and
X-ray photoelectron spectroscopy, the site occupancies and ionic states of the
cations in the pyrochlore structure were investigated.Polycrystalline samples
of Fe2BiMO7 (M = Sb, Ta) compounds with pyrochlore-type structure were
synthesized for the first time by the molten salts method. The compounds were
obtained in one hour at 950 C. The structures were determined by Rietveld
refinement. Through M\""ossbauer spectroscopy and X-ray photoelectron
spectroscopy, the site occupancies and ionic states of the cations in the
pyrochlore structure were investigated.",1811.08989v1
2020-01-21,Hybrid Semantic Recommender System for Chemical Compounds,"Recommending Chemical Compounds of interest to a particular researcher is a
poorly explored field. The few existent datasets with information about the
preferences of the researchers use implicit feedback. The lack of Recommender
Systems in this particular field presents a challenge for the development of
new recommendations models. In this work, we propose a Hybrid recommender model
for recommending Chemical Compounds. The model integrates
collaborative-filtering algorithms for implicit feedback (Alternating Least
Squares (ALS) and Bayesian Personalized Ranking(BPR)) and semantic similarity
between the Chemical Compounds in the ChEBI ontology (ONTO). We evaluated the
model in an implicit dataset of Chemical Compounds, CheRM. The Hybrid model was
able to improve the results of state-of-the-art collaborative-filtering
algorithms, especially for Mean Reciprocal Rank, with an increase of 6.7% when
comparing the collaborative-filtering ALS and the Hybrid ALS_ONTO.",2001.07440v1
2017-04-24,Electronic transport properties of intermediately coupled superconductors: PdTe2 and Cu0.04PdTe2,"We have investigated the electrical resistivity, Seebeck coefficient and
thermal conductivity of PdTe2 and 4% Cu intercalated PdTe2 compounds.
Electrical resistivity for the compounds shows Bloch-Gruneisen type linear
temperature (T) dependence for 100 K < T < 480 K, and Fermi liquid behavior (~
T^2) below 50 K. Seebeck coefficient data exhibit strong competition between
Normal (N) and Umklapp (U) scattering processes at low T. Though our results
indicate the transfer of charge carriers to PdTe2 upon Cu intercalation, it is
difficult to discern any change in the Fermi surface of the compound by
Nordheim-Gorter plots. The estimated Fermi energies of the compounds are quite
comparable to good metals Cu, Ag and Au. The low T, thermal conductivity (k) of
the compounds is strongly dominated by the electronic contribution, and
exhibits a rare linear T dependence below 10 K. However, high T, k(T) shows
usual 1/T dependence, dominated by U scattering process. The electron phonon
coupling parameters, estimated from the low T, specific heat data and first
principle electronic structure calculations suggest that PdTe2 and Cu0.04PdTe2
are intermediately coupled superconductors.",1704.07194v2
2017-05-08,Theoretical prediction of sandwiched two-dimensional phosphide binary compounds sheets with tunable bandgaps and anisotropic physical properties,"New allotropes of two-dimensional (2D) GaP and InP binary compounds were
predicted from the structural optimization and dynamical stability analysis in
the framework of the density functional calculations. These stabilized GaP and
InP monolayers possess unique high buckled orthorhombic lattices symmetry with
their cohesive energies of ~0.14 and ~0.17 eV/pair lower than those of 2D low
buckled honeycomb GaP and InP binary compounds, demonstrating that these newly
predicted 2D GaP and InP binary compounds are energetically preferential. More
interesting, their energy band gaps are even ~ 0.52 eV (for GaP) and ~1.49 eV
(for InP) wider than their bulk counterparts. Such band gaps are also tunable
under the strain along armchair/zigzag direction, and the direct/indirect band
gap transitions occur under certain strain, providing their promising
applications in band gap engineering for nanoscale electronic and
optoelectronic devices. A feasible way to synthesize these novel 2D phosphide
compounds is also provided in this study.",1705.02718v2
2019-01-04,Manifestation of electron correlation effect in $\mathrm{U}~5f$ states of uranium compounds revealed by $\mathrm{U}~4d-5f$ resonant photoemission spectroscopy,"We have elucidated the nature of the electron correlation effect in uranium
compounds by imaging the partial $\mathrm{U}~5f$ density of states (pDOS) of
typical itinerant, localized, and heavy fermion uranium compounds by using the
$\mathrm{U}~4d-5f$ resonant photoemission spectroscopy. Obtained
$\mathrm{U}~5f$ pDOS exhibit a systematic trend depending on the physical
properties of compounds. The coherent peak at the Fermi level can be described
by the band-structure calculation, but an incoherent peak emerges on the higher
binding energy side ($\lesssim 1~\mathrm{eV}$) in the \Uf pDOS of localized and
heavy fermion compounds. As the $\mathrm{U}~5f$ state is more localized, the
intensity of the incoherent peak is enhanced and its energy position is shifted
to higher binding energy. These behaviors are consistent with the prediction of
the Mott metal-insulator transition, suggesting that the Hubbard-$U$ type
mechanism takes an essential role in the $5f$ electronic structure of actinide
materials.",1901.00956v1
2019-01-08,Zeeman-type spin splitting in non-magnetic three-dimensional compounds: Materials prediction and electrical control,"Despite its potential for device application, the non-magnetic Zeeman effect
has only been predicted and observed in two-dimensional compounds. We
demonstrate that non-centrosymmetric three-dimensional compounds can also
exhibit a Zeeman-type spin splitting, allowing the splitting control by
changing the growth direction of slabs formed by these compounds. We determine
the required conditions for this effect: $i$) non-centrosymmetric including
polar and non-polar point groups, $ii$) valence band maximum or conduction band
minimum in a generic $k$-point, i.e., non-time-reversal-invariant momentum, and
$iii$) zero magnetic moment. Using these conditions as filters, we perform a
material screening to systematically search for these systems in the aflow-ICSD
database. We find 20 material candidates featuring the Zeeman-type effect. We
also found that the spin-splitting in confined systems can be controlled by an
external electric field, which in turns can induce a metal-insulator
transition. We believe that the Zeeman-type effect in three-dimensional
compounds can potentially be used for spin-filtering devices.",1901.02276v1
2019-10-22,"Electronic and magnetic properties of perovskite selenite and tellurite compounds: CoSeO$_3$, NiSeO$_3$, CoTeO$_3$ and NiTeO$_3$","Selenium and tellurium are among the few elements that form $AB$O$_3$
perovskite structures with a four valent ion in the $A$ site. This leads to
highly distorted structures and unusual magnetic behavior. Here we investigate
the Co and Ni selenite and tellurite compounds, CoSeO$_3$, CoTeO$_3$, NiSeO$_3$
and NiTeO$_3$ using first principles calculations. We find an interplay of
crystal field and Jahn-Teller distortions that underpin the electronic and
magnetic properties. While all compounds are predicted to show an insulating
G-type antiferromagnetic ground state, there is a considerable difference in
the anisotropy of the exchange interactions between the Ni and Co compounds.
This is related to the Jahn-Teller distortion. Finally, we observe that these
four compounds show characteristics generally associated with Mott insulators,
even when described at the level of standard density functional theory. These
are then dense bulk band or Slater, Mott-type insulators.",1910.09923v1
2018-02-08,Frustration and anisotropic exchange in ytterbium magnets with edge-shared octahedra,"We consider the structure of anisotropic exchange interactions in
ytterbium-based insulating rare-earth magnets built from edge-sharing
octahedra. We argue the features of trivalent ytterbium and this structural
configuration allow for a qualitative determination of the different
anisotropic exchange regimes that may manifest in such compounds. The validity
of such super-exchange calculations is tested through comparison to the
well-characterized breathing pyrochlore compound Ba$_3$Yb$_2$Zn$_5$O$_{11}$.
With this in hand, we then consider application to three-dimensional pyrochlore
spinels as well as two-dimensional honeycomb and triangular lattice systems
built from such edge-sharing octahedra. We find an extended regime of robust
emergent weak anisotropy with dominant antiferromagnetic Heisenberg
interactions as well as smaller regions with strong anisotropy. We discuss the
implications of our results for known compounds with the above structures, such
as the spinels AYb$_2$X$_4$ (A = Cd, Mg, X = S, Se), the triangular compound
YbMgGaO$_4$, which have recently emerged as promising candidates for observing
unconventional magnetic phenomena. Finally, we speculate on implications for
the R$_2$M$_2$O$_7$ pyrochlore compounds and some little studied honeycomb
ytterbium magnets.",1802.03024v1
2018-02-19,Hill plot focusing on Ce compounds with high magnetic-ordering-temperatures and consequent study of Ce2AuP3,"Hill plot is a well-known criterion of the f-electron element interatomic
threshold-distance separating the nonmagnetic state from the magnetic one in
actinides or lanthanides. We have reinvestigated the Hill plot of Ce compounds
using a commercial crystallographic database CRYSTMET, focusing on a
relationship between the Ce-Ce distance and the magnetic ordering temperature,
because a Ce compound with no other magnetic elements scarcely has a magnetic
ordering temperature higher than 20 K. The Hill plot of approximately 730
compounds has revealed that a Ce compound, especially for ferromagnet, showing
the high magnetic-ordering-temperature would require a short Ce-Ce distance
with a suppression of valence instability of Ce ion. Through the study, we had
interest in Ce2AuP3 with the Curie temperature of 31 K. The ferromagnetic
nature has been examined by a doping effect, which suggests a possible increase
of magnetic anisotropy energy.",1802.06899v1
2018-08-02,The Icosahedral (H$_2)_{13}$ Supermolecule,"We investigate a range of possible materials containing the supermolecular
form of hydrogen comprising 13 hydrogen molecules arranged in an icosahedral
arrangement. This supermolecule consists of freely rotating 12 hydrogen
molecules in an icosahedral arrangement, enclosing another freely rotating
molecule. To date, this supermolecule has only been observed in a compound with
Iodane (HI). The extremely high hydrogen content suggests possible application
in hydrogen storage so we examine the possibility of supermolecule formation at
ambient pressures. We show that ab initio molecular dynamics calculations give
a good description of the known properties of the HI(H2)13 material, and make
predictions of the existence of related compounds Xe(H2)1, HBr(H2)13 and
HCl(H2)13, including a symmetry-breaking phase transition at low temperature.
The icosahedral (H2)13 supermolecule, remains stable in all these compounds.
This suggests (H2)13 is a widespread feature in hydrogen compounds, and that
appropriately-sized cavities could hold hydrogen supermolecules even at low
pressure. The structure of the supermolecule network is shown to be independent
of the compound at equivalent density.",1808.00884v1
2018-08-09,First-principles calculations of Sc2CdS4 and Y2CdS4 compounds,"Direct energy bandgap materials are crucial for the efficient optoelectronics
devices. Therefore, the investigation of new direct gap materials is important.
In the present work, two novel d-metal sulfides Sc2CdS4 and Y2CdS4 compounds
are investigated by using the all electron full potential linearized augment
plane wave method. Both the compounds show semiconducting nature and direct
band gap with a value 1.886eV for Sc2CdS4 and 2.209eV for Y2CdS4, respectively.
Strong hybridization between S-p and Sc/Y-d orbitals present among valence and
conduction bands which is beneicial to electrical transport. Key optical
parameters are calculated. The static value of the reflectivity R(0) and
refractive index n(0) are vary inversely with the energy band gap (Eg). Both
the compounds Sc2CdS4 and Y2CdS4 are P-type thermoelectric materials because
the Hole carriers dominate the electronic transport. High optical and thermal
response for all compounds reveals that they are potential candidates for
optical and thermoelectric devices.",1808.03039v2
2019-06-06,Measuring the compositionality of noun-noun compounds over time,"We present work in progress on the temporal progression of compositionality
in noun-noun compounds. Previous work has proposed computational methods for
determining the compositionality of compounds. These methods try to
automatically determine how transparent the meaning of the compound as a whole
is with respect to the meaning of its parts. We hypothesize that such a
property might change over time. We use the time-stamped Google Books corpus
for our diachronic investigations, and first examine whether the vector-based
semantic spaces extracted from this corpus are able to predict compositionality
ratings, despite their inherent limitations. We find that using temporal
information helps predicting the ratings, although correlation with the ratings
is lower than reported for other corpora. Finally, we show changes in
compositionality over time for a selection of compounds.",1906.02563v2
2019-06-09,Learning to Predict Novel Noun-Noun Compounds,"We introduce temporally and contextually-aware models for the novel task of
predicting unseen but plausible concepts, as conveyed by noun-noun compounds in
a time-stamped corpus. We train compositional models on observed compounds,
more specifically the composed distributed representations of their
constituents across a time-stamped corpus, while giving it corrupted instances
(where head or modifier are replaced by a random constituent) as negative
evidence. The model captures generalisations over this data and learns what
combinations give rise to plausible compounds and which ones do not. After
training, we query the model for the plausibility of automatically generated
novel combinations and verify whether the classifications are accurate. For our
best model, we find that in around 85% of the cases, the novel compounds
generated are attested in previously unseen data. An additional estimated 5%
are plausible despite not being attested in the recent corpus, based on
judgments from independent human raters.",1906.03634v2
2020-04-01,DeepSIBA: Chemical Structure-based Inference of Biological Alterations,"Predicting whether a chemical structure shares a desired biological effect
can have a significant impact for in-silico compound screening in early drug
discovery. In this study, we developed a deep learning model where compound
structures are represented as graphs and then linked to their biological
footprint. To make this complex problem computationally tractable, compound
differences were mapped to biological effect alterations using Siamese Graph
Convolutional Neural Networks. The proposed model was able to learn new
representations from chemical structures and identify structurally dissimilar
compounds that affect similar biological processes with high precision.
Additionally, by utilizing deep ensembles to estimate uncertainty, we were able
to provide reliable and accurate predictions for chemical structures that are
very different from the ones used during training. Finally, we present a novel
inference approach, where the trained models are used to estimate the signaling
pathways affected by a compound perturbation in a specific cell line, using
only its chemical structure as input. As a use case, this approach was used to
infer signaling pathways affected by FDA-approved anticancer drugs.",2004.01028v1
2020-04-04,Lattice distortion in TmCo$_2$: a poly- and single- crystal study,"Within the RCo$_2$ family of compounds, a structural distortion linked with
the onset of magnetic ordering around the critical temperature can be observed.
One of the less explored RCo$_2$ compounds is TmCo$_2$ probably due to its low
Curie temperature. Exceptionally this compound, given its position at the end
of the ferrimagnetic series, shows discrepancies in the ordering of the Co
sub-lattice because of a weak Weiss molecular field. In this paper we focus on
the structural distortion in TmCo$_2$, which appears together with the magnetic
ordering around the critical temperature of $T_{C}\sim3.6$~K. Poly-crystals as
well as single-crystals of TmCo$_2$ were used in our experiments. For both
kinds of samples we observed the same type of the rhombohedral distortion along
the [111] direction from the cubic Fd$\bar{3}$m to R$\bar{3}$m space group. The
relation between observed magnetic and structural properties in this compound
is discussed.",2004.01938v1
2020-04-08,The Rashba Scale: Emergence of Band Anti-Crossing as a Design Principle for Materials with Large Rashba coefficient,"The spin-orbit -induced spin splitting of energy bands in low symmetry
compounds (the Rashba Effect) has a long-standing relevance to spintronic
applications and to the fundamental understanding of symmetry breaking in
solids, yet the knowledge of what controls its magnitude in different materials
is difficult to anticipate. Indeed, rare discoveries of compounds with large
Rashba coefficients are invariably greeted as pleasant surprises. We advance
the understanding of the ""Rashba Scale"" using the ""inverse design"" approach by
formulating theoretically the relevant design principle and then identifying
compounds that satisfy it. We show that the presence of energy band
anti-crossing provides a causal design principle of compounds with large Rashba
coefficients, leading to the identification via first-principles calculations
of 34 rationally designed strong-Rashba compounds. Since topological insulators
must have band anti crossing, this leads us to establish an interesting cross
functionality of ""Topological Rashba Insulators"" (TRI) that may provide a
platform for the simultaneous control of spin splitting and spin-polarization.",2004.07293v1
2020-05-04,"Synthesis and characterization of novel benzimidazole embedded 1,3,5-trisubstituted pyrazolines as antimicrobial agents","Efficient syntheses of some new substituted pyrazoline derivatives linked to
substituted benzimidazole scaffold were performed by multistep reaction
sequences. All the synthesized compounds were characterized using elemental
analysis and spectral studies (IR, 1D/2D NMR techniques and mass spectrometry).
The synthesized compounds were screened for their antimicrobial activity
against selected Gram-positive and Gram-negative bacteria, and fungi strain.
The compounds with halo substituted phenyl group at C5 of the 1-phenyl
pyrazoline ring (15, 16 and 17) showed significant antibacterial activity.
Among the screened compounds, 17 showed most potent inhibitory activity (MIC =
64 {\mu}g mL-1) against a bacterial strain. The tested compounds werefound to
be almost inactive against the fungal strain C. albicans, apart from
pyrazoline-1-carbothiomide 21, which was moderately active.",2005.01375v1
2020-05-24,"Multiband effect in elastoresistance of Fe(Se,Te)","We have investigated the elastoresistance of two FeSe${}_{1-x}$Te${}_{x}$ (x
about 0.4 - 0.5) compounds that have a close chemical composition but differ
significantly in electronic properties. The first compound has a negative
temperature coefficient of resistance and does not show any phase transitions
other than superconducting. The elastoresistance of this compound approximately
follows $1/T$ low as it usually occurs in Fe(Se,S) with metallic conductivity.
The second compound has a metallic type of conductivity and in addition to the
superconducting transition, there is also a phase transition at a temperature
of about 30 K. The elastoresistance of the second compound is sign-reversing
and can be approximated with the sum of two Curie-Weiss type terms with
opposite signs and different critical temperatures which suggest a competition
of contributions to the elastoresistance from different band valleys.",2005.11765v1
2020-08-12,"Insights into the structural, electronic and optical properties of X$_2$MgZ$_4$($X=$ Sc, Y; $Z=$ S, Se) spinel compounds: Materials for the future optoelectronic applications","Direct bandgap bulk materials are very important for the optical
applications. It is therefore important to predict new materials with the
desired properties. In the present work, density functional theory is applied
to study different physical properties of X$_2$MgZ$_4$($X=$ Sc, Y; $Z=$ S, Se)
spinel compounds. Generalized gradient approximation is used to analyze the
structural and elastic parameters while modified Becke Johnson exchange
potential is applied to calculate electric band profiles and optical
properties. All the studied compounds are stable in the cubic structure. Also
the energy bandgap is of direct nature. Therefore these compounds can find
useful applications in the optoelectrics devices. Optical properties of the
compounds are studied in terms of dielectric function, refractive index,
extinction coefficient, optical conductivity and reflectivity. The transport
parameters like electrical conductivity, Seebeck coefficient, and thermal
conductivity are also evaluated.",2008.05126v1
2022-03-03,Effect of symmetry reduction on the magnetic properties of LnIr$_2$Si$_2$ polymorphs,"Many tetragonal compounds LnIr$_2$Si$_2$ (Ln = lanthanoid) occur in two
polymorphous phases and are therefore well suited to study the relationship
between crystal structure and magnetic properties. We have grown GdIr$_2$Si$_2$
single crystals of both polymorphs from a high-temperature indium flux and
investigated their anisotropic magnetic properties. The higher symmetric form
with the ThCr$_2$Si$_2$ structure (space group $I4/mmm$) orders
antiferromagnetically at $T_{\rm N}=87\,\rm K$ while for the lower symmetric
compound in the CaBe$_2$Ge$_2$ structure (space group $P4/nmm$) we determined a
much lower \neel temperature $T_{\rm N}=12\,\rm K$. Our magnetic
characterization of the single crystals reveals that for both compounds the
magnetic moments are aligned in the $a-a$ plane of the tetragonal lattice, but
that the change of the symmetry strongly effects the inplane alignment of the
moment orientation. For Ln$=$Er and Ho, we confirmed the existence of
LnIr$_2$Si$_2$ in the space group $P4/nmm$. The magnetic properties of these
lower symmetric compounds are in remarkable difference to their related
compounds in the space group $I4/mmm$.",2203.01790v1
2017-06-27,Risk Model Based on General Compound Hawkes Process,"In this paper, we introduce a new model for the risk process based on general
compound Hawkes process (GCHP) for the arrival of claims. We call it risk model
based on general compound Hawkes process (RMGCHP). The Law of Large Numbers
(LLN) and the Functional Central Limit Theorem (FCLT) are proved. We also study
the main properties of this new risk model, net profit condition, premium
principle and ruin time (including ultimate ruin time) applying the LLN and
FCLT for the RMGCHP. We show, as applications of our results, similar results
for risk model based on compound Hawkes process (RMCHP) and apply them to the
classical risk model based on compound Poisson process (RMCPP).",1706.09038v1
2017-06-29,On magic factors in Stein's method for compound Poisson approximation,"One major obstacle in applications of Stein's method for compound Poisson
approximation is the availability of so-called magic factors (bounds on the
solution of the Stein equation) with favourable dependence on the parameters of
the approximating compound Poisson random variable. In general, the best such
bounds have an exponential dependence on these parameters, though in certain
situations better bounds are available. In this paper, we extend the region for
which well-behaved magic factors are available for compound Poisson
approximation in the Kolmogorov metric, allowing useful compound Poisson
approximation theorems to be established in some regimes where they were
previously unavailable. To illustrate the advantages offered by these new
bounds, we consider applications to runs, reliability systems, Poisson mixtures
and sums of independent random variables.",1706.09642v1
2017-10-03,Keep It Real: Tail Probabilities of Compound Heavy-Tailed Distributions,"We propose an analytical approach to the computation of tail probabilities of
compound distributions whose individual components have heavy tails. Our
approach is based on the contour integration method, and gives rise to a
representation of the tail probability of a compound distribution in the form
of a rapidly convergent one-dimensional integral involving a discontinuity of
the imaginary part of its moment generating function across a branch cut. The
latter integral can be evaluated in quadratures, or alternatively represented
as an asymptotic expansion. Our approach thus offers a viable (especially at
high percentile levels) alternative to more standard methods such as Monte
Carlo or the Fast Fourier Transform, traditionally used for such problems. As a
practical application, we use our method to compute the operational Value at
Risk (VAR) of a financial institution, where individual losses are modeled as
spliced distributions whose large loss components are given by power-law or
lognormal distributions. Finally, we briefly discuss extensions of the present
formalism for calculation of tail probabilities of compound distributions made
of compound distributions with heavy tails.",1710.01227v1
2017-10-10,"Ternary inorganic compounds containing carbon, nitrogen, and oxygen at high pressures","Ternary C_{x}N_{y}O_{z} compounds are actively researched as novel high
energy density and ultrahard materials. Although some synthesis work has been
performed at ambient conditions, very little is known about the high pressure
chemistry of of C_{x}N_{y}O_{z} compounds. In this work, first principles
variable-composition evolutionary structure prediction calculations are
performed with the goal of discovering novel mixed C_{x}N_{y}O_{z} materials at
ambient and high pressure conditions. By systematically searching ternary
variable composition crystalline materials, the full ternary phase diagram is
constructed in the range of pressures from 0 to 100 GPa. The search finds the
C_{2}N_{2}O crystal containing extended covalent network of C, N, and O atoms,
having space group symmetry Cmc2_{1}, and stable above just 10 GPa. Several
other novel metastable (CO)_{x}-(N)_{y} crystalline compounds discovered during
the search, including two polymorphs of C_{2}NO_{2} and two polymorphs of
C_{3}N_{2}O_{3} crystals are found to be energetically favorable compared to
polymeric carbon monoxide (CO) and nitrogen. Predicted new compounds are
characterized by their Raman spectra and equations of state.",1710.03652v1
2019-05-06,Controlled exploration of chemical space by machine learning of coarse-grained representations,"The size of chemical compound space is too large to be probed exhaustively.
This leads high-throughput protocols to drastically subsample and results in
sparse and non-uniform datasets. Rather than arbitrarily selecting compounds,
we systematically explore chemical space according to the target property of
interest. We first perform importance sampling by introducing a Markov chain
Monte Carlo scheme across compounds. We then train an ML model on the sampled
data to expand the region of chemical space probed. Our boosting procedure
enhances the number of compounds by a factor 2 to 10, enabled by the ML model's
coarse-grained representation, which both simplifies the structure-property
relationship and reduces the size of chemical space. The ML model correctly
recovers linear relationships between transfer free energies. These linear
relationships correspond to features that are global to the dataset, marking
the region of chemical space up to which predictions are reliable---a more
robust alternative to the predictive variance. Bridging coarse-grained
simulations with ML gives rise to an unprecedented database of drug-membrane
insertion free energies for 1.3 million compounds.",1905.01897v2
2019-12-19,Perfect anomalous reflection using compound metallic metagratings,"Metagrating is a new concept for wavefront manipulation that, unlike phase
gradient metasurfaces, does not suffer from low efficiency and also has a less
complicated fabrication process. In this paper, a compound metallic grating (a
periodic structure with more than one slit in each period) is proposed for
anomalous reflection. The electromagnetic response of this grating is analyzed
by a proposed analytical method and then a closed-form and analytical
expressions are presented for the reflection coefficients of the higher
diffracted orders. The proposed method is verified by full-wave simulations and
the results are in excellent agreement. Thanks to the geometrical asymmetry of
compound metallic grating, we use it for designing anomalous reflection in the
normal incident. Given analytical expressions for reflection coefficients, a
perfect anomalous reflector is designed via transferring all the incident power
to (-1) diffraction order. The structure designed in this study has an
unprecedented near-to-unitary efficiency of 99.9%. Finally, a multi-element
compound metallic grating is proposed for reflecting the normal incident to
angles of below 30, which is a challenging accomplishment. This excellent
performance of compound metallic grating shows its high potential for microwave
and terahertz wave-front manipulation applications.",1912.09139v1
2020-03-13,Evolutionary construction of formation energy convex hull: Practical scheme and application to carbon-hydrogen binary system,"We present an evolutionary construction technique of formation energy convex
hull to search for thermodynamically stable compounds. In this technique,
candidates with a wide variety of chemical compositions and crystal structures
are created by systematically applying evolutionary operators, ""mating"",
""mutation"", and ""adaptive mutation"", to two target compounds, and the convex
hull is directly updated through the evolution. We applied the technique to
carbon-hydrogen binary system at 10 GPa and obtained 15 hydrocarbons within the
convex hull distance less than 0.5 mRy/atom: graphane, polybutadiene,
polyethylene, butane, ethane, methane, three molecular compounds of ethane and
methane, and six molecular compounds of methane and hydrogen. These results
suggest that our evolutionary construction technique is useful for the
exploration of stable phases under extreme conditions and the synthesis of new
compounds.",2003.06098v1
2020-03-25,Wavelet Compressibility of Compound Poisson Processes,"In this paper, we precisely quantify the wavelet compressibility of compound
Poisson processes. To that end, we expand the given random process over the
Haar wavelet basis and we analyse its asymptotic approximation properties. By
only considering the nonzero wavelet coefficients up to a given scale, what we
call the greedy approximation, we exploit the extreme sparsity of the wavelet
expansion that derives from the piecewise-constant nature of compound Poisson
processes. More precisely, we provide lower and upper bounds for the mean
squared error of greedy approximation of compound Poisson processes. We are
then able to deduce that the greedy approximation error has a sub-exponential
and super-polynomial asymptotic behavior. Finally, we provide numerical
experiments to highlight the remarkable ability of wavelet-based dictionaries
in achieving highly compressible approximations of compound Poisson processes.",2003.11646v2
2020-07-02,Compounds of symmetric informationally complete measurements and their application in quantum key distribution,"Symmetric informationally complete measurements (SICs) are elegant,
celebrated and broadly useful discrete structures in Hilbert space. We
introduce a more sophisticated discrete structure compounded by several SICs. A
SIC-compound is defined to be a collection of $d^3$ vectors in $d$-dimensional
Hilbert space that can be partitioned in two different ways: into $d$ SICs and
into $d^2$ orthonormal bases. While a priori their existence may appear
unlikely when $d>2$, we surprisingly answer it in the positive through an
explicit construction for $d=4$. Remarkably this SIC-compound admits a close
relation to mutually unbiased bases, as is revealed through quantum state
discrimination. Going beyond fundamental considerations, we leverage these
exotic properties to construct a protocol for quantum key distribution and
analyze its security under general eavesdropping attacks. We show that
SIC-compounds enable secure key generation in the presence of errors that are
large enough to prevent the success of the generalisation of the six-state
protocol.",2007.01007v1
2020-07-10,A characterization of progressively equivalent probability measures preserving the structure of a compound mixed renewal process,"Generalizing earlier works of Delbaen & Haezendonck [5] as well as of [18]
and [16] for given compound mixed renewal process S under a probability measure
P, we characterize all those probability measures Q on the domain of P such
that Q and P are progressively equivalent and S remains a compound mixed
renewal process under Q with improved properties. As a consequence, we prove
that any compound mixed renewal process can be converted into a compound mixed
Poisson process through a change of measures. Applications related to the ruin
problem and to the computation of premium calculation principles in an
insurance market without arbitrage opportunities are discussed in [26] and
[27], respectively.",2007.05289v2
2020-09-19,Stochastic Threshold Model Trees: A Tree-Based Ensemble Method for Dealing with Extrapolation,"In the field of chemistry, there have been many attempts to predict the
properties of unknown compounds from statistical models constructed using
machine learning. In an area where many known compounds are present (the
interpolation area), an accurate model can be constructed. In contrast, data in
areas where there are no known compounds (the extrapolation area) are generally
difficult to predict. However, in the development of new materials, it is
desirable to search this extrapolation area and discover compounds with
unprecedented physical properties. In this paper, we propose Stochastic
Threshold Model Trees (STMT), an extrapolation method that reflects the trend
of the data, while maintaining the accuracy of conventional interpolation
methods. The behavior of STMT is confirmed through experiments using both
artificial and real data. In the case of the real data, although there is no
significant overall improvement in accuracy, there is one compound for which
the prediction accuracy is notably improved, suggesting that STMT reflects the
data trends in the extrapolation area. We believe that the proposed method will
contribute to more efficient searches in situations such as new material
development.",2009.09171v1
2020-09-19,Nominal Compound Chain Extraction: A New Task for Semantic-enriched Lexical Chain,"Lexical chain consists of cohesion words in a document, which implies the
underlying structure of a text, and thus facilitates downstream NLP tasks.
Nevertheless, existing work focuses on detecting the simple surface lexicons
with shallow syntax associations, ignoring the semantic-aware lexical compounds
as well as the latent semantic frames, (e.g., topic), which can be much more
crucial for real-world NLP applications. In this paper, we introduce a novel
task, Nominal Compound Chain Extraction (NCCE), extracting and clustering all
the nominal compounds that share identical semantic topics. In addition, we
model the task as a two-stage prediction (i.e., compound extraction and chain
detection), which is handled via a proposed joint framework. The model employs
the BERT encoder to yield contextualized document representation. Also, HowNet
is exploited as external resources for offering rich sememe information. The
experiments are based on our manually annotated corpus, and the results prove
the necessity of the NCCE task as well as the effectiveness of our joint
approach.",2009.09173v1
2020-09-30,Designing of Magnetic MAB Phases for Energy Applications,"Based on high-throughput density functional theory calculations, we performed
screening for stable magnetic MAB compounds and predicted potential strong
magnets for permanent magnet and magnetocaloric applications. The
thermodynamical, mechanical, and dynamical stabilities are systematically
evaluated, resulting in 21 unreported compounds on the convex hull, and 434
materials being metastable considering convex hull tolerance to be 100
meV/atom. Analysis based on the Hume-Rothery rules revealed that the valence
electron concentration and size factor difference are of significant importance
in determining the stability, with good correspondence with the local atomic
bonding. We found 71 compounds with the absolute value of magneto-crystalline
anisotropy energy above 1.0 MJ/m$^3$ and 23 compounds with a uniaxial
anisotropy greater than 0.4 MJ/m$^3$, which are potential gap magnets. Based on
the magnetic deformation proxy, 99 compounds were identified as potential
materials with interesting magnetocaloric performance.",2009.14543v1
2020-10-23,Magnetic and structural properties of Ni-substituted magnetoelectric Co$_4$Nb$_2$O$_9$,"The magnetic and structural properties of polycrystalline Co$_{4-x}$ Ni$_x$
Nb$_2$ O$_9$ (x=1,2) have been investigated by neutron powder diffraction,
magnetization and heat capacity measurements, and density functional theory
(DFT) calculations. For x=1, the compound crystallizes in the trigonal
P$\bar{3}$c1 space group. Below T$_N$ = 31 K it develops a weakly non-collinear
antiferromagnetig structure with magnetic moments in the ab-plane. The compound
with x=2 has crystal structure of the orthorhombic Pbcn space group and shows a
hard ferrimagnetic behavior below T$_C$ =47 K. For this compound a weakly
non-collinear ferrimagnetic structure with two possible configurations in ab
plane was derived from ND study. By calculating magnetic anisotropy energy via
DFT, the ground-state magnetic configuration was determined for this compound.
The heat capacity study in magnetic fields up to 140 kOe provide further
information on the magnetic structure of the compounds.",2010.12285v1
2020-11-24,Good and Bad Boundaries in Ultrasound Compounding: Preserving Anatomic Boundaries While Suppressing Artifacts,"Ultrasound 3D compounding is important for volumetric reconstruction, but as
of yet there is no consensus on best practices for compounding. Ultrasound
images depend on probe direction and the path sound waves pass through, so when
multiple intersecting B-scans of the same spot from different perspectives
yield different pixel values, there is not a single, ideal representation for
compounding (i.e. combining) the overlapping pixel values. Current popular
methods inevitably suppress or altogether leave out bright or dark regions that
are useful, and potentially introduce new artifacts. In this work, we establish
a new algorithm to compound the overlapping pixels from different view points
in ultrasound. We uniquely leverage Laplacian and Gaussian Pyramids to preserve
the maximum boundary contrast without overemphasizing noise and speckle. We
evaluate our algorithm by comparing ours with previous algorithms, and we show
that our approach not only preserves both light and dark details, but also
somewhat suppresses artifacts, rather than amplifying them.",2011.11962v3
2020-11-27,d0 Ferromagnetism in Mg-doped Rutile TiO2 Nanoparticles,"In a quest of enriching the area of d0 magnetism in oxide materials, we have
undertaken to study Mg-doped TiO2 compounds. The Ti1-xMgxO2 (x=0, 0.02, 0.04
and 0.06) nanoparticles were prepared by solid-state reaction route. The X-ray
diffractions (XRD) patterns of these samples indicate single phase of
tetragonal rutile-structure of TiO2. The refinement of the XRD patterns reveals
no change in the crystallographic lattice parameters in comparison to pure TiO2
upon Mg doping and it indicates that Mg2+ ions do not enter core grains and
form core/shell structure. SEM observations reveal the uniform morphology with
nanometric grains in the range of 150-200 nm. The measurement of magnetic
properties of these compounds indicates that pure TiO2 and Ti0.98Mg0.02
compounds exhibit paramagnetic behavior and Ti0.96Mg0.04 compound exhibits
ferromagnetic (FM) phase superimposed with the dominating paramagnetic phase.
However, Ti0.94Mg0.06 compound exhibits ferromagnetic to paramagnetic
transition with FM transition temperature of 180.2 K. The measurements of zero
field and field cooled magnetization data indicate low temperature magnetic
irreversibility for x=0.06 sample and it was attributed to the competing AFM
(core) and the FM (shell) interactions. The measurement of hysteresis curves at
various temperatures indicates domain wall pinning and an exchange-bias
behavior.",2011.13718v1
2020-12-24,Generalization of the multiplicative and additive compounds of square matrices and contraction in the Hausdorff dimension,"The $k$ multiplicative and $k$ additive compounds of a matrix play an
important role in geometry, multi-linear algebra, the asymptotic analysis of
nonlinear dynamical systems, and in bounding the Hausdorff dimension of fractal
sets. These compounds are defined for integer values of $k$. Here, we introduce
generalizations called the $\alpha$ multiplicative and $\alpha$ additive
compounds of a square matrix, with $\alpha$ real. We study the properties of
these new compounds and demonstrate an application in the context of the Douady
and Oesterl\'{e} Theorem. This leads to a generalization of contracting systems
to $\alpha$ contracting systems, with $\alpha$ real. Roughly speaking, the
dynamics of such systems contracts any set with Hausdorff dimension larger than
$\alpha$. For $\alpha=1$ they reduce to standard contracting systems.",2012.13441v1
2021-09-20,Random magnetic anisotropy in a new compound $\mbox{Sm}_2\mbox{Ag}\mbox{Si}_3$,"We report the experimental study on the structural and magnetic properties of
a new ternary intermetallic compound $\mathrm{Sm_2AgSi_3}$. The properties of
the sample were investigated in detail by X-ray diffraction, dc-magnetization,
and heat capacity measurements. The polycrystalline compound of
$\mathrm{Sm_2AgSi_3}$ crystallizes in the $\mathrm{ThSi_2}$-type tetragonal
structure (space group ${I_{4_1}/amd}$). The temperature-dependent
dc-magnetization and heat capacity results demonstrate that the compound
undergoes ferromagnetic behaviour with a Curie temperature ($T_C$) of 14 K. The
large coercive field in hysteresis loops and the thermomagnetic irreversibility
in the ferromagnetic region revealed that the compound exhibits a large
magnetic anisotropy. The magnitude of the applied field and the coercivity
obtained from the M-H loops corroborate with the thermomagnetic irreversibility
in the magnetization data. The magnetic contribution of the heat capacity
reveals a broad Schottky-type anomaly above $T_C$, due to the presence of the
crystal electric field effect of $\mathrm{Sm^{3+}}$ in $\mathrm{Sm_2AgSi_3}$.",2109.09608v1
2021-10-01,Iron-rich Fe-O compounds with closest-packed layers at core pressures,"Oxygen solubility in solid iron is extremely low, even at high pressures and
temperatures. Thus far, no Fe-O compounds between Fe and FeO endmembers have
been reported experimentally. We observed chemical reactions of Fe with FeO or
Fe$_2$O$_3$ $in\ situ$ x-ray diffraction experiments at 220-260 GPa and
3,000-3,500 K. The refined diffraction patterns are consistent with a series of
Fe$_n$O (n $>$ 1) compounds (e.g., Fe$_{25}$O$_{13}$ and Fe$_{28}$O$_{14}$)
identified using the adaptive genetic algorithm. Like $\epsilon$-Fe in the
hexagonal close-packed (hcp) structure, the structures of Fe$_n$O compounds
consist of oxygen-only close-packed monolayers distributed between iron-only
layers. $Ab\ initio$ calculations show systematic electronic properties of
these compounds that have ramifications for the physical properties of Earth's
inner core.",2110.00524v1
2021-12-01,Superconductivity in the layered cage compound Ba3Rh4Ge16,"We report the synthesis and superconducting properties of a layered cage
compound Ba3Rh4Ge16. Similar to Ba3Ir4Ge16, the compound is composed of 2D
networks of cage units, formed by noncubic Rh-Ge building blocks, in marked
contrast to the reported rattling compounds. The electrical resistivity,
magnetization, specific heat capacity, and muSR measurements unveiled
moderately coupled s-wave superconductivity with a critical temperature Tc =
7.0 K, the upper critical field ~ 2.5 T, the electron-phonon coupling strength
~ 0.80, and the Ginzburg-Landau parameter ~ 7.89. The mass reduction by the
substitution of Ir by Rh is believed to be responsible for the enhancement of
Tc and coupling between the cage and guest atoms. Our results highlight the
importance of the atomic weight of the framework in cage compounds in
controlling the electron-phonon coupling strength and Tc.",2112.00644v1
2022-06-12,Electronic and magnetic properties of intermetallic Kagome magnets $R$V$_6$Sn$_6$ ($R$ = Tb - Tm),"We present a systematic study of the structure, electronic, and magnetic
properties of a new branch of intermetalllic compounds, $R$V$_6$Sn$_6$ ($R$ =
Tb - Tm) by using X-ray diffraction, magnetic susceptibility, magnetization,
electrical transport, and heat-capacity measurements. These compounds feature a
combination of a non-magnetic vanadium kagome sublattice and a magnetic
rare-earth triangular sublattice that supports various spin anisotropies based
on different $R$ ions. We find magnetic orders for the $R$ = Tb, Dy, and Ho
compounds at 4.4, 3, 2.5 K, respectively, while no ordering is detected down to
0.4 K for the $R$ = Er and Tm compounds with easy-plane anisotropies.
Electronically, we found no superconductivity or charge ordering transition
down to 0.4 K for any member of this family, while all compounds exhibit
multi-band transport properties that originate from the band topology of the
vanadium kagome sublattice.",2206.05653v1
2022-06-29,Designing shape-memory-like microstructures in intercalation materials,"During the reversible insertion of ions, lattices in intercalation materials
undergo structural transformations. These lattice transformations generate
misfit strains and volume changes that, in turn, contribute to the structural
decay of intercalation materials and limit their reversible cycling. In this
paper, we draw on insights from shape-memory alloys, another class of phase
transformation materials, that also undergo large lattice transformations but
do so with negligible macroscopic volume changes and internal stresses. We
develop a theoretical framework to predict structural transformations in
intercalation compounds and establish crystallographic design rules necessary
for forming shape-memory-like microstructures in intercalation materials. We
use our framework to systematically screen open-source structural databases
comprising n > 5000 pairs of intercalation compounds. We identify candidate
compounds, such as Li$_x$Mn$_2$O$_4$ (Spinel), Li$_x$Ti$_2$(PO$_4$)$_3$
(NASICON), that approximately satisfy the crystallographic design rules and can
be precisely doped to form shape-memory-like microstructures. Throughout, we
compare our analytical results with experimental measurements of intercalation
compounds. We find a direct correlation between structural transformations,
microstructures, and increased capacity retention in these materials. These
results, more generally, show that crystallographic designing of intercalation
materials could be a novel route to discovering compounds that do not decay
with continuous usage.",2206.14948v1
2022-08-29,Resonant Kushi-comb-like multi-frequency radiation of oscillating two-color soliton molecules,"Nonlinear waveguides with two distinct domains of anomalous dispersion can
support the formation of molecule-like two-color pulse compounds. They consist
of two tightly bound subpulses with frequency loci separated by a vast
frequency gap. Perturbing such a two-color pulse compound triggers periodic
amplitude and width variations, reminiscent of molecular vibrations. With
increasing strength of perturbation, the dynamics of the pulse compound changes
from harmonic to nonlinear oscillations. The periodic amplitude variations
enable coupling of the pulse compound to dispersive waves, resulting in the
resonant emission of multi-frequency radiation. We demonstrate that the
location of the resonances can be precisely predicted by phase-matching
conditions. If the pulse compound consists of a pair of identical subpulses,
inherent symmetries lead to degeneracies in the resonance spectrum. Weak
perturbations lift existing degeneracies and cause a splitting of the resonance
lines into multiple lines. Strong perturbations result in more complex emission
spectra, characterized by well separated spectral bands caused by resonant
Cherenkov radiation and additional four-wave mixing processes.",2208.13829v1
2022-09-16,"Highly Tunable Band Inversion in AB2X4 (A=Ge, Sn, Pb; B=As, Sb, Bi; X=Se, Te) Compounds","Topological materials have been discovered so far largely by searching for
existing compounds in crystallographic databases, but there are potentially new
topological materials with desirable features that have not been synthesized.
One of the desirable features is high tunability resulted from the band
inversion with a very small direct band gap, which can be tuned by changes in
pressure or strain to induce a topological phase transition. Using density
functional theory (DFT) calculations, we have studied the septuple layered
AB2X4 series compounds, where A=(Ge, Sn and Pb), B=(As, Sb and Bi) and X=(Se
and Te). With the DFT thermodynamic stability validated by the already reported
compounds in these series, we predict new stable Se compounds, which are not
found in crystallographic database. Among them, we find that GeBi2Se4 and
GeSb2Se4 having a small direct band gap at the Z point are very close to a
strong topological insulator, which can be tuned by a moderate pressure to
induce the band inversion. Importantly, the topological features with the small
direct band gap are well isolated in both momentum and energy windows, which
offers high tunability for studying the topological phase transition.",2209.07984v1
2022-10-08,Energy transition density of driven chaotic systems: A compound trace formula,"Oscillations in the probability density of quantum transitions of the
eigenstates of a chaotic Hamiltonian within classically narrow energy ranges
have been shown to depend on closed compound orbits. These are formed by a pair
of orbit segments, one in the energy shell of the original Hamiltonian and the
other in the energy shell of the driven Hamiltonian, with endpoints which
coincide. Viewed in the time domain, the same pair of trajectory segments
arises in the semiclassical evaluation of the trace of a compound propagator:
the product of the complex exponentials of the original Hamiltonian and of its
driven image. It is shown here that the probability density is the double
Fourier transform of this trace, so that the closed compound orbits emulate the
role played by periodic orbits in Gutzwiller's trace formula in its
semiclassical evaluation. The phase of the oscillations with the energies or
evolution parameters agree with those previously obtained, whereas the
amplitude of the contribution of each closed compound orbit is more compact and
independent of any feature of the Weyl-Wigner representation in which the
calculation was carried out.",2210.04078v3
2022-10-24,"""Covid vaccine is against Covid but Oxford vaccine is made at Oxford!"" Semantic Interpretation of Proper Noun Compounds","Proper noun compounds, e.g., ""Covid vaccine"", convey information in a
succinct manner (a ""Covid vaccine"" is a ""vaccine that immunizes against the
Covid disease""). These are commonly used in short-form domains, such as news
headlines, but are largely ignored in information-seeking applications. To
address this limitation, we release a new manually annotated dataset, ProNCI,
consisting of 22.5K proper noun compounds along with their free-form semantic
interpretations. ProNCI is 60 times larger than prior noun compound datasets
and also includes non-compositional examples, which have not been previously
explored. We experiment with various neural models for automatically generating
the semantic interpretations from proper noun compounds, ranging from few-shot
prompting to supervised learning, with varying degrees of knowledge about the
constituent nouns. We find that adding targeted knowledge, particularly about
the common noun, results in performance gains of upto 2.8%. Finally, we
integrate our model generated interpretations with an existing Open IE system
and observe an 7.5% increase in yield at a precision of 85%. The dataset and
code are available at https://github.com/dair-iitd/pronci.",2210.13039v1
2022-12-20,"Atomic, electronic, and superconducting properties of Zr$_2$Ir compound","We have investigated the structural, electronic, mechanical, phononic, and
superconducting properties of the Zr$_2$Ir compound with a body-centered
tetragonal crystal structure using first-principles calculations. Our analysis
reveals that the Zr$_2$Ir compound shows mechanical and dynamically stable by
using with and without spin-orbit coupling (SOC) effect. After calculating some
properties such as elastic constants, Bulk modulus, Young's modulus, Poisson
ratio, Debye temperature, and sound velocity, we found that Zr$_2$Ir is
ductile. When the elastic constants $C_{11}$ and $C_{33}$ are compared, it is
determined that the situation changes in the opposite direction under the
effect of SOC, that is, more compressibility along the x-axis turns into the
z-axis. Here, the electronic band structure and intensity of the states
calculated for the compound show a metallic character. The superconducting
critical temperature ($T_c$) and electron-phonon coupling constant ($\lambda$)
were found to be 7.50 K and 0.93 without SOC and 7.62 K and 0.96 with SOC,
respectively. We determined that although the Zr$_2$Ir compound has a strong
electron-phonon coupling regime, the inclusion of SOC slightly reduces its
critical temperature and electron-phonon coupling constant.",2212.10611v1
2023-02-13,"Signature of topological crystalline insulating behavior in new B2X2Zn (X=Ir, Rh, Co) compound from first-principles Computation","Recent attempts at topological materials have revealed a large class of
materials that show gapless surface states protected by time-reversal symmetry
and crystal symmetries. Among them, topological insulating states protected by
crystal symmetries, rather than time-reversal symmetry are classified as
topological crystalline insulators. We computationally predict the signature of
new three-dimensional topological crystalline insulating compounds of space
group 139(I/4mmm). After conducting a full volume optimization process by
allowing to rearrange of atomic positions and lattice parameters, the first
principles calculation with a generalized gradient approximation is utilized to
identify multiple Dirac-type crossings around X and P symmetric points near
Fermi energy. Importantly the band inversion at point P is recognized. Further,
We investigate the compound for topological crystalline insulating behavior and
identify metallic surface states on high-symmetry crystal surfaces with the
projection to the plane (001). Additionally, we performed formation energy,
elastic properties, and phonon modes calculations to verify the structural,
mechanical, and dynamical stability of the compounds. Therefore, we suggest the
compounds for further investigation and experimental realization.",2302.06056v1
2023-02-27,Novel supercell compounds of layered Bi-Rh-O with $p$-type metallic conduction materialized as a thin film form,"Layered oxides have been intensively studied due to their high degree of
freedom in designing various electromagnetic properties and functionalities.
While Bi-based layered supercell (LSC) compounds
[Bi$_n$O$_{n+\delta}$]-[$M$O$_2$] ($M$ = Mn, Mn/Al, Mn/Fe, or Mn/Ni; $n=2, 3$)
are a group of prospective candidates, all of the reported compounds are
insulators. Here, we report on the synthesis of two novel metallic LSC
compounds [Bi$_{n}$O$_{n+\delta}$]-[RhO$_2$] ($n=2, 3$) by pulsed laser
deposition and subsequent annealing. With tuning the thickness of the
sublattice from Bi$_2$O$_{2+\delta}$ to Bi$_3$O$_{3+\delta}$, a
dimensionality-dependent electrical transport is revealed from a conventional
metallic transport in $n=2$ to a localized transport in $n=3$. Our successful
growth will be an important step for further exploring novel layered oxide
compounds.",2302.13538v1
2023-03-02,"DFT based investigation of bulk mechanical, thermophysical and optoelectronic properties of PbTaSe2 topological semimetal","PbTaSe2 is a non-centrosymmetric topological semimetal. In this work we have
explored the structural, elastic, mechanical, bonding, electronic, acoustic,
thermal, and optical properties of PbTaSe2. The electronic bond structure
calculations confirm semi-metallic character. Fermi surface topology shows both
electron and hole sheets. The single crystal elastic constants reveal that
PbTaSe2 is elastically stable. The compound is soft, brittle, and highly
machinable at the same time. It also possesses very high level of dry
lubricity. Various anisotropy indicators suggest that PbTaSe2 is elastically
anisotropic with layered character. The phonon dynamics has been investigated.
Phonon dispersion plot shows that the compound is dynamically stable with a
clear frequency gap between the acoustic and optical branches. The Debye
temperature, phonon thermal conductivity, and melting temperature of PbTaSe2 is
low. The compound has medium Gr\""uneisen parameter. The bonding character is
mainly dominated by ionic bonding with some metallic contribution. The optical
parameters have been studied in detail. The optical spectra reveal metallic
features. The compound reflects visible light very efficiently (reflectance
above 60%). It is also an efficient absorber of the ultraviolet light. The
compound exhibits significant optical anisotropy with respect to the
polarization directions of the incident electric field.",2303.01319v1
2023-11-19,Identifying regions of concomitant compound precipitation and wind speed extremes over Europe,"The task of simplifying the complex spatio-temporal variables associated with
climate modeling is of utmost importance and comes with significant challenges.
In this research, our primary objective is to tailor clustering techniques to
handle compound extreme events within gridded climate data across Europe.
Specifically, we intend to identify subregions that display asymptotic
independence concerning compound precipitation and wind speed extremes. To
achieve this, we utilise daily precipitation sums and daily maximum wind speed
data derived from the ERA5 reanalysis dataset spanning from 1979 to 2022. Our
approach hinges on a tuning parameter and the application of a divergence
measure to spotlight disparities in extremal dependence structures without
relying on specific parametric assumptions. We propose a data-driven approach
to determine the tuning parameter. This enables us to generate clusters that
are spatially concentrated, which can provide more insightful information about
the regional distribution of compound precipitation and wind speed extremes. In
the process, we aim to elucidate the respective roles of extreme precipitation
and wind speed in the resulting clusters. The proposed method is able to
extract valuable information about extreme compound events while also
significantly reducing the size of the dataset within reasonable computational
timeframes.",2311.11292v1
2024-01-05,"Single Crystal Growth and Transport Properties of van der Waals Materials $AB$Te$_\mathbf{4}$ ($A/B$ = Ti, Zr, Hf)","Monolayers of $AB$Te$_4$ ($A$/$B$ = Ti, Zr, Hf) were theoretically predicted
to be two-dimensional topological insulators, but little has been known about
the physical properties of these compounds. Here, we report on the single
crystal growth, bulk transport properties, and band structure calculations of
these compounds. The magnetotransport properties indicate that all three
compounds are multi-carrier systems. The experimental results of ZrTiTe$_4$ and
HfTiTe$_4$ can be well fitted by the multi-carrier formula assuming two types
of carriers, while three carrier components were necessary for HfZrTe$_4$.
Interestingly, one of the carrier mobilities of HfZrTe$_4$ exceeded 1000
cm$^2$V$^{-1}$s$^{-1}$, which was nearly one order in magnitude larger than the
carrier mobilities of ZrTiTe$_4$ and HfTiTe$_4$. Our band structure
calculations showed that all three compounds are semimetals consistent with the
magnetotransport properties. The band structure around the $\Gamma$-point of
HfZrTe$_4$ exhibits features that are distinct from the other two compounds,
which is likely the reason of the different carrier properties.",2401.02704v1
2024-01-30,Prediction of ambient pressure superconductivity in cubic ternary hydrides with MH$_6$ octahedra,"Exploring high-temperature superconducting (high-$T_c$) material at ambient
pressure holds immense significance for physics, chemistry, and materials
science. In this study, we perform a high-throughput screening of strong
electron-phonon interactions in X$_2$MH$_6$ compounds (X = Li, Na, Mg, Al, K,
Ca, Ga, Rb, Sr, and In; M are $3d$, $4d$, and $5d$ transition metals). These
compounds have a cubic structure featuring an MH$_6$ octahedron motif. Our
screening calculations suggest that 26 compounds exhibit dynamic stability and
strong electron-phonon coupling. Among these 26 compounds, Mg$_2$RhH$_6$,
Mg$_2$IrH$_6$, Al$_2$MnH$_6$, and Li$_2$CuH$_6$ show promising energetic
stability and $T_c$ of more than 50 K at ambient pressure. This study
underscores promising high-$T_c$ compounds at ambient pressure with distinctive
MH$_6$ motifs.",2401.17024v2
2024-03-04,Tuning charge density wave of kagome metal ScV6Sn6,"Compounds with a kagome lattice exhibit intriguing properties and the charge
density wave (CDW) adds an additional layer of interest to research on them. In
this study, we investigate the temperature and magnetic field dependent
electrical properties under a chemical substitution and hydrostatic pressure of
ScV6Sn6, a non-magnetic charge density wave (CDW) compound. Substituting 5 % Cr
at the V site or applying 1.5 GPa of pressure shifts the CDW to 50 K from 92 K.
This shift is attributed to the movement of the imaginary phonon band, as
revealed by the phonon dispersion relation. The longitudinal and Hall
resistivities respond differently under these stimuli. The magnetoresistance
(MR) maintains its quasilinear behavior under pressure, but it becomes
quadratic after Cr substitution. The anomalous Hall-like behavior of the parent
compound persists up to the respective CDW transition under pressure, after
which it sharply declines. In contrast, the longitudinal and Hall resistivities
of Cr substituted compounds follow a two-band model and originates from the
multi carrier effect. These results clearly highlight the role of phonon
contributions in the CDW transition and call for further investigation into the
origin of the anomalous Hall-like behavior in the parent compound.",2403.02463v1
2024-03-08,Design of Magnetic Polar Double-Double Perovskite Oxides through Cation Ordering,"Commencing from the centrosymmetric MnRMnSbO$_6$ compound, we explore the
realm of magnetic polar double-double perovskite oxides characterized by
significant ferroelectric polarization. Employing symmetry operations,
first-principles methodologies, and Monte Carlo simulations, our investigation
delves into the structural, magnetic, ferroelectric, and electronic attributes
of the polar LaFeMnNiO$_6$ and LaTiMnNiO$_6$ compounds. The structural analysis
uncovers that the paraelectric-ferroelectric phase transition is intricately
linked to the Fe/Ti-displacement of square planar Fe/TiO$_4$. Notably, the
magnetic LaFeMnNiO$_6$ and LaTiMnNiO$_6$ compounds demonstrate robust
ferroelectric polarizations, measuring 20.0 $\mu$C/cm$^2$ and 21.8
$\mu$C/cm$^2$, respectively, accompanied by minimalist forbidden energy gaps of
1.40 eV and 1.18 eV using the GGA+U method. Furthermore, we pinpoint elevated
magnetic transition temperatures for these compounds. Additionally, our study
scrutinizes the energies associated with diverse spin configurations and
identifies potential minimum decomposition pathways into stable oxides. This
comprehensive analysis ensures the meticulous formation of the LaFeMnNiO$_6$
and LaTiMnNiO$_6$ compounds.",2403.05498v1
2024-03-18,Zero-shot Compound Expression Recognition with Visual Language Model at the 6th ABAW Challenge,"Conventional approaches to facial expression recognition primarily focus on
the classification of six basic facial expressions. Nevertheless, real-world
situations present a wider range of complex compound expressions that consist
of combinations of these basics ones due to limited availability of
comprehensive training datasets. The 6th Workshop and Competition on Affective
Behavior Analysis in-the-wild (ABAW) offered unlabeled datasets containing
compound expressions. In this study, we propose a zero-shot approach for
recognizing compound expressions by leveraging a pretrained visual language
model integrated with some traditional CNN networks.",2403.11450v1
2024-03-19,Audio-Visual Compound Expression Recognition Method based on Late Modality Fusion and Rule-based Decision,"This paper presents the results of the SUN team for the Compound Expressions
Recognition Challenge of the 6th ABAW Competition. We propose a novel
audio-visual method for compound expression recognition. Our method relies on
emotion recognition models that fuse modalities at the emotion probability
level, while decisions regarding the prediction of compound expressions are
based on predefined rules. Notably, our method does not use any training data
specific to the target task. Thus, the problem is a zero-shot classification
task. The method is evaluated in multi-corpus training and cross-corpus
validation setups. Using our proposed method is achieved an F1-score value
equals to 22.01% on the C-EXPR-DB test subset. Our findings from the challenge
demonstrate that the proposed method can potentially form a basis for
developing intelligent tools for annotating audio-visual data in the context of
human's basic and compound emotions.",2403.12687v2
1995-07-24,"Prediction of an undimerized, insulating, antiferromagnetic ground-state in halogen-bridged linear-chain Ni compounds","A parameter-free, mean-field, multi-orbital Hubbard model with nonspherical
Coulomb and exchange interactions, implemented around all-electron
local-density approximation (LDA) calculations, correctly predicts the band-gap
energy, the absence of dimerization, and the antiferromagnetic ground state of
halogen-bridged linear-chain Ni compounds. This approach also reproduces the
insulating ground state and dimerization in PtX linear-chain compounds in
agreement with experiment and previous calculations. Three ""ps"" figures are
included at the end of the RevTex file and compressed using uufiles.",9507104v1
1996-05-20,Ab Initio Calculation of Crystalline Electric Fields and Kondo Temperatures in Ce-Compounds,"We have calculated the band-$f$ hybridizations for Ce$_x$La$_{1-x}$M$_3$
compounds ($x=1$ and $x\rightarrow 0$; M=Pb, In, Sn, Pd) within the local
density approximation and fed this into a non-crossing approximation for the
Anderson impurity model applied to both dilute and concentrated limits. Our
calculations produce crystalline electric field splittings and Kondo
temperatures with trends in good agreement with experiment and demonstrate the
need for detailed electronic structure information on hybridization to describe
the diverse behaviors of these Ce compounds.",9605126v1
1997-10-29,Magnetic Resonance in the Spin-Peierls compound $α'-NaV_2O_5$,"We present results from magnetic resonance measurements for 75-350 GHz in
$\alpha$'-NaV$_{2}$O$_{5}$. The temperature dependence of the integrated
intensity indicates that we observe transitions in the excited state. A
quantitative description gives resonances in the triplet state at high symmetry
points of the excitation spectrum of this Spin-Peierls compound. This energy
has the same temperature dependence as the Spin-Peierls gap. Similarities and
differences with the other inorganic compound CuGeO$_{3}$ are discussed.",9710318v1
1997-11-11,Optical spectroscopy on the spin-Peierls compound CuGeO$_3$,"An overview is given of Raman and infrared spectroscopic studies of the
inorganic spin-Peierls compound CuGeO$_3$, with an emphasis on the magnetic
fluctuations in the uniform, dimerized, and high field phases of this quasi one
dimensional magneto-elastic compound.",9711091v1
1998-12-11,Crystal stability and optical properties of organic chain compounds,"The solution to the long standing problem of the cohesion of organic chain
compounds is proposed. We consider the tight-binding dielectric matrix with two
electronic bands per chain, determine the corresponding hybridized collective
modes, and show that three among them are considerably softened due to strong
dipole-dipole and monopole-dipole interactions. By this we explain the unusual
low frequency optical activity of TTF-TCNQ, including the observed 10meV
anomaly. The softening of the modes also explains the cohesion of the
mixed-stack lattice, the fractional charge transfer almost independent of the
material, and the formation of the charged sheets in some compounds.",9812194v1
2000-05-26,Theory of the solid-state physics on the turn: II. Importance of the spin-orbit coupling for 3d-ion compounds: the case of NiO,"The orbital and spin moment of the Ni2+ ion in NiO has been calculated at 0 K
to be 0.54mB and 1.99 mB respectively. Such large orbital moment, more than 20%
of the total moment of 2.53 mB, proves the need for the ''unquenching'' of the
orbital moment in compounds containing 3d ions. It turns out that the
spin-orbit coupling is indispensable for description of magnetic and electronic
properties of 3d-ion compounds. These two findings, largely ignored at the
nowadays in-fashion solid-state thories, call for an advanced solid-state
physics theory.",0005471v1
2001-02-02,Superconductivity in Ru(1-x)Sr2GdCu(2+x)O(8-y) Compounds,"We report on the properties of new ruthenocuprates Ru(1-x)Sr2GdCu(2+x)O(8-y)
(x=0, 0.1, 0.2, 0.3, 0.4, 0.75) that extend the superconductivity found
previously in RuSr2GdCu2O8 (Tc=45 K) to the solid solution with varied Ru/Cu
ratios. The compounds have been synthesized in high-pressure oxygen atmosphere.
The maximum temperature of the superconducting transition is 72 K for the x=0.3
and 0.4 compositions. The reported behavior of magnetization at low
temperatures can be qualitatively explained assuming a quasi-two-dimensional
character of the superconducting regions in compounds studied.",0102023v2
2001-07-23,Monte Carlo Methods for Small Molecule High-Throughput Experimentation,"By analogy with Monte Carlo algorithms, we propose new strategies for design
and redesign of small molecule libraries in high-throughput experimentation, or
combinatorial chemistry. Several Monte Carlo methods are examined, including
Metropolis, three types of biased schemes, and composite moves that include
swapping or parallel tempering. Among them, the biased Monte Carlo schemes
exhibit particularly high efficiency in locating optimal compounds. The Monte
Carlo strategies are compared to a genetic algorithm approach. Although the
best compounds identified by the genetic algorithm are comparable to those from
the better Monte Carlo schemes, the diversity of favorable compounds identified
is reduced by roughly 60%.",0107484v1
2002-03-29,"Superparamagnetic-like ac susceptibility behavior in a ""partially disordered antiferromagnetic"" compound, Ca$_3$CoRhO$_6$","We report the results of dc and ac magnetization measurements as a function
of temperature (1.8 - 300 K) for the spin chain compound, Ca$_3$CoRhO$_6$,
which has been recently reported to exhibit a partially disordered
antiferromagnetic (PDAF) structure in the range 30 - 90 K and spin-glass
freezing below 30 K. We observe an unexpectedly large frequency dependence of
ac susceptibility in the T range 30 - 90 K, typical of superparamagnets. In
addition, we find that there is no difference in the isothermal remanent
magnetization behavior for the two regimes below 90 K. These findings call for
more investigations to understand the magnetism of this compound.",0203605v1
2002-08-15,Superconductivity in Ba_2Sn_3Sb_6 and SrSn_3Sb_4,"Resistivity and ac magnetic susceptibility measurements on Ba2Sn3Sb6 and
SrSn3Sb4 indicate that these Zintl compounds display a transition to a
superconducting phase at Tc = 3.9 K. The Meissner effect was observed for
Ba2Sn3Sb6 under an applied field of 25 Oe. The signatures for
superconductivity, such as high and low velocity conduction electrons and lone
pairs, are present for both of these compounds.",0208313v1
2002-11-14,Breakdown of the Fermi liquid theory in heavy fermion compounds,"We review the anomalous properties of heavy fermion compounds like
CeCu$_{6-x}$Au$_x$ or CeMIn$_5$ close to a zero temperature phase transition
called a quantum critical point. Anomalous behavior of the resistivity,
specific heat and magnetic properties observed in various compounds suggests a
fundamental breakdown of the Fermi liquid theory. Recent measurements on
YbRh$_2$Si$_2$, field-tuned through the quantum critical point, provide
interesting insights on the evolution of the Fermi liquid close to criticality.
We discuss the possibility of a kind of spin-charge separation at the quantum
critical point and make some remarks about its possible link with the
underscreened Kondo model.",0211284v1
2003-12-15,Influence of the incommensurability in $Sr_{14-x}Ca_xCu_{24}O_{41}$ family compounds,"The present paper studies the influence of the structural modulation on the
low energy physics of the $Sr_{14-x}Ca_xCu_{24}O_{41}$ oxides, using ab-initio
determination of the on-site and nearest neighbor effective parameters. The
structural modulations appears to be the key degree of freedom, responsible for
the low energy properties, such as the electron localization, the formation of
dimers in the $x=0$ compound or the anti-ferromagnetic order in the $x=13.6$
compound.",0312369v2
2004-01-20,The spin excitation spectrum in striped bilayer compounds,"The spin dynamics of bilayer cuprate compounds are studied in a basic model.
The magnetic spectral properties are calculated in linear spin-wave theory for
several stripe configurations which differ by the relative location of the
stripes in the layers. We focus on the bilayer splitting of the magnon bands
near the incommensurate low energy peaks as well as near the $\pi$ resonance,
distinguishing between the odd and even channel. We find that a x-shaped
dispersion near the $\pi$ resonance is generic for stripes. By comparison of
our results to neutron scattering data for $\mathrm{YBa_2Cu_3O_{6+x}}$ we
conclude that the stripe model is consistent with characteristic features of
bilayer high-$T_c$ compounds.",0401354v1
2004-01-23,Optical properties and Raman scattering of vanadium ladder compounds,"We investigate electronic and optical properties of the V-based ladder
compounds NaV2O5, the iso-structural CaV2O5, as well as MgV2O5, which differs
from NaV2O5 and CaV2O5 in the c axis stacking. We calculate ab initio the A_g
phonon modes in these compounds as a basis for the investigation of the
electron-phonon and spin-phonon coupling. The phonon modes together with the
dielectric tensors as a function of the corresponding ion displacements are the
starting point for the calculation of the A_g Raman scattering.",0401458v1
2004-06-24,Single crystals of the anisotropic Kagome staircase compounds Ni3V2O8 and Co3V2O8,"Compounds with a Kagome type lattice are known to exhibit magnetic
frustration. Large single crystals of two compounds Ni3V2O8 and Co3V2O8, which
are variants of a Kagome net lattice, have been grown successfully by the
floating zone technique using an optical image furnace. The single crystals are
of high quality and exhibit intriguing magnetic properties.",0406601v1
2004-11-16,An Interesting Magnetoresistive System: Sr2FeMoO6,"Ordered double perovskite oxides of the general formula, A2BB'O6, have been
known for several decades to have interesting electronic and magnetic
properties. However, a recent report of a spectacular negative
magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6,
has brought this class of compounds under intense scrutiny. In this small
review, we present few theoretical and experimental results, describing mainly
the effects of Fe/Mo antisite defects on the properties of this compound and
also briefly discuss few other puzzling facts about this fascinating compound",0411400v1
2005-02-03,Charge order in the incommensurate compounds $Sr\_{14-x}Ca\_xCu\_{24}O\_{41}$,"The present paper studies, using ab-initio calculations, the influence of the
incommensurate structural modulations on the low energy physics of the
$Sr\_{14-x}Ca\_xCu\_{24}O\_{41}$ oxides. On-site, nearest-neighbor and
next-nearest-neighbor effective parameters were computed within a $t-J+V$ model
based on the copper magnetic orbitals. The structural modulations appear to be
the key degree of freedom, responsible for the low energy properties such as
the electron localization, the formation of dimers in the $x=0$ compound or the
anti-ferromagnetic order in the $x=13.6$ compound.",0502105v1
2005-06-10,"Symmetry analysis of k = (1/3,1/3,0) three-sublattice ordering in A14B51 compounds","Bulk magnetic, X-ray and neutron diffraction measurements were performed on
polycrystalline Tb14Ag51 in the temperature range from 1.5 K to room
temperature. Its chemical Gd14Ag51 type structure corresponds to space group
P6/m. Combined with group theoretical symmetry analysis, we show that the
magnetic structure of this intermetallic compound is of a new k = (1/3,1/3,0)
type with three magnetic Tb sublattices ordering simultaneously below TN =
27.5(5) K according to the combined irreducible representations tau4 and tau6.
Here we present a general analysis of possible magnetic A ordering for k =
(1/3,1/3,0) in A14B51 compounds.",0506249v1
2005-07-17,Electronic structure and the Fermi surface of ThRhIn$_5$ in comparison with uranium and transuranium compounds,"By using a relativistic linear augmented-plane-wave method, we clarify energy
band structure and the Fermi surfaces of recently synthesized thorium compound
ThRhIn$_5$. We find several cylindrical Fermi surface sheets, which are similar
to those of CeTIn$_5$ (T=Ir and Co), PuTGa$_5$ (T=Co and Rh), and AmCoGa$_5$.
We discuss such similarity among the compounds including rare-earth or actinide
ions with different $f$ electron numbers.",0507401v1
2005-11-30,Theoretical analysis of the double spin chain compound KCuCl_3,"We investigate thermal and magnetic properties of the double spin chain
compound KCuCl_3 via an exactly solved ladder model with strong rung
interaction. Results from the analysis of the thermodynamic Bethe Ansatz
equations suggests the critical field values H_{c1}=22.74T and H_{c2}=51.34T,
in good agreement with the experimental observations. The temperature dependent
magnetic properties are directly evaluated from the exact free energy. Good
overall agreement is seen between the theoretical and experimental
susceptibility curves. Our results suggest that this compound lies in the
strong dimerized phase with an energy gap $\Delta \approx 35$K at zero
temperature.",0511725v1
2006-01-25,"Single-ion Kondo behavior of a novel Kondo lattice, CeNi9Si4","The compound, CeNi9Si4 has been recently reported to be an unusual Kondo
lattice with a large Ce-Ce separation, with a breakdown of Kadowaki-Woods
relationship governing low temperature electrical resistivity and
heat-capacity. Here we report the results of magnetic susceptibility,
heat-capacity and electrical resistivity of the solid solution,
Ce(1-x)La(x)Ni9Si4 to understand the Kondo behavior of this compound. The
results establish that the observed properties of Ce in this compound are
single-ionic in character.",0601577v1
2006-06-20,Orthorhombic to tetragonal phase transition and superconductivity in the Ba2Cu3O4Cl2 compound,"In this work we have investigated the orthorhombic to tetragonal phase
transition in the Ba2Cu3O4Cl2 compound. This transition was observed by X-ray
powder diffractometry carried out in samples heat treated between 700 and 750OC
and also in samples with Ba2ZnCu2O4Cl2 composition. Results of X-ray
diffractograms simulation confirm the phase transition. dc-Magnetization
measurements performed in SQUID showed the existence of diamagnetism signal.
The results suggest the existence of localized superconductivity and can
explain the different magnetic properties reported in literature for the
Ba2Cu3O4Cl2 compound.",0606524v1
2006-07-05,"Exchange integrals and magnetization distribution in BaCu2X2O7 (X=Ge,Si)","Estimating the intrachain and interchain exchange constants in BaCu2X2O7
(X=Ge,Si) by means of density-functional calculations within the local
spin-density approximation (LSDA) we find the Ge compound to be a more ideal
realization of a one-dimensional spin chain with Dzyaloshinskii-Moriya
interaction than its Si counterpart. Both compounds have a comparable magnitude
of interchain couplings in the range of 5-10 K, but the nearest neighbor
intrachain exchange of the Ge compound is nearly twice as large as for the Si
one. Using the LSDA+U method we predict the detailed magnetization density
distribution and especially remarkable magnetic moments at the oxygen sites.",0607108v1
2006-08-26,Superconductivity in Mg10Ir19B16,"Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system,
is found to be superconducting at temperatures near 5 K. The fact that the
compound exhibits a range of superconducting temperatures between 4 and 5 K
suggests that a range of stoichiometries is allowed, though no structural
evidence for this is observed. The compound has a large, noncentrosymmetric,
body centered cubic unit cell with a = 10.568 Angstrom, displaying a structure
type for which no previous superconductors have been reported.",0608576v1
2006-08-31,On hydrogen bond correlations at high pressures,"In situ high pressure neutron diffraction measured lengths of O H and H O
pairs in hydrogen bonds in substances are shown to follow the correlation
between them established from 0.1 MPa data on different chemical compounds. In
particular, the conclusion by Nelmes et al that their high pressure data on ice
VIII differ from it is not supported. For compounds in which the O H stretching
frequencies red shift under pressure, it is shown that wherever structural data
is available, they follow the stretching frequency versus H O (or O O) distance
correlation. For compounds displaying blue shifts with pressure an analogy
appears to exist with improper hydrogen bonds.",0608697v1
2006-10-04,Magnetic phase diagrams of the Kagome staircase compounds Co3V2O8 and Ni3V2O8,"An extensive low temperature magnetisation study of high quality single
crystals of the Kagome staircase compounds Ni3V2O8 and Co3V2O8 has been
performed, and the H-T phase diagrams have been determined from these
measurements. The magnetisation and susceptibility curves for Co3V2O8 are
analysed in terms of their compatibility with the different ferromagnetic and
antiferromagnetic structures proposed for this compound. For Ni3V2O8, the phase
diagram is extended to magnetic fields higher than previously reported; for a
field applied along the a-axis, the low temperature incommensurate phase is
found to close at around 90 kOe.",0610123v1
1999-08-07,Analysis on Poisson and Gamma spaces,"We study the spaces of Poisson, compound Poisson and Gamma noises as special
cases of a general approach to non-Gaussian white noise calculus, see
\cite{KSS96}. We use a known unitary isomorphism between Poisson and compound
Poisson spaces in order to transport analytic structures from Poisson space to
compound Poisson space. Finally we study a Fock type structure of chaos
decomposition on Gamma space.",9908033v1
1994-12-15,"Effects of T- and P-odd weak nucleon interaction in nuclei: renormalizations due to residual strong interaction, matrix elements between compound states and their correlations with P-violating matrix elements","Manifestations of P-,T-odd weak interaction between nucleons in nucleus are
considered. Renormalization of this interaction due to residual strong
interaction is studied. Mean squared matrix elements of P-,T-odd weak
interaction between compound states are calculated. Correlators between
P-,T-odd and P-odd, T-even weak interaction matrix elements between compound
states are considered and estimates for these quantities are obtained.",9412022v2
1999-01-08,Saturation of product's exoticity in compound nuclear reactions and its role in the production of new n-deficient nuclei with radioactive projectiles,"Representation in terms of a new parameter, exoticity, a measure of
n-deficiency or p-richness, clearly brings out the saturation tendency of the
product's maximum exoticity in a compound nuclear reaction as the compound
nucleus is made more and more exotic using radioactive projectile (RIBs). The
effect of this saturation on the production of new proton-rich species with
RIBs over a wide Z-range has been discussed.",9901015v1
1999-07-06,Probing the width of compound states with rotational gamma rays,"The intrinsic width of (multiparticle-multihole) compound states is an
elusive quantity, of difficult direct access, as it is masked by damping
mechanisms which control the collective response of nuclei. Through microscopic
cranked shell model calculations, it is found that the strength function
associated with two-dimensional gamma-coincidence spectra arising from
rotational transitions between states lying at energies >1 MeV above the yrast
line, exhibits a two-component structure controlled by the rotational (wide
component) and compound (narrow component) damping width. This last component
is found to be directly related to the width of the multiparticle-multihole
autocorrelation function.",9907016v1
2002-12-11,Rotational Damping and Compound Formation in Warm Rotating Nuclei,"The rotational damping width \Gamma_{rot} and the compound damping width
\Gamma_{comp} are two fundamental quantities that characterize rapidly rotating
compound nuclei having finite thermal excitation energy. A two-component
structure in the strength function of consecutive E2 transitions reflects the
two widths, and it causes characteristic features in the double and triple
gamma-ray spectra. We discuss a new method to extract experimentally values of
\Gamma_{rot} and \Gamma_{comp}. The first preliminary result of this method is
presented.",0212050v1
2006-04-27,An extension of the Hirsch Index: Indexing scientific topics and compounds,"An interesting twist of the Hirsch index is given, in terms of an index for
topics and compounds. By comparing both the hb index and m for a number of
compounds and topics, it can be used to differentiate between a new so-called
hot topic with older topics. This quick method is shown to help new comers to
identify how much interest and work has already been achieved in their chosen
area of research.",0604216v2
2007-03-06,Compounding Fields and Their Quantum Equations in the Sedenion Space,"The sedenion compounding fields and their quantum interplays can be presented
by analogy with the octonionic electromagnetic, gravitational, strong and weak
interactions. In sedenion fields which are associated with electromagnetic,
gravitational, strong and weak interactions, the study deduces some conclusions
of field source particles and intermediate particles which are consistent with
current electro-weak theory. In the sedenion fields which are associated with
the hyper-strong and strong-weak fields, the paper draws some predicts and
conclusions of the field source particles and intermediate particles. The
researches results show that there may exist some new field source particles in
the sedenion compounding fields.",0703055v4
2000-08-11,Structural Characterization of Compoundness,"We recover the rays in the tensor product of Hilbert spaces within a larger
class of so called `states of compoundness', structured as a complete lattice
with the `state of separation' as its top element. At the base of the
construction lies the assumption that the cause of actuality of a property of
one of the (as individual considered) entities in the compound system can be
actuality of a property of the other one.",0008054v2
2007-08-29,"Tuning the Competing magnetic interactions in RTiGe (R = Tb, Er) Compounds and tailoring the Magnetocaloric effect","The tetragonal layered compounds TbTiGe and ErTiGe order
antiferromagnetically at 276 K and 39 K, respectively. Partial substitution of
Mo for Ti in these two compounds modifies the magnetic interactions giving rise
to a ferromagnetic ground state which results in an enhanced magnetocaloric
effect. The magnetic entropy change in ErTi0.85Mo0.15Ge for a magnetic field
change of 5 T is ~10.5 J/kg/K against ~0.8 J/kg/K for ErTiGe in the vicinity of
the magnetic transition. Thus, magnetocaloric properties of such layered
materials may be tunable by suitable chemical substitutions.",0708.3887v1
2007-09-26,Compound-specific isotope analysis,"The isotopic composition, for example, 14C/12C, 13C/12C, 2H/1H, 15N/14N and
18O/16O, of the elements of matter is heterogeneous. It is ruled by physical,
chemical and biological mechanisms. Isotopes can be employed to follow the fate
of mineral and organic compounds during biogeochemical transformations. The
determination of the isotopic composition of organic substances occurring at
trace level in very complex mixtures such as sediments, soils and blood, has
been made possible during the last 20 years due to the rapid development of
molecular level isotopic techniques. After a brief glance at pioneering studies
revealing isotopic breakthroughs at the molecular and intramolecular levels,
this paper reviews selected applications of compound-specific isotope analysis
in various scientific fields.",0709.4164v1
2007-12-12,Magnetic phase transition and magnetocaloric effect in PrCo9Si4 and NdCo9Si4,"The compounds, PrCo9Si4 and NdCo9Si4, have been recently reported to exhibit
first-order ferromagnetic transitions near 24 K. We have subjected this
compound for further characterization by magnetization, heat-capacity and
electrical resistivity measurements at low temperatures in the presence of
magnetic fields, particularly to probe magnetocaloric effect and
magnetoresistance. The compounds are found to exhibit rather modest
magnetocaloric effect at low temperatures peaking at Curie temperature,
tracking the behavior of magnetoresistance. The magnetic transition does not
appear to be first order in its character.",0712.1989v1
2007-12-24,Cryptanalysis of an Image Encryption Scheme Based on a Compound Chaotic Sequence,"Recently, an image encryption scheme based on a compound chaotic sequence was
proposed. In this paper, the security of the scheme is studied and the
following problems are found: (1) a differential chosen-plaintext attack can
break the scheme with only three chosen plain-images; (2) there is a number of
weak keys and some equivalent keys for encryption; (3) the scheme is not
sensitive to the changes of plain-images; and (4) the compound chaotic sequence
does not work as a good random number resource.",0712.3964v2
2008-04-07,The compound Poisson distribution and return times in dynamical systems,"Previously it has been shown that some classes of mixing dynamical systems
have limiting return times distributions that are almost everywhere Poissonian.
Here we study the behaviour of return times at periodic points and show that
the limiting distribution is a compound Poissonian distribution. We also derive
error terms for the convergence to the limiting distribution. We also prove a
very general theorem that can be used to establish compound Poisson
distributions in many other settings.",0804.1032v1
2008-06-12,Magnetic behavior of nanocrystalline LaMn2Ge2,"The compound, LaMn2Ge2, crystallizing in ThCr2Si2-type tetragonal crystal
structure, has been known to undergo ferromagnetic order below (T_C=) 326 K. In
this article, we report the magnetic behavior of nanocrystalline form of this
compound, obtained by high-energy ball-milling. T_C of this compound is reduced
maginally for the nanoform, whereas there is a significant reduction of the
magnitude of the saturation magnetic moment with increasing milling time. The
coercive field however increases with decreasing particle size. Thus, this work
provides a route to tune these parameters by reducing the particle size in this
ternary family.",0806.2030v1
2008-06-18,Compound Node-Kayles on Paths,"In his celebrated book ""On Number and Games"" (Academic Press, New-York,
1976), J.H. Conway introduced twelve versions of compound games. We analyze
these twelve versions for the Node-Kayles game on paths. For usual disjunctive
compound, Node-Kayles has been solved for a long time under normal play, while
it is still unsolved under mis\`ere play. We thus focus on the ten remaining
versions, leaving only one of them unsolved.",0806.3033v2
2008-07-25,Magnetism and Electronic Correlations in Quasi-One-Dimensional Compounds,"In this contribution on the celebration of the 80th birthday anniversary of
Prof. Ricardo Ferreira, we present a brief survey on the magnetism of
quasi-one-dimensional compounds. This has been a research area of intense
activity particularly since the first experimental announcements of magnetism
in organic and organometallic polymers in the mid 80s. We review experimental
and theoretical achievements on the field, featuring chain systems of
correlated electrons in a special AB2 unit cell structure present in inorganic
and organic compounds.",0807.4156v1
2008-07-31,Superconductivity in nickel-based compound GdONiBi and hole doped Gd0.9Sr0.1ONiBi,"We successfully synthesized the nickel-based compound GdONiBi with
superconducting transition temperature about 4.5 K. By partially substituting
the element Gd with Sr to introduce holes into the material, we got new
superconductor Gd0.9Sr0.1ONiBi with critical temperature about 4.7 K. The
normal state resistivity in nickel-based samples shows a metallic behavior. The
magnetoresistance measurements show a different behavior compared to those in
iron-based compounds which indicates that the mechanism in the two kinds of
superconductors maybe different.",0807.5045v1
2008-11-10,Alternative descriptions and bipartite compound quantum systems,"We analyze some features of alternative Hermitian and quasi-Hermitian quantum
descriptions of simple and bipartite compound systems. We show that alternative
descriptions of two interacting subsystems are possible if and only if the
metric operator of the compound system can be obtained as tensor product of
positive operators on component spaces. Some examples also show that such
property could be strictly connected with symmetry properties of the
non-Hermitian Hamiltonian.",0811.1415v1
2008-12-01,High - Temperature Superconductivity in Iron Based Layered Compounds,"We present a review of basic experimental facts on the new class of high -
temperature superconductors - iron based layered compounds like REOFeAs
(RE=La,Ce,Nd,Pr,Sm...), AFe_2As_2 (A=Ba,Sr...), AFeAs (A=Li,...) and FeSe(Te).
We discuss electronic structure, including the role of correlations, spectrum
and role of collective excitations (phonons, spin waves), as well as the main
models, describing possible types of magnetic ordering and Cooper pairing in
these compounds.",0812.0302v1
2009-05-15,Superconducting phases of f-electron compounds,"Intermetallic compounds containing f-electron elements display a wealth of
superconducting phases, that are prime candidates for unconventional pairing
with complex order parameter symmetries. For instance, superconductivity has
been found at the border of magnetic order as well as deep within ferro- and
antiferromagnetically ordered states, suggesting that magnetism may promote
rather than destroy superconductivity. Superconductivity near valence
transitions, or in the vicinity of magneto-polar order are candidates for new
superconductive pairing interactions such as fluctuations of the conduction
electron density or the crystal electric field, respectively. The experimental
status of the study of the superconducting phases of f-electron compounds is
reviewed.",0905.2625v1
2009-05-23,On spectrum and approximations of one class of sign-symmetric matrices,"A new class of sign-symmetric matrices is introduced in this paper. Such
matrices are named J--sign-symmetric. The spectrum of a J--sign-symmetric
irreducible matrix is studied under assumptions that its second compound matrix
is also J--sign-symmetric and irreducible. The conditions, when such matrices
have complex eigenvalues on the largest spectral circle, are given. The
existence of two positive simple eigenvalues $\lambda_1 > \lambda_2 > 0$ of a
J--sign-symmetric irreducible matrix A is proved under some additional
conditions. The question, when the approximation of a J--sign-symmetric matrix
with a J--sign-symmetric second compound matrix by strictly J--sign-symmetric
matrices with strictly J--sign-symmetric compound matrices is possible, is also
studied in this paper.",0905.3799v1
2009-11-26,Bose-Einstein condensation of semi-hard bosons in S=1 dimerized organic compound F2PNNNO,"An analysis of the energy spectrum and the magnetization curve of
two-dimensional organic antiferromagnet F2PNNNO with a spin-one dimerized
structure shows that a behavior of the compound in an external magnetic field
can be explained within a lattice boson model with an extended Pauli's
exclusion principle, i.e. no more than two bosons per a dimer. The unusual
magnetization curve observed experimentally in the compound reflects a sequence
of phase transitions intrinsic for a lattice boson system with strong on-site
and inter-site repulsions due to a tuning of magnon density by the applied
magnetic field.",0911.5039v1
2010-04-30,Magnetic structure of the edge-sharing copper oxide chain compound NaCu2O2,"Single-crystal neutron diffraction has been used to determine the
incommensurate magnetic structure of NaCu2O2, a compound built up of chains of
edge-sharing CuO4 plaquettes. Magnetic structures compatible with the lattice
symmetry were identified by a group-theoretical analysis, and their magnetic
structure factors were compared to the experimentally observed Bragg
intensities. In conjunction with other experimental data, this analysis yields
an elliptical helix structure in which both the helicity and the polarization
plane alternate among copper-oxide chains. This magnetic ground state is
discussed in the context of the recently reported multiferroic properties of
other copper-oxide chain compounds.",1004.5526v1
2010-06-23,The Poisson Compound Decision Problem Revisited,"The compound decision problem for a vector of independent Poisson random
variables with possibly different means has half a century old solution.
However, it appears that the classical solution needs smoothing adjustment even
when there are many observations and relatively small means such that the
empirical distribution is close to its mean. We discuss three such adjustments.
We also present another approach that first transforms the problem into the
normal compound decision problem.",1006.4582v2
2010-06-30,Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2,"The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a
superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent
compound, TiSe2, which shows a charge density wave transition and no
superconductivity. The crystal structure, characterized by high resolution
electron microscopy and powder x-ray diffraction, consists of two layers of
1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements
suggest that the superconductivity is induced by charge transfer from the PbSe
layers to the TiSe2 layers.",1006.5946v1
2010-09-17,Applicability of Anderson and Hubbard model for Ce metal and cerium heavy fermion compounds,"The importance of taking into account inter-site $f-f$ hybridization in
electron structure calculations for Ce metal and cerium heavy fermion compounds
was studied. We demonstrate that for heavy-fermion systems such as cerium
compound CeCu$_2$Si$_2$ $f-f$ hybridization can be neglected and Anderson model
application is well justified. On another hand for cerium metal $f-f$
hybridization is strong enough to provide the contribution to hybridization
function comparable to hybridization between $4f$ and itinerant electrons. We
argue that in the case of Ce only the most general Hamiltonian combining
Hubbard and Anderson models should be used.",1009.3382v1
2010-10-12,"Phonon, Two-Magnon and Electronic Raman Scattering of Fe1+yTe1-xSex","We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4
(T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In
the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5
and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree
with the calculated results. Two-magnon excitation has been observed around
2300 cm-1 for both compounds. Temperature dependence between the electronic
Raman spectra below and above T_c has been observed and 2\Delta and
2\Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.",1010.2374v2
2010-11-19,Plasmonic-dielectric compound grating with high group-index and transmission,"We propose a compound system consisting of a dielectric grating and a
plasmonic resonance cavity embedded in the grating. Based on the interference
effect between the surface mode supported by the dielectric grating and the
plasmonic-induced cavity mode, this system could achieve slow light with group
index more than 200 and transmission more than 75%. Meanwhile, we examine the
effects of the period numbers of the compound system and photonic crystal
superlattice made up of alternate layers of the grating and air on the
properties of slow light.",1011.4358v1
2011-03-09,Antiferromagnetic Heisenberg S=5/2 spin chain compound SrMn$_2$V$_2$O$_8$,"Large single crystals of the new compound SrMn$_2$V$_2$O$_8$ have been grown
by the floating-zone method. This transition-metal based oxide is isostructural
to SrNi$_2$V$_2$O$_8$, described by the tetragonal space group $I4_1cd$.
Magnetic properties were investigated by means of susceptibility,
magnetization, and specific heat measurements. The title compound behaves like
a one-dimensional magnetic system above the ordering temperature ($T_N$ = 43
K). The magnetic ground state can be described as a classical long-range
ordered antiferromagnet with weak anisotropy.",1103.1830v1
2011-06-27,Charge redistribution at the antiferromagnetic phase transition in SrFeAsF compound,"The relationship between spin, electron, and crystal structure has been one
of the foremost issues in understanding the superconducting mechanism since the
discovery of iron-based high temperature superconductors. Here, we report
M\""ossbauer and first-principles calculations studies of the parent compound
SrFeAsF with the largest temperature gap ($\sim$50\,K) between the structural
and antiferromagnetic (AFM) transitions. Our results reveal that the structural
transition has little effect on the electronic structure of the compound
SrFeAsF while the development of the AFM order induces a redistribution of the
charges near the Fermi level.",1106.5370v2
2011-07-11,Exchange bias effect in alloys and compounds,"The phenomenology of exchange bias effects observed in structurally
single-phase alloys and compounds but composed of a variety of coexisting
magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic,
spin-glass, cluster-glass and disordered magnetic states are reviewed. The
investigations on exchange bias effects are discussed in diverse types of
alloys and compounds where qualitative and quantitative aspects of magnetism
are focused based on macroscopic experimental tools such as magnetization and
magnetoresistance measurements. Here, we focus on improvement of fundamental
issues of the exchange bias effects rather than on their technological
importance.",1107.1978v1
2012-04-17,The Debye temperature of sigma-phase Fe-Mo compounds as determined with Mössbauer spectroscopy,"The Debye temperature, T_D, of sigma-phase Fe_(100-x)Mo_x compounds with 47 <
x < 56.7 was determined from the temperature dependence of the centre shift of
M\""ossbauer spectra recorded in the temperature range of 80 - 300 K. Its
compositional dependence shows a weak increase with x whose rate, in a linear
approximation, is equal to 3.1 K/at%. The results are compared with the
corresponding ones found previously for the sigma-phase in Fe-Cr and Fe-V
compounds.",1204.3792v1
2012-05-15,An isolated Dirac cone on the surface of ternary tetradymite-like topological insulators,"We have extended the search for topological insulators to the ternary
tetradymite-like compounds M2X2Y (M = Bi or Sb; X and Y = S, Se or Te), which
are variations of the well-known binary compounds Bi2Se3 and Bi2Te3. Our
first-principles computations suggest that five existing compounds are strong
topological insulators with a single Dirac cone on the surface. In particular,
stoichiometric Bi2Se2S, Sb2Te2Se and Sb2Te2S are predicted to have an isolated
Dirac cone on their naturally cleaved surface. This finding paves the way for
the realization of the topological transport regime.",1205.3467v1
2012-08-15,New layered fluorosulfide SrFBiS2,"We have synthesized a new layered BiS$_{2}$-based compound SrFBiS2. This
compound has similar structure to BiS2. It is built up by stacking up SrF
layers and NaCl-type BiS2 layers alternatively along the c axis. Electric
transport measurement indicates that SrFBiS2 is a semiconductor. Thermal
transport measurement shows that SrFBiS2 has a small thermal conductivity and
large Seebeck coefficient. First principle calculations are in agreement with
experimental results and show that SrFBiS2 is very similar to LaOBiS2 which
becomes superconductor with F doping. Therefore, SrFBiS2 may be a parent
compound of new superconductors.",1208.3189v2
2012-10-10,Comment on Synthesis of rhenium nitride crystal with MoS2 structure,"Kawamura et. al. recently published an article about the synthesis of rhenium
nitride with MoS2-type structure [APL 100, 251910(2012)]. We disagree with the
composition proposed by Kawamura. The compound synthesized by Kawamura is ReN3,
or a compound of similar composition. What Kawamura did is to find the Re
atomic positions of a compound where the nitrogen concentration remains
unknown. This paper was rejected form APL. The reviewer comments (and our
reply) are included here.",1210.3054v2
2013-01-16,"Magnetic, magnetocaloric and transport properties of HoRuSi compound","Magnetic, thermal, magnetocaloric and transport properties of polycrystalline
HoRuSi have been studied. It was found that the compound shows magnetic
transitions at T1=18 K and T2=8 K. Magnetization data reveal that the
ferromagnetic ordering is dominant in this compound. Magnetocaloric effect has
been estimated from M-H-T data and the -{\Delta}SM has been found to be 12.8
J/kg K for field of 50 kOe, which is comparable to some potential refrigerant
materials in same temperature regime.",1301.3670v1
2013-03-04,Compound Perfect Squared Squares of the Order Twenties,"P. J. Federico used the term low-order for perfect squared squares with at
most 28 squares in their dissection. In 2010 low-order compound perfect squared
squares (CPSSs) were completely enumerated. Up to symmetries of the square and
its squared subrectangles there are 208 low-order CPSSs in orders 24 to 28. In
2012 the CPSSs of order 29 were completely enumerated, giving a total of 620
CPSSs up to order 29.",1303.0599v3
2013-03-15,van der Waals interaction in iron-chalcogenide superconductors,"We demonstrate that the inclusion of van der Waals dispersive interaction
sensibly improves the prediction of lattice constants by density functional
theory in iron-chalcogenides (FeCh) superconductor compounds, namely FeSe and
FeTe. We show how generalized gradient approximation (GGA) for the exchange
correlation potential overestimates the out-of-plane lattice constants in both
compounds when compared with experiments. In addition, GGA predicts a too weak
bonding between the neutral FeCh layers, with a sensible underestimation of the
bulk modulus. van der Waals corrected simulations completely solve both
problems, reconciling theoretical results with experiments. These findings must
be considered when dealing with theoretical predictions in FeCh compounds.",1303.3747v2
2013-09-23,"Superconductivity and physical properties of LanRu3n-1B2n (n = 1, 2, and 3)","We examined the physical properties of homologous LanRu3n-1B2n (n = 1 - 3)
series including a new compound of n = 2. All of these compounds showed strong
electron-electron correlation characterized by large Wilson ratio. In contrast
to LaRu2B2 and La2Ru5B4 that show normal metal behaviors down to 1.8 K, we
discover La3Ru8B6 is an intermediately coupled BCS superconductor with Tc ~ 3.2
K. The experimental and theoretical calculation results suggest that the
emergence of superconductivity in La3Ru8B6 attributes to the rather large
density of states at EF when compared to other two compounds.",1309.5776v2
2014-02-07,An Extended Hückel Study of the Electronic Properties of III-V Compounds and Their Alloys,"In this work, we performed tight binding calculations of the electronic
structure of III-V semiconductors compounds and their alloys based on the
Extended H\""uckel Theory (EHT), where the H\""uckel parameters for the binary
compounds were generated following a simulated annealing procedure. In
particular, this article is focused on the dependency between band gap and the
applied pressure and also the alloy composition.",1402.1610v1
2014-02-26,Spin nematic interaction in multiferroic compound Ba$_{2}$CoGe$_{2}$O$_{7}$,"We demonstrate the existence of the spin nematic interactions in an
easy-plane type antiferromagnet Ba$_{2}$CoGe$_{2}$O$_{7}$ by exploring the
magnetic anisotropy and spin dynamics. Combination of neutron scattering and
magnetic susceptibility measurements reveals that the origin of the in-plane
anisotropy is an antiferro-type interaction of the spin nematic operator. The
relation between the nematic operator and the electric polarization in the
ligand symmetry of this compound is presented. The introduction of the spin
nematic interaction is useful to understand the physics of spin and electric
dipole in multiferroic compounds.",1402.6436v1
2014-03-04,Theoretical descriptions of compound-nuclear reactions: open problems & challenges,"Compound-nuclear processes play an important role for nuclear physics
applications and are crucial for our understanding of the nuclear many-body
problem. Despite intensive interest in this area, some of the available
theoretical developments have not yet been fully tested and implemented. We
revisit the general theory of compound-nuclear reactions, discuss descriptions
of pre-equilibrium reactions, and consider extensions that are needed in order
to get cross section information from indirect measurements.",1403.0923v1
2014-08-21,$J_{eff}=1/2$ Mott Insulating State in Rh and Ir Fluorides,"Discovery of new transition metal compounds with large spin orbit coupling
(SOC) coexisting with strong electron-electron correlation among the $d$
electrons is essential for understanding the physics that emerges from the
interplay of these two effects. In this study, we predict a novel class of
$J_{eff}=1/2$ Mott insulators in a family of fluoride compounds that are
previously synthesized, but not characterized extensively. First principles
calculations in the level of all electron Density Functional Theory + Dynamical
Mean Field Theory (DFT+DMFT) indicate that these compounds have large Mott gaps
and some of them exhibit unprecedented proximity to the ideal, $SU(2)$
symmetric $J_{eff}=1/2$ limit.",1408.4852v2
2015-02-16,"Superconductivity in the elements, alloys and simple compounds","We give a brief review of superconductivity at ambient pressure in elements,
alloys, and simple three-dimensional compounds. Historically these were the
first superconducting materials studied, and based on the experimental
knowledge gained from them the BCS theory of superconductivity was developed in
1957. Extended to include the effect of phonon retardation, the theory is
believed to describe the subset of superconducting materials known as
`conventional superconductors', where superconductivity is caused by the
electron-phonon interaction. These include the elements, alloys and simple
compounds discussed in this article and several other classes of materials
discussed in other articles in this Special Issue.",1502.04724v1
2015-03-12,Thermodynamics of point defects and diffusion mechanisms in B2-ordered compounds,"The point defect thermodynamics in a general family of binary compounds,
including B2 compounds as a specific representative, are classified by way of
two non-trivial energy parameters. The scheme is applied to published ab initio
defect formation energies, and the variety of resulting phenomena is
demonstrated. Further, by introducing model assumptions the consequences for
the active diffusion mechanisms are deduced. It is shown that particularly for
the off-stoichiometric case, the assumed prevalence of either the six-jump
cycle or the triple-defect mechanism has to be reconsidered, as a number of
qualitatively different mechanisms emerge as likely candidates for the dominant
effect. Two of those, the 4+2-jump cycles and the waltzing-step mechanism, are
introduced here.",1503.03798v1
2015-05-20,Superconductivity in MgPtSi: An orthorhombic variant of MgB2,"A ternary compound, MgPtSi, was synthesized by solid-state reaction. An
examination of the compound by powder X-ray diffraction revealed that it
crystallizes in the orthorhombic TiNiSi-type structure with the Pnma space
group. The structure comprises alternately stacked layers of Mg and PtSi
honeycomb network, which is reminiscent of MgB2, and the buckling of the
honeycomb network causes orthorhombic distortion. Electrical and magnetic
studies revealed that MgPtSi exhibited superconductivity with a transition
temperature of 2.5 K. However, its isostructural compounds, namely, MgRhSi and
MgIrSi, were not found to exhibit superconductivity.",1505.05301v1
2015-07-09,A note on functional limit theorems for compound Cox processes,"An improved version of the functional limit theorem is proved establishing
weak convergence of random walks generated by compound doubly stochastic
Poisson processes (compound Cox processes) to L{\'e}vy processes in the
Skorokhod space under more realistic moment conditions. As corollaries,
theorems are proved on convergence of random walks with jumps having finite
variances to L{\'e}vy processes with variance-mean mixed normal distributions,
in particular, to stable L{\'e}vy processes, generalized hyperbolic and
generalized variance-gamma L{\'e}vy processes.",1507.02534v1
2015-09-13,Compound structure one-dimensional photonic crystal,"In this paper, we have proposed a new compound structure one-dimensional
photonic crystal, which include series connection, parallel connection and
positive and negative feedback compound structure photonic crystal. We have
studied their transmission characteristics and obtained some new results, which
should be help to design new type optical devices, such as optical amplifier,
photonic crystal laser and so on.",1509.03824v1
2016-01-07,"Exchange interactions and Curie temperatures of the tetrametal nitrides Cr4N, Mn4N, Fe4N, Co4N, and Ni4N","The exchange interactions of Cr4N, Mn4N, Fe4N, Co4N, and Ni4N compounds with
perovskite structure were calculated to obtain the Curie temperatures for these
compounds from Monte Carlo calculations. Contrary to naive expectation, the
exchange interactions vary markedly among these five compounds. In Fe4N, the
intra-sublattice interaction of the Fe 3c atoms is strongly negative, leading
to a significant reduction of the Curie temperature. The calculated Curie
temperatures are 291K (Cr4N), 710K (Mn4N), 668K (Fe4N), 827K (Co4N), and 121K
(Ni4N), in good agreement with experimental observations where available. The
much lower Curie temperature of Ni4N compared to fcc Ni is explained on the
basis of the exchange interactions.",1601.01522v1
2016-08-31,On subexponential tails for the maxima of negatively driven compound renewal and Lévy processes,"We study subexponential tail asymptotics for the distribution of the maximum
$M_t:=\sup_{u\in[0,t]}X_u$ of a process $X_t$ with negative drift for the
entire range of $t>0$. We consider compound renewal processes with linear drift
and L\'evy processes. For both we also formulate and prove the principle of a
single big jump for their maxima. The class of compound renewal processes
particularly includes Cram\'er-Lundberg risk process.",1608.09004v2
2016-11-09,The mechanocaloric potential of spin crossover compounds,"We present a first evaluation of the potential for spin crossover (SCO)
compounds to be considered as a new class of giant mechanocaloric effect
material. From literature data on the variation of the spin crossover
temperature with pressure, we estimate the maximum available adiabatic
temperature change for several compounds and the relatively low pressures that
may be required to observe these effects.",1611.03032v1
2017-03-11,"Investigation on different physical aspects such as structural, elastic, mechanical, optical properties and Debye temperature of Fe2ScM (M = P and As) semiconductors: a DFT based first principles study","With the help of first principles calculation method based on the density
functional theory we have investigated the structural, elastic, mechanical
properties and Debye temperature of Fe2ScM (M = P and As) compounds under
pressure up to 60 GPa. The optical properties have been investigated under zero
pressure. Our calculated optimized structural parameters of both the compounds
are in good agreement with the other theoretical results. The calculated
elastic constants show that Fe2ScM (M = P and As) compounds are mechanically
stable up to 60 GPa.",1703.03980v2
2017-08-25,Chisio: A Compound Graph Editing and Layout Framework,"We introduce a new free, open-source compound graph editing and layout
framework named Chisio, based on the Eclipse Graph Editing Framework (GEF) and
written in Java. Chisio can be used as a finished graph editor with its
easy-to-use graphical interface. The framework has an architecture suitable for
easy customization of the tool for end-user's specific needs as well. Chisio
comes with a variety of graph layout algorithms, most supporting compound
structures and non-uniform node dimensions. Furthermore, new algorithms are
straightforward to add, making Chisio an ideal test environment for layout
algorithm developers.",1708.07762v1
2017-12-01,"Frustrated antiferromagnetic honeycomb-tunnel-like lattice CuRE2Ge2O8 (RE=Pr, Nd, Sm, and Eu)","New frustrated antiferromagnetic compounds CuRE2Ge2O8 (RE=Pr, Nd, Sm, Eu)
have been investigated using high-resolution x-ray diffraction, magnetic and
heat capacity measurements. These systems show different magnetic lattices
depending on rare-earth element. The nonmagnetic Eu compound is a S=1/2
two-dimensional triangular antiferromagnetic lattice oriented in the ac plane
with geometrical frustration. On the other hand, the Pr, Nd, and Sm compounds
show a three-dimensional honeycomb-tunnel-like lattice made of RE^3+ running
along the a axis with the characteristic behavior of frustrated
antiferromagnets.",1712.00183v1
2018-03-21,"Olive Oil is Made of Olives, Baby Oil is Made for Babies: Interpreting Noun Compounds using Paraphrases in a Neural Model","Automatic interpretation of the relation between the constituents of a noun
compound, e.g. olive oil (source) and baby oil (purpose) is an important task
for many NLP applications. Recent approaches are typically based on either
noun-compound representations or paraphrases. While the former has initially
shown promising results, recent work suggests that the success stems from
memorizing single prototypical words for each relation. We explore a neural
paraphrasing approach that demonstrates superior performance when such
memorization is not possible.",1803.08073v1
2018-09-18,Transfer and Multi-Task Learning for Noun-Noun Compound Interpretation,"In this paper, we empirically evaluate the utility of transfer and multi-task
learning on a challenging semantic classification task: semantic interpretation
of noun--noun compounds. Through a comprehensive series of experiments and
in-depth error analysis, we show that transfer learning via parameter
initialization and multi-task learning via parameter sharing can help a neural
classification model generalize over a highly skewed distribution of relations.
Further, we demonstrate how dual annotation with two distinct sets of relations
over the same set of compounds can be exploited to improve the overall accuracy
of a neural classifier and its F1 scores on the less frequent, but more
difficult relations.",1809.06748v1
2019-11-26,On Optimal Solutions to Compound Statistical Decision Problems,"In a compound decision problem, consisting of $n$ statistically independent
copies of the same problem to be solved under the sum of the individual losses,
any reasonable compound decision rule $\delta$ satisfies a natural symmetry
property, entailing that $\delta(\sigma(\boldsymbol{y})) =
\sigma(\delta(\boldsymbol{y}))$ for any permutation $\sigma$. We derive the
greatest lower bound on the risk of any such decision rule. The classical
problem of estimating the mean of a homoscedastic normal vector is used to
demonstrate the theory, but important extensions are presented as well in the
context of Robbins's original ideas.",1911.11422v2
2020-01-29,Subexponential densities of compound Poisson sums and the supremum of a random walk,"We characterize the subexponential densities on $(0,\infty)$ for compound
Poisson distributions on $[0,\infty)$ with absolutely continuous L\'evy
measures. As a corollary, we show that the class of all subexponential
probability density functions on $\mathbb R_+$ is closed under generalized
convolution roots of compound Poisson sums. Moreover, we give an application to
the subexponential density on $(0,\infty)$ for the distribution of the supremum
of a random walk.",2001.11362v1
2019-07-05,Predicting Gene Expression Between Species with Neural Networks,"We train a neural network to predict human gene expression levels based on
experimental data for rat cells. The network is trained with paired human/rat
samples from the Open TG-GATES database, where paired samples were treated with
the same compound at the same dose. When evaluated on a test set of held out
compounds, the network successfully predicts human expression levels. On the
majority of the test compounds, the list of differentially expressed genes
determined from predicted expression levels agrees well with the list of
differentially expressed genes determined from actual human experimental data.",1907.03041v1
2019-07-10,The evolution of electron dispersion in the series of rare-earth tritelluride compounds obtained from their charge-density-wave properties and susceptibility calculations,"We calculated electron susceptibility of rare-earth tritelluride compounds
RTe$_3$ as a function of temperature, wave vector and electron-dispersion
parameters. Comparison of results obtained with the available experimental data
on the transition temperature and on the wave vector of a charge-density wave
in these compounds allowed us to predict values and the evolution of
electron-dispersion parameters with the variation of atomic number of
rare-earth element R.",1907.04815v1
2017-12-06,Surface Tension Prediction for Pure Fluids,"In this paper we propose an analytic expression for surface tension of
organic compounds. This new expression, originally derived from the
statistical-mechanics is shown to represent the experimental surface tension
data of 94 different organic compounds within 1.05 AAD%. We also propose
another simpler expression. When this generalized expression is used surface
tensions for all the 94 compounds can be predicted within 2.57 AAD% for all
temperatures investigated.",1802.02201v1
2018-11-06,General Compound Hawkes Processes in Limit Order Books,"In this paper, we study various new Hawkes processes. Specifically, we
construct general compound Hawkes processes and investigate their properties in
limit order books. With regards to these general compound Hawkes processes, we
prove a Law of Large Numbers (LLN) and a Functional Central Limit Theorems
(FCLT) for several specific variations. We apply several of these FCLTs to
limit order books to study the link between price volatility and order flow,
where the volatility in mid-price changes is expressed in terms of parameters
describing the arrival rates and mid-price process.",1812.02298v1
2020-07-31,Multivariate General Compound Point Processes in Limit Order Books,"In this paper, we focus on a new generalization of multivariate general
compound Hawkes process (MGCHP), which we referred to as the multivariate
general compound point process (MGCPP). Namely, we applied a multivariate point
process to model the order flow instead of the Hawkes process. Law of large
numbers (LLN) and two functional central limit theorems (FCLTs) for the MGCPP
were proved in this work. Applications of the MGCPP in the limit order market
were also considered. We provided numerical simulations and comparisons for the
MGCPP and MGCHP by applying Google, Apple, Microsoft, Amazon, and Intel trading
data.",2008.00124v1
2022-03-17,Heuristics and Uncertainty Quantification in Rational and Inverse Compound and Catalyst Design,"The goal of inverse (quantum) approaches is to devise methods and approaches
capable of efficiently searching chemical space in such a way that the design
of novel materials and compounds with specific properties is as direct and
efficient as possible. Here, we review the current state of the field with a
focus on the most recent developments. We discuss the importance of heuristic
rules and human intuition for rational compound design. Moreover, we elaborate
on options for reliable uncertainty quantification for computational results,
which is crucial for a truly predictive application of any in silico method.",2203.09315v1
2016-03-14,Conformal Predictors for Compound Activity Prediction,"The paper presents an application of Conformal Predictors to a
chemoinformatics problem of identifying activities of chemical compounds. The
paper addresses some specific challenges of this domain: a large number of
compounds (training examples), high-dimensionality of feature space, sparseness
and a strong class imbalance. A variant of conformal predictors called
Inductive Mondrian Conformal Predictor is applied to deal with these
challenges. Results are presented for several non-conformity measures (NCM)
extracted from underlying algorithms and different kernels. A number of
performance measures are used in order to demonstrate the flexibility of
Inductive Mondrian Conformal Predictors in dealing with such a complex set of
data.
  Keywords: Conformal Prediction, Confidence Estimation, Chemoinformatics,
Non-Conformity Measure.",1603.04506v1
2017-06-01,Electronic and magnetic properties of low dimensional system Co2TeO3Cl2,"The electronic and magnetic properties of transition metal oxyhalide compound
Co2TeO3Cl2 is investigated using first principle calculations within the
framework of density functional theory. In order to find underlying spin
lattice of this compound, various hopping integrals and exchange interactions
are calculated. The calculations reveal that the dominant inter-chain and
intra-chain interactions are in ab plane. The exchange path is visualised by
Wannier function plotting. The nearest neighbour and next nearest neighbour
exchange interactions are antiferromagnetic, making the system frustrated in
low dimension. The importance of spin orbit coupling in this compound is also
investigated. The spin quantization axis is favoured along the crystallographic
b direction.",1706.00259v1
2017-06-22,General Compound Hawkes Processes in Limit Order Books,"In this paper, we study various new Hawkes processes, namely, so-called
general compound and regime-switching general compound Hawkes processes to
model the price processes in the limit order books. We prove Law of Large
Numbers (LLN) and Functional Central Limit Theorems (FCLT) for these processes.
The latter two FCLTs are applied to limit order books where we use these
asymptotic methods to study the link between price volatility and order flow in
our two models by studying the diffusion limits of these price processes. The
volatilities of price changes are expressed in terms of parameters describing
the arrival rates and price changes.",1706.07459v2
2017-10-25,Free deterministic equivalent Z-scores of compound Wishart models: A goodness of fit test of 2DARMA models,"We introduce a new method to qualify the goodness of fit parameter estimation
of compound Wishart models. Our method based on the free deterministic
equivalent Z-score, which we introduce in this paper. Furthermore, an
application to two dimensional autoregressive moving-average model is provided.
  Our proposal method is a generalization of statistical hypothesis testing to
one dimensional moving average model based on fluctuations of real compound
Wishart matrices, which is a recent result by Hasegawa, Sakuma and Yoshida.",1710.09497v1
2019-04-30,Quasiparticle self-consistent $GW$ band structures of Mg-IV-N$_2$ compounds: the role of semicore $d$ states,"We present improved band structure calculations of the Mg-IV-N$_2$ compounds
in the quasiparticle self-consistent $GW$ approximation. Compared to previous
calculations (Phys. Rev. B 94, 125201 (2016)) we here include the effects of
the Ge-3$d$ and Sn-4$d$ semicore states and find that these tend to reduce the
band gap significantly. This places the band gap of MgSnN$_2$ in the difficult
to reach green region of the visible spectrum. The stability of the materials
with respect to competing binary compounds is also evaluated and details of the
valence band maximum manifold splitting and effective masses are provided.",1905.00049v1
2019-05-18,A characterization of martingale-equivalent compound mixed Poisson process,"If a given aggregate process $S$ is a compound mixed Poisson process under a
probability measure $P$, a characterization of all probability measures $Q$ on
the domain of $P$, such that $P$ and $Q$ are progressively equivalent and $S$
remains a compound mixed Poisson process with improved properties, is provided.
This result generalizes earlier work of Delbaen & Haezendonck (1989).
Implications related to the computation of premium calculation principles in an
insurance market possessing the property of no free lunch with vanishing risk
are also discussed.",1905.07629v1
2020-10-24,New compound control algorithm in sliding mode control to reduce the chattering phenomenon: experimental validation,"In this work, a new SMS is proposed to achieve high tracking and suitable
robustness. However, the chattering phenomenon should be regarded as the main
drawback of the SMC. Therefore, a new compound control algorithm is used for
reducing the chattering phenomenon. The applied compound control law constantly
evaluates the error and send the correct value to the system. This
significantly will reduce the chattering phenomenon. The performance of the
control methods validated by applying on a robot arm experimentally.",2010.12778v2
2021-01-01,"Extraction, isolation, structure elucidation and evaluation of toxicity, anti-inflammatory and analgesic activity of Pituranthos scoparius constituents","The present work aimed to investigate an ethnobotanical survey about
Pituranthos scoparius and assess the toxicity, anti-inflammatory (in vitro, and
in vivo) potential, in vitro antioxidant, and analgesic effects of stems and
roots of Pituranthos scoparius. Furthermore; to isolate and elucidate the
chemical constituents of the n-butanol stem extract of P. scoparius (ButE) and
determine the toxicity and anti-inflammatory effects of these compounds added
to the ButE. Data from an ethnopharmacological study showed that 24.47 % of
people used this plant in folk medicine. Four compounds were isolated from
ButE. These compounds were characterized by means of NMR and high-resolution
mass spectral (HRMS) data.",2101.01548v1
2021-04-04,The Malliavin-Stein method for Hawkes functionals,"In this paper, following Nourdin-Peccati's methodology, we combine the
Malliavin calculus and Stein's method to provide general bounds on the
Wasserstein distance between functionals of a compound Hawkes process and a
given Gaussian density. To achieve this, we rely on the Poisson embedding
representation of an Hawkes process to provide a Malliavin calculus for the
Hawkes processes, and more generally for compound Hawkes processes. As an
application, we close a gap in the literature by providing the first
Berry-Ess\'een bounds associated to Central Limit Theorems for the compound
Hawkes process.",2104.01583v1
2021-09-24,Compound Krylov subspace methods for parametric linear systems,"In this work, we propose a reduced basis method for efficient solution of
parametric linear systems. The coefficient matrix is assumed to be a linear
matrix-valued function that is symmetric and positive definite for admissible
values of the parameter $\mathbf{\sigma}\in \mathbb{R}^s$. We propose a
solution strategy where one first computes a basis for the appropriate compound
Krylov subspace and then uses this basis to compute a subspace solution for
multiple $\mathbf{\sigma}$. Three kinds of compound Krylov subspaces are
discussed. Error estimate is given for the subspace solution from each of these
spaces. Theoretical results are demonstrated by numerical examples related to
solving parameter dependent elliptic PDEs using the finite element method
(FEM).",2109.12206v1
2021-10-08,Polyhalogenated Molecules in the Polarizable Ellipsoidal Force Field Model,"Polyhalogenated compounds are common in industrial, agricultural, and
environmental applications. These compounds contain more halogen bonds than
monohalogenated compounds. The presence of coupled {\sigma}-holes in the
covalent halogen atoms, which demonstrates strong interplay in halogen bonds,
should be carefully evaluated in force field optimization. In this study, a
polarizable ellipsoidal force field model was successfully applied to many
possible halogenated benzenes. The symmetry of the fitted parameters was
reproduced without any additional restrictions. The optimized parameters for
the anisotropic electrostatic potential showed good accuracy, stability, and
transferability with reasonable physical meanings. The parameter fitting
protocol was efficiently performed on a laptop, showing the potential of being
completely parallelized for thousands of halogenated homologues.",2110.04189v3
2022-07-07,Tunable anomalous Hall and Nernst effects in MM'X compounds,"Based on first-principles calculations, the anomalous Hall (AHC) and
anomalous Nernst conductivities (ANC) of the XMnP (X=Ti, Zr, Hf) compounds were
evaluated, and the possibility to tailor such properties by changing the
magnetization directions was also investigated. We observed that nodal lines
and small gap areas consist the dominant contributions to AHC and ANC, where
the significant variations in AHC and ANC when altering the magnetization
direction originate from the whole Brillouin zone. Our studies gave a promising
clue on engineering magnetic intermetallic compounds for tunable transverse
thermoelectric applications.",2207.03320v1
2022-09-13,ESG-valued discrete option pricing in complete markets,"We consider option pricing using replicating binomial trees, with a two fold
purpose. The first is to introduce ESG valuation into option pricing. We
explore this in a number of scenarios, including enhancement of yield due to
trader information and the impact of the past history of a market driver. The
second is to emphasize the use of discrete dynamic pricing, rather than
continuum models, as the natural model that governs actual market practice. We
further emphasize that discrete option pricing models must use discrete
compounding (such as risk-free rate compounding of $1+r_f \Delta t$) rather
than continuous compounding (such as $e^{r_f \Delta t})$.",2209.06276v1
2023-12-05,Effective mass and field-reinforced superconductivity in uranium compounds,"A theory of strong coupling superconductivity in uranium compounds has been
developed, based on electron-electron interaction through magnetic fluctuations
described by frequency-dependent magnetic susceptibility. The magnetic field
dependence of the electron effective mass is expressed through the field
dependence of the magnetic susceptibility components. It is shown that the
intensity of triplet pairing, and hence the critical temperature of the
transition to the superconducting state, is also determined by the
field-dependent susceptibility. The results are discussed in relation to the
properties of ferromagnetic uranium compounds URhGe and UCoGe, as well as the
recently discovered UTe2.",2312.02893v4
2023-12-12,Top-Down Drawings of Compound Graphs,"Bottom-up layout algorithms for compound graphs are suitable for presenting
the microscale view of models and are often used in model-driven engineering.
However, they have difficulties at the macroscale where maintaining the
overview of large models becomes challenging. We propose top-down layout, which
utilizes scale to hide low-level details at high zoom levels. The entire
high-level view can fit into the viewport and remain readable, while the
ability to zoom in to see the details is still maintained. Top-down layout is
an abstract high-level layout process that can be used in conjunction with
classic layout algorithms to produce visually compelling and readable diagrams
of large compound graphs.",2312.07319v1
2003-07-24,Crystal Structure of the Sodium Cobaltate Deuterate Superconductor NaxCoO2o4xD2O (x=1/3),"Neutron and x-ray powder diffraction have been used to investigate the
crystal structures of a sample of the newly-discovered superconducting sodium
cobaltate deuterate compound with composition Na0.31(3)CoO2o1.25(2)D2O and its
anhydrous parent compound Na0.61(1)CoO2. The deuterate superconducting compound
is formed by coordinating four D2O molecules (two above and two below) to each
Na ion in a way that gives Na-O distances nearly equal to those in the parent
compound. One deuteron of the D2O molecule is hydrogen bonded to an oxygen atom
in the CoO2 plane and the oxygen atom and the second deuteron of each D2O
molecule lie approximately in a plane between the Na layer and the CoO2 layers.
This coordination of Na by four D2O molecules leads to ordering of the Na ions
and D2O molecules. The sample studied here, which has Tc=4.5 K, has a refined
composition of Na0.31(3)CoO2o1.25(2)D2O, in agreement with the expected 1:4
ratio of Na to D2O. These results show that the optimal superconducting
composition should be viewed as a specific hydrated compound, not a solid
solution of Na and D2O (H2O) in NaxCoO2oyD2O. Studies of physical properties
vs. Na or D2O composition should be viewed with caution until it is verified
that the compound remains in the same phase over the composition range of the
study.",0307627v1
2005-02-04,"Interplay of magnetic ordering and CEF anisotropy in the hexagonal compounds RPtIn, R = Y, Gd - Lu","Single crystals of RPtIn, $R~=$ Y, Gd - Lu were grown out of In-rich ternary
solution. Powder X-ray diffraction data on all of these compounds were
consistent with the hexagonal ZrNiAl-type structure (space group P $\bar{6}$ 2
m). The $R~=$ Tb and Tm members of the series appear to order
antiferromagnetically ($T_N~=$ 46.0 K, and 3.0 K respectively), whereas the
$R~=$ Gd, Dy - Er compounds have at least a ferromagnetic component of the
magnetization along the c-axis. The magnetic ordering temperatures of all of
these systems seem to scale well with the de Gennes factor dG, whereas the
curious switching from ferromagnetic to antiferromagnetic ordering across the
series is correlated with a change in anisotropy, such that, in the low
temperature paramagnetic state, $\chi_{ab} > \chi_c$ for the antiferromagnetic
compounds, and $\chi_c > \chi_{ab}$ for the rest. In order to characterize the
magnetic ordering across the RPtIn series, a three-dimensional model of the
magnetic moments in Fe$_2$P-type systems was developed, using the \textit{three
co-planar Ising-like systems model} previously introduced for the extremely
planar TbPtIn compound: given the orthorhombic point symmetry of the R sites,
we assumed the magnetic moments to be confined to six non-planar easy axes,
whose in-plane projections are rotate by $60^0$ with respect to each other.
Such a model is consistent with the reduced high-field magnetization values
observed for the RPtIn compounds, R$~=$ Tb - Tm, and qualitatively reproduces
the features of the angular dependent magnetization of Ho$_x$Y$_{1-x}$PtIn at
$H~=$ 55 kG.",0502131v1
2006-07-24,Effect of Y substitution on the structural and magnetic properties of Dy1-xYxCo5 compounds,"Structural and magnetization studies were carried out on Dy1-xYxCo5 [x = 0,
0.2, 0.4, 0.6, 0.8, 1] compounds which crystallize in the hexagonal CaCu5-type
structure. Lattice parameters and unit-cell volume increase with Y
concentration. Large thermomagnetic irreversibility between the field-cooled
and the zero-field cooled magnetization data has been observed in all the
compounds, which has been attributed to the domain wall pinning effect.
Temperature dependence of magnetization data shows that except DyCo5 and YCo5,
all the compounds show spin reorientation transitions in the range of 5-300 K.
The spin reorientation temperature decreases from 266 K for x=0.2 to 100 K for
x=0.8. Powder x-ray diffractograms of the magnetically aligned samples show
that DyCo5 has planar anisotropy at room temperature whereas all the other
compounds possess axial anisotropy. The spin reorientation transition has been
attributed to a change in the easy magnetization direction from the ab-plane to
the c-axis, as the temperature is increased. The anisotropy field and the first
order anisotropy constant are found to be quite high in all the compounds
except DyCo5. The magnetic properties have been explained by taking into
account the variations in contributions arising from the rare earth and
transition metal sublattices.",0607597v1
2008-02-27,Co-Accretion of Chondrules and Dust in the Solar Nebula,"We present a mechanism for chondrules to stick together by means of
compaction of a porous dust rim they sweep up as they move through the dusty
nebula gas. It is shown that dust aggregates formed out of micron-sized grains
stick to chondrules, forming a porous dust rim. When chondrules collide, this
dust can be compacted by means of rolling motions within the porous dust layer.
This mechanism dissipates the collisional energy, compacting the rim and
allowing chondrules to stick. The structure of the obtained chondrule-dust
agglomerates (referred to as compounds) then consists of three phases:
chondrules, porous dust, and dust that has been compacted by collisions.
Subsequently, these compounds accrete their own dust and collide with other
compounds. The evolution of the compound size distribution and the relative
importance of the phases is calculated by a Monte Carlo code. Growth ends, and
a simulation is terminated when all the dust in the compounds has been
compacted. Numerous runs are performed, reflecting the uncertainty in the
physical conditions at the chondrule formation time. It is found that compounds
can grow by 1-2 orders of magnitudes in radius, upto dm-sizes when turbulence
levels are low. However, relative velocities associated with radial drift form
a barrier for further growth. Earlier findings that the dust sweep-up by
chondrules is proportional to their sizes are confirmed. We contrast two
scenarios regarding how this dust evolved further towards the densely packed
rims seen in chondrites.",0802.4048v1
2009-07-24,Monolayer honeycomb structures of group IV elements and III-V binary compounds,"Using first-principles plane wave calculations, we investigate two
dimensional honeycomb structure of Group IV elements and their binary
compounds, as well as the compounds of Group III-V elements. Based on structure
optimization and phonon mode calculations, we determine that 22 different
honeycomb materials are stable and correspond to local minima on the
Born-Oppenheimer surface. We also find that all the binary compounds containing
one of the first row elements, B, C or N have planar stable structures. On the
other hand, in the honeycomb structures of Si, Ge and other binary compounds
the alternating atoms of hexagons are buckled, since the stability is
maintained by puckering. For those honeycomb materials which were found stable,
we calculated optimized structures, cohesive energies, phonon modes, electronic
band structures, effective cation and anion charges, and some elastic
constants. The band gaps calculated within Density Functional Theory using
Local Density Approximation are corrected by GW0 method. Si and Ge in honeycomb
structure are semimetal and have linear band crossing at the Fermi level which
attributes massless Fermion character to charge carriers as in graphene.
However, all binary compounds are found to be semiconductor with band gaps
depending on the constituent atoms. We present a method to reveal elastic
constants of 2D honeycomb structures from the strain energy and calculate the
Poisson's ratio as well as in-plane stiffness values. Preliminary results show
that the nearly lattice matched heterostructures of ...",0907.4350v1
2009-12-03,"Log-concavity, ultra-log-concavity, and a maximum entropy property of discrete compound Poisson measures","Sufficient conditions are developed, under which the compound Poisson
distribution has maximal entropy within a natural class of probability measures
on the nonnegative integers. Recently, one of the authors [O. Johnson, {\em
Stoch. Proc. Appl.}, 2007] used a semigroup approach to show that the Poisson
has maximal entropy among all ultra-log-concave distributions with fixed mean.
We show via a non-trivial extension of this semigroup approach that the natural
analog of the Poisson maximum entropy property remains valid if the compound
Poisson distributions under consideration are log-concave, but that it fails in
general. A parallel maximum entropy result is established for the family of
compound binomial measures. Sufficient conditions for compound distributions to
be log-concave are discussed and applications to combinatorics are examined;
new bounds are derived on the entropy of the cardinality of a random
independent set in a claw-free graph, and a connection is drawn to Mason's
conjecture for matroids. The present results are primarily motivated by the
desire to provide an information-theoretic foundation for compound Poisson
approximation and associated limit theorems, analogous to the corresponding
developments for the central limit theorem and for Poisson approximation. Our
results also demonstrate new links between some probabilistic methods and the
combinatorial notions of log-concavity and ultra-log-concavity, and they add to
the growing body of work exploring the applications of maximum entropy
characterizations to problems in discrete mathematics.",0912.0581v2
2011-02-05,Compound Outage Probability and Capacity of a Class of Fading MIMO Channels with Channel Distribution Uncertainty,"Outage probability and capacity of a class of block-fading MIMO channels are
considered with partial channel distribution information. Specifically, the
channel or its distribution are not known but the latter is known to belong to
a class of distributions where each member is within a certain distance
(uncertainty) from a nominal distribution. Relative entropy is used as a
measure of distance between distributions. Compound outage probability defined
as min (over the transmit signal distribution) -max (over the channel
distribution class) outage probability is introduced and investigated. This
generalizes the standard outage probability to the case of partial channel
distribution information. Compound outage probability characterization (via
one-dimensional convex optimization), its properties and approximations are
given. It is shown to have two-regime behavior: when the nominal outage
probability decreases (e.g. by increasing the SNR), the compound outage first
decreases linearly down to a certain threshold (related to relative entropy
distance) and then only logarithmically (i.e. very slowly), so that no
significant further decrease is possible. The compound outage depends on the
relative entropy distance and the nominal outage only, all other details
(nominal fading and noise distributions) being irrelevant. The transmit signal
distribution optimized for the nominal channel distribution is shown to be also
optimal for the whole class of distributions. The effect of swapping the
distributions in relative entropy is investigated and an error floor effect is
established. The compound outage probability under Lp distance constraint is
also investigated. The obtained results hold for a generic channel model
(arbitrary nominal fading and noise distributions).",1102.1103v1
2012-12-03,"Magnetic properties and magnetocaloric effects in NaZn13-type La(Fe, Al)13-based compounds","In this article, our recent progresses about the effects of atomic
substitution, magnetic field and temperature on the magnetic and magnetocaloric
properties of the LaFe13-xAlx compounds are reviewed. With the increase of
aluminum content, the compounds exhibit successively an antiferromagnetic
(AFM), a ferromagnetic (FM), and a mictomagnetic state. Furthermore, the AFM
coupling of LaFe13-xAlx can be converted to a FM coupling by substituting Si
for Al, Co for Fe and magnetic rare-earth R for La, or introducing interstitial
C or H atom. However, low doping levels lead to FM clusters embedded in AFM
matrix, and the resultant compounds can undergo, under appropriate applied
fields, first an AFM-FM and then a FM-AFM phase transition while heated, with
significant magnetic relaxation in the vicinity of the transition temperature.
The Curie temperature of LaFe13-xAlx can be shifted to room temperature by
choosing appropriate contents of Co, C or H, and strong magnetocaloric effect
can be obtained around the transition temperature. For example, for the
LaFe11.5Al1.5C0.2H1.0 compound, the maximal entropy change reaches 13.8 J/kg K
for a field change of 0-5 T, occurring around the room temperature. It is 42%
higher than that of Gd and, therefore, this compound is a promising
room-temperature magnetic refrigerant.",1212.0315v1
2013-03-18,A study of volatile compounds in the breath of children with type 1 diabetes,"A pilot study of exhaled volatile compounds and their correlation with blood
glucose levels in eight children with type 1 diabetes is reported. Five paired
blood and breath samples were obtained from each child over a 6 hour period.
The blood glucose concentration ranged from 41.4 to 435.6 mg/dL. Breath samples
were collected in Tedlar bags and immediately evacuated through thermal
desorption tubes packed with Carbopack B and C. The VOCs were later recovered
by thermal desorption and analysed using gas chromatography mass spectrometry.
The study identified 74 volatile compounds present in at least 10% of the
patient samples. Of these 74 volatiles 36 were found in all patient samples
tested. Further analysis of the 36 compounds found that none showed significant
overall correlation with blood glucose levels. Isoprene showed a weak negative
correlation with blood glucose levels. Acetone was found to have no correlation
with blood glucose levels for the patients studied. Some patients showed
significant individual correlation between the relative peak areas of certain
compounds and blood glucose levels. However, there was no consistent pattern
observed within these results across all 8 patients. Additional breath samples
were collected in Tedlar bags and analysed using SIFTMS for 3 of the patients
and a healthy control. The levels of 24 volatiles are reported and were found
to be generally consistent with previously reported SIFT-MS data. In agreement
with the GCMS data, no compounds exhibited a significant overall correlation
with blood glucose level.",1303.4210v1
2013-04-05,Fermi surface topology and de Hass-van Alphen orbits in PuIn$_{\rm 3}$ and PuSn$_{\rm 3}$ compounds,"Since the recent discovery of plutonium-based superconductors such as
PuCoIn$_{\rm 5}$, systematic studies of the electronic properties for plutonium
compounds are providing insight into the itinerancy-localization crossover of
Pu 5$f$ electrons. We are particularly interested in understanding the Fermi
surface properties of PuIn$_{3}$ compound, which serves as the building block
for the PuCoIn$_{\rm 5}$ superconductor. Motivated by the first observation of
quantum oscillation and renewed interest in the de-Hass van-Alphen (dHvA)
measurements on PuIn$_{\rm 3}$, we study the Fermi surface (FS) topology and
the band dispersion in both paramagnetic and antiferromagnetic state of
PuIn$_{\rm 3}$, based on density functional theory with generalized gradient
approximation. We compare the results with its isostructural paramagnetic
compound PuSn$_{\rm 3}$. We show the detailed Fermi surfaces of compounds
PuIn$_{\rm 3}$ and PuSn$_{\rm 3}$ and conclude that the FS topology of an
antiferromagnetic PuIn$_3$ agrees better with dHvA measurements. In addition,
we show the magnetization of the antiferromagnetic order can alter the angle
dependence and values of the effective mass for the dHvA orbits. We point out
the accurate determination of the magnetic order orientation with respect to
the crystal orientation is crucial to advance the understanding of the
electronic structures of the PuIn$_{\rm 3}$ compound.",1304.1833v2
2013-07-30,Analysis of the volatiles in the headspace above the plasmodium and sporangia of the slime mould (Physarum polycephalum) by SPME-GCMS,"Solid phase micro-extraction (SPME) coupled with Gas Chromatography Mass
Spectrometry (GC-MS) was used to extract and analyse the volatiles in the
headspace above the plasmodial and sporulating stages of the slime mould
Physarum Polycephalum. In total 115 compounds were identified from across a
broad range of chemical classes. Although more (87) volatile organic compounds
(VOCs) were identified when using a higher incubation temperature of 75oC, a
large number of compounds (79) were still identified at the lower extraction
temperature of 30oC and where the plasmodial stage was living. Far fewer
compounds were extracted after sporulation at the two extraction temperatures.
There were some marked differences between the VOCs identified in the
plasmodial stage and after sporulation. In particular the nitrogen containing
compounds acetonitrile, pyrrole, 2, 5-dimethyl-pyrazine and trimethyl pyrazine
seemed to be associated with the sporulating stage. There were many compounds
associated predominantly with the plasmodial stage including a number of furans
and alkanes. Interestingly, a number of known fungal metabolites were
identified including 1-octen-3-ol, 3-octanone, 1-octen-3-one, 3-octanol. In
addition known metabolites of cyanobacteria and actinobacteria in particular
geosmin was identified in the headspace. Volatile metabolites that had
previously been identified as having a positive chemotactic response to the
plasmodial stage of P. polycephalum were also identified including
{\beta}-farnesene, {\beta}-myrcene, limonene and 3-octanone. This study
constitutes the first comprehensive analysis of the headspace volatiles emitted
from Physarum Polycephalum. Further work to understand the origin and function
of the volatiles identified is required.",1307.8017v1
2013-08-12,"Spin reorientation behavior in YMn1-xMxO3 (M = Ti, Fe, Ga; x = 0, 0.1)","The structural and magnetic properties of polycrystalline YMn1-xMxO3 (M = Ti,
Fe, Ga; x = 0, 0.1) have been studied by neutron powder diffraction and
magnetic measurements to probe the effect of Mn site doping on the frustration
behavior and magnetic structure of these compounds. The compounds are
isostructural and crystallize with hexagonal structure in P63cm space group. We
find that doping with these three ions, Ti4+ (d0), Fe3+ (d5) and Ga3+ (d10),
influences both the TN and magnetic structure, unlike other Mn-site dopants
reported previously. The magnetic structure of YMnO3 is described by
considering a linear combination of irreducible representations {\Gamma}3 and
{\Gamma}4 below TN ~ 75K and with decrease in temperature the ratio of
{\Gamma}3 and {\Gamma}4 changes. The mixing ratio of these two irreducible
representations remains constant on lowering of temperature in the Ga doped
compounds. The magnetic structure is modified on doping with nonmagnetic ion
Ti4+ (d0). It is described by the basis vectors of the irreducible
representation {\Gamma}2 with moment 2.3{\mu}B at 6 K. On doping with Fe3+ (d5)
the magnetic structure immediately below TN is explained by considering the
{\Gamma}3 irreducible representation. On further lowering of temperature, a
spin reorientation at ~ 35 K is observed. Below this temperature, the magnetic
structure of YMn0.9Fe0.1O3 is explained by considering {\Gamma}3 representation
with 51% mixing of {\Gamma}4. The ordered moments are found to be reduced from
the expected value for a Mn3+ ion in all these compounds indicating the
frustrated nature of these compounds. However, the frustration parameter, f is
significantly reduced in the case of Ti doped compound with {\Gamma}2
representation.",1308.2482v1
2014-05-18,Laboratory Studies on the Carbon Kinetic Isotope Effects on the Production Mechanism of Particulate Phenolic Compounds Formed by Toluene Photooxidation: A Tool to Constrain Reaction Pathways,"Compound-specific stable carbon isotope ratios for phenolic compounds in
secondary particulate organic matter (POM) formed by photooxidation of toluene
were studied. Secondary POM generated by photooxidation of toluene using a
continuous-flow reactor and an 8 cubic meter indoor smog chamber was collected,
and then extracted with acetonitrile. Eight phenolic compounds were identified
in the extracts by a gas chromatograph coupled with a mass spectrometer, and
their compound-specific stable carbon isotope ratios were determined by a gas
chromatograph coupled with a combustion furnace followed by an isotope ratio
mass spectrometer. The majority of the products, including methylnitrophenols
and methylnitrocatechols, were isotopically depleted by 5 to 6 permil compared
to the initial isotope ratio for toluene, whereas the isotope ratio for
4_nitrophenol remained the same as the initial isotope ratio for toluene. Based
on the reaction mechanisms postulated in literature, stable carbon isotope
ratios of these products were calculated. Comparison of the observed isotope
ratios with the predicted implies that a reaction channel of
methylhydroxycyclohexadienyl radical with NO2 is a possible production pathway
for the particulate phenolic compounds.",1405.4508v2
2014-05-29,"High Pressure Structural Stability, and Optical Properties of Scheelite type ZrGeO$_4$ and HfGeO$_4$ X-ray Phosphor Hosts","\emph{Ab-initio} calculations were performed on the scheelite type MGeO$_4$
(M = Hf, and Zr) compounds which find wide range of applications such as in
x-ray imaging. We have studied the high pressure structural stability, elastic
constants, electronic structure and optical properties of these compounds
through density functional theory calculations. Two different density
functional approaches namely plane wave pseudopotential method (PW-PP) and full
potential linearized augmented plane wave method (FP-LAPW) were used for the
present study. The ground state structural and vibrational properties are
calculated and found to be in good agreement with experimental data. The
compressibility of Zr and Hf germanates is found to be anisotropic as the
a-axis is less compressible over c-axis due to the presence of Ge-O bonds along
a-axis which is further confirmed from the ordering of the elastic constants
that follows C$_{11}$ $>$ C$_{33}$. The electronic structure of the compounds
has been calculated through recently developed Tran Blaha-modified Becke
Johnson potential. The calculated electronic structure shows that the compounds
are insulators with a gap of 5.39 eV for ZrGeO$_4$ and 6.25 eV for HfGeO$_4$
respectively. Optical anisotropy of these compounds are revealed from the
computed optical properties such as complex dielectric function, refractive
index, and absorption coefficient. In addition, it is observed that Ti doped
ZrGeO$_4$ and HfGeO$_4$ turns out to be a good phosphor as the pristine
compounds have the energy gap greater than the visible range upon Ti doping
bandgap reduces as a result emission spectra occurs in the visible region and
is well explained in the present study.",1405.7526v1
2014-07-30,Mesophase behaviour of binary mixtures of bent-core and calamitic compounds,"The mesophase behaviour of binary mixtures of bent-core and calamitic liquid
crystals is presented. The nematogenic 4,6-dichloro-1,3-phenylene
bis[4'-(10-undecen-1-yloxy)-1,1'-biphenyl-4-carboxylate] (I) was the
banana-shaped component. As the calamitic compound ethyl
4'-(9-decen-1-yloxy)-1,1'-biphenyl-4-carboxylate (II), similar to one arm of
the bent-core molecule, was used which exhibits smectic phases in a wide
temperature range. A total of 6 mixtures with different compositions were
prepared and studied by polarising optical microscopy, differential scanning
calorimetry and X-ray diffraction on non-oriented samples. In the mixtures a
nematic phase is not concomitant with smectic A phase, and the temperature
range of both phases highly depends on the concentration of the comprising
compounds. Lowered melting temperatures have been observed for all mixtures
with respect to that of the pure compounds. Unforeseen finding is the induction
of a monotropic SmC phase in mixtures with lowest concentration of the
bent-core compound. Semi-empirical quantum-chemical calculations have also been
performed. Based on the calculated molecular conformation, as well as on
collected X-ray diffraction data, a model for a possible self-assembly of the
banana-shaped and calamitic compounds is proposed.",1407.7992v1
2014-11-15,Limitations of unconstrained LSDA+$U$ calculations in predicting the electronic and magnetic ground state of a geometrically frustrated ZnV$_{2}$O$_{4}$ compound,"In the present work, we investigate the applicability of the LSDA+$U$ method
in understanding the electronic and magnetic properties of a geometrically
frustrated ZnV$_2$O$_4$ compound, where the delicate balance of electrons,
lattice, orbital and spin interactions play an important role in deciding its
physical properties. In the ferromagnetic solution of the compound, only one
type of orbital solution is found to exist in all ranges of $U$ studied here.
However, in antiferromagnetic (AFM) phase, two types of orbital solutions,
AFM(OS1) and AFM(OS2), exist for $U >$3 eV. If the difference of the electronic
occupancy of $d_{xz}$ and $d_{yz}$ orbitals is less than 0.25, then AFM(OS1)
solution is stabilized, whereas for higher values AFM(OS2) solution is
stabilized. The use of unconstrained calculations within the fully localized
double counting scheme is unable to predict the AFM ground state for $U
\leqslant$3 eV. Our results clearly suggest the importance of constrained
calculations in understanding the electronic and magnetic properties of a
compound, where various competing interactions are present. In the AFM
solution, the orbital ground state of the compound changes with varying $U$,
where AFM(OS1) is found to be the ground state for $U \leqslant$3 eV and for
higher values of $U$, AFM(OS2) is the ground state. The analysis of the band
gap suggests that the AFM(OS2) is the real ground state of the compound.",1411.4119v2
2015-06-29,Compound surface-plasmon-polariton waves guided by a thin metal layer sandwiched between a homogeneous isotropic dielectric material and a periodically multilayered isotropic dielectric material,"Multiple p- and s-polarized compound surface plasmon-polariton (SPP) waves at
a fixed frequency can be guided by a structure consisting of a metal layer
sandwiched between a homogeneous isotropic dielectric (HID) material and a
periodic multilayered isotropic dielectric (PMLID) material. For any thickness
of the metal layer, at least one compound SPP wave must exist. It possesses the
p-polarization state, is strongly bound to the metal/HID interface when the
metal thickness is large but to both metal/dielectric interfaces when the metal
thickness is small. When the metal layer vanishes, this compound SPP wave
transmutes into a Tamm wave. Additional compound SPP waves exist, depending on
the thickness of the metal layer, the relative permittivity of the HID
material, and the period and the composition of the PMLID material. Some of
these are p polarized, the others being s polarized. All of them differ in
phase speed, attenuation rate, and field profile, even though all are excitable
at the same frequency. The multiplicity and the dependence of the number of
compound SPP waves on the relative permittivity of the HID material when the
metal layer is thin could be useful for optical sensing applications.",1506.08753v1
2015-10-01,Compound lensing: Einstein Zig-Zags and high multiplicity lensed images,"Compound strong gravitational lensing is a rare phenomenon, but a handful of
such lensed systems are likely to be discovered in forthcoming surveys. In this
work, we use a double SIS lens model to analytically understand how the
properties of the system impact image multiplicity for the final source. We
find that up to six images of a background source can form, but only if the
second lens is multiply imaged by the first and the Einstein radius of the
second lens is comparable to, but does not exceed that of the first. We then
build a model of compound lensing masses in the Universe, using SIE lenses, and
assess how the optical depth for multiple imaging by a galaxy-galaxy compound
lens varies with source redshift. For a source redshift of 4, we find optical
depths of $6 \times 10^{-6}$ for multiple imaging and $5 \times 10^{-8}$ for
multiplicity of 6 or greater. We find that extreme magnifications are possible,
with magnifications of 100 or more for $6 \times 10^{-9}$ of $z=10$ sources
with 0.1 kpc radii. We show some of the image configurations that can be
generated by compound lenses, and demonstrate that they are qualitatively
different to those generated by single-plane lenses; dedicated compound lens
finders will be necessary if these systems are to be discovered in forthcoming
surveys.",1510.00242v1
2016-04-08,Representing high throughput expression profiles via perturbation barcodes reveals compound targets,"High throughput mRNA expression profiling can be used to characterize the
response of cell culture models to perturbations such as pharmacologic
modulators and genetic perturbations. As profiling campaigns expand in scope,
it is important to homogenize, summarize, and analyze the resulting data in a
manner that captures significant biological signals in spite of various noise
sources such as batch effects and stochastic variation. We used the L1000
platform for large-scale profiling of 978 genes, chosen to be representative of
the genome as whole, across thousands of compound treatments. Here, a method is
described that uses deep learning techniques to convert the expression changes
of the landmark genes into a perturbation barcode that reveals important
features of the underlying data, performing better than the raw data in
revealing important biological insights. The barcode captures compound
structure and target information, in addition to predicting a compound's high
throughput screening promiscuity, to a higher degree than the original data
measurements, indicating that the approach uncovers underlying factors of the
expression data that are otherwise entangled or masked by noise. Furthermore,
we demonstrate that visualizations derived from the perturbation barcode can be
used to more sensitively assign functions to unknown compounds through a
guilt-by-association approach, which we use to predict and experimentally
validate the activity of compounds on the MAPK pathway. The demonstrated
application of deep metric learning to large-scale chemical genetics projects
highlights the utility of this and related approaches to the extraction of
insights and testable hypotheses from big, sometimes noisy data.",1604.02399v1
2016-11-16,Two-dimensional materials from high-throughput computational exfoliation of experimentally known compounds,"We search for novel two-dimensional materials that can be easily exfoliated
from their parent compounds. Starting from 108423 unique, experimentally known
three-dimensional compounds we identify a subset of 5619 that appear layered
according to robust geometric and bonding criteria. High-throughput
calculations using van-der-Waals density-functional theory, validated against
experimental structural data and calculated random-phase-approximation binding
energies, allow to identify 1825 compounds that are either easily or
potentially exfoliable, including all that are commonly exfoliated
experimentally. In particular, the subset of 1036 easily exfoliable
cases---layered materials held together mostly by dispersion interactions and
with binding energies up to $30-35$ meV$\cdot\text{\AA}^{-2}$---provides a
wealth of novel structural prototypes and simple ternary compounds, and a large
portfolio to search materials for optimal properties. For the 258 compounds
with up to 6 atoms per primitive cell we comprehensively explore vibrational,
electronic, magnetic, and topological properties, identifying in particular 56
ferromagnetic and antiferromagnetic systems, including half-metals and
half-semiconductors.",1611.05234v2
2017-11-19,Spin-order-induced multiferroicity in LiCuFe2(VO4)3 and disorder effects in NaCuFe2(VO4)3,"Mixed spin chain compounds, ACuFe2(VO4)3 (A= Li,Na), reach magnetically
ordered state at TN ~ 11 K (Li) or ~ 9 K (Na) and experience further
transformation of magnetic order at T* ~ 7 K (Li) or ~ 5 K (Na), evidenced in
magnetic susceptibility chi and specific heat Cp measurements. While no anomaly
has been detected in dielectric property of NaCuFe2(VO4)3, the step-like
feature precedes a sharp peak in permittivity epsilon at TN in LiCuFe2(VO4)3.
These data suggest the spin-order-induced ferroelectricity in Li compound and
no such thing in Na compound. On the contrary, the Moessbauer spectroscopy
study suggests similarly wide distribution of hyperfine field in between T* and
TN for both the compounds. The first principles calculations also provide
similar values for magnetic exchange interaction parameters in both compounds.
These observations lead us to conclude on the crucial role of alkali metals
mobility within the channels of the crystal structure needed to be considered
in explaining the improper multiferroicity in one compound and its absence in
other.",1711.06990v1
2017-11-20,Phonons and Anomalous Thermal Expansion Behaviour in Crystalline Solids,"Anomalous thermal expansion behaviour of several open frame-work compounds
has been extensively investigated using the techniques of inelastic neutron
scattering and lattice dynamics. These compounds involve increasing level of
structural complexity and flexibility, which leads to increased values of
thermal expansion coefficients approaching colossal values. In several
compounds, neutron inelastic scattering experiments have produced quantitative
estimates of the anharmonicity of phonons over a range of low energies, and
thereby explained the observed thermal expansion quantitatively. The
anharmonicity is found to be an order of magnitude larger than that in usual
materials. Lattice dynamical calculations have correctly predicted the observed
anharmonicity in the neutron experiments and revealed the overall nature of
phonons involved. In compounds showing negative thermal expansion, the phonons
responsible have rather low energies up to 10 meV. In most compounds, the
anharmonic phonons span all over the Brillouin zone, while in some cases the
specific phonons are limited to certain wave-vectors. The nature of specific
phonons responsible for anomalous behavior is found to be different in all
these compounds. These phonons generally involve transverse vibrations,
librations and internal distortions of the polyhedral units. The paper reviews
recent advances in the understanding of anomalous thermal expansion behaviour.",1711.07267v1
2021-07-19,Compound Figure Separation of Biomedical Images with Side Loss,"Unsupervised learning algorithms (e.g., self-supervised learning,
auto-encoder, contrastive learning) allow deep learning models to learn
effective image representations from large-scale unlabeled data. In medical
image analysis, even unannotated data can be difficult to obtain for individual
labs. Fortunately, national-level efforts have been made to provide efficient
access to obtain biomedical image data from previous scientific publications.
For instance, NIH has launched the Open-i search engine that provides a
large-scale image database with free access. However, the images in scientific
publications consist of a considerable amount of compound figures with
subplots. To extract and curate individual subplots, many different compound
figure separation approaches have been developed, especially with the recent
advances in deep learning. However, previous approaches typically required
resource extensive bounding box annotation to train detection models. In this
paper, we propose a simple compound figure separation (SimCFS) framework that
uses weak classification annotations from individual images. Our technical
contribution is three-fold: (1) we introduce a new side loss that is designed
for compound figure separation; (2) we introduce an intra-class image
augmentation method to simulate hard cases; (3) the proposed framework enables
an efficient deployment to new classes of images, without requiring resource
extensive bounding box annotations. From the results, the SimCFS achieved a new
state-of-the-art performance on the ImageCLEF 2016 Compound Figure Separation
Database. The source code of SimCFS is made publicly available at
https://github.com/hrlblab/ImageSeperation.",2107.08650v1
2021-07-28,Effect of transition metal doping on magnetic hardness of CeFe$_{12}$-based compounds,"In this work, compositions of CeFe11X and CeFe10X2 with all 3d, 4d, and 5d
transition metal substitutions are considered. Since many previous studies have
focused on the CeFe11Ti compound, this particular compound became the starting
point of our considerations and we gave it special attention. We first
determined the optimal symmetry of the simplest CeFe11Ti structure model. We
then observed that the calculated magnetocrystalline anisotropy energy (MAE)
correlates with the magnetic moment, which in turn strongly depends on the
choice of the exchange-correlation potential. MAE, magnetic moments, and
magnetic hardness were determined for all compositions considered. Moreover,
the calculated dependence of the MAE on the spin magnetic moment allowed us to
predict the upper limits of the MAE. We also showed that it does not depend on
the choice of the exchange-correlation potential form. The economically
justifiable compositions with the highest magnetic hardness values are CeFe11W,
CeFe10W2, CeFe11Mn, CeFe10Mn2, CeFe11Mo, CeFe10Mo2, and CeFe10Nb2. However,
calculations suggest that, like CeFe12, these compounds are not chemically
stable and could require additional treatments to stabilize the composition.
Further alloying of the selected compositions with elements embedded in
interstitial positions confirms the positive effect of such dopants on hard
magnetic properties. Subsequent calculations performed for comparison for
selected isostructural La-based compounds lead to similar MAE results as for
Ce-based compounds, suggesting a secondary effect of 4f electrons. Calculations
were performed using the full-potential local-orbital electronic structure code
FPLO18, whose unique fully relativistic implementation of the fixed spin moment
method allowed us to calculate the MAE dependence of the magnetic moment.",2107.13352v3
2018-09-28,Domain-Adversarial Multi-Task Framework for Novel Therapeutic Property Prediction of Compounds,"With the rapid development of high-throughput technologies, parallel
acquisition of large-scale drug-informatics data provides huge opportunities to
improve pharmaceutical research and development. One significant application is
the purpose prediction of small molecule compounds, aiming to specify
therapeutic properties of extensive purpose-unknown compounds and to repurpose
novel therapeutic properties of FDA-approved drugs. Such problem is very
challenging since compound attributes contain heterogeneous data with various
feature patterns such as drug fingerprint, drug physicochemical property, drug
perturbation gene expression. Moreover, there is complex nonlinear dependency
among heterogeneous data. In this paper, we propose a novel domain-adversarial
multi-task framework for integrating shared knowledge from multiple domains.
The framework utilizes the adversarial strategy to effectively learn target
representations and models their nonlinear dependency. Experiments on two
real-world datasets illustrate that the performance of our approach obtains an
obvious improvement over competitive baselines. The novel therapeutic
properties of purpose-unknown compounds we predicted are mostly reported or
brought to the clinics. Furthermore, our framework can integrate various
attributes beyond the three domains examined here and can be applied in the
industry for screening the purpose of huge amounts of as yet unidentified
compounds. Source codes of this paper are available on Github.",1810.00867v1
2019-01-16,"Magnetic properties of double perovskite $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho): hetero-tri-spin $3d$-$5d$-$4f$ systems","The field of double perovskites is now advancing to three magnetic elements
on the A, B and B$'$ sites. A series of iridium-based double perovskite
compounds, $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho) with three magnetic elements
were synthesized as polycrystalline samples. The compounds crystalize in
monoclinic structures with the space group $P2_1/n$. Magnetic properties of
these hetero-tri-spin $3d$-$5d$-$4f$ systems were studied by magnetic
susceptibility and field dependent magnetization in both DC and pulsed magnetic
fields. All these compounds show ferrimagnetic transitions at temperatures
$T_C$ above 100 K, which are attributable to antiferromagnetic coupling between
Co$^{2+}$ and Ir$^{4+}$ spins. For Eu$_2$CoIrO$_6$, the magnetic properties are
similar to those of La$_2$CoIrO$_6$. The Eu$^{3+}$ spins show Van Vleck
paramagnetism that don't significantly interact with transition-metal cations.
By contrast, Tb$_2$CoIrO$_6$ and Ho$_2$CoIrO$_6$ reveal a second transition to
antiferromagnetic order below a lower temperature $T_N$. The
temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might
be explained by a spin-reorientation transition. Moreover, a
magnetic-field-induced spin-flop transition with a small hysteresis was
observed below $T_N$ in these two compounds. The magnetic moment of all three
compounds do not saturate up to 60 T at low temperatures. Moderate
magnetocaloric effect was also observed in all three compounds. Our results
should motivate further investigation of the spin configuration on single
crystals of these iridium-based double perovskites.",1901.05412v1
2019-04-21,Compound chondrule formation in optically thin shock waves,"Shock-wave heating within the solar nebula is one of the leading candidates
for the source of chondrule-forming events. Here, we examine the possibility of
compound chondrule formation via optically thin shock waves. Several features
of compound chondrules indicate that compound chondrules are formed via the
collisions of supercooled precursors. We evaluate whether compound chondrules
can be formed via the collision of supercooled chondrule precursors in the
framework of the shock-wave heating model by using semi-analytical methods and
discuss whether most of the crystallized chondrules can avoid destruction upon
collision in the post-shock region. We find that chondrule precursors
immediately turn into supercooled droplets when the shock waves are optically
thin and they can maintain supercooling until the condensation of evaporated
fine dust grains. Owing to the large viscosity of supercooled melts,
supercooled chondrule precursors can survive high-speed collisions on the order
of $1\ {\rm km}\ {\rm s}^{-1}$ when the temperature is below $\sim 1400\ {\rm
K}$. From the perspective of the survivability of crystallized chondrules,
shock waves with a spatial scale of $\sim 10^{4}\ {\rm km}$ may be potent
candidates for the chondrule formation mechanism. Based on our results from
one-dimensional calculations, a fraction of compound chondrules can be
reproduced when the chondrule-to-gas mass ratio in the pre-shock region is
$\sim 2 \times 10^{-3}$, which is approximately half of the solar metallicity.",1904.09580v1
2018-08-26,Phase transition in CaFeAsH: bridging 1111 and 122 iron-based superconductors,"Iron-based superconductors can be categorized as two types of parent
compounds by considering the nature of their temperature-induced phase
transitions; namely, first order transitions for 122- and 11-type compounds and
second-order transitions for 1111-type compounds. This work examines the
structural and magnetic transitions (ST and MT) of CaFeAsH by specific heat,
X-ray diffraction, neutron diffraction, and electrical resistivity
measurements. Heat capacity measurements revealed a second-order phase
transition accompanies an apparent single peak at 96 K. However, a clear ST
from the tetragonal to orthorhombic phase and a MT from the paramagnetic to
antiferromagnetic phase were detected. The structural (Ts) and N\'eel
temperatures (TN) were respectively determined to be 95(2) and 96 K by X-ray
and neutron diffraction and resistivity measurements. This small temperature
difference, Ts - TN, was attributed to strong magnetic coupling in the
inter-layer direction owing to CaFeAsH having the shortest lattice constant c
among parent 1111-type iron arsenides. Considering that a first-order
transition takes place in 11- and 122-type compounds with a short inter-layer
distance, we conclude that the nature of the ST and MT in CaFeAsH is
intermediate in character, between the second-order transition for 1111-type
compounds and the first-order transition for other 11- and 122-type compounds.",1808.08564v1
2020-08-12,"Investigation of the lead-free double perovskites Cs2AgSbX6 (X= Cl, Br, I) for optoelectronic and thermoelectric applications","Perovskite compounds have the potential to harvest solar energy as well as
exploit the thermoelectric potential of a number of available materials. Here,
we present the electronic, structural, thermoelectric, and optical properties
of Cs2AgSbX6 (X = Cl, Br, I) perovskite with the help of the density functional
theory (DFT). The WC-GGA approximation was used to calculate the structural
parameters. All these compounds crystalize in a cubic unit cell with lattice
constant increasing from 10.65 {\AA} (Cl) to 11.14 {\AA} (Br) to 11.86 {\AA}
(I). The mBJ-functional shows a semiconducting nature for these compounds with
an indirect band gap lying at the L-X symmetry points. The optical conductivity
and absorption coefficient show their peaks in the ultraviolet region, moving
towards a lower energy range by inserting large size anion. The band gap of
these compounds (2.08, 1.37, 0.64 eV) indicates their potential in single and
multijunction solar cells. The value of refractive index at zero energy was
evaluated to be 3.1, 2.2, and 1.97 for Cs2AgSbCl6, Cs2AgSbBr6 and Cs2AgSbI6.
Effective mass of electrons is smaller than those of holes resulting in higher
carrier mobility for electrons. The Seebeck coefficient, power factor, and the
figure of merit were computed using the BoltzTrap code. The negative
temperature coefficient of resistivity also supports the semiconductor nature
of these compounds. The high electrical, small thermal conductivity, positive
Seebeck coefficient, and the optimum figure of merit make these compounds
suitable for thermoelectric applications.",2008.06384v3
2021-03-13,Dilute dispersion of compound particles: deformation dynamics and rheology,"Compound particles are a class of composite systems in which solid particles
encapsulated in a fluid droplet are suspended in another fluid. They are
encountered in various natural and biological processes, for e.g., nucleated
cells, hydrogels, microcapsules etc. In this work, we analyze the flow in and
around a concentric compound particle and investigate the deformation and
reorientation dynamics of the confining drop and its stability against breakup
in imposed linear flows. We obtain analytical expressions for the flow fields
upto O(Ca) (capillary number) and the deformed shape of the confining drop upto
O(Ca^2) using a domain perturbation technique. Further, we develop an O(Ca)
constitutive equation for the volume-averaged stress for a dilute dispersion of
compound particles. Compared to linear theory, O(Ca^2) calculations are found
to be important as they make qualitatively different predictions in some linear
flows. We find that the strong hydrodynamic interaction between the
encapsulated particle and the confining interface results in an increased
deformation of the confining drop compared to that of a simple drop, and
enhances the rheological quantities such as the effective shear viscosity,
extensional viscosity, and normal stress differences in a dilute dispersion.
These measures pertaining to particles, drops, and particles coated with a
fluid film are also derived as limiting cases of compound particles. Moreover,
linear viscoelastic behavior of a dilute dispersion of compound particles is
characterized in terms of complex modulus by subjecting the dispersion to a
small amplitude oscillatory shear flow.",2103.07664v1
2019-03-18,Optical and electronic properties in ferroelectric barium titanate-based compounds,"The bandgap energy values for the ferroelectric BaTiO3-based solid solutions
with isovalent substitution Ba1-x SrxTiO3, BaZrxTi1-xO3 and BaSnxTi1-xO3 were
determined using diffuse reflectance spectra. While the corresponding unit cell
volume follows Vegard's law in accordance with the different ionic radii of the
ionic substitutions, the bandgap values depict non-linear compositional
dependences for all the solid solutions. The effect is considerably large for
BaZrxTi1-xO3 and BaSnxTi1-xO3 solutions, depicting a bandgap linear
compositional dependence up to x=0.6, for x>0.6 BaZrxTi1-xO3 compounds present
much larger bandgap values than BaSnxTi1-xO3 counterparts. Electronic
properties have been investigated through X-ray photoelectron spectroscopy in
BaSnxTi1-xO3 compounds, indicating that the Sn 3d and Ti 2p core levels shift
against the Ba 3d ones within the whole compositional range with the same
energy trend as that observed for the optical bandgap. Since for Ba1-x SrxTiO3
compounds no major bandgap variation is observed, we conclude that the bandgap
compositional dependences observed for BaSnxTi1-xO3 compounds and BaZrxTi1-xO3
ones are originated from the structural sensitivity of the O, Ti and Sn or Zr
electronic bands involved in the bandgap transition of these compounds. With
this work, we underline the reliability of the bandgap determined from diffuse
reflectance spectrometry experiments, as a means to non-invasively evaluate the
electronic properties of powder materials.",1903.07443v1
2019-05-30,High Performance Ternary Alkali Nitrides for Renewable Energy Applications,"Rapid decline in fossil fuel energy necessitates the immediate need for
renewable energy resources. Here, we report a previously unexplored class of
nitrides AMN$_2$ keeping renewable energy applications in mind. Using a
detailed structure and stability analysis using first principles simulation, we
discovered twelve such compounds (few of which are already synthesized before),
which are chemically, mechanically and dynamically stable. These twelve
compounds were then evaluated for their suitability for three renewable energy
applications, (i) photovoltaics, (ii) water splitting, and (iii)
thermoelectrics. Careful analysis of electronic structure reveals high optical
transition strength resulting in sharp rise in absorption. This in turn yields
high short circuit current and hence excellent solar efficiency for few
compounds namely CsVN$_2$ and RbVN$_2$. Along with excellent absorption
quality, some compounds show favorable band edge positions compared to water
redox levels and hence are promising as photoelectrodes in
photo(electro)chemical water splitting devices. Mixture of flat and dispersive
bands in the band structure yields both high Seebeck and electrical
conductivity, thus excellent power factor for seven compounds. Simulated
lattice thermal conductivity shows moderate to ultralow values and thus the
possibility of achieving high thermoelectric figure of merit (ZT), even at
lower temperatures. From the experimental perspective, we discuss the possible
challenges that may arise while utilizing these compounds for the desired
applications, and suggest possible pathways to overcome them. We believe such
theoretical prediction of promising materials are extremely useful for new
materials discovery and anticipate rapid response from the experimental
community.",1905.13069v2
2020-02-23,ChemGrapher: Optical Graph Recognition of Chemical Compounds by Deep Learning,"In drug discovery, knowledge of the graph structure of chemical compounds is
essential. Many thousands of scientific articles in chemistry and
pharmaceutical sciences have investigated chemical compounds, but in cases the
details of the structure of these chemical compounds is published only as an
images. A tool to analyze these images automatically and convert them into a
chemical graph structure would be useful for many applications, such drug
discovery. A few such tools are available and they are mostly derived from
optical character recognition. However, our evaluation of the performance of
those tools reveals that they make often mistakes in detecting the correct bond
multiplicity and stereochemical information. In addition, errors sometimes even
lead to missing atoms in the resulting graph. In our work, we address these
issues by developing a compound recognition method based on machine learning.
More specifically, we develop a deep neural network model for optical compound
recognition. The deep learning solution presented here consists of a
segmentation model, followed by three classification models that predict atom
locations, bonds and charges. Furthermore, this model not only predicts the
graph structure of the molecule but also produces all information necessary to
relate each component of the resulting graph to the source image. This solution
is scalable and could rapidly process thousands of images. Finally, we compare
empirically the proposed method to a well-established tool and observe
significant error reductions.",2002.09914v1
2020-06-11,Targeting Receptor Binding Domain and Cryptic Pocket of Spike glycoprotein from SARS-CoV-2 by biomolecular modeling,"SARS-CoV-2, the causative agent of the disease known as Covid-19, has so far
reported around 3,435,000 cases of human infections, including more than
239,000 deaths in 187 countries, with no effective treatment currently
available. For this reason, it is necessary to explore new approaches for the
development of a drug capable of inhibiting the entry of the virus into the
host cell. Therefore, this work includes the exploration of potential
inhibitory compounds for the Spike protein of SARS-CoV-2 (PDB ID: 6VSB), which
were obtained from The Patogen Box. Later, they were filtered through virtual
screening and molecular docking techniques, thus obtaining a top of 1000
compounds, which were used against a binding site located in the Receptor
Binding Domain (RBD) and a cryptic site located in the N-Terminal Domain (NTD),
resulting in good pharmaceutical targets for the blocking the infection. From
the top 1000, the best compound (TCMDC-124223) was selected for the binding
site. It interacts with specific residues that intervene in the recognition and
subsequent entry into the host cell, resulting in a more favorable binding free
energy in comparison to the control compounds (Hesperidine and Emodine). In the
same way, the compound TCMDC-133766 was selected for the cryptic site. These
identified compounds are potential inhibitors that can be used for the
development of new drugs that allow effective treatment for the disease.",2006.06452v1
2020-09-05,Analysis and representation of Igbo text document for a text-based system,"The advancement in Information Technology (IT) has assisted in inculcating
the three Nigeria major languages in text-based application such as text
mining, information retrieval and natural language processing. The interest of
this paper is the Igbo language, which uses compounding as a common type of
word formation and as well has many vocabularies of compound words. The issues
of collocation, word ordering and compounding play high role in Igbo language.
The ambiguity in dealing with these compound words has made the representation
of Igbo language text document very difficult because this cannot be addressed
using the most common and standard approach of the Bag-Of-Words (BOW) model of
text representation, which ignores the word order and relation. However, this
cause for a concern and the need to develop an improved model to capture this
situation. This paper presents the analysis of Igbo language text document,
considering its compounding nature and describes its representation with the
Word-based N-gram model to properly prepare it for any text-based application.
The result shows that Bigram and Trigram n-gram text representation models
provide more semantic information as well addresses the issues of compounding,
word ordering and collocations which are the major language peculiarities in
Igbo. They are likely to give better performance when used in any Igbo
text-based system.",2009.06376v1
2020-09-30,"Ab initio study of structural, electronic and magnetic properties of XSn$_3$ (X = Gd, Cm) and Gd$_x$Cm$_{1-x}$Sn$_3$ compounds","In this paper, the structural, electronic and magnetic properties of the
GdSn$_3$, CmSn$_3$ and Gd$_x$Cm$_{1-x}$Sn$_3$ compounds ($x = 0.25$, $0.5$ and
$0.75$) were studied using the full-potential linearized augmented plane wave
method, within the generalized gradient approximation$+U$. The ground-state
properties are determined for the bulk materials GdSn$_3$, CmSn$_3$ and
Gd$_x$Cm$_{1-x}$Sn$_3$ crystallized in AuCu$_3$-type structure. The calculated
structural, electronic and magnetic properties of GdSn$_3$ compound are in good
agreement with the existing experimental and theoretical data. It is found that
the most stable magnetic configurations of both compounds CmSn$_3$ and GdSn$_3$
are anti-ferromagnetic type A (AFM-A) and have a metallic behavior. The
magnetic moment found decreases with increasing the Cm composition in
Gd$_x$Cm$_{1-x}$Sn$_3$ compounds. The results show that the GdSn$_3$, CmSn$_3$
and Gd$_x$Cm$_{1-x}$Sn$_3$ compounds share some properties, and may well be
useful for spintronic applications.",2009.14708v2
2020-11-23,Microalgae-based bioremediation of water contaminated by pesticides in peri-urban agricultural areas,"The present study evaluated the capacity of a semi-closed, tubular horizontal
photobioreactor (PBR) to remove pesticides from agricultural run-off. The study
was carried out in July to study its efficiency under the best conditions
(highest solar irradiation). A total of 51 pesticides, including 10
transformation products, were selected and investigated based on their
consumption rate and environmental relevance. Sixteen of them were detected in
the agricultural run-off, and the estimated removal efficiencies ranged from
negative values, obtained for 3 compounds, namely terbutryn, diuron, and
imidacloprid, to 100%, achieved for 10 compounds. The acidic herbicide MCPA was
removed by 88% on average, and the insecticides 2,4-D and diazinon showed
variable removals, between 100% and negative values. The environmental risk
associated with the compounds still present in the effluent of the PBR was
evaluated using hazard quotients (HQs), calculated using the average and
highest measured concentrations of the compounds. HQ values > 10 (meaning high
risk) were obtained for imidacloprid (21), between 1 and 10 (meaning moderate
risk) for 2,4-D (2.8), diazinon (4.6) and terbutryn (1.5), and < 1 (meaning low
risk) for the remaining compounds diuron, linuron, and MCPA. The PBR treatment
yielded variable removals depending on the compound, similar to conventional
wastewater treatment plants. This study provides new data on the capacity of
icroalgae-based treatment systems to eliminate a wide range of priority
pesticides under real/environmental conditions.",2011.11546v1
2021-01-15,Production of super-heavy nuclei in cold fusion reactions,"The model for the cold-fusion reactions related to the synthesis of
super-heavy nuclei in collisions of heavy projectile-nuclei with $^{208}$Pb
target nucleus is discussed. In the framework of this model the production of
the compound nucleus by two paths through, the di-nuclear system and the fusion
way, are taken into account simultaneously. The formation of the compound
nucleus in the framework of the di-nuclear system is related to the transfer of
nucleons from the light nucleus to the heavy one. The fusion way is linked to
the sequential evolution of the nuclear shape from the system of contacting
nuclei to the compound nucleus. It is shown that the compound nucleus is mainly
formed by the fusion way in the cold-fusion reactions. The landscape of the
potential energy related to the fusion path is discussed in detail. This
landscape for very heavy nucleus-nucleus systems has the intermediate state,
which is linked to the formation of both the compound nucleus and the
quasi-fission fragments. The decay of the intermediate state is taken into
account in the calculation of the compound nucleus production cross sections
and the quasi-fission cross sections. The values of the cold-fusion cross
sections obtained in the model are well agreed with the experimental data.",2101.06037v1
2021-08-25,Magnetic properties of BiFeO$_3$-BaTiO$_3$ ceramics in the morphotropic phase boundary: a role of crystal structure and structural parameters,"A correlation between the crystal structure and magnetic properties of system
(1-x)BiFeO$_3$-(x)BaTiO$_3$ with compounds across the morphotropic phase
boundary was studied using X-ray and neutron diffraction, magnetometry, and
Mossbauer spectroscopy measurements. Increase in the dopants content leads to
the structural transition from the rhombohedral phase to the cubic phase via a
formation of the two-phase region (0.2 < x < 0.33), wherein the magnetic
structure changes from the modulated G-type antiferromagnetic to the collinear
antiferromagnetic via a stabilization of the non-collinear antiferromagnetic
phase with non-zero remanent magnetization. The value of magnetic moment
calculated per iron ion based on the Mossbauer and neutron diffraction data
decreases from m = 4.4 mB for the compound with x=0.25 to m=3.2 mB for the
compound with x=0.35 testifying a dominance of 3+ oxidation state of the iron
ions. Increase in the amount of the cubic phase leads to a reduction in the
remanent magnetization from 0.02 emu.g for the compounds with the dominant
rhombohedral phase (x < 0.27) down to about 0.001 emu/g for the compounds with
dominant cubic structure (x >= 0.27). Rapid decrease in the remanent
magnetization observed in the compounds across the phase coexistence region
points at no direct correlation between the type of structural distortion and
non-zero remanent magnetization, while the oxygen octahedra tilting is the key
factor determining the presence of non-zero remanent magnetization.",2108.11447v1
2022-08-30,Tailoring Molecules for Protein Pockets: a Transformer-based Generative Solution for Structured-based Drug Design,"Structure-based drug design is drawing growing attentions in computer-aided
drug discovery. Compared with the virtual screening approach where a
pre-defined library of compounds are computationally screened, de novo drug
design based on the structure of a target protein can provide novel drug
candidates. In this paper, we present a generative solution named TamGent
(Target-aware molecule generator with Transformer) that can directly generate
candidate drugs from scratch for a given target, overcoming the limits imposed
by existing compound libraries. Following the Transformer framework (a
state-of-the-art framework in deep learning), we design a variant of
Transformer encoder to process 3D geometric information of targets and
pre-train the Transformer decoder on 10 million compounds from PubChem for
candidate drug generation. Systematical evaluation on candidate compounds
generated for targets from DrugBank shows that both binding affinity and
drugability are largely improved. TamGent outperforms previous baselines in
terms of both effectiveness and efficiency. The method is further verified by
generating candidate compounds for the SARS-CoV-2 main protease and the
oncogenic mutant KRAS G12C. The results show that our method not only
re-discovers previously verified drug molecules , but also generates novel
molecules with better docking scores, expanding the compound pool and
potentially leading to the discovery of novel drugs.",2209.06158v1
2022-11-02,Virtual screening of DrugBank database for hERG blockers using topological Laplacian-assisted AI models,"The human {\it ether-a-go-go} (hERG) potassium channel (K$_\text{v}11.1$)
plays a critical role in mediating cardiac action potential. The blockade of
this ion channel can potentially lead fatal disorder and/or long QT syndrome.
Many drugs have been withdrawn because of their serious hERG-cardiotoxicity. It
is crucial to assess the hERG blockade activity in the early stage of drug
discovery. We are particularly interested in the hERG-cardiotoxicity of
compounds collected in the DrugBank database considering that many DrugBank
compounds have been approved for therapeutic treatments or have high potential
to become drugs. Machine learning-based in silico tools offer a rapid and
economical platform to virtually screen DrugBank compounds. We design accurate
and robust classifiers for blockers/non-blockers and then build regressors to
quantitatively analyze the binding potency of the DrugBank compounds on the
hERG channel. Molecular sequences are embedded with two natural language
processing (NPL) methods, namely, autoencoder and transformer. Complementary
three-dimensional (3D) molecular structures are embedded with two advanced
mathematical approaches, i.e., topological Laplacians and algebraic graphs.
With our state-of-the-art tools, we reveal that 227 out of the 8641 DrugBank
compounds are potential hERG blockers, suggesting serious drug safety problems.
Our predictions provide guidance for the further experimental interrogation of
DrugBank compounds' hERG-cardiotoxicity .",2211.00861v1
2022-12-06,Novel superhard structures of high-pressure C-N compounds,"Through machine learning force field accelerated structure search combined
with first-principles calculations, we have studied the structures of new C-N
compounds with different stoichiometric ratios, and found twelve new superhard
C-N compounds, the energies of these structures are similar to c-C3N4 , which
is possibly synthesized by high pressure experiment, the XRD of Pa-3(C4N)
P3(C4N) and C2/m(C2N) are consistent with previous experimental data and can be
used as the structural candidate. According to the macro hardness model, they
are all superhard structures, with Vickers hardness over 40GPa, even, the
hardness of Pa-3 (C4N) as high as 82.2GPa, and Pa-3 (C4N) combines high tensile
and shear resistance. Compared with the hardness calculated by macro hardness
model and bond resistance model, we obtained the relationship between the
hardness and chemical concentration of C-N compounds under the two models,
besides that, we also calculated the fracture toughness of these structures.
According to Niu's model, P2_1/c(C4N) has the best fracture toughness, which is
higher than WC in calculation, This also indicated the superior mechanical
properties of the novel C-N compounds. Moreover, for nitrogen-rich structures,
they have the potential to be used as high energy density, the energy density
of Pa-3(CN3), P-3c1 (CN4), and I-42d (CN4) are 7.076kJ/g, 7.742kJ/g and
8.045kJ/g, which is close or higher than CL-20, therefore, the C-N compounds
synthesized under high pressure have great potential as ideally superhard
materials and high energy density materials(HEDMs).",2212.03009v3
2023-02-24,Effect of hydrostatic strain on the mechanical properties and topological phase transition of bi-alkali pnictogen NaLi$_{2}$Bi,"The bi-alkali pnictogens have attracted significant attention for
optoelectronic and photocathodic device applications. However, in most of the
compounds belonging to this family, there has been less effort put into
investigating the mechanical properties and topological phase transitions (TPT)
of the compounds. Here, in the framework of density functional theory, the
mechanical properties and topological phase transition of NaLi$_{2}$Bi under
hydrostatic pressures are investigated. Elastic constants and phonon
calculations have shown the mechanical and dynamical stability of this compound
under hydrostatic tension and compression. The analysis of the elastic
constants shows that the NaLi$_{2}$Bi in the equilibrium state is an auxetic
material with a negative Poisson's ratio of -0.285, which changes to a material
with a positive Poisson's ratio under hydrostatic tension. Meanwhile, Poisson's
ratio and Pugh ratio indicate that this compound has brittle behavior and
maintains it under hydrostatic pressures. The calculated results of the band
structure within the generalized gradient approximation (GGA) (Tran-Blaha
modified Becke-Johnson exchange potential approximation (TB-mBJ)) show that
NaLi$_{2}$Bi is a nontrivial topological material (trivial topological
material). It was found that hydrostatic compression (tension) in the GGA
(TB-mBJ) approach leads to a transition from a nontrivial (trivial) to a
trivial (nontrivial) topological phase for this compound. Moreover, the
calculated Wannier charge centers confirm the TPT. Identifying the mechanisms
controlling the auxetic behavior and TPT of this compound offers a valuable
feature for designing and developing high-performance nanoscale
electromechanical and spintronic devices.",2302.12605v1
2023-03-01,Machine-learning Repurposing of DrugBank Compounds for Opioid Use Disorder,"Opioid use disorder (OUD) is a chronic and relapsing condition that involves
the continued and compulsive use of opioids despite harmful consequences. The
development of medications with improved efficacy and safety profiles for OUD
treatment is urgently needed. Drug repurposing is a promising option for drug
discovery due to its reduced cost and expedited approval procedures.
Computational approaches based on machine learning enable the rapid screening
of DrugBank compounds, identifying those with the potential to be repurposed
for OUD treatment. We collected inhibitor data for four major opioid receptors
and used advanced machine learning predictors of binding affinity that fuse the
gradient boosting decision tree algorithm with two natural language processing
(NLP)-based molecular fingerprints and one traditional 2D fingerprint. Using
these predictors, we systematically analyzed the binding affinities of DrugBank
compounds on four opioid receptors. Based on our machine learning predictions,
we were able to discriminate DrugBank compounds with various binding affinity
thresholds and selectivities for different receptors. The prediction results
were further analyzed for ADMET (absorption, distribution, metabolism,
excretion, and toxicity), which provided guidance on repurposing DrugBank
compounds for the inhibition of selected opioid receptors. The pharmacological
effects of these compounds for OUD treatment need to be tested in further
experimental studies and clinical trials. Our machine learning studies provide
a valuable platform for drug discovery in the context of OUD treatment.",2303.00240v1
2023-05-23,Multi-BVOC Super-Resolution Exploiting Compounds Inter-Connection,"Biogenic Volatile Organic Compounds (BVOCs) emitted from the terrestrial
ecosystem into the Earth's atmosphere are an important component of atmospheric
chemistry. Due to the scarcity of measurement, a reliable enhancement of BVOCs
emission maps can aid in providing denser data for atmospheric chemical,
climate, and air quality models. In this work, we propose a strategy to
super-resolve coarse BVOC emission maps by simultaneously exploiting the
contributions of different compounds. To this purpose, we first accurately
investigate the spatial inter-connections between several BVOC species. Then,
we exploit the found similarities to build a Multi-Image Super-Resolution
(MISR) system, in which a number of emission maps associated with diverse
compounds are aggregated to boost Super-Resolution (SR) performance. We compare
different configurations regarding the species and the number of joined BVOCs.
Our experimental results show that incorporating BVOCs' relationship into the
process can substantially improve the accuracy of the super-resolved maps.
Interestingly, the best results are achieved when we aggregate the emission
maps of strongly uncorrelated compounds. This peculiarity seems to confirm what
was already guessed for other data-domains, i.e., joined uncorrelated
information are more helpful than correlated ones to boost MISR performance.
Nonetheless, the proposed work represents the first attempt in SR of BVOC
emissions through the fusion of multiple different compounds.",2305.14180v3
2023-06-04,"Ab-initio insights into the structural, elastic, bonding, and thermophysical properties of UHx (x = 1, 2, 3, 5, 6, 7, 8) under pressure: possible relevance to high-Tc superconductivity","Binary uranium hydrides, UHx (x = 1, 2, 3, 5, 6, 7, 8), with different
crystal symmetries are potentially interesting compounds for high-Tc
superconductivity and as hydrogen storage systems. In this work we have
explored the structural, elastic, mechanical, bonding, and thermophysical
properties of these systems under uniform pressure via density functional
theory based computations. Most of the results disclosed in this work are
novel. From the calculations of the cohesive energy and enthalpy of formation,
we have found that the titled compounds are chemically stable. The computed
elastic constants at different pressures ensure elastic stability. All the
binary hydrides are mechanically anisotropic. Pressure induced brittle-ductile
transition takes place under high pressure. The compounds are machinable with
the cubic {\alpha}-UH3-Pm-3n showing very high value of the machinability
index. All the compounds are fairly hard with cubic UH8 showing superhard
character. The Debye temperatures and acoustic velocities of these compounds
are high; the highest value is found for the cubic UH8. The melting
temperature, Gr\""uneisen parameter, minimal phonon thermal conductivity, and
the thermal expansion coefficient of these compounds have also been studied at
different pressures. All these parameters show excellent correspondence with
the estimated Debye temperature, elastic parameters and bonding
characteristics.",2306.02269v1
2023-08-01,Data Collaboration Analysis applied to Compound Datasets and the Introduction of Projection data to Non-IID settings,"Given the time and expense associated with bringing a drug to market,
numerous studies have been conducted to predict the properties of compounds
based on their structure using machine learning. Federated learning has been
applied to compound datasets to increase their prediction accuracy while
safeguarding potentially proprietary information. However, federated learning
is encumbered by low accuracy in not identically and independently distributed
(non-IID) settings, i.e., data partitioning has a large label bias, and is
considered unsuitable for compound datasets, which tend to have large label
bias. To address this limitation, we utilized an alternative method of
distributed machine learning to chemical compound data from open sources,
called data collaboration analysis (DC). We also proposed data collaboration
analysis using projection data (DCPd), which is an improved method that
utilizes auxiliary PubChem data. This improves the quality of individual
user-side data transformations for the projection data for the creation of
intermediate representations. The classification accuracy, i.e., area under the
curve in the receiver operating characteristic curve (ROC-AUC) and AUC in the
precision-recall curve (PR-AUC), of federated averaging (FedAvg), DC, and DCPd
was compared for five compound datasets. We determined that the machine
learning performance for non-IID settings was in the order of DCPd, DC, and
FedAvg, although they were almost the same in identically and independently
distributed (IID) settings. Moreover, the results showed that compared to other
methods, DCPd exhibited a negligible decline in classification accuracy in
experiments with different degrees of label bias. Thus, DCPd can address the
low performance in non-IID settings, which is one of the challenges of
federated learning.",2308.00280v1
2023-09-28,"Ab-initio insights into the physical properties of XIr3 (X = La, Th) superconductors: A comparative analysis","Here we report the structural, elastic, bonding, thermo-mechanical,
optoelectronic and superconducting state properties of recently discovered XIr3
(X = La, Th) superconductors utilizing the density functional theory (DFT). The
elastic, bonding, thermal and optical properties of these compounds are
investigated for the first time. The calculated lattice and superconducting
state parameters are in reasonable agreement to those found in the literature.
In the ground state, both the compounds are mechanically stable and possess
highly ductile character, high machinability, low Debye temperature, low bond
hardness and significantly high melting point. The thermal conductivities of
the compounds are found to be very low which suggests that they can be used for
thermal insulation purpose. The population analysis and charge density
distribution map confirm the presence of both ionic and covalent bonds in the
compounds with ionic bond playing dominant roles. The calculated band structure
and DOS profiles indicate metallic character. Unlike the significant anisotropy
observed in elastic and thermal properties, all the optical constants of these
compounds exhibit almost isotropic behavior. The optical constants correspond
very well with the electronic band structure and DOS features. We have
estimated the superconducting transition temperature of the compounds in this
work.",2309.16151v1
2023-10-03,Magnetic phenomena in equiatomic ternary rare earth compounds,"The chapter discusses the structural and magnetic properties of equiatomic
ternary RTX compounds, where R represents rare earth, T is transition metal,
and X belongs to the p block elements. RTX compounds exhibit a variety of
crystal structures, which leads to a range of magnetic phenomenon ranging from
long range antiferromagnetic-ferromagnetic ordering, unconventional
superconductivity, magnetic frustration to spin ices. Coexistence of various
magnetic phenomenon result in many exotic properties, which make these
materials promising for next generation technological applications. In RTX
family of compounds, most transition metals, except manganese, Mn do not
contribute significantly to the magnetic moment and behave as non-magnetic. The
lack of magnetic behaviour in the transition metal sublattices of these ternary
compounds may be attributed to hybridization between p electron states of X
atom and d electron states of the transition metal, resulting in the filling of
the d band. The dominant interaction in these compounds is of Ruderman Kittel
Kasuya Yosida type due to the localized nature of the 4f electrons in the rare
earths. The magnetic transition temperature in these materials varies from
ultra-low to high temperatures, making them suitable for integration into
devices operating at room temperature. The RTX series discussed here
encompasses all rare earth elements, a range of transition metals, and various
p-block elements such as Al, Ga, In, Si, Ge, Sn, Sb, and Bi. Most of the
materials studied are arc melted polycrystalline materials with some in the
form of single crystal or thin films.",2310.02103v1
2023-11-09,"High-frequency dielectric anomalies in a highly frustrated square kagome lattice nabokoite family compounds ACu$_7$(TeO$_4$)(SO$_4$)$_5$Cl (A=Na, K, Rb, Cs)","Nabokoite family compounds ACu$_7$(TeO$_4$)(SO$_4$)$_5$Cl (A=Na, K, Cs, Rb)
are candidates for the experimental realization of highly-frustrated 2D square
kagome lattice (SKL). Their magnetic subsystem includes SKL layers decorated by
additional copper ions. All members of this family are characterized by quite
high Curie-Weiss temperatures ($\sim 80-200$ K), but magnetic ordering was
reported only for Na and K compounds at a much lower temperatures below 4 K. We
report here results of the study of high-frequency ($\sim 10$ GHz) dielectric
properties of this family of compounds. Our study revealed presence of the
strong dielectric anomaly both in the real and imaginary parts of
high-frequency dielectric permittivity for Na and K compounds approx. 100 and
26 K, correspondingly, presumably related to antiferroelectric ordering.
Additionally, much weaker anomalies were observed at approximately 5K
indicating possible interplay of magnetic and lattice degrees of freedom. We
discuss possible relation between the structure rearrangements accompanying
dielectric anomalies and a delayed magnetic ordering in the nabokoite family
compounds.",2311.05209v2
2023-12-03,Evolutionary search for superconducting phases in the lanthanum-nitrogen-hydrogen system with universal neural network potential,"Recently, Grockowiak $\textit{et al.}$ reported ""hot superconductivity"" in
ternary or multinary compounds based on lanthanum hydride [A. D. Grockowiak
$\textit{et al.}$, Front. Electron. Mater. $\textbf{2}$, 837651 (2022)]. In
this paper, we explored thermodynamically stable phases and superconducting
phases in the lanthanum-nitrogen-hydrogen system (La$_{x}$N$_{y}$H$_{1-x-y}$,
$0 \leq x \leq 1$, $0 \leq y \leq 1$) at pressure of 20$\,$GP. We rapidly and
accurately constructed the formation-enthalpy convex hull using an evolutionary
construction scheme based on density functional theory calculations, extracting
the candidates for stable and moderately metastable compounds by the universal
neural network potential calculations. The convex hull diagram shows that more
than fifty compounds emerge as stable and moderately metastable phases in the
region of $\Delta H \leq 4.4$$\,$mRy/atom. In particular, the compounds are
concentrated on the line of $x = 0.5$ connecting between LaH and LaN. We found
that the superconductivity is gradually enhanced due to N doping for LaH and
the superconducting critical temperature $T_{\rm c}$ reaches 8.77$\,$K in
La$_2$NH with $y = 0.25$. In addition, we predicted that metastable
La$_2$NH$_2$ shows the highest $T_{\rm c}$ value, 14.41$\,$K, of all the
ternary compounds predicted in this study. These results suggest that it is
difficult to obtain the hot superconductivity in the La-H compounds with N at
20$\,$GPa.",2312.01290v1
2023-12-26,"Ternary Alkali Metal Copper Chalcogenides ACuX (A= Na, K and X= S, Se, Te): Promising Candidate for Solar Harvesting Applications","We report a comprehensive first-principles study of the relative stability of
the various possible crystal structures, and the electronic and optical
properties of ternary alkali metal chalcogenides ACuX (A= Na/K and X= S/Se/Te)
compounds through density functional theory (DFT) calculations. The energetics
and phonon spectra of greater than 700 structures were compared, and seven
possible stabilized structures of six ACuX compounds were identified using the
fixed composition evolutionary search method. Our electronic band structure
simulation confirms that all the ternary ACuX compounds are direct band gap
semiconductors, with the band gap lying between 0.83 eV to 2.88 eV. These
compounds exhibit directly allowed electronic transitions from the valence band
to the conduction band, which leads to a significant strength of optical
transition probability. This yields a sharp rise in the optical absorption
spectra (ranging between 10$^4$ to 10$^5$ cm$^{-1}$) near the energy gap. The
estimated spectroscopic limited maximum efficiency (SLME) is about 18% for an 8
$\mu$m thick NaCuTe film. For other ACuX compounds, the SLME ranges between 10%
to 13%. In addition, we also explored the feasibility of these ternary ACuX
compounds for photocatalytic water splitting applications and found that they
can be promising candidates as photocathodes for hydrogen evolution reactions.
With a large spread in the band gap and interesting band topology near Fermi
level, these chalcogenides can be quite fertile for other energy applications
such as thermoelectric, LED, etc.",2312.16063v1
2024-01-14,An extension of the compound flow theory with shear and friction,"Compound flows consist of two or more parallel compressible streams inside a
duct. Its theoretical treatment has recently been applied to model ejectors,
but also to post-process and to interpret CFD results. More precisely, it has
been observed that compound flows can choke upstream of the geometrical throat.
While it is widely known that friction can push the sonic section downstream,
no mechanism has been identified to explain the movement in the opposite
direction.
  In this work, we extend the existing compound flow theory with shear and
friction. The resulting model captures the up- and downstream movement of the
sonic section. We show analytically that shear between the streams is the
driving force behind the upstream movement by analysing the singularity of the
governing equations in the sonic section. Additionally, we provide a
quasi-third order approximation of the governing equations in the vicinity of
the sonic section to alleviate potential numerical issues. Finally, we compare
the predictions of the model with post-processed CFD results of a compound
nozzle. We study the individual effects of shear and friction through an
inviscid simulation for the isentropic case and a viscid simulation with a slip
or no-slip condition at the wall to include shear with or without friction.
  The proposed extension offers new possibilities in modelling and analysis of
compound flows.",2401.07236v1
2024-01-20,Pressure dependent physical properties of a potential high-TC superconductor ScYH6: insights from first-principles study,"We have investigated the structural, elastic, electronic, thermophysical,
superconducting, and optical properties of ScYH6 under uniform hydrostatic
pressures up to 25 GPa, using the density functional theory (DFT) formalism.
Most of results reported here are novel. The compound ScYH6 has been found to
be elastically and thermodynamically stable within the pressure range
considered. The compound is brittle; the brittleness decreases with increasing
pressure. The elastic anisotropy is low and the machinability index is moderate
which increases gradually with rising pressure. The compound is a hard
material. The electronic band structure shows weakly metallic character with
low density of states at the Fermi level. The Debye temperature of the compound
is high and increases with increasing pressure. The Gr\""uneisen parameter of
ScYH6 is low and the phonon thermal conductivity is high at room temperature.
The compound is a very efficient reflector of infrared radiation. The compound
is also an efficient absorber of visible and ultraviolet light. The overall
effect of pressure on optical parameters is small. We have also investigated
the pressure induced changes in the predicted superconducting state properties
by considering the changes in the electronic density of states at the Fermi
level, Debye temperature, and the repulsive Coulomb pseudopotential. The
superconducting transition temperature is found to increase gradually with
increasing pressure.",2401.11121v1
2024-03-19,"Thermoelectric properties of marcasite-type compounds MSb$_2$ (M = Ta, Nb): A combined experimental and computational study","Here, we investigate the thermoelectric properties of the marcasite-type
compounds MSb$_2$ (M = Ta, Nb) in the temperature range of 310-730 K. These
compounds were synthesized by a solid-state reaction followed by the spark
plasma sintering process. The Rietveld refinement method confirms the
monoclinic phase with space group C2/m for both compounds. The observed values
of Seebeck coefficients exhibit non-monotonic behaviour in the studied
temperature range, with the maximum magnitude of -14.4 and -22.7 $\mu$V
K$^{-1}$ for TaSb$_2$ and NbSb$_2$, respectively at ~444 K. The negative sign
of S in the full temperature window signifies the n-type behaviour of these
compounds. Both electrical and thermal conductivities show an increasing trend
with temperature. The experimentally observed thermoelectric properties are
understood through the first-principles DFT and Boltzmann transport equation. A
pseudogap in the density of states around the Fermi level characterizes the
semimetallic behaviour of these compounds. The multi-band electron and hole
pockets were found to be mainly responsible for the temperature dependence of
transport properties. The experimental power factors are found to be ~0.09 and
~0.42 mW m$^{-1}$ K$^{-2}$ at 310 K for TaSb2 and NbSb2, respectively. From the
DFT-based calculations, the maximum possible power factors for p-type
conduction are predicted as ~1.14 and ~1.74 mW m$^{-1}$ K$^{-2}$, while these
values are found to be ~1.16 and ~1.80 mW m$^{-1}$ K$^{-2}$ for n-type TaSb$_2$
and NbSb$_2$, respectively at 300 K with the corresponding doping
concentrations. The present study suggests that the combined DFT and Boltzmann
transport theory are found to be reasonably good at explaining the experimental
transport properties, and moderate power factors are predicted.",2403.12484v1
1996-10-08,Electronic Properties Of Buckminsterfullerenes: Degeneracies and Surprises,"Buckminsterfullerene compounds exibit remarkable physics at low temperatures,
e.g. high temperature superconductivity in alkali-fullerenes, and
ferromagnetism in TDAE -C60. Here we review recent theoretical studies of
electron correlations in these compounds. In particular, we discuss models of
electron-vibron interactions, electron-electron interactions, and
intermolecular hopping. We show that the origin of novel electronic phases lies
in {\em local} degeneracies of C60; a direct consequence of the high molecular
symmetry.",9610058v1
1998-10-31,Charge screening and magnetic anisotropy in RCo5 compounds,"An analysis of magnetic anisotropy in RCo5 compounds is performed with
account of screening of ion point charges by conduction electrons. A crucial
role of non-uniform distribution of screening electrons (the terms containing
derivatives of charge density) is demonstrated. Influence of anisotropy of
screening, that is connected with the anisotropy of the Fermi surface, on the
magnetic anisotropy sign is discussed.",9811004v1
1999-05-04,Heavy-Fermions in a Transition-Metal Compound: $LiV_2O_4$,"The recent discovery of heavy-Fermion properties in Lithium Vanadate and the
enormous difference in its properties from the properties of Lithium Titanate
as well as of the manganite compounds raise some puzzling questions about
strongly correlated Fermions. These are disscussed as well as a solution to the
puzzles provided.",9905041v1
2000-03-13,Unconventional odd-parity superconductivity in the ladder compounds,"Superconductive properties of the two-leg ladder compounds are studied
theoretically. The antiferromagnetic fluctuations are considered because of the
good nesting of the Fermi surfaces. The attractive interaction which is most
likely due to the electron-phonon coupling is also taken into account. Under
this circumstance, it is shown that the superconductivity has two sets of
spin-triplet pairings. The gaps for both pairings have no node.",0003211v1
2002-01-12,Carrier relaxation dynamics in heavy fermion compounds,"The first femtosecond carrier relaxation dynamics studies in heavy fermion
compounds are presented. The carrier relaxation time shows a dramatic
hundred-fold increase below the Kondo temperature revealing a dramatic
sensitivity to the electronic density of states near the Fermi level.",0201194v1
2002-10-27,Specific Heat Study on Heavy-Fermion Pr compounds with filled skutterudite structure,"Rare 4f^2-based heavy-fermion behaviors have been revealed recently in
Pr-based filled skutterudites PrFe4P12 and PrOs4Sb12. Recent studies on the
thermal properties on both compounds are reported, putting emphasis on the
field-induced ordered phase found in PrOs4Sb12.",0210596v1
2003-05-23,Metallo-Anti-aromatic Al4Na4 and Al4Na3- compounds: A theoretical investigation,"We propose a theoretical investigation in this paper to understand the
bonding and structural properties of neutral Al4Na4 and anion Al4Na3- clusters.
We show that the Al4 species in Al4Na4 and Al4Na3- clusters is a rectangular
planar structure with alternate pi-bonds and hence satisfying the basic
criteria for anti-aromaticity. We prove that the Al4Na4 and Al4Na3- clusters
are metallo-anti-aromatic compounds.",0305553v1
2004-12-15,Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?,"Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are
explained by an elaborately modified spin-wave theory. We give a strong
evidence of the major contribution to 1/T_1_ being made by the three-magnon
scattering rather than the Raman one.",0412389v1
2003-02-22,Empirical Methods for Compound Splitting,"Compounded words are a challenge for NLP applications such as machine
translation (MT). We introduce methods to learn splitting rules from
monolingual and parallel corpora. We evaluate them against a gold standard and
measure their impact on performance of statistical MT systems. Results show
accuracy of 99.1% and performance gains for MT of 0.039 BLEU on a
German-English noun phrase translation task.",0302032v1
2002-07-02,Spectrum of the Multi-Reggeon Compound States in Multi-Colour QCD,"We study the properties of the colour-singlet compound states of reggeized
gluons in multi-colour QCD. Applying the methods of integrable models, we
calculate their spectrum and discuss the application of the obtained results to
high-energy asymptotics of the scattering amplitudes in perturbative QCD.",0207033v1
1998-02-22,Bounds on norms of compound matrices and on products of eigenvalues,"An upper bound on operator norms of compound matrices is presented, and
special cases that involve the $\ell_1$, $\ell_2$ and $\ell_\infty$ norms are
investigated. The results are then used to obtain bounds on products of the
largest or smallest eigenvalues of a matrix.",9802106v1
2006-08-22,Mixtures of compound Poisson processes as models of tick-by-tick financial data,"A model for the phenomenological description of tick-by-tick share prices in
a stock exchange is introduced. It is based on mixtures of compound Poisson
processes. Preliminary results based on Monte Carlo simulation show that this
model can reproduce various stylized facts.",0608217v1
2006-12-17,Aromaticity in Polyacene Analogues of Inorganic Ring Compounds,"The aromaticity in the polyacene analogues of several inorganic ring
compounds (BN-acenes, CN-acenes, BO-acenes and Na6-acenes) is reported here for
the first time. Conceptual density functional theory based reactivity
descriptors and the nucleus independent chemical shift (NICS) values are used
in this analysis.",0612165v1
2007-09-11,The extremal values of the Wiener index of a tree with given degree sequence,"The Wiener index of a graph is the sum of the distances between all pairs of
vertices, it has been one of the main descriptors that correlate achemical
compound's molecular graph with experimentally gathered data regarding the
compound's characteristics. The tree that minimizes the Wiener index among
trees of given maximal degree was studied. We characterize trees that achieve
the maximum and minimum Wiener index, given the number of vertices and the
degree sequence.",0709.1679v1
2008-05-12,The probability of exceeding a piecewise deterministic barrier by the heavy-tailed renewal compound process,"We analyze the asymptotics of crossing a high piecewise linear barriers by a
renewal compound process with the subexponential jumps. The study is motivated
by ruin probabilities of two insurance companies (or two branches of the same
company) that divide between them both claims and premia in some specified
proportions when the initial reserves of both companies tend to infinity.",0805.1631v1
2008-12-18,Charge and Spin Ordering in the Mixed Valence Compound LuFe2O4,"Landau theory and symmetry considerations are invoked to give a unified
treatment of charge and spin ordering in the mixed valence compound LuFe2O4. In
particular, the unusual evolution of charge ordering correlations can be
explained by invoking phonon mediated interactions.",0812.3575v1
2010-01-26,"Reply to ""Comment on <Emergence of a superconducting state from an antiferromagnetic phase in single crystals of the heavy fermion compound Ce2PdIn8> by Uhlirova et al.""","Reply to ""Comment on <Emergence of a superconducting state from an
antiferromagnetic phase in single crystals of the heavy fermion compound
Ce2PdIn8> by Uhlirova et al.""",1001.4609v1
2011-01-27,Exit problems for oscillating compound Poisson process,"In this article we determine the Laplace transforms of the main boundary
functionals of the oscillating compound Poisson process. These are the first
passage time of the level, the joint distribution of the first exit time from
the interval and the value of the overshoot through the boundary. Under certain
conditions we establish the asymptotic behaviour of the mentioned functionals.",1101.5279v1
2011-04-28,Notional portfolios and normalized linear returns,"The vector of periodic, compound returns of a typical investment portfolio is
almost never a convex combination of the return vectors of the securities in
the portfolio. As a result the ex post version of Harry Markowitz's ""standard
mean-variance portfolio selection model"" does not apply to compound return
data. We propose using notional portfolios and normalized linear returns to
remedy this problem.",1104.5393v1
2011-10-24,Compound Poisson approximation for triangular arrays with application to threshold estimation,"We prove weak convergence of triangular arrays to the compound Poisson limit
using Tikhomirov's method. The result is applied to statistical estimation of
the threshold parameter in autoregressive models.",1110.5381v3
2012-05-10,Sliding charge-density-wave in two-dimensional rare-earth tellurides,"Nonlinear transport properties are reported in the layered DyTe$_3$ compound
at temperature below the charge-density-wave (CDW) transition, $T_P=302$ K.
Conductivity is increasing sharply above the threshold electric field. Under
application of a rf field Shapiro steps are clearly observed. These features
demonstrate for the first time CDW sliding in two-dimensional compounds.",1205.2214v1
2012-05-24,Principles of crystal growth of intermetallic and oxide compounds from molten solutions,"We present a tutorial on the principles of crystal growth of intermetallic
and oxide compounds from molten solutions, with an emphasis on the fundamental
principles governing the underlying phase equilibria and phase diagrams of
multicomponent systems.",1205.5592v1
2012-11-22,Poisson and Compound Poisson Approximations in a Nonconventional Setup,"We show that for all $\psi$-mixing shifts distributions of the numbers of
multiple recurrencies to shrinking cylindrical neighborhoods of all points are
close either to Poisson or to compound Poisson distributions. We also describe
completely the asymptotic behavior of these distributions.",1211.5238v2
2012-12-01,Fissibility of compound nuclei,"Collisions between $^{248}$Cm and $^{48}$Ca are systematically investigated
by time-dependent density functional calculations with evaporation
prescription. Depending on the incident energy and impact parameter, fusion,
deep-inelastic and fission events are expected to appear. In this paper, a
microscopic method of calculating the fissibility of compound nuclei is
presented.",1212.0161v1
2013-01-31,Spin-rotation coupling in compound spin objects,"We generalize spin-rotation coupling to compound spin systems. In the case of
muons bound to nuclei in a storage ring the decay process acquires a
modulation. Typical frequencies for $Z/A\sim 1/2$ are $\sim 3\times 10^6$Hz, a
factor 10 higher than the modulation observed in $g-2$ experiments.",1301.7561v1
2013-03-01,Smoothing effect of Compound Poisson approximation to distribution of weighted sums,"The accuracy of compound Poisson approximation to the sum
$S=w_1S_1+w_2S_2+...+w_NS_N$ is estimated.
  Here $S_i$ are sums of independent or weakly dependent random variables, and
$w_i$ denote weights. The overall smoothing effect of $S$ on $w_iS_i$ is
estimated by L\' evy concentration function.",1303.0159v1
2013-11-18,Superconductivity in BiS2-Based Layered Compounds,"Crystal structure and physical properties of the novel BiS2-based layered
superconductors are briefly reviewed. Superconductivity in the BiS2-based
layered compounds is induced by electron doping into the BiS2 conduction
layers. The superconducting properties seem to correlate with the crystal
structure. Possible strategies for increasing transition temperature in this
family are discussed.",1311.4270v1
2014-08-14,Review on magnetic and related properties of RTX compounds,"RTX (R=rare earths, T= 3d/4d/5d, transition metals such as Sc, Ti, Mn, Fe,
Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, and X=p-block elements such as Al,
Ga, In, Si, Ge, Sn, As, Sb, Bi) series is a huge family of intermetallics
compounds. These compounds crystallize in different crystal structures
depending on the constituents. Though these compounds have been known for a
long time, they came to limelight recently in view of the large magnetocaloric
effect (MCE) and magnetoresistance (MR) shown by many of them. Most of these
compounds crystallize in hexagonal and tetragonal crystal structures. Some of
them show crystal structure modification with annealing temperature; while a
few of them show iso-structural transition in the paramagnetic regime. Their
magnetic ordering temperatures vary from very low temperatures to temperatures
well above room temperature (~510 K). Depending on the crystal structure, they
show a variety of magnetic and electrical properties. These compounds have been
characterized by means of a variety of techniques/measurements such as x-ray
diffraction, neutron diffraction, magnetic properties, heat capacity,
magnetocaloric properties, electrical resistivity, magnetoresistance,
thermoelectric power, thermal expansion, Hall effect, optical properties, XPS,
M\""ossbauer spectroscopy, ESR, {\mu}SR, NMR, NQR etc. Some amount of work on
theoretical calculations on electronic structure, crystal field interaction and
exchange interactions has also been reported. The interesting aspect of this
series is that they show a variety of physical properties such as Kondo effect,
heavy fermion behavior, spin glass state, intermediate valence,
superconductivity, multiple magnetic transitions, metamagnetism, large MCE,
large positive as well as negative MR, spin orbital compensation, magnetic
polaronic behavior, pseudo gap effect etc.",1408.3238v1
2014-12-08,On the Optimality of Treating Interference as Noise: Compound Interference Networks,"In a K-user Gaussian interference channel, it has been shown by Geng et al.
that if for each user the desired signal strength is no less than the sum of
the strengths of the strongest interference from this user and the strongest
interference to this user (all values in dB scale), then power control and
treating interference as noise (TIN) is optimal from the perspective of
generalized degrees of freedom (GDoF) and achieves the entire channel capacity
region to within a constant gap. In this work, we generalize the optimality of
TIN to compound networks. We show that for a K-user compound Gaussian
interference channel, if in every possible state for each receiver, the channel
always satisfies the TIN-optimality condition identified by Geng et al., then
the GDoF region of the compound channel is the intersection of the GDoF regions
of all possible network realizations, which is achievable by power control and
TIN. Furthermore, we demonstrate that for a general K-user compound
interference channel, regardless of the number of states of each receiver, we
can always construct a counterpart K-user regular interference channel that has
the same TIN region as the original compound channel. The regular interference
channel has only one state for each receiver, which may be different from all
of the original states. Solving the GDoF-based power control problem for the
compound channel is equivalent to solving the same problem in its regular
counterpart. Exploring the power control problem further we develop a
centralized power control scheme for K-user compound interference channels, to
achieve all the Pareto optimal GDoF tuples. Finally, based on this scheme, we
devise an iterative power control algorithm which requires at most K updates to
obtain the globally optimal power allocation for any feasible GDoF tuple.",1412.2711v1
2015-12-06,Magnetic properties of bismuth-cobalt oxides doped by erbium,"We synthesized bismuth - cobalt oxide doped by erbium with general formula
Bi3-xErxCoO3-y. Compound has structure of delta-form bismuth oxide. Magnetic
properties of the compound were measured by Faraday's method using quartz
scales in the temperature range of 80-500 K. The magnetic susceptibility and
effective magnetic moment were calculated.",1512.01782v1
2015-12-07,Metalloboranes from first-principles calculations: A candidate for high-density hydrogen storage,"Using first principles calculations, we show the high hydrogen storage
capacity of a new class of compounds, metalloboranes. Metalloboranes are
transition metal (TM) and borane compounds that obey a novel-bonding scheme. We
have found that the transition metal atoms can bind up to 10 H2 molecules.",1512.02128v1
2016-06-05,Understanding the Thermoelectric Properties of LaCoO$_{3}$ Compound,"We present the thermoelectric (TE) properties of LaCoO$_{3}$ compound in the
temperature range 300-600 K. The experimental value of Seebeck coefficient
($\alpha$) at 300 K is found to be $\sim$635 $\mu$V/K. The value of $\alpha$
decreases continuously with increase in temperature and reaches to $\sim$46
$\mu$V/K at $\sim$600 K. The electronic and TE properties of the compound have
also been investigated by combining the \textit{ab-initio} electronic
structures and Boltzmann transport calculations. LSDA plus Hubbard U (U= 2.75
eV) calculation on low spin configuration of the compound gives an energy gap
of $\sim$0.5 eV, which is close to the experimentally reported energy gap. The
effective mass of holes (\textit{m$^{*}_h$}) at $\Gamma$ point is nearly two
times larger than the value of effective mass of electrons (\textit{m$^{*}_e$})
at FB point along the L and T directions, whereas the \textit{m$^{*}_e$} at FB
point along the $\Gamma$ direction is nearly eight times larger than the value
of \textit{m$^{*}_h$} at $\Gamma$ point along the FB direction. The large
effective mass at FB point along the $\Gamma$ direction suggests that the TE
property of this compound is mainly decided by the effective mass of the charge
carriers in this direction. The calculated temperature dependent values of
$\alpha$ are in fairly good agreement with experimental data in the temperature
range 300-360 K, and above this temperature slight deviation is observed. The
value of power factor (PF) for \textit{n}-type is $\sim$1.3 times larger the
value of \textit{p}-type doped compound at 1100 K. The value of
\textit{figure-of-merit} (\textit{ZT}) for \textit{n}-type doped compound is
obtained $\sim$0.35 in the temperature range 600-1100 K, which suggests that
with appropriate \textit{n}-type doping this compound can be used as a good TE
material in the high temperature region.",1606.01539v3
2016-09-12,"Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM$_2$Al$_{20}$ [R = Eu,Gd and La ; TM = V,Ti]","Single crystals of Frank-Kasper compounds RTM$_2$Al$_{20}$ (R = Eu, Gd and
La; TM = V and Ti) were grown by self-flux method and their physical properties
were investigated through magnetization ($M$), magnetic susceptibility
($\chi$), specific heat ($C_P$) and electrical resistivity ($\rho$)
measurements. Powder x-ray diffraction studies and structural analysis showed
that these compounds crystallize in the cubic crystal structure with the space
group $Fd\overline{3}m$. The magnetic susceptibility for the compounds
EuTi$_2$Al$_{20}$ and GdTi$_2$Al$_{20}$ showed a sudden jump below the N{\'e}el
temperature $T_N$ indicative of plausible double magnetic transition. Specific
heat ($C_P$) and electrical resistivity ($\rho$) measurements also confirm the
first-order magnetic transition (FOMT) and possible double magnetic
transitions. Temperature variation of heat capacity showed a sharp phase
transition and huge $C_P$ value for the (Eu/Gd)Ti$_2$Al$_{20}$ compounds Full
width at half-maximum (FWHM) $<$ 0.2 K) which is reminiscent of a first-order
phase transition and a unique attribute among RTM$_2$Al$_{20}$ compounds. We
observed clear anomaly between heating and cooling cycle in temperature-time
relaxation curve for the compounds GdTi$_2$Al$_{20}$ (2.38 $K$) and
EuTi$_2$Al$_{20}$ (3.2 $K$) which is indicating a thermal arrest due to the
latent heat. The temperature variation of $S_{mag}$ for GdTi$_2$Al$_{20}$
saturates to a value $0.95R\ln8$ while the other magnetic systems exhibited
still lower entropy saturation values in the high temperature limit.
Resistivity measurements showed that all the samples behave as normal Fermi
liquid type compounds and $\rho(T)$ due to electron-phonon scattering follows
Bloch-Gr$\ddot{\textrm u}$neisen-Mott relation in the paramagnetic region.",1609.03458v1
2016-09-10,Fractional Euler Limits and Their Applications,"Generalisations of the classical Euler formula to the setting of fractional
calculus are discussed. Compound interest and fractional compound interest
serve as motivation. Connections to fractional master equations are
highlighted. An application to the Schlogl reactions with Mittag-Leffler
waiting times is described.",1609.04772v1
2017-07-21,Integrability conditions for Compound Random Measures,"Compound random measures (CoRM's) are a flexible and tractable framework for
vectors of completely random measure. In this paper, we provide conditions to
guarantee the existence of a CoRM. Furthermore, we prove some interesting
properties of CoRM's when exponential scores and regularly varying L\'evy
intensities are considered.",1707.06768v2
2018-06-19,The determinant of the second additive compound of a square matrix: a formula and applications,"A formula is presented for the determinant of the second additive compound of
a square matrix in terms of coefficients of its characteristic polynomial. This
formula can be used to make claims about the eigenvalues of polynomial
matrices, with sign patterns as an important special case. A number of
corollaries and applications of this formula are given.",1806.07162v1
2018-09-27,Some Nontrivial Properties of a Formula for Compound Interest,"We analyze the classical model of compound interest with a constant
per-period payment and interest rate. We examine the outstanding balance
function as well as the periodic payment function and show that the outstanding
balance function is not generally concave in the interest rate, but instead may
be initially convex on its domain and then concave.",1809.10566v1
2019-01-14,Transmission coefficients in compound-nucleus reaction theory,"A recent article (D.A. Brown, et al., Phys. Rev. C98 024616 (2018)) rproposed
a modification of the cross section formula used in practical calculations of
compound nucleus reactions. We discuss the main concepts and approximations of
statistical reaction theory and conclude that the standard practical
implementations of the cross section formula remain the preferred choice.",1901.04534v1
2012-09-27,Fission Dynamics of Compound Nuclei,"Collisions between $^{248}$Cm and $^{48}$Ca are systematically investigated
by time-dependent density functional calculations with evaporation
prescription. Depending on the incident energy and impact parameter, fusion,
deep-inelastic and quasi-fission events are expected to appear. In this paper,
possible fission dynamics of compound nuclei is presented.",1209.6142v1
2018-02-23,The Sprague-Grundy function for some selective compound games,"We analyze the Sprague-Grundy functions for a class of almost disjoint
selective compound games played on Nim heaps. Surprisingly, we find that these
functions behave chaotically for smaller Sprague-Grundy values of each
component game yet predictably when any one heap is sufficiently large.",1802.08700v1
2020-04-16,Some martingale characterizations of compound mixed Poisson processes,"Some martingale characterizations of compound mixed Poisson processes are
proven, extending S. Watanabe's (1964) martingale characterization of Poisson
processes as well as the main result of Lyberopoulos and Macheras (2012),
concerning martingale characterizations of mixed Poisson processes.",2004.07835v1
2020-05-04,Subordinated Compound Poisson processes of order $k$,"In this article, the compound Poisson processes of order $k$ (CPPoK) is
introduced and its properties are discussed. Further, using mixture of tempered
stable subordinator (MTSS) and its right continuous inverse, the two
subordinated CPPoK with various distributional properties are studied. It is
also shown that space and tempered space fractional versions of CPPoK and PPoK
can be obtained, which generalize the results in the literature.",2005.01337v1
2022-03-22,Compound Optics,"Simple optics are defined using actions of monoidal categories. Compound
optics arise, for instance, as natural transformations between polynomial
functors. Since a monoidal category is a special case of a bicategory, we
formulate complex optics using the action of a bicategory. We show that
polynomial optics are a special case of complex optics defined by the action of
bicategory $\mathbf{Prof}$ on co-presheaves.",2203.12022v1
2019-05-12,The compound product distribution; a solution to the distributional equation X=AX+1,"The solution of $ X=AX+1 $ is analyzed for a discrete variable $ A $ with $
\mathbb{P}\left[A=0\right]>0 $. Accordingly, a fast algorithm is presented to
calculate the obtained heavy tail density. To exemplify, the compound product
distribution is studied in detail for some particular families of
distributions.",1905.04758v1
2019-12-04,Max-compound Cox processes. III,"Extreme values are considered in samples with random size that has a mixed
Poisson distribution being generated by a doubly stochastic Poisson process. We
prove some inequalities providing bounds on the rate of convergence in limit
theorems for the distributions of max-compound Cox processes.",1912.02237v2
2020-05-30,Approximation of the fixed-probability level for a compound renewal process,"Dealing with compound renewal process with generally distributed jump sizes
and inter-renewal intervals, we focus on the approximation for the
fixed-probability level, which is the core of inverse level crossing problem.
We are developing an analytical technique presented in [15]-[17] and based on
Kendall's identity; this yields (see [18]) inverse Gaussian approximation in
the direct level crossing problem. These issues are of great importance in risk
theory.",2006.00370v1
2020-07-15,Applications of a change of measures technique for compound mixed renewal processes to the ruin problem,"In the present paper the change of measures technique for compound mixed
renewal processes, developed in Tzaninis & Macheras [24], is applied to the
ruin problem in order to compute the ruin probability and to find upper and
lower bounds for it.",2007.09266v1
2020-07-30,"Tunable spin Hall and spin Nernst effects in Dirac line-node semimetals XCuYAs (X=Zr, Hf; Y=Si, Ge)","The quaternary arsenide compounds XCuYAs (X=Zr, Hf; Y= Si, Ge) belong to the
vast family of the 1111-type quaternary compounds, which possess outstanding
physical properties ranging from $p$-type transparent semiconductors to
high-temperature Fe-based superconductors. In this paper, we study the
electronic structure topology, spin Hall effect (SHE) and spin Nernst effect
(SNE) in these compounds based on density functional theory calculations. First
we find that the four considered compounds are Dirac semimetals with the
nonsymmorphic symmetry-protected Dirac line nodes along the Brillouin zone
boundary $A$-$M$ and $X$-$R$ and low density of states (DOS) near the Fermi
level ($E_F$). Second, the intrinsic SHE and SNE in some of these considered
compounds are found to be large. In particular, the calculated spin Hall
conductivity (SHC) of HfCuGeAs is as large as -514 ($\hbar$/e)(S/cm). The spin
Nernst conductivity (SNC) of HfCuGeAs at room temperature is also large, being
-0.73 ($\hbar$/e)(A/m-K). Moreover, both the magnitude and sign of the SHC and
SNC in these compounds can be manipulated by varying either the applied
electric field direction or spin current direction. The SHE and SNE in these
compounds can also be enhanced by tuning the Fermi level via chemical doping or
electric gating. Finally, a detailed analysis of the band-decomposed and
$k$-resolved spin Berry curvatures reveals that these large SHC and SNC as well
as their notable tunabilities originate largely from the presence of a large
number of spin-orbit coupling-gapped Dirac points near the Fermi level as well
as the gapless Dirac line-nodes, which give rise to large spin Berry
curvatures. Our findings thus suggest that the four XCuYAs compounds not only
provide a valuable platform for exploring the interplay between SHE, SNE and
band topology but also have promising applications in spintronics and spin
caloritronics.",2007.15303v1
2021-01-31,"Origin of high hardness and optoelectronic and thermo-physical properties of boron-rich compounds B6X (X = S, Se): a comprehensive study via DFT approach","In the present study, the structural and hitherto uninvestigated mechanical
(elastic stiffness constants, machinability index, Cauchy pressure, anisotropy
indices, brittleness/ductility, Poissons ratio), electronic, optical, and
thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have
been explored using density functional theory. The estimated structural lattice
parameters were consistent with the prior report. The mechanical and dynamical
stability of these compounds have been established theoretically. The materials
are brittle in nature and elastically anisotropic. The value of fracture
toughness, KIC for the B6S and B6Se are ~ 2.07 MPam0.5, evaluating the
resistance to limit the crack propagation inside the materials. Both B6S and
B6Se compounds possess high hardness values in the range 31-35 GPa, and have
the potential to be prominent members of the class of hard compounds. Strong
covalent bonding and sharp peak at low energy below the Fermi level confirmed
by partial density of states (PDOS) resulted in the high hardness. The profile
of band structure, as well as DOS, assesses the indirect semiconducting nature
of the titled compounds. The comparatively high value of Debye temperature
({\Theta}D), minimum thermal conductivity (Kmin), lattice thermal conductivity
(kph), low thermal expansion coefficient, and low density suggest that both
boron-rich chalcogenides might be used as thermal management materials. Large
absorption capacities in the mid ultraviolet region (3.2-15 eV) of the studied
materials and low reflectivity (~16 %) are significantly noted. Such favorable
features give promise to the compounds under investigation to be used in UV
surface-disinfection devices as well as medical sterilizer equipment
applications. Excellent correlations are found among all the studied physical
properties of these compounds.",2102.00446v1
2021-04-27,The Ordered Join of Impartial Games,"Inspired by the theory of poset games, we introduce a new compound of
impartial combinatorial games and provide a complete analysis in the spirit of
the Sprague-Grundy theory. Furthermore, we establish several substitution and
reduction principles for this compound and consider its computational aspects.",2104.13131v2
2021-06-23,On the compounding of higher order monotonic pseudo-Boolean functions,"Compounding submodular monotone (i.e. 2-alternating) set functions on a
finite set preserves this property, as shown in 2010. A natural generalization
to k-alternating functions was presented in 2018, however hardly readable
because of page long formulas. We give an easier proof of a more general
result, exploiting known properties of higher order monotonic functions.",2106.12221v1
2021-10-30,Comparison of $pp$ and $p \bar{p}$ differential elastic cross sections and observation of the exchange of a Colorless $C$-odd gluonic compound,"We describe the discovery of the colorless $C$-odd gluonic compound, the
odderon, by the D0 and TOTEM Collaborations by comparing elastic differential
cross sections measured in $pp$ and $p \bar{p}$ interactions at high energies",2111.00245v1
2021-12-17,Large deviations principle for terminating multidimensional compound renewal processes with application to polymer pinning models,"Large deviations principle is obtained for terminating multidimensional
compound renewal processes. We also obtained the asymptotic of large deviations
for the case when a Gibbs change of the original probability measure takes
place. The random processes mentioned in the paper are widely used in polymer
pinning models.",2112.09640v1
2022-11-09,Asymptotics of joint orderings of compound Poisson fields,"We are developing a new method for the analysis of queuing systems with
heterogeneous in time and space compound (marked) Poisson input flow. The state
space of the input flow is embedded in a higher-dimensional space with a
homogeneous marked Poisson field on it. We prove limit theorems for partial
sums of marks under the ordering of field points by coordinates.",2211.04723v1
2023-09-15,"A comparative ab-initio investigation of the physical properties of cubic Laves phase compounds XBi$_2$ (X = K, Rb)","In this study, we looked into a number of physical properties of
alkali-bismuth compounds KBi$_2$ and RbBi$_2$ in the cubic Laves phase using
the density functional theory (DFT). The structural, elastic, anisotropy
indices, hardness, thermo-physical parameters, electronic band structure, and
optoelectronic properties have been explored. Most of the results presented in
this work are novel in nature.",2309.08307v1
1997-04-20,Inelastic Neutron scattering in CeSi_{2-x}Ga_x ferromagnetic Kondo lattice compounds,"Inelastic neutron scattering investigation on ferromagnetic Kondo lattice
compounds belonging to CeSi_{2-x}Ga_{x}, x = 0.7, 1.0 and 1.3, system is
reported. The thermal evolution of the quasielastic response shows that the
Kondo interactions dominate over the RKKY interactions with increase in Ga
concentration from 0.7 to 1.3. This is related to the increase in k-f
hybridization with increasing Ga concentration. The high energy response
indicates the ground state to be split by crystal field in all three compounds.
Using the experimental results we have calculated the crystal field parameters
in all three compounds studied here.",9704174v2
1999-04-08,Properties of the ferrimagnetic double-perovskite A_{2}FeReO_{6} (A=Ba and Ca),"Ceramics of A_{2}FeReO_{6} double-perovskite have been prepared and studied
for A=Ba and Ca. Ba_{2}FeReO_{6} has a cubic structure (Fm3m) with $a\approx
$8.0854(1) \AA whereas Ca_{2}FeReO_{6} has a distorted monoclinic symmetry with
$a\approx 5.396(1) \AA, b\approx 5.522(1) \AA, c\approx 7.688(2) \AA$ and
$\beta =90.4^{\circ} (P21/n)$. The barium compound is metallic from 5 K to 385
K, i.e. no metal-insulator transition has been seen up to 385 K, and the
calcium compound is semiconducting from 5 K to 385 K. Magnetization
measurements show a ferrimagnetic behavior for both materials, with T_{c}=315 K
for Ba_{2}FeReO_{6} and above 385 K for Ca_{2}FeReO_{6}. A specific heat
measurement on the barium compound gave an electron density of states at the
Fermi level, N(E_{F}) equal to 6.1$\times 10^{24} eV^{-1}mole^{-1}$. At 5 K, we
observed a negative magnetoresistance of 10 % in a magnetic field of 5 T, but
only for Ba_{2}FeReO_{6}. Electrical, thermal and magnetic properties are
discussed and compared to the analogous compounds Sr_{2}Fe(Mo,Re)O_{6}.",9904119v1
2000-04-18,"Metallic and nonmetallic double perovskites: A case study of A$_2$FeReO$_6$ (A= Ca, Sr, Ba)","We have investigated the structure and electronic properties of ferrimagnetic
double perovskites, A2FeReO6 (A= Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m)
and metallic, while the A=Ca phase is monoclinic (P21/n) and nonmetallic.
  57Fe Mossbauer spectroscopy shows that iron is present mainly in the
high-spin (S=5/2) Fe3+ state in the Ca compound, while it occurs in an
intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. It is
argued that a direct Re t2g - Re t2g interaction is the main cause for the
metallic character of the Ba compound; the high covalency of Ca-O bonds and the
monoclinic distortion (which lifts the degeneracy of t2g states) seem to
disrupt the Re-Re interaction in the case of the Ca compound, making it
non-metallic for the same electron count.",0004315v1
2001-06-26,Superconductivity in a pyrochlore oxide Cd2Re2O7,"We make the first report that a metallic pyrochlore oxide \Cd2Re2O7, exhibits
type II superconductivity at 1.1 K. The pyrochlore oxide is known to be a
geometrical frustrated system, which includes the tetrahedral network of
magnetic ions. A large number of compounds are classified in the family of
pyrochlore oxides, and these compounds exhibit a wide variety of physical
properties ranging from insulator through semiconductor and from bad metal to
good metal. Until now, however, no superconductivity has been reported for
frustrated pyrochlore oxides. The bulk superconductivity of this compound is
confirmed by measurements of the resistivity and the a. c. magnetic
susceptibility. The \Hc2, which is extrapolated to 0 K, is estimated as about
0.8 T, using the resistivity measurements under aplied field. The plot of \Hc2
vs $T$ indicates that the Cooper pairs are composed of rather heavy
quasiparticles. This fact suggests that frustrated heavy electrons become
superconducting in this compound.",0106521v1
2001-07-03,"Sr$_3$CuIrO$_6$, a spin-chain compound with random ferromagnetic-antiferromagnetic interactions","Ac and dc magnetization and heat-capacity (C) measurements performed on the
pseudo-one-dimensional compound Sr$_3$CuIrO$_6$ reveal a competition between
antiferromagnetic (AF) and ferromagnetic (F) exchange couplings, as evidenced
by frequency dependence of ac susceptibility and by the absence of a C anomaly
at the magnetic transition. The value of the saturation moment (about 0.35
$\mu_B$/formula unit) is much smaller than expected for ferromagnetism from the
two S=1/2 ions (Cu and Ir). Thus, this compound is not a ferromagnet in zero
magnetic field, in contrast to earlier beliefs. Of particular importance is the
finding that the value of the magnetic ordering temperature is sample
dependent, sensitive to synthetic conditions resulting from deviations in
oxygen/Cu content. We propose that this compound serves as a unique model
system to test theories on random AF-F interaction in a chain system,
considering that this competition can be tuned without any chemical
substitution.",0107069v1
2002-07-08,Magnetic behavior of single crystalline Ho$_2$PdSi$_3$,"The magnetic behavior of single-crystal Ho$_2$PdSi$_3$, crystallizing in an
AlB$_2$-derived hexagonal structure, is investigated by magnetic susceptibility
($\chi$) and electrical resistivity ($\rho$) measurements along two directions.
There is no dramatic anisotropy in the high temperature Curie-Weiss parameter
or in the $\rho$ and isothermal magnetization data, though there is a
noticeable anisotropy in the magnitude of $\rho$ between two perpendicular
orientations. The degree of anisotropy is overall less prominent than in the Gd
(which is an S-state ion!) and Tb analogues. A point of emphasis is that this
compound undergoes long range magnetic ordering below 8 K as in the case of
analogous Gd and Dy compounds. Considering this fact for these compounds with
well-localised f-orbital, the spin glass freezing noted for isomorphous U
compounds in the recent literature could be attributed to the role of the
f-ligand hybridization, rather than just Pd-Si disorder.",0207199v1
2002-07-09,Anderson lattice in CeNiSi$_2$ intermediate valence compound,"We present experimental results of electrical resistivity, Hall coefficient,
magnetic susceptibility, and specific heat for single crystals of Ce-based
intervalent compound CeNiSi$_2$. The results show similar behaviors observed in
Yb-based intervalent compounds and support recent thoery of the Anderson
lattice, in which the Fermi-liquid coherence is gloval over the whole lattice.
There is a low-temperature scale $T_{coh} \sim$ 50 K for the onset of
Fermi-liquid coherence, in addition to a high-temperature scale $T_K^* \sim$
150 K for the Kondo-lattice condensation. Therefore, we conclude that two
energy scales are generic in intermediate valence compounds based on Ce where
the orbital degeneracy is smaller and where the size of the $4f$ orbital is
larger than those based on Yb.",0207240v1
2002-07-19,Magnetic character of the empty density of states in uranium compounds from X-ray magnetic circurlar dichroism,"We present a discussion of published x-ray magnetic circular dichroism (XMCD)
measurements performed at the uranium M_4,5 edges of metallic uranium
compounds, focusing on the shape of the dichroic signal at the M_5 edge. A well
resolved double lobe structure, comprised of a positive and a negative peak, is
sometimes observed. Out of the twelve metallic uranium compounds so far
investigated by XMCD, six exhibit an intense double-lobe structure at the M_5
edge. This line shape gives information on the empty 5f magnetic density of
states with angular quantum number j=7/2. Conclusions about the difference
between these two families of compounds are given regarding the splitting of
the j=7/2 band and the occupation among the different m_7/2 sublevels.",0207474v1
2003-04-15,"Anisotropic spin-glass-like and quasi-one-dimensional magnetic behaviour in an intermetallic compound, Tb2PdSi3","We report temperature dependent ac susceptibility ($\chi$) measurements on a
high quality single crystal of Tb$_2$PdSi$_3$, crystallizing in a
AlB$_2$-derived hexagonal structure. This compound is found to exhibit features
attributable to quasi-low-dimensional magnetism at high temperatures and {\it
anisotropic} spin-glass-like behavior at low temperatures ($<$ 10 K) with an
unusually large frequency dependence of peak temperature in ac $\chi$(T). This
compound thus presents a novel situation in {\it metallic magnetism},
considering that the former phenomenon is normally encountered only among
insulators, whereas the anisotropic spin-glass-like behavior, to our knowledge,
has not been known in stoichiometric intermetallic compounds.",0304325v1
2003-04-18,Magnetoresistance and percolation in the LaNi(1-x)Co(x)O3 solid solution,"A detailed study of the zero-field electrical resistivity and
magnetoresistance for the metallic members of the LaNi_{1-x}Co{x}O3 solid
solution with 0.3<=x<=0.6 is reported. The low temperature resistivity of the
compounds with 0.3<=x<=0.5 exhibits a logarithmic dependence that is
characteristic of systems with spin fluctuations. It is suggested that the
effect of the magnetic field dependence on the spin fluctuations plays a vital
role in determining the magnetoresistive behavior of these compounds. Concrete
experimental evidence that classify the chemically induced metal-to-insulator
transition (x_{c}=0.65) as a percolative phenomenon is provided. The
resistivity data for the x=0.6 metallic compound are analyzed in the framework
of cluster percolation threshold theory. The results of this analysis are
consistent with the suggestion that the growth of magnetic metallic clusters in
the presence of a magnetic field is mainly responsible for the observed giant
magnetoresistance effect at low temperatures for the compounds with x>=0.6.",0304423v2
2003-06-06,"Long range magnetic ordering in a spin-chain compound, Ca$_3$CuMnO$_6$, with multiple bond distances","The results of ac and dc magnetization and heat capacity measurements as a
function of temperature (T = 1.8 to 300 K) are reported for a
quasi-one-dimensional compound, Ca$_3$CuMnO$_6$, crystallizing in a
triclinically distorted K$_4$CdCl$_6$-type structure. The results reveal that
this compound undergoes antiferromagnetic ordering close to 5.5 K. In addition,
there is another magnetic transition below 3.6 K. Existence of two long-range
magnetic transitions is uncommon among quasi-one-dimensional systems. It is
interesting to note that both the magnetic transitions are of long-range type,
instead of spin-glass type, in spite of the fact that the Cu-O and Mn-O bond
distances are multiplied due to this crystallographic distortion. In view of
this, this compound could serve as a nice example for studying
""order-in-disorder"" phenomena.",0306166v1
2003-10-02,Magnetic susceptibility and heat capacity investigations of the unconventional spin-chain compound Sr3CuPtO6,"The Heisenberg spin chain compound Sr3CuPtO6 is investigated by magnetic
susceptibility and heat capacity measurements. Sr3CuPtO6 has an unconventional
chain structure in the sense that i) the spin half copper atoms are arranged in
a zigzag chain structure, and ii) neighboring Cu atoms along the chains are
separated by spin zero platinum atoms. We report that this compound shows broad
features in the temperature dependence of both the magnetic contribution to the
heat capacity and the magnetic susceptibility. Despite the unconventional
nature of the spin chain structure, this set of data exhibits good agreement
with theoretical models for a classical S = 1/2 Heisenberg spin chain compound.
The values of the intra-chain coupling constant, obtained by different
techniques, are found to be very close to each other. The low temperature heat
capacity data (below ~ 6 K) exhibit a deviation from the theoretically expected
behavior, which could be related to a small energy gap in the spin excitation
spectrum.",0310034v2
2003-11-25,Comparison of the superconducting critical transition temperature of LaBaCaCu3O7-d and NdBaCaCu3O7-d,"LaBaCaCu3O7 (La:1113) and NdBaCaCu3O7 (Nd:1113) compounds are synthesized by
solid state reaction route. Both compounds crystallize in tetragonal structure.
  Four probe resistivity measurements showed that superconducting transition
temperature (Tc) is 73 K and 41 K respectively for La:1113 and Nd:1113
compounds. Considering the fact that for RE:123 (REBa2Cu3O7) compounds the Tc
hardly depends upon the choice of RE (Rare earth, except Ce, Pr and Tb), the
current nearly two fold increase in Tc of La:1113 when compared to Nd:1113,
warrants serious discussion.",0311565v1
2003-12-09,Phonon anomalies in trilayer high-Tc superconductors,"We present an extension of the model proposed recently to account for
dramatic changes below Tc (anomalies) of some c-axis polarized infrared-active
phonons in bilayer cuprate superconductors, that applies to trilayer high-Tc
compounds. We discuss several types of phonon anomalies that can occur in these
systems and demonstrate that our model is capable of explaining the spectral
changes occurring upon entering the superconducting state in the trilayer
compound Tl2Ba2Ca2Cu3O10. The low-temperature spectra of this compound obtained
by Zetterer and coworkers display an additional broad absorption band, similar
to the one observed in underdoped YBa2Cu3O7-delta and Bi2Sr2CaCu2O8. In
addition, three phonon modes are strongly anomalous. We attribute the
absorption band to the transverse Josephson plasma resonance, similar to that
of the bilayer compounds. The phonon anomalies are shown to result from a
modification of the local fields induced by the formation of the resonance. The
spectral changes in Tl2Ba2Ca2Cu3O10 are compared with those occurring in
Bi2Sr2Ca2Cu3O10, reported recently by Boris and coworkers.",0312219v1
2004-05-13,Quantum phase transitions and magnetization of an integrable spin ladder with new parameters in bridging to real compounds,"We study the field-induced quantum phase transitions (QPT) and the relevant
magnetic properties of a spin-1/2 two-leg integrable spin ladder (ISL), of
which the system parameters in bridging to the real compounds are determined by
setting the extra interactions in the Hamiltonian of the ISL relative to the
Heisenberg spin ladder to vanish in the expectation in the ground state (GS).
Such an ISL analytically has the correct leading terms of both the critical
fields of the two QPT's as in the real strongly-coupled compounds: g\mu
_BH_{c1}=J_{\perp}-J_{\parallel} and g\mu_BH_{c2}=J_{\perp}+2J_{\parallel} in
terms of the experimental leg (J_{\parallel}) and rung (J_{\perp})
interactions. The symmetric magnetization inflection point is located at g\mu
_BH_{IP}=J_{\perp}+J_{\parallel}/2. The magnetizations for the GS and at finite
temperatures, as well as the susceptibility, show good agreements in various
comparisons with the finite-site exact diagonalization, the transfer-matrix
renormalization group numerical result, the perturbation theory, and the
compounds (5IAP)_2CuBr_4\cdot 2H_2O, Cu_2(C_5H_{12}N_2)_2Cl_4 and
(C_5H_{12}N)_2CuBr_4.",0405274v1
2004-05-21,"Incommensurate magnetic ordering in $Cu_2 Te_2 O_5 X_2$ (X=Cl,Br) studied by neutron diffraction","We present the results of the first neutron powder and single crystal
diffraction studies of the coupled spin tetrahedra systems ${\CuTeX}$ (X=Cl,
Br). Incommensurate antiferromagnetic order with the propagation vectors
${\bf{k}_{Cl}}\approx[0.150,0.422,\half]$,
${\bf{k}_{Br}}\approx[0.158,0.354,\half]$ sets in below $T_{N}$=18 K for X=Cl
and 11 K for X=Br. No simple collinear antiferromagnetic or ferromagnetic
arrangements of moments within Cu${}^{2+}$ tetrahedra fit these observations.
Fitting the diffraction data to more complex but physically reasonable models
with multiple helices leads to a moment of 0.67(1)$\mu_B$/Cu${}^{2+}$ at 1.5 K
for the Cl-compound. The reason for such a complex ground state may be
geometrical frustration of the spins due to the intra- and inter-tetrahedral
couplings having similar strengths. The magnetic moment in the Br- compound,
calculated assuming it has the same magnetic structure as the Cl compound, is
only 0.51(5)$\mu_B$/Cu${}^{2+}$ at 1.5 K. In neither compound has any evidence
for a structural transition accompanying the magnetic ordering been found.",0405513v3
2004-05-30,Electronic structure of crystalline binary and ternary Cd-Te-O compounds,"The electronic structure of crystalline CdTe, CdO, $\alpha$-TeO$_2$,
CdTeO$_3$ and Cd$_3$TeO$_6$ is studied by means of first principles
calculations. The band structure, total and partial density of states, and
charge densities are presented. For $\alpha$-TeO$_2$ and CdTeO$_3$, Density
Functional Theory within the Local Density Approximation (LDA) correctly
describes the insulating character of these compounds. In the first four
compounds, LDA underestimates the optical bandgap by roughly 1 eV. Based on
this trend, we predict an optical bandgap of 1.7 eV for Cd$_3$TeO$_6$. This
material shows an isolated conduction band with a low effective mass, thus
explaining its semiconducting character observed recently. In all these oxides,
the top valence bands are formed mainly from the O 2p electrons. On the other
hand, the binding energy of the Cd 4d band, relative to the valence band
maximum, in the ternary compounds is smaller than in CdTe and CdO.",0405700v1
2004-08-09,Excitonic effect on optical response in one-dimensional two-band Hubbard model,"Motivated by the gigantic nonlinear optical response in the halogen-bridged
Ni-compounds, the underlying electronic states of the compounds are examined in
the one-dimensional two-band Hubbard model, by studying the current-current
correlation function and the charge density in the ground state. The dynamical
density matrix renormalization group method is employed. We find that the
low-energy peak of the correlation function consists of a single Lorentzian
component for a parameter range appropriate to the compounds. This is due to an
excitonic state induced by the intersite Coulomb repulsion between holes on the
metal and halogen ions. This is consistent with the optical absorption spectra
of the compounds. We suggest that the localization of holes on the metal ions
in the ground state brings about the formation of the excitonic state.",0408172v1
2004-12-10,"Short-range charge-order in $R$NiO$_{3}$ perovskites ($R$=Pr,Nd,Eu) probed by X-ray absorption spectroscopy","The short-range organization around Ni atoms in orthorhombic $R$NiO$_{3}$
($R$=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni
K-edge x-ray absorption spectroscopy. Our results demonstrate that two
different Ni sites, with different average Ni-O bond lengths, coexist in those
orthorhombic compounds and that important modifications in the Ni nearest
neighbors environment take place across the metal-insulator transition. We
report evidences for the existence of short-range charge-order in the
insulating state, as found in the monoclinic compounds. Moreover, our results
suggest that the two different Ni sites coexists even in the metallic state.
The coexistence of two different Ni sites, independently on the $R$ ion,
provides a common ground to describe these compounds and shed new light in the
understanding of the phonon-assisted conduction mechanism and unusual
antiferromagnetism present in all $R$NiO$_{3}$ compounds.",0412277v1
2005-01-19,Magnetism and Transport in YbMn2Sb2,"A new ternary intermetallic compound, namely, YbMn2Sb2, has been synthesized
and its magnetic and electrical transport properties have been studied in the
temperature range of 2 to 300 K. This compound crystallizes in a trigonal,
La2O2S type structure (space group P3bm1, No. 164) and is found to be
ferromagnetically ordered at room temperature. The magnetism is attributed to
the ordering of Mn sublattice. M5 xray absorption spectrum of YbMn2Sb2 obtained
at room temperature suggests that the valency of Yb in this compound is close
to 2. Electrical resistivity of this compound is metal like and a positive
magnetoresistance of 13 percent is observed at 5 K in an applied field of 9T.
Key words Rare earth intermetallics and alloys, Magnetic properties, Xray
absorption spectroscopy, Electrical transport.",0501450v1
2005-01-24,"Magnetic and Transport Properties of Ternary Indides of type R2CoIn8 (R = Ce, Pr and Dy)","We have synthesized and investigated the magnetic and transport properties of
a series of compounds, R2CoIn8 (R = rare earth). Compounds form in single phase
with a tetragonal structure (space group P4/mmm, no. 162). The Ce compound
shows heavy fermion behavior. The magnetic susceptibility of Pr2CoIn8 shows a
marked deviation from the Curie-Weiss behavior at low temperatures, which is
attributed to the crystalline electric field effects. Heat capacity and
magnetization measurements show that Dy2CoIn8 undergoes a magnetic transition
at 17 K and a second transition near 5 K, the latter of which may be due to
spin reorientation. Magnetization of this compound shows two metamagnetic
transitions approximately at 3.6 T and 8.3 T.",0501553v1
2005-09-14,Magnetic ordering in trigonal chain compounds,"We present electronic structure calculations for the one-dimensional magnetic
chain compounds Ca_3CoRhO_6 and Ca_3FeRhO_6. The calculations are based on
density functional theory and the local density approximation. We use the
augmented spherical wave (ASW) method. The observed alternation of low- and
high-spin states along the Co-Rh and Fe-Rh chains is related to differences in
the oxygen coordination of the transition metal sites. Due to strong
hybridization the O 2p states are polarized, giving rise to extended localized
magnetic moments centered at the high-spin sites. Strong metal-metal overlap
along the chains leads to a substantial contribution of the low-spin Rh
4d_{3z^2-r^2} orbitals to the exchange coupling of the extended moments.
Interestingly, this mechanism holds for both compounds, even though the
coupling is ferromagnetic for the cobalt and antiferromagnetic for the iron
compound. However, our results allow to understand the different types of
coupling from the filling dependence of the electronic properties.",0509374v1
2005-10-06,Ca_25Co_22O_56(OH)_28: a layered misfit compound,"The high pressure synthesis, structure and magnetic properties of
Ca_25Co_22O_56(OH)_28 are reported. The compound has a misfit structure,
consisting of double, square calcium oxide hydroxide rock-salt-like layers
between hexagonal CoO_2 layers. The misfit compound crystallizes in the
monoclinic space group C2/m, and can be characterized by the coexistence of two
subsystems with common a=4.893(5)A, c=8.825(9)A and b=95.745(8) parameters, and
different b parameters: b_RS=4.894(5)A, and b_HEX=2.809(3)A, for the rock-salt
and hexagonal type planes respectively. The compound shows Curie-Weiss
paramagnetism with an antiferromagnetic Weiss temperature of -43K and a reduced
Co moment. Substantial deviations from Curie-Weiss behavior are seen below 50K
with no indication of magnetic ordering. No superconductivity was observed down
to a temperature of 2K.",0510137v2
2005-12-21,"Field-induced first-order magnetic phase transition in an intermetallic compound, Nd7Rh3: Evidence for kinetic-hindrance, phase co-existence and percolative conduction","The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, was
previously known to exhibit two magnetic transitions, one at 32 K and the other
at 10 K (in zero magnetic field). Here, we report the existence of a
field-induced first-order antiferromagnetic to ferromagnetic transition at 1.8
K in this compound. On the basis of the measurements of isothermal
magnetization and magnetoresistance, we provide evidence for the occurence of
kinetic-hindrance, proposed in the literature, resulting in phase co-existence
(super-cooled ferromagnetic + antifferomagnetic) and percolative electrical
conduction in this stoichiometric intermetallic compound. A point of emphasis,
as inferred from ac susceptibility data, is that such a co-existing phase is
different from spin-glasses, thereby clarifying a question raised in the field
of phase-separation.",0512542v1
2006-02-14,Correlation between molecular orbitals and doping dependence of the electrical conductivity in electron-doped Metal-Phthalocyanine compounds,"We have performed a comparative study of the electronic properties of six
different electron-doped metal phthalocyanine (MPc) compounds (ZnPc, CuPc,
NiPc, CoPc, FePc, and MnPc), in which the electron density is controlled by
means of potassium intercalation. In spite of the complexity of these systems,
we find that the nature of the underlying molecular orbitals produce observable
effects in the doping dependence of the electrical conductivity of the
materials. For all the MPc's in which the added electrons are expected to
occupy orbitals centered on the ligands (ZnPc, CuPc, and NiPc), the doping
dependence of the conductivity has an essentially identical shape. This shape
is different from that observed in MPc materials in which electrons are also
added to orbitals centered on the metal atom (CoPc, FePc, and MnPc). The
observed relation between the macroscopic electronic properties of the MPc
compounds and the properties of the molecular orbitals of the constituent
molecules, clearly indicates the richness of the alkali-doped
metal-phthalocyanines as a model class of compounds for the investigation of
the electronic properties of molecular systems.",0602329v1
2006-09-01,Texture transitions in binary mixtures of 6OBAC with compounds of its homologous series,"Recently we have observed in compounds of the 4,n-alkyloxybenzoic acid
series, with the homologous index n ranging from 6 to 9, a texture transition
in the nematic range which subdivides the nematic phase in two sub-phases
displaying different textures in polarised light analysis. To investigate a
persistence of texture transitions in nematic phases, we prepared binary
mixtures of 4,6-alkyloxybenzoic acid (6OBAC) with other members (7-,8-,9-,12-,
16OBAC) of its homologous series. Binary mixtures exhibit a broadening in the
temperature ranges of both smectic and nematic phases. A nematic temperature
range of 75 C is observed. In the nematic phase, in spite of the microscopic
disorder introduced by mixing two components, the polarised light optics
analysis of the liquid crystal cells reveals a texture transition. In the case
of the binary mixture of 6OBAC with 12OBAC and with 16OBAC, that is of
compounds with monomers of rather different lengths, the texture transition
temperature is not homogeneous in the cell, probably due to a local variation
in the relative concentrations of compounds.",0609008v1
2006-09-10,An anomalous magnetic phase transition at 10 K in Nd7Rh3,"The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has
been shown recently by us to exhibit a signature of magnetic phase-coexistence
phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric
intermetallic compounds, bearing a relevance to the trends in the field of
electronic phase-separation. In order to characterize this compound further, we
have carried out dc magnetic susceptibility (chi), electrical resistivity,
magnetoresistance and heat-capacity measurements as a function temperature (T=
1.8 to 300 K). The results reveal that this compound exhibits another unusual
finding at the 10K-transition in the sense that the plot of chi(T) shows a
sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve
shows a downturn below the transition. In addition, the sign of
magnetoresistance is negative and the magnitude is large over a wide
temperature range in the vicinity of magnetic ordering temperature, with a
sharp variation at 10 K. The results indicate that the transition below 10 K is
first-order in its character.",0609232v1
2006-09-14,Role of coexisting ferromagnetic and antiferromagnetic phases on the magnetocaloric effect in metamagnetic Tb2Ni2Sn,"We report the anomalous magnetocaloric behavior in the polycrystalline
compound Tb2Ni2Sn. The magnetization measurements show that this compound shows
multiple magnetic transitions, which are attributed to the coexistence of
ferromagnetic and antiferromagnetic phases at low temperatures. With increase
in field and temperature, the compound undergoes a metamagnetic transition to a
ferromagnetic state. In the temperature range where the antiferromagnetic phase
is dominant, it exhibits inverse (negative) magnetocaloric effect. At
temperatures close to the Neel temperature, the compound shows positive
magnetocaloric effect. Below the critical field needed for the metamagnetic
transition, the temperature variation of the magnetocaloric effect is seen to
be correlated with the ferromagnetic fraction.",0609335v2
2006-10-30,Hybridization functions of intermetallic Ce compounds with group VI elements,"Among the Cerium compounds, the heavier monochalcogenides CeY (Y=S,Se,Te) of
cerium provide a class of compounds which together with the heavier
monopnictides CeX (X=N,P,As,Sb,Bi) exhibit extremely interesting physical
properties. The hybridization of the partially delocalized f-electrons seems to
be responsible for the unusual properties, in particular the magnetic ones
which show great chemical sensitivity. As compared to the monopnictides, the
monochalcogenides have an additional anion p-electron which shifts the Fermi
energy into the p-region of the Cerium 5d-derived density of states, and which
should affect the hybridization function of the electrons in the conduction
band. In this contribution we analyze the 4f-hybridization function and the
crystal-field splittings of the compounds under study.
  KEY WORDS: Highly correlated systems, crystal fields, p-electron.",0610807v1
2006-12-12,Magnetic and Resonance Properties of the Compound (NH3)2(CH2)3CoCl4 - an Antiferromagnet with the Dzyaloshinskii Interaction,"The static magnetic and dynamic properties of the compound (NH3)2(CH2)3CoCl4
are investigated in the temperature interval 0.5-50 K. It is shown that at TN
=2.05 K this compound undergoes a transition to a magnetically ordered
antiferromagnet state. A distinctive feature of this compound is the presence
of temperature hysteresis at the transition to the ordered state (corresponding
to a first order magnetic phase transition) and of a spontaneous magnetic
moment along the x axis. The paramagnetic Curie temperatures are determined.
The frequency-field curves of the AFMR spectrum in the xy plane are
investigated at a temperature below TN. The main magnetic parameters of the
biaxial AFM - the value of the low-frequency gap and the effective magnetic
anisotropy field - are determined.",0612285v1
2007-01-15,Electron-phonon interaction in Graphite Intercalation Compounds,"Motivated by the recent discovery of superconductivity in Ca- and
Yb-intercalated graphite (CaC$_{6}$ and YbC$_{6}$) and from the ongoing debate
on the nature and role of the interlayer state in this class of compounds, in
this work we critically study the electron-phonon properties of a simple model
based on primitive graphite. We show that this model captures an essential
feature of the electron-phonon properties of the Graphite Intercalation
Compounds (GICs), namely, the existence of a strong dormant electron-phonon
interaction between interlayer and $\pi ^{\ast}$ electrons, for which we
provide a simple geometrical explanation in terms of NMTO Wannier-like
functions. Our findings correct the oversimplified view that
nearly-free-electron states cannot interact with the surrounding lattice, and
explain the empirical correlation between the filling of the interlayer band
and the occurrence of superconductivity in Graphite-Intercalation Compounds.",0701347v1
2007-03-02,"Ab-initio design of half-metallic fully-compensated ferrimagnets: the case of Cr$_2$MnZ (Z= P, As, Sb, Bi) compounds","Electronic structure calculations from first-principles are employed to
design some new half-metallic fully-compensated ferrimagnets (or as they are
widely known half-metallic antiferromagnets) susceptible of finding
applications in spintronics. Cr$_2$MnZ (Z= P, As, Sb, Bi) compounds have 24
valence electrons per unit cell and calculations show that their total spin
moment is approximately zero for a wide range of lattice constants in agreement
with the Slater-Pauling behavior for ideal half-metals. Simultaneously, the
spin magnetic moments of Cr and Mn atoms are antiparallel and the compounds are
ferrimagnets. Mean-field approximation is employed to estimate their Curie
temperature, which exceeds room temperature for the alloy with Sb. Our findings
suggest that Cr$_2$MnSb is the compound of choice for further experimental
investigations. Contrary to the alloys mentioned above half-metallic
antiferromagnetism is unstable in the case of the Cr$_2$FeZ (Z= Si, Ge, Sn)
alloys.",0703078v1
2005-07-08,Compound nuclear decay and the liquid to vapor phase transition: a physical picture,"Analyses of multifragmentation in terms of the Fisher droplet model (FDM) and
the associated construction of a nuclear phase diagram bring forth the problem
of the actual existence of the nuclear vapor phase and the meaning of its
associated pressure. We present here a physical picture of fragment production
from excited nuclei that solves this problem and establishes the relationship
between the FDM and the standard compound nucleus decay rate for rare particles
emitted in first-chance decay. The compound thermal emission picture is
formally equivalent to a FDM-like equilibrium description and avoids the
problem of the vapor while also explaining the observation of Boltzmann-like
distribution of emission times. In this picture a simple Fermi gas thermometric
relation is naturally justified and verified in the fragment yields and time
scales. Low energy compound nucleus fragment yields scale according to the FDM
and lead to an estimate of the infinite symmetric nuclear matter critical
temperature between 18 and 27 MeV depending on the choice of the surface energy
coefficient of nuclear matter.",0507015v1
2001-05-19,A Representation for Compound Quantum Systems as Individual Entities: Hard Acts of Creation and Hidden Correlations,"We introduce an explicit definition for 'hidden correlations' on individual
entities in a compound system: when one individual entity is measured, this
induces a well-defined transition of the 'proper state' of the other individual
entities. We prove that every compound quantum system described in the tensor
product of a finite number of Hilbert spaces can be uniquely represented as a
collection of individual(ized) (peudo-)entities between which there exist such
hidden correlations. We investigate the significance of these hidden
correlation representations within the so-called
``creation-discovery-approach'' and in particular their compatibility with the
``hidden measurement formalism''. This leads us to the introduction of the
notions of 'soft' and 'hard' 'acts of creation' and to the observation that our
approach can be seen as a theory of (pseudo-)individuals when compared to the
standard quantum theory. (For a presentation of the ideas proposed in this
paper within a quantum logical setting, yielding a structural theorem for the
representation of a compound quantum system in terms of the Hilbert space
tensor product, we refer to quant-ph/0008054.)",0105093v1
2007-06-26,Correlation between transport properties and lattice effects in the NdCoO3 based catalysts and sensor materials,"This study presents correlations between the structural and transport
properties of pure and doped neodymium cobaltate, a compound of great interest
for its foreseen applications as catalyst, sensor and thermoelectric material.
Neutron and x-ray powder diffraction data have been combined to carefully
determine lattice constants and atomic positions and four probe direct current
conductivity and thermoelectric power measurements allowed us to follow the
thermal evolution of the transport properties of these compounds. The dramatic
improvement of the room temperature conductivity of Nd0.8Ca0.2CoO3 with respect
to the pure and the Na-doped compound is explained in terms of a different
spin-state for the Co ions within this structure. The higher conductivity and
the absence of anomalies in the thermal expansion makes the Ca-doped compound
more attractive than the pure NdCoO3 in view of possible applications. The
experimental data and the Co environment analysis here discussed, in particular
bond lengths distortion and bending angles, are fully consistent with a spin
state (low to intermediate) transition in NdCoO3",0706.3760v1
2007-07-17,Positive and negative pressure effects on the magnetic ordering and the Kondo effect in the compound Ce2RhSi3,"The competition between magnetic ordering and the Kondo effect in Ce2RhSi3,
ordering antiferromagnetically at 7 K, is investigated by the measurements of
magnetization, heat capacity and electrical resistivity on the solid solutions,
Ce(2-x)La(x)RhSi3, Ce(2-y)Y(y)RhSi3, and Ce2RhSi(3-z)Ge(z), as well as by high
pressure studies on this compound. The trends in the Kondo and Neel temperature
variations among these alloys are compared to infer the roles of unit-cell
volume and electronic structure changes. On the basis of the results, we infer
that this compound lies at the peak of Doniach-magnetic-phase-diagram. The high
pressure electrical resistivity data indicate that the quantum critical point
for this compound is in the vicinity of 4 GPa.",0707.2518v1
2007-08-03,Equilibrium Low Temperature Heat Capacity of the Spin Density Wave compound (TMTTF)2 Br: effect of a Magnetic Field,"We have investigated the effect of the magnetic field (B) on the very
low-temperature equilibrium heat capacity ceq of the quasi-1 D organic compound
(TMTTF)2Br, characterized by a commensurate Spin Density Wave (SDW) ground
state. Below 1K, ceq is dominated by a Schottky-like contribution, very
sensitive to the experimental time scale, a property that we have previously
measured in numerous DW compounds. Under applied field (in the range 0.2- 7 T),
the equilibrium dynamics, and hence ceq extracted from the time constant,
increases enormously. For B = 2-3 T, ceq varies like B2, in agreement with a
magnetic Zeeman coupling. Another specific property, common to other
Charge/Spin density wave (DW) compounds, is the occurrence of metastable
branches in ceq, induced at very low temperature by the field exceeding a
critical value. These effects are discussed within a generalization to SDWs in
a magnetic field of the available Larkin-Ovchinnikov local model of strong
pinning. A limitation of the model when compared to experiments is pointed out.",0708.0540v1
2007-12-19,Madelung Energy of the Valence Skipping Compound BaBiO$_3$,"Several elements show valence skip fluctuation, for instance, Tl forms the
compounds in valence states +1 and +3, and Bi forms in +3 and +5 states. This
kind of fluctuation gives rise to a negative effective attractive interaction
and the Kondo effect. In the compounds of valence skipping elements, the
carrier doping will induce superconductivity with high critical temperature.
For example, Ba$_{1-x}$K$_x$BiO$_3$ shows high $T_c$ which is unlikely from the
conventional electron-phonon mechanism. The reason for the missing of some
valence states in such valence skip compounds remains a mystery. We have
performed the evaluation of the Madelung potential for BaBiO$_3$, and have
shown for the first time that charge-ordered state is stabilized if we take
into account the polarization of the oxygen charge. We argue that the effective
Coulomb interaction energy $U$ may be negative evaluating the local excitation
energy.",0712.3097v1
2008-06-09,Hydration-induced anisotropic spin fluctuations in Na_{x}CoO_{2}\cdot1.3H_{2}O superconductor,"We report ^{59}Co NMR studies in single crystals of cobalt oxide
superconductor Na_{0.42}CoO_{2}\cdot1.3H_{2}O (T_c=4.25K) and its parent
compound Na_{0.42}CoO_{2}. We find that both the magnitude and the temperature
(T) dependence of the Knight shifts are identical in the two compounds above
T_c. The spin-lattice relaxation rate (1/T_1) is also identical above T_0
\sim60 K for both compounds. Below T_0, the unhydrated sample is found to be a
non-correlated metal that well conforms to Fermi liquid theory, while spin
fluctuations develop in the superconductor. These results indicate that water
intercalation does not change the density of states but its primary role is to
bring about spin fluctuations. Our result shows that, in the hydrated
superconducting compound, the in-plane spin fluctuation around finite wave
vector is much stronger than that along the c-axis, which indicates that the
spin correlation is quasi-two-dimensional.",0806.1412v1
2008-06-13,Extraterrestrial nucleobases in the Murchison meteorite,"Carbon-rich meteorites, carbonaceous chondrites, contain many biologically
relevant organic molecules and delivered prebiotic material to the young Earth.
We present compound-specific carbon isotope data indicating that measured
purine and pyrimidine compounds are indigenous components of the Murchison
meteorite. Carbon isotope ratios for uracil and xanthine of delta13C=+44.5per
mil and +37.7per mil, respectively, indicate a non-terrestrial origin for these
compounds. These new results demonstrate that organic compounds, which are
components of the genetic code in modern biochemistry, were already present in
the early solar system and may have played a key role in life's origin.",0806.2286v1
2008-08-14,Half-metallic ferromagnetism in binary compounds of alkali metals with nitrogen: Ab initio calculations,"The first-principles full-potential linearized augmented plane-wave method
based on density functional theory is used to investigate electronic structure
and magnetic properties of hypothetical binary compounds of I$^{A}$ subgroup
elements with nitrogen (LiN, NaN, KN and RbN) in assumed three types of
cristalline structure (rock salt, wurtzite and zinc-blende). We find that, due
to the spin polarized \textit{p} orbitas of N, all four compounds are
half-metallic ferromagnets with wide energy bandgaps (up to 2.0 eV). The
calculated total magnetic moment in all investigated compounds for all three
types of crystal structure is exactly 2.00 $\mu_{\text{B}}$ per formula unit.
The predicted half-metallicity is robust with respect to lattice-constant
contraction. In all the cases ferromagnetic phase is energetically favored with
respect to the paramagnetic one. The mechanism leading to half-metallic
ferromagnetism and synthesis possibilities are discussed.",0808.1951v2
2008-09-25,Magnetic Behavior of Single Crystalline Pr_{5}Ge_{3} and Tb_{5}Ge_{3}Compounds,"The results of the magnetization studies on Pr_{5}Ge_{3}and Tb_{5}Ge_{3}
single crystals are reported. Single Crystals of Pr_{5}Ge_{3} and Tb_{5}Ge_{3}
compounds were successfully grown by Czochralski method. These compounds
crystallize in a Mn_{5}Si_{3} type hexagonal structure with space group
P6_{3}/mcm. Ferromagnetic correlations set in at around 36 K in Pr_{5}Ge_{3} in
the ab plane followed by an antiferromagnetic transition at 13 K. Along the
c-axis the magnetization shows a ferromagnetic transition around 13 K with an
overall ferrimagnetic behavior. At 2K, the magnetic isotherm of the compound
along [0001] direction is typical for a ferromagnet, while a field induced
ferromagnetic type response is observed along the [10\overline{\mathit{1}}0]
direction. Hexagonal ab plane or [10\overline{\mathit{1}}0] direction was found
to be the easy axis of magnetization. Tb_{5}Ge_{3} orders antiferromagneticaly
at 85 K with the hexagonal ab plane as easy axis of magnetization. The compound
shows a field induced ferromagnetic behavior in its magnetic isotherm at 2 K.",0809.4467v2
2008-10-13,Tunable Hydrogen Storage in Magnesium - Transition Metal Compounds,"Magnesium dihydride ($\mgh$) stores 7.7 weight % hydrogen, but it suffers
from a high thermodynamic stability and slow (de)hydrogenation kinetics.
Alloying Mg with lightweight transition metals (TM = Sc, Ti, V, Cr) aims at
improving the thermodynamic and kinetic properties. We study the structure and
stability of Mg$_x$TM$_{1-x}$H$_2$ compounds, $x=[0$-1], by first-principles
calculations at the level of density functional theory. We find that the
experimentally observed sharp decrease in hydrogenation rates for $x\gtrsim0.8$
correlates with a phase transition of Mg$_x$TM$_{1-x}$H$_2$ from a fluorite to
a rutile phase. The stability of these compounds decreases along the series Sc,
Ti, V, Cr. Varying the transition metal (TM) and the composition $x$, the
formation enthalpy of Mg$_x$TM$_{1-x}$H$_2$ can be tuned over the substantial
range 0-2 eV/f.u. Assuming however that the alloy Mg$_x$TM$_{1-x}$ does not
decompose upon dehydrogenation, the enthalpy associated with reversible
hydrogenation of compounds with a high magnesium content ($x=0.75$) is close to
that of pure Mg.",0810.2254v1
2008-11-26,"Magnetic order in CaFe1-xCoxAsF (x = 0, 0.06, 0.12) superconductor compounds","A Neutron Powder Diffraction (NPD) experiment has been performed to
investigate the structural phase transition and magnetic order in CaFe1-xCoxAsF
superconductor compounds (x = 0, 0.06, 0.12). The parent compound CaFeAsF
undergoes a tetragonal to orthorhombic phase transition at 134(3) K, while the
magnetic order in form of a spin-density wave (SDW) sets in at 114(3) K. The
antiferromagnetic structure of the parent compound has been determined with a
unique propagation vector k = (1,0,1) and the Fe saturation moment of 0.49(5)uB
aligned along the long a-axis. With increasing Co doping, the long range
antiferromagnetic order has been observed to coexist with superconductivity in
the orthorhombic phase of the underdoped CaFe0.94Co0.06AsF with a reduced Fe
moment (0.15(5)uB). Magnetic order is completely suppressed in optimally doped
CaFe0.88Co0.12AsF. We argue that the coexistence of SDW and superconductivity
might be related to mesoscopic phase separation.",0811.4418v2
2008-12-03,"Superconductivity in LnFePO (Ln = La, Pr, and Nd) single crystals","Single crystals of the compounds LaFePO, PrFePO, and NdFePO have been
prepared by means of a flux growth technique and studied by electrical
resistivity, magnetic susceptibility and specific heat measurements. We have
found that PrFePO and NdFePO display superconductivity with values of the
superconducting critical temperature T_c of 3.2 K and 3.1 K, respectively. The
effect of annealing on the properties of LaFePO, PrFePO, and NdFePO is also
reported. The LnFePO (Ln = lanthanide) compounds are isostructural with the
LnFeAsO_{1-x}F_x compounds that become superconducting with T_c values as high
as 55 K for Ln = Sm. A systematic comparison of the occurrence of
superconductivity in the series LnFePO and LnFeAsO_{1-x}F_x points to a
possible difference in the origin of the superconductivity in these two series
of compounds.",0812.0774v1
2008-12-12,"Spin diffusion and magnetic eigenoscillations confined to single molecular layers in the organic conductors kappa-(BEDT-TTF)_2Cu[N(CN)_2X (X=Cl, Br)","The layered organic compounds, kappa-(BEDT-TTF)_2Cu[N(CN)_2X (X=Cl, Br) are
metals at ambient temperatures. At low temperatures, the Cl compound is a
weakly ferromagnetic Mott insulator while the isostructural Br compound is a
superconductor. We find by conduction electron spin resonance (CESR) and
antiferromagnetic resonance (AFMR) an extreme anisotropy of spin transport and
magnetic interactions in these materials. In the metallic state spin diffusion
is confined to single molecular layers within the spin lifetime of 10^-9 s.
Electrons diffuse several hundreds of nm without hopping to the next molecular
layer. In the magnetically ordered insulating phase of the Cl compound we
observe and calculate the four AFMR modes of the weakly coupled single
molecular layers. The inter-plane exchange field is comparable or less than the
typically 1 mT dipolar field and almost 10^6 times less than the intra-layer
exchange field.",0812.2383v1
2009-02-01,Magnetic anomalies in Nd6Co(1.67)Si3: Surprising first order transitions in the low-temperature isothermal magnetization,"We present the results of magnetic measurements on Nd6Co(1.67)Si3, a compound
recently reported to crystallize in a hexagonal structure (space group P6_3/m)
and to undergo long range magnetic ordering below 84 K. The results reveal that
the magnetism of this compound is quite complex with additional magnetic
anomalies near 50 and 20 K. There are qualitative changes in the isothermal
magnetization behavior with the variation of temperature. Notably, there is a
field-induced spin reorientation as the temperature is lowered below 20 K. A
finding we stress is that this transition is discontinuous for 1.8K in the
virgin curve, but the first order character appears only after a field-cycling
for a narrow higher temperature range near 5 K. Thus, this compound serves as
an example for the stabilisation of first-order transition induced by
magnetic-field-cycling. The issues of 'Phase co-existence' and 'meta-stability'
after a field-cycling at low temperatures in this compound are also addressed.",0902.0150v1
2009-02-01,Magnetic anomalies in Gd6Co1.67Si3 and Tb6Co1.67Si3,"The compounds, Gd6Co1.67Si3 and Tb6Co1.67Si3, recently reported to form in a
Ce6Ni2Si3-derived hexagonal structure (space group: P6_3 / m) and to order
magnetically below 295 and 190 K respectively, have been investigated by
detailed magnetization (M) studies in the temperature interval 1.8-330 K as a
function of magnetic field (H). The points of emphasis are: We observe multiple
steps in the M(H) curve for the Tb compound at 1.8 K while increasing H, but
these steps do not appear in the reverse cycle of H. At higher temperatures,
such steps are absent. However, this 'staircase' behavior of M(H) is not
observed for the Gd compound at any temperature and the isothermal
magnetization is not hysteretic unlike in Tb compound. From the M(H) data
measured at close intervals of temperature, we have derived isothermal entropy
change (Delta S) and it is found that Delta S follows a theoretically predicted
H^2/3-dependence.",0902.0151v1
2009-02-08,Magnetic and magnetoelectric studies in pure and cation doped BiFeO3,"We report magnetic and magnetoelectric studies on BiFeO3 and divalent cation
(A) suvtitute Bi0.7A0.3FeO3 (A = Sr,Ba, and Sr0.5Ba0.5). It is shown that the
rapid increase of magnetization at the Neel temperature (TN = 642 K) is
suppressed in the co-doped compound A = Sr0.5Ba0.5. All the divalent subtituted
compounds show enhanced magnetization and hysteresis loop. Both longitudinal
and transverse magnetoelectric coefficients were measured using the dynamical
lock-in technique. The co-doped compound shows the highest magnetoelectric
coefficient at room temperature although it is not the compound with the
highest saturation magnetization. It is found that as the size of the A-site
cation increses, the transverse magnetoelectric coeffient increases and exceeds
the longitudinal magnetoelectric coefficient. It is suggested that changes in
magnetic domain structure and magnetostriction are possible reasons for the
observed changes in the magnetoelectric coefficients.",0902.1283v1
2009-03-10,Effect of the chemical pressure on superconductivity and SDW in undoped and 15%F doped La1-yYyFeAsO compounds,"We present a study concerning the partial substitution of yttrium at the
lanthanum site of the undoped LaFeAsO and superconducting LaFeAsO0.85F0.15
compounds. We prepared samples with a nominal yttrium content up to 70%
producing simultaneous shrinkage of both the a- and c-lattice parameters by
1.8% and 1.7%, respectively. The chemical pressure provided by the partial
substitution with this smaller ion size causes a lowering of the spin density
wave temperature in the undoped compounds, as well as an increase of the
superconducting transition temperatures in the doped ones. The 15%
fluorine-doped samples reach a maximum critical temperature of 40.2 K for the
50% yttrium substitution. Comparison with literature data indicates that
chemical pressure cannot be the only mechanism which tunes drastically both
TSDW and Tc in 1111 compounds. Our data suggest that structural disorder
induced by the partial substitution in the La site or by doping could play an
important role as well.",0903.1825v2
2009-03-28,"Magnetic and dielectric properties in the langasite-type compounds : A3BFe3D2O14 with A=Ba, Sr, Ca, B=Ta, Nb, Sb and D=Ge, Si","The Fe-based langasites are the first reported compounds presenting a
magnetic ordering in this rich family, besides being well known for
piezo-electric properties and optical activity. The structural, magnetic and
dielectric properties of the Fe langasite compounds, with various substitution
of non-magnetic cations, have been studied with x-ray and neutron diffraction,
magnetostatic measurements, M\""ossbauer spectroscopy, and dielectric
measurements. The title compounds (trigonal, space group P321) display a
helical magnetic order with signatures of frustration below TN ~24- 35 K where
an anomaly of the dielectric permittivity is observed. The influence of the
cationic substitutions and the nature of the magnetoelectric coupling is
hereafter addressed.",0903.4950v1
2009-04-06,Computing Tails of Compound Distributions Using Direct Numerical Integration,"An efficient adaptive direct numerical integration (DNI) algorithm is
developed for computing high quantiles and conditional Value at Risk (CVaR) of
compound distributions using characteristic functions. A key innovation of the
numerical scheme is an effective tail integration approximation that reduces
the truncation errors significantly with little extra effort. High precision
results of the 0.999 quantile and CVaR were obtained for compound losses with
heavy tails and a very wide range of loss frequencies using the DNI, Fast
Fourier Transform (FFT) and Monte Carlo (MC) methods. These results,
particularly relevant to operational risk modelling, can serve as benchmarks
for comparing different numerical methods. We found that the adaptive DNI can
achieve high accuracy with relatively coarse grids. It is much faster than MC
and competitive with FFT in computing high quantiles and CVaR of compound
distributions in the case of moderate to high frequencies and heavy tails.",0904.0830v3
2009-06-02,Measurement of electron correlations in LixCoO2 (x=0.0 - 0.35) using 59Co nuclear magnetic resonance and nuclear quadrupole resonance techniques,"CoO2 is the parent compound for the superconductor NaxCoO2\cdot1.3H2O and was
widely believed to be a Mott insulator. We performed 59Co nuclear magnetic
resonance (NMR) and nuclear quadrupole resonance (NQR) studies on LixCoO2 (x =
0.35, 0.25, 0.12, and 0.0) to uncover the electronic state and spin
correlations in this series of compounds which was recently obtained through
electrochemical de-intercalation of Li from pristine LiCoO2. We find that
although the antiferromagnetic spin correlations systematically increase with
decreasing Li-content (x), the end member, CoO2 is a non-correlated metal that
well satisfies the Korringa relation for a Fermi liquid. Thus, CoO2 is not
simply located at the limit of x->0 for AxCoO2 (A = Li, Na) compounds. The
disappearance of the electron correlations in CoO2 is due to the three
dimensionality of the compound which is in contrast to the highly two
dimensional structure of AxCoO2.",0906.0400v1
2009-06-06,Low Temperature Crystal Structures and Magnetic Properties of the V4-Cluster Compounds Ga1-xGexV4S8,"The solid solution Ga1-xGexV4S8 (x = 0 - 1) was synthesized by solid state
reactions and characterized by temperature-dependent x-ray powder diffraction
and static magnetic susceptibility measurements. The compounds crystallize in
the cubic GaMo4S8-type structure (space group F-43m), built up by
heterocubane-like [V4S4](5-x)+ cubes and [Ga1-xGexS4](5-x)- tetrahedra arranged
in a NaCl-like manner. The successive substitution of Ga3+ by Ge4+ increases
the electron count in the molecular orbital (MO) of the V4-cluster gradually
from seven to eight. We observe an almost linear increase of the magnetic
moments, connected with a transition from ferromagnetic to antiferromagnetic
ordering around x <= 0.5. Remarkably, the low temperature structural phase
transitions as known from the ternary compounds were also detected in the solid
solution. The gallium-rich compounds (0 < x < 0.5) undergo rhombohedral
distortions like GaV4S8 (space group R3m), whereas distortions to orthorhombic
symmetry (space group Imm2) as known from GeV4S8 occur in the germanium-rich
part of the solid solution (0.5 <= x < 1).",0906.1278v1
2009-06-26,Insensitivity of magnetic anomalies in Sr3NiPtO6 to positive and negative pressures,"The compound, Sr3NiPtO6, belonging to a K4CdCl6-type rhombohedral structure,
has been reported not to exhibit magnetic ordering at least down to 1.8 K,
despite a relatively large value of paramagnetic Curie temperature. This is
attributable to geometrical frustration. Here we report the results of our
efforts to gradually replace Sr by Ba and to probe the influence of positive
(external) and negative (chemical) pressure on the magnetic behavior of this
compound. In the Ba substituted series, single phase is formed up to x= 1.0
with Ba substituting for Sr. The magnetic properties of the parent compound in
the entire temperature range of investigation are not influenced at all in any
of the compositions studied as well as under external pressure (investigated up
to 10 kbar). Spin-liquid-like heat-capacity behavior (finite linear term) is
observed even in Ba substituted specimens. Thus, the magnetic anomalies of this
compound are quite robust.",0906.4890v1
2009-06-29,Upper critical fields of the 11-system iron-chalcogenide superconductor FeSe$_{0.25}$Te$_{0.75}$,"We have performed electrical resistivity measurements of a polycrystalline
sample of FeSe$_{0.25}$Te$_{0.75}$, which exhibits superconductivity at $T_{\rm
c} \sim 14$ K, in magnetic fields up to 55 T to determine the upper critical
field $\mu_{0}H_{\rm c2}$. In this compound, very large slopes of
$\mu_{0}H_{\rm c2}$ at the onset, the mid-point, the zero-resistivity
temperatures on superconductivity are determined to be -13.7, -10.1, and -6.9
T/K, respectively. The observed $\mu_{0}H_{\rm c2}(T)$s of this compound are
considerably smaller than those expected from the Werthamer-Helfand-Hohenberg
model, manifesting the Pauli limiting behavior. These results suggest that this
compound has a large Maki parameter, but it is smaller than that calculated for
a weak-coupling superconductor, indicating a large superconducting gap of this
compound as a strong-coupling superconductor.",0906.5248v1
2009-07-29,Hafnium binary alloys from experiments and first principles,"Despite the increasing importance of hafnium in numerous technological
applications, experimental and computational data on its binary alloys is
sparse. In particular, data is scant on those binary systems believed to be
phase separating. We performed a comprehensive study of 44 hafnium binary
systems with alkali metals, alkaline earths, transition metals and metals,
using high-throughput first principles calculations. These computations predict
novel unsuspected compounds in six binary systems previously believed to be
phase separating They also predict a few unreported compounds in additional
systems and indicate that some reported compounds may actually be unstable at
low temperatures. We report the results for the following systems: AgHf, AlHf,
AuHf, BaHf*, BeHf, BiHf, CaHf*, CdHf, CoHf, CrHf, CuHf, FeHf, GaHf, HfHg, HfIn,
HfIr, HfK*, HfLa*, HfLi*, HfMg, HfMn, HfMo, HfNa*, HfNb*, HfNi, HfOs, HfPb,
HfPd, HfPt, HfRe, HfRh, HfRu, HfSc, HfSn, HfSr*, HfTa*, HfTc, HfTi, HfTl, HfV*,
HfW, HfY*, HfZn, and HfZr. (* = systems in which the ab initio method predicts
that no compounds are stable).",0907.5131v1
2009-09-23,"Muon-Spin Spectroscopy of the organometallic spin 1/2 kagome-lattice compound Cu(1,3-benzenedicarboxylate)","Using muon spin resonance we examine the organometallic hybrid compound
Cu(1,3-benzenedicarboxylate) [Cu(1,3-bdc)], which has structurally perfect spin
1/2 copper kagome planes separated by pure organic linkers. This compound has
antiferromagnetic interactions with Curie-Weiss temperature of -33 K. We found
slowing down of spin fluctuations starting at T=1.8 K, and that the state at
T->0 is quasi-static with no long-range order and extremely slow spin
fluctuations at a rate of 3.6 1/usec. This indicates that Cu(1,3-bdc) behaves
as expected from a kagome magnet and could serve as a model kagome compound.",0909.4187v1
2009-10-11,"Magnetic and electrical properties of RCo2Mn (R=Ho, Er) compounds","The RCo2Mn (R= Ho and Er) alloys, crystallizing in the cubic MgCu2-type
structure, are isostructural to RCo2 compounds. The excess Mn occupies both the
R and the Co atomic positions. Magnetic, electrical and heat capacity
measurements have been done in these comounds. The Curie temperature is found
to be 248 K and 222 K for HoCo2Mn and ErCo2Mn respectively, which are
considerably higher than that of the corresponding RCo2 compounds. Saturation
magnetization values calculated in these samples are less compared to that of
the corresponding RCo2 compounds. Heat capacity data have been fitted with the
nonmagnetic contribution with Debye temperature =250 K and electronic
coefficient=26 mJ mol^-1K^-2.",0910.2001v1
2009-10-28,"Magnetocrystalline anisotropy in RAu_{2}Ge_{2} (R = La, Ce and Pr) single crystals","Anisotropic magnetic properties of single crystalline RAu_{2}Ge_{2} (R = La,
Ce and Pr) compounds are reported. LaAu_{2}Ge_{2} exhibit a Pauli-paramagnetic
behavior whereas CeAu_{2}Ge_{2} and PrAu_{2}Ge_{2} show an antiferromagnetic
ordering with N\grave{e}el temperatures T_{N} = 13.5 and 9 K, respectively. The
anisotropic magnetic response of Ce and Pr compounds establishes [001] as the
easy axis of magnetization and a sharp spin-flip type metamagnetic transition
is observed in the magnetic isotherms. The resistance and magnetoresistance
behavior of these compounds, in particular LaAu_{2}Ge_{2}, indicate an
anisotropic Fermi surface. The magnetoresistivity of CeAu_{2}Ge_{2} apparently
reveals the presence of a residual Kondo interaction. A crystal electric field
analysis of the anisotropic susceptibility in conjunction with the
experimentally inferred Schottky heat capacity enables us to propose a crystal
electric field level scheme for Ce and Pr compounds. For CeAu_{2}Ge_{2} our
values are in excellent agreement with the previous reports on neutron
diffraction. The heat capacity data in LaAu_{2}Ge_{2} show clearly the
existence of Einstein contribution to the heat capacity.",0910.5310v1
2009-12-25,Doping Dependence of Spin Dynamics in Electron-Doped Ba(Fe1-xCox)2As2,"The spin dynamics in single crystal, electron-doped Ba(Fe1-xCox)2As2 has been
investigated by inelastic neutron scattering over the full range from undoped
to the overdoped regime. We observe damped magnetic fluctuations in the normal
state of the optimally doped compound (x=0.06) that share a remarkable
similarity with those in the paramagnetic state of the parent compound (x=0).
In the overdoped superconducting compound (x=0.14), magnetic excitations show a
gap-like behavior, possibly related to a topological change in the hole Fermi
surface (Lifshitz transition), while the imaginary part of the spin
susceptibility prominently resembles that of the overdoped cuprates. For the
heavily overdoped, non-superconducting compound (x=0.24) the magnetic
scattering disappears, which could be attributed to the absence of a hole
Fermi-surface pocket observed by photoemission.",0912.4945v2
2010-02-24,Interference Alignment for the Multi-Antenna Compound Wiretap Channel,"We study a wiretap channel model where the sender has $M$ transmit antennas
and there are two groups consisting of $J_1$ and $J_2$ receivers respectively.
Each receiver has a single antenna. We consider two scenarios. First we
consider the compound wiretap model -- group 1 constitutes the set of
legitimate receivers, all interested in a common message, whereas group 2 is
the set of eavesdroppers. We establish new lower and upper bounds on the secure
degrees of freedom. Our lower bound is based on the recently proposed
\emph{real interference alignment} scheme. The upper bound provides the first
known example which illustrates that the \emph{pairwise upper bound} used in
earlier works is not tight.
  The second scenario we study is the compound private broadcast channel. Each
group is interested in a message that must be protected from the other group.
Upper and lower bounds on the degrees of freedom are developed by extending the
results on the compound wiretap channel.",1002.4548v2
2010-03-28,Anomalous Hall Effect due to Non-collinearily in Pyrochlore Compounds: Role of Orbital Aharonov-Bohm Effect,"To elucidate the origin of spin structure-driven anomalous Hall effect (AHE)
in pyrochlore compounds, we construct the $t_{2g}$-orbital kagome lattice model
and analyze the anomalous Hall conductivity (AHC). We reveal that a conduction
electron acquires a Berry phase due to the complex d-orbital wavefunction in
the presence of spin-orbit interaction. This ``orbital Aharonov-Bohm (AB)
effect'' produces the AHC that is drastically changed in the presence of
non-collinear spin structure. In both ferromagnetic compound Nd$_2$Mo$_2$O$_7$
and paramagnetic compound Pr$_2$Ir$_2$O$_7$, the AHC given by the orbital AB
effect totally dominates the spin chirality mechanism, and succeeds in
explaining the experimental relation between the spin structure and the AHC.
Especially, ``finite AHC in the absence of magnetization'' observed in
Pr$_2$Ir$_2$O$_7$ can be explained in terms of the orbital mechanism by
assuming small magnetic order of Ir 5d-electrons.",1003.5339v2
2010-04-21,Compound Poisson Approximation via Information Functionals,"An information-theoretic development is given for the problem of compound
Poisson approximation, which parallels earlier treatments for Gaussian and
Poisson approximation. Let $P_{S_n}$ be the distribution of a sum $S_n=\Sumn
Y_i$ of independent integer-valued random variables $Y_i$. Nonasymptotic bounds
are derived for the distance between $P_{S_n}$ and an appropriately chosen
compound Poisson law. In the case where all $Y_i$ have the same conditional
distribution given $\{Y_i\neq 0\}$, a bound on the relative entropy distance
between $P_{S_n}$ and the compound Poisson distribution is derived, based on
the data-processing property of relative entropy and earlier Poisson
approximation results. When the $Y_i$ have arbitrary distributions,
corresponding bounds are derived in terms of the total variation distance. The
main technical ingredient is the introduction of two ""information functionals,""
and the analysis of their properties. These information functionals play a role
analogous to that of the classical Fisher information in normal approximation.
Detailed comparisons are made between the resulting inequalities and related
bounds.",1004.3692v1
2010-04-27,On the Capacity of Compound State-Dependent Channels with States Known at the Transmitter,"This paper investigates the capacity of compound state-dependent channels
with non-causal state information available at only the transmitter. A new
lower bound on the capacity of this class of channels is derived. This bound is
shown to be tight for the special case of compound channels with stochastic
degraded components, yielding the full characterization of the capacity.
Specific results are derived for the compound Gaussian Dirty-Paper (GDP)
channel. This model consists of an additive white Gaussian noise (AWGN) channel
corrupted by an additive Gaussian interfering signal, known at the transmitter
only, where the input and the state signals are affected by fading coefficients
whose realizations are unknown at the transmitter. Our bounds are shown to be
tight for specific cases. Applications of these results arise in a variety of
wireless scenarios as multicast channels, cognitive radio and problems with
interference cancellation.",1004.4917v1
2010-05-18,Strength of Correlations in electron and hole doped cuprates,"High temperature superconductivity was achieved by introducing holes in a
parent compound consisting of copper oxide layers separated by spacer layers.
It is possible to dope some of the parent compounds with electrons, and their
physical properties are bearing some similarities but also significant
differences from the hole doped counterparts. Here, we use a recently developed
first principles method, to study the electron doped cuprates and elucidate the
deep physical reasons why their behavior is so different than the hole doped
materials. We find that electron doped compounds are Slater insulators, e.g. a
material where the insulating behavior is the result of the presence of
magnetic long range order. This is in sharp contrast with the hole doped
materials, where the parent compound is a Mott charge transfer insulator,
namely a material which is insulating due to the strong electronic correlations
but not due to the magnetic order.",1005.3095v1
2010-06-03,Ab Initio Exchange Interactions and Magnetic Properties of Intermetallic Compound Gd(2)Fe(17-x)Ga(x),"Intermetallic compounds R2Fe17 are perspective for applications as permanent
magnets. Technologically these systems must have Curie temperature Tc much
higher than room temperature and preferably have easy axis anisotropy. At the
moment highest Tc among stoichiometric R2Fe17 materials is 476 K, which is not
high enough. There are two possibilities to increase Tc: substitution of Fe
ions with non-magnetic elements or introduction of light elements into
interstitial positions. In this work we have focused our attention on
substitution scenario of Curie temperature rising observed experimentally in
Gd(2)Fe(17-x)Ga(x) (x=0,3,6) compounds. In the framework of the LSDA approach
electronic structure and magnetic properties of the compounds were calculated.
Ab initio exchange interaction parameters within the Fe sublattice for all
nearest Fe ions were obtained. Employing the theoretical values of exchange
parameters Curie temperatures Tc of Gd(2)Fe(17-x)Ga(x) within mean-field theory
were estimated. Obtained values of Tc agree well with experiment. Also LSDA
computed values of total magnetic moment coincide with experimental ones.",1006.0591v1
2010-06-18,"A New Iron Pnictide Oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and a New Phase in Fe-As-Ca-Mg-Ti-O system","A new layered iron arsenide oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and its structural
derivative were found in the Fe-As-Ca-Mg-Ti-O system. The crystal structure of
(Fe2As2)(Ca5(Mg,Ti)4Oy) is identical to that of (Fe2As2)(Ca5(Sc,Ti)4Oy), which
was reported in our previous study. The lattice constants of this compound are
a = 3.86(4) A and c = 41.05(2) A. In addition, another phase with a thicker
blocking layer was found. The structure of the compound and its derivative was
tentatively assigned through STEM observation as (Fe2As2)(Ca8(Mg,Ti)6Oy) with
sextuple perovskite-type sheets divided by a rock salt layer. The interlayer
Fe-Fe distance of this compound is ~30 A. The compound and its derivative
exhibited bulk superconductivity, as found from magnetization and resistivity
measurements.",1006.3769v4
2010-12-25,"Effective moment of inertia for several fission reaction systems induced by nucleons, light particles and heavy ions","Compound nucleus effective moment of inertia has been calculated for several
fission reaction systems induced by nucleons, light particles, and heavy ions.
Determination of this quantity for these systems is based upon the comparison
between the experimental data of the fission fragment angular distributions as
well as the prediction of the standard saddle-point statistical model (SSPSM).
For the systems, the two cases, namely with and without neutron emission
corrections were considered. In these calculations, it is assumed that all the
neutrons are emitted before reaching the saddle point.It should be noted that
the above method for determining of the effective moment of inertia had not
been reported until now and this method is used for the first time to determine
compound nucleus effective moment of inertia. Hence, our calculations are of
particular importance in obtaining this quantity, and have a significant rule
in the field of fission physics. Afterwards, our theoretical results have been
compared with the data obtained from the rotational liquid drop model as well
as the Sierk model, and satisfactory agreements were found. Finally, we have
considered the effective moment of inertia of compound nuclei for the systems
that formed similar compound nuclei at similar excitation energies.",1012.5459v1
2011-01-11,Enhanced electrical resistance at the field-induced magnetic transitions in some stoichiometric and nonstoichiometric Tb-based ternary germanides,"We present the magnetic and transport behavior of some Tb compounds, viz.,
TbIrGe2, TbFe(0.4)Ge2, and TbCo(0.4)Ge2. The stoichoometric germanide TbIrGe2
exhibits at least two distinct magnetic transitions in a close temperature
interval around 10 K. The non-stoichiometric compounds, TbFe(0.4)Ge2 and
TbCo(0.4)Ge2, undergo magnetic ordering around 17 and 19 K respectively. The
magnetic state of these compouds appears to be antiferromagnetic-like.
Qualitatively, there is a correlation between the field response of the
magnetization (M), the magnetoresistance (MR) and the entropy change curve in
all these compouds. That is, these Tb compounds exhibit a ""positive"" MR and
entropy change beyond a magnetic field where M also shows a field-induced
transition. On the basis of this correlaion, we conclude that magnetic
disorder/fluctuations beyond a critical field - ""a phenomenon called inverse
metamagnetism"" - rather than metamagnetism,is induced in these compounds.",1101.2013v2
2011-03-01,Capacity results for compound wiretap channels,"We derive a lower bound on the secrecy capacity of the compound wiretap
channel with channel state information at the transmitter which matches the
general upper bound on the secrecy capacity of general compound wiretap
channels given by Liang et al. and thus establishing a full coding theorem in
this case. We achieve this with a quite strong secrecy criterion and with a
decoder that is robust against the effect of randomisation in the encoding.
This relieves us from the need of decoding the randomisation parameter which is
in general not possible within this model. Moreover we prove a lower bound on
the secrecy capacity of the compound wiretap channel without channel state
information.",1103.0135v2
2011-03-12,"Metal-insulator transition in layered nickelates La$_3$Ni$_2$O$_{7-δ}$ ($δ$=0.0, 0.5, 1)","Three low-valence layered nickelates with general formula
La$_3$Ni$_2$O$_{7-\delta}$ ($\delta$=0.0, 0.5, 1) are studied by ab initio
techniques. Both the insulating and metallic limits are analyzed, together with
the compound at the Mott transition ($\delta$= 0.5; Ni$^{2+}$), that shows
insulating behavior, with all Ni atoms in a S=1 high-spin state. The compound
in the $\delta$= 1 limit (La$_3$Ni$_2$O$_6$), with mean formal valence
Ni$^{1.5+}$ and hence nominally metallic, nevertheless shows a correlated {\it
molecular} insulating state, produced by the quantum confinement of the NiO$_2$
bilayers and the presence of mainly d$_{z^2}$ bands (bonding-antibonding split)
around the gap. The metallic compound shows a larger bandwidth of the e$_g$
states that can sustain the experimentally observed paramagnetic metallic
properties. The evolution of the in-plane antiferromagnetic coupling with the
oxygen content is discussed, and also the similarities of this series of
compounds with the layered superconducting cuprates.",1103.2407v1
2011-06-10,Secrecy Results for Compound Wiretap Channels,"We derive a lower bound on the secrecy capacity of the compound wiretap
channel with channel state information at the transmitter which matches the
general upper bound on the secrecy capacity of general compound wiretap
channels given by Liang et al. and thus establishing a full coding theorem in
this case. We achieve this with a stronger secrecy criterion and the maximum
error probability criterion, and with a decoder that is robust against the
effect of randomisation in the encoding. This relieves us from the need of
decoding the randomisation parameter which is in general not possible within
this model. Moreover we prove a lower bound on the secrecy capacity of the
compound wiretap channel without channel state information and derive a
multi-letter expression for the capacity in this communication scenario.",1106.2013v2
2011-07-07,Atomic scale chemical fluctuation in LaSrVMoO6: A proposed halfmetallic antiferromagnet,"Half metallic antiferromagnets (HMAFM) have been proposed theoretically long
ago but have not been realized experimentally yet. Recently, a double
perovskite compound, LaSrVMoO6, has been claimed to be an almost real HMAFM
system. Here, we report detailed experimental and theoretical studies on this
compound. Our results reveal that the compound is neither a half metal nor an
ordered antiferromagnet. Most importantly, an unusual chemical fluctuation is
observed locally, which finally accounts for all the electronic and magnetic
properties of this compound.",1107.1309v1
2011-08-02,"Structural, elastic, electronic and optical properties of a newly predicted layered-ternary Ti4SiN3: A First-principles study","We study a newly predicted layered-ternary compound Ti4SiN3 in its {\alpha}-
and {\beta}-phases. We calculate their mechanical, electronic and optical
properties and then compare these with those of other compounds M4AX3 (M = V,
Ti, Ta; A = Si, Al; X = N, C). The results show that the hypothetical Ti4SiN3
shows an improved behavior of the resistance to shape change and uniaxial
tensions and a slight elastic anisotropy. The electronic band structures for
both {\alpha}- and {\beta}-Ti4SiN3 show metallic conductivity in which Ti 3d
states dominate. The hybridization peak of Ti 3d and N 2s lies lower in energy
than that of Ti 3d and Si 3p states which suggests that the Ti 3d - N 2s bond
is stronger than the Ti 3d - Si 3p bond. Using band structure we discuss the
origin of different features of optical properties. The {\alpha}-phase of
predicted compound has improved behavior in reflectivity compared to those of
similar types of compounds.
  Keywords: Ternary nitride; First-principles; Mechanical properties;
Electronic band structure; Optical properties",1108.0553v1
2011-10-25,Ba{1-x}KxMn2As2: An Antiferromagnetic Local-Moment Metal,"The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a
local-moment antiferromagnetic insulator with a Neel temperature TN = 625 K and
a large ordered moment mu = 3.9 mu_B/Mn. We demonstrate that this compound can
be driven metallic by partial substitution of Ba by K, while retaining the same
crystal and antiferromagnetic structures together with nearly the same high TN
and large mu. Ba_{1-x}K_xMn2As2 is thus the first metallic ThCr2Si2-type
MAs-based system containing local 3d transition metal M magnetic moments, with
consequences for the ongoing debate about the local moment versus itinerant
pictures of the FeAs-based superconductors and parent compounds. The
Ba_{1-x}K_xMn2As2 class of compounds also forms a bridge between the layered
iron pnictides and cuprates and may be useful to test theories of high Tc
superconductivity.",1110.5546v2
2012-01-30,Synthesis and superconductivity of CeNi0.8Bi2: New entrant in superconductivity kitchen?,"CeNi0.8Bi2 is very recent entrant in superconductivity kitchen [1], and the
same seeks reproduction from other groups. We report synthesis, structural
details and superconductivity in CeNi0.8Bi2 compound. The CeNi0.8Bi2 compound
is synthesized by solid state reaction route via vacuum encapsulation of high
purity mixed Ce, Ni, Bi and subsequent heating of the same at 500 0C for 10
hours followed by annealing at 750 0C for 20 hours. As synthesized compounds
are dark grey in color and do crystallize in tetragonal structure with space
group P4/nmm. The lattice parameters are a = 3.61 {\AA} and c = 10.20 {\AA}. AC
susceptibility measurements showed that synthesized CeNi0.8Bi2 compound is
weakly superconducting below 4.2K. We believe our article will regenerate fresh
activity to look for bulk superconductivity in CeNi0.8Bi2.",1201.6131v4
2012-02-15,Local kernel canonical correlation analysis with application to virtual drug screening,"Drug discovery is the process of identifying compounds which have potentially
meaningful biological activity. A major challenge that arises is that the
number of compounds to search over can be quite large, sometimes numbering in
the millions, making experimental testing intractable. For this reason
computational methods are employed to filter out those compounds which do not
exhibit strong biological activity. This filtering step, also called virtual
screening reduces the search space, allowing for the remaining compounds to be
experimentally tested. In this paper we propose several novel approaches to the
problem of virtual screening based on Canonical Correlation Analysis (CCA) and
on a kernel-based extension. Spectral learning ideas motivate our proposed new
method called Indefinite Kernel CCA (IKCCA). We show the strong performance of
this approach both for a toy problem as well as using real world data with
dramatic improvements in predictive accuracy of virtual screening over an
existing methodology.",1202.3302v1
2012-02-17,Electronic and Magnetic Structures of Chain Structured Iron Selenide Compounds,"Electronic and magnetic structures of iron selenide compounds Ce2O2FeSe2
(2212\ast) and BaFe2Se3(123\ast) are studied by the first-principles
calculations. We find that while all these compounds are composed of
one-dimensional (1D) Fe chain (or ladder) structures, their electronic
structures are not close to be quasi-1D. The magnetic exchange couplings
between two nearest-neighbor (NN) chains in 2212\ast and between two NN
two-leg-ladders in 123\ast are both antiferromagnetic (AFM), which is
consistent with the presence of significant third NN AFM coupling, a common
feature shared in other iron-chalcogenides, FeTe (11\ast) and KyFe2-xSe2
(122\ast). In magnetic ground states, each Fe chain of 2212\ast is
ferromagnetic and each two-leg ladder of 123\ast form a block-AFM structure. We
suggest that all magnetic structures in iron-selenide compounds can be unified
into an extended J1-J2-J3 model. Spin-wave excitations of the model are
calculated and can be tested by future experiments on these two systems.",1202.4016v1
2012-03-04,Posterior Mean Super-Resolution with a Compound Gaussian Markov Random Field Prior,"This manuscript proposes a posterior mean (PM) super-resolution (SR) method
with a compound Gaussian Markov random field (MRF) prior. SR is a technique to
estimate a spatially high-resolution image from observed multiple
low-resolution images. A compound Gaussian MRF model provides a preferable
prior for natural images that preserves edges. PM is the optimal estimator for
the objective function of peak signal-to-noise ratio (PSNR). This estimator is
numerically determined by using variational Bayes (VB). We then solve the
conjugate prior problem on VB and the exponential-order calculation cost
problem of a compound Gaussian MRF prior with simple Taylor approximations. In
experiments, the proposed method roughly overcomes existing methods.",1203.0781v3
2012-03-28,New Method for Quantitative Determination of Volatile Compounds in Spirit Drinks by Gas Chromatography. Ethanol as Internal Standard,"The new methodical approach of using ethanol as internal standard in gas
chromatographic analysis of volatile compounds in spirit drinks in daily
practice of testing laboratories is proposed. This method provides
determination of volatile compounds concentrations in spirit drinks directly
expressed in milligrams per liter (mg/L) of absolute alcohol according to
official methods without measuring of alcohol strength of analyzed sample. The
experimental demonstration of this method for determination of volatile
compounds in spirit drinks by gas chromatography is described.",1203.6202v2
2012-04-07,KFe_2Se_2 is the parent compound of K-doped iron selenide superconductors,"We elucidate the existing controversies in the newly discovered K-doped iron
selenide (KxFe2-ySe2-z) superconductors. The stoichiometric KFe2Se2 with
\surd2\times\surd2 charge ordering was identified as the parent compound of
KxFe2-ySe2-z superconductor using scanning tunneling microscopy and
spectroscopy. The superconductivity is induced in KFe2Se2 by either Se
vacancies or interacting with the anti-ferromagnetic K2Fe4Se5 compound. Totally
four phases were found to exist in KxFe2-ySe2-z: parent compound KFe2Se2,
superconducting KFe2Se2 with \surd2\times\surd5 charge ordering,
superconducting KFe2Se2-z with Se vacancies and insulating K2Fe4Se5 with
\surd5\times\surd5 Fe vacancy order. The phase separation takes place at the
mesoscopic scale under standard molecular beam epitaxy condition.",1204.1588v1
2012-04-16,Signature of an antiferromagnetic metallic ground state in heavily electron doped Sr2FeMoO6,"Sr$_{2}$FeMoO$_6$ is a double perovskite compound, known for its high
temperature behavior. Combining different magnetic and spectroscopic tools, we
show that this compound can be driven to rare example of antiferromagnetic
metallic state through heavy electron doping. Considering synthesis of
Sr$_{2-x}$La$_x$FeMoO$_6$ (1.0 $\le{x}\le$ 1.5) compounds, we find compelling
evidences of antiferromagnetic metallic ground state for $x\ge$1.4. The local
structural study on these compounds reveal unusual atomic scale phase
distribution in terms of La, Fe and Sr, Mo-rich regions driven by strong La-O
covalency: a phenomenon hitherto undisclosed in double perovskites. The general
trend of our findings are in agreement with theoretical calculations carried
out on realistic structures with the above mentioned local chemical
fluctuations, which reconfirms the relevance of the kinetic energy driven
magnetic model.",1204.3378v1
2012-04-17,Van der Waals bonding in layered compounds from advanced first-principles calculations,"Although the precise microscopic knowledge of van der Waals interactions is
crucial for understanding bonding in weakly bonded layered compounds, very
little quantitative information on the strength of interlayer interaction in
these materials is available, either from experiments or simulations. Here,
using many-body perturbation and advanced density-functional theory techniques,
we calculate the interlayer binding and exfoliation energies for a large number
of layered compounds and show that, independent of the electronic structure of
the material, the energies for most systems are around 20 meV/\AA$^2$. This
universality explains the successful exfoliation of a wide class of layered
materials to produce two-dimensional systems, and furthers our understanding
the properties of layered compounds in general.",1204.3753v1
2012-05-15,Field-induced high coercive ferromagnetic state and magnetoresistance in the antiferromagnetically ordered compound Fe0.5TiS2,"The measurements of the magnetic susceptibility, magnetization, electrical
resistivity and magnetoresistance have been performed for the Fe intercalated
compound Fe0.5TiS2. According to X-ray diffraction measurements the Fe0.5TiS2
compound synthesized in the present work has a monoclinic crystal structure
(space group I12/m1) which results from the ordering of Fe ions and vacancies
between S-Ti-S tri-layres. The changes in the heat-treatment conditions at
temperatures below 1100 Celsius degrees do not lead to an order-disorder
transition within the subsystem of intercalated Fe ions. It has been shown that
this compound exhibits an antiferromagnetic (AF) ground state below the Neel
temperature TN = 140 K. Application of the magnetic field at T < TN induces a
metamagnetic phase transition to the ferromagnetic (F) state, which is
accompanied by the large magnetoresistance effect (up to 27 %). The
field-induced AF-F transition is found to be irreversible below ~ 100 K. The
magnetization reversal in the metastable F state at low temperatures is
accompanied by substantial hysteresis (~ 100 kOe) which is associated with the
Ising character of Fe ions.",1205.3242v1
2012-05-30,Superconductivity in the YIr2Si2 and LaIr2Si2 Polymorphs,"We report on existence of superconductivity in YIr2Si2 and LaIr2Si2 compounds
in relation to crystal structure. The two compounds crystallize in two
structural polymorphs, both tetragonal. The high temperature polymorph (HTP)
adopts the CaBe2Ge2-structure type (space group P4/nmm) while the low
temperature polymorph (LTP) is of the ThCr2Si2 type (I4/mmm). By studying
polycrystals prepared by arc melting we have observed that the rapidly cooled
samples retain the HTP even at room temperature (RT) and below. Annealing such
samples at 900C followed by slow cooling to RT provides the LTP. Both, the HTP
and LTP were subsequently studied with respect to magnetism and
superconductivity by electrical resistivity, magnetization, AC susceptibility
and specific heat measurements. The HTP and LTP of both compounds respectively,
behave as Pauli paramagnets. Superconductivity has been found exclusively in
the HTP of both compounds below Tsc (= 2.52 K in YIr2Si2 and 1.24 K in
LaIr2Si2). The relations of magnetism and superconductivity with the electronic
and crystal structure are discussed with comparing experimental data with the
results of first principles electronic structure calculations.",1205.6667v2
2012-07-04,Solvent effect on the Thermodynamics of the Oxidation of Potential Antioxidant Garlic Compounds,"Antioxidant capacity of garlic has been attributed to organic sulfur
compounds such us allyl methyl disulfide. Using quantum chemical calculations
at B3LYP/6-31+G (d) and G3MP2B3/6-31+G (d) levels of theory, we study three
possible oxidation reactions of this compound against hydrogen peroxide, a
reactive oxygen species, from a thermodynamic point of view. Because these
reactions are supposed to occur in biological media, solvent effect was taken
into consideration. Oxidation over the double bond that leads to the formation
of an epoxide is more thermodynamically feasible, limiting the antioxidant
capacity of this compound.",1207.1092v2
2012-07-13,Harvesting and storing laser energy with graphene-cu compound structure,"Graphene-metal compound structure has been reported as a novel and
outstanding component used in electrical and optical devices. We report on a
first-principles study of graphene-cu compound structure, showing its capacity
of converting laser energy into electrical power and storing the harvested
energy for a long time. A real-time and real-space time-dependent density
functional method (TDDFT) is applied for the simulation of electrons dynamics
and energy absorption. The laser-induced charge transfer from copper layer to
graphene layer is observed and represented by plane-averaged electron
difference and dipoles. The effects of laser frequency on the excitation energy
and charge transfer are studied as well. The enhancement of C-C {\sigma}-bond
and decreasing of electron density corresponding to {\pi}-bond within graphene
layer indicate the way in which the transferred-charges are stored. In
addition, the shift and oscillations of dipole along z-direction after the
application of laser pulse offer a concept that the compound structure has the
ability of storing the harvested energy for a long time.",1207.3131v2
2012-07-20,Quantum Phase Transition from a Spin-liquid State to a Spin-glass State in the Quasi-1D Spin-1 System Sr1-xCaxNi2V2O8,"We report a quantum phase transition from a spin-liquid state to a spin-glass
state in the quasi-one dimensional (1D) spin-1 system Sr1-xCaxNi2V2O8, induced
by a small amount of Ca-substitution at Sr site. The ground state of the parent
compound (x = 0) is found to be a spin-liquid type with a finite energy gap of
26.6 K between singlet ground state and triplet excited state. Both
dc-magnetization and ac-susceptibility studies on the highest Ca-substituted
compound (x = 0.05) indicate a spin-glass type magnetic ground state. With
increasing Ca-concentration, the spin-glass ordering temperature increases from
4.5 K (for the x = 0.015 compound) to 6.25 K (for the x = 0.05 compound). The
observed results are discussed in the light of the earlier experimental reports
and the theoretical predictions for a quasi-1D spin-1 system.",1207.4946v1
2012-08-29,Magnetic Phase Diagram of the new Heavy Fermion Compound Ce2PtIn8,"We report on the discovery and investigation of a new 218 heavy fermion
compound. Crystals have been synthesized from In-flux. Structurally, Ce2PtIn8
is located between the cubic CeIn3 and the more two-dimensional CeTIn5 (T =
transition metal) type of compounds. The weak anisotropy of the paramagnetic
susceptibility suggests rather 3D magnetic correlations. Specific heat,
electrical resistivity and magnetization measurements revealed that Ce2PtIn8
orders antiferromagnetically below Tn = 2.1 K. An order-to-order transition is
observed at Tm = 2 K. Similarities in the H - T phase diagram to other
CenTmIn3n+2m (T = Rh, Pt) compounds point to a pressure-induced quantum phase
transition (QPT) which, according to the tentative location of Ce2PtIn8 in the
recent proposed global phase diagram for QPT, would be of spin density wave
type.",1208.5856v3
2012-11-01,Tune of Magnetism and Electronic Structures of Alkali Metal Carbides with Rocksalt Structure,"Electronic structures of carbides with the rocksalt structure were calculated
by full potential electronic codes solving the Kohn-Sham equation. Bonding
characters were analyzed by constructing tight-binding Hamiltonian based on
maximally-localized Wannier functions. It was found that the cations in these
compounds act as an electron provider and the frame is formed by the carbon
atoms. The electronic states in the vicinity of the Fermi level are mainly from
the p-orbitals of C. Pressure and doping are two efficient ways to tune the
magnetic and electronic properties of these compounds. It turns out that a spin
gapless semiconductor can be obtained by applying hydrostatic pressure up to
tens of gigaPascal. Higher pressure induced an insulator to metal transition
because of band broadening. Compounds of IA group (Na, K, Rb, Cs) were magnetic
semiconductor at ambient conditions. Alloying with IIA elements decrease the
magnetic moment according to the law of $3-x$, where $x$ is the relative atomic
ratio of the IIA elements to the IA ones. The behaviors of the compounds under
the pressure and the doping effects can be understood by a rigid band model.",1211.0162v2
2013-01-10,Hyperfine interaction in CoCl$_2$ investigated by high resolution neutron spectroscopy,"We investigated low energy nuclear spin excitations in the layered compound
CoCl$_2$ by high resolution back-scattering neutron spectroscopy. We detected
inelastic peaks at $E = 1.34 \pm 0.03$ $\mu$eV on both energy loss and energy
sides of the central elastic peak at $T = 2$ K. The energy of the inelastic
peaks decrease with temperature continuously and become zero at $T_N \approx
25$ K at which the two ielastic peaks merge with the central elastic peak. We
interpret the low energy excitations to be due to the transition between
hyperfine field split nuclear levels. The present data together with the data
on other Co compounds show that the energy of the nuclear spin excitations of a
number of compounds follow a linear relationship with the electronic magnetic
moment of the Co ion whereas that of other compounds deviate appreciably from
this linear behaviour. We ascribe this anomalous behaviour to the presence of
unquenched orbital moments of the Co ions.",1301.2099v1
2013-01-14,Pressure-Induced Superconductivity and Its Scaling with Doping-Induced Superconductivity in the Iron Pnictide with Skutterudite Intermediary Layers,"The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide
superconductors whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers
in a unit cell. When n=3 (the 10-3-8 phase), the undoped compound is an
antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the
undoped compound is a superconductor with the transition temperature of 26K.
Here we report the results of high-pressure studies on the 10-3-8 compound
obtained through a combination of in-situ resistance, magnetic susceptibility,
and Hall coefficient measurements. We find that its AFM order can be suppressed
completely at 3.5 GPa and then superconducting state appears in the pressure
range of 3.5-7 GPa. The pressure dependence of superconducting transition
temperature displays a dome-like shape.",1301.2863v2
2013-02-07,"Crystal Structure and Magnetic Properties of the Ba3TeCo3P2O14, Pb3TeCo3P2O14, and Pb3TeCo3V2O14 Langasites","We report the structural and magnetic characterizations of Ba3TeCo3P2O14,
Pb3TeCo3P2O14, and Pb3TeCo3V2O14, compounds that are based on the mineral
Dugganite, which is isostructural to Langasites. The magnetic part of the
structure consists of layers of Co2+ triangles. Nuclear and magnetic structures
were determined through a co-refinement of synchrotron and neutron powder
diffraction data. In contrast to the undistorted P321 Langasite structure of
Ba3TeCo3P2O14, a complex structural distortion yielding a large supercell is
found for both Pb3TeCo3P2O14 and Pb3TeCo3V2O14. Comparison of the three
compounds studied along with the zinc analog Pb3TeZn3P2O14, also characterized
here, suggests that the distortion is driven by Pb2+ lone pairs; as such, the
Pb compounds crystallize in a pyroelectric space group, P2. Magnetic
susceptibility, magnetization, and heat capacity measurements were performed to
characterize the magnetic behavior. All three compounds become
antiferromagnetic with N\'eel temperatures TN ~ 21 K (Ba3TeCo3P2O14), ~ 13 K
(Pb3TeCo3P2O14), and ~ 8 K (Pb3TeCo3V2O14), and they exhibit magnetic
transitions at high applied magnetic fields, suggesting intrinsically complex
magnetic behavior for tetrahedrally coordinated d7 Co2+ in this structure type.",1302.1636v1
2013-02-07,Magnetic phase diagram of $Sr_3 Fe_2 O_{7-x}$,"Magnetometry, electrical transport, and neutron scattering measurements were
performed on single crystals of the Fe^{4+}-containing perovskite-related phase
Sr_3Fe_2O_7-x as a function of oxygen content. Although both the crystal
structure and electron configuration of this compound are closely similar to
those of well-studied ruthenates and manganates, it exhibits very different
physical properties. The fully-oxygenated compound (x=0) exhibits a
charge-disproportionation transition at T_D = 340 K, and an antiferromagnetic
transition at T_N = 115 K. For temperatures T \leq T_D, the material is a
small-gap insulator; the antiferromagnetic order is incommensurate, which
implies competing exchange interactions between the Fe^{4+} moments. The
fully-deoxygenated compound (x=1) is highly insulating, and its Fe^{3+} moments
exhibit commensurate antiferromagnetic order below T_N ~ 600 K. Compounds with
intermediate x exhibit different order with lower T_N, likely as a consequence
of frustrated exchange interactions between Fe^{3+} and Fe^{4+} sublattices. A
previous proposal that the magnetic transition temperature reaches zero is not
supported.",1302.1815v2
2013-02-13,Ferromagnetism and the formation of interlayer As2-dimers in Ca(Fe1-xNix)2As2,"The compounds Ca(Fe1-xNix)2As2 with the tetragonal ThCr2Si2-type structure
(space group I4/mmm) show a continuous transition of the interlayer As-As
distances from a non-bonding state in CaFe2As2 (dAs-As = 313 pm) to
single-bonded As2-dimers in CaNi2As2 (dAs-As = 260 pm). Magnetic measurements
reveal weak ferromagnetism which develops near the composition
Ca(Fe0.5Ni0.5)2As2, while the compounds with lower and higher nickel
concentrations both are Pauli-paramagnetic. DFT band structure calculations
reveal that the As2-dimer formation is a consequence of weaker metal-metal in
MAs4-layers (M = Fe1-xNix) of Ni-richer compounds, and depends not on
depopulation or shift of As-As antibonding states as suggested earlier. Our
results also indicate that the ferromagnetism of Ca(Fe0.5Ni0.5)2As2 and related
compounds like SrCo2(Ge0.5P0.5)2 is probably not induced by dimer breaking as
recently suggested, but arises from the high density of states generated by the
transition metal 3d bands near the Fermi level without contribution of the
dimers.",1302.3046v1
2013-03-28,Topological Insulators in Hexagonal Wurtzite-type Binary Compounds,"We propose new topological insulators in hexagonal wurtzite-type binary
compounds based on the first principles calculations. It is found that two
compounds AgI and AuI are three-dimensional topological insulators with a
naturally opened band-gap at Fermi level. From band inversion mechanism point
view, this new family of topological insulators is similar with HgTe, which has
s (Gamma 6) - p (Gamma 8) band inversion. Our results strongly support that the
spin-orbit coupling is not an essential factor to the band inversion mechanism;
on the contrary, it is mainly responsible to the formation of a global band gap
for the studied topological insulators. We further theoretically explore the
feasibility of tuning the topological order of the studied compounds with two
types of strains. The results show that the uniaxial strain can contribute
extremely drastic impacts to the band inversion behavior, which provide an
effective approach to induce topological phase transition.",1303.7040v1
2013-05-01,Electronic structure of the kagome staircase compounds Ni3V2O8 and Co3V2O8,"The electronic structure of the kagome staircase compounds, Ni3V2O8 and
Co3V2O8, has been investigated using soft x-ray absorption, soft x-ray
emission, and resonant inelastic x-ray scattering (RIXS). Comparison between
the two compounds, and with first principles band structure calculations and
crystal-field multiplet models, provide unique insight into the electronic
structure of the two materials. Whereas the location of the narrow (Ni,Co) d
bands is predicted to be close to EF, we experimentally find they lie deeper in
the occupied O 2p and unoccupied V 3d manifolds, and determine their energy via
measured charge-transfer excitations. Additionally, we find evidence for a dd
excitation at 1.5 eV in Ni3V2O8, suggesting the V d states may be weakly
occupied in this compound, contrary to Co3V2O8. Good agreement is found between
the crystal-field dd excitations observed in the experiment and predicted by
atomic multiplet theory.",1305.0198v1
2013-06-03,Pre-saddle neutron multiplicity for fission reactions induced by heavy ions and light particles,"Pre-saddle neutron multiplicity has been calculated for several fission
reactions induced by heavy ions and light particles. Experimentally, it is
impossible to determine the contribution of neutrons being emitted before the
saddle point and those emitted between the saddle and the scission points.
Determination of the pre-saddle neutron multiplicity in our research is based
on the comparison between the experimental anisotropies and those predicted by
the standard saddle-point statistical model. Analysis of the results shows that
the pre-saddle neutron multiplicity depends on the fission barrier height and
stability of the compound nucleus. In heavy ion induced fission, the number of
pre-saddle neutrons decreases with increasing the excitation energy of the
compound nucleus. A main cause of this behavior is due to a reduction in the
ground state-to-saddle point transition time with increasing the excitation
energy of the compound nucleus. Whereas in induced fission by light particles,
the number of pre-saddle neutrons increases with increasing the excitation
energy of the compound nucleus.",1306.0310v1
2013-06-03,"Bonds, bands, and bandgaps in tetrahedrally bonded ternary compounds: the role of group V Lone Pairs","An interesting class of tetrahedrally coordinated ternary compounds have
attracted considerable interest because of their potential as good
thermoelectrics. These compounds, denoted as I$_3$-V-VI$_4$, contain three
monovalent-I (Cu, Ag), one nominally pentavalent-V (P, As, Sb, Bi), and four
hexavalent-VI (S, Se, Te) atoms; and can be visualized as ternary derivatives
of the II-VI zincblende or wurtzite semiconductors, obtained by starting from
four unit cells of (II-VI) and replacing four type II atoms by three type I and
one type V atoms. In trying to understand their electronic structures and
transport properties, some fundamental questions arise: whether V atoms are
indeed pentavalent and if not how do these compounds become semiconductors,
what is the role of V lone pair electrons in the origin of band gaps, and what
are the general characteristics of states near the valence band maxima and the
conduction band minima. We answer some of these questions using ab initio
calculations (density functional methods with both local and nonlocal
exchange-correlation potential).",1306.0503v3
2013-06-18,Glassy magnetic behavior in the metamagnetic DyAlO3 doped with Cr,"Magnetic properties of DyAl$_{0.926}$Cr$_{0.074}$O$_3$ and DyAlO$_3$ were
studied. We found that both compounds are antiferromagnetic with a low N\'eel
transition temperature. At higher temperatures the magnetic characteristics
show a Curie-Weiss dependence. The N\'eel temperature disappears when a field
of about 2 T is applied, the system changes from an antiferromagnetic to a weak
ferromagnetic behavior due to a metamagnetic transition. Furthermore, AC
magnetic measurements in the Cr doped compound, at different frequencies, show
a spin glass-like behavior. These transitions were studied and corroborated by
specific heat measurements. We found the presence of metamagnetism and spin
glass in the compound doped with chromium, determining that the small addition
of chromium atoms modifies the magnetic properties of the compound DyAlO$_3$,
resulting in new features such as the spin glass-like behavior.",1306.4378v1
2013-08-26,Stable ordered structures of binary technetium alloys from first principles,"Technetium, element 43, is the only radioactive transition metal. It occurs
naturally on earth in only trace amounts. Experimental investigation of its
possible compounds is thus inherently difficult and limited. Half of the
Tc-transition-metal systems (14 out of 28) are reported to be phase separating
or lack experimental data. Using high-throughput first-principles calculations,
we present a comprehensive investigation of the binary alloys of technetium
with the transition metals. The calculations predict stable, ordered structures
in nine of these 14 binary systems. They also predict additional compounds in
all nine known compound-forming systems and in two of the five systems reported
with disordered \c{hi} or {\sigma} phases. These results accentuate the
incompleteness of the current knowledge of technetium alloys and should guide
experimental studies to obtain accurate structural information on potential
compounds, obviating some of the difficulties associated with such work.",1308.5721v1
2013-08-28,Mechanism of formation and peculiarities of structure of bulk MgB2 compound specimens,"The existence of two phases within one and the same hexagonal lattice of MgB2
compound, differing in Mg and B (in the homogeneity region) and especially in
impurity oxygen content, as well as in microstructure, is demonstrated by
various techniques. The regions corresponding to these two phases of MgB2 have
the sizes of 100-500 {\mu}m, and they fill the whole bulk of specimens,
alternating with each other. It is suggested that the two-phase state of MgB2
compound is caused by specific features of its formation mechanism (as a result
of synthesis at 800-1000{\deg}C), including the stages of Mg melting,
dissolution of solid boron in it up to the composition of MgB2 and further
crystallization of the MgB2 compound from the melt with the formation of
dendrite-like structure with corresponding redistribution of main components
and impurities.",1308.6084v1
2013-09-12,"First-principles study of band alignments in the p-type hosts BaM2X2 (M = Cu, Ag; X = S, Se)","The electronic structures of four semiconductor compounds BaCu2S2, BaCu2Se2,
BaAg2S2, and BaAg2Se2 are studied by density functional theory using both
semi-local and hybrid functionals. The ionization energies and electron
affinities were determined by aligning the electronic states with the vacuum
level by calculating the electrostatic profile within a supercell slab model.
The ionization energy and electron affinity of the compounds were calculated
using the Heyd-Scuseria-Ernzerhof (HSE) functionals and range from 4.5 to 5.4
eV and 3.1 to 3.4 eV, respectively. The replacement of Cu by Ag slightly
increases the ionization energy and electron affinity, while the replacement of
S by Se decreases the ionization energy but slightly increases the electron
affinity. Overall, the low ionization energies and small electron affinities
suggest that these compounds possess good p-type doping propensities. The band
gaps are somewhat small to be ideal candidates for transparent semiconducting
behavior. The replacement of Cu with Ag in the barium sulfide compounds can
increase the band gap from 1.62 eV to 2.01 eV.",1309.3041v1
2013-11-27,Quasi-2D $J_1$-$J_2$ Antiferromagnet $Zn_2VO(PO_4)_2$ and its $Ti$-substituted Derivative - A Spin-wave Analysis,"In this study, we present non-linear spin wave analysis of a quasi 2D
spin-$\frac{1}{2}$ $J_1-J_2$ antiferromagnet at the parameter regime relevant
for the recently studied compound $Zn_2VO(PO_4)_2$. We obtain the temperature
dependence of the spin wave energy, susceptibility and magnetization using
Green's function technique and Hartree-Fock factorization or Tyablikov's
decoupling approximation. The comparison of our numerical results with the
experimental findings is discussed. Magnetic structure factor is calculated and
compared with powder neutron diffraction data. We also study the spin wave
behavior of the compound $Zn_2Ti_{0.25}V_{0.75}O(PO_4)_2$ obtained by partial
chemical substitution of $Ti$ at $V$ sites of the compound $Zn_2VO(PO_4)_2$
(Phys. Rev. B87, 054431). Due to the superlattice structure of the spin
lattice, the substituted compound possess multiple spin wave modes. The spin
wave analysis confirms the quasi-1D nature of the substituted system.",1311.6915v1
2014-03-19,Stronger findings from mass spectral data through multi-peak modeling,"Mass spectrometry-based metabolomic analysis depends upon the identification
of spectral peaks by their mass and retention time. Statistical analysis that
follows the identification currently relies on one main peak of each compound.
However, a compound present in the sample typically produces several spectral
peaks due to its isotopic properties and the ionization process of the mass
spectrometer device. In this work, we investigate the extent to which these
additional peaks can be used to increase the statistical strength of
differential analysis.
  We present a Bayesian approach for integrating data of multiple detected
peaks that come from one compound. We demonstrate the approach through a
simulated experiment and validate it on ultra performance liquid
chromatography-mass spectrometry (UPLC-MS) experiments for metabolomics and
lipidomics. Peaks that are likely to be associated with one compound can be
clustered by the similarity of their chromatographic shape. Changes of
concentration between sample groups can be inferred more accurately when
multiple peaks are available.
  When the sample-size is limited, the proposed multi-peak approach improves
the accuracy at inferring covariate effects. An R implementation, data and the
supplementary material are available at
http://research.ics.aalto.fi/mi/software/peakANOVA/ .",1403.4732v1
2014-03-31,Orbital-dependent singlet dimers and orbital-selective Peierls transitions in transition metal compounds,"We show that in transition metal compounds containing structural metal dimers
there may exist in the presence of different orbitals a special state with
partial formation of singlets by electrons on one orbital, while others are
effectively decoupled and may give e.g. long-range magnetic order or stay
paramagnetic. Similar situation can be realized in dimers spontaneously formed
at structural phase transitions, which can be called orbital-selective Peierls
transition. This can occur in case of strongly nonuniform hopping integrals for
different orbitals and small intra-atomic Hund's rule coupling JH. Yet another
consequence of this picture is that for odd number of electrons per dimer there
exist competition between double exchange mechanism of ferromagnetism, and the
formation of singlet dimer by electron on one orbital, with remaining electrons
giving a net spin of a dimer. The first case is realized for strong Hund's rule
coupling, typical for 3d compounds, whereas the second is more plausible for
4d-5d compounds. We discuss some implications of these phenomena, and consider
examples of real systems, in which orbital-selective phase seems to be
realized.",1403.7871v2
2014-04-16,"Coherent and stochastic contributions of compound resonances in atomic processes: Electron recombination, photoionization and scattering","In open-shell atoms and ions, processes such as photoionization, combination
(Raman) scattering, electron scattering and recombination, are often mediated
by many-electron compound resonances. We show that their interference
(neglected in the independent-resonance approximation) leads to a coherent
contribution, which determines the energy-averaged total cross sections of
electron- and photon-induced reactions obtained using the optical theorem. In
contrast, the partial cross sections (e.g., electron recombination, or photon
Raman scattering) are dominated by the stochastic contributions. Thus, the
optical theorem provides a link between the stochastic and coherent
contributions of the compound resonances. Similar conclusions are valid for
reactions via compound states in molecules and nuclei.",1404.4151v3
2014-05-13,Stability of numerous novel potassium chlorides at high pressure,"K-Cl is a simple system displaying all four main types of bonding, as it
contains (i) metallic potassium, (ii) elemental chlorine made of covalently
bonded Cl2 molecules held together by van der Waals forces, and (iii) an
archetypal ionic compound KCl. Well-known octet rule (and its special case, the
charge balance rule, assigning classical charges of +1 to K and -1 to Cl)
predicts that no compounds other than KCl are possible. However, our
quantum-mechanical variable-composition evolutionary simulations predict new
stable compounds. The phase diagram of the K-Cl system turned out to be
extremely complicated, featuring new thermodynamically compounds K3Cl, K2Cl,
K3Cl2, K4Cl3, K5Cl4, K3Cl5, KCl3, KCl7. Of particular interest are 2D-metallic
homologs Kn+1Cln, the presence of positively charged Cl atoms in KCl7, and the
predicted stability of KCl3 already at the atmospheric pressure.",1405.3007v1
2014-05-13,Local structural distortions and their role in superconductivity in SmFeAsO$_{1-x}$F$_x$ superconductors,"EXAFS studies at the As K edge as a function of temperature have been carried
out in SmFeAsO$_{1-x}$F$_x$ ($x$ = 0 and 0.2) compounds to understand the role
of local structural distortions superconductivity observed in F doped compound.
A significant correlation between thermal variation of local structural
parameters like anion height and superconducting onset is found in the
fluorinated compound. Such a variation in anion height is absent in
non-superconducting compound. Increase in Fe-As bond distance just below
superconducting onset temperature indicates a similarity in distortions
observed in high T$_C$ cuprates and these Fe based superconductors.",1405.3086v1
2014-07-28,Magneto Seebeck effect in REFeAsO (RE=rare earth) compounds: probing the magnon drag scenario,"We investigate Seebeck effect in REFeAsO (RE=rare earth)compounds as a
function of temperature and magnetic field up to 30T. The Seebeck curves are
characterized by a broad negative bump around 50K, which is sample dependent
and strongly enhanced by the application of a magnetic field. A model for the
temperature and field dependence of the magnon drag contribution to the Seebeck
effect by antiferromagnetic (AFM) spin fluctuation is developed. It accounts
for the magnitude and scaling properties of such bump feature in our
experimental data. This analysis allows to extract precious information on the
coupling between electrons and AFM spin fluctuations in these parent compound
systems, with implications on the pairing mechanism of the related
superconducting compounds.",1407.7358v1
2014-11-12,"A comparative study of HoSn1.1Ge0.9 and DySn1.1Ge0.9 compounds using magnetic, magneto-thermal and magneto-transport measurements","Polycrystalline HoSn1.1Ge0.9 and DySn1.1Ge0.9 compounds have been studied by
means of different experimental probes. Both the compounds are
antiferromagnetic and show metamagnetic transition at low temperatures.
HoSn1.1Ge0.9 shows a sign change in magnetocaloric effect (MCE) and
magnetoresistance (MR) with field, which is attributed to the metamagnetic
transition. DySn1.1Ge0.9 shows characteristics of a typical antiferromagnet, as
evidenced by magnetization, MCE and MR data. 119Sn M\""ossbauer studies show
hyperfine splitting at low temperatures, consistent with magnetization data.
Thermoelectric power and resistivity measurements reveal metallic behavior in
these compounds. Magnetic, magnetocaloric and the magnetoresistance data
clearly show that the antiferromagnetic coupling in DySn1.1Ge0.9 is stronger
than in HoSn1.1Ge0.9.",1411.3129v1
2014-11-14,A mini review on NiFe-based materials as highly active oxygen evolution reaction electrocatalysts,"Oxygen evolution reaction (OER) electrolysis, as an important reaction
involved in water splitting and rechargeable metal-air battery, has attracted
increasing attention for clean energy generation and efficient energy storage.
Nickel/iron (NiFe)-based compounds have been known as active OER catalysts
since the last century, and renewed interest has been witnessed in recent years
on developing advanced NiFe-based materials for better activity and stability.
In this review, we present the early discovery and recent progress on
NiFe-based OER electrocatalysts in terms of chemical properties, synthetic
methodologies and catalytic performances. The advantages and disadvantages of
each class of NiFe-based compounds are summarized, including NiFe alloys,
electro-deposited films and layered-double hydroxide nanoplates. Some
mechanistic studies of the active phase of NiFe-based compounds are introduced
and discussed to give insight into the nature of active catalytic site, which
could facilitate further improving NiFe based OER electrocatalysts. Finally,
some applications of NiFe-based compounds for OER are described, including the
development of electrolyzer operating with a single AAA battery with voltage
below 1.5V and high performance rechargeable Zn-air batteries.",1411.4677v1
2014-12-11,Synthesis of ultra-incompressible sp3-hybridized carbon nitride,"Search of materials with C-N composition hold a great promise in creating
materials which would rival diamond in hardness due to the very strong and
relatively low-ionic C-N bond. Early experimental and theoretical works on C-N
compounds were based on structural similarity with binary A3B4 structural-
types; however, the synthesis of C3N4 remains elusive. Here we explored an
unbiased synthesis from the elemental materials at high pressures and
temperatures. Using in situ synchrotron X-ray diffraction and Raman
spectroscopy we demonstrate synthesis of highly incompressible Pnnm CN compound
with sp3 hybridized carbon is synthesized above 55 GPa and 7000 K. This result
is supported by first principles evolutionary search, which finds that Pnnm CN
is the most stable compound above 10.9 GPa. On pressure release below 6 GPa the
synthesized CN compound amorphizes reattaining its 1:1 stoichiometry as
confirmed by Energy-Dispersive X-ray Spectroscopy. This work underscores the
importance of understanding of novel high-pressure chemistry rules and it opens
a new route for synthesis of superhard materials.",1412.3755v1
2015-01-04,Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridate Y2Ir2O7,"Pyrochlore iridates have recently attracted growing interest in condensed
matter physics because of their potential for realizing new topological states.
In order to achieve such quantum states, it is essential to understand
themagnetic properties of these compounds, as their electronic structures are
strongly coupled with theirmagnetic ground states. In this work, we report a
systematic study of the magnetic properties of pyrochlore Y2Ir2O7 and its
hole-doped compounds by performing magnetic, electron spin resonance,
electrical transport, and x-ray photoelectron spectroscopy (XPS) measurements.
We demonstrate the existence of weak ferromagnetism on top of a large
antiferromagnetic background in the undoped compound. Hole doping by calcium
was found to enhance both the ferromagnetism and the electrical conductivity.
The XPS characterization shows the coexistence of Ir4+ and Ir5+ in the undoped
compound, and the amount of Ir5+ increases with Ca doping, which highlights the
possible origins of the weak ferromagnetism associated with the formation of
Ir5+.We also observe a vertical shift in the M-H curves after field cooling,
which may arise from a strong coupling between the ferromagnetic phase and the
antiferromagnetic background.",1501.00615v1
2015-01-15,Shape Evolution of CdSe Nanoparticles controlled by Halogen Compounds,"Halogen compounds are capable of playing an important role in the
manipulation of nanoparticle shapes and properties. In a new approach, we
examined the shape evolution of CdSe nanorods to hexagonal pyramids in a
hot-injection synthesis under the influence of halogenated additives in the
form of organic chlorine, bromine and iodine compounds. Supported by DFT
calculations, this shape evolution is explained as a result of X-type ligand
coordination to sloped and flat Cd-rich facets and an equilibrium shape
strongly influenced by halides. Synchrotron XPS measurements and TXRF results
show that the shape evolution is accompanied by a modification in the chemical
composition of the ligand sphere. Our experimental results suggest that the
molecular structure of the halogenated compound is related to the degree of the
effect on both rod growth and further shape evolution. This presents a new
degree of freedom in nanoparticle shape control and highlights the role of
additives in nanoparticle synthesis and their possible in situ formation of
ligands.",1501.03633v1
2015-02-04,Disordered Fe vacancies and superconductivity in potassium-intercalated iron selenide (K2-xFe4+ySe5),"The parent compound of an unconventional superconductor must contain unusual
correlated electronic and magnetic properties of its own. In the high-Tc
potassium intercalated FeSe, there has been significant debate regarding what
the exact parent compound is. Our studies unambiguously show that the
Fe-vacancy ordered K2Fe4Se5 is the magnetic, Mott insulating parent compound of
the superconducting state. Non-superconducting K2Fe4Se5 becomes a
superconductor after high temperature annealing, and the overall picture
indicates that superconductivity in K2-xFe4+ySe5 originates from the Fe-vacancy
order to disorder transition. Thus, the long pending question whether magnetic
and superconducting state are competing or cooperating for cuprate
superconductors may also apply to the Fe-chalcogenide superconductors. It is
believed that the iron selenides and related compounds will provide essential
information to understand the origin of superconductivity in the iron-based
superconductors, and possibly to the superconducting cuprates.",1502.01116v2
2015-02-04,Compound Chondrules fused Cold,"About 4-5% of chondrules are compound: two separate chondrules stuck
together. This is commonly believed to be the result of the two component
chondrules having collided shortly after forming, while still molten. This
allows high velocity impacts to result in sticking. However, at T ~ 1100K, the
temperature below which chondrules collide as solids (and hence usually
bounce), coalescence times for droplets of appropriate composition are measured
in tens of seconds. Even at 1025K, at which temperature theory predicts that
the chondrules must have collided extremely slowly to have stuck together, the
coalescence time scale is still less than an hour. These coalescence time
scales are too short for the collision of molten chondrules to explain the
observed frequency of compound chondrules. We suggest instead a scenario where
chondrules stuck together in slow collisions while fully solid; and the
resulting chondrule pair was subsequently briefly heated to a temperature in
the range of 900-1025K. In that temperature window the coalescence time is
finite but long, covering a span of hours to a decade. This is particularly
interesting because those temperatures are precisely the critical window for
thermally ionized MRI activity, so compound chondrules provide a possible probe
into that vital regime.",1502.01299v1
2015-02-19,Anomalous impact of hydrostatic pressure on superconductivity of polycrystalline LaO0.5F0.5BiSe2,"We report bulk superconductivity at 2.5K in LaO0.5F0.5BiSe2 compound through
the DC magnetic susceptibility and electrical resistivity measurements. The
synthesized LaO0.5F0.5BiSe2 compound is crystallized in tetragonal structure
with space group P4/nmm and Reitveld refined lattice parameters are a= 4.15(1)A
and c=14.02(2)A. The lower critical field of Hc1= 40Oe, at temperature 2K is
estimated through the low field magnetization measurements. The LaO0.5F0.5BiSe2
compound showed metallic normal state electrical resistivity with residual
resistivity value of 1.35m{\Omega}-cm. The compound is type-II superconductor,
and the estimated Hc2(0) value obtained by WHH formula is above 20kOe for
90percent Rn criteria. The superconducting transition temperature decreases
with applied pressure till around 1.68GPa and with further higher pressures a
high Tc phase emerges with possible onset Tc of above 5K for 2.5GPa.",1502.05502v3
2015-02-25,Prediction of new thermodynamically stable aluminum oxides,"Recently, it has been shown that under pressure, unexpected and
counterintuitive chemical compounds become stable. Laser shock experiments (A.
Rode, unpublished) on alumina (Al2O3) have shown non-equilibrium decomposition
of alumina with the formation of free Al and a mysterious transparent phase.
Inspired by these observations, with have explored the possibility of the
formation of new chemical compounds in the system Al-O. Using the
variable-composition structure prediction algorithm USPEX, in addition to the
well-known Al2O3, we have found two extraordinary compounds Al4O7 and AlO2 to
be thermodynamically stable in the pressure range 330-443 GPa and above 332
GPa, respectively. Both of these compounds at the same time contain oxide O2-
and peroxide O22- ions, and both are insulating. Peroxo-groups are responsible
for gap states, which significantly reduce the electronic band gap of both
Al4O7 and AlO2.",1502.07012v1
2015-03-20,"Collapse of the magnetic moment under pressure of AFe$_2$ (A = Y, Zr, Lu and Hf) in the cubic Laves phase","The electronic structures of four Laves phase iron compounds (e.g. YFe$_2$,
ZrFe$_2$, LuFe$_2$ and HfFe$_2$) have been calculated by the state-of-the-art
full potential electronic structure code. The magnetic moments collapse under
hydrostatic pressure. This feature is found to be universal in these materials.
Its electronic origin is provided by the sharp peaks in the density of states
near the Fermi level. It is shown that a first order quantum phase transition
can be expected under pressure in Y(Zr, or Lu)Fe$_2$, while a second order one
in HfFe$_2$. The bonding characteristics are discussed to elucidate the
equilibrium lattice constant variation. The large spontaneous volume
magnetostriction gives one of the most important character of these compounds.
Invar anomalies in these compounds can be partly explained by the current work
when the fast continuous magnetic moment decrease at the decrease of the
lattice constant was properly considered. This work may remind the
experimentalists of these ""old"" compounds and exploration of the quantum
properties under high pressures are greatly encouraged.",1503.06017v1
2015-03-27,Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3,"We investigated the iron-based ladder compounds (Ba,Cs)Fe$_2$Se$_3$. Their
parent compounds, BaFe$_2$Se$_3$ and CsFe$_2$Se$_3$, have different space
groups, formal valences of Fe and magnetic structures. Electrical resistivity,
specific heat, magnetic susceptibility, X-ray diffraction and powder neutron
diffraction measurements were conducted to obtain temperature and composition
phase diagram of this system. Block magnetism observed in BaFe$_2$Se$_3$ is
drastically suppressed with Cs doping. In contrast, stripe magnetism observed
in CsFe$_2$Se$_3$ is not so fragile against Ba doping. New type of magnetic
structure appears in intermediate compositions, which is similar to stripe
magnetism of CsFe$_2$Se$_3$, but inter-ladder spin configuration is different.
Intermediate compounds show insulating behavior, nevertheless finite $T$-linear
contribution in specific heat was obtained at low temperatures.",1503.08129v1
2015-04-25,Novel lithium-nitrogen compounds at ambient and high pressures,"Using ab initio evolutionary simulations, we predict the existence of five
novel stable Li-N compounds at pressures from 0 to 100 GPa (Li13N, Li5N, Li3N2,
LiN2, and LiN5). Structures of these compounds contain of isolated N ions, N2
dimers, polyacetylene-like N chains and N5 rings, respectively. The structure
of Li13N consists of Li atoms and Li12N icosahedra (with N atom in the center
of the Li12 icosahedron) such icosahedra are notdescribed by Wade-Jemmis
electron counting rules and are unique. Electronic structure of Li-N compounds
is found to dramatically depend on composition and pressure, making this system
ideal for studying metal-insulator transitions. For example, LiN3 undergoes a
sequence of pressure-induced transitions: metal-insulator-metal-insulator. This
work resolves the previous controversies of theory and experiment on Li2N2.",1504.06677v1
2015-05-20,Compound droplets on fibers,"Droplets on fibers have been extensively studied in the recent years.
Although the equilibrium shapes of simple droplets on fibers are well
established, the situation becomes more complex for compound fluidic systems.
Through experimental and numerical investigations, we show herein that compound
droplets can be formed on fibers and that they adopt specific geometries. We
focus on the various contact lines formed at the meeting of the different
phases and we study their equilibrium state. It appears that, depending on the
surface tensions, the triple contact lines can remain separate or merge
together and form quadruple lines. The nature of the contact lines influences
the behavior of the compound droplets on fibers. Indeed, both experimental and
numerical results show that, during the detachment process, depending on
whether the contact lines are triple or quadruple, the characteristic length is
the inner droplet radius or the fiber radius.",1505.05267v2
2015-06-22,Discovery of low thermal conductivity compounds with first-principles anharmonic lattice dynamics calculations and Bayesian optimization,"Compounds of low lattice thermal conductivity (LTC) are essential for seeking
thermoelectric materials with high conversion efficiency. Some strategies have
been used to decrease LTC. However, such trials have yielded successes only
within a limited exploration space. Here we report the virtual screening of a
library containing 54,779 compounds. Our strategy is to search the library
through Bayesian optimization using for the initial data the LTC obtained from
first-principles anharmonic lattice dynamics calculations for a set of 101
compounds. We discovered 221 materials with very low LTC. Two of them have even
an electronic band gap < 1 eV, what makes them exceptional candidates for
thermoelectric applications. In addition to those newly discovered
thermoelectric materials, the present strategy is believed to be powerful for
many other applications in which chemistry of materials are required to be
optimized.",1506.06439v1
2015-07-16,Semiclassical evolution of correlations between observables,"The trace of an arbitrary product of quantum operators with the density
operator is rendered as a multiple phase space integral of the product of their
Weyl symbols with the Wigner function. Interspersing the factors with various
evolution operators, one obtains an evolving correlation. The kernel for the
matching multiple integral that evolves within the Weyl representation is
identified with the trace of a single compound unitary operator. Its evaluation
within a semiclassical approximation then becomes a sum over the periodic
trajectories of the corresponding classical compound canonical transformation.
  The search for periodic trajectories can be bypassed by an exactly equivalent
initial value scheme, which involves a change of integration variable and a
reduced compound unitary operator. Restriction of all the operators to
observables with smooth non-oscillatory Weyl symbols reduces the evolving
correlation to a single phase space integral. If each observable undergoes
independent Heisenberg evolution, the overall correlation evolves classically.
Otherwise, the kernel acquires a nonclassical phase factor, though it still
depends on a purely classical compound trajectory: e.g. the fase for a double
return of the quantum Loschmidt echo does not coincide with twice the phase for
a single echo.",1507.04707v1
2015-08-24,"A Method to Calculate Fission-Fragment Yields $Y(Z,N)$ versus Proton and Neutron Number in the Brownian Shape-Motion Model. Application to calculations of U and Pu charge yields","We propose a method to calculate the two-dimensional (2D) fission-fragment
yield $Y(Z,N)$ versus both proton and neutron number, with inclusion of
odd-even staggering effects in both variables. The approach is to use Brownian
shape-motion on a macroscopic-microscopic potential-energy surface which, for a
particular compound system is calculated versus four shape variables:
elongation (quadrupole moment $Q_2$), neck $d$, left nascent fragment
spheroidal deformation $\epsilon_{\rm f1}$, right nascent fragment deformation
$\epsilon_{\rm f2}$ and two asymmetry variables, namely proton and neutron
numbers in each of the two fragments. The extension of previous models 1)
introduces a method to calculate this generalized potential-energy function and
2) allows the correlated transfer of nucleon pairs in one step, in addition to
sequential transfer. In the previous version the potential energy was
calculated as a function of $Z$ and $N$ of the compound system and its shape,
including the asymmetry of the shape. We outline here how to generalize the
model from the ""compound-system"" model to a model where the emerging fragment
proton and neutron numbers also enter, over and above the compound system
composition.",1508.05964v1
2015-10-02,"Electronic structure and magnetic properties of FeTe, BiFeO$_3$, SrFe$_{12}$O$_{19}$ and SrCoTiFe$_{10}$O$_{19}$ compounds","The electronic energy structures and magnetic properties of iron-based
compounds with group VI elements (FeTe, BiFeO$_3$, SrFe$_{12}$O$_{19}$ and
SrCoTiFe$_{10}$O$_{19}$) are studied using the density functional theory (DFT)
methods. Manifestations of different types of chemical bonds in magnetism of
these compounds are studied theoretically. Calculations of electronic
structures of these systems were performed using the generalized gradient
approximation (GGA) for description of the exchange and correlation effects
within DFT. For SrFe$_{12}$O$_{19}$ and SrCoTiFe$_{10}$O$_{19}$ hexaferrites
the GGA+$U$ method was also employed to deal with strongly correlated
3$d$-electrons. The calculations have revealed distinctive features of
electronic structure of the investigated iron-based compounds with strongly
correlated 3$d$-electrons, which can be responsible for their peculiar
structural and magnetic properties.",1510.00513v1
2015-11-16,"A model for the compositions of non-stoichiometric intermediate phases formed by diffusion reactions, and its application to Nb3Sn superconductors","In this work we explore the compositions of non-stoichiometric intermediate
phases formed by diffusion reactions: a mathematical framework is developed and
tested against the specific case of Nb3Sn superconductors. In the first part,
the governing equations for the bulk diffusion and inter-phase interface
reactions during the growth of a compound are derived, numerical solutions to
which give both the composition profile and growth rate of the compound layer.
The analytic solutions are obtained with certain approximations made. In the
second part, we explain an effect that the composition characteristics of
compounds can be quite different depending on whether it is the bulk diffusion
or grain boundary diffusion that dominates in the compounds, and that frozen
bulk diffusion leads to unique composition characteristics quite distinct from
equilibrium expectations; then the model is modified for the case of grain
boundary diffusion. Finally, we apply this model to the Nb3Sn superconductors
and propose the approaches to control their compositions.",1511.05086v1
2015-11-16,Compound Poisson process with a Poisson subordinator,"A compound Poisson process whose randomized time is an independent Poisson
process is called compound Poisson process with Poisson subordinator. We
provide its probability distribution, which is expressed in terms of the Bell
polynomials, and investigate in detail both the special cases in which the
compound Poisson process has exponential jumps and normal jumps. Then for the
iterated Poisson process we discuss some properties and provide convergence
results to a Poisson process. The first-crossing-time problem for the iterated
Poisson process is finally tackled in the cases of (i) a decreasing and
constant boundary, where we provide some closed-form results, and (ii) a
linearly increasing boundary, where we propose an iterative procedure to
compute the first-crossing-time density and survival functions.",1511.05192v1
2015-12-24,Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metal(s),"The magnetocaloric effect (MCE) in many rare earth (RE) based intermetallic
compounds has been extensively investigated during last two decades, not only
due to their potential applications for magnetic refrigeration but also for
better understanding of the fundamental problems of the materials. This paper
reviews our recent progress of magnetic properties and MCE in some binary or
ternary intermetallic compounds of RE with low boiling point metal(s) (Zn, Mg,
and Cd). Some of them are exhibiting promising MCE properties which make them
also attractive for low temperature magnetic refrigeration. Characteristics of
the magnetic transition, origin of large MCE as well as the potential
application of these compounds were thoroughly discussed. Additionally, a brief
review of the magnetic and magnetocaloric properties in the quaternary rare
earth nickel boroncarbides RENi2B2C superconductors is also presented.",1512.07692v1
2016-01-13,Hybrid Crystals of Cuprates and Iron-Based Superconductors,"We propose two possible new compounds, Ba$_2$CuO$_2$Fe$_2$As$_2$ and
K$_2$CuO$_2$Fe$_2$Se$_2$, which hybridize the building blocks of two high
temperature superconductors, cuprates and iron-based superconductors. These
compounds consist of square CuO$_2$ layers and antifluorite-type Fe$_2$X$_2$
(X=As,Se) layers separated by Ba/K. The calculations of binding energies and
phonon spectrums indicate that they are dynamically stable, which ensures that
they may be experimentally synthesized. The Fermi surfaces and electronic
structures of the two compounds inherit the characteristics of both cuprates
and iron-based superconductors. These compounds can be superconductors with
intriguing physical properties to help to determine pairing mechanisms of high
$T_c$ superconductivity.",1601.03220v1
2016-01-21,"Method ""Ethanol as Internal Standard"" for determination of volatile compounds in alcohol products by gas chromatography in daily practice","Recently proposed new method ""Ethanol as Internal Standard"" for determination
of volatile compounds in alcohol products by gas chromatography (GC) is
investigated from different sides including method testing on prepared standard
solutions like cognac and brandy, different ethanol-water solutions and
certified reference material CRM LGC5100 Whisky-Congeners. Analysis of obtained
results of experimental study from four different laboratories shows that
relative bias between the experimentally measured concentrations calculated in
accordance with proposed method and the values of concentrations assigned
during the preparation by gravimetric method for all analyzed compounds does
not exceed 10 %. It is shown that relative response factors (RRF) between
analyzed volatile compounds and ethanol do not depend on time of analysis and
are constant for every model of GC. It is shown the possibility to use
predetermined RRF in daily practice of testing laboratories and to implement
this new method in the international standards of measurement procedure.",1601.05587v1
2016-02-26,Thermal noise and optomechanical features in the emission of a membrane-coupled compound cavity laser diode,"We demonstrate the use of a compound optical cavity as linear displacement
detector, by measuring the thermal motion of a silicon nitride suspended
membrane acting as the external mirror of a near-infrared Littrow laser diode.
Fluctuations in the laser optical power induced by the membrane vibrations are
collected by a photodiode integrated within the laser, and then measured with a
spectrum analyzer. The dynamics of the membrane driven by a piezoelectric
actuator is investigated as a function of air pressure and actuator
displacement in a homodyne configuration. The high Q-factor ($\sim 3.4\cdot
10^4$ at $8.3 \cdot 10^{-3}$ mbar) of the fundamental mechanical mode at $\sim
73$ kHz guarantees a detection sensitivity high enough for direct measurement
of thermal motion at room temperature ($\sim 87$ pm RMS). The compound cavity
system here introduced can be employed as a table-top, cost-effective linear
displacement detector for cavity optomechanics. Furthermore, thanks to the
strong optical nonlinearities of the laser compound cavity, these systems open
new perspectives in the study of non-Markovian quantum properties at the
mesoscale.",1602.08453v1
2016-08-10,Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3,"We report a detailed investigation of magnetization, magnetocaloric effect
and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to
perovskite family. Our results reveal that the compound is in canted magnetic
state (CMS) where ferromagnetic correlations are present in an
antiferromagnetic state. Magnetic entropy change of this compound follows a
power law (deltaS_M ~ H^m) dependence of magnetic field. In this compound,
inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional
magnetocaloric effect (CMCE) above it. The exponent m is found to be
independent of temperature and field only in the IMCE region. Investigation of
temperature and magnetic field dependence studies of exchange bias, reveal a
competition between effective Zeeman energy of the ferromagnetic regions and
anisotropic exchange energy at the interface between ferromagnetic and
antiferromagnetic regions. Variation of exchange bias due to temperature and
field cycling is also investigated.",1608.03223v1
2016-08-26,Nombre de résidus quadratiques d'un nombre entier inférieurs à sa moitié,"We propose a criterion that allows one to distinguish prime numbers from
compound ones. This criterion is based on the counting of small quadratic
residues.",1609.05776v1
2016-10-17,Tunable bandgap and spin-orbit coupling by composition control of MoS$_{2}$ and MoO$_{x}$ (X=2 and 3) compounds,"We report on composition controlled MoS$_{2}$ and MoO$_{x}$ (x=2 and 3)
compounds electrodeposited on Flourine dopped Tin Oxide (FTO) substrate. It was
observed that the relative content has systematic electrical and optical
changes for different thicknesses of layers ranging from $\approx$20 to 540 nm.
Optical and electrical bandgaps reveals a tuneable behavior by controlling the
relative content of compounds as well as a sharp transition from p to n-type of
semiconductivity. Moreover, spin-orbit interaction of Mo 3d doublet enhances by
reduction of MoO$_{3}$ content in thicker films. Our results convey path-way of
applying such compounds in optoelectronics and nanoelectronics devices.",1610.05110v1
2017-01-16,Relationship between the parent charge transfer gap and maximum transition temperature in cuprates,"One of the biggest puzzles concerning the cuprate high temperature
superconductors is what determines the maximum transition temperature (Tc,max),
which varies from less than 30 K to above 130 K in different compounds. Despite
this dramatic variation, a robust trend is that within each family, the
double-layer compound always has higher Tc,max than the single-layer
counterpart. Here we use scanning tunneling microscopy to investigate the
electronic structure of four cuprate parent compounds belonging to two
different families. We find that within each family, the double layer compound
has a much smaller charge transfer gap size ($\Delta_{CT}$), indicating a clear
anticorrelation between $\Delta_{CT}$ and Tc,max. These results suggest that
the charge transfer gap plays a key role in the superconducting physics of
cuprates, which shed important new light on the high Tc mechanism from doped
Mott insulator perspective.",1701.04190v2
2017-07-07,A characterization of equivalent martingale measures in a renewal risk model with applications to premium calculation principles,"Generalizing earlier work of Delbaen and Haezendonck for given compound
renewal process $S$ under a probability measure $P$ we characterize all
probability measures $Q$ on the domain of $P$ such that $Q$ and $P$ are
progressively equivalent and $S$ remains a compound renewal process under $Q$.
As a consequence, we prove that any compound renewal process can be converted
into a compound Poisson process through a change of measures and we show how
this approach is related to premium calculation principles.",1707.02149v5
2017-08-28,Insight into the physical properties of two niobium based compounds Nb3Be and Nb3Be2 via first principles calculation,"We investigate the structural, electronic, mechanical and elastic properties
of two niobium based intermetallic compounds Nb3Be and Nb3Be2 by using the DFT
based theoretical method. A good agreement is found among the structural
parameters of both the phases with experimentally evaluated parameters. For
both the phases metallic conductivity is observed while Nb3Be phase is more
conducting than that of Nb3Be2 phase. Evaluated DOS at Fermi level indicates
that Nb3Be2 phase is electrically more stable than Nb3Be phase. For both phases
Nb-4d states is mostly responsible for metallic conductivity. The study of
total charge density and Mulliken atomic population reveal the existence of
covalent, metallic and ionic bonds in both intermetallics. Both the phases are
mechanically stable in nature while Nb3Be phase is more ductile than Nb3Be2
phase. The study of Vickers hardness exhibits that Nb3Be2 phase is harder than
that of Nb3Be. Both compounds are anisotropic in nature while Nb3Be phase
possesses large anisotropic characteristics than that of Nb3Be2 phase. The
Debye temperature of both the compounds are also calculated and discussed.",1708.08386v2
2017-09-07,"Elastic, electronic, thermodynamic and transport properties of XOsSi (X=Nb, Ta) superconductors: A first-principles exploration","A first-principles calculation has been performed to study elastic,
electronic, thermodynamic, transport and superconducting properties of recently
reported osmium based two superconductors, XOsSi (X=Nb, Ta). We have calculated
elastic constants and elastic moduli of XOsSi for the first time. The
calculated values of bulk, Youngs, shear moduli are reasonably larger than the
average value obtained from the rule of mixtures of the constituents. NbOsSi
and TaOsSi both compounds are found to be relatively hard material, elastically
stable and ductile in nature. The obtained directional bulk modulus and shear
anisotropic factors indicate that both compounds have high elastic anisotropy.
The shear anisotropic factors show higher elastic anisotropy than the
percentage anisotropy in these compounds. The Debye temperature and bulk
modulus increases with pressure but decreases with temperature as usual for
metals. The magnetic susceptibility of TaOsSi follow the Curie law but NaOsSi
do not follow due to its delocalized magnetic moment and electronic specific
heat slightly deviates from the linear relationship with temperature. The
calculated band structures of XOsSi compounds show metallic nature. In both
cases d-orbitals have the dominating contribution to the total density of
states. The smaller electron-phonon coupling constant implies that XOsSi (X=Nb,
Ta) are weakly coupled superconductors.",1709.02173v1
2017-09-13,"Compound Poisson Point Processes, Concentration and Oracle Inequalities","This note aims at presenting several new theoretical results for the compound
Poisson point process, which follows the work of Zhang \emph{et al.}
[Insurance~Math.~Econom.~59(2014), 325-336]. The first part provides a new
characterization for a discrete compound Poisson point process (proposed by
{Acz{\'e}l} [Acta~Math.~Hungar.~3(3)(1952), 219-224]), it extends the
characterization of the Poisson point process given by Copeland and Regan
[Ann.~Math.~(1936): 357-362]. Next, we derive some concentration inequalities
for discrete compound Poisson point process (negative binomial random variable
with unknown dispersion is a significant example). These concentration
inequalities are potentially useful in count data regressions. We give an
application in the weighted Lasso penalized negative binomial regression whose
KKT conditions of penalized likelihood hold with high probability and then we
derive non-asymptotic oracle inequalities for a weighted Lasso estimator.",1709.04159v3
2017-09-21,Electron-Phonon Interaction in Ternary Rare-Earth Copper Antimonides LaCuSb2 and La(Cu0.8Ag0.2)Sb2 probed by Yanson Point-Contact Spectroscopy,"Investigation of the electron-phonon interaction (EPI) in LaCuSb2 and
La(Cu0.8Ag0.2)Sb2 compounds by Yanson point-contact spectroscopy (PCS) has been
carried out. Point-contact spectra display a pronounced broad maximum in the
range of 10{\div}20 mV caused by EPI. Variation of the position of this maximum
is likely connected with anisotropic phonon spectrum in these layered
compounds. The absence of phonon features after the main maximum allows the
assessment of the Debye energy of about 40 meV. The EPI constant for the
LaCuSb2 compound was estimated to be {\lambda}=0.2+/-0.03. A zero-bias minimum
in differential resistance for the latter compound is observed for some point
contacts, which vanishes at about 6 K, pointing to the formation of
superconducting phase under point contact, while superconducting critical
temperature of the bulk sample is only 1K.",1709.07318v1
2017-11-28,Novel Rubidium Poly-Nitrogen Materials at High Pressure,"First-principles crystal structure search is performed to predict novel
rubidium poly-nitrogen materials at high pressure by varying the stoichiometry,
i. e. relative quantities of the constituent rubidium and nitrogen atoms. Three
compounds of high nitrogen content, RbN_{5}, RbN_{2}, and Rb_{4}N_{6}, are
discovered. Rubidium pentazolate (RbN5) becomes thermodynamically stable at
pressures above \unit[30]{GPa}. The charge transfer from Rb to N atoms enables
aromaticity in cyclo-N_{^{_{5}}}^{-} while increasing the ionic bonding in the
crystal. Rubidium pentazolate can be synthesized by compressing rubidium azide
(RbN3) and nitrogen (N2) precursors above \unit[9.42]{GPa}, and its
experimental discovery is aided by calculating the Raman spectrum and
identifying the features attributed to N_{^{_{5}}}^{-} modes. The two other
interesting compounds, RbN2 containing infinitely-long single-bonded nitrogen
chains, and Rb_{4}N_{6} consisting of single-bonded N_{6} hexazine rings,
become thermodynamically stable at pressures exceeding \unit[60]{GPa}. In
addition to the compounds with high nitrogen content, Rb_{3}N_{3}, a new
compound with 1:1 RbN stoichiometry containing bent N_{3} azides is found to
exist at high pressures.",1711.10415v1
2017-11-30,Nature of optical excitations in the frustrated kagome compound Herbertsmithite,"Optical conductivity measurements are combined with density functional theory
calculations in order to understand the electrodynamic response of the
frustrated Mott insulators Herbertsmithite $\mathrm{ZnCu_{3}(OH)_{6}Cl_{2}}$
and the closely-related kagome-lattice compound
$\mathrm{Y_{3}Cu_{9}(OH)_{19}Cl_{8}}$. We identify these materials as
charge-transfer rather than Mott-Hubbard insulators, similar to the high-$T_c$
cuprate parent compounds. The band edge is at 3.3 and 3.6 eV, respectively,
establishing the insulating nature of these compounds. Inside the gap, we
observe dipole-forbidden local electronic transitions between the Cu $3d$
orbitals in the range 1--2 eV. With the help of \textit{ab initio} calculations
we demonstrate that the electrodynamic response in these systems is directly
related to the role of on-site Coulomb repulsion: while charge-transfer
processes have their origin on transitions between the ligand band and the Cu
$3d$ upper Hubbard band, \textit{local} $d$-$d$ excitations remain rather
unaffected by correlations.",1711.11340v1
2017-12-16,A Possible Family of Ni-based High Temperature Superconductors,"We suggest that a family of Ni-based compounds, which contain
[Ni$_2$M$_2$O]$^{2-}$(M=chalcogen) layers with an antiperovskite structure
constructed by mixed-anion Ni complexes, NiM$_4$O$_2$, can be potential high
temperature superconductors upon doping or applying pressure. The layer
structures have been formed in many other transitional metal compounds such as
La$_2$B$_2$Se$_2$O$_3$(B=Mn, Fe,Co). For the Ni-based compounds, we predict
that the parental compounds host collinear antiferromagnetic states similar to
those in the iron-based high temperature superconductors. The electronic
physics near Fermi energy is controlled by two e$_{g}$ d-orbitals with
completely independent in-plane kinematics. We predict that the
superconductivity in this family is characterized by strong competition between
extended s-wave and d-wave pairing symmetries.",1712.05962v1
2017-12-18,Signature of partially frustrated moments and a new magnetic phase in CeNiGe2,"We report the magnetic, thermodynamic, and transport properties of a heavy
fermion compound CeNiGe2. This compound undergoes two antiferromagnetic
transitions around 4.1 and 3 K. It is observed in heat capacity that as
magnetic field is increased to ~ 1 T, the two peak merge into a single peak
around 3 K. However this peak is not suppressed under the application of
magnetic field. Instead a new feature develops at 3.6 K above 1 T. The magnetic
field induced new feature is investigated through entropy evolution, magnetic
Gruneisen parameter and resistivity studies. These studies emphasis the fact
that partial magnetic frustration due to field induced spin fluctuation is
responsible for this observed feature. This partially frustrated regime
develops a new antiferromagnetically ordered phase at high fields. In this
compound magnetic field induced QCP is absent implying that the behavior of
CeNiGe2 is not in accordance to Doniach model proposed for heavy fermions
compounds.",1712.06394v1
2018-01-01,Sanskrit Sandhi Splitting using seq2(seq)^2,"In Sanskrit, small words (morphemes) are combined to form compound words
through a process known as Sandhi. Sandhi splitting is the process of splitting
a given compound word into its constituent morphemes. Although rules governing
word splitting exists in the language, it is highly challenging to identify the
location of the splits in a compound word. Though existing Sandhi splitting
systems incorporate these pre-defined splitting rules, they have a low accuracy
as the same compound word might be broken down in multiple ways to provide
syntactically correct splits.
  In this research, we propose a novel deep learning architecture called Double
Decoder RNN (DD-RNN), which (i) predicts the location of the split(s) with 95%
accuracy, and (ii) predicts the constituent words (learning the Sandhi
splitting rules) with 79.5% accuracy, outperforming the state-of-art by 20%.
Additionally, we show the generalization capability of our deep learning model,
by showing competitive results in the problem of Chinese word segmentation, as
well.",1801.00428v4
2018-06-20,Topological Critical Materials of Ternary Compounds,"We review topological properties of two series of ternary compounds AMgBi
(A=K, RB, Cs) and ABC with a hexagonal ZrBeSi type structure. The first series
of materials AMgBi are predicted to be topological critical Dirac semimetals.
The second series of ternary compounds, such as KZnP, BaAgAs, NaAuTe and KHgSb,
can be used to realize various topological insulating states and semimetal
states. The states are highly tunable as the realization of these topological
states depends on the competition between several energy scales, including the
energy of atomic orbitals, the energy of crystal splitting, the energy
difference between bonding and antibonding states, and the strength of
spin-orbit coupling. The exotic surface states in these series of compounds are
predicted and are closely related to their unique crystal structures.",1806.07656v1
2018-09-27,Electrical property of Half Metallic Ferromagnet Pr0.95Mn0.939O3,"Half metallic ferromagnetic compounds (HMF) are intensively explored for
their potential in spintronics application. According to theoretical studies,
HMF are those materials where the conduction mechanism is due to one type of
spin state, either up or down. Band theory strongly predicts that Praseodymium
(Pr) based transition metal compound (TMC) is HMF whose electrical properties
are a consequence of the contribution from both the 4f and 3d orbitals of Pr
and TMC ions. Hence, an investigation has been made by preparing
Pr0.95Mn0.939O3 by ball milling assisted sintering process. The phase
confirmation of the prepared compound is carried out using X-Ray diffraction
technique. Impedance analysis with respect to temperature indicates a
decreasing trend in electrical conductivity with respect to temperature,
confirming the semiconductor behaviour of the sample. This may be due to the
consequence of the interaction of 4f and 3d orbitals of the rare-earth (Pr) and
transition metal compound (Manganese).",1809.10350v1
2018-11-05,Syntheses and First-Principles Calculations of the Pseudobrookite Compound AlTi2O5,"We synthesize a new titanium-oxide compound AlTi2O5 with pseudobrookite-type
structure. The formal valence of Ti is 3.5+ that is the same as the Magneli
compound Ti4O7 and the spinel compound LiTi2O4. AlTi2O5 exhibits insulating
behavior in resistivity. Using experimentally determined crystal structure, we
perform the first-principles calculations for the electronic structures.
Experimentally suggested random distribution of Al and Ti is not the origin of
the insulating behavior. The Fermi surfaces for nonrandom AlTi2O5 show
cylindrical shapes reflecting a layered structure, which indicates a possible
nesting-driven order. Constructing a tight-binding model from the
first-principles calculations, we calculate the spin and charge
susceptibilities using the random phase approximation. We suggest possible
charge-density-wave state forming Ti3+ chains separated from each other by Ti4+
chains, similar to the low-temperature phase of Ti4O7.",1811.01471v1
2018-11-07,Constraints on Compound Chondrule Formation from Laboratory High-Temperature Collisions,"In laboratory experiments, spherical 1 mm-wide glass and basalt particles are
heated, and the hot particles collide at about 1m/s with a flat glass target
that is at room temperature. When the particles are heated below 900 K, the
collisions are essentially elastic with coefficients of restitution of about
0.9, but above 900K collisions become increasingly inelastic and the
coefficient of restitution decreases with increasing temperature. At 1100K the
glass particles approach sticking but, simultaneously, at the same temperature
the particles melt on timescales of minutes. The basalt particles approach
sticking at 1200 K. Only above 1400K do basalt grains in contact with each
other fuse together, forming compounds on timescales of hours, and at 1500K
basalt grains completely fuse together. Therefore, cooling basalt grains only
have a 100K window for compound formation, and velocities very likely have to
be below 1m/s for sticking in the first place. We predict that this puts
constraints on compound chondrule formation and particle densities in the solar
nebula.",1811.02905v1
2019-11-13,Weighted Network Analysis of Biologically Relevant Chemical Spaces,"In cheminformatics, network representations of the space of compounds have
been suggested extensively. Among these, the threshold-network consists of
nodes representing molecules. In this network representation, two molecules are
connected by a link if the Tanimoto coefficient, a similarity measure, between
them exceeds a preset threshold. However, the topology of the threshold-network
is affected significantly by the preset threshold. In this study, we collected
the data of biologically relevant compounds and bioactivities. We defined the
weighted network where the weight of each link between the nodes equals the
Tanimoto coefficient between the bioactive compounds (nodes) without using the
threshold. We investigated the relationship between the strength of the link
connection and the bioactivity closeness in the weighted networks. We found
that compounds with significantly high or low bioactivity have a stronger
connection than those in the overall network.",1911.05259v1
2019-11-22,Exploring Chemical Compound Space with Quantum-Based Machine Learning,"Rational design of compounds with specific properties requires conceptual
understanding and fast evaluation of molecular properties throughout chemical
compound space (CCS) -- the huge set of all potentially stable molecules.
Recent advances in combining quantum mechanical (QM) calculations with machine
learning (ML) provide powerful tools for exploring wide swaths of CCS. We
present our perspective on this exciting and quickly developing field by
discussing key advances in the development and applications of QM-based ML
methods to diverse compounds and properties and outlining the challenges ahead.
We argue that significant progress in the exploration and understanding of CCS
can be made through a systematic combination of rigorous physical theories,
comprehensive synthetic datasets of microscopic and macroscopic properties, and
modern ML methods that account for physical and chemical knowledge.",1911.10084v2
2019-11-23,SemEval-2013 Task 4: Free Paraphrases of Noun Compounds,"In this paper, we describe SemEval-2013 Task 4: the definition, the data, the
evaluation and the results. The task is to capture some of the meaning of
English noun compounds via paraphrasing. Given a two-word noun compound, the
participating system is asked to produce an explicitly ranked list of its
free-form paraphrases. The list is automatically compared and evaluated against
a similarly ranked list of paraphrases proposed by human annotators, recruited
and managed through Amazon's Mechanical Turk. The comparison of raw paraphrases
is sensitive to syntactic and morphological variation. The ""gold"" ranking is
based on the relative popularity of paraphrases among annotators. To make the
ranking more reliable, highly similar paraphrases are grouped, so as to
downplay superficial differences in syntax and morphology. Three systems
participated in the task. They all beat a simple baseline on one of the two
evaluation measures, but not on both measures. This shows that the task is
difficult.",1911.10421v1
2021-07-19,Discarded gems: Thermoelectric performance of materials with band gap emerging at the hybrid-functional level,"A finite electronic band gap is a standard filter in high-throughput
screening of materials using density functional theory (DFT). However, because
of the systematic underestimation of band gaps in standard DFT approximations,
a number of compounds may incorrectly be predicted metallic. In a more accurate
treatment, such materials may instead appear as low band gap materials and
could e.g. have good thermoelectric properties if suitable doping is feasible.
To explore this possibility, we performed hybrid functional calculations on
1093 cubic materials listed in the MaterialsProjects database with four atoms
in the primitive unit cell, spin-neutral ground state, and a formation energy
within 0.3 eV of the convex hull. Out of these materials, we identified eight
compounds for which a finite band gap emerges. Evaluating electronic and
thermal transport properties of these compounds, we found the compositions
MgSc2 Hg and Li2 CaSi to exhibit promising thermoelectric properties. These
findings underline the potential of reassessing band gaps and band structures
of compounds to indentify additional potential thermoelectric materials.",2107.09159v1
2017-05-04,Link Mining for Kernel-based Compound-Protein Interaction Predictions Using a Chemogenomics Approach,"Virtual screening (VS) is widely used during computational drug discovery to
reduce costs. Chemogenomics-based virtual screening (CGBVS) can be used to
predict new compound-protein interactions (CPIs) from known CPI network data
using several methods, including machine learning and data mining. Although
CGBVS facilitates highly efficient and accurate CPI prediction, it has poor
performance for prediction of new compounds for which CPIs are unknown. The
pairwise kernel method (PKM) is a state-of-the-art CGBVS method and shows high
accuracy for prediction of new compounds. In this study, on the basis of link
mining, we improved the PKM by combining link indicator kernel (LIK) and
chemical similarity and evaluated the accuracy of these methods. The proposed
method obtained an average area under the precision-recall curve (AUPR) value
of 0.562, which was higher than that achieved by the conventional Gaussian
interaction profile (GIP) method (0.425), and the calculation time was only
increased by a few percent.",1705.01667v2
2017-05-12,Molecular Generation with Recurrent Neural Networks (RNNs),"The potential number of drug like small molecules is estimated to be between
10^23 and 10^60 while current databases of known compounds are orders of
magnitude smaller with approximately 10^8 compounds. This discrepancy has led
to an interest in generating virtual libraries using hand crafted chemical
rules and fragment based methods to cover a larger area of chemical space and
generate chemical libraries for use in in silico drug discovery endeavors. Here
it is explored to what extent a recurrent neural network with long short term
memory cells can figure out sensible chemical rules and generate synthesizable
molecules by being trained on existing compounds encoded as SMILES. The
networks can to a high extent generate novel, but chemically sensible
molecules. The properties of the molecules are tuned by training on two
different datasets consisting of fragment like molecules and drug like
molecules. The produced molecules and the training databases have very similar
distributions of molar weight, predicted logP, number of hydrogen bond
acceptors and donors, number of rotatable bonds and topological polar surface
area when compared to their respective training sets. The compounds are for the
most cases synthesizable as assessed with SA score and Wiley ChemPlanner.",1705.04612v2
2017-05-23,"Magnetic behavior of new compounds, Gd3RuSn6 and Tb3RuSn6","We report temperature (T) dependence of dc magnetization, electrical
resistivity (rho(T)), and heat-capacity of rare-earth (R) compounds, Gd3RuSn6
and Tb3RuSn6, which are found to crystallize in the Yb3CoSn6-type orthorhombic
structure (space group: Cmcm). The results establish that there is an onset of
antiferromagnetic order near (T_N) 19 and 25 K respectively. In addition, we
find that there is another magnetic transition for both the cases around 14 and
17 K respectively. In the case of the Gd compound, the spin-scattering
contribution to rho is found to increase below 75 K as the material is cooled
towards T_N, thereby resulting in a minimum in the plot of rho(T) unexpected
for Gd based systems. Isothermal magnetization at 1.8 K reveals an upward
curvature around 50 kOe. Isothermal magnetoresistance plots show interesting
anomalies in the magnetically ordered state. There are sign reversals in the
plot of isothermal entropy change versus T in the magnetically ordered state,
indicating subtle changes in the spin reorientation with T. The results reveal
that these compounds exhibit interesting magnetic properties.",1705.08436v2
2018-07-24,Efficient Edelstein effects in one-atom-layer Tl-Pb compound,"We have investigated direct and inverse Edelstein effects in a one-atom-layer
Tl-Pb compound with a large Rashba-type spin splitting. In spin pumping
experiments at room temperature, spin-to-charge conversion voltage due to the
inverse Edelstein effect is clearly observed in Py/Cu/Tl-Pb trilayer samples.
To confirm efficient spin-charge interconversion in Tl-Pb compounds, the direct
Edelstein effect is also studied in the same trilayer samples by measuring
modulation of the effective magnetization damping in the Py layer via the
charge-to-spin conversion in the Tl-Pb layer. Using both the results of direct
and inverse Edelstein effects, the Edelstein length is estimated to be ~0.1 nm
for Tl-Pb compounds.",1807.08958v1
2019-01-11,Quasiparticle self-consistent $GW$ electronic band structures of Be-IV-N$_2$ compounds,"The electronic band structures of BeSiN$_2$ and BeGeN$_2$ compounds are
calculated using the quasiparticle self-consistent $GW$ method. The lattice
parameters are calculated for the wurtzite based crystal structure commonly
found in other II-IV-N$_2$ compounds with the $Pbn$2$_1$ space group. They are
determined both in the local density approximation (LDA) and generalized
gradient approximation (GGA), which provide lower and upper limits. At the GGA
lattice constants, which gives lattice constants closer to the experimental
ones, BeSiN$_2$ is found to have an indirect band gap of 6.88 eV and its direct
gap at $\Gamma$ is 7.77 eV, while in BeGeN$_2$ the gap is direct at $\Gamma$
and equals 5.03 eV. To explain the indirect gap in BeSiN$_2$, comparisons are
made with the parent III-N compound w-BN band structure. The effective mass
parameters are also evaluated and found to decrease from BeSiN$_2$ to
BeGeN$_2$.",1901.03722v2
2019-01-22,Semiconducting nature and thermal transport studies of ZrTe3,"We report electrical and thermal transport properties of polycrystalline
ZrTe3. The polycrystalline sample shows semiconducting behavior in contrast to
the established semi-metallic character of the compound. However the charge
density wave (CDW) transition remains intact and its clear signatures are
observed in thermal conductivity and Seebeck coefficient, in the wide
temperature range 50 - 100 K. The thermal conductivity points to additional
scattering from the low frequency phonons (phonon softening) in the vicinity of
CDW transition. The transport in the polycrystalline compounds is governed by
smaller size polarons in the variable range hopping (VRH) region. However, the
increasing disorder in polycrystalline compounds suppresses the CDW transition.
The VRH behavior is also observed in the Seebeck coefficient data in the
similar temperature range. The Seebeck coefficient suggests a competition
between the charge carriers (electrons and hole).",1901.07286v1
2019-01-28,Effect of Bi Substitution on Thermoelectric Properties of SbSe2-based Layered Compounds NdO$_{0.8}$F$_{0.2}$Sb$_{1-x}$Bi$_x$Se$_2$,"Although SbSe2-based layered compounds have been predicted to be
high-performance thermoelectric materials and topological materials, most of
these compounds obtained experimentally have been insulators so far. Here, we
present the effect of Bi substitution on the thermoelectric properties of
SbSe2-based layered compounds NdO0.8F0.2Sb1-xBixSe2 (x = 0-0.4). The room
temperature electrical resistivity is decreased to 8.0 * 10^-5 ohmm for x =
0.4. The electrical power factor is calculated to be 1.4 * 10^-4 W/mK^2 at 660
K, which is in reasonable agreement with combined Jonker and Ioffe analysis.
The room-temperature lattice thermal conductivity of less than 1 W/mK is almost
independent of x, in contrast to the point-defect scattering model for
conventional alloys. The present work provides an avenue for exploring
SbSe2-based insulating and BiSe2-based conducting systems.",1901.09909v1
2019-04-09,"Physical properties of RIr3 (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases","The binary compounds GdIr3, TbIr3 and HoIr3 are synthesized successfully and
found to form in macroscopic co-existence of two polymorphic phases: C15b and
AuCu3-type. The dc magnetization and heat capacity studies confirm that C15b
phase orders ferromagnetically, whereas the AuCu3 phase remains paramagnetic
down to 2 K. The frequency dependent ac-susceptibility data, time dependent
magnetic relaxation behavior and magnetic memory effect studies suggest that
TbIr3 and HoIr3 are cannonical spin-glass system, but no glassy feature could
be found in GdIr3. The critical behavior of all the three compounds has been
investigated from the magnetization and heat capacity measurements around the
transition temperature (TC). The critical exponents alpha, beta, gamma and
delta have been estimated using different techniques such as Arrott-Noaks plot,
Kouvel-Fisher plot, critical isotherm as well as analysis of specific heat data
and study of magnetocaloric effect. The critical analysis study identifies the
type of universal magnetic class in which the three compounds belong.",1904.04807v1
2019-07-24,Understanding Magnetic Properties of Actinide-Based Compounds from Machine Learning,"Actinide and lanthanide-based materials display exotic properties that
originate from the presence of itinerant or localized f-electrons and include
unconventional superconductivity and magnetism, hidden order; and heavy fermion
behavior. Due to the strongly correlated nature of the 5f electrons, magnetic
properties of these compounds depend sensitively on applied magnetic field and
pressure, as well as on chemical doping. However, precise connection between
the structure and magnetism in actinide-based materials is currently unclear.
In this investigation, we established such structure-property links by
assembling and mining two datasets that aggregate, respectively, the results of
high-throughput DFT simulations and experimental measurements for the families
of uranium and neptunium based binary compounds. Various regression algorithms
were utilized to identify correlations among accessible attributes (features or
descriptors) of the material systems and predict their cation magnetic moments
and general forms of magnetic ordering. Descriptors representing compound
structural parameters and cation f-subshell occupation numbers were identified
as most important for accurate predictions. The best machine learning model
developed employs the Random Forest Regression algorithm and can predict
magnetic moment sizes and ordering forms in actinide-based systems with 10-20%
of root mean square error.",1907.10587v1
2019-10-08,Magnetic Weyl semimetals with diamond structure realized in spinel compounds,"Diamond-structure materials have been extensively studied for decades, which
form the foundation for most semiconductors and their modern day electronic
devices. Here, we discover a e$_g$-orbital ($d_{z^2}$,$d_{x^2-y^2}$ ) model
within the diamond lattice (e$_g$-diamond model) that hosts novel topological
states. Specifically, the e$_g$-diamond model yields a 3D nodal cage (3D-NC),
which is characterized by a $d$-$d$ band inversion protected by two types of
degenerate states (i.e., e$_g$-orbital and diamond-sublattice degeneracies). We
demonstrate materials realization of this model in the well-known spinel
compounds (AB$_2$X$_4$), where the tetrahedron-site cations (A) form the
diamond sub-lattice. An ideal half metal with one metallic spin channel formed
by well-isolated and half-filled e$_g$-diamond bands, accompanied by a large
spin gap (4.36 eV) is discovered in one 4-2 spinel compound (VMg$_2$O$_4$),
which becomes a magnetic Weyl semimetal when spin-orbit coupling effect is
further considered. Our discovery greatly enriches the physics of diamond
structure and spinel compounds, opening a door to their application in
spintronics.",1910.03195v1
2019-10-08,"AFeSe2 (A=Tl, K, Rb, or Cs): Iron-based superconducting analog of the cuprates","It has long been a challenging task to find compounds with similar crystal
and electronic structures as cuprate superconductors with low dimensionality
and strong antiferromagnetic fluctuations. The parent compounds of cuprate
superconductors are Mott insulators with strong in-plane antiferromagnetic
exchange interactions between Cu moments. Here we show, based on
first-principles density functional calculations, that AFeSe2 (A=Tl, K, Rb, or
Cs) exhibit many of the physical properties common to the cuprate parent
compounds: (1) the FeSe2 layer in AFeSe2 is similar in crystalline and
electronic structures to the CuO2 plane in cuprates, although Se atoms are not
coplanar to the square Fe-lattice; (2) they are antiferromagnetic insulators,
but with relatively small charge excitation gaps; (3) their ground states are
Neel antiferromagnetic ordered, similar as in cuprates; and (4) the
antiferromagnetic exchange interactions between Fe moments are larger than in
other iron-based superconducting materials, but comparable to those in
cuprates. Like cuprates, these compounds may become high-Tc superconductors
upon doping of charge carriers either by chemical substitution or intercalation
or by liquid or solid gating.",1910.03545v2
2019-04-15,"Theoretical studies on anisotropic charge mobility, band structure, and non-linear optical calculations of ambipolar type organic semiconductors","The anisotropic charge carrier mobilities of two phenancene series compounds
such as dibenzo[a,c]picene (DBP) and tribenzo[a,c,k]tetraphene (TBT) is
investigated based on the first-principle calculations and Marcus-Hush theory.
The molecular packing patterns in organic crystal play an important role for
determing the charge carrier mobility and hence the device efficiencies
designed from the organic materials. Among the studied molecules, TBT shows a
maximum anisotropic hole ($\mu_h=0.129\ cm^2V^{-1}s^{-1}$) and electron
($\mu_h=1.834\ cm^2V^{-1}s^{-1}$) mobility, hence possesses an ambipolar
semiconducting character. The frontier molecular orbital analyses proved the
better air-stability of the studied compounds than the conventional pentacene,
because of their higher HOMO energy levels. Band structure calculations of the
studied compounds have also been investigated. From non-linear optical (NLO)
properties anysis, we found the TBT compound shows more NLO response than DBP.",1910.11462v1
2012-09-11,Design of Low Band Gap Double Perovskites from First Principles,"Using density functional theory (DFT)-based calculations, we propose a family
of metastable, as-yet unmade V5+ and Cr6+ double perovskite compounds with low
band gaps spanning much of the visible region of the solar spectrum. Through
analysis of a related set of measured optical gaps of d0 ABO3 perovskites and
A2B'BO6 double perovskites, an ad hoc procedure is developed to correct DFT and
many-body perturbation theory gaps, bringing them into quantitative agreement
with experiment for measured compounds, and predicting that V5+ and Cr6+ double
perovskites would have gaps ranging from approximately 1.1-2.4 eV,
significantly lower than previous materials studied in this class. DFT
calculations also establish that these V5+ and Cr6+ compounds are likely able
to be synthesized, either in bulk form or as epitaxial thin films. These
compounds would comprise a new class of semiconducting double perovskites for
potential use in solar energy conversion and other optoelectronic applications.",1209.2187v2
2012-09-23,First principles view on chemical compound space: Gaining rigorous atomistic control of molecular properties,"A well-defined notion of chemical compound space (CCS) is essential for
gaining rigorous control of properties through variation of elemental
composition and atomic configurations. Here, we review an atomistic first
principles perspective on CCS. First, CCS is discussed in terms of variational
nuclear charges in the context of conceptual density functional and molecular
grand-canonical ensemble theory. Thereafter, we revisit the notion of compound
pairs, related to each other via ""alchemical"" interpolations involving
fractional nuclear chargens in the electronic Hamiltonian. We address Taylor
expansions in CCS, property non-linearity, improved predictions using reference
compound pairs, and the ounce-of-gold prize challenge to linearize CCS.
Finally, we turn to machine learning of analytical structure property
relationships in CCS. These relationships correspond to inferred, rather than
derived through variational principle, solutions of the electronic
Schr\""odinger equation.",1209.5033v3
2018-08-17,Material Development and Physical Properties of BiS2-Based Layered Compounds,"In 2012, we discovered superconductivity in Bi4O4S3 and LaO1-xFxBiS2, whose
crystal structures are composed of alternate stacks of a BiS2-type conduction
layer and a blocking layer. Since the discovery, many related superconductors
and functional materials have been synthesized. Furthermore, the possibility of
unconventional superconductivity has been proposed in recent theoretical and
experimental studies. In addition, notable correlations between local structure
and physical properties have been revealed in the BiS2-based systems. In this
review article, we summarize the material development (probably all the
compounds) and physical properties of BiS2-related materials developed in the
last six years. The key parameters for the emergence of bulk superconductivity
in the BiS2-based compounds are carrier doping to the parent phase (band
insulator), pressure-induced structural transition, in-plane chemical pressure,
and the suppression of in-plane disorder. We systematically review those
parameters and the method of designing new superconductors with BiS2 layers. In
addition, studies of BiS2-based compounds as thermoelectric materials are
briefly reviewed.",1808.05782v3
2018-08-20,"First-principles prediction of phonon-mediated superconductivity in XBC (X= Mg, Ca, Sr, Ba)","From first-principles calculations, we predict four new intercalated
hexagonal $X$BC ($X$=Mg, Ca, Sr, Ba) compounds to be dynamically stable and
phonon-mediated superconductors. These compounds form a LiBC like structure but
are metallic. The calculated superconducting critical temperature, $T{_c}$, of
MgBC is 51 K. The strong attractive interaction between $\sigma$-bonding
electrons and the B${_{1g}}$ phonon mode gives rise to a larger electron-phonon
coupling constant (1.135) and hence high $T_c$; notably, higher than that of
MgB$_2$. The other compounds have a low superconducting critical temperature
(4-17 K) due to the interaction between $\sigma$-bonding electrons and low
energy phonons (E${_{2u}}$ modes). Due to their energetic and dynamic
stability, we envisage that these compounds can be synthesized experimentally.",1808.06700v2
2018-12-04,Effect of (Cu/Fe)O5 bipyramid size and separation on magnetic and dielectric properties of rare earth layered perovskite LaBaCuFeO5 and LuBaCuFeO5,"We report structural, magnetic and dielectric properties of layered
perovskite materials LnBaCuFeO5 (Ln = La and Lu). LaBaCuFeO5 shows magnetic
cluster glass behavior below 60 K owing to the competing ferromagnetic and
antiferromagnetic exchange interactions. Glassy dynamics of electric dipoles
has also been observed in the vicinity of the magnetic glass transition
temperature. The presence of significant coupling between spin and polar
degrees of freedom results in the multiglass feature in LaBaCuFeO5. The
LuBaCuFeO5 compound undergoes YBaCuFeO5 like commensurate to incommensurate
antiferromagnetic transition at 175 K. Large magnetic irreversibility below 17
K in this compound suggests the presence of strong spin anisotropy. In
addition, in this compound the interaction between the dipoles is not strong
enough, which results in the absence of glassy dynamics of electric dipoles.
The contrasting behavior of two compounds is possibly due to variation in the
ferromagnetic and antiferromagnetic interactions along c-axis, which is the
manifestation of structural modification arising out of the difference in the
ionic radii of La and Lu.",1812.01239v2
2018-12-06,Ternary mixed-anion semiconductors with tunable band gaps from machine-learning and crystal structure prediction,"We report the computational investigation of a series of ternary X$_4$Y$_2$Z
and X$_5$Y$_2$Z$_2$ compounds with X={Mg, Ca, Sr, Ba}, Y={P, As, Sb, Bi}, and
Z={S, Se, Te}. The compositions for these materials were predicted through a
search guided by machine learning, while the structures were resolved using the
minima hopping crystal structure prediction method. Based on $\textit{ab
initio}$ calculations, we predict that many of these compounds are
thermodynamically stable. In particular, 21 of the X$_4$Y$_2$Z compounds
crystallize in a tetragonal structure with $\textit{I-42d}$ symmetry, and
exhibit band gaps in the range of 0.3 and 1.8 eV, well suited for various
energy applications. We show that several candidate compounds (in particular
X$_4$Y$_2$Te and X$_4$Sb$_2$Se) exhibit good photo absorption in the visible
range, while others (e.g., Ba$_4$Sb$_2$Se) show excellent thermoelectric
performance due to a high power factor and extremely low lattice thermal
conductivities.",1812.02708v1
2018-12-19,"Dynamically screened Coulomb interaction in the parent compounds of hole-doped cuprates, trends and exceptions","Although the cuprate high-temperature superconductors were discovered already
1986 the origin of the pairing mechanism remains elusive. While the doped
compounds are superconducting with high transition temperatures $T_{c}$ the
undoped compounds are insulating due to the strong effective Coulomb
interaction between the Cu $3d$ holes. We investigate the dependence of the
maximum superconducting transition temperature, $T_{c\text{ max}}$, on the
onsite effective Coulomb interaction $U$ using the constrained random-phase
approximation. We focus on the commonly used one-band model of the cuprates,
including only the antibonding combination of the Cu $d_{x^2-y^2}$ and O $p_x$
and $p_y$ orbitals, and find a clear screening dependent trend between the
static value of $U$ and $T_{c\text{ max}}$ for the parent compounds of a large
number of hole-doped cuprates. Our results suggest that superconductivity is
favored by a large onsite Coulomb repulsion. We analyze both the trend in the
static value of $U$ and its frequency dependence in detail and, by comparing to
other works, speculate on the mechanisms behind the trend.",1812.07898v1
2019-02-06,"Spectroscopic and first principle DFT+eDMFT study of complex structural, electronic, and vibrational properties of $M_2$Mo$_3$O$_8$ ($M$=Fe, Mn) polar magnets","Optical spectroscopy, X-ray diffraction measurements, density functional
theory (DFT) and density functional theory + embedded dynamical mean field
theory (DFT+eDMFT) have been used to characterize structural and electronic
properties of hexagonal $M_2$Mo$_3$O$_8$ ($M$=Fe, Mn) polar magnets. Our
experimental data are consistent with the room temperature structure belonging
to the space group P6$_3$mc for both compounds. The experimental structural and
electronic properties at room temperature are well reproduced within DFT+eDMFT
method, thus establishing its predictive power in the paramagnetic phase. With
decreasing temperature, both compounds undergo a magnetic phase transition and
we argue that this transition is concurrent with a structural phase transition
(symmetry change from P6$_3$mc) in the Fe compound and an isostructural
transition (no symmetry change from P6$_3$mc) in the Mn compound. In addition,
the unusual temperature dependent behavior of electronic d-d transitions in
Fe$^{2+}$ ions is discussed.",1902.02325v2
2020-04-29,Solving Nonsmooth Nonconvex Compound Stochastic Programs with Applications to Risk Measure Minimization,"This paper studies a structured compound stochastic program (SP) involving
multiple expectations coupled by nonconvex and nonsmooth functions. We present
a successive convex-programming based sampling algorithm and establish its
subsequential convergence. We describe stationarity properties of the limit
points for several classes of the compound SP. We further discuss probabilistic
stopping rules based on the computable error-bound for the algorithm. We
present several risk measure minimization problems that can be formulated as
such a compound stochastic program; these include generalized deviation
optimization problems based on optimized certainty equivalent and buffered
probability of exceedance (bPOE), a distributionally robust bPOE optimization
problem, and a multiclass classification problem employing the cost-sensitive
error criteria with bPOE risk measure.",2004.14342v3
2020-05-06,Two-Dimensional Rare Earth -- Gold Intermetallic Compounds on Au(111) by Surface Alloying,"Surface alloying is a straightforward route to control and modify the
structure and electronic properties of surfaces. Here, We present a
systematical study on the structural and electronic properties of three novel
rare earth-based intermetallic compounds, namely ReAu2 (Re = Tb, Ho, and Er),
on Au(111) via directly depositing rare-earth metals onto the hot Au(111)
surface. Scanning tunneling microscopy/spectroscopy measurements reveal the
very similar atomic structures and electronic properties, e.g. electronic
states, and surface work functions, for all these intermetallic compound
systems due to the physical and chemical similarities between these rare earth
elements. Further, these electronic properties are periodically modulated by
the moir\'e structures caused by the lattice mismatches between ReAu2 and
Au(111). These periodically modulated surfaces could serve as templates for the
self-assembly of nanostructures. Besides, these two-dimensional rare
earth-based intermetallic compounds provide platforms to investigate the rare
earth related catalysis, magnetisms, etc., in the lower dimensions.",2005.02660v1
2020-05-08,Modulating the electronic and optical properties of a ternary chalcogenide CdTl2Te4 via external electric field: A DFT study,"Various ternary chalcogenide systems and their properties are one of the hot
topics for researchers nowadays. In this article, one of the ternary
chalcogenide compounds, CdTl2Te4 is studied including its electronic structures
and optical properties via first principles calculations using SIESTA code. The
structure of the compound has a tetragonal crystal system and the unit cell is
periodic in all directions. The band structure showed it is a direct band gap
semiconductor which is explained by the density of states. The energy gap
obtained is seen to increase on employing external electric field perpendicular
to the xy plane, but does not increase on increasing the magnitude of field
strength. The optical properties which includes absorption coefficient,
reflectance, real & imaginary parts of dielectric function, refractive index
and extinction coefficient were calculated for polarized light both in plane
and out of the plane, but the interesting modulation in properties were seen
for the latter which can open up applications of the compound in UV absorbers,
making solar cells, etc. So, the compound being a narrow-gap semiconductor
along with its tunable electronic and optical properties can have potential
application in the fields such as optoelectronics.",2005.03877v1
2021-03-29,"An ab initio study of structural, elastic and electronic properties of hexagonal MAuGe (M = Lu, Sc) compounds","In this paper, we performed a detailed theoretical study of structural,
elastic and electronic properties of two germanides LuAuGe and ScAuGe by means
of first-principles calculations using the pseudopotential plane-wave method
within the generalized gradient approximation. The crystal lattice parameters
and the internal coordinates are in good agreement with the existing
experimental and theoretical reports, which proves the reliability of the
applied theoretical method. The hydrostatic pressure effect on the structural
parameters is shown. The monocrystalline elastic constants were calculated
using the stress-strain technique. The calculated elastic constants of the
MAuGe (M = Lu, Sc) compounds meet the mechanical stability criteria for
hexagonal crystals and these constants were used to analyze the elastic
anisotropy of the MAuGe compounds through three different indices.
Polycrystalline isotropic elastic moduli, namely bulk modulus, shear modulus,
Young's modulus, Poisson's ratio, and the related properties are also estimated
using Voigt-Reuss-Hill approximations. Finally, we studied the electronic
properties of the considered compounds by calculating their band structures,
their densities of states and their electron density distributions.",2103.15579v1
2022-01-31,A Search for Alternative Solid Rocket Propellant Oxidizers,"Carbon-based caged and heterocyclic compounds tend to have strained molecular
structures leading to high heats of formation and energetic behavior. In the
current paper, molecular modelling calculations for 10 caged compounds of this
type along with 2 strained aliphatic compounds and 4 simple cyclic chains are
presented in view of their possible use as oxidizers in propulsion
applications. Density functional theory (B3LYP) was employed for the geometry
optimization of the proposed molecular structure using the 6-311++G(d,p) basis
set. Heats of formation of the compounds were calculated using the molecular
modeling results and their specific impulses were computed using the NASA CEA
[1] software package to evaluate their potentials as propellant oxidizers.",2202.02370v1
2022-02-17,Pressure-induced superconductivity in iron-based spin-ladder compound BaFe2+δ(S1-Sex)3,"The iron-based superconductors had a significant impact on condensed matter
physics. They have a common structural motif of a two-dimensional square iron
lattice and exhibit fruitful physical properties as a strongly correlated
electron system. During the extensive investigations, quasi-one-dimensional
iron-based spin-ladder compounds attracted much attention as a platform for
studying the interplay between magnetic and orbital ordering. In these
compounds, BaFe2S3 and BaFe2Se3 were found to exhibit superconductivity under
high pressure, having a different crystal and magnetic structure at low
temperature. We report a brief review of the iron-based spin-ladder compound
and recent studies for BaFe2+d(S1-xSex)3. BaFe2(S0.75 Se0.25)3 is in the
vicinity of the boundary of two different magnetic phases and it is intriguing
to perform high pressure experiments for studying superconductivity, since
effects of large magnetic fluctuations on superconductivity are expected. The
effect of iron stoichiometry on the interplay between magnetism and
superconductivity is also studied by changing the iron concentration in
BaFe2+dSe3.",2202.08525v1
2022-02-23,Superconductive materials with MgB2-like structures from data-driven screening,"Finding viable superconducting materials is of interest to the physics
community as the superconductors are the playground to manifest many appealing
quantum phenomena. This work exemplifies an end-to-end materials discovery
towards novel MgB2-like superconductors, starting from the data-driven compound
screening all the way to the experimental materialization. In addition to the
known superconducting compounds, CaB2 (Tc = 9.4 ~ 28.6 K), SrGa2 (Tc = 0.1 ~
2.4 K), BaGa2 (Tc = 0.3 ~ 3.3 K), BaAu2 (Tc = 0.0 ~ 0.5 K), and LaCu2 (Tc = 0.1
~ 2.2 K) are newly discovered, out of ~182,000 starting structures, to be the
most promising superconducting compounds that share similar atomic structures
with MgB2. Moreover, BaGa2 is experimentally synthesized and measured to
confirm that the compound is a BCS superconductor with Tc = 0.36 K, in good
agreement with our theoretical predictions. This work provides a ""once and for
all"" study for the MgB2-like superconductors and showcases that it is feasible
to discover new materials via a data-driven approach.",2202.11355v1
2022-02-26,Single-channel or multi-channel thermal transport? Effect of higher-order anharmonic corrections on the predicted phonon thermal transport properties of semiconductors,"The phonon thermal transport properties of eight ternary intermetallic
semiconductors are investigated by accounting for higher-order four-phonon
scattering, phonon renormalization, and multi-channel thermal transport. The
commonly used lowest-order theory, which accounts only for three-phonon
scattering and without phonon renormalization, fails drastically for considered
materials and underpredicts the thermal conductivity by up to a factor of two.
The thermal conductivity decreases for three compounds and increases for five
compounds with the application of higher-order corrections owing to a
contrasting role of four-phonon scattering and phonon stiffening on the
predicted thermal conductivity. Using the higher-order theory, at a temperature
of 300 K, the lowest obtained thermal conductivity is 0.31 W/m-K for BiCsK2 and
three other compounds (SbCsK2, SbRbNa2, and SbRbK2) have thermal conductivities
lower than 0.5 W/m-K via the particle-like phonon transport channel. The
contribution from the wave-like coherent transport channel is lower than 0.05
W/m-K in all of these ultra-low thermal conductivity compounds. The
higher-order theory is a must for the correct description of thermal transport
physics, failing which the thermal transport is wrongly characterized as
multi-channel transport by the lowest-order theory.",2202.13211v1
2022-03-03,Symmetry-protected Dirac nodal lines and large spin Hall effect in $\mathbf{V_6Sb_4}$ with kagome bilayer,"Recently, a family of nonmagnetic kagome metals \textit{A}$\mathrm{V_3Sb_5}$
(\textit{A}=K, Rb, and Cs) has attracted significant attention for realizing
the intertwining of quantum order and nontrivial topology. However, these
compounds have been identified to host complex band structures. Therefore, it
is desirable to design and synthesize novel kagome materials with a simple band
topology and good transport properties. In this study, using first-principles
calculations, we present the electronic properties and the intrinsic spin Hall
effect of V$_6$Sb$_4$, the latest experimentally synthesized vanadium-based
compounds with a kagome bilayer. In the absence of spin-orbital coupling (SOC),
this compound is a Dirac nodal line semimetal with symmetry-protected nodal
rings near the Fermi level. Within the SOC, the spin-rotation symmetry breaks
the gaps of the nodal rings with a small band gap. Furthermore, based on the
Wannier tight-binding approach and the Kubo formula, we propose a large spin
Hall effect in V$_6$Sb$_4$, which intrinsically originates from the spin Berry
curvature. Our work further expands nonmagnetic kagome compounds for
applications in spintronics accompanied by exotic quantum order.",2203.01558v1
2022-03-11,New Buckled Honeycomb Lattice Compound Sr3CaOs2O9 Exhibiting Antiferromagnetism above Room Temperature,"Synthesis, crystal structure and magnetic properties of a new 2:1 ordered
triple perovskite Sr3CaOs2O9 are reported. The compound crystallizes in P21/c
space group and features a unique buckled honeycomb lattice of osmium. It
exhibits long-range antiferromagnetic ordering with a high Neel temperature of
385 K as confirmed by susceptibility, heat capacity and neutron diffraction
measurements and is electrically insulating. This compound is also the first
example of a 2:1 ordered osmate perovskite. Theoretical investigations indicate
that Sr3CaOs2O9 features a sizeable antiferromagnetic exchange between the
puckered planes resulting in a high TN. The magnetic properties of the known
compound Sr3CaRu2O9 are elucidated in comparison. It shows antiferromagnetic
order below TN = 200 K.",2203.05942v1
2022-03-14,Stability of xenon-sodium compounds at moderately low pressures,"A growing body of theoretical and experimental evidence suggests that inert
gases (He, Ne, Ar, Kr, Xe, Rn) become less and less inert under increasing
pressure. Here we use the ab initio evolutionary algorithm to predict stable
compounds of Xe and Na at pressures below 100 GPa, and find three stable
compounds, NaXe, NaXe$_3$ and NaXe$_4$. The NaXe belongs to a well-known cubic
CsCl structure type. The NaXe$_4$'s structure is common in amphiboles, whereas
the NaXe$_3$ has a unique structure, analogous to the ""post-perovskite""
orthorhombic CaIrO$_3$-type structure with Ir atoms removed. This is the first
time that a cation-vacant version of the CaIrO$_3$ is found in any compound.
NaXe, NaXe$_3$ and NaXe$_4$ are found to be metallic.",2203.06815v2
2022-03-17,Investigating Compounding Prediction Errors in Learned Dynamics Models,"Accurately predicting the consequences of agents' actions is a key
prerequisite for planning in robotic control. Model-based reinforcement
learning (MBRL) is one paradigm which relies on the iterative learning and
prediction of state-action transitions to solve a task. Deep MBRL has become a
popular candidate, using a neural network to learn a dynamics model that
predicts with each pass from high-dimensional states to actions. These
""one-step"" predictions are known to become inaccurate over longer horizons of
composed prediction - called the compounding error problem. Given the
prevalence of the compounding error problem in MBRL and related fields of
data-driven control, we set out to understand the properties of and conditions
causing these long-horizon errors. In this paper, we explore the effects of
subcomponents of a control problem on long term prediction error: including
choosing a system, collecting data, and training a model. These detailed
quantitative studies on simulated and real-world data show that the underlying
dynamics of a system are the strongest factor determining the shape and
magnitude of prediction error. Given a clearer understanding of compounding
prediction error, researchers can implement new types of models beyond
""one-step"" that are more useful for control.",2203.09637v1
2016-03-08,Pressure-induced stabilization of carbonic acid and other compounds in the C-H-O system,"The physicochemical behavior of elements and compounds is heavily altered by
high pressure. The occurrence of pressure-induced reactions and phase
transitions can be revealed by crystal structure prediction approaches. In this
work, we explore the C-H-O phase diagram up to 400 GPa exploiting an
evolutionary algorithm for crystal structure predictions along with ab initio
calculations. Besides uncovering new stable polymorphs of high-pressure
elements and known molecules, we predicted the formation of new compounds. A
2CH4:3H2 inclusion compound forms at low pressure and remains stable up to 215
GPa. Carbonic acid (H2CO3), highly unstable at ambient conditions, was
predicted to form exothermically at mild pressure (about 1 GPa). As pressure
rises, it polymerizes and, above 300 GPa, reacts with water to form
orthocarbonic acid (H4CO4). This unexpected high-pressure chemistry is
rationalized by analyzing charge density and electron localization function
distributions, and implications for general chemistry and planetary science are
also discussed.",1603.02425v1
2016-03-19,Characteristics study of projectiles lightest fragment for 84Kr36 - emulsion interaction at around 1 A GeV,"The present article significantly investigated projectiles lightest fragments
(proton) multiplicity distribution and probability distribution with 84Kr36
emulsion collision at around 1 A GeV. The multiplicity and normalized
multiplicity of projectiles lightest fragments (proton) is correlated with the
compound particles, shower particles, black particles, grey particles, helium
fragments particles and heavily ionizing charged particles. It is found that
projectiles lightest fragments (proton) are strongly correlated with compound
particles and shower particles rather than other particles and the average
multiplicity of projectiles lightest fragments (proton) increases with
increasing compound, shower and heavy ionizing particles. Normalized
projectiles lightest fragments (proton) are strongly correlated with compound
particles, shower particles and heavy ionizing charge particles. The
multiplicity distribution of the projectiles lightest fragments (proton)
emitted in the 84Kr36 + emulsion interaction at around 1 A GeV with different
target has well explained by KNO scaling. The mean multiplicity of projectiles
lightest fragments (proton) depends on the mass number of the projectile and
does not significantly dependent of the projectile energy. The mean
multiplicity projectiles lightest fragment (proton) increases with increasing
the target mass number.",1603.06081v1
2016-03-24,"Ab initio Investigation of Vibrational, Thermodynamic, and Optical properties of Sc2AlC MAX compound","The structural, vibrational, thermodynamical and optical properties of
technologically important, weakly coupled MAX compound, Sc2AlC are calculated
using density functional theory (DFT). The structural properties of Sc2AlC are
compared with results reported earlier. The vibrational, thermodynamical, and
optical properties are theoretically estimated for the first time. The phonon
dispersion curve has been calculated and the dynamical stability of this
compound has been investigated. The optical and acoustic modes are observed
clearly. We have calculated the Helmholtz free energy (F), internal energy (E),
entropy (S) and specific heat capacity (Cv) from the phonon density of states.
Various optical parameters have also been calculated. The reflectance spectrum
shows that it this compound has the potential to be used as a solar reflector.",1603.07530v1
2016-03-29,Multidimensional Compound Poisson Distributions in Free Probability,"Inspired by R. Speicher's multidimensional free central limit theorem and
semicircle families, we prove an infinite dimensional compound Poisson limit
theorem in free probability, and define infinite dimensional compound free
Poisson distributions in a non-commutative probability space. Infinite
dimensional free infinitely divisible distributions are defined and
characterized in terms of its free cumulants. It is proved that for a
distribution of a sequence of random variables, the following statements are
equivalent. (1) The distribution is multidimensional free infinitely divisible.
(2) The distribution is the limit distribution of triangular trays of families
of random variables. (3) The distribution is the distribution of $\{a_1^{(i)}:
i=1, 2, \cdots\}$ of a multidimensional free Levy process $\{\{a_t^{(i)}:i=1,
2, \cdots\}: t\ge 0\}$. (4) The distribution is the limit distribution of a
sequence of multidimensional compound free Poisson distributions.",1603.08612v3
2017-02-09,"$J_1-J_2$ Square-Lattice Heisenberg Antiferromagnets with 4$d^1$ spins: AMoOPO$_4$Cl (A = K, Rb)","Magnetic properties of AMoOPO$_4$Cl (A = K, Rb) with Mo$^{5+}$ ions in the
4$d^1$ electronic configuration are investigated by magnetization, heat
capacity and NMR measurements on single crystals, combined with powder neutron
diffraction experiments. The magnetization measurements reveal that they are
good model compounds for the spin-1/2 $J_1-J_2$ square lattice magnet with the
first and second nearest-neighbor interactions. Magnetic transitions are
observed at around 6 and 8 K in the K and Rb compounds, respectively. In
contrast to the normal N\'eel-type antiferromagnetic order, the NMR and neutron
diffraction experiments find a columnar antiferromagnetic order for each
compound, which is stabilized by a dominant antiferromagnetic $J_2$. Both
compounds realize the unusual case of two interpenetrating $J_2$ square
lattices weakly coupled to each other by $J_1$.",1702.02660v1
2017-02-16,Universality of density waves in p-doped La2CuO4 and n-doped Nd2CuO4+y,"The contribution of $O^{2-}$ ions to antiferromagnetism in
$La_{2-x}Ae_xCuO_4$ ($Ae = Sr, Ba)$ is highly sensitive to doped holes. In
contrast, the contribution of $Cu^{2+}$ ions to antiferromagnetism in
$Nd_{2-x}Ce_xCuO_{4+y}$ is much less sensitive to doped electrons. The
difference causes the precarious and, respectively, robust antiferromagnetic
phase of these cuprates. The same sensitivities affect the doping dependence of
the incommensurability of density waves, $\delta (x)$. In the hole-doped
compounds this gives rise to a doping offset for magnetic and charge density
waves, $\delta_{m,c}^p(x) \propto \sqrt{x-x_{0p}^N}$. Here $x_{0p}^N$ is the
doping concentration where the N\'{e}el temperature vanishes, $T_N(x_{0p}^N) =
0$. No such doping offset occurs for density waves in the electron-doped
compound. Instead, excess oxygen (necessary for stability in crystal growth) of
concentration $y$ causes a different doping offset in the latter case,
$\delta_{m,c}^n(x) \propto \sqrt{x- 2y}$. The square-root formulas result from
the assumption of superlattice formation through partitioning of the $CuO_2$
plane by pairs of itinerant charge carriers. Agreement of observed
incommensurability $\delta(x)$ with the formulas is very good for the
hole-doped compounds and reasonable for the electron-doped compound. The
deviation in the latter case may be caused by residual excess oxygen.",1702.05364v1
2017-09-20,Matrix- and tensor-based recommender systems for the discovery of currently unknown inorganic compounds,"Chemically relevant compositions (CRCs) and atomic arrangements of inorganic
compounds have been collected as inorganic crystal structure databases.
Machine-learning is a unique approach to search for currently unknown CRCs from
vast candidates. Herein we propose matrix- and tensor-based recommender system
approaches to predict currently unknown CRCs from database entries of CRCs.
Firstly, the performance of the recommender system approaches to discover
currently unknown CRCs is examined. A Tucker decomposition recommender system
shows the best discovery rate of CRCs as the majority of the top 100
recommended ternary and quaternary compositions correspond to CRCs. Secondly,
systematic density functional theory (DFT) calculations are performed to
investigate the phase stability of the recommended currently unknown CRCs. The
phase stability of the 27 compositions reveals that 23 currently unknown
compounds are stable. These results indicate that the recommender system has
great potential to accelerate the discovery of new compounds.",1710.00659v1
2017-10-16,The Fano Signature in the Optical Response of a Waveguide-excited Compound Plasmonic Nanoantenna,"While long-range propagating plasmons have been extensively investigated for
implementing on-chip optical sensing platforms, waveguide-excited localized
surface plasmon resonance (LSPR) based sensing systems have not yet received
much attention. Waveguide excitation and readout as an alternative to
free-space light based single-particle spectroscopy are particularly attractive
for high-throughput sensing and on-chip drug discovery platforms. Here we
present a numerical investigation of the optical response of a
waveguide-excited plasmonic dolmen-shaped compound nanoantenna that exhibits a
Fano signature in its spectral response. Although only evanescently coupled to
the waveguide, the compound nanoantenna is seen to induce a high-contrast
extinction in the transmission spectrum of the waveguide. The compound
plasmonic nanoantenna configuration presented here is of interest in hybrid
photonic-plasmonic sensing approaches with high-throughput capabilities.",1710.05624v1
2017-10-26,Lattice Boltzmann modeling of wall-bounded ternary fluid flows,"In this paper, a wetting boundary scheme used to describe the interactions
among ternary fluids and solid is proposed in the framework of the lattice
Boltzmann method. This scheme for three-phase fluids can preserve the reduction
consistency property with the diphasic situation such that it could give
physically relevant results. Combining this wetting boundary scheme and the
lattice Boltzmann (LB) ternary fluid model based on the multicomponent
phase-field theory, we simulated several ternary fluid flow problems involving
solid substrate, including the spreading of binary drops on the substrate, the
spreading of a compound drop on the substrate, and the shear of a compound
liquid drop on the substrate. The numerical results are found to be good
agreement with the analytical solutions or some available results. Finally, as
an application, we use the LB model coupled with the present wetting boundary
scheme to numerically investigate the impact of a compound drop on a solid
circular cylinder. It is found that the dynamics of a compound drop can be
remarkably influenced by the wettability of the solid surface and the
dimensionless Weber number.",1710.09534v1
2019-03-24,Semantically Secure Lattice Codes for Compound MIMO Channels,"We consider compound multi-input multi-output (MIMO) wiretap channels where
minimal channel state information at the transmitter (CSIT) is assumed. Code
construction is given for the special case of isotropic mutual information,
which serves as a conservative strategy for general cases. Using the flatness
factor for MIMO channels, we propose lattice codes universally achieving the
secrecy capacity of compound MIMO wiretap channels up to a constant gap
(measured in nats) that is equal to the number of transmit antennas. The
proposed approach improves upon existing works on secrecy coding for MIMO
wiretap channels from an error probability perspective, and establishes
information theoretic security (in fact semantic security). We also give an
algebraic construction to reduce the code design complexity, as well as the
decoding complexity of the legitimate receiver. Thanks to the algebraic
structures of number fields and division algebras, our code construction for
compound MIMO wiretap channels can be reduced to that for Gaussian wiretap
channels, up to some additional gap to secrecy capacity.",1903.09954v2
2019-05-15,Compound Dirichlet Processes,"The compound Poisson process and the Dirichlet process are the pillar
structures of Renewal theory and Bayesian nonparametric theory, respectively.
Both processes have many useful extensions to fulfill the practitioners needs
to model the particularities of data structures. Accordingly, in this
contribution, we joined their primal ideas to construct the compound Dirichlet
process and the compound Dirichlet process mixture. As a consequence, these new
processes had a fruitful structure to model the time occurrence among events,
with also a flexible structure on the arrival variables. These models have a
direct Bayesian interpretation of their posterior estimators and are easy to
implement. We obtain expressions of the posterior distribution, nonconditional
distribution and expected values. In particular to find these formulas we
analyze sums of random variables with Dirichlet process priors. We assessed our
approach by applying our model on a real data example of a contagious zoonotic
disease.",1905.06411v1
2019-05-17,Superconductivity in the $η$-carbide-type oxides Zr4Rh2Ox,"We report on the synthesis and the superconductivity of Zr$_4$Rh$_2$O$_{x}$
($x$ = 0.4, 0.5, 0.6, 0.7, 1.0). These compounds crystallize in the
$\eta$-carbide structure, which is a filled version of the complex
intermetallic Ti$_2$Ni structure. We find that in the system
Zr$_4$Rh$_2$O$_{x}$, already a small amount ($x$ $\geq$ 0.4) of oxygen addition
stabilizes the $\eta$-carbide structure over the more common intermetallic
CuAl$_2$ structure-type, in which Zr$_2$Rh crystallizes. We show that
Zr$_4$Rh$_2$O$_{0.7}$ and Zr$_4$Rh$_2$O are bulk superconductors with critical
temperatures of $T_c \approx$ 2.8 K and 4.7 K in the resistivity, respectively.
Our analysis of the superconducting properties reveal both compounds to be
strongly type-II superconductors with critical fields up to $\mu_0 H_{c1}$(0)
$\approx$ 8.8 mT and $\mu_0 H_{c2}$(0) $\approx$ 6.08 T. Our results support
that the $\eta$-carbides are a versatile family of compounds for the
investigation of the interplay of interstitial doping on physical properties,
especially for superconductivity.",1905.07402v1
2019-08-06,"Quaternary compounds Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge) as novel potential thermoelectric materials","Experimental results have shown that the quaternary compound Cu2ZnSnSe4 is an
excellent thermoelectric material. This inspires us to seek the other
quaternary compounds with similar chemical formula to Cu2ZnSnSe4 as
thermoelectric materials. In this paper, we use the first-principle method to
systematically explore the electronic and phonon structures, mechanical,
thermal and thermoelectric properties of p- and n-type Ag2XYSe4 (X=Ba, Sr;
Y=Sn, Ge). It is found that the ZT maximum for n-type Ag2SrGeSe4 can reach up
to 1.22 at 900 K, and those for p-type Ag2SrSnSe4, Ag2SrGeSe4 and Ag2BaSnSe4
can reach up to 1.20, 1.13 and 1.12, respectively. Our work not only shows that
Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge) are a kind of potential thermoelectric materials,
but also can inspire more theoretical and experimental researches on
thermoelectric properties of quaternary compounds.",1908.02305v4
2019-08-20,Phonons and Anomalous Lattice Behaviour in KMnAg3(CN)6 and KNiAu3(CN)6: Inelastic Neutron Scattering and First-Principles Calculations,"Cyanide based framework compounds are known to show large negative thermal
expansion behaviour. Here we report the phonon and anomalous lattice behavior
of two metal cyanide framework compounds i.e. KMnAg3(CN)6 and KNiAu3(CN)6. We
have studied the role of van der Waals dispersion and magnetic interactions on
structural stability of these compounds. The behavior of these compounds under
isotropic compression shows the presence of negative linear compressibility.
The calculated phonon spectra, validated by inelastic neutron scattering
measurements and elastic constants are used to study the negative thermal
expansion behavior which is found to arise from low energy phonon modes
involving the folding of A-NC-B-CN-A linkage about B atoms.",1908.07289v1
2019-07-31,On the Magnetism of C14 Nb(Fe89.4Al10.6)2 Laves Phase Intermetallic Compound,"C14 Nb(Fe89.4Al10.6)2 Laves phase intermetallic compound was investigated by
DC magnetization (M) measurements performed in the temperature (T) interval of
20 to 175 K,under an applied magnetic field (H) ranging between 50 and 1250 Oe.
Magnetization curves were recorded in the field-cooled (FC) and in the
zero-field-cooled (ZFC) modes. They clearly showed an irreversible character
that vanished at H=1250 Oe. Both magnetization curves exhibited well-defined
peaks around T_N =72.3 K whose positions were H-independent, so they were
identified as the compound's N\'eel temperature. The existence of
irreversibility which decreases with H testify to a re-entrant character of
magnetism in the studied compound. An increase of both MFC and MZFC observed
below TN likely indicates a mixed i.e. ferromagnetic and antiferromagnetic
ground magnetic state of the studied system.",1908.07995v1
2019-12-09,Monte Carlo simulations study of the intermetallic compound NdCo$_2$Si$_2$ Magnetic properties,"Magnetic properties of the intermetallic compound NdCo$_2$Si$_2$ are
investigated by using the Monte Carlo simulation (MCs) under Metropolis
algorithm. The magnetism of the compound is caused by the existence of the rare
earth (Nd3+) ions with a magnetic moment taking the value 2.7 muB. Firstly, the
ground state phase diagrams are presented and discussed in different planes
corresponding to different physical parameters of the system. The stable phases
are explored for different configurations of the Hamiltonian of the system.
These stable phases are determined by the minimal energies. For non-null
temperature values, we compute the magnetizations and susceptibilities
behaviors as a function of temperature by using the Monte Carlo simulations
(MCS). Also, we present the magnetization behaviors as a function of the
exchange coupling interactions, the crystal field and the external magnetic
field. Finally, we present and discuss the magnetic hysteresis loops of the
intermetallic NdCo2Si2 compound as a function of the external magnetic field
for fixed values of temperature and the other physical parameters.",1912.04245v1
2019-12-14,"Electron doping and correlation effects on crystal, electronic and magnetic structures of A$_2$NRuO$_6$ (A2 = Ba$_2$, BaLa; N = V, Cr, Fe)","Density functional methods have been used to study the crystal, electronic
and magnetic structures of new ordered double perovskites A2NRuO6 (A2 = Ba2,
BaLa; N = V, Cr, Fe). In the doped compounds, the A-site was replaced by 1:1 of
Ba and La cations, BaLaNRuO6. All compounds of A2NRuO6 crystallize in cubic
symmetry with space group Fm-3m and tilt system a0a0a0. The electronic and
magnetic calculations were performed by the full-potential linear muffin-tin
orbital method using both the generalized gradient approximation and GGA plus
on-site electron correlation effect GGA+U. In GGA, Ba2NRuO6 shows
half-metallic, semiconducting and metallic behavior for N = V, Cr, Fe,
respectively, completely change to half-metallic when A2 = BaLa. While, GGA+U
method yields clearly half-metallic in all compounds, except for Ba2FeRuO6,
shows an insulating behavior. Also, the results of magnetic structures
calculations reveal that the A2NRuO6 compounds have ferrimagnetic nature if N =
V and Cr, switch to ferromagnetic when N = Fe. The V3+, Cr3+, Fe3+ and Ru5+
ions are in high spin magnetic moments states due to the antiferromagnetic
coupling.",1912.06843v1
2019-12-21,Black Box Recursive Translations for Molecular Optimization,"Machine learning algorithms for generating molecular structures offer a
promising new approach to drug discovery. We cast molecular optimization as a
translation problem, where the goal is to map an input compound to a target
compound with improved biochemical properties. Remarkably, we observe that when
generated molecules are iteratively fed back into the translator, molecular
compound attributes improve with each step. We show that this finding is
invariant to the choice of translation model, making this a ""black box""
algorithm. We call this method Black Box Recursive Translation (BBRT), a new
inference method for molecular property optimization. This simple, powerful
technique operates strictly on the inputs and outputs of any translation model.
We obtain new state-of-the-art results for molecular property optimization
tasks using our simple drop-in replacement with well-known sequence and
graph-based models. Our method provides a significant boost in performance
relative to its non-recursive peers with just a simple ""for"" loop. Further,
BBRT is highly interpretable, allowing users to map the evolution of newly
discovered compounds from known starting points.",1912.10156v1
2019-12-29,Explainable Deep Relational Networks for Predicting Compound-Protein Affinities and Contacts,"Predicting compound-protein affinity is critical for accelerating drug
discovery. Recent progress made by machine learning focuses on accuracy but
leaves much to be desired for interpretability. Through molecular contacts
underlying affinities, our large-scale interpretability assessment finds
commonly-used attention mechanisms inadequate. We thus formulate a hierarchical
multi-objective learning problem whose predicted contacts form the basis for
predicted affinities. We further design a physics-inspired deep relational
network, DeepRelations, with intrinsically explainable architecture.
Specifically, various atomic-level contacts or ""relations"" lead to
molecular-level affinity prediction. And the embedded attentions are
regularized with predicted structural contexts and supervised with partially
available training contacts. DeepRelations shows superior interpretability to
the state-of-the-art: without compromising affinity prediction, it boosts the
AUPRC of contact prediction 9.5, 16.9, 19.3 and 5.7-fold for the test,
compound-unique, protein-unique, and both-unique sets, respectively. Our study
represents the first dedicated model development and systematic model
assessment for interpretable machine learning of compound-protein affinity.",1912.12553v1
2020-02-06,Superconductivity of Carbon Compounds with Sodalite Structure,"We investigate the superconductivity of carbon compounds with a sodalite
structure, which are similar to hydrogen compounds showing the high-temperature
superconductivity. A systematic analysis by first-principles calculations is
carried out, including examination of mechanical and dynamic instabilities
under external pressure $P$. These instabilities are classified on the phase
diagram for the effective doping charge versus the lattice constant of the
system. We also present the superconducting transition temperature $T_{\rm c}$
as a function of $P$ for many carbon compounds and a pure carbon system with
the sodalite structure. Some of them have $T_{\rm c}$ of up to about 100 K at
$P > \sim 30$ GPa, and the results suggest that the sodalite structure of
carbon may be a key to producing phonon-mediated high-$T_{\rm c}$
superconductivity.",2002.02174v2
2020-06-11,Helium Incorporation Stabilized Direct-gap Silicides,"The search of direct-gap Si-based semiconductors is of great interest due to
the potential application in many technologically relevant fields. This work
examines the incorporation of He as a possible route to form a direct band gap
in Si. Structure predictions and first-principles calculations have shown that
He reacts with Si at high pressure, to form the stable compounds Si2He and
Si3He. Both compounds have host-guest structures consisting of a channel-like
Si host framework filled with He guest atoms. The Si frameworks in two
compounds could be persisted to ambient pressure after removal of He, forming
two pure Si allotropes. Both Si-He compounds and both Si allotropes exhibit
direct or quasi-direct band gaps of 0.84-1.34 eV, close to the optimal value
(~1.3 eV) for solar cell applications. Analysis shows that Si2He with an
electric-dipole-transition allowed band gap possesses higher absorption
capacity than diamond cubic Si, which makes it to be a promising candidate
material for thin-film solar cell.",2006.06319v1
2020-09-07,Predicting second virial coefficients of organic and inorganic compounds using Gaussian Process Regression,"We show that by using intuitive and accessible molecular features it is
possible to predict the temperature-dependent second virial coefficient of
organic and inorganic compounds using Gaussian process regression. In
particular, we built a low dimensional representation of features based on
intrinsic molecular properties, topology and physical properties relevant for
the characterization of molecule-molecule interactions. The featurization was
used to predict second virial coefficients in the interpolative regime with a
relative error $\lesssim 1\% $ and to extrapolate the prediction to
temperatures outside of the training range for each compound in the dataset
with a relative error of 2.14\%. Additionally, the model's predictive abilities
were extended to organic molecules unseen in the training process, yielding a
prediction with a relative error of 2.66\%. Therefore, apart from being robust,
the present Gaussian process regression model is extensible to a variety of
organic and inorganic compounds.",2009.03073v2
2020-10-29,Stabilization of hexazine rings in potassium polynitride at high pressure,"Polynitrogen molecules represent the ultimate high energy-density materials
as they have a huge potential chemical energy originating from their high
enthalpy. However, synthesis and storage of such compounds remain a big
challenge because of difficulties to find energy efficient synthetic routes and
stabilization mechanisms. Compounds of metals with nitrogen represent promising
candidates for realization of energetic polynitrogen compounds, which are also
environmentally benign. Here we report the synthesis of polynitrogen planar N6
hexazine rings, stabilized in K2N6 compound, which was formed from K azide upon
laser heating in a diamond anvil cell at high pressures in excess of 45 GPa and
remains metastable down to 20 GPa. Synchrotron X-ray diffraction and Raman
spectroscopy are used to identify this material, also exhibiting metallic
luster, being all consistent with theoretically predicted structural,
vibrational and electronic properties. The documented here N6 hexazine rings
represent new highly energetic polynitrogens, which have a potential for future
recovery and utilization.",2010.15995v1
2020-11-02,Development of antibacterial compounds that block evolutionary pathways to resistance,"Antibiotic resistance is a worldwide challenge. A potential approach to block
resistance is to simultaneously inhibit WT and known escape variants of the
target bacterial protein. Here we applied an integrated computational and
experimental approach to discover compounds that inhibit both WT and
trimethoprim (TMP) resistant mutants of E. coli dihydrofolate reductase (DHFR).
We identified a novel compound (CD15-3) that inhibits WT DHFR and its TMP
resistant variants L28R, P21L and A26T with IC50 50-75 micromoles against WT
and TMP-resistant strains. Resistance to CD15-3 was dramatically delayed
compared to TMP in in vitro evolution. Whole genome sequencing of CD15-3
resistant strains showed no mutations in the target folA locus. Rather, gene
duplication of several efflux pumps gave rise to weak (about twofold increase
in IC50) resistance against CD15-3. Altogether, our results demonstrate the
promise of strategy to develop evolution drugs - compounds which block
evolutionary escape routes in pathogens.",2011.01098v1
2020-11-03,Machine Learning and Evolutionary Prediction of Superhard B-C-N Compounds,"We build random forests models to predict elastic properties and mechanical
hardness of a compound, using only its chemical formula as input. The model
training uses over 10,000 target compounds and 60 features based on
stoichiometric attributes, elemental properties, orbital occupations, and ionic
bonding levels. Using the models, we construct triangular graphs for B-C-N
compounds to map out their bulk and shear moduli, as well as hardness values.
The graphs indicate that a 1:1 B-N ratio can lead to various superhard
compositions. We also validate the machine learning results by evolutionary
structure prediction and density functional theory. Our study shows that
BC$_{10}$N, B$_4$C$_5$N$_3$, and B$_2$C$_3$N exhibit dynamically stable phases
with hardness values $>40$GPa, which are potentially new superhard materials
that could be synthesized by low-temperature plasma methods.",2011.02038v1
2020-11-11,Bayes Optimal Informer Sets for Early-Stage Drug Discovery,"An important experimental design problem in early-stage drug discovery is how
to prioritize available compounds for testing when very little is known about
the target protein. Informer based ranking (IBR) methods address the
prioritization problem when the compounds have provided bioactivity data on
other potentially relevant targets. An IBR method selects an informer set of
compounds, and then prioritizes the remaining compounds on the basis of new
bioactivity experiments performed with the informer set on the target. We
formalize the problem as a two-stage decision problem and introduce the Bayes
Optimal Informer SEt (BOISE) method for its solution. BOISE leverages a
flexible model of the initial bioactivity data, a relevant loss function, and
effective computational schemes to resolve the two-step design problem. We
evaluate BOISE and compare it to other IBR strategies in two retrospective
studies, one on protein-kinase inhibition and the other on anti-cancer drug
sensitivity. In both empirical settings BOISE exhibits better predictive
performance than available methods. It also behaves well with missing data,
where methods that use matrix completion show worse predictive performance. We
provide an R implementation of BOISE at
https://github.com/wiscstatman/esdd/BOISE",2011.06122v1
2020-11-26,On stable H-C-N-O compounds at high pressure,"The make-up of the outer planets, and many of their moons, are dominated by
matter from the H-C-N-O chemical space, commonly assumed to originate from
mixtures of hydrogen and the planetary ices H$_2$O, CH$_4$, and NH$_3$. In
their interiors, these ices experience extreme pressure conditions, around 5
Mbar at the Neptune mantle-core boundary, and it is expected that they undergo
phase transitions, decompose, and form entirely new compounds. In turn, this
determines planets' interior structure, thermal history, magnetic field
generation, etc. Despite its importance, the H-C-N-O space has not been
surveyed systematically. Asked simply: at high-pressure conditions, what
compounds emerge within this space, and what governs their stability? Here, we
report on results from an unbiased crystal structure search amongst H-C-N-O
compounds at 5 Mbar to answer this question.",2011.13285v1
2020-11-14,Cross-Modality Protein Embedding for Compound-Protein Affinity and Contact Prediction,"Compound-protein pairs dominate FDA-approved drug-target pairs and the
prediction of compound-protein affinity and contact (CPAC) could help
accelerate drug discovery. In this study we consider proteins as multi-modal
data including 1D amino-acid sequences and (sequence-predicted) 2D residue-pair
contact maps. We empirically evaluate the embeddings of the two single
modalities in their accuracy and generalizability of CPAC prediction (i.e.
structure-free interpretable compound-protein affinity prediction). And we
rationalize their performances in both challenges of embedding individual
modalities and learning generalizable embedding-label relationship. We further
propose two models involving cross-modality protein embedding and establish
that the one with cross interaction (thus capturing correlations among
modalities) outperforms SOTAs and our single modality models in affinity,
contact, and binding-site predictions for proteins never seen in the training
set.",2012.00651v1
2020-12-19,Accelerated Discovery of a Large Family of Quaternary Chalcogenides with very Low Lattice Thermal Conductivity,"The development of efficient thermal energy management devices such as
thermoelectrics, barrier coatings, and thermal data-storage disks often relies
on compounds that possess very low lattice thermal conductivity ($\kappa_l$).
Here, we present the computational prediction of a large family of 628
thermodynamically stable quaternary chalcogenides, AMM'Q$_3$ (A =
alkali/alkaline earth/post-transition metals; M/M' = transition metals,
lanthanides; Q = chalcogens) using high-throughput density functional theory
(DFT) calculations. We validate the presence of low-$\kappa_l$ in this family
of materials by calculating $\kappa_l$ of several predicted stable compounds
using the Peierls-Boltzmann transport equation within a first-principles DFT
framework. Our analysis reveals that the low-$\kappa_l$ in the AMM'Q$_3$
compounds originates from the presence of either a strong lattice anharmonicity
that enhances the phonon scatterings or rattlers cations that lead to multiple
scattering channels in their crystal structures. Our predictions suggest new
experimental research opportunities in the synthesis and characterization of
these stable, low-$\kappa_l$ compounds.",2012.10778v1
2020-12-30,"Anisotropic magnetic interactions in hexagonal AB-stacked kagome lattice structures: Applications to $\mathrm{Mn}_3\mathrm{X}$ ($\mathrm{X}$ = $\mathrm{Ge}$, $\mathrm{Sn}$, $\mathrm{Ga}$) compounds","$\mathrm{Mn}_3\mathrm{X}$ compounds in which the magnetic $\mathrm{Mn}$ atoms
form AB-stacked kagome lattices have received a tremendous amount of attention
since the observation of the anomalous Hall effect in
$\mathrm{Mn}_3\mathrm{Ge}$ and $\mathrm{Mn}_3\mathrm{Sn}$. Although the
magnetic ground state has been known for some time to be an inverse triangular
structure with an induced in-plane magnetic moment, there have been several
controversies about the minimal magnetic Hamiltonian. We present a general
symmetry-based model for these compounds that includes a previously unreported
interplane Dzyaloshinskii-Moriya interaction, as well as anisotropic exchange
interactions. The latter are shown to compete with the single-ion anisotropy
which strongly affects the ground state configurations and elementary spin-wave
excitations. Finally, we present the calculated elastic and inelastic neutron
scattering intensities and point to experimental assessment of the types of
magnetic anisotropy in these compounds that may be important.",2012.15280v2
2021-01-05,"Observation of unconventional six-fold, four-fold and three-fold excitations in rare-earth-metal carbide Re2C3","Unconventional fermions, such as three-fold, four-fold, six-fold, and
eight-fold fermions have attracted intense attention in recent years. However,
the concrete materials hosting unconventional fermions are still in urgent
scarcity. In this work, based first-principle calculations and symmetry
analysis, we reveal rich unconventional fermions in existing compound Re2C3 (Re
= Y, La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, Yb, Lu). We show that these
compounds host quadratic dispersive three-fold (TP), linear dispersive
four-fold (FP) and six-fold points (SP) near the Fermi level in their electric
band structures when spin-orbital coupling (SOC) is not included. Notably, the
FP is charge-2 Dirac-like point. More importantly, among compound Re2C3, the
compound Yb2C3 has very clean band structure, and its unconventional fermions
are closed to the Fermi level. We also find that a uniaxial strain can
transform the unconventional fermions into other types fermions, depending on
the directions of strain. When SOC is considered, a SP transform to an
eightfold degenerate point and a fourfold degenerate point. Overall, our work
provides a family of realistic materials to study the unconventional fermions.",2101.01413v1
2021-01-17,Generalized Image Reconstruction over T-Algebra,"Principal Component Analysis (PCA) is well known for its capability of
dimension reduction and data compression. However, when using PCA for
compressing/reconstructing images, images need to be recast to vectors. The
vectorization of images makes some correlation constraints of neighboring
pixels and spatial information lost. To deal with the drawbacks of the
vectorizations adopted by PCA, we used small neighborhoods of each pixel to
form compounded pixels and use a tensorial version of PCA, called TPCA
(Tensorial Principal Component Analysis), to compress and reconstruct a
compounded image of compounded pixels. Our experiments on public data show that
TPCA compares favorably with PCA in compressing and reconstructing images. We
also show in our experiments that the performance of TPCA increases when the
order of compounded pixels increases.",2101.06650v3
2021-02-03,Evolutionary search for cobalt-rich compounds in the yttrium-cobalt-boron system,"Modern high-performance permanent magnets are made from alloys of rare earth
and transition metal elements, and large magnetization is achieved in the
alloys with high concentration of transition metals. We applied evolutionary
search scheme based on first-principles calculations to the Y-Co-B system and
predicted 37 cobalt-rich compounds with high probability of being stable.
Focusing on remarkably cobalt-rich compounds, YCo$_{16}$ and YCo$_{20}$, we
found that, although they are metastable phases, the phase stability is
increased with increase of temperature due to the contribution of vibrational
entropy. The magnetization and Curie temperature are higher by 0.22 T and 204 K
in YCo$_{16}$ and by 0.29 T and 204 K in YCo$_{20}$ than those of
Y$_{2}$Co$_{17}$ which has been well studied as strong magnetic compounds.",2102.02097v1
2021-02-09,Substitutional effects in TiFe for hydrogen storage: a comprehensive review,"The search for suitable materials for solid-state stationary storage of green
hydrogen is pushing the implementation of efficient renewable energy systems.
This involves rational design and modification of cheap alloys for effective
storage in mild conditions of temperature and pressure. Among many
intermetallic compounds described in the literature, TiFe-based systems have
recently regained vivid interest as materials for practical applications since
they are low-cost and they can be tuned to match required pressure and
operation conditions. This work aims to provide a comprehensive review of
publications involving chemical substitution in TiFe-based compounds for
guiding compound design and materials selection in current and future hydrogen
storage applications. Mono- and multi-substituted compounds modify TiFe
thermodynamics and are beneficial for many hydrogenation properties. They will
be reviewed and deeply discussed, with a focus on manganese substitution.",2102.04766v1
2021-04-15,Unconventional iron-magnesium compounds at terapascal pressures,"Being a lithophile element at ambient pressure, magnesium is long believed to
be immiscible with iron. A recent study by Gao et al. [1] showed that pressure
turns magnesium into a siderophile element and can produce unconventional Fe-Mg
compounds. Here, we extend the investigation to exoplanetary pressure
conditions using an adaptive genetic algorithm-based variable-composition
structural prediction approach. We identify several Fe-Mg phases up to 3 TPa.
Our cluster alignment analysis reveals that most of the predicted Fe-Mg
compounds prefer a BCC packing motif at terapascal pressures. This study
provides a more comprehensive structure database to support future
investigations of the high-pressure structural behavior of Fe-Mg and ternary,
quaternary, etc. compounds involving these elements.",2104.07700v1
2021-05-04,Magnetic properties and magnetocaloric effect of $\mathrm{Tb_2Rh_3Ge}$,"We report the structural, magnetic properties, and magnetocaloric effect of a
new polycrystalline compound of $\mathrm{Tb_2Rh_3Ge}$. This present compound
crystallizes with $\mathrm{Mg_2Ni_3Si}$-type of rhombohedral Laves phases
(space group $R\overline{3}m$, hR18). The magnetic properties and
magnetocaloric effect of the $\mathrm{Tb_2Rh_3Ge}$ is explored through
dc-magnetization measurements. Temperature dependence of magnetization revealed
that the compound exhibits ferromagnetic behavior with $T_C$$=$56 K. The field
dependence of magnetization indicates that $\mathrm{Tb_2Rh_3Ge}$ is a soft
ferromagnet. The obtained isothermal magnetic entropy changes ($\Delta S_m$),
and refrigeration capacity (relative power cooling) for a change of magnetic
field 0-9 T are 12.74 J/kg-K, and 497(680) J/kg respectively. The Arrott plots
and universal curve of normalized $\Delta S_m$ indicate that this compound
undergoes second order ferromagnetic phase transition",2105.01364v2
2021-06-09,Automated charting of the visual space of insect compound eyes,"This paper describes the automatic measurement of the spatial organization of
the visual axes of insect compound eyes, which consist of several thousands of
visual units called ommatidia. Each ommatidium samples the optical information
from a small solid angle, with an approximately Gaussian-distributed
sensitivity (half-width of the order of one degree) centered around a visual
axis. Together, the ommatidia gather the optical information from virtually the
full surroundings. The spatial distribution of the visual axes thus determines
the eye's spatial resolution. Knowledge of the optical organization of a
compound eye and its visual acuity is crucial for quantitative studies of the
neural processing of visual information. Here we present an automated procedure
for mapping a compound eye's visual axes, using an intrinsic optical
phenomenon, the pseudopupil. We outline the optomechanical setup for scanning
insect eyes, and use experimental results obtained from a housefly, Musca
domestica, to illustrate the steps in the measurement procedure.",2106.05077v1
2021-08-27,Compound twin beams without the need of genuine photon-number-resolving detection,"The scheme for building stronger multi-mode twin beams from a greater number
of identical twin beams sufficiently weak so that single-photon sensitive
on/off detectors suffice in their detection is studied. Statistical properties
of these compound twin beams involving the non-classicality are analyzed for
intensities up to hundreds of photon pairs. Their properties are compared with
those of the genuine twin beams that require photon-number-resolving detectors
in their experimental investigations. The use of such compound twin beams for
the generation of sub-Poissonian light and measurement of absorption with
sub-shot-noise precision is analyzed. A suitable theoretical model for the
compound twin beams is developed to interpret the experimental data.",2108.12449v1
2021-09-14,Valence state determines the band magnetocrystalline anisotropy in 2D rare-earth/noble-metal compounds,"In intermetallic compounds with zero-orbital momentum ($L=0$) the magnetic
anisotropy and the electronic band structure are interconnected. Here, we
investigate this connection on divalent Eu and trivalent Gd intermetallic
compounds. We find by X-ray magnetic circular dichroism an out-of-plane easy
magetization axis in 2D atom-thick EuAu$_2$. Angle-resolved photoemission and
density-functional theory prove that this is due to strong $f-d$ band
hybridization and Eu$^{2+}$ valence. In contrast, the easy in-plane
magnetization of the structurally-equivalent GdAu$_2$ is ruled by
spin-orbit-split $d$-bands, notably Weyl nodal lines, occupied in the Gd$^{3+}$
state. Regardless of the $L$ value, we predict a similar itinerant electron
contribution to the anisotropy of analogous compounds.",2109.06769v2
2021-09-20,"Electron Spin Resonance of the itinerant ferromagnets LaCrGe3, CeCrGe3 and PrCrGe3","We report Electron Spin Resonance of the itinerant ferromagnets LaCrGe3,
CeCrGe3, and PrCrGe3. These compounds show well defined and very similar
spectra of itinerant Cr 3d spins in the paramagnetic temperature region. Upon
cooling and crossing the Cr-ferromagnetic ordering (below around 90 K) strong
spectral structures start to dominate the resonance spectra in a quite
different manner in the three compounds. In the Ce- and Pr-compounds the
resonance is only visible in the paramagnetic region whereas in the La-compound
the resonance can be followed far below the ferromagnetic ordering temperature.
This behavior will be discussed in terms of the specific interplay between the
4f and 3d magnetism which appears quite remarkable since CeCrGe3 displays heavy
fermion behavior even in the magnetically ordered state.",2109.09341v1
2021-09-20,Magnetic properties and magnetocaloric effect in a Laves phase compound ~$\mbox{Er}_2\mbox{Rh}_{3}\mbox{Si}$,"The magnetic properties and magnetocaloric effect of an intermetallic
compound $\mathrm{Er_2Rh_3Si}$ was investigated by performing temperature
dependence of dc- and ac-magnetic susceptibility and isothermal magnetizations.
Polycrystalline $\mathrm{Er_2Rh_3Si}$ compound with $\mathrm{Mg_2Ni_3Si}$-type
of rhombohedral Laves phases (space group $R\overline{3}m$, hR18) structure was
synthesized by arc-melting method. The ac- and dc-magnetic susceptibility
results revealed that the compound exhibited ferromagnetic order with $T_C$
$\approx$ 18 K. The obtained isothermal magnetic entropy changes ($\Delta
S_m$), and relative power cooling for a change of magnetic field 0-9 T are
10.1~$\mathrm{J.~kg^{-1}.~K^{-1}}$, and 255 J. kg$^{-1}$ respectively. Arrott
plots and also the universal scaling plot by rescaled temperature axis and
normalized $\Delta S_m$ collapse onto a one curve for independent of magnetic
fields, confirming a second-order ferromagnetic to paramagnetic phase
transition in $\mathrm{Er_2Rh_3Si}$.",2109.09632v1
2021-09-30,Hypothetical FrAu: An outlier in the B2 compounds,"The ordered alloys of alkali metals (Rb and Cs) and gold (Au) have the B2
(CsCl-type) structure and show a semiconducting property, irrespective to the
metallic constituents. Francium (Fr) is classed as an alkali metal and is
expected to form the B2 structure with Au. However, it is difficult to
synthesize such a compound experimentally due to a half-life of a few ten
minutes in the Fr atom. In this paper, by using the first-principles method, we
study the structural and electronic properties of FrAu in the B2 structure. The
FrAu has a relatively large lattice constant and a relatively small bulk
modulus among 310 B2 compounds. The profiles of the electron and phonon band
structures of the FrAu are quite similar to those of the CsAu. We predict that
the FrAu is included to one of the ionic compounds as well as the RbAu and
CsAu.",2109.14836v1
2021-10-25,A Heavy-Fermion Zn-deficient CaBe2Ge2-Type Phase with Rare Ce-based Ferromagnetism and Large Magnetoresistance,"We report on the hitherto unknown compound CeZn2-dGe2 (d approx 0.41). We
find this compound to crystallize in a defect version of the well-known
CaBe2Ge2 structure type. The phase forms in a Zn/In flux and with Zn-deficiency
on one of its crystallographic sites. We find the compound to display uncommon
localized Ce-based (4f1) ferromagnetism with a Tc = 6.6 K, a large positive
magnetoresistance reaching an MR of approximately 32 % below $T$ = 10 K, and
strongly correlated electrons, as evidenced by a Kadowaki-Woods ratio A/gamma^2
close to known heavy fermion compounds. The here discovered material is
therefore a promising model platform for the investigation of these entangled
interacting and potentially competing electronic states paired with complex
crystal chemistry.",2110.13096v4
2021-11-01,Crystal Structure of Silver Pentazolates AgN5 and AgN6,"Silver pentazolate, a high energy density compound containing cyclo-N5-
anion, has recently been synthesized at ambient conditions. However, due to
high sensitivity to irradiation, its crystal structure has not been determined.
In this work, silver-nitrogen crystalline compounds at ambient conditions and
high pressures, up to 100 GPa, are predicted and characterized by performing
first-principles evolutionary crystal structure searching with variable
stoichiometry. It is found that newly discovered AgN5 and AgN6 are the only
thermodynamically stable silver-nitrogen compounds at pressures between 42 and
80 GPa. In contrast to AgN5, pentazolate AgN6 compound contains N2 diatomic
molecules in addition to cyclo-N5-. These AgN5 and AgN6 crystals are metastable
at ambient conditions with positive formation enthalpies of 54.95 kJ/mol and
46.24 kJ/mol, respectively. The underlying cause of the stability of cyclo-N5-
silver pentazolates is the enhanced aromaticity enabled by the charge transfer
from silver atoms to nitrogen rings. To aid in experimental identification of
these materials, calculated Raman spectra are reported at ambient pressure: the
frequencies of N5- vibrational modes of AgN5 are in good agreement with those
measured in experiment.",2111.01240v1
2021-11-17,Machine Learning for compositional disorder: A Comparison Between Different Descriptors and Machine Learning Frameworks,"Compositional disorder is common in crystal compounds. In these compounds,
some atoms are randomly distributed at some crystallographic sites. For such
compounds, randomness forms many non-identical independent structures. Thus,
calculating the energy of all structures using ordinary quantum ab initio
methods can be significantly time-consuming. Machine learning can be a reliable
alternative to ab initio methods. We calculate the energy of these compounds
with an accuracy close to that of density functional theory calculations in a
considerably shorter time using machine learning. In this study, we use kernel
ridge regression and neural network to predict energy. In the KRR, we employ
sine matrix, Ewald sum matrix, SOAP, ACSF, and MBTR. To implement the neural
network, we use two important classes of application of the neural network in
material science, including high-dimensional neural network and convolutional
neural network based on crystal graph representation. We show that kernel ridge
regression using MBTR and neural network using ACSF can provide better accuracy
than other methods.",2111.09368v3
2021-11-30,Navigating the Ti-C-O and Al-C-O ternary systems through theory-driven discovery,"Computational searches for new materials are naturally turning from binary
systems, to ternary and other multicomponent systems, and beyond. Here, we
select the industrially-relevant metals titanium and aluminium and report the
results of an extensive structure prediction study on the ternary
titanium-carbon-oxygen (Ti-C-O) and aluminium-carbon-oxygen (Al-C-O) systems.
We map out for the first time the full phase stability of Ti-C-O and Al-C-O
compounds using first-principles calculations, through simple, efficient and
highly parallel random structure searching in conjunction with techniques based
on complex network theory. These phase stabilities emerge naturally from our
`data agnostic' approach, in which we map stable compounds without recourse to
structural databases or other prior knowledge. A surprising find is the
predicted ambient pressure stability of octet-rule-fulfiling titanium and
aluminium carbonate: Ti(CO3)$_2$ and Al$_2$(CO3)$_3$, neither of which has to
our knowledge been synthesised before. These materials could potentially act as
carbon sequestering compounds. Our searches discover several additional stable
and metastable ternary compounds supported by the Ti-C-O and Al-C-O systems.",2111.15247v1
2021-12-17,A Binded VAE for Inorganic Material Generation,"Designing new industrial materials with desired properties can be very
expensive and time consuming. The main difficulty is to generate compounds that
correspond to realistic materials. Indeed, the description of compounds as
vectors of components' proportions is characterized by discrete features and a
severe sparsity. Furthermore, traditional generative model validation processes
as visual verification, FID and Inception scores are tailored for images and
cannot then be used as such in this context. To tackle these issues, we develop
an original Binded-VAE model dedicated to the generation of discrete datasets
with high sparsity. We validate the model with novel metrics adapted to the
problem of compounds generation. We show on a real issue of rubber compound
design that the proposed approach outperforms the standard generative models
which opens new perspectives for material design optimization.",2112.09570v1
2021-12-17,Inorganic Synthesis Reaction Condition Prediction with Generative Machine Learning,"Data-driven synthesis planning with machine learning is a key step in the
design and discovery of novel inorganic compounds with desirable properties.
Inorganic materials synthesis is often guided by chemists' prior knowledge and
experience, built upon experimental trial-and-error that is both time and
resource consuming. Recent developments in natural language processing (NLP)
have enabled large-scale text mining of scientific literature, providing open
source databases of synthesis information of synthesized compounds, material
precursors, and reaction conditions (temperatures, times). In this work, we
employ a conditional variational autoencoder (CVAE) to predict suitable
inorganic reaction conditions for the crucial inorganic synthesis steps of
calcination and sintering. We find that the CVAE model is capable of learning
subtle differences in target material composition, precursor compound
identities, and choice of synthesis route (solid-state, sol-gel) that are
present in the inorganic synthesis space. Moreover, the CVAE can generalize
well to unseen chemical entities and shows promise for predicting reaction
conditions for previously unsynthesized compounds of interest.",2112.09612v1
2022-01-06,High fill factor confocal compound eyes fabricated by direct laser writing for better imaging quality,"We fabricate two kinds of 100% fill factor compound eye structures using
direct laser writing, including conventional compound eyes (CVCEs) with the
same focal length of each microlens unit, and specially designed confocal
compound eyes (CFCEs). For CFCEs, the focal length of each microlens unit is
determined by its position and is equal to the distance between the microlens
unit and the image sensor. In this letter, the optical properties of CVCEs and
CFCEs are tested and compared. It is found that compared with CVCEs, CFCEs can
improve the focusing efficiency by about 7%, enlarge the imaging area by about
25%, and have better imaging quality at the edge of the field of view.",2201.01915v1
2022-04-12,First-principles electronic structure investigation of HgBa$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{2n+2+x}$ with the SCAN density functional,"We perform first-principles calculation to study the electronic structure of
HgBa$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{2n+2+x}$ copper oxides up to $n = 6$ for the
undoped parent compound $(x = 0)$ and up to $n = 3$ for the doped compound $(x
> 0)$ by means of the SCAN meta-GGA density functional. Our calculations
predict an antiferromagnetic insulator ground state for the parent compounds
with an energy gap that decreases with the number of CuO$_{2}$ planes. We
report structural, electronic and magnetic order evolution with $x$ which agree
with experiments. We find an enhanced density of states at Fermi level at $x
\approx 0.25$ for the single-layered compound manifesting in a peak of the
Sommerfeld parameter, which recently has been discussed as a possible signature
of quantum criticality generic to all cuprates.",2204.05719v3
2022-04-06,Machine learning identification of organic compounds using visible light,"Identifying chemical compounds is essential in several areas of science and
engineering. Laser-based techniques are promising for autonomous compound
detection because the optical response of materials encodes enough electronic
and vibrational information for remote chemical identification. This has been
exploited using the fingerprint region of infrared absorption spectra, which
involves a dense set of absorption peaks that are unique to individual
molecules, thus facilitating chemical identification. However, optical
identification using visible light has not been realized. Using decades of
experimental refractive index data in the scientific literature of pure organic
compounds and polymers over a broad range of frequencies from the ultraviolet
to the far-infrared, we develop a machine learning classifier that can
accurately identify organic species based on a single-wavelength dispersive
measurement in the visible spectral region, away from absorption resonances.
The optical classifier proposed here could be applied to autonomous material
identification protocols or applications.",2204.11832v2
2022-04-29,Compound conditionals as random quantities and Boolean algebras,"Conditionals play a key role in different areas of logic and probabilistic
reasoning, and they have been studied and formalized from different angles. In
this paper we focus on the de Finetti's notion of conditional as a three-valued
object, with betting-based semantics, and its related approach as random
quantity as mainly developed by two of the authors. Compound conditionals have
been studied in the literature, but not in full generality. In this paper we
provide a natural procedure to explicitly attach conditional random quantities
to arbitrary compound conditionals that also allows us to compute their
previsions. By studying the properties of these random quantities, we show
that, in fact, the set of compound conditionals can be endowed with a Boolean
algebraic structure. In doing so, we pave the way to build a bridge between the
long standing tradition of three-valued conditionals and a more recent proposal
of looking at conditionals as elements from suitable Boolean algebras.",2204.14131v2
2022-07-12,Unveiling Unconventional Ferroelectric Switching in Multiferroic Ga0.6 Fe1.4O3 Thin Films Through Multiscale Electron Microscopy Investigations,"Understanding the polarization switching mechanisms at play in ferroelectric
materials is crucial for their exploitation in electronic devices. The
conventional centrosymmetric reference structure-based mechanism which accounts
for ferroelectricity in most of the usual displacive ferroelectric materials is
too energy-demanding for some newly diagnosed ferroelectric materials such as
the Ga2-xFexO3 (0.8 < x < 1.4) compounds. Some alternative theoretical
propositions have been made and need experimental confirmation. A dual-scale
electron microscopy study is performed on thin films of the Ga0.6Fe1.4O3
multiferroic compound. A wide scale precession-assisted electron diffraction
tomography study first allows the determination of the structure the compound
adopts in thin films, and even permits the refinement of the atomic positions
within this structure. Cationic mobility is suggested for two of the atomic
positions through the existence of extra electronic density. A local in situ
high resolution scanning transmission electron microscopy study then allows
confirming these mobilities by directly spotting the cationic displacements on
successively acquired images. The whole study confirms an unconventional
switching mechanism via local domain wall motion in this compound.",2207.05813v1
2022-09-13,A probabilistic virtual process chain to quantify process-induced uncertainties in Sheet Molding Compounds,"The manufacturing process of Sheet Molding Compound (SMC) influences the
properties of a component in a non-deterministic fashion. To predict this
influence on the mechanical performance, we develop a virtual process chain
acting as a digital twin for SMC specimens from compounding to failure. More
specifically, we inform a structural simulation with individual fields for
orientation and volume fraction computed from a direct bundle simulation of the
manufacturing process. The structural simulation employs an interpolated direct
deep material network to upscale a tailored SMC damage model. We evaluate
hundreds of virtual specimens and conduct a probabilistic analysis of the
mechanical performance. We estimate the contribution to uncertainty originating
from the process-induced inherent random microstructure and from varying
initial SMC stack configurations. Our predicted results are in good agreement
with experimental tensile tests and thermogravimetric analysis.",2209.05873v1
2022-09-16,Self-Supervised Learning of Phenotypic Representations from Cell Images with Weak Labels,"We propose WS-DINO as a novel framework to use weak label information in
learning phenotypic representations from high-content fluorescent images of
cells. Our model is based on a knowledge distillation approach with a vision
transformer backbone (DINO), and we use this as a benchmark model for our
study. Using WS-DINO, we fine-tuned with weak label information available in
high-content microscopy screens (treatment and compound) and achieve
state-of-the-art performance in not-same-compound mechanism of action
prediction on the BBBC021 dataset (98%), and not-same-compound-and-batch
performance (96%) using the compound as the weak label. Our method bypasses
single cell cropping as a pre-processing step, and using self-attention maps we
show that the model learns structurally meaningful phenotypic profiles.",2209.07819v2
2022-10-19,Axis thermal expansion switching in transition-metal zirconides TrZr2 by tuning the c/a ratio,"This study examines the temperature-dependent evolution of the lattice
constants for various CuAl2-type compounds, including NiZr2, (Co,Rh,Ir)Zr2,
(Fe,Co,Rh,Ir)Zr2, and (Co,Ni,Cu,Rh,Ir)Zr2, in the pursuit of negative or zero
thermal expansion. Results reveal that NiZr2 has positive thermal expansion,
while the other compounds exhibit uniaxial negative thermal expansion along the
c-axis contraction. The study suggests that the c-axis thermal expansion can be
controlled by manipulating the c/a ratio through Tr-site substitution,
providing a design principle for achieving negative thermal expansion of the
c-axis and potentially zero thermal expansion in a single compound in TrZr2
compounds.",2210.10367v2
2022-10-28,"Measurement of the transverse asymmetry of $γ$-rays in the $^{117}$Sn(n,$γ$)$^{118}$Sn reaction","Largely enhanced parity-violating effects observed in compound resonances
induced by epithermal neutrons are currently attributed to the mixing of
parity-unfavored partial amplitudes in the entrance channel of the compound
states. Furthermore, it is proposed that the same mechanism that enhances the
parity-violation also enhances the breaking of time-reversal-invariance in the
compound nucleus. The entrance-channel mixing induces energy-dependent
spin-angular correlations of individual $\gamma$-rays emitted from the compound
nuclear state. For a detailed study of the mixing model, a $\gamma$-ray yield
in the reaction of $^{117}$Sn(n,$\gamma$)$^{118}$Sn was measured using the
pulsed beam of polarized epithermal neutrons and Ge detectors. An angular
dependence of asymmetric $\gamma$-ray yields for the orientation of the neutron
polarization was observed.",2210.15807v1
2022-10-28,"Pressure-dependent semiconductor-metal transition and elastic, electronic, optical, and thermophysical properties of SnS binary chalcogenide","Density functional theory based study of the pressure dependent physical
properties of binary SnS compound has been carried out. The computed elastic
constants reveal that SnS is mechanically stable and brittle under ambient
conditions. With increasing pressure, the compound becomes ductile. The
Poisson's ratio also indicates brittle-ductile transition with increasing
pressure. The hardness of SnS increases significantly with pressure. The
compound possesses elastic anisotropy. The ground state electronic band
structure is semiconducting with a small band gap which becomes metallic under
pressure. The band becomes more and more dispersive with the increase in
pressure while the electronic correlations decrease as pressure is raised. Both
the Debye temperature and the phonon thermal conductivity of SnS increase
sharply with pressure. The Melting temperature of the compound is low. Mixed
bonding characteristics are found with ionic and covalent contributions. SnS is
a good absorber of ultraviolet light. The reflectivity of the material
increases with the increase in pressure. The reflectivity is nonselective over
a wide spectral range. The low energy refractive index is high. All these
optical characteristics are useful for prospective optoelectronic device
applications. The optical anisotropy is low.",2210.16055v1
2023-04-01,Knowledge Graph Embedding with 3D Compound Geometric Transformations,"The cascade of 2D geometric transformations were exploited to model relations
between entities in a knowledge graph (KG), leading to an effective KG
embedding (KGE) model, CompoundE. Furthermore, the rotation in the 3D space was
proposed as a new KGE model, Rotate3D, by leveraging its non-commutative
property. Inspired by CompoundE and Rotate3D, we leverage 3D compound geometric
transformations, including translation, rotation, scaling, reflection, and
shear and propose a family of KGE models, named CompoundE3D, in this work.
CompoundE3D allows multiple design variants to match rich underlying
characteristics of a KG. Since each variant has its own advantages on a subset
of relations, an ensemble of multiple variants can yield superior performance.
The effectiveness and flexibility of CompoundE3D are experimentally verified on
four popular link prediction datasets.",2304.00378v1
2023-04-05,A+2n compound nuclei and the unitary limit in nuclear physics,"This contribution discusses a new perception of the structure of compound
nuclei by introducing intermediate states of the Feshbach formalism of nuclear
reactions in the Interacting Boson Model of nuclear structure. The stake is to
explore the manifestation of the unitary limit in heavy, even-even nuclei.
Interactions that govern Feshbach resonances of cold and dilute atomic gases
suggest the formulation of an IBM-compound Hamiltonian for scattering two
neutrons (2n) from a heavy, even-even target (A). The solutions of the
corresponding coupled channel equations host a 2n-IBM state resonance. It turns
out that the unitary limit is measurable in a heavy A+2n compound nucleus at
low temperatures. That measurement is feasible through the fluctuations of the
cross-sections that tune the 2n-A scattering length.",2304.02400v1
2023-04-17,Transformation of hexagonal Lu to cubic LuH$_{2+x}$ single-crystalline films,"With the recent report of near ambient superconductivity at room temperature
in the N-doped lutetium hydride (Lu-H-N) system, the understanding of cubic
Lu-H compounds has attracted worldwide attention. Generally, compared to
polycrystal structures with non-negligible impurities, the single-crystalline
form of materials with high purity can provide an opportunity to show their
hidden properties. However, the experimental synthesis of single-crystalline
cubic Lu-H compounds has not been reported thus far. Here, we developed an easy
way to synthesize highly pure LuH$_{2+x}$ single-crystalline films by the
post-annealing of Lu single-crystalline films (purity of 99.99%) in the H$_2$
atmosphere. The crystal and electronic structures of films were characterized
by X-ray diffraction, Raman spectroscopy, and electrical transport.
Interestingly, Lu films are silver-white and metallic, whereas their
transformed LuH$_{2+x}$ films become purple-red and insulating, indicating the
formation of an unreported electronic state of Lu-H compounds possibly. Our
work provides a novel route to synthesize and explore more single-crystalline
Lu-H compounds.",2304.07966v2
2023-04-20,"Magnetic behavior of cubic Dy4RhAl with respect to isostructural Dy4PtAl, revealing a novel 4f d-band interaction","We have investigated for the first time the magnetic behaviour of an
intermetallic compound, Dy4RhAl, crystallizing in Gd4RhIn type cubic structure
containing 3 sites for rare-earth (R), by several bulk measurements down to 1.8
K. This work is motivated by the fact that the isostructural Dy compound in the
R4PtAl family surprisingly orders ferromagnetically unlike other members of
this series, which order antiferromagnetically. The results reveal that the
title compound undergoes antiferromagnetic order at about 18 K, similar to
other heavy R members of R4RhAl family, unlike its Pt counterpart, indicating a
subtle difference in the role of conduction electrons to decide magnetism of
these compounds. Besides, spin-glass features coexisting with antiferromagnetic
order could be observed, which could mean cluster antiferromagnetism. The
electrical resistivity and magnetoresistance behaviours in the magnetically
ordered state are typical of magnetic materials exhibiting antiferromagnetic
gap. Features attributable to spin-reorientation as a function of temperature
and magnetic field can be seen in the magnetization data.",2304.10122v1
2023-05-08,Quantum oscillations revealing topological band in kagome metal ScV6Sn6,"Compounds with kagome lattice structure are known to exhibit Dirac cones,
flat bands, and van Hove singularities, which host numerous versatile quantum
phenomena. Inspired by these intriguing properties, we investigate the
temperature and magnetic field dependent electrical transports along with the
theoretical calculations of ScV6Sn6, a nonmagnetic charge density wave (CDW)
compound. At low temperatures, the compound exhibits Shubnikov-de Haas quantum
oscillations, which help to design the Fermi surface (FS) topology. This
analysis reveals the existence of several small FSs in the Brillouin zone,
combined with a large FS. Among them, the FS possessing Dirac band is a
non-trivial and generates a non-zero Berry phase. In addition, the compound
also shows the anomalous Hall-like behaviour up to the CDW with the CDW phase,
ScV6Sn6 presents a unique material example of the versatile HfFe6Ge6 family and
provides various promising opportunities to explore the series further.",2305.04683v2
2023-05-28,Understanding Blockchain Governance: Analyzing Decentralized Voting to Amend DeFi Smart Contracts,"Governance protocols define the means for amending or changing smart
contracts without any centralized authority. They distribute the
decision-making power to every user of the smart contract: Users vote on
accepting or rejecting every change. In this work, we review and characterize
decentralized governance in practice, using Compound and Uniswap -- two widely
used governance protocols -- as a case study. We reveal a high concentration of
voting power in both Compound and Uniswap: 10 voters hold together 57.86% and
44.72% of the voting power, respectively. Although proposals to change or amend
the protocol receive, on average, a substantial number of votes (i.e., 89.39%)
in favor within the Compound protocol, they require fewer than three voters to
obtain 50% or more votes. We show that voting on Compound proposals can be
unfairly expensive for small token holders, and we discover voting coalitions
that can further marginalize these users.",2305.17655v2
2023-06-01,Structural Trends and Itinerant Magnetism of the New Cage-structured Compound HfMn$_{2}$Zn$_{20}$,"A new cage-structured compound - HfMn$_{2}$Zn$_{20}$ - belonging to the
AB$_{2}$C$_{20}$ (A, B = transition or rare earth metals, and C = Al, Zn, or
Cd) family of structures has been synthesized via the self-flux method. The new
compound crystallizes in the space group Fd-3m with lattice parameter a =
14.0543(2) \r{A} (Z = 8) and exhibits non-stoichiometry due to Mn/Zn mixing on
the Mn-site and an underoccupied Hf-site. The structure refines to
Hf$_{0.93}$Mn$_{1.63}$Zn$_{20.37}$ and follows lattice size trends when
compared to other HfM$_{2}$Zn$_{20}$ (M = Fe, Co, and Ni) structures. The
magnetic measurements show that this compound displays a modified Curie-Weiss
behavior with a transition temperature around 22 K. The magnetization shows no
saturation, a small magnetic moment, and near negligible hysteresis, all signs
of the itinerant magnetism. The Rhodes-Wohlfarth ratio and the spin fluctuation
parameters ratio both confirm the itinerant nature of the magnetism in
HfMn$_{2}$Zn$_{20}$.",2306.01146v3
2023-06-12,Compound Poisson particle approximation for McKean-Vlasov SDEs,"We present a comprehensive discretization scheme for linear and nonlinear
stochastic differential equations (SDEs) driven by either Brownian motions or
$\alpha$-stable processes. Our approach utilizes compound Poisson particle
approximations, allowing for simultaneous discretization of both the time and
space variables in McKean-Vlasov SDEs. Notably, the approximation processes can
be represented as a Markov chain with values on a lattice. Importantly, we
demonstrate the propagation of chaos under relatively mild assumptions on the
coefficients, including those with polynomial growth. This result establishes
the convergence of the particle approximations towards the true solutions of
the McKean-Vlasov SDEs. By only imposing moment conditions on the intensity
measure of compound Poisson processes, our approximation exhibits universality.
In the case of ordinary differential equations (ODEs), we investigate scenarios
where the drift term satisfies the one-sided Lipschitz assumption. We prove the
optimal convergence rate for Filippov solutions in this setting. Additionally,
we establish a functional central limit theorem (CLT) for the approximation of
ODEs and show the convergence of invariant measures for linear SDEs. As a
practical application, we construct a compound Poisson approximation for
2D-Navier Stokes equations on the torus and demonstrate the optimal convergence
rate.",2306.06816v2
2023-07-07,Identifying metabolites from protein identifiers with P2M,"The identification of metabolites from complex biological samples often
involves matching experimental mass spectrometry data to signatures of
compounds derived from massive chemical databases. However, misidentifications
may result due to the complexity of potential chemical space that leads to
databases containing compounds with nearly identical structures. Prior
knowledge of compounds that may be enzymatically consumed or produced by an
organism can help reduce misidentifications by restricting initial database
searching to compounds that are likely to be present in a biological system.
While databases such as UniProt allow for the identification of small molecules
that may be consumed or generated by enzymes encoded in an organism's genome,
currently no tool exists for identifying SMILES strings of metabolites
associated with protein identifiers and expanding R-containing substructures to
fully defined, biologically relevant chemical structures. Here we present
Proteome2Metabolome (P2M), a tool that performs these tasks using external
database querying behind a simple command line interface. Beyond mass
spectrometry based applications, P2M can be generally used to identify
biologically relevant chemical structures likely to be observed in a biological
system.",2307.03865v1
2023-07-20,Sampling the Whole Materials Space for Conventional Superconducting Materials,"We perform a large scale study of conventional superconducting materials
using a machine-learning accelerated high-throughput workflow. We start by
creating a comprehensive dataset of around 7000 electron-phonon calculations
performed with reasonable convergence parameters. This dataset is then used to
train a robust machine learning model capable of predicting the electron-phonon
and superconducting properties based on structural, compositional, and
electronic ground-state properties. Using this machine, we evaluate the
transition temperature (Tc ) of approximately 200000 metallic compounds, all of
which on the convex hull of thermodynamic stability (or close to it) to
maximize the probability of synthesizability. Compounds predicted to have Tc
values exceeding 5 K are further validated using density-functional
perturbation theory. As a result, we identify 545 compounds with Tc values
surpassing 10 K, encompassing a variety of crystal structures and chemical
compositions. This work is complemented with a detailed examination of several
interesting materials, including nitrides, hydrides, and intermetallic
compounds. Particularly noteworthy is LiMoN2 , which we predict to be
superconducting in the stoichiometric trigonal phase, with a Tc exceeding 38 K.
LiMoN2 has been previously synthesized in this phase, further heightening its
potential for practical applications.",2307.10728v1
2023-07-23,Fractional Generalizations of the Compound Poisson Process,"This paper introduces the Generalized Fractional Compound Poisson Process
(GFCPP), which claims to be a unified fractional version of the compound
Poisson process (CPP) that encompasses existing variations as special cases. We
derive its distributional properties, generalized fractional differential
equations, and martingale properties. Some results related to the governing
differential equation about the special cases of jump distributions, including
exponential, Mittag-Leffler, Bernst\'ein, discrete uniform, truncated
geometric, and discrete logarithm. Some of processes in the literature such as
the fractional Poisson process of order $k$, P\'olya-Aeppli process of order
$k$, and fractional negative binomial process becomes the special case of the
GFCPP. Classification based on arrivals by time-changing the compound Poisson
process by the inverse tempered and the inverse of inverse Gaussian
subordinators are studied. Finally, we present the simulation of the sample
paths of the above-mentioned processes.",2307.12252v1
2023-08-15,Different phase leads to different transport behavior in Pb$_9$Cu(PO$_4$)$_6$O compounds,"The recent claimed room-temperature superconductivity in Cu-doped lead
apatite at ambient pressure are under highly debate. To identify its physical
origin, we studied the crystal structures, energy band structures, lattice
dynamics and magnetic properties of the parent Pb$_{10}$(PO$_4$)$_6$O compound,
in which two different phases of the LK-99 compound are analyzed in detail. Our
results show that the Pb$_{10}$(PO$_4$)$_6$O compound is an indirect band gap
semiconductor, where Cu doping at the 4$f$ site of Pb leads to a semiconducting
to half-metallic transition. Two half-filled flat bands spanning the Fermi
energy levels are present in the 4$f$-phase of LK-99, which are mainly formed
by hybridization of the $d_{x^2-y^2}$ and $d_{zy}$ orbitals of Cu with the 2$p$
orbitals of O. In addition, 6$h$-phase of LK-99 always has spin polarity at the
bottom of the conduction band and at the top of the valence band, making the
material a bipolar magnetic semiconductor. Our results are basically consistent
with the recent experimental transport properties of LK-99 posted on
arXiv:2308.05778.",2308.08454v1
2023-09-05,Towards data-driven mass spectrometry in atmospheric science,"Aerosols found in the atmosphere affect the climate and worsen air quality.
To mitigate these adverse impacts, aerosol formation and aerosol chemistry in
the atmosphere need to be better mapped out and understood. Currently, mass
spectrometry is the single most important analytical technique in atmospheric
chemistry and is used to track and identify compounds and processes. Vast
amounts of data are collected in each measurement of current time-of-flight and
orbitrap mass spectrometers using modern rapid data acquisition practices.
However, compound identification remains as a major bottleneck during data
analysis due to lacking reference libraries and analysis tools. Data-driven
compound identification approaches could alleviate the problem, yet remain rare
to non-existent in atmospheric science. In this perspective, we review the
current state of data-driven compound identification with mass spectrometry in
atmospheric science, and discuss current challenges and possible future steps
towards a digital mass spectrometry era in atmospheric science.",2309.02268v2
2023-10-10,Prediction of Ambient Pressure Conventional Superconductivity above 80K in Thermodynamically Stable Hydride Compounds,"The primary challenge in the field of high-temperature superconductivity in
hydrides is to achieve a superconducting state at ambient pressure rather than
the extreme pressures that have been required in experiments so far. Here, we
propose a family of compounds, of composition Mg$_2$XH$_6$ with X$=$Rh, Ir, Pd,
or Pt, that achieves this goal. These materials were identified by scrutinizing
more than a million compounds using a machine-learning accelerated
high-throughput workflow. They are thermodynamically stable, indicating that
they are serious candidates for experimental synthesis. We predict that their
superconducting transition temperatures are in the range of 45-80K, or even
above 100K with appropriate electron doping of the Pt compound. These results
indicate that, although very rare, high-temperature superconductivity in
thermodynamically stable hydrides is achievable at room pressure.",2310.06804v1
2023-10-19,Pressure-induced Superconductivity and Structure Phase Transition in SnAs-based Zintl Compound SrSn2As2,"Layered SnAs-based Zintl compounds exhibit a distinctive electronic
structure, igniting extensive research efforts in areas of superconductivity,
topological insulators and quantum magnetism. In this paper, we systematically
investigate the crystal structures and electronic properties of the Zintl
compound SrSn2As2 under high-pressure. At approximately 20.8 GPa,
pressure-induced superconductivity is observed in SrSn2As2 with a
characteristic dome-like evolution of Tc. Theoretical calculations together
with high pressure synchrotron X-ray diffraction and Raman spectroscopy have
identified that SrSn2As2 undergoes a structural transformation from a trigonal
to a monoclinic structure. Beyond 28.3 GPa, the superconducting transition
temperature is suppressed due to a reduction of the density of state at the
Fermi level. The discovery of pressure-induced superconductivity, accompanied
by structural transitions in SrSn2As2, greatly expands the physical properties
of layered SnAs-based compounds and provides a new ground states upon
compression.",2310.12824v1
2023-10-23,Compound Poisson process approximation under $β$-mixing and stabilization,"We establish Poisson and compound Poisson approximations for stabilizing
statistics of $\beta$-mixing point processes and give explicit rates of
convergence. Our findings are based on a general estimate of the total
variation distance of a stationary $\beta$-mixing process and its Palm version.
As main contributions, this article (i) extends recent results on Poisson
process approximation to non-Poisson/binomial input, (ii) gives concrete bounds
for compound Poisson process approximation in a Wasserstein distance and (iii)
illustrates the applicability of the general result in an example on minimal
angles in the stationary Poisson-Delaunay tessellation. The latter is among the
first (nontrivial) situations in Stochastic Geometry, where compound Poisson
approximation can be established with explicit extremal index and cluster size
distribution.",2310.15009v1
2023-10-25,Unsupervised Learning of Molecular Embeddings for Enhanced Clustering and Emergent Properties for Chemical Compounds,"The detailed analysis of molecular structures and properties holds great
potential for drug development discovery through machine learning. Developing
an emergent property in the model to understand molecules would broaden the
horizons for development with a new computational tool. We introduce various
methods to detect and cluster chemical compounds based on their SMILES data.
Our first method, analyzing the graphical structures of chemical compounds
using embedding data, employs vector search to meet our threshold value. The
results yielded pronounced, concentrated clusters, and the method produced
favorable results in querying and understanding the compounds. We also used
natural language description embeddings stored in a vector database with
GPT3.5, which outperforms the base model. Thus, we introduce a similarity
search and clustering algorithm to aid in searching for and interacting with
molecules, enhancing efficiency in chemical exploration and enabling future
development of emergent properties in molecular property prediction models.",2310.18367v1
2023-11-12,First-principles pressure dependent investigation of the physical properties of KB2H8: a prospective high-TC superconductor,"Using the density functional theory (DFT) based first-principles
investigation, the structural, mechanical, hardness, elastic anisotropy,
optoelectronic, and thermal properties of cubic KB2H8 have been studied within
the uniform pressure range of 0 - 24 GPa. The calculated structural parameters
are in good agreement with the previous theoretical work. The compound KB2H8 is
found to be structurally and thermodynamically stable in the pressure range
from 8 GPa to 24 GPa. Single crystal elastic constants Cij and bulk elastic
moduli (B, G and Y) increase systematically with pressure from 8 GPa to 24 GPa.
In the stable phase, KB2H8 is moderately elastically anisotropic and ductile in
nature. The compound is highly machinable and fracture resistant. The Debye
temperature, melting temperature and thermal conductivity increases with
pressure. The results of electronic band structure calculations and optical
parameters at different pressures are consistent with each other. The compound
is optically isotropic. The compound KB2H8 has potential to be used as a very
efficient solar energy reflector. The electronic energy density of states at
the Fermi level decreases systematically with increasing pressure. The same
trend is found for the repulsive Coulomb pseudopotential. Possible relevance of
the studied properties to superconductivity has also been discussed in this
paper.",2311.06709v1
2023-11-30,Highly sensitive magnetic properties and large linear magnetoresistance in antiferromagnetic CrxSe(0.875\lex\le1)single crystals,"CrxSe (x\le1) is a class of quasi-layered binary compounds with potential
applications in spintronics due to its intriguing antiferromagnetic properties.
In this work, CrxSe single crystals with high Cr content (x=0.87, 0.91 and
0.95) were grown, and their magnetic and transport properties were investigated
in detail. It is found that with small increase of Cr content, the N\'eel
temperature (TN) of the samples can dramatically increase from 147 K to 257 K,
accompanied with obvious changes in the magnetic anisotropy and hysteresis. The
phenomena of field-induced spin-flop transitions were unveiled in these alloys,
indicating their comparatively low anisotropy. The magnetoresistance (MR) of
the three compounds showed positive dependence at low temperatures and
particularly, non-saturated linear positive MR was observed in Cr0.91Se and
Cr0.95Se, with a large value of 16.2% achieved in Cr0.91Se (10K, 9T). The
calculated Fermi surface and MR showed that the quasi-linear MR is a product of
carrier compensation. Our work revealed highly sensitive magnetic and transport
properties in the Cr-Se compounds, which can lay foundation when constructing
further antiferromagnetic spintronic devices based on them.",2311.18349v1
2023-12-01,Compensated Ferrimagnets with Colossal Spin Splitting in Organic Compounds,"The study of the magnetic order has recently been invigorated by the
discovery of exotic collinear antiferromagnets with time-reversal symmetry
breaking. Examples include altermagnetism and compensated ferrimagnets, which
show spin splittings of the electronic band structures even at zero net
magnetization, leading to several unique transport phenomena, notably
spin-current generation. Altermagnets demonstrate anisotropic spin splitting,
such as $d$-wave, in momentum space, whereas compensated ferrimagnets exhibit
isotropic spin splitting. However, methods to realize compensated ferrimagnets
are limited. Here, we demonstrate a method to realize a fully compensated
ferrimagnet with isotropic spin splitting utilizing the dimer structures
inherent in organic compounds. Moreover, based on $ab$ $initio$ calculations,
we find that this ferrimagnet can be realized in the recently discovered
organic compound (EDO-TTF-I)$_2$ClO$_4$. Our findings provide an unprecedented
strategy for using the dimer degrees of freedom in organic compounds to realize
fully compensated ferrimagnets with colossal spin splitting.",2312.00367v2
2023-12-15,Full-Envelope Flight Control and a Transition Strategy for Compound eVTOL aircrafts,"This paper presents a flight control design for compound Electric Vertical
Takeoff and Landing (eVTOL) vehicles. With their multitude of degrees of
controllability as well as the significant variations in their flight
characteristics, VTOL vehicles present challenges when it comes to designing
their flight control system, especially for the transition phase where the
vehicle transitions between near-hovering and high-speed wing-borne flights.
This work extends previous research on the design of unified and generic
control laws that can be applied to a broad class of vehicles such as hovering
vehicles and fixed-wing aircraft. This paper exploits this unifying property
and presents an extension for the case of compound VTOL vehicles. The proposed
control approach consists of nonlinear geometric control laws that are
continuously applicable over the entire flight envelope, excluding the use of
switching policies between different control algorithms. A transition strategy
consisting of a sequence of high-level setpoints is associated with the flight
control laws, it is defined with respect to flight envelope limitations and is
applied in this work to a commercially available compound UAV. The control
algorithms are implemented on a Pixhawk controller, they are evaluated via
Hardware-In-The-Loop (HIL) simulations, and finally validated in a flight
experiment.",2312.09629v1
2024-01-17,Study of the structural and electronic properties of semimetallic InBi: first-principles calculation of compound with peculiarities of the electronic structure,"The electronic properties as well as the structural characteristics and their
pressure dependence of the semi-metallic $B10$-structured compound
$\mathrm{InBi}$ were investigated. It is found that the structural values of
$\mathrm{InBi}$ calculated in the first-principles calculations reproduce the
experimental values worse than those for other heavy III-V pnictides, which are
characterized by cubic $B3$ and $B2$ structures, as well as for IV-VI compounds
$\mathrm{SnO}$ and $\mathrm{PbO}$ having the same $B10$ structure. The low
accuracy of the first-principles calculations is a consequence of the
peculiarities of the band structure inherent to $\mathrm{InBi}$ and not
observed in all the other above-mentioned compounds. To improve the agreement
with the experiment, it is proposed to take into account the distortion of the
compensated half-metal condition at the highly symmetric points of the
Brillouin zone, where the electronic and hole pockets are located.",2401.09326v1
2024-01-25,Common Randomness Generation from Finite Compound Sources,"We investigate the problem of generating common randomness (CR) from finite
compound sources aided by unidirectional communication over rate-limited
perfect channels. The two communicating parties, often referred to as
terminals, observe independent and identically distributed (i.i.d.) samples of
a finite compound source and aim to agree on a common random variable with a
high probability for every possible realization of the source state. Both
parties know the set of source states as well as their statistics. However,
they are unaware of the actual realization of the source state. We establish a
single-letter lower and upper bound on the compound CR capacity for the
specified model. Furthermore, we present two special scenarios where the
established bounds coincide.",2401.14323v1
2024-02-06,Compound Returns Reduce Variance in Reinforcement Learning,"Multistep returns, such as $n$-step returns and $\lambda$-returns, are
commonly used to improve the sample efficiency of reinforcement learning (RL)
methods. The variance of the multistep returns becomes the limiting factor in
their length; looking too far into the future increases variance and reverses
the benefits of multistep learning. In our work, we demonstrate the ability of
compound returns -- weighted averages of $n$-step returns -- to reduce
variance. We prove for the first time that any compound return with the same
contraction modulus as a given $n$-step return has strictly lower variance. We
additionally prove that this variance-reduction property improves the
finite-sample complexity of temporal-difference learning under linear function
approximation. Because general compound returns can be expensive to implement,
we introduce two-bootstrap returns which reduce variance while remaining
efficient, even when using minibatched experience replay. We conduct
experiments showing that two-bootstrap returns can improve the sample
efficiency of $n$-step deep RL agents, with little additional computational
cost.",2402.03903v1
2024-02-16,MFBind: a Multi-Fidelity Approach for Evaluating Drug Compounds in Practical Generative Modeling,"Current generative models for drug discovery primarily use molecular docking
to evaluate the quality of generated compounds. However, such models are often
not useful in practice because even compounds with high docking scores do not
consistently show experimental activity. More accurate methods for activity
prediction exist, such as molecular dynamics based binding free energy
calculations, but they are too computationally expensive to use in a generative
model. We propose a multi-fidelity approach, Multi-Fidelity Bind (MFBind), to
achieve the optimal trade-off between accuracy and computational cost. MFBind
integrates docking and binding free energy simulators to train a multi-fidelity
deep surrogate model with active learning. Our deep surrogate model utilizes a
pretraining technique and linear prediction heads to efficiently fit small
amounts of high-fidelity data. We perform extensive experiments and show that
MFBind (1) outperforms other state-of-the-art single and multi-fidelity
baselines in surrogate modeling, and (2) boosts the performance of generative
models with markedly higher quality compounds.",2402.10387v1
2024-02-20,On Generalization Bounds for Deep Compound Gaussian Neural Networks,"Algorithm unfolding or unrolling is the technique of constructing a deep
neural network (DNN) from an iterative algorithm. Unrolled DNNs often provide
better interpretability and superior empirical performance over standard DNNs
in signal estimation tasks. An important theoretical question, which has only
recently received attention, is the development of generalization error bounds
for unrolled DNNs. These bounds deliver theoretical and practical insights into
the performance of a DNN on empirical datasets that are distinct from, but
sampled from, the probability density generating the DNN training data. In this
paper, we develop novel generalization error bounds for a class of unrolled
DNNs that are informed by a compound Gaussian prior. These compound Gaussian
networks have been shown to outperform comparative standard and unfolded deep
neural networks in compressive sensing and tomographic imaging problems. The
generalization error bound is formulated by bounding the Rademacher complexity
of the class of compound Gaussian network estimates with Dudley's integral.
Under realistic conditions, we show that, at worst, the generalization error
scales $\mathcal{O}(n\sqrt{\ln(n)})$ in the signal dimension and
$\mathcal{O}(($Network Size$)^{3/2})$ in network size.",2402.13106v1
2024-03-02,A Bayesian Committee Machine Potential for Oxygen-containing Organic Compounds,"Understanding the pivotal role of oxygen-containing organic compounds in
serving as an energy source for living organisms and contributing to protein
formation is crucial in the field of biochemistry. This study addresses the
challenge of comprehending protein-protein interactions (PPI) and developing
predicitive models for proteins and organic compounds, with a specific focus on
quantifying their binding affinity. Here, we introduce the active Bayesian
Committee Machine (BCM) potential, specifically designed to predict
oxygen-containing organic compounds within eight groups of CHO. The BCM
potential adopts a committee-based approach to tackle scalability issues
associated with kernel regressors, particularly when dealing with large
datasets. Its adaptable structure allows for efficient and cost-effective
expansion, maintaing both transferability and scalability. Through systematic
benchmarking, we position the sparse BCM potential as a promising contender in
the pursuit of a universal machine learning potential.",2403.01158v1
2024-03-11,Human and Automatic Interpretation of Romanian Noun Compounds,"Determining the intended, context-dependent meanings of noun compounds like
""shoe sale"" and ""fire sale"" remains a challenge for NLP. Previous work has
relied on inventories of semantic relations that capture the different meanings
between compound members. Focusing on Romanian compounds, whose morphosyntax
differs from that of their English counterparts, we propose a new set of
relations and test it with human annotators and a neural net classifier.
Results show an alignment of the network's predictions and human judgments,
even where the human agreement rate is low. Agreement tracks with the frequency
of the selected relations, regardless of structural differences. However, the
most frequently selected relation was none of the sixteen labeled semantic
relations, indicating the need for a better relation inventory.",2403.06360v1
2024-03-19,Compound Expression Recognition via Multi Model Ensemble,"Compound Expression Recognition (CER) plays a crucial role in interpersonal
interactions. Due to the existence of Compound Expressions , human emotional
expressions are complex, requiring consideration of both local and global
facial expressions to make judgments. In this paper, to address this issue, we
propose a solution based on ensemble learning methods for Compound Expression
Recognition. Specifically, our task is classification, where we train three
expression classification models based on convolutional networks, Vision
Transformers, and multi-scale local attention networks. Then, through model
ensemble using late fusion, we merge the outputs of multiple models to predict
the final result. Our method achieves high accuracy on RAF-DB and is able to
recognize expressions through zero-shot on certain portions of C-EXPR-DB.",2403.12572v1
2009-09-23,On the Degrees of Freedom of Finite State Compound Wireless Networks - Settling a Conjecture by Weingarten et. al,"We explore the degrees of freedom (DoF) of three classes of finite state
compound wireless networks in this paper. First, we study the multiple-input
single-output (MISO) finite state compound broadcast channel (BC) with
arbitrary number of users and antennas at the transmitter. In prior work,
Weingarten et. al. have found inner and outer bounds on the DoF with 2 users.
The bounds have a different character. While the inner bound collapses to unity
as the number of states increases, the outer bound does not diminish with the
increasing number of states beyond a threshold value. It has been conjectured
that the outer bound is loose and the inner bound represents the actual DoF. In
the complex setting (all signals, noise, and channel coefficients are complex
variables) we solve a few cases to find that the outer bound -and not the inner
bound- of Weingarten et. al. is tight. For the real setting (all signals, noise
and channel coefficients are real variables) we completely characterize the
DoF, once again proving that the outer bound of Weingarten et. al. is tight. We
also extend the results to arbitrary number of users. Second, we characterize
the DoF of finite state scalar (single antenna nodes) compound X networks with
arbitrary number of users in the real setting. Third, we characterize the DoF
of finite state scalar compound interference networks with arbitrary number of
users in both the real and complex setting. The key finding is that scalar
interference networks and (real) X networks do not lose any DoF due to channel
uncertainty at the transmitter in the finite state compound setting. The finite
state compound MISO BC does lose DoF relative to the perfect CSIT scenario.
However, what is lost is only the DoF benefit of joint processing at transmit
antennas, without which the MISO BC reduces to an X network.",0909.4177v1
2011-06-24,Semantic Inference using Chemogenomics Data for Drug Discovery,"Background Semantic Web Technology (SWT) makes it possible to integrate and
search the large volume of life science datasets in the public domain, as
demonstrated by well-known linked data projects such as LODD, Bio2RDF, and
Chem2Bio2RDF. Integration of these sets creates large networks of information.
We have previously described a tool called WENDI for aggregating information
pertaining to new chemical compounds, effectively creating evidence paths
relating the compounds to genes, diseases and so on. In this paper we examine
the utility of automatically inferring new compound-disease associations (and
thus new links in the network) based on semantically marked-up versions of
these evidence paths, rule-sets and inference engines.
  Results Through the implementation of a semantic inference algorithm, rule
set, Semantic Web methods (RDF, OWL and SPARQL) and new interfaces, we have
created a new tool called Chemogenomic Explorer that uses networks of
ontologically annotated RDF statements along with deductive reasoning tools to
infer new associations between the query structure and genes and diseases from
WENDI results. The tool then permits interactive clustering and filtering of
these evidence paths.
  Conclusions We present a new aggregate approach to inferring links between
chemical compounds and diseases using semantic inference. This approach allows
multiple evidence paths between compounds and diseases to be identified using a
rule-set and semantically annotated data, and for these evidence paths to be
clustered to show overall evidence linking the compound to a disease. We
believe this is a powerful approach, because it allows compound-disease
relationships to be ranked by the amount of evidence supporting them.",1106.4880v1
2017-08-24,Ab initio effective Hamiltonians for cuprate superconductors,"Ab initio low-energy effective Hamiltonians of two typical high-temperature
copper-oxide superconductors, whose mother compounds are La$_2$CuO$_4$ and
HgBa$_2$CuO$_4$, are derived by utilizing the multi-scale ab initio scheme for
correlated electrons (MACE). The effective Hamiltonians obtained in the present
study serve as platforms of future studies to accurately solve the low-energy
effective Hamiltonians beyond the density functional theory. It allows further
study on the superconducting mechanism from the first principles and
quantitative basis without adjustable parameters not only for the available
cuprates but also for future design of higher Tc in general. More concretely,
we derive effective Hamiltonians for three variations, 1)one-band Hamiltonian
for the antibonding orbital generated from strongly hybridized Cu
$3d_{x^2-y^2}$ and O $2p_\sigma$ orbitals 2)two-band Hamiltonian constructed
from the antibonding orbital and Cu $3d_{3z^2-r^2}$ orbital hybridized mainly
with the apex oxygen $p_z$ orbital 3)three-band Hamiltonian consisting mainly
of Cu $3d_{x^2-y^2}$ orbitals and two O $2p_\sigma$ orbitals. Differences
between the Hamiltonians for La$_2$CuO$_4$ and HgBa$_2$CuO$_4$, which have
relatively low and high critical temperatures, respectively, at optimally doped
compounds, are elucidated. The main differences are summarized as i) the oxygen
$2p_\sigma$ orbitals are farther(~3.7eV) below from the Cu $d_{x^2-y^2}$
orbital for the La compound than the Hg compound(~2.4eV) in the three-band
Hamiltonian. This causes a substantial difference in the character of the
$d_{x^2-y^2}-2p_\sigma$ antibonding band at the Fermi level and makes the
effective onsite Coulomb interaction U larger for the La compound than the Hg
compound for the two- and one-band Hamiltonians. ii)The ratio of the
second-neighbor to the nearest transfer t'/t is also substantially different
(~0.26) for the Hg and ~0.15 for the La compound in the one-band Hamiltonian.",1708.07498v2
2018-05-09,"Effects of transition metals on physical properties of M2BC (M = V, Nb, Mo and Ta): a DFT calculation","The electronic band structures along with Fermi surface, anisotropy, Vickers
hardness, analysis of Mulliken populations, optical and thermodynamic
properties were studied for the first time. The optimized unit cell parameters
are compared with available theoretical and experimental results and a
reasonable agreement is recorded. The mechanical stability of these compounds
is confirmed. All the compounds herein exhibit metallic conductivity where
major contribution comes from d-orbital electrons. The hardness values of
10.71, 12.44, 8.52 and 16.80 GPa were recorded for M2BC (M = V, Nb, Mo and Ta)
compounds, respectively. The value of bulk modulus, B is found to increase in
the sequence B (V2BC) < B (Nb2BC) < B (Ta2BC) < B (Mo2BC), indicates Mo2BC is
highly stiff among all compounds. The Mo2BC and Ta2BC compound might be
considered as potential candidates for protection of cutting and forming tools
due to the moderately ductile and highly stiff behavior compared to other
benchmark hard coating materials such as TiN, TiAlN, Ti0.5Al0.5N and c-BN.
Ta2BC compound could also be a promising thermal barrier coating (TBC) material
due to the reasonable results of minimum thermal conductivity, Debye
temperature and damage tolerance behavior. Various optical functions such as
dielectric constants, refractive index, photo-conductivity, absorption, loss
function and reflectivity) are calculated and discussed in details. The amount
of reflectivity was always more than around 50% with no significant change in
the near infrared, visible light and near ultraviolet region (up to ~6 eV),
which results a promising coating material to diminish solar heating as well.",1805.03392v2
2018-11-22,KekuleScope: prediction of cancer cell line sensitivity and compound potency using convolutional neural networks trained on compound images,"The application of convolutional neural networks (ConvNets) to harness
high-content screening images or 2D compound representations is gaining
increasing attention in drug discovery. However, existing applications often
require large data sets for training, or sophisticated pretraining schemes.
Here, we show using 33 IC50 data sets from ChEMBL 23 that the in vitro activity
of compounds on cancer cell lines and protein targets can be accurately
predicted on a continuous scale from their Kekule structure representations
alone by extending existing architectures, which were pretrained on unrelated
image data sets. We show that the predictive power of the generated models is
comparable to that of Random Forest (RF) models and fully-connected Deep Neural
Networks trained on circular (Morgan) fingerprints. Notably, including
additional fully-connected layers further increases the predictive power of the
ConvNets by up to 10%. Analysis of the predictions generated by RF models and
ConvNets shows that by simply averaging the output of the RF models and
ConvNets we obtain significantly lower errors in prediction for multiple data
sets, although the effect size is small, than those obtained with either model
alone, indicating that the features extracted by the convolutional layers of
the ConvNets provide complementary predictive signal to Morgan fingerprints.
Lastly, we show that multi-task ConvNets trained on compound images permit to
model COX isoform selectivity on a continuous scale with errors in prediction
comparable to the uncertainty of the data. Overall, in this work we present a
set of ConvNet architectures for the prediction of compound activity from their
Kekule structure representations with state-of-the-art performance, that
require no generation of compound descriptors or use of sophisticated image
processing techniques.",1811.09036v2
2017-05-30,Combining electronic structure and many-body theory with large data-bases: a method for predicting the nature of 4f states in Ce compounds,"Here we present the first large scale investigation of electronic properties
and correlated magnetism in Ce-based compounds accompanied by a systematic
study of the electronic structure and 4f-hybridization function of a large body
of Ce compounds. We systematically study the electronic structure and
4f-hybridization function of a large body of Ce compounds with the goal of
elucidating the nature of the 4f states and their interrelation with the
measured Kondo energy in these compounds. The hybridization function has been
analyzed for more than 350 data sets of cubic Ce compounds using electronic
structure theory that relies on a full-potential approach. We demonstrate that
the strength of the hybridization function, evaluated in this way, allows us to
draw precise conclusions about the degree of localization of the 4f states in
these compounds. The theoretical results are entirely consistent with all
experimental information, relevant to the degree of 4f localization for all
investigated materials. Furthermore, a more detailed analysis of the electronic
structure and the hybridization function allows us to make precise statements
about Kondo correlations in these systems. The calculated hybridization
functions, together with the corresponding density of states, reproduce the
expected exponential behavior of the observed Kondo temperatures and prove a
consistent trend in real materials. This trend allows us to predict which
systems may be correctly identified as Kondo systems. A strong anti-correlation
between the size of the hybridization function and the volume of the systems
has been observed. Our approach demonstrates the predictive power of materials
informatics when a large number of materials is used to establish significant
trends which can be used to design new materials with desired properties.",1705.10674v2
2019-07-18,Characterization and decomposition of the natural van der Waals heterostructure SnSb2Te4 under compression,"This joint experimental and theoretical study of the structural, vibrational
and electrical properties of rhombohedral SnSb2Te4 at high pressure unveils the
internal mechanisms of its compression. The equation of state and the internal
polyhedral compressibility, the symmetry and behavior of the Raman-active modes
and the electrical behavior of this topological insulator under compression
have been discussed and compared with the parent binary alpha-Sb2Te3 and SnTe
compounds and with related ternary compounds. Our X-ray diffraction and Raman
measurements together with theoretical calculations, which include topological
electron density and electronic localization function analysis, evidence the
presence of an isostructural phase transition around 2 GPa and a Fermi
resonance around 3.5 GPa. The Raman spectrum of SnSb2Te4 shows vibrational
modes that are forbidden in rocksalt SnTe; thus showing a novel way to
experimentally observe the forbidden vibrational modes of some compounds.
Additionally, since SnSb2Te4 is an incipient metal, like its parent binary
compounds, we establish a new criterion to identify the recently proposed
metavalent bonding in complex materials when different bond characters coexist
in the system. Finally, SnSb2Te4 exhibits a pressure-induced decomposition into
the high-pressure phases of its parent binary compounds above 7 GPa, which is
supported by an analysis of their formation enthalpies. We have framed the
behavior of SnSb2Te4 within the extended orbital radii map of BA2Te4 compounds,
which paves the way to understand the pressure behavior and stability ranges of
other layered van der Waals-type compounds with similar stoichiometry.",1907.08317v1
2022-08-30,Compound Figure Separation of Biomedical Images: Mining Large Datasets for Self-supervised Learning,"With the rapid development of self-supervised learning (e.g., contrastive
learning), the importance of having large-scale images (even without
annotations) for training a more generalizable AI model has been widely
recognized in medical image analysis. However, collecting large-scale
task-specific unannotated data at scale can be challenging for individual labs.
Existing online resources, such as digital books, publications, and search
engines, provide a new resource for obtaining large-scale images. However,
published images in healthcare (e.g., radiology and pathology) consist of a
considerable amount of compound figures with subplots. In order to extract and
separate compound figures into usable individual images for downstream
learning, we propose a simple compound figure separation (SimCFS) framework
without using the traditionally required detection bounding box annotations,
with a new loss function and a hard case simulation. Our technical contribution
is four-fold: (1) we introduce a simulation-based training framework that
minimizes the need for resource extensive bounding box annotations; (2) we
propose a new side loss that is optimized for compound figure separation; (3)
we propose an intra-class image augmentation method to simulate hard cases; and
(4) to the best of our knowledge, this is the first study that evaluates the
efficacy of leveraging self-supervised learning with compound image separation.
From the results, the proposed SimCFS achieved state-of-the-art performance on
the ImageCLEF 2016 Compound Figure Separation Database. The pretrained
self-supervised learning model using large-scale mined figures improved the
accuracy of downstream image classification tasks with a contrastive learning
algorithm. The source code of SimCFS is made publicly available at
https://github.com/hrlblab/ImageSeperation.",2208.14357v1
2022-09-12,A deep Aurum reservoir: Stable compounds of two bulk-immiscible metals under pressure,"The Earth's crust is known to be depleted of gold, among other slightly heavy
noble metals transported by magma from the Earth's mantle to the crust. The
bulk silicate Earth (BSE) model also suggests significant depletion of Au in
the silicate mantle itself, which cannot be explained by the amount of Au in
the mantle's magma. This implies that Au could remain in the lower mantle and
form stable compounds, especially with iron, which is the predominant element
within the core. While Fe does not form binary compounds or a bulk alloy with
Au under ambient conditions, it may do so at the elevated pressures found in
the Earth's interior. Here, using density-functional methods, we investigated
the possibility of identifying stable, binary Fe-Au compounds at pressures up
to 210 GPa. We found three such Fe-Au compounds, which are stabilized by
pressure and notable electron transfer, including an orthorhombic AuFe$_4$
phase that is ferromagnetic in nature with Au possessing a significant magnetic
moment. While our results suggest that thermal convection due to the
conductivities and the heat flux from the Fe-Au compounds could be an energy
source to power the Earth's geodynamo, they also point towards changes in Au's
chemical properties, as it can exist as either an anion or cation under
pressure. In addition, the sound velocity and the density predicted for the
various Fe-Au compounds suggest that they could shed light on the composition
of the core-mantle boundary and the Earth's core, while demonstrating how the
presence of trace amounts of Au could influence agreement with seismic data.",2209.05652v1
2022-10-31,"A comparative study of the structural, elastic, thermophysical, and optoelectronic properties of CaZn$_2$X$_2$ (X = N, P, As) semiconductors via ab-initio approach","We present a detailed density functional theory based calculations of the
structural, elastic, lattice dynamical, thermophysical, and optoelectronic
properties of ternary semiconductors CaZn$_2$X$_2$ (X = N, P, As) in this
paper. The obtained lattice parameters are in excellent agreement with the
experimental values and other theoretical findings. These elastic constants
satisfy the mechanical stability criteria. Moreover, many thermophysical
parameters of these compounds are estimated, including the Debye temperature,
average sound velocity, melting temperature, heat capacity, lattice thermal
conductivity, etc. The comprehensive analysis of the elastic constants and
moduli show that CaZn$_2$X$_2$ compounds possess reasonably good machinability,
relatively high Vickers hardness and relatively low Debye temperature. The
phonon dispersion curves and phonon density of states are investigated for the
first time for the compounds CaZn$_2$P$_2$ and CaZn$_2$As$_2$. It is observed
from the phonon dispersion curves that the bulk CaZn$_2$X$_2$ (X = N, P, As)
compounds are dynamically stable. Electronic properties have been studied
through the band structures and electronic energy density of states. The
electronic band structures show that CaZn$_2$N$_2$ and CaZn$_2$As$_2$ possess
direct band gaps while the compound CaZn$_2$P$_2$ show indirect band gap. The
bonding characters of CaZn$_2$X$_2$ (X = N, P, As) compounds are investigated.
Energy dependent optical parameters exhibit good correspondence with the
electronic energy density of states features. We have thoroughly discussed the
reflectivity, absorption coefficient, refractive index, dielectric function,
optical conductivity and loss function of these semiconductors. The optical
absorption, reflectivity spectra and the refractive index of CaZn$_2$X$_2$ (X =
N, P, As) show that the compounds hold promise to be used in optoelectronic
devices.",2210.17275v1
2023-06-27,Crystal structure and magnetic properties of spin-$1/2$ frustrated two-leg ladder compounds (C$_4$H$_{14}$N$_2$)Cu$_2X_6$ ($X$= Cl and Br),"We have successfully synthesized single crystals, solved the crystal
structure, and studied the magnetic properties of a new family of copper
halides (C$_4$H$_{14}$N$_2$)Cu$_2X_6$ ($X$= Cl, Br). These compounds
crystallize in an orthorhombic crystal structure with space group $Pnma$. The
crystal structure features Cu$^{2+}$ dimers arranged parallel to each other
that makes a zig-zag two-leg ladder-like structure. Further, there exists a
diagonal interaction between two adjacent dimers which generates inter-dimer
frustration. Both the compounds manifest a singlet ground state with a large
gap in the excitation spectrum. Magnetic susceptibility is analyzed in terms of
both interacting spin-$1/2$ dimer and two-leg ladder models followed by exact
diagonalization calculations. Our theoretical calculations in conjunction with
the experimental magnetic susceptibility establish that the spin-lattice can be
described well by a frustrated two-leg ladder model with strong rung coupling
($J_0/k_{\rm B} \simeq 116$ K and 300 K), weak leg coupling
($J^{\prime\prime}/k_{\rm B} \simeq 18.6$ K and 105 K), and equally weak
diagonal coupling ($J^{\prime }/k_{\rm B} \simeq 23.2$ K and 90 K) for Cl and
Br compounds, respectively. These exchange couplings set the critical fields
very high, making them experimentally inaccessible. The correlation function
decays exponentially as expected for a gapped spin system. The structural
aspects of both the compounds are correlated with their magnetic properties.
The calculation of entanglement witness divulges strong entanglement in both
the compounds which persists upto high temperatures, even beyond 370~K for the
Br compound.",2306.15205v1
2004-06-05,Role of shuffles and atomic disorder in Ni-Mn-Ga,"We report results of \textit{ab-initio} calculations of the ferromagnetic
Heusler alloy Ni-Mn-Ga. Particular emphasis is placed on the stability of the
low temperature tetragonal structure with $c/a = 0.94$. This structure cannot
be derived from the parent L2$_1$ structure by a simple homogeneous strain
associated with the soft elastic constant $C'$. In order to stabilise the
tetragonal phase, one has to take into account shuffles of atoms, which form a
wave-like pattern of atomic displacements with a well defined period
(modulation). While the modulation is related to the soft acoustic [110]-TA$_2$
phonon mode observed in Ni$_2$MnGa, we obtain additional atomic shuffles, which
are related to acoustic-optical coupling of the phonons in Ni$_2$MnGa. In
addition, we have simulated an off-stoichiometric systems, in which 25 % of Mn
atoms are replaced by Ni. The energy of this structure also exhibits a local
minimum at $c/a = 0.94$. This allows us to conclude that both shuffles and
atomic disorder stabilize the $c/a = 0.94$ structure. In both cases the
stability seems to be associated with a dip in the minority-spin density of
states (DOS) at the Fermi level, being related to the formation of hybrid
states of Ni-\textit{d} and Ga-\textit{p} minority-spin orbitals.",0406139v1
2006-11-23,Half-Metallic Graphene Nanoribbons,"Electrical current can be completely spin polarized in a class of materials
known as half-metals, as a result of the coexistence of metallic nature for
electrons with one spin orientation and insulating for electrons with the
other. Such asymmetric electronic states for the different spins have been
predicted for some ferromagnetic metals - for example, the Heusler compounds-
and were first observed in a manganese perovskite. In view of the potential for
use of this property in realizing spin-based electronics, substantial efforts
have been made to search for half-metallic materials. However, organic
materials have hardly been investigated in this context even though
carbon-based nanostructures hold significant promise for future electronic
device. Here we predict half-metallicity in nanometre-scale graphene ribbons by
using first-principles calculations. We show that this phenomenon is realizable
if in-plane homogeneous electric fields are applied across the zigzag-shaped
edges of the graphene nanoribbons, and that their magnetic property can be
controlled by the external electric fields. The results are not only of
scientific interests in the interplay between electric fields and electronic
spin degree of freedom in solids but may also open a new path to explore
spintronics at nanometre scale, based on graphene.",0611600v1
2010-11-01,Modeling materials with optimized transport properties,"Following demands for materials with peculiar transport properties, e.g. in
magnetoelectronics or thermoelectrics, there is a need for materials modeling
at the quantum-mechanical level. We combine density-functional with various
scale-bridging tools to establish correlations between the macroscopic
properties and the atomic structure of materials. For examples, magnetic memory
devices exploiting the tunneling magneto-resistance (TMR) effect depend
crucially on the spin polarization of the electrodes. Heusler alloys, e.g.
Co2MnSi, if perfectly ordered, are ferromagnetic half-metals with (ideally)
100% spin polarization. Their performance as electrodes in TMR devices is
limited by atomic disorder and deviations from perfect stoichiometry, but also
by interface states at the tunneling barrier. We use ab initio thermodynamics
in conjunction with the cluster expansion technique to show that excess
manganese in the alloy and at the interface helps to preserve the desired
half-metallic property. As another example, nanostructured materials with a
reduced thermal conductivity but good electrical conductivity are sought for
applications in thermoelectrics. Semiconductor heterostructures with a regular
arrangement of nanoscale inclusions ('quantum dot superlattices') hold the
promise of a high thermoelectric figure of merit. Our theoretical analysis
reveals that an increased figure of merit is to be expected if the quantum dot
size, the superlattice period and the doping level are all suitably fine-tuned.
Such a superlattice thus constitutes a material whose transport properties are
controlled by geometrical features at the nanoscale.",1011.0324v1
2011-02-10,An effective quantum parameter for strongly correlated metallic ferromagnets,"The correlated motion of electrons in multi-orbital metallic ferromagnets is
investigated in terms of a realistic Hubbard model with {\cal N}-fold orbital
degeneracy and arbitrary intra- and inter-orbital Coulomb interactions U and J
using a Goldstone-mode-preserving non-perturbative scheme. An effective quantum
parameter '\hbar'=\frac{U^2+({\cal N}-1)J^2}{(U+({\cal N}-1)J)^2} is obtained
which determines, in analogy with 1/S for quantum spin systems and 1/N for the
N-orbital Hubbard model, the strength of correlation-induced quantum
corrections to magnetic excitations. The rapid suppression of this quantum
parameter with Hund's coupling J, especially for large {\cal N}, provides
fundamental insight into the phenomenon of strong stabilization of metallic
ferromagnetism by orbital degeneracy and Hund's coupling. This approach is
illustrated for the case of ferromagnetic iron and the half metallic Heusler
alloy Co_2 Mn Si. For realistic values for iron, the calculated spin stiffness
and Curie temperature values obtained are in quantitative agreement with
measurements. Significantly, the contribution of long wavelength modes is shown
to yield a nearly ~25% reduction in the calculated Curie temperature. Finally,
an outline is presented for extending the approach to generic multi-band
metallic ferromagnets including realistic band-structure features of
non-degenerate orbitals and inter-orbital hopping as obtained from LDA
calculations.",1102.2115v1
2011-11-28,Reduction of spin polarization by incoherent tunneling in Co2FeAl/MgO/CoFe magnetic tunnel junctions with thick MgO barriers,"We report on spin polarization reduction by incoherent tunneling in realistic
single crystal Co2FeAl/MgO/Co50Fe50 magnetic tunnel junctions (MTJ) compared to
reference Fe/MgO/Fe. A large density of misfit dislocations in the Heusler
based MTJs has been insured by a thick MgO barrier and its 3.8% lattice
mismatch with the Co2FeAl electrode. Our analysis implicates a correlated
structural-transport approach. The crystallographic coherence, in the real
space, is investigated using High Resolution Transmission Electron Microscopy
phase analysis. The electronic transport experiments in variable temperature,
fitted with a theoretical extended-Glazman-Matveev model, address different
levels of the tunneling mechanisms from direct to multi-center hopping. We
demonstrate a double negative impact of dislocations, as extended defects, on
the tunneling polarization. Firstly, the breaking of the crystal symmetry
destroys the longitudinal and lateral coherence of the propagating Bloch
functions. This affects the symmetry filtering efficiency of the Delta_1 states
across the (100) MgO barriers and reduces the associated effective tunneling
polarization. Secondly, dislocations provide localized states within the MgO
gap. This determines temperature activated spin-conserving inelastic tunneling
through chains of defects which are responsible for the one order of magnitude
drop of the tunnel magnetoresistance from low to room temperature.",1111.6442v3
2012-10-19,"Ferromagnetic structures in Mn2CoGa and Mn2CoAl doped by Co, Cu, V, and Ti","The structure and magnetic properties in doped Heusler alloys of Mn2CoGa and
Mn2CoAl have been investigated by experiments and calculations. The main group
elements of Ga and Al are substituted by the magnetic or non-magnetic
transition metals, Co, Cu, V, and Ti in the alloy systems. Three kinds of local
ferromagnetic structures, Co-Mn-Co, Mn-Co-Mn and Mn-Co-V, have been found. They
embed in the native ferrimagnetic matrix and increase the magnetization with
different increments. The Co-Mn-Co ferromagnetic structure shows the largest
increment of 6.18{\mu}B /atom. In addition, interesting results for
non-magnetic Cu increasing the magnetization and the V atom having a large
ferromagnetic moment of about 1.0{\mu}B have been obtained. The exchange
interaction energy can be increased by the newly added Co and depleted by
supporting a ferromagnetic coupling in other substitution cases, and showing
the variation of the TC. Our calculation of electronic structure verifies the
strong d-d hybridization when the three ferromagnetic structures are achieved.
It has also been found that the covalent effect from the Ga and Al determines
the generation of the local ferromagnetic structure and the tolerance for
dopant content.",1210.5357v1
2013-10-23,Magnetoelastic coupling induced magnetic anisotropy in Co$_2$(Fe/Mn)Si thin films,"The influence of epitaxial strain on uniaxial magnetic anisotropy of
Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on
(001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is
susceptible to tune by varying the thickness of the films on STO, while on MgO
the films show in-plane easy axis for magnetization (\overrightarrow{M})
irrespective of their thickness. A variational analysis of magnetic free energy
functional within the Stoner-Wohlfarth coherent rotation model with
out-of-plane uniaxial anisotropy for the films on STO showed the presence of
magnetoelastic anisotropy with magnetostriction constant $\approx$
(12.22$\pm$0.07)$\times 10^{-6}$ and (2.02$\pm$0.06)$\times 10^{-6}$, in
addition to intrinsic magnetocrystalline anisotropy $\approx$ -1.72$\times
10^{6}$ erg/cm$^{3}$ and -3.94$\times 10^{6}$ erg/cm$^{3}$ for CFS and CMS,
respectively. The single-domain phase diagram reveals a gradual transition from
in-plane to out-of-plane orientation of magnetization with the decreasing film
thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane
is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The
distinct behaviour of \overrightarrow{M} in the films with lower thickness on
STO is attributed to strain-induced tetragonal distortion.",1310.6204v1
2014-01-17,Co2FeAl Heusler thin films grown on Si and MgO substrates: annealing temperature effect,"10 nm and 50 nm Co$_{2}$FeAl (CFA) thin films have been deposited on MgO(001)
and Si(001) substrates by magnetron sputtering and annealed at different
temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth
(according to the relation CFA(001)[110]//MgO(001)[100] epitaxial relation),
respectively for CFA films grown on a Si and on a MgO substrate. For these
later, the chemical order varies from the A2 phase to the B2 phase when
increasing the annealing temperature (Ta) while only the A2 disorder type has
been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR)
measurements revealed that the in-plane anisotropy results from the
superposition of a uniaxial and of a fourfold symmetry term for CFA grown on
MgO substrates. This fourfold anisotropy, which disappears completely for
samples grown on Si, is in accord with the crystal structure of the samples.
The fourfold anisotropy field decreases when increasing Ta while the uniaxial
anisotropy field is nearly unaffected by Ta within the investigated range. The
MS-FMR data also allow for concluding that the gyromagnetic factor remains
constant and that the exchange stiffness constant increases with $T_{a}$.
Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement
of the chemical order. We derive a very low intrinsic damping parameter
(1.3*10^-3 and 1.1*10^-3 for films of 50 nm thickness annealed at 615 {\deg}C
grown on MgO and on Si, respectively).",1401.4397v1
2014-12-02,"Structural, electrical and magnetic properties of nanostructured Mn2Ni1.6Sn0.4 melt spun ribbons","Nanocrystalline ribbons of inverse Heusler alloy Mn2Ni1.6Sn0.4 have been
synthesised by melt spinning of the arc melted bulk precursor. The single phase
ribbons crystallize into a cubic structure and exhibit very fine crystallite
size of < 2 nm. Temperature dependent magnetization (M-T) measurements reveal
that austenite (A)-martensite (M) phase transition begins at T~248 K and
finishes at T~238 K during cooling cycle and these values increase to T~267 K
and T~259 K while warming. In cooling cycle, the A-phase shows ferromagnetic
(FM) ordering with a Curie temperature T~267 K, while both the
FM-antiferromagnetic (AFM) and M-transitions occur at T~242 K. The M-phase
undergoes FM transition at T~145 K. These transitions are also confirmed by
temperature dependent resistivity measurements. The observed hysteretic
behaviour of magnetization and resistivity in the temperature regime spanned by
the A-M transition is a manifestation of the first order phase transition.
Magnetization and susceptibility data also provide unambiguous evidence in
favour of spin glass . The scaling of the glass freezing temperature (Tf) with
frequency, extracted from the frequency dependent AC susceptibility
measurements, confirms the existence of canonical spin glass at T<145 K. The
occurrence of canonical spin glass has been explained in terms of the
nanostructuring modified interactions between the FM correlations in the
martensitic phase and the coexisting AFM.",1412.0859v1
2015-01-16,Direct measurement of the magnetic anisotropy field in Mn--Ga and Mn--Co--Ga Heusler films,"The static and dynamic magnetic properties of tetragonally distorted Mn--Ga
based alloys were investigated. Static properties are determined in magnetic
fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film,
the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial
substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The
saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is
increased to 1~T.
  Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the
high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency
extrapolated to zero-field is found to be 125~GHz with a Gilbert damping,
$\alpha$, of 0.019. The anisotropy field is determined from both SQUID and
TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of
0.81~MJ/m$^3$.
  Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film,
pulsed magnetic fields up to 60~T are used to determine the field strength
required to saturate the film in the plane. For this, the extraordinary Hall
effect was employed as a probe of the local magnetisation. By integrating the
reconstructed in--plane magnetisation curve, the effective anisotropy energy
density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.",1501.03973v1
2015-10-01,Creating Nanostructured Superconductors On Demand by Local Current Annealing,"Superconductivity results from a Bose condensate of Cooper-paired electrons
with a macroscopic quantum wavefunction. Dramatic effects can occur when the
region of the condensate is shaped and confined to the nanometer scale. Recent
progress in nanostructured superconductors has revealed a route to topological
superconductivity, with possible applications in quantum computing. However,
challenges remain in controlling the shape and size of specific superconducting
materials. Here, we report a new method to create nanostructured
superconductors by partial crystallization of the half-Heusler material, YPtBi.
Superconducting islands, with diameters in the range of 100 nm, were
reproducibly created by local current annealing of disordered YPtBi in the
tunneling junction of a scanning tunneling microscope (STM). We characterize
the superconducting island properties by scanning tunneling spectroscopic
measurements to determine the gap energy, critical temperature and field,
coherence length, and vortex formations. These results show unique properties
of a confined superconductor and demonstrate that this new method holds promise
to create tailored superconductors for a wide variety of nanometer scale
applications.",1510.00362v1
2015-11-25,Accelerated screening of thermoelectric materials by first-principles computations of electron-phonon scattering,"Recent discovery of new materials for thermoelectric energy conversion is
enabled by efficient prediction of materials' performance from
first-principles, without empirically fitted parameters. The novel simplified
approach for computing electronic transport properties is described, which
achieves good accuracy and transferability while greatly reducing complexity
and computation cost compared to the existing methods. The first-principles
calculations of the electron-phonon coupling demonstrate that the energy
dependence of the electron relaxation time varies significantly with chemical
composition and carrier concentration, suggesting that it is necessary to go
beyond the commonly used approximations to screen and optimize materials'
composition, carrier concentration, and microstructure. The new method is
verified using high accuracy computations and validated with experimental data
before applying it to screen and discover promising compositions in the space
of half-Heusler alloys. By analyzing data trends the effective electron mass is
identified as the single best general descriptor determining material's
performance. The Lorenz number is computed from first principles and the
universality of the Wiedemann-Franz law in thermoelectrics is discussed.",1511.08115v7
2016-01-22,Phase Separation and Superparamagnetism in the Martensitic Phase of $Ni_{50-x}Co_{x}Mn_{40}Sn_{10}$,"$Ni_{50-x}Co_{x}Mn_{40}Sn_{10}$ shape memory alloys in the approximate range
$5 \le x \le 10$ display desirable properties for applications as well as
intriguing magnetism. These off-stoichiometric Heusler alloys undergo a
martensitic phase transformation at a temperature $T_{M}$ of 300 - 400 K, from
ferromagnetic (F) to nonferromagnetic, with unusually low thermal hysteresis
and a large change in magnetization. The low temperature magnetic structures in
the martensitic phase of such alloys, which are distinctly inhomogeneous, are
of great interest but are not well understood. Our present use of spin echo
NMR, in the large hyperfine fields at $^{55}Mn$ sites, provides compelling
evidence that nanoscale magnetic phase separation into F and antiferromagnetic
(AF) regions occurs below $T_{M}$ in alloys with x in the range 0 to 7. At
finite Co substitution the F regions are found to be of two distinct types,
corresponding to high and low local concentrations of Co on Ni sites. Estimates
of the size distributions of both the F and AF nanoregions have been made. At x
= 7 the AF component is not long-range ordered, even below 4 K, and is quite
different to the AF component found at x = 0; by x = 14 the F phase is
completely dominant. Of particular interest, we find, for x = 7, that field
cooling leads to dramatic changes in the AF regions. These findings provide
insight into the origins of magnetic phase separation and superparamagnetism in
these complex alloys, particularly their intrinsic exchange bias, which is of
considerable current interest.",1601.05993v1
2016-08-05,Ternary Semiconductors NiZrSn and CoZrBi with half-Heusler structure: a first-principles study,"The ternary semiconductors NiZrSn and CoZrBi with C1_b crystal structure are
introduced by calculating their basic structural, electronic and phononic
properties using density functional theory. Both the gradient-corrected PBE
functional and the hybrid functional HSE06 are employed. While NiZrSn is found
to be a small-band-gap semiconductor (E_g = 0.46 eV in PBE and 0.60 eV in
HSE06), CoZrBi has a band gap of 1.01 eV in PBE (1.34 eV in HSE06). Moreover,
effective masses and deformation potentials are reported. In both materials
ABC, the intrinsic point defects introduced by species A (Ni or Co) are
calculated. The Co-induced defects in CoZrBi are found to have a higher
formation energy compared to Ni-induced defects in NiZrSn. The interstitial Ni
atom (Ni_i ) as well as the V_Ni Ni_i complex introduce defect states in the
band gap, whereas the Ni vacancy (V_Ni) only reduces the size of the band gap.
Motivated by the reported use of NiZrSn for thermoelectric applications, the
Seebeck coefficient of both materials is calculated. We find that CoZrBi
displays a rather large thermopower of up to 500 micro-V/K when p-doped,
whereas NiZrSn possesses its maximum thermopower in the n-type regime. The
reported difficulties in achieving p-type doping in NiZrSn could be
rationalized by the unintended formation of Ni_i^2+ in conjunction with
extrinsic acceptors, resulting in their compensation. Moreover, it is found
that all types of defects considered, when present in concentrations as large
as 3%, tend to reduce the thermopower compared to ideal bulk crystals at
T=600K. For NiZrSn, the calculated thermodynamic data suggest that additional
Ni impurities could be removed by annealing, leading to precipitation of a
metallic Ni_2ZrSn phase.",1608.01957v1
2017-08-03,Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co$_2$FeAl/MgO interface upon annealing,"We investigate thickness series of films of the Heusler alloy Co$_2$FeAl in
order to study the effect of annealing on the interface with a MgO layer and on
the bulk magnetic properties. Our results reveal that while the perpendicular
interface anisotropy constant $K^{\perp}_{\rm S}$ is zero for the as-deposited
samples, its value increases with annealing up to a value of $1.14\, \pm
\,0.07$~mJ/m$^2$ for the series annealed at 320$^{\rm o}$C and of $2.07\, \pm
\,0.7$~mJ/m$^2$ for the 450$^{\rm o}$C annealed series owing to a strong
modification of the interface during the thermal treatment. This large value
ensures a stabilization of a perpendicular magnetization orientation for a
thickness below 1.7~nm. The data additionally shows that the in-plane biaxial
anisotropy constant has a different evolution with thickness in as-deposited
and annealed systems. The Gilbert damping parameter $\alpha$ shows minima for
all series for a thickness of 40~nm and an absolute minimum value of
$2.8\pm0.1\cdot10^{-3}$. The thickness dependence is explained in terms of an
inhomogenous magnetization state generated by the interplay between the
different anisotropies of the system and by crystalline disorder.",1708.01126v2
2017-09-13,Pairing states of spin-3/2 fermions: Symmetry-enforced topological gap functions,"We study the topological properties of superconductors with paired
$j=\frac{3}{2}$ quasiparticles. Higher spin Fermi surfaces can arise, for
instance, in strongly spin-orbit coupled band-inverted semimetals. Examples
include the Bi-based half-Heusler materials, which have recently been
established as low-temperature and low-carrier density superconductors.
Motivated by this experimental observation, we obtain a comprehensive
symmetry-based classification of topological pairing states in systems with
higher angular momentum Cooper pairing. Our study consists of two main parts.
First, we develop the phenomenological theory of multicomponent (i.e., higher
angular momentum) pairing by classifying the stationary points of the free
energy within a Ginzburg-Landau framework. Based on the symmetry classification
of stationary pairing states, we then derive the symmetry-imposed constraints
on their gap structures. We find that, depending on the symmetry quantum
numbers of the Cooper pairs, different types of topological pairing states can
occur: fully gapped topological superconductors in class DIII, Dirac
superconductors and superconductors hosting Majorana fermions. Notably, we find
a series of nematic fully gapped topological superconductors, as well as
double-Dirac superconductors with quadratic dispersion. Our approach, applied
here to the case of $j=\frac{3}{2}$ Cooper pairing, is rooted in the symmetry
properties of pairing states, and can therefore also be applied to other
systems with higher angular momentum and high-spin pairing. We conclude by
relating our results to experimentally accessible signatures in thermodynamic
and dynamic probes.",1709.04487v2
2018-11-30,Spin Gapless Semiconducting Nature in Co-rich Co1+xFe1-xCrGa: Insight and Advancements,"In this report, we present structural, electronic, magnetic and transport
properties of Co-rich spin gapless semiconductor CoFeCrGa using both
theoretical and experimental techniques. The key advantage of Co-rich samples
$\mathrm{Co_{1+x}Fe_{1-x}CrGa}$ is the high Curie temperature (T$\mathrm{_C}$)
and magnetization, without compromising the SGS nature (up to x = 0.4), and
hence our choice. The quaternary Heusler alloys $\mathrm{Co_{1+x}Fe_{1-x}CrGa}$
(x = 0.1 to 0.5) are found to crystallize in LiMgPdSn-type structure having
space group $F\bar{4}3m$ (\# 216). The measured Curie temperature increases
from 690 K (x = 0) to 870 K (x = 0.5). Observed magnetization values follow the
Slater-Pauling rule. Measured electrical resistivity, in the temperature range
of 5-350 K, suggests that the alloys retain the SGS behavior up to x = 0.4,
beyond which it reflects metallic character. Unlike conventional
semiconductors, the conductivity value ($\mathrm{\sigma_{xx}}$) at 300 K lies
in the range of 2289 S $\mathrm{cm^{-1}}$ to 3294 S $\mathrm{cm^{-1}}$, which
is close to that of other reported SGS materials. The anomalous Hall effect is
comparatively low. The intrinsic contribution to the anomalous Hall
conductivity increase with x, which can be correlated with the enhancement in
chemical order. The anomalous Hall coefficient is found to increase from 38
S/cm for x = 0.1 to 43 S/cm for 0.3. Seebeck coefficients turn out to be
vanishingly small below 300 K, another signature for being SGS. All the alloys
(for different x) are found to be both chemically and thermally stable.
Simulated magnetization agrees fairly with the experiment. As such Co-rich
CoFeCrGa is a promising candidate for room temperature spintronic applications,
with enhanced T$\mathrm{_C}$, magnetic properties and SGS nature.",1811.12684v1
2019-11-13,"Thermoelectric properties, efficiency and thermal expansion of ZrNiSn half-Heusler by first-principles calculations","In this work, we try to understand the experimental thermoelectric (TE)
properties of a ZrNiSn sample with DFT and semiclassical transport calculations
using SCAN functional. SCAN and mBJ provide the same band gap $E_{g}$ of
$\sim$0.54 eV. This $E_{g}$ is found to be inadequate to explain the
experimental data. The better explanation of experimental Seebeck coefficient
$S$ is done by considering $E_{g}$ of 0.18 eV which suggests the
non-stoichiometry and/or disorder in the sample. Further improvement in the $S$
is done by the inclusion of temperature dependence on chemical potential. In
order to look for the possible enhanced TE properties obtainable in ZrNiSn with
$E_{g}$ of $\sim$0.54 eV, power factor and optimal carrier concentrations are
calculated. The optimal electron and hole concentrations required to attain
highest power factors are $\sim$7.6x10$^{19}$ cm$^{-3}$ and $\sim$1.5x10$^{21}$
cm$^{-3}$, respectively. The maximum figure of merit $ZT$ calculated at 1200 K
for n-type and p-type ZrNiSn are $\sim$0.6 and $\sim$0.7, respectively. The %
efficiency obtained for n-type ZrNiSn is $\sim$5.1 % while for p-type ZrNiSn is
$\sim$6.1 %. The $ZT$ are expected to be further enhanced to $\sim$1.2 (n-type)
and $\sim$1.4 (p-type) at 1200 K by doping with heavy elements for thermal
conductivity reduction. The phonon properties are also studied by calculating
dispersion, total and partial density of states. The calculated Debye
temperature of 382 K is in good agreement with experimental value of 398 K. The
thermal expansion behaviour in ZrNiSn is studied under quasi-harmonic
approximation. The average linear thermal expansion coefficient
$\alpha_{ave}(T)$ of $\sim$7.8x10$^{-6}$ K$^{-1}$ calculated in our work is
quite close to the experimental values.",1911.05680v1
2020-01-28,Anomalous transverse response of Co$_2$MnGa and universality of the room-temperature $α^A_{ij}/σ^A_{ij}$ ratio across topological magnets,"The off-diagonal (electric, thermal and thermoelectric) transport
coefficients of a solid can acquire an anomalous component due to the
non-trivial topology of the Bloch waves. We present a study of the anomalous
Hall (AHE), Nernst (ANE) and thermal Hall effects (ATHE) in the Heusler Weyl
ferromagnet Co$_2$MnGa. The Anomalous Wiedemann-Franz law, linking electric and
thermal responses, was found to be valid over the whole temperature window.
This indicates that the AHE has an intrinsic origin and the Berry spectrum is
smooth in the immediate vicinity of the Fermi level. From the ANE data, we
extract the magnitude and temperature dependence of $\alpha^A_{ij}$ and put
under scrutiny the $\alpha^A_{ij}/\sigma^A_{ij}$ ratio, which approaches
k$_B$/e at room temperature. We show that in various topological magnets the
room-temperature magnitude of this ratio is a sizeable fraction of k$_B$/e and
argue that the two anomalous transverse coefficients depend on universal
constants, the Berry curvature averaged over a window set by either the Fermi
wavelength (for Hall) or the de Broglie thermal length (for Nernst). Since the
ratio of the latter two is close to unity at room temperature, such a universal
scaling finds a natural explanation in the intrinsic picture of anomalous
transverse coefficients.",2001.10264v1
2018-07-12,Giant anomalous Nernst effect and quantum-critical scaling in a ferromagnetic semimetal,"In metallic ferromagnets, the Berry curvature of underlying quasiparticles
can cause an electric voltage perpendicular to both magnetization and an
applied temperature gradient, a phenomenon called the anomalous Nernst effect
(ANE). Here, we report the observation of a giant ANE in the full-Heusler
ferromagnet Co$_2$MnGa, reaching $S_{yx}\sim -6$ $\mu$V/K at room $T$, one
order of magnitude larger than the maximum value reported for a magnetic
conductor. With increasing temperature, the transverse thermoelectric
conductivity or Peltier coefficient $\alpha_{yx}$ shows a crossover between
$T$-linear and $-T \log(T)$ behaviors, indicating the violation of Mott formula
at high temperatures. Our numerical and analytical calculations indicate that
the proximity to a quantum Lifshitz transition between type-I and type-II
magnetic Weyl fermions is responsible for the observed crossover properties and
an enhanced $\alpha_{yx}$. The $T$ dependence of $\alpha_{yx}$ in experiments
and numerical calculations can be understood in terms of a quantum critical
scaling function predicted by the low energy effective theory over more than a
decade of temperatures. Moreover, the observation of chiral anomaly or an
unsaturated positive longitudinal magnetoconductance also provide evidence for
the existence of Weyl fermions in Co$_2$MnGa.",1807.04761v1
2018-10-04,Anisotropic electrical and thermal magnetotransport in the magnetic semimetal GdPtBi,"The half-Heusler rare-earth intermetallic GdPtBi has recently gained
attention due to peculiar magnetotransport phenomena that have been associated
with the possible existence of Weyl fermions, thought to arise from the
crossings of spin-split conduction and valence bands. On the other hand,
similar magnetotransport phenomena observed in other rare-earth intermetallics
have often been attributed to the interaction of itinerant carriers with
localized magnetic moments stemming from the $4f$-shell of the rare-earth
element. In order to address the origin of the magnetotransport phenomena in
GdPtBi, we performed a comprehensive study of the magnetization, electrical and
thermal magnetoresistivity on two single-crystalline GdPtBi samples. In
addition, we performed an analysis of the Fermi surface via Shubnikov-de Haas
oscillations in one of the samples and compared the results to \emph{ab initio}
band structure calculations. Our findings indicate that the electrical and
thermal magnetotransport in GdPtBi cannot be solely explained by Weyl physics
and is strongly influenced by the interaction of both itinerant charge carriers
and phonons with localized magnetic Gd-ions and possibly also paramagnetic
impurities.",1810.02300v3
2018-10-23,Uncovering the puzzle of complex magnetism in Fe16N2: a first-principles based study,"The electronic structure and magnetic exchange interactions in pure and
V-doped Fe16N2 are studied within the framework of density functional theory.
The Curie temperatures were obtained with both mean field approximation (MFA)
as well as Monte Carlo (MC) calculations. The Curie temperature (TC) for pure
Fe16N2 obtained within MFA are significantly larger than the experimental
value, suggesting the importance of thermal fluctuations in these systems, and
has a resemblance of a lower dimensional spin system. We also briefly discuss
about the various possible factors which may lead to a large magnetic moment in
this material. The calculated magnetic susceptibility at zero field shows sharp
peak at T=TC which resemble a local moment system. From the nature of exchange
interactions we try to figure out the nature of the Fesites which might contain
localized d-states. Finally, we point out that Fe16N2 can also act as a good
spin injector for the III-V semiconductors in addition to its well promised
application as permanent magnet since it has a very high spin polarization
(larger compared to elemental ferromagnets) as well as quite smaller lattice
mismatch (compared to half-metallic Heusler alloys) with the conventional III-V
semiconductors such as GaAs or InGaAs. We further demonstrate this through our
calculations for Fe16N2(001)/InGaAs(001) heterostructures which shows the
non-negligible spin polarization in the semiconductor (InGaAs) region implying
a long spin diffusion length.",1810.09818v1
2019-07-24,Nonlinear anomalous Hall effect for Néel vector detection,"Antiferromagnetic (AFM) spintronics exploits the N\'eel vector as a state
variable for novel spintronic devices. Recent studies have shown that the
field-like and antidamping spin-orbit torques (SOT) can be used to switch the
N\'eel vector in antiferromagnets with proper symmetries. However, the precise
detection of the N\'eel vector remains a challenging problem. In this letter,
we predict that the nonlinear anomalous Hall effect (AHE) can be used to detect
the N\'eel vector in most compensated antiferromagnets supporting the
antidamping SOT. We show that the magnetic crystal group symmetry of these
antiferromagnets combined with spin-orbit coupling produce a sizable Berry
curvature dipole and hence the nonlinear AHE. As a specific example, we
consider half-Heusler alloy CuMnSb, which N\'eel vector can be switched by the
antidamping SOT. Based on density functional theory calculations, we show that
the nonlinear AHE in CuMnSb results in a measurable Hall voltage under
conventional experimental conditions. The strong dependence of the Berry
curvature dipole on the N\'eel vector orientation provides a new detection
scheme of the N\'eel vector based on the nonlinear AHE. Our predictions enrich
the material platform for studying non-trivial phenomena associated with the
Berry curvature and broaden the range of materials useful for AFM spintronics.",1907.10696v3
2012-09-22,Structural and electronic properties of superconducting Heusler alloy Ni$_{2}$Nb$_{1+x}$Sn$_{1-x}$: \textit{Ab initio} approach,"Using \textit{ab initio} calculation, we investigate systematically the
structural and electronic properties of Ni$_{2}$Nb$_{1+x}$Sn$_{1-x}$ ($x$ = 0,
0.25, 0.50). Here, projector augmented wave approach (PAW) implemented in the
Vienna \textit{ab initio} simulation package (VASP) within generalized gradient
approximation (GGA) for the exchange-correlation functional has been used. In
this article, it is reported that though Ni$_{2}$NbSn and
Ni$_{2}$Nb$_{1.25}$Sn$_{0.75}$ have no structural transformation,
Ni$_{2}$Nb$_{1.5}$Sn$_{0.5}$ can transform to tetragonal structure from cubic
L2$_{1}$ phase. The cubic lattice parameter decreases with Nb doping at Sn
sites in off-stoichiometric alloys. The alloys are in paramagnetic phase in all
the structures. The hybridization between Ni and Nb 3d states triggers the
tetragonal distortion. Due to Nb doping in cubic L2$_{1}$ phase, there is a
significant change in total density of states (DOSs) at Fermi energy (E$_{F}$)
(N(E$_{F}$)). N(E$_{F}$) increases with increasing Nb doping. But, N(E$_{F}$)
decreases during structural transformation of Ni$_{2}$Nb$_{1.5}$Sn$_{0.5}$. The
superconducting critical temperature (T$_{C}$) also changes with Nb doping in
cubic phase and tetragonal distortion because T$_{C}$ very much depends on
N(E$_{F}$).",1209.4964v3
2018-08-16,Tunnel magneto-Seebeck effect,"The interplay of charge, spin and heat transport is investigated in the
fascinating research field of spin caloritronics, the marriage of spintronics
and thermoelectrics. Here, many new spin-dependent thermal transport phenomena
in magnetic nanostructures have been explored in the recent years. One of them
is the tunnel magneto-Seebeck (TMS) effect in magnetic tunnel junctions (MTJs)
that has large potential for future nanoelectronic devices, such as
nanostructured sensors for three-dimentional thermal gradients, or scanning
tunneling microscopes driven by temperature differences. The TMS describes the
dependence of the MTJ's thermopower on its magnetic cofiguration when a thermal
gradient is applied. In this review, we highlight the successful way from first
observation of the TMS in 2011 to current ongoing developments in this research
area. We emphasize on different heating techniques, material designs,
applications, and additional physical aspects such as the role of the thermal
conductivity of the barrier material. We further demonstrate the efficient
interplay between ab initio calculations and experiments within this field, as
this has led, e.g., to the detection of large TMS ratios in MTJs with
half-metallic Heusler electrodes.",1808.05638v2
2019-02-20,On the inexistence of solitons in Einstein-Maxwell-scalar models,"Three non-existence results are established for self-gravitating solitons in
Einstein-Maxwell-scalar models, wherein the scalar field is, generically,
non-minimally coupled to the Maxwell field via a scalar function $f(\Phi)$.
Firstly, a trivial Maxwell field is considered, which yields a consistent
truncation of the full model. In this case, using a scaling (Derrick-type)
argument, it is established that no stationary and axisymmetric
self-gravitating scalar solitons exist, unless the scalar potential energy is
somewhere negative in spacetime. This generalises previous results for the
static and strictly stationary cases. Thus, rotation alone cannot support
self-gravitating scalar solitons in this class of models. Secondly, constant
sign couplings are considered. Generalising a previous argument by Heusler for
electro-vacuum, it is established that no static self-gravitating
electromagnetic-scalar solitons exist. Thus, a varying (but constant sign)
electric permittivity alone cannot support static Einstein-Maxwell-scalar
solitons. Finally, the second result is generalised for strictly stationary,
but not necessarily static, spacetimes, using a Lichnerowicz-type argument,
generalising previous results in models where the scalar and Maxwell fields are
not directly coupled. The scope of validity of each of these results points out
the possible paths to circumvent them, in order to obtain self-gravitating
solitons in Einstein-Maxwell-scalar models.",1902.07721v3
2019-06-14,Stability of Long-lived Antiskyrmions in Mn-Pt-Sn Material,"The lifetime of antiskyrmions at room temperature in a Mn-Pt-Sn tetragonal
Heusler material has been calculated using an atomic scale representation
including nearly a million spins. The evaluation of the pre-exponential factor
in the Arrhenius rate expression for this large system is made possible by an
implementation of harmonic transition state theory that avoids evaluation of
the eigenvalues of the Hessian matrix.The parameter values in the extended
Heisenberg Hamiltonian, including anisotropic Dzyaloshinskii-Moriya
interaction, are chosen to reproduce experimental observations [A. K. Nayak
$\it{et\,al.}$, Nature $\textbf{548}$, 561 (2017)], in particular the 150 nm
diameter. The calculated results are consistent with the long lifetime observed
in the laboratory and this exceptional stability of the antiskyrmions is found
to result from large activation energy for collapse due to strong exchange
coupling while the pre-exponential factor in the Arrhenius expression for the
lifetime is found to have a typical magnitude of 10$^{-12}$ s, despite the
large number of spins. The long lifetime is, therefore, found to result from
energetic effects rather than entropic effects in this system.",1906.06383v5
2020-05-10,Phase stability and the effect of lattice distortions on electronic properties and half-metallic ferromagnetism of Co2FeAl Heusler alloy: An ab initio study,"Density functional theory calculations within the generalized gradient
approximation are employed to study the ground state of Co2FeAl. Various
magnetic configurations are considered to find out its most stable phase. The
ferromagnetic ground state of the Co2FeAl is energetically observed with an
optimized lattice constant of 5.70 {\AA}. Thereafter, the system was subjected
under uniform and non-uniform strains to see their effects on spin polarization
(P) and half-metallicity. The effect of spin orbit coupling is considered in
the present study. Half-metallicity (and 100 % P) is only retained under
uniform strains started from 0 to +4%, and dropped rapidly from 90% to 16% for
the negative strains started from -1% to -6%. We find that the present system
is much sensitive under tetragonal distortions as half-metallicity (and 100% P)
is preserved only for the cubic case. The main reason for the loss of
half-metallicity is due to the shift of the bands with respect to the Fermi
level. We also discuss the influence of these results on spintronics devices.",2005.04634v2
2022-02-04,Bipolar conduction asymmetries lead to ultra-high thermoelectric power factor,"Low band gap thermoelectric materials suffer from bipolar effects at high
temperatures, with increased electronic thermal conductivity and reduced
Seebeck coefficient, leading to reduced power factor and low ZT figure of
merit. In this work we show that the presence of strong transport asymmetries
between the conduction and valence bands can allow high phonon-limited
electronic conductivity at finite Seebeck coefficient values, leading to
largely enhanced power factors. The power factors that can be achieved can be
significantly larger compared to their maximum unipolar counterparts, allowing
for doubling of the ZT figure of merit. We identify this behavior in low band
gap cases from the half-Heusler materials family. Using both, advanced
electronic Boltzmann transport calculations for realistic material
bandstructures, as well as model parabolic electronic bands, we elaborate on
the parameters that determine this effect. We then develop a series of
descriptors which can guide machine learning studies in identifying such
classes of materials with extraordinary power factors at nearly pristine
conditions. For this we test more than 3000 analytical bandstructures and their
features, and more than 120 possible descriptors, to identify the most
promising ones that contain: i) only band structure features for easy
identification from material databases, and ii) band structure and transport
parameters that provide much higher correlations, but for which parameter
availability can be somewhat scarce.",2202.02128v1
2016-12-10,Chaos and regularity in the doubly magic nucleus 208Pb,"High resolution experiments have recently lead to a complete identification
(energy, spin, and parity) of 151 nuclear levels up to an excitation Energy of
Ex= 6.20 MeV in 208Pb. We present a thorough study of the fluctuation
properties in the energy spectra of the unprecedented set of nuclear bound
states. In a first approach we grouped states with the same spin and parity
into 14 subspectra, analyzed standard statistical measures for short- and
long-range correlations and then computed their ensemble average. Their
comparison with a random matrix ensemble which interpolates between Poisson
statistics expected for regular systems and the Gaussian Orthogonal Ensemble
(GOE) predicted for chaotic systems shows that the data are well described by
the GOE. In a second approach, following an idea of Rosenzweig and Porter we
considered the complete spectrum composed of the independent subspectra. We
analyzed their fluctuation properties using the method of Bayesian inference
involving a quantitative measure, called the chaoticity parameter f, which also
interpolates between Poisson (f=0) and GOE statistics (f=1). It turns out to be
f~0.9. This is so far the closest agreement with GOE observed in spectra of
bound states in a nucleus. The same analysis has also been performed with
spectra computed on the basis of shell model calculations with different
interactions (SDI, KB, M3Y). While the simple SDI exhibits features typical for
nuclear many-body systems with regular dynamics, the other, more realistic
interactions yield chaoticity parameters f close to the experimental values.",1612.03260v1
2018-04-11,NMR and the antiferromagnetic crystal phase regions in rapidly quenched ribbons and in alloys of the type $Cu-Mn-Al$,"It was shown that anomalous resistivity behavior of the $Cu-Mn-Al$ ribbons is
explained by the s-d interaction between conduction electrons and the clustered
Mn atoms. While nuclear magnetic resonance measurements show the
antiferromagnetic and ferromagnetic clusters of Mn atom coexisting without
long-range order, it is an interesting problem to study magnetic resonance
properties also for the antiferromagnetic crystal phase regions (which have
long-range order for larger regions) and which may also occur in these ribbons.
The Heusler Type $Cu-Mn-Al$ Alloy has a composition half way between
$Cu_{2}MnAl$ and $Cu_{3}Al$. Electron microscopy of the premartensitic $\beta
Cu-Zn-Al$ alloy has shown that the $\beta Cu-Zn-Al$ alloy quenched from high
temperature has the electron diffraction patterns of this alloy well explained
by the model with the existence of small particles with an orthorhombic
structure. It was noted that an important aspect of improvement in the material
properties is to create a nanostructured state in matrix, which has significant
advantages in magnetic and mechanical characteristics in contrast to the bulk
materials in crystalline or amorphous state. It is an interesting problem to
study magnetic resonance properties not only for the Mn atoms and clusters
without long-range order but also for the antiferromagnetic crystal phase
regions (which have long-range order for larger regions) which may also occur
in ribbons. This is the aim of our paper.",1804.04196v1
2019-12-20,Defect charging and resonant levels in half-Heusler Nb$_{1-x}$Ti$_x$FeSb,"We report $^{93}$Nb and $^{121}$Sb NMR and $^{57}$Fe M\""{o}ssbauer studies
combined with DFT calculations of Nb$_{1-x}$Ti$_x$FeSb ($0\leqslant x
\leqslant0.3$), one of the most promising thermoelectric systems for
applications above 1000 K. These studies provide local information about
defects and electronic configurations in these heavily $p$-type materials. The
NMR spin-lattice relaxation rate provides a measure of states within the
valence band. With increasing $x$, changes of relaxation rate vs carrier
concentration for different substitution fractions indicate the importance of
resonant levels which do not contribute to charge transport. The local
paramagnetic susceptibility is significantly larger than expected based on DFT
calculations, which we discuss in terms of an enhancement of the susceptibility
due to a Coulomb enhancement mechanism. The M\""{o}ssbauer spectra of
Ti-substituted samples show small departures from a binomial distribution of
substituted atoms, while for unsubstituted $p$-type NbFeSb, the amplitude of a
M\""{o}ssbauer satellite peak increases vs temperature, a measure of the
$T$-dependent charging of a population of defects residing about 30 meV above
the valence band edge, indicative of an impurity band at this location.",1912.09643v3
2020-03-18,Neutron diffraction and symmetry analysis of the martensitic transformation in Co-doped Ni$_2$MnGa,"Martensitic transformations are strain driven displacive transitions
governing the mechanical and physical properties in intermetallic materials.
This is the case in Ni$_2$MnGa, where the martensite transition is at the heart
of the striking magnetic shape memory and magneto-caloric properties.
Interestingly, the martensitic transformation is preceded by a pre-martensite
phase, and the role of this precursor and its influence on the martensitic
transition and properties is still a matter of debate. In this work, we report
on the influence of Co doping (Ni$_{50-x}$Co$_x$Mn$_{25}$Ga$_{25}$ with x = 3
and 5) on the martensitic transformation path in stoichiometric Ni$_2$MnGa by
neutron diffraction. The use of the superspace formalism to describe the
crystal structure of the modulated martensitic phases, joined with a group
theoretical analysis allows unfolding the different distortions featuring the
structural transitions. Finally, a general Landau thermodynamic potential of
the martensitic transformation, based on the symmetry analysis is outlined. The
combined use of phenomenological and crystallographic studies highlights the
close relationship between the lattice distortions at the core of the
Ni$_2$MnGa physical properties and, more in general, on the properties of the
martensitic transformations in the Ni-Mn based Heusler systems.",2003.08261v1
2020-06-09,Effect of partial substitution of iso-valent Mo at Cr-site on electronic structure and physical properties of Fe2CrAl,"Heusler alloy Fe2CrAl exhibits a ferromagnetic behaviour below Curie
temperature (TC) ~ 202 K along with presence of cluster glass (CG) phase near
freezing temperature (Tf) ~ 3.9 K and Griffiths phase (GP) above 300 K. The
physical properties of this alloy are very sensitive to substitutions and
anti-site disorder. Here, we investigate the effect of partial substitution of
Mo at Cr-site on physical properties of Fe2CrAl. Structural and morphological
analysis confirms the single cubic structure of the substituted alloys.
Increment in Mo concentration shifts the TC towards lower temperature, which is
ascribed to the effect of increased hybridization strength between 3d-4d states
of Fe/Cr/Mo. Additionally, systematic analysis of AC susceptibility, magnetic
memory effect and time dependent magnetization studies confirm the presence of
CG-like phase near (Tf) ~ 3.5 K in Fe2Cr0.95Mo0.05Al. Such feature gets
suppressed towards lower temperature with an increase of Mo concentration, i.e.
below 1.8 K in Fe2Cr0.85Mo0.15Al. The origin of the glassy signature is
ascribed to the decrement in magnetic anisotropy with Mo concentration. A
partial increment in magnetic entropy change is also noted near TC with the
increase in Mo substitution. Interestingly, at high temperatures (above 350 K),
GP phase persists in both the alloys due to the presence of anti-site disorder.",2006.05111v2
2020-11-01,Bipolar Magnetic Semiconducting Behavior in VNbRuAl: A New Spintronic Material for Spin Filters,"We report the theoretical prediction of a new class of spintronic materials,
namely bipolar magnetic semiconductor (BMS), which is also supported by our
experimental data. BMS acquires a unique band structure with unequal band gaps
for spin up and down channels, and thus are useful for tunable spin transport
based applications such as spin filters. The valence band (VB) and conduction
band (CB) in BMS approach the Fermi level through opposite spin channels, and
hence facilitate to achieve reversible spin polarization which are controllable
via applied gate voltage. We report the quaternary Heusler alloy VNbRuAl to
exactly possess the band structure of BMS. The alloy is found to crystallize in
LiMgPdSn prototype structure (space group $F\bar{4}3m$) with B$2$ disorder and
lattice parameter 6.15 \AA . The resistivity and Hall measurements show a two
channel semiconducting behavior and a quasi linear dependence of negative
magneto resistance (MR) indicating the possible semiconducting nature.
Interestingly, VNbRuAl also shows a fully compensated ferrimagnetic (FCF)
behavior with vanishing net magnetization (m$_s$$\sim$ $10^{-3}$ $\mu_B/f.u.$)
and significantly high ordering temperature ($> 900$ K). Unlike conventional
FCF, vanishing moment in this case appears to be the result of a combination of
long range antiferromagnetic (AFM) ordering and the inherent B2 disorder of the
crystal. This study opens up the possibility of finding a class of materials
for AFM spintronics, with great significance both from fundamental and applied
fronts.",2011.00533v1
2021-01-22,Structural and transport properties of 4f electron doped Y1-x(Dy)xPdBi topological semi-metallic thin films,"We report the effect of 4f electron doping on structural, electrical and
magneto-transport properties of Dy doped half Heusler Y1-x(Dy)xPdBi (x =0, 0.2,
0.5, 1) thin films grown by pulsed laser deposition. The Dy doping leads to
lattice contraction which increases from 0% for the parent x =0 sample to
approx 1.3% for x=1 sample with increase in Dy doping. The electrical transport
measurements show a typical semi-metallic behaviour in the temperature range 3K
to 300K and a sharp drop in resistivity at low temperatures (less than 3K) for
all the samples. Magnetotransport measurements and Shubnikov de-Hass
oscillations at high magnetic fields demonstrate that for these topologically
non-trivial samples, Dy doping induced lattice contraction plays an active role
in modifying the Fermi surface, carrier concentration and the effective
electron mass. There is an uniform suppression of the onset of
superconductivity with increased Dy doping which is possibly related to the
increasing local exchange field arising from the 4f electrons in Dy. Our
results indicate that we can tune various band structure parameters of YPdBi by
f electron doping and strained thin films of Y1-x(Dy)xPdBi show surface
dominated relativistic carrier transport at low temperatures.",2101.09185v2
2021-02-25,Unidirectional magnetoresistance and spin-orbit torque in NiMnSb,"Spin-dependent transport phenomena due to relativistic spin-orbit coupling
and broken space-inversion symmetry are often difficult to interpret
microscopically, in particular when occurring at surfaces or interfaces. Here
we present a theoretical and experimental study of spin-orbit torque and
unidirectional magnetoresistance in a model room-temperature ferromagnet NiMnSb
with inversion asymmetry in the bulk of this half-heusler crystal. Besides the
angular dependence on magnetization, the competition of Rashba and
Dresselhaus-like spin-orbit couplings results in the dependence of these
effects on the crystal direction of the applied electric field. The
phenomenology that we observe highlights potential inapplicability of commonly
considered approaches for interpreting experiments. We point out that, in
general, there is no direct link between the current-induced non-equilibrium
spin polarization inferred from the measured spin-orbit torque and the
unidirectional magnetiresistance. We also emphasize that the unidirectional
magnetoresistance has not only longitudinal but also transverse components in
the electric field -- current indices which complicates its separation from the
thermoelectric contributions to the detected signals in common experimental
techniques. We use the theoretical results to analyze our measurements of the
on-resonance and off-resonance mixing signals in microbar devices fabricated
from an epitaxial NiMnSb film along different crystal directions. Based on the
analysis we extract an experimental estimate of the unidirectional
magnetoresistance in NiMnSb.",2102.12838v1
2022-05-16,First principle studies on electronic and thermoelectric properties of Fe$_{2}$TiSn based multinary Heusler alloys,"The alloys with 8/18/24 valence electron count (VEC) are promising candidates
for efficient energy conversion and refrigeration applications at low as well
as high temperatures. The full potential linearized augmented plane wave method
as implemented in WIEN2k code was used to investigate electronic structure and
TE transport properties with the PBE$-$GGA and TB$-$mBJ exchange potentials and
Boltzmann transport theory. The calculated single crystal elastic constants,
phonon dispersion and phonon density of states confirm that these systems are
mechanically and dynamically stable. The TE transport properties is calculated
by including the lattice part of thermal conductivity ($\kappa_{L}$) obtained
from two methods one from the calculated elastic properties calculation
($\kappa^{elastic}_{L}$) and the other from phonon dispersion curve
($\kappa^{phonon}_{L}$). The strong phonon$-$phonon scattering by large mass
difference/strain fluctuation of isovalent/aliovalent substitution at Ti/Sn
sites of Fe$_{2}$TiSn reduces the lattice thermal conductivity which results in
high \textit{ZT} value of 0.81 at 900\,K for
Fe$_{2}$Sc$_{0.25}$Ti$_{0.5}$Ta$_{0.25}$Al$_{0.5}$Bi$_{0.5}$. The comparative
analysis of TE transport properties using the band structures calculated with
the PBE$-$GGA and TB$-$mBJ functional shows that the \textit{ZT} value obtained
from TB$-$mBJ scheme is found to be significantly higher than that based on
PBE$-$GGA. The calculated relatively low lattice thermal conductivity and high
\textit{ZT} values suggest that isovalent/aliovalent substituted Fe$_{2}$TiSn
are promising candidates for medium to high temperature waste heat recovery.",2205.07688v1
2022-05-28,Helicity-independent all-optical switching of magnetization in ferrimagnetic alloys,"We review and discuss the process of single-shot helicity-independent
all-optical switching of magnetization by which a single suitably-ultrafast
excitation, under the right conditions, toggles magnetization from one stable
state to another. For almost a decade, this phenomenon was only consistently
observed in specific rare-earth-transition-metal ferrimagnetic alloys of
GdFeCo, but breakthrough experiments in recent years have revealed that the
same behavior can be achieved in a wide range of multi-sublattice magnets
including TbCo alloys doped with minute amounts of Gd, Gd/Co and Tb/Co
synthetic ferrimagnets, and the rare-earth-free Heusler alloy Mn$_2$Ru$_x$Ga.
Aiming to resolve the conditions that allow switching, a series of experiments
have shown that the process in the ferrimagnetic alloys GdFeCo and
Mn$_2$Ru$_x$Ga is highly sensitive to the pulse duration, starting temperature
and the alloy composition. We argue here that the switching displayed by these
two very different ferrimagnetic alloys can be generally understood within a
single phenomenological framework describing the flow of angular momentum
between the constituent sublattices and from the sublattices to the
environment. The conditions that facilitate switching stem from the properties
of these channels of angular momentum flow in combination with the size of the
angular momentum reservoirs. We conclude with providing an outlook in this
vibrant research field, with emphasis on the outstanding open questions
pertaining to the underlying physics along with noting the advances in
exploiting this switching process in technological applications.",2205.14342v1
2022-08-03,"Machine Learning-Based Classification, Interpretation, and Prediction of High-Entropy-Alloy Intermetallic Phases","The design of high-entropy alloys (HEA) with desired properties is
challenging due to their large compositional space. While various machine
learning (ML) models can predict specific HEA solid-solution phases (SS),
predicting high-entropy intermetallic phases (IM) is underdeveloped due to
limited datasets and inadequate ML features. This paper introduces feature
engineering-assisted ML models that achieve detailed phase classification and
high accuracy. By combining phase-diagram-based and physics-based features, it
is found that the ML models trained on the Random Forest (RF) and Support
Vector Machine (SVM) regressors, are able to classify individual SS and common
IM (Sigma, Laves, Heusler, and refractory B2 phases) with accuracies ranging
from 80 - 94%. The machine-learned features also enable the interpretation of
IM formation. Furthermore, the efficacies of the RF, SVM, and neural network
(NN) models are critically evaluated. The phase classification accuracies are
found to decrease upon utilizing the NN model to train the datasets. The
accuracy of the model prediction is validated by synthesizing 86 new alloys.
This approach provides a practical and robust framework for guiding HEA phase
design, particularly for technologically significant IM phases.",2208.02141v3
2022-08-09,"Structural, magnetic and transport properties of Co$_2$CrAl epitaxial thin films","We report the physical properties of Co$_2$CrAl Heusler alloy epitaxial thin
films grown on single crystalline MgO(001) substrate using pulsed laser
deposition technique. The x-ray diffraction pattern in $\theta$-2$\theta$ mode
showed the film growth in single phase B2-type ordered cubic structure with the
presence of (002) and (004) peaks, and the film oriented along the MgO(001)
direction. The $\phi$~scan along the (220) plane confirms the four-fold
symmetry and the epitaxial growth relation found to be
Co$_2$CrAl(001)[100]$\vert$$\vert$MgO(001)[110]. The thickness of about 12~nm
is extracted through the analysis of x-ray reflectivity data. The isothermal
magnetization (M--H) curves confirm the ferromagnetic (FM) nature of the thin
film having significant hysteresis at 5 and 300~K. From the in-plane M--H
curves, the saturation magnetization values are determined to be
2.1~$\mu$$_{\rm B}$/f.u.~at 5~K and 1.6~$\mu$$_{\rm B}$/f.u. at 300~K, which
suggests the soft FM behavior in the film having the coercive field $\approx$
522~Oe at 5~K. The thermo-magnetization measurements at 500~Oe magnetic field
show the bifurcation between field-cooled and zero-field-cooled curves below
about 100~K. The normalized field-cooled magnetization curve follows the T$^2$
dependency, and the analysis reveal the Curie temperature around 335$\pm$11~K.
Moreover, the low-temperature resistivity indicates semiconducting behavior
with the temperature, and we find a negative temperature coefficient of
resistivity (5.2 $\times$ 10$^{-4}$ /K).",2208.04687v1
2023-01-03,Ab-initio study of phononic thermal conduction in ScAgC half-Heusler,"We present a first-principles lattice calculations to comprehend the thermal
expansion $\alpha(T)$ and lattice thermal conductivity $\kappa_{ph}$ of ScAgC.
The obtained positive frequencies of phonon dispersion shows the dynamical
stability of ScAgC in FCC structure. The estimated $\alpha(T)$ from
quasi-harmonic approximation (QHA) at 300(1200) K is
$\sim$4(4.6)$\times$$10^{-6}$ K$^{-1}$. The predicted value of total
$\kappa_{ph}$ from phonon-phonon interaction (PPI) at 300(1200) K is
$\sim$7.4(1.8) Wm$^{-1}$K$^{-1}$. The highest group velocity for acoustic $\&$
optical branches (AB $\&$ OB) is $\sim$6.7 and $\sim$3.5 km/s, respectively.
The predicted average phonon lifetime ($\tau_{\lambda}$) for AB(OB) is
$\sim$2.5(1.65) ps at 300 K, whereas it is $\sim$0.6(0.4) ps at 1200 K. The
estimated highest heat capacity ($C_{\lambda}$) at 200 K for AB(OB) is
$\sim$23.5 (19.5) meV/K. We fitted the equation
$A_{\kappa}$T$^{-x_{\kappa}}$($A_{\tau}$T$^{-x_{\tau}}$) in the
$\kappa_{ph}$($\tau_{\lambda}$) curve to gain a thorough understanding of
temperature-dependent $\kappa_{ph}$ trend. The $x_{\kappa}$ for total branches
is calculated to be $\sim$1.02. The $x_{\tau}$ value due to total AB(OB) is
estimated to be $\sim$1.04(1.02), while it is $\sim$1.03 for total branches.
The calculated $x_{\kappa}$ for total AB(OB) is $\sim$1.04(0.95), implying that
AB contributes more to the total $\kappa_{ph}$. This research could be
important for enhancing the properties of ScAgC regarding thermoelectric and
photovoltaic applications.",2301.01029v1
2023-01-19,Ab initio comparison of spin-transport properties in MgO-spaced ferrimagnetic tunnel junctions based on Mn$_3$Ga and Mn$_3$Al,"We report on first-principles spin-polarised quantum transport calculations
(from NEGF+DFT) in MgO-spaced magnetic tunnel junctions (MTJs) based on two
different Mn-based Heusler ferrimagnetic metals, namely Mn$_3$Al and Mn$_3$Ga
in their tetragonal DO$_{22}$ phase. The former is a fully compensated
half-metallic ferrimagnet, while the latter is a low-moment
high-spin-polarisation ferrimagnet, both with a small lattice mismatch from
MgO. In identical symmetric and asymmetric interface reconstructions across a
3-monolayer thick MgO barrier for both ferrimagets, the linear response
(low-voltage) spin-transfer torque (STT) and tunneling magneto-resistance (TMR)
effects are evaluated. A larger staggered in-plane STT is found in the Mn$_3$Ga
case, while the STT in Mn$_3$Al vanishes quickly away from the interface
(similarly to STT in ferromagnetic MTJs). The roles are reversed for the TMR,
which is practically 100\% in the half-metallic Mn$_3$Al-based MTJs (using the
conservative definition) as opposed to 60\% in the Mn$_3$Ga case. The weak
dependence on the exact interface reconstruction would suggest
Mn$_3$Ga-Mn$_3$Al solid solutions as a possible route towards optimal trade-off
of STT and TMR in the low-bias, low-temperature transport regime.",2301.08300v1
2023-02-13,The impact of an interactive visualization and simulation tool on learning quantum physics: Results of an eye-tracking study,"Employing scientific practices to obtain and use information is one of the
central facets of next generation science standards. Especially in quantum
technology education, the ability to employ such practices is an essential
skill to foster both academic success and technological development. In order
to help educators design effective instructions, the comparison between
novices' and experts' eye movements allows the identification of efficient
information extraction and integration strategies. In this work, we compare the
gaze behavior of experts and novices while solving problems in quantum physics
using an interactive simulation tool, Quantum Composer, which displays
information via multiple external representations (numerical values, equations,
graphs). During two reasoning tasks, we found that metarepresentational
competences were crucial for successful engagement with the simulation tool.
The analysis of the gaze behavior revealed that visual attention on a graph
plays a major role and redundant numerical information is ignored. Furthermore,
the total dwell time on relevant and irrelevant areas is predictive for the
score in the second task. Therefore, the results demonstrate which difficulties
novices encounter when using simulation tools and provides insights for how to
design effective instructions in quantum technology education guided by
experts' gaze behavior.",2302.06286v1
2023-08-20,A Framework for Curriculum Transformation in Quantum Information Science and Technology Education,"The field of Quantum Information Science and Technology (QIST) is booming.
Due to this, many new educational courses and university programs are needed in
order to prepare a workforce for the developing industry. Owing to its
specialist nature, teaching approaches in this field can suffer with being
disconnected from the substantial degree of science education research which
aims to support the best approaches to teaching in STEM fields. In order to
connect these two communities with a pragmatic and repeatable methodology, we
have synthesised this educational research into a decision-tree based
theoretical model for the transformation of QIST curricula, intended to provide
a didactical perspective for practitioners. The QCTF consists of four steps: 1.
choose a topic, 2. choose one or more targeted skills, 3. choose a learning
goal and 4. choose a teaching approach that achieves this goal. We show how
this can be done using an example curriculum and more specifically quantum
teleportation as a basic concept of quantum communication within this
curriculum. By approaching curriculum creation and transformation in this way,
educational goals and outcomes are more clearly defined which is in the
interest of the individual and the industry alike. The framework is intended to
structure the narrative of QIST teaching, and with future testing and
refinement it will form a basis for further research in the didactics of QIST.",2308.10371v2
2023-10-05,Exotic rare earth-based materials for emerging spintronic technology,"The progress in materials science has always been associated with the
development of functional materials systems, which enables us to design
proof-of-concept devices. To advance further, theoretical predictions of new
novel materials and their experimental realization is very important. This
chapter reviews the intriguing properties of rare earth-based materials and
their applications in spintronics. Spintronics is an emerging technology, which
exploits spin degree of freedom of an electron along with its charge property.
Discovery of various physical phenomena and their industrial applications in
the field of magnetic sensors, magnetic recording and non-volatile memories
such as magnetic random access memory (MRAM) and spin-transfer torque (STT)
MRAM opens several new directions in this field. Materials with large spin
polarization, strong spin-orbit coupling, and tunable electronic and magnetic
properties offer an excellent platform for the spintronics technology.
Combination of rare earths with other elements such as transition metals show
broad range of structural, electronic, and magnetic properties which make them
excellent candidates for various spintronic applications. This chapter
discusses many such materials ranging from Heusler alloys, topological
insulators to two-dimensional ferromagnets and their potential applications.
The review gives an insight of how rare-earth materials can play a key role in
emerging future technology and have great potential in many new spintronic
related applications.",2310.03541v1
2023-11-07,The role of electronic bandstructure shape in improving the thermoelectric power factor of complex materials,"The large variety of complex electronic structure materials and their alloys,
offer highly promising directions for improvements in thermoelectric (TE) power
factors (PF). Their electronic structure contains rich features, referred to as
'surface complexity', one of them being the highly anisotropic warped energy
surface shapes with elongated features and threads in some cases. In this work
we use Boltzmann transport simulations to quantify the influence that the shape
of the electronic structure energy surfaces has on the PF. Using both
analytical ellipsoidal bands, as well as realistic bands from the group of
half-Heuslers, we show that band shape complexity alone can offer an advantage
to the PF of ~3x in realistic cases. The presence of anisotropic scattering
mechanisms such as ionized impurity or polar optical phonon scattering,
however, can reduce these improvements by up to ~50%. We show that expressions
based on the simple ratio of the density-of-states to the conductivity
effective masses, mDOS/mC, together with the number of valleys, can capture the
anisotropy shape with a moderate to high degree of correlation. For this, we
use a convenient way to extract these masses by mapping the complex
bandstructures of materials to parabolic electronic structures, without the
need for Boltzmann transport codes. Despite the fact that the PF depends on
many parameters, information about the benefits of the band shape alone, would
be very useful for identifying and understanding the performance of novel
thermoelectric materials.",2311.03935v1
2023-11-30,Vanishing of the anomalous Hall effect and enhanced carrier mobility in the spin-gapless ferromagnetic Mn2CoGa1-xAlx alloys,"Spin gapless semiconductor (SGS) has attracted long attention since its
theoretical prediction, while concrete experimental hints are still lack in the
relevant Heusler alloys. Here in this work, by preparing the series alloys of
Mn2CoGa1-xAlx (x=0, 0.25, 0.5, 0.75 and 1), we identified the vanishing of
anomalous Hall effect in the ferromagnetic Mn2CoGa (or x=0.25) alloy in a wide
temperature interval, accompanying with growing contribution from the ordinary
Hall effect. As a result, comparatively low carrier density (1020 cm-3) and
high carrier mobility (150 cm2/Vs) are obtained in Mn2CoGa (or x=0.25) alloy in
the temperature range of 10-200K. These also lead to a large dip in the related
magnetoresistance at low fields. While in high Al content, despite the
magnetization behavior is not altered significantly, the Hall resistivity is
instead dominated by the anomalous one, just analogous to that widely reported
in Mn2CoAl. The distinct electrical transport behavior of x=0 and x=0.75 (or 1)
is presently understood by their possible different scattering mechanism of the
anomalous Hall effect due to the differences in atomic order and conductivity.
Our work can expand the existing understanding of the SGS properties and offer
a better SGS candidate with higher carrier mobility that can facilitate the
application in the spin-injected related devices.",2311.18335v1
2023-12-29,"Effect of Point Defects and Lattice Distortions on the Structural, Electronic, and Magnetic properties of Co$_2$MnAl Heusler alloy","The effects of various point defects and lattice distortions on the
structural, electronic, and magnetic properties of Co$_2$MnAl alloy are
investigated using density functional theory calculations. For the point
defects, six types of binary antisites, three types of ternary antisites, and
three kinds of vacancies have been simulated with different disorder degrees,
up to a maximum of 12.50%. For the lattice distortions, cubic strain within
-10% $\leq$$\Delta{V/V_0}$$\leq$ 10% (corresponding to 5.50\r{A} $\leq$ a
$\leq$5.88\r{A}) and tetragonal distortions with
0.5$\leq$$\textit{c/a}$$\leq$1.5 at three different unit-cell volumes -
$\textit{V}_0$ and ($\textit{V}_0$$\pm5$%$\textit{V}_0$) have been considered.
The Co$_{Al}$ and Mn$_{Al}$ binary antisite disordered structures (namely,
Co$_{2.0625}$MnAl$_{0.9375}$, Co$_{2.125}$MnAl$_{0.875}$,
Co$_2$Mn$_{1.0625}$Al$_{0.9375}$ and Co$_2$Mn$_{1.125}$Al$_{0.875}$) and
(Co$_{Al}$+Mn$_{Al}$) ternary antisite disordered structure
(Co$_{2.0625}$Mn$_{1.0625}$Al$_{0.875}$) exhibit perfect half-metallicity. The
rest of the antisite disorders have a marginal effect on the half-metallic
properties of Co$_2$MnAl, along with high spin polarization ($\textit{P}$
$\geq$ 70%) and nearly same magnetization ($\textit{M$_s$}$) as that for ideal
structure. Conversely, the vacancy defects significantly affect the electronic
and magnetic properties. The cubic strained structures exhibit high
$\textit{P}$ and constant $\textit{M$_s$}$. Under negative strain within -10%
$\leq$$\Delta{V/V_0}$$\leq$ -7% (for 5.50\r{A} $\leq$ a $\leq$ 5.58\r{A}), the
strained structures have perfect half-metallicity. On the other hand,
tetragonal distortions lead to significant degradation in half-metallic
behavior, except for small distortion values $\Delta{c/a}$, irrespective of
their volume.",2312.17545v1
2024-02-29,Enhanced metamagnetic shape memory effect in Heusler-type Ni37Co11Mn43Sn9 polycrystalline ferromagnetic shape memory alloy,"Polycrystalline Ni-Co-Mn-Sn based ferromagnetic shape memory alloys (FSMAs)
show promise as actuator materials, but their practical application involving
magnetic field induced strain (MFIS) is often limited by three factors: the
requirement for high magnetic fields (> 5 T), martensitic transition
temperature away from room temperature, and limited recovery of pre-strain
applied to the martensite phase. Current work investigates the martensitic
transition (MT) and shape memory effect under the application of magnetic field
for bulk polycrystalline Ni37Co11Mn43Sn9 alloy. The outcome of the study
reveals a metamagnetic transition from the martensitic phase to the austenitic
phase at a low field of 2.8 T at 300 K which results 0.25% spontaneous MFIS.
Interestingly, 1.3% pre-strained specimen registers a 100% recovery with the
application of magnetic field of 4.5 T. Furthermore, the pre-strained specimen
exhibited a two-way shape memory effect between a strain value of 1.0% to 1.55%
during the field loading and unloading sequences. Notably, this study also
demonstrates, to the best of our knowledge , for the first time, that the
spontaneous strain and pre-strain add together. This finding paves the way for
achieving a giant MFIS by pre-straining a Ni-Mn-Sn/In class of FSMAs which
shows large spontaneous MFIS.",2402.18992v1
1999-02-10,Thermodynamics of the incommensurate state in Rb_2WO_4: on the Lifshitz point in A`A``BX_4 compounds,"We consider the evolution of the phase transition from the parent hexagonal
phase $P6_{3}/mmc$ to the orthorhombic phase $Pmcn$ that occurs in several
compounds of $A'A''BX_{4}$ family as a function of the hcp lattice parameter
$c/a$. For compounds of $K_{2}SO_{4}$ type with $c/a$ larger than the threshold
value 1.26 the direct first-order transition $Pmcn-P6_{3}/mmc$ is characterized
by the large entropy jump $Rln2$. For compounds $Rb_{2}WO_{4}$, $K_{2}MoO_{4}$,
$K_{2}WO_{4}$ with $c/a<1.26$ this transition occurs via an intermediate
incommensurate $(Inc)$ phase. DSC measurements were performed in $Rb_{2}WO_{4}$
to characterize the thermodynamics of the $Pmcn-Inc-P6_{3}/mmc$ transitions. It
was found that both transitions are again of the first order with entropy jumps
$0.2Rln2 and $0.3Rln2$. Therefore, at $c/a ~ 1.26$ the $A'A''BX_{4}$ compounds
reveal an unusual Lifshitz point where three first order transition lines meet.
We propose the coupling of crystal elasticity with $BX_{4}$ tetrahedra
orientation as a possible source of the transitions discontinuity.",9902138v1
2001-04-07,Correlation between the Josephson coupling energy and the condensation energy in bilayer cuprate superconductors,"We review some previous studies concerning the intra-bilayer Josephson
plasmons and present new ellipsometric data of the c-axis infrared response of
almost optimally doped Bi_{2}Sr_{2}CaCu_{2}O_{8}. The c-axis conductivity of
this compound exhibits the same kind of anomalies as that of underdoped
YBa_{2}Cu_{3}O_{7-delta}. We analyze these anomalies in detail and show that
they can be explained within a model involving the intra-bilayer Josephson
effect and variations of the electric field inside the unit cell. The Josephson
coupling energies of different bilayer compounds obtained from the optical data
are compared with the condensation energies and it is shown that there is a
reasonable agreement between the values of the two quantities. We argue that
the Josephson coupling energy, as determined by the frequency of the
intra-bilayer Josephson plasmon, represents a reasonable estimate of the change
of the effective c-axis kinetic energy upon entering the superconducting state.
It is further explained that this is not the case for the estimate based on the
use of the simplest ``tight-binding'' sum rule. We discuss possible
interpretations of the remarkable agreement between the Josephson coupling
energies and the condensation energies. The most plausible interpretation is
that the interlayer tunneling of the Cooper pairs provides the dominant
contribution to the condensation energy of the bilayer compounds; in other
words that the condensation energy of these compounds can be accounted for by
the interlayer tunneling theory. We suggest an extension of this theory, which
may also explain the high values of T_{c} in the single layer compounds
Tl_{2}Ba_{2}CuO_{6} and HgBa_{2}CuO_{4}, and we make several experimentally
verifiable predictions.",0104123v1
2003-03-29,Unusual Ground State Properties of the Kondo-Lattice Compound Yb2Ir3Ge5,"We report sample preparation, structure, electrical resistivity, magnetic
susceptibility and heat capacity studies of a new compound Yb$_2$Ir$_3$Ge$_5$.
We find that this compound crystallizes in an orthorhombic structure with a
space group PMMN unlike the compound Ce$_2$Ir$_3$Ge$_5$ which crystallizes in
the tetragonal IBAM (U$_2$Co$_3$Si$_5$ type) structure. Our resistivity
measurements indicate that the compound Yb$_2$Ir$_3$Ge$_5$ behaves like a
typical Kondo lattice system with no ordering down to 0.4 K. However, a
Curie-Weiss fit of the inverse magnetic susceptibility above 100 K gives an
effective moment of only 3.66 $\mu$$_B$ which is considerably less than the
theoretical value of 4.54 $\mu$$_B$ for magnetic Yb$^3+$ ions. The value of
$\theta_{P}$ = -15.19 K is also considerably higher indicating the presence of
strong hybridization. An upturn in the low temperature heat capacity gives an
indication that the system may order magnetically just below the lowest
temperature of our heat capacity measurements (0.4 K). The structure contains
two sites for Yb ions and the present investigation suggests that Yb may be
trivalent in one site while it may be significantly lower (close to divalent)
in the other.",0303618v1
2003-08-26,Ferromagnetic materials in the zinc-blende structure,"New materials are currently sought for use in spintronics applications.
Ferromagnetic materials with half metallic properties are valuable in this
respect. Here we present the electronic structure and magnetic properties of
binary compounds consisting of 3d transition metals and group V elements viz.
P, Sb and As in the zinc-blende structure. We demonstrate that compounds of V,
Cr and Mn show half metallic behavior for appropriate lattice constants.
  By comparing the total energies in the ferromagnetic and antiferromagnetic
structures, we have ascertained that the ferromagnetic phase is stable over the
antiferromagnetic one. Of the different compounds studied, the Cr based systems
exhibit the strongest interatomic exchange interactions, and are hence
predicted to have the highest critical temperatures. Also, we predict that VAs
under certain growth conditions should be a semiconducting ferromagnet.
Moreover, critical temperatures of selected half metallic compounds have been
estimated from mean field theory and Monte Carlo simulations using parameters
obtained from a {\it ab-initio} non-collinear, tight binding linearized
muffin-tin orbital method. From a simple model, we calculate the reflectance
from an ideal MnAs/InAs interface considering the band structures of MnAs and
InAs. Finally we present results on the relative stabilities of MnAs and CrSb
compounds in the NiAs and zinc-blende structures, and suggest a parameter space
in substrate lattice spacings for when the zinc-blende structure is expected to
be stable.",0308524v1
2003-10-14,Structural and magnetic properties of MSr2Y1.5Ce0.5Cu2Oz (M-1222) compounds with M = Fe and Co,"MSr2Y1.5Ce0.5Cu2Oz (M-1222) compounds, with M = Fe and Co, have been
synthesized through a solid-state reaction route. Both compounds crystallize in
a tetragonal structure (space group I4/mmm). A Rietveld structural refinement
of room-temperature neutron diffraction data for Fe-1222 reveals that nearly
half the Fe remains at the M site, while the other half goes to the Cu site in
the CuO2 planes. Existence of Fe at two different lattice sites, is also
confirmed by 57Fe Mossbauer spectroscopy from which it is inferred that nearly
50% of the total Fe occupies the Cu site in the CuO2 planes as Fe3+, whereas
the other 50 % is located at the M site with nearly 40 % as Fe4+ and around 10%
as Fe3+. For the M = Co compound, nearly 84 % of Co remains at its designated M
site, while the rest occupies the Cu site in the CuO2 planes. The oxygen
content, z, based on oxygen occupancies refined from the neutron diffraction
data, comes close to 9.0 for both the samples The ZFC and FC magnetization
curves as a function of temperature show a complex behavior for both Fe-1222
and Co-1222 compounds.",0310294v1
2004-01-29,"Magnetic and transport anomalies in the compounds, RCuAs2 (R= Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er)","The results of dc magnetization, heat capacity, electrical resistivity (rho)
and magnetoresistance measurements are reported in detail for the compounds,
RCuAs2 for R= Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, crystallizing in HfCuSi2-type
tetragonal structure, with the aim of bringing out anomalies among 'normal'
(that is, other than Ce and Yb) rare-earths. The results establish that all
these compounds order antiferromagnetically at low temperatures with deviations
from de Gennes scaling. Isothermal magnetization (M) data below respective Neel
temperatures (TN) reveal the existence of field-induced metamagnetic-like
transitions for most of the compounds (except R= Sm and Gd), whereas in Sm and
Gd compounds M varies essentially linearly with magnetic field. With respect to
the rho behavior, there appears to be a subtle difference in the temperature
dependence beyond 50 K between Sm on the one hand and the rest on the other. In
addition, the unexpected rho(T) minimum reported recently for R = Sm, Gd, Tb
and Dy in the paramagnetic state (around 20 to 30 K) is essentially absent for
R = Ho and Er. The results overall reveal that the normal rare-earths in this
series present an interesting situation in magnetism, warranting a new
theoretical approach to describe the transport behavior in the paramagnetic
state particularly in the vicinity of TN.",0401599v1
2004-02-03,"Anomalous f-electron Hall Effect in the Heavy-Fermion System CeTIn$_{5}$ (T = Co, Ir, or Rh)","The in-plane Hall coefficient $R_{H}(T)$ of CeRhIn$_{5}$, CeIrIn$_{5}$, and
CeCoIn$_{5}$ and their respective non-magnetic lanthanum analogs are reported
in fields to 90 kOe and at temperatures from 2 K to 325 K. $R_{H}(T)$ is
negative, field-independent, and dominated by skew-scattering above $\sim$ 50 K
in the Ce compounds. $R_{H}(H \to 0)$ becomes increasingly negative below 50 K
and varies with temperature in a manner that is inconsistent with skew
scattering. Field-dependent measurements show that the low-T anomaly is
strongly suppressed when the applied field is increased to 90 kOe. Measurements
on LaRhIn$_{5}$, LaIrIn$_{5}$, and LaCoIn$_{5}$ indicate that the same
anomalous temperature dependence is present in the Hall coefficient of these
non-magnetic analogs, albeit with a reduced amplitude and no field dependence.
Hall angle ($\theta_{H}$) measurements find that the ratio
$\rho_{xx}/\rho_{xy}=\cot(\theta_{H})$ varies as $T^{2}$ below 20 K for all
three Ce-115 compounds. The Hall angle of the La-115 compounds follow this
T-dependence as well. These data suggest that the electronic-structure
contribution dominates the Hall effect in the 115 compounds, with $f$-electron
and Kondo interactions acting to magnify the influence of the underlying
complex band structure. This is in stark contrast to the situation in most $4f$
and $5f$ heavy-fermion compounds where the normal carrier contribution to the
Hall effect provides only a small, T-independent background to $R_{H}.$",0402076v1
2004-05-03,"Compressibility of $Ce M In_5$ and $Ce_2 M In_8$ (M = Rh, Ir and Co) Compounds","The lattice parameters of the tetragonal compounds Ce$M$In$_{5}$ and
Ce$_{2}M$In$_{8}$($M=$Rh, Ir and Co) have been studied as a function of
pressure up to 15 GPa using a diamond anvil cell under both hydrostatic and
quasihydrostatic conditions at room temperature. The addition of $M$In$_{2}$
layers to the parent CeIn$_{3}$ compound is found to stiffen the lattice as the
2-layer systems (average of bulk modulus values $B_{0}$ is 70.4 GPa) have a
larger $B_{0}$ than CeIn$_{3}$ (67 GPa), while the 1-layer systems with the are
even stiffer (average of $B_{0}$ is 81.4 GPa). Estimating the hybridization
using parameters from tight binding calculations shows that the dominant
hybridization is $fp$ in nature between the Ce and In atoms. The values of
$V_{pf}$ at the pressure where the superconducting transition temperature
$T_{c}$ reaches a maximum is the same for all Ce$M$In$_{5}$ compounds. By
plotting the maximum values of the superconducting transition temperature
$T_{c}$ versus $c/a$ for the studied compounds and Pu-based superconductors, we
find a universal $T_{c}$ versus $c/a$ behavior when these quantities are
normalized appropriately. These results are consistent with magnetically
mediated superconductivity.",0405043v2
2004-12-07,High pressure high temperature (HPHT) synthesis and magnetization of Magneto-Superconducting RuSr2(LnCe2)Cu2O12.25 (Ru-1232) compounds (Ln = Y and Dy),"RuSr2(LnCe2)Cu2O12.25 (Ru-1232) compounds with Ln = Y and Dy being
synthesized by high pressure high temperature (6GPa, 12000C) solid state
synthesis route do crystallize in space group P4/mmm in near single phase form
with small quantities of SrRuO3 and RuSr2(RE1.5Ce0.5)Cu2O10 (Ru-1222). Both
samples exhibit magnetic transitions (Tmag.) at ~90 K with significant
branching of zfc (zero-field-cooled) and fc (field-cooled) magnetization and a
sharp cusp in zfc at ~ 70 K, followed by superconducting transitions at ~ 30 K.
Both compounds show typical ferromagnetic hysteresis loops in magnetic moment
(M) versus field (H) magnetization right upto Tmag. i.e. < 90K. To our
knowledge these are the first successfully synthesized Ru-1232 compounds in
near single phase with lanthanides including Y and Dy. The results are compared
with widely reported Gd/Ru-1222 and Ru-1212 (RuSr2GdCu2O8) compounds. In
particular, it seems that the Ru moments magnetic ordering temperature (Tmag.)
scales with the c-direction distance between magnetic RuO6 octahedras in
Ru-1212/1222 or 1232 systems.",0412153v1
2006-01-06,Phase formation and superconductivity of Fe-tube encapsulated and vacuum annealed MgB2,"We report optimization of the synthesis parameters viz. heating temperature
(TH), and hold time (thold) for vacuum (10-5 torr) annealed and LN2 (liquid
nitrogen) quenched MgB2 compound. These are single-phase compounds
crystallizing in the hexagonal structure (space group P6/mmm) at room
temperature. Our XRD results indicated that for phase-pure MgB2, the TH for
10-5 torr annealed and LN2 quenched samples is 750 0C. The right stoichiometry
i.e., MgB2 of the compound corresponding to 10-5 Torr and TH of 750 0C is found
for the hold time (thold) of 2.30 hours. With varying thold from 1- 4 hours at
fixed TH (750 0C) and vacuum (10-5 torr), the c-lattice parameter decreases
first and later increases with thold (hours) before a near saturation, while
the a-lattice parameter first increase and later decreases beyond thold of 2.30
hours. c/a ratio versus thold plot showed an inverted bell shape curve,
touching the lowest value of 1.141 which is reported value for perfect
stoichiometry of MgB2. The optimized stoichimetric MgB2 compound exhibited
superconductivity at 39.2 K with transition width of 0.6 K. In conclusion, the
synthesis parameters for phase pure stoichimetric vacuum annealed MgB2 compound
are optimized and are compared with widely reported Ta tube encapsulated
samples.",0601112v1
2006-01-06,Local distortion of MnO$_6$ octahedron in La$_{1-x}$Sr$_x$MnO$_{3+δ}$ (x = 0.1 to 0.9): an EXAFS study,"Room temperature Mn K-edge extended x-ray absorption fine structure (EXAFS)
studies were carried out on La$_{1-x}$Sr$_x$MnO$_{3+\delta}$ (x = 0.1 to 0.9)
compounds. It is found from the detailed EXAFS analysis that the local
structure around Mn sites is different from the global structure inferred from
x-ray diffraction, especially for x <= 0.4, indicating presence of local
distortions in MnO$_6$ octahedra. For the rhombohedral compounds, x = 0.1 to
0.3 the distortion is maximum for x = 0.1 and two bond lengths are seen- short
one in basal plane and long one in apical plane. For compounds with x = 0.4 to
0.8 two short bonds in basal plane and four long bonds- two in the basal plane
and remaining two in the apical plane are seen. For the compounds up to x = 0.3
compositions long bond length decreases and short bond length increases with
increase in x whereas for the compounds 0.4 <= x <= 0.8 both types of bond
lengths decrease. Such behaviour of bond lengths is an indication of the
changed nature of distortion from Jahn-Teller type to breathing type at x = 0.4
composition.",0601117v1
2006-05-12,Hard x-ray spectroscopy in NaxCoO2 and superconducting NaxCoO2 - yH2O: A view on the bulk Co electronic properties,"The electronic properties of Co in bulk Na0.7CoO2 and the superconducting
hydrated compound Na0.35CoO2 - y H2O have been investigated by x-ray absorption
spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) using hard
x-rays. The XAS spectra at the Co K-edge were measured in both compounds with
two different polarization directions. The changes in the XAS spectra upon
hydration and their polarization dependence are well accounted for by linear
muffin- tin orbital calculations in the local density approximation. The
underlying electronic structure indicates the strong hybridization between the
Co 3d and O 2p states in both compounds, while the electron localization is
enhanced in the hydrated compound due to the increase of the Co-Co interplanar
distance. The Co K pre-edge further highlights the splitting of the d band as a
result of the crystal field effect and demonstrates the Co valency increase
when Na0.7CoO2 is hydrated. The RIXS spectra measured at the Co K-edge show an
energy loss feature around 10 eV in both compounds in fair agreement with the
calculated dynamical structure factor. The RIXS feature is associated to a
damped plasmon excitation.",0605328v1
2006-06-02,The study of nearest- and next-nearest-neighbour magnetic interactions in seven tetragonal compounds V(IV) containing linear chains and square lattices,"A new crystal chemical method was used to calculate the sign and strength not
only of the nearest-neighbor (NN)interactions, but also of the
next-nearest-neighbor (NNN) ones in tetragonal compounds Zn2(VO)(PO4)2
(I),(VO)(H2PO4)2 (II), (VO)SiP2O8 (III), (VO)SO4 (IV), (VO)MoO4 (V),
Li2(VO)SiO4 (VI) and Li2(VO)GeO4 (VII) with similar sublattices of V4+ ions on
the basis of the room-temperature structural data. The reason for difference
between respective magnetic interactions characteristics of these compounds was
established. It is shown that the characteristic feature of these compounds is
a strong dependence of the strength of magnetic interactions and the magnetic
moments ordering type on slight displacements of XO4 (X = P, Mo, Si or Ge)
groups even without change of the crystal symmetry. In addition to extensively
studied square lattice, other specific geometrical configurations of V4+ were
discovered. These configurations can result in frustration of magnetic
interactions, namely linear chains along the c-axis with competing nearest- and
next-to-nearest-neighbor interactions; rectangular (in I) and triangular (in
II-VII) lattices with non-equivalent nearest-to-neighbor interactions, which
can be also considered as n-leg ladders; one extra square lattice in the
ab-plane with longer range interactions. It was concluded that virtually all
magnetic interactions in these compounds were frustrated.",0606053v2
2006-07-05,Coexistence of open and closed gallery spaces in intercalation compounds,"A series of molybdenum disulfide intercalation compounds was prepared to
study the effect of varying loadings of the samples with intercalated
molecules. The molecules, (5,7,7,12,14,14-hexamethyl-1,4,8,11-
tetraazacyclotetradeca-4,11-diene) macrocycles, occupy the gallery spaces
between the MoS2 layers in a single layer. The samples were characterized by
thermogravimetry, wide angle X-ray scattering, scanning electron microscopy and
transmission electron microscopy (TEM). TEM images reveal the layer stacking as
the filling of the gallery spaces with macrocycles increases gradually up to
one monolayer per gallery space. Fourier transforms of these images are in
excellent agreement with the X-ray scattering of the bulk compound. X-ray
scattering by these compounds was simulated by evaluating the Debye sum for
weighted averages of model particles that have sequences of open and closed
gallery spaces. Open and closed gallery spaces coexist in the samples with less
than one monolayer of intercalated molecules per gallery space. The fraction of
open gallery spaces increases with macrocycle loading, from zero for restacked
MoS2 without macrocycles to one for a fully intercalated compound. The sequence
of open and closed spaces is approximately random, and the MoS2 layers stack
with the same orientation but with random lateral shifts. The binding enthalpy
of the macrocycles in the gallery spaces is about 14 meV.",0607131v1
2006-08-18,"YSix closely related YbT$_2$Zn$_{20}$ (T = Fe, Co, Ru, Rh, Os, Ir) heavy fermion compounds with large local moment degeneracy","Heavy fermion compounds represent one of the most strongly correlated forms
of electronic matter and give rise to low temperature states that range from
small moment ordering to exotic superconductivity, both of which are often in
close proximity to quantum critical points. These strong electronic
correlations are associated with the transfer of entropy from the local moment
degrees of freedom to the conduction electrons, and, as such, are intimately
related to the low temperature degeneracy of the (originally) moment bearing
ion. Here we report the discovery of six closely related Yb-based heavy fermion
compounds, YbT$_2$Zn$_{20}$, that are members of the larger family of dilute
rare earth bearing compounds: RT$_2$Zn$_{20}$ (T = Fe, Co, Ru, Rh, Os, Ir).
This discovery doubles the total number of Yb-based heavy fermion materials.
Given these compounds' dilute nature, systematic changes in T only weakly
perturb the Yb site and allow for insight into the effects of degeneracy on the
thermodynamic and transport properties of these model correlated electron
systems.",0608422v3
2003-01-22,Alkali and Alkaline Earth Metal Compounds: Core-Valence Basis Sets and Importance of Subvalence Correlation,"Core-valence basis sets for the alkali and alkaline earth metals Li, Be, Na,
Mg, K, and Ca are proposed. The basis sets are validated by calculating
spectroscopic constants of a variety of diatomic molecules involving these
elements. Neglect of $(3s,3p)$ correlation in K and Ca compounds will lead to
erratic results at best, and chemically nonsensical ones if chalcogens or
halogens are present. The addition of low-exponent $p$ functions to the K and
Ca basis sets is essential for smooth convergence of molecular properties.
Inclusion of inner-shell correlation is important for accurate spectroscopic
constants and binding energies of all the compounds. In basis set
extrapolation/convergence calculations, the explicit inclusion of alkali and
alkaline earth metal subvalence correlation at all steps is essential for K and
Ca, strongly recommended for Na, and optional for Li and Mg, while in Be
compounds, an additive treatment in a separate `core correlation' step is
probably sufficient. Consideration of $(1s)$ inner-shell correlation energy in
first-row elements requires inclusion of $(2s,2p)$ `deep core' correlation
energy in K and Ca for consistency. The latter requires special CCV$n$Z `deep
core correlation' basis sets. For compounds involving Ca bound to
electronegative elements, additional $d$ functions in the basis set are
strongly recommended. For optimal basis set convergence in such cases, we
suggest the sequence CV(D+3d)Z, CV(T+2d)Z, CV(Q+$d$)Z, and CV5Z on calcium.",0301056v1
2008-04-24,The Influence of A-site Ionic Radii on the Magnetic Structure of Charge Ordered La0.5Ca0.5-xSrxMnO3 Manganites,"The influence of the A-site ionic radii (<rA>) on the magnetic structure has
been investigated in La0.5Ca0.5-xSrxMnO3 compounds (0 .GE. x .LE. 0.5) using
neutron diffraction, magnetization, and resistivity techniques. All compounds
in the composition range x .LE. 0.3 crystallize in the orthorhombic structure
(Space Group Pnma). No further structural transition is observed as temperature
is lowered below 300K. The compound x = 0.4, is a mixture of two orthorhombic
phases crystallizing in Pnma and Fmmm space group. The x = 0.5 compound has a
tetragonal structure in the space group, I4/mcm. The charge ordered (CO) state
with CE-type antiferromagnetic order remains stable for x .LE. 0.3. Above x =
0.3, the CE-type antiferromagnetic state is suppressed. In x = 0.4 compound,
A-type antiferromagnetic ordering is found at temperatures below 200K. Orbital
ordering accompanying the spin ordering is found in all the samples with x .LE.
0.4. The system becomes ferromagnetic at x = 0.5 and no signature of orbital
ordering is observed. As a function of <rA>, the charge ordered state is stable
up to <rA> ~ 1.24A, and is suppressed thereafter. The magnetic structure
undergoes a transformation from CE-type antiferromagnetic state to a
ferromagnetic state with an intermediate A-type antiferromagnetic state.",0804.3923v1
2008-06-30,"The Superconducting Gap Behavior in the Antiferromagnetic Nickel-Borocarbide Compounds RNi2B2C (R=Dy, Ho, Er, Tm) Studied by Point-Contacts Spectroscopy","An general survey of the superconducting (SC) gap study in the title
compounds by point-contact (PC) spectroscopy is presented. The SC gap was
determined from dV/dI of PCs employing the well-known theory of conductivity
for normal metal-superconductor PCs accounting Andreev reflection. The theory
was modified by including pair-breaking effects considering the presence of
magnetic rare-earth ions. A possible multiband structure of these compounds was
also taken into account. The PC study of the gap in the Er-compound
(TN=6K<Tc=11K) gives =evidence for the presence of two SC gaps. Additionally, a
distinct decrease of both gaps is revealed for R = Er in the antiferromagnetic
(AF) state. For R = Tm (TN=1.5K<Tc=10.5K) a decrease of the SC gap is observed
below 4-5K, while for R = Dy (TN=10.5K>Tc=6.5K) the SC gap has a BCS-like
dependence in the AF state. The SC gap for R = Ho (TN=5.2K<Tc=8.5K) exhibits
below T*=5.6K a single-band BCS-like dependence vanishing above T*, where a
specific magnetic order occurs. The difference in the SC gap behavior in the
title compounds is attributed to different AF ordering.",0806.4814v2
2008-11-26,Synthesis of SmFeAsO by an Easy and Versatile Route and its Physical Property Characterization,"We report synthesis, structure, electrical transport and heat capacity of
SmFeAsO. The title compound is synthesized by one-step encapsulation of
stoichiometric FeAs, Sm, and Sm2O3 in an evacuated (10-5 Torr) quartz tube by
prolong (72 hours) annealing at 1100oC. The as synthesized compound is
crystallized in tetragonal structure with P4/nmm space group having lattice
parameters a = 3.93726(33) A and c = 8.49802(07) A. The resistance (R-T)
measurements on the compound exhibited ground state spin-density-wave
(SDW)-like metallic steps below 140 K. Heat capacity CP(T) measurements on the
title compound, showed an anomaly at around 140 K, which is reminiscent of the
SDW ordering of the compound. At lower temperatures the CP(T) shows a clear
peak at around 4.5 K. At lower temperature below 20 K, Cp(T) is also measured
under an applied field of 7 Tesla. It is concluded that the CP(T) peak at 4.5 K
is due to the anti-ferromagnetic(AFM) ordering of Sm3+ spins. These results are
in confirmation with ordering of Sm in Sm2-xCexCuO4.",0811.4223v2
2010-02-22,Handwritten Bangla Basic and Compound character recognition using MLP and SVM classifier,"A novel approach for recognition of handwritten compound Bangla characters,
along with the Basic characters of Bangla alphabet, is presented here. Compared
to English like Roman script, one of the major stumbling blocks in Optical
Character Recognition (OCR) of handwritten Bangla script is the large number of
complex shaped character classes of Bangla alphabet. In addition to 50 basic
character classes, there are nearly 160 complex shaped compound character
classes in Bangla alphabet. Dealing with such a large varieties of handwritten
characters with a suitably designed feature set is a challenging problem.
Uncertainty and imprecision are inherent in handwritten script. Moreover, such
a large varieties of complex shaped characters, some of which have close
resemblance, makes the problem of OCR of handwritten Bangla characters more
difficult. Considering the complexity of the problem, the present approach
makes an attempt to identify compound character classes from most frequently to
less frequently occurred ones, i.e., in order of importance. This is to develop
a frame work for incrementally increasing the number of learned classes of
compound characters from more frequently occurred ones to less frequently
occurred ones along with Basic characters. On experimentation, the technique is
observed produce an average recognition rate of 79.25 after three fold cross
validation of data with future scope of improvement and extension.",1002.4040v2
2010-03-17,Neutron scattering and scaling behavior in URu2Zn20 and YbFe2Zn20,"The dynamic susceptibility chi""(deltaE), measured by inelastic neutron
scattering measurements, shows a broad peak centered at Emax = 16.5 meV for the
cubic actinide compound URu2Zn20 and 7 meV at the (1/2, 1/2, 1/2) zone boundary
for the rare earth counterpart compound YbFe2Zn20. For URu2Zn20, the low
temperature susceptibility and magnetic specific heat coefficient gamma =
Cmag/T take the values chi = 0.011 emu/mole and gamma = 190 mJ/mole-K2 at T = 2
K. These values are roughly three times smaller, and Emax is three times
larger, than recently reported for the related compound UCo2Zn20, so that chi
and gamma scale inversely with the characteristic energy for spin fluctuations,
Tsf = Emax/kB. While chi(T), Cmag(T), and Emax of the 4f compound YbFe2Zn20 are
very well described by the Kondo impurity model, we show that the model works
poorly for URu2Zn20 and UCo2Zn20, suggesting that the scaling behavior of the
actinide compounds arises from spin fluctuations of itinerant 5f electrons.",1003.3484v1
2010-07-14,Synchrotron X-ray Diffraction Study of BaFe2As2 and CaFe2As2 at High Pressures up to 56 GPa: Ambient and Low-Temperatures Down to 33 K,"We report high pressure powder synchrotron x-ray diffraction studies on
MFe2As2 (M=Ba, Ca) over a range of temperatures and pressures up to about 56
GPa using a membrane diamond anvil cell. A phase transition to a collapsed
tetragonal phase is observed in both compounds upon compression. However, at
300 (33) K in the Ba-compound the transition occurs at 26 (29) GPa, which is a
much higher pressure than 1.7 (0.3) GPa at 300 (40) K in the Ca-compound, due
to its larger volume. It is important to note that the transition in both
compounds occurs when they are compressed to almost the same value of the unit
cell volume and attain similar ct/at ratios. We also show that the FeAs4
tetrahedra are much less compressible and more distorted in the collapsed
tetragonal phase than their nearly regular shape in the ambient pressure phase.
We present a detailed analysis of the pressure dependence of the structures as
well as equation of states in these important BaFe2As2 and CaFe2As2 compounds.",1007.2320v2
2010-08-16,"Second Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]","We have discovered a new homologous series of iron pnictide oxides
(Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]. These compounds have perovskite-like
blocking layers between Fe2As2 layers. The structure of new compounds are
tetragonal with space groups of P4/nmm for n = 2 and 4 and P4mm for n = 3,
which are similar to those of (Fe2As2)(Can+1(Sc,Ti)nOy)[n = 3,4,5] found in our
previous study. Compounds with n = 3 and 4 have new crystal structures with 3
and 4 sheets of perovskite layers, respectively, including a rock salt layer in
each blocking layer. The a-axis lengths of the three compounds are
approximately 3.8 A, which are close to those of FeSe and LiFeAs.
(Fe2As2)(Ca6(Al,Ti)4Oy) exhibited bulk superconductivity in magnetization
measurement with Tc(onset)~36 K and resistivity drop was observed at ~39 K.
(Fe2As2)(Ca5(Al,Ti)3Oy) also showed large diamagnetism at low temperatures.
These new compounds indicate considerable rooms are still remaining for new
superconductors in layered iron pnictides.",1008.2582v4
2010-09-17,"First-principles studies of Ce-doped RE2M2O7 (RE=Y,La;M=Ti,Zr,Hf): A class of non-scintillators","Lanthanum and yttrium compounds with composition RE2M2O7 (RE=Y, La; M = Ti,
Zr, Hf) have high density and high Z and can be doped with Ce onto the La and Y
sites. This makes these compounds good candidates for Ce activated scintillator
gamma-ray detectors particularly for the hafnate systems which have a very high
density. There is disagreement in the literature concerning La2Hf2O7:Ce as it
has been reported to show both bright as well as no Ce activated luminescence
by different experimental groups. We have performed first-principles electronic
structure calculations of these compounds doped with Ce using the
pseudopotential method based on the generalized gradient approximation in
density functional theory. The positions of the Ce 4f states relative to the
valence band maximum and the position of the Ce 5d states relative to the
conduction band minimum (CBM) of the host material are determined. We find,
unlike Ce activated La and Y compounds where the CBM is typically of La 5d or Y
4d character, that, in these systems the CBM is predominately of d character on
the Ti, Zr, Hf atoms. For all these compounds we also find that the Ce 5d state
lies above the CBM which would prevent any luminescence from the Ce site.",1009.3381v1
2010-09-28,Absence of Ferromagnetism in Mn-doped Tetragonal Zirconia,"In a recent letter, it has been predicted within first principle studies that
Mn-doped ZrO2 compounds could be good candidate for spintronics application
because expected to exhibit ferromagnetism far beyond room temperature. Our
purpose is to address this issue experimentally for Mn-doped tetragonal
zirconia. We have prepared polycrystalline samples of Y0.15(Zr0.85-yMny)O2
(y=0, 0.05, 0.10, 0.15 & 0.20) by using standard solid state method at
equilibrium. The obtained samples were carefully characterized by using x-ray
diffraction, scanning electron microscopy, elemental color mapping, X-ray
photoemission spectroscopy and magnetization measurements. From the detailed
structural analyses, we have observed that the 5% Mn doped compound
crystallized into two symmetries (dominating tetragonal & monoclinic), whereas
higher Mn doped compounds are found to be in the tetragonal symmetry only. The
spectral splitting of the Mn 3s core-level x-ray photoelectron spectra confirms
that Mn ions are in the Mn3+ oxidation state and indicate a local magnetic
moment of about 4.5 {\mu}B/Mn. Magnetic measurements showed that compounds up
to 10% of Mn doping are paramagnetic with antiferromagnetic interactions.
However, higher Mn doped compound exhibits local ferrimagnetic ordering. Thus,
no ferromagnetism has been observed for all Mn-doped tetragonal ZrO2 samples.",1009.5583v2
2011-11-28,"4f-hybridization effect on the magnetism of Nd2PdSi3, an anomalous magnetic compound","Among the members of the series R2PdSi3 (R= Rare-earths), the magnetic
behavior of the Nd compound is interesting in some respects. This compound is
considered to order ferromagnetically (below 16 K), unlike other members of
this series which order antiferromagnetically. In addition, magnetic ordering
temperature (To) is significantly enhanced with respect to de Gennes scaled
value. In order to understand the magnetism of this compound better, we have
investigated the magnetic behavior in detail (under external pressure as well)
and also of its solid solutions based on substitutions at Nd and at Si sites,
viz., on the series, Nd(2-x)(Y,La)(x)PdSi(3-y)Ge(y) (x, y= 0.2, 0.4, 0.8, and
1.2) by bulk measurements. The results overall establish that Nd2PdSi3 orders
ferromagnetically below 16 K, but antiferromagnetic component seems to set in
at very low temperatures. Notably, there is a significant suppression of To for
Y and Ge substitutions, compared to La substitution, for a given magnitude of
unit-cell volume change, however qualitatively correlating with the separation
between the layers of Nd and Pd-Si(Ge). On the basis of this observation, we
conclude that 4f(Nd) hybridization plays a major role on the magnetism of the
former solid solutions. To our knowledge, this work serves as a rare
demonstration of 4f-hybridization effects on the magnetism of a Nd-based
intermetallic compound.",1111.6485v1
2012-05-09,Phonons and Colossal Thermal Expansion Behavior of Ag3Co(CN)6 and Ag3Fe(CN)6,"Recently colossal positive volume thermal expansion has been found in the
framework compounds Ag3Co(CN)6 and Ag3Fe(CN)6. Phonon spectra have been
measured using the inelastic neutron scattering technique as a function of
temperature and pressure. The data has been analyzed using ab-initio
calculations. We find that the bonding is very similar in both compounds. At
ambient pressure modes in the intermediate frequency part of the vibrational
spectra in the Co compound are shifted to slightly higher energies as compared
to the Fe compound. The temperature dependence of the phonon spectra gives
evidence for large explicit anharmonic contribution to the total anharmonicity
for low-energy modes below 5 meV. We found that modes are mainly affected by
the change in the size of unit cell, which in turn changes the bond lengths and
vibrational frequencies. Thermal expansion has been calculated via the volume
dependence of phonon spectra. Our analysis indicates that Ag phonon modes in
the energy range from 2 to 5 meV are strongly anharmonic and major contributors
to thermal expansion in both compounds. The application of pressure hardens the
low-energy part of the phonon spectra involving Ag vibrations and confirms the
highly anharmonic nature of these modes.",1205.1945v1
2012-08-07,Nuclear evaporation process with simultaneous multiparticle emission,"The nuclear evaporation process is reformulated by taking into account
simultaneous multiparticle emission from a hot compound nucleus appearing as an
intermediate state in many nuclear reaction mechanisms. The simultaneous
emission of many particles is particularly relevant for high excitation energy
of the compound nucleus.These channels are effectively open in competition with
the single particle emissions and fission in this energy regime. Indeed, the
inclusion of these channels along the decay evaporating chain shows that the
yield of charged particles and occurrence of fission are affected by these
multiparticle emission processes of the compounded nucleus, when compared to
the single sequential emission results. The effect also shows a qualitative
change in the neutron multiplicity of different heavy compound nucleus
considered. This should be an important aspect for the study of spallation
reaction in Acceleration Driven System (ADS) reactors. The majority of neutrons
generated in these reactions come from the evaporation stage of the reaction,
the source of neutron for the system. A Monte Carlo simulation is employed to
determine the effect of these channels on the particle yield and fission
process. The relevance of the simultaneous particle emission with the
increasing of excitation energy of the compound nucleus is explicitly shown.",1208.1543v1
2012-08-31,Simultaneous fitting of statistical-model parameters to symmetric and asymmetric fission cross sections,"The de-excitation of compound nuclei has been successfully described for
several decades by means of statistical models. However, accurate predictions
require some fine-tuning of the model parameters. This task can be simplified
by studying several entrance channels, which populate different regions of the
parameter space of the compound nucleus.
  Fusion reactions play an important role in this strategy because they
minimise the uncertainty on the entrance channel by fixing mass, charge and
excitation energy of the compound nucleus. If incomplete fusion is negligible,
the only uncertainty on the compound nucleus comes from the spin distribution.
However, some de-excitation channels, such as fission, are quite sensitive to
spin. Other entrance channels can then be used to discriminate between
equivalent parameter sets.
  The focus of this work is on fission and intermediate-mass-fragment emission
cross sections of compound nuclei with 70<=A<=240. The statistical
de-excitation model is GEMINI++. The choice of the observables is natural in
the framework of GEMINI++, which describes fragment emission using a
fission-like formalism. Equivalent parameter sets for fusion reactions can be
resolved using the spallation entrance channel. This promising strategy can
lead to the identification of a minimal set of physical ingredients necessary
for a unified quantitative description of nuclear de-excitation.",1208.6520v1
2013-09-01,Xe anions in stable Mg-Xe compounds: the mechanism of missing Xe in earth atmosphere,"The reactivity of noble gas elements is important for both fundamental
chemistry and geological science. The discovery of the oxidation of Xe extended
the doctrinal boundary of chemistry that a complete shell is inert to reaction.
The oxidations of Xe by various geological substances have been researched in
order to explain the missing Xe in earth atmosphere. Among many proposals, the
chemistry mechanisms are straightforward as they identify chemical processes
that can capture Xe in earth interior. However, all the mechanisms based on
current noble gas chemistry face the same difficulty: the earth lower mantle
and core are rich in metals and therefore their chemical environment is
reductive. On the other hand, up till now, the opposite chemical inclination,
the reductive propensity, i.e. gaining electrons and forming anions, has not
been proposed and examined for noble gas elements. In this work, we
demonstrate, using first principles calculations and an efficient structure
prediction method, that Xe and Kr can form stable MgXe and MgKr compounds under
high pressure. These compounds are intermetallic and Xe or Kr is negatively
charged. We also find that elevated temperature has large effect in stabilizing
MgXe and MgKr compounds. Our results show that the earth has the capability of
capturing Xe but not Kr, which is consistent to the depletion of Xe in earth
atmosphere. The stability of these compounds suggests that chemical species
with completely filled shell may still gain more electrons filling their outer
shell in chemical reactions.",1309.0696v2
2013-10-01,The Strain Derivatives of $T_c$ in HgBa$_2$CuO$_{4+δ}$: CuO$_2$ Plane Alone is Not Enough,"The strain derivatives of $T_c$ along the $a$ and $c$ axes have been
determined for HgBa$_2$CuO$_{4+\delta}$ (Hg1201), the simplest monolayer
cuprate with the highest $T_c$ of all monolayer cuprates ($T_c$ = 97 K at
optimal doping). The underdoped compound with the initial $T_c$ of 65 K has
been studied as a function of pressure up to 20 GPa by magnetic susceptibility
and X-ray diffraction (XRD). The observed linear increase in $T_c$ with
pressure is the same as previously been found for the optimally-doped compound.
The above results have enabled the investigation of the origins of the
significantly different $T_c$ values of optimally doped Hg1201 and the
well-studied compound La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO), the latter value of
$T_c$ = 40 K being only about 40% of the former. Hg1201 can have almost
identical CuO$_6$ octahedra as LSCO if specifically strained. When the apical
and in-plane CuO$_2$ distances are the same for the two compounds, a large
discrepancy in their $T_c$ remains. Differences in crystal structures and
interactions involving the Hg-O charge reservoir layers of Hg1201 may be
responsible for the different $T_c$ values exhibited by the two compounds.",1310.0148v2
2013-12-13,"Physical properties of the thermoelectric cubic lanthanum chalcogenides La3-yX4 (X=S,Se,Te) from first-principles","We report ab-initio calculations of the stability, lattice dynamics,
electronic and thermoelectric properties of cubic La3-yX4 (X=S,Se,Te) materials
in view of analyzing their potential for thermoelectric applications. The
lanthanum motions are strongly coupled to the tellurium motions in the
telluride, whereas the motions of both types of atoms are decoupled in the
sulfides. Nevertheless, this has no impact on their thermal properties because
experimentally all compounds have low thermal conductivity. We believe that
this is due to Umklapp scattering of the acoustical modes, notably by the low
energy optical modes at about 7-8 meV found in all three chalcogenides, as in
cage compounds such as skutterudites or clathrates, even though there are no
cages in the cubic Th3P4 structure. We find that the energy bandgap increases
from the telluride to the sulfide in good agreement with the experiments.
However, due to their similar band structure, we find that all three compounds
have almost identical thermoelectric properties. Our results agree
qualitatively with the experiments, especially in the case of the telluride for
which a great amount of data exists. All our results indicate that the sulfides
have strong potential for thermoelectricity and could replace the tellurides if
the charge carrier concentration is optimized. Finally, we predict also a
larger maximum ZT for the p-type doped materials than for the n-type doped
ones, even though compounds with p-doping have still to be synthesized. Thus
our results indicate the possibility to make high temperature performing
thermo-generators based only on La3X4 compounds.",1312.3778v1
2014-02-17,Pressure decoupled magnetic and structural transitions of the parent compound of iron based 122 superconductors BaFe2As2,"The recent discovery of iron ferropnictide superconductors has received
intensive concerns on magnetic involved superconductors. Prominent features of
ferropnictide superconductors are becoming apparent: the parent compounds
exhibit antiferromagnetic (AFM) ordered spin density wave (SDW) state; the
magnetic phase transition is always accompanied to a crystal structural
transition; superconductivity can be induced by suppressing the SDW phase via
either chemical doping or applied external pressure to the parent state. These
features generated considerable interests on the interplay between magnetism
and structure in chemical doped samples, showing crystal structure transitions
always precedes to or coincide with magnetic transition. Pressure tuned
transition on the other hand would be more straightforward to superconducting
mechanism studies since there are no disorder effects caused by chemical
doping; however, remarkably little is known about the interplay in the parent
compounds under controlled pressure due to the experimental challenge of in
situ measuring both of magnetic & crystal structure evolution at high pressure
& low temperatures. Here we show from combined synchrotron Mossbauer and x-ray
diffraction at high pressures that the magnetic ordering surprisingly precedes
the structural transition at high pressures in the parent compound BaFe2As2, in
sharp contrast to the chemical doping case. The results can be well understood
in terms of the spin fluctuations in the emerging nematic phase before the long
range magnetic order that sheds new light on understanding how parent compound
evolves from a SDW state to a superconducting phase, a key scientific inquiry
of iron based superconductors.",1402.4086v1
2014-04-30,Synthesis and Pharmacology of Ester Modified (+/-)-threo-Methylphenidate Analogs,"As part of a program to develop compounds with potential to treat cocaine
abuse, eleven (+/-)-threo-methylphenidate (TMP; Ritalin) derivatives were
synthesized and tested in rat striatal tissue preparations for inhibitory
potency against [3H]WIN 35,428 binding (WIN) to the dopamine (DA) transporter,
[3H]citalopram binding (CIT) to the serotonin transporter, and [3H]DA uptake.
The ester function was replaced by other functional groups in all of the
compounds; some also contained substituents on the phenyl ring and/or the
piperidine nitrogen. Potencies against WIN, measured as IC50, ranged from 27 nM
to 7,000 nM, compared to an IC50 of 83 nM for TMP itself. Potency against
[3H]DA uptake was approximately two-fold less than that against WIN, but
generally exhibited the same rank order. With one exception, the compounds were
significantly less potent against CIT than WIN. The one exception, which has a
rigid planar conformation at the altered ester position, is unique in that it
also is much less potent against [3H]DA uptake relative to WIN, compared to the
other derivatives. The three compounds with dichloro groups on the phenyl ring
did not exhibit positive cooperativity, as has been observed with several
previously synthesized halogenated TMP derivatives. Taken together, these
compounds should help to further our understanding of the stimulant binding
sites on both the dopamine and serotonin transporters.",1404.7842v1
2015-01-09,Single crystal study of layered U$_{n}$RhIn$_{3n+2}$ materials: case of the novel U$_{2}$RhIn$_{8}$ compound,"We report on the single crystal properties of the novel U$_{2}$RhIn$_{8}$
compound studied in the context of parent URhIn$_{5}$ and UIn$_{3}$ systems.
The compounds were prepared by In self-flux method. U$_{2}$RhIn$_{8}$ adopts
the Ho$_{2}$CoGa$_{8}$-type structure with lattice parameters a $= 4.6056(6)$
\AA\ and c $= 11.9911(15)$ \AA. The behavior of U$_{2}$RhIn$_{8}$ strongly
resembles that of the related URhIn$_{5}$ and UIn$_{3}$ with respect to
magnetization, specific heat and resistivity except for magnetocrystalline
anisotropy developing with lowering dimensionality in the series UIn$_{3}$ vs.
U$_{2}$RhIn$_{8}$ and URhIn$_{5}$. U$_{2}$RhIn$_{8}$ orders
antiferromagnetically below T$_{\textrm{N}}$ $= 117$ K and exhibits a slightly
enhanced Sommerfeld coefficient $\gamma = 47$ mJ$\cdot$mol$^{-1}\cdot$K$^{-2}$.
Magnetic field leaves the value of N\'{e}el temperature for both URhIn$_{5}$
and U$_{2}$RhIn$_{8}$ unaffected up to 9 T. On the other hand, T$_{\textrm{N}}$
is increasing with applying hydrostatic pressure up to 3.2 GPa. The weak
temperature dependence of $\chi(T)$ in all studied compounds might be
attributed to the mainly itinerant nature of 5f electrons. The character of
uranium 5f electron states of U$_{2}$RhIn$_{8}$ was studied by first principles
calculations based on the density functional theory. The overall phase diagram
of U$_{2}$RhIn$_{8}$ is discussed in the context of magnetism in the related
URhX$_{5}$ and UX$_{3}$ (X = In, Ga) compounds.",1501.02154v1
2015-08-06,Emergence of novel hydrogen chlorides under high pressure,"HCl, a 'textbook' example of a polar covalent molecule, is a well-known
compound of hydrogen and chlorine. Inspired by the discovery of unexpected
stable stoichiometries of sodium chlorides, we performed systematic searches
for all stable compounds in the H-Cl system from ambient pressure to higher
pressures up to 500 GPa using variable-composition ab initio evolutionary
algorithm USPEX. We found several compounds that are stable under pressure,
i.e. HCl, H$_2$Cl, H$_3$Cl, H$_5$Cl and H$_4$Cl$_7$, which display a rich
variety of chemical bonding types. At ambient pressure, H$_2$, Cl$_2$ and HCl
molecular crystals are formed by weak intermolecular van der Waals interactions
and adjacent HCl molecules connect with each other to form asymmetric zigzag
chains, which become symmetric under high pressure. In hydrogen-rich chlorides,
H$_2$ and HCl react to form the thermodynamically stable H$_3$Cl crystalline
compound in which molecular cyclic H$_3^+$ cations are stabilised by the Cl$^-$
sublattice. Increasing the amount of hydrogen leads to stable solid-state
H$_5$Cl, in which H$_2$ formally combines with H$_3^+$ to form H$_5^+$ cations.
Additionally, chlorine-based Kagom\'e layers are formed with intercalated
zigzag HCl chains in chlorine-rich hydrides. These discoveries help to
understand how varied bonding features can co-exist and evolve in one compound
under extreme conditions.",1508.01395v1
2015-10-11,Prediction of novel stable compounds in the Mg-Si-O system under exoplanet pressures,"The Mg-Si-O system is the major Earth and rocky planet-forming system. Here,
through quantum variable-composition evolutionary structure explorations, we
have discovered several unexpected stable binary and ternary compounds in the
Mg-Si-O system. Besides the well-known SiO2 phases, we have found two
extraordinary silicon oxides, SiO3 and SiO, which become stable at pressures
above 0.51 TPa and 1.89 TPa, respectively. In the Mg-O system, we have found
one new compound, MgO3, which becomes stable at 0.89 TPa. We find that not only
the (MgO)x(SiO2)y compounds, but also two (MgO3)x(SiO3)y compounds, MgSi3O12
and MgSiO6, have stability fields above 2.41 TPa and 2.95 TPa, respectively.
The highly oxidized MgSi3O12 can form in deep mantles of mega-Earths with
masses above 20 M+ (M+:Earth's mass). Furthermore, the dissociation pathways of
pPv-MgSiO3 are also clarified, and found to be different at low and high
temperatures. The low-temperature pathway is MgSiO3 -> Mg2SiO4 + MgSi2O5 ->
SiO2 + Mg2SiO4 -> MgO + SiO2, while the high-temperature pathway is MgSiO3 ->
Mg2SiO4 + MgSi2O5 -> MgO + MgSi2O5 -> MgO + SiO2. Present results are relevant
for models of the internal structure of giant exoplanets, and for understanding
the high-pressure behavior of materials.",1510.03061v1
2015-10-13,Atomically thin binary V-V compound semiconductor: a first-principles study,"Searching the novel 2D semiconductor is crucial to develop the
next-generation low-dimensional electronic device. Using first-principles
calculations, we propose a class of unexplored binary V-V compound
semiconductor (PN, AsN, SbN, AsP, SbP and SbAs) with monolayer black
phosphorene ($\alpha$) and blue phosphorene ($\beta$) structure. Our phonon
spectra and room-temperature molecular dynamics (MD) calculations indicate that
all compounds are very stable. Moreover, most of compounds are found to present
a moderate energy gap in the visible frequency range, which can be tuned
gradually by in-plane strain. Especially, $\alpha$-phase V-V compounds have a
direct gap while $\beta$-SbN, AsN, SbP, and SbAs may be promising candidates of
2D solar cell materials due to a wide gap separating acoustic and optical
phonon modes. Furthermore, vertical heterostructures can be also built using
lattice matched $\alpha$($\beta$)-SbN and phosphorene, and both vdW
heterostructures are found to have intriguing direct band gap. The present
investigation not only broads the scope of layered group V semiconductors but
also provides an unprecedented route for the potential applications of 2D V-V
families in optoelectronic and nanoelectronic semiconductor devices.",1510.04108v5
2015-11-04,Asymptotic Approximations for TCP Compound,"In this paper, we derive an approximation for throughput of TCP Compound
connections under random losses. Throughput expressions for TCP Compound under
a deterministic loss model exist in the literature. These are obtained assuming
the window sizes are continuous, i.e., a fluid behaviour is assumed. We
validate this model theoretically. We show that under the deterministic loss
model, the TCP window evolution for TCP Compound is periodic and is independent
of the initial window size. We then consider the case when packets are lost
randomly and independently of each other. We discuss Markov chain models to
analyze performance of TCP in this scenario. We use insights from the
deterministic loss model to get an appropriate scaling for the window size
process and show that these scaled processes, indexed by p, the packet error
rate, converge to a limit Markov chain process as p goes to 0. We show the
existence and uniqueness of the stationary distribution for this limit process.
Using the stationary distribution for the limit process, we obtain
approximations for throughput, under random losses, for TCP Compound when
packet error rates are small. We compare our results with ns2 simulations which
show a good match.",1511.01344v4
2016-01-25,"Synthesis, crystal structure, and magnetic properties of RE3Sb3Mg2O14 (RE=La, Pr, Sm, Eu, Tb, Ho): new 2D Kagome materials","We present the crystal structures and magnetic properties of RE3Sb3Mg2O14
(La3Sb3Mg2O14, Pr3Sb3Mg2O14, Sm3Sb3Mg2O14, Eu3Sb3Mg2O14, Tb3Sb3Mg2O14, and
Ho3Sb3Mg2O14), a family of novel materials based on a perfect geometry 2D rare
earth Kagome lattice. Structure refinements were performed by the Rietveld
method using X-ray diffraction data, indicating that the layered compounds are
fully structurally ordered. The compounds crystallize in a rhombohedral
supercell of the cubic pyrochlore structure, in the space group R-3m. As
indicated by magnetic susceptibility measurements, they exhibit predominantly
antiferromagnetic interactions between rare earth moments. Except for possibly
Pr3Sb3Mg2O14 and Eu3Sb3Mg2O14, none of the compounds show any signs of magnetic
ordering above 2 K. This RE3Sb3Mg2O14 family of compounds is similar to that of
RE3Sb3Zn2O14, except the series reported here features a fully ordered
distribution of cations in both the nonmagnetic antimony and magnesium sites
and the magnetic rare earth kagome sites. The compounds appear to be relatively
defect-free and are therefore model systems for investigating magnetic
frustration on an ideal 2D rare earth Kagome lattice.",1601.06639v2
2016-02-22,Structure and magnetic properties of {\it Ln}MnSbO ({\it Ln} = La and Ce) and CeMnAsO,"Neutron powder diffraction (NPD) study of \textit{Ln}MnSbO (\textit{Ln }$=$
La or Ce) reveals differences between the magnetic ground state of the two
compounds due to the strong Ce-Mn coupling compared to La-Mn. The two compounds
adopt the \textit{P4/nmm} space group down to 2 K and whereas magnetization
measurements do not show obvious anomaly at high temperatures, NPD reveals a
C-type antiferromagnetic (AFM) order below $T_{\mathrm{N}} = 255 $ K for
LaMnSbO and 240 K for CeMnSbO. While the magnetic structure of LaMnSbO is
preserved to base temperature, a sharp transition at $T_{\mathrm{SR}} = 4.5 $K
is observed in CeMnSbO due to a spin-reorientation (SR) transition of the
Mn$^{\mathrm{2+}}$ magnetic moments from pointing along the $c$-axis to the
\textit{ab}-plane. The SR transition in CeMnSbO is accompanied by a
simultaneous long-range AFM ordering of the Ce moments which indicates that the
Mn SR transition is driven by the Ce-Mn coupling. The ordered moments are found
to be somewhat smaller than those expected for Mn$^{\mathrm{2+}}$ ($S = 5/2$)
in insulators, but large enough to suggest that these compounds belong to the
class of local-moment antiferromagnets. The lower $T_{\mathrm{N\thinspace }}$
found in these two compounds compared to the As-based counterparts
($T_{\mathrm{N}} = 317$ for LaMnAsO, $T_{\mathrm{N}} = 347$ K for CeMnAsO)
indicates that the Mn-$Pn$ ($Pn=$ As or Sb) hybridization that mediates the
superexchange Mn-$Pn$-Mn coupling is weaker for the Sb-based compounds.",1602.06993v1
2016-05-04,Investigation of the Thermoelectric Properties of ZnV$_{2}$O$_{4}$ Compound in High Temperature Region,"In the present work, we report the experimental thermopower ($\alpha$) data
for ZnV$_{2}$O$_{4}$ compound in the high temperature range 300-600 K. The
value of $\alpha$ is found to be $\sim$184 and $\sim$126 $\mu$V/K at $\sim$300
and $\sim$600 K, respectively. The temperature dependent behavior of $\alpha$
is almost linear in the measured temperature range. To understand the large and
positive $\alpha$ value observed in this compound, we have also investigated
the electronic and thermoelectric properties by combining the
\textit{ab-initio} electronic structures calculations with Boltzmann transport
theory. Within the local spin density approximation plus Hubbard U, the
anti-ferromagnetic ground state calculation gives an energy gap $\sim$0.33 eV
for U=3.7 eV, which is in accordance with the experimental results. The
effective mass for holes in the valance band is found nearly four times that of
electrons in conduction band. The large effective mass of holes are mainly
responsible for the observed positive and large $\alpha$ value in this
compound. There is reasonably good matching between calculated and experimental
$\alpha$ data in the temperature range 300-410 K. The power factor calculation
shows that thermoelectric properties in high temperature region can be enhanced
by tuning the sample synthesis conditions and suitable doping. The estimated
value of \textit{figure-of-merit}, ZT, at different absolute temperature
suggest that ZnV$_{2}$O$_{4}$ compound can be a good thermoelectric material in
high temperature range.",1605.01428v2
2016-09-11,"Crystal structure and anisotropic magnetic properties of new ferromagnetic Kondo lattice compound Ce(Cu,Al,Si)2","Single crystals of the new compound CeCu0.18Al0.24Si1.58 have been grown by
high-temperature solution growth method using a eutectic Al-Si mixture as flux.
This compound is derived from the binary CeSi2 (tetragonal ThSi2-type, Pearson
symbol tI12, space group I41/amd) obtained by partial substitution of Si by Cu
and Al atoms but showing full occupation of the Si crystal site (8e). While
CeSi2 is a well-known valence-fluctuating paramagnetic compound, the
CeCu0.18Al0.24Si1.58 phase orders ferromagnetically at TC = 9.3 K. At low
temperatures the easy-axis of magnetization is along the a-axis, which
re-orients itself along the c-axis above 30 K. The presence of hysteresis in
the magnetization curve, negative temperature coefficient of resistivity at
high temperatures, reduced jump in the heat capacity and a relatively lower
entropy released up to the ordering temperature, and enhanced Sommerfeld
coefficient (~100 mJ/mol K2) show that CeCu0.18Al0.24Si1.58 is a Kondo lattice
ferromagnetic, moderate heavy fermion compound. Analysis of the high
temperature heat capacity data in the paramagnetic region lets us infer that
the crystal electric field split doublet levels are located at 178 and 357 K,
respectively, and Kondo temperature (8.4 K) is of the order of TC in
CeCu0.18Al0.24Si1.58.",1609.03166v1
2017-03-06,Computational Search for Novel Hard Chromium-Based Materials,"Nitrides, carbides and borides of transition metals are an attractive class
of hard materials. Our recent preliminary explorations of the binary chemical
compounds indicated that chromium-based materials are among the hardest
transition metal compounds. Motivated by this, here we explore in detail the
binary Cr-B, Cr-C and Cr-N systems using global optimization techniques.
Calculated enthalpy of formation and hardness of predicted materials were used
for Pareto optimization to define the hardest materials with lowest energy. Our
calculations recover all numerous known stable compounds (except $Cr_{23}C_6$
with its large unit cell) and discover a novel stable phase $Pmn2_1$-$Cr_2C$.
We resolve the structure of $Cr_2N$ and find it to be of anti-$CaCl_2$ type
(space group Pnnm). Many of these phases possess remarkable hardness, but only
$CrB_4$ is superhard (Vickers hardness 48 GPa). Among chromium compounds,
borides generally possess highest hardnesses and greatest stability. Under
pressure, we predict stabilization of a TMDC-like phase of $Cr_2N$, a WC-type
phase of CrN, and a new compound $CrN_4$. Nitrogen-rich chromium nitride
$CrN_4$ is a high energy-density material featuring polymeric nitrogen chains.
In the presence of metal atoms polymerization of nitrogen takes place at much
lower pressures: $CrN_4$ becomes stable at 15 GPa.",1703.02115v1
2017-09-07,Importance of elastic finite-size effects: neutral defects in ionic compounds,"Small system sizes are a well known source of error in DFT calculations, yet
computational constraints frequently dictate the use of small supercells, often
as small as 96 atoms in oxides and compound semiconductors. In ionic compounds,
electrostatic finite size effects have been well characterised, but
self-interaction of charge neutral defects is often discounted or assumed to
follow an asymptotic behaviour and thus easily corrected with linear elastic
theory. Here we show that elastic effects are also important in the description
of defects in ionic compounds and can lead to qualitatively incorrect
conclusions if inadequately small supercells are used; moreover, the spurious
self-interaction does not follow the behaviour predicted by linear elastic
theory. Considering the exemplar cases of metal oxides with fluorite structure,
we show that numerous previous studies, employing 96-atom supercells,
misidentify the ground state structure of (charge neutral) Schottky defects. We
show that the error is eliminated by employing larger cells (324, 768 and 1500
atoms), and careful analysis determines that elastic effects, not
electrostatic, are responsible. The spurious self-interaction was also observed
in non-oxide ionic compounds and irrespective of the computational method used,
thereby resolving long standing discrepancies between DFT and force-field
methods, previously attributed to the level of theory. The surprising magnitude
of the elastic effects are a cautionary tale for defect calculations in ionic
materials, particularly when employing computationally expensive methods or
when modelling large defect clusters. We propose two computationally
practicable methods to test the magnitude of the elastic self-interaction in
any ionic system.",1709.02037v1
2018-03-04,Pressure-stabilized binary compounds of magnesium and silicon,"The family of binary compounds composed of magnesium and silicon is rather
rich. In addition to the well-known magnesium silicide Mg$_2$Si, other
compounds, including MgSi$_2$, Mg$_4$Si$_7$, Mg$_5$Si$_6$, MgSi, and
Mg$_9$Si$_5$, have also been identified and/or proposed in precipitated
Al-Mg-Si solid solutions. Nevertheless, computational studies show that only
Mg$_2$Si is thermodynamically stable at ambient conditions while certain
non-zero hydrostatic pressure can stabilize Mg$_9$Si$_5$ so that it can
co-exist with Mg$_2$Si. We conduct a comprehensive search for viable binary
compounds of Mg$_x$Si$_{1-x}$ ($1/3\leq x \leq 2/3$), discovering numerous new
structures for all the compounds. On the one hand, we find that MgSi$_2$, MgSi,
and Mg$_9$Si$_5$ are likely pressure-stabilized materials, while, on the other
hand, supporting previous studies, raising doubt on the existence of
Mg$_5$Si$_6$, and claiming that the existence of Mg$_4$Si$_7$ remains an open
question. Therefore, we recommend that (hydrostatic and/or non-hydrostatic)
pressure should be explicitly considered when discussing the stability of these
solids (and maybe other solids as well) by computations. We also find that
MgSi$_2$ can potentially exhibit superconducting behaviors within a wide range
of pressure with the critical temperature of up to $7$ K.",1803.01279v1
2018-05-25,Drug-membrane permeability across chemical space,"Unraveling the relation between the chemical structure of small drug-like
compounds and their rate of passive permeation across lipid membranes is of
fundamental importance for pharmaceutical applications. The elucidation of a
comprehensive structure-permeability relationship expressed in terms of a few
molecular descriptors is unfortunately hampered by the overwhelming number of
possible compounds. In this work, we reduce a priori the size and diversity of
chemical space to solve an analogous---but smoothed out---structure-property
relationship problem. This is achieved by relying on a physics-based
coarse-grained model that reduces the size of chemical space, enabling a
comprehensive exploration of this space with greatly reduced computational
cost. We perform high-throughput coarse-grained (HTCG) simulations to derive a
permeability surface in terms of two simple molecular descriptors---bulk
partitioning free energy and pKa. The surface is constructed by exhaustively
simulating all coarse-grained compounds that are representative of small
organic molecules (ranging from 30 to 160 Da) in a high-throughput scheme. We
provide results for acidic, basic and zwitterionic compounds. Connecting back
to the atomic resolution, the HTCG predictions for more than 500,000 compounds
allow us to establish a clear connection between specific chemical groups and
the resulting permeability coefficient, enabling for the first time an inverse
design procedure. Our results have profound implications for drug synthesis:
the predominance of commonly-employed chemical moieties narrows down the range
of permeabilities.",1805.10158v2
2018-05-28,Evidence for Multiple Underlying Fermi Surface and Isotropic Energy Gap in the Cuprate Parent Compound Ca$_2$CuO$_2$Cl$_2$,"The parent compounds of the high-temperature cuprate superconductors are Mott
insulators. It has been generally agreed that understanding the physics of the
doped Mott insulators is essential to understanding the mechanism of high
temperature superconductivity. A natural starting point is to elucidate the
basic electronic structure of the parent compound. Here we report comprehensive
high resolution angle-resolved photoemission measurements on
Ca$_2$CuO$_2$Cl$_2$, a Mott insulator and a prototypical parent compound of the
cuprates. Multiple underlying Fermi surface sheets are revealed for the first
time. The high energy waterfall-like band dispersions exhibit different
behavior near the nodal and antinodal regions. Two distinct energy scales are
identified: a d-wave-like low energy peak dispersion and a nearly isotropic
lower Hubbard band gap. These observations provide new information on the
electronic structure of the cuprate parent compound, which is important for
understanding the anomalous physical properties and superconductivity mechanism
of the high temperature cuprate superconductors.",1805.10991v1
2018-11-16,PaccMann: Prediction of anticancer compound sensitivity with multi-modal attention-based neural networks,"We present a novel approach for the prediction of anticancer compound
sensitivity by means of multi-modal attention-based neural networks (PaccMann).
In our approach, we integrate three key pillars of drug sensitivity, namely,
the molecular structure of compounds, transcriptomic profiles of cancer cells
as well as prior knowledge about interactions among proteins within cells. Our
models ingest a drug-cell pair consisting of SMILES encoding of a compound and
the gene expression profile of a cancer cell and predicts an IC50 sensitivity
value. Gene expression profiles are encoded using an attention-based encoding
mechanism that assigns high weights to the most informative genes. We present
and study three encoders for SMILES string of compounds: 1) bidirectional
recurrent 2) convolutional 3) attention-based encoders. We compare our devised
models against a baseline model that ingests engineered fingerprints to
represent the molecular structure. We demonstrate that using our
attention-based encoders, we can surpass the baseline model. The use of
attention-based encoders enhance interpretability and enable us to identify
genes, bonds and atoms that were used by the network to make a prediction.",1811.06802v2
2019-11-14,"Minimal model for the magnetic phase diagram of CeTi$_{1-x}$Sc$_{x}$Ge, GdFe$_{1-x}$Co$_{x}$Si, and related materials","We present a theoretical analysis of the magnetic phase diagram of
CeTi$_{1-x}$Sc$_{x}$Ge and GdFe$_{1-x}$Co$_{x}$Si as a function of the
temperature and the Sc and Co concentration $x$, respectively. CeScGe and
GdCoSi, as many other RTX (R=rare earth, T=transition metal, X=p-block element)
compounds, present a tetragonal crystal structure where bilayers of R are
separated by layers of T and X. While GdFeSi and CeTi$_{0.75}$Sc$_{0.25}$Ge are
ferromagnetic, CeScGe and GdCoSi order antiferromagnetically with the R 4f
magnetic moments on the same bilayer aligned ferromagnetically and magnetic
moments in nearest neighbouring bilayers aligned antiferromagnetically. The
antiferromagnetic transition temperature $T_N$ decreases with decreasing
concentration $x$ in both compounds and for low enough values of $x$ the
compounds show a ferromagnetic behavior. Based on these observations we
construct a simplified model Hamiltonian that we solve numerically for the
specific heat and the magnetization. We find a good qualitative agreement
between the model and the experimental data. Our results show that the main
magnetic effect of the Sc $\to$ Ti and Co $\to$ Fe substitution in these
compounds is consistent with a change in the sign of the exchange coupling
between magnetic moments in neighbouring bilayers. We expect a similar
phenomenology for other magnetic RTX compounds with the same type of crystal
structure.",1911.06235v1
2021-07-11,Magnetic frustration and paramagnetic state transport anomalies in Ho4RhAl and Er4RhAl: Possible test cases for newly identified roles of itinerant electrons,"We report the results of magnetic, heat-capacity, electrical and
magnetoresistance measurements on Ho4RhAl and Er4RhAl, characterized by 3 sites
for rare-earths (R). Antiferromagnetic ordering sets in at (T_N =) about 8.8
and 4.0 K respectively. While Ho compound appears to enter into a complex
spin-glass phase at T less thanT_N (at nearly 5 K), spin-glass component
appears to set in essentially almost at T_N for the Er case. The loss of the
spin-disorder contribution in the magnetically ordered state is not pronounced,
mimicking that in Gd2PdSi3, a compound which now attracts interest in the area
of topological Hall effect and magnetic skyrmions, indicating complex Fermi
surface. There is a minimum in the temperature dependence of electrical
resistivity in the case of only Ho above T_N, but significant negative
magnetoresistance is observed over a wide temperature range in the paramagnetic
state increasing with decreasing temperature for both the cases. This finding
establishes that these compounds belong to a select group of intermetallics in
which spin-disorder contribution apparently increases gradually as one
approaches respective TN with decreasing temperature. This could be an
experimental signature for the effect due to classical spin-liquid above T_N.
In view of these properties analogous to those of Gd2PdSi3, it is of interest
to investigate these 4:1:1 compounds further to understand possible
unconventional roles of itinerant electrons, not only in the magnetically
ordered state but also in the paramagnetic state, predicted by some theories in
recent years for which this Gd compound is considered to be a classic
example.Besides, magnetoresistance and isothermal entropy change
(magnetocaloric effect) track each other.",2107.04981v1
2021-07-29,Superionic silica-water and silica-hydrogen compounds under high pressure,"Silica, water and hydrogen are known to be the major components of celestial
bodies, and have significant influence on the formation and evolution of giant
planets, such as Uranus and Neptune. Thus, it is of fundamental importance to
investigate their states and possible reactions under the planetary conditions.
Here, using advanced crystal structure searches and first-principles
calculations in the Si-O-H system, we find that a silica-water compound
(SiO2)2(H2O) and a silica-hydrogen compound SiO2H2 can exist under high
pressures above 450 and 650 GPa, respectively. Further simulations reveal that,
at high pressure and high temperature conditions corresponding to the interiors
of Uranus and Neptune, these compounds exhibit superionic behavior, in which
protons diffuse freely like liquid while the silicon and oxygen framework is
fixed as solid. Therefore, these superionic silica-water and silica-hydrogen
compounds could be regarded as important components of the deep mantle or core
of giants, which also provides an alternative origin for their anomalous
magnetic fields. These unexpected physical and chemical properties of the most
common natural materials at high pressure offer key clues to understand some
abstruse issues including demixing and erosion of the core in giant planets,
and shed light on building reliable models for solar giants and exoplanets.",2107.13728v1
2017-05-03,Prefer Nested Segmentation to Compound Segmentation,"Introduction: Intra-organ radiation dose sensitivity is becoming increasingly
relevant in clinical radiotherapy. One method for assessment involves
partitioning delineated regions of interest and comparing the relative
contributions or importance to clinical outcomes. We show that an intuitive
method for dividing organ contours, compound (sub-)segmentation, can
unintentionally lead to sub-segments with inconsistent volumes, which will bias
relative importance assessment. An improved technique, nested segmentation, is
introduced and compared. Methods: Clinical radiotherapy planning parotid
contours from 510 patients were segmented. Counts of radiotherapy dose matrix
voxels interior to sub-segments were used to determine the equivalency of
sub-segment volumes. The distribution of voxel counts within sub-segments were
compared using Kolmogorov-Smirnov tests and characterized by their dispersion.
Analytical solutions for 2D/3D analogues were derived and sub-segment
area/volume were compared directly. Results: Both parotid and 2D/3D region of
interest analogue segmentation confirmed compound segmentation intrinsically
produces sub-segments with volumes that depend on the region of interest shape
and selection location. Significant volume differences were observed when
sub-segmenting parotid contours into 18ths, and vanishingly small sub-segments
were observed when sub-segmenting into 96ths. Central sub-segments were
considerably smaller than sub-segments on the periphery. Nested segmentation
did not exhibit these shortcomings and produced sub-segments with equivalent
volumes when dose grid and contour collinearity was addressed, even when
dividing the parotid into 96ths. Nested segmentation was always faster or
equivalent in runtime to compound segmentation. Conclusions: Nested
segmentation is more suited than compound segmentation for analyses requiring
equal weighting of sub-segments.",1705.01643v1
2017-05-14,"Magnetic behavior of metallic kagome lattices, Tb3Ru4Al12 and Er3Ru4Al12","We report magnetic behavior of two intermetallics-based kagome lattices,
Tb3Ru4Al12 and Er3Ru4Al12, crystallizing in the Gd3Ru4Al12-type hexagonal
crystal structure, by measurements in the range 1.8-300 K with bulk
experimental techniques (ac and dc magnetization, heat-capacity and
magnetoresistance). The main finding is that the Tb compound, known to order
antiferromagnetically below (T_N=) 22 K, shows glassy characteristics at lower
temperatures (<15K), thus characterizing this compound as a re-entrant
spin-glass. The data reveal that glassy phase is quite complex and is of a
cluster type. Since the glassy behavior was not seen for the Gd analogue in the
past literature, this finding for the Tb compound emphasizes that this kagome
family could provide an opportunity to explore the role of higher order (such
as quadrupole) in bringing out magnetic frustration. Additional findings
reported here for this compound are: (i) The temperature dependence of magnetic
susceptibility and electrical resistivity in the range 12 - 20 K are found to
be hysteretic leading to a magnetic phase in this temperature range, mimicking
disorder-induced first-order magnetic phase-transition. (ii) Features
attributable to an interesting magnetic phase co-existence phenomenon in the
magnetoresistance in zero field, after cycling across metamagnetic transition
fields, are observed. With respect to the Er compound, we do not find any
evidence for long-range magnetic ordering down to 2 K, but this appears to be
on the verge of magnetic order at 2 K.",1705.04921v2
2018-10-09,Unexpected Xe cations and superconductivity in Y-Xe compounds under pressure,"The metal-based noble gas compounds exhibit interesting behavior of
electronic valence states under pressure. For example, Xe upon compression can
gain electrons from the alkali metal, or lose electrons unexpectedly to Fe and
Ni, toward formation of stable metal compounds. In addition, the Na2He is not
even stabilized by the local chemical bonds but via the long-range Coulomb
interactions. Herein, by using the first-principles calculations and the
unbiased structure searching techniques, we uncover that the transition metal Y
is able to react with Xe above 60 GPa within various Y-Xe stochiometries,
namely the YXe, YXe2, YXe3 and Y3Xe structures. Surprisingly, it is found that
all the resulting compounds are intermetallic and Xe atoms are positively
charged. We also argue that the pressure-induced changes of the energy orbital
filling are responsible for the electron transfer from Xe to Y. Meanwhile, the
Peierls-like mechanism is found to stabilize the energetically most favorable
YXe-Pbam phase. Furthermore, the predicted YXe-Pbam, YXe-Pnnm, and YXe3-I4/mcm
phases are discovered to be phonon-mediated superconductors under pressure,
with the critical superconducting temperatures in the range of approximately
3-4K, 7-10K, and 5-6K, respectively. In summary, our work promotes further
understanding of the crystal structures and electronic properties of the
metal-based noble gas compounds.",1810.03860v2
2019-01-18,"Magnetic, Transport, and Phonon Properties of the Trivalent Eu Metallic Compound EuBe13","Magnetic susceptibility, specific heat, and electrical resistivity
measurements have been performed on single-crystal EuBe13 in the temperature
range between 2 and 300 K to investigate its phonon property and the valence
state of the Eu ion. The obtained temperature dependence of the magnetic
susceptibility curves obey a typical Van Vleck susceptibility for Eu3+ with a
nonmagnetic ground state in the entire measured temperature range. In the case
of the specific heat, we observed the coexistence of Debye and Einstein phonon
modes with characteristic Debye and Einstein temperatures of ~ 835 K and ~167
K, respectively, which are in good agreement with those previously reported for
other isostructural MBe13 compounds (M = rare earths and actinides). The
temperature dependence of the resistivity for EuBe13 shows an unusual T-cubed
like dependence at low temperatures, as also observed for the nonmagnetic
isostructural compound LaBe13, which can be reproduced well by calculations
based on electron--phonon scattering using the estimated Debye temperature and
Einstein temperature. We also summarized the relationship between the
Eu-valence state and the free distance between the Eu ion and the
first-nearest-neighbor atoms in several Eu-based cubic compounds, and argued
that EuBe13 takes the Eu3+ state despite its larger free distance than other
Eu3+ compounds.",1901.06120v1
2019-01-20,"Structural, Elastic, Electronic, and Optical Properties of Layered TiNX (X = F, Cl, Br, I) Compounds: a Density Functional Theory Study","Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the {\alpha}-phase
(orthorhombic) are exciting quasi two-dimensional (2D) electronic systems
exhibiting a fascinating series of electronic ground states under different
conditions. Pristine TiNX are semiconductors with varying energy gaps and
possess attractive properties for potential applications in the fields of
optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated
TiNCl becomes superconducting at reasonably high temperature in the
{\alpha}-phase. We have revisited the electronic band structure of these
compounds using density functional theory (DFT) based first-principles
calculations. The atomic species and orbital resolved partial electronic energy
density of states are calculated together with the total density of states
(TDOS). The structural and elastic properties have been investigated in details
for these layered compounds for the first time. The elastic anisotropy has been
explored. The optical properties, including energy dependent real and imaginary
parts of the dielectric constant, optical conductivity, reflectivity, and loss
function of TiNX are studied for the first time. The Debye temperatures of
these compounds have been calculated and the related thermal and phonon
parameters are discussed. The calculated physical parameters are compared with
existing theoretical and experimental results and show fair agreement, where
available. All these compounds are found to reflect electromagnetic radiation
strongly in the mid ultraviolet region. The elastic properties show high degree
of anisotropy. The lattice is highly compressible along the crystallographic
c-direction. The effect of halogen atoms on various structural, elastic,
electronic, and thermal properties in TiNX are also discussed in detail.",1901.06643v1
2019-07-16,Compound-tunable embedding potential method and its application to fersmite crystal,"Compound-tunable embedding potential (CTEP) method is proposed. A fragment of
some chemical compound, ""main cluster"" in the present paper, is limited by
boundary anions such that the nearest environmental atoms are cations. The CTEP
method is based on constructing the embedding potential as linear combination
of short-range ""electron-free"" spherical ""tunable"" pseudopotentials for cations
from nearest environment of the main cluster, whereas the long-range CTEP part
consists of Coulomb potentials from optimized fractional point charges centered
on both environmental cations and anions.
  A pilot application of the CTEP method to the fersmite crystal,
CaNb$_2$O$_6$, is performed and a remarkable agreement of the electronic
density and interatomic distances within the fragment with those of the
original periodic crystal calculation is attained. Characteristics of
""atoms-in-compounds"" which are of great importance for compound of $f$- and
$d$-elements (Nb in fersmite) are considered on examples of chemical shifts of
$K_{{\alpha}_{1,2}}\ $ and $K_{{\beta}_{1,2}}\ $ lines of X-ray emission
spectra in niobium. A very promising potential of this approach in studying
variety of properties of point defects containing $f$- and heavy $d$-elements
with relativistic effects, extended basis set and broken crystal symmetry
considered is discussed.",1907.06947v2
2021-03-10,Binary and ternary ionic compounds in the outer crust of a cold nonaccreting neutron star,"The outer crust of a cold nonaccreting neutron star has been generally
assumed to be stratified into different layers, each of which consists of a
pure body-centered cubic ionic crystal in a charge compensating background of
highly degenerate electrons. The validity of this assumption is examined by
analyzing the stability of multinary ionic compounds in dense stellar matter.
It is thus shown that their stability against phase separation is uniquely
determined by their structure and their composition irrespective of the stellar
conditions. However, equilibrium with respect to weak and strong nuclear
processes imposes very stringent constraints on the composition of multinary
compounds, and thereby on their formation. By examining different cubic and
noncubic lattices, it is found that substitutional compounds having the same
structure as cesium chloride are the most likely to exist in the outer crust of
a nonaccreting neutron star. The presence of ternary compounds is also
investigated. Very accurate analytical expressions are obtained for the
threshold pressure, as well as for the densities of the different phases
irrespective of the degree of relativity of the electron gas. Finally,
numerical calculations of the ground-state structure and of the equation of
state of the outer crust of a cold nonaccreting neutron star are carried out
using recent experimental and microscopic nuclear mass tables.",2103.06073v1
2021-03-12,Strong correlation between bonding network and critical temperature in hydrogen-based superconductors,"Recent experimental discoveries show that hydrogen-rich compounds can reach
room temperature superconductivity, at least at high pressures. Also that there
exist metallic hydrogen-abundant systems with critical temperatures of few
Kelvin, or even with no trace of superconductivity at all. By analyzing through
first-principles calculations the structural and electronic properties of more
than one hundred compounds predicted to be superconductors in the literature,
we determine that the capacity of creating a bonding network of connected
localized units is the key to enhance the critical temperature in
hydrogen-based superconductors, explaining the large variety of critical
temperatures of superconducting hydrogen-rich materials. We define a magnitude
named as the {\it networking value}, which correlates well with the predicted
critical temperature, much better than any other descriptor analyzed thus far.
This magnitude can be easily calculated for any compound by analyzing
isosurfaces of the electron localization function. By classifying the studied
compounds according to their bonding nature, we observe that the {\it
networking value} correlates with the critical temperature for all bonding
types. Our analysis also highlights that systems with weakened covalent bonds
are the most promising candidates for reaching high critical temperatures. The
discovery of the positive correlation between superconductivity and the bonding
network offers the possibility of screening easily hydrogen-based compounds
and, at the same time, sets clear paths for chemically engineering better
superconductors.",2103.07320v1
2022-02-21,Ligandformer: A Graph Neural Network for Predicting Compound Property with Robust Interpretation,"Robust and efficient interpretation of QSAR methods is quite useful to
validate AI prediction rationales with subjective opinion (chemist or biologist
expertise), understand sophisticated chemical or biological process mechanisms,
and provide heuristic ideas for structure optimization in pharmaceutical
industry. For this purpose, we construct a multi-layer self-attention based
Graph Neural Network framework, namely Ligandformer, for predicting compound
property with interpretation. Ligandformer integrates attention maps on
compound structure from different network blocks. The integrated attention map
reflects the machine's local interest on compound structure, and indicates the
relationship between predicted compound property and its structure. This work
mainly contributes to three aspects: 1. Ligandformer directly opens the
black-box of deep learning methods, providing local prediction rationales on
chemical structures. 2. Ligandformer gives robust prediction in different
experimental rounds, overcoming the ubiquitous prediction instability of deep
learning methods. 3. Ligandformer can be generalized to predict different
chemical or biological properties with high performance. Furthermore,
Ligandformer can simultaneously output specific property score and visible
attention map on structure, which can support researchers to investigate
chemical or biological property and optimize structure efficiently. Our
framework outperforms over counterparts in terms of accuracy, robustness and
generalization, and can be applied in complex system study.",2202.10873v3
2016-12-09,Discovery of ferromagnetism with large magnetic anisotropy in ZrMnP and HfMnP,"ZrMnP and HfMnP single crystals are grown by a self-flux growth technique and
structural as well as temperature dependent magnetic and transport properties
are studied. Both compounds have an orthorhombic crystal structure. ZrMnP and
HfMnP are ferromagnetic with Curie temperatures around $370$~K and $320$~K
respectively. The spontaneous magnetizations of ZrMnP and HfMnP are determined
to be $1.9$~$\mu_\textrm{B}$/f.u. and $2.1$~$\mu_\textrm{B}$/f.u. respectively
at $50$~K. The magnetocaloric effect of ZrMnP in term of entropy change
($\Delta S$) is estimated to be $-6.7$ kJm$^{-3}$K$^{-1}$ around $369$~K. The
easy axis of magnetization is [100] for both compounds, with a small anisotropy
relative to the [010] axis. At $50$~K, the anisotropy field along the [001]
axis is $\sim4.6$~T for ZrMnP and $\sim10$~T for HfMnP. Such large magnetic
anisotropy is remarkable considering the absence of rare-earth elements in
these compounds. The first principle calculation correctly predicts the
magnetization and hard axis orientation for both compounds, and predicts the
experimental HfMnP anisotropy field within 25 percent. More importantly, our
calculations suggest that the large magnetic anisotropy comes primarily from
the Mn atoms suggesting that similarly large anisotropies may be found in other
3d transition metal compounds.",1612.03166v1
2016-12-20,Feedback Does Not Increase the Capacity of Compound Channels with Additive Noise,"A discrete compound channel with memory is considered, where no stationarity,
ergodicity or information stability is required, and where the uncertainty set
can be arbitrary. When the discrete noise is additive but otherwise arbitrary
and there is no cost constraint on the input, it is shown that the causal
feedback does not increase the capacity. This extends the earlier result
obtained for general single-state channels with full transmitter (Tx) channel
state information (CSI) to the compound setting. It is further shown that, for
this compound setting and under a mild technical condition on the additive
noise, the addition of the full Tx CSI does not increase the capacity either,
so that the worst-case and compound channel capacities are the same. This can
also be expressed as a saddle-point in the information-theoretic game between
the transmitter (who selects the input distribution) and the nature (who
selects the channel state), even though the objective function (the
inf-information rate) is not convex/concave in the right way. Cases where the
Tx CSI does increase the capacity are identified.
  Conditions under which the strong converse holds for this channel are
studied. The ergodic behaviour of the worst-case noise in otherwise
information-unstable channel is shown to be both sufficient and necessary for
the strong converse to hold, including feedback and no feedback cases.",1612.06900v1
2018-04-18,Performance of the strongly constrained and appropriately normed density functional for solid-state materials,"Constructed to satisfy all known exact constraints and appropriate norms for
a semilocal density functional, the strongly constrained and appropriately
normed (SCAN) meta-generalized gradient approximation functional has shown
early promise for accurately describing the electronic structure of molecules
and solids. One open question is how well SCAN predicts the formation energy, a
key quantity for describing the thermodynamic stability of solid-state
compounds. To answer this question, we perform an extensive benchmark of SCAN
by computing the formation energies for a diverse group of nearly one thousand
crystalline compounds for which experimental values are known. Due to an
enhanced exchange interaction in the covalent bonding regime, SCAN
substantially decreases the formation energy errors for strongly-bound
compounds, by approximately 50% to 110 meV/atom, as compared to the generalized
gradient approximation of Perdew, Burke, and Ernzerhof (PBE). However, for
intermetallic compounds, SCAN performs moderately worse than PBE with an
increase in formation energy error of approximately 20%, stemming from SCAN's
distinct behavior in the weak bonding regime. The formation energy errors can
be further reduced via elemental chemical potential fitting. We find that SCAN
leads to significantly more accurate predicted crystal volumes, moderately
enhanced magnetism, and mildly improved band gaps as compared to PBE. Overall,
SCAN represents a significant improvement in accurately describing the
thermodynamics of strongly-bound compounds.",1804.06914v1
2019-03-11,Compound Regularization of Full-waveform Inversion for Imaging Piecewise Media,"The nonlinear and ill-posed nature of full waveform inversion (FWI) requires
us to use sophisticated regularization techniques to solve it. In most
applications, the model parameters may be described by physical properties
(e.g., wave speeds, density, attenuation, anisotropic parameters) which are
piecewise functions of space. Compound regularizations are thus necessary to
reconstruct properly such parameters by FWI. We consider different
implementations of compound regularizations in the wavefield reconstruction
inversion (WRI) method, a formulation of FWI that extends its search space and
prevent the so-called cycle skipping pathology. Our hybrid regularizations rely
on Tikhonov and total variation (TV) functionals, from which we build two
classes of hybrid regularizers: the first class is simply obtained by a convex
combination (CC) of the two functionals, while the second relies on their
infimal convolution (IC). In the former class, the model of parameters is
required to simultaneously satisfy different priors, while in the latter the
model is broken into its basic components, each satisfying a distinct prior
(e.g. smooth, piecewise constant, piecewise linear). We implement these types
of compound regularizations in the WRI optimization problem using the
alternating direction method of multipliers (ADMM). Then, we assess our
regularized WRI in the framework of seismic imaging applications. Using a wide
range of subsurface models, we conclude that compound regularizer based on IC
leads to the lowest error in the parameter reconstruction compared to that
obtained with the CC counterpart and the Tikhonov and TV regularizers when used
independently.",1903.04405v1
2019-12-10,"Magnetic couplings and magnetocaloric effect in the GdTX (T=Sc, Ti, Co, Fe; X=Si, Ge) compounds","We compute the magnetocaloric effect (MCE) in the GdTX (T=Sc, Ti, Co, Fe;
X=Si, Ge) compounds as a function of the temperature and the external magnetic
field. To this end we use a density functional theory approach to calculate the
exchange-coupling interactions between Gd$^{3+}$ ions on each compound. We
consider a simplified magnetic Hamiltonian and analyze the dependence of the
exchange couplings on the transition metal T, the p-block element X, and the
crystal structure (CeFeSi-type or CeScSi-type). The most significant effects
are observed for the replacements Ti $\to$ Sc or Fe $\to$ Co which have an
associated change in the parity of the electron number in the 3d level. These
replacements lead to an antiferromagnetic contribution to the magnetic
couplings that reduces the Curie temperature and can even lead to an
antiferromagnetic ground state. We solve the magnetic models through mean field
and Monte Carlo calculations and find large variations among compounds in the
magnetic transition temperature and in the magnetocaloric effect, in agreement
with the available experimental data. The magnetocaloric effect shows a
universal behavior as a function of temperature and magnetic field in the
ferromagnetic compounds after a scaling of the relevant energy scales by the
Curie temperature $T_C$.",1912.04990v1
2020-02-06,Exotic multiferroic properties of spinel structured $AB_2O_4$ compounds: A Monte Carlo Study,"Spinel structured compounds, $AB_2O_4$, are special because of their exotic
multiferroic properties. In $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$), a switchable
polarization has been observed experimentally due to a non-collinear magnetic
spin order. In this article, we demonstrated the microscopic origin behind such
magnetic spin order, hysteresis, polarisation and the so-called magnetic
compensation effect in $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$, $Ni$) using Monte Carlo
simulation. With a careful choice of the exchange interaction, we were able to
explain various experimental findings such as magnetization vs. temperature (T)
behavior, conical stability, unique magnetic ordering and polarization in a
representative compound $CoCr_2O_4$ which is the best known multiferroic
compound in the $AB_2O_4$ spinel family. We have also studied the effect of
$Fe$-substitution in $CoCr_2O_4$, with an onset of few exotic phenomena such as
magnetic compensation and sign reversible exchange bias effect. These effects
are investigated using an effective interactions mimicking the effect of
substitution. Two other compounds in this family, $CoMn_2O_4$ and $CoFe_2O_4$,
are also studied where no conical magnetic order and polarisation was observed,
as hence provide a distinct contrast. Here all calculations are done using the
polarisation calculated by the spin-current model. This model has certain
limitation and it works quite good for low temperature and low magnetic field.
But the model despite its limitation it can reproduce sign reversible exchange
bias and magnetic compensation like phenomena quite well.",2002.02180v1
2020-06-09,Optical System Design of Bionic Compound Eye with Broad Field of View,"In nature, many common insects have compound eyes composed of many small eyes
arranged on a curved retina. This kind of vision systems have many advantages,
such as small size, large FOV (field of view) and high sensitivity, which have
attracted extensive attention and research from world-wide researchers. It has
good application prospects in military strikes and mechanical vision. In this
paper, a new type of miniature compound eye system with large FOV is designed,
which contains a micro-lens array and a relay system. Hexagonal micro-lens
array are spliced seamlessly as a curved shell in the designed compound eye
system. The intermediate curved image formed by the curved array is converted
to a planar image by introducing a relay system. After combination and
optimization of the micro-lens array and the relay system, the MTF values at
89.3lp/mm for each FOV within 120.5{\deg} are greater than 0.3, and the
corresponding RMS spot radii less than the radius of the Airy disk, which
proves the good imaging quality for the compound eye. The clear aperture of a
single micro lens is 250{\mu}m with FOV 6{\deg}. After tolerance analysis, the
results show the image quality still holds good enough performance and meets
the requirements of the additive manufacturing process.",2006.05090v2
2020-06-29,Phonon dispersions and electronic structures of two-dimensional IV-V compounds,"One novel family of two-dimensional IV-V compounds have been proposed, whose
dynamical stabilities and electronic properties have been systematically
investigated using the density functional theory. Extending from our previous
work, two phases of carbon phosphorus bilayers \alpha- and \beta-C$_{2}$P$_{2}$
have been proposed. Both of them are dynamically stable and thermally stable at
300K. They possess intrinsic HSE gaps of 2.70 eV and 2.67 eV, respectively.
Similar \alpha- and \beta-C$_{2}$Y$_{2}$ (Y= As, Sb, and Bi) can be obtained if
the phosphorus atoms in the \alpha- and \beta-C$_{2}$P$_{2}$ replaced by other
pnictogens, respectively. If the C atoms in the \alpha- and
\beta-C$_{2}$Y$_{2}$ (Y= P, As, Sb, and Bi) are further replaced by other IV
elements X (X=Si, Ge, Sn, and Pb), respectively, more derivatives of \alpha-
and \beta-X$_{2}$Y$_{2}$ (Y=N, P, As, Sb, and Bi) also can be obtained. It was
found that the majority of them are dynamically stable. The proposed compounds
range from metal to insulators depending on their constitutions. All insulated
compounds can undergo a transition from insulator to metal induced by biaxial
strain. Some of them can undergo a transition from indirect band gap to direct
band gap. These new compounds can become candidates as photovoltaic device,
thermoelectric material field as well as lamellated superconductors.",2006.16173v2
2020-07-09,Investigation of H Sorption and Corrosion Properties of Sm2MnxNi7-x (0<x<0.5) Intermetallic Compounds Forming Reversible Hydrides,"Intermetallic compounds are key materials for energy transition as they form
reversible hydrides that can be used for solid state hydrogen storage or as
anodes in batteries. ABy compounds (A = Rare Earth (RE); B = transition metal;
2 < y < 5) are good candidates to fulfill the required properties for practical
applications. They can be described as stacking of AB5 and AB2 sub-units along
the c crystallographic axis. The latter sub-unit brings a larger capacity,
while the former one provides a better cycling stability. However, ABy binaries
do not show good enough properties for applications. Upon hydrogenation, they
exhibit multiplateau behavior and poor reversibility, attributed to H induced
amorphization. These drawbacks can be overcome by chemical substitutions on the
A and/or the B sites leading to stabilized reversible hydrides. The present
work focuses on the pseudo-binary Sm2MnxNi7-x system (0 <= x < 0.5). The
structural, thermodynamic and corrosion properties are analyzed and interpreted
by means of X-ray diffraction, chemical analysis, scanning electron microscopy,
thermogravimetric analysis and magnetic measurements. Unexpected cell parameter
variations are reported and interpreted regarding possible formation of
structural defects and uneven Mn distribution within the Ni sublattice.
Reversible capacity is improved for x > 0.3 leading to larger and flatter
isotherm curves, allowing for reversible capacity >1.4 wt %. Regarding
corrosion, the binary compound corrodes in alkaline medium to form rare earth
hydroxide and nanoporous nickel. As for the Mn-substituted compounds, a new
corrosion product is formed in addition to those above mentioned, as manganese
initiates a sacrificial anode mechanism taking place at the early corrosion
stage.",2007.04695v1
2020-07-27,Thermodynamic and corrosion study of Sm$_{1-x}$Mg$_x$Ni$_y$ (y = 3.5 or 3.8) compounds forming reversible hydrides,"AB5 compounds (A = rare earth, B = transition metal) have been widely studied
as anodes for Ni-MH applications. However, they have reached their technical
limitations and the search for new promising materials with high capacity is
foreseen. ABy compounds (2 < y < 5) are good candidates. They are made by
stacking [AB5] and [A2B4] units along the c crystallographic axis. The latter
unit allows a large increase in capacity, while the [AB5] unit provides good
cycling stability. Consequently, the AB3.8 composition (i.e. A5B19 with three
[AB5] for one [A2B4]) is expected to exhibit better cycling stability than the
AB3.5 (i.e. A2B7 with two [AB5] for one [A2B4]). Furthermore, substitution of
rare earth by light magnesium improves both the capacity and cycling stability.
In this paper, we compare the hydrogenation and corrosion properties of two
binary compounds SmNi$_{3.5}$ and SmNi$_{3.8}$ and two pseudo-binary ones
(Sm,Mg)Ni$_{3.5}$ and (Sm,Mg)Ni$_{3.8}$. A better solid-gas cycling stability
is highlighted for the binary SmNi$_{3.8}$. The pseudo-binary compounds also
exhibit higher cycling stability than the binary ones. Furthermore, their
resistance to corrosion was investigated.",2007.13456v1
2020-09-03,Universal $T/B$ scaling behavior of heavy fermion compounds,"In our mini-review, we address manifestations of $T/B$ scaling behavior of
heavy-fermion (HF) compounds, where $T$ and $B$ are respectively temperature
and magnetic field. Using experimental data and the fermion condensation
theory, we show that this scaling behavior is typical of HF compounds including
HF metals, quasicrystals, and quantum spin liquids. We demonstrate that such
scaling behavior holds down to the lowest temperature and field values, so that
$T/B$ varies in a wide range, provided the HF compound is located near the
topological fermion condensation quantum phase transition (FCQPT). Due to the
topological properties of FCQPT, the effective mass $M^*$ exhibits a universal
behavior, and diverges as $T$ goes to zero. Such a behavior of $M^*$ has
important technological applications. We also explain how to extract the
universal scaling behavior from experimental data collected on different
heavy-fermion compounds. As an example, we consider the HF metal $\rm
YbCo_2Ge_4$, and show that its scaling behavior is violated at low
temperatures. Our results obtained show good agreement with experimental facts.",2009.01620v4
2020-10-29,Seq2Mol: Automatic design of de novo molecules conditioned by the target protein sequences through deep neural networks,"De novo design of molecules has recently enjoyed the power of generative deep
neural networks. Current approaches aim to generate molecules either resembling
the properties of the molecules of the training set or molecules that are
optimized with respect to specific physicochemical properties. None of the
methods generates molecules specific to a target protein. In the approach
presented here, we introduce a method which is conditioned on the protein
target sequence to generate de novo molecules that are relevant to the target.
We use an implementation adapted from Google's ""Show and Tell"" image caption
generation method, to generate SMILES strings of molecules from protein
sequence embeddings generated by a deep bi-directional language model ELMo.
ELMo is used to generate contextualized embedding vectors of the protein
sequence. Using reinforcement learning, the trained model is further optimized
through augmented episodic likelihood to increase the diversity of the
generated compounds compared to the training set. We used the model to generate
compounds for two major drug target families, i.e. for GPCRs and Tyrosine
Kinase targets. The model generated compounds which are structurally different
form the training set, while also being more similar to compounds known to bind
to the two families of drug targets compared to a random set of molecules. The
compounds further display reasonable synthesizability and drug-likeness scores.",2010.15900v1
2020-12-10,"Growth of Two-dimensional Compound Materials: Controllability, Material Quality, and Growth Mechanism","CONSPECTUS: Two-dimensional (2D) compound materials are promising materials
for use in electronics, optoelectronics, flexible devices, etc. because they
are ultrathin and cover a wide range of properties. Among all methods to
prepare 2D materials, chemical vapor deposition (CVD) is promising because it
produces materials with a high quality and reasonable cost. So far, much
efforts have been made to produce 2D compound materials with large domain size,
controllable number of layers, fast-growth rate, and high quality features,
etc. However, due to the complicated growth mechanism like sublimation and
diffusion processes of multiple precursors, maintaining the controllability,
repeatability, and high quality of CVD grown 2D binary and ternary materials is
still a big challenge, which prevents their widespread use. Here, taking 2D
transition metal dichalcogenides (TMDCs) as examples, we review current
progress and highlight some promising growth strategies for the growth of 2D
compound materials. The key technology issues which affect the CVD process,
including non-metal precursor, metal precursor, substrate engineering,
temperature, and gas flow, are discussed. Also, methods in improving the
quality of CVD-grown 2D materials and current understanding on their growth
mechanism are highlighted. Finally, challenges and opportunities in this field
are proposed. We believe this review will guide the future design of
controllable CVD systems for the growth of 2D compound materials with good
controllability and high quality, laying the foundations for their potential
applications.",2012.05486v1
2021-02-04,"Lattice dynamics effects on finite-temperature stability of $R_{1-x}$Fe$_{x}$ ($R$ = Y, Ce, Nd, Sm, and Dy) alloys from first principles","We report the effects of lattice dynamics on thermodynamic stability of
binary $R_{1-x}$Fe$_x$ $(0<x<1)$ compounds ($R$: rare-earth elements, Y, Ce,
Nd, Sm, and Dy) at finite temperature predicted by first-principles calculation
based on density functional theory (DFT). We first demonstrate that the
thermodynamic stability of $R_{1-x}$Fe$_x$ $(0<x<1)$ alloys cannot be predicted
accurately by the conventional approach, where only the static DFT energy at $T
= 0$ K is used. This issue can be overcome by considering the entropy
contribution, including electronic and vibrational free energies, and we
obtained convex hull plots at finite temperatures that successfully explain the
thermodynamic stability of various known compounds. Our systematic calculation
indicates that vibrational entropy helps stabilize various $R_{1-x}$Fe$_x$
compounds with increasing temperature. In particular, experimentally reported
$R_2$Fe$_{17}$ compounds are predicted to become thermodynamically stable above
$\sim$800 K. We also show that thermodynamic stability is rare-earth dependent
and discuss its origin. Besides the experimentally reported structures, the
stability of two new monoclinic $R$Fe$_{12}$ structures found by Ishikawa
\textit{et al.} [Phys. Rev. Mater.~\textbf{4}, 104408 (2020)] based on a
genetic algorithm are investigated. These monoclinic phases are found to be
dynamically stable and have larger magnetization than the ThMn$_{12}$-type
$R$Fe$_{12}$. Although they are thermodynamically unstable, the formation
energies decrease significantly with increasing temperature, indicating the
possibility of synthesizing these compounds at high temperatures.",2102.02590v1
2021-02-08,"Improvement of reversible H storage capacity by fine tuning of the composition in the pseudo-binary systems A2-xLaxNi7 (A = Gd, Sm, Y, Mg)","A2B7 compounds (A = rare earth or Mg, B = transition metal) are widely
studied as active materials for negative electrode in Ni-MH batteries. By
playing on the substitution rate of both A and B elements, it is possible to
prepare various compositions. This strategy will help to improve the
properties, for example get a higher reversible hydrogen capacity and a
well-adapted hydrogen sorption pressure. Indeed, A can be almost all light rare
earths (La to Gd), yttrium and alkaline earth metals (Mg or Ca), whereas B can
contain various late transition metals (Mn to Ni). To understand the effects of
composition on the physicochemical properties of La2Ni7-based compound, various
pseudo-binary systems have been investigated: Gd2 xLaxNi7 (x = 0, 0.6, 1, 1.5),
Sm2-xLaxNi7 (x = 0, 0.5, 1, 1.5), Y2-xLaxNi7 (x = 0, 0.4, 0.5, 0.6, 0.8, 1,
1.5, 1.75) and A0.5La1.1Mg0.4Ni7 (A = Sm, Gd and Y). To determine their
crystallographic properties, X-ray diffraction analysis was performed followed
by Rietveld refinement. Thermodynamic properties regarding reversible hydrogen
sorption were investigated at room temperature. Quaternary compounds present
drastically improved sorption properties in the frame of practical energy
storage applications with reversible capacity equivalent to 400 mAh/g for the
compound La1.1Sm0.5Mg0.4Ni7.",2102.04161v1
2021-04-29,"Competing magnetic interactions and magnetoresistance anomalies in cubic intermetallic compounds, Gd4RhAl and Tb4RhAl, and enhanced magnetocaloric effect for the Tb case","We report complex magnetic, magnetoresistance (MR) and magnetocaloric
properties of Gd4RhAl and Tb4RhAl forming in the Gd4RhIn type cubic structure.
Though the synthesis of the compounds was reported long ago, to our knowledge,
no attempt was made to investigate the properties of these compounds. The
present results of ac and dc magnetization, electrical resistivity and
heat-capacity measurements down to 1.8 K establish that these compounds undergo
antiferromagnetic order initially, followed by complex spin-glass features with
decreasing temperature. These characteristic temperatures are: For Gd case, TN
is about 46K and TG is about 21 K, and for Tb, about 32 and 28 K respectively.
Additionally, there are field induced magnetic effects, interestingly leading
to non-monotonic variations in MR. There is a significant MR over a wide
temperature range above TN, similar to the behavior of magnetocaloric effect
(MCE) as measured by isothermal entropy change (DeltaS). An intriguing finding
we made is that DeltaS at the onset of magnetic order is significantly larger
for the Tb compound than that observed for the Gd analogue near its TN. On the
basis of this observation in a cubic material, we raise a question whether
aspherical nature of the 4f orbital can play a role to enhance MCE under
favorable circumstances, a clue that could be useful to find materials for
magnetocaloric applications.",2104.14521v1
2021-05-18,Unsupervised Compound Domain Adaptation for Face Anti-Spoofing,"We address the problem of face anti-spoofing which aims to make the face
verification systems robust in the real world settings. The context of
detecting live vs. spoofed face images may differ significantly in the target
domain, when compared to that of labeled source domain where the model is
trained. Such difference may be caused due to new and unknown spoof types,
illumination conditions, scene backgrounds, among many others. These varieties
of differences make the target a compound domain, thus calling for the problem
of the unsupervised compound domain adaptation. We demonstrate the
effectiveness of the compound domain assumption for the task of face
anti-spoofing, for the first time in this work. To this end, we propose a
memory augmentation method for adapting the source model to the target domain
in a domain aware manner. The adaptation process is further improved by using
the curriculum learning and the domain agnostic source network training
approaches. The proposed method successfully adapts to the compound target
domain consisting multiple new spoof types. Our experiments on multiple
benchmark datasets demonstrate the superiority of the proposed method over the
state-of-the-art.",2105.08463v1
2021-05-23,"Ab-initio investigations for Structural, Mechanical, Optoelectronic, and Thermoelectric properties of Ba2SbXO6 (X=Nb, Ta) compounds","We report the structural, mechanical, electronic, optical, thermoelectric
properties and spectroscopic limited maximum efficiency (SLME) of oxide double
perovskite structure Ba2SbNbO6 and Ba2SbTaO6 compounds. All the investigations
were performed through the first-principles density functional theory (DFT).
The obtained values for the elastic constants reveal the mechanical stability
of the studied compounds. The calculated data of bulk modulus (B), shear
modulus (G), and Young's modulus (E) for Ba2SbTaO6 are found to be greater than
those of Ba2SbNbO6. The ratio of Bulk to shear ratio (B/G) shows that Ba2SbNbO6
and Ba2SbTaO6 are ductile. The computed electronic band structure reveals the
semiconducting nature of both compounds. We have also studied the electron
relaxation time-dependent thermoelectric properties, such as Seebeck
coefficient, thermal conductivity, electrical conductivity, thermoelectric
power factor, and the figure of merit as a function of chemical potential at
various temperatures for p-type and n-type charge carriers. The high absorption
spectra and good figure of merit (ZT) reveal that both the studied compounds,
Ba2SbXO6 (X = Nb, Ta) are promising materials for photovoltaic and
thermoelectric applications. The calculated SLME of 26.8% reveals that Ba2SNbO6
is an appealing candidate for single-junction solar cells.",2105.10976v2
2021-08-23,Understanding the Seebeck coefficient of LaNiO3 compound in the temperature range 300-620 K,"Transition metal oxides have been attracted much attention in thermoelectric
community from the last few decades. In the present work, we have synthesized
LaNiO$_{3}$ by a simple solution combustion process. To analyze the crystal
structure and structural parameters we have used Rietveld refinement method
wherein FullProf software is employed. The room temperature x-ray diffraction
indicates the trigonal structure with space group $R \, \overline{3} \, c$ (No.
167). The refined values of lattice parameters are a = b = 5.4615 \AA\, $\&$ c
= 13.1777 \AA. Temperature dependent Seebeck coefficient (S) of this compound
has been investigated by using experimental and computational tools. The
measurement of S is conducted in the temperature range $300-620$ K. The
measured values of S in the entire temperature range have negative sign that
indicates \textit{n}-type character of the compound. The value of S is found to
be $\sim$ $-$8 $\mu$V/K at 300 K and at 620 K this value is $\sim$ $-$12
$\mu$V/K. The electronic structure calculation is carried out using
DFT+\textit{U} method due to having strong correlation in LaNiO$_{3}$. The
calculation predicts the metallic ground state of the compound. Temperature
dependent S is calculated using BoltzTraP package and compared with experiment.
The best matching between experimental and calculated values of S is observed
when self-interaction correction is employed as double counting correction in
spin-polarized DFT + \textit{U} (= 1 eV) calculation. Based on the
computational results maximum power factors are also calculated for
\textit{p}-type and \textit{n}-type doping of this compound.",2108.09969v1
2021-09-22,First-principles study of the electronic structure of CaKRu$_4$P$_4$,"The recent discovery and studies of 1144-phase compounds, e.g.,
CaKFe$_4$As$_4$, have attracted significant research interest. In this paper,
based on the first-principles density functional calculations, we present a
systematic study on the electronic structure of the recently synthetized
1144-type quaternary compound CaKRu$_4$P$_4$. We find that the Ru-based
1144-type compound possesses a different electronic structure from that of
iron-based superconductors, even though they share very similar
crystallographic structures. In CaKRu$_4$P$_4$, there is no hole-type carrier
if spin-orbit interaction is not considered. And a long-range magnetic order is
absent in its ground state. With the application of pressure, the electronic
structure of CaKRu$_4$P$_4$ becomes similar to those of the ternary 122-type
compounds LaRu$_2$P$_2$ and LaRu$_2$As$_2$. CaKRu$_4$P$_4$ is very likely to be
a phonon-mediated medium coupled BCS superconductor. Furthermore, type-I and
type-II Dirac fermions can be created and regulated in this system with
pressure. The quaternary compound CaKRu$_4$P$_4$ therefore has a potential to
be an attractive platform for the study of topological physics and
superconductivity.",2109.10851v2
2021-10-20,Selective crystal growth of indium selenide compounds from saturated solutions grown in a selenium vapor,"Indium selenide compounds are promising materials for energy conversion,
spintronic applications, and chemical sensing. However, it is difficult to grow
stoichiometric indium selenide crystals due to the high equilibrium selenium
vapor pressure and the complicated phase equilibrium system of indium selenide
compounds. In this paper, we apply a novel and convenient crystal growth
method, in which the saturated solution is grown by the application of a
selenium vapor. In this method, selenium vapor at a pressure higher than the
saturated vapor pressure is applied to molten indium, such that the selenium
continuously dissolves into the indium solution until the solubility at the
growth temperature is reached; then a slow cooling process results in
crystallization. The selenium dose is matched to its solubility so that indium
selenide compounds can be selectively grown just by controlling the temperature
without the need to consider the chemical ratio in the solution. The pressure
of the vapor is controlled during the whole growth process so that any
deviation from a stoichiometric composition in the crystal can be controlled.
Both InSe and In2Se3 were successfully grown using this method, and we have
investigated the growth mechanism and found the growth window for each
compound. This study presents a novel and convenient approach to fabricating
transitional metal chalcogenides without deficiencies in the chalcogen element.",2110.10345v1
2021-10-23,Influence of vacancies on phonons and pressure phase transitions in TiO: a DFT study,"Since recently, some interests appeared in TiO as a thin film coating
material due to its promising physical properties. Moreover, because of the
existence of intrinsic vacancies, TiO demonstrates memristive properties. To
use these compounds in active region for memristive switching, the
investigation of the dynamical stability of these compounds is of importance.
Therefore, the structural, electronic, and dynamical properties of TiO in two
different phases, namely cubic and monoclinic structures along with vacancies,
are debated from the framework of density functional theory. The structural
calculations show that the vacancies have quite an impact on the bulk modulus
of these compounds. The electronic band structure remarks that these structures
are metallic. In addition, there is an energy gap between O-2p and Ti-3d states
in these compounds below the Fermi level that can be altered via vacancy
concentration. The phonon calculations reveal that monoclinic structure is
dynamically stable whereas the cubic phase is unstable at room temperature.
Considering ~12.5% of both Ti and O vacancy concentration, eliminate the
imaginary modes for the cubic structure. Moreover, the vacancy-free cubic
structure can be stable above ~ 10 GPa applied pressure, which is consistent
with the experiment. Additionally, phonon dispersion curves of TiOx compounds
suggest that these materials are not favorable for thermal conductivity. The
pressure phase transition results indicate the transition from monoclinic to
vacant cubic TiO at ~8 GPa, whereas the monoclinic to vacancy-free cubic TiO
transition occurs at ~ 44 GPa, which are in a good agreement with the recent
reports. Therefore, it can be concluded that engineering of the vacancy sites
and their concentration in TiO phases can play an important role in applying
them in technological applications.",2110.12267v1
2021-11-01,Compound eruptions of twin flux ropes in a solar active region,"Compound eruptions represent that multiple closely spaced magnetic structures
erupt consecutively within a short interval, and then lead to a single flare
and a single CME. However, it is still subtle for the links between multiple
eruptions and the associated single flare or/and single CME. In this Letter, we
report the compound eruptions of twin close flux ropes (FR1 and FR2) within a
few minutes that resulted in a flare with a single soft X-ray peak and a CME
with two cores. The successive groups of expanding loops and double peaks of
intensity flux in AIA cool wavelengths indicate two episodes of internal
magnetic reconnections during the compound eruptions. Following the eruption of
FR2, the erupting FR1 was accelerated, and then the expanding loops overlying
FR2 were deflected. Moreover, the eruption of FR2 likely involved the external
magnetic reconnection between the bottom of the overlying stretching field
lines and the rebounding loops that were previously pushed by the eruption of
FR1, which was evidenced by a pair of groups of newly-formed loops. All results
suggest that the compound eruptions involved both internal and external
magnetic reconnections, and two erupting structures of twin FRs interacted at
the initial stage. We propose that two episodes of internal magnetic
reconnections were likely united within a few minutes to form the continuous
impulsive phase of the single peaked flare, and two separated cores of the CME
was possibly because that the latter core was too slow to merge with the former
one.",2111.00713v1
2022-04-20,Graph neural networks and attention-based CNN-LSTM for protein classification,"This paper focuses on three critical problems on protein classification.
Firstly, Carbohydrate-active enzyme (CAZyme) classification can help people to
understand the properties of enzymes. However, one CAZyme may belong to several
classes. This leads to Multi-label CAZyme classification. Secondly, to capture
information from the secondary structure of protein, protein classification is
modeled as graph classification problem. Thirdly, compound-protein interactions
prediction employs graph learning for compound with sequential embedding for
protein. This can be seen as classification task for compound-protein pairs.
This paper proposes three models for protein classification. Firstly, this
paper proposes a Multi-label CAZyme classification model using CNN-LSTM with
Attention mechanism. Secondly, this paper proposes a variational graph
autoencoder based subspace learning model for protein graph classification.
Thirdly, this paper proposes graph isomorphism networks (GIN) and
Attention-based CNN-LSTM for compound-protein interactions prediction, as well
as comparing GIN with graph convolution networks (GCN) and graph attention
networks (GAT) in this task. The proposed models are effective for protein
classification. Source code and data are available at
https://github.com/zshicode/GNN-AttCL-protein. Besides, this repository
collects and collates the benchmark datasets with respect to above problems,
including CAZyme classification, enzyme protein graph classification,
compound-protein interactions prediction, drug-target affinities prediction and
drug-drug interactions prediction. Hence, the usage for evaluation by benchmark
datasets can be more conveniently.",2204.09486v2
2022-05-27,Magnetic Ordering in GdAuAl$_4$Ge$_2$ and TbAuAl$_4$Ge$_2$: layered compounds with triangular lanthanide nets,"We report the synthesis of the entire $Ln$AuAl$_4$Ge$_2$ ($Ln$ = Y, Pr, Nd,
Sm, Gd, Tb, Dy, Ho, Er, and Tm) series and focus on the magnetic properties of
GdAuAl$_4$Ge$_2$ and TbAuAl$_4$Ge$_2$. Temperature and magnetic field dependent
magnetization, heat capacity, and electrical resistivity measurements reveal
that both compounds exhibit several magnetically ordered states at low
temperatures, with evidence for magnetic fluctuations extending into the
paramagnetic temperature region. For magnetic fields applied in the $ab$-plane
there are several ordered state regions that are associated with metamagnetic
phase transitions, consistent with there being multiple nearly degenerate
ground states. Despite Gd being an isotropic $S$-state ion and Tb having an
anisotropic $J$-state, there are similarities in the phase diagrams for the two
compounds, suggesting that factors such as the symmetry of the crystalline
lattice, which features well separated triangular planes of lanthanide ions, or
the Ruderman-Kittel-Kasuya-Yosida interaction as defined by the Fermi surface
topography control the magnetism. We also point out similarities to other
centrosymmetric compounds that host skyrmion lattices such as Gd$_2$PdSi$_3$,
and propose that the $Ln$AuAl$_4$Ge$_2$ family of compounds are of interest as
reservoirs for complex magnetism and electronic behaviors such as the
topological Hall effect.",2205.14063v1
2022-06-21,A method to computationally screen for tunable properties of crystalline alloys,"Conventionally, high-throughput computational materials searches start from
an input set of bulk compounds extracted from material databases, and this set
is screened for candidate materials for specific applications. In contrast,
many functional materials, and especially semiconductors, are heavily
engineered alloys or solid solutions of multiple compounds rather than a single
bulk compound. To improve our ability to design functional materials, in this
work we propose a framework and open-source code to automatically construct
possible ""alloy pairs"" and ""alloy systems"" and detect ""alloy members"" from a
set of existing, experimental or calculated ordered compounds, without
requiring any additional metadata beyond their crystal structure. We provide
analysis tools to estimate stability across each alloy. As a demonstration, we
apply this framework to all inorganic materials in the Materials Project
database to create a new database of over 600,000 unique alloy pair entries
that can then be used in materials discovery studies to search for materials
with tunable properties. This new database has been incorporated into the
Materials Project website and linked with corresponding material identifiers
for any user to query and explore. Using an example of screening for p-type
transparent conducting materials, we demonstrate how using this methodology
reveals candidate material systems that might otherwise have been excluded by a
traditional screening. This work lays a foundation from which materials
databases can go beyond stoichiometric compounds, and approach a more realistic
description of compositionally tunable materials.",2206.10715v3
2022-07-19,ML-BPM: Multi-teacher Learning with Bidirectional Photometric Mixing for Open Compound Domain Adaptation in Semantic Segmentation,"Open compound domain adaptation (OCDA) considers the target domain as the
compound of multiple unknown homogeneous subdomains. The goal of OCDA is to
minimize the domain gap between the labeled source domain and the unlabeled
compound target domain, which benefits the model generalization to the unseen
domains. Current OCDA for semantic segmentation methods adopt manual domain
separation and employ a single model to simultaneously adapt to all the target
subdomains. However, adapting to a target subdomain might hinder the model from
adapting to other dissimilar target subdomains, which leads to limited
performance. In this work, we introduce a multi-teacher framework with
bidirectional photometric mixing to separately adapt to every target subdomain.
First, we present an automatic domain separation to find the optimal number of
subdomains. On this basis, we propose a multi-teacher framework in which each
teacher model uses bidirectional photometric mixing to adapt to one target
subdomain. Furthermore, we conduct an adaptive distillation to learn a student
model and apply consistency regularization to improve the student
generalization. Experimental results on benchmark datasets show the efficacy of
the proposed approach for both the compound domain and the open domains against
existing state-of-the-art approaches.",2207.09045v1
2022-07-23,A Ligand-and-structure Dual-driven Deep Learning Method for the Discovery of Highly Potent GnRH1R Antagonist to treat Uterine Diseases,"Gonadotrophin-releasing hormone receptor (GnRH1R) is a promising therapeutic
target for the treatment of uterine diseases. To date, several GnRH1R
antagonists are available in clinical investigation without satisfying multiple
property constraints. To fill this gap, we aim to develop a deep learning-based
framework to facilitate the effective and efficient discovery of a new orally
active small-molecule drug targeting GnRH1R with desirable properties. In the
present work, a ligand-and-structure combined model, namely LS-MolGen, was
firstly proposed for molecular generation by fully utilizing the information on
the known active compounds and the structure of the target protein, which was
demonstrated by its superior performance than ligand- or structure-based
methods separately. Then, a in silico screening including activity prediction,
ADMET evaluation, molecular docking and FEP calculation was conducted, where
~30,000 generated novel molecules were narrowed down to 8 for experimental
synthesis and validation. In vitro and in vivo experiments showed that three of
them exhibited potent inhibition activities (compound 5 IC50 = 0.856 nM,
compound 6 IC50 = 0.901 nM, compound 7 IC50 = 2.54 nM) against GnRH1R, and
compound 5 performed well in fundamental PK properties, such as half-life, oral
bioavailability, and PPB, etc. We believed that the proposed
ligand-and-structure combined molecular generative model and the whole
computer-aided workflow can potentially be extended to similar tasks for de
novo drug design or lead optimization.",2207.11547v1
2022-08-22,A Novel Multi-Task Learning Approach for Context-Sensitive Compound Type Identification in Sanskrit,"The phenomenon of compounding is ubiquitous in Sanskrit. It serves for
achieving brevity in expressing thoughts, while simultaneously enriching the
lexical and structural formation of the language. In this work, we focus on the
Sanskrit Compound Type Identification (SaCTI) task, where we consider the
problem of identifying semantic relations between the components of a compound
word. Earlier approaches solely rely on the lexical information obtained from
the components and ignore the most crucial contextual and syntactic information
useful for SaCTI. However, the SaCTI task is challenging primarily due to the
implicitly encoded context-sensitive semantic relation between the compound
components.
  Thus, we propose a novel multi-task learning architecture which incorporates
the contextual information and enriches the complementary syntactic information
using morphological tagging and dependency parsing as two auxiliary tasks.
Experiments on the benchmark datasets for SaCTI show 6.1 points (Accuracy) and
7.7 points (F1-score) absolute gain compared to the state-of-the-art system.
Further, our multi-lingual experiments demonstrate the efficacy of the proposed
architecture in English and Marathi languages.The code and datasets are
publicly available at https://github.com/ashishgupta2598/SaCTI",2208.10310v2
2022-09-02,Verifying $k$-Contraction without Computing $k$-Compounds,"Compound matrices have found applications in many fields of science including
systems and control theory. In particular, a sufficient condition for
$k$-contraction is that a logarithmic norm (also called matrix measure) of the
$k$-additive compound of the Jacobian is uniformly negative. However, this may
be difficult to check in practice because the $k$-additive compound of an
$n\times n$ matrix has dimensions $\binom{n}{k}\times \binom{n}{k}$. For an
$n\times n$ matrix $A$, we prove a duality relation between the $k$ and $(n-k)$
compounds of $A$. We use this duality relation to derive a sufficient condition
for $k$-contraction that does not require the computation of any $k$-compounds.
  We demonstrate our results by deriving a sufficient condition for
$k$-contraction of an $n$-dimensional Hopfield network that does not require to
compute any compounds. In particular, for $k=2$ this sufficient condition
implies that the network is $2$-contracting and this implies a strong
asymptotic property: every bounded solution of the network converges to an
equilibrium point, that may not be unique. This is relevant, for example, when
using the Hopfield network as an associative memory that stores patterns as
equilibrium points of the dynamics.",2209.01046v1
2022-09-11,Operational and Economy-Wide Impacts of Compound Cyberattacks and Extreme Weather Events on Electric Power Networks,"The growing frequencies of extreme weather events and cyberattacks give rise
to a novel threat where a malicious cyber actor aims to disrupt stressed
components of critical infrastructure systems immediately before, during, or
shortly after an extreme weather event. In this paper, we initiate the study of
Compound Cyber-Physical Threats and develop a two-stage framework for the
analysis of operational disruptions in electric power networks and economy-wide
impacts under three scenarios: a Heatwave, a Cyberattack, and a Compound
scenario when the Cyberattack is timed with the Heatwave. In the first stage,
we use a bilevel optimization problem to represent the adversarial rationale of
a cyberattacker in the upper level. In the lower level, we model disruptions in
the electric power network using an optimal power flow model. In the second
stage, we couple the disruption of electricity supply with a Computable General
Equilibrium model to elucidate the impacts on all economic sectors. For the New
York Independent System Operator, we find that a 9% demand increase in a
Heatwave may not lead to unserved load. The Cyberattack can lead to 4% of
unserved electric load in Long Island, while the Compound scenario can increase
unserved electric load in Long Island to 13% and affect almost 600,000
customers. Our results show that the activity of state and local government
enterprises can decrease by 30% in the Compound scenario. We conclude that the
vulnerability of federal, state, and local government enterprises to
electricity disruptions can affect a broad range of populations.",2209.04927v1
2022-10-15,Tetragonal-phase SnOFeSe: A possible parent compound of FeSe-based superconductor,"Recent experiments have reported that inserting metal atoms or small
molecules in between the FeSe layers of $\beta$-FeSe can significantly enhance
the superconducting transition temperature. Here, based on first-principles
electronic structure calculations, we propose a stable compound SnOFeSe by
alternatively stacking the SnO and $\beta$-FeSe layers. The predicted SnOFeSe
has the same tetragonal structure as the well-known FeAs-based compound
LaOFeAs, meanwhile their electronic structures in the nonmagnetic state are
quite similar. The magnetic ground state of SnOFeSe is predicted to be the
dimer antiferromagnetic (AFM) state, which is energetically only 2.77 (2.15)
meV/Fe lower than the trimer (dimer-trimer-dimer-trimer) AFM state, indicating
that strong magnetic fluctuations might be induced via slight modulation.
Interestingly, SnOFeSe is at the verge of metal-insulator transition in these
low-energy magnetic states, hence bridging the metallic parent compounds of
iron-based superconductors and the insulating ones of cuprate superconductors.
With the reduced dimensionality, monolayer SnOFeSe also shows great
similarities in the electronic and magnetic properties to its bulk phase. Given
that SnOFeSe is adjacent to magnetic frustration and resembles LaOFeAs in both
crystal and electronic structures, we suggest that SnOFeSe is a possible
superconductor parent compound, which may provide a promising platform to study
the interplay between magnetism and unconventional superconductivity in
FeSe-derived materials.",2210.08146v1
2022-11-05,Identification and Molecular Dynamic Simulation of Flavonoids from Mediterranean species of Oregano against the Zika NS2B-NS3 Protease,"The Zika virus, is an emerging infectious disease causing severe
complications such as microcephaly in infants and Guillain Barre syndrome in
adults. There is no licensed vaccination or approved medicine to treat ZIKV
infection. Therefore, extensive research is being carried out to find compounds
that can be used effectively as therapeutic molecules to treat ZIKV infection.
Oregano, a commonly found herb in the Mediterranean region, has been used
predominantly for culinary purposes. The fact that the members of the Origanum
species are a storehouse of various bioactive compounds gives us a solid reason
to study compounds extracted from it for therapeutic purposes. In this study,
were retrieved 20 Flavonoids found in various Origanum species belonging to the
Mediterranean region from the PubChem database and pharmacological analysis
using SwissADME and Molecular docking using AutoDock Vina 4.0. were carried out
against the NS2B NS3 protease since it serves as an effective drug target owing
to its role in viral replication and immune evasion within the host. The best
hit compounds were subjected to MD simulation at 100 ns using Desmond
Schrodinger to analyze the molecule's stability. We observed Cirsiliol as the
best hit compound against the NS2B NS3 complex with a binding affinity of -8.5
kcal per mol. It also showed good stability during MD simulation. We recommend
the use of Cirsiliol for in vitro and in vivo studies for further investigation
concerning the ZIKA virus.",2211.02826v1
2022-10-19,An efficient graph generative model for navigating ultra-large combinatorial synthesis libraries,"Virtual, make-on-demand chemical libraries have transformed early-stage drug
discovery by unlocking vast, synthetically accessible regions of chemical
space. Recent years have witnessed rapid growth in these libraries from
millions to trillions of compounds, hiding undiscovered, potent hits for a
variety of therapeutic targets. However, they are quickly approaching a size
beyond that which permits explicit enumeration, presenting new challenges for
virtual screening. To overcome these challenges, we propose the Combinatorial
Synthesis Library Variational Auto-Encoder (CSLVAE). The proposed generative
model represents such libraries as a differentiable, hierarchically-organized
database. Given a compound from the library, the molecular encoder constructs a
query for retrieval, which is utilized by the molecular decoder to reconstruct
the compound by first decoding its chemical reaction and subsequently decoding
its reactants. Our design minimizes autoregression in the decoder, facilitating
the generation of large, valid molecular graphs. Our method performs fast and
parallel batch inference for ultra-large synthesis libraries, enabling a number
of important applications in early-stage drug discovery. Compounds proposed by
our method are guaranteed to be in the library, and thus synthetically and
cost-effectively accessible. Importantly, CSLVAE can encode out-of-library
compounds and search for in-library analogues. In experiments, we demonstrate
the capabilities of the proposed method in the navigation of massive
combinatorial synthesis libraries.",2211.04468v1
2022-11-08,Insights into the Limitations of Parameter Transferability in Heteronuclear SAFT-type Equations of State,"The use of heteronuclear models are often viewed as ways to improve the
predictive ability and parameter transferability of advanced association
models, such as those derived from the Statistical Associating Fluid Theory
(SAFT). Indeed, several results in the literature have suggested that this
approach can be useful to accurately describe a given family/series of
homologous compounds and their mixtures, with accuracies competitive (and in
some cases better) than those obtained using the more traditional SAFT
variants. However, the parameter transferability of the different groups, i.e.
between different families of compounds, without the introduction of new groups
or refitting existing ones, is seldom reported, and often overlooked, making an
accurate evaluation of the heteronuclear models difficult. This work analyzes
whether the increased complexity of a heteronuclear treatment of a SAFT-type
EoS, namely the SAFT-{\gamma}-Mie EoS, results in a significant increase on
both the predictive ability and parameter transferability of the model, across
different families of compounds. This is done by using a case study involving
some different (yet related) families of compounds, containing a small number
of common functional groups. The results obtained show that the transferability
of group parameters, across different families of compounds, in a heteronuclear
SAFT-type EoS does not allow an adequate description of the phase equilibria of
these systems. Therefore, to achieve a reasonable accuracy in the description
of these systems, a specific refitting of group parameters is required for a
given family, or even for a particular system, destroying the predictive
capability of these models. Moreover, this increases the number of adjustable
parameters to numbers similar to those used in homonuclear approaches, further
reducing the advantages of using heteronuclear models.",2211.04606v1
2022-12-13,Antiferromagnetic iron based magnetoelectric compounds,"The Landau free-energy of a compound that benefits from a linear coupling of
an electric field and a magnetic field includes a product of the two fields,
one polar and time-even and one axial and time-odd. In ME compounds,
expectation values of some atomic magnetic tensors are invariant with respect
to anti-inversion. An invariance shared by the Dirac monopole (an element of
charge allowed in Maxwell's equations that has not been observed) and a
Zeldovich anapole, also known as a Dirac dipole. From the science of materials
perspective, it has been established that Dirac multipoles contribute to the
diffraction of x-rays and neutrons. We identify Dirac monopoles in bulk
magnetic properties of iron tellurate (Fe2TeO6) and a spin ladder (SrFe2S2O).
Both cited compounds present a simple antiferromagnetic configuration of axial
dipoles, and their different magnetic crystal classes allow a linear ME effect.
However, the Kerr effect is symmetry allowed in the spin ladder and forbidden
in iron tellurate. Anapoles are forbidden in iron tellurate and allowed in the
spin ladder compound, a difference evident in diffraction patterns fully
informed by symmetry. More generally, we identify a raft of Dirac multipoles,
and axial multipoles beyond dipoles, visible in future experiments using
standard techniques with beams of neutrons or x-rays tuned in energy to an iron
atomic resonance. ME invariance imposes a phase relationship between nuclear
(charge) and magnetic contributions to neutron (x-ray) diffraction amplitudes.
In consequence, intensities of Bragg spots in an x-ray pattern do not change
when helicity in the primary beam is reversed. A like effect occurs in the
magnetic diffraction of polarized neutrons.",2212.06403v1
2023-02-06,Proposing Novel Extrapolative Compounds by Nested Variational Autoencoders,"Materials informatics (MI), which uses artificial intelligence and data
analysis techniques to improve the efficiency of materials development, is
attracting increasing interest from industry. One of its main applications is
the rapid development of new high-performance compounds. Recently, several deep
generative models have been proposed to suggest candidate compounds that are
expected to satisfy the desired performance. However, they usually have the
problem of requiring a large amount of experimental datasets for training to
achieve sufficient accuracy. In actual cases, it is often possible to
accumulate only about 1000 experimental data at most. Therefore, the authors
proposed a deep generative model with nested two variational autoencoders
(VAEs). The outer VAE learns the structural features of compounds using
large-scale public data, while the inner VAE learns the relationship between
the latent variables of the outer VAE and the properties from small-scale
experimental data. To generate high performance compounds beyond the range of
the training data, the authors also proposed a loss function that amplifies the
correlation between a component of latent variables of the inner VAE and
material properties. The results indicated that this loss function contributes
to improve the probability of generating high-performance candidates.
Furthermore, as a result of verification test with an actual customer in
chemical industry, it was confirmed that the proposed method is effective in
reducing the number of experiments to $1/4$ compared to a conventional method.",2302.02555v1
2023-02-24,Statistical Principles for Platform Trials,"While within a clinical study there may be multiple doses and endpoints,
across different studies each study will result in either an approval or a lack
of approval of the drug compound studied. The False Approval Rate (FAR) is the
proportion of drug compounds that lack efficacy incorrectly approved by
regulators. (In the U.S., compounds that have efficacy and are approved are not
involved in the FAR consideration, according to our reading of the relevant
U.S. Congressional statute).
  While Tukey's (1953) Error Rate Familwise (ERFw) is meant to be applied
within a clinical study, Tukey's (1953) Error Rate per Family (ERpF), defined
alongside ERFw,is meant to be applied across studies. We show that controlling
Error Rate Familwise (ERFw) within a clinical study at 5% in turn controls
Error Rate per Family (ERpF) across studies at 5-per-100, regardless of whether
the studies are correlated or not. Further, we show that ongoing regulatory
practice, the additive multiplicity adjustment method of controlling ERpF, is
controlling False Approval Rate FAR exactly (not conservatively) at 5-per-100
(even for Platform trials).
  In contrast, if a regulatory agency chooses to control the False Discovery
Rate (FDR) across studies at 5% instead, then this change in policy from ERpF
control to FDR control will result in incorrectly approving drug compounds that
lack efficacy at a rate higher than 5-per-100, because in essence it gives the
industry additional rewards for successfully developing compounds that have
efficacy and are approved. Seems to us the discussion of such a change in
policy would be at a level higher than merely statistical, needing
harmonizsation/harmonization. (In the U.S., policy is set by the Congress.)",2302.12728v1
2023-04-14,Symbiotic Message Passing Model for Transfer Learning between Anti-Fungal and Anti-Bacterial Domains,"Machine learning, and representation learning in particular, has the
potential to facilitate drug discovery by screening billions of compounds. For
example, a successful approach is representing the molecules as a graph and
utilizing graph neural networks (GNN). Yet, these approaches still require
experimental measurements of thousands of compounds to construct a proper
training set. While in some domains it is easier to acquire experimental data,
in others it might be more limited. For example, it is easier to test the
compounds on bacteria than perform in-vivo experiments. Thus, a key question is
how to utilize information from a large available dataset together with a small
subset of compounds where both domains are measured to predict compounds'
effect on the second, experimentally less available domain. Current transfer
learning approaches for drug discovery, including training of pre-trained
modules or meta-learning, have limited success. In this work, we develop a
novel method, named Symbiotic Message Passing Neural Network (SMPNN), for
merging graph-neural-network models from different domains. Using routing new
message passing lanes between them, our approach resolves some of the potential
conflicts between the different domains, and implicit constraints induced by
the larger datasets. By collecting public data and performing additional
high-throughput experiments, we demonstrate the advantage of our approach by
predicting anti-fungal activity from anti-bacterial activity. We compare our
method to the standard transfer learning approach and show that SMPNN provided
better and less variable performances. Our approach is general and can be used
to facilitate information transfer between any two domains such as different
organisms, different organelles, or different environments.",2304.07017v1
2023-06-26,Nanoextraction from a flow of a highly diluted solution for much-improved sensitivity in offline chemical detection and quantification,"Preconcentration of the target compound is a critical step that ensures the
accuracy of the subsequent chemical analysis. In this work, we present a
straightforward yet effective liquid-liquid extraction approach based on
surface nanodroplets (i.e., nanoextraction) for offline analysis of highly
diluted sample solutions. The extraction and sample collection were streamlined
in a 3-m microcapillary tube. The concentration of the target analyte in
surface nanodroplets was significantly increased compared to the concentration
in the sample solution, reaching several orders of magnitudes. A limit of
detection (LOD) was decreased by a factor of $\sim 10^3$ for an organic model
compound in Fourier-transform infrared spectroscopy (FTIR) measurements and
$\sim 10^5$ for a model fluorescent dye in fluorescence detection. The
quantitative analysis of the organic compound was also achieved in a wide
concentration region from $10^{-3}$ M to $10^{-4}$ M. The total volume of
surface nanodroplets can be manipulated to further enhance extraction
efficiency, according to the principle that governs droplet formation by
solvent exchange. Additionally, our method exhibited significantly improved
sensitivity compared to traditional dispersive liquid-liquid microextraction
(DLLME). The LOD of the fluorescent dye and the organic model compound obtained
with DLLME was 3 orders of magnitude and 20 times higher than the LOD achieved
through nanoextraction approach. The nanoextraction developed in this work can
be applied to preconcentrate multi-compounds from river water samples, without
clear interference from each other. This can further extend its applicability
for the detection and quantification of target analytes in complex aqueous
samples by common analytical instruments.",2306.14860v1
2023-06-28,Exploring chemical compound space with a graph-based recommender system,"With the availability of extensive databases of inorganic materials,
data-driven approaches leveraging machine learning have gained prominence in
materials science research. In this study, we propose an innovative adaptation
of data-driven concepts to the mapping and exploration of chemical compound
space. Recommender systems, widely utilized for suggesting items to users,
employ techniques such as collaborative filtering, which rely on bipartite
graphs composed of users, items, and their interactions. Building upon the Open
Quantum Materials Database (OQMD), we constructed a bipartite graph where
elements from the periodic table and sites within crystal structures are
treated as separate entities. The relationships between them, defined by the
presence of ions at specific sites and weighted according to the thermodynamic
stability of the respective compounds, allowed us to generate an embedding
space that contains vector representations for each ion and each site. Through
the correlation of ion-site occupancy with their respective distances within
the embedding space, we explored new ion-site occupancies, facilitating the
discovery of novel stable compounds. Moreover, the graph's embedding space
enabled a comprehensive examination of chemical similarities among elements,
and a detailed analysis of local geometries of sites. To demonstrate the
effectiveness and robustness of our method, we conducted a historical
evaluation using different versions of the OQMD and recommended new compounds
with Kagome lattices, showcasing the applicability of our approach to practical
materials design.",2306.16496v1
2023-07-09,"Neutron scattering and muon-spin spectroscopy studies of the magnetic triangular-lattice compounds $A_2$La$_2$NiW$_2$O$_{12}$ ($A$ = Sr, Ba)","We report on the geometrically frustrated two-dimensional triangular-lattice
magnets $A_2$La$_2$NiW$_2$O$_{12}$ ($A$ = Sr, Ba) studied mostly by means of
neutron powder diffraction (NPD) and muon-spin rotation and relaxation
($\mu$SR) techniques. The chemical pressure induced by the Ba-for-Sr
substitution suppresses the ferromagnetic (FM) transition from 6.3 K in the
Ba-compound to 4.8 K in the Sr-compound. We find that the $R\bar{3}$ space
group reproduces the NPD patterns better than the previously reported
$R\bar{3}m$ space group. Both compounds adopt the same magnetic structure with
a propagation vector $\boldsymbol{k} = (0, 0, 0)$, in which the Ni$^{2+}$
magnetic moments are aligned ferromagnetically along the $c$-axis. The
zero-field {\textmu}SR results reveal two distinct internal fields (0.31 and
0.10 T), caused by the long-range ferromagnetic order. The small transverse
muon-spin relaxation rates reflect the homogeneous internal field distribution
in the ordered phase and, thus, further support the simple FM arrangement of
the Ni$^{2+}$ moments. The small longitudinal muon-spin relaxation rates, in
both the ferromagnetic- and paramagnetic states of A$_2$La$_2$NiW$_2$O$_{12}$,
indicate that spin fluctuations are rather weak. Our results demonstrate that
chemical pressure indeed changes the superexchange interactions in
$A_2$La$_2$NiW$_2$O$_{12}$ compounds, with the FM interactions being dominant.",2307.04116v1
2023-09-12,Optoelectronic and Transport Properties of Vacancy Ordered Double Perovskite Halides: A First-principles Study,"In the search for stable lead (Pb) free perovskites, Vacancy ordered double
perovskite (VODP), A$_2$BX$_6$ has emerged as a promising class of materials
for solar harvesting owing to their nontoxicity, better stability, and unique
optoelectronic properties. Here, we present the stability and the key physical
attributes of few selected compounds in a systematic manner using
state-of-the-art first-principle calculations. A careful structural and
stability analysis via simulating convex hull and compositional phase diagrams
for different structural prototypes discloses 14 stable and 1 metastable
compounds in this class. The electronic structure calculations using hybrid
functional reveals six compounds to acquire band gap in the ideal visible
region. These six compounds, namely Cs$_2$SnI$_6$, Cs$_2$PdI$_6$,
Cs$_2$TeI$_6$, Cs$_2$TiI$_6$, Cs$_2$PtI$_6$, and Cs$_2$PdBr$_6$, show high
optical absorption ($\approx$ 10$^{5}$ cm $^{-1}$) giving rise to high
spectroscopic limited maximum efficiency, SLME (15-23\%) in the thin-film
thickness range. Close inspection of transport properties reveals polar optical
phonon scattering to be the dominant mechanism limiting the overall mobility.
Further analysis of the polaron excitations discloses the possibility of large
polaron formation at low to moderate defect concentrations. At high defect
concentrations, ionized impurity scattering takes over. This suggests that, a
simulation based guided control of defect concentrations during synthesis can
yield a desired candidate for promissing device application. Additionally, few
selected compounds show moderate to high electron mobility values ($\sim$13-63
cm$^2$V$^{-1}$ s$^{-1}$) at room temperature. Overall, the present study paves
an important path to help design VODP as Pb-free potential candidates for
future optoelectronic applications.",2309.06153v1
2023-09-13,Lattice Thermal Conductivity from First Principles and Active Learning with Gaussian Process Regression,"The lattice thermal conductivity ($\kappa_{\ell}$) is a key materials
property in power electronics, thermal barriers, and thermoelectric devices.
Identifying a wide pool of compounds with low $\kappa_{\ell}$ is particularly
important in the development of materials with high thermoelectric efficiency.
The present study contributed to this with a reliable machine learning (ML)
model based on a training set consisting of 268 cubic compounds. For those,
$\kappa_{\ell}$ was calculated from first principles using the
temperature-dependent effective potential (TDEP) method based on forces and
phonons calculated by density functional theory (DFT). 238 of these were
preselected and used to train an initial ML model employing Gaussian process
regression (GPR). The model was then improved with active learning (AL) by
selecting the 30 compounds with the highest GPR uncertainty as new members of
an expanded training set. This was used to predict $\kappa_{\ell}$ of the 1574
cubic compounds in the \textsc{Materials Project} (MP) database with a
validation R2-score of 0.81 and Spearman correlation of 0.93. Out of these, 27
compounds were predicted to have very low values of $\kappa_{\ell}$ ($\leq 1.3$
at 300~K), which was verified by DFT calculations. Some of these have not
previously been reported in the literature, suggesting further investigations
of their electronic thermoelectric properties.",2309.06786v1
2023-09-19,Multi-Object Graph Affordance Network: Enabling Goal-Oriented Planning through Compound Object Affordances,"Learning object affordances is an effective tool in the field of robot
learning. While the data-driven models delve into the exploration of
affordances of single or paired objects, there is a notable gap in the
investigation of affordances of compound objects that are composed of an
arbitrary number of objects with complex shapes. In this study, we propose
Multi-Object Graph Affordance Network (MOGAN) that models compound object
affordances and predicts the effect of placing new objects on top of the
existing compound. Given different tasks, such as building towers of specific
heights or properties, we used a search based planning to find the sequence of
stack actions with the objects of suitable affordances. We showed that our
system was able to correctly model the affordances of very complex compound
objects that include stacked spheres and cups, poles, and rings that enclose
the poles. We demonstrated the applicability of our system in both simulated
and real-world environments, comparing our systems with a baseline model to
highlight its advantages.",2309.10426v2
2023-09-20,Large-scale Pretraining Improves Sample Efficiency of Active Learning based Molecule Virtual Screening,"Virtual screening of large compound libraries to identify potential hit
candidates is one of the earliest steps in drug discovery. As the size of
commercially available compound collections grows exponentially to the scale of
billions, brute-force virtual screening using traditional tools such as docking
becomes infeasible in terms of time and computational resources. Active
learning and Bayesian optimization has recently been proven as effective
methods of narrowing down the search space. An essential component in those
methods is a surrogate machine learning model that is trained with a small
subset of the library to predict the desired properties of compounds. Accurate
model can achieve high sample efficiency by finding the most promising
compounds with only a fraction of the whole library being virtually screened.
In this study, we examined the performance of pretrained transformer-based
language model and graph neural network in Bayesian optimization active
learning framework. The best pretrained models identifies 58.97% of the
top-50000 by docking score after screening only 0.6% of an ultra-large library
containing 99.5 million compounds, improving 8% over previous state-of-the-art
baseline. Through extensive benchmarks, we show that the superior performance
of pretrained models persists in both structure-based and ligand-based drug
discovery. Such model can serve as a boost to the accuracy and sample
efficiency of active learning based molecule virtual screening.",2309.11687v1
2023-09-25,"Magnetic States and Electronic Properties of Manganese-Based Intermetallic Compounds Mn$_2$YAl and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni; Z = Al, Ge, Sn, Si, Pt)","We present a brief review of experimental and theoretical papers on studies
of electron transport and magnetic properties in manganese-based compounds
Mn$_2$YZ and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni, etc.; Z = Al, Ge, Sn, Si, Pt,
etc.). It has been shown that in the electronic subsystem of Mn$_2$YZ
compounds, the states of a half-metallic ferromagnet and a spin gapless
semiconductor can arise with the realization of various magnetic states, such
as a ferromagnet, a compensated ferrimagnet, and a frustrated antiferromagnet.
Binary compounds Mn$_3$Z have the properties of a half-metallic ferromagnet and
a topological semimetal with a large anomalous Hall effect, spin Hall effect,
spin Nernst effect, and thermal Hall effect. Their magnetic states are also
very diverse: from a ferrimagnet and an antiferromagnet to a compensated
ferrimagnet and a frustrated antiferromagnet, as well as an antiferromagnet
with a kagome-type lattice. It has been demonstrated that the electronic and
magnetic properties of such materials are very sensitive to external influences
(temperature, magnetic field, external pressure), as well as the processing
method (cast, rapidly quenched, nanostructured, etc.). Knowledge of the
regularities in the behavior of the electronic and magnetic characteristics of
Mn$_2$YAl and Mn$_3$Z compounds can be used for applications in micro- and
nanoelectronics and spintronics.",2309.14140v1
2023-12-02,"The electronic, thermodynamic, thermoelectric and optical properties of Ca(InP)2 compound: DFT study","In this study, we investigate the electronic, optical, thermoelectric, and
thermodynamic properties of Ca(InP)2 through comprehensive theoretical
calculations Ca(InP)2 is a compound with promising applications in materials
science and electronics. Using the density functional theory (DFT) with
Generalized Gradient Approximation (GGA) and modified Becke_Johnson
approximation (mBJ), we determine the band structure, density of states, and
optical properties of Ca(InP)2. The obtained results reveal that the Ca(InP)2
compound exhibits a direct band gap of 0 eV and 0,645 eV for PBE-GGA and
GGA+mBJ, respectively. This direct band gap is found at the Gamma point of the
Brillouin zone, making it well-suited for optoelectronic applications.
Furthermore, we analyze the thermoelectric properties such as the Seebeck
coefficient, the lattice thermal conductivity, and optical properties like
dielectric function, absorption coefficient, conductivity, and extinction
coefficient. Thermodynamic properties, including heat capacity and Debye
temperature, are also calculated, providing a deeper understanding of the
compound's thermal behavior. The findings of this study highlight the
fundamental characteristics of Ca(InP)2 and offer valuable information for its
potential use in electronic and optoelectronic devices. A comprehensive
understanding of the electronic, optical, and thermodynamic properties of the
Ca(InP)2 compound can serve as a guide for future experimental research and aid
in the design of novel materials for a wide range of technological
applications.",2312.01102v1
2024-01-16,Simultaneous Coherent and Displacement Compounding for 2D Noninvasive Carotid Strain Imaging: a Proof of Principle Study,"Arteriosclerosis results from lipid buildup in artery walls, leading to
plaque formation, and is a leading cause of death. Plaque rupture can cause
blood clots that might lead to a stroke. Distinguishing plaque types is a
challenge, but ultrasound elastography can help by assessing plaque composition
based on strain values. Since the artery has a circular structure, an accurate
axial and lateral displacement strategy is needed to derive the radial and
circumferential strains. A high precision lateral displacement is challenging
due to the lack of phase information in the lateral direction of the beamformed
RF data. Previously, our group has developed a compounding technique in which
the lateral displacement is estimated using tri-angulation of the axial
displacement estimated from transmitting and beamforming ultrasound beams at
+-20 degree. However, its applicability to in vivo is challenging due to the
imaging noise and the low contrast of the arterial wall, caused by a single
plane wave transmission. In this paper, we combine our displacement compounding
with coherent compounding. Instead of transmitting a single plane wave,
multiple plane waves are transmitted at certain angles with respect to the
angle of the beamforming grids, and then the backscattered wavefronts are
beamformed and coherently compounded on the center of the transmit beams (-20,
+20 and 0 degree). ...",2401.08218v1
2024-02-13,PSC-CPI: Multi-Scale Protein Sequence-Structure Contrasting for Efficient and Generalizable Compound-Protein Interaction Prediction,"Compound-Protein Interaction (CPI) prediction aims to predict the pattern and
strength of compound-protein interactions for rational drug discovery. Existing
deep learning-based methods utilize only the single modality of protein
sequences or structures and lack the co-modeling of the joint distribution of
the two modalities, which may lead to significant performance drops in complex
real-world scenarios due to various factors, e.g., modality missing and domain
shifting. More importantly, these methods only model protein sequences and
structures at a single fixed scale, neglecting more fine-grained multi-scale
information, such as those embedded in key protein fragments. In this paper, we
propose a novel multi-scale Protein Sequence-structure Contrasting framework
for CPI prediction (PSC-CPI), which captures the dependencies between protein
sequences and structures through both intra-modality and cross-modality
contrasting. We further apply length-variable protein augmentation to allow
contrasting to be performed at different scales, from the amino acid level to
the sequence level. Finally, in order to more fairly evaluate the model
generalizability, we split the test data into four settings based on whether
compounds and proteins have been observed during the training stage. Extensive
experiments have shown that PSC-CPI generalizes well in all four settings,
particularly in the more challenging ``Unseen-Both"" setting, where neither
compounds nor proteins have been observed during training. Furthermore, even
when encountering a situation of modality missing, i.e., inference with only
single-modality protein data, PSC-CPI still exhibits comparable or even better
performance than previous approaches.",2402.08198v1
2024-03-04,Are More LLM Calls All You Need? Towards Scaling Laws of Compound Inference Systems,"Many recent state-of-the-art results in language tasks were achieved using
compound systems that perform multiple Large Language Model (LLM) calls and
aggregate their responses. However, there is little understanding of how the
number of LLM calls -- e.g., when asking the LLM to answer each question
multiple times and taking a consensus -- affects such a compound system's
performance. In this paper, we initiate the study of scaling laws of compound
inference systems. We analyze, theoretically and empirically, how the number of
LLM calls affects the performance of one-layer Voting Inference Systems -- one
of the simplest compound systems, which aggregates LLM responses via majority
voting. We find empirically that across multiple language tasks, surprisingly,
Voting Inference Systems' performance first increases but then decreases as a
function of the number of LLM calls. Our theoretical results suggest that this
non-monotonicity is due to the diversity of query difficulties within a task:
more LLM calls lead to higher performance on ""easy"" queries, but lower
performance on ""hard"" queries, and non-monotone behavior emerges when a task
contains both types of queries. This insight then allows us to compute, from a
small number of samples, the number of LLM calls that maximizes system
performance, and define a scaling law of Voting Inference Systems. Experiments
show that our scaling law can predict the performance of Voting Inference
Systems and find the optimal number of LLM calls to make.",2403.02419v1
2000-01-11,Magnetic Susceptibilities of Spin-1/2 Antiferromagnetic Heisenberg Ladders and Applications to Ladder Oxide Compounds,"A comprehensive theoretical and experimental study is presented of the
magnetic susceptibility versus temperature \chi(T) of spin S = 1/2 two- and
three-leg Heisenberg ladders and ladder oxide compounds. Extensive quantum
Monte Carlo simulations of \chi(T) were carried out for both isolated and
coupled two-leg ladders with spatially anisotropic intraladder exchange.
Accurate fits to these and related literature QMC data were obtained. We have
also calculated the one- and two-magnon dispersion relations and the dynamical
spin structure factor for anisotropic isolated 2 x 12 ladders. The exchange
constants in the two-leg ladder compound SrCu2O3 are estimated from LDA+U
calculations. We report the detailed crystal structure of SrCu2O3 and of the
three-leg ladder compound Sr2Cu3O5. New experimental \chi(T) data are reported
for the two-leg ladder cuprates SrCu2O3 and LaCuO_{2.5}, and for the
(nominally) two-leg ladder vanadates CaV2O5 and MgV2O5. The new and literature
\chi(T) data for these compounds and for Sr2Cu3O5 are modeled using our QMC
\chi(T) simulation fits, and the exchange coupling constants between the
spins-1/2 are thereby estimated for each material. The surpisingly strong
spatial anisotropy of the bilinear intraladder exchange constants in the
cuprate compounds is discussed together with the results of other experiments
sensitive to this anisotropy. Recent theoretical predictions are discussed
including those which indicate that a four-spin cyclic exchange interaction
within a Cu4 plaquette is important to determining the magnetic properties and
which can significantly influence the exchange interactions estimated from
\chi(T) data assuming the presence of only bilinear exchange.",0001147v1
2005-03-23,Electronic structure of superconducting graphite intercalate compounds: The role of the interlayer state,"Although not an intrinsic superconductor, it has been long--known that, when
intercalated with certain dopants, graphite is capable of exhibiting
superconductivity. Of the family of graphite--based materials which are known
to superconduct, perhaps the most well--studied are the alkali metal--graphite
intercalation compounds (GIC) and, of these, the most easily fabricated is the
C${}_8$K system which exhibits a transition temperature $\bm{T_c\simeq 0.14}
$K. By increasing the alkali metal concentration (through high pressure
fabrication techniques), the transition temperature has been shown to increase
to as much as $\bm 5 $K in C${}_2$Na. Lately, in an important recent
development, Weller \emph{et al.} have shown that, at ambient conditions, the
intercalated compounds \cyb and \cca exhibit superconductivity with transition
temperatures $\bm{T_c\simeq 6.5} $K and $\bm{11.5} $K respectively, in excess
of that presently reported for other graphite--based compounds. We explore the
architecture of the states near the Fermi level and identify characteristics of
the electronic band structure generic to GICs. As expected, we find that charge
transfer from the intercalant atoms to the graphene sheets results in the
occupation of the $\bm\pi$--bands. Yet, remarkably, in all those -- and only
those -- compounds that superconduct, we find that an interlayer state, which
is well separated from the carbon sheets, also becomes occupied. We show that
the energy of the interlayer band is controlled by a combination of its
occupancy and the separation between the carbon layers.",0503569v2
2013-12-04,Structure and Properties of α-NaFeO2-type Ternary Sodium Iridates,"The synthesis, structure, and elementary magnetic and electronic properties
are reported for layered compounds of the type Na3-xMIr2O6 and Na3-xM2IrO6,
where M is a transition metal from the 3d series (M=Zn, Cu, Ni, Co, Fe and Mn).
The rhombohedral structures, in space group R-3m, were determined by refinement
of neutron and synchrotron powder diffraction data. No clear evidence for long
range 2:1 or 1:2 honeycomb-like M/Ir ordering was found in the neutron powder
diffraction patterns except in the case of M = Zn, thus in general the
compounds are best designated as sodium deficient {\alpha}-NaFeO2-type phases
with formulas Na1-xM1/3Ir2/3O2 or Na1-xM2/3Ir1/3O2. Synchrotron powder
diffraction patterns indicate that several of the compounds likely have
honeycomb in-plane metal-iridium ordering with disordered stacking of the
layers. All the compounds are sodium deficient under our synthetic conditions
and are black and insulating. Weiss constants derived from magnetic
susceptibility measurements indicate that Na0.62Mn0.61Ir0.39O2,
Na0.80Fe2/3Ir1/3O2, Na0.92Ni1/3Ir2/3O2, Na0.86Cu1/3Ir2/3O2, and
Na0.89Zn1/3Ir2/3O2 display dominant antiferromagnetic interactions. For
Na0.90Co1/3Ir2/3O2 the dominant magnetic interactions at low temperature are
ferromagnetic while at high temperatures they are antiferromagnetic; there is
also a change in the effective moment. Low temperature specific heat
measurements (to 2 K) on Na0.92Ni1/3Ir2/3O2 indicate the presence of a broad
magnetic ordering transition. X-ray absorption spectroscopy shows that iridium
is at or close to the 4+ oxidation state in all compounds. 23Na nuclear
magnetic resonance measurements comparing Na2IrO3 to Na0.92Ni1/3Ir2/3O2 and
Na0.89Zn1/3Ir2/3O2 provide strong indications that the electron spins are
short-range ordered in the latter two materials. All of the compounds are spin
glasses.",1312.0995v1
2013-12-11,From stellar nebula to planets: the refractory components,"We computed the abundance of refractory elements in planetary bodies formed
in stellar systems with solar chemical composition by combining models for
chemical composition and planet formation. We also consider the formation of
refractory organic compounds, which have been ignored in previous studies on
this topic. We used the commercial software package HSC Chemistry in order to
compute the condensation sequence and chemical composition of refractory
minerals incorporated into planets. The problem of refractory organic material
is approached with two distinct model calculations: the first considers that
the fraction of atoms used in the formation of organic compounds is removed
from the system (i.e. organic compounds are formed in the gas phase and are
nonreactive); and the second assumes that organic compounds are formed by the
reaction between different compounds that had previously condensed from the gas
phase. Results show that refractory material represents more than 50 wt % of
the mass of solids accreted by the simulated planets, with up to 30 wt % of the
total mass composed of refractory organic compounds. Carbide and silicate
abundances are consistent with C/O and Mg/Si elemental ratios of 0.5 and 1.02
for the Sun. Less than 1 wt % of carbides; pyroxene and olivine in similar
quantities are formed. The model predicts planets that are similar in
composition to those of the Solar system. It also shows that, starting from a
common initial nebula composition, a wide variety of chemically different
planets can form, which means that the differences in planetary compositions
are due to differences in the planetary formation process. We show that a model
in which refractory organic material is absent from the system is more
compatible with observations. The use of a planet formation model is essential
to form a wide diversity of planets in a consistent way.",1312.3085v2
2014-01-22,Correct quantitative determination of ethanol and volatile compounds in alcohol products,"Determination of the volume content of ethanol in the alcohol products in
practice is usually determined by pycnometry, electronic densimetry, or
densimetry using a hydrostatic balance in accordance with Commission Regulation
No 2870/2000. However, these methods determine directly only density of the
tested liquid sample and does not take into account the effects of other
volatile components such as aldehydes, esters and higher alcohols. So they are
appropriate only for binary water-ethanol solutions in accordance with
international table adopted by the International Legal Metrology Organization
in its Recommendation No 22. Availability notable concentrations of the higher
alcohols and ethers in different alcohol-based products, e. g. in whisky,
cognac, brandy, wine as well as in waste alcohol and alcohol beverage
production, leads to the significant contribution of these compounds in the
value of the density of tested alcohol-containing sample. As a result,
determination of the volume of ethanol content for such alcohol products in
gives the value of the strength, which may significantly differ from the true
one. Using incorrectly calculated volume content of ethyl alcohol leads to
incorrect results determining the quantities of volatile compounds in the
alcohol-containing products, expressed in milligrams per liter of absolute
alcohol. We propose experimental results of the method of correct determination
of ethanol and other volatile compounds content in waste products of alcohol
and alcoholic beverage industry by gas chromatography. Calculations are based
on the measured value of sample density and volatile compound concentrations
expressed in mg per liter of absolute alcohol [JAFC 61(2013)2950]. The method
can be easily incorporated into daily practice of analytical and control
laboratories with no additional material, financial or time costs.",1401.5599v1
2014-03-11,Finding the stable structures of W$_x$N$_1$$_-$$_x$ with an $ab$$-$$initio$ high-throughput approach,"Using density functional theory calculations, many researchers have predicted
that various tungsten-nitride compounds WN$_x$ ($x$ > 1) will be
""ultra-compressible"" or ""superhard"", $i.e.$ as hard as or harder than diamond.
These compounds are predicted to have large bulk and shear moduli (> 200 GPa)
and to be elastically and vibrationally stable.
  Compounds with such desirable properties must be energetically stable against
decomposition into other compounds. This stability can only be found after the
determination of the convex hull for W$_x$N$_1$$_-$$_x$ lines which connect the
lowest enthalpy structures as a function of composition. The phase diagram of
the W-N structure is uncertain, both experimentally and computationally.
Complex van der Waals forces play a significant role in determining the
structure of solid N$_2$.
  Here we use high-throughput calculations to map out the convex hull and other
low energy structures for the W-N system. We find that the ground state of the
system is the NbO structure, and that the WN$_2$ structures found by Wang $et$
$al$. are also stable when the van der Waals forces are neglected. Other
proposed structures are above the convex hull of the W-N system. We show how
the choice of density functional influences the shape of the curve and the
structures that form the hull. In nitrogen-rich compounds, the choice of
functional can dramatically change the structural parameters and mechanical
behavior. Using any of the functionals, the bulk and shear moduli of the NbO
phase are comparable to the WN$_x$ compounds that have been claimed to be
ultra-compressible for superhard.",1403.2762v1
2014-03-18,"Single crystal study of the layered heavy fermion compounds Ce$_2$PdIn$_8$, Ce$_3$PdIn$_{11}$, Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$","We report on single crystal growth and crystallographic parameters results of
Ce$_2$PdIn$_8$, Ce$_3$PdIn$_{11}$, Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$. The
Pt-systems Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$ are synthesized for the first
time. All these compounds are member of the Ce$_n$T$_m$In$_{3n+2m}$ (n = 1,
2,..; m = 1, 2,.. and T = transition metal) to which the extensively studied
heavy fermion superconductor CeCoIn$_5$ belongs. Single crystals have been
grown by In self-flux method. Differential scanning calorimetry studies were
used to derive optimal growth conditions. Evidently, the maximum growth
conditions for these materials should not exceed 750 $^{\circ}$C. Single
crystal x-ray data show that Ce$_2$TIn$_8$ compounds crystallize in the
tetragonal Ho$_2$CoGa$_8$ phase (space group P4/mmm) with lattice parameters a
=4.6898(3) $\AA$ and c =12.1490(8) $\AA$ for the Pt-based one (Pd: a =
4.6881(4) $\AA$ and c = 12.2031(8) \AA). The Ce$_3$TIn$_{11}$ compounds adopt
the Ce$_3$PdIn$_{11}$ structure with a = 4.6874(4) $\AA$ and c = 16.8422(12)
$\AA$ for the Pt-based one (Pd: a = 4.6896 $\AA$ and c = 16.891 \AA). Specific
heat experiments on Ce$_3$PtIn$_{11}$ and Ce$_3$PdIn$_{11}$ have revealed that
both compounds undergo two successive magnetic transitions at T$_1$ ~ 2.2 K
followed by T$_N$ ~ 2.0 K and T$_1$ ~ 1.7 K and T$_N$ ~ 1.5 K, respectively.
Additionally, both compounds exhibit enhanced Sommerfeld coefficients yielding
{\gamma}$_{Pt}$ = 0.300 J/mol K$^2$ Ce ({\gamma}$_{Pd}$ = 0.290 J/mol K$^2$
Ce), hence qualifying them as heavy fermion materials.",1403.4363v1
2014-12-05,Ferromagnetic behavior of the Kondo lattice compound $Np_2PtGa_3$,"In this study we report the results of study of novel ternary $Np_2PtGa_3$
compound. The x-ray-powder diffraction analysis reveals that the compound
crystallizes in the orthorhombic CeCu$_2$-type crystal structure (space group
Imma) with lattice parameters $a$ = 0.4409(2) nm, $b$ = 0.7077(3) nm and $c$ =
0.7683(3) nm at room temperature. The measurements of dc magnetization,
specific heat and electron transport properties in the temperature range 1.7 -
300 K and in magnetic fields up to 9 T imply that this intermetallic compound
belongs to a class of ferromagnetic Kondo systems. The Curie temperature of
$T_C \sim$ 26 K is determined from the magnetization and specific heat data. An
enhanced coefficient of the electronic specific heat of $\gamma$ = 180 mJ/(mol
at. Np K$^2$) and -ln\T dependence of the electrical resistivity indicate the
presence of Kondo effect, which can be described in terms of the S = 1
underscreened Kondo-lattice model. The estimated Kondo temperature $T_K \sim$
24 K, Hall mobility of $\sim$ 16.8 cm$^2$/Vs and effective mass of $\sim$ 83
$m_e$ are consistent with assumption that the heavy-fermion state develops in
$Np_2PtGa_3$ at low temperatures. We compare the observed properties of
$Np_2PtGa_3$ to that found in $Np_2PtGa_3$ and discuss their difference in
regard to change in the exchange interaction between the conduction and
localized 5f electrons. We have used the Fermi wave vector $k_F$ to evaluate
the Rudermann-Kittel-Kasuya-Yosida (RKKY) exchange. Based on experimental data
of the (U, Np)$_2$(Pd, Pt)Ga$_3$ compounds we suggest that the evolution of the
magnetic ground states in these actinide compounds can be explained within the
RKKY formalism.",1412.1962v1
2016-11-24,"Magnetic behavior of Ni substituted LiCoO2, magnetization and electron paramagnetic resonance studies","Single phase Ni substituted LiCo1-xNixO2 solid solutions with x < 0.15 have
been synthesized to study the effect of substitution on the magnetic behavior.
Two different techniques, magnetic susceptibility and electron paramagnetic
resonance, EPR which provide information in two different time windows have
been used. The solid solutions have been found to be single phase with large
grains conforming to R-3m rhombohedral structure. The lattice parameters c and
a increase with increasing Ni substitution but with a nearly constant c/a ratio
of about 4.99 in all the cases indicating that the CoO6 and LiO6 octahedra do
not undergo any Jahn-Teller distortions. The room temperature EPR absorption
spectra clearly shows a peak in all the compounds at a field of 314 mT
corresponding to a g-factor of 2.14. The peak width however is found to be a
strong function of Ni substitution; increasing with increasing Ni from 3.6 mT
to 6.5 mT for x = 0.08. The magnetization increases with decreasing temperature
in all the compounds, a paramagnetic behavior, unlike Li-deficient compounds
which show a Pauli paramagnetic susceptibility. Also, the magnetization
exhibits thermal irreversibility which vanishes at large magnetic fields in all
the compounds. The unsubstituted compound has discontinuities at 200 K and 50 K
corresponding to magnetic transitions which disappear on substitution with 2 %
Ni for Co. The effective magnetic moment is found to increase from 0.32 Bohr
magnetons to 0.66 Bohr magnetons on increasing the substitution to 0.15. The
unique feature however is that all the compounds exhibit a clear magnetic
hysteresis at room temperature with a finite coercivity. The coercivity
increases from 31 Oe to 168 Oe for x = 0.04 and then decreases on further
increasing of x. A deconvolution of the hysteresis loops clearly shows an
increasing paramagnetic component with substitution.",1611.08153v1
2019-04-09,CsMn$_4$As$_3$: A layered tetragonal transition-metal pnictide compound with antiferromagnetic ground state,"We report the synthesis and properties of a new layered tetragonal ternary
compound CsMn$_4$As$_3$ (structure: KCu$_4$S$_3$-type, space group: $P4/mmm$,
No. 123 and $Z = 2$). The material is a small band-gap semiconductor and
exhibits an antiferromagnetic ground state associated with Mn spins. The
compound exhibits a signature of a distinct magnetic moment canting event at
150(5)~K with a canting angle of $\approx 0.3^{\circ}$. Although, some features
of the magnetic characteristics of this new compound are qualitatively similar
to those of the related BaMn$_2$As$_2$, the underlying Mn sublattices of the
two materials are quite different. While the Mn square-lattice layers in
BaMn$_2$As$_2$ are equally spaced along the $c$-direction with the interlayer
distance $d_{\rm L\,Ba} = 6.7341(4)$ Ang., the Mn sublattice forms bilayers in
CsMn$_4$As$_3$ with the interlayer distance within a bilayer $d_{\rm L\,Cs} =
3.1661(6)$ Ang. and the distance between the two adjacent bilayers $d_{\rm B} =
7.290(6)$ Ang. This difference in the Mn sublattice is bound to significantly
alter the energy balance between the $J_{1}$, $J_{2}$ and $J_{c}$ exchange
interactions within the J1-J2-Jc model compared to that in BaMn$_2$As$_2$ and
the other related 122 compounds including the well-known iron-arsenide
superconductor parent compound BaFe$_2$As$_2$. Owing to the novelty of its
transition metal sublattice, this new addition to the family of tetragonal
materials related to the iron-based superconductors brings prospects for doping
and pressure studies in the search of new superconducting phases as well as
other exciting correlated-electron properties.",1904.04598v1
2019-04-25,Towards Explainable Anticancer Compound Sensitivity Prediction via Multimodal Attention-based Convolutional Encoders,"In line with recent advances in neural drug design and sensitivity
prediction, we propose a novel architecture for interpretable prediction of
anticancer compound sensitivity using a multimodal attention-based
convolutional encoder. Our model is based on the three key pillars of drug
sensitivity: compounds' structure in the form of a SMILES sequence, gene
expression profiles of tumors and prior knowledge on intracellular interactions
from protein-protein interaction networks. We demonstrate that our multiscale
convolutional attention-based (MCA) encoder significantly outperforms a
baseline model trained on Morgan fingerprints, a selection of encoders based on
SMILES as well as previously reported state of the art for multimodal drug
sensitivity prediction (R2 = 0.86 and RMSE = 0.89). Moreover, the
explainability of our approach is demonstrated by a thorough analysis of the
attention weights. We show that the attended genes significantly enrich
apoptotic processes and that the drug attention is strongly correlated with a
standard chemical structure similarity index. Finally, we report a case study
of two receptor tyrosine kinase (RTK) inhibitors acting on a leukemia cell
line, showcasing the ability of the model to focus on informative genes and
submolecular regions of the two compounds. The demonstrated generalizability
and the interpretability of our model testify its potential for in-silico
prediction of anticancer compound efficacy on unseen cancer cells, positioning
it as a valid solution for the development of personalized therapies as well as
for the evaluation of candidate compounds in de novo drug design.",1904.11223v3
2020-04-03,In Silico Screening of Some Naturally Occurring Bioactive Compounds Predicts Potential Inhibitors against SARS-COV-2 (COVID-19) Protease,"SARS-COV-2 identified as COVID-19 in Wuhan city of China in the month of
December, 2019 has now been declared as pandemic by World Health Organization
whose transmission chain and cure both have emerged as a tough problem for the
medical fraternity. The reports pertaining to the treatment of this pandemic
are still lacking. We firmly believe that Nature itself provides a simple
solution for any complicated problem created in it which motivated us to carry
out In Silico investigations on some bioactive natural compounds reportedly
found in the fruits and leaves of Anthocephalus Cadamba which is a miraculous
plant found on the earth aiming to predict the potential inhibitors against
aforesaid virus. Having modeled the ground state ligand structure of the such
nine natural compounds applying density functional theory at B3LYP/631+G (d, p)
level we have performed their molecular docking with SARS-COV-2 protease to
calculate the binding affinity as well as to screen the binding at S-protein
site during ligand-protein interactions. Out of these nine studied naturally
occurring compounds; Oleanic Acid has been appeared to be potential inhibitor
for COVID-19 followed by Ursolic Acid,
IsoVallesiachotamine,Vallesiachotamine,Cadambine,Vincosamide-N-Oxide,
Isodihydroamino-cadambine, Pentyle Ester of Chlorogenic Acid and
D-Myo-Inositol. Hence these bioactive natural compounds or their structural
analogs may be explored as anti-COVID19 drug agent which will be possessing the
peculiar feature of cost-less synthesis and less or no side effect due to their
natural occurrence. The solubility and solvent-effect related to the
phytochemicals may be the point of concern. The In-vivo investigations on these
proposed natural compounds or on their structural analogs are invited for
designing and developing the potential medicine/vaccine for the treatment of
COVID-19 pandemic.",2004.01634v1
2020-08-19,Prediction of low-Z collinear and noncollinear antiferromagnetic compounds having momentum-dependent spin splitting even without spin-orbit coupling,"Recent study (Yuan et. al., Phys. Rev. B 102, 014422 (2020)) revealed a
SOC-independent spin splitting and spin polarization effect induced by
antiferromagnetic ordering which do not necessarily require breaking of
inversion symmetry or the presence of SOC, hence can exist even in
centrosymmetric, low-Z light element compounds, considerably broadening the
material base for spin polarization. In the present work we develop the
magnetic symmetry conditions enabling such effect, dividing the 1651 magnetic
space groups into 7 different spin splitting prototypes (SST-1 to SST-7). We
use the 'Inverse Design' approach of first formulating the target property
(here, spin splitting in low-Z compounds not restricted to low symmetry
structures), then derive the enabling physical design principles to search
realizable compounds that satisfy these a priori design principles. This
process uncovers 422 magnetic space groups (160 centrosymmetric and 262
non-centrosymmetric) that could hold AFM-induced, SOC-independent spin
splitting and spin polarization. We then search for stable compounds following
such enabling symmetries. We investigate the electronic and spin structures of
some selected prototype compounds by density functional theory (DFT) and find
spin textures that are different than the traditional Rashba-Dresselhaus
patterns. We provide the DFT results for all antiferromagnetic spin splitting
prototypes (SST-1 to SST-4) and concentrate on revealing of the AFM-induced
spin splitting prototype (SST-4). The symmetry design principles along with
their transformation into an Inverse Design material search approach and DFT
verification could open the way to their experimental examination.M). The
symmetry design principles along with their transformation into an Inverse
Design material search approach and DFT verification could open the way to
their experimental examination.",2008.08532v1
2017-10-02,Cluster formation in pre-compound nuclei in the time-dependent framework,"Background: Applications of nuclear time-dependent density functional theory
(TDDFT) are often capable of providing quantitative description of heavy ion
reactions. However, the structure of pre-compound states produced in heavy ion
reactions are difficult to assess theoretically in TDDFT as the s.p. density
alone is a weak indicator of shell structure and cluster states. Purpose: We
employ the time-dependent nucleon localization function (NLF) to reveal
structure of pre-compound states in nuclear reactions involving light and
medium-mass ions. We primarily focus on spin saturated systems with N = Z.
Furthermore, we study reactions with oxygen and carbon ions, for which
experimental evidence for {\alpha} clustering in pre-compound states exists.
Method: We utilize the symmetry-free TDDFT approach and compute the NLFs to
describe $^{16}$O + $^{16}$O, $^{40}$Ca + $^{16}$O, $^{40}$Ca + $^{40}$Ca, and
$^{16,18}$O + $^{12}$C collisions at energies above the Coulomb barrier.
Results: We show that NLFs reveal a variety of time-dependent modes involving
cluster structures. For instance, the $^{16}$O + $^{16}$O collision results in
a vibrational mode of a quasi-molecular \alpha-$^{12}$C-$^{12}$C-\alpha{}
state. For heavier ions, a variety of cluster configurations are predicted. For
the collision of $^{16,18}$O + $^{12}$C, we showed that the pre-compound system
has a tendency to form {\alpha} clusters. This result supports the experimental
findings that the presence of cluster structures in the projectile and target
nuclei gives rise to strong entrance channel effects and enhanced {\alpha}
emission. Conclusion: The time-dependent NLF is a good indicator of clusters
structures in complex pre-compound states formed in heavy-ion fusion reactions.
The localization reveals the presence of collective vibrations involving
cluster structures, which dominate the initial dynamics of the fusing system.",1710.00579v1
2019-05-06,Correlations between stacked structures and weak itinerant magnetic properties of La$_{2-x}$ Y$_x $ Ni$_7$ compounds,"Hexagonal La$_2$Ni$_7$ and rhombohedral Y$_2$Ni$_7$ are weak itinerant
antiferromagnet (wAFM) and ferromagnet (wFM), respectively. The crystal
structure and magnetic properties of $A_2B_7$ intermetallic compounds ($A$ =
La, Y, $B$ = Ni) have been investigated combining X-ray powder diffraction and
magnetic measurements. The La$_{2-x}$Y$_x$Ni$_7$ intermetallic compounds with
$0 \leq x \leq 1$ crystallize in the Ce$_{2}$Ni$_7$-type hexagonal structure
with Y preferentially located in the [$AB_2$] units. The compounds with larger
Y content ($1.2 \leq x < 2$) crystallize in both hexagonal and rhombohedral
(Gd$_2$Co$_7$-type) structures with a progressive substitution of Y for La in
the $A$ sites belonging to the [$AB_5$] units. Y$_2$Ni$_7$ crystallizes in the
rhombohedral structure only. The average cell volume decreases linearly versus
Y content, whereas the c/a ratio presents a minimum at $x = 1$ due to geometric
constrains. The magnetic properties are strongly dependent on the structure
type and the Y content. La$_{2}$Ni$_7$ displays a complex metamagnetic behavior
with split AFM peaks. Compounds with x = 0.25 and 0.5 display a wAFM ground
state and two metamagnetic transitions, the first one towards an intermediate
wAFM state and the second one towards a FM state.T$_N$ and the second critical
field increase with the Y content, indicating a stabilization of the AFM state.
LaYNi$_7$, which is as the boundary between the two structure types, presents a
very wFM state at low field and an AFM state as the applied field increases.
All the compounds with $x > 1$ and containing a rhombohedral phase are wFM with
$T_C$ = 53(2) K. In addition to the experimental studies, first principles
calculations using spin polarization have been performed to interpret the
evolution of both structural phase stability and magnetic ordering for $0 \leq
x < 2$.",1905.01985v2
2019-08-29,PaccMann$^{RL}$: Designing anticancer drugs from transcriptomic data via reinforcement learning,"With the advent of deep generative models in computational chemistry, in
silico anticancer drug design has undergone an unprecedented transformation.
While state-of-the-art deep learning approaches have shown potential in
generating compounds with desired chemical properties, they disregard the
genetic profile and properties of the target disease. Here, we introduce the
first generative model capable of tailoring anticancer compounds for a specific
biomolecular profile. Using a RL framework, the transcriptomic profiles of
cancer cells are used as a context for the generation of candidate molecules.
Our molecule generator combines two separately pretrained variational
autoencoders (VAEs) - the first VAE encodes transcriptomic profiles into a
smooth, latent space which in turn is used to condition a second VAE to
generate novel molecular structures on the given transcriptomic profile. The
generative process is optimized through PaccMann, a previously developed drug
sensitivity prediction model to obtain effective anticancer compounds for the
given context (i.e., transcriptomic profile). We demonstrate how the molecule
generation can be biased towards compounds with high predicted inhibitory
effect against individual cell lines or specific cancer sites. We verify our
approach by investigating candidate drugs generated against specific cancer
types and find the highest structural similarity to existing compounds with
known efficacy against these cancer types. We envision our approach to
transform in silico anticancer drug design by leveraging the biomolecular
characteristics of the disease in order to increase success rates in lead
compound discovery.",1909.05114v4
2019-12-07,Computational design of $f$-electron Kitaev magnets: honeycomb and hyperhoneycomb compounds $A_2$PrO$_3$ ($A=$ alkali metals),"The Kitaev spin model offers an exact quantum spin liquid in the ground
state, which has stimulated exploration of its material realization over the
last decade. Thus far, most of the candidates are found in $4d$- and
$5d$-electron compounds, in which the low-spin $d^5$ electron configuration
subject to strong spin-orbit coupling comprises a Kramers doublet with the
effective angular momentum $j_{\rm eff}=1/2$ and gives rise to the
bond-dependent anisotropic interactions in the Kitaev model. Here we
theoretically investigate other candidates in $4f$-electron compounds with the
$f^1$ electron configuration on both quasi-two-dimensional honeycomb and
three-dimensional hyperhoneycomb structures, $A_2$PrO$_3$ with $A$=Li, Na, K,
Rb, and Cs. Based on {\it ab initio} calculations, we show that the electronic
structures of these compounds host a spin-orbital entangled Kramers doublet
with $j_{\rm eff}=1/2$ in the $\Gamma_7$ state. By constructing the
tight-binding Hamiltonian and performing a perturbation expansion, we find that
the low-energy magnetic properties of $A_2$PrO$_3$ are well described by an
effective spin model with the $J$-$K$-$\Gamma'$ model. The most remarkable
feature is that the Kitaev interaction $K$ is antiferromagnetic, in contrast to
the ferromagnetic one in the $d^5$ candidates at hand. The exchange
interactions are systematically modulated by changing the $A$-site cations. As
a consequence, the compounds with $A$=Li and Na may have a dominant
antiferromagnetic $K$, but $J$ dominates $K$ and $\Gamma'$ in the cases with
$A$=Rb and Cs. Also, by computing the ground states of the $J$-$K$-$\Gamma'$
model by using the exact diagonalization, we map out the systematic evolution
of the model parameters in the phase diagram. Our results will stimulate
material exploration of the antiferromagnetic Kitaev interaction in
$f$-electron compounds.",1912.03422v1
2020-10-05,Influence of Se doping in recently synthesized NaInS2-xSex solid solutions for potential thermo-mechanical applications studied via first-principles method,"In the present work, the structural and hitherto unexplored thermal and
mechanical properties of NaInS2-xSex (x = 0, 0.5, 1.0, 1.5 and 2.0) compounds
have been studied using the density functional theory. Besides, the elastic
anisotropy indices and hardnesses of NaInS2-xSex have been investigated as Se
content is varied. The mechanical stability of all the compounds under study
has been confirmed. The ratio of shear to bulk modulus (G/B) is low suggesting
that the NaInS2-xSex (x = 0.5 and 1.5) compounds exhibit damage tolerant
(ductility) properties while rest of the compositions are brittle in nature.
The predicted hardness (H) values are also influenced with the Se content in
the following order: H (NaInSSe) > H (NaInS2) > H (NaInSe2) > H (NaInS1.5Se0.5)
> H (NaInS0.5Se1.5). All the anisotropic indices under study indicate that
NaInS2-xSex compounds are anisotropic in nature. The Mulliken bond population
analysis suggests that the degree of covalency of In-S/Se bonds decreases when
S is substituted by Se. The origin of low Debye temperature ({\Theta}D) and low
minimum thermal conductivity (Kmin) have been successfully explained by
considering the mean atomic weight (M/n) and average bond strength of the
compounds. Temperature dependence of heat capacities (Cv, Cp) and linear
thermal expansion coefficient ({\alpha} ) are also estimated using the
quasi-harmonic Debye model and discussed. The low values of Kmin, {\Theta}D and
{\alpha} and damage tolerant behavior clearly indicate that the NaInS2-xSex (x
= 0.5 and 1.5) compounds can be used as promising thermal barrier coating
materials for high temperature applications.",2010.01796v1
2021-08-19,"Newly synthesized 3D boron-rich chalcogenides B12X (X = S, Se): Theoretical characterization of physical properties for optoelectronic and mechanical applications","Boron rich chalcogenides have been predicted to have excellent properties for
optical and mechanical applications in recent times. In this regard, we report
the electronic, optical and mechanical properties of recently synthesized boron
rich chalcogenide compounds, B12X (X = S and Se) using density functional
theory for the first time. The effects of exchange and correlation functional
on these properties are also investigated. The consistency of the obtained
crystal structure with the reported experimental results has been checked in
terms of lattice parameters. The considered materials are mechanically stable,
brittle and elastically anisotropic. Furthermore, the elastic moduli and
hardness parameters are calculated, which show that B12S is likely to be a
prominent member of hard materials family compared to B12Se. The origin of
different in hardness is explained on the basis of density of states near the
Fermi level. Reasonably good values of fracture toughness and machinability
index for B12X (X= S and Se) are reported. The melting point, Tm for the B12S
and B12Se compounds suggests that both solids are stable, at least up to 4208
and 3577 K, respectively. Indirect band gap of B12S (2.27 eV) and B12Se (1.30
eV) are obtained using the HSE06 functional.The electrons of B12Se compound
show lighter average effective mass compared to that of B12S compound, which
signifies higher mobility of charge carriers in B12Se. The optical properties
are characterized using GGA-PBE and HSE06 method and discussed in detail. These
compounds possess bulk optical anisotropy and excellent absorption coefficients
in visible light region along with very low static value of reflectivity
spectra (range: 7.42-14.0% using both functionals) are noted. Such useful
features of the compounds under investigation show promise for applications in
optoelectronic and mechanical sectors.",2108.08493v1
2022-08-01,"MAFW: A Large-scale, Multi-modal, Compound Affective Database for Dynamic Facial Expression Recognition in the Wild","Dynamic facial expression recognition (FER) databases provide important data
support for affective computing and applications. However, most FER databases
are annotated with several basic mutually exclusive emotional categories and
contain only one modality, e.g., videos. The monotonous labels and modality
cannot accurately imitate human emotions and fulfill applications in the real
world. In this paper, we propose MAFW, a large-scale multi-modal compound
affective database with 10,045 video-audio clips in the wild. Each clip is
annotated with a compound emotional category and a couple of sentences that
describe the subjects' affective behaviors in the clip. For the compound
emotion annotation, each clip is categorized into one or more of the 11
widely-used emotions, i.e., anger, disgust, fear, happiness, neutral, sadness,
surprise, contempt, anxiety, helplessness, and disappointment. To ensure high
quality of the labels, we filter out the unreliable annotations by an
Expectation Maximization (EM) algorithm, and then obtain 11 single-label
emotion categories and 32 multi-label emotion categories. To the best of our
knowledge, MAFW is the first in-the-wild multi-modal database annotated with
compound emotion annotations and emotion-related captions. Additionally, we
also propose a novel Transformer-based expression snippet feature learning
method to recognize the compound emotions leveraging the expression-change
relations among different emotions and modalities. Extensive experiments on
MAFW database show the advantages of the proposed method over other
state-of-the-art methods for both uni- and multi-modal FER. Our MAFW database
is publicly available from https://mafw-database.github.io/MAFW.",2208.00847v2
2023-03-12,"Molecular Identifification, Antioxidant Effifficacy of Phenolic Compounds, and Antimicrobial Activity of Beta-Carotene Isolated from Fruiting Bodies of Suillus sp","Suillus species, in general, are edible mushrooms, and environmentally
important that are associated mostly with pine trees in the tropics regions.
These fungi considered a remarkable source of phenolic compounds that play a
crucial role as antioxidants which may reduce the risk of most human chronic
diseases such as cancer, diabetes, asthma, atherosclerosis, Alzheimer, and
others. On the other hand, carotenoids (\b{eta} carotene) are the most popular
natural pigments which play an important role to protect the plants from
photo-oxidative reactions. In human, these compounds prevent oxidative stress
and expects to have antimicrobial activity. Here, the phenolic compounds were
extracted with Ethyl acetate from fruiting bodies of Suillus sp and analyzed by
HPLC, the antioxidant activity (reducing power%) of phenolic compounds was
determined at the concentrations of 1, 2.5, and 5 mg/mL. Antimicrobial activity
of \b{eta} carotene pigment was measured at a concentration of 100 mg/mL
against some human pathogenic bacteria such as Escherichia coli, Pseudomonas
aeruginosa, Klebsiella pneumonia, and Staphylococcus aureus. The specific DNA
region ITS was amplified and sequenced using ITS1 and ITS4 primers with some
bioinformatics analyses. The phenolic extract isolated from fruiting bodies of
Suillus sp showed a remarkable antioxidant activity by increasing the reducing
power percent (from F+3 ions to F+2 ions) comparing with the industrial
antioxidant (Propyl gallate) at all used concentrations. Percent of reducing
power of phenolic compounds were 75.5, 84.9 and 95.7% at concentrations of 1,
2.5, and 5 mg/mL respectively; comparing with PG were 65.9, 81.3, and 93.3 at
1, 2.5, and 5 mg/mL respectively. The \b{eta} carotene pigment revealed a
significant antimicrobial activity at a concentration of 100 mg/mL against K.
pneumonia, E. coli, and S. aureus.",2303.08768v1
2023-10-27,"Dirac surface states, multiorbital dimerization and superconductivity in Nb- and Ta-based A15 compounds","Using first-principle calculations, we investigate the electronic,
topological and superconducting properties of Nb$_3$X (X = Ge, Sn, Sb) and
Ta$_3$Y (Y = As, Sb, Bi) A15 compounds. We demonstrate that these compounds
host Dirac surface states which are related to a nontrivial Z$_2$ topological
value. The spin-orbit coupling (SOC) splits the eightfold degenerate R point
close to the Fermi level enhancing the amplitude of the spin Hall conductance.
Indeed, despite the moderate spin-orbit of the Nb-compounds, a large spin Hall
effect is also obtained in Nb$_3$Ge and Nb$_3$Sn compounds. We show that the
Coulomb interaction opens the gap at the R point thus making more evident the
occurrence of Dirac surface states. We then investigate the superconducting
properties by determining the strength of the electron-phonon BCS coupling. The
evolution of the critical temperature is tracked down to the 2D limit
indicating a reduction of the transition temperature which mainly arises from
the suppression of the density of states at the Fermi level. Finally, we
propose a minimal tight-binding model based on three coupled
Su-Schrieffer-Heeger chains with t$_{2g}$ Ta- and Nb-orbitals reproducing the
spin-orbit splittings at the R point among the $\pi$-bond bands in this class
of compounds. We separate the kinetic parameters in $\pi$ and $\delta$-bonds,
in intradimer and interdimer hoppings and discuss their relevance for the
topological electronic structure. We point out that Nb$_3$Ge might represent a
Z$_2$ topological metal with the highest superconducting temperature ever
recorded.",2310.18245v2
1997-09-20,Secure Communication using Compound Signal from Generalized Synchronizable Chaotic Systems,"By considering generalized synchronizable chaotic systems, the
drive-auxiliary system variables are combined suitably using encryption key
functions to obtain a compound chaotic signal. An appropriate feedback loop is
constructed in the response-auxiliary system to achieve synchronization among
the variables of the drive-auxiliary and response-auxiliary systems. We apply
this approach to transmit analog and digital information signals in which the
quality of the recovered signal is higher and the encoding is more secure.",9709025v1
1995-04-28,Corpus Statistics Meet the Noun Compound: Some Empirical Results,"A variety of statistical methods for noun compound analysis are implemented
and compared. The results support two main conclusions. First, the use of
conceptual association not only enables a broad coverage, but also improves the
accuracy. Second, an analysis model based on dependency grammar is
substantially more accurate than one based on deepest constituents, even though
the latter is more prevalent in the literature.",9504033v2
1993-08-18,Tuning of the CDW in the Halogen-Bridged Transition-Metal Linear-Chain Compounds,"Local-density-approximation calculations are used to show that the
metal-metal distance along the chains controls the charge-density wave (CDW) in
halogen-bridged transition-metal linear-chain (MX) compounds. The strength of
the CDW can be understood in terms of a two band Su-Schrieffer-Heeger model if
a hard-core ion-ion repulsion potential is also added. We predict a
second-order phase transition from an insulating to a semi-metallic ground
state and explain trends in dimerization, bond-length ratios, band gaps, and
Raman breathing modes in terms of the metal-metal distance. Three ""ps"" figures
are included at the end of the file.",9308025v1
1993-09-17,Understanding Far-Infrared Absorption in the S=1 Antiferromagnetic Chain Compound NENP,"Infrared transmission measurements on the $S=1$ antiferromagnetic chain
compound NENP in applied magnetic fields show a sharp absorption line at the
field-shifted Haldane gap. This violates a wave-vector selection rule of the
Hamiltonian normally used for NENP, as the gap excitations occur at the
Brillouin zone boundary. We argue that the crystal structure admits terms which
can explain the absorption lines. In addition, in an applied field, staggered
orientations of the g-tensors produce a staggered magnetic field. This can
explain the observation of a finite gap at all applied fields.",9309022v1
1993-10-26,The relationship between perturbation theory and direct calculations of rare-earth transition intensities,"We use a simplified calculation to demonstrate the equivalence between three
different methods for calculating transition line strengths [B.R. Judd and D.
R. Pooler, J. Phys. C 15 (1982) 591; G. W. Burdick and M. F. Reid, Phys. Rev.
Lett. 70 (1993) 2491; G. W. Burdick, H. J. Kooy, and M. F. Reid, J. Phys.:
Condens. Matter 5 (1993) L323]. These calculations demonstrate the complex
interplay between spin-orbit and correlation contributions to two-photon
transitions in rare-earth ions.",9310057v1
1994-06-08,Mean-field phase diagrams of $AT_2X_2$ compounds,"Magnetic-field -- temperature phase diagrams of the axial
next-nearest-neighbor Ising model are calculated within the framework of a
Landau-type expansion of the free energy derived from molecular-field theory.
Good qualitative agreement is found with recently reported results on
body-centered-tetragonal $UPd_2Si_2$. This work is expected to also be relevant
for related compounds.",9406042v1
1996-05-29,Quasiparticle energy dispersion in doped two dimensional quantum antiferromagnets,"The quasiparticle dispersion in the one-hole t-t'-t""-J model is studied. Both
the finite-size diagonalization and the self-consistent Born approximation
calculations have been performed and compared. The quasiparticle band
structures in the hole and electron doped high-Tc cuprates are qualitatively
different. In the hole doped compounds, the band maxima locate at (pi/2 ,
pi/2), while in the electron doped compounds the band maxima locate at (pi, 0)
and its equivalent points. The angle-resolved photoemission data for the
quasiparticle dispersion of Sr_2CuO_2Cl_2 can be quantitatively reproduced
using the one band t-t'-t""-J model with the three-site hopping term.",9605182v1
1996-06-14,Two dimensional bulk bands and surfaces resonances originated from (100) surfaces of III-V semiconductor compounds,"We have calculated the electronic band structure of the (100) surface of the
III--V zinc blende semiconductor compounds, using the standard tight binding
method and the surface Green's function matching method. We have found that the
creation of the surface gives place to new states in the electronic structure:
surface resonances and two dimensional bulk states. The two dimensional bulk
states are of the same character of those reported recently in CdTe(100) [Phys.
Rev. {\bf 50}, 1980 (1994)]. We analyze the states in the valence band region
and compare with photoemission spectroscopy data.",9606096v1
1996-06-19,The Magnetization of Cu_2(C_5H_{12}N_2)_2Cl_4 : A Heisenberg Spin Ladder System,"We study the magnetization of a Heisenberg spin ladder using exact
diagonalization techniques, finding three distinct magnetic phases. We consider
the results in relation to the experimental behaviour of the new copper
compound Cu_2(C_5H_{12}N_2)_2Cl_4 and deduce that the compound is well
described by such a model with a ratio of `chain' to `rung' bond strengths
(J/J^\prime) of the order of 0.2, consistent with results from the magnetic
susceptibility. The effects of temperature, spin impurities and additional
diagonal bonds are presented and we give evidence that these diagonal bonds are
indeed of a ferromagnetic nature.",9606145v1
1996-07-05,Towards a Statistical Theory of Finite Systems and Compound States: Random Two-Body Interaction Approach,"The model of Fermi particles with random two-body interaction is
investigated. This model allows to study the origin and accuracy of statistical
laws in few-body systems, the role of interaction and chaos in thermalization,
Fermi-Dirac distribution for quasi-particles with spreading widths, matrix
elements of external field and enhancement of weak perturbation in chaotic
compound states.",9607035v1
1996-07-09,Anomalous magnetic response of the valence-fluctuating compound YbInCu4,"The exact solution of the spin one-half Falicov-Kimball model, with random
hopping between the lattice sites, is used to explain the anomalous magnetic
response of Yb-based valence-fluctuating intermetallic compounds. The anomalous
behavior arises from an entropy-driven local-moment--nonmagnetic transition of
unhybridized Yb ions in these materials which can also be used to explain the
observed metamagnetism and resistivity anomalies.",9607068v1
1997-03-08,"Weak pseudogap in crystals of Pb2Sr2(Y,Ca)Cu3O8+d","We report on NMR measurements in underdoped Pb2Sr2(Y,Ca)Cu3O8+d crystals. A
pseudogap is observed in the Knight shift and spin-lattice relaxation rate. In
contrast to other underdoped compounds, the pseudogap observed in the Knight
shift is weak and occurs at a significantly lower temperature. On the other
hand, the effect the pseudogap has on spin-lattice relaxation is quite similar
to that in other compounds. The contrast between weak and strong pseudogaps is
discussed.",9703083v1
1997-04-30,Anharmonic effects in the A15 compounds induced by sublattice distortions,"We demonstrate that elastic anomalies and lattice instabilities in the the
A15 compounds are describable in terms of first-principles LDA electronic
structure calculations. We show that at T=0 V_3Si, V_3Ge, and Nb_3Sn are
intrinsically unstable against shears with elastic moduli C_11-C_12 and C_44,
and that the zone center phonons, Gamma_2 and Gamma_12, are either unstable or
extremely soft. We demonstrate that sublattice relaxation (internal strain)
effects are key to understanding the behavior of the A15 materials.",9704251v2
1997-05-20,Magnetic Excitations in quasi two-dimensional Spin-Peierls Systems,"A study is presented of a two-dimensional frustrated and dimerized quantum
spin-system which models the effect of inter-chain coupling in a spin-Peierls
compound. Employing a bond-boson method to account for quantum disorder in the
ground state the elementary excitations are evaluated in terms of gapful
triplet modes. Results for the ground state energy and the spin gap are
discussed. The triplet dispersion is found to be in excellent agreement with
inelastic neutron scattering data in the dimerized phase of the spin-Peierls
compound CuGeO_3. Moreover, consistent with these neutron scattering
experiments, the low-temperature dynamic structure factor exhibits a
high-energy continuum split off from the elementary triplet mode.",9705193v1
1997-11-18,Basal-plane Incommensurate Phases in HCP Structures,"An Ising model with competing interaction is used to study the appearance of
incommensurate phases in the basal plane of an hexagonal closed-packed
structure. The calculated mean-field phase diagram reveals various
1q-incommensurate and lock-in phases. The results are applied to explain the
basal-plane incommensurate phase in some compounds of the A'A""BX_4 family, like
K_2MoO_4, K_2WO_4, Rb_2WO4 and to describe the sequence of high-temperature
phase transitions in other compounds of this family.",9711174v1
1998-01-22,The Heisenberg model on the 1/5-depleted square lattice and the CaV4O9 compound,"We investigate the ground state structure of the Heisenberg model on the
1/5-depleted square lattice for arbitrary values of the first- and
second-neighbor exchange couplings. By using a mean-field Schwinger-boson
approach we present a unified description of the rich ground-state diagram,
which include the plaquette and dimer resonant-valence-bond phases, an
incommensurate phase and other magnetic orders with complex magnetic unit
cells. We also discuss some implications of ours results for the experimental
realization of this model in the CaV4O9 compound.",9801235v1
1998-11-16,Metal-Insulator Transition in Mn Perovskite Compounds,"We discuss Mott insulating and metallic phases of a model with $e_g$ orbital
degeneracy to understand physics of Mn perovskite compounds. Quantum Monte
Carlo and Lanczos diagonalization results are discussed in this model. To
reproduce experimental results on charge gap and Jahn-Teller distortions, we
show that a synergy between the strong correlation effects and the Jahn-Teller
coupling is important. The incoherent charge dynamics and strong charge
fluctuations are characteristic of the metallic phase accompanied with critical
enhancement of short-ranged orbital correlation near the insulator.",9811221v1
1998-11-16,Superconductivity in a magnetically ordered background,"Borocarbide compounds with the formula RNi2B2C show interesting
superconducting and magnetic properties and the coexistence of the two
phenomena. BCS theory is extended to systems with underlying commensurate
magnetic order. In the case of helical phases the technique may be extended to
any Q-vector and there exists a well defined limit for incommensurate values.
The way magnetic order influences superconductivity depends crucially on the
details of both the magnetic structure and the electron bands, but some
qualitative criteria may be given. As an example we give a brief analysis of
the compound HoNi2B2C.",9811226v1
1998-12-12,On possible superconductivity in the doped ladder compound La_(1-x)Sr_xCuO_2.5,"LaCuO_2.5 is a system of coupled, two-chain, cuprate ladders which may be
doped systematically by Sr substitution. Motivated by the recent synthesis of
single crystals, we investigate theoretically the possibility of
superconductivity in this compound. We use a model of spin fluctuation-mediated
superconductivity, where the pairing potential is strongly peaked at \pi in the
ladder direction. We solve the coupled gap equations on the bonding and
antibonding ladder bands to find superconducting solutions across the range of
doping, and discuss their relevance to the real material.",9812211v1
1999-05-21,"Comment on ""Theory of Unconventional Spin Density Wave: A Possible Mechanism of the Micromagnetism in U-based Heavy Fermion Compounds""","In the recent letter [1] by H. Ikeda and Y. Ohashi, a new, very attractive
idea is proposed for the explanation of the micromagnetism in U-based heavy
fermion compounds. For this sake a nontrivial spin density wave (d-SDW) is
introduced. Our goal is to claim, that in the model considered, the mean-field
analysis is incomplete: the ferromagnetic state missed by [1] overcomes d-SDW
in a large region of the phase diagram (Fig.1 in [1]).",9905321v1
1999-08-30,Direct Observation of Antiferro-Quadrupolar Ordering - Resonant X-ray Scattering Study of DyB2C2,"Antiferroquadrupolar (AFQ) ordering has been conjectured in several
rare-earth compounds to explain their anomalous magnetic properties. No direct
evidences for AFQ ordering, however, have been reported. Using the resonant
x-ray scattering technique near the Dy L_III absorption edge, we have succeeded
in observing the AFQ order parameter in DyB2C2 and analyzing the energy and
polarization dependence. Much weaker coupling between orbital degrees of
freedom and lattice in 4f electron systems than in 3d compounds provides an
ideal platform to study orbital interactions originated from electronic
mechanisms.",9908436v2
1999-09-03,Effective Dimensionality and Band Structure of alpha-Nav_2o_5 Compound: 1D or 2D?,"The AV_nO_{2n+1} mixed valence compounds (n=1, A=Na) are classified as
dimerized layered system with strongly interacting d-electrons of vanadium
ions. The derived band gaps, energy dispersion relations and density of
electronic states are in a good agreement with available experimental and
theoretical data. The correlated band gap provides the insulating state of the
high-temperature alpha-NaV_2O_5 phase whereas the state, earlier misrepresented
as the spin-Peierls state, is governed, in fact, by opening of the Coulomb gap.",9909046v1
1999-10-25,Heavy Fermion Behaviors in LiV_{2}O_{4},"Experiments of various types on the metallic transition metal oxide compound
LiV_{2}O_{4} with the fcc normal-spinel structure are reviewed. The
low-temperature T < 10 K data consistently indicate heavy fermion (HF)
behaviors characteristic of those of the heaviest-mass f-electron HF compounds.
A crossover is observed above about 50 K in the magnetic susceptibility, ^{7}Li
spin-lattice relaxation rate and neutron magnetic scattering function to a
magnetic state variously described as an antiferromagnetically-coupled
local-moment metal or, at the opposite extreme, as an itinerant
nearly-ferromagnetic metal. Recent theoretical investigations to understand
these properties of LiV_{2}O_{4} are discussed.",9910404v1
1999-11-11,Excitonic Strings in one dimensional organic compounds,"Important questions concern the existence of excitonic strings in organic
compounds and their signatures in the photophysics of these systems. A model in
terms of Hard Core Bosons is proposed to study this problem in one dimension.
Mainly the cases with two and three particles are studied for finite and
infinite lattices, where analytical results are accessible. It is shown that if
bi-excitonic states exist, three-excitonic and even, n-excitonic strings, at
least in a certain range of parameters, will exist. Moreover, the behaviour of
the transitions from one exciton to the biexciton is fully clarified. The
results are in agreement with exact finite cluster diagonalizations of several
model Hamiltonians.",9911160v1
1999-11-29,Explanation of Giant Cluster Coexistence in Doped Manganites and Other Compounds,"Computational studies show the generation of large coexisting metallic and
insulating clusters with equal electronic density in models for manganites. The
clusters are induced by disorder on exchange and hopping amplitudes near
first-order transitions of the non-disordered strongly coupled system. The
random-field Ising model is used to explain the qualitative aspects of our
results. Percolative characteristics are natural in this context. Our results
explain the recently experimentally discovered micrometer size inhomogeneities
in manganites. The conclusions are general and apply to a variety of compounds.",9911448v1
2000-02-18,"Ab initio Hartree-Fock Born effective charges of LiH, LiF, LiCl, NaF, and NaCl","We use the Berry-phase-based theory of macroscopic polarization of dielectric
crystals formulated in terms of Wannier functions, and state-of-the-art
Gaussian basis functions, to obtain benchmark ab initio Hartree-Fock values of
the Born effective charges of ionic compounds LiH, LiF, LiCl, NaF, and NaCl. We
find excellent agreement with the experimental values for all the compounds
except LiCl and NaCl, for which the disagreement with the experiments is close
to 10% and 16%, respectively. This may imply the importance of many-body
effects in those systems.",0002285v1
2000-06-06,The preservation of the individuality of 3d atoms in a solid,"On basis of analysis of experimental results for more than 200 compounds with
3d and 4f elements we conjecture that atoms with unfilled 3d and 4f shells
preserve much of their atomic properties, manifested by the discrete electronic
structure, even then when they become the part of a solid. As a consequence,
electronic and magnetic properties of the 3d-ion containing compounds are
strongly affected by the existence of the atomic-like crystal-field fine
electronic structure.",0006092v1
2000-06-13,Long-range antiferromagnetic order in the S=1 chain compound LiVGe2O6,"The phase transition in the compound LiVGe2O6 has been proposed as a unique
example of a spin-Peierls transition in an S=1 antiferromagnetic chain. We
report neutron and x-ray diffraction measurements of LiVGe2O6 above and below
the phase transition at T=24 K. No evidence is seen for any structural
distortion associated with the transition. The neutron results indicate that
the low temperature state is antiferromagnetic, driven by ferromagnetic
interchain couplings.",0006216v1
2000-06-20,A simple theory for high $Δ/ T_{c}$ ratio in d-wave superconductors,"We investigate a simple explanation for the high maximum gap to $T_{c}$ ratio
found experimentally in high $T_{c}$ compounds. We ascribe this observation to
the lowering of $T_{c}$ by boson scattering of electrons between parts of the
Fermi surface with opposite sign for the order parameter. We study the simplest
possible model within this picture. Our quantitative results show that we can
account for experiment for a rather small value of the coupling constant, all
the other ingredients of our model being already known to exist in these
compounds. A striking implication of this theory is the fairly high value of
the critical temperature in the absence of boson scattering.",0006296v1
2000-06-30,Theory of valence transitions in ytterbium-based compounds,"The anomalous behavior of YbInCu4 and similar compounds is modeled by the
exact solution of the spin one-half Falicov-Kimball model in infinite
dimensions. The valence-fluctuating transition is related to a metal-insulator
transition caused by the Falicov-Kimball interaction, and triggered by the
change in the f-occupancy.",0006495v1
2000-09-18,Ground-State Phase Diagram for the Three-Dimensional Orthogonal-Dimer System,"We investigate quantum phase transitions in the three-dimensional
orthogonal-dimer system of the compound $\rm SrCu_2(BO_3)_2$ by means of the
series expansion technique. We then discuss the phase diagram where the dimer
phase, the Haldane phase, the frustration-induced disordered phase and the
magnetically ordered phase compete with each other. It is found that the
compound $\rm SrCu_2(BO_3)_2$ is located in the dimer phase close to the phase
boundary.",0009266v1
2000-10-02,"Large Orbital Magnetic Moment in Feo, Fes and Febr2","Magnetic moment of the Fe2+ ion in FeO, FeS and FeBr2 has been calculated
within the quantum atomistic solid-state theory to substantially exceed a value
of 4 muB in the magnetically-ordered state at 0 K. In all compounds the large
orbital moment, of 0.7 - 1.1 muB, has been revealed. Our calculations show that
for the meaningful analysis of electronic and magnetic properties of FeO, FeS
and FeBr2 the intra-atomic spin-orbit coupling is essentially important and
that the orbital moment is largely unquenched in 3d- ion containing compounds.",0010032v1
2000-12-01,Incommensurate structure factor in a hole-doped spin-1 system,"The nickelate compound Y_{2}BaNiO_{5} is a spin-1 Haldane-gap
antiferromagnet. The compound is doped with holes on replacing the off-chain
Y^{3+} ions by Ca^{2+} ions. Inelastic neutron scattering (INS) experiments
reveal the existence of sub-gap states on doping. A recent INS experiment
provides evidence for an incommensurate double-peaked structure factor S(q)
corresponding to the sub-gap states. In this paper, we formulate a microscopic
theory for the origin of the incommensurate peak.",0012006v1
2001-02-06,"Observation of superconductivity in Y$_2$PdGe$_3$, structurally same as MgB$_2$","The results of electrical resistance (1.4 - 300 K), magnetization (2-300 K)
and heat-capacity (2 - 50 K) measurements in Y$_2$PdGe$_3$, found to
crystallize in a AlB$_2$-derived hexagonalstructure, are reported. The results
establish that this compound is superconducting below 3 K. This obervation is
interesting considering that this compound is the first superconductor among
the ternary members derived from the hexagonal AlB$_2$ structure. With
superconductivity being uncommon even among binary alloys derived from AlB$_2$
structure and with recent excitement on the observation of high temperature
superconductivity in Mg$B_2$, this finding gains importance.",0102110v1
2001-03-02,Lattice Properties of MgB2 versus Temperature and Pressure,"We have determined the structural properties of the superconducting compound
MgB2 as a function of temperature from 11 K to 297 K and as a function of
hydrostatic pressure up to 0.62 GPa using neutron powder diffraction. This
compound, when compared to other diborides with the same structure, is
characterized by unusually large anisotropies of both the thermal expansion and
compressibility, with the c-axis responses being substantially larger in both
cases. We speculate that the comparatively weaker metal-boron bonding in MgB2,
manifest by these lattice responses, is important for establishing the
structural features that give rise to high Tc superconductivity in this
structure type.",0103069v1
2001-06-18,Metal-Nonmetal Changeover in Pyrochlore Iridates,"We report the low temperature properties of a new series of pyrochlore
iridates R2Ir2O7 (R = rare-earth elements). We found that the compounds with R
= Pr, Sm, Nd, and Eu exhibit metallic conductivity, whereas those with smaller
rare-earth ions are nonmetallic. Such metal-nonmetal changeover is attributable
to the importance of electron correlation among the Ir 5d electrons. Reflecting
the geometrical frustration in the pyrochlore lattice, the rare-earth moments
do not exhibit magnetic ordering to temperatures well below the
antiferromagnetic Weiss temperature. We have not found any sign of
superconductivity down to 0.3 K in these compounds.",0106330v1
2001-06-18,Investigation of ferroelectric order-disorder type compounds with asymmetric double-well potential,"The Mitsui model for the order-disorder type ferroelectrics is studied within
the mean field approximation. The phase diagram of the model is obtained, its
dependence on the transverse field is obtained. A scheme of setting the values
of the model parameters is proposed; all the dielectric characteristics of
Rochelle salt are calculated with the found parameters. Within the Mitsui model
we study the physical characteristics of RbHSO4 type crystals; the found values
of the model parameters provide a good description of both dielectric and
thermodynamic properties of these compounds.",0106351v1
2001-07-10,Nature of insulating state in NaV$_{2}$O$_{5}$ above charge-ordering transition: a cluster DMFT study,"The nature of insulating state driven by electronic correlations in the
quarter-filled ladder compound $\alpha'$NaV$_{2}$O$_{5}$ is investigated within
a cluster dynamical mean-field approach. An extended Hubbard model with
first-principle tight-binding parameters have been used. It is shown that the
insulating state in the charge-disordered phase of this compound is formed due
to the transfer of spectral density and dynamical charge fluctuations where for
the latter, the role of inter-site Coulomb interaction is found to be of
crucial importance.",0107200v1
2001-08-27,Quasiparticles and Energy Scaling in Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4}$ ($\it{n}$=1-3): Angle-Resolved Photoemission Spectroscopy,"Angle-resolved photoemission spectroscopy (ARPES) has been performed on the
single- to triple-layered Bi-family high-{\it T$_c$} superconductors
(Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4}$, $\it{n}$=1-3). We found a sharp
quasiparticle peak as well as a pseudogap at the Fermi level in the
triple-layered compound. Comparison among three compounds has revealed a
universal rule that the characteristic energies of superconducting and
pseudogap behaviors are scaled with the maximum {\it T$_c$}.",0108415v1
2001-10-02,Sweeping of Lattice Disorder and Associated Phenomena in Colossal Magnetoresistance Compounds,"We show through a variational calculation that in a large range of parameters
the paramagnetic to ferromagnetic transition in colossal magnetoresistance
compounds is accompanied by a collapse of polaronic lattice disorder in
addition to that of spin disorder. The spin-lattice disordered state is shown
to be localized and the ordered state itinerant as observed. The observed
dramatic change in the diffuse scattering at the transition as well as the
isotope effect are also explained.",0110047v1
2001-10-22,"Crystal structures, magnetic and superconducting properties of the RuSr_2NdCu_2O_x and RuSr_2GdCu_2O_y compounds","We report the magnetization and the susceptibility measurements of the
RuSr_2GdCu_2O_y and RuSr_2NdCu_2O_x perovskite materials. We find that
RuSr_2GdCu_2O_y compound exhibits a magnetic transition at Tn=135 K followed by
a superconducting one with an onset Tc=35 K. Samples of RuSr_2NdCu_2O_x
material have shown neither superconductivity nor magnetic transition. XRD
measurements show that in RuSr_2NdCu_2O_x the Nd ions tend to substitute to Sr
ions in very high percentages. The relevance of this phenomenon on the absence
of superconductivity in RuSr_2NdCu_2O_x is discussed.",0110482v1
2002-01-28,Magnetic Properties of the Novel Low-Dimensional Cuprate Na5RbCu4(AsO4)4Cl2,"The magnetic properties of a new compound, Na5RbCu4(AsO4)4Cl2 are reported.
The material has a layered structure comprised of square Cu4O4 tetramers. The
Cu ions are divalent and the system behaves as a low-dimensional S=1/2
antiferromagnet. Spin exchange in Na5RbCu4(AsO4)4Cl2 appears to be
quasi-two-dimensional and non-frustrated. Measurements of the bulk magnetic
susceptibility and heat capacity are consistent with low-dimensional magnetism.
The compound has an interesting, low-entropy, magnetic transition at T = 17 K.",0201522v2
2002-02-25,Electrical and magnetic properties of the new Kondo-lattice compound Ce3Pd4Ge4,"We have measured the electric resistivity, magnetoresistance, magnetic
susceptibility and magnetization of the new Kondo-lattice compound Ce3Pd4Ge4.
The electrical resistivity exhibits a rapid drop at temperatures below 6 K,
while the magnetic susceptibility does not show any corresponding anomaly at
that temperature. This phenomenon is similar to that of Ce3Pd20Ge6 which shows
quadrupolar interation. We suggest that there is the possibility of quadrupolar
interaction in the orthorhombic 4f-electron system Ce3Pd4Ge4. In addition, it
is realized that the spin-dependent scattering effect is responsible for the
magnetotransport.",0202451v1
2002-03-06,First Principle Electronic Model for High-Temperature Superconductivity,"Using the structural data of the La2CuO4 compound both in the low temperature
tetragonal phase and in the isotropic phase we have derived an effective t-J
model with hoppings t and superexchange interactions J extended up to fourth
and second neareast neighbors respectively. By numerically studying this
hamiltonian we have then reproduced the main experimental features of this HTc
compound: d-wave superconductivity is stabilized at small but finite doping
delta>6% away from the antiferromagnetic region and some evidence of dynamical
stripes is found at commensurate filling 1/8.",0203117v1
2002-03-22,Superconductivity in the Infinite Layer Compound CaCuO2,"Superconductivity in the electric field-effect doped infinite layer compound
CaCuO2 is considered. It is argued that in the superconducting CuO2 layer, next
to the insulating Al2O3 overlayer, the coordination of the Cu2+ ions by oxygens
is pyramidal rather than square planar. This view stems from existing NEXAFS
and the analysis of HRETM results, as well as chemical considerations, and is
discussed mainly for the hole doped but also the electron doped region of the
phase diagramm.",0203457v1
2002-06-10,Realization of La2MnVO6: Search for half-metallic antiferromagnetism?,"Single-phase polycrystalline La2MnVO6 samples were synthesized by arc melting
and characterized by X-ray diffraction, magnetization and resistivity
measurements. We find that the compound has cubic (space group), partly ordered
double perovskite structure. The sample exhibits ferrimagnetic behavior and
variable-range hopping conductivity. We conclude based on the magnetic
properties that both Mn and V ions are trivalent; moreover, the Mn3+ ions are
in a high-spin state, which is the reason that the compound is not a
half-metallic antiferromagnet.",0206146v1
2002-06-13,Mixed moment wave function for magnetic heavy fermion compounds,"We propose a variational wave function for the ground state of the magnetic
heavy fermion (HF) systems, in which both the Kondo and the RKKY interactions
are variationally incorporated and the local f-orbital state exists as a linear
combination of a full local moment state and a fully compensated state (mixed
moment state). We describe the mechanism for the mixed moment ground state
based on the large-N treatment of the Kondo lattice Hamiltonian added with RKKY
interaction. With the mixed moment ground state we can explain several puzzling
experiments in magnetic HF compounds such as a small value of local moment,
coexistence of the antiferromagnetic (AFM) and the paramagnetic (PM) phases,
local quantum criticality, etc.",0206247v2
2002-07-18,Spin dynamics in a structurally ordered non-Fermi liquid compound: YbRh_2Si_2,"Muon spin relaxation (muSR) experiments have been carried out at low
temperatures in the non-Fermi-liquid heavy-fermion compound YbRh_2Si_2. The
longitudinal-field muSR relaxation function is exponential, indicative that the
dynamic spin fluctuations are homogeneous. The relaxation rate 1/T_1 varies
with applied field as H^{-y}, y = 1.0 \pm 0.1, which implies a scaling law of
the form \chi''(\omega) \propto \omega^{-y} f(\omega/T), \lim_{x\to0} f(x) = x
for the dynamic spin susceptibility.",0207464v1
2002-08-07,Carbon cage-like materials as potential low work function metallic compounds: Case of clathrates,"We present an ab-initio calculation of the electronic affinity of the
hypothetical C-46 clathrate by studying its bare and hydrogenated (100)
surfaces. We show that such a system shares with the diamond phase a small
electronic affinity. Further, contrary to the diamond phase, the possibility of
doping endohedrally these cage-like systems allows to significantly raise the
position of the Fermi level, resulting in a true metal with a small work
function. This is illustrated in the case of the Li8@C-46 doped compound. Such
a class of materials might be of much interest for the design of
electron-emitting devices.",0208132v1
2002-09-02,"Towards New Half-Metallic Systems: Zinc-Blende Compounds of Transition Elements with N, P, As, Sb, S, Se, and Te","We report systematic first-principles calculations for ordered zinc-blende
compounds of the transition metal elements V, Cr, Mn with the sp elements N, P,
As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb,
and MnAs. They show ferromagnetic half-metallic behavior for a wide range of
lattice constants. We discuss the origin and trends of half-metallicity,
present the calculated equilibrium lattice constants, and examine the
half-metallic behavior of their transition element terminated (001) surfaces.",0209039v2
2002-09-25,Superconducting Properties of Atomic-Disordered Compound MgCNi_3,"The effect of radiation-induced disordering in a nuclear reactor (fast
neutrons fluence \Phi = 5\cdot10^{19} cm^2, T_{\text{irr}} = 340 K) on
resistivity \rho, superconducting transition temperature T_C and upper critical
field H_{C_2} of polycrystalline MgCNi_3 samples was investigated. It was found
that T_C decreases under irradiation from 6.5 to 2.9 K and completely recovers
after annealing at 600 ^\circC. Temperature dependences \rho(T) are
characteristic of compounds with strong electron-phonon interaction. The
dH_{C_2}/dT behaviour testifies to a considerable decrease in density of
electronic state at Fermi level N(E_F) in the course of disordering.",0209575v1
2002-10-02,Direct evidence for superconductivity in the organic charge density-wave compound alpha-(BEDT-TTF)_2KHg(SCN)_4 under hydrostatic pressure,"We present direct evidence of a superconducting state existing in the title
compound below 300 mK under quasi-hydrostatic pressure. The superconducing
transition is observed in the whole pressure range studied, 0 < P < 4 kbar.
However, the character of the transition drastically changes with suppressing
the charge-density wave state.",0210062v1
2002-11-12,Electron Correlations in the High Tc-Compounds,"Ab-initio correlation results for an idealized high Tc-compound are compared
to density functional (DF) calculations for the same system. It is shown that
and why the DF-charge distribution is wrong. The largest deficiency arises for
the Cu-d(x2-y2)-occupation, originating from strong atomic correlations but
mostly from anomalous neighbor Cu-spin correlations. Both features are beyound
the range of the homogeneous electron gas approximation underlying the
DF-schemes. The ab-initio results also exclude a description of the real system
in a Mott-Hubbard scenario, that is mostly chosen in theory.",0211230v1
2002-11-14,"Comment on ""Short-range magnetic interactions in the spin-ice compound Ho2Ti2O7""","In their recent communication (Phys. Rev. B 64, 060406(R) (2001)) Cornelius
and Gardner have reported the results of magnetization and susceptibility
studies on single crystals of the pyrochlore Ho2Ti2O7. The observed field
dependence of magnetization is totally unexpected, as it seems to suggest that
the magnetic moments in this compound do not obey the 'ice-rule'. We have
re-measured the magnetization curves for Ho2Ti2O7 single crystal for the three
principal directions of an applied magnetic field and found nearly perfect
agreement with the predictions for a nearest-neighbor spin-ice model.",0211282v1
2002-11-20,Symmetry Considerations for detection of Time-reversal Breaking Phases in Cuprates by X-ray Diffraction and Absorption,"Time-reversal and inversion breaking in the pseudogap region of the cuprate
compounds have been proposed and detected by means of ARPES in the compound
Bi-2212. Given the implication of the effect in the physics of the cuprate
superconductors, it is important to check the conclusions through quite
independent experimental techniques. We show how time-reversal and inversion
breaking may be revealed in the Cuprates through resonant x-ray scattering and
through non-reciprocal or magnetochiral dichroism.",0211433v1
2003-02-12,"Octahedral Tilting in ACu3Ru4O12 (A=Na,Ca,Sr,La,Nd)","The perovskite-like compounds ACu3Ru4O12 (A=Na,Ca,Sr,La,Nd) are studied by
means of density functional theory based electronic structure calculations
using the augmented spherical wave (ASW) method. The electronic properties are
strongly influenced by covalent type bonding between transition metal d and
oxygen p states. The characteristic tilting of the RuO6 octahedra arises mainly
from the Cu--O bonding, allowing for optimal bond lengths between these two
atoms. Our results provide a deeper understanding of octahedral tilting as a
universal mechanism, applicable to a large variety of multinary compounds.",0302240v1
2003-02-17,Deviation from the Kadowaki-Woods relation in Yb-based intermediate-valent systems,"The T^2 coefficient of electrical resistivity, A, is compared with the
electronic specific-heat coefficient, \gamma, for a number of Yb-based
compounds. It is revealed that many systems including YbCuAl, YbInCu4, YbAl3
and YbCu5 show A/\gamma^2 values close to 0.4*10^{-6} \mu\Omega cm(mol K/mJ)^2,
which is remarkably smaller than that known as the Kadowaki-Woods relation,
A/\gamma^2 = 1.0*10^{-5} \mu\Omega cm(mol K/mJ)^2. Empirically, the compounds
with the smaller A/\gamma^2 values appear to show weak intersite
magnetic-correlation and/or to have almost fully-degenerated (J = 5/2 or 7/2)
ground states.",0302325v1
2003-03-19,Heavy fermion superconductivity in the filled skutterudite compound PrOs$_4$Sb$_{12}$,"The filled skutterudite compound \PrOsSb{} has been found to exhibit
superconductivity with a critical temperature $T_\mathrm{c} = 1.85$ K that
develops out of a heavy Fermi liquid with an effective mass $m^{*} \approx 50
m_\mathrm{e}$. The current experimental situation regarding the heavy fermion
state, the superconducting state, and a high field, low temperature phase that
is apparently associated with magnetic or quadrupolar order in \PrOsSb{} is
briefly reviewed herein.",0303371v1
2003-05-18,Non-adiabatic small polaron hopping in the n=3 Ruddlesden-Popper compound Ca4Mn3O10,"Magnetotransport properties of the compound Ca4Mn3O10 are interpreted in
terms of activated hopping of small magnetic polarons in the non-adiabatic
regime. Polarons are most likely formed around Mn3+ sites created by oxygen
substoichiometry. The application of an external field reduces the size of the
magnetic contribution to the hopping barrier and thus produces an increase in
the conductivity .We argue that the change in the effective activation energy
around TN is due to the crossover to VRH conduction as antiferromagnetic order
sets in.",0305421v1
2003-05-26,Quasiparticle relaxation dynamics in heavy fermion compounds,"We present the first femtosecond studies of electron-phonon (e-ph)
thermalization in heavy fermion compounds. The e-ph thermalization time
tau_{ep} increases below the Kondo temperature by more than two orders of
magnitude as T = 0 K is approached. Analysis using the two-temperature model
and numerical simulations based on Boltzmann's equations suggest that this
anomalous slowing down of the e-ph thermalization derives from the large
electronic specific heat and the suppresion of scattering between heavy
electrons and phonons.",0305597v1
2003-06-03,The suppression of superconductivity in Mn substituted MgCNi$_{3}$,"We report the effect of doping Mn in the isostructural MgCNi$_{3-x}$Mn$_{x}$
(x = 0-0.05) compounds. Magnetic susceptibility, resistivity,
magneto-resistance, and specific heat studies show evidence of localized
moments and Kondo effect in samples with x$\neq$0. The rapid suppression of
superconductivity ($\sim$ -21K/at.% Mn) in these compounds is a consequence of
pair breaking effects due to moment formation on Mn.",0306052v2
2003-06-18,Evidence for the coexistence of low-dimensional magnetism and long-range order in Ca3CoRhO6,"We report the results of neutron powder diffraction studies on the spin-chain
compound Ca3CoRhO6 in the temperature range 3 to 293 K. Bragg peaks due to
magnetic ordering start appearing below about 100 K. The most interesting
observation is that there is a diffuse magnetic peak superimposed over the
strongest magnetic Bragg peak. The diffuse magnetic intensity is observed below
as well above 100 K. This finding provides a new insight into the physics of
this compound as though the low-dimensional magnetic interaction coexists with
long range magnetic order - a novel situation among quasi one-dimensional
oxides.",0306481v1
2003-08-01,A New structural parameter for Perovskite type compounds and its application to 'Stripe Phases',"A new parameter named PESATc (Parametro Estructural de los Superconductores
de Alta Temperatura critica) is presented and used to discuss an aproach to the
'Stripe Phases' in (La,Ca)MnO3 superconductors. The PESATc parameter is based
on the superposition of an Octahedrical Moebius Strip over the CuO planes and
apical oxygen O(4). The linear correlation between PESATc and Tc for Rare Earth
based perovskite compound is shown.",0308004v2
2003-09-16,Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario,"Field-induced magnetization jumps with similar characteristics are observed
at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent
manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even
the existence- of these jumps depends critically on the magnetic field sweep
rate used to record the data. It is proposed that, for both compounds, the
martensitic character of their antiferromagnetic-to-ferromagnetic transitions
is at the origin of the magnetization steps.",0309389v1
2003-11-11,First-principles study of the electrooptic effect in ferroelectric oxides,"We present a method to compute the electrooptic tensor from first principles,
explicitly taking into account the electronic, ionic and piezoelectric
contributions. It allows us to study the non-linear optic behavior of three
ferroelectric ABO_3 compounds : LiNbO_3, BaTiO_3 and PbTiO_3. Our calculations
reveal the dominant contribution of the soft mode to the electrooptic
coefficients in LiNbO_3 and BaTiO_3 and identify the coupling between the
electric field and the polar atomic displacements along the B-O chains as the
origin of the large electrooptic response in these compounds.",0311240v2
2003-12-02,Single Crystal Growth of Skutterudite CoP3 under High Pressure,"A new method to grow single crystals of skutterudite compounds is examined.
Using a wedge-type, cubic-anvil, high-pressure apparatus, single crystals of
CoP3 were grown from stoichiometric melts under a pressure of 3.5 GPa. Powder
x-ray diffraction and electron probe microanalysis measurements indicate that
the as-grown boules are a single phase of CoP3. The results suggest that CoP3
is a congruent melting compound under high pressure.",0312059v1
2003-12-15,Magnetic ligands in the $Pt_2(dta)_4I$ compound,"We report a reinterpretation of the electronic structure of the
$(Pt)_2I(dta)_4$ compound, based on {\em ab initio} embedded fragment
calculations. Our major results are the following. First, the usually assumed
electronic intra-dimer charge ordering is unrealistic. Second, the $(dta)$
ligands take part actively in the magnetic properties of the system. The
proposed electronic structure is favorably confronted to experimental data. In
particular, the unexplained $3:1$ $Pt^{2+}/Pt^{3+}$ abundances ratio of the XPS
spectra is rationalized.",0312374v1
2003-12-28,"XANES Pb LIII spectra of mixed-valence compound: Minium, Pb3O4","Mixed-valence compound Pb3O4 (minium) has been studied using X-ray absorption
near-edge structure (XANES) spectroscopy and DFT calculations. In spite of
presence of two valence states of lead [Pb(II) and Pb(IV)], the XANES spectrum
of studied system is corresponding to apparently unified, an intermediate
valence state of Pb. On the other hand, the 207Pb NMR spectra definitely show
two different spectral bands corresponding to different Pb2+ and Pb4+ ions in
Pb3O4 crystal structure. The explanation of this contradiction is related to
the basics of XANES and NMR spectroscopy.",0312663v1
2004-01-30,Comparison of the Electronic Structures of Hydrated and Unhydrated Na_xCoO_2: The Effect of H_2O,"We report electronic structure calculations within density functional theory
for the hydrated superconductor Na_{1/3}CoO_2(1.33)H_2O and compare the results
with the parent compound Na_{0.3}CoO_2. We find that the intercalation of water
into the parent compound has little effect on the Fermi surface outside of the
predictable effects expansion, in particular increased two-dimensionality. This
implies an intimate connection between the electronic properties of the
hydrated and unhydrated phases.",0401646v1
2004-02-09,Superconductivity in metal rich Li-Pd-B ternary Boride,"8K superconductivity was observed in the metal rich Li-Pd-B ternary system.
Structural, microstructural, electrical and magnetic investigations for various
compositions proved that Li2Pd3B compound, which has a cubic structure composed
of distorted Pd6B octahedrons, is responsible for the superconductivity. This
is the first observation of superconductivity in metal rich ternary borides
containing alkaline metal and Pd as a late transition metal. The compound
prepared by arc melting has high density, is stable in the air and has an upper
critical field, Hc2(0), of 6T.",0402232v1
2004-02-14,Crystal-field-induced magnetostrictions in the spin reorientation process of Nd$_2$Fe$_{14}$B-type compounds,"Volume expansion $\Delta V / V$ associated with the spin reorientation
process of Nd$_2$Fe$_{14}$B-type compounds has been investigated in terms of
simple crystalline-electric-field (CEF) model. In this system, $\Delta V / V$
is shown to be a direct measure of second order CEF energy. Calculated
anomalies in $\Delta V / V$ associated with the first-order magnetization
process of Nd$_2$Fe$_{14}$B are presented, which well reproduced the
observations.",0402384v1
2004-06-11,Electronic Structure of a Chain-like Compound: TlSe,"An ab-initio pseudopotential calculation using density functional theory
within the local density approximation has been performed to investigate the
electronic properties of TlSe which is of chain-like crystal geometry. The
energy bands and effective masses along high symmetry directions, the density
of states and valence charge density distributions cut through various planes
are presented. The results have been discussed in terms of previously existing
experimental and theoretical data, and comparisons with similar compounds have
been made.",0406287v1
2004-08-03,Electrical resistivity and tunneling anomalies in CeCuAs2,"The compound CeCuAs2 is found to exhibit negative temperature (T) coefficient
of electrical resistivity (rho) under ambient pressure conditions in the entire
T-range of investigation (45 mK to 300 K), even in the presence of high
magnetic fields. Preliminary tunneling spectroscopic measurements indicate the
existence of a psuedo-gap at least at low temperatures, thereby implying that
this compound could be classified as a Kondo semi-conductor, though rho(T)
interestingly is not found to be of an activated type.",0408060v1
2004-09-07,Optical conductivity of filled skutterudites,"A simple tight-binding model is constructed for the description of the
electronic structure of some Ce-based filled skutterudite compounds showing an
energy gap or pseudogap behavior. Assuming band-diagonal electron interactions
on this tight-binding model, the optical conductivity spectrum is calculated by
applying the second-order self-consistent perturbation theory to treat the
electron correlation. The correlation effect is found to be of great importance
on the description of the temperature dependence of the optical conductivity.
The rapid disappearance of an optical gap with increasing temperature is
obtained as observed in the optical experiment for Ce-based filled-skutterudite
compounds.",0409165v1
2004-09-23,On the Multi-channel Anderson Model of Uranium Compounds,"In this talk we will present the solution of the two-channel Anderson
impurity model, proposed in the context of the heavy fermion compound UBe13,
and discuss briefly the more general multi-channel case. We will show results
for the thermodynamics in the full range of temperature and fields and make the
connection with the current experimental situation.",0409616v1
2004-12-17,Temperature dependence of the EPR linewidth of Yb3+ - ions in Y0.99Yb0.01Ba2Cu3OX compounds: Evidence for an anomaly near TC,"Electron paramagnetic resonance experiments on doped Yb3+ ions in YBaCuO
compounds with different oxygen contents have been made. We have observed the
strong temperature dependence of the EPR linewidth in the all investigated
samples caused by the Raman processes of spin-lattice relaxation. The
spin-lattice relaxation rate anomaly revealed near TC in the superconducting
species can be assigned to the phonon density spectrum changes",0412474v2
2004-12-21,"EPR study of some rare-earth ions (Dy3+, Tb3+ and Nd3+) in YBa2Cu3O6 compound","We investigate the low temperature X-band electron paramagnetic resonance
(EPR) of YBa2Cu3O6 compounds with x = 6.0 doped with Dy3+, Tb3+, and Nd3+. The
EPR spectra of Dy3+ and Tb3+ have been identified. The EPR of Tb3+ is used also
to study the effect of suppression of high Tc superconductivity. The EPR of
Nd3+ is probably masked by the intense resonance of Cu2+. All experimental EPR
results compare well with theoretical estimations.",0412567v1
2005-01-24,Low energy spin fluctuations in the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$,"We report inelastic neutron scattering measurements performed on a single
crystal of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$,
which is at the borderline between an antiferromagnetically ordered and a
paramagnetic ground state. Intensity maps as a function of wavevector and
energy ($0.1<E<1.2$ meV) were obtained at temperatures $T=0.1$ and 2 K, using
the time-of-flight spectrometer IRIS. An unexpected saturation of the
relaxation rate and static susceptibility of the spin fluctuations is found at
low temperatures.",0501574v1
2005-02-18,"Neutron inelastic scattering investigation of the magnetic excitations in Cu_2Te_2O_5X_2 (X=Br, Cl)","Neutron inelastic scattering investigations have been performed on the spin
tetrahedral system Cu_2Te_2O_5X_2 (X = Cl, Br). We report the observation of
magnetic excitations with a dispersive component in both compounds, associated
with the 3D incommensurate magnetic order that develops below $T^{Cl}_{N}$=18.2
K and $T^{Br}_{N}$=11.4 K. The excitation in Cu_2Te_2O_5Cl_2 softens as the
temperature approaches $T^{Cl}_{N}$, leaving diffuse quasi-elastic scattering
above the transition temperature. In the bromide, the excitations are present
well above $T^{Br}_{N}$, which might be attributed to the presence of a degree
of low dimensional correlations above $T^{Br}_{N}$ in this compound.",0502445v1
2005-02-23,"Crystal-field effects in the mixed-valence compounds Yb2M3Ga9 (M= Rh, Ir)","Magnetic susceptibility, heat capacity, and electrical resistivity
measurements have been carried out on single crystals of the intermediate
valence compounds Yb2Rh3Ga9 and Yb2Ir3Ga9. These measurements reveal a large
anisotropy due apparently to an interplay between crystalline electric field
(CEF) and Kondo effects. The temperature dependence of magnetic susceptibility
can be modelled using the Anderson impurity model including CEF within an
approach based on the Non-Crossing Approximation.",0502562v1
2005-04-07,"Structural and magnetic properties of hexagonal perovskites La1.2Sr2.7MO7+d (M=Ru,Ir)","The structures of the new compound La1.2Sr2.7IrO7+d and the recently
discovered La1.2Sr2.7RuO7+d have been solved using a combination of X-ray and
neutron diffraction. Both compounds crystallize in the trigonal space group
R-3m and contain isolated MO6 (M=Ru,Ir) octahedra, which are arranged in
well-defined layers. Results of the magnetic susceptibility and XANES
measurements show that the transition metal cations are in a pentavalent state.
While in La1.2Sr2.7RuO7+d an antiferromagnetic interaction between the Ru5+
ions is found, La1.2Sr2.7IrO7+d shows a very small temperature-independent
paramagnetism down to 1.8 K due to the strong spin-orbit coupling
characteristic for the 5d element iridium.",0504171v1
2005-05-09,Dynamical properties of S=1 bond-alternating Heisenberg chains in transverse magnetic fields,"We calculate dynamical structure factors of the S=1 bond-alternating
Heisenberg chain with a single-ion anisotropy in transverse magnetic fields,
using a continued fraction method based on the Lanczos algorithm. In the
Haldane-gap phase and the dimer phase, dynamical structure factors show
characteristic field dependence. Possible interpretations are discussed. The
numerical results are in qualitative agreement with recent results for
inelastic neutron-scattering experiments on the S=1 bond-alternating
Heisenberg-chain compound $\rm{Ni(C_{9}D_{24}N_{4})(NO_{2})ClO_{4}}$ and the
S=1 Haldane-gap compound $\rm{Ni(C_{5}D_{14}N_{2})_{2}N_{3}(PF_{6})}$ in
transverse magnetic fields.",0505196v1
2005-06-03,Superconductivity of bulk CaC6,"We have obtained bulk samples of the graphite intercalation compound, CaC6,
by a novel method of synthesis from highly oriented pyrolytic graphite. The
crystal structure has been completely determined showing that it is the only
member of the MC6, metal-graphite compounds, which has rhombohedral symmetry.
We have clearly shown the occurrence of superconductivity in the bulk sample at
11.5K, using magnetization measurements.",0506093v1
2005-06-21,Multiband superconductivity in the heavy fermion compound PrOs4Sb12,"The thermal conductivity of the heavy fermion superconductor PrOs4Sb12 was
measured down to Tc/40 throughout the vortex state. At lowest temperatures and
for magnetic fields H ~ 0.07Hc2, already 40% of the normal state thermal
conductivity is restored. This behaviour (similar to that observed in MgB2) is
a clear signature of multiband superconductivity in this compound.",0506522v1
2005-07-28,Optical study of interactions in a d-electron Kondo lattice with ferromagnetism,"We report on a comprehensive optical, transport and thermodynamic study of
the Zintl compound Yb$_{14}$MnSb$_{11}$, demonstrating that it is the first
ferromagnetic Kondo lattice compound in the underscreened limit. We propose a
scenerio whereby the combination of Kondo and Jahn-Teller effects provides a
consistent explanation of both transport and optical data.",0507693v1
2005-08-04,Kondo Lattice Behavior in the Ordered Dilute Magnetic Semiconductor Yb_{14-x}La_xMnSb_{11},"We report Hall, magnetic, heat capacity and doping studies from single
crystals of Yb_14MnSb_11 and Yb_13.3La_0.7MnSb_11. These heavily doped
semiconducting compounds are ferromagnetic below 53 K and 39 K respectively.
The renormalization of the carrier mass from 2 me near room temperature to 15
me at 5 K, plus the magnetic evidence for partial screening of the Mn magnetic
moments suggest that these compounds represent rare examples of an
underscreened Kondo lattice with T_K = 350 K.",0508132v1
2005-08-23,First-principles calculations of a high-pressure synthesized compound PtC,"First-principles density-functional method is used to study the recently
high-pressure synthesized compound PtC. It is confirmed by our calculations
that the platinum carbide has a zinc-blende ground-state phase at zero pressure
and the rock-salt structure is a high-pressure phase. The theoretical
transition pressure from zinc-blende to rock-salt is determined to be 52GPa.
Furthermore, our calculation shows the possibility that the experimentally
synthesized PtC by Ono et al. under high pressure condition might undergo a
transition from rock-salt structure to zinc-blende after the pressure quench to
ambient condition.",0508533v2
2005-09-05,"Large magnetoresistance and magnetocaloric effect above 70 K in Gd2Co2Al, Gd2Co2Ga and Gd7Rh3","The electrical resistivity, magnetization and heat-capacity behavior of the
Gd-based compounds, Gd2Co2Al, Gd2Co2Ga and Gd7Rh3, ordering magnetically at TC=
78 K, TC= 76 K and TN= 140 K have been investigated as a function of
temperature and magnetic field. All these compounds are found to show large
magnetoresistance (with a negative sign) in the paramagnetic state at rather
high temperatures with the magnitude peaking at respective magnetic ordering
temperatures. There is a corresponding behavior in the magnetocaloric effect as
inferred from the entropy derived from these data.",0509107v1
2005-11-24,Superconductivity in a Molecular Metal Cluster Compound,"Compelling evidence for band-type conductivity and even bulk
superconductivity below $T\_{\text{c}}\approx 8$ K has been found in
$^{69,71}$Ga-NMR experiments in crystalline ordered, giant Ga$\_{84}$
cluster-compounds. This material appears to represent the first realization of
a theoretical model proposed by Friedel in 1992 for superconductivity in
ordered arrays of weakly coupled, identical metal nanoparticles.",0511612v2
2005-12-14,Acoustic emission across the magnetostructural transition of the giant magnetocaloric Gd5Si2Ge2 compound,"We report on the existence of acoustic emission during the
paramagnetic-monoclinic to ferromagnetic-orthorhombic magnetostructural phase
transition in the giant magnetocaloric Gd5Si2Ge2 compound. The transition
kinetics have been analyzed from the detected acoustic signals. It is shown
that this transition proceeds by avalanches between metastable states.",0512303v1
2006-01-04,Tunable temperature induced magnetization jump in a GdVO3 single crystal,"We report a novel feature of the temperature induced magnetization jump
observed along the a-axis of the GdVO3 single crystal at temperature TM = 0.8
K. Below TM, the compound shows no coercivity and remanent magnetization
indicating a homogenous antiferromagnetic structure. However, we will
demonstrate that the magnetic state below TM is indeed history dependent and it
shows up in different jumps in the magnetization only when warming the sample
through TM. Such a magnetic memory effect is highly unusual and suggesting
different domain arrangements in the supposedly homogenous antiferromagnetic
phase of the compound.",0601066v1
2006-02-16,"Anomalous charge transport in dodecaborides RB12 (R- Ho, Er, Tm, Lu)","High precision measurements of Hall RH(T) and Seebeck S(T) coefficients have
been carried out for the first time on single crystals of rare earth
dodecaborides RB12 (R - Ho, Er, Tm, Lu) at temperatures 1.8 - 300K. Low
temperature anomalies associated with antiferromagnetic phase transitions in
HoB12, ErB12 and TmB12 compounds have been detected on the temperature
dependencies of RH(T) and S(T). The estimated values of charge carriers
mobility allowed us to conclude about the appreciable influence of spin
fluctuations on the charge transport in these compounds with B12 atomic
clusters.",0602380v1
2006-03-22,Spin thermal conductivity of the Haldane chain compound Y2BaNiO5,"We have measured the thermal conductivity of the spin S=1 chain compound
Y2BaNiO5. Analyzing the anisotropy of the thermal transport allows to identify
a definite spin-mediated thermal conductivity \kappa_s along the chain
direction. The calculated spin-related energy diffusion constant D_E(T) shows a
broad peak around 120 K. Close to room temperature, D_E(T) approaches the
theoretically predicted high-temperature value, while scattering of spin
excitations by magnetic impurities seems to be the major limiting factor of
\kappa_s at low temperature.",0603586v2
2006-04-07,The Jahn-Teller theorem for 3d ions and their compounds,"In contrary to customarily consideration of the Jahn-Teller theorem for
3d-ion compounds in the orbital space only we point out that it has to be
considered in the spin-orbital space. It is despite the weakness of the
intraatomic spin-orbit coupling. A direct motivation for this paper is an
erroneous claim of a recent Phys. Rev. Lett. 96 (2006) 027201 paper that the
high-spin t2g4eg2 state of the 3d6 configuration is not Jahn-Teller active.",0604207v1
2006-04-26,Synthesis and physical characterization of superconductivity-magnetism crossover compound RuSr2EuCeCu2O10,"We carefully studied the nonsuperconducting sample of the
magneto-superconducting RuSr2(Eu1-xCex)Cu2O10 series with composition
RuSr2EuCeCu2O10. This compound seems to exhibit a complex magnetic state as
revealed by host of techniques like resistivity, thermopower, magnetic
susceptibility and MR measurements.",0604586v1
2006-06-15,Interplay between phase defects and spin polarization in the specific heat of the spin density wave compound (TMTTF)_2Br in a magnetic field,"Equilibrium heat relaxation experiments provide evidence that the ground
state of the commensurate spin density wave (SDW) compound (TMTTF)$_2$Br after
the application of a sufficient magnetic field is different from the
conventional ground state. The experiments are interpreted on the basis of the
local model of strong pinning as the deconfinement of soliton-antisoliton pairs
triggered by the Zeeman coupling to spin degrees of freedom, resulting in a
magnetic field induced density wave glass for the spin carrying phase
configuration.",0606403v1
2006-09-07,A compound figure of merit for photonic applications of metal nanocomposites,"Selecting nanocomposites for photonic switching applications requires
optimizing their thermal, nonlinear and two-photon absorption characteristics.
We simplify this step by defining a compound figure of merit (FOM_{C}) for
nanocomposites of noble metals in dielectric based on criteria that limit these
structures in photonic applications, i.e. thermal heating and two-photon
absorption. The device independent results predict extremely large values of
FOM_{C} for a specific combination of the metal and insulator dielectric
constant given by \epsilon_{h}=\frac{\epsilon_{1}-\epsilon_{2}}{2}, where
\epsilon_{h} is the dielectric constant of the host and \epsilon_{1} and
\epsilon_{2} are the real and imaginary parts for the metal.",0609176v1
2006-10-05,Magnetic excitations in the Kagome staircase compounds,"Inelastic neutron scattering measurements have been performed on single
crystal samples of Co3V2O8 and Ni3V2O8. The magnetic system in these compounds
is believed to be frustrated, as the magnetic ions Co2+ with S=3/2 and Ni2+
with S=1 adopt a buckled version of the Kagome lattice. Magnetic excitations
have been observed in both samples using a time-of-flight neutron spectrometer.
The excitation spectrum is dispersive for both samples and has a considerable
gap in the low temperature phases, while the intermediate temperature phases
are marked by a significant softening of the excitations energy.",0610143v1
2006-10-19,Heat capacity and magnetocaloric effect in polycrystalline Gd1-xSmxMn2Si2,"We report the magnetocaloric effect in terms of isothermal magnetic entropy
change as well as adiabatic temperature change, calculated using the heat
capacity data. Using the zero field heat capacity data, the magnetic
contribution to the heat capacity has been estimated. The variations in the
magnetocaloric behavior have been explained on the basis of the magnetic
structure of these compounds. The refrigerant capacities have also been
calculated for these compounds.",0610551v1
2007-01-23,Hyperfine Interaction in USb2 Crystal,"The hyperfine interactions at the uranium site in the antiferromagnetic USb2
compound were calculated within the density functional theory (DFT) employing
augmented plane wave plus local orbital (APW+lo) method. We investigated the
dependence of the nuclear quadruple interaction to the magnetic structure in
USb2 compound. The result shows that the 5f-electrons have the tendency to be
hybridized with the conduction electrons.",0701563v1
2007-02-06,Magnetic structure and phase diagram in a spin-chain system: Ca$_3$Co$_2$O$_6$,"The low-temperature structure of the frustrated spin-chain compound
Ca$_3$Co$_2$O$_6$ is determined by the ground state of the 2D Ising model on
the triangular lattice. At high-temperatures it transforms to the honeycomb
magnetic structure. It is shown that the crossover between the two magnetic
structures at 12 K arises from the entropy accumulated in the disordered
chains. This interpretation is in an agreement with the experimental data.
General rules for for the phase diagram of frustrated Ising chain compounds are
formulated.",0702155v1
1999-02-23,"End states, ladder compounds, and domain wall fermions","A magnetic field applied to a cross linked ladder compound can generate
isolated electronic states bound to the ends of the chain. After exploring the
interference phenomena responsible, I discuss a connection to the domain wall
approach to chiral fermions in lattice gauge theory. The robust nature of the
states under small variations of the bond strengths is tied to chiral symmetry
and the multiplicative renormalization of fermion masses.",9902028v2
2001-11-15,Solution of the multi-reggeon compound state problem in multi-colour QCD,"We study the properties of the colour-singlet compound states of reggeized
gluons in multi-colour QCD using their relation with noncompact Heisenberg spin
magnets. Applying the methods of integrable models, we calculate their spectrum
and discuss the application of the obtained results to high-energy asymptotics
of the scattering amplitudes in perturbative QCD.",0111185v2
2002-12-30,On certain organic compounds with one mono-substitution and at least three di-substitution homogeneous derivatives,"In this paper parent substances with molecules which can be divided into a
skeleton and six univalent substituents, and that have the properties mentioned
in the title, are considered. Two instances are the molecules of benzene and
cyclopropane. The Lunn-Senior's symmetry groups of substitution isomerism of
these compounds are described and upper bounds of the numbers of their
di-substitution and tri-substitution homogeneous derivatives are found. Lists
of the possible simple substitution reactions among di-substitution homogeneous
derivatives, on one hand, and di-substitution heterogeneous, and
tri-substitution homogeneous derivatives, on the other, are given. These
substitution reactions allow for some derivatives to be identified with their
structural formulae.",0212374v1
2005-06-21,Measure Concentration for Compound Poisson Distributions,"We give a simple development of the concentration properties of compound
Poisson measures on the nonnegative integers. A new modification of the Herbst
argument is applied to an appropriate modified logarithmic-Sobolev inequality
to derive new concentration bounds. When the measure of interest does not have
finite exponential moments, these bounds exhibit optimal polynomial decay.
Simple new proofs are also given for earlier results of Houdr{\'e} (2002) and
Wu (2000).",0506435v1
2006-04-18,Asymptotic expansions for distributions of compound sums of light subexponential random variables,"We derive an asymptotic expansion for the distribution of a compound sum of
independent random variables, all having the same light-tailed subexponential
distribution. The examples of a Poisson and geometric number of summands serve
as an illustration of the main result. Complete calculations are done for a
Weibull distribution, with which we derive, as examples and without any
difficulties, 7 terms expansions.",0604378v1
2004-07-16,Non-linear hydrodynamics of incommensurate intergrowth compounds and quasicrystals,"Hamiltonian structures for non-linear hydrodynamics of incommensurate
intergrowth compounds (IIC) and quasicrystals (IQ) are constructed. We discuss
also the way to account for internal friction of phason nature. We show that
the existence of a self-force in IIC and IQ is not only matter of constitutive
issues, rather it is related with questions of SO(3) invariance. The covariant
mechanics of discontinuity surfaces in quasiperiodic structures is also
analyzed. The attention is mainly focused on the interaction between `diffuse'
grain boundaries and sharp discontinuity (moving possibly) surfaces.",0407036v1
1994-11-17,Competing structural instabilities in cubic perovskites,"We study the antiferrodistortive instability and its interaction with
ferroelectricity in cubic perovskite compounds. Our first-principles
calculations show that coexistence of both instabilities is very common. We
develop a first-principles scheme to study the thermodynamics of these
compounds when both instabilities are present, and apply it to SrTiO$_3$. We
find that increased pressure enhances the antiferrodistortive instability while
suppressing the ferroelectric one. Moreover, the presence of one instability
tends to suppress the other. A very rich $P$--$T$ phase diagram results.",9411005v1
1998-07-24,Evaporation of alpha particles from $^31$P nucleus,"The energy spectra of alpha particles have been measured in coincidence with
the evaporation residues for the decay of the compound nucleus $^31$P produced
in the reaction $^19$F (96 MeV) + $^12$C. The data have been compared with the
predictions of the statistical model code CASCADE. It has been observed that
significant deformation effect in the compound nucleus need to be considered in
order to explain the shape of the evaporated alpha particle energy spectra.",9807005v1
2003-06-04,Main parameters of the 118Sn compound-state cascade gamma-decay,"Main properties of the excited states of $^{118}$Sn manifesting themselves in
cascade gamma-decay of its compound state were studied. As in other heavier
nuclei studied earlier, qualitative interpretation of the totality of the
observed properties of this nucleus is impossible without accounting for
coexistence and interaction of quasi-particle and collective nuclear
excitations and their considerable influence on the main parameters of the
process under study.",0306008v1
1994-05-13,Molecular dynamics approach: from chaotic to statistical properties of compound nuclei,"Statistical aspects of the dynamics of chaotic scattering in the classical
model of $\alpha$-cluster nuclei are studied. It is found that the dynamics
governed by hyperbolic instabilities which results in an exponential decay of
the survival probability evolves to a limiting energy distribution whose
density develops the Boltzmann form. The angular distribution of the
corresponding decay products shows symmetry with respect to $\pi/2$ angle. Time
estimated for the compound nucleus formation ranges within the order of
$10^{-21}$s.",9405013v1
1994-10-28,Time Reversal Symmetry Breaking Effects in Resonant Nuclear Reactions,"We incorporate time reversal symmetry breaking (TRSB) effects into the theory
of compound nuclear reactions. We show that the only meaningful test of TRSB in
the overlapping resonances regime is through the study of cross-section
correlations. The effect is channel-dependent. In the isolated resonance
regime, we employ $K$-matrix theory to show the impact of TRSB using the fact
that when only one eigen-channel participates in populating and depopulating
the compound resonance.",9410047v1
2003-11-26,Modelling of compound nucleus formation in fusion of heavy nuclei,"A new model that includes the time-dependent dynamics of the single-particle
(s.p.) motion in conjunction with the macroscopic evolution of the system is
proposed for describing the compound nucleus (CN) formation in fusion of heavy
nuclei. The diabaticity initially keeps the entrance system around its contact
configuration, but the gradual transition from the diabatic to the adiabatic
potential energy surface (PES) leads to fusion or quasifission. Direct
measurements of the probability for CN formation are crucial to discriminate
between the current models.",0311093v1
2000-11-29,Compound Poisson Statistics and Models of Clustering of Radiation Induced DNA Double Strand Breaks,"According to the experimental evidence damage induced by densely ionizing
radiation in mammalian cells is distributed along the DNA molecule in the form
of clusters. The most critical constituent of DNA damage are double-strand
breaks (DSBs) which are formed when the breaks occur in both DNA strands and
are directly opposite or separated by only a few base pairs. The paper
discusses a model of clustered DSB formation viewed in terms of compound
Poisson process along with the predictive assay of the formalism in application
to experimental data.",0011071v1
2003-05-02,On the Compound Structures of the Neutrino Mass and Charge,"The mass and charge of a particle correspond to the most diverse form of the
same regularity of the nature of this field. As a consequence, each of all
possible types of charges testifies in favor of the existence of a kind of
inertial mass. Therefore, to investigate these features, we have established
the compound structures of mass and charge. They can explain also the
availability of fundamental differences in the masses as well as in the charges
of Dirac and Majorana neutrinos.",0305008v2
2004-06-30,Nanoporous compound materials for optical applications - microlasers and microresonators,"This book chapter is the first part of a review of nanoporous materials for
optical applications. Whereas the second part [J.Sauer, F. Marlow and
F.Schueth, pp. 153-172 of the same volume] discusses material properties, this
part gives a self-contained discussion of fluorescence and lasing in dielectric
microresonators, with special emphasis on the hexagonal morphology found in
molecular-sieve-dye compounds.",0406155v1
2005-05-24,Calculation of single-beam two-photon absorption transition rate of rare-earth ions using effective operator and diagrammatic representation,"Effective operators needed in single-beam two-photon transition calculations
have been represented with modified Goldstone diagrams similar to the type
suggested by Duan and co-workers [J. Chem. Phys. 121, 5071 (2004) ]. The rules
to evaluate these diagrams are different from those for effective Hamiltonian
and one-photon transition operators. It is verified that the perturbation terms
considered contain only connected diagrams and the evaluation rules are
simplified and given explicitly.",0505162v1
2006-10-12,Compound Pendulum to Monitor Hurricanes and Tropical Storms,"The period of an undamped compound pendulum has been selected to maximize the
instrument's response to microseisms, when functioning as a type of horizontal
seismometer. When functioning as a tiltmeter, the instrument is also capable of
monitoring eigenmode oscillations of the Earth. Other instruments designed by
the author, some of which were monitored during hurricanes, suggest that storm
seismicity in the frequency range of this pendulum could aid the process of
hurricane forecasting.",0610092v1
1999-01-09,Searching in Grover's Algorithm,"Grover's algorithm is usually described in terms of the iteration of a
compound operator of the form $Q = - H I_{0} H I_{x_0}$. Although it is quite
straightforward to verify the algebra of the iteration, this gives little
insight into why the algorithm works. What is the significance of the compound
structure of $Q$? Why is there a minus sign? Later it was discovered that $H$
could be replaced by essentially any unitary $U$. What is the freedom involved
here? We give a description of Grover's algorithm which provides some
clarification of these questions.",9901021v1
2003-02-19,Compressing compound states,"Quantum compression can be thought of not only as compression of a signal,
but also as a form of cooling. In this view, one is interested not in the
signal, but in obtaining purity. In compound systems, one may be interested to
cool the system to obtain {\it local purity} by use of local operations and
classical communication [Oppenheim et al. Phys. Rev. Lett. 89,180402 (2002)].
Here we compare it with usual compression and find that it can be represented
as compression with suitably restricted means.",0302139v1
2007-04-02,Compounding Fields and Their Quantum Equations in the Trigintaduonion Space,"The 32-dimensional compounding fields and their quantum interplays in the
trigintaduonion space can be presented by analogy with octonion and sedenion
electromagnetic, gravitational, strong and weak interactions. In the
trigintaduonion fields which are associated with the electromagnetic,
gravitational, strong and weak interactions, the study deduces some conclusions
of field source particles (quarks and leptons) and intermediate particles which
are consistent with current some sorts of interaction theories. In the
trigintaduonion fields which are associated with the hyper-strong and
strong-weak fields, the paper draws some predicts and conclusions of the field
source particles (sub-quarks) and intermediate particles. The research results
show that there may exist some new particles in the nature.",0704.0136v2
2007-04-04,Thermally Stimulated Luminescence and Current in new heterocyclic materials for Organic field transistors and organic light emitting diodes,"The present work is focused on theoretical and experimental study of
localised levels in organic materials suitable for light-emitting devices and
field effect transistors by means of thermal techniques. In our work we focused
on low molecular compounds as well as on polymers, especially of two classes of
materials: oxadiazoles and quinoxalines. Both organic compounds are well know
as electron transport materials in OLEDs.",0704.0568v1
2007-04-10,Electronic structure of the zigzag spin-chain compound In$_2$VO$_5$,"Band structure calculations within the local spin-density approximation are
presented in order to investigate the electronic and magnetic properties of the
zigzag spin-chain compound In$_2$VO$_5$. The essential structural feature of
the system is a double chain of VO$_6$-octahedra, which leads to competing
intrachain and interchain magnetic couplings. Frustration of the spin-chains is
expected for the proposed antiferromagnetic ordering at low temperatures.
However, the band calculations show that the experimental room temperature
crystal structure is incompatible with antiferromagnetism. Both the intrachain
and interchain coupling is found to be ferromagnetic.",0704.1205v2
2007-04-22,Sm2Al: Another ferromagnet with spin-orbital compensation?,"We report the observation of a compensation point in the temperature
dependence of magnetization data of polycrystalline Sm2Al. Magnetization
measurements show that this compound magnetically orders at about 150 K. Below
this temperature, the magnetization data shows a compensation point, which
shifts with field. Hysteresis loops obtained below the compensation temperature
show that the compound possesses exchange anisotropy. Both the exchange
anisotropy field and the coercive field are found to be quite large and
comparable to those of the classical spin-orbit compensated ferromagnet
(Sm,Gd)Al2. The heat capacity data also suggest that there are similarities
between (Sm,Gd)Al2 and Sm2Al.",0704.2864v1
2007-07-11,Orbital-Driven Electronic Structure Changes and the Resulting Optical Anisotropy of the Quasi-Two-Dimensional Spin Gap Compound La4Ru2O10,"We investigated the electronic response of the quasi-two-dimensional spin gap
compound La4Ru2O10 using optical spectroscopy. We observed drastic changes in
the optical spectra as the temperature decreased, resulting in anisotropy in
the electronic structure of the spin-singlet ground state. Using the
orbital-dependent hopping analysis, we found that orbital ordering plays a
crucial role in forming the spin gap state in the non-one-dimensional material.",0707.1564v1
2007-08-24,Single-crystal growth and magnetic properties of the metallic molybdate pyrochlore Sm2Mo2O7,"We have successfully grown cm3-size single crystals of the
metallic-ferromagnet Sm2Mo2O7 by the floating-zone method using an infrared-red
image furnace. The growth difficulties and the remedies found using a 2-mirror
image furnace are discussed. Magnetization studies along the three crystalline
axes of the compound are presented and discussed based on our recent proposal
of an ordered spin-ice ground state for this compound",0708.3324v1
2007-08-27,Polarized neutron scattering study on antiferromagnetic states in CeRh0.6Co0.4In5,"Polarized neutron scattering experiments were performed on mixed compound
CeRh0.6Co0.4In5 to clarify the nature of the low-temperature ordered states.
Three nonequivalent Bragg peaks, characterized by the wave vectors of q_h ~
(1/2,1/2,0.3), q_1 ~ (1/2,1/2,0.4) and q_c=(1/2,1/2,1/2), were observed at 1.4
K. These Bragg peaks are found to occur entirely in spin-flip channel. This
indicates that these Bragg peaks originate from the magnetic scattering, i.e.,
the antiferromagnetic orders with three different modulations appear in this
compound.",0708.3523v1
2007-08-28,An elementary sieve,"In this paper we review the properties of families of numbers of the form
$6n\pm1$, with $n$ integer (in which there are all prime numbers greater than 3
and other compound numbers with particular properties) to later use them in a
new sieve that allows the separation of numbers $n$ that generate primes from
those that only generate compounds. In principle, this can be used to find the
amount of prime numbers up to a given number $h$; this means, $\pi(h)$.",0708.3709v1
2007-09-20,A Kondo lattice antiferromagnet CePd5Al2,"We report on the electrical resistivity, magnetic susceptibility and
heat-capacity measurements on a new intermetallic compound CePd5Al2,
crystallizing in the ZrNi2Al5-type tetragonal structure, with lattice
parameters a = 4.156 A and c = 14.883 A. The compound presents Kondo lattice
behavior and an easy-plane antiferromagnetic ground state with two magnetic
transitions at 2.9 K and 3.9 K. The Sommerfeld coefficient is estimated as 60
mJ/mol K^2.",0709.3135v1
2007-11-26,Experimental evidence for the separability of compound-nucleus and fragment properties in fission,"The large body of experimental data on nuclear fission is analyzed with a
semi-empirical ordering scheme based on the macro-microscopic approach and the
separability of compound-nucleus and fragment properties on the fission path.
We apply the statistical model to the non-equilibrium descent from saddle to
scission, taking the influence of dynamics into account by an early freeze out.
The present approach reveals a large portion of common features behind the
variety of the complex observations made for the different systems. General
implications for out-of-equilibrium processes are mentioned.",0711.3967v1
2007-12-13,"Optical properties of the charge-density-wave polychalcogenide compounds $R_2$Te$_5$ ($R$=Nd, Sm and Gd)","We investigate the rare-earth polychalcogenide $R_2$Te$_5$ ($R$=Nd, Sm and
Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption
spectrum we extract the excitation energy of the CDW gap and estimate the
fraction of the Fermi surface which is gapped by the formation of the CDW
condensate. In analogy to previous findings on the related $R$Te$_n$ (n=2 and
3) families, we establish the progressive closing of the CDW gap and the
moderate enhancement of the metallic component upon chemically compressing the
lattice.",0712.2206v1
2008-01-07,Origin of the Structural and Magnetic Anomaly of the Layered Compound SrFeO2: A Density Functional Investigation,"The structural and magnetic anomaly of the layered compound SrFeO$_{2}$ were
examined by first principles density functional calculations and Monte Carlo
simulations. The down-spin Fe 3$d$ electron occupies the $d_{z^2}$ level rather
than the degenerate ($d_{xz}$, $d_{yz}$) levels, which explains the absence of
Jahn-Teller instability, the easy ab-plane magnetic anisotropy and the observed
three-dimensional (0.5, 0.5, 0.5) antiferromagnetic order. Monte Carlo
simulations show that the strong inter-layer spin exchange is essential for the
high N\'eel temperature.",0801.1137v2
2008-01-21,The Two User Gaussian Compound Interference Channel,"We introduce the two user finite state compound Gaussian interference channel
and characterize its capacity region to within one bit. The main contributions
involve both novel inner and outer bounds. The inner bound is multilevel
superposition coding, but the decoding of the levels is opportunistic,
depending on the channel state. The genie aided outer bound is motivated by the
typical error events of the achievable scheme.",0801.3112v3
2008-01-30,"Concerning Olga, the Beautiful Little Street Dancer (Adjectives as Higher-Order Polymorphic Functions)","In this paper we suggest a typed compositional seman-tics for nominal
compounds of the form [Adj Noun] that models adjectives as higher-order
polymorphic functions, and where types are assumed to represent concepts in an
ontology that reflects our commonsense view of the world and the way we talk
about it in or-dinary language. In addition to [Adj Noun] compounds our
proposal seems also to suggest a plausible explana-tion for well known
adjective ordering restrictions.",0801.4746v5
2008-02-10,Asymptotic efficiency of simple decisions for the compound decision problem,"We consider the compound decision problem of estimating a vector of $n$
parameters, known up to a permutation, corresponding to $n$ independent
observations, and discuss the difference between two symmetric classes of
estimators. The first and larger class is restricted to the set of all
permutation invariant estimators. The second class is restricted further to
simple symmetric procedures. That is, estimators such that each parameter is
estimated by a function of the corresponding observation alone. We show that
under mild conditions, the minimal total squared error risks over these two
classes are asymptotically equivalent up to essentially O(1) difference.",0802.1319v1
2008-03-05,Superconductivity in the Mo_2Re_3B compound,"We report on the synthesis and on basic superconducting properties of a
completely new Mo_2Re_3B ternary boride. The crystal structure of the Mo_2Re_3B
compound is characterised by Pmmm space group and the cell parameters: a=11.626
A, b=8.465 A and c=8.026 A. The critical temperature is Tc=8.5 K, whereas the
lower and the upper-critical fields at zero temperature are equal to
Hc1(0)=19.2 mT and to Hc2(0)=3.7 T, respectively. The corresponding
Ginzburg-Landau parameter is equal to k=16.5 and the superconducting gap is
estimated to be 2delta/kTc=3.2.",0803.0644v1
2008-03-09,Correlated electronic structure of LaOFeAs,"We compute the electronic structure, momentum resolved spectral function and
optical conductivity of the new superconductor LaO$_{1-x}$F$_x$FeAs within the
combination of the Density functional theory and the Dynamical Mean Field
Theory. We find that the compound in the normal state is a strongly correlated
metal and the parent compound is a bad metal at the verge of the metal
insulator transition. We argue that the superconductivity is not phonon
mediated.",0803.1279v1
2008-03-11,Substantial magneto-electric coupling near room temperature in Bi2Fe4O9,"We report remarkable multiferroic effects in polycrystalline Bi2Fe4O9.
High-resolution X-ray diffraction shows that this compound has orthorhombic
structure. Magnetic measurements confirm an antiferromagnetic transition around
260 K. A pronounced inverse S-shape anomaly in the loss tangent of dielectric
measurement is observed near the Neel temperature. This feature shifts with the
application of magnetic field. These anomalies are indicative of substantial
coupling between the electric and magnetic orders in this compound.",0803.1539v1
2008-03-19,Unconventional sign-reversing superconductivity in LaFeAsO_(1-x)F_x,"We argue that the newly discovered superconductivity in a nearly magnetic,
Fe-based layered compound is unconventional and mediated by antiferromagnetic
spin fluctuations, though different from the usual superexchange and specific
to this compound. This resulting state is an example of extended s-wave pairing
with a sign reversal of the order parameter between different Fermi surface
sheets. The main role of doping in this scenario is to lower the density of
states and suppress the pair-breaking ferromagnetic fluctuations.",0803.2740v4
2008-03-31,Hole superconductivity in Arsenic-Iron compounds,"Superconductivity above 25K, and possibly above 40K, has recently been
discovered in $LaO_{1-x}F_xFeAs$ and related compounds. We propose that this is
another example of the mechanism of hole superconductivity at play. This
requires the existence of hole carriers at the Fermi energy, which appears to
contradict current observations. We propose that two-band conduction is taking
place in these materials, that the negative ion $As^{-3}$ plays a key role, and
that superconductivity is non-phononic and driven by pairing and undressing of
heavily dressed hole carriers to lower their kinetic energy. We make several
predictions of future observations based on our theory.",0804.0002v1
2008-04-29,Muon spin relaxation study of LaTiO3 and YTiO3,"We report muon spin relaxation measurements on two Ti3+ containing
perovskites, LaTiO3 and YTiO3, which display long range magnetic order at low
temperature. For both materials, oscillations in the time-dependence of the
muon polarization are observed which are consistent with three-dimensional
magnetic order. From our data we identify two magnetically inequivalent muon
stopping sites. The muon spin relaxation results are compared with the magnetic
structures of these compounds previously derived from neutron diffraction and
muon spin relaxation studies on structurally similar compounds.",0804.4591v1
2008-05-02,"Magnetic properties of the charge density wave compounds RTe3, R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er & Tm","The antiferromagnetic transition is investigated in the rare-earth (R)
tritelluride RTe3 family of charge density wave (CDW) compounds via specific
heat, magnetization and resistivity measurements. Observation of the opening of
a superzone gap in the resistivity of DyTe3 indicates that additional nesting
of the reconstructed Fermi surface in the CDW state plays an important role in
determining the magnetic structure.",0805.0175v1
2008-06-19,Possible unconventional superconductivity in iron-based layered compound LaFePO: Study of heat capacity,"Heat capacity measurements were performed on recently discovered iron based
layered superconductors, non doped LaFePO and fluorine doped LaFePO. A
relatively large electronic heat capacity coefficient and a small normalized
heat capacity jump at Tc = 3.3 K were observed in LaFePO. LaFePO0.94F0.06 had a
smaller electronic heat capacity coefficient and a larger normalized heat
capacity jump at Tc = 5.8 K. These values indicate that these compounds have
strong electron electron correlation and magnetic spin fluctuation, which are
the signatures of unconventional superconductivity mediated by spin
fluctuation.",0806.3139v1
2008-07-04,Lattice dynamical calculations of infinite layer iron oxides SrFeO2 and CaFeO2,"We report extensive lattice dynamical calculations of the newly discovered
infinite-layer iron oxides SrFeO2 and CaFeO2. For SrFeO2, the parameters of the
interatomic potential have been determined to reproduce the zone-centre phonon
frequencies reported using ab-initio calculations. Further we have extended the
potential model for calculations of CaFeO2. The potential parameters are found
to be transferable between the two compounds, and are used to calculate the
phonon spectra in the whole Brillouin zone and several thermodynamic properties
for these compounds. The calculations show fair agreement with the available
experimental data of structure, thermal expansion, and mean-squared amplitudes
of the atoms.",0807.0716v1
2008-07-14,Structure and superconductivity of LiFeAs,"The lithium ions in Lithium iron arsenide phases with compositions close to
LiFeAs have been located using powder neutron diffraction. These phases exhibit
superconductivity at temperatures at least as high as 16 K demonstrating that
superconductivity in compounds with [FeAs]- anti-PbO-type anionic layers occurs
in compounds with at least three different structure types and occurs for a
wide range of As-Fe-As bond angles.",0807.2228v2
2008-08-07,Incommensurate spin density modulation in a copper-oxide chain compound with commensurate charge order,"Neutron diffraction has been used to determine the magnetic structure of
Na$_8$Cu$_5$O$_{10}$, a stoichiometric compound containing chains based on
edge-sharing CuO$_4$ plaquettes. The chains are doped with 2/5 hole per Cu site
and exhibit long-range commensurate charge order with an onset well above room
temperature. Below $T_N = 23$ K, the neutron data indicate long-range collinear
magnetic order with a spin density modulation whose propagation vector is
commensurate along and incommensurate perpendicular to the chains. Competing
interchain exchange interactions are discussed as a possible origin of the
incommensurate magnetic order.",0808.1009v1
2008-08-07,Tetragonal to orthorhombic phase transition in SmFeAsO: a synchrotron powder diffraction investigation,"The crystal structure of SmFeAsO has been investigated by means of Rietveld
refinement of high resolution synchrotron powder diffraction data collected at
300 K and 100 K. The compound crystallizes in the tetragonal P4/nmm space group
at 300 K and in the orthorhombic Cmma space group at 100 K; attempts to refine
the low temperature data in the monoclinic P112/n space group diverged. On the
basis of both resistive and magnetic analyses the tetragonal to orthorhombic
phase transition can be located at T about 140 K.",0808.1024v1
2008-08-30,A new family of iron pnictides: BaFeAs2 and BaFeSb2,"We investigate the structural, electronic, and magnetic properties of the
hypothetical compound BaFePn2 (Pn = As and Sb), which is isostructural to the
parent compound of the high temperature superconductor LaFeAsO1-xFx. Using
density functional theory, we show that the Fermi surface, electronic structure
and the spin density wave instability of BaFePn2 are very similar to the Fe
based superconductors. Additionally, there are very dispersive metallic bands
of a spacer Pn layer, which are almost decoupled from FePn layer. Our results
show that experimental study of BaFePn2 can test the role of charge and
polarization fluctuation, importance of two dimensionality in mechanism of
superconductivity.",0809.0041v2
2008-09-05,Interacting Dipoles in Type-I Clathrates: Why Glass-like though Crystal?,"Almost identical thermal properties of type-I clathrate compounds to those of
glasses follow naturally from the consideration that off-centered guest ions
possess electric dipole moments. Local fields from neighbor dipoles create many
potential minima in the configuration space. A theoretical analysis based on
two-level tunneling states demonstrates that interacting dipoles are a key to
quantitatively explain the glass-like behaviors of low-temperature thermal
properties of type-I clathrate compounds with off-centered guest ions.From this
analysis, we predict the existence of a glass transition.",0809.1070v2
2008-09-09,"Doping and Temperature Dependence of Raman Scattering of NdFeAsO1-xFx (x=0.0, 0.1, 0.2) Superconductor","Raman spectra of polycrystalline NdFeAsO1-xFx (x=0.0, 0.1, 0.2) compound have
been systematically investigated as functions of temperature and fluorine
concentration. Scanning electron microscopic and Raman microscopic
characterization demonstrates that the polycrystalline samples mainly contain
two phases, i.e. superconductor NdFeAsO1-xFx compound and a MnP-type FeAs
phase, with dissimilar characteristic Raman bands. It was found that fluorine
doping leads to structure disorder in the insulator Nd-O layers and high
temperature coefficient of Fe-As vibrational mode.",0809.1474v1
2008-10-23,Spin-1/2 kagome compounds: volborthite vs herbertsmithite,"Two kagome compounds, volborthite Cu3V2O7(OH)2-2H2O and herbertsmithite
ZnCu3(OH)6Cl2, are compared in order to derive information about the intrinsic
properties of the spin-1/2 kagome antiferromagnet. Volborthite shows a broad
maximum at T ~ J / 4 and the approach at T = 0 to a large finite value of the
bulk magnetic susceptibility chi_bulk as well as the local susceptibility
chi_local from NMR measurements. These must be intrinsic properties for the
spin-1/2 kagome antiferromagnet, as similar behavior has also been reported in
chi_local for herbertsmithite [Olariu A et al. 2008 Phys. Rev. Lett., 100
087202]. Impurity effects that may significantly influence the bulk properties
are discussed.",0810.4202v1
2008-12-11,Undulation textures at the phase transitions of some alkyloxybenzoic acids,"We observed undulated smectic textures for some compounds of the
4,n-alkyloxybenzoic (nOBAC) acid series, at transitions between the smectic and
the isotropic phase and between the smectic and nematic phase. Studied
compounds were 12OBAC, 16OBAC and a binary mixture of 12- and 16OBAC. The
undulations are dressing a usual Schlieren texture. In the case of the binary
mixture, an interesting fingerprint pattern is observed too.",0812.2178v2
2009-01-12,Correlated electrons in Fe-As compounds: a quantum chemical perspective,"State-of-the-art quantum chemical methods are applied to the study of the
multiorbital correlated electronic structure of a Fe-As compound, the recently
discovered LiFeAs. Our calculations predict a high-spin, S=2, ground-state
configuration for the Fe ions, which shows that the on-site Coulomb
interactions are substantial. Also, orbital degeneracy in the (xz,yz) sector
and a three-quarter filling of these levels suggest the presence of strong
fluctuations and are compatible with a low metallic conductivity in the normal
state. The lowest electron-removal states have As 4p character, in analogy to
the ligand hole states in p-type cuprate superconductors.",0901.1594v1
2009-01-19,Possible Kondo effect in the iron arsenides,"The normal state of the iron arsenides shows the poor metallic behavior mixed
with strong magnetic fluctuations. In particular, some FeAs-1111 and FeAs-122
compounds show the linear-T dependence of susceptibility above the spin-density
wave (SDW) transition and the logarithmic upturn of resistivity at low
temperatures. We suggest that this is due to the spin-flip scattering between
the charge carriers and the local moments in the undoped FeAs layer where Kondo
effect coexists with the SDW. This scenario is also accounted for the change of
the magnetoresistance from positive to negative in the Sr3Sc2O5Fe2As2 compound.",0901.2787v2
2009-02-03,Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne,"In the catalytic addition of water to propyne the Au(III) catalyst is not
stable under non-relativistic conditions and dissociates into a Au(I) compound
and Cl2. This implies that one link in the chain of events in the catalytic
cycle is broken and relativity may well be seen as the reason why Au(III)
compounds are effective catalysts.",0902.0426v2
2009-03-07,Impurity effects in multiferroic compounds,"We investigate the effect of impurities in multiferroic materials using an
equation of motion approach for the spin dynamics of the host multiferroic
compound. We model the impurities as a two-level system and focus on the regime
where the impurity spins relax slowly. When the impurity strength is weak the
host spins oscillate with no decay and the electric polarization is not
affected. However as the impurity strength is increased the host spin
components get damped and the electrion polarization is suppressed. Since
polarization in multiferroic materials is driven by magnetic ordering we
conclude that the presence of impurities is detrimental to multiferroicity.",0903.1319v1
2009-03-26,Nonparametric estimation of the heterogeneity of a random medium using Compound Poisson Process modeling of wave multiple scattering,"In this paper, we present a nonparametric method to estimate the
heterogeneity of a random medium from the angular distribution of intensity
transmitted through a slab of random material. Our approach is based on the
modeling of forward multiple scattering using Compound Poisson Processes on
compact Lie groups. The estimation technique is validated through numerical
simulations based on radiative transfer theory.",0903.4502v1
2009-04-01,Inverse magnetocaloric effect in polycrystalline La$_{0.125}$Ca$_{0.875}$MnO$_{3}$,"Recently the inverse magnetocaloric effect is observed for different
compounds. However there is very rare for any manifestation of the effect to be
seen in manganites. We have found inverse magnetocaloric effect in the case of
polycrystalline La$_{0.125}$Ca$_{0.875}$MnO$_{3}$. Such phenomenon is
attributed to the stabilization of antiferromagnetic state associated with
inherent magnetic inhomogeneous phases for this compound.",0904.0074v2
2009-04-06,Dynamic Disorder in Negative Thermal Expansion Compound Zn(CN)2,"Dynamical disorder in negative thermal expansion compound Zn(CN)2 is
investigated by quasielastic neutron scattering technique in the temperature
range 170-320 K. Significant quasielastic broadening is observed above the
phase transition temperature of about 250 K, however no broadening is observed
at 220 K and below. Data at high temperatures are analyzed assuming the CN
reorientation. Characteristic time associated with the CN orientation is
estimated as 16 ps and 11 ps at 270 and 320 K respectively.",0904.0963v2
2009-04-20,Successive phase transitions under high pressure in FeTe0.92,"We performed magnetization and electrical resistivity measurements under high
pressures of up to 19 GPa for FeTe0.92. The compound shows an anomaly in
magnetization and resistivity at atmospheric pressure due to a structural
distortion accompanied by a magnetic transition. We also observed magnetic and
resistive anomalies under high pressure, suggesting that two pressure-induced
phases exist at a low temperature. Unlike in FeAs-based compounds, no
superconductivity was detected under high pressures of up to 19 GPa, although
the anomaly at atmospheric pressure was suppressed by applying pressure.",0904.2945v2
2009-06-02,dHvA Oscillations in High-Tc Compounds,"Recent de Haas-van Alphen (dHvA) experiments on high-Tc compounds have been
interpreted using Lifshitz-Kosevich (LK) theory, which ignores many-body
effects. However in quasi-2d systems, interactions plus Landau level
quantization give strong singularities in the self-energy $\Sigma$ and the
thermodynamic potential $\Omega$. These are rapidly suppressed as one increases
the c-axis tunneling amplitude $t_\perp$ and/or impurity scattering. We show
that 2d-3d crossover and interaction effects should show up in these
experiments, and that they can lead to strong deviations from LK behaviour.
Moreover, dHvA experiments in quasi-2d systems should clearly distinguish
between Fermi liquid and non-Fermi liquid states, for sufficiently weak
impurity scattering.",0906.0621v1
2009-06-10,Emergence of a superconducting state from an antiferromagnetic phase in single crystals of the heavy fermion compound Ce2PdIn8,"Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility,
electrical resistivity and specific heat measurements. The compound was found
to be a heavy fermion clean-limit superconductor with Tc = 0.68 K. Most
remarkably, the superconductivity in this system emerges out of the
antiferromagnetic state that sets in at TN = 10 K, and both cooperative
phenomena coexist in a bulk at ambient pressure conditions.",0906.1881v2
2009-08-27,A new 111 type iron pnictide superconductor LiFeP,"A new iron pnictide LiFeP superconductor was found. The compound crystallizes
into a Cu2Sb structure containing an FeP layer showing superconductivity with
maximum Tc of 6K. This is the first 111 type iron pnictide superconductor
containing no arsenic. The new superconductor is featured with itinerant
behavior at normal state that could helpful to understand the novel
superconducting mechanism of iron pnictide compounds.",0908.4043v1
2009-08-27,Annealing effects on superconductivity in SrFe2-xNixAs2,"Superconductivity has been explored in single crystals of the Ni-doped
FeAs-compound SrFe2-xNixAs2 grown by self-flux solution method. The
antiferromagnetic order associated with the magnetostructural transition of the
parent compound SrFe2As2 is gradually suppressed with increasing Ni
concentration x and bulk-phase superconductivity with full diamagnetic
screening is induced near the optimal doping of x = 0.15 with a maximum
transition temperature Tc ~9.8 K. An investigation of high-temperature
annealing on as-grown samples indicate that the heat treatment can enhance Tc
as much as ~50 %.",0908.4095v2
2009-09-18,Microscopic Calculation of Pre-Compound Excitation Energies for Heavy-Ion Collisions,"We introduce a microscopic approach for calculating the excitation energies
of systems formed during heavy-ion collisions. The method is based on
time-dependent Hartree-Fock (TDHF) theory and allows the study of the
excitation energy as a function of time or ion-ion separation distance. We
discuss how this excitation energy is related to the estimate of the excitation
energy using the reaction $Q$-value, as well as its implications for dinuclear
pre-compound systems formed during heavy-ion collisions.",0909.3469v1
2009-11-18,Evidence of Kinetic Energy Driven Antiferromagnetism in Double Perovskites : A First-principles Study,"Using first principles density functional calculations, together with exact
diagonalization of Fe-Mo Hamiltonian constructed in a first principles Wannier
function basis, we studied the electronic structure of La doped double
perovskite compound Sr$_2$FeMoO$_6$. Our calculation show stabilization of
kinetic energy driven antiferromagnetic phase for La rich compounds, in
agreement with the results obtained on the basis of previous model
calculations.",0911.3525v1
2009-12-04,On the mechanism of negative compressibility in layered compounds,"A mechanism of negative compressibility occurring in compressed layered
compounds in the presence of a pressure transmitting fluid medium is discussed
within a simple model. It takes into account the excluded volume effects and
soft fluid-matrix repulsion. It is demonstrated that a non-monotonic behavior
of the interlayer spacing with the applied pressure results from a competition
between the applied pressure and the internal one induced by the adsorbed
fluid. Recent experimental data on the graphite oxide ""structure breathing""
under compression in the presence of water are analyzed in the light of these
theoretical results.",0912.0892v1
2010-02-13,Spectral properties of one class of sign-symmertic matrices,"A $n\times n$ matrix $A$, which has a certain sign-symmetric structure
($J$--sign-symmetric), is studied in this paper. It is shown that such a matrix
is similar to a nonnegative matrix. The existence of the second in modulus
positive eigenvalue $\lambda_2$ of a $J$--sign-symmetric matrix $A$, or an odd
number $k$ of simple eigenvalues, which coincide with the $k$-th roots of
$\rho(A)^k$, is proved under the additional condition that its second compound
matrix is also $J$--sign-symmetric. The conditions when a $J$--sign-symmetric
matrix with a $J$--sign-symmetric second compound matrix has complex
eigenvalues, which are equal in modulus to $\rho(A)$, are given.",1002.2696v1
2010-03-25,Magnetic phase diagram of the S=1/2 triangular layered compound NaNiO2: a single crystal study,"Using magnetic torque measurement on a NaNiO2 single crystal, we have
established the magnetic phase diagram of this triangular compound. It presents
5 different phases depending on the temperature (4 K - 300 K) and magnetic
field (0 - 22 T) revealing several spin reorientations coupled to different
magnetic anisotropies.",1003.4848v1
2010-03-31,Half-metallic ferromagnetism in transition-metal doped germanium nitride: A first-principles study,"The electronic and magnetic properties of transition-metal doped
$\beta$-Ge3N4 have been studied using first-principles calculations. The
results show that the substitutional transition-metal impurities tend to
cluster. The V and Cr doped Ge3N4 compounds are ferromagnetic semiconductors,
while the compounds with Mn and Fe doping show a half-metallic ferromagnetic
character.",1003.5982v2
2010-04-20,An Achievability Scheme for the Compound Channel with State Noncausally Available at the Encoder,"A new achievability scheme for the compound channel with discrete memoryless
(DM) state noncausally available at the encoder is established. Achievability
is proved using superposition coding, Marton coding, joint typicality encoding,
and indirect decoding. The scheme is shown to achieve strictly higher rate than
the straightforward extension of the Gelfand-Pinsker coding scheme for a single
DMC with DM state, and is optimal for some classes of channels.",1004.3427v2
2010-04-28,On limiting cluster size distributions for processes of exceedances for stationary sequences,"It is well known that, under broad assumptions, the time-scaled point process
of exceedances of a high level by a stationary sequence converges to a compound
Poisson process as the level grows. The purpose of this note is to demonstrate
that, for any given distribution G on the natural numbers, there exists a
stationary sequence for which the compounding law of this limiting process of
exceedances will coincide with G.",1004.4955v1
2010-05-07,"Convergence of the enhancement of the effective mass under pressure and magnetic field in heavy-fermion compounds: CeRu2Si2, CeRh2Si2, and CeIn3","Emphasis is given on the observation of a convergence to a critical value of
the effective mass of a heavy fermion compound by tuning it through a quantum
instability either by applying pressure or magnetic field from an
antiferromagnetic (AF) to a paramagnetic (PM) ground state. Macroscopic and
microscopic results are discussed and the main message is to rush to the
discovery of an ideal material whose Fermi surface could be fully observed on
both sides of each quantum phase transition.",1005.1202v1
2010-07-09,Galaxy Modeling with Compound Elliptical Shapelets,"Gauss-Hermite and Gauss-Laguerre (""shapelet"") decompositions of images have
become important tools in galaxy modeling, particularly for the purpose of
extracting ellipticity and morphological information from astronomical data.
However, the standard shapelet basis functions cannot compactly represent
galaxies with high ellipticity or large Sersic index, and the resulting
underfitting bias has been shown to present a serious challenge for
weak-lensing methods based on shapelets. We present here a new convolution
relation and a compound ""multi-scale"" shapelet basis to address these problems,
and provide a proof-of-concept demonstration using a small sample of nearby
galaxies.",1007.1681v2
2010-08-16,Quasiparticle interference of C2-symmetric surface states in LaOFeAs parent compound,"We present scanning tunneling microscopy studies of the LaOFeAs parent
compound of iron pnictide superconductors. Topographic imaging reveals two
types of atomically flat surfaces, corresponding to the exposed LaO layer and
FeAs layer respectively. On one type of surface, we observe strong standing
wave patterns induced by quasiparticle interference of two-dimensional surface
states. The distribution of scattering wavevectors exhibits pronounced two-fold
symmetry, consistent with the nematic electronic structure found in the
Ca(Fe1-xCox)2As2 parent state.",1008.2642v1
2010-09-15,Phonons and superconductivity in YbC$_6$ and related compounds,"The out-of-plane intercalate phonons of superconducting YbC6 have been
measured with inelastic x-ray scattering. Model fits to this data, and
previously measured out-of-plane intercalate phonons in graphite intercalation
compounds (GICs), reveal surprising trends with the superconducting transition
temperature. These trends suggest that superconducting GICs should be viewed as
electron-doped graphite.",1009.3056v1
2010-09-16,Exchange bias-like magnetic properties in Sr2LuRuO6,"Exchange bias properties are observed in a double perovskite compound,
Sr2LuRuO6. The observed exchange bias properties have been analyzed on the
basis of some of the available theoretical models. Detailed magnetization
measurements show that the exchange bias properties are associated with the
Dzyaloshinsky-Moria (D-M) interaction among the antiferromagnetically ordered
Ru moments (TN~32K). In addition to the usual canting of the antiferromagnetic
moments, D-M interaction in this compound also causes a magnetization reversal
at T~26K, which seems to trigger the exchange bias properties. Heat capacity
measurements confirm the two magnetic anomalies.",1009.3162v1
2010-12-07,Compound decision in the presence of proxies with an application to spatio-temporal data,"We study the problem of incorporating covariates in a compound decision
setup. It is desired to estimate the means of $n$ response variables, which are
independent and normally distributed, and each is accompanied by a vector of
covariates. We suggest a method that involves non-parametric empirical Bayes
techniques and may be viewed as a generalization of the celebrated Fay-Herriot
(1979) method.
  Some optimality properties of our method are proved. We also compare it
numerically with Fay-Herriot and other methods, using a `semi-real' data set
that involves spatio-temporal covariates, where the goal is to estimate certain
proportions in many small areas (Statistical-Areas)",1012.1563v1
2011-01-25,Ferron Type of Coductivity in Metal CuFeSe2,"It is pointed out, that the charge transfer in the compound in paramagnetic
region has a ferron type of transport with ferrons of a small radius, predicted
by N. Mott. For some another specimen the charge transfer may be carried out by
ferrons of a large radius at very low temperatures. The results are well
confirmed by the temperature dependence of resistivity and by metal type of the
compound.",1101.4904v2
2011-01-28,Spin glass behavior of insulating K0.8Fe2-xS2,"We report the discovery of KxFe2-yS2 single crystals, isostructural to
KxFe2-ySe2 superconductors. The sulfide compound is a small gap semiconductor
and shows spin-glass behavior below 32 K. Our results indicate that
stoichiometry, defects, and the local environment of FeCh (Ch = S,Se)
tetrahedra have important effects on the physical properties of isostructural
and isoelectronic KxFe2-yCh2 compounds.",1101.5616v2
2011-03-23,Computational Design of Axion Insulators Based on 5d Spinels Compounds,"Based on density functional calculation with LDA+U method, we propose that
hypothetical Osmium compounds such as CaOs2O4 and SrOs2O4 can be stabilized in
the geometrically frustrated spinel crystal structure. They also show some
exotic electronic and magnetic properties in a reasonable range of on-site
Coulomb correlation U such as ferromagnetism and orbital magnetoelectric effect
characteristic to Axion electrodynamics. Other electronic phases including 3D
Dirac metal and Mott insulator exist and would make perspective 5d spinels
ideal for applications.",1103.4634v1
2011-04-20,High-Field de Haas-van Alphen Effect in non-centrosymmetric CeCoGe3 and LaCoGe3,"We report on de Haas-van Alphen effect measurements in the
non-centrosymmetric systems CeCoGe3 and LaCoGe3 in magnetic field up to 28
Tesla. In both compounds, two new high frequencies were observed in high
fields. The frequencies were not detected in previous lower field measurements.
The frequencies do not originate from magnetic breakdown, and, therefore, are
likely to be intrinsic features of the compounds. In CeCoGe3, the corresponding
effective masses are strongly enhanced, being of the order of 30 bare electron
masses.",1104.3952v1
2011-05-17,Spin-dependent observables in surrogate reactions,"Observables emitted from various spin states in compound U nuclei are
investigated to validate usefulness of the surrogate reaction method. It was
found that energy spectrum of cascading $\gamma$-rays and their multiplicities,
spectrum of evaporated neutrons, and mass-distribution of fission fragments
show clear dependence on the spin of decaying nuclei. The present results
indicate that they can be used to infer populated spin distributions which
significantly affect the decay branching ratio of the compound system produced
by the surrogate reactions.",1105.3278v1
2011-05-18,Magnetism in doped two-dimensional honeycomb structures of III-V binary compounds,"Using first-principles plane-wave calculations systematic study of magnetic
properties of doped two-dimensional honeycomb structures of III-V binary
compounds have been conducted, either for magnetic or nonmagnetic dopants.
Calculations show, that all cases where magnetic moment is non-zero are
energetically more favorable. For such cases band structure and (partial)
density of states were calculated and analyzed in detail. The possible
applications of these structures were also discussed.",1105.3589v1
2011-05-19,Temperature dependence of low-energy phonons in magnetic nonsuperconducting TbNi2B2C,"We report temperature dependence of low-energy phonons in magnetic
nonsuperconducting TbNi2B2C single crystals measured by inelastic neutron
scattering. We observed a low-temperature softening and broadening of two
phonon branches, qualitatively similar to that previously reported for
superconducting RNi2B2C (R= rare earth, Y) compounds. This result suggests that
the superconductivity in TbNi2B2C compounds is absent not because of a weak
electron-phonon coupling but as a result of pairbreaking due to magnetism.",1105.3966v2
2011-06-06,Chiral spin-wave excitations of the spin-5/2 trimers in the langasite compound Ba3NbFe3Si2O14,"The inelastic scattering of neutrons from magnetic excitations in the
antiferromagnetic phase of the langasite compound Ba3NbFe3Si2O14 is analyzed
theoretically. In the calculations presented, the strongly coupled spin-5/2 Fe
triangles are accounted for as trimerized units. The weaker interactions
between the trimers are included within the mean-field/random-phase
approximation. The theory is compared with linear spin-wave theory, and a model
is developed which leads to good agreement with the published results from
unpolarized and polarized neutron-scattering experiments.",1106.1052v1
2011-06-24,Distribution fitting 12. Sampling distribution of compounds abundance from plant species measured by instrumentation. Application to plants metabolism classification,"A series of ten plant species belonging to Magnoliopsida - Dicotyledons class
were analyzed in terms of chemical compounds distribution of abundance,
starting from the assumption that these distributions should give a picture of
similarities and differences between plants metabolism. From a pool of
theoretical distributions, log-normal distribution was selected giving the best
accuracy with the modeled phenomena and agreement with the observed data. From
obtained lognormal distributions statistics a classification were constructed
and were compared with the classification based on phylogeny.",1106.4954v2
2011-08-12,Ferromagnetism in semiconductors and oxides: prospects from a ten years' perspective,"Over the last decade the search for compounds combining the resources of
semiconductors and ferromagnets has evolved into an important field of
materials science. This endeavour has been fuelled by continual demonstrations
of remarkable low-temperature functionalities found for ferromagnetic
structures of (Ga,Mn)As, p-(Cd,Mn)Te, and related compounds as well as by ample
observations of ferromagnetic signatures at high temperatures in a number of
non-metallic systems. In this paper, recent experimental and theoretical
developments are reviewed emphasising that, from the one hand, they disentangle
many controversies and puzzles accumulated over the last decade and, on the
other, offer new research prospects.",1108.2582v1
2011-09-13,Large Magnetoresistance Effects in $Ln$CoAsO with a Ferromagnetic-Antiferromagnetic Transition,"A large magnetoresistance (MR) effect was observed in the layered compounds
NdCoAsO and SmCoAsO, in which ferromagnetically ordered itinerant-electrons of
Co are sandwiched by localized 4$f$-electrons of $Ln^{3+}$, below
ferromagnetic-antiferromagnetic transition (FAFT) temperature $T_\mathrm{N}$ as
observed in other FAFT compounds. In SmCoAsO, the large MR effect is also
observed up to the Curie temperature $T_\mathrm{C}$, and it is found to be
originating in the presence of another antiferromagnetic phase in the
low-magnetic field region of the ferromagnetic phase.",1109.2730v2
2011-10-09,Channel Coding in Random Access Communication over Compound Channels,"Due to the short and bursty incoming messages, channel access activities in a
wireless random access system are often fractional. The lack of frequent data
support consequently makes it difficult for the receiver to estimate and track
the time varying channel states with high precision. This paper investigates
random multiple access communication over a compound wireless channel where
channel realization is known neither at the transmitters nor at the receiver.
An achievable rate and error probability tradeoff bound is derived under the
non-asymptotic assumption of a finite codeword length. The results are then
extended to the random multiple access system where the receiver is only
interested in decoding messages from a user subset.",1110.1891v1
2011-11-09,Tuning the spin dynamics of kagome systems,"Despite the conceptional importance of realizing spin liquids in solid states
only few compounds are known. On the other side the effect of lattice
distortions and anisotropies on the magnetic exchange topology and the
fluctuation spectrum are an interesting problem. We compare the excitation
spectra of the two s=1/2 kagome lattice compounds volborthite and vesignieite
using Raman scattering. We demonstrate that even small modifications of the
crystal structure may have a huge effect on the phonon spectrum and low
temperature properties.",1111.2167v1
2011-11-18,Stripes and Superconductivity in Cuprates,"Holes doped into the CuO2 planes of cuprate parent compounds frustrate the
antiferromagnetic order. The development of spin and charge stripes provides a
compromise between the competing magnetic and kinetic energies. Static stripe
order has been observed only in certain particular compounds, but there are
signatures which suggest that dynamic stripe correlations are common in the
cuprates. Though stripe order is bad for superconducting phase coherence,
stripes are compatible with strong pairing. Ironically, magnetic-field-induced
stripe order appears to enhance the stability of superconducting order within
the planes.",1111.4268v1
2011-11-24,Effect of neutron irradiation on the properties of FeSe compound in superconducting and normal states,"Effect of atomic disordering induced by irradiation with fast neutrons on the
properties of the normal and superconducting states of polycrystalline samples
FeSe has been studied. The irradiation with fast neutrons of fluencies up to
1.25\cdot10^20 cm^-2 at the irradiation temperature Tirr ~ 50 \degree C results
in relatively small changes in the temperature of the superconducting
transition T_c and electrical resistivity Rho_25. Such a behavior is considered
to be traceable to rather low, with respect to that possible at a given
irradiation temperature, concentration of radiation defects, which is caused by
a simpler crystal structure, considered to other layered compounds.",1111.5677v1
2012-02-18,"Superconductivity in Ce- and U-based ""122"" heavy-fermion compounds","This review discusses the heavy-fermion superconductivity in Ce- and U-based
compounds crystallizing in the body-centered tetragonal ThCr2Si2 structure.
Special attention will be paid to the theoretical background of these systems
which are located close to a magnetic instability.",1202.4114v2
2012-03-02,"From first-order magneto-elastic to magneto-structural transition in (Mn,Fe)1.95P0.50Si0.50 compounds","We report on structural, magnetic and magnetocaloric properties of
MnxFe1.95-xP0.50Si0.50 (x > 1.10) compounds. With increasing the Mn:Fe ratio, a
first-order magneto-elastic transition gradually changes into a first-order
magneto-structural transition via a second-order magnetic transition. The study
also shows that thermal hysteresis can be tuned by varying the Mn:Fe ratio.
Small thermal hysteresis (less than 1 K) can be obtained while maintaining a
giant magnetocaloric effect. This achievement paves the way for real
refrigeration applications using magnetic refrigerants.",1203.0555v2
2012-04-09,"Reply to Comment by Calandra et al on ""Electronic Structure of Superconducting KC$_8$ and Nonsuperconducting LiC$_6$ Graphite Intercalation Compounds: Evidence for a Graphene-Sheet-Driven Superconducting State""","In their comment Calandra \textit{et al} \cite{Calandra}, assert two points:
(1) the estimate of charge transfer from Li to graphene layers in LiC$_6$ in
our letter \cite{Pan2011c} is incorrect because of the three dimensional (3D)
character of the electronic structure in bulk LiC$_6$; (2) our main claim that
the superconductivity in graphite intercalation compounds (GICs) is
graphene-sheet-driven is therefore invalid.",1204.1898v1
2012-04-19,"Electronic structure and magnetism in M(=IA, IIA)C compounds with the rocksalt structure","Electronic structures of MC where M is the alkali and alkaline earth metals
with the rocksalt structure are calculated by full potential density functional
codes. We find that the spin magnetic moment in the compounds is mainly
contributed by the spin polarized p-orbitals of carbon. The large distance
between the carbon makes the p-orbitals localized, which induces magnetic
instability according to the Stoner criterion. The electronic structure can be
mapped to the rigid band model. SrC, BaC and RaC are half-metals, while KC, RbC
and CsC are magnetic semiconductors",1204.4233v2
2012-05-30,Type-I superconductivity in ScGa3 and LuGa3 single crystals,"We present evidence of type-I superconductivity in single crystals of ScGa3
and LuGa3, from magnetization, specific heat, and resistivity measurements: low
critical temperatures Tc = 2.1-2.2 K; field-induced secondto first-order phase
transition in the specific heat, critical fields less than 240 Oe; and low
Ginzburg-Landau coefficients {\kappa} approx 0.23 and 0.30 for ScGa3 and LuGa3,
respectively, are all traits of a type-I superconducting ground state. These
observations render ScGa3 and LuGa3 two of only several type-I superconducting
compounds, with most other superconductors being type II (compounds and alloys)
or type I (elemental metals and metaloids).",1205.6836v1
2012-05-31,Bose-Einstein Condensation of Magnons in NiCl2-4SC(NH2)2,"A Bose-Einstein condensation (BEC) has been observed in magnetic insulators
in the last decade. The bosons that condensed are magnons, associated with an
ordered magnetic phase induced by a magnetic field. We review the experiments
in the spin-gap compound NiCl2-4SC(NH2)2, in which the formation of BEC occurs
by applying a magnetic field at low temperatures. This is a contribution to the
celebration for the 50th anniversary of the Solid State and Low Temperature
Laboratory of the University of S\~ao Paulo, where this compound was first
magnetically characterized.",1206.0035v1
2012-06-08,"Superconductivity at 5.2 K in ZrTe3 polycrystals and the effect of Cu, Ag intercalation","We report the occurrence of superconductivity in polycrystalline samples of
ZrTe3 at 5.2 K temperature at ambient pressure. The superconducting state
coexists with the charge density wave (CDW) phase, which sets in at 63K. The
intercalation of Cu or Ag, does not have any bearing on the superconducting
transition temperature but suppresses the CDW state. The feature of CDW anomaly
in these compounds is clearly seen in the DC magnetization data. Resistivity
data is analysed to estimate the relative loss of carriers and reduction in the
nested Fermi surface area upon CDW formation in the ZrTe3 and the intercalated
compounds.",1206.1700v1
2012-06-08,"Effect of Ni, Fe Intercalation on the Superconducting Properties of ZrTe3","We report the superconductivity at enhanced temperature of 5.2 K in the
polycrystalline sample of ZrTe3 and Ni intercalated ZrTe3. ZrTe3 is a Charge
Density Wave (T = 63K) compound, which is known to superconduct only below 2K
in single crystalline form. We discuss that the intergrain strains in the
polycrystalline samples induces an intrinsic pressure and thus enhances the
transition temperature. Fe intercalation of ZrTe3 kills both the charge density
wave and superconducting states, gives rise to the magnetic ordering in the
compound.",1206.1716v1
2012-06-26,Multiferroic behavior of Aurivillius Bi4Mn3O12 from first-principles,"The multiferroic behavior of the hypothetical Aurivillius compound Bi4Mn3O12
has been explored on the basis of density functional calculations. We find that
the tetragonal paraelectric phase of this material is ferromagnetic, showing
ferroelectric and antiferrodistortive instabilities similar to the ones
observed in its ferroelectric parent compound Bi4Ti3O12 . Our results indicate,
however, that the presence of Mn+4 ions at the B-sites shrinks the cell volume
and consequently the unstable polar mode, associated with the ferroelectric
polarization, is overcame by an antiferrodistortive distortion. In this way,
Bi4Mn3O12 exhibits incipient ferroelectricity at its equilibrium volume. We
show that the ferroelectric state can be favored by strain or partial
substitution of Mn with Ti.",1206.6090v1
2012-08-05,Image encryption schemes for JPEG and GIF formats based on 3D baker with compound chaotic sequence generator,"This paper proposed several methods to transplant the compound chaotic image
encryption scheme with permutation based on 3D baker into image formats as
Joint Photographic Experts Group (JPEG) and Graphics Interchange Format (GIF).
The new method averts the lossy Discrete Cosine Transform and quantization and
can encrypt and decrypt JPEG images lossless. Our proposed method for GIF keeps
the property of animation successfully. The security test results indicate the
proposed methods have high security. Since JPEG and GIF image formats are
popular contemporarily, this paper shows that the prospect of chaotic image
encryption is promising.",1208.0999v1
2012-08-07,"Density functional theory study of phase stability, vibrational and electronic properties of $Mo_3Al_2C$","Based on density functional theory the noncentrosymmetric superconductor
Mo_3Al_2C in its well established {\beta}-Mn type ($P4_{1}32$) crystal
structure is investigated. In particular, its thermodynamical and dynamical
stabilities are studied by calculating lattice vibrations within the harmonic
approximation. It is found that the fully stoichiometric compound is
dynamically unstable. However, compounds with carbon vacancies, i.e.,
Mo_3Al_2C_{1-x}, can be dynamically stabilized for vacancy concentrations x >
0.09. By means of a simple thermodynamical model we estimate x ~ 0.13-0.14 for
Mo_3Al_2C_{1-x} at the experimental preparation temperatures. The influence of
the carbon vacancy concentration on the electronic structure is investigated.",1208.1391v1
2012-08-20,Strongly correlated electrons: Estimates of model parameters,"The determination of renormalized parameters in model Hamiltonians is
discussed. A simple model of a 3d compound is studied, and it is shown how
higher states can be projected out, resulting in a simpler model with
renormalized parameters. This is applied to the calculation of effective
Coulomb integrals for 3d and 4f compounds. Effects left out in this approach
are discussed. We then focus on fullerides and compare theoretical and
experimental data for the Coulomb interaction and the electron-phonon strength.",1208.4044v1
2012-10-01,Electron-phonon superconductivity and charge density wave instability in the layered titanium-based pnictide BaTi$_2$Sb$_2$O,"I present the results of first principles calculations of the phonon
dispersions and electron-phonon coupling for BaTi$_2$Sb$_2$O. The phonon
dispersions show a weak lattice instability near the zone corners that leads to
a charge-density wave phase. The calculations of the electron-phonon coupling
reveal strong coupling, especially to the in-plane Ti modes. The total coupling
is large enough to readily explain the superconductivity in this compound. As
the Fermi surfaces are disconnected with different orbital character weights,
this compound is likely to host a multiband superconductivity.",1210.0499v2
2012-10-05,Electronic structure and superconductivity of BiS2-based compounds LaO1-xFxBiS2,"Using the density-functional perturbation theory with structural
optimization, we investigate the electronic structure, phonon spectra, and
superconductivity of BiS2-based layered compounds LaO1-xFxBiS2. For
LaO0.5F0.5BiS2, the calculated electron-phonon coupling constant is equal to
lambda = 0.8, and obtained Tc = 9.1 K is very close to its experimental value,
indicating that it is a conventional electron-phonon superconductor.",1210.1743v2
2012-10-15,Temperature dependent tunneling spectroscopy in the heavy fermion CeRu2Si2 and in the antiferromagnet CeRh2Si2,"CeRu2Si2 and CeRh2Si2 are two similar heavy fermion stoichiometric compounds
located on the two sides of the magnetic quantum critical phase transition.
CeRh2Si2 is an antiferromagnet below T_N=36 K with moderate electronic masses
whereas CeRu2Si2 is a paramagnetic metal with particularly heavy electrons.
Here we present tunneling spectroscopy measurements as a function of
temperature (from 0.15 K to 45 K). The tunneling conductance at 0.15 K reveals
V-shaped dips around the Fermi level in both compounds, which disappear in
CeRu2Si2 above the coherence temperature, and above the N\'eel temperature in
CeRh2Si2. In the latter case, two different kinds of V-shaped tunneling
conductance dips are found.",1210.4085v1
2012-11-02,Perovskite BaCrO_{3}: completing a materials system with an anomalous Mott transition,"We have synthesized and characterized laser-deposited film samples of
perovskite BaCrO_{3}, a missing member of the perovskite-chromate family. The
BaCrO_{3} films have a substantially larger lattice constant than other
chromates, are insulating, and exhibit weak ferromagnetism likely associated
with canted antiferromagnetism. Comparison with the other sister compounds
CaCrO_{3} and SrCrO_{3} suggest an anomalous Mott transition where magnetism is
independent of whether the compound is metallic or insulating",1211.0534v2
2012-11-20,"Stoichiometry, structure, and transport in the quasi-one-dimensional metal, Li(0.9)Mo(6)O(17)","A correlation between lattice parameters, oxygen composition, and the
thermoelectric and Hall coefficients is presented for single-crystal
Li(0.9)Mo(6)O(17), a quasi-one-dimensional (Q1D) metallic compound. The
possibility that this compound is a compensated metal is discussed in light of
a substantial variability observed in the literature for these transport
coefficients.",1211.4822v1
2012-12-01,Parameter estimation of a Levy copula of a discretely observed bivariate compound Poisson process with an application to operational risk modelling,"A method is developed to estimate the parameters of a Levy copula of a
discretely observed bivariate compound Poisson process without knowledge of
common shocks. The method is tested in a small sample simulation study. Also,
the method is applied to a real data set and a goodness of fit test is
developed. With the methodology of this work, the Levy copula becomes a
realistic tool of the advanced measurement approach of operational risk.",1212.0092v1
2012-12-20,Thermoelectricity in ternary rare-earth systems,"Crystallographic data, Seebeck coefficient, electrical resistance and thermal
conductivity are reported for a large number of rare-earth compounds,
manifestations of the Kondo effect being discussed. In more detail,
thermoelectric properties of Yb3Co4Ge13 and Yb3Co4Sn13 compounds and
Yb2CeCo4Ge13 and Yb2.3La0.7Co4Ge13 solid solutions are presented.",1212.4995v1
2013-01-30,Discrete approximations for sums of m-dependent random variables,"Sums of of 1-dependent integer-valued random variables are approximated by
compound Poisson, negative binomial and Binomial distributions and signed
compound Poisson measures. Estimates are obtained for total variation and local
metrics. The results are then applied to statistics of $m$-dependent
$(k_1,k_2)$ events and 2-runs. Heinrich's method and smoothing properties of
convolutions are used for the proofs.",1301.7196v3
2013-02-20,Non-magnetic doping induced magnetism in Li doped SnO2 nanoparticles,"We address the possibility of non-magnetic doping induced magnetism, in Li
doped SnO2 nano-particles. The compounds have been prepared by solid state
route at equilibrium and were found to be crystallized in single rutile phase.
The magnetization measurements have shown that Li-doping induces magnetism in
SnO2 for a particular range of Li concentration. However, for other Li
concentrations, including pure SnO2, the samples exhibit diamagnetism. To
investigate the possible origin of the induced magnetism, we have studied the
variation of the magnetization as a function of the average nano-particle
radius. Possible scenarios for the appearance of magnetism in these compounds
are discussed.",1302.4869v1
2013-04-19,Electron-phonon coupling in 122 Fe pnictides analyzed by femtosecond time-resolved photoemission,"Based on results from femtosecond time-resolved photoemission, we compare
three different methods for determination of the electron-phonon coupling
constant {\lambda} in Eu and Ba-based 122 FeAs compounds. We find good
agreement between all three methods, which reveal a small {\lambda} < 0.2. This
makes simple electron-phonon mediated superconductivity unlikely in these
compounds.",1304.5355v1
2013-05-08,Optimal dividend problem for a generalized compound Poisson risk model,"In this note we study the optimal dividend problem for a company whose
surplus process, in the absence of dividend payments, evolves as a generalized
compound Poisson model in which the counting process is a generalized Poisson
process. This model including the classical risk model and the Polya-Aeppli
risk model as special cases. The objective is to find a dividend policy so as
to maximize the expected discounted value of dividends which are paid to the
shareholders until the company is ruined. We show that under some conditions
the optimal dividend strategy is formed by a barrier strategy.",1305.1747v2
2013-05-16,Comments on the thermoelectric power of the f-electron metallic compounds,"The anomalous temperature variation of the thermoelectric power in the
f-electron metallic compounds, namely the sign reversal or the maxima, is
sometimes interpreted as resulting from the conduction electrons scattering in
Born approximation on the acoustic phonons and on the localized spins in the
s-f exchange interaction. The experimenters rely on the results of some
theoretical works where such thermoelectric power behavior was obtained within
these simple models. In the present paper we prove that neither the
electron-phonon scattering nor the magnetic s-f scattering in the Born
approximation (nor both of them) do lead to the effects mentioned above.",1305.3948v1
2013-05-31,Why MgFeGe is not a superconductor,"The recently synthesized MgFeGe compound is isostructural and isoelectronic
with superconducting LiFeAs. Both materials are paramagnetic metals at room
temperature. Inspection of their electronic structures without spin
polarization reveals hardly any difference between the two. This fact was
interpreted as evidence against popular theories relating superconductivity in
Fe-based materials with spin fluctuations. We show that in the magnetic domain
the two compounds are dramatically different, and the fact that MgFeGe does not
superconduct, is, on the contrary, a strong argument in favor of theories based
on spin fluctuations.",1305.7368v1
2013-06-03,Ab initio GW calculation for organic compounds (TMTSF)2PF6,"We present an ab initio GW calculation to study dynamical effects on an
organic compound (TMTSF)2PF6. Calculated polarized reflectivities reproduce
experimental plasma edges at around 0.2 eV for E||b' and 1.0 eV for E||a. The
low-energy plasmons come out from the low-energy narrow bands energetically
isolated from other higher-energy bands, and affect the low-energy electronic
structure via the GW-type self-energy. Because of the quasi-one-dimensional
band structure, a large plasmon-induced electron scattering is found in the
low-energy occupied states along the X-M line.",1306.0354v1
2013-09-11,Non compound nucleus fission events and standard saddle-point statistical model,"The large body of experimental data on the fission fragments anisotropies are
analyzed in several heavy-ion induced fission reaction systems. The entrance
channel mass asymmetry parameters of these systems put on the both sides of the
Businaro-Gallone mass asymmetry parameters. The role of the mass numbers of the
projectile and the target in the prediction of a normal or an anomalous
behavior in angular anisotropy, as well as the validity of standard
saddle-point statistical model are considered. The average contribution of non
compound nucleus fission for the systems with an anomalous behavior in
anisotropy are also determined. PACS numbers: 25.70.Jj *Corresponding author:
s.soheyli@basu.ac.ir",1309.2738v1
2013-09-15,Crystal fields and Kondo effect: specific heat for Cerium compounds,"The thermodynamic Bethe ansatz equations for the N = 6 Coqblin-Schrieffer
model with crystal fields have been solved numerically. The realistic case of
three Kramers doublets with arbitrary splittings has been studied for the first
time. The specific heat has been calculated for representative combinations of
the ionic energy splittings providing ample material for comparison with
experimental results for Cerium impurities and compounds.",1309.3749v3
2013-09-20,Fluctuation theory for upwards skip-free Lévy chains,"A fluctuation theory and, in particular, a theory of scale functions is
developed for upwards skip-free L\'evy chains, i.e. for right-continuous random
walks embedded into continuous time as compound Poisson processes. This is done
by analogy to the spectrally negative class of L\'evy processes -- several
results, however, can be made more explicit/exhaustive in our compound Poisson
setting. In particular, the scale functions admit a linear recursion, of
constant order when the support of the jump measure is bounded, by means of
which they can be calculated -- some examples are considered.",1309.5328v3
2013-10-19,"First-principles studies of the structural, electronic, and optical properties of a novel thorium compound Rb2Th7Se15","The structural, electronic, and optical properties of a recently synthesized
thorium compound Rb2Th7Se15 have been calculated in the density functional
theory framework for the first time. The calculated direct band gap was 1.471
eV (generalized gradient approximation) and 1.171 eV (local density
approximation), with both results being close to the experimental result of
1.83 eV. High covalency/iconicity of the Th-Se/Rb-Se bonds was demonstrated by
calculating effective Mulliken charges of all ions. The polarized calculations
of the complex dielectric function are presented; dependence of the calculated
index of refraction was fitted to the Sellmeyer equation in the wavelength
range from 500 to 2500 nm.",1310.5210v1
2013-11-05,Hysteresis and Relaxation Effects in the Spin-Ice Compound Dy$_2$Ti$_2$O$_7$ studied by Heat Transport,"The low-temperature thermal conductivity $\kappa$ of the spin-ice compound
Dy$_2$Ti$_2$O$_7$ shows pronounced hysteresis as a function of magnetic field.
Here, we investigate how these hysteresis effects depend on temperature, the
magnetic-field direction, the rate of magnetic-field change, and on the
direction of the heat current. In addition, the time-dependent relaxation of
the heat conductivity is investigated. These measurements yield information
about possible equilibrium states and reveal that in the low-field and
low-temperature region extremely slow relaxation processes occur.",1311.1139v1
2013-12-01,Modeling of aging processes in the insertion compounds,"The aging phenomena occurring in the course of cycling processes in the
insertion host-guest compounds are discussed in the framework of a simple
model. It takes into account two types of effects. One can be attributed to
modifications of the host/guest solution interface in a form of an effective
energetic barrier. The other is associated with the host matrix disordering
that is translated into a change in the distribution of the host site energies
as a function of the applied potential or the concentration of the guest
species. It is found that the aging properties depend on the preparation mode,
the cycling conditions and the insertion induced transformations. The impact of
these transformations on the aging is determined by the matrix sensibility.",1312.0196v1
2013-12-04,Li-containing scintillating bolometers for low background physics,"We present the performances of Li-based compounds used as scintillating
bolometer for rare decay studies such as double-beta decay and direct dark
matter investigations. The compounds are tested in a dilution refrigerator
installed in the underground laboratory of Laboratori Nazionali del Gran Sasso
(Italy). Low temperature scintillating properties are investigated by means of
different radioactive sources, and the radio-purity level for internal
contaminations are estimated for possible employment for next generation
experiments.",1312.1276v1
2014-02-02,A Compound Poisson Convergence Theorem for Sums of $m$-Dependent Variables,"We prove the Simons-Johnson theorem for the sums $S_n$ of $m$-dependent
random variables, with exponential weights and limiting compound Poisson
distribution $\CP(s,\lambda)$. More precisely, we give sufficient conditions
for $\sum_{k=0}^\infty\ee^{hk}\ab{P(S_n=k)-\CP(s,\lambda)\{k\}}\to 0$ and
provide an estimate on the rate of convergence. It is shown that the
Simons-Johnson theorem holds for weighted Wasserstein norm as well. %limiting
sum of two Poisson variables defined on %different lattices. The results are
then illustrated for $N(n;k_1,k_2)$ and $k$-runs statistics.",1402.0183v1
2014-02-09,First passage time law for some Lévy processes with compound Poisson: Existence of a conditional density with incomplete observation,"We study the default risk in incomplete information. That means, we model the
value of a firm by one L\'evy process which is the sum of brownian motion with
drift and compound Poisson process. This L\'evy process can not be observed
completely and we let an other process which representes the available
information on the firm. We obtain an equation safisfied by the conditional
density of the default time given the available information and closed form
expression for the density.",1402.2000v2
2014-02-24,Compound orbits break-up in constituents: an algorithm,"In this paper decomposition of periodic orbits in bifurcation diagrams are
derived in unidimensional dynamics system $x_{n+1}=f(x_{n};r)$, being $f$ an
unimodal function. We proof a theorem which states the necessary and sufficient
conditions for the break-up of compound orbits in their simpler constituents. A
corollary to this theorem provides an algorithm for the computation of those
orbits. This process closes the theoretical framework initiated in (Physica D,
239:1135--1146, 2010).",1402.5893v1
2014-02-26,Deconstruction of compound objects from image sets,"We propose a method to recover the structure of a compound object from
multiple silhouettes. Structure is expressed as a collection of 3D primitives
chosen from a pre-defined library, each with an associated pose. This has
several advantages over a volume or mesh representation both for estimation and
the utility of the recovered model. The main challenge in recovering such a
model is the combinatorial number of possible arrangements of parts. We address
this issue by exploiting the sparse nature of the problem, and show that our
method scales to objects constructed from large libraries of parts.",1402.6416v1
2014-02-25,Magnetic field control of ferroelectric polarization and magnetization of LiCu2O2 compound,"A spin model of LiCu2O2 compound with ground state of ellipsoidal helical
structure has been adopted. Taking into account the interchain coupling and
exchange anisotropy, we focus on the magnetoelectric properties in a rotating
magnetic field and perform the Monte Carlo simulation on a two-dimensional
lattice. A prominent anisotropic response is observed in the magnetization and
polarization curves, qualitatively coinciding with the behaviors that detected
in the experiment. In addition, the influences of the magnetic field with
various magnitudes are also explored and analyzed in detail. As the magnetic
field increases, a much smoother polarization of angle dependence is exhibited,
indicating the strong correlation between the magnetic and ferroelectric
orders.",1402.6648v1
2014-03-01,Anomalies of transport properties in antiferromagnetic YbMn2Sb2 compound,"The low-temperature transport properties (resistivity, thermal conductivity,
thermoelectric power) are experimentally investigated for the compound
YbMn2Sb2. Large Seebeck coefficient and nearly linear temperature dependence of
resistivity are obtained. The thermal conductivity is large and has mainly
phonon origin. Appreciable anomalies of transport characteristics near the
antiferromagnetic transition point are found. Possible influence of
pseudo-Kondo scattering is discussed.",1403.0077v2
2014-03-19,Enthalpy of formation for Cu-Zn-Sn-S (CZTS),"Herein we report an analytical procedure to calculate the enthalpy of
formation for thin film multinary compounds from sputtering rates measured
during ion bombardment. The method is based on Sigmund's sputtering theory and
the Born-Haber cycle. Using this procedure, an enthalpy of formation for a CZTS
film of the composition Cu$_{1.9}$Zn$_{1.5}$Sn$_{0.8}$S$_4$ was measured as
-930$\pm$98 kJ/mol. This value is much more negative than the sum of the
enthalpies of formation for the constituent binary compounds, meaning the
multinary formation reaction is predicted to be exothermic.",1403.4922v1
2014-04-07,A hybrid vanadium fluoride with structurally isolated S = 1 kagome layers,"A new organically-templated vanadium (III) fluoride, (NH4)2(C2H8N)[V3F12],
has been prepared using an ionothermal approach. This compound has a unique
layered structure featuring distorted S = 1 kagome planes separated by the
cationic species. The compound exhibits magnetic frustration, with a canted
antiferromagnetic ground state. On further cooling within the ground state a
pronounced change in magnetisation kinetics is observed.",1404.1755v1
2014-07-25,Hydrostatic Pressure Studies on Parent Phase SrFBiS2 of BiS2-based Superconducting Family,"In the present work, we measure the temperature dependent electrical
resistivity from 300K down to 2K under applied hydrostatic pressure of upto
2.5GPa for SrFBiS2, which is the parent compound for the BiS2 based
superconductors. Though the normal state resistivity of the compound decreases
with pressure, the same is not superconducting down to 2K under applied
pressure of up to 2.5Gpa.",1407.6793v4
2014-11-08,"Correlations among magnetic, magnetocaloric and magneto-transport properties in HoNiSi","Magnetic, magnetocaloric and magneto-transport properties of polycrystalline
HoNiSi have been studied. The compound crystallizes in orthorhombic crystal
structure and orders antiferromagnetically at TN=4.6 K. Magnetization isotherms
show curvature at small fields, revealing a field induced metamagnetic
transition. Magnetocalroic effect (MCE) has been estimated using magnetization
data and is found to be 12.8 J/kg K for a field of 50 kOe. Application of field
reduces the resistivity near TN, which results in a large negative MR. The
maximum value of MR has been found to be -24% at 4 K for 50 kOe. Below 4 K, the
compound shows positive MR with shape changing with field.",1411.2135v1
2014-12-17,Connecting thermoelectric performance and topological-insulator behavior: Bi$_2$Te$_3$ and Bi$_{2}$Te$_{2}$Se from first principles,"Thermoelectric performance is of interest for numerous applications such as
waste heat recovery and solid state energy conversion, and will be seen to be
closely connected to topological insulator behavior. In this context we here
report first principles transport and defect calculations for
Bi$_{2}$Te$_{2}$Se in relation to Bi$_{2}$Te$_{3}$. The two compounds are found
to contain remarkably different electronic structures in spite of being
isostructural and isoelectronic. We discuss these results in terms of the
topological insulator characteristics of these compounds.",1412.5407v1
2014-12-26,Screened exchange dynamical mean field theory and its relation to density functional theory: SrVO3 and SrTiO3,"We present the first application of a recently proposed electronic-structure
scheme to transition metal oxides: screened exchange dynamical mean-field
theory includes non-local exchange beyond the local density approximation and
dynamical correlations beyond standard dynamical mean-field theory. Our results
for the spectral function of SrVO3 are in agreement with the available
experimental data, including photoemission spectroscopy and thermodynamics.
Finally, the 3d0 compound SrTiO3 serves as a test case to illustrate how the
theory reduces to the band structure of standard electronic-structure
techniques for weakly correlated compounds.",1412.7971v1
2015-03-12,Compound droplet manipulations on fiber arrays,"Recent works demonstrated that fiber arrays may constitue the basis of an
open digital microfluidics. Various processes, such as droplet motion,
fragmentation, trapping, release, mixing and encapsulation, may be achieved on
fiber arrays. However, handling a large number of tiny droplets resulting from
the mixing of several liquid components is still a challenge for developing
microreactors, smart sensors or microemulsifying drugs. Here, we show that the
manipulation of tiny droplets onto fiber networks allows for creating compound
droplets with a high complexity level. Moreover, this cost-effective and
flexible method may also be implemented with optical fibers in order to develop
fluorescence-based biosensor.",1503.03747v1
2015-03-20,Numerical semigroups on compound sequences,"We generalize the geometric sequence $\{a^p, a^{p-1}b, a^{p-2}b^2,...,b^p\}$
to allow the $p$ copies of $a$ (resp. $b$) to all be different. We call the
sequence $\{a_1a_2a_3\cdots a_p, b_1a_2a_3\cdots a_p, b_1b_2a_3\cdots
a_p,\ldots, b_1b_2b_3\cdots b_p\}$ a \emph{compound sequence}. We consider
numerical semigroups whose minimal set of generators form a compound sequence,
and compute various semigroup and arithmetical invariants, including the
Frobenius number, Ap\'ery sets, Betti elements, and catenary degree. We compute
bounds on the delta set and the tame degree.",1503.05993v3
2015-04-24,Compound geometric approximation under a failure rate constraint,"We consider compound geometric approximation for a nonnegative,
integer-valued random variable $W$. The bound we give is straightforward but
relies on having a lower bound on the failure rate of $W$. Applications are
presented to M/G/1 queuing systems, for which we state explicit bounds in
approximations for the number of customers in the system and the number of
customers served during a busy period. Other applications are given to
birth-death processes and Poisson processes.",1504.06498v2
2015-05-28,Study of the new superconducting compound Zr0.97V0.03B2 with point-contact spectroscopy,"We present a study of the superconducting energy gap performed with point
contact spectroscopy in a single crystal of the superconductor Zr0:97V0:03B2.
We determined the size and evolution with temperature of the energy gap, the
transition temperature in the compound occurs at the onset of Tc = 9.3 K. The
point contact junctions were measured from 1.7 to 20 K. The differential
conductance as a function of bias voltage was analyzed with the
Blonder-Tinkham-Klapwijk model, the evolution of the gap with temperature was
compared with the BCS theory, the ratio 2{\Delta}(0)/KBTC was of the order of
8.95 indicative of a very strong coupling limit.",1505.07874v1
2015-05-31,Single- and double-wall carbon nanotubes fully covered with tetraphenylporphyrins: Stability and optoelectronic properties from ab-initio calculations,"The optoelectronic properties of single- and double-wall carbon nanotubes
(CNTs) noncovalently functionalized with tetraphenylporphyrins (TPPs) are
addressed by dispersion-corrected ab initio calculations. Five CNT species with
different chiralities were considered. We find that the most stable
configurations are those where the CNTs are fully covered by TPPs, exhibiting
binding energy of about 2~eV/TPP. The semiconducting CNT-TPP compounds show
optical response characterized by a strong absorption associated to the TPP
bands, with increasing intensity with the TPP concentration. In addition,
molecular dynamic simulations show that the compounds would be stable at
temperatures as high as 100$^{\circ}$C.",1506.00191v1
2015-07-17,The centrifugal Jahn-Teller effect in rare-earth cage systems,"The analysis of the properties of rare-earth based materials relies on the
Crystalline Electric Field theory. This theory has to be reconsidered in case
of cage-type compounds, where the rare-earth ion can substantially depart from
its, high symmetry, average position. It is shown that, in case of an orbital
degeneracy at the cage center, a specific Jahn-Teller effect develops in the
paramagnetic range: at low temperature, the distribution of the magnetic ion
spreads inside the cage, the magnetic entropy is reduced, whereas the cage
multipolar susceptibilities are increased. These consequences are put in
relation with the properties of some metallic rare-earth cage compounds.",1507.04918v1
2015-07-21,Multivariate fractional Poisson processes and compound sums,"In this paper we present multivariate space-time fractional Poisson processes
by considering common random time-changes of a (finite-dimensional) vector of
independent classical (non-fractional) Poisson processes. In some cases we also
consider compound processes. We obtain some equations in terms of some suitable
fractional derivatives and fractional difference operators, which provides the
extension of known equations for the univariate processes.",1507.05805v1
2015-07-21,"Towards a Better Understanding of CAR, CDR, CADR and the Others","This paper describes the IBM 704 architecture and the genesis of the names
for CAR, and CDR, which, as it turns out, probably don't quite make sense. The
paper suggests that this may not be all bad, as the names lend themselves to
compounding. Indeed that the compound function names , such as CADR, or even
CADADR, etc. may be read as little access programs.",1507.05956v6
2015-07-22,Strain induced topological phase transitions in monolayer honeycomb structures of group-V binary compounds,"We present first-principles calculations of electronic structures of a class
of two-dimensional (2D) honeycomb structures of group-V binary compounds. Our
results show these new 2D materials are stable semiconductors with direct or
indirect band gaps. The band gap can be tuned by applying lattice strain.
During their stretchable regime, they all exhibit metal-indirect gap
semiconductor-direct gap semiconductor-topological insulator (TI) transitions
with increasing strain from negative (compressive) to positive (tensile)
values. The topological phase transition results from the band inversion at
$\Gamma$ point due to lattice strain and is irrelevant to spin-orbit coupling
(SOC).",1507.06068v1
2015-07-22,MOCVD synthesis of compositionally tuned topological insulator nanowires,"Device applications involving topological insulators (TIs) will require the
development of scalable methods for fabricating TI samples with sub-micron
dimensions, high quality surfaces, and controlled compositions. Here we use
Bi-, Se-, and Te-bearing metalorganic precursors to synthesize TIs in the form
of nanowires. Single crystal nanowires can be grown with compositions ranging
from Bi2Se3 to Bi2Te3, including the ternary compound Bi2Te2Se. These high
quality nanostructured TI compounds are suitable platforms for on-going
searches for Majorana Fermions.",1507.06360v1
2015-07-23,Finite-temperature scaling of spin correlations in a partially magnetized Heisenberg $S=1/2$ chain,"Inelastic neutron scattering is employed to study transverse spin
correlations of a Heisenberg $S=1/2$ chain compound in a magnetic field of 7.5
T. The target compound is the antiferromagnetic Heisenberg $S=1/2$ chain
material 2(1,4-Dioxane)$\cdot$2(H$_2$O)$\cdot$CuCl$_2$, or CuDCl for short. The
validity and the limitations of the scaling relation for the transverse dynamic
structure factor are tested, discussed and compared to the Tomonaga-Luttinger
spin liquid theory and to Bethe-ansatz results for the Heisenberg model.",1507.06487v2
2015-09-01,Argon difluoride stabilized at high pressure,"On account of the rapid development of noble gas chemistry in the past
half-century both xenon and krypton compounds can now be isolated in
macroscopic quantities. The same though does not hold true for the next lighter
group 18 element, argon, which forms only isolated molecules stable solely in
low-temperature matrices or supersonic jet streams. Here we present theoretical
investigations into a new high-pressure reaction pathway which enables
synthesis of Ar-bearing compounds in bulk and at room temperature.",1509.00188v2
2015-09-14,Refined total variation bounds in the multivariate and compound Poisson approximation,"We consider the approximation of a convolution of possibly different
probability measures by (compound) Poisson distributions and also by related
signed measures of higher order. We present new total variation bounds having a
better structure than those from the literature. A numerical example
illustrates the usefulness of the bounds, and an application in the Poisson
process approximation is given. The proofs use arguments from Kerstan (Z.
Wahrscheinlichkeitstheorie und Verw. Gebiete 2 (1964) 173-179) and Roos (J.
Multivariate Anal. 69 (1999) 120-134) in combination with new smoothness
inequalities, which could be of independent interest.",1509.04167v2
2015-10-29,Effect of antimony substitution in iron pnictide compounds,"In the present study we have examined the effect of negative chemical
pressure in iron pnictides. We have synthesized substitution series replacing
arsenic by antimony in a number of 1111- and 122-iron arsenides and present
their crystallographic and physical properties. The SDW transition temperature
in LaFeAs$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$O decreases with increasing antimony
content, while the superconducting transition temperature in
LaFeAs$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$O$_{\mathrm{0.85}}$F$_{\mathrm{0.15}}$
initially increases with Sb substitution. 1111-compounds with samarium instead
of lanthanum have a smaller unit cell volume. In these phases, no Sb solubility
is observed. There is also no apparent solubility of antimony in the 122-iron
arsenides.",1510.08665v1
2015-12-15,Ab-initio modeling of an anion $C_{60}^-$ pseudopotential for fullerene-based compounds,"A pseudopotential of $C_{60}^-$ has been constructed from ab-initio
quantum-mechanical calculations. Since the obtained pseudopotential can be
easily fitted by rather simple analytical approximation it can be effectively
used both in classical and quantum molecular dynamics of fullerene-based
compounds.",1512.04841v1
2016-02-09,"The structural, elastic and optical properties of ScM (M = Rh, Cu, Ag, Hg) intermetallic compounds under pressure by ab initio simulations","The influence of pressure on the structural and elastic properties of ScM (M
= Rh, Cu, Ag, Hg) compounds has been performed by using ab initio approach
pseudopotential plane- wave method based on the density functional theory
within the generalized gradient approximation (GGA). The optical properties
have been investigated under zero pressure. It is found that the optimized
lattice parameters for all metals are in good agreement with the experimental
data and other available theoretical values.",1602.03152v3
2016-02-22,Analysis of Multiple Flows using Different High Speed TCP protocols on a General Network,"We develop analytical tools for performance analysis of multiple TCP flows
(which could be using TCP CUBIC, TCP Compound, TCP New Reno) passing through a
multi-hop network. We first compute average window size for a single TCP
connection (using CUBIC or Compound TCP) under random losses. We then consider
two techniques to compute steady state throughput for different TCP flows in a
multi-hop network. In the first technique, we approximate the queues as M/G/1
queues. In the second technique, we use an optimization program whose solution
approximates the steady state throughput of the different flows. Our results
match well with ns2 simulations.",1602.06653v1
2016-04-05,Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2,"We performed magnetic susceptibility and neutron powder diffraction
experiments on the ternary compound Pr5Ru3Al2. It belongs to the
noncentrosymmetric and nonmirrorsymmetric cubic I213 space group. The
previously reported ferromagnetic transition at 24 K was not detected in our
improved quality samples. Instead, magnetic ordering was observed in the DC
magnetic susceptibility at 3.8 K. Neutron powder diffraction further indicates
that an incommensurate magnetic structure is established below 3.8 K, with the
magnetic modulation vector (0.066, 0.066, 0.066) (r.l.u.). Using the magnetic
representation analysis, we propose the block helical structure as a candidate
for the incommensurate magnetic structure.",1604.01149v1
2016-05-06,Investigation of magnetic phases in parent compounds of Iron-chalcogenides via quasiparticle scattering interference,"We employ a five-orbital tight-binding model to develop the mean field
solution for various possible spin density wave states in the
iron-chalcogenides. The quasiparticle interference (QPI) technique is applied
to detect signatures of these states due to scatterings arising from
non-magnetic impurities. Apart from the experimentally observed double striped
structure with ordering vector $(\pi/2,\pi/2)$, the QPI method is investigated
for the extended-stripe as well as the orthogonal double stripe phase. We
discuss QPI as a possible tool to detect and classify various magnetic
structures with different electronic structure reconstruction within framework
of the Fe$_{1+y}$Te compound.",1605.01798v1
2016-05-13,Competing magnetic interactions in the orthorhombic GdNiAl3,"Magnetization and heat capacity measurements of ternary rare earth
intermetallic compound GdNiAl3 demonstrate para to ferromagnetic transition at
Tc=165.5K. In addition multiple short range magnetic transitions observed below
Tc are suggestive of competing interactions in this compound. As a result of
this a weak Griffiths phase type behaviour is observed in the paramagnetic
region. This complex behaviour is rather supported by the random orientation of
Ni centered tricapped trigonal prisms with additional Al atoms in the
structure. Heat capacity and resistivity data display an interesting peak at 72
K, which is highly unaffected by magnetic fields up to 90KOe.",1605.04264v1
2016-07-28,Canonical singularities of dimension three in characteristic 2 which do not follow Reid's rules,"We continue to study and present concrete examples in characteristic 2 of
compound Du Val singularities defined over an algebraically closed field which
have one dimensional singular loci but cannot be written as products (a
rational double point) x (a curve) up to analytic isomorphism at any point of
the loci. Unlike in other characteristics, we find a large number of such
examples whose general hyperplane sections have rational double points of type
D. We consider these compound Du Val singularities as a special class of
canonical singularities, intend to complete classification in arbitrary
characteristic reinforcing Miles Reid's result in characteristic zero.",1607.08664v2
2016-09-20,Multiferroic phases of the frustrated quantum spin-chain compound linarite,"The dielectric properties of the prototypical frustrated ferromagnetic
spin-chain compound PbCuSO$_4$(OH)$_2$ known as linarite, are studied across
its strongly anisotropic magnetic phase diagram in single crystal samples. The
ferroelectric character of the principal low-field spin spiral phase is
confirmed. The measured polarization is fully consistent with the previously
proposed magnetic structure. Spontaneous polarization is also detected in two
other field-induced phases but in some cases is incompatible with previously
suggested models for the spin arrangement.",1609.06087v2
2016-09-22,Resistivity Minimum in Granular Composites and Thin Metallic Films,"We analyze the temperature dependence of conductivity in thick granular
ferromagnetic compounds NiSiO2 and in thin weakly coupled films of Fe, Ni and
Py in vicinity of metal-insulator transition. Development of resistivity
minimum followed by a logarithmic variation of conductivity at lower
temperatures is attributed to granular structure of compounds and thin films
fabricated by conventional deposition techniques. Resistivity minimum is
identified as a transition between temperature dependent intra-granular
metallic conductance and thermally activated inter-granular tunneling.",1609.06850v1
2016-10-29,Large Deviations for Processes on Half-Line: Random Walk and Compound Poisson,"We establish, under the Cramer exponential moment condition in a
neighbourhood of zero, the Extended Large Deviation Principle for the Random
Walk and the Compound Poisson processes in the metric space $\V$ of functions
of finite variation on $[0,\infty)$ with the modified Borovkov metric $\r(f,g)=
\r_\B(\hat{f},\hat{g}) $, where $ \hat f(t)= f(t)/(1+t)$, $t\in \R$, and
$\r_\B$ is the Borovkov metric. LDP in this space is ""more precise"" than that
with the usual metric of uniform convergence on compacts.",1610.09472v1
2016-11-25,"Magnetism in the KBaRE(BO3)2 (RE=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) series: materials with a triangular rare earth lattice","We report the magnetic properties of compounds in the KBaRE(BO3)2 family (RE=
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), materials with a planar triangular lattice
composed of rare earth ions. The samples were analyzed by x-ray diffraction and
crystallize in the space group R-3m. Physical property measurements indicate
the compounds display predominantly antiferromagnetic interactions between
spins without any signs of magnetic ordering above 1.8 K. The ideal 2D rare
earth triangular layers in this structure type make it a potential model system
for investigating magnetic frustration in rare-earth-based materials.",1611.08548v1
2017-07-04,CrCTe$_3$: Computational design of a robust two-dimensional anti-ferromagnetic semiconductor,"Using density functional theory calculations we establish the hitherto
unknown compound CrCTe$_3$ to be a stable anti-ferromagnetic semiconductor in
the R$\bar{3}$ crystal structure with an indirect fundamental gap . Successive
layers in the bulk compound are weakly bound by van der Waals forces so that
individual layers can be easily exfoliated. A monolayer of CrCTe$_3$ is also an
anti-ferromagnetic semiconductor. The monolayer is structurally stable over a
large range of compressive and tensile strains, and the anti-ferromagnetic
state is robust over this strain range. Band gap of the monolayer can be tuned
by as much as 50% by applying strain in this range.",1707.00878v1
2017-07-17,Magnetic properties of the intermetallic compound HoCuBi,"We present an investigation on the intermetallic compound formed by HoCuBi
which has a monoclinic crystalline P2 structure with lattice parameters; a =
9:8012(26)A, b = 6:0647(6)A, c = 6:1663(13)A. In this report we performed an
extensive analysis of the magnetic characteristics, specific heat at low
temperature mainly close to the region of the observed antiferromagnetic
transition with Neel temperature about 7 K, and to the field induced
spin-crossover; the metamagnetic transition typically observed in
antiferromagnetic systems by measurements of M-H, (Magnetization - Magnetic
Field) at low temperatures.",1707.06086v1
2017-07-29,Thermodynamics of the SmCo5 compound doped with Fe and Ni: an ab initio study,"SmCo5 permanent magnets exhibit enormous uniaxial magnetocrystalline
anisotropy energy and have a high Curie temperature. However, a low energy
product presents a significant drawback in the performance of SmCo5 permanent
magnets. In order to increase the energy product in SmCo5, we propose
substituting fixed amount of cobalt with iron in a new magnet, SmFe3CoNi, where
inclusion of nickel metal makes this magnet thermodynamically stable. We
further discuss some basic theoretical magnetic properties of the SmCo5
compound.",1707.09447v1
2017-07-29,First-principles study of the thermoelectric properties of Zintl compound KSnSb,"The unique structure of Zintl phase makes it an ideal system to realize the
concept of phonon-glass and electron-crystal in the thermoelectric community.
In this work, by combining first-principles calculations and Boltzmann
transport theory for both electrons and phonons, we demonstrate that the ZT
value of Zintl compound KSnSb can reach ~2.6 at 800 K. Such extraordinary
thermoelectric performance originates from the large Seebeck coefficient due to
multi-valley band structures and particularly very small lattice thermal
conductivity caused by mixed-bond characteristics.",1707.09456v1
2017-09-04,Revealing correlation effect of Co 3d electrons in La$_3$Co$_4$Sn$_{13}$ and Ce$_3$Co$_4$Sn$_{13}$ by infrared spectroscopy study,"We report resistivity, specific heat and optical spectroscopy measurements on
single crystal samples of La$_3$Co$_4$Sn$_{13}$ and Ce$_3$Co$_4$Sn$_{13}$. We
observed clear temperature-induced spectral weight suppression below 4000 \cm
for both compounds in conductivity spectra $\sigma_1(\omega)$, indicating the
progressive formation of gap-like features with decreasing temperature. The
suppressed spectral weight transfers mostly to the higher energy region. The
observation reflects the presence of correlation effect in the compounds. We
attribute the correlation effect to the Co 3d electrons.",1709.00816v1
2017-09-07,Computing optimal experimental designs with respect to a compound Bayes risk criterion,"We consider the problem of computing optimal experimental design on a finite
design space with respect to a compound Bayes risk criterion, which includes
the linear criterion for prediction in a random coefficient regression model.
We show that the problem can be restated as constrained A-optimality in an
artificial model. This permits using recently developed computational tools,
for instance the algorithms based on the second-order cone programming for
optimal approximate design, and mixed-integer second-order cone programming for
optimal exact designs. We demonstrate the use of the proposed method for the
problem of computing optimal designs of a random coefficient regression model
with respect to an integrated mean squared error criterion.",1709.02317v1
2017-09-13,Towards microscopic studies of survival probabilities of compound superheavy nuclei,"The microscopic approach of fission rates and neutron emission rates in
compound nuclei have been applied to $^{258}$No and $^{286}$Cn. The microscopic
framework is based on the finite-temperature Skyrme-Hartree-Fock+BCS
calculations, in which the fission barriers and mass parameters are
self-consistently temperature dependent. The fission rates from low to high
temperatures can be obtained based on the imaginary free energy method. The
neutron emission rates are obtained with neutron gases at surfaces. Finally the
survival probabilities of superheavy nuclei can be calculated microscopically.
The microscopic approach has been compared with the widely used statistical
models. Generally, there are still large uncertainties in descriptions of
fission rates.",1709.04350v1
2017-09-23,Quest for consistent modelling of statistical decay of the compound nucleus,"A statistical model description of heavy ion induced fusion-fission reactions
is presented where shell effects, collective enhancement of level density,
tilting away effect of compound nuclear spin and dissipation are included. It
is shown that the inclusion of all these effects provides a consistent picture
of fission where fission hindrance is required to explain the experimental
values of both pre-scission neutron multiplicities and evaporation residue
cross-sections in contrast to some of the earlier works where a fission
hindrance is required for pre-scission neutrons but a fission enhancement for
evaporation residue cross-sections.",1709.08029v1
2017-11-16,Distribution of Off-Diagonal Cross Sections in Quantum Chaotic Scattering: Exact Results and Data Comparison,"The recently derived distributions for the scattering-matrix elements in
quantum chaotic systems are not accessible in the majority of experiments,
whereas the cross sections are. We analytically compute distributions for the
off-diagonal cross sections in the Heidelberg approach, which is ap- plicable
to a wide range of quantum chaotic systems. We thus eventually fully solve a
problem which already arose more than half a century ago in compound-nucleus
scattering. We compare our results with data from microwave and
compound-nucleus experiments, particularly addressing the transition from
isolated resonances towards the Ericson regime of strongly overlapping ones.",1711.08320v1
2017-11-23,Limit Theorems for the Fractional Non-homogeneous Poisson Process,"The fractional non-homogeneous Poisson process was introduced by a
time-change of the non-homogeneous Poisson process with the inverse
$\alpha$-stable subordinator. We propose a similar definition for the
(non-homogeneous) fractional compound Poisson process. We give both
finite-dimensional and functional limit theorems for the fractional
non-homogeneous Poisson process and the fractional compound Poisson process.
The results are derived by using martingale methods, regular variation
properties and Anscombe's theorem. Eventually, some of the limit results are
verified in a Monte Carlo simulation.",1711.08768v1
2017-12-12,Non-Gaussianity of multiple photon subtracted thermal states in terms of compound-Poisson photon number distribution parameters: theory and experiment,"The multiphoton-subtracted thermal states are an interesting example of
quantum states of light which are both classical and non-Gaussian. All the
properties of such states can be described by just two parameters of
compound-Poisson photon number distribution. The non-Gaussianity dependency on
these parameters has been calculated numerically and analytically. The loss of
non-Gaussianity during the optical damping has been also studied
experimentally.",1712.04174v2
2018-06-11,Properties of Poisson processes directed by compound Poisson-Gamma subordinators,"In the paper we consider time-changed Poisson processes where the time is
expressed by compound Poisson-Gamma subordinators $G(N(t))$ and derive the
expressions for their hitting times. We also study the time-changed Poisson
processes where the role of time is played by the processes of the form
$G(N(t)+at)$ and by the iteration of such processes.",1806.03833v1
2018-06-12,Magnetic properties of YCo$_5$ compound at high pressure,"The crystal structure and magnetic properties of YCo$_5$ compound have been
studied by neutron diffraction, in the pressure range $0 \le p \le 7.2 \ GPa$.
The experimental data are analyzed together with results from the combined
Density Functional and Dynamical Mean-Field Theory. A good agreement between
the experimentally determined and calculated values of cobalt moments is shown.
Our scenario for the behavior of YCo$_5$ under pressure, is the combined action
of the Lifshitz transition with a strong local electron-electron interaction.",1806.04650v1
2018-09-04,Superconductivity in BaPtSb with an Ordered Honeycomb Network,"Superconductivity in BaPtSb with the SrPtSb-type structure (space group
$P\bar{6}m2$, $D_{3h}^1$, No. 187) is reported. The structure consists of a
PtSb ordered honeycomb network that stacks along the $c$-axis so that spatial
inversion symmetry is broken globally. Electrical resistivity and specific-heat
measurements revealed that the compound exhibited superconductivity at 1.64 K.
The noncentrosymmetric structure and the strong spin-orbit coupling of Pt and
Sb make BaPtSb an attractive compound for studying the exotic superconductivity
predicted for a honeycomb network.",1809.00756v1
2018-11-15,"Local theorems for arithmetic compound renewal processes, when Cramer's condition holds","We continue the study of the compound renewal processes (c.r.p.), where the
moment Cramer's condition holds (see [1]-[10], where the study of c.r.p. was
started). In the paper arithmetic c.r.p. Z(n) are studied. In such processes
random vector {\xi} = ({\tau},{\zeta}) has the arithmetic distribution, where
{\tau} > 0 defines the distance between jumps, {\zeta} defines the values of
jumps. For this processes the fine asymptotics in the local limit theorem for
probabilities P(Z(n) = x) has been obtained in Cramer's deviation region of x
$\in$ Z. In [6]-[10] the similar problem has been solved for non-lattice
c.r.p., when the vector {\xi} = ({\tau},{\zeta}) has the non-lattice
distribution.",1811.06299v1
2019-11-27,"Structural, Electronic and Elastic Properties of zincblende III-Arsenide Binary Compounds: First-Principles Study","First-principles calculations were performed, and the results from the study
of structural, electronic and elastic properties of zincblende III-arsenide
binary compounds (BAs, AlAs, GaAs and InAs) are presented. These properties
have been calculated using an ab initio pseudopotential method based on density
functional theory (DFT) with the local density approximation (LDA) for the
exchange-correlation potential. The results obtained for the calculated
properties have been compared with experimental data and other computational
works. It has also been found that our results with LDA are in good agreement
with other computational work wherever these are available.",1911.12234v1
2019-04-06,"Structural, elastic, thermal and lattice dynamic properties of new 321 MAX phases","A new series of MAX family designated as 321 phases are recently reported
with Nb3As2C, V3As2C, Nb3P2C and Ta3P2C. Most of the physical properties of
these new MAX phase compounds are unexplored and the present study aims to
investigate their structural, elastic, thermal, and lattice dynamical
properties. Their mechanical and dynamical stabilities are examined. All the
phases are elastically anisotropic and brittle in nature. The Debye
temperatures and lattice thermal conductivities have been calculated. Lattice
dynamical features are investigated in detail and infrared and Raman modes are
identified. High melting temperature of these compounds are favorable for their
applications at elevated temperatures.",1904.03459v1
2019-04-08,Native point defects in $Ti_3GeC_2$ and $Ti_2GeC$,"Using density functional theory, we calculated the formation energy of native
point defects (vacancies, interstitials and antisites) in MAX phase $Ti_2GeC$
and $Ti_3GeC_2$ compounds. Ge vacancy with formation energy of 2.87 eV was the
most stable defect in $Ti_2GeC$ while C vacancy with formation energy of 2.47
eV was the most stable defect in $Ti_3GeC_2$. Ge vacancies, in particular, were
found to be strong phonon scattering centres that reduce the lattice
contribution to thermal conductivity in $Ti_2GeC$. In both compounds, the
reported high thermal and electrical conductivity is attributed to the
electronic contribution that originates from the high density of states at the
Fermi level.",1904.03852v1
2019-06-29,Most abundant isotope peaks and efficient selection on $Y=X_1+X_2+\cdots + X_m$,"The isotope masses and relative abundances for each element are fundamental
chemical knowledge. Computing the isotope masses of a compound and their
relative abundances is an important and difficult analytical chemistry problem.
We demonstrate that this problem is equivalent to sorting
$Y=X_1+X_2+\cdots+X_m$. We introduce a novel, practically efficient method for
computing the top values in $Y$. then demonstrate the applicability of this
method by computing the most abundant isotope masses (and their abundances)
from compounds of nontrivial size.",1907.00278v1
2019-07-27,Escape probabilities of compound renewal processes with drift,"We consider the problem of determining escape probabilities from an interval
of a general compound renewal process with drift. This problem is reduced to
the solution of a certain integral equation. In an actuarial situation where
only negative jumps arise we give a general solution for escape and survival
probabilities under Erlang$(n)$ and hypo-exponential arrivals. These ideas are
generalized to the class of arrival distributions having rational Laplace
transforms. In a general situation with two-sided jumps we also identify
important families of solvable cases. A parallelism with the ""scale function""
of diffusion processes is drawn.",1907.11894v1
2012-09-15,H4O and other hydrogen-oxygen compounds at giant-planet core pressures,"Water and hydrogen at high pressure make up a substantial fraction of the
interiors of giant planets. Using ab initio random structure search methods we
investigate the ground-state crystal structures of water, hydrogen, and
hydrogen-oxygen compounds. We find that, at pressures beyond 14 Mbar, excess
hydrogen is incorporated into the ice phase to form a novel structure with H4O
stoichiometry. We also predict two new ground state structures, P2_1/m and
I4/mmm, for post-C2/m water ice.",1209.3448v1
2014-06-03,Generalizing the divisibility property of rectangle domino tilings,"We introduce a class of graphs called compound graphs, generalizing
rectangles, which are constructed out of copies of a planar bipartite base
graph. The main result is that the number of perfect matchings of every
compound graph is divisible by the number of matchings of its base graph. Our
approach is to use Kasteleyn's theorem to prove a key lemma, from which the
divisibility theorem follows combinatorially. This theorem is then applied to
provide a proof of Problem 21 of Propp's Enumeration of Matchings, a
divisibility property of rectangles. Finally, we present a new proof, in the
same spirit, of Ciucu's factorization theorem.",1406.0669v2
2014-06-09,Phase separation near half-filling point in superconducting compounds,"We present the model of superconducting ceramics using the single band
extended Hubbard Hamiltonian. We investigate the simultaneous presence of
antiferromagnetism (AF) and d-wave superconductivity (SC) in the coherent
potential (CP) approximation applied to the on-site Coulomb repulsion $U$. We
consider the hopping interaction, $\Delta t$, the inter-site charge-charge
interaction, $V$, (creating SC), and the single site Hund's type exchange
interaction, $F_{in}$, (creating AF). The influence of these interactions on
the separation of superconducting and antiferromagnetic phases near the
half-filling point is investigated. Results are compared with the experimental
data for YBaCuO and NdCeCuO compounds.",1406.2090v1
2014-06-24,"Comprehensive verification of new method ""Ethanol as Internal Standard"" for determination of volatile compounds in alcohol products by gas chromatography","Recently proposed new method ""Ethanol as Internal Standard"" for determination
of volatile compounds in alcohol products by gas chromatography is investigated
from different sides. Results of experimental study from three different
laboratories from Belarus and Russian Federation are presented.",1406.6358v2
2018-02-16,InP femtosecond mode-locked laser in a compound feedback cavity with a switchable repetition rate,"A monolithically integrated mode-locked semiconductor laser is proposed. The
compound ring cavity is composed of a colliding pulse mode-locking (ML)
subcavity and a passive Fabry-Perot feedback subcavity. These two 1.6 mm long
subcavities are coupled by using on-chip reflectors at both ends, enabling
harmonic mode locking. By changing DC-bias conditions, optical mode spacing
from 50 to 450 GHz is experimentally demonstrated. Ultrafast pulses shorter
than 0.3 ps emitted from this laser diode are shown in autocorrelation traces.",1802.06154v1
2018-02-21,Spin-fluctuations drive the inverse magnetocaloric effect in Mn5Si3,"Inelastic neutron scattering measurements were performed on single crystals
of the antiferromagnetic compound Mn5Si3 in order to investigate the relation
between the spin dynamics and the magneto-thermodynamic properties. It is shown
that among the two stable antiferromagnetic phases of this compound, the high
temperature one has an unusual magnetic excitation spectrum where propagative
spin-waves and diffuse spin-fluctuations coexist. Moreover, it is evidenced
that the inverse magnetocaloric effect of Mn5Si3, the cooling by adiabatic
magnetization, is associated with field induced spin-fluctuations.",1802.07511v1
2018-12-02,Fast recovery of the pristine magnetic and structural phases in superconducting LaFeAsO$_{0.89}$F$_{0.11}$ by Mn/Fe substitution,"We report on an experimental study of the effect of Mn impurities in the
optimally doped LaFeAsO$_{0.89}$F$_{0.11}$ compound. The results show that a
very tiny amount of Mn, of the order of 0.1\%, is enough to destroy
superconductivity and to recover at low temperatures both the magnetic ground
state and the orthorhombic structure of the pristine LaFeAsO parent compound.
The results are discussed within a model where electron correlations enhance
the Ruderman-Kittel-Kasuya-Yosida interaction among impurities.",1812.00443v1
2019-02-04,The H$_x$Li$_{1-x}$TaWO$_6.n$H$_2$O trirutile structure characterization through Raman and IR spectra comparison: The non-center symmetric case,"We have performed the LiTaWO$_6$ vibrational studies for both Raman and
infrared actives modes. Although we do not have crystalline samples, the study
was conducted qualitatively, firstly comparing the sample with similar
compounds in the literature, and secondly comparing both Raman and infrared
spectra of the LiTaWO$_6$ compound. Although the procedure is limited, we can
assign 8 of the 10 Raman-IR active modes expected by Group Theory.",1902.05127v1
2020-04-01,Packing fraction related distortion of Mn$_6$C octahedra and its effect on the first order magnetic transition in Mn based antiperovskites,"In this paper, we attempt to understand the cause of magnetostructural
transformation in Mn-based antiperovskites by calculating EXAFS at the K edges
of constituent metal atoms in three antiperovskite compounds, Mn$_3$GaC,
Mn$_3$SnC and Mn$_3$InC. These three compounds have very different magnetic
ground states despite the similar cubic structure. Our calculations show that
the distortions of Mn$_6$C octahedra, which are responsible for the first-order
magnetic transition to antiferromagnetic state, depends on the packing fraction
of the lattice.",2004.00258v1
2020-04-23,Covalency a Pathway for Achieving High Magnetisation in $TMFe_2O_4$ Compounds,"The interplay between covalency and magnetism is non-trivial and can be
harnessed for designing new functional magnetic materials. Based on a survey
using density functional calculations, we show that $TM\unicode{x2013}O$ bond
covalency can increase the total magnetic moment of spinel compounds of
$TMFe_2O_4$ composition ($TM = V-Ni, Nb-Pd$) which are isomorphic to the
much-researched magnetite. Accordingly, $PdFe_2O_4$ was found to exhibit the
highest magnetic moment of 7.809 ${\mu}_B$ per formula unit which is
approximately twice that of $Fe_3O_4$ with $T_c$ predicted to be well above
ambient. We further propose a practical method for synthesising $PdFe_2O_4$.",2004.10948v1
2020-05-20,Riemannian geometry for Compound Gaussian distributions: application to recursive change detection,"A new Riemannian geometry for the Compound Gaussian distribution is proposed.
In particular, the Fisher information metric is obtained, along with
corresponding geodesics and distance function. This new geometry is applied on
a change detection problem on Multivariate Image Times Series: a recursive
approach based on Riemannian optimization is developed. As shown on simulated
data, it allows to reach optimal performance while being computationally more
efficient.",2005.10087v1
2020-08-07,Generating Sparse Stochastic Processes Using Matched Splines,"We provide an algorithm to generate trajectories of sparse stochastic
processes that are solutions of linear ordinary differential equations driven
by L\'evy white noises. A recent paper showed that these processes are limits
in law of generalized compound-Poisson processes. Based on this result, we
derive an off-the-grid algorithm that generates arbitrarily close
approximations of the target process. Our method relies on a B-spline
representation of generalized compound-Poisson processes. We illustrate
numerically the validity of our approach.",2008.03181v1
2021-03-02,Thermal entanglement in $2\otimes3$ Heisenberg chains via distance between states,"Most of the work involving entanglement measurement focuses on systems that
can be modeled by two interacting qubits. This is due to the fact that there
are few studies presenting entanglement analytical calculations in systems with
spins $s > 1/2$. In this paper we present for the first time an analytical way
of calculating thermal entanglement in a dimension $2\otimes3$ Heisenberg chain
through the distance between states. We use the Hilbert-Schmidt norm to obtain
entanglement. The result obtained can be used to calculate entanglement in
chains with spin-$1/2$ coupling with spin-$1$, such as ferrimagnetic compounds
as well as compounds with dimer-trimer coupling.",2103.02019v1
2021-03-12,"The expected values of Sombor indices in random hexagonal chains, phenylene chains and Sombor indices of some chemical graphs","Hexagonal chains are a special class of catacondensed benzenoid system and
phenylene chains are a class of polycyclic aromatic compounds. Recently, A
family of Sombor indices was introduced by Gutman in the chemical graph theory.
It had been examined that these indices may be successfully applied on modeling
thermodynamic properties of compounds. In this paper, we study the expected
values of the Sombor indices in random hexagonal chains, phenylene chains, and
consider the Sombor indices of some chemical graphs such as graphene, coronoid
systems and carbon nanocones.",2103.07172v3
2021-03-18,A Pilot Study For Fragment Identification Using 2D NMR and Deep Learning,"This paper presents a method to identify substructures in NMR spectra of
mixtures, specifically 2D spectra, using a bespoke image-based Convolutional
Neural Network application. This is done using HSQC and HMBC spectra separately
and in combination. The application can reliably detect substructures in pure
compounds, using a simple network. It can work for mixtures when trained on
pure compounds only. HMBC data and the combination of HMBC and HSQC show better
results than HSQC alone.",2103.12169v1
2016-03-07,Entanglement-assisted capacities of compound quantum channels,"We study universal quantum codes for entanglement-assisted quantum
communication over compound quantum channels. In this setting, sender and
receiver do not know the specific channel that will be used for communication,
but only know the set that the channel is selected from. We investigate
different variations of the problem: uninformed users, informed receiver,
informed sender, and feedback assistance. We derive single-letter formulas for
all corresponding channel capacities. Our proofs are based on one-shot
decoupling bounds and properties of smooth entropies.",1603.02282v2
2016-03-12,Novel Laves phase superconductor NbBe2: A theoretical investigation,"A new Laves phase superconductor NbBe2, prototype with MgCu2, having maximum
Tc ~2.6 K has been reported very recently. Based on first-principle
calculations, we systematically study the structural, elastic, mechanical,
electronic, thermal and superconducting properties of the newly reported
superconducting intermetallic compound NbBe2. Finally, we investigate the
electron-phonon coupling constant, phonon dispersion curve and density of
states which indicates that the compound under study is a weakly coupled BCS
superconductor.",1603.03917v1
2016-12-14,On Sylvester sums of compound sequence semigroup complements,"In this paper, we consider the set $\textit{NR}(G)$ of natural numbers which
are not in the numerical semigroup generated by a compound sequence $G$. We
generalize a result of Tuenter which completely characterizes $\textit{NR}(G)$.
We use this result to compute Sylvester sums, and we give a direct application
to the computation of weights of higher-order Weierstrass points on some
families of complex algebraic curves.",1612.04766v3
2017-02-14,Structural and electronic changes of pentacene induced by potassium doping,"Potassium is introduced into the crystalline herringbone structure of
pentacene searching for a compound showing metallic electronic transport
properties and, hopefully, superconductivity at small enough temperatures.
Several possible structures for stoichiometric KPentacene (1:1), K2Pentacene
(2:1) and K3Pentacene (3:1) compounds are theoretically investigated. Detailed
densities of states for all of them are presented. As a more prominent result,
a new monoclinic structure has been stabilized for the potassium richer
material that could correspond to the recently synthesized superconducting
phase of K3Pentacene. Although energetically unfavorable, it is the only
metallic candidate found to date.",1702.04141v1
2017-06-08,Ab initio studies of carbon dioxide affinity to carbon compounds and minerals,"We have performed quantum chemical computational studies to determine carbon
dioxide affinity to carbon compounds and minerals, which could be present in
shales. These studies shed light on the microscopic mechanisms of the possible
carbon oxide sequestration processes. Our studies reveal that the carbon oxide
can be adsorbed to various forms of carbon structures and also minerals such as
periclase or illite. We find out that the strongest affinity of carbon oxide
towards carbon structures occurs when the carbon structures exhibit $sp^3$
bonds.",1706.02572v1
2017-09-25,Statistical Analysis of $σ$-Holes: A Novel Complementary View on Halogen Bonding,"To contribute to the understanding of noncovalent binding of halogenated
molecules with a biological activity, electrostatic potential (ESP) maps of
more than 2,500 compounds were thoroughly analysed. A peculiar region of
positive ESP, called $\sigma$-hole, is a concept of central importance for
halogen bonding. We aim at simplifying the view on $\sigma$-holes and provide
general trends in organic drug-like molecules. The results are in fair
agreement with crystallographic surveys of small molecules as well as of
biomolecular complexes and attempt to improve the intuition of chemists when
dealing with halogenated compounds.",1710.02202v1
2018-04-09,Halogens in the synthesis of colloidal semiconductor nanocrystals,"In this review, we highlight the role of halogenated compounds in the
colloidal synthesis of nanostructured semiconductors. Halogen-containing
metallic salts used as precursors and halogenated hydrocarbons used as ligands
allow stabilizing different shapes and crystal phases, and enable the formation
of colloidal systems with different dimensionality. We summarize recent reports
on the tremendous influence of these compounds on the physical properties of
nanocrystals, like field-effect mobility and solar cell performance and outline
main analytical methods for the nanocrystal surface control.",1804.02977v1
2018-04-12,Peculiar magnetic properties of NC6 and NC12 layered compounds from first principles,"In the context of characterizing nitrogen poor carbo-nitrides for different
applications, identification of an unusual onset of spin polarization of N(p)
states has been shown. A full saturation up to 3 Bohr magnetons is demonstrated
in extended two-dimensional carbon networks of C6N and C12N hexagonal
structures refined based on density functional theory calculations. From
establishing the energy-volume equations of states in both compounds assuming
spin degenerate (non spin polarized) and spin-polarized configurations, the
ground state is identified as ferromagnetic. The variation of magnetization
with volume points to strongly ferromagnetic behavior",1804.04441v1
2019-08-30,Superconductivity in PtSbS with a Noncentrosymmetric Cubic Crystal Structure,"We report the synthesis, electronic properties, and electronic structure of
ullmannite-type PtSbS, which has a cubic crystal structure without space
inversion symmetry. Electrical resistivity and magnetization measured at low
temperatures suggested that this compound is a bulk superconductor with a
superconducting transition temperature of Tc = 0.15 K. First principles
calculations indicated that Fermi surfaces of PtSbS include strongly nested
hole pockets, which can make this compound interesting if they contribute to
the emergence of superconductivity.",1908.11507v1
2019-12-12,"Cluster glass behavior of frustrated birnessites AxMnO2*yH2O (A = Na, K)","We report on the synthesis and magnetic properties of frustrated
Na0.22MnO2*0.39H2O and K0.6MnO2*0.48H2O with the birnessite structure. The
structure, static and dynamic magnetic properties of the compounds are
investigated in detail. A combination of DC and AC magnetic susceptibility
measurements and magnetization decay measurements reveal cluster glass behavior
below the freezing temperature of 4 K for Na-birnessite and 6 K for
K-birnessite. The frequency dependence of the freezing temperature is analyzed
on the basis of dynamic scaling laws including the critical slowing down
formula and the Vogel-Fulcher law, which further confirm cluster glass
formation in both compounds.",1912.05997v1
2019-12-13,Magnetic spiral order in the square-lattice spin system (CuBr)Sr$_{2}$Nb$_{3}$O$_{10}$,"We address quantum spin helical states in the strongly frustrated Heisenberg
model. Contrary to conventional Dzyaloshinskii-Moriya approach we show that
such states appear without central symmetry breaking. As an example, we
demonstrate that the magnetic and thermodynamic properties of the
quasi-two-dimensional square-lattice compound
$\mathrm{(CuBr)Sr_{2}Nb_{3}O_{10}}$ can be interpreted within 2D $S = 1/2$
$J_1-J_2-J_3$ Heisenberg model. In this compound neutron experiment indicates
helical spin order while central symmetry does hold.",1912.06399v1
2020-02-16,Effect of Carbon on the Compound Layer Properties of AISI H13 Tool Steel in Pulsed Plasma Nitrocarburizing,"Due to the mechanical and inertness properties of the Epsilon phase, its
formation as a compact monolayer is most wanted in plasma surface treatments of
steels. This phase can be obtained by the inclusion of carbon species in the
plasma. In this work, we present a systematic study of the carbon influence on
the compound layer in an AISI H13 tool steel by pulsed plasma nitrocarburizing
process with different gaseous ratios.",2002.06688v1
2020-03-19,Dependence of nonthermal metallization kinetics on bond ionicity of compounds,"It is known that covalently bonded materials undergo nonthermal structure
transformations upon ultrafast excitation of an electronic system, whereas
metals exhibit phonon hardening. Here we study how ionic bonds react to
electronic excitation. Density-functional molecular dynamics predicts that
ionic crystals may melt nonthermally, however, into an electronically
insulating state, in contrast to covalent materials. We demonstrate that the
band gap behavior during nonthermal transitions depends on a bonding type: it
is harder to collapse the band gap in more ionic compounds, which is
illustrated by transformations in Y2O3 vs. NaCl, LiF and KBr.",2003.08887v1
2020-06-17,"Magnetic properties of two-dimensional M$_2$N$_3$ (M-metal, N=S,Se,Te) compounds","Using \textit{ab-initio} methods we study structural, electronic and magnetic
properties of two dimensional compounds with stoichiometry M$_2$N$_3$ (M-metal,
N=S,Se,Te). Our study shows that structures with Cr, Ti, and Mn are stable,
with significant binding energy. Also, such structures are semiconductors with
narrow band gaps. We also show that Cr$_2$Se$_3$, Cr$_2$Te$_3$ and Mn$_2$Te$_3$
have considerable magnetic moments. The negative values of magnetic anisotropy
energy suggest, that these materials can maintain ferromagnetic ordering in
non-zero temperatures with estimated Curie temperatures in the range of 30-55
K.",2006.09757v1
2020-07-31,On $q$-scale functions of spectrally negative compound Poisson processes,"Scale functions play a central role in the fluctuation theory of spectrally
negative L\'evy processes. For spectrally negative compound Poisson processes
with positive drift, a new representation of the $q$-scale functions in terms
of the characteristics of the process is derived. Moreover, similar
representations of the derivatives and the primitives of the $q$-scale
functions are presented. The obtained formulae for the derivatives allow for a
complete exposure of the smoothness properties of the considered $q$-scale
functions. Some explicit examples of $q$-scale functions are given for
illustration.",2007.15880v1
2020-10-24,New compound fractional sliding mode control and super-twisting control of a MEMS gyroscope,"In this research we propose a new compound Fractional Order Sliding Mode
Controller (FOSMC) and SuperTwisting Controller (FOSMC+STC) to control of a
MEMS gyroscope. A new sliding mode surface has been defined to design the
proposed new sliding mode controller. The main advantages of a FOSMC is its
high tracking performance and robustness against external perturbation, but it
is susceptible to chattering. By augmenting a STC with a FOSMC, the chattering
phenomenon is eliminated, singularity problem is solved and systems robustness
has significatnetly improved. Simulation results validate the effectiveness of
the proposed control approach.",2010.12774v1
2020-11-25,Cavity-modulated ionization potentials and electron affinities from quantum electrodynamics coupled-cluster theory,"Quantum electrodynamics coupled-cluster (QED-CC) theory is used to model
vacuum-field-induced changes to ground-state properties of a series of sodium
halide compounds (NaX, X = F, Cl, Br, I) strongly coupled to an optical cavity.
Ionization potentials (IPs) and electron affinities (EAs) are presented, and it
is demonstrated that EAs are easily modulated by cavity interactions, while IPs
for these compounds are far less sensitive to the presence of the cavity. EAs
predicted by QED-CC can be reduced by as much 0.22 eV (or ~50%) when
considering experimentally-accessible coupling parameters.",2011.12768v2
2021-01-02,Birational geometry of sextic double solids with a compound $A_n$ singularity,"Sextic double solids, double covers of $\mathbb P^3$ branched along a sextic
surface, are the lowest degree Gorenstein Fano 3-folds, hence are expected to
behave very rigidly in terms of birational geometry. Smooth sextic double
solids, and those which are $\mathbb Q$-factorial with ordinary double points,
are known to be birationally rigid. In this article, we study sextic double
solids with an isolated compound $A_n$ singularity. We prove a sharp bound $n
\leq 8$, describe models for each $n$ explicitly and prove that sextic double
solids with $n > 3$ are birationally non-rigid.",2101.00501v1
2021-04-23,Symplectic cohomology of compound Du Val singularities,"We compute symplectic cohomology for Milnor fibres of certain compound Du Val
singularities that admit small resolution by using homological mirror symmetry.
Our computations suggest a new conjecture that the existence of a small
resolution has strong implications for the symplectic cohomology and
conversely. We also use our computations to give a contact invariant of the
link of the singularities and thereby distinguish many contact structures on
connected sums of $S^2 \times S^3$.",2104.11713v3
2021-04-29,"Influence of the organic cation disorder on photoconductivity in ethylenediammonium lead iodide, NH3CH2CH2NH3PbI4","We report the synthesis and crystal structure of an organic inorganic
compound, ethylenediammonium lead iodide, NH3CH2CH2NH3PbI4. Synchrotron based
single crystal X-ray diffraction experiments revealed that the pristine and
thermally treated crystals differ in the organic cation behaviour, which is
characterized by a partial disorder in the thermally treated crystal. Based on
current voltage measurements, increased disorder of the organic cation is
associated with enhanced photoconductivity. This compound could be a potential
candidate for interface engineering in lead halide perovskite-based
optoelectronic devices.",2104.14178v1
2021-05-10,High-pressure synthesis of boron-rich chalcogenides B12S and B12Se,"Two boron-rich chalcogenides B12S and B12Se isostructural to
{\alpha}-rhombohedral boron were synthesized by chemical reaction of the
elements at high-pressure - high-temperature conditions. The crystal structures
and stoichiometries of both compounds were confirmed by Rietveld refinement and
elemental analysis. The experimental Raman spectra of B12S and B12Se were
investigated for the first time. All observed Raman bands have been attributed
to the theoretically calculated phonon modes, and the mode assignment has been
performed.",2105.04450v1
2021-05-19,Free carrier induced ferroelectricity in layered perovskites,"Doping ferroelectrics with carriers is often detrimental to polarization.
This makes the design and discovery of metals that undergo a ferroelectric-like
transition challenging. In this letter, we show from first principles that the
oxygen octahedral rotations in perovskites are often enhanced by electron
doping, and this can be used as a means to strengthen the structural
polarization in certain hybrid-improper ferroelectrics -- compounds in which
the polarization is not stabilized by the long range Coulomb interactions but
is instead induced by a trilinear coupling to octahedral rotations. We use this
design strategy to predict a cation ordered Ruddlesden-Popper compound that can
be driven into a metallic ferroelectric-like phase via electrolyte gating.",2105.08905v1
2021-06-27,Shift of Infrared Absorption and Emission Spectra of Transition Metal Ions in Solid Solutions of Semiconductor Compounds,"A universal theoretical model is proposed that explains the observed shift of
IR absorption and emission bands in the spectra of transition metal ions in
solid solutions of semiconductor compounds. The model has been used for
estimating the long-wavelength shift of luminescence bands in the spectra of
semiconductor solid solutions with increasing concentration in application to
crystals of the ternary systems ZnMgSe(Cr2+) and CdMnTe(Fe2+). Description of
the phenomenon is generalized to the case of multicomponent solid solutions.",2106.14164v1
2021-08-17,"First-principles investigation of Nd(Fe,M)12 (M = K--Br) and Nd(Fe,Cr,Co,Ni,Ge,As)12: Possible enhancers of Curie temperature for NdFe12 magnetic compounds","We investigate the effects of various dopants (M = K--Br) on the Curie
temperature of the magnetic compound NdFe12 through first-principles
calculations. Analysis by the Korringa--Kohn--Rostoker method with the coherent
potential approximation reveals that doping the Fe sites with optimal
concentrations of Ge and As is a promising strategy for increasing the Curie
temperature. To search over a wider space, we also perform Bayesian
optimization. Out of over 180,000 candidate compositions, co-doped systems with
Co, Ge, and As are found to have the highest Curie temperatures.",2108.07452v1
2021-08-17,Similarity law and critical properties in ionic systems,"Using molecular simulations, we determine the locus of ideal compressibility,
or Zeno line, for a series of ionic compounds. We find that the shape of this
thermodynamic contour follows a linear law, leading to the determination of the
Boyle parameters. We also show that a similarity law, based on the Boyle
parameters, yields accurate critical data when compared to the experiment.
Furthermore, we show that the Boyle density scales linearly with the
size-asymmetry, providing a direct route to establish a correspondence between
the thermodynamic properties of different ionic compounds.",2108.07831v1
2021-09-13,On directional convolution equivalent densities,"We propose a definition of directional multivariate subexponential and
convolution equivalent densities and find a useful characterization of these
notions for a class of integrable and almost radial decreasing functions. We
apply this result to show that the density of the absolutely continuous part of
the compound Poisson measure built on a given density $f$ is directionally
convolution equivalent and inherits its asymptotic behaviour from $f$ if and
only if $ f$ is directionally convolution equivalent. We also extend this
characterization to the densities of more general infinitely divisible
distributions on $\mathbb{R}^d$, $d \geq 1$, which are not pure compound
Poisson.",2109.06336v2
2021-09-16,Non-central moderate deviations for compound fractional Poisson processes,"The term ""moderate deviations"" is often used in the literature to mean a
class of large deviation principles that, in some sense, fill the gap between a
convergence in probability to zero (governed by a large deviation principle)
and a weak convergence to a centered Normal distribution. We talk about
""non-central moderate deviations"" when the weak convergence is towards a
non-Gaussian distribution. In this paper we study non-central moderate
deviations for compound fractional Poisson processes with light-tailed jumps.",2109.07862v2
2021-09-24,Convergence to infinite-dimensional compound Poisson distributions on convex polyhedra,"The aim of the present work is to provide a supplement to the authors' paper
(2018). It is shown that our results on the approximation of distributions of
sums of independent summands by the accompanying compound Poisson laws and the
estimates of the proximity of sequential convolutions of multidimensional
distributions on convex polyhedra may be almost automatically transferred to
the infinite-dimensional case.",2109.11845v2
2021-09-25,Improved statistical machine translation using monolingual paraphrases,"We propose a novel monolingual sentence paraphrasing method for augmenting
the training data for statistical machine translation systems ""for free"" -- by
creating it from data that is already available rather than having to create
more aligned data. Starting with a syntactic tree, we recursively generate new
sentence variants where noun compounds are paraphrased using suitable
prepositions, and vice-versa -- preposition-containing noun phrases are turned
into noun compounds. The evaluation shows an improvement equivalent to 33%-50%
of that of doubling the amount of training data.",2109.15119v1
2021-11-18,CSI: Contrastive Data Stratification for Interaction Prediction and its Application to Compound-Protein Interaction Prediction,"Accurately predicting the likelihood of interaction between two objects
(compound-protein sequence, user-item, author-paper, etc.) is a fundamental
problem in Computer Science. Current deep-learning models rely on learning
accurate representations of the interacting objects. Importantly, relationships
between the interacting objects, or features of the interaction, offer an
opportunity to partition the data to create multi-views of the interacting
objects. The resulting congruent and non-congruent views can then be exploited
via contrastive learning techniques to learn enhanced representations of the
objects.",2111.09467v2
2022-01-04,Compound photon blockade based on three mode system,"Based on the four wave mixing, a three mode nonlinear system is proposed. The
single photon blockade is discussed through analytical analysis and numerical
calculation. The analytical analysis shows that the conventional photon
blockade and unconventional photon blockade can be realized at the same time,
and the analytical conditions of the two kinds of blockade are the same. The
numerical results show that the system not only has the maximum average photon
number in the blockade region, but also can have strong photon anti-bunching in
the region with small nonlinear coupling coefficient, which greatly reduces the
experimental difficulty of the system. This optical system which can realize
the compound photon blockade effect is helpful to realize the high-purity
single photon source.",2201.01127v1
2022-01-24,Superconducting hydrides on a quantum landscape,"Reaching superconductivity at ambient conditions is one of the biggest
scientific dreams. The discoveries in the last few years at high pressures
place hydrogen-based compounds as the best candidates for making it true. As
the recent history shows, first-principles calculations are expected to
continue guiding the experimental quest in the right track in the coming years.
Considering that ionic quantum fluctuations largely affect the structural and
vibrational properties of superconducting hydrides, in many cases making them
stable at much lower pressures than expected, it will be crucial to include
such effects on the future ab initio predictions. The prospects for
low-pressure high critical-temperature compounds are wide open, even at ambient
pressure.",2201.09500v1
2022-04-07,Editorial on Research Topic: High-Tc Superconductivity in Electron-Doped Iron Selenide and Related Compounds,"In this editorial, we first give a brief survey of the field of iron-selenide
superconductivity, both in the case of bulk FeSe characterized by the
co-existence of superconductivity and nematic order, and in the case of
electron-doped FeSe characterized by high-temperature superconductivity. We
next review the 8 contributions to the Frontiers in Physics research topic
""High-Tc Superconductivity in Electron-Doped Iron Selenide and Related
Compounds"".",2204.03735v2
2022-05-10,FlavorDB2: An Updated Database of Flavor Molecules,"Flavor is expressed through interaction of molecules via gustatory and
olfactory mechanisms. Knowing the utility of flavor molecules in food and
fragrances, it is valuable to add a comprehensive repository of flavor
compounds characterizing their flavor profile, chemical properties, regulatory
status, consumption statistics, taste/aroma threshold values, reported uses in
food categories, and synthesis. FlavorDB2
(https://cosylab.iiitd.edu.in/flavordb2/) is an updated database of flavor
molecules with an user-friendly interface. This repository simplifies the
search for flavor molecules, their attributes and offers a range of
applications including food pairing. FlavorDB2 serves as a standard repository
of flavor compounds.",2205.05451v1
2022-06-09,Some Compound Fractional Poisson Processes,"In this paper, we introduce and study fractional versions of three compound
Poisson processes, namely, the Bell-Touchard process, the Poisson-logarithmic
process and the generalized P\'olya-Aeppli process. It is shown that these
processes are limiting cases of a recently introduced process by Di Crescenzo
et al. (2016), namely, the generalized counting process. We obtain the mean,
variance, covariance, long-range dependence property etc. for these processes.
Also, we obtain several equivalent forms of the one-dimensional distribution of
fractional versions of these processes.",2206.04377v1
2022-08-03,Electrical transport and magnetic properties of the triangular-lattice compound Zr$_2$NiP$_2$,"We report the first investigation of the electrical and magnetic properties
of the triangular-lattice compound Zr$_2$NiP$_2$ (space group $P$6$_3$/$mmc$).
The temperature evolution of electrical resistivity follows the
Bloch-Gr\""uneisen-Mott law, and exhibits a typically metallic behavior. No
transition is visible by both electrical and magnetic property measurements,
and nearly no magnetization is detected ($M_0$ $<$ 0.002$\mu_\mathrm{B}$/Ni)
down to 1.8 K up to 7 T. The metallic and nonmagnetic characters are well
understood by the first-principles calculations for Zr$_2$NiP$_2$.",2208.01799v1
2022-08-03,Towards hydrogen-rich ionic (NH4)(BH3NH2BH2NH2BH3) and related molecular NH3BH2NH2BH2NH2BH3,"Attempts of synthesis of ionic (NH4)(BH3NH2BH2NH2BH3) using metathetical
approach resulted in a mixture of the target compound and a partly
dehydrogenated molecular NH3BH2NH2BH2NH2BH3 product. The mixed specimen was
characterized by NMR and vibrational spectroscopies, and the crystal structure
of their cocrystal was solved from powder x-ray diffraction data, and
supplemented by theoretical density functional theory calculations. Despite
their impressive hydrogen content, and similarly to ammonia borane, both title
compounds release hydrogen substantially polluted with borazine, and traces of
ammonia and diborane.",2208.01979v1
2022-08-09,Literature Review: Graph Kernels in Chemoinformatics,"The purpose of this review is to introduce the reader to graph kernels and
the corresponding literature, with an emphasis on those with direct application
to chemoinformatics. Graph kernels are functions that allow for the inference
of properties of molecules and compounds, which can help with tasks such as
finding suitable compounds in drug design. The use of kernel methods is but one
particular way two quantify similarity between graphs. We restrict our
discussion to this one method, although popular alternatives have emerged in
recent years, most notably graph neural networks.",2208.04929v2
2022-11-02,A brief perspective of high temperature superconductivity in the cuprates: Strong correlations combined with superexchange match experiment,"High temperature superconductivity encompasses the cuprates, nickelates, iron
pnictides, and LaH$_x$ compounds. The first three groups of compounds involve
in the pairing electrons, which are strongly to moderately correlated, whereas
in the last class of systems specific phonon excitations. In this overview we
concentrate first on the (semi)quantitative theory of high T$_{C}$
superconductivity in the cuprates based on our original vibrational approach
beyond the renormalized mean field theory. The model we explore mainly is
$t$-$J$-$U$ model containing both the superexchange (kinetic energy) combined
with strong interelectronic correlations. Selected equilibrium and
dynamic-excitation properties are analyzed briefly. General questions regarding
the pseudogap and two--dimensional character of those systems are raised.",2211.01024v1
2022-12-12,Decentralized lending and its users: Insights from Compound,"Permissionless blockchains offer an information environment where users can
interact privately without fear of censorship. Financial services can be
programmatically coded via smart contracts to automate transactions without the
need for human intervention or knowing user identity. This new paradigm is
known as decentralized finance (DeFi). We investigate Compound (a leading DeFi
lending protocol) to show how it works in this novel information environment,
who its users are, and what factors determine their participation. On-chain
transaction data shows that loan durations are short (31 days on average), and
many users borrow to support leveraged investment strategies (yield farming).
We show that systemic risk in DeFi arises from concentration and
interconnection, and how traditional risk management practices can be
challenging for DeFi.",2212.05734v1
2022-12-19,Compound Poisson approximation for simple transient random walks in random sceneries,"Given a simple transient random walk $(S_n)_{n\geq 0}$ in $\mathbf{Z}$ and a
stationary sequence of real random variables $(\xi(s))_{s\in \mathbf{Z}}$, we
investigate the extremes of the sequence $(\xi(S_n))_{n\geq 0}$. Under suitable
conditions, we make explicit the extremal index and show that the point process
of exceedances converges to a compound Poisson point process. We give two
examples for which the cluster size distribution can be made explicit.",2212.09395v1
2022-12-31,High-pliability Fano hypersurfaces,"We show that five of Reid's Fano 3-fold hyperurfaces containing at least one
compound Du Val singularity of type $cA_n$ have pliability at least two. The
two elements of the pliability set are the singular hypersurface itself, and
another non-isomorphic Fano hypersurface of the same degree, embedded in the
same weighted projective space, but with different compound Du Val
singularities. The birational map between them is the composition of two
birational links initiated by blowing up two Type I centres on a codimension 4
Fano 3-fold of $\mathbb{P}^2 \times \mathbb{P}^2$-type having Picard rank 2.",2301.00154v2
2023-02-06,Spectral comparison of compound cocycles generated by delay equations in Hilbert spaces,"We study linear cocycles generated by nonautonomous delay equations in a
proper Hilbert space and their extensions (compound cocycles) to exterior
powers. Armed with the recently developed version of the Frequency Theorem, we
develop analytic perturbation techniques for comparison of spectral properties
(e.g., uniform exponential dichotomies) between such cocycles and cocycles
generated by stationary equations. In the basis, there lies an interplay
between regularity and structure in PDEs associated with delay equations. In
particular, the developed machinery results in effective robust criteria for
the absence of closed invariant contours on global attractors arising in
nonlinear problems.",2302.02537v3
2023-02-08,Quantum anomalous Hall effect induced by circularly polarized light on samarium hexaboride surface,"We consider a time-dependent, surface Hamiltonian for the 3D compound
samarium hexaboride based on the slave boson protocol linked version of the
periodic Anderson model reported earlier. We show the possible access to the
quantum anomalous Hall state due to the normal incidence of circularly
polarized light on the surface of the compound in the high frequency limit
within the framework of the Floquet theory. The chern number is found to be
unity for the right-handed as well as the left-handed circularly polarized
light.",2302.04039v4
2023-02-25,Two-Disk Compound Symmetry Groups,"Symmetry is at the heart of much of mathematics, physics, and art.
Traditional geometric symmetry groups are defined in terms of isometries of the
ambient space of a shape or pattern. If we slightly generalize this notion to
allow the isometries to operate on overlapping but non-identical metric spaces,
we obtain what we call compound symmetry groups. A natural example is that of
the groups generated by discrete rotations of overlapping disks in the plane.
Investigation of these groups reveals a new family of fractals, as well as a
rich structure that is intriguing both mathematically and artistically. We
report on our initial investigations.",2302.12950v1
2023-03-30,Maxima over random time intervals for heavy-tailed compound renewal and Lévy processes,"We derive subexponential tail asymptotics for the distribution of the maximum
of a compound renewal process with linear component and of a L\'evy process,
both with negative drift, over random time horizon $\tau$ that does not depend
on the future increments of the process. Our asymptotic results are uniform
over the whole class of such random times. Particular examples are given by
stopping times and by $\tau$ independent of the processes. We link our results
with random walk theory.",2303.17315v2
2023-05-15,Synthesis and scintillation properties of some dense X-ray phosphors,"Many ultra-dense lutetium or gadolinium based compounds doped with Eu 3+ have
been prepared. This paper reports on the major scintillation performances of
these compounds. One of them (Lu 2 O 3 :Eu) is particularly promising and have
been deposited on a screen. Performances of such a screen are presented.",2305.08485v1
2023-05-17,Crystal structure informed mesoscale deformation model for HCP Cu6Sn5 intermetallic compound,"In the electronic packaging and energy storage sectors, the study of Cu6Sn5
intermetallic compound (IMC) is getting more attention. At temperatures above
186 oC, this IMC exists in a hexagonal closed packed (HCP) crystalline
structure. Crystal plasticity finite element simulations are performed on
Cu6Sn5 IMC by taking the information about its lattice parameters and direction
dependent elastic properties. Three types of models corresponding to
deformations in basal, prismatic and pyramidal modes are developed. With the
same type of loading in the elastic regime and boundary conditions, the results
of the computations reveal the differences in displacement magnitudes among the
three model types.",2305.10582v2
2023-05-11,Predictive ability comparison of different versions of some well known degree dependent topological indices,"To avoid extensive lab work on properties of chemical compounds, QSPR/QSAR
analysis for topological descriptors is a productive statistical approach to
analyze various physicochemical properties of chemical compounds. Many
researchers have investigated on correlation of degree-based topological
descriptors. In this article we present the predictive ability of 6 well known
degree dependant topological indices of 22 lower poly cyclic aromatic
hydrocarbons in three versions, and we have done a comparison analysis of three
versions of considered topological indices for their predictive ability.",2305.13260v1
2023-07-31,Erbium-based multifuncional compounds as molecular microkelvin-tunable driving-sensing units,"We demonstrate the selective control of the magnetic response and
photoluminescence properties of Er3+ centers with light, by associating them
with a highly conjugated beta-diketonate (1,3-di(2-naphthyl)-1,3-propanedione)
ligand. We demonstrate this system to be an optically-pumped molecular compound
emittingin infra-red, which can be employed as a precise heat-driving and
detecting unit for low temperatures",2307.16476v1
2023-09-19,DeFi composability as MEV non-interference,"Complex DeFi services are usually constructed by composing a variety of
simpler smart contracts. The permissionless nature of the blockchains where
these smart contracts are executed makes DeFi services exposed to security
risks, since adversaries can target any of the underlying contracts to
economically damage the compound service. We introduce a new notion of secure
composability of smart contracts, which ensures that adversaries cannot
economically harm the compound contract by interfering with its dependencies.",2309.10781v2
2023-10-10,A conditional compound Poisson process approach to the sparse Erdős-Rényi random graphs: moderate deviations,"We construct a compound Poisson process conditioned on its random summation
that represents the sizes of the connected components in the sparse
Erd\H{o}s-R\'enyi random graph $G(n,c/n)$. This new representation depicts a
connection between the phase transition in the sparse random graph and the
condensation transition in the zero-range model. Under this framework, we can
derive moderate deviation principles for the maximun component, total number of
connected components and empirical measure of the sizes in the non-critical
regimes. Large deviation results are discussed.",2310.06348v2
2023-10-26,Distinct contiguous versus separated triplet-pair multiexcitons in an intramolecular singlet fission chromophore,"We show from many-body quantum mechanical calculations that there occur
structurally distinct triplet-pair eigenstates in the intramolecular singlet
fission (iSF) compound pentacene-tetracene-pentacene. Triplet excitons occupy
neigboring pentacene and tetracene monomers in the higher energy doubly
degenerate triplet-triplet multiexcitons, and terminal pentacene chromophores
in the lower energy multiexciton. The lowest energy multiexciton is reached by
ultrafast triplet migration within the triplet-triplet manifold, a result with
profound implication for the design of superior iSF compounds.",2310.17818v1
2024-04-07,Directional Invariants of Doubly Periodic Tangles,"In this paper we define novel topological invariants of doubly periodic
tangles (DP tangles). DP tangles are embeddings of curves in the thickened
plane that are repeated periodically in two directions. We first organize the
components of a DP tangle into different it interlinked compounds, which are
invariants of a DP tangle. The notion of interlinked compound leads to the
classification of DP tangles according to their it directional type. We then
prove that the directional type is an invariant of DP tangles using the concept
of axis-motif, which can be viewed as the blueprint of a DP tangle.",2404.05092v1
2024-04-15,A Note on Loss Functions and Error Compounding in Model-based Reinforcement Learning,"This note clarifies some confusions (and perhaps throws out more) around
model-based reinforcement learning and their theoretical understanding in the
context of deep RL. Main topics of discussion are (1) how to reconcile
model-based RL's bad empirical reputation on error compounding with its
superior theoretical properties, and (2) the limitations of empirically popular
losses. For the latter, concrete counterexamples for the ""MuZero loss"" are
constructed to show that it not only fails in stochastic environments, but also
suffers exponential sample complexity in deterministic environments when data
provides sufficient coverage.",2404.09946v1
1998-08-25,"Unconventional Transition from Metallic to Insulating Resistivity in the Spin-ladder Compound (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$","Spin-ladder compounds make interesting analogs of the high-temperature
superconductors, because they contain layers of nearly one-dimensional
""ladders"" consisting of a square array of copper and oxygen atoms. Increasing
the number of legs in the ladders provides a step-wise approach toward the
two-dimensional copper-oxygen plane, that structure believed to be a key to
high temperature superconductivity. Short-range spin correlations in ladders
have been predicted to lead to formation of hole pairs favorable for
superconductivity, once enough holes are introduced onto the ladders by doping.
Indeed, superconductivity has been discovered in the two-leg ladder compound
(Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$ under high pressure. Here we show that charge
transport in the non-superconducting state of (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$
shares three distinct regimes in common with high-temperature superconductors,
including an unexplained insulating behavior at low temperatures in which the
resistivity increases as the logarithm of the temperature. These observations
suggest that the logarithmic divergence arises from a new localization
mechanism common to the ladder compounds and the high-temperature
superconductors, which may arise from nearly one-dimensional charge transport
in the presence of a spin gap.",9808284v2
1999-02-22,Hall-effect in LuNi_2B_2C and YNi_2B_2C borocarbides: a comparative study,"The Hall effect in LuNi_2B_2C and YNi_2B_2C borocarbides has been
investigated in normal and superconducting mixed states. The Hall resistivity
rho_{xy} for both compounds is negative in the normal as well as in the mixed
state and has no sign reversal below T_c typical for high-T_c superconductors.
In the mixed state the behavior of both systems is quite similar. The scaling
relation rho_{xy}\sim\rho_{xx}^\beta (\rho_{xx} is the longitudinal
resistivity) was found with \beta=2.0 and 2.1 for annealed Lu- and Y-based
compounds, respectively. The scaling exponent \beta decreases with increasing
degree of disorder and can be varied by annealing. This is attributed to a
variation of the strength of flux pinning. In the normal state weakly
temperature dependent Hall coefficients were observed for both compounds. A
distinct nonlinearity in the \rho_{xy} dependence on field H was found for
LuNi_2B_2C in the normal state below 40K, accompanied by a large
magnetoresistance (MR) reaching +90% for H=160kOe at T=20K. At the same time
for YNi_2B_2C only linear \rho_{xy}(H) dependences were observed in the normal
state with an approximately three times lower MR value. This difference in the
normal state behavior of the very similar Lu- and Y-based borocarbides seems to
be connected with the difference in the topology of the Fermi surface of these
compounds.",9902299v1
1999-03-18,Interlayer Josephson vortices in the high-T_c superconducting cuprates,"We comment on the work by Moler, et al., [Science 279, 1193 (1998)]
concerning determination of the c-axis penetration depth in the single-layer
compound Tl-2201 through measuring the magnetic flux due to isolated interlayer
Josephson vortices.",9903284v1
1999-06-15,"Electronic Structure of Cu_(1-x)Ni_xRh_2S_4 and CuRh_2Se_4: Band Structure Calculations, X-ray Photoemission and Fluorescence Measurements","The electronic structure of spinel-type Cu_(1-x)Ni_xRh_2S_4 (x = 0.0, 0.1,
0.3, 0.5, 1.0) and CuRh_2Se_4 compounds has been studied by means of X-ray
photoelectron and fluorescent spectroscopy. Cu L_3, Ni L_3, S L_(2,3) and Se
M_(2,3) X-ray emission spectra (XES) were measured near thresholds at Beamline
8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES
measurements of the constituent atoms of these compounds, reduced to the same
binding energy scale, are found to be in excellent agreement with XPS valence
bands. The calculated XES spectra which include dipole matrix elements show
that the partial density of states reproduce experimental spectra quite well.
States near the Fermi level (E_F) have strong Rh d and S(Se) p character in all
compounds. In NiRh_2S_4 the Ni 3d states contribute strongly at E_F, whereas in
both Cu compounds the Cu 3d bands are only ~1 eV wide and centered ~2.5 eV
below E_F, leaving very little 3d character at E_F. The density of states at
the Fermi level is less in NiRh_2S_4 than in CuRh_2S_4. This difference may
contribute to the observed decrease, as a function of Ni concentration, in the
superconducting transition temperature in Cu_(1-x)Ni_xRh_2S_4. The density of
states of the ordered alloy Cu_(1/2)Ni_(1/2)Rh_2S_4 shows behavior that is more
``split-band''-like than ``rigid band''-like.",9906209v1
2000-06-14,The Jahn-Teller theorem for the 3d magnetic ions,"We argue that the Jahn-Teller theorem, if applied to 3d-ion compounds, has to
be considered in the orbital+spin space. It is despite of the weakness of the
intraatomic spin-orbit coupling.",0006231v1
2001-02-28,Absence of Superconductivity in BeB2,"The hexagonal BeB2 compound has been prepared and found to be paramagnetic
down to 5 K. The mixed (Mg,Be)B2 system has the same TC =39 K as pure MgB2,
indicating that Be does not replace the Mg atoms.",0102508v1
2001-04-19,"Optical phonons of superconducting infinite-layer compounds Sr_{0.9}Ln_{0.1}CuO_2 (Ln = La, Gd, Sm)","We have identifies the otical phonon modes of the superconducting
infinite-layer compounds Sr$_{0.9}Ln_{0.1}$CuO$_2$ ($Ln$ = La, Gd, Sm; $T_c$ =
43 K for all) from their infrared reflectivity spectra obtained with a
Fourier-transform infrared spectrometer on high-quality high-purity samples
synthesized under high pressure. The La- and the Gd-doped compounds exhibited
only four (2$A_{\rm 2u}$+2$E_{\rm u}$) out of the five (2$A_{\rm 2u}$+3$E_{\rm
u}$) infrared-active phonon modes predicted by a group theoretical analysis
whereas the Sm-doped compound exhibited all five modes. We propose the atomic
displacement pattern for each phonon mode based on reported lattice dynamics
calculations and through comparison with the phonon modes of other single-layer
high-$T_{\rm c}$ cuprate superconductors.",0104352v1
2001-08-05,EXAFS study of Tl$_{0.75}$Cu$_{.25}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ and Cu$_{0.68}$C$_{.32}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ superconductors [bulk] at 300 K,"The results of EXAFS measurements at 300 K for the superconducting compounds
Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ [Tl-1234],
TlBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Tl-1212], and
CuBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Cu-1234]. are reported. We have measured the
EXAFS spectrum for Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ in the
range 10K-300K, however here we limit our discussion to the spectrum at 300 K.
This material is prepared under high pressure [3.5 GPa] from precursors with
small carbon concentrations and exhibits a T$_c$ of $~127$ K. We have also
performed ``aging'' study by looking at XRD for this material after
approximately one year. The XRD results at 300 K are ``unchanged''. It is of
interest to compare the EXAFS spectrum of this compound with the corresponding
compound Cu-1234. Remarks on the choice of appropriate EXAFS standard for this
and related compounds are also given. Based on our data analysis we quantify
disorder in these systems. By using the Cu-O in-plane distance we give values
for the microstrain parameter, which can be related to the charge ordering
transition.",0108085v1
2001-10-08,"Structural and electronic properties of the Nb$_4$-cluster compound Ga$_{1.33}$Nb$_4$X$_8$ (X = S, Se)","We report resistivity, thermopower and magnetic susceptibility measurements
on the Nb$_4$-cluster compounds Ga$_{1.33}$Nb$_4$X$_{8}$ (X = S, Se), derived
from vacancy ordered spinels A$_x$T$_4$X$_8$. The cubic selenide phase is
insulating and its resistivity crosses over from $\ln{\rho} \sim T^{-1}$ to
$\sim T^{-1/2}$ on cooling below 150 K, indicating variable range hopping (VRH)
conduction at low temperatures. This is similar to that previously reported for
V$_4$ and Mo$_4$ cluster compounds. The rhombohedrally distorted sulfide is
metallic and shows a minimum in resistance at $\sim $ 56 K below which the
resistivity varies as $\rho(T) \sim T^{-1/2}$. The thermopower of the selenide
becomes temperature independent below the crossover temperature. These Nb$_4$
compounds exhibit enhanced Pauli-paramagnetic magnetic susceptibility ($\chi$)
irrespective of their transport properties and both undergo a similar
transition in $\chi(T) \sim 30$ K. We discuss these properties in the model of
hopping conduction under long-range Coulomb repulsion effects and derive
consistency between some of the transport and magnetic parameters.",0110155v1
2001-10-16,Intercalation and High Temperature Superconductivity of Fullerides II,"Based on the mechanism described by the authors in cond-mat/0109553, we
predict that the compound C60/CHI3 will have Tc~140K, which would be the
highest value obtained sofar for intercalated materials.",0110327v1
2002-01-14,"Comment on ""Reaction-Limited Island Nucleation in Molecular Beam Epitaxy of Compound Semiconductors""","A Comment on the Letter by P. Kratzer and M. Scheffler,
  Phys. Rev. Lett. 88, 036102 (2002).",0201203v2
2003-05-28,Note on the thermodynamic Bethe Ansatz approach to the quantum phase diagram of the strong coupling ladder compounds,"We investigate the low-temperature phase diagram of the exactly solved su(4)
two-leg spin ladder as a function of the rung coupling $J_{\perp}$ and magnetic
field $H$ by means of the thermodynamic Bethe Ansatz (TBA). In the absence of a
magnetic field the model exhibits three quantum phases, while in the presence
of a strong magnetic field there is no singlet ground state for ferromagnetic
rung coupling. For antiferromagnetic rung coupling, there is a gapped phase in
the regime H < H_{c1}, a fully polarized gapped phase for H > H_{c2} and a
Luttinger liquid magnetic phase in the regime H_{c1} < H < H_{c2}. The critical
behaviour derived using the TBA is consistent with the existing experimental,
numerical and perturbative results for the strong coupling ladder compounds.
This includes the spin excitation gap and the critical fields H_{c1} and
H_{c2}, which are in excellent agreement with the experimental values for the
known strong coupling ladder compounds (5IAP)_2CuBr_4 2H_2 O, Cu_2(C_5 H_{12}
N_2)_2 Cl_4 and (C_5 H_{12} N)_2 CuBr_4. In addition we predict the spin gap
$\Delta \approx J_{\perp}-{1/2}J_{\parallel}$ for the weak coupling compounds
with $J_{\perp} \sim J_{\parallel}$, such as (VO)_2 P_2 O_7, and also show that
the gap opens for arbitrary $J_{\perp}/ J_{\parallel}$.",0305633v1
2004-12-07,Revival of Superconductivity by Y3+/Ca2+ substitution in YBa2Cu2.7Co0.3O7 without reported phase transformation,"Results of phase formation, resistivity (r), and thermo-electric power (S),
are reported on Y1-xCaxBa2Cu2.7Co0.3O7 compounds with x = 0.1 and 0.2. Pristine
compound i.e. without Co or Ca substitution crystallizes in orthorhombic
structure with space group P/mmm. Cu-site Co substituted compound i.e.
YBa2Cu2.7Co0.3O7 is tetragonal. With simultaneous doping of Ca at Y site in Co
substituted compound i.e. Y1-xCaxBa2Cu2.7Co0.3O7 the tetragonal nature still
remains. r(T) measurements showed superconducting transition temperature (Tc)
to decrease from 90K (YBa2Cu3O7) to 33 K for YBa2Cu2.7Co0.3O7 which with
further Ca substitution increases from 33K to 53K (Y0.9 Ca0.1Ba2Cu2.7Co0.3O7)
and 67 K for Y0.8 Ca0.2Ba2Cu2.7Co0.3O7. Tc decreases first with Cu-site Co
substitution by hole-filling and later recovers by simultaneous hole creation
by Y site Ca substitution. Room temperature thermoelectric power S(300 K),
which is an indirect measure of mobile carriers shows the decrease of carriers
with Co doping and creation by Ca substitution. Our results demonstrate the
hole filling by Co substitution is compensated by simultaneous Ca substitution.",0412152v1
2005-07-14,On the role of Calcium in inducing superconductivity - the study of La-2125 superconductors,"Ever since high Tc superconductivity was discovered in La-based mixed oxide
system by Bednorz and Muller, enormous efforts have been put in by several
researchers around the world in understanding the origin and mechanism of
superconductivity in these, as well as in systems derived from them. It is a
proven fact that the superconductivity in RE-123 superconductors is governed by
the oxygen content, which in turn is responsible for the carrier concentration
in the system. Due to their dependence on oxygen content, RE-123
superconductors undergo structural transformation from orthorhombic to
tetragonal as a function of oxygen content making them very difficult compounds
to work with, in terms of technological applications, such as device
fabrication. Hence, it would be interesting to obtain a stable compound whose
superconducting properties, are not only insensitive directly to oxygen content
but, having dependence of its carrier concentration and Tc on the nature and
amount of the substituted cation. In the present work, we focus our
investigations for such a compound, which has been derived from a tetragonal
RE-123 superconducting system.
  In this chapter, we present a brief review of the studies carried out on
La-2125 compounds to elucidate the role of dopants in modifying the
superconducting properties and establish a structure-property correlation in
them.",0507346v2
2005-09-05,"Negative chemical pressure effects induced by Y substitution for Ca on the exotic magnetic behavior of spin-chain compound, Ca3Co2O6","The magnetic behavior of a solid solution, Ca3-xYxCo2O6, based on an exotic
spin-chain compound, Ca3Co2O6, crystallizing in K4CdCl6-derived rhombohedral
structure is investigated. Among the compositions investigated (x= 0.0, 0.3,
0.5, 0.75 and 1.0), single phase formation persists up to x= 0.75, with the
elongation of the c-axis. The present investigations reveal that the
temperature at which the partially disordered antiferromagnetic structure sets
in (which occurs at 24 K for the parent compound, x= 0.0) undergoes gradual
reduction with the substitution of Y for Ca, attaining the value of about 2.2 K
for the nominal x = 1.0. The trend observed in this characteristic temperature
is opposite to that reported under external pressure, thereby establishing that
Y substitution exerts negative chemical pressure. Anomalous steps observed in
the isothermal magnetization at very low temperatures (around 2 K) for x= 0.0,
which have been proposed to arise from quantum tunneling effects are found to
vanish by a small substitution (x = 0.3) of Y for Ca. Systematics in ac and dc
magnetic susceptibility behavior with Y substitution for Ca have also been
probed. We believe that the present results involving the expansion of chain
length without disrupting the magnetic chain may be useful to the overall
understanding of the novel magnetism of the parent compound.",0509106v1
2006-02-26,Physical properties and magnetic structure of TbRhIn5 intermetallic compound,"In this work we report the physical properties of the new intermetallic
compound TbRhIn5 investigated by means of temperature dependent magnetic
susceptibility, electrical resistivity, heat-capacity and resonant x-ray
magnetic diffraction experiments. TbRhIn5 is an intermetallic compound that
orders antiferromagnetically at TN = 45.5 K, the highest ordering temperature
among the existing RRhIn5 (1-1-5, R = rare earth) materials. This result is in
contrast to what is expected from a de Gennes scaling along the RRhIn5 series.
The X-ray resonant diffraction data below TN reveal a commensurate
antiferromagnetic (AFM) structure with a propagation vector (1/2 0 1/2) and the
Tb moments oriented along the c-axis. Strong (over two order of magnitude)
dipolar enhancements of the magnetic Bragg peaks were observed at both Tb
absorption edges LII and LIII, indicating a fairly high polarization of the Tb
5d levels. Using a mean field model including an isotropic first-neighbors
exchange interaction J(R-R) and the tetragonal crystalline electrical field
(CEF), we were able to fit our experimental data and to explain the direction
of the ordered Tb-moments and the enhanced TN of this compound. The evolution
of the magnetic properties along the RRhIn5 series and its relation to CEF
effects for a given rare-earth is discussed.",0602612v1
2006-06-09,First-principles study on the intermediate compounds of LiBH$_4$,"We report the results of the first-principles calculation on the intermediate
compounds of LiBH$_4$. The stability of LiB$_3$H$_8$ and Li$_2$B$_n$H$_n
(n=5-12)$ has been examined with the ultrasoft pseudopotential method based on
the density functional theory. Theoretical prediction has suggested that
monoclinic Li$_2$B$_{12}$H$_{12}$ is the most stable among the candidate
materials. We propose the following hydriding/dehydriding process of LiBH$_4$
via this intermediate compound : LiBH$_4 \leftrightarrow
{1/12}$Li$_{2}$B$_{12}$H$_{12} + {5/6}$ LiH $+ {13/12}$H$_2 \leftrightarrow
$LiH $+$ B $+ {3/2} $H$_2$. The hydrogen content and enthalpy of the first
reaction are estimated to be 10 mass% and 56 kJ/mol H$_2$, respectively, and
those of the second reaction are 4 mass% and 125 kJ/mol H$_2$. They are in good
agreement with experimental results of the thermal desorption spectra of
LiBH$_4$. Our calculation has predicted that the bending modes for the
$\Gamma$-phonon frequencies of monoclinic Li$_2$B$_{12}$H$_{12}$ are lower than
that of LiBH$_4$, while stretching modes are higher. These results are very
useful for the experimental search and identification of possible intermediate
compounds.",0606228v1
2006-09-06,Mapping High-Temperature Superconductors - A Scientometric Approach,"This study has been carried out to analyze the research field of
high-temperature superconductivity and to demonstrate the potential of modern
databases and search systems for generating meta-information. The alkaline
earth (A2) rare earth (RE) cuprate high-temperature superconductors as a
typical inorganic compound family and the corresponding literature were
analyzed by scientometric methods. The time-dependent overall number of
articles and patents and of the publications related to specific compound
subsets and subject categories are given. The data reveal a significant
decrease of basic research activity in this research field. The A2 RE cuprate
species covered by the CAS compound file were analyzed with respect to the
occurrence of specific elements in order to visualize known and unknown
substances and to identify characteristic patterns. The quaternary and
quinternary cuprates were selected and the number of compound species as
function of specific combinations of A2 and RE elements is given. The Cu/O and
RE/A2 ratios of the quaternary cuprate species as function of A2 and RE atoms
are shown. In addition, the research landscape of the MgB2 related publications
was established using STN AnaVist, an analysis tool recently developed by STN
International.",0609114v2
2006-09-10,"Magnetic and magnetoresistance behavior of Tb7Rh3, an intermetallic compound with a negative temperature coefficient of electrical resistivity in the paramagnetic state, and Paramagnetic Giant Magnetoresistance Phenomenon","The results of dc magnetization, electrical and magnetoresistance and heat
capacity measurements (2-300 K) on Tb7Rh3, crystallizing in Th7Fe3-type
hexagonal structure, are reported. In this compound, magnetic ordering sets in
around 90 K with additional transitions at low temperatures and the temperature
coefficient of resistivity (R), dR/dT, is negative over a wide temperature
range in the paramagnetic state. The present magnetization results reveal that
this compound is apparently characterized by rich features in the
magnetic-field-temperature phase diagram. A point of major emphasis is that the
sign of dR/dT in the paramagnetic state can be gradually changed by the
application of magnetic field. As a result, the magnitude of the
magnetoresistance (MR) is rather large even in the vicinity of room temperature
(far above magnetic ordering temperature), in addition to giant MR behavior in
the magnetically ordered state. Viewed together With similar behavior for other
heavy rare-earth members of this series, this class of compounds can be
classified as Paramagnetic Giant Magnetoresistance Systems. A new theoretical
approach is warranted to understand this phenomenon.",0609231v1
2007-02-05,"Infrared study on the electronic structure of alkaline-earth-filled skutterudites AT4Sb12 (A = Sr, Ba; M = Fe, Ru, Os)","The optical conductivity [$\sigma(\omega)$] spectra of alkaline-earth-filled
skutterudites with the chemical formula $A^{2+}M_{4}$Sb$_{12}$ ($A$ = Sr, Ba,
$M$ = Fe, Ru, Os) and a reference material La$^{3+}$Fe$_{4}$Sb$_{12}$ were
obtained and compared with the corresponding band structure calculations and
with calculated $\sigma(\omega)$ spectra to investigate their electronic
structures. At high temperatures, the energy of the plasma edge decreased with
the increasing valence of the guest atoms $A$ in the Fe$_{4}$Sb$_{12}$ cage
indicating hole-type conduction. A narrow peak with a pseudogap of 25 meV was
observed in SrFe$_{4}$Sb$_{12}$, while the corresponding peak were located at
200 and 100 meV in the Ru- and Os-counterparts, respectively. The order of the
peak energy in these compounds is consistent with the thermodynamical
properties in which the Os-compound is located between the Fe- and
Ru-compounds. This indicated that the electronic structure observed in the
infrared $\sigma(\omega)$ spectra directly affects the thermodynamical
properties. The band structure calculation implies the different electronic
structure among these compounds originates from the different $d$ states of the
$M$ ions.",0702090v1
1997-12-08,The Possibility of Large Direct CP Violation in B to K pi-Like Modes Due to Long Distance Rescattering Effects and Implications for the Angle gamma,"We consider the strong rescattering effects that can occur in the decays such
as B -> K pi, K* pi, K rho... and their impact on direct CP violation in these
modes. First we discuss, in general, how the CPT theorem constrains the
resulting pattern of partial rate asymmetries leading to different brands of
direct CP. Traditional discussions have centered around the absorptive part of
the penguin graph which has Delta I=0 in b -> s transitions and as a result
causes ``simple'' CP violation; long-distance final state rescattering effects,
in general, will lead to a different pattern of CP: ``compound'' CP violation.
Predictions of simple CP are quite distinct from that of compound CP. Final
states rescattering phases in B decays are unlikely to be small possibly
causing large compound CP violating partial rate asymmetries in these modes.
CPT theorem requires a cancellation of PRA due to compound CP amongst the
$K\pi$ states themselves; thus there can be no net cancellation with other
states such as K*\pi, K\rho etc. Therefore, each class of such modes, namely K
pi, K rho, K^*pi, K a_1 etc. can have large direct CP emanating from
rescattering effects. Various repercussions for the angle $\gamma$ are also
discussed.",9712287v2
2000-10-22,Divisorial contractions in dimension three which contract divisors to compound A_1 points,"We deal with a divisorial contraction in dimension 3 which contracts its
exceptional divisor to a cA_1 point. We prove that any such contraction is
obtained by a suitable weighted blow-up.",0010207v1
2001-11-12,Effects of shell structure in reactions leading to the same compound nucleus or different isotopes,"The role of the entrance channel in fusion-fission reactions was studied by
the theoretical analysis of the experimental evaporation residue excitation
functions for reactions leading to the same compound nucleus. The evaporation
residues cross sections for xn-channels were calculated in the frame of the
combined dinuclear system concept and advanced statistical model. The revealed
differences between experimental data on the evaporation residues in the
^{40}Ar+^{176}Hf, ^{86}Kr + ^{130}Xe and ^{124}Sn + ^{92}Zr reactions leading
to the ^{216}Th^* compound nucleus are explained by the different spin
distributions of compound nuclei which are formed. It is shown that the
intrinsic fusion barrier B^*_{fus} and size of potential well are different for
every entrance channel.",0111034v2
2000-05-31,Adiabatic Elimination in Compound Quantum Systems with Feedback,"Feedback in compound quantum systems is effected by using the output from one
sub-system (``the system'') to control the evolution of a second sub-system
(``the ancilla'') which is reversibly coupled to the system. In the limit where
the ancilla responds to fluctuations on a much shorter time scale than does the
system, we show that it can be adiabatically eliminated, yielding a master
equation for the system alone. This is very significant as it decreases the
necessary basis size for numerical simulation and allows the effect of the
ancilla to be understood more easily. We consider two types of ancilla: a
two-level ancilla (e.g. a two-level atom) and an infinite-level ancilla (e.g.
an optical mode). For each, we consider two forms of feedback: coherent (for
which a quantum mechanical description of the feedback loop is required) and
incoherent (for which a classical description is sufficient). We test the
master equations we obtain using numerical simulation of the full dynamics of
the compound system. For the system (a parametric oscillator) and feedback
(intensity-dependent detuning) we choose, good agreement is found in the limit
of heavy damping of the ancilla. We discuss the relation of our work to
previous work on feedback in compound quantum systems, and also to previous
work on adiabatic elimination in general.",0005127v1
2006-02-28,Relations Between Quantum Maps and Quantum States,"The relation between completely positive maps and compound states is
investigated in terms of the notion of quantum conditional probability.",0602228v2
2007-04-02,Bonding of H in O vacancies of ZnO,"We investigate the bonding of H in O vacancies of ZnO using density
functional calculations. We find that H is anionic and does not form
multicenter bonds with Zn in this compound.",0704.0173v1
2007-08-07,"Hydrostatic pressure study of pure and doped La1-xRxAgSb2 (R = Ce, Nd) charge-density-wave compounds","The intermetallic compound LaAgSb2 displays two charge-density-wave (CDW)
transitions, which were detected with measurements of electrical resistivity
(rho), magnetic susceptibility, and X-ray scattering; the upper transition
takes place at T1 approx. 210 K, and it is accompanied by a large anomaly in
rho(T), whereas the lower transition is marked by a much more subtle anomaly at
T2 approx. 185 K. We studied the effect of hydrostatic pressure (P) on the
formation of the upper CDW state in pure and doped La1-xRxAgSb2 (R = Ce, Nd)
compounds, by means of measurements of rho(T) for P < 23 kbar. We found that
the hydrostatic pressure, as well as the chemical pressure introduced by the
partial substitution of the smaller Ce and Nd ions for La, result in the
suppression of the CDW ground state, e.g. the reduction of the ordering
temperature T1. The values of dT1/dP are approx. 2-4 times higher for the
Ce-doped samples as compared to pure LaAgSb2, or even La0.75Nd0.25AgSb2
Nd-doped with a comparable T1 (P=0). This increased sensitivity to pressure may
be due to increasing Ce- hybridization under pressure. The magnetic ordering
temperature of the cerium-doped compounds is also reduced by pressure, and the
high pressure behavior of the Ce-doped samples is dominated by Kondo impurity
scattering.",0708.1098v2
2007-11-19,Probing phase coexistence and stabilization of the spin-ordered ferrimagnetic state by Calcium addition in the YBa_{1-x}Ca_{x}Co_{2}O_{5.5} layered cobaltites using neutron diffraction,"In this article we study the effects of a partial substitution of Ba with the
smaller cation Ca in the layered cobaltites YBaCo_2O_{5+\delta} for \delta
\approx 0.5. Neutron thermodiffractograms are reported for the compounds
YBa_{0.95}Ca_{0.05}Co_2O_{5.5} (x_{Ca}=0.05) and YBa_{0.90}Ca_{0.10}Co_2O_{5.5}
(x_{Ca}=0.10) in the temperature range 20 K \leq T \leq 300 K, as well as high
resolution neutron diffraction experiments at selected temperatures for the
samples x_{Ca}=0.05, x_{Ca}=0.10 and the parent compound x_{Ca}=0. We have
found the magnetic properties to be strongly affected by the cationic
substitution. Although the ""122"" perovskite structure seems unaffected by Ca
addition, the magnetic arrangements of Co ions are drastically modified: the
antiferromagnetic (AFM) long-range order is destroyed, and a ferrimagnetic
phase with spin state order is stabilized below T \sim 290 K. For the sample
with x_{Ca}=0.05 a fraction of AFM phase coexists with the ferrimagnetic one
below T \sim 190 K, whereas for x_{Ca}=0.10 the AFM order is completely lost.
The systematic refinement of the whole series has allowed for a better
understanding of the observed low-temperature diffraction patterns of the
parent compound, YBaCo_2O_{5.5}, which had not yet been clarified. A two-phase
scenario is proposed for the x_{Ca}=0 compound which is compatible with the
phase coexistence observed in the x_{Ca}=0.05 sample.",0711.3002v1
2008-03-11,Crucial inputs to nucleosynthesis calculations,"The first part of the paper discusses nuclear properties relevant to predict
compound reactions. The second part addresses direct reactions with special
emphasis on direct neutron capture.",0803.1622v1
2008-06-02,Common Features in Electronic Structure of the Fe-Based Layered Superconductors from Photoemission Spectroscopy,"High resolution photoemission measurements have been carried out on
non-superconducting LaOFeAs parent compound and various superconducting
R(O1-xFx)FeAs (R=La, Ce and Pr) compounds. We found that the parent LaOFeAs
compound shows a metallic character. Through extensive measurements, we have
identified several common features in the electronic structure of these
Fe-based compounds: (1). 0.2 eV feature in the valence band; (2). A universal
13~16 meV feature; (3). A clear Fermi cutoff showing zero leading-edge shift in
the superconducting state;(4). Lack of superconducting coherence peak(s); (5).
Near EF spectral weight suppression with decreasing temperature. These
universal features can provide important information about band structure,
superconducting gap and pseudogap in these Fe-based materials.",0806.0291v2
2008-06-03,Magnetic Anomalies in a New Manganocuprate Gd3Ba2Mn2Cu2O12,"The manganocuprate compound Gd3Ba2Mn2Cu2O12 (Gd-3222) has been synthesized by
conventional solid state reaction method and its magnetic behavior has been
studied by dc and ac magnetization (M) and heat capacity (C) measurements as a
function of temperature (T). This compound crystallizes in a tetragonal
structure (space group I4/mmm). We find that this compound exhibits three
magnetic transitions, around 2.5, 4.8 and 9 K, as inferred from dc and ac
magnetic susceptibility (chi) data. However, no evidence for a well-defined
lambda-anomaly is found in C(T) above 1.8 K, though there is a gradual upturn
below about 10 K. An application of a magnetic field results in a peak around
5K, while ac chi appears to show a very weak frequency dependence below 9 K.
Isothermal M curve at 1.8 K exhibits a weak hysteresis without any evidence for
saturation even at fields as high as 120 kOe. These results imply that this
compound undergoes a spin-glass-like freezing at low temperatures, though the
exact nature of the magnetic transition at 10 K is not clear. The magnitude of
the magnetocaloric effect, as inferred from M and C data, is quite large over a
wide temperature range below 50 K peaking around 4 K.",0806.0456v1
2008-06-30,Coexistence of Supercondcutivity and Magnetism in LaFeAs(O0.94F0.06) Probed by Muon Spin Relaxation,"Recent discovery of oxypnictide superconductor LaFeAs(O,F) (LFAO-F) with the
critical temperature (Tc) of 26 K and succeeding revelation of much increased
Tc upon substitution of La for other rare earth elements (such as Sm, leading
to ~43 K) and application of pressure for LFAO-F (~ 43 K) has triggered broad
interest in the mechanism yielding relatively high Tc in this new class of
compounds. While they share a feature with high-Tc cuprates that
superconductivity occurs upon carrier doping to pristine compound which
exhibits magnetism, they also resemble the heavy-fermion compounds in the sense
that superconductivity appears in the vicinity of magnetic phase. Investigation
of electronic states near the boundary between these two phases might provide
some useful information on the mechanism of superconductivity, as it has been
proved to be the case in many exotic superconductors. Here we show by muon
experiment in the LFAO-F compound that a macroscopic phase separation into
superconducting and spin glass-like magnetic phases occurs at x=0.06 that is
near the phase boundary, where both the magnetism and superconductivity develop
simultaneously below a common Tc ~ 18 K. This accordance strongly suggests
intimate relationship between magnetism and superconductivity typically found
in heavy-fermion systems near the quantum critical point.",0806.4798v2
2008-07-14,Isotope dependence of band-gap energy,"The results of the quantitative investigations of the renormalization of the
absorption edge of different compounds by the isotope effect are described.",0807.2152v1
2008-07-15,Superconductivity in the PbO-type Structure alpha-FeSe,"The recent discovery of superconductivity with relatively high transition
temperature Tc in the layered iron-based quaternary oxypnictides La[ O1-xFx]
FeAs was a real surprise. The excitement generated can be seen by the number of
subsequent works published within a very short period of time. Although there
exists superconductivity in alloy that contains Fe element, LaOMPn (with M= Fe,
Ni; and Pn=P and As) is the first system where Fe-element plays the key role to
the occurrence of superconductivity. LaOMPn has a layered crystal structure
with an Fe-based plane. It is quite natural to ask whether there exists other
Fe based planar compounds that exhibit superconductivity. Here we report the
observation of superconductivity with zero resistance transition temperature at
8K in the PbO-type alpha-FeSe compound. Although FeSe has been studied quite
extensively, a key observation is that the clean superconducting phase exists
only in those samples prepared with intentional Se deficiency. What is truly
striking, is that this compound has the same, perhaps simpler, planar crystal
sublattice as the layered oxypnictides. Furthermore, FeSe is, compared with
LaOFeAs, much easier to handle and fabricate. In view of the abundance of
compounds with PbO type structure, this result opens a new route to the search
for unconventional superconductors.",0807.2369v2
2008-07-20,"Nearly Isotropic superconductivity in (Ba,K)Fe2As2","Superconductivity was recently observed in the iron-arsenic-based compounds
with a superconducting transition temperature (Tc) as high as 56K [1-7],
naturally raising comparisons with the high Tc copper oxides. The copper oxides
have layered crystal structures with quasi-two-dimensional electronic
properties, which led to speculations that reduced dimensionality (that is,
extreme anisotropy) is a necessary prerequisite for superconductivity at
temperatures above 40 K [8,9]. Early work on the iron-arsenic compounds seemed
to support this view [7,10]. Here we report measurements of the electrical
resistivity in single crystals of (Ba,K)Fe2As2 in a magnetic field up to 60 T.
We find that the superconducting properties are in fact quite isotropic, being
rather independent of the direction of the applied magnetic fields at low
temperature. Such behaviour is strikingly different from all previously-known
layered superconductors [9,11], and indicates that reduced dimensionality in
these compounds is not a prerequisite for high-temperature superconductivity.
We suggest that this situation arises because of the underlying electronic
structure of the iron-arsenide compounds, which appears to be much more three
dimensional than that of the copper oxides. Extrapolations of low-field
single-crystal data incorrectly suggest a high anisotropy and a greatly
exaggerated zero-temperature upper critical field.",0807.3137v4
2008-11-28,Metastable states influence on the magnetic behavior of the triangular lattice: Application to the spin-chain compound Ca3Co2O6,"It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting
plateaus in the magnetization as a function of the magnetic field at low
temperatures. The origin of them is still controversial. In this paper we study
the thermal behavior of this compound with a single-flip Monte Carlo simulation
on a triangular lattice and demonstrate the decisive influence of metastable
states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We
consider the [Co2O6]n chains as giant magnetic moments described by large Ising
spins on planar clusters with open boundary conditions. With this simple
frozen-moment model we obtain stepped magnetization curves which agree quite
well with the experimental results for different sweeping rates. We describe
particularly the out-of-equilibrium states that split the low-temperature 1/3
plateau into three steps. They relax thermally to the 1/3 plateau, which has
long-range order at the equilibrium. Such states are further analyzed with
snapshots unveiling a domain-wall structure that is responsible for the
observed behavior of the 1/3 plateau. A comparison is also given of the exact
results in small triangular clusters with our Monte Carlo results, providing
further support for our thermal description of this compound.",0811.4772v1
2009-01-28,"Magnetic, Thermal, and Transport Properties of Layered Arsenides BaRu2As2 and SrRu2As2","The magnetic, thermal and transport properties of polycrystalline BaRu2As2
and SrRu2As2 samples with the ThCr2Si2 structure were investigated by means of
magnetic susceptibility chi(T), electrical resistivity rho(T), and heat
capacity Cp(T) measurements. The temperature (T) dependence of rho indicates
metallic character for both compounds with residual resistivity ratios rho(310
K)/rho(2 K) of 17 and 5 for the Ba and Sr compounds, respectively. The Cp(T)
results reveal a low-T Sommerfeld coefficient gamma = 4.9(1) and 4.1(1) mJ/mol
K^2 and Debye temperature \Theta_D = 271(7) K and 271(4) K for the Ba and Sr
compounds, respectively. The chi (T) was found to be diamagnetic with a small
absolute value for both compounds. No transitions were found for BaRu2As2 above
1.8 K. The chi(T) data for SrRu2As2 exhibit a cusp at \sim 200 K, possibly an
indication of a structural and/or magnetic transition. We discuss the
properties of BaRu2As2 and SrRu2As2 in the context of other ThCr2Si2-type and
ZrCuSiAs-type transition metal pnictides.",0901.4582v2
2009-02-03,Optical and Raman spectroscopy studies on Fe-based superconductors,"A brief review of optical and Raman studies on the Fe-based superconductors
is given, with special emphasis on the competing phenomenon in this system.
Optical investigations on ReFeAsO (Re=rare-earth element) and AFe$_2$As$_2$
(A=alkaline-earth metal) families provide clear evidence for the gap formation
in the broken symmetry states, including the partial gaps in the spin-density
wave states of parent compounds, and the pairing gaps in the superconducting
states for doped compounds. Especially, the superconducting gap has an s-wave
pairing lineshape in hole-doped BaFe$_2$As$_2$. Optical phonons at zone center
detected by Raman and infrared techniques are classified for several Fe-based
compounds. Related issues, such as the electron-phonon coupling and the effect
of spin-density wave and superconducting transitions on phonons, are also
discussed. Meanwhile, open questions including the \emph{T}-dependent
mid-infrared peak at 0.6-0.7 eV, electronic correlation, and the
similarities/differences between high-\Tc cuprates and Fe-based superconductors
are also briefly discussed. Important results from other experimental probes
are compared with optical data to better understand the spin-density wave
properties, the superconductivity, and the multi-band character in Fe-based
compounds.",0902.0435v1
2009-02-26,Phonon spectra in CaFe2As2 and Ca0.6Na0.4Fe2As2: Measurement of the pressure and temperature dependence and comparison with ab-initio and shell model calculations,"We report the pressure and temperature dependence of the phonon
density-of-states in superconducting Ca0.6Na0.4Fe2As2 (Tc=21 K) and the parent
compound CaFe2As2, using inelastic neutron scattering. We observe no
significant change in the phonon spectrum for Ca0.6Na0.4Fe2As2 at 295 K up to
pressures of 5 kbar. The phonon spectrum for CaFe2As2 shows softening of the
low-energy modes by about 1 meV when decreasing the temperature from 300 K to
180 K. There is no appreciable change in the phonon density of states across
the structural and anti-ferromagnetic phase transition at 172 K. These results,
combined with our earlier temperature dependent phonon density of states
measurements for Ca0.6Na0.4Fe2As2, indicate that the softening of low-energy
phonon modes in these compounds may be due to the interaction of phonons with
electron or short-range spin fluctuations in the normal state of the
superconducting compound as well as in the parent compound. The phonon spectra
are analyzed with ab-initio and empirical model calculations giving partial
densities of states and dispersion relations.",0902.4590v1
2009-08-27,Competition and/or Coexistence of Antiferromagnetism and Superconductivity in CeRhIn$_5$ and CeCoIn$_5$,"The Ce compounds CeCoIn$_5$ and CeRhIn$_5$ are ideal model systems to study
the competition of antiferromagnetism (AF) and superconductivity (SC). Here we
discuss the pressure--temperature and magnetic field phase diagrams of both
compounds. In CeRhIn$_5$ the interesting observation is that in zero magnetic
field a coexistence AF+SC phase exist inside the AF phase below the critical
pressure $p_{\rm c}^\star \approx 2$ GPa. Above $p_{\rm c}^\star$ AF is
suppressed in zero field but can be re-induced by applying a magnetic field.
The collapse of AF under pressure coincides with the abrupt change of the Fermi
surface.
  In CeCoIn$_5$ a new phase appears at low temperatures and high magnetic field
(LTHF) which vanishes at the upper critical field $H_{\rm c2}$. In both
compounds the paramagnetic pair breaking effect dominates at low temperature.
We discuss the evolution of the upper critical field under high pressure of
both compounds and propose a simple picture of the glue of reentrant magnetism
to the upper critical field in order to explain the interplay of
antiferromagnetic order and superconductivity.",0908.3980v1
2009-12-09,Phonon dynamics in SrFe2As2 and SrFeAsF parent pnictide compounds: How different/similar when compared to Ca- and Ba-compounds?,"We report detailed measurements of temperature dependence and ab initio
lattice dynamical calculations of the phonon density-of-states of two Sr based
iron pnictide parent compounds; SrFe2As2 and SrFeAsF. Although both compounds
undergo a magnetic as well as a tetragonal-to-orthorhombic structural phase
transitions, no drastic change of their phonon spectra is found in the
temperature range from 2 to 300 K.. In both the systems the Fe-As stretching
modes at 32 meV react to the temperature change and shift towards higher
energies with decreasing temperature. Furthermore, we found that in the
antiferromagnetic phase of SrFe2As2 at 180 K a peak at 25 meV, due to Fe
vibrations, moves slightly to higher energies and become narrower on cooling
from 300 K. However we did not find any evidence of softening of low energy
phonon modes in both SrFe2As2 and SrFeAsF on decreasing the temperature from
300 K in their paramagnetic phase. This is contrary to our earlier observation
of phonon softening in CaFe2As2, Ca0.6Na0.4Fe2As2 and Sr0.6K0.4Fe2As2. For the
sake of comparison, the previously studied Ca- and Ba-cases are also presented
and the role of the magnetic ordering on the calculated phonon spectra in these
two families of pnictides is reported.",0912.1782v3
2009-12-22,Cd-doping effects in Ce2MIn8 (M = Rh and Ir) heavy fermion compounds,"Low temperature magnetic properties of Cd-doped Ce2MIn8 (M = Rh and Ir)
single crystals are investigated. Experiments of temperature dependent magnetic
susceptibility, heat capacity and electrical resistivity measurements revealed
that Cd-doping enhances the antiferromagnetic (AFM) ordering temperature from
TN = 2.8 K (x = 0) to TN = 4.8 K (x = 0.21) for Ce2RhIn8-xCdx and induces long
range AFM ordering with TN = 3.8 K (x = 0.21) for Ce2IrIn8-xCdx. Additionally,
X-ray and neutron magnetic scattering studies showed that Cd-doped samples
present below TN a commensurate antiferromagnetic structure with a propagation
vector (1/2,1/2,0). The resolved magnetic structures for both compounds
indicate that the Cd-doping tends to rotate the direction of the ordered
magnetic moments toward the ab-plane. This result suggests that the Cd-doping
affects the Ce3+ ground state single ion anisotropy modifying the crystalline
electrical field (CEF) parameters at the Ce3+ site. Indications of CEF
evolution induced by Cd-doping were also found in the electrical resistivity
measurements. Comparisons between our results and the general effects of
Cd-doping on the related compounds CeMIn5 (M = Co, Rh and Ir) confirms the
claims that the Cd-doping induced electronic tuning is the main effect favoring
AFM ordering in these compounds.",0912.4467v1
2009-12-28,Iron pnictide superconductors: Electrons on the verge,"An optical analysis reveals that the electronic correlations in the `parent'
compounds of the iron pnictide superconductors are sufficiently strong to
significantly impede the mobility of the electrons.",0912.4989v1
2010-01-25,"Comment on ""Emergence of a Superconducting State from an Antiferromagnetic Phase in Single Crystals of the Heavy Fermion Compound Ce2PdIn8""","Comment to D. Kaczorowski et al., Phys. Rev. Lett. 103, 027003 (2009).",1001.4397v1
2010-04-12,Magnetism in Fe-based superconductors,"In this review, we present a summary of experimental studies of magnetism in
Fe-based superconductors. The doping dependent phase diagram shows strong
similarities to the generic phase diagram of the cuprates. Parent compounds
exhibit magnetic order together with a structural phase transition both of
which are progressively suppressed with doping allowing superconductivity to
emerge. The stripe-like spin arrangement of Fe moments in the magnetically
ordered state shows the identical in-plane structure for the RFeAsO (R=rare
earth) and AFe2As2 (A=Sr, Ca, Ba, Eu and K) parent compounds, notably different
than the spin configuration of the cuprates. Interestingly, Fe1+yTe orders with
a different spin order despite very similar Fermi surface topology. Studies of
the spin dynamics in the parent compounds shows that the interactions are best
characterized as anisotropic three-dimensional (3D) interactions. Despite the
room temperature tetragonal structure, analysis of the low temperature spin
waves under the assumption of a Heisenberg Hamiltonian indicates strong
in-plane anisotropy with a significant next-near neighbor interaction. In the
superconducting state, a resonance, localized in both wavevector and energy is
observed in the spin excitation spectrum as in the cuprates. This resonance is
observed at a wavevector compatible with a Fermi surface nesting instability
independent of the magnetic ordering of the relevant parent compound. The
resonance energy (Er) scales with superconducting transition temperature (TC)
as Er ~4.9 kBTC consistent with the canonical value of ~5 kBTC observed in the
cuprates. Moreover, the relationship between the resonance energy and the
superconducting gap, \Delta, is similar to that observed in many unconventional
superconductors (Er/2\Delta ~ 0.64).",1004.1969v1
2010-10-04,Distributed Storage Codes Meet Multiple-Access Wiretap Channels,"We consider {\it i)} the overhead minimization of maximum-distance separable
(MDS) storage codes for the repair of a single failed node and {\it ii)} the
total secure degrees-of-freedom (S-DoF) maximization in a multiple-access
compound wiretap channel. We show that the two problems are connected.
Specifically, the overhead minimization for a single node failure of an {\it
optimal} MDS code, i.e. one that can achieve the information theoretic overhead
minimum, is equivalent to maximizing the S-DoF in a multiple-access compound
wiretap channel. Additionally, we show that maximizing the S-DoF in a
multiple-access compound wiretap channel is equivalent to minimizing the
overhead of an MDS code for the repair of a departed node. An optimal MDS code
maps to a full S-DoF channel and a full S-DoF channel maps to an MDS code with
minimum repair overhead for one failed node. We also state a general framework
for code-to-channel and channel-to-code mappings and performance bounds between
the two settings. The underlying theme for all connections presented is
interference alignment (IA). The connections between the two problems become
apparent when we restate IA as an optimization problem. Specifically, we
formulate the overhead minimization and the S-DoF maximization as rank
constrained, sum-rank and max-rank minimization problems respectively. The
derived connections allow us to map repair strategies of recently discovered
repair codes to beamforming matrices and characterize the maximum S-DoF for the
single antenna multiple-access compound wiretap channel.",1010.0485v1
2010-10-14,"Bipolaron Model of the Superconductivity of an Iron-Based Layered Compound LnO_{1-x}F_xFePn (Ln =La, Sm, Nd, Pr, Ce, Pn=P, As)","A bipolaron model is proposed as a superconductivity mechanism for iron-based
superconductivity. The results are consistent with the experiments.",1010.3026v1
2011-02-17,Analytic Loss Distributional Approach Model for Operational Risk from the alpha-Stable Doubly Stochastic Compound Processes and Implications for Capital Allocation,"Under the Basel II standards, the Operational Risk (OpRisk) advanced
measurement approach is not prescriptive regarding the class of statistical
model utilised to undertake capital estimation. It has however become well
accepted to utlise a Loss Distributional Approach (LDA) paradigm to model the
individual OpRisk loss process corresponding to the Basel II Business
line/event type. In this paper we derive a novel class of doubly stochastic
alpha-stable family LDA models. These models provide the ability to capture the
heavy tailed loss process typical of OpRisk whilst also providing analytic
expressions for the compound process annual loss density and distributions as
well as the aggregated compound process annual loss models. In particular we
develop models of the annual loss process in two scenarios. The first scenario
considers the loss process with a stochastic intensity parameter, resulting in
an inhomogeneous compound Poisson processes annually. The resulting arrival
process of losses under such a model will have independent counts over
increments within the year. The second scenario considers discretization of the
annual loss process into monthly increments with dependent time increments as
captured by a Binomial process with a stochastic probability of success
changing annually. Each of these models will be coupled under an LDA framework
with heavy-tailed severity models comprised of $\alpha$-stable severities for
the loss amounts per loss event. In this paper we will derive analytic results
for the annual loss distribution density and distribution under each of these
models and study their properties.",1102.3582v1
2011-04-18,Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides,"The iron pnictide and chalcogenide compounds are a subject of intensive
investigations due to their high temperature superconductivity.\cite{a-LaFeAsO}
They all share the same structure, but there is significant variation in their
physical properties, such as magnetic ordered moments, effective masses,
superconducting gaps and T$_c$. Many theoretical techniques have been applied
to individual compounds but no consistent description of the trends is
available \cite{np-review}. We carry out a comparative theoretical study of a
large number of iron-based compounds in both their magnetic and paramagnetic
states. We show that the nature of both states is well described by our method
and the trends in all the calculated physical properties such as the ordered
moments, effective masses and Fermi surfaces are in good agreement with
experiments across the compounds. The variation of these properties can be
traced to variations in the key structural parameters, rather than changes in
the screening of the Coulomb interactions. Our results provide a natural
explanation of the strongly Fermi surface dependent superconducting gaps
observed in experiments\cite{Ding}. We propose a specific optimization of the
crystal structure to look for higher T$_c$ superconductors.",1104.3454v1
2011-04-18,Thermal Expansion in 3d-Metal Prussian Blue Analogs - A Survey Study,"We present a comprehensive study of the structural properties and the thermal
expansion behavior of 17 different Prussian Blue Analogs (PBAs) with
compositions MII3[(M')III(CN)6]2.nH2O and MII2[FeII(CN)6].nH2O, where MII = Mn,
Fe, Co, Ni, Cu and Zn, (M')III = Co, Fe and n is the number of water molecules,
which range from 5 to 18 for these compounds. The PBAs were synthesized via
standard chemical precipitation methods, and temperature-dependent X-ray
diffraction studies were performed in the temperature range between -150oC (123
K) and room-temperature. The vast majority of the studied PBAs were found to
crystallize in cubic structures of space groups, and . The temperature
dependence of the lattice parameters was taken to compute an average
coefficient of linear thermal expansion in the studied temperature range. Of
the 17 compounds, 9 display negative values for the average coefficient of
linear thermal expansion, which can be as large as 39.7 x 10-6 K-1 for
Co3[Co(CN)6]2.12H2O. All of the MII3[CoIII(CN)6]2.nH2O compounds show negative
thermal expansion behavior, which correlates with the Irving-Williams series
for metal complex stability. The thermal expansion behavior for the PBAs of the
MII3[FeIII(CN)6]2.nH2O family are found to switch between positive (for M = Mn,
Co, Ni) and negative (M = Cu, Zn) behavior, depending on the choice of the
metal cation (M). On the other hand, all of the MII2[FeII(CN)6].nH2O compounds
show positive thermal expansion behavior.",1104.3554v2
2011-05-25,"Antiferromagnetism, superconductivity, and pseudogap in three-layered high-T_c cuprates Ba_2Ca_2Cu_3O_6(F,O)_2 probed by Cu-NMR","We report on the phase diagram of antiferromagnetism (AFM) and
superconductivity (SC) in three-layered Ba_2Ca_2Cu_3O_6(F,O)_2 by means of
Cu-NMR measurements. It is demonstrated that AFM and SC uniformly coexist in
three-layered compounds as well as in four- and five-layered ones. The critical
hole density p_c for the long range AFM order is determined as p_c ~ 0.075,
which is larger than p_c ~ 0.02 and 0.055 in single- and bi-layered compounds,
and smaller than p_c ~ 0.08-0.09 and 0.10-0.11 in four- and five-layered
compounds, respectively. This variation of p_c is attributed to the magnetic
interlayer coupling which becomes stronger as the stacking number of CuO_2
layers increases; that is, the uniform coexistence of AFM and SC is a universal
phenomenon in underdoped regions when a magnetic interlayer coupling is strong
enough to stabilize an AFM ordering. In addition, we highlight an unusual
pseudogap behavior in three-layered compounds -- the gap behavior in low-energy
magnetic excitations collapses in an underdoped region where the ground state
is the AFM-SC mixed phase.",1105.5168v1
2011-07-12,Complex magneto-elastic properties in the frustrated kagome-staircase compounds (Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$,"High resolution heat capacity and thermal expansion experiments performed on
single crystalline kagome-staircase compounds (Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$
are presented. The parent compounds Co$_3$V$_2$O$_8$ and Ni$_3$V$_2$O$_8$
undergo a complex sequence of first- and second-order magnetic phase
transitions. The low-temperature ($T<40$ K) magnetic entropy evolves
monotonously with the doping content $x$, from the full S=1 Ni$^{2+}$ magnetic
entropy in Ni$_3$V$_2$O$_8$ to half of the S=3/2 Co$^{2+}$ magnetic entropy in
Co$_3$V$_2$O$_8$. Thermal expansion coefficients $\alpha_i$ ($i = a$, $b$ and
$c$) show a strong anisotropy for all (Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$
compounds. The low-temperature magnetic distortion indicates that Co-doping
(Ni-doping) has similar effects to applying a uniaxial pressures along $a$ or
$b$ ($c$). Linear Gr\""{u}neisen parameters $\Gamma_i$ are extracted for the
three main axes $i$ and exhibit a complex behavior with both temperature and
doping. For each axis, $\Gamma_i$ and $\alpha_i$ exhibit a sign change (at low
temperature) at the critical concentration $x_c\simeq0.25$, at which the
incommensurate magnetic propagation vector changes. Beyond our study, an
understanding of the multiple and complex parameters (magnetic frustration,
magnetic anisotropy, mixture of S=1 and S=3/2 ions, etc.) is now necessarily to
bring light to the rich magneto-elastic properties of
(Co$_{1-x}$Ni$_x$)$_3$V$_2$O$_8$.",1107.2230v1
2011-08-01,Sn1-xBixO2 and Sn1-xTaxO2 (0 \leq x \leq 0.75): A first-principles study,"The structural, elastic, electronic and optical (x = 0) properties of doped
Sn1-xBixO2 and Sn1-xTaxO2 (0 \leq x \leq 0.75) are studied by using the
first-principles pseudopotential plane-wave method within the local density
approximation. The independent elastic constants Cij and other elastic
parameters of these compounds have been calculated for the first time. The
mechanical stability of the compounds with different doping concentrations has
also been studied. The electronic band structure and density of states are
calculated and the effect of doping on these properties is also analyzed. It is
seen that the band gap of the undoped compound narrowed with dopant
concentration which disappeared for x = 0.26 for Bi doping and 0.36 for Ta
doping. The materials thus become conductive oxides through the change in the
electronic properties of the compound for x \leq 0.75 which may be useful for
potential application. The calculated optical properties, e.g. dielectric
function, refractive index, absorption spectrum, loss-function, reflectivity
and conductivity of the undoped SnO2 in two polarization directions are
compared with both previous calculations and measurements.
  Keywords: Doped SnO2; First-principles; Mechanical properties; Electronic
band structure; Optical properties.",1108.0245v2
2011-10-20,Phase stability and physical properties of hypothetical V4SiC3,"We study the phase stability, mechanical, electronic, optical properties and
Vicker's hardness of the newly predicted layered compound V4SiC3 using the
first-principles method. This hypothetical compound is found to possess higher
bulk modulus as well as higher hardness than those of a similar V4AlC3. The
Mulliken bond population analysis indicates that the substitution of Al atom
with the Si atom increases the Vicker's hardness of this compound. The
electronic band structure shows that the conductivity is metallic and the main
contribution comes from V 3d states. The partial density of states (PDOS) shows
that the hybridization peak of V 3d and C 2s lies lower in energy than that of
V 3d and Si 3p states which suggests that the V 3d - C 2s bond is stronger than
the V 3d - Si 3p bond. The results are consistent with our bond analysis.
Further we have discussed the origin of the features that appear in the optical
properties. V4SiC3 is seen as a promising dielectric material showing a much
better candidate material as a coating to avoid solar heating than those of
V4AlC3, {\alpha}-Nb4SiC3 and Ti4AlN3 compounds.
  Keywords: MAX phase V4SiC3; Phase stability; Electronic properties; Optical
properties; Vicker's hardness.
  PACS: 61.66.Fn, 62.20.-x, 62.20.Dc, 71.15Mb, 78.20.Ci",1110.4452v2
2011-11-03,"Phase stability and physical properties of Ta5Si3 compounds from first-principles calculations,","We present a study of the thermodynamic and physical properties of Ta5Si3
compounds by means of density functional theory based calculations. Among the
three different structures (D8m, D8l, D88), the D8l structure (Cr5B3-prototype)
is the low temperature phase with a high formation enthalpy of -449.20kJ/mol,
the D8m structure (W5Si3-prototype) is the high temperature phase with a
formation enthalpy of -419.36kJ/mol, and the D88 structure (Mn5Si3-prototype)
is a metastable phase. The optimized lattice constants of the different Ta5Si3
compounds are also in good agreement with the experimental data. The electronic
density of states (DOS) and the bonding charge density have also been
calculated to elucidate the bonding mechanism in these compounds and the
results indicate that bonding is mostly of covalent nature. The elastic
constants of the D8m and D8l structures have been calculated together with the
different moduli. Finally, by using a quasiharmonic Debye model, the Debye
temperature, the heat capacity, the coefficient of thermal expansion and the
Gr\""uneisen parameter have also been obtained in the present work. The
transformation temperature (2303.7K) between the D8m and the D8l structures has
been predicted by means of the Gibbs energy, and this predicted temperature
(2303.7K) is close to the experimental value (2433.5K).",1111.0792v1
2012-04-17,Chaos-induced enhancement of resonant multielectron recombination in highly charged ions: Statistical theory,"A statistical theory of resonant multielectron recombination based on
properties of chaotic eigenstates is developed. The level density of many-body
states increases exponentially with the number of excited electrons. When the
residual electron-electron interaction exceeds the interval between these
levels, the eigenstates (called compound states or compound resonances if these
states are in the continuum) become ""chaotic"" superpositions of large numbers
of Hartree-Fock configurational basis states. This situation takes place in
some rare-earth atoms and many open-shell multiply charged ions excited in the
process of electron recombination. Our theory describes resonant multielectron
recombination via dielectronic doorway states leading to such compound
resonances. The result is a radiative capture cross section averaged over a
small energy interval containing several compound resonances. In many cases
individual resonances are not resolved experimentally (since the interval
between them is small, e.g., $\le 1$ meV, possibly even smaller than their
radiative widths), therefore, our statistical theory should correctly describe
the experimental data. We perform numerical calculations of the recombination
cross sections for tungsten ions W$^{q+}$, $q=18$--25. The recombination rate
for W$^{20+}$ measured recently [Phys. Rev. A {\bf 83}, 012711 (2011)] is
$10^3$ greater than the direct radiative recombination rate at low energies,
and our result for W$^{20+}$ agrees with the measurements.",1204.3707v1
2012-04-30,The monetary growth order,"Growth of monetary assets and debts is commonly described by the formula of
compound interest which for the case of continuous compounding is the
exponential growth law. Its differential form is dc/dt = i c where dc/dt
describes the rate of monetary growth, i the compounded interest rate and c the
actual principal. Exponential growth of this type is fixed to be neither
resource-limited nor self-limiting which is in contrast to real economic growth
(such as the GDP) which may have exponential, but also subexponential, linear,
saturation, and even decline phases. As a result assets and debts commonly
outgrow their economic fundament giving rise to the financial equivalent of
Malthusian catastrophes after a certain interval of time. We here introduce an
alternative for exponential compounding and propose to replace dc/dt = i c by
dc/dt = i c^p where the exponent p (called reaction order in chemistry) is a
quantity which will be termed monetary growth order. The monetary growth order
p is seen as a tuning handle which enables to adjust gross monetary growth to
real economic growth. It is suggested that the central banks take a serious
look to this control instrument which allows tuning in crisis situations and
immediate return to the exponential norm if needed.",1204.6590v1
2012-05-27,Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of K$_x$Fe$_{2-y}$Se$_2$,"The recently discovered K-Fe-Se high temperature superconductor has caused
heated debate regarding the nature of its parent compound. Transport,
angle-resolved photoemission spectroscopy, and STM measurements have suggested
that its parent compound could be insulating, semiconducting or even metallic
[M. H. Fang, H.-D. Wang, C.-H. Dong, Z.-J. Li, C.-M. Feng, J. Chen, and H. Q.
Yuan, Europhys. Lett. 94, 27009 (2011); F. Chen et al. Phys. Rev. X 1, 021020
(2011); and W. Li et al.,Phys. Rev. Lett. 109, 057003 (2012)]. Because the
magnetic ground states associated with these different phases have not yet been
identified and the relationship between magnetism and superconductivity is not
fully understood, the real parent compound of this system remains elusive.
Here, we report neutron-diffraction experiments that reveal a semiconducting
antiferromagnetic (AFM) phase with rhombus iron vacancy order. The magnetic
order of the semiconducting phase is the same as the stripe AFM order of the
iron pnictide parent compounds. Moreover, while the root5*root5 block AFM phase
coexists with superconductivity, the stripe AFM order is suppressed by it. This
leads us to conjecture that the new semiconducting magnetic ordered phase is
the true parent phase of this superconductor.",1205.5992v2
2012-06-13,Magnetic anomalies in single crystalline Tb5Si3,"The polycrystalline form of the compound, Tb5Si3, crystallizing in
Mn5Si3-type hexagonal structure, which was earlier believe to order
antiferromagnetically below 69 K, has been recently reported by us to exhibit
interesting magnetoresistance (MR) anomalies. In order to understand the
magnetic anomalies of this compound better, we synthesized single crystals of
this compound and subjected them to intense magnetization and MR studies. The
results reveal that the magnetic behavior is strongly anisotropic as the easy
axis is along a basal plane. There appear to be multiple magnetic features in
the close vicinity of 70 K. In addition, there are multiple steps in isothermal
magnetization (which could not be resolved in the data for polycrystalline
data) for magnetic-field (H) along a basal plane. The sign of MR is positive in
the magnetically ordered state, and, interestingly, the magnitude dramatically
increases at the initial step for H parallel to basal plane, but decreases at
subsequent steps as though the origin of these steps are different. However,
for the perpendicular orientation (H || [0 0 0 1]), there is no evidence for
any step either in M(H) or in MR(H). These results establish this compound is
an interesting magnetic material.",1206.2738v1
2012-06-15,"Comment on ""Anisotropic Critical Magnetic Fluctuations in the Ferromagnetic Superconductor UCoGe""","We have presented the potential explanation of nonvanishing at q=0 Landau
damping measured experimentally in ferromagnetic compounds UGe2 and UCoGe based
on possible intersection of the Fermi sheets corresponding different bands.",1206.3468v1
2012-08-06,Electronic structure of Pt-doped superconductor CaFe1-xPtxAs2,"We have computed complete electronic structure of new Pt-doped superconductor
CaFe1-xPtxAs2. Our findings for the parent compound of this superconductor
agree well with experimental predictions.",1208.1219v1
2012-08-23,Capacity of Compound MIMO Gaussian Channels with Additive Uncertainty,"This paper considers reliable communications over a multiple-input
multiple-output (MIMO) Gaussian channel, where the channel matrix is within a
bounded channel uncertainty region around a nominal channel matrix, i.e., an
instance of the compound MIMO Gaussian channel. We study the optimal transmit
covariance matrix design to achieve the capacity of compound MIMO Gaussian
channels, where the channel uncertainty region is characterized by the spectral
norm. This design problem is a challenging non-convex optimization problem.
However, in this paper, we reveal that this problem has a hidden convexity
property, which can be exploited to map the problem into a convex optimization
problem. We first prove that the optimal transmit design is to diagonalize the
nominal channel, and then show that the duality gap between the capacity of the
compound MIMO Gaussian channel and the min-max channel capacity is zero, which
proves the conjecture of Loyka and Charalambous (IEEE Trans. Inf. Theory, vol.
58, no. 4, pp. 2048-2063, 2012). The key tools for showing these results are a
new matrix determinant inequality and some unitarily invariant properties.",1208.4656v5
2013-02-16,Generic Strategies for Chemical Space Exploration,"Computational approaches to exploring ""chemical universes"", i.e., very large
sets, potentially infinite sets of compounds that can be constructed by a
prescribed collection of reaction mechanisms, in practice suffer from a
combinatorial explosion. It quickly becomes impossible to test, for all pairs
of compounds in a rapidly growing network, whether they can react with each
other. More sophisticated and efficient strategies are therefore required to
construct very large chemical reaction networks.
  Undirected labeled graphs and graph rewriting are natural models of chemical
compounds and chemical reactions. Borrowing the idea of partial evaluation from
functional programming, we introduce partial applications of rewrite rules.
Binding substrate to rules increases the number of rules but drastically prunes
the substrate sets to which it might match, resulting in dramatically reduced
resource requirements. At the same time, exploration strategies can be guided,
e.g. based on restrictions on the product molecules to avoid the explicit
enumeration of very unlikely compounds. To this end we introduce here a generic
framework for the specification of exploration strategies in graph-rewriting
systems. Using key examples of complex chemical networks from sugar chemistry
and the realm of metabolic networks we demonstrate the feasibility of a
high-level strategy framework.
  The ideas presented here can not only be used for a strategy-based chemical
space exploration that has close correspondence of experimental results, but
are much more general. In particular, the framework can be used to emulate
higher-level transformation models such as illustrated in a small puzzle game.",1302.4006v2
2013-04-15,Thermodynamic stability of alkali metal/zinc double-cation borohydrides at low temperatures,"We study the thermodynamic stability at low temperatures of a series of
alkali metal/zinc double-cation borohydrides, including LiZn(BH$_4$)$_3$,
LiZn$_2$(BH$_4$)$_5$, NaZn(BH$_4$)$_3$, NaZn$_2$(BH$_4$)$_5$, KZn(BH$_4$)$_3$,
and KZn$_2$(BH$_4$)$_5$. While LiZn$_2$(BH$_4$)$_5$, NaZn(BH$_4$)$_3$,
NaZn$_2$(BH$_4$)$_5$ and KZn(BH$_4$)$_3$ were recently synthesized,
LiZn(BH$_4$)$_3$ and KZn$_2$(BH$_4$)$_5$ are hypothetical compounds. Using the
minima-hopping method, we discover two new lowest-energy structures for
NaZn(BH$_4$)$_3$ and KZn$_2$(BH$_4$)$_5$ which belong to the $C2/c$ and $P2$
space groups, respectively. These structures are predicted to be both
thermodynamically stable and dynamically stable, implying that their existence
may be possible. On the other hand, the lowest-energy $P1$ structure of
LiZn(BH$_4$)$_3$ is predicted to be unstable, suggesting a possible reason
elucidating why this compound has not been experimentally identified. In
exploring the low-energy structures of these compounds, we find that their
energetic ordering is sensitive to the inclusion of the van der Waals
interactions. We also find that a proper treatment of these interactions, e.g.,
as given by a non-local density functional such as vdW-DF2, is necessary to
address the stability of the low-energy structures of these compounds.",1304.4088v2
2013-04-16,"Magnetoelectric coupling in Haldane spin chain system, Dy2BaNiO5","We report the results of various measurements, namely magnetization, complex
dielectric permittivity and electric polarization (P) on Dy2BaNiO5 as a
function of temperature (T) and magnetic-field (H), apart from heat-capacity
(C), with the primary motivation of exploring the existence of magnetoelectric
(ME) coupling among Haldane spin-chain systems. The M(T) and C(T) data
establish long range magnetic ordering at 58K. The most noteworthy observations
are: (i) Distinct anomalies are observed in dielectric constant ({\epsilon}')
vs T and loss (tan{\delta}) vs T at different temperatures, i.e. 12.5, 30, 50
and 58K; at low temperatures, three magnetic-field-induced transitions are
observed in {\epsilon}' vs H at 6, 40 and 60 kOe. These transition temperatures
and critical magnetic fields track those obtained from magnetization data. This
establishes the existence of strong magnetoelectric coupling in this compound.
(ii) Correspondingly, electric polarization could be observed as a function of
T and H in the magnetically ordered state, thereby indicating magnetism-induced
ferroelectricity in this compound; this result suggests that this compound is a
possible new multiferroic material among spin = 1 (nickel containing) compounds
with successive magnetic transitions and strong magnetoelectric coupling.",1304.4550v2
2013-05-02,Magnetic and electric properties of CaMn7O12 based multiferroic compounds: effect of electron doping,"The mixed-valent multiferroic compound CaMn7O12 is studied for its magnetic
and electric properties. The compound undergoes magnetic ordering below 90 K
with a helimagnetic structure followed by a low temperature magnetic anomaly
observed around 43 K. The present study shows that the magnetic anomaly at 43 K
is associated with thermal hysteresis indicating first order nature of the
transition. The compound also shows field-cooled magnetic memory and relaxation
below 43 K, although no zero-field-cooled memory is present. Clear magnetic
hysteresis loop is present in the magnetization versus field measurements
signifying the presence of some ferromagnetic clusters in the system. We doped
trivalent La at the cite of divalent Ca expecting to enhance the fraction of
Mn$^{3+}$ ions. The La doped samples show reduced magnetization, although the
temperatures associated with the magnetic anomalies remain almost unaltered.
Interestingly, the spontaneous electrical polarization below 90 K increases
drastically on La substitution. We propose that the ground state of the pure as
well as the La doped compositions contain isolated superparamagnetic like
clusters, which can give rise to metastability in the form of field-cooled
memory and relaxation. The ground state is not certainly spin glass type as it
is evident from the absence of zero-field-cooled memory and frequency shift in
the ac suceptibility measurements.",1305.0351v1
2013-06-04,"The reltation between the electronic structure and thermoelectric transport properties for Zintl compounds M2Zn5As4 (M=K, Rb)","The electronic structure and thermoelectric properties of are studied by the
first principles and the semiclassical BoltzTrap theory.",1306.0648v1
2013-08-05,"Enhancement of superconductivity near the pressure-induced semiconductor-metal transition in BiS2-based compounds LnO(0.5)F(0.5)BiS2 (Ln = La, Ce, Pr, Nd)","Measurements of electrical resistivity were performed between 3 and 300 K at
various pressures up to 2.8 GPa on the BiS2-based superconductors
LnO0.5F0.5BiS2 (Ln = Pr, Nd). At lower pressures, PrO0.5F0.5BiS2 and
NdO0.5F0.5BiS2 exhibit superconductivity with critical temperatures Tc of 3.5
and3.9 K, respectively. As pressure is increased, both compounds undergo a
transition at a pressure Pt from a low Tc superconducting phase to a high Tc
superconducting phase in which Tc reaches maximum values of 7.6 and 6.4 K for
PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced
transition is characterized by a rapid increase in Tc within a small range in
pressure of ~0.3 GPa for both compounds. In the normal state of PrO0.5F0.5BiS2,
the transition pressure Pt correlates with the pressure where the suppression
of semiconducting behaviour saturates. In the normal state of NdO0.5F0.5BiS2,
Pt is coincident with a semiconductor-metal transition. This behaviour is
similar to the results recently reported for the LnO0.5F0.5BiS2 (Ln = La, Ce)
compounds. We observe that Pt and the size of the jump in Tc between the two
superconducting phases both scale with the lanthanide element in LnO0.5F0.5BiS2
(Ln = La, Ce, Pr, Nd).",1308.1072v3
2013-08-12,Spin ladders and quantum simulators for Luttinger liquids,"Magnetic insulators have proven to be usable as quantum simulators for
itinerant interacting quantum systems. In particular the compound
(C$_{5}$H$_{12}$N)$_{2}$CuBr$_{4}$ (short (Hpip)$_{2}$CuBr$_{4}$) was shown to
be a remarkable realization of a Tomonaga-Luttinger liquid (TLL) and allowed to
quantitatively test the TLL theory. Substitution weakly disorders this class of
compounds and allows thus to use them to tackle questions pertaining to the
effect of disorder in TLL as well, such as the formation of the Bose glass. As
a first step in this direction we present in this paper a study of the
properties of the related (Hpip)$_{2}$CuCl$_{4}$ compound. We determine the
exchange couplings and compute the temperature and magnetic field dependence of
the specific heat, using a finite temperature Density Matrix Renormalization
group (DMRG) procedure. Comparison with the measured specific heat at zero
magnetic field confirms the exchange parameters and Hamiltonian for the
(Hpip)$_{2}$CuCl$_{4}$ compound, giving the basis needed to start studying the
disorder effects.",1308.2712v1
2013-09-16,A stable compound of helium and sodium at high pressure,"Helium is generally understood to be chemically inert and this is due to its
extremely stable closed-shell electronic configuration, zero electron affinity
and an unsurpassed ionization potential. It is not known to form
thermodynamically stable compounds, except a few inclusion compounds. Here,
using the ab initio evolutionary algorithm USPEX and subsequent high-pressure
synthesis in a diamond anvil cell, we report the discovery of a
thermodynamically stable compound of helium and sodium, Na2He, which has a
fluorite-type structure and is stable at pressures >113 GPa. We show that the
presence of He atoms causes strong electron localization and makes this
material insulating. This phase is an electride, with electron pairs localized
in interstices, forming eight-centre two-electron bonds within empty Na8 cubes.
We also predict the existence of Na2HeO with a similar structure at pressures
above 15 GPa.",1309.3827v4
2013-11-05,Cluster glass magnetism in the phase-separated Nd2/3Ca1/3MnO3 perovskite,"A detailed study of the low-temperature magnetic state and the relaxation in
the phase-separated colossal magnetoresistance Nd2/3Ca1/3MnO3 perovskite has
been carried out. Clear experimental evidence of the cluster-glass magnetic
behavior of this compound has been revealed. Well defined maxima in the
in-phase linear ac susceptibility $\chi ^{/}(T)$ were observed, indicative of
the magnetic glass transition at $T_{g}$ = 60 K. Strongly divergent
zero-field-cooled and field-cooled static magnetizations and frequency
dependent ac susceptibility are evident of the glassy-like magnetic state of
the compound at low temperatures. The frequency dependence of the cusp
temperature Tmax of the $\chi ^{/}(T)$ susceptibility was found to follow the
critical slowing down mechanism. The Cole-Cole analysis of the dynamic
susceptibility at low temperature has shown extremely broad distribution of
relaxation times, indicating that spins are frozen at ""macroscopic"" time scale.
Slow relaxation in the zero-field-cooled magnetization has been experimentally
revealed. The obtained results do not agree with a canonical spin-glass state
and indicate a cluster glass magnetic state of the compound below $T_{g}$,
associated with its antiferromagnetic-ferromagnetic nano-phase segregated
state. It was found that the relaxation mechanisms below the cluster glass
freezing temperature $T_{g}$ and above it are strongly different. Magnetic
field up to about $\mu_{0}$H = 0.4 T suppresses the glassy magnetic state of
the compound.",1311.1123v2
2013-11-06,First-principles evidence of Mn moment canting in hole-doped Ba$_{1-2x}$K$_{2x}$Mn$_{2}$As$_{2}$,"The compound BaFe$_{2}$As$_{2}$ is the proptotypical example of the 122
family of high-$T_{c}$ Fe-based superconductors that crystallize in the
ThCr$_{2}$Si$_{2}$ structure. Isostructural compounds can be formed by
replacing Fe with another transition metal; using Mn produces the material
BaMn$_{2}$As$_{2}$, which unlike its Fe-based cousin has an insulating ground
state with a large magnetic moment of $3.9 \mu_{B}$ and G-type
antiferromagnetic order. Despite its lack of superconductivity, the material is
interesting in its own right. Recent experimental studies have shown that
hole-doping the compound by substituting K for Ba leads to metallic behavior
and a spontaneous, weak, in-plane magnetization, which was attributed to the
holes fully polarizing independent of the Mn moments, producing half-metallic
behavior. However the observed in-plane magnetization can also be understood as
a small canting of the Mn moments. Using density functional theory, we
demonstrate that a Mn moment canting occurs upon hole-doping the compound. We
argue that this is due to the competition between the super- and double
exchange interactions, which we support using a simple tight-binding model of
the superexchange-double exchange interaction and the Andersen Force Theorem.
Our calculations also rule out an in-plane polarization of As holes as an
explanation for the in-plane magnetization.",1311.1537v1
2013-12-04,Mössbauer studies of the peculiar magnetism in parent compounds of the iron-based superconductors,"A review of the magnetism in the parent compounds of the iron-based
superconductors is given based on the transmission Moessbauer spectroscopy of
57Fe and 151Eu. It was found that the 3d magnetism is of the itinerant
character with varying admixture of the spin-polarized covalent bonds. For the
122 compounds a longitudinal spin density wave (SDW) develops. In the case of
the EuFe2As2 a divalent europium orders antiferromagnetically at much lower
temperature as compared to the onset of SDW. These two magnetic systems remain
almost uncoupled one to another. For the non-stoichiometric Fe(1+x)Te parent of
the 11 family one has a transversal SDW and magnetic order of the interstitial
iron with relatively high and localized magnetic moments. These two systems are
strongly coupled one to another. For the grand parent of the iron-based
superconductors FeAs one observes two mutually orthogonal phase-related
transversal SDW on the iron sites. There are two sets of such spin arrangements
due to two crystallographic iron sites. The FeAs exhibits the highest covalency
among compounds studied, but it has still a metallic character.",1312.1152v1
2014-01-26,Lattice parameters and stability of the spinel compounds in relation to the ionic radii and electronegativities of constituting chemical elements,"A thorough consideration of the relation between the lattice parameters of
185 binary and ternary spinel compounds, on one side, and ionic radii and
electronegativities of the constituting ions, on the other side, allowed for
establishing a simple empirical model and finding its linear equation, which
links together the above-mentioned quantities. The derived equation gives good
agreement between the experimental and modeled values of the lattice parameters
in the considered group of spinels, with an average relative error of about 1%
only. The proposed model was improved further by separate consideration of
several groups of spinels, depending on the nature of the anion (oxygen,
sulfur, selenium/tellurium, nitrogen). The developed approach can be
efficiently used for prediction of lattice constants for new isostructural
materials. In particular, the lattice constants of new hypothetic spinels
ZnRE2O4, CdRE2S4, CdRE2Se4 (RE=rare earth elements) are predicted in the
present paper. In addition, the upper and lower limits for the variation of the
ionic radii, electronegativities and certain their combinations were
established, which can be considered as stability criteria for the spinel
compounds. The findings of the present paper offer a systematic overview of the
structural properties of spinels and can serve as helpful guides for synthesis
of new spinel compounds.",1401.6631v2
2014-04-16,Improvement upon Mahler's transference theorem,"In this paper we obtain new transference theorems improving some classical
theorems which belong to Kurt Mahler. We formulate those theorems in terms of
consecutive minima of pseudo-compound parallelepipeds.",1404.4375v1
2014-09-22,Analysis of charge states in the mixed valent ionic insulator AgO,"The doubly ionized $d^9$ copper ion provides, originally in La$_2$CuO$_4$ and
later in many more compounds, the platform for high temperature
superconductivity when it is forced toward higher levels of oxidation. The
nearest chemical equivalent is Ag$^{2+}$, which is almost entirely avoided in
nature. AgO is an illustrative example, being an unusual nonmagnetic insulating
compound with an open $4d$ shell on one site. This compound has been
interpreted in terms of one Ag$^{3+}$ ion at the fourfold site and one Ag$^{+}$
ion that is twofold coordinated. We analyze more aspects of this compound,
finding that indeed the Ag$^{3+}$ ion supports only four occupied $4d$-based
Wannier functions per spin, while Ag$^+$ supports five, yet their physical
charges are nearly equal. The oxygen $2p$ Wannier functions display two
distinct types of behavior, one type of which includes conspicuous Ag $4d$
tails. Calculation of the Born effective charge tensor shows that the mean
effective charges of the Ag ions differ by about a factor of two, roughly
consistent with the assigned formal charges. We analyze the $4d$ charge density
and discuss it in terms of recent insights into charge states of insulating
(and usually magnetic) transition metal oxides. What might be expected in
electron- and hole-doped AgO is discussed briefly.",1409.6371v1
2014-10-20,On the Compound Broadcast Channel: Multiple Description Coding and Interference Decoding,"This work investigates the general two-user Compound Broadcast Channel (BC)
where an encoder wishes to transmit common and private messages to two
receivers while being oblivious to two possible channel realizations
controlling the communication. The focus is on the characterization of the
largest achievable rate region by resorting to more evolved encoding and
decoding techniques than the conventional coding for the standard BC. The role
of the decoder is first explored, and an achievable rate region is derived
based on the principle of ""Interference Decoding"" (ID) where each receiver
decodes its intended message and chooses to (non-uniquely) decode or not the
interfering message. This inner bound is shown to be capacity achieving for a
class of non-trivial compound BEC/BSC broadcast channels while the worst-case
of Marton's inner bound -based on ""Non Interference Decoding"" (NID)- fails to
achieve the capacity region. The role of the encoder is then studied, and an
achievable rate region is derived based on ""Multiple Description"" (MD) coding
where the encoder transmits a common as well as multiple dedicated private
descriptions to the many instances of the users channels. It turns out that MD
coding outperforms the single description scheme -Common Description (CD)
coding- for a class of compound Multiple Input Single Output Broadcast Channels
(MISO BC).",1410.5187v1
2014-11-17,Experimental and theoretical investigations on magnetic and related properties of ErRuSi,"We report experimental and theoretical studies of magnetic and related
properties of ErRuSi compound. Various experimental techniques such as neutron
diffraction, magnetization, magneto-thermal, magneto-transport, optical have
been used to study the compound. Neutron diffraction shows ferromagnetic
ordering at low temperatures with moments aligned in ab plane. Neutron
diffraction and magnetization data show reduction in magnetic moment, which may
be due to crystalline electric field effects at low temperatures. The compound
shows good magnetocaloric properties with a low field adiabatic temperature
change of 4.7 K, which is larger than that of many proposed materials for
magnetic refrigeration at low temperatures. Magnetoresistance shows large
negative value at 8 K, which changes its sign and increases in magnitude, with
decrease in temperature and/or increase in field. The positive MR at low
temperatures attributed to the Lorentz force effect. The electronic structure
calculations accounting for electronic correlations of the 4f electrons of Er
reproduces the ferromagnetic ordering and effective magnetic moment. Interband
transitions between the Ru and Er d states and Er f states in one spin
projection are found to form the main features of the measured optical
conductivity in this compound.",1411.4391v1
2014-12-31,"What superconducts in sulfur hydrides under pressure, and why","The recent discovery of superconductivity at 190~K in highly compressed
H$_{2}$S is spectacular not only because it sets a record high critical
temperature, but because it does so in a material that appears to be, and we
argue here that it is, a conventional strong-coupling BCS superconductor.
Intriguingly, superconductivity in the observed pressure and temperature range
was predicted theoretically in a similar compound H$_{3}$S. Several important
questions about this remarkable result, however, are left unanswered: (1) Does
the stoichiometry of the superconducting compound differ from the nominal
composition, and could it be the predicted H$_{3}$S compound? (2) Is the
physical origin of the anomalously high critical temperature related only to
the high H phonon frequencies, or does strong electron-ion coupling play a
role? We show that at experimentally relevant pressures H$_2$S is unstable,
decomposing into H$_3$S and S, and that H$_3$S has a record high $T_c$ due to
its covalent bonds driven metallic. The main reason for this extraordinarily
high $T_c$ in H$_3$S as compared with MgB$_2$, another compound with a similar
superconductivity mechanism, is the high vibrational frequency of the much
lighter H atoms.",1501.00196v1
2015-02-26,"Structural and Dielectric Properties of (La, Nd) (Mg1/2Ti1/2)O3 Perovskites","Using the high-resolution x-ray diffraction (XRD) analysis, scanning electron
microscopy (SEM), and the temperature-dependent microwave resonator
characterization, structural properties, phase assemblage and dielectric
properties of La(Mg1/2Ti1/2)O3 (LMT) and Nd(Mg1/2Ti1/2)O3 (NMT) ceramics
prepared via the mixed oxide route were investigated in this study.
Single-phase ceramics were synthesized for both LMT and NMT at sintering
temperatures from 1250 degree C to 1675 degree C. On the basis of the XRD
analysis we have found that the LMT and NMT compounds have cubic and monoclinic
crystal structures, respectively. We have also observed that the relative
densities of LMT and NMT vary between about 93 and 99% of the theoretical
density, depending on the sintering temperature. Finally, concerning the
dielectric properties of the microwave resonators made of LMT and NMT compounds
we have measured their temperature coefficient of the resonant frequency
({\tau}f) and the quality factor (Q). It is interesting to notice that
({\tau}f) in the case of the NMT compound (-16 ppm 1/K) is essentially smaller
than in the case of the LMT compound (-72 ppm 1/K), therefore proving a better
stability against temperature variations in the NMT based resonators. On the
other hand, the Q values are very similar, being 34000 at the resonance
frequency of 8.07 GHz and 38000 at the resonance frequency of 9.76 GHz in the
LMT and NMT cases, respectively.
  Keywords: dielectric properties; microstructure-final: grain growth; single
phase Ln(Mg0.5Ti0.5)O3 (Ln=Nd,La); Lanthanum magnesium titanium oxide.",1502.07547v1
2015-01-26,Learning Immune-Defectives Graph through Group Tests,"This paper deals with an abstraction of a unified problem of drug discovery
and pathogen identification. Pathogen identification involves identification of
disease-causing biomolecules. Drug discovery involves finding chemical
compounds, called lead compounds, that bind to pathogenic proteins and
eventually inhibit the function of the protein. In this paper, the lead
compounds are abstracted as inhibitors, pathogenic proteins as defectives, and
the mixture of ""ineffective"" chemical compounds and non-pathogenic proteins as
normal items. A defective could be immune to the presence of an inhibitor in a
test. So, a test containing a defective is positive iff it does not contain its
""associated"" inhibitor. The goal of this paper is to identify the defectives,
inhibitors, and their ""associations"" with high probability, or in other words,
learn the Immune Defectives Graph (IDG) efficiently through group tests. We
propose a probabilistic non-adaptive pooling design, a probabilistic two-stage
adaptive pooling design and decoding algorithms for learning the IDG. For the
two-stage adaptive-pooling design, we show that the sample complexity of the
number of tests required to guarantee recovery of the inhibitors, defectives,
and their associations with high probability, i.e., the upper bound, exceeds
the proposed lower bound by a logarithmic multiplicative factor in the number
of items. For the non-adaptive pooling design too, we show that the upper bound
exceeds the proposed lower bound by at most a logarithmic multiplicative factor
in the number of items.",1503.00555v3
2015-03-20,Magnetic excitations of perovskite rare-earth nickelates: RNiO$_3$,"The perovskite nickelates RNiO$_3$ (R: rare-earth) have been studied as
potential multiferroic compounds. A certain degree of charge disproportionation
in the Ni ions has been confirmed by high resolution synchrotron power
diffraction: instead of the nominal Ni$^{3+}$ valence, they can have the
mixed-valence state Ni$^{(3-\delta)+}$ and Ni$^{(3+\delta)+}$, though agreement
has not been reached on the precise value of $\delta$ (e.g. for NdNiO$_3$,
$\delta=0.0$ and $\delta=0.29$ were reported). Also, the magnetic ground state
is not yet clear: collinear and non-collinear Ni-O magnetic structures have
been proposed to explain neutron diffraction and soft X-ray resonant
sccattering results in these compounds, and more recently a canted
antiferromagnetic spin arrangement was proposed on the basis of magnetic
susceptibility measurements. This scenario is reminiscent of the situation in
the half-doped manganites.
  In order to gain insight into the ground state of these compounds, we studied
the magnetic excitations of some of the different phases proposed, using a
localized spin model for a simplified spin chain which could describe these
compounds. We first analize the stability of the collinear, orthogonal, and
intermediate phases in the classical case. We then explore the quantum ground
state indirectly, calculating the spin excitations obtained for each phase,
using the Holstein-Primakoff transformation and the linear spin-wave
approximation. For the collinear and orthogonal ($\theta=\pi/2$) phases, we
predict differences in the magnon spectrum which would allow to distinguish
between them in future inelastic neutron scattering experiments.",1503.06102v1
2015-04-07,Potential ring of Dirac nodes in a new polymorph of Ca$_3$P$_2$,"We report the crystal structure of a new polymorph of Ca$_3$P$_2$, and an
analysis of its electronic structure. The crystal structure was determined
through Rietveld refinements of powder synchrotron x-ray diffraction data.
Ca$_3$P$_2$ is found to be a variant of the Mn$_5$Si$_3$ structure type, with a
Ca ion deficiency compared to the ideal 5:3 stoichiometry to yield a
charge-balanced compound. We also report the observation of a secondary phase,
Ca$_5$P$_3$H, in which the Ca and P sites are fully occupied and the presence
of interstitial hydride ions creates a closed-shell electron-precise compound.
We show via electronic structure calculations of Ca$_3$P$_2$ that the compound
is stabilized by a gap in the density of states compared to the hypothetical
compound Ca$_5$P$_3$. Moreover, the calculated band structure of Ca$_3$P$_2$
indicates that it should be a three-dimensional Dirac semimetal with a highly
unusual ring of Dirac nodes at the Fermi level. The Dirac states are protected
against gap opening by a mirror plane in a manner analogous to graphene. The
results suggest that further study of the electronic properties of Ca$_3$P$_2$
will be of interest.",1504.01731v1
2015-05-06,"Curvature-driven, One-step Assembly of Reconfigurable Smectic Liquid Crystal ""Compound Eye"" Lenses","Confined smectic A liquid crystals (SmA LCs) form topological defects called
focal conic domains (FCDs) that focus light as gradient-index lenses. Here, we
exploit surface curvature to self-assemble FCDs in a single step into a
hierarchical structure (coined ""flower pattern"") molded by the fluid interface
that is pinned at the top of a micropillar. The structure resembles the
compound eyes of some invertebrates, which consist of hundreds of microlenses
on a curved interface, able to focus and construct images in three dimensions.
Here we demonstrate that these flowers are indeed ""compound eyes"" with
important features which have not been demonstrated previously in the
literature. The eccentric FCDs gradually change in size with radial distance
from the edge of the micropillar, resulting in a variable microlens focal
length that ranges from a few microns to a few tens of microns within a single
""flower"". We show that the microlenses can construct a composite 3D image from
different depth of field. Moreover, the smectic ""compound eye"" can be
reconfigured by heating and cooling at the LC phase transition temperature; its
field of view can be manipulated by tuning the curvature of the LC interface,
and the lenses are sensitive to light polarization.",1505.01449v1
2015-11-05,High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt,"YbBiPt is a heavy-fermion compound possessing significant short-range
antiferromagnetic correlations below a temperature of $T^{\textrm{*}}=0.7$ K,
fragile antiferromagnetic order below $T_{\rm{N}}=0.4$ K, a Kondo temperature
of $T_{\textrm{K}} \approx1$ K, and crystalline-electric-field splitting on the
order of $E/k_{\textrm{B}}=1\,\textrm{-}\,10$ K. Whereas the compound has a
face-centered-cubic lattice at ambient temperature, certain experimental data,
particularly those from studies aimed at determining its
crystalline-electric-field scheme, suggest that the lattice distorts at lower
temperature. Here, we present results from high-resolution, high-energy x-ray
diffraction experiments which show that, within our experimental resolution of
$\approx6\,\textrm{-}\,10\times10^{-5}$ \AA, no structural phase transition
occurs between $T=1.5$ and $50$ K. In combination with results from dilatometry
measurements, we further show that the compound's thermal expansion has a
minimum at $\approx18$ K and a region of negative thermal expansion for
$9<T<18$ K. Despite diffraction patterns taken at $1.6$ K which indicate that
the lattice is face-centered cubic and that the Yb resides on a
crystallographic site with cubic point symmetry, we demonstrate that the linear
thermal expansion may be modeled using crystalline-electric-field level schemes
appropriate for Yb$^{3+}$ residing on a site with either cubic or less than
cubic point symmetry.",1511.01822v1
2015-12-07,Superconductivity in metastable phases of phosphorus-hydride compounds under high pressure,"Hydrogen-rich compounds have been extensively studied both theoretically and
experimentally in the quest for novel high-temperature superconductors. Reports
on sulfur-hydride attaining metallicity under pressure and exhibiting
superconductivity at temperatures as high as 200 K have spurred an intense
search for room-temperature superconductors in hydride materials. Recently,
compressed phosphine was reported to metallize at pressures above 45 GPa,
reaching a superconducting transition temperature (T$_{c}$) of 100 K at 200
GPa. However, neither the exact composition nor the crystal structure of the
superconducting phase have been conclusively determined. In this work the phase
diagram of PH$_n$ ($n=1,2,3,4,5,6$) was extensively explored by means of {\it
ab initio} crystal structure predictions using the Minima Hopping Method (MHM).
The results do not support the existence of thermodynamically stable PH$_n$
compounds, which exhibit a tendency for elemental decomposition at high
pressure even when vibrational contributions to the free energies are taken
into account. Although the lowest energy phases of PH$_{1,2,3}$ display
T$_{c}$'s comparable to experiments, it remains uncertain if the measured
values of T$_{c}$ can be fully attributed to a phase-pure compound of PH$_n$.",1512.02132v1
2015-12-22,A generalization of product construction of multimagic squares,"In this paper, constructions of multimagic squares are investigated. Diagonal
Latin squares and Kronecker products are used to get some constructions of
multimagic squares. Consequently, some new families of compound multimagic
squares are obtained.",1512.07287v1
2016-01-13,Quantitative study of the f occupation in CeMIn5 and other cerium compounds with hard x-rays,"We present bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) data
of the Ce3d core levels and lifetime-reduced L edge x-ray absorption
spectroscopy (XAS) in the partial fluorescence yield (PFY) mode of the CeMIn5
family with M = Co, Rh, and Ir. The HAXPES data are analyzed quantitatively
with a combination of full multiplet and configuration interaction model which
allows correcting for the strong plasmons in the CeMIn5 HAXPES data, and
reliable weights wn of the different fn contributions in the ground state are
determined. The CeMIn5 results are compared to HAXPES data of other heavy
fermion compounds and a systematic decrease of the hybridization strength Veff
from CePd3 to CeRh3B2 to CeRu2Si2 is observed, while it is smallest for the
three CeMIn5 compounds. The f-occupation, however, increases in the same
sequence and is close to one for the CeMIn5 family. The PFY-XAS data confirm an
identical f-occupation in the three CeMIn5 compounds and a phenomenological fit
to these PFY-XAS data combined with a configuration interaction model yields
consistent results.",1601.03270v1
2016-02-20,Covalent bonds against magnetism in transition metal compounds,"Magnetism in transition metal compounds is usually considered starting from a
description of isolated ions, as exact as possible, and treating their
(exchange) interaction at a later stage. We show that this standard approach
may break down in many cases, especially in $4d$ and $5d$ compounds. We argue
that there is an important intersite effect -- an orbital-selective formation
of covalent metal-metal bonds, which leads to an ""exclusion"" of corresponding
electrons from the magnetic subsystem, and thus strongly affects magnetic
properties of the system. This effect is especially prominent for noninteger
electron number, when it results in suppression of the famous double exchange,
the main mechanism of ferromagnetism in transition metal compounds. We study
this novel mechanism analytically and numerically and show that it explains
magnetic properties of not only several $4d-5d$ materials, including
Nb$_2$O$_2$F$_3$ and Ba$_5$AlIr$_2$O$_{11}$, but can also be operative in $3d$
transition metal oxides, e.g. in CrO$_2$ under pressure. We also discuss the
role of spin-orbit coupling on the competition between covalency and magnetism.
Our results demonstrate that strong intersite coupling may invalidate the
standard single-site starting point for considering magnetism, and can lead to
a qualitatively new behaviour.",1602.06425v2
2016-04-24,Cooling rate dependence of simulated ${\rm Cu_{64.5}Zr_{35.5}}$ metallic glass structure,"Using molecular dynamics simulations with embedded atom model potential, we
study structural evolution of ${\rm Cu_{64.5}Zr_{35.5}}$ alloy during the
cooling in a wide range of cooling rates $\gamma\in(1.5\cdot 10^{9},10^{13})$
K/s. Investigating short- and medium-range order, we show that structure of
${\rm Cu_{64.5}Zr_{35.5}}$ metallic glass essentially depends on cooling rate.
In particular, a decrease of the cooling rate leads to a increase of abundances
of both the icosahedral-like clusters and Frank-Kasper Z16 polyhedra. The
amounts of these clusters in the glassy state drastically increase at the
$\gamma_{\rm min}=1.5\cdot 10^{9}$ K/s. Analysing the structure of the glass at
$\gamma_{\rm min}$, we observe the formation of nano-sized crystalline grain of
${\rm Cu_2Zr}$ intermetallic compound with the structure of ${\rm Cu_2Mg}$
Laves phase. The structure of this compound is isomorphous with that for ${\rm
Cu_5Zr}$ intermetallic compound. Both crystal lattices consist of two type of
clusters: Cu-centered 13-atom icosahedral-like cluster and Zr-centered 17-atom
Frank-Kasper polyhedron Z16. That suggests the same structural motifs for the
metallic glass and intermetallic compounds and explains the drastic increase of
the abundances of these clusters observed at $\gamma_{\rm min}$.",1604.07024v1
2016-05-04,"Insight into the magnetism of a distorted Kagome lattice, Dy3Ru4Al12, based on polycrystalline studies","The layered compound with distorted Kagome nets, Dy3Ru4Al12, was previously
reported to undergo antiferromagnetic ordering below (TN=) 7 K, based on
investigations on single crystals. Here, we report the results of our
investigation of ac and dc magnetic susceptibility (\c{hi}), isothermal remnant
magnetization (MIRM), heat-capacity, magnetocaloric effect and
magnetoresistance measurements on polycrystals. The present results reveal that
there is an additional magnetic anomaly around 20 K, as though the N\'eel order
is preceded by the formation of ferromagnetic clusters. We attribute this
feature to geometric frustration of magnetism. In view of the existence of this
phase, the interpretation of the linear-term in the heat-capacity in terms of
spin-fluctuations from the Ru 4d band needs to be revisited. Additionally, in
the vicinity of TN, AC \c{hi} shows a prominent frequency dependence and, below
TN, MIRM exhibits a slow decay with time. This raises a question whether the
antiferromagnetic structure in this compound is characterized by
spin-glass-like dynamics. In contrast to what was reported earlier, there is a
change in the sign of the magnetoresistance (MR) at the metamagnetic
transition. A butter-fly-shaped (isothermal) MR loop (interestingly spanning
over all the four quadrants) is observed at 2 K with distinct evidence for the
magnetic phase co-existence phenomenon in zero field after travelling through
metamagnetic transition field. The results on polycrystals thus provide
additional information about the magnetism of this compound, revealing that the
magnetism of this compound is more complex than what is believed, due to
geometric frustration intrinsic to Kagome net.",1605.01147v1
2016-05-11,"Magnetic behavior of Gd3Ru4Al12, a layered compound with a distorted Kagome net","The magnetic behavior of the compound, Gd3Ru4Al12, which has been reported to
crystallize in a hexagonal structure about two decades ago, had not been
investigated in the past literature despite interesting structural features
(that is, magnetic layers and triangles as well as Kagome-lattice features
favouring frustrated magnetism) characterizing this compound. We report here
the results of magnetization, heat-capacity, and magnetoresistance studies in
the temperature (T) range 1.8-300 K. The results establish that there is a
long-range magnetic order of an antiferromagnetic type below (TN= ) 18.5 K,
despite a much large value (about 80 K) of paramagnetic Curie temperature with
a positive sign characteristic of ferromagnetic interaction. We attribute this
to geometric frustration. The most interesting finding is that there is an
additional magnetic anomaly below about 55 K before the onset of long range
order in the magnetic susceptibility data. Concurrent with this observation,
the sign of isothermal entropy change remains positive above TN with a broad
peak above TN. This observation indicates the presence of ferromagnetic
clusters before the onset of long range magnetic order. Thus, this compound may
serve as an example for a situation in which magnetic frustration due to
geometrical reasons is faced by competition with such precursor effects. There
is also a reversal of the sign of entropy-change in the curves for lower final
fields (for H less than 30 kOe) on entering into magnetically ordered state
consistent with the entrance into antiferromagnetic state. The
magnetoresistance behavior is consistent with above conclusions.",1605.03528v1
2016-06-10,"Systematic analysis of structural and magnetic properties of spinel $CoB_2O_4$(B=Cr,Mn and Fe)compounds from their electronic structures","The structural and magnetic properties of spinel compounds $CoB_2O_4$
(B=Cr,Mn and Fe) are studied using the DFT+U method and generalized gradient
approximation (GGA). We concentrate on understanding the trends in the
properties of these materials as the B cation changes, in terms of relative
strengths of crystal fields and exchange fields through an analysis of their
electronic densities of states. We find that the electron-electron correlation
plays a significant role in obtaining the correct structural and electronic
ground states. Significant structural distortion in CoMn$_{2}$O$_{4}$ and
""inverted"" sublattice occupancy in CoFe$_{2}$O$_{4}$ affects the magnetic
exchange interactions substantially. The trends in the magnetic exchange
interactions are analysed in terms of the structural parameters and the
features in their electronic structures. We find that the Fe states in
CoFe$_{2}$O$_{4}$ are extremely localised, irrespective of the symmetry of the
site, which makes it very different from the features of the states of the B
cations in other two compounds. These results provide useful insights into the
trends in the properties of CoB$_{2}$O$_{4}$ compounds with variation of B
cation which would help in understanding the results of recent experiments on
doping of Mn and Cr in multiferroic CoCr$_{2}$O$_{4}$.",1606.03176v2
2016-06-21,Tuning the electronic hybridization in the heavy fermion cage compound YbFe$_{2}$Zn$_{20}$ with Cd-doping,"Tuning of the electronic properties of heavy fermion compounds by chemical
substitutions provides excellent opportunities to further understand the
physics of hybridized ions in crystal lattices. Here we present an
investigation on the effects of Cd doping in flux-grown single crystals of the
complex intermetallic cage compound YbFe$_{2}$Zn$_{20}$, that has been
described as a heavy fermion with Sommerfeld coefficient of 535 mJ/mol.K$^{2}$.
Substitution of Cd for Zn disturbs the system by expanding the unit cell and,
in this case, the size of the Zn cages that surround Yb and Fe. With increasing
amount of Cd, the hybridization between Yb $4f$ electrons and the conduction
electrons is weakened, as evidenced by a decrease in the Sommerfeld
coefficient, which should be accompanied by a valence shift of the Yb$^{3+}$
due to the negative chemical pressure effect. This scenario is also supported
by the low temperature dc-magnetic susceptibility, that is gradually suppressed
and evidences an increment of the Kondo temperature, based on a shift to higher
temperatures of the characteristic broad susceptibility peak. Furthermore, the
DC resistivity decreases with the isoelectronic Cd substitution for Zn,
contrary to the expectation for an increasingly disordered system, and implying
that the valence shift is not related to charge carrier doping. The combined
results demonstrate excellent complementarity between positive physical
pressure and negative chemical pressure, and point to a rich playground for
exploring the physics and chemistry of strongly correlated electron systems in
the general family of Zn$_{20}$ compounds, despite their structural complexity.",1606.06722v1
2016-07-01,EuCo2P2: A Model Molecular-Field Helical Heisenberg Antiferromagnet,"The metallic compound EuCo2P2 with the body-centered tetragonal ThCr2Si2
structure containing Eu spins 7/2 was previously shown from single-crystal
neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM)
structure below TN = 66.5 K with the helix axis along the c axis and with the
ordered moments aligned within the ab-plane. Here we report crystallography,
electrical resistivity, heat capacity, magnetization and magnetic
susceptibility measurements on single crystals of this compound. We demonstrate
that EuCo2P2 is a model molecular-field helical Heisenberg antiferromagnet from
comparisons of the anisotropic magnetic susceptibility chi, high-field
magnetization and magnetic heat capacity of EuCo2P2 single crystals at
temperature T < TN with the predictions of our recent formulation of molecular
field theory. Values of the Heisenberg exchange interactions between the Eu
spins are derived from the data. The low-T magnetic heat capacity ~ T^3 arising
from spin-wave excitations with no anisotropy gap is calculated and found to be
comparable to the lattice heat capacity. The density of states at the Fermi
energy of EuCo2P2 and the related compound BaCo2P2 are found from the heat
capacity data to be large, 10 and 16 states/eV per formula unit for EuCo2P2 and
BaCo2P2, respectively. These values are enhanced by a factor of ~2.5 above
those found from DFT electronic structure calculations for the two compounds.
The calculations also find ferromagnetic Eu-Eu exchange interactions within the
ab-plane and AFM interactions between nearest- and next-nearest planes, in
agreement with the MFT analysis of chi{ab}(T < TN).",1607.00247v1
2016-07-05,Two new parent compounds for FeSe-based superconducting phases,"It is well established that the occurrence of superconductivity in iron
pnictides is closely related to the tetragonal to orthorhombic structural and
antiferromagnetic (AFM) phase transitions. It, however, has not been clear
whether the same scenario is appropriate for iron chalcogenide counterparts due
to the absence of parent compounds for the latter family of superconductors.
Here, we report the synthesis and structure determination of two novel phases
in ethylenediamine intercalated FeSe, one is tetragonal and the other
orthorhombic in room temperature, which can be stabilized with neutral spacer
layers. Both phases can be regarded as the parent compounds for
superconductivity as they are non-superconducting (non-SC) in pristine form and
superconducting (SC) with Tc up to 38K and 46K, respectively after Na doping,
and the switch between SC and no-SC is reversible. Moreover, the two non-SC
parent compounds show no evidence of long-range magnetic ordering down to 2K,
only with dynamic spin fluctuations at low temperatures, suggesting that no
competition between SC and AFM ordering. Our results reveal that undoped iron
selenides are quantum paramagnetic in ground state, implying that they are
distinct from their pnictide counterparts in pairing mechanism.",1607.01103v1
2016-08-16,Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles,"Motivated by the resurgence of electronic and optical property design in
ordered fluoride and oxyfluoride compounds, we present a density functional
theory (DFT) study on 19 materials with structures, ranging from simple to
complex, and variable oxygen-to-fluorine ratios. We focus on understanding the
accuracy of the exchange-correlation potentials ($V_{xc}$) to DFT for the
prediction of structural, electronic, and lattice dynamical properties at four
different levels of theory, \emph{i.e.}, the local density approximation (LDA),
generalized gradient approximation (GGA), metaGGA, and hybrid functional level
which includes fractions of exact exchange. We investigate in detail the
metaGGA functionals MS2 [Sun \emph{et al}., Phys.\ Rev.\ Lett., \textbf{111},
106401 (2013)] and SCAN [Sun \emph{et al}., Phys.\ Rev.\ Lett., \textbf{115},
036402 (2015)], and show that although the metaGGAs show improvements over the
LDA and GGA functionals in describing the electronic structure and phonon
frequencies, the static structural properties of fluorides and oxyfluorides are
often more accurately predicted by the GGA-level functional PBEsol. Results
from LDA calculations are unsatisfactory for any compound regardless of oxygen
concentration. PBEsol or HSE06 gives good performance in all oxide or all
fluoride compounds. For the oxyfluorides, PBEsol is consistently more accurate
for structural properties across all oxygen concentrations, however, we stress
the need for detailed property assessment with various functionals for
oxyfluorides with variable composition. The ""best"" functional is anticipated to
be more strongly dependent on the property of interest. Our study provides
useful insights in selecting an $V_{xc}$ that achieves the best performance
comprise, enabling more accurate predictive design of functional fluoride-based
materials with density functional theory.",1608.04450v2
2016-11-01,Experimental evidence for the importance of Hund's exchange interaction for the incoherence of the charge carriers in iron-based superconductors,"Angle-resolved photoemission spectroscopy (ARPES) is used to study the
scattering rates of charge carriers from the hole pockets near Gamma in the
iron-based high-Tc hole doped superconductors KxBa1-xFe2As2 x=0.4 and
KxEu1-xFe2As2 x=0.55$ and the electron doped compound Ba(Fe1-xCox)2As2 x=0.075.
The scattering rate for any given band is found to depend linearly on energy,
indicating a non-Fermi liquid regime. The scattering rates in the hole-doped
compound are considerably larger than those in the electron-doped compounds. In
the hole-doped systems the scattering rate of the charge carriers of the inner
hole pocket is about three times bigger than the binding energy indicating that
the spectral weight is heavily incoherent. The strength of the scattering rates
and the difference between electron and hole doped compounds signals the
importance of Hund's exchange coupling for correlation effects in these
iron-based high-Tc superconductors. The experimental results are in qualitative
agreement with theoretical calculations in the framework of combined density
functional dynamical mean-field theory.",1611.00239v1
2017-01-26,3D Printing of Polymer Bonded Rare-Earth Magnets With a Variable Magnetic Compound Density for a Predefined Stray Field,"Additive manufacturing of polymer bonded magnets is a recently developed
technique, for single-unit production, and for structures that have been
impossible to manufacture previously. Also new possibilities to create a
specific stray field around the magnet are triggered. The current work presents
a method to 3D print polymer bonded magnets with a variable magnetic compound
density distribution. A low-cost, end-user 3D printer with a mixing extruder is
used to mix permanent magnetic filaments with pure PA12 filaments. The magnetic
filaments are compounded, extruded, and characterized for the printing process.
To deduce the quality of the manufactured magnets with a variable compound
density, an inverse stray field framework is used. The effectiveness of the
printing process and the simulation method is shown. It can also be used to
manufacture magnets that produce a predefined stray field in a given region.
Examples for sensor applications are presented. This setup and simulation
framework allows the design and manufacturing of polymer bonded permanent
magnets which are impossible to create with conventional methods.",1701.07703v1
2017-01-25,Probabilistic inferences from conjoined to iterated conditionals,"There is wide support in logic, philosophy, and psychology for the hypothesis
that the probability of the indicative conditional of natural language,
$P(\textit{if } A \textit{ then } B)$, is the conditional probability of $B$
given $A$, $P(B|A)$. We identify a conditional which is such that $P(\textit{if
} A \textit{ then } B)= P(B|A)$ with de Finetti's conditional event, $B|A$. An
objection to making this identification in the past was that it appeared
unclear how to form compounds and iterations of conditional events. In this
paper, we illustrate how to overcome this objection with a probabilistic
analysis, based on coherence, of these compounds and iterations. We interpret
the compounds and iterations as conditional random quantities which, given some
logical dependencies, may reduce to conditional events. We show how the
inference to $B|A$ from $A$ and $B$ can be extended to compounds and iterations
of both conditional events and biconditional events. Moreover, we determine the
respective uncertainty propagation rules. Finally, we make some comments on
extending our analysis to counterfactuals.",1701.07785v5
2017-08-08,Quantum interference in coherent tunnelling through branched molecular junctions containing ferrocene centers,"In our theoretical study where we combine a nonequilibrium Green's function
(NEGF) approach with density functional theory (DFT) we investigate branched
compounds containing ferrocene moieties in both branches which due to their
metal centers are designed to allow for asymmetry induced by local charging. In
these compounds the ferrocene moieties are connected to pyridyl anchor groups
either directly or via acetylenic spacers in a meta-connection where we also
compare our results with those obtained for the respective single-branched
molecules with both meta- and para-connections between the metal center and the
anchors. We find a destructive quantum interference (DQI) feature in the
transmission function slightly below the lowest unoccupied molecular orbital
(LUMO) which dominates the conductance even for the uncharged branched compound
with spacer groups inserted. In an analysis based on mapping the structural
characteristics of the range of molecules in our article onto tight-binding
models, we identify the structural source of the DQI minimum as the
through-space coupling between the pyridyl anchor groups. We also find that
local charging on one of the branches only changes the conductance by about one
order of magnitude which we explain in terms of the spatial distributions of
the relevant molecular orbitals for the branched compounds.",1708.02522v1
2017-08-10,"Observation of Dirac surface states in the hexagonal PtBi2, a possible origin of the linear magnetoresistance","The nonmagnetic compounds showing extremely large magnetoresistance are
attracting a great deal of research interests due to their potential
applications in the field of spintronics. PtBi$_2$ is one of such interesting
compounds showing large linear magnetoresistance (MR) in its both the hexagonal
and pyrite crystal structure. We use angle-resolved photoelectron spectroscopy
(ARPES) and density functional theory (DFT) calculations to understand the
mechanism of liner MR observed in the hexagonal PtBi$_2$. Our results uncover
for the first time linear dispersive surface Dirac states at the
$\bar{\Gamma}$-point, crossing Fermi level with node at a binding energy of
$\approx$ 900 meV, in addition to the previously reported Dirac states at the
$\bar{M}$-point in the same compound. We further notice from our dichroic
measurements that these surface states show an asymmetric spectral intensity
when measured with left and right circularly polarized light, hinting at a
substantial spin polarization of the bands. Following these observations, we
suggest that the linear dispersive Dirac states at the $\bar{\Gamma}$ and
$\bar{M}$-points are likely to play a crucial role for the linear field
dependent magnetoresistance recorded in this compound.",1708.03233v1
2018-01-08,The effect of heavy tars (toluene and naphthalene) on the electrochemical performance of an anode-supported SOFC running on bio-syngas,"The effect of heavy tar compounds on the performance of a Ni-YSZ anode
supported solid oxide fuel cell was investigated. Both toluene and naphthalene
were chosen as model compounds and tested separately with a simulated
bio-syngas. Notably, the effect of naphthalene is almost negligible with pure
H2 feed to the SOFC, whereas a severe degradation is observed when using a
bio-syngas with an H2:CO = 1. The tar compound showed to have a remarkable
effect on the inhibition of the WGS shift-reaction, possibly also on the CO
direct electro-oxidation at the three-phase-boundary. An interaction through
adsorption of naphthalene on nickel catalytic and electrocatalytic active sites
is a plausible explanation for observed degradation and strong performance
loss. Different sites seem to be involved for H2 and CO electro-oxidation and
also with regard to catalytic water gas shift reaction. Finally, heavy tars
(C>=10) must be regarded as a poison more than a fuel for SOFC applications,
contrarily to lighter compounds such benzene or toluene that can directly
reformed within the anode electrode. The presence of naphthalene strongly
increases the risk of anode re-oxidation in a syngas stream as CO conversion to
H2 is inhibited and also CH4 conversion is blocked.",1801.02557v1
2018-01-19,Combined computational and experimental investigation of the La-Cu-S-O quaternary system,"The lack of a mechanistic framework for chemical reactions forming inorganic
extended solids presents a challenge to accelerated materials discovery. We
demonstrate here a combined computational and experimental methodology to
tackle this problem, in which in situ X-ray diffraction measurements monitor
solid state reactions and deduce reaction pathways, while theoretical
computations rationalize reaction energetics. The method has been applied to
the La-Cu-S-O quaternary system, following an earlier prediction that enhanced
superconductivity could be found in these of new lanthanum copper(II)
oxysulfide compounds. In situ diffraction measurements show that reactants
containing Cu(II) and S(2-) ions undergo redox reactions, leaving their ions in
oxidation states that are incompatible with forming the desired new compounds.
Computations of the reaction energies confirm that the observed synthetic
pathways are indeed favored over those that would hypothetically form the
suggested compounds. The consistency between computation and experiment in the
La-Cu-S-O system suggests a new role for predictive theory: to identify and to
explicate new synthetic routes for forming predicted compounds.",1801.06262v1
2018-01-19,High pressure effects on non-fluorinated BiS2-based superconductors La$_{1-x}$M$_x$OBiS$_2$ (M = Ti and Th),"Layered \textit{Ln}OBiS$_2$ compounds with \textit{Ln} = La, Ce, Pr, Nd, and
Yb can be rendered conducting and superconducting via two routes, substitution
of F for O or the tetravalent ions Ti, Zr, Hf, and Th for trivalent \textit{Ln}
ions. Electrical resistivity measurements on non-fluorinated
La$_{0.80}$Ti$_{0.20}$OBiS$_2$ and La$_{0.85}$Th$_{0.15}$OBiS$_2$
superconductors were performed between $\sim$1.5 K and 300 K and under pressure
up to 2.4 GPa. For both compounds, the superconducting transition temperature
$T_c$, which is $\sim$2.9 K at ambient pressure, gradually increases with
pressure to 3.2-3.7 K at $\sim$1 GPa, above which it is suppressed and the
superconducting transitions become very broad. Measurements of the normal state
electrical resistivity of the two compounds reveal discontinuous changes of the
resistivity as a function of pressure at $\sim$0.6 GPa. Surprisingly, above 1.3
GPa, semiconducting-like behavior reappears in La$_{0.80}$Ti$_{0.20}$OBiS$_2$.
This study reveals a new high-pressure phase of La$_{1-x}$$M$$_x$OBiS$_2$
containing the tetravalent ions $M$ = Ti, Th which does not favor
superconductivity. In contrast, application of pressure to fluorinated
LaO$_0.5$F$_0.5$BiS$_2$ produces an abrupt tetragonal-monoclinic transition to
a metallic phase with an enhanced $T_c$. These results demonstrate that the
response of the normal and superconducting properties of LaOBiS$_2$-based
compounds depends strongly on the atomic site where the electron donor ions are
substituted.",1801.06568v1
2018-01-31,"The Physical Properties of ThCr2Si2-type Nickel-based Superconductors BaNi2T2 (T = P, As): An ab-initio study","Employing the first-principles computations based on the density functional
theory (DFT), we have investigated the structural, mechanical, electronic,
bonding, optical and thermodynamics properties of newly discovered bulk
superconductors BaNi2P2 (Tc ~3 K) and BaNi2As2 (Tc ~0.7 K). Our optimized
lattice parameters are in good concurrence with the experimental records. The
positive elastic constants reveal that both the superconductors are stable in
nature. The analysis of the mechanical properties insures that both the phases
are ductile in nature and show anisotropic behaviors. The analysis of the
electronic band structures and density of states (TDOS and PDOS) reveals the
metallic manners for both the compounds and the major contribution comes from
Ni-3d states for both the phases. The calculations of the chemical bonding
specify that a mixture of covalent, ionic and metallic bonds exist in both the
superconductors. The high value of the dielectric constant of BaNi2As2 ensures
that this compound may be used to manufacture high value capacitors. The large
reflectivity in the low energy region indicates that both the compounds might
be useful as coating materials to reduce solar heating. By using the elastic
constants data the calculated Debye temperatures of BaNi2P2 and BaNi2As2 are
323.70 K and 272.94 K respectively, which are in good accordance with the
experimental values. Finally we have calculated the thermal conductivity of
these compounds which is 0.56 for BaNi2P2 and 0.46 for BaNi2As2.",1801.10573v1
2018-06-08,"Physical properties of niobium based intermetallics (Nb3B; B = Os, Pt, Au): a DFT based ab-initio study","Structural, elastic and electronic band structure properties of A-15 type
Nb-based intermetallic compounds Nb3B (B = Os, Pt, Au) have been revisited
using first principles calculations based on the density functional theory
(DFT). All these show excellent agreement with previous reports. More
importantly, electronic bonding, charge density distribution and Fermi surface
features have been studied in detail for the first time. Vickers hardness of
these compounds is also studied. The Fermi surfaces of Nb3B contain both hole-
and electron-like sheets, the features of which change systematically as one
move from Os to Au. The electronic charge density distribution implies that
Nb3Os, Nb3Pt and Nb3Au have a mixture of ionic and covalent bondings with a
substantial metallic contribution. The charge transfer between the atomic
species in these compounds has been explained via the Mulliken bond population
analysis and the Hirshfeld population analysis. The bonding properties show a
good correspondence to the electronic band structure derived electronic density
of states (DOS) near the Fermi level. Debye temperature of Nb3B (B = Os, Pt,
Au) have been estimated from the elastic constants and show a systematic
behavior as a function of the B atomic species. We have discussed implications
of the results obtained in this study in details in this paper.",1806.04007v1
2018-06-20,DeepAffinity: Interpretable Deep Learning of Compound-Protein Affinity through Unified Recurrent and Convolutional Neural Networks,"Motivation: Drug discovery demands rapid quantification of compound-protein
interaction (CPI). However, there is a lack of methods that can predict
compound-protein affinity from sequences alone with high applicability,
accuracy, and interpretability.
  Results: We present a seamless integration of domain knowledges and
learning-based approaches. Under novel representations of
structurally-annotated protein sequences, a semi-supervised deep learning model
that unifies recurrent and convolutional neural networks has been proposed to
exploit both unlabeled and labeled data, for jointly encoding molecular
representations and predicting affinities. Our representations and models
outperform conventional options in achieving relative error in IC$_{50}$ within
5-fold for test cases and 20-fold for protein classes not included for
training. Performances for new protein classes with few labeled data are
further improved by transfer learning. Furthermore, separate and joint
attention mechanisms are developed and embedded to our model to add to its
interpretability, as illustrated in case studies for predicting and explaining
selective drug-target interactions. Lastly, alternative representations using
protein sequences or compound graphs and a unified RNN/GCNN-CNN model using
graph CNN (GCNN) are also explored to reveal algorithmic challenges ahead.
  Availability: Data and source codes are available at
https://github.com/Shen-Lab/DeepAffinity
  Supplementary Information: Supplementary data are available at
http://shen-lab.github.io/deep-affinity-bioinf18-supp-rev.pdf",1806.07537v2
2018-09-27,Charge-doping-induced variation of BaFe$_2$As$_2$ electronic structure and the emerging physical effects,"We studied the relationship between the charge doping and the correlation,
and its effects on the spectral function of the BaFe$_2$As$_2$ compound in the
framework of the density functional theory combined with the dynamical mean
field theory (DFT+DMFT). The calculated mass enhancements showed that the
electronic correlation varies systematically from weak to strong when moving
from the heavily electron-doped regime to the heavily hole-doped one. Since the
compound has a multi-orbital nature, the correlation is orbital-dependent and
it increases as hole-doping increases. The Fe-3d$_{xy}$ (xy) orbital is much
more correlated than the other orbitals, because it reaches its half-filled
situation and has a narrower energy scale around the Fermi energy. Our findings
can be consistently understood as the tendency of the heavily hole-doped
BaFe$_2$As$_2$ compound to an orbital-selective Mott phase (OSMP). Moreover,
the fact that the superconducting state of the heavily hole-doped
BaFe$_2$As$_2$ is an extreme case of such a selective Mottness constrains the
non-trivial role of the electronic correlation in iron-pnictide
superconductors. In addition, the calculated spectral function shows a behavior
that is compatible with experimental results reported for every charge-doped
BaFe$_2$As$_2$ compound and clarifies the importance of the characterization of
its physical effects on the material.",1809.10509v1
2018-11-19,"Elastic anisotropy and thermal properties of extended linear chain compounds MV$_2$Ga$_4$ (M = Sc, Zr, Hf) from ab-initio calculations","MV$_2$Ga$_4$ (M = Sc, Zr, Hf) compounds belong to an emerging class of
materials showing a unique combination of unusual superconducting behavior with
extended linear chains in the crystal structure. In order to gain insights
{into} its mechanical and thermal properties, we have performed
first-principles electronic-structure calculations in the framework of the
Density Functional Theory (DFT). From the calculated second-order elastic
constants, we have systematically shown that the extended linear vanadium chain
substructures indeed give rise to an anisotropic regime in the elastic and
mechanical moduli. The high density of valence and conduction electrons along
the linear vanadium chains leads to a directional dependence of the reciprocal
linear compressibility, Young's modulus and shear modulus. Poisson's ratio for
several elongation directions is also drastically affected by the presence of
extended V chains. If the elongation is along the V chains, all compounds
exhibit {practically} the same Poisson ratio in directions perpendicular to it,
further highlighting the importance of the V chains to the mechanical
properties. Moreover, based on our results, we have discussed the possible
consequences of the elastic anisotropy on the superconducting properties of the
compounds. Finally, using the Debye-Gr\""uneisen approximation, our calculations
of thermal properties show {a good agreement with the available experimental
low temperature heat capacity data above the superconducting critical
temperature.",1811.07814v1
2019-11-15,Achieving high figure-of-merit in Nb-doped Na$_{0.74}$CoO$_{2}$ compound at high temperature region,"We report the thermoelectric (TE) properties of
Na$_{0.74}$Co$_{0.95}$Nb$_{0.05}$O$_{2}$ in the temperature range $300-1200$ K,
as a potential candidate for p-type thermoelectric material. The experimental
values of Seebeck coefficient (S) are $ \sim $ $82-121$ $ \mu $V/K measured in
the temperature range $300-620$ K. The positive values of S in the entire
temperature range indicates p-type behaviour of the compound. At 300 K the
experimental value of thermal conductivity ($ \kappa $) is $ \sim $ 1.88 W/m-K
that increases up to $ \sim $ 420 K, then decreases till 620 K with
corresponding value $ \sim $ 1.86 W/m-K. To understand the experimentally
observed transport properties, we have calculated S and $\rho$ of this
compound. Then, based on theoretical understanding, we have estimated
\textit{figure-of-merit} (ZT) up to 1200 K by using calculated S and $\rho$
values with extrapolated experimental $\kappa$. The value of ZT is found to be
$\sim$ 0.03 at 300 K, whereas, the highest value is observed as $\sim$ 1.7 at
1200 K. Finally, we have calculated the efficiency ($\eta$) by keeping the cold
end temperature (T$_{c}$) fixed at 500 K and varying hot end temperature
(T$_{h}$) from 500 to 1200 K, respectively. The maximum value of $\eta$ is
found to be $\sim$ 8 %, when T$_{c}$ and T$_{h}$ are fixed at 500 and 1200 K,
respectively. This result suggests that
Na$_{0.74}$Co$_{0.95}$Nb$_{0.05}$O$_{2}$ compound can be used as a p-leg for
making high temperature TE generator (TEG).",1911.06584v1
2019-12-20,Shear Stress Distribution Prediction in Symmetric Compound Channels Using Data Mining and Machine Learning Models,"Shear stress distribution prediction in open channels is of utmost importance
in hydraulic structural engineering as it directly affects the design of stable
channels. In this study, at first, a series of experimental tests were
conducted to assess the shear stress distribution in prismatic compound
channels. The shear stress values around the whole wetted perimeter were
measured in the compound channel with different floodplain widths also in
different flow depths in subcritical and supercritical conditions. A set of,
data mining and machine learning models including Random Forest (RF), M5P,
Random Committee (RC), KStar and Additive Regression Model (AR) implemented on
attained data to predict the shear stress distribution in the compound channel.
Results indicated among these five models, RF method indicated the most precise
results with the highest R2 value of 0.9. Finally, the most powerful data
mining method which studied in this research (RF) compared with two well-known
analytical models of Shiono and Knight Method (SKM) and Shannon method to
acquire the proposed model functioning in predicting the shear stress
distribution. The results showed that the RF model has the best prediction
performance compared to SKM and Shannon models.",2001.01558v1
2020-01-28,A critical examination of compound stability predictions from machine-learned formation energies,"Machine learning has emerged as a novel tool for the efficient prediction of
materials properties, and claims have been made that machine-learned models for
the formation energy of compounds can approach the accuracy of Density
Functional Theory (DFT). The models tested in this work include five recently
published compositional models, a baseline model using stoichiometry alone, and
a structural model. By testing seven machine learning models for formation
energy on stability predictions using the Materials Project database of DFT
calculations for 85,014 unique chemical compositions, we show that while
formation energies can indeed be predicted well, all compositional models
perform poorly on predicting the stability of compounds, making them
considerably less useful than DFT for the discovery and design of new solids.
Most critically, in sparse chemical spaces where few stoichiometries have
stable compounds, only the structural model is capable of efficiently detecting
which materials are stable. The non-incremental improvement of structural
models compared with compositional models is noteworthy and encourages the use
of structural models for materials discovery, with the constraint that for any
new composition, the ground-state structure is not known a priori. This work
demonstrates that accurate predictions of formation energy do not imply
accurate predictions of stability, emphasizing the importance of assessing
model performance on stability predictions, for which we provide a set of
publicly available tests.",2001.10591v2
2020-01-30,Normally Hyperbolic Invariant Cylinders Passing Through Multiple Resonance,"We study the continuation of periodic orbits from various compound of
homoclinics in classical system. Together with the homoclinics, the periodic
orbits make up a $C^1$-smooth, normally hyperbolic invariant cylinder with
holes. It plays a key role to cross multiple resonant point.",2001.11223v1
2021-07-20,Pressure-stabilized Planar N4-ring and Bonding Properties in Manganese Nitrides,"Manganese nitrides should be with amazing properties and promised
application, because manganese atom is particular for its magnetism, valence
states, high electron density, etc., and N atoms in compounds form different
substructures. It is hard to good synthesize manganese nitride crystals with
all established means, therefore, theoretical studies are highly welcome. In
this study, we systematically examined the stoichiometric phases spaces of Mn-N
compounds from 0 to 100 GPa based on ab initio calculations, and constructed
the high pressure magnetic phase diagram. Remarkably, N-rich MnN4 with a planar
N4 ring was discovered for the first time in the pressure range from 40 to 100
GPa. The electronic structures reveal that the N4 ring is driven by the sp2
hybridization of nitrogen atoms. This phase with Tc=1.6 K and high bulk modulus
B =381 GPa, which make it potentially interesting as a hard superconductive
material. Moreover, the phase transition sequence for the MnN compound is
summarized renewedly, the semi-conducting NM-zb phase (5 GPa) first transforms
to metallic AFM-NiAs (40 GPa), which further transforms to the more stable
metallic FM-rs phase. The mechanical properties show that covalent interaction
has a great effect on N-rich structures' hardness and hardly effect on Mn-rich
structures in Mn-N compounds.",2107.09279v2
2021-07-30,Partially Diffusive Helium-Silica Compound in the Deep Interiors of Giant Planets,"Helium is the second most abundant element in the universe, and together with
silica, they are major components of giant planets. Exploring the reactivity
and state of helium and silica under high pressure is of fundamental importance
for developing and understanding of the evolution and internal structure of
giant planets. Here, using first-principles calculations and crystal structure
predictions, we identify four stable phases of a helium-silica compound with
seven/eight-coordinated silicon atoms at pressure range of 600-4000 GPa,
corresponding to the interior condition of the outer planets in the solar
system. The density of HeSiO2 agrees with current structure models of the
planets. This helium-silica compound exhibits a superionic-like helium
diffusive state at the high pressure and high temperature conditions along the
isentropes of Saturn, a metallic fluid state in Jupiter, and a solid state in
the deep interiors of Uranus and Neptune. The reaction of helium and silica may
lead to the erosion of the rocky core of giant planets and form a diluted core
region. These results highlight the reactivity of helium under high pressure to
form new compounds, and also provides evidence to help build more sophisticated
interior models of giant planets.",2107.14416v1
2017-04-09,Generalized Sylvester Formulas and skew Giambelli Identities,"We obtain a common generalization of two types of Sylvester formulas for
compound determinants and its Pfaffian analogue. As applications, we give
generalizations of the Giambelli identity to skew Schur functions and the Schur
identity to Schur's skew $Q$-functions.",1704.02585v1
2017-04-18,Unified phase diagram for iron-based superconductors,"High-temperature superconductivity is closely adjacent to a long-range
antiferromagnet, which is called a parent compound. In cuprates, all parent
compounds are alike and carrier doping leads to superconductivity, so a unified
phase diagram can be drawn. However, the properties of parent compounds for
iron-based superconductors show significant diversity and both carrier and
isovalent dopings can cause superconductivity, which casts doubt on the idea
that there exists a unified phase diagram for them. Here we show that the
ordered moments in a variety of iron pnictides are inversely proportional to
the effective Curie constants of their nematic susceptibility. This unexpected
scaling behavior suggests that the magnetic ground states of iron pnictides can
be achieved by tuning the strength of nematic fluctuations. Therefore, a
unified phase diagram can be established where superconductivity emerges from a
hypothetical parent compound with a large ordered moment but weak nematic
fluctuations, which suggests that iron-based superconductors are strongly
correlated electron systems.",1704.05182v2
2017-05-17,First-principles study of superconducting ScRhP and ScIrP pnictides,"For the first time, we have reported in this study an ab initio investigation
on elastic properties, Debye temperature, Mulliken population, Vickers
hardness, and charge density of superconducting ScRhP and ScIrP phosphides. The
optimized cell parameters show fair agreement with experimental results. The
elastic constants and moduli, Poisson's as well as Pugh's ratio and elastic
anisotropy factors have also been calculated to understand the mechanical
behavior of these ternary compounds. Their mechanical stability is confirmed
via the calculated elastic constants. The calculated values for Poisson's and
Pugh's ratio indicate the ductile nature of these compounds. ScIrP is expected
to be elastically more anisotropic than ScRhP. The estimated value of Debye
temperature predicts that ScRhP is thermally more conductive than ScIrP and the
phonon frequency in ScRhP is higher than that in ScIrP. The hardness of ScRhP
is lower due to the presence of anti-bonding Rh-Rh in ScRhP. The investigated
electronic structure predict that the metallic conductivity of ScRhP reduces
significantly when Rh is replaced with Ir. The main contribution to the total
density of states (TDOS) at Fermi-level (EF) comes from the d-electrons of Sc
and Rh/Ir in both compounds. These two ternary compounds are characterized
mainly by metallic and covalent bonding with little ionic contribution. As far
as superconductivity is concerned, the matrix elements of electron-phonon
interaction are noticeably enhanced in ScIrP compared to that in ScRhP.",1705.06083v1
2018-07-12,"Profiles for ion activities are multiphasic, not curvilinear","In agreement with previous findings (Nissen 2017a,b), data (Wilczek-Vera et
al. 2004) for the ion activities of a variety of simple inorganic compounds are
shown to be precisely represented as multiphasic, i.e. as a series of straight
lines separated by discontinuous transitions.",1807.07125v1
2018-07-25,PADME: A Deep Learning-based Framework for Drug-Target Interaction Prediction,"In silico drug-target interaction (DTI) prediction is an important and
challenging problem in biomedical research with a huge potential benefit to the
pharmaceutical industry and patients. Most existing methods for DTI prediction
including deep learning models generally have binary endpoints, which could be
an oversimplification of the problem, and those methods are typically unable to
handle cold-target problems, i.e., problems involving target protein that never
appeared in the training set. Towards this, we contrived PADME (Protein And
Drug Molecule interaction prEdiction), a framework based on Deep Neural
Networks, to predict real-valued interaction strength between compounds and
proteins without requiring feature engineering. PADME takes both compound and
protein information as inputs, so it is capable of solving cold-target (and
cold-drug) problems. To our knowledge, we are the first to combine Molecular
Graph Convolution (MGC) for compound featurization with protein descriptors for
DTI prediction. We used multiple cross-validation split schemes and evaluation
metrics to measure the performance of PADME on multiple datasets, including the
ToxCast dataset, and PADME consistently dominates baseline methods. The results
of a case study, which predicts the binding affinity between various compounds
and androgen receptor (AR), suggest PADME's potential in drug development. The
scalability of PADME is another advantage in the age of Big Data.",1807.09741v4
2019-01-08,Successive Convexification for 6-DoF Powered Descent Guidance with Compound State-Triggered Constraints,"This paper introduces a continuous formulation for compound state-triggered
constraints, which are generalizations of the recently introduced
state-triggered constraints. State-triggered constraints are different from
ordinary constraints found in optimal control in that they use a
state-dependent trigger condition to enable or disable a constraint condition,
and can be expressed as continuous functions that are readily handled by
successive convexification. Compound state-triggered constraints go a step
further, giving designers the ability to compose trigger and constraint
conditions using Boolean and and or operations. Simulations of the
6-degree-of-freedom (DoF) powered descent guidance problem obtained using
successive convexification are presented to illustrate the utility of
state-triggered and compound state-triggered constraints. The examples employ a
velocity-triggered angle of attack constraint to alleviate aerodynamic loads,
and a collision avoidance constraint to avoid large geological formations. In
particular, the velocity-triggered angle of attack constraint demonstrates the
ability of state-triggered constraints to introduce new constraint phases to
the solution without resorting to combinatorial techniques.",1901.02181v1
2019-01-17,Compositional dependence of epitaxial Tin+1SiCn MAX-phase thin films grown from a Ti3SiC2 compound target,"We investigate sputtering of a Ti3SiC2 compound target at temperatures
ranging from RT (no applied external heating) to 970 oC as well as the
influence of the sputtering power at 850 oC for the deposition of Ti3SiC2 films
on Al2O3(0001) substrates. Elemental composition obtained from time-of-flight
energy elastic recoil detection analysis shows an excess of carbon in all
films, which is explained by differences in angular distribution between C, Si
and Ti, where C scatters the least during sputtering. The oxygen content is 2.6
at.% in the film deposited at RT and decreases with increasing deposition
temperature, showing that higher temperatures favor high purity films. Chemical
bonding analysis by X-ray photoelectron spectroscopy shows C-Ti and Si-C
bonding in the Ti3SiC2 films and Si-Si bonding in the Ti3SiC2 compound target.
X-ray diffraction reveals that the phases Ti3SiC2, Ti4SiC3, and Ti7Si2C5 can be
deposited from a Ti3SiC2 compound target at substrate temperatures above 850 oC
and with growth of TiC and the Nowotny phase Ti5Si3Cx at lower temperatures.
High-resolution scanning transmission electron microscopy shows epitaxial
growth of Ti3SiC2, Ti4SiC3, and Ti7Si2C5 on TiC at 970 oC. Four-point probe
resistivity measurements give values in the range 120 to 450 micro-Ohm-cm and
with the lowest values obtained for films containing Ti3SiC2, Ti4SiC3, and
Ti7Si2C5.",1901.05904v1
2019-04-03,Platonic Compounds of Cylinders,"Generalizing the octahedral configuration of six congruent cylinders touching
the unit sphere, we exhibit configurations of congruent cylinders associated to
a pair of dual Platonic bodies.",1904.02043v1
2019-04-03,Ultrahigh Elastically Compressible and Strain-Engineerable Intermetallic Compounds Under Uniaxial Mechanical Loading,"Intermetallic compounds possess unique atomic arrangements that often lead to
exceptional material properties, but their extreme brittleness usually causes
fracture at a limited strain of less than 1% and prevents their practical use.
Therefore, it is critical for them to exhibit either plasticity or some form of
structural transition to absorb and release a sufficient amount of mechanical
energy before failure occurs. This study reports that the ThCr2Si2-structured
intermetallic compound (CaFe2As2) and a hybrid of its structure (CaKFe4As4)
with 2 {\mu}m in diameter and 6 {\mu}m in height can exhibit superelasticity
with strain up to 17% through a reversible, deformation-induced, lattice
collapse, leading to a modulus of resilience orders of magnitude higher than
that of most engineering materials. Such superelasticity also can enable strain
engineering, which refers to the modification of material properties through
elastic strain. Density Functional Theory calculations and cryogenic
nanomechanical tests predict that superconductivity in CaKFe4As4 could be
turned on/off through the superelasticity process, before fracture occurs, even
under uniaxial compression, which is the favorable switching loading mode in
most engineering applications. Our results suggest that other members with the
same crystal structure (more than 2500 intermetallic compounds), and
substitution series based on them should be examined for the possibility of
manifesting similar superelastic and strain-engineerable functional properties.",1904.02256v1
2019-04-08,"Local study of the insulating quantum kagome antiferromagnets YCu3(OH)6OxCl3-x (x=0,1/3)","The quantum kagome antiferromagnets YCu3(OH)6OxCl3-x (x=0,1/3) are produced
using a unified solid state synthesis route for polycrystalline samples. From
structural refinements based on neutron diffraction data, we clarify the
structure of the Y3Cu9(OH)18OCl8 (x=1/3) compound and provide a revised
chemical formula. We use muon spin relaxation, as a local probe of magnetism,
to investigate the exotic low temperature properties in the two compounds. In
agreement with the low temperature neutron diffraction data, we find no
evidence for long range ordering in both materials but they exhibit distinct
ground states: while disordered static magnetism develops in the x=0 compound,
we conclude on the stabilization of a quantum spin liquid in the x=1/3 one,
since the local fields remain fully dynamical. Our findings are in contrast to
previous reports based on thermodynamical measurements only. We then discuss
their origin on the basis of structural details and specific heat measurements.
In particular, the x=1/3 compound appears to realize an original spatially
anisotropic kagome model.",1904.04125v1
2019-07-05,"Reentrant spin-glass and transport behavior of Gd4PtAl, a compound with three sites for Gd","We report temperature (T) dependence (2-330 K) of DC and AC magnetization
(M), isothermal remnant magnetization (M_IRM), heat capacity (C), electrical
resistivity (rho), and magnetoresistance (MR) of a ternary intermetallic
compound, Gd4PtAl, crystallizing in a cubic (space group F-43m) structure. In
this structure, there are three sites for the rare-earth. The magnetization
data reveal that, in addition to a magnetic transition at 64 K, there is
another magnetic feature below 20 K. The C(T) data reveal an upturn below 64 K,
shifting to a lower temperature with increasing field, which establishes that
the onset of magnetic order is of an antiferromagnetic type. However, there is
no worthwhile feature near 20 K in the C(T) curve. AC susceptibility peak
undergoes an observable change with frequency and, in particular, the peak
around 20 K gets suppressed with the application of a dc magnetic field; in
addition, M_IRM undergoes a slow decay with time and isothermal M exhibits
low-field hysteresis below 20 K only, which is typical of spin-glasses. The
results overall suggest that this compound is a reentrant spin-glass in
zero-field. There are experimental signatures pointing to the existence of both
antiferromagnetic and ferromagnetic components, competing with the variation of
temperature and magnetic field, as a result of which electrical and
magnetoresistance behaviors are peculiar. The results overall suggest this
compound exhibits interesting magnetic and transport properties.",1907.02812v1
2019-10-01,A novel compound synapse using probabilistic spin-orbit-torque switching for MTJ based deep neural networks,"Analog electronic non-volatile memories mimicking synaptic operations are
being explored for the implementation of neuromorphic computing systems.
Compound synapses consisting of ensembles of stochastic binary elements are
alternatives to analog memory synapses to achieve multilevel memory operation.
Among existing binary memory technologies, magnetic tunneling junction (MTJ)
based Magnetic Random Access Memory (MRAM) technology has matured to the point
of commercialization. More importantly for this work, stochasticity is natural
to the MTJ switching physics e.g devices referred as p-bits which mimic binary
stochastic neurons. In this article, we experimentally demonstrate a novel
compound synapse that uses stochastic spin-orbit torque (SOT) switching of an
ensemble of nano-magnets that are located on one shared spin Hall effect (SHE)
material channel, i.e. tantalum. By using a properly chosen pulse scheme, we
are able to demonstrate linear potentiation and depression in the synapse, as
required for many neuromorphic architectures. In addition to this experimental
effort, we also performed circuit simulations on an SOT-MRAM based 784*200*10
deep belief network (DBN) consisting of p-bit based neurons and compound
synapses. MNIST pattern recognition was used to evaluate the system
performance, and our findings indicate that a significant reduction in
recognition error rates can be achieved when using our incremental pulse scheme
rather than a non-linear potentiation and depression as obtained when employing
identical pulses.",1910.00171v1
2019-10-03,"Structural, dielectric and magnetic properties of multiferroic (1-x) La0.5Ca0.5MnO3-(x) BaTi0.8Sn0.2O3 laminated composites","High performance lead-free multiferroic composites are desired to replace the
lead-based ceramics in multifunctional devices applications. Laminated
compounds were prepared from ferroelectric and ferromagnetic materials. In this
work, we present laminated ceramics compound by considering the ferromagnetic
La0.5Ca0.5MnO3 (LCMO) and the ferroelectric BaTi0.8Sn0.2O3 (BTSO) in two
different proportions. Compounds (1-x) LCMO-(x) BTSO with x=1 and 0 (pure
materials) were synthesized by the sol gel method and x=0.7 and 0.5 (laminated)
compounds were elaborated by welding appropriate mass ratios of each pure
material by using the silver paste technique. Structural, dielectric,
ferroelectric, microstructure and magnetic characterization were conducted on
these samples. X-ray scattering results showed pure perovskite phases
confirming the successful formation of both LCMO and BTSO. SEM images evidenced
the laminated structure and good quality of the interfaces. The laminated
composite materials have demonstrated a multiferroic behavior characterized by
the ferroelectric and the ferromagnetic hysteresis loops. Furthermore, the
enhancement of the dielectric constant in the laminated composite samples is
mainly attributed to the Maxwell-Wagner polarization.",1910.01538v1
2019-10-09,Decoupling of itinerant and localized $d$-orbital electrons in the compound Sc$_{0.5}$Zr$_{0.5}$Co,"By using the arc-melting method, we successfully synthesized the compound
Sc$_{0.5}$Zr$_{0.5}$Co with the space group of $Pm$-$3m$. Both the resistivity
and magnetic susceptibility measurements reveal a phase transition at about 86
K. This transition might be attributed to the establishment of an
antiferromagnetic order. The magnetization hysteresis loop measurements in wide
temperature region show a weak ferromagnetic feature, which suggests a possible
canted arrangement of the magnetic moments. Bounded by the phase transition
temperature, the resistivity at ambient pressure shows a change from Fermi
liquid behavior to a super-linear behavior as temperature increases. By
applying pressures up to 32.1 GPa, the transition temperature does not show a
clear change and no superconductivity is observed above 2 K. The density
functional theory (DFT) calculations confirm the existence of the
antiferromagnetic order and reveal a gap between the spin-up and spin-down
$d$-orbital electrons. This kind of behavior may suggest that the
antiferromagnetic order in this compound originates from the localized
$d$-electrons which do not contribute to the conductance. Thus the itinerant
and localized $d$-orbital electrons in the compound are decoupled.",1910.03966v1
2019-10-27,"Synthesis of La0.5Ca0.5-x xMnO3 nanocrystalline manganites by sucrose assisted auto combustion route and study of their structural, magnetic and magnetocaloric properties","Perovskite manganite La0.5Ca0.5-x xMnO3 (LCMO) nanomaterials were elaborated
using the sucrose modified auto combustion method. Rietveld refinements of the
X-ray diffraction patterns of the crystalline structure confirm a single-phase
orthorhombic state with Pbnm space group (No. 62). The Ca-vacancies were
voluntarily created in the LCMO structure in order to study their influence on
the magnetic behaviour in the system. The magnetic susceptibility was found to
be highly enhanced in the sample with Ca-vacancies.
Paramagnetic-to-ferromagnetic phase transition was evidenced in both samples
around 254 K. This transition is, characterized by a drastic jump of the
susceptibility in the sample with Ca-vacancies. The maximum of entropy change,
observed for both compounds at magnetic field of 6T was 2.30 J kg-1K-1 and 2.70
J kg-1K-1 for the parent compound and the lacunar one respectively. The
magnetocaloric adiabatic temperature change value calculated by indirect method
was 5.6 K and 5.2 K for the non-lacunar and Ca-vacancy compound, respectively.
The Ca-lacunar La0.5Ca0.5-x xMnO3 (x=0.05) reported in this work demonstrated
overall enhancement of the magnetocaloric effect over the LCMO. The technique
used to elaborate LCMO materials was beneficial to enhance the magnetocaloric
effect and magnetic behaviour. Therefore, we conclude that this less costly
environmentally friendly system can be considered as more advantageous
candidate for magnetic refrigeration applications then the commonly Gd-based
compounds.",1910.12245v1
2012-09-24,Small quantum dots of diluted magnetic III-V semiconductor compound,"In this chapter quantum many body theoretical methods have been used to study
properties of GaAs - and InAs - based, small semiconductor compound quantum
dots (QDs) containing manganese or vanadium atoms. Interest to such systems has
grown since experimental synthesis of nanoscale magnetic semiconductors, that
is, nanoscale semiconductor compounds with enhanced magnetic properties. This
enhancement is achieved by several methods, and in particular by doping common
semiconductor compounds with some atoms, such as Mn or V. Experimental studies
indicate that the electron spin density in the case of thin nanoscale magnetic
semiconductor films and QDs may be delocalized. As described in this chapter,
quantum many body theory-based, computational synthesis (i.e., virtual
synthesis) of tetrahedral symmetry GaAs and InAs small pyramidal QDs doped with
sabstitutional Mn or V atoms proves that such QDs are small magnetic molecules
that indeed, possess delocalized and polarized electron spin density. Such
delocalization provides a physical mechanism responsible for stabilization of
these nanoscale molecular magnets, and leads to the development of what can be
described as spin-polarized holes of the electron charge deficit. In some QDs,
numerical values of the electron spin density distribution are relatively
large, indicating that such semiconductor systems may be used as nanomaterials
for spintronic and magneto-optical sensor applications.",1209.5341v1
2014-06-02,Superconductivity in titanium-based pnictide oxide compounds,"Superconductivity in a novel class of layered materials, Ti-based pnictide
oxides, was recently discovered. These compounds have attracted interest since
they combine features of copper oxide and iron pnictide superconductors. Here
the transition metal (titanium) forms two-dimensional Ti$_2$O layers (anti
structure to the CuO$_2$ planes), capped by pnictogen ions (similar to
Fe$_2$As$_2$ layers). The pnictide oxide compounds show a spin or charge
density wave phase which coexists with superconductivity in some members of the
family. Unlike the cuprates, but similar to iron pnictides, the parent
compounds of pnictide oxides are metals with specific nesting properties of the
Fermi surface which leads to the density wave instability. The nature of the
superconductivity, coexisting with the density wave order, and the possible
competition or mutual interaction between both states is one of the central
questions of recent studies. This short review summarizes the current knowledge
from an experimental as well as theoretical point of view and discusses some of
the open questions and possible future developments.",1406.0442v1
2014-06-20,Optical properties of BiTeBr and BiTeCl,"We present a comparative study of the optical properties - reflectance,
transmission and optical conductivity - and Raman spectra of two layered
bismuth-tellurohalides BiTeBr and BiTeCl at 300 K and 5 K, for light polarized
in the a-b planes. Despite different space groups, the optical properties of
the two compounds are very similar. Both materials are doped semiconductors,
with the absorption edge above the optical gap which is lower in BiTeBr (0.62
eV) than in BiTeCl (0.77 eV). The same Rashba splitting is observed in the two
materials. A non-Drude free carrier contribution in the optical conductivity,
as well as three Raman and two infrared phonon modes, are observed in each
compound. There is a dramatic difference in the highest infrared phonon
intensity for the two compounds, and a difference in the doping levels. Aspects
of the strong electron-phonon interaction are identified. Several interband
transitions are assigned, among them the low-lying absorption $\beta$ which has
the same value 0.25 eV in both compounds, and is caused by the Rashba spin
splitting of the conduction band. An additional weak transition is found in
BiTeCl, caused by the lower crystal symmetry.",1406.5356v1
2018-08-24,Inverse Statics Optimization for Compound Tensegrity Robots,"Robots built from cable-driven tensegrity (`tension-integrity') structures
have many of the advantages of soft robots, such as flexibility and robustness,
while still obeying simple statics and dynamics models. However, existing
tensegrity modeling approaches cannot natively describe robots with arbitrary
rigid bodies in their tension network. This work presents a method to calculate
the cable tensions in static equilibrium for such tensegrity robots, here
defined as compound tensegrity. First, a static equilibrium model for compound
tensegrity robots is reformulated from the standard force density method used
with other tensegrity structures. Next, we pose the problem of calculating
tension forces in the robot's cables under our proposed model. A solution is
proposed as a quadratic optimization problem with practical constraints.
Simulations illustrate how this inverse statics optimization problem can be
used for both the design and control of two different compound tensegrity
applications: a spine robot and a quadruped robot built from that spine.
Finally, we verify the accuracy of the inverse statics model through a hardware
experiment, demonstrating the feasibility of low-error open-loop control using
our proposed methodology.",1808.08252v2
2018-12-12,Observing a Lévy process up to a stopping time,"It is proved that the law of a possibly killed L\'evy process $X$, seen up to
and including (resp. up to strictly before) a stopping time, determines already
the law of $X$ (resp. up to a compound Poisson component and killing).",1812.05128v1
2018-12-20,A Density Functional Theory Based Electron Transport Study of Coherent Tunneling Through Cyclic Molecules Containing Ru and Os as Redox Active Centers,"In our theoretical study in which we combine a nonequilibrium Green's
function (NEGF) approach with density functional theory (DFT) we investigate
branched compounds containing Ru or Os metal complexes in two branches, which
due to their identical or different metal centers are symmetric or asymmetric.
In these compounds the metal atoms are connected to pyridyl anchor groups via
acetylenic and phenyl spacer groups in a meta-connection. We find there is no
destructive quantum interference (DQI) feature in the transmission function
near the Fermi level for the investigated molecules regardless of their
symmetry, neither in their neutral states nor in their charged states. We map
the structural characteristics of the range of molecules onto a simplified
tight-binding model in order to identify the main differences between the
molecules in this study and previously investigated ferrocene compounds in
order to clarify the structural sources for DQI, which we found for the latter
but not for the former. We also find that local charging on one of the branches
only changes the conductance by about one order of magnitude which we explain
in terms of the spatial distributions and charge-induced energy shifts of the
relevant molecular orbitals for the branched compounds.",1812.08841v1
2018-12-21,Electric field- induced Pinch-off of a migrating compound droplet in confined micro channel,"The present study looks into the pinch-off dynamics of a compound droplet,
which is suspended in another fluid in a parallel plate microchannel. The
droplet is subjected to a transverse electric field in the presence of an
imposed pressure driven flow. For the present study, a leaky dielectric model
have been taken into consideration. When a concentric compound droplet migrates
in a pressure driven flow, the inner droplet shifts from the concentric
position and forms a eccentric configuration that finally leads to the rupture
of the outer shell. The present investigation have uncovered that the temporal
evolution of droplet eccentricity as well as the kinetics of the thinning of
the outer droplet are markedly influenced by the strength of the electric field
as well as the electric properties of the system. The present study also shows
that the conversion of different modes of droplet pinch-off mode , such as the
equatorial cap breaking-off or the hole-puncturing mode can be attained by
altering the electric field strength and its electrical properties. Finally the
present study depicts that these factors also alter the pinch-off time as well
as its location on the outer interface. Therefore the outcomes of the present
study offers an effective means of modulating the morphology of compound
droplets in a confined channel by applying an electric field.",1812.09033v1
2018-12-26,Realization of predicted exotic materials: The burden of proof,"Trove of exotic topoloid structures has recently been predicted by searching
for compounds whose calculated band structure crossing points fulfill specific
symmetry requirements. Discovery of exciting physical phenomena by experimental
studies of such predicted compounds is just around the corner. Yet, the
examination of some of these assumed high-symmetry structures suggests that not
always will assembly of atoms in a configuration that yields exotic topological
properties be protected against energy-lowering symmetry breaking modes.
Indeed, although bulk topological characteristics lead to protected
surface/edge states, nothing protects bulk states from structural instability.
The burden of proof for theoretical predictions of exciting physical phenomena
should include some compelling hints that such phenomena can live in
thermodynamically stable (or near stable) compounds. Herein, we illustrate how
the use of the calculated total (electron + ion) energies of candidate
structures can remove false-positive predicted topoloids from the list of
likely realizable compounds, to the benefit of the much-cherished iterative
process of theory-experiment materials discovery.",1812.10573v5
2019-02-25,Real-Time Quad-Rotor Path Planning Using Convex Optimization and Compound State-Triggered Constraints,"The contribution of this paper is the application of compound state-triggered
constraints (STCs) to real-time quad-rotor path planning. Originally developed
for rocket landing applications, STCs are made up of a trigger condition and a
constraint condition that are arranged such that satisfaction of the former
implies satisfaction of the latter. Compound STCs go a step further by allowing
multiple trigger and constraint conditions to be combined via Boolean ""and"" or
""or"" operations. The logical implications embodied by STCs can be formulated
using continuous variables, and thus enable the incorporation of discrete
decision making into a continuous optimization framework. In this paper,
compound STCs are used to solve quad-rotor path planning problems that would
typically require the use of computationally expensive mixed-integer
programming techniques. Two scenarios are considered: (1) a quad-rotor flying
through a hoop, and (2) a pair of quad-rotors carrying a beam-like payload
through an obstacle course. Successive convexification is used to solve the
resulting non-convex optimization problem. Monte-Carlo simulation results show
that our approach can reliably generate trajectories at rates upwards of 3 and
1.5 Hz for the first and second scenarios, respectively.",1902.09149v1
2019-02-25,Empirical Evidence of Isospin Memory in Compound Nuclear Fission,"We present empirical evidence of isospin dependence in the compound nuclear
fission cross-sections and fission widths, which suggests that the compound
nucleus (CN) possibly retains the memory of the isospin when it is formed. We
examine the idea, first proposed by Yadrovsky [1], for three pairs of reactions
where experimental data of fission cross section at various excitation energies
are available. One of the pairs of reactions is the same as used by Yadrovsky
i.e. $^{209}$Bi($p$, f) and $^{206}$Pb($\alpha$, f) leading to the CN
$^{210}$Po but with an improved experimental data set. The other two pairs of
reaction sets are, $^{185}$Re($p$, f) and $^{182}$W($\alpha$, f) leading to the
CN $^{186}$Os and, $^{205}$Tl($p$, f) and $^{202}$Hg($\alpha$, f) leading to
the CN $^{206}$Pb. An observable difference between the fission branching
ratios in two different isospin states suggests that the CN seems to remember
its isospin at the point of formation. This possibility is further supported by
another method, where additional empirical evidence for four CN, viz.
$^{210}$Po, $^{209}$Bi, $^{207}$Bi, and $^{198}$Hg, is obtained from the
experimental data in Zhukova et al. [2]. Further, the data also suggest a
possible new signature of the weakening of CN process and gradual transition to
non-compound processes as the energy rises. Fresh experimental efforts as
proposed, are required to confirm these findings.",1902.09319v1
2019-06-27,First-principles study of LaOPbBiS$_3$ and its analogous compounds as thermoelectric materials,"LaOBiPbS$_3$ is a kind of pnictogen-dichalcogenide layered compounds, which
have recently been experimentally investigated as thermoelectric materials
owing to their low thermal conductivity and high controllability of constituent
elements. However, thermoelectric performance of LaOBiPbS$_3$ is at present not
very high and that of its analogous compounds remains to be unknown. In this
study, we theoretically investigate thermoelectric properties of 24 possible
variations of the constituent elements in LaOBiPbS$_3$ from the viewpoint of
the electronic structure. We find that some compounds can have much better
thermoelectric performance than LaOBiPbS$_3$; in particular, LaOSbPbSe$_3$ is
predicted to have a power factor five times as large as that of LaOBiPbS$_3$.
Here, the choice of the pnictogen atom (As, Sb, and Bi), of which the
low-energy conduction bands mainly consist, correlates with the calculated
power factor and the dimensionless figure of merit, $ZT$. Such correlation
comes from the fact that the low-dimensionality of the electronic structure,
which enhances the density of states near the band edge, strongly depends on
the pnictogen atom through, e.g., the strength of the spin-orbit coupling.
Moreover, hybridization of the wave functions in the pnictogen-dichalcogenide
layer and those in the rock-salt layer plays a key role in gap opening, and
thus is important for achieving high thermoelectric performance. In
LaOSbPbSe$_3$, such hybridization also pushes up the conduction band bottom,
which enhances the density of states near the band edge and thus the power
factor.",1906.11505v1
2020-04-10,Hydrogen storage properties of Mn and Cu for Fe substitution in TiFe0.9 intermetallic compound,"The present study investigates the partial substitutions of Mn and Cu for Fe
in the TiFe-system to gain better understanding of the role of elemental
substitution on its hydrogen storage properties. The TiFe0.88-xMn0.02Cux (x =
0, 0.02, 0.04) compositions were studied. From X-Ray Diffraction (XRD) and
Electron Probe Micro-Analysis (EPMA), it was found that all alloys are
multi-phase, with TiFe as a major phase, together with \b{eta}-Ti and
Ti4Fe2O-type as secondary precipitates, of all them containing also Mn and Cu.
Increasing the Cu content augments the secondary phase amounts. Low quantity of
secondary phases helps the activation of the main TiFe phase for the first
hydrogen absorption, but on increasing their amounts, harsher activation
occurs. Both Mn and Cu substitutions increase the cell parameter of TiFe, thus
decreasing the first plateau pressure. However, Cu substitution rises the
second plateau pressure revealing the predominancy of electronic effects
associated to this substitution. All samples have fast kinetics and high
hydrogen capacity making these substituted compounds promising for large scale
stationary applications.",2004.04947v2
2021-03-30,A comprehensive study of the physical properties of Nb2P5 via ab-initio technique,"Binary metallic phosphide, Nb2P5, belongs to technologically important class
of materials. Quite surprisingly, a large number of physical properties of
Nb2P5, including elastic properties and their anisotropy, acoustic, electronic
(DOS, charge density distribution, electron density difference),
thermo-physical, bonding characteristics, and optical properties have not been
investigated at all. In the present work we have explored all these properties
in details for the first time employing density functional theory based
first-principles method. Nb2P5 is found to be a mechanically stable,
elastically anisotropic compound with weak brittle character. The bondings
among the atoms are dominated by covalent and ionic contributions with small
signature of metallic feature. The compound possesses high level of
machinability. Nb2P5 is a moderately hard compound. The band structure
calculations reveal metallic conduction with a large electronic density of
states at the Fermi level. Calculated values of different thermal properties
indicate that Nb2P5 has the potential to be used as a thermal barrier coating
material. The energy dependent optical parameters show close agreement with the
underlying electronic band structure. The optical absorption and reflectivity
spectra and the static index of refraction of Nb2P5 show that the compound
holds promise to be used in optoelectronic device sector. Unlike notable
anisotropy in elastic and mechanical properties, the optical parameters are
found to be almost isotropic.",2103.16027v1
2022-01-31,Performance Analysis of Novel Propellant Oxidizers using Molecular Modelling and Nozzle Flow Simulations,"The primary target of this paper is to present novel compounds in view of
their possible use as oxidizers in propulsion applications using molecular
modeling calculations and supersonic flow simulations. Carbon-based
heterocyclic compounds tend to have strained molecular structures leading to
high heats of formation and energetic behavior. In the present work, molecular
modeling calculations for molecules of 37 such potential propellant oxidizers
are presented. Density functional theory (B3LYP) was employed for the geometry
optimization of the proposed molecular structures using the 6-311++G(d,p) basis
set. Heats of formation of the compounds were calculated using the molecular
modeling results. Appropriate propellant compositions were considered with the
proposed compounds as oxidizer components and Ideal specific impulse
(Ivac,ideal*) was calculated for each composition assuming isentropic flow,
computed using the NASA CEA software package. To predict the actual delivered
specific impulse (Ivac,act*), supersonic nozzle flow simulations of equilibrium
product gases of each propellant composition have been carried out using
OpenFOAM. The standard k-epsilon turbulence model for compressible flows
including rapid distortion theory (RDT) based compression term, has been
employed. As the problem is inherently transient in nature, local time stepping
(LTS) methodology has been further implemented to reach a steady-state
solution. These simulations accounted for divergence losses, turbulence losses
and boundary layer losses and gave a more realistic estimation of the specific
impulse. It was observed that the Ivac,act* for all propellant compositions lie
between 88% to 91% of the corresponding ideal value. The newly proposed
oxidizers showed considerable improvement in propulsion performance as compared
to ammonium perchlorate.",2202.00107v2
2022-02-01,Option Pricing and CVA Calculations using the Monte Carlo-Tree (MC-Tree) Method,"The binomial tree method and the Monte Carlo (MC) method are popular methods
for solving option pricing problems. However in both methods there is a
trade-off between accuracy and speed of computation, both of which are
important in applications. We introduce a new method, the MC-Tree method, that
combines the MC method with the binomial tree method. It employs a mixing
distribution on the tree parameters, which are restricted to give prescribed
mean and variance. For the family of mixing densities proposed here, the
corresponding compound densities of the tree outcomes at final time are
obtained. Ideally the compound density would be (after a logarithmic
transformation of the asset prices) Gaussian. Using the fact that in general,
when mean and variance are prescribed, the maximum entropy distribution is
Gaussian, we look for mixing densities for which the corresponding compound
density has high entropy level. The compound densities that we obtain are not
exactly Gaussian, but have entropy values close to the maximum possible
Gaussian entropy. Furthermore we introduce techniques to correct for the
deviation from the ideal Gaussian pricing measure. One of these (distribution
correction technique) ensures that expectations calculated with the method are
taken with respect to the desired Gaussian measure. The other one
(bias-correction technique) ensures that the probability distributions used are
risk-neutral in each of the trees. Apart from option pricing, we apply our
techniques to develop an algorithm for calculation of the Credit Valuation
Adjustment (CVA) to the price of an American option. Numerical examples of the
workings of the MC-Tree approach are provided, which show good performance in
terms of accuracy and computational speed.",2202.00785v1
2022-02-12,High-throughput discovery of chemical structure-polarity relationships combining automation and machine learning techniques,"As an essential attribute of organic compounds, polarity has a profound
influence on many molecular properties such as solubility and phase transition
temperature. Thin layer chromatography (TLC) represents a commonly used
technique for polarity measurement. However, current TLC analysis presents
several problems, including the need for a large number of attempts to obtain
suitable conditions, as well as irreproducibility due to non-standardization.
Herein, we describe an automated experiment system for TLC analysis. This
system is designed to conduct TLC analysis automatically, facilitating
high-throughput experimentation by collecting large experimental data under
standardized conditions. Using these datasets, machine learning (ML) methods
are employed to construct surrogate models correlating organic compounds'
structures and their polarity using retardation factor (Rf). The trained ML
models are able to predict the Rf value curve of organic compounds with high
accuracy. Furthermore, the constitutive relationship between the compound and
its polarity can also be discovered through these modeling methods, and the
underlying mechanism is rationalized through adsorption theories. The trained
ML models not only reduce the need for empirical optimization currently
required for TLC analysis, but also provide general guidelines for the
selection of conditions, making TLC an easily accessible tool for the broad
scientific community.",2202.05962v1
2022-03-01,Cu-doping effects on the ferromagnetic semimetal CeAuGe,"We present a study of Cu-substitution effects in 4f-Ce intermetallic compound
CeAu1-xCuxGe, with potentially unusual electronic states, in the whole
concentration range (x = 0.0 - 1.0). The parent CeAuGe compound, crystallizing
in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with
Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu1-xCuxGe, changes
the crystal structure from the non-centrosymmetric (P63mc) to centrosymmetric
(P63/mmc) space group at the concentration x ~ 0.5, where the c-lattice
constant has a maximum value. Magnetic susceptibility and electrical
resistivity measurements reveal that all Cu-doped compounds undergo magnetic
phase transition near 10 K, with the maximum transition temperature of 12 K for
x = 0.5. The neutron powder diffraction experiments show the ferromagnetic
ordering of Ce3+ magnetic moments with a value of ~ 1.2 Bohr magneton at 1.8 K,
oriented perpendicular to the hexagonal c-axis. By using symmetry analysis, we
have found the solutions for the magnetic structure in the ferromagnetic
Shubnikov space groups Cmc'21' and P21'/m' for x < 0.5 and x >= 0.5,
respectively. Electrical resistivity exhibits a metallic temperature behaviour
in all compounds. The resistivity has a local minimum in the paramagnetic state
due to Kondo effects at high doping x = 0.8 and 1.0. At the small Cu-doping
level, x = 0.2, the resistivity shows a broad feature at the ferromagnetic
transition temperature and an additional transition-like peculiarity at 2.5 K
in the ferromagnetic state.",2203.00335v1
2022-03-04,Machine-learning enabled thermodynamic model for the design of new rare-earth compounds,"We employ a descriptor based machine-learning approach to assess the effect
of chemical alloying on formation-enthalpy of rare-earth intermetallics.
Application of machine-learning approaches in rare-earth intermetallic design
have been sparse due to limited availability of reliable datasets. In this
work, we developed an `in-house' rare-earth database with more than 600$+$
compounds, each entry was populated with formation enthalpy and related atomic
features using high-throughput density-functional theory (DFT). The SISSO (sure
independence screening and sparsifying operator) based machine-learning method
with meaningful atomic features was used for training and testing the formation
enthalpies of rare earth compounds. The complex lattice function coupled with
the machine-learning model was used to explore the effect of transition metal
alloying on the energy stability of Ce based cubic Laves phases (MgCu$_{2}$
type). The SISSO predictions show good agreement with high-fidelity DFT
calculations and X$-$ray powder diffraction measurements. Our study provides
quantitative guidance for compositional considerations within a
machine-learning model and discovering new metastable materials. The
electronic-structure of Ce$-$Fe$-$Cu based compound was also analyzed
in$-$depth to understand the electronic origin of phase stability. The
interpretable analytical models in combination with density$-$functional theory
and experiments provide a fast and reliable design guide for discovering
technologically useful materials.",2203.02391v1
2022-03-20,Semiclassical energy transition of driven chaotic systems: phase coherence on scar disks,"A trajectory segment in an energy shell, which combines to form a closed
curve with a segment in another canonically driven energy shell, adds an
oscillatory semiclassical contribution to the smooth classical background of
the quantum probability density for a transition between their energies. If
either segment is part of a Bohr-quantized periodic orbit of either shell, the
centre of its endpoints lies on a scar disk of the spectral Wigner function for
single static energy shell and the contribution to the transition is reinforced
by phase coherence. The exact representation of the transition density as an
integral over spectral Wigner functions, which was previously derived for the
special case where the system undergoes a reflection in phase space, is here
generalized to arbitrary unitary transformations. If these are generated
continuously by a driving Hamiltonian, there will be a finite lapse in the
driving time for the transition to start, until the initially nested shells
touch each other and then start to overlap.
  The stationary phase evaluation of the multidimensional integral for the
transition density selects the pair of matching trajectory segments on each
shell, which close to form a piecewise smooth compound orbit. Each compound
orbit shows up as a fixed point of a product of mappings that generalize
Poincar\'e maps on the intersection of the shells. Thus, the closed compound
orbits are isolated if the original Hamiltonian is chaotic. The actions of the
compound orbits depend on the driving time, or on any other parameter of the
transformation of the original eigenstates.",2203.10668v2
2022-03-30,Pressure-induced superconductivity in flat-band Kagome compounds Pd$_3$P$_2$(S$_{1-x}$Se$_x$)$_8$,"We performed high-pressure transport studies on the flat-band Kagome
compounds, Pd$_3$P$_2$(S$_{1-x}$Se$_x$)$_8$ ($x$ = 0, 0.25), with a diamond
anvil cell. For both compounds, the resistivity exhibits an insulating behavior
with pressure up to 17 GPa. With pressure above 20 GPa, a metallic behavior is
observed at high temperatures in Pd$_3$P$_2$S$_8$, and superconductivity
emerges at low temperatures. The onset temperature of superconducting
transition $T_{\rm C}$ rises monotonically from 2 K to 4.8 K and does not
saturate with pressure up to 43 GPa. For the Se-doped compound
Pd$_3$P$_2$(S$_{0.75}$Se$_{0.25}$)$_8$, the $T_{\rm C}$ is about 1.5 K higher
than that of the undoped one over the whole pressure range, and reaches 6.4 K
at 43 GPa. The upper critical field with field applied along the $c$ axis at
typical pressures is about 50$\%$ of the Pauli limit, suggesting a 3D
superconductivity. The Hall coefficient in the metallic phase is low and
exhibits a peaked behavior at about 30 K, which suggests either a multi-band
electronic structure or an electron correlation effect in the system.",2203.15957v2
2016-03-10,Thermodynamic Screening of Metal-Substituted MOFs for Carbon Capture,"Metal-organic frameworks (MOFs) have emerged as promising materials for
carbon capture applications due to their high CO2 capacities and tunable
properties. Amongst the many possible MOFs, metal-substituted compounds based
on M-DOBDC and M-HKUST-1 have demonstrated amongst the highest CO2 capacities
at the low pressures typical of flue gasses. Here we explore the possibility
for additional performance tuning of these compounds by computationally
screening 36 metal-substituted variants (M = Be, Mg, Ca, Sr, Sc, Ti, V, Cr, Mn,
Fe, Co, Ni, Cu, Zn, Mo, W, Sn, and Pb) with respect to their CO2 adsorption
enthalpy, $\Delta$H (T=300K). Supercell calculations based on van der Waals
density functional theory (vdW-DF) yield enthalpies in good agreement with
experimental measurements, out-performing semi-empirical (DFT-D2) and
conventional (LDA and GGA) functionals. Our screening identifies 13 compounds
having $\Delta$H values within the targeted thermodynamic window 40 $\leq$
$\Delta$H $\leq$ 75 kJ/mol: 8 are based on M-DODBC (M=Mg, Ca, Sr, Sc, Ti, V,
Mo, and W), and 5 on M-HKUST-1 (M= Be, Mg, Ca, Sr and Sc). Variations in the
electronic structure and the geometry of the structural building unit are
examined and used to rationalize trends in CO2 affinity. In particular, the
partial charge on the coordinatively unsaturated metal sites is found to
correlate with $\Delta$H, suggesting that this property may be used as a simple
performance descriptor. The ability to rapidly distinguish promising MOFs from
those that are ""thermodynamic dead-ends"" will be helpful in guiding synthesis
efforts towards promising compounds.",1603.03192v1
2016-03-17,"Rattling enhanced superconductivity in MV$_2$Al$_{20}$ (M = Sc, Lu, Y) intermetallic cage compounds","Polycrystalline samples of four intermetallic compounds: MV$_2$Al$_{20}$ (M =
Sc, Y, La, and Lu) were synthesized using an arc-melting technique. The crystal
structures were analyzed by means of powder x-ray diffraction and Rietveld
analysis, and the physical properties were studied by means of heat capacity,
electrical resistivity and magnetic susceptibility measurements down to 0.4 K.
For ScV$_2$Al$_{20}$, LuV$_2$Al$_{20}$, and YV$_2$Al$_{20}$, superconductivity
was observed with critical temperatures T$_c$ = 1.00 K, 0.57 K, and 0.60 K,
respectively. Superconductivity for the Lu compound is reported for the first
time. Theoretical calculations of the electronic and phonon structures were
conducted in order to analyze the superconductivity and dynamics in
ScV$_2$Al$_{20}$, YV$_2$Al$_{20}$, and LuV$_2$Al$_{20}$ and to explain the lack
of a superconducting transition in LaV$_2$Al$_{20}$ down to 0.4 K. The results
of the experimental and theoretical studies show that all the compounds are
weakly-coupled type II BCS superconductors, and reveal the importance of the
M-atom anharmonic ""rattling"" modes for the superconductivity in these
materials, which seem to enhance T$_c$, especially for ScV$_2$Al$_{20}$.",1603.05320v1
2016-12-02,Unusual mixed valence of Eu in two new materials EuSr2Bi2S4F4 and Eu2SrBi2S4F4: Mössbauer and X-ray photoemission Spectroscopy investigations,"We have synthesized two new Eu-based compounds, EuSr2Bi2S4F4 and Eu2SrBi2S4F4
which are derivatives of Eu3Bi2S4F4, an intrinsic superconductor with Tc = 1.5
K. They belong to a tetragonal structure (SG: I4/mmm, Z = 2), similar to the
parent compound Eu3Bi2S4F4. Our structural and 151Eu M\""ossbauer spectroscopy
studies show that in EuSr2Bi2S4F4, Eu-atoms exclusively occupy the
crystallographic 2a-sites. In Eu2SrBi2S4F4, 2a-sites are fully occupied by
Eu-atoms and the other half of Eu-atoms and Sr-atoms together fully occupy
4e-sites in a statistical distribution. In both compounds Eu atoms occupying
the crystallographic 2a-sites are in a homogeneous mixed valent state ~ 2.6 -
2.7. From our magnetization studies in an applied H = 9 Tesla, we infer that
the valence of Eu-atoms in Eu2SrBi2S4F4 at the 2a-sites exhibits a shift
towards 2+. Our XPS studies corroborate the occurrence of valence fluctuations
of Eu and after Ar-ion sputtering show evidence of enhanced population of
Eu2+-states. Resistivity measurements, down to 2 K suggest a semi-metallic
nature for both compounds.",1612.00639v1
2016-12-09,Comparative study of Mo2Ga2C with superconducting MAX phase Mo2GaC: a first-principles calculations,"The structural, electronic, optical and thermodynamic properties of Mo2Ga2C
are investigated using density functional theory (DFT) within the generalized
gradient approximation (GGA). The optimized crystal structure is obtained and
the lattice parameters are compared with available experimental data. The
electronic density of states (DOS) is calculated and analyzed. The metallic
behavior for the compound is confirmed and the value of DOS at Fermi level is
4.2 states per unit cell per eV. Technologically important optical parameters
(e.g., dielectric function, refractive index, absorption coefficient, photo
conductivity, reflectivity, and loss function) have been calculated for the
first time. The study of dielectric constant (e1) indicates the Drude-like
behavior. The absorption and conductivity spectra suggest that the compound is
metallic. The reflectance spectrum shows that this compound has the potential
to be used as a solar reflector. The thermodynamic properties such as the
temperature and pressure dependent bulk modulus, Debye temperature, specific
heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from
the quasi-harmonic Debye model with phononic effect also for the first time.
Analysis of Tc expression using available parameter values (DOS, Debye
temperature, atomic mass etc.) suggests that the compound is less likely to be
superconductor.",1612.02907v1
2016-12-16,Pressure-Induced Metallization in Iron-Based Ladder Compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$,"Electrical resistivity measurements have been performed on the iron-based
ladder compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$ ($x$ = 0, 0.25, 0.65, and 1)
under high pressure. A cubic anvil press was used up to 8.0 GPa, whereas
further higher pressure was applied using a diamond anvil cell up to 30.0 GPa.
Metallic behavior of the electrical conductivity was confirmed in the $x$ =
0.25 and 0.65 samples for pressures greater than 11.3 and 14.4 GPa,
respectively, with the low-temperature $\log T$ upturn being consistent with
weak localization of 2D electrons due to random potential. At pressures higher
than 23.8 GPa, three-dimensional Fermi-liquid-like behavior was observed in the
latter sample. No metallic conductivity was observed in the parent compounds
BaFe$_2$Se$_3$ ($x $ = 0) up to 30.0 GPa and CsFe$_2$Se$_3$ ($x$ = 1) up to
17.0 GPa. The present results indicate that the origins of the insulating
ground states in the parent and intermediate compounds are intrinsically
different; the former is a Mott insulator, whereas the latter is an Anderson
insulator owing to the random substitution of Cs for Ba.",1612.05394v1
2016-12-25,Conformally correct tilings,"We discuss the art and science of producing conformally correct euclidean and
hyperbolic tilings of compact surfaces. As an example, we present a tiling of
the Chmutov surface by hyperbolic (2, 4, 6) triangles.",1612.08299v1
2017-02-08,Chlorine and Bromine Isotope Fractionation of Halogenated Organic Compounds in Electron Ionization Mass Spectrometry,"Revelation of chlorine and bromine isotope fractionation of halogenated
organic compounds (HOCs) in electron ionization mass spectrometry (EI-MS) is
crucial for compound-specific chlorine/bromine isotope analysis (CSIA-Cl/Br)
using gas chromatography EI-MS (GC-EI-MS). This study systematically
investigated chlorine/bromine isotope fractionation in EI-MS of HOCs including
12 organochlorines and 5 organobromines using GC-double focus magnetic-sector
high resolution MS (GC-DFS-HRMS). Chlorine/bromine isotope fractionation
behaviors of the HOCs in EI-MS showed varied isotope fractionation patterns and
extents depending on compounds. Besides, isotope fractionation patterns and
extents varied at different EI energies, demonstrating potential impacts of EI
energy on the chlorine/bromine isotope fractionation. Hypotheses of inter-ion
and intra-ion isotope fractionations were applied to interpreting the isotope
fractionation behaviors. The inter-ion and intra-ion isotope fractionations
counteractively contributed to the apparent isotope ratio for a certain
dehalogenated product ion. The isotope fractionation mechanisms were
tentatively elucidated on basis of the quasi-equilibrium theory. In the light
of the findings of this study, isotope ratio evaluation scheme using complete
molecular ions and the EI source with sufficient stable EI energies may be
helpful to achieve optimal precision and accuracy of CSIA-Cl/Br data. The
method and results of this study can help to predict isotope fractionation of
HOCs during dehalogenation processes and further to reveal the dehalogenation
pathways.",1702.02323v2
2017-06-27,Computational Study of Halide Perovskite-Derived A$_2$BX$_6$ Inorganic Compounds: Chemical Trends in Electronic Structure and Structural Stability,"The electronic structure and energetic stability of A$_2$BX$_6$ halide
compounds with the cubic and tetragonal variants of the perovskite-derived
K$_2$PtCl$_6$ prototype structure are investigated computationally within the
frameworks of density-functional-theory (DFT) and hybrid (HSE06) functionals.
The HSE06 calculations are undertaken for seven known A$_2$BX$_6$ compounds
with A = K, Rb and Cs, and B = Sn, Pd, Pt, Te, and X = I. Trends in band gaps
and energetic stability are identified, which are explored further employing
DFT calculations over a larger range of chemistries, characterized by A = K,
Rb, Cs, B = Si, Ge, Sn, Pb, Ni, Pd, Pt, Se and Te and X = Cl, Br, I. For the
systems investigated in this work, the band gap increases from iodide to
bromide to chloride. Further, variations in the A site cation influences the
band gap as well as the preferred degree of tetragonal distortion. Smaller A
site cations such as K and Rb favor tetragonal structural distortions,
resulting in a slightly larger band gap. For variations in the B site in the
(Ni, Pd, Pt) group and the (Se, Te) group, the band gap increases with
increasing cation size. However, no observed chemical trend with respect to
cation size for band gap was found for the (Si, Sn, Ge, Pb) group. The findings
in this work provide guidelines for the design of halide A$_2$BX$_6$ compounds
for potential photovoltaic applications.",1706.08674v1
2017-10-03,"Long-range dynamical magnetic order and spin tunneling in the cooperative paramagnetic states of the pyrochlore analogous spinel antiferromagnets CdYb2X4 (X = S, Se)","Magnetic systems with spins sitting on a lattice of corner sharing regular
tetrahedra have been particularly prolific for the discovery of new magnetic
states for the last two decades. The pyrochlore compounds have offered the
playground for these studies, while little attention has been comparatively
devoted to other compounds where the rare earth R occupies the same
sub-lattice, e.g. the spinel chalcogenides CdR2X4 (X = S, Se). Here we report
measurements performed on powder samples of this series with R = Yb using
specific heat, magnetic susceptibility, neutron diffraction and
muon-spin-relaxation measurements. The two compounds are found to be
magnetically similar. They long-range order into structures described by the
\Gamma_5 irreducible representation. The magnitude of the magnetic moment at
low temperature is 0.77 (1) and 0.62 (1) mu_B for X = S and Se, respectively.
Persistent spin dynamics is present in the ordered states. The spontaneous
field at the muon site is anomalously small, suggesting magnetic moment
fragmentation. A double spin-flip tunneling relaxation mechanism is suggested
in the cooperative paramagnetic state up to 10 K. The magnetic space groups
into which magnetic moments of systems of corner-sharing regular tetrahedra
order are provided for a number of insulating compounds characterized by null
propagation wavevectors.",1710.01062v1
2017-10-18,Fingerprinting of Compound-Specific Chlorine Isotopologue Distribution of Organochlorines by GC-HRMS,"This study developed a method to measure compound-specific chlorine
isotopologue distribution of organochlorines for source identification and
apportionment. Complete chlorine isotopologues of individual model
organochlorines were detected by gas chromatography-high resolution mass
spectrometry (GC-HRMS). The measured relative abundances (RAmea), simulated
relative abundances (RAsim), and relative variations between RAmea and RAsim
(${\Delta}$RA) were obtained on basis of the detected MS signal intensities of
individual isotopologues. The method has been partially validated in precision,
injection-amount dependency and temporal drifts. The standard deviations (SDs)
of RAmea of all istotopologues of perchlorethylene (PCE) and trichloroethylene
(TCE) from different manufacturers were 0.002%-0.069%. The SDs of ${\Delta}$RA
of the first three isotopologues of PCE and TCE from different manufacturers
were 0.026%-0.155%. The ${\Delta}$RA and ${\Delta}$RA patterns of the standards
of PCE and TCE from different manufacturers were able to be differentiated with
statistical significance. The method has been successfully applied to an
analogous case of source identification and apportionment for two
trichlorodiphenyls that exhibited significant chlorine isotope fractionation on
the GC-HRMS system. The results demonstrate that the ${\Delta}$RA in
conjunction with isotope ratios can be applied to source identification and
present high-validity identification outcomes. Moreover, the RAmea can be used
to implement source apportionment for organochlorines from more sources with
more reliable outcomes compared with the methods using isotope ratios only.
This method opens a new way to perform fingerprinting analysis of
compound-specific chlorine isotopologue distribution of organochlorines, and
will be a promising high-performance approach in source delineation and
apportionment for chlorinated organic compounds.",1710.06597v1
2017-10-29,Survey of the class of isovalent antiperovskite alkaline earth-pnictide compounds,"The few reported members of the antiperovskite structure class $Ae_3Pn_APn_B$
of alkaline earth ($Ae$ = Ca,Sr,Ba) pnictides ($Pn$ = N,P,As,Sb,Bi) compounds
are all based on the B-site anion $Pn_B$=N. All fit can be categorized as
narrow gap semiconductors, making them of interest for several reasons. Because
chemical reasoning suggests that more members of this class may be stable, we
provide here a density functional theory (DFT) based survey of this entire
class of $3\times5\times5$ compounds. We determine first the relative energetic
stability of the distribution of pairs of $Pn$ ions in the A and B sites of the
structure, finding that the $B$ site always favors the small pnictogen anion.
The trends of the calculated energy gaps with $Ae$ cation and $Pn$ anions are
determined, and we study effects of spin-orbit coupling as well as two types of
gap corrections to the conventional DFT electronic spectrum. Because there have
been suggestions that this class harbors topological insulating phases, we have
given this possibility attention and found that energy gap corrections indicate
the cubic structures will provide at most a few topological insulators.
Structural instability is addressed by calculating phonon dispersion curves for
a few compounds, with one outcome being that distorted structures should be
investigated further for thermoelectric and topological character. Examples of
the interplay between spin-orbit coupling and strain on the topological nature
are provided. A case study of $\mathrm{Ca_3BiP}$ including the effect of strain
illustrates how a topological semimetal can be transformed into topological
insulator and Dirac semimetal.",1710.10716v1
2019-03-19,"Ab initio Investigation of Structural Stability and Exfoliation Energies in Transition Metal Dichalcogenides based on Ti-, V-, and Mo-Group Elements","In this work, we report an ab initio investigation based on density
functional theory of the structural, energetic and electronic properties of 2D
layered chalcogenides compounds based in the combination of the
transition-metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and chalcogenides (S, Se,
Te) in three polymorphic phases: trigonal prismatic (2H), octahedral (1T) and
distorted octahedral (1T$_{\text{d}}$). We determined the most stable phases
for each compound, verifying the existence of the 1T$_{\text{d}}$ phase for a
small number of the compounds and we have also identified the magnetic
compounds. In addition, with the determination of the exfoliation energies, we
indicated the potential candidates to form one layer material and we have also
found a relation between the exfoliation energy and the effective Bader charge
in the metal, suggesting that when the materials present small exfoliation
energy, it is due to the Coulomb repulsion between the chalcogen planes.
Finally, we analyzed the electronic properties, identifying the semiconductor,
semimetal and metal materials and predicting the band gap of the
semiconductors. In our results, the dependence of the band gap on the
$d$-orbital is explicit. In conclusion, we have investigated the properties of
stable and metastable phases for a large set of TMD materials, and our findings
may be auxiliary in the synthesis of metastable phases and in the development
of new TMDs applications.",1903.08112v1
2019-05-23,Hierarchical Reinforcement Learning for Concurrent Discovery of Compound and Composable Policies,"A common strategy to deal with the expensive reinforcement learning (RL) of
complex tasks is to decompose them into a collection of subtasks that are
usually simpler to learn as well as reusable for new problems. However, when a
robot learns the policies for these subtasks, common approaches treat every
policy learning process separately. Therefore, all these individual
(composable) policies need to be learned before tackling the learning process
of the complex task through policies composition. Moreover, such composition of
individual policies is usually performed sequentially, which is not suitable
for tasks that require to perform the subtasks concurrently. In this paper, we
propose to combine a set of composable Gaussian policies corresponding to these
subtasks using a set of activation vectors, resulting in a complex Gaussian
policy that is a function of the means and covariances matrices of the
composable policies. Moreover, we propose an algorithm for learning both
compound and composable policies within the same learning process by exploiting
the off-policy data generated from the compound policy. The algorithm is built
on a maximum entropy RL approach to favor exploration during the learning
process. The results of the experiments show that the experience collected with
the compound policy permits not only to solve the complex task but also to
obtain useful composable policies that successfully perform in their
corresponding subtasks.",1905.09668v2
2019-09-04,Spin--lattice coupling and the emergence of the trimerized phase in the $S=1$ Kagome antiferromagnet Na$_2$Ti$_3$Cl$_8$,"Spin-1 antiferromagnets are abundant in nature, but few theories or results
exist to understand their general properties and behavior, particularly in
situations when geometric frustration is present. Here we study the $S=1$
Kagome compound Na$_2$Ti$_3$Cl$_8$ using a combination of Density Functional
Theory, Exact Diagonalization, and Density Matrix Renormalization Group methods
to achieve a first principles supported explanation of exotic magnetic phases
in this compound. We find that the effective magnetic Hamiltonian includes
essential non-Heisenberg terms that do not stem from spin-orbit coupling, and
both trimerized and spin-nematic magnetic phases are relevant. The
experimentally observed structural transition to a breathing Kagome phase is
driven by spin--lattice coupling, which favors the trimerized magnetic phase
against the quadrupolar one. We thus show that lattice effects can be necessary
to understand the magnetism in frustrated magnetic compounds, and surmise that
Na$_2$Ti$_3$Cl$_8$ is a compound which cannot be understood from only
electronic or only lattice Hamiltonians, very much like VO$_2$.",1909.02020v1
2019-09-09,"Deposition of MAX phase containing thin films from a (Ti,Zr)2AlC compound target","This work reports on sputter depositions carried out from a compound
(Ti,Zr)2AlC target, whereupon Al-containing (Ti,Zr)C thin films (30-40 nm in
thickness) were deposited on MgO(111) and Al2O3(0001) substrates at
temperatures ranging between 500 and 900 {\deg}C. The presence of Al within the
carbide structure was evidenced by lattice parameter variations. Furthermore,
chemical analyses showed that the Al distribution throughout the film thickness
was fairly homogeneous. Thicker films (80-90 nm) deposited from the same
compound target consisted of the pseudo-binary (Ti,Zr)C and intermetallic
compounds in the Ti-Zr-Al system up to 800 {\deg}C, as well as solid solution
MAX phases with different Ti:Zr ratios at 900 {\deg}C. X-ray diffraction and
transmission electron microscopy showed that both (Ti,Zr)2AlC and (Ti,Zr)3AlC2
solid solution MAX phases were formed. Moreover, this work discusses the growth
mechanism of the thicker films, which started with the formation of the mixed
(Ti,Zr)C carbide, followed by the nucleation and growth of aluminides,
eventually leading to the formation of the MAX phases, which was the primary
objective of the sputter depositions.",1909.04097v3
2019-12-04,High-pressure phase transitions of zinc difluoride up to 55 GPa,"Studying the effect of high pressure (exceeding 10 kbar) on the structure of
solids allows to gain deeper insight in the mechanism governing crystal
structure stability. Here we report a study on the high-pressure behaviour of
zinc difluoride (ZnF2) - an archetypical ionic compound which at ambient
pressure adopts the rutile (TiO2) structure. Previous investigations, limited
to a pressure of 15 GPa, revealed that this compound undergoes two
pressure-induced phase transitions: TiO2 - CaCl2 at 4.5 GPa, and CaCl2 -
HP-PdF2 at 10 GPa. Within this joint experimental-theoretical study we extend
the room temperature phase diagram of ZnF2 up to 55 GPa. By means of Raman
spectroscopy measurements we identify two new phase transitions: HP-PdF2 -
HP1-AgF2 at 30 GPa and HP1 AgF2 - PbCl2 at 44 GPa. These results are confirmed
by Density Functional Theory calculations which indicate that in the HP1-AgF2
polymorph the coordination sphere of Zn2+ undergoes drastic changes upon
compression. Our results point to important differences in the high-pressure
behaviour of ZnF2 and MgF2, despite the fact that both compounds contain
cations of similar size. We also argue that the HP1-AgF2 structure, previously
observed only for AgF2, might be observed at large compression in other AB2
compounds.",1912.01850v1
2020-03-10,Machine-learning assisted cross-domain prediction of ionic conductivity in sodium and lithium-based superionic conductors,"Solid state lithium- and sodium-ion batteries utilize solid ionicly
conducting compounds as electrolytes. However, the ionic conductivity of such
materials tends to be lower than their liquid counterparts, necessitating
research efforts into finding suitable alternatives. The process of electrolyte
screening is often based on a mixture of domain expertise and trial-and-error,
both of which are time and resource-intensive. Data-driven and machine learning
approaches have recently come to the fore to accelerate learnings towards
discovery. In this work, we present a simple machine-learning based approach to
predict the ionic conductivity of sodium and lithium-based SICON compounds.
Using primarily theoretical elemental feature descriptors derivable from
tabulated information on the unit cell and the atomic properties of the
components of a target compound on a limited dataset of 70 NASICON-examples, we
have designed a logistic regression-based model capable of distinguishing
between poor and good superionic conductors with a cross-validation accuracy of
over 82%. Moreover, we demonstrate how such a system is capable of cross-domain
classification on lithium-based examples at the same accuracy, despite being
introduced to zero lithium-based compounds during training. Through a
systematic permutation-based evaluation process, we reduced the number of
considered features from 47 to 7, reduction of over 83%, while simultaneously
improving model performance. The contributions of different electronic and
structural features to overall ionic conductivity is also discussed, and
contrasted with accepted theories in literature. Our results demonstrate the
utility of such a simple, yet interpretable tool provides opportunities for
initial screening of potential candidates as solid-state electrolytes through
the use of existing data.",2003.04922v1
2020-03-22,The emergence of magnetic skyrmions,"This is a narrative of the basic theoretical ideas of axisymmetric
two-dimensional solitons and of their connection to basic experiments on
magnetic compounds. A shortened and edited version appeared in Physics Today.",2003.09836v1
2020-06-12,A Bivariate Compound Dynamic Contagion Process for Cyber Insurance,"As corporates and governments become more digital, they become vulnerable to
various forms of cyber attack. Cyber insurance products have been used as risk
management tools, yet their pricing does not reflect actual risk, including
that of multiple, catastrophic and contagious losses. For the modelling of
aggregate losses from cyber events, in this paper we introduce a bivariate
compound dynamic contagion process, where the bivariate dynamic contagion
process is a point process that includes both externally excited joint jumps,
which are distributed according to a shot noise Cox process and two separate
self-excited jumps, which are distributed according to the branching structure
of a Hawkes process with an exponential fertility rate, respectively. We
analyse the theoretical distributional properties for these processes
systematically, based on the piecewise deterministic Markov process developed
by Davis (1984) and the univariate dynamic contagion process theory developed
by Dassios and Zhao (2011). The analytic expression of the Laplace transform of
the compound process and its moments are presented, which have the potential to
be applicable to a variety of problems in credit, insurance, market and other
operational risks. As an application of this process, we provide insurance
premium calculations based on its moments. Numerical examples show that this
compound process can be used for the modelling of aggregate losses from cyber
events. We also provide the simulation algorithm for statistical analysis,
further business applications and research.",2007.04758v1
2020-07-10,"Dynamical stability, Vibrational and optical properties of anti-perovskite A3BX (Ti3TlN, Ni3SnN and Co3AlC) phases: a first principles study","We have investigated various physical properties including phonon dispersion,
thermodynamic parameters, optical constants, Fermi surface, Mulliken bond
population, theoretical Vickers hardness and damage tolerance of
anti-perovskite A3BX phases for the first time by employing density functional
theory (DFT) methodology based on first principles method. Initially we
assessed nine A3BX phases in total and found that only three phases (Ti3TlN,
Ni3SnN and Co3AlC) are mechanically and dynamically stable based on analysis of
computed elastic constants and phonon dispersion along with phonon density of
states. We revisited the structural, elastic and electronic properties of the
compounds to judge the reliability of our calculations. Absence of band gap at
the Fermi level characterizes the phases under consideration as metallic in
nature. The values of Pugh ratio, Poisson ratio and Cauchy factor have
predicted the ductile nature associated with strong metallic bonding in these
compounds. High temperature feasibility study of the phases has also been
performed using the thermodynamic properties, such as the free energy,
enthalpy, entropy, heat capacity and Debye temperature. The Vickers hardness of
the compounds are estimated to be around 4 GPa which is comparable to many
well-known MAX phases, indicating their reasonable hardness and easily
machinable nature. The static refractive index n(zero) has been found around
8.0 for the phases under study that appeals as potential candidate to design
optoelectronics appliances. The reflectivity is found above 44 percent for the
Ti3TlN compound in the energy range of 0 to 14.8 eV demonstrating that this
material holds significant promise as a coating agent to avoid solar heating.",2007.05135v1
2020-07-13,Molecule Oxygen Induced Ferromagnetism and Half-metallicity in α-BaNaO4: A First Principles Study,"Molecule oxygen resembles 3d and 4f metals in exhibiting long-range spin
ordering and electron strong correlated behaviors in compounds. The
ferromagnetic spin ordering and half-metallicity, however, are quite elusive
and have not been well acknowl-edged. In this article, we address this issue to
study how spins will interact each other if the oxygen dimers are arranged in a
dif-ferent way from that in the known super- and per-oxides by first principles
calculations. Based on the results of structure search, thermodynamic study and
lattice dynamics, we show that tetragonal {\alpha}-BaNaO4 is a stable
half-metal with a Curie temperature at 120 K, a first example in this class of
compounds. Like 3d and 4f metals, the O2 dimer carries a local magnetic moment
0.5 {\mu}B due to the unpaired electrons in its {\pi}* orbitals. This compound
can be regarded as forming from the O2 dimer layers stacking in a head to head
way. Different from that in AO2 (A=K, Rb, Cs), the spins are both
ferromagnetically coupled within and between the layers. Spin polarization
occurs in {\pi}* orbitals with spin-up electrons fully occupying the valence
band and spin-down electrons partially the conduction band, forming the
semiconducting and metallic channels, respectively. Our results highlight the
im-portance of geometric arrangement of O2 dimers in inducing ferromagnetism
and other novel properties in O2 dimer containing compounds.",2007.06433v1
2020-07-30,Magnetotransport Properties of Square-Net Compounds of NbSiSb and NbGeSb Single Crystals,"We successfully grew single crystals of Si- and Ge-square-net compounds of
NbSiSb and NbGeSb whose excellent crystalline quality are verified using
single-crystal x-ray diffraction, rocking curves, scanning and transmission
electron microscopies. Since these two compounds share major crystallographic
similarity with the topological nodal-line semimetals of ZrSiS family, we
employ density functional theory (DFT) calculations and magnetotransport
measurements to demonstrate their band structures as well as the electron
scattering mechanisms. DFT calculations show that the fermiology shows strong
anisotropy from the crystallographic c-axis to the ab-plane and weak anisotropy
within the ab plane, which is consistent with the strong anisotropic
magnetotransport behaviors. Following the Kohler's scaling rule we prove that
similar interband and intraband electron-phonon scattering mechanisms work in
both the NbSiSb and NbGeSb compounds. The study of electronic transport
mechanism in the presence of external magnetic field renders deep insight into
topological behavior together with it's Fermi surface, and the high similarity
of crystallography and strong difference in band structures between the present
single crystals and that of ZrSiS family provides the possibility to tune the
band structure via element doping",2007.15437v1
2020-09-29,ChemoVerse: Manifold traversal of latent spaces for novel molecule discovery,"In order to design a more potent and effective chemical entity, it is
essential to identify molecular structures with the desired chemical
properties. Recent advances in generative models using neural networks and
machine learning are being widely used by many emerging startups and
researchers in this domain to design virtual libraries of drug-like compounds.
Although these models can help a scientist to produce novel molecular
structures rapidly, the challenge still exists in the intelligent exploration
of the latent spaces of generative models, thereby reducing the randomness in
the generative procedure. In this work we present a manifold traversal with
heuristic search to explore the latent chemical space. Different heuristics and
scores such as the Tanimoto coefficient, synthetic accessibility, binding
activity, and QED drug-likeness can be incorporated to increase the validity
and proximity for desired molecular properties of the generated molecules. For
evaluating the manifold traversal exploration, we produce the latent chemical
space using various generative models such as grammar variational autoencoders
(with and without attention) as they deal with the randomized generation and
validity of compounds. With this novel traversal method, we are able to find
more unseen compounds and more specific regions to mine in the latent space.
Finally, these components are brought together in a simple platform allowing
users to perform search, visualization and selection of novel generated
compounds.",2009.13946v1
2020-10-26,Structure and magnetism of the skyrmion hosting family GaV$_4$S$_{8-y}$Se$_y$ with low levels of substitutions between $0 \leq y \leq 0.5$ and $7.5 \leq y\leq 8$,"Polycrystalline members of the GaV$_4$S$_{8-y}$Se$_y$ family of materials
with small levels of substitution between $0 \leq y \leq 0.5$ and $7.5 \leq
y\leq 8$ have been synthesized in order to investigate their magnetic and
structural properties. Substitutions to the skyrmion hosting parent compounds
GaV$_4$S$_8$ and GaV$_4$Se$_8$, are found to suppress the temperature of the
cubic to rhombohedral structural phase transition that occurs in both end
compounds and to create a temperature region around the transition where there
is a coexistence of these two phases. Similarly, the magnitude of the
magnetization and temperature of the magnetic transition are both suppressed in
all substituted compounds until a glassy-like magnetic state is realized. There
is evidence from the $ac$ susceptibility data that skyrmion lattices with
similar dynamics to those in GaV$_4$S$_8$ and GaV$_4$Se$_8$ are present in
compounds with very low levels of substitution, $0 < y< 0.2$ and $7.8 < y < 8$,
however, these states vanish at higher levels of substitution. The magnetic
properties of these substituted materials are affected by the substitution
altering exchange pathways and resulting in the creation of increasingly
disordered magnetic states.",2010.13450v1
2020-11-06,Simulating multiscale gated field emitters -- a hybrid approach,"Multi-stage cathodes are promising candidates for field emission due to the
multiplicative effect in local field predicted by the Schottky conjecture and
its recent corrected counterpart [J. Vac. Sci. Technol. B 38, 023208 (2020)].
Due to the large variation in length scales even in a 2-stage compound
structure consisting of a macroscopic base and a microscopic protrusion, the
simulation methodology of a gated field emitting compound diode needs to be
revisited. As part of this strategy, the authors investigate the variation of
local field on the surface of a compound emitter near its apex and find that
the generalized cosine law continues to hold locally near the tip of a
multi-scale gated cathode. This is used to emit charges with appropriate
distributions in position and velocity components with a knowledge of only the
electric field at the apex. The distributions are consistent with contemporary
free-electron field emission model and follow from the joint distribution of
launch angle, total energy, and normal energy. For a compound geometry with
local field enhancement by a factor of around 1000, a hybrid model is used
where the vacuum field calculated using COMSOL is imported into the
Particle-In-Cell code PASUPAT where the emission module is implemented. Space
charge effects are incorporated in a multi-scale adaptation of PASUPAT using a
truncated geometry with `open electrostatic boundary' condition. The space
charge field, combined with the vacuum field, is used for particle-emission and
tracking.",2011.03278v2
2020-11-08,Analysis of Dimensional Influence of Convolutional Neural Networks for Histopathological Cancer Classification,"Convolutional Neural Networks can be designed with different levels of
complexity depending upon the task at hand. This paper analyzes the effect of
dimensional changes to the CNN architecture on its performance on the task of
Histopathological Cancer Classification. The research starts with a baseline
10-layer CNN model with (3 X 3) convolution filters. Thereafter, the baseline
architecture is scaled in multiple dimensions including width, depth,
resolution and a combination of all of these. Width scaling involves
inculcating greater number of neurons per CNN layer, whereas depth scaling
involves deepening the hierarchical layered structure. Resolution scaling is
performed by increasing the dimensions of the input image, and compound scaling
involves a hybrid combination of width, depth and resolution scaling. The
results indicate that histopathological cancer scans are very complex in nature
and hence require high resolution images fed to a large hierarchy of
Convolution, MaxPooling, Dropout and Batch Normalization layers to extract all
the intricacies and perform perfect classification. Since compound scaling the
baseline model ensures that all the three dimensions: width, depth and
resolution are scaled, the best performance is obtained with compound scaling.
This research shows that better performance of CNN models is achieved by
compound scaling of the baseline model for the task of Histopathological Cancer
Classification.",2011.04057v2
2020-11-17,Metric-driven search for structurally stable inorganic compounds,"We report a facile `metric' for the identification of structurally and
dynamically (positive definite phonon structure) stable inorganic compounds.
The metric considers charge-imbalance within the local substructures in
crystalline compounds calculated using first-principles density-functional
theory. To exemplify, we chose carbon-based nitrides as it provides a large
pool of structurally stable and unstable phases. We showcase how local
structural information related to Wyckoff symmetry uniquely identifies four new
carbon-nitride phases. The metric predicts three new structurally stable phases
of 4 (C)$:$3 (N) stoichiometry, i.e., C$_{4}$N$_{3}$, which is further
confirmed by direct phonon calculations. The structurally stable phases also
satisfy the thermodynamic stability and mechanical stability criteria. New
phases possess extraordinary mechanical properties, similar to diamond, and
show insulating bandgap ranging from optimal, 1.45 eV (optimal) to 5.5 eV
(large gap). The structural, electronic, and optical properties of
Pm(1)-C$_{4}$N$_{3}$, discussed in detail, indicate possible application in
optoelectronic and photovoltaic technologies. The way metric is design, it can
be used to predict stability of any material with three-dimensional bonding
network. The metric was also able to predict structural stability of other
nitride polymorphs with 100$\%$ accuracy. We believe that the proposed `Metric'
will accelerate the search of unknown and unexplored inorganic compounds by
quick filtering of dynamically stable phases without expensive
density-functional theory calculations.",2011.08947v1
2020-12-02,"Soft elastic constants from phonon spectroscopy in hole-doped Ba$_{1-x}$(K,Na)$_x$Fe$_2$As$_2$ and Sr$_{1-x}Na$_x$Fe$_2$As$_2$","We report inelastic x-ray scattering measurements of the in-plane polarized
transverse acoustic phonon mode propagating along $q\parallel$[100] in various
hole-doped compounds belonging to the 122 family of iron-based superconductors.
The slope of the dispersion of this phonon mode is proportional to the square
root of the shear modulus $C_{66}$ in the $q \rightarrow 0$ limit and, hence,
sensitive to the tetragonal-to-orthorhombic structural phase transition
occurring in these compounds. In contrast to a recent report for
Ba(Fe$_{0.94}$Co$_{0.06}$)$_2$As$_2$ [F. Weber et al., Phys. Rev. B 98, 014516
(2018)], we find qualitative agreement between values of $C_{66}$ deduced from
our experiments and those derived from measurements of the Youngs modulus in
Ba$_{1-x}$(K,Na)$_x$Fe$_2$As$_2$ at optimal doping. These results provide an
upper limit of about 50 {\AA} for the nematic correlation length for the
optimally hole-doped compounds. Furthermore, we also studied compounds at lower
doping levels exhibiting the orthorhombic magnetic phase, where $C_{66}$ is not
accessible by volume probes, as well as the C4 tetragonal magnetic
phase.investigated",2012.01051v1
2020-12-15,"Cluster, Split, Fuse, and Update: Meta-Learning for Open Compound Domain Adaptive Semantic Segmentation","Open compound domain adaptation (OCDA) is a domain adaptation setting, where
target domain is modeled as a compound of multiple unknown homogeneous domains,
which brings the advantage of improved generalization to unseen domains. In
this work, we propose a principled meta-learning based approach to OCDA for
semantic segmentation, MOCDA, by modeling the unlabeled target domain
continuously. Our approach consists of four key steps. First, we cluster target
domain into multiple sub-target domains by image styles, extracted in an
unsupervised manner. Then, different sub-target domains are split into
independent branches, for which batch normalization parameters are learnt to
treat them independently. A meta-learner is thereafter deployed to learn to
fuse sub-target domain-specific predictions, conditioned upon the style code.
Meanwhile, we learn to online update the model by model-agnostic meta-learning
(MAML) algorithm, thus to further improve generalization. We validate the
benefits of our approach by extensive experiments on synthetic-to-real
knowledge transfer benchmark datasets, where we achieve the state-of-the-art
performance in both compound and open domains.",2012.08278v1
2020-12-29,Predicting Kovats Retention Indices Using Graph Neural Networks,"The \kovats retention index is a dimensionless quantity that characterizes
the rate at which a compound is processed through a gas chromatography column.
This quantity is independent of many experimental variables and, as such, is
considered a near-universal descriptor of retention time on a chromatography
column. The \kovats retention indices of a large number of molecules have been
determined experimentally. The ""NIST 20: GC Method\slash Retention Index
Library"" database has collected and, more importantly, curated retention
indices of a subset of these compounds resulting in a highly valued reference
database. The experimental data in the library form an ideal data set for
training machine learning models for the prediction of retention indices of
unknown compounds. In this article, we describe the training of a graph neural
network model to predict the \kovats retention index for compounds in the NIST
library and compare this approach with previous work \cite{2019Matyushin}. We
predict the \kovats retention index with a mean unsigned error of 28 index
units as compared to 44, the putative best result using a convolutional neural
network \cite{2019Matyushin}. The NIST library also incorporates an estimation
scheme based on a group contribution approach that achieves a mean unsigned
error of 114 compared to the experimental data. Our method uses the same input
data source as the group contribution approach, making its application
straightforward and convenient to apply to existing libraries. Our results
convincingly demonstrate the predictive powers of systematic, data-driven
approaches leveraging deep learning methodologies applied to chemical data and
for the data in the NIST 20 library outperform previous models.",2012.14798v1
2021-01-25,Collisions and compositional variability in chondrule-forming events,"Compound chondrules, i.e. chondrules fused together, make a powerful probe of
the density and compositional diversity in chondrule-forming environments, but
their abundance among the dominating porphyritic textures may have been
drastically underestimated. I report herein microscopic observations and
LA-ICP-MS analyses of lobate chondrules in the CO3 chondrites Miller Range
07193 and 07342. Lobes in a given chondrule show correlated volatile and
moderately volatile element abundances but refractory element concentrations
are essentially independent. This indicates that they formed by the collision
of preexisting droplets whose refractory elements behaved in closed system,
while their more volatile elements were buffered by the same gaseous medium.
The presence of lobes would otherwise be difficult to explain, as surface
tension should have rapidly imposed a spherical shape at the temperature peak.
In fact, since most chondrules across chondrite groups are nonspherical, a
majority are probably compounds variously relaxed toward sphericity. The lack
of correlation of refractory elements between conjoined compound chondrule
components is inconsistent with derivation of chondrules from the disruption of
homogenized melt bodies as in impact scenarios and evokes rather the melting of
independent mm-size nebular aggregates. Yet a ""nebular"" setting for chondrule
formation would need to involve not only increased solid concentration, e.g. by
settling to the midplane, but also a boost in relative velocities between
droplets during chondrule-forming events to account for observed compound
chondrule frequencies .",2101.10083v1
2021-02-16,Low-dimensional magnetism of BaCuTe$_{2}$O$_{6}$,"X-ray diffraction, thermodynamic measurements, and density-functional
band-structure calculations are used to study the magnetic behavior of
BaCuTe$_{2}$O$_{6}$, a member of the $A$CuTe$_2$O$_6$ structural family that
hosts complex three-dimensional frustrated spin networks with possible
spin-liquid physics. Temperature-dependent magnetic susceptibility and heat
capacity of the Ba compound are well described by the one-dimensional
spin-$\frac12$ Heisenberg chain model reminiscent of the Sr analog
SrCuTe$_2$O$_6$. While the intrachain coupling $J/k_{\rm B}\simeq 37$ K is
reduced compared to 49 K in the Sr compound, the N\'eel temperature increases
from 5.5 K (Sr) to 6.1 K (Ba). Unlike the Sr compound, BaCuTe$_2$O$_6$
undergoes only one magnetic transition as a function of temperature and shows
signatures of weak spin canting. We elucidate the microscopic difference
between the Sr and Ba compounds and suggest that one of the interchain
couplings changes sign as a result of negative pressure caused by the Sr/Ba
substitution. The N\'eel temperature of BaCuTe$_2$O$_6$ is remarkably
insensitive to the magnetic dilution with Zn$^{2+}$ up to the highest reachable
level of about 20%.",2102.08046v2
2021-02-20,Designation of Intra-layer and Intercalated High Entropy Quasi-2D Compounds,"Here, we designed two promising schemes to realize the high-entropy structure
in a series of quasi-two-dimensional compounds, transition metal
dichalcogenides (TMDCs). In the intra-layer high-entropy plan, (HEM)X2
compounds with high-entropy structure in the MX2 slabs were obtained, here HEM
means high-entropy metals, such as TiZrNbMoTa. And superconductivity with a
Tc~7.4 K was found in a Mo-rich HEMX2. On the other hand, in the intercalation
plan, we intercalated HEM-atoms (FeCoCrNiMn) into the gap between the
sandwiched-MX2 slabs resulting in a series of (HEM)xMX2 compounds, x in the
range of 0~0.5, in which HEM is mainly composed of 3d transition metal
elements, such as FeCoCrNiMn. As the introduction of multi-component magnetic
atoms, ferromagnetic spin-glass states with strong 2D characteristics ensued.
Tuning the x content, three kinds of two in the high-entropy intercalated layer
were observed including the 1*1 triangular lattice and two kinds of
superlattices \sqrt3*\sqrt3 and \sqrt3*2 in x=0.333 and x>0.5, respectively.
Meanwhile, the spin frustration in the two-dimensional high-entropy magnetic
plane will be enhanced with the development of \sqrt3*\sqrt3 and will be
reduced significantly when changing into the \sqrt3*2 phase. The high-entropy
TMDCs and versatile two-dimensional high-entropy structures found by us possess
great potentials to find new physics in low-dimensional high-entropy structures
and future applications.",2102.10306v2
2021-02-24,"Structural, elastic, bonding, optoelectronic, and some thermo-physical properties of transition metal dichalcogenides ZrX2 (X = S, Se, Te): Insights from ab-initio calculations","Transition metal dichalcogenides (TMDCs) belong to technologically important
compounds. We have explored the structural, elastic, bonding, optoelectronic
and some thermo-physical properties of ZrX2 (X = S, Se, Te) TMDCs in details
via ab-initio technique in this study. Elastic anisotropy indices, atomic
bonding character, optoelectronic properties and thermo-physical parameters
including melting temperature and minimum phonon thermal conductivity are
investigated for the first time. All the TMDCs under investigation possess
significant elastic anisotropy and layered structural features. ZrX2 (X = S,
Se, Te) compounds are fairly machinable, and ZrS2 and ZrSe2 are moderately
hard. ZrTe2, on the other hand, is significantly softer. Both covalent and
ionic bondings contribute in the crystals. Electronic band structure
calculations display semiconducting behavior for ZrS2 and ZrSe2 and metallic
behavior for ZrTe2. Energy dependent optoelectronic parameters exhibit good
correspondence with the underlying electronic energy density of states
features. ZrX2 (X = S, Se, Te) compounds absorb ultraviolet radiation
effectively. The reflectivity spectrum, R(w), remains over 50% in the energy
range from 0 eV to 20 eV for ZrTe2. Therefore, this TMDC has wide band and
nonselective high reflectivity and can be used as an efficient reflector to
reduce solar heating. Debye temperature, melting point and minimum phonon
thermal conductivity of the compounds under study are low and show excellent
correspondence with each other and also with the elastic and bonding
characteristics.",2102.12097v1
2021-04-05,Anisotropic Triangular Lattice Realized in Rhenium Oxychlorides A3ReO5Cl2 (A = Ba and Sr),"We report the synthesis, crystal structure, and magnetic properties of two
new quantum antiferromagnets A3ReO5Cl2 (A = Sr and Ba). The crystal structure
is isostructural with the mineral pinalite Pb3WO5Cl2, in which the Re6+ ion is
square-pyramidally coordinated by five oxide atoms, and forms an anisotropic
triangular lattice (ATL) made of S = 1/2 spins. The magnetic interactions J and
J' in the ATL are estimated from magnetic susceptibilities to be 19.5 (44.9)
and 9.2 (19.3) K, respectively, with J'/J = 0.47 (0.43) for A = Ba (Sr). For
each compound, heat capacity at low temperatures shows a large T-linear
component with no signature of long-range magnetic order above 2 K, which
suggests a gapless spin liquid state of one-dimensional character of the J
chains in spite of the significantly large J' couplings. This is a consequence
of one-dimensionalization by geometrical frustration in the ATL magnet; a
similar phenomenon has been observed in two compounds with slightly smaller
J'/J values: Cs2CuCl4 (J'/J = 0.3) and the related compound Ca3ReO5Cl2 (0.32).
Our findings demonstrate that 5d mixed-anion compounds provide a unique
opportunity to explore novel quantum magnetism.",2104.01838v1
2021-04-15,Morphotropic Phase Boundary in Sm-Substituted BiFeO3 Ceramics: Local vs Microscopic Approaches,"Samarium substituted bismuth ferrite (BiFeO3) ceramics prepared by sol-gel
synthesis method were studied using both local scale and microscopic
measurement techniques in order to clarify an evolution of the crystal
structure of the compounds across the morphotropic phase boundary region. X-ray
diffraction analysis, transmission and scanning electron microscopies, XPS,
EDS/EDX experiments and piezoresponse force microscopy were used to study the
structural transitions from the polar active rhombohedral phase to the
anti-polar orthorhombic phase and then to the non-polar orthorhombic phase,
observed in the Bi1-xSmxFeO3 compounds within the concentration range of 0.08 <
x < 0.2. The results obtained by microscopic techniques testify that the
compounds in the range of 0.12 < x < 0.15 are characterized by two phase
structural state formed by a coexistence of the rhombohedral and the anti-polar
orthorhombic phases; two phase structural state observed in the compounds with
0.15 < x < 0.18 is associated with a coexistence of the anti-polar orthorhombic
and the non-polar orthorhombic phases. Local scale measurements have revealed a
notable difference in the concentration range ascribed to the morphotropic
phase boundary estimated by microscopic measurements, the obtained results
testify a wider concentration range ascribed to a coexistence of different
structural phases, the background of the mentioned difference is discussed.",2104.07401v1
2021-05-06,First-order transitions at the Neel temperatures of trigonal SrMn2P2 and CaMn2P2 single crystals containing corrugated-honeycomb Mn sublattices,"Single crystals of SrMn2P2 and CaMn2P2 were grown using Sn flux and
characterized by single-crystal x-ray diffraction, electrical resistivity rho,
heat capacity Cp, and magnetic susceptibility chi = M/H measurements versus
temperature T and magnetization M versus applied magnetic field H isotherm
measurements. The x-ray diffraction results show that both compounds adopt the
trigonal CaAl2Si2-type structure. The rho(T) measurements demonstrate
insulating ground states for both compounds. The chi(T) and Cp(T) data reveal a
weak first-order antiferromagnetic (AFM) transition at the Neel temperature TN
= 53(1) K for SrMn2P2 and a strong first-order AFM transition at TN = 69.8(3) K
for CaMn2P2. Both compounds show an isotropic and nearly T-independent chi(T <
TN). {31}P NMR measurements confirm the strong first-order transition in
CaMn2P2 but show critical slowing down near TN for SrMn2P2 thus evidencing
second-order character. The NMR measurements also indicate that the AFM
structure of CaMn2P2 is commensurate with the lattice whereas that of SrMn2P2
is incommensurate. These first-order AFM transitions are unique among the class
of trigonal (Ca, Sr, Ba)Mn2(P, As, Sb, Bi)2 compounds which otherwise exhibit
second-order AFM transitions. This result presents a challenge to understand
the systematics of magnetic ordering in this class of materials in which
magnetically-frustrated antiferromagnetism is quasi-two-dimensional.",2105.02394v1
2021-05-11,A comprehensive DFT based insights into the physical properties of tetragonal Mo5PB2,"Tetragonal Mo5PB2 compound, a recently discovered superconductor, belongs to
technologically important class of materials. It is quite surprising to note
that a large number of physical properties of Mo5PB2, including elastic
properties and their anisotropy, acoustic behavior, electronic (charge density
distribution, electron density difference), thermo-physical, bonding
characteristics, and optical properties have not been carried out at all. In
the present work we have explored all these properties in details for the first
time with density functional theory based first-principles method. Mo5PB2 is
found to be a mechanically stable, elastically anisotropic compound with
ductile character. Moreover, the chemical bonding is interpreted by calculating
the electronic energy density of states, electron density distribution, elastic
properties and Mulliken bond population analysis. Mo5PB2 has a combination of
mainly ionic, metallic, and some covalent bonding characteristics. The compound
possesses high level of machinability. The band structure along with a large
electronic density of states at the Fermi level reveals metallic character.
Calculated values of different thermal parameters of Mo5PB2 are closely related
to the elastic properties. The energy dependent optical parameters show close
assent to the underlying electronic band structure. The optical absorption and
reflectivity spectra and the low energy index of refraction of Mo5PB2 show that
the compound holds promise to be used in optoelectronic device sector. Unlike
the notable anisotropy found in elastic, mechanical properties and minimum
thermal conductivity, the optical parameters are found to be almost isotropic
with respect to the polarization direction of the incident electric field.",2105.04786v1
2021-05-11,Observation of nearly identical superconducting transition temperatures in pressurized Weyl semimetal MIrTe4 (M=Nb and Ta),"Here we report the observation of pressure-induced superconductivity in
type-II Weyl semimetal (WSM) candidate NbIrTe4 and the evolution of its Hall
coefficient (RH), magnetoresistance (MR), and lattice with increasing pressure
to ~57 GPa. These results provide a significant opportunity to investigate the
universal high-pressure behavior of ternary WSMs, including the sister compound
TaIrTe4 that has been known through our previous studies. We find that the
pressure-tuned evolution from the WSM to the superconducting (SC) state in
these two compounds exhibit the same trend, i.e., a pressure-induced SC state
emerges from the matrix of the non-superconducting WSM state at ~ 27 GPa, and
then the WSM state and the SC state coexist up to 40 GPa. Above this pressure,
an identical high-pressure behavior, characterized by almost the same value of
RH and MR in its normal state and the same value of Tc in its SC state, appears
in both compounds. Our results not only reveal a universal connection between
the WSM state and SC state, but also demonstrate that NbIrTe4 and TaIrTe4 can
make the same contribution to the normal and SC states that inhabit in the
high-pressure phase, although these two compounds have dramatically different
topological band structure at ambient pressure.",2105.05032v1
2021-05-13,Charge-order phase transition in the quasi one-dimensional organic conductor (TMTTF)$_2$NO$_3$,"Low-dimensional organic conductors show a rich phase diagram, which has,
despite all efforts, still some unexploed regions. Charge ordered phases
present in many compounds of the (TMTTF)$_2 X$ family are typically studied
with their unique electronic properties in mind. An influence on the spin
arrangement is, however, not expected at first glance. Here, we report
temperature and angle dependent electron spin resonance (ESR) measurements on
the quasi one-dimensional organic conductor (TMTTF)$_2$NO$_3$. We found that
the (TMTTF)$_2$NO$_3$ compound develops a peculiar anisotropy with a doubled
periodicity ($ab'$-plane) of the ESR linewidth below about $T_\text{CO}=250\pm
10$ K. This behavior is similar to observations in the related compounds
(TMTTF)$_2 X$ ($X$ = PF$_6$, SbF$_6$ and AsF$_6$), where it has been attributed
to relaxation processes of magnetically inequivalent sites in the
charge-ordered state. For the structural analogous (TMTTF)$_2$ClO$_4$, known
for the absence of charge order, such angular dependence of the ESR signal is
not observed. Therefore, our ESR measurements lead us to conclude that a
charge-order phase is stabilized in the title compound below $T_\text{CO}
\approx 250$ K.",2105.06362v1
2021-06-07,Chiral phonons in honeycomb sublattice of layered CoSn-like compounds,"Hexagonal and kagome lattices exhibit extraordinary electronic properties. It
is a natural consequence of additional discrete degree of freedom associated
with a valley or the occurence of electronic flat-bands. Combination of both
types of lattices, observed in CoSn-like compounds, leads not only to the
topological electronic behavior, but also to the emergence of chiral phonon
modes. Here, we study CoSn-like compounds in the context of realization of
chiral phonons. Previous theoretical studies demonstrated that the chiral
phonons can be found in ideal two-dimensional hexagonal or kagome lattices.
However, it turns out that in the case of CoSn-like systems with the $P6/mmm$
symmetry, the kagome lattice formed by $d$-block element is decorated by the
additional $p$-block atom. This results in a two dimensional triangular lattice
of atoms with non-equal masses and the absence of chiral phonons in the kagome
plane. Contrary to this, the interlayer hexagonal lattice of $p$-block atoms is
preserved and allows for the realization of chiral phonons. We discuss
properties of these chiral phonons in seven CoSn-like compounds and demonstrate
that they do not depend on atomic mass ratio or the presence of intrinsic
magnetic order. The chiral phonons of $d$-block atoms can be restored by
removing the inversion symmetry. The latter is possible in the crystal
structure of CoGe and RhPb with the reduced symmetry ($P\bar{6}2m$) and
distorted-kagome-like lattice.",2106.03740v1
2021-06-01,Raman spectral analysis of mixtures with one-dimensional convolutional neural network,"Recently, the combination of robust one-dimensional convolutional neural
networks (1-D CNNs) and Raman spectroscopy has shown great promise in rapid
identification of unknown substances with good accuracy. Using this technique,
researchers can recognize a pure compound and distinguish it from unknown
substances in a mixture. The novelty of this approach is that the trained
neural network operates automatically without any pre- or post-processing of
data. Some studies have attempted to extend this technique to the
classification of pure compounds in an unknown mixture. However, the
application of 1-D CNNs has typically been restricted to binary classifications
of pure compounds. Here we will highlight a new approach in spectral
recognition and quantification of chemical components in a multicomponent
mixture. Two 1-D CNN models, RaMixNet I and II, have been developed for this
purpose. The former is for rapid classification of components in a mixture
while the latter is for quantitative determination of those constituents. In
the proposed method, there is no limit to the number of compounds in a mixture.
A data augmentation method is also introduced by adding random baselines to the
Raman spectra. The experimental results revealed that the classification
accuracy of RaMixNet I and II is 100% for analysis of unknown test mixtures; at
the same time, the RaMixNet II model may achieve a regression accuracy of 88%
for the quantification of each component.",2106.05316v1
2021-06-18,Merging of bivariate compound Binomial processes with shocks,"The paper investigates a discrete time Binomial risk model with different
types of polices and shock events may influence some of the claim sizes. It is
shown that this model can be considered as a particular case of the classical
compound Binomial model. As far as we work with parallel Binomial counting
processes in infinite time, if we consider them as independent, the probability
of the event they to have at least once simultaneous jumps would be equal to
one. We overcome this problem by using thinning instead of convolution
operation. The bivariate claim counting processes are expressed in two
different ways. The characteristics of the total claim amount processes are
derived. The risk reserve process and the probabilities of ruin are discussed.
The deficit at ruin is thoroughly investigated when the initial capital is
zero. Its mean, probability mass function and probability generating function
are obtained. We show that although the probability generating function of the
global maxima of the random walk is uniquely determined via its probability
mass function and vice versa, any compound geometric distribution with
non-negative summands has uncountably many stochastically equivalent compound
geometric presentations. The probability to survive in much more general
settings, than those, discussed here, for example in the Anderson risk model,
has uncountably many Beekman's convolution series presentations.",2106.10007v1
2021-08-11,Spin-orbital entangled state and realization of Kitaev physics in 3d cobalt compounds: a progress report,"The realization of Kitaev's honeycomb magnetic model in real materials has
become one of the most pursued topics in condensed matter physics and materials
science. If found, it is expected to host exotic quantum phases of matter and
offers potential realizations of fault$-$tolerant quantum computations. Over
the past years, much effort was made on 4d$-$ or 5d$-$ heavy transition metal
compounds because of their intrinsic strong spin$-$orbit coupling. But more
recently, there have been growing shreds of evidence that the Kitaev model
could also be realized in 3d$-$transition metal systems with much weaker
spin$-$orbit coupling. This review intends to serve as a guide to this
fast$-$developing field focusing on systems with d$^7$ transition metal
occupation. It overviews the current theoretical and experimental progress on
realizing the Kitaev model in those systems. We examine the recent experimental
observations of candidate materials with Co$^{2+}$ ions: e.g., CoPS$_3$,
Na$_3$Co$_2$SbO$_6$, and Na$_2$Co$_2$TeO$_6$, followed by a brief review of
theoretical backgrounds. We conclude this article by comparing experimental
observations with density functional theory (DFT) calculations. We stress the
importance of inter$-t_{2g}$ hopping channels and Hund's coupling in the
realization of Kitaev interactions in Co$-$based compounds, which has been
overlooked in previous studies. This review suggests future directions in the
search for Kitaev physics in 3d cobalt compounds and beyond.",2108.05044v3
2021-08-17,Pressure induced Lifshitz transition and anomalous crystal field splitting in AFeAs (A=Li/Na) Fe-based superconducting compounds: A first principles study,"The effect of hydrostatic pressure on the electronic structures of iron
pnictide superconducting compounds LiFeAs and NaFeAs through density functional
theory based first principles studies are presented, using the predicted
crystal structures at very high pressure by Zhang et al. [1]. The orbital
selective pressure induced modifications in the partial density of states and
electronic band structures reveal mixed multi-band multi-orbital nature of
these compounds, with energetically degenerate dxz/dyz orbitals at ambient
pressure. Due to larger hydrostatic pressures some of the electron/hole bands
crosses the Fermi level, leading to significant topological modifications in
Fermi surfaces known as Lifshitz transition. Interrelation between Lifshitz
transition and superconductivity-an important subject matter of current
research are described. Based on such interconnection the current study
predicts the superconducting-Tc in 111 compounds can not be raised at such high
pressures. Wannier functions based electronic structure investigation reveal a
relatively larger hybridization between the Fe-3d and As-4p orbitals at higher
pressures, as an effect of which the orbital degeneracy of dxz and dyz orbitals
are lifted. Different hybridization contributions in the crystal-field
splitting are separated using the Wannier functions based formalism, by
incorporating different bands with a particular orbital character in the
Wannier function construction. Pressure dependence of the intra/inter orbital
hopping amplitudes between Fe-d orbitals has been discussed using low energy
tight binding model.",2108.07623v1
2021-08-27,"Superexchange interactions in AgMF4 (M = Co, Ni, Cu) polymorphs","Magnetic properties of silver(II) compounds have been of interest in recent
years. In covalent compounds, the main mechanism of interaction between
paramagnetic sites is the superexchange via the connecting ligand. To date,
little is known of magnetic interactions between Ag(II) cations and other
paramagnetic centres. It is because only a few compounds bearing Ag(II) cation
and other paramagnetic transition metal cation are known experimentally.
Recently the high-pressure synthesis of ternary silver(II) fluorides with 3d
metal cations AgMF4 (M = Co, Ni, Cu) was predicted to be feasible. Here, we
investigate the magnetic properties of these compounds in their diverse
polymorphic forms. Using well established computational methods we predict
superexchange pathways in AgMF4, evaluate coupling constants and calculate the
impact of Ag(II) presence on superexchange between the other cations. The
results indicate that the low-pressure form of AgCuF4, the only composed of
stacked layers as the parent AgF2, would hold mainly Ag-Ag and Cu-Cu
superexchange interactions. Upon compression, or with the nickel(II) cation,
the Ag-M interactions in AgMF4 intensify, which is emphasized by an increase of
Ag-M superexchange coupling constants and Ag-F-M angles. All the strongest Ag-M
superexchange pathways are quasi-linear, leading to the formation of
antiferromagnetic chains along the crystallographic directions. The impact of
Ag(II) on M-M superexchange turns out to be moderate, due to factors connected
to the crystal structure.",2108.12241v1
2021-09-01,Synthesis and Anisotropic Magnetism in Quantum Spin Liquid Candidates $A$YbSe$_2$ ($A$ = K and Rb),"Quantum spin liquid (QSL) state in rare-earth triangular lattice has
attracted much attention recently due to its potential application in quantum
computing and communication. Here we report the single-crystal growth
synthesis, crystal structure characterizations and magnetic properties of
$A$YbSe$_{2}$ ($A$= K, Rb) compounds. The X-ray diffraction analysis shows that
$A$YbSe$_{2}$ ($A$ = K and Rb) crystallizes in a trigonal space group, $R$-3$m$
(No. 166) with Z = 3. $A$YbSe$_{2}$ possesses a two-dimensional (2D) Yb-Se-Yb
layered structure formed by edged-shared YbSe$_6$ octahedra. The magnetic
properties are highly anisotropic for both title compounds and no long-range
order is found down to 0.4 K, revealing the possible QSL ground state in these
compounds. The isothermal magnetization exhibits one-third magnetization
plateau when the magnetic fields are applied in $ab$-plane. Heat capacity is
performed along both $ab$-plane and $c$-axis, and features the characteristic
dome for triangular magnetic lattice compounds as a function of magnetic
fields. Due to the change of the interlayer and intralayer distance of
Yb$^{3+}$, the dome shifts to low fields from KYbSe$_2$ to RbYbSe$_2$. All
these results indicate the $A$YbSe$_2$ family presents unique frustrated
magnetism close to the possible QSL and noncolinear spin states.",2109.00384v2
2021-09-22,Data-Driven Design of Novel Halide Perovskite Alloys,"The great tunability of the properties of halide perovskites presents new
opportunities for optoelectronic applications as well as significant challenges
associated with exploring combinatorial chemical spaces. In this work, we
develop a framework powered by high-throughput computations and machine
learning for the design and prediction of mixed cation halide perovskite
alloys. In a chemical space of ABX$_{3}$ perovskites with a selected set of
options for A, B, and X atoms, pseudo-cubic structures of compounds with B-site
mixing are simulated using density functional theory (DFT) and several
properties are computed, including stability, lattice constant, band gap,
vacancy formation energy, refractive index, and optical absorption spectrum,
using both semi-local and hybrid functionals. Neural networks (NN) are used to
train predictive models for every property using tabulated elemental properties
of A, B, and X site atoms as descriptors. Starting from the DFT dataset of 229
points, we use the trained NN models to predict the structural, energetic,
electronic and optical properties of a complete dataset of 17,955 compounds,
and perform high-throughput screening in terms of stability, band gap and
defect tolerance, to obtain 574 promising compounds that are ranked as
potential absorbers according to their photovoltaic figure of merit.
Compositional trends in the screened set of attractive mixed cation halide
perovskites are revealed and additional computations are performed on selected
compounds. The data-driven design framework developed here is promising for
designing novel mixed compositions and can be extended to a wider perovskite
chemical space in terms of A, B, and X atoms, different kinds of mixing at the
A, B, or X sites, non-cubic phases, and other properties of interest.",2109.10798v1
2021-10-12,Vapor transport growth of MnBi2Te4 and related compounds,"Motivated by fine tuning of the magnetic and topological properties of
MnBi$_2$Te$_4$ via defect engineering, in this work, we report the crystal
growth of MnBi$_2$Te$_4$ and related compounds using vapor transport method and
characterization of vapor transported crystals by measuring elemental analysis,
magnetic and transport properties, and scanning tunneling microscopy. For the
growth of MnBi$_2$Te$_4$ single crystals, I$_2$, MnI$_2$ , MnCl$_2$, TeCl$_4$,
or MoCl$_5$ are all effective transport agents; chemical transportation occurs
faster in the presence of iodides than chlorides. MnBi$_2$Te$_4$ crystals can
be obtained in the temperature range 500$^\circ$C-590$^\circ$C using I$_2$ as
the transport agent. We further successfully grow MnSb$_2$Te$_4$,
MnBi$_{2-x}$Sb$_x$Te$_4$, and Sb-doped MnBi$_4$Te$_7$ crystals. A small
temperature gradient $<$20$^\circ$C between the hot and cold ends of the growth
cmpoule is critical for the successful crystal growth of MnBi$_2$Te$_4$ and
related compounds. Compared to flux grown crystals, vapor transported crystals
tend to be Mn stoichiometric, and Sb-bearing compositions have more Mn/Sb site
mixing. The vapor transport growth provides a new materials synthesis approach
to fine tuning the magnetic and topological properties of these intrinsic
magnetic topological insulators.",2110.06034v1
2021-10-13,Compositional Generalization in Dependency Parsing,"Compositionality -- the ability to combine familiar units like words into
novel phrases and sentences -- has been the focus of intense interest in
artificial intelligence in recent years. To test compositional generalization
in semantic parsing, Keysers et al. (2020) introduced Compositional Freebase
Queries (CFQ). This dataset maximizes the similarity between the test and train
distributions over primitive units, like words, while maximizing the compound
divergence: the dissimilarity between test and train distributions over larger
structures, like phrases. Dependency parsing, however, lacks a compositional
generalization benchmark. In this work, we introduce a gold-standard set of
dependency parses for CFQ, and use this to analyze the behavior of a
state-of-the art dependency parser (Qi et al., 2020) on the CFQ dataset. We
find that increasing compound divergence degrades dependency parsing
performance, although not as dramatically as semantic parsing performance.
Additionally, we find the performance of the dependency parser does not
uniformly degrade relative to compound divergence, and the parser performs
differently on different splits with the same compound divergence. We explore a
number of hypotheses for what causes the non-uniform degradation in dependency
parsing performance, and identify a number of syntactic structures that drive
the dependency parser's lower performance on the most challenging splits.",2110.06843v2
2021-10-19,A new class of bilayer kagome lattice compounds with Dirac nodal lines and pressure-induced superconductivity,"Kagome lattice composed of transition-metal ions provides a great opportunity
to explore the intertwining between geometry, electronic orders and band
topology. The discovery of multiple competing orders that connect intimately
with the underlying topological band structure in nonmagnetic kagome metals
$A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) further pushes this topic to the quantum
frontier. Here we report the discovery and characterization of a new class of
vanadium-based compounds with kagome bilayers, namely $A$V$_6$Sb$_6$ ($A$ = K,
Rb, Cs) and V$_6$Sb$_4$, which, together with $A$V$_3$Sb$_5$, compose a series
of kagome compounds with a generic chemical formula
($A_{m-1}$Sb$_{2m}$)(V$_3$Sb)$_n$ (m = 1, 2; n = 1, 2). Theoretical
calculations combined with angle-resolved photoemission measurements reveal
that these compounds feature Dirac nodal lines in close vicinity to the Fermi
level. Pressure-induced superconductivity in $A$V$_6$Sb$_6$ further suggests
promising emergent phenomena in these materials. The establishment of a new
family of layered kagome materials paves the way for designer of fascinating
kagome systems with diverse topological nontrivialities and collective ground
states.",2110.09782v2
2021-10-19,A magnetic excitation linking quasi-1D Chevrel-type selenide and arsenide superconductors,"The quasi-one-dimensional Chevrel phases, $A_2$Mo$_6$Se$_6$ ($A$ = Tl, In, K,
Rb, Cs), are of interest due to their atypical electronic properties. The Tl
and In analogues undergo a superconducting transition whereas the alkali metal
analogues undergo metal-to-insulator transitions, neither of which is fully
understood. We report the results of inelastic neutron scattering on
polycrystalline In$_2$Mo$_6$Se$_6$ ($T_c$ = 2.85$\,$K) and Rb$_2$Mo$_6$Se$_6$
($T_{MIT}$ $\approx \,$170K) which reveal a highly dispersive column of
intensity present in both compounds near $Q$ = 1.0 $\r{A}^{-1}$. The excitation
is nearly indistinguishable from another excitation observed in the
structurally related superconducting compound K$_2$Cr$_3$As$_3$, which has been
interpreted as magnetic in origin and related to Fermi surface nesting.
However, the calculated Fermi surface of K$_2$Cr$_3$As$_3$ differs
substantially from the $A_2$Mo$_6$Se$_6$ compounds, and many consider them
distinct classes of materials. Nevertheless, the new observation is most
consistent with a magnetic origin, linking the physics of both classes. These
findings suggest that the selenide and arsenide compounds are more closely
related than originally thought, with properties falling on the same continuum.",2110.10226v2
2021-10-21,Discovery of two families of VSb-based compounds with V-kagome lattice,"We report the structure and physical properties of two newly-discovered
compounds AV8Sb12 and AV6Sb6 (A = Cs, Rb), which have C2 (space group: Cmmm)
and C3 (space group: R-3m) symmetry, respectively. The basic V-kagome unit is
present in both compounds, but stacking differently. A V2Sb2 layer is
sandwiched between two V3Sb5 layers in AV8Sb12, altering the V-kagome lattice
and lowering the symmetry of kagome layer from hexagonal to orthorhombic. In
AV6Sb6, the building block is a more complex slab made up of two half-V3Sb5
layers that are intercalated by Cs cations along the c-axis. Transport property
measurements demonstrate that both compounds are nonmagnetic metals, with
carrier concentrations at around 1021cm-3. No superconductivity has been
observed in CsV8Sb12 above 0.3 K under in-situ pressure up to 46 GPa. In
contrast to CsV3Sb5, theoretical calculations and angle-resolved photoemission
spectroscopy (ARPES) reveal a quasi-two-dimensional electronic structure in
CsV8Sb12 with C2 symmetry and no van Hove singularities near the Fermi level.
Our findings will stimulate more research into V-based kagome quantum
materials.",2110.11311v2
2021-10-22,EvoGAN: An Evolutionary Computation Assisted GAN,"The image synthesis technique is relatively well established which can
generate facial images that are indistinguishable even by human beings.
However, all of these approaches uses gradients to condition the output,
resulting in the outputting the same image with the same input. Also, they can
only generate images with basic expression or mimic an expression instead of
generating compound expression. In real life, however, human expressions are of
great diversity and complexity. In this paper, we propose an evolutionary
algorithm (EA) assisted GAN, named EvoGAN, to generate various compound
expressions with any accurate target compound expression. EvoGAN uses an EA to
search target results in the data distribution learned by GAN. Specifically, we
use the Facial Action Coding System (FACS) as the encoding of an EA and use a
pre-trained GAN to generate human facial images, and then use a pre-trained
classifier to recognize the expression composition of the synthesized images as
the fitness function to guide the search of the EA. Combined random searching
algorithm, various images with the target expression can be easily sythesized.
Quantitative and Qualitative results are presented on several compound
expressions, and the experimental results demonstrate the feasibility and the
potential of EvoGAN.",2110.11583v1
2021-11-30,A Review on Parallel Virtual Screening Softwares for High Performance Computers,"Drug discovery is the most expensive, time demanding and challenging project
in biopharmaceutical companies which aims at the identification and
optimization of lead compounds from large-sized chemical libraries. The lead
compounds should have high affinity binding and specificity for a target
associated with a disease and in addition they should have favorable
pharmacodynamic and pharmacokinetic properties (grouped as ADMET properties).
Overall, drug discovery is a multivariable optimization and can be carried out
in supercomputers using a reliable scoring function which is a measure of
binding affinity or inhibition potential of the drug-like compound. The major
problem is that the number of compounds in the chemical spaces is huge making
the computational drug discovery very demanding. However, it is cheaper and
less time consuming when compared to experimental high throughput screening. As
the problem is to find the most stable (global) minima for numerous
protein-ligand complexes (at the order of 10$^6$ to 10$^{12}$), the parallel
implementation of in-silico virtual screening can be exploited to make the drug
discovery in affordable time. In this review, we discuss such implementations
of parallelization algorithms in virtual screening programs. The nature of
different scoring functions and search algorithms are discussed, together with
a performance analysis of several docking softwares ported on high-performance
computing architectures.",2112.00116v1
2022-06-03,"Dissociative electron attachment to gold(i) based compounds: 4,5-dichloro 1,3-diethyl imidazolylidene trifluoromethyl gold(i)","With the use of proton-NMR and powder XRD (XRPD) studies, the suitability of
specific Au FEBID precursors has been investigated to low electron energy,
structure, excited states and resonances, structural crystal modifications,
flexibility, and vaporization level. Uniquely designed precursor to meet the
needs of focused electron beam induced deposition (FEBID) at the nanostructure
level, the 4,5-dichloro 1,3-diethyl imidazolylidene trifluoromethyl gold(i) is
a compound that proves its capability to create high purity structures, and its
growing importance between other AuImx and AuClnB (where x, n are the number of
radicals, B = CH, CH3 or Br) compounds in the radiation cancer therapy
increases the efforts to design more suitable bonds in processes of SEM
deposition and in gas-phase studies. The investigation done to its powder shape
using the XRPD XPERT3 Panalytical diffractometer based on CoK{\alpha} lines
show changes to its structure with temperature, level of vacuum, and light; the
sensitivity of this compound makes it highly interesting to radiation research
in particular. Used for FEBID, through its smaller number of C, H, and O atoms
has lower levels of C contamination in the structures and on the surface, but
it replaces these bonds with C-Cl and C-N bonds that have a lower bond breaking
energy but still needing an extra purification step in the deposition process,
whether is H2O, O2 or H jets.",2206.01420v1
2022-06-27,Hybridization and Correlation between f- and d-orbital electrons in a valence fluctuating compound EuNi2P2,"The interaction between localized f and itinerant conduction electrons is
crucial in the electronic properties of heavy fermion and valence fluctuating
compounds. Using high-resolution angle-resolved photoemission spectroscopy, we
systematically investigate the electronic structure of the archetypical valence
fluctuating compound EuNi2P2 that hosts multiple f electrons. At low
temperatures, we reveal the hybridization between Eu 4f and Ni 3d states, which
contributes to the electron mass enhancement, consistent with the periodic
Anderson model. With increasing temperature, interestingly, we observe opposite
temperature evolution of electron spectral function above and below the Kondo
coherence temperature near 110 K, which is in contrast to the monotonic valence
change and beyond the expectation of the periodic Anderson model. We argue that
both f-d hybridization and correlation are imperative in the electronic
properties of EuNi2P2. Our results shed light on the understanding of novel
properties, such as heavy fermion behaviors and valence fluctuation, of
rare-earth transition-metal intermetallic compounds with multiple f electrons.",2206.13030v1
2022-06-30,Antipolar transitions in GaNb$_4$Se$_8$ and GaTa$_4$Se$_8$,"We present dielectric, polarization, resistivity, specific heat, and magnetic
susceptibility data on single crystals of the lacunar spinels GaNb4Se8 and
GaTa4Se8, tetrahedral cluster-based materials with substantial spin-orbit
coupling. We concentrate on the possible occurrence of antipolar order in these
compounds, as previously reported for the isoelectronic GaNb4S8, where
spin-orbit coupling plays a less important role. Our broadband
dielectric-spectroscopy investigations reveal clear anomalies of the intrinsic
dielectric constant at the magneto-structural transitions in both systems that
are in accord with the expectations for antipolar transitions. A similar
anomaly is also observed at the cubic-cubic transition of the Nb compound
leading to an intermediate phase. Similar to other polar and antipolar lacunar
spinels, we find indications for dipolar relaxation dynamics at low
temperatures. Polarization measurements on GaNb4Se8 reveal weak ferroelectric
ordering below the magneto-structural transition, either superimposed to
antipolar order or emerging at structural domain walls. The
temperature-dependent dc resistivity evidences essentially thermally-activated
charge transport with different activation energies in the different phases. A
huge step-like increase of the resistivity at the magneto-structural transition
of the Ta compound points to a fundamental change in the electronic structure
or the mechanism of the charge transport. At low temperatures, charge transport
is governed by in-gap impurity states, as also invoked to explain the resistive
switching in these compounds.",2206.15200v2
2022-07-06,Pressure-temperature magnetostructural phase diagrams of slowly cooled Co$_{1-x}$Cu$_x$MnGe $(0.05 \leq x \leq 0.35)$,"Polycrystalline samples of Co$_{1-x}$Cu$_x$MnGe ($x=0.05, 0.10, 0.15, 0.22$
and 0.35), prepared by arc melting under argon atmosphere, have been annealed
at 1123 K with final furnace cooling. The samples have been investigated by
powder X-ray diffraction (in function of temperature) and ac magnetic
measurements (in function of temperature and applied hydrostatic pressure up to
12 kbar). On the basis of the experimental data, the $(p,T)$ phase diagrams
have been determined. For the low Cu content ($x=0.05$, 0.10 and 0.15), the
compounds show a martensitic transition between the low-temperature
orthorhombic crystal structure of the TiNiSi-type (space group: $Pnma$) and the
high-temperature hexagonal structure of the Ni$_2$In-type (space group:
$P6_3/mmc$). For the high Cu content ($x=0.22$ and 0.35) only the hexagonal
structure is observed. All compounds undergo a transition from para- to
ferromagnetic state with decreasing temperature (in case of $x=0.22$ through an
intermediate antiferromagnetic phase). The para- to ferromagnetic transition is
fully coupled with the martensitic one for $x=0.05$ at the intermediate
pressure range (6 kbar $\le p \le 8$ kbar). Partial magnetostructural coupling
is observed for $x=0.10$ at ambient pressure. The Curie temperature at ambient
pressure decreases from 313 K for $x=0.05$ (in the orthorhombic phase) to about
250 K for the remaining compounds (in the hexagonal phase). For the
Co$_{0.85}$Cu$_{0.15}$MnGe compound, entropy change associated with the
martensitic transition has been calculated using Clausius-Clapeyron equation.",2207.02570v2
2022-08-20,Evaluation of the suitable analytical techniques for the investigation of the toxic elements and compounds in the Pyrotechnic materials (Green crackers),"The present manuscript reports the elemental as well as molecular study of
the Green Crackers. Laser-induced breakdown spectroscopy has been used for
elemental analysis, UV-Vis and Photoacoustic Spectroscopy (PAS) are used for
molecular study of the green crackers. The spectral lines of several elements
including heavy/toxic such as Al, Ba, Sr, Cr, Cu are observed in the LIBS
spectra of green crackers like present in normal crackers. In addition to this,
the electronic bands of diatomic molecules like AlO, SrO, and CaO are also
observed in LIB spectra of the green crackers. PAS, which is non-destructive,
useful for scattering & opaque substances, is more suitable than the UV-VIS
method for the investigation of the various organic compounds/molecules present
in the firecrackers. Molecular bands of these molecules (AlO, SrO and CaO) are
also in the absorption spectra of the crackers recorded using PAS technique and
UV-Vis spectroscopy technique. In addition to these, absorption bands of some
additional compounds/molecules like AlO, SrO, CaCO3, KNO3, NH4NO3, NHClO4 are
also observed in the PA spectra of the green crackers, which show that PAS is
more appropriate technique than the UV-VIS method for the investigation of the
organic compounds/molecules in firecrackers. To determine the exact
concentration of the constituents (Al, Cr, Cu) in green crackers AAS has been
used. The results of the present manuscript show that the green crackers are
also toxic for the environment as well as for humans although with lesser
intensity than traditional/normal crackers.",2208.09655v1
2022-10-02,Large-scale machine-learning-assisted exploration of the whole materials space,"Crystal-graph attention networks have emerged recently as remarkable tools
for the prediction of thermodynamic stability and materials properties from
unrelaxed crystal structures. Previous networks trained on two million
materials exhibited, however, strong biases originating from underrepresented
chemical elements and structural prototypes in the available data. We tackled
this issue computing additional data to provide better balance across both
chemical and crystal-symmetry space. Crystal-graph networks trained with this
new data show unprecedented generalization accuracy, and allow for reliable,
accelerated exploration of the whole space of inorganic compounds. We applied
this universal network to perform machine-learning assisted high-throughput
materials searches including 2500 binary and ternary structure prototypes and
spanning about 1 billion compounds. After validation using density-functional
theory, we uncover in total 19512 additional materials on the convex hull of
thermodynamic stability and ~150000 compounds with a distance of less than 50
meV/atom from the hull. Combining again machine learning and ab-initio methods,
we finally evaluate the discovered materials for applications as
superconductors, superhard materials, and we look for candidates with large gap
deformation potentials, finding several compounds with extreme values of these
properties.",2210.00579v1
2022-10-20,Novel materials in the Materials Cloud 2D database,"Two-dimensional (2D) materials are among the most promising candidates for
beyond-silicon electronic, optoelectronic and quantum computing applications.
Recently, their recognized importance sparked a push to discover and
characterize novel 2D materials. Within a few years, the number of
experimentally exfoliated or synthesized 2D materials went from a couple of
dozens to more than a hundred, with the number of theoretically predicted
compounds reaching a few thousands. In 2018 we first contributed to this effort
with the identification of 1825 compounds that are either easily (1036) or
potentially (789) exfoliable from experimentally known 3D compounds. Here, we
report on a major expansion of this 2D portfolio thanks to the extension of the
screening protocol to an additional experimental database (MPDS) as well as to
the updated versions of the two databases (ICSD and COD) used in our previous
work. This expansion has led to the discovery of additional 1252 unique
monolayers, bringing the total to 3077 compounds and, notably, almost doubling
the number of easily exfoliable materials (2004). Moreover, we optimized the
structural properties of all these monolayers and explored their electronic
structure with a particular emphasis on those rare large-bandgap 2D materials
that could be precious to isolate 2D field effect transistors channels.
Finally, for each material containing up to 6 atoms per unit cell, we
identified the best candidates to form commensurate heterostructures, balancing
requirements on the supercells size and minimal strain.",2210.11301v1
2022-11-16,A natural ionic liquid: low molecular mass compounds of aggregate glue droplets on spider orb webs,"The aggregate glue of spider orb web is an excellent natural adhesive.
Orb-weaver spiders use micron-scale aggregate glue droplets to retain prey in
the capture spiral silks of their orb web. In aggregate glue droplets, highly
glycosylated and phosphorylated proteins dissolve in low molecular mass
compounds. The aggregate glue droplets show a heterogeneous structural
distribution after attaching to the substrate. Although components of the
aggregate glue droplets have been well analyzed and determined in past studies,
visualization of the spatial distribution of their chemical components before
and after their attachment is the key to exploring their adhesion mechanisms.
Here, we investigated the distribution of low molecular mass compounds and
glycoproteins in aggregate glue droplets using the in situ measurement methods
and visualized the role of specific low molecular mass compounds in promoting
glycoprotein modification in the aggregate glue. The results of the analysis
suggest that the constituents of aggregate glue droplets include at least one
ionic liquid: hydrated choline dihydrogen phosphate, while the modification of
glycoproteins in aggregate glue depends on the concentration of this ionic
liquid. This natural ionic liquid does not affect the fluorescence activity of
fluorescent proteins, indicating that proteins of aggregate glue droplets can
be dissolved well and maintain the stability of their higher-order structures
in that ionic liquid. As a natural ionic liquid, aggregate glue droplets from
the spider orb webs may be an excellent ionic liquid material model.",2211.08818v1
2022-12-16,Test-time Adaptation in the Dynamic World with Compound Domain Knowledge Management,"Prior to the deployment of robotic systems, pre-training the deep-recognition
models on all potential visual cases is infeasible in practice. Hence,
test-time adaptation (TTA) allows the model to adapt itself to novel
environments and improve its performance during test time (i.e., lifelong
adaptation). Several works for TTA have shown promising adaptation performances
in continuously changing environments. However, our investigation reveals that
existing methods are vulnerable to dynamic distributional changes and often
lead to overfitting of TTA models. To address this problem, this paper first
presents a robust TTA framework with compound domain knowledge management. Our
framework helps the TTA model to harvest the knowledge of multiple
representative domains (i.e., compound domain) and conduct the TTA based on the
compound domain knowledge. In addition, to prevent overfitting of the TTA
model, we devise novel regularization which modulates the adaptation rates
using domain-similarity between the source and the current target domain. With
the synergy of the proposed framework and regularization, we achieve consistent
performance improvements in diverse TTA scenarios, especially on dynamic domain
shifts. We demonstrate the generality of proposals via extensive experiments
including image classification on ImageNet-C and semantic segmentation on GTA5,
C-driving, and corrupted Cityscapes datasets.",2212.08356v3
2023-01-10,Magnetic anisotropy and low-energy spin dynamics in the van der Waals compounds Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$,"We report the detailed high-field and high-frequency electron spin resonance
(HF-ESR) spectroscopic study of the single-crystalline van der Waals compounds
Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$. Analysis of magnetic excitations
shows that in comparison to Mn$_{2}$P$_{2}$S$_{6}$ increasing the Ni content
yields a larger magnon gap in the ordered state and a larger g-factor value and
its anisotropy in the paramagnetic state. The studied compounds are found to be
strongly anisotropic having each the unique ground state and type of magnetic
order. Stronger deviation of the g-factor from the free electron value in the
samples containing Ni suggests that the anisotropy of the exchange is an
important contributor to the stabilization of a certain type of magnetic order
with particular anisotropy. At temperatures above the magnetic order, we have
analyzed the spin-spin correlations resulting in a development of slowly
fluctuating short-range order. They are much stronger pronounced in
MnNiP$_{2}$S$_{6}$ compared to Mn$_{2}$P$_{2}$S$_{6}$. The enhanced spin
fluctuations in MnNiP$_{2}$S$_{6}$ are attributed to the competition of
different types of magnetic order. Finally, the analysis of the temperature
dependent critical behavior of the magnon gaps below the ordering temperature
in Mn$_{2}$P$_{2}$S$_{6}$ suggests that the character of the spin wave
excitations in this compound undergoes a field induced crossover from a 3D-like
towards 2D XY regime.",2301.04239v2
2023-01-16,Antiferromagnetic order and its interplay with superconductivity in CaK(Fe$_{1-x}$Mn$_x$)$_4$As$_4$,"The magnetic order for several compositions of
CaK(Fe$_{1-x}$Mn$_x$)$_4$As$_4$ has been studied by nuclear magnetic resonance
(NMR), M\""ossbauer spectroscopy, and neutron diffraction. Our observations for
the Mn-doped 1144 compound are consistent with the hedgehog spin vortex crystal
(hSVC) order which has previously been found for Ni-doped
$\text{Ca}\text{K}\text{Fe}_4\text{As}_4$. The hSVC state is characterized by
the stripe-type propagation vectors $(\pi\,0)$ and $(0\,\pi)$ just as in the
doped 122 compounds. The hSVC state preserves tetragonal symmetry at the Fe
site, and only this SVC motif with simple AFM stacking along $\textbf{c}$ is
consistent with all our observations using NMR, M\""ossbauer spectroscopy, and
neutron diffraction. We find that the hSVC state in the Mn-doped 1144 compound
coexists with superconductivity (SC), and by combining the neutron scattering
and M\""ossbauer spectroscopy data we can infer a quantum phase transition,
hidden under the superconducting dome, associated with the suppression of the
AFM transition temperature ($T_\text{N}$) to zero for $x\approx0.01$. In
addition, unlike several 122 compounds and Ni-doped 1144, the ordered magnetic
moment is not observed to decrease at temperatures below the superconducting
transition temperature ($T_\text{c}$).",2301.06336v1
2023-02-28,Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds,"The iron-based compounds of the so-called 12442 family are very peculiar in
various respects. They originate from the intergrowth of 122 and 1111 building
blocks, display a large in-plane vs. out-of-plane anisotropy, possess double
layers of FeAs separated by insulating layers, and are generally very similar
to double-layer cuprates. Moreover, they are stoichiometric superconductors
because of an intrinsic hole doping. Establishing their superconducting
properties, and in particular the symmetry of the order parameter, is thus
particularly relevant in order to understand to what extent these compounds can
be considered as the iron-based counterpart of cuprates. In this work we review
the results of various techniques from the current literature and compare them
with ours, obtained in Rb-12442 by combining point-contact Andreev-reflection
spectroscopy and coplanar waveguide resonator measurements of the superfluid
density. It turns out that the compound possesses at least two gaps, one of
which is certainly nodal. The compatibility of this result with the
theoretically allowed gap structures, as well as with the other results in
literature, is discussed in detail.",2302.14767v2
2023-03-06,SPARTA: Spatial Acceleration for Efficient and Scalable Horizontal Diffusion Weather Stencil Computation,"Fast and accurate climate simulations and weather predictions are critical
for understanding and preparing for the impact of climate change. Real-world
weather and climate modeling consist of complex compound stencil kernels that
do not perform well on conventional architectures. Horizontal diffusion is one
such important compound stencil found in many climate and weather prediction
models. Recent works propose using FPGAs as an alternative to traditional CPU
and GPU-based systems to accelerate compound stencil kernels. However, we
observe that compound stencil computations cannot leverage the bit-level
flexibility available on an FPGA because of its complex memory access patterns,
leading to high hardware resource utilization and low peak performance. We
introduce SPARTA, a novel spatial accelerator for horizontal diffusion weather
stencil computation. We exploit the two-dimensional spatial architecture to
efficiently accelerate horizontal diffusion stencil by designing the first
scaled-out spatial accelerator using MLIR (Multi-Level Intermediate
Representation) compiler framework. We evaluate its performance on a real
cutting-edge AMD-Xilinx Versal AI Engine spatial architecture. Our real-system
evaluation results demonstrate that SPARTA outperforms the state-of-the-art
CPU, GPU, and FPGA implementations by 17.1x, 1.2x, and 2.1x, respectively. Our
results reveal that balancing workload across the available processing
resources is crucial in achieving high performance on spatial architectures. We
also implement and evaluate five elementary stencils that are commonly used as
benchmarks for stencil computation research. We freely open-source all our
implementations to aid future research in stencil computation and spatial
computing systems at https://github.com/CMU-SAFARI/SPARTA.",2303.03509v2
2023-03-25,Prediction of novel final phases in aged uranium-niobium alloys,"Ordered intermetallics are long believed to be the final products of the
aging of U-Nb solid solutions at low temperatures, a crucial property for the
practical applications of this alloy in engineering and industry. However, such
conjectured ordered compounds have not been experimentally or theoretically
established. Herein, numerical evidence for ordered intermetallic U-Nb
compounds is presented using thorough first-principles structure predictions up
to 500 GPa. Two stable U2Nb compounds and one metastable U2Nb and one
metastable U3Nb were discovered. A unique hybridized transition driven by
pressure was observed in U2Nb, which is a superposition of one first-order
transition and another second-order transition, leading to striking features
near the transition pressure of 21.6 GPa. The decomposition limit of these
compounds at high temperature was also investigated. The strong stability of
U2Nb in the region of low pressure and high temperature was revealed. This
discovery of ordered U2Nb and its strong stability over a wide pressure range
completely changed the phase diagram of U-Nb alloys and shed new light on the
dynamic response and aging mechanism of U-Nb alloys.",2303.14442v1
2023-05-12,Ab-initio investigation of the physical properties of BaAgAs Dirac semimetal and its possible thermo-mechanical and optoelectronic applications,"BaAgAs is a ternary Dirac semimetal which can be tuned across a number of
topological orders. In this study we have investigated the bulk physical
properties of BaAgAs using density functional theory based computations. Most
of the results presented in this work are novel. The optimized structural
parameters are in good agreement with previous results. The elastic constants
indicate that BaAgAs is mechanically stable and brittle in nature. The compound
is moderately hard and possesses fair degree of machinability. There is
significant mechanical/elastic anisotropy in BaAgAs. The Debye temperature of
the compound is medium and the phonon thermal conductivity and melting
temperature are moderate as well. The bonding character is mixed with notable
covalent contribution. The electronic band structure calculations reveal clear
semimetallic behavior with a Dirac node at the Fermi level. BaAgAs has a small
ellipsoidal Fermi surface centered at the G-point of the Brillouin zone. The
phonon dispersion curves show dynamical stability. There is a clear phonon band
gap between the acoustic and the optical branches. The energy dependent optical
constants conform to the band structure calculations. The compound is an
efficient absorber of the ultraviolet light and has potential to be used as an
anti-reflection coating. Optical anisotropy of BaAgAs is moderate. The computed
repulsive Coulomb pseudopotential is low indicating that the electronic
correlations in this compound are not strong.",2305.07427v1
2023-04-28,ALMERIA: Boosting pairwise molecular contrasts with scalable methods,"Searching for potential active compounds in large databases is a necessary
step to reduce time and costs in modern drug discovery pipelines. Such virtual
screening methods seek to provide predictions that allow the search space to be
narrowed down. Although cheminformatics has made great progress in exploiting
the potential of available big data, caution is needed to avoid introducing
bias and provide useful predictions with new compounds. In this work, we
propose the decision-support tool ALMERIA (Advanced Ligand Multiconformational
Exploration with Robust Interpretable Artificial Intelligence) for estimating
compound similarities and activity prediction based on pairwise molecular
contrasts while considering their conformation variability. The methodology
covers the entire pipeline from data preparation to model selection and
hyperparameter optimization. It has been implemented using scalable software
and methods to exploit large volumes of data -- in the order of several
terabytes -- , offering a very quick response even for a large batch of
queries. The implementation and experiments have been performed in a
distributed computer cluster using a benchmark, the public access DUD-E
database. In addition to cross-validation, detailed data split criteria have
been used to evaluate the models on different data partitions to assess their
true generalization ability with new compounds. Experiments show
state-of-the-art performance for molecular activity prediction (ROC AUC:
$0.99$, $0.96$, $0.87$), proving that the chosen data representation and
modeling have good properties to generalize. Molecular conformations --
prediction performance and sensitivity analysis -- have also been evaluated.
Finally, an interpretability analysis has been performed using the SHAP method.",2305.13254v1
2023-05-28,"Large Language Models, scientific knowledge and factuality: A systematic analysis in antibiotic discovery","Inferring over and extracting information from Large Language Models (LLMs)
trained on a large corpus of scientific literature can potentially drive a new
era in biomedical research, reducing the barriers for accessing existing
medical evidence. This work examines the potential of LLMs for dialoguing with
biomedical background knowledge, using the context of antibiotic discovery. The
systematic analysis is applied to ten state-of-the-art models, from models
specialised on biomedical scientific corpora to general models such as ChatGPT,
GPT-4 and Llama 2 in two prompting-based tasks: chemical compound definition
generation and chemical compound-fungus relation determination. The work
provides a systematic assessment on the ability of LLMs to encode and express
these relations, verifying for fluency, prompt-alignment, semantic coherence,
factual knowledge and specificity of generated responses. Results show that
while recent models have improved in fluency, factual accuracy is still low and
models are biased towards over-represented entities. The ability of LLMs to
serve as biomedical knowledge bases is questioned, and the need for additional
systematic evaluation frameworks is highlighted. The best performing GPT-4
produced a factual definition for 70% of chemical compounds and 43.6% factual
relations to fungi, whereas the best open source model BioGPT-large 30% of the
compounds and 30% of the relations for the best-performing prompt. The results
show that while LLMs are currently not fit for purpose to be used as biomedical
factual knowledge bases, there is a promising emerging property in the
direction of factuality as the models become domain specialised, scale-up in
size and level of human feedback.",2305.17819v2
2023-08-20,A probabilistic analysis of selected notions of iterated conditioning under coherence,"It is well know that basic conditionals satisfy some desirable basic logical
and probabilistic properties, such as the compound probability theorem, but
checking the validity of these becomes trickier when we switch to compound and
iterated conditionals. We consider de Finetti's notion of conditional as a
three-valued object and as a conditional random quantity in the betting
framework. We recall the notions of conjunction and disjunction among
conditionals in selected trivalent logics. First, in the framework of specific
three-valued logics we analyze the notions of iterated conditioning introduced
by Cooper-Calabrese, de Finetti and Farrell, respectively. We show that the
compound probability theorem and other basic properties are not preserved by
these objects, by also computing some probability propagation rules. Then, for
each trivalent logic we introduce an iterated conditional as a suitable random
quantity which satisfies the compound prevision theorem and some of the
desirable properties. We also check the validity of two generalized versions of
Bayes' Rule for iterated conditionals. We study the p-validity of generalized
versions of Modus Ponens and two-premise centering for iterated conditionals.
Finally, we observe that all the basic properties are satisfied only by the
iterated conditional mainly developed in recent papers by Gilio and Sanfilippo
in the setting of conditional random quantities.",2308.10338v1
2023-10-05,Comparison of Gd addition effect on the superconducting properties of FeSe0.5Te0.5 bulks under ambient and high-pressure conditions,"We have prepared a series of (FeSe0.5Te0.5 + xGd) bulk samples, with x = 0,
0.03, 0.05, 0.07, 0.1 and 0.2, through the convenient solid-state reaction
method at ambient pressure (CSP). High gas pressure and high-temperature
synthesis methods (HP-HTS) are also applied to grow the parent compound (x = 0)
and 5-wt% of Gd-added bulks. Structural, microstructural, transport and
magnetic characterizations have been performed on these samples in order to
draw the final conclusion. Our analysis results that the HP-HTS applied for the
parent compound enhances the transition temperature (Tc) and the critical
current density (Jc) with the improved sample density and intergrain
connections. The lattice parameter c is increased with Gd additions, suggesting
a small amount of Gd enters the tetragonal lattice of FeSe0.5Te0.5 and the Gd
interstitial sites are along the c-axis. A systematic decrease of the onset
transition temperature Tc is observed with Gd additions, however, the
calculated Jc of these Gd-added samples is almost the same as that of the
parent compound prepared by CSP. It specifies that there is no improvement of
the grain connections or pinning properties due to these rare earth additions.
However, Gd-added FeSe0.5Te0.5 bulks prepared by HP-HTS have revealed a
slightly improved critical current density due to improved grain connections
and sample density but have a lower transition temperature than that of the
parent compounds.",2310.03531v1
2023-10-10,Improved charge storage capacity of supercapacitor electrodes by engineering surfaces: the case of Janus MXenes,"Surface Engineering in two-dimensional(2D) materials has turned out to be an
useful technique to improve their functional properties. By designing Janus
compounds MM$^{\prime}$C in MXene family of compounds M$_{2}$C where the two
surfaces are constituted by two different transition metal M and M$^{\prime}$,
we have explored their potentials as electrodes in a supercapacitor with acidic
electrolyte. Using Density functional Theory (DFT) \cite{dft} in conjunction
with classical solvation model we have made an in depth analysis of the
electrochemical parameters of three Janus MXenes, passivated by oxygen - NbVC,
MnVC and CrMnC. Comparisons with the corresponding end point MXenes Nb$_{2}$C,
V$_{2}$C, Mn$_{2}$C and Cr$_{2}$C are also made. We find that the surface redox
activity enhances due to formation of Janus, improving the charge storage
capacities of MXene electrodes significantly. Our analysis reveals that the
improved functionality has its root in the variations in the charge state of
one of the constituents in the Janus compound which, in turn, has its origin in
the electronic structure changes due to the surface manipulation. Our work,
which is the first on the electrochemical properties of Janus MXenes for
supercapacitor applications, suggests the surface engineering by forming
appropriate Janus compounds as a possible route to extract high power density
in a MXene electrode-acidic electrolyte based energy storage devices.",2310.06334v1
2023-11-13,High Rectification Ratio at Room Temperature in Rhenium(I) Compound,"Electrical current rectification is an interesting electronic feature,
popularly known as a diode. Achieving a high rectification ratio in a molecular
junction has been a long-standing goal in molecular electronics. The present
work describes mimicking electrical current rectification with pi-stacked
rhenium(I) compound sandwiched between two electrical contacts. Among the two
mononuclear rhenium compounds studied here, [Re(CO)4(PPh3){(N)-saccharinate}]
(1) and [Re(CO)3(phen){(N)-saccharinate}] (2), the latter show strong pi-pi
interactions-induced high rectification ratio of ~ 4000 at 2.0 V at room
temperature. Alternating current (AC)-based electrical measurements ensuring AC
to DC electrical signal conversion at a frequency f of 1 KHz showing 2 can act
as an excellent half-wave rectifier. Asymmetric charge injection barrier height
at the electrode/Re(I) interfaces of the devices with a stacking configuration
of p++-Si/Re compound31nm(2)/ITO originates the flow of electrical current
unidirectionally. The charge transport mechanism governed by thermally
activated hopping phenomena, and charge carrier propagation is explained
through an energy profile considering the Fermi levels of two electrodes, and
the energy of frontier molecular orbitals, HOMO, and LUMO, confirming
rectification is of a molecular origin. The present work paves the way to
combine different organometallic compounds as circuit elements in
nanoelectronic devices to achieve numerous exciting electronic features.",2311.07258v1
2023-12-11,"DFT based investigation of structural, elastic, optoelectronic, thermophysical and superconducting state properties of binary Mo3P at different pressures","In recent years, the investigation of novel materials for various
technological applications has gained much importance in materials science
research. Tri-molybdenum phosphide (Mo3P), a promising transition metal
phosphide (TMP), has gathered significant attention due to its unique
structural and electronic properties, which already make it potentially
valuable system for catalytic and electronic device applications. Through an
in-depth study using the density functional theory (DFT) calculations, this
work aims to clarify the basic properties of the Mo3P compound at different
pressures. In this work, we have studied the structural, elastic,
optoelectronic and thermophysical properties of binary Mo3P compound. In this
investigation, we varied uniform hydrostatic pressure from 0 GPa to 30 GPa. A
complete geometrical optimization for structural parameters is performed and
the obtained values are in good accord with the experimental values where
available. It is also found that Mo3P possesses very low level of elastic
anisotropy, reasonably good machinability, ductile nature, relatively high
Vickers hardness, high Debye temperature and high melting temperature.
Thermomechanical properties indicate that the compound has potential to be used
as a thermal barrier coating material. The bonding nature in Mo3P has been
explored. The electronic band structure shows that Mo3P has no band gap and
exhibits conventional metallic behavior. All of the energy dependent optical
characteristics demonstrate apparent metallic behavior and agree exactly with
the electronic density of states calculations. The compound has excellent
reflective and absorptive properties suitable for optical applications.
Pressure dependent variations of the physical properties are explored and their
possible link with superconductivity has been discussed.",2312.06073v1
2023-12-16,Exploring the effect of strong electronic correlations in Seebeck Coefficient of the NdCoO3 compound : Using experimental and DFT+U approach,"The presence of complexity in the electronic structure of strongly correlated
electron system NdCoO$_3$ (NCO) have sparked interest in the investigation of
its physical properties. Here, we study the the Seebeck coefficient ($\alpha $)
of NCO by using the combined experimental and DFT+$U$ based methods. The
experimentally measured $\alpha $ is found to be $\sim$ 444 $\mu V/K$ at 300 K,
which decreases to 109.8 $\mu V/K$ at 600 K. In order to understand the
measured $\alpha $, we have calculated the PDOS and band structure of the NCO.
Furthermore, the calculated occupancy of 6.4 for Co $3d$ orbitals and presence
of large unoccupied O $2p$ states indicate the covalent nature of the bonding.
Apart from this, the maximum effective mass is found to be 36.75 (28.13) for
the spin-up (dn) channel in conduction band indicates the n-type behaviour of
the compound in contrast to our experimentally observed p-type behaviour.
While, the calculated $\alpha $ at the temperature-dependent chemical potential
($\mu$) at 300 K shows the p-type behaviour of the compound. Fairly good
agreement is seen between the calculated and measured values of $\alpha $ at
U$_f$$_f$ = 5.5 eV and U$_d$$_d$ = 2.7 eV. The maximum power factor (PF) is
found to be 47.6 (114.4) $\times$ $10^1$$^4 $ $\mu
$$W$$K^-$$^2$$cm^-$$^1$$s^-$$^1$ at 1100 K, which corresponds to p (n)-type
doping of $\sim$ 1.4 (0.7) $\times$ 10$^2$$^1$ cm$^-$$^3$. This study suggests
the importance of strong on-site electron correlation in understanding the
thermoelectric property of the compound.",2312.10449v1
2024-01-02,Accelerating Discovery of Novel and Bioactive Ligands With Pharmacophore-Informed Generative Models,"Deep generative models have gained significant advancements to accelerate
drug discovery by generating bioactive chemicals against desired targets.
Nevertheless, most generated compounds that have been validated for potent
bioactivity often exhibit structural novelty levels that fall short of
satisfaction, thereby providing limited inspiration to human medicinal
chemists. The challenge faced by generative models lies in their ability to
produce compounds that are both bioactive and novel, rather than merely making
minor modifications to known actives present in the training set. Recognizing
the utility of pharmacophores in facilitating scaffold hopping, we developed
TransPharmer, an innovative generative model that integrates ligand-based
interpretable pharmacophore fingerprints with generative pre-training
transformer (GPT) for de novo molecule generation. TransPharmer demonstrates
superior performance across tasks involving unconditioned distribution
learning, de novo generation and scaffold elaboration under pharmacophoric
constraints. Its distinct exploration mode within the local chemical space
renders it particularly useful for scaffold hopping, producing compounds that
are structurally novel while pharmaceutically related. The efficacy of
TransPharmer is validated through two case studies involving the dopamine
receptor D2 (DRD2) and polo-like kinase 1 (PLK1). Notably in the case of PLK1,
three out of four synthesized designed compounds exhibit submicromolar
activities, with the most potent one, IIP0943, demonstrating a potency of 5.1
nM. Featuring a new scaffold of 4-(benzo[b]thiophen-7-yloxy)pyrimidine, IIP0943
also exhibits high selectivity for PLK1. It was demonstrated that TransPharmer
is a powerful tool for discovery of novel and bioactive ligands.",2401.01059v1
2024-01-12,Symmetry Lowering Through Surface Engineering and Improved Thermoelectric Properties in MXenes,"Despite ample evidence of their influences on the transport properties of
two-dimensional solids, the interrelations of reduced symmetry, electronic and
thermal transport, have rarely being discussed in the context of thermoelectric
materials. With the motivation to design new thermoelectric materials with
improved properties, we have addressed these by performing first-principles
Density Functional Theory based calculations in conjunction with semi-classical
Boltzmann transport theory on a number of compounds in the MXene family. The
symmetry lowering in parent M$_{2}$CO$_{2}$ MXenes are done by replacing
transition metal $M$ on one surface, resulting in Janus compounds
MM$^{\prime}$CO$_{2}$. Our calculations show that the thermoelectric
figure-of-merit can be improved significantly by such surface engineering. We
discuss in detail, both qualitatively and quantitatively, the origin behind
high thermoelectric parameters for these compounds. Our in-depth analysis shows
that the modifications in the electronic band structures and degree of
anharmonicity driven by the dispersions in the bond strengths due to lowering
of symmetry, an artefact of surface engineering, are the factors behind the
trends in the thermoelectric parameters of the MXenes considered. The results
also substantiate that the compositional flexibility offered by the MXene
family of compounds can generate complex interplay of symmetry, electronic
structure, bond strengths and anharmonicity which can be exploited to engineer
thermoelectric materials with improved properties.",2401.06335v1
2024-01-29,Dual-adatom diffusion-limited growth model for compound nanowires: Application to InAs nanowires,"We propose a dual-adatom diffusion-limited model for the growth of compound
semiconductor nanowires via the vapor-liquid-solid or the vapour-solid-solid
mechanisms. The growth is catalyzed either by a liquid or a solid nanoparticle.
We validate the model using experimental data from the growth of InAs nanowires
catalyzed by a gold nanoparticle in a molecular beam epitaxy reactor.
Initially, we determine the parameters (diffusion lengths, flux to the seed,
Kelvin effect) that describe the growth of nanowires under an excess of one of
the two beams (for instance, group III or group V atoms). The diffusion-limited
model calculates the growth rate resulting from the current of atoms reaching
the seed. Our dual-adatom diffusion-limited model calculates for a compound
semiconductor, the instantaneous growth rate resulting from the smallest
current of the two types of atoms at a given time. We apply the model to
analyze the length-radius dependence of our InAs nanowires for growth
conditions covering the transition from the As-limited to the In-limited
regime. Finally, the model also describes the complex dependence of the
transition between both regimes on the nanowire radius and length. This
approach is generic and can be applied to study the growth of any compound
semiconductor nanowires.",2401.16269v1
2024-02-02,Emerging topological states in EuMn$_2$Bi$_2$: A first principles prediction,"New materials with magnetic order driven topological phases are hugely sought
after for their immense application potential. In this work, we propose a new
compound EuMn$_2$Bi$_2$ from our first principles density functional theory
calculations to host novel topological phases such as Dirac/Weyl semimetal and
topological insulator in its different magnetic states which are energetically
close to one another. We started with an isostructural compound EuMn$_2$As$_2$
where the magnetic structure has been studied experimentally. From our
calculations we could explain the nature of two magnetic transitions observed
experimentally in this system and could also establish the correct magnetic
ground state. Our electronic structure calculations reveal the insulating
nature of the ground state consistent with the experiments. By replacing all As
by Bi in EuMn$_2$As$_2$ and by optimizing the new structure, we obtained the
new compound EuMn$_2$Bi$_2$. We observe this compound to be dynamically stable
from our phonon calculations supporting its experimental preparation in future.
By comparing the total energies of various possible magnetic structures we
identified the ground state. Though the magnetic ground state is found to be
insulating in nature with tiny band gap which is an order of magnitude less
than the same in EuMn$_2$As$_2$, there were other magnetic states energetically
very close to the ground state which display remarkable non-trivial band
topology such as Dirac/Weyl points close to the Fermi level and topological
insulator state. The energetic proximity of these magnetic order driven
topological phases makes them tunable via external handle which indicates that
the proposed new material EuMn$_2$Bi$_2$ would be a very versatile magnetic
topological material.",2402.01328v1
2024-02-13,Chemical tuning of photo- and persistent luminescence of Cr3+-activated beta-Ga2O3 by alloying with Al2O3 and In2O3,"An effect of alloying of the monoclinic beta- Ga2O3 with Al2O3 and In2O3 on
the photoluminescent, thermoluminescent and persistent luminescent properties
of Cr3+ ions has been comprehensively investigated. For this purpose, various
series of Cr3+ and Ca2+ co-doped microcrystalline phosphors were synthesized by
the solution combustion method, including pseudobinary compounds like
(Ga-Al)2O3 with up to 20% Al and (Ga-In)2O3 with up to 50% In as well as
pseudoternary compounds (Ga Al In)2O3 with balanced proportion of Al, Ga and
In. The phase composition and crystal structure of the obtained materials were
examined by X-ray powder diffraction technique. Detailed luminescence studies
were conducted for the (Ga-Al)2O3 and (Ga-In)2O3 compounds which exhibited a
single-phase monoclinic structure. Low-temperature and time-resolved
photoluminescence investigations of the Cr-doped pseudobinary compounds
unveiled several types of Cr3+ centres, attributed to the Al-, Ga- and
In-centred octahedra in the studied alloys. The obtained results underscore the
benefit of bandgap engineering through alteration in the host lattice chemical
composition for efficient tuning of the thermoluminescent and persistent
luminescent properties of the near-infrared-emitting beta Ga2O3:Cr based
phosphors. Furthermore, it was demonstrated that modification of the chemical
composition of the host lattice also adjusts the thermometric performance of
the studied phosphors. Indeed, the specific sensitivity of the beta- Ga2O3:Cr3+
decay time luminescence thermometer showed nearly twofold enhancement when the
host lattice was alloyed with 30% of In2O3.",2402.08542v2
2024-02-19,"Revisiting thermodynamics in (LiF, NaF, KF, CrF2)-CrF3 by first-principles calculations and CALPHAD modeling","The thermodynamic description of the (LiF, NaF, KF, CrF2)-CrF3 systems has
been revisited, aiming for a better understanding of the effects of Cr on the
FLiNaK molten salt. First-principles calculations based on density functional
theory (DFT) were performed to determine the electronic and structural
properties of each compound, including the formation enthalpy, volume, and bulk
modulus. DFT-based phonon calculations were carried out to determine the
thermodynamic properties of compounds, for example, enthalpy, entropy, and heat
capacity as functions of temperature. Phonon-based thermodynamic properties
show a good agreement with experimental data of binary compounds LiF, NaF, KF,
CrF3, and CrF2, establishing a solid foundation to determine thermodynamic
properties of ternary compounds as well as to verify results estimated by the
Neumann-Kopp rule. Additionally, DFT-based ab initio molecular dynamics (AIMD)
simulations were employed to predict the mixing enthalpies of liquid salts.
Using DFT-based results and experimental data in the literature, the (LiF, NaF,
KF, CrF2)-CrF3 system has been remodeled in terms of the CALculation of PHAse
Diagrams (CALPHAD) approach using the modified quasichemical model with
quadruplet approximation (MQMQA) for liquid. Calculated phase stability in the
present work shows an excellent agreement with experiments, indicating the
effectiveness of combining DFT-based total energy, phonon, and AIMD
calculations, and CALPHAD modeling to provide the thermodynamic description in
complex molten salt systems.",2402.12574v2
2024-02-22,Spin ice evidence in the frustrated Gd2GaSbO7 and Gd2InSbO7 pyrochlore compounds,"Gd2GaSbO7 and Gd2InSbO7 pyrochlore compounds have exhibited spin ice
behavior. These compounds have not been adequately reported based on the
concept of magnetic frustration. Here, we have synthesized and characterized
Gd2GaSbO7 and Gd2InSbO7 to study the ground state magnetic properties. We
confirmed the cubic pyrochlore structure via X-ray powder diffraction. Magnetic
and heat capacity measurements show an absence of magnetic order down to 400
mK. Interestingly, the low-temperature magnetic heat capacity exhibited a broad
maximum around Tmax = 0.9 K for Gd2GaSbO7 and Tmax = 1 K for Gd2InSbO7,
suggesting the presence of spin fluctuations and following the T^1.71 and
T^1.49 dependence for Gd2GaSbO7 and Gd2InSbO7 respectively. We scale the ratio
between nearest-neighbour exchange and dipolar interaction of all the reported
Gd-based pyrochlores, where Gd2InSbO7 has the lowest and weaker exchange
interaction of all among others. It states that chemical pressure has an impact
on exchange interaction due to the different pathways of mediators between
magnetic ions. This study reveals the robust spin ice behaviour in the ground
state like Dy2Ti2O7 and Ho2Ti2O7. It is in stark contrast with other
Gd-Pyrochlore compounds that hold the long-range magnetic order.",2402.14413v2
2024-03-04,"Double magnetic transition, complex field-induced phases, and large magnetocaloric effect in the frustrated garnet compound Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$","A detailed study of the magnetic and magnetocaloric properties of a garnet
compound Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$ is carried out using x-ray
diffraction, magnetization, heat capacity, and neutron diffraction measurements
as well as \textit{ab initio} band-structure calculations. This compound
manifests two successive magnetic transitions at $T_{\rm N1} \simeq 4.5$ K and
$T_{\rm N2} \simeq 2.7$ K. Neutron powder diffraction experiments reveal that
these two transitions correspond to the collinear and non-collinear
antiferromagnetic ordering of the nonfrustrated Cr$^{3+}$ and frustrated
Mn$^{2+}$ sublattices, respectively. The interactions within each of the Cr and
Mn sublattices are antiferromagnetic, while the inter-sublattice interactions
are ferromagnetic. The $H-T$ phase diagram is quite complex and displays
multiple phases under magnetic field, which can be attributed to the frustrated
nature of the spin lattice. Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$ shows a large
magnetocaloric effect with a maximum value of isothermal entropy change $\Delta
S_{\rm m} \simeq -23$ J/kg-K and adiabatic temperature change $\Delta T_{\rm
ad} \simeq 9$ K for a field change of 7 T. Further, a large value of the
relative cooling power ($RCP \simeq 360$ J/kg) demonstrates the promise of
using this compound in magnetic refrigeration.",2403.02082v2
2024-03-07,Non-equilibrium Green's function approach to low-energy fission dynamics,"The concept of a compound nucleus was proposed by Bohr in 1936 to explain
narrow resonances in neutron scattering off a nucleus. While a compound nucleus
has been understood in terms of statistical mechanics, its description based on
a many-body Hamiltonian has yet to be developed. Here we present a microscopic
modeling of a compound nucleus starting from a nucleonic degree of freedom. We
focus in particular on a decay of a heavy compound nucleus, that is, fission
and radiative capture. To this end, we develop an approach based on a
non-equilibrium Green's function, which is combined with a configuration
interaction (CI) approach based on a constrained density-functional theory
(DFT). We apply this approach to a barrier-top fission of $^{236}$U,
restricting the model space to seniority zero configurations of neutrons and
protons. Our calculation with a Skyrme energy functional yields the
fission-to-capture branching ratio of around 0.07. While this value is still
reasonable, the calculation underestimates the branching ratio by about a
factor of 40 as compared to the empirical value, indicating a necessity of
seniority non-zero configurations in the model space. We also find that the
distribution of the fission probability approximately follows the chi-squared
distribution with the number of degrees of freedom of the order of 1, which is
consistent with the experimental finding.",2403.04255v2
2024-03-19,Predicting Winning Lottery Numbers,"We use mathematical statistics theory to derive the
Compound-Dirichlet-Multinomial (CDM) prediction model. We then use this model
to predict winning numbers for the 6-number, 5-number, pick-4 and pick-3
lottery games. We also develop a strategy which we call the 3-strategy, for
generating profit by predicting winning numbers for the pick-3 lottery game.",2403.12836v1
1994-09-06,Conceptual Association for Compound Noun Analysis,"This paper describes research toward the automatic interpretation of compound
nouns using corpus statistics. An initial study aimed at syntactic
disambiguation is presented. The approach presented bases associations upon
thesaurus categories. Association data is gathered from unambiguous cases
extracted from a corpus and is then applied to the analysis of ambiguous
compound nouns. While the work presented is still in progress, a first attempt
to syntactically analyse a test set of 244 examples shows 75% correctness.
Future work is aimed at improving this accuracy and extending the technique to
assign semantic role information, thus producing a complete interpretation.",9409002v2
1996-09-25,Designing Statistical Language Learners: Experiments on Noun Compounds,"The goal of this thesis is to advance the exploration of the statistical
language learning design space. In pursuit of that goal, the thesis makes two
main theoretical contributions: (i) it identifies a new class of designs by
specifying an architecture for natural language analysis in which probabilities
are given to semantic forms rather than to more superficial linguistic
elements; and (ii) it explores the development of a mathematical theory to
predict the expected accuracy of statistical language learning systems in terms
of the volume of data used to train them.
  The theoretical work is illustrated by applying statistical language learning
designs to the analysis of noun compounds. Both syntactic and semantic analysis
of noun compounds are attempted using the proposed architecture. Empirical
comparisons demonstrate that the proposed syntactic model is significantly
better than those previously suggested, approaching the performance of human
judges on the same task, and that the proposed semantic model, the first
statistical approach to this problem, exhibits significantly better accuracy
than the baseline strategy. These results suggest that the new class of designs
identified is a promising one. The experiments also serve to highlight the need
for a widely applicable theory of data requirements.",9609008v1
1997-06-24,Automatic Discovery of Non-Compositional Compounds in Parallel Data,"Automatic segmentation of text into minimal content-bearing units is an
unsolved problem even for languages like English. Spaces between words offer an
easy first approximation, but this approximation is not good enough for machine
translation (MT), where many word sequences are not translated word-for-word.
This paper presents an efficient automatic method for discovering sequences of
words that are translated as a unit. The method proceeds by comparing pairs of
statistical translation models induced from parallel texts in two languages. It
can discover hundreds of non-compositional compounds on each iteration, and
constructs longer compounds out of shorter ones. Objective evaluation on a
simple machine translation task has shown the method's potential to improve the
quality of MT output. The method makes few assumptions about the data, so it
can be applied to parallel data other than parallel texts, such as word
spellings and pronunciations.",9706027v1
1994-06-29,Cross relaxation and the bilayer coupling in YBCO,"There is strong experimental evidence for substantial antiferromagnetic
coupling between the CuO$_2$ planes of the bilayers in YBCO compounds. The
acoustic mode of the spin excitation spectrum has been measured but the optic
mode has not been observed. Theoretical estimates suggest values for the
antiferromagnetic interplane coupling as large as 10 meV. It has been proposed
that this coupling is responsible for the spin gap in the underdoped YBCO
compounds. In the recently synthesized compounds Y$_2$Ba$_4$Cu$_7$O$_{15}$ with
alternating single/double chain blocks, it is possible to distinguish between
the CuO$_2$ planes in a bilayer. We propose a nuclear magnetic cross relaxation
experiment to directly measure the strength of the coupling between the two
planes of a bilayer. The temperature dependence and magnitude of this cross
relaxation rate is predicted.",9406118v1
1994-08-05,NMR in ``underdoped'' and ``overdoped'' YBaCuO compounds: fermi-liquid approach,"We examine the NMR experimental data for the normal state of
YBa$_2$Cu$_3$O$_{7-\delta}$ within the Fermi-liquid approach. We show that the
observed temperature dependence of the Knight shift and $^{17}$O ($^{89}$Y)
relaxation rate in ``underdoped'' ( $T_c=60\,$K ) compound can be interpreted
as resulting from a peak in the density of states near the Fermi level. The
possible origin of such peak is the quasi-one-dimensional van Hove singularity
in the fermionic spectrum, conjectured by Abrikosov, Gofron and Campuzano. The
proposed spectrum allows us to account for the qualitatively different NMR data
for ``underdoped'' and ``overdoped''( $T_c=90\,$K ) compounds by varying the
value of chemical potential only.",9408021v1
1997-05-15,Tight-binding parameters and exchange integrals of Ba_2Cu_3O_4Cl_2,"Band structure calculations for Ba_2Cu_3O_4Cl_2 within the local density
approximation (LDA) are presented. The investigated compound is similar to the
antiferromagnetic parent compounds of cuprate superconductors but contains
additional Cu_B atoms in the planes. Within the LDA, metallic behavior is found
with two bands crossing the Fermi surface (FS). These bands are built mainly
from Cu 3d_{x^2-y^2} and O 2p_{x,y} orbitals, and a corresponding tight-binding
(TB) model has been parameterized. All orbitals can be subdivided in two sets
corresponding to the A- and B-subsystems, respectively, the coupling between
which is found to be small. To describe the experimentally observed
antiferromagnetic insulating state, we propose an extended Hubbard model with
the derived TB parameters and local correlation terms characteristic for
cuprates. Using the derived parameter set we calculate the exchange integrals
for the Cu_3O_4 plane. The results are in quite reasonable agreement with the
experimental values for the isostructural compound Sr_2Cu_3O_4Cl_2.",9705153v1
1998-01-27,NaV_2O_5 as a quarter-filled ladder compound,"A new X-ray diffraction study of the one-dimensional spin-Peierls compound
\alpha-NaV_2O_5 reveals a centrosymmetric (Pmmn) crystal structure with one
type of V site, contrary to the previously postulated non-centrosymmetric
P2_1mn structure with two types of V sites (V^{+4} and V^{+5}). Density
functional calculations indicate that NaV_2O_5 is a quarter-filled ladder
compound with the spins carried by V-O-V molecular orbitals on the rungs of the
ladder. Estimates of the charge-transfer gap and the exchange coupling agree
well with experiment and explain the insulating behavior of NaV_2O_5 and its
magnetic properties.",9801276v2
1998-05-01,The physics of dynamical atomic charges: the case of ABO3 compounds,"Based on recent first-principles computations in perovskite compounds,
especially BaTiO3, we examine the significance of the Born effective charge
concept and contrast it with other atomic charge definitions, either static
(Mulliken, Bader...) or dynamical (Callen, Szigeti...). It is shown that static
and dynamical charges are not driven by the same underlying parameters. A
unified treatment of dynamical charges in periodic solids and large clusters is
proposed. The origin of the difference between static and dynamical charges is
discussed in terms of local polarizability and delocalized transfers of charge:
local models succeed in reproducing anomalous effective charges thanks to large
atomic polarizabilities but, in ABO3 compounds, ab initio calculations favor
the physical picture based upon transfer of charges. Various results concerning
barium and strontium titanates are presented. The origin of anomalous Born
effective charges is discussed thanks to a band-by-band decomposition which
allows to identify the displacement of the Wannier center of separated bands
induced by an atomic displacement. The sensitivity of the Born effective
charges to microscopic and macroscopic strains is examined. Finally, we
estimate the spontaneous polarization in the four phases of barium titanate.",9805013v1
1998-05-05,Rare earth contributions to the X-ray magnetic circular dichroism at the Co K edge in rare earth-cobalt compounds investigated by multiple-scattering calculations,"The X-ray magnetic circular dichroism (XMCD) has been measured at the Co K
edge in Co-hcp and R-Co compounds (R=La, Tb, Dy). The structure of the
experimental XMCD spectra in the near-edge region has been observed to be
highly sensitive to the magnetic environment of the absorbing site.
Calculations of the XMCD have been carried out at the Co K edge in Co metal,
LaCo$_5$ and TbCo$_5$ within the multiple-scattering framework including the
spin-orbit coupling. In the three systems, the XMCD spectra in the near-edge
region are well reproduced. The possibility to separate and quantitatively
estimate the local effects from those due to the neighboring atoms in the XMCD
cross section makes possible a more physical understanding of the spectra. The
present results emphasize the major role played by the $d$ states of the Tb
ions in the XMCD spectrum at the Co K edge in the TbCo$_5$ compound.",9805062v3
1998-05-19,Anomalous relaxations and chemical trends at III-V nitride non-polar surfaces,"Relaxations at nonpolar surfaces of III-V compounds result from a competition
between dehybridization and charge transfer. First principles calculations for
the (110) and (10$\bar{1}$0) faces of zincblende and wurtzite AlN, GaN and InN
reveal an anomalous behavior as compared with ordinary III-V semiconductors.
Additional calculations for GaAs and ZnO suggest close analogies with the
latter. We interpret our results in terms of the larger ionicity (charge
asymmetry) and bonding strength (cohesive energy) in the nitrides with respect
to other III-V compounds, both essentially due to the strong valence potential
and absence of $p$ core states in the lighter anion. The same interpretation
applies to Zn II-VI compounds.",9805220v2
1998-08-07,"Scaling relations in charge and spin excitations for (La,Sr)MnO3","Scaling relations in the charge and spin excitations of (La,Sr)MnO3 are
studied from both theoretical and experimental points of view. In the
ferromagnetic metal phase, we investigate optical conductivity and neutron
inelastic scattering, and compare with a theoretical calculation based on the
dynamical mean-field theory of the double-exchange hamiltonian. Spin and charge
dynamics of (La,Sr)MnO3 exhibit typical behaviors of half metals. In these
manganite compounds with high Curie temperature, various behaviors in spin and
charge properties are explained by the double-exchange hamiltonian alone.
Magnetoresistance of these compounds as well as other compounds with lower
Curie temperature are also discussed.",9808076v1
1999-01-08,Anisotropy and magnetism of high temperature oxides superconductors,"Phonon or electron mediated weak BCS attraction is enough to have high
critical temperature if a van Hove anomaly is at work. This could apply to
electron doped compounds and also to compounds with CuO$_2$ planes overdoped in
holes, where $T_c$ decreases with increasing doping. If phonons dominate, it
should lead to an anisotropic but mainly $s$ superconductive gap, as observed
recently in overdoped LaSrCuO, and probably also in electron doped compounds.
If electrons dominate, a $d$ gap should develop as observed in a number of
cases. In the underdoped range, the observed decrease of $T_c$ with hole doping
can be related in all cases to the development of antiferromagnetic
fluctuations which produces a magnetic pseudogap, thus lowering the density of
states at the Fermi level. The observed mainly $d$ superconductive gap then can
be due to a prevalent superconductive coupling through antiferromagnetic
fluctuations; it could also possibly be attributed to the same phonon coupling
as in the overdoped range, now acting on Bloch functions scattered in the
magnetic pseudogap. More systematic studies of superconductive gap anisotropy
and of magnetic fluctuations would be in order.",9901065v2
1999-02-22,1D Quantum transport in the even-chain spin-ladder compound Sr2.5Ca11.5Cu24O41 and YBa2Cu4O8,"The temperature dependence of the resistivity r(T) of the novel
Sr2.5Ca11.5Cu24O41 ladder compound under hydrostatic pressure of up to 8 GPa
has been explained by assuming that the relevant length scale for electrical
transport is given by the magnetic correlation length related to the opening of
a spin-gap in a 1D even-chain spin-ladder (1D-SL). The pressure dependence of
the gap was extracted by applying this model to r(T) data obtained at different
pressures. The r(T) dependence of the underdoped cuprate YBa2Cu4O8 demonstrates
a remarkable scaling with the r(T) of the 1D-SL compound Sr2.5Ca11.5Cu24O41.
This scaling implies that underdoped cuprates at Tc < T < T* are in the 1D
regime and their pseudo-gap below T* is the spin-gap in the even-chain 1D-SL
formed at T < T* in these materials.",9902297v1
1999-06-15,Incorporation of a non-amphiphilic nematic liquid crystal into a host monolayer,"Many nematic liquid crystals are not able to form stable monolayers at the
air/water interface because of the lack of a polar headgroup. A possible way to
obtain a monomolecular film with these compounds is to incorporate them into
host monolayers of amphiphilic compounds. Stable monolayers containing a high
fraction of the liquid crystal can be obtained. We have prepared stable and
transferable monolayers of MBBA (which is not an amphiphilic compound) using
octadecylmalonic acid (OMA) as host. The monolayers at the air/water interface
have been characterized by measurements of surface-pressure/area and
surface-potential/area isotherms. The monolayers deposited on quartz plates
have been characterized by determining the transfer ratio and by spectroscopic
measurements.",9906225v1
1999-11-21,Charge Ordering in Organic ET Compounds,"The charge ordering phenomena in quasi two-dimensional 1/4-filled organic
compounds (ET)_2X (ET=BEDT-TTF) are investigated theoretically for the $\theta$
and $\alpha$-type structures, based on the Hartree approximation for the
extended Hubbard models with both on-site and intersite Coulomb interactions.
It is found that charge ordered states of stripe-type are stabilized for the
relevant values of Coulomb energies, while the spatial pattern of the stripes
sensitively depends on the anisotropy of the models. By comparing the results
of calculations with the experimental facts, where the effects of quantum
fluctuation is incorporated by mapping the stripe-type charge ordered states to
the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating
phases of $\theta$-(ET)_2MM'(SCN)_4 and $\alpha$-(ET)_2I_3 are deduced.
Furthermore, to obtain a unified view among the $\theta$, $\alpha$ and
$\kappa$-(ET)_2X families, the stability of the charge ordered state in
competition with the dimeric antiferromagnetic state viewed as the Mott
insulating state, which is typically realized in $\kappa$-type compounds, and
with the paramagnetic metallic state, is also pursued by extracting essential
parameters.",9911329v2
2000-01-08,Field Dependent Specific-Heat of Rare Earth Manganites,"The low temperature specific heat C(H) of several rare-earth manganites
(La_(0.7)Sr_(0.3)MnO_(3), Nd_(0.5)Sr_(0.5)MnO_(3), Pr_(0.5)Sr_(0.5)MnO_(3),
La_(0.67)Ca_(0.33)MnO$_(3), La_(0.5)Ca_(0.5)MnO_(3), La_(0.45)Ca_(0.55)MnO_(3)
and La_(0.33)Ca_(0.67)MnO_(3)) was measured as a function of magnetic field. We
observed behaviour consistent with thermodynamic expectations, i.e., C(H)
decreases with field for ferromagnetic metallic compounds by an amount which is
in quantitative agreement with spin wave theory. We also find that C(H)
increases with field in most compounds with a charge-ordered antiferromagnetic
ground state. In compounds which show evidence of a coexistence of
ferromagnetic metallic and antiferromagnetic charge-ordered states, C(H)
displays some unusual non-equilibrium effects presumably associated with the
phase-separation of the two states. We also observe a large anomalous low
temperature specific heat at the doping induced metal-insulator transition (at
x = 0.50) in La_(1-x)Ca_(x)MnO_(3).",0001089v1
2000-02-08,Spin quantization axis dependent magnetic properties and x-ray magnetic circular dichroism of FePt and CoPt,"We have performed a theoretical study of the magnetic circular dichroism in
the x-ray absorption spectra (XMCD) of the equiatomic CoPt and FePt ordered
alloys as a function of the spin quantization axis. We found that the
magnetization axis is along the [001] direction and the magneto-crystalline
anisotropy energy (MCA) for the FePt compound is twice as large as that of the
CoPt compound in agreement with experiment. The band structure and the total
density of states confirm that all electronic states contribute to the MCA, and
not just the states at the vicinity of the Fermi level. The orbital magnetic
moments decrease with respect to the angle between the [001] axis and the spin
quantization axis, and are much larger for the CoPt compound. We show that the
orbital moment anisotropy is reflected in the XMCD signal.",0002110v1
2000-02-14,Transition Temperature and Magnetoresistance in Double-Exchange Compounds with Moderate Disorder,"We develop a variational mean-field theory of the ferromagnetic transition in
compounds like Lanthanum-Manganite within the framework of the Double-Exchange
Model supplemented by modest disorder. We obtain analytical expressions for the
transition temperature, its variation with the valence electron-density and its
decrease with disorder.
  We derive an expression for the conductivity for both the paramagnetic and
the ferromangetic metallic phases, and study its dependence on the temperature
and magnetic field. A simple relation between the resistivity in the
ferromagnetic phase and the spontaneous magnetization is found. Our results are
in a good agreement with the experimental data on transition temperatures and
resistivity in the manganite compounds with relatively small disorder. We
comment on the effects of increased disorder.",0002191v1
2000-02-17,"Silence of magnetic layers to magnetoresistive process and electronic separation at low temperatures in (La, Sm)Mn$_2$Ge$_2$","A closer look at the temperature (T) dependence of magnetoresistance (MR) of
two polycrystalline magnetic compounds, LaMn$_2$Ge$_2$ and SmMn$_2$Ge$_2$,
previously reported by us, is made. A common feature for both these compounds
is that the low temperature MR is positive (say, below, 30 K) in spite of the
fact that both are ferromagnetic at such low temperatures; in addition, MR as a
function of magnetic field (H) does not track magnetization (M) in the sense
that M saturates at low fields, while MR varies linearly with H. These
observations suggest that the magnetic layers interestingly do not dominate low
temperature magnetotransport process. Interestingly enough, as the T is
increased, say around 100 K, these magnetic layers dominate MR process as
evidenced by the tracking of M and MR in SmMn$_2$Ge$_2$. These results tempts
us to propose that there is an unusual ""electronic separation"" for MR process
as the T is lowered in this class of compounds.",0002275v1
2000-03-14,"Magnetic and electrical resistance behaviour of the oxides, Ca$_{3-x}$Y$_x$LiRuO$_6$ (x= 0.0, 0.5 and 1.0)","We have investigated the magnetic and electrical resistance behaviour of
  Ca$_{3-x}$Y$_x$LiRuO$_6$. The parent compound exhibits magnetic ordering from
Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic
  Curie temperature ($\theta$$_p$) is negative indicative of antiferromagnetic
ordering, the large magnitude (-250 K) of $\theta$$_p$ reveals complex nature
of the magnetism in this compound. Ru ions appear to be in the pentavalent
state. We note that the N\'eel temperature undergoes only a marginal reduction
by Y substitution. All these compositions are found to be insulators and thus
the electron doping does not result in metallicity. Thus the overall magnetic
and transport behaviour are found to be essentially insensitive to Y
substitution for Ca, a finding which may favour the idea of
quasi-one-dimensional magnetism in these compounds.",0003227v1
2000-07-06,X-ray magnetic circular dichroism spectra on the superparamagnetic transition metal-ion clusters [Mn12O12(CH3COO)16(H2O)24].2CH3COOH.4H2O (Mn12) and [Fe8O2(OH)12(tacn)6]Br8 9H2O (Fe8),"The first X-ray magnetic circular dichroism (XMCD) spectra on the title
compounds are presented. In Mn12 the Mn(III) and Mn(IV) contributions are
clearly apparent and evidence the opposite spin arrangement of the two ions.
For Fe8 the typical two peak structure of Fe(III) compounds is found.
Quantitative analysis yielded for both compounds a negligible <Lz>. This is the
first direct experimental evidence of the quenching of the angular momentum in
these systems. For Fe8 we found <Sz>=1.14 in mB units per Fe atom, in
reasonable agreement with the S=10 ground state assumed for in this system.",0007092v1
2000-08-02,Andreev-reflection and Point-Contact Spectroscopy of Superconducting Rare Earth Transition Metal Borocarbides,"The superconducting energy gap and quasiparticle density of states (DOS) is
measured by means of Andreev-reflection spectroscopy in normal metal -
superconductor point contacts. It is found that both in paramagnetic and in
antiferromagnetically ordered states (Tm- and Dy-compounds) the DOS has the
BCS-like form while in Er- the dip in the temperature dependence of the gap is
observed at the Neel temperature. In Ho-compound, the non-BCS-like form of DOS
is observed in the temperature region where the incommensurate spin density
waves exist along the axes a and c .
  Inelastic point-contact spectroscopy performed on these compounds shows that
the low-frequency phonons are important for the superconducting state which are
strongly mixed with the magnetic excitation branches in magnetic
superconductors.",0008030v1
2000-10-26,Magnetic Phase Transitions in the double spin-chains compound $\rm LiCu_2O_2$,"We report high-resolution x-ray diffraction, muon-spin-rotation spectroscopic
and specific heat measurements in the double spin-chains compound $\rm
LiCu_2O_2$. The x-ray diffraction results show that the crystal structure of
$\rm LiCu_2O_2$ ~is orthorhombic down to T=10K. Anisotropic line-broadening of
the diffraction peaks is observed, indicating disorder along the spin chains.
Muon spin relaxation and specific heat measurements show that $\rm LiCu_2O_2$
\~undergoes a phase transition to a magnetic ordered state at $\rm T_1\sim24K$.
The specific heat data exhibits a second $\rm \lambda$-like peak at $\rm
T_2\sim22.5 K$, which increases with increasing magnetic field similarly way to
that found in spin-ladder compounds.",0010404v1
2000-11-13,Electronic Structure of the Chevrel-Phase Compounds Sn$_{x}$Mo$_{6}$Se$_{7.5}$: Photoemission Spectroscopy and Band-structure Calculations,"We have studied the electronic structure of two Chevrel-phase compounds,
Mo$_6$Se$_{7.5}$ and Sn$_{1.2}$Mo$_6$Se$_{7.5}$, by combining photoemission
spectroscopy and band-structure calculations. Core-level spectra taken with
x-ray photoemission spectroscopy show systematic core-level shifts, which do
not obey a simple rigid-band model. The inverse photoemission spectra imply the
existence of an energy gap located $\sim 1$ eV above the Fermi level, which is
a characteristic feature of the electronic structure of the Chevrel compounds.
Quantitative comparison between the photoemission spectra and the
band-structure calculations have been made. While good agreement between theory
and experiment in the wide energy range was obtained as already reported in
previous studies, we found that the high density of states near the Fermi level
predicted theoretically due to the Van Hove singularity is considerably reduced
in the experimental spectra taken with higher energy resolution than in the
previous reports. Possible origins are proposed to explain this observation.",0011231v1
2000-12-21,Ferromagnetism and large negative magnetoresistance in Pb doped Bi-Sr-Co-O misfit-layer compound,"Ferromagnetism and accompanying large negative magnetoresistance in
Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail.
Recent structural analysis of (Bi,Pb)${}_2$Sr${}_{3}$Co${}_2$O${}_9$, which has
been believed to be a Co analogue of
Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta}$, revealed that it has a more complex
structure including a CoO${}_2$ hexagonal layer [T. Yamamoto {\it et al.}, Jpn.
J. Appl. Phys. {\bf 39} (2000) L747]. Pb substitution for Bi not only
introduces holes into the conducting CoO${}_2$ layers but also creates a
certain amount of localized spins. Ferromagnetic transition appears at $T$ =
3.2 K with small spontaneous magnetization along the $c$ axis, and around the
transition temperature large and anisotropic negative magnetoresistance was
observed. This compound is the first example which shows ferromagnetic
long-range order in a two-dimensional metallic hexagnonal CoO${}_2$ layer.",0012395v1
2000-12-28,Hybridization Mechanism for Cohesion of Cd-based Quasicrystals,"Cohesion mechanism of cubic approximant crystals of newly discovered binary
quasicrystals, Cd$_6$M (M=Yb and Ca), are studied theoretically. It is found
that stabilization due to alloying is obtained if M is an element with
low-lying unoccupied $d$ states. This leads to conclusion that the cohesion of
the Cd-based compounds is due to the hybridization of the $d$ states of Yb and
Ca with a wide $sp$ band. %unlike known stable quasicrystals without transition
elements %such as Al-Li-Cu and Zn-Mg-RE (RE:rare earth). Although a diameter of
the Fermi sphere coincides with the strong Bragg peaks for Cd-Yb and Cd-Ca, the
Hume-Rothery mechanism does not play a principal role in the stability because
neither distinct pseudogap nor stabilization due to alloying is obtained for
isostructural Cd-Mg. In addition to the electronic origin, matching of the
atomic size is very crucial for the quasicrystal formation of the Cd-based
compounds. It is suggested that the glue atoms, which do not participate in the
icosahedral cluster, play an important role in stabilization of the compound.",0012485v3
2001-02-14,Loss of superconductivity and structural transition in Mg1-xAlxB2,"The basic magnetic and electronic properties of most binary compounds have
been well known for decades. Therefore the recent announcement of
superconductivity at 39 K in the simple binary ceramic compound MgB2 is
surprising. This compound, available from common chemical suppliers, and used
as a starting material for chemical metathesis reactions, has been known and
structurally characterized since the mid 1950's. Here we show that the addition
of electrons to MgB2 through partial substitution of Al for Mg results in the
loss of superconductivity. Associated with the Al substitution is a subtle but
distinct structural transition, reflected in the partial collapse of the
spacing between boron layers near 10% Al content. This indicates that
superconducting MgB2 is poised very near a structural instability at slightly
higher electron concentrations.",0102262v1
2001-02-23,Three-Dimensional Superconductivity in the Infinite-Layer Compound Sr_{0.9}La_{0.1}CuO_2 in Entire Region below $T_c$,"The infinite-layer compound ACuO$_{2}$ (A $=$ alkaline-earth ions) is
regarded as the most suitable material for exploring the fundamental nature of
the CuO$_2$ plane because it does not contain a charge-reservoir block, such as
a rock-salt or a fluorite like block. We report that superconductivity in the
infinite-layer compound Sr$_{0.9}$La$_{0.1}$CuO$_2$ is of a three-dimensional
nature, in contrast to the quasi two-dimensional superconducting behavior of
all other cuprates. The key observation is that the $c$-axis coherence length
is longer than the $c$-axis lattice constant even at zero temperature. This
means that the superconducting order parameter of one CuO$_{2}$ plane overlaps
with those of neighboring CuO$_{2}$ planes all the temperatures below the
$T_c$. Among all cuprates, only the infinite-layer superconductor shows such a
feature.",0102420v3
2001-02-27,A new class of magnetic materials: Sr2FeMoO6 and related compounds,"Ordered double perovskite oxides of the general formula, A2BB'O6, have been
known for several decades to have interesting electronic and magnetic
properties. However, a recent report of a spectacular negative
magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6,
has brought this class of compounds under intense scrutiny. It is now believed
that the origin of magnetism in this class of compounds is based on a novel
kinetically-driven mechanism. This new mechanism is also likely to be
responsible for the unusually high temperature ferromagnetism in several other
systems, such as dilute magnetic semiconductors, as well as in various
half-metallic ferromagnetic systems, such as Heussler alloys.",0102502v1
2001-03-14,Superconductivity in the non-oxide Perovskite MgCNi3,"The oxide perovskites are a large family of materials with many important
physical properties. Of particular interest has been the fact that this
structure type provides an excellent structural framework for the existence of
superconductivity. The high Tc copper oxides are the most famous examples of
superconducting perovskites, but there are many others [1]. Intermetallic
compounds have been the source of many superconducting materials in the past,
but they have been eclipsed in recent years by the perovskite oxides. The
recent discovery of superconductivity in MgB2 [2] suggests that intermetallic
compounds with simple structure types are worth serious reconsideration as
sources of new superconducting materials. Here we report the observation of
superconductivity at 8 K in the perovskite structure intermetallic compound
MgCNi3, linking what appear at first sight to be mutually exclusive classes of
superconducting materials. The observation of superconductivity in MgCNi3
indicates that MgB2 will not be the only one of its kind within the chemical
paradigm that it suggests for new superconducting materials.",0103296v1
2001-04-06,Nonadiabatic Pauli susceptibility in fullerene compounds,"Pauli paramagnetic susceptibility $\chi$ is unaffected by the electron-phonon
interaction in the Migdal-Eliashberg context. Fullerene compounds however do
not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic
effects are expected to be relevant in these materials. In this paper we
investigate the Pauli spin susceptibility in nonadiabatic regime by following a
conserving approach based on Ward's identity. We find that a sizable
renormalization of $\chi$ due to electron-phonon coupling appears when
nonadiabatic effects are taken into account. The intrinsic dependence of $\chi$
on the electron-phonon interaction gives rise to a finite and negative isotope
effect which could be experimentally detected in fullerides. In addition, we
find an enhancement of the spin susceptibility with temperature increasing, in
agreement with the temperature dependence of $\chi$ observed in fullerene
compounds. The role of electronic correlation is also discussed.",0104108v1
2001-06-13,"Electronic and structural properties of superconducting MgB$_2$, CaSi$_2$ and related compounds","We report a detailed study of the electronic and structural properties of the
39K superconductor \mgbtwo and of several related systems of the same family,
namely \mgalbtwo, \bebtwo, \casitwo and \cabesi. Our calculations, which
include zone-center phonon frequencies and transport properties, are performed
within the local density approximation to the density functional theory, using
the full-potential linearized augmented plane wave (FLAPW) and the
norm-conserving pseudopotential methods. Our results indicate essentially
three-dimensional properties for these compounds; however, strongly
two-dimensional $\sigma$-bonding bands contribute significantly at the Fermi
level. Similarities and differences between \mgbtwo and \bebtwo (whose
superconducting properties have not been yet investigated) are analyzed in
detail. Our calculations for \mgalbtwo show that metal substitution cannot be
fully described in a rigid band model. \casitwo is studied as a function of
pressure, and Be substitution in the Si planes leads to a stable compound
similar in many aspects to diborides.",0106239v1
2001-07-03,Thickness dependence of the ground-state properties in thin films of the heavy-fermion compound CeCu_6,"High-quality thin polycrystalline films of the heavy-fermion compound CeCu_6
were prepared by sputter deposition. The thicker of these films (with thickness
up to around 200 nm) reproduce the properties of the bulk compound CeCu_6. As
the thickness of the films is decreased, our measurements display strong
deviations from the bulk properties, namely, a suppression of the heavy-fermion
state. We show that possible `external' effects, like disorder, oxidation and
morphology can be excluded and that this size effect is therefore an intrinsic
property of CeCu_6. In addition, we investigate possible scenarios explaining
the size effect, and find that the proximity of CeCu_6 to a quantum phase
transition can account for this striking result.",0107049v1
2001-10-12,Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12,"The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron
diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the
compounds were found to comprise linear-chains at inter-chain distance of
approximately 10 A. The parent chain compound (x = 0), however, shows less
anisotropic magnetic behavior above 2 K, although it is of substantially
antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain
system. A magnetic cusp gradually appears at about 100 K in T vs chi with the
Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore
suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold
electrically insulating in the composition range.",0110262v1
2002-01-18,Electronic structure of metallic antiperovskite compound GaCMn$_3$,"We have investigated electronic structures of antiperovskite GaCMn$_3$ and
related Mn compounds SnCMn$_3$, ZnCMn$_3$, and ZnNMn$_3$. In the paramagnetic
state of GaCMn$_3$, the Fermi surface nesting feature along the $\Gamma{\rm R}$
direction is observed, which induces the antiferromagnetic (AFM) spin ordering
with the nesting vector {\bf Q} $\sim \Gamma{\rm R}$. Calculated
susceptibilities confirm the nesting scenario for GaCMn$_3$ and also explain
various magnetic structures of other antiperovskite compounds. Through the band
folding effect, the AFM phase of GaCMn$_3$ is stabilized. Nearly equal
densities of states at the Fermi level in the ferromagnetic and AFM phases of
GaCMn$_3$ indicate that two phases are competing in the ground state.",0201328v1
2002-08-15,Crystal growth of MgB2 from Mg-Cu-B melt flux and superconducting properties,"A new method for preparation of single crystals of the superconducting
intermetallic MgB2 compound from a Mg-Cu-B melt flux is presented. The high
vapour pressure of Mg at elevated temperature is a serious challenge of the
preparation process. The approximate thermodynamic calculations of the ternary
Mg-Cu-B phase diagram show a beneficial effect of Cu, which extends the range
of formation of MgB2 to lower temperatures. Within the as-solidified Mg-Cu-B
melt flux the MgB2 compound forms plate-like single crystals up to a size of
0.2 x 0.2 x 0.05 mm3 or alternatively rims peritectically grown around MgB4
particles. AC-susceptibility measurements were conducted with specimen selected
from different parts of the as-solidified flux containing MgB2 particles.
Peritectically formed MgB2-particles display the highest transition temperature
of Tc = 39.2 K and a relatively narrow transition width of DTc = 1.3 K. Other
sections of the sample exhibit various superconducting transitions from Tc = 39
K to 7.2 K. This variation of Tc is attributed to a finite homogeneity range of
the MgB2 compound whereas significant Cu solid solubility in MgB2 can be
excluded.",0208300v1
2002-08-16,"Superconductivity in the C32 Intermetallic Compounds AAl(2-x)Si(x), with A=Ca and Sr, and 0.6<x<1.2","The intermetallic compounds AAl2-xSix, where A = Ca, Sr or Ba, crystallize in
the C32 structure, same as the recently discovered MgB2 with a high
superconducting transition temperature of 39 K. For x = 1, superconductivity
has been observed in AAlSi with A = Ca and Sr, but not with A = Ba. The
transition temperatures are 7.8 and 5.1 K, respectively for CaAlSi and SrAlSi.
The CaAl2-xSix compound system display a Tc-peak at x = 1, a possible x-induced
electronic transition at x ~ 0.75 and a possible miscibility gap near x ~ 1.1
which results in a very broad superconducting transition. The Seebeck
coefficients of AAlSi indicate that their carriers are predominantly electrons
in nature, in contrast to the holes in MgB2.",0208341v1
2002-09-17,Schwinger-Boson Mean-Field Theory of Mixed-Spin Antiferromagnet $L_2BaNiO_5$,"The Schwinger-boson mean-field theory is used to study the three-dimensional
antiferromagnetic ordering and excitations in compounds $L_2BaNiO_5$, a large
family of quasi-one-dimensional mixed-spin antiferromagnet. To investigate
magnetic properties of these compounds, we introduce a three-dimensional
mixed-spin antiferromagnetic Heisenberg model based on experimental results for
the crystal structure of $L_2BaNiO_5$. This model can explain the experimental
discovery of coexistence of Haldane gap and antiferromagnetic long-range order
below N\'{e}el temperature. Properties such as the low-lying excitations,
magnetizations of $Ni$ and rare-earth ions, N\'{e}el temperatures of different
compounds, and the behavior of Haldane gap below the N\'{e}el temperature are
investigated within this model, and the results are in good agreement with
neutron scattering experiments.",0209388v2
2002-12-12,Low-energy spin fluctuations of the heavy-Fermion compound CeNi_2Ge_2: origin of non-Fermi liquid behavior,"Neutron scattering shows that non-Fermi-liquid behavior of the heavy-Fermion
compound CeNi_2Ge_2 is brought about by development of low-energy spin
fluctuations with an energy scale of 0.6 meV. They appear around
antiferromagnetic wave vectors $({1/2} {1/2} 0)$ and $(0 0 {3/4})$ at low
temperatures, and coexist with high-energy spin fluctuations with an energy
scale of 4 meV and a modulation vector $(0.23, 0.23, {1/2})$. The energy
dependence of the spin fluctuations is a peculiar character of CeNi_2Ge_2 which
differs from typical heavy-Fermion compounds, and suggests importance of
low-energy structures of quasiparticle bands.",0212265v1
2003-01-23,Average Lattice Symmetry and Nanoscale Structural Correlations in Magnetoresistive Manganites,"We report x-ray scattering studies of nanoscale structural correlations in
the paramagnetic phases of the perovskite manganites
La$_{0.75}$(Ca$_{0.45}$Sr$_{0.55}$)$_{0.25}$MnO$_3$,
La$_{0.625}$Sr$_{0.375}$MnO$_3$, and Nd$_{0.45}$Sr$_{0.55}$MnO$_3$. We find
that these correlations are present in the orthorhombic $O$ phase in
La$_{0.75}$(Ca$_{0.45}$Sr$_{0.55}$)$_{0.25}$MnO$_3$, but they disappear
abruptly at the orthorhombic-to-rhombohedral transition in this compound. The
orthorhombic phase exhibits increased electrical resistivity and reduced
ferromagnetic coupling, in agreement with the association of the nanoscale
correlations with insulating regions. In contrast, the correlations were not
detected in the two other compounds, which exhibit rhombohedral and tetragonal
phases. Based on these results, as well as on previously published work, we
propose that the local structure of the paramagnetic phase correlates strongly
with the average lattice symmetry, and that the nanoscale correlations are an
important factor distinguishing the insulating and the metallic phases in these
compounds.",0301466v2
2003-03-06,Anisotropy and Ising-like transition of the S=5/2 two-dimensional Heisenberg antiferromagnet Mn-formate di-Urea,"Recently reported measurements of specific heat on the compound Mn-formate
di-Urea (Mn-f-2U) by Takeda et al. [Phys. Rev. B 63, 024425 (2001)] are
considered. As a model to describe the overall thermodynamic behavior of such
compound, the easy-axis two-dimensional Heisenberg antiferromagnet is proposed
and studied by means of the 'pure quantum self-consistent harmonic
approximation' (PQSCHA). In particular it is shown that, when the temperature
decreases, the compound exhibits a crossover from 2D-Heisenberg to 2D-Ising
behavior, followed by a 2D-Ising-like phase transition, whose location allows
to get a reliable estimate of the easy-axis anisotropy driving the transition
itself. Below the critical temperature T_N=3.77 K, the specific heat is well
described by the two-dimensional easy-axis model down to a temperature T*=1.47
K where a T^3-law sets in, possibly marking a low-temperature crossover of
magnetic fluctuations from two to three dimensions.",0303119v1
2003-04-16,Enhancement of Tc by Sr substitution for Ba in Hg-2212 superconductor,"The Ba substitution by Sr has been studied in two Hg-2212 series:
Hg2(Ba(1-y)Sr(y))2YCu2O8-d and Hg2(Ba(1-y)Sr(y))2(Y0.80Ca0.20)Cu2O8-d. In both
series a Tc enhancement of about 40 K is observed when Sr substitutes Ba from y
= 0 to y = 1.0.
  The y = 0 compound of the first series is the non superconducting
Hg2Ba2YCu2O8-d prototype. In the second series, this y = 0 compound is already
superconducting at 21 K. Indeed the members of this series present a higher
charge carrier density in their CuO2 superconducting planes than their
homologues of the first series due to the doping introduced by the substitution
of 20% of Y by Ca. The compounds of both series were synthesized in high
pressure (3.5 GPa) - high temperature (950 - 1050C) conditions. In both cases
Sr substitution was successful up to the full replacement of Ba (y = 1.0). The
Hg-2212 phases were characterized by XRD, SEM, EDX and a.c. susceptibility.",0304373v2
2003-09-04,Study of Crystal-field Effects in Rare-earth (RE) - Transition-metal Intermetallic Compounds and in RE-based Laser Crystals,"Rare-earth (RE) based compounds and alloys are of great interest both for
their fundamental physical properties and for applications. In order to tailor
the required compounds for a specific task, one must be able to predict the
energy level structure and transition intensities for any magnetic ion in any
crystalline environment. The crystal-field (CF) analysis is one of the most
powerful theoretical methods to deal with the physics of magnetic ions. In the
present work, this technique is used to analyze peculiar physical properties of
some materials employed in the production of new-generation solid-state laser
and high-performance permanent magnets.",0309100v1
2003-09-10,Exact results for the thermal and magnetic properties of strong coupling ladder compounds,"We investigate the thermal and magnetic properties of the integrable su(4)
ladder model by means of the quantum transfer matrix method. The magnetic
susceptibility, specific heat, magnetic entropy and high field magnetization
are evaluated from the free energy derived via the recently proposed method of
high temperature expansion for exactly solved models. We show that the
integrable model can be used to describe the physics of the strong coupling
ladder compounds. Excellent agreement is seen between the theoretical results
and the experimental data for the known ladder compounds
(5IAP)$_2$CuBr$_4$$\cdot$2H$_2$O, Cu$_{2}$(C$_5$H$_{12}$N$_2$)$_2$Cl$_4$ etc.",0309244v1
2003-09-12,Thermodynamic and transport properties of RAgGe (R=Tb-Lu) single crystals,"Single crystals of the title compounds were grown out of an AgGe-rich ternary
solution. Powder x-ray diffraction data confirmed the hexagonal AlNiZr-type
structure ($P\bar{6}2m$ space group), an ordered variant of the Fe$_2$P
structure type. Antiferromagnetic ordering can be inferred from magnetization,
resistance and specific heat measurements, with values of T$_N$ between 28.5 K
for TbAgGe, and 1.0 K for YbAgGe, which scale roughly with the de Gennes
factor. Anisotropic $M(H)$ measurements indicate one or more metamagnetic
transitions when the external field is applied along the c-axis (for R=Tb) or
perpendicular to it (R = Ho, Er, Tm), or even in both orientations as in the
case of DyAgGe. Furthermore, the extreme anisotropy of the magnetization in
TmAgGe, where magnetic moments lie in the $ab$-plane, provides the possibility
of studying the angular dependence of metamagnetism in hexagonal compounds with
the rare earth in orthorhombic point symmetry.
  YbAgGe has distinct properties from the rest of the series: an enhanced
electronic specific heat coefficient ($\gamma
\approx$(154.2$\pm$2.5)mJ/mol*K$^2$), and apparently small moment magnetic
ordering below 1.0 K. This compound appears to be close to a quantum critical
point.",0309327v1
2003-12-19,Unconventional Superconductivity and Magnetism in Lanthanide and Actinide Intermetallic Compounds,"In this review article we present a survey of unconventional superconductors
and their coexistence behaviour with magnetism.
  We focus on Ce- and U-based heavy fermion superconductors, in addition we
discuss the rare earth borocarbide and skutterudite superconductors. We show
that heavy fermion behaviour in Ce- and U- compounds should be described
differently. While the Kondo-lattice model with localised 4f-electrons is
appropriate for Ce-compounds, dual models including localised and itinerant
5f-electrons are necessary for U-compounds. We demonostrate that this leads to
consistent results for Fermi surface topology and mass enhancement in various
U-compounds. We also show that virtual exchange of localised 5f-electron
excitations provides a new mechanism for unconventional superconductivity in
addition to the known itinerant spin-fluctuation exchange mechanism. We discuss
symmetry properties and coexistence of unconventional superconducting and
density wave (hidden) order parameters and methods for their detection, notably
the new angle resolved magntetotransport methods. The latter have been very
succesful for the investigtion of gap anisotropies in the nonmagnetic
borocarbide superconductors. Recent results on the new multiphase
Pr-skutterudite superconductor are also reviewed.",0312540v1
2004-02-19,Spin and orbital frustration in MnSc_2S_4 and FeSc_2S_4,"Crystal structure, magnetic susceptibility, and specific heat were measured
in the normal cubic spinel compounds MnSc_2S_4 and FeSc_2S_4. Down to the
lowest temperatures, both compounds remain cubic and reveal strong magnetic
frustration. Specifically the Fe compound is characterized by a Curie-Weiss
temperature \Theta_{CW}= -45 K and does not show any indications of order down
to 50 mK. In addition, the Jahn-Teller ion Fe^{2+} is orbitally frustrated.
Hence, FeSc_2S_4 belongs to the rare class of spin-orbital liquids. MnSc_2S_4
is a spin liquid for temperatures T > T_N \approx 2 K.",0402495v1
2004-02-19,Unusual Single-Ion Non-Fermi Liquid Behavior in Ce_(1-x)La_xNi_9Ge_4,"We report on specific heat, magnetic susceptibility and resistivity
measurements on the compound Ce_(1-x)La_xNi_9Ge_4 for various concentrations
ranging from the stoichiometric system with x=0 to the dilute limit x=0.95. Our
data reveal single-ion scaling with the Ce-concentration and the largest ever
recorded value of the electronic specific heat c/T approximately 5.5 J
K^(-2)mol^(-1) at T=0.08K for the stoichiometric compound x=0 without any trace
of magnetic order. While in the doped samples c/T increases logarithmically
below 3K down to 50mK, their magnetic susceptibility behaves Fermi liquid like
below 1K. These properties make the compound Ce_(1-x)La_xNi_9Ge_4 a unique
system on the borderline between Fermi liquid and non-Fermi liquid physics.",0402498v2
2004-03-29,Quantum Tunneling of the Magnetization in the Ising Chain Compound Ca3Co2O6,"The magnetic behavior of the Ca3Co2O6 spin chain compound is characterized by
a large Ising-like character of its ferromagnetic chains, set on triangular
lattice, that are antiferromagnetically coupled. At low temperature, T < 7K,
the 3D antiferromagnetic state evolves towards a spin frozen state. In this
temperature range, magnetic field driven magnetization of single crystals
(H//chains) exhibits stepped variations. The occurrence of these steps at
regular intervals of the applied magnetic field, Hstep=1.2T, is reminiscent of
the quantum tunneling of the magnetization (QTM) of molecular based magnets.
Magnetization relaxation experiments also strongly support the occurrence of
this quantum phenomenon. This first observation of QTM in a magnetic oxide
belonging to the large family of the A3BBO6 compounds opens new opportunities
to study a quantum effect in a very different class of materials from molecular
magnets.",0403695v1
2004-04-20,Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in Rb${}_{2}$Cu${}_{2}$Mo${}_{3}$O${}_{12}$,"We have investigated magnetic properties of Rb$_2$Cu$_2$Mo$_3$O$_{12}$
powder. Temperature dependence of magnetic susceptibility and magnetic-field
dependence of magnetization have shown that this cuprate is a model compound of
a one-dimensional spin-1/2 Heisenberg system with ferromagnetic
first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor
(2NN) competing interactions (competing system). Values of the 1NN and 2NN
interactions are estimated as $J_1 = -138$ K and $J_2 = 51$ K ($\alpha \equiv
J_2 / J_1 = -0.37$). This value of $\alpha$ suggests that the ground state is a
spin-singlet incommensurate state. In spite of relatively large $J_1$ and
$J_2$, no magnetic phase transition appears down to 2 K, while an
antiferromagnetic transition occurs in other model compounds of the competing
system with ferromagnetic 1NN interaction. For that reason,
Rb$_2$Cu$_2$Mo$_3$O$_{12}$ is an ideal model compound to study properties of
the incommensurate ground state that are unconfirmed experimentally.",0404463v1
2004-04-27,Phase Separation in Li$_x$FePO$_4$ Induced by Correlation Effects,"We report on a significant failure of LDA and GGA to reproduce the phase
stability and thermodynamics of mixed-valence Li$_x$FePO$_4$ compounds.
Experimentally, Li$_x$FePO$_4$ compositions ($0 \leq x \leq 1$) are known to be
unstable and phase separate into Li FePO$_4$ and FePO$_4$. However,
first-principles calculations with LDA/GGA yield energetically favorable
intermediate compounds an d hence no phase separation. This qualitative failure
of LDA/GGA seems to have its origin in the LDA/GGA self-interaction which de
localizes charge over the mixed-valence Fe ions, and is corrected by explicitly
considering correlation effects in this material. This is demonstrated with
LDA+U calculations which correctly predict phase separation in Li$_x$FePO$_4$
for $U-J \gtrsim 3.5$eV. T he origin of the destabilization of intermediate
compounds is identified as electron localization and charge ordering at
different iron sites. Introduction of correlation also yields more accurate
electrochemical reaction energies between FePO$_4$/Li$_x$FePO$_ 4$ and
Li/Li$^+$ electrodes.",0404631v2
2004-05-27,"Magnetic behavior of spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, from heat capacity and ac susceptibility studies","Heat-capacity (C) and ac susceptibility measurements have been performed on
the spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, to establish their magnetic
behavior and to explore whether there are magnetic frustration effects due to
antiferromagnetic coupling of the chains arranged in a triangular fashion.
While the paramagnetic Curie temperatures have been known to be large with a
negative sign, as though antiferromagnetic interaction is very strong, the
results establish that (i) the former apparently undergoes inhomogeneous
magnetic ordering only around 15 K, however without spin-glass anomalies, and
(ii) the latter orders antiferromagnetically at a relatively low temperature
(17 K). Thus, the magnetic frustration manifests differently in these
compounds.",0405639v1
2004-06-07,Valence and magnetic instabilities in Sm compounds at high pressures,"We report on the study of the response to high pressures of the electronic
and magnetic properties of several Sm-based compounds, which span at ambient
pressure the whole range of stable charge states between the divalent and the
trivalent. Our nuclear forward scattering of synchrotron radiation and specific
heat investigations show that in both golden SmS and SmB6 the pressure-induced
insulator to metal transitions (at 2 and about 4-7 GPa, respectively) are
associated with the onset of long-range magnetic order, stable up to at least
19 and 26 GPa, respectively. This long-range magnetic order, which is
characteristic of Sm(3+), appears already for a Sm valence near 2.7. Contrary
to these compounds, metallic Sm, which is trivalent at ambient pressure,
undergoes a series of pressure-induced structural phase transitions which are
associated with a progressive decrease of the ordered 4f moment.",0406166v1
2004-06-14,Doping Effects on the two-dimensional Spin Dimer Compound $SrCu_2(BO_3)_2$,"A series of compounds M$_{0.1}$Sr$_{0.9}$Cu$_2$(BO$_3$)$_2$ with Sr
substituted by M=Al, La, Na and Y were prepared by solid state reaction. XRD
analysis showed that these doping compounds are isostructural to
SrCu$_2$(BO$_3$)$_2$. The magnetic susceptibility from 1.9K to 300K in an
applied magnetic field of 1.0T and the specific heat from 1.9K to 25K in
applied fields up to 14T were measured. The spin gap is deduced from the low
temperature susceptibility as well as the specific heat. It is found that the
spin gap is strongly suppressed by magnetic fields. No superconductivity is
observed in all four samples.",0406306v1
2004-06-16,First-principles prediction of redox potentials in transition-metal compounds with LDA+U,"First-principles calculations within the Local Density Approximation (LDA) or
Generalized Gradient Approximation (GGA), though very successful, are known to
underestimate redox potentials, such as those at which lithium intercalates in
transition metal compounds. We argue that this inaccuracy is related to the
lack of cancellation of electron self-interaction errors in LDA/GGA and can be
improved by using the DFT+$U$ method with a self-consistent evaluation of the
$U$ parameter. We show that, using this approach, the experimental lithium
intercalation voltages of a number of transition metal compounds, including the
olivine Li$_{x}$MPO$_{4}$ (M=Mn, Fe Co, Ni), layered Li$_{x}$MO$_{2}$ ($x=$Co,
Ni) and spinel-like Li$_{x}$M$_{2}$O$_{4}$ (M=Mn, Co), can be reproduced
accurately.",0406382v2
2004-09-13,Thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies,"The thermal and magnetic properties of spin-1 magnetic chain compounds with
large single-ion and in-plane anisotropies are investigated via the integrable
su(3) model in terms of the quantum transfer matrix method and the recently
developed high temperature expansion method for exactly solved models. It is
shown that large single-ion anisotropy may result in a singlet gapped phase in
the spin-1 chain which is significantly different from the standard Haldane
phase. A large in-plane anisotropy may destroy the gapped phase. On the other
hand, in the vicinity of the critical point a weak in-plane anisotropy leads to
a different phase transition than the Pokrovsky-Talapov transition. The
magnetic susceptibility, specific heat and magnetization evaluated from the
free energy are in excellent agreement with the experimental data for the
compounds NiC_2H_8N_2)_2Ni(CN)_4 and Ni(C_{10}H_8N_2)_2Ni(CN)_4.H_2O.",0409310v1
2004-11-04,Orbital-based Scenario for Magnetic Structure of Neptunium Compounds,"In order to understand a crucial role of orbital degree of freedom in the
magnetic structure of recently synthesized neptunium compounds NpTGa_5 (T=Fe,
Co, and Ni), we propose to discuss the magnetic phase of an effective
two-orbital model, which has been constructed based on a j-j coupling scheme to
explain the magnetic structure of uranium compounds UTGa_5. By analyzing the
model with the use of numerical technique such as exact diagonalization, we
obtain the phase diagram including several kinds of magnetic states. An
orbital-based scenario is discussed to understand the change in the magnetic
structure among C-, A-, and G-type antiferromagnetic phases, experimentally
observed in NpFeGa_5, NpCoGa_5, and NpNiGa_5.",0411100v1
2004-11-12,Peculiarities of crystal structure of terbium (III) trifluoroacetate trihydrate,"A comparative study of the crystalline and molecular structures of
trifluoroacetate trihydrates of Tb(III) prepared from Tb(OH)_3 and Tb_2(CO_3)_3
by reaction with trifluoroacetic acid is made. Elemental analysis of the two
reaction products in indicated them to be compounds of the same C_6H_6F_9O_9Tb.
According to the X-ray structural analysis the molecular structure of the first
product is described by the average statistical formula
Tb_2(CF_3COO)_5(CF_3COOH)(H_2O)_5(OH) (Tb-I) and the compound is a dimer with a
centre of inversion. In the second case the product is also a centrosymmetric
dimer but its formula is Tb_2(CF_3COO)_6(H_2O)_6 (Tb-II). The compounds only
difference is in the crystallographic positions of their hydrogen atoms. A
luminescent analysis using Tb^{3+} ^5D_4-> ^7F_0 transition indicated the
presence within the structure of Tb-I of the structure of Tb-II. Magnetic
measurements showed that Tb-II has an antiferromagnetic ordering at low
temperatures. In the case of Tb-I there also appears a ferromagnetic ordering.
On the basis of the available experimental results such a behaviour was
explained to be the result of some peculiar features of the hydrogen bonds in
the molecules.",0411327v1
2004-11-24,"Nature of magnetism in the spin-chain compound, Ca3CuRuO6","A quasi one-dimensional compound, Ca3CuRuO6, has been synthesized by
solid-state reaction method and studied using magnetization (M) and heat
capacity (C) measurements. This compound undergoes magnetic ordering (T_o)
around 40 K, as evidenced by the dc magnetic susceptibility (chi) behavior.
However, the magnitude of the paramagnetic
  Curie temperature (theta_p) obtained from the high temperature linear region
is large (-277 K, with the negative sign indicating antiferromagnetic
interaction). The reduction of T_o, compared to theta_p, is attributed to
geometrical frustration effect arising from the triangular arrangement of
antiferromagnetically coupled magnetic chains. The absence of a feature in ac
chi around 40 K rules out possible spin-glass freezing. However, we find that
the peak in C(T) around 40 K is weak, with the entropy change associated with
the transition being negligible, typical of a disordered magnetism. We infer
that this material thus exhibits inhomogeneous magnetism, despite being
stoichiometric, presumably due to an interplay between disorder in the Cu-Ru
chain.",0411601v1
2005-01-21,Theory of the thermoelectricity of intermetallic compounds with Ce or Yb ions,"The thermoelectric properties of intermetallic compounds with Ce or Yb ions
are explained by the single-impurity Anderson model which takes into account
the crystal-field splitting of the 4{\it f} ground-state multiplet, and assumes
a strong Coulomb repulsion which restricts the number of {\it f} electrons or
{\it f} holes to $n_f\leq 1$ for Ce and $n_f^{hole}\leq 1$ for Yb ions. Using
the non-crossing approximation and imposing the charge neutrality constraint on
the local scattering problem at each temperature and pressure, the excitation
spectrum and the transport coefficients of the model are obtained. The
thermopower calculated in such a way exhibits all the characteristic features
observed in Ce and Yb intermetallics. Calculating the effect of pressure on
various characteristic energy scales of the model, we obtain the $(T,p)$ phase
diagram which agrees with the experimental data on CeRu$_{2}$Si$_2$,
CeCu$_{2}$Si$_2$, CePd$_{2}$Si$_2$, and similar compounds. The evolution of the
thermopower and the electrical resistance as a function of temperature,
pressure or doping is explained in terms of the crossovers between various
fixed points of the model and the redistribution of the single-particle
spectral weight within the Fermi window.",0501519v1
2005-01-24,"Heat capacity and magnetoresistance in Dy(Co,Si)2 compounds","Magnetocaloric effect and magnetoresistance have been studied in
Dy(Co1-xSix)2 [x=0, 0.075 and 0.15] compounds. Magnetocaloric effect has been
calculated in terms of adiabatic temperatue change (Delta Tad) as well as
isothermal magnetic entropy change (Delta SM) using the heat capacity data. The
maximum values of DeltaSM and DeltaTad for DyCo2 are found to be 11.4 JKg-1K-1
and 5.4 K, respectively. Both DSM and DTad decrease with Si concentration,
reaching a value of 5.4 JKg-1K-1 and 3 K, respectively for x=0.15. The maximum
magnetoresistance is found to about 32% in DyCo2, which decreases with increase
in Si. These variations are explained on the basis of itinerant electron
metamagnetism occurring in these compounds.",0501552v1
2005-02-08,Magnetocaloric effect in the intermetallic compound DyNi,"Magnetic and heat capacity measurements have been carried out on the
polycrystalline sample of DyNi which crystallizes in the orthorhombic FeB
structure (space group Pnma). This compound is ferromagnetic with a Curie
temperature of 59 K. Magnetization-field isotherms at low temperatures shows a
step-like behavior characteristic of metamagnetic transitions. The
magnetocaloric effect has been measured both in terms of isothermal magnetic
entropy change and adiabatic temperature change for various applied magnetic
fields. The maximum values of the entropy change and the temperature change are
found to be 19 Jkg-1K-1 and 4.5 K, respectively, for a field of 60 kOe. The
large magnetocaloric effect is attributed to the field-induced spin-flop
metamagnetism occurring in this compound, which has a noncollinear magnetic
structure at low fields.",0502188v1
2005-04-08,On the crystal field in the modern solid-state theory,"We point out the high physical correctness of the use and the concept of the
crystal-field approach, even if is used to metallic magnetic materials of
transition-metal 3d/4f/5f compounds. We discuss the place of the crystal-field
theory in modern solid-state physics and we point out the necessity to consider
the crystal-field approach with the spin-orbit coupling and strong electron
correlations, as a contrast to the single-electron version of the crystal field
customarily used for 3d electrons. We have extended the strongly-correlated
crystal-field theory to a Quantum Atomistic Solid-State Theory (QUASST) to
account for the translational symmetry and inter-site spin-dependent
interactions indispensable for formation of magnetically-ordered state. We have
correlated macroscopic magnetic and electronic properties with the atomic-scale
electronic structure for ErNi5, UPd2Al3, FeBr2, LaCoO3 and LaMnO3. In QUASST we
have made unification of 3d and rare-earth compounds in description of the
low-energy electronic structures and magnetism of open 3d-/4f-/5f-shell
electrons. QUASST offers consistent description of zero-temperature properties
and thermodynamic properties of 4f-/5f-/3d-atom containing compounds. Our
studies indicate that it is the highest time to unquench the orbital magnetism
in 3d oxides.",0504199v1
2005-04-19,High temperature magnetic ordering in La2RuO5,"Magnetic susceptibility, heat capacity and electrical resistivity
measurements have been carried out on a new ruthenate, La2RuO5 (monoclinic,
space group P21/c) which reveal that this compound is a magnetic semiconductor
with a high magnetic ordering temperature of 170K. The entropy associated with
the magnetic transition is 8.3 J/mole-K -close to that expected for the low
spin (S=1) state of Ru4+ ions. The low temperatures specific heat coefficient g
is found to be nearly zero consistent with the semiconducting nature of the
compound. The magnetic ordering temperature of La2RuO5 is comparable to the
highest known Curie temperature of another ruthenate, namely, metallic SrRuO3,
and in both these compounds the nominal charge state of Ru is 4+.",0504489v1
2005-05-09,Spin and orbital degrees of freedom in transition metal oxides and oxide thin films studied by soft x-ray absorption spectroscopy,"The class of transition metal compounds shows an enormous richness of
physical properties, such as metal-insulator transitions, colossal
magneto-resistance, super-conductivity, magneto-optics and spin-depend
transport. It now becomes more and more clear that in order to describe
transition metal compounds the charge, orbital, spin and lattice degrees of
freedom should all be taken into account. With the recognition that the local
orbital occupation plays an important role in many of the transition metal
compounds there is a need for experimental techniques that can measure the
orbital occupation. This technique is soft x-ray absorption spectroscopy.
Within this PhD. Thesis we will illustrate the usefulness of this technique by
some examples: 1) Magnetic versus crystal-field linear dichroism in NiO thin
films. 2) The importance of spin-orbit coupling in CoO bulk and CoO thin films.
3) Aligning spins in anti ferromagneticfilms using antiferromagnets. 4) The
spin-state puzzle in the cobaltates. 5) Determination of the orbital momentum
and crystal-field splitting in LaTiO3. 6) Orbital-assisted metal-insulator
transition in VO2.",0505214v1
2005-06-02,"Influence of magnetic interaction between impurity and impurity-liberated spins on the magnetism in the doped Haldane chain compounds PbNi${}_{2-x${A}${}_{x}$V${}_{2}$O${}_{8}$ (A = Mg, Co)","A comprehensive study of impurity-induced magnetism in nonmagnetically
(Mg${}^{2+}$) and magnetically (Co${}^{2+}$) doped
PbNi${}_{2}$V${}_{2}$O${}_{8}$ compounds is given, using both macroscopic dc
susceptibility and local-probe electron spin resonance (ESR) techniques.
Magnetic coupling between impurity-liberated spins is estimated from a
linewidth of low-temperature ESR signal in Mg-doped samples. In addition, in
the case of magnetic cobalt dopants the impurity-host magnetic exchange is
evaluated from the Co-induced contribution to the linewidth in the paramagnetic
phase. The experimentally observed severe broadening of the ESR lines in the
magnetically doped compounds with respect to nonmagnetic doping is attributed
to a rapid spin-lattice relaxation of the Co${}^{2+}$ ions, which results in a
bottleneck-type of temperature dependence of the induced linewidth. The
exchange parameters obtained from the ESR analysis offer a satisfactory
explanation of the observed low-temperature magnetization in doped samples.",0506056v1
2005-06-30,Magnetic versus nonmagnetic doping effects on the magnetic ordering in the Haldane chain compound PbNi2V2O8,"A study of an impurity driven phase-transition into a magnetically ordered
state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both,
macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR)
measurements reveal that the spin nature of dopants has a crucial role in
determining the stability of the induced long-range magnetic order. In the case
of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition
is observed in relatively low magnetic fields. On the other hand, the magnetic
order in magnetically (Co2+) doped compounds survives at much higher magnetic
fields and temperatures, which is attributed to a significant anisotropic
impurity-host magnetic interaction. The NMR measurements confirm the predicted
staggered nature of impurity-liberated spin degrees of freedom, which are
responsible for the magnetic ordering. In addition, differences in the
broadening of the NMR spectra and the increase of nuclear spin-lattice
relaxation in doped samples, indicate a diverse nature of electron spin
correlations in magnetically and nonmagnetically doped samples, which begin
developing at rather high temperatures with respect to the antiferromagnetic
phase transition.",0506808v1
2005-07-11,Inter-cluster reactivity of Metallo-aromatic and anti-aromatic Compounds and Their Applications in Molecular Electronics: A Theoretical Investigation,"Local reactivity descriptors such as the condensed local softness and Fukui
function have been employed to investigate the inter-cluster reactivity of the
metallo-aromatic (Al4Li- and Al4Na-) and anti-aromatic (Al4Li4 and Al4Na4)
compounds. We use the concept of group softness and group Fukui function to
study the strength of the nucleophilicity of the Al4 unit in these compounds.
Our analysis shows that the trend of nucleophilicity of the Al4 unit in the
above clusters is as follows;
  Al4Li- > Al4Na- > Al4Li4 > Al4Na 4
  For the first time we have used the reactivity descriptors to show that these
clusters can act as electron donating systems and thus can be used as a
molecular cathode.",0507236v1
2005-08-12,Dynamical mean-field theory of photoemission spectra of actinide compounds,"A model of photoemission spectra of actinide compounds is presented. The
complete multiplet spectrum of a single ion is calculated by exact
diagonalization of the two-body Hamiltonian of the f^n shell. A coupling to
auxiliary fermion states models the interaction with a conduction sea. The
ensuing self-energy function is combined with a band Hamiltonian of the
compound, calculated in the local-density approximation, to produce a solid
state Green's function. The theory is applied to PuSe and elemental Am. For
PuSe a sharp resonance at the Fermi level arises from mixed valent behavior,
while several features at larger binding energies can be identified with
quantum numbers of the atomic system. For Am the ground state is dominated by
the |f^6;J=0> singlet but the strong coupling to the conduction electrons mixes
in a significant amount of f^7 character.",0508311v2
2005-09-05,Magnetic behavior of EuCu2As2: Delicate balance between antiferromagnetic and ferromagnetic order,"The Eu-based compound, EuCu2As2, crystallizing in the ThCr2Si2-type
tetragonal structure, has been synthesized and its magnetic behavior has been
investigated by magnetization (M), heat-capacity (C) and electrical resistivity
(rho) measurements as a function of temperature (T) and magnetic field (H) as
well as by 151Eu Moessbauer measurements. The results reveal that Eu is
divalent ordering antiferromagnetically below 15 K in the absence of magnetic
field, apparently with the formation of magnetic Brillouin-zone boundary gaps.
A fascinating observation is made in a narrow temperature range before
antiferromagnetism sets in: That is, there is a remarkable upturn just below 20
K in the plot of magnetic susceptibility versus T even at low fields, as though
the compound actually tends to order ferromagnetically. There are corresponding
anomalies in the magnetocaloric effect data as well. In addition, a small
application of magnetic field (around 1 kOe at 1.8 K) in the antiferromagnetic
state causes spin-reorientation effect. These results suggest that there is a
close balance between antiferromagnetism and ferromagnetism in this compound",0509108v1
2005-09-19,Raman spectroscopy on cubic and hexagonal SrMnO$_3$,"We report on the first optical characterization of both cubic and hexagonal
SrMnO$_3$. Room-temperature Raman spectra collected by means of a micro-Raman
spectrometer are shown. The spectrum of the cubic compound is characterized by
weak and broad bands in agreement with group-theory which predicts no
Raman-active phonons for this compound. On the other hand, the spectrum of the
hexagonal compound shows six narrow peaks ascribed to one-phonon processes. A
complete polarization analysis of the spectra collected from a single
crystallite allows us to completely assign the symmetries of the six observed
peaks. Atomic displacements for each phonon peaks are also proposed.",0509468v1
2005-09-27,Memory and aging effect in hierarchical spin orderings of stage-2 CoCl_{2} graphite intercalation compound,"Stage-2 CoCl$_{2}$ graphite intercalation compound undergoes two magnetic
phase transitions at $T_{cl}$ (= 7.0 K) and $T_{cu}$ (= 8.9 K). The aging
dynamics of this compound is studied near $T_{cl}$ and $T_{cu}$. The
intermediate state between $T_{cl}$ and $T_{cu}$ is characterized by a spin
glass phase extending over ferromagnetic islands. A genuine thermoremnant
magnetization (TRM) measurement indicates that the memory of the specific spin
configurations imprinted at temperatures between $T_{cl}$ and $T_{cu}$ during
the field-cooled (FC) aging protocol can be recalled when the system is
re-heated at a constant heating rate. The zero-field cooled (ZFC) and TRM
magnetization is examined in a series of heating and reheating process. The
magnetization shows both characteristic memory and rejuvenation effects. The
time $(t)$ dependence of the relaxation rate
$S_{ZFC}(t)=(1/H)$d$M_{ZFC}(t)$/d$\ln t$ after the ZFC aging protocol with a
wait time $t_{w}$, exhibits two peaks at characteristic times $t_{cr1}$ and
$t_{cr2}$ between $T_{cl}$ and $T_{cu}$. An aging process is revealed as the
strong $t_{w}$ dependence of $t_{cr2}$. The observed aging and memory effect is
discussed in terms of the droplet model.",0509696v1
2005-12-21,In-plane substitution effect on the magnetic properties of two-dimensional Spin-gap system SrCu$_2$(BO$_3$)$_2$,"A series of in-plane substituted compounds, including Cu-site
(SrZn$_x$Cu$_{2-x}$(BO$_3$)$_2$), and B-site
(SrCu$_2$(Si$_x$B$_{1-x}$O$_3$)$_2$) substitution, were synthesized by solid
state reaction. X-ray diffraction measurements reveal that these compounds are
single-phase materials and their in-plane lattice parameter depends
systematically on the substituting content $x$. The magnetic susceptibility in
different magnetic fields, the magnetization at different temperatures, and the
resistivity at room temperature were measured, respectively. It is found that
the spin gap deduced from the magnetic susceptibility measurements decreases
with increasing of $x$ in both Cu- and B-site substitution. No
superconductivity was found in these substituted compounds.",0512521v1
2006-01-04,Incommensurate structure of the spin-Peierls compound TiOCl,"We report on a detailed single crystal x-ray diffraction study of the
unconventional spin-Peierls compound TiOCl. The intermediate phase of TiOCl is
characterized by an incommensurate modulation which is virtually identical to
that recently found in the homologue compound TiOBr. The first order phase
transition between the spin-Peierls ground state and the incommensurate phase
reveals the same kind of thermal hysteresis in both, its crystal structure and
magnetic susceptibility. A weak, but significant magnetic field effect is found
for this phase transition with a field induced shift of the transition
temperature of Delta Tc1= -0.13 K for an applied field of B=10 T along the
chain direction. The field induced changes of the incommensurate crystal
structure are compatible with a scenario of competing intra- and inter-chain
interactions.",0601079v1
2006-01-25,Aging dynamics of ferromagnetic and reentrant spin glass phases in stage-2 Cu$_{0.80}$C$_{0.20}$Cl$_{2}$ graphite intercalation compound,"Aging dynamics of a reentrant ferromagnet stage-2
Cu$_{0.8}$Co$_{0.2}$Cl$_{2}$ graphite intercalation compound has been studied
using DC magnetic susceptibility. This compound undergoes successive
transitions at the transition temperatures $T_{c}$ ($\approx 8.7$ K) and
$T_{RSG}$ ($\approx 3.3$ K). The relaxation rate $S_{ZFC}(t)$ exhibits a
characteristic peak at $t_{cr}$ below $T_{c}$. The peak time $t_{cr}$ as a
function of temperature $T$ shows a local maximum around 5.5 K, reflecting a
frustrated nature of the ferromagnetic phase. It drastically increases with
decreasing temperature below $T_{RSG}$. The spin configuration imprinted at the
stop and wait process at a stop temperature $T_{s}$ ($<T_{c}$) during the
field-cooled aging protocol, becomes frozen on further cooling. On reheating,
the memory of the aging at $T_{s}$ is retrieved as an anomaly of the
thermoremnant magnetization at $T_{s}$. These results indicate the occurrence
of the aging phenomena in the ferromagnetic phase ($T_{RSG}<T<T_{c}$) as well
as in the reentrant spin glass phase ($T<T_{RSG}$).",0601561v1
2006-02-28,Magnetic field dependence of the magnetic phase separation in Pr1-xCaxMnO3 manganites studied by small-angle neutron scattering,"Transport properties of manganese oxides suggest that their colossal
magnetoresistance (CMR) is due to percolation between ferromagnetic metallic
(FM) clusters in an antiferromagnetic insulating (AFI) matrix. We have studied
small-angle neutron scattering under applied magnetic field in CMR Pr1-xCaxMnO3
crystals for x around 0.33. Quantitative analysis of the small-angle magnetic
neutron scattering shows that the magnetic heterogeneities take place at
different scales. At the mesoscopic scale (200nm), the inhomogeneities
correspond to the percolation of the conducting ferromagnetic phase into the
insulating phases. It is at the origin of the colossal magnetoresistance of the
compound. The other inhomogeneities are nanoscopic: inside the
antiferromagnetic phase (AFI), there exist small ferromagnetic clusters. Inside
the ferromagnetic phase which exists in absence of magnetic field in some
compounds and is in fact insulating (FI), there also exist small non
ferromagnetic objects. No evolution of this nanostructure is observed when the
magnetic field is applied. The existence of such nanoscale objects is discussed
in relation to the cationic disorder of these compounds.",0602668v1
2006-03-10,Prediction of new crystal structure phases in metal borides: a lithium monoboride analog to MgB2,"Modern compound prediction methods can efficiently screen large numbers of
crystal structure phases and direct the experimental search for new materials.
One of the most challenging problems in alloy theory is the identification of
stable phases with a never seen prototype; such predictions do not always
follow rational strategies. While performing ab initioa data mining of
intermetallic compounds we made an unexpected discovery: even in such a
well-studied class of systems as metal borides there are previously unknown
layered phases comparable in energy to the existing ones. With ab initio
calculations we show that the new metal-sandwich (MS) lithium monoboride phases
are marginally stable under ambient conditions but become favored over the
known stoichiometric compounds under moderate pressures. The MS lithium
monoboride exhibits electronic features similar to those in magnesium diboride
and is expected to be a good superconductor.",0603304v2
2006-06-16,Chemical pressure and hidden one-dimensional behavior in rare earth tri-telluride charge density wave compounds,"We report on the first optical measurements of the rare-earth tri-telluride
charge-density-wave systems. Our data, collected over an extremely broad
spectral range, allow us to observe both the Drude component and the
single-particle peak, ascribed to the contributions due to the free charge
carriers and to the charge-density-wave gap excitation, respectively. The data
analysis displays a diminishing impact of the charge-density-wave condensate on
the electronic properties with decreasing lattice constant across the
rare-earth series. We propose a possible mechanism describing this behavior and
we suggest the presence of a one-dimensional character in these two-dimensional
compounds. We also envisage that interactions and umklapp processes might play
a relevant role in the formation of the charge-density-wave state in these
compounds.",0606451v3
2006-07-19,Effect of strain and electric field on the electronic soft matter in manganite thin films,"We have studied the effect of substrate-induced strain on the properties of
the hole-doped manganite (La$_{1-y}$Pr$_{y}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ ($y$
= 0.4, 0.5 and 0.6) in order to distinguish between the roles played by
long-range strain interactions and quenched atomic disorder in forming the
micrometer-scale phase separated state. We show that a fluid phase separated
(FPS) state is formed at intermediate temperatures similar to the strain-liquid
state in bulk compounds, which can be converted to a metallic state by applying
an external electric field. In contrast to bulk compounds, at low temperatures
a strain stabilized ferromagnetic metallic (FMM) state is formed in the $y$ =
0.4 and 0.5 samples. However, in the $y$ = 0.6 sample a static phase separated
(SPS) state is formed similar to the strain-glass phase in bulk compounds.
Hence, we show that long-range strain interaction plays a dominant role in
forming the micrometer-scale phase separated state in manganite thin films.",0607502v2
2006-08-02,Magnetic frustration in the spinel compounds Ge Co_2 O_4 and Ge Ni_2 O_4,"In both spinel compounds GeCo$_2$O$_4$ and GeNi$_2$O$_4$ which order
antiferromagnetically (at $T_N = 23.5 K$ and $T_{N_1} = 12.13 K$, $T_{N_2} =
11.46 K$) with different Curie Weiss temperatures ($T_{CW}$=80.5 K and -15 K),
the usual magnetic frustration criterion $f=|T_{CW}|/T_N>>1$ is not fulfilled.
Using neutron powder diffraction and magnetization measurements up to 55 T,
both compounds are found with a close magnetic ground state at low temperature
and a similar magnetic behavior (but with a different energy scale), even
though spin anisotropy and first neighbor exchange interactions are quite
different. This magnetic behavior can be understood when considering the main
four magnetic exchange interactions. Frustration mechanisms are then
enlightened.",0608061v1
2006-08-28,"Microscopic model for the novel frustrated Cu(II)-spin tetrahedron-based Cu4Te5O12X4 (X=Cl, Br) systems","We present a microscopic study of the electronic and magnetic properties of
the newly synthesized Cu(II)-spin tetrahedron-based Cu4Te5O12Cl4 compound based
on Density Functional calculations and on ab initio-derived effective models.
In view of these results, we discuss the origin of the observed differences in
behavior between this system and the structurally similar and much studied
Cu2Te2O5Cl2. Since the Br analog of the title compound has not been synthesized
yet, we derive the crystal structure of Cu4Te5O12Br4 by geometry optimization
in an ab initio molecular dynamics calculation and investigate the effect of
substituting Cl by Br as well as the possible magnetic behavior of this system
and compare with the recently studied sister compound, Cu2Te2O5Br2.",0608598v1
2006-09-08,Coexistence of ferromagnetism and Kondo effect in uranium compounds,"Coexistence between ferromagnetic order and Kondo behavior has been observed
in some uranium compounds. The underscreened Kondo lattice model can provide a
possible description of this coexistence. Here we present a model of a lattice
of S=1 spins coupled to the conduction electrons through an intra-site exchange
interaction $J_{K}$ and an inter-site ferromagnetic exchange $f-f$ interaction
$J_{H}$. Finite temperature results show that the Kondo temperature is larger
than the Curie ordering temperature, $T_{C}$, providing a possible scenario for
the coexistence of Kondo effect and magnetic order. Also, the Kondo behavior
disappears abruptly for low values of $J_{K}$ and smoothly when changing the
band occupation. These results are in qualitative agreement with the
experimental situation for the above mentioned uranium compounds.",0609199v1
2006-09-26,Structure and basic magnetic properties of the honeycomb lattice compounds Na2Co2TeO6 and Na3Co2SbO6,"The synthesis, structure, and basic magnetic properties of Na2Co2TeO6 and
Na3Co2SbO6 are reported. The crystal structures were determined by neutron
powder diffraction. Na2Co2TeO6 has a two-layer hexagonal structure (space group
P6322) while Na3Co2SbO6 has a single-layer monoclinic structure (space group
C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge
sharing octahedra form planes interleaved by sodium ions. Both compounds have
full ordering of the Co2+ and Te6+/Sb5+ ions in the ab plane such that the Co2+
ions form a honeycomb array; the stacking of the honeycomb arrays differ in the
two compounds. Both Na2Co2TeO6 and Na3Co2SbO6 reveal antiferromagnetic ordering
at low temperatures, with a metamagnetic transition displayed by Na3Co2SbO6.",0609670v1
2006-11-01,A review of the electronic and magnetic properties of tetrahedrally bonded half-metallic ferromagnets,"The emergence of the field of spintronics brought half-metallic ferromagnets
to the center of scientific research. A lot of interest was focused on newly
created transition-metal pnictides (such as CrAs) and chalcogenides (such as
CrTe) in the metastable zinc-blende lattice structure. These compounds were
found to present the advantage of high Curie temperature values in addition to
their structural similarity to semiconductors. Significant theoretical activity
has been devoted to the study of the electronic and magnetic properties of
these compounds in an effort to achieve a better control of their experimental
behaviour in realistic applications. This review is devoted to an overview of
the studies of these compounds, with emphasis on theoretical results, covering
their bulk properties (electronic structure, magnetism, stability of the
zinc-blende phase, stability of ferromagnetism) as well as low-dimensional
structures (surfaces, interfaces, nanodots and transition-metal delta-doped
semiconductors) and phenomena that can possibly destroy the half-metallic
property, like structural distortions or defects.",0611006v1
2006-11-16,Valence Instability and Superconductivity in Heavy Fermion Systems,"Many cerium-based heavy fermion (HF) compounds have pressure-temperature
phase diagrams in which a superconducting region extends far from a magnetic
quantum critical point. In at least two compounds, CeCu2Si2 and CeCu2Ge2, an
enhancement of the superconducting transition temperature was found to coincide
with an abrupt valence change, with strong circumstantial evidence for pairing
mediated by critical valence, or charge transfer, fluctuations. This pairing
mechanism, and the valence instability, is a consequence of a f-c Coulomb
repulsion term U_fc in the hamiltonian. While some non-superconducting Ce
compounds show a clear first order valence instability, analogous to the Ce
alpha-gamma transition, we argue that a weakly first order valence transition
may be a general feature of Ce-based HF systems, and both magnetic and critical
valence fluctuations may be responsible for the superconductivity in these
systems.",0611429v1
2006-11-20,Graphite intercalation compounds under pressure,"Motivated by recent experimental work, we use first-principles density
functional theory methods to conduct an extensive search for low enthalpy
structures of C$_6$Ca under pressure. As well as a range of buckled structures,
which are energetically competitive over an intermediate range of pressures, we
show that the high pressure system ($\gtrsim 18$ GPa) is unstable towards the
formation of a novel class of layered structures, with the most stable compound
involving carbon sheets containing five- and eight-membered rings. As well as
discussing the energetics of the different classes of low enthalpy structures,
we comment on the electronic structure of the high pressure compound and its
implications for superconductivity.",0611511v1
2006-12-13,Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8,"The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline
compound has been measured as function of temperature and magnetic field up to
14T. It is found that the application of an external magnetic field suppresses
the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic
field dependence reveals a negative magnetocapacitance which is proportional to
the magnetic susceptibility, suggesting a common magnetostrictive origin for
the magnetic field dependence of the two quantities. This result is very
different from that obtained from the isostructural compound Ni3V2O8 that
presents a peak in the dielectric constant at the incommensurate magnetic phase
transition coupled to a sign change of the magnetocapacitance.",0612335v1
2006-12-21,Universality in one dimensional orbital wave ordering in spinel and related compounds: an experimental perspective,"Recent state-of-the-art crystallographic investigations of transition metal
spinel compounds have revealed that the d- orbital charge carriers undergo
ordering transitions with the formation of local ""molecular bonding"" units such
as dimers in MgTi2O4, octomers in CuIr2S4, and heptamers in AlV2O4. Herein, we
provide a unifying scheme involving one- dimensional orbital wave ordering
applicable to all of these spinels. The relative phase of the orbitals in the
chains is shown to be crucial to the formation of different local units, and
thus both the amplitude and phase of the orbital wave play important roles.
Examination of Horibe et al.'s [1] structure for AlV2O4 serves as the vehicle
for developing the general behavior for such orbital wave ordering. Ordered
AlV2O4 will be seen to organize into three equivalent chains in 2D Kagome
planes coupled so as to form units of three dimer bonds. Three additional
equivalent chains manifest a more complex tetramerization with three different
charge states and two different bonding schemes. The orbital wave ordering
scheme developed is extended to other spinel and related compounds with local
triangular transition metal coordination and partial filling of the t2g-d
orbitals.",0612564v2
2007-01-04,Spin-phonon coupling in antiferromagnetic chromium spinels,"The temperature dependence of eigenfrequencies and intensities of the IR
active modes has been investigated for the antiferromagnetic chromium spinel
compounds CdCr2O4, ZnCr2O4, ZnCr2S4, ZnCr2Se4, and HgCr2S4 by IR spectroscopy
for temperatures from 5 K to 300 K. At the transition into the magnetically
ordered phases, and driven by spin-phonon coupling, most compounds reveal
significant splittings of the phonon modes. This is true for geometrically
frustrated CdCr2O4, and ZnCr2O4, for bond frustrated ZnCr2S4 and for ZnCr2Se4,
which also is bond frustrated, but dominated by ferromagnetic exchange. The
pattern of splitting is different for the different compounds and crucially
depends on the nature of frustration and of the resulting spin order. HgCr2S4,
which is almost ferromagnetic, exhibits no splitting of the eigenfrequencies,
but shows significant shifts due to ferromagnetic spin fluctuations.",0701080v1
2007-01-19,A Physical Mechanism Underlying the Increase of Aqueous Solubility of Nonpolar Compounds and the Denaturation of Proteins upon Cooling,"The increase of aqueous solubility of nonpolar compounds upon cooling and the
cold denaturation of proteins are established experimental facts. Both
phenomena have been hypothesized to be related to restructuring of the hydrogen
bond network of water around small nonpolar solutes or hydrophobic amino acid
side chains. However, an underlying physical mechanism has yet to be
identified. We assume the solute particles and the monomers of a polymer
interact via a hard sphere potential. We further assume that the solvent
molecules interact via the two-scale spherically symmetric Jagla potential,
which qualitatively reproduces the anomalies of water, such as expansion on
cooling. We find that this model correctly predicts the increase in solubility
of nonpolar compounds and the swelling of polymers on cooling. Our findings are
consistent with the possibility that the presence of two length scales in the
Jagla potential--a rigid hard core and a more flexible soft core--is
responsible for both phenomena. At low temperatures, the solvent particles
prefer to remain at the soft core distance, leaving enough space for small
nonpolar solutes to enter the solvent thus increasing solubility. We support
this hypothesized mechanism by molecular dynamic simulations.",0701485v1
2007-01-19,Electronic structure and electric-field gradients analysis in $CeIn_3$,"Electric field gradients (EFG's) were calculated for the $CeIn_3$ compound at
both $^{115}In$ and $^{140}Ce$ sites. The calculations were performed within
the density functional theory (DFT) using the augmented plane waves plus local
orbital (APW+lo) method employing the so-called LDA+U scheme. The $CeIn_3$
compound were treated as nonmagnetic, ferromagnetic, and antiferromagnetic
cases. Our result shows that the calculated EFG's are dominated at the
$^{140}Ce$ site by the Ce-4f states. An approximately linear relation is
intuited between the main component of the EFG's and total density of states
(DOS) at Fermi level. The EFG's from our LDA+U calculations are in better
agreement with experiment than previous EFG results, where appropriate
correlations had not been taken into account among 4f-electrons. Our result
indicates that correlations among 4f-electrons play an important role in this
compound and must be taken into account.",0701486v2
2007-02-05,Multiple magnetic transitions and magnetocaloric effect in Gd1-xSmxMn2Ge2 compounds,"Magnetic and magnetocaloric properties of polycrystalline samples of
Gd1-xSmxMn2Ge2 have been studied. All the compounds except GdMn2Ge2 show
re-entrant ferromagnetic behavior. Multiple magnetic transitions observed in
these compounds are explained on the basis of the temperature dependences of
the exchange strengths of the rare earth and Mn sublattices. Magnetocaloric
effect is found to be positive at the re-entrant ferromagnetic transition,
whereas it is negative at the antiferro-ferromagnetic transition. In SmMn2Ge2,
the magnetic entropy change associated with the re-entrant transition is found
to decrease with field, which is attributed to the admixture effect of the
crystal field levels. The isothermal magnetic entropy change is found to
decrease with increase in Sm concentration.",0702082v1
2007-02-22,"Magnetization reversal in the orthovanadate RVO3 compounds (R = La, Nd, Sm, Gd, Er and Y): Inhomogeneities caused by defects in the orbital sector of quasi-one-dimensional orbital systems","We report on a study of various RVO3 single-crystal samples (R = La, Nd, Sm,
Gd, Er and Y) which show temperature-induced magnetization reversal. For
compounds with lighter rare-earths (R = La, Nd and Sm), magnetization reversal
can be observed for magnetic field applied in the ab plane and along the c
axis, whereas for the heavy rare-earths (R = Gd, Er) magnetization reversal is
only observed when the field is applied along the a axis. YVO3 has a
magnetization reversal along all the main crystallographic axes in a modest
applied field. We have found that some compounds are very sensitive to small
trapped fields present in the superconducting solenoid of the magnetometer
during the cooling. Based on the observed results, we argue that inhomogeniety
caused by defects in the orbital sector in the quasi one-dimensional orbital
systems could account for the unusual magnetization reversal.",0702527v1
2007-03-07,Semimetal to semimetal charge density wave transition in 1T-TiSe$_2$,"We report an infrared study on 1$T$-TiSe$_2$, the parent compound of the
newly discovered superconductor Cu$_x$TiSe$_2$. Previous studies of this
compound have not conclusively resolved whether it is a semimetal or a
semiconductor: information that is important in determining the origin of its
unconventional CDW transition. Here we present optical spectroscopy results
that clearly reveal that the compound is metallic in both the high-temperature
normal phase and the low-temperature CDW phase. The carrier scattering rate is
dramatically different in the normal and CDW phases and the carrier density is
found to change with temperature. We conclude that the observed properties can
be explained within the scenario of an Overhauser-type CDW mechanism.",0703167v2
2007-03-23,111Cd- TDPAC study of pressure-induced valence transition in YbAl2,"The quadrupole interaction at 111Cd impurity nuclei in the
intermediate-valence compound YbAl2 has been measured under pressure up to 80
kbar by the TDPAC spectroscopy. It was found that the quadrupole frequency nQ
measured on the 111Cd located at the Al sites in YbAl2, varies nonlinearly and
increases by almost four times with the pressure increase up to 80 kbar. A
linear correlation between the mean Yb valence, derived from Yb L3 OFY-XAS and
RXES measurements, and the electric field gradient (the quadrupole frequency
nQ=eQVzz/h) has been observed. The quadrupole frequencies on 111Cd in the
GdAl2, YbAl3, TmAl3 and CaAl2 compounds have been measured, also. The
possibility of determining the valence of Yb in the Yb compounds with p-metals
from the relation nQ (u(P)) = n2 + (n3 - n2) u(P) has been considered.",0703608v1
2006-02-13,Analysis of LDGM and compound codes for lossy compression and binning,"Recent work has suggested that low-density generator matrix (LDGM) codes are
likely to be effective for lossy source coding problems. We derive rigorous
upper bounds on the effective rate-distortion function of LDGM codes for the
binary symmetric source, showing that they quickly approach the rate-distortion
function as the degree increases. We also compare and contrast the standard
LDGM construction with a compound LDPC/LDGM construction introduced in our
previous work, which provably saturates the rate-distortion bound with finite
degrees. Moreover, this compound construction can be used to generate nested
codes that are simultaneously good as source and channel codes, and are hence
well-suited to source/channel coding with side information. The sparse and
high-girth graphical structure of our constructions render them well-suited to
message-passing encoding.",0602046v1
1995-06-29,Spin-polarization-induced structural selectivity in Pd$_3X$ and Pt$_3X$ ($X=3d$) compounds,"Spin-polarization is known to lead to important {\it magnetic} and {\it
optical} effects in open-shell atoms and elemental solids, but has rarely been
implicated in controlling {\it structural} selectivity in compounds and alloys.
Here we show that spin-polarized electronic structure calculations are crucial
for predicting the correct $T=0$ crystal structures for Pd$_3X$ and Pt$_3X$
compounds. Spin-polarization leads to (i) stabilization of the $L1_2$ structure
over the $DO_{22}$ structure in Pt$_3$Cr, Pd$_3$Cr, and Pd$_3$Mn, (ii) to the
stabilization of the $DO_{22}$ structure over the $L1_2$ structure in Pd$_3$Co
and to (iii) ordering (rather than phase-separation) in Pt$_3$Co and Pd$_3$Cr.
The results are analyzed in terms of first-principles local spin density
calculations.",9506007v1
2000-10-05,A Diffusion Model for Classical Chaotic Compound Scattering,"We consider the classical map proposed previously to be the exact classical
analogue of Rydberg Molecules calculated with the approximations relevant to
the multi-channel quantum defect theory. The resulting classical map is
analyzed at energies above the threshold for the Rydberg electron. At energies
very near to this threshold we find the possibility of bounded motion for
positive energy due to conserved tori as well as the possibility of forming a
compound system, i.e. a system where the particle is trapped for long times
before emerging again to the continuum. The compound scattering displays
unusual features for short time behavior. A diffusion model explains these
features.",0010014v2
2005-09-15,Change of 7Be decay rate in exohedral and endohedral C60 fullerene compounds and its implications,"The half-life of 7Be implanted in a C60 pellet and gold foil has been
measured to be about the same within about 0.2%. Using a radiochemical
technique, we also measured that the probability of formation of endohedral
7Be@C60 by nuclear implantation technique was (5.6+-0.45)%. It is known from
earlier works that the half-life of endohedral 7Be@C60 is about 1.2% shorter
than that of 7Be implanted in gold. An analysis of these results using linear
muffin-tin orbital method calculations indicates that most of the implanted 7Be
ions in fullerene C60 stay at a distance of about 5.3 Angstrom from the centers
of nearest C60 molecules forming exohedral compounds and those who enter the
fullerene cages go to the centers of the cages forming endohedral 7Be@C60
compounds.",0509021v1
1994-08-28,"Nearby Doorways, Parity Doublets and Parity Mixing in Compound Nuclear States","We discuss the implications of a doorway state model for parity mixing in
compound nuclear states. We argue that in order to explain the tendency of
parity violating asymmetries measured in $^{233}$Th to have a common sign,
doorways that contribute to parity mixing must be found in the same energy
neighbourhood of the measured resonance. The mechanism of parity mixing in this
case of nearby doorways is closely related to the intermediate structure
observed in nuclear reactions in which compound states are excited. We note
that in the region of interest ($^{233}$Th) nuclei exhibit octupole
deformations which leads to the existence of nearby parity doublets. These
parity doublets are then used as doorways in a model for parity mixing. The
contribution of such mechanism is estimated in a simple model.",9408027v1
1996-09-06,Entrance-channel Mass-asymmetry Dependence of Compound-nucleus Formation Time in Light Heavy-ion Reactions,"The entrance-channel mass-asymmetry dependence of the compound nucleus
formation time in light heavy-ion reactions has been investigated within the
framework of semiclassical dissipative collision models. the model calculations
have been succesfully applied to the formation of the $^{38}$Ar compound
nucleus as populated via the $^{9}$Be+$^{29}$Si, $^{11}$B+$^{27}$Al,
$^{12}$C+$^{26}$Mg and $^{19}$F+$^{19}$F entrance channels. The shape evolution
of several other light composite systems appears to be consistent with the
so-called ""Fusion Inhibition Factor"" which has been experimentally observed. As
found previously in more massive systems for the fusion-evaporation process,
the entrance-channel mass-asymmetry degree of freedom appears to determine the
competition between the different mechanisms as well as the time scales
involved.",9609016v1
1997-06-04,Matrix Elements between Nuclear Compound States and Dynamical Enhancement of the Weak Interaction,"A method to calculate the mean squared matrix element of weak interaction
between compound states is developed. The result is expressed in terms of
matrix elements of the nucleon-nucleon strong and weak interactions times the
Fermi distribution functions at finite temperature. Numerical calculations for
$^{233}$Th are in excellent agreement with recent measurements of parity
nonconservation effects in neutron capture. In fact, our calculations prove
that the factor of dynamical enhancement (ratio of compound-nucleus effect to
single-particle one) really exceeds 100, thus making it unnesessary to assume a
value of the weak constant bigger than standard one ($g\simeq 10^{8} \epsilon
\sim 1\div 4$).",9706014v1
2001-07-13,Parity Violation in Neutron Capture Reactions,"In the last decade, the scattering of polarized neutrons on compound nucleus
resonances proved to be a powerful experimental technique for probing nuclear
parity violation. Longitudinal analyzing powers in neutron transmission
measurements on p-wave resonances in nuclei such as $^{139}$La and $^{232}$Th
were found to be as large as 10%. Here we examine the possibilities of carrying
out a parallel program to measure asymmetries in the $(n,\gamma$) reaction on
these same compound nuclear resonances. Symmetry-violating $(n,\gamma$) studies
can also show asymmetries as large as 10%, and have the advantage over
transmission experiments of allowing parity-odd asymmetries in several
different gamma-decay branches from the same resonance. Thus, studies of parity
violation in the $(n,\gamma)$ reaction using high efficiency germanium
detectors at the Los Alamos Lujan facility, for example, could determine the
parity-odd nucleon-nucleon matrix elements in complex nuclei with high
accuracy. Additionally, simultaneous studies of the E1 and $V_{PNC}$ matrix
elements invol ved in these decays could be used to help constrain the
statistical theory of parity non-conservation in compound nuclei.",0107041v1
2006-09-16,Possibility of synthesizing doubly closed superheavy nucleus,"The possibility of synthesizing a doubly magic superheavy nucleus,
$^{298}114_{184}$, is investigated on the basis of fluctuation-dissipation
dynamics. In order to synthesize this nucleus, we must generate more
neutron-rich compound nuclei because of the neutron emissions from excited
compound nuclei. The compound nucleus $^{304}114$ has two advantages to
achieving a high survival probability. First, because of small neutron
separation energy and rapid cooling, the shell correction energy recovers
quickly. Secondly, owing to neutron emissions, the neutron number of the
nucleus approaches that of the double closed shell and the nucleus obtains a
large fission barrier. Because of these two effects, the survival probability
of $^{304}114$ does not decrease until the excitation energy $E^{*}= 50$ MeV.
These properties lead to a rather high evaporation reside cross section.",0609043v1
2006-11-02,Collective effects in a medium and a model of compound flow in relativistic heavy ion collisions,"A new analytical approach is presented for analysis of two-particle azimuthal
correlations in heavy ion collisions at relativistic energies. This approach
suggests that elliptic flow measured by experiment has a compound structure,
namely, that it may come from superposition of several components. General
expressions have been derived for the two-particle correlation function
isolating the contribution due to anisotropic flow. The model of compound flow
takes into account the number of jets per event, average multiplicity per jet,
dependence of jet yield on the orientation with respect to the reaction plane,
and independent ""soft"" particle production.",0611005v3
2003-03-10,Statistical Yield Modeling for IC Manufacture: Hierarchical Fault Distributions,"A hierarchical approach to the construction of compound distributions for
process-induced faults in IC manufacture is proposed. Within this framework,
the negative binomial distribution and the compound binomial distribution are
treated as level-1 models. The hierarchical approach to fault distribution
offers an integrated picture of how fault density varies from region to region
within a wafer, from wafer to wafer within a batch, and so on. A theory of
compound-distribution hierarchies is developed by means of generating
functions. With respect to applications, hierarchies of yield means and yield
probability-density functions are considered and an in-process measure of yield
loss is introduced. It is shown that the hierarchical approach naturally
embraces the Bayesian approach.",0303039v1
2007-02-23,Bandwidth control of forbidden transmission gaps in compound structures with subwavelength slits,"Phase resonances in transmission compound structures with subwavelength slits
produce sharp dips in the transmission response. For all equal slits, the
wavelengths of these sharp transmission minima can be varied by changing the
width or the length of all the slits. In this paper we show that the width of
the dip, i.e., the frequency range of minimum transmittance, can be controlled
by making at least one slit different from the rest within a compound unit
cell. In particular, we investigate the effect that a change in the dielectric
filling, or in the length of a single slit produces in the transmission
response. We also analyze the scan angle behavior of these structures by means
of band diagrams, and compare them with previous results for all-equal slit
structures.",0702207v1
2000-03-18,"Subnormal operators regarded as generalized observables and compound-system-type normal extension related to su(1,1)","In this paper, subnormal operators, not necessarily bounded, are discussed as
generalized observables. In order to describe not only the information about
the probability distribution of the output data of their measurement but also a
framework of their implementations, we introduce a new concept
compound-system-type normal extension, and we derive the compound-system-type
normal extension of a subnormal operator, which is defined from an irreducible
unitary representation of the algebra su(1,1). The squeezed states are
characterized as the eigenvectors of an operator from this viewpoint, and the
squeezed states in multi-particle systems are shown to be the eigenvectors of
the adjoints of these subnormal operators under a representation. The affine
coherent states are discussed in the same context, as well.",0003079v3
2000-04-18,Entanglements and compound states in quantum information theory,"Quantum entanglements, describing truly quantum couplings, are stu died and
classified from the point of view of quantum compound states. We show that c
lassical-quantum correspondences such as quantum encodings can be treated as
d-entanglements leading to a special class of the separable compound states.
The mutual information of the d-compound and entangled states lead to two di
fferent types of entropies for a given quantum state: the von Neumann entrop y,
which is achieved as the supremum of the information over all d-entanglem ents,
and the dimensional entropy, which is achieved at the standard entangl ement,
the true quantum entanglement, coinciding with a d-entanglement only in the
commutative case. The q-capacity of a quantum noiseless channel, defi ned as
the supremum over all entanglements, is given as the logarithm of the
dimensionality of the input von Neumann algebra. It can double the classical
capacity, achieved as the supremum over all semi-quantum couplings (d-entang
lements, or encodings), which is bounded by the logarithm of the dimensional
ity of a maximal Abelian subalgebra.",0004069v1
2001-05-19,A (Classical) Representation for a Spin-S Entity as a compound system in R^3 consisting of 2S Individual Spin-1/2 Entities,"We generalize the results of [B. Coecke, Helv. Phys. Acta 68, 396 (1995)] for
the representation of coherent states of a spin-1 entity to spin-S entities
with S>1 and to non-coherent spin states: through the introduction of 'hidden
correlations' (see quant-ph/0105093) we introduce a representation for a spin-S
entity as a compound system consisting of 2S 'individual' spin-1/2 entities,
each of them represented by a 'proper state', and such that we are able to
consider a measurement on the spin-S entity as a measurement on each of the
individual spin-1/2 entities. If the spin-S entity is in a maximal spin state,
the 2S individual spin-1/2 entities behave as a collection of indistinguishable
but separated entities. If not so, we have to introduce the same kind of hidden
correlations as required for a hidden correlation representation of a compound
quantum systems described by a symmetrical superposition. Moreover, by applying
the Majorana representation and Aerts' representation for a spin-1/2 entity,
this hidden correlation representation yields a classical mechanistic
representation of a spin-S entity in R^3.",0105094v2
2004-10-12,Orthocomplementation and compound systems,"In their 1936 founding paper on quantum logic, Birkhoff and von Neumann
postulated that the lattice describing the experimental propositions concerning
a quantum system is orthocomplemented. We prove that this postulate fails for
the lattice L_sep describing a compound system consisting of so called
separated quantum systems. By separated we mean two systems prepared in
different ``rooms'' of the lab, and before any interaction takes place. In that
case the state of the compound system is necessarily a product state. As a
consequence, Dirac's superposition principle fails, and therefore L_sep cannot
satisfy all Piron's axioms. In previous works, assuming that L_sep is
orthocomplemented, it was argued that L_sep is not orthomodular and fails to
have the covering property. Here we prove that L_sep cannot admit and
orthocomplementation. Moreover, we propose a natural model for L_sep which has
the covering property.",0410085v2
2007-04-11,Magnetic structure of Sm2IrIn8,"The magnetic structure of the intermetallic antiferromagnet Sm2IrIn8 was
determined using x-ray resonant magnetic scattering (XRMS). Below TN = 14.2,
Sm2IrIn8 has a commensurate antiferromagnetic structure with a propagation
vector (1/2,0,0). The Sm magnetic moments lie in the ab plane and are rotated
roughly 18 degrees away from the a axis. The magnetic structure of this
compound was obtained by measuring the strong dipolar resonant peak whose
enhancement was of over two orders of magnitude at the L2 edge. At the L3 edge
both quadrupolar and dipolar features were observed in the energy line shape.
The magnetic structure and properties of Sm2IrIn8 are found to be consistent
with the general trend already seen for the Nd-, Tb- and the Ce-based compounds
from the RmMnIn3m+2n family (R = rare earth; M=Rh or Ir, m = 1, 2; n = 0, 1),
where the crystalline electrical field (CEF) effects determine the direction of
magnetic moments and the TN evolution in the series. The measured Neel
temperature for Sm2IrIn8 is slightly suppressed when compared to the TN of the
parent cubic compound SmIn3.",0704.1480v2
2007-05-21,Compound basis for the space of symmetric functions,"The aim of this note is to introduce a compound basis for the space of
symmetric functions. Our basis consists of products of Schur functions and
$Q$-functions. The basis elements are indexed by the partitions. It is well
known that the Schur functions form an orthonormal basis for our space. A
natural question arises. How are these two bases connected? In this note we
present some numerical results of the transition matrix for these bases. In
particular we will see that the determinant of the transition matrix is a power
of 2. This is not a surprising fact. However the explicit formula involves an
interesting combinatorial feature.
  Our compound basis comes from the twisted homogeneous realization of the
basic representation of the affine Lie algebras.
  This note is not written in a standard style of mathematical articles. It is
more like a draft of a talk. In particular proofs are not given here. Details
and proofs will be published elsewhere.",0705.2932v1
2007-05-28,Theory of Thermal Conductivity in High-Tc Superconductors below Tc: Comparison between Hole-Doped and Electron-Doped Systems,"In hole-doped high-Tc superconductors, thermal conductivity increases
drastically just below Tc, which has been considered as a hallmark of a nodal
gap. In contrast, such a coherence peak in thermal conductivity is not visible
in electron-doped compounds, which may indicate a full-gap state such as a
(d+is)-wave state. To settle this problem, we study the thermal conductivity in
the Hubbard model using the fluctuation-exchange (FLEX) approximation, which
predicts that the nodal d-wave state is realized in both hole-doped and
electron-doped compounds. The contrasting behavior of thermal conductivity in
both compounds originates from the differences in the hot/cold spot structure.
In general, a prominent coherence peak in thermal conductivity appears in
line-node superconductors only when the cold spot exists on the nodal line.",0705.3988v1
2007-06-05,Superconductivity in Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$ without Inversion Symmetry,"Superconductivity with $T_{\rm c}$ $\simeq$ 2 K was discovered in the
intermetallic binary compounds Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$. This is the first
observation of superconductivity in the Rh-Ga and Ir-Ga binary systems. Both
compounds crystallize in a distorted Co$_2$Al$_9$-type structure (monoclinic,
space group: $Pc$), which lacks spatial inversion symmetry. Specific heat
measurements revealed that both compounds are weak-coupling BCS superconductors
having an isotropic superconducting gap. Measurements in magnetic fields
indicated type-I superconductivity with a critical field $H_{\rm c}(0)$
$\simeq$ 130 Oe for Rh$_2$Ga$_9$ and type-II superconductivity with an upper
critical field $H_{\rm c2}(0)$ $\simeq$ 250 Oe for Ir$_2$Ga$_9$.",0706.0577v1
2007-06-09,Geometrically frustrated magnetic behavior of Sr3NiRhO6 and Sr3NiPtO6,"The results of ac and dc magnetic susceptibility isothermal magnetization and
heat-capacity measurements as a function of temperature (T) are reported for
Sr3NiRhO6 and Sr3NiPtO6 containing magnetic chains arranged in a triangular
fashion in the basal plane and crystallizing in K4CdCl6-derived rhombohedral
structure. The results establish that both the compounds are magnetically
frustrated, however in different ways. In the case of the Rh compound, the
susceptibility data reveal that there are two magnetic transitions, one in the
range 10 -15 K and the other appearing as a smooth crossover near 45 K, with a
large frequency dependence of ac susceptibility in the range 10 to 40 K; in
addition, the features in C(T) are smeared out at these temperatures. The
magnetic properties are comparable to those of previously known few compounds
with partially disordered antiferromagnetic structure. On the other hand, for
Sr3NiPtO6, there is no evidence for long-range magnetic ordering down to 1.8 K
despite large value of paramagnetic Curie temperature.",0706.1308v2
2007-07-20,The Ba2LnFeNb4O15 Tetragonal Tungsten Bronze: towards RT composite multiferroics,"Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd)
with the Tetragonal Tungsten Bronze (TTB) structure have been synthesised by
conventional solid-state methods. The Neodymium, Samarium and Europium
compounds are ferroelectric with Curie temperature ranging from 320 to 440K.
The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300
K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium
compounds exhibit magnetic hysteresis loops at room temperature originating
from traces of a barium ferrite secondary phase. The presence of both
ferroelectric and magnetic hysteresis loops at room temperature allows
considering these materials as composites multiferroic. Based on
crystal-chemical analysis we propose some relationships between the
introduction of Ln3+ ions in the TTB framework and the chemical, structural and
physical properties of these materials.",0707.3112v2
2007-08-01,"Crystal Structure and Physical Properties of Mg6Cu16Si7-type M6Ni16Si7, for M = Mg, Sc, Ti, Nb, and Ta","Five compounds were investigated for magnetic character and
superconductivity, all with non-magnetic nickel and band structures containing
flat bands and steep bands. The syntheses and crystal structures, refined by
powder X-ray diffraction, are reported for M6Ni16Si7, where M = Mg, Sc, Ti, Nb,
and Ta. All compounds form in the Mg6Cu16Si7 structure type. Resistance
measurements are also reported on M6Ni16Si7 (M = Mg, Sc, Ti, and Nb) down to
0.3 K, with all four showing metallic conductivity. No superconductivity is
observed. Magnetization measurements for all compounds reveal essentially
temperature independent paramagnetism, with a tendency toward more enhanced low
temperature paramagnetism for the cases of Mg6Ni16Si7 and Sc6Ni16Si7.",0708.0179v2
2007-08-05,Structures of the reduced niobium oxides Nb12O29 and Nb22O54,"The crystal structure of Nb22O54 is reported for the first time, and the
structure of orthorhombic Nb12O29 is reexamined, resolving previous
ambiguities. Single crystal x-ray and electron diffraction were employed. These
compounds were found to crystallize in the space groups P2/m (a = 15.7491(2) A,
b = 3.8236(3) A, c = 17.8521(2) A, beta = 102.029(3)) and Cmcm (a = 3.8320(2)
A, b = 20.7400(9) A, c = 28.8901(13) A) respectively and share a common
structural unit, a 4x3 block of corner sharing NbO6 octahedra. Despite
different constraints imposed by symmetry these blocks are very similar in both
compounds. Within a block, it is found that the niobium atoms are not located
in the centers of the oxygen octahedra, but rather are displaced inward toward
the center of the block forming an apparent antiferroelectric state. Bond
valence sums and bond lengths do not show the presence of charge ordering,
suggesting that all 4d electrons are delocalized in these compounds at the
temperature studied, T = 200 K.",0708.0673v1
2007-08-28,"Doniach diagram for ordered, disordered and underscreened Kondo lattices","The Doniach's diagram has been originally proposed to describe the
competition between the local Kondo effect and the intersite RKKY interactions
in cerium compounds. Here we discuss the extension of this diagram to different
variations of Kondo lattice model. We consider a) ordered cerium compounds
where the competition between magnetic order and Kondo effect plays an
important role, as $CeRh_2Si_2$, b) disordered cerium systems with competing
spin glass phase, magnetic ordered phases and a Kondo phase, as the heavy
fermion cerium alloy $CeCu_xNi_{1-x}$ and, c) uranium compounds where a
coexistence between Kondo effect and ferromagnetic order has been observed, as
UTe. We show that all these cases can be described by a generalized Doniach
phase diagram.",0708.3807v1
2007-09-06,Magneto-optical behaviour of EuIn_2P_2,"We report results of a magneto-optical investigation of the Zintl-phase
compound EuIn$_2$P$_2$. The compound orders magnetically at $T_C$=24 K and
exhibits concomitant large magnetoresistance effects. For $T\le$50 K and
increasing magnetic fields we observe a transfer of spectral weight in
$\sigma_1(\omega)$ from energies above 1 eV into the low-energy metallic
component as well as into a mid-infrared signal centered at about 600
cm$^{-1}$. This latter absorption is reminiscent to what has been seen in a
large variety of so-called Kondo materials and ascribed to excitations across
the hybridization gap. The observed gain of Drude weight upon increasing
magnetic field suggests an enhancement of the itinerant charge-carrier
concentration due to the increasing magnetization, a phenomenon that was
previously observed in other compounds which exhibit colossal magnetoresistive
effects.",0709.0791v1
2007-09-14,Electronic structure of the ferromagnetic superconductor UCoGe from first principles,"The superconductor UCoGe is analyzed with electronic structure calculations
using Linearized Augmented Plane Wave method based on Density Functional
Theory. Ferromagnetic and antiferromagnetic calculations with and without
correlations (via LDA+U) were done. In this compound the Fermi level is
situated in a region where the main contribution to DOS comes from the U-5f
orbital. The magnetic moment is mainly due to the Co-3d orbital with a small
contribution from the U-5f orbital. The possibility of fully non-collinear
magnetism in this compound seems to be ruled out. These results are compared
with the isostructural compound URhGe, in this case the magnetism comes mostly
from the U-5f orbital.",0709.2351v4
2007-09-17,Growth of toric domains in the smectic phase of oxadiazoles,"In a previous paper (Phase Transitions, 80(9), 987, 2007) we discussed the
smectic and nematic textures of some mesomorphic oxadiazole compounds with
terminal Cl-substituent. Optical microscope investigations showed a very
interesting behaviour of smectic and nematic phases; the smectic phase has
fan-shaped and toric textures and the nematic phase has spherulitic domains,
which disappear as the sample is further heated, the texture changing into a
smooth one. Here, we investigate four oxadiazole compounds with the same
structure but terminal Br-substituent. The behaviour of the smectic and nematic
phases is like that observed in the compounds with Cl. The focus of the paper
is on the growth of toric domains from the nematic melt and on the role of
defects in the domain structure.",0709.2659v1
2007-10-16,Classical Capacities of Averaged and Compound Quantum Channels,"We determine the capacity of compound classical-quantum channels. As a
consequence we obtain the capacity formula for the averaged classical-quantum
channels. The capacity result for compound channels demonstrates, as in the
classical setting, the existence of reliable universal classical-quantum codes
in scenarios where the only a priori information about the channel used for the
transmission of information is that it belongs to a given set of memoryless
classical-quantum channels. Our approach is based on the universal classical
approximation of the quantum relative entropy which in turn relies on the
universal hypothesis testing results.",0710.3027v2
2007-10-20,Spin-Dependent Mass Enhancement under Magnetic Field in the Periodic Anderson Model,"In order to study the mechanism of the mass enhancement in heavy fermion
compounds in the presence of magnetic field, we study the periodic Anderson
model using the fluctuation exchange approximation. The resulting value of the
mass enhancement factor z^{-1} can become up to 10, which is significantly
larger than that in the single-band Hubbard model. We show that the difference
between the magnitude of the mass enhancement factor of up spin (minority spin)
electrons z^{-1}_up and that of down spin (majority spin) electrons z^{-1}_down
increases by the applied magnetic field B//z, which is consistent with de
Haas-van Alphen measurements for CeCoIn_5, CeRu_2Si_2 and CePd_2Si_2. We
predict that z^{-1}_up >z^{-1}_down in many Ce compounds, whereas z^{-1}_up <
z^{-1}_down in Yb compounds.",0710.3830v1
2007-10-22,Observation of magnetization reversal and negative magnetization in a double perovskite compound Sr2YbRuO6,"Detailed magnetic properties of the compound Sr2YbRuO6 are presented here.
The compound belongs to the family of double perovskites forming a monoclinic
structure. Magnetization meas-urements reveal clear evidence for two components
of magnetic ordering aligned opposite to each other, leading to a magnetization
reversal, compensation temperature (T* = 34 K) and neg-ative magnetization at
low temperatures and low magnetic fields. Heat capacity measurements
corroborate the presence of two components in the magnetic ordering and a
noticeable third anomaly at low temperatures (~15 K) which cannot be attributed
the Schottky effect. The calcu-lated magnetic entropy is substantially lower
than that expected for the ground states of the or-dered moments of Ru5+ and
Yb3+, indicating the presence of large crystal field effects and/ or
in-complete magnetic ordering and/or magnetic frustrations well above the
magnetic ordering. An attempt is made to explain the magnetization reversal
within the frameworks of available models.",0710.4043v3
2008-01-03,Resonant Inelastic X-ray Scattering (RIXS) Spectra for Ladder Cuprates,"The ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ is of interest both as a
quasi-one-dimensional analog of the superconducting cuprates and as a
superconductor in its own right when Sr is substituted by Ca. In order to model
resonant inelastic x-ray scattering (RIXS) spectra for this compound, we
investigate the simpler SrCu$_{2}$O$_{3}$ system in which the crystal structure
contains very similar ladder planes. We approximate the LDA dispersion of
SrCu$_{2}$O$_{3}$ by a Cu only two-band tight-binding model. Strong correlation
effects are incorporated by assuming an anti-ferromagnetic ground state. The
available angle-resolved photoemission (ARPES) and RIXS data on the ladder
compound are found to be in reasonable accord with our theoretical predictions.",0801.0604v1
2008-02-11,"Synthesis and structural characterization of uranium-doped Ca2CuO3, a 1D quantum antiferromagnet","The technological settings of a modified sol-gel method for preparation of
highly fine homogeneous powder Ca2CuO3 doped with uranium 238 (x=0-0.05) is
presented. The analysis of structure, purity of phases and the justification
for the role of uranium in the given compounds are provided together with
almost complete classification of observed optical phonons by means of the
Raman, IR measurements and ab initio calculation. The significant reduction in
particle size was achieved by doping and the strong correlation between
resistivity and doping concentration was observed and explained using the
phonon-assisted electron hopping conduction model. The persistence of covalent
insulation state in all compounds is a key feature of this class of compounds.",0802.1423v2
2008-02-20,Anomalous Magnetic Properties of Sr2YRuO6,"Anomalous magnetic properties of the double perovskite ruthenates compound
Sr2YRuO6 are reported here. Magnetization measurements as a function of
temperature in low magnetic fields show clear evidence for two components of
magnetic order (TM1 ~ 32K and TM2 ~ 27K) aligned opposite to each other with
respect to the magnetic field direction even though only Ru5+moments can order
magnetically in this compound. The second component of the magnetic order at
TM2 ~ 27K results only in a magnetization reversal, and not in the negative
magnetization when the magnetization is measured in the field cooled (FC) mode.
Isothermal magnetization (M-H) measurements show hysteresis with maximum
coercivity (Hc) and remnant magnetization (Mr) at T ~ 27 K, corroborating the
presence of the two oppositely aligned magnetic moments, each with a
ferromagnetic component. The two components of magnetic ordering are further
confirmed by the double peak structure in the heat capacity measurements. These
anomalous properties have significance to some of the earlier results obtained
for the Cu-substituted superconducting Sr2YRu1-xCuxO6 compounds.",0802.2953v2
2008-03-22,Iron-based layered superconductor LaO$_{1-x}$F$_x$FeAs: an antiferromagnetic semimetal,"We have studied the newly found superconductor compound LaO$_{1-x}$F$_x$FeAs
through the first-principles density functional theory calculations. We find
that the parent compound LaOFeAs is a quasi-2-dimensional antiferromgnetic
semimetal with most carriers being electrons and with a magnetic moment of
$2.3\mu_B$ located around each Fe atom on the Fe-Fe square lattice. Furthermore
this is a commensurate antiferromagnetic spin density wave due to the Fermi
surface nesting, which is robust against the F-doping. The observed
superconduction happens on the Fe-Fe antiferromagnetic layer, suggesting a new
superconductivity mechanism, mediated by the spin fluctuations. An abrupt
change on the Hall measurement is further predicted for the parent compound
LaOFeAs.",0803.3286v1
2008-03-31,Hall effect measurements on YbRh2Si2 and relatives in the light of electronic structure calculations,"We report experimental and theoretical investigations of the Hall effect in
YbRh2Si2 and its reference compounds LuRh2Si2 and YbIr2Si2. Based on
band-structure calculations we identify two bands dominating the Hall
coefficient in all these compounds. For the case of LuRh2Si2 - the non-magnetic
reference compound of YbRh2Si2 - the temperature dependence of the Hall
coefficient is described quantitatively to arise from two hole-like bands. For
YbIr2Si2 and YbRh2Si2, renormalized band calculations yield two bands of
opposite character. In YbRh2Si2 these two bands almost compensate each other.
We present strong indications that the sample dependences of the
low-temperature Hall coefficient observed for YbRh2Si2 arise from slight
variations of the relative scattering rates of the two bands. Minute changes of
the composition appear to be the origin.",0803.4428v3
2008-04-02,"Physical properties of the new Uranium ternary compounds U3Bi4M3 (M=Ni, Rh)","We report the properties of two new isostructural compounds, U3Bi4Ni3 and
U3Bi4Rh3. The first of these compounds is non-metallic, and the second is a
nearly ferromagnetic metal, both as anticipated from their electron count
relative to other U-based members of the larger 3-4-3 family. For U3Bi4Rh3, a
logarithmic increase of C/T below 3 K, a resistivity proportional to T^4/3, and
the recovery of Fermi-liquid behavior in both properties with applied fields
greater than 3T, suggest that U3Bi4Rh3 may be a new example of a material
displaying ferromagnetic quantum criticality.",0804.0393v1
2008-04-03,"Phonon density of states, anharmonicity, electron-phonon coupling and possible multigap superconductivity in the clathrate superconductors Ba8Si46 and Ba24Si100: Why is Tc different in these two compounds?","We report a detailed study of specific heat, electrical resistivity and
thermal expansion in combination with inelastic neutron and inelastic X-ray
scattering to investigate the origin of superconductivity in the two silicon
clathrate superconductors Ba8Si46 and Ba24Si100. Both compounds have a similar
structure based on encaged barium atoms in oversized silicon cages. However,
the transition temperatures are rather different: 8 K and 1.5 K respectively.
By extracting the superconducting properties, phonon density of states,
electron-phonon coupling function and phonon anharmonicity from these
measurements we discuss the important factors governing Tc and explain the
difference between the two compounds.",0804.0535v1
2008-04-10,Electronic properties and phase transitions in low-dimensional semiconductors,"We present the first review of the current state of the literature on
electronic properties and phase transitions in TlX and TlMX2 (M = Ga, In; X =
Se, S, Te) compounds. These chalcogenides belong to a family of the
low-dimensional semiconductors possessing chain or layered structure. They are
of significant interest because of their highly anisotropic properties, semi-
and photoconductivity, non-linear effects in their I-V characteristics
(including a region of negative differential resistance), switching and memory
effects, second harmonic optical generation, relaxor behavior and potential
applications for optoelectronic devices. We review the crystal structure of TlX
and TlMX2 compounds, their transport properties under ambient conditions,
experimental and theoretical studies of the electronic structure, transport
properties and semiconductor-metal phase transitions under high pressure, and
sequences of temperature-induced structural phase transitions with intermediate
incommensurate states. Electronic nature of the ferroelectric phase transitions
in the above-mentioned compounds, as well as relaxor behavior, nanodomains and
possible occurrence of quantum dots in doped and irradiated crystals is
discussed.",0804.1639v2
2008-05-26,Superconducting Gap and Pseudogap in Sm(O$_{1-x}$F$_x$)FeAs Layered Superconductor from Photoemission Spectroscopy,"High resolution photoemission measurements have been carried out on
non-superconducting SmOFeAs parent compound and superconducting
Sm(O$_{1-x}$F$_x$)FeAs (x=0.12, and 0.15) compounds. The momentum-integrated
spectra exhibit a clear Fermi cutoff that shows little leading-edge shift in
the superconducting state which suggests the Fermi surface sheet(s) around the
$\Gamma$ point may not be gapped in this multiband superconductors. A robust
feature at 13 meV is identified in all these samples. Spectral weight
suppression near E$_F$ with decreasing temperature is observed in both undoped
and doped samples that points to a possible existence of a pseudogap in these
Fe-based compounds.",0805.3821v1
2008-05-29,Superconductivity at 38 K in the iron arsenide (Ba1-xKx)Fe2As2,"The ternary iron arsenide BaFe2As2 becomes superconducting by hole doping,
which was achieved by partial substitution of the barium site with potassium.
We have discovered bulk superconductivity up to Tc = 38 K in (Ba1-xKx)Fe2As2
with x = 0.4. The parent compound BaFe2As2 as well as KFe2As2 both crystallize
in the tetragonal ThCr2Si2-type structure, which consists of (FeAs)- iron
arsenide layers separated by barium or potassium ions. BaFe2As2 is a poor metal
and exhibits a SDW anomaly at 140 K. By substituting Ba2+ for K+ ions we have
introduced holes in the (FeAs)- layers, which suppress the SDW anomaly and
induce superconductivity. This scenario is very similar to the recently
discovered arsenide-oxide superconductors. The Tc of 38 K in (Ba1-xKx)Fe2As2 is
the highest observed critical temperature in hole doped iron arsenide
superconductors so far. Therefore, we were able to expand this class of
superconductors by oxygen-free compounds with the ThCr2Si2-type structure. Our
results suggest, that superconductivity in these systems essentially evolves
from the (FeAs)- layers and may occur in other related compounds.",0805.4630v2
2008-06-06,Electromagnons in multiferroic RMn2O5 compounds and their microscopic origin,"We summarize the existing experimental data on electromagnons in multiferroic
RMn2O5 compounds, where R denotes a rare earth ion, Y or Bi, and discuss a
realistic microscopic model of these materials based on assumption that the
microscopic mechanism of magnetically-induced ferroelectricity and
electromagnon absorption relies entirely on the isotropic Heisenberg exchange
and magnetostrictive coupling of spins to a polar lattice mode and does not
involve relativistic effects. This model explains many magnetic and optical
properties of RMn2O5 manganites, such as the spin re-orientation transition,
magnetically-induced polarisation, appearance of the electromagnon peak in the
non-collinear spin state and the polarisation of light for which this peak is
observed. We compare experimental and theoretical results on electromagnons in
RMn2O5 and RMnO3 compounds.",0806.1207v1
2008-06-06,Superconductivity in hole-doped (Sr$_{1-x}$K$_x$)Fe$_2$As$_2$,"A series of layered (Sr$_{1-x}$K$_x$)Fe$_2$As$_2$ compounds with nominal x=0
to 0.40 are synthesized by solid state reaction method. Similar to other parent
compounds of iron-based pnictide superconductors, the pure SrFe$_2$As$_2$ shows
a strong resistivity anomaly near 210 K, which was ascribed to the
spin-density-wave instability. The anomaly temperature is much higher than
those observed in LaOFeAs and BaFe$_2$As$_2$, the two prototype parent
compounds with ZrCuSiAs- and ThCr$_2$Si$_2$-type structures. K-doping strongly
suppresses this anomaly and induces superconductivity. Like in the case of
K-doped BaFe$_2$As$_2$, sharp superconducting transitions at T$_c\sim$38 K was
observed. We performed the Hall coefficient measurement, and confirmed that the
dominant carriers are hole-type. The carrier density is enhanced by a factor of
3 in comparison to F-doped LaOFeAs superconductor.",0806.1209v1
2008-06-10,An Experimental and Theoretical Study of the Variation of 4f Hybridization Across the La1-xCexIn3 Series,"Crystal structures of a series of La1-xCexIn3 (x = 0.02, 0.2, 0.5, or 0.8)
intermetallic compounds have been investigated by both neutron and X-ray
diffraction, and their physical properties have been characterized by magnetic
susceptibility and specific heat measurements. Our results emphasize atypical
atomic displacement parameters (ADP) for the In and the rare-earth sites.
Depending on the x value, the In ADP presents either an ""ellipsoidal""
elongation (La-rich compounds) or a ""butterfly-like"" distortion (Ce-rich
compounds). These deformations have been understood by theoretical techniques
based on the band theory and are the result of hybridization between conduction
electrons and 4f-electrons.",0806.1756v1
2008-06-16,Antiferromagnetic transition in EuFe$_2$As$_2$: A possible parent compound for superconductors,"Ternary iron arsenide EuFe$_2$As$_2$ with ThCr$_2$Si$_2$-type structure has
been studied by magnetic susceptibility, resistivity, thermopower, Hall and
specific heat measurements. The compound undergoes two magnetic phase
transitions at about 200 K and 20 K, respectively. The former was found to be
accompanied with a slight drop in magnetic susceptibility (after subtracting
the Curie-Weiss paramagnetic contribution), a rapid decrease in resistivity, a
large jump in thermopower and a sharp peak in specific heat with decreasing
temperature, all of which point to a spin-density-wave-like antiferromagnetic
transition. The latter was proposed to be associated with an A-type
antiferromagnetic ordering of Eu$^{2+}$ moments. Comparing with the physical
properties of the iso-structural compounds BaFe$_2$As$_2$ and SrFe$_2$As$_2$,
we expect that superconductivity could be induced in EuFe$_2$As$_2$ through
appropriate doping.",0806.2591v2
2008-06-16,Electronic structure and exotic exchange splitting in spin-density-wave states of BaFe$_2$As$_2$,"The magnetic properties in the parent compounds are often intimately related
to the microscopic mechanism of superconductivity. Here we report the first
direct measurements on the electronic structure of a parent compound of the
newly discovered iron-based superconductor, BaFe$_2$As$_2$, which provides a
foundation for further studies. We show that the energy of the spin density
wave (SDW) in BaFe$_2$As$_2$ is lowered through exotic exchange splitting of
the band structure, rather than Fermi surface nesting of itinerant electrons.
This clearly demonstrates that a metallic SDW state could be solely induced by
interactions of local magnetic moments, resembling the nature of
antiferromagnetic order in cuprate parent compounds.",0806.2627v2
2008-06-17,Crystal growth of copper-rich ytterbium compounds: The predicted giant unit cell structures YbCu4.4 and YbCu4.25,"Two new phases YbCu4.4 and YbCu4.25 are found as a result of careful phase
diagram investigations. Between the congruent and peritectic formation of
YbCu4.5 and YbCu3.5, respectively, the phases YbCu4.4 and YbCu4.25 are formed
peritectically at 934(2)degC and 931(3)degC. Crystal growth was realised using
a Bridgman technique and single crystalline grains of about 50-100 10^{-6}m
were analyzed by electron diffraction and single crystal X-ray diffraction. Due
to the only slight differences in both compositions and formation temperatures
the growth of larger single crystals of a defined superstructure is
challenging. The compounds YbCu4.4 and YbCu4.25 fit in Cerny`s (J. Solid State
Chem. 174 (2003) 125) building principle {(RECu5)n(RECu2)} where RE = Yb with n
= 4 and 3. YbCu4.4 and YbCu4.25 base on AuBe5/MgCu2-type substructures and
contain approximately 4570 and 2780 atoms per unit cell. The new phases close
the gap in the series of known copper-rich rare earth compounds for n = 1, 2
(DyCu3.5, DyCu4.0) and n = 5 (YbCu4.5, DyCu4.5).",0806.2778v1
2008-06-24,On the importance of the electron-phonon coupling function on the superconducting transition temperature in dodecaboride superconductors: A comparison of LuB12 with ZrB12,"We report a detailed study of specific heat, electrical resistivity and
optical spectroscopy in the superconducting boride LuB12 (Tc = 0.4 K) and
compare it to the higher Tc compound ZrB12 (Tc = 6 K). Both compounds have the
same structure based on enclosed metallic Lu or Zr ions in oversized boron
cages. The infrared reflectivity and ellipsometry in the visible range allow us
to extract the optical conductivity from 6 meV to 4 eV in the normal state from
20 to 280 K. By extracting the superconducting properties, phonon density of
states and electron-phonon coupling function from these measurements we discuss
the important factors governing Tc and explain the difference between the two
compounds. The phonon density of states seems to be insignificantly modified by
substitution of Zr with Lu. However, the soft vibrations of the metal ions in
boron cages, responsible for the relatively high Tc in ZrB12, have almost no
contribution to the electron-phonon coupling in LuB12.",0806.3850v1
2008-07-15,LiFeAs: An Intrinsic FeAs-based Superconductor with Tc = 18K,"The synthesis and properties of LiFeAs, a high-Tc Fe-based superconducting
stoichiometric compound, are reported. Single crystal x-ray studies reveal that
it crystallizes in the tetragonal PbFCl type (P4/nmm) with a=3.7914(7) A and
c=6.364(2) A. Unlike the known isoelectronic undoped intrinsic FeAs compounds,
LiFeAs does not show any spin-density wave behavior but exhibits
superconductivity at ambient pressures without chemical doping. It exhibits a
respectable transition temperature of Tc=18 K with electronlike carriers and a
very high critical field, Hc2(0)>80 T. LiFeAs appears to be the chemical
equivalent of the infinite layered compound of the high-Tc cuprates.",0807.2274v2
2008-07-27,"Density functional study of FeS, FeSe and FeTe: Electronic structure, magnetism, phonons and superconductivity","We report density functional calculations of the electronic structure, Fermi
surface, phonon spectrum, magnetism and electron-phonon coupling for the
superconducting phase FeSe, as well as the related compounds FeS and FeTe. We
find that the Fermi surface structure of these compounds is very similar to
that of the Fe-As based superconductors, with cylindrical electron sections at
the zone corner, cylindrical hole surface sections, and depending on the
compound, other small hole sections at the zone center. As in the Fe-As based
materials, these surfaces are separated by a 2D nesting vector at
($\pi$,$\pi$). The density of states, nesting and Fermi surface size increase
going from FeSe to FeTe. Both FeSe and FeTe show spin density wave ground
states, while FeS is close to an instability. In a scenario where
superconductivity is mediated by spin fluctuations at the SDW nesting vector,
the strongest superconductor in this series would be doped FeTe.",0807.4312v2
2008-08-15,X-ray absorption spectroscopy measurement on the LaO1-xFxFeAs system,"Results of Fe K-, As K-, and La L3-edge x-ray absorption near edge structure
(XANES) measurements on LaO1-xFxFeAs compounds are presented. The Fe K- edge
exhibits a chemical shift to lower energy, near edge feature modifications, and
pre-edge feature suppression as a result of F substitution for O. The former
two changes provide evidence of electron charge transfer to the Fe sites and
the latter directly supports the delivery of this charge into the Fe-3d
orbitals. The As K- edge measurements show spectral structures typical of
compounds with planes of transition-metal tetrahedrally coordinated to p-block
elements as is illustrated by comparison to other such materials. The
insensitivity of the As-K edge to doping, along with the strong Fe-K doping
response, is consistent with band structure calculations showing essentially
pure Fe-d character near the Fermi energy in these materials. The energy of the
continuum resonance feature above the La-L3 edge is shown to be quantitatively
consistent with the reported La-O inter-atomic separation and with other oxide
compounds containing rare earth elements.",0808.2134v2
2008-08-19,Possible Superconductivity in Fe-Sb Based Materials: Density Functional Study of LiFeSb,"We investigate the electronic and other properties of the hypothetical
compound LiFeSb in relation to superconducting LiFeAs and FeSe using density
functional calculations. The results show that LiFeSb in the LiFeAs structure
would be dynamically stable in the sense of having no unstable phonon modes,
and would have very similar electronic and magnetic properties to the layered
Fe based superconductors. Importantly, a very similar structure for the Fermi
surface and a spin density wave related to but stronger than that in the
corresponding As compound is found. These results are indicative of possible
superconductivity analogous to the Fe-As based compounds if the spin density
wave can be suppressed by doping or other means. Prospects for synthesizing
this material in pure form or in solid solution with FeTe are discussed.",0808.2653v3
2008-09-30,Linear Universal Decoding for Compound Channels: a Local to Global Geometric Approach,"Over discrete memoryless channels (DMC), linear decoders (maximizing additive
metrics) afford several nice properties. In particular, if suitable encoders
are employed, the use of decoding algorithm with manageable complexities is
permitted. Maximum likelihood is an example of linear decoder. For a compound
DMC, decoders that perform well without the channel's knowledge are required in
order to achieve capacity. Several such decoders have been studied in the
literature. However, there is no such known decoder which is linear. Hence, the
problem of finding linear decoders achieving capacity for compound DMC is
addressed, and it is shown that under minor concessions, such decoders exist
and can be constructed. This paper also develops a ""local geometric analysis"",
which allows in particular, to solve the above problem. By considering very
noisy channels, the original problem is reduced, in the limit, to an inner
product space problem, for which insightful solutions can be found. The local
setting can then provide counterexamples to disproof claims, but also, it is
shown how in this problem, results proven locally can be ""lifted"" to results
proven globally.",0809.5217v1
2008-10-15,From protein binding to pharmacokinetics: a novel approach to active drug absorption prediction,"Due to inherent complexity active transport presents a landmark hurdle for
oral absorption properties prediction. We present a novel approach
carrier-mediated drug absorption parameters calculation based on entirely
different paradigm than QSPR. We capitalize on recently emerged ideas that
molecule activities against a large protein set can be used for prediction of
biological effects and performed a large scale numerical docking of drug-like
compounds to a large diversified set of proteins. As a result we identified for
the first time a protein, binding to which correlates well with the intestinal
permeability of many actively absorbed compounds. Although the protein is not a
transporter, we speculate that it has the binding site force field similar to
that of an important intestinal transporter. The observation helped us to
improve the passive absorption model by adding non-liner flux associated with
the transporting protein to obtain a quantitative model of active transport.
This study demonstrates that binding data to a sufficiently representative set
of proteins can serve as a basis for active absorption prediction for a given
compound.",0810.2617v1
2008-10-24,Phonon dynamics in Sr0.6K0.4Fe2As2 and Ca0.6Na0.4Fe2As2,"We report inelastic neutron scattering measurements of the phonon
density-of-states in superconducting Sr0.6K0.4Fe2As2 (Tc=30 K) and
Ca0.6Na0.4Fe2As2 (Tc=18 K). Compared with the parent compound BaFe2As2 doping
affects mainly the lower and intermediate frequency part of the vibrations.
Mass effects and lattice contraction cannot explain these changes. A lattice
dynamical model has been used to identify the character of the various phonon
bands. Softening of phonon modes below 10 meV has been observed in both samples
on cooling from 300 K to 140 K. In the Ca doped compound the softening amounts
to about 1 meV while for the Sr doped compound the softening is about 0.5 meV.
There is no appreciable change in the phonon density of states when crossing
Tc.",0810.4498v1
2008-12-29,"Magnetic structures of quaternary intermetallic borocarbides RCo2B2C (R=Dy, Ho, Er)","The magnetic structures of the title compounds have been studied by neutron
diffraction. In contrast to the isomorphous RNi2B2C compounds wherein a variety
of exotic incommensurate modulated structures has been observed, the magnetic
structure of ErCo2B2C is found to be collinear antiferromagnet with
k=((1/2),0,(1/2)) while that of HoCo2B2C and DyCo2B2C are observed to be simple
ferromagnets. For all studied compounds, the moments are found to be confined
within the basal plane and their magnitudes are in good agreement with the
values obtained from the low-temperature isothermal magnetization measurements.
The absence of modulated magnetic structures in the RCo2B2C series (for
ErCo2B2C, verified down to 50 mK) is attributed to the quenching of the Fermi
surface nesting features.",0812.4867v1
2009-02-14,"ARPES studies of the electronic structure of LaOFe(P,As)","We report a comparison study of LaOFeP and LaOFeAs, two parent compounds of
recently discovered iron-pnictide superconductors, using angle-resolved
photoemission spectroscopy. Both systems exhibit some common features that are
very different from well-studied cuprates. In addition, important differences
have also been observed between these two ferrooxypnictides. For LaOFeP,
quantitative agreement can be found between our photoemission data and the LDA
band structure calculations, suggesting that a weak coupling approach based on
an itinerant ground state may be more appropriate for understanding this new
superconducting compound. In contrast, the agreement between LDA calculations
and experiments in LaOFeAs is relatively poor, as highlighted by the unexpected
Fermi surface topology around (pi,pi). Further investigations are required for
a comprehensive understanding of the electronic structure of LaOFeAs and
related compounds.",0902.2503v1
2009-02-16,Lattice effects in the La$_{\rm 2-x}$Sr$_{\rm x}$CuO$_{\rm 4}$ compounds,"Systematic Raman studies on several cuprates (YBa$_{\rm 2}$Cu$_{\rm
3}$O$_{\rm x}$, YBa$_{\rm 2}$Cu$_{\rm 4}$O$_{\rm 8}$ or Bi$_{\rm 2}$Sr$_{\rm
2}$CaCu$_{\rm 2}$O$_{\rm 8}$) have shown that at optimal doping the compounds
are at the edge of lattice instability; once this level is exceeded, by means
of doping or applying external hydrostatic pressure, the changes in the
transition temperature are accompanied by spectral modifications. There are
strong indications that the reduction in T$_{\rm c}$ is correlated with a
separation into nanoscale phases, which involve the oxygen atoms of the
CuO$_{\rm 2}$ planes. In this work, modifications with doping in the Raman
spectra of the La$_{\rm 2-x}$Sr$_{\rm x}$CuO$_{\rm 4}$ compound are presented,
which show that spin or charge ordering is coupled with lattice distortions in
the whole doping region.",0902.2664v1
2009-02-23,Superconductivity at 14K in the Co-doped SmFe0.9Co0.1AsO,"We report superconductivity in the SmFe0.9Co0.1AsO system being prepared by
most easy and versatile single step solid-state reaction route. The parent
compound SmFeAsO is non-superconducting but shows the spin density wave (SDW)
like antiferromagnetic ordering at around 140K. To destroy the
antiferromagnetic ordering and to induce the superconductivity in the parent
system, the Fe2+ is substituted partially by Co3+. Superconductivity appears in
SmFe0.9Co0.1AsO system at around 14K. The Co doping suppresses the SDW anomaly
in the parent compound and induces the superconductivity. Magnetization
measurements show clearly the onset of superconductivity with Tcdia at 14K. The
isothermal magnetization measurements exhibit the lower critical fields (Hc1)
to be around 200Oe at 2 K. The bulk superconductivity of the studied
SmFe0.9Co0.1AsO sample is further established by open diamagnetic M(H) loops at
2, and 5K. Normal state (above Tc) linear isothermal magnetization M(H) plots
excluded presence of any ordered magnetic impurity in the studied compound.",0902.3894v2
2009-02-24,Network of two-Chinese-character compound words in Japanese language,"Some statistical properties of a network of two-Chinese-character compound
words in Japanese language are reported. In this network, a node represents a
Chinese character and an edge represents a two-Chinese-character compound word.
It is found that this network has properties of ""small-world"" and ""scale-free.""
A network formed by only Chinese characters for common use ({\it joyo-kanji} in
Japanese), which is regarded as a subclass of the original network, also has
small-world property. However, a degree distribution of the network exhibits no
clear power law. In order to reproduce disappearance of the power-law property,
a model for a selecting process of the Chinese characters for common use is
proposed.",0902.4060v1
2009-02-25,"Magnetic excitations in the spinel compound Li$_x$[Mn$_{1.96}$Li$_{0.04}$]O$_4$ (x= 0.2, 0.6, 0.8, 1.0): how a classical system can mimic quantum critical scaling","We present neutron scattering results on the magnetic excitations in the
spinel compounds Li$_x$[Mn$_{1.96}$Li$_{0.04}$]O$_4$ (x= 0.2, 0.6, 0.8, 1.0).
We show that the dominant excitations below T ~ 70 K are determined by clusters
of Mn^4+ ions, and that these excitations mimic the E/T-scaling found in
quantum critical systems that also harbor magnetic clusters, such as
CeRu$_{0.5}$Fe$_{1.5}$Ge$_2$. We argue that our results for this classical
spinel compound show that the unusual response at low temperatures as observed
in quantum critical systems is (at least) partially the result of the
fragmentation of the magnetic lattice into smaller units. This fragmentation in
quantum critical systems is the direct and unavoidable result of intrinsic
disorder.",0902.4412v1
2009-03-04,"Resistivity Anisotropy of $AE$Fe$_2$As$_2$ ($AE$ =Ca, Sr, Ba): direct versus Montgomery technique measurements","The anisotropy of electrical resistivity was measured in parent compounds of
the iron-arsenic high temperature superconductors, AEFe2As2 with Alkali Earth
elements AE=Ca,Sr, Ba. Measurements were performed using both the Montgomery
technique and direct resistivity measurements on samples cut along principal
crystallographic directions. The anisotropy ratio \gamma_\rho=\rho_c/\rho_a is
well below 10 for all compounds in the whole temperature range studied (4 to
300 K), in notable contrast to previous reports. The anisotropy at room
temperature increases from about 2 in Ca, to about 4 in Sr and Ba. In all
compounds the resistivity ratio decreases on cooling through the
structural/antiferromagnetic transition temperature T_{SM}, with the change
mainly coming from stronger variation in \rho_a as compared with \rho_c. This
suggests that the transitions stronger affect the two-dimensional parts of the
Fermi surface. We compare our experimental observations with band structure
calculations, and find similar trend in the evolution of anisotropy with the
size of AE ion. Our results show that the electronic structure of the iron
pnictides has large contribution from three-dimensional areas of the Fermi
surface.",0903.0820v1
2009-03-30,"New iron-based arsenide oxides (Fe2As2)(Sr4M2O6)(M = Sc, Cr)","We have discovered new layered oxyarsenides (Fe2As2)(Sr4M2O6) (M = Sc, Cr:
M-22426). These materials are isostructural with (Fe2P2)(Sr4Sc2O6), which was
found in our previous study. The new compounds are tetragonal with a space
group of P4/nmm and consist of the anti-fluorite type FeAs layer and
perovskite-type blocking layer. The lattice constants are a = 4.050 A, c =
15.809 A for M = Sc and a = 3.918 A, c = 15.683 A for M = Cr. These compounds
have long interlayer Fe-Fe distances corresponding to the c-axis length, the
15.8 A in Sc-22426 is the longest in the iron-based oxypnictide systems.
Chemical flexibility of the perovskite block in this system was probed by
chromium containing (Fe2As2)(Sr4Cr2O6). Different trends were found in bond
angle and bond length of the new oxypnictides compared to the reported systems,
such as REFePnO. Absence of superconductivity in these compounds is considered
to be due to insufficient carrier concentration as in the case of undoped
REFeAsO.",0903.5124v3
2009-03-31,Structure and Physical properties of New layered oxypnictides $Sr_4Sc_2O_6M_2As_2$ (M=Fe and Co),"We have successfully prepared the new layered oxypnictides
$Sr_4Sc_2O_6M_2As_2$ (M=Fe and Co). They adopt the tetragonal structure, being
the same as that of $Sr_4Sc_2O_6Fe_2P_2$. The lattice constants are a=0.4045 nm
and c= 0.5802 nm for M=Fe, and a=0.4045 nm and c=1.5695 nm for M=Co,
respectively. Their transport and magnetic properties have been systematically
studied. The temperature dependence of Hall coefficient and thermoelectric
powder for $Sr_4Sc_2O_6Fe_2As_2$ compound show complicated behavior, similar to
that of iron-based parent compounds LnOFeAs and $BaFe_2As_2$. It suggests that
the $Sr_4Sc_2O_6Fe_2As_2$ could be considered a new parent compound as
iron-based superconductors.",0903.5484v1
2009-06-08,$\mathcal{G}$-SELC: Optimization by sequential elimination of level combinations using genetic algorithms and Gaussian processes,"Identifying promising compounds from a vast collection of feasible compounds
is an important and yet challenging problem in the pharmaceutical industry. An
efficient solution to this problem will help reduce the expenditure at the
early stages of drug discovery. In an attempt to solve this problem, Mandal, Wu
and Johnson [Technometrics 48 (2006) 273--283] proposed the SELC algorithm.
Although powerful, it fails to extract substantial information from the data to
guide the search efficiently, as this methodology is not based on any
statistical modeling. The proposed approach uses Gaussian Process (GP) modeling
to improve upon SELC, and hence named $\mathcal{G}$-SELC. The performance of
the proposed methodology is illustrated using four and five dimensional test
functions. Finally, we implement the new algorithm on a real pharmaceutical
data set for finding a group of chemical compounds with optimal properties.",0906.1433v1
2009-07-02,Thermal expansion of the spin-1/2 Heisenberg-chain compound Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$,"Compounds containing magnetic subsystems representing simple model spin
systems with weak magnetic coupling constants are ideal candidates to test
theoretical predictions for the generic behavior close to quantum phase
transitions. We present measurements of the thermal expansion and
magnetostriction of the spin-1/2-chain compound copper pyrazine dinitrate
Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$. Of particular interest is the low-temperature
thermal expansion close to the saturation field $H_c \simeq 13.9 \mathrm{T}$,
which defines a quantum phase transition from the gapless Luttinger liquid
state to the fully saturated state with a finite excitation gap. We observe a
sign change of the thermal expansion for the different ground states, and at
the quantum critical point $H_c$ the low-temperature expansion approaches a
$1/\sqrt{T}$ divergence. Thus, our data agree very well with the expected
quantum critical behaviour.",0907.0400v1
2009-07-16,Dependence of Band Renormalization Effect on the Number of Copper-oxide Layers in Tl-based Copper-oxide Superconductor using Angle-resolved Photoemission Spectroscopy,"Here we report the first angle-resolved photoemission measurement on nearly
optimally-doped multi-layer Tl-based superconducting cuprates (Tl-2212 and
Tl-1223) and a comparison study to single layer (Tl-2201) compound. A ""kink"" in
the band dispersion is found in all three compounds but exhibits different
momentum dependence for the single layer and multi-layer compounds, reminiscent
to that of Bi-based cuprates. This layer number dependent renormalization
effect strongly implies that the spin resonance mode is unlikely responsible
for the dramatic renormalization effect near the antinodal region.",0907.2747v1
2009-07-16,"Anisotropic thermal expansion of AEFe2As2 (AE = Ba, Sr, Ca) single crystals","We report anisotropic thermal expansion of the parent, AEFe2As2 (AE = Ba, Sr,
and Ca), compounds. Above the structural/antiferromagnetic phase transition
anisotropy of the thermal expansion coefficients is observed, with the
coefficient along the a-axis being significantly smaller than the coefficient
for the c-axis. The high temperature (200 K < T < 300 K) coefficients
themselves have similar values for the compounds studied. The sharp anomalies
associated with the structural/antiferromagnetic phase transitions are clearly
seen in the thermal expansion measurements. For all three pure compounds the
""average"" a-value increases and the c-lattice parameter decreases on warming
through the transition with the smallest change in the lattice parameters
observed for SrFe2As2. The data are in general agreement with the literature
data from X-ray and neutron diffraction experiments.",0907.2936v1
2009-08-01,Origin of infrared peaks in the optical conductivity of ytterbium compounds,"We have calculated optical conductivity [$\sigma(\omega)$] spectra of
ytterbium compounds (YbAl$_3$, YbAl$_2$, YbCu$_2$Si$_2$, YbNi$_2$Ge$_2$,
YbInCu$_4$, YbRh$_2$Si$_2$, YbIr$_2$Si$_2$, and YbB$_{12}$) based on the direct
interband transition derived from first-principle band calculation and compared
the results with the experimentally obtained $\sigma(\omega)$ spectra. The
spectral feature of a peak in the middle-infrared region (mid-IR peak) and a
shoulder structure in the far-infrared region (far-IR shoulder) in the
experimental $\sigma(\omega)$ spectra can be described by the band calculation
with a common renormalization factor. This result indicates that the infrared
spectra of Yb compounds originate from the interband transition from the Yb
$4f$ state but that the Yb $4f$ state shifts to the Fermi level with strong
electron correlation.",0908.0048v1
2009-08-12,Universal $\sqrt{2}\times\sqrt{2}$ structure and short-range charge order at the surfaces of BaFe$_{2-x}$Co$_{x}$As$_{2}$ compounds with various Co doping levels,"The structure and electronic order at the cleaved (001) surfaces of the
newly-discovered pnictide superconductors BaFe$_{2-x}$Co$_{x}$As$_{2}$ with x
ranging from 0 to 0.32 are systematically investigated by scanning tunneling
microscopy. A $\sqrt{2}\times\sqrt{2}$ surface structure is revealed for all
the compounds, and is identified to be Ba layer with half Ba atoms lifted-off
by combination with theoretical simulation. A universal short-range charge
order is observed at this $\sqrt{2}\times\sqrt{2}$ surface associated with an
energy gap of about 30 meV for all the compounds.",0908.1710v1
2009-09-16,"Superconductivity at 39 K in New Iron Pnictide Oxide (Fe2As2)(Sr4(Mg,Ti)2O6)","We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6)
(M = Sc, Cr), which was found in our previous study. The structure of this
compound is tetragonal with a space group of P4/nmm and consists of the
anti-fluorite type FeAs and perovskite-type blocking layers. The lattice
constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). In both
magnetization and resistivity measurements, this compound exhibits
superconductivity below 10 K. Moreover, ratio of Mg and Ti in this compound can
be changed toward Ti-rich composition. (Fe2As2)(Sr4Mg1-xTi1+xO6) phase is
obtained at 0 < x as a main phase, and Tc and superconducting volume fraction
increase with increasing x. The highest Tc(onset) was confirmed at 39 K for x =
0.6 in resistivity measurement.",0909.2945v3
2009-10-20,"Sharp fall of electrical resistance for a small application of magnetic field on a metastable form of a compound, Tb5Si3, under pressure","We report an unusual sensitivity of electrical resistivity (rho) to an
application of a small magnetic field in an intermetallic compound, Tb5Si3,
under pressure. In this compound, there is a magnetic field-induced first-order
magnetic transition at 1.8 K. Under pressure, there is a metastable magnetic
phase after reducing the field to zero. This metastable phase is relatively of
higher rho and interestingly a small magnetic field (less than 2 kOe) in the
reverse direction results in a sharp fall of rho to restore virgin state rho.
The present finding could be relevant to spintronic applications.",0910.3794v1
2009-12-11,"Magnetic and electrical transport anomalies in RMAs2 (R= Pr and Sm, M= Ag and Au)","The results of magnetization, heat-capacity, and electrical resistivity (rho)
studies of the compounds, RMAs2 (R= Pr and Sm; M= Ag, Au), crystallizing in
HfCuSi2-derived structure are reported. PrAgAs2 orders antiferromagnetically at
T_N= 5 K. The Au analogue, however, does not exhibit long range magnetic order
down to 1.8 K. We infer that this is due to subtle differences in their
crystallographic features, particularly noting that both the Sm compounds with
identical crystal structure as that of former order magnetically nearly at the
same temperature (about 17 K). It appears that, in PrAgAs2, SmAgAs2, and
SmAuAs2, there is an additional magnetic transition at a lower temperature, as
though the similarity in the crystal structure results in similarities in
magnetism as well. The rho for PrAgAs2 and PrAuAs2 exhibits negative
temperature coefficient in some temperature range in the paramagnetic state.
SmAuAs2 exhibits magnetic Brillouin-zone gap effect in rho at T_N, while
SmAgAs2 shows a well-defined broad minimum well above T_N around 45 K. Thus,
these compounds reveal interesting magnetic and transport properties.",0912.2277v1
2009-12-17,"Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFe$_2$As$_2$, an Fe-pnictide superconductor parent compound","Using angle resolved photoemission it is shown that the low lying electronic
states of the iron pnictide parent compound EuFe$_2$As$_2$ are strongly
modified in the magnetically ordered, low temperature, orthorhombic state
compared to the tetragonal, paramagnetic case above the spin density wave
transition temperature. Back-folded bands, reflected in the orthorhombic/
anti-ferromagnetic Brillouin zone boundary hybridize strongly with the
non-folded states, leading to the opening of energy gaps. As a direct
consequence, the large Fermi surfaces of the tetragonal phase fragment, the low
temperature Fermi surface being comprised of small droplets, built up of
electron and hole-like sections. These high resolution ARPES data are therefore
in keeping with quantum oscillation and optical data from other undoped
pnictide parent compounds.",0912.3434v1
2010-01-09,Correlation induced half-metallicity in a ferromagnetic single-layered compound: Sr$_2$CoO$_4$,"The electronic and magnetic properties of Sr$_2$CoO$_4$ compound have been
studied using $\emph{ab initio}$ electronic structure calculations. As opposed
to GGA calculation, which gives ferromagnetic metallic solution, GGA+$U$
calculations provide two kind of ferromagnetic solutions: (i) half-metallic and
(ii) metallic. The half-metallic solution is a ground state of the system and
the metallic one is a metastable state. The strong hybridization between Co
3$d$ and O 2$p$ orbitals decides the electronic and magnetic properties of the
compound. The total magnetic moment per formula unit is found to be $\sim$ 3
$\mu_B$ ($S$ = 3/2). Our calculations give the magnetocrystalline anisotropy
energy of $\sim$ 2.7 meV, which provides a good description of experimentally
observed large magnetocrystalline anisotropy. The Heisenberg exchange
parameters up to fourth nearest neighbours are also calculated. The mean-field
theory gives the $T_C$ = 887 K. The possible physical implications of the
ferromagnetic half-metallic ground state are also discussed.",1001.1405v1
2010-01-14,Segmentation algorithm for non-stationary compound Poisson processes,"We introduce an algorithm for the segmentation of a class of regime switching
processes. The segmentation algorithm is a non parametric statistical method
able to identify the regimes (patches) of the time series. The process is
composed of consecutive patches of variable length, each patch being described
by a stationary compound Poisson process, i.e. a Poisson process where each
count is associated to a fluctuating signal. The parameters of the process are
different in each patch and therefore the time series is non stationary. Our
method is a generalization of the algorithm introduced by Bernaola-Galvan, et
al., Phys. Rev. Lett., 87, 168105 (2001). We show that the new algorithm
outperforms the original one for regime switching compound Poisson processes.
As an application we use the algorithm to segment the time series of the
inventory of market members of the London Stock Exchange and we observe that
our method finds almost three times more patches than the original one.",1001.2549v2
2010-02-10,Heat conductivity of the spin-Peierls compounds TiOCl and TiOBr,"We report experimental results on the heat conductivity \kappa of the S=1/2
spin chain compounds TiOBr and TiOCl for temperatures 5K<T<300K and magnetic
fields up to 14. Surprisingly, we find no evidence of a significant magnetic
contribution to \kappa, which is in stark contrast to recent results on S=1/2
spin chain cuprates. Despite this unexpected result, the thus predominantly
phononic heat conductivity of these spin-Peierls compounds exhibits a very
unusual behavior. In particular, we observe strong anomalies at the phase
transitions Tc1 and Tc2. Moreover, we find an overall but anisotropic
suppression of \kappa in the intermediate phase which extends even to
temperatures higher than Tc2. An external magnetic field causes a slight
downshift of the transition at Tc1 and enhances the suppression of \kappa up to
Tc2. We interprete our findings in terms of strong spin-phonon coupling and
phonon scattering arising from spin-driven lattice distortions.",1002.2112v1
2010-02-28,Compound Markov counting processes and their applications to modeling infinitesimally over-dispersed systems,"We propose an infinitesimal dispersion index for Markov counting processes.
We show that, under standard moment existence conditions, a process is
infinitesimally (over-) equi-dispersed if, and only if, it is simple
(compound), i.e. it increases in jumps of one (or more) unit(s), even though
infinitesimally equi-dispersed processes might be under-, equi- or
over-dispersed using previously studied indices. Compound processes arise, for
example, when introducing continuous-time white noise to the rates of simple
processes resulting in Levy-driven SDEs. We construct multivariate
infinitesimally over-dispersed compartment models and queuing networks,
suitable for applications where moment constraints inherent to simple processes
do not hold.",1003.0173v1
2010-03-08,Orbital-transverse density-wave instabilities in iron-based superconductors,"Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFe$_2$As$_2$ (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional $d_{xy}$-like Fermi surface around (0,0) being only in 1111
parent compounds.",1003.1660v2
2010-03-13,Fermi surface evolution through a heavy fermion superconductor-to-antiferromagnet transition: de Haas-van Alphen effect in Cd-substituted CeCoIn$_5$,"We report the results of de-Haas-van-Alphen (dHvA) measurements in Cd doped
CeCoIn$_5$ and LaCoIn$_5$. Cd doping is known to induce an antiferromagnetic
order in the heavy fermion superconductor CeCoIn$_5$, whose effect can be
reversed with applied pressure. We find a slight but systematic change of the
dHvA frequencies with Cd doping in both compounds, reflecting the chemical
potential shift due to the addition of holes. The frequencies and effective
masses are close to those found in the nominally pure compounds with similar
changes apparent in the Ce and La compounds with Cd substitution. We observe no
abrupt changes to the Fermi surface in the high field paramagnetic state for $x
\sim x_c$ corresponding to the onset of antiferromagnetic ordering at H=0 in
CeCo(In$_{1-x}$Cd$_x$)$_5$. Our results rule out $f-$electron localization as
the mechanism for the tuning of the ground state in CeCoIn$_5$ with Cd doping.",1003.2720v1
2010-03-20,Electronic structure of superconducting KC$_8$ and non-superconducting LiC$_6$ graphite intercalation compounds: Evidence for a graphene-sheet-driven superconducting state,"We have performed photoemission studies of the electronic structure in
LiC$_6$ and KC$_8$, a non-superconducting and a superconducting graphite
intercalation compound, respectively. We have found that the charge transfer
from the intercalant layers to graphene layers is larger in KC$_8$ than in
LiC$_6$, opposite of what might be expected from their chemical composition. We
have also measured the strength of the electron-phonon interaction on the
graphene-derived Fermi surface to carbon derived phonons in both materials and
found that it follows a universal trend where the coupling strength and
superconductivity monotonically increase with the filling of graphene
$\pi^{\ast}$ states. This correlation suggests that both graphene-derived
electrons and graphene-derived phonons are crucial for superconductivity in
graphite intercalation compounds.",1003.3903v2
2010-05-04,NMR evidence for antiferromagnetic order in a planar 3d9/3d8 nickelate,"We report La-139 Nuclear Magnetic Resonance (NMR) data in La4Ni3O8 which
reveals the presence of antiferromagnetic order below T_N ~ 105 K. This
compound contains two-dimensional layers of NiO2 that are isostructural to the
copper oxide planes of the high temperature superconductors. This compound is
remarkable because the average Ni valence of 1.33+ for formally 2Ni1+ + Ni2+
indicates a 3d9/3d8 electronic configuration. Nickel oxides with Ni1+ valence
are rare and unstable, yet may provide new routes to high temperature
superconductivity. La4Ni3O8, with antiferromagnetic order of S=1/2 Ni1+ spins,
is analogous to the parent compounds of the cuprate superconductors. Our data
clearly reveal dramatic spectral changes and low energy antiferromagnetic
correlations associated with the onset of long range order below T_N.",1005.0435v1
2010-05-05,Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems,"We report a theoretical study of the quasiparticle lifetime and the
quasiparticle mean free path caused by inelastic electron-electron scattering
in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based
on spin-polarized calculations, which are performed within the $GW$
approximation for equiatomic and Co- and Ni-rich compounds, as well as for
their constituents. We mainly focus on the spin asymmetry of the quasiparticle
properties, which leads to the spin-filtering effect experimentally observed in
spin-dependent transport of hot electrons and holes in the systems under study.
By comparing with available experimental data on the attenuation length, we
estimate the contribution of the inelastic mean free path to the latter.",1005.0679v2
2010-05-10,Magnetic and neutron spectroscopic properties of the tetrameric nickel compound $[Mo_{12}O_{28}(μ_2-OH)_9(μ_3-OH)_3{Ni(H_2O)_3}_4] $\cdot$ 13H_2O$,"We present results of inelastic neutron scattering experiments performed for
the compound Magnetic and neutron spectroscopic properties of the tetrameric
nickel compound $[Mo_{12}O_{28}(\mu_2-OH)_9(\mu_3-OH)_3{Ni(H_2O)_3}_4] $\cdot$
13H_2O$, which is a molecular magnet with antiferromagnetically coupled Ni2+
ions forming nearly ideal tetrahedra in a diamagnetic molybdate matrix. The
neutron spectroscopic data are analyzed together with high-field magnetization
data (taken from the literature) which exhibit four steps at non-equidistant
field intervals. The experimental data can be excellently described by
antiferromagnetic Heisenberg-type exchange interactions as well as an axial
single-ion anisotropy within a distorted tetrahedron of Ni2+ ions characterized
by X-ray single-crystal diffraction. Our analysis contrasts to recently
proposed models which are based on the existence of extremely large biquadratic
(and three-ion) exchange interactions and/or on a strong field dependence of
the Heisenberg coupling parameters.",1005.1498v1
2010-05-18,Superconductivity induced by doping Rh in CaFe2-xRhxAs2,"In this paper we report the synthesis of iron-based superconductors
CaFe2-xRhxAs2 using one-step solid state reaction method, which crystallizes in
the ThCr2Si2-type structure with a space group I4/mmm. The systematic evolution
of the lattice constants demonstrates that the Fe ions are successfully
replaced by the Rh. By increasing the doping content of Rh, the
spin-density-wave (SDW) transition in the parent compound is suppressed and
superconductivity emerges. The maximum superconducting transition temperature
is found at 18.5 K with the doping level of x = 0.15. The temperature
dependence of DC magnetization confirms superconducting transitions at around
15 K. The general phase diagram was obtained and found to be similar to the
case of Rh-doping Sr122 system. Our results explicitly demonstrate the
feasibility of inducing superconductivity in Ca122 compounds by higher
d-orbital electrons doping, however, different Rh-doping effect between FeAs122
compounds and FeAs1111 systems still remains an open question.",1005.3172v2
2010-06-25,A systematic description of evaporation spectra for light and heavy compound nuclei,"To systematically describe evaporation spectra for light and heavy compound
nuclei over a large range of excitation energies, it was necessary to consider
three ingredients in the statistical model. Firstly, transmission coefficients
or barrier penetration factors for charged-particle emission are typically
taken from global fits to elastic-scattering data. However, such transmission
coefficients do not reproduce the barrier region of evaporation spectra and
reproduction of the data requires a distributions of Coulomb barriers. This is
possibly associated with large fluctuations in the compound-nucleus shape or
density profile. Secondly for heavy nuclei, an excitation-energy dependent
level-density parameter is required to describe the slope of the exponential
tails of these spectra. The level-density parameter was reduced at larger
temperatures, consistent with the expected fadeout of long-range correlation,
but the strong $A$ dependence of this effect is unexpected. Lastly to describe
the angular-momentum dependence of the level density in light nuclei at large
spins, the macroscopic rotational energy of the nucleus has to be reduced from
the values predicted with the Finite-Range Liquid-Drop model.",1006.5018v1
2010-07-01,Multiferroicity and hydrogen-bond ordering in (C2H5NH3)2CuCl4 featuring dominant ferromagnetic interactions,"We demonstrate that ethylammonium copper chloride, (C2H5NH3)2CuCl4, a member
of the hybrid perovskite family is an electrically polar and magnetic compound
with dielectric anomaly around the Curie point (247 K). We have found large
spontaneous electric polarization below this point accompanied with a color
change in the sample. The system is also ferroelectric, with large remnant
polarization (37{\mu}C/cm2) that is comparable to classical ferroelectric
compounds. The results are ascribed to hydrogen-bond ordering of the organic
chains. The coexistence of ferroelectricity and dominant ferromagnetic
interactions allows to relate the sample to a rare group of magnetic
multiferroic compounds. In such hybrid perovskites the underlying hydrogen
bonding of easily tunable organic building blocks in combination with the 3d
transition-metal layers offers an emerging pathway to engineer multifuctional
multiferroics.",1007.0099v1
2010-07-02,Spin glassiness and power law scaling in a quasi-triangular spin-1/2 compound,"We present data on the magnetic properties of two classes of layered spin
S=1/2 antiferromagnetic quasi-triangular lattice materials:
$Cu_{2(1-x)}Zn_{2x}(OH)_3NO_3$ ($0 < x < 0.65$) and its long chain organic
derivatives $Cu_{2(1-x)}Zn_{2x}(OH)_3(C_7H_{15}COO)\cdot mH_2O$ ($0 < x <
0.29$), where non-magnetic Zn substitutes Cu isostructurally. It is found that
the long-chain compounds, even in a clean system in the absence of dilution,
$x\!=\!0$, show spin-glass behavior, as evidenced by DC and AC susceptibility,
and by time dependent magnetization measurements. A striking feature is the
observation of a sharp crossover between two successive power law regimes in
the DC susceptibility above the freezing temperature. Specific heat data are
consistent with a conventional phase transition in the unintercalated
compounds, and glassy behavior in the long chain compunds.",1007.0442v1
2010-07-16,On Compound Poisson Processes Arising in Change-Point Type Statistical Models as Limiting Likelihood Ratios,"Different change-point type models encountered in statistical inference for
stochastic processes give rise to different limiting likelihood ratio
processes. In a previous paper of one of the authors it was established that
one of these likelihood ratios, which is an exponential functional of a
two-sided Poisson process driven by some parameter, can be approximated (for
sufficiently small values of the parameter) by another one, which is an
exponential functional of a two-sided Brownian motion. In this paper we
consider yet another likelihood ratio, which is the exponent of a two-sided
compound Poisson process driven by some parameter. We establish, that similarly
to the Poisson type one, the compound Poisson type likelihood ratio can be
approximated by the Brownian type one for sufficiently small values of the
parameter. We equally discuss the asymptotics for large values of the parameter
and illustrate the results by numerical simulations.",1007.2758v1
2010-07-23,"Helical spin-waves, magnetic order, and fluctuations in the langasite compound Ba3NbFe3Si2O14","We have investigated the spin fluctuations in the langasite compound
Ba3NbFe3Si2O14 in both the ordered state and as a function of temperature. The
low temperature magnetic structure is defined by a spiral phase characterized
by magnetic Bragg peaks at q=(0,0,tau ~ 1/7) onset at TN=27 K as previously
reported by Marty et al. The nature of the fluctuations and temperature
dependence of the order parameter is consistent with a classical second order
phase transition for a two dimensional triangular antiferromagnet. We will show
that the physical properties and energy scales including the ordering
wavevector, Curie-Weiss temperature, and the spin-waves can be explained
through the use of only symmetric exchange constants without the need for the
Dzyaloshinskii-Moriya interaction. This is accomplished through a set of
``helical"" exchange pathways along the c direction imposed by the chiral
crystal structure and naturally explains the magnetic diffuse scattering which
displays a strong vector chirality up to high temperatures well above the
ordering temperature. This illustrates a strong coupling between magnetic and
crystalline chirality in this compound.",1007.4216v1
2010-09-08,Multi-Orbital Molecular Compound (TTM-TTP)I_3: Effective Model and Fragment Decomposition,"The electronic structure of the molecular compound (TTM-TTP)I_3, which
exhibits a peculiar intra-molecular charge ordering, has been studied using
multi-configuration ab initio calculations. First we derive an effective
Hubbard-type model based on the molecular orbitals (MOs) of TTM-TTP; we set up
a two-orbital Hamiltonian for the two MOs near the Fermi energy and determine
its full parameters: the transfer integrals, the Coulomb and exchange
interactions. The tight-binding band structure obtained from these transfer
integrals is consistent with the result of the direct band calculation based on
density functional theory. Then, by decomposing the frontier MOs into two
parts, i.e., fragments, we find that the stacked TTM-TTP molecules can be
described by a two-leg ladder model, while the inter-fragment Coulomb energies
are scaled to the inverse of their distances. This result indicates that the
fragment picture that we proposed earlier [M.-L. Bonnet et al.: J. Chem. Phys.
132 (2010) 214705] successfully describes the low-energy properties of this
compound.",1009.1503v2
2010-10-08,A new method for obtaining sharp compound Poisson approximation error estimates for sums of locally dependent random variables,"Let $X_1,X_2,...,X_n$ be a sequence of independent or locally dependent
random variables taking values in $\mathbb{Z}_+$. In this paper, we derive
sharp bounds, via a new probabilistic method, for the total variation distance
between the distribution of the sum $\sum_{i=1}^nX_i$ and an appropriate
Poisson or compound Poisson distribution. These bounds include a factor which
depends on the smoothness of the approximating Poisson or compound Poisson
distribution. This ""smoothness factor"" is of order $\mathrm{O}(\sigma ^{-2})$,
according to a heuristic argument, where $\sigma ^2$ denotes the variance of
the approximating distribution. In this way, we offer sharp error estimates for
a large range of values of the parameters. Finally, specific examples
concerning appearances of rare runs in sequences of Bernoulli trials are
presented by way of illustration.",1010.1625v1
2010-10-29,Interplay of Spin-Orbit Interaction and Electron Correlation on the Van Vleck Susceptibility in Transition Metal Compounds,"We have studied the effects of electron correlation on Van Vleck
susceptibility ($\chi_{\rm{VV}}$) in transition metal compounds. A typical
crossover behavior is found for the correlation effect on $\chi_{\rm{VV}}$ as
sweeping spin-orbit interaction, $\lambda$. For a small $\lambda$, orbital
fluctuation plays a dominant role in the correlation enhancement of
$\chi_{\rm{VV}}$; however, the enhancement rate is rather small. In contrast,
for an intermediate $\lambda$, $\chi_{\rm{VV}}$ shows a substantial increase,
accompanied by the development of spin fluctuation. We will discuss the
behavior of $\chi_{\rm{VV}}$ in association with the results of Knight-shift
experiments on Sr$_2$RuO$_4$ and an anomalously large magnetic susceptibility
observed for $5d$ Ir compounds.",1010.6133v2
2010-11-08,Consistent model of magnetism in ferropnictides,"The discovery of superconductivity in LaFeAsO introduced the ferropnictides
as a major new class of superconducting compounds with critical temperatures
second only to cuprates. The presence of magnetic iron makes ferropnictides
radically different from cuprates. Antiferromagnetism of the parent compounds
strongly suggests that superconductivity and magnetism are closely related.
However, the character of magnetic interactions and spin fluctuations in
ferropnictides, in spite of vigorous efforts, has until now resisted
understanding within any conventional model of magnetism. Here we show that the
most puzzling features can be naturally reconciled within a rather simple
effective spin model with biquadratic interactions, which is consistent with
electronic structure calculations. By going beyond the Heisenberg model, this
description explains numerous experimentally observed properties, including the
peculiarities of the spin wave spectrum, thin domain walls, crossover from
first to second order phase transition under doping in some compounds, and
offers new insight in the occurrence of the nematic phase above the
antiferromagnetic phase transition.",1011.1715v2
2010-12-01,Persistence of magnons in a site-diluted dimerized frustrated antiferromagnet,"We present inelastic neutron scattering and thermodynamic measurements
characterizing the magnetic excitations in a disordered non-magnetic
substituted spin-liquid antiferromagnet. The parent compound Ba3Mn2O8 is a
dimerized, quasi-two-dimensional geometrically frustrated quantum disordered
antiferromagnet. We substitute this compound with non-magnetic vanadium for the
S = 1 manganese atoms, Ba3(Mn1-xVx)2O8, and find that the singlet-triplet
excitations which dominate the spectrum of the parent compound persist for the
full range of substitution examined, x = 0.02 to 0.3. We also observe
additional low-energy magnetic fluctuations which are enhanced at the greatest
substitution values. These excitations may be a precursor to a low-temperature
random singlet phase which may exist in Ba3(Mn1-xVx)2O8",1012.0099v1
2010-12-09,The magnetocaloric and barocaloric effects in Gd5Si2Ge2 compound,"The caloric effect in Gd5Si2Ge2 compound is studied experimentally and
theoretically. The first-order phase transition is sensitive to both magnetic
field and pressure. It indicates that the influences of magnetic field and
pressure on the phase transition are virtually equivalent. Moreover, the
theoretical analyses reveal that the total entropy change is almost definite at
a certain Curie temperature whether the applied external field is magnetic
field or pressure. On the basis of theoretical analyses, the entropy change
simultaneously induced by magnetic field and hydrostatic pressure can be
obtained experimentally. As for Gd5Si2Ge2 compound, the entropy change curve is
broadened dramatically, and the refrigerant capacity is improved from 284.7 to
447.0 J/kg. Additionally, the required magnetic field in magnetic refrigeration
technique may be reduced by the application of hydrostatic pressure.",1012.2102v2
2010-12-17,First-principles study of phase stability of Gd-doped EuO and EuS,"Phase diagrams of isoelectronic Eu$_{1-x}$Gd$_x$O and Eu$_{1-x}$Gd$_{x}$S
quasi-binary alloy systems are constructed using first-principles calculations
combined with the standard cluster expansion approach and Monte-Carlo
simulations. The oxide system has a wide miscibility gap on the Gd-rich side
but forms ordered compounds on the Eu-rich side, exhibiting a deep asymmetric
convex hull in the formation enthalpy diagram. The sulfide system has no stable
compounds. The large difference in the formation enthalpies of the oxide and
sulfide compounds is due to the contribution of local lattice relaxation, which
is sensitive to the anion size. The solubility of Gd in both EuO and EuS is in
the range of 10-20% at room temperature and quickly increases at higher
temperatures, indicating that highly doped disordered solid solutions can be
produced without the precipitation of secondary phases. We also predict that
rocksalt GdO can be stabilized under appropriate experimental conditions.",1012.4026v1
2010-12-20,Application of the S=1 underscreened Anderson lattice model to Kondo uranium and neptunium compounds,"Magnetic properties of uranium and neptunium compounds showing the
coexistence of Kondo screening effect and ferromagnetic order are investigated
within the Anderson lattice Hamiltonian with a two-fold degenerate $f$-level in
each site, corresponding to $5f^2$ electronic configuration with $S=1$ spins. A
derivation of the Schrieffer-Wolff transformation is presented and the
resulting Hamiltonian has an effective $f$-band term, in addition to the
regular exchange Kondo interaction between the $S=1$ $f$-spins and the $s=1/2$
spins of the conduction electrons. The obtained effective Kondo lattice model
can describe both the Kondo regime and a weak delocalization of $5f$-electron.
Within this model we compute the Kondo and Curie temperatures as a function of
model parameters, namely the Kondo exchange interaction constant $J_K$, the
magnetic intersite exchange interaction $J_H$ and the effective $f$-bandwidth.
We deduce, therefore, a phase diagram of the model which yields the coexistence
of Kondo effect and ferromagnetic ordering and also accounts for the pressure
dependence of the Curie temperature of uranium compounds such as UTe.",1012.4229v1
2011-01-09,Semiconducting (Half-Metallic) Ferromagnetism in Mn(Fe) Substituted Pt and Pd Nitrides,"Using first principles calculations as based on density functional theory, we
propose a class of so far unexplored diluted ferromagnetic semiconductors and
half-metals. Here, we study the electronic properties of recently synthesized $
4d $ and $ 5d $ transition metal dinitrides. In particular, we address Mn- and
Fe-substitution in PtN$_2$ and PdN$_2$. Structural relaxation shows that the
resulting ordered compounds, Pt$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$ and
Pd$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$, maintain the cubic crystal symmetry of the
parent compounds. On substitution, all compounds exhibit long-range
ferromagnetic order. While both Pt$_{0.75}$Mn$_{0.25}$N$_2$ and
Pd$_{0.75}$Mn$_{0.25}$N$_2$ are semiconducting, Fe-substitution causes
half-metallic behavior for both parent materials.",1101.1635v1
2011-01-19,Critical Phenomena in Long-Range RKKY Ising Spin Glasses,"We have investigated critical phenomena in spin glasses RxY1-xRu2Si2 (R = Dy,
Tb, Gd). These compounds, where the magnetic moments of rare-earth ions
interact by the long-range Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction
via conduction electrons, has uniaxial magnetic anisotropy. The separation of
the zero-field-cooled and field-cooled magnetization was found only along the
c-axis in all compounds, and hence, they are classified into the long-range
Ising spin glass. The magnetic anisotropic energies in these compounds are
different from each other in two orders of magnitude, from 330 K to 1.8 K,
however, the critical exponents are similar. It clearly indicates a presence of
the universality of the long-range RKKY Ising spin glasses.",1101.3618v2
2011-01-20,Compound transfer matrices: Constructive and destructive interference,"Scattering from a compound barrier, one composed of a number of distinct
non-overlapping sub-barriers, has a number of interesting and subtle
mathematical features. If one is scattering classical particles, where the wave
aspects of the particle can be ignored, the transmission probability of the
compound barrier is simply given by the product of the transmission
probabilities of the individual sub-barriers. In contrast if one is scattering
waves (whether we are dealing with either purely classical waves or quantum
Schrodinger wavefunctions) each sub-barrier contributes phase information (as
well as a transmission probability), and these phases can lead to either
constructive or destructive interference, with the transmission probability
oscillating between nontrivial upper and lower bounds. In this article we shall
study these upper and lower bounds in some detail, and also derive bounds on
the closely related process of quantum excitation (particle production) via
parametric resonance.",1101.4014v2
2011-02-21,Stein's method and locally dependent point process approximation,"Random events in space and time often exhibit a locally dependent structure.
When the events are very rare and dependent structure is not too complicated,
various studies in the literature have shown that Poisson and compound Poisson
processes can provide adequate approximations. However, the accuracy of
approximations does not improve or may even deteriorate when the mean number of
events increases. In this paper, we investigate an alternative family of
approximating point processes and establish Stein's method for their
approximations. We prove two theorems to accommodate respectively the
positively and negatively related dependent structures. Three examples are
given to illustrate that our approach can circumvent the technical difficulties
encountered in compound Poisson process approximation [see Barbour &
M{\aa}nsson (2002)] and our approximation error bound decreases when the mean
number of the random events increases, in contrast to increasing bounds for
compound Poisson process approximation.",1102.4153v1
2011-02-28,"Charge transfer on the metallic atom pair bond, and the crystal structures adopted by intermetallic compounds","Pauling had proposed that charge is transferred from the more electronegative
atom to the less electronegative one during metallic alloying. An expression
has recently been derived for the energy of the unlike atom-pair bond using
that concept. In this paper, Pauling's view is further supported by showing
that the electronegativity and valence differences between unlike atoms in
binary metallic alloys are of the required magnitude and direction so as to
bring the metallic radii ratio R_A/R_B by charge transfer to a value r_A/r_B
for ideal packing in an intermetallic compound. It is also demonstrated that
lattice parameters of intermetallic compounds belonging to several crystal
structure types can be obtained with excellent accuracy from the length of the
atom-pair bond.",1102.5655v1
2011-03-09,Incommensurate spin Luttinger liquid phase in a model for the spin-Peierls materials TiOBr and TiOCl,"In the present work we aim to characterize the lattice configurations and the
magnetic behavior in the incommensurate phase of spin-Peierls systems. This
phase emerges when the magnetic exchange interaction is coupled to the
distortions of an underlying triangular lattice and has its experimental
realization in the quasi-one dimensional compound family TiOX (X = Cl, Br).
With a simple model of spin-1/2 chains inserted in a planar triangular geometry
which couples them elastically, we are able to obtain the
uniform-incommensurate and incommensurate-dimerized phase transitions seen in
these compounds. Moreover, we follow the evolution of the wave-vector of the
distortions with temperature inside the incommensurate phase. Finally, we
predict gapless spin excitations for the intermediate phase of TiOX compounds
along with incommensurate spin-spin correlations. This exotic Luttinger
liquid-like behavior could be observed in future experiments.",1103.1792v1
2011-03-16,Magnetization Plateaus in the Spin-1/2 Kagome Antiferromagnets: Volborthite and Vesignieite,"The magnetization of two spin-1/2 kagome antiferromagnets, volborthite and
vesignieite, has been measured in pulsed magnetic fields up to 68 T. A
magnetization plateau is observed for each compound near the highest magnetic
field. Magnetizations at saturation are approximately equal to 0.40Ms for both
compounds, where Ms is the fully saturated magnetization, irrespective of a
difference in the distortion of the kagome lattice between the two compounds.
It should be noted that these values of magnetizations are significantly larger
than Ms/3 predicted theoretically for the one-third magnetization plateau in
the spin-1/2 kagome antiferromagnet. The excess magnetization over Ms/3 is
nearly equal to the sum of the magnetizations gained at the second and third
magnetization steps in volborthite, suggesting that there is a common origin
for the excess magnetization and the magnetization steps.",1103.3116v1
2011-03-27,Isotope exponent in disordered underdoped and overdoped La214,"The effect of oxygen isotope substitution on Tc has been analyzed for heavily
underdoped and overdoped La2-xSrxCu1-yZnyO4 compounds with different Zn
contents in the CuO2 plane. The effect of Zn on the isotope exponent, {\alpha},
was more pronounced in the case of the underdoped (x = 0.09) compounds compared
to the overdoped (x = 0.22) ones. The variation of {\alpha} with in-plane
disorder can be described quite well within a model based solely on impurity
induced Cooper pair-breaking in the case of the underdoped compounds. This
model, on the other hand, fails to describe the behavior of {\alpha}(y) for the
overdoped samples, even though Zn still breaks pairs very effectively at this
hole (Sr) content. We discuss the implications of these finding in details by
considering the Zn induced magnetism, stripe correlations, and possible changes
in the superconducting order parameter as number of charge carriers in the CuO2
plane, p (\equiv x), is varied.",1103.5200v2
2011-04-03,Band Structure Engineering of Multinary Chalcogenide Topological Insulators,"Topological insulators (TIs) have been found in strained binary HgTe and
ternary I-III-VI2 chalcopyrite compounds such as CuTlSe2 which have inverted
band structures. However, the non-trivial band gaps of these existing binary
and ternary TIs are limited to small values, usually around 10 meV or less. In
this work, we reveal that a large non-trivial band gap requires the material
having a large negative crystal field splitting $\Delta_{CF}$ at top of the
valence band and a moderately large negative $s-p$ band gap $E_g^{s-p}$. These
parameters can be better tuned through chemical ordering in multinary
compounds. Based on this understanding, we show that a series of quaternary
I2-II-IV-VI4 compounds, including Cu2HgPbSe4, Cu2CdPbSe4, Ag2HgPbSe4 and
Ag2CdPbTe4 are TIs, in which Ag2HgPbSe4 has the largest TI band gap of 47 meV
because it combines the optimal values of $\Delta_{CF}$ and $E_g^{s-p}$.",1104.0353v1
2011-04-12,Possible routes for synthesis of new boron-rich Fe-B and Fe(1-x)Cr(x)B4 compounds,"We use ab initio calculations to examine thermodynamic factors that could
promote the formation of recently proposed unique oP10-FeB4 and oP12-FeB2
compounds. We demonstrate that these compact boron-rich phases are stabilized
further under pressure. We also show that chromium tetraboride is more stable
in the new oP10 rather than the reported oI10 structure which opens up the
possibility of realizing an oP10-Fe(x)Cr(1-x)B4 pseudobinary material. In
addition to exhibiting remarkable electronic features, oP10-FeB4 and oP12-FeB2
are expected to be harder than the known Fe-B compounds commonly used for hard
coating applications.",1104.2136v1
2011-04-21,"Seeking Meaning in a Space Made out of Strokes, Radicals, Characters and Compounds","Chinese characters can be compared to a molecular structure: a character is
analogous to a molecule, radicals are like atoms, calligraphic strokes
correspond to elementary particles, and when characters form compounds, they
are like molecular structures. In chemistry the conjunction of all of these
structural levels produces what we perceive as matter. In language, the
conjunction of strokes, radicals, characters, and compounds produces meaning.
But when does meaning arise? We all know that radicals are, in some sense, the
basic semantic components of Chinese script, but what about strokes?
Considering the fact that many characters are made by adding individual strokes
to (combinations of) radicals, we can legitimately ask the question whether
strokes carry meaning, or not. In this talk I will present my project of
extending traditional NLP techniques to radicals and strokes, aiming to obtain
a deeper understanding of the way ideographic languages model the world.",1104.4321v1
2011-05-04,A modeling-based evaluation of isothermal rebreathing for breath gas analyses of highly soluble volatile organic compounds,"Isothermal rebreathing has been proposed as an experimental technique for
estimating the alveolar levels of hydrophilic volatile organic compounds (VOCs)
in exhaled breath. Using the prototypic test compound acetone we demonstrate
that the end-tidal breath profiles of such substances during isothermal
rebreathing show characteristics that contradict the conventional pulmonary
inert gas elimination theory due to Farhi. On the other hand, these profiles
can reliably be captured by virtue of a previously developed mathematical model
for the general exhalation kinetics of highly soluble, blood-borne VOCs, which
explicitly takes into account airway gas exchange as major determinant of the
observable breath output.
  This model allows for a mechanistic analysis of various rebreathing protocols
suggested in the literature. In particular, it clarifies the discrepancies
between in vitro and in vivo blood-breath ratios of hydrophilic VOCs and yields
further quantitative insights into the physiological components of isothermal
rebreathing.",1105.0864v2
2011-05-10,The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5,"The crystal and magnetic structure of the magnetocaloric compound
FeMnP0.5Si0.5 have been studied by means of neutron and X-ray powder
diffraction. Single phase samples of nominal composition FeMnP0.5Si0.5 have
been prepared by the drop synthesis method. The compound crystallizes in the
Fe2P-type structure (P-62m) with the magnetic moments aligned along the aaxis.
It is found that the Fe atoms are mainly situated in the tetrahedral 3g site
while the Mn atoms prefer the pyramidal 3f position. The material is
ferromagnetic (TC = 382 K) and at 296 K the total magnetic moment is 4.4 \mu
B/f.u. It is shown that the magnetic moment in the 3f site is larger (2.5 \mu
B) than in the 3g site (1.9 \mu B).",1105.1942v1
2011-05-19,High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopy,"We report optical spectroscopic measurements on electron- and hole-doped
BaFe2As2. We show that the compounds in the normal state are not simple metals.
The optical conductivity spectra contain, in addition to the free carrier
response at low frequency, a temperature-dependent gap-like suppression at
rather high energy scale near 0.6 eV. This suppression evolves with the
As-Fe-As bond angle induced by electron- or hole-doping. Furthermore, the
feature becomes much weaker in the Fe-chalcogenide compounds. We elaborate that
the feature is caused by the strong Hund's rule coupling effect between the
itinerant electrons and localized electron moment arising from the multiple Fe
3d orbitals. Our experiments demonstrate the coexistence of itinerant and
localized electrons in iron-based compounds, which would then lead to a more
comprehensive picture about the metallic magnetism in the materials.",1105.3939v1
2011-06-08,Superconductivity in Iron Compounds,"Kamihara and coworkers' report of superconductivity at Tc = 26 K in
fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of
the superconductivity in this new class of compounds. These iron pnictide and
chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface,
plus an unusual Fermiology that can change rapidly with doping, which lead to
normal and superconducting state properties very different from those in
standard electron-phonon coupled 'conventional' superconductors. Clearly
superconductivity and magnetism/magnetic fluctuations are intimately related in
the FePn/Ch - and even coexist in some. Open questions, including the
superconducting nodal structure in a number of compounds, abound and are often
dependent on improved sample quality for their solution. With Tc values up to
56 K, the six distinct Fe-containing superconducting structures exhibit complex
but often comparable behaviors. The search for correlations and explanations in
this fascinating field of research would benefit from an organization of the
large, seemingly disparate data set. This review attempts to provide an
overview, using numerous references, with a focus on the materials and their
superconductivity.",1106.1618v1
2011-06-15,Thermodynamic modeling of the LiF-YF3 phase diagram,"A thermodynamic optimization of the LiF-YF3 binary phase diagram was
performed by fitting the Gibbs energy functions to experimental data that were
taken from the literature, as well as from own thermoanalytic measurements (DTA
and DSC) on HF-treated samples. The Gibbs energy functions for the end member
compounds were taken from the literature. Excess energy terms, which describe
the effect of interaction between the two fluoride compounds in the liquid
phase, were expressed by the Redlich-Kister polynomial function. The calculated
phase diagram and thermodynamic properties for the unique formed compound,
LiYF4, are in reasonable agreement with the experimental data.",1106.2964v2
2011-07-06,Maximum-Likelihood Non-Decreasing Response Estimates,"Let $x_{i,j}$, $1 \le i \le m$, $1 \le j \le n_i$, be observations from a
doubly-indexed sequence $\{X_{i,j}\}$ of independent random variables (all of
them discrete, or all of them absolutely continuous). Suppose that each
$X_{i,j}$ has the PDF $f(x\mid\theta_i)$ from a one-parameter family of PDFs
$f(x\mid \theta)$. Mild assumptions are described under which there is a
unique, non-decreasing compound response estimate of $\mathbf \theta=<\theta_1,
\hdots \theta_m>$ that maximizes the compound likelihood function among all
non-decreasing response estimates. An efficient algorithm is described to
compute this unique estimate.
  The same theory and algorithm also give the unique non-increasing compound
response estimate that maximizes likelihood among all non-increasing response
estimates. One simply reverses the order represented by the index $i$.",1107.1025v1
2011-07-15,Satellites and large doping- and temperature-dependence of electronic properties in hole-doped BaFe2As2,"Over the last years, superconductivity has been discovered in several
families of iron-based compounds. Despite intense research, even basic
electronic properties of these materials, such as Fermi surfaces, effective
electron masses, or orbital characters are still subject to debate. Here, we
address an issue that has not been considered before, namely the consequences
of dynamical screening of the Coulomb interactions among Fe-d electrons. We
demonstrate its importance not only for correlation satellites seen in
photoemission spectroscopy, but also for the low-energy electronic structure.
From our analysis of the normal phase of BaFe2As2 emerges the picture of a
strongly correlated compound with strongly doping- and temperature-dependent
properties. In the hole overdoped regime, an incoherent metal is found, while
Fermi-liquid behavior is recovered in the undoped compound. At optimal doping,
the self-energy exhibits an unusual square-root energy dependence which leads
to strong band renormalizations near the Fermi level.",1107.3128v1
2011-08-02,"Elastic, electronic and optical properties of hypothetical SnNNi3 and CuNNi3 in comparison with superconducting ZnNNi3","The elastic, electronic and optical properties of MNNi3 (M= Zn, Sn and Cu)
have been calculated using the plane-wave ultrasoft pseudopotential technique
which is based on the first-principles density functional theory (DFT) with
generalized gradient approximation (GGA). The optimized lattice parameters,
independent elastic constants (C11, C12, and C44), bulk modulus B,
Compressibility K, shear modulus G, and Poisson's ratio \u{psion}, as well as
the band structures, total and atom projected densities of states and finally
the optical properties of MNNi3 have been evaluated and discussed. The
electronic band structures of the two hypothetical compounds show metallic
behavior just like the superconducting ZnNNi3. Using band structures, the
origin of features that appear in different optical properties of all the three
compounds have been discussed. The large reflectivity of the predicted
compounds in the low energy region might be good candidate materials as a
coating to avoid solar heating. Key words: MNNi3, Ab initio calculations,
Elastic properties, Electronic band structure, Optical properties.",1108.0557v1
2011-08-02,"Systematical, experimental investigations on LiMgZ (Z= P, As, Sb) wide band gap semiconductors","This work reports on the experimental investigation of the wide band gap
compounds LiMgZ (Z = P, As, Sb), which are promising candidates for
opto-electronics and anode materials for Lithium batteries. The compounds
crystallize in the cubic (C1_b) MgAgAs structure (space group F-43m). The
polycrystalline samples were synthesized by solid state reaction methods. X-ray
and neutron diffraction measurements show a homogeneous, single-phased samples.
The electronic properties were studied using the direct current (DC) method.
Additionally UV-VIS diffuse reflectance spectra were recorded in order to
investigate the band gap nature. The measurements show that all compounds
exhibit semiconducting behavior with direct band gaps of 1.0 eV to 2.3 eV
depending on the Z element. A decrease of the peak widths in the static 7Li
nuclear magnetic resonance (NMR) spectra with increasing temperature was
observed, which can directly be related to an increase of Li ion mobility.",1108.0584v1
2011-08-15,Iron Displacements and Magnetoelastic Coupling in the Spin-Ladder Compound BaFe2Se3,"We report long-range ordered antiferromagnetism concomitant with local iron
displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic
correlations, present at room temperature, develop into long-range
antiferromagnetic order below T$_N$ = 256 K, with no superconductivity down to
1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, the magnetic ground state
correlates with local displacements of the Fe atoms. These iron displacements
imply significant magnetoelastic coupling in FeX$_4$-based materials, an
ingredient hypothesized to be important in the emergence of superconductivity.
This result also suggests that knowledge of these local displacements is
essential for properly understanding the electronic structure of these systems.
As with the copper oxide superconductors two decades ago, our results highlight
the importance of reduced dimensionality spin ladder compounds in the study of
the coupling of spin, charge, and atom positions in superconducting materials.",1108.2928v2
2011-09-06,The effects of competing magnetic interactions on the electronic properties of CuCrS2 and CuCrSe2,"We present a detail study of the electrical resistivity, thermoelectric
power, magnetic susceptibility \c{hi} and the heat capacity CP in
antiferromagnetic layered compounds CuCrS2 and CuCrSe2 at 2K-300K. CuCrS2
showed sharp cusp in \c{hi} and a lambda-like peak in CP at TN = 40K as
expected for a 3D- magnetic order, while more metallic CuCrSe2 showed a rounded
maximum in \c{hi} and the absence of sharp peak in CP around 55K, the CP at low
temperature has T2-dependence in it which suggests the absence of the long
range order and 2D spin-liquid like excitation in its magnetic phase. We
explain the absence of the magnetic order in the selenide compound as resulting
from the effective competition of the magnetic interactions from the distant
neighbors; the indirect exchange among the intra-layer Cr-atoms increases in
more metallic selenide compound which competes with the direct
antiferromagnetic interactions between the Cr-atoms of different layers which
destroys the long range magnetic order.",1109.1071v1
2011-10-10,Magnetic order and transitions in the spin-web compound Cu3TeO6,"The spin-web compound Cu3TeO6, belongs to an intriguing group of materials
where magnetism is governed by 3d9 copper Cu2+ ions. This compound has been
sparsely experimentally studied and we here present the first investigation of
its local magnetic properties using muon-spin relaxation/rotation ({\mu}+SR).
Our results show a clear long-range 3D magnetic order below TN as indicated by
clear zero-field (ZF) muon-precessions. At TN = 61.7 K a very sharp transition
is observed in the weak transverse-field (wTF) as well as ZF data. Contrary to
suggestions by susceptibility measurements and inelastic neutron scattering, we
find no evidence for either static or dynamic (on the time-scale of {\mu}+SR)
spin-correlations above TN.",1110.2073v1
2011-10-19,Synthesis of novel rare earth - iron oxide chalcogenides with the La2Fe2O3Se2 structure,"Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and
Zn resulted in preparation of two new compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 which
are isostructural to La2Fe2O3Se2 and Sm2Ti2O3Sb2. Crystal structures of the new
compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 were determined from powder X-ray
diffraction data. Magnetic measurements were performed for Ce2Fe2O3S2 and
revealed behavior very similar to that of isostructural oxide chalcogenides of
iron and pnictides of titanium. In particular, no superconductivity was
observed down to 4 K. Crystal chemical factors determining the stability of the
La2Fe2O3Se2 structure type are discussed.",1110.4234v1
2011-11-13,Experimental Evidence of the Role of Compound Counting Processes in Random Walk Approaches to Fractional Dynamics,"We present dielectric spectroscopy data obtained for gallium-doped
Cd$_{0.99}$Mn$_{0.01}$Te:Ga mixed crystals which exhibit a very special case of
the two-power-law relaxation pattern with the high-frequency power-law exponent
equal to 1. We explain this behavior, which cannot be fitted by none of the
well-known empirical relaxation functions, in a subordinated diffusive
framework. We propose diffusion scenario based on a renormalized clustering of
random number of spatio-temporal steps in the continuous time random walk. Such
a construction substitutes the renewal counting process, used in the classical
continuous time random walk methodology, by a compound counting one. As a
result, we obtain a novel relaxation function governing the observed
non-standard pattern, and we show the importance of the compound counting
processes in studying fractional dynamics of complex systems.",1111.3030v1
2011-11-15,Extending the adverbial coverage of a NLP oriented resource for French,"This paper presents a work on extending the adverbial entries of LGLex: a NLP
oriented syntactic resource for French. Adverbs were extracted from the
Lexicon-Grammar tables of both simple adverbs ending in -ment '-ly' (Molinier
and Levrier, 2000) and compound adverbs (Gross, 1986; 1990). This work relies
on the exploitation of fine-grained linguistic information provided in existing
resources. Various features are encoded in both LG tables and they haven't been
exploited yet. They describe the relations of deleting, permuting, intensifying
and paraphrasing that associate, on the one hand, the simple and compound
adverbs and, on the other hand, different types of compound adverbs. The
resulting syntactic resource is manually evaluated and freely available under
the LGPL-LR license.",1111.3462v1
2011-11-17,Competition between commensurate and incommensurate magnetic ordering in Fe(1+y)Te,"The Fe1+y Te1-x Sex compounds belong to the family of iron-based high
temperature superconductors, in which superconductivity often appears upon
doping antiferromagnetic parent compounds. Unlike other Fe-based
superconductors (in which the antiferromagnetic order is at the Fermi surface
nesting wavevector [1/2,1/2,1]), the Fe1+y Te1-x Sex parent compound Fe1+y Te
orders at a different wavevector, [1/2, 0, 1/2]. Furthermore, the ordering
wavevector depends on y, the occupation of interstitial sites with excess iron;
the origin of this behavior is controversial. Using inelastic neutron
scattering on Fe1.08 Te, we find incommensurate magnetic fluctuations above the
Neel temperature, even though the ordered state is bicollinear and commensurate
with gapped spin waves. This behavior can be understood in terms of a
competition between commensurate and incommensurate order, which we explain as
a lock-in transition caused by the magnetic anisotropy.",1111.4236v2
2011-11-25,Flavor network and the principles of food pairing,"The cultural diversity of culinary practice, as illustrated by the variety of
regional cuisines, raises the question of whether there are any general
patterns that determine the ingredient combinations used in food today or
principles that transcend individual tastes and recipes. We introduce a flavor
network that captures the flavor compounds shared by culinary ingredients.
Western cuisines show a tendency to use ingredient pairs that share many flavor
compounds, supporting the so-called food pairing hypothesis. By contrast, East
Asian cuisines tend to avoid compound sharing ingredients. Given the increasing
availability of information on food preparation, our data-driven investigation
opens new avenues towards a systematic understanding of culinary practice.",1111.6074v1
2011-11-27,A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3,"We present magnetic characterization of a binary rare-earth intermetallic
compound Er5Si3, crystallizing in Mn5Si3-type hexagonal structure, through
magnetization, heat-capacity, electrical resistivity, and magnetoresistance
measurements. Our investigations confirm that the compound exhibits two
magnetic transitions with decreasing temperature, first one at 35 K and the
second one at 15 K. The present results reveal that the second magnetic
transition is a disorder-broadened first-order transition, as shown by thermal
hysteresis in the measured data. Another important finding is that, below 15 K,
there is a magnetic-field-induced transition with a hysteretic effect with the
electrical resistance getting unusually enhanced at this transition and the
magnetorsistance (MR) is found to exhibit intriguing magnetic-field dependence
indicating novel magnetic phase-co-existence phenomenon. It thus appears that
this compound is characterized by interesting magnetic anomalies in the
temperature-magnetic-field phase diagram.",1111.6240v1
2011-11-29,Modules of differential operators of order 2 on Coxeter arrangements,"We prove that the modules of differential operators of order 2 on the
classical Coxeter arrangements are free by exhibiting bases. For this purpose,
we use Cauchy-Sylvester's theorem on compound determinants and Saito-Holm's
criterion. In the case type $A$, we apply Cauchy-Sylvester's theorem on
compound determinants to Vandermond determinant. By using the Schur
polynomials, we define operators which form a part of a basis of modules of
differential operators on the classical Coxeter arrangements of type $A$. In
the cases of type $B$ and type $D$, the proofs go similarly to the case of type
$A$ with some adjustments of operators and determinants.",1111.6712v2
2011-12-23,Thermodynamic properties of quantum sine-Gordon spin chain system KCuGaF6,"We investigated the thermodynamic properties of the spin-1/2 one-dimensional
Heisenberg antiferromagnet KCuGaF6 by measuring the specific heat in magnetic
fields. When this compound is subjected to a uniform magnetic field H a
transverse staggered magnetic field h is induced in this compound owing to the
staggered component of the g tensor and the Dzyaloshinskii-Moriya interaction
with an alternating D vector. Consequently, the quantum sine-Gordon (SG) model
is an effective model of this compound in a uniform magnetic field. In three
different field directions, we observed a magnetic-field-induced gap, which
increases with H. We analyzed experimental results using specific heat theory
based on quantum SG theory. The thermodynamic property for H // c is very well
described in terms of the elementary excitations characteristic of the quantum
SG model, while for the other field directions, significant contributions from
other excitation modes beyond the framework of the quantum SG model were
observed. For H // b, a quantum phase transition between gapless and gapped
ground states was observed.",1112.5531v1
2012-01-21,Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound,"We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray
and neutron powder diffraction show that the crystal structure is rhombohedral
with View the MathML source space group (Th2Zn17-type). The investigated
compound exhibits a broad isothermal magnetic entropy change {\Delta}SM(T)
associated with the ferro-to-paramagnetic phase transition (TC \approx 290 K).
The |{\Delta}SM| (\approx 2.3 J kg-1 K-1) and the relative cooling power
(\approx 100 J kg-1) have been calculated for applied magnetic field changes up
to 1.5 T. A single master curve for {\Delta}SM under different values of the
magnetic field change can be obtained by a rescaling of the temperature axis.
The results are compared and discussed in terms of the magneto-caloric effect
in the isostructural R2Fe17 (R = Y, Pr and Nd) binary intermetallic alloys.",1201.4411v1
2012-01-26,Non standard functional limit laws for the increments of the compound empirical distribution function,"Let $(Y_i,Z_i)_{i\geq 1}$ be a sequence of independent, identically
distributed (i.i.d.) random vectors taking values in $\RRR^k\times\RRR^d$, for
some integers $k$ and $d$. Given $z\in \RRR^d$, we provide a nonstandard
functional limit law for the sequence of functional increments of the compound
empirical process, namely $$\mathbf{\Delta}_{n,\cc}(h_n,z,\cdot):=
\frac{1}{nh_n}\sliin 1_{[0,\cdot)}\poo \frac{Z_i-z}{{h_n}^{1/d}}\pff Y_i.$$
Provided that $nh_n\sim c\log n $ as $\nif$, we obtain, under some natural
conditions on the conditional exponential moments of $Y\mid Z=z$, that
$$\mathbf{\Delta}_{n,\cc}(h_n,z,\cdot)\leadsto \Gam\text{almost surely},$$
where $\leadsto$ denotes the clustering process under the sup norm on $\Idd$.
Here, $\Gam$ is a compact set that is related to the large deviations of
certain compound Poisson processes.",1201.5528v1
2012-02-12,Theory of High-Tc Superconductivity: Accurate Predictions of Tc,"The superconducting transition temperatures of high-Tc compounds based on
copper, iron, ruthenium and certain organic molecules are discovered to be
dependent on bond lengths, ionic valences, and Coulomb coupling between
electronic bands in adjacent, spatially separated layers [1]. Optimal
transition temperature, denoted as T_c0, is given by the universal expression
$k_BT_c0 = e^2 \Lambda / \ell\zeta$; $\ell$ is the spacing between interacting
charges within the layers, \zeta is the distance between interacting layers and
\Lambda is a universal constant, equal to about twice the reduced electron
Compton wavelength (suggesting that Compton scattering plays a role in
pairing). Non-optimum compounds in which sample degradation is evident
typically exhibit Tc < T_c0. For the 31+ optimum compounds tested, the
theoretical and experimental T_c0 agree statistically to within +/- 1.4 K. The
elemental high Tc building block comprises two adjacent and spatially separated
charge layers; the factor e^2/\zeta arises from Coulomb forces between them.
The theoretical charge structure representing a room-temperature superconductor
is also presented.",1202.2480v2
2012-03-09,Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution,"We introduce an approach to calculate the thermodynamic oxidation and
reduction potentials of semiconductors in aqueous solution. By combining a
newly-developed ab initio calculation for compound formation energy and band
alignment with electrochemistry experimental data, this approach can be used to
predict the stability of almost any compound semiconductor in aqueous solution.
30 photocatalytic semiconductors have been studied, and a graph (a simplified
Pourbaix diagram) showing their valence/conduction band levels and
oxidation/reduction potentials is produced. Based on this graph, we have
studied the stabilities and trends against the oxidative and reductive
photocorrosion for compound semiconductors. We found that, only metal oxides
can be thermodynamically stable when used as the n-type photoanodes. All the
non-oxides are unstable due to easy oxidation by the photogenerated holes, but
they can be resistant to the reduction by electrons, thus stable as the p-type
photocathodes.",1203.1970v1
2012-03-14,Adaptive wavelet estimation of a compound Poisson process,"We study the nonparametric estimation of the jump density of a compound
Poisson process from the discrete observation of one trajectory over $[0,T]$.
We consider the microscopic regime when the sampling rate
$\Delta=\Delta_T\rightarrow0$ as $T\rightarrow\infty$. We propose an adaptive
wavelet threshold density estimator and study its performance for the $L_p$
loss, $p\geq 1$, over Besov spaces. The main novelty is that we achieve minimax
rates of convergence for sampling rates $\Delta_T$ that vanish with $T$ at
arbitrary polynomial rates. More precicely, our estimator attains minimax rates
of convergence provided there exists a constant $K\geq 1$ such that the
sampling rate $\Delta_T$ satisfies $T\Delta_T^{2K+2}\leq 1.$ If this condition
cannot be satisfied we still provide an upper bound for our estimator. The
estimating procedure is based on the inversion of the compounding operator in
the same spirit as Buchmann and Gr\""ubel (2003).",1203.3135v1
2012-03-19,"Study of Structural, Magnetic and Electrical properties on Ho - substituted BiFeO3","The polycrystalline Bi1-xHoxFeO3 (x=0, 0.05, 0.1) compounds were synthesized
by conventional solid-state route. Rietveld refinement reveals that all the
compounds were stabilized in rhombohedral structure with R3c (IUCr No. 161)
space group. A competing ferro and anti-ferro magnetic interaction was observed
in Ho-substituted compounds. A change in the Fe-O-Fe bond-angle and Fe-O bond
distance increase the Neel Transition temperature with increasing Ho
concentration. The appearance of peak in imaginary part of impedance (Z"") for
each concentration and shifting of this peak with temperature towards higher
frequency side indicated that the presence of electric relaxations. Correlated
Barrier Hopping model (CBH) was employed to explain the frequency and
temperature dependence of ac conductivity and the mechanism of transport in the
material BFO and Ho substituted BFO. Density of states near Fermi level was
calculated by using the ac conductivity data.",1203.4083v1
2012-03-23,Phase-sensitive evidence for dx2-y2-pairing symmetry in the parent-structure high-Tc cuprate superconductor Sr1-xLaxCuO2,"Even after 25 years of research the pairing mechanism and - at least for
electron doped compounds - also the order parameter symmetry of the high
transition temperature (high-Tc) cuprate superconductors is still under debate.
One of the reasons is the complex crystal structure of most of these materials.
An exception are the infinite layer (IL) compounds consisting essentially of
CuO2 planes. Unfortunately, these materials are difficult to grow and, thus,
there are only few experimental investigations. Recently, we succeeded in
depositing high quality films of the electron doped IL compound Sr1-xLaxCuO2
(SLCO), with x approximately 0.15, and on the fabrication of well-defined grain
boundary Josephson junctions (GBJs) based on such SLCO films. Here we report on
a phase sensitive study of the superconducting order parameter based on GBJ
SQUIDs from a SLCO film grown on a tetracrystal substrate. Our results show
that also the parent structure of the high-Tc cuprates has dx2-y2-wave
symmetry, which thus seems to be inherent to cuprate superconductivity.",1203.5237v1
2012-04-05,The compound class of extended Weibull power series distributions,"In this paper, we introduce a new class of distributions which is obtained by
compounding the extended Weibull and power series distributions. The
compounding procedure follows the same set-up carried out by Adamidis and
Loukas (1998) and defines at least new 68 sub-models. This class includes some
well-known mixing distributions, such as the Weibull power series (Morais and
Barreto-Souza, 2010) and exponential power series (Chahkandi and Ganjali, 2009)
distributions. Some mathematical properties of the new class are studied
including moments and generating function. We provide the density function of
the order statistics and obtain their moments. The method of maximum likelihood
is used for estimating the model parameters and an EM algorithm is proposed for
computing the estimates. Special distributions are investigated in some detail.
An application to a real data set is given to show the flexibility and
potentiality of the new class of distributions.",1204.1303v1
2012-04-17,"Pressure study of the noncentrosymmetric 5d-electron superconductors CaMSi3 (M= Ir, Pt)","We report hydrostatic pressure study on the Rashba-type noncentrosymmetric
superconduc- tors CaMSi3 (M= Ir, Pt). The temperature dependence of the
resistivity for both compounds is well described by the conventional
Bloch-Gr\""uneisen formalism at each pressure. This fact suggests that
electron-phonon scattering is dominant in these compounds. The superconducting
critical temperature Tc decreases by pressure as \sim 0.2 K/GPa above 0.41 GPa
to 2 GPa for both compounds. This behavior of Tc can be explained with a modest
decrease of the density of states based on the conventional BCS theory.",1204.3796v2
2012-04-18,"First principles prediction of the elastic, electronic, and optical properties of Sb2S3 and Sb2Se3 compounds","We have performed a first principles study of structural, mechanical,
electronic, and optical properties of orthorhombic Sb2S3 and Sb2Se3 compounds.
The calculations have been carried out within the local density approximation
using norm conserving pseudopotentials. The lattice parameters, bulk modulus,
and its pressure derivatives of the these compounds have been obtained. The
second-order elastic constants have been calculated, and the other related
quantities such as the Young's modulus, shear modulus, Poisson's ratio,
anisotropy factor, sound velocities and Debye temperature have also been
estimated in the present work. The linear photon-energy dependent dielectric
functions and some optical properties such as the energy-loss function, the
effective number of valance electrons and the effective optical dielectric
constant are calculated. Our structural estimation and some other results are
in agreement with the available experimental and theoretical data.",1204.4062v1
2012-04-22,Optimal simulation schemes for Lévy driven stochastic differential equations,"We consider a general class of high order weak approximation schemes for
stochastic differential equations driven by L\'evy processes with infinite
activity. These schemes combine a compound Poisson approximation for the jump
part of the L\'evy process with a high order scheme for the Brownian driven
component, applied between the jump times. The overall approximation is
analyzed using a stochastic splitting argument. The resulting error bound
involves separate contributions of the compound Poisson approximation and of
the discretization scheme for the Brownian part, and allows, on one hand, to
balance the two contributions in order to minimize the computational time, and
on the other hand, to study the optimal design of the approximating compound
Poisson process. For driving processes whose L\'evy measure explodes near zero
in a regularly varying way, this procedure allows to construct discretization
schemes with arbitrary order of convergence.",1204.4877v1
2012-04-26,Raman response of Stage-1 graphite intercalation compounds revisited,"We present a detailed in-situ Raman analysis of stage-1 KC8, CaC6, and LiC6
graphite intercalation compounds (GIC) to unravel their intrinsic finger print.
Four main components were found between 1200 cm-1 and 1700 cm-1, and each of
them were assigned to a corresponding vibrational mode. From a detailed line
shape analysis of the intrinsic Fano-lines of the G- and D-line response we
precisely determine the position ({\omega}ph), line width ({\Gamma}ph) and
asymmetry (q) from each component. The comparison to the theoretical calculated
line width and position of each component allow us to extract the
electron-phonon coupling constant of these compounds. A coupling constant
{\lambda}ph < 0.06 was obtained. This highlights that Raman active modes alone
are not sufficient to explain the superconductivity within the electron-phonon
coupling mechanism in CaC6 and KC8.",1204.5971v3
2012-05-15,"Elastic, electronic, and optical properties of Sb2S3 and Sb2Se3 compounds: ab initio calculation","We have performed a first principles study of structural, mechanical,
electronic, and optical properties of orthorhombic Sb2S3 and Sb2Se3 compounds
using the density functional theory within the local density approximation. The
lattice parameters, bulk modulus, and its pressure derivatives of these
compounds have been obtained. The second-order elastic constants have been
calculated, and the other related quantities such as the Young's modulus, shear
modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye
temperature, and hardness have also been estimated in the present work. The
linear photon-energy dependent dielectric functions and some optical properties
such as the energy-loss function, the effective number of valance electrons and
the effective optical dielectric constant are calculated. Our structural
estimation and some other results are in agreement with the available
experimental and theoretical data.",1205.3344v1
2012-05-16,"Spin-phonon coupling in multiferroic RCrO$_3$ (R-Y, Lu, Gd, Eu, Sm): A Raman study","Raman study on a select few orthochromites, RCrO$_3$ (R = Y, Lu, Gd, Eu and
Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd
and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu).
While anomalies in most of the observed phonon frequencies in all these
compounds may result from the distortion of CrO$_6$ octahedra due to size
effect and magnetostriction arising from Cr-ordering, the anomalous behavior of
their linewidths observed at TN for the compounds with only magnetic R-ion
suggests spin-phonon coupling. The presence of spin-phonon coupling and the
anomalies in the low frequency modes related to R-ion motion in orthochromites
(R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments
play important role in inducing switchable electric polarization.",1205.3551v2
2012-06-11,Mössbauer Studies of Coordination Compounds using Synchrotron Radiation,"Nuclear resonant forward scattering (NFS) and nuclear inelastic scattering
(NIS) of synchrotron radiation are fairly recent spectroscopic methods for the
investigation of complexes containing M\""ossbauer-active transition metal ions.
NFS, which can be regarded as M\""ossbauer spectroscopy in the time domain,
overcomes some limitations of conventional M\""ossbauer spectroscopy as has been
demonstrated especially for bioinorganic compounds. NIS extends the energy
range of conventional M\""ossbauer spectroscopy to the range of molecular
vibrations. Since NIS is sensitive only to the mean-square displacement of
M\""ossbauer nuclei it can be used as site-selective vibrational spectroscopy.
It complements usefully comparable techniques such as IR or Raman spectroscopy.
Examples are given for applications to spin crossover complexes, nitroprusside
compounds, heme model complexes and myoglobin.",1206.2137v1
2012-06-17,Asymptotic behavior of local times of compound Poisson processes with drift in the infinite variance case,"Consider compound Poisson processes with negative drift and no negative
jumps, which converge to some spectrally positive L\'evy process with non-zero
L\'evy measure. In this paper we study the asymptotic behavior of the local
time process, in the spatial variable, of these processes killed at two
different random times: either at the time of the first visit of the L\'evy
process to 0, in which case we prove results at the excursion level under
suitable conditionings; or at the time when the local time at 0 exceeds some
fixed level. We prove that finite-dimensional distributions converge under
general assumptions, even if the limiting process is not c\`adl\`ag. Making an
assumption on the distribution of the jumps of the compound Poisson processes,
we strengthen this to get weak convergence. Our assumption allows for the
limiting process to be a stable L\'evy process with drift.
  These results have implications on branching processes and in queueing
theory, namely, on the scaling limit of binary, homogeneous Crump-Mode-Jagers
processes and on the scaling limit of the Processor-Sharing queue length
process.",1206.3800v2
2012-06-25,Spin-induced symmetry breaking in orbitally ordered NiCr_2O_4 and CuCr_2O_4,"At room temperature, the normal oxide spinels NiCr_2O_4 and CuCr_2O_4 are
tetragonally distorted and crystallize in the I4_1/amd space group due to
cooperative Jahn-Teller ordering driven by the orbital degeneracy of
tetrahedral Ni$^{2+}$ ($t_2^4$) and Cu$^{2+}$ ($t_2^5$). Upon cooling, these
compounds undergo magnetic ordering transitions; interactions being somewhat
frustrated for NiCr_2O_4 but not for CuCr_2O_4. We employ variable-temperature
high-resolution synchrotron X-ray powder diffraction to establish that at the
magnetic ordering temperatures there are further structural changes, which
result in both compounds distorting to an orthorhombic structure consistent
with the Fddd space group. NiCr_2O_4 exhibits additional distortion, likely
within the same space group, at a yet-lower transition temperature of $T$ = 30
K. The tetragonal to orthorhombic structural transition in these compounds
appears to primarily involve changes in NiO_4 and CuO_4 tetrahedra.",1206.5760v1
2012-07-01,On the magnetic structure of Sr3Ir2O7: an x-ray resonant scattering study,"This report presents azimuthal dependent and polarisation dependent x-ray
resonant magnetic scattering at the Ir L3 edge for the bilayered iridate
compound, Sr3Ir2O7. Two magnetic wave vectors, k1=(1/2,1/2,0) and
k2=(1/2,-1/2,0), result in domains of two symmetry-related G-type
antiferromagnetic structures, noted A and B, respectively. These domains are
approximately 0.02 mm^2 and are independent of the thermal history. An
understanding of this key aspect of the magnetism is necessary for an overall
picture of the magnetic behaviour in this compound. Azimuthal and polarisation
dependence of magnetic reflections, relating to both magnetic wave vectors,
show that the Ir magnetic moments in the bilayer compound are oriented along
the c axis. This contrasts with single layer Sr2IrO4 where the moments are
confined to the ab plane.",1207.0173v1
2012-07-13,Ab Initio Discovery of Novel Crystal Structure Stability in Barium and Sodium-Calcium Compounds under Pressure using DFT,"Group I/II materials exhibit unexpected structural phase transitions at high
pressures, providing potential insight into the origins of elemental
superconductivity. We present here a computational study of elemental barium
and binary sodium-calcium alloys to identify both known and unknown phases of
barium under pressure, as well as stable high-pressure compounds in the
immiscible Na-Ca system. To predict stability, we performed density functional
theory calculations on randomly generated structures and evolved them using a
genetic algorithm. For barium, we observed all of the expected phases and a
number of new metastable structures, excluding the incommensurate Ba-IV
structure. We also observed a heretofore unreported structure (\alpha-Sm)
predicted to be the ground state from 30-42 GPa. In the Na-Ca system, we
demonstrate feasibility of our search method, but have been unable to predict
any stable compounds. These results have improved the efficacy of the genetic
algorithm, and should provide many promising directions for future work.",1207.3320v1
2012-07-31,Pr magnetism and its interplay with the Fe spin density wave in PrFeAsO,"We have studied the magnetism of the Pr3+ ions in PrFeAsO_1-xF_x (x = 0;
0.15) and its interaction with the Fe magnetic order (for x = 0). Specific heat
data confirm the presence of a first excited crystal electric field (CEF) level
around 3.5 meV in the undoped compound PrFeAsO. This finding is in agreement
with recent neutron scattering experiments. The doped compound is found to have
a much lower first CEF splitting of about 2.0 meV. The Pr ordering in PrFeAsO
gives rise to large anomalies in the specific heat and the thermal expansion
coefficient. In addition, a field-induced transition is found at low
temperatures that is most pronounced for the magnetostriction coefficient. This
transition, which is absent in the doped compound, is attributed to a reversal
of the Fe spin canting as the antiferromagnetic Pr order is destroyed by the
external magnetic field.",1207.7186v1
2012-08-03,"First-principles study on the effective masses of zinc-blend-derived Cu_2Zn-IV-VI_4 (IV = Sn, Ge, Si and VI = S, Se)","The electron and hole effective masses of kesterite (KS) and stannite (ST)
structured Cu_2Zn-IV-VI_4 (IV = Sn, Ge, Si and VI = S, Se) semiconductors are
systematically studied using first-principles calculations. We find that the
electron effective masses are almost isotropic, while strong anisotropy is
observed for the hole effective mass. The electron effective masses are
typically much smaller than the hole effective masses for all studied
compounds. The ordering of the topmost three valence bands and the
corresponding hole effective masses of the KS and ST structures are different
due to the different sign of the crystal-field splitting. The electron and hole
effective masses of Se-based compounds are significantly smaller compared to
the corresponding S-based compounds. They also decrease as the atomic number of
the group IV elements (Si, Ge, Sn) increases, but the decrease is less notable
than that caused by the substitution of S by Se.",1208.0774v1
2012-08-29,Synthesis and superconductivity of new BiS2 based superconductor PrO0.5F0.5BiS2,"We report synthesis and superconductivity at 3.7K in PrO0.5F0.5BiS2. The
newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2
compounds having ZrCuSiAs type structure. The bulk polycrystalline compound is
synthesized by vacuum encapsulation technique at 7800C in single step. Detailed
structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is
crystallized in tetragonal P4/nmm space group with lattice parameters a =
4.015(5) {\AA}, c = 13.362(4) {\AA}. Bulk superconductivity is observed in
PrO0.5F0.5BiS2 below 4K from magnetic and transport measurements. Electrical
transport measurements showed superconducting transition temperature (Tc) onset
at 3.7K and Tc ({\rho}=0) at 3.1K. Hump at Tc related to superconducting
transition is not observed in heat capacity measurement and rather a
Schottky-type anomaly is observed at below ~6K. The compound is slightly
semiconducting in normal state. Isothermal magnetization (MH) exhibited typical
type II behavior with lower critical field (Hc1) of around 8Oe.",1208.5873v3
2012-10-29,High-pressure phases of a hydrogen-rich compound: tetramethylgermane,"The vibrational and structural properties of a hydrogen-rich Group IVa
hydride, Ge(CH$_3$)$_4$, are studied by combining Raman spectroscopy and
synchrotron X-ray diffraction measurements at room temperature and at pressures
up to 30.2 GPa. Both techniques allow the obtaining of complementary
information on the high-pressure behaviors and yield consistent phase
transitions at 1.4 GPa for the liquid to solid and 3.0, 5.4, and 20.3 GPa for
the solid to solid. The four high-pressure solid phases are identified to have
the cubic, orthorhombic, monoclinic and monoclinic crystal structures with
space groups of Pa-3 for phase I, Pnma for phase II, P2$_1$/c for phase III,
and P2$_1$ for phase IV, respectively. These transitions are suggested to
result from the changes in the inter- and intra-molecular bonding of this
compound. The softening of some Raman modes on CH$_3$ groups and their sudden
disappearance indicate that Ge(CH$_3$)$_4$ might be an ideal compound to
realize metallization and even high-temperature superconductivity at modest
static pressure for laboratory capability.",1210.7560v1
2012-11-01,Large Diamagnetism of AV2Al20 (A = Y and La),"We find anomalously large diamagnetic responses in the cage compounds AV2Al20
where A = Y and La, not A = Al0.3, Sc0.4, and Lu, despite the apparent
similarities in crystal and electronic structures among these compounds. The
magnetic susceptibilities of the Y and La compounds become -1.94 and -7.44 x
10-4 cm3 mol-1 at 10 K, respectively, the latter of which corresponds to
approximately one-quarter of that of bismuth, a well-known diamagnetic
material, in terms of unit volume. The origin is not clear but may be related
to a specific evolution in the band structure, as the diamagnetic response
increases with increasing lattice constant.",1211.0066v1
2012-11-07,Study on the formation and the decomposition of AgN3 and a hypothetical compound ReN3 by using density functional calculations,"We present a comparative study between ReN3 and AgN3 by using density
functional theory. The ReN3 is a hypothetical compound proposed by us to
interpret the Re to Re interplanar spacing of thin films grown by sputtering.
Both, the AgN3 as the ReN3, are calculated as positive enthalpy compounds. The
enthalpy might give a clue about the spontaneous decomposition of the solid
form, but it cannot be interpreted as a restriction of its synthesizability. As
from the calculated total-energy, we discuss the route for the formation of
AgN3 starting from atomic species in aqueous solution. We propose that their
synthesizability is conditioned by the energy of free nitrogen atoms, and the
kinetics of reaction. We conclude that the intrinsic stability of a certain
atomic arrangement depends only of the equilibrium of atomic forces, and not
from the energy value associated with that structure.",1211.1704v1
2012-11-26,In-plane antiferromagnetism in $Na_{0.5}CoO_2$ induced by $Sb_{Co}$ dopants,"$Na_xCoO_2$ has a fascinating and complex magnetic phase diagram that can be
further manipulated by doping. Here, we investigated the effect of electron
doping on the magnetic coupling among $Co^{4+}$ ions in $Na_xCoO_2$ using
density functional theory based on Hartree-Fock hybrid functional. We found
that electron doping through substitutional $Sb_{Co}$ dopants flip the in-plane
ferromagnetic coupling among $Co^{4+}$ ions in the undoped compound to
antiferromagnetic. Electron doping through interstitial $Cu_{Int}$, however,
does not have a similar effect as $Cu_{Int}$ dopant leaves the compound
ferromagnetic, just like the case of the undoped compound. The results
demonstrate the critical dependence of magnetic phase in $Na_{0.5}CoO_2$ on the
dopant and its incorporation site.",1211.6167v3
2012-11-28,Stability of xenon oxides at high pressures,"Xenon, which is quite inert under ambient conditions, may become reactive
under pressure. The possibility of formation of stable xenon oxides and
silicates in the interior of the Earth could explain the atmospheric missing
xenon paradox. Using the ab initio evolutionary algorithm, we predict the
thermodynamical stabilization of Xe-O compounds at high pressures (XeO, XeO2
and XeO3 at pressures above 83, 102 and 114 GPa, respectively). Our
calculations indicate large charge transfer in these oxides, suggesting that
large electronegativity difference and pressure are the key factors favoring
the formation of xenon compounds. Xenon compounds in the Earth's mantle,
however, cannot directly explain the missing xenon paradox: xenon oxides are
unstable in equilibrium with metallic iron in the Earth's lower mantle, while
xenon silicates are predicted to spontaneously decompose at all mantle
pressures (<136 GPa). This does not preclude Xe atoms from being retained in
defects of mantle silicates and oxides.",1211.6520v2
2012-11-28,Unexpected Stoichiometries in Mg-O System under High Pressure,"Using ab initio evolutionary simulations, we explore all the possible
stoichiometries for Mg-O system at pressures up to 850 GPa. In addition to MgO,
our calculations find that two extraordinary compounds MgO2 and Mg3O2 become
thermodynamically stable at 116 GPa and 500 GPa, respectively. Detailed
chemical bonding analysis shows large charge transfer in all magnesium oxides.
MgO2 contains peroxide ions [O-O]2-, while non-nuclear electron density maxima
play the role of anions in the electride compound Mg3O2. The latter compound is
calculated to have a much narrower band gap compared to MgO and MgO2. We
discuss conditions at which MgO2 and Mg3O2 might exist in planetary conditions.",1211.6521v3
2012-12-04,Three-dimensional topological insulators: A review on host materials,"In recent years, three-dimensional topological insulators (3DTI) as a novel
state of quantum matter have become a hot topic in the fields of condensed
matter physics and materials sciences. To fulfill many spectacularly novel
quantum phenomena predicted in 3DTI, real host materials are of crucial
importance. In this review paper, we first introduce general methods of
searching for new 3DTI based on the density-functional theory. Then, we review
the recent progress on materials realization of 3DTI including simple elements,
binary compounds, ternary compounds, and quaternary compounds. In these
potential host materials, some of them have already been confirmed by
experiments while the others are not yet. The 3DTI discussed here does not
contain the materials with strong electron-electron correlation. Lastly, we
give a brief summary and some outlooks in further studies.",1212.0602v1
2012-12-10,YCr6Ge6 as a Candidate Compound for a Kagome Metal,"We show that YCr6Ge6, comprising a kagome lattice made up of Cr atoms, is a
plausible candidate compound for a kagome metal that is expected to exhibit
anomalous phenomena such as flat-band ferromagnetism. Resistivity,
magnetization, and heat capacity are measured on single crystals of YCr6Ge6,
and band structure calculations are performed to investigate the electronic
structure. Curie-Weiss-like behavior in magnetic susceptibility, T2 dependence
in resistivity, and a Sommerfeld coefficient doubly enhanced from a calculated
value indicate a moderately strong electron correlation. Interestingly, the
in-plane resistivity is twice as large as the interplane resistivity, which is
contrary to the simple expectation from the layered structure. Band structure
calculations demonstrate that there are partially flat bands slightly below the
Fermi level near the {\Gamma} point, which is ascribed to Cr 3d3z2-r2 bands and
may govern the properties of this compound.",1212.1976v1
2012-12-11,Appearance of Antiferromagnetism and Superconductivity in Superconducting Cuprates,"We represent the superconducting ceramic compounds by the single band
extended Hubbard model. We solve this model for the simultaneous presence of
antiferromagnetism and the d-wave superconductivity in the Hartree-Fock (H-F)
and in the coherent potential (CP) approximation, which is applied to the
on-site Coulomb repulsion U. The hopping interaction used in addition to the
Coulomb repulsion causes rapid expansion of the band at carrier concentrations
departing from unity. This expansion shifts the d-wave superconductivity away
from the half filled point reducing its occupation range approximately to the
experimental range in the YBaCuO compound. The CP approximation used for the
Coulomb repulsion is justified by the large ratio of Coulomb repulsion to the
effective width of perturbed density of states being reduced by the hopping
interaction. Fast disappearance of antiferromagnetism observed experimentally
is supported by the relatively large value of the total width of unperturbed
density of states. It is shown that our model is capable of describing the
electron doped compounds as well.",1212.2352v1
2013-01-11,Perspectives of the disproportionation driven superconductivity in strongly correlated 3d compounds,"Disproportionation in 3d compounds can give rise to an unconventional
electron-hole Bose liquid with a very rich phase diagram from a Bose metal,
charge ordering insulator to an inhomogeneous Bose superfluid. Optimal
conditions for the disproportionation driven high-T_c superconductivity are
shown to realize only for several Jahn-Teller d^n configurations that permit
the formation of well defined local composite bosons. These are the high-spin
d^4, low-spin d^7, and d^9 configurations given the octahedral crystal field,
and the d^1, high-spin d^6 configurations given the tetrahedral crystal field.
The disproportionation reaction has a peculiar anti-Jahn- Teller character
lifting the bare orbital degeneracy. Superconductivity in the d^4 and d^6
systems at variance with d^1, d^7, and d^9 systems implies an unavoidable
coexistence of the spin-triplet composite bosons and a magnetic lattice. We
argue that unconventional high-T_c superconductivity observed in quasi-2D
cuprates with tetragonally distorted CuO_6 octahedra and iron-based layered
pnictides/chalcogenides with tetrahedrally coordinated Fe^2+ ions can be a key
argument supporting the disproportionation scenario is at work in these
compounds.",1301.2395v1
2013-01-19,On the Uniqueness of the Canonical Polyadic Decomposition of third-order tensors --- Part I: Basic Results and Uniqueness of One Factor Matrix,"Canonical Polyadic Decomposition (CPD) of a higher-order tensor is
decomposition in a minimal number of rank-1 tensors. We give an overview of
existing results concerning uniqueness. We present new, relaxed, conditions
that guarantee uniqueness of one factor matrix. These conditions involve
Khatri-Rao products of compound matrices. We make links with existing results
involving ranks and k-ranks of factor matrices. We give a shorter proof, based
on properties of second compound matrices, of existing results concerning
overall CPD uniqueness in the case where one factor matrix has full column
rank. We develop basic material involving $m$-th compound matrices that will be
instrumental in Part II for establishing overall CPD uniqueness in cases where
none of the factor matrices has full column rank.",1301.4602v1
2013-02-07,Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3d-5d Transition-Metal Compound Sr3CuIrO6,"We report a combined experimental and theoretical study of the unusual
ferromagnetism in the one-dimensional copper-iridium oxide Sr$_3$CuIrO$_6$.
Utilizing Ir $L_3$ edge resonant inelastic x-ray scattering, we reveal a large
gap magnetic excitation spectrum. We find that it is caused by an unusual
exchange anisotropy generating mechanism, namely, strong ferromagnetic
anisotropy arising from antiferromagnetic superexchange, driven by the
alternating strong and weak spin-orbit coupling on the $5d$ Ir and 3d Cu
magnetic ions, respectively. From symmetry consideration, this novel mechanism
is generally present in systems with edge-sharing Cu$^{2+}$O$_4$ plaquettes and
Ir$^{4+}$O$_6$ octahedra. Our results point to unusual magnetic behavior to be
expected in mixed 3d-5d transition-metal compounds via exchange pathways that
are absent in pure 3d or 5d compounds.",1302.1818v2
2013-02-08,Superconducting Transition Temperatures for Spin-Fluctuation Promoted Superconductivity in Heavy Fermion Compounds,"The quantum critical Antiferromagnetic (AFM) fluctuation spectra measured by
inelastic neutron scattering recently in two heavy fermion superconductors are
used together with their other measured properties to calculate their D-wave
superconducting transition temperatures $T_{\rm c}$. To this end, the
linearized Eliashberg equations for D-wave superconductivity induced by AFM
fluctuations are solved in models of fermions with various levels of nesting.
The results for the ratio of $T_{\rm c}$ to the characteristic spin-fluctuation
energy are well parametrized by a dimensionless coupling constant and the AFM
correlation length. Comparing the results with experiments suggests that one
may reasonably conclude that superconductivity in these compounds is indeed
caused by AFM fluctuations. This conclusion is strengthened by a calculation
with the same parameters of the measured coefficient of the normal state
quantum-critical resistivity $\propto T^{3/2}$ characteristic of {\it gaussian}
AFM quantum-critical fluctuations. The calculations give details of the
superconducting coupling as a function of the correlation length and the
integrated fluctuation spectra useful in other compounds.",1302.2160v2
2013-03-09,Adiabatic transformation as a search tool for new topological insulators: distorted ternary Li$_2$AgSb-class semiconductors and related compounds,"We demonstrate that first-principles based adiabatic continuation approach is
a very powerful and efficient tool for constructing topological phase diagrams
and locating non-trivial topological insulator materials. Using this technique,
we predict that the ternary intermetallic series Li$_2M'X$ where $M'$=Cu, Ag,
Au, or Cd, and $X$=Sb, Bi, or Sn, hosts a number of topological insulators with
remarkable functional variants and tunability. We also predict that several
III-V semimetallic compounds are topologically non-trivial. We construct a
topological phase diagram in the parameter space of the atomic numbers of atoms
in Li$_2M'X$ compounds, which places a large number of topological materials
presented in this work as well as in earlier studies within a single unified
topological framework. Our results demonstrate the efficacy of adiabatic
continuation as a useful tool for exploring topologically nontrivial alloying
systems and for identifying new topological insulators even when the underlying
lattice does not possess inversion symmetry, and the approaches based on parity
analysis are not viable.",1303.2228v1
2013-03-12,Reentrant Superconductivity in Eu(Fe1-xIrx)2As2,"The interplay between superconductivity and Eu$^{2+}$ magnetic ordering in
Eu(Fe$_{1-x}$Ir$_{x}$)$_{2}$As$_{2}$ is studied by means of electrical
transport and magnetic measurements. For the critically doped sample
Eu(Fe$_{0.86}$Ir$_{0.14}$)$_{2}$As$_{2}$, we witnessed two distinct transitions
: a superconducting transition below 22.6 K which is followed by a resistivity
reentrance caused by the ordering of the Eu$^{2+}$ moments. Further, the low
field magnetization measurements show a prominent diamagnetic signal due to
superconductivity which is remarkable in presence of a large moment
magnetically ordered system. The electronic structure for a 12.5% Ir doped
EuFe$_{1.75}$Ir$_{0.25}$As$_{2}$ is investigated along with the parent compound
EuFe$_{2}$As$_{2}$. As compared to EuFe$_{2}$As$_{2}$, the doped compound has
effectively lower value of density of states throughout the energy scale with
more extended bandwidth and stronger hybridization involving Ir. Shifting of
Fermi energy and change in band filling in EuFe$_{1.75}$Ir$_{0.25}$As$_{2}$
with respect to the pure compound indicate electron doping in the system.",1303.2855v2
2013-03-16,Dispersive spin excitations in highly overdoped cuprates revealed by resonant inelastic x-ray scattering,"Using resonant inelastic x-ray scattering (RIXS) at the Cu $L$-absorption
edge, we have observed intense, dispersive spin excitations in highly overdoped
Tl$_2$Ba$_2$CuO$_{6+\delta}$ (superconducting $T_c =6$ K), a compound whose
normal-state charge transport and thermodynamic properties have been studied
extensively and shown to exhibit canonical Fermi-liquid behavior. Complementary
RIXS experiments on slightly overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$ ($T_c =89$
K) and on Y$_{1-x}$Ca$_{x}$Ba$_2$Cu$_3$O$_{6+\delta}$ compounds spanning a wide
range of doping levels indicate that these excitations exhibit energies and
energy-integrated spectral weights closely similar to those of
antiferromagnetic magnons in undoped cuprates. The surprising coexistence of
Fermi-liquid-like charge excitations and high-energy spin excitations
reminiscent of antiferromagnetic insulators in highly overdoped compounds poses
a challenge to current theoretical models of the cuprates.",1303.3947v1
2013-04-06,Effect of activation procedure on Sm-Co-Fe-Zr-B compound for low temperature efficient hydrogen storage,"The present research work is focused on the effect of activation procedure on
the hydrogen absorption-desorption properties of new rare earth transition
metal compound based on Sm(Co0.6Fe0.2Zr0.16B0.04)7.5 composition. Crystal
structure and composition is always connected to the maximum capacity of the
intermetallic hydrides. For composite materials the thermodynamic properties of
hydrogenation & dehydrogenation procedure are mostly explained through
microstructure-microchemistry characteristics. Efficient hydrogen storage is
direct connected to the desorbed hydrogen amount. The as hydrogenated material
Sm(Co0.6Fe0.2Zr0.16B0.04)7.5 seems to have in the desorption a pressure plateau
below the atmospheric pressure at room temperature while the absorbed hydrogen
almost remains in the material having capacity of ~0.8 wt. % at 0.1 MPa - 30
oC. After the proper activation procedure, the hydrogenated material desorbs
very high amount of hydrogen ~1.9 wt. % at 0.1 MPa - 100 oC. Subsequently, the
treatment of the composite materials before hydrogenation & dehydrogenation
procedures could play a crucial role on the efficiency.",1304.1901v1
2013-04-11,Electronic structure of KTi(SO4)2.H2O - a S=1/2 frustrated chain antiferromagnet,"The compound KTi(SO4)2.H2O was recently reported as a quasi one-dimensional
spin 1/2 compound with competing antiferromagnetic nearest neighbor exchange J1
and next-nearest neighbor exchange J2 along the chain with a frustration ratio
alpha = J2/J1 ~ 0.29 [Chem. Mater. vol. 20, pg. 8 (2008)]. Here, we report a
microscopically based magnetic model for this compound derived from density
functional electronic structure calculations along with respective
tight-binding models. Our calculations confirm the quasi one-dimensional nature
of the system with antiferromagnetic J1 and J2, but suggest a significantly
larger frustration ratio alpha ~ 1.1 +- 0.2. Based on transfer matrix
renormalization group calculations we found that, due to an intrinsic symmetry
of the J1-J2 model, our larger frustration ratio alpha is also consistent with
the previous thermodynamic data. To resolve this issue, we propose performing
high-field magnetization measurements and low temperature susceptibility
measurements which should allow to precisely identify the frustration ratio
alpha.",1304.3361v1
2013-06-21,Magnetic properties of a family of quinternary oxalates,"We report on the magnetic properties of four isomorphous compounds of a
family of quinternary oxalates down to 60 mK. In all these materials, the
magnetic FeII ions with a strong magneto-crystalline anisotropy form a
distorted kagome lattice, topologically equivalent to a perfect kagome one if
nearest-neighbor interactions only are considered. All the compounds order at
low temperature in an antiferromagnetic arrangement with magnetic moments at
120{\deg}. A remarkable magnetic behavior emerges below the N\'eel temperature
in three compounds (with inter-kagome-layer Zr, Sn, Fe but not with Al): the
spin anisotropy combined with a low exchange path network connectivity lead to
domain walls intersecting the kagome planes through strings of free spins.
These produce an unfamiliar slow spin dynamics in the ordered phase observed by
AC susceptibility, evolving from exchange-released spin-flips towards a
cooperative behavior on decreasing the temperature.",1306.5188v1
2013-07-20,"NMR and NQR Studies on Non-centrosymmetric Superconductors Re7B3, LaBiPt, and BiPd","We report the nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) measurements for non-centrosymmetric superconductors Re7B3,
LaBiPt, and BiPd containing heavy elements. For all three compounds, the
spin-lattice relaxation rate 1/T1 shows a coherence peak just below Tc and
decreases exponentially at low temperatures, which indicates that an isotropic
superconducting gap is dominant in these compounds. In BiPd, the height of the
coherence peak just below Tc is much suppressed, which suggests that there
exists a substantial component of gap with nodes in this compound. Our results
indicate that heavy element is not the only factor, but the extent of inversion
symmetry breaking is also important to induce a large spin-orbit coupling and
an unconventional superconducting state.",1307.5382v1
2013-07-23,Exploration of iron-chalcogenide superconductors,"Iron-chalcogenide compounds with FeSe(Te, S) layers did not attract much
attention until the discovery of high-Tc superconductivity (SC) in the
iron-pnictide compounds at the begining of 2008. Compared with FeAs-based
superconductors, iron-chalcogenide superconductors have aroused enormous
enthusiasm to study the relationship between SC and magnetisms with several
distinct features, such as different antiferromagnetic ground states with
relatively large moments in the parents, indicating possibly different
superconducting mechanisms, the existence of the excess Fe atoms or Fe
vacancies in the crystal lattice. Another reason is that the large single
crystals are easily grown for the iron-chalcogenide compounds. This review will
focus on our exploration for the iron-chalcogenide superconductors and
discussion on several issues, including the crystal structure, magnetic
properties, superconductivity, and phase separation. Some of them reach a
consensus but some important questions still remain to be answered.",1307.5991v1
2013-08-21,Superconductivity in the Mn5Si3-type Zr5Sb3 system,"We report the discovery of superconductivity at 2.3 K in Zr5Sb3, the first
superconducting member in the large compound family of the Mn5Si3-structure
type. Transport, magnetic, and calorimetric measurements and band structure
calculations show it to be a phonon-mediated BCS superconductor, with a
relatively large density of states at the Fermi level associated with the
d-electrons of Zr and substantially larger electron-phonon coupling compared to
the Sn counterpart compound Zr5Sn3. More superconductors with even higher
transition temperatures are expected to be found in this family of compounds.",1308.4649v1
2013-08-28,"Compound Poisson Processes, Latent Shrinkage Priors and Bayesian Nonconvex Penalization","In this paper we discuss Bayesian nonconvex penalization for sparse learning
problems. We explore a nonparametric formulation for latent shrinkage
parameters using subordinators which are one-dimensional L\'{e}vy processes. We
particularly study a family of continuous compound Poisson subordinators and a
family of discrete compound Poisson subordinators. We exemplify four specific
subordinators: Gamma, Poisson, negative binomial and squared Bessel
subordinators. The Laplace exponents of the subordinators are Bernstein
functions, so they can be used as sparsity-inducing nonconvex penalty
functions. We exploit these subordinators in regression problems, yielding a
hierarchical model with multiple regularization parameters. We devise ECME
(Expectation/Conditional Maximization Either) algorithms to simultaneously
estimate regression coefficients and regularization parameters. The empirical
evaluation of simulated data shows that our approach is feasible and effective
in high-dimensional data analysis.",1308.6069v3
2013-09-05,3d-4f spin interaction induced giant magnetocaloric effect in zircon-type DyCrO4 and HoCrO4 compounds,"We have investigated the influence of 3d-4f spin interaction on magnetic and
magnetocaloric properties of DyCrO$_4$ and HoCrO$_4$ compounds by magnetization
and heat capacity measurements. Both the compounds exhibit complicated magnetic
properties and huge magnetic entropy change around the ferromagnetic transition
due to the strong competition between ferromagnetic and antiferromagnetic
superexchange interactions. For a field change of 8 T, the maximum values of
magnetic entropy change ($\Delta S_{M}^{max}$), adiabatic temperature change
($\Delta T_{ad}$), and refrigerant capacity (RC) reach 29 J kg$^{-1}$ K$^{-1}$,
8 K, and 583 J kg$^{-1}$, respectively for DyCrO$_4$ whereas the corresponding
values for HoCrO$_4$ are 31 J kg$^{-1}$ K$^{-1}$, 12 K, and 622 J kg$^{-1}$.
$\Delta S_{M}^{max}$, $\Delta T_{ad}$, and RC are also quite large for a
moderate field change. The large values of magnetocaloric parameters suggest
that the zircon-type DyCrO$_4$ and HoCrO$_4$ could be the potential magnetic
refrigerant materials for liquefaction of hydrogen.",1309.1242v1
2013-09-24,Chemical capacitance proposed for manganite-based ceramics,"The measured value of effective electric permittivity \varepsilon_{eff} of
several compounds, e.g., (BiNa)(MnNb)O_{3}, (BiPb)(MnNb)O_{3}, and BiMnO_{3}
increases from a value \approx 10-100 at the low temperature range (100-300 K)
up to the high value reaching the value 10^5 at high temperature range, e.g.,
500-800 K. Such features suggest the manifestation of thermally activated space
charge carriers, which effect the measured capacitance. The measured high-value
effective permittivity of several manganite compounds can be ascribed to the
chemical capacitance C_{\mu}=e^2\partial N_{i}/\partial \mu_{i} expressed in
terms of the chemical potential \mu. The chemical capacitance C_{\mu}^{(cb)} =
e^2 n_{C}/k_{B}T depends on temperature when the conduction electrons with
density n_{C} = N_{C} \exp(\mu_{n}- E_{C})/k_{B}T are considered. The
experimental results obtained for the manganite compounds, at high temperature
range, are discussed in the framework of the chemical capacitance model.
However, the measured capacitance dependence on geometrical factors is analysed
for BiMnO_{3} indicating that the non-homogeneous electrostatic capacitor model
is valid in 300-500 K range.",1309.6127v1
2013-11-14,Structural variations and magnetic properties of the quantum antiferromagnets Cs2CuCl4-xBrx,"Depending on the crystal growth conditions, an orthorhombic (O-type) or a
tetragonal (T-type) structure can be found in the solid solution Cs2CuCl4-xBrx
(0 < x < 4). Here we present measurements of the temperature-dependent magnetic
susceptibility and isothermal magnetization on the T-type compounds x = 1.6 and
1.8 and compare these results with the magnetic properties recently derived for
the O-type variant by Cong et al., Phys. Rev. B 83, 064425 (2011). The systems
were found to exhibit quite dissimilar magnetic properties which can be
assigned to differences in the Cu coordination in these two structural
variants. Whereas the tetragonal compounds can be classified as quasi-2D
ferromagnets, characterized by ferromagnetic layers with a weak
antiferromagnetic inter-layer coupling, the orthorhombic materials, notably the
border compounds x = 0 and 4, are model systems for frustrated 2D Heisenberg
antiferromagnets",1311.3351v1
2013-11-19,Interplay of superconductivity and magnetism in FeSe$_{1-x}$Te$_x$ compounds. Pressure effects,"The influence of uniform pressures $P$ up to 5 kbar on the superconducting
transition temperature $T_c$ was studied for the FeSe$_{1-x}$Te$_x$ ($x=0$,
0.85, 0.88 and 0.9) system. For the first time, we observed a change in sign of
the pressure effect on $T_c$ when going from FeSe to tellurium rich alloys.
This has allowed to specify the pressure derivative d$T_c$/d$P$ for the system
as a function of composition. The observed dependence was compared with results
of the {\em ab initio} calculations of electronic structure and magnetism of
FeSe, FeTe and FeSe$_{0.5}$Te$_{0.5}$, and also with our recent experimental
data on pressure effects on magnetic susceptibilities of FeSe and FeTe
compounds in the normal state. This comparison demonstrates a competing
interplay between superconductivity and magnetism in tellurium rich
FeSe$_{1-x}$Te$_x$ compounds",1311.4656v1
2013-12-02,Thermodynamic properties of LiCu$_{2}$O$_{2}$ multiferroic compound,"A spin model of quasi-one dimensional LiCu$_{2}$O$_{2}$ compound with ground
state of ellipsoidal helical structure in which the helical axis is along the
diagonal of CuO$_{4}$ squares has been adopted. By taking into account the
interchain coupling and exchange anisotropy, the exotic magnetic properties and
ferroelectricity induced by spiral spin order have been studied by performing
Monte Carlo simulation. The simulation results qualitatively reproduce the main
characters of ferroelectric and magnetic behaviors of LiCu$_{2}$O$_{2}$
compound and confirm the low-temperature incollinear spiral ordering.
Furthermore, by performing the calculations of spin structure factor, we
systematically investigate the effects of different exchange coupling on the
lower-temperature magnetic transition, and find that the spiral spin order
depends not only on the ratio of nearest and next-nearest neighbor inchain spin
coupling but also strongly on the exchange anisotropy.",1312.0293v1
2013-12-05,p-Type Zinc Oxide Spinels: Application to Transparent Conductors and Spintronics,"We report on the electronic and optical properties of two theoretically
predicted stable spinel compounds of the form ZnB2O4, where B = Ni or Cu;
neither compound has been previously synthesized, so we compare them to the
previously studied p-type ZnCo2O4 spinel. These new materials exhibit spin
polarization that is ideal for spintronics applications, and broad conductivity
maxima near the valence band edge that facilitate p-type dopability. We show
that 3d electrons on the octahedrally coordinated Zn atom fall deep within the
valence band and do not contribute significantly to the electronic structure of
the material, while the O 2p and tetrahedrally coordinated B 3d electrons
hybridize broadly in the shallow valence states, resulting in increasing
curvature (i.e., decreased electron effective mass) of valence bands near the
band edge. In particular, ZnCu2O4 exhibits high electrical conductivities near
the valence band edge that, at sigma = 2 x 10^4 S/cm, are twice the maximum
found for ZnCo2O4, a previously synthesized compound in this class of
materials. This material also exhibits ferromagnetism in all of its most stable
structures, which makes it a good candidate for further study as a dilute
magnetic semiconductor.",1312.1728v1
2013-12-13,Dielectric and Magnetic Properties of (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 Ceramics Prepared from Mechanically Synthesized Powders,"Multiferroic (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 ceramics was prepared from
mechanical synthesized nanopowders. The XRD studies revealed the tetragonal
structure and the tetragonality decreased with La content. Dielectric response
of the compounds was found to contain three anomalies: 1) relaxor-like behavior
due to lattice disorder (below 300 K); 2) dielectric permittivity maxima at~400
K attributed to the presence of oxygen vacancies; 3) grain boundary effect
above 475 K. The Curie point at ~500 K was observed for the compound with
x=0.5. The composition near the morphotropic boundary:
(Bi0.8La0.2FeO3)0.5(PbTiO3)0.5 shoved the highest remnant magnetization. The
irreversible magnetic properties of the (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 compounds
can be explained in terms of disorder induced spin-glass behavior due to random
substitution of La or Pb ions for Bi sites. A sharp step in magnetization about
250 K is caused by the A-site distortion associated with tilts of FeO6
octahedra leading to modification of Fe-O-Fe angles and of antiferromagnetic
coupling between magnetic Fe3+ moments.",1312.3886v1
2014-01-30,Revealing multiple density wave orders in non-superconducting titanium oxypnictide Na$_2$Ti$_2$As$_2$O,"We report an optical spectroscopy study on the single crystal of
Na$_2$Ti$_2$As$_2$O, a sister compound of superconductor BaTi$_2$Sb$_2$O. The
study reveals unexpectedly two density wave phase transitions. The first
transition at 320 K results in the formation of a large energy gap and removes
most part of the Fermi surfaces. But the compound remains metallic with
residual itinerant carriers. Below 42 K, another density wave phase transition
with smaller energy gap scale occurs and drives the compound into
semiconducting ground state. These experiments thus enable us to shed light on
the complex electronic structure in the titanium oxypnictides.",1401.7853v1
2014-03-02,Nodeless superconducting gaps in Ca$_{10}$(Pt$_{4-δ}$As$_8$)((Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$)$_5$ probed by quasiparticle heat transport,"The in-plane thermal conductivity of iron-based superconductor
Ca$_{10}$(Pt$_{4-\delta}$As$_8$)((Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$)$_5$ single
crystal (``10-4-8"", $T_c$ = 22 K) was measured down to 80 mK. In zero field,
the residual linear term $\kappa_0/T$ is negligible, suggesting nodeless
superconducting gaps in this multiband compound. In magnetic fields,
$\kappa_0/T$ increases rapidly, which mimics those of multiband superconductor
NbSe$_2$ and LuNi$_2$B$_2$C with highly anisotropic gap. Such a field
dependence of $\kappa_0/T$ is an evidence for multiple superconducting gaps
with quite different magnitudes or highly anisotropic gap. Comparing with the
London penetration depth results of
Ca$_{10}$(Pt$_3$As$_8$)((Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$)$_5$ (``10-3-8"")
compound, the 10-4-8 and 10-3-8 compounds may have similar superconducting gap
structure.",1403.0194v1
2014-03-06,Ordered Phases and Quantum Criticality in Cubic Heavy Fermion Compounds,"Quantum criticality in cubic heavy fermion compounds remains much less
explored than in quasi-two-dimensional systems. However, such materials are
needed to broadly test the recently suggested global phase diagram for heavy
fermion quantum criticality. Thus, to boost these activities, we review the
field, with focus on Ce-based systems with temperature-magnetic field or
temperature-pressure phase diagrams that may host a quantum critical point. To
date, CeIn3 and Ce3Pd20Si6 are the only two among these compounds where quantum
critical behaviour has been systematically investigated. Interestingly, both
show Fermi surface reconstructions as function of the magnetic field that may
be understood in terms of Kondo destruction quantum criticality.",1403.1386v1
2014-03-12,Spin Gap in the Single Spin-1/2 Chain Cuprate Sr$_{1.9}$Ca$_{0.1}$CuO$_3$,"We report $^{63}$Cu nuclear magnetic resonance and muon spin rotation
measurements on the S=1/2 antiferromagnetic Heisenberg spin chain compound
Sr$_{1.9}$Ca$_{0.1}$CuO$_3$. An exponentially decreasing spin-lattice
relaxation rate 1/T$_1$ indicates the opening of a spin gap. This behavior is
very similar to what has been observed for the cognate zigzag spin chain
compound Sr$_{0.9}$Ca$_{0.1}$CuO$_2$, and confirms that the occurrence of a
spin gap upon Ca doping is independent of the interchain exchange coupling
$J'$. Our results therefore generally prove the appearance of a spin gap in an
antiferromagnetic Heisenberg spin chain induced by a local bond disorder of the
intrachain exchange coupling $J$. A low temperature upturn of 1/T$_1$ evidences
growing magnetic correlations. However, zero field muon spin rotation
measurements down to 1.5 K confirm the absence of magnetic order in this
compound which is most likely suppressed by the opening of the spin gap.",1403.2890v1
2014-03-17,"Magnetic structures of non-cerium analogues of heavy-fermion Ce2RhIn8: case of Nd2RhIn8, Dy2RhIn8 and Er2RhIn8","R2RhIn8 compounds (space group P4/mmm, R is a rare-earth element) belong to a
large group of structurally related tetragonal materials which involves several
heavy-fermion superconductors based on Ce. We have succeeded to grow single
crystals of compounds with Nd, Dy and Er and following our previous bulk
measurements, we performed neutron-diffraction studies to determine their
magnetic structures. The Laue diffraction experiment showed that the
antiferromagnetic order below the N\'eel temperature is in all three compounds
characterized by the propagation vector k = (1/2, 1/2, 1/2). The amplitude and
direction of the magnetic moments, as well as the invariance symmetry of the
magnetic structure, were determined by subsequent experiments using two- and
four-circle diffractometers. The critical exponents were determined from the
temperature dependence of the intensities below TN.",1403.4159v1
2014-03-26,Mechanism of charge transfer/disproportionation in LnCu3Fe4O12 (Ln: Lanthanides),"The Fe-Cu intersite charge transfer and Fe charge disproportionation are
interesting phenomena observed in some LnCu3Fe4O12 (Ln: Lanthanides) compounds
containing light and heavy Ln atoms, respectively. We show that a change in the
spin state is responsible for the intersite charge transfer in the light Ln
compounds. At the high spin state, such systems prefer an unusual Cu-d^8
configuration, whereas at the low spin state they retreat to the normal Cu-d^9
configuration through a charge transfer from Fe to Cu-3d_{xy} orbital. We find
that the strength of the crystal field splitting and the relative energy
ordering between Cu-3d_{xy} and Fe-3d states are the key parameters,
determining the intersite charge transfer (charge disproportionation) in light
(heavy) Ln compounds. It is further proposed that the size of Ln affects the
onsite interaction strength of Cu-3d states, leading to a strong modification
of the Cu-L_3 edge spectrum, as observed by the X-ray absorption spectroscopy.",1403.6589v1
2014-04-30,Enhanced superconductivity in F-doped LaO1-xFxBiSSe,"The layered compound LaOBiSSe was successfully synthesized by a two-step
solid-state reaction method, which is isostructural with the quaternary
compound LaOBiS2 indicated by the powder X-ray diffraction characterization,
and the crystal lattice parameters are slightly expanded by the substitution of
Se atoms. Electrical transport measurement shows that LaOBiSSe exhibits
semiconducting behavior similar with the parent compound LaOBiS2, while by
F-doping the samples can be much more easily turned to be metallic and
superconducting at low temperature with a small amount of F. Under the optimal
carrier doping concentration of F ~ 0.5, the superconducting critical
temperature of LaO0.5F0.5BiSSe is clearly enhanced up to a value of 3.8 K than
the 3.2 K of LaO0.5F0.5BiS2.",1404.7562v1
2014-05-02,Mott insulator-to-metal transition in yttrium-doped CaIrO3,"We report on the study of insulator-to-metal transition in post-perovskite
compound CaIrO3. It is discovered that a gradual chemical substitution of
calcium by yttrium leads to the onset of strong metallic behavior in this
compound. This observation is in stark contrast to BaIrO3, which preserves its
Mott insulating behavior despite excess of charge carriers due to yttrium
doping. Magnetic measurements reveal that both compounds tend to exhibit
magnetic character irrespective of the chemical substitution of Ca or Ba. We
analyze these unusual observations in light of recent researches that suggest
that unlike BaIrO3, CaIrO3 does not necessarily possess j = 1/2 ground state
due to structural distortion. The insulator-to-metal transition in CaIrO3 will
spur new researches to explore more exotic ground state, including
superconductivity, in post-perovskite Mott insulators.",1405.0512v2
2014-05-09,Structure and modeling of the network of two-Chinese-character compound words in the Japanese language,"This paper proposes a numerical model of the network of two-Chinese-character
compound words (two-character network, for short). In this network, a Chinese
character is a node and a two-Chinese-character compound word links two nodes.
The basic framework of the model is that an important character gets many
edges. As the importance of a character, we use the frequency of each character
appearing in publications. The direction of edge is given according to a random
number assigned to nodes. The network generated by the model is small-world and
scale-free, and reproduces statistical properties in the actual two-character
network quantitatively.",1405.2167v1
2014-05-23,Significant enhancement of superconductivity under hydrostatic pressure in CeO0.5F0.5BiS2 superconductor,"We report the effect of hydrostatic pressure (0-1.97GPa) on the
superconductivity of BiS2 based CeO0.5F0.5BiS2 compound. The CeO0.5F0.5BiS2
superconductor was synthesized by the solid state reaction route and the
compound is crystallized in tetragonal P4/nmm space group. The studied compound
shows superconductivity with transition temperature of 2.5K (Tconset) at
ambient pressure, which has been enhanced to 8 K at applied pressure of 1.97
GPa. The observed normal resistivity exhibited semiconducting behavior. The
data of normal state resistivity R(T) has been fitted by activation type
equation and it is found that the energy gap is significantly reduced with
pressure. Resistivity measurements under magnetic field for the highest applied
pressure of 1.97GPa (Tconset = 8K) exhibits the upper critical field of above
5Tesla. The observation of fourfold increase in Tc accompanied with improved
normal state conduction under hydrostatic pressure on CeO0.5F0.5BiS2
superconductor calls for the attention of solid state physics community.",1405.5976v2
2014-07-03,"Superconductivity by rare earth doping in the 1038-type compounds (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) with RE = Y, La-Nd, Sm-Lu","We report superconductivity in polycrystalline samples of the 1038-type
compounds (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) up to T$_c$ = 35
K with RE = Y, La-Nd, Sm, Gd-Lu. The critical temperatures are independent of
the trivalent rare earth element used, yielding an universal T$_c$($x$) phase
diagram for electron doping in all these systems. The absence of
superconductivity in Eu$^{2+}$ doped samples, as well as the close resemblance
of (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) to the 1048 compound
substantiate that the electron doping scenario in the RE-1038 and 1048 phases
is completely analogous to other iron-based superconductors with simpler
crystal structures.",1407.1007v1
2014-07-11,"Superconductivity by transition metal doping in Ca$_{10}$(Fe$_{1-x}$M$_x$As)$_{10}$(Pt$_3$As$_8$) (M = Co, Ni, Cu)","We report the successful substitution of cobalt, nickel, and copper for iron
in the 1038 phase parent compound Ca$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) yielding
Ca$_{10}$(Fe$_{1-x}$Co$_x$As)$_{10}$(Pt$_3$As$_8$),
Ca$_{10}$(Fe$_{1-x}$Ni$_x$As)$_{10}$(Pt$_3$As$_8$), and
Ca$_{10}$(Fe$_{1-x}$Cu$_x$As)$_{10}$(Pt$_3$As$_8$), respectively.
Superconductivity is induced in Co and Ni doped compounds reaching critical
temperatures up to 15 K, similar to known Pt substituted
Ca$_{10}$(Fe$_{1-x}$Pt$_x$As)$_{10}$(Pt$_3$As$_8$), whereas no
superconductivity was detected in
Ca$_{10}$(Fe$_{1-x}$Cu$_x$As)$_{10}$(Pt$_3$As$_8$). The obtained Tc(x) phase
diagrams are very similar to those of other iron arsenide superconductors
indicating rather universal behavior despite the more complex structures of the
1038-type compounds, where the physics is primarily determined by the FeAs
layer.",1407.3100v1
2014-07-19,Magnetic states of iron-based superconducting compounds calculated by using GGA$+U$ method with negative \emph{U},"The magnetic moments per Fe atom in high-$T{_\textrm{c}}$ iron-based
superconducting compounds, BaFe$_{2}$As$_{2}$ and LaFeAsO obtained from the
first-principles calculation with local-spin-density approximation are much
larger than those obtained from experiments. To resolve the contradictory
results between theory and experiment we employed the so-called LDA$+ U$ (or
more exactly GGA$+ U$) technique with negative \emph{U} in the first-principles
calculation. The calculated values with negative \emph{U}, $- 0.09$ Ry and $-
0.10$ Ry for BaFe$_{2}$As$_{2}$ and LaFeAsO, respectively, are in excellent
agreement with the experimental ones. By comparing the differences in
\emph{d}-orbital occupation numbers and spin densities calculated by using a
simple GGA and GGA$+ U$ with negative $U$, the magnetic moments of the two
compounds are found to be similar to the case of low-spin state of metamagnetic
Fe$_{3}$Al alloy.",1407.5137v1
2014-08-06,"Synthesis, single crystal growth and properties of $Sr_5Pb_3ZnO_{12}$","The novel $Sr_5Pb_3ZnO_{12}$ oxide was synthesized by the solid-state
reaction method. The crystal structure was studied by means of the powder x-ray
diffraction Rietveld method and was found to be similar to 3 other previously
known $Sr_5Pb_3MO_{12}$ compounds (M = Co, Ni, Cu). Crystals of several hundred
microns in size of the new phase were grown in molten sodium chloride and
imaged using confocal optical and scanning electron microscopy. Electrical
properties were studied using the impedance spectroscopy technique. It was
found that $Sr_5Pb_3ZnO_{12}$ is a dielectric material with rather high
relative permittivity ($\epsilon_r$ = 22 at 300K) and with activation energy of
the dielectric relaxation process $E_A$ = 0.80(4) eV. The heat capacity studies
reveal the Debye temperature $\Theta_D$ = 324(1) K.",1408.1241v1
2014-08-12,"First-Principles Calculation of the Bulk Photovoltaic Effect in the Polar Compounds LiAsS$_\text{2}$, LiAsSe$_\text{2}$, and NaAsSe$_\text{2}$","We calculate the shift current response, which has been identified as the
dominant mechanism for the bulk photovoltaic effect, for the polar compounds
LiAsS$_\text{2}$, LiAsSe$_\text{2}$, and NaAsSe$_\text{2}$. We find that the
magnitudes of the photovoltaic responses in the visible range for these
compounds exceed the maximum response obtained for BiFeO$_\text{3}$ by 10 - 20
times. We correlate the high shift current response with the existence of $p$
states at both the valence and conduction band edges, as well as the dispersion
of these bands, while also showing that high polarization is not a requirement.
With low experimental band gaps of less than 2 eV and high shift current
response, these materials have potential for use as bulk photovoltaics.",1408.2819v2
2014-08-18,"Magnetoelectric properties of $A_2$[FeCl$_5$(H$_2$O)] with $A = $ K, Rb, Cs","The compounds $A_2$[FeCl$_5$(H$_2$O)] with $A=$ K, Rb, Cs are identified as
new linear magnetoelectric materials. We present a detailed investigation of
their linear magnetoelectric properties by measurements of pyroelectric
currents, dielectric constants and magnetization. The anisotropy of the linear
magnetoelectric effect of the K-based and Rb-based compound is consistent with
the magnetic point group $m'm'm'$, already reported in literature. A symmetry
analysis of the magnetoelectric effect of the Cs-based compound allows to
determine the magnetic point group $mmm'$ and to develop a model for its
magnetic structure. In addition, magnetic-field versus temperature phase
diagrams are derived and compared to the closely related multiferroic
(NH$_4$)$_2$[FeCl$_5$(H$_2$O)].",1408.3997v2
2014-08-27,Localised Wannier orbital basis for the Mott insulators GaV4S8 and GaTa4Se8,"We study the electronic properties of GaV4S8 (GVS) and GaTaSe8 (GTS), two
distant members within the large family of chalcogenides AM4X8, with A={Ga,
Ge}, M={V, Nb, Ta, Mo} and X={S, Se}. While all these compounds are Mott
insulators, their ground state show many types of magnetic order, with GVS
being ferromagnetic and GTS non-magnetic. Based on their bandstructures,
calculated with Density Functional Theory methods, we compute an effective
tight binding Hamiltonian in a localised Wannier basis set, for each one of the
two compounds. The localised orbitals provide a very accurate representation of
the bandstructure, with hopping amplitudes that rapidly decrease with distance.
We estimate the super-exchange interactions and show that the Coulomb repulsion
with the Hund's coupling may account the for the different ground states
observed in GVS and GTS. Our localised Wannier basis provides a starting point
for realistic Dynamical Mean Field Theory studies of strong correlation effects
in this family compounds.",1408.6458v1
2014-09-03,Backbone NxH Compounds at High Pressures,"Optical and synchrotron x-ray diffraction diamond anvil cell experiments have
been combined with first principles theoretical structure predictions to
investigate mixed N2 and H2 up to 55 GPa. We found the formation of oligomeric
NxH (x>1) compounds using mechano- and photochemistry at pressures above 47 and
10 GPa, respectively, and room temperature. These compounds can be recovered to
ambient pressure at T<130 K, whereas at room temperature, they can be
metastable down to 3.5 GPa. Our results suggest new pathways for synthesis of
environmentally benign high energy-density materials and alternative planetary
ice.",1409.1181v1
2014-09-08,Prediction of pressure-induced stabilization of noble-gas-atom compounds with alkali oxides and alkali sulfides,"The cubic antifluorite structure comprises a face-centered cubic sublattice
of anions with cations on the tetrahedral sites. The voids in the antifluorite
structure that are crucial for superionicity in Li2O might also act as atomic
traps. Trapping of guest atoms and small molecules within voids of a host
structure leads to the formation of what are known as clathrate compounds. Here
we investigate the possibility of trapping helium or larger neon guest atoms
under pressure within alkali metal oxide and sulfide structures. We find stable
helium and neon-bearing compounds at very low pressures. These structures are
stabilized by a reduction in volume from incorporation of helium or neon atoms
within the antifluorite structure. We predict that NeCs2S could be stable at
ambient pressure. Our study suggests a novel class of alkali oxide and sulfide
materials incorporating noble gas atoms that might potentially be useful for
gas storage.",1409.2227v2
2014-10-24,"Defect propagation in one-, two-, and three-dimensional compounds doped by magnetic atoms","Inelastic neutron scattering experiments were performed to study
manganese(II) dimer excitations in the diluted one-, two-, and
three-dimensional compounds CsMn(x)Mg(1-x)Br(3), K(2)Mn(x)Zn(1-x)F(4), and
KMn(x)Zn(1-x)F(3) (x<0.10), respectively. The transitions from the ground-state
singlet to the excited triplet, split into a doublet and a singlet due to the
single-ion anisotropy, exhibit remarkable fine structures. These unusual
features are attributed to local structural inhomogeneities induced by the
dopant Mn atoms which act like lattice defects. Statistical models support the
theoretically predicted decay of atomic displacements according to 1/r**2, 1/r,
and constant (for three-, two-, and one-dimensional compounds, respectively)
where r denotes the distance of the displaced atoms from the defect. The
observed fine structures allow a direct determination of the local exchange
interactions J, and the local intradimer distances R can be derived through the
linear law dJ/dR.",1410.6617v1
2014-11-03,Ultrafast structural dynamics of the Fe-pnictide parent compound BaFe2As2,"Using femtosecond time-resolved x-ray diffraction we investigate the
structural dynamics of the coherently excited A1g phonon mode in the
Fe-pnictide parent compound BaFe2As2. The fluence dependent intensity
oscillations of two specific Bragg reflections with distinctly different
sensitivity to the pnictogen height in the compound allow us to quantify the
coherent modifications of the Fe-As tetrahedra, indicating a transient increase
of the Fe magnetic moments. By a comparison with time-resolved photoemission
data we derive the electron-phonon deformation potential for this particular
mode. The value of Delta mu/Delta z = -(1.0 - 1.5) eV/A is comparable with
theoretical predictions and demonstrates the importance of this degree of
freedom for the electron-phonon coupling in the Fe pnictides.",1411.0718v1
2014-12-05,Fragmentation trees reloaded,"Metabolites, small molecules that are involved in cellular reactions, provide
a direct functional signature of cellular state. Untargeted metabolomics
experiments usually relies on tandem mass spectrometry to identify the
thousands of compounds in a biological sample. Today, the vast majority of
metabolites remain unknown. Fragmentation trees have become a powerful tool for
the interpretation of tandem mass spectrometry data of small molecules. These
trees are found by combinatorial optimization, and aim at explaining the
experimental data via fragmentation cascades. To obtain biochemically
meaningful results requires an elaborate optimization function. We present a
new scoring for computing fragmentation trees, transforming the combinatorial
optimization into a maximum a posteriori estimator. We demonstrate the
superiority of the new scoring for two tasks: Both for the de novo
identification of molecular formulas of unknown compounds, and for searching a
database for structurally similar compounds, our methods performs significantly
better than the previous scoring, as well as other methods for this task. Our
method can expedite the workflow for untargeted metabolomics, allowing
researchers to investigate unknowns using automated computational methods.",1412.1929v3
2014-12-22,Understanding the multiple magnetic structures of the intermetallic compound NdMn1.4Co0.6Si2,"Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been
investigated at various temperatures by dc magnetization, neutron diffraction
and neutron depolarization. Our study shows multiple magnetic phase transitions
with temperature (T) over 1.5-300 K. In agreement with dc-magnetization and
neutron depolarization results, the temperature dependence of the neutron
diffraction patterns shows five distinct regions with different magnetic
phases. These temperature regions are (i) T >= 215 K, (ii) 215 K > T >= 50 K,
(iii) 50 K > T >= 40 K, (iv) 40 K > T > 15 K, and (v) T =< 15 K. The
corresponding magnetic structures are paramagnetic, commensurate collinear
antiferromagnetic (AFM-I), incommensurate AFM (AFM-II), mixed ferromagnetic and
AFM (FM+AFM-II), and incommensurate AFM (AFM-II), respectively.",1412.7182v1
2015-01-04,Distribution of phonon lifetime in Brillouin zone,"Lattice thermal conductivities of zincblende- and wurtzite-type compounds
with 33 combinations of elements are calculated with the single-mode
relaxation-time approximation and linearized phonon Boltzmann equation from
first-principles anharmonic lattice dynamics calculations. In 9 zincblende-type
compounds, distributions of phonon linewidths (inverse phonon lifetimes) are
discussed in detail. The phonon linewidths vary non-smoothly with respect to
wave vector, which is explained from the imaginary parts of the self energies.
It is presented that detailed combination of phonon-phonon interaction strength
and three phonon selection rule is critically important to determine phonon
lifetime for these compounds. This indicates difficulty to predict phonon
lifetime quantitatively without anharmonic force constants. However it is shown
that joint density of states weighted by phonon numbers, which is calculated
only from harmonic force constants, can be potentially used for a screening of
the lattice thermal conductivity of materials.",1501.00691v3
2015-01-10,Crystal growth of the non-magnetic Zn$^{2+}$ and magnetic Co$^{2+}$ doped quasi one-dimensional spin chain compound SrCuO$_{2}$ using the travelling solvent floating zone method,"We report on the crystal growth of the quasi one-dimensional quantum spin
chain compound SrCuO$_{2}$ and its doped variants containing magnetic cobalt
(0.25%, 0.5%, 1% and 2.5%) and non-magnetic zinc (0.5\% and 1\%) impurities.
Crystals are grown using the travelling solvent floating zone (TSFZ) method in
a four-mirror optical furnace. Some crucial factors, key to the stability of a
TSFZ process, including the choice of solvent composition and its associated
melting behavior, are discussed in detail. The grown crystals were
characterized using x-ray powder diffraction, scanning electron microscopy,
optical microscopy, neutron single crystal diffraction and magnetic
susceptibility measurements. Co-doping induces magnetic anisotropy and a
corresponding change of magnetic behavior characterized by the presence of a
sharp peak in the magnetic susceptibility at low-temperatures (T = 5 K), which
is not seen for the pristine compound. The peak position is shown to scale
linearly with Co-concentration for low doping levels upto 2.5%.",1501.02333v1
2015-02-01,"Partially-ordered vortex lattices in the high-field, low-temperature mixed state of quasi two-dimensional organic superconductors","We report the results of high-field, low-temperature MuSR measurements of the
quasi two-dimensional organic superconductors \k{appa}-(ET)2Cu(NCS)2 and
\k{appa}-(ET)2Cu[N(CN)2]Br. The MuSR lineshapes for these compounds indicate
the existence of partially-ordered vortex lattice phases in the high magnetic
field regime, up to 2.5 T for the former compound and 4 T for the latter
compound. The observed sharp loss of order is found to be consistent with a
vortex-lattice melting transition that is predicted by numerical simulations of
weakly coupled layers of pancake vortices. It is argued that the robustness of
the partially-ordered vortex lattice phases could be due to strong flux-line
pinning by a dilute ensemble of defects.",1502.00310v1
2015-02-10,A large new family of filled skutterudites stabilized by electron count,"Based on the interplay of theory and experiment, a large new family of filled
group 9 (Co, Rh and Ir) skutterudites is designed and synthesized. The new
materials fill the empty cages in the structures of the known binary CoSb3,
RhSb3 and IrSb3 skutterudites with alkaline, alkaline earth, and rare earth
atoms to create compounds of the type AyB4X12; A atoms fill the cages to a
fraction y, B are the group 9 transition metals, and X is a mixture of
electronegative main group elements chosen to achieve chemical stability by
adjusting the electron counts to electron-precise values. Forty-three new
compounds are reported, antimony-tin and phosphorous-silicon based, with 63
compositional variations presented. The new family of compounds is large and
general. The results described here can be extended to the synthesis of
hundreds of new group 9 filled skutterudites.",1502.03127v2
2015-02-12,Short-range Magnetic Ordering in the Geometrically Frustrated Layered Compound YBaCo4O7 with an Extended Kagomé Structure,"Structural and magnetic properties of the geometrically frustrated layered
compound YBaCo4O7 have been studied by magnetization and neutron diffraction. A
layered type crystal structure, with alternating tetrahedral layers of Kagom\'e
and triangular types, along the c axis (hexagonal symmetry, space group P63mc)
has been found. The oxygen content of the present compound was determined by
iodometric titration to be 7.00{\pm}0.01. Presence of a short-range
antiferromagnetic ordering (below TN ~ 110 K) has been concluded from the
appearance of an addition broad magnetic peak (at Q ~ 1.35 {\AA}-1) in the
neutron diffraction pattern. A staggered chiral type (\sqrt{3}\mult \sqrt{3} )
spin structure in the Kagom\'e layers has been found. Presence of a significant
magneto-structural coupling is concluded from the changes in lattice parameters
across the magnetic ordering temperature TN ~ 110 K.",1502.03588v1
2015-03-03,Visualizing the Pt doping effect on surface and electronic structure in Ir_{1-x}Pt_{x}Te_{2} by scanning tunneling microscopy and spectroscopy,"We report on the Pt doping effect on surface and electronic structure in
Ir$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$Te$_ {\mathrm{2}}$ by scanning tunneling
microscopy (STM) and spectroscopy (STS). The surface prepared by cleavage at
4.2 K shows a triangular lattice of topmost Te atoms. The compounds that
undergo structural transition have supermodulation with a fixed wave vector $q
= \frac{2\pi}{5a_m}$ (where $a_m$ is the lattice constant in the monoclinic
phase) despite the different Pt concentrations. The superconducting compounds
show patch structures. The surface of the compound that exhibits neither the
superconductivity nor the structural transition shows no superstructure. In all
doped samples, the dopant is observed as a dark spot in STM images. The
tunneling spectra near the dopant show the change in the local density of state
at approximately -200 mV. Such microscopic effects of the dopant give us the
keys for establishing a microscopic model of this material.",1503.00898v1
2015-03-07,Compounding approach for univariate time series with non-stationary variances,"A defining feature of non-stationary systems is the time dependence of their
statistical parameters. Measured time series may exhibit Gaussian statistics on
short time horizons, due to the central limit theorem. The sample statistics
for long time horizons, however, averages over the time-dependent parameters.
To model the long-term statistical behavior, we compound the local distribution
with the distribution of its parameters. Here we consider two concrete, but
diverse examples of such non-stationary systems, the turbulent air flow of a
fan and a time series of foreign exchange rates. Our main focus is to
empirically determine the appropriate parameter distribution for the
compounding approach. To this end we have to estimate the parameter
distribution for univariate time series in a highly non-stationary situation.",1503.02177v1
2015-03-23,Giant magnetothermal conductivity and magnetostriction effect in charge ordered Nd$_{0.8}$Na$_{0.2}$MnO$_{3}$ compound,"We present results on resistivity ($\rho$), magnetization ($M$), thermal
conductivity ($\kappa$), magnetostriction ($\frac{\Delta L}{L(0)}$) and
specific heat ($C_{p}$) of charge-orbital ordered antiferromagnetic
Nd$_{0.8}$Na$_{0.2}$MnO$_{3}$ compound. Magnetic field-induced
antiferromagnetic/charge-orbital ordered insulating to ferromagnetic metallic
transition leads to giant magnetothermal conductivity and magnetostriction
effect. The low-temperature irreversibility behavior in $\rho$, $M$, $\kappa$
and $\frac{\Delta L}{L(0)}$ due to field cycling together with striking
similarity among the field and temperature dependence of these parameters
manifest the presence of strong and complex spin-charge-lattice coupling in
this compound. The giant magnetothermal conductivity is attributed mainly to
the suppression of phonon scattering due to the destabilization of spin
fluctuations and static/dynamic Jahn-Teller distortion by the application of
magnetic field.",1503.06552v2
2015-03-23,Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4Si2 and CeIrAl4Si2,"We have investigated the magnetic ground state of the antiferromagnetic
Kondo-lattice compounds CeMAl$_{4}$Si$_{2}$ (M = Rh, Ir) using neutron powder
diffraction. Although both of these compounds show two magnetic transitions
$T_{N1}$ and $T_{N2}$ in the bulk properties measurements, evidence for
magnetic long-range order was only found below the lower transition $T_{N2}$.
Analysis of the diffraction profiles reveals a commensurate antiferromagnetic
structure with a propagation vector $\mathbf{k}$= (0, 0, 1/2). The magnetic
moment in the ordered state of CeRhAl$_{4}$Si$_{2}$ and CeIrAl$_{4}$Si$_{2}$
were determined to be 1.14(2) and 1.41(3) $\mu_{B}$/Ce, respectively, and are
parallel to the crystallographic $c$-axis in agreement with magnetic
susceptibility measurements.",1503.06860v1
2015-04-23,Anomalous charge and negative-charge-transfer insulating state in cuprate chain-compound KCuO_2,"Using a combination of X-ray absorption spectroscopy experiments with first
principle calculations, we demonstrate that insulating KCuO_2 contains Cu in an
unusually-high formal-3+ valence state, the ligand-to-metal (O to Cu) charge
transfer energy is intriguingly negative (Delta~ -1.5 eV) and has a dominant
(~60%) ligand-hole character in the ground state akin to the high Tc cuprate
Zhang-Rice state. Unlike most other formal Cu^{3+} compounds, the Cu 2p XAS
spectra of KCuO_2 exhibits pronounced 3d^8 (Cu^{3+}) multiplet structures,
which accounts for ~40% of its ground state wave-function. Ab-initio
calculations elucidate the origin of the band-gap in KCuO_2 as arising
primarily from strong intra-cluster Cu 3d - O 2p hybridizations (t_{pd}); the
value of the band-gap decreases with reduced value of t_{pd}. Further, unlike
conventional negative charge-transfer insulators, the band-gap in KCuO_2
persists even for vanishing values of Coulomb repulsion U, underscoring the
importance of single-particle band-structure effects connected to the
one-dimensional nature of the compound.",1504.06268v2
2015-04-25,Relevance of $4f$-$3d$ exchange to finite-temperature magnetism of rare-earth permanent magnets: an ab-initio-based spin model approach for NdFe$_{12}$N,"A classical spin model derived ab initio for rare-earth-based permanent
magnet compounds is presented. Our target compound, NdFe$_{12}$N, is a material
that goes beyond today's champion magnet compound Nd$_{2}$Fe$_{14}$B in its
intrinsic magnetic properties with a simpler crystal structure. Calculated
temperature dependence of the magnetization and the anisotropy field agree with
the latest experimental results in the leading order. Having put the realistic
observables under our numerical control, we propose that engineering
$5d$-electron-mediated indirect exchange coupling between $4f$-electrons in Nd
and $3d$-electrons from Fe would most critically help to enhance the material's
utility over the operation-temperature range.",1504.06697v2
2015-05-06,Structural instability of the ground state of the U2Mo compound,"This work reports the structural instability at T=0 K of the U2Mo compound in
the structure C11b under the distortion related to the C66 elastic constant.
The electronic properties of U2Mo such density of states (DOS), bands and Fermi
surface (FS) are studied to understand the source of the instability. The C11b
structure can be interpreted as formed by parallel linear chains along the
z-directions each one composed by successive U-Mo-U blocks. The hybridization
due to electronic interactions inside the U-Mo-U blocks is slightly modified
under the D6 distortion. The change in distance among chains modifies the U-U
interaction and produces the split of f-states. The distorted structure is
stabilized by the energy lowering of the hybridized states, mainly between d-Mo
and f-U states, together with the f-band split. Consequently, an induced
Peierls distortion is produced in U2Mo due to the D6 distortion. In addition,
the results of this work remarks that the structure of the ground state of the
U2Mo compound is other than the assumed C11b structure.",1505.01473v1
2015-05-11,High-efficient thermoelectric materials: The case of orthorhombic IV-VI compounds,"Improving the thermoelectric efficiency is one of the greatest challenges in
materials science. The recent discovery of excellent thermoelectric performance
in simple orthorhombic SnSe crystal offers new promise in this prospect [Zhao
et al. Nature 508, 373 (2014)]. By calculating the thermoelectric properties of
orthorhombic IV-VI compounds GeS,GeSe,SnS,and SnSe based on the
first-principles combined with the Boltzmann transport theory, we show that the
Seebeck coefficient, electrical conductivity, and thermal conductivity of
orthorhombic SnSe are in agreement with the recent experiment. Importantly,
GeS,GeSe,and SnS exhibit comparative thermoelectric performance compared to
SnSe. Especially, the Seebeck coefficients of GeS,GeSe,and SnS are even larger
than that of SnSe under the studied carrier concentration and temperature
region. We also use the Cahill's model to estimate the lattice thermal
conductivities at the room temperature. The large Seebeck coefficients, high
power factors, and low thermal conductivities make these four orthorhombic
IV-VI compounds promising candidates for high-efficient thermoelectric
materials.",1505.02477v1
2015-05-21,Screening for Two dimensional MX$_2$ semiconductors with possible high room temperature mobility,"We calculated the electron mobility of 14 two dimensional semiconductors with
composition of MX$_2$, where M (= Mo, W, Sn, Hf, Zr and Pt) is the transition
metal, and X is S, Se and Te. We treated the scattering matrix by deformation
potential approximation. Long wave longitudinal acoustical and optical phonon
scatterings are included. Piezoelectric scattering in the compounds without
inversion symmetry is also taken into account. We found that out of the 14
compounds, WSe$_2$, PtS$_2$ and PtSe$_2$, are promising regarding to the
possible high electron mobility and finite band gap. The phonon limited
mobility in PtSe$_2$ reaches about 3000 cm$^2$V$^{-1}$s$^{-1}$ at room
temperature which is the highest among the compounds. The bandgap under the
local density approximation is 1.25 eV. Our results can be a guide for
experiments to search for better two-dimensional materials for future
semiconductor devices.",1505.05698v1
2015-05-29,Designing isoelectronic counterparts to layered group V semiconductors,"In analogy to III-V compounds, which have significantly broadened the scope
of group IV semiconductors, we propose IV-VI compounds as isoelectronic
counterparts to layered group V semiconductors. Using {\em ab initio} density
functional theory, we study yet unrealized structural phases of silicon
mono-sulfide (SiS). We find the black-phosphorus-like $\alpha$-SiS to be almost
equally stable as the blue-phosphorus-like $\beta$-SiS. Both $\alpha$-SiS and
$\beta$-SiS monolayers display a significant, indirect band gap that depends
sensitively on the in-layer strain. Unlike 2D semiconductors of group V
elements with the corresponding nonplanar structure, different SiS allotropes
show a strong polarization either within or normal to the layers. We find that
SiS may form both lateral and vertical heterostructures with phosphorene at a
very small energy penalty, offering an unprecedented tunability in structural
and electronic properties of SiS-P compounds.",1506.00513v1
2015-06-03,Filaments in the TGBA phase,"A model of filaments of the TGBA phase arising from the homeotropic smectic A
phase and nucleating on the sample surface is proposed. The model is based on
the concept of finite blocks of parallel smectic layers forming a helical
structure. The blocks are surrounded by dislocation loops. The model describes
the filament structure near the sample surface and explains the observed
inclination of the filament axis with respect to the easy direction of the
molecular anchoring on the surface. The model is based on the observations of
filament textures of the TGBA phase in a new chiral liquid crystalline
compound, but can be applied for forming of TGBA filaments in any compound. The
compression modulus of the compound has been estimated using such parameters as
anchoring energy, estimated from the field necessary to transform the structure
into the homeotropic smectic A, and the observed filament width.",1506.01177v3
2015-06-04,Prediction of Band Structure of $Bi_2Te_3$-related Binary and Ternary Thermoelectric Materials,"Density functional calculations have performed to study the band structures
of $Bi_2Te_3$-related binary ($Bi_2Te_3$, $Sb_2Te_3$, $Bi_2Se_3$, and
$Sb_2Se_3$) and $Sb$/$Se$ doped ternary compounds [$(Bi_{1-x}Sb_x)_2Te_3$ and
$Bi_2(Te_{1-y}Se_y)_3$]. It is found that the band gap can be increased by $Sb$
doping and it is monotonically increased by $Se$ doping. In ternary compounds,
the change of the conduction band structure is more significant, as compared to
the change of valence band. The band degeneracy of valence band maximum is
maintained to be 6 in binaries and ternaries. However, as going from $Bi_2Te_3$
to $Sb_2Te_3$ ($Bi_2Se_3$), the degeneracy of conduction band minimum is
reduced from 6 to 2(1). Based on the results of band structures, we suggest the
suitable stoichiometries of ternary compounds for high thermoelectric
performance.",1506.01592v2
2015-06-04,Superconductivity in graphite intercalation compounds,"The field of superconductivity in the class of materials known as graphite
intercalation compounds has a history dating back to the 1960s. This paper
recontextualizes the field in light of the discovery of superconductivity in
CaC6 and YbC6 in 2005. In what follows, we outline the crystal structure and
electronic structure of these and related compounds. We go on to experiments
addressing the superconducting energy gap, lattice dynamics, pressure
dependence, and how this relates to theoretical studies. The bulk of the
evidence strongly supports a BCS superconducting state. However, important
questions remain regarding which electronic states and phonon modes are most
important for superconductivity and whether current theoretical techniques can
fully describe the dependence of the superconducting transition temperature on
pressure and chemical composition.",1506.01663v1
2015-06-23,"New class of compounds - variators - are reprogramming substrate specificity of H4K12Ac, H4K16Ac and H4K20Ac epigenetic marks reading bromodomain of BPTF protein","Previously reported [http://arxiv.org/abs/1506.06433] reprogramming of
substrate specificity of H3K4Me3 epigenetic marks reading PHD domain of BPTF
protein illustrates therapeutic potential of a new class of non-inhibitor small
organic compounds - variators. Here we address the question about
reproducibility of rational design of variators by reprogramming of the second
epigenetic marks reading domain of BPTF protein - bromodomain. Bromodomain of
BPTF binds to epigenetic marks in form of acetylated lysine of histone H4
(H4K12Ac, H4K16Ac and H4K20Ac), which physicochemical properties and binding
mode differs considerably from those of methylated H3K4 marks. Thus, detailed
description of computational approach for reprogramming of bromodomain
substrate specificity illustrates both general and target specific attributes
of computer aided variators design.",1506.06845v1
2015-07-15,Feasibility study of heavy ion beams and compound target materials for muon production,"We have investigated the feasibility of using compound materials as target
for muon production by virtue of simulations using a GEANT4 toolkit. A graphite
and two thermostable compound materials, beryllium oxide (BeO) and boron
carbide (B4C) were considered as muon production targets and their muon
production rates for 600-MeV proton beam were calculated and compared. For
thermal analysis, total heat deposited on the targets by the proton beams and
the secondary particles was calculated with a MCNPX code, and then the
temperature distribution of target was derived from the calculated heat by
using an ANSYS code with consideration for heat transfer mechanisms, such as
thermal conduction and thermal radiation. In addition, we have investigated
whether the heavy ion beams can be utilized for muon production. For various
beam species such as 3He2, 4He, 7Li, 10B and 12C, their muon production rates
were calculated and compared with that obtained for a proton beam.",1507.04071v1
2015-08-12,RCR: Robust Compound Regression for Robust Estimation of Errors-in-Variables Model,"The errors-in-variables (EIV) regression model, being more realistic by
accounting for measurement errors in both the dependent and the independent
variables, is widely adopted in applied sciences. The traditional EIV model
estimators, however, can be highly biased by outliers and other departures from
the underlying assumptions. In this paper, we develop a novel nonparametric
regression approach - the robust compound regression (RCR) analysis method for
the robust estimation of EIV models. We first introduce a robust and efficient
estimator called least sine squares (LSS). Taking full advantage of both the
new LSS method and the compound regression analysis method developed in our own
group, we subsequently propose the RCR approach as a generalization of those
two, which provides a robust counterpart of the entire class of the maximum
likelihood estimation (MLE) solutions of the EIV model, in a 1-1 mapping.
Technically, our approach gives users the flexibility to select from a class of
RCR estimates the optimal one with a predefined regression efficiency criterion
satisfied. Simulation studies and real-life examples are provided to illustrate
the effectiveness of the RCR approach.",1508.02925v1
2015-08-08,"Possible coexistence of Cycloidal Phases, Magnetic Field Reversal of Polarization and Memory Effect in Multiferroic \emph{R}$_{0.5}$Dy$_{0.5}$MnO$_3$ (\emph{R}=Eu and Gd)","We report the occurrence of both \emph{ab} and \emph{bc} cycloidal ordering
of Mn-spins at different temperatures and their possible coexistence at low
temperatures in the polycrystalline mixed rare-earth compounds,
\emph{R}$_{0.5}$Dy$_{0.5}$MnO$_3$ (\emph{R} = Eu and Gd), which exhibit
extraordinary magnetoelectric properties. While the polarization of
Gd$_{0.5}$Dy$_{0.5}$MnO$_3$ is comparable to TbMnO$_3$, the compound
Eu$_{0.5}$Dy$_{0.5}$MnO$_3$ shows high value of polarization. However, both of
them show giant magnetic tunability and exhibit large magnetocapacitance whose
sign changes across the two cycloidal ordering temperatures. Intriguingly, the
electric polarization can be reversed upon ramping up or ramping down the
magnetic field, which has not been observed for any of the \emph{R}MnO$_3$
system. Most strikingly, these compounds show non-volatile ferroelectric memory
effect even in the paraelectric and paramagnetic region (T$_C$ $\leq$ T $\leq$
80 K). We attribute these remarkable properties to the coexistence of \emph{ab}
and \emph{bc} cycloidal ordered phases.",1508.03659v1
2015-08-25,Tuning the carrier concentration to improve the thermoelectric performance of CuInTe2 compound,"The electronic and transport properties of CuInTe2 chalcopyrite are
investigated using density functional calculations combined with Boltzmann
theory. The band gap predicted from hybrid functional is 0.92 eV, which agrees
well with experimental data and leads to relatively larger Seebeck coefficient
compared with those of narrow-gap thermoelectric materials. By fine tuning the
carrier concentration, the electrical conductivity and power factor of the
system can be significantly optimized. Together with the inherent low thermal
conductivity, the ZT values of CuInTe2 compound can be enhanced to as high as
1.72 at 850 K, which is obviously larger than those measured experimentally and
suggests there is still room to improve the thermoelectric performance of this
chalcopyrite compound.",1508.06009v1
2015-08-26,Potassium carbonate under pressure: common structural trend for alkaline carbonates and binary compounds,"The behaviour of alkaline carbonates at high pressure is poorly understood.
Indeed, theoretical and experimental investigations of general trends of
pressure induced structural changes appear in the literature only sporadically.
In this article we use a combination of ab-initio calculations and
high-pressure experiments in diamond anvil cell to determine crystal structures
of high-pressure phases of K2CO3. The comparison with experimental data on
Li2CO3 allows to reconstruct the common structural trend, which is consistent
with the simple rule that the structure of high-pressure polymorph is the same
as the ambient structure of a heavier element compound from the same group of
the periodic table. The correctness of the constructed trend is confirmed by
the perfect consistency with pressure-induced structural transformations in a
wide range of binary A2B compounds.",1508.06456v1
2015-08-29,"Magnetic properties of Gd$T_2$Zn$_{20}$ (T = Fe, Co) investigated by X-ray diffraction and spectroscopy","We investigate the magnetic and electronic properties of the Gd$T_2$Zn$_{20}$
($T$ = Fe and Co) compounds using X-ray resonant magnetic scattering (XRMS),
X-ray absorption near-edge structure (XANES) and X-ray magnetic circular
dichroism (XMCD) techniques. The XRMS measurements reveal that the
GdCo$_2$Zn$_{20}$ compound has a commensurate antiferromagnetic spin structure
with a magnetic propagation vector $\vec{\tau}$ =
$(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ below the N\'eel temperature ($T_N
\sim$ 5.7 K). Only the Gd ions carry a magnetic moment forming an
antiferromagnetic structure with magnetic representation $\Gamma_6$. For the
ferromagnetic GdFe$_2$Zn$_{20}$ compound, an extensive investigation was
performed at low temperature and under magnetic field using XANES and XMCD
techniques. A strong XMCD signal of about 12.5 $\%$ and 9.7 $\%$ is observed
below the Curie temperature ($T_C \sim$ 85 K) at the Gd-$L_2$ and $L_3$ edges,
respectively. In addition, a small magnetic signal of about 0.06 $\%$ of the
jump is recorded at the Zn $K$-edge suggesting that the Zn 4$p$ states are spin
polarized by the Gd 5$d$ extended orbitals.",1508.07495v1
2015-08-30,Generalized Gompertz-power series distributions,"In this paper, we introduce the generalized Gompertz-power series class of
distributions which is obtained by compounding generalized Gompertz and power
series distributions. This compounding procedure follows same way that was
previously carried out by Silva et al. (2013) and Barreto-Souza et al. (2011)
in introducing the compound class of extended Weibull-power series distribution
and the Weibull-geometric distribution, respectively. This distribution
contains several lifetime models such as generalized Gompertz, generalized
Gompertz-geometric, generalized Gompertz-poisson, generalized Gompertz-binomial
distribution, and generalized Gompertz-logarithmic distribution as special
cases. The hazard rate function of the new class of distributions can be
increasing, decreasing and bathtub-shaped. We obtain several properties of this
distribution such as its probability density function, Shannon entropy, its
mean residual life and failure rate functions, quantiles and moments. The
maximum likelihood estimation procedure via a EM-algorithm is presented, and
sub-models of the distribution are studied in details.",1508.07634v1
2015-09-01,Pressure induced novel compounds in the Hf-O system from first-principles calculations,"Using first-principles evolutionary simulations, we have systematically
investigated phase stability in the Hf-O system at pressure up to 120 GPa. New
compounds Hf5O2, Hf3O2, HfO and HfO3 are discovered to be thermodynamically
stable at certain pressure ranges and a new stable high-pressure phase is found
for Hf2O with space group Pnnm and anti-CaCl2-type structure. Both P62m-HfO and
P4m2-Hf2O3 show semimetallic character. Pnnm-HfO3 shows interesting structure,
simultaneously containing oxide O2- and peroxide [O-O]2- anions. Remarkably, it
is P62m-HfO rather than OII-HfO2 that exhibits the highest mechanical
characteristics among Hf-O compounds. Pnnm-Hf2O, Imm2-Hf5O2, P31m-Hf2O and
P4m2-Hf2O3 phases also show superior mechanical properties, these phases can be
quenched to ambient pressure and their properties can be exploited.",1509.00326v1
2015-10-01,CuAlTe$_2$: A promising bulk thermoelectric material,"Transport properties of Cu-based chalcopyrite materials are presented using
the full potential linear augmented plane wave method and Boltzmann
Semi-classical theory. All the studied compounds appear to be direct band gap
semiconductors evaluated based on the Tran-Blaha modified Becke-Johnson
potential. The heavy and light band combination found near the valence band
maximum (VBM) drive these materials to possess good thermoelectric properties.
Among the studied compounds, CuAlTe$_2$ is found to be more promising, in
comparison with CuGaTe$_2$, which is reported to be an efficient thermoelectric
material with appreciable figure of merit. Another interesting fact about
CuAlTe$_2$ is the comparable thermoelectric properties possessed by both $n-$
type and $p-$ type carriers, which might attract good device applications and
are explained in detail using the electronic structure calculations.",1510.00231v1
2015-10-02,On the Extraction of Exchange Parameters in Transition-Metal Perovskites,"The extraction of exchange parameters from measured spin-wave dispersion
relations has severe limitations particularly for magnetic compounds such as
the transition-metal perovskites, where the nearest-neighbor exchange parameter
usually dominates the couplings between the further-distant-neighbor spins.
Very precise exchange parameters beyond the nearest-neighbor spins can be
obtained by neutron spectroscopic investigations of the magnetic excitation
spectra of isolated multimers in magnetically diluted compounds. This is
exemplified for manganese trimers in the mixed three- and two-dimensional
perovskite compounds KMnxZn1-xF3 and K2MnxZn1-xF4, respectively. It is shown
that the small exchange couplings between the second-nearest and the
third-nearest neighboring spins can be determined unambiguously and with equal
precision as the dominating nearest-neighbor exchange coupling.",1510.00569v1
2015-10-27,MeV Neutron Production from Thermal Neutron Capture in {6}^Li Simulated with Geant4,"Various Li compounds are commonly used at neutron facilities as neutron
absorbers. These compounds provide one of the highest ratios of neutron
attenuation to $\gamma$-ray production. Unfortunately, the usage of these
compounds can also give rise to fast neutron emission with energies up to
almost 16 MeV. Historically, some details in this fast neutron production
mechanism can be absent from some modeling packages under some optimization
scenarios. In this work, we tested Geant4 to assess the performance of this
simulation toolkit for the fast neutron generation mechanism. We compare the
results of simulations performed with Geant4 to available measurements. The
outcome of our study shows that results of the Geant4 simulations are in good
agreement with the available measurements for $^6$Li fast neutron production,
and suitable for neutron instrument background evaluation at spallation neutron
sources.",1510.07937v1
2015-12-07,"First principles investigation of structural, electronic and optical properties of MgRh intermetallic compound","The structural electronic and optical properties of intermetallic compound
MgRh were investigated by using the ab-initio technique from CASTEP code. In
this study we have carried out the pseudo-potential plane-wave (PP-PW) method
based on the density functional theory (DFT), within the generalized gradient
approximation (GGA). Our calculated structural parameters and corresponding
graphical values fit with other previous available experimental data and other
theoretical observations. The calculated electronic band structure reveals
metallic conductivity and the major contribution comes from Rh-d states.
Comparison between our investigated properties and experimental data shows good
agreement. The optical functions (dielectric functions, refractive index,
absorption spectrum, conductivity, energy loss spectrum and reflectivity) have
been calculated and discussed. This is the first quantitative prediction of the
electronic and optical properties of intermetallic compound MgRh alloy, since
it has not been reported yet. The calculated optical functions reveal that the
reflectivity is high in the ultraviolet region up to 73 eV for MgRh, showing
this to be promising coating materials.",1512.02118v1
2015-12-21,"Novel synthesis method of nonstoichiometric Na2-xIrO3. Crystal structure, transport and magnetic properties","Transition metal oxides with 4d or 5d metals are of great interest due to the
competing interactions, of the Coulomb repulsion and the itineracy of the
d-electrons, opening a possibility of building new quantum ground states.
Particularly the 5d metal oxides containing Iridium have received significant
attention within the last years, due to their unexpected physical properties,
caused by a strong spin orbit coupling observed in Ir(IV). A prominent example
is the Mott-insulator Sr2IrO4. Another member of this family, the honeycomb
lattice compound Na2IrO3, also being a Mott-insulator having, most probably, a
Kitaev spin liquid ground state. By deintercalating sodium from Na2IrO3, we
were able to synthesize a new honeycomb lattice compound with more than 50%
reduced sodium content. The reduction of the sodium content in this layered
compound leads to a change of the oxidation state of iridium from +IV to +V/+VI
and a symmetry change from C2/c to P-3. This goes along with significant
changes of the physical properties. Besides the vanishing magnetic ordering at
15K, also the transport properties changes and instead insulating
semiconducting properties are observed.",1512.06627v1
2015-12-22,(C$_{4}$H$_{12}$N$_{2}$)[CoCl$_{4}$] -tetrahedrally coordinated Co$^{2+}$ without the orbital degeneracy,"We report on the synthesis, crystal structure, and magnetic properties of a
previously unreported Co$^{2+}$ $S={3 \over 2}$ compound,
(C$_{4}$H$_{12}$N$_{2}$)[CoCl$_{4}$], based upon a tetrahedral crystalline
environment. The $S={3 \over 2}$ magnetic ground state of Co$^{2+}$, measured
with magnetization, implies an absence of spin-orbit coupling and orbital
degeneracy. This contrasts with compounds based upon an octrahedral and even
known tetrahedral Co$^{2+}$ based systems where a sizable spin-orbit coupling
is measured. The compound is characterized with single crystal x-ray
diffraction, magnetic susceptibility, infrared, and ultraviolet/visible
spectroscopy. Magnetic susceptibility measurements find no magnetic ordering
above 2 K. The results are also compared with the previously known monoclinic
hydrated analogue.",1512.07124v1
2016-01-12,Theory of Superconductivity in Graphite Intercalation Compounds,"On the basis of the model that was successfully applied to KC8, RbC8, and
CsC8 in 1982, we have calculated the superconducting transition temperature Tc
for CaC6 and YbC6 to find that the same model reproduces the observed Tc in
those compounds as well, indicating that it is a standard model for
superconductivity in the graphite intercalation compounds with Tc ranging over
three orders of magnitude. Further enhancement of Tc well beyond 10 K is also
predicted. The present method for calculating Tc from first principles is
compared with that in the density functional theory for superconductors, with
paying attention to the feature of determining Tc without resort to the concept
of the Coulomb pseudopotential.",1601.02753v1
2016-01-16,Estimation of the Accuracy of Method for Quantitative Determination of Volatile Compounds in Alcohol Products,"Results of the estimation of the precision for determination volatile
compounds in alcohol-containing products by gas chromatography: acetaldehyde,
methyl acetate, ethyl acetate, methanol, isopropyl alcohol, propyl alcohol,
isobutyl alcohol, butyl alcohol, isoamyl alcohol are presented. To determine
the accuracy, measurements were planned in accordance with ISO 5725 and held at
the gas chromatograph Chromatec-Crystal 5000. Standard deviation of
repeatability, intermediate precision and their limits are derived from
obtained experimental data. The uncertainty of the measurements was calculated
on the base of an ""empirical"" method. The obtained values of accuracy indicate
that the developed method allows measurement uncertainty extended from 2 to 20%
depending on the analyzed compound and measured concentration.",1601.04159v2
2016-01-25,Large Magnetoresistance in Compensated Semimetals TaAs$_2$ and NbAs$_2$,"We report large magnetoresistance (MR) at low temperatures in
single-crystalline nonmagnetic compounds TaAs$_2$ and NbAs$_2$. Both compounds
exhibit parabolic-field-dependent MR larger than $5\times10^3$ in a magnetic
field of 9 Tesla at 2 K. The MR starts to deviate from parabolic dependence
above 10 T and intends to be saturated in 45 T for TaAs$_2$ at 4.2 K. The Hall
resistance measurements and band structural calculations reveal their
compensated semimetal characteristics. The large MR at low temperatures is
ascribed to a resonance effect of the balanced electrons and holes with large
mobilities. We also discuss the relation of the MR and samples' quality for
TaAs$_2$ and other semimetals. We found that the magnitudes of MR are strongly
dependent on the samples' quality for different compounds.",1601.06482v1
2016-04-19,Fabrication of FeSi and Fe3Si compounds by electron beam induced mixing of [Fe/Si]2 and [Fe3/Si]2 multilayers grown by focused electron beam induced deposition,"Fe-Si binary compounds have been fabricated by focused electron beam induced
deposition by the alternating use of iron pentacarbonyl, Fe(CO)5, and
neopentasilane, Si5H12 as precursor gases. The fabrication procedure consisted
in preparing multilayer structures which were treated by low-energy electron
irradiation and annealing to induce atomic species intermixing. In this way we
are able to fabricate FeSi and Fe3Si binary compounds from [Fe=Si]2 and
[Fe3=Si]2 multilayers, as shown by transmission electron microscopy
investigations. This fabrication procedure is useful to obtain nanostructured
binary alloys from precursors which compete for adsorption sites during growth
and, therefore, cannot be used simultaneously.",1604.05536v1
2016-05-24,Infrared properties of heavy-fermions: evolution from weak to strong hybridizations,"In this article, we review the charge excitations of heavy fermion compounds
probed by infrared spectroscopy. The article is not meant to be a comprehensive
survey of experimental investigations. Rather it focuses on the dependence of
charge excitations on the hybridization strength. In this context, the infrared
properties of the Ce$_m$M$_n$In$_{3m+2n}$ family are discussed in detail since
the hybridization strengths differ dramatically in different members despite
their similar lattice structures. Investigations on some mixed valent compounds
are also presented aiming to elucidate the generic trend on the evolution. In
particular, we address the scaling between hybridization energy gap
$\Delta_{dir}$ and the hybridization strength $\tilde{V}$($\propto\sqrt{WT_K}$)
in a wide range of heavy fermions compounds which demonstrates that the
periodic Anderson model can generally and quantitatively describe the
low-energy charge excitations.",1605.07446v1
2016-06-06,First-principles calculation of the stabilities of LMP/LAMP lithium superionic conductors against sodium-ion exchange in seawater,"Electronic structure calculations carried out to estimate the free energies
of Na(aq)+ exchange for lithium in LiM2(PO4)3 (LMP, M=Si4+,Ge4+,Ti4+,Sn4+,Zr4+)
and Li1+xAlxM2-x(PO4)3 (LAMP; M=Ge4+,Ti4+, between 0 and 0.5) compounds in
seawater. The calculations show that resistance to sodium-ion exchange
increases with decreasing cell volume. For the pure LMP compounds, only the
hypothetical LiSi2(PO4)3 is predicted to be stable against sodium ion exchange
in aqueous solution. The calculations indicate that increasing the extent of
Al3+ substitution for M4+ in the LAMP compounds increases the resistance to
exchange, and that both LAGP and LATP can be stabilized against sodium exchange
for x greater than or equal to approximately 0.5 Li1+xAlxM2-x(PO4)3.",1606.02177v1
2016-06-20,Extended homologous series of Sn-O layered systems: a first-principles study,"Apart from the most studied tin-oxide compounds, SnO and SnO2, intermediate
states have been claimed to exist for more than a hundred years. In addition to
the known homologous series (Seko et al., Phys. Rev. Lett. 100, 045702 (2008)),
we here predict the existence of several new compounds with an O concentration
between 50 % (SnO) and 67 % (SnO2). All these intermediate compounds are
constructed from removing one or more (101) oxygen layers of SnO2. Since the
van der Waals (vdW) interaction is known to be important for the Sn-Sn
interlayer distances, we use a vdW-corrected functional, and compare these
results with results obtained with PBE and hybrid functionals. We present the
electronic properties of the intermediate structures and we observe a decrease
of the band gap when (i) the O concentration increases and (ii) more SnO-like
units are present for a given concentration. The contribution of the different
atoms to the valence and conduction band is also investigated.",1606.06187v1
2016-06-29,The magnetic precursor of the pressure-induced superconductivity in Fe-ladder compound,"The pressure effects on the antiferromagentic orders in iron-based ladder
compounds CsFe$_2$Se$_3$ and BaFe$_2$S$_3$ have been studied using neutron
diffraction. With identical crystal structure and similar magnetic structures,
the two compounds exhibit highly contrasting magnetic behaviors under moderate
external pressures. In CsFe$_2$Se$_3$ the ladders are brought much closer to
each other by pressure, but the stripe-type magnetic order shows no observable
change. In contrast, the stripe order in BaFe$_2$S$_3$, undergoes a quantum
phase transition where an abrupt increase of N$\acute{e}$el temperature by more
than 50$\%$ occurs at about 1 GPa, accompanied by a jump in the ordered moment.
With its spin structure unchanged, BaFe$_2$S$_3$ enters an enhanced magnetic
phase that bears the characteristics of an orbital selective Mott phase, which
is the true neighbor of superconductivity emerging at higher pressures.",1606.09223v1
2016-06-30,Entanglement-assisted classical capacities of compound and arbitrarily varying quantum channels,"We consider classical message transmission under entanglement assistance for
compound memoryless and arbitrarily varying quantum channels. In both cases, we
prove general coding theorems together with corresponding weak converse bounds.
In this way, we obtain single-letter characterizations of the
entanglement-assisted classical capacities for both channel models. Moreover,
we show that the entanglement-assisted classical capacity does exhibit no
strong converse property for some compound quantum channels for the average as
well as the maximal error criterion. A strong converse to the
entanglement-assisted classical capacities does hold for each arbitrarily
varying quantum channel.",1606.09314v3
2016-06-30,Superconductivity at 5.5 K in Nb2PdSe5 compound,"We report superconductivity in as synthesized Nb2PdSe5, which is similar to
recently discovered Nb2PdS5 compound having very high upper critical field,
clearly above the Pauli paramagnetic limit [Sci. Rep. 3, 1446 (2013)]. A bulk
polycrystalline Nb2PdSe5 sample is synthesized by solid state reaction route in
phase pure structure. The structural characterization has been done by X ray
diffraction, followed by Rietveld refinements, which revealed that Nb2PdSe5
sample is crystallized in monoclinic structure with in space group C2/m.
Structural analysis revealed the formation of sharing of one dimensional PdSe2
chains. Electrical and magnetic measurements confirmed superconductivity in
Nb2PdSe5 compound at 5.5K. Detailed magneto-resistance results, exhibited the
value of upper critical field to be around 8.2Tesla. The estimated Hc2(0) is
within Pauli Paramagnetic limit, which is unlike the Nb2PdS5.",1606.09369v2
2016-07-03,Spin waves and magnetic exchange interactions in the spin ladder compound RbFe$_2$Se$_3$,"We report an inelastic neutron scattering study of the spin waves of the
one-dimensional antiferromagnetic spin ladder compound RbFe$_2$Se$_3$. The
results reveal that the products, $SJ$'s, of the spin $S$ and the magnetic
exchange interactions $J$'s along the antiferromagnetic (leg) direction and the
ferromagnetic (rung) direction are comparable with those for the stripe ordered
phase of the parent compounds of the iron-based superconductors. The
universality of the $SJ$'s implies nearly universal spin wave dynamics and the
irrelevance of the fermiology for the existence of the stripe antiferromagnetic
order among various Fe-based materials.",1607.00639v1
2016-07-31,"X-ray powder diffraction of high-absorption materials at the XRD1 beamline off the best conditions: Application to (Gd,Nd)5Si4 compounds","Representative compounds of the new family of magnetic materials Gd5-xNdxSi4
were analyzed by X-ray diffraction at the XRD1 beamline at LNLS. To reduce
X-ray absorption, thin layers of the powder samples were mounted outside the
capillaries and measured in Debye-Scherrer geometry as usual. The X-ray
diffraction analyses and the magnetometry results indicate that the behavior of
the magnetic transition temperature as a function of Nd content may be directly
related to the average of the four smallest interatomic distances between
different rare earth sites of the majority phase of each compound. The quality
and consistency of the results show that the XRD1 beamline is able to perform
satisfactory X-ray diffraction experiments on high-absorption materials even
off the best conditions.",1608.00565v2
2016-08-30,Superconductivity in the ternary iridium-arsenide BaIr2As2,"Here we report the synthesis and discovery of superconductivity in a novel
ternary iridium-arsenide compound BaIr2As2. The polycrystalline BaIr2As2 sample
was synthesized by a high temperature and high pressure method. Crystal
structural analysis indicates that BaIr2As2 crystallizes in the ThCr2Si2-type
layered tetragonal structure with space group I4/mmm (No. 139), and the lattice
parameters were refined to be a = 4.052(9) {\AA} and c = 12.787(8) {\AA}. By
the electrical resistivity and magnetic susceptibility measurements we found
type-II superconductivity in the new BaIr2As2 compound with a Tc (critical
temperature) of 2.45 K, and an upper critical field u0Hc2(0) about 0.2 T. Low
temperature specific heat measurements gave a Debye temperature about 202 K and
a distinct specific jump with delta Ce/{\gamma}Tc = 1.36, which is close to the
value of BCS weak coupling limit and confirms the bulk superconductivity in
this new BaIr2As2 compound.",1608.08352v1
2016-09-29,Prediction of superconducting iron-bismuth intermetallic compounds at high pressure,"The synthesis of materials in high-pressure experiments has recently
attracted increasing attention, especially since the discovery of record
breaking superconducting temperatures in the sulfur-hydrogen and other
hydrogen-rich systems. Commonly, the initial precursor in a high pressure
experiment contains constituent elements that are known to form compounds at
ambient conditions, however the discovery of high-pressure phases in systems
immiscible under ambient conditions poses an additional materials design
challenge. We performed an extensive multi component $ab\,initio$ structural
search in the immiscible Fe--Bi system at high pressure and report on the
surprising discovery of two stable compounds at pressures above $\approx36$
GPa, FeBi$_2$ and FeBi$_3$. According to our predictions, FeBi$_2$ is a metal
at the border of magnetism with a conventional electron-phonon mediated
superconducting transition temperature of $T_{\rm c}=1.3$ K at 40 GPa. In
analogy to other iron-based materials, FeBi$_2$ is possibly a non-conventional
superconductor with a real $T_{\rm c}$ significantly exceeding the values
obtained within Bardeen-Cooper-Schrieffer (BCS) theory.",1609.09536v1
2016-11-05,Oscillating magnetoresistance due to fragile spin structure in metallic GdPd$_3$,"Studies on the phenomenon of magnetoresistance (MR) have produced intriguing
and application-oriented outcomes for decades--colossal MR, giant MR and
recently discovered extremely large MR of millions of percents in semimetals
can be taken as examples. We report here the investigation of oscillating MR in
a cubic intermetallic compound GdPd$_3$, which is the only compound that
exhibits MR oscillations between positive and negative values. Our study shows
that a very strong correlation between magnetic, electrical and
magnetotransport properties is present in this compound. The magnetic structure
in GdPd$_3$ is highly fragile since applied magnetic fields of moderate
strength significantly alter the spin arrangement within the system--a behavior
that manifests itself in the oscillating MR. Intriguing magnetotransport
characteristics of GdPd$_3$ are appealing for field-sensitive device
applications, especially if the MR oscillation could materialize at higher
temperature by manipulating the magnetic interaction through perturbations
caused by chemical substitutions.",1611.01672v2
2016-11-10,"Antiferroelectric instability in kagome francisites Cu$_3$Bi(SeO$_3$)$_2$O$_2$X (X = Cl, Br)","Density-functional calculations of lattice dynamics and high-resolution
synchrotron powder diffraction uncover antiferroelectric distortion in the
kagome francisite Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl below 115K. Its Br-containing
analogue is stable in the room-temperature crystal structure down to at least
10K, although the Br compound is on the verge of a similar antiferroelectric
instability and reveals local displacements of Cu and Br atoms. The
I-containing compound is stable in its room-temperature structure according to
density-functional calculations. We show that the distortion involves
cooperative displacements of Cu and Cl atoms, and originates from the
optimization of interatomic distances for weakly bonded halogen atoms. The
distortion introduces a tangible deformation of the kagome spin lattice and may
be responsible for the reduced net magnetization of the Cl compound compared to
the Br one. The polar structure of Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl is only
slightly higher in energy than the non-polar antiferroelectric structure, but
no convincing evidence of its formation could be obtained.",1611.03317v1
2017-01-09,"Static and Dynamic Magnetic Properties of Spin-1/2 Inequilateral Diamond-Chain Compounds $A_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ ($A$=K, Rb, and Cs)","Spin-1/2 compounds A3Cu3AlO2(SO4)4 (A=K, Rb, and Cs) have one-dimensional
(1D) inequilateral diamond chains. We analyze the temperature dependence of the
magnetic susceptibility and determine the magnetic exchange interactions. In
contrast to the azurite, a dimer is formed on one of the sides of the diamond.
From numerical analyses of the proposed model, we find that the dimer together
with a nearly isolated 1D Heisenberg chain characterizes magnetic properties
including magnetization curve and magnetic excitations. This implies that a
dimer-monomer composite chain without frustration is a good starting point for
describing these compounds.",1701.02198v3
2017-01-10,"Ru-doping on iron based pnictides: the ""unfolded"" dominant role of structural effects for superconductivity","We present an ab-initio study of Ru substitution in two different compounds,
BaFe2As2 and LaFeAsO, pure and F-doped. Despite the many similarities among
them, Ru substitution has very different effects on these compounds. By means
of an unfolding technique, which allows us to trace back the electronic states
into the primitive cell of the pure compounds, we are able to disentangle the
effects brought by the local structural deformations and by the impurity
potential to the states at the Fermi level. Our results are compared with
available experiments and show: i) satisfying agreement of the calculated
electronic properties with experiments, confirming the presence of a magnetic
order on a short range scale; ii) Fermi surfaces strongly dependent on the
internal structural parameters, more than on the impurity potential. These
results enter a widely discussed field in the literature and provide a better
understanding of the role of Ru in iron pnictides: although isovalent to Fe,
the Ru-Fe substitution leads to changes in the band structure at the Fermi
level mainly related to local structural modifications.",1701.02498v1
2017-01-10,Superconductivity and Dirac Fermions in 112-phase Pnictides,"This article reviews the status of current research on the 112-phase of
pnictides. The 112-phase has gained augmented attention due to the recent
discovery of high-temperature superconductivity in $\cl$ with a maximum
critical temperature $\tc\sim$ 47\,K upon Sb substitution. The structural,
magnetic, and electronic properties of $\cl$ bear some similarities with other
superconducting pnictide phases, however, the different valence states of the
pnictogen and the presence of a metallic spacer layer are unique features of
the 112-system. Low-temperature superconductivity which coexists with
antiferromagnetic order was observed in transition metal (Ni, Pd) deficient
112-compounds like $\cn$, $\lpb$, $\lps$, $\lns$. Besides superconductivity,
the presence of naturally occurring anisotropic Dirac Fermionic states were
observed in the layered 112-compounds $\smb$, $\cmb$, $\lab$ which are of
significant interest for future nanoelectronics as an alternative to graphene.
In these compounds, the linear energy dispersion resulted in a high
magnetoresistance that stayed unsaturated even at the highest applied magnetic
fields. Here, we describe various 112-type materials systems combining
experimental results and theoretical predictions to stimulate further research
on this less well-known member of the pnictide family.",1701.02700v1
2017-01-26,Comparing robustness properties of optimal designs under standard and compound criteria,"Standard optimality criteria (e.g. A-, D-optimality criterion, etc.) have
been commonly used for obtaining optimal designs. For a given statistical
model, standard criteria assume the error variance is known at the design
stage. However, in practice the error variance is estimated to make inference
about the model parameters. Modified criteria are defined as a function of the
standard criteria and the corresponding error degrees of freedom, which may
lead to extreme optimal design. Compound criteria are defined as the function
of different modified criteria and corresponding user specified weights.
Standard, modified, and compound criteria based optimal designs are obtained
for $3^3$ factorial design. Robustness properties of the optimal designs are
also compared.",1701.07577v1
2017-03-03,Magnetic and Hyperfine interactions in HoFe1-xCrxO3 compounds,"We report on the magnetic and Mossbauer properties of polycrystalline
HoFe1-xCrxO3 compounds. Magnetization data reveals the continuous tailoring of
magnetic transition due to weakening of Ho3+ Fe3+ and Fe3+ Fe3+ interactions in
the entire temperature range by replacing the Fe3+ ions with Cr3+ ions. The
observed decrease in Neel temperature (TN) and increase in spin re-orientation
transition temperature (TSR) with the replacement of Fe3+ with Cr3+ is ascribed
to the weakening of Fe(Cr) O Fe(Cr) antiferromagnetic exchange interaction. In
addition, we also attribute such a change in TN to the enhancement of
ferromagnetic interaction of adjacent Cr3+ moments through t e hybridization as
a result of the structural distortion. The decrease in isomer shift (IS)
suggests enhancement of the interaction between nuclear charge with the 3s
electrons as a result of decrease in radial part of 3d wave function with Cr
addition. In this paper we also discuss about the variation of quadrupole
splitting (QS) and hyperfine fields (Hhf) with Cr addition in HoFe1-xCrxO3
compounds.",1703.02094v1
2017-03-07,How the Chemical Composition Alone Can Predict Vibrational Free Energies and Entropies of Solids,"Computing vibrational free energies ($F_{vib}$) and entropies ($S_{vib}$) has
posed a long standing challenge to the high-throughput ab initio investigation
of finite temperature properties of solids. Here we use machine-learning
techniques to efficiently predict $F_{vib}$ and $S_{vib}$ of crystalline
compounds in the Inorganic Crystal Structure Database. By employing descriptors
based simply on the chemical formula and using a training set of only 300
compounds, mean absolute errors of less than 0.04 meV/K/atom (15 meV/atom) are
achieved for $S_{vib}$ ($F_{vib}$), whose values are distributed within a range
of 0.9 meV/K/atom (300 meV/atom.) In addition, for training sets containing
fewer than 2,000 compounds the chemical formula alone is shown to perform as
well as, if not better than, four other more complex descriptors previously
used in the literature. The accuracy and simplicity of the approach mean that
it can be advantageously used for the fast screening of phase diagrams or
chemical reactions at finite temperatures.",1703.02309v1
2017-03-17,Structural and magnetic properties of spin-$1/2$ dimer compound Cu$_2$(IPA)$_2$(DMF)(H$_2$O) with a large spin gap,"We present the synthesis and a detailed investigation of structural and
magnetic properties of metal-organic compound Cu$_2$(IPA)$_2$(DMF)(H$_2$O) by
means of x-ray diffraction, magnetization, and heat capacity measurements.
Single crystals of the title compound were synthesized by judicious selection
of organic ligand and employing a selective hydrothermal reaction route. It
crystallizes in an orthorhombic structure with space group $Cmca$. The
structural analysis revealed that two Cu$^{2+}$ ions are held together by the
organic component (-O-C-O-) in a square paddle-wheel to form spin dimers which
are aligned perpendicular to each other and are further coupled through organic
ligands (isophthalic acid) forming two-dimensional layers. Temperature
dependent magnetic susceptibility $\chi(T)$ could be described well using
spin-$1/2$ dimer model. The spin susceptibility $\chi_{\rm spin} (T)$ shows an
exponential decrease in the low temperature region, below the broad maximum,
confirming the singlet ground state with a large spin gap of $\Delta/k_{\rm B}
\simeq 409$~K. The heat capacity $C_{\rm p}$ measured as a function of
temperature also confirms the absence of magnetic long-range-order down to 2~K.",1703.05896v1
2017-07-03,Fair Pipelines,"This work facilitates ensuring fairness of machine learning in the real world
by decoupling fairness considerations in compound decisions. In particular,
this work studies how fairness propagates through a compound decision-making
processes, which we call a pipeline. Prior work in algorithmic fairness only
focuses on fairness with respect to one decision. However, many decision-making
processes require more than one decision. For instance, hiring is at least a
two stage model: deciding who to interview from the applicant pool and then
deciding who to hire from the interview pool. Perhaps surprisingly, we show
that the composition of fair components may not guarantee a fair pipeline under
a $(1+\varepsilon)$-equal opportunity definition of fair. However, we identify
circumstances that do provide that guarantee. We also propose numerous
directions for future work on more general compound machine learning decisions.",1707.00391v1
2017-08-03,Type-II Dirac cone and Dirac cone protected by nonsymmorphic symmetry in carbon-lithium compound (C4Li),"In this work, we predict a novel band structure for Carbon-Lithium(C4Li)
compound using the first-principles method. We show that it exhibits two Dirac
points near the Fermi level; one located at W point originating from the
nonsymmophic symmetry of the compound, and the other one behaves like a type-II
Dirac cone with higher anisotropy along the {\Gamma} to X line. The obtained
Fermi surface sheets of the hole-pocket and the electron-pocket near the
type-II Dirac cone are separated from each other, and they would touch each
other when the Fermi level is doped to cross the type-II Dirac cone. The
evolution of Fermi surface with doping is also discussed. The bands crossing
from T to W make a line-node at the intersection of kx={\pi} and ky={\pi}
mirror planes. The C4Li is a novel material with both nonsymmorphic protected
Dirac cone and type-II Dirac cone near the Fermi level which may exhibit
exceptional topological property for electronic applications.",1708.01202v1
2017-08-15,"Emergence of Topological Nodal Lines and Type II Weyl Nodes in Strong Spin--Orbit Coupling System InNbX2(X=S,Se)","Using first--principles density functional calculations, we systematically
investigate electronic structures and topological properties of InNbX2 (X=S,
Se). In the absence of spin--orbit coupling (SOC), both compounds show nodal
lines protected by mirror symmetry. Including SOC, the Dirac rings in InNbS2
split into two Weyl rings. This unique property is distinguished from other
dicovered nodal line materials which normally requires the absence of SOC. On
the other hand, SOC breaks the nodal lines in InNbSe2 and the compound becomes
a type II Weyl semimetal with 12 Weyl points in the Brillouin Zone. Using a
supercell slab calculation we study the dispersion of Fermi arcs surface states
in InNbSe2, we also utilize a coherent potential approximation to probe their
tolernace to the surface disorder effects. The quasi two--dimensionality and
the absence of toxic elements makes these two compounds an ideal experimental
platform for investigating novel properties of topological semimetals.",1708.04556v1
2017-09-02,Compound Poisson law for hitting times to periodic orbits in two-dimensional hyperbolic systems,"We show that a compound Poisson distribution holds for scaled exceedances of
observables $\phi$ uniquely maximized at a periodic point $\zeta$ in a variety
of two-dimensional hyperbolic dynamical systems with singularities $(M,T,\mu)$,
including the billiard maps of Sinai dispersing billiards in both the finite
and infinite horizon case. The observable we consider is of form $\phi (z)=-\ln
d(z,\zeta)$ where $d$ is a metric defined in terms of the stable and unstable
foliation. The compound Poisson process we obtain is a P\'olya-Aeppli
distibution of index $\theta$. We calculate $\theta$ in terms of the derivative
of the map $T$. Furthermore if we define $M_n=\max\{\phi,\ldots,\phi\circ
T^n\}$ and $u_n (\tau)$ by $\lim_{n\to \infty} n\mu (\phi >u_n (\tau) )=\tau$
the maximal process satisfies an extreme value law of form $\mu (M_n \le
u_n)=e^{-\theta \tau}$. These results generalize to a broader class of
functions maximized at $\zeta$, though the formulas regarding the parameters in
the distribution need to be modified.",1709.00530v1
2017-09-21,Investigation on the Physical Properties of Two Laves Phase Compounds HRh2 (H = Ca and La): A DFT Study,"Structural, elastic, electronic and optical properties of laves phase
intermetallic compounds CaRh2 and LaRh2 prototype with MgCu2 are investigated
by using the first principle calculations. These calculations stand on density
functional theory (DFT) from CASTEP code. The calculated lattice parameters are
consistent with the experimental values. The significant elastic properties,
like as bulk modulus, shear modulus, Youngs modulus and the Poissons ratio are
determined by applying the Voigt Reuss Hill (VRH) approximation. The analysis
of Pughs ratio shows the ductile nature of both the phases. Metallic
conductivity is observed for both the compounds. Most of the contribution
originates from Rh 4d states at Fermi level in DOS. The study of bonding
characteristics reveals the existence of ionic and metallic bonds in both
intermetallics. The study of optical properties indicates that maximum
reflectivity occurs in low energy region implying the characteristics of high
conductance of both the phases. Absorption quality of both the phases is good
in the visible region.",1709.07173v1
2017-09-22,Tin-selenium compounds at ambient and high pressures,"SnxSey crystalline compounds consisting of Sn and Se atoms of varying
composition are systematically investigated at pressures from 0 to 100 GPa
using the first-principles evolutionary crystal structure search method based
on density functional theory (DFT). All known experimental phases of SnSe and
SnSe2 are found without any prior input. A second order polymorphic phase
transition from SnSe-Pnma phase to SnSe-Cmcm phase is predicted at 2.5 GPa.
Initially being semiconducting, this phase becomes metallic at 7.3 GPa. Upon
further increase of pressure up to 36.6 GPa, SnSe-Cmcm phase is transformed to
CsCl-type SnSe-Pm3m phase, which remains stable at even higher pressures. A
metallic compound with different stoichiometry, Sn3Se4-I43d, is found to be
thermodynamically stable from 18 GPa to 70 GPa. Known semiconductor tin
diselenide SnSe2-P3m1 phase is found to be thermodynamically stable from
ambient pressure up to 18 GPa. Initially being semiconducting, it experiences
metalization at pressures above 8 GPa.",1709.07570v1
2017-09-22,Universality in the Electronic Structure of 3d Transition Metal Oxides,"Electronic structure of strongly correlated transition metal oxides (TMOs) is
a complex phenomenon due to competing interaction among the charge, spin,
orbital and lattice degrees of freedom. Often individual compounds are examined
to explain certain properties associated with these compounds or in rare cases
few members of a family are investigated to define a particular trend exhibited
by that family. Here, with the objective of generalization, we have
investigated the electronic structure of three families of compounds, namely,
highly symmetric cubic mono-oxides, symmetry-lowered spinels and asymmetric
olivine phosphates, through density functional calculations. From the results
we have developed empirical hypotheses involving electron hopping,
electron-lattice coupling, Hund's rule coupling, strong correlation and d-band
filling. These hypotheses, classified through the point group symmetry of the
transition metal - oxygen complexes, can be useful to understand and predict
the electronic and magnetic structure of 3d TMOs.",1709.07868v1
2017-09-29,Theoretical Study of Thermopower Behavior of LaFeO$_{3}$ Compound in High Temperature Region,"The electronic structure and thermopower ($\alpha$) behavior of LaFeO$_{3}$
compound were investigated by combining the ab-initio electronic structures and
Boltzmann transport calculations. LSDA plus Hubbard U (U = 5 eV) calculation on
G-type anti-ferromagnetic (AFM) configuration gives an energy gap of $\sim$2
eV, which is very close to the experimentally reported energy gap. The
calculated values of effective mass of holes (m$^{*}$$_{h}$) in valance band
(VB) are found $\sim$4 times that of the effective mass of electrons
(m$^{*}$$_{e}$) in conduction band (CB). The large effective masses of holes
are responsible for the large and positive thermopower exhibited by this
compound. The calculated values of $\alpha$ using BoltzTraP code are found to
be large and positive in the 300-1200 K temperature range, which is in
agreement with the experimentally reported data.",1709.10327v1
2017-11-15,Anisotropy of the Seebeck and Nernst coefficients in parent compounds of the iron-based superconductors,"In-plane longitudinal and transverse thermoelectric phenomena in two parent
compounds of iron-based superconductors are studied. Namely, the Seebeck (S)
and Nernst (n) coefficients were measured in the temperature range 10 - 300 K
for BaFe2As2 and CaFe2As2 single crystals that were detwinned in-situ. The
thermoelectric response shows sizeable anisotropy in the spin density wave
state (SDW) for both compounds, while some dissimilarities in the vicinity of
the SDW transition can be attributed to the different nature of the phase
change in BaFe2As2 and CaFe2As2. Temperature dependences of S and n can be
described within a two-band model that contains a contribution from highly
mobile, probably Dirac, electrons. The Dirac band seems to be rather isotropic,
whereas most of the anisotropy in the transport phenomena could be attributed
to ""regular"" hole-like charge carriers. We also observe that the off-diagonal
element of the Peltier tensor axy is not the same for the a and b orthorhombic
axes, which indicates that the widely used Mott formula is not applicable to
the SDW state of iron-based superconductors.",1711.05831v2
2017-11-13,PRE-render Content Using Tiles (PRECUT). 1. Large-Scale Compound-Target Relationship Analyses,"Visualizing a complex network is computationally intensive process and
depends heavily on the number of components in the network. One way to solve
this problem is not to render the network in real time. PRE-render Content
Using Tiles (PRECUT) is a process to convert any complex network into a
pre-rendered network. Tiles are generated from pre-rendered images at different
zoom levels, and navigating the network simply becomes delivering relevant
tiles. PRECUT is exemplified by performing large-scale compound-target
relationship analyses. Matched molecular pair (MMP) networks were created using
compounds and the target class description found in the ChEMBL database. To
visualize MMP networks, the MMP network viewer has been implemented in COMBINE
and as a web application, hosted at http://cheminformatic.com/mmpnet/.",1711.06328v1
2017-11-21,Application of generative autoencoder in de novo molecular design,"A major challenge in computational chemistry is the generation of novel
molecular structures with desirable pharmacological and physiochemical
properties. In this work, we investigate the potential use of autoencoder, a
deep learning methodology, for de novo molecular design. Various generative
autoencoders were used to map molecule structures into a continuous latent
space and vice versa and their performance as structure generator was assessed.
Our results show that the latent space preserves chemical similarity principle
and thus can be used for the generation of analogue structures. Furthermore,
the latent space created by autoencoders were searched systematically to
generate novel compounds with predicted activity against dopamine receptor type
2 and compounds similar to known active compounds not included in the training
set were identified.",1711.07839v1
2017-12-04,Sequential fission of highly excited compound nuclei in a 4D Langevin approach,"In highly dissipative collisions between heavy ions, the optimal conditions
to investigate different de-excitation channels of hot nuclei such as
evaporation, fission or multifragmentation are well known. One crucial issue
remains the excitation energy region where fission gives way to
multifragmentation. In this paper, the onset of multi-fragment exit channels is
investigated in terms of sequential fission. For the first time, the dynamical
approach based on solving Langevin transport equations in multidimensional
collective coordinate space is used to follow the de-excitation of highly
excited (up to E* =223-656 MeV) 248Rf compound nuclei. The sequential fission
model we propose contains two steps: (1) time evolution of the compound nucleus
up to either scission or residue formation, followed by (2) dynamical
calculations of each primary fragment separately. This procedure allows to
obtain from one to four cold fragments correlated with the light particles
emitted during the de-excitation process. Experimental data measured with the
INDRA detector for the 129Xe+ natSn reaction at beam energies 8, 12 and 15
MeV/nucleon provide strong constraints for this sequential fission scenario.",1712.00999v1
2017-12-07,Compound Hawkes Processes in Limit Order Books,"In this paper we introduce two new Hawkes processes, namely, compound and
regime-switching compound Hawkes processes, to model the price processes in
limit order books. We prove Law of Large Numbers and Functional Central Limit
Theorems (FCLT) for both processes. The two FCLTs are applied to limit order
books where we use these asymptotic methods to study the link between price
volatility and order flow in our two models by using the diffusion limits of
these price processes. The volatilities of price changes are expressed in terms
of parameters describing the arrival rates and price changes. We also present
some numerical examples.",1712.03106v1
2017-12-11,Observation of non-Fermi liquid behavior in hole doped Eu2Ir2O7,"The Weyl semimetallic compound Eu2Ir2O7 along with its hole doped derivatives
(which is achieved by substituting trivalent Eu by divalent Sr) are
investigated through transport, magnetic and calorimetric studies. The
metal-insulator transition (MIT) temperature is found to get substantially
reduced with hole doping and for 10% Sr doping the composition is metallic down
to temperature as low as 5 K. These doped compounds are found to violate the
Mott-Ioffe-Regel condition for minimum electrical conductivity and show
distinct signature of non-Fermi liquid behavior at low temperature. The MIT in
the doped compounds does not correlate with the magnetic transition point and
Anderson-Mott type disorder induced localization may be attributed to the
ground state insulating phase. The observed non-Fermi liquid behavior can be
understood on the basis of disorder induced distribution of spin orbit coupling
parameter which is markedly different in case of Ir4+ and Ir5+ ions.",1712.03737v1
2017-12-15,Unusual effects of manual grinding and subsequent annealing process observed in Gd5.09Ge2.03Si1.88 compound,"The Gd5.09Ge2.03Si1.88 compound, as well as other magnetocaloric materials,
certainly will not be used in their un-manufactured as-cast condition in future
magnetic refrigeration applications or other devices. In this work, we have
studied the Gd5.09Ge2.03Si1.88 compound processed in different ways, mainly,
the as-cast powder, the annealed powder and the pressed and sintered powder.
The annealed powder (1370 K / 20 hours) does not present the monoclinic phase
and the first-order-magneto-structural transition observed in the as-cast
powder. The pressed and sintered powder also do not present the first-order
transition. Furthermore, the compacting pressure shifts the
second-order-magnetic transition to lower temperatures. The behavior of cell
parameters as a function of the compacting pressure indicates that TC is
directly affected by parameter c change.",1712.05820v2
2017-12-18,Magnetic and universal magnetocaloric behavior of rare-earth substituted DyFe0.5Cr0.5O3,"We report the effect of partial substitution of Dy-site by rare-earths (R=Gd,
Er and La)on the magnetic and magnetocaloric behavior of a mixed metal oxide
DyFe0.5Cr0.5O3.Structural studies reveal that substitution of Dy by R has a
minimal influence on the crystal structure. Magnetic and heat capacity studies
show that the magnetic transition around 121 K observed for DyFe0.5Cr0.5O3
remains unchanged with rare-earth substitution, whereas the lower magnetic
transition temperature is suppressed/enhanced by magnetic/non-magnetic
substitution. In all these compounds, the second order nature of magnetic
transition is confirmed by Arrott plots. As compared to DyFe0.5Cr0.5O3, the
values of magnetic entropy change and relative cooling power are increased with
magnetic rare-earth substitution while it decreases with non-magnetic
rare-earth substitution. In all these compounds, magnetic entropy change
follows the power law dependence of magnetic field and the value of the
exponent n indicate the presence of ferromagnetic correlation in an
antiferromagnetic state. A phenomenological universal master curve is also
constructed for all the compounds by normalizing the entropy change with
rescaled temperature using a single reference temperature. This master curve
also reiterates the second order nature of the magnetic phase transition in
such mixed metal oxides.",1712.06396v1
2017-12-30,First-principles study of the effects of electron-phonon coupling on the thermoelectric properties: a case study of SiGe compound,"It is generally assumed in the thermoelectric community that the lattice
thermal conductivity of a given material is independent of the electronic
properties. This perspective is however questionable since the electron-phonon
coupling could have certain effects on both the carrier and phonon transport,
which in turn will affect the thermoelectric properties. Using SiGe compound as
a prototypical example, we give an accurate prediction of the carrier
relaxation time by considering scattering from all the phonon modes, as opposed
to the simple deformation potential theory. It is found that the carrier
relaxation time does not change much with the concentration, which is however
not the case for the phonon transport where the lattice thermal conductivity
can be significantly reduced by electron-phonon coupling at higher carrier
concentration. As a consequence, the figure-of-merit of SiGe compound is
obviously enhanced at optimized carrier concentration, and becomes more
pronounced at elevated temperature.",1801.00130v1
2018-01-10,Quantum Theory of Rare-Earth Magnets,"Strong permanent magnets mainly consist of rare earths ($R$) and transition
metals ($T$). The main phase of the neodymium magnet, which is the strongest
magnet, is Nd$_2$Fe$_{14}$B. Sm$_{2}$Fe$_{17}$N$_{3}$ is another magnet
compound having excellent magnetic properties comparable to those of
Nd$_{2}$Fe$_{14}$B. Their large saturation magnetization, strong
magnetocrystalline anisotropy, and high Curie temperature originate from the
interaction between the $T$-3d electrons and $R$-4f electrons. This article
discusses the magnetism of rare-earth magnet compounds. The basic theory and
first-principles calculation approaches for quantitative description of the
magnetic properties are presented, together with applications to typical
compounds such as Nd$_2$Fe$_{14}$B, Sm$_{2}$Fe$_{17}$N$_{3}$, and the recently
synthesized NdFe$_{12}$N.",1801.03455v1
2018-01-11,Universal random codes: Capacity regions of the compound quantum multiple-access channel with one classical and one quantum sender,"We consider the compound memoryless quantum multiple-access channel (QMAC)
with two sending terminals. In this model, the transmission is governed by the
memoryless extensions of a completely positive and trace preserving map which
can be any element of a prescribed set of possible maps. We study a
communication scenario, where one of the senders aims for transmission of
classical messages while the other sender sends quantum information. Combining
powerful universal random coding results for classical and quantum information
transmission over point-to-point channels, we establish universal codes for the
mentioned two-sender task. Conversely, we prove that the two-dimensional rate
region achievable with these codes is optimal. In consequence, we obtain a
multi-letter characterization of the capacity region of each compound QMAC for
the considered transmission task.",1801.03692v2
2018-03-21,"Coexistence of Triple Nodal Points, Nodal Links, and Unusual Flat Bands in intermetallic ${\cal A}$Pd$_3$ (${\cal A}$=Pb, Sn)","We investigate the electronic structure and several properties, and
topological character, of the cubic time-reversal invariant intermetallic
compounds PbPd$_3$ and SnPd$_3$ using density functional theory based methods.
These compounds have a dispersionless band along the $\Gamma-X$ line, forming
the top of the Pd $4d$ bands and lying within a few meV of the Fermi level
$E_F$. Effects of the flat band on transport and optical properties have been
inspected by varying the doping concentration treated with the virtual crystal
approximation for substitution on the Pb site. In the absence of spin-orbit
coupling (SOC), we find triple nodal points and three-dimensional nodal loops,
which are known to lead to surface bands and drumhead states, respectively,
which we discuss for PbPd$_3$. SOC removes degeneracy in most of the zone,
providing a topological index $Z_2$=1 on the $k_z=0$ plane that indicates a
topological character on that plane. The isovalent and isostructural compound
SnPd$_3$ shows only minor differences in its electronic structures, so it is
expected to display similar electronic, transport, and topological properties.",1803.08172v2
2018-05-01,Experimental and theoretical studies on the photodegradation of 2-ethylhexyl 4-methoxycinnamate in the presence of reactive oxygen and chlorine species,"2-Ethylhexyl 4-methoxycinnamate (EHMC) is one of the most commonly used
sunscreen ingredient. In this study we investigated photodegradation of EHMC in
the presence of such common oxidizing and chlorinating systems as H2O2,
H2O2/HCl, H2O2/UV, and H2O2/HCl/UV. Reaction products were detected by gas
chromatography with a mass spectrometric detector (GC-MS). As a result of
experimental studies chloro-substituted 4-methoxycinnamic acid (4-MCA),
4-methoxybenzaldehyde (4-MBA) and 4-methoxyphenol (4-MP) were identified.
Experimental studies were enriched with DFT and MP2 calculations. We found that
reactions of 4-MCA, 4-MBA and 4-MP with Cl2 and HOCl were in all cases
thermodynamically favorable. However, reactivity indices provide a better
explanation of the formation of particular chloroorganic compounds. Generally,
those isomeric forms of mono- and dichlorinated compounds which exhibits the
highest hardness were identified. Nucleophilicity of the chloroorganic
compounds precursors were examined by means of the Fukui function.",1805.00234v1
2018-05-18,Band crossings in honeycomb-layered transition metal compounds,"Two-dimensional electron dispersions with peculiar band crossings provide a
platform for realizing topological phases of matter. Here we theoretically show
that the $e_g$-orbital manifold of honeycomb-layered transition metal compounds
accommodates a plethora of peculiar band crossings, such as multiple Dirac
point nodes, quadratic band crossings, and line nodes. From the tight-binding
analysis, we find that the band topology is systematically changed by the
orbital dependent transfer integrals on the honeycomb network of edge-sharing
octahedra, which can be modulated by distortions of the octahedra as well as
chemical substitutions. The band crossings are gapped out by the spin-orbit
coupling, which brings about a variety of topological phases distinguished by
the spin Chern numbers. The results provide a comprehensive understanding of
the previous studies on various honeycomb compounds. We also propose another
candidate materials by ab initio calculations.",1805.07068v2
2018-05-21,A general approach for the synthesis of two-dimensional binary compounds,"Only a few of the vast range of potential two-dimensional materials have been
isolated or synthesised to date. Typically, 2D materials are discovered by
mechanically exfoliating naturally occurring bulk crystals to produce
atomically thin layers, after which a material-specific vapour synthesis method
must be developed to grow interesting candidates in a scalable manner. Here we
show a general approach for synthesising thin layers of two-dimensional binary
compounds. We apply the method to obtain high quality, epitaxial MoS2 films,
and extend the principle to the synthesis of a wide range of other materials -
both well-known and never-before isolated - including transition metal
sulphides, selenides, tellurides, and nitrides. This approach greatly
simplifies the synthesis of currently known materials, and provides a general
framework for synthesising both predicted and unexpected new 2D compounds.",1805.08002v1
2018-05-26,Ionic vs. van der Waals Layered Materials: Identification and Comparison of Elastic Anisotropy,"In this work, we expand the set of known layered compounds to include ionic
layered materials, which are well known for superconducting, thermoelectric,
and battery applications. Focusing on known ternary compounds from the ICSD, we
screen for ionic layered structures by expanding upon our previously developed
algorithm for identification of van der Waals (vdW) layered structures, thus
identifying over 1,500 ionic layered compounds. Since vdW layered structures
can be chemically mutated to form ionic layered structures, we have developed a
methodology to structurally link binary vdW to ternary ionic layered materials.
We perform an in-depth analysis of similarities and differences between these
two classes of layered systems and assess the interplay between layer geometry
and bond strength with a study of the elastic anisotropy. We observe a rich
variety of anisotropic behavior in which the layering direction alone is not a
simple predictor of elastic anisotropy. Our results enable discovery of new
layered materials through intercalation or de- intercalation of vdW or ionic
layered systems, respectively, as well as lay the groundwork for studies of
anisotropic transport phenomena such as sound propagation or lattice thermal
conductivity.",1805.10489v1
2018-06-09,Quantitative trends in 8 physical properties of 115000 inorganic compounds gained by machine learning,"We applied the decision trees (random forest) machine-learning technique for
the large experimental materials dataset PAULING FILE, compiled from the
world's peer-reviewed literature. The training and validation data were
extracted from the hundreds of thousands of publications in materials science
(1891-2017). Then, for the nearly 115'000 distinct inorganic compounds we
predicted 8 thermodynamic, mechanical, and electronic properties, using the
only crystalline structures as an input. For the predicted physical properties
we observed certain periodical patterns in all unary, binary, ternary, and
quaternary compounds. We also solved a reversed task of predicting the possible
crystalline structure based on a given combination of values of the 8 mentioned
properties. Therefore our observations may play a role of the periodic table,
formulated not for the chemical elements, but for the entire set of materials.",1806.03553v2
2018-06-12,ToxicBlend: Virtual Screening of Toxic Compounds with Ensemble Predictors,"Timely assessment of compound toxicity is one of the biggest challenges
facing the pharmaceutical industry today. A significant proportion of compounds
identified as potential leads are ultimately discarded due to the toxicity they
induce. In this paper, we propose a novel machine learning approach for the
prediction of molecular activity on ToxCast targets. We combine extreme
gradient boosting with fully-connected and graph-convolutional neural network
architectures trained on QSAR physical molecular property descriptors, PubChem
molecular fingerprints, and SMILES sequences. Our ensemble predictor leverages
the strengths of each individual technique, significantly outperforming
existing state-of-the art models on the ToxCast and Tox21 toxicity-prediction
datasets. We provide free access to molecule toxicity prediction using our
model at http://www.owkin.com/toxicblend.",1806.04449v1
2018-11-03,Superconductivity in Li6P electride,"Electrides are unique compounds where most of the electrons reside at
interstitial regions of the crystal behaving as anions, which strongly
determines its physical properties. Interestingly, the magnitude and
distribution of interstitial electrons can be effectively modified either by
modulating its chemical composition or external conditions (e.g. pressure).
Most of the electrides under high pressure are non-metallic, and
superconducting electrides are very rare. In this work we report that a
pressure-induced stable Li6P electride becomes superconductor with a Tc of 39.3
K, which is the highest among already known electrides. The interstitial
electrons in Li6P, with dumbbell-like connected electride states, play a
dominant role in the superconducting transition. Other Li-rich phosphides, Li5P
and Li8P, are also predicted to be superconducting electrides, but with a lower
Tc. Superconductivity in all these compounds can be attributed to a combination
of a weak electronegativity of P with a strong electropositivity of Li, and
opens up the interest to explore high-temperature superconductivity in similar
binary compounds.",1811.01169v1
2018-11-12,"Spin Triplet Ground-State in the Copper Hexamer Compounds A2Cu3O(SO4)3 (A=Na,K)","The compounds A2Cu3O(SO4)3 (A=Na,K) are characterized by copper hexamers
which are weakly coupled along the b-axis to realize one-dimensional
antiferromagnetic chains below TN=3 K, whereas the interchain interactions
along the a- and c-axes are negligible. We investigated the energy-level
splittings of the copper hexamers by inelastic neutron scattering below and
above TN. The eight lowest-lying hexamer states could be unambiguously assigned
and parametrized in terms of a Heisenberg exchange Hamiltonian, providing
direct experimental evidence for an S=1 triplet ground-state associated with
the copper hexamers. Therefore, the compounds A2Cu3O(SO4)3 serve as novel
cluster-based spin-1 antiferromagnets to support Haldane's conjecture that a
gap appears in the excitation spectrum below TN, which was verified by
inelastic neutron scattering.",1811.04674v1
2018-11-27,Spin-polarization control driven by a Rashba-type effect breaking the mirror symmetry in two-dimensional dual topological insulators,"Three-dimensional topological insulators protected by both the time reversal
(TR) and mirror symmetries were recently predicted and observed.
Two-dimensional materials featuring this property and their potential for
device applications have been less explored. We find that in these systems, the
spin-polarization of edge states can be controlled with an external electric
field breaking the mirror symmetry. This symmetry requires that the
spin-polarization is perpendicular to the mirror plane, therefore, the electric
field induces spin-polarization components parallel to the mirror plane. Since
this field preserves the TR topological protection, we propose a transistor
model using the spin-direction of protected edge states as a switch. In order
to illustrate the generality of the proposed phenomena, we consider compounds
protected by mirror planes parallel and perpendicular to the structure, e.g.,
Na$_3$Bi and half-functionalized (HF) hexagonal compounds, respectively. For
this purpose, we first construct a tight-binding effective model for the
Na$_3$Bi compound and predict that HF-honeycomb lattice materials are also dual
topological insulators.",1811.11014v2
2019-11-15,Modelling phase imperfections in compound refractive lenses,"Compound refractive lenses (CRL) offer outstanding potential for probe
formation in X-ray micro- and nano-analysis as well as for imaging
applications, but effective aberration-free focusing of X-rays is a key
consideration when high spatial resolution and intensities are required.
Available refractive optics have non-negligible aberrations which degrade their
final performance. We describe a framework based on physical-optics for
simulating the effect of imperfect CRL upon an X-ray beam, taking into account
measured phase errors obtained from at-wavelength metrology. We model, with
increasing complexity, a CRL stack as a single thin phase element, then as a
more realistic compound-element including absorption and thickness effects and
finally, we add realistic optical imperfections to the CRL. Coherent and
partially-coherent simulations using the ""Synchrotron Radiation Workshop"" (SRW)
are used to evaluate the different models, the effects of the phase errors and
to check the validity of the design equations and suitability of the figures of
merit.",1911.06712v3
2019-11-25,First Principles Calculations of Superconducting Critical Temperature of ThCr$_2$Si$_2$-Type Structure,"High critical temperature (T$_c$) superconductor has a great potential in
many industrial applications. However, discovering a compound having high T$_c$
is still remaining a big challenge for experimental approach due to
time-consuming and high cost. In this paper, we investigated the critical
temperature (T$_c$) of several compounds of ThCr$_2$Si$_2$-type structure
(space group I4/mmm) since some of them had already been investigated and
trusted as the potential candidates for superconductivity. First principle
calculation was performed to compute the critical temperature (T$_c$) based on
allen-dynes equation modification of McMillian formula. In order to confirm our
calculation scheme, we compared our result with compounds which had been
experimentally determined obtained from $NIMS$ database. The result showed a
very good agreement with experimental data. Based on this scheme, finally, we
found ThCu$_2$Si$_2$ and ThAu$_2$Si$_2$ which were most likely to exhibit a
superconductivity around 3.88 K and 4.27.
  $keywords$ : superconductivity, ThCr$_2$Si$_2$-type structure,
ThCu$_2$Si$_2$, ThAu$_2$Si$_2$, critical temperature",1911.10716v1
2019-11-26,Effect of compound nucleus spin correlations on fission fragment angular distribution,"We extend a conventional description of the fusion-fission fragment angular
distributions by introducing the correlation between compound nucleus states
carrying different total angular momenta. This correlation results in the
strong anisotropy and mass-angle correlation of fission fragments for compact
saddle-point nuclear shapes for which the conventional description predicts
almost isotropic angular distributions. The spin off-diagonal phase relaxation
timescale, $\simeq 10^{-19}$ sec, obtained from analysis of anomalous fission
fragment angular distributions in $^{12}$C+$^{236}$U, $^{16}$O+$^{232}$Th and
$^{16}$O+$^{238}$U collisions at the sub-barrier energies is three orders of
magnitude longer than the timescale of the compound nucleus thermalization.
Expression for the angle-dependent time power spectrum for quasifission is also
presented.",1911.11832v1
2019-11-27,A Class of Compounds Featuring Frustrated Triangular Magnetic Lattice CsRESe$_2$ (RE=La-Lu): Quantum Spin-Liquid Candidates,"A triangular lattice selenide series of rare earth (RE), CsRESe2, were
synthesized as large single crystals using a flux growth method. This series
stabilized in either trigonal (R-3m) or hexagonal (P63/mmc) crystal systems.
Physical properties of CsRESe2 were explored by magnetic susceptibility and
heat capacity measurements down to 0.4 K. Antiferromagnetic interaction was
observed in all magnetic compounds, while no long-range magnetic order was
found, indicating the frustrated magnetism. CsDySe2 presents spin freezing at
0.7 K, revealing a spin-glass state. CsCeSe2 and CsYbSe2 present broad peaks at
0.7 K and 1.5 K in the magnetization, respectively, suggesting the short-range
interactions between magnetic rare earth ions. The lack of signature for
long-range magnetic order and spin freezing down to 0.4 K in these compounds
(RE = Ce, Yb) implies their candidacy for quantum spin liquid state.",1911.12278v1
2021-07-23,Multivariate Methods for Detection of Rubbery Rot in Storage Apples by Monitoring Volatile Organic Compounds: An Example of Multivariate Generalised Mixed Models,"This article is a case study illustrating the use of a multivariate
statistical method for screening potential chemical markers for early detection
of post-harvest disease in storage fruit. We simultaneously measure a range of
volatile organic compounds (VOCs) and two measures of severity of disease
infection in apples under storage: the number of apples presenting visible
symptoms and the lesion area. We use multivariate generalised linear mixed
models (MGLMM) for studying association patterns of those simultaneously
observed responses via the covariance structure of random components.
Remarkably, those MGLMMs can be used to represent patterns of association
between quantities of different statistical nature. In the particular example
considered in this paper, there are positive responses (concentrations of VOC,
Gamma distribution based models), positive responses possibly containing
observations with zero values (lesion area, Compound Poisson distribution based
models) and binomially distributed responses (proportion of apples presenting
infection symptoms). We represent patterns of association inferred with the
MGLMMs using graphical models (a network represented by a graph), which allow
us to eliminate spurious associations due to a cascade of indirect correlations
between the responses.",2107.11233v1
2021-07-30,Distributed Representations of Atoms and Materials for Machine Learning,"The use of machine learning is becoming increasingly common in computational
materials science. To build effective models of the chemistry of materials,
useful machine-based representations of atoms and their compounds are required.
We derive distributed representations of compounds from their chemical formulas
only, via pooling operations of distributed representations of atoms. These
compound representations are evaluated on ten different tasks, such as the
prediction of formation energy and band gap, and are found to be competitive
with existing benchmarks that make use of structure, and even superior in cases
where only composition is available. Finally, we introduce a new approach for
learning distributed representations of atoms, named SkipAtom, which makes use
of the growing information in materials structure databases.",2107.14664v1
2017-04-26,Beyond the network of plants volatile organic compounds,"Plants emission of volatile organic compounds (VOCs) is involved in a wide
class of ecological functions, as VOCs play a crucial role in plants
interactions with biotic and abiotic factors. Accordingly, they vary widely
across species and underpin differences in ecological strategy. In this paper,
VOCs spontaneously emitted by 109 plant species (belonging to 56 different
families) have been qualitatively and quantitatively analysed in order to
classify plants species. By using bipartite networks methodology, based on
recent advancements in Complex Network Theory, and through the application of
complementary classical and advanced community detection algorithms, the
possibility to classify species according to chemical classes such as terpenes
and sulfur compounds is suggested. This indicates complex network analysis as
an advantageous methodology to uncover plants relationships also related to the
way they react to the environment where they evolve and adapt.",1704.08062v1
2017-05-02,A regression-based feature selection study of the Curie temperature of transition-metal rare-earth compounds: prediction and understanding,"The Curie temperature ($T_C$) of binary alloy compounds consisting of 3$d$
transition-metal and 4$f$ rare-earth elements is analyzed by a machine learning
technique. We first demonstrate that nonlinear regression can accurately
reproduce $T_C$ of the compounds. The prediction accuracy for $T_C$ is
maximized when five to ten descriptors are selected, with the rare-earth
concentration being the most relevant. We then discuss an attempt to utilize a
regression-based model selection technique to learn the relation between the
descriptors and the actuation mechanism of the corresponding physical
phenomenon, i.e., $T_C$ in the present case.",1705.00978v2
2017-05-11,Predicted novel insulating electride compound between alkali metals lithium and sodium under high pressure,"The application of high pressure can fundamentally modify the crystalline and
electronic structures of elements as well as their chemical reactivity, which
could lead to the formation of novel materials. Here, we explore the reactivity
of lithium with sodium under high pressure, using a swarm structure searching
techniques combined with first-principles calculations, which identify a
thermodynamically stable LiNa compound adopting an orthorhombic oP8 phase at
pressure above 355 GPa. The formation of LiNa may be a consequence of strong
concentration of electrons transfer from the lithium and the sodium atoms into
the interstitial sites, which also leads to opening a relatively wide band gap
for LiNa-op8. This is substantially different from the picture that share or
exchange electrons in common compounds and alloys. In addition, lattice-dynamic
calculations indicate that LiNa-op8 remains dynamically stable when pressure
decompresses down to 70 GPa.",1705.04213v1
2018-06-30,Stability of charges in titanium compounds and charge transfer to oxygen in titanium dioxide,"We investigate the charge density distribution in titanium dioxide, molecular
titanium complexes and a variety of periodic titanium compounds using
delocalization indices and Bader charge analysis. Our results are in agreement
with previous experimental and theoretical investigations on the charge
stability and deviation from formal oxidation states in transition metal
compounds. We present examples for practically relevant redox processes, using
molecular titanium dioxide model systems, that illustrate the failure of formal
oxidation states to account for some redox phenomena. We observe a pronounced
charge stability on titanium for trial systems which are expected to be mainly
ionic. No environment tested by us is capable to reduce the local titanium
charge remainder below one electron.",1807.00115v1
2018-07-04,Predicting Dirac semimetals based on Sodium Ternary Compounds,"Predicting a new Dirac semimetal (DSM), as well as other topological
materials, is quite challenging, since the relationship between crystal
structure, composing atoms and the band topology is complex and elusive. Here,
we demonstrate an approach to design DSMs via exploring the chemical degree of
freedom. Based on the understanding of the well-known DSM Na$_3$Bi, three
compounds in one family, namely Na$_2$MgSn, Na$_2$MgPb and Na$_2$CdSn, have
been exactly located. Further hybrid-functional calculations with improved
estimation of band inversion show that two of them, Na$_2$MgPb and Na$_2$CdSn,
have band topology of DSMs. The nontrivial surface states with Fermi arcs on
the (010) and (100) side surfaces are shown to connect the projection of bulk
Dirac nodes. Most importantly, the candidate compounds are dynamically stable
and have been experimentally synthesized. The ideas in this work would
stimulate more designs on locating topological materials based on the
understanding of existing ones.",1807.01434v4
2018-07-08,"Simultaneously high electron and hole mobilities in cubic boron-V compounds: BP, BAs and BSb","Through first-principles calculations, the phonon-limited transport
properties of cubic boron-V compounds (BP, BAs and BSb) are studied. We find
that the high optical phonon frequency in these compounds leads to the
substantial suppression of polar scattering and the reduction of inter-valley
transition mediated by large-wavevector optical phonons, both of which
significantly facilitate charge transport. We also discover that BAs
simultaneously has a high hole mobility (2110 cm2/V-s) and electron mobility
(1400 cm2/V-s) at room temperature, which is rare in semiconductors. Our
findings present a new insight in searching high mobility polar semiconductors,
and point to BAs as a promising material for electronic and photovoltaic
devices in addition to its predicted high thermal conductivity.",1807.02732v1
2018-07-10,"Ideal inner nodal chain semimetals in Li2XY (X = Ca, Ba; Y = Si, Ge) materials","The chain-type nodal loops in the reciprocal space can generate exotic nodal
chain fermions. Here, we report that Li2XY (X = Ca, Ba; Y = Si, Ge) compounds
are ideal inner nodal chain semimetals. Their band structures are composed of
two connecting nodal loops with either hybrid or type-I band dispersion. The
signatures of the nodal chain, such as the nontrivial surface states, are quite
pronounced in these Li2XY compounds since there is only a single inner nodal
chain without other extraneous bands near the Fermi level. These compounds are
existing materials and ambient-stable, which is available to realize the
experimental detection of inner nodal chain fermions or further the practical
applications.",1807.03447v1
2018-07-11,Dynamical coupling of dilute magnetic impurities with quantum spin liquid state in the S = 3/2 dimer compound Ba3ZnRu2O9,"We have investigated the dilute magnetic impurity effect on the magnetic
properties of a quantum spin liquid candidate Ba3ZnRu2O9 and a spin gapped
compound Ba3CaRu2O9. The magnetic ground state of each compound stands against
2% substitution of magnetic impurities for Zn or Ca. We have found that the
magnetic response of these impurities, which behave as paramagnetic spins,
depends on the host materials and the difference of the two manifests itself in
the Weiss temperature, which can hardly be explained by the dilute magnetic
impurities alone in the case of Ba3ZnRu2O9. We consider a contribution from the
Ru5+ ions which would appear only in the substituted Ba3ZnRu2O9 and discuss a
possible physical meaning of the observed Weiss temperature.",1807.04076v1
2018-07-12,Superconductivity in layered Oxychalcogenide La2O2Bi3AgS6,"We report the superconductivity in layered oxychalcogenide La2O2Bi3AgS6
compound. The La2O2Bi3AgS6 compound has been reported recently by our group,
which has a tetragonal structure with the space group P4/nmm. The crystal
structure of La2O2Bi3AgS6 can be regarded as alternate stacks of LaOBiS2-type
layer and rock-salt-type (Bi,Ag)S layer. We measured low-temperature electrical
resistivity and observed superconductivity at 0.5 K. The observation of
superconductivity in the La2O2Bi3AgS6 should provide us with the successful
strategy for developing new superconducting phases by the insertion of a
rock-salt-type chalcogenide layer into the van der Waals gap of BiS2-based
layered compound like LaOBiS2.",1807.04582v1
2018-07-14,Compound Metaoptics for Amplitude and Phase Control of Wavefronts,"Metasurfaces allow tailored control over electromagnetic wavefronts. However,
due to the local conservation of power flow, a passive, lossless, and
reflectionless metasurface is limited to imparting phase discontinuities -- and
not power density discontinuities -- onto a wavefront. Here, we show how the
phase and power density profiles of a wavefront can be independently controlled
using two closely-spaced, phase-discontinuous metasurfaces. The two
metasurfaces, each designed to exhibit specific refractive properties, are
separated by a wavelength-scale distance and together form a compound
metaoptic. A systematic design procedure is presented, which allows
transformation between arbitrary complex-valued field distributions without
reflection, absorption, or active components. Such compound metaoptics may find
applications in optical trapping of particles, displaying three-dimensional
holographic images, shrinking the size of optical systems, or producing custom
(shaped and steered) far-field radiation patterns.",1807.05461v1
2018-07-17,First principle calculations with SIC correction of Fe-doped CuO compound,"In this work the electronic properties of Fe doped CuO thin films are studied
by using a standard density functional theory. This approach is based on the
abinitio calculations under the Korringa Kohn Rostoker coherent potential
approximation. We carried out our investigations in the framework of the
general gradient approximation and self interaction corrected. The density of
states in the energy diagrams are presented and discussed. The computed
electronic properties of the studied compound confirm the half metalicity
nature of this material. In addition, the absorption spectra of the studied
compound within the Generalized Gradient Approximation, as proposed by Perdew
Burke Ernzerhof approximations are examined. When compared with the pure CuO,
the Fermi levels of doped structures are found to move to the higher energy
directions. To complete this study, the effect of Fe doping method in CuO has
transformed the material to half metallic one. We found a high wide impurity
band in two cases of approximations methods.",1807.06319v1
2018-07-19,Magnetocrystalline anisotropy in the Kondo lattice compound CeAgAs$_2$,"We report on the single crystal growth and anisotropic physical properties of
CeAgAs$_2$. The compound crystallizes as on ordered variant of the
HfCuSi$_2$-type crystal structure and adopts the orthorhombic space group
$Pmca$~(\#57) with two symmetry inequivalent cerium atomic positions in the
unit cell. The orthorhombic crystal structure of our single crystal was
confirmed from the powder x-ray diffraction and from electron diffraction
patterns obtained from the transmission electron microscope. The anisotropic
physical properties have been investigated on a good quality single crystal by
measuring the magnetic susceptibility, isothermal magnetization, electrical
transport and heat capacity. The magnetic susceptibility and magnetization
measurements revealed that this compound orders antiferromagnetically with two
closely spaced magnetic transitions at $T_{\rm N1} = 6$~K and $T_{\rm N2} =
4.9$~K. Magnetization studies have revealed a large magnetocrystalline
anisotropy due to the crystalline electric field (CEF) with an easy axis of
magnetization along the [010] direction. The magnetic susceptibility measured
along the [001] direction exhibited a broad hump in the temperature range 50 to
250~K, while typical Curie-Weiss behaviour was observed along the other two
orthogonal directions. The electrical resistivity and the heat capacity
measurements revealed that CeAgAs$_2$ is a Kondo lattice system with a magnetic
ground state.",1807.07265v1
2018-07-27,Superconductivity in a misfit layered compound (SnSe)$_{1.16}$(NbSe$_2$),"The large size single crystals of (SnSe)$_{1.16}$(NbSe$_2$) misfit layered
compound were grown and superconductivity with $T_c$ of 3.4 K was first
discovered in this system. Powder X-ray diffraction (XRD) and high resolution
transmission electron microscopy (HRTEM) clearly display the misfit feature
between SnSe and NbSe$_2$ subsystems. The Sommerfeld coefficient $\gamma$
inferred from specific-heat measurements is 16.73 mJ mol$^{-1}$ K$^{-2}$,
slightly larger than the usual misfit compounds. The normalized specific heat
jump $\Delta$$C_e$/$\gamma$$T_{\rm c}$ is about 0.98, and the electron-phonon
coupling constant $\lambda$$_{e-ph}$ is estimated to be 0.80. The estimated
value of the in-plane upper critical magnetic field, $H_{c2}^{ab}$(0), is about
7.82 T, exceeding the Pauli paramagnetic limit slightly. Both the specific-heat
and $H_{c2}$ data suggest that (SnSe)$_{1.16}$(NbSe$_2$) is a multi-band
superconductor.",1807.10410v1
2018-10-02,New Families of Large Band Gap 2D Topological Insulators in Ethynyl-Derivative Functionalized Compounds,"The search for large band gap systems with dissipationless edge states is
essential to developing materials that function under a wide range of
temperatures. Two-dimensional (2D) topological insulators (TIs) have recently
attracted significant attention due to their dissipationless transport, robust
properties and excellent compatibility with device integration. However, a
major barrier of 2D TIs is their small bulk band gap, which allows for
applications only in extremely low temperatures. In this work, first principle
calculations were used to analyze the geometric, electronic, and topological
properties of PbC2X and BiC2X (X = H, Cl, F, Br, I) compounds. The band gap
values are remarkably large, ranging from 0.79eV to 0.99eV. The nanoribbons of
these compounds exhibited nontrivial topological order in the simulation, thus
proving ethynyl-derivative functionalized Pb and Bi films to be new classes of
giant band gap 2D TIs. In addition, these findings indicate that chemical
functionalization with ethynyl-derivatives is an effective method to tune the
band gap and preserve the nontrivial topological order. These novel materials
that are applicable at both room temperature and high temperatures open the
door to a new generation of electronics.",1810.01060v1
2018-10-29,"Material design of indium based compounds: possible candidates for charge, valence, and bond disproportionation and superconductivity","We design and investigate the physical properties of new indium compounds
AInX$_{3}$ (A = alkali metals, X = F or Cl). We find nine new In based
materials in their ground state and are thermodynamically stable but are not
reported in ICSD (Inorganic Crystal Structure Database). We also discuss
several metastable structures. This new series of materials display multiple
valences, charge and bond disproportionation, and dimerization. The most common
valence of In is 3+. We also find two rare alternatives, one has In$^{2+}$ with
In-In dimerization and the other shows valence disproportionation to In$^{1+}$
and In$^{3+}$ with bond disproportionation. We study the possibility of
superconductivity in these new In compounds and find that CsInF$_{3}$ has a
transition temperature about 24 K with sufficient hole doping and pressure.",1810.12410v2
2018-10-30,"Optoelectronic and thermoelectric properties of Ba3DN (D = Sb, Bi): A DFT investigation","We have investigated the optoelectronic and thermoelectric properties of
hexagonal antiperovskites Ba$_3$DN (D = Sb, Bi) using DFT calculations. The
calculated equilibrium lattice parameters of both compounds are in good
agreement with the available data. The calculated electronic structures
indicate that they are direct bandgap semiconductors and the values of bandgaps
are 1.35 and 1.33 eV for Ba3SbN and Ba3BiN, respectively. The inclusion of the
spin-orbit effect split the conduction bands and the band gap of Ba$_3$BiN is
much reduced. These two compounds have a high absorption coefficient, notably
higher than that for GaAs and close to that for silicon. The obtained static
refractive index is ~2.8 and 3.26, for Ba$_3$SbN and Ba$_3$BiN, respectively.
We predict that both materials are suitable for a high-efficiency solar cell.
Both compounds exhibit a high Seebeck coefficient and high power factor. Our
analysis predicts that the studied materials are potential candidates in
thermoelectric device applications.",1810.12526v1
2019-01-10,Magnetization plateau and supersolid phases in the spin-1/2 antiferromagnetic Heisenberg model on a tetragonally distorted fcc lattice,"The Heisenberg model on a face center cubic (fcc) lattice is a typical
three-dimensional frustrated spin system expected to have magnetization
plateaus and supersolid phases. There are model compounds $A_2$CoTeO$_6$ ($A$ =
Ca, Sr, Pb) for the fcc lattice but with lattice distortions. Motivated by the
presence of the compounds, we investigate the ground state of the spin-1/2
antiferromagnetic Heisenberg model on a tetragonally distorted fcc lattice in
the magnetic field using a large-size cluster mean-field method for the sake of
finding new supersolid phases. We find five supersolid phases in the model,
indicating possibility to observe supersolid phases in these compounds. We also
find that one of the supersolid phases is similar to the nonclassical coplanar
phase obtained in the XXZ model on the triangular lattice.",1901.02996v2
2019-01-21,Raman spectra of Nontraditional Compound KO4 and Novel Chemical Reaction of KCl-O2,"The non-traditional compound KO4 still existing at ambient conditions was
synthesized by the reaction of KCl-O2 under high pressure and high temperature
(HPHT) using the diamond anvil cell and the laser heating technology. The
KCl-O2 sample was heated at 37 GPa (1800 K) and then the products were measured
by Raman technology at room temperature. The acquired 1386 cm-1 characteristic
vibration band of KO4 reflects the O-O pair with fractional negative charge.
The other reaction products include another non-traditional compound KCl3, a
bit KClO4 and intermediate product Cl2. The KCl3 can distinguish 11 Raman peaks
and decompose into KCl and Cl2 below 10 GPa during decompression. These novel
products show that high pressure promotes oxygen and chlorine forming
unconventional pair-anions and polyanions, the novel chemical reaction provides
new perspectives for developing new batteries materials and studying batteries
reactions.",1901.06784v1
2019-01-23,Computing Defects Associated to Bounded Domain Wall Structures: The $\operatorname{Vec}(\mathbb{Z}/p\mathbb{Z})$ Case,"A domain wall structure consists of a planar graph with faces labeled by
fusion categories/topological phases. Edges are labeled by bimodules/domain
walls. When the vertices are labeled by point defects we get a compound defect.
We present an algorithm, called the domain wall structure algorithm, for
computing the compound defect. We apply this algorithm to show that the
\emph{bimodule associator}, related to the $O_3$ obstruction of [Etingof et
al., Quantum Topol. 1, 209 (2010), arXiv:0909.3140], is trivial for all domain
walls of $\operatorname{Vec}(\mathbb{Z}/p\mathbb{Z})$.
  In the language of this paper, the ground states of the Levin-Wen model are
compound defects. We use this to define a generalization of the Levin-Wen model
with domain walls and point defects. The domain wall structure algorithm can be
used to compute the ground states of these generalized Levin-Wen type models.",1901.08069v2
2019-01-25,"Low temperature magnetic and dielectric properties of LnBaCuFeO5 (Ln = Nd, Eu, Gd, Ho and Yb)","The layered perovskite compounds are interesting due to their intriguing
physical properties. In this article we report the structural, magnetic and
dielectric properties of LnBaCuFeO5 (Ln=Nd, Eu, Gd, Ho and Yb). The structural
parameters decrease from Nd to Yb due to the decrease in the ionic radii of the
rare earth ions. An antiferromagnetic transition is observed for EuBaCuFeO5
near 120 K along with the glassy dynamics of the electric dipoles below 100 K.
The magnetic transition is absent in other compounds, which may be due to the
dominance of the magnetic moment of the rare earth ions. The dielectric
constant does not show any anomaly, except in the case of HoBaCuFeO5 where it
shows a weak frequency dependence around 54 K. These compounds show a
significant enhancement of dielectric constant at high temperatures which have
been attributed to Maxwell-Wagner effect. However, no significant
magneto-dielectric coupling has been observed in these layered perovskites.",1901.08835v1
2019-01-28,Computational Analysis of Composition-Structure-Property-Relationships in NZP-type Materials for Li-Ion Batteries,"Compounds crystallizing in the structure of NaZr$_2$(PO$_4$)$_3$ (NZP) are
considered as promising materials for solid state electrolytes in Li-ion
batteries. Using density functional theory (DFT), a systematic computational
screening of 18 NZP compounds, namely LiX$_2$(LO$_4$)$_3$ with X = Ti, V, Fe,
Zr, Nb, Ru, Hf, Ta, Os, and L = P, Mn is performed with respect to their
activation energies for vacancy-mediated Li migration. It is shown how the
different ionic radii of the cationic substitutions influence structural
characteristics such as the octahedron volumes around Li ions on the initial
and transition state sites, which affect the activation energies
(''composition-structure-property'' relationships). The prevalent assumption
that structural bottlenecks formed by triangularly arranged oxygen atoms at a
certain location along the migration path determine the energy barriers for Li
migration is not supported by the DFT results. Instead, the ionic neighborhood
of the migrating ion in the initial and in the transition state needs to be
taken into account to relate the structure to the activation energies. This
conclusion applies to Na containing NZP compounds as well.",1901.09759v1
2019-01-29,"Optimal uni-axial ferromagnetism in (La,Ce)$_2$Fe$_{14}$B for permanent magnets","Prospects for light-rare-earth-based permanent magnet compound
R$_{2}$Fe$_{14}$B (R=La$_{1-x}$Ce$_{x}$ with $0 \le x\le 1$) are inspected from
first principles referring to the latest experimental data. Ce-rich 2:14:1
compounds come with good structure stability, reasonably good combination of
magnetization and magnetic anisotropy, while a drawback lies in the low Curie
temperature that is only 120~K above the room temperature at the
Ce$_2$Fe$_{14}$B limit. Best compromise is inspected on the basis of ab initio
data for (La$_{1-x}$Ce$_{x}$)$_2$Fe$_{14}$B referring to the magnetic
properties of the champion magnet compound Nd$_{2}$Fe$_{14}$B and prerequisite
conditions imposed by practical utility.",1901.10119v1
2019-04-12,Structure map of AB$_2$ type 2D materials by high-throughput DFT calculations,"By high-throughput calculations based on the density functional theory, we
construct a structure map for AB$_2$ type monolayers of 3844 compounds which
are all the combinations of 62 elements selected from the periodic table. The
structure map and its web version (www.openmx-square.org/2d-ab2/) provide
comprehensive structural trends of the 3844 compounds in two dimensional (2D)
structures, and predict correctly structures of most of existing 2D compounds
such as transition metal dichalcogenides and MXenes having 1T or 1H type
structures. We also summarize all the families of 1T/1H type AB$_2$ monolayers
for each combination of groups in the periodic table on the basis of our
structure map, and propose new types of structures such as a memory structure,
which may be a candidate material for data storage applications with an
extremely high areal density. In addition, planar and distorted planar
structures and other geometrically characteristic structures are found through
the high-throughput calculations. These characteristic structures might give
new viewpoints and directions to search unknown 2D materials. Our structure map
and database will promote efforts towards synthesizing undiscovered 2D
materials experimentally and investigating properties of the new structures
theoretically.",1904.06047v1
2019-07-05,Destruction of multiferroicity in Tb2BaNiO5 by Sr doping and its implication to magnetoelectric coupling,"The Haldane spin-chain compound, Tb2BaNiO5, with two antiferromagnetic
transitions, one at T1=63K, and the other at T2=25K, has been recently shown by
us to be an exotic multiferroic below T2. Here, we report the results of our
investigations of Sr doping at the Ba site by magnetization, heat-capacity,
magnetoelectric (MDE), and pyrocurrent measurements. An intriguing finding,
which we stress, is that the ferroelectricity is lost even for a doping level
of 10 atomic percent, though magnetic ordering prevails. The doped specimens
however retain significant magnetodielectric behaviour, but with reduced
magnitudes and qualitative changes with respect to the behaviour of the parent
compound. This implies that ferroelectric order is also crucial for the
anomalously large MDE in the parent compound, in addition to the role of 4f
single-ion anisotropy.",1907.02816v1
2019-07-16,Improved alkali intercalation of carbonaceous materials in ammonia solution,"Alkali intercalated graphite compounds represent a compelling modification of
carbon with significant application potential and various fundamentally
important phases. We report on the intercalation of graphite with alkali atoms
(Li and K) using liquid ammonia solution as mediating agent. Alkali atoms
dissolve well in liquid ammonia which simplifies and speeds up the
intercalation process, and it also avoids the high temperature formation of
alkali carbides. Optical microscopy, Raman, and electron spin resonance
spectroscopy attest that the prepared samples are highly and homogeneously
intercalated to a level approaching Stage-I intercalation compounds. The method
and the synthesis route may serve as a starting point for the various forms of
alkali atom intercalated carbon compounds (including carbon nanotubes and
graphene), which could be exploited in energy storage and further chemical
modifications.",1907.07058v1
2019-10-02,"Investigation of structural and elastic properties of monoclinic Ba$_2$P$_7$X (X $=$ Cl, Br, I) Zintl Salts compounds","Structural and elastic properties of Ba$_{2}$P$_{7}$X (X=Cl, Br, I) (Barium
Phosphide Halides) Zintl compounds have been investigated using the
pseudo-potential plane-wave (PP-PW) method based on the density functional
theory (DFT) within the generalized gradient approximation (GGA-PBESOL). The
calculated lattice constants and internal parameters are in a good agreement
with the experimental results reported in literature. In this paper, we present
an investigation of the relative changes of the structural parameters and
elastic constants as function of hydrostatic pressure. Isotropic elastic moduli
and their related properties for single-crystal and polycrystalline phase,
including the namely bulk modulus, shear modulus, Young's modulus, Poisson's
ratio, elastic anisotropy indexes, Pugh's indicator of brittle/ductile
behavior, elastic wave velocities and Debye temperature have been estimated
from $C_{ij}$ using Voigt, Russ and Hill approximations. Two different methods
have been used to study the elastic anisotropy of these compounds.",1910.00915v1
2019-10-07,"One-Pot Preparation of Mechanically Robust, Transparent, Highly Conductive and Memristive Metal-Organic Ultrathin Film","The future of 2D flexible electronics relies on the preparation of conducting
ultrathin films of materials with mechanical robustness and flexibility in a
simple but controlled manner. In this respect, metal-organic compounds present
advantages over inorganic laminar crystals owing to their structural, chemical
and functional diversity. While most metal-organic compounds are usually
prepared in bulk, recent work has shown that some of them are processable down
to low dimensional forms. Here we report the one-pot preparation, carried out
at the water-air interface, of ultrathin (down to 4 nm) films of the
metal-organic compound [Cu2I2(TAA)]n (TAA= thioacetamide). The films are shown
to be homogenous over mm2 areas, smooth, highly transparent, mechanically
robust and good electrical conductors with memristive behavior at low
frequencies. This combination of properties, as well as the industrial
availability of the two building blocks required for the preparation,
demonstrates their wide range potential in future flexible and transparent
electronics.",1910.02809v1
2019-10-13,Regression for Copula-linked Compound Distributions with Applications in Modeling Aggregate Insurance Claims,"In actuarial research, a task of particular interest and importance is to
predict the loss cost for individual risks so that informative decisions are
made in various insurance operations such as underwriting, ratemaking, and
capital management. The loss cost is typically viewed to follow a compound
distribution where the summation of the severity variables is stopped by the
frequency variable. A challenging issue in modeling such outcome is to
accommodate the potential dependence between the number of claims and the size
of each individual claim. In this article, we introduce a novel regression
framework for compound distributions that uses a copula to accommodate the
association between the frequency and the severity variables, and thus allows
for arbitrary dependence between the two components. We further show that the
new model is very flexible and is easily modified to account for incomplete
data due to censoring or truncation. The flexibility of the proposed model is
illustrated using both simulated and real data sets. In the analysis of
granular claims data from property insurance, we find substantive negative
relationship between the number and the size of insurance claims. In addition,
we demonstrate that ignoring the frequency-severity association could lead to
biased decision-making in insurance operations.",1910.05676v1
2019-10-25,Local magnetic anisotropy by polarized neutron powder diffraction: application of magnetically induced preferred crystallite orientation,"Polarized neutron diffraction allows to determine the local susceptibility
tensor on the magnetic site both in single crystals and powders. It is widely
used in the studies of single crystals, but it is still hardly applicable to a
number of highly interesting powder materials, like molecular magnets or
nanoscale systems because of the low luminosity of existing instruments and the
absence of an appropriate data analysis software. We show that these
difficulties can be overcome by using a large area detector in combination with
the two-dimensional Rietveld method and powder samples with magnetically
induced preferred crystallite orientation. This is demonstrated by revisiting
two test powder compounds, namely, low anisotropy (soft) ferrimagnetic compound
Fe3O4 and spin-ice compound Ho2Ti2O7 with high local anisotropy. The values of
magnetic moments in Fe3O4 and the susceptibility tensors of Ho2Ti2O7 at various
temperatures and fields were found in perfect agreement with these found
earlier in single crystal experiments. The magnetically induced preferred
crystallite orientation was used to study the local susceptibility of a
single-molecule magnet Co([(CH3)2N]2CS)2Cl2. Hence, the studies of local
magnetic anisotropy in powder systems might now become accessible.",1910.11822v1
2012-09-05,"Half-metallicity and magnetism of GeTe doped with transition metals V, Cr and Mn: a theoretical study from the viewpoint of application in spintronics","This work presents results for the magnetic properties of the compound GeTe
doped with 3d transition metals V, Cr and Mn from the viewpoint of potential
application in spintronics. We report a systematic density-functional study of
the electronic structure, magnetic and cohesive properties of these ternary
compounds in both rock salt and zinc blende structures. In both cases, it is
the Ge sublattice that is doped with the three transition metals. Some of these
compounds are found to be half-metallic at their optimized cell volumes. For
these particular cases, we calculate both exchange interactions and the Curie
temperatures in order to provide some theoretical guidance to experimentalists
trying to fabricate materials suitable for spintronic devices. Discussions
relating our results to the existing experimental studies are provided whenever
applicable and appropriate. Apparent discrepancy between experimental
observations and our theoretical result for the case of Mn-doping is discussed
in detail, pointing out various physical reasons and possible resolutions of
the apparent discrepancy.",1209.1063v1
2012-09-10,Epitaxially Stabilized EuMoO3: A New Itinerant Ferromagnet,"Synthesizing metastable phase often opens new functions in materials but is a
challenging topic. Thin film techniques have advantages to form materials which
do not exist in nature since nonequilibrium processes are frequently utilized.
In this study, we successfully synthesize epitaxially stabilized new compound
of perovskite Eu2+Mo4+O3 as a thin film form by a pulsed laser deposition.
Analogous perovskite SrMoO3 is a highly conducting paramagnetic material, but
Eu2+ and Mo4+ are not compatible in equilibrium and previous study found more
stable pyrochlore Eu23+Mo24+O7 prefers to form. By using isostructural
perovskite substrates, the gain of the interface energy between the film and
the substrate stabilizes the matastable EuMoO3 phase. This compound exhibits
high conductivity and large magnetic moment, originating from Mo 4d2 electrons
and Eu 4f7 electrons, respectively. Our result indi-cates the epitaxial
stabilization is effective not only to stabilize crystallographic structures
but also to from a new compound which contains unstable combinations of ionic
valences in bulk form.",1209.2032v1
2014-06-07,Optical conductivity of iron-based superconductors,"The new family of unconventional iron-based superconductors discovered in
2006 immediately relieved their copper-based high-temperature predecessors as
the most actively studied superconducting compounds in the world. The
experimental and theoretical effort made in order to unravel the mechanism of
superconductivity in these materials has been overwhelming. Although our
understanding of their microscopic properties has been improving steadily, the
pairing mechanism giving rise to superconducting transition temperatures up to
55 K remains elusive. And yet the hope is strong that these materials, which
possess a drastically different electronic structure but similarly high
transition temperatures compared to the copper-based compounds, will shed
essential new light onto the several-decade-old problem of unconventional
superconductivity. In this work we review the current understanding of the
itinerant-charge-carrier dynamics in the iron-based superconductors and parent
compounds largely based on the optical-conductivity data the community has
gleaned over the past seven years using such experimental techniques as
reflectivity, ellipsometry, and terahertz transmission measurements and analyze
the implications of these studies for the microscopic properties of the
iron-based materials as well as the mechanism of superconductivity therein.",1406.1879v1
2014-06-16,Handling non-compositionality in multilingual CNLs,"In this paper, we describe methods for handling multilingual
non-compositional constructions in the framework of GF. We specifically look at
methods to detect and extract non-compositional phrases from parallel texts and
propose methods to handle such constructions in GF grammars. We expect that the
methods to handle non-compositional constructions will enrich CNLs by providing
more flexibility in the design of controlled languages. We look at two specific
use cases of non-compositional constructions: a general-purpose method to
detect and extract multilingual multiword expressions and a procedure to
identify nominal compounds in German. We evaluate our procedure for multiword
expressions by performing a qualitative analysis of the results. For the
experiments on nominal compounds, we incorporate the detected compounds in a
full SMT pipeline and evaluate the impact of our method in machine translation
process.",1406.3976v1
2014-06-16,Na-ion dynamics in Quasi-1D compound NaV2O4,"We have used the pulsed muon source at ISIS to study high-temperature Na-ion
dynamics in the quasi-one-dimensional (Q1D) metallic antiferromagnet NaV2O4. By
performing systematic zero-field and longitudinal-field measurements as a
function of temperature we clearly distinguish that the hopping rate increases
exponentially above Tdiff=250 K. The data is well fitted to an Arrhenius type
equation typical for a diffusion process, showing that the Na-ions starts to be
mobile above Tdiff . Such results makes this compound very interesting for the
tuning of Q1D magnetism using atomic-scale ion-texturing through the periodic
potential from ordered Na-vacancies. Further, it also opens the door to
possible use of NaV2O4 and related compounds in energy related applications.",1406.3982v1
2014-06-17,"Effect of hydrostatic pressures on the superconductivity of new BiS2 based REO0.5F0.5BiS2 (RE-La, Pr and Nd) superconductors","We study the impact of hydrostatic pressure on superconductivity of new BiS2
based layered REO0.5F0.5BiS2 (RE-La, Pr, and Nd) compounds through the
measurements of dc electrical resistivity. The REO0.5F0.5BiS2 (RE-La, Pr and
Nd) compounds synthesized by solid state reaction route via vacuum
encapsulation are crystallized in the tetragonal P4/nmm space group. At ambient
pressure the superconducting transition onset temperatures are 2.7K, 3.5K and
4.5K which are enhanced substantially under external hydrostatic pressure to
10.5K, 7.8K and 7.5K for LaO0.5F0.5BiS2, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2
respectively at 1.68GPa. The normal state electrical resistivity decreases with
applied pressure for REO0.5F0.5BiS2 (RE-La, Pr and Nd). The electrical
resistivity under magnetic field and applied pressure has been measured to
estimate upper critical field, the values of which are 15.9Tesla, 8.8Tesla and
8.2Tesla for LaO0.5F0.5BiS2, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 compounds.
Substantial enhancement of superconductivity under moderate pressures in
studied new BiS2 based superconductors call for the attention of condensed
matter physics community.",1406.4231v2
2018-02-16,"Superconductivity in Cage Compounds La$Tr_{2}$Al$_{20}$ with $Tr$ = Ti, V, Nb, and Ta","Electrical resistivity, magnetic susceptibility, and specific heat
measurements on single crystals of La$Tr_{2}$Al$_{20}$ ($Tr$ = Ti, V, Nb, and
Ta) revealed that these four compounds exhibit weak-coupling superconductivity
with transition temperatures $T_{\rm c}$ = 0.46, 0.15, 1.05, and 1.03 K,
respectively. LaTi$_{2}$Al$_{20}$ is most probably a type-I superconductor,
which is quite rare among intermetallic compounds. Single-crystal X-ray
diffraction suggests ""rattling"" anharmonic large-amplitude oscillations of Al
ions (16$c$ site) on the Al$_{16}$ cage, while no such feature is suggested for
the cage-center La ion. Using a parameter $d_{\rm GFS}$ quantifying the ""guest
free space"" of the cage-center ion, we demonstrate that nonmagnetic
$RTr_{2}$Al$_{20}$ superconductors are classified into two groups, i.e., (A)
$d_{\rm GFS} \ne 0$ and $T_{\rm c}$ correlates with $d_{\rm GFS}$, and (B)
$d_{\rm GFS} \simeq 0$ and $T_{\rm c}$ seems to be governed by other factors.",1802.06119v1
2018-02-19,Exploring the high-pressure materials genome,"A thorough in situ characterization of materials at extreme conditions is
challenging, and computational tools such as crystal structural search methods
in combination with ab initio calculations are widely used to guide experiments
by predicting the composition, structure, and properties of high-pressure
compounds. However, such techniques are usually computationally expensive and
not suitable for large-scale combinatorial exploration. On the other hand,
data-driven computational approaches using large materials databases are useful
for the analysis of energetics and stability of hundreds of thousands of
compounds, but their utility for materials discovery is largely limited to
idealized conditions of zero temperature and pressure. Here, we present a novel
framework combining the two computational approaches, using a simple linear
approximation to the enthalpy of a compound in conjunction with
ambient-conditions data currently available in high-throughput databases of
calculated materials properties. We demonstrate its utility by explaining the
occurrence of phases in nature that are not ground states at ambient conditions
and estimating the pressures at which such ambient-metastable phases become
thermodynamically accessible, as well as guiding the exploration of
ambient-immiscible binary systems via sophisticated structural search methods
to discover new stable high-pressure phases.",1802.06900v1
2018-08-15,"Crystal Field Levels and Magnetic Anisotropy in the Kagome Compounds $\rm{Nd_3Sb_3Mg_2O_{14}}$, $\rm{Nd_3Sb_3Zn_2O_{14}}$, and $\rm{Pr_3Sb_3Mg_2O_{14}}$","We report the crystal field levels of several newly-discovered rare-earth
kagome compounds: $\rm{Nd_3Sb_3Mg_2O_{14}}$, $\rm{Nd_3Sb_3Zn_2O_{14}}$, and
$\rm{Pr_3Sb_3Mg_2O_{14}}$. We determine the CEF Hamiltonian by fitting to
neutron scattering data using a point-charge Hamiltonian as an intermediate
fitting step. The fitted Hamiltonians accurately reproduce bulk susceptibility
measurements, and the results indicate easy-axis ground state doublets for
$\rm{Nd_3Sb_3Mg_2O_{14}}$ and $\rm{Nd_3Sb_3Zn_2O_{14}}$, and a singlet ground
state for $\rm{Pr_3Sb_3Mg_2O_{14}}$. These results provide the groundwork for
future investigations of these compounds and a template for CEF analysis of
other low-symmetry materials.",1808.05111v1
2018-08-17,Magnetic and structural studies of G-phase compound Mn$_6$Ni$_{16}$Si$_7$,"Transition metal compounds with complex crystal structures tend to
demonstrate interesting magnetic coupling resulting in unusual magnetic
properties. In this work, the structural and magnetic characterization of a
single crystal of the Ni-Mn-Si based G-phase compound, Mn$_6$Ni$_{16}$Si$_7$,
grown by the Czochralski method, is reported. In this structure isolated
octahedral Mn$_6$ clusters form a f.c.c. lattice. As each octahedron consists
of eight edge-sharing equilateral triangles, the possibility for geometric
frustration exists. Magnetization and specific heat measurements showed two
magnetic phase transitions at 197 K and 50 K, respectively. At 100 K neutron
diffraction on powder samples shows a magnetic structure with k = (001) in
which only four of the six Mn spins per cluster order along $<100>$ directions
giving a two dimensional magnetic structure consistent with intra-cluster
frustration. Below the 50 K phase transition the Mn spins cant away from
$<100>$ directions and a weak moment develops on the two remaining Mn
octahedral sites.",1808.05741v2
2018-08-30,"Topological Nontrivial Phase in Hexagonal Antiperovskites A3BiB (A=Ba,Sr; B=P,N)","In this article, we predict the occurrence of topological non-trivial phase
in hexagonal antiperovskite systems. By carefully investigating the evolution
of band structure, we have studied the pressure induced topological phase
transition in Ba$_{3}$BiP, Ba$_{3}$BiN, and Sr$_{3}$BiN compounds using the
hybrid functional calculations. The non-trivial topology has been verified by
computing Dirac like surface dispersion and topological invariant {\it Z$_2$}
index via parity analysis. The unconventional spin texture has been analyzed
which guaranteed the absence of impurity induced backscattering on boundary of
the sample while respecting the time reversal symmetry. Our simulation confirms
the chemical and mechanical stability of all the three compounds. The present
study introduces an important new class of hexagonal antiperovskite compounds
in the topological regime and are believed to capture ample of attention both
from theoretical as well as experimental front.",1808.10215v1
2018-12-20,Dynamical splitting of cubic crystal field levels in rare-earth cage compounds,"The Crystalline Electric Field (CEF) influence is usually described by
considering an ideally symmetrical rare-earth site. In the case of cage
compounds, ample excursions of the rare-earth inside the cage require an
adapted CEF description. A corrective, position dependent, CEF term accounts
for the deviation from the perfect symmetry. In the paramagnetic range, a CEF
level with orbital degeneracy thus acquires a width reflecting the rare-earth
spatial distribution. In the case, frequent in cubic systems, of an orbitally
degenerate CEF ground state at the center, this width introduces an additional
energy scale, influential at low temperature. A spherical simplification allows
to identify the major consequences of a cage-split ground multiplet: a
Schottky-like anomaly appears in the specific heat with associated reduction of
the magnetic entropy and alteration of the magnetic properties. Concomitantly,
a centrifugal Jahn-Teller effect develops that expands the distribution of the
magnetic ion and softens the rattling phonons. These effects are confronted
with anomalous paramagnetic properties of rare-earth cage compounds, notably
rare-earth filled skutterudites and hexaborides.",1812.08722v3
2018-12-25,Type-II superconductivity in W5Si3-type Nb5Sn2Al,"We report the discovery of superconductivity in the ternary aluminide
Nb$_{5}$Sn$_{2}$Al, which crystallizes in the W$_{5}$Si$_{3}$-type structure
with one-dimensional Nb chains along the $c$-axis. It is found that the
compound has a multiband nature and becomes a weakly coupled, type-II
superconductor below 2.0 K. The bulk nature of superconductivity is confirmed
by the specific heat jump, whose temperature dependence shows apparent
deviation from a single isotropic gap behavior. The lower and upper critical
fields are estimated to be 2.0 mT and 0.3 T, respectively. From these values,
we derive the penetration depth, coherence length and Ginzburg-Landau parameter
to be 516 nm, 32.8 nm and 15.6, respectively. By contrast, the isostructural
compound Ti$_{5}$Sn$_{2}$Al dose not superconduct above 0.5 K. A comparison of
these results with other W$_{5}$Si$_{3}$-type superconductors suggests that
$T_{\rm c}$ of these compounds correlates with the average number of valence
electrons per atom.",1812.10009v2
2019-02-06,Mol-CycleGAN - a generative model for molecular optimization,"Designing a molecule with desired properties is one of the biggest challenges
in drug development, as it requires optimization of chemical compound
structures with respect to many complex properties. To augment the compound
design process we introduce Mol-CycleGAN - a CycleGAN-based model that
generates optimized compounds with high structural similarity to the original
ones. Namely, given a molecule our model generates a structurally similar one
with an optimized value of the considered property. We evaluate the performance
of the model on selected optimization objectives related to structural
properties (presence of halogen groups, number of aromatic rings) and to a
physicochemical property (penalized logP). In the task of optimization of
penalized logP of drug-like molecules our model significantly outperforms
previous results.",1902.02119v1
2019-02-27,Atomistic structure learning,"One endeavour of modern physical chemistry is to use bottom-up approaches to
design materials and drugs with desired properties. Here we introduce an
atomistic structure learning algorithm (ASLA) that utilizes a convolutional
neural network to build 2D compounds and layered structures atom by atom. The
algorithm takes no prior data or knowledge on atomic interactions but inquires
a first-principles quantum mechanical program for physical properties. Using
reinforcement learning, the algorithm accumulates knowledge of chemical
compound space for a given number and type of atoms and stores this in the
neural network, ultimately learning the blueprint for the optimal structural
arrangement of the atoms for a given target property. ASLA is demonstrated to
work on diverse problems, including grain boundaries in graphene sheets,
organic compound formation and a surface oxide structure. This approach to
structure prediction is a first step toward direct manipulation of atoms with
artificially intelligent first principles computer codes.",1902.10501v1
2019-06-03,Physical properties of CeIrSi with trillium-lattice frustrated magnetism,"Magnetic ($\chi$), transport ($\rho$) and heat capacity ($C_m$)properties of
CeIrSi are investigated to elucidate the effect of geometric frustration in
this compound with trillium type structure because, notwithstanding its robust
effective moment, $\mu_{\rm eff}\approx 2.46\mu_B$, this Ce-lattice compound
does not undergo a magnetic transition. In spite of that it shows broad
$C_m(T)/T$ and $\chi(T)$ maxima centered at $T_{max}\approx 1.5$\,K, while a
$\rho \propto T^2$ thermal dependence, characteristic of electronic spin
coherent fluctuations, is observed below $T_{coh} \approx 2.5$\,K. Magnetic
field does not affect significantly the position of the mentioned maxima up to
$\approx 1$\,T, though $\chi(T)$ shows an incipient structure that completely
vanishes at $\mu_0 H \approx 1$\,T. Concerning the $\rho \propto T^2$
dependence, it is practically not affected by magnetic field up to $\mu_0 H =
9$\,T, with the residual resistivity $\rho_0(H)$ slightly decreasing and
$T_{coh}(H)$ increasing. These results are compared with the physical
properties observed in other frustrated intermetallic compounds",1906.00832v2
2019-06-16,Covert Communication Over a Compound Channel,"In this paper, we consider fundamental communication limits over a compound
channel. Covert communication in the information-theoretic context has been
primarily concerned with fundamental limits when the transmitter wishes to
communicate to legitimate receiver(s) while ensuring that the communication is
not detected by an adversary. This paper, however, considers an alternative,
and no less important, setting in which the object to be masked is the state of
the compound channel. Such a communication model has applications in the
prevention of malicious parties seeking to jam the communication signal when,
for example, the signal-to-noise ratio of a wireless channel is found to be
low. Our main contribution is the establishment of bounds on the throughput-key
region when the covertness constraint is defined in terms of the total
variation distance. In addition, for the scenario in which the key length is
infinite, we provide a sufficient condition for when the bounds coincide for
the scaling of the throughput, which follows the square-root law. Numerical
examples, including that of a Gaussian channel, are provided to illustrate our
results.",1906.06675v1
2020-04-21,Fusion hindrance of $^{48}$Ti + $^{138}$Ba reaction,"We have already measured the ER excitation function of $^{48}$Ti + $^{138}$Ba
reaction around the Coulomb barrier. While a detailed report of measurement of
ER excitation function of $^{48}$Ti + $^{138}$Ba is available in literature,
the present paper compares it with other channels forming the same compound
nucleus. The experiment was performed at IUAC, New Delhi for lab energies from
189.3 to 234.4 MeV, where the ER cross sections show an abrupt fall beyond
160.03 MeV. The decrease in ER cross section is attributed to non compound
nuclear reaction such as quasi-fission (QF). A comparison with statistical
model code PACE 4 also shows significant deviation of the experimental data
from theoretical predictions. When this reaction is compared with $^{86}$Kr +
$^{100}$Mo and $^{64}$Ni + $^{122}$Sn forming the same compound nucleus
$^{186}Pt^{*}$, the symmetric systems show more ERs than the asymmetric one and
it is against the general trend. Preliminary study predict the influence of
deformation and isospin asymmetry in the abrupt fall of ER cross section than
that of the symmetric systems. A detailed theoretical analysis of the systems
are in progress and will be published shortly.",2004.09827v1
2020-04-29,High throughput computational screening for two-dimensional magnetic materials based on experimental databases of three-dimensional compounds,"We perform a computational screening for two-dimensional magnetic materials
based on experimental bulk compounds present in the Inorganic Crystal Structure
Database and Crystallography Open Database. A recently proposed geometric
descriptor is used to extract materials that are exfoliable into
two-dimensional derivatives and we find 85 ferromagnetic and 61
anti-ferromagnetic materials for which we obtain magnetic exchange and
anisotropy parameters using density functional theory. For the easy-axis
ferromagnetic insulators we calculate the Curie temperature based on classical
Monte Carlo simulations of anisotropic Heisenberg models. We find good
agreement with the experimentally reported Curie temperatures of known 2D
ferromagnets and identify 10 potentially exfoliable two-dimensional
ferromagnets that have not been reported previously. In addition, we find 18
easy-axis anti-ferromagnetic insulators with several compounds exhibiting very
strong exchange coupling and magnetic anisotropy.",2004.14460v1
2020-05-02,Stress-Induced Intercalation Instability,"We present a linear stability analysis to demonstrate that a flat coherent
phase boundary formed by the (de)intercalation of solutes into a compound is
unstable against perturbations with wavelengths larger than a critical
wavelength. This critical wavelength is controlled by the competition between
the interface energy and the elastic strain energy caused by the misfit between
the solute-rich and solute-poor phases. It increases with the distance between
the phase boundary and free surface of the compound, and so the instability is
most pronounced when the boundary is close to the surface at the early stage of
the (de)intercalation process. Numerical calculations show that such
instability leads to non-uniform intercalation behavior. We find that uniform
intercalation cannot be achieved unless the phase boundary moves at a speed
greater than a critical velocity. Estimate of the magnitude of this velocity
suggests that the stress-induced intercalation instability is generally
operative in intercalation compounds used for battery applications.",2005.00884v1
2020-05-26,First-order ferromagnetic transitions of lanthanide local moments in divalent compounds: An itinerant electron positive feedback mechanism and Fermi surface topological change,"Around discontinuous (first-order) magnetic phase transitions the strong
caloric response of materials to the application of small fields is widely
studied for the development of solid-state refrigeration. Typically strong
magnetostructural coupling drives such transitions and the attendant
substantial hysteresis dramatically reduces the cooling performance. In this
context we describe a purely electronic mechanism which pilots a first-order
paramagnetic-ferromagnetic transition in divalent lanthanide compounds and
which explains the giant non-hysteretic magnetocaloric effect recently
discovered in a Eu$_2$In compound. There is positive feedback between the
magnetism of itinerant valence electrons and the ferromagnetic ordering of
local $f$-electron moments, which appears as a topological change to the Fermi
surface. The origin of this electronic mechanism stems directly from Eu's
divalency, which explains the absence of a similar discontinuous transition in
Gd$_2$In.",2005.12659v1
2020-08-05,NMR study of the spin correlations in the $S=1$ armchair chain Ni$_2$NbBO$_6$,"We report our nuclear magnetic resonance (NMR) study on the structurally spin
chain compound Ni$_2$NbBO$_6$ with complex magnetic coupling. The
antiferromagnetic transition is monitored by the line splitting resulting from
the staggered internal hyperfine field. The magnetic coupling configuration
proposed by the first-principle density functional theory (DFT) is supported by
our NMR spectral analysis. For the spin dynamics, a prominent peak at $T\sim35$
K well above the N\'{e}el temperature ($T_N\sim20$ K at $\mu_0H=10$ T) is
observed from the spin-lattice relaxation data. As compared with the
dc-susceptibility, this behavior indicates a antiferromagnetic coupling with
the typical energy scale of $\sim3$ meV. Thus, the Ni$_2$NbBO$_6$ compound can
be viewed as strongly ferromagnetically coupled armchair spin chains along the
crystalline $b$-axis. These facts place strong constraints to the theoretical
model for this compound.",2008.01949v1
2020-08-12,Prediction on Properties of Rare-earth 2-17-X Magnets Ce2Fe17-xCoxCN : A Combined Machine-learning and Ab-initio Study,"We employ a combination of machine learning and first-principles calculations
to predict magnetic properties of rare-earth lean magnets. For this purpose,
based on training set constructed out of experimental data, the machine is
trained to make predictions on magnetic transition temperature (Tc), largeness
of saturation magnetization ({\mu}0Ms), and nature of the magnetocrystalline
anisotropy (Ku). Subsequently, the quantitative values of {\mu}0Ms and Ku of
the yet-to-be synthesized compounds, screened by machine learning, are
calculated by first-principles density functional theory. The applicability of
the proposed technique of combined machine learning and first-principles
calculations is demonstrated on 2-17-X magnets, Ce2Fe17-xCoxCN. Further to this
study, we explore stability of the proposed compounds by calculating vacancy
formation energy of small atom interstitials (N/C). Our study indicates a
number of compounds in the proposed family, offers the possibility to become
solution of cheap, and efficient permanent magnet.",2008.05125v1
2020-08-23,"Frierson's 1907 Parameterization of Compound Magic Squares Extended to Orders 3^{l}, l=1,2,3,..., with Information Entropy","Frierson used a powerful parameterization of the pattern of the order 3
associative magic square to construct a family of six related order 9 compound
(or composite) magic squares, several of them ancient. Stimulated by Bellew's
1997 extension to order 27, we extend these ideas to all orders that are powers
of 3, and in addition find simple formulae for the matrix spectra and entropic
measures for all those orders. This construction is fractal and we give
numerical results to order 243 which show an information entropy measure
converging to a constant value of about 1.168.. for the lowest entropy members.
We also briefly consider compounding of an order 4 magic square with the lowest
entropy, for which we find a similar trend to constant entropy.",2008.11020v2
2020-07-24,Deep Inverse Reinforcement Learning for Structural Evolution of Small Molecules,"The size and quality of chemical libraries to the drug discovery pipeline are
crucial for developing new drugs or repurposing existing drugs. Existing
techniques such as combinatorial organic synthesis and High-Throughput
Screening usually make the process extraordinarily tough and complicated since
the search space of synthetically feasible drugs is exorbitantly huge. While
reinforcement learning has been mostly exploited in the literature for
generating novel compounds, the requirement of designing a reward function that
succinctly represents the learning objective could prove daunting in certain
complex domains. Generative Adversarial Network-based methods also mostly
discard the discriminator after training and could be hard to train. In this
study, we propose a framework for training a compound generator and learning a
transferable reward function based on the entropy maximization inverse
reinforcement learning paradigm. We show from our experiments that the inverse
reinforcement learning route offers a rational alternative for generating
chemical compounds in domains where reward function engineering may be less
appealing or impossible while data exhibiting the desired objective is readily
available.",2008.11804v2
2020-08-26,Revealing charge anisotropies in metal compounds via high-purity x-ray polarimetry,"Linear polarization analysis of hard x-rays is employed to probe electronic
anisotropies in metal-containing complexes with very high selectivity. We use
the pronounced linear dichroism of nuclear resonant x-ray scattering to
determine electric field gradients in an iron(II) containing compound as they
evolve during a temperature-dependent high-spin/low-spin phase transition. This
method constitutes a novel approach to analyze changes in the electronic
structure of metal-containing molecules as function of external parameters or
stimuli. The polarization selectivity of the technique allows us to monitor
defect concentrations of electronic valence states across phase transitions.
This opens new avenues to trace electronic changes and their precursors that
are connected to structural and electronic dynamics in the class of metal
compounds ranging from simple molecular solids to biological molecules.",2008.11820v1
2020-08-28,Rethinking the Objectives of Extractive Question Answering,"This work demonstrates that using the objective with independence assumption
for modelling the span probability $P(a_s,a_e) = P(a_s)P(a_e)$ of span starting
at position $a_s$ and ending at position $a_e$ has adverse effects. Therefore
we propose multiple approaches to modelling joint probability $P(a_s,a_e)$
directly. Among those, we propose a compound objective, composed from the joint
probability while still keeping the objective with independence assumption as
an auxiliary objective. We find that the compound objective is consistently
superior or equal to other assumptions in exact match. Additionally, we
identified common errors caused by the assumption of independence and manually
checked the counterpart predictions, demonstrating the impact of the compound
objective on the real examples. Our findings are supported via experiments with
three extractive QA models (BIDAF, BERT, ALBERT) over six datasets and our
code, individual results and manual analysis are available online.",2008.12804v4
2021-02-27,"High-$T_c$ ternary metal hydrides, YKH$_{12}$ and LaKH$_{12}$, discovered by machine learning","The search for hydride compounds that exhibit high $T_c$ superconductivity
has been extensively studied. Within the range of binary hydride compounds, the
studies have been developed well including data-driven searches as a topic of
interest. Toward the search for the ternary systems, the number of possible
combinations grows rapidly, and hence the power of data-driven search gets more
prominent. In this study, we constructed various regression models to predict
$T_c$ for ternary hydride compounds and found the extreme gradient boosting
(XGBoost) regression giving the best performance. The best performed regression
predicts new promising candidates realizing higher $T_c$, for which we further
identified their possible crystal structures. Confirming their lattice and
thermodynamical stabilities, we finally predicted new ternary hydride
superconductors, YKH$_{12}$ [$C2/m$ (No.12), $T_c$=143.2 K at 240 GPa] and
LaKH$_{12}$ [$R\bar{3}m$ (No.166), $T_c$=99.2 K at 140 GPa] from first
principles.",2103.00193v1
2021-02-28,eQuilibrator 3.0 -- a platform for the estimation of thermodynamic constants,"eQuilibrator (equilibrator.weizmann.ac.il) is a calculator for biochemical
equilibrium constants and Gibbs free energies, originally designed as a
web-based interface. While the website now counts ${\sim}1000$ distinct monthly
users, its design could not accommodate larger compound databases and it lacked
an application programming interface (API) for integration in other tools
developed by the systems biology community. Here, we report a new python-based
package for eQuilibrator, that comes with many new features such as a 50-fold
larger compound database, the ability to add novel compound structures,
improvements in speed and memory use, and correction for Mg2+ ion
concentrations. Moreover, it adds the ability to compute the covariance matrix
of the uncertainty between estimates, for which we show the advantages and
describe the application in metabolic modeling. We foresee that these
improvements will make thermodynamic modeling more accessible and facilitate
the integration of eQuilibrator into other software platforms.",2103.00621v1
2021-03-29,Classicality of the heat produced by quantum measurements,"Quantum measurement is ultimately a physical process, resulting from an
interaction between the measured system and a measuring apparatus. Considering
the physical process of measurement within a thermodynamic context naturally
raises the following question: How can the work and heat be interpreted? In the
present paper we model the measurement process for an arbitrary discrete
observable as a measurement scheme. Here the system to be measured is first
unitarily coupled with an apparatus and subsequently the compound system is
objectified with respect to a pointer observable, thus producing definite
measurement outcomes. The work can therefore be interpreted as the change in
internal energy of the compound system due to the unitary coupling. By the
first law of thermodynamics, the heat is the subsequent change in internal
energy of this compound due to pointer objectification. We argue that the
apparatus serves as a stable record for the measurement outcomes only if the
pointer observable commutes with the Hamiltonian and show that such
commutativity implies that the uncertainty of heat will necessarily be
classical.",2103.15749v3
2021-03-30,Integer vs. half-integer spin on an approximate honeycomb lattice,"Recent interest in honeycomb lattice materials has focused on their potential
to host quantum spin liquid (QSL) states. Variations in bond angles and spin
allow a range of interesting behaviors on this lattice, from the predicted QSL
ground state of the Kitaev model to exotic magnetic orders. Here we report the
physical properties of two compounds with rare earths on an approximate
honeycomb lattice. The isostructural compounds Nd$_2$S$_5$Sn (J =
$\frac{9}{2}$) and Pr$_2$S$_5$Sn (J = 4) permit a direct comparison of
half-integer versus integer spins on this lattice. We find strikingly different
magnetic properties for the two compounds. Nd$_2$S$_5$Sn orders
antiferromagnetically at T$_N$ $\approx$ 2.5 K, and undergoes several magnetic
transitions to other ordered states under applied field. Pr$_2$S$_5$Sn displays
no magnetic ordering transition above T = 0.41 K, and may be proximate to a
spin liquid state.",2103.16684v1
2022-02-01,Magnetic structures and electronic properties of cubic-pyrochlore ruthenates from first principles,"The magnetic ground states of $R_2$Ru$_2$O$_7$ and $A_2$Ru$_2$O$_7$ with $R=$
Pr, Gd, Ho, and Er, as well as $A=$ Ca, Cd are predicted devising a combination
of the cluster-multipole (CMP) theory and spin-density-functional theory
(SDFT). The strong electronic correlation effects are estimated by the
constrained-random-phase approximation (cRPA) and taken into account within the
dynamical-mean-field theory (DMFT). The target compounds feature $d$-orbital
magnetism on Ru$^{4+}$ and Ru$^{5+}$ ions for $R$ and $A$, respectively, as
well as $f$-orbital magnetism on the $R$ site, which leads to an intriguing
interplay of magnetic interactions in a strongly correlated system. We find
CMP+SDFT is capable of describing the magnetic ground states in these
compounds. The cRPA captures a difference in the screening strength between
$R_2$Ru$_2$O$_7$ and $A_2$Ru$_2$O$_7$ compounds, which leads to a qualitative
and quantitative understanding of the electronic properties within DMFT.",2202.00277v1
2022-02-13,Data standardization for robust lip sync,"Lip sync is a fundamental audio-visual task. However, existing lip sync
methods fall short of being robust to the incredible diversity of videos taken
in the wild, and the majority of the diversity is caused by compound
distracting factors that could degrade existing lip sync methods. To address
these issues, this paper proposes a data standardization pipeline that can
produce standardized expressive images while preserving lip motion information
from the input and reducing the effects of compound distracting factors. Based
on recent advances in 3D face reconstruction, we first create a model that can
consistently disentangle expressions, with lip motion information embedded.
Then, to reduce the effects of compound distracting factors on synthesized
images, we synthesize images with only expressions from the input,
intentionally setting all other attributes at predefined values independent of
the input. Using synthesized images, existing lip sync methods improve their
data efficiency and robustness, and they achieve competitive performance for
the active speaker detection task.",2202.06198v2
2022-03-07,"Dynamical properties of magnetic topological insulator $T$Bi$_{2}$Te$_{4}$ ($T=$Mn, Fe): phonons dispersion, Raman active modes, and chiral phonons study","Recently discovered magnetic topological insulators $T$Bi$_{2}$Te$_{4}$
($T=$Mn, Fe) crystallize into the $R\bar{3}m$ rhombohedral structure and
exhibit the antiferromagnetic order. Here, we discuss the lattice dynamics of
these compounds to confirm the stability of these systems. We show that the
phonon dispersion does not contain soft modes, so both compounds are
dynamically stable in the $R\bar{3}m$ phase. We perform theoretical analyses of
the mode activity at $\Gamma$ point for the discussed compounds. In the case of
the Raman active modes, our results are in agreement with the experimentally
observed frequencies. Finally, we also discuss the possibility of realization
of chiral phonons.",2203.03337v1
2022-03-16,Does (TaSe4)2I really harbor an axionic charge density wave?,"A recent experimental work has reported an excess of the non-linear
conductivity in the charge density wave (CDW) sliding mode of the quasi
one-dimensional compound (TaSe4)2I, when a magnetic field is applied
co-linearly to the electric field [Gooth et al., Nature 575, 315 (2019)]. This
result has opened a conceptual approach, where the CDW gap in (TaSe4)2I is
opened between Weyl fermions of opposite chirality with the assumption that
this compound is a Weyl semi-metal in its undistorted high temperature phase.
We report measurements in the sliding state of (TaSe4)2I performed in similar
conditions. We have found no increase in the magnetoconductivity. In our
attempts for understanding this unsettling discrepancy, we stress the specific
nature of the Peierls transition in (TaSe4)2I and the strong electron-phonon
coupling present in this compound. Given the lack of further evidence, we think
that it is premature to assert that (TaSe4)2I is an axionic insulator.",2203.08743v1
2022-03-17,Observation of banded spherulite in a pure compound by rhythmic growth,"Banded spherulitic growth of crystal is observed in some materials with
spherically symmetric growth front and periodic radial variation of
birefringence. This variation of birefringence in quasi two dimensional
geometry produces concentric interference colour bands when viewed through
crossed polarisers. In most materials, the banded spherulites are found to be
formed by radially oriented periodically twisted fibrillar crystallites. Here,
we report the formation of banded spherulites due to the rhythmic growth of
concentric crystallite-rich and crystallite-poor bands for a pure compound
consisting of strongly polar rod like molecules. The compound exhibits
coexistence of untwisted fibrillar crystallites and an amorphous phase in its
most stable solid state. On sufficient supercooling of the sample from its
melting point, the banded spherulites are formed with a periodic variation of
composition of untwisted radially aligned fibrillar crystallites and an
amorphous solid phase. We have developed a time dependent Ginzburg-Landau model
to account for the observed banded spherulitic growth.",2203.09222v1
2022-03-18,"Orbital physics: glorious past, bright future","Transition metal (TM) compounds present a very big class of materials with
quite diverse properties. There are among them insulators, metals, systems with
insulator-metal transitions; most magnetic systems are TM compounds; there are
among them also (high-Tc) superconductors. Their very rich properties are
largely determined by the strong interplay of different degrees of freedom:
charge; spin; orbital; lattice. Orbital effects play a very important role in
these systems -- and not only in them! The study of this field, initiated by
Goodenough almost 70 years ago, turned out to be very fruitful and produced a
lot of important results. In this short review I first discuss the basics of
orbital physics, summarize the main achievements in this big field, in which
Goodenough played a pivotal role and which are nowadays widely used to explain
many properties of TM compounds. In the main part of the text I discuss novel
developments and perspectives in orbital physics, which is still a very active
field of research, constantly producing new surprises.",2203.10151v1
2016-03-02,On the formation of molecules and solid-state compounds from the AGB to the PN phases,"During the asymptoyic giant branch (AGB) phase, different elements are
dredge-up to the stellar surface depending on progenitor mass and metallicity.
When the mass loss increases at the end of the AGB, a circumstellar dust shell
is formed, where different (C-rich or O-rich) molecules and solid-state
compounds are formed. These are further processed in the transition phase
between AGB stars and planetary nebulae (PNe) to create more complex organic
molecules and inorganic solid-state compounds (e.g., polycyclic aromatic
hydrocarbons, fullerenes, and graphene precursors in C-rich environments and
oxides and crystalline silicates in O-rich ones). We present an observational
review of the different molecules and solid-state materials that are formed
from the AGB to the PN phases. We focus on the formation routes of complex
fullerene (and fullerene-based) molecules as well as on the level of dust
processing depending on metallicity.",1603.00723v1
2016-03-07,Study of compound nucleus formation via bremsstrahlung emission in proton $α$-particle scattering,"In this paper a role of many-nucleon dynamics in formation of the compound
$^{5}{\rm Li}$ nucleus in the scattering of protons off $\alpha$-particles at
the proton incident energies up to 20 MeV is investigated. We propose a
bremsstrahlung model allowing to extract information about probabilities of
formation of such nucleus on the basis of analysis of experimental
cross-sections of the bremsstrahlung photons. In order to realize this
approach, the model includes elements of microscopic theory and also
probabilities of formation of the short-lived compound nucleus. Results of
calculations of the bremsstrahlung spectra are in good agreement with the
experimental cross-sections.",1603.01924v1
2016-03-07,"High-pressure melt growth and transport properties of SiP, SiAs, GeP, and GeAs 2D layered semiconductors","Silicon and Germanium monopnictides SiP, SiAs, GeP and GeAs form a family of
2D layered semiconductors. We have succeeded in growing bulk single crystals of
these compounds by melt-growth under high pressure (0.5-1 GPa) in a cubic anvil
hot press. Large (mm-size), shiny, micaceous crystals of GeP, GeAs and SiAs
were obtained, and could be exfoliated into 2D flakes. Small and brittle
crystals of SiP were yielded by this method. High-pressure sintered
polycrystalline SiP and GeAs have also been successfully used as a precursor in
the Chemical Vapor Transport growth of these crystals in the presence of
I$_{2}$ as a transport agent. All compounds are found to crystallize in the
expected layered structure and do not undergo any structural transition at low
temperature, as shown by Raman spectroscopy down to T=5K. All materials exhibit
a semiconducting behavior. The electrical resistivity of GeP, GeAs and SiAs is
found to depend on temperature following a 2D-Variable Range Hopping conduction
mechanism. The availability of bulk crystals of these compounds opens new
perspectives in the field of 2D semiconducting materials for device
applications.",1603.02134v1
2016-03-29,Role of Sn impurity on electronic topological transitions in 122 Fe-based superconductors,"We show that only a few percentage of Sn doping at the Ba site on
BaFe$_2$As$_2$, can cause electronic topological transition, namely, the
Lifshitz transition. A hole like d$_{xy}$ band of Fe undergoes electron like
transition due to 4\% Sn doping. Lifshitz transition is found in BaFe$_2$As$_2$
system around all the high symmetry points. Our detailed first principles
simulation predicts absence of any Lifshitz transition in other 122 family
compounds like SrFe$_2$As$_2$, CaFe$_2$As$_2$. This work bears practical
significance due to the facts that a few percentage of Sn impurity is in-built
in tin-flux grown single crystals method of synthesizing 122 materials and
inter-relationship among the Lifshitz transition, magnetism and
superconductivity.",1603.08772v1
2016-12-06,High-Pressure Synthesis of a Pentazolate Salt,"The pentazolates, the last all-nitrogen members of the azole series, have
been notoriously elusive for the last hundred years despite enormous efforts to
make these compounds in either gas or condensed phases. Here we report a
successful synthesis of a solid state compound consisting of isolated
pentazolate anions N5-, which is achieved by compressing and laser heating
cesium azide (CsN3) mixed with N2 cryogenic liquid in a diamond anvil cell. The
experiment was guided by theory, which predicted the transformation of the
mixture at high pressures to a new compound, cesium pentazolate salt (CsN5).
Electron transfer from Cs atoms to N5 rings enables both aromaticity in the
pentazolates as well as ionic bonding in the CsN5 crystal. This work provides a
critical insight into the role of extreme conditions in exploring unusual
bonding routes that ultimately lead to the formation of novel high nitrogen
content species.",1612.01918v1
2016-12-09,New Tl2LaBr5: Ce3+ Crystal Scintillator for γ-Rays Detection,"In this study we present our preliminary report on the scintillation
properties of new Ce-doped Tl2LaBr5 single crystal. Two zones vertical Bridgman
technique is used for the growth of this compound. Pure and Ce-doped samples
showed maximum emission peaks at 435 nm and 415 nm, respectively. Best light
yield of 43,000+-4300 ph/MeV with 6.3% (FWHM) energy resolution is obtained for
5% Ce-doped sample under {\gamma}-ray excitation. Single exponential decay time
constant of 25 ns is observed for 5% Ce doped sample. Effective Z-number is
found to be 67, therefore efficient detection of X- and {\gamma}-ray will be
possible. Preliminary results revealed that this compound will be an ideal
candidate for the medical imaging techniques. Further investigations are under
way for the determination of optimized conditions of this compound.",1612.02918v1
2016-12-09,"Water/ice phase transition: the role of Zirconium Acetate, a compound with ice-shaping properties","Few compounds feature ice-shaping properties. The only compound reported to
have ice-shaping properties similar to that of ice-shaping proteins,
encountered in many organisms living at low temperature, is Zirconium Acetate.
When a Zirconium Acetate solution is frozen, oriented and perfectly hexagonal
ice crystals can be formed and their growth follows the temperature gradient.
To shed light on the water/ice phase transition while freezing Zirconium
Acetate solution we carried out differential scanning calorimetry measurements.
From our results, we estimate how many water molecules do not freeze because of
their interaction with Zr cations. We estimate the colligative properties of
the Zr concentration on the apparent critical temperature. We further show the
phase transition is unaffected by the nature of the base which is used to
adjust the pH. Our results provide thus new hints on the ice-shaping mechanism
of Zirconium Acetate.",1612.02934v1
2016-12-12,New Ternary Superconducting Compound LaRu2As2: Physical Properties from DFT Calculations,"In this paper, we have presented the density functional theory (DFT) based
calculations performed within the first-principles pseudopotential method to
investigate the physical properties of the newly discovered superconductor
LaRu2As2 for the first time. The optimized structural parameters are in good
agreement with the experimental results. The calculated independent elastic
constants ensure mechanical stability of the compound. The calculated Cauchy
pressure, Pugh's ratio as well as Poisson's ratio indicate that LaRu2As2 should
behave as a ductile material. Due to low Debye temperature, LaRu2As2 may be
used as a thermal barrier coating (TBC) material. The new compound should
exhibit metallic nature as its valence bands overlap considerably with the
conduction bands. LaRu2As2 is expected to be a soft material and easily
machineable because of its low hardness value of 6.8 Gpa. The multi-band nature
is observed in calculated Fermi surface. A highly anisotropic combination of
ionic, covalent, and metallic interactions is expected in accordance with
charge density calculations.",1612.03569v1
2016-12-26,Magnetic excitations in a three-orbital model for the strongly spin-orbit coupled iridates: Effect of mixing between the J=1/2 and 3/2 sectors,"A three-orbital-model approach for studying spin wave excitations in the
strongly spin-orbit coupled layered perovskite iridates is presented which
provides a unified description of magnetic excitations as well as the
electronic band structure. The calculated spin wave dispersions with realistic
three-band parameters are in excellent agreement with the RIXS data for
iridates, including the strong AF zone boundary dispersion in the single-layer
compound $\rm Sr_2 Ir O_4$ and the large anisotropy gap in the bilayer compound
$\rm Sr_3 Ir_2 O_7$. The RIXS spin wave data is shown to provide evidence of
mixing between the J=1/2 and 3/2 sectors in both compounds.",1612.08360v1
2016-12-30,Antiferromagnetic Kondo lattice compound CePt$_{3}$P,"A new ternary platinum phosphide CePt$_{3}$P was synthesized and
characterized by means of magnetic, thermodynamic and transport measurements.
The compound crystallizes in an antiperovskite tetragonal structure similar to
that in the canonical family of platinum-based superconductors $A$Pt$_{3}$P
($A$ = Sr, Ca, La) and closely related to the noncentrosymmetric heavy fermion
superconductor CePt$_{3}$Si. In contrast to all the superconducting
counterparts, however, no superconductivity is observed in CePt$_{3}$P down to
0.5 K. Instead, CePt$_{3}$P displays a coexistence of antiferromagnetic
ordering, Kondo effect and crystalline electric field effect. A field-induced
spin-flop transition is observed below the magnetic ordering temperature
$T_{N1}$ of 3.0 K while the Kondo temperature is of similar magnitude as
$T_{N1}$. The obtained Sommerfeld coefficient of electronic specific heat is
${\gamma}_{Ce}$ = 86 mJ/molK$^{2}$ indicating that CePt$_{3}$P is a moderately
correlated antiferromagnetic Kondo lattice compound.",1612.09389v1
2017-02-02,High-pressure phases of group II difluorides: polymorphism and superionicity,"We investigate the high-pressure behaviour of beryllium, magnesium and
calcium difluorides using ab initio random structure searching and density
functional theory (DFT) calculations, over the pressure range 0-70 GPa.
Beryllium fluoride exhibits extensive polymorphism at low pressures, and we
find two new phases for this compound - the silica moganite and CaCl2
structures - which are stable over the wide pressure range 12-57 GPa. For
magnesium fluoride, our searching results show that the orthorhombic `O-I' TiO2
structure (Pbca, Z=8) is stable for this compound between 40 and 44 GPa. Our
searches find no new phases at the static-lattice level for calcium difluoride
between 0 and 70 GPa; however, a phase with P62m symmetry is close to stability
over this pressure range, and our calculations predict that this phase is
stabilised at high temperature. The P62m structure exhibits an unstable phonon
mode at large volumes which may signal a transition to a superionic state at
high temperatures. The Group-II difluorides are isoelectronic to a number of
other AB2-type compounds such as SiO2 and TiO2, and we discuss our results in
light of these similarities.",1702.00746v1
2017-02-22,"Antiferroelectric topological insulators in orthorhombic $A$MgBi compounds ($A=$ Li, Na, K)","We introduce antiferroelectric topological insulators as a new class of
functional materials in which an electric field can be used to control
topological order and induce topological phase transitions. Using first
principles methods, we predict that several alkali-MgBi orthorhombic members of
an $ABC$ family of compounds are antiferroelectric topological insulators. We
also show that epitaxial strain and hydrostatic pressure can be used to tune
the topological order and the band gap of these $ABC$ compounds.
Antiferroelectric topological insulators could enable precise control of
topology using electric fields, enhancing the applicability of topological
materials in electronics and spintronics.",1702.06958v2
2017-10-07,Robust Radar Detection of a Mismatched Steering Vector Embedded in Compound Gaussian Clutter,"The problem of radar detection in compound Gaussian clutter when a radar
signature is not completely known has not been considered yet and is addressed
in this paper. We proposed a robust technique to detect, based on the
generalized likelihood ratio test, a point-like target embedded in compound
Gaussian clutter. Employing an array of antennas, we assume that the actual
steering vector departs from the nominal one, but lies in a known interval. The
detection is then secured by employing a semi-definite programming. It is
confirmed via simulation that the proposed detector experiences a negligible
detection loss compared to an adaptive normalized matched filter in a perfectly
matched case, but outperforms in cases of mismatched signal. Remarkably, the
proposed detector possesses constant false alarm rate with respect to the
clutter covariance matrix.",1710.02656v1
2017-10-10,Ambient and high pressure phases of tin sulfide compounds,"Tin sulfides SnxSy are important class of materials that are actively
investigated as novel photovoltaic and water splitting materials.
First-principles evolutionary crystal structure search is performed with the
goal of constructing the complete phase diagram of SnxSy and discover new
phases as well as new compounds of varying stoichiometry at ambient conditions
and pressures up to 100 GPa. The ambient phase of SnS2 with P3m1 symmetry
remains stable up to 30 GPa. Another ambient phase, SnS experiences a series of
phase transformations: including \alpha-SnS to \beta-SnS at 9 GPa, followed by
\beta-SnS to \gamma-SnS at 40 GPa. \gamma-SnS is a new high-pressure metallic
phase with Pm3m space group symmetry stable up to 100 GPa, which becomes a
superconductor with a maximum Tc= 9.6 K at 40 GPa. Another new metallic
compound, Sn3S4 with I43d space group symmetry, is predicted to be stable at
pressures above 15 GPa, which also becomes a superconductor with a maximum
Tc=21.8 K at 30 GPa.",1710.03642v1
2017-10-17,Compound Poisson approximation of subgraph counts in stochastic block models with multiple edges,"We use the Stein-Chen method to obtain compound Poisson approximations for
the distribution of the number of subgraphs in a generalised stochastic block
model which are isomorphic to some fixed graph. This model generalises the
classical stochastic block model to allow for the possibility of multiple edges
between vertices. Both the cases that the fixed graph is a simple graph and
that it has multiple edges are treated. The former results apply when the fixed
graph is a member of the class of strictly balanced graphs and the latter
results apply to a suitable generalisation of this class to graphs with
multiple edges. We also consider a further generalisation of the model to
pseudo-graphs, which may include self-loops as well as multiple edges, and
establish a parameter regime in the multiple edge stochastic block model in
which Poisson approximations are valid. The results are applied to obtain
Poisson and compound Poisson approximations (in different regimes) for subgraph
counts in the Poisson stochastic block model and degree corrected stochastic
block model of Karrer and Newman \cite{kn11}.",1710.06341v2
2017-10-30,Influence of fusion dynamics on fission observables: A multi-dimensional analysis,"An attempt to unfold the respective influence of the fusion and fission
stages on typical fission observables, and namely the neutron pre-scission
multiplicity, is proposed. A four-dimensional dynamical stochastic Langevin
model is used to calculate the decay by fission of excited compound nuclei
produced in a wide set of heavy-ion collisions. The comparison of the results
from such a calculation and experimental data is discussed, guided by
predictions of the dynamical deterministic HICOL code for the compound-nucleus
formation time. While the dependence of the latter on the entrance-channel
properties can straigthforwardly explain some observations, a complex interplay
between the various parameters of the reaction can occur in other cases. A
multi-dimensional analysis of the respective role of these parameters,
including entrance-channel asymmetry, bombarding energy, compound-nucleus
fissility, angular momentum and excitation energy, is proposed. It is shown
that, depending on the size of the system, apparent unconsistencies may be
deduced when projecting onto specific ordering parameters. The work suggests
the possibility of delicate compensation effects in governing the measured
fission observables, thereby highlighting the necessity of a multi-dimensional
discussion.",1710.10926v1
2018-04-01,The silver route to cuprate analogs,"The parent compound of high-Tc superconducting cuprates is a unique Mott
state consisting of layers of spin-1/2 ions arranged on a square lattice and
with a record high antiferromagnetic coupling within the layers. Compounds with
similar characteristics have long been searched for. Nickelates and iridates
had been proposed as cuprate analogs but so far have not reached a satisfactory
similarity. Here we use a combination of experimental and theoretical tools to
show that the commercial compound AgF2 is an excellent cuprate analog with
remarkably similar electronic parameters to La2CuO4 but larger buckling of
planes. Two-magnon Raman scattering reveals a superexchange constant which
reaches 70% of that of a typical cuprate. We argue that structures that reduce
or eliminate the buckling of the AgF2 planes could have an antiferromagnetic
coupling that matches or surpasses the cuprates.",1804.00329v1
2018-04-11,"Structural, electronic and magnetic properties of the Manganese telluride layers AMnTe2 (A=K, Rb, Cs) from first-principles calculations","Using first-principles electronic structure calculations based on density
functional theory (DFT), we investigate the structural, electronic and magnetic
properties of the layered ternary manganese tellurides: AMnTe2 (A = K, Rb, and
Cs). Calculations are accomplished within the full-potential linearized
augmented plane wave (FP-LAPW) using the generalized gradient approximation GGA
formalism for the exchange correlation term. We have treated all ferromagnetic,
antiferromagnetic and non-magnetic phases and found that the ferromagnetic is
the ground-state for all studied compounds. Moreover, all three compounds under
study are half-metals with a total spin magnetic per formula unit of 4 mu_B
which is mainly localized at the Mn atoms. We express for these compounds a new
version of the Slater-Pauling rule and discuss in detail the origin of the
minority-spin gap. Finally, we have also calculated some other relevant
quantities such as the bulk modulus B, the pressure derivative B', the virtual
semiconducting gap Eg, and the half-metallic gap E_HM.",1804.04189v1
2018-04-27,Electrodynamics of quantum spin liquids,"Quantum spin liquids attract great interest due to their exceptional magnetic
properties characterized by the absence of long-range order down to low
temperatures despite the strong magnetic interaction. Commonly, these compounds
are strongly correlated electron systems, and their electrodynamic response is
governed by the Mott gap in the excitation spectrum. Here we summarize and
discuss the optical properties of several two-dimensional quantum spin liquid
candidates. First we consider the inorganic material Herbertsmithite
ZnCu$_3$(OH)$_6$Cl$_2$ and related compounds, which crystallize in a kagome
lattice. Then we turn to the organic compounds
$\beta^{\prime}$-EtMe$_3$\-Sb\-[Pd(dmit)$_2$]$_2$,
$\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$ and
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, where the spins are arranged in an
almost perfect triangular lattice, leading to strong frustration. Due to
differences in bandwidth, the effective correlation strength varies over a wide
range, leading to a rather distinct behavior as far as the electrodynamic
properties are concerned. We discuss the spinon contributions to the optical
conductivity in comparison to metallic quantum fluctuations in the vicinity of
the Mott transition.",1804.10702v1
2019-03-07,Superconductivity in Bi3O2S2Cl with Bi-Cl Planar Layers,"A quaternary compound Bi3O2S2Cl, which consists of novel [BiS2Cl]2-layers, is
reported. It adopts a layered structure of the space group I4/mmm (No. 139)
with lattice parameters: a = 3.927(1) {\AA}, c = 21.720(5) {\AA}. In this
compound, bismuth and chlorine atoms form an infinite planar layer, which is
unique among the bismuth halides. Superconductivity is observed in both
polycrystals and single crystals, and is significantly enhanced in the samples
prepared with less sulfur or at higher temperatures. By tuning the content of
sulfur, Bi3O2S2Cl can be converted from a semiconductor into a superconductor.
The superconducting critical temperature ranges from 2.6 K to 3.5 K. Our
discovery of the [BiS2Cl]2- layer opens another door in searching for the
bismuth compounds with novel physical properties.",1903.02698v1
2019-03-22,"Al$_{5+α}$Si$_{5+δ}$N$_{12}$, a new Nitride compound","We report on the synthesis of new nitride-based compound by using annealing
of AlN heteroepitaxial layers under a Si-atmosphere at temperatures between
1350$^\circ$C and 1550$^\circ$C. The structure and stoichiometry of this
compound are investigated by high-resolution scanning transmission electron
microscopy (HRSTEM), energy dispersive X-Ray (EDX) spectroscopy, and density
functional theory (DFT) calculations. The identified structure is a derivative
of the parent wurtzite AlN crystal where anion sublattice is fully occupied by
N atoms and the cation sublattice is the stacking of 2 different planes along
<0001>. The first one exhibits a $\times$3 periodicity along <10-10> with 1/3
of the sites being vacant. The rest of the sites in the cation sublattice are
occupied by equal number of Si and Al atoms. Assuming a semiconducting alloy,
which is expected to have a wide band gap, a range of stoichiometries is
proposed, Al$_{5+\alpha}$Si$_{5+\delta}$N$_{12}$, with $\alpha$ being between 0
and 1/3 and $\delta$ between 0 and 1/4.",1903.09400v1
2019-05-22,"Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5","YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits
magnetic ordering and dielectric anomaly above 200 K. Partial substitution of
Fe with other magnetic and non-magnetic ion affects the magnetic and the
structural properties of the system. We report detailed investigation of
structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M=Co, Ni
and Ga). We observed that the partial replacement of Ni and Co in place of Fe,
results in magnetic dilution and broadening of the magnetic transition and
shifting towards lower temperature. The replacement of Fe with non-magnetic Ga
also results in shifting of the magnetic transition to the lower temperature
side. The observed dielectric relaxation behavior in these compounds is due to
the charge carrier hoping. This study highlights the impacts of magnetic and
non-magnetic doping at the magnetic site on magnetic and dielectric properties
in layered perovskite compound YBaCuFeO5.",1905.08982v2
2019-05-30,Combating the Compounding-Error Problem with a Multi-step Model,"Model-based reinforcement learning is an appealing framework for creating
agents that learn, plan, and act in sequential environments. Model-based
algorithms typically involve learning a transition model that takes a state and
an action and outputs the next state---a one-step model. This model can be
composed with itself to enable predicting multiple steps into the future, but
one-step prediction errors can get magnified, leading to unacceptable
inaccuracy. This compounding-error problem plagues planning and undermines
model-based reinforcement learning. In this paper, we address the
compounding-error problem by introducing a multi-step model that directly
outputs the outcome of executing a sequence of actions. Novel theoretical and
empirical results indicate that the multi-step model is more conducive to
efficient value-function estimation, and it yields better action selection
compared to the one-step model. These results make a strong case for using
multi-step models in the context of model-based reinforcement learning.",1905.13320v1
2019-08-02,Materials informatics based on evolutionary algorithms: Application to search for superconducting hydrogen compounds,"We present materials informatics approach to search for superconducting
hydrogen compounds, which is based on a genetic algorithm and a genetic
programming. This method consists of four stages: (i) search for stable crystal
structures of materials by a genetic algorithm, (ii) collection of physical and
chemical property data by first-principles calculations, (iii) development of
superconductivity predictor based on the database by a genetic programming, and
(iv) discovery of potential candidates by regression analysis. By repeatedly
performing the process as (i) $\rightarrow$ (ii) $\rightarrow$ (iii)
$\rightarrow$ (iv) $\rightarrow$ (i) $\rightarrow$ $\dots$, the
superconductivity of the discovered candidates is validated by first-principles
calculations, and the database and predictor are further improved, which leads
to an efficient search for superconducting materials. We applied this method to
hypothetical ternary hydrogen compounds and predicted KScH$_{12}$ with a
modulated hydrogen cage showing the superconducting critical temperature of 122
K at 300 GPa and GaAsH$_{6}$ showing 98 K at 180 GPa.",1908.00746v1
2019-08-09,On the Compound Beta-Binomial Risk Model with Delayed Claims and Randomized Dividends,"In this paper, we propose the discrete time Compound Beta-Binomial Risk Model
with by-claims, delayed by-claims and randomized dividends. We then analyze the
Gerber-Shiu function for the cases where the dividend threshold $d=0$ and $d>0$
under the assumption that the constant discount rate $\nu \in (0,1)$. More
specifically, we study the discrete time compound binomial risk model subject
to the assumption that the probabilities with which the claims, by-claims occur
and the dividends are issued are not fixed(constant), instead the probabilities
are random and follow a Beta distribution with parameters $a_{i}$ and $b_{i}$,
$i = 1, 2, 3$. Recursive expressions for the Gerber-Shiu function corresponding
to the proposed model are obtained. The recursive relations are further
utilized to obtain significant ruin related quantities of interest. Recursive
relations for probability of ruin, the probability of the deficit at ruin, the
generating function of the deficit at ruin and the probability of surplus at
ruin and for the probability of the claim causing ruin are obtained.",1908.03407v1
2019-08-16,Vibrational signatures of diamondoid dimers with large intramolecular London dispersion interactions,"We analyze the vibrational properties of diamondoid compounds via Raman
spectroscopy. The compounds are interconnected with carbon-carbon single bonds
that exhibit exceptionally large bond lengths up to 1.71 A. Attractive
dispersion interactions caused by well-aligned intramolecular H--H contact
surfaces determine the overall structures of the diamondoid derivatives. The
strong van-der-Waals interactions alter the vibrational properties of the
compounds in comparison to pristine diamondoids. Supported by
dispersion-corrected density functional theory (DFT) computations, we analyze
and explain their experimental Raman spectra with respect to unfunctionalized
diamondoids. We find a new set of dispersion-induced vibrational modes
comprising characteristic CH/CH$_{2}$ vibrations with exceptionally high
energies. Further, we find structure-induced dimer modes that are indicative of
the size of the dimers.",1908.05933v1
2019-08-29,A New Method for Employing Feedback to Improve Coding Performance,"We introduce a novel mechanism, called timid/bold coding, by which feedback
can be used to improve coding performance. For a certain class of DMCs, called
compound-dispersion channels, we show that timid/bold coding allows for an
improved second-order coding rate compared with coding without feedback. For
DMCs that are not compound dispersion, we show that feedback does not improve
the second-order coding rate. Thus we completely determine the class of DMCs
for which feedback improves the second-order coding rate. An upper bound on the
second-order coding rate is provided for compound-dispersion DMCs. We also show
that feedback does not improve the second-order coding rate for very noisy
DMCs. The main results are obtained by relating feedback codes to certain
controlled diffusions.",1908.11428v1
2019-09-04,Unconventional Multi-gap Superconductivity and Antiferromagnetic Spin Fluctuations in New Iron-arsenide LaFe2As2 in Heavily Electron-doped Regime,"We report 75As-NMR/NQR results on new iron-arsenide compounds
(La0.5-xNa0.5+x)Fe2As2. The parent compound x=0 exhibits a stripe-type
antiferromagnetic (AFM) order below T_N=130 K. The measurement of nuclear spin
relaxation rate at hole-doped x=+0.3 and heavily electron-doped x=-0.5 revealed
that the normal-state properties are dominated by AFM spin fluctuations
(AFMSFs), which are more significant at x=+0.3 than at x=-0.5. Their
superconducting (SC) phases are characterized by unconventional multi-gap SC
state, where the smaller SC gaps are particularly weaken in common. The
experimental results indicate the close relationship between the AFMSFs and the
SC from the hole-doped state to heavily electron-doped state, which shed light
on a unique SC phase emerged in the heavily electron-doped regime being
formally equivalent to non-SC compound Ba(Fe0.5Co0.5)Fe2As2.",1909.01569v2
2019-09-04,Image Processing Based on Compound Flat Optics,"Image processing has become a critical technology in a variety of science and
engineering disciplines. While most image processing is performed digitally,
optical analog processing has the advantages of being low-power and high-speed
though it requires a large volume. Here, we demonstrate optical analog imaging
processing using a flat optic for direct image differentiation allowing one to
significantly shrink the required optical system size. We first demonstrate how
the image differentiator can be combined with traditional imaging systems such
as a commercial optical microscope and camera sensor for edge detection.
Second, we demonstrate how the entire analog processing system can be realized
as a monolithic compound flat optic by integrating the differentiator with a
metalens. The compound nanophotonic system manifests the advantage of thin form
factor optics as well as the ability to implement complex transfer functions
and could open new opportunities in applications such as biological imaging and
machine vision.",1909.02132v1
2020-02-05,"Explicit Wiretap Channel Codes via Source Coding, Universal Hashing, and Distribution Approximation, When the Channels' Statistics are Uncertain","We consider wiretap channels with uncertainty on the eavesdropper channel
under (i) noisy blockwise type II, (ii) compound, or (iii) arbitrarily varying
models. We present explicit wiretap codes that can handle these models in a
unified manner and only rely on three primitives, namely source coding with
side information, universal hashing, and distribution approximation. Our
explicit wiretap codes achieve the best known single-letter achievable rates,
previously obtained non-constructively, for the models considered. Our results
are obtained for strong secrecy, do not require a pre-shared secret between the
legitimate users, and do not require any symmetry properties on the channel. An
extension of our results to compound main channels is also derived via new
capacity-achieving polar coding schemes for compound settings.",2002.01924v3
2020-02-13,Kitaev Spin Liquid in 3d Transition Metal Compounds,"We study the exchange interactions and resulting magnetic phases in the
honeycomb cobaltates. For a broad range of trigonal crystal fields acting on
Co2+ ions, the low-energy pseudospin-1/2 Hamiltonian is dominated by
bond-dependent Ising couplings that constitute the Kitaev model. The non-Kitaev
terms nearly vanish at small values of trigonal field \Delta, resulting in spin
liquid ground state. Considering Na3Co2SbO6 as an example, we find that this
compound is proximate to a Kitaev spin liquid phase, and can be driven into it
by slightly reducing \Delta by \sim 20 meV, e.g., via strain or pressure
control. We argue that due to the more localized nature of the magnetic
electrons in 3d compounds, cobaltates offer the most promising search area for
Kitaev model physics.",2002.05441v2
2020-02-17,Monte Carlo study of the magnetic properties of the spinel ZnFe$_2$O$_4$ compound,"In this work, a study of the magnetic behavior of the spinel ZnFe2O4 is
presented by using the Monte Carlo simulations (MCS). The iron atoms provide
the magnetism in this material. In fact, the magnetic spin of moment of the
Fe3+ ions is S=5/2. In this context, we propose a Hamiltonian describing and
modeling this compound. Firstly, at zero temperature we have studied the ground
state phase diagrams of the system in order to find the more stable
configurations. On the other hand, for a non-null temperature values, we
obtained the results of the Monte Carlo simulations, namely: the magnetizations
and the susceptibilities as a function of temperature. The behavior of those
physical parameters shows an anti-ferromagnetic behavior with a
Neel-temperature of about TN=12 K. This value is found to be in good agreement
with the literature. Moreover, the effect of varying the crystal field, the
exchange coupling interactions and the external magnetic field is studied and
discussed on the behavior of the magnetizations. To complete this study, we
presented the magnetic hysteresis loops deducing the antiferromagnetic behavior
of the ZnFe2O4 compound.",2002.06889v1
2020-03-09,Ab initio description of the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ electronic structure,"Bi-based cuprate superconductors are important materials for both fundamental
research and applications. As in other cuprates, the superconducting phase in
the Bi compounds lies close to an antiferromagnetic phase. Our density
functional theory calculations based on the
strongly-constrained-and-appropriately-normed (SCAN) exchange correlation
functional in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ reveal the persistence of
magnetic moments on the copper ions for oxygen concentrations ranging from the
pristine phase to the optimally hole-doped compound. We also find the existence
of ferrimagnetic solutions in the heavily doped compounds, which are expected
to suppress superconductivity.",2003.04034v3
2020-03-20,Partial Hessian vibrational analysis: vapour pressure isotope effects and their relation with non-covalent interactions,"In this study equilibrium isotope effects (EIEs) on evaporation to several
organic solvents (bromobenzene, dibromomethane, ethanol, methanol, and
trichloromethane) in the pure phase are estimated employing Kohn-Sham Density
functional theory (KS-DFT) along with full Hessian vibrational analysis (FHVA)
and partial Hessian vibrational analysis (PHVA). Both FHVA and PHVA
qualitatively predict compounds EIEs. Weakly interacting systems (bromobenzene,
dibromomethane, and trichloromethane) display identical EIE values for both,
FHVA and PHVA. Whereas for strongly interacting systems (ethanol and methanol),
PHVA estimates slightly smaller EIE compared to FHVA. By employing the
symmetry-adapted perturbation theory (SAPT) along with independent gradient
model (IGM), it was possible to establish how minimal changes in compounds
interaction energy affected carbon and bromine EIEs estimation in
dibromomethane. Moreover, SAPT and IGM revealed how in ethanol, apparently
insignificant intermolecular interactions possessed an enormous impact in
carbon position specific isotope effects, which highlight the importance of
solvent effects for strongly interacting compounds. The presented results have
important implications for correctly comprehending and characterising the role
of non-covalent interactions in the prediction of isotope effects, as well as
providing a robust test to PHVA for the prediction of EIEs.",2003.09509v1
2020-03-29,Dominant role of orbital splitting in determining cathode potential in $O3$ $NaTMO_2$ compounds,"Designing high potential cathodes for Na-ion batteries, which are comparable
in performance to Li-ion cathodes, remains a challenging task. Through
comprehensive density functional calculations, we disentangle the relationship
between the cathode potential and the ionicity of $TM-O$ bonds in $O3$
$NaTMO_2$ compounds in which TM ions is a fourth- or fifth-row transition
metal. We demonstrate that the magnetic exchange interaction and the local
distortions in the coordination environment of TM ions play more significant
roles in determining the cathode potential of the $TM^{3+}$ $\to$ $TM^{4+}+
e^-$ reaction than the ionicity of the $TM-O$ bonds in these compounds. These
results indicate that designing cathode materials solely based on empirical
electronegativity values to achieve high potential may not be a feasible
strategy without taking into account a detailed structural assessment.",2003.13046v1
2020-06-01,Magnetocaloric effect and spin-phonon correlations in RFe0.5Cr0.5O3 (R = Er and Yb) compounds,"We report the results of our investigation of the physical properties of
mixed metal oxides RFe0.5Cr0.5O3 (R = Er and Yb). ErFe0.5Cr0.5O3 undergoes an
antiferromagnetic ordering around 270 K followed by spin reorientation (SR)
transitions around 150 and 8 K respectively. In contrast, in YbFe0.5Cr0.5O3 a
single SR transition is noted at 36 K, below the AFM ordering temperature of
280 K. In ErFe0.5Cr0.5O3, a significant value of magnetic entropy change
({\Delta}SM) ~ -12.4 J/kg-K is noted near the 2nd SR transition, however, this
value is suppressed in YbFe0.5Cr0.5O3. Temperature dependent dielectric
permittivity of ErFe0.5Cr0.5O3 and YbFe0.5Cr0.5O3 at different frequencies,
reveal the presence of Debye-like relaxation behaviour in both compounds, which
can be due to the effect of charge carrier hopping between localized states of
Fe and Cr ions. Temperature dependent Raman scattering studies divulge that
spin-phonon coupling plays a crucial role in defining the physical properties
of these compounds.",2006.00736v1
2020-06-08,Maximum Entropy Model Rollouts: Fast Model Based Policy Optimization without Compounding Errors,"Model usage is the central challenge of model-based reinforcement learning.
Although dynamics model based on deep neural networks provide good
generalization for single step prediction, such ability is over exploited when
it is used to predict long horizon trajectories due to compounding errors. In
this work, we propose a Dyna-style model-based reinforcement learning
algorithm, which we called Maximum Entropy Model Rollouts (MEMR). To eliminate
the compounding errors, we only use our model to generate single-step rollouts.
Furthermore, we propose to generate \emph{diverse} model rollouts by
non-uniform sampling of the environment states such that the entropy of the
model rollouts is maximized. We mathematically derived the maximum entropy
sampling criteria for one data case under Gaussian prior. To accomplish this
criteria, we propose to utilize a prioritized experience replay. Our
preliminary experiments in challenging locomotion benchmarks show that our
approach achieves the same sample efficiency of the best model-based
algorithms, matches the asymptotic performance of the best model-free
algorithms, and significantly reduces the computation requirements of other
model-based methods.",2006.04802v2
2020-06-09,Electronic and Magnetic Properties of Topological Semimetal Candidate NdSbTe,"ZrSiS-type materials represent a large material family with unusual
coexistence of topological nonsymmorphic Dirac fermions and nodal-line
fermions. As a special group of ZrSiS-family, LnSbTe (Ln = Lanthanide rare
earth) compounds provide a unique opportunity to explore new quantum phases due
to the intrinsic magnetism induced by Ln. Here we report the single crystal
growth and characterization of NdSbTe, a previously unexplored LnSbTe compound.
NdSbTe has an antiferromagnetic ground state with field-driven metamagnetic
transitions similar to other known LnSbTe, but exhibits distinct enhanced
electronic correlations characterized by large a Sommerfeld coefficient of 115
mJ/mol $K^2$, which is the highest among the known LnSbTe compounds.
Furthermore, our transport studies have revealed the coupling with magnetism
and signatures of Kondo localization. All these findings establish NdSbTe as a
new platform for observing novel phenomena arising from the interplay between
magnetism, topology, and electron correlations.",2006.05536v1
2020-06-10,Understanding and adjusting the selection bias from a proof-of-concept study to a more confirmatory study,"It has long been noticed that the efficacy observed in small early phase
studies is generally better than that observed in later larger studies.
Historically, the inflation of the efficacy results from early proof-of-concept
studies is either ignored, or adjusted empirically using a frequentist or
Bayesian approach. In this article, we systematically explained the underlying
reason for the inflation of efficacy results in small early phase studies from
the perspectives of measurement error models and selection bias. A systematic
method was built to adjust the early phase study results from both frequentist
and Bayesian perspectives. A hierarchical model was proposed to estimate the
distribution of the efficacy for a portfolio of compounds, which can serve as
the prior distribution for the Bayesian approach. We showed through theory that
the systematic adjustment provides an unbiased estimator for the true mean
efficacy for a portfolio of compounds. The adjustment was applied to paired
data for the efficacy in early small and later larger studies for a set of
compounds in diabetes and immunology. After the adjustment, the bias in the
early phase small studies seems to be diminished.",2006.05795v1
2020-06-19,Predicting the phase stability of multi-component high entropy compounds,"A generic method to estimate the relative feasibility of formation of high
entropy compounds in a single phase, directly from first principles, is
developed. As a first step, the relative formation abilities of 56
multi-component, AO, oxides were evaluated. These were constructed from 5
cation combinations chosen from A={Ca, Co, Cu, Fe, Mg, Mn, Ni, Zn}. Candidates
for multi-component oxides are predicted from descriptors related to the
enthalpy and configurational entropy obtained from the mixing enthalpies of two
component oxides. The utility of this approach is evaluated by comparing the
predicted combinations with the experimentally realized entropy stabilized
oxide, (MgCoCuNiZn)O. In the second step, Monte Carlo simulations are utilized
to investigate the phase composition and local ionic segregation as a function
of temperature. This approach allows for the evaluation of potential secondary
phases, thereby making realistic predictions of novel multi-component compounds
that can be synthesized.",2006.11231v2
2020-06-23,Cation Order Control of Correlations in Double Perovskite Sr$_2$VNbO$_6$,"Double perovskites extend the design space for new materials, and they often
host phenomena that don't exist in their parent perovskite compounds. Here, we
present a detailed first principles study of the correlated double perovskite
Sr$_2$VNbO$_6$, where inter-cationic charge transfer and strength of electronic
correlations depend strongly on the cation order. By using Density Functional
Theory + Embedded Dynamical Mean Field Theory, we show that this compound has a
completely different electronic structure than either of its parent compounds
despite V and Nb being from the same group in the periodic table. We explain
how the electronic correlations' effect on the crystal structural parameters
determines on which side of the Hund's metal-Mott insulator transition the
material is. Our results demonstrate the emergence of Hund's metallic behavior
in a double perovskite that has $d^1$ parents, and underlines the importance of
electronic correlation effects on the crystal structure.",2006.13195v1
2020-07-03,Magnetic correlations in the semimetallic hyper-kagome iridate Na3Ir3O8,"We present a microscopic study of a doped quantum spin liquid candidate, the
hyperkagome Na$_3$Ir$_3$O$_8$ compound by using $^{23}$Na NMR. We determine the
intrinsic behavior of the uniform \textbf{q} $ = 0$ susceptibility via shift
measurements and the dynamical response by probing the spin-lattice relaxation
rate. Throughout the studied temperature range, the susceptibility is
consistent with a semimetal behavior, though with electronic bands
substantially modified by correlations. Remarkably, the antiferromagnetic
fluctuations present in the insulating parent compound Na$_4$Ir$_3$O$_8$
survive in the studied compound. The spin dynamics are consistent with 120$^o$
excitations modes displaying short-range correlations.",2007.01633v2
2020-07-07,Speed-of-sound imaging by differential phase contrast with angular compounding,"We describe a technique to reveal speed-of-sound (SoS) variations within an
echogenic sample. The technique uses the same receive data as standard
pulse-echo imaging based on plane-wave compounding, and can be operated in
parallel. Point-like scatterers randomly distributed throughout the sample
serve as local probes of the downstream transmit-beam phase shifts caused by
aberrating structures within the sample. Phase shifts are monitored in a
differential manner, providing signatures of transverse gradients of the local
sample SoS. The contrast of the signatures is augmented by a method of angular
compounding, which provides ``focus"" control of the image sharpness, which, in
turn, enables a visual localization of aberrating inclusions within the sample
on the fly. The localization can be performed in 2D when operated with standard
B-mode imaging, or in 3D when operated with C-mode imaging. Finally, we present
a wave-acoustic forward model that provides insight into the principle of
differential phase contrast (DPC) imaging, and roughly recapitulates
experimental results obtained with an elastography phantom. In particular, we
demonstrate that our technique easily reveals relative SoS variations as small
as 0.5\% in real time. Such imaging may ultimately be useful for clinical
diagnosis of pathologies in soft tissue.",2007.03156v1
2020-09-02,GNN-PT: Enhanced Prediction of Compound-protein Interactions by Integrating Protein Transformer,"The prediction of protein interactions (CPIs) is crucial for the in-silico
screening step in drug discovery. Recently, many end-to-end representation
learning methods using deep neural networks have achieved significantly better
performance than traditional machine learning algorithms. Much effort has
focused on the compound representation or the information extraction from the
compound-protein interaction to improve the model capability by taking the
advantage of the neural attention mechanism. However, previous studies have
paid little attention to representing the protein sequences, in which the
long-range interactions of residue pairs are essential for characterizing the
structural properties arising from the protein folding. We incorporate the
self-attention mechanism into the protein representation module for CPI
modeling, which aims at capturing the long-range interaction information within
proteins. The proposed module concerning protein representation, called Protein
Transformer, with an integration with an existing CPI model, has shown a
significant improvement in the prediction performance when compared with
several existing CPI models.",2009.00805v2
2020-09-10,Integrated nanoextraction and colorimetric reactions in surface nanodroplets for combinative analysis,"A combinative approach for chemical analysis makes it possible to distinguish
a mixture of a large number of compounds from other mixtures in a single step.
This work demonstrates a combinative analysis approach by using surface
nanodroplets for integrating nanoextraction and colorimetric reactions for the
identification of multi-component mixtures. The model analytes are acidic
compounds dissolved in oil that are extracted into aqueous droplets on a solid
substrate. The proton from acid dissociation reacts with the halochromic
chemical compounds inside the droplets, leading to the color change of the
droplets. The rate of the colorimetric reaction exhibits certain specificity
for the acid type, distinguishing acid mixtures with the same pH value. The
underlying principle is that the acid transport rate is associated with the
partition coefficient and the dissociation constant of the acid, in addition to
the concentration in oil. As a demonstration, we showed that droplet-based
combinative analysis can be applied for anti-counterfeiting of various
alcoholic spirits by comparing decolor time of organic acid mixtures in the
spirits. The readout can be done by using a common hand-hold mobile phone.",2009.04672v1
2020-09-23,Effect of reduced local lattice disorder on the magnetic properties of B-site substituted La0.8Sr0.2MnO3,"Disorder induced by chemical inhomogeneity and Jahn-Teller (JT) distortions
is often observed in mixed valence perovskite manganites. The main reasons for
the evolution of this disorder are connected with the cationic size differences
and the ratio between JT active and non-JT active ions. The quenched disorder
leads to a spin-cluster state above the magnetic transition temperature. The
effect of Cu, a B-site substitution in the La0.8Sr0.2MnO3 compound, on the
disordered phase has been addressed here. X-ray powder diffraction reveals
rhombohedral (R-3c) structures for the two compounds with negligible change of
lattice volume. The chemical compositions of the two compounds were verified by
ion beam analysis technique. With the change of electronic bandwidth, the
magnetic phase transition temperature has been tuned towards room temperature
(318 K), an important requirement for room temperature magnetic refrigeration.
However, a small decrease of the isothermal entropy was observed with
Cu-substitution, related to the decrease of the saturation magnetization.",2009.11157v2
2020-09-25,Antiferromagnetic phase diagram of the cuprate superconductors,"Taking the spin-fermion model as the starting point for describing the
cuprate superconductors, we obtain an effective nonlinear sigma-field
hamiltonian, which takes into account the effect of doping in the system. We
obtain an expression for the spin-wave velocity as a function of the chemical
potential. For appropriate values of the parameters we determine the
antiferromagnetic phase diagram for the YBa$_2$Cu$_3$O$_{6+x}$ compound as a
function of the dopant concentration in good agreement with the experimental
data. Furthermore, our approach provides a unified description for the phase
diagrams of the hole-doped and the electron doped compounds, which is
consistent with the remarkable similarity between the phase diagrams of these
compounds, since we have obtained the suppression of the antiferromagnetic
phase as the modulus of the chemical potential increases. The aforementioned
result then follows by considering positive values of the chemical potential
related to the addition of holes to the system, while negative values
correspond to the addition of electrons.",2009.14030v1
2020-10-06,Superconductivity in Infinite-layer Nickelates : Role of Non-zero f-ness,"Employing first-principles density functional theory calculations and
Wannierization of the low energy band structure, we analyze the electronic
structure of undoped, infinite-layer nickelate compounds, NdNiO$_2$, PrNiO$_2$
and LaNiO$_2$. Our study reveals important role of non-zero $f$-ness of Nd and
Pr atoms, as opposed to $f^{0}$ occupancy of La. The non-zero $f$-ness becomes
effective in lowering the energy of the rare-earth 5$d$ hybridized axial
orbital, thereby enhancing the electron pockets and influencing the Fermi
surface topology. The Fermi surface topology of NdNiO$_2$ and PrNiO$_2$ is
strikingly similar, while differences are observed for LaNiO$_2$. This
difference shows up in computed doping dependent superconducting properties of
the three compounds within a weak coupling theory. We find two gap
superconductivity for NdNiO$_2$ and PrNiO$_2$, and possibility of a single gap
superconductivity for LaNiO$_2$ with the strength of superconductivity
suppressed by almost a factor of two, compared to Nd or Pr compound.",2010.02527v1
2020-10-06,"Theoretical study of ternary silver fluorides AgMF4 (M = Co, Ni, Cu) formation at pressures up to 20 GPa","Only several compounds bearing Ag(II) cation and other transition metal
cation have been known. Herein, we predict stability and crystal structures of
hypothetical ternary silver(II) fluorides with copper, nickel and cobalt in 1:1
stoichiometry at pressure range from 0 GPa up to 20 GPa within the frame of
Density Functional Theory. Calculations show that AgCoF4 could be synthesized
already at ambient conditions but this compound would host diamagnetic Ag(I)
and high-spin Co(III). However, at increased pressure ternary fluorides of
Ag(II) featuring Cu and Ni could be synthesized, in the pressure windows of
7-14 and 8-15 GPa, respectively. All title compounds would be semiconducting
and magnetically ordered.",2010.02544v1
2020-10-07,Computational compound screening of biomolecules and soft materials by molecular simulations,"Decades of hardware, methodological, and algorithmic development have
propelled molecular dynamics (MD) simulations to the forefront of
materials-modeling techniques, bridging the gap between electronic-structure
theory and continuum methods. The physics-based approach makes MD appropriate
to study emergent phenomena, but simultaneously incurs significant
computational investment. This topical review explores the use of MD outside
the scope of individual systems, but rather considering many compounds. Such an
in silico screening approach makes MD amenable to establishing coveted
structure--property relationships. We specifically focus on biomolecules and
soft materials, characterized by the significant role of entropic contributions
and heterogeneous systems and scales. An account of the state of the art for
the implementation of an MD-based screening paradigm is described, including
automated force-field parametrization, system preparation, and efficient
sampling across both conformation and composition. Emphasis is placed on
machine-learning methods to enable MD-based screening. The resulting framework
enables the generation of compound--property databases and the use of advanced
statistical modeling to gather insight. The review further summarizes a number
of relevant applications.",2010.03298v3
2020-10-17,"Electron-phonon coupling in APd3O4: A = Ca, Sr, and Sr0.85Li0.15","Here we have investigated the role of electron-phonon coupling on the Raman
spectrum of narrow bandgap semiconductors APd3O4 (A = Ca, Sr) and hole-doped
system Sr0.85Li0.15Pd3O4. Four Raman active phonons are observed at room
temperature for all three compounds as predicted by factor group analysis. The
lowest energy phonon (~190/202 cm-1) associated with Pd vibrations is observed
to exhibit an asymmetric Fano-like lineshape in all the three compounds,
indicating the presence of an interaction between the phonon and the electronic
continuum. The origin of the electronic continuum states and electron-phonon
coupling are discussed based on our laser power- and temperature-dependent
Raman results. We have observed an enhanced strength of electron-phonon
coupling in Sr0.85Li0.15Pd3O4 at low temperatures which can be attributed to
the metallicity in this doped compound.",2010.08813v1
2020-10-24,Neural Compound-Word (Sandhi) Generation and Splitting in Sanskrit Language,"This paper describes neural network based approaches to the process of the
formation and splitting of word-compounding, respectively known as the Sandhi
and Vichchhed, in Sanskrit language. Sandhi is an important idea essential to
morphological analysis of Sanskrit texts. Sandhi leads to word transformations
at word boundaries. The rules of Sandhi formation are well defined but complex,
sometimes optional and in some cases, require knowledge about the nature of the
words being compounded. Sandhi split or Vichchhed is an even more difficult
task given its non uniqueness and context dependence. In this work, we propose
the route of formulating the problem as a sequence to sequence prediction task,
using modern deep learning techniques. Being the first fully data driven
technique, we demonstrate that our model has an accuracy better than the
existing methods on multiple standard datasets, despite not using any
additional lexical or morphological resources. The code is being made available
at https://github.com/IITD-DataScience/Sandhi_Prakarana",2010.12940v1
2020-11-04,"Study of the superconducting ground state of topological superconducting candidates Ti$_{3}$X (X = Ir, Sb)","The topologically non-trivial band structure of A15 compounds has drawn
attention owing to the possible realization of topological superconductivity.
Here, we report a microscopic investigation of the superconducting ground state
in A15 compound Ti$_{3}$X (X = Ir, Sb) by muon spectroscopy measurements. Zero
field muon measurements have shown that time-reversal symmetry is preserved in
these materials. Furthermore, specific heat and a transverse field muon
spectroscopy measurement rule out any possibility to have a nodal or
anisotropic superconducting gap, revealing a conventional s-wave nature in the
superconducting ground state. This work classifies A15 compound Ti$_{3}$X (X =
Ir, Sb) as a time-reversal preserved topological superconductor.",2011.02350v1
2020-11-05,Causal Imputation via Synthetic Interventions,"Consider the problem of determining the effect of a compound on a specific
cell type. To answer this question, researchers traditionally need to run an
experiment applying the drug of interest to that cell type. This approach is
not scalable: given a large number of different actions (compounds) and a large
number of different contexts (cell types), it is infeasible to run an
experiment for every action-context pair. In such cases, one would ideally like
to predict the outcome for every pair while only having to perform experiments
on a small subset of pairs. This task, which we label ""causal imputation"", is a
generalization of the causal transportability problem. To address this
challenge, we extend the recently introduced synthetic interventions (SI)
estimator to handle more general data sparsity patterns. We prove that, under a
latent factor model, our estimator provides valid estimates for the causal
imputation task. We motivate this model by establishing a connection to the
linear structural causal model literature. Finally, we consider the prominent
CMAP dataset in predicting the effects of compounds on gene expression across
cell types. We find that our estimator outperforms standard baselines, thus
confirming its utility in biological applications.",2011.03127v3
2020-11-25,Direct evidence of electron-hole compensation for XMR in topologically trivial YBi,"The prediction of topological states in rare earth monopnictide compounds has
attracted renewed interest. Extreme magnetoresistance (XMR) has also been
observed in several nonmagnetic rare earth monopnictide compounds. The origin
of XMR in these compounds could be attributed to several mechanisms, such as
topologically nontrivial electronic structures and electron-hole carrier
balance. YBi is a typical rare earth monopnictide exhibiting XMR, and expected
to have a nontrivial electronic structure. In this work, we performed a direct
investigation of the electronic structure of YBi by combining angle resolved
photoemission spectroscopy and theoretical calculations. Our results show that
YBi is topologically trivial without the expected band inversion, and they rule
out the topological effect as the cause of XMR in YBi. Furthermore, we directly
observed perfect electron-hole compensation in the electronic structure of YBi,
which could be the primary mechanism accounting for the XMR.",2011.12474v1
2020-11-27,Understanding doping of quantum materials,"Doping mobile carriers into ordinary semiconductors such as Si, GaAs, and ZnO
was the enabling step in the electronic and optoelectronic revolutions. The
recent emergence of a class of ""Quantum Materials"", where uniquely quantum
interactions between the components produce specific behaviors such as
topological insulation, unusual magnetism, superconductivity,
spin-orbit-induced and magnetically-induced spin splitting, polaron formation,
and transparency of electrical conductors, pointed attention to a range of
doping-related phenomena associated with chemical classes that differ from the
traditional semiconductors. These include wide-gap oxides, compounds containing
open-shell d electrons, and compounds made of heavy elements yet having
significant band gaps. The atomistic electronic structure theory of doping that
has been developed over the past two decades in the sub-field of semiconductor
physics has recently been extended and applied to quantum materials. The
present review focuses on explaining the main concepts needed for a basic
understanding of the doping phenomenology and indeed peculiarities in quantum
materials from the perspective of condensed matter theory, with the hope of
forging bridges to the chemists that have enabled the synthesis of some of the
most interesting compounds in this field.",2011.13521v1
2020-12-06,Bulk Superconductivity in the Dirac Semimetal TlSb,"A feasible strategy to realize the Majorana fermions is searching for a
simple compound with both bulk superconductivity and Dirac surface states. In
this paper, we performed calculations of electronic band structure, the Fermi
surface and surface states, as well as measured the resistivity, magnetization,
specific heat for TlSb compound with a CsCl-type structure. The band structure
calculations show that TlSb is a Dirac semimetal when spin-orbit coupling is
taken into account. Meanwhile, we first found that TlSb is a type-II
superconductor with $T_c$ = 4.38 K, $H_{c1}$(0) = 148 Oe, $H_{c2}$(0) = 1.12 T
and $\kappa_{GL}$ = 10.6, and confirmed it to be a moderately coupled s-wave
superconductor. Although we can not determine which bands near the Fermi level
$E_F$ to be responsible for superconductivity, its coexistence with the
topological surface states implies that TlSb compound may be a simple material
platform to realize the fault-tolerant quantum computations.",2012.03274v1
2020-12-08,Rare-earth effect on the physical properties of Na$_{0.5}$Bi$_{0.5}$TiO$_3$ system: A Density Functional Theory investigation,"Na$_{0.5}$(Bi$_3$/4RE$_{1/4}$)$_{0.5}$TiO$_3$ (RENBT, RE = Nd, Gd, Dy, and
Ho) compounds were investigated in the framework of first-principles
calculations using the full potential linearized augmented plane wave (FP-LAPW)
method based on the spin-polarized density functional theory implemented in the
WIEN2k code. Combined charge density distribution and Ti K-edge x-ray
absorption spectra revealed that the RENBT compositions with high polarization
values were accompanied by a higher TiO$_6$ distortion, DyNBT, and NdNBT
compounds. The effect of the rare-earth elements on the polarization were
confirmed experimentally with the collection of the hysteresis loops. The
investigation of the electronic properties of the compounds highlighted the
emergence of a magnetization owing to the 4f orbital effect of the rare-earth
elements. Besides, the investigation of the chemical ordering showed a
short-range chemical ordering for the pure composition and an increased A-site
disorder for dysprosium doped NBT system. The increased disorder may speak for
increased relaxor properties in the RE doped compositions.",2012.04319v1
2020-12-16,Experimental and theoretical study of the correlated compound YbCdSn: Evidence for large magnetoresistance and mass enhancement,"The unusual features of topological semimetals arise from its nontrivial band
structure. The impact of strong electron correlations on the topological states
remains largely unexplored in real materials. Here, we report the
magnetotransport properties of YbCdSn single crystals. We found two fundamental
experimental evidences of electron correlations through magnetic susceptibility
and specific heat. The electron correlations in this compound lead to an
intermediate valence state and enhance the effective mass of the charge
carriers. This correlated state exhibits large nonsaturating magnetoresistance,
low carrier density, magnetic field induced metal-semiconductor-like crossover
and a plateau in resistivity at low temperatures. This compound also shows a
cusp-like magnetoconductivity at low magnetic field which indicates the
presence of weak antilocalization effect. Our band structure calculations of
Yb$^{2+}$ state predict YbCdSn to be a topological nodal-line semimetal.",2012.09095v1
2020-12-17,Fluorides of silver under large compression,"The silver-fluorine phase diagram has been scrutinized as a function of
external pressure using theoretical methods. Our results indicate that two
novel stoichiometries containing Ag+ and Ag2+ cations (Ag3F4 and Ag2F3) are
thermodynamically stable at ambient and low pressure. Both are computed to be
magnetic semiconductors at ambient pressure conditions. For Ag2F5, containing
both Ag2+ and Ag3+, we find that strong 1D antiferromagnetic coupling is
retained throughout the pressure-induced phase transition sequence up to 65
GPa. Our calculations show that throughout the entire pressure range of their
stability the mixed valence fluorides preserve a finite band gap at the Fermi
level. We also confirm the possibility of synthesizing AgF4 as a paramagnetic
compound at high pressure. Our results indicate that this compound is metallic
in its thermodynamic stability region. Finally, we present general
considerations on the thermodynamic stability of mixed valence compounds of
silver at high pressure.",2012.09583v1
2020-12-18,Structure and composition of C-S-H compounds up to 143 GPa,"We synthesized two C-S-H compounds from a mixture of carbon and sulfur in
hydrogen and from sulfur in mixed methane-hydrogen fluids at 4 GPa. X-ray
synchrotron single-crystal diffraction and Raman spectroscopy have been applied
to these samples up to 58 and 143 GPa, respectively. Both samples show a
similar Al2Cu type I4/mcm basic symmetry, while the hydrogen subsystem evolves
with pressure via variously ordered molecular and extended modifications. The
methane bearing sample lowers symmetry to an orthorhombic Pnma structure after
laser heating to 1400 K at 143 GPa. The results suggest that superconducting
C-S-H compounds are structurally different from a common Im-3m H3S.",2012.10528v1
2021-01-09,A simple counterexample for the permanent-on-top conjecture,"The permanent-on-top conjecture states that the largest eigenvalue of the
Schur power matrix of a positive semi-definite Hermitian matrix H is per(H). A
counterexample has been found with the help of computers, but here, I present
another counterexample that can be checked by hand. My method is to use linear
representations of groups to connect the spectrum of the Schur power matrix
with the spectra of the entrywise(Hadamard) product matrices of permanental
compound matrices. By that, we are able to study the properties of the spectrum
of the Schur power matrix through the entrywise(Hadamard) product matrices of
permanental compound matrices. The counterexample we find is in fact also a
counterexample to a weaker conjecture related to permanental compound matrices.
This conjecture was also known to be false, but the new counterexample is
smaller than the known one.",2101.03428v5
2021-01-26,Understanding Magnetism in Double Double Perovskites: A Complex Multiple Magnetic Sublattice System,"Understanding magnetism in multiple magnetic sublattice system, driven by the
interplay of varied nature of magnetic exchanges, is on one hand challenging
and on other hand intriguing. Motivated by the recent synthesis of AA'BB'O_6
double double perovskites with multiple magnetic ions both at A- and B-sites,
we investigate the mechanism of magnetic behavior in these interesting class of
compounds. We find that the magnetism in such multiple sublattice compounds is
governed by the interplay and delicate balance between two distinct mechanisms,
a) kinetic energy-driven multiple sublattice double exchange mechanism and b)
the conventional super-exchange mechanism. The derived spin Hamiltonian based
on first-principles calculations is solved by the classical Monte Carlo
technique which reproduces the observed magnetic properties. Finally, the
influence of off-stoichiometry, as in experimental samples, is discussed. Some
of these double double perovskite compounds are found to possess large total
magnetic moment and also are found to be half-metallic, which raises the hope
of future applications of these large magnetic moment half-metallic oxides in
spintronics and memory devices.",2101.10822v1
2021-01-28,Heterogeneous Graph based Deep Learning for Biomedical Network Link Prediction,"Multi-scale biomedical knowledge networks are expanding with emerging
experimental technologies that generates multi-scale biomedical big data. Link
prediction is increasingly used especially in bipartite biomedical networks to
identify hidden biological interactions and relationshipts between key entities
such as compounds, targets, gene and diseases. We propose a Graph Neural
Networks (GNN) method, namely Graph Pair based Link Prediction model (GPLP),
for predicting biomedical network links simply based on their topological
interaction information. In GPLP, 1-hop subgraphs extracted from known network
interaction matrix is learnt to predict missing links. To evaluate our method,
three heterogeneous biomedical networks were used, i.e. Drug-Target Interaction
network (DTI), Compound-Protein Interaction network (CPI) from NIH Tox21, and
Compound-Virus Inhibition network (CVI). Our proposed GPLP method significantly
outperforms over the state-of-the-art baselines. In addition, different network
incompleteness is analysed with our devised protocol, and we also design an
effective approach to improve the model robustness towards incomplete networks.
Our method demonstrates the potential applications in other biomedical
networks.",2102.01649v4
2021-02-05,"Generalized scaling of spin qubit coherence in over 12,000 host materials","Spin defect centers with long quantum coherence times ($T_2$) are key
solid-state platforms for a variety of quantum applications. Recently, cluster
correlation expansion (CCE) techniques have emerged as a powerful tool to
simulate the $T_2$ of defect electron spins in these solid-state systems with
good accuracy. Here, based on CCE, we uncover an algebraic expression for $T_2$
generalized for host compounds with dilute nuclear spin baths, which enables a
quantitative and comprehensive materials exploration with a near instantaneous
estimate of the coherence. We investigate more than 12,000 host compounds at
natural isotopic abundance, and find that silicon carbide (SiC), a prominent
widegap semiconductor for quantum applications, possesses the longest coherence
times among widegap non-chalcogenides. In addition, more than 700 chalcogenides
are shown to possess a longer $T_2$ than SiC. We suggest new potential host
compounds with promisingly long $T_2$ up to 47 ms, and pave the way to explore
unprecedented functional materials for quantum applications.",2102.02986v1
2021-02-05,Temperature-driven hidden 5f itinerant-localized crossover in heavy-fermion compound PuIn3,"The temperature-dependent evolution pattern of 5f electrons helps to
elucidate the long-standing itinerant-localized dual nature in plutonium-based
compounds. In this work, we investigate the correlated electronic states of
PuIn3 dependence on temperature by using a combination of the density
functional theory and the dynamical mean-field theory. Not only the
experimental photoemission spectroscopy is correctly reproduced, but also a
possible hidden 5f itinerant-localized crossover is identified. Moreover, it is
found that the quasiparticle multiplets from the many-body transitions
gradually enhance with decreasing temperature, accompanied by the
hybridizations with 5f electrons and conduction bands. The temperature-induced
variation of Fermi surface topology suggests a possible electronic Lifshitz
transition and the onset of magnetic order at low temperature. Finally, the
ubiquitous existence orbital selective 5f electron correlation is also
discovered in PuIn3. These illuminating results shall enrich the understanding
on Pu-based compounds and serve as critical predictions for ongoing
experimental research.",2102.03085v1
2021-02-08,Double magnetic phase transitions and magnetotransport anomalies in a new compound Gd$_\textbf{2}$AgSi$_\textbf{3}$,"Dc and ac-magnetic susceptibility ($\chi$), specific heat ($C_\mathrm{P}$),
electrical resistivity ($\rho$) and magnetoresistance measurements performed on
the new polycrystalline compound $\mathrm{Gd_2AgSi_3}$, crystallizing in the
$\alpha$-$\mathrm{ThSi_2}$ tetragonal structure, are reported. Two magnetic
phase transitions were observed in dc and ac susceptibility, specific heat, and
resistivity measurements at temperatures $\mathrm{T_{N_1}} = 11$ K and
$\rm{T_{N_2}} = 20$ K, despite a single site occupied by Gd atom, which is an
indication of the complex magnetic behavior. $\mathrm{Gd_2AgSi_3}$ turns out to
be one of the rare Gd compound in which a minimum is observed in the
temperature dependence of resistivity in the paramagnetic state and also
negative magnetoresistance over a wide temperature range (above
$\rm{T_{N_2}}$), mimicking the behavior of exotic $\mathrm{Gd_2PdSi_3}$, in
this ternary family. The isothermal magnetic entropy and adiabatic temperature
changes reach a value of 9.5 J/kg-K and 7.5 K respectively for the field change
of 9 T.",2102.04096v2
2021-04-05,Possible quadrupole order in tetragonal Ba2CdReO6 and chemical trend in the ground states of 5d1 double perovskites,"The synthesis and physical properties of the double perovskite (DP) compound
Ba2CdReO6 with the 5d1 electronic configuration are reported. Three successive
phases originating from a spin-orbit-entangled Jeff = 3/2 state, confirmed by
the reduced effective magnetic moment of 0.72 {\mu}B, were observed upon
cooling. X-ray diffraction measurements revealed a structural transition from a
high-temperature cubic structure to a low-temperature tetragonal structure at
Ts = 170 K, below which the Jeff = 3/2 state was preserved. Magnetization, heat
capacity, and thermal expansion measurements showed two more electronic
transitions to a possible quadrupole ordered state at Tq = 25 K, and an
antiferromagnetic order of dipoles accompanied by a ferromagnetic moment of ~
0.2 {\mu}B at Tm = 12 K. These properties were compared with those of the
sister compounds Ba2BReO6 (B = Mg, Zn, and Ca) and the chemical trend is
discussed in terms of the mean-field theory for spin-orbit-coupled 5d electrons
[G. Chen et al., Phys. Rev. B 82, 174440 (2010)]. The DP compound Ba2BReO6
provides a unique opportunity for a systematic investigation on symmetry
breaking in the presence of multipolar degrees of freedom.",2104.01833v1
2021-04-14,Crystal Growth of the Quasi-2D Quarternary Compound AgCrP$_2$S$_6$ by Chemical Vapor Transport,"We report optimized crystal growth conditions for the quarternary compound
AgCrP$_2$S$_6$ by chemical vapor transport. Compositional and structural
characterization of the obtained crystals were carried out by means of
energy-dispersive X-ray spectroscopy and powder X-ray diffraction.
AgCrP$_2$S$_6$ is structurally closely related to the $M_2$P$_2$S$_6$ family,
which contains several compounds that are under investigation as 2D magnets.
As-grown crystals exhibit a plate-like, layered morphology as well as a
hexagonal habitus. AgCrP$_2$S$_6$ crystallizes in monoclinic symmetry in the
space group $P2/a$ (No. 13). The successful growth of large high-quality single
crystals paves the way for further investigations of low dimensional magnetism
and its anisotropies in the future and may further allow for the manufacturing
of few-layer (or even monolayer) samples by exfoliation.",2104.06760v1
2021-04-16,Ab initio determination of ultrahigh thermal conductivity in ternary compounds,"Discovering new materials with ultrahigh thermal conductivity has been a
critical research frontier and driven by many important technological
applications ranging from thermal management to energy science. Here we have
rigorously investigated the fundamental lattice vibrational spectra in ternary
compounds and determined the thermal conductivity using a predictive ab initio
approach. Phonon transport in B-X-C (X = N, P, As) groups is systematically
quantified with different crystal structures and high-order anharmonicity
involving a four-phonon process. Our calculation found an ultrahigh
room-temperature thermal conductivity through strong carbon-carbon bonding up
to 2100 W/mK beyond most common materials and the recently discovered boron
arsenide. This study provides fundamental insight into the atomistic design of
thermal conductivity and opens up opportunities in new materials searching
towards complicated compound structures.
  DOI: 10.1103/PhysRevB.103.L041203",2104.07833v1
2021-04-18,On-Surface Synthesis of Graphene Nanoribbons on Two-Dimensional Rare Earth-Gold Intermetallic Compounds,"Here, we demonstrate two reliable routes for the fabrication of armchair-edge
graphene nanoribbons (GNRs) on TbAu2/Au(111), belonging to a class of
two-dimensional ferromagnetic rare earth-gold intermetallic compounds.
On-surface synthesis directly on TbAu2 leads to the formation of GNRs, which
are short and interconnected with each other. In contrast, the intercalation
approach - on-surface synthesis of GNRs directly on Au(111) followed by rare
earth intercalation - yields GNRs on TbAu2/Au(111), where both the ribbons and
TbAu2 are of high quality comparable with those directly grown on clean
Au(111). Besides, the as-grown ribbons retain the same band gap while changing
from p-doping to weak n-doping mainly due to a change in the work function of
the substrate after the rare earth intercalation. The intercalation approach
might also be employed to fabricate other types of GNRs on various rare earth
intermetallic compounds, providing platforms to tailor the electronic and
magnetic properties of GNRs on magnetic substrates.",2104.08719v1
2021-04-29,"Universal spin-glass behaviour in bulk LaNiO2, PrNiO2 and NdNiO2","Motivated by the recent discovery of superconductivity in infinite-layer
nickelate thin films, we report on a synthesis and magnetization study on bulk
samples of the parent compounds ${R}$NiO$_{2}$ (${R}$=La, Pr, Nd). The
frequency-dependent peaks of the AC magnetic susceptibility, along with
remarkable memory effects, characterize spin-glass states. Furthermore, various
phenomenological parameters via different spin glass models show strong
similarity within these three compounds as well as with other rare-earth metal
nickelates. The universal spin-glass behaviour distinguishes the nickelates
from the parent compound CaCuO$_{2}$ of cuprate superconductors, which has the
same crystal structure and $d^9$ electronic configuration but undergoes a
long-range antiferromagnetic order. Our investigations may indicate a
distinctly different nature of magnetism and superconductivity in the bulk
nickelates than in the cuprates.",2104.14324v2
2021-05-03,Essential properties of AlCl4-related graphite intercalation compounds of aluminum-ion-based battery cathodes,"Up to now, many guest atoms/molecules/ions have been successfully synthesized
into graphite to form the various compounds. For example, alkali-atom graphite
intercalation compounds are verified to reveal the stage-n structures,
including LiC6n and LiM8n [M=K. Rb and Cs; n=1, 2, 3; 4]. On the other side,
AlCl4-ion/molecule ones are examined to show stage-4 and stage-3 cases at room
and lower temperatures, respectively. Stage-1 and stage-2 configurations, with
the higher intercalant concentrations, are unable to synthesize in experimental
laboratories. This might arise from the fact that it is quite difficult to
build the periodical arrangements along the longitudinal z and transverse
directions simultaneously for the large ions or molecules. Our works are mainly
focused on stage-1 and stage-2 systems in terms of geometric and electronic
properties. The critical features, being associated with the atom-dominated
energy spectra and wave function within the specific energy ranges, the active
multi-orbital hybridization in distinct chemical bonds, and atom- &
orbital-decomposed van Hove singularities, will be thoroughly clarified by the
delicate simulations and analyses.",2105.01113v1
2021-05-12,Metastability relationship between two- and three-dimensional crystal structures: A case study of the Cu-based compounds,"Some of the three-dimensional (3D) crystal structures are constructed by
stacking two-dimensional (2D) layers. It remains unclear whether this geometric
concept is related to the stability of ordered compounds and whether this can
be used to computational materials design. Here, using first principles
calculations, we investigate the dynamical stability of copper-based compounds
Cu$X$ (a metallic element $X$) in the B$_h$ and L1$_1$ structures constructed
from the buckled honeycomb (BHC) structure and in the B2 and L1$_0$ structures
constructed from the buckled square (BSQ) structure. We demonstrate that (i) if
Cu$X$ in the BHC structure is dynamically stable, those in the B$_h$ and L1$_1$
structures are also stable. Although the interrelationship of the metastability
between the BSQ and the 3D structures (B2 and L1$_0$) is not clear, we find
that (ii) if Cu$X$ in the B2 (L1$_0$) structure is dynamically stable, that in
the L1$_0$ (B2) is unstable, analogous to the metastability relationship
between the bcc and the fcc structures in elemental metals. The total energy
curves for Cu$X$ along the tetragonal and trigonal paths are also investigated.",2105.05499v1
2021-05-24,Machine learning approaches for feature engineering of the crystal structure: Application to the prediction of the formation energy of cubic compounds,"In this study, we present a novel approach along with the needed
computational strategies for efficient and scalable feature engineering of the
crystal structure in compounds of different chemical compositions. This
approach utilizes a versatile and extensible framework for the quantification
of a three-dimensional (3-D) voxelized crystal structure in the form of 2-point
spatial correlations of multiple atomic attributes and performs principal
component analysis to extract the low-dimensional features that could be used
to build surrogate models for material properties of interest. An application
of the proposed feature engineering framework is demonstrated on a case study
involving the prediction of the formation energies of crystalline compounds
using two vastly different surrogate model building strategies - local Gaussian
process regression and neural networks. Specifically, it is shown that the top
25 features (i.e., principal component scores) identified by the proposed
framework serve as good regressors for the formation energy of the crystalline
substance for both model building strategies.",2105.11319v1
2021-05-30,Systematic studies of rubidium-exposed surfaces by X-ray photoelectron spectroscopy and light-induced atom desorption,"We systematically investigated various types of surfaces on which rubidium
(Rb) atoms were deposited by X-ray photoelectron spectroscopy (XPS) and
measured the light-induced atom desorption (LIAD) from those surfaces. The main
surfaces of interest included synthetic quartz, yttrium metal, and paraffin.
The Rb atoms deposited on quartz and yttrium surfaces by exposure to Rb vapor
at room temperature were detected by XPS. Quartz is originally silicon dioxide.
The yttrium surfaces were also oxidized, and Rb atoms reacted with oxygen on
both surfaces. Conversely, Rb deposition was observed only at low temperatures
on paraffin. Specifically, Rb atoms deposited on paraffin, which is not an
oxygen compound, also formed oxygen compounds under ultrahigh vacuum conditions
by reaction with the background gas. All examined surfaces showed a similar
light wavelength or photon energy dependence, such that the LIAD rates
increased with decreasing light wavelength. We presume that some types of
compounds of alkali metal and oxygen can be ubiquitous sources for LIAD from
many types of surfaces of alkali-metal vapor cells.",2105.14451v1
2021-08-06,Helical spin order in EuFe2As2 and EuRbFe4As4 single crystals,"In this work, fabrication and characterization of magnetic properties of
EuFe2As2 and EuRbFe4As4 single crystals is reported. Magnetization measurements
of samples with well defined thin film geometry and crystal orientation
demonstrate a striking similarity in ferromagnetic properties of Eu subsystems
in these two compounds. Measurements with magnetic field applied along ab
crystal planes reveal meta-magnetic transition in both compounds. Numerical
studies employing the Jz1-Jz2 Heisenberg model suggest that the ground state of
the magnetic order in Eu subsystem for both compounds is the helical spin order
with the helical angle about 2pi/5, while the meta-magnetic transition is the
helix-to-fan first order phase transition.",2108.03184v1
2021-08-08,"Atomic structure, electronic structure and optical absorption of inorganic perovskite compounds Cs2SnI6-nXn (X=F, Cl, Br; n= 0~6): A first-principles study","As a possible alternative to organic-inorganic hybrid perovskite halide,
inorganic Cs2SnI6 has drawn more and more research attention recently. In order
to find more Cs2SnI6 derivatives as the potential solar cell absorber
materials, I- ions in Cs2SnI6 are replaced by other halogen ions and forms the
Cs2SnI6-nXn (X=F, Cl, Br; n=1~6) compounds, whose atomic structures, electronic
structures and optical absorption are investigated by first principles
calculation. When the alloying level n increases, the mean lattice constants,
the weighted Sn-X and Cs-X bond lengths all decreases linearly; the bond length
of each Sn-X diminishes slightly inside the octahedral structure; Eg of
Cs2SnI6-nXn increases nonlinearly. Eleven Cs2SnI6-nXn compounds have an Eg
between 1.0 eV and 2.0 eV and so can be potentially used as the light
absorption layer of solar cells. Their partial DOS demonstrate that as the
alloying level n increases, I 5p orbital in VBM and CBM is gradually
substituted by Br 4p, or Cl 3p, or F 2p orbital. The eleven Cs2SnI6-nXn alloys
all have a direct bandgap although the lattice distortion induced by the
alloyed X- ion.",2108.03597v1
2021-08-21,Superconductivity of Light-Elements Doped H$ {}_{3} $S,"Pressurized hydrogen-rich compounds, which could be viewed as precompressed
metallic hydrogen, exhibit high superconductivity, thereby providing a viable
route toward the discovery of high-temperature superconductors. Of particular
interest is to search for high-temperature superconductors with low stable
pressure in terms of pressure-stabilized hydrides. In this work, with the aim
of obtaining high-temperature superconducting compounds at low pressure, we
attempt to study the doping effects for high-temperature superconductive $
\mathrm{H_3S} $ with supercells up to 64 atoms using first principle electronic
structure simulations. As a result of various doping, we found that Na doping
for $ \mathrm{H_3S} $ could lower the dynamically stable pressure by 40 GPa.
The results also indicate P doping could enhance the superconductivity of $
\mathrm{H_3S} $ system, which is in agreement with previous calculations.
Moreover, our work proposed an approach that could reasonably estimate the
superconducting critical temperature ($ T_{c} $) of a compound containing a
large number of atoms, saving the computational cost significantly for
large-scale elements-doping superconductivity simulations.",2108.09437v1
2021-08-24,Magnetic Topological Semimetal Phase with Electronic Correlation Enhancement in SmSbTe,"The ZrSiS family of compounds hosts various exotic quantum phenomena due to
the presence of both topological nonsymmorphic Dirac fermions and nodal-line
fermions. In this material family, the LnSbTe (Ln= lanthanide) compounds are
particularly interesting owing to the intrinsic magnetism from magnetic Ln
which leads to new properties and quantum states. In this work, the authors
focus on the previously unexplored compound SmSbTe. The studies reveal a rare
combination of a few functional properties in this material, including
antiferromagnetism with possible magnetic frustration, electron correlation
enhancement, and Dirac nodal-line fermions. These properties enable SmSbTe as a
unique platform to explore exotic quantum phenomena and advanced
functionalities arising from the interplay between magnetism, topology, and
electronic correlations.",2108.10983v1
2021-08-25,"Comprehensive search for buckled honeycomb binary compounds based on noble metals (Cu, Ag, and Au)","Honeycomb structure has been frequently observed in two-dimensional (2D)
materials. CuAu in the buckled honeycomb (BHC) structure has been synthesized
recently, which is the first case of 2D intermetallic compounds. Here, the
dynamical stability of 2D $AX$ in the BHC structure, where $A=$ Cu, Ag, and Au
and $X$ is a metallic element in the periodic table, is systematically studied
by calculating phonon dispersions from first-principles. Among 135 $AX$, more
than 50 $AX$ are identified to be dynamically stable. In addition, (i) a
relationship between the dynamical stability and the formation energy, (ii) a
correlation of dynamical stability between different constituents $A$, (iii) a
trend of lattice parameters, and (iv) electronic and magnetic properties are
discussed. Furthermore, a stable phase of B11-type AuZr is predicted based on
both the result (ii) and the stability relationship between 2D and
three-dimensional structures. The present findings stimulate future studies
exploring physics and chemistry of 2D intermetallic compounds.",2108.11060v1
2021-09-04,Simulation of X-ray diffraction in Mn$_x$Bi$_2$Te$_{3+x}$ epitaxic films,"Disordered heterostructures stand as a general description for compounds that
are part of homologous series such as bismuth chalcogenides. In device
engineering, van der Waals epitaxy of these compounds is very promising for
applications in spintronic and quantum computing. Structural analysis methods
are essential to control and improve their synthesis in the form of thin films.
Recently, X-rays tools have been proposed for structural modeling of disordered
heterostructures [arXiv:2107.12280]. Here, we further evaluate the use of these
tools to study the compound Mn$_x$Bi$_2$Te$_{3+x}$ in the grazing incidence
region of the reflectivity curves, as well as the effect of thickness
fluctuation in the wide angle region.",2109.01914v1
2021-09-13,Anisotropic Nodal-Line-Derived Large Anomalous Hall Conductivity in ZrMnP and HfMnP,"The nontrivial band structure of semimetals has attracted substantial
research attention in condensed matter physics and materials science in recent
years owing to its intriguing physical properties. Within this class, a group
of non-trivial materials known as nodal-line semimetals is particularly
important. Nodal-line semimetals exhibit the potential effects of electronic
correlation in nonmagnetic materials, whereas they enhance the contribution of
the Berry curvature in magnetic materials, resulting in high anomalous Hall
conductivity (AHC). In this study, two ferromagnetic compounds, namely ZrMnP
and HfMnP, are selected, wherein the abundance of mirror planes in the crystal
structure ensures gapped nodal lines at the Fermi energy. These nodal lines
result in one of the largest AHC values of 2840 ohm^-1cm^-1, with a high
anomalous Hall angle of 13.6 % in these compounds. First-principles
calculations provide a clear and detailed understanding of nodal line-enhanced
AHC. Our finding suggests a guideline for searching large AHC compounds.",2109.06134v1
2021-10-08,"Discover, Hallucinate, and Adapt: Open Compound Domain Adaptation for Semantic Segmentation","Unsupervised domain adaptation (UDA) for semantic segmentation has been
attracting attention recently, as it could be beneficial for various
label-scarce real-world scenarios (e.g., robot control, autonomous driving,
medical imaging, etc.). Despite the significant progress in this field, current
works mainly focus on a single-source single-target setting, which cannot
handle more practical settings of multiple targets or even unseen targets. In
this paper, we investigate open compound domain adaptation (OCDA), which deals
with mixed and novel situations at the same time, for semantic segmentation. We
present a novel framework based on three main design principles: discover,
hallucinate, and adapt. The scheme first clusters compound target data based on
style, discovering multiple latent domains (discover). Then, it hallucinates
multiple latent target domains in source by using image-translation
(hallucinate). This step ensures the latent domains in the source and the
target to be paired. Finally, target-to-source alignment is learned separately
between domains (adapt). In high-level, our solution replaces a hard OCDA
problem with much easier multiple UDA problems. We evaluate our solution on
standard benchmark GTA to C-driving, and achieved new state-of-the-art results.",2110.04111v1
2021-10-11,High-T$_c$ Superconductivity in doped boron-carbon clathrates,"We report a high-throughput ab-initio study of the thermodynamic and
superconducting proper- ties of the recently synthesized XB$_3$C$_3$
clathrates. These compounds, in which boron and carbon form a sponge-like
network of interconnected cages each enclosing a central X atom, are attractive
candidates to achieve high-Tc conventional superconductivity at ambient
pressure, due to the simultaneous presence of a stiff B-C covalent network and
a tunable charge reservoir, provided by the guest atom. Ternary compounds like
CaB$_3$C$_3$, SrB$_3$C$_3$ and BaB$_3$C$_3$ are predicted to exhibit T$_c$
$\lt$ 50 K at moderate or ambient pressures, which may further increase up to
77 K if the original compounds are hole-doped by replacing the divalent
alkaline earth with a monovalent alkali metal to form ordered $XY$B$_6$C$_6$
alloys.",2110.05333v1
2021-10-28,Identification over Compound Multiple-Input Multiple-Output Broadcast Channels,"The identification capacity region of the compound broadcast channel is
determined under an average error criterion, where the sender has no channel
state information. We give single-letter identification capacity formulas for
discrete channels and multiple-input multiple-output Gaussian channels under an
average input constraint. The capacity theorems apply to general discrete
memoryless broadcast channels. This is in contrast to the transmission setting,
where the capacity is only known for special cases, notably the degraded
broadcast channel and the multiple-input multiple-output broadcast channel with
private messages. Furthermore, the identification capacity region of the
compound multiple-input multiple-output broadcast channel can be larger than
the transmission capacity region. This is a departure from the single-user
behavior of identification, since the identification capacity of a single-user
channel equals the transmission capacity.",2110.15101v2
2021-11-03,Insulator-to-superconductor transition in quasi-one-dimensional HfS3 under pressure,"Various transition metal trichalcogenides (TMTC) show the charge-density-wave
and superconductivity, which provide an ideal platform to study the correlation
between these two orderings and the mechanism of superconductivity. Currently,
almost all metallic TMTC compounds can show superconductivity either at ambient
pressure or at high pressure. However, most TMTC compounds are semiconductors
and even insulators. Does the superconductivity exist in any non-metal TMTC
compound? In this work, we managed to manipulate the electronic behavior of
highly insulating HfS3 in term of pressure. HfS3 underwent an
insulator-semiconductor transition near 17 GPa with a band gap reduce of ~1 eV.
The optical absorption and Raman measurement provide the consistent results,
suggesting the structural origin of the electronic transition. Upon further
compression, HfS3 becomes a superconductor. The superconducting transition was
initialized as early as 50.6 GPa and the zero-resistance is reached above 91.2
GPa. The superconducting behavior is further confirmed by both the magnetic
field effect and current effect. This work sheds the light that all TMTC may be
superconductors, and opens a new avenue to explore the abundant emergence
phenomena in TMTC material family.",2111.02060v1
2021-11-24,Assessing the correlated electronic structure of lanthanum nickelates,"The series of nickel-oxide compounds LaNiO$_3$ (formal Ni$(d^7)$),
La$_2$NiO$_4$ (formal Ni$(d^8)$) and LaNiO$_2$ (formal Ni$(d^9)$) is
investigated by first-principles many-body, using a combination of density
functional theory, self-interaction correction and dynamical mean-field theory.
The characteristics of these different nickelates, in good agreement with
available experimental data, is revealed by employing a compound-independent
choice for the local Coulomb interactions. The dichotomy within the low-energy
dominant Ni-$e_g$ sector of $\{d_{z^2},d_{x^2-y^2}\}$ kind is rising with
growing Ni$(3d)$ filling across the series. An intermediate-coupling scheme for
spin-polarized calculations is introduced, which leads to very weak Ni ordered
moments for the infinite-layer compound LaNiO$_2$ in contrast to the
robust-moment system La$_2$NiO$_4$.",2111.12473v1
2021-11-25,Discovering Superhard B-N-O Compounds by Iterative Machine Learning and Evolutionary Structure Predictions,"We search for new superhard B-N-O compounds with an iterative machine
learning (ML) procedure, where ML models are trained using sample crystal
structures from evolutionary algorithm. We first use cohesive energy to
evaluate the thermodynamic stability of varying B$_x$N$_y$O$_z$ compositions,
and then gradually focus on compositional regions with high cohesive energy and
high hardness. The results converge quickly after a few iterations. Our
resulting ML models show that B$_{x+2}$N$_{x}$O$_{3}$ compounds with $x \geq 3$
(like B$_5$N$_3$O$_3$, B$_6$N$_4$O$_3$, etc.) are potentially superhard and
thermodynamically favorable. Our meta-GGA density functional theory
calculations indicate that these materials are also wide bandgap ($\ge 4.4$ eV)
insulators, with the valence band maximum related to the $p$-orbitals of
nitrogen atoms near vacant sites. This study demonstrates that an iterative
method combining ML and ab initio simulations provides a powerful tool for
discovering novel materials.",2111.12923v1
2021-12-05,Structural instabilities of infinite-layer nickelates from first-principles simulations,"Rare-earth nickelates RNiO$_2$ adopting an infinite-layer phase show
superconductivity once La, Pr or Nd are substituted by a divalent cation.
Either in the pristine or doped form, these materials are reported to adopt a
high symmetry, perfectly symmetric, P4/mmm tetragonal cell. Nevertheless, bulk
compounds are scarce, hindering a full understanding of the role of chemical
pressure or strain on lattice distortions that in turn could alter magnetic and
electronic properties of the 2D nickelates. Here, by performing a full analysis
of the prototypical YNiO$_2$ compound with first-principles simulations, we
identify that these materials are prone to exhibit O$_4$ group rotations whose
type and amplitude are governed by the usual R-to-Ni cation size mismatch. We
further show that these rotations can be easily tuned by external stimuli
modifying lattice parameters such as pressure or strain. Finally, we reveal
that H intercalation is favored for any infinite-layer nickelate member and
pushes the propensity of the compounds to exhibit octahedra rotations.",2112.02642v1
2021-12-09,Global and local approaches to population analysis: bonding patterns in superheavy element compounds,"Relativistic effective atomic configurations of superheavy elements Cn, Nh
and Fl and their lighter homologues (Hg, Tl and Pb) in their simple compounds
with fluorine and oxygen are determined using the analysis of local properties
of molecular Kohn-Sham density matrices in the vicinity of heavy nuclei. The
difference in populations of atomic spinors with the same orbital angular
momentum and different total angular momenta is demonstrated to be essential
for understanding the peculiarities of chemical bonding in superheavy element
compounds. The results are fully compatible with those obtained by the
relativistic iterative version of conventional projection analysis of global
density matrices.",2112.04738v1
2021-12-20,Computational design of a new layered superconductor LaOTlF2,"A new layered compound LaOTlF2 is designed and investigated using
first-principles calculations in this work. The parent compound is an insulator
with an indirect band gap of 2.65 eV. Electron-doping of the parent compound
makes the material metallic. In the meantime, several lattice vibrational modes
couple strongly to the conduction band, leading to a large electron-phonon
coupling constant and conventional superconductivity. The highest
superconducting transition temperature Tc is predicted to be approximately 8.6
K with {\lambda} about 1.25 in the optimally doped LaO0.95F0.05TlF2, where
{\lambda} is calculated using the Wannier interpolation technique.",2112.10687v1
2021-12-20,A Constraint Programming Approach to Weighted Isomorphic Mapping of Fragment-based Shape Signatures,"Fragment-based shape signature techniques have proven to be powerful tools
for computer-aided drug design. They allow scientists to search for target
molecules with some similarity to a known active compound. They do not require
reference to the full underlying chemical structure, which is essential to deal
with chemical databases containing millions of compounds. However, finding the
optimal match of a part of the fragmented compound can be time-consuming. In
this paper, we use constraint programming to solve this specific problem. It
involves finding a weighted assignment of fragments subject to connectivity
constraints. Our experiments demonstrate the practical relevance of our
approach and open new perspectives, including generating multiple, diverse
solutions. Our approach constitutes an original use of a constraint solver in a
real time setting, where propagation allows to avoid an enumeration of weighted
paths. The model must remain robust to the addition of constraints making some
instances not tractable. This particular context requires the use of unusual
criteria for the choice of the model: lightweight, standard propagation
algorithms, data structures without prohibitive constant cost. The objective is
not to design new, complex algorithms to solve difficult instances.",2112.10892v2
2021-12-23,Deep Proximal Learning for High-Resolution Plane Wave Compounding,"Plane Wave imaging enables many applications that require high frame rates,
including localisation microscopy, shear wave elastography, and ultra-sensitive
Doppler. To alleviate the degradation of image quality with respect to
conventional focused acquisition, typically, multiple acquisitions from
distinctly steered plane waves are coherently (i.e. after time-of-flight
correction) compounded into a single image. This poses a trade-off between
image quality and achievable frame-rate. To that end, we propose a new deep
learning approach, derived by formulating plane wave compounding as a linear
inverse problem, that attains high resolution, high-contrast images from just 3
plane wave transmissions. Our solution unfolds the iterations of a proximal
gradient descent algorithm as a deep network, thereby directly exploiting the
physics-based generative acquisition model into the neural network design. We
train our network in a greedy manner, i.e. layer-by-layer, using a combination
of pixel, temporal, and distribution (adversarial) losses to achieve both
perceptual fidelity and data consistency. Through the strong model-based
inductive bias, the proposed architecture outperforms several standard
benchmark architectures in terms of image quality, with a low computational and
memory footprint.",2112.12410v1
2021-12-24,Forecasting number of corner kicks taken in association football using compound Poisson distribution,"This article presents a holistic compound Poisson regression model framework
to forecast number of corner kicks taken in association football. Corner kick
taken events are often decisive in the match outcome and inherently arrive in
batch with serial clustering pattern. Providing parameter estimates with
intuitive interpretation, a class of compound Poisson regression including a
Bayesian implementation of geometric-Poisson distribution is introduced. With a
varying shape parameter, the corner counts serial correlation between matches
is handled naturally within the Bayesian model. In this study, information
elicited from cross-market betting odds was used to improve the model
predictability. Margin application methods to adjust market inefficiency in raw
odds are also discussed.",2112.13001v3
2021-12-28,Topological viewpoint of two-dimensional group III-V and IV-IV compounds in the presence of electric field and spin-orbit coupling by density functional theory and tight-binding model,"Using the tight-binding model and density functional theory, the topological
invariant of the two-dimensional (2D) group III-V and IV-IV compounds are
studied in the absence and the presence of an external perpendicular electric
field and spin-orbit coupling. It will be recognized that a critical value of
these parameters changes the topological invariant of 2D graphene-like
compounds. The significant effects of an external electric field and spin-orbit
coupling are considered to the two-center overlap integrals of the
Slater-Koster model involved in band structures, changing band-gap, and tuning
the topological phase transition between ordinary and quantum spin Hall regime.
These declare the good consistency between two theories: tight-binding and
density functional. So, this study reveals topological phase transition in
these materials. Our finding paves a way to extend an effective Hamiltonian,
and may instantly clear some computation aspects of the study in the field of
spintronic based on the first-principles methods.",2112.14155v2
2021-12-29,Photochemical Synthesis of P-S-H Ternary Hydride at High Pressures,"The recent discovery of room temperature superconductivity (283 K) in
carbonaceous sulfur hydride (C-S-H) has attracted lots of interests in ternary
hydrogen rich materials. In this report, ternary hydride P-S-H has been
synthesized through photochemical reaction from elemental sulfur (S),
phosphorus (P) and molecular hydrogen (H2) at high pressures and room
temperature. The Raman spectroscopy under pressure shows that H2S and PH3
compounds are synthesized after laser heating at 0.9 GPa and a ternary van der
Waals compound P-S-H is synthesized with a further compression to 4.6 GPa. The
P-S-H compound is probably a mixed alloy of PH3 and (H2S)2H2 with a guest-host
structure similar to the C-S-H system. The ternary hydride can persist up to
35.6 GPa at least and shows two phase transitions at approximately 23.6 GPa and
32.8 GPa, respectively. The P-S-H ternary hydride in this report is a
competitive candidate for new hydride superconductors with near
room-temperature transitions.",2112.14348v1
2022-01-09,Joint Successive Cancellation List Decoding for the Double Polar codes,"As a new joint source-channel coding scheme, the double polar (D-Polar) codes
have been proposed recently. In this letter, a novel joint source-channel
decoder, namely the joint successive cancellation list (J-SCL) decoder, is
proposed to improve the decoding performance of the D-Polar codes. We merge the
trellis of the source polar code and that of the channel polar code to
construct a compound trellis. In this compound trellis, the joint
source-channel nodes represent both of the information bits and the
high-entropy bits. Based on the compound trellis, the J-SCL decoder is designed
to recover the source messages by combining the source SCL decoding and channel
SCL decoding. The J-SCL decoder doubles the number of the decoding paths at
each decoding level and then reserves the L paths with the smallest joint
path-metric (JPM). For the JSC node, the JPM is updated considering both the
channel decision log-likelihood ratios (LLRs) and the source decision LLRs.
Simulation results show that the J-SCL decoder outperforms the turbo-like BP
(TL-BP) decoder with lower complexity.",2201.02924v1
2022-01-17,Handling Compounding in Mobile Keyboard Input,"This paper proposes a framework to improve the typing experience of mobile
users in morphologically rich languages. Smartphone keyboards typically support
features such as input decoding, corrections and predictions that all rely on
language models. For latency reasons, these operations happen on device, so the
models are of limited size and cannot easily cover all the words needed by
users for their daily tasks, especially in morphologically rich languages. In
particular, the compounding nature of Germanic languages makes their vocabulary
virtually infinite. Similarly, heavily inflecting and agglutinative languages
(e.g. Slavic, Turkic or Finno-Ugric languages) tend to have much larger
vocabularies than morphologically simpler languages, such as English or
Mandarin. We propose to model such languages with automatically selected
subword units annotated with what we call binding types, allowing the decoder
to know when to bind subword units into words. We show that this method brings
around 20% word error rate reduction in a variety of compounding languages.
This is more than twice the improvement we previously obtained with a more
basic approach, also described in the paper.",2201.06469v1
2022-01-20,Sub-barrier fusion reactions,"The concept of compound nucleus was proposed by Niels Bohr in 1936 to explain
narrow resonances observed in scattering of a slow neutron off atomic nuclei. A
compound nucleus is a metastable state with a long lifetime, in which all the
degrees of freedom are in a sort of thermal equilibrium. Fusion reactions are
defined as reactions to form such compound nucleus by merging two atomic
nuclei. Here a short description of heavy-ion fusion reactions at energies
close the Coulomb barrier is presented. This includes: (i) an overview of a
fusion process, (ii) a strong interplay between nuclear structure and fusion,
(iii) fusion and multi-dimensional/multi-particle quantum tunneling, and (iv)
fusion for superheavy elements.",2201.08061v1
2022-04-01,Experimental control of Tc in AlB2-type compounds using an applied voltage,"We utilize the van de Pauw technique combined with Density Functional Theory
to show that an external voltage applied to superconducting AlB2-type
compounds, such as MgB2 and Mg(B1.9C0.1), effects substantive changes in
transition temperature due to modification of electronic band structure. An
applied voltage results in a symmetric split of degenerate sigma bands in MgB2
similar to that calculated for atom displacement along the B-B bond aligned
with E2g phonon mode directions. For AlB2, similar splitting of sigma bands
occurs albeit with higher voltage requirement compared to MgB2. Experimental
data show that Tc values for MgB2 and Mg(B1.9C0.1) reduce consistently with
increased increments of applied voltage. Zero resistance is limited by an upper
applied voltage depending on the compound.",2204.00151v1
2022-04-01,Tuning of Carrier Concentration and Superconductivity in High-Entropy-Alloy-Type Metal Telluride (AgSnPbBi)(1-x)/4InxTe,"High-entropy-alloy-type (HEA-type) compound superconductors have been drawing
much attention as a new class of exotic superconductors with local structural
inhomogeneity. NaCl-type (Ag,In,Sn,Pb,Bi)Te is a typical HEA-type
superconductor, but the carrier doping mechanism had been unclear. In this
study, we synthesized (Ag,In,Sn,Pb,Bi)Te with various In concentration using
high-pressure synthesis: the studied system is (AgSnPbBi)(1-x)/4InxTe (x =
0-0.4). Single-phase samples were obtained for x = 0-0.3. A semiconductor-like
temperature dependence of resistivity was observed for x = 0, while
superconductivity appeared for the In-doped samples. The highest transition
temperature (Tc) was 3.0 K for x = 0.3. The Seebeck coefficient decreases with
increase of x, which suggests that In3+ generates electron carriers in
(AgSnPbBi)(1-x)/4InxTe. Tuning of carrier concentration and superconducting
properties of (Ag,In,Sn,Pb,Bi)Te would be useful for further investigation of
exotic superconductivity in the HEA-type compound.",2204.00407v1
2022-04-09,Crystallographic design of intercalation materials,"Intercalation materials are promising candidates for reversible energy
storage and are, for example, used as lithium-battery electrodes,
hydrogen-storage compounds, and electrochromic materials. An important issue
preventing the more widespread use of these materials is that they undergo
structural transformations (of up to ~10% lattice strains) during
intercalation, which expand the material, nucleate microcracks, and,
ultimately, lead to material failure. Besides the structural transformation of
lattices, the crystallographic texture of the intercalation material plays a
key role in governing ion-transport properties, generating phase separation
microstructures, and elastically interacting with crystal defects. In this
review, I provide an overview of how the structural transformation of lattices,
phase transformation microstructures, and crystallographic defects affect the
chemo-mechanical properties of intercalation materials. In each section, I
identify the key challenges and opportunities to crystallographically design
intercalation compounds to improve their properties and lifespans. I
predominantly cite examples from the literature of intercalation cathodes used
in rechargeable batteries, however, the identified challenges and opportunities
are transferable to a broader range of intercalation compounds.",2204.04525v1
2022-04-19,Antiferromagnetic structure and magnetic properties of Dy2O2Te: An isostructural analog of the rare-earth superconductors R2O2Bi,"The rare-earth compounds R2O2Bi (R=Tb, Dy, Er, Lu, Y) are newly discovered
superconductors in the vicinity of a rare-earth magnetic long-range order. In
this work, we determine the magnetic order of the parent compound Dy2O2Te by
neutron scattering as the A-type antiferromagnetic structure below the N\'eel
temperature TN=9.7K. The large staggered magnetic moment 9.4(1) {\mu}B per Dy
at T=3.5K lies in the basal ab plane. In a magnetic field, anomalous magnetic
properties including the bifurcation between zero-field- and field-cooling
magnetization, a butterfly-shaped magnetic hysteresis, and slow magnetic
relaxation emerge, which are related to the field-induced metamagnetic
transitions in Dy2O2Te. Our experimental findings could stimulate further
research on the relation between antiferromagnetism and superconductivity in
these rare-earth compounds.",2204.09103v1
2022-04-20,Infusing Linguistic Knowledge of SMILES into Chemical Language Models,"The simplified molecular-input line-entry system (SMILES) is the most popular
representation of chemical compounds. Therefore, many SMILES-based molecular
property prediction models have been developed. In particular,
transformer-based models show promising performance because the model utilizes
a massive chemical dataset for self-supervised learning. However, there is no
transformer-based model to overcome the inherent limitations of SMILES, which
result from the generation process of SMILES. In this study, we grammatically
parsed SMILES to obtain connectivity between substructures and their type,
which is called the grammatical knowledge of SMILES. First, we pretrained the
transformers with substructural tokens, which were parsed from SMILES. Then, we
used the training strategy 'same compound model' to better understand SMILES
grammar. In addition, we injected knowledge of connectivity and type into the
transformer with knowledge adapters. As a result, our representation model
outperformed previous compound representations for the prediction of molecular
properties. Finally, we analyzed the attention of the transformer model and
adapters, demonstrating that the proposed model understands the grammar of
SMILES.",2205.00084v1
2022-05-19,Towards Understanding Gender-Seniority Compound Bias in Natural Language Generation,"Women are often perceived as junior to their male counterparts, even within
the same job titles. While there has been significant progress in the
evaluation of gender bias in natural language processing (NLP), existing
studies seldom investigate how biases toward gender groups change when
compounded with other societal biases. In this work, we investigate how
seniority impacts the degree of gender bias exhibited in pretrained neural
generation models by introducing a novel framework for probing compound bias.
We contribute a benchmark robustness-testing dataset spanning two domains, U.S.
senatorship and professorship, created using a distant-supervision method. Our
dataset includes human-written text with underlying ground truth and paired
counterfactuals. We then examine GPT-2 perplexity and the frequency of gendered
language in generated text. Our results show that GPT-2 amplifies bias by
considering women as junior and men as senior more often than the ground truth
in both domains. These results suggest that NLP applications built using GPT-2
may harm women in professional capacities.",2205.09830v1
2022-06-05,Exponential densities and compound Poisson measures,"We prove estimates at infinity of convolutions $f^{n\star}$ and densities of
the corresponding compound Poisson measures for a class of radial decreasing
densities on $\mathbb{R}^d$, $d \geq 1$, which are not convolution equivalent.
Existing methods and tools are limited to the situation in which the
convolution $f^{2\star}(x)$ is comparable to initial density $f(x)$ at
infinity. We propose a new approach which allows one to break this barrier. We
focus on densities which are products of exponential functions and smaller
order terms -- they are common in applications. In the case when the smaller
order term is polynomial estimates are given in terms of the generalized Bessel
function. Our results can be seen as the first attempt to understand the
intricate asymptotic properties of the compound Poisson and more general
infinitely divisible measures constructed for such densities.",2206.02258v2
2022-06-16,Optimal Parallel Sequential Change Detection under Generalized Performance Measures,"This paper considers the detection of change points in parallel data streams,
a problem widely encountered when analyzing large-scale real-time streaming
data. Each stream may have its own change point, at which its data has a
distributional change. With sequentially observed data, a decision maker needs
to declare whether changes have already occurred to the streams at each time
point.Once a stream is declared to have changed, it is deactivated permanently
so that its future data will no longer be collected. This is a compound
decision problem in the sense that the decision maker may want to optimize
certain compound performance metrics that concern all the streams as a whole.
Thus, the decisions are not independent for different streams. Our contribution
is three-fold. First, we propose a general framework for compound performance
metrics that includes the ones considered in the existing works as special
cases and introduces new ones that connect closely with the performance metrics
for single-stream sequential change detection and large-scale hypothesis
testing. Second, data-driven decision procedures are developed under this
framework. Finally, optimality results are established for the proposed
decision procedures. The proposed methods and theory are evaluated by
simulation studies and a case study.",2206.08435v1
2022-07-14,Covy: An AI-powered Robot with a Compound Vision System for Detecting Breaches in Social Distancing,"This paper introduces a compound vision system that enables robots to
localize people up to 15m away using a cheap camera. And, it proposes a robust
navigation stack that combines Deep Reinforcement Learning (DRL) and a
probabilistic localization method. To test the efficacy of these systems, we
prototyped a low-cost mobile robot that we call Covy. Covy can be used for
applications such as promoting social distancing during pandemics or estimating
the density of a crowd. We evaluated Covy's performance through extensive sets
of experiments both in simulated and realistic environments. Our results show
that Covy's compound vision algorithm doubles the range of the used depth
camera, and its hybrid navigation stack is more robust than a pure DRL-based
one.",2207.06847v2
2022-07-26,Microscopic study of the compound nucleus formation in cold-fusion reactions,"The understanding of the fusion probability is of particular importance to
reveal the mechanism of producing superheavy elements. We present a microscopic
study of the compound nucleus formation by combining time-dependent density
functional theory, coupled-channels approach, and dynamical diffusion models.
The fusion probability and compound nucleus formation cross sections for
cold-fusion reactions $^{48}$Ca+$^{208}$Pb, $^{50}$Ti+$^{208}$Pb, and
$^{54}$Cr+$^{208}$Pb are investigated and it is found that the deduced capture
barriers, capture cross sections for these reactions are consistent with
experimental data. Above the capture barrier, our calculations reproduce the
measured fusion probability reasonably well. Our studies demonstrate that the
restrictions from the microscopic dynamic theory improve the predictive power
of the coupled-channels and diffusion calculations.",2207.12924v1
2022-08-09,Bridging the gap between target-based and cell-based drug discovery with a graph generative multi-task model,"Drug discovery is vitally important for protecting human against disease.
Target-based screening is one of the most popular methods to develop new drugs
in the past several decades. This method efficiently screens candidate drugs
inhibiting target protein in vitro, but it often fails due to inadequate
activity of the selected drugs in vivo. Accurate computational methods are
needed to bridge this gap. Here, we propose a novel graph multi task deep
learning model to identify compounds carrying both target inhibitory and cell
active (MATIC) properties. On a carefully curated SARS-CoV-2 dataset, the
proposed MATIC model shows advantages comparing with traditional method in
screening effective compounds in vivo. Next, we explored the model
interpretability and found that the learned features for target inhibition (in
vitro) or cell active (in vivo) tasks are different with molecular property
correlations and atom functional attentions. Based on these findings, we
utilized a monte carlo based reinforcement learning generative model to
generate novel multi-property compounds with both in vitro and in vivo
efficacy, thus bridging the gap between target-based and cell-based drug
discovery.",2208.04944v1
2022-08-22,Learning Ball-balancing Robot Through Deep Reinforcement Learning,"The ball-balancing robot (ballbot) is a good platform to test the
effectiveness of a balancing controller. Considering balancing control,
conventional model-based feedback control methods have been widely used.
However, contacts and collisions are difficult to model, and often lead to
failure in balancing control, especially when the ballbot tilts a large angle.
To explore the maximum initial tilting angle of the ballbot, the balancing
control is interpreted as a recovery task using Reinforcement Learning (RL). RL
is a powerful technique for systems that are difficult to model, because it
allows an agent to learn policy by interacting with the environment. In this
paper, by combining the conventional feedback controller with the RL method, a
compound controller is proposed. We show the effectiveness of the compound
controller by training an agent to successfully perform a recovery task
involving contacts and collisions. Simulation results demonstrate that using
the compound controller, the ballbot can keep balance under a larger set of
initial tilting angles, compared to the conventional model-based controller.",2208.10142v1
2022-09-09,$GW$+EDMFT investigation of Pr$_{1-x}$Sr$_x$NiO$_2$ under pressure,"Motivated by the recent experimental observation of a large pressure effect
on $T_c$ in Pr$_{1-x}$Sr$_x$NiO$_2$, we study the electronic properties of this
compound as a function of pressure for $x=0$ and $0.2$ doping using
self-consistent $GW$+EDMFT. Our numerical results demonstrate a non-trivial
interplay between chemical doping and physical pressure, and small but
systematic changes in the orbital occupations, local level energies, and
interaction parameters with increasing pressure. The proper treatment of
correlation effects, beyond density function theory, is shown to play an
important role in revealing these trends. While the pressure dependent changes
in the electronic structure of the undoped compound suggest a more
single-band-like behavior in the high-pressure regime, a qualitatively
different behavior is found in the doped system. We also point out that the
fluctuations in the orbital occupations and spin states are not consistent with
a single-band picture, and that at least a two-band model is necessary to
reproduce the full result. This multi-orbital nature manifests itself most
clearly in the doped compound.",2209.04349v1
2022-09-12,Phase Transitions and Superconductivity in Ternary Hydride Li$_2$SiH$_6$ at High Pressures,"We predicted a new ternary hydride Li$_2$SiH$_6$ at high pressures. A
systematic structure search in Li$_2$SiH$_6$ compound reveals novel stable
phases with intriguing electronic and phonon properties. It is found that
Li$_2$SiH$_6$ is dynamically stable from ambient pressure up to 400 GPa with
three novel phases: P312, P$\bar{3}$, and P$\bar{6}$2m. The calculation of
electron-phonon coupling combined with Bardeen-Cooper-Schrieffer's argument
indicates that this compound may be a candidate for high $T_c$ superconductors
under high pressures. In particular, the maximum $T_c$ of
$P\bar{6}2m$-Li$_2$SiH$_6$ at 400 GPa reaches 56 K. These findings may pave the
way for obtaining room temperature superconductors in dense hydrogen-rich
compounds.",2209.05014v1
2022-10-11,New Gd-based magnetic compound GdPt$_2$B with a chiral crystal structure,"Herein, we report the discovery of a novel Gd-based magnetic compound
GdPt$_2$B with a chiral crystal structure. X-ray diffraction and chemical
composition analyses reveal a CePt$_2$B-type crystal structure (space group:
$P6_422$) for GdPt$_2$B. Moreover, we successfully grew single crystals of
GdPt$_2$B using the Czochralski method. Magnetization measurements and the
Curie$-$Weiss analysis demonstrate that the ferromagnetic interaction is
dominant in GdPt$_2$B. A clear transition is observed in the temperature
dependence of electrical resistivity, magnetic susceptibility, and specific
heat at $T_{\rm O}$ = 87 K. The magnetic phase diagram of GdPt$_2$B, which
consists of a field-polarized ferromagnetic region and a magnetically ordered
region, resembles those of known chiral helimagnets. Furthermore, magnetic
susceptibility measurements reveal a possible spin reorientation within the
magnetically ordered phase in magnetic fields perpendicular to the screw axis.
The results demonstrate that GdPt$_2$B is a suitable platform for investigating
the competing effects of ferromagnetic and antisymmetric exchange interactions
in rare-earth-based chiral compounds.",2210.05099v1
2022-09-30,Prioritizing emergency evacuations under compounding levels of uncertainty,"Well-executed emergency evacuations can save lives and reduce suffering.
However, decision makers struggle to determine optimal evacuation policies
given the chaos, uncertainty, and value judgments inherent in emergency
evacuations. We propose and analyze a decision support tool for pre-crisis
training exercises for teams preparing for civilian evacuations and explore the
tool in the case of the 2021 U.S.-led evacuation from Afghanistan. We use
different classes of Markov decision processes (MDPs) to capture compounding
levels of uncertainty in (1) the priority category of who appears next at the
gate for evacuation, (2) the distribution of priority categories at the
population level, and (3) individuals' claimed priority category. We compare
the number of people evacuated by priority status under eight heuristic
policies. The optimized MDP policy achieves the best performance compared to
all heuristic baselines. We also show that accounting for the compounding
levels of model uncertainty incurs added complexity without improvement in
policy performance. Useful heuristics can be extracted from the optimized
policies to inform human decision makers. We open-source all tools to encourage
robust dialogue about the trade-offs, limitations, and potential of integrating
algorithms into high-stakes humanitarian decision-making.",2210.08975v1
2022-10-19,Electronic and Excitonic Properties of MSi2Z4 Monolayers,"MA2Z4 monolayers form a new class of hexagonal non-centrosymmetric materials
hosting extraordinary spin-valley physics. While only two compounds (MoSi2N4
and WSi2N4) were recently synthesized, theory predicts interesting
(opto)electronic properties of a whole new family of such two-dimensional
materials. Here, the chemical trends of band gaps and spin-orbit splittings of
bands in selected MSi2Z4 (M = Mo, W; Z = N, P, As, Sb) compounds are studied
from first-principles. Effective Bethe-Salpeter-equation-based calculations
reveal high exciton binding energies. Evolution of excitonic energies under
external magnetic field is predicted by providing their effective g-factors and
diamagnetic coefficients, which can be directly compared to experimental
values. In particular, large positive g-factors are predicted for excitons
involving higher conduction bands. In view of these predictions, MSi2Z4
monolayers yield a new platform to study excitons and are attractive for
optoelectronic devices, also in the forms of heterostructures. In addition, a
spin-orbit induced bands inversion is observed in the heaviest studied
compound, WSi2Sb4, a hallmark of its topological nature.",2210.10679v1
2022-10-21,Deep Reinforcement Learning for Inverse Inorganic Materials Design,"A major obstacle to the realization of novel inorganic materials with
desirable properties is the inability to perform efficient optimization across
both materials properties and synthesis of those materials. In this work, we
propose a reinforcement learning (RL) approach to inverse inorganic materials
design, which can identify promising compounds with specified properties and
synthesizability constraints. Our model learns chemical guidelines such as
charge and electronegativity neutrality while maintaining chemical diversity
and uniqueness. We demonstrate a multi-objective RL approach, which can
generate novel compounds with targeted materials properties including formation
energy and bulk/shear modulus alongside a lower sintering temperature synthesis
objectives. Using this approach, the model can predict promising compounds of
interest, while suggesting an optimized chemical design space for inorganic
materials discovery.",2210.11931v1
2022-10-21,Triangular Kondo lattice in $\mathrm{YbV_6Sn_6}$ and its quantum critical behaviors in magnetic field,"We report magnetization, heat capacity and electrical resistivity for a newly
discovered heavy fermion (HF) compound $\mathrm{YbV_6Sn_6}$ which is
crystallized in a hexagonal $\mathrm{HfFe_6Ge_6}$-type structure, highlighted
by the stacking of triangular ytterbium sublattice and kagome vanadium
sublattice. Above 2 K, $\mathrm{YbV_6Sn_6}$ shows typical HF properties due to
the Kondo effect on the Kramers doublet of $\mathrm{Yb^{3+}}$ ions in crystal
electric field. A remarkable magnetic ordering occurs at $T_{\mathrm{N}}$ =
0.40 K in zero field while a weak external field suppresses the ordering and
induces non-Fermi liquid (NFL) behavior. In strong magnetic field the compound
shows a heavy Fermi liquid state. $\mathrm{YbV_6Sn_6}$ presents as one of the
few examples of Yb-based HF compounds hosting triangular Kondo lattice on which
a magnetic field induces quantum criticality near zero temperature.",2210.12117v1
2022-10-29,Magnetotransport Properties and Fermi Surface Topology of Nodal line Semimetal InBi,"In the present study, we have discussed the up-turn behavior in the
resistivity pattern of the topological nodal line semimetal InBi. We argued
that such nature could be generalized with a mathematical model, that can be
applied to any compounds exhibiting similar behavior. The extremely high
magnetoresistance (XMR) has also been explained by the carrier compensation in
the compound, estimated from the Hall conductivity. Moreover, from the study of
Subhnikov-de Haas (SdH) oscillation and density functional theory (DFT), we
obtained the complete three-dimensional (3D) Fermi surface topology of the
compound InBi. A detailed understanding of carriers' behavior has been
discussed using those studies. We have also unfurled the topology of each
electron and hole pocket and its possible modulation with electron and hole
doping.",2210.16527v1
2022-11-04,"Determination of photo-nuclear cross section of $^{61}$Ni($γ$,xp) reaction via surrogate ratio technique","The photo nuclear reaction cross section of $^{61}$Ni($\gamma$,xp) reaction
have been measured by employing surrogate reaction technique. This indirect
method is used for the first time to obtain the cross section of photo nuclear
reaction. The compound nucleus $^{61}$Ni$^{*}$ was populated using the transfer
reaction $^{59}$Co($^{6}$Li,$\alpha$) at E$_{lab}=$ 40.5 MeV. To calculate the
surrogate ratio, $^{60}$Ni($\gamma$,xp) was selected as reference reaction and
the corresponding compound nucleus $^{60}$Ni$^{*}$ was populated using the
transfer reaction $^{56}$Fe($^{6}$Li,d) at E$_{lab}=$ 35.9 MeV. The
experimental cross section data of the reference reaction has been taken from
EXFOR data libraries. Compound nuclear cross section calculations have been
done using EMPIRE 3.2.3 code.",2211.02393v2
2022-11-30,Compound Multivariate Hawkes Processes: Large Deviations and Rare Event Simulation,"In this paper, we establish a large deviations principle for a multivariate
compound process induced by a multivariate Hawkes process with random marks.
Our proof hinges on showing essential smoothness of the limiting cumulant of
the multivariate compound process, resolving the inherent complication that
this cumulant is implicitly characterized through a fixed-point representation.
We employ the large deviations principle to derive logarithmic asymptotic
results on the marginal ruin probabilities of the associated multivariate risk
process. We also show how to conduct rare event simulation in this multivariate
setting using importance sampling and prove the asymptotic efficiency of our
importance sampling based estimator. The paper is concluded with a systematic
assessment of the performance of our rare event simulation procedure.",2211.16848v2
2022-12-15,Vanishing RKKY interactions in Ce-based cage compounds,"We report the results of thermodynamic measurements in external magnetic
field of the cubic Ce-based cage compounds Ce$T_{2}$Cd$_{20}$ ($T$ = Ni,Pd).
Our analysis of the heat-capacity data shows that the $\Gamma_7$ doublet is the
ground state multiplet of the Ce$^{3+}$ ions. Consequently, for the $\Gamma_7$
doublet it can be theoretically shown that the Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction between the localized Ce moments mediated by the conduction
electrons, must vanish at temperatures much lower than the energy separating
the ground state doublet from the first excited $\Gamma_8$ quartet. Our
findings provide an insight as to why no long range order has been observed in
these compounds down to temperatures in the millikelvin range.",2212.07586v1
2022-12-23,Statistical inference with normal-compound gamma priors in regression models,"Scale-mixture shrinkage priors have recently been shown to possess robust
empirical performance and excellent theoretical properties such as model
selection consistency and (near) minimax posterior contraction rates. In this
paper, the normal-compound gamma prior (NCG) resulting from compounding on the
respective inverse-scale parameters with gamma distribution is used as a prior
for the scale parameter. Attractiveness of this model becomes apparent due to
its relationship to various useful models. The tuning of the hyperparameters
gives the same shrinkage properties exhibited by some other models. Using
different sets of conditions, the posterior is shown to be both strongly
consistent and have nearly-optimal contraction rates depending on the set of
assumptions. Furthermore, the Monte Carlo Markov Chain (MCMC) and Variational
Bayes algorithms are derived, then a method is proposed for updating the
hyperparameters and is incorporated into the MCMC and Variational Bayes
algorithms. Finally, empirical evidence of the attractiveness of this model is
demonstrated using both real and simulated data, to compare the predicted
results with previous models.",2212.13144v1
2022-12-27,Conjugate Bayesian analysis of compound-symmetric Gaussian models,"We discuss Bayesian inference for a known-mean Gaussian model with a compound
symmetric variance-covariance matrix. Since the space of such matrices is a
linear subspace of that of positive definite matrices, we utilize the methods
of Pisano (2022) to decompose the usual Wishart conjugate prior and derive a
closed-form, three-parameter, bivariate conjugate prior distribution for the
compound-symmetric half-precision matrix. The off-diagonal entry is found to
have a non-central Kummer-Beta distribution conditioned on the diagonal, which
is shown to have a gamma distribution generalized with Gauss's hypergeometric
function. Such considerations yield a treatment of maximum a posteriori
estimation for such matrices in Gaussian settings, including the Bayesian
evidence and flexibility penalty attributable to Rougier and Priebe (2019). We
also demonstrate how the prior may be utilized to naturally test for the
positivity of a common within-class correlation in a random-intercept model
using two data-driven examples.",2212.13612v2
2022-12-30,Preparation of CuxCe$_{0.3-X}$Ni$_{0.7}$Fe$_2$O$_4$ ferrite nanoparticles as a nitrogen dioxide gas sensor,"In this work, the ferrite nanocomposite CuxCe$_{0.3-X}$Ni$_{0.7}$Fe$_2$O$_4$
is prepared (where: x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) was prepared using the
auto combustion technique (sol-gel), and citric acid was utilized as the fuel
for Auto combustion. The results of X-ray diffraction (XRD), emitting field
scanning electron microscope (FE-SEM), and energy dispersive X-ray analyzer
(EDX) tests revealed that the prepared compound has a face-centered cubic
structure (FCC) polycrystalline, and the lattice constant increases with an
increase in the percentage of doping for the copper ion, and decreases for the
cerium ion and that the compound is porous, and its molecules are spherical,
and there are no additional elements present other than those used in the
synthesis of the compound, indicating that it is of high purity, and the
combination has a high sensitivity to Nitrogen dioxide (NO$_2$) gas, as
determined by the gas detecting equipment.",2212.14861v1
2023-01-06,Multi-Genre Music Transformer -- Composing Full Length Musical Piece,"In the task of generating music, the art factor plays a big role and is a
great challenge for AI. Previous work involving adversarial training to produce
new music pieces and modeling the compatibility of variety in music (beats,
tempo, musical stems) demonstrated great examples of learning this task. Though
this was limited to generating mashups or learning features from tempo and key
distributions to produce similar patterns. Compound Word Transformer was able
to represent music generation task as a sequence generation challenge involving
musical events defined by compound words. These musical events give a more
accurate description of notes progression, chord change, harmony and the art
factor. The objective of the project is to implement a Multi-Genre Transformer
which learns to produce music pieces through more adaptive learning process
involving more challenging task where genres or form of the composition is also
considered. We built a multi-genre compound word dataset, implemented a linear
transformer which was trained on this dataset. We call this Multi-Genre
Transformer, which was able to generate full length new musical pieces which is
diverse and comparable to original tracks. The model trains 2-5 times faster
than other models discussed.",2301.02385v1
2023-01-26,Joint action loss for proximal policy optimization,"PPO (Proximal Policy Optimization) is a state-of-the-art policy gradient
algorithm that has been successfully applied to complex computer games such as
Dota 2 and Honor of Kings. In these environments, an agent makes compound
actions consisting of multiple sub-actions. PPO uses clipping to restrict
policy updates. Although clipping is simple and effective, it is not efficient
in its sample use. For compound actions, most PPO implementations consider the
joint probability (density) of sub-actions, which means that if the ratio of a
sample (state compound-action pair) exceeds the range, the gradient the sample
produces is zero. Instead, for each sub-action we calculate the loss
separately, which is less prone to clipping during updates thereby making
better use of samples. Further, we propose a multi-action mixed loss that
combines joint and separate probabilities. We perform experiments in
Gym-$\mu$RTS and MuJoCo. Our hybrid model improves performance by more than
50\% in different MuJoCo environments compared to OpenAI's PPO benchmark
results. And in Gym-$\mu$RTS, we find the sub-action loss outperforms the
standard PPO approach, especially when the clip range is large. Our findings
suggest this method can better balance the use-efficiency and quality of
samples.",2301.10919v1
2023-03-08,Spontaneous off-stoichiometry as the knob to control dielectric properties of gapped metals,"Using the first-principles calculations and La3Te4 as an example of an n-type
gapped metal, we demonstrate that gapped metals can develop spontaneous defect
formation resulting in off-stoichiometric compounds. Importantly, these
compounds have different free carrier concentrations and can be realized by
optimizing synthesis conditions. The ability to manipulate the free carrier
concentration allows to tailor intraband and interband transitions, thus
controlling the optoelectronic properties of materials in general.
Specifically, by realizing different off-stochiometric La3-xTe4 compounds, it
is possible to reach specific crossings of the real part of the dielectric
function with the zero line, reduce plasma frequency contribution to absorption
spectra, or, more generally, induce metal-to-insulator transition. This is
particularly important in the context of optoelectronic, plasmonic, and
epsilon-near-zero materials, as it enables materials design with a target
functionality. While this work is limited to the specific gapped metal, we
demonstrate that the fundamental physics is transferable to other gapped metals
and can be generally used to design a wide class of new
optoelectronic/plasmonic materials.",2303.04872v1
2023-03-17,Towards a Foundation Model for Neural Network Wavefunctions,"Deep neural networks have become a highly accurate and powerful wavefunction
ansatz in combination with variational Monte Carlo methods for solving the
electronic Schr\""odinger equation. However, despite their success and favorable
scaling, these methods are still computationally too costly for wide adoption.
A significant obstacle is the requirement to optimize the wavefunction from
scratch for each new system, thus requiring long optimization. In this work, we
propose a novel neural network ansatz, which effectively maps uncorrelated,
computationally cheap Hartree-Fock orbitals, to correlated, high-accuracy
neural network orbitals. This ansatz is inherently capable of learning a single
wavefunction across multiple compounds and geometries, as we demonstrate by
successfully transferring a wavefunction model pre-trained on smaller fragments
to larger compounds. Furthermore, we provide ample experimental evidence to
support the idea that extensive pre-training of a such a generalized
wavefunction model across different compounds and geometries could lead to a
foundation wavefunction model. Such a model could yield high-accuracy ab-initio
energies using only minimal computational effort for fine-tuning and evaluation
of observables.",2303.09949v1
2023-03-17,"On Trivalent Logics, Compound Conditionals, and Probabilistic Deduction Theorems","In this paper we recall some results for conditional events, compound
conditionals, conditional random quantities, p-consistency, and p-entailment.
Then, we show the equivalence between bets on conditionals and conditional
bets, by reviewing de Finetti's trivalent analysis of conditionals. But our
approach goes beyond de Finetti's early trivalent logical analysis and is based
on his later ideas, aiming to take his proposals to a higher level. We examine
two recent articles that explore trivalent logics for conditionals and their
definitions of logical validity and compare them with our approach to compound
conditionals. We prove a Probabilistic Deduction Theorem for conditional
events. After that, we study some probabilistic deduction theorems, by
presenting several examples. We focus on iterated conditionals and the
invalidity of the Import-Export principle in the light of our Probabilistic
Deduction Theorem. We use the inference from a disjunction, ""$A$ or $B$"", to
the conditional,""if not-$A$ then $B$"", as an example to show the invalidity of
the Import-Export principle. We also introduce a General Import-Export
principle and we illustrate it by examining some p-valid inference rules of
System P. Finally, we briefly discuss some related work relevant to AI.",2303.10268v1
2023-03-21,Lu-H-N phase diagram from first-principles calculations,"Using a comprehensive structure search and high-throughput first-principles
calculations of 1483 compounds, this study presents the phase diagram of
Lu-H-N. The formation energy landscape of Lu-H-N was derived and utilized to
assess the thermodynamic stability of compounds. Results indicate that there
are no stable Lu-H-N ternary structures in this system, but metastable ternary
structures, such as Lu20H2N17 (C2/m), Lu2H2N (P3-m1), were observed with small
Ehull (< 100 meV/atom). Moreover, applying hydrostatic pressure up to 10 GPa
causes the energy convex hull of the Lu-H-N to shift its shape and stabilizes
binary phases such as LuN9 and Lu10H21. Additionally, interstitial empty sites
in LuH2 were noted, which may explain the formation of Lu10H21 and LuH3-xNy. To
provide a basis for comparison, X-ray diffraction patterns and electronic
structures of some compounds are also presented.",2303.11683v2
2023-04-27,Spin-Peierls transition to a Haldane phase,"We present an organic compound exhibiting a spin-Peierls (SP) transition to
an effective spin-1 antiferromagnetic uniform chain, that is, the Haldane
chain. The clear disappearance of magnetization, accompanied by a structural
phase transition, is well explained by the deformation to an effective spin-1
Haldane chain. The flexibility of the molecular orbitals in the organic radical
compound allows the transformation of the exchange interactions into the
Haldane state with different topologies. The SP transition in the present
compound demonstrates a mechanism different from that of the conventional
systems, paving another path for research in quantum phenomena originating from
spin-lattice couplings.",2304.13970v1
2023-05-14,A Stochastic Compound Failure Model for Testing Resilience of Autonomous Fixed-Wing Aircraft I: Formulation and Simulation,"This paper presents a Markov chain model to dynamically emulate the effects
of adverse (failure) flight conditions on fixed-wing, autonomous aircraft
system actuators. It implements a PX4 Autopilot flight stack module that
perturbs the attitude control inputs to the plane's actuator mixer. We apply
this approach in simulation on a fixed-wing autonomous aircraft to test the
controller response to stochastic compound failures on a range of turning
radii. Statistical measures of the differences between target and simulated
flight paths demonstrate that a well-tuned PID controller remains competitive
with adaptive control in a cascading, compound, transient failure regime.",2305.08262v2
2023-06-08,SequenceMatch: Imitation Learning for Autoregressive Sequence Modelling with Backtracking,"In many domains, autoregressive models can attain high likelihood on the task
of predicting the next observation. However, this maximum-likelihood (MLE)
objective does not necessarily match a downstream use-case of autoregressively
generating high-quality sequences. The MLE objective weights sequences
proportionally to their frequency under the data distribution, with no guidance
for the model's behaviour out of distribution (OOD): leading to compounding
error during autoregressive generation. In order to address this compounding
error problem, we formulate sequence generation as an imitation learning (IL)
problem. This allows us to minimize a variety of divergences between the
distribution of sequences generated by an autoregressive model and sequences
from a dataset, including divergences with weight on OOD generated sequences.
The IL framework also allows us to incorporate backtracking by introducing a
backspace action into the generation process. This further mitigates the
compounding error problem by allowing the model to revert a sampled token if it
takes the sequence OOD. Our resulting method, SequenceMatch, can be implemented
without adversarial training or major architectural changes. We identify the
SequenceMatch-$\chi^2$ divergence as a more suitable training objective for
autoregressive models which are used for generation. We show that empirically,
SequenceMatch training leads to improvements over MLE on text generation with
language models.",2306.05426v2
2023-06-13,Multi-objective Molecular Optimization for Opioid Use Disorder Treatment Using Generative Network Complex,"Opioid Use Disorder (OUD) has emerged as a significant global public health
issue, with complex multifaceted conditions. Due to the lack of effective
treatment options for various conditions, there is a pressing need for the
discovery of new medications. In this study, we propose a deep generative model
that combines a stochastic differential equation (SDE)-based diffusion modeling
with the latent space of a pretrained autoencoder model. The molecular
generator enables efficient generation of molecules that are effective on
multiple targets, specifically the mu, kappa, and delta opioid receptors.
Furthermore, we assess the ADMET (absorption, distribution, metabolism,
excretion, and toxicity) properties of the generated molecules to identify
drug-like compounds. To enhance the pharmacokinetic properties of some lead
compounds, we employ a molecular optimization approach. We obtain a diverse set
of drug-like molecules. We construct binding affinity predictors by integrating
molecular fingerprints derived from autoencoder embeddings, transformer
embeddings, and topological Laplacians with advanced machine learning
algorithms. Further experimental studies are needed to evaluate the
pharmacological effects of these drug-like compounds for OUD treatment. Our
machine learning platform serves as a valuable tool in designing and optimizing
effective molecules for addressing OUD.",2306.07484v1
2023-06-21,Designing Pr-based Advanced Photoluminescent Materials using Machine Learning and Density Functional Theory,"This work presents a machine learning approach to predict novel perovskite
oxide materials in the Pr-Al-O and Pr-Sc-O compound families with the potential
for photoluminescence applications. The predicted materials exhibit a large
bandgap and high Debye temperature, and have remained unexplored thus far. The
predicted compounds (Pr$_3$AlO$_6$, Pr$_4$Al$_2$O$_9$, Pr$_3$ScO$_6$ and
Pr$_3$Sc$_5$O$_{12}$) are screened using machine learning approach, which are
then confirmed by density functional theory calculations. The study includes
the calculation of the bandgap and density of states to determine electronic
properties, and the optical absorption and emission spectra to determine
optical properties. Mechanical stability of the predicted compounds, as
demonstrated by satisfying the Born-Huang criterion. By combining machine
learning and density functional theory, this work offers a more efficient and
comprehensive approach to materials discovery and design.",2306.11978v1
2023-06-24,Limits of stability for compounds of pentavalent praseodymium,"Eleven possible candidates for compounds of pentavalent praseodymium were
investigated with relativistic density functional theory using the B3LYP
functional with ZORA scalar relativistic correction and including spin orbit
coupling effects. Two of those candidates had previously been synthesized and
another two of them were previously theoretically predicted. Three new species
were proposed here as possible candidates for the compounds of Pr in its fifth
oxidation state: PrF4+, PrO2F2- and PrOF2+. The main technical obstacle in
synthesizing these ions is their high reactivity due to large electron
affinity; decomposition via bimolecular reaction pathways and low energy of
excitation to the triplet state constitute other stability limiting factors.",2306.13939v1
2023-07-03,Unveiling Real Triple Degeneracies in Crystals: Exploring Link and Compound Structures,"With their non-Abelian topological charges, real multi-bandgap systems
challenge the conventional topological phase classifications. As the minimal
sector of multi-bandgap systems, real triple degeneracies (RTPs), which serve
as real 'Weyl points', lay the foundation for the research on real topological
phases. However, experimental demonstration of physical systems with global
band configurations consisting of multiple RTPs in crystals has not been
reported. Here we present experimental evidence of RTPs in photonic
meta-crystals, characterizing them using the Euler number, and establishing
their connection with both Abelian and non-Abelian charges. By considering RTPs
as the basic elements, we further propose the concept of a topological
compound, akin to a chemical compound, where we find that certain phases are
not topologically allowed. The topological classification of RTPs in crystals
demonstrated in our work plays a similar role as the 'no-go' theorem in Weyl
systems.",2307.01228v2
2023-07-06,Misfit layer compounds as ultra-tunable field effect transistors: from charge transfer control to emergent superconductivity,"Misfit layer compounds are heterostructures composed of rocksalt units
stacked with few layers transition metal dichalcogenides. They host Ising
superconductivity, charge density waves and good thermoelectricity. The design
of misfits emergent properties is, however, hindered by the lack of a global
understanding of the electronic transfer among the constituents. Here, by
performing first principles calculations, we unveil the mechanism controlling
the charge transfer and demonstrate that rocksalt units are always donor and
dichalcogenides acceptors. We show that misfits behave as a periodic
arrangement of ultra-tunable field effect transistors where a charging as large
as 6\times10^{14} e^-cm^{-2} can be reached and controlled efficiently by the
La-Pb alloying in the rocksalt. Finally, we identify a strategy to design
emergent superconductivity and demonstrate its applicability in
(LaSe)_{1.27}(SnSe_2)_2. Our work paves the way to the design synthesis of
misfit compounds with tailored physical properties.",2307.02886v1
2023-07-08,Superconducting Gap Structure of Filled Skutterudite LaOs$_4$As$_{12}$ Compound through $μ$SR Investigations,"Filled skutterudite compounds have gained attention recently as an innovative
platforms for studying intriguing low-temperature superconducting properties.
Regarding the symmetry of the superconducting gap, contradicting findings from
several experiments have been made for LaRu$_{4}$As$_{12}$ and its
isoelectronic counterpart, LaOs$_{4}$As$_{12}$. In this vein, we report
comprehensive bulk and microscopic results on LaOs$_{4}$As$_{12}$ utilizing
specific heat analysis and muon-spin rotation/relaxation ($\mu$SR)
measurements. Bulk superconductivity with $T_C$ = 3.2 K was confirmed by heat
capacity. The superconducting ground state of the filled-skutterudite
LaOs$_{4}$As$_{12}$ compound is found to have two key characteristics:
superfluid density exhibits saturation type behavior at low temperature, which
points to a fully gapped superconductivity with gap value of $2\Delta/k_BT_C$ =
3.26; additionally, the superconducting state does not show any sign of
spontaneous magnetic field, supporting the preservation of time-reversal
symmetry. These results open the door for the development of La-based
skutterudites as special probes for examining the interplay of single- and
multiband superconductivity in classical electron-phonon systems.",2307.03946v1
2023-07-09,Profiling Of Volatiles In Tissues Of Salacia Reticulata Wight. With Anti-Diabetic Potential Using GC-MS And Molecular Docking,"Type 2 diabetes mellitus is a global pandemic, it is a chronic, progressive
and an incompletely understood metabolic condition. The disease is
characterized by higher levels of sugar in blood caused either due to
insufficient production of insulin or because of insulin resistance. Major
drugs used for the treatment of the condition are fraught with side effects.
Hence, it is becoming an obligation to gaze at alternative agents showing
marginal adverse effects. An important source of such agents are the medicinal
plants. Several plants have been positively identified to show anti-diabetic
effects. The species Salacia reticulata Wight., belonging to the family
Celastraceae which is found in the forests of Southern India is one such
promising plant to tackle type 2 diabetics. In this study, numerous volatile
compounds were identified from various tissues through GC-MS analysis. Among
these the compounds possessed suitable ADMET properties, and high binding
affinities were compared with two approved {\alpha}-glucosidase inhibitors,
Acarbose and Miglitol. The analysis indicated that the compounds with PubChem
IDs, CID-240051 and CID-533471 exhibited potential as inhibitors of Human
Maltase-Glucoamylase enzyme.",2307.04109v1
2023-07-12,Purely antiferromagnetic frustrated Heisenberg model in spin ladder compound BaFe$_2$Se$_3$,"The spin dynamics in the block magnetic phase of the iron-based ladder
compound \bfs\ has been studied by means of single crystal inelastic neutron
scattering. Using linear spin wave theory and Monte-Carlo simulations, our
analysis points to a magnetic Heisenberg model with effective frustrated
antiferromagnetic couplings only, able to describe both the exotic block order
and its dynamics. This new and purely antiferromagnetic picture offers a
fruitful perspective to describe multiferroic properties but also understand
the origin of the stripe-like magnetic instability observed under pressure as
well as in other parent compounds with similar crystalline structure.",2307.06193v1
2023-07-13,Zero-field magnetic structure and metamagnetic phase transitions of the cobalt chain compound Li$_2$CoCl$_4$,"Exploring the uncharacterized magnetic phases of Co$^{2+}$ chain compounds is
critical for finding new low-dimensional magnets hosting quantized excitations.
We map the unexplored magnetic phases of the Co$^{2+}$ chain compound
Li$_2$CoCl$_4$. Magnetometry reveals magnetic ordering below 7 K with a
metamagnetic transition near 16.5 kOe and a gradual transition to a
field-aligned paramagnetic state above 31 kOe. Curie-Weiss fits to the high
temperature susceptibility reveal a high-spin (spin-$\frac{3}{2}$) state for
cobalt. Heat capacity data, though, give a magnetic entropy change of 5.46
J/mol, consistent with cobalt effective spin-$\frac{1}{2}$ systems. To
characterize the zero-field antiferromagnetic ordering, we separately
calculated the energy of proposed magnetic structures with density functional
theory and collected 3.5 K neutron diffraction data, finding that
Li$_2$CoCl$_4$ has ferromagnetic chains with antiferromagnetic interactions
between them. Increasing field rotates these spin chains, producing the
antiferromagnetic to intermediate to paramagnetic transition sequence.",2307.06899v1
2023-07-24,Vibrational Entropic Stabilization of Layered Chalcogenides: From Ordered Vacancy Compounds to 2D Layers,"Despite the rapid pace of computationally and experimentally discovering new
two-dimensional layered materials, a general criteria for a given compound to
prefer a layered structure over a non-layered one remains unclear. Articulating
such criteria would allow one to identify materials at the verge of an
inter-dimensional structural phase transition between a 2D layered phase and 3D
bulk one, with potential applications in phase change memory devices. Here we
identify a general stabilization effect driven by vibrational entropy that can
favor 2D layered structures over 3D bulk structures at higher temperatures,
which can manifest in ordered vacancy compounds where phase competition is
tight. We demonstrate this vibrational-entropy stabilization effect for three
prototypical ordered vacancy chalcogenides, ZnIn2S4 and In2S3, and Cu3VSe4,
either by vacancy rearrangement or by cleaving through existing vacancies. The
relative vibrational entropy advantage of the 2D layered phase originates
mainly from softened out-of-plane dilation phonon modes.",2307.12640v1
2023-07-27,The rule of four: anomalous stoichiometries of inorganic compounds,"Why are materials with specific characteristics more abundant than others?
This is a fundamental question in materials science and one that is
traditionally difficult to tackle, given the vastness of compositional and
configurational space. We highlight here the anomalous abundance of inorganic
compounds whose primitive unit cell contains a number of atoms that is a
multiple of four. This occurrence - named here the 'rule of four' - has to our
knowledge not previously been reported or studied. Here, we first highlight the
rule's existence, especially notable when restricting oneself to experimentally
known compounds, and explore its possible relationship with established
descriptors of crystal structures, from symmetries to energies. We then
investigate this relative abundance by looking at structural descriptors, both
of global (packing configurations) and local (the smooth overlap of atomic
positions) nature. Contrary to intuition, the overabundance does not correlate
with low-energy or high-symmetry structures; in fact, structures which obey the
'rule of four' are characterized by low symmetries and loosely packed
arrangements maximizing the free volume. We are able to correlate this
abundance with local structural symmetries, and visualize the results using a
hybrid supervised-unsupervised machine learning method.",2307.14742v1
2023-09-03,Phase space geometry of general quantum energy transitions,"The mixed density operator for coarsegrained eigenlevels of a static
Hamiltonian is represented in phase space by the spectral Wigner function,
which has its peak on the corresponding classical energy shell. The action of
trajectory segments along the shell determine the phase of the Wigner
oscillations in its interior. The classical transitions between any pair of
energy shells, driven by a general external time dependent Hamiltonian, also
have a smooth probability density. It is shown here that a further contribution
to the transition between the corresponding pair of coarsegrained energy
levels, which oscillates with either energy, or the driving time, is determined
by four trajectory segments (two in the pair of energy shells and two generated
by the driving Hamiltonian) that join exactly to form a closed compound orbit.
In its turn, this sequence of segments belongs to the semiclassical expression
of a compound unitary operator that combines four quantum evolutions: a pair
generated by the static internal Hamiltonian and a pair generated by the
driving Hamiltonian. The closed compound orbits are shown to belong to
continuous families, which are initially seeded at points where the classical
flow generated by both Hamiltonians commute.",2309.01178v2
2023-09-07,T2IW: Joint Text to Image & Watermark Generation,"Recent developments in text-conditioned image generative models have
revolutionized the production of realistic results. Unfortunately, this has
also led to an increase in privacy violations and the spread of false
information, which requires the need for traceability, privacy protection, and
other security measures. However, existing text-to-image paradigms lack the
technical capabilities to link traceable messages with image generation. In
this study, we introduce a novel task for the joint generation of text to image
and watermark (T2IW). This T2IW scheme ensures minimal damage to image quality
when generating a compound image by forcing the semantic feature and the
watermark signal to be compatible in pixels. Additionally, by utilizing
principles from Shannon information theory and non-cooperative game theory, we
are able to separate the revealed image and the revealed watermark from the
compound image. Furthermore, we strengthen the watermark robustness of our
approach by subjecting the compound image to various post-processing attacks,
with minimal pixel distortion observed in the revealed watermark. Extensive
experiments have demonstrated remarkable achievements in image quality,
watermark invisibility, and watermark robustness, supported by our proposed set
of evaluation metrics.",2309.03815v1
2023-09-13,Large Diameter Bulk Crystal Growth and Scintillation Characterization of Thallium-Based Ternary Halide Crystals for Detection and Imaging,"Scintillators cover an important wide range of applications in detection and
imaging. In this paper we are presenting growth and performance results of
several advanced large diameter thallium-based ternary halide crystals are
presented. Intrinsic crystals of TlMgCl3, TlCaCl3, TlCaBr3, and TlCa(Cl,Br)3,
as well as europium-doped TlCa2Br5 and TlCa(Cl,Br)3 are melt-grown by the
Bridgman method. These compounds have high Zeff due to thallium and expected to
have high physical densities. The best crystal quality and energy resolution
(FWHM) at 662 keV are observed for intrinsic TlMgCl3. The primary decay
constants for these compounds are in the range of 0.45 to 0.55 microseconds.
All of these compounds have proportional or linear response to gamma-ray above
100 keV.",2309.07093v1
2023-09-19,Prediction of superconductivity in metallic boron-carbon compounds from 0 to 100 GPa by high-throughput screening,"Boron carbon compounds have been shown to have feasible superconductivity. In
our earlier paper [Zheng et al., Phys. Rev. B 107, 014508 (2023)], we
identified a new conventional superconductor of LiB3C at 100 GPa. Here, we aim
to extend the investigation of possible superconductivity in this structural
framework by replacing Li atoms with 27 different cations under pressures
ranging from 0 to 100 GPa. Using the high-throughput screening method of
zone-center electron-phonon interaction, we find that ternary compounds like
CaB3C, SrB3C, TiB3C, and VB3C are promising candidates for superconductivity.
The consecutive calculations using the full Brillouin zone confirm that they
have Tc < 31 K at moderate pressures. Our study demonstrates that fast
screening of superconductivity by calculating zone-center electron-phonon
coupling strength is an effective strategy for high-throughput identification
of new superconductors.",2309.10274v1
2023-09-19,Stability of AuSn$_{4}$ compound in low temperature,"$\mathrm{AuSn_4}$ is the example of an orthorhombic compound that exhibits
topological properties. Recent XRD measurements reveal an ambiguous nature of
the crystal structure, as it can be realized with either Aea2 or Ccca symmetry.
Motivated by this, we analyze the dynamical stability of the compound with
these symmetries. Interestingly, our main result indicates that
$\mathrm{AuSn_4}$ is unstable with both Aea2 and Ccca symmetries, due to the
soft modes in the phonon spectra. We find that the $\mathrm{AuSn_4}$ can be
stable with Pbcm at low temperatures using the soft mode analysis. We also show
that the theoretical electronic spectra are well reproduced, and have a good
resemblance with the experimental ARPES spectra. Our findings may be valuable
to the theoretical investigations of $\mathrm{AuSn_4}$ in future.",2309.10571v1
2023-10-02,Estimation of In-Vitro Free Radical Scavenging and Cytotoxic Activities of Thiocarbohydrazones Derivatives,"Objective: To investigate free radical scavenging potential of
thiocarbohydrazones derivatives for the discovery of antioxidant compounds of
synthetic origin. Method: Eighteen thiocarbohydrazones derivatives were
screened for antioxidant activities by using in vitro radical inhibition assay.
Cytotoxicity all derivatives were evaluated using invitro cytotoxicity assay on
mouse fibroblast cell line. Results: various compounds of the have shown
significant radical scavenging activities as compared with the standard drug
butylated hydroxytoluene. In addition in an in vitro cell cytotoxicity assay
selected analogues were found to be non-cytotoxic against fibroblast 3T3 cell
line. Conclusion: Taken together, these findings all compound this series could
be further evaluated in in vivo model of oxidative stress to develop as a
therapeutic agent against oxidative stress related disorders due to exhibiting
excellent free radical scavenging properties and having their non cytotoxic
nature against normal cells.",2310.00939v1
2023-10-02,"Benzophenone Semicarbazones as Potential alpha-glucosidase and Prolyl Endopeptidase Inhibitor: In-vitro free radical scavenging, enzyme inhibition, mechanistic, and molecular docking studies","$\alpha$-glucosidase and prolylendopeptidase has altered expression and
activity patterns in neurological disease, type 2diabetes respectively and
several cancers. Here we screened a series 1-29 benzophenone semicarbazone
derivatives for in vitro free radical scavenging, alpha-glucosidase and
prolylendopeptidase inhibition activities. Seven derivatives were identified as
potential free radical scavengers, 14 as alpha-glucosidase, and 9 as
prolylendopeptidase inhibitors. Kinetic studies on the most promising
inhibitors were performed. Compounds 23, 27, 25 and 28 were found as inhibitor
of alpha-glucosidase, while compound 26 inhibited both prolylendopeptidase and
alpha-glucosidase. The binding modes and binding free energy of the multi
targeted inhibitor 26 were predicted by molecular docking studies. These
results provide insights on prolylendopeptidase and alpha-glucosidase
inhibition of compound 26 for further development as therapeutic agents for
neoplastic, neurological, and endocrine disorders.",2310.00947v1
2023-10-06,"Weberite Na$_2$MM'F$_7$ (M,M'=Redox-Active Metal) as Promising Fluoride-Based Sodium-Ion Battery Cathodes","Sodium-ion batteries are a viable alternative to lithium-ion technology due
to the plentiful sodium resources. However, certain commercialization
challenges, such as low specific energies and poor cycling performance of
current Na-ion cathodes, still need to be addressed. To overcome these hurdles,
this study explored the potential of a novel class of fluoride-based materials,
specifically trigonal-type Na$_2$MM'F$_7$ (M and M' are redox-active metals)
belonging to the weberite-type compounds, as promising candidates for Na-ion
cathodes. Through a comprehensive assessment utilizing ab initio calculations,
twelve prospective compounds were identified, demonstrating high thermodynamic
stability, large gravimetric capacities (>170 mAh/g), and low net Na-ion
migration barriers (<600 meV). Significantly, ten out of the twelve screened
compounds exhibit high specific energies exceeding 580 Wh/kg (approximately
equals to the specific energy of LiFePO$_4$), indicating their exceptional
electrochemical performance. This study will pave the way for further
advancements in fluoride-based electrode materials.",2310.04222v1
2023-10-09,Molecular De Novo Design through Transformer-based Reinforcement Learning,"In this work, we introduce a method to fine-tune a Transformer-based
generative model for molecular de novo design. Leveraging the superior sequence
learning capacity of Transformers over Recurrent Neural Networks (RNNs), our
model can generate molecular structures with desired properties effectively. In
contrast to the traditional RNN-based models, our proposed method exhibits
superior performance in generating compounds predicted to be active against
various biological targets, capturing long-term dependencies in the molecular
structure sequence. The model's efficacy is demonstrated across numerous tasks,
including generating analogues to a query structure and producing compounds
with particular attributes, outperforming the baseline RNN-based methods. Our
approach can be used for scaffold hopping, library expansion starting from a
single molecule, and generating compounds with high predicted activity against
biological targets.",2310.05365v5
2023-10-18,Mack's estimator motivated by large exposure asymptotics in a compound Poisson setting,"The distribution-free chain ladder of Mack justified the use of the chain
ladder predictor and enabled Mack to derive an estimator of conditional mean
squared error of prediction for the chain ladder predictor. Classical insurance
loss models, i.e. of compound Poisson type, are not consistent with Mack's
distribution-free chain ladder. However, for a sequence of compound Poisson
loss models indexed by exposure (e.g. number of contracts), we show that the
chain ladder predictor and Mack's estimator of conditional mean squared error
of prediction can be derived by considering large exposure asymptotics. Hence,
quantifying chain ladder prediction uncertainty can be done with Mack's
estimator without relying on the validity of the model assumptions of the
distribution-free chain ladder.",2310.12056v1
2023-10-05,Zero-shot Learning of Drug Response Prediction for Preclinical Drug Screening,"Conventional deep learning methods typically employ supervised learning for
drug response prediction (DRP). This entails dependence on labeled response
data from drugs for model training. However, practical applications in the
preclinical drug screening phase demand that DRP models predict responses for
novel compounds, often with unknown drug responses. This presents a challenge,
rendering supervised deep learning methods unsuitable for such scenarios. In
this paper, we propose a zero-shot learning solution for the DRP task in
preclinical drug screening. Specifically, we propose a Multi-branch
Multi-Source Domain Adaptation Test Enhancement Plug-in, called MSDA. MSDA can
be seamlessly integrated with conventional DRP methods, learning invariant
features from the prior response data of similar drugs to enhance real-time
predictions of unlabeled compounds. We conducted experiments using the GDSCv2
and CellMiner datasets. The results demonstrate that MSDA efficiently predicts
drug responses for novel compounds, leading to a general performance
improvement of 5-10\% in the preclinical drug screening phase. The significance
of this solution resides in its potential to accelerate the drug discovery
process, improve drug candidate assessment, and facilitate the success of drug
discovery.",2310.12996v1
2023-10-29,Valence band electronic structure of Pd based ternary chalcogenide superconductors,"We present a comparative study of the valence band electronic structure of Pd
based ternary chalcogenide superconductors Nb2Pd0.95S5, Ta2Pd0.97S6 and
Ta2Pd0.97Te6 using experimental photoemission spectroscopy and density
functional based theoretical calculations. We observe a qualitatively
similarity between valence band (VB) spectra of Nb2Pd0.95S5 and Ta2Pd0.97S6.
Further, we find a pseudogap feature in Nb2Pd0.95S5 at low temperature, unlike
other two compounds. We have correlated the structural geometry with the
differences in VB spectra of these compounds. The different atomic packing in
these compounds could vary the strength of inter-orbital hybridization among
various atoms which leads to difference in their electronic structure as
clearly observed in our DOS calculations.",2310.19016v1
2023-10-29,Valence band electronic structure of Nb2Pd1.2Se5 and Nb2Pd0.95S5 superconductors,"We present a comparative study of our valence band photoemission results on
Nb2Pd1.2Se5 and Nb2Pd0.95S5 superconductors which is supported by our DFT based
electronic structure calculations. We observe that the VB spectra of both the
compounds are qualitatively similar, except slight difference in the binding
energy position of all features between the two compounds which could be the
result of different electronegativity of Se and S atom. The calculated density
of states reveal that the VB features are mainly composed of Pd Se S hybridized
states. The nature of DOS originating from the distinctly coordinated Pd atoms
is different. Further, the involvement of the various Pd 4d and Nb 4d states in
crossing of Fermi level signifies the multiband character of these compounds.
In addition, we find a temperature dependent pseudogap in Nb2Pd0.95S5 which is
absent in Nb2Pd1.2Se5.",2310.19082v1
2023-11-24,LLamol: A Dynamic Multi-Conditional Generative Transformer for De Novo Molecular Design,"Generative models have demonstrated substantial promise in Natural Language
Processing (NLP) and have found application in designing molecules, as seen in
General Pretrained Transformer (GPT) models. In our efforts to develop such a
tool for exploring the organic chemical space in search of potentially
electro-active compounds, we present ""LLamol"", a single novel generative
transformer model based on the LLama 2 architecture, which was trained on a 13M
superset of organic compounds drawn from diverse public sources. To allow for a
maximum flexibility in usage and robustness in view of potentially incomplete
data, we introduce ""Stochastic Context Learning"" as a new training procedure.
We demonstrate that the resulting model adeptly handles single- and
multi-conditional organic molecule generation with up to four conditions, yet
more are possible. The model generates valid molecular structures in SMILES
notation while flexibly incorporating three numerical and/or one token sequence
into the generative process, just as requested. The generated compounds are
very satisfactory in all scenarios tested. In detail, we showcase the model's
capability to utilize token sequences for conditioning, either individually or
in combination with numerical properties, making LLamol a potent tool for de
novo molecule design, easily expandable with new properties.",2311.14407v1
2023-11-30,Combining deep generative models with extreme value theory for synthetic hazard simulation: a multivariate and spatially coherent approach,"Climate hazards can cause major disasters when they occur simultaneously as
compound hazards. To understand the distribution of climate risk and inform
adaptation policies, scientists need to simulate a large number of physically
realistic and spatially coherent events. Current methods are limited by
computational constraints and the probabilistic spatial distribution of
compound events is not given sufficient attention. The bottleneck in current
approaches lies in modelling the dependence structure between variables, as
inference on parametric models suffers from the curse of dimensionality.
Generative adversarial networks (GANs) are well-suited to such a problem due to
their ability to implicitly learn the distribution of data in high-dimensional
settings. We employ a GAN to model the dependence structure for daily maximum
wind speed, significant wave height, and total precipitation over the Bay of
Bengal, combining this with traditional extreme value theory for controlled
extrapolation of the tails. Once trained, the model can be used to efficiently
generate thousands of realistic compound hazard events, which can inform
climate risk assessments for climate adaptation and disaster preparedness. The
method developed is flexible and transferable to other multivariate and spatial
climate datasets.",2311.18521v1
2023-12-18,Quantum criticality in quasi-binary compounds of iron-based superconductors,"In this work, we present the studies of structural phase transitions in
Fe(Se,Te) crystals in the range of about 30% selenium substitution by
tellurium. We found a significant change in the properties of the ordered state
of these compositions compared to the case of pure FeSe. The resistivity at low
temperatures for the studied Fe(Se,Te) is proportional to the square of the
temperature while for pure FeSe below the structural transition it depends
almost linearly on temperature. The NMR data show a noticeable line broadening
below the structural transition and an anomaly in the temperature dependence of
the relaxation rate in the tellurium-substituted compounds, which was not
observed in the pure FeSe. This reveals in quasi-binary compounds of iron-based
superconductors a region of quantum criticality similar to that which exists
when the nematicity of FeSe is suppressed under pressure and which precedes the
emergence of high-temperature superconductivity in FeSe under hydrostatic
pressure.",2312.10901v1
2023-09-10,Predicting the activity of chemical compounds based on machine learning approaches,"Exploring methods and techniques of machine learning (ML) to address specific
challenges in various fields is essential. In this work, we tackle a problem in
the domain of Cheminformatics; that is, providing a suitable solution to aid in
predicting the activity of a chemical compound to the best extent possible. To
address the problem at hand, this study conducts experiments on 100 different
combinations of existing techniques. These solutions are then selected based on
a set of criteria that includes the G-means, F1-score, and AUC metrics. The
results have been tested on a dataset of about 10,000 chemical compounds from
PubChem that have been classified according to their activity",2401.01004v1
2024-01-05,Correlation-enhanced viable core in metabolic networks,"Cellular ingredient concentrations can be stabilized by adjusting generation
and consumption rates through multiple pathways. To explore the portion of
cellular metabolism equipped with multiple pathways, we categorize individual
metabolic reactions and compounds as viable or inviable: A compound is viable
if processed by two or more reactions, and a reaction is viable if all of its
substrates and products are viable. Using this classification, we identify the
maximal subnetwork of viable nodes, referred to as the {\it viable core}, in
bipartite metabolic networks across thousands of species. The obtained viable
cores are remarkably larger than those in degree-preserving randomized
networks, while their broad degree distributions commonly enable the viable
cores to shrink gradually as reaction nodes are deleted. We demonstrate that
the positive degree-degree correlations of the empirical networks may underlie
the enlarged viable cores compared to the randomized networks. By investigating
the relation between degree and cross-species frequency of metabolic compounds
and reactions, we elucidate the evolutionary origin of the correlations.",2401.02624v1
2024-01-15,Growth and Characterization of Superconducting Bulk Crystal [(SnSe)$_{1+δ}$]$_m$(NbSe$_2$) Misfit Layer Compounds,"[(SnSe)$_{1+\delta}$]$_m$(NbSe$_2$) ($m$ = 1-6, 8, and 12) highly orientated
crystals 1-2 mm in size and well-defined c-planes were successfully grown using
CsCl/KCl flux, including the first growth of crystals with $m = 12$. The
stacked layers along the $c$ axis in the obtained crystals were directly
observed by transmission electron microscopy as m alternating layers of SnSe
and single layers of NbSe$_2$. The superconducting transition temperature of
the obtained [(SnSe)$_{1+\delta}$]$_m$(NbSe$_2$) crystals decreased with an
increase in the number of SnSe layers per unit cell. As the superconducting
anisotropy parameters increase, a significant increase is observed between $m =
4$ and 5. This indicates that the superconducting dimensionality becomes more
two-dimensional with an increasing $m$.",2401.07407v1
2024-01-15,"Superconductivity in Breathing Kagome-Structured C14 Laves Phase XOs2(X = Zr, Hf)","Recently, the emergence of superconductivity in kagome metals has generated
significant interest due to its interaction with flat bands and topological
electronic states, which exhibit a range of unusual quantum characteristics.
This study thoroughly investigates largely unexplored breathing Kagome
structure C14 laves phase compounds XOs$_{2}$ (X = Zr, Hf) by XRD, electrical
transport, magnetization, and specific heat measurements. Our analyses confirm
the presence of the MgZn$_{2}$-type structure in ZrOs$_{2}$ and HfOs$_{2}$
compounds, exhibiting type-II superconductivity with critical temperature
(T$_{C}$) values of 2.90(3) K and 2.69(6) K, respectively. Furthermore,
specific heat measurements and an electron-phonon coupling constant suggest the
presence of weakly coupled BCS superconductivity in both compounds.",2401.07610v1
2024-01-19,Extremely strong spin-orbit coupling effect in light element altermagnetic materials,"Spin-orbit coupling is a key to realize many novel physical effects in
condensed matter physics, but the mechanism to achieve strong spin-orbit
coupling effect in light element antiferromagnetic compounds has not been
explored. In this work, based on symmetry analysis and the first-principles
electronic structure calculations, we demonstrate that strong spin-orbit
coupling effect can be realized in light element altermagnetic materials, and
propose a mechanism for realizing the corresponding effective spin-orbit
coupling. This mechanism reveals the cooperative effect of crystal symmetry,
electron occupation, electronegativity, electron correlation, and intrinsic
spin-orbit coupling. Our work not only promotes the understanding of light
element compounds with strong spin-orbit coupling effect, but also provides an
alternative for realizing light element compounds with an effective strong
spin-orbit coupling.",2401.11065v1
2024-01-24,High-throughput screening for boride superconductors,"A high-throughput screening using density functional calculations is
performed to search for stable boride superconductors from the existing
materials database. The workflow employs the fast frozen phonon method as the
descriptor to evaluate the superconducting properties quickly. 23 stable
candidates are identified from the screening. For almost all found binary
compounds, the superconductivity was obtained earlier experimentally or
computationally. For ternary borides, previous studies are very limited. Our
extensive search among ternary systems confirmed superconductivity in known
systems and found several new compounds. Among these discovered superconducting
ternary borides, Ta(MoB)$_2$ shows the highest superconducting temperature of
~12K. Most predicted compounds were synthesized previously; therefore, our
predictions can be examined experimentally. Our work also demonstrates that the
boride systems can have diverse structural motifs that lead to
superconductivity.",2401.13211v1
2024-01-24,Quantum Oscillations in kagome metals CsTi3Bi5 and RbTi3Bi5,"We report quantum oscillation measurements on the kagome compounds
ATi$_3$Bi$_5$ (A=Rb, Cs) in magnetic fields up to 41.5 T and temperatures down
to 350 mK. In addition to the frequencies observed in previous studies, we have
observed multiple unreported frequencies above 2000 T in CsTi$_3$Bi$_5$ using a
tunnel diode oscillator technique. We compare these results against density
functional theory calculations and find good agreement with the calculations in
the number of peaks observed, frequency, and the dimensionality of the Fermi
surface. For RbTi$_3$Bi$_5$ we have obtained a different quantum oscillation
spectrum, although calculated quantum oscillation frequencies for the Rb
compound are remarkably similar to the Cs compound, calling for further
studies.",2401.13628v1
2024-02-10,"All ""roads"" lead to rocksalt structure","Rocksalt is the most common crystal structure among binary compounds.
Moreover, no long-lived, metastable polymorphs are observed in compounds with
the rocksalt ground state. We investigate the absence of polymorphism and the
dominance of the rocksalt structure via first-principles random structure
sampling and transformation kinetics modeling of three rocksalt compounds: MgO,
TaC, and PbTe. Random structure sampling reveals that for all three systems the
rocksalt local minimum on the potential energy surface is far larger than any
other, making it statistically the most significant structure. The kinetics
modeling shows that virtually all other relevant structures, including most of
the 457 known A$_1$B$_1$ prototypes, transform rapidly to rocksalt, making it
the only option at ambient conditions. These results explain the absence of
polymorphism in binary rocksalts, answer why rocksalt is the structure of
choice for high-entropy ceramics and disordered ternary nitrides, and help
understand/predict metastable states in crystalline solids more generally.",2402.06843v1
2024-02-12,Non-Hermitian bonding and electronic reconfiguration of Ba$_2$ScNbO$_6$ and Ba$_2$LuNbO$_6$,"Despite the extensive applications of perovskite compounds, the precise
nature of non-Hermitian bonding in these materials remains poorly understood.
In this study, density functional theory calculations were performed to
determine the electronic structures of perovskite compounds. In particular, the
bandgaps of Ba$_2$ScNbO$_6$ and Ba$_2$LuNbO$_6$ were found to be 2.617 and
2.629 eV, respectively, and the deformation bond energies and non-Hermitian
bonding of these compounds were calculated. The relationship between the
non-Hermitian zeros of the O-Nb bond of Ba$_2$ScNbO$_6$ and the non-Hermitian
zeros of the Sc-O bond was found to be similar but with varying sizes. Further,
in-depth research on the non-Hermitian chemistry verified that precise control
of atomic bonding and electron states can be achieved, providing new insights
into the study of chemical bonds.",2402.07615v1
2024-02-23,"Ab-initio insights into the mechanical, phonon, bonding, electronic, optical and thermal properties of hexagonal W2N3 for potential applications","We investigated the structural, elastic, electronic, vibrational, optical,
thermodynamic and a number of thermophysical properties of W2N3 in this study
using DFT based formalisms. The mechanical and dynamical stabilities have been
confirmed. The Pugh and Poisson ratios are located quite close to the brittle
to ductile borderline. The electronic band structure and energy density of
states show metallic behavior. The Fermi surface features are investigated. The
analysis of charge density distribution map clearly shows that W atoms have
comparatively high electron density around than the N atoms. Presence of
covalent bondings are anticipated. High melting temperature and high phonon
thermal conductivity at room temperature of W2N3 imply that the compound has
potential to be used as a heat sink system. The optical characteristics
demonstrate anisotropy for W2N3. The compound can be used in optoelectronic
device applications due to its high absorption coefficient and low reflectivity
in the visible to ultraviolet spectrum. Furthermore, the quasiharmonic Debye
model is used to examine temperature and pressure dependent thermal
characteristics for the first time.",2402.15342v1
2024-02-24,Prediction of Superionic State in LiH2 at Conditions Enroute to Nuclear Fusion,"Hydrogen and lithium, along with their compounds, are crucial materials for
nuclear fusion research. High-pressure studies have revealed intricate
structural transitions in all these materials. However, research on lithium
hydrides beyond LiH has mostly focused on the low-temperature regime. Here, we
use density functional theory and ab initio molecular dynamics simulations to
investigate the behavior of LiH2, a hydrogen-rich compound, near its melting
point. Our study is particularly relevant to the low-pressure region of the
compression pathway of lithium hydrides toward fusion. We discovered a
premelting superionic phase transition in LiH2 that has significant
implications for its mass transportation, elastic properties, and sound
velocity. The theoretical boundary for the superionic transition and melting
temperature was then determined. In contrast, we also found that the primary
compound of lithium hydrides, LiH, does not exhibit a superionic transition.
These findings have important implications for optimizing the compression path
to achieve the ignition condition in inertial confinement fusion research,
especially when lithium tritium-deuteride(LiTD) are used as the fuel.",2402.15791v1
2024-02-27,In-plane ordering and tunable magnetism in Cr-based MXenes,"MXene, the two-dimensional derivatives of MAX compounds, due to their
structural and compositional flexibility, is an ideal family of compounds to
study a number of structure-property relations. In this work, we have
investigated the tunability of magnetic properties in Cr-based MXenes that have
an in-plane ordering arising out of alloying Cr with another non-magnetic
transition metal atom. Using Density Functional Theory based calculations we
have explored the effects of composition and surface functionalisations on the
electronic and magnetic properties of these in-plane ordered MXenes known as
i-MXenes. We found that the electronic and magnetic ground states are quite
sensitive to the structure and composition. This provides enough tunability in
these compounds so that they can be used for practical applications. Our
calculated results of magnetic transition temperatures and magnetic anisotropy
energies are comparable to many a established two-dimensional magnets. These
put together widen the prospect of these i-MXenes for multiple usage as
magnetic devices making them attractive for further investigation.",2402.17577v1
2024-03-13,Layered Kagome Compound Na$_2$Ni$_3$S$_4$ with Topological Flat Band,"We report structural and electronic properties of Na$_2$Ni$_3$S$_4$, a
quasi-two-dimensional compound composed of alternating layers of
[Ni$_3$S$_4$]$^{2-}$ and Na$^{+}$. The compound features a remarkable Ni-based
kagome lattice with a square planar configuration of four surrounding S atoms
for each Ni atom. Magnetization and electrical measurements reveal a weak
paramagnetic insulator with a gap of about 0.5 eV. Our band structure
calculation highlights a set of topological flat bands of the kagome lattice
derived from the rotated d$_{xz}$-orbital with $C_\mathrm{3}$ + $T$ symmetry in
the presence of crystal-field splitting.",2403.08456v1
2024-03-14,Leap: molecular synthesisability scoring with intermediates,"Assessing whether a molecule can be synthesised is a primary task in drug
discovery. It enables computational chemists to filter for viable compounds or
bias molecular generative models. The notion of synthesisability is dynamic as
it evolves depending on the availability of key compounds. A common approach in
drug discovery involves exploring the chemical space surrounding
synthetically-accessible intermediates. This strategy improves the
synthesisability of the derived molecules due to the availability of key
intermediates. Existing synthesisability scoring methods such as SAScore,
SCScore and RAScore, cannot condition on intermediates dynamically. Our
approach, Leap, is a GPT-2 model trained on the depth, or longest linear path,
of predicted synthesis routes that allows information on the availability of
key intermediates to be included at inference time. We show that Leap surpasses
all other scoring methods by at least 5% on AUC score when identifying
synthesisable molecules, and can successfully adapt predicted scores when
presented with a relevant intermediate compound.",2403.13005v2
2024-03-21,Assessing exchange-correlation functionals for heterogeneous catalysis of nitrogen species,"Increasing interest in sustainable synthesis of ammonia, nitrates, and urea
has led to an increase in studies of catalytic conversion between
nitrogen-containing compounds using heterogeneous catalysts. Density functional
theory (DFT) is commonly employed to obtain molecular-scale insight into these
reactions, but there have been relatively few assessments of the
exchange-correlation functionals that are best suited for heterogeneous
catalysis of nitrogen compounds. Here, we assess a range of functionals ranging
from the generalized gradient approximation (GGA) to the random phase
approximation (RPA) for the formation energies of gas-phase nitrogen species,
the lattice constants of representative solids from several common classes of
catalysts (metals, oxides, and metal-organic frameworks (MOFs)), and the
adsorption energies of a range of nitrogen-containing intermediates on these
materials. The results reveal that the choice of exchange-correlation
functional and van der Waals correction can have a surprisingly large effect
and that increasing the level of theory does not always improve the accuracy
for nitrogen-containing compounds. This suggests that the selection of
functionals should be carefully evaluated on the basis of the specific reaction
and material being studied.",2403.14482v1
2024-04-02,FraGNNet: A Deep Probabilistic Model for Mass Spectrum Prediction,"The process of identifying a compound from its mass spectrum is a critical
step in the analysis of complex mixtures. Typical solutions for the mass
spectrum to compound (MS2C) problem involve matching the unknown spectrum
against a library of known spectrum-molecule pairs, an approach that is limited
by incomplete library coverage. Compound to mass spectrum (C2MS) models can
improve retrieval rates by augmenting real libraries with predicted spectra.
Unfortunately, many existing C2MS models suffer from problems with prediction
resolution, scalability, or interpretability. We develop a new probabilistic
method for C2MS prediction, FraGNNet, that can efficiently and accurately
predict high-resolution spectra. FraGNNet uses a structured latent space to
provide insight into the underlying processes that define the spectrum. Our
model achieves state-of-the-art performance in terms of prediction error, and
surpasses existing C2MS models as a tool for retrieval-based MS2C.",2404.02360v1
2024-04-03,High-throughput calculations of antiferromagnets hosting anomalous transport phenomena,"We develop a high-throughput computational scheme based on cluster multipole
theory to identify new functional antiferromagnets. This approach is applied to
228 magnetic compounds listed in the AtomWork-Adv database, known for their
elevated N\'eel temperatures. We conduct systematic investigations of both
stable and metastable magnetic configurations of these materials. Our findings
reveal that 34 of these compounds exhibit antiferromagnetic structures with
zero propagation vectors and magnetic symmetries identical to conventional
ferromagnets, rendering them potentially invaluable for spintronics
applications. By cross-referencing our predictions with the existing MAGNDATA
database and published literature, we verify the reliability of our findings
for 26 out of 28 compounds with partially or fully elucidated magnetic
structures in the experiments. These results not only affirm the reliability of
our scheme but also point to its potential for broader applicability in the
ongoing quest for the discovery of new functional magnets.13",2404.02437v1
2024-04-04,Electronic structure of noncentrosymmetric B20 compound HfSn and tuning of multifold band-crossing points,"We present a detailed theoretical study of the electronic structure of
hafnium tin HfSn crystallizing in a B$20$ structure, renowned for the diversity
of physical and peculiar topological properties. The chiral crystal structure
of these materials protects multifold band crossings located at high symmetry
points. We employ density functional methods to reveal basic features of the
band structure and Fermi surface topology of HfSn, on top of which an effective
tight-binding model is built. The compound exhibits a fourfold band crossing
pinned at the ${\Gamma}$ point. We investigate routes that can shift such
crossings towards the Fermi level, offering a unique way to possibly tune the
compound`s properties. Specifically, we show that the energy position of the
fourfold crossing can be easily manipulated via external perturbations such as
strain and pressure. Considering that this point carries a topological charge
larger than one, such tuning is of great importance. We anticipate that the
approach presented in the current study can be utilized to investigate symmetry
protected crossings in a wide class of materials.",2404.03365v1
2024-04-05,"Willkommens-Merkel, Chaos-Johnson, and Tore-Klose: Modeling the Evaluative Meaning of German Personal Name Compounds","We present a comprehensive computational study of the under-investigated
phenomenon of personal name compounds (PNCs) in German such as
Willkommens-Merkel ('Welcome-Merkel'). Prevalent in news, social media, and
political discourse, PNCs are hypothesized to exhibit an evaluative function
that is reflected in a more positive or negative perception as compared to the
respective personal full name (such as Angela Merkel). We model 321 PNCs and
their corresponding full names at discourse level, and show that PNCs bear an
evaluative nature that can be captured through a variety of computational
methods. Specifically, we assess through valence information whether a PNC is
more positively or negatively evaluative than the person's name, by applying
and comparing two approaches using (i) valence norms and (ii) pretrained
language models (PLMs). We further enrich our data with personal,
domain-specific, and extra-linguistic information and perform a range of
regression analyses revealing that factors including compound and modifier
valence, domain, and political party membership influence how a PNC is
evaluated.",2404.04031v1
2024-04-11,Low-symmetry polymorph of GaP upends bonding paradigms of metallic high-pressure III-V compounds,"The pressure-induced polymorphism of binary octect compounds has long been
considered a settled problem although the possible atomic disordering of some
phases remains a puzzling observation. Taking GaP as a case study, we conclude,
through x-ray microdiffraction and first-principles calculations, that its
high-pressure phase II (previously reported as being disordered) adopts in fact
an ordered base-centered monoclinic structure previously unknown in this class
of compounds. The formation of layered patterns with variable degrees of
interlayer dimerization, as observed in GaP, marks a paradigm shift of our
understanding of ordering in octect high-pressure phases which calls for a more
extensive re-examination. A rich polymorphism with fine tuning of chemical and
physical properties can be envisioned.",2404.07758v1
2024-04-13,Emergent Griffiths-phase-like behavior in the ball-milled nanocrystalline Dy4RhAl and its implication,"We report the results of dc susceptibility and heat capacity measurements on
the (ball-milled) nanocrystalline rare-earth (R) ternary compound,
crystallizing in Gd4RhIn type, cubic Dy4RhAl compound. The bulk form of this
compound has been known to undergo antiferromagnetic ordering at (TN=) 18 K
with concomitant cluster spin glass anomalies. The present studies on the
nano-form obtained by ball milling reveal that this antiferromagnetic ordering
is suppressed with the reduction of particle size with no feature attributable
to a well defined long-range magnetic ordering down to 1.8 K, but showing an
inhomogeneous magnetism below 10 K. The point being stressed is that the
results show the dominance of a feature around 30 K in the magnetic
susceptibility data (well above TN of the bulk form) mimicking Griffiths phase.
We infer that surface magnetism dominates before long range magnetic ordering
occurs in this material.",2404.08956v1
2013-11-21,Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloy as magnetic electrodes,"HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning
spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance
(FMR) techniques are used in view of comparing (static and dynamic) magnetic
and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel
magnetic junctions (TMJ), deposited on various single crystalline substrates
(a-plane sapphire, MgO(100) and Si(111)). They allow for providing a
correlation between these magnetic properties and the fine structure
investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and
contains a large concentration of Co atoms, which, however, is significantly
reduced when using a sapphire substrate. The Co layer is polycrystalline and
shows larger grains for films grown on a sapphire substrate. The VSM
investigation reveals in-plane anisotropy only for samples grown on a sapphire
substrate. The FMR spectra of the TMJs are compared to the obtained ones with a
single Co and Co2MnGe films of identical thickness deposited on a sapphire
substrate. As expected, two distinct modes are detected in the TMJs while only
one mode is observed in each single film. For the TMJ grown on a sapphire
substrate the FMR behavior does not significantly differ from the superposition
of the individual spectra of the single films, allowing for concluding that the
exchange coupling between the two magnetic layers is too small to give rise to
observable shifts. For TMJs grown on a Si or on a MgO substrate the resonance
spectra reveal one mode which is nearly identical to the obtained one in the
single Co film, while the other observed resonance shows a considerably smaller
intensity and cannot be described using the magnetic parameters appropriate to
the single Co2MnGe film.",1311.5589v1
2015-09-30,Roadmap for Emerging Materials for Spintronic Device Applications,"The Technical Committee of the IEEE Magnetics Society has selected 7 research
topics to develop their roadmaps, where major developments should be listed
alongside expected timelines; (i) hard disk drives, (ii) magnetic random access
memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and
actuators, (vi) magnetic materials and (vii) organic devices. Among them,
magnetic materials for spintronic devices have been surveyed as the first
exercise. In this roadmap exercise, we have targeted magnetic tunnel and
spin-valve junctions as spintronic devices. These can be used for example as a
cell for a magnetic random access memory and spin-torque oscillator in their
vertical form as well as a spin transistor and a spin Hall device in their
lateral form. In these devices, the critical role of magnetic materials is to
inject spin-polarised electrons efficiently into a non-magnet. We have
accordingly identified 2 key properties to be achieved by developing new
magnetic materials for future spintronic devices: (1) Half-metallicity at room
temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For
the first property, 5 major magnetic materials are selected for their
evaluation for future magnetic/spintronic device applications: Heusler alloys,
ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys
have been reported or predicted to be half-metallic ferromagnets at RT. They
possess a bandgap at the Fermi level EF only for its minority spins, achieving
100% spin polarisation at EF. We have also evaluated L10-alloys and
D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet
with large spin polarisation. We have listed several key milestones for each
material on their functionality improvements, property achievements, device
implementations and interdisciplinary applications within 35 years time scale.",1509.08997v1
2017-07-16,Competing magnetic and spin gap-less semiconducting behaviour in fully compensated ferrimagnet CrVTiAl: Theory and Experiment,"We report the structural, magnetic and transport properties of
polycrystalline CrVTiAl alloy along with first principles calculations. It
crystallizes in the LiMgPdSn type structure with lattice parameter 6.14 \AA\ at
room temperature. Absence of (111) peak along with the presence of a weak (200)
peak indicates the antisite disorder of Al with Cr and V atoms. The
magnetization measurements reveal a ferrimagnetic transition near 710 K and a
coercive field of 100 Oe at 3 K. Very low moment and coercive field indicate
fully compensated ferrimagnetism in the alloy. Temperature coefficient of
resistivity is found to be negative, indicating a characteristic of
semiconducting nature. Absence of exponential dependence of resistivity on
temperature indicates a gapless/spin-gapless semiconducting behaviour.
Electronic and magnetic properties of CrVTiAl for three possible
crystallograpic configurations are studied theoretically. All the three
configurations are found to be different forms of semiconductors. Ground state
configuration is a fully compensated ferrimagnet with band gaps 0.58 eV and
0.30 eV for up and down spin bands respectively. The next higher energy
configuration is also ferrimagnetic, but has spin-gapless semiconducting
nature. The highest energy configuration corresponds to a non-magnetic gapless
semiconductor. The energy differences among these configurations are quite
small ($<$ 1 $\mathrm{mRy/atom}$) which hints that at finite temperatures, the
alloy exists in a disordered phase, which is a mixture of the three
configurations. By taking into account the theoretical and the experimental
findings, we conclude that CrVTiAl is a fully compensated ferrimagnet with
predominantly spin gap-less semiconductor nature.",1707.04854v1
2018-11-29,Interacting spin-3/2 fermions in a Luttinger semimetal: Competing phases and their selection in the global phase diagram,"We compute the effects of electronic interactions on gapless spin-3/2
excitations that in a noninteracting system emerge at a bi-quadratic touching
of Kramers degenerate valence and conduction bands, known as Luttinger
semimetal. This model can describe the low-energy physics of HgTe, gray-Sn, 227
pyrochlore iridates and half-Heuslers. For the sake of concreteness we only
consider the short-range components of the Coulomb interaction. By combining
mean-field analysis with a renormalization group (RG) calculation, we construct
multiple cuts of the global phase diagram of interacting spin-3/2 fermions at
zero and finite temperature and chemical doping. Such phase diagrams display a
rich confluence of competing orders, among which rotational symmetry breaking
nematic insulators and time reversal symmetry breaking magnetic orders are the
prominent excitonic phases. We also show that even repulsive interactions can
be conducive for both s-wave and d-wave pairings. The reconstructed band
structure inside the ordered phases allows us to organize them according to the
energy (entropy) gain in the following (reverse) order: s-wave pairing, nematic
phases, magnetic orders and d-wave pairings, at zero chemical doping. But, the
paired states are always energetically superior over the excitonic ones for
finite doping. The phase diagrams obtained from the RG analysis show that an
ordered phase with higher energy (entropy) gain is realized at low (high)
temperature. In addition, we establish a ""selection rule"" between the
interaction channels and the resulting ordered phases, suggesting that
repulsive interactions in the magnetic (nematic) channels are conducive for the
nucleation of d-wave (s-wave) pairing. The proposed methodology can shed light
on the global phase diagram of other strongly interacting multi-band systems,
such as doped Dirac semimetal, topological insulators and the like.",1811.12415v2
2019-07-25,Superconducting switching due to triplet component in the Pb/Cu/Ni/Cu/Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$ spin-valve structure,"We report the superconducting properties of the
Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$/Cu/Ni/Cu/Pb spin-valve structure which magnetic
part comprises the Heusler alloy layer HA = Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$ with a
high degree of spin polarization (DSP) of the conduction band and the Ni layer
of variable thickness. We obtained that the separation between the
superconducting transition curves measured for the parallel ($\alpha =
0^\circ$) and perpendicular ($\alpha = 90^\circ$) orientation of the
magnetizations of the HA and Ni layers reaches up to 0.5 K ($\alpha$ is an
angle between the magnetization of two ferromagnetic layers). For all studied
samples the dependence of the superconducting transition temperature $T_c$ on
$\alpha$ demonstrates a deep minimum in the vicinity of the perpendicular
configuration of magnetizations. This suggests that the observed minimum and
the corresponding full switching effect of the spin valve is caused by the
long-range triplet component of the superconducting condensate in the
multilayer. Such a large effect can be attributed to a half-metallic nature of
the HA layer which in the orthogonal configuration efficiently draws off the
spin-polarized Cooper pairs from the space between the HA and Ni layers. Our
results indicate a significant potential of the concept of the superconducting
spin-valve multilayer comprising a half-metallic ferromagnet recently proposed
by A. Singh et al., Phys. Rev. X 5, 021019 (2015) in achieving large values of
the switching effect.",1907.11176v2
2016-03-10,Beyond Triplet: Unconventional Superconductivity in a Spin-3/2 Topological Semimetal,"In all known fermionic superfluids, Cooper pairs are composed of spin-1/2
quasi-particles that pair to form either spin-singlet or spin-triplet bound
states. The ""spin"" of a Bloch electron, however, is fixed by the symmetries of
the crystal and the atomic orbitals from which it is derived, and in some cases
can behave as if it were a spin-3/2 particle. The superconducting state of such
a system allows pairing beyond spin-triplet, with higher spin quasi-particles
combining to form quintet or septet pairs. Here, we report evidence of
unconventional superconductivity emerging from a spin-3/2 quasiparticle
electronic structure in the half-Heusler semimetal YPtBi, a low-carrier density
noncentrosymmetric cubic material with a high symmetry that preserves the
$p$-like $j=3/2$ manifold in the Bi-based $\Gamma_8$ band in the presence of
strong spin-orbit coupling. With a striking linear temperature dependence of
the London penetration depth, the existence of line nodes in the
superconducting order parameter $\Delta$ is directly explained by a
mixed-parity Cooper pairing model with high total angular momentum, consistent
with a high-spin fermionic superfluid state. We propose a $\mathbf{k\cdot p}$
model of the $j=3/2$ fermions to explain how a dominant $J$=3 septet pairing
state is the simplest solution that naturally produces nodes in the mixed
even-odd parity gap. Together with the underlying topologically non-trivial
band structure, the unconventional pairing in this system represents a truly
novel form of superfluidity that has strong potential for leading the
development of a new generation of topological superconductors.",1603.03375v4
2020-12-10,Magnetic order and magneto-transport in half-metallic ferrimagnetic Mn$_y$Ru$_x$Ga thin films,"The ruthenium content of half-metallic Mn$_2$Ru$_x$Ga thin films, with a
biaxially-strained inverse Heusler structure, controls the ferrimagnetism that
determines their magnetic and electronic properties. An extensive study of
Mn$_y$Ru$_x$Ga films on MgO (100) substrates with $1.8 \leq y \leq 2.6$ and $x
= 0.5$, 0.7 or 0.9, including crystallographic, magnetic order,
magneto-transport and spin polarisation is undertaken to map specific
composition-dependent properties in this versatile ternary system. A comparison
of experimental densities obtained from X-ray reflectivity with calculated
densities indicates full site occupancy for all compositions, which implies
chemical disorder. All moments lie on the Slater-Pauling plot with slope 1 and
all except $x = 0.5$, $y = 2.2$ exhibit magnetic compensation at \tcmp~below
500~K. The coercivity near \tcmp~exceeds 10~T. Increasing the Mn or Ru content
raises \tcmp, but increasing Ru also decreases the spin polarisation determined
by point contact Andreev reflection. Molecular field theory is used to model
the temperature dependence of the net ferrimagnetic moment and three principal
exchange coefficients are deduced. Marked differences in the shape of anomalous
Hall and net magnetisation hysteresis loops are explained by substantial
canting of the small net moment by up to \SI{40}{\degree} relative to the
$c$-axis in zero field, which is a result of slight non-collinearity of the
Mn$^{4c}$ sublattice moments due to competing intra-sublattice exchange
interactions arising from antisite disorder and excess Mn in the unit cell.
Consequences are reduced spin polarisation and an enhanced intrinsic
contribution to the anomalous Hall effect. The systematic investigation of the
physical properties as a function of $x$ and $y$ will guide the selection of
compositions to meet the requirements for magnonic and spintronic MRG-based
devices.",2012.05736v5
2021-01-25,Computing and Memory Technologies based on Magnetic Skyrmions,"Solitonic magnetic excitations such as domain walls and, specifically,
skyrmionics enable the possibility of compact, high density,
ultrafast,all-electronic, low-energy devices, which is the basis for the
emerging area of skyrmionics. The topological winding of skyrmion spins affects
their overall lifetime, energetics and dynamical behavior. In this review, we
discuss skyrmionics in the context of the present day solid state memory
landscape, and show how their size, stability and mobility can be controlled by
material engineering, as well as how they can be nucleated and detected.
Ferrimagnetsnear their compensation points are important candidates for this
application, leading to detailed exploration of amorphous CoGd as well as the
study of emergent materials such as Mn$_4$N and Inverse Heusler alloys. Along
with material properties, geometrical parameters such as film thickness, defect
density and notches can be used to tune skyrmion properties, such as their size
and stability. Topology, however, can be a double-edged sword, especially for
isolated metastable skyrmions, as it brings stability at the cost of additional
damping and deflective Magnus forces compared to domain walls. Skyrmion
deformation in response to forces also makes them intrinsically slower than
domain walls. We explore potential analog applications of skyrmions, including
temporal memory at low density, and decorrelator for stochastic computing at a
higher density that capitalizes on their interactions. We summarize the main
challenges to achieve a skyrmionics technology, including maintaining
positional stability with very high accuracy, electrical readout, especially
for small ferrimagnetic skyrmions, deterministic nucleation and annihilation,
and overall integration with digital circuits with the associated circuit
overhead.",2101.09947v4
2021-02-26,Role of chemical disorder in tuning the Weyl points in vanadium doped Co$_2$TiSn,"The lack of time-reversal symmetry and Weyl fermions give exotic transport
properties to Co-based Heusler alloys. In the present study, we have
investigated the role of chemical disorder on the variation of Weyl points in
Co\textsubscript{2}Ti\textsubscript{1-x}V\textsubscript{x}Sn magnetic Weyl
semimetal candidate. We employ the first principle approach to track the
evolution of the nodal lines responsible for the appearance of Weyl node in
Co$_2$TiSn as a function of V substitution in place of Ti. By increasing the V
concentration in place of Ti, the nodal line moves toward Fermi level and
remains at Fermi level around the middle composition. Further increase of the V
content, leads shifting of nodal line away from Fermi level. Density of state
calculation shows half-metallic behavior for the entire range of composition.
The magnetic moment on each Co atom as a function of V concentration increases
linearly up to x=0.4, and after that, it starts decreasing. We also
investigated the evolution of the Weyl nodes and Fermi arcs with chemical
doping. The first-principles calculations reveal that via replacing almost half
of the Ti with V, the intrinsic anomalous Hall conductivity increased twice as
compared to the undoped composition. Our results indicate that the composition
close to the 50\% V doped Co$_2$TiSn, will be an ideal composition for the
experimental investigation of Weyl physics.",2102.13389v2
2021-11-03,Antiskyrmions and their electrical footprint in crystalline mesoscale structures of Mn$_{1.4}$PtSn,"Skyrmionic materials hold the potential for future information technologies,
such as racetrack memories. Key to that advancement are systems that exhibit
high tunability and scalability, with stored information being easy to read and
write by means of all-electrical techniques. Topological magnetic excitations
such as skyrmions and antiskyrmions, give rise to a characteristic topological
Hall effect. However, the electrical detection of antiskyrmions, in both thin
films and bulk samples has been challenging to date. Here, we apply
magneto-optical microscopy combined with electrical transport to explore the
antiskyrmion phase as it emerges in crystalline mesoscale structures of the
Heusler magnet Mn$_{1.4}$PtSn. We reveal the Hall signature of antiskyrmions in
line with our theoretical model, comprising anomalous and topological
components. We examine its dependence on the vertical device thickness, field
orientation, and temperature. Our atomistic simulations and experimental
anisotropy studies demonstrate the link between antiskyrmions and a complex
magnetism that consists of competing ferromagnetic, antiferromagnetic, and
chiral exchange interactions, not captured by micromagnetic simulations.",2111.02494v3
2022-12-26,In plane reorientation induced single laser pulse magnetization reversal in rare-earth based multilayer,"Single Pulse All Optical Helicity Independent Switching (AO-HIS) represents
the ability to reverse the magnetic moment of a nanostructure using a
femtosecond single laser pulse. It is an ultrafast method to manipulate
magnetization without the use of any applied field. Since the first switching
experiments carried on GdFeCo ferrimagnetic systems, single pulse AO-HIS has
been restricted for a while to Gd-based alloys or Gd/FM bilayers where FM is a
ferromagnetic layer. Only recently has AO-HIS been extended to a few other
materials: MnRuGa ferrimagnetic Heusler alloys and Tb/Co multilayers with a
very specific range of thickness and composition. Here, we demonstrate that
single pulse AO-HIS observed in Tb/Co results from a different mechanism than
the one for Gd based samples and that it can be obtained for a large range of
rare earth-transition metal (RE-TM) multilayers, making this phenomenon much
more general. Surprisingly, in this large family of (RE-TM) multilayer systems,
the threshold fluence for switching is observed to be independent of the pulse
duration, up to at least 12 ps. Moreover, at high laser intensities, concentric
ring domain structures are induced, unveiling multiple fluence thresholds.
These striking switching features, which are in contrast to those of AO-HIS in
GdFeCo alloys, concomitant with the demonstration of an in-plane reorientation
of the magnetization, point towards an intrinsic precessional reversal
mechanism. Our results allow expanding the variety of materials with tunable
magnetic properties that can be integrated in complex heterostructures and
provide a pathway to engineer materials for future applications based on
all-optical control of magnetic order.",2212.13279v1
2023-01-14,CoRuVSi: A potential candidate for spin semimetal with promising spintronic and thermoelectric properties,"Based on our experimental and theoretical studies, we report the
identification of the quaternary Heusler alloy, CoRuVSi as a new member of the
recently discovered spin semimetals class. Spin polarised semimetals possess a
unique band structure in which one of the spin bands shows semimetallic nature,
while the other shows semiconducting/insulating nature. Our findings show that
CoRuVSi possesses interesting spintronic and thermoelectric properties.
Magnetization data reveal a weak ferri-/antiferro magnetic ordering at low
temperatures, with only a very small moment $\sim$ 0.13 $\mu_B$/f.u.,
attributed to the disorder. Transport results provide strong evidence of
semimetallicity dominated by two-band conduction, while magnetoresistance data
show a non-saturating, linear, positive, magnetoresistance. Spin polarization
measurements using point-contact Andreev reflection spectra reveal a reasonably
high spin polarization of $\sim$ 50\%, which matches fairly well with the
simulated result. Furthermore, CoRuVSi shows a high thermopower value of $0.7$
$m Watt/ m-K^{2}$ at room temperature with the dominant contribution from the
semimetallic bands, rendering it as a promising thermoelectric material as
well. Our ab-initio simulation not only confirms a unique semimetallic feature,
but also reveals that the band structure hosts a linear band crossing at $\sim$
-0.4 eV below the Fermi level incorporated by a band-inversion. In addition,
the observed topological non-trivial features of the band structure is
corroborated with the simulated Berry curvature, intrinsic anomalous Hall
conductivity and the Fermi surface. The coexistence of many interesting
properties relevant for spintronic, topological and thermoelectric applications
in a single material is extremely rare and hence this study could promote a
similar strategy to identify other potential materials belonging to same class.",2301.05854v1
2024-03-19,PH-NODE: A DFPT and finite displacement supercell based python code for searching nodes in topological phononic materials,"Exploring the topological physics of phonons is fundamentally important for
understanding various practical applications. Here, we present a
density-functional perturbation theory and finite displacement supercell based
Python 3 software package called PH-NODE for efficiently computing phonon nodes
present in real material through a first-principle approach. The present
version of the code is interfaced with the WIEN2k, Elk, and ABINIT packages. In
order to benchmark the code, four different types of materials are considered,
which include (i) FeSi, a well-known double-Weyl point; (ii) LiCaAs, a
half-Heusler single-type-I Weyl topological phonon (TP); and (iii) ScZn,
coexisting nodal-line and nodal-ring TPs; (iv) TiS, six pairs of bulk Weyl
nodes. In FeSi, the node points are found at ${\Gamma}$(0, 0, 0) and R(0.5,
0.5, 0.5) high symmetric points. Also, there are 21 energy values at which the
node points are situated, corresponding to the full Brillouin Zone. For LiCaAs,
the previously reported literature claims that there is a node point along the
W-X high symmetry direction between the highest longitudinal acoustic and the
lowest transverse optical branch, while in our DFT calculations, a gap of 0.17
meV is found. Furthermore, ScZn hosts six nodal-ring TPs phonons at the
boundary planes of the Brillouin Zone in the vicinity of the M high-symmetric
point. In addition to this, straight-line TPs are also found along the
${\Gamma}$-X and ${\Gamma}$-R high symmetric directions. Moreover, for TiS, six
weyl node points (WP1, WP2, WP3, WP4, WP5 and WP6) are found along H-K
high-symmetric direction. The results obtained from the PH-NODE code are in
good agreement with the experimentally and theoretically reported data for each
material.",2403.12643v1
2002-09-30,"Magnetism and superconductivity in Ru(1-x)Sr2RECu(2+x)O(8-d) (RE=Gd, Eu) and RuSr2Gd(1-y)Ce(y)Cu2O8 compounds","We discuss the properties of new superconducting compositions of
Ru(1-x)Sr2RECu(2+x)O(8-d) (RE=Gd, Eu) ruthenocuprates that were synthesized at
600 atm. of oxygen at 1080 C. By changing ratio between the Ru and Cu, the
temperature of superconducting transition (Tc) raises up to Tc max=72 K for
x=0.3, 0.4. The hole doping achieved along the series increases with Cu->Ru
substitution. For x different than x=0, Tc can be subsequently tuned between Tc
max and 0 K by changing oxygen content in the compounds. The magnetic
characteristics of the RE=Gd and Eu based compounds are interpreted as
indicative of constrained dimensionality of the superconducting phase. Muon
spin rotation experiments reveal the presence of the magnetic transitions at
low temperatures (Tm=14-2 K for x=0.1-0.4) that can originate in the response
of Ru/Cu sublattices. RuSr2Gd(1-y)Ce(1-y)Cu2O8 (0<y<0.1) compounds show the
simultaneous increase of TN and decrease of Tc with y. The effect should be
explained by the electron doping that occurs with Ce->Gd substitution.
Properties of these two series allow us to propose phase diagram for 1212-type
ruthenocuprates that links their properties to the hole doping achieved in the
systems. Non-superconducting single-phase RuSr2GdCu2O8 and RuSr2EuCu2O8 are
reported and discussed in the context of the properties of substituted
compounds.",0209668v1
2004-12-28,Magnetic state of plutonium ion in metallic Pu and its compounds,"By LDA+U method with spin-orbit coupling (LDA+U+SO) the magnetic state and
electronic structure have been investigated for plutonium in \delta and \alpha
phases and for Pu compounds: PuN, PuCoGa5, PuRh2, PuSi2, PuTe, and PuSb. For
metallic plutonium in both phases in agreement with experiment a nonmagnetic
ground state was found with Pu ions in f^6 configuration with zero values of
spin, orbital, and total moments. This result is determined by a strong
spin-orbit coupling in 5f shell that gives in LDA calculation a pronounced
splitting of 5f states on f^{5/2} and f^{7/2} subbands. A Fermi level is in a
pseudogap between them, so that f^{5/2} subshell is already nearly completely
filled with six electrons before Coulomb correlation effects were taken into
account. The competition between spin-orbit coupling and exchange (Hund)
interaction (favoring magnetic ground state) in 5f shell is so delicately
balanced, that a small increase (less than 15%) of exchange interaction
parameter value from J_H=0.48eV obtained in constrain LDA calculation would
result in a magnetic ground state with nonzero spin and orbital moment values.
For Pu compounds investigated in the present work, predominantly f^6
configuration with nonzero magnetic moments was found in PuCoGa5, PuSi2, and
PuTe, while PuN, PuRh2, and PuSb have f^5 configuration with sizeable magnetic
moment values. Whereas pure jj coupling scheme was found to be valid for
metallic plutonium, intermediate coupling scheme is needed to describe 5f shell
in Pu compounds. The results of our calculations show that both spin-orbit
coupling and exchange interaction terms in the Hamiltonian must be treated in a
general matrix form for Pu and its compounds.",0412724v2
2010-09-28,Relationship Between Phonons and Thermal Expansion in Zn(CN)2 and Ni(CN)2 from Inelastic Neutron Scattering and Ab-Initio Calculations,"Zn(CN)2 and Ni(CN)2 are known for exhibiting anomalous thermal expansion over
a wide temperature range. The volume thermal expansion coefficient for the
cubic, three dimensionally connected material, Zn(CN)2, is negative ({\alpha}V
= -51 x 10-6 K-1) while for Ni(CN)2, a tetragonal material, the thermal
expansion coefficient is negative in the two dimensionally connected sheets
({\alpha}a=-7 x 10-6 K-1), but the overall thermal expansion coefficient is
positive ({\alpha}V=48 x 10-6 K-1). We have measured the temperature dependence
of phonon spectra in these compounds and analyzed them using ab-initio
calculations. The spectra of the two compounds show large differences that
cannot be explained by simple mass renormalization of the modes involving Zn
(65.38 amu) and Ni (58.69 amu) atoms. This reflects the fact that the structure
and bonding are quite different in the two compounds. The calculated pressure
dependence of the phonon modes and of the thermal expansion coefficient,
{\alpha}V, are used to understand the anomalous behavior in these compounds.
Our ab-initio calculations indicate that it is the low-energy rotational modes
in Zn(CN)2, which are shifted to higher energies in Ni(CN)2, that are
responsible for the large negative thermal expansion. The measured temperature
dependence of the phonon spectra has been used to estimate the total
anharmonicity of both compounds. For Zn(CN)2, the temperature- dependent
measurements (total anharmonicity), along with our previously reported pressure
dependence of the phonon spectra (quasiharmonic), is used to separate the
explicit temperature effect at constant volume (intrinsic anharmonicity).",1009.5540v1
2011-08-01,"Ferrimagnetism, Antiferromagnetism and Magnetic Frustration in La$_{2-x}$Sr$_{x}$CuRuO$_{6}$ (0 <= x <= 1)","We studied structural and magnetic properties of a series of insulating
double perovskite compounds, La$_{2-x}$Sr$_{x}$CuRuO$_{6}$ (0 $\le$ x $\le$ 1),
representing doping via \textit{A}-site substitution. The end members
La$_{2}$CuRuO$_{6}$ and LaSrCuRuO$_{6}$ form in monoclinic structure while the
intermediate Sr doped compounds stabilise in triclinic structure. The Cu and Ru
ions sit on alternate B-sites of the perovskite lattice with $\sim$15%
anti-site defects in the undoped sample while the Sr doped samples show a
tendency to higher ordering at B-sites. The undoped (x = 0) compound shows a
ferrimagnetic-like behaviour at low temperatures. In surprising contrast to the
usual expectation of an enhancement of ferromagnetic interaction on doping, an
antiferromagnetic-like ground state is realized for all doped samples (x $>$
0). Heat capacity measurements indicate the absence of any long range magnetic
order in any of these compounds. The magnetic relaxation and memory effects
observed in all compounds suggest glassy dynamical properties associated with
magnetic disorder and frustration. We show that the observed magnetic
properties are dominated by the competition between the nearest neighbour Ru --
O -- Cu 180$^\circ$ superexchange interaction and the next nearest neighbour Ru
-- O -- O -- Ru 90$^\circ$ superexchange interaction as well as by the
formation of anti-site defects with interchanged Cu and Ru positions. Our
calculated exchange interaction parameters from first principles calculations
for $x$ = 0 and $x$ = 1 support this interpretation.",1108.0334v3
2013-07-27,Universal Polar Codes,"Polar codes, invented by Arikan in 2009, are known to achieve the capacity of
any binary-input memoryless output-symmetric channel. One of the few drawbacks
of the original polar code construction is that it is not universal. This means
that the code has to be tailored to the channel if we want to transmit close to
capacity.
  We present two ""polar-like"" schemes which are capable of achieving the
compound capacity of the whole class of binary-input memoryless
output-symmetric channels with low complexity.
  Roughly speaking, for the first scheme we stack up $N$ polar blocks of length
$N$ on top of each other but shift them with respect to each other so that they
form a ""staircase."" Coding then across the columns of this staircase with a
standard Reed-Solomon code, we can achieve the compound capacity using a
standard successive decoder to process the rows (the polar codes) and in
addition a standard Reed-Solomon erasure decoder to process the columns.
Compared to standard polar codes this scheme has essentially the same
complexity per bit but a block length which is larger by a factor $O(N
\log_2(N)/\epsilon)$, where $\epsilon$ is the gap to capacity.
  For the second scheme we first show how to construct a true polar code which
achieves the compound capacity for a finite number of channels. We achieve this
by introducing special ""polarization"" steps which ""align"" the good indices for
the various channels. We then show how to exploit the compactness of the space
of binary-input memoryless output-symmetric channels to reduce the compound
capacity problem for this class to a compound capacity problem for a finite set
of channels. This scheme is similar in spirit to standard polar codes, but the
price for universality is a considerably larger blocklength.
  We close with what we consider to be some interesting open problems.",1307.7223v2
2013-09-05,Magnetic interactions in disordered perovskite PbFe_{1/2}Nb_{1/2}O_3 and related compounds. Dominance of nearest-neighbor interaction,"We show that the magnetism of double perovskite AFe_{1/2}M_{1/2}O_3 systems
may be described by the Heisenberg model on the simple cubic lattice, where
only half of sites are occupied by localized magnetic moments. The
nearest-neighbor interaction J_1 is more than 20 times the next-nearest
neighbor interaction J_2, the third-nearest interaction along the space
diagonal of the cube being negligible. We argue that the variety of magnetic
properties observed in different systems is connected with the variety of
chemical ordering in them. We analyze six possible types of the chemical
ordering in 2x2x2 supercell, and argue that the probability to find them in a
real compound does not correspond to a random occupation of lattice sites by
magnetic ions. The exchange J_2 rather than J_1 define the magnetic energy
scale of most double perovskite compounds that means the enhanced probability
of 1:1 short range ordering. Two multiferroic compounds PbFe_{1/2}M_{1/2}O_3
(M=Nb, Ta) are exceptions. We show that the relatively high temperature of
antiferromagnetic transition is compatible with a layered short-range chemical
order, which was recently shown to be most stable for these two compounds [I.
P. Raevski, {\em et al.}, Phys.\ Rev.\ B \textbf{85}, 224412 (2012)]. We show
also that one of the types of ordering has ferrimagnetic ground state. The
clusters with short-range order of this type may be responsible for a
room-temperature superparamagnetism, and may form the cluster glass at low
temperatures.",1309.1318v3
2013-11-04,Fermion condensate generates a new state of matter by making flat bands,"Belyaev's ideas associated with the condensate state in Bose interacting
systems have stimulated intensive studies of the possible manifestation of such
a condensation in Fermi systems. In many Fermi systems and compounds at zero
temperature a phase transition happens that leads to a quite specific state
called fermion condensation. As a signal of such a fermion condensation quantum
phase transition (FCQPT) serves unlimited increase of the effective mass of
quasiparticles that determines the excitation spectrum and creates flat bands.
We show that the class of Fermi liquids with the fermion condensate forms a new
state of matter. We discuss the phase diagrams and the physical properties of
systems located near that phase transition. It is demonstrated that a huge
amount of experimental data collected on different compounds suggests that
they, starting from some temperature and down, form the new state of matter,
and are governed by the fermion condensation. Our discussion shows that the
theory of fermion condensation develops completely good description of the NFL
behavior of strongly correlated Fermi systems. Moreover, the fermion
condensation can be considered as the universal reason for the NFL behavior
observed in various HF metals, liquids, compounds with quantum spin liquids,
and quasicrystals. We show that these systems exhibit universal scaling
behavior of their thermodynamic properties. Therefore, the quantum critical
physics of different strongly correlated compounds is universal, and emerges
regardless of the underlying microscopic details of the compounds. This uniform
behavior, governed by the universal quantum critical physics, allows us to view
it as the main characteristic of the new state of matter.",1311.0629v1
2014-08-26,Search and design of nonmagnetic centrosymmetric layered crystals with large local spin polarization,"Until recently, spin-polarization in nonmagnetic materials was the exclusive
territory of non- centrosymmetric structures. It was recently shown that a form
of hidden spin polarization (named the Rashba-2 or R-2 effect) could exist in
globally centrosymmetric crystals provided the individual layers belong to
polar point group symmetries. This realization could considerably broaden the
range of materials that might be considered for spin-polarization spintronic
applications to include the hitherto forbidden spintronic compound that belong
to centrosymetric symmetries. Here we take the necessary steps to transition
from such general, material-agnostic condensed matter theory arguments to
material-specific design principles that could aid future laboratory search of
R-2 materials. Specifically, we (i) classify different prototype layered
structures that have been broadly studied in the literature in terms of their
expected R-2 behavior, including the Bi2Se3-structure type (a prototype
topological insulator), MoS2-structure type (a prototype valleytronic compound)
and LaBiOS2-structure type (a host of superconductivity upon doping); (ii)
formulate the properties that ideal R-2 compounds should have in terms of
combination of their global unit cell symmetries with specific point group
symmetries of their constituent sectors; (iii) use first-principles band theory
to search for compounds from the prototype family of LaOBiS2-type structures
that satisfy these R-2 design metrics. We initially consider both stable and
hypothetical compounds to establish an understanding of trends of R-2 with
composition, and then indicate the predictions that are expected to be stable
and synthesizable. We predict large spin splittings (up to ~ 200 meV for holes
in LaOBiTe2) as well as surface Rashba states. Experimental testing of such
predictions is called for.",1408.6004v2
2014-11-05,"Why the Co-based 115 compounds are different?: The case study of GdMIn$_5$ (M=Co, Rh, Ir)","The discovery in 2001 of superconductivity in some heavy fermion compounds of
the RMIn$_5$ (R=4f or 5f elements, M=Co, Rh, Ir) family, has triggered enormous
amount of research pointing to understand the physical origin of
superconductivity and its relation with magnetism. Although many properties
have been clarified, there are still crutial questions that remain unanswered.
One of these questions is the particular role of the transition metal in
determining the value of critical superconducting temperature (Tc). In this
work, we analyse an interesting regularity that is experimentally observed in
this family of compounds, where the lowest N\'eel temperatures are obtained in
the Co-based materials. We focus our analysis on the GdMIn$_5$ compounds and
perform density-functional-theory based total-energy calculations to obtain the
parameters for the exchange coupling interactions between the magnetic moments
located at the Gd$^{3+}$ ions. Our calculations indicate that the ground state
of the three compounds is a $C$-type antiferromagnet determined by the
competition between the first- and second-neighbor exchange couplings inside
GdIn$_3$ planes and stabilized by the couplings across MIn$_2$ planes. We then
solve a model with these magnetic interactions using a mean-field approximation
and Quantum Monte Carlo simulations. The results obtained for the calculated
N\'eel and Curie-Weiss temperatures, the specific heat and the magnetic
susceptibility are in very good agreement with the existent experimental data.
Remarkably, we show that the first neighbor interplane exchange coupling in the
Co-based material is much smaller than in the Rh and Ir analogues due to a more
two dimensional behaviour in the former. This result explains the observed
lower N\'eel temperature in Co-115 systems and may shed light on the fact that
the Co-based 115 superconductors present the highest Tc.",1411.1396v2
2014-11-26,Entrance channel effects on the evaporation residue yields in reactions leading to the $^{220}$Th compound nucleus,"The evaporation residue yields from compound nuclei $^{220}$Th formed in the
$^{16}$O+$^{204}$Pb, $^{40}$Ar+$^{180}$Hf, $^{82}$Se+$^{138}$Ba,
$^{124}$Sn+$^{96}$Zr reactions are analyzed to study the entrance channel
effects by comparison of the capture, fusion and evaporation residue cross
sections calculated by the combined dinuclear system (DNS) and advanced
statistical models. The difference between evaporation residue (ER) cross
sections can be related to the stages of compound nucleus formation or/and at
its surviving against fission. The sensitivity of the both stages in the
evolution of DNS up to the evaporation residue formation to the angular
momentum of DNS is studied. The difference between fusion excitation functions
are explained by the hindrance to complete fusion due to the larger intrinsic
fusion barrier $B^*_{\rm fus}$ for the transformation of the DNS into a
compound nucleus and the increase of the quasifission contribution due to the
decreasing of quasifission barrier $B_{\rm qf}$ as a function of the angular
momentum. The largest value of the ER residue yields in the very mass
asymmetric $^{16}$O+$^{204}$Pb reaction is related to the large fusion
probability and to the relatively low threshold of the excitation energy of the
compound nucleus. Due to the large threshold of the excitation energy (35 MeV)
of the $^{40}$Ar+$^{180}$Hf reaction, it produces less the ER yields than the
almost mass symmetric $^{82}$Se+$^{138}$Ba reaction having the lowest threshold
value (12 MeV).",1411.7239v1
2015-01-01,"Kondo lattice and antiferromagnetic behavior in quaternary CeTAl$_4$Si$_2$ (T~=~Rh, Ir) single crystals","We report the synthesis and the magnetic properties of single crystalline
CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$ and their non magnetic La-analogs. The
single crystals of these quaternary compounds were grown using Al-Si binary
eutectic as flux. The anisotropic magnetic properties of the cerium compounds
were explored in detail by means of magnetic susceptibility, isothermal
magnetization, electrical resistivity, magnetoresistivity and heat capacity
measurements. Both CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$ undergo two
antiferromagnetic transitions, first from the paramagnetic to an
antiferromagnetic state at $T_{\rm N1}$~=~12.6~K and 15.5~K, followed by a
second transition at lower temperatures $T_{\rm N2}$~=~9.4~K and 13.8~K,
respectively. The paramagnetic susceptibility is highly anisotropic and its
temperature dependence in the magnetically ordered state suggests the $c$-axis
to be the relatively easy axis of magnetization. Concomitantly, isothermal
magnetization at 2~K along the $c$-axis shows a sharp spin-flop transition
accompanied by a sizeable hysteresis, while it varies nearly linearly with
field along the [100] direction up to the highest field 14~T, of our
measurement. The electrical resistivity provides evidence of the Kondo
interaction in both compounds, inferred from its $-lnT$ behavior in the
paramagnetic region. The heat capacity data confirm the bulk nature of the two
magnetic transitions in each compound, and further confirm the presence of
Kondo interaction by a reduced value of the entropy associated with the
magnetic ordering. From the heat capacity data below 1~K, the coefficient of
the linear term in the electronic heat capacity, $\gamma$, is inferred to be
195.6 and 49.4~mJ/mol K$^2$ in CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$,
respectively classifying these materials as moderate heavy fermion compounds.",1501.00250v2
2015-03-08,Structural instability of the rutile compounds and its relevance to the metal-insulator transition of VO2,"The metal-insulator transition (MIT) of VO2 is discussed with particular
emphasis on the structural instability of the rutile compounds toward
dimerization. Ti substitution experiments reveal that the MIT is robust up to
20% Ti substitutions and occurs even in extremely thin V-rich lamellas in
spinodally decomposed TiO2-VO2 composites, indicating that the MIT is
insensitive to hole doping and essentially takes on a local character. These
observations suggest that either electron correlation in the Mott-Hubbard sense
or Peierls (Fermi-surface) instability plays a minor role on the MIT. Through a
broad perspective of crystal chemistry on the rutile-related compounds, it is
noted that VO2 and another MIT compound NbO2 in the family eventually lie just
near the borderline between the two structural groups with the regular rutile
structure and the distorted structures characterized by the formation of dimers
with direct metal-metal bonding. The MITs of VO2 and NbO2 are natural
consequences of structural transitions between the two groups, as all the d
electrons are trapped in the bonding molecular orbitals of dimers at low
temperatures. Such dimer crystals are ubiquitously found in early transition
metal compounds having chain-like structures, such as MoBr3, NbCl4, Ti4O7, and
V4O7, the latter two of which also exhibit MITs probably of the same origin. In
a broader sense, the dimer crystal is a kind of molecular orbital crystals in
which virtual molecules made of transition metal atoms with partially-filled
t2g shells, such as dimers, trimers or larger ones, are generated by
metal-metal bonding and are embedded into edge- or face-sharing octahedron
networks of various kinds. The molecular orbital crystallization opens a
natural route to stabilization of unpaired t2g electrons in crystals.",1503.02262v1
2015-04-22,Gradual localization of 5f states in orthorhombic UTX ferromagnets - polarized neutron diffraction study of Ru substituted UCoGe,"We report on a microscopic study of the evolution of ferromagnetism in the Ru
substituted ferromagnetic superconductor (FM SC) UCoGe crystallizing in the
orthorhombic TiNiSi-type structure. For that purpose, two single crystals with
composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge have been prepared and
characterized by magnetization, AC susceptibility, specific heat and electrical
resistivity measurements. Both compounds have been found to order
ferromagnetically below TC = 6.5 K and 7.5 K, respectively, which is
considerably higher than the TC = 3 K of the parent compound UCoGe. The higher
values of TC are accompanied by enhanced values of the spontaneous moment
mspont. = 0.11 mB/f.u. and mspont. = 0.21 mB/f.u., respectively in comparison
to the tiny spontaneous moment of UCoGe (about 0.07mB/f.u.). No sign of
superconductivity was detected in either compound. The magnetic moments of the
samples were investigated on the microscopic scale using polarized neutron
diffraction (PND) and for UCo0.88Ru0.12Ge also by soft X-ray magnetic circular
dichroism (XMCD). The analysis of the PND results indicates that the observed
enhancement of ferromagnetism is mainly due to the growth of the orbital part
of the uranium 5f moment mL(U), reflecting a gradual localization of the 5f
electrons with Ru substitution. In addition, the parallel orientation of the U
and Co moments has been established in both substituted compounds. The results
are discussed and compared with related isostructural ferromagnetic UTX
compounds (T - transition metals, X - Si, Ge) in the context of a varying
degree of the 5f-ligand hybridization.",1504.05645v1
2015-04-22,Complex Organic and Inorganic Compounds in Shells of Lithium-rich K Giant Stars,"Hydrocarbon organic material, as found in the interstellar medium, exists in
complex mixtures of aromatic and aliphatic forms. It is considered to be
originated from carbon enriched giant stars during their final stages of
evolution, when very strong mass loss occurs in a few thousand years on their
way to become planetary nebulae. We show here that the same organic compounds
appear to be formed in previous stages of the evolution of giant stars. More
specifically, during the first ascending giant branch K-type stars. According
to our model this happens only when these stars are being abruptly enriched
with lithium together with the formation of a circumstellar shell with a strong
mass loss during just a few thousand years. This sudden mass loss is, on an
average, a thousand times larger than that of normal Li-poor K giant stars.
This shell would later be detached, specially when the star stops its Li
enrichment and a rapid photospheric Li depletion occurs. In order to gain extra
carbon-based material to form the organic hydrocarbons, and also to explain the
presence of complex inorganic compounds in these stars, we propose an
interaction of these strong winds with remaining asteroidal/cometary disks that
already existed around these stars since they were dwarf A-type stars. The
mechanism of interaction presented here is successful to explain the presence
of inorganic compounds, however it is unable to produce new carbon free atoms
to form the organic hydrocarbon compounds. Finally, we discuss some suggestions
and speculations that can eventually help solving the long-standing puzzle of
Li-rich giants.",1504.05983v1
2015-05-30,Superconducting interaction charge in thallium-based high-Tc cuprates: Roles of cation oxidation state and electronegativity,"Superconductivity in the Tl-based cuprates encompasses a notably broad range
of measured optimal transition temperatures Tc0, ranging from lowest in the
charge-depleted Tl-1201 compounds
(Tl$_{1-x}$(Ba/Sr)$_{1+y}$La$_{1-y}$CuO$_{5-{\delta}}$), such as
Tl$_{0.7}$LaSrCuO$_5$ (37 K) and TlBa$_{1.2}$La$_{0.8}$CuO$_5$ (45.4 K), to
highest in the Tl-1223 compound TlBa$_2$Ca$_2$Cu$_3$O$_{9{\pm}{\delta}}$ (133.5
K). Seven Tl-based cuprates are considered and compared using the model of
superconductive pairing via electronic interactions between two physically
separated charge reservoirs, where Tc0 $\propto$
({\sigma}{\eta}/A)$^{1/2}${\zeta}$^{-1}$ is determined by the superconducting
interaction charge fraction {\sigma} the number {\eta} of CuO$_2$ layers, and
the basal-plane area A, each per formula unit, and the transverse distance
{\zeta} between interacting layers. Herein it is demonstrated that {\sigma}
follows from the elemental electronegativity and the oxidation state of Tl, and
other structurally analogous cations. The comparatively lower elemental
electronegativity of Tl, in conjunction with its oxidation state, explains the
higher {\sigma} and Tc0 values in the Tl-based compounds relative to their
Bi-based cuprate homologues. A derivation of {\sigma} is introduced for the
optimal Tl$_2$Ba$_2$Ca$_{{\eta}-1}$Cu$_{\eta}$O$_{2{\eta}+4}$ (for {\eta} = 1,
2, 3) compounds, which exhibit a Tl oxidation state at or near +3, obtaining
the fundamental value {\sigma}$_0$ = 0.228 previously established for
YBa$_2$Cu$_3$O$_{6.92}$. Also reported is the marked enhancement in {\sigma}
associated with Tl$^{+1}$ and analogous inner-layer cations relative to
higher-valence cations. For a model proposition of {\sigma} = {\sigma}$_0$, the
fractional Tl$^{+1}$ content of the mixed-valence compound,
TlBa$_2$Ca$_2$Cu$_3$O$_{9{\pm}{\delta}}$, is predicted to be 1/3 at
optimization, in agreement ...",1506.00065v1
2017-08-28,Machine learning the band gap properties of kesterite I$_2$-II-IV-V$_4$ quaternary compounds for photovoltaics applications,"Kesterite I$_2$-II-IV-V$_4$ semiconductors are promising solar absorbers for
photovoltaics applications. The band gap and it's character, either direct or
indirect, are fundamental properties determining photovoltaic-device
efficiency. We use a combination of accurate first-principles calculations and
machine learning to predict the properties of the band gap for a large number
of kesterite I$_2$-II-IV-V$_4$ semiconductors. In determining the magnitude of
the fundamental gap, we compare results for a number of machine-learning
models, and achieve a root mean squared error as low as 283 meV; the best
results are achieved using support-vector regression with a radial-bias kernel.
This error is well within the uncertainty of even the most advanced
first-principles methods for calculating semiconductor band gaps. Predicting
the direct--indirect property of the band gap is more challenging. After
significant feature engineering, we are able to train a classifier that
predicts the nature of the band gap with an accuracy of 89 \% using logistic
regression. Using these trained models, the band gap properties of 1568
kesterite I$_2$-II-IV-V$_4$ compounds are predicted. We find 717 compounds with
band gaps in the range 0.5 -- 2.5 eV that can potentially act as solar
absorbers, and 242 materials with a band gap in the ``\emph{optimum range}"" of
1.2 -- 1.8 eV. The stability of these 242 compounds is assessed by calculating
the Energy Above Hull using the Materials Project database, and the band gaps
are verified using hybrid functional calculations; in the end, we identify 25
compounds that are expected to be synthesizable, and have a band gap in the
range 1.2 -- 1.8 eV -- most of which are previously unexplored. These results
will be useful in the materials engineering of efficient photovoltaic devices.",1708.08530v2
2018-06-30,A Study of a Compound Solar Eruption with Two Consecutive Erupting Magnetic Structures,"We report a study of a compound solar eruption that was associated with two
consecutively erupting magnetic structures and correspondingly two distinct
peaks, during impulsive phase, of an M-class flare (M8.5). Simultaneous
multi-viewpoint observations from $\textit{SDO}$, $\textit{GOES}$ and
$\textit{STEREO-A}$ show that this compound eruption originated from two
pre-existing sigmoidal magnetic structures lying along the same polarity
inversion line. Observations of the associated pre-existing filaments further
show that these magnetic structures are lying one on top of the other,
separated by 12 Mm in height, in a so-called ""double-decker"" configuration. The
high-lying magnetic structure became unstable and erupted first, appearing as
an expanding hot channel seen at extreme ultraviolet wavelengths. About 12
minutes later, the low-lying structure also started to erupt and moved at an
even faster speed compared to the high-lying one. As a result, the two erupting
structures interacted and merged with each other, appearing as a single coronal
mass ejection in the outer corona. We find that the double-decker configuration
is likely caused by the persistent shearing motion and flux cancellation along
the source active region's strong-gradient polarity inversion line. The
successive destabilization of these two separate but closely spaced magnetic
structures, possibly in the form of magnetic flux ropes, led to a compound
solar eruption. The study of the compound eruption provides a unique
opportunity to reveal the formation process, initiation, and evolution of
complex eruptive structures in solar active regions.",1807.00206v1
2019-07-09,Resolution limit of data-driven coarse-grained models spanning chemical space,"Increasing the efficiency of materials design and discovery remains a
significant challenge, especially given the prohibitively large size of
chemical compound space. The use of a chemically transferable coarse-grained
model enables different molecular fragments to map to the same bead type, while
also reducing computational expense. These properties further increase
screening efficiency, as many compounds are screened through the use of a
single coarse-grained simulation, effectively reducing the size of chemical
compound space. Here, we propose new criteria for the rational design of
coarse-grained models that allows for the optimization of their chemical
transferability and evaluate the Martini model within this framework. We
further investigate the scope of this chemical transferability by
parameterizing three Martini-like models, in which the number of bead types
ranges from five to sixteen for the different force fields. We then implement a
Bayesian approach to determining which chemical groups are more likely to be
present on fragments corresponding to specific bead types for each model. We
demonstrate that a level of performance and accuracy comparable to Martini can
be obtained by using a force field with fewer bead types. However, the
advantage of including more bead types is a reduction of uncertainty with
respect to back-mapping these bead types to specific chemistries. Just as
reducing the size of the coarse-grained particles leads to a finer mapping of
conformational space, increasing the number of bead types yields a finer
mapping of chemical compound space. Finally, we note that, due to the
relatively large size of the chemical fragments that map to a single martini
bead, a clear resolution limit arises when using the water/octanol partition
free energy as the only descriptor when coarse-graining chemical compound
space.",1907.04082v1
2021-03-23,Automated fragment identification for electron ionisation mass spectrometry: application to atmospheric measurements of halocarbons,"Non-target screening consists in searching a sample for all present
substances, suspected or unknown, with very little prior knowledge about the
sample. This approach has been introduced more than a decade ago in the field
of water analysis, together with dedicated compound identification tools, but
is still very scarce for indoor and atmospheric trace gas measurements, despite
the clear need for a better understanding of the atmospheric trace gas
composition.For a systematic detection of emerging trace gases in the
atmosphere, a new and powerful analytical method is gas chromatography (GC) of
preconcentrated samples, followed by electron ionisation, high resolution mass
spectrometry (EI-HRMS). In this work, we present data analysis tools to enable
automated fragment formula annotation for unknown compounds measured by
GC-EI-HRMS. Based on co-eluting mass/charge fragments, we developed an
innovative data analysis method to reliably reconstruct the chemical formulae
of the fragments, using efficient combinatorics and graph theory. The method
does not require the presence of the molecular ion, which is absent in ~40% of
EI spectra. Our method has been trained and validated on \textgreater50
halocarbons and hydrocarbons, with 3 to 20 atoms and molar masses of 30 to 330
g mol-1, measured with a mass resolution of approx.~3500. For 90% of the
compounds, more than 90% of the annotated fragment formulae are correct. Cases
of wrong identification can be attributed to the scarcity of detected fragments
per compound or the lack of isotopic constraint (no minor isotopocule
detected).Our method enables to reconstruct most probable chemical formulae
independently from spectral databases. Therefore, it demonstrates the
suitability of EI-HRMS data for non-target analysis and paves the way for the
identification of substances for which no EI mass spectrum is registered in
databases. We illustrate the performances of our method for atmospheric trace
gases and suggest that it may be well suited for many other types of samples.
The L-GPL licenced Python code is released under the name ALPINAC for
ALgorithmic Process for Identification of Non-targeted Atmospheric Compounds.",2103.13807v2
2022-02-07,Understanding nature's purpose in starting all new lives with compound growth -- New science for individual systems,"We often associate compound growth with the Anthropocene and our overwhelming
economic impacts on the Earth. Today our actual choices for future society
appear to lie with studying the class of emergent natural systems that first
develop by compound growth, called 'new lives' here, or ""natural complex
adaptive systems"" (NCAS). The key to their success is first starting with
compound growth, a system for growing the system. Its self-organization needs
to shift resources from multiplying its scale to maturing and adapting its
design for its new environment, a challenging environmental coordination
process.
  We see that taking place in biological reproduction all the time, of course,
but it all needs to occur for businesses, economies, cultures, and even for
creative work and personal relationships to survive their initial periods of
compound growth. Why economic growth as a process that accelerates ever faster
still seems unlimited to some seems to come from representing growth as a
numerical rather than organizational development process. For example, all
kinds of adaptive system organization have limits to how fast they can
rearrange their systems.
  To understand the kinds of limits and adaptations that lead to a successful
growth climax and perhaps a long creative life to follow, we combine the most
notable observed milestones of successful growth found in nature, divided into
3 main development periods. Those milestones of new lives (MNL) teach us
alternative paths to follow The primary milestones include 3 critical events,
initiating 3 feedback periods, for 3 organizational development stages,
occurring in 3 environments. Together they can be called the A, B, C, egg,
nest, world, or natural growth pattern. By observing them in familiar cases, we
learn the patterns that also apply in others.",2202.03404v1
2022-02-25,Detecting gravitational lenses using machine learning: exploring interpretability and sensitivity to rare lensing configurations,"Forthcoming large imaging surveys such as Euclid and the Vera Rubin
Observatory Legacy Survey of Space and Time are expected to find more than
$10^5$ strong gravitational lens systems, including many rare and exotic
populations such as compound lenses, but these $10^5$ systems will be
interspersed among much larger catalogues of $\sim10^9$ galaxies. This volume
of data is too much for visual inspection by volunteers alone to be feasible
and gravitational lenses will only appear in a small fraction of these data
which could cause a large amount of false positives. Machine learning is the
obvious alternative but the algorithms' internal workings are not obviously
interpretable, so their selection functions are opaque and it is not clear
whether they would select against important rare populations. We design, build,
and train several Convolutional Neural Networks (CNNs) to identify strong
gravitational lenses using VIS, Y, J, and H bands of simulated data, with F1
scores between 0.83 and 0.91 on 100,000 test set images. We demonstrate for the
first time that such CNNs do not select against compound lenses, obtaining
recall scores as high as 76\% for compound arcs and 52\% for double rings. We
verify this performance using Hubble Space Telescope (HST) and Hyper
Suprime-Cam (HSC) data of all known compound lens systems. Finally, we explore
for the first time the interpretability of these CNNs using Deep Dream, Guided
Grad-CAM, and by exploring the kernels of the convolutional layers, to
illuminate why CNNs succeed in compound lens selection.",2202.12776v1
2016-12-20,Pressure Induced Thermodynamically Stable and Mechanically Robust Li-rich Unknown Li-Sn Compounds: A Step Towards Improvement of Li-Sn Batteries,"Volume expansion and elastic softening of Sn anode on lithiation result in
mechanical degradation and pulverization of Sn, affecting the overall
performance of Li-Sn batteries. It can however be overcome by using exotic high
pressure quenched phase as prelithiated reagent. Moreover, it is known that
under pressure many unusual stoichiometric which are basically impossible at
ambient pressure, can be synthesized, that may even survive the decompression
from high to ambient pressure.We therefore have performed a comprehensive study
using evolutionary algorithm and density functional theory based simulations to
understand the lithiation of Sn anode at pressure ranging from 1 atm to 20 GPa.
The ground state structures of all stable and metastable Li-Sn compounds have
been identified at ambient and moderate pressures and their properties have
been studied to understand the role of pressure in re-defining the reaction
mechanism during charging-discharging process in Li-ion batteries. Besides the
well-known existing Li-Sn compounds, our studies reveal the existence of five
unreported stoichiometries (Li8Sn3, Li3Sn1, Li4Sn1, Li5Sn1, and Li7Sn1) and
their associated crystal structures at ambient and high pressure. While Li8Sn3
has been identified as one of the most stable Li-Sn compound in the entire
pressure range (1 atm-20 GPa), the pressure induced Li-rich compounds like
Li5Sn1 and Li7Sn1 have been classified as providing higher theoretical
gravimetric capacity of 1129 and 1580 mAh/g), respectively, than the capacity
of the known most lithiated phase, i.e., Li17Sn4 (960 mAh/g).Most importantly,
our calculations show reduction in volume expansion by ~ 50% at 20 GPa, and
reveal that the application of pressure can reduce the chance of Li plating and
improve the mechanical properties, which are desired to make the battery safer
and its life longer.",1612.06770v1
2017-10-09,Pressure-induced spin pairing transition of Fe$^{3+}$ in oxygen octahedra,"High pressure can provoke spin transitions in transition metal-bearing
compounds. These transitions are of high interest not only for fundamental
physics and chemistry, but also may have important implications for
geochemistry and geophysics of the Earth and planetary interiors. Here we have
carried out a comparative study of the pressure-induced spin transition in
compounds with trivalent iron, octahedrally coordinated by oxygen.
High-pressure single-crystal M\""{o}ssbauer spectroscopy data for FeBO$_3$,
Fe$_2$O$_3$ and Fe$_3$(Fe$_{1.766(2)}$Si$_{0.234(2)}$)(SiO$_4$)$_3$ are
presented together with detailed analysis of hyperfine parameter behavior. We
argue that $\zeta$-Fe$_2$O$_3$ is an intermediate phase in the reconstructive
phase transition between $\iota$-Fe$_2$O$_3$ and $\theta$-Fe$_2$O$_3$ and
question the proposed perovskite-type structure for $\zeta$-Fe$_2$O$_3$.The
structural data show that the spin transition is closely related to the volume
of the iron octahedron. The transition starts when volumes reach 8.9-9.3
\AA$^3$, which corresponds to pressures of 45-60 GPa, depending on the
compound. Based on phenomenological arguments we conclude that the spin
transition can proceed only as a first-order phase transition in
magnetically-ordered compounds. An empirical rule for prediction of cooperative
behavior at the spin transition is proposed. The instability of iron octahedra,
together with strong interactions between them in the vicinity of the critical
volume, may trigger a phase transition in the metastable phase. We find that
the isomer shift of high spin iron ions depends linearly on the octahedron
volume with approximately the same coefficient, independent of the particular
compounds and/or oxidation state. For eight-fold coordinated Fe$^{2+}$ we
observe a significantly weaker nonlinear volume dependence.",1710.03192v1
2019-03-27,"Relation between the weak itinerant magnetism in $A_2$Ni$_7$ compounds ($A$ = Y, La) and their stacked crystal structures","The weak itinerant magnetic properties of $A_2$Ni$_7$ compounds with $A$ =
{Y, La} have been investigated using electronic band structure calculations in
the relation with their polymorphic crystal structures. These compounds
crystallizes in two structures resulting from the stacking of two and three
blocks of [$A_2$Ni$_4$ + 2 $A$Ni$_5$] units for hexagonal $2H$-La$_2$Ni$_7$
(Ce$_2$Ni$_7$ type) and rhombohedral $3R$-Y$_2$Ni$_7$ (Gd$_2$Co$_7$ type)
respectively. Experimentally, $2H$-La$_2$Ni$_7$ is a weak itinerant
antiferromagnet whereas $3R$-Y$_2$Ni$_7$ is a weak itinerant ferromagnet. From
the present first principles calculation within non-spin polarized state, both
compounds present an electronic density of state with a sharp and narrow peak
centered at the Fermi level corresponding to flat bands from $3d$-Ni. This
induces a magnetic instability and both compounds are more stable in a
ferromagnetic (FM) order compared to a paramagnetic state ($\Delta E \simeq$
-35 meV/f.u.). The magnetic moment of each of the five Ni sites varies with
their positions relative to the [$A_2$Ni$_4$] and [$A$Ni$_5$] units: they are
minimum in the [$A_2$Ni$_4$] unit and maximum at the interface between two
[$A$Ni$_5$] units. For $2H$-La$_2$Ni$_7$, an antiferromagnetic (AFM) structure
has been proposed and found with an energy comparable to that of the FM state.
This AFM structure is described by two FM unit blocks of opposite Ni spin sign
separated by a non-magnetic layer at z = 0 and $\frac12$. The Ni ($2a$) atoms
belonging to this intermediate layer are located in the [La$_2$Ni$_4$] unit and
are at a center of symmetry of the hexagonal cell ($P6_3/mmc$) where the
resultant molecular field is cancelled. Further non-collinear spin calculations
have been performed to determine the Ni moment orientations which are found
preferentially parallel to the $c$ axis for both FM and AFM structures.",1903.11423v2
2019-03-29,"Magnetic and physical properties of new hexagonal compounds PrPt$_4X$ ($X$ = Ag, Au)","We have synthesized PrPt$_4$Ag and PrPt$_4$Au compounds for the first time
and report their crystal structure, as well as magnetic and physical properties
in the temperature range of 1.9~K to 300~K. Both compounds are derived from the
substitution of Pt with Ag and Au, respectively in the parent compound PrPt$_5$
which crystallizes in the hexagonal CaCu$_5$-type structure. Here we observed
the preservation of the hexagonal CaCu$_5$-type structure under such
substitutions, which is in contrast to the observations in PrCu$_4$Ag and
PrCu$_4$Au adopting the cubic MgCu$_4$Sn-type structure upon substitution on
parent hexagonal PrCu$_5$. The temperature dependences of specific heat
$C_p(T)$, and electrical resistivity $\rho(T)$ of PrPt$_4$Ag show an anomaly at
7.6~K. This is absent in the magnetic susceptibility $\chi(T)$, thus suggesting
a possible multipolar ordering of the Pr$^{3+}$ moment. PrPt$_4$Au on the other
hand does not show any anomaly but an upturn in $C_p(T)/T$ below about 10~K and
attains 1.23~J/(mol K$^2$) at 1.9~K. In addition, $\rho(T)$ $\sim T$ for nearly
a decade in temperature. These observations for PrPt$_4$Au are the hallmark of
a non-Fermi liquid (nFL) behavior and is characteristic of a system near a
quantum critical point. The analyses of the low-temperature $C_p(T)$ for
PrPt$_4$Ag and PrPt$_4$Au give values of the Sommerfeld coefficient, $\gamma =
728.5~$mJ/(mol K$^2$) and 509.1~mJ/(mol K$^2$), respectively, indicating a
significant enhancement of the quasiparticle mass in the two compounds.",1903.12362v1
2019-05-16,Search for stabilizing effects of $\bm{Z=82}$ shell closure against fission,"Presence of closed proton and/or neutron shells causes deviation from
macroscopic properties of nuclei which are understood in terms of the liquid
drop model. It is important to investigate experimentally the stabilizing
effects of shell closure, if any, against fission. This work aims to
investigate probable effects of proton shell ($Z = 82$) closure in the compound
nucleus, in enhancing survival probability of the evaporation residues formed
in heavy ion-induced fusion-fission reactions. Evaporation residue cross
sections have been measured for the reactions $^{19}$F+$^{180}$Hf,
$^{19}$F+$^{181}$Ta and $^{19}$F+$^{182}$W from $\simeq9\%$ below to
$\simeq42\%$ above the Coulomb barrier, leading to formation of compound nuclei
with same number of neutrons ($N = 118$) but different number of protons across
$Z = 82$. Measured excitation functions have been compared with statistical
model calculation, in which reduced dissipation coefficient is the only
adjustable parameter. Evaporation residue cross section, normalized by capture
cross section, is found to decrease gradually with increasing fissility of the
compound nucleus. Measured evaporation residue cross sections require inclusion
of nuclear viscosity in the model calculations. Reduced dissipation coefficient
in the range of 1\textendash3 $\times$ $10^{21}$ s$^{-1}$ reproduces the data
quite well. No abrupt enhancement of evaporation residue cross sections has
been observed in the reaction forming compound nucleus with $Z = 82$. Thus,
this work does not find enhanced stabilizing effects of $Z = 82$ shell closure
against fission in the compound nucleus. One may attempt to measure cross
sections of individual exit channels for further confirmation of our
observation.",1905.06525v1
2019-09-13,Statistical-model description of $γ$ decay from compound-nucleus resonances,"The statistical model of compound-nucleus reactions predicts that the
fluctuations of the partial $\gamma$-decay widths for a compound-nucleus
resonance are governed by the Porter-Thomas distribution (PTD), and that
consequently the distribution of total $\gamma$-decay widths is very narrow.
However, a recent experiment [Koehler, Larsen, Guttormsen, Siem, and Guber,
Phys. Rev. C 88, 041305(R) (2013)] reported large fluctuations of the total
$\gamma$-decay widths in the $^{95}$Mo$(n,\gamma)^{96}$Mo* reaction, contrary
to this expectation. Furthermore, in recent theoretical works it was argued
that sufficiently strong channel couplings can cause deviations of the partial
width distributions from PTD. Here, we investigate whether the combined
influence of a large number of nonequivalent $\gamma$-decay channels, each of
which couples weakly to the compound-nucleus resonances, can modify the
statistics of the partial widths. We study this effect in neutron scattering
off $^{95}$Mo within a random-matrix model that includes coupling to the
entrance neutron channel and to the large number of $\gamma$ channels. Using
realistic coupling parameters obtained from empirical models for the level
density and the $\gamma$ strength function, we find that the PTD describes well
the distribution of partial widths for all decay channels, in agreement with
the statistical-model expectation. Furthermore, we find that the width of the
distribution of the total $\gamma$-decay widths is insensitive to wide
variations in the parameters of the $\gamma$ strength function, as well as to
deviations of the partial-width distributions from the PTD. Our results rule
out an explanation of the recent experimental data within a statistical-model
description of the compound nucleus.",1909.06250v2
2020-06-27,Spin qubit based on the nitrogen-vacancy center analog in a diamond-like compound C3BN,"The Nitrogen-vacancy (NV) center in diamond plays important roles in emerging
quantum technologies. Currently available methods to fabricate the NV center
often involve complex processes such as N implantation. By contrast, in a
diamond-like compound C3BN, creating a boron (B) vacancy immediately leads to
an NV center analog. We use the strongly constrained and appropriately normed
(SCAN) semilocal density functional - this functional leads to nearly the same
zero-phonon line (ZPL) energy as the experiment and as obtained from the more
time-consuming hybrid density functional calculations - to explore the
potential of this NV center analog as a novel spin qubit for applications in
quantum information processing. We show that the NV center analog in C3BN
possesses many similar properties to the NV center in diamond including a wide
band gap, weak spin-orbit coupling, an energetically stable negatively charged
state, a highly localized spin density, a paramagnetic triplet ground state,
and strong hyperfine interactions, which are the properties that make the NV
center in diamond stand out as a suitable quantum bit (qubit). We predict the
NV center analog in C3BN to exhibit two ZPL energies that correspond to longer
wavelengths close to the ideal telecommunication band for quantum
communications. C3BN studied here represents only one example of A3XY (A: group
IV element; X/Y: group III/V elements) compounds. We expect many other
compounds of this family to have similar NV center analogs with a wide range of
ZPL energies and functional properties, promising to be new hosts of qubits for
quantum technology applications. Furthermore, A3XY compounds often contain
group IV elements such as silicon and germanium, so they are compatible with
the sophisticated semiconductor processing techniques. Our work opens up ample
opportunities towards scalable qubit host materials and novel quantum devices.",2006.15407v1
2020-07-14,Excitations in the spin-1 trimer chain compound CaNi3P4O14: gapped dispersive spinwaves to gapless magnetic excitations,"Magnetic excitations and the spin Hamiltonian of the spin-1 J1-J1-J2 trimer
chain compound CaNi3P4O14 have been investigated by inelastic neutron
scattering. Experimental data reveal gapped dispersive spin wave excitations in
the 3D long-range ordered magnetic state (TC = 16 K), and gapless magnetic
excitations above the TC. Simulated magnetic excitations, by using the linear
spin wave theory, for a model of coupled trimer spin-chains provide a good
description of the observed experimental data. The analysis reveals both
ferromagnetic J1 and J2 interactions within the chains, and an
antiferromagnetic interchain interaction J3 between chains. The strengths of
the J1 and J2 are found to be closer (J2/J1 ~ 0.81), and J3 is determined to be
weaker (J3/ J1 ~ 0.69), which is consistent with the spin chain type crystal
structure. Presence of a weak single-ion-anisotropy (D/J=0.19) is also
revealed. The strengths and signs of exchange interactions explain why the 1/3
magnetization is absent in the studied spin-1 compound CaNi3P4O14 in contrast
to its S= 5/2 counterpart Mn based isostructural compound. The signs of the
exchange interactions are in agreement with that obtained from the reported DFT
calculations, whereas, their strengths are found to be significantly different.
The relatively strong value of the J3 in CaNi3P4O14 gives a conventional 3D
type magnetic ordering below the TC, however, retains its 1D character above
the TC. The present experimental study also reveals a sharp change of
single-ion anisotropy across the TC indicating that the stability of the 3D
magnetic ordering in CaNi3P4O14 is ascribed to the local magnetic anisotropy in
addition to interchain interactions. The present study divulges the importance
of full knowledge of the exchange interactions in trimer spin chain compounds
to understand their exotic magnetic properties, such as 1/3 magnetization
plateau.",2007.07233v1
2020-10-29,Evolution of the crystal structure and magnetic properties of Sm-doped BiFeO3 ceramics across the phase boundary region,"Samarium doped BiFeO3 compounds having nano-size crystallites were prepared
by the ethylene glycol assisted sol-gel synthesis method. X-ray diffraction and
SEM measurements as well as Raman spectroscopy and FTIR experiments were used
to clarify the evolution of the crystal structure on microscopic and local
scale levels in the compounds having formula Bi1-xSmxFeO3, where x equals from
0 to 1. Magnetization measurements along with the structural data were used to
determine a correlation between magnetic properties and crystal structure of
the compounds. The compounds with from x 0.1-0.2 are characterized by the
sequence of the structural transitions driven by the dopant increase, from the
polar rhombohedral phase to the non-polar orthorhombic phase via two-phase
regions characterized by the presence of the anti-polar orthorhombic phase. The
concentration regions ascribed to a coexistence of the rhombohedral and the
anti-polar orthorhombic phases as well as theanti-polar orthorhombic and the
non-polar orthorhombic phases are observed in the ranges from 0.12 to 0.15 and
from 0.15 to 0.18 respectively. The compounds having single-phase rhombohedral
structure are characterized by a release of remnant magnetization as compared
to ceramics with similar chemical compositions but synthesized by the
solid-state reaction method and having microscopic size crystallites. A
correlation between the type of structural distortion, morphology of
crystallites and an onset of remnant magnetization is discussed highlighting a
difference in the evolution of crystal structure and magnetization observed for
the Sm-doped ceramics prepared by modified sol-gel method and conventional
solid-state reaction technique.",2010.15439v1
2020-12-05,"Synthesis, crystal structure, polymorphism and microscopic luminescence properties of anthracene derivative compounds","Anthracene derivative compounds are currently investigated because of their
unique physical properties (e.g., bright luminescence and emission tunability),
which make them ideal candidates for advanced optoelectronic devices.
Intermolecular interactions are the basis of the tunability of the optical and
electronic properties of these compounds, whose prediction and exploitation
benefit from the knowledge of the crystal structure and the packing
architecture. Polymorphism can occur due to the weak intermolecular
interactions, asking for detailed structural analysis clarifying the origin of
observed material property modifications. Here, two silylethyne-substituted
anthracene compounds are characterized by single-crystal synchrotron X-ray
diffraction, identifying a new polymorph. Additionally, laser confocal
microscopy and fluorescence lifetime imaging microscopy confirm the results
obtained by the X-ray diffraction characterization, i.e., shifting the
substituents towards the external benzene rings of the anthracene unit favours
{\pi}-{\pi} interactions, impacting on both the morphology and the microscopic
optical properties of the crystals. The compounds with more isolated anthracene
units feature shorter lifetime and emission spectra more similar to those ones
of isolated molecules. The crystallographic study, supported by the optical
investigation, sheds light on the influence of non-covalent interactions on the
crystal packing and luminescence properties of anthracene derivatives,
providing a further step towards their efficient use as building blocks in
active components of light sources and photonic networks.",2012.03067v1
2021-10-21,Deep Learning Model of Dock by Dock Process Significantly Accelerate the Process of Docking-based Virtual Screening,"Docking-based virtual screening (VS process) selects ligands with potential
pharmacological activities from millions of molecules using computational
docking methods, which greatly could reduce the number of compounds for
experimental screening, shorten the research period and save the research cost.
Howerver, a majority of compouds with low docking scores could waste most of
the computational resources. Herein, we report a novel and practical
docking-based machine learning method called MLDDM (Machince Learning
Docking-by-Docking Models). It is composed of a regression model and a
classification model that simulates a classical docking by docking protocol
ususally applied in many virtual screening projects. MLDDM could quickly
eliminate compounds with low docking scores and the retained compounds with
potential high docking scores would be examined for further real docking
program. We demonstrated that MLDDM has a good ability to identify active
compounds in the case studies for 10 specific protein targets. Compared to pure
docking by docking based VS protocol, the VS process with MLDDM can achieve an
over 120 times speed increment on average and the consistency rate with
corresponding docking by docking VS protocol is above 0.8. Therefore, it would
be promising to be used for examing ultra-large compound libraries in the
current big data era.",2110.10918v2
2021-10-26,Anomalous Lattice Thermal Conductivity in Rocksalt IIA-VIA Compounds,"Materials with an intrinsic (ultra)low lattice thermal conductivity (k$_L$)
are critically important for the development of efficient energy conversion
devices. In the present work, we have investigated microscopic origins of low
k$_L$ behavior in BaO, BaS and MgTe by exploring lattice dynamics and phonon
transport of 16 iso-structural MX (Mg, Ca, Sr, Ba and X = O, S, Se and Te)
compounds in the rocksalt (NaCl)-type structure by comparing their lattice
transport properties with the champion thermoeletric iso-structural material,
PbTe. Anomalous trends are observed for k$_L$ in MX compounds except the MgX
series in contrast to the expected trend from their atomic mass. The underlying
mechanisms for such low k$_L$ behavior in relatively low atomic mass systems
namely BaO, BaS and MgTe compounds are thoroughly analyzed. We propose the
following dominant factors that might be responsible for low k$_L$ behavior in
these materials: 1) softening of transverse acoustic (TA) phonon modes despite
low atomic mass, 2) low lying optic (LLO) phonon modes fall deep into acoustic
mode region which enhances overlap between longitudinal acoustic (LA) and LLO
phonon modes which increases scattering phase space, 3) short phonon lifetimes
and high scattering rates, 4) relatively high density (\r{ho}) and large
Gr\""uneisen parameter. Moreover, tensile strain also causes a further reduction
in k$_L$ for BaO, BaS and MgTe through phonon softening and near ferroelectric
instability. Our comprehensive study on 16 binary MX compounds might provide a
pathway for designing (ultra)low k$_L$ materials even with simple crystal
systems through phonon engineering.",2110.13857v1
2022-09-02,Exploiting Pretrained Biochemical Language Models for Targeted Drug Design,"Motivation: The development of novel compounds targeting proteins of interest
is one of the most important tasks in the pharmaceutical industry. Deep
generative models have been applied to targeted molecular design and have shown
promising results. Recently, target-specific molecule generation has been
viewed as a translation between the protein language and the chemical language.
However, such a model is limited by the availability of interacting
protein-ligand pairs. On the other hand, large amounts of unlabeled protein
sequences and chemical compounds are available and have been used to train
language models that learn useful representations. In this study, we propose
exploiting pretrained biochemical language models to initialize (i.e. warm
start) targeted molecule generation models. We investigate two warm start
strategies: (i) a one-stage strategy where the initialized model is trained on
targeted molecule generation (ii) a two-stage strategy containing a
pre-finetuning on molecular generation followed by target specific training. We
also compare two decoding strategies to generate compounds: beam search and
sampling.
  Results: The results show that the warm-started models perform better than a
baseline model trained from scratch. The two proposed warm-start strategies
achieve similar results to each other with respect to widely used metrics from
benchmarks. However, docking evaluation of the generated compounds for a number
of novel proteins suggests that the one-stage strategy generalizes better than
the two-stage strategy. Additionally, we observe that beam search outperforms
sampling in both docking evaluation and benchmark metrics for assessing
compound quality.
  Availability and implementation: The source code is available at
https://github.com/boun-tabi/biochemical-lms-for-drug-design and the materials
are archived in Zenodo at https://doi.org/10.5281/zenodo.6832145",2209.00981v1
2022-12-14,"Characterization of magnetic properties, including magnetocaloric effect, of RE$_{5}$Pt$_2$In$_4$ (RE = Gd-Tm) compounds","The RE$_{5}$Pt$_2$In$_4$ (RE = Gd-Tm) rare earth compounds have been
investigated by means of X-ray diffraction (XRD) as well as by DC and AC
magnetometric measurements. The compounds crystallize in an orthorhombic
crystal structure of the Lu$_{5}$Ni$_2$In$_4$-type (\textit{Pbam} space group,
No.~55). With decreasing temperature the intermetallics undergo a transition
from para- to ferro-/ferri- (RE~=~Gd, Tb, Ho, Er) or antiferromagnetic state
(RE~=~Tm). In case of Dy$_{5}$Pt$_2$In$_4$, the ferromagnetic state is reached
through an intermediate antiferromagnetic order present in a limited
temperature range. The critical temperatures of magnetic ordering range from
4.1~K (RE~=~Tm) up to 108~K (RE~=~Tb). For the majority of investigated
compounds, a cascade of additional magnetic transitions is found below the
respective critical temperatures of magnetic ordering. The magnetic moments are
found solely on the rare earth atoms, while the moments of the remaining Pt and
In atoms are absent or are too small to be detected while accompanied by the
strong rare earth's moments. The magnetocaloric (MCE) performance of
RE$_{5}$T$_2$In$_4$ (RE~=~Gd-Tm) is found quite good, especially while taking
into account the compounds with RE = Ho and Er. Maximum magnetic entropy change
($-\Delta S_M^{max}$) reaches 11.8 (RE~=~Ho) or
11.4~J$\cdot$kg$^{-1}\cdot$K$^{-1}$ (RE~=~Er) under magnetic flux density
change of 0-9~T. Under the same conditions, the relative cooling power (RCP)
and refrigerant capacity (RC) equal 607 and 495~J$\cdot$kg$^{-1}$ (RE~=~Ho) or
434 and 341~J$\cdot$kg$^{-1}$ (RE~=~Er).",2212.07171v4
2023-01-31,Exploring QSAR Models for Activity-Cliff Prediction,"Pairs of similar compounds that only differ by a small structural
modification but exhibit a large difference in their binding affinity for a
given target are known as activity cliffs (ACs). It has been hypothesised that
quantitative structure-activity relationship (QSAR) models struggle to predict
ACs and that ACs thus form a major source of prediction error. However, a study
to explore the AC-prediction power of modern QSAR methods and its relationship
to general QSAR-prediction performance is lacking. We systematically construct
nine distinct QSAR models by combining three molecular representation methods
(extended-connectivity fingerprints, physicochemical-descriptor vectors and
graph isomorphism networks) with three regression techniques (random forests,
k-nearest neighbours and multilayer perceptrons); we then use each resulting
model to classify pairs of similar compounds as ACs or non-ACs and to predict
the activities of individual molecules in three case studies: dopamine receptor
D2, factor Xa, and SARS-CoV-2 main protease. We observe low AC-sensitivity
amongst the tested models when the activities of both compounds are unknown,
but a substantial increase in AC-sensitivity when the actual activity of one of
the compounds is given. Graph isomorphism features are found to be competitive
with or superior to classical molecular representations for AC-classification
and can thus be employed as baseline AC-prediction models or simple
compound-optimisation tools. For general QSAR-prediction, however,
extended-connectivity fingerprints still consistently deliver the best
performance. Our results provide strong support for the hypothesis that indeed
QSAR methods frequently fail to predict ACs. We propose twin-network training
for deep learning models as a potential future pathway to increase
AC-sensitivity and thus overall QSAR performance.",2301.13644v1
2023-02-28,Quantifying interaction mechanism in infinite layer nickelate superconductors,"The relationship between the long-range antiferromagnetic order in cuprates
and the high-temperature superconductivity in these compounds represents
unresolved, nearly four-decades long scientific problem. Because recently
discovered nickelate superconductors are crystallographical counterparts of
cuprates, many properties and difficulties into describing these compounds are
common to both families. Recently, Fowlie et al (2022 Nature Physics 18 1043)
aimed to detect the antiferromagnetic order in $R_{1-x}Sr_{x}NiO_{2}$ (R = Nd,
Pr, La, x ~ 0.2) films by using the muon spin rotation (muSR) technique. This
research group reported on the existence of short-range antiferromagnetic order
in all studied nickelates. Here, we aimed to reveal the existence of this
interaction in the same nickelate films by analyzing the temperature dependent
resistivity, $\rho(T)$, reported by the same research group. Global $\rho(T)$
data fits to the advanced Bloch-Gr\""uneisen model showed that each of
R1-xSrxNiO2 compounds can be characterized by a unique power-law exponent, p
(where p=2 for the electron-electron scattering, p=3 for the electron-magnon
scattering, and p=5 for the electron-phonon scattering), and global
characteristic temperature, $T_{\omega}$ (which has the meaning of the Debye
temperature at p=5). We found that p=2.0 in Nd- and Pr-based compounds, and
p=1.3 for La-based compound. The latter value does not have any interpretation
within established theoretical models. We also analyzed $\rho(T)$ data for
$Nd_{1-x}Sr_{x}NiO_{2}$ (0.125 < x < 0.325) reported by Lee et al (2022
arXiv2203.02580). Because our analysis showed that p-values in nickelates are
remarkably different from p=3, we call for the developent of a new theoretical
model to describe $\rho(T)$ in materials exhibiting a short-range
antiferromagnetic order.",2302.14729v3
2023-06-20,A Unified Understanding of Minimum Lattice Thermal Conductivity,"We propose a first-principles model of minimum lattice thermal conductivity
($\kappa_{\rm L}^{\rm min}$) based on a unified theoretical treatment of
thermal transport in crystals and glasses. We apply this model to thousands of
inorganic compounds and discover a universal behavior of $\kappa_{\rm L}^{\rm
min}$ in crystals in the high-temperature limit: the isotropically averaged
$\kappa_{\rm L}^{\rm min}$ is independent of structural complexity and bounded
within a range from $\sim$0.1 to $\sim$2.6 W/[m$\cdot$K], in striking contrast
to the conventional phonon gas model which predicts no lower bound. We unveil
the underlying physics by showing that for a given parent compound $\kappa_{\rm
L}^{\rm min}$ is bounded from below by a value that is approximately
insensitive to disorder, but the relative importance of different heat
transport channels (phonon gas versus diffuson) depends strongly on the degree
of disorder. Moreover, we propose that the diffuson-dominated $\kappa_{\rm
L}^{\rm min}$ in complex and disordered compounds might be effectively
approximated by the phonon gas model for an ordered compound by averaging out
disorder and applying phonon unfolding. With these insights, we further bridge
the knowledge gap between our model and the well-known Cahill-Watson-Pohl (CWP)
model, rationalizing the successes and limitations of the CWP model in the
absence of heat transfer mediated by diffusons. Finally, we construct graph
network and random forest machine learning models to extend our predictions to
all compounds within the Inorganic Crystal Structure Database (ICSD), which
were validated against thermoelectric materials possessing experimentally
measured ultralow $\kappa_{\rm L}$. Our work offers a unified understanding of
$\kappa_{\rm L}^{\rm min}$, which can guide the rational engineering of
materials to achieve $\kappa_{\rm L}^{\rm min}$.",2306.11917v1
2023-07-11,"Dynamics of orbital degrees of freedom probed via isotope $^{121,123}$ Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors","Isotope $^{121,123}$Sb nuclei with large electric quadrupole moments are
applied to investigate the dynamics of orbital degrees of freedom in
Sb-substituted iron(Fe)-based compounds. In the parent compound
LaFe(As$_{0.6}$Sb$_{0.4}$)O, the nuclear spin relaxation rate
$^{121,123}(T_{1}^{-1})$ at $^{121,123}$Sb sites was enhanced at structural
transition temperature ($T_{s}\sim$ 135 K), which is higher than N\'eel
temperature ($T_{\rm N}\sim$125 K). The isotope ratio
$^{123}(T_{1}^{-1})/^{121}(T_{1}^{-1})$ indicates that the electric quadrupole
relaxation due to the dynamical electric field gradient at Sb site increases
significantly toward $T_{s}$. It is attributed to the critically enhanced
nematic fluctuations of stripe-type arrangement of Fe-$3d_{xz}$ (or $3d_{yz}$)
orbitals. In the lightly electron-doped superconducting (SC) compound
LaFe(As$_{0.7}$Sb$_{0.3}$)(O$_{0.9}$F$_{0.1}$), the nematic fluctuations are
largely suppressed in comparison with the case of the parent compound, however,
it remains a small enhancement below 80 K down to the $T_c$($\sim$ 20 K). The
results indicate that the fluctuations from both the spin and orbital degrees
of freedom on the $3d_{xz}$(or $3d_{yz}$) orbitals can be seen in lightly
electron-doped SC state of LaFeAsO-based compounds. We emphasize that isotope
$^{121,123}$Sb quadrupole moments are sensitive local probe to identify the
dynamics of orbital degrees of freedom in Fe-pnictides, which provides with a
new opportunity to discuss the microscopic correlation between the
superconductivity and both nematic and spin fluctuations simultaneously even in
the polycrystalline samples.",2307.05112v1
1997-07-11,Intermediate Valence Model for the Colossal Magnetoresistance in Tl_{2}Mn_{2}O_{7},"The colossal magnetoresistance exhibited by Tl_{2}Mn_{2}O_{7} is an
interesting phenomenon, as it is very similar to that found in perovskite
manganese oxides although the compound differs both in its crystalline
structure and electronic properties from the manganites. At the same time,
other pyrochlore compounds, though sharing the same structure with
Tl_{2}Mn_{2}O_{7}, do not exhibit the strong coupling between magnetism and
transport properties found in this material. Mostly due to the absence of
evidence for significant doping into the Mn-O sublattice, and the tendency of
Tl to form conduction bands, the traditional double exchange mechanism
mentioned in connection with manganites does not seem suitable to explain the
experimental results in this case. We propose a model for Tl_{2}Mn_{2}O_{7}
consisting of a lattice of intermediate valence ions fluctuating between two
magnetic configurations, representing Mn-3d orbitals, hybridized with a
conduction band, which we associate with Tl. This model had been proposed
originally for the analysis of intermediate valence Tm compounds. With a
simplified treatment of the model we obtain the electronic structure and
transport properties of Tl_{2}Mn_{2}O_{7}, with good qualitative agreement to
experiments. The presence of a hybridization gap in the density of states seems
important to understand the reported Hall data.",9707130v2
1997-11-11,Transport Properties of Heavy Fermion Compounds,"A technique for measuring the electrical resistivity and absolute thermopower
is presented for pressures up to 30 GPa, temperatures down to 25 mK and
magnetic fields up to 10 T. With the examples of CeCu2Ge2 and CeCu2Si2 we focus
on the interplay of normal phase and superconducting properties. With
increasing pres- sure, the behaviour of CeCu2Ge2 evolves from that of an
antiferromagnetically ordered Kondo system to that characteristic of an
intermediate valence compound as the Kondo temperature increases by about two
orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a
superconducting phase occurs which com- petes at low pressure with magnetic
ordering. For CeCu2Si2 the effective mass of carriers is probed by both the
coefficient of the Fermi liquid law and the ini- tial slope of the upper
critical field. The magnetic instability is studied no- tably for CeRu2Ge2 and
Yb-based compounds for which pressure-induced magnetic ordering tends to
develop. Finally, contrary to conventional wisdom, we argue that in heavy
fermions a large part of the residual resistivity is most likely not
independent of temperature; tentatively ascribed to Kondo hole, it can be very
pressure as well as sample dependent. [electrical resistivity, thermoelectric
power, heavy fermion, magnetic order, superconductivity]",9711089v1
1999-07-07,Low energy valence photoemission in the Anderson impurity model for Ce compounds,"The valence level photoemission spectra in the Anderson impurity model for Ce
compounds at zero temperature are studied as a function of the photon energy
$\omega$. Most of former studies on Ce compounds are based on the sudden
approximation, which is valid in high energy region. For the photoemission in
the adiabatic limit of low energy region, one should consider the dipole matrix
elements and the hole-induced photoelectron scattering potential. We can manage
it by combining the time-evolution formalism and the $1/N_f$ scheme in a large
$f$-level degeneracy $N_f$. This gives the exact results as $N_f\to\infty$. In
view of experiments on the valence photoemission, two contributions of $4f$-
and band emissions are mixed. We study the separate $4f$ and band contributions
(from Ce $5d$) and total emission including the interference between two on an
equal footing with varying the photon energy. In the $4f$-emission case, we
also explore the effects of hole-induced scattering potential of the
photoelectron with respect to $\omega$. Its effects are found very similar to
the core level photoemission in shake down case with a localized charge
transfer excitation. Additionally, we examine the adiabatic-sudden transition
in valence level photoemission for the present localized system through the
simplified two-level model.",9907097v1
1999-10-23,High-resolution Ce 3d-edge resonant photoemission study of CeNi_2,"Resonant photoemission (RPES) at the Ce 3d -> 4f threshold has been performed
for alpha-like compound CeNi_2 with extremely high energy resolution (full
width at half maximum < 0.2 eV) to obtain bulk-sensitive 4f spectral weight.
The on-resonance spectrum shows a sharp resolution-limited peak near the Fermi
energy which can be assigned to the tail of the Kondo resonance. However, the
spin-orbit side band around 0.3 eV binding energy corresponding to the f_{7/2}
peak is washed out, in contrast to the RPES spectrum at the Ce 3d -> 4f RPES
threshold. This is interpreted as due to the different surface sensitivity, and
the bulk-sensitive Ce 3d -> 4f RPES spectra are found to be consistent with
other electron spectroscopy and low energy properties for alpha-like
Ce-transition metal compounds, thus resolves controversy on the interpretation
of Ce compound photoemission. The 4f spectral weight over the whole valence
band can also be fitted fairly well with the Gunnarsson-Schoenhammer
calculation of the single impurity Anderson model, although the detailed
features show some dependence on the hybridization band shape and (possibly) Ce
5d emissions.",9910373v1
2000-03-03,Theory of the first-order isostructural valence phase transitions in mixed valence compounds YbIn_{x}Ag_{1-x}Cu_{4},"For describing the first-order isostructural valence phase transition in
mixed valence compounds we develop a new approach based on the lattice Anderson
model. We take into account the Coulomb interaction between localized f and
conduction band electrons and two mechanisms of electron-lattice coupling. One
is related to the volume dependence of the hybridization. The other is related
to local deformations produced by f- shell size fluctuations accompanying
valence fluctuations. The large f -state degeneracy allows us to use the 1/N
expansion method. Within the model we develop a mean-field theory for the
first-order valence phase transition in YbInCu_{4}. It is shown that the
Coulomb interaction enhances the exchange interaction between f and conduction
band electron spins and is the driving force of the phase transition. A
comparison between the theoretical calculations and experimental measurements
of the valence change, susceptibility, specific heat, entropy, elastic
constants and volume change in YbInCu_{4} and YbAgCu_{4} are presented, and a
good quantitative agreement is found. On the basis of the model we describe the
evolution from the first-order valence phase transition to the continuous
transition into the heavy-fermion ground state in the series of compounds
YbIn_{1-x}Ag_{x}Cu_{4}. The effect of pressure on physical properties of
YbInCu_{4} is studied and the H-T phase diagram is found.",0003045v1
2000-05-22,Néel ordered versus quantum disordered behavior in doped spin-Peierls and Haldane gap systems,"I consider a theoretical description of recent experiments on doping the
spin-Peierls compound CuGeO$_3$ and the Haldane gap compounds
PbNi$_2$V$_2$O$_8$ and Y$_2$BaNiO$_5$. The effective theory is the one of
randomly distributed spin-$1/2$ moments interacting with an exchange decaying
exponentially with distance. The model has two phases in the (doping,
interchain coupling) plane: (i) A N\'eel ordered phase at small doping; (ii) A
quantum disordered phase at larger doping and small interchain interactions.
The spin-Peierls compound CuGeO$_3$ and the Haldane gap Nickel oxides
PbNi$_2$V$_2$O$_8$ and Y$_2$BaNiO$_5$ fit well into this phase diagram. At
small temperature, the N\'eel phase is found to be reentrant into the quantum
disordered region. The N\'eel transition relevant for CuGeO$_3$ and
PbNi$_2$V$_2$O$_8$ can be described in terms of a classical disordered model. A
simplified version of this model is introduced, and is solved on a hierarchical
lattice structure, which allows to discuss the renormalization group flow of
the model. It is found that the system looks non disordered at large scale,
which is not against available susceptibility experiments. In the quantum
disordered regime relevant for Y$_2$BaNiO$_5$, the two spin model and the
cluster RG in the 1D regime show a power law susceptibility, in agreement with
recent experiments on Y$_2$BaNiO$_5$. It is found that there is a succession of
two distinct quantum disordered phases as the temperature is decreased. The
classical disordered model of the doped spin-$1$ chain contains already a
physics relevant to the quantum disordered phase.",0005361v2
2000-06-08,Slow crossover in YbXCu4 intermediate valence compounds,"We compare the results of measurements of the magnetic susceptibility Chi(T),
the linear coefficient of specific heat Gamma(T)=C(T)/T and 4f occupation
number nf(T) for the intermediate valence compounds YbXCu4 (X = Ag, Cd, In, Mg,
Tl, Zn) to the predictions of the Anderson impurity model, calculated in the
non-crossing approximation (NCA). The crossover from the low temperature Fermi
liquid state to the high temperature local moment state is substantially slower
in the compounds than predicted by the NCA; this corresponds to the
''protracted screening'' recently predicted for the Anderson Lattice. We
present results for the dynamic susceptibility, measured through neutron
scattering experiments, to show that the deviations between theory and
experiment are not due to crystal field effects, and we present
x-ray-absorption fine-structure (XAFS) results that show the local crystal
structure around the X atoms is well ordered, so that the deviations probably
do not arise from Kondo Disorder. The deviations may correlate with the
background conduction electron density, as predicted for protracted screening.",0006147v2
2000-08-22,"Hole distribution for (Sr,Ca,Y,La)_14 Cu_24 O_41 ladder compounds studied by x-ray absorption spectroscopy","The unoccupied electronic structure for the Sr_14Cu_24O_41 family of two-leg
ladder compounds was investigated for different partial substitutions of Sr^2+
by Ca^2+, leaving the nominal hole count constant, and by Y^3+ or La^3+,
reducing the nominal hole count from its full value of 6 per formula unit.
Using polarization-dependent x-ray absorption spectroscopy on single crystals,
hole states on both the chain and ladder sites could be studied. While for
intermediate hole counts all holes reside on O sites of the chains, a partial
hole occupation on the ladder sites in orbitals oriented along the legs is
observed for the fully doped compound Sr_14Cu_24O_41. On substitution of Ca for
Sr orbitals within the ladder planes but perpendicular to the legs receive some
hole occupation as well.",0008320v1
2001-04-13,Detailed electronic structure studies on superconducting MgB$_2$ and related compounds,"In order to understand the unexpected superconducting behavior of MgB$_2$
compound we have made electronic structure calculations for MgB$_2$ and closely
related systems. Our calculated Debye temperature from the elastic properties
indicate that the average phonon frequency is very large in MgB$_2$ compared
with other superconducting intermetallics and the exceptionally high $T_c$ in
this material can be explained through BCS mechanism only if phonon softening
occurs or the phonon modes are highly anisotropic. We identified a
doubly-degenerate quasi-two dimensional key-energy band in the vicinity of
$E_{F}$ along $\Gamma$-A direction of BZ which play an important role in
deciding the superconducting behavior of this material. Based on this result,
we have searched for similar kinds of electronic feature in a series of
isoelectronic compounds such as BeB$_2$, CaB$_2$, SrB$_2$, LiBC and
MgB$_2$C$_2$ and found that MgB$_2$C$_2$ is one potential material from the
superconductivity point of view. There are contradictory experimental results
regarding the anisotropy in the elastic properties of MgB$_2$ ranging from
isotropic, moderately anisotropic to highly anisotropic. In order to settle
this issue we have calculated the single crystal elastic constants for MgB$_2$
by the accurate full-potential method and derived the directional dependent
linear compressibility, Young's modulus, shear modulus and relevant elastic
properties. We have observed large anisotropy in the elastic properties. Our
calculated polarized optical dielectric tensor shows highly anisotropic
behavior even though it possesses isotropic transport property. MgB$_2$
possesses a mixed bonding character and this has been verified from density of
states, charge density and crystal orbital Hamiltonian population analyses.",0104253v1
2001-06-16,Towards an understanding of CMR pyrochlore Tl2Mn2O7,"Tl2Mn2O7 exhibits important differences with other colossal magnetoresistance
(CMR) compounds, like the Mn-perovskites, in its crystal structure and
electronic properties, indicating the possibility of different mechanisms for
CMR being present. The larger experimental background now existent, has
received diverse interpretations. We aim to contribute to the understanding of
the properties of Tl2Mn2O7 through the study of a generic model for the
compound, including Hund and superexchange couplings as well as hybridization
effects. It includes two kinds of electronic orbitals, as widely believed to be
present: one, directly related to magnetism, involving localized Mn magnetic
moments, and a narrow band strongly Hund-coupled to them. Also, more extended
electronic orbitals, related to the carriers in Tl2Mn2O7, appear and hybridize
with the narrow band. The possibility of a superexchange coupling between the
localized spins is also allowed for. This generic model allows exploration of
many of the proposals put forward by other researchers for Tl2Mn2O7. As a first
approach to the problem, we study the phase diagram and electronic structure
employing simplifications, for sets of parameters including previous
suggestions for the compound. Furthermore, we are able to exhibit similarities
with results obtained in 1997 using an intermediate valence model for Tl2Mn2O7,
in particular, for the electronic structure in the ferromagnetic phase.",0106319v1
2001-07-23,"New two dimensional S=1/2 Heisenberg antiferromagnets: synthesis, structure and magnetic properties","The magnetic susceptibility and magnetization of two new layered S=1/2
Heisenberg antiferromagnets with moderate exchange are reported. The two
isostructural compounds, (2-amino-5-chloropyridinium)2CuBr4 ((5CAP)2CuBr4) and
(2-amino-5-methylpyridinium)2CuBr4 ((5MAP)2CuBr4), contain S=1/2, Cu(II) ions
related by C-centering, yielding four equivalent nearest neighbors. The crystal
structure of newly synthesized compound, (5CAP)2CuBr4, shows the existence of
layers of distorted copper(II)-bromide tetrahedra parallel to the ab plane,
separated by the organic cations along the c axis. Magnetic pathways are
available through the bromide-bromide contacts within the layers and provide
for moderate antiferromagnetic exchange. Susceptibility measurements indicate
interaction strengths to be 8.5(1) K, and 6.5(1) K and ordering temperatures of
5.1(2) K and 3.8(2) K for (5CAP)2CuBr4 and (5MAP)2CuBr4 respectively. High
field magnetization experiments on both compounds show upward curvature of
M(H,T). Magnetization measurements made at T = 1.3 K show saturation occurs in
(5MAP)2CuBr4 at 18.8 T and in (5CAP)2CuBr4 at 24.1 T. The magnetization curves
are consistent with recent theoretical predictions. Single crystal
magnetization measured at 2.0 K indicate a spin flop transition at 0.38 T and
0.63 T for (5CAP)2CuBr4 and (5MAP)2CuBr4 respectively.",0107483v3
2001-12-10,Angle-resolved photoemission study of MX-chain compound [Ni(chxn)$_2$Br]Br$_2$,"We report on the results of angle-resolved photoemission experiments on a
quasi-one-dimensional $MX$-chain compound [Ni(chxn)$_2$Br]Br$_2$ (chxn =
1$R$,2$R$-cyclohexanediamine), a one-dimensional Heisenberg system with $S=1/2$
and $J \sim 3600$ K, which shows a gigantic non-linear optical effect. A ""band""
having about 500 meV energy dispersion is found in the first half of the
Brillouin zone $(0\le kb/\pi <1/2)$, but disappears at $kb / \pi \sim 1/2$. Two
dispersive features, expected from the spin-charge separation, as have been
observed in other quasi-one-dimensional systems like Sr$_2$CuO$_3$, are not
detected. These characteristic features are well reproduced by the $d$-$p$
chain model calculations with a small charge-transfer energy $\Delta$ compared
with that of one-dimensional Cu-O based compounds. We propose that this smaller
$\Delta$ is the origin of the absence of clear spin- and charge-separation in
the photoemission spectra and strong non-linear optical effect in
[Ni(chxn)$_2$Br]Br$_2$.",0112154v2
2001-12-14,Decomposition of the spin-1/2 Heisenberg chain compound Sr2CuO3 in air and water: An EPR and magnetic susceptibility study of Sr2Cu(OH)6,"The reaction of Sr2CuO3 with air and liquid water was studied to address the
origin of the reported variable Curie-Weiss impurity contribution to the
magnetic susceptibility X of this compound at low temperatures. Sr2CuO3 was
found to decompose upon exposure to either of these environments. The compound
Sr2Cu(OH)6 was identified as the primary reaction product. A pure sample of
Sr2Cu(OH)6 was then prepared separately. Electron paramagnetic resonance (EPR),
isothermal magnetization versus magnetic field M(H) and X versus temperature T
measurements demonstrate that Sr2Cu(OH)6 contains weakly interacting Cu+2
magnetic moments with spin S = 1/2 and average g-factor 2.133. From a fit of
X(T) by the Curie-Weiss law and of the M(H) isotherms by modified Brillouin
functions, the exchange interaction between adjacent Cu+2 spins was found to be
J/kB = -1.06(4)K, a weakly antiferromagnetic interaction. Our results indicate
that the previously reported, strongly sample-dependent, Curie-Weiss
contribution to X(T) of a polycrystalline Sr2CuO3 sample most likely arises
from exposing the sample to air, resulting in a variable amount of paramagnetic
Sr2Cu(OH)6 on the surface of the sample.",0112268v1
2002-09-04,Electrical resistivity at large temperatures: Saturation and lack thereof,"Many transition metal compounds show saturation of the resistivity at high
temperatures, T, while the alkali-doped fullerenes and the high-Tc cuprates are
usually considered to show no saturation. We present a model of transition
metal compounds, showing saturation, and a model of alkali-doped fullerenes,
showing no saturation. To analyze the results we use the f-sum rule, which
leads to an approximate upper limit for the resistivity at large T. For some
systems and at low T, the resistivity increases so rapidly that this upper
limit is approached for experimental T. The resistivity then saturates. For a
model of transition metal compounds with weakly interacting electrons, the
upper limit corresponds to a mean free path consistent with the Ioffe-Regel
condition. For a model of the high Tc cuprates with strongly interacting
electrons, however, the upper limit is much larger than the Ioffe-Regel
condition suggests. Since this limit is not exceeded by experimental data, the
data are consistent with saturation also for the cuprates. After ""saturation""
the resistivity usually grows slowly. For the alkali-doped fullerenes,
""saturation"" can be considered to have happened already for T=0, due to
orientational disorder. For these systems, however, the resistivity grows so
rapidly after ""saturation"" that this concept is meaningless. This is due to the
small band width and to the coupling to the level energies of the important
phonons.",0209099v1
2002-09-06,"Raman phonons as a probe of disorder, fluctuations and local structure in doped and undoped orthorhombic and rhombohedral manganites","We present a rationalization of the Raman spectra of orthorhombic and
rhombohedral, stoichiometric and doped, manganese perovskites. In particular we
study RMnO3 (R= La, Pr, Nd, Tb, Ho, Er, Y and Ca) and the different phases of
Ca or Sr doped RMnO3 compounds as well as cation deficient RMnO3. The spectra
of manganites can be understood as combinations of two kinds of spectra
corresponding to two structural configurations of MnO6 octahedra and
independently of the average structure obtained by diffraction techniques. The
main peaks of compounds with regular MnO6 octahedra, as CaMnO3, highly Ca doped
LaMnO3 or the metallic phases of Ca or Sr doped LaMnO3, are bending and tilt
MnO6 octahedra modes which correlate to R-O(1) bonds and Mn-O-Mn angles
respectively. In low and optimally doped manganites, the intensity and width of
the broad bands are related to the amplitude of the dynamic fluctuations
produced by polaron hopping in the paramagnetic insulating regime. The
activation energy, which is proportional to the polaron binding energy, is the
measure of this amplitude. This study permits to detect and confirm the
coexistence, in several compounds, of a paramagnetic matrix with lattice
polaron together with regions without dynamic or static octahedron distortions,
identical to the ferromagnetic metallic phase. We show that Raman spectroscopy
is an excellent tool to obtain information on the local structure of the
different micro or macro-phases present simultaneously in many manganites.",0209156v1
2002-11-14,The magnetic state of Yb in Kondo-lattice YbNi2B2C,"We report neutron scattering experiments performed to investigate the dynamic
magnetic properties of the Kondo-lattice compound YbNi2B2C. The spectrum of
magnetic excitations is found to be broad, extending up to at least 150 meV,
and contains inelastic peaks centred near 18 meV and 43 meV. At low energies we
observe quasielastic scattering with a width Gamma = 2.1 meV. The results
suggest a Yb3+ ground state with predominantly localized 4f electrons subject
to (i) a crystalline electric field (CEF) potential, and (ii) a Kondo
interaction, which at low temperatures is about an order of magnitude smaller
than the CEF interaction. From an analysis of the dynamic magnetic response we
conclude that the crystalline electric field acting on the Yb ions has a
similar anisotropy to that in other RNi2B2C compounds, but is uniformly
enhanced by almost a factor of 2. The static and dynamic magnetic properties of
YbNi2B2C are found to be reconciled quite well by means of an approximation
scheme to the Anderson impurity model, and this procedure also indicates that
the effective Kondo interaction varies with temperature due to the crystal
field splitting. We discuss the nature of the correlated-electron ground state
of YbNi2B2C based on these and other experimental results, and suggest that
this compound might be close to a quantum critical point on the non-magnetic
side.",0211277v3
2003-04-24,Superconductivity of the two-component non-stoichiometric compounds with incommensurate sublattices,"There exists a class of non-stoichiometric materials (berthollides) that can
be considered as constituted by two sublattices, which have specific
physicochemical properties. These properties can be essentially modified by
even rather weak interaction between these components. One of them can be
regarded as a rigid matrix, while another one as a filling in the form of
isolated atoms, molecules or clusters. Structures containing voids of the
diameter up to D ~ (1 - 2)nm in diameter in the stoichiometric sublattice
belong to this class of compounds. These voids are filled by the second
component (of diameter d_{0}), which can be compressed or stretched because of
the sublattice parameters misfit. A stretched matter (D - d_{0} = h > 0) can
exist in a unique intermediate state between the metal and the dielectric; this
state cannot be implemented by another way. The period doubling occurs and a
weak modulation of the metal lattice constant leads to forming not only the
energy gap, but the bound electronic states of the molecular type with two
paired electrons as well. Validity of this model with the Peierls-type lattice
instability for explanation of the well known experimental data on
superconducting transition temperature (T_{c}) in such systems (fullerides,
perovskite-type compounds like Na-WO_{3}, high temperature superconductors) is
considered in this work. The transition temperature T_{c} of fullerides is
proportional to h/D; for the tungsten-bronzes with Na, Rb, or Cs, T_{c} > 0 for
h > 0, and T_{c} ~ 0 for h < 0.",0304561v1
2003-08-13,Nonlinear magnetic susceptibility and aging phenomena in reentrant ferromagnet: Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Linear and nonlinear dynamic properties of a reentrant ferromagnet
Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound are
studied using AC and DC magnetic susceptibility. This compound undergoes
successive phase transitions at the transition temperatures $T_{h}$ (= 16 K),
$T_{c}$ (= 9.7 K), and $T_{RSG}$ (= 3.5 K). The static and dynamic behaviors of
the reentrant spin glass phase below $T_{RSG}$ are characterized by those of
normal spin glass phase with critical exponent $\beta$ = 0.57 $\pm$ 0.10, a
dynamic critical exponent $x$ = 8.5 $\pm$ 1.8, and an exponent $p$ (= 1.55
$\pm$ 0.13) for the de Almeida -Thouless line. A prominent nonlinear
susceptibility is observed between $T_{RSG}$ and $T_{c}$ and around $T_{h}$,
suggesting a chaotic nature of the ferromagnetic phase ($T_{RSG} \leq T \leq
T_{c}$) and the helical spin ordered phase ($T_{c} \leq T \leq T_{h}$). The
aging phenomena are observed both in the RSG and FM phases, with the same
qualitative features as in normal spin glasses. The aging of zero-field cooled
magnetization indicates a drastic change of relaxation mechanism below and
above $T_{RSG}$. The time dependence of the absorption $\chi^{\prime \prime}$
is described by a power law form ($\approx t^{-b^{\prime \prime}}$) in the
ferromagnetic phase, where $b^{\prime \prime} \approx 0.074 \pm 0.016$ at $f$ =
0.05 Hz and $T$ = 7 K. No $\omega t$-scaling law for $\chi^{\prime \prime}$
[$\approx (\omega t)^{-b^{\prime \prime}}$] is observed.",0308247v1
2003-11-19,"Pressure effects on charge, spin, and metal-insulator transitions in narrow bandwidth manganite Pr$_{1-x}$Ca$_{x}$MnO$_{3}$","Pressure effects on the charge and spin states and the relation between the
ferromagnetic and metallic states were explored on the small bandwidth
manganite Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ (x = 0.25, 0.3, 0.35). Under pressure,
the charge ordering state is suppressed and a ferromagnetic metallic state is
induced in all three samples. The metal-insulator transition temperature
(T$_{MI}$) increases with pressure below a critical point P*, above which
T$_{MI}$ decreases and the material becomes insulating as at the ambient
pressure. The e$_{g}$ electron bandwidth and/or band-filling mediate the
pressure effects on the metal-insulator transition and the magnetic transition.
In the small bandwidth and low doping concentration compound (x = 0.25), the
T$_{MI}$ and Curie temperature (T$_{C}$) change with pressure in a reverse way
and do not couple under pressure. In the x = 0.3 compound, the relation of
T$_{MI}$ and T$_{C}$ shows a critical behavior: They are coupled in the range
of $\sim$0.8-5 GPa and decoupled outside of this range. In the x = 0.35
compound, T$_{MI}$ and T$_{C}$ are coupled in the measured pressure range where
a ferromagnetic state is present.",0311431v2
2003-12-10,"G-type antiferromagnetism and orbital ordering due to the crystal field from the rare-earth ions induced by the GdFeO_3-type distortion in RTiO_3 with R=La, Pr, Nd and Sm","The origin of the antiferromagnetic order and puzzling properties of LaTiO_3
as well as the magnetic phase diagram of the perovskite titanates are studied
theoretically. We show that in LaTiO_3, the t_{2g} degeneracy is eventually
lifted by the La cations in the GdFeO_3-type structure, which generates a
crystal field with nearly trigonal symmetry. This allows the description of the
low-energy structure of LaTiO_3 by a single-band Hubbard model as a good
starting point. The lowest-orbital occupation in this crystal field stabilizes
the AFM(G) state, and well explains the spin-wave spectrum of LaTiO_3 obtained
by the neutron scattering experiment. The orbital-spin structures for RTiO_3
with R=Pr, Nd and Sm are also accounted for by the same mechanism. We point out
that through generating the R crystal field, the GdFeO_3-type distortion has a
universal relevance in determining the orbital-spin structure of the perovskite
compounds in competition with the Jahn-Teller mechanism, which has been
overlooked in the literature. Since the GdFeO_3-type distortion is a universal
phenomenon as is seen in a large number of perovskite compounds, this mechanism
may also play important roles in other compounds of this type.",0312244v2
2003-12-29,Influence of Co$^{3+}$ spin-state on optical properties of LaCoO$_3$ and HoCoO$_3$,"Optical properties of the isoelectronic compounds LaCoO$_3$ and HoCoO$_3$ has
been experimentally and theoretically investigated. We've measured the real
$\epsilon_1(\omega)$ and imaginary $\epsilon_2(\omega)$ parts of the dielectric
function, reflectance $R(\omega)$ and optical conductivity at room temperature.
The shift of the most pronounced spectral features to the high energy region on
0.3 eV associated with larger distortions due to the smaller rare earth ionic
radii in HoCoO$_3$ in comparison with LaCoO$_3$ was observed. Also there was
found an enhancement of absorption intensity in the range 1.3-2.3 eV in all
kinds of spectra in HoCoO$_3$, which can be attributed basing on the results of
LDA+U calculations to the different spin-states of Co$^{3+}$ ion in these
compounds. The shift of the onset of the absorption from less than 0.1 eV in
LaCoO$_3$ to 0.7 eV in HoCoO$_3$ and an absorption intensity enhancement in a
narrow spectral range 1.2-2.6 eV in HoCoO$_3$ are clearly seen from the
calculated convolution of partial densities of states obtained in the LDA+U
approach. Such changes are assumed to be induced by the different Co$^{3+}$
spin-state in these compounds at room temperature.",0312679v1
2004-03-09,Possible Competition between superconductivity and magnetism in RuSr2Gd1.5Ce0.5Cu2O10-d (Ru-1222) Rutheno-cuprate compounds,"The RuSr2Gd1.5Ce0.5Cu2O10-d (Ru-1222) compounds, with varying oxygen content,
crystallize in a tetragonal crystal structure (space group I4/mmm).
  Resistance (R) versus temperature (T) measurements show that the air-annealed
samples exhibit superconductivity with superconducting transition temperature
(Tc) onset at around 32 K and R=0 at 3.5 K. On the other hand, the N2-annealed
sample is semiconducting down to 2 K. Magneto-transport measurements on
air-annealed sample in applied magnetic fields of 3 and 6 Tesla show a decrease
in both Tc onset and TR=0. Magnetoresistance of up to 20% is observed in
N2-annealed sample at 2 K and 3 T applied field. The DC magnetization data (M
vs. T) reveal magnetic transitions (Tmag.) at 100 K and 106 K, respectively,
for both air- and N2-annealed samples. Ferromagnetic components in the
magnetization are observed for both samples at 5K and 20 K. The superconducting
transition temperature (Tc) seems to compete with the magnetic transition
temperature (Tmag.). Our results suggest that the magnetic ordering temperature
(Tmag.) of Ru moments in RuO6 octahedra may have direct influence/connection
with the appearance of superconductivity in Cu-O2 planes of Ru-1222 compounds.
Key words: Ruthenocuprates, Superconductivity and Magnetism, Magneto transport
and Magneto resistance. PACS: 74.25. Ha, 74.72. Jt, 75.25. +z, 75.30. Cr.",0403229v2
2004-06-21,Aging dynamics in reentrant ferromagnet: Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Aging dynamics of a reentrant ferromagnet
Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound has
been studied using AC and DC magnetic susceptibility. This compound undergoes
successive transitions at the transition temperatures $T_{c}$ ($= 9.7$ K) and
$T_{RSG}$ ($= 3.5$ K). The relaxation rate $S(t)$ exhibits a characteristic
peak at $t_{cr}$ close to a wait time $t_{w}$ below $T_{c}$, indicating that
the aging phenomena occur in both the reentrant spin glass (RSG) phase below
$T_{RSG}$ and the ferromagnetic (FM) phase between $T_{RSG}$ and $T_{c}$. The
relaxation rate $S(t)$ ($=\text{d}\chi_{ZFC}(t)/\text{d}\ln t$) in the FM phase
exhibits two peaks around $t_{w}$ and a time much shorter than $t_{w}$ under
the positive $T$-shift aging, indicating a partial rejuvenation of domains. The
aging state in the FM phase is fragile against a weak magnetic-field
perturbation. The time ($t$) dependence of $\chi_{ZFC}(t)$ around $t \approx
t_{cr}$ is well approximated by a stretched exponential relaxation:
$\chi_{ZFC}(t) \approx \exp[-(t/\tau)^{1-n}]$. The exponent $n$ depends on
$t_{w}$, $T$, and $H$. The relaxation time $\tau$ ($\approx t_{cr}$) exhibits a
local maximum around 5 K, reflecting a chaotic nature of the FM phase. It
drastically increases with decreasing temperature below $T_{RSG}$.",0406473v1
2004-08-05,Angular dependent planar metamagnetism in the hexagonal compounds TbPtIn and TmAgGe,"Detailed magnetization measurements, M(T,H,theta), were performed on single
crystals of TbPtIn and TmAgGe (both members of the hexagonal Fe_2P/ZrNiAl
structure type), for the magnetic field H applied perpendicular to the
crystallographic c axis. These data allowed us to identify, for each compound,
the easy-axes for the magnetization, which coincided with high symmetry
directions ([120] for TbPtIn and [110] for TmAgGe). For fixed orientations of
the field along each of the two six-fold symmetry axes, a number of
magnetically ordered phases is being revealed by M(H,T) measurements below T_N.
Moreover, T ~ 2 K, M(H)|_theta measurements for both compounds (with H applied
parallel to the basal plane), as well as T = 20 K data for TbPtIn, reveal five
metamagnetic transitions with simple angular dependencies: H_{ci,j} ~
1/cos(theta +/- phi), where phi = 0^0 or 60^0. The high field magnetization
state varies with theta like 2/3*mu_{sat}(R^{3+})*cos(theta), and corresponds
to a crystal field limited saturated paramagnetic, CL-SPM, state. Analysis of
these data allowed us to model the angular dependence of the locally saturated
magnetizations M_{sat} and critical fields H_c with a three coplanar Ising-like
model, in which the magnetic moments are assumed to be parallel to three
adjacent easy axes. Furthermore, net distributions of moments were inferred
based on the measured data and the proposed model.",0408121v1
2004-10-26,Orbital Physics in the Perovskite Ti Oxides,"In the perovskite Ti oxide RTiO3 (R=rare-earth ions), the Ti t2g orbitals and
spins in the 3d^1 state couple each other through the strong electron
correlations, resulting in a rich variety of orbital-spin phases. The origin
and nature of orbital-spin states of these Mott insulators have been
intensively studied. In this article, we review the studies on orbital physics
in the perovskite titanates. We focus on the following three topics: (1) the
origin and nature of the ferromagnetism as well as the orbital ordering in the
compounds with relatively small R ions such as GdTiO3 and YTiO3, (2) the origin
of the G-type antiferromagnetism and the orbital state in LaTiO3, and (3) the
orbital-spin structures in other AFM(G) compounds with relatively large R ions
(R=Ce, Pr, Nd and Sm). On the basis of these discussions, we discuss the whole
phase diagram together with mechanisms of the magnetic phase transition. We
also show that the Ti t2g degeneracy is inherently lifted in the titanates,
which allows the single-band descriptions of the ground-state and low-energy
electronic structures as a good starting point. Our analyses indicate that
these compounds offer touchstone materials described by the single-band Hubbard
model on the cubic lattice. From this insight, we also reanalyze the hole-doped
titanates. Experimentally revealed filling-dependent and bandwidth-dependent
properties and the critical behavior of the metal-insulator transitions are
discussed in the light of theories based on the single-band Hubbard models.",0410650v1
2004-11-17,"Effects of Space Charge, Dopants, and Strain Fields on Surfaces and Grain Boundaries in YBCO Compounds","Statistical thermodynamical and kinetically-limited models are applied to
study the origin and evolution of space charges and band-bending effects at low
angle [001] tilt grain boundaries in YBa$_2$Cu$_3$O$_7$ and the effects of Ca
doping upon them. Atomistic simulations, using shell models of interatomic
forces, are used to calculate the energetics of various relevant point defects.
The intrinsic space charge profiles at ideal surfaces are calculated for two
limits of oxygen contents, i.e. YBa$_2$Cu$_3$O$_6$ and YBa$_2$Cu$_3$O$_7$. At
one limit, O$_6$, the system is an insulator, while at O$_7$, a metal. This is
analogous to the intrinsic and doping cases of semiconductors. The site
selections for doping calcium and creating holes are also investigated by
calculating the heat of solution. In a continuum treatment, the volume of
formation of doping calcium at Y-sites is computed. It is then applied to study
the segregation of calcium ions to grain boundaries in the Y-123 compound. The
influences of the segregation of calcium ions on space charge profiles are
finally studied to provide one guide for understanding the improvement of
transport properties by doping calcium at grain boundaries in Y-123 compound.",0411432v2
2004-12-06,"Resistivity and Thermoelectric power of NaxCoO2 (x =1.0, 0.7 and 0.6) system","Results of thermo-electric power (S) and electrical resistivity (r)
measurements are reported on NaxCoO2 compounds with x = 1.0, 0.7 and 0.6. These
are single-phase compounds crystallizing in the hexagonal structure (space
group P63/mmc) at room temperature. Thermo-electric power values at 300K
(S300K) are, 80mV/K, 39mV/K and 37mV/K for x = 1.0, 0.7 and 0.6 samples,
respectively. The samples with x=0.7 and 1.0 are metallic down to 5 K, while
the x = 0.6 sample is semiconducting. The value of r300K for x = 1.0 sample is
\~0.895 mW-cm and the power factor (S2/r) is = 7.04 x 10-3 W/mK2 which
qualifies it as a good thermo-electric material. In x =1.0 sample, S(T) is
positive throughout 300-5K temperature range and decreases monotonically to
zero as temperature T= 0. In contrast, S(T) of x = 0.7 and 0.6 samples changes
sign and shows negative values between 90 K and 16 K before approaching zero as
T = 0. Anomalous S(T) behavior of x = 0.6 and 0.7 samples, which are
coincidentally the precursor materials to the reported superconductivity in
this class of materials, indicates a dramatic change in the electronic
structure of these compounds on lowering the Na content.",0412122v1
2005-08-30,Effect of annealing on glassy dynamics and non-Fermi liquid behavior in UCu_4Pd,"Longitudinal-field muon spin relaxation (LF-muSR) experiments have been
performed in unannealed and annealed samples of the heavy-fermion compound
UCu_4Pd to study the effect of disorder on non-Fermi liquid behavior in this
material. The muon spin relaxation functions G(t,H) obey the time-field scaling
relation G(t,H) = G(t/H^gamma) previously observed in this compound. The
observed scaling exponent gamma = 0.3 pm 0.1, independent of annealing. Fits of
the stretched-exponential relaxation function G(t) = exp[-(Lambda t)^K] to the
data yielded stretching exponentials K < 1 for all samples. Annealed samples
exhibited a reduction of the relaxation rate at low temperatures, indicating
that annealing shifts fluctuation noise power to higher frequencies. There was
no tendency of the inhomogeneous spread in rates to decrease with annealing,
which modifies but does not eliminate the glassy spin dynamics reported
previously in this compound. The correlation with residual resistivity
previously observed for a number of NFL heavy-electron materials is also found
in the present work.",0508742v1
2005-10-03,New Misfit-Layered Cobalt Oxide (CaOH)1.14CoO2,"We found a new cobalt oxide (CaOH)1.14CoO2 by utilizing the high-pressure
technique. X-ray and electron diffraction studies revealed that the compound
has layer structure which consists of CdI2-type CoO2 layers and rock-salt-type
double CaOH atomic layers. The two subcells have incommensurate periodicity
along the a-axis, resulting in modulated crystal structure due to the
inter-subcell interaction. The structural modulation affects carrier conduction
through the potential randomness. We found that the two-dimensional (2-D)
variable-range hopping (VRH) regime with hole conduction is dominant at low
temperature for this compound, and that the conduction mechanism undergoes
crossover from the 2-D VRH regime to thermal activation-energy type one with
increasing temperature. Based on the experimental results of resistivity,
thermoelectric power, magnetic susceptibility and specific heat measurements,
we suggested a possible electronic-band structure model to explain these
results. The cobalt t2g-derivative band crosses Fermi energy level near the
band edge, yielding small finite density of localized states at the Fermi level
in the band. The observed resistivity, Seebeck coefficient, large Pauli
paramagnetic component in the magnetic susceptibility and comparatively small
Sommerfeld constant in the specific heat are principally attributed to the
holes in the t2g-derivative band. We estimated the Wilson ratio to be about
2.8, suggesting the strong electron correlation realized in this compound.",0510031v1
2005-11-04,Valence and magnetic ordering in intermediate valence compounds : TmSe versus SmB6,"The intermediate valent systems TmSe and SmB6 have been investigated up to 16
and 18 GPa by ac microcalorimetry with a pressure (p) tuning realized in situ
at low temperature. For TmSe, the transition from an antiferromagnetic
insulator for p<3 GPa to an antiferromagnetic metal at higher pressure has been
confirmed. A drastic change in the p variation of the Neel temperature (Tn) is
observed at 3 GPa. In the metallic phase (p>3 GPa), Tn is found to increase
linearly with p. A similar linear p increase of Tn is observed for the
quasitrivalent compound TmS which is at ambiant pressure equivalent to TmSe at
p=7 GPa. In the case of SmB6 long range magnetism has been detected above p=8
GPa, i.e. at a pressure slightly higher than the pressure of the insulator to
metal transition. However a homogeneous magnetic phase occurs only above 10
GPa. The magnetic and electronic properties are related to the renormalization
of the 4f wavefunction either to the divalent or the trivalent configurations.
As observed in SmS, long range magnetism in SmB6 occurs already far below the
pressure where a trivalent Sm3+ state will be reached. It seems possible, to
describe roughly the physical properties of the intermediate valence
equilibrium by assuming formulas for the Kondo lattice temperature depending on
the valence configuration. Comparison is also made with the appearance of long
range magnetism in cerium and ytterbium heavy fermion compounds.",0511106v1
2006-01-01,Classical and ab initio preparation of reliable structures for polymeric coordination compounds,"The detailed investigation of electronic and magnetic properties of polymeric
coordination materials with accurate ab initio quantum mechanical methods is
often computationally extremely demanding because of the large number of atoms
in the unit cell. Moreover, usually the available structural data are
insufficient or poorly determined, especially when the structure contains
hydrogen atoms. In order to be able to perform controlled ab initio
calculations on reliable structures, we use a two-step approach to
systematically prepare model structures for polymeric coordination compound
systems and to relax them to their equilibrium configuration. First, a
structure is constructed on the basis of a crystallographic database and
optimized by force field methods; in the second step, the structure is relaxed
by ab initio quantum mechanical molecular dynamics. With this structure, we
perform accurate electronic structure calculations. We will apply this
procedure to a Fe(II) triazole compound and to a coordination polymer of Cu(II)
ions with 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene.",0601010v3
2006-01-18,Competition between phonon superconductivity and Kondo screening in mixed valence and heavy fermion compounds,"We consider competition of Kondo effect and s-wave superconductivity in heavy
fermion and mixed valence superconductors, using the phenomenological approach
for the periodic Anderson model. Similar to the well known results for
single-impurity Kondo effect in superconductors, we have found principal
possibility of a re-entrant regime of the superconducting transition
temperature, $T_c$, in heavy fermion superconductors in a narrow range of model
parameters and concentration of f-electrons. Suppression of $T_c$ in mixed
valence superconductors is much weaker. Our theory has most validity in the
low-temperature Fermi liquid regime, without re-entrant behavior of $T_c$. To
check its applicability, we performed the fit for the $x$-dependence of $T_c$
in Ce$_{1-x}$La$_x$Ru$_3$Si$_2$ and obtained an excellent agreement with the
experimental data, although no re-entrance was found in this case. Other
experimental data are discussed in the light of our theoretical analysis. In
particular, we compare temperatures of the superconducting transition for some
known homologs, i.e., the analog periodic lattice compounds with and without
f-elements. For a few pairs of homologs superconductivity exists only in the
heavy fermion materials, thus confirming uniqueness of superconductivity
mechanisms for the latter. We suggest that for some other compounds the value
of $T_c$ may remain of the same order in the two homologs, if superconductivity
originates mainly on some light Fermi surface, but induces sizable
superconducting gap on another Fermi surface,for which hybridization or other
heavy fermion effects are more significant.",0601412v1
2006-03-03,Antiferromagnetic superconductors with effective mass anisotropy in magnetic fields,"We derive critical field H_c2 equations for antiferromagnetic
\textit{s}-wave, d_{x^2-y^2}-wave, and d_{xy}-wave superconductors with
effective mass anisotropy in three dimensions, where we take into account (i)
the Jaccarino-Peter mechanism of magnetic-field-induced superconductivity
(FISC) at high fields, (ii) an extended Jaccarino-Peter mechanism that reduces
the Pauli paramagnetic pair-breaking effect at low fields where
superconductivity and an antiferromagnetic long-range order with a canted spin
structure coexist, and (iii) the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or
LOFF) state. As an example, experimental phase diagrams observed in organic
superconductor kappa-(BETS)_2FeBr_4 are theoretically reproduced. In
particular, the upper critical field of low-field superconductivity is well
reproduced without any additional fitting parameter other than those determined
from the critical field curves of the FISC at high fields. Therefore, the
extended Jaccarino-Peter mechanism seems to occur actually in the present
compound. It is predicted that the FFLO state does not occur in the FISC at
high fields in contrast to the compound lambda-(BETS)_2FeCl_4, but it may occur
in low-field superconductivity for s-wave and d_{x^2-y^2}-wave pairings. We
also briefly discuss a possibility of compounds that exhibit unconventional
behaviors of upper critical fields.",0603068v3
2006-05-17,Pressure Induced Changes in the Antiferromagnetic Superconductor YbPd2Sn,"Low temperature ac magnetic susceptibility measurements of the coexistent
antiferromagnetic superconductor YbPd2Sn have been made in hydrostatic
pressures < 74 kbar in moissanite anvil cells. The superconducting transition
temperature is forced to T(SC) = 0 K at a pressure of 58 kbar. The initial
suppression of the superconducting transition temperature is corroborated by
lower hydrostatic pressure (p < 16 kbar) four point resisitivity measurements,
made in a piston cylinder pressure cell. At ambient pressure, in a modest
magnetic field of ~ 500 G, this compound displays reentrant superconducting
behaviour. This reentrant superconductivity is suppressed to lower temperature
and lower magnetic field as pressure is increased. The antiferromagnetic
ordering temperature, which was measured at T(N) = 0.12 K at ambient pressure
is enhanced, to reach T(N) = 0.58 K at p = 74 kbar. The reasons for the
coexistence of superconductivity and antiferromagnetism is discussed in the
light of these and previous findings. Also considered is why superconductivity
on the border of long range magnetic order is so much rarer in Yb compounds
than in Ce compounds. The presence of a new transition visible by ac magnetic
susceptibility under pressure and in magnetic fields greater than 1.5 kG is
suggested.",0605429v1
2006-06-22,Metal-insulator transition in Nd$_{1-x}$Eu$_{x}$NiO$_{3}$ compounds,"Polycrystalline Nd$_{1-x}$Eu$_{x}$NiO$_3$ ($0 \leq x \leq 0.5$) compounds
were synthesized in order to investigate the character of the metal-insulator
(MI) phase transition in this series. Samples were prepared through the sol-gel
route and subjected to heat treatments at $\sim$1000 $^\circ$C under oxygen
pressures as high as 80 bar. X-ray Diffraction (XRD) and Neutron Powder
Diffraction (NPD), electrical resistivity $\rho(T)$, and Magnetization $M(T)$
measurements were performed on these compounds. The results of NPD and XRD
indicated that the samples crystallize in an orthorhombic distorted perovskite
structure, space group $Pbnm$. The analysis of the structural parameters
revealed a sudden and small expansion of $\sim$0.2% of the unit cell volume
when electronic localization occurs. This expansion was attributed to a small
increase of $\sim$0.003 \AA{} of the average Ni-O distance and a simultaneous
decrease of $\sim$$- 0.5^\circ$ of the Ni-O-Ni superexchange angle. The
$\rho(T)$ measurements revealed a MI transition occurring at temperatures
ranging from $T_{\rm MI}\sim 193$ to 336 K for samples with $x = 0$ and 0.50,
respectively. These measurements also show a large thermal hysteresis in
NdNiO$_{3}$ during heating and cooling processes suggesting a first-order
character of the phase transition at $T_{\rm MI}$. The width of this thermal
hysteresis was found to decrease appreciably for the sample
Nd$_{0.7}$Eu$_{0.3}$NiO$_{3}$. The results indicate that cation disorder
associated with increasing substitution of Nd by Eu is responsible for changing
the first order character of the transition in NdNiO$_{3}$.",0606573v1
2006-06-23,"High temperature ferromagnetism in GdFe2Zn20: large, local moments embedded in the nearly ferromagnetic Fermi liquid compound YFe2Zn20","The RFe$_2$Zn$_{20}$ series manifests strongly correlated electron behavior
for the non-magnetic R = Y member and remarkably high temperature,
ferromagnetic ordering ($T_C$ = 86 K) for the local moment bearing R = Gd
member (a compound that is less than 5% atomic Gd). In contrast, the
isostructural RCo$_2$Zn$_{20}$ series manifests a more typical ordering
temperature ($T_N$ = 5.7 K for GdCo$_2$Zn$_{20}$) and YCo$_2$Zn$_{20}$ does not
show signs of correlated electron behavior. Studies of
R(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ (R = Gd, Y), combined with bandstructure
calculations for the end members, reveal that YFe$_2$Zn$_{20}$ is a nearly
ferromagnetic Fermi liquid and that the remarkably high $T_C$ associated with
GdFe$_2$Zn$_{20}$ is the result of submerging a large local moment into such a
highly polarizable matrix. These results indicate that the RFe$_2$Zn$_{20}$
series, and more broadly the RT$_2$Zn$_{20}$ (T = Fe, Co, Ni, Mn, Ru, Rh, Os,
Ir, Pt) isostructural family of compounds, offer an exceptionally promising
phase space for the study of the interaction between local moment and
correlated electron effects near the dilute R limit.",0606615v2
2006-09-25,Ground-state of fractional and integral quantum Hall systems at $ν \leq 1$ and it excitations,"Many-body variational ground-state wave function of two-dimensional electron
system (2DES), localized in the main strip (MS)$L_{x}^{\square} \times L_{y}$
of the finite width $L_{x}^{\square}=\sqrt{2 \pi m} \ell_{0}$ (and the periodic
boundary condition (PBC) imposed along $x-$direction), is presented at the
fractional and the integral filling factors $\nu=1/m$ for two different ion
backgrounds: microscopical uniform ion background (UIB) and classical ion
jellium background (IJB); $\ell_{0}$ is the magnetic length, $m=2\ell+1$ and
$\ell=0, 1, 2,...$. It is shown that the ground-state and the lowest
excited-state can correspond to partial crystal-like correlation order among
$N$ electrons of the main region (MR) $L_{x} \times L_{y}$; then the study of
2DES of $N$ electrons within MR is exactly reduced to the treatment of 2DES of
$\tilde{N}=N L_{x}^{\square}/L_{x}$ electrons localized within MS, with PBC
along $x$. The ground-state manifests the broken symmetry liquid-crystal state
with 2DES density that is periodic along the $y-$ direction, with the period
$L_{x}^{\square}/m$, and independent of $x$. For IJB, at $m=3, 5$, the
ground-state has essentially lower energy per electron than the Laughlin,
uniform liquid, ground-state (the Laughlin model uses IJB); the same holds at
$m=1$. Obtained compound exciton and compound spin-exciton states show finite
excitation gaps. The excited compound electron (hole) is composed, within MS,
from $m$ strongly correlated quasielectrons (quasiholes) of the charge $e/m$
($-e/m$. Quantized Hall conductance $\sigma_{H}=e^{2}/(2 m \pi \hbar)$ is
obtained. The theory is in good agreement with experiments.",0609649v3
2002-06-09,Japanese/English Cross-Language Information Retrieval: Exploration of Query Translation and Transliteration,"Cross-language information retrieval (CLIR), where queries and documents are
in different languages, has of late become one of the major topics within the
information retrieval community. This paper proposes a Japanese/English CLIR
system, where we combine a query translation and retrieval modules. We
currently target the retrieval of technical documents, and therefore the
performance of our system is highly dependent on the quality of the translation
of technical terms. However, the technical term translation is still
problematic in that technical terms are often compound words, and thus new
terms are progressively created by combining existing base words. In addition,
Japanese often represents loanwords based on its special phonogram.
Consequently, existing dictionaries find it difficult to achieve sufficient
coverage. To counter the first problem, we produce a Japanese/English
dictionary for base words, and translate compound words on a word-by-word
basis. We also use a probabilistic method to resolve translation ambiguity. For
the second problem, we use a transliteration method, which corresponds words
unlisted in the base word dictionary to their phonetic equivalents in the
target language. We evaluate our system using a test collection for CLIR, and
show that both the compound word translation and transliteration methods
improve the system performance.",0206015v1
1995-01-08,"Bethe Ansatz for QCD Pomeron,","The equivalence is found between high-energy QCD in the generalized leading
logarithmic approximation and the one-dimensional Heisenberg magnet. According
to Regge theory, the high energy asymptotics of hadronic scattering amplitudes
are related to singularities of partial waves in the complex angular momentum
plane. In QCD, the partial waves are determined by nontrivial two-dimensional
dynamics of the transverse gluonic degrees of freedom. The ""bare"" gluons
interact with each other to form a collective excitation, the Reggeon. The
partial waves of the scattering amplitude satisfy the Bethe-Salpeter equation
whose solutions describe the color singlet compound states of Reggeons --
Pomeron, Odderon and higher Reggeon states. We show that the QCD Hamiltonian
for reggeized gluons coincides in the multi-color limit with the Hamiltonian of
XXX Heisenberg magnet for spin s=0 and spin operators the generators of the
conformal SL(2,C) group. As a result, the Schrodinger equation for the compound
states of Reggeons has a sufficient number of conservation laws to be
completely integrable. A generalized Bethe ansatz is developed for the
diagonalization of the QCD Hamiltonian and for the calculation of hadron-hadron
scattering. Using the Bethe Ansatz solution of high-energy QCD we investigate
the properties of the Reggeon compound states which govern the Regge behavior
of the total hadron-hadron cross sections and the small-x behavior of the
structure functions of deep inelastic scattering.",9501232v2
1995-08-06,Quasiclassical QCD Pomeron,"The Regge behaviour of the scattering amplitudes in perturbative QCD is
governed in the generalized leading logarithmic approximation by the
contribution of the color--singlet compound states of Reggeized gluons. The
interaction between Reggeons is described by the effective hamiltonian, which
in the multi--color limit turns out to be identical to the hamiltonian of the
completely integrable one--dimensional XXX Heisenberg magnet of noncompact spin
$s=0$. The spectrum of the color singlet Reggeon compound states - perturbative
Pomerons and Odderons, is expressed by means of the Bethe Ansatz in terms of
the fundamental $Q-$function, which satisfies the Baxter equation for the XXX
Heisenberg magnet. The exact solution of the Baxter equation is known only in
the simplest case of the compound state of two Reggeons, the BFKL Pomeron. For
higher Reggeon states the method is developed which allows to find its general
solution as an asymptotic series in powers of the inverse conformal weight of
the Reggeon states. The quantization conditions for the conserved charges for
interacting Reggeons are established and an agreement with the results of
numerical solutions is observed. The asymptotic approximation of the energy of
the Reggeon states is defined based on the properties of the asymptotic series,
and the intercept of the three--Reggeon states, perturbative Odderon, is
estimated.",9508025v3
2004-09-28,Integral Equations for Heat Kernel in Compound Media,"By making use of the potentials of the heat conduction equation the integral
equations are derived which determine the heat kernel for the Laplace operator
$-a^2\Delta$ in the case of compound media. In each of the media the parameter
$a^2$ acquires a certain constant value. At the interface of the media the
conditions are imposed which demand the continuity of the `temperature' and the
`heat flows'. The integration in the equations is spread out only over the
interface of the media. As a result the dimension of the initial problem is
reduced by 1. The perturbation series for the integral equations derived are
nothing else as the multiple scattering expansions for the relevant heat
kernels. Thus a rigorous derivation of these expansions is given. In the one
dimensional case the integral equations at hand are solved explicitly (Abel
equations) and the exact expressions for the regarding heat kernels are
obtained for diverse matching conditions. Derivation of the asymptotic
expansion of the integrated heat kernel for a compound media is considered by
making use of the perturbation series for the integral equations obtained. The
method proposed is also applicable to the configurations when the same medium
is divided, by a smooth compact surface, into internal and external regions, or
when only the region inside (or outside) this surface is considered with
appropriate boundary conditions.",0409289v3
2006-08-03,Upper Bounds on Parity Violating Gamma-Ray Asymmetries in Compound Nuclei from Polarized Cold Neutron Capture,"Parity-odd asymmetries in the electromagnetic decays of compound nuclei can
sometimes be amplified above values expected from simple dimensional estimates
by the complexity of compound nuclear states. In this work we use a statistical
approach to estimate the root mean square (RMS) of the distribution of expected
parity-odd correlations $\vec{s_{n}} \cdot \vec{k_{\gamma}}$, where $\vec
{s_{n}}$ is the neutron spin and $\vec{k_{\gamma}}$ is the momentum of the
gamma, in the integrated gamma spectrum from the capture of cold polarized
neutrons on Al, Cu, and In and we present measurements of the asymmetries in
these and other nuclei. Based on our calculations, large enhancements of
asymmetries were not predicted for the studied nuclei and the statistical
estimates are consistent with our measured upper bounds on the asymmetries.",0608006v1
1999-12-03,Unusual statistics of interference effects in neutron scattering from compound nuclei,"We consider interference effects between p-wave resonance scattering
amplitude and background s-wave amplitude in low-energy neutron scattering from
a heavy nucleus which goes through the compound nucleus stage. The first effect
is in the difference between the forward and backward scattering cross
sections. Because of the chaotic nature of the compound states, this effect is
a random variable with zero mean. However, a statistical consideration shows
that the probability distribution of this effect does not obey the standard
central limit theorem. That is, the probability density for the effect averaged
over n resonances does not become a Gaussian distribution with the variance
decreasing as 1/sqrt(n) (``violation'' of the theorem!). We derive the
probability distribution of the effect and the limit distribution of the
average. It is found that the width of this distribution does not decrease with
the increase of n, i.e., fluctuations are not suppressed by averaging.
Furthermore, we consider the correlation between the neutron spin and the
scattering plane and find that this effect, although much smaller, shows
fluctuations which actually increase upon averaging over many measurements.
Limits of the effects due to finite resonance widths are also considered. In
the appendix we present a simple derivation of the limit theorem for the
average of random variables with infinite variances.",9912010v2
2003-06-24,An algebraic solution of the multichannel problem applied to low energy nucleon-nucleus scattering,"Compound resonances in nucleon-nucleus scattering are related to the discrete
spectrum of the target. Such resonances can be studied in a unified and general
framework by a scattering model that uses sturmian expansions of postulated
multichannel interactions between the colliding nuclei. Associated with such
expanded multichannel interactions are algebraic multichannel scattering
matrices. The matrix structure of the inherent Green functions not only
facilitates extraction of the sub-threshold (compound nucleus) bound state
spin-parity values and energies but also readily gives the energies and widths
of resonances in the scattering regime. We exploited also the ability of the
sturmian-expansion method to deal with non-local interactions to take into
account the strong non-local effects introduced by the Pauli principle. As an
example, we have used the collective model (to second order) to define a
multichannel potential matrix for low energy neutron-C12 scattering allowing
coupling between the 0+ (ground), 2+ (4.4389 MeV), and 0+ (7.64 MeV) states.
The algebraic S matrix for this system has been evaluated and the sub-threshold
bound states as well as cross sections and polarizations as functions of energy
are predicted. The results are reflected in the actual measured data, and are
shown to be consistent with expectations as may be based upon a shell model
description of the target and of the compound nucleus.",0306068v1
2000-11-15,Correlation consistent valence basis sets for use with the Stuttgart-Dresden-Bonn relativistic effective core potentials: the atoms Ga-Kr and In-Xe,"We propose large-core correlation-consistent pseudopotential basis sets for
the heavy p-block elements Ga-Kr and In-Xe. The basis sets are of cc-pVTZ and
cc-pVQZ quality, and have been optimized for use with the large-core
(valence-electrons only) Stuttgart-Dresden-Bonn relativistic pseudopotentials.
Validation calculations on a variety of third-row and fourth-row diatomics
suggest them to be comparable in quality to the all-electron cc-pVTZ and
cc-pVQZ basis sets for lighter elements. Especially the SDB-cc-pVQZ basis set
in conjunction with a core polarization potential (CPP) yields excellent
agreement with experiment for compounds of the later heavy p-block elements.
For accurate calculations on Ga (and, to a lesser extent, Ge) compounds,
explicit treatment of 13 valence electrons appears to be desirable, while it
seems inevitable for In compounds. For Ga and Ge, we propose correlation
consistent basis sets extended for (3d) correlation. For accurate calculations
on organometallic complexes of interest to homogenous catalysis, we recommend a
combination of the standard cc-pVTZ basis set for first- and second-row
elements, the presently derived SDB-cc-pVTZ basis set for heavier p-block
elements, and for transition metals, the small-core [6s5p3d] Stuttgart-Dresden
basis set-RECP combination supplemented by (2f1g) functions with exponents
given in the Appendix to the present paper.",0011030v1
2006-03-19,Theory and Application of Dissociative Electron Capture in Molecular Identification,"The coupling of an electron monochromator (EM) to a mass spectrometer (MS)
has created a new analytical technique, EM-MS, for the investigation of
electrophilic compounds. This method provides a powerful tool for molecular
identification of compounds contained in complex matrices, such as
environmental samples. EM-MS expands the application and selectivity of
traditional MS through the inclusion of a new dimension in the space of
molecular characteristics--the electron resonance energy spectrum. However,
before this tool can realize its full potential, it will be necessary to create
a library of resonance energy scans from standards of the molecules for which
EM-MS offers a practical means of detection. Here, an approach supplementing
direct measurement with chemical inference and quantum scattering theory is
presented to demonstrate the feasibility of directly calculating resonance
energy spectra. This approach makes use of the symmetry of the
transition-matrix element of the captured electron to discriminate between the
spectra of isomers. As a way of validating this approach, the resonance values
for twenty-five nitrated aromatic compounds were measured along with their
relative abundance. Subsequently, the spectra for the isomers of nitrotoluene
were shown to be consistent with the symmetry-based model. The initial success
of this treatment suggests that it might be possible to predict negative ion
resonances and thus create a library of EM-MS standards.",0603156v1
2007-05-16,"Nucleon-induced fission cross-sections of tantalum and separated tungsten isotopes and ""compound nucleus"" effect in intermediate energy region","Neutron- and proton-induced fission cross-sections of separated isotopes of
tungsten (182W, 183W, 184W, and 186W) and 181Ta relative to 209Bi have been
measured in the incident nucleon energy region 50 - 200 MeV using fission
chambers based on thin-film breakdown counters (TFBC) using quasi-monoenergetic
neutrons from the 7Li(p,n) reaction and at the proton beams of The Svedberg
Laboratory (TSL), Uppsala University (Uppsala, Sweden). The results are
compared with predictions by the CEM03.01 event generator, as well as with the
recent data for nuclei in the lead-bismuth region. The effect of ""compound
nucleus"" in the intermediate energy region is discussed, displaying in
exponential dependence of nucleon-induced fission cross-sections on the
parameter Z^2/A of the composite system (projectile+target nucleus), and in
other characteristics of the fission process for which parameter Z^2/A plays a
role similar to the one of the usual liquid-drop parameter Z^2/A of compound
nuclei.",0705.2387v2
2007-07-31,Renormalized spin wave excitations in the antiferromagnetic Heisenberg-Kondo model for heavy fermions,"Recent inelastic neutron scattering experiments in CeIn3 and CePd2Si2 single
crystals, measured spin wave excitations at low temperatures. These two heavy
fermion compounds exhibit antiferromagnetic long-range order, but a strong
competition between the Ruderman-Kittel-Kasuya-Yosida(RKKY) interaction and
Kondo effect is evidenced by their nearly equal Neel and Kondo temperatures.
Our aim is to show how magnons such as measured in the antiferromagnetic phase
of these Ce compounds, can be described with a microscopic Heisenberg-Kondo
model as introduced by J.R.Iglesias, C.Lacroix and B.Coqblin, used before for
studies of the non-magnetic phase. The model includes the correlated Ce-4f
electrons hybridized with the conduction band, and we consider competing RKKY
(Heisenberg-like J_{H}) and Kondo (J_{K}) antiferromagnetic couplings. Carrying
on a series of unitary transformations, we perturbatively derive a second-order
effective Hamiltonian which, projected onto the antiferromagnetic electron
ground state, describes the spin wave excitations, renormalized by their
interaction with correlated itinerant electrons. We numerically study how the
different parameters of the model influence the renormalization of the magnons,
yielding useful information for the analysis of inelastic neutron scattering
experiments in antiferromagnetic heavy fermion compounds. We also compare our
results with available experimental data, finding good agreement with the spin
wave measurements in cubic CeIn3.",0708.0023v1
2007-12-04,A suggestion for B-10 imaging during boron neutron capture therapy,"Selective accumulation of B-10 compound in tumour tissue is a fundamental
condition for the achievement of BNCT (Boron Neutron Capture Therapy), since
the effectiveness of therapy irradiation derives just from neutron capture
reaction of B-10. Hence, the determination of the B-10 concentration ratio,
between tumour and healthy tissue, and a control of this ratio, during the
therapy, are essential to optimise the effectiveness of the BNCT, which it is
known to be based on the selective uptake of B-10 compound. In this work,
experimental methods are proposed and evaluated for the determination in vivo
of B-10 compound in biological samples, in particular based on neutron
radiography and gammaray spectroscopy by telescopic system. Measures and Monte
Carlo calculations have been performed to investigate the possibility of
executing imaging of the 10B distribution, both by radiography with thermal
neutrons, using 6LiF/ZnS:Ag scintillator screen and a CCD camera, and by
spectroscopy, based on the revelation of gamma-ray reaction products from B-10
and the H. A rebuilding algorithm has been implemented. The present study has
been done for the standard case of B-10 uptake, as well as for proposed case in
which, to the same carrier, is also synthesized Gd-157, in the amount of is
used like a contrast agent in NMRI.",0712.0501v1
2007-12-18,"Variation of the magnetic ordering in GdT$_2$Zn$_{20}$ (T= Fe, Ru, Os, Co, Rh and Ir) and its correlation with the electronic structure of isostructural YT$_2$Zn$_{20}$","Magnetization, resistivity and specific heat measurements were performed on
the solution-grown, single crystals of six GdT$_2$Zn$_{20}$ (T = Fe, Ru, Os,
Co, Rh and Ir) compounds, as well as their Y analogues. For the Gd compounds,
the Fe column members manifest a ferromagnetic (FM) ground state (with an
enhanced Curie temperature, $T_{\mathrm{C}}$, for T = Fe and Ru), whereas the
Co column members manifest an antiferromagnetic (AFM) ground state.
Thermodynamic measurements on the YT$_2$Zn$_{20}$ revealed that the enhanced
$T_{\mathrm{C}}$ for GdFe$_2$Zn$_{20}$ and GdRu$_2$Zn$_{20}$ can be understood
within the framework of Heisenberg moments embedded in a nearly ferromagnetic
Fermi liquid. Furthermore, electronic structure calculations indicate that this
significant enhancement is due to large, close to the Stoner FM criterion,
transition metal partial density of states at Fermi level, whereas the change
of FM to AFM ordering is associated with filling of electronic states with two
additional electrons per formula unit. The degree of this sensitivity is
addressed by the studies of the pseudo-ternary compounds
Gd(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ and Y(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ which
clearly reveal the effect of 3d band filling on their magnetic properties.",0712.2855v1
2007-12-28,"Half Semimetallic Antiferromagnetism in the Sr$_2$CrTO$_6$ System, T=Os, Ru","Double perovskite Sr$_2$CrOsO$_6$ is (or is very close to) a realization of a
spin-asymmetric semimetallic compensated ferrimagnet, according to first
principles calculations. This type of near-half metallic antiferromagnet is an
unusual occurrence, and more so in this compound because the zero gap is
accidental rather than being symmetry determined. The large spin-orbit coupling
(SOC) of osmium upsets the spin balance (no net spin moment without SOC): it
reduces the Os spin moment by 0.27 $\mu_B$ and induces an Os orbital moment of
0.17 $\mu_B$ in the opposite direction. The effects combine (with small oxygen
contributions) to give a net total moment of 0.54 $\mu_B$ per cell in \scoo,
reflecting a large impact of SOC in this compound. This value is in moderately
good agreement with the measured saturation moment of 0.75 $\mu_B$. The value
of the net moment on the Os ion obtained from neutron diffraction (0.73 $\mu_B$
at low temperature) differs from the calculated value (1.14 $\mu_B$). Rather
surprisingly, in isovalent Sr$_2$CrRuO$_6$ the smaller SOC-induced spin changes
and orbital moments (mostly on Ru) almost exactly cancel. This makes
Sr$_2$CrRuO$_6$ a ""half (semi)metallic antiferromagnet"" (practically vanishing
net total moment) even when SOC is included, with the metallic channel being a
small-band-overlap semimetal. Fixed spin moment (FSM) calculations are
presented for each compound, illustrating how they provide different
information than in the case of a nonmagnetic material. These FSM results
indicate that the Cr moment is an order of magnitude stiffer against
longitudinal fluctuations than is the Os moment.",0712.4308v1
2008-05-13,"Synthesis, Infra-red, Raman, NMR and structural characterization by X-ray Diffraction of [C12H17N2]2CdCl4 and [C6H10N2]2Cd3Cl10 compounds","The synthesis, infra-red, Raman and NMR spectra and crystal structure of 2,
4, 4- trimethyl-4, 5- dihydro-3H-benzo[b] [1, 4] diazepin-1-ium
tetrachlorocadmate, [C12H17N2]2CdCl4 and benzene-1,2-diaminium
decachlorotricadmate(II) [C6H10N2]2Cd3Cl10 are reported.
  The [C12H17N2]2CdCl4 compound crystallizes in the triclinic system (P-1 space
group) with Z = 2 and the following unit cell dimensions: a = 9.6653(8)
angstrom, b = 9.9081(9) angstrom, c = 15.3737(2) angstrom, alpha =
79.486(1)degrees, beta = 88.610(8)degrees and gamma = 77.550(7)degrees. The
structure was solved by using 4439 independent reflections down to R value of
0.029. In crystal structure, the tetrachlorocadmiate anion is connected to two
organic cations through N-H...Cl hydrogen bonds and Van Der Waals interaction
as to build cation-anion-cation cohesion. The [C6H10N2]2Cd3Cl10 crystallizes in
the triclinic system (P-1 space group). The unit cell dimensions are a = 6.826
(5)angstrom, b = 9.861 (7)angstrom, c = 10.344 (3)angstrom, alpha = 103.50
(1)degrees, beta = 96.34 (4)degrees and gamma = 109.45 (3)degrees, Z=2. The
final R value is 0.053 (Rw=0.128). Its crystal structure consists of organic
cations and polymeric chains of [Cd3Cl10]4- anions running along the [011]
direction, In The [C6H10N2]2Cd3Cl10 compounds hydrogen bond interactions
between the inorganic chains and the organic cations, contribute to the crystal
packing.
  PACS Codes: 61.10.Nz, 61.18.Fs, 78.30.-j",0805.1804v2
2008-05-28,57Fe Mossbauer spectroscopy and magnetic measurements of oxygen deficient LaFeAsO,"We report on the magnetic behavior of oxygen deficient LaFeAsO1-x (x-0.10)
compound, prepared by one-step synthesis, which crystallizes in the tetragonal
(S.G. P4/nmm) structure at room temperature. Resistivity measurements show a
strong anomaly near 150 K, which is ascribed to the spin density wave (SDW)
instability. On the other hand, dc magnetization data shows paramagnetic-like
features down to 5 K, with an effective moment of 0.83 mB/Fe. 57Fe Mossbauer
studies (MS) have been performed at 95 and 200 K. The spectra at both
temperatures are composed of two sub-spectra. At 200 K the major one (88%), is
almost a singlet, and corresponds to those Fe nuclei, which have two oxygen
ions in their close vicinity. The minor one, with a large quadrupole splitting,
corresponds to Fe nuclei, which have vacancies in their immediate neighborhood.
The spectrum at 95 K, exhibits a broadened magnetic split major (84%)
sub-spectrum and a very small magnetic splitting in the minor subspectrum. The
relative intensities of the subspectra facilitate in estimating the actual
amount of oxygen vacancies in the compound to be 7.0(5)%, instead of the
nominal LaFeAsO0.90. These results, when compared with reported 57Fe MS of
non-superconducting LaFeAsO and superconducting LaFeAsO0.9F0.1, confirm that
the studied LaFeAsO0.93 is a superconductivity-magnetism crossover compound of
the newly discovered Fe based superconducting family.",0805.4251v2
2008-07-03,Spin wave excitations in the antiferromagnetic Heisenberg-Kondo model for heavy fermions,"Recent inelastic neutron scattering experiments in CeIn$_{3}$ and
CePd$_{2}$Si$_{2}$ single crystals measured spin wave excitations at low
temperatures. These two heavy fermion compounds exhibit antiferromagnetic
long-range order, but a strong competition between the
Ruderman-Kittel-Kasuya-Yosida(RKKY) interaction and Kondo effect is evidenced
by their nearly equal N\'eel and Kondo temperatures. Our aim is to show how
magnons such as measured in the antiferromagnetic phase of these Ce compounds,
can be described with a microscopic Heisenberg-Kondo model introduced by
J.R.Iglesias, C.Lacroix and B.Coqblin, used before for studies of the
non-magnetic phase. The model includes the correlated Ce-$4 f$ electrons
hybridized with the conduction band, where we also allow for correlations, and
we consider competing
  RKKY (Heisenberg-like $J_{H} $) and Kondo ($J_{K}$) antiferromagnetic
couplings. Carrying on a series of unitary transformations, we perturbatively
derive a second-order effective Hamiltonian which, projected onto the
antiferromagnetic electron ground state, describes the spin wave excitations,
renormalized by their interaction with correlated itinerant electrons. We
numerically study how the different parameters of the model influence the
renormalization of the magnons, yielding useful information for the analysis of
inelastic neutron scattering experiments in antiferromagnetic heavy fermion
compounds. We also compare our results with the available experimental data,
finding good agreement with the spin wave measurements in cubic CeIn$_3$.",0807.1246v1
2008-07-17,High pressure behavior of Ga-doped LaMnO_3: a combined X-ray diffraction and optical spectroscopy study,"The pressure effects on the JT distortion of three representative compounds
belonging to the LaMn_1-xGa_xO_3 (x= 0.2, 0.3, 0.4) family was widely
investigated by means of X-ray diffraction and Raman spectroscopy. A compound
with a fully JT distorted structure (x=0.2), one with regular octahedra (x=0.6)
and one in an intermediate configuration (x=0.3) were selected. A pressure
induced transitions from the orthorhombic Pbnm phase towards structures with
higher symmetry were observed in all the samples. Both Raman and X-ray data
confirm that the most important structural effect of pressure is that of
reducing the octahedral distortion. The appearance of a feature in the lattice
parameter behavior connected to a structural instability was also detected,
pointing out the key role of the JT distortion in stabilizing the manganite
structures. On the other hand, the complete suppression of the JT distortion in
the high-pressure phases cannot be claimed. The Raman spectra collected from
more distorted compounds (x=0.2, 0.3) reveal clearly the coexistence of domains
of distorted and more regular octahedra in a certain pressure range. The first
sketch of the Pressure vs. Ga-content phase diagram was drawn.",0807.2848v1
2008-07-24,Resonant Spin Excitation in the High Temperature Superconductor Ba0.6K0.4Fe2As2,"The recent observations of superconductivity at temperatures up to 55K in
compounds containing layers of iron arsenide have revealed a new class of high
temperature superconductors that show striking similarities to the more
familiar cuprates. In both series of compounds, the onset of superconductivity
is associated with the suppression of magnetic order by doping holes and/or
electrons into the band leading to theories in which magnetic fluctuations are
either responsible for or strongly coupled to the superconducting order
parameter. In the cuprates, theories of magnetic pairing have been invoked to
explain the observation of a resonant magnetic excitation that scales in energy
with the superconducting energy gap and is suppressed above the superconducting
transition temperature, Tc. Such resonant excitations have been shown by
inelastic neutron scattering to be a universal feature of the cuprate
superconductors, and have even been observed in heavy fermion superconductors
with much lower transition temperatures. In this paper, we show neutron
scattering evidence of a resonant excitation in Ba0.6K0.4Fe2As2, which is a
superconductor below 38K, at the momentum transfer associated with magnetic
order in the undoped compound, BaFe2As2, and at an energy transfer that is
consistent with scaling in other strongly correlated electron superconductors.
As in the cuprates, the peak disappears at Tc providing the first experimental
confirmation of a strong coupling of the magnetic fluctuation spectrum to the
superconducting order parameter in the new iron arsenide superconductors.",0807.3932v1
2008-08-27,Magnetic phase evolution in the spinel compounds Zn$_{1-x}$Co$_x$Cr$_2$O$_4$,"We present the magnetic properties of complete solid solutions of
ZnCr$_2$O$_4$ and CoCr$_2$O$_4$: two well-studied oxide spinels with very
different magnetic ground states. ZnCr$_2$O$_4$, with non-magnetic $d^{10}$
cations occupying the A site and magnetic $d^3$ cations on the B site, is a
highly frustrated antiferromagnet. CoCr$_2$O$_4$, with magnetic $d^7$ cations
(three unpaired electrons) on the A site as well, exhibits both N\'eel
ferrimagnetism as well as commensurate and incommensurate non-collinear
magnetic order. More recently, CoCr$_2$O$_4$ has been studied extensively for
its polar behavior which arises from conical magnetic ordering. Gradually
introducing magnetism on the A site of ZnCr$_2$O$_4$ results in a transition
from frustrated antiferromagnetism to glassy magnetism at low concentrations of
Co, and eventually to ferrimagnetic and conical ground states at higher
concentrations. Real-space Monte-Carlo simulations of the magnetic
susceptibility suggest that the first magnetic ordering transition and features
of the susceptibility across $x$ are captured by near-neighbor self- and
cross-couplings between the magnetic A and B atoms. We present as a part of
this study, a method for displaying the temperature dependence of magnetic
susceptibility in a manner which helps distinguish between compounds possessing
purely antiferromagnetic interactions from compounds where other kinds of
ordering are present.",0808.3789v3
2008-09-26,High-pressure x-ray diffraction study on the structure and phase transitions of the defect-stannite ZnGa2Se4 and defect-chalcopyrite CdGa2S4,"X-ray diffraction measurements on the sphalerite-derivatives ZnGa2Se4 and
CdGa2S4 have been performed upon compression up to 23 GPa in a diamond-anvil
cell. ZnGa2Se4 exhibits a defect tetragonal stannite-type structure (I-42m) up
to 15.5 GPa and in the range from 15.5 GPa to 18.5 GPa the low-pressure phase
coexists with a high-pressure phase, which remains stable up to 23 GPa. In
CdGa2S4, we find the defect tetragonal chalcopyrite-type structure (I-4) is
stable up to 17 GPa. Beyond this pressure a pressure-induced phase transition
takes place. In both materials, the high-pressure phase has been characterized
as a defect-cubic NaCl-type structure (Fm-3m). The occurrence of the pressure
induced phase transitions is apparently related with an increase of the cation
disorder on the semiconductors investigated. In addition, the results allow the
evaluation of the axial compressibility and the determination of the equation
of state for each compound. The obtained results are compared with those
previously reported for isomorphic digallium sellenides. Finally, a systematic
study of the pressure-induced phase transition in twenty-three different
sphalerite-related ABX2 and AB2X4 compounds indicates that the transition
pressure increases as the ratio of the cationic radii and anionic radii of the
compounds increases.",0809.4620v1
2008-11-03,Ab initio calculation of structural and electronic properties of Al$_x$Ga$_{1-x}$N and In$_x$Ga$_{1-x}$N alloys,"Using the density functional theory (DFT) with the generalized gradient
approximation (GGA), the structural and electronic properties of wurtzite AlN,
GaN, InN, and their related alloys, Al$_x$Ga$_{1-x}$N and In$_x$Ga$_{1-x}$N,
were calculated. We have performed accurate {\it ab initio} total energy
calculations using the full--potential linearized augmented plane wave
(FP--LAPW) method to investigate the structural and electronic properties. In
both alloys we found that the fundamental parameters do not follow Vegard's
law. The lattice parameters, $a, c,$ and $u$, for the Al$_x$Ga$_{1-x}$N alloy
are found to exhibit downward bowing, while for In$_x$Ga$_{1-x}$N there is an
upward bowing for the $a$ and $c$ parameters and a downward bowing for the
internal parameter, $u$. Furthermore, we found that for both alloys, the band
gap value does not follow Vegard's law. As a by--product of our electronic band
structure calculations, the effective masses of the binary compounds as well as
their related alloys were calculated. We show that the calculated properties
for the binary compounds, as well as for the studied alloys, show good
agreement with most of the previously reported results. Finally, using the
frozen phonon approach, the A$_1(TO)$ mode for the different systems studied in
this work was calculated. Our calculations show good agreement with
experimental values reported for the binary compounds. For the ternary alloys,
our calculations reproduce experimental values for Al$_x$Ga$_{1-x}$N as well as
theoretical predictions for In$_x$Ga$_{1-x}$N.",0811.0380v1
2008-12-31,Entropy and set cardinality inequalities for partition-determined functions,"A new notion of partition-determined functions is introduced, and several
basic inequalities are developed for the entropy of such functions of
independent random variables, as well as for cardinalities of compound sets
obtained using these functions. Here a compound set means a set obtained by
varying each argument of a function of several variables over a set associated
with that argument, where all the sets are subsets of an appropriate algebraic
structure so that the function is well defined. On the one hand, the entropy
inequalities developed for partition-determined functions imply entropic
analogues of general inequalities of Pl\""unnecke-Ruzsa type. On the other hand,
the cardinality inequalities developed for compound sets imply several
inequalities for sumsets, including for instance a generalization of
inequalities proved by Gyarmati, Matolcsi and Ruzsa (2010). We also provide
partial progress towards a conjecture of Ruzsa (2007) for sumsets in nonabelian
groups. All proofs are elementary and rely on properly developing certain
information-theoretic inequalities.",0901.0055v3
2009-02-07,Development of an IMS Type Device for Volatile Organic Compunds Detection: Simulation and Comparision of the Ion Distributions,"Ion Mobility Spectrometry (IMS) is a well-known, sensitive and rapid
technique to detect dangerous organic compounds. We propose a system in which a
crown type discharge generates a ionic flow that is swept towards an array of
collectors by a transverse electric field. The ions are separated as they enter
the cell according to their mobility. Thus, the distribution of the charge
deposited at the detector assembly constitutes a {\em fingerprint} for each
organic compound. Simulations of our cell and experiments were performed for
small amounts of acetone, ethanol and toluene. The dependence on the cell
parameters of the current and charge versus time of flight was analyzed. Our
simulation reproduces only qualitatively the experimental results. However, a
PCA statistical analysis of the results obtained by simulation of the proposed
design shows that the fingerprint is useful for a clear identification of such
compounds.",0902.1206v2
2009-03-16,Spin Waves and Magnetic Exchange Interactions in CaFe2As2,"Antiferromagnetism is relevant to high temperature (high-Tc)
superconductivity because copper oxide and iron arsenide high-Tc
superconductors arise from electron- or hole-doping of their antiferromagnetic
(AF) ordered parent compounds. There are two broad classes of explanation for
the phenomenon of antiferromagnetism: in the local moment picture, appropriate
for the insulating copper oxides, AF interactions are well described by a
Heisenberg Hamiltonian; while in the itinerant model, suitable for metallic
chromium, AF order arises from quasiparticle excitations of a nested Fermi
surface. There has been contradictory evidence regarding the microscopic origin
of the AF order in iron arsenide materials, with some favoring a localized
picture while others supporting an itinerant point of view. More importantly,
there has not even been agreement about the simplest effective ground state
Hamiltonian necessary to describe the AF order. Here we report inelastic
neutron scattering mapping of spin-wave excitations in CaFe2As2, a parent
compound of the iron arsenide family of superconductors. We find that the spin
waves in the entire Brillouin zone can be described by an effective
three-dimensional local moment Heisenberg Hamiltonian, but the large in-plane
anisotropy cannot. Therefore, magnetism in the parent compounds of iron
arsenide superconductors is neither purely local nor purely itinerant; rather
it is a complicated mix of the two.",0903.2686v1
2009-03-27,Coupling between phonons and magnetic excitations in orthorhombic Eu_{1-x}Y_xMnO_3,"In this work we present a detailed study of the structural and lattice
dynamic properties of Y-doped EuMnO3 ceramics (Eu1-xYxMnO3, with 0<x<0.55). A
thorough analysis towards the correlation between both structural and Raman
modes parameters has been undertaken. Our results provide evidence for two main
structural distortions of MnO6 octahedra, arising from a cooperative
Jahn-Teller and rotational distortions in these compounds. The temperature
dependence of the B1g symmetric stretching mode of the MnO6 units has revealed
either a positive or negative shift regarding the pure anharmonic temperature
dependence of the phonon frequency, which strongly depends on the
Y-concentration. This frequency renormalization is explained in terms of a
competition between ferro and antiferromagnetic interactions. The pronounced
frequency renormalization of the symmetric stretching mode for x=0.2 evidences
the predominance of the ferromagnetic interactions against the
antiferromagnetic ones, which is in good correlation with the spontaneous
magnetization measured in this compound. The emerging of the shifts referred
well above the Neel temperature is likely associated with the coupling between
phonons and dynamical fluctuations of the magnetic system, which provides
further grounds for the existence of strong spin-phonon coupling in this
compound.",0903.4753v1
2009-06-15,Progress and perspectives on the electron-doped cuprates,"Although the vast majority of high-$T_c$ cuprate superconductors are
hole-doped, a small family of electron-doped compounds exists. Under
investigated until recently, there has been tremendous recent progress in their
characterization. A consistent view is being reached on a number of formerly
contentious issues, such as their order parameter symmetry, phase diagram, and
normal state electronic structure. Many other aspects have been revealed
exhibiting both their similarities and differences with the hole-doped
compounds. This review summarizes the current experimental status of these
materials, with a goal to providing a snapshot of our current understanding of
electron-doped cuprates. When possible we put our results in the context of the
hole-doped compounds. We attempt to synthesize this information into a
consistent view on a number of topics important to both this material class as
well as the overall cuprate phenomenology including the phase diagram, the
superconducting order parameter symmetry, phase separation, pseudogap effects,
the role of competing orders, the spin-density wave mean-field description of
the normal state, and electron-phonon coupling.",0906.2931v2
2009-06-19,DNA Nucleobase Synthesis at Titan Atmosphere Analog by Soft X-rays,"Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of
N2 and CH4 and includes traces of many simple organic compounds. This
atmosphere also partly consists of haze and aerosol particles which during the
last 4.5 gigayears have been processed by electric discharges, ions, and
ionizing photons, being slowly deposited over the Titan surface. In this work,
we investigate the possible effects produced by soft X-rays (and secondary
electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic
photochemistry. The experiments have been performed inside a high vacuum
chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian
Synchrotron Light Source, Campinas, Brazil. In-situ sample analyses were
performed by a Fourier transform infrared spectrometer. The infrared spectra
have presented several organic molecules, including nitriles and aromatic CN
compounds. After the irradiation, the brownish-orange organic residue (tholin)
was analyzed ex-situ by gas chromatographic (GC/MS) and nuclear magnetic
resonance (1H NMR) techniques, revealing the presence of adenine (C5H5N5), one
of the constituents of the DNA molecule. This confirms previous results which
showed that the organic chemistry on the Titan surface can be very complex and
extremely rich in prebiotic compounds. Molecules like these on the early Earth
have found a place to allow life (as we know) to flourish.",0906.3675v1
2009-08-24,Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface,"Recent theories and experiments have suggested that strong spin-orbit
coupling effects in certain band insulators can give rise to a new phase of
quantum matter, the so-called topological insulator, which can show macroscopic
entanglement effects. Such systems feature two-dimensional surface states whose
electrodynamic properties are described not by the conventional Maxwell
equations but rather by an attached axion field, originally proposed to
describe strongly interacting particles. It has been proposed that a
topological insulator with a single spin-textured Dirac cone interfaced with a
superconductor can form the most elementary unit for performing fault-tolerant
quantum computation. Here we present an angle-resolved photoemission
spectroscopy study and first-principle theoretical calculation-predictions that
reveal the first observation of such a topological state of matter featuring a
single-surface-Dirac-cone realized in the naturally occurring Bi$_2$Se$_3$
class of materials. Our results, supported by our theoretical predictions and
calculations, demonstrate that undoped compound of this class of materials can
serve as the parent matrix compound for the long-sought topological device
where in-plane surface carrier transport would have a purely quantum
topological origin. Our study further suggests that the undoped compound
reached via n-to-p doping should show topological transport phenomena even at
room temperature.",0908.3513v1
2009-08-26,Valence fluctuation in Ce$_{2}$Co$_{3}$Ge$_{5}$ and crystal field effect in Pr$_{2}$Co$_{3}$Ge$_{5}$,"Polycrystalline samples of ternary rare earth germanides
R$_{2}$Co$_{3}$Ge$_{5}$(R = La, Ce and Pr) have been prepared and investigated
by means of magnetic susceptibility, isothermal magnetization, electrical
resistivity and specific heat measurements. All these compounds crystallize in
orthorhombic U$_{2}$Co$_{3}$Si$_{5}$ structure (space group \textit{Ibam}). No
evidence of magnetic or superconducting transition is observed in any of these
compounds down to 2 K. The unit cell volume of Ce$_{2}$Co$_{3}$Ge$_{5}$
deviates from the expected lanthanide contraction, indicating non trivalent
state of Ce ions in this compound. The reduced value of effective moment
($\mu_{eff}$ $\approx$ 0.95 $\mu_{B}$) compared to that expected for trivalent
Ce ions further supports valence fluctuating nature of Ce in
Ce$_{2}$Co$_{3}$Ge$_{5}$. The observed temperature dependence of magnetic
susceptibility is consistent with ionic interconfiguration fluctuation (ICF)
model. Although no sharp anomaly due to a phase transition is seen, a broad
Schottky-type anomaly is observed in the magnetic part of specific heat of
Pr$_{2}$Co$_{3}$Ge$_{5}$. An analysis of $C_{mag}$ data suggests a singlet
ground state in Pr$_{2}$Co$_{3}$Ge$_{5}$ separated from the singlet first
excited state by 22 K and a doublet second excited state at 73 K.",0908.3880v1
2009-09-28,On the Degrees of Freedom of the Compound MIMO Broadcast Channels with Finite States,"Multiple-antenna broadcast channels with $M$ transmit antennas and $K$
single-antenna receivers is considered, where the channel of receiver $r$ takes
one of the $J_r$ finite values. It is assumed that the channel states of each
receiver are randomly selected from $\mathds{R}^{M\times 1}$ (or from
$\mathds{C}^{M\times 1}$). It is shown that no matter what $J_r$ is, the
degrees of freedom (DoF) of $\frac{MK}{M+K-1}$ is achievable. The achievable
scheme relies on the idea of interference alignment at receivers, without
exploiting the possibility of cooperation among transmit antennas. It is proven
that if $J_r \geq M$, $r=1,...,K$, this scheme achieves the optimal DoF. This
results implies that when the uncertainty of the base station about the channel
realization is considerable, the system loses the gain of cooperation. However,
it still benefits from the gain of interference alignment. In fact, in this
case, the compound broadcast channel is treated as a compound X channel.
  Moreover, it is shown that when the base station knows the channel states of
some of the receivers, a combination of transmit cooperation and interference
alignment would achieve the optimal DoF.
  Like time-invariant $K$-user interference channels, the naive vector-space
approaches of interference management seem insufficient to achieve the optimal
DoF of this channel. In this paper, we use the Number-Theory approach of
alignment, recently developed by Motahari et al.[1]. We extend the approach of
[1] to complex channels as well, therefore all the results that we present are
valid for both real and complex channels.",0909.5006v3
2009-10-16,Degraded Compound Multi-receiver Wiretap Channels,"In this paper, we study the degraded compound multi-receiver wiretap channel.
The degraded compound multi-receiver wiretap channel consists of two groups of
users and a group of eavesdroppers, where, if we pick an arbitrary user from
each group of users and an arbitrary eavesdropper, they satisfy a certain
Markov chain. We study two different communication scenarios for this channel.
In the first scenario, the transmitter wants to send a confidential message to
users in the first (stronger) group and a different confidential message to
users in the second (weaker) group, where both messages need to be kept
confidential from the eavesdroppers. For this scenario, we assume that there is
only one eavesdropper. We obtain the secrecy capacity region for the general
discrete memoryless channel model, the parallel channel model, and the Gaussian
parallel channel model. For the Gaussian multiple-input multiple-output (MIMO)
channel model, we obtain the secrecy capacity region when there is only one
user in the second group. In the second scenario we study, the transmitter
sends a confidential message to users in the first group which needs to be kept
confidential from the second group of users and the eavesdroppers. Furthermore,
the transmitter sends a different confidential message to users in the second
group which needs to be kept confidential only from the eavesdroppers. For this
scenario, we do not put any restriction on the number of eavesdroppers. As in
the first scenario, we obtain the secrecy capacity region for the general
discrete memoryless channel model, the parallel channel model, and the Gaussian
parallel channel model. For the Gaussian MIMO channel model, we establish the
secrecy capacity region when there is only one user in the second group.",0910.3033v1
2009-12-15,Unusual Electronic Structure and Observation of Dispersion Kink in CeFeAsO Parent Compound of FeAs-Based Superconductors,"We report the first comprehensive high-resolution angle-resolved
photoemission measurements on CeFeAsO, a parent compound of FeAs-based high
temperature superconductors with a mangetic/structural transition at $\sim$150
K. In the magnetic ordering state, four hole-like Fermi surface sheets are
observed near $\Gamma$(0,0) and the Fermi surface near M(+/-$\pi$,+/-$\pi$)
shows a tiny electron-like pocket at M surrounded by four Dirac cone-like
strong spots. The unusual Fermi surface topology deviates strongly from the
band structure calculations. The electronic signature of the
magnetic/structural transition shows up in the dramatic change of the
quasiparticle scattering rate. A dispersion kink at $\sim$ 25meV is for the
first time observed in the parent compound of Fe-based superconductors.",0912.2838v4
2010-02-19,Uniaxial strain detwinning of CaFe2As2 and BaFe2As2: optical and transport study,"TThe parent compounds of iron-arsenide superconductors, $A$Fe$_{2}$As$_{2}$
($A$=Ca, Sr, Ba), undergo a tetragonal to orthorhombic structural transition at
a temperature $T_{\mathrm{TO}}$ in the range 135 to 205K depending on the
alkaline earth element. Below $T_{\mathrm{TO}}$ the free standing crystals
split into equally populated structural domains, which mask intrinsic,
in-plane, anisotropic properties of the materials. Here we demonstrate a way of
mechanically detwinning CaFe$_{2}$As$_{2}$ and BaFe$_{2}$As$_{2}$. The
detwinning is nearly complete, as demonstrated by polarized light imaging and
synchrotron $X$-ray measurements, and reversible, with twin pattern restored
after strain release. Electrical resistivity measurements in the twinned and
detwinned states show that resistivity, $\rho$, decreases along the
orthorhombic $a_{o}$-axis but increases along the orthorhombic $b_{o}$-axis in
both compounds. Immediately below $T_{\mathrm{TO}}$ the ratio $\rho_{bo}/
\rho_{ao}$ = 1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to
CaFe$_{2}$As$_{2}$, BaFe$_{2}$As$_{2}$ reveals an anisotropy in the nominally
tetragonal phase, suggesting that either fluctuations play a larger role above
$T_{\mathrm{TO}}$ in BaFe$_{2}$As$_{2}$ than in CaFe$_{2}$As$_{2}$, or that
there is a higher temperature crossover or phase transition.",1002.3801v3
2010-03-10,"Diffuse Neutron Scattering Study of Magnetic Correlations in half-doped La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) Manganites","The short range ordered magnetic correlations have been studied in half doped
La0.5Ca0.5-xSrxMnO3 (x = 0.1, 0.3 and 0.4) compounds by polarized neutron
scattering technique. On doping Sr2+ for Ca2+ ion, these compounds with x =
0.1, 0.3, and 0.4 exhibit CE-type, mixture of CE-type and A-type, and A-type
antiferromagnetic ordering, respectively. Magnetic diffuse scattering is
observed in all the compounds above and below their respective magnetic
ordering temperatures and is attributed to magnetic polarons. The correlations
are primarily ferromagnetic in nature above T\_N, although a small
antiferromagnetic contribution is also evident. Additionally, in samples x =
0.1 and 0.3 with CE-type antiferromagnetic ordering, superlattice diffuse
reflections are observed indicating correlations between magnetic polarons. On
lowering temperature below T\_N the diffuse scattering corresponding to
ferromagnetic correlations is suppressed and the long range ordered
antiferromagnetic state is established. However, the short range ordered
correlations indicated by enhanced spin flip scattering at low Q coexist with
long range ordered state down to 3K. In x = 0.4 sample with A-type
antiferromagnetic ordering, superlattice diffuse reflections are absent.
Additionally, in comparison to x = 0.1 and 0.3 sample, the enhanced spin flip
scattering at low Q is reduced at 310K, and as temperature is reduced below
200K, it becomes negligibly low. The variation of radial correlation function,
g(r) with temperature indicates rapid suppression of ferromagnetic correlations
at the first nearest neighbor on approaching TN. Sample x = 0.4 exhibits growth
of ferromagnetic phase at intermediate temperatures (~ 200K). This has been
further explored using SANS and neutron depolarization techniques.",1003.2026v1
2010-03-17,"Kondo behavior, ferromagnetic correlations, and crystal fields in the heavy Fermion compounds Ce3X (X=In, Sn)","We report measurements of inelastic neutron scattering, magnetic
susceptibility, magnetization, and the magnetic field dependence of the
specific heat for the heavy Fermion compounds Ce$_3$In and Ce$_3$Sn. The
neutron scattering results show that the excited crystal field levels have
energies $E_1$ = 13.2 meV, $E_2$ = 44.8 meV for Ce$_3$In and $E_1$ = 18.5 meV,
$E_2$ = 36.1 meV for Ce$_3$Sn. The Kondo temperature deduced from the
quasielastic linewidth is 17 K for Ce$_3$In and 40 K for Ce$_3$Sn. The low
temperature behavior of the specific heat, magnetization, and susceptibility
can not be well-described by J=1/2 Kondo physics alone, but require
calculations that include contributions from the Kondo effect, broadened
crystal fields, and ferromagnetic correlations, all of which are known to be
important in these compounds. We find that in Ce$_3$In the ferromagnetic
fluctuation makes a 10-15 % contribution to the ground state doublet entropy
and magnetization. The large specific heat coefficient $\gamma$ in this heavy
fermion system thus arises more from the ferromagnetic correlations than from
the Kondo behavior.",1003.3462v1
2010-04-18,Charge dynamics of the Co-doped BaFe$_2$As$_2$,"We report on a thorough optical investigation over a broad spectral range and
as a function of temperature of the charge dynamics in
Ba(Co$_x$Fe$_{1-x}$)$_2$As$_2$ compounds for Co-doping ranging between 0 and
18%. For the parent compound as well as for $x$=0.025 we observe the opening of
a pseudogap, due to the spin-density-wave phase transition and inducing a
reshuffling of spectral weight from low to high frequencies. For compounds with
0.051$\le x \le$ 0.11 we detect the superconducting gap, while at $x$=0.18 the
material stays metallic at all temperatures. We describe the effective metallic
contribution to the optical conductivity with two Drude terms, representing the
combination of a coherent and incoherent component, and extract the respective
scattering rates. We establish that the $dc$ transport properties in the normal
phase are dominated by the coherent Drude term for 0$\le x \le$0.051 and by the
incoherent one for 0.061$\le x \le$0.18, respectively. Finally through spectral
weight arguments, we give clear-cut evidence for moderate electronic
correlations for 0$\le x \le$0.061, which then crossover to values appropriate
for a regime of weak interacting and nearly-free electron metals for
$x\ge$0.11.",1004.3022v1
2010-04-23,Spin dynamics in the frustrated three-dimensional hyperkagom{é} compound $Gd_3 Ga_5 O_{12}$,"We present the first neutron inelastic scattering results on the low
temperature magnetic state of the three dimensional hyperkagom\'e compound
Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG). GGG is often classified as a strongly
frustrated system with a manifold of continuously connected states. However, in
contrast to the expectation of a continuum of gap-less excitations above a spin
liquid-like ground state our results reveal three distinct inelastic modes
found at 0.04(1), 0.12(2) an 0.58(3) meV at 0.06 K. The inelastic modes can be
attributed to the magnetic ground state with the lowest and highest energy
excitations showing spatial dependencies indicative of dimerized short range
antiferromagnetic correlations. Short range correlations, reminiscent of spin
liquid-like order, are static within the instrumental resolution (50 $\mu$eV)
and represent 82% of the spectral weight. Longer range correlations, first
observed by Petrenko, et al.\cite{Petrenko1998, develop below 0.14 ~K within
the elastic cross section. The short range static correlations and dynamic
components survive to high temperatures, comparable to the nearest neighbor
exchange interactions. Our results suggest that the ground state of a three
dimensional hyperkagom\'e compound differs distinctly from its frustrated
counterparts on a pyrochlore lattice and reveals a juxtaposition of spin liquid
order and strong dimerised coupling.",1004.4140v1
2010-04-27,Construction of a Microscopic Model for Yb and Tm Compounds on the Basis of a $\mib{j}$-$\mib{j}$ Coupling Scheme,"We provide a prescription to construct a microscopic model for heavy
lanthanide systems such as Yb and Tm compounds by exploiting a $j$-$j$ coupling
scheme. Here we consider a situation with a large spin-orbit coupling, in which
$j$=5/2 sextet is fully occupied, while $j$=7/2 octet is partially occupied,
where $j$ denotes total angular momentum. We evaluate crystalline electric
field potentials and Coulomb interactions among the states of the $j$=7/2 octet
to construct a local Hamiltonian in the $j$-$j$ coupling scheme. Then, it is
found that the local $f$-electron states composed of the $j$=7/2 octet agree
quite well with those of seven $f$ orbitals even for a realistic value of the
spin-orbit coupling. As an example of the application of the present model, we
discuss low-temperature multipole states of Yb- and Tm-based filled
skutterudites by analyzing multipole susceptibility of the Anderson model in
the $j$-$j$ coupling scheme with the use of a numerical renormalization group
technique. From the comparison with the numerical results of the seven-orbital
Anderson model, it is concluded that the multipole state is also well
reproduced by the $j$-$j$ coupling model, even when we include the
hybridization between conduction and $f$ electrons for the realistic value of
the spin-orbit coupling. Finally, we briefly discuss future applications of the
present prescription for theoretical research on heavy lanthanide compounds.",1004.4707v1
2010-05-08,Non-Resonant X-ray Magnetic Scattering on Rare-Earth Iron Borates RFe$_3$(BO$_3$)$_4$,"Hard x-ray scattering (HXS) experiments with a photon energy of 100keV were
performed as a function of temperature and applied magnetic field on selected
compounds of the RFe$_3$(BO$_3$)$_4$ family. The results show the presence of
several unexpected diffraction features, in particular non-resonant magnetic
reflections in the magnetically ordered phase, and structural reflections that
violate the diffraction conditions for the low temperature phase $P3_121$ of
the rare-earth iron borates. The temperature and field dependence of the
magnetic superlattice reflections corroborate the magnetic structures of the
borate compounds obtained by neutron diffraction. The detailed analysis of the
intensity and scattering cross section of the magnetic reflection reveals
details of the magnetic structure of these materials such as the spin domain
structure of NdFe$_3$(BO$_3$)$_4$ and GdFe$_3$(BO$_3$)$_4$. Furthermore we find
that the correlation length of the magnetic domains is around 100 \AA{} for all
the compounds and that the Fe moments are rotated $53^\circ\pm3^\circ$ off from
the hexagonal basal plane in GdFe$_3$(BO$_3$)$_4$",1005.1333v2
2010-06-02,"Electric and magnetic polarizabilities of hexagonal Ln2CuTiO6 (Ln=Y, Dy, Ho, Er and Yb)","We investigated the rare-earth transition metal oxide series, Ln2CuTiO6
(Ln=Y, Dy, Ho, Er and Yb), crystallizing in the hexagonal structure with
non-centrosymmetric P63cm space group for possible occurrences of multiferroic
properties. Our results show that while these compounds, except Ln=Y, exhibit a
low temperature antiferromagnetic transition due to the ordering of the
rare-earth moments, the expected ferroelectric transition is frustrated by the
large size difference between Cu and Ti at the B-site. Interestingly, this
leads these compounds to attain a rare and unique combination of desirable
paraelectric properties with high dielectric constants, low losses and weak
temperature and frequency dependencies. First-principles calculations establish
these exceptional properties result from a combination of two effects. A
significant difference in the MO5 polyhedral sizes for M = Cu and M = Ti
suppress the expected co-operative tilt pattern of these polyhedra, required
for the ferroelectric transition, leading to relatively large values of the
dielectric constant for every compound investigated in this series.
Additionally, it is shown that the majority contribution to the dielectric
constant arises from intermediate-frequency polar vibrational modes, making it
relatively stable against any temperature variation. Changes in the temperature
stability of the dielectric constant amongst different members of this series
are shown to arise from changes in relative contributions from soft polar
modes.",1006.0417v2
2010-06-25,FeCl3 based Few-Layer Graphene Intercalation Compounds: Single Linear Dispersion Electronic Band Structure and Strong Charge Transfer Doping,"Graphene has attracted great attentions since its first discovery in 2004.
Various approaches have been proposed to control its physical and electronic
properties. Here, we report that graphene based intercalation compounds is an
efficient method to modify the electronic properties of few layer graphene
(FLG). FeCl3 intercalated FLG were successfully prepared by two-zone vapor
transport method. This is the first report on full intercalation for graphene
samples. The features of the Raman G peak of such few-layer graphene
intercalation compounds (FLGIC) are in good agreement with their full
intercalation structures. The FLGIC presents single Lorentzian 2D peak, similar
to that of single layer graphene, indicating the loss of electronic coupling
between adjacent graphene layers. First principle calculations further reveal
that the band structure of FLGIC is similar to single layer graphene but with
strong doping effect due to the charge transfer from graphene to FeCl3. The
successful fabrication of FLGIC opens a new way to modify properties of FLG for
fundamental studies and future applications.",1006.4961v1
2010-08-11,The magnetic structure of the $zigzag$ chain family Na$_{x}$Ca$_{1-x}$V$_2$O$_4$ determined by muon-spin rotation,"We present muon-spin rotation measurements on polycrystalline samples of the
complete family of the antiferromagnetic (AF) $zigzag$ chain compounds,
Na$_x$Ca$_{1-x}$V$_2$O$_4$. In this family, we explore the magnetic properties
from the metallic NaV$_2$O$_4$ to the insulating CaV$_2$O$_4$. We find a
critical $x_c(\sim0.833)$ which separates the low and high Na-concentration
dependent transition temperature and its magnetic ground state. In the $x<x_c$
compounds, the magnetic ordered phase is characterized by a single homogenous
phase and the formation of incommensurate spin-density-wave order. Whereas in
the $x>x_c$ compounds, multiple sub-phases appear with temperature and $x$.
Based on the muon data obtained in zero external magnetic field, a careful
dipolar field simulation was able to reproduce the muon behavior and indicates
a modulated helical incommensurate spin structure of the metallic AF phase. The
incommensurate modulation period obtained by the simulation agrees with that
determined by neutron diffraction.",1008.2022v1
2010-08-12,The interparticle interaction and crossover in critical lines on field-temperature plane in Pr$_{0.5}$Sr$_{0.5}$MnO$_{3}$ nanoparticles,"The magnetic properties and the effects of interparticle interaction on it
have been studied in nanoparticles of half doped Pr$_{0.5}$Sr$_{0.5}$MnO$_{3}$.
Three samples consisting of nanoparticles of different average particle sizes
are synthesized to render the variation in interparticle interaction. Though
all the samples crystallize in the same structure to that of their bulk
compound, the low temperature ferromagnetic-antiferromagnetic transition, which
is present in bulk compound, is not evident in the nanoparticles. Linear as
well as nonlinear ac susceptibility coupled with dc magnetic measurements have
shown the superparamagnetic behavior of these nanoparticles where the blocking
temperature increases with the increasing particle size. Presence of
interparticle interaction is confirmed from the temperature variation of
coercive field and the analysis of frequency dependent ac susceptibility. We
have identified the nature of this interaction to be of dipolar type, and show
that its strength decreases with the increasing particle size. The effect of
this dipolar interaction on magnetic properties is intriguing as the compounds
exhibit crossover from de Almeida-Thouless to Gabay-Toulouse like critical
lines on field-temperature plane above their respective interaction field. In
agreement with theoretical prediction, we infer that this crossover is induced
by the unidirectional anisotropy arising from interparticle interaction, and
this is confirmed from the presence of exchange bias phenomenon.",1008.2090v1
2010-08-30,"Intriguing complex magnetism of Co in RECoAsO (RE=La, Nd and Sm)","We synthesized bulk polycrystalline samples of RECoAsO (RE=La, Nd and Sm) by
solid state reaction route in an evacuated sealed quartz tube. All these
compounds are crystallized in a tetragonal structure with space group P4/nmm.
The Co, in these compounds is in itinerant ferromagnetic state with its
paramagnetic moment above 1.5 microB and the same orders ferromagnetically (FM)
with small saturation moment of around 0.20 microB below say 80K. This bulk
intrinsic magnetism of Co changes dramatically when nonmagnetic La is changed
by magnetic Sm and Nd. Although the itinerant ferromagnetism occurs below
80-100K with small saturation moment, typical anti-ferromagnetic (AFM)
transitions (TN1, TN2) are observed at 57K and 45K for Sm and at 69K and 14K
for Nd. The transition of Co spins from FM to AFM, for magnetic Sm and Nd in
RECoAsO is both field and temperature dependent. For applied fields below
100Oe, both TN1 and TN2 are seen, with intermediate fields below 1-2kOe only
TN1 and above say 5kOe the AFM transition is not observed. This is evidenced in
isothermal magnetization (MH) plots as well. It is clear that Sm/Nd magnetic
moments interact with the ordered Co spins in adjacent layer and thus
transforms the FM ordering to AFM. All the studied compounds are metallic in
nature, and their magneto-transport R(T)H follows the temperature and field
dependent FM-AFM transition of ordered Co spins.",1008.4999v3
2010-09-02,Band Calculations for Ce Compounds with AuCu$_{3}$-type Crystal Structure on the basis of Dynamical Mean Field Theory I. CePd$_{3}$ and CeRh$_{3}$,"Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure
were carried out on the basis of dynamical mean field theory (DMFT). The
auxiliary impurity problem was solved by a method named NCA$f^{2}$vc
(noncrossing approximation including the $f^{2}$ state as a vertex correction).
The calculations take into account the crystal-field splitting, the spin-orbit
interaction, and the correct exchange process of the $f^{1} \rightarrow
f^{0},f^{2}$ virtual excitation. These are necessary features in the
quantitative band theory for Ce compounds and in the calculation of their
excitation spectra. The results of applying the calculation to CePd$_{3}$ and
CeRh$_{3}$ are presented as the first in a series of papers. The experimental
results of the photoemission spectrum (PES), the inverse PES, the
angle-resolved PES, and the magnetic excitation spectra were reasonably
reproduced by the first-principles DMFT band calculation. At low temperatures,
the Fermi surface (FS) structure of CePd$_{3}$ is similar to that of the band
obtained by the local density approximation. It gradually changes into a form
that is similar to the FS of LaPd$_{3}$ as the temperature increases, since the
$4f$ band shifts to the high-energy side and the lifetime broadening becomes
large.}",1009.0327v1
2010-09-29,A dynamical model of surrogate reactions,"A new dynamical model is developed to describe the whole process of surrogate
reactions; transfer of several nucleons at an initial stage, thermal
equilibration of residues leading to washing out of shell effects and decay of
populated compound nuclei are treated in a unified framework. Multi-dimensional
Langevin equations are employed to describe time-evolution of collective
coordinates with a time-dependent potential energy surface corresponding to
different stages of surrogate reactions. The new model is capable of
calculating spin distributions of the compound nuclei, one of the most
important quantity in the surrogate technique. Furthermore, various observables
of surrogate reactions can be calculated, e.g., energy and angular distribution
of ejectile, and mass distributions of fission fragments. These features are
important to assess validity of the proposed model itself, to understand
mechanisms of the surrogate reactions and to determine unknown parameters of
the model. It is found that spin distributions of compound nuclei produced in
$^{18}$O+$^{238}$U $\rightarrow ^{16}$O+$^{240*}$U and $^{18}$O+$^{236}$U
$\rightarrow ^{16}$O+$^{238*}$U reactions are equivalent and much less than
10$\hbar$, therefore satisfy conditions proposed by Chiba and Iwamoto (PRC 81,
044604(2010)) if they are used as a pair in the surrogate ratio method.",1009.5924v1
2010-10-11,Topological Insulators in Ternary Compounds with a Honeycomb Lattice,"One of the most exciting subjects in solid state physics is a single layer of
graphite which exhibits a variety of unconventional novel properties. The key
feature of its electronic structure are linear dispersive bands which cross in
a single point at the Fermi energy. This so-called Dirac cone is closely
related to the surface states of the recently discovered topological
insulators. The ternary compounds, such as LiAuSe and KHgSb with a honeycomb
structure of their Au-Se and Hg-Sb layers feature band inversion very similar
to HgTe which is a strong precondition for existence of the topological surface
states. In contrast to graphene with two Dirac cones at K and K' points, these
materials exhibit the surface states formed by only a single Dirac cone at the
\Gamma -point together with the small direct band gap opened by a strong
spin-orbit coupling (SOC) in the bulk. These materials are centro-symmetric,
therefore, it is possible to determine the parity of their wave functions, and
hence, their topological character. Surprisingly, the compound KHgSb with the
strong SOC is topologically trivial, whereas LiAuSe is found to be a
topological non-trivial insulator.",1010.2195v1
2010-11-02,Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68K0.32Fe2As2 single crystals,"Early work on the iron-arsenide compounds supported the view, that a reduced
dimensionality might be a necessary prerequisite for high-Tc superconductivity.
Later, however, it was found that the zero-temperature upper critical magnetic
field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we
report measurements of the temperature dependence of the electrical
resistivity, \Gamma(T), in Ba0.5K0.5Fe2As2 and Ba0.68K0.32Fe2As2 single
crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and
pulsed magnetic fields up to 60 T. We find that the resistivity of both
compounds in zero field is well described by an exponential term due to
inter-sheet umklapp electron-phonon scattering between light electrons around
the M point to heavy hole sheets at the \Gamma point in reciprocal space. From
our data, we construct an H-T phase diagram for the inter-plane (H || c) and
in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data
for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic
in optimally doped samples down to low temperatures. The anisotropy parameter,
{\gamma} = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find
a concave curvature of the Hc2 lines with decreasing anisotropy and saturation
towards lower temperature. Taking into account Pauli spin paramagnetism we
perfectly can describe Hc2(T) and its anisotropy.",1011.0698v1
2010-11-28,Structural and Magnetic Properties of the Layered Manganese Oxychalcogenides:(LaO)$_2$Mn$_2$Se$_2$O and (BaF)$_2$Mn$_2$Se$_2$O,"The new layered manganese oxychalcogenides (LaO)$_2$Mn$_2$Se$_2$O and
(BaF)$_2$Mn$_2$Se$_2$O, isostructural to (LaO)$_2$Fe$_2$Se$_2$O, were
synthesized by using solid state reaction. The single crystals of former
compound were also successfully grown by using high temperature fusion method.
The polycrytalline samples showed the insulating behavior, with the activation
energy gaps of about 278 meV and 416 meV for (LaO)$_2$Mn$_2$Se$_2$O and
(BaF)$_2$Mn$_2$Se$_2$O, respectively. The magnetic susceptibility indicated an
antiferromagnetic (AFM) transition at around 160K and strong anisotropic
magnetic properties below T$_N$ for the former compound, which suggests a
long-range canted AFM ordering. A broad maximum of the susceptibility can be
observed for the two compound at high temperatures, say 360 K and 210 K
respectively, suggesting that strong magnetic correlation gives rise to
low-dimensional AFM or short-range ordering at high temperatures in these rare
transition metal oxychalcogenides with a frustrated AFM checkerboard spin
lattice.",1011.6052v2
2010-12-16,Linearization effect in multifractal analysis: Insights from the Random Energy Model,"The analysis of the linearization effect in multifractal analysis, and hence
of the estimation of moments for multifractal processes, is revisited borrowing
concepts from the statistical physics of disordered systems, notably from the
analysis of the so-called Random Energy Model. Considering a standard
multifractal process (compound Poisson motion), chosen as a simple
representative example, we show: i) the existence of a critical order $q^*$
beyond which moments, though finite, cannot be estimated through empirical
averages, irrespective of the sample size of the observation; ii) that
multifractal exponents necessarily behave linearly in $q$, for $q > q^*$.
Tayloring the analysis conducted for the Random Energy Model to that of
Compound Poisson motion, we provide explicative and quantitative predictions
for the values of $q^*$ and for the slope controlling the linear behavior of
the multifractal exponents. These quantities are shown to be related only to
the definition of the multifractal process and not to depend on the sample size
of the observation. Monte-Carlo simulations, conducted over a large number of
large sample size realizations of compound Poisson motion, comfort and extend
these analyses.",1012.3688v2
2011-03-14,Character of the structural and magnetic phase transitions in the parent and electron doped BaFe2As2 compounds,"We present a combined high-resolution x-ray diffraction and x-ray resonant
magnetic scattering (XRMS) study of as-grown BaFe2As2. The structural/magnetic
transitions must be described as a two-step process. At T_S = 134.5 K we
observe the onset of a second-order structural transition from the
high-temperature paramagnetic tetragonal structure to a paramagnetic
orthorhombic phase, followed by a discontinuous step in the structural order
parameter that is coincident with a first-order antiferromagnetic (AFM)
transition at T_N = 133.75 K. These data, together with detailed
high-resolution x-ray studies of the structural transition in lightly doped
Ba(Fe{1-x}Co{x})2As2 and Ba(Fe{1-x}Rh{x})2As2 compounds, show that the
structural and AFM transitions do, in fact, occur at slightly different
temperatures in the parent BaFe2As2 compound, and evolve towards split
secondorder transitions as the doping concentration is increased. We estimate
the composition for the tricritical point for Co-doping and employ a mean-field
approach to show that our measurements can be explained by the inclusion of an
anharmonic term in the elastic free energy and magneto-elastic coupling in the
form of an emergent Ising-nematic degree of freedom.",1103.2752v1
2011-03-24,Dynamics of dinuclear system formation and its decay in heavy ion collisions,"A variety of phenomena connected with the formation of a dinuclear complex is
observed in the heavy ion collisions at low energies. The dinuclear system
model allows us to analyze the experimental data and to interpret them by
comparison of the partial capture, fusion and evaporation residue cross
sections measured for the different reactions leading to the same compound
nucleus. The comparison of theoretical and experimental values of the mass and
angular distributions of the reaction products gives us a detailed information
about reaction mechanism forming the observed yields. The observed very small
cross sections of the evaporation residues may be explained by the strong
fusion hindrance and/or instability of the heated and rotating compound nucleus
and smallness of its survival probability. The fusion hindrance arises due to
competition between complete fusion and quasifission while the smallness of
survival probability is connected with the decrease of the fission barrier at
large excitation energy and angular momentum of compound nucleus.",1103.4847v2
2011-04-06,Chiral criticality in doped Mn$_{1-y}$Fe$_y$Si compounds,"The critical spin fluctuations in doped compounds Mn$_{1-y}$Fe$_y$Si have
been studied by means of ac-susceptibility measurements, polarized neutron
small angle scattering and spin echo spectroscopy. It is shown that these
compounds undergo the transition from the paramagnetic to helimagnetic phase
through continuous, yet well distinguishable crossovers: (i) from paramagnetic
to partially chiral, (ii) from partially chiral to highly chiral fluctuating
state. The crossover points are identified on the basis of combined analysis of
the temperature dependence of ac-susceptibility and polarized SANS data. The
whole transition is marked by two inflection point of the temperature
dependence of ac-susceptibility: the upper one corresponds to the crossover to
partially chiral state at $T^*$, where the inverse correlation length $\kappa
\approx 2 k$, the lower one corresponds to the transition to the spin helix
structure. The intermediate crossover to the highly chiral phase is observed at
the inflection point $T_k$ of the first derivative of ac-susceptibility, where
$\kappa \approx k$. The temperature crossovers to the highly chiral fluctuating
state is associated with the enhancing influence of the Dzyaloshinskii-Moria
interaction close to $T_c$.",1104.1119v2
2011-05-03,Comparison between two simple numerical models for the magnetoelectric interaction in multiferroics,"We developed numerical calculations to simulate the magnetoelectric coupling
in multiferroic compounds, using the Monte Carlo technique. Two simple models
were used to simulate the compounds. In the first one, the magnetic ions are
represented by a spin 1/2 2D Ising lattice of ions, and the electric lattice by
classical moments, coupled one to one with the magnetic moments. The coupling
between both lattices allows to the leading lattice, that is, the magnetic one,
to change the orientation of the electrical dipoles in one direction
perpendicular to the magnetic dipoles. This direction was chosen to accomplish
the symmetry requirements of the magnetoelectric effect. In the second case,
the magnetic lattice is also a 2D Ising lattice, but the electric momenta are
in a lattice that also behaves as an Ising lattice, perpendicular to the
magnetic moments. In this case, the one-to-one coupling of the electric and
magnetic momenta is represented by a two-valued energy parameter, allowing the
possibility of independent transition temperatures for both lattices. Both
models contain three independent parameters. We studied the physical properties
obtained with both models, as functions of the ratio of the three parameters.
The results in both cases allowed us to compare changes in the physics of the
models, and with the physics of compounds measured experimentally.",1105.0642v1
2011-05-05,"Synthesis, magnetization and magneto transport study of RECoPO (RE = La, Nd & Sm)","We report the electrical, magneto transport and specific heat of the layered
polycrystalline RECoPO (RE = La, Nd and Sm) samples. These compounds are
iso-structural to recently discovered superconductor LaFeAs(O/F). Bulk
polycrystalline samples are synthesized by solid state reaction route in an
evacuated sealed quartz tube. All these compounds are crystallized in a
tetragonal structure with space group P4/nmm. The Cobalt in these compounds is
in itinerant state with its paramagnetic moment above 1.4\muB and the same
orders ferromagnetically (FM) with saturation moment of around 0.20\muB below
say 80K. Though, LaCoPO shows single paramagnetic (PM) to ferromagnetic (FM)
transition near 35K, the NdCoPO and SmCoPO exhibit successive PM-FM-AFM
transitions. Both FM and AFM transition temperatures vary with applied field.
Although the itinerant ferromagnetism occurs with small saturation moment,
typical anti-ferromagnetic (AFM) transitions (TN1, TN2) are observed at 69K and
14K for Nd and 57K and 45K for Sm. This FM-AFM transition of Co spins in NdCoPO
and SmCoPO is both field and temperature dependent. The Magneto-transport of
NdCoPO and SmCoPO distinctly follows their successive PM-FM-AFM transitions. It
is clear that Sm/Nd (4f) interacts with the Co (3d) in first time synthesized
Sm/NdCoPO.",1105.0971v2
2011-06-09,Fibrations of financial events,"In this paper we shall prove that the plane of financial events, introduced
and applied to financial problems by the author himself (see [2], [3] and [4])
can be considered as a fibration in two different ways. The first one, the
natural one, reveals itself to be isomorphic to the tangent- bundle of the real
line, when the last one is considered as a differentiable manifold in the
natural way; the second one is a fibration induced by the status of compound
interest capitalization at a given rate i in the interval ] - 1, \rightarrow [.
Moreover, in the paper we define on the first fibration an affine connection,
also in this case induced by the status of compound interest at a given rate i.
The final goal of this paper is the awareness that all the effects determined
by the status of compound interest are nothing but the consequences of the fact
that the space of financial events is a fibration endowed with a particular
affine connection, so they are consequences of purely geometric properties, at
last, depending upon the curvature determined by the connection upon the
fibration. A natural preorder upon the set of fibers of the second fibration is
considered. Some remarks about the applicability to economics and finance of
the theories presented in the paper and about the possible developments are
made in the directions followed in papers [1], [5], [6], [7], [8] of the
author.",1106.1774v1
2011-06-20,"Magnetotransport in La(Fe,Ru)AsO as a probe of band structure and mobility","In this work we investigate the Ru substituted LaFeAsO compound, by studying
the magnetotransport behaviour and its relationship with the band structure, in
different regimes of temperature, magnetic field and Ru content. In particular
we analyse the magnetoresistance of LaFe1-xRuxAsO (0 <= x <= 0.6) samples with
the support of ab initio calculations and we find out that in the whole series:
(i) the transport is dominated by electron bands only; (ii) the
magnetoresistance exhibits distinctive features related to the presence of
Dirac cones; indeed, ab initio calculations confirm the presence of anisotropic
Dirac cones in the band structure; (iii) the low temperature mobility is
exceptionally high and reaches 18.6 m2/(Vs) in the Ru-free sample at T=2K, in
the extreme limit of a single Landau level occupied in the Dirac cones; (iv)
the mobility drops abruptly above 10K-15K; (v) the disorder has a very weak
effect on the band mobilities and on the transport properties; (vi) there
exists a correlation between the temperature ranges of Dirac cones and SDW
carrier condensation. These findings may be of crucial importance in the
investigation of the pairing mechanism in the F-doped superconducting
La(Fe,Ru)As(O,F) compounds related to this series of parent compounds.",1106.3973v4
2011-06-21,Transport properties and anisotropy in rare earth doped CaFe2As2 single crystals with Tc above 40 K,"In this paper we report the superconductivity above 40 K in the electron
doping single crystal Ca1-xRexFe2As2 (Re = La, Ce, Pr). The x-ray diffraction
patterns indicate high crystalline quality and c-axis orientation. the
resistivity anomaly in the parent compound CaFe2As2 is completely suppressed by
partial replacement of Ca by rare earth and a superconducting transition
reaches as high as 43 K, which is higher than the value in electron doping
FeAs-122 compounds by substituting Fe ions with transition metal, even
surpasses the highest values observed in hole doping systems with a transition
temperature up to 38 K. The upper critical field has been determined with the
magnetic field along ab-plane and c-axis, yielding the anisotropy of 2~3.
Hall-effect measurements indicate that the conduction in this material is
dominated by electron like charge carriers. Our results explicitly demonstrate
the feasibility of inducing superconductivity in Ca122 compounds via electron
doping using aliovalent rare earth substitution into the alkaline earth site,
which should add more ingredients to the underlying physics of the iron-based
superconductors.",1106.4208v1
2011-07-01,Glass-like ordering and spatial inhomogeneity of magnetic structure in Ba3FeRu2O9 : The role of Fe/Ru-site disorder,"Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9,
have been studied over a significant period of time in order to understand the
unusual magnetism of ruthenium metal. However, among them, the M=Fe compound
appears different since it is observed that unlike others, the 3d Fe ions and
4d Ru ions can easily exchange their crystallographic positions and as a result
many possible magnetic interactions become realizable. The present study
involving several experimental methods on this compound establish that the
magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H
ruthenates. Local structural study reveals that the possible Fe/Ru-site
disorder further extends to create local chemical inhomogeneity, affecting the
high temperature magnetism of this material. There is a gradual decrease of
57Fe M\""ossbauer spectral intensity with decreasing temperature (below 100 K),
which reveals that there is a large spread in the magnetic ordering
temperatures, corresponding to many spatially inhomogeneous regions. However,
finally at about 25 K, the whole compound is found to take up a global
glass-like magnetic ordering.",1107.0121v1
2011-07-15,"A combined high-pressure experimental and theoretical study of the electronic band-structure of scheelite-type AWO4 (A = Ca, Sr, Ba, Pb) compounds","The optical-absorption edge of single crystals of CaWO4, SrWO4, BaWO4, and
PbWO4 has been measured under high pressure up to ~20 GPa at room temperature.
From the measurements we have obtained the evolution of the band-gap energy
with pressure. We found a low-pressure range (up to 7-10 GPa) where
alkaline-earth tungstates present a very small Eg pressure dependence (-2.1 <
dEg/dP < 8.9 meV/GPa). In contrast, in the same pressure range, PbWO4 has a
pressure coefficient of -62 meV/GPa. The high-pressure range is characterized
in the four compounds by an abrupt decrease of Eg followed by changes in
dEg/dP. The band-gap collapse is larger than 1.2 eV in BaWO4. We also
calculated the electronic-band structures and their pressure evolution.
Calculations allow us to interpret experiments considering the different
electronic configuration of divalent metals. Changes in the pressure evolution
of Eg are correlated with the occurrence of pressure-induced phase transitions.
The band structures for the low- and high-pressure phases are also reported. No
metallization of any of the compounds is detected in experiments nor is
predicted by calculations.",1107.3014v1
2011-07-26,Interplay between magnetism and superconductivity in EuFe(2-x)Co(x)As2 studied by 57Fe and 151Eu Mössbauer spectroscopy,"The compound EuFe(2-x)Co(x)As2 was investigated by means of the 57Fe and
151Eu Moessbauer spectroscopy versus temperature (4.2 - 300 K) for x=0
(parent), x=0.34 - 0.39 (superconductor) and x=0.58 (overdoped). It was found
that spin density wave (SDW) is suppressed by Co-substitution, however it
survives in the region of superconductivity, but iron spectra exhibit some
non-magnetic component in the superconducting region. Europium orders
anti-ferromagnetically regardless of the Co concentration with the spin
re-orientation from the a-axis in the parent compound toward c-axis with the
increasing replacement of iron by cobalt. The re-orientation takes place close
to the a-c plane. Some trivalent europium appears in EuFe(2-x)Co(x)As2 versus
substitution due to the chemical pressure induced by Co-atoms and it
experiences some transferred hyperfine field from Eu2+. Iron experiences some
transferred field due to the europium ordering for substituted samples in the
SDW and non-magnetic state both, while the transferred field is undetectable in
the parent compound. Superconductivity coexists with the 4f-europium magnetic
order within the same volume. It seems that superconductivity has some
filamentary character in EuFe(2-x)Co(x)As2 and it is confined to the
non-magnetic component seen by the iron Moessbauer spectroscopy.",1107.5271v2
2011-09-14,Analytical modelling of stable isotope fractionation of volatile organic compounds in the unsaturated zone,"Analytical models were developed that simulate stable isotope ratios of
volatile organic compounds (VOCs) near a point source contamination in the
unsaturated zone. The models describe diffusive transport of VOCs,
biodegradation and source ageing. The mass transport is governed by Fick's law
for diffusion, and the equation for reactive transport of VOCs in the soil gas
phase was solved for different source geometries and for different boundary
conditions. Model results were compared to experimental data from a
one-dimensional laboratory column and a radial-symmetric field experiment, and
the comparison yielded a satisfying agreement. The model results clearly
illustrate the significant isotope fractionation by gas-phase diffusion under
transient state conditions. This leads to an initial depletion of heavy
isotopes with increasing distance from the source. The isotope evolution of the
source is governed by the combined effects of isotope fractionation due to
vaporization, diffusion and biodegradation. The net effect can lead to an
enrichment or depletion of the heavy isotope in the remaining organic phase
depending on the compound and element considered. Finally, the isotope
evolution of molecules migrating away from the source and undergoing
degradation is governed by a combined degradation and diffusion isotope effect.
This suggests that in the unsaturated zone, the interpretation of
biodegradation based on isotope data must always be based on a model combining
gas-phase diffusion and degradation.",1109.3141v1
2011-10-03,Raman scattering study of delafossite magnetoelectric multiferroic compounds: CuFeO2 and CuCrO2,"Ultrasonic velocity measurements on the magnetoelectric multiferroic compound
CuFeO2 reveal that the antiferromagnetic transition observed at TN1 = 14 K
might be induced by an R-3m -> C2/m pseudoproper ferroelastic transition (G.
Quirion, M. J. Tagore, M. L. Plumer, O. A. Petrenko, Phys. Rev. B 77, 094111
(2008)). In that case, the group theory states that the order parameter
associated with the structural transition must belong to a two dimensional
irreducible representation Eg (x^2 - y^2, xy). Since this type of transition
can be driven by a Raman Eg mode, we performed Raman scattering measurements on
CuFeO2 between 5 K and 290 K. Considering that the isostructural multiferroic
compound CuCrO2 might show similar structural deformations at the
antiferromagnetic transition TN1 = 24.3 K, Raman measurements have also been
performed for comparison. At ambient temperature, the Raman modes in CuFeO2 are
observed at omega_Eg = 352 cm^-1 and omega_Ag = 692 cm^-1, while these modes
are detected at omega_E_g = 457 cm^-1 and omega_Ag = 709 cm^-1 in CuCrO2. The
analysis of the temperature dependence of modes shows that the frequency of all
modes increases down to 5 K. This typical behavior can be attributed to
anharmonic phonon-phonon interactions. These results clearly indicate that none
of the Raman active modes observed in CuFeO2 and CuCrO2 drive the pseudoproper
ferroelastic transition observed at the N\'eel temperature TN1. Finally, a
broad band at about 550 cm^-1 observed in the magnetoelectric phase of CuCrO2
below TN2 could be attributed to a magnon mode.",1110.0473v1
2011-10-28,Mott Transition and Phase Diagram of $κ$-(BEDT-TTF)2Cu(NCS)2 Studied by Two-Dimensional Model Derived from Ab initio Method,"We present an ab initio analysis for the ground-state properties of a
correlated organic compound $\kappa$-(BEDT-TTF)2Cu(NCS)2. First, we derive an
effective two-dimensional low-energy model from first principles, having
short-ranged transfers and short-ranged Coulomb and exchange interactions.
Then, we perform many-variable variational Monte Carlo calculations for this
model and draw a ground-state phase diagram as functions of scaling parameters
for the onsite and off-site interactions. The phase diagram consists of three
phases; a paramagnetic metallic phase, an antiferromagnetic (Mott) insulating
phase, and a charge-ordered insulating phase. In the phase diagram, the
parameters for the real compound are close to the first-order Mott transition,
being consistent with experiments. We show that the off-site Coulomb and
exchange interactions affect the phase boundary; (i) they appreciably stabilize
the metallic state against the Mott insulating phase and (ii) enhance charge
fluctuations in a wide parameter region in the metallic phase.
  We observe arc-like structure in Fermi surface around the region where the
charge fluctuations are enhanced. Possible relevance of the charge fluctuations
to the experimentally observed dielectric anomaly in the $\kappa$-BEDT-TTF
family compounds is also pointed out.",1110.6299v2
2011-11-13,"On the anomalous thermal evolution of the low-temperature, normal-state specific heat of various nonmagnetic intermetallic compounds","The low-temperature normal-state specific heat and resistivity curves of
various nonmagnetic intermetallic compounds manifest an anomalous thermal
evolution. Such an anomaly is exhibited as a break in the slope of the
linearized C/T versus T^2 curve and as a drop in the R versus T curve, both at
the same T_{\beta}{\gamma}. It is related, not to a thermodynamic phase
transition, but to an anomaly in the density of states curves of the phonon or
electron subsystems. On representing these two anomalies as additional
Dirac-type delta functions, situated respectively at kB.{\theta}_L (for
lattice) and kB.{\theta}_E (for electrons), an analytical expression for the
total specific heat can be obtained. A least-square fit of this expression to
experimental specific heat curves of various compounds reproduced
satisfactorily all the features of the anomalous thermal evolution. The
obtained fit parameters (in particular the Sommerfeld constant, {\gamma}_{0},
and Debye temperatures, {\theta}_D, compare favorably with the reported values.
Furthermore, the analysis shows that (i) (T_{\beta}{\gamma}) / ({\theta}_D) =
0.2(1\pm1/\surd6) and (ii) {\gamma}_{0} {\propto} ({\theta}_D)^2; both
relations are in a reasonable agreement with the experimental results. Finally,
this analysis (based on the above arguments) justifies the often-used procedure
that treats the above anomaly in terms of either a thermal variation of
{\theta}_D or an additional Einstein mode.",1111.3070v1
2011-12-12,"Crystal Growth and Physical Properties of SrCu2As2, SrCu2Sb2 and BaCu2Sb2","We report the growth of single crystals of SrCu2As2, SrCu2Sb2,
SrCu2(As{0.84}Sb{0.16})2 and BaCu2Sb2 using the self-flux technique and their
structural, magnetic, thermal and transport properties that were investigated
by powder x-ray diffraction (XRD), magnetic susceptibility chi, specific heat
Cp and electrical resistivity rho measurements versus temperature T from 1.8 to
350 K. Rietveld refinements of XRD patterns for crushed crystals confirm that
SrCu2As2 crystallizes in the ThCr2Si2-type structure and SrCu2Sb2 crystallizes
in the CaBe2Ge2-type structure. However, BaCu2Sb2 is found to have a large unit
cell consisting of three blocks. Here a ThCr2Si2-type block is sandwiched
between two CaBe2Ge2-type blocks along the c-axis, as reported, but likely with
a monoclinic distortion. The chi data of all these compounds are diamagnetic
and reveal nearly T-independent anisotropic behavior. The finite values of the
Sommerfeld linear specific heat coefficients gamma and the T dependences of rho
reveal metallic character of all four compounds. The electronic and magnetic
properties indicate that these compounds are sp metals with Cu in the 3d^{10}
electronic configuration corresponding to the oxidation state Cu^{+1}, as
previously predicted theoretically for (Sr,Ba)Cu2As2 by D. J. Singh. We find
that SrCu2As2 has a collapsed-tetragonal structure. The electronic character of
the Cu and the strength of the As-As interlayer bonding are both expected to
drastically change between weakly Cu-substituted BaFe2As and pure BaCu2As2.",1112.2722v2
2012-02-02,"The Superconducting Transition Temperatures of Fe1+xSe1--y, Fe1+xSe1--yTey and (K/Rb/Cs)zFe2--xSe2","In a recent contribution to this journal, it was shown that the transition
temperatures of optimal high-Tc compounds obey the algebraic relation, Tc0 =
kB-1{\beta}/\ell{\zeta}, where \ell is related to the mean spacing between
interacting charges in the layers, {\zeta} is the distance between interacting
electronic layers, {\beta} is a universal constant and kB is Boltzmann's
constant. The equation was derived assuming pairing based on interlayer Coulomb
interactions between physically separated charges. This theory was initially
validated for 31 compounds from five different high-Tc families (within an
accuracy of \pm1.37 K). Herein we report the addition of Fe1+xSe1-y and
Fe1+xSe1-yTey (both optimized under pressure) and AzFe2-xSe2 (for A = K, Rb, or
Cs) to the growing list of Coulomb-mediated superconducting compounds in which
Tc0 is determined by the above equation. Doping in these materials is
accomplished through the introduction of excess Fe and/or Se deficiency, or a
combination of alkali metal and Fe vacancies. Consequently, a very small number
of vacancies or interstitials can induce a superconducting state with a
substantial transition temperature. The confirmation of the above equation for
these Se-based Fe chalcogenides increases to six the number of superconducting
families for which the transition temperature can be accurately predicted.",1202.0329v1
2012-02-07,Effect of internal chemical pressure on transport properties and TCR for sensors applications,"In this work, the structural and transport properties of
(Nd0.7-xLax)Sr0.3MnO3 manganites with x = 0, 0.1 and 0.2 prepared by solid
state reaction route are studied. These compounds are found to be crystallized
in orthorhombic structural form. The influence of La substitution in place of
Nd at A-site shifts the metal to semiconductor/insulator transition temperature
(TMI) peak towards room temperature with x = 0, 0.1 and 0.2. A composition
prepared with the value of x = 0.2 in (Nd0.7-xLax)0.7Sr0.3MnO3 manganites (i.e.
(Nd0.5La0.2)0.7Sr0.3MnO3), TMI was observed at 289 K which is close to room
temperature. The maximum percentage of TCR values of compounds are increasing
with average radius <r_A> but %TCR are slightly equal in x = 0.1 and 0.2 as
compared to the parent compound. The maximum %TCR value is almost independent
with A-site average radius <r_A> in x = 0.1 and 0.2. The electrical resistivity
data are explored by different theoretical models and it has been concluded
that at low temperature (ferromagnetic metallic region) conduction mechanism
presumably due to the combined effect of electron-electron, electron-phonon and
electron-magnon scattering, while in paramagnetic semiconducting regime, the
variation of resistivity with temperature are explained by (1) Mott variable
range hopping mechanism, (2) Adiabatic small polaron hopping and (3) Thermally
activated hopping. The polaron hopping and thermal activation energies are
decreasing with increase of an average A-site ionic radius (<rA>). An
appropriate enlightenment for the observed behavior is discussed in detail.",1202.1355v1
2012-02-29,Selective Response of Mesoporous Silicon to Adsorbants with Nitro Groups,"We demonstrate that the electronic structure of mesoporous silicon is
affected by adsorption of nitro-based explosive molecules in a
compound-selective manner. This selective response is demonstrated by probing
the adsorption of two nitro-based molecular explosives (trinitrotoluene and
cyclotrimethylenetrinitramine) and a nonexplosive nitro-based arematic molecule
(nitrotoluene) on mesoporous silicon using soft X-ray spec- troscopy. The Si
atoms strongly interact with adsorbed molecules to form Si-O and Si-N bonds, as
evident from the large shifts in emission energy present in the Si L2,3 X-ray
emission spectroscopy (XES) measurements. Furthermore, we find that the energy
gap of mesoporous silicon changes depending on the adsorbant, as estimated from
the Si L2,3 XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab
initio molecular dynamics calculations of model compounds suggest that these
changes are due to spontaneous breaking of the nitro groups upon contacting
surface Si atoms. This compound-selective change in electronic structure may
provide a powerful tool for the detection and identification of trace
quantities of airborne explosive molecules.",1202.6656v1
2012-03-22,"Crystal Chemistry and Magnetic Properties of Manganese Zinc Alloy ""YMn2Zn20"" Comprising a Mn Pyrochlore Lattice","The chemical composition, crystal structure, and magnetic properties of a
manganese zinc alloy with an ideal composition of YMn2Zn20, which comprises a
pyrochlore lattice made of Mn atoms, are reported. The compound is stable only
when In or Al is partially substituted for Zn. We have determined the actual
chemical formula as YMn2+dZn20-x-dMx, with M = In or Al, and have identified
the characteristic preferences with which the incorporated M and excess Mn
atoms occupy the three crystallographic sites for Zn atoms. The Mn atoms in the
pyrochlore lattice possess small magnetic moments that interact with each other
antiferromagnetically but exhibit no long-range order above 0.4 K, probably
owing to the geometrical frustration of the pyrochlore lattice. As a result,
the effective mass of the conduction electrons is considerably enhanced, as
observed in the related pyrochlore-lattice compounds (Y,Sc)Mn2 and LiV2O4.
However, the presence of excess Mn atoms with large localized magnetic moments
comparable to spin 5/2 tends to mask the inherent magnetism of the pyrochlore
Mn atoms. It is suggested that ""YMn2Zn18In2"" with neither excess Mn atoms nor
site disorder would be an ideal compound for further study.",1203.4887v1
2012-03-30,The role of different negatively charged layers in Ca10(Fe1-xPtxAs)10(Pt3+yAs8) and superconductivity at 30 K in electron-doped (Ca0.8La0.2)10(FeAs)10(Pt3As8),"The recently discovered compounds Ca10(Fe1-xPtxAs)10(Pt3+yAs8) exhibit
superconductivity up to 38 K, and contain iron arsenide (FeAs) and platinum
arsenide (Pt3+yAs8) layers separated by layers of Ca atoms. We show that high
Tc's above 15 K only emerge if the iron-arsenide layers are at most free of
platinum-substitution (x \rightarrow 0) in contrast to recent reports. In fact
Pt-substitution is detrimental to higher Tc, which increases up to 38 K only by
charge doping of pure FeAs layers. We point out, that two different negatively
charged layers [(FeAs)10]n- and (Pt3+yAs8)m- compete for the electrons provided
by the Ca2+ ions, which is unique in the field of iron-based superconductors.
In the parent compound Ca10(FeAs)10(Pt3As8), no excess charge dopes the
FeAs-layer, and superconductivity has to be induced by Pt-substitution, albeit
below 15 K. In contrast, the additional Pt-atom in the Pt4As8layer shifts the
charge balance between the layers equivalent to charge doping by 0.2 electrons
per FeAs. Only in this case Tc raises to 38 K, but decreases again if
additionally platinum is substituted for iron. This charge doping scenario is
supported by our discovery of superconductivity at 30 K in the electron-doped
La-1038 compound (Ca0.8La0.2)10(FeAs)10(Pt3As8) without significant
Pt-substitution.",1203.6767v1
2012-04-10,The compound Poisson limit ruling periodic extreme behaviour of non-uniformly hyperbolic dynamics,"We prove that the distributional limit of the normalised number of returns to
small neighbourhoods of periodic points of non-uniformly hyperbolic dynamical
systems is compound Poisson. The returns to small balls around a fixed point in
the phase space correspond to the occurrence of rare events, or exceedances of
high thresholds, so that there is a connection between the laws of Return Times
Statistics and Extreme Value Laws. The fact that the fixed point in the phase
space is a repelling periodic point implies that there is a tendency for the
exceedances to appear in clusters whose average sizes is given by the Extremal
Index, which depends on the expansion of the system at the periodic point.
  We recall that for generic points, the exceedances, in the limit, are
singular and occur at Poisson times. However, around periodic points, the
picture is different: the respective point processes of exceedances converge to
a compound Poisson process, so instead of single exceedances, we have entire
clusters of exceedances occurring at Poisson times with a geometric
distribution ruling its multiplicity.
  The systems to which our results apply include: general piecewise expanding
maps of the interval (Rychlik maps), maps with indifferent fixed points
(Manneville-Pomeau maps) and Benedicks-Carleson quadratic maps.",1204.2304v2
2012-04-18,Controlling bulk conductivity in topological insulators: Key role of anti-site defects,"The binary Bi-chalchogenides, Bi2Ch3, are widely regarded as model examples
of a recently discovered new form of quantum matter, the three-dimensional
topological insulator (TI) [1-4]. These compounds host a single spin-helical
surface state which is guaranteed to be metallic due to time reversal symmetry,
and should be ideal materials with which to realize spintronic and quantum
computing applications of TIs [5]. However, the vast majority of such compounds
synthesized to date are not insulators at all, but rather have detrimental
metallic bulk conductivity [2, 3]. This is generally accepted to result from
unintentional doping by defects, although the nature of the defects responsible
across different compounds, as well as strategies to minimize their detrimental
role, are surprisingly poorly understood. Here, we present a comprehensive
survey of the defect landscape of Bi-chalchogenide TIs from first-principles
calculations. We find that fundamental differences in the energetics of native
defect formation in Te- and Se-containing TIs enables precise control of the
conductivity across the ternary Bi-Te-Se alloy system. From a systematic
angle-resolved photoemission (ARPES) investigation of such ternary alloys,
combined with bulk transport measurements, we demonstrate that this method can
be utilized to achieve true topological insulators, with only a single Dirac
cone surface state intersecting the chemical potential. Our microscopic
calculations reveal the key role of anti-site defects for achieving this, and
predict optimal growth conditions to realize maximally-resistive ternary TIs.",1204.4063v1
2012-05-16,"Electronic correlations, Jahn-Teller distortions and Mott transition to superconductivity in alkali-C60 compounds","The discovery in 1991 of high temperature superconductivity (SC) in A3C60
compounds, where A is an alkali ion, has been rapidly ascribed to a BCS
mechanism, in which the pairing is mediated by on ball optical phonon modes.
While this has lead to consider that electronic correlations were not important
in these compounds, further studies of various AnC60 with n=1, 2, 4 allowed to
evidence that their electronic properties cannot be explained by a simple
progressive band filling of the C60 six-fold degenerate t1u molecular level.
This could only be ascribed to the simultaneous influence of electron
correlations and Jahn-Teller Distortions (JTD) of the C60 ball, which
energetically favour evenly charged C60 molecules. This is underlined by the
recent discovery of two expanded fulleride Cs3C60 isomeric phases which are
Mott insulators at ambient pressure. Both phases undergo a pressure induced
first order Mott transition to SC with a (p, T) phase diagram displaying a dome
shaped SC, a common situation encountered nowadays in correlated electron
systems. NMR experiments allowed us to study the magnetic properties of the
Mott phases and to evidence clear deviations from BCS expectations near the
Mott transition. So, although SC involves an electron-phonon mechanism, the
incidence of electron correlations has an importance on the electronic
properties, as had been anticipated from DMFT calculations.",1205.3622v1
2012-05-18,"Magnetic ordering in double perovskites R$_2$CoMnO$_6$ (R= Y,Tb) investigated by high resolution neutron spectroscopy","We have investigated low energy nuclear spin excitations in double perovskite
compounds R$_2$CoMnO$_6$ (R = Y,Tb) by inelastic neutron scattering with a
high-resolution back-scattering spectrometer. We observed inelastic signals at
about 2.1 $\mu$eV for Y$_2$CoMnO$_6$ and also for Tb$_2$CoMnO$_6$ at T = 2 K in
both energy loss and energy gain sides. We interpret these inelastic peaks to
be due to the transitions between the hyperfine split nuclear levels of
$^{59}$Co nucleus. The inelastic peaks move towards the central elastic peak
and finally merge with it at the magnetic ordering temperature $T_C$. The
energy of the low energy excitations decreases continuously and becomes zero at
$T_C \approx 75$ K for Y$_2$CoMnO$_6$ and $T_C \approx 100$ K for
Tb$_2$CoMnO$_6$. For Tb$_2$CoMnO$_6$, which contains magnetic rare-earth ions,
additional quasielastic scattering due presumably to the fluctuations of large
Tb magnetic moments was observed. The present study reveals the magnetic
ordering of the Co sublattice. The results of this investigation along with
that obtained by us for other compounds indicate the presence of unquenched
orbital moments in some of the Co compounds.",1205.4099v1
2012-05-30,Band Calculations for Ce Compounds with AuCu$_{3}$-type Crystal Structure on the basis of Dynamical Mean Field Theory II. - CeIn$_{3}$ and CeSn$_{3}$,"Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure
were carried out on the basis of dynamical mean field theory (DMFT). The
results of applying the calculation to CeIn$_{3}$ and CeSn$_{3}$ are presented
as the second in a series of papers. The Kondo temperature and crystal-field
splitting are obtained, respectively, as 190 and 390 K (CeSn$_{3}$), 8 and 160
K (CeIn$_{3}$ under ambient pressure), and 30 and 240 K (CeIn$_{3}$ at a
pressure of 2.75 GPa). Experimental results for the photoemission spectrum are
reasonably well reproduced. In CeSn$_{3}$, a Fermi surface (FS) structure
similar to that obtained by a refined calculation based on the local density
approximation (LDA) is obtained. In CeIn$_{3}$, the topology of the FS
structure is different from that obtained by the LDA calculation but seems to
be consistent with the results of de Haas-van Alphen experiments. Cyclotron
mass of the correct magnitude is obtained in both compounds. The experimental
result for the angular correlation of the electron-positron annihilation
radiation is reasonably well reproduced on the basis of the itinerant 4f
picture. A band calculation for CeIn$_{3}$ in the antiferromagnetic state was
carried out, and it was shown that the occupied 4f state should have a very
shallow level.",1205.6469v1
2012-06-04,Topological Surface States and Dirac point tuning in ternary Bi2Te2Se class of topological insulators,"Using angle-resolved photoemission spectroscopy, we report electronic
structure for representative members of ternary topological insulators. We show
that several members of this family, such as Bi2Se2Te, Bi2Te2Se, and GeBi2Te4,
exhibit a singly degenerate Dirac-like surface state, while Bi2Se2S is a fully
gapped insulator with no measurable surface state. One of these compounds,
Bi2Se2Te, shows tunable surface state dispersion upon its electronic alloying
with Sb (SbxBi2-xSe2Te series). Other members of the ternary family such as
GeBi2Te4 and BiTe1.5S1.5 show an in-gap surface Dirac point, the former of
which has been predicted to show nonzero weak topological invariants such as
(1;111); thus belonging to a different topological class than BiTe1.5S1.5. The
measured band structure presented here will be a valuable guide for
interpreting transport, thermoelectric, and thermopower measurements on these
compounds. The unique surface band topology observed in these compounds
contributes towards identifying designer materials with desired flexibility
needed for thermoelectric and spintronic device fabrication.",1206.0695v2
2012-06-07,Effect of inelastic scattering on the nuclear magnetic relaxation rate 1/T1T in iron-based superconductors,"We present a microscopic study of the nuclear magnetic relaxation rate 1/T1
based on the five-orbital model for iron-based superconductors. We mainly
discuss the effect of the ""inelastic"" quasi-particle damping rate {\gamma} due
to many-body interaction on the size of the coherence peak, for both s++ and
s+- wave superconducting states. We focus on Ba(Fe1-xCox)2As2, and
systematically evaluate {\gamma} in the normal state from the experimental
resistivity, from optimally to over-doped compounds. Next, {\gamma} in the
superconducting state is calculated microscopically based on the second order
perturbation theory. In optimally doped compounds (Tc ~ 30 K), it is revealed
that the coherence peak on 1/T1T is completely suppressed due to large {\gamma}
for both s++ and s+- wave states. On the other hand, in heavily over doped
compounds with Tc < 10 K, the coherence peak could appear for both pairing
states, since {\gamma} at Tc is quickly suppressed in proportion to Tc^2. By
making careful comparison between theoretical and experimental results, we
conclude that it is difficult to discriminate between s++ and s+- wave states
from the present experimental results.",1206.1399v2
2012-07-06,Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors,"Upon introducing charge carriers into the copper-oxygen sheets of the
enigmatic lamellar cuprates the ground state evolves from an insulator into a
superconductor, and eventually into a seemingly conventional metal (a Fermi
liquid). Much has remained elusive about the nature of this evolution and about
the peculiar metallic state at intermediate hole-carrier concentrations (p).
The planar resistivity of this unconventional metal exhibits a linear
temperature dependence (\rho $\propto$ T) that is disrupted upon cooling toward
the superconducting state by the opening of a partial gap (the pseudogap) on
the Fermi surface. Here we first demonstrate for the quintessential compound
HgBa$_2$CuO$_{4+\delta}$ a dramatic switch from linear to purely quadratic
(Fermi-liquid-like, \rho $\propto$ T$^2$) resistive behavior in the pseudogap
regime. Despite the considerable variation in crystal structures and disorder
among different compounds, our result together with prior work gives new
insight into the p-T phase diagram and reveals the fundamental resistance per
copper-oxygen sheet in both linear (\rho_S = A_{1S} T) and quadratic (\rho_S =
A_{2S} T$^2$) regimes, with A_{1S} $\propto$ A_{2S} $\propto$ 1/p. Theoretical
models can now be benchmarked against this remarkably simple universal
behavior. Deviations from this underlying behavior can be expected to lead to
new insights into the non-universal features exhibited by certain compounds.",1207.1504v2
2012-07-24,Thermodynamic behavior of Ce compounds tuned at T_ord = 0,"Based on specific heat (C_m) and entropy evaluation, different magnetic phase
diagrams of Ce compounds can be recognized: I) with the entropy of the ordered
phase (S_MO) decreasing with their order temperature (T_ord): S_MO => 0 as
T_ord => 0, being these systems the only candidates for Quantum Critical
behavior. II) with phase boundaries ending at a finite temperature Critical
Point because their Cm(T_ord) jumps (\Delta C_m) do not decrease sufficiently
with T_ord producing a S_MO bottleneck, and III) those showing a transference
of degrees of freedom to a non-magnetic heavy fermion (HF) component, with
their \Delta C_m vanishing at T >> 0. There is also a IV) group of Ce HF
fermions which do not order magnetically because they are tuned at T_ord = 0.
These compounds are at the top of the lim(T=>0) of \delta S_m/\delta T = \gamma
. values because they collect the highest density of low energy excitations.
From the analysis of Cm(T)=T and S_m(T) results performed on these selected Ce
ternaries, a quantitative determination of an upper limit for the density of
excitations is obtained, excluding any evidence of C_m(T)/T divergency at T =>
0 in agreement with thermodynamic laws.",1207.5829v2
2012-08-07,"(CuCl)LaTa2O7 and quantum phase transition in the (CuX)LaM2O7 family (X = Cl, Br; M = Nb, Ta)","We apply neutron diffraction, high-resolution synchrotron x-ray diffraction,
magnetization measurements, electronic structure calculations, and quantum
Monte-Carlo simulations to unravel the structure and magnetism of
(CuCl)LaTa2O7. Despite the pseudo-tetragonal crystallographic unit cell, this
compound features an orthorhombic superstructure, similar to the Nb-containing
(CuX)LaNb2O7 with X = Cl and Br. The spin lattice entails dimers formed by the
antiferromagnetic fourth-neighbor coupling J4, as well as a large number of
nonequivalent interdimer couplings quantified by an effective exchange
parameter Jeff. In (CuCl)LaTa2O7, the interdimer couplings are sufficiently
strong to induce the long-range magnetic order with the Neel temperature TN~7 K
and the ordered magnetic moment of 0.53 mu_B, as measured with neutron
diffraction. This magnetic behavior can be accounted for by Jeff/J4~1.6 and
J4~16 K. We further propose a general magnetic phase diagram for the
(CuCl)LaNb2O7-type compounds, and explain the transition from the gapped
spin-singlet (dimer) ground state in (CuCl)LaNb2O7 to the long-range
antiferromagnetic order in (CuCl)LaTa2O7 and (CuBr)LaNb2O7 by an increase in
the magnitude of the interdimer couplings Jeff/J_4, with the (CuCl)LaM2O7 (M =
Nb, Ta) compounds lying on different sides of the quantum critical point that
separates the singlet and long-range-ordered magnetic ground states.",1208.1477v1
2012-08-15,Superconductivity at 5K in NdO0.5F0.5BiS2,"We report appearance of superconductivity at 5K in NdO0.5F0.5BiS2 and
supplement the discovery [1] of the same in layered sulfide based ZrCuSiAs type
compounds. The bulk polycrystalline compound is synthesized by conventional
solid state route via vacuum encapsulation technique. Detailed structural
analysis showed that the studied compound is crystallized in tetragonal P4/nmm
space group with lattice parameters a = 3.9911(3) {\AA}, c = 13.3830(2) {\AA}.
Bulk superconductivity is established in NdO0.5F0.5BiS2 at 5K by both transport
and magnetic measurements. Electrical transport measurements showed
superconducting Tc onset at 5.2K and Tc ({\rho}=0) at 4.7K. Under applied
magnetic field both Tc onset and Tc ({\rho} =0) decrease to lower temperatures
and an upper critical field [Hc2(0)] of above 23kOe is estimated. Both AC and
DC magnetic susceptibility measurements showed bulk superconductivity below 5K.
Isothermal magnetization (MH) exhibited typical type II behavior with lower
critical field (Hc1) of around 15Oe. Isothermal magnetization (MH) exhibited
typical type-II behavior with lower critical field (Hc1) of around 15Oe.
Specific heat [Cp(T)] is investigated in the temperature range of 1.9-50K in
zero external magnetic field. A Schottky-type anomaly is observed at low
temperature below 7K. This low temperature Schottky can be attributed to the
change in the entropy of the system.",1208.3077v4
2012-10-06,"X-ray magnetic circular dichroism in (Ge,Mn) compounds: experiments and modeling","X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra
at the L$_{2,3}$ edges of Mn in (Ge,Mn) compounds have been measured and are
compared to the results of first principles calculation. Early \textit{ab
initio} studies show that the Density Functional Theory (DFT) can very well
describe the valence band electronic properties but fails to reproduce a
characteristic change of sign in the L$_{3}$ XMCD spectrum of Mn in
Ge$_3$Mn$_5$, which is observed in experiments. In this work we demonstrate
that this disagreement is partially related to an underestimation of the
exchange splitting of Mn 2$p$ core states within the local density
approximation. It is shown that the change in sign experimentally observed is
reproduced if the exchange splitting is accurately calculated within the
Hartree-Fock approximation, while the final states can be still described by
the DFT. This approach is further used to calculate the XMCD in different
(Ge,Mn) compounds. It demonstrates that the agreement between experimental and
theoretical spectra can be improved by combining state of the art calculations
for the core and valence states respectively.",1210.1991v5
2012-10-20,Tunable spin reorientation transition and magnetocaloric effect in Sm0.7-xLaxSr0.3MnO3 series,"We report electrical resistivity, magnetic and magnetocaloric properties in
Sm0.7-xLaxSr0.3MnO3 series for x= 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, and
0.7. All the compounds show second order paramagnetic to ferromagnetic
transition at T = Tc which is tunable anywhere between 83 K and 373 K with a
proper choice of the doping level (x). The insulating ferromagnet x= 0
transforms to ferromagnetic metal below Tc for x= 0.1 and the insulator-metal
transition temperature shifts up with increasing x. The magnetization (M)
exhibits an interesting behavior as a function of temperature and doping level.
The field-cooled M(T) of all but x= 0.7 compound show a cusp at a temperature
T* much below Tc. While the Tc increases monotonically with increasing x, T*
increases gradually, attains a maximum value (T*= 137 K) for x= 0.6 and
decreases rapidly thereafter. It is suggested that the decrease of M(T) below
T* is due to ferrimagnetic interaction between Sm(4f) and Mn(3d) sublattices
that promotes spin-reorientation transition of the Mn-sublattice. The observed
anomalous feature in M(T) does not have impact on the dc resistivity. Magnetic
entropy change (delta Sm) was estimated from magnetization isotherms. The sign
of delta Sm is found to change from negative above T* to positive below T*
indicating the coexistence of normal and inverse magnetocaloric effects. delta
Sm is nearly composition independent (-delta Sm is about 1.5 J/Kg K for delta H
= 1 Tesla) and refrigeration capacity lies between 50 and 80 J/kg K for x =
0.1-0.6. The tunability of Curie temperature with a nearly constant delta Sm
value along with high refrigeration capacity makes this series of compounds
interesting for magnetic refrigeration over a wide temperature range.",1210.5595v1
2012-10-24,Non-linear lattice response of SmFeAsO_{1-x}F_{x} superconductor to hydrostatic pressure,"Hydrostatic pressure Raman measurements have been carried out on the SmFeAsO
series of oxypnictides with varying amount of doping (F substitution for O and
Co for Fe) and transition temperature (T_{c}), in order to investigate lattice
modifications and their connection to doping and superconductivity. Synchrotron
XRD data on some of these compounds indicated that at low doping the lattice
constants vary smoothly with pressure, but with increasing F concentration
there is a deviation from the normal equation of state and these effects are
related with modifications in the superconducting FeAs4 tetrahedra. The
hydrostatic pressure Raman measurements show that the A1g mode of the rare
earth atom for the superconducting compounds deviates from the linear pressure
dependence at the same pressures where the XRD results indicate
pressure-induced lattice anomalies. A similar anomaly is found for the As
phonon of same symmetry. As in cuprates, the effect is diminished in the
undoped compounds and it is not related with the F substitution being present
in the Sm(Fe_{1-x}Co_{x})AsO as well. The calculated Gr\""uneisen parameter for
the Sm phonon ({\gamma \approx}1.5) is very similar to the corresponding values
of cuprates and it does not vary with doping. For the Fe mode it has higher
value ({\gamma \approx}1.8) than for As ({\gamma \approx}1) indicating a more
anharmonic phonon.",1210.6451v1
2012-11-15,Unexpected stable stoichiometries of sodium chlorides,"At ambient pressure, sodium, chlorine, and their only known compound NaCl,
have well-understood crystal structures and chemical bonding. Sodium is a
nearly-free-electron metal with the bcc structure. Chlorine is a molecular
crystal, consisting of Cl2 molecules. Sodium chloride, due to the large
electronegativity difference between Na and Cl atoms, has highly ionic chemical
bonding, with stoichiometry 1:1 dictated by charge balance, and rocksalt
(B1-type) crystal structure in accordance with Pauling's rules. Up to now,
Na-Cl was thought to be an ultimately simple textbook system. Here, we show
that under pressure the stability of compounds in the Na-Cl system changes and
new materials with different stoichiometries emerge at pressure as low as 25
GPa. In addition to NaCl, our theoretical calculations predict the stability of
Na3Cl, Na2Cl, Na3Cl2, NaCl3 and NaCl7 compounds with unusual bonding and
electronic properties. The bandgap is closed for the majority of these
materials. Guided by these predictions, we have synthesized cubic NaCl3 at
55-60 GPa in the laser-heated diamond anvil cell at temperatures above 2000 K.",1211.3644v1
2012-12-13,Destruction of Kondo effect in cubic heavy fermion compound Ce3Pd20Si6,"How ground states of quantum matter transform between one another reveals
deep insights into the mechanisms stabilizing them. Correspondingly, quantum
phase transitions are explored in numerous materials classes, with heavy
fermion compounds being among the most prominent ones. Recent studies in an
anisotropic heavy fermion compound have shown that different types of
transitions are induced by variations of chemical or external pressure [1-3],
raising the question of the extent to which heavy fermion quantum criticality
is universal. To make progress, it is essential to broaden both the materials
basis and the microscopic parameter variety. Here, we identify a cubic heavy
fermion material as exhibiting a field-induced quantum phase transition, and
show how the material can be used to explore one extreme of the dimensionality
axis. The transition between two different ordered phases is accompanied by an
abrupt change of Fermi surface, reminiscent of what happens across the
field-induced antiferromagnetic to paramagnetic transition in the anisotropic
YbRh2Si2. This finding leads to a materials-based global phase diagram -- a
precondition for a unified theoretical description.",1212.3166v2
2012-12-27,Cs in high oxidation states and as a p-block element,"The major chemical feature of an element is the number of electrons available
for forming chemical bonds. A doctrine rooted in the atomic shell model states
that the atoms will maintain a complete inner shell while interacting with
other atoms. Therefore, group IA elements, for example, are invariably stable
in the +1 charge state because the p electrons of their inner shells do not
react with other chemical species. This general rule governs our understanding
of the structures and reactions of matter and has never been challenged. In
this work, we show for the first time that while mixing with fluorine under
pressure, Cs atoms will share their 5p electrons and become oxidized to a
higher charge state. The formal oxidation state can be as high as +5 within the
pressure range of our study (<200 GPa) and stable Cs2+ and Cs3+ compounds can
form at lower pressures. While sharing its 5p electrons, Cs behaves like a
p-block element forming compounds with molecular, covalent, ionic and metallic
features. Considering the pressure range required for the CsFn compounds, the
inner shell electrons in other group IA and IIA elements may also bond with F
or other chemical species under higher pressure.",1212.6290v1
2013-01-17,"63,65Cu Nuclear Resonance Study of the Coupled Spin Dimers and Chains Compound Cu2Fe2Ge4O13","Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) of Cu
have been measured in a coupled spin dimers and chains compound Cu2Fe2Ge4O13.
Cu NQR has also been measured in an isostructural material Cu2Sc2Ge4O13
including only spin dimers. Comparison of the temperature dependence of the
63Cu nuclear spin-lattice relaxation rate between the two compounds reveals
that the Fe chains in Cu2Fe2Ge4O13 do not change a spin gap energy of the Cu
dimers from that in Cu2Sc2Ge4O13, contributing additionally to the relaxation
rate at the Cu site. A modestly large internal field of 3.39 T was observed at
the Cu site in the antiferromagnetic state of Cu2Fe2Ge4O13 at 4.2 K, which is
partly because of quantum reduction of the ordered moment of a Cu atom. The
internal field and the ordered moment of Cu are noncollinear due to large
anisotropy of the hyperfine interaction at the Cu site. A model analysis of the
internal field based on the fourfold planar coordination of Cu suggests that a
3d hole of the Cu2+ ion is mainly in the d(x2-y2) orbital state.",1301.3974v2
2013-02-04,"ThermInfo: Collecting, Retrieving, and Estimating Reliable Thermochemical Data","Standard enthalpies of formation are used for assessing the efficiency and
safety of chemical processes in the chemical industry. However, the number of
compounds for which the enthalpies of formation are available is many orders of
magnitude smaller than the number of known compounds. Thermochemical data
prediction methods are therefore clearly needed. Several commercial and free
chemical databases are currently available, the NIST WebBook being the most
used free source. To overcome this problem a cheminformatics system was
designed and built with two main objectives in mind: collecting and retrieving
critically evaluated thermochemical values, and estimating new data. In its
present version, by using cheminformatics techniques, ThermInfo allows the
retrieval of the value of a thermochemical property, such as a gas-phase
standard enthalpy of formation, by inputting, for example, the molecular
structure or the name of a compound. The same inputs can also be used to
estimate data (presently restricted to non-polycyclic hydrocarbons) by using
the Extended Laidler Bond Additivity (ELBA) method. The information system is
publicly available at http://www.therminfo.com or
http://therminfo.lasige.di.fc.ul.pt. ThermInfo's strength lies in the data
quality, availability (free access), search capabilities, and, in particular,
prediction ability, based on a user-friendly interface that accepts inputs in
several formats.",1302.0710v1
2013-02-05,A Compound model for the origin of Earth's water,"One of the most important subjects of debate in the formation of the solar
system is the origin of Earth's water. Comets have long been considered as the
most likely source of the delivery of water to Earth. However, elemental and
isotopic arguments suggest a very small contribution from these objects. Other
sources have also been proposed, among which, local adsorption of water vapor
onto dust grains in the primordial nebula and delivery through planetesimals
and planetary embryos have become more prominent. However, no sole source of
water provides a satisfactory explanation for Earth's water as a whole. In view
of that, using numerical simulations, we have developed a compound model
incorporating both the principal endogenous and exogenous theories, and
investigating their implications for terrestrial planet formation and
water-delivery. Comets are also considered in the final analysis, as it is
likely that at least some of Earth's water has cometary origin. We analyze our
results comparing two different water distribution models, and complement our
study using D/H ratio, finding possible relative contributions from each
source, focusing on planets formed in the habitable zone. We find that the
compound model play an important role by showing more advantage in the amount
and time of water-delivery in Earth-like planets.",1302.1233v2
2013-02-13,Towards Quantifying the electrostatic transduction mechanism in carbon nanotube molecular sensors,"Despite the great promise of carbon nanotube field effect transistors (CNT
FETs) for applications in chemical and biochemical detection, a quantitative
understanding of sensor responses is lacking. To explore the role of
electrostatics in sensor transduction, experiments were conducted with a set of
highly similar compounds designed to adsorb onto the CNT FET via a pyrene
linker group and take on a set of known charge states under ambient conditions.
Acidic and basic species were observed to induce threshold voltage shifts of
opposite sign, consistent with gating of the CNT FET by local charges due to
protonation or deprotonation of pyrene compounds by interfacial water. The
magnitude of the gate voltage shift was controlled by the distance between the
charged group and the CNT. Additionally, functionalization with an un-charged
pyrene compound showed a threshold shift ascribed to its molecular dipole
moment. This work illustrates a method to produce CNT FETs with controlled
values of the turnoff gate voltage, and more generally, these results will
inform the development of quantitative models for the response of CNT FET
chemical and biochemical sensors.",1302.2960v1
2013-02-24,"A universal, operational theory of unicast multi-user communication with fidelity criteria","This is a three part paper.
  Optimality of source-channel separation for communication with a fidelity
criterion when the channel is compound as defined by Csiszar and Korner in
their book and general as defined by Verdu and Han, is proved in Part I. It is
assumed that random codes are permitted. The word ""universal"" in the title of
this paper refers to the fact that the channel model is compound. The proof
uses a layered black-box or a layered input-output view-point. In particular,
only the end-to-end description of the channel as being capable of
communicating a source to within a certain distortion level is used when
proving separation. This implies that the channel model does not play any role
for separation to hold as long as there is a source model. Further implications
of the layered black-box view-point are discussed.
  Optimality of source-medium separation for multi-user communication with
fidelity criteria over a general, compound medium in the unicast setting is
proved in Part II, thus generalizing Part I to the unicast, multi-user setting.
  Part III gets to an understanding of the question, ""Why is a channel which is
capable of communicating a source to within a certain distortion level, also
capable of communicating bits at any rate less than the infimum of the rates
needed to code the source to within the distortion level"": this lies at the
heart of why optimality of separation for communication with a fidelity
criterion holds. The perspective taken to get to this understanding is a
randomized covering-packing perspective, and the proof is operational.",1302.5860v1
2013-03-11,X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds,"The actinide cubic Laves compounds NpAl2, NpOs2, NpFe2, and PuFe2 have been
examined by X-ray magnetic circular dichroism (XMCD) at the actinide M4,5
absorption edges and Os L2,3 absorption edges. The XMCD experiments performed
at the M4,5 absorption edges of Np and Pu allow us to determine the
spectroscopic branching ratio, which gives information on the coupling scheme
in these materials. In all materials the intermediate coupling scheme is found
appropriate. Comparison with the SQUID data for NpOs2 and PuFe2 allows a
determination of the individual orbital and spin magnetic moments and the
magnetic dipole contribution mmd. The resulting orbital and spin magnetic
moments are in good agreement with earlier values determined by neutron
diffraction, and the values of mmd are non-negligible, and close to those
predicted for intermediate coupling. There is a comparatively large induced
moment on the Os atom in NpOs2 such that the Os contribution to the total
moment per formula unit is ~30% of the total. The spin and orbital moments at
the Os site are parallel, in contrast to the anti-parallel configuration of Os
impurities in 3d ferromagnetic transition metals. Calculations using the LDA+U
technique are reported. The ab initio computed XMCD spectra show good agreement
with experimental spectra for small values (0-1eV) of the Hubbard U parameter,
which underpins that 5f electrons in these compounds are relatively
delocalized.",1303.2496v1
2013-03-20,Ensembling classification models based on phalanxes of variables with applications in drug discovery,"Statistical detection of a rare class of objects in a two-class
classification problem can pose several challenges. Because the class of
interest is rare in the training data, there is relatively little information
in the known class response labels for model building. At the same time the
available explanatory variables are often moderately high dimensional. In the
four assays of our drug-discovery application, compounds are active or not
against a specific biological target, such as lung cancer tumor cells, and
active compounds are rare. Several sets of chemical descriptor variables from
computational chemistry are available to classify the active versus inactive
class; each can have up to thousands of variables characterizing molecular
structure of the compounds. The statistical challenge is to make use of the
richness of the explanatory variables in the presence of scant response
information. Our algorithm divides the explanatory variables into subsets
adaptively and passes each subset to a base classifier. The various base
classifiers are then ensembled to produce one model to rank new objects by
their estimated probabilities of belonging to the rare class of interest. The
essence of the algorithm is to choose the subsets such that variables in the
same group work well together; we call such groups phalanxes.",1303.4805v4
2013-04-09,Magnetocaloric effect and its implementation in critical behavior study of Mn4FeGe3-xSix intermetallic compounds,"Magnetocaloric effect in Mn4FeGe3-xSix compounds has been studied by dc
magnetization measurements. For the parent compound Mn4FeGe3, the paramagnetic
to ferromagnetic transition temperature TC is above room temperature (320 K),
which initially remains constant for small Si substitution at the Ge site and
then decreases marginally with an increase in Si concentration. A large change
in magnetic entropy at the TC, under a magnetic field variation of 50 kOe, with
typical values of 5.9, 6.5, 5.9 and 4.4 J kg-1 K-1 for x = 0, 0.2, 0.6, and 1
samples, respectively, along with a broad operating temperature range and a
negligible hysteresis make Mn4FeGe3-xSix series a promising candidate for
magnetic refrigerant material around room temperature. Mn4FeGe3-xSix series is
found to undergo a second-order magnetic phase transition. The field dependence
of the magnetic entropy change has been brought out and implemented it to
deduce the critical exponents. The critical behavior study shows that the
magnetic interactions for x = 0 and 0.2 samples have two different behaviors
below and above TC. Below TC, it follows the mean field theory with long-range
magnetic interaction and above TC it follows the Heisenberg three-dimensional
model with short-range or local magnetic interaction. The magnetic exchange
interactions for the x = 0.6 and 1 samples follow the mean-field theory.",1304.2465v1
2013-04-28,Point Contact Spectroscopy of Fe Pnictides & Chalcogenides In The Normal State,"We review the current status of point contact spectroscopy on the iron based
superconductors, focusing on their normal state. Point contact spectroscopy is
generally used to study superconductors via Andreev reflection, but in recent
years it has also proved to be a useful bulk probe of strongly correlated
electron systems. Point contact spectroscopy picks up a conductance enhancement
in the normal state, above the structural phase transition, of certain iron
based compounds. These include Co doped $\rm{BaFe_2As_2}$, $\rm{SrFe_2As_2}$,
$\rm{Fe_{1+y}Te}$ and F doped $\rm{SmFeAsO}$ and $\rm{LaFeAsO}$. Two materials
which do not show this conductance enhancement are $\rm{CaFe_2As_2}$ and K
doped $\rm{BaFe_2As_2}$. This conductance enhancement is thought to be tied to
orbital fluctuations. Orbital fluctuations in the normal state of these
compounds increases the single particle density of states at the Fermi level,
indicating that PCS is sensitive to this excess density of states. The
enhancement is only observed at those temperatures and dopings where an
in-plane resisitve anisotropy in the detwinned compounds is known to occur.
Thus point contact spectroscopy provides strong indications of electronic
nematicity in such materials. We also present diagnostics on how to judge if a
junction is impacted by joule heating or not. We conclude with the outstanding
challenges in the field and the new experiments that need to be carried out.",1304.7426v1
2013-05-06,Study of Ni and Zn doped CeOFeAs: Effect on the structural transition and specific heat capacity,"We have systematically studied the substitution of nonmagnetic Zn and
magnetic Ni at iron sites in Ce based oxypnictide. The parent compound
(CeOFeAs) shows an anomaly in resistivity around 150 K due to structural
transition from tetragonal (space group: P4/nmm) to orthorhombic structure
(space group: Cmma). Substitution of Zn suppresses this anomaly to lower
temperature (~130 K) but Ni substitution does not show any anomaly around this
temperature and the compound behaves like a metal. Further, we find that non
magnetic (Zn) doping leads to higher impurity scattering as compared to
magnetic Ni doping. Similar to the resistivity measurement, the specific heat
shows another jump near 4 K for CeOFeAs. This is attributed to the ordering of
Ce3+ moments. This peak shifts to 3.8 K for Zn substituted compound and there
is no change in the ordering temperature in the Ni substituted CeOFeAs. These
peaks are broadened in applied magnetic field (5 T) and the calculated magnetic
entropy tends to saturate at the same value for 0 T and 5 T external magnetic
field.",1305.1088v2
2013-06-27,Superconductivity in Topological Insulator Sb2Te3 Induced by Pressure,"Topological superconductivity is one of most fascinating properties of
topological quantum matters that was theoretically proposed and can support
Majorana Fermions at the edge state. Superconductivity was previously realized
in a Cu-intercalated Bi2Se3 topological compound or a Bi2Te3 topological
compound at high pressure. Here we report the discovery of superconductivity in
the topological compound Sb2Te3 when pressure was applied. The crystal
structure analysis results reveal that superconductivity at a low-pressure
range occurs at the ambient phase. The Hall coefficient measurements indicate
the change of p-type carriers at a low-pressure range within the ambient phase,
into n-type at higher pressures, showing intimate relation to superconducting
transition temperature. The first principle calculations based on experimental
measurements of the crystal lattice show that Sb2Te3 retains its Dirac surface
states within the low-pressure ambient phase where superconductivity was
observed, which indicates a strong relationship between superconductivity and
topology nature.",1306.6484v1
2013-07-16,"Pressure-induced enhancement of superconductivity and suppression of semiconducting behavior in Ln(O0.5F0.5)BiS2 (Ln = La, Ce) compounds","Electrical resistivity measurements as a function of temperature between 1 K
and 300 K were performed at various pressures up to 3 GPa on the
superconducting layered compounds Ln(O0.5F0.5)BiS2 (Ln = La, Ce). At
atmospheric pressure, La(O0.5F0.5)BiS2 and Ce(O0.5F0.5)BiS2 have
superconducting critical temperatures, Tc, of 3.3 K and 2.3 K, respectively.
For both compounds, the superconducting critical temperature Tc initially
increases, reaches a maximum value of 10.1 K for La(O0.5F0.5)BiS2 and 6.7 K for
CeO(0.5F0.5)BiS2, and then gradually decreases with increasing pressure. Both
samples also exhibit transient behavior in the region between the lower Tc
phase near atmospheric pressure and the higher Tc phase. This region is
characterized by a broadening of the superconducting transition, in which Tc
and the transition width, delta Tc, are reversible with increasing and
decreasing pressure. There is also an appreciable pressure-induced and
hysteretic suppression of semiconducting behavior up to the pressure at which
the maximum value of Tc is found. At pressures above the value at which the
maximum in Tc occurs, there is a gradual decrease of Tc and further suppression
of the semiconducting behavior with pressure, both of which are reversible.",1307.4157v5
2013-08-16,Appreciable magnetic moment and energy density in single step normal route synthesized MnBi,"We study the structural and magnetic properties of the MnBi inter-metallic
compound. The LTP (Low Temperature Phase) MnBi compound is successfully
synthesized in single step by vacuum encapsulation technique and rapid
quenching from phase formation temperature. The phase purity and the magnetic
moments of MnBi are highly dependent on heat treating schedule. The best phase
purity and the magnetic moment are found for a sample heat treated at 310oC for
48h. Rietveld fitted X-ray diffraction (XRD) patterns revealed that the studied
MnBi compound is crystallized in hexagonal P63/mmc space group with minute
presence of unreacted Bi and Mn phases. The scanning electron microscopy (SEM)
study is carried out to visualize the grains morphology and phase
identification. The bulk MnBi powder showed appreciable magnetic moment of
(62emu/g at 6Tesla) and maximum energy product (BHmax of 4.01MGOe at 6Tesla).
The magnetic properties of synthesized MnBi show that it could be a potential
candidate for rare earth free permanent magnets.",1308.3556v2
2013-08-31,First-principles Study On The Electronic And Optical Properties Of Cubic ABX3 Halide Perovskites,"The electronic properties of ABX3 (A = Cs, CH3NH3, NH2CHNH2; B = Sn, Pb; X =
Cl, Br, I) type compounds in the cubic phase are systematically studied using
the first-principles calculations. We find that these compounds have direct
band gaps at R point where the valance band maximum is an anti-bonding state of
B s-X p coupling, while the conduction band minimum is a non-bonding state with
B p characters. The chemical trend of their properties as A or B or X varies is
fully investigated, which is of great importance to understand and optimize
this kind of solar cell materials. We find that: (i) as the size of A
increases, the band gap of ABX3 will increase; (ii) as B varies from Sn to Pb,
the band gap of ABX3 will increase; and (iii) as X ranges from Cl to Br to I,
the band gap will decrease. We explained these trends by analyzing their band
structures. Furthermore, optical properties of the ABX3 compounds are
investigated. Our calculations show that taking into account the spin-orbit
coupling effect is crucial for predicting the accurate band gap of these halide
perovskites. We predict that CH3NH3SnBr3 is a promising material for solar
cells absorber with a perfect band gap and good optical absorption.",1309.0070v1
2013-08-31,Nature of the magnetic ground state in the mixed valence compound CeRuSn: a single-crystal study,"We report on detailed low temperature measurements of the magnetization, the
specific heat and the electrical resistivity on high quality CeRuSn single
crystals. The compound orders antiferromagnetically at $T_{\rm N} = 2.8$ K with
the Ce$^{3+}$ ions locked within the $a-c$ plane of the monoclinic structure.
Magnetization shows that below $T_{\rm N}$ CeRuSn undergoes a metamagnetic
transition when applying a magnetic field of 1.5 and 0.8 T along the $a$ and
$c$--axis, respectively. This transition manifests in a tremendous negative
jump of $\sim 25$% in the magnetoresistance. The value of the saturated
magnetization along the easy magnetization direction ($c$--axis) and the
magnetic entropy above $T_{\rm N}$ derived from specific heat data correspond
to the scenario where only one third of the Ce ions in the compound being
trivalent and carrying a stable Ce$^{3+}$ magnetic moment, whereas the other
two thirds of the Ce ions are in a nonmagnetic tetravalent and/or mixed valence
state. This is consistent with the low temperature CeRuSn crystal structure
i.\,e.\,, a superstructure consisting of three unit cells of the CeCoAl-type
piled up along the $c$--axis, and in which the Ce$^{3+}$ ions are characterized
by large distances from the Ru ligands while the Ce-Ru distances of the other
Ce ions are much shorter causing a strong 4{\it f}-ligand hybridization and
hence leading to tetravalent and/or mixed valence Ce ions.",1309.0106v1
2013-10-01,Field Induced Magnetic Ordering and Single-ion Anisotropy in the Quasi-1D Haldane Chain Compound SrNi2V2O8: A Single Crystal investigation,"Field-induced magnetic ordering in the Haldane chain compound
SrNi$_{2}$V$_{2}$O$_{8}$ and effect of anisotropy have been investigated using
single crystals. Static susceptibility, inelastic neutron scattering,
high-field magnetization, and low temperature heat-capacity studies confirm a
non-magnetic spin-singlet ground state and a gap between the singlet ground
state and triplet excited states. The intra-chain exchange interaction is
estimated to be $J \sim 8.9{\pm}$0.1 meV. Splitting of the dispersions into two
modes with minimum energies 1.57 and 2.58 meV confirms the existence of
single-ion anisotropy $D(S^z){^2}$. The value of {\it D} is estimated to be
$-0.51{\pm}0.01$ meV and the easy axis is found to be along the
crystallographic {\it c}-axis. Field-induced magnetic ordering has been found
with two critical fields [$\mu_0H_c^{\perp c} = 12.0{\pm}$0.2 T and
$\mu_0H_c^{\parallel c} = 20.8{\pm}$0.5 T at 4.2 K]. Field-induced
three-dimensional magnetic ordering above the critical fields is evident from
the heat-capacity, susceptibility, and high-field magnetization study. The
Phase diagram in the {\it H-T} plane has been obtained from the high-field
magnetization. The observed results are discussed in the light of theoretical
predictions as well as earlier experimental reports on Haldane chain compounds.",1310.0221v1
2013-10-25,NMR investigation of the pressure induced Mott transition to superconductivity in Cs3C60 isomeric compounds,"The discovery in 1991 of high temperature superconductivity (SC) in A3C60
compounds, where A is an alkali ion, has been initially ascribed to a BCS
mechanism, with a weak incidence of electron correlations. However various
experimental evidences taken for compounds with distinct alkali content
established the interplay of strong correlations and Jahn Teller distortions of
the C60 ball. The importance of electronic correlations even in A3C60 has been
highlighted by the recent discovery of two expanded fulleride Cs3C60 isomeric
phases that are Mott insulators at ambient pressure. Both phases undergo a
pressure induced first order Mott transition to SC with a (p, T) phase diagram
displaying a dome shaped SC, a common situation encountered nowadays in
correlated electron systems. NMR experiments allowed us to establish that the
bipartite A15 phase displays N\'eel order at 47K, while magnetic freezing only
occurs at lower temperature in the fcc phase. NMR data do permit us to conclude
that well above the critical pressure, the singlet superconductivity found for
light alkalis is recovered. However deviations from BCS expectations linked
with electronic correlations are found near the Mott transition. So, although
SC involves an electron-phonon mechanism, correlations have a significant
incidence on the electronic properties, as had been anticipated from DMFT
calculations.",1310.6969v1
2013-10-28,Coding theorems for compound problems via quantum Rényi divergences,"Recently, a new notion of quantum R\'enyi divergences has been introduced by
M\""uller-Lennert, Dupuis, Szehr, Fehr and Tomamichel, J.Math.Phys. 54:122203,
(2013), and Wilde, Winter, Yang, Commun.Math.Phys. 331:593--622, (2014), that
has found a number of applications in strong converse theorems. Here we show
that these new R\'enyi divergences are also useful tools to obtain coding
theorems in the direct domain of various problems. We demonstrate this by
giving new and considerably simplified proofs for the achievability parts of
Stein's lemma with composite null hypothesis, universal state compression, and
the classical capacity of compound classical-quantum channels, based on
single-shot error bounds already available in the literature, and simple
properties of the quantum R\'enyi divergences. The novelty of our proofs is
that the composite/compound coding theorems can be almost directly obtained
from the single-shot error bounds, with essentially the same effort as for the
case of simple null-hypothesis/single source/single channel.",1310.7525v4
2013-11-14,Improved design and screening of high bioactivity peptides for drug discovery,"The discovery of peptides having high biological activity is very challenging
mainly because there is an enormous diversity of compounds and only a minority
have the desired properties. To lower cost and reduce the time to obtain
promising compounds, machine learning approaches can greatly assist in the
process and even replace expensive laboratory experiments by learning a
predictor with existing data. Unfortunately, selecting ligands having the
greatest predicted bioactivity requires a prohibitive amount of computational
time. For this combinatorial problem, heuristics and stochastic optimization
methods are not guaranteed to find adequate compounds.
  We propose an efficient algorithm based on De Bruijn graphs, guaranteed to
find the peptides of maximal predicted bioactivity. We demonstrate how this
algorithm can be part of an iterative combinatorial chemistry procedure to
speed up the discovery and the validation of peptide leads. Moreover, the
proposed approach does not require the use of known ligands for the target
protein since it can leverage recent multi-target machine learning predictors
where ligands for similar targets can serve as initial training data. Finally,
we validated the proposed approach in vitro with the discovery of new cationic
anti-microbial peptides.
  Source code is freely available at
http://graal.ift.ulaval.ca/peptide-design/.",1311.3573v3
2013-11-24,How Soil Organic Matter Composition Controls Hexachlorobenzene-Soil-Interactions: Adsorption Isotherms and Quantum Chemical Modelling,"Hazardous persistent organic pollutants (POPs) interact in soil with the soil
organic matter (SOM) but this interaction is insufficiently understood at the
molecular level. We investigated the adsorption of hexachlorobenzene (HCB) on
soil samples with systematically modified SOM. These samples included the
original soil, the soil modified by adding a hot water extract (HWE) fraction
(soil+3 HWE and soil+6 HWE), and the pyrolyzed soil. The SOM contents increased
in the order pyrolyzed soil < original soil < soil+3 HWE < soil+6 HWE. For the
latter three samples this order was also valid for the HCB adsorption. The
pyrolyzed soil adsorbed more HCB than the other samples at low initial
concentrations, but at higher concentrations the HCB adsorption became weaker
than in the samples with HWE addition. This adsorption behaviour combined with
the differences in the chemical composition between the soil samples suggested
that alkylated aromatic, phenol, and lignin monomer compounds contributed most
to the HCB adsorption. To obtain a molecular level understanding, a test set
has been developed on the basis of elemental analysis which comprises 32
representative soil constituents. The calculated binding free energy for HCB
with each representative system shows that HCB binds to SOM stronger than to
soil minerals. For SOM, HCB binds to alkylated aromatic, phenols, lignin
monomers, and hydrophobic aliphatic compounds stronger than to polar aliphatic
compounds confirming the above adsorption isotherms. Moreover, quantitative
structure-activity relationship (QSAR) of the binding free energy with
independent physical properties of the test set systems for the first time
indicated that the polarizability, the partial charge on the carbon atoms, and
the molar volume are the most important properties controlling HCB-SOM
interactions.",1311.6157v1
2013-11-25,"muSR and inelastic neutron scattering investigations of the caged type Kondo semimetals: CeT2Al10 (T=Fe, Ru and Os)","Recently the Ce-based caged-type compounds having general formula CeT2Al10
(T=Fe, Ru and Os) have generated considerable interest due to the Kondo
semiconducting paramagnetic ground state (down to 40 mK) observed in CeFe2Al10
and anomalously high magnetic ordering temperature with a spin gap formation at
low temperatures in Kondo semimetals CeRu2Al10 and CeOs2Al10. The formation of
long-range magnetic ordering out of the Kondo semiconducting/semimetallic state
itself is extraordinary and these are the first examples of this enigmatic
coexistence of electronic ground states. These compounds also exhibit strong
anisotropy in the magnetic and transport properties, which has been explained
on the basis of single ion crystal electric field (CEF) anisotropy in the
presence of strongly anisotropic hybridization between localised 4f-electron
and conduction electrons. Further they also exhibit a remarkable modification
of magnetic and transport properties with doping on Ce, or T or Al sites. In
this review we briefly discuss the bulk properties of these compounds, giving a
detailed discussion on our muon-spin-relaxation (muSR) investigations and
inelastic neutron scattering (INS) results.",1311.6380v1
2013-12-11,Structural and electronic properties of the mu-phase Fe-Mo compounds,"Structural (lattice parameters and sublattice occupancies) and electronic
(charge-density and electric field gradient) properties in a series of
compounds mu-Fe_(100-x)Mo_x were studied experimentally (X-ray diffraction and
Mossbauer spectroscopy) and theoretically (charge and spin self-consistent
KorringaKohnRostoker Green function method). The lattice parameters a and c
showed a linear increase with x while all five lattice sites were found to be
populated by both alloying elements: A and B predominantly by Fe atoms whereas
C and D by Mo atoms hardly depending on the composition. The population of Fe
atoms on the site E was ranging between ca. 50% at x=37.5 and ca. 20% at
x=44.5. Fe-site charge-density (isomer shift) and the electric field gradient
(quadrupole splitting, QS) were revealed to be characteristic of the lattice
site and both of them were almost x-independent. The difference in the
charge-density at Fe-atoms at the sites B (the highest value) and those at the
sites D (the lowest value) was estimated as equivalent to 0.18 electrons. The
average charge-density increases linearly with x. The largest QS-values were
those at the sites A and C, while the smallest ones at the site D.",1312.3130v2
2014-01-21,Nearly compensated exchange in the dimer compound callaghanite Cu$_2$Mg$_2$(CO$_3$)(OH)$_6$$\cdot$2H$_2$O,"A combined theoretical and experimental study of the natural Cu(2+)-mineral
callaghanite is presented. Its crystal structure features well separated
Cu$_2$(OH)$_6$ structural dimers with weakly bonded carbonate groups and water
molecules in between. Susceptibility, field-dependent magnetization and
specific heat measurements reveal a compound with a small spin gap of about 7
K. The observed magnetic properties are well described by a model of isolated
antiferromagnetic spin dimers. Possible ferromagnetic interactions between the
dimers amount to -1.5 K, at most. Different flavors of electronic structure
calculations have been employed to locate the magnetic dimers in the crystal
structure, i.e., to determine whether they coincide with the structural dimers
or not. Calculations of the coupling between the structural dimers clearly show
that magnetic and structural dimers are the same. For the intradimer coupling,
however, the computational results confirmed a coupling strength close to zero
but the sign of the coupling could not be determined unambiguously. Based on
this finding, we then discuss how the reliability of the numerical methods
depends on the characteristics of exchange pathways and on structural features
of the compound in general. Eventually, we try to provide a minimum coupling
strength that is needed for a reliable computational description.",1401.5239v1
2014-01-23,Resource cost results for one-way entanglement distillation and state merging of compound and arbitrarily varying quantum sources,"We consider one-way quantum state merging and entanglement distillation under
compound and arbitrarily varying source models. Regarding quantum compound
sources, where the source is memoryless, but the source state an unknown member
of a certain set of density matrices, we continue investigations begun in the
work of Bjelakovi\'c et. al. [Universal quantum state merging, J. Math. Phys.
54, 032204 (2013)] and determine the classical as well as entanglement cost of
state merging. We further investigate quantum state merging and entanglement
distillation protocols for arbitrarily varying quantum sources (AVQS). In the
AVQS model, the source state is assumed to vary in an arbitrary manner for each
source output due to environmental fluctuations or adversarial manipulation. We
determine the one-way entanglement distillation capacity for AVQS, where we
invoke the famous robustification and elimination techniques introduced by R.
Ahlswede. Regarding quantum state merging for AVQS we show by example, that the
robustification and elimination based approach generally leads to suboptimal
entanglement as well as classical communication rates.",1401.6063v3
2014-02-06,Magneto-elastic couplings in the distorted diamond-chain compound azurite,"We present results of ultrasonic measurements on a single crystal of the
distorted diamond-chain compound azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$. Pronounced
elastic anomalies are observed in the temperature dependence of the
longitudinal elastic mode $c_{22}$ which can be assigned to the relevant
magnetic interactions in the system and their couplings to the lattice degrees
of freedom. From a quantitative analysis of the magnetic contribution to
$c_{22}$ the magneto-elastic coupling $G$ = $\partial J_2$/$\partial
\epsilon_b$ can be determined, where $J_2$ is the intra-dimer coupling constant
and $\epsilon_b$ the strain along the intra-chain $b$ axis. We find an
exceptionally large coupling constant of $|G| \sim ($3650 $\pm$ 150) K
highlighting an extraordinarily strong sensitivity of $J_2$ against changes of
the $b$-axis lattice parameter. These results are complemented by measurements
of the hydrostatic pressure dependence of $J_2$ by means of thermal expansion
and magnetic susceptibility measurements performed both at ambient and finite
hydrostatic pressure. We propose that a structural peculiarity of this
compound, in which Cu$_2$O$_6$ dimer units are incorporated in an unusually
stretched manner, is responsible for the anomalously large magneto-elastic
coupling.",1402.1306v1
2014-02-07,Heavy fermion and Kondo lattice behavior in the itinerant ferromagnet CeCrGe3,"Physical properties of polycrystalline CeCrGe$_{3}$ and LaCrGe$_{3}$ have
been investigated by x-ray absorption spectroscopy, magnetic susceptibility
$\chi(T)$, isothermal magnetization M(H), electrical resistivity $\rho(T)$,
specific heat C($T$) and thermoelectric power S($T$) measurements. These
compounds are found to crystallize in the hexagonal perovskite structure (space
group \textit{P6$_{3}$/mmc}), as previously reported. The $\rho(T)$, $\chi(T)$
and C($T$) data confirm the bulk ferromagnetic ordering of itinerant Cr moments
in LaCrGe$_{3}$ and CeCrGe$_{3}$ with $T_{C}$ = 90 K and 70 K respectively. In
addition a weak anomaly is also observed near 3 K in the C($T$) data of
CeCrGe$_{3}$. The T dependences of $\rho$ and finite values of Sommerfeld
coefficient $\gamma$ obtained from the specific heat measurements confirm that
both the compounds are of metallic character. Further, the $T$ dependence of
$\rho$ of CeCrGe$_{3}$ reflects a Kondo lattice behavior. An enhanced $\gamma$
of 130 mJ/mol\,K$^{2}$ together with the Kondo lattice behavior inferred from
the $\rho(T)$ establish CeCrGe$_{3}$ as a moderate heavy fermion compound with
a quasi-particle mass renormalization factor of $\sim$ 45.",1402.1609v1
2014-03-04,The Structural Diversity of ABS3 Compounds with d0 Electronic Configuration for the B-cation,"We use first-principles density functional theory (DFT) within the local
density approx- imation (LDA) to ascertain the ground state structure of real
and theoretical compounds with the formula ABS3 (A = K, Rb, Cs, Ca, Sr, Ba, Tl,
Sn, Pb, and Bi; and B = Sc, Y, Ti, Zr, V, and Nb) under the constraint that B
must have a d0 electronic configuration. Our findings indicate that none of
these AB combinations prefer a perovskite ground state with corner-sharing BS6
octahedra, but that they prefer phases with either edge- or face-sharing
motifs. Further, a simple two-dimensional structure field map created from A
and B ionic radii provides a neat demarcation between combinations preferring
face-sharing versus edge- sharing phases for most of these combinations. We
then show that by modifying the common Goldschmidt tolerance factor with a
multiplicative term based on the electronegativity dif- ference between A and
S, the demarcation between predicted edge-sharing and face-sharing ground state
phases is enhanced. We also demonstrate that, by calculating the free energy
contribution of phonons, some of these compounds may assume multiple phases as
synthesis temperatures are altered, or as ambient temperatures rise or fall.",1403.0919v3
2014-07-08,Physical properties and magnetic structure of the intermetallic CeCuBi2 compound,"In this work, we combined magnetization, pressure dependent electrical
resistivity, heat-capacity, 63Cu Nuclear Magnetic Resonance (NMR) and X-ray
resonant magnetic scattering experiments to investigate the physical properties
of the intermetallic CeCuBi2 compound. Our single crystals show an
antiferromagnetic ordering at TN ~ 16 K and the magnetic properties indicate
that this compound is an Ising antiferromagnet. In particular, the low
temperature magnetization data revealed a spin-flop transition at T = 5 K when
magnetic fields about 5.5 T are applied along the c-axis. Moreover, the X-ray
magnetic diffraction data below TN revealed a commensurate antiferromagnetic
structure with propagation wavevector (0 0 1/2) with the Ce^3+ moments oriented
along the c-axis. Furthermore, our heat capacity, pressure dependent
resistivity and temperature dependent 63Cu NMR data suggest that CeCuBi2
exhibits a weak heavy fermion behavior with strongly localized Ce^3+ 4f
electrons. We thus discuss a scenario taking into account the anisotropic
magnetic interaction between the Ce^3+ ions along with the tetragonal
crystalline electric field effects in CeCuBi2.",1407.2277v2
2014-07-11,Optical characterization of RTV615 silicone rubber compound,"Room Temperature Vulcanized (RTV) silicone compounds are commonly used to
bond optical components. For our application, we needed to identify an adhesive
with good ultraviolet transmission characteristics, to couple photomultipliers
to quartz windows in a Heavy Gas Cerenkov detector that is being constructed
for Experimental Hall C of Jefferson Lab to provide pi/K separation up to 11
GeV/c. To this end, we present the light transmission results for Momentive
RTV615 silicone rubber compound for wavelengths between 195-400 nm, obtained
with an adapted reflectivity apparatus at Jefferson Lab. All samples cured at
room temperature have transmissions ~93% for wavelengths between 360-400 nm and
fall sharply below 230 nm. Wavelength dependent absorption coefficients were
extracted with four samples of different thicknesses cured at normal
temperature (25oC for 7 days). The absorption coefficient drops approximately
two orders in magnitude from 220-400 nm, exhibiting distinct regions of
flattening near 250 nm and 330 nm. We also investigated the effect of a high
temperature curing method (100oC for 1 hour) and found 5-10% better
transmission than with the normal method. The effect was more significant with
larger sample thickness (3.35 mm) over the wavelength range of 220-280 nm.",1407.3258v1
2014-07-22,New Superconductor (Na0.25K0.45) Ba3Bi4O12: A First-principles Study,"A new superconductor (Na0.25K0.45)Ba3Bi4O12, having an A-site-ordered double
perovskite structure, with a maximum Tc ~ 27 K has very recently been
discovered through hydrothermal synthesis at 593 K. The structural, elastic,
electronic, and thermal properties of the new synthesized compound have been
investigated theoretically. Here we have employed the pseudo-potential
plane-wave (PP-PW) approach based on the density functional (DFT) theory,
within the generalized gradient approximation (GGA). The elastic constants
(Cij), Pugh`s ratio, Cauchy`s pressure and other elastic parameters are derived
and analyzed using energy strain method for the first time. We have discussed
the bonding nature in the light of the electronic valence charge density. Both
electron and hole-like Fermi surfaces are present in the compound under study
which indicate the multiple-band nature of (Na0.25K0.45)Ba3Bi4O12. The compound
is indicated to be a strongly coupled superconductor which is based on the
estimated e-ph coupling constant. The thermodynamic properties such as bulk
modulus, Debye temperature, heat capacities and volume thermal expansion
coefficient at elevated temperature and pressure are calculated and analyzed
for the first time by using quasi-harmonic model.
  Key words: double perovskite, superconductor, elastic properties, electronic
properties, thermal properties",1407.5733v1
2014-08-12,Magnetic properties of geometrically frustrated SrGd2O4,"A study of the magnetic properties of the frustrated rare earth oxide SrGd2O4
has been completed using bulk property measurements of magnetization,
susceptibility and specific heat on single crystal samples. Two zero-field
phase transitions have been identified at 2.73 and 0.48 K. For the field, H,
applied along the a and b axes, a single boundary is identified that delineates
the transition from a low field, low temperature magnetically ordered regime to
a high field, high temperature paramagnetic phase. Several field-induced
transitions, however, have been observed with H || c. The measurements have
been used to map out the magnetic phase diagram of SrGd2O4, suggesting that it
is a complex system with several competing magnetic interactions. The
low-temperature magnetic behavior of SrGd2O4 is very different compared to the
other SrLn2O4 (Ln = Lanthanide) compounds, even though all of the SrLn2O4
compounds are isostructural, with the magnetic ions forming a low-dimensional
lattice of zigzag chains that run along the c axis. The differences are likely
to be due to the fact that in the ground state Gd3+ has zero orbital angular
momentum and therefore the spin-orbit interactions, which are crucial for other
SrLn2O4 compounds, can largely be neglected. Instead, given the relatively
short Gd3+-Gd3+ distances in SrGd2O4, dipolar interactions must be taken into
account for this antiferromagnet alongside the Heisenberg exchange terms.",1408.2771v1
2014-09-13,Microscopic description of neutron emission rates in compound nuclei,"The neutron emission rates in thermal excited nuclei are conventionally
described by statistical models with a phenomenological level density parameter
that depends on excitation energies, deformations and mass regions. In the
microscopic view of hot nuclei, the neutron emission rates can be determined by
the external neutron gas densities without any free parameters. Therefore the
microscopic description of thermal neutron emissions is desirable that can
impact several understandings such as survival probabilities of superheavy
compound nuclei and neutron emissivity in reactors.
  To describe the neutron emission rates microscopically, the external thermal
neutron gases are self-consistently obtained based on the Finite-Temperature
Hartree-Fock-Bogoliubov (FT-HFB) approach. The results are compared with the
statistical model to explore the connections between the FT-HFB approach and
the statistical model.
  The Skyrme FT-HFB equation is solved by HFB-AX in deformed coordinate spaces.
Based on the FT-HFB approach, the thermal properties and external neutron gas
are properly described with the self-consistent gas substraction procedure.
Then neutron emission rates can be obtained based on the densities of external
neutron gases.
  The thermal statistical properties of $^{238}$U and $^{258}$U are studied in
detail in terms of excitation energies. The thermal neutron emission rates in
$^{238, 258}$U and superheavy compound nuclei $_{112}^{278}$Cn and
$_{114}^{292}$Fl are calculated, which agree well with the statistical model by
adopting an excitation-energy-dependent level density parameter.
  The coordinate-space FT-HFB approach can provide reliable microscopic
descriptions of neutron emission rates in hot nuclei, as well as microscopic
constraints on the excitation energy dependence of level density parameters for
statistical models.",1409.3958v2
2014-09-16,On the Continuity of the Secrecy Capacity of Compound and Arbitrarily Varying Wiretap Channels,"The wiretap channel models secure communication between two users in the
presence of an eavesdropper who must be kept ignorant of transmitted messages.
The performance of such a system is usually characterized by its secrecy
capacity which determines the maximum transmission rate of secure
communication. In this paper, the issue of whether or not the secrecy capacity
is a continuous function of the system parameters is examined. In particular,
this is done for channel uncertainty modeled via compound channels and
arbitrarily varying channels, in which the legitimate users know only that the
true channel realization is from a pre-specified uncertainty set. In the former
model, this realization remains constant for the entire duration of
transmission, while in the latter the realization varies from channel use to
channel use in an unknown and arbitrary manner. These models not only capture
the case of channel uncertainty, but are also suitable for modeling scenarios
in which a malicious adversary jams or otherwise influence the legitimate
transmission. The secrecy capacity of the compound wiretap channel is shown to
be robust in the sense that it is a continuous function of the uncertainty set.
Thus, small variations in the uncertainty set lead to small variations in
secrecy capacity. On the other hand, the deterministic secrecy capacity of the
\emph{arbitrarily varying wiretap channel} is shown to be discontinuous in the
uncertainty set meaning that small variations can lead to dramatic losses in
capacity.",1409.4752v3
2014-09-22,First-Principles Description of Charge Transfer in Donor-Acceptor Compounds from Self-Consistent Many-Body Perturbation Theory,"We investigate charge transfer in prototypical molecular donor-acceptor
compounds using hybrid density functional theory (DFT) and the GW approximation
at the perturbative level (G0W0) and at full self-consistency (sc-GW). For the
systems considered here, no charge transfer should be expected at large
intermolecular separation according to photoemission experiment and accurate
quantum-chemistry calculations. The capability of hybrid exchange-correlation
functionals of reproducing this feature depends critically on the fraction of
exact exchange $\alpha$, as for small values of $\alpha$ spurious fractional
charge transfer is observed between the donor and the acceptor. G0W0 based on
hybrid DFT yields the correct alignment of the frontier orbitals for all values
of $\alpha$. However, G0W0 has no capacity to alter the ground-state properties
of the system, because of its perturbative nature. The electron density in
donor-acceptor compounds thus remains incorrect for small $\alpha$ values. In
sc-GW, where the Green's function is obtained from the iterative solution of
the Dyson equation, the electron density is updated and reflects the correct
description of the level alignment at the GW level, demonstrating the
importance of self-consistent many-body approaches for the description of
ground- and excited-state properties in donor-acceptor systems.",1409.6196v1
2014-10-08,"Electronic properties of single-layer and multilayer transition metal dichalcogenides $MX_2$ ($M=$ Mo, W and $X=$ S, Se)","Single- and few-layer transition metal dichalcogenides have recently emerged
as a new family of layered crystals with great interest, not only from the
fundamental point of view, but also because of their potential application in
ultrathin devices. Here we review the electronic properties of semiconducting
$MX_2$, where $M=$Mo or W and $X=$ S or Se. Based on of density functional
theory calculations, which include the effect of spin-orbit interaction, we
discuss the band structure of single-layer, bilayer and bulk compounds. The
band structure of these compounds is highly sensitive to elastic deformations,
and we review how strain engineering can be used to manipulate and tune the
electronic and optical properties of those materials. We further discuss the
effect of disorder and imperfections in the lattice structure and their effect
on the optical and transport properties of $MX_2$. The superconducting
transition in these compounds, which has been observed experimentally, is
analyzed, as well as the different mechanisms proposed so far to explain the
pairing. Finally, we include a discussion on the excitonic effects which are
present in these systems.",1410.2154v1
2014-10-27,Solution based synthesis of mixed phase materials in the Li2TiO3 - Li4SiO4 system,"As candidate tritium breeder materials for use in the ITER helium cooled
pebble bed, ceramic multiphasic compounds lying in the region of the
quasi-binary lithium metatitanate- lithium orthosilicate system may exhibit
mechanical and physical advantages relative to single phase materials. Here we
present an organometallic solution-based synthesis procedure for the
low-temperature fabrication of compounds in the Li2TiO3 - Li4SiO4 region and
investigate phase stability and transformations through temperature varied
X-ray diffraction and scanning calorimetry. Results demonstrate that the
metatitanate and metasilicate phases Li2TiO3 and Li2SiO3 readily crystallise in
nanocrystalline form at temperatures below 180{\deg}C. Lithium deficiency in
the region of 5% results from Li sublimation from Li4SiO4 and/or from excess Li
incorporation in the metatitanate phase and brings about a stoichiometry shift
and product compounds with mixed lithium orthosilicate/ metasilicate content
towards the Si rich region and predominantly Li2TiO3 content towards the Ti
rich region. Above 1150{\deg}C the transformation of monoclinic to cubic
{\gamma}-Li2TiO3 disordered solid-solution occurs while the melting of silicate
phases indicates a likely monotectic type system with a solidus line in the
region 1050{\deg}-1100{\deg}C. Synthesis procedures involving a lithium
chloride precursor are not likely to be a viable option for breeder pebble
synthesis as this route was found to yield materials with a more significant
Li-deficiency exhibiting the crystallisation of the Li2TiSiO5 phase at
intermediate compositions.",1410.7128v1
2014-11-17,Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3,"Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3,
Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators
and demonstrated through experimental efforts. The counterpart compound Sb2Se3
on the other hand was found to be topological trivial, but further theoretical
studies indicated that the pressure might induce Sb2Se3 into a topological
nontrivial state. Here, we report on the discovery of superconductivity in
Sb2Se3 single crystal induced via pressure. Our experiments indicated that
Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a
pressure induced insulator to metal like transition at ~3 GPa which should be
related to the topological quantum transition. The superconducting transition
temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it
keeps ambient structure. High pressure Raman revealed that new modes appeared
around 10 GPa and 20 GPa, respectively, which correspond to occurrence of
superconductivity and to the change of TC slop as the function of high pressure
in conjunction with the evolutions of structural parameters at high pressures.",1411.4533v1
2014-11-20,Two maxentropic approaches to determine the probability density of compound risk losses,"Here we present an application of two maxentropic procedures to determine the
probability density distribution of compound sums of random variables, using
only a finite number of empirically determined fractional moments. The two
methods are the Standard method of Maximum Entropy (SME), and the method of
Maximum Entropy in the Mean (MEM). We shall verify that the reconstructions
obtained satisfy a variety of statistical quality criteria, and provide good
estimations of VaR and TVaR, which are important measures for risk management
purposes. We analyze the performance and robustness of these two procedures in
several numerical examples, in which the frequency of losses is Poisson and the
individual losses are lognormal random variables. As side product of the work,
we obtain a rather accurate description of the density of the compound random
variable. This is an extension of a previous application based on the Standard
Maximum Entropy approach (SME) where the analytic form of the Laplace transform
was available to a case in which only observed or simulated data is used. These
approaches are also used to develop a procedure to determine the distribution
of the individual losses through the knowledge of the total loss. Then, in the
case of having only historical total losses, it is possible to decompound or
disaggregate the random sums in its frequency/severity distributions, through a
probabilistic inverse problem.",1411.5625v2
2014-11-24,"Experimental demonstration of hybrid improper ferroelectricity and presence of abundant charged walls in (Ca,Sr)$_{3}$Ti$_{2}$O$_{7}$ crystals","Standing on successful first principles predictions for new functional
ferroelectric materials, a number of new ferroelectrics have been
experimentally discovered. Utilizing trilinear coupling of two types of
octahedron rotations, hybrid improper ferroelectricity has been theoretically
predicted in ordered perovskites and the Ruddlesden-Popper compounds
(Ca$_{3}$Ti$_{2}$O$_{7}$, Ca$_{3}$Mn$_{2}$O$_{7}$, and
(Ca/Sr/Ba)$_{3}$(Sn/Zr/Ge)$_{2}$O$_{7}$). However, the ferroelectricity of
these compounds has never been experimentally confirmed and even their polar
nature has been under debate. Here we provide the first experimental
demonstration of room-temperature switchable polarization in the bulk crystals
of Ca$_{3}$Ti$_{2}$O$_{7}$ as well as Sr-doped Ca$_{3}$Ti$_{2}$O$_{7}$. In
addition, (Ca,Sr)$_{3}$Ti$_{2}$O$_{7}$ is found to exhibit an intriguing
ferroelectric domain structure resulting from orthorhombic twins and
(switchable) planar polarization. The planar domain structure accompanies
abundant charged domain walls with conducting head-to-head and insulating
tail-to-tail configurations, which exhibit two-order-of-magnitude conduction
difference. These discoveries provide new research opportunities not only on
new stable ferroelectrics of Ruddlesden-Popper compounds, but also on
meandering conducting domain walls formed by planar polarization.",1411.6315v1
2014-11-25,Tuning the Ferroelectric Polarization in $AA^{\prime}$MnWO$_6$ Double Perovskites through $A$ Cation Substitution,"Recent experimental and theoretical work has shown that the double perovskite
NaLaMnWO$_6$ exhibits antiferromagnetic ordering owing to the Mn $d$ states,
and computational studies further predict it to exhibit a spontaneous electric
polarization due to an improper mechanism for ferroelectricity [King \textit{et
al., Phys.\ Rev.\ B}, 2009, \textbf{79}, 224428; Fukushima \textit{et al.,
Phys.\ Chem.\ Chem.\ Phys.}, 2011, \textbf{13}, 12186], which make it a
candidate multiferroic material. Using first-principles density functional
calculations, we investigate nine isostructural and isovalent
$AA^{\prime}$MnWO$_6$ double perovskites ($A$=Na, K, and Rb; $A^{\prime}$=La,
Nd, and Y) with the aim of articulating crystal-chemistry guidelines describing
how to enhance the magnitude of the electric polarization through chemical
substitution of the $A$-site while retaining long-range magnetic order. We find
that the electric polarization can be enhanced by up to 150\% in compounds
which maximize the difference in the ionic size of the $A$ and $A^{\prime}$
cations. By examining the tolerance factors, bond valences, and structural
distortions (described by symmetry-adapted modes) of the nine compounds, we
identify the atomic scale features that are strongly correlated with the ionic
and electronic contributions to the electric polarization. We also find that
each compound exhibits a purely electronic remnant polarization, even in the
absence of a displacive polar mode. The analysis and design strategies
presented here can be further extended to additional members of this family
($B$=Fe, Co, etc.), and the improper ferroelectric nature of the mechanism
allows for the decoupling of magnetic and ferroelectric properties and the
targeted design of novel multiferroics.",1411.6891v1
2014-12-08,Resonant spin excitations in unconventional heavy fermion superconductors and Kondo lattice compounds,"The heavy quasiparticle bands in Kondo materials which originate in the
hybridization of f- and conduction electrons exhibit numerous, sometimes
coexisting, broken symmetry phases. Most notable are unconventional
superconductivity, itinerant small moment antiferromagnetism and hidden order
of higher order multipoles of f-electrons which all lead to a gapping of the
heavy bands. In rare cases the chemical potential lies within the hybridization
gap and the ground state is a Kondo semiconductor without ordering. The
dynamical magnetic response of such gapped f-electron systems has been
investigated with inelastic neutron scattering. It was found that collective
spin exciton modes which are due to residual quasiparticle interactions appear
below the threshold of superconducting or hidden order gap or directly the
hybridzation gap. The spin exciton resonance is commonly located around a zone
boundary vector $Q$ with nesting properties in the normal state. In the
superconducting case its appearance gives a strong criterion for the gap
symmetry requesting a sign change $\Delta_{{\bf k}+{\bf Q}}=-\Delta_{\bf k}$
due to the coherence factors. Therefore this many body effect with fundamental
importance may also be used as a tool to discriminate between proposed gap
models. While the spin resonance has been observed for many compounds we
restrict our discussion here exclusively to the small group of f-electron
superconductors CeCoIn5, CeCu2Si2 and UPd2Al3, hidden order Kondo compounds
CeB6 and URu2Si2 as well as the Kondo semiconductor YbB12 .",1412.2523v2
2015-01-01,Tripling the critical temperature of KFe$_{2}$As$_{2}$ by carrier switch,"Superconductivity of high critical temperature ($T_{c}$) superconductors is
usually realized through chemical dopant or application of pressure in a
similar way to induce charge carriers of either electrons or holes into their
parent compounds. For chemical doping, superconductivity behaves asymmetrically
with the maximum $T_{c}$ often higher for optimal hole-doping than that of
optimal electron-doping on the same parent compound. However, whether electron
carriers could be in favour of higher $T_{c}$ than holes in such high-$T_{c}$
superconductors is unknown but attractive. Here we show that the application of
pressure can drive KFe$_{2}$As$_{2}$ from hole- to electron-superconductivity
after passing the previously reported $V$-shape or oscillation regime. The
maximum $T_{c}$ in the electron-dominated region is tripled to the initial
value of 3.5 K or the average in the low-pressure hole-dominated region. The
structural transition takes place from the tetragonal to collapsed tetragonal
phase when the carrier characteristic is changed upon compression. Our results
unambiguously offer a new route to further improve superconductivity with huge
$T_{c}$ enhancement for a compound through carrier switch. The strong
electronic correlations in KFe$_{2}$As$_{2}$ are suggested to account for the
unexpected enhancement of superconductivity in the collapsed tetragonal phase.",1501.00330v1
2015-02-24,$S$ = 1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain in a zinc-verdazyl complex,"We successfully synthesized the zinc-verdazyl complex
[Zn(hfac)$_2$]$\cdot$($o$-Py-V) [hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate;
$o$-Py-V = 3-(2-pyridyl)-1,5-diphenylverdazyl], which is an ideal model
compound with an $S$ = 1/2 ferromagnetic-antiferromagnetic alternating
Heisenberg chain (F-AF AHC). $Ab$ $initio$ molecular orbital (MO) calculations
indicate that two dominant interactions $J_{\rm{F}}$ and $J_{\rm{AF}}$ form the
$S=1/2$ F-AF AHC in this compound. The magnetic susceptibility and magnetic
specific heat of the compound exhibit thermally activated behavior below
approximately 1 K. Furthermore, its magnetization curve is observed up to the
saturation field and directly indicates a zero-field excitation gap of 0.5 T.
These experimental results provide evidence for the existence of a Haldane gap.
We successfully explain the results in terms of the $S=1/2$ F-AF AHC through
quantum Monte Carlo calculations with $|J_{\rm{AF}}/J_{\rm{F}}|$ = 0.22. The
$ab$ $initio$ MO calculations also indicate a weak AF interchain interaction
$J'$ and that the coupled F-AF AHCs form a honeycomb lattice. The $J'$
dependence of the Haldane gap is calculated, and the actual value of $J'$ is
determined to be less than 0.01$|J_{\rm{F}}|$.",1502.06804v1
2015-03-03,Magnetic properties and complex magnetic phase diagram in non centrosymmetric EuRhGe$_3$ and EuIrGe$_3$ single crystals,"We report the magnetic properties of two Eu based compounds, single
crystalline EuIrGe$_3$ and EuRhGe$_3$, inferred from magnetisation, electrical
transport, heat capacity and $^{151}$Eu M\""{o}ssbauer spectroscopy. These
previously known compounds crystallise in the non-centrosymmetric, tetragonal,
$I4mm$, BaNiSn$_3$-type structure. Single crystals of EuIrGe$_3$ and EuRhGe$_3$
were grown using high temperature solution growth method using In as flux.
EuIrGe$_3$ exhibits two magnetic orderings at $T_{\rm N1}$ = 12.4 K, and
$T_{\rm N2}$ = 7.3 K. On the other hand EuRhGe$_3$ presents a single magnetic
transition with a $T_{\rm N}$ = 12 K. $^{151}$Eu M\""{o}ssbauer spectra present
evidence for a cascade of transitions from paramagnetic to incommensurate
amplitude modulated followed by an equal moment antiferromagnetic phase at
lower temperatures in EuIrGe$_3$, the transitions having a substantial first
order character. On the other hand the $^{151}$Eu M\""{o}ssbauer spectra at 4.2
and 9 K in EuRhGe$_3$ present evidence of a single magnetic transition. In both
compounds a superzone gap is observed for the current density $J\parallel$
[001], which enhances with transverse magnetic field. The magnetisation
measured up to 14 T shows the occurrence of field induced transitions, which
are well documented in the magnetotransport data as well. The magnetic phase
diagram constructed from these data is complex, revealing the presence of many
phases in the $H-T$ phase space.",1503.00936v1
2015-03-18,Gold-Gold Bonding: The Key to Stabilizing the 19-Electron Ternary Phases LnAuSb (Ln = La-Nd and Sm) as New Dirac Semimetals,"We report a new family of ternary 111 hexagonal LnAuSb (Ln = La-Nd, Sm)
compounds that, with a 19 valence electron count, has one extra electron
compared to all other known LnAuZ compound. The ""19th"" electron is accommodated
by Au-Au bonding between the layers; this Au-Au interaction drives the phases
to crystallize in the YPtAs-type structure rather than the more common
LiGaGe-type. This is critical, as the YPtAs structure type has the
symmetry-allowed band crossing necessary for the formation of Dirac semimetals.
Band structure, density of stats, and crystal orbital calculations confirm this
picture, which results in a nearly complete band gap between full and empty
electronic states and stable compounds; we can thus present a structural
stability phase diagram for the LnAuZ (Ln = Ge, As, Sn, Sb, Pb, Bi) family of
phases. Those calculations also show that LaAuSb has a bulk Dirac cone below
the Fermi level. The YPtAs-type LnAuSb family reported here is an example of
the uniqueness of gold chemistry applied to a rigidly closed shell system in an
unconventional way.",1503.05424v1
2015-03-23,A unified description of superconducting pairing symmetry in electron-doped Fe-based-122 compounds,"The pairing symmetry is examined in highly electron-doped
Ba(Fe$_{1-x}$Co$_x$As)$_2$ and A$_y$Fe$_2$Se$_2$ (with A=K, Cs) compounds, with
similar crystallographic and electronic band structures. Starting from a
phenomenological two-orbital model, we consider nearest-neighbor and
next-nearest-neighbor intraorbital pairing interactions on the Fe square
lattice. In this model, we find a unified description of the evolution from
$s_\pm$-wave pairing ($2.0 < n \lesssim 2.4$) to $d$-wave pairing ($2.4
\lesssim n \lesssim 2.5$) as a function of electron filling. In the crossover
region a novel time-reversal symmetry breaking state with $s_\pm+id$ pairing
symmetry emerges. This minimal model offers an overall picture of the evolution
of superconductivity with electron doping for both $s_\pm$-wave
[Ba(Fe$_{1-x}$Co$_x$As)$_2$] and $d$-wave [A$_y$Fe$_2$Se$_2$] pairing, as long
as the dopants only play the role of a charge reservoir. However, the situation
is more complicated for Ba(Fe$_{1-x}$Co$_x$As)$_2$. A real-space study further
shows that when the impurity scattering effects of Co dopants are taken into
account, the superconductivity is completely suppressed for $n > 2.4$. This
preempts any observation of $d$-wave pairing in this compound, in contrast to
A$_y$Fe$_2$Se$_2$.",1503.06706v1
2015-06-08,Decay analysis of compound nuclei with mass A$\sim 30-200$ formed in the reactions involving loosely bound projectiles,"The dynamics of the reactions forming compound nuclei using loosely bound
projectiles is analysed within the framework of dynamical cluster decay model
(DCM) of Gupta and Collaborators. We have analysed different reactions with
$^{7}Li$, $^{9}Be$ and $^{7}Be$ as neutron rich and neutron deficient
projectiles, respectively, on different targets at the three $E_{lab}$ values,
forming compound nuclei within the mass region A$\sim 30-200$. The
contributions of light particles LPs ($A\le4$) cross sections $\sigma_{LP}$,
energetically favoured intermediate mass fragments IMFs ($5 \le A_2 \le 20$)
cross sections $\sigma_{IMF}$ as well as fusion-fission $\it{ff}$ cross
sections $\sigma_{ff}$ constitute the $\sigma_{fus}$
(=$\sigma_{LP}$+$\sigma_{IMF}$+$\sigma_{ff}$) for these reactions. The
contribution of the emitted LPs, IMFs and ff fragments is added for all the
angular momentum upto the $\ell_{max}$ value, for the resepctive reactions.
Interestingly, we find that the $\Delta R^{emp}$, the only parameter of model
and uniquely fixed to address the $\sigma_{fus}$ for all other reactions having
$\it same$ loosely bound projectile at the chosen incident energy. It may be
noted that the dynamical collective mass motion of preformed LPs, IMFs and ff
fragments or clusters through the modified interaction potential barrier are
treated on parallel footing. We see that the values of modified interaction
barrier heights $\Delta V_{B}^{emp}$ for such reactions are almost of the same
amount specifically at the respective $\ell_{max}$ values.",1506.02451v1
2015-06-23,Shape evolution and collective dynamics of quasifission in TDHF,"Background: At energies near the Coulomb barrier, capture reactions in
heavy-ion collisions result either in fusion or in quasifission. The former
produces a compound nucleus in statistical equilibrium, while the second leads
to a reseparation of the fragments after partial mass equilibration without
formation of a compound nucleus. Extracting the compound nucleus formation
probability is crucial to predict superheavy-element formation cross-sections.
It requires a good knowledge of the fragment angular distribution which itself
depends on quantities such as moments of inertia and excitation energies which
have so far been somewhat arbitrary for the quasifission contribution.
  Methods: We investigate the evolution of the nuclear density in
time-dependent Hartree-Fock (TDHF) calculations leading to quasifission. Our
main goal is to extract ingredients of the formula used in the analysis of
experimental angular distributions. These include the moment-of-inertia and
temperature. We study the dependence of these quantities on various initial
conditions of the reaction process.
  Results: The evolution of the moment of inertia is clearly non-trivial and
depends strongly on the characteristics of the collision. The temperature rises
quickly when the kinetic energy is transformed into internal excitation. Then,
it rises slowly during mass transfer.
  Conclusions: Fully microscopic theories are useful to predict the complex
evolution of quantities required in macroscopic models of quasifission.",1506.06880v1
2015-08-22,Low Temperature metamagnetism and Hall effect anomaly in Kondo compound CeAgBi2,"Heavy fermion (HF) materials exhibit a rich array of phenomena due to the
strong Kondo coupling between their localized moments and itinerant electrons.
A central question in their study is to understand the interplay between
magnetic order and charge transport, and its role in stabilizing new quantum
phases of matter. Particularly promising in this regard is a family of
tetragonal intermetallic compounds Ce{$TX$}$_2$ ($T=$ transition metal, $X=$
pnictogen), that includes a variety of HF compounds showing $T$-linear
electronic specific heat $\bf{C_e \sim \gamma T}$, with $\gamma\sim$ 20-500
mJ$\cdot$mol$^{-1}$~K$^{-2}$, reflecting an effective mass enhancement ranging
from small to modest. Here, we study the low-temperature field-tuned phase
diagram of high-quality CeAgBi$_2$ using magnetometry and transport
measurements. We find an antiferromagnetic transition at ${T_{N} = 6.4}$~K with
weak magnetic anisotropy and the easy axis along the $c$-axis, similar to
previous reports (${T_{N} = 6.1}$~K). This scenario, along with the presence of
two anisotropic Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, leads to a
rich field-tuned magnetic phase diagram, consisting of five metamagnetic
transitions of both first and second order. In addition, we unveil an anomalous
Hall contribution for fields $H<54$ kOe which is drastically altered when $H$
is tuned through a trio of transitions at 57, 78, and 84~kOe, suggesting that
the Fermi surface is reconstructed in a subset of the metamagnetic transitions.",1508.05444v2
2015-09-01,Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Ag doping,"We report the impact of silver addition on granularity of NdFeAsO0.8F0.2
superconductor. The ac susceptibility and electrical resistivity under magnetic
field are measured to study the improvement in weak links of NdFeAsO0.8F0.2
with addition of Ag. The Ag free NdFeAsO0.8F0.2 compound shows
superconductivity at around 51.8K. Typical two step superconducting transitions
due to the inter and intra grain contributions, induced from the combined
effect of superconducting grains and the inter-granular weak-coupled medium
respectively are clearly seen in susceptibility plots. In comparison to the
pure NdFeAsO0.8F0.2 compound, the coupling between the superconducting grains
is significantly improved for 20Ag silver doped sample, and the same is
deteriorated for higher Ag content i.e., for 30wt Ag sample. The magneto
transport measurements R(T)H of polycrystalline 20Ag doped NdFeAsO0.8F0.2,
exhibited the upper critical filed [Hc2(0)] of up to 334Tesla, which is
slightly higher than the one observed for pure NdFeAsO0.8F0.2. The flux flow
activation energy varies from 7143.38K to 454.77K with magnetic field ranging
from 0Tesla to 14Tesla for 20wtAg doped NdFeAsO0.8F0.2. In this investigation,
our results show that limited addition of Ag improves the granular coupling of
superconducting grains of NdFeAsO0.8F0.2 compound.",1509.00182v2
2015-09-11,Theoretical investigation of the behavior of CuSe2O5 compound in high magnetic fields,"Based on analytical and numerical approaches, we investigate thermodynamic
properties of CuSe2O5 at high magnetic fields which is a candidate for the
strong intra-chain interaction in quasi one-dimensional (1D) quantum magnets.
Magnetic behavior of the system can be described by the 1D spin-1/2 XXZ model
in the presence of the Dzyaloshinskii-Moriya (DM) interaction. Un- der these
circumstances, there is one quantum critical field in this compound. Below the
quantum critical field the spin chain system is in the gapless Luttinger liquid
(LL) regime, whereas above it one observes a crossover to the gapped saturation
magnetic phase. Indications on the thermodynamic curves confirm the occurrence
of such a phase transition. The main characteristics of the LL phase are
gapless and spin-spin correlation functions decay algebraic. The effects of
zero-temperature quantum phase transition are observed even at rather high
temperatures in comparison with the counterpart compounds. In addition, we
calculate the Wilson ratio in the model. The Wilson ratio at a fixed
temperature remains almost independent of the field in the LL region. In the
vicinity of the quantum critical field, the Wilson ratio increases and exhibits
anomalous enhancement.",1509.03414v1
2015-09-11,Local lattice distortions vs. structural phase transition in NdFeAsO1-xFx,"The lattice properties at low temperatures of two samples of NdFeAsO1-xFx
(x=0.05 and 0.25) have been examined in order to investigate possible
structural phase transition that may occur in the optimally doped
superconducting sample with respect to the non-superconducting low-F
concentration compound. In order to detect small modifications in the ion
displacements with temperature micro-Raman and high resolution synchrotron
powder diffraction measurements were carried out. No increase of the width of
the (220) or (322) tetragonal diffraction peaks and microstrains could be found
in the superconducting sample from synchrotron XRD measurements. On the other
hand, the atomic displacement parameters deviate from the expected behavior, in
agreement with modifications in the phonon width, as obtained by Raman
scattering. These deviations occur around 150 K for both F dopings, with
distinct differences among the two compounds, i.e., they decrease at low doping
and increase for the superconducting sample. The data do not support a hidden
phase transition to an orthorhombic phase in the superconducting compound, but
point to an isostructural lattice deformation. Based on the absence of magnetic
effects in this temperature range for the superconducting sample, we attribute
the observed lattice anomalies to the formation of local lattice distortions
that, being screened by the carriers, can only acquire long-range coherence by
means of a structural phase transition at low doping levels.",1509.03519v1
2015-09-11,Multipolar phases and magnetically hidden order: Review of the heavy-fermion compound Ce(1-x)La(x)B6,"Cerium hexaboride is a cubic f-electron heavy-fermion compound that displays
a rich array of low-temperature magnetic ordering phenomena which have been the
subject of investigation for more than 50 years. Its complex behaviour is the
result of competing interactions, with both itinerant and local electrons
playing important roles. Investigating this material has proven to be a
substantial challenge, in particular because of the appearance of a
""magnetically hidden order"" phase, which remained elusive to neutron-scattering
investigations for many years. It was not until the development of modern x-ray
scattering techniques that the long suspected multipolar origin of this phase
was confirmed. Doping with non-magnetic lanthanum dilutes the magnetic cerium
sublattice and reduces the f-electron count, bringing about substantial changes
to the ground state with the emergence of new phases and quantum critical
phenomena. To this day, Ce(1-x)La(x)B6 and its related compounds remain a
subject of intense interest. Despite the substantial progress in understanding
their behaviour, they continue to reveal new and unexplained physical
phenomena. Here we present a review of the accumulated body of knowledge on
this family of materials in order to provide a firm standpoint for future
investigations.",1509.03588v1
2015-09-15,Characterization and Dielectric Properties of Microwave Rare Earth Ceramics Materials for Telecommunications,"The rare-earth-metal-oxide based electronic materials were produced via a
conventional mixed-oxide route. Thermal analysis, XRD and SEM were used to
follow phase evolution and demonstrate the phase purity. Analytical TEM were
used to analyze crystal structural defects and to track the presence of
secondary phases, especially at grain boundaries. A crystal structure
determination was also performed. Phonon modes were analyzed with FTIR and
Raman spectroscopies and correlated with the origin of dielectric permittivity
({\epsilon}r) and radiation losses (tan {\delta}) characteristics. In some
compound and mixed compound Raman band mode exist, but this band is absent in
simple perovskite indicating that this band is associated with distribution of
B-site cations ordering. Some of compound shows long range order in B-site,
while it does not present in other material. A photo-acoustic sampling
technique in conjunction with the FTIR spectroscopy was employed, allowing the
analysis of neat materials with minimal sample preparation. Measurements of the
quality factor (Qf), {\epsilon}r and the temperature coefficient of the
resonant frequency ({\tau}f) characteristics were made at the microwave
resonant frequency using a vector or network analyzer.
  These perovskite have low tolerance factor because of considerable size
misfit of constituting atoms. For determination of atomic size and
characterization of constitution atoms, the test of samples and Rietveld
refinement using GSAS programs were used to do this examination. These
materials have attractive dielectric properties are being evaluated extensively
for substrates for multi-chip-module (MCM) devices and microwave
telecommunications.",1509.04445v2
2015-10-14,Spin dynamics near a putative antiferromagnetic quantum critical point in Cu substituted BaFe$_2$As$_2$ and its relation to high-temperature superconductivity,"We present the results of elastic and inelastic neutron scattering
measurements on non-superconducting
Ba(Fe${_{0.957}}$Cu${_{0.043}}$)${_2}$As${_2}$, a composition close to a
quantum critical point between AFM ordered and paramagnetic phases. By
comparing these results with the spin fluctuations in the low Cu composition as
well as the parent compound BaFe$_2$As$_2$ and superconducting
Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ compounds, we demonstrate that paramagnon-like
spin fluctuations are evident in the antiferromagnetically ordered state of
Ba(Fe$_{0.957}$Cu$_{0.043}$)$_2$As$_2$, which is distinct from the AFM-like
spin fluctuations in the superconducting compounds. Our observations suggest
that Cu substitution decouples the interaction between quasiparticles and the
spin fluctuations. We also show that the spin-spin correlation length,
${\xi(T)}$, increases rapidly as the temperature is lowered and find
${\omega/T}$ scaling behavior, the hallmark of quantum criticality, at an
antiferromagnetic quantum critical point.",1510.04167v1
2015-11-04,Interstellar Fullerene Compounds and Diffuse Interstellar Bands,"Recently, the presence of fullerenes in the interstellar medium (ISM) has
been confirmed especially with the first confirmed identification of two strong
diffuse interstellar bands (DIBs) with C60+. This justifies reassesing the
importance of interstellar fullerenes of various sizes with endohedral or
exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of
fullerenes is complex. In addition to fullerene formation in shock shattering,
fully dehydrogenated PAHs in diffuse interstellar (IS) clouds could perhaps
efficiently transform into fullerenes including EEHFs. But it is extremely
difficult to assess their expected abundance, composition and size
distribution, except for C60+. EEHFs share many properties with C60, as regards
stability, formation/destruction and chemical processes, and many basic
spectral features. We address the interstellar importance of various EEHFs as
possible DIB carriers. Specifically, we discuss IS properties and the
contributions of fullerenes of various sizes and charge such as C60+,
metallofullerenes, heterofullerenes, fulleranes, fullerene-PAH compounds,
H2@C60. We conclude that the landscape of interstellar fullerenes is probably
much richer than heretofore realized. EEHFs, together with pure fullerenes of
various sizes, have properties necessary to be suitably carriers of DIBs:
carbonaceous nature; stability and resilience in the ISM; various heteroatoms
and ionization states; relatively easy formation; few stable isomers; right
spectral range; energy internal conversion; Jahn-Teller fine structure. This is
supported by the C60+ DIBs. But, the lack of information about optical spectra
other than C60 and IS abundances still precludes definitive assessment of the
importance of fullerenes as DIB carriers. Their compounds could significantly
contribute to DIBs, but it still seems difficult that they are the only
important DIB carriers.",1511.01250v2
2015-12-10,Investigation of magnetic characteristics of oxygen adsorbed YbFe2As2 single crystals,"Recent discovery of superconductivity in iron pnictides had attracted immense
attention of the scientific community. The parent compounds were spin density
wave (SDW) metals unlike the high-TC superconductors which were Mott
insulators. In this present study, we synthesized single crystal of a new
compound YbFe2As2 by using high temperature solution growth technique without
flux. The YbFe2As2 single crystals had been systematically characterized by
energy dispersive X-ray analysis (EDAX). The presence of oxygen was found by
EDAX on the surfaces of grown YbFe2As2 single crystals which had been kept in
air ambience for few months. The measurement of magnetization (M) versus
temperature (T) using SQUID at constant magnetic field (H = 100 Oe) for
YbFe2As2 had revealed an occurrence of sharp slope change around 140 K which
was the known SDW transition temperature for the parent compound BaFe2As2. An
additional slope change had been observed around 40 K. M vs T data at H= 10000
Oe had exhibited paramagnetic behavior. Result of M versus H measurements for
YbFe2As2 at 2 K had shown that the saturation had not been achieved at H =
80000 Oe. We had carried out magnetization measurements for oxygen adsorbed
YbFe2As2 (YbFe2As2 : O2 ) and BaFe2As2 (BaFe2As2 : O2) for comparative study
also.",1512.03197v1
2016-01-11,High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides,"In the family of the iron-based superconductors, the $RE$FeAsO-type compounds
(with $RE$ being a rare-earth metal) exhibit the highest bulk superconducting
transition temperatures ($T_{\mathrm{c}}$) up to $55\ \textrm{K}$ and thus hold
the key to the elusive pairing mechanism. Recently, it has been demonstrated
that the intrinsic electronic structure of SmFe$_{0.92}$Co$_{0.08}$AsO
($T_{\mathrm{c}}=18\ \textrm{K}$) is highly nontrivial and consists of multiple
band-edge singularities in close proximity to the Fermi level. However, it
remains unclear whether these singularities are generic to the $RE$FeAsO-type
materials and if so, whether their exact topology is responsible for the
aforementioned record $T_{\mathrm{c}}$. In this work, we use angle-resolved
photoemission spectroscopy (ARPES) to investigate the inherent electronic
structure of the NdFeAsO$_{0.6}$F$_{0.4}$ compound with a twice higher
$T_{\mathrm{c}}=38\ \textrm{K}$. We find a similarly singular Fermi surface and
further demonstrate that the dramatic enhancement of superconductivity in this
compound correlates closely with the fine-tuning of one of the band-edge
singularities to within a fraction of the superconducting energy gap $\Delta$
below the Fermi level. Our results provide compelling evidence that the
band-structure singularities near the Fermi level in the iron-based
superconductors must be explicitly accounted for in any attempt to understand
the mechanism of superconducting pairing in these materials.",1601.02686v1
2016-01-16,"Lattice specific heat for the RMIn$_5$ (R = Gd, La, Y, M = Co, Rh) compounds: non-magnetic contribution subtraction","We analyze theoretically a common experimental process used to obtain the
magnetic contribution to the specific heat of a given magnetic material. In the
procedure, the specific heat of a non-magnetic analog is measured and used to
subtract the non-magnetic contributions, which are generally dominated by the
lattice degrees of freedom in a wide range of temperatures. We calculate the
lattice contribution to the specific heat for the magnetic compounds GdMIn$_5$
(M = Co, Rh) and for the non-magnetic YMIn$_5$ and LaMIn$_5$ (M = Co, Rh),
using density functional theory based methods. We find that the best
non-magnetic analog for the subtraction depends on the magnetic material and on
the range of temperatures. While the phonon specific heat contribution of
YRhIn$_5$ is an excellent approximation to the one of GdCoIn$_5$ in the full
temperature range, for GdRhIn$_5$ we find a better agreement with LaCoIn$_5$,
in both cases, as a result of an optimum compensation effect between masses and
volumes. We present measurements of the specific heat of the compounds
GdMIn$_5$ (M = Co, Rh) up to room temperature where it surpasses the value
expected from the Dulong-Petit law. We obtain a good agreement between theory
and experiment when we include anharmonic effects in the calculations.",1601.04214v1
2016-01-22,Transforming common III-V and II-VI semiconductor compounds into topological heterostructures: The case of CdTe/InSb superlattices,"Currently known topological insulators (TIs) are limited to narrow gap
compounds incorporating heavy elements, thus severely limiting the material
pool available for such applications. We show via first-principle calculations
how a heterovalent superlattice made of common semiconductor building blocks
can transform its non-TI components into a topological nanostructure,
illustrated by III-V/II-VI superlattice InSb/CdTe. The heterovalent nature of
such interfaces sets up, in the absence of interfacial atomic exchange, a
natural internal electric field that along with the quantum confinement leads
to band inversion, transforming these semiconductors into a topological phase
while also forming a giant Rashba spin splitting. We reveal the relationship
between the interfacial stability and the topological transition, finding a
window of opportunity where both conditions can be optimized. Once a critical
InSb layer thickness above ~ 1.5 nm is reached, both [111] and [100]
superlattices have a relative energy of 5-14 meV/A2 higher than that of the
atomically exchanged interface and an excitation gap up to ~150 meV, affording
room-temperature quantum spin Hall effect in semiconductor superlattices. The
understanding gained from this study could significantly broaden the current,
rather restricted repertoire of functionalities available from individual
compounds by creating next-generation super-structured functional materials.",1601.06210v2
2016-02-04,Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A comparative study,"New classes two-dimensional (2D) materials beyond graphene, including layered
and non-layered, and their heterostructures, are currently attracting
increasing interest due to their promising applications in nanoelectronics,
optoelectronics and clean energy, where thermal transport property is one of
the fundamental physical parameters. In this paper, we systematically
investigated the phonon transport properties of 2D orthorhombic group IV-VI
compounds of $GeS$, $GeSe$, $SnS$ and $SnSe$ by solving the Boltzmann transport
equation (BTE) based on first-principles calculations. Despite the similar
puckered (hinge-like) structure along the armchair direction as phosphorene,
the four monolayer compounds possess diverse anisotropic properties in many
aspects, such as phonon group velocity, Young's modulus and lattice thermal
conductivity ($\kappa$), etc. Especially, the $\kappa$ along the zigzag and
armchair directions of monolayer $GeS$ shows the strongest anisotropy while
monolayer $SnS$ and $SnSe$ shows an almost isotropy in phonon transport. The
origin of the diverse anisotropy is fully studied and the underlying mechanism
is discussed in detail. With limited size, the $\kappa$ could be effectively
lowered, and the anisotropy could be effectively modulated by nanostructuring,
which would extend the applications in nanoscale thermoelectrics and thermal
management. Our study offers fundamental understanding of the anisotropic
phonon transport properties of 2D materials, and would be of significance for
further study, modulation and aplications in emerging technologies.",1602.01766v2
2016-02-11,Effects of quantum impurity spins on the magnetic properties of zigzag and linear spin chains,"We investigated the magnetic ground state and low-energy excitations of the
spin chains compounds SrCuO$_{2}$ (zigzag chains) and Sr$_{2}$CuO$_{3}$ (linear
chains) in the presence of quantum impurities induced by lightly doping ($\leq
1 \%$) with Zn$^{2+}$ ($S = 0$), Co$^{2+}$ ($S =1/2$) and Ni$^{2+}$ ($S = 1$)
impurities at the Cu$^{2+}$ site. We show that the ground states and the nature
of low-lying excitations (i.e., gapped or gapless) depend on the spin state and
symmetry of the defects. For Ni doped chains a spin gap is observed but for Zn
and Co doping the excitations remain gapless. Co-doped chains exhibit magnetic
order with critical temperatures significantly enhanced compared to those of
the pristine compounds. In the specific case of 1 \% Co impurities, the linear
chains exhibit long-range order below 11 K, while the zigzag chain is
characterized by a quasi-long range ordered phase below 6 K with correlation
lengths of about 12\textit{a} and 40\textit{c} units along the crystal axes
\textit{a} and \textit{c}, respectively. The different magnetic behaviours of
these two compounds with comparable intra- and interchain couplings underpin
the role of spin frustration in the zigzag chains.",1602.03677v1
2016-04-07,The super-super exchange mechanism in iron-based antiperovskite chalco-halides,"By using the first-principles electronic structure calculations, we have
systematically studied the magnetism in three recently synthesized iron-based
antiperovskite chalco-halides: Ba$_3$(FeS$_4$)Cl, Ba$_3$(FeS$_4$)Br, and
Ba$_3$(FeSe$_4$)Br. These compounds consist of edge-sharing Ba$Q_6$ ($Q$=Cl or
Br) octahedra intercalated with isolated Fe$X_4$ ($X$=S or Se) tetrahedra. We
find that even though the shortest distances between the nearest-neighboring Fe
atoms in these three compounds already exceed 6 \AA, much larger than the bond
length of a chemical bonding, they all remarkably show antiferromagnetic (AFM)
coupling along $b$ axis with very weak spin-spin correlation along $a$ axis.
Our study shows that the mechanism underlying this novel AFM coupling is such a
new type of exchange interaction between the nearest-neighboring Fe-based
super-moments mediated by Ba cations, which we call the super-super exchange
interaction, in which each magnetic Fe atom partially polarizes its four
nearest-neighboring $X$ atoms to form a super-moment through $p$-$d$ orbital
hybridization and the $X$ atoms in neighboring Fe$X_4$ tetrahedra along $b$
axis antiferromagnetically couple with each others through the intermediate Ba
cations. Different from the conventional superexchange, here it is cations
rather than anions that mediate two neighboring super-moments. According to the
calculated strength of the AFM coupling, we predict that among these compounds
the highest AFM phase transition temperature $T_N$ may reach 110 K in
Ba$_3$(FeSe$_4$)Br, in comparison with the observed $T_N$s of 84 K in
Ba$_3$(FeS$_4$)Br and 95 K in Ba$_3$(FeS$_4$)Cl.",1604.02044v1
2016-04-14,"Longitudinal magnon, inversion breaking and magnetic instabilities in the pseudo-Kagome francisites Cu3Bi(SeO3)2O2X with X=Br, Cl","We performed Raman studies and a dielectric characterization of the
pseudo-kagome Cu3Bi(SeO3)2O2X (X = Cl, Br). These compounds share competing
nearest-neighbour ferromagnetic exchange and frustrating next-nearest-neighbour
antiferromagnetic exchange as well as highly noncollinear magnetic ground
state. However, at low temperature they differ with respect to the existence of
inversion symmetry. For both compounds there exists a pronounced interplay of
polar phonon modes with quantum magnetic fluctuations. A novel Raman mode
appears for temperatures below the Neel temperature with a Fano lineshape and
an enormous intensity that exceeds most of the phonon lines. We discuss a
possible contribution of longitudinal magnons to this signal. In contrast, one
magnon scattering based on linear transvers magnons is excluded based on a
symmetry analysis of spin wave representations and Raman tensor calculations.
There exists evidence that in these pseudo-kagome compounds magnetic quantum
fluctuations carry an electric dipole moment. Our data as well as a comparison
with previous far-infrared spectra allow us to conclude that Cu3Bi(SeO3)2O2Cl
changes its symmetry most likely from Pmmn to P21mn with a second order
structural phase transition at T*=120 K and becomes multiferroic.
Cu3Bi(SeO3)2O2Br represents an interesting counter part as it does not show
this instability and stays inversion symmetric down to lowest temperatures,
investigated.",1604.04249v1
2016-04-19,Distillation of secret key from a class of compound memoryless quantum sources,"We consider secret-key distillation from tripartite compound
classical-quantum-quantum (cqq) sources with free forward public communication
under strong security criterion. We design protocols which are universally
reliable and secure in this scenario. These are shown to achieve asymptotically
optimal rates as long as a certain regularity condition is fulfilled by the the
set of its generating density matrices. We derive a multi-letter formula which
describes the optimal forward secret-key capacity for all compound cqq sources
being regular in this sense. We also determine the forward secret-key
distillation capacity for situations, where the legitimate sending party has
perfect knowledge of his/her marginal state deriving from the source
statistics. In this case regularity conditions can be dropped. Our results show
that the capacities with and without the mentioned kind of state knowledge are
equal as long as the source is generated by a regular set of density matrices.
We demonstrate that regularity of cqq sources is not only a technical but also
an operational issue. For this reason, we give an example of a source which has
zero secret-key distillation capacity without sender knowledge, while achieving
positive rates is possible if sender marginal knowledge is provided.",1604.05530v2
2016-04-27,"Investigation of the physical properties of the Ce2MAl7Ge4 (M = Co, Ir, Ni, Pd) heavy fermion compounds","We report the synthesis, crystal structure and characterization by means of
single crystal x-ray diffraction, neutron powder diffraction, magnetic, thermal
and transport measurements of the new heavy fermion compounds
Ce$_{2}$MAl$_{7}$Ge$_{4}$ (M = Co, Ir, Ni, Pd). These compounds crystallize in
a noncentrosymmetic tetragonal space group P\={4}2$_{1}$m, consisting of layers
of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks.
Ce$_{2}$CoAl$_{7}$Ge$_{4}$, Ce$_{2}$IrAl$_{7}$Ge$_{4}$ and
Ce$_{2}$NiAl$_{7}$Ge$_{4}$ order magnetically behavior below $T_{M}=$ 1.8, 1.6,
and 0.8 K, respectively. There is no evidence of magnetic ordering in
Ce$_{2}$PdAl$_{7}$Ge$_{4}$ down to 0.4 K. The small amount of entropy released
in the magnetic state of Ce$_{2}$MAl$_{7}$Ge$_{4}$ (M = Co, Ir, Ni) and the
reduced specific heat jump at $T_M$ suggest a strong Kondo interaction in these
materials. Ce$_{2}$PdAl$_{7}$Ge$_{4}$ shows non-Fermi liquid behavior, possibly
due to the presence of a nearby quantum critical point.",1604.07927v1
2016-05-02,"Active role of the nonmagnetic cations in magnetic interactions for the double-perovskite Sr2BOsO6 (B=Y, In, Sc)","Using first-principles density functional theory, we have investigated the
electronic and magnetic properties of recently synthesized and characterized 5d
double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure
calculations show that in all compounds, the Os5+ (5d3) site is the only
magnetically active one, while Y3+, In3+ and Sc3+ remain in nonmagnetic states,
with Sc/Y and In featuring d0 and d10 electronic configurations, respectively.
Our studies reveal the important role of closed-shell (d10) versus open-shell
(d0) electronic configurations of the nonmagnetic sites in determining the
overall magnetic exchange interactions. Although the magnetic Os5+ (5d3) site
is the same in all compounds, the magnetic super-exchange interactions mediated
by non-magnetic Y/In/Sc species are strongest for Sr2ScOsO6, weakest for
Sr2InOsO6, and intermediate in case of the Y (d0), due to different energy
overlaps between Os-5d and Y/In/Sc-d states. This explains the experimentally
observed substantial differences in the magnetic transition temperatures of
these materials, despite of an identical magnetic site and underlying magnetic
ground state. Furthermore, short range Os-Os exchange-interactions are more
prominent than long range Os-Os interactions in these compounds, which
contrasts with the behavior of other 3d-5d double-perovskites.",1605.00540v1
2016-05-06,Antiferromagnetism in trigonal SrMn2As2 and CaMn2As2 single crystals,"Crystallographic, electronic transport, thermal and magnetic properties are
reported for SrMn2As2 and CaMn2As2 single crystals grown using Sn flux.
Rietveld refinements of powder x-ray diffraction data show that the two
compounds are isostructural and crystallize in the trigonal CaAl2Si2-type
structure (space group P-3m1), in agreement with the literature. Electrical
resistivity rho versus temperature T measurements demonstrate insulating ground
states for both compounds with activation energies of 85 meV for SrMn2As2 and
61 meV for CaMn2As2. In a local-moment picture, the Mn^{+2} 3d^5 ions are
expected to have high-spin S = 5/2 with spectroscopic splitting factor g = 2.
Magnetic susceptibility chi and heat capacity measurements versus T reveal
antiferromagnetic (AFM) transitions at TN = 120(2) K and 62(3) K for SrMn2As2
and CaMn2As2, respectively. The anisotropic chi(T < TN) data indicate that the
hexagonal c axis is the hard axis and hence that the ordered Mn moments are
aligned in the ab plane. The chi(T) for both compounds and Cp(T) data for
SrMn2As2 show strong dynamic short-range AFM correlations from TN up to at
least 900 K, likely associated with quasi-two-dimensional connectivity of
strong AFM exchange interactions between the Mn spins within the corrugated
honeycomb Mn layers parallel to the ab plane.",1605.02052v2
2016-05-19,Hydration induced spin glass state in a frustrated Na-Mn-O triangular lattice,"Birnessite compounds are stable across a wide range of compositions that
produces a remarkable diversity in their physical, electrochemical and
functional properties. These are hydrated analogues of the magnetically
frustrated, mixed-valent manganese oxide structures, with general formula,
NaxMnO2. Here we demonstrate that the direct hydration of layered rock-salt
type a-NaMnO2, with the geometrically frustrated triangular lattice topology,
yields the birnessite type oxide, Na0.36MnO2 0.2H2O, transforming its magnetic
properties. This compound has a much-expanded interlayer spacing compared to
its parent a-NaMnO2 compound. We show that while the parent a-NaMnO2 possesses
a Neel temperature of 45 K as a result of broken symmetry in the Mn3+
sub-lattice, the hydrated derivative undergoes collective spin-freezing at 29 K
within the Mn3+/Mn4+ sub-lattice. Scaling-law analysis of the frequency
dispersion of the AC susceptibility, as well as the temperature-dependent,
low-field DC magnetization confirm a cooperative spin-glass state of strongly
interacting spins. This is supported by complementary spectroscopic analysis
(HAADF-STEM, EDS, EELS) as well as by a structural investigation
(high-resolution TEM, X-ray and neutron powder diffraction) that yield insights
into the chemical and atomic structure modifications. We conclude that the
spin-glass state in birnessite is driven by the spin-frustration imposed by the
underlying triangular lattice topology that is further enhanced by the in-plane
bond-disorder generated by the mixed-valent character of manganese in the
layers.",1605.06067v1
2016-06-21,Experimental and first-principles studies of magnetism and magnetoelectric effect in Co4Nb2O9 and Co4Ta2O9,"We report results of joint experimental and theoretical studies on
magnetoelectric (ME) compounds Co4Nb2O9 and Co4Ta2O9. On the experimental side,
we present results of the magnetization and dielectric permittivity
measurements in the magnetic field. On the theoretical side, we construct the
low-energy Hubbard-type model for the magnetically active Co 3d bands in the
Wannier basis, using the input of first-principles electronic structure
calculations, solve this model in the mean-field Hartree-Fock approximation,
and evaluate the electric polarization in terms of the Berry phase theory. Both
experimental and theoretical results suggest that Co4Ta2O9 is magnetically
softer than Co4Nb2O9. Therefore, it is reasonable to expect that the
antiferromagnetic structure of Co4Ta2O9 can be easier deformed by the external
magnetic field, yielding larger polarization. This trend is indeed reproduced
by our theoretical calculations, but does not seem to be consistent with the
experimental behavior of the polarization and dielectric permittivity. Thus, we
suggest that there should be a hidden mechanism controlling the ME coupling in
these compounds, probably related to the magnetic striction or a spontaneous
change of the magnetic structure, which breaks the inversion symmetry.
Furthermore, we argue that unlike in other ME systems (e.g. Cr2O3), in Co4Nb2O9
and Co4Ta2O9 there are two crystallographic sublattices, which contribute to
the ME effect. These contributions are found to be of the opposite sign and
tend to compensate each other. The latter mechanism can be also used to control
and reverse the electric polarization in these compounds.",1606.06394v1
2016-06-29,Reorientation of the bicollinear antiferromagnetic structure at the surface of Fe$_{1+y}$Te bulk and thin films,"Establishing the relation between the ubiquitous antiferromagnetism in the
non-superconducting parent compounds of unconventional superconductors and
their superconducting phase is believed to be important for the understanding
of the complex physics in these materials. Going from the bulk systems to thin
films strongly affects the phase diagram of unconventional superconductors. For
Fe$_{1+y}$Te, the parent compound of the Fe$_{1+y}$Se$_{1-x}$Te$_x$
superconductors, bulk sensitive neutron diffraction has revealed an in-plane
oriented bicollinear antiferromagnetic structure. Here, we show by
spin-resolved scanning tunneling microscopy that on the surfaces of bulk
Fe$_{1+y}$Te, as well as on thin films grown on the topological insulator
Bi$_2$Te$_3$, the spin direction is canted both away from the surface plane and
from the high-symmetry directions of the surface unit cell, while keeping the
bicollinear magnetic structure. Our results demonstrate that the magnetism at
the Fe-chalcogenide surface markedly deviates from a simple in-plane oriented
bicollinear antiferromagnetic structure, which implies that the pairing at the
surface of the related superconducting compounds might be different from that
in the bulk.",1606.09192v1
2016-07-26,"Neutron Larmor diffraction investigation of the rare earth pyrochlores $R_2$Ti$_2$O$_7$ ($R$ = Tb, Dy, Ho)","In this work we present a neutron Larmor diffraction study of the rare earth
pyrochlores $R_2$Ti$_2$O$_7$, with $R$ = Tb, Dy, Ho. We measured the
temperature dependence of the lattice parameter with precision $10^{-5}$,
between 0.5 K and 300 K in each of the three compounds. The lattice parameter
of the spin ices Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$ enters into the
derivation of the charge of the emergent magnetic monopole excitations
suggested to exist in these materials. We found that throughout the range of
applicability of the theory of emergent monopoles in the spin ices there will
be no renormalization of the monopole charge due to lattice contraction. In
Tb$_2$Ti$_2$O$_7$ strong magnetoelastic interactions have been reported. We
found no sign of the previously reported negative thermal expansion, but did
observe anomalies in the thermal expansion that can be correlated with
previously observed interactions between phonon and crystal field excitations.
Other features in the thermal expansion of all three compounds can be related
to previously observed anomalies the elastic constants, and explained by the
phonon band structure of the rare earth titanates. The temperature dependence
of the lattice strain in all three compounds can be correlated with the thermal
population of excited crystal field levels.",1607.07688v1
2016-07-29,"A rock-salt type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers","The area of research to discover new Li containing materials and to
understand their physical properties has been of constant interest due to
applications potential for rechargeable batteries. Here, we present the results
of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to
be a ferrimagnet below 80K. While our neutron diffraction (ND) and isothermal
magnetization (M) data support ferrimagnetism, more detailed magnetic studies
establish that this ferrimagnetic phase exhibits some features similar to
spin-glasses. In addition, we find another broad magnetic anomaly around 40-55
K in magnetic susceptibility, attributable to cluster spin-glass phenomenon.
Gradual dominance of cluster spin-glass dynamics with a decrease of temperature
(T) and the apparent spread in freezing temperature suggest that the
ferrimagnetism of this compound is a chaotic one. The absence of a unique
freezing temperature for a crystalline material is interesting. In addition,
pyroelectric current data reveals a feature in the range 40-50 K, attributable
to thermally stimulated depolarization current. We hope this finding motivates
future work to explore whether there is any intriguing correlation of such a
feature with spin-glass dynamics. We attribute these magnetic and electric
dipole anomalies to the crystallographic disorder intrinsic to this compound.",1607.08689v1
2016-08-01,Magnetism in Sr$_{2}$CrMoO$_{6}$: A combined abinitio and model study,"Using a combination of first-principles density functional theory (DFT)
calculations and exact diagonalization studies of a first-principles derived
model, we carry out a microscopic analysis of the magnetic properties of the
half-metallic double perovskite compound, Sr$_2$CrMoO$_6$, a sister compound of
the much discussed material Sr$_2$FeMoO$_6$. The electronic structure of
Sr$_2$CrMoO$_6$, though appears similar to Sr$_2$FeMoO$_6$ at first glance,
shows non trivial differences with that of Sr$_2$FeMoO$_6$ on closer
examination. In this context, our study highlights the importance of charge
transfer energy between the two transition metal sites. The change in charge
transfer energy due to shift of Cr $d$ states in Sr$_2$CrMoO$_6$ compared to Fe
$d$ in Sr$_2$FeMoO$_6$ suppresses the hybridization between Cr $t_{2g}$ and Mo
$t_{2g}$. This strongly weakens the hybridization-driven mechanism of magnetism
discussed for Sr$_2$FeMoO$_6$. Our study reveals that, nonetheless, the
magnetic transition temperature of Sr$_2$CrMoO$_6$ remains high since
additional superexchange contribution to magnetism arises with a finite
intrinsic moment developed at the Mo site. We further discuss the situation in
comparison to another related double perovskite compound, Sr$_2$CrWO$_6$. We
also examine the effect of correlation beyond DFT, using dynamical mean field
theory (DMFT).",1608.00380v1
2016-08-22,Peculiar Magnetism of UAu$_{2}$Si$_{2}$,"Single-crystalline UAu$_2$Si$_2$ has been grown by a floating-zone melting
method, and its magnetic, thermal and transport properties have been
investigated through measurements of magnetization, specific heat and
electrical resistivity to reveal its peculiar magnetism. It is shown that
UAu$_2$Si$_2$ undergoes a second-order phase transition at \tm = 19 K, which
had been believed to be ferromagnetic ordering in the literature, from a
paramagnetic phase to an uncompensated antiferromagnetic phase with spontaneous
magnetization along the tetragonal $c$-axis (the easy magnetization direction).
The magnetic entropy analysis points to the itinerant character of 5f electrons
in the magnetic ordered state of UAu$_2$Si$_2$ with large enhancement of the
electronic specific heat coefficient of $\gamma$ $\sim$ 150 mJ/K$^2$mol at 2 K.
It also reveals the relatively isotropic crystalline electric field effect of
this compound, with contrast to the other relative isostructural compounds. The
observed magnetization curves strongly suggest that there is a parasitic
ferromagnetic component developing below $\sim$ 50 K in high coercivity with
the easy axis along the tetragonal $c$-axis. The results are discussed in the
context of evolution of magnetism within the entire family of isostructural
U$T_2$Si$_2$ compounds.",1608.06035v2
2016-08-23,Mott transition and magnetism on the anisotropic triangular lattice,"Spin-liquid behavior was recently suggested experimentally in the moderately
one-dimensional organic compound $\kappa$-H$_3$(Cat-EDT-TTF)$_2$. This compound
can be modeled by the one-band Hubbard model on the anisotropic triangular
lattice with $t^\prime/t \simeq 1.5$, where $t'$ is the minority hopping. It
thus becomes important to extend previous studies, that were performed in the
range $0 \leq t'/t \leq 1.2$, to find out whether there is a regime where Mott
insulating behavior can be found without long-range magnetic order. To this
end, we study the above model in the range $1.2 \leq t'/t \leq 2$ using cluster
dynamical mean-field theory (CDMFT). We argue that it is important to choose a
symmetry-preserving cluster rather than a quasi one-dimensional cluster. We
find that, upon increasing $t'/t$ beyond $t^\prime/t \approx 1.3$, the Mott
transition at zero-temperature is replaced by a first-order transition
separating a metallic state from a collinear magnetic insulating state.
Nevertheless, at the physically relevant value $t^\prime/t \simeq 1.5$, the
transitions toward the magnetic and the Mott insulating phases are very close.
The phase diagram obtained in this study can provide a working basis for
moderately one-dimensional compounds on the anisotropic triangular lattice.",1608.06640v1
2016-09-05,Field-induced Conductance Switching by Charge-state Alternation in Organometallic Single-Molecule Junctions,"Charge transport through single molecules can be influenced by the charge and
spin states of redox-active metal centres placed in the transport pathway.
These molecular intrinsic properties are usually addressed by varying the
molecules electrochemical and magnetic environment, a procedure that requires
complex setups with multiple terminals. Here we show that oxidation and
reduction of organometallic compounds containing either Fe, Ru or Mo centres
can solely be triggered by the electric field applied to a two-terminal
molecular junction. Whereas all compounds exhibit bias-dependent hysteresis,
the Mo-containing compound additionally shows an abrupt voltage-induced
conductance switching, yielding high to low current ratios exceeding 1000 at
voltage stimuli of less than 1.0 V. DFT calculations identify a localized,
redox active molecular orbital that is weakly coupled to the electrodes and
closely aligned with the Fermi energy of the leads because of the
spin-polarised ground state unique to the Mo centre. This situation opens an
additional slow and incoherent hopping channel for transport, triggering a
transient charging effect of the entire molecule and a strong hysteresis with
unprecedented high low-to-high current ratios.",1609.01200v1
2016-10-05,Electric field gradients in Zr$_8$Ni$_{21}$ and Hf$_8$Ni$_{21}$ intermetallic compounds; Results from perturbed angular correlation measurements and first-principles density functional theory,"Numerous technological applications of Ni-based Zr and Hf intermetallic
alloys promoted comprehensive studies in Zr$_8$Ni$_{21}$ and Hf$_8$Ni$_{21}$ by
perturbed angular correlation (PAC) spectroscopy, which were not studied
earlier until this report. The different phases produced in the samples have
been identified by PAC and X-ray diffraction (XRD) measurements. Using
$^{181}$Hf probe, two non-equivalent Zr/Hf sites have been observed in both
Zr$_8$Ni$_{21}$ and Hf$_8$Ni$_{21}$ compounds. From present PAC measurements in
Zr$_8$Ni$_{21}$, a component due to the production of Zr$_7$Ni$_{10}$ by
eutectic reaction from the liquid metals is also observed. The phase
Zr$_7$Ni$_{10}$, however, is not found from the XRD measurement. In
Zr$_8$Ni$_{21}$, while the results do not change appreciably up to 973 K
exhibit drastic changes at 1073 K. In Hf$_8$Ni$_{21}$, similar results for the
two non-equivalent sites have been found but site fractions are in reverse
order. In this alloy, a different contaminating phase, possibly due to
HfNi$_3$, has been found from PAC measurements but is not found from XRD
measurement. Density functional theory (DFT) based calculations of electric
field gradient (EFG) and asymmetry parameter ($\eta$) at the sites of
$^{181}$Ta probe nucleus allowed us to assign the observed EFG fractions to the
various lattice sites in (Zr/Hf)$_8$Ni$_{21}$ compounds.",1610.01414v3
2016-10-13,"Strong, anisotropic anomalous Hall effect and spin Hall effect in chiral antiferromagnetic compounds Mn$_3X$ ($X$ = Ge, Sn, Ga, Ir, Rh and Pt)","We have carried out a comprehensive study of the intrinsic anomalous Hall
effect and spin Hall effect of several chiral antiferromagnetic compounds,
Mn$_3X$ ($X$ = Ge, Sn, Ga, Ir, Rh and Pt) by $ab~initio$ band structure and
Berry phase calculations. These studies reveal large and anisotropic values of
both the intrinsic anomalous Hall effect and spin Hall effect. The Mn$_3X$
materials exhibit a non-collinear antiferromagnetic order which, to avoid
geometrical frustration, forms planes of Mn moments that are arranged in a
Kagome-type lattice. With respect to these Kagome planes, we find that both the
anomalous Hall conductivity (AHC) and the spin Hall conductivity (SHC) are
quite anisotropic for any of these materials. Based on our calculations, we
propose how to maximize AHC and SHC for different materials. The band
structures and corresponding electron filling, that we show are essential to
determine the AHC and SHC, are compared for these different compounds. We point
out that Mn$_3$Ga shows a large SHC of about 600 $(\hbar/e)(\Omega\cdot
cm)^{-1}$. Our work provides insights into the realization of strong anomalous
Hall effects and spin Hall effects in chiral antiferromagetic materials.",1610.04034v2
2016-10-31,Chromium analogues of Iron-based superconductors,"We theoretically investigate the $d^4$ (Cr$^{2+}$) compound BaCr$_2$As$_2$
and show that, despite non-negligible differences in the electronic structure,
its many-body physics mirrors that of BaFe$_2$As$_2$, which has instead a $d^6$
(Fe$^{2+}$) configuration. This reflects a symmetry of the electron correlation
effects around the half-filled $d^5$ Mott insulating state. The experimentally
known metallic antiferromagnetic phase is correctly modeled by dynamical
mean-field theory, and for realistic values of the interaction it shows a
moderate mass enhancement of order $\sim$2. This value decreases if the ordered
moment grows as a result of a stronger interaction. The antiferromagnetic phase
diagram for this $d^4$ shows similarities with that calculated for the $d^6$
systems. Correspondingly, in the paramagnetic phase the influence of the
half-filled Mott insulator shows up as a crossover from a weakly correlated to
an orbitally differentiated ""Hund's metal"" phase which reflects an analogous
phenomenon in $d^6$ iron compounds including a strong enhancement of the
compressibility in a zone just inside the frontier between the normal and the
Hund's metal. The experimental evidence and our theoretical description place
BaCr$_2$As$_2$ at interaction strength slightly below the crossover which
implies that negative pressures and/or electron doping (e.g. Cr $\rightarrow$
Mn,Fe or Ba $\rightarrow$ Sc,Y,La) might strongly enhance the compressibility,
thereby possibly inducing a pairing instability in this non-superconducting
compound.",1610.10054v1
2017-01-11,Antiferromagnetic structure and electronic properties of BaCr2As2 and BaCrFeAs2,"The chromium arsenides BaCr2As2 and BaCrFeAs2 with ThCr2Si2 type structure
(space group I4/mmm; also adopted by '122' iron arsenide superconductors) have
been suggested as mother compounds for possible new superconductors. DFT-based
calculations of the electronic structure evidence metallic antiferromagnetic
ground states for both compounds. By powder neutron diffraction we confirm for
BaCr2As2 a robust ordering in the antiferromagnetic G-type structure at T_N =
580 K with mu_Cr = 1.9 mu_B at T = 2K. Anomalies in the lattice parameters
point to magneto-structural coupling effects. In BaCrFeAs2 the Cr and Fe atoms
randomly occupy the transition-metal site and G-type order is found below 265 K
with mu_Cr/Fe = 1.1 mu_B. 57Fe Moessbauer spectroscopy demonstrates that only a
small ordered moment is associated with the Fe atoms, in agreement with
electronic structure calculations with mu_Fe ~ 0. The temperature dependence of
the hyperfine field does not follow that of the total moments. Both compounds
are metallic but show large enhancements of the linear specific heat
coefficient gamma with respect to the band structure values. The metallic state
and the electrical transport in BaCrFeAs2 is dominated by the atomic disorder
of Cr and Fe and partial magnetic disorder of Fe. Our results indicate that
Neel-type order is unfavorable for the Fe moments and thus it is destabilized
with increasing iron content.",1701.03127v1
2017-01-25,On The Compound MIMO Wiretap Channel with Mean Feedback,"Compound MIMO wiretap channel with double sided uncertainty is considered
under channel mean information model. In mean information model, channel
variations are centered around its mean value which is fed back to the
transmitter. We show that the worst case main channel is anti-parallel to the
channel mean information resulting in an overall unit rank channel. Further,
the worst eavesdropper channel is shown to be isotropic around its mean
information. Accordingly, we provide the capacity achieving beamforming
direction. We show that the saddle point property holds under mean information
model, and thus, compound secrecy capacity equals to the worst case capacity
over the class of uncertainty. Moreover, capacity achieving beamforming
direction is found to require matrix inversion, thus, we derive the null
steering (NS) beamforming as an alternative suboptimal solution that does not
require matrix inversion. NS beamformer is in the direction orthogonal to the
eavesdropper mean channel that maintains the maximum possible gain in mean main
channel direction. Extensive computer simulation reveals that NS performs very
close to the optimal solution. It also verifies that, NS beamforming
outperforms both maximum ratio transmission (MRT) and zero forcing (ZF)
beamforming approaches over the entire SNR range. Finally, An equivalence
relation with MIMO wiretap channel in Rician fading environment is established.",1701.07518v4
2017-01-30,Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe3,"The crystallographic, magnetic, and transport properties of the van der Waals
bonded, layered compound CrTe3 have been investigated on single crystal and
polycrystalline materials. The crystal structure contains layers made up of
lozenge shaped Cr_4 tetramers. Electrical resistivity measurements show the
crystals to be semiconducting, with a temperature dependence consistent with a
band gap of 0.3eV. The magnetic susceptibility exhibits a broad maximum near
300K characteristic of low dimensional magnetic systems. Weak anomalies are
observed in the susceptibility and heat capacity near 55K, and single crystal
neutron diffraction reveals the onset of long range antiferromagnetic order at
this temperature. Strongly dispersive spin-waves are observed in the ordered
state. Significant magneto-elastic coupling is indicated by the anomalous
temperature dependence of the lattice parameters and is apparent in structural
optimization in van der Waals density functional theory calculations for
different magnetic configurations. The cleavability of the compound is apparent
from its handling and is confirmed by first principles calculations, which
predict a cleavage energy 0.5J/m^2, similar to graphite. Based on these
results, CrTe3 is identified as a promising compound for studies of low
dimensional magnetism in bulk crystals as well as magnetic order in monolayer
materials and van der Waals heterostructures.",1701.08621v2
2017-03-03,Structural studies of the bond-orientational order and hexatic-smectic transition in liquid crystals of various compositions,"We report on X-ray studies of freely suspended hexatic films of three
different liquid crystal compounds. By applying angular X-ray cross-correlation
analysis (XCCA) to the measured diffraction patterns the parameters of the
bond-orientational (BO) order in the hexatic phase were directly determined.
The temperature evolution of the BO order parameters was analyzed on the basis
of the multicritical scaling theory (MCST). Our results confirmed the validity
of the MCST in the whole temperature range of existence of the hexatic phase
for all three compounds. The temperature dependence of the BO order parameters
in the vicinity of the hexatic-smectic transition was fitted by a conventional
power law with a critical exponent $\beta\approx0.1$ of extremely small value.
We found that the temperature dependence of higher order harmonics of the BO
order scales as the powers of the first harmonic, with exponent equal to
harmonic number. This indicates a nonlinear coupling of the BO order parameters
of different order. It is shown that compounds of various composition,
possessing different phase sequences, display the same thermodynamic behavior
in the hexatic phase and in the vicinity of the smectic-hexatic phase
transition.",1703.01198v1
2017-03-03,High-pressure behavior of the Fe-S system and composition of the Earth's inner core,"Using evolutionary crystal structure prediction algorithm USPEX, we identify
the compositions and crystal structures of stable compounds in the Fe-S system
at pressures in the range 100-400 GPa. We find that at pressures of the Earth's
solid inner core (330-364 GPa) two compounds are stable - Fe2S and FeS. In
equilibrium with iron, only Fe2S can exist in the inner core. Using the
equation of state of Fe2S, we find that in order to reproduce the density of
the inner core by adding sulfur alone, 10.6-13.7 mol.% (6.4-8.4 wt.%) sulfur is
needed. Analogous calculation for silicon (where the only stable compound at
inner core pressures is FeSi) reproduces the density of the inner core with
9.0-11.8 mol.% (4.8-6.3 wt.%) silicon. In both cases, a virtually identical
mean atomic mass M in the range 52.6-53.3 results for in the inner core, which
is much higher than M = 49.3 determined for the inner core from Birch's law.
For oxygen (where the relevant stable oxide at conditions of the inner core is
Fe2O) we find the matching concentration in the range 13.2-17.2 mol.% (4.2-5.6
wt.%), which corresponds to M in the range 49.0-50.6. Combining our results and
previous works, we find that inner core density and M can be explained by only
four models (in atomic %): (a) 86%(Fe+Ni) + 14%C, (b) 84%(Fe+Ni) + 16%O, (c)
84%(Fe+Ni) + 7%S + 9%H, (d) 85%(Fe+Ni) + 6%Si + 9%H, and some of their linear
combinations (primarly, models (c) and (d)).",1703.01214v2
2017-03-25,Structure and physical properties of superconducting compounds Y(La)-Ba(Sr)-Cu-O,"The structure and physical properties of superconducting compounds
Y(La)-Ba(Sr)-Cu-O are studied, the compounds being prepared by the method of
cryogenic dispersion of a charge consisting of premix oxides and carbonates.
Electrical conductivity and critical current density of the superconductors are
measured over a wide temperature range of 10~$mK$ to 300~$K$. Degradation of
the superconductor critical parameters in time and structural characteristics,
magnetic susceptibility, heat capacity and acoustic properties are studied, and
current-voltage characteristics are determined.",1703.08707v1
2017-03-29,Identification of phase components in Zr-Ni and Hf-Ni intermetallic compounds; Investigations by perturbed angular correlation spectroscopy and first principles calculations,"Time-differential perturbed angular correlation (TDPAC) measurements have
been carried out in stoichiometric ZrNi$_3$ and HfNi$_3$ intermetallic
compounds using $^{181}$Ta probe in the temperature range 77-1073 K considering
the immense technological applications of Zr-Ni and Hf-Ni intermetallic
compounds. In ZrNi$_3$, four components due to the production of Zr$_2$Ni$_7$,
Zr$_8$Ni$_{21}$, Zr$_7$Ni$_{10}$ and ZrNi$_3$ have been found at room
temperature. The HfNi$_3$ sample produces five electric quadrupole interaction
frequencies at room temperature. The phase HfNi$_3$ is strongly produced in
stoichiometric sample of HfNi$_3$ where two non-equivalent Hf sites are found
to be present. Besides this phase, two other phases due to Hf$_2$Ni$_7$ and
Hf$_8$Ni$_{21}$ have been found but, we do not observe any phase due to
Hf$_7$Ni$_{10}$. X-ray diffraction, TEM/energy dispersive X-ray spectroscopy
(EDX) and TEM-selected area electron diffraction (SAED) measurements were used
to further characterize the investigated materials and it was found that these
results agree with the TDPAC results. In order to confirm findings from TDPAC
measurements, density functional theory (DFT) based calculations of electric
field gradients (EFG) and asymmetry parameters at the sites of $^{181}$Ta probe
nucleus were performed. Our calculated results are found to be in excellent
agreement with the experimental results.",1703.10035v2
2017-07-12,Filamentary superconductivity in semiconducting policrystalline ZrSe2 compound with Zr vacancies,"ZrSe2 is a band semiconductor studied long time ago. It has interesting
electronic properties, and because its layers structure can be intercalated
with different atoms to change some of the physical properties. In this
investigation we found that Zr deficiencies alter the semiconducting behavior
and the compound can be turned into a superconductor. In this paper we report
our studies related to this discovery. The decreasing of the number of Zr atoms
in small proportion according to the formula ZrxSe2, where x is varied from
about 8.1 to 8.6 K, changing the semiconducting behavior to a superconductor
with transition temperatures ranging between 7.8 to 8.5 K, it depending of the
deficiencies. Outside of those ranges the compound behaves as semiconducting
with the properties already known. In our experiments we found that this new
superconductor has only a very small fraction of superconducting material
determined by magnetic measurements with applied magnetic field of 10 Oe. Our
conclusions is that superconductivity is filamentary. However, in one studied
sample the fraction was about 10.2 %, whereas in others is only about 1 % or
less. We determined the superconducting characteristics; the critical fields
that indicate a type two superonductor with Ginzburg-Landau ? parameter of the
order about 2.7. The synthesis procedure is quite normal fol- lowing the
conventional solid state reaction. In this paper are included, the electronic
characteristics, transition temperature, and evolution with temperature of the
critical fields.",1707.03875v1
2017-08-01,"Rare-earth/transition-metal magnetic interactions in pristine and (Ni,Fe)-doped YCo5 and GdCo5","We present an investigation into the intrinsic magnetic properties of the
compounds YCo5 and GdCo5, members of the RETM5 class of permanent magnets (RE =
rare earth, TM = transition metal). Focusing on Y and Gd provides direct
insight into both the TM magnetization and RE-TM interactions without the
complication of strong crystal field effects. We synthesize single crystals of
YCo5 and GdCo5 using the optical floating zone technique and measure the
magnetization from liquid helium temperatures up to 800 K. These measurements
are interpreted through calculations based on a Green's function formulation of
density-functional theory, treating the thermal disorder of the local magnetic
moments within the coherent potential approximation. The rise in the
magnetization of GdCo5 with temperature is shown to arise from a faster
disordering of the Gd magnetic moments compared to the antiferromagnetically
aligned Co sublattice. We use the calculations to analyze the different Curie
temperatures of the compounds and also compare the molecular (Weiss) fields at
the RE site with previously published neutron scattering experiments. To gain
further insight into the RE-TM interactions, we perform substitutional doping
on the TM site, studying the compounds RECo4.5Ni0.5, RECo4Ni, and RECo4.5Fe0.5.
Both our calculations and experiments on powdered samples find an
increased/decreased magnetization with Fe/Ni doping, respectively. The
calculations further reveal a pronounced dependence on the location of the
dopant atoms of both the Curie temperatures and the Weiss field at the RE site.",1708.00288v1
2017-08-29,Dielectric and multiferroic behavior in a Haldane spin-chain compound Sm2BaNiO5 due to an interplay between crystal-field effect and exchange interaction,"The Haldane spin-chain (S=1) insulating compound, Sm2BaNiO5, which has been
proposed to order antiferromagnetically around (T_N=) 55 K, was investigated
for its complex dielectric permittivity, magnetodielectric and pyrocurrent
behavior as a function of temperature (T). In order to enable meaningful
discussions, the results of ac and dc magnetizatioin and heat-capacity studies
are also reported. We emphasize on the following findings: (i) There is a
pyrocurrent peak near T_N, but it is shown not to arise from ferroelectricity,
but possibly due to 'thermally stimulated depolarization current', unlike in
many other members of this rare-earth series, in which case ferroelectric
features were reported at or above T_N; (ii) however, the pyrocurrent measured
in the presence of a bias electric field (after cooling in zero electric field)
as well as dielectric constant reveal a weak peak with increasing T around 22 K
- the temperature around which population of the exchange-split excited state
of Kramers doublet has been known to occur. This finding suggests that this
compound presents a novel situation in which multiferroicity is induced by an
interplay between crystal-field effects and exchange interaction. No multiglass
features could be observed down to 2 K unlike in many members of this family.",1708.08699v1
2017-09-01,"Two-dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A = Ba, Sr)","We report infrared studies of AFe$_{2}$As$_{2}$ (A = Ba, Sr), two
representative parent compounds of iron-arsenide superconductors, at magnetic
fields (B) up to 17.5 T. Optical transitions between Landau levels (LLs) were
observed in the antiferromagnetic states of these two parent compounds. Our
observation of a $\sqrt{B}$ dependence of the LL transition energies, the
zero-energy intercepts at B = 0 T under the linear extrapolations of the
transition energies and the energy ratio ($\sim$ 2.4) between the observed LL
transitions, combined with the linear band dispersions in two-dimensional (2D)
momentum space obtained by theoretical calculations, demonstrates the existence
of massless Dirac fermions in antiferromagnetic BaFe$_{2}$As$_{2}$. More
importantly, the observed dominance of the zeroth-LL-related absorption
features and the calculated bands with extremely weak dispersions along the
momentum direction $k_{z}$ indicate that massless Dirac fermions in
BaFe$_{2}$As$_{2}$ are 2D. Furthermore, we find that the total substitution of
the barium atoms in BaFe$_{2}$As$_{2}$ by strontium atoms not only maintains 2D
massless Dirac fermions in this system, but also enhances their Fermi velocity,
which supports that the Dirac points in iron-arsenide parent compounds are
topologically protected.",1709.00203v1
2017-09-06,Magnetic ground states and magnetodielectric effect in $R$Cr(BO$_3$)$_2$ ($R$ = Y and Ho),"The layered perovskites $R$Cr(BO$_3$)$_2$ ($R$ = Y and Ho) with magnetic
triangular lattices were studied by performing ac/dc susceptibility, specific
heat, elastic and inelastic neutron scattering, and dielectric constant
measurements. The results show (i) both samples' Cr$^{3+}$ spins order in a
canted antiferromagnetic structure with $T_N$ around 8-9 K, while the Ho$^{3+}$
ions do not order down to $T$ = 1.5 K in HoCr(BO$_3$)$_2$; (ii) when a critical
magnetic field H$_{C}$ around 2-3 T is applied below $T_{N}$, the Cr$^{3+}$
spins in the Y-compound and both the Cr$^{3+}$ and Ho$^{3+}$ spins in the
Ho-compound order in a ferromagnetic state; (iii) both samples exhibit
dielectric constant anomalies around the transition temperature and critical
field, but the Ho-compound displays a much stronger magnetodielectric response.
We speculate that this is due to the magnetostriction which depends on both of
the Cr$^{3+}$ and the Ho$^{3+}$ ions' ordering in the Ho-compound. Moreover, by
using linear spin wave theory to simulate the inelastic neutron scattering
data, we estimated the Y-compound's intralayer and interlayer exchange
strengths as ferromagnetic J$_{1}$ = -0.12 meV and antiferromagnetic J$_{2}$ =
0.014 meV, respectively. The competition between different kinds of
superexchange interactions results in the ferromagnetic intralayer interaction.",1709.03493v1
2017-07-23,Dithymoquinone as a novel inhibitor for 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) to prevent renal failure,"3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) is a major
endogenous ligand found in the human serum albumin (HSA) of renal failure
patients. It gets accumulated in the HSA and its concentration in sera of
patients may reflect the chronicity of renal failure [1-4]. It is considered
uremic toxin due to its damaging effect on the renal cells. The high
concentrations of CMPF inhibit the binding of other ligands to HSA. Removal of
CMPF is difficult through conventional hemodialysis due to its strong binding
affinity. We hypothesized that the competitive inhibition may be helpful in
removal of CMPF binding to HSA. A compound with higher HSA binding affinity
than CMPF could be useful to prevent CMPF from binding so that CMPF could be
excreted by the body through the urine. We studied an active compound
dihydrothymoquinone/ dithymoquinone (DTQ) found in black cumin seed (Nigella
sativa), which has higher binding affinity for HSA. Molecular docking
simulations were performed to find the binding affinity of CMPF and DTQ with
HSA. DTQ was found to have higher binding affinity possessing more interactions
with the binding residues than the CMPF. We studied the binding pocket
flexibility of CMPF and DTQ to analyze the binding abilities of both the
compounds. We have also predicted the ADME properties for DTQ which shows
higher lipophilicity, higher gastrointestinal (GI) absorption, and blood-brain
barrier (BBB) permeability. We discovered that DTQ has potential to act as an
inhibitor of CMPF and can be considered as a candidate for the formation of the
therapeutic drug against CMPF.",1709.03813v1
2017-09-16,"Mixed eldfellite compounds \ce{Na(Fe_{1/2}M_{1/2})(SO4)2} (M = Mn, Co, Ni): A new family of high electrode potential cathodes for the sodium-ion battery","Natural abundance of sodium and its similar behavior to lithium triggered
recent extensive studies of cost-effective sodium-ion batteries (SIBs) for
large-scale energy storage systems. A challenge is to develop electrode
materials with a high electrode potential, specific capacity and a good rate
capability. In this work we propose mixed eldfellite compounds
\ce{Na_x(Fe_{1/2}M_{1/2})(SO4)2} (M = Mn, Co, Ni) as a new family of high
electrode potential cathodes of SIBs and present their material properties
predicted by first-principles calculations. The structural optimizations show
that these materials have significantly small volume expansion rates below 5\%
upon Na insertion/desertion with negative Na binding energies. Through the
electronic structure calculations, we find band insulating properties and hole
(and/or electron) polaron hoping as a possible mechanism for the charge
transfer. Especially we confirm the high electrode voltages over 4 V with
reasonably high specific capacities. We also investigate the sodium ion
mobility by estimating plausible diffusion pathways and calculating the
corresponding activation barriers, demonstrating the reasonably fast migrations
of sodium ions during the operation. Our calculation results indicate that
these mixed eldfellite compounds can be suitable materials for high performance
SIB cathodes.",1709.05523v1
2017-09-27,Carrier and strain tunable intrinsic magnetism in two-dimensional MAX$_3$ transition metal chalcogenides,"We present a density functional theory study of the carrier-density and
strain dependence of magnetic order in two-dimensional (2D) MAX$_3$ (M= V, Cr,
Mn, Fe, Co, Ni; A= Si, Ge, Sn, and X= S, Se, Te) transition metal
trichalcogenides. Our {\em ab initio} calculations show that this class of
compounds includes wide and narrow gap semiconductors and metals and
half-metals, and that most of these compounds are magnetic. Although
antiferromagnetic order is most common, ferromagnetism is predicted in
MSiSe$_3$ for M= Mn, Ni, in MSiTe$_3$ for M= V, Ni, in MnGeSe$_3$, in MGeTe$_3$
for M=Cr, Mn, Ni, in FeSnS$_3$, and in MSnTe$_3$ for M= V, Mn, Fe. Among these
compounds CrGeTe$_3$ and VSnTe$_3$ are ferromagnetic semiconductors. Our
calculations suggest that the competition between antiferromagnetic and
ferromagnetic order can be substantially altered by strain engineering, and in
the semiconductor case also by gating. The associated critical temperatures can
be substantially enhanced by means of carrier doping and strains.",1709.09386v1
2017-11-15,Orbital physics in transition metal compounds: new trends,"In the present review different effects related to the orbital degrees of
freedom are discussed. Leaving aside such aspects as the superexchange
mechanism of the cooperative Jahn-Teller distortions and different properties
of ""Kugel-Khomskii""-like models, we mostly concentrate on other phenomena,
which are in the focus of the modern condensed matter physics. After a general
introduction we start with the discussion of the concept of effective reduction
of dimensionality due to orbital degrees of freedom and consider such phenomena
as the orbitally-driven Peierls effect and the formation of small clusters of
ions in the vicinity of a Mott transition, which behave like ""molecules""
embedded in a solid. The second large section is devoted to the
orbital-selective effects such as the orbital-selective Mott transition and the
suppression of magnetism due to the fact that part of the orbitals start to
form singlet molecular orbitals. At the end the rapidly growing field of the
so-called ""spin-orbit-dominated"" transition metal compounds is briefly reviewed
including such topics as the interplay between the spin-orbit coupling and the
Jahn-Teller effect, the formation of the spin-orbit driven Mott and Peierls
states, the role of orbital degrees of freedom in generation of the Kitaev
exchange coupling, and the singlet (excitonic) magnetism in $4d$ and $5d$
transition metal compounds.",1711.05409v2
2017-11-23,Complex Fluid-Fluid Interface may Non Trivially Dictate Droplet Deformation in an Incipient Flow,"The present study theoretically predicts the effect of interfacial viscosity
on the deformation of a compound drop as well as on the bulk rheology. The
system at hand comprises of a dilute emulsion of concentric compound drops,
laden with surfactants and suspended in a linear flow. Two types of linear
flows are considered in this study, namely, a uniaxial extensional flow and a
simple shear flow. Presence of surfactants along the drop surface leads to the
generation of an interfacial viscosity, which is different from the bulk. This
interfacial viscosity generates a viscous drag that along with bulk
flow-induced nonuniform surfactant distribution on the drop surface
significantly alters drop dynamics. For the present study an asymptotic
approach is used to solve the flow field under the limiting case of
diffusion-dominated-surfactant transport. Assuming the surfactants to be
bulk-insoluble and negligible inertia to be present in fluid flow, it is shown
that presence of interfacial viscosity reduces the deformation of a compound
drop and enhances the stability of a dilute double emulsion. At the same time
the effective viscosity of the emulsion also increases with rise in interfacial
viscosity. For large values of interfacial dilatational viscosity the drop
deformation is seen to increase and hence the stability of the double emulsion
is questionable.",1711.08738v1
2017-11-29,Deep Reinforcement Learning for De-Novo Drug Design,"We propose a novel computational strategy for de novo design of molecules
with desired properties termed ReLeaSE (Reinforcement Learning for Structural
Evolution). Based on deep and reinforcement learning approaches, ReLeaSE
integrates two deep neural networks - generative and predictive - that are
trained separately but employed jointly to generate novel targeted chemical
libraries. ReLeaSE employs simple representation of molecules by their SMILES
strings only. Generative models are trained with stack-augmented memory network
to produce chemically feasible SMILES strings, and predictive models are
derived to forecast the desired properties of the de novo generated compounds.
In the first phase of the method, generative and predictive models are trained
separately with a supervised learning algorithm. In the second phase, both
models are trained jointly with the reinforcement learning approach to bias the
generation of new chemical structures towards those with the desired physical
and/or biological properties. In the proof-of-concept study, we have employed
the ReLeaSE method to design chemical libraries with a bias toward structural
complexity or biased toward compounds with either maximal, minimal, or specific
range of physical properties such as melting point or hydrophobicity, as well
as to develop novel putative inhibitors of JAK2. The approach proposed herein
can find a general use for generating targeted chemical libraries of novel
compounds optimized for either a single desired property or multiple
properties.",1711.10907v2
2017-12-12,Ultrahigh permittivity in core-shell ferroelectric ceramics: Theoretical approach and practical conclusions,"Ferroelectric anomalies in most classical ferroelectric materials such as
BaTiO3 (BT) and related compounds tend to become diffuse and eventually vanish
when the grain size decreases. This has led to question the very existence of
ferroelectricity for very small particles. However there are also reports in
the literature of ultra-high values of permittivity when specific processes or
doping are performed, for instance in the BT-family, or in the CaCu3Ti4O12-
family and interpretations using (IBLC) have been proposed. We have considered
these effects in the framework of a core-shell model of ceramics. The ultrahigh
values mentioned above could be reproduced by considering that the core (be it
dielectric or ferroelectric) have non-zero conductivity. In particular a huge
background of permittivity and a Maxwell Wagner relaxation were obtained in
agreement with the experimental situation. Different types of inhomogeneity
(grain size distribution, mixing of conductive and non-conductive phases,
porosity) have also been considered and their effects are discussed. Finally we
have evaluated the potentiality of energy storage in IBLC compounds and
observed a reduction (compared with non-conductive ferroelectrics) by a factor
2-4 depending on the structuration of the ceramic, which shows that the
performance of such compounds are lower than in optimal insulating core-shell
structures.",1712.04197v1
2017-12-19,Li doping kagome spin liquid compounds,"Herbertsmithite and Zn-doped barlowite are two compounds for experimental
realization of twodimensional gapped kagome spin liquid. Theoretically, it has
been proposed that charge doping a quantum spin liquid gives rise to exotic
metallic states, such as high-temperature superconductivity. However, one
recent experiment about herbertsmithite with successful Li-doping shows
surprisingly the insulating state even under the heavy doped scenario, which
can hardly be explained by many-body physics. Using first-principles
calculation, we performed a comprehensive study about the Li intercalated
doping effect of these two compounds. For the Li-doped herbertsmithite, we
identified the optimized Li position at the Cl-(OH)$_3$-Cl pentahedron site
instead of previously speculated Cl-(OH)$_3$ tetrahedral site. With the
increase of Li doping concentration, the saturation magnetization decreases
linearly due to the charge transfer from Li to Cu ions. Moreover, we found that
Li forms chemical bonds with the nearby (OH)$^-$ and Cl$^-$ ions, which lowers
the surrounding chemical potential and traps the electron, as evidenced by the
localized charge distribution, explaining the insulating behavior measured
experimentally. Though with different structure from herbertsmithite, Zn-doped
Barlowite shows the same features upon Li doping. We conclude that Li doping
this family of kagome spin liquid cannot realize exotic metallic states, other
methods should be further explored, such as element substitution with different
valence electrons.",1712.06791v2
2017-12-21,The Role of Molecular Properties on the Dimerization of Aromatic Compounds,"Recent results have shown the presence and importance of oxygen chemistry
during the growth of aromatic compounds, leading to the formation of oxygenated
structures that have been identified in various environments. Since the
formation of polycyclic aromatic compounds (PAC) bridge the formation of
gas-phase species with particle inception, in this work we report a detailed
analysis of the effects of molecular characteristics on physical growth of PAC
via dimerization. We have included oxygen content, mass, type of bonds (rigid
versus rotatable), and shape as main properties of the molecules and studied
their effect on the propensity of these structures to form homo-molecular and
hetero-molecular dimers. Using enhanced sampling molecular dynamics techniques,
we have computed the free energy of dimerization in the temperature range
$500-1680$~K. Initial structures used in this study were obtained from
experimental data. The results show that although the effects of shape,
presence of oxygen, mass, and internal bonds are tightly intertwined, and their
relative importance changes with temperature. In general, mass and the presence
of rotatable bonds are the best indicators. The results provide knowledge on
the inception step and the role that particle characteristics play during
inception. In addition, our study highlights the fact that current models that
use stabilomers as monomers for physical aggregation are overestimating the
importance of this process during particle nucleation.",1712.08187v1
2018-01-18,"Material Discovery and Design Principles for Stable, High Activity Perovskite Cathodes for Solid Oxide Fuel Cells","Critical to the development of improved solid oxide fuel cell (SOFC)
technology are novel compounds with high oxygen reduction reaction (ORR)
catalytic activity and robust stability under cathode operating conditions.
Approximately 2145 distinct perovskite compositions are screened for potential
use as high activity, stable SOFC cathodes, and it is verified that the
screening methodology qualitatively reproduces the experimental activity,
stability, and conduction properties of well-studied cathode materials. The
calculated oxygen p-band center is used as a first principle-based descriptor
of the surface exchange coefficient (k*), which in turn correlates with cathode
ORR activity. Convex hull analysis is used under operating conditions in the
presence of oxygen, hydrogen, and water vapor to determine thermodynamic
stability. This search has yielded 52 potential cathode materials with good
predicted stability in typical SOFC operating conditions and predicted k* on
par with leading ORR perovskite catalysts. The established trends in predicted
k* and stability are used to suggest methods of improving the performance of
known promising compounds. The material design strategies and new materials
discovered in the computational search help enable the development of high
activity, stable compounds for use in future solid oxide fuel cells and related
applications.",1801.06109v2
2018-03-02,Antiferroelectric and Magnetodielectric Coupling Response of La0.2Sr0.7Fe12O19 Ceramics,"Multiferroics is a class of functional materials that simultaneously exhibit
ferroelectricity and ferromagnetism in a single structure. We report here the
integration of anti-ferroelectricity and ferromagnetism in a new M-type
hexaferrite compound, in which 0.3 Sr ions was substituted by 0.2 La3+ ions in
SrFe12O19 so as to keep the charge balance. This doped compound is expressed as
a molecular formula of La0.2Sr0.7Fe12O19, which was confirmed by XRD to have
the same structure as SrFe12O19 with a lattice contraction of 0.59%.
Surprisingly, the doping effect turns La0.2Sr0.7Fe12O19 from ferroelectric to
antiferroelectric phase, which displays double hysteresis loops with a maximum
polarization of 154 uC/cm2 and a remnant one of 38uC/cm2. The dielectric
constant is also greatly improved from 1462 to 1451778 at 10.2Hz by this
substitution. This compound simultaneously demonstrates strong ferromagnetism,
the remnant magnetic moment and coercive field are 52 emu/g and 5876 Oe,
respectively. In addition, La0.2Sr0.7Fe12O19 also exhibits strong
magnetodielectric (MD) response, in which a applying magnetic field B lifts the
whole e1-f spectra up and right shifts e2-f spectra to higher frequency side.
Both real and imaginary parts of the dielectric constant varies with frequency
and B field and obey Debye relaxation model. The maximum MD increment in e1
reaches as high as 540830 upon a B field of 926mT. The capacitance of the
La0.2Sr0.7Fe12O19 ceramics could be much more enhanced by applying a magnetic
field B, which could induce an additional polarization P(H) upon the
conventional P(E) by the cycloid conical spin in the intermediate phases. These
results suggest that La0.2Sr0.7Fe12O19 exhibits a strong interplay between
magnetic ordering and ferroelectricity, which makes it a good magnetoelectric
coupling candidate.",1803.00731v1
2018-05-10,Magnetic phase diagram of Ca-substituted EuFe$_2$As$_2$,"The simultaneous presence of a Fe-related spin-density wave and
antiferromagnetic order of Eu$^{2+}$ moments ranks EuFe$_2$As$_2$ among the
most interesting parent compounds of iron-based pnictide superconductors. Here
we explore the consequences of the dilution of Eu$^{2+}$ magnetic lattice
through on-site Ca substitution. By employing macro- and microscopic
techniques, including electrical transport and magnetometry, as well as
muon-spin spectroscopy, we study the evolution of Eu magnetic order in both the
weak and strong dilution regimes, achieved for Ca concentration $x(\mathrm{Ca})
= 0.12$ and 0.43, respectively. We demonstrate the localized character of the
Eu antiferromagnetism mediated via RKKY interactions, in contrast with the
largely itinerant nature of Fe magnetic interactions. Our results suggest a
weak coupling between the Fe and Eu magnetic sublattices and a rapid decrease
of the Eu magnetic interaction strength upon Ca substitution. The latter is
confirmed both by the depression of the ordering temperature of the Eu$^{2+}$
moments, $T_\mathrm{N}$, and the decrease of magnetic volume fraction with
increasing $x(\mathrm{Ca})$. We establish that, similarly to the EuFe$_2$As$_2$
parent compound, the investigated Ca-doped compounds have a twinned structure
and undergo a permanent detwinning upon applying an external magnetic field.",1805.03896v2
2018-05-21,Physical descriptor for the Gibbs energy of inorganic crystalline solids and temperature-dependent materials chemistry,"The Gibbs energy, G, determines the equilibrium conditions of chemical
reactions and materials stability. Despite this fundamental and ubiquitous
role, G has been tabulated for only a small fraction of known inorganic
compounds, impeding a comprehensive perspective on the effects of temperature
and composition on materials stability and synthesizability. Here, we use the
SISSO (sure independence screening and sparsifying operator) approach to
identify a simple and accurate descriptor to predict G for stoichiometric
inorganic compounds with ~50 meV/atom (~1 kcal/mol) resolution, and with
minimal computational cost, for temperatures ranging from 300-1800 K. We then
apply this descriptor to ~30,000 known materials curated from the Inorganic
Crystal Structure Database (ICSD). Using the resulting predicted thermochemical
data, we generate thousands of temperature-dependent phase diagrams to provide
insights into the effects of temperature and composition on materials
synthesizability and stability and to establish the temperature-dependent scale
of metastability for inorganic compounds.",1805.08155v2
2018-05-21,Insights on unconventional superconductivity in HfV$_2$Ga$_4$ and ScV$_2$Ga$_4$ from first principles electronic structure calculations,"The HfV$_2$Ga$_4$ compound was recently reported to exhibit unusual bulk
superconducting properties, with the possibility of multiband behavior. To gain
insight into its properties, we performed ab-initio electronic structure
calculations based on the Density Functional Theory (DFT). Our results show
that the density of states at the Fermi energy is mainly composed by V--$d$
states. The McMillan formula predicts a superconducting critical temperature
($T_{c}$) of approximately $3.9\,$K, in excellent agreement with the
experimental value at $4.1\,$K, indicating that superconductivity in this new
compound may be explained by the electron-phonon mechanism. Calculated valence
charge density maps clearly show directional bonding between Hf and V atoms
with 1D highly populated V-chains, and some ionic character between Hf--Ga and
V--Ga bonds. Finally, we have shown that there are electrons occupying two
distinct bands at the Fermi level, with different characters, which supports
experimental indications of possible multiband superconductivity. Based on the
results, we propose the study of a related compound, ScV$_2$Ga$_4$, showing
that it has similar electronic properties, but probably with a higher $T_c$
than HfV$_2$Ga$_4$.",1805.08285v1
2018-06-06,High performance magnetic material with Ce and La: an alternative to Nd-Fe-B magnet,"A systematic study of magnetocrystalline anisotropy is performed for
R(La/Ce/Nd)2Fe14B tetragonal compound with the site substitution mechanism.
Theoretical calculation suggests the 50% doping with Ce at 4f-site can lead to
competitive magnetic anisotropy to that of the champion magnet Nd2Fe14B.
Electronic structure calculations are performed using the full-potential
linearized augmented plane wave method by inclusion of the spin-orbit coupling
and Hubbard (U) interaction in the calculation for the rare-earth elements to
get the correct influence of the localized 4f orbitals. Detailed analysis of
the magnetic moment and magnetic anisotropy change has been studied by
individually inserting the La and Ce atoms at the two inequivalent sites (4g
and 4f sites) of the 2-14-B tetragonal structure. Accurate prediction of the
total magnetic moment with the orbital contribution in the 2-14-B structure
shows the maximum moment for Ce2Fe14B (3.86 {\mu}B/f.u less) compared to
Nd2Fe14B. Theoretical analysis confirms that regardless of the anti-parallel
spin moment emerging in the Ce atom the complex structure of the Ce substituted
compound at 4f-site gives the maximum anisotropy of 2.27 meV/cell with lowering
the magnetic moment by 1.26 {\mu}B/f.u. compared to the Nd2Fe14B compound.",1806.01990v1
2018-06-19,"Magnetic, electronic and transport properties of high-pressure-synthesized chiralmagnets Mn$_{1-x}$Rh$_x$Ge (B20)","We report on structural, magnetic and transport properties of a new set of
the high-pressuresynthesized compounds Mn$_{1-x}$Rh$x$Ge ($0 \leq x \leq 1$)
with the chiral magnetic ordering. The magnetic and transport properties depend
substantially on the concentration of rhodium (x) and the pressure. The
saturation magnetic moment corresponds to a known high-spin value for pristine
MnGe (x = 0) and decreases almost linearly with increasing concentration $x$.
In addition, XMCD spectra taken at 10 K and 2 T indicate magnetic polarization
of the Rh 4d electron states and Ge $4p$ states, which decreases with $x$, too.
In rhodium rich compounds ($x \geq 0.5$) the temperature of the magnetic
ordering increases significantly with pressure, whereas in manganese rich
compounds ($x < 0.5$) the temperature decreases. Three different tendencies are
also found for several structural and transport properties. In the intermediate
range ($0.3 \leq x \leq 0.7$) samples are semiconducting in the paramagnetic
phase, but become metallic in the magnetically ordered state. We carried out ab
initio density-functional calculations of Mn$_{1-x}$Rh$_x$Ge at various
concentrations $x$ and traced the evolution of electronic and magnetic
properties. The calculation results are in good agreement with the measured
magnetic moments and qualitatively explain the observed trends in transport
properties.",1806.07165v1
2018-09-10,Diffusion of Mn in gallium nitride: Experiment and modelling,"The control over the structural homogeneity is of paramount importance for
ternary nitride compounds - the second most important semiconducting
material-class after Si, due to its unrivalled applicability in
optoelectronics, and high power/high frequency electronics. Therefore it is
timely to investigate possible mechanisms influencing the crystallographic
constitution of the material. In this work the diffusion mechanism of manganese
in gallium nitride is investigated in two types of epilayers: Mn implanted
metalorganic vapour phase epitaxy grown GaN and (Ga,Mn)N solid solution grown
by molecular beam epitaxy. The extent of the Mn diffusion is established by
secondary ion mass spectrometry. Analysis of the Mn profiles in the implanted
samples in the frame of the infinite source diffusion led to the establishment
for the first time of the pre-exponential factor DO = 2x10-4 cm2/s and
diffusion activation energy EA = 1.8 eV describing the diffusion coefficient of
Mn in GaN. Modelling of the out-diffusion of Mn from (Ga,Mn)N layers based on
these values in turn allows to provide an explanation of the origin of the
ubiquitously observed near-the-surface sizable depletion of Mn in (Ga,Mn)N,
resulting from the blocking of the Mn out-diffusion by Mn-oxide and the
correspondingly formed space-charge layer on the surface.",1809.03247v1
2018-09-11,Nonparametric Bayesian analysis of the compound Poisson prior for support boundary recovery,"Given data from a Poisson point process with intensity $(x,y) \mapsto n
\mathbf{1}(f(x)\leq y),$ frequentist properties for the Bayesian reconstruction
of the support boundary function $f$ are derived. We mainly study compound
Poisson process priors with fixed intensity proving that the posterior
contracts with nearly optimal rate for monotone and piecewise constant support
boundaries and adapts to H\""older smooth boundaries with smoothness index at
most one. We then derive a non-standard Bernstein-von Mises result for a
compound Poisson process prior and a function space with increasing parameter
dimension. As an intermediate result the limiting shape of the posterior for
random histogram type priors is obtained. In both settings, it is shown that
the marginal posterior of the functional $\vartheta =\int f$ performs an
automatic bias correction and contracts with a faster rate than the MLE. In
this case, $(1-\alpha)$-credible sets are also asymptotic
$(1-\alpha)$-confidence intervals. As a negative result, it is shown that the
frequentist coverage of credible sets is lost for linear functions indicating
that credible sets only have frequentist coverage for priors that are
specifically constructed to match properties of the underlying true function.",1809.04140v1
2018-09-16,Curriculum-Based Neighborhood Sampling For Sequence Prediction,"The task of multi-step ahead prediction in language models is challenging
considering the discrepancy between training and testing. At test time, a
language model is required to make predictions given past predictions as input,
instead of the past targets that are provided during training. This difference,
known as exposure bias, can lead to the compounding of errors along a generated
sequence at test time.
  In order to improve generalization in neural language models and address
compounding errors, we propose a curriculum learning based method that
gradually changes an initially deterministic teacher policy to a gradually more
stochastic policy, which we refer to as \textit{Nearest-Neighbor Replacement
Sampling}. A chosen input at a given timestep is replaced with a sampled
nearest neighbor of the past target with a truncated probability proportional
to the cosine similarity between the original word and its top $k$ most similar
words. This allows the teacher to explore alternatives when the teacher
provides a sub-optimal policy or when the initial policy is difficult for the
learner to model. The proposed strategy is straightforward, online and requires
little additional memory requirements. We report our main findings on two
language modelling benchmarks and find that the proposed approach performs
particularly well when used in conjunction with scheduled sampling, that too
attempts to mitigate compounding errors in language models.",1809.05916v1
2018-09-19,Intermolecular Coupling and Superconductivity in Chevrel Phase Compounds,"To understand superconductivity in Chevrel phase compounds and guide the
search for interesting properties in materials created with Chevrel phase
molecules as building blocks, we use ab-initio methods to study the properties
of single Mo$_6$X$_8$ molecules with $X=S$, $Se$, $Te$ as well as the bulk
solid PbMo$_6$S$_8$. In bulk PbMo$_6$S$_8$, the different energy scales from
strong to weak are: the band kinetic energy, the intra-molecular Coulomb
interaction, the on-molecule Jahn-Teller energy and the Hund's exchange
coupling. The metallic state is stable with respect to Mott and polaronic
insulating states. The bulk compound is characterized by a strong
electron-phonon interaction with the largest coupling involving phonon modes
with energies in the range from 11 meV to 17 meV and with a strong
inter-molecule (Peierls) character. A two-band Eliashberg equation analysis
shows that the superconductivity is strong-coupling, with different gaps on the
two Fermi surface sheets. A Bergman-Rainer analysis of the functioanl
derivative of the transition temperature with respect to the electron-phonon
coupling reveals that the Peierls modes provide the most important contribution
to the superconductivity. This work illustrates the importance of
inter-molecular coupling for collective phenomena in molecular solids.",1809.07000v1
2018-09-20,Role of charged particle emission on the evaporation residue formation in the $^{82}$Se+$^{138}$Ba reaction leading to the $^{220}$Th compound nucleus,"We present detailed results of a theoretical investigation on the production
of evaporation residue nuclei obtained in a heavy ion reaction when charged
particles (proton and $\alpha$-particle) are also emitted with the neutron
evaporation along the deexcitation cascade of the formed compound nucleus. The
almost mass symmetric $^{82}$Se+$^{138}$Ba reaction has been studied since
there are many experimental results on individual evaporation residue (ER)
cross sections after few light particle emissions along the cascade of the
$^{220}$Th compound nucleus (CN) covering the wide 12--70 MeV excitation energy
range. Our specific theoretical results on the ER cross sections for the
$^{82}$Se+$^{138}$Ba are in good agreement with the available experimental
measurements, but our overall theoretical results concerning all possible
relevant contributions of evaporation residues are several times greater than
the ERs measured in experiment. The discrepancy could be due to the
experimental difficulties in the identification of ER nuclei after the emission
of multiple neutral and charged particles, nevertheless the analysis of ER data
is very important to test the reliability of the model and to stress the
importance on the investigation of ER nuclei also obtained after charged
particle emissions.",1809.07798v1
2018-09-20,Phase components in Zr7Ni10 and Hf7Ni10 binary alloys; investigations by perturbed angular correlation spectroscopy and first principles calculations,"Intermetallic compounds Zr7Ni10 and Hf7Ni10 have been studied by perturbed
angular correlation (PAC) spectroscopy considering the fact that Zr7Ni10 has
application as hydrogen storage material in fuel cell. In stoichiometric
Zr7Ni10, the phase Zr2Ni7 is found to be dominant (~38%) while a fraction of
~25% is found for the Zr7Ni10 phase at room temperature. In this compound, a
phase due to Zr8Ni21 (~10%) is found from room temperature up to 773 K but,
this is not found at 873 K and above. In the stoichiometric Hf7Ni10 sample, the
phase due to Hf7Ni10 is found as a minor phase (~22%) at room temperature. In
this system, no phase of Hf2Ni7 is observed but, a different phase due to HfNi3
is found to be dominant (~62%). It is found that the site fraction of Hf7Ni10
enhances with temperature at the expense of HfNi3 and this phase becomes
predominant (~57%) at 673 K and above. The change of phase fractions of HfNi3
and Hf7Ni10 with temperature is found to be reversible. The phase components in
Zr7Ni10 and Hf7Ni10 have been determined also from X-ray powder diffraction
(XRD) and transmission electron microscopy/selected area electron diffraction
(TEM/SAED) measurements. Ab-initio calculations using the all electron full
potential (linearized) augmented plane wave [FP-(L)APW] method, within the
framework of the density functional theory (DFT), have been performed to
determine the electric field gradients at the 181Ta impurity sites and
therefrom to assign the different components observed from PAC measurements.
Present experimental and calculated results of EFG support the Cmca space group
for both Zr7Ni10 and Hf7Ni10 compounds.",1809.08114v1
2018-09-26,A Generalized Index for Static Voltage Stability of Unbalanced Polyphase Power Systems including Thévenin Equivalents and Polynomial Models,"This paper proposes a Voltage Stability Index (VSI) suitable for unbalanced
polyphase power systems. To this end, the grid is represented by a polyphase
multiport network model (i.e., compound hybrid parameters), and the aggregate
behavior of the devices in each node by Th\'evenin Equivalents (TEs) and
Polynomial Models (PMs), respectively. The proposed VSI is a generalization of
the known L-index, which is achieved through the use of compound electrical
parameters, and the incorporation of TEs and PMs into its formal definition.
Notably, the proposed VSI can handle unbalanced polyphase power systems,
explicitly accounts for voltage-dependent behavior (represented by PMs), and is
computationally inexpensive. These features are valuable for the operation of
both transmission and distribution systems. Specifically, the ability to handle
the unbalanced polyphase case is of particular value for distribution systems.
In this context, it is proven that the compound hybrid parameters required for
the calculation of the VSI do exist under practical conditions (i.e., for lossy
grids). The proposed VSI is validated against state-of-the-art methods for
voltage stability assessment using a benchmark system which is based on the
IEEE 34-node feeder.",1809.09922v3
2018-11-26,Magnetic Dynamics in Heavy-Fermion Systems with Multipolar Ordering Studied by Neutron Scattering,"Despite more than half a century of studies in heavy-fermion compounds, a
full understanding of the various possible magnetic ordering phenomena is still
far from complete. Some heavy-fermion materials show so-called hidden-order
phases, which are invisible to conventional diffraction techniques. The
multipolar moments of the $f$-electrons in their specific crystal field
environment play a decisive role in the formation of these phases. Such
hidden-order phases have been observed in a variety of compounds containing
$4f$ and $5f$ elements, like URu$_2$Si$_2$, NpO$_2$, YbRu$_2$Ge$_2$, and
CeB$_6$. The competition or coexistence of multipolar ordering with more
conventional magnetic order parameters, such as ferro- or antiferromagnetism,
gives rise to complex magnetic-field$-$temperature phase diagrams in these
compounds that provide a rich playground for experimental and theoretical
investigations. Here I examine the pure and La-doped $f$-electron system
CeB$_6$, as well as Ce$_{3}$Pd$_{20}$Si$_{6}$, by means of neutron scattering.
The magnetic field dependence of the zone center exciton mode in CeB$_6$ was
studied in fields up to 14.5 T and compared with the existing theory. A long
standing question of the applicability of the phenomenological temperature
dependence $\Gamma=k_{\text B}T_{\text K}+A \sqrt{T}$, where $T_{\text K}$ is
the Kondo temperature, for two limiting cases, the Kondo lattice and Kondo
impurity, has been investigated on a set of samples diluted with lanthanum. In
Ce$_{3}$Pd$_{20}$Si$_{6}$, the order parameter of the AFQ phase was uncovered,
and its field dependence was studied in fields up to 9 T.",1811.10502v1
2019-11-08,Reconstruction for Diverging-Wave Imaging Using Deep Convolutional Neural Networks,"In recent years, diverging-wave (DW) ultrasound imaging has become a very
promising methodology for cardiovascular imaging due to its high temporal
resolution. However, if they are limited in number, DW transmits provide lower
image quality compared with classical focused schemes. A conventional
reconstruction approach consists in summing series of ultrasound signals
coherently, at the expense of the frame rate. To deal with this limitation, we
propose a convolutional neural networks (CNN) architecture for high-quality
reconstruction of DW ultrasound images using a small number of transmissions.
Given the spatially varying properties of DW images along depth, we adopted the
inception model composed of the concatenation of multi-scale convolutional
kernels. Incorporating inception modules aims at capturing different image
features with multi-scale receptive fields. A mapping between low-quality
images and corresponding high-quality compounded reconstruction was learned by
training the network using in vitro and in vivo samples. The performance of the
proposed approach was evaluated in terms of contrast-to-noise ratio and lateral
resolution, and compared with standard compounding method and conventional CNN
methods. The results demonstrate that our method could produce high-quality
images using only three DWs, yielding an image quality equivalent to the one
obtained with standard compounding of 31 DWs and outperforming more
conventional CNN architectures in terms of complexity, inference time and image
quality.",1911.03416v3
2019-11-18,Elastic Response in the Dilute non-Kramers System Y$_{1-x}$Pr$_x$Ir$_2$Zn$_{20}$,"Ultrasonic investigations of the single-site quadrupolar Kondo effect in
diluted Pr system Y$_{0.966}$Pr$_{0.034}$Ir$_2$Zn$_{20}$ are reported. The
elastic constant $(C_{11}-C_{12})/2$ is measured down to ~40 mK using
ultrasound for the dilute system Y$_{0.966}$Pr$_{0.034}$Ir$_2$Zn$_{20}$ and the
pure compound YIr$_2$Zn$_{20}$. We found that the elastic constant
$(C_{11}-C_{12})/2$ of the Pr-dilute system exhibits a logarithmic temperature
dependence below $T_0$ ~0.3 K, where non-Fermi-liquid (NFL) behavior in the
specific heat and electrical resistivity is observed. This logarithmic
temperature variation manifested in the $\Gamma_3$-symmetry quadrupolar
susceptibility is consistent with the theoretical prediction of the quadrupolar
Kondo effect by D. L. Cox. On the other hand, the pure compound
YIr$_2$Zn$_{20}$ without $4f$-electron contributions shows nearly no change in
its elastic constants evidencing negligible phonon contributions. In addition,
clear acoustic de Haas-van Alphen (dHvA) oscillations in the elastic constant
were detected for both compounds on applying magnetic field. This is mainly
interpreted as contribution from the Fermi surface of YIr$_2$Zn$_{20}$.",1911.07462v1
2019-11-27,Spin-dimer ground state driven by consecutive charge and orbital ordering transitions in the anionic mixed-valence compound Rb$_4$O$_6$,"Recently, a Verwey-type transition in the mixed-valence alkali sesquioxide
Cs$_4$O$_6$ was deduced from the charge ordering of molecular peroxide
O$_2^{2-}$ and superoxide O$_2^-$ anions accompanied by the structural
transformation and a dramatic change in electronic conductivity [Adler et al,
Sci. Adv 4, eaap7581 (2018)]. Here, we report that in the sister compound
Rb$_4$O$_6$ a similar Verwey-type charge ordering transition is strongly linked
to O$_2^-$ orbital and spin dynamics. On cooling, a powder neutron diffraction
experiment reveals a charge ordering and a cubic-to-tetragonal transition at
$T_{\rm CO}=290$ K, which is followed by a further structural instability at
$T_{\rm s}=92$ K that involves an additional reorientation of magnetic O$_2^-$
anions. Magnetic resonance techniques supported by density functional theory
computations suggest the emergence of a peculiar type of $\pi^*$-orbital
ordering of the magnetically active O$_2^-$ units, which promotes the formation
of a quantum spin state composed of weakly coupled spin dimers. These results
reveal that similarly as in 3$d$ transition metal compounds, also in in the
$\pi^*$ open-shell alkali sesquioxides the interplay between Jahn-Teller-like
electron-lattice coupling and Kugel-Khomskii-type superexchange determines the
nature of orbital ordering and the magnetic ground state.",1911.12049v1
2020-01-07,Ab Initio Many-Body Perturbation Theory Calculations of the Electronic and Optical Properties of Cyclometalated Ir(III) Complexes,"Cyclometalled Ir(III) compounds are the preferred choice as organic emitters
in Organic Light Emitting Diodes. In practice, the presence of the transition
metals surrounded by carefully designed ligands allows the fine tuning of the
emission frequency as well as a good efficiency of the device. To support the
development of new compounds the experimental measurements are generally
compared with ab-initio calculation of the absorption and emission spectra. The
standard approach for these calculations is TDDFT with hybrid exchange and
correlation functional like the B3LYP. Due to the size of these compounds the
application of more complex quantum chemistry approaches can be challenging. In
this work we used Many Body Perturbation Theory approaches (in particular the
GW approximation with the Bethe-Salpeter equation) implemented in gaussian
basis sets, to calculate the quasiparticle properties and the adsorption
spectra of six cyclometalled Ir(III) complexes going behind TDDFT. In the
presented results we compared standard TDDFT simulation with BSE calculations
performed on top on perturbative G 0 W 0 and accounting for eigenvalue self
consistency. Moreover, in order to investigate in detail the effect of the DFT
starting point, we concentrate on Ir(ppy) 3 performing GW-BSE simulations
starting from different DFT exchange and correlation potentials.",2001.01959v1
2019-11-28,Few-layer flakes of Molybdenum Disulphide produced by anodic arc discharge in pulsed mode,"Here, the synthesis of Molybdenum Disulphide (MoS2) flakes by means of anodic
atmospheric arc discharge is reported for the first time. The vertical
electrode configuration consisted of a compound anode (hollow graphite anode
filled with MoS2 powder) and a solid graphite cathode placed just above of the
compound anode. Arc processes were operated in pulsed mode to preferentially
evaporate the powder component from the anode and to minimize Carbon ablation.
Pulsed anodic arc discharges were conducted at 2 Hz and 10% duty cycle in 300
Torr of Helium with a peak current of 250-300 A and peak voltage of 35 V. A
probe made of Tungsten wire was placed in the vicinity of the arc column to
collect the evaporated material. The measured thickness profile was correlated
to the particle flux distribution and it was fitted by a simple model of plasma
expansion. During pulse phase, electron density was estimated around 5E22 m-3
or higher, and ion current density was of the order of 10 A/mm2. Morphology,
structure and composition of the samples were characterized by Raman
spectroscopy, atomic force microscopy (AFM), scanning electron microscopy
(SEM), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The
study shows that pulsed arc discharge of the compound anode leads to moderate C
deposition combined with MoS2 deposition in the form of fragmented nanocrystals
and few atomic monolayers of MoS2. Such synthesis technique is promising to
produce new 2D nanomaterials with tailored structure and functionality thanks
to the flexibility of pulsed power.",2001.02041v1
2019-12-17,Theoretical study of structure and magnetism of Ga$_{1-x}$V$_x$Sb compounds for spintronic applications,"In this paper, the structural, electronic and magnetic properties of
Zinc-blende Ga1-xVxSb compounds, with x from dilute doping situation to extreme
doping limiting, were systematically investigated by first-principles
calculations. V atoms prefer to substitute the Ga atoms and the formation
energy is lower in Sb-rich than Ga-rich growth condition. Meantime, the SbGa
antisite defects can effectively decrease the energy barrier of substitution
process, from 0.85 eV to 0.53 eV. The diffusion of V atom in GaSb lattice is
through meta-stable interstitial sites with an energy barrier of 0.6 eV. At a
low V concentration x = 0.0625, V atoms prefer a homogeneous distribution and
an antiferromagnetic coupling among them. However, starting from x = 0.5, the
magnetic coupling among V atoms changes to be ferromagnetic, due to enhanced
superexchange interaction between eg and t2g states of neighbouring V atoms. At
the extreme limiting of x = 1.00, we found that Zinc-blende VSb as well as its
analogs VAs and VP are intrinsic ferromagneitc semiconductors, with a large
change of light absorption at the curie temperature. These results indicate
that Ga1-xVxSb compounds can provide a platform to design the new electronic,
spintronic and optoelectronic devices.",2001.02054v1
2021-07-02,Negative thermal expansion and itinerant ferromagnetism in Mn$_{1.4}$Fe$_{3.6}$Si$_{3}$,"We report the thermal expansion, critical behavior, magnetocaloric effect
(MCE), and magnetoresistance ($MR$) on the polycrystalline
Mn$_{1.4}$Fe$_{3.6}$Si$_{3}$ compound around the ferromagnetic transition. A
large negative volume thermal expansion ($\alpha_{\rm V}\sim -20 \times
10^{-6}$ K$^{-1}$) is observed across the transition temperature with a strong
anisotropic variation of lattice parameters in the $ab$-plane. The anisotropic
magnetoelasticity arises from the competition between magnetic ordering and
structural deformation which could be responsible for the large MCE ($\Delta
S_{\rm m} \simeq -6$ J/Kg-K) across the magnetic transition in this compound.
The large and negative $MR$ ($\sim -3\%$ in 80 kOe) is also observed at the
transition temperature which can be attributed to the suppression of spin
disorder. Further, the Rhodes-Wolfarth ratio (RWR $> 1$) and identical field
dependence of $MR$ and MCE isotherms indicate the itinerant character of the
$3d$ electrons. The critical exponents determined from the analysis of
magnetization and MCE are consistent with the quasi-two-dimensional (2D) Ising
model with long range exchange interactions which decays as $J(r)\sim
r^{-3.41}$. This unconventional quasi-2D Ising character with long-range
interactions can be ascribed to strong $ab$-plane anisotropy and the
delocalized $3d$ electrons in the studied compound.",2107.01245v1
2021-07-11,Exploring low lattice thermal conductivity materials using chemical bonding principles,"Semiconductors with very low lattice thermal conductivities are highly
desired for applications relevant to thermal energy conversion and management,
such as thermoelectrics and thermal barrier coatings. Although the crystal
structure and chemical bonding are known to play vital roles in shaping heat
transfer behavior, material design approaches of lowering lattice thermal
conductivity using chemical bonding principles are uncommon. In this work, we
present an effective strategy of weakening interatomic interactions and
therefore suppressing lattice thermal conductivity based on chemical bonding
principles and develop a high-efficiency approach of discovering low
$\kappa_{\rm L}$ materials by screening the local coordination environments of
crystalline compounds. The followed first-principles calculations uncover 30
hitherto unexplored compounds with (ultra)low lattice thermal conductivities
from thirteen prototype crystal structures contained in the inorganic crystal
structure database. Furthermore, we demonstrate an approach of rationally
designing high-performance thermoelectrics by additionally incorporating
cations with stereochemically active lone-pair electrons. Our results not only
provide fundamental insights into the physical origin of the low lattice
thermal conductivity in a large family of copper-based compounds but also offer
an efficient approach to discovery and design materials with targeted thermal
transport properties.",2107.04955v1
2021-07-11,"Electronic structure of $A$Co$_2$As$_2$ ($A=$ Ca, Sr, Ba, Eu) studied using angle-resolved photoemission spectroscopy and theoretical calculations","We present a comprehensive study of the low-energy band structure and Fermi
surface (FS) topology of $A$Co$_2$As$_2$ ($A=$ Ca, Sr, Ba, Eu) using
high-resolution angle-resolved photoemission spectroscopy. The experimental FS
topology and band dispersion data are compared with theoretical full-potential
linearized augmented-plane-wave (FP-LAPW) calculations, which yielded
reasonably good agreement. We demonstrate that the FS maps of $A$Co$_2$As$_2$
are significantly different from those of the parent compounds of Fe-based
high-temperature superconductors. Further, the FSs of CaCo$_2$As$_2$ do not
show significant changes across its antiferromagnetic transition temperature.
The band dispersions extracted in different momentum $(k_{\it x}, k_{\it y})$
directions show a small electron pocket at the center and a large electron
pocket at the corner of the Brillouin zone (BZ). The absence of the hole FS in
these compounds does not allow nesting between pockets at the Fermi energy
({\it E}$_{\rm F}$), which is in contrast to $A$Fe$_2$As$_2$-type parent
compounds of the iron-based superconductors. Interestingly, we find that the
hole bands are moved 300--400~meV below $E_{\rm F}$ depending on the $A$
element. Moreover, the existence of nearly flat bands in the vicinity of
$E_{\rm F}$ are consistent with the large density of states at $E_{\rm F}$.
These results are important to understand the physical properties as well as
the possibility of the emergence of superconductivity in related materials.",2107.04961v1
2021-07-13,Motion-Aware Robotic 3D Ultrasound,"Robotic three-dimensional (3D) ultrasound (US) imaging has been employed to
overcome the drawbacks of traditional US examinations, such as high
inter-operator variability and lack of repeatability. However, object movement
remains a challenge as unexpected motion decreases the quality of the 3D
compounding. Furthermore, attempted adjustment of objects, e.g., adjusting
limbs to display the entire limb artery tree, is not allowed for conventional
robotic US systems. To address this challenge, we propose a vision-based
robotic US system that can monitor the object's motion and automatically update
the sweep trajectory to provide 3D compounded images of the target anatomy
seamlessly. To achieve these functions, a depth camera is employed to extract
the manually planned sweep trajectory after which the normal direction of the
object is estimated using the extracted 3D trajectory. Subsequently, to monitor
the movement and further compensate for this motion to accurately follow the
trajectory, the position of firmly attached passive markers is tracked in
real-time. Finally, a step-wise compounding was performed. The experiments on a
gel phantom demonstrate that the system can resume a sweep when the object is
not stationary during scanning.",2107.05998v1
2021-07-15,"Magnetic properties of {M$_4$} coordination clusters with different magnetic cores (M=Co, Mn)","We present a joint experimental and theoretical characterization of the
magnetic properties of coordination clusters with an antiferromagnetic core of
four magnetic ions. Two different compounds are analyzed, with Co and Mn ions
in the core. While both molecules are antiferromagnetic, they display different
sensitivities to external magnetic field, according to the different strength
of the intra-molecular magnetic coupling. In particular, the dependence of the
magnetization versus field of the two molecules switches with temperatures: at
low temperature the magnetization is smaller in \{Mn$_4$\}, while the opposite
happens at high temperature. Through a detailed analysis of the electronic and
magnetic properties of the two compounds we identify a stronger magnetic
interaction between the magnetic ions in \{Mn$_4$\} with respect to \{Co$_4$\}.
Moreover \{Co$_4$\} displays not negligible spin-orbit related effects that
could affect the spin lifetime in future antiferromagnetic spintronic
applications. We highlight the necessity to account for these spin-orbit
effects for a reliable description of these compounds.",2107.07237v2
2021-07-16,Exploiting generative self-supervised learning for the assessment of biological images with lack of annotations: a COVID-19 case-study,"Computer-aided analysis of biological images typically requires extensive
training on large-scale annotated datasets, which is not viable in many
situations. In this paper we present GAN-DL, a Discriminator Learner based on
the StyleGAN2 architecture, which we employ for self-supervised image
representation learning in the case of fluorescent biological images. We show
that Wasserstein Generative Adversarial Networks combined with linear Support
Vector Machines enable high-throughput compound screening based on raw images.
We demonstrate this by classifying active and inactive compounds tested for the
inhibition of SARS-CoV-2 infection in VERO and HRCE cell lines. In contrast to
previous methods, our deep learning based approach does not require any
annotation besides the one that is normally collected during the sample
preparation process. We test our technique on the RxRx19a Sars-CoV-2 image
collection. The dataset consists of fluorescent images that were generated to
assess the ability of regulatory-approved or in late-stage clinical trials
compound to modulate the in vitro infection from SARS-CoV-2 in both VERO and
HRCE cell lines. We show that our technique can be exploited not only for
classification tasks, but also to effectively derive a dose response curve for
the tested treatments, in a self-supervised manner. Lastly, we demonstrate its
generalization capabilities by successfully addressing a zero-shot learning
task, consisting in the categorization of four different cell types of the
RxRx1 fluorescent images collection.",2107.07761v2
2021-07-27,"Pressure-induced anomalies in the magnetic transitions of the exotic multiferroic material, Tb2BaNiO5","We have studied the influence of external pressure up to 1 GPa on the
magnetic transitions of the orthorhombic Haldane-spin chain compound Tb2BaNiO5
an exotic multiferroic material. This parent compound is known to undergo
N\'eel ordering at TN1= 63 K and another magnetic transition at TN2= 25K at
which ferroelectricity sets in, however, without any change in the magnetic
symmetry, but with only a sharp change in the canting angle of Tb 4f and Ni 3d
magnetic moments. There is a subtle difference in the antiferromagnetic state
above and below TN2, which is supported by the fact that there is a
metamagnetic transition below TN2only (for 5 K, at about 60 kOe). We report
here that, with the application of external pressure, there is an upward shift
of TN1, while TN2 shifts towards lower temperatures. It is interesting that the
two magnetic transitions in the same compound behave differently under pressure
and the opposite behavior at TN2 is attributed to local distortion leading to
ferroelectricity. The results are augmented by temperature dependent x-ray
diffraction and positive chemical pressure studies. The chemical pressure
caused by the isoelectronic doping at Ba site by Sr reduces both the transition
temperatures. Clearly, the external pressure favors antiferromagnetic coupling
(that is, leading to TN1 enhancement), whereas the chemical pressure reduces
TN1, suggesting important role of the changes in local hybridization induced by
doping on magnetism in this material.",2107.12729v1
2017-04-20,"Electronic structure of RSb (R = Y, Ce, Gd, Dy, Ho, Tm, Lu) studied by angle-resolved photoemission spectroscopy","We use high resolution angle-resolved photoemission spectroscopy (ARPES) and
electronic structure calculations to study the electronic properties of
rare-earth monoantimonides RSb (R = Y, Ce, Gd, Dy, Ho, Tm, Lu). The
experimentally measured Fermi surface (FS) of RSb consists of at least two
concentric hole pockets at the $\Gamma$ point and two intersecting electron
pockets at the $X$ point. These data agree relatively well with the electronic
structure calculations. Detailed photon energy dependence measurements using
both synchrotron and laser ARPES systems indicate that there is at least one
Fermi surface sheet with strong three-dimensionality centered at the $\Gamma$
point. Due to the ""lanthanide contraction"", the unit cell of different
rare-earth monoantimonides shrinks when changing rare-earth ion from CeSb to
LuSb. This results in the differences in the chemical potentials in these
compounds, which is demonstrated by both ARPES measurements and electronic
structure calculations. Interestingly, in CeSb, the intersecting electron
pockets at the $X$ point seem to be touching the valence bands, forming a
four-fold degenerate Dirac-like feature. On the other hand, the remaining
rare-earth monoantimonides show significant gaps between the upper and lower
bands at the $X$ point. Furthermore, similar to the previously reported results
of LaBi, a Dirac-like structure was observed at the $\Gamma$ point in YSb,
CeSb, and GdSb, compounds showing relatively high magnetoresistance. This
Dirac-like structure may contribute to the unusually large magnetoresistance in
these compounds.",1704.06237v1
2017-04-28,Experimental probe on the production of $^{97}$Ru from $^{7}$Li+$^{93}$Nb reaction: A study on the precompound emissions,"Background: Interaction of weakly bound heavy-ions with an intermediate or
heavy target is not yet understood completely due to the scarcity of
experimental data. In order to develop a clear understanding of breakup fusion
or preequilibrium emission even at low energy range, 3--10 MeV/nucleon, more
experimental investigations are necessary. Purpose: Study of reaction
mechanisms involved in the weakly bound heavy-ion induced reaction, $^7$Li +
$^{93}$Nb, at low energies by measuring the production cross sections of the
residual radionuclides. Method: Natural niobium ($^{93}$Nb) foil, backed by
aluminium (Al) catcher, arranged in a stack was bombarded by $^{7}$Li ions of
20-45 MeV energy. Activity of the residues produced in each $^{93}$Nb target
was measured by off-line $\gamma$-ray spectrometry after the end of bombardment
(EOB) and cross sections were calculated. Experimental cross sections were
compared with those computed using compound and precompound models. Results: In
general, measured excitation functions of all residues produced in $^{7}$Li +
$^{93}$Nb reaction showed good agreement with the model calculations based on
Hauser-Feshbach formalism and exciton model for compound and precompound
processes, respectively. Significant preequilibrium emission of neutrons was
observed at the relatively high energy tail of the excitation function of
$^{97}$Ru. Conclusions: Preequilibrium process played an important role for the
enhancement of cross-section in $xn$ reaction channel over the compound
reaction mechanism at higher energies for $^{7}$Li + $^{93}$Nb reaction.
Additionally, indirect evidence of incomplete or breakup fusion was also
perceived.",1704.08811v1
2017-05-25,Topological Weyl and Node-Line Semimetals in Ferromagnetic Vanadium-Phosphorous-Oxide $β$-V$_2$OPO$_4$ Compound,"We propose that the topological semimetal features can co-exist with
ferromagnetic ground state in vanadium-phosphorous-oxide $\beta$-V$_2$OPO$_4$
compound from first-principles calculations. In this magnetic system with
inversion symmetry, the direction of magnetization is able to manipulate the
symmetric protected band structures from a node-line type to a Weyl one in the
presence of spin-orbital-coupling. The node-line semimetal phase is protected
by the mirror symmetry with the reflection-invariant plane perpendicular to
magnetic order. Within mirror symmetry breaking due to the magnetization along
other directions, the gapless node-line loop will degenerate to only one pair
of Weyl points protected by the rotational symmetry along the magnetic axis,
which are largely separated in momentum space. Such Weyl semimetal phase
provides a nice candidate with the minimum number of Weyl points in a condensed
matter system. The results of surface band calculations confirm the non-trivial
topology of this proposed compound. This findings provide a realistic candidate
for the investigation of topological semimetals with time-reversal symmetry
breaking, particularly towards the realization of quantum anomalous Hall effect
in Weyl semimetals.",1705.09234v1
2018-07-03,Etude de la composition chimique et du potentiel pharmacologique associ{é} de Phyllanthus amarus Schum et Thonn (1827),"In August 2013, the French pharmacopoeia was enriched with 43 plants used in
French overseas territories, including 15 proposed by APLAMEDAROM association
of Guadeloupe. However, for most of them, no data on the chemical composition,
qualitatively and quantitatively is available in the literature for these
specimens; this is an issue to their commercialization in dispensary,
pharmacists wishing to know their composition in order to avoid the problems of
dosage and drug interactions. Among these plants, Phyllanthus amarus Schum. \&
Thonn. (1827), commonly called 'Grenn anba f{\`e}y' [1], is well known for its
potent medicinal properties especially hepatoprotective, antidiabetic,
antiviral (flu), anti-inflammatory, anti-cholesterol [2]. In Guadeloupe, this
plant is generally used freshly harvested in infusion but also in aqueous
decoction [3]. Besides, these studies are conducted in association with
APLAMEDAROM association in order to identify the polar constituents and then to
understand better the origin of the observed properties. Therefore, using
UHPLC-MS, we were able to identify the presence of bioactive polyphenolic
compounds, including phyllanthin, rutin and gallic acid. Phyllanthin,
characteristic of the specie, is a very active lignan with high antioxidant,
hepatoprotective and anticancer properties [2]. Rutin is known for its
antioxidant and anti-hypertensive properties [2]. Gallic acid is distinguished
by antioxidant, anti-inflammatory, antidiabetic, antiviral and anticancer
properties and has the advantage of being a bioavailable compound. Similarly,
many compounds never listed to date in this specie were also highlighted and
are currently purified.",1807.01039v1
2018-07-11,"Magnetodielectric coupling in a Ru-based 6H-perovskite, Ba3NdRu2O9","A large spin-orbit coupling is a way to control strong magnetodielectric (MD)
coupling in a higher d-orbital materials. However reports are rare on such
compounds due to often leaky conductive behavior. Here, we demonstrate MD
coupling in a Ru-based 6H-perovskite system, Ba3NdRu2O9. The rare-earth ion in
a 6H-perovskite makes the system insulating enough to carry out MD
investigation. The compound is ferromagnetically ordered below 24 K (TC),
followed by another magnetic feature at T~ 17 K (T2). The dielectric constant
clearly traces the magnetic ordering, manifesting a peak at the onset of TC,
which is suppressed by the application of an external magnetic field (H). The
results indicate the presence of MD coupling in this compound, which is further
confirmed by the H-dependence of the dielectric constant. Interestingly, a
cross-over of the sign of MD coupling is observed at T ~ T2. We conclude that
two different mechanism controls the MD coupling which yields positive and
negative coupling, respectively. Both mechanisms are competing as a function of
temperature and magnetic field. This brings us a step closer to design and
control the magnetodielectric effect in 6H-perovskites containing higher
d-orbital elements.",1807.04231v2
2018-10-26,Essential properties of Li/Li$^+$ graphite intercalation compounds,"The essential properties of graphite-based 3D systems are thoroughly
investigated by the first-principles method. Such materials cover a simple
hexagonal graphite, a Bernal graphite, and the stage-1 to stage-4 Li/Li$^+$
graphite intercalation compounds. The delicate calculations and the detailed
analyses are done for their optimal stacking configurations, bong lengths,
interlayer distances, free electron $\&$ hole densities, Fermi levels,
transferred charges in chemical bondings, atom- or ion-dominated energy bands,
spatial charge distributions and the significant variations after
intercalation, Li-/Li$^+$- $\&$ C-orbital-decomposed DOSs. The above-mentioned
physical quantities are sufficient in determining the critical orbital
hybridizations responsible for the unusual fundamental properties. How to
dramatically alter the low-lying electronic structures by modulating the
quest-atom/quest-ion concentration is one of focuses, e.g., the drastic changes
on the Fermi level, band widths, and number of energy bands. The theoretical
predictions on the stage-n-dependent band structures could be examined by the
high-resolution angle-resolved photoemission spectroscopy (ARPES). Most
important, the low-energy DOSs near the Fermi might provide the reliable data
for estimating the free carrier density due to the interlayer atomic
interactions or the quest-atom/quest-ion intercalation. The van Hove
singularities, which mainly arise from the critical points in
energy-wave-vector space, could be directly examined by the experimental
measurements of scanning tunneling spectroscopy (STS). Their features should be
very useful in distinguishing the important differences among the stage-$n$
graphite intercalation compounds, and the distinct effects due to the atom or
ion decoration.",1810.11166v1
2019-01-08,Ferromagnetic ordering along the hard axis in the Kondo lattice YbIr3Ge7,"Ferromagnetic Kondo lattice compounds are far less common than their
antiferromagnetic analogs. In this work, we report the discovery of a new
ferromagnetic Kondo lattice compound, YbIr3Ge7. Like almost all ferromagnetic
Kondo lattice systems, YbIr3Ge7 shows magnetic order with moments aligned
orthogonal to the crystal electric field (CEF) easy axis. YbIr3Ge7 is unique in
that it is the only member of this class of compounds that crystallizes in a
rhombohedral structure with a trigonal point symmetry of the magnetic site, and
it lacks broken inversion symmetry at the local moment site. AC magnetic
susceptibility, magnetization, and specific heat measurements show that
YbIr3Ge7 has a Kondo temperature TK = 14 K and a Curie temperature TC = 2.4 K.
Ferromagnetic order occurs along the crystallographic [100] hard CEF axis
despite the large CEF anisotropy of the ground state Kramers doublet with a
saturation moment along [001] almost four times larger than the one along
[100]. This implies that a mechanism which considers the anisotropy in the
exchange interaction to explain the hard axis ordering is unlikely. On the
other hand, the broad second-order phase transition at TC favors a
fluctuation-induced mechanism.",1901.02489v1
2019-01-14,First-principles calculations of the magnetocrystalline anisotropy of the prototype 2:17 cell boundary phase Y(Co$_{1-x-y}$Fe$_x$Cu$_y$)$_5$,"We present a computational study of the compound
Y(Co$_{1-x-y}$Fe$_x$Cu$_y$)$_5$ for 0 $\leq x,y \leq 0.2$. This compound was
chosen as a prototype for investigating the cell boundary phase believed to
play a key role in establishing the high coercivity of commercial Sm-Co 2:17
magnets. Using density-functional theory, we have calculated the magnetization
and magnetocrystalline anisotropy at zero temperature for a range of
compositions, modeling the doped compounds within the coherent potential
approximation. We have also performed finite temperature calculations for
YCo$_5$, Y(Co$_{0.838}$Cu$_{0.162}$)$_5$ and
Y(Co$_{0.838}$Fe$_{0.081}$Cu$_{0.081}$)$_5$ within the disordered local moment
picture. Our calculations find that substituting Co with small amounts of
either Fe or Cu boosts the magnetocrystalline anisotropy $K$, but the change in
$K$ depends strongly on the location of the dopants. Furthermore, the
calculations do not show a particularly large difference between the magnetic
properties of Cu-rich Y(Co$_{0.838}$Cu$_{0.162}$)$_5$ and equal Fe-Cu
Y(Co$_{0.838}$Fe$_{0.081}$Cu$_{0.081}$)$_5$, despite these two compositions
showing different coercivity behavior when found in the cell boundary phase of
2:17 magnets. Our study lays the groundwork for studying the rare earth
contribution to the anisotropy of Sm(Co$_{1-x-y}$Fe$_x$Cu$_y$)$_5$, and also
shows how a small amount of transition metal substitution can boost the
anisotropy field of YCo$_5$.",1901.04185v1
2019-01-18,Layered semiconductor EuTe 4 with charge density wave order in square tellurium sheets,"We report a novel quasi-two dimensional compound of EuTe4 hosting charge
density waves (CDW) instability. The compound has a crystallographic structure
in a orthorhombic space group Pmmn (No.59) with cell parameters a =
4.6347(2){\AA}, b = 4.5119(2){\AA}, c = 15.6747(10){\AA} at room temperature.
The pristine structure contains consecutive near-square Te sheets separated by
corrugated Eu-Te slabs. Upon cooling, the compound experiences a phase
transition near 255 K. X-ray crystallographic analysis and transmission
electron microscopy (TEM) measurements reveal strong structural distortions in
the low temperature phase, showing a superstructure with a periodic formation
of Te-trimers in the monolayer Te sheets, yielding evidence for the formation
of CDW order. The charge transport properties show a semiconducting behavior in
the CDW state. Density functional theory calculations reveals a Fermi surface
nesting driven instability with a nesting vector in good agreement with the one
observed experimentally. Our finding provides a promising system for the study
of CDW driven 2D semiconducting mechanisms, which would shed a new light on
exploring novel 2D semiconductors with collective electronic states.",1901.06061v1
2019-01-29,"Chemical pressure effect on the optical conductivity of the nodal-line semimetals ZrSi$Y$ ($Y$=S, Se, Te) and ZrGe$Y$ ($Y$=S, Te)","ZrSiS is a nodal-line semimetal, whose electronic band structure contains a
diamond-shaped line of Dirac nodes. We carried out a comparative study on the
optical conductivity of ZrSiS and related compounds ZrSiSe, ZrSiTe, ZrGeS, and
ZrGeTe by reflectivity measurements over a broad frequency range combined with
density functional theory calculations. The optical conductivity exhibits a
distinct U shape, ending at a sharp peak at around 10000~cm$^{-1}$ for all
studied compounds, except for ZrSiTe. The U shape of the optical conductivity
is due to transitions between the linearly dispersing bands crossing each other
along the nodal line. The sharp high-energy peak is related to transitions
between almost parallel bands, and its energy position depends on the
interlayer bonding correlated with the $c$/$a$ ratio, which can be tuned by
either chemical or external pressure. For ZrSiTe, another pair of crossing
bands appears in the vicinity of the Fermi level, corrugating the nodal-line
electronic structure and leading to the observed difference in optical
conductivity. The findings suggest that the Dirac physics in Zr$XY$ compounds
with $X$=Si, Ge and $Y$=S, Se, Te is closely connected to the interlayer
bonding.",1901.10256v2
2019-01-31,"Successive magnetic ordering sequence observed from muon spin rotation in T'-structured R2CuO4 (R = Eu, Nd)","The magnetic behavior and effects of oxygen-reduction annealing on the
magnetism of T'-structured R2CuO4 (R = Eu and Nd), which is the parent compound
of electron-doped cuprate superconductors, have been investigated from muon
spin rotation (muSR) measurements. In the muon time spectra of as-sintered
R2CuO4, an oscillation component with a small amplitude and a dominant
exponential-type decay component were observed for the temperature range
between 150 K and TN1 (=250-270 K). This observation suggests an inhomogeneous
magnetic phase of a fluctuating spin state and a locally ordered spin state at
these temperatures. With decreasing temperature,the small oscillation component
disappears, and the exponential one develops below 150 K. Upon further cooling,
well-defined oscillation spectra corresponding to uniform long-ranged magnetic
order emerge below TN2 = 110 K. Except for the absence of the small oscillation
component, similar magnetic behavior is confirmed for the annealed compounds.
Therefore, the successive development of magnetism characterized by the
fluctuating spin state over a wide temperature range is a common feature for
T'-R2CuO4. We discuss a possible picture for the ordering sequence in T'-R2CuO4
and the origin of the small oscillation component in the as-sintered compounds
from the viewpoint of local defects.",1901.11233v1
2019-04-01,From Trivial Kondo Insulator Ce$_3$Pt$_3$Bi$_4$ to Topological Nodal-line Semimetal Ce$_3$Pd$_3$Bi$_4$,"Using the density functional theory combined with dynamical mean-field
theory, we have performed systematic study of the electronic structure and its
band topology properties of Ce$_3$Pt$_3$Bi$_4$ and Ce$_3$Pd$_3$Bi$_4$. At high
temperatures ($\sim$290K), the electronic structures of both compounds resemble
the open-core 4$f$ density functional calculation results. For
Ce$_3$Pt$_3$Bi$_4$, clear hybridization gap can be observed below 72K, and its
coherent momentum-resolved spectral function below 18K exhibits an
topologically trivial indirect gap of $\sim$6 meV and resembles density
functional band structure with itinerant 4$f$ state. For Ce$_3$Pd$_3$Bi$_4$, no
clear hybridization gap can be observed down to 4K, and its momentum-resolved
spectral function resembles electron-doped open-core 4$f$ density functional
calculations. The band nodal points of Ce$_3$Pd$_3$Bi$_4$ at 4K are protected
by the gliding-mirror symmetry and form ring-like structure. Therefore, the
Ce$_3$Pt$_3$Bi$_4$ compound is topologically trivial Kondo insulator while the
Ce$_3$Pd$_3$Bi$_4$ compound is topological nodal-line semimetal.",1904.00675v2
2019-04-05,"Osmium-Nitrosyl Oxalato-Bridged Lanthanide-Centered Pentanuclear Complexes - Synthesis, Crystal Structures and Magnetic Properties","A series of pentanuclear heterometallic coordination compounds of the general
formula (Bu 4 N) 5 [Ln{Os(NO)($\mu$-ox)-Cl 3 } 4 (H 2 O) n ] [Ln = Y (for 2)
and Dy (for 3) when n = 0; Ln = Dy (for 3), Tb (for 4), and Gd (for 5) when n =
1] were synthesized by the reaction of the precursor (Bu 4 N) 2 [Os(NO)(ox)-Cl
3 ] (1) with the respective lanthanide(III) (Gd, Tb, Dy) or yttrium(III)
chloride. For the five new complexes, the coordination numbers eight or nine
are found for the central metal ion. The compounds were fully characterized by
elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis,
magnetic susceptibility measurements, and ESI mass spectrometry. In addition,
compound 1 was studied by UV/Vis spectroscopy and cyclic voltammetry. The X-ray
dif-fraction analyses revealed that the anionic complexes consist of a
lanthanide or yttrium core bridged through oxalato li-gands to four octahedral
osmium-nitrosyl moieties. This picture , in which the central ion is
eight-coordinate, holds for",1904.02913v1
2019-04-11,Repurposing of Ring Framework through TR screening,"In the drug repurposing approach, the chemically diverse and potentially safe
molecules can be explored as therapeutic potential out of those originally
targeted indications. However, the intellectual property rights, and
competitive over-heating issue from sharing the same drug pipeline information
are drawback of the approach. In current paradigm of drug discovery, despite
approval of new chemical entity, the finding of a new ring system for drug
discovery have stagnated. In addition, there are still rarely used ring systems
from FDA approved drug that can be optimized and used for repurposing purpose.
In the present work, these rarely used drug ring system were re-purposed with
our bidirectional target and ring screening (TR- dual screening) approach
within our defined objectives. The TR-dual screening suggested RARbeta and
cyproheptadine as a pair of target and ring system. The selected ring system
was virtually grown with predefined criterion, ranking of molecular docking and
top score poses made us select test compounds for synthesis and biological
proof. Among the tested compounds, 6c proved RARbeta agonist activity. The
concept of TR dual optimization can contribute to picking either a compound
having acceptable ADMET profile or a target for a selected drug scaffold.",1904.09243v1
2019-04-23,Momentum-resolved lattice dynamics of parent and electron-doped Sr$_{2}$IrO$_{4}$,"The mixing of orbital and spin character in the wave functions of the $5d$
iridates has led to predictions of strong couplings among their lattice,
electronic and magnetic degrees of freedom. As well as realizing a novel
spin-orbit assisted Mott-insulating ground state, the perovskite iridate
Sr$_{2}$IrO$_{4}$ has strong similarities with the cuprate La$_{2}$CuO$_{4}$,
which on doping hosts a charge-density wave that appears intimately connected
to high-temperature superconductivity. These phenomena can be sensitively
probed through momentum-resolved measurements of the lattice dynamics, made
possible by meV-resolution inelastic x-ray scattering. Here we report the first
such measurements for both parent and electron-doped Sr$_{2}$IrO$_{4}$. We find
that the low-energy phonon dispersions and intensities in both compounds are
well described by the same nonmagnetic density functional theory calculation.
In the parent compound, no changes of the phonons on magnetic ordering are
discernible within the experimental resolution, and in the doped compound no
anomalies are apparent due to charge-density waves. These measurements extend
our knowledge of the lattice properties of (Sr$_{1-x}$La$_{x}$)$_{2}$IrO$_{4}$
and constrain the couplings of the phonons to magnetic and charge order.",1904.10391v2
2019-07-02,A comprehensive first-principles analysis of phonon thermal conductivity and electron-phonon coupling in different metals,"Separating electron and phonon thermal conductivity components is imperative
for understanding the principle thermal transport mechanisms in metals and
highly desirable in many applications. In this work, we predict the
mode-dependent electron and phonon thermal conductivities of 18 different
metals at room-temperature from first-principles. Our first-principles
predictions, in general, agree well with experimental data. We find that the
phonon thermal conductivity is in the range of 2 - 18 $W/mK$, which accounts
for 1% - 40% of the total thermal conductivity. It is also found that the
phonon thermal conductivities in transition metals and
transition-intermetallic-compounds (TICs) are non-negligible compared to noble
metals due to their high phonon group velocities. Besides, the electron-phonon
coupling effect on phonon thermal conductivity in transition metals and
intermetallic compounds is stronger than that of nobles, which is attributed to
the larger electron-phonon coupling constant with a high electron density of
state within Fermi window and high phonon frequency. The noble metals have
higher electron thermal conductivities compared to transition metals and TICs,
which is mainly due to the weak electron-phonon coupling in noble metals. It is
also shown that the Lorenz ratios of transition metals and
transition-intermetallic-compounds hold larger deviations from the Sommerfeld
value $L_0=2.44 \times 10^{-8} W \Omega K^{-2}$. We also find the mean free
paths (MFPs) for phonon (within 10 nm) are smaller than those of electron (5 -
25 nm). The electrical conductivity and electron thermal conductivity are
strongly related to the MFPs of the electron.",1907.01364v1
2019-07-21,Ascertaining hydrogen-abstraction reaction efficiencies of halogenated organic compounds on electron ionization mass spectrometry,"H-abstraction reactions occurring on electron ionization mass spectrometry
(EI-MS) are a long-standing and crucial topic in MS research. Yet some critical
relevant mechanisms are controversial and ambiguous, and information about the
EI-induced H-abstraction reactions of halogenated organic compounds (HOCs) is
completely in the dark. This study provides a systematic investigation of
H-abstraction reactions of HOCs taking place on EI source using
13C6-hexachlorobenzene (13C6-HCB) and 13C6-hexabromobenzene (13C6-HBB) as
exemplary compounds by gas chromatography high resolution mass spectrometry
(GC-HRMS). The H-abstraction efficiencies were evaluated with the MS signal
intensity ratios of ions with H-abstraction relative to the corresponding
original ions (without H-abstraction). Ion source temperatures, EI energies and
numbers of heavy isotope atoms (37Cl or 81Br) of isotopologues were
investigated in terms of their effects on the H-abstraction efficiencies. The
H-abstraction efficiencies of individual isotopologues generally decreased from
the first to the last isotopologues of respective ions, and those of individual
ions were different from each other, with the highest values of 0.017 and 0.444
for 13C6-HCB and 13C6-HBB, respectively. The overall H-abstraction efficiencies
involving all measured ions of 13C6-HCB and 13C6-HBB were 0.004 and 0.128,
respectively. EI energies and emission currents could impact the H-abstraction
efficiencies. The H-abstraction reactions were inferred to belong to
ion-molecule reactions. Some strategies were proposed for eliminating or
alleviating the interference triggered by the H-abstraction reactions on EI-MS
in identification of halogenated organic pollutants (HOPs). Our findings
provide a better understanding for the EI-induced H-abstraction reactions of
HOCs, and may benefit identification of HOPs in environmental analysis,
especially for novel HOPs.",1907.08904v1
2019-07-23,Magnetic structure and magnetoelastic coupling of GdNiSi3 and TbNiSi3,"The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows
interesting magnetic properties evolving with $R$ and metamagnetic transitions
under applied magnetic field for some of the compounds. The microscopic
magnetic structures must be determined to rationalize such rich behavior. Here,
resonant x-ray magnetic diffraction experiments are performed on single
crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic
unit cell matches the chemical cell below the N\'eel temperatures $T_{N}$ =
22.2 and 33.2 K, respectively. The magnetic structure is determined to be the
same for both compounds (magnetic space group $Cmmm'$). It features
ferromagnetic {\it ac} planes that are stacked in an antiferromagnetic $+-+-$
pattern, with the rare-earth magnetic moments pointing along the $\vec{a}$
direction, which contrasts with the $+--+$ stacking and moment direction along
the $\vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign
reversal of the coupling constant between second-neighbor $R$ planes as $R$ is
varied from Gd and Tb to Yb. The long {\it b} lattice parameter of GdNiSi$_{3}$
and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$,
pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice
expansion. A competition between distinct magnetic stacking patterns with
similar exchange energies tuned by the size of $R$ sets the stage for the
magnetic ground state instability observed along this series.",1907.09830v1
2019-10-24,Persistent gapless surface states in MnBi2Te4/Bi2Te3 superlattice antiferromagnetic topological insulator,"Magnetic topological quantum materials (TQMs) provide a fertile ground for
the emergence of fascinating topological magneto-electric effects. Recently,
the discovery of intrinsic antiferromagnetic (AFM) topological insulator
MnBi2Te4 that could realize quantized anomalous Hall effect and axion insulator
phase ignited intensive study on this family of TQM compounds. Here, we
investigated the AFM compound MnBi4Te7 where Bi2Te3 and MnBi2Te4 layers
alternate to form a superlattice. Using spatial- and angle-resolved
photoemission spectroscopy, we identified ubiquitous (albeit termination
dependent) topological electronic structures from both Bi2Te3 and MnBi2Te4
terminations. Unexpectedly, while the bulk bands show strong temperature
dependence correlated with the AFM transition, the topological surface states
show little temperature dependence and remain gapless across the AFM
transition. The detailed electronic structure of MnBi4Te7 and its temperature
evolution, together with the results of its sister compound MnBi2Te4, will not
only help understand the exotic properties of this family of magnetic TQMs, but
also guide the design for possible applications.",1910.11014v1
2012-09-27,Arbitrarily varying and compound classical-quantum channels and a note on quantum zero-error capacities,"We consider compound as well as arbitrarily varying classical-quantum channel
models. For classical-quantum compound channels, we give an elementary proof of
the direct part of the coding theorem. A weak converse under average error
criterion to this statement is also established. We use this result together
with the robustification and elimination technique developed by Ahlswede in
order to give an alternative proof of the direct part of the coding theorem for
a finite classical-quantum arbitrarily varying channels with the criterion of
success being average error probability. Moreover we provide a proof of the
strong converse to the random coding capacity in this setting.The notion of
symmetrizability for the maximal error probability is defined and it is shown
to be both necessary and sufficient for the capacity for message transmission
with maximal error probability criterion to equal zero. Finally, it is shown
that the connection between zero-error capacity and certain arbitrarily varying
channels is, just like in the case of quantum channels, only partially valid
for classical-quantum channels.",1209.6325v2
2014-06-11,Dynamic behavior of magnetic avalanches in the spin-ice compound Dy$_2$Ti$_2$O$_7$,"Avalanches of the magnetization, that is to say an abrupt reversal of the
magnetization at a given field, have been previously reported in the spin-ice
compound Dy$_{2}$Ti$_{2}$O$_{7}$. This out-of-equilibrium process, induced by
magneto-thermal heating, is quite usual in low temperature magnetization
studies. A key point is to determine the physical origin of the avalanche
process. In particular, in spin-ice compounds, the origin of the avalanches
might be related to the monopole physics inherent to the system. We have
performed a detailed study of the avalanche phenomena in three single crystals,
with the field oriented along the [111] direction, perpendicular to [111] and
along the [100] directions. We have measured the changing magnetization during
the avalanches and conclude that avalanches in spin ice are quite slow compared
to the avalanches reported in other systems such as molecular magnets. Our
measurements show that the avalanches trigger after a delay of about 500 ms and
that the reversal of the magnetization then occurs in a few hundreds of
milliseconds. These features suggest an unusual propagation of the reversal,
which might be due to the monopole motion. The avalanche fields seem to be
reproducible in a given direction for different samples, but they strongly
depend on the initial state of magnetization and on how the initial state was
achieved.",1406.2954v1
2018-02-24,Revealing the formation and electrochemical properties of bis(trifluoromethanesulfonyl) imide intercalated graphite with first-principles calculations,"Graphite has been reported to have anion as well as cation intercalation
capacities as both cathode and anode host materials for the dual ion battery.
In this work, we study the intercalation of bis(trifluoromethanesulfonyl) imide
(TFSI) anion from ionic liquid electrolyte into graphite with first-principles
calculations. We build models for TFSI-C$_n$ compounds with systematically
increasing unit cell sizes of graphene sheet and investigate their stabilities
by calculating the formation energy, resulting in the linear decrease and
arriving at the limit of stability. With identified unit cell sizes for stable
compound formation, we reveal that the interlayer distance and relative volume
expansion ratio of TFSI-C$_n$ increase as increasing the concentration of TFSI
intercalate during the charge process. The electrode voltage is determined to
be ranged from 3.8 V to 3.0 V at the specific capacity ranging from 30 mAh
g$^{-1}$ to 54 mAh g$^{-1}$ in agreement with experiment. Moreover, a very low
activation barrier of under 50 meV for TFSI migration and good electronic
conductivity give a proof of using these compounds as a promising cathode.
Through the analysis of charge transfer, we clarify the mechanism of TFSI-C$_n$
formation, and reveal new prospects for developing graphite based cathode.",1802.08775v1
2018-08-11,Compound Poisson Noise Sources in Diffusion-based Molecular Communication,"Diffusion-based molecular communication (DMC) is one of the most promising
approaches for realizing nano-scale communications for healthcare applications.
The DMC systems in in-vivo environments may encounter biological entities that
release molecules identical to the molecules used for signaling as part of
their functionality. Such entities in the environment act as external noise
sources from the DMC system's perspective. In this paper, the release of
molecules by biological external noise sources is particularly modeled as a
compound Poisson process. The impact of compound Poisson noise sources (CPNSs)
on the performance of a point-to-point DMC system is investigated. To this end,
the noise from the CPNS observed at the receiver is characterized. Considering
a simple on-off keying (OOK) modulation and formulating symbol-by-symbol
maximum likelihood (ML) detector, the performance of DMC system in the presence
of the CPNS is analyzed. For special case of CPNS in high-rate regime, the
noise received from the CPNS is approximated as a Poisson process whose rate is
normally distributed. In this case, it is proved that a simple single-threshold
detector (STD) is an optimal ML detector. Our results reveal that in general,
adopting the conventional simple homogeneous Poisson noise model may lead to
overly optimistic performance predictions, if a CPNS is present.",1808.03876v2
2018-08-13,Electrohydrodynamics of compound droplet in a microfluidic confinement,"The present study deals with the dynamics of a double emulsion confined in a
microchannel under the presence of a uniform electric field. Towards
investigating the non-trivial electrohydrodynamics of a compound droplet,
confined in between two parallel plate electrodes, a phase field approach has
been adopted. Under the assumption of negligible fluid inertia and small shape
deformation, an asymptotic model is also developed to predict the transient as
well as the steady state droplet dynamics in the limiting case of an unbounded
suspending medium. The phases involved are either assumed to be perfect
dielectric or leaky dielectric. Subsequent investigation shows that shape
deformation of either of the interfaces of the droplet increase with rise in
the channel confinement for a perfect dielectric system. However, for a leaky
dielectric system, the deformation of inner droplet and outer droplet can
increase or decrease with the rise in channel confinement depending on the
electric properties (conductivity and permittivity) of the system. The present
study further takes into account the effect of eccentricity of the inner
droplet. Depending on the relative magnitude of the permittivity and
conductivity of the system, the inner droplet, if eccentrically located, may
exhibit a to and fro or a simple translational motion. It is seen that increase
in the channel confinement results in a translational motion of the inner
droplet thus rendering its motion independent of any electrical properties.
Since the compound droplet model approximately mimics the structure of a cell,
the current investigation is expected to provide a significant impact towards
predicting the effect of an externally imposed electrical field on the dynamics
of a cell in any fluidic confinement and hence has the potential towards
widespread applications in the field of medical diagnostics.",1808.04110v1
2018-08-16,Unravelling the mechanism of the semiconducting-like behavior and its relation to superconductivity in (CaFe$_{1-x}$Pt$_{x}$As)$_{10}$Pt$_{3}$As$_{8}$,"The temperature-dependence of the in-plane optical properties of
(CaFe$_{1-x}$Pt$_{x}$As)$_{10}$Pt$_{3}$As$_{8}$ have been investigated for the
undoped ($x=$0) parent compound, and the optimally-doped ($x=$0.1)
superconducting material ($T_{c}\simeq$ 12 K) over a wide frequency range. The
optical conductivity has been described using two free-carrier (Drude)
components, in combination with oscillators to describe interband transitions.
At room temperature, the parent compound may be described by a strong, broad
Drude term, as well as a narrow, weaker Drude component. Below the structural
and magnetic transitions at $\simeq$ 96 and 83 K, respectively, strength is
transferred from the free-carrier components into a bound excitation at
$\simeq$ 1000 cm$^{-1}$, and the material exhibits semiconducting-like
behavior. In the optimally-doped sample, at room temperature the optical
properties are again described by narrow and broad Drude responses comparable
to the parent compound; however, below $T^\ast \simeq$ 100 K, strength from the
narrow Drude is transferred into a newly-emergent low-energy peak at $\simeq$
120 cm$^{-1}$, which arises from a localization process, resulting in
semiconducting-like behavior. Interestingly, below $T_{c}$, this peak also
contributes to the superfluid weight, indicating that some localized electrons
condense into Cooper pairs; this observation may provide insight into the
pairing mechanism in iron-based superconductors.",1808.05682v2
2019-02-04,"Magneto-structural properties of the layered quasi-2D triangular-lattice antiferromagnets Cs$_2$CuCl$_{4-x}$Br$_x$ for ${x}$ = 0,1,2 and 4","We present a study of the magnetic susceptibility $\chi_{mol}$ under variable
hydrostatic pressure on single crystals of Cs$_2$CuCl$_{4-x}$Br$_x$. This
includes the border compounds \textit{x} = 0 and 4, known as good realizations
of the distorted triangular-lattice spin-1/2 Heisenberg antiferromagnet, as
well as the isostructural stoichiometric systems Cs$_2$CuCl$_{3}$Br$_1$ and
Cs$_2$CuCl$_{2}$Br$_2$. For the determination of the exchange coupling
constants $J$ and $J^{\prime}$, $\chi_{mol}$ data were fitted by a
$J-J^{\prime}$ model \cite{Schmidt2015}. Its application, validated for the
border compounds, yields a degree of frustration $J^{\prime}$/$J$ = 0.47 for
Cs$_2$CuCl$_3$Br$_1$ and $J^{\prime}$/$J$ $\simeq$ 0.63 - 0.78 for
Cs$_2$CuCl$_2$Br$_2$, making these systems particular interesting
representatives of this family. From the evolution of the magnetic
susceptibility under pressure up to about 0.4\,GPa, the maximum pressure
applied, two observations were made for all the compounds investigated here.
First, we find that the overall energy scale, given by $J_c = (J^2$ +
$J^{\prime 2}$)$^{1/2}$, increases under pressure, whereas the ratio
$J^{\prime}$/$J$ remains unchanged in this pressure range. These experimental
observations are in accordance with the results of DFT calculations performed
for these materials. Secondly, for the magnetoelastic coupling constants,
extraordinarily small values are obtained. We assign these observations to a
structural peculiarity of this class of materials.",1902.01099v1
2019-02-04,Position Representation of Effective Electron-Electron Interactions in Solids,"An essential ingredient in many model Hamiltonians, such as the Hubbard
model, is the effective electron-electron interaction $U$, which enters as
matrix elements in some localized basis. These matrix elements provide the
necessary information in the model, but the localized basis is incomplete for
describing $U$. We present a systematic scheme for computing the manifestly
basis-independent dynamical interaction in position representation, $U({\bf
r},{\bf r}';\omega)$, and its Fourier transform to time domain, $U({\bf r},{\bf
r}';\tau)$. These functions can serve as an unbiased tool for the construction
of model Hamiltonians. For illustration we apply the scheme within the
constrained random-phase approximation to the cuprate parent compounds
La$_2$CuO$_4$ and HgBa$_2$CuO$_4$ within the commonly used 1- and 3-band
models, and to non-superconducting SrVO$_{3}$ within the $t_{2g}$ model. Our
method is used to investigate the shape and strength of screening channels in
the compounds. We show that the O 2$p_{x,y}-$Cu 3$d_{x^2-y^2}$ screening gives
rise to regions with strong attractive static interaction in the minimal
(1-band) model in both cuprates. On the other hand, in the minimal ($t_{2g}$)
model of SrVO$_3$ only regions with a minute attractive interaction are found.
The temporal interaction exhibits generic damped oscillations in all compounds,
and its time-integral is shown to be the potential caused by inserting a frozen
point charge at $\tau=0$. When studying the latter within the three-band model
for the cuprates, short time intervals are found to produce a negative
potential.",1902.01176v1
2019-02-14,Nitrogen-containing Anions and Tholin Growth in Titan's Ionosphere: Implications for Cassini CAPS-ELS Observations,"The Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) instrument
onboard Cassini revealed an unexpected abundance of negative ions above 950 km
in Titan's ionosphere. \textit{In situ} measurements indicated the presence of
negatively charged particles with mass-over-charge ratios up to 13,800
\textit{u/q}. At present, only a handful of anions have been characterized by
photochemical models, consisting mainly of C$_n$H$^-$ carbon chain and
C$_{n-1}$N$^-$ cyano compounds ($n=2-6$); their formation occurring essentially
through proton abstraction from their parent neutral molecules. However,
numerous other species have yet to be detected and identified. Considering the
efficient anion growth leading to compounds of thousands of \textit{u/q}, it is
necessary to better characterize the first light species. Here, we present new
negative ion measurements with masses up to 200 \textit{u/q} obtained in an
\ce{N2}:\ce{CH4} dusty plasma discharge reproducing analogous conditions to
Titan's ionosphere. We perform a comparison with high altitude CAPS-ELS
measurements near the top of Titan's ionosphere from the T18 encounter. The
main observed peaks are in agreement with the observations. However, a number
of other species (\textit{e.g.} \ce{CNN-}, \ce{CHNN-}) previously not
considered suggests an abundance of N-bearing compounds, containing two or
three nitrogen atoms, consistent with certain adjacent doubly-bonded nitrogen
atoms found in tholins. These results suggest that an N-rich incorporation into
tholins may follow mechanisms including anion chemistry, further highlighting
the important role of negative ions in Titan's aerosol growth.",1902.05585v1
2019-06-12,Developing an improved Crystal Graph Convolutional Neural Network framework for accelerated materials discovery,"The recently proposed crystal graph convolutional neural network (CGCNN)
offers a highly versatile and accurate machine learning (ML) framework by
learning material properties directly from graph-like representations of
crystal structures (""crystal graphs""). Here, we develop an improved variant of
the CGCNN model (iCGCNN) that outperforms the original by incorporating
information of the Voronoi tessellated crystal structure, explicit 3-body
correlations of neighboring constituent atoms, and an optimized chemical
representation of interatomic bonds in the crystal graphs. We demonstrate the
accuracy of the improved framework in two distinct illustrations: First, when
trained/validated on 180,000/20,000 density functional theory (DFT) calculated
thermodynamic stability entries taken from the Open Quantum Materials Database
(OQMD) and evaluated on a separate test set of 230,000 entries, iCGCNN achieves
a predictive accuracy that is significantly improved, i.e., 20% higher than
that of the original CGCNN. Second, when used to assist high-throughput search
for materials in the ThCr2Si2 structure-type, iCGCNN exhibited a success rate
of 31% which is 310 times higher than an undirected high-throughput search and
2.4 times higher than that of the original CGCNN. Using both CGCNN and iCGCNN,
we screened 132,600 compounds with elemental decorations of the ThCr2Si2
prototype crystal structure and identified a total of 97 new unique stable
compounds by performing 757 DFT calculations, accelerating the computational
time of the high-throughput search by a factor of 130. Our results suggest that
the iCGCNN can be used to accelerate high-throughput discoveries of new
materials by quickly and accurately identifying crystalline compounds with
properties of interest.",1906.05267v1
2019-06-20,SMILES-X: autonomous molecular compounds characterization for small datasets without descriptors,"There is more and more evidence that machine learning can be successfully
applied in materials science and related fields. However, datasets in these
fields are often quite small ($\ll1000$ samples). It makes the most advanced
machine learning techniques remain neglected, as they are considered to be
applicable to big data only. Moreover, materials informatics methods often rely
on human-engineered descriptors, that should be carefully chosen, or even
created, to fit the physicochemical property that one intends to predict. In
this article, we propose a new method that tackles both the issue of small
datasets and the difficulty of task-specific descriptors development. The
SMILES-X is an autonomous pipeline for molecular compounds characterisation
based on a \{Embed-Encode-Attend-Predict\} neural architecture with a
data-specific Bayesian hyper-parameters optimisation. The only input to the
architecture -- the SMILES strings -- are de-canonicalised in order to
efficiently augment the data. One of the key features of the architecture is
the attention mechanism, which enables the interpretation of output predictions
without extra computational cost. The SMILES-X shows new state-of-the-art
results in the inference of aqueous solubility ($\overline{RMSE}_{test} \simeq
0.57 \pm 0.07$ mols/L), hydration free energy ($\overline{RMSE}_{test} \simeq
0.81 \pm 0.22$ kcal/mol, which is $\sim 24.5\%$ better than molecular dynamics
simulations), and octanol/water distribution coefficient
($\overline{RMSE}_{test} \simeq 0.59 \pm 0.02$ for LogD at pH 7.4) of molecular
compounds. The SMILES-X is intended to become an important asset in the toolkit
of materials scientists and chemists. The source code for the SMILES-X is
available at
\href{https://github.com/GLambard/SMILES-X}{github.com/GLambard/SMILES-X}.",1906.09938v2
2019-06-25,A neutron scattering measurement of crystalline-electric fields in magnesium rare-earth selenide spinels,"The symmetry of local moments plays a defining role in the nature of exotic
grounds states stabilized in frustrated magnetic materials. We present
inelastic neutron scattering (INS) measurements of the crystal electric field
(CEF) excitations in the family of compounds MgRE$_2$Se$_4$ (RE $\in$ $\{$Ho,
Tm, Er and Yb$\}$). These compounds form in the spinel structure, with the rare
earth ions comprising a highly frustrated pyrochlore sublattice. Within the
symmetry constraints of this lattice, we fit both the energies and intensities
of observed modes in the INS spectra to determine the most likely CEF
Hamiltonian for each material and comment on the ground state wavefunctions in
the local electron picture. In this way, we experimentally confirm
MgTm$_2$Se$_4$ has a non-magnetic ground state, and MgYb$_2$Se$_4$ has
effective $S=\frac{1}{2}$ spins with $g_\parallel = 5.188(79)$ and $g_\perp =
0.923(85)~\mu_B$. The spectrum of MgHo$_2$Se$_4$ indicates a ground state
doublet containing Ising spins with $g_\parallel = 2.72(46)$, though low-lying
CEF levels are also seen at thermally accessible energies $\delta_E =
0.591(36)$, 0.945(30) and 2.88(7)~meV, which can complicate interpretation.
These results are used to comment on measured magnetization data of all
compounds, and are compared to published results on the material
MgEr$_2$Se$_4$.",1906.10767v2
2020-04-07,"Magnetic and transport anomalies in R2RhSi3 (R= Gd, Tb, and Dy), resembling those of an exotic magnetic skyrmion Gd2PdSi3","We have carried out magnetization, heat capacity, electrical and
magnetoresistance measurements (2-300 K) for the polycrystalline form of
intermetallic compounds, R2RhSi3 (R= Gd, Tb, and Dy), forming in a AlB2 derived
hexagonal structure with a triangular R network. This work was primarily
motivated by a revival of interest on Gd2PdSi3 after about two decades in the
field of Toplogical Hall Effect due to magnetic skyrmions. We report here that
these compounds are characterized by double antiferromagnetic transitions (T_N=
13.5 and 12 K for Gd, 13.5 and 6.5 K for Tb; 6.5 and 2.5 for Dy), but
antiferromagnerism seems to be complex. The most notable observations common to
all these compounds are: (i) There are many features in the data mimicking
those seen for Gd2PdSi3, including the two field-induced changes in isothermal
magnetization as though there are two metamagnetic transitions well below T_N.
In view of such a resemblance of the properties, we speculate that these
Rh-based materials offer a good playground to study toplogical Hall effect in a
centrosymmetric structure, with its origin lying in triangular lattice of
magnetic R ions; (ii) There is an increasing contribution of electronic
scattering with decreasing temperature towards T_N in all cases, similar to
Gd2PdSi3, thereby serving as examples for a theoretical prediction for a
classical spin-liquid phase in metallic systems due to geometrical frustration.",2004.03144v1
2020-04-15,Prediction of potential inhibitors for RNA-dependent RNA polymerase of SARS-CoV-2 using comprehensive drug repurposing and molecular docking approach,"The pandemic prevalence of COVID-19 has become a very serious global health
issue. Scientists all over the world have been heavily invested in the
discovery of a drug to combat SARS-CoV-2. It has been found that RNA-dependent
RNA Polymerase (RdRp) plays a crucial role in SARS-CoV-2 replication, and thus
could be a potential drug target. Here, comprehensive computational approaches
including drug repurposing and molecular docking were employed to predict an
effective drug candidate targeting RdRp of SARS-CoV-2. This study revealed that
Rifabutin, Rifapentine, Fidaxomicin,
7-methyl-guanosine-5'-triphosphate-5'-guanosine and Ivermectin have a potential
inhibitory interaction with RdRp of SARS-CoV-2, and could be effective drugs
for COVID-19. In addition, virtual screening of the compounds from ZINC
database also allowed the prediction of two compounds (ZINC09128258 and ZINC
09883305) with pharmacophore features that interact effectively with RdRp of
SARS-CoV-2; indicating their potentiality as effective inhibitors of the
enzyme. Furthermore, ADME analysis along with analysis of toxicity was also
investigated to check the pharmacokinetics and drug-likeness properties of the
two compounds. Comparative structural analysis of protein-inhibitor complexes
revealed that positions of the amino acid Y32, K47, Y122, Y129, H133, N138,
D140, T141, S709 and N781 are crucial for drug surface hotspot in the RdRp of
SARS-CoV-2.",2004.07086v1
2020-05-17,Linkage between scattering rates and superconductivity in doped ferropnictides,"We report an angle-resolved photoemission study of a series of hole and
electron doped iron-based superconductors, their parent compound BaFe2As2, and
their cousins BaCr2As2 and BaCo2As2. We focus on the energy (E) dependent
scattering rate Gamma(E) as a function of the 3d count and on the
renormalization function Z(E) of the inner hole pocket, which is the hot spot
in these compounds. We obtain a non-Fermi-liquid-like linear in energy
scattering rate Gamma(E>> kBT), independent of the dopant concentration. The
main result is that the slope beta=Gamma(E >> kBT)/E, reaches its maxima near
optimal doping and scales with the superconducting transition temperature. This
supports the spin fluctuation model for superconductivity for these materials.
In the optimally hole-doped compound, the slope of the scattering rate of the
inner hole pocket is about three times bigger than the Planckian limit
Gamma(E)/E~1. This result together with the energy dependence of the
renormalization function Z(E) signals very incoherent charge carriers in the
normal state which transform at low temperatures to a coherent unconventional
superconducting state.",2005.08216v3
2020-05-19,Speciation of FeS and FeS$_2$ by means of X-ray Emission Spectroscopy using a compact full-cylinder von Hamos spectrometer,"We present Fe K$\beta$ X-ray emission (XES) and Fe K X-ray absorption spectra
(XAS) of Iron(II)sulfide (FeS) and Iron(II)disulfide (FeS$_2$). While XES and
XAS offer different discrimination capabilities for chemical speciation,
depending on the valence states of the compounds probed, XES allows for using
different excitation sources. The XES data was measured using polychromatic
X-ray radiation with a full-cylinder von Hamos spectrometer being characterized
by an energy window of up to 700 eV and a spectral resolving power of $E/
\Delta E = 800$. The large energy window at a single position of the
spectrometer components is made profit of to circumvent the instrumental
sensitivity of wavelength-dispersive spectrometers to sample positioning. This
results in a robust energy scale which is used to compare experimental data
with ab initio valence-to-core calculations, which are carried out using the
OCEAN package. To validate the reliability of the OCEAN package for the two
sample systems, near edge X-ray absorption fine structure measurements of the
Fe K absorption edge are compared to theory using the same input parameters as
in the case of the X-ray emission calculations. Based on the example of iron
sulfide compounds, the combination of XES experiments and OCEAN calculations
allows unravelling the electronic structure of different transition metal
sulfides and qualifying XES investigations for the speciation of different
compounds.",2005.09509v1
2020-05-27,Prediction of exotic magnetic states in the alkali metal quasi-one-dimensional iron selenide compound Na$_2$FeSe$_2$,"The magnetic and electronic phase diagram of a model for the
quasi-one-dimensional alkali metal iron selenide compound Na$_2$FeSe$_2$ is
presented. The novelty of this material is that the valence of iron is
Fe$^{2+}$ contrary to most other iron-chain compounds with valence Fe$^{3+}$.
Using first-principles techniques, we developed a three-orbital tight-binding
model that reproduces the {\it ab initio} band structure near the Fermi level.
Including Hubbard and Hund couplings and studying the model via the density
matrix renormalization group and Lanczos methods, we constructed the ground
state phase diagram. A robust region where the block state $\uparrow \uparrow
\downarrow \downarrow \uparrow \uparrow \downarrow \downarrow$ is stabilized
was unveiled. The analog state in iron ladders, employing 2$\times$2
ferromagnetic blocks, is by now well-established, but in chains a block
magnetic order has not been observed yet in real materials. The phase diagram
also contains a large region of canonical staggered spin order $\uparrow
\downarrow \uparrow \downarrow \uparrow \downarrow \uparrow$ at very large
Hubbard repulsion. At the block to staggered transition region, a novel phase
is stabilized with a mixture of both states: an inhomogeneous orbital-selective
charge density wave with the exotic spin configuration $\uparrow \uparrow
\downarrow \uparrow \downarrow \downarrow \uparrow \downarrow$. Our predictions
for Na$_2$FeSe$_2$ may guide crystal growers and neutron scattering
experimentalists towards the realization of block states in one-dimensional
iron-selenide chain materials.",2005.13132v1
2020-08-10,Feature Ranking for Semi-supervised Learning,"The data made available for analysis are becoming more and more complex along
several directions: high dimensionality, number of examples and the amount of
labels per example. This poses a variety of challenges for the existing machine
learning methods: coping with dataset with a large number of examples that are
described in a high-dimensional space and not all examples have labels
provided. For example, when investigating the toxicity of chemical compounds
there are a lot of compounds available, that can be described with information
rich high-dimensional representations, but not all of the compounds have
information on their toxicity. To address these challenges, we propose
semi-supervised learning of feature ranking. The feature rankings are learned
in the context of classification and regression as well as in the context of
structured output prediction (multi-label classification, hierarchical
multi-label classification and multi-target regression). To the best of our
knowledge, this is the first work that treats the task of feature ranking
within the semi-supervised structured output prediction context. More
specifically, we propose two approaches that are based on tree ensembles and
the Relief family of algorithms. The extensive evaluation across 38 benchmark
datasets reveals the following: Random Forests perform the best for the
classification-like tasks, while for the regression-like tasks Extra-PCTs
perform the best, Random Forests are the most efficient method considering
induction times across all tasks, and semi-supervised feature rankings
outperform their supervised counterpart across a majority of the datasets from
the different tasks.",2008.03937v1
2020-08-23,"Item Quality Control in Educational Testing: Change Point Model, Compound Risk, and Sequential Detection","In standardized educational testing, test items are reused in multiple test
administrations. To ensure the validity of test scores, the psychometric
properties of items should remain unchanged over time. In this paper, we
consider the sequential monitoring of test items, in particular, the detection
of abrupt changes to their psychometric properties, where a change can be
caused by, for example, leakage of the item or change of the corresponding
curriculum. We propose a statistical framework for the detection of abrupt
changes in individual items. This framework consists of (1) a multi-stream
Bayesian change point model describing sequential changes in items, (2) a
compound risk function quantifying the risk in sequential decisions, and (3)
sequential decision rules that control the compound risk. Throughout the
sequential decision process, the proposed decision rule balances the trade-off
between two sources of errors, the false detection of pre-change items and the
non-detection of post-change items. An item-specific monitoring statistic is
proposed based on an item response theory model that eliminates the confounding
from the examinee population which changes over time. Sequential decision rules
and their theoretical properties are developed under two settings: the oracle
setting where the Bayesian change point model is completely known and a more
realistic setting where some parameters of the model are unknown. Simulation
studies are conducted under settings that mimic real operational tests.",2008.10104v2
2020-08-27,"Different universality classes of isostructural U$TX$ compounds ($T$ = Rh, Co, Co$_{0.98}$Ru$_{0.02}$; $X$ = Ga, Al)","Magnetization isotherms of the 5f-electron ferromagnets URhGa, UCoGa and
UCo0.98Ru0.02Al were measured at temperatures in the vicinity of their Curie
temperature in order to investigate the critical behavior near the
ferromagnetic phase transition. These compounds adopt the layered hexagonal
ZrNiAl-type structure and exhibit huge uniaxial magnetocrystalline anisotropy.
The critical \b{eta}, {\gamma} and {\delta} exponents were determined by
analyzing Arrott-Noakes plots, Kouvel-Fisher plots, critical isotherms, scaling
theory and Widom scaling relations. The values obtained for URhGa and UCoGa can
be explained by the results of the renormalization group theory for a 2D Ising
system with long-range interactions similar to URhAl reported by other
investigators. On the other hand, the critical exponents determined for
UCo0.98Ru0.02Al are characteristic of a 3D Ising ferromagnet with short-range
interactions suggested in previous studies also for the itinerant 5f-electron
paramagnet UCoAl situated near a ferromagnetic transition. The change from the
2D to the 3D Ising system is related to the gradual delocalization of 5f
electrons in the series of the URhGa, URhAl, UCoGa to UCo0.98Ru0.02Al and UCoAl
compounds and appears close to the strongly itinerant nonmagnetic limit. This
indicates possible new phenomena that may be induced by the change of
dimensionality in the vicinity of the quantum critical point.",2008.12061v1
2020-08-30,ChemVA: Interactive Visual Analysis of Chemical Compound Similarity in Virtual Screening,"In the modern drug discovery process, medicinal chemists deal with the
complexity of analysis of large ensembles of candidate molecules. Computational
tools, such as dimensionality reduction (DR) and classification, are commonly
used to efficiently process the multidimensional space of features. These
underlying calculations often hinder interpretability of results and prevent
experts from assessing the impact of individual molecular features on the
resulting representations. To provide a solution for scrutinizing such complex
data, we introduce ChemVA, an interactive application for the visual
exploration of large molecular ensembles and their features. Our tool consists
of multiple coordinated views: Hexagonal view, Detail view, 3D view, Table
view, and a newly proposed Difference view designed for the comparison of DR
projections. These views display DR projections combined with biological
activity, selected molecular features, and confidence scores for each of these
projections. This conjunction of views allows the user to drill down through
the dataset and to efficiently select candidate compounds. Our approach was
evaluated on two case studies of finding structurally similar ligands with
similar binding affinity to a target protein, as well as on an external
qualitative evaluation. The results suggest that our system allows effective
visual inspection and comparison of different high-dimensional molecular
representations. Furthermore, ChemVA assists in the identification of candidate
compounds while providing information on the certainty behind different
molecular representations.",2008.13150v1
2021-03-01,Mixed-valence compounds as polarizing agents for Overhauser dynamic nuclear polarization in solids,"In this paper we investigate a novel set of polarizing agents --
mixed-valence compounds -- by theoretical and experimental methods and
demonstrate their performance in high-field Dynamic Nuclear Polarization (DNP)
experiments in the solid state. Mixed-valence compounds constitute a group of
molecules, in which molecular mobility persists even in solids. Consequently,
such polarizing agents can be used to perform Overhauser-DNP experiments in
solid-state, with favorable conditions for dynamic nuclear polarization
formation at ultra-high magnetic fields.",2103.00997v1
2021-03-04,Reference Energies for Intramolecular Charge-Transfer Excitations,"In the aim of completing our previous efforts devoted to local and Rydberg
transitions in organic compounds, we provide a series of highly-accurate
vertical transition energies for intramolecular charge-transfer transitions
occurring in ($\pi$-conjugated) molecular compounds. To this end we apply a
composite protocol consisting of linear-response CCSDT excitation energies
determined with Dunning's double-$\zeta$ basis set corrected by CC3/CCSDT-3
energies obtained with the corresponding triple-$\zeta$ basis. Further basis
set corrections (up to \emph{aug}-cc-pVQZ) are obtained at the CCSD and CC2
level. We report 30 transitions obtained in 17 compounds. These reference
values are then used to benchmark a series of wave function (CIS(D), SOPPA,
RPA(D), EOM-MP2, CC2, CCSD, CCSD(T)(a)*, CCSDR(3), CCSDT-3, CC3, ADC(2),
ADC(3), and ADC(2.5)), the Green's function-based Bethe-Salpeter equation (BSE)
formalism performed on top of the partially self-consistent ev$GW$ scheme
considering two different starting points (BSE/ev$GW$@HF and BSE/ev$GW$@PBE0),
and TD-DFT combined with several exchange-correlation functionals (B3LYP, PBE0,
M06-2X, CAM-B3LYP, LC-$\omega$HPBE, $\omega$B97X, $\omega$B97X-D, and M11).",2103.02947v2
2021-03-23,57Fe and 151Eu Mössbauer studies of 3d-4f spin interplay in EuFe(2-x)Ni(x)As2,"The EuFe(2-x)Ni(x)As2 compounds exhibiting 3d and/or 4f magnetic order were
investigated by means of 57Fe and 151Eu M\""ossbauer spectroscopy. Additionally,
results for the end members of this system, i.e. EuFe2As2 and EuNi2As2, are
reported for comparison. It was found that spin-density-wave order of the Fe
itinerant moments is monotonically suppressed by Ni-substitution. However, the
3d magnetic order survives at the lowest temperature up to at least x = 0.12
and it is certainly completely suppressed for x = 0.20. The Eu localized
moments order regardless of the Ni concentration, but undergo a spin
reorientation with increasing x from the alignment parallel to the a-axis in
the parent compound, toward c-axis alignment for x > 0.07. The change of the 4f
spins ordering from antiferromagnetic to ferromagnetic takes place
simultaneously with a disappearance of the 3d spins order what is the evidence
of a strong coupling between magnetism of Eu2+ ions and the conduction
electrons of [Fe(2-x)Ni(x)As2]2- layers. The Fe nuclei experience the
transferred hyperfine magnetic field due to the Eu2+ ordering for
Ni-substituted samples with x > 0.04, while the transferred field is
undetectable in EuFe2As2 and for compound with a low Ni-substitution level. It
seems that the 4f ferromagnetic component arising from a tilt of the Eu2+
moments to the crystallographic c-axis leads to the transferred magnetic field
at the Fe atoms.",2103.12698v2
2022-02-09,Amplitude Spectrum Transformation for Open Compound Domain Adaptive Semantic Segmentation,"Open compound domain adaptation (OCDA) has emerged as a practical adaptation
setting which considers a single labeled source domain against a compound of
multi-modal unlabeled target data in order to generalize better on novel unseen
domains. We hypothesize that an improved disentanglement of domain-related and
task-related factors of dense intermediate layer features can greatly aid OCDA.
Prior-arts attempt this indirectly by employing adversarial domain
discriminators on the spatial CNN output. However, we find that latent features
derived from the Fourier-based amplitude spectrum of deep CNN features hold a
more tractable mapping with domain discrimination. Motivated by this, we
propose a novel feature space Amplitude Spectrum Transformation (AST). During
adaptation, we employ the AST auto-encoder for two purposes. First, carefully
mined source-target instance pairs undergo a simulation of cross-domain feature
stylization (AST-Sim) at a particular layer by altering the AST-latent. Second,
AST operating at a later layer is tasked to normalize (AST-Norm) the domain
content by fixing its latent to a mean prototype. Our simplified adaptation
technique is not only clustering-free but also free from complex adversarial
alignment. We achieve leading performance against the prior arts on the OCDA
scene segmentation benchmarks.",2202.04287v1
2022-02-17,Properties and challenges of hot-phonon physics in metals: MgB$_2$ and other compounds,"The ultrafast dynamics of electrons and collective modes in systems out of
equilibrium is crucially governed by the energy transfer from electronic
degrees of freedom, where the energy of the pump source is usually absorbed, to
lattice degrees of freedom. In conventional metals such process leads to an
overall heating of the lattice, usually described by an effective lattice
temperature $T_{\rm ph}$, until final equilibrium with all the degrees of
freedom is reached. In specific materials, however, few lattice modes provide a
preferential channel for the energy transfer, leading to a non-thermal
distribution of vibrations and to the onset of {\em hot phonons}, i.e., lattice
modes with a much higher population than the other modes. Hot phonons are
usually encountered in semiconductors or semimetal compounds, like graphene,
where the preferential channel towards hot modes is dictated by the reduced
electronic phase space. Following a different path, the possibility of
obtaining hot-phonon physics also in metals has been however also recently
prompted in literature, as a result of a strong anisotropy of the
electron-phonon (el-ph) coupling. In the present paper, taking MgB$_2$ as a
representative example, we review the physical conditions that allow a
hot-phonon scenario in metals with anisotropic el-ph coupling, and we discuss
the observable fingerprints of hot phonons. Novel perspectives towards the
prediction and experimental observation of hot phonons in other metallic
compounds are also discussed.",2202.08597v1
2022-03-07,MS2MP: A Min-Sum Message Passing Algorithm for Motion Planning,"Gaussian Process (GP) formulation of continuoustime trajectory offers a fast
solution to the motion planning problem via probabilistic inference on factor
graph. However, often the solution converges to in-feasible local minima and
the planned trajectory is not collision-free. We propose a message passing
algorithm that is more sensitive to obstacles with fast convergence time. We
leverage the utility of min-sum message passing algorithm that performs local
computations at each node to solve the inference problem on factor graph. We
first introduce the notion of compound factor node to transform the factor
graph to a linearly structured graph. We next develop an algorithm denoted as
Min-sum Message Passing algorithm for Motion Planning (MS2MP) that combines
numerical optimization with message passing to find collision-free
trajectories. MS2MP performs numerical optimization to solve non-linear least
square minimization problem at each compound factor node and then exploits the
linear structure of factor graph to compute the maximum a posteriori (MAP)
estimation of complete graph by passing messages among graph nodes. The
decentralized optimization approach of each compound node increases sensitivity
towards avoiding obstacles for harder planning problems. We evaluate our
algorithm by performing extensive experiments for exemplary motion planning
tasks for a robot manipulator. Our evaluation reveals that MS2MP improves
existing work in convergence time and success rate.",2203.03201v1
2022-03-24,Compound Domain Generalization via Meta-Knowledge Encoding,"Domain generalization (DG) aims to improve the generalization performance for
an unseen target domain by using the knowledge of multiple seen source domains.
Mainstream DG methods typically assume that the domain label of each source
sample is known a priori, which is challenged to be satisfied in many
real-world applications. In this paper, we study a practical problem of
compound DG, which relaxes the discrete domain assumption to the mixed source
domains setting. On the other hand, current DG algorithms prioritize the focus
on semantic invariance across domains (one-vs-one), while paying less attention
to the holistic semantic structure (many-vs-many). Such holistic semantic
structure, referred to as meta-knowledge here, is crucial for learning
generalizable representations. To this end, we present Compound Domain
Generalization via Meta-Knowledge Encoding (COMEN), a general approach to
automatically discover and model latent domains in two steps. Firstly, we
introduce Style-induced Domain-specific Normalization (SDNorm) to re-normalize
the multi-modal underlying distributions, thereby dividing the mixture of
source domains into latent clusters. Secondly, we harness the prototype
representations, the centroids of classes, to perform relational modeling in
the embedding space with two parallel and complementary modules, which
explicitly encode the semantic structure for the out-of-distribution
generalization. Experiments on four standard DG benchmarks reveal that COMEN
exceeds the state-of-the-art performance without the need of domain
supervision.",2203.13006v1
2022-03-29,Accurate electronic properties and intercalation voltages of olivine-type Li-ion cathode materials from extended Hubbard functionals,"The design of novel cathode materials for Li-ion batteries would greatly
benefit from accurate first-principles predictions of structural, electronic,
and magnetic properties as well as intercalation voltages in compounds
containing transition-metal elements. For such systems, density-functional
theory (DFT) with standard (semi-)local exchange-correlation functionals is of
limited use as it often fails due to strong self-interaction errors that are
especially relevant in the partially filled $d$ shells. Here, we perform a
detailed comparative study of the phospho-olivine cathode materials
Li$_x$MnPO$_4$, Li$_x$FePO$_4$, and the mixed transition metal
Li$_x$Mn$_{1/2}$Fe$_{1/2}$PO$_4$ ($x=0, 1/4, 1/2, 3/4, 1$) using four
electronic-structure methods: DFT, DFT+$U$, DFT+$U$+$V$, and HSE06. We show
that DFT+$U$+$V$, with onsite $U$ and intersite $V$ Hubbard parameters
determined from first principles and self-consistently with respect to the
structural parameters by means of density-functional perturbation theory
(linear response), provides the most accurate description of the electronic
structure of these challenging compounds. In particular, we demonstrate that
DFT+$U$+$V$ displays very clearly ""digital"" changes in oxidation states of the
transition-metal ions in all compounds, including the mixed-valence phases
occurring at intermediate Li concentrations, leading to voltages in remarkable
agreement with experiments. We show that the inclusion of intersite Hubbard
interactions is essential for the accurate prediction of thermodynamic
quantities, balancing the drive for localization induced by the onsite $U$ with
intersite $V$ orbital hybridizations.",2203.15732v2
2016-03-15,Coexistence of superconductivity and antiferromagnetism in Ca$_{0.74(1)}$La$_{0.26(1)}$(Fe$_{1-x}$Co$_{x}$)As$_{2}$ single crystals,"We report the transport, thermodynamic, $\mu$SR and neutron study of the
Ca$_{0.74(1)}$La$_{0.26(1)}$(Fe$_{1-x}$Co$_{x}$)As$_{2}$ single crystals,
mapping out the temperature-doping level phase diagram. Upon Co substitution on
the Fe site, the structural/magnetic phase transitions in this 112 compound are
suppressed and superconductivity up to 20 K occurs. Our measurements of the
superconducting and magnetic volume fractions show that these two phases
coexist microscopically in the underdoped region, in contrast to the related
10-3-8 Ca$_{10}$(Pt$_{3}$As$_{8}$)((Fe$_{1-x}$Pt$_x$)$_{2}$As$_{2}$)$_{5}$
compound, where coexistence is absent. Supported by model calculations, we
discuss the differences in the phase diagrams of the 112 and 10-3-8 compounds
in terms of the FeAs interlayer coupling, whose strength is affected by the
character of the spacer layer, which is metallic in the 112 and insulating in
the 10-3-8.",1603.04899v1
2016-12-05,Sn(II)-containing phosphates as optoelectronic materials,"We theoretically investigate Sn(II) phosphates as optoelectronic materials
using first principles calculations. We focus on known prototype materials
Sn$_n$P$_2$O$_{5+n}$ (n=2, 3, 4, 5) and a previously unreported compound,
SnP$_2$O$_6$ (n=1), which we find using global optimization structure
prediction. The electronic structure calculations indicate that these compounds
all have large band gaps above 3.2 eV, meaning their transparency to visible
light. Several of these compounds show relatively low hole effective masses
($\sim$2-3 m$_0$), comparable the electron masses. This suggests potential
bipolar conductivity depending on doping. The dispersive valence band-edges
underlying the low hole masses, originate from the anti-bonding hybridization
between the Sn 5s orbitals and the phosphate groups. Analysis of
structure-property relationships for the metastable structures generated during
structure search shows considerable variation in combinations of band gap and
carrier effective masses, implying chemical tunability of these properties. The
unusual combinations of relatively high band gap, low carrier masses and high
chemical stability suggests possible optoelectronic applications of these
Sn(II) phosphates, including p-type transparent conductors. Related to this,
calculations for doped material indicate low visible light absorption, combined
with high plasma frequencies.",1612.01372v1
2016-12-12,"Synthesis and properties of A$_x$V$_2$Al$_{20}$ (A = Th, U, Np, Pu) ternary actinide aluminides","Polycrystalline samples of A$_x$V$_2$Al$_{20}$ (A = Ce, Th, U, Np, Pu; 0.7 =<
x =< 1.0) actinide intermetallics were synthesized using the arc-melting
method. Crystal structure studies were performed by means of powder x-ray
diffraction and the Rietveld refinement method. All studied compounds
crystallize in the CeCr$_{2}$Al$_{20}$-type structure (space group Fd-3m, no.
227) with the actinide or Ce atom located in the oversized cage formed by Al
atoms. Comparison of the crystallographic results with the reported data for
LnV$_{2}$Al$_{20}$ (Ln = lanthanoids) counterparts reveals distinctly different
behavior of the lanthanide- and actinide-bearing compounds. This difference is
suggested to be caused by fairly localized character of the 4f electrons,
whereas itinerant character of the 5f electrons is likely seen for U- and
Np-containing phases. Magnetic susceptibility and specific heat measurements
did not reveal any magnetic ordering in U$_{0.8}$V$_{2}$Al$_{20}$,
Np$_{0.8}$V$_{2}$Al$_{20}$ and Pu$_{0.8}$V$_{2}$Al$_{20}$ down to 2.5 K. A
small anomaly in low-temperature specific heat of Ce$_{0.8}$V$_{2}$Al$_{20}$,
U$_{0.8}$V$_{2}$Al$_{20}$, and Np$_{0.8}$V$_{2}$Al$_{20}$ is observed, likely
arising from a low-energy Einstein mode.",1612.03609v1
2017-02-10,"Mechanical behavior, bonding nature, and defect processes of Mo2ScAlC2: a new ordered MAX phase","In the present study we employed density functional theory calculations to
investigate the mechanical behavior, bonding nature and defect processes of the
new ordered MAX phase Mo2ScAlC2. The mechanical stability of the compound is
verified with its single crystal elastic constants. The new phase Mo2ScAlC2 is
anticipated to be prone to shear along the crystallographic b and c axes, when
a rational force is applied to the crystallographic a axis. The compressibility
along the <001> direction under uniaxial stress is expected to be easier in
Mo2ScAlC2. Additionally, the volume deformation should be easier in Mo2ScAlC2
than in the isostructural Mo2TiAlC2. Mo2ScAlC2 is predicted to behave in a
brittle manner. Due to its higher Debye temperature, Mo2ScAlC2 is expected to
be thermally more conductive than Mo2TiAlC2. The cross-slip pinning procedure
should be significantly easier in Mo2ScAlC2 as compared to Mo2TiAlC2. The new
ordered MAX phase Mo2ScAlC2 has a mixed character of strong covalent and
metallic bonding with limited ionic nature. Both Mo-C and Mo-Al bonds are
expected to be more covalent in Mo2ScAlC2 than those of Mo2TiAlC2. the level of
covalency of Sc-C bond is somewhat low compared to a similar bond Ti-C in
Mo2TiAlC2. Due to its reduced hardness, Mo2ScAlC2 should be softer and more
easily machinable compared to Mo2TiAlC2. Fermi surface topology of the new
compound is formed mainly due to the low-dispersive Mo 4d-like bands. The
intrinsic defect processes reveal that the level of radiation tolerance in
Mo2ScAlC2 is not as high as in other MAX phases such as Ti3AlC2.",1702.03048v1
2017-02-22,Effect of Sr doping on the magnetic exchange interactions in manganites,"Strontium doping transforms manganites of type La(1-x)Sr(x)MnO(3) from an
insulating antiferromagnet (x=0) to a metallic ferromagnet (x>0.16) due to the
induced charge carriers (holes). Neutron scattering experiments were employed
to investigate the effect of Sr doping on a tailor-made compound of composition
La(0.7)Sr(0.3)Mn(0.1)Ti(0.3)Ga(0.6)O(3). By the simultaneous doping with Sr2+
and Ti4+ ions the compound remains in the insulating state, so that the
magnetic interactions for large Sr doping can be studied in the absence of
charge carriers. At TC=215 K there is a first-order reconstructive phase
transition from the trigonal R-3c structure to the orthorhombic Pnma structure
via an intermediate virtual configuration described by the common monoclinic
subgroup P21/c. The magnetic excitations associated with Mn3+ dimers give
evidence for two different nearest-neighbor ferromagnetic exchange
interactions, in contrast to the undoped compound LaMnyA(1-y)O(3) where both
ferromagnetic and antiferromagnetic interactions are present. The doping
induced changes of the exchange coupling originates from different Mn-O-Mn bond
angles determined by neutron diffraction. The large fourth-nearest-neighbor
interaction found for metallic manganites is absent in the insulating state. We
argue that the Ruderman-Kittel-Kasuya-Yosida interaction reasonably accounts
for all the exchange couplings derived from the spin-wave dispersion in
metallic manganites.",1702.06802v1
2017-06-28,Prediction of the High Thermoelectric Performance of Pnictogen Dichalcogenide Layered Compounds with Quasi-One-Dimensional Gapped Dirac-like Band Dispersion,"Thermoelectric power generation has been recognized as one of the most
important technologies, and high-performance thermoelectric materials have long
been pursued. However, because of the large number of candidate materials, this
quest is extremely challenging, and it has become clear that a firm theoretical
concept from the viewpoint of band-structure engineering is needed. In this
study, we theoretically demonstrate that pnictogen-dichalcogenide layered
compounds, which originally attracted attention as a family of superconductors
and have recently been investigated as thermoelectric materials, can exhibit
very high thermoelectric performance with elemental substitution. In
particular, we clarify a promising guiding principle for materials design and
find that LaOAsSe$_2$, a material that has yet to be synthesized, has a
powerfactor that is six times as large as that of the known compound LaOBiS$_2$
and can exhibit a very large $ZT$ under some plausible assumptions. This large
enhancement of the thermoelectric performance originates from the
quasi-one-dimensional gapped Dirac-like band dispersion, which is realized by
the square-lattice network. Our study offers one ideal limit of the band
structure for thermoelectric materials. Because our target materials have high
controllability of constituent elements and feasibility of carrier doping,
experimental studies along this line are strongly awaited.",1706.09271v2
2017-10-09,Angular Distribution of $γ$-rays from Neutron-Induced Compound States of $^{140}$La,"Angular distribution of individual $\gamma$-rays, emitted from a
neutron-induced compound nuclear state via radiative capture reaction of
${}^{139}$La(n,$\gamma$) has been studied as a function of incident neutron
energy in the epithermal region by using germanium detectors.
  An asymmetry $A_{\mathrm{LH}}$ was defined as $(N_{\mathrm L}-N_{\mathrm
H})/(N_{\mathrm L}+N_{\mathrm H})$, where $N_{\mathrm L}$ and $N_{\mathrm H}$
are integrals of low and high energy region of a neutron resonance
respectively, and we found that $A_{\mathrm{LH}}$ has the angular dependence of
$(A\cos\theta_\gamma+B)$, where $\theta_\gamma$ is emitted angle of
$\gamma$-rays, with $A= -0.3881\pm0.0236$ and $B=-0.0747\pm0.0105$ in 0.74 eV
p-wave resonance.
  This angular distribution was analyzed within the framework of interference
between s- and p-wave amplitudes in the entrance channel to the compound
nuclear state, and it is interpreted as the value of the partial p-wave neutron
width corresponding to the total angular momentum of the incident neutron
combined with the weak matrix element, in the context of the mechanism of
enhanced parity-violating effects. Additionally we used the result to quantify
the possible enhancement of the breaking of the time-reversal invariance in the
vicinity of the p-wave resonance.",1710.03065v5
2017-10-16,Antiferromagnetism in semiconducting SrMn2Sb2 and BaMn2Sb2 single crystals,"Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized
by powder and single-crystal x-ray diffraction, respectively, and by
single-crystal electrical resistivity rho, heat capacity Cp, and magnetic
susceptibility chi measurements versus temperature T, and magnetization versus
field M(H) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2-type
structure whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2-type
structure. The rho(T) data indicate semiconducting behaviors for both compounds
with activation energies of 0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2. The
chi(T) and Cp(T) data reveal antiferromagnetic (AFM) ordering at TN = 110 K for
SrMn2Sb2 and 450~K for BaMn2Sb2. The anisotropic chi(T < TN) data also show
that the ordered moments in SrMn2Sb2 are aligned in the hexagonal ab plane
whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the
tetragonal c axis. The ab-plane M(H) data for SrMn2Sb2 exhibit a continuous
metamagnetic transition at low fields 0 < H < 1 T, whereas BaMn2Sb2 exhibits no
metamagnetic transitions up to 5.5 T. The chi(T) data for both compounds and
the Cp(T) data for SrMn2Sb2 and BaMn2Sb2 indicate strong dynamic short-range
AFM correlations above their respective TN up to at least 900 K within a
local-moment picture, corresponding to quasi-two-dimensional magnetic behavior.
The present results and a survey of the literature for Mn pnictides with the
CaAl2Si2 and ThCr2Si2 crystal structures show that the TN values for the
CaAl2Si2-type compounds are much smaller than those for the ThCr2Si2-type
materials.",1710.05976v1
2017-10-24,Mössbauer study of Eu0.57Ca0.43Fe2As2 and Eu0.73Ca0.27(Fe0.87Co0.13)2As2: A comparison to 122 iron-based superconductors parent compounds EuFe2As2 and CaFe2As2,"57Fe and 151Eu Moessbauer spectra were obtained versus temperature for
Eu0.57Ca0.43Fe2As2 compound with 3d and 4f magnetic order and
Eu0.73Ca0.27(Fe0.87Co0.13)2As2 re-entrant superconductor, where the finite
resistivity reappears while approaching the ground state. They were compared
with previously obtained spectra for parent compounds EuFe2As2 and CaFe2As2. It
was found that substitution beyond the Fe-As layers does not lead to the
rotation (canting) of the Eu2+ magnetic moments and does not generate Eu3+
states. On the other hand, re-entrant superconductor exhibits rotation
(canting) of the Eu2+ moments on the c-axis of the unit cell leading to the
transferred hyperfine magnetic field on iron nuclei. Divalent europium orders
magnetically within the bulk of the re-entrant superconducting phase. The
re-entrant superconductor remains in the inhomogeneous state close to the
ground state with about 27 % of the volume being free of 3d magnetism, while
the remainder exhibits weak spin density wave. Those two regions slightly
differ by the electric field gradient and electron density on iron nuclei.",1710.08887v3
2017-10-27,Universal superconducting precursor in the cuprates,"The nature of the superconducting (SC) precursor in the cuprates has been the
subject of intense interest, with profound implications for both the normal and
the SC states. Different experimental probes have led to vastly disparate
conclusions on the temperature range of superconducting fluctuations. The main
challenges have been to separate the SC response from complex normal-state
behavior, and to distinguish the underlying behavior of the quintessential
CuO$_{2}$ layers from compound-specific properties. Here we reveal remarkably
simple and universal behavior of the SC precursor using torque magnetometry, a
unique thermodynamic probe with extremely high sensitivity to SC diamagnetism.
We comprehensively study four distinct cuprate compounds:
single-CuO$_{2}$-layer La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO),
Bi$_{2}$(Sr,La)$_{2}$CuO$_{6+\delta}$ (Bi2201) and HgBa$_{2}$CuO$_{4+\delta}$
(Hg1201), and double-layer
Bi$_{2}$Sr$_{2}$Ca$_{0.95}$Y$_{0.05}$CuO$_{8+\delta}$ (Bi2212). Our approach,
which focuses on the nonlinear diamagnetic response, completely removes
normal-state contributions and thus allows us to trace the diamagnetic signal
above Tc with great precision. We find that SC diamagnetism vanishes in an
unusual, yet surprisingly simple exponential manner, marked by a universal
temperature scale that is independent of compound and Tc. We discuss the
distinct possibility that this unusual behavior signifies the proliferation of
SC clusters as a result of the intrinsic inhomogeneity known to be an inherent
property of the cuprates.",1710.10957v1
2018-04-04,Heterobimetallic Dy-Cu coordination compound as a classical-quantum ferrimagnetic chain of regularly alternating Ising and Heisenberg spins,"A classical-quantum chain composed of regularly alternating Ising and
Heisenberg spins is rigorously solved by considering two distinct local
anisotropy axes of the Ising spins. The ground-state phase diagram and
magnetization curves are examined depending on a spatial orientation of the
applied magnetic field. The phase diagram totally consists of four distinct
phases and a few macroscopically degenerate points, where an outstanding
coexistence of perfect order and complete disorder occurs within the so-called
'half-fire, half-ice' state. The zero-temperature magnetization curves
generally exhibit a smooth dependence on a magnetic field owing to a canting
angle between two coplanar anisotropy axes of the Ising spins, which enforces a
misalignment of the magnetization vector from a direction of the applied
magnetic field. It is evidenced that the investigated spin-chain model
reproduces magnetic features of the heterobimetallic coordination compound
Dy(NO)$_{3}$(DMSO)$_{2}$Cu(opba)(DMSO)$_{2}$ (DMSO=dimethylsulfoxide,
opba=orthophenylenebisoxamato). The high-field magnetization data reported for
the powder sample of this polymeric coordination compound generally display a
substantial smoothing on account of a powder averaging.",1804.01551v2
2018-04-09,Pressure effects on the structural and superconducting transitions in La3Co4Sn13,"La3Co4Sn13 is a superconducting material with transition temperature at Tc =
2.70 K, which presents a superlattice structural transition at T* ~ 150 K, a
common feature for this class of compounds. However, for this material, it is
not clear that at T* the lattice distortions arise from a charge density wave
(CDW) or from a distinct microscopic origin. Interestingly, it has been
suggested in isostructural non-magnetic intermetallic compounds that T* can be
suppressed to zero temperature, by combining chemical and external pressure,
and a quantum critical point is argued to be observed near these critical
doping/pressure. Our study shows that application of pressure on
single-crystalline La3Co4Sn13 enhances Tc and decreases T*. We observe thermal
hysteresis loops for cooling/heating cycles around T* for P > 0.6 GPa, in
electrical resistivity measurements, which are not seen in x-ray diffraction
data. The hysteresis in electrical measurements may be due to the pinning of
the CDW phase to impurities/defects, while the superlattice structural
transition maintains its ambient pressure second-order transition nature under
pressure. From our experiments we estimate that T* vanishes at around 5.5 GPa,
though no quantum critical behavior is observed up to 2.53 GPa.",1804.03215v2
2018-04-12,"The melilite-type compound (Sr$_{1-x}$,$A_x$)$_2$MnGe$_2$S$_6$O ($A$=K, La) being a room temperature ferromagnetic semiconductor","The seeking of room temperature ferromagnetic semiconductors, which take
advantages of both the charge and spin degrees of freedom of electrons to
realize a variety of functionalities in devices integrated with electronic,
optical, and magnetic storage properties, has been a long-term goal of
scientists and engineers. Here, by using the spin-polarized density functional
theory calculations, we predict a new series of high temperature ferromagnetic
semiconductors based on the melilite-type oxysulfide Sr$_2$MnGe$_2$S$_6$O
through hole (K) and electron (La) doping. Due to the lack of strong
antiferromagnetic superexchange between Mn ions, the weak antiferromagnetic
order in the parent compound Sr$_2$MnGe$_2$S$_6$O can be suppressed easily by
charge doping with either $p$-type or $n$-type carriers, giving rise to the
expected ferromagnetic order. At a doping concentration of 25%, both the
hole-doped and electron-doped compounds can achieve a Curie temperature
($T_\text{c}$) above 300 K. The underlying mechanism is analyzed. Our study
provides an effective approach for exploring new types of high temperature
ferromagnetic semiconductors.",1804.04519v1
2018-04-27,Intrinsic permanent magnetic characteristics beyond Ce2Co17 with Ce/Co substitutions,"By understanding the small easy axis magnetocrystalline anisotropy energy
(MAE) of hexagonal Ce2Co17, an attempt has been made to improve anisotropy and
consequently to obtain better characteristics for a high energy permanent
magnet via site selective substitutional doping of Ce/Co with suitable
elements. The present calculations of the electronic and magnetic properties of
Ce2Co17 and related substituted compounds have been performed using the full
potential linear augmented plane wave (FPLAPW) method within the generalized
gradient approximation (GGA). Sm-substituted compounds were simulated using
Coulomb corrected GGA (GGA+U) to provide a better representation of energy
bands due to the strongly correlated Sm-f electrons. The formation energies for
all substituted compounds are found to be negative which indicate their
structural stability. Of the substitutions, Zr substitution at the Co-dumbbell
site enhances uniaxial anisotropy of Ce2Co17. Furthermore, Sm-substitution at
Ce-2c sites favors incremental MAE whereas a La-substitution at both 2b- and
2c-sites depletes the tiny MAE in Ce2Co17. These observed trends in the MAE
have been examined in terms of contributions from various electronic states.
Finally, Ce2Zr2Co15 and SmCeCo17 are foreseen as suitable materials for
designing permanent magnets derived from the crystal lattice structure of
hexagonal Ce2Co17.",1804.10310v2
2018-04-27,"Low-Temperature X-ray Crystal Structure Analysis of the Cage-Structured Compounds MBe13 (M = La, Sm, and U)","The beryllides MBe13 (M = rare earths and actinides) crystallize in a
NaZn13-type cubic structure, which can be categorized as a cage-structured
compound. In this study, powder X-ray diffraction measurements have been
performed on LaBe13, SmBe13, and UBe13 in the temperature range between 7 and
300 K in order to investigate their crystallographic characteristics
systematically. They keep the NaZn13-type cubic structure down to the lowest
temperature. We estimated their Debye temperature to be 600 - 750 K from
analyses of the temperature dependence of a lattice parameter, being in good
agreement with the values reported previously. Rietveld refinements on the
obtained powder patterns revealed that the M atom in the 8a site is located in
an almost ideal snub cube formed by 24 Be atoms in the 96i site, whose caged
structure is unchanged even at the low temperatures. In addition, it is argued
from the temperature variation of an isotropic mean-square displacement
parameter that the MBe13 compounds commonly have a low-energy phonon mode,
which can be described by a model assuming an Einstein oscillation of the M
atom with a characteristic temperature of ~ 160 K.",1804.10311v2
2019-03-19,"Structural, electronic, and dynamical properties of the tetragonal and collapsed tetragonal phases of KFe$_2$As$_2$","Compounds with a tetragonal ThCr$_{2}$Si$_{2}$-type structure are
characterized by the possibility of the isostructural phase transition from the
tetragonal phase to the collapsed tetragonal phase induced by the external
pressure. An example of a compound with such a phase transition is
KFe$_{2}$As$_{2}$, which belongs to the family of the iron-based
superconductors. In this paper, we investigate the effects of the phase
transition on the structural, electronic, and dynamical properties of this
compound. Performing the ab initio calculations, we reproduce the dependence of
the lattice constants on pressure and analyze the changes of the inter-atomic
distances in the tetragonal and collapsed tetragonal phases. Using the tight
binding model with maximally localized Wannier orbitals, we calculate and
discuss the influence of pressure on the electronic band structure as well as
on the shape of the Fermi surface. We found a precursor of the phase transition
in the form of enhancement of overlapping between two Wannier orbitals of As
atoms. In order to better understand the superconducting properties of
KFe$_{2}$As$_{2}$, we study the orbital-projected Cooper pairs susceptibility
as a function of pressure. We found a decrease of susceptibility with the
increasing pressure in a good qualitative agreement with experimental
observation. The structural transition also influences the phonon spectrum of
KFe$_{2}$As$_{2}$, which exhibits pronounced changes induced by pressure. Some
phonon modes related with the vibrations of Fe and As atoms show an anomalous,
nonmonotonic dependence on pressure close to the phase transition.",1903.07953v1
2019-03-22,Bayesian optimization of chemical composition: a comprehensive framework and its application to $R$Fe$_{12}$-type magnet compounds,"We propose a framework for optimization of the chemical composition of
multinary compounds with the aid of machine learning. The scheme is based on
first-principles calculation using the Korringa-Kohn-Rostoker method and the
coherent potential approximation (KKR-CPA). We introduce a method for
integrating datasets to reduce systematic errors in a dataset, where the data
are corrected using a smaller and more accurate dataset. We apply this method
to values of the formation energy calculated by KKR-CPA for nonstoichiometric
systems to improve them using a small dataset for stoichiometric systems
obtained by the projector-augmented-wave (PAW) method. We apply our framework
to optimization of $R$Fe$_{12}$-type magnet compounds
(R$_{1-\alpha}$Z$_{\alpha}$)(Fe$_{1-\beta}$Co$_{\beta}$)$_{12-\gamma}$Ti$_{\gamma}$,
and benchmark the efficiency in determination of the optimal choice of elements
(R and Z) and ratio ($\alpha$, $\beta$ and $\gamma$) with respect to
magnetization, Curie temperature and formation energy. We find that the
optimization efficiency depends on descriptors significantly. The variable
$\beta$, $\gamma$ and the number of electrons from the R and Z elements per
cell are important in improving the efficiency. When the descriptor is
appropriately chosen, the Bayesian optimization becomes much more efficient
than random sampling.",1903.09385v2
2019-05-22,Crystal structure and thermodynamic properties of the non-centrosymmetric PrRu$_4$Sn$_6$ caged compound,"PrRu$_4$Sn$_6$ is a tetragonal, non-centrosymmetric structure compound. It is
isostructural to the extensively studied Kondo insulator CeRu$_4$Sn$_6$ which
crystallizes in the YRu$_4$Sn$_6$-type structure with space group $I$\={4}2$m$.
In this structure, the Pr atom fills the void formed by the octahedral
Ru$_4$Sn$_6$ units which results in a tetragonal body-centred arrangement. Here
we present reports on the physical and magnetic properties of PrRu$_4$Sn$_6$.
The temperature dependences of specific heat, $C_p(T)$, electrical resistivity,
$\rho(T)$, and magnetic susceptibility, $\chi(T)$, reveal the absence of a
long-range magnetic ordering down to 2 K. $\chi(T)$ follows a Curie-Weiss
behaviour above 100 K with an effective magnetic moment, $\mu_\mathrm{eff}$ =
3.34 $\mu_B$/Pr and paramagnetic Weiss temperature, $\theta_p$ = $-$19.47 K
indicating a dominant antiferromagnetic interaction. The magnetization at 2 K
is quasi-linear in nature and attains a value of 0.86 $\mu_B$/Pr at 7 T which
is well reduced compared to the calculated value of 3.32 $\mu_B$/Pr expected
for a free Pr$^{3+}$ ion. This is attributed to possible magneto-crystalline
anisotropy in the system. $C_p(T)$ indicates the presence of a optical-phonon
mode which is supported by a glass-like thermal conductivity above $\sim$45 K.
This observation is associated with caged structured compounds where the
low-frequency optical-phonon mode of the guest atom interacts with the host
lattice, resulting in the scattering of heat-carrying quasiparticles.",1905.09008v1
2019-04-29,New Strategies in Modeling Electronic Structures and Properties with Applications to Actinides,"This chapter discusses contemporary quantum chemical methods and provides
general insights into modern electronic structure theory with a focus on
heavy-element-containing compounds. We first give a short overview of
relativistic Hamiltonians that are frequently applied to account for
relativistic effects. Then, we scrutinize various quantum chemistry methods
that approximate the $N$-electron wave function. In this respect, we will
review the most popular single- and multi-reference approaches that have been
developed to model the multi-reference nature of heavy element compounds and
their ground- and excited-state electronic structures. Specifically, we
introduce various flavors of post-Hartree--Fock methods and optimization
schemes like the complete active space self-consistent field method, the
configuration interaction approach, the Fock-space coupled cluster model, the
pair-coupled cluster doubles ansatz, also known as the antisymmetric product of
1 reference orbital geminal, and the density matrix renormalization group
algorithm. Furthermore, we will illustrate how concepts of quantum information
theory provide us with a qualitative understanding of complex electronic
structures using the picture of interacting orbitals. While modern quantum
chemistry facilitates a quantitative description of atoms and molecules as well
as their properties, concepts of quantum information theory offer new
strategies for a qualitative interpretation that can shed new light onto the
chemistry of complex molecular compounds.",1908.03916v2
2019-08-16,A case study of bilayered spin-$1/2$ square lattice compound [VO(HCOO)$_2\cdot$(H$_2$O)],"We present the synthesis and a detail investigation of structural and
magnetic properties of polycrystalline [VO(HCOO)$_2\cdot$(H$_2$O)] by means of
x-ray diffraction, magnetic susceptibility, high-field magnetization, heat
capacity, and electron spin resonance measurements. It crystallizes in a
orthorhombic structure with space group $Pcca$. It features distorted VO$_6$
octahedra connected via HCOO linker (formate anions) forming a two-dimensional
square lattice network with a bilayered structure. Analysis of magnetic
susceptibility, high field magnetization, and heat capacity data in terms of
the frustrated square lattice model unambiguously establish
quasi-two-dimensional nature of the compound with nearest neighbour interaction
$J_1/k_{\rm B} \simeq 11.7$~K and next-nearest-neighbour interaction
$J_2/k_{\rm B} \simeq 0.02$~K. It undergoes a N\'eel antiferromagnetic ordering
at $T_{\rm N} \simeq 1.1$~K. The ratio $\theta_{\rm CW}/T_{\rm N} \simeq 10.9$
reflects excellent two-dimensionality of the spin-lattice in the compound. A
strong in-plane anisotropy is inferred from the linear increase of $T_{\rm N}$
with magnetic field, consistent with the structural data.",1908.06032v1
2019-08-20,DeepScaffold: a comprehensive tool for scaffold-based de novo drug discovery using deep learning,"The ultimate goal of drug design is to find novel compounds with desirable
pharmacological properties. Designing molecules retaining particular scaffolds
as the core structures of the molecules is one of the efficient ways to obtain
potential drug candidates with desirable properties. We proposed a
scaffold-based molecular generative model for scaffold-based drug discovery,
which performs molecule generation based on a wide spectrum of scaffold
definitions, including BM-scaffolds, cyclic skeletons, as well as scaffolds
with specifications on side-chain properties. The model can generalize the
learned chemical rules of adding atoms and bonds to a given scaffold.
Furthermore, the generated compounds were evaluated by molecular docking in
DRD2 targets and the results demonstrated that this approach can be effectively
applied to solve several drug design problems, including the generation of
compounds containing a given scaffold and de novo drug design of potential drug
candidates with specific docking scores. Finally, a command line interface is
created.",1908.07209v4
2019-08-23,Strong bulk photovoltaic effect in chiral crystal in the visible spectrum,"Structurally chiral materials hosting multifold fermions with large
topological number have attracted considerable attention because of their
naturally long surface Fermi arcs and bulk quantized circular photogalvanic
effect (CPGE). Multifold fermions only appear in metallic states, and
therefore, most studies so far have only focused on the semimetals in compounds
with chiral crystal structures. In this work, we show that the structurally
chiral topological trivial insulators are also exotic states, which is
interesting from the application point of view, owing to their natural
advantage to host a large bulk photovoltaic effect in the visible wavelength
region. In the last decades, the shift current in the visible wavelength region
was limited to be 10 uA/V2 . By scanning the insulators with chiral structure,
we found a class of compounds with photoconductivity ranging from 20 to 80
uA/V2 , which is approximately one order of magnitude larger than that reported
in other real materials. This work illustrates that the compounds with chiral
structure can host both quantum CPGE and a strong shift current in the second
order optical response. Moreover, this work offers a good platform for the
study of the shift current and its future application by putting the focus on
insulator with chiral lattices, so far overlooked in photovoltaic technologies.",1908.08878v2
2019-09-08,Open Compound Domain Adaptation,"A typical domain adaptation approach is to adapt models trained on the
annotated data in a source domain (e.g., sunny weather) for achieving high
performance on the test data in a target domain (e.g., rainy weather). Whether
the target contains a single homogeneous domain or multiple heterogeneous
domains, existing works always assume that there exist clear distinctions
between the domains, which is often not true in practice (e.g., changes in
weather). We study an open compound domain adaptation (OCDA) problem, in which
the target is a compound of multiple homogeneous domains without domain labels,
reflecting realistic data collection from mixed and novel situations. We
propose a new approach based on two technical insights into OCDA: 1) a
curriculum domain adaptation strategy to bootstrap generalization across
domains in a data-driven self-organizing fashion and 2) a memory module to
increase the model's agility towards novel domains. Our experiments on digit
classification, facial expression recognition, semantic segmentation, and
reinforcement learning demonstrate the effectiveness of our approach.",1909.03403v2
2019-09-16,Magnetic ground state of the frustrated spin-1/2 chain compound $β$-TeVO$_4$ at high magnetic fields,"Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit
remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave
(SDW) and multipolar/spin-nematic phases as a function of the magnetic field.
Here we report a study of $\beta$-TeVO$_4$, an archetype of such compounds,
based on magnetization and neutron diffraction measurements up to 25 T. We find
the transition from the helical VC ground state to the SDW state at $\sim$3 T
for the magnetic field along the $a$ and $c$ crystal axes, and at $\sim$9 T for
the field along the $b$ axis. The high-field (HF) state, existing above
$\sim$18 T, i.e., above $\sim$1/2 of the saturated magnetization, is an
incommensurate magnetically ordered state and not the spin-nematic state, as
theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF
state is likely driven by sizable interchain interactions and symmetric
intrachain anisotropies uncovered in previous studies. Consequently, the
potential existence of the spin nematic phase in $\beta$-TeVO$_4$ is limited to
a narrow field range, i.e., a few tenths of a tesla bellow the saturation of
the magnetization, as also found in other frustrated spin-1/2 chain compounds.",1909.07085v1
2019-11-30,High-Temperature Charge-Stripe Correlations in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$,"We use resonant inelastic x-ray scattering to investigate charge-stripe
correlations in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$. By differentiating
elastic from inelastic scattering, it is demonstrated that charge-stripe
correlations precede both the structural low-temperature tetragonal phase and
the transport-defined pseudogap onset. The scattering peak amplitude from
charge stripes decays approximately as $T^{-2}$ towards our detection limit.
The in-plane integrated intensity, however, remains roughly temperature
independent. Therefore, although the incommensurability shows a remarkably
large increase at high temperature, our results are interpreted via a single
scattering constituent. In fact, direct comparison to other stripe-ordered
compounds (La$_{1.875}$Ba$_{0.125}$CuO$_4$,
La$_{1.475}$Nd$_{0.4}$Sr$_{0.125}$CuO$_4$ and La$_{1.875}$Sr$_{0.125}$CuO$_4$)
suggests a roughly constant integrated scattering intensity across all these
compounds. Our results therefore provide a unifying picture for the
charge-stripe ordering in La-based cuprates. As charge correlations in
La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$ extend beyond the low-temperature
tetragonal and pseudogap phase, their emergence heralds a spontaneous symmetry
breaking in this compound.",1912.00194v2
2019-12-03,A generalised linear Ramsey graph construction,"A construction described by the current author in 2017 uses two linear
`prototype' graphs to build a compound graph with Ramsey properties inherited
from the prototypes.
  This paper describes a generalisation of that construction which has produced
improved lower bounds in many cases for multicolour Ramsey numbers. The
resulting graphs are linear, as before, and under certain specific conditions
set out here, they can be cyclic.
  The mechanism of the new construction requires that the first prototype
contains a triangle-free `template' in one colour, with defined properties.
This paper shows that in the compound graph, clique numbers in the colours of
the first prototype may exceed those of the prototype. However, it proves
necessary only to test for a limited subset of the possible cliques using these
colours, in order to evaluate the relevant clique numbers for the entire graph.
Clique numbers in the colours of the second prototype are equal to those of
that prototype. These attributes enable the efficient searching of a new family
of graphs based on the `template' approach.
  It has also been found that there are a number of useful cases in which the
clique numbers of the first prototype are not increased by the compounding
process.
  As a result of this construction many lower bounds can be improved. The
improvements include $R_4(5) \ge 4073$, $R_5(5) \ge 38914$, $R_3(6) \ge 1106$,
$R_4(6) \ge 21302$, $R_4(7) \ge 84623$ and $R_3(9) \ge 14034$.
  It is also shown that $R_3(9) \ge 14081$ using a non-linear construction.",1912.01164v3
2019-12-11,"Ab initio approach to the elastic, electronic, and optical properties of MoTe2: A topological Weyl semimetal","The topological Weyl semimetal MoTe2, in the orthorhombic phase, is an
important system both from the point of view of fundamental physics and
potential applications. In this study we have investigated the elastic,
electronic, bonding and optical properties of MoTe2 using density functional
theory. Study of the elastic constants and moduli indicates that MoTe2 is a
relatively soft material with high level of machinability. Mechanical stability
conditions are fulfilled. The compound possesses elastic and mechanical
anisotropy and is prone to brittle fracture. Elastic parameters indicate that
both covalent and metallic bondings are present in MoTe2. This is supported by
the charge density distribution mapping and Mulliken and Hirshfeld bond
population analyses. Debye temperature has been calculated. A relatively low
value of Debye temperature also supports the scenario where bonding strengths
are weak. The bulk electronic band structure calculations reveal clear
indications of semi-metallic character. A pseudogap in the electronic energy
density of states at the Fermi level indicates high level of electronic
stability. Features reminiscent of the Dirac cone is observed close to the
Fermi level. There is significant electronic anisotropy. Bands running in the
crystallographic c-direction are non-dispersive with high carrier effective
mass. Investigation of optical constants demonstrate that MoTe2 possess
excellent reflecting characteristics over a wide spectral range encompassing
the infrared to ultraviolet regions. The compound also has high refractive
index in the visible range. MoTe2 is optically anisotropic, reflecting the
anisotropic nature of the electronic band structure. The energy dependent
optical parameters show metallic features and are in complete accord with the
electronic density of states calculations.",1912.05112v1
2020-02-03,Direct and real-time analysis in a plasma reactor using a compact FTICR/MS: degradation of acetone in nitrogen and by-products formation,"Methods for reduction of Volatile Organic Compounds (VOCs) content in air
depend on the 10 application considered. For low concentration and low flux,
non-thermal plasma methods are often considered as efficient. However, the
complex chemistry involved is still not well understood as there is a lack of
datasets of byproducts formation. So as to overcome this issue, rapid
analytical methods are needed. We present the coupling of a rapid chemical
ionization mass spectrometer (CIMS) for the real-time analysis of the VOCs
formed during a degradation experiment. The high resolution instrument used 15
allows for chemical ionization and direct quantification of non-targeted
compounds. We present degradation experiments of acetone in a photo-triggered
nitrogen plasma discharge. Two regimes were highlighted: efficient conversion
at low concentrations (<100ppm) and moderate efficiency conversion at higher
concentrations (>100ppm). Those two regimes were clearly delimited as the sum
of two exponential curves occuring at respectively low and high concentrations.
Many by-products were detected, in 20 particular HCN presented a significantly
high yield. Nitrile compounds (acetonitrile, propionitrile,...) are formed as
well. To a lower extent, ketene, acetaldehyde and formaldehyde are observed.
The association of the high resolution mass spectrometer to the plasma reactor
will allow further insights into the plasma chemistry and comparison to
modelisation.",2002.00873v1
2020-02-15,"Understanding high ordering temperature in Gd$_6$FeBi$_2$ magnet: critical behavior, electronic structure and crystal-field analysis","Gd6FeBi2 is reported as the only one room-temperature magnet with a Curie
temperature (Tc) of ca. 350 K among more than hundreds of compounds with its
structural type, which makes it more attractive in potential applications. To
reveal the origin of such high ordering temperature, critical behaviors,
electronic structure and crystal-field effects of Gd6FeBi2 are investigated in
this work. The short-range Gd-Fe ferrimagnetic interaction is supported by the
non-Curie-Weiss paramagnetic behavior, crystal and electronic structure
analyses, in agreement with previous DFT calculations. Unlike the strong TM-TM
exchange interactions, the Gd-Fe exchange interaction shows limited influence
on the critical exponents determined by long-range exchange interactions, which
seems a common feature in RE-TM based alloys without TM-TM exchange
interactions. However, the strong Gd-Fe hybridization reduces the influence of
vibronic couplings on the short-range exchange interaction and thus allows a
high Tc. The broadening or splitting mechanism of Gd 4f-electron bands is
addressed based on crystal-field analysis and likely another factor for
elevated Tc in Gd6FeBi2 and Gd-based compounds with non-magnetic elements.
Different magnetic behaviors among isostructural compounds, and the
relationship between the band splitting and crystal-field effects is also
discussed.",2002.06402v1
2020-02-18,Computational Study of Defect variant Perovskites A2BX6 for Photovoltaic Applications,"A comprehensive study of the structural, electronic, and optical properties
of lead-free perovskites has been carried out by means of first principles
method based on DFT. The calculations are performed for the compound of the
type A2BX6 with A=Rb, and Cs; B=Sn, Pd, and Pt; and X=Cl, Br, and I. The
calculated structural parameters (lattice constants and bond lengths) agree
well with the experiments. The computed band gap reveals a semiconducting
profile for all these compounds showing a decreasing trend of the band gap
energy by changing the halide ions consecutively from Cl to Br and Br to I.
However, for variation in the B-site cation, the band gap increases by changing
the cation from Pd to Pt via Sn. The most likely compounds, Rb2PdBr6 and
Cs2PtI6, exhibit a band gap within the optimal range of 0.9-1.6 eV for
single-junction photovoltaic applications. The optical properties in terms of
the optimal value of the dielectric constant, optical conductivity, and
absorption coefficient are also investigated upto the photon energy of 10 eV.
Our results indicate that upon changing the halogen ions (Cl by Br and Br by I)
the optical properties altered significantly. Maximum dielectric constants and
high optical absorption are found for Rb2PdI6 and Cs2PtI6. The unique
optoelectronic properties such as ideal band gap, high dielectric constants,
and optimum absorption of A2BX6 perovskites could be efficiently utilized in
designing high performance single and multi-junction perovskite solar cells.",2002.07543v2
2020-03-23,Evolution of Griffiths Phase and Critical Behaviour of La1-xPbxMnO3+-y Solid Solutions,"Polycrystalline La1-xPbxMnO3+-y (x = 0.3, 0.35, 0.4) solid solutions were
prepared by solid state reaction method and their magnetic properties have been
investigated. Rietveld refinement of X-ray powder diffraction patterns showed
that all samples are single phase and crystallized with the rhombohedral
structure in the R-3c space group. A second order paramagnetic to ferromagnetic
phase transition was observed for all materials. The Griffiths phase (GP),
identified from the temperature dependence of the inverse susceptibility, was
suppressed by increasing magnetic field and showed a significant dependence on
A-site chemical substitution. The critical behaviour of the compounds was
investigated near to their Curie temperatures, using intrinsic magnetic field
data. The critical exponents (\b{eta}, {\gamma} and {\delta}) are close to the
mean-field approximation values for all three compounds. The observed
mean-field like behaviour is a consequence of the GP and the formation of
ferromagnetic clusters. Long-range ferromagnetic order is established as the
result of long-range interactions between ferromagnetic clusters. The
magnetocaloric effect was studied in terms of the isothermal entropy change.
Our study shows that the material with the lowest chemical substitution (x =
0.3) has the highest potential (among the three compounds) as magnetic
refrigerant, owing to its higher relative cooling power (258 J/kg at 5 T field)
and a magnetic phase transition near room temperature.",2003.10207v2
2020-03-31,Application and Assessment of Deep Learning for the Generation of Potential NMDA Receptor Antagonists,"Uncompetitive antagonists of the N-methyl D-aspartate receptor (NMDAR) have
demonstrated therapeutic benefit in the treatment of neurological diseases such
as Parkinson's and Alzheimer's, but some also cause dissociative effects that
have led to the synthesis of illicit drugs. The ability to generate NMDAR
antagonists in silico is therefore desirable both for new medication
development and for preempting and identifying new designer drugs. Recently,
generative deep learning models have been applied to de novo drug design as a
means to expand the amount of chemical space that can be explored for potential
drug-like compounds. In this study, we assess the application of a generative
model to the NMDAR to achieve two primary objectives: (i) the creation and
release of a comprehensive library of experimentally validated NMDAR
phencyclidine (PCP) site antagonists to assist the drug discovery community and
(ii) an analysis of both the advantages conferred by applying such generative
artificial intelligence models to drug design and the current limitations of
the approach. We apply, and provide source code for, a variety of ligand- and
structure-based assessment techniques used in standard drug discovery analyses
to the deep learning-generated compounds. We present twelve candidate
antagonists that are not available in existing chemical databases to provide an
example of what this type of workflow can achieve, though synthesis and
experimental validation of these compounds is still required.",2003.14360v1
2020-06-03,Stochastic-based Neural Network hardware acceleration for an efficient ligand-based virtual screening,"Artificial Neural Networks (ANN) have been popularized in many science and
technological areas due to their capacity to solve many complex pattern
matching problems. That is the case of Virtual Screening, a research area that
studies how to identify those molecular compounds with the highest probability
to present biological activity for a therapeutic target. Due to the vast number
of small organic compounds and the thousands of targets for which such
large-scale screening can potentially be carried out, there has been an
increasing interest in the research community to increase both, processing
speed and energy efficiency in the screening of molecular databases. In this
work, we present a classification model describing each molecule with a single
energy-based vector and propose a machine-learning system based on the use of
ANNs. Different ANNs are studied with respect to their suitability to identify
biochemical similarities. Also, a high-performance and energy-efficient
hardware acceleration platform based on the use of stochastic computing is
proposed for the ANN implementation. This platform is of utility when screening
vast libraries of compounds. As a result, the proposed model showed appreciable
improvements with respect previously published works in terms of the main
relevant characteristics (accuracy, speed and energy-efficiency).",2006.02505v1
2020-06-05,An Accurate Current Model for III-V Field Effect Transistors Using a Novel Concept of Effective Transmission Coefficient,"In this work, we investigate the transport phenomena in compound
semiconductor material based buried channel Quantum Well MOSFET with a view to
developing a simple and effective model for the device current. Device
simulation has been performed in quantum ballistic regime using non-equilibrium
Greens function (NEGF) formalism. The simulated current voltage characteristics
using a novel concept of effective transmission coefficient has been found to
define the reported experimental data with high accuracy. The proposed model
has also been effective to capture the transport characteristics reported for
other compound semiconductor material based field effect transistors. The
concept of the proposed effective transmission coefficient and hence the model
lends itself to be a simple and powerful device analysis tool which can be
extensively used to predict the performance of a wide variety of compound
semiconductor devices in the pre fabrication stage. It has also demonstrated
consistency with device characteristics for doping concentration and channel
length scaling. Thus the model can help the device or process engineers to tune
the devices for the best possible performance.",2006.03681v1
2020-06-17,Electronic structure of a Si-containing topological Dirac semimetal CaAl2Si2,"There has been an upsurge in the discovery of topological quantum materials,
where various topological insulators and semimetals have been theoretically
predicted and experimentally observed. However, only very few of them contains
silicon, the most widely used element in electronic industry. Recently, ternary
compound CaAl2Si2 has been predicted to be a topological Dirac semimetal,
hosting Lorentz-symmetry-violating quasiparticles with a strongly tilted
conical band dispersion. In this work, by using high-resolution angle-resolved
photoemission spectroscopy (ARPES), we investigated the comprehensive
electronic structure of CaAl2Si2. A pair of topological Dirac crossings is
observed along the kz direction, in good agreement with the ab initio
calculations, confirming the topological Dirac semimetal nature of the
compound. Our study expands the topological material family on Si-containing
compounds, which have great application potential in realizing low-cost,
nontoxic electronic device with topological quantum states.",2006.09633v1
2020-06-29,Irreversible Heat Flow Across Phase Boundaries in Phase-Separated Manganites,"We have investigated the change in entropy with direct measurements of heat
flow as a function of magnetic field at fixed temperatures across the entire
phase diagram of the phase-separated (PS) compound
La$_{0.25}$Pr$_{0.375}$Ca$_{0.375}$MnO$_3$ (LPCMO). At this composition, the
compound shows competing charge-ordered/antiferromagnetic (CO/AF) ground
states. At a fixed temperature, we observe an increase in hysteresis in the
entropy as a function of the applied field. The heat flux shows progressively
irreversible hysteresis, which characterizes the energy barriers between the
two competing ground states, as the temperature is lowered. The increase in the
heat loss correlates with the increase in magnetic viscosity in the
phase-separated state.
  Keywords: manganites, avalanche effect, phase transition, heat flow, DSC,
entropy. Corresponding author: allimas@sandia.gov . On 10 April 2020, this
JAC-Elsevier article was accepted. Yet, its online publication shows numerous
errors: Cut-off text, missing Figure Captions, incomplete Table ... None of
which is our fault! This makes our paper hard to read, study and/or understand.
This reproduction is our final (error-free!) revision. When citing our refereed
paper, please also refer to this arXiv print. Thank you for understanding",2006.16381v2
2020-07-09,Quantification of Coulomb Interactions in layered Lithium and Sodium Battery Cathode Materials,"Despite the importance of the electron correlation in the first-principles
description of the Li-ion cathode materials, the Coulomb interaction parameter,
U is often treated as an ad hoc value. In practice, one usually relies on
empirical ways of parametric treatment of U to optimally match the
experimentally observed physical properties such as band gap or reaction
energy. Here, using constrained random phase approximation (cRPA) method, we
self-consistently evaluate the Coulomb U and Hund J values for representative
layered cathode materials including not only Li compounds but also Na
compounds; LiCoO2, LiNiO2, LiMnO2, NaCoO2, NaNiO2, and NaMnO2. We found that
the Coulomb interaction parameters for Li and Na compounds and their polymorphs
with different layer stackings do not deviate much, which shows the dominant
role of local environment rather than of global structural features. We have
analyzed the origin of variable Coulomb parameters, which is mainly due to the
competition between the localization and screening. We provided cRPA Coulomb
parameters for battery cathode materials and validate the values by observing
systematic improvement in describing the experimentally observed average
intercalation voltage and lattice parameters. These results can be applied for
the first-principles calculations as well as model-based simulations for the
theoretical investigation of cathode systems.",2007.04652v1
2020-09-28,Liquidations: DeFi on a Knife-edge,"The trustless nature of permissionless blockchains renders
overcollateralization a key safety component relied upon by decentralized
finance (DeFi) protocols. Nonetheless, factors such as price volatility may
undermine this mechanism. In order to protect protocols from suffering losses,
undercollateralized positions can be liquidated. In this paper, we present the
first in-depth empirical analysis of liquidations on protocols for loanable
funds (PLFs). We examine Compound, one of the most widely used PLFs, for a
period starting from its conception to September 2020. We analyze participants'
behavior and risk-appetite in particular, to elucidate recent developments in
the dynamics of the protocol. Furthermore, we assess how this has changed with
a modification in Compound's incentive structure and show that variations of
only 3% in an asset's dollar price can result in over 10m USD becoming
liquidable. To further understand the implications of this, we investigate the
efficiency of liquidators. We find that liquidators' efficiency has improved
significantly over time, with currently over 70% of liquidable positions being
immediately liquidated. Lastly, we provide a discussion on how a false sense of
security fostered by a misconception of the stability of non-custodial
stablecoins, increases the overall liquidation risk faced by Compound
participants.",2009.13235v6
2020-10-03,Flood Evacuation During Pandemic: A multi-objective Framework to Handle Compound Hazard,"The evacuation of the population from flood-affected regions is a
non-structural measure to mitigate flood hazards. Shelters used for this
purpose usually accommodate a large number of flood evacuees for a temporary
period. Floods during pandemic result in a compound hazard. Evacuations under
such situations are difficult to plan as social distancing is nearly impossible
in the highly crowded shelters. This results in a multi-objective problem with
conflicting objectives of maximizing the number of evacuees from flood-prone
regions and minimizing the number of infections at the end of the shelter's
stay. To the best of our knowledge, such a problem is yet to be explored in
literature. Here we develop a simulation-optimization framework, where multiple
objectives are handled with a max-min approach. The simulation model consists
of an extended Susceptible Exposed Infectious Recovered Susceptible (SEIRS)
model.We apply the proposed model to the flood-prone Jagatsinghpur district in
the state of Odisha, India. We find that the proposed approach can provide an
estimate of people required to be evacuated from individual flood-prone
villages to reduce flood hazards during the pandemic. At the same time, this
does not result in an uncontrolled number of new infections. The proposed
approach can generalize to different regions and can provide a framework to
stakeholders to manage conflicting objectives in disaster management planning
and to handle compound hazards.",2010.01386v1
2020-10-09,"DFT insights into new B-containing 212 MAX phases: Hf2AB2 (A = In, Sn)","212 MAX phase borides are new additions to the MAX phase family with enhanced
thermo-mechanical properties. In this article, first-principles calculations
have been carried out to explore the mechanical properties, Vickers hardness,
elastic anisotropy, thermal properties, and optical properties of predicted
thermodynamically stable MAX compounds Hf2AB2 (A = In, Sn). The structural
properties are compared with the available data to assess the validity of
calculations. The mechanical stability of Hf2AB2 (A = In, Sn) compounds is
established with the help of the computed stiffness constants (Cij). The
possible reason for enhanced mechanical properties and Vickers hardness of
Hf2SnB2 is explained based on the analysis of bonding strength, followed by the
electronic density of states. Higher mechanical strength and Vickers hardness
of Hf2AB2 (A = In, Sn) compared to Hf2AC (A = In, Sn) are also indicated in the
light of charge density mapping. The values of Pugh ratio, Poissons ratio and
Cauchy pressure predict brittle character of the studied compounds. Besides,
the anisotropic nature of the titled borides is investigated by 2D and 3D plots
of elastic moduli along with some well established anisotropy indices. Thermal
properties were investigated by calculating the Debye temperature, minimum
thermal conductivity, Gr\""uneisen parameter, and melting temperature. The
thermal properties of Hf2AB2 (A = In, Sn) are also superior to Hf2AC (A = In,
Sn). The optical constants such as real and imaginary parts of the dielectric
function, refractive index, extinction coefficient, absorption coefficient,
photoconductivity, reflectivity, and loss function are investigated.",2010.04675v1
2020-10-14,Weakly coupled alternating $S=1/2$ chains in the distorted honeycomb lattice compound Na$_2$Cu$_2$TeO$_6$,"Spin-1/2 chains with alternating antiferromagnetic (AF) and ferromagnetic
(FM) couplings exhibit quantum entanglement like the integer-spin Haldane
chains and might be similarly utilized for quantum computations. Such
alternating AF-FM chains have been proposed to be realized in the distorted
honeycomb-lattice compound Na$_2$Cu$_2$TeO$_6$, but to confirm this picture a
comprehensive understanding of the exchange interactions including terms
outside of the idealized model is required. Here we employ neutron scattering
to study the spin dynamics in Na$_2$Cu$_2$TeO$_6$ and accurately determine the
coupling strengths through the random phase approximation and density
functional theory (DFT) approaches. We find the AF and FM intrachain couplings
are the dominant terms in the spin Hamiltonian, while the interchain couplings
are AF but perturbative. This hierarchy in the coupling strengths and the
alternating signs of the intrachain couplings can be understood through their
different exchange paths. Our results establish Na$_2$Cu$_2$TeO$_6$ as a
weakly-coupled alternating AF-FM chain compound and reveal the robustness of
the gapped ground state in alternating chains under weak interchain couplings.",2010.06745v2
2020-10-17,Dependency of XC functionals and role of 3s(2p) orbitals of Co(Si) as core/valence states on the vibrational and thermodynamic properties of CoSi,"First-principles phonon calculations along with density functional theory
(DFT) play an important role to study the dynamical and thermal properties of
materials. Here, we investigate the effect of exchange correlation (XC)
functionals on the vibrational and thermodynamic properties of CoSi. The role
of 3s(2p) orbitals of Co(Si) as core/valence states on the phonon properties of
this compound is also studied. Phonon calculations are carried out by finite
displacement method with supercell approach using equilibrium crystal
structures obtained from DFT calculations. The calculated results are compared
with the existing experiment. Three XC functionals, viz., LDA, PBEsol and SCAN
are used for calculating the phonon dispersion, phonon density of states
(DOS)/partial DOS and thermal properties of this compound. SCAN is found to
give the highest phonon frequency of $\sim$56 meV which is in good agreement
with the experimental value, while LDA (PBEsol) gives $\sim$54 ($\sim$55) meV.
The zero-point energy is calculated as $\sim$ 10 kJ/mol for all the
functionals. The Debye temperatures ($\Theta_{D}$) are computed as $\sim$626 K,
$\sim$638 K and $\sim$650 K for LDA, PBEsol and SCAN, respectively. The
$\Theta_{D}$ obtained from LDA gives the good agreement with the reported
value. The phonon dispersion and phonon DOS are found to be dependent whether
3s(2p) orbitals of Co(Si) are considered as core or valence states. But, this
orbital dependency is seemed to be insignificant on the thermal properties of
this compound.",2010.08780v1
2020-10-23,Misfit layer compounds: a platform for heavily-doped two-dimensional transition metal dichalcogenides,"Transition metal dichalcogenides (TMDs) display a rich variety of
instabilities such as spin and charge orders, Ising superconductivity and
topological properties. Their physical properties can be controlled by doping
in electric double-layer field-effect transistors (FET). However, for the case
of single layer NbSe$_2$, FET doping is limited to $\approx 1\times 10^{14}$
cm$^{-2}$, while a somewhat larger charge injection can be obtained via
deposition of K atoms. Here, by performing ARPES, STM, quasiparticle
interference measurements, and first principles calculations we show that a
misfit compound formed by sandwiching NbSe$_2$ and LaSe layers behaves as a
NbSe$_2$ single layer with a rigid doping of $0.55-0.6$ electrons per Nb atom
or $\approx 6\times 10^{14}$ cm$^{-2}$. Due to this huge doping, the $3\times3$
charge density wave is replaced by a $2\times2$ order with very short coherence
length. As a tremendous number of different misfit compounds can be obtained by
sandwiching TMDs layers with rock salt or other layers, our work paves the way
to the exploration of heavily doped 2D TMDs over an unprecedented wide range of
doping.",2010.12314v1
2020-11-04,Spin reorientations and crystal field modification in Ho$_{1-y}$Gd$_y$Al$_2$ compounds,"We have performed an experimental and theoretical investigation on the spin
reorientation transitions Ho$_{1-y}$Gd$_y$Al$_2$ compounds. Crystallographic,
magnetic and calorimetric measurements have been performed for five selected
samples in the Ho$_{1-y}$Gd$_y$Al$_2$ series ($y$ = 0, 0.25, 0.5, 0.75 and
1.0). From the results, a linear increase in the lattice parameter as a
function of Gd-content ($x$) is observed. Magnetization measurements show that
all samples present collinear ferromagnetism. Specific heat measurements were
performed in order to detail the first-order spin reorientation transition
(FOSRT) that appears for HoAl$_2$ around 20 K. Furthermore, we investigated how
the increase in Gd content affects the character of such phase transition. Our
results show a slightly modification in the spin reorientation transition
temperature, which moves to lower temperatures as Gd is increased in HoAl$_2$,
whereas for the selected concentrations up to x = 0.75 the first-order
character of the transition is maintained. Such behavior may lead to a large
refrigerant capacity (RC) over a wide temperature range, which is an important
parameter to evaluate the magnetocaloric effect (MCE) of such compounds. The
theoretical analysis by means of a model Hamiltonian that includes crystal
field, exchange and Zeeman interactions reveals a modification in the
crystal-field acting on Ho ions as Gd-content is increased.",2011.02571v1
2020-11-13,The elastic properties and lattice dynamics for selected 211 MAX phases: A DFT study,"The elastic properties and lattice dynamics of Ti$_2$AlC, Ti$_2$AlN,
Ti$_2$GaC, Ti$_2$GaN, Ti$_2$PbC, Ti$_2$CdC and Ti$_2$SnC have been investigated
using the density functional theory within the generalized gradient
approximations as expressed in Quantum Espresso and VASP codes. The obtained
lattice parameters are in agreement with the previous theoretical research and
available experimental data. The elastic properties of the MAX phases under
study have been calculated. The values of elastic anisotropy, Young's modulus,
Poisson ratio and shear modulus reveal that the compounds are stable and
ductile and that Ti$_2$PbC and Ti$_2$CdC are more stable than the other
considered compounds. Thus, the seven compounds may be useful for industrial
applications. The calculated phonon spectra confirm that the studied MAX phases
are dynamically stable because of the absence of imaginary phonon modes. The
temperature dependent lattice thermal conductivity of MAX phases have been
determined using the Debye theory as outlined by Slack. The obtained
$\kappa_{ph}$ for Ti$_2$AlC at 1300 K agree with experimental findings within
9$\%$. The estimated minimum thermal conductivities ($\kappa_{min}$) of the MAX
phases obtained by using empirical formula suggested by Clarke show that
Ti$_2$PbC possesses the lowest minimum thermal conductivity.",2011.07102v1
2020-11-25,Electrochemical Ion Insertion: From Atoms to Devices,"Electrochemical ion insertion involves coupled ion-electron transfer
reactions, transport of guest species, and redox of the host. The hosts are
typically anisotropic solids with two-dimensional conduction planes, but can
also be materials with one-dimensional or isotropic transport pathways. These
insertion compounds have traditionally been studied in the context of energy
storage, but also find extensive applications in electrocatalysis,
optoelectronics, and computing. Recent developments in operando, ultrafast, and
high-resolution characterization methods, as well as accurate theoretical
simulation methods, have led to a renaissance in the understanding of
ion-insertion compounds. In this Review, we present a unified framework for
understanding insertion compounds across time and length scales ranging from
atomic to device levels. Using graphite, transition metal dichalcogenides,
layered oxides, oxyhydroxides, and olivines as examples, we explore
commonalities in these materials in terms of point defects, interfacial
reactions, and phase transformations. We illustrate similarities in the
operating principles of various ion-insertion devices ranging from batteries
and electrocatalysts to electrochromics and thermal transistors, with the goal
of unifying research across disciplinary boundaries.",2011.12991v1
2020-11-27,d0 Ferromagnetism in Li-doped ZnO Compounds,"Recently, d0 ferromagnetic materials have been projected as one of the
promising novel materials for spintronics applications. In this work, we have
studied Li-doped ZnO compounds, i.e. Zn1-xLixO (x=0, 0.02, 0.04, and 0.06)
samples, prepared by the solid-state reaction route method. From the study of
crystal structure using X-ray diffraction (XRD) patterns, it is evident that
the prepared materials have been formed in a single-phase of the hexagonal
wurtzite structure. The refinement of the XRD patterns suggests that there are
very small changes in the lattice parameters upon Li-incorporation in ZnO. The
average crystallite size (SC), estimated from XRD patterns was found to be in
the range of 35-50 nm. The microstructural study by scanning electron
microscope reveals the uniform morphology of the grains of the order of 50-70
nm. The energy dispersive spectrum indicates that no unwanted ferromagnetic
impurities have crept into the final prepared samples. The measurement of the
temperature (T) variation of magnetization (M) with SQUID magnetometer
indicates that undoped ZnO exhibits diamagnetic property but all Li-doped
compounds exhibit room-temperature ferromagnetism and with a magnetic
irreversibility behavior between zero-field cooled and field cooled M-T data.
From the magnetization versus field measurements at 3 and 300 K, it is observed
that Li-doped samples exhibit ferromagnetic loops with ultra-soft coercivity
(~50 Oe) and with a maximum saturation magnetization of 0.10 emu/gm for x= 0.02
sample, which decreases with the increase in Li concentration.",2011.13713v1
2020-12-06,Evolution of possible Weyl semimetal states across the hole-doping induced Mott transition in pyrochlore iridates,"We study possible Weyl semimetals of strongly-correlated electrons by
investigating magnetotransport properties in pyrochlore R2Ir2O7 (R=rare-earth
ions), choosing three types of R ions to design the exchange coupling scheme
between R 4f and Ir 5d moments; non-magnetic Eu (4f6), isotropic Gd (4f7), and
anisotropic Tb (4f8). In the doping-induced semimetallic state, distinctive
features of magnetoresistance and Hall effect are observed in R=Gd and Tb
compounds due to the effects of the exchange-enhanced isotropic and anisotropic
Zeeman fields, respectively, exemplifying the double Weyl semimetal and the
2-in 2-out line-node semimetal as predicted by theories. In particular, a Hall
angle of R=Gd compound is strongly enhanced to 1.5 % near above the critical
doping for the Mott transition. Furthermore, an unconventional Hall
contribution is discerned for a lower doping regime of R=Gd compound, which can
be ascribed to the emergence of Weyl points with the field-distorted all-in
all-out order state. These findings indicate that the hole-doping induced Mott
transition as well as the characteristic f-d exchange interaction stabilizes
versatile topological semimetal states in a wide range of material parameter
space.",2012.03251v2
2020-12-08,Complex impedance and Raman spectroscopy of Na$_{0.5}$(Bi$_{1-x}$Dy$_x$)$_{0.5}$TiO$_3$ ceramics,"In this work structural refinement, complex impedance spectroscopy, and Raman
spectroscopy have been investigated on
Na$_{0.5}$(Bi$_{1-x}$Dy$_x$)$_{0.5}$TiO$_3$ (xDyNBT) ceramic systems. The pure
NBT, 2DyNBT and 5DyNBT compounds crystallize in a rhombohedral structure while
the 15DyNBT composition crystallizes in an orthorhombic Pnma structure. We
reported that dysprosium addition affects the phase transition temperatures as
well as the dielectric losses. The electrical transport at high temperatures
was investigated using the CIS over a wide frequency range. The studied samples
showed a non-Debye type process, with a short-range relaxation for the pure NBT
and a coexistence of both localized and long-range relaxations of charge
carriers for the 2DyNBT and 5DyNBT compounds. For the high concentration,
15DyNBT, a short-range relaxation is observed. Moreover, using a brick-layer
model we discuss the resistance and capacitance of the different contributors
(grain and grain boundaries) in our samples. High temperature Raman
spectroscopy investigation was performed in order to follow the temperature
evolution of the structural transformations on ferroelectric compounds.
Anomalies in the temperature evolution of the vibrational modes are seen to
correlate well with the temperature transitions observed from dielectric
measurements.",2012.04325v1
2020-12-08,Hurricane-blackout-heatwave Compound Hazard Risk and Resilience in a Changing Climate,"Hurricanes have caused power outages and blackouts, affecting millions of
customers and inducing severe social and economic impacts. The impacts of
hurricane-caused blackouts may worsen due to increased heat extremes and
possibly increased hurricanes under climate change. We apply hurricane and
heatwave projections with power outage and recovery process analysis to
investigate how the emerging hurricane-blackout-heatwave compound hazard may
vary in a changing climate, for Harris County in Texas (including major part of
Houston City) as an example. We find that, under the high-emissions scenario
RCP8.5, the expected percent of customers experiencing at least one
longer-than-5-day hurricane-induced power outage in a 20-year period would
increase significantly from 14% at the end of the 20th century to 44% at the
end of the 21st century in Harris County. The expected percent of customers who
may experience at least one longer-than-5-day heatwave without power (to
provide air conditioning) would increase alarmingly, from 0.8% to 15.5%. These
increases of risk may be largely avoided if the climate is well controlled
under the stringent mitigation scenario RCP2.6. We also reveal that a moderate
enhancement of critical sectors of the distribution network can significantly
improve the resilience of the entire power grid and mitigate the risk of the
future compound hazard. Together these findings suggest that, in addition to
climate mitigation, climate adaptation actions are urgently needed to improve
the resilience of coastal power systems.",2012.04452v1
2020-12-17,Ab initio study and assignment of electronic states in molecular RaCl,"Radium compounds have attracted recently considerable attention due to both
development of experimental techniques for high-precision laser spectroscopy of
molecules with short-lived nuclei and amenability of certain radium compounds
for direct cooling with lasers. Currently, radium monofluoride (RaF) is one of
the most studied molecules among the radium compounds, both theoretically and
recently also experimentally. Complementary studies of further diatomic radium
derivatives are highly desired to assess the influence of chemical substitution
on diverse molecular parameters, especially on those connected with laser
cooling, such as vibronic transition probabilities, and those related to
violations of fundamental symmetries. In this article high-precision \emph{ab
initio} studies of electronic and vibronic levels of diatomic radium
monochloride (RaCl) are presented. Recently developed approaches for treating
electronic correlation with Fock-space coupled cluster methods are applied for
this purpose. Theoretical results are compared to an early experimental
investigation by Lagerqvist and used to partially reassign the experimentally
observed transitions and molecular electronic levels of RaCl. Effective
constants of $\mathcal{P}$-odd hyperfine interaction $W_{\rm{a}}$ and
$\mathcal{P,T}$-odd scalar-pseudoscalar nucleus-electron interaction
$W_{\rm{s}}$ in the ground electronic state of RaCl are estimated within the
framework of a quasirelativistic Zeroth-Order Regular Approximation approach
and compared to parameters in RaF and RaOH.",2012.09818v1
2020-12-18,Carbon-Doped Sulfur Hydrides as Room-Temperature Superconductors at 270 GPa,"To understand the most-recent experiment on room-temperature
superconductivity in carbonaceous sulfur hydride (CSH) systems under high
pressure, we have performed extensive stoichiometry and structure searches of
ternary CSH compounds using generic evolutionary algorithms. Judged from the
formation enthalpy of different CSH compounds, our studies conclude that
certain levels of carbon doping (~5%-6%) in sulfur hydride (H$_3$S) in its R3m
and phases gives rise to the most-stable structure (second to the H$_3$S
itself) among the various CSH systems found. The replacement of a small amount
of sulfur atoms by carbon in compounds like C$_1$S$_{15}$H$_{48}$ and
C$_1$S$_{17}$H$_{54}$ results in a stronger electron-phonon coupling and a
higher averaged phonon frequency that increases with pressure, thereby leading
to room-temperature superconductivity at ~270 GPa. The calculated
superconducting transition temperature T$_c$ of C$_1$S$_{15}$H$_{48}$ and
C$_1$S$_{17}$H$_{54}$ as a function of pressure shows reasonably good agreement
with experimental measurements. Before transition to superconducting states at
~80 GPa, the CSH system is predicted to have a stoichiometry of
C$_2$S$_2$H$_{10}$ with a stable structure of P1 symmetry, which is supported
by the direct comparison of its Raman spectrum with experiment.",2012.10259v1
2021-01-01,"Structure and magnetic properties of melilite-type compounds RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) with Rare-Earth ions on Shastry-Sutherland lattice","Rare-earth (RE) based frustrated magnets as typical systems of combining
strong spin-orbit coupling, geometric frustration and anisotropic exchange
interactions, can give rise to diverse exotic magnetic ground states such as
quantum spin liquid (QSL). The discovery of new RE-based frustrated materials
is crucial for exploring the exotic magnetic phases. Herein, we report the
synthesis, structure and magnetic properties of a family of melilite-type
RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) compounds crystallized in a tetragonal
structure, where magnetic RE3+ ions lay out on Shastry-Sutherland lattice (SSL)
within ab-plane and are well separated by nonmagnetic GeBe2O7 polyhedrons along
c-axis. Temperature-dependent susceptibilities and isothermal magnetization
M(H) measurements reveal that most RE2Be2GeO7 compounds except RE=Tb show no
magnetic ordering down to 2 K despite the dominant antiferromagnetic (AFM)
interactions, where Tb2Be2GeO7 undergoes AFM transition with Neel temperature
TN~ 2.5 K and field-induced spin flop behaviors (T< TN). In addition, the
calculated magnetic entropy change from the isothermal M(H) curves reveal a
viable magnetocaloric effect (MCE) for RE2Be2GeO7 (RE =Gd, Dy) in liquid helium
temperature regimes, Gd2Be2GeO7 shows maximum Sm up to 54.8 J K-1 Kg-1 at H= 7
T and Dy2Be2GeO7 has largest value Sm=16.1 J K-1 kg-1 at H= 2 T in this family.
More excitingly, rich diversity of RE ions in this family enables an archetype
for exploring exotic quantum magnetic phenomena with large variability of spin
located on SSL lattice.",2101.00156v1
2021-01-01,A catastrophic charge density wave in BaFe$_2$Al$_9$,"Charge density waves (CDW) are modulations of the electron density and the
atomic lattice that develop in some crystalline materials at low temperature.
We report an unusual example of a CDW in BaFe$_2$Al$_9$ below 100 K. In
contrast to the canonical CDW phase transition, temperature dependent physical
properties of single crystals reveal a first-order phase transition. This is
accompanied by a discontinuous change in the size of the crystal lattice. In
fact, this large strain has catastrophic consequences for the crystals causing
them to physically shatter. Single crystal x-ray diffraction reveals
super-lattice peaks in the low-temperature phase signaling the development of a
CDW lattice modulation. No similar low-temperature transitions are observed in
BaCo$_2$Al$_9$. Electronic structure calculations provide one hint to the
different behavior of these two compounds; the d-orbital states in the Fe
compound are not completely filled. Iron compounds are renowned for their
magnetism and partly filled d-states play a key role. It is therefore
surprising that BaFe$_2$Al$_9$ develops a structural modulation instead at low
temperature instead of magnetic order.",2101.00321v2
2021-01-13,Quasi-one-dimensional magnetism in the spin-$\frac12$ antiferromagnet BaNa$_{2}$Cu(VO$_{4}$)$_{2}$,"We report synthesis and magnetic properties of quasi-one-dimensional
spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain compound
BaNa$_2$Cu(VO$_4$)$_2$. This orthovanadate has a centrosymmetric crystal
structure, $C2/c$, where the magnetic Cu$^{2+}$ ions form spin chains. These
chains are arranged in layers, with the chain direction changing by 62$^0$
between the two successive layers. Alternatively, the spin lattice can be
viewed as anisotropic triangular layers upon taking the inter-chain
interactions into consideration. Despite this potential structural complexity,
temperature-dependent magnetic susceptibility, heat capacity, ESR intensity,
and NMR shift agree well with the uniform spin-$1/2$ Heisenberg chain model
with an intrachain coupling of $J/k_{\rm B} \simeq 5.6$ K. The saturation field
obtained from the magnetic isotherm measurement consistently reproduces the
value of $J/k_{\rm B}$. Further, the $^{51}$V NMR spin-lattice relaxation rate
mimics the 1D character in the intermediate temperature range, whereas magnetic
long-range order sets in below $T_{\rm N} \simeq 0.25$ K. The effective
interchain coupling is estimated to be $J_{\perp}/k_{\rm B} \simeq 0.1$ K. The
theoretical estimation of exchange couplings using band-structure calculations
reciprocate our experimental findings and unambiguously establish the 1D
character of the compound. Finally, the spin lattice of BaNa$_2$Cu(VO$_4$)$_2$
is compared with the chemically similar but not isostructural compound
BaAg$_2$Cu(VO$_4)_2$.",2101.05120v1
2021-01-24,Optical evidence of local and itinerant states in Ce- and Yb-heavy-fermion compounds,"The electronic properties of Cerium (Ce) and ytterbium (Yb) intermetallic
compounds may display a more local or more itinerant character depending on the
interplay of the exchange interactions among the $4f$ electrons and the Kondo
coupling between $4f$ and conduction electrons. For the more itinerant case,
the materials form heavy-fermions once the Kondo effect is developed at low
temperatures. Hence, a temperature variation occurs in the electronic structure
that can be traced by investigating the optical conductivity ($\sigma(\omega)$)
spectra. Remarkably, the temperature variation in the $\sigma(\omega)$ spectrum
is still present in the more localized case, even though the Kondo effect is
strongly suppressed. Here, we clarify the local and itinerant character in the
electronic structure by investigating the temperature dependence in the
$\sigma(\omega)$ spectra of various Ce and Yb compounds with a tetragonal
ThCr$_2$Si$_2$-type crystal structure. We explain the temperature change in a
unified manner. Above temperatures of about 100 K, the temperature dependence
of the $\sigma(\omega)$ spectra is mainly due to the electron-phonon
interaction, while the temperature dependence below is due to the Kondo effect.",2101.09696v2
2021-01-25,The Origin of Aromaticity: Aromatic Compounds as Intrinsic Topological Superconductors with Majorana Fermion,"Topological superconductors have been discovered with recent advances in
understanding the topological properties of condensed matters. These states
have a full pairing gap in the bulk and gapless counter-propagating Majorana
states at the boundary. A pair of Majorana zero modes is associated with each
vortex. This understanding had a great influence on the theory of
superconductivity and their following experiments, but its relevantce to
organic compounds was not closely observed. Here, we analyze the topological
states of various polyaromatic hydrocarbons (PAHs), including benzene, and
reveal that they are topological superconductors. We have analyzed the momentum
vectors of benzene and other PAHs through a semi-classical approach to confirm
their non-trivial state. Their unique properties might be originated from the
odd number of Kramers doublets in PAHs. The H\""uckel rule describing
aromaticity can be reinterpreted with a topological viewpoint. It suggests that
the (4n+2) rule can be split into two pairs of (2n+1) electrons each, namely,
electrons and holes with spin up and down. Therefore, it always forms an odd
number of Kramers` doublet. Moreover, n in the H\""uckel rule can be interpreted
as the winding number in global next-nearest-neighbor(NNN) hopping. This work
will re-establish the definition of aromaticity that has been known so far and
extend the use of aromatic compounds as topological superconductors to quantum
computers.",2101.09958v1
2021-02-02,Distinct magnetic ground states of $R_2$ZnIrO$_6$ ($R$ = La and Nd) determined by neutron powder diffraction,"Double perovskite iridates $A_2$ZnIrO$_6$ ($A$ = alkaline or lanthanide) show
complex magnetic behaviors ranging from weak ferromagnetism to successive
antiferromagnetic transitions. Here we report the static ($dc$) and dynamic
($ac$) magnetic susceptibility, and neutron powder diffraction measurements for
$A$ = La and Nd compounds to elucidate the magnetic ground state. Below 10~K,
the $A$ = La compound is best described as canted iridium moments in an
antiferromagnet arrangement with a propagation vector \textbf{k} = 0 and a net
ferromagnetic component along the $c$-axis. On the other hand, Nd$_2$ZnIrO$_6$
is described well as an antiferromagnet with a propagation vector \textbf{k} =
(1/2~1/2~0) below $T_\mathrm{N} \sim$ 17 K. Scattering from both the Nd and Ir
magnetic sublattices were required to describe the data and both were found to
lie almost completely within the $ab$-plane. $Dc$ susceptibility revealed a
bifurcation between the zero-field-cooled and field-cooled curves below
$\sim$13 K in Nd$_2$ZnIrO$_6$. A glassy state was ruled out by $ac$
susceptibility but detailed magnetic isotherms revealed the opening of the loop
below 13~K. These results suggest a delicate balance exists between the
Dzyaloshinskii-Moriya, crystal field schemes, and $d$-$f$ interaction in this
series of compounds.",2102.01276v1
2021-02-02,Complex Dirac-like Electronic Structure in Atomic Site Ordered Rh3In3.4Ge3.6,"We report the synthesis via an indium flux method of a novel
single-crystalline compound Rh3In3.4Ge3.6 that belongs to the cubic Ir3Ge7
structure type. In Rh3In3.4Ge3.6, the In and Ge atoms choose to preferentially
occupy, respectively, the 12d and 16f sites of the Im-3m space group, thus
creating a colored version of the Ir3Ge7 structure. Like the other compounds of
the Ir3Ge7 family, Rh3In3.4Ge3.6 shows potential as a thermoelectric displaying
a relatively large power factor, PF ~ 2 mW/cmK2, at a temperature T ~ 225 K
albeit showing a modest figure of merit, ZT = 8 x 10-4, due to the lack of a
finite band gap. These figures might improve through a use of chemical
substitution strategies to achieve band gap opening. Remarkably, electronic
band structure calculations reveal that this compound displays a complex
Dirac-like electronic structure relatively close to the Fermi level. The
electronic structure is composed of several Dirac type-I and type-II nodes, and
even Dirac type-III nodes that result from the touching between a flat band and
a linearly dispersing band. This rich Dirac-like electronic dispersion offers
the possibility to observe Dirac type-III nodes and study their role in the
physical properties of Rh3In3.4Ge3.6 and related Ir3Ge7-type materials.",2102.01793v1
2021-02-08,"Structural, magnetic, thermodynamic and electrical transport properties of a new compound $\mbox{Pr}_2\mbox{Rh}_{2}\mbox{Ga}$","A new ternary intermetallic compound $\mathrm{Pr_2Rh_2Ga}$ was synthesized by
arc-melting and was characterized by powder X-ray diffraction (PXRD),
magnetization, heat capacity $\mathrm{C}_p(\textit{T})$, and electrical
resistivity $\rho(T)$ measurements. PXRD patterns revealed that
$\mathrm{Pr_2Rh_2Ga}$ crystallizes in the $\rm{La_2Ni_3}$-type of orthorhombic
structure with the space group $Cmca$. The temperature variation of magnetic
susceptibility, $\mathrm {C}_p(\textit{T})$ and $\rho(T)$ confirmed that
$\mathrm{Pr_2Rh_2Ga}$ exhibits a ferromagnetic behavior with the transition
temperature of 18 K. The estimated Sommerfeld coefficient $\gamma$ = 640
mJ/($\mathrm{Pr.mole.K^2}$) from the $\mathrm {C}_p(\textit{T})$ results in the
paramagnetic region just above $T_{C}$~was large in comparison to ordinary
metals. In the paramagnetic region $\rho(T)$ data showed a metallic behavior
characteristic of electron - phonon scattering. The maximum negative
magneto-resistance at high field occurs in the region near the magnetic phase
transition temperature. The maximum value of magnetic entropy change ($\rm
-\Delta \textit{S}_{M}$) and adiabatic temperature change ($\rm \Delta
\textit{T}_{ad}$) are $\rm8.2~J/kg.K$ and $\rm3.6~K$, respectively, around the
transition temperature for the change of magnetic field 0-9 T. The calculated
refrigerant capacity is $\rm70~J/kg$, and $\rm135~J/kg$ for a change of
magnetic field 0-5 T and 0-9 T, respectively. Arrott plot derived from
isothermal magnetization and the universal scaling plot by normalizing $\rm
-\Delta \textit{S}_{M}$ confirm that the compound undergoes a second order
ferromagnetic to paramagnetic phase transition.",2102.04106v2
2021-02-10,Searching for Fast Model Families on Datacenter Accelerators,"Neural Architecture Search (NAS), together with model scaling, has shown
remarkable progress in designing high accuracy and fast convolutional
architecture families. However, as neither NAS nor model scaling considers
sufficient hardware architecture details, they do not take full advantage of
the emerging datacenter (DC) accelerators. In this paper, we search for fast
and accurate CNN model families for efficient inference on DC accelerators. We
first analyze DC accelerators and find that existing CNNs suffer from
insufficient operational intensity, parallelism, and execution efficiency.
These insights let us create a DC-accelerator-optimized search space, with
space-to-depth, space-to-batch, hybrid fused convolution structures with
vanilla and depthwise convolutions, and block-wise activation functions. On top
of our DC accelerator optimized neural architecture search space, we further
propose a latency-aware compound scaling (LACS), the first multi-objective
compound scaling method optimizing both accuracy and latency. Our LACS
discovers that network depth should grow much faster than image size and
network width, which is quite different from previous compound scaling results.
With the new search space and LACS, our search and scaling on datacenter
accelerators results in a new model series named EfficientNet-X. EfficientNet-X
is up to more than 2X faster than EfficientNet (a model series with
state-of-the-art trade-off on FLOPs and accuracy) on TPUv3 and GPUv100, with
comparable accuracy. EfficientNet-X is also up to 7X faster than recent RegNet
and ResNeSt on TPUv3 and GPUv100.",2102.05610v1
2021-02-15,Magic thickness of 25 Å makes periodic metal-insulator transitions,"Novel quantum phenomena, including high-temperature superconductivity,
topological properties, and charge/spin density waves, appear in
low-dimensional conductive materials. It is possible to artificially create
low-dimensional systems by fabricating ultrathin films, quantum wires, or
quantum dots with flat interfaces. Some experiments have been performed on
ultrathin compounds of strongly correlated electron systems. However, since it
is technically difficult to control multiple elements precisely, most of the
properties of artificially fabricated low-dimensional compounds fall into
uncharted territory. Here we show that extraordinary metal-insulator
transitions that oscillate depending on the scale occur in CaRuO_3 films with a
thickness of around several unit cells. We grow high-crystalline CaRuO_3
ultrathin films, whose surface roughness is controlled at 199 pm, by molecular
beam epitaxy. We observe that resistivity oscillates with a magic thickness of
25 {\AA}, which changes by 3 and 9 orders of magnitude at room temperature and
at low temperature, respectively. These changes are much larger than quantum
size effects. We also confirm the same periodicity with photoelectron
spectroscopy by etching the ultrathin film. Considering the large energy,
periodicity and anisotropy, we conclude that the oscillating transitions
originate from the commensurability of Mott insulation triggered by Peierls
instability arising from a dual restriction on the dimensions in wavenumber
space and real space. We have shown the possibility of producing new functional
materials by controlling film thickness on electron correlated compounds at the
picometer level.",2102.07323v1
2021-04-10,Role of polyhedron unit in distinct photodynamics of zero-dimensional organic-inorganic hybrid tin halide compounds,"The zero-dimensional (0D) metal halides comprise periodically distributed and
isolated metal-halide polyhedra, which act as the smallest inorganic quantum
systems and can accommodate quasi-localized Frenkel excitons. These excitons
exhibit unique photophysics including broadband photon emission, huge Stokes
shift, and long decay lifetime. The polyhedra can have different symmetries due
to the coordination degree of the metal ions. Little is known about how the
polyhedron type affects the characteristics of the 0D metal halide crystals. We
synthesize and comparatively study three novel kinds of 0D organic-inorganic
hybrid tin halide compounds. They are efficient light emitters with a highest
quantum yield of 92.3%. Although they have the same compositional organic
group, the most stable phases are composed of octahedra for the bromide and
iodide but disphenoids (see-saw structures) for the chloride. They separately
exhibit biexponential and monoexponential luminescence decays due to different
symmetries (Ci group for octahedra and C2 group for disphenoids) and
corresponding different electronic structures. The chloride has the largest
absorption photon energy among the three halides, but it has the smallest
emission photon energy. A model regarding the unoccupied energy band degeneracy
is proposed based on the experiments and density functional theory
calculations, which explains well the experimental phenomena and reveals the
crucial role of polyhedron type in determining the optical properties of the 0D
tin halide compounds.",2104.04677v2
2021-04-14,"On the complexity of spinels: Magnetic, electronic, and polar ground states","This review summarizes more than 100 years of research on spinel compounds,
mainly focusing on the progress in understanding their magnetic, electronic,
and polar properties during the last two decades. Many spinel compounds are
magnetic insulators or semiconductors; however, a number of spinel-type metals
exists including superconductors and some rare examples of d-derived
heavy-fermion compounds. In the early days, they gained importance as
ferrimagnetic or even ferromagnetic insulators with relatively high saturation
magnetization and high ordering temperatures, with magnetite being the first
magnetic mineral known to mankind. However, spinels played an outstanding role
in the development of concepts of magnetism, in testing and verifying the
fundamentals of magnetic exchange, in understanding orbital-ordering and
charge-ordering phenomena. In addition, the A- site as well as the B-site
cations in the spinel structure form lattices prone to strong frustration
effects resulting in exotic ground-state properties. In case the A-site cation
is Jahn-Teller active, additional entanglements of spin and orbital degrees of
freedom appear, which can give rise to a spin-orbital liquid or an orbital
glass state. The B-site cations form a pyrochlore lattice, one of the strongest
contenders of frustration in three dimensions. In addition, in spinels with
both cation lattices carrying magnetic moments, competing magnetic exchange
interactions become important, yielding ground states like the time-honoured
triangular Yafet-Kittel structure. Finally, yet importantly, there exists a
long-standing dispute about the possibility of a polar ground state in spinels,
despite their reported overall cubic symmetry. Indeed, over the years number of
multiferroic spinels were identified.",2104.06889v1
2021-04-16,Thiols in the ISM: first detection of HC(O)SH and confirmation of C$_2$H$_5$SH,"The chemical compounds carrying the thiol group (-SH) have been considered
essential in recent prebiotic studies regarding the polymerization of amino
acids. We have searched for this kind of compounds toward the Galactic Centre
quiescent cloud G+0.693-0.027. We report the first detection in the
interstellar space of the trans-isomer of monothioformic acid (t-HC(O)SH) with
an abundance of $\sim\,$1$\,\times\,$10$^{-10}$. Additionally, we provide a
solid confirmation of the gauche isomer of ethyl mercaptan (g-C$_2$H$_5$SH)
with an abundance of $\sim\,$3$\,\times\,$10$^{-10}$, and we also detect methyl
mercaptan (CH$_3$SH) with an abundance of $\sim\,$5$\,\times\,$10$^{-9}$.
Abundance ratios were calculated for the three SH-bearing species and their
OH-analogues, revealing similar trends between alcohols and thiols with
increasing complexity. Possible chemical routes for the interstellar synthesis
of t-HC(O)SH, CH$_3$SH and C$_2$H$_5$SH are discussed, as well as the relevance
of these compounds in the synthesis of prebiotic proteins in the primitive
Earth.",2104.08036v2
2021-05-02,"BAARD: Blocking Adversarial Examples by Testing for Applicability, Reliability and Decidability","Adversarial defenses protect machine learning models from adversarial
attacks, but are often tailored to one type of model or attack. The lack of
information on unknown potential attacks makes detecting adversarial examples
challenging. Additionally, attackers do not need to follow the rules made by
the defender. To address this problem, we take inspiration from the concept of
Applicability Domain in cheminformatics. Cheminformatics models struggle to
make accurate predictions because only a limited number of compounds are known
and available for training. Applicability Domain defines a domain based on the
known compounds and rejects any unknown compound that falls outside the domain.
Similarly, adversarial examples start as harmless inputs, but can be
manipulated to evade reliable classification by moving outside the domain of
the classifier. We are the first to identify the similarity between
Applicability Domain and adversarial detection. Instead of focusing on unknown
attacks, we focus on what is known, the training data. We propose a simple yet
robust triple-stage data-driven framework that checks the input globally and
locally, and confirms that they are coherent with the model's output. This
framework can be applied to any classification model and is not limited to
specific attacks. We demonstrate these three stages work as one unit,
effectively detecting various attacks, even for a white-box scenario.",2105.00495v2
2021-05-03,Co-existence of Topological Non-trivial and Spin Gapless Semiconducting Behavior in MnPO$_4$: A Composite Quantum Compound,"Composite quantum compounds (CQC) are classic example of quantum materials
which host more than one apparently distinct quantum phenomenon in physics.
Magnetism, topological superconductivity, Rashba physics etc. are few such
quantum phenomenon which are ubiquitously observed in several functional
materials and can co-exist in CQCs. In this letter, we use {\it ab-initio}
calculations to predict the co-existence of two incompatible phenomena, namely
topologically non-trivial Weyl semimetal and spin gapless semiconducting (SGS)
behavior, in a single crystalline system. SGS belong to a special class of
spintronics material which exhibit a unique band structure involving a
semiconducting state for one spin channel and a gapless state for the other. We
report such a SGS behavior in conjunction with the topologically non-trivial
multi-Weyl Fermions in MnPO$_4$. Interestingly, these Weyl nodes are located
very close to the Fermi level with the minimal trivial band density. A drumhead
like surface state originating from a nodal loop around Y-point in the
Brillouin zone is observed. A large value of the simulated anomalous Hall
conductivity (1265 $\Omega^{-1} cm^{-1}$) indirectly reflects the topological
non-trivial behavior of this compound. Such co-existent quantum phenomena are
not common in condensed matter systems and hence it opens up a fertile ground
to explore and achieve newer functional materials.",2105.00907v2
2021-05-24,"High-Pressure Na3(N2)4, Ca3(N2)4, Sr3(N2)4, and Ba(N2)3 Featuring Nitrogen Dimers with Non-Integer Charges and Anion-Driven Metallicity","Charged nitrogen dimers are ubiquitous in high-pressure binary metal-nitrogen
systems. They are known to possess integer formal charges x varying from one
through four. Here, we present the investigation of the binary alkali- and
alkaline earth metal-nitrogen systems, Na-N, Ca-N, Sr-N, Ba-N to 70 GPa. We
report on compounds-Na3(N2)4, Ca3(N2)4, Sr3(N2)4, and Ba(N2)3-featuring charged
nitrogen dimers with paradigm-breaking non-integer charges, x = 0.67, 0.75 and
1.5. The metallic nature of all four compounds is deduced from ab initio
calculations. The conduction electrons occupy the pi* antibonding orbitals of
the charged nitrogen dimers that results in anion-driven metallicity.
Delocalization of these electrons over the pi* antibonding states enables the
non-integer electron count of the dinitrogen species. Anion-driven metallicity
is expected to be found among a variety of compounds with homoatomic anions
(e.g., polynitrides, carbides, and oxides), with the conduction electrons
playing a decisive role in their properties.",2105.11288v1
2021-05-26,BioNavi-NP: Biosynthesis Navigator for Natural Products,"Nature, a synthetic master, creates more than 300,000 natural products (NPs)
which are the major constituents of FDA-proved drugs owing to the vast chemical
space of NPs. To date, there are fewer than 30,000 validated NPs compounds
involved in about 33,000 known enzyme catalytic reactions, and even fewer
biosynthetic pathways are known with complete cascade-connected enzyme
catalysis. Therefore, it is valuable to make computer-aided bio-retrosynthesis
predictions. Here, we develop BioNavi-NP, a navigable and user-friendly
toolkit, which is capable of predicting the biosynthetic pathways for NPs and
NP-like compounds through a novel (AND-OR Tree)-based planning algorithm, an
enhanced molecular Transformer neural network, and a training set that combines
general organic transformations and biosynthetic steps. Extensive evaluations
reveal that BioNavi-NP generalizes well to identifying the reported
biosynthetic pathways for 90% of test compounds and recovering the verified
building blocks for 73%, significantly outperforming conventional rule-based
approaches. Moreover, BioNavi-NP also shows an outstanding capacity of
biologically plausible pathways enumeration. In this sense, BioNavi-NP is a
leading-edge toolkit to redesign complex biosynthetic pathways of natural
products with applications to total or semi-synthesis and pathway elucidation
or reconstruction.",2105.13121v1
2021-06-13,Protein-Ligand Docking Surrogate Models: A SARS-CoV-2 Benchmark for Deep Learning Accelerated Virtual Screening,"We propose a benchmark to study surrogate model accuracy for protein-ligand
docking. We share a dataset consisting of 200 million 3D complex structures and
2D structure scores across a consistent set of 13 million ""in-stock"" molecules
over 15 receptors, or binding sites, across the SARS-CoV-2 proteome. Our work
shows surrogate docking models have six orders of magnitude more throughput
than standard docking protocols on the same supercomputer node types. We
demonstrate the power of high-speed surrogate models by running each target
against 1 billion molecules in under a day (50k predictions per GPU seconds).
We showcase a workflow for docking utilizing surrogate ML models as a
pre-filter. Our workflow is ten times faster at screening a library of
compounds than the standard technique, with an error rate less than 0.01\% of
detecting the underlying best scoring 0.1\% of compounds. Our analysis of the
speedup explains that to screen more molecules under a docking paradigm,
another order of magnitude speedup must come from model accuracy rather than
computing speed (which, if increased, will not anymore alter our throughput to
screen molecules). We believe this is strong evidence for the community to
begin focusing on improving the accuracy of surrogate models to improve the
ability to screen massive compound libraries 100x or even 1000x faster than
current techniques.",2106.07036v2
2021-06-17,Synthesis of Murunskite Single Crystals: A Bridge Between Cuprates and Pnictides,"Numerous contemporary investigations in condensed matter physics are devoted
to high temperature (high-$T_c$ ) cuprate superconductors. Despite its unique
effulgence among research subjects, the enigma of the high-$T_c$ mechanism
still persists. One way to advance its understanding is to discover and study
new analogous systems. Here we begin a novel exploration of the natural mineral
murunskite, K$_2$FeCu$_3$S$_4$, as an interpolation compound between cuprates
and ferropnictides, the only known high-$T_c$ superconductors at ambient
pressure. Because in-depth studies can be carried out only on single crystals,
we have mastered the synthesis and growth of high quality specimens. Similar to
the cuprate parent compounds, these show semiconducting behavior in resistivity
and optical transmittance, and an antiferromagnetic ordering at 100 K.
Spectroscopy (XPS) and calculations (DFT) concur that the sulfur 3$p$ orbitals
are partially open, making them accessible for charge manipulation, which is a
prerequisite for superconductivity in analogous layered structures. DFT
indicates that the valence band is more cuprate-like, while the conduction band
is more pnictide-like. With appropriate doping strategies, this parent compound
promises exciting future developments.",2106.09555v1
2021-06-24,Competing magnetic interactions and magnetocaloric effect in Ho$_5$Sn$_3$,"The rare-earth intermetallic compound Ho$_5$Sn$_3$ demonstrates fascinating
magnetic properties which include temperature-driven multiple magnetic
transitions and field driven metamagnetism. We address the magnetic character
of this exciting compound through a combined experimental and theoretical
studies. Ho$_5$Sn$_3$ orders antiferromagnetically below $~28$ K, and shows
further spin reorientation transitions at 15 K and 12 K. We observe a sizable
amount of low-temperature magnetocaloric effect in Ho$_5$Sn$_3$ with a maximum
value of entropy change $\Delta S$ = -9.5 JKg$^{-1}$K$^{-1}$ for an applied
field of $H$ = 50 kOe at around 30 K. The field hysteresis is almost zero above
15 K where magneto-caloric effect is important. Interestingly, $\Delta S$ is
found to change its sign from positive to negative as the temperature is
increased above about 8 K, which can be linked to the multiple spin
reorientation transitions. The signature of the metamagnetism is visible in the
$\Delta S$ versus $H$ plot. The magnetic ground-state, obtained from the
density functional theory based calculation, is susceptible to the effective
Coulomb interaction ($U_{\rm eff}$) between electrons. Depending upon the value
of $U_{\rm eff}$, the ground-state can be ferromagnetic or antiferromagnetic.
The compound shows large relaxation (14\% change in magnetization in 60 min) in
the field cooled state with a logarithmic time variation, which may be
connected to the competing magnetic ground-states observed in our theoretical
calculations. The competing magnetic ground-states is also evident from the
small value of the paramagnetic Curie-Weiss temperature.",2106.13173v1
2021-08-15,Vector-Decomposed Disentanglement for Domain-Invariant Object Detection,"To improve the generalization of detectors, for domain adaptive object
detection (DAOD), recent advances mainly explore aligning feature-level
distributions between the source and single-target domain, which may neglect
the impact of domain-specific information existing in the aligned features.
Towards DAOD, it is important to extract domain-invariant object
representations. To this end, in this paper, we try to disentangle
domain-invariant representations from domain-specific representations. And we
propose a novel disentangled method based on vector decomposition. Firstly, an
extractor is devised to separate domain-invariant representations from the
input, which are used for extracting object proposals. Secondly,
domain-specific representations are introduced as the differences between the
input and domain-invariant representations. Through the difference operation,
the gap between the domain-specific and domain-invariant representations is
enlarged, which promotes domain-invariant representations to contain more
domain-irrelevant information. In the experiment, we separately evaluate our
method on the single- and compound-target case. For the single-target case,
experimental results of four domain-shift scenes show our method obtains a
significant performance gain over baseline methods. Moreover, for the
compound-target case (i.e., the target is a compound of two different domains
without domain labels), our method outperforms baseline methods by around 4%,
which demonstrates the effectiveness of our method.",2108.06685v1
2021-08-20,4/-hybridization strength in CemMnIn3m+2n heavy-fermion compounds studied by Angle-Resolved Photoemission Spectroscopy,"We systemically investigate the nature of Ce 4f electrons in structurally
layered heavy-fermion compounds CcmMnIn3m+2n (with M =Co, Rh, Ir, and Pt, m=l,
2, n=0 - 2), at low temperature using on-resonance angle-resolved photoemission
spectroscopy. Three heavy quasiparticle bands f^0, f^1_7/2 and f^1_5/2 are
observed in all compounds, but their intensities and energy locations vary
greatly with materials. The strong f^0 states imply that the localized electron
behavior dominates the Ce 4f states. The Ce 4f electrons are partially
hybridized with the conduction electrons, making them have the dual nature of
localization and itinerant. Our quantitative comparison reveals that the
f^1_5/2 / f^0 intensity ratio is more suitable to reflect the 4f-state
hybridization strength.",2108.09090v1
2021-08-22,On the product selectivity in the electrochemical reductive cleavage of lignin model compounds,"Research towards the production of renewable chemicals for fuel and energy
industries has found lignin valorization as key. With a high carbon content and
aromaticity, a fine-tuning of the depolymerization process is required to
convert lignin into valuable chemicals. In context, model compounds have been
used to understand the electrocatalyzed depolymerization for mimicking the
typical linkages of lignin. In this investigation, 2-phenoxyacetophenone, a
model compound for lignin \b{eta}-O-4 linkage, was electro-catalytically
hydrogenated (ECH) in distinct three-electrode setups: an open and a membrane
cell. A deep eutectic solvent based on ethylene-glycol and choline chloride was
used to pursue sustainable routes to dissolve lignin. Copper was used as
electrocatalyst due to the economic feasibility and low activity towards
hydrogen evolution reaction (HER), a side reaction of ECH. By varying the cell
type, we demonstrate a simple ECH route for the generation of different
monomers and oligomers from lignin. Gas chromatography of the products revealed
a higher content of carbonyl groups in those using the membrane cell, whereas
the open cell produced mostly hydroxyl-end chemicals. Aiming at high
value-added products, our results disclose the cell type influence on
electrochemical reductive depolymerization of lignin. This approach encompasses
cheap transition metal electrodes and sustainable solvents.",2108.09771v1
2021-08-26,Infrared dielectric functions and Brillouin zone center phonons of $α$-Ga$_2$O$_3$ compared to $α$-Al$_2$O$_3$,"We determine the anisotropic dielectric functions of rhombohedral
$\alpha$-Ga$_2$O$_3$ by far-infrared and infrared generalized spectroscopic
ellipsometry and derive all transverse optical and longitudinal optical phonon
mode frequencies and broadening parameters. We also determine the high
frequency and static dielectric constants. We perform density functional theory
computations and determine the phonon dispersion for all branches in the
Brillouin zone, and we derive all phonon mode parameters at the Brillouin zone
center including Raman-active, infrared-active, and silent modes. Excellent
agreement is obtained between our experimental and computation results as well
as among all previously reported partial information from experiment and
theory. We also compute the same information for $\alpha$-Al$_2$O$_3$, the
binary parent compound for the emerging alloy of
$\alpha$-(Al$_{x}$Ga$_{1-x}$)$_2$O$_3$, and use results from previous
investigations [Schubert, Tiwald, and Herzinger, Phys. Rev. B 61, 8187 (2000)]
to compare all properties among the two isostructural compounds. From both
experimental and theoretical investigations we compute the frequency shifts of
all modes between the two compounds. Additionally, we calculate overlap
parameters between phonon mode eigenvectors and discuss the possible evolution
of all phonon modes into the ternary alloy system and whether modes may form
single mode or more complex mode behaviors.",2108.12058v1
2021-08-30,Effect of small cation occupancy and anomalous Griffiths phase disorder in nonstoichiometric magnetic perovskites,"The structural, magnetic, magnetocaloric and Griffiths phase (GP) disorder of
non-stoichiometric perovskite manganites La_(0.8-x) Sr_(0.2-y) Mn_(1+x+y) O_3
are reported here. Determination of valence states and structural phases
evidenced that the smaller cations Mn2+ and Mn3+ will not occupy the A-site of
a perovskite under atmospheric synthesis conditions. The same analysis also
supports that the vacancy in the A-site of a perovskite induces a similar
vacancy in the B-site. The La3+ and Sr2+ cation substitutions in the A-site
with vacancy influences the magnetic phase transition temperature (TC)
inversely, which is explained in terms of the electronic bandwidth change. An
anomalous non-linear change of the GP has been observed in the Sr-substituted
compounds. The agglomeration of Mn3+-Mn4+ pairs (denoted as dimerons), into
small ferromagnetic clusters, has been identified as the reason for the
occurrence of the GP. A threshold limit of the dimeron formation explains the
observed non-linear behaviour of the GP formation. The Sr-substituted compounds
show a relatively large value of isothermal entropy change (maximum 3.27 J/kgK
at {\mu}_0 H=2T) owing to its sharp magnetic transition, while the broad change
of magnetization in the La-substituted compound enhances the relative cooling
power (maximum 98 J/kg at {\mu}_0 H=2T).",2108.13251v2
2021-08-31,Competing control scenarios in probabilistic SIR epidemics on social-contact networks,"A probabilistic approach to the epidemic evolution on realistic
social-contact networks allows for characteristic differences among subjects,
including the individual number and structure of social contacts, and the
heterogeneity of the infection and recovery rates according to age or medical
preconditions. Within our probabilistic Susceptible-Infectious-Removed (SIR)
model on social-contact networks, we evaluate the `infection load' or
`activation margin' of various control scenarios; by confinement, by
vaccination, and by their combination. We compare the epidemic burden for
subpopulations which apply competing or co-operative control strategies. The
simulation experiments are conducted on randomised social-contact graphs that
are designed to exhibit realistic person-person contact characteristics and
which follow near `homogeneous' or `block-localised' subpopulation spreading.
The scalarization method is used for the multi-objective optimization problem
in which both the infection load is minimized and the extent to which each
subpopulation's control strategy preference ranking is adhered to is maximized.
We obtain the compounded payoff matrices for two subpopulations which impose
contrasting control strategies, each according to their proper ranked control
strategy preferences. The Nash equilibria, according to each subpopulation's
compounded objective, and according to their proper ranking intensity, are
discussed. Finally, the interaction effects of the control strategies are
discussed and related to the type of spreading of the two subpopulations.",2108.13714v3
2021-09-09,Investigation of the phase occurrence and H sorption properties in the Y33.33Ni66.67-xAlx (0 <= x <= 33.33) system,"The Y33.33Ni66.67-xAlx system has been investigated in the region 0 <= x <=
33.3. The alloys were synthesized by induction melting. Phase occurrence and
structural properties were studied by X-Ray powder Diffraction (XRD). The Al
solubility in each phase has been investigated by XRD and Electron Probe
Micro-Analysis (EPMA). The hydrogenation properties were characterized by
pressure-composition isotherm measurements and kinetic curves at 473 K. For x =
0, the binary Y33.33Ni66.67 alloy crystallizes in the cubic superstructure with
F4-3m space group and ordered Y vacancies. For 1.67 <= x <= 8.33, the alloys
contain mainly Y(Ni, Al)2 and Y(Ni, Al)3 pseudobinary phases; while for 16.67
<= x <= 33.33 they are mainly formed by ternary line compounds Y3Ni6Al2,
Y2Ni2Al and YNiAl. Contrary to the binary Y33.33Ni66.67, Y(Ni, Al)2
pseudo-binary compounds crystalize in C15 phase (space group Fd-3m ) with
disordered Y vacancies. The solubility limit of Al in the C15 YNi2-yAly phase
is y = 0.11 (i.e., x = 3.67). The Y(Ni, Al)3 phase changes from rhombohedral
(PuNi3-type, R-3m) to hexagonal (CeNi3-type, P63/mmc) structure for x
increasing from 5.00 to 6.67. Upon hydrogenation, the disproportion of C15
Y(Ni, Al)2 and losses of crystallinity of YNi and Y2Ni2Al are the main reasons
causing capacity decay of Y33.33Ni66.67-xAlx (0 <= x <= 33.33) alloys upon
cycling.",2109.04182v1
2021-09-15,Study of the electronic properties of topological kagome metals YV$_6$Sn$_6$ and GdV$_6$Sn$_6$,"The synthesis and characterization of vanadium-based kagome metals
YV$_6$Sn$_6$ and GdV$_6$Sn$_6$ are presented. X-ray diffraction, magnetization,
magnetotransport, and heat capacity measurements reveal an ideal kagome network
of V-ions coordinated by Sn and separated by triangular lattice planes of
rare-earth ions. The onset of low-temperature, likely noncollinear, magnetic
order of Gd spins is detected in GdV$_6$Sn$_6$, while V-ions in both compounds
remain nonmagnetic. Density functional theory calculations are presented
modeling the band structures of both compounds, which can be classified as
$\mathbb{Z}_2$ topological metals in the paramagnetic state. Both compounds
exhibit high mobility, multiband transport and present an interesting platform
for controlling the interplay between magnetic order associated with the
$R$-site sublattice and nontrivial band topology associated with the V-based
kagome network. Our results invite future exploration of other $R$V$_6$Sn$_6$
($R$=rare earth) variants where this interplay can be tuned via $R$-site
substitution.",2109.07394v2
2021-09-18,Stabilization of S3O4 at High Pressure-Implications for the Sulfur Excess Paradox,"The geological conundrum of sulfur excess refers to the finding that
predicted amounts of sulfur, in the form of SO2, discharged in volcanic
eruptions much exceeds the sulfur available for degassing from the erupted
magma. Exploring the source of the excess sulfur has been the subject of
considerable interest. Here, from a systematic computational investigation of
sulfur-oxygen compounds under pressure, a hitherto unknown S3O4 compound
containing a mixture of sulfur oxidation states +II and +IV emerges and is
predicted to be stabilized above a pressure of 79 GPa. We predict that S3O4 can
be produced via multiple redox reactions involving subducted S-bearing minerals
(e.g., sulfates and sulfides) at high pressure conditions relevant to the deep
lower mantle, and conversely be decomposed into SO2 and S at shallow depths of
Earth. Therefore, S3O4 can be considered as a key intermediate compound to
promote the decomposition of sulfates to release SO2, which offers an
alternative source of the excess sulfur released during explosive eruptions.
These findings provide a possible resolution to the geological paradox of
excess sulfur degassing and a viable mechanism for the understanding of S
exchange between surface and the lower mantle for the deep sulfur cycle.",2109.08891v1
2021-09-28,Transport anomalies in the layered compound BaPt4Se6,"We report a layered ternary selenide BaPt4Se6 featuring sesqui-selenide
Pt2Se3 layers sandwiched by Ba atoms. The Pt2Se3 layers in this compound can be
derived from the Dirac-semimetal PtSe2 phase with Se vacancies that form a
honeycomb structure. This structure results in a Pt (VI) and Pt (II)
mixed-valence compound with both PtSe6 octahedra and PtSe4 square net
coordination configurations. Temperature dependent electrical transport
measurements suggest two distinct anomalies: a resistivity crossover, mimic to
the metal-insulator (M-I) transition at ~150K, and a resistivity plateau at
temperatures below 10K. The resistivity crossover is not associated with any
structural, magnetic or charge order modulated phase transitions.
Magnetoresistivity, Hall and heat capacity measurements concurrently suggest an
existing hidden state below 5K in this system. Angle-resolved photoemission
spectroscopy measurements reveal a metallic state and no dramatic
reconstruction of the electronic structure up to 200K.",2109.13902v1
2021-10-07,Local atomic configuration control of superconductivity in the undoped pnictide parent compound BaFe2As2,"Emergent superconductivity is strongly correlated with the symmetry of local
atomic configuration in the parent compounds of iron-based superconductors.
While chemical doping or hydrostatic pressure can change the local geometry,
these conventional approaches do not provide a clear pathway in tuning the
detailed atomic arrangement predictably, due to the parent compounds
complicated structural deformation in the presence of the
tetragonal-to-orthorhombic phase transition. Here, we demonstrate a systematic
approach to manipulate the local structural configurations in BaFe2As2
epitaxial thin films by controlling two independent structural factors
orthorhombicity (in-plane anisotropy) and tetragonality (out-of-plane/in-plane
balance) from lattice parameters. We tune superconductivity without chemical
doping utilizing both structural factors separately, controlling local
tetrahedral coordination in designed thin film heterostructures with substrate
clamping and bi-axial strain. We further show that this allows quantitative
control of both the structural phase transition, associated magnetism, and
superconductivity in the parent material BaFe2As2. This approach will advance
the development of tunable thin film superconductors in reduced dimension.",2110.03640v1
2021-10-19,"Dynamical Study of the Origin of the Charge Density Wave in $A$V$_{3}$Sb$_{5}$ ($A=$K, Rb, Cs) Compounds","Systems containing the ideal kagome lattice can exhibit several distinct and
novel exotic states of matter. One example of such systems is a recently
discovered $A$V$_{3}$Sb$_{5}$ ($A$ = K, Rb, and Cs) family of compounds. Here,
the coexistence of the charge density wave (CDW) and superconductivity is
observed. In this paper, we study the dynamic properties of the
$A$V$_{3}$Sb$_{5}$ systems in context of origin of the CDW phase. We show and
discuss the structural phase transition from $P6/mmm$ to $C2/m$ symmetry that
are induced by the presence of phonon soft modes. We conclude that the CDW
observed in this family of compounds is a consequence of the atom displacement,
from the high symmetry position of the kagome net, in low-temperature phase.
Additionally, using the numerical {\it ab initio} methods, we discuss the
charge distribution on the $A$V$_{3}$Sb$_{5}$ surface. We show that the
observed experimental %$4\times 1$ stripe-like modulation of the surface, can
be related to surface reconstruction and manifestation of the three dimensional
$2 \times 2 \times 2$ bulk CDW. Finally, the consequence of realization of the
$C2/m$ structure on the electronic properties are discussed. We show that the
electronic band structure reconstruction and the accompanying modification of
density of states correspond well to the experimental data.",2110.09816v1
2021-10-25,"Correlations between the structural, magnetic, and ferroelectric properties of BaMO3: M = Ti1-x(Mn/Fe)x compounds: A Raman study","Multiferroics possess two or more switchable states such as polarization,
magnetization, etc. Phonon excitations in multiferroic phase are strongly
modified by magnetoelectric coupling, spin-phonon coupling, and anharmonic
phonon-phonon interactions. Here, we have investigated the correlation between
phonons and multiferroic order parameters in hexagonal BaMO3: M = Ti1-x(Mn/Fe)x
systems using powder x-ray diffraction (PXRD), Raman spectroscopic, and
magnetic measurements. The structural transformation from a polar tetragonal to
a non-polar 6H-type hexagonal phase is observed as a function of doping
(Mn/Fe). Magnetic measurements reveal that the BaTi1-xMnxO3 is paramagnetic
while BaTi1-xFexO3 exhibits composition-dependent ferromagnetic order.
Importantly, Anomalous temperature-dependence is observed for two phonons (E1g
at ~ 152 cm-1 and A1g at ~ 636 cm-1) in both the systems exhibiting similar
trend with the doping (Mn/Fe) irrespective of the differences in their magnetic
ground state. Hence, we attribute the phonon anomalies in both the (Fe/Mn
doped) systems to strong anharmonic phonon-phonon interactions arising from
large atomic displacements involved in the vibrations. In addition, we have
also observed signatures of correlation of phonons with ferroelectric phase as
well as magnetically ordered state suggesting the presence of a strain-induced
magnetoelectric coupling in the doped compounds.",2110.12673v1
2021-10-26,Structural and electrical characterization of the monolayer Kondo-lattice compound CePt$_6$/Pt(111),"We report the growth process, structure, and electronic states of 1 unit
layer (u.l.) of a Ce-Pt intermetallic compound on Pt(111) using scanning
tunneling microscopy/spectroscopy (STM/STS) and low-energy electron
diffraction. An ordered $(2 \times 2)$ structure was observed in the form of
films or nanoislands depending on Ce dose by annealing at around 700 K. A
structural model constructed from atomically resolved STM images and
quasiparticle interference (QPI) patterns indicates the formation of a new
surface compound 1 u.l. CePt$_6$ on Pt(111) terminated by a Pt layer. A lateral
lattice constant of the 1 u.l. CePt$_6$ on Pt(111) is expanded from the value
of a bulk CePt$_5$ crystal to match the Pt(111) substrate. By measuring
d$I$/d$V$ spectra and QPI, we observed an onset energy of the surface state
found on Pt(111) above Fermi energy ($E_F$) shifts below $E_F$ on the Pt layer
of the 1 u.l. CePt$_6$ due to charge transfer from the underneath CePt$_2$
layer. We discuss a possible two-dimensional coherent Kondo effect with the
observed spectra on the 1 u.l. CePt$_6$.",2110.13469v1
2021-11-15,Superconductivity in compressed SnPS3,"Metal phosphorous trichalcogenides, MPX3, is a group of van der Waals
materials with rich electronic properties and even exotic magnetic behavior.
These properties can be well manipulated by pressure/strain via effective
control of interlayer interaction, lattice parameters and crystal structure.
Superconducting transition has been observed in compressed FePSe3. However, it
is the only one superconductor reported in the large MPX3 family. Is it
possible to achieve superconducting transition in other MPX3 compounds,
especially in a trisulfide compound? In this work, we tentatively compressed
the SnPS3 (an insulator with large band gap at ambient condition) up to 48.9
GPa, and managed to achieve the superconducting transition above 31.7 GPa with
Tc ranging from ~2.2 K to ~2.8 K. The upper critical field is estimated to be
~3.03 T at 40.5 GPa. Optical absorption measurements together with Raman
spectroscopy show a series of transitions under pressure, which is well
consistent with the electric transport results. This work provides direct
experimental evidence that SnPS3 undergoes an insulator-metal transition near
31.7 GPa. More importantly, it demonstrates that superconductivity can exist in
MPS3 compounds, which not only further enriches the electronic properties of
this kind of material but also paves a new avenue to explore the abundant
emergence phenomena in the whole MPX3 family, and it also benefits the study of
superconductor mechanism.",2111.07604v1
2021-12-10,Singular jets in compound drop impact,"Compound drop impacting on a solid surface is of considerable importance in
industrial applications, such as combustion, food industry, and drug
encapsulation. An intriguing phenomenon associated with this process is the
occurrence of singular jets that are up to dozens of times faster than the
impact velocity. These jets break into micro-droplets, which can produce
aerosols and affect the quality of printing technologies. Here, we investigate
experimentally and numerically the jetting process after a coaxial water-in-oil
compound drop impacts on a glass substrate with different releasing heights and
volumetric ratios. After impact, the water core spreads and retracts, giving
rise to a vertical jet initially made of oil. For certain values of the
impacting velocity, high speed and very thin jets are observed, the so-called
singular jets. Depending on the volumetric ratio, one or two velocity peaks can
be observed when varying the impact velocity, triggered by the contraction
dynamics of a deep and cylindrical cavity. The self-similar time-evolution of
the collapse for the first singularity regime follows a 1/2 power law in time,
which can be derived from bubble pinch-off. In contrast, the collapse at the
second peak follows a 2/3 power law, which can be accounted for by a balance
between inertial and capillary forces.",2112.05284v1
2021-12-18,Investigations on Cmc2$_1$-Si$_2$P$_2$X structures and physical properties by first-principles calculations,"The new structures, Cmc2$_1$-Si$_2$P$_2$X (X=S, Se, Te, and Po), are
predicted, and their mechanical, electronic and optical properties are
investigated with the density functional theory, by first principles
calculations. The elastic constants of the four compounds are calculated by the
stress-strain method. The calculations of the elastic stability criteria and
phonon dispersion spectra imply that they are mechanically and dynamically
stable at zero pressure. The mechanical parameters, such as shear moduli $G$,
bulk moduli $B$, Young's moduli $E$ and Poisson's ratios $v$ are evaluated by
the Voigt-Reuss-Hill approach. The Cmc2$_1$-Si$_2$P$_2$X has the largest
hardness due to the largest Young's modulus in the four compounds, and it is a
covalent crystal. The anisotropies of their mechanical properties are also
analyzed. The band structures and densities of states, which are calculated by
using HSE06, show that Cmc2$_1$-Si$_2$P$_2$X compounds are indirect bandgap
semiconductors, and the values of the band gaps decrease with increasing atomic
number from S, Se, Te, to Po. In addition, the longitudinal sound velocity and
transverse sound velocity for Cmc2$_1$-Si$_2$P$_2$X have been investigated. The
dielectric constant, electron energy loss, refractive index, reflectivity,
absorption and conductivity are analyzed to gain the optical properties of
Si$_2$P$_2$X.",2112.09928v1
2021-12-31,The thermodynamic trends of intrinsic defects in primary halide perovskites: A first-principles study,"Defects in halide perovskites play an essential role in determining the
efficiency and stability of the resulting optoelectronic devices. Here, we
present a systematic study of intrinsic point defects in six primary metal
halide perovskites, MAPbI$_3$, MAPbBr$_3$, MAPbCl$_3$, FAPbI$_3$, CsPbI$_3$ and
MASnI$_3$, using density functional theory calculations with the SCAN+rVV10
functional. We analyse the impact of changing anions and cations on the defect
formation energies and the charge state transitions levels and identify the
physical origins underlying the observed trends. Dominant defects in the
lead-iodide compounds are the A$^+$ cation interstitials (A = Cs, MA, FA),
charge-compensated by I$^-$ interstitials or lead $({2-})$ vacancies. In the
lead-bromide and -chloride compounds, halide vacancies become relatively more
prominent, and for MAPbBr$_3$, the Pb$^{2+}$ interstitial also becomes
important. The trends can be explained in terms of the changes in electrostatic
interactions and chemical bonding upon replacing cations and anions. Defect
physics in MASnI$_3$ is strongly dominated by tin $({2-})$ vacancies, promoted
by the easy oxidation of the tin perovskite. Intrinsically, all compounds are
mildly p-doped, except for MASnI$_3$, which is strongly p-doped. All acceptor
levels created by defects in the six perovskites are shallow. Some defects,
halide vacancies and Pb or Sn interstitials in particular, create deep donor
traps. Although these traps might hamper the electronic behavior of MAPbBr$_3$
and MAPbCl$_3$, in iodine-based perovskites their equilibrium concentrations
are too small to affect the materials' properties.",2112.15251v1
2022-01-01,"First-principles insights into the mechanical, optoelectronic, thermophysical, and lattice dynamical properties of binary topological semimetal BaGa2","In the present study we have investigated the structural properties,
electronic band dispersion, elastic constants, acoustic behavior, phonon
spectrum, optical properties, and a number of thermophysical parameters of
binary topological semimetal BaGa2 in details via first-principles calculations
using the density functional theory (DFT) based formalisms. The electronic band
structure and density of states calculations with spin orbit coupling reveal
semimetallic nature with clear topological signature. The minimum thermal
conductivities and anisotropies of the compound are calculated. The elastic
constants, phonon dispersion calculations show that the compound under study is
both mechanically and dynamically stable. Comprehensive study of elastic
constants and moduli shows that BaGa2 possesses fairly isotropic mechanical
properties, reasonably good machinability, low Debye temperature and melting
point. The chemical bonding in BaG2 is interpreted via the electronic energy
density of states, electron density distribution, elastic properties and
Mulliken bond population analysis. The compound possesses both ionic and
covalent bondings. The reflectivity spectra show strong anisotropy with respect
to polarization of the incident electric field in the visible to
mid-ultraviolet regions. High reflectivity over wide spectral range makes BaGa2
suitable as a reflecting material. BaGa2 is also an efficient absorber of
ultraviolet radiation. Furthermore, the refractive index is quite high in the
infrared to visible range. All the energy dependent optical parameters show
metallic features and are in complete accord with the underlying bulk
electronic density of states calculations. Most of the results presented in
this study are novel and should serve as useful reference for future study.",2201.00172v1
2022-01-03,Phase Diagram of Infinite-layer Nickelate Compounds from First- and Second-principles Calculations,"The fundamental properties of infinite-layer rare-earth nickelates (RNiO2)
are carefully revisited and compared with those of CaCuO2 and RNiO3
perovskites. Combining first-principles and finite-temperature
second-principles calculations, we highlight that bulk NdNiO2 compound are far
from equivalent to CaCuO2, together at the structural, electronic, and magnetic
levels. Structurally, it is shown to be prone to spin-phonon coupling induced
oxygen square rotation motion, which might be responsible for the intriguing
upturn of the resistivity. At the electronic and magnetic levels, we point out
orbital-selective Mott localization with strong out-of-plane band dispersion,
which should result in the isotropic upper critical fields and weakly
three-dimensional magnetic interactions with in-plane local moment and
out-of-plane itinerant moment. We further demonstrate that as in RNiO3
perovskites, oxygen rotation motion and rare-earth ion controlled electronic
and magnetic properties can give rise in RNiO2 compounds to a rich phase
diagram and high tunability of various appealing properties. In line with that,
we reveal that key ingredients of high-Tc superconductor such as orbital
polarization, Fermi surface, and antiferromagnetic interactions can be
deliberately controlled in NdNiO2 through epitaxial strain. Exploiting
strain-orbital engineering, a crossover from three- to two-dimensional magnetic
transition can be established, making then NdNiO2 thin film a true analog of
high-Tc cuprates.",2201.00709v1
2022-01-19,Extending the Lorentz Factor Range and Sensitivity of Transition Radiation with Compound Radiators,"Transition radiation detectors (TRDs) have been used to identify high-energy
particles (in particular, to separate electrons from heavier particles) in
accelerator experiments. In space, they have been used to identify cosmic-ray
electrons and measure the energies of cosmic-ray nuclei. To date, radiators
have consisted of regular configurations of foils with fixed values of foil
thickness and spacing (or foam or fiber radiators with comparable average
dimensions) that have operated over a relatively restricted range of Lorentz
factors. In order to extend the applicability of future TRDs (for example, to
identify 0.5 - 3 TeV pions, kaons, and protons in the far forward region in a
future accelerator experiment or to measure the energy spectrum of cosmic-ray
nuclei up to 20 TeV/nucleon or higher), there is a need to increase the signal
strength and extend the range of Lorentz factors that can be measured in a
single detector. A possible approach is to utilize compound radiators
consisting of varying radiator parameters. We discuss the case of a compound
radiator and derive the yield produced in a TRD with an arbitrary configuration
of foil thicknesses and spacings.",2201.07901v1
2022-01-25,Rare Isotope Formation in Complete Fusion and Multinucleon Transfer Reactions in Collisions of 48Ca +248Cm around Coulomb Barrier Energies,"Within the framework of the dinuclear system model, the reaction mechanisms
for synthesizing target-like isotopes from Bk to compound nuclei Lv are
thoroughly investigated in complete and incomplete fusion reaction of $^{48}$Ca
+$^{248}$Cm around Coulomb barrier energies. Production cross-section of
$^{292,293}$Lv as a function of excitation energy in fusion-evaporation
reactions and target-like isotopic yields in multinucleon transfer reactions
are evaluated, in which a statistical approach is used to describe the decay
process of excited nuclei. The available experimental data can be reproduced
well with the model reasonably. The products of all possible formed isotopes in
the dynamical pre-equilibrium process for collision partners at incident energy
$E_{\rm lab}$ = 5.5 MeV/nucleon are exported, systematically. It is found that
the quasi-fission fragments are dominant in the yields. The optimal pathway
from the target to compound nuclei shows up along the valley of potential
surface energy. The effective impact parameter of two colliding partners
leading to compound nuclei is selected from head-on collision to semi-central
collision with $L$ = 52 $\rm \hbar$. The timescale boundary between complete
fusion and multinucleon transfer reactions is about 5.7$\times 10^{-21}$ s with
effective impact parameters. Synthesis cross-section of unknown neutron-rich
actinides from Bk to Rf have been predicted around several nanobarns.",2201.10077v1
2022-01-29,Machine Learning Study of the Magnetic Ordering in 2D Materials,"Magnetic materials have been applied in a large variety of technologies, from
data storage to quantum devices. The development of 2D materials has opened new
arenas for magnetic compounds, even when classical theories discourage their
examination. Here we propose a machine-learning-based strategy to predict and
understand magnetic ordering in 2D materials. This strategy couples the
prediction of the existence of magnetism in 2D materials using random forest
and the SHAP method with material maps defined by atomic features predicting
the magnetic ordering (ferromagnetic or antiferromagnetic). While the random
forest model predicts magnetism with an accuracy of 86%, the material maps
obtained by the SISSO method have an accuracy of about 90% in predicting the
magnetic ordering. Our model indicates that 3d transition metals, halides, and
structural clusters with regular transition metals sublattices have a positive
contribution in the total weight deciding the existence of magnetism in 2D
compounds. This behavior is associated with the competition between crystal
field and exchange splitting. The machine learning model also indicates that
the atomic SOC is a determinant feature for the identification of the patterns
separating ferro- from antiferro-magnetic order. The proposed strategy is used
to identify novel 2D magnetic compounds which, together with the fundamental
trends in the chemical and structural space, paves novel routes for
experimental exploration.",2201.12630v1
2022-04-07,Assessing the accuracy of compound formation energies with quantum Monte Carlo,"Accurately predicting the formation energy of a compound, which describes its
thermodynamic stability, is a key challenge in materials physics. Here, we
employ many-body quantum Monte Carlo (QMC) with single-reference trial
functions to compute the formation energy of two electronically disparate
compounds, the intermetallic VPt$_2$ and the semiconductor CuI, for which
standard density functional theory (DFT) predictions using both the
Perdew-Burke Ernzerhof (PBE) and the strongly constrained and appropriately
normed (SCAN) density functional approximations deviate markedly from available
experimental values. For VPt$_2$, we find an agreement between QMC, SCAN, and
PBE0 estimates, which therefore remain in disagreement with the much less
exothermic experimental value. For CuI, the QMC result agrees with neither SCAN
nor PBE pointing towards DFT exchange-correlation biases, likely related to the
localized Cu $3d$ electrons. Compared to the behavior of some density
functional approximations within DFT, spin-averaged QMC exhibits a smaller but
still appreciable deviation when compared to experiment. The QMC result is
slightly improved by incorporating spin-orbit corrections for CuI and solid
I$_2$, so that experiment and theory are brought into imperfect but reasonable
agreement within about 120~meV/atom.",2204.03441v2
2022-04-08,Magnetic measures of purity for MnBi$_2$Te$_4$,"The intrinsically anti-ferromagnetic topological insulator, MnBi$_2$Te$_4$
(MBT), has garnered significant attention recently. The excitement for this
layered van der Waals bonded compound stems from its potential to host numerous
exotic topological quantum states. For instance, quantum anomalous Hall states
are predicted for odd-layer compounds and axion insulator states for the
even-layer compounds. Unfortunately, the realization of these phenomena has
been hindered by experimental challenges such as the existence of negative
charge carriers, i.e., electron doping, which have been linked to anti-site
defects among the Mn and Bi sub-lattices. Based on high level diffusion Monte
Carlo (DMC) and DMC-tuned DFT+U calculations, we provide benchmark quality
results for the bulk Mn magnetization as well as for Mn$_{Bi}$ and Bi$_{Mn}$
defects. We use this information to refine and extend models that estimate the
anti-site defect concentration in actual MBT samples when combined with data
from magnetic susceptibility and intermediate field magnetization measurements.
Our models are validated through favorable comparison with prior experimental
studies that obtained both magnetic and site occupancy data. We then extend our
estimates to a larger set of prior samples to identify a probable zone of low
defect density that has yet to be reached in synthesis. We anticipate our
theoretically based magnetic purity measures may be used as minimization
targets in the cycle of refinement needed to synthesize MBT samples with low
anti-site defect concentrations and more reproducible topological properties.",2204.04268v1
2022-04-09,"A Family of Lanthanide Noncentrosymmetric Superconductors La$_4$$TX$ ($T$ = Ru, Rh, Ir; $X$ = Al, In)","We report the discovery of superconductivity in a series of
noncentrosymmetric compounds La$_4$$TX$ ($T$ = Ru, Rh, Ir; $X$ = Al, In), which
have a cubic crystal structure with space group $F\bar{4}3m$. La$_4$RuAl,
La$_4$RhAl, La$_4$IrAl, La$_4$RuIn and La$_4$IrIn exhibit bulk superconducting
transitions with critical temperatures $T_c$ of 1.77 K, 3.05 K, 1.54 K, 0.58 K
and 0.93 K, respectively. The specific heat of the La$_4$$T$Al compounds are
consistent with an $s$-wave model with a fully open superconducting gap. In all
cases, the upper critical fields are well described by the
Werthamer-Helfand-Hohenberg model, and the values are well below the Pauli
limit, indicating that orbital limiting is the dominant pair-breaking
mechanism. Density functional theory (DFT) calculations reveal that the degree
of band splitting by the antisymmetric spin-orbit coupling (ASOC) shows
considerable variation between the different compounds. This indicates that the
strength of the ASOC is highly tunable across this series of superconductors,
suggesting that these are good candidates for examining the relationship
between the ASOC and superconducting properties in noncentrosymmetric
superconductors.",2204.04463v1
2022-04-12,Enhanced superconductivity and moderate spin fluctuations suppressed at low energies in heavily electron-doped La1111-based superconductor,"To elucidate the origin of re-enhanced high-$T_c$ phase in the heavily
electron-doped Fe-pnictides, systematic $^{75}$As NMR studies are performed on
heavily electron-doped LaFe$Pn$O$_{0.75}$H$_{0.25}$ by controlling the
pnictogen height ($h_{Pn}$) from the Fe plane through the substitution at
$Pn$(=As) site with Sb or P. The measurements of nuclear spin relaxation rate
(1/$T_1$) and Knight shift ($K$) reveal that the moderate spin fluctuations at
high temperatures are suppressed toward low temperatures. Such characteristic
spin fluctuations with gap like feature at low energies are more enlarged in
higher $T_c$ compounds with higher $h_{Pn}$, while those are totally suppressed
in non-superconducting compounds with lower $h_{Pn}$. This implies that the
contribution of the finite energy part in the spin fluctuation spectrum is
crucial for enhancing $T_c$ in the heavily electron-doped regime. This is in
contrast to many cases of typical Fe-based compounds with hole and electron
Fermi surfaces of similar sizes, where the spin fluctuations at low energies
develop significantly at low temperatures. The features in the heavily
electron-doped states are discussed in relation with the characteristics of the
faint hole Fermi surface derived from $d_{xy}$ orbital that rises when $h_{Pn}$
is high, together with the enhanced electron correlation effects.",2204.05686v2
2022-04-24,"An ab initio approach to understand the structural, thermophysical, electronic, and optical properties of binary silicide SrSi2: A double Weyl semimetal","A large number of hitherto unexplored elastic, thermophysical, acoustic, and
optoelectronic properties of a double Weyl semimetal SrSi2 have been
investigated in this study. Density functional theory (DFT) based methodology
has been employed. Analyses of computed elastic parameters reveal that SrSi2 is
a mechanically stable, ductile, moderately machinable, and relatively soft
material. The compound is predicted to be dynamically stable and possesses
significant metallic bonding. Study of thermophysical properties, namely, Debye
temperature, Gr\""uneisen parameter, acoustic parameters, melting temperature,
heat capacity, thermal expansion coefficient, and dominant phonon mode is also
indicative of soft nature of SrSi2. The electronic band structure calculations
without and with spin-orbit coupling disclose semimetallic character with clear
Weyl nodes close to the Fermi level. The electronic dispersion is anisotropic
characterized by nearly flat and linear regions within the Brillouin zone.
Optical parameters at different photon energies are investigated. SrSi2 shows
excellent nonselective reflection spectrum across an extended range of energy
encompassing the visible region implying that the compound under study has
significant potential to be used as an efficient solar energy reflector. SrSi2
absorbs ultraviolet light quite efficiently. The compound also possesses high
refractive index in the low energy. All these optical features can be useful in
optoelectronic device applications.",2204.11238v1
2022-04-26,A DFT computational design and exploration of novel direct band gap silver-thallium double perovskites,"Researchers have addressed the non-traditional power generation schemes as
alternatives to the traditional fossil-fuel methods enormously since the
scientific community has serious concerns about shortages of energy on our
planet for future generations. In this scenario, the innovative materials for
photovoltaic and thermoelectric device applications are required by addressing
current issues of instability and efficiency. Perovskites are very popular in
this regard particularly having higher power conversion efficiency of 25.2% in
the case of solar cells. In the current article, we investigated innovative
small direct band gap double perovskites (elapsolite) Cs$_2$AgTlX$_6$ (X= Cl,
Br) with a comprehensive discussion on structural, electronic, optical, and
thermoelectric properties using a first-principles approach. The compounds
under investigation are found stable, efficient, and economical with alluring
optical and thermoelectric properties. The higher absorption peaks in the
visible range, substantial optical conductivities (~10$^{16}$ sec$^{-1}$), and
a lower percentage of reflection in the visible range make these compounds
fascinating for solar cell applications. Whereas large values of Seebeck
coefficients, electrical conductivities, the figure of merits (greater than
unity), and small values of thermal conductivities suggest the applications of
these compounds in thermoelectric generators.",2204.12123v2
2022-05-08,Spin interaction and magnetism in cobaltate Kitaev candidate materials: an $ab$ $initio$ and model Hamiltonian approach,"In the quest for materials hosting Kitaev spin liquids, much of the efforts
have been focused on the fourth- and fifth-row transition metal compounds,
which are spin-orbit coupling assisted Mott insulators. Here, we study the
structural and magnetic properties of 3$d$ transition metal oxides,
Na$_2$Co$_2$TeO$_6$ and Na$_3$Co$_2$SbO$_6$. The partial occupancy of sodium in
former compound is addressed using a cluster expansion, and a honeycomb lattice
of sodiums is found to be energetically favored. Starting from the \textit{ab
initio} band structures, a many-body second order perturbation theory leads to
a pseudospin-$\frac{1}{2}$ Hamiltonian with estimated magnetic interactions. We
show that the experimentally observed zigzag magnetic state is stabilized only
when the first neighbor Kitaev coupling dominates over the Heisenberg term,
both of which are highly suppressed due to presence of $e_g$ orbitals. A third
neighbor Heisenberg interaction is found dominant in both these compounds. We
also present a phase diagram for Na$_2$Co$_2$TeO$_6$ by varying the
electron-electron and spin-orbit interactions. The computed spin excitation
spectra are found to capture essential features of recent experimental magnon
spectrum, lending support to our results.",2205.03836v2
2022-05-09,Charge density wave in kagome lattice intermetallic ScV6Sn6,"Materials hosting kagome lattices have drawn interest for the diverse
magnetic and electronic states generated by geometric frustration. In the
$A$V$_3$Sb$_5$ compounds ($A$ = K, Rb, Cs), stacked vanadium kagome layers give
rise to unusual charge density waves (CDW) and superconductivity. Here we
report single-crystal growth and characterization of ScV$_6$Sn$_6$, a hexagonal
HfFe$_6$Ge$_6$-type compound that shares this structural motif. We identify a
first-order phase transition at 92 K. Single crystal X-ray and neutron
diffraction reveal a charge density wave modulation of the atomic lattice below
this temperature. This is a distinctly different structural mode than that
observed in the $A$V$_3$Sb$_5$ compounds, but both modes have been anticipated
in kagome metals. The diverse HfFe$_6$Ge$_6$ family offers more opportunities
to tune ScV$_6$Sn$_6$ and explore density wave order in kagome lattice
materials.",2205.04582v2
2022-05-11,One-dimensional electronic states in a natural misfit structure,"Misfit compounds are thermodynamically stable stacks of two-dimensional
materials, forming a three-dimensional structure that remains incommensurate in
one direction parallel to the layers. As a consequence, no true bonding is
expected between the layers, with their interaction being dominated by charge
transfer. In contrast to this well-established picture, we show that interlayer
coupling can strongly influence the electronic properties of one type of layer
in a misfit structure, in a similar way to the creation of modified band
structures in an artificial moir\'e structure between two-dimensional
materials. Using angle-resolved photoemission spectroscopy with a micron-scale
light focus, we selectively probe the electronic properties of hexagonal
NbSe$_2$ and square BiSe layers that terminate the surface of the
(BiSe)$_{1+\delta}$NbSe$_2$ misfit compound. We show that the band structure in
the BiSe layers is strongly affected by the presence of the hexagonal NbSe$_2$
layers, leading to quasi one-dimensional electronic features. The electronic
structure of the NbSe$_2$ layers, on the other hand, is hardly influenced by
the presence of the BiSe. Using density functional theory calculations of the
unfolded band structures, we argue that the preferred modification of one type
of bands is mainly due to the atomic and orbital character of the states
involved, opening a promising way to design novel electronic states that
exploit the partially incommensurate character of the misfit compounds.",2205.05470v1
2022-06-07,A generative recommender system with GMM prior for cancer drug generation and sensitivity prediction,"Recent emergence of high-throughput drug screening assays sparkled an
intensive development of machine learning methods, including models for
prediction of sensitivity of cancer cell lines to anti-cancer drugs, as well as
methods for generation of potential drug candidates. However, a concept of
generation of compounds with specific properties and simultaneous modeling of
their efficacy against cancer cell lines has not been comprehensively explored.
To address this need, we present VADEERS, a Variational Autoencoder-based Drug
Efficacy Estimation Recommender System. The generation of compounds is
performed by a novel variational autoencoder with a semi-supervised Gaussian
Mixture Model (GMM) prior. The prior defines a clustering in the latent space,
where the clusters are associated with specific drug properties. In addition,
VADEERS is equipped with a cell line autoencoder and a sensitivity prediction
network. The model combines data for SMILES string representations of
anti-cancer drugs, their inhibition profiles against a panel of protein
kinases, cell lines biological features and measurements of the sensitivity of
the cell lines to the drugs. The evaluated variants of VADEERS achieve a high
r=0.87 Pearson correlation between true and predicted drug sensitivity
estimates. We train the GMM prior in such a way that the clusters in the latent
space correspond to a pre-computed clustering of the drugs by their inhibitory
profiles. We show that the learned latent representations and new generated
data points accurately reflect the given clustering. In summary, VADEERS offers
a comprehensive model of drugs and cell lines properties and relationships
between them, as well as a guided generation of novel compounds.",2206.03555v1
2022-06-23,A Hybrid Adjacency and Time-Based Data Structure for Analysis of Temporal Networks,"Dynamic or temporal networks enable representation of time-varying edges
between nodes. Conventional adjacency-based data structures used for storing
networks such as adjacency lists were designed without incorporating time and
can thus quickly retrieve all edges between two sets of nodes (a node-based
slice) but cannot quickly retrieve all edges that occur within a given time
interval (a time-based slice). We propose a hybrid data structure for storing
temporal networks that stores edges in both an adjacency dictionary, enabling
rapid node-based slices, and an interval tree, enabling rapid time-based
slices. Our hybrid structure also enables compound slices, where one needs to
slice both over nodes and time, either by slicing first over nodes or slicing
first over time. We further propose an approach for predictive compound
slicing, which attempts to predict whether a node-based or time-based compound
slice is more efficient. We evaluate our hybrid data structure on many real
temporal network data sets and find that they achieve much faster slice times
than existing data structures with only a modest increase in creation time and
memory usage.",2206.11444v1
2022-07-12,Compound Prototype Matching for Few-shot Action Recognition,"Few-shot action recognition aims to recognize novel action classes using only
a small number of labeled training samples. In this work, we propose a novel
approach that first summarizes each video into compound prototypes consisting
of a group of global prototypes and a group of focused prototypes, and then
compares video similarity based on the prototypes. Each global prototype is
encouraged to summarize a specific aspect from the entire video, for example,
the start/evolution of the action. Since no clear annotation is provided for
the global prototypes, we use a group of focused prototypes to focus on certain
timestamps in the video. We compare video similarity by matching the compound
prototypes between the support and query videos. The global prototypes are
directly matched to compare videos from the same perspective, for example, to
compare whether two actions start similarly. For the focused prototypes, since
actions have various temporal variations in the videos, we apply bipartite
matching to allow the comparison of actions with different temporal positions
and shifts. Experiments demonstrate that our proposed method achieves
state-of-the-art results on multiple benchmarks.",2207.05515v6
2022-07-15,Spin-split collinear antiferromagnets: a large-scale ab-initio study,"It was recently discovered that, depending on their symmetries, collinear
antiferromagnets can actually break the spin degeneracy in momentum space, even
in the absence of spin-orbit coupling. Such systems, recently dubbed
altermagnets, are signalled by the emergence of a spin-momentum texture set
mainly by the crystal and magnetic structure, relativistic effects playing a
secondary role. Here we consider all collinear $q$=0 antiferromagnetic
compounds in the MAGNDATA database allowing for spin-split bands. Based on
density-functional calculations for the experimentally reported crystal and
magnetic structures, we study more than sixty compounds and introduce numerical
measures for the average momentum-space spin splitting. We highlight some
compounds that are of particular interest, either due to a relatively large
spin splitting, such as CoF$_2$ and FeSO$_4$F, or because of their low-energy
electronic structure. The latter include LiFe$_2$F$_6$, which hosts nearly flat
spin-split bands next to the Fermi energy, as well as RuO$_2$, CrNb$_4$S$_8$,
and CrSb, which are spin-split antiferromagnetic metals.",2207.07592v2
2022-07-21,Low cost prediction of probability distributions of molecular properties for early virtual screening,"While there is a general focus on predictions of values, mathematically more
appropriate is prediction of probability distributions: with additional
possibilities like prediction of uncertainty, higher moments and quantiles. For
the purpose of the computer-aided drug design field, this article applies
Hierarchical Correlation Reconstruction approach, previously applied in the
analysis of demographic, financial and astronomical data. Instead of a single
linear regression to predict values, it uses multiple linear regressions to
independently predict multiple moments, finally combining them into predicted
probability distribution, here of several ADMET properties based on
substructural fingerprint developed by Klekota\&Roth. Discussed application
example is inexpensive selection of a percentage of molecules with properties
nearly certain to be in a predicted or chosen range during virtual screening.
Such an approach can facilitate the interpretation of the results as the
predictions characterized by high rate of uncertainty are automatically
detected. In addition, for each of the investigated predictive problems, we
detected crucial structural features, which should be carefully considered when
optimizing compounds towards particular property. The whole methodology
developed in the study constitutes therefore a great support for medicinal
chemists, as it enable fast rejection of compounds with the lowest potential of
desired physicochemical/ADMET characteristic and guides the compound
optimization process.",2207.11174v1
2022-07-29,Flipping of antiferromagnetic to superconducting states in pressurized quasi-one-dimensional manganese-based compounds,"One of the universal features of unconventional superconductors is that the
superconducting (SC) state is developed in the proximity of an
antiferromagnetic (AFM) state. Understanding the interplay between these two
states is one of the key issues to uncover the underlying physics of
unconventional SC mechanism. Here, we report a pressure-induced flipping of the
AFM state to SC state in the quasi-one-dimensional AMn6Bi5 (A = K, Rb, and Cs)
compounds. We find that at a critical pressure the AFM state suddenly
disappears at a finite temperature and a SC state simultaneously emerges at a
lower temperature without detectable structural changes. Intriguingly, all
members of the family present the AFM-SC transition at almost the same critical
pressures (Pc), though their ambient-pressure unit-cell volumes vary
substantially. Our theoretical calculations indicate that the increasing weight
of dxz orbital electrons near Fermi energy under the pressure may be the origin
of the flipping. These results reveal a diversity of competing nature between
the AFM and SC states among the 3d-transition-metal compounds.",2207.14697v1
2022-08-02,Spin-Orbital States and Strong Antiferromagnetism of Layered Eu$_2$SrFe$_2$O$_6$ and Sr$_3$Fe$_2$O$_4$Cl$_2$,"The insulating iron compounds Eu$_2$SrFe$_2$O$_6$ and Sr$_3$Fe$_2$O$_4$Cl$_2$
have high-temperature antiferromagnetic (AF) order despite their different
layered structures. Here we carry out density functional calculations and Monte
Carlo simulations to study their electronic structures and magnetic properties
aided with analyses of the crystal field, magnetic anisotropy, and
superexchange. We find that both compounds are Mott insulators and in the
high-spin (HS) Fe$^{2+}$ state ($S$ = 2) accompanied by the weakened crystal
field. Although they have different local coordination and crystal fields, the
Fe$^{2+}$ ions have the same level sequence and ground-state configuration
$(3z^2-r^2)^2(xz,yz)^2(xy)^1(x^2-y^2)^1$. Then, the multiorbital superexchange
produces strong AF couplings, and the $(3z^2-r^2)/(xz,yz)$ mixing via the
spin-orbit coupling (SOC) yields a small in-plane orbital moment and
anisotropy. Indeed, by tracing a set of different spin-orbital states, our
density functional calculations confirm the strong AF couplings and the easy
planar magnetization for both compounds. Moreover, using the derived magnetic
parameters, our Monte Carlo simulations give the N\'eel temperature $T_{\rm N}$
= 420 K (372 K) for the former (the latter), which well reproduce the
experimental results. Therefore, the present study provides a unified picture
for Eu$_2$SrFe$_2$O$_6$ and Sr$_3$Fe$_2$O$_4$Cl$_2$ concerning their electronic
and magnetic properties.",2208.01318v1
2022-08-09,Discovery of Superconductivity in Nb$_4$SiSb$_2$ with a V$_4$SiSb$_2$-Type Structure and Implications of Interstitial Doping on its Physical Properties,"We report on the discovery, structural analysis, and the physical properties
of Nb$_4$SiSb$_2$ -- a hitherto unknown compound crystallizing in the
V$_4$SiSb$_2$-type structure with the tetragonal space group $I4/mcm$ and unit
cell parameters $a$ = 10.3638(2) $\mathring{\mathrm{A}}$ and $c$ = 4.9151(2)
$\mathring{\mathrm{A}}$. We find Nb$_4$SiSb$_2$ to be a metal undergoing a
transition to a superconducting state at a critical temperature of $T_{\rm c}
\approx$ 1.6 K. The bulk nature of the superconductivity in this material is
confirmed by the observation of a well defined discontinuity in specific heat
with a normalized specific heat jump of $\Delta C(T_{\rm c})/\gamma T_{\rm c} =
1.33\, {\rm mJ}\, {\rm mol}^{-1}\, {\rm K}^{-2}$. We find that for
Nb$_4$SiSb$_2$, the unoccupied sites on the $4b$ Wyckoff position can be
partially occupied with Cu, Pd, or Pt. Low-temperature resistivity measurements
show transitions to superconductivity for all three compounds at $T_{\rm c}
\approx\, 1.2\, {\rm K}$ for Nb$_4$Cu$_{0.2}$SiSb$_2$, and $T_{\rm c} \approx\,
0.8\, {\rm K}$ for Nb$_4$Pd$_{0.2}$SiSb$_2$ as well as for
Nb$_4$Pt$_{0.14}$SiSb$_2$. The addition of electron-donor atoms into these void
positions, henceforth, lowers the superconducting transition temperature in
comparison to the parent compound.",2208.04834v1
2022-08-12,Weak antilocalization effect and triply degenerate state in Cu-doped CaAuAs,"The effect of 50\% Cu doping at the Au site in the topological Dirac
semimetal CaAuAs is investigated through electronic band structure
calculations, electrical resistivity, and magnetotransport measurements.
Electronic structure calculations a suggest broken-symmetry-driven topological
phase transition from the Dirac to triple-point state in CaAuAs via alloy
engineering. The electrical resistivity of both the CaAuAs and
CaAu$_{0.5}$Cu$_{0.5}$As compounds shows metallic behavior. Nonsaturating
quasilinear magnetoresistance (MR) behavior is observed in CaAuAs. On the other
hand, MR of the doped compound shows a pronounced cusplike feature in the
low-field regime. Such behavior of MR in CaAu$_{0.5}$Cu$_{0.5}$As is attributed
to the weak antilocalization (WAL) effect. The WAL effect is analyzed using
different theoretical models, including the semiclassical $\sim\sqrt{B}$ one
which accounts for the three-dimensional WAL and modified Hikami-Larkin-Nagaoka
model. Strong WAL effect is also observed in the longitudinal MR, which is well
described by the generalized Altshuler-Aronov model. Our study suggests that
the WAL effect originates from weak disorder and the spin-orbit coupled bulk
state. Interestingly, we have also observed the signature of chiral anomaly in
longitudinal MR, when both current and field are applied along the $c$ axis.
The Hall resistivity measurements indicate that the charge conduction mechanism
in these compounds is dominated by the holes with a concentration
$\sim$10$^{20}$ cm$^{-3}$ and mobility $\sim 10^2$ cm$^2$ V$^{-1}$ S$^{-1}$.",2208.06208v1
2022-08-15,Self-Assembled Ligand-Capped Plasmonic Au Nanoparticle Films in the Kretschmann Configuration for Sensing of Volatile Organic Compounds,"Films of close-packed Au nanoparticles are coupled electrodynamically through
their collective plasmon resonances. This collective optical response results
in enhanced light-matter interactions, which can be exploited in various
applications. Here, we demonstrate their application in sensing volatile
organic compounds, using methanol as a test-case. Ordered films over several
cm2 were obtained by interfacial self-assembly of colloidal Au nanoparticles
(~10 nm diameter) through controlled evaporation of the solvent. Even though
isolated nanoparticles of this size are inherently non-scattering, when
arranged in a close-packed film the plasmonic coupling results in a strong
reflectance and absorbance. The in-situ tracking of vapor phase methanol
concentration through UV-Vis transmission measurements of the nanoparticle film
is first demonstrated. Next, in-situ ellipsometry of the self-assembled films
in the Kretschmann (also known as ATR) configuration is shown to yield enhanced
sensitivity, especially with phase difference measurements. Our study shows the
excellent agreement between theoretical models of the spectral response of
self-assembled films with experimental in-situ sensing experiments. At the same
time, the theoretical framework provides the basis for the interpretation of
the various observed experimental trends. Combining periodic nanoparticle films
with ellipsometry in the Kretschmann configuration is a promising strategy
towards highly sensitive and selective plasmonic thin-film devices based on
colloidal fabrication methods for volatile organic compound (VOC) sensing
applications.",2208.07034v1
2022-09-07,Atypical magnetic behavior in the incommensurate $[CH_3NH_3][Ni(HCOO)_3]$ hybrid perovskite,"A plethora of temperature induced phase transitions have been observed in
$[CH_3NH_3][M(HCOO)_3]$ compounds, where M is Co(II) or Ni(II). Among them, the
nickel compound exhibits a combination of magnetic and nuclear
incommensurabil-ity below N\'eel temperature. Despite the fact that the
zero-field behavior has been previously addressed, here we study in depth the
macroscopic magnetic behavior of this compound to unveil the origin of the
atypical magnetic response found in it and in its parent family of formate
perovskites. In particular, they show a puzzling magnetization reversal in the
curves measured starting from low temperatures, after cooling under zero field.
The first atypical phenomena is the im-possibility of reaching zero
magnetization, even by nullifying the applied external field and even
compensating it for the influence earth's magnetic field. Relatively large
magnetic fields are needed to switch the magnetization from negative to
positive values or vice versa, which is compatible with a soft-ferromagnetic
system. The atypical path found in its first magnetization curve and hysteresis
loop at low temperatures is the most noticeable feature. The magnetization
curve switches from more than 1200 Oe from the first magnetization loop to the
subsequent magnetization loops. A feature that cannot be explained using a
model based on unbalanced pair of domains. As a result, we decipher this
behavior in light of the incommensurate structure of this material. We propose,
in particular, that the applied magnetic field induces a mag-netic phase
transition from a magnetically incommensurate structure to a magnetically
commensurate structure.",2209.03093v1
2022-09-16,Unveiling new quantum phases in the Shastry-Sutherland compound SrCu2(BO3)2up to the saturation magnetic field,"Under magnetic fields, quantum magnets often undergo exotic phase transitions
with various kinds of order. The discovery of a sequence of fractional
magnetization plateaus in the Shastry-Sutherland compound SrCu2(BO3)2 has
played a central role in the high-field research on quantum materials, but so
far this system could only be probed up to half the saturation value of the
magnetization. Here, we report the first experimental and theoretical
investigation of this compound up to the saturation magnetic field of 140 T and
beyond. Using ultrasound and magnetostriction techniques combined with
extensive tensor-network calculations (iPEPS), several spin-supersolid phases
are revealed between the 1/2 plateau and saturation (1/1 plateau). Quite
remarkably, the sound velocity of the 1/2 plateau exhibits a drastic decrease
of -50%, related to the tetragonal-to-orthorhombic instability of the
checkerboard-type magnon crystal. The unveiled nature of this paradigmatic
quantum system is a new milestone for exploring exotic quantum states of matter
emerging in extreme conditions.",2209.07652v2
2022-09-27,Gap opening mechanism for correlated Dirac electrons in organic compounds $α$-(BEDT-TTF)$_2$I$_3$ and $α$-(BEDT-TSeF)$_2$I$_3$,"To determine how electron correlations open a gap in two-dimensional massless
Dirac electrons in the organic compounds $\alpha$-(BEDT-TTF)$_2$I$_3$
[$\alpha$-(ET)$_2$I$_3$] and $\alpha$-(BEDT-TSeF)$_2$I$_3$
[$\alpha$-(BETS)$_2$I$_3$], we derive and analyze $ab$ $initio$ low-energy
effective Hamiltonians for these two compounds. We find that the horizontal
stripe charge ordering opens a gap in the massless Dirac electrons in
$\alpha$-(ET)$_2$I$_3$, while an insulating phase without explicit symmetry
breaking appears in $\alpha$-(BETS)$_2$I$_3$. We clarify that the combination
of the anisotropic transfer integrals and the electron correlations induces a
dimensional reduction in the spin correlations, i.e., one-dimensional spin
correlations develop in $\alpha$-(BETS)$_2$I$_3$. We show that the
one-dimensional spin correlations open a gap in the massless Dirac electrons.
Our finding paves the way for opening gaps for massless Dirac electrons using
strong electronic correlations.",2209.13460v4
2022-09-29,Site-specific atomic substitution in a giant magnetocaloric Fe$_2$P-type system,"Giant magnetocaloric (GMC) materials constitute a requirement for near room
temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with
strong magnetoelastic coupling. The main hindrance towards application of this
material is a comparably large temperature hysteresis, which can be reduced by
metal site substitution with a nonmagnetic element. However, the
(Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the
tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The
magnetic and magnetocaloric properties of such compounds are highly sensitive
to the site specific occupancy of the magnetic atoms. Here we have attempted to
study separately the effect of $3f$ and $3g$ site substitution with equal
amounts of vanadium. Using formation energy calculations, the site preference
of vanadium and its influence on the magnetic phase formation are described. A
large difference in the isothermal entropy change (as high as 44\%) with
substitution in the $3f$ and $3g$ sites is observed. The role of the lattice
parameter change with temperature and the strength of the magnetoelastic
coupling on the magnetic properties are highlighted.",2209.14962v1
2022-10-10,Simulations of magnetic Bragg scattering in transmission electron microscopy,"We have simulated the magnetic Bragg scattering in transmission electron
microscopy in two antiferromagnetic compounds, NiO and LaMnAsO. This weak
magnetic phenomenon was experimentally observed in NiO by Loudon. We have
computationally reproduced Loudon's experimental data, and for comparison we
have performed calculations for the LaMnAsO compound as a more challenging
case, containing lower concentration of magnetic elements and strongly
scattering heavier non-magnetic elements. We have also described thickness and
voltage dependence of the intensity of the antiferromagnetic Bragg spot for
both compounds. We have considered lattice vibrations within two computational
approaches, one assuming a static lattice with Debye-Waller smeared potentials,
and another explicitly considering the atomic vibrations within the quantum
excitations of phonons model (thermal diffuse scattering). The structural
analysis shows that the antiferromagnetic Bragg spot appears in between (111)
and (000) reflections for NiO, while for LaMnAsO the antiferromagnetic Bragg
spot appears at the position of the (010) reflection in the diffraction
pattern, which corresponds to a forbidden reflection of the crystal structure.
Calculations predict that the intensity of the magnetic Bragg spot in NiO is
significantly stronger than thermal diffuse scattering at room temperature. For
LaMnAsO, the magnetic Bragg spot is weaker than the room-temperature thermal
diffuse scattering, but its detection can be facilitated at reduced
temperatures.",2210.04679v2
2022-10-11,Ultrafast electron localization and screening in a transition metal dichalcogenide,"The coupling of light to electrical charge carriers in semiconductors is the
foundation of many technological applications. Attosecond transient absorption
spectroscopy measures simultaneously how excited electrons and the vacancies
they leave behind dynamically react to the applied optical fields. In compound
semiconductors, these dynamics can be probed via any of their atomic
constituents. Often, the atomic species forming the compound contribute
comparably to the relevant electronic properties of the material. One therefore
expects to observe similar dynamics, irrespective of the choice of atomic
species via which it is probed. Here, we show in the two-dimensional transition
metal dichalcogenide semiconductor $MoSe_2$, that through a selenium-based
transition we observe charge carriers acting independently from each other,
while when probed through molybdenum, the collective, many-body motion of the
carriers dominates. Such unexpectedly contrasting behavior can be traced back
to a strong localization of electrons around molybdenum atoms following
absorption of light, which modifies the local fields acting on the carriers. We
show that similar behavior in elemental titanium metal carries over to
transition metal-containing compounds and is expected to play an essential role
for a wide range of such materials. Knowledge of independent particle and
collective response is essential for fully understanding these materials.",2210.05465v1
2022-10-13,Fermi-liquid nonadiabatic highly-compressed cesium iodide superconductor,"Experimental discovery that compressed sulphur hydride exhibits
superconducting transition temperature Tc=203 K (Drozdov et al 2015 Nature 525
73) sparked intensive studies of superconducting hydrides. However, this
discovery was not a straight forward experimental examination of theoretically
predicted phase, instead it was nearly five-decade long experimental quest for
superconductivity in highly-compressed matters, which varied from pure elements
(hydrogen, oxygen, sulphur, lithium), cuprates, and hydrides (SiH4, YH3, and
AlH3), to semiconductors and ionic salts. One of these salts was cesium iodide,
CsI, which converts into metallic state at P=115 GPa and at P=180 GPa this
compound exhibits the onset of the superconducting transition temperature Tc~2
K (Eremets et al 1998 Science 281 1333). Detailed first principles calculations
(Xu et al 2009 Phys Rev B 79 144110) showed that within Eliashberg theory of
superconductivity, the CsI should exhibits Tc=0.03 K at pressure P=180 GPa,
which is by two orders of magnitude lower than the observed value. In attempt
to understand the nature of this discrepancy, here we analyzed temperature
dependent resistance in compressed CsI and found that this compound is perfect
Fermi liquid metal which exhibits extremely high (~ 17) ratio of the Debye
temperature, Td, to the Fermi energy, Tf. This implies that direct utilization
of the Eliashberg theory is incorrect for this compound, because the theory
valid for the ratio Td/Tf << 1. We also showed that highly-compressed CsI
exhibits the ratio of Tc/Tf = 0.04-0.07 and it falls in unconventional
superconductors band in the Uemura plot.",2210.07205v1
2022-10-18,In-plane electronic anisotropy revealed by interlayer resistivity measurements on the iron-based superconductor parent compound CaFeAsF,"Both cuprates and iron-based superconductors demonstrate nematicity, defined
as the spontaneous breaking of rotational symmetry in electron systems. The
nematic state can play a role in the high-transition-temperature
superconductivity of these compounds. However, the microscopic mechanism
responsible for the transport anisotropy in iron-based compounds remains
debatable. Here, we investigate the electronic anisotropy of CaFeAsF by
measuring its interlayer resistivity under magnetic fields with varying field
directions. Counterintuitively, the interlayer resistivity was larger in the
longitudinal configuration ($B \parallel I \parallel c$) than in the transverse
one ($B \perp I \parallel c$). The interlayer resistivity exhibited a so-called
coherence peak under in-plane fields and was highly anisotropic with respect to
the in-plane field direction. At $T$ = 4 K and $B$ = 14 T, the
magnetoresistance $\Delta\rho/\rho_0$ was seven times larger in the $B
\parallel b_o$ than in the $B \parallel a_o$ configuration. Our theoretical
calculations of the conductivity based on the first-principles electronic band
structure qualitatively reproduced the above observations but underestimated
the magnitudes of the observed features. The proposed methodology can be a
powerful tool for probing the nematic electronic state in various materials.",2210.09533v2
2022-10-26,Evolution of the optical response of the magnetic topological insulators Mn(Bi$_{1-x}$Sb$_{x}$)$_2$Te$_4$ with Sb content,"MnBi$_2$Te$_4$ is a promising representative of intrinsic antiferromagnetic
topological insulators, which could enable rare quantum mechanical effects like
the quantum anomalous Hall effect. Especially at low temperatures, numerous
studies have been reported, demonstrating the great potential of this compound
in the magnetically ordered state below $T_{\mathrm{N}}$. Among recent
findings, the alloy compound Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ has been suggested
to be an interesting candidate for the realization of an ideal Weyl semimetal
state. By exchanging Bi by Sb, the electronic structure is influenced in terms
of a shift of the Fermi energy, and a decrease in the energy gap has been
predicted. In this work, we investigate and compare the optical conductivity of
Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ single crystals with various Sb doping levels
$x$ by infrared reflectivity measurements. We observe a big impact of the Sb
content on the low-energy excitations characterizing the metallic state of our
samples. Different $x$=0.26 crystals show significant differences in their
optical response and also a strong position dependence. The findings are
compared to the recently reported optical conductivity spectrum of the pure
compound MnBi$_2$Te$_4$.",2210.14538v1
2022-10-26,"Unconventional magneto-resistance, and electronic transition in Mn$_3$Ge Weyl semimetal","Weyl semimetals are well known for their anomalous transport effects caused
by a large fictitious magnetic field generated by the non-zero Berry curvature.
We performed the analysis of the electrical transport measurements of the
magnetic Weyl semimetal Mn$_{3}$Ge in the a-b and a-c plane. We have observed
negative longitudinal magneto-resistance (LMR) at a low magnetic field ($B<1.5$
T) along all the axes. The high field LMR shows different behavior along x and
z axes. A similar trend has been observed in the case of planar Hall effect
(PHE) measurements as well. The nature of high field LMR along the x axis
changes near 200 K. Dominant carrier concentration type, and metallic to
semimetallic transition also occur near 200 K. These observations suggest two
main conclusions: (i) The high field LMR in Mn$_3$Ge is driven by the metallic
- semimetallic nature of the compound. (ii) Mn$_3$Ge compound goes through an
electronic band topological transition near 200 K. Single crystal neutron
diffraction does not show any change in the magnetic structure below 300 K.
However, the in-plane lattice parameter (a) shows a maximum near 230 K.
Therefore, it is possible that the change in electronic band structure near 200
K is driven by the a lattice parameter of the compound.",2210.14683v1
2022-10-23,Identifying Crisis Response Communities in Online Social Networks for Compound Disasters: The Case of Hurricane Laura and Covid-19,"Online social networks allow different agencies and the public to interact
and share the underlying risks and protective actions during major disasters.
This study revealed such crisis communication patterns during hurricane Laura
compounded by the COVID-19 pandemic. Laura was one of the strongest (Category
4) hurricanes on record to make landfall in Cameron, Louisiana. Using the
Application Programming Interface (API), this study utilizes large-scale social
media data obtained from Twitter through the recently released academic track
that provides complete and unbiased observations. The data captured publicly
available tweets shared by active Twitter users from the vulnerable areas
threatened by Laura. Online social networks were based on user influence
feature ( mentions or tags) that allows notifying other users while posting a
tweet. Using network science theories and advanced community detection
algorithms, the study split these networks into twenty-one components of
various sizes, the largest of which contained eight well-defined communities.
Several natural language processing techniques (i.e., word clouds, bigrams,
topic modeling) were applied to the tweets shared by the users in these
communities to observe their risk-taking or risk-averse behavior during a major
compounding crisis. Social media accounts of local news media, radio,
universities, and popular sports pages were among those who involved heavily
and interacted closely with local residents. In contrast, emergency management
and planning units in the area engaged less with the public. The findings of
this study provide novel insights into the design of efficient social media
communication guidelines to respond better in future disasters.",2210.14970v1
2022-12-07,Symmetry-based computational search for novel binary and ternary 2D materials,"We present a symmetry-based exhaustive approach to explore the structural and
compositional richness of two-dimensional materials. We use a ``combinatorial
engine'' that constructs potential compounds by occupying all possible Wyckoff
positions for a certain space group with combinations of chemical elements.
These combinations are restricted by imposing charge neutrality and the Pauling
test for electronegativities. The structures are then pre-optimized with a
specially crafted universal neural-network force-field, before a final step of
geometry optimization using density-functional theory is performed. In this way
we unveil an unprecedented variety of two-dimensional materials, covering the
whole periodic table in more than 30 different stoichiometries of form
A$_n$B$_m$ or A$_n$B$_m$C$_k$. Among the found structures we find examples that
can be built by decorating nearly all Platonic and Archimedean tesselations as
well as their dual Laves or Catalan tilings. We also obtain a rich, and
unexpected, polymorphism for some specific compounds. We further accelerate the
exploration of the chemical space of two-dimensional materials by employing
machine-learning-accelerated prototype search, based on the structural types
discovered in the exhaustive search. In total, we obtain around 6500 compounds,
not present in previous available databases of 2D materials, with an energy of
less than 250~meV/atom above the convex hull of thermodynamic stability.",2212.03975v2
2023-01-03,Semantic Units: Organizing knowledge graphs into semantically meaningful units of representation,"Knowledge graphs and ontologies are becoming increasingly important as
technical solutions for Findable, Accessible, Interoperable, and Reusable data
and metadata (FAIR Guiding Principles). We discuss four challenges that impede
the use of FAIR knowledge graphs and propose semantic units as their potential
solution. Semantic units structure a knowledge graph into identifiable and
semantically meaningful subgraphs. Each unit is represented by its own
resource, instantiates a corresponding semantic unit class, and can be
implemented as a FAIR Digital Object and a nanopublication in RDF/OWL and
property graphs. We distinguish statement and compound units as basic
categories of semantic units. Statement units represent smallest, independent
propositions that are semantically meaningful for a human reader. They consist
of one or more triples and mathematically partition a knowledge graph. We
distinguish assertional, contingent (prototypical), and universal statement
units as basic types of statement units and propose representational schemes
and formal semantics for them (including for absence statements, negations, and
cardinality restrictions) that do not involve blank nodes and that translate
back to OWL. Compound units, on the other hand, represent semantically
meaningful collections of semantic units and we distinguish various types of
compound units, representing different levels of representational granularity,
different types of granularity trees, and different frames of reference.
Semantic units support making statements about statements, can be used for
graph-alignment, subgraph-matching, knowledge graph profiling, and for managing
access restrictions to sensitive data. Organizing the graph into semantic units
supports the separation of ontological, diagnostic (i.e., referential), and
discursive information, and it also supports the differentiation of multiple
frames of reference.",2301.01227v1
2023-01-12,The collision frequency in two unconventional superconductors,"The collision frequency (also known as the inverse scattering lifetime) can
be self-consistently calculated from the imaginary part of the zero-temperature
elastic scattering cross-section in unconventional superconductors. We find
these types of studies helpful to describe a hidden self-consistent damping due
to incoherent fermions in two physical spaces: The Phase Space of the
Nonequilibrium Statistical Mechanics, and the Configuration Space of
Nonrelativistic Quantum Mechanics. The direct relation of the collision
frequency with those well-known Physical Spaces is addressed in a singular way
this time. Since the use of collisions for different elastic scattering
regimes, is a well-developed formalism using retarded, and advanced Green
functions in Many Body Physics; in order to describe our findings, we define
and characterize a Reduced Phase Space for collision frequencies in the triplet
strontium ruthenate compound and the singlet doped with strontium lanthanum
cuprate ceramic. Both compounds display different nodal behavior of the
superconducting order parameter. In this work, their zero gap behavior is
numerically scanned and used to give some illustrative examples. Finally, it
intuitively explores the geometrical nonlocality of the collision frequency of
this type of hidden self-consistency in the Boltzmann equation, when the zero
superconducting gap value drives the physics below the transition temperature,
and incoherent fermions quasiparticles govern several nonequilibrium phenomena
since the macroscopic behavior remarkably changes with the strontium atomic
potential strength, and the concentration inherent to both compounds.",2301.05322v2
2023-01-16,"Tomographic imaging of microvasculature with a purpose-designed, polymeric X-ray contrast agent","Imaging of microvasculature is primarily performed with X-ray contrast
agents, owing to the wide availability of absorption-contrast laboratory source
microCT compared to phase contrast capable devices. Standard commercial
contrast agents used in angiography are not suitable for high-resolution
imaging ex vivo, however, as they are small molecular compounds capable of
diffusing through blood vessel walls within minutes. Large nanoparticle-based
blood pool contrast agents on the other hand exhibit problems with aggregation,
resulting in clogging in the smallest blood vessels. Injection with solidifying
plastic resins has, therefore, remained the gold standard for microvascular
imaging, despite the considerable amount of training and optimization needed to
properly perfuse the viscous compounds. Even with optimization, frequent gas
and water inclusions commonly result in interrupted vessel segments. This lack
of suitable compounds has led us to develop the polymeric, cross-linkable X-ray
contrast agent XlinCA. As a water-soluble organic molecule, aggregation and
inclusions are inherently avoided. High molecular weight allows it to be
retained even in the highly fenestrated vasculature of the kidney filtration
system. It can be covalently crosslinked using the same aldehydes used in
tissue fixation protocols, leading to stable and permanent contrast. These
properties allowed us to image whole mice and individual organs in 6 to
12-month-old C57BL/6J mice without requiring lengthy optimizations of injection
rates and pressures, while at the same time achieving greatly improved filling
of the vasculature compared to resin-based vascular casting. This work aims at
illuminating the rationales, processes and challenges involved in creating this
recently developed contrast agent.",2301.06351v1
2023-01-17,Magnetic frustration driven by conduction carrier blocking in Nd$_2$Co$_{0.85}$Si$_{2.88}$,"The intermetallic compound Nd$_2$Co$_{0.85}$Si$_{2.88}$ having a triangular
lattice could be synthesized in single-phase only with defect crystal
structure. Investigation through different experimental techniques indicate the
presence of two magnetic transitions in the system. As verified experimentally
and theoretically, the high-temperature transition T$_H$ ~ 140 K is associated
with the development of ferromagnetic interaction between itinerant Co moments,
whereas the low-temperature transition at T$_L$ ~ 6.5 K is due to the coupling
among Nd-4f and Co-3d moments, which is antiferromagnetic in nature. Detailed
studies of temperature-dependent dc magnetic susceptibility, field dependence
of isothermal magnetization, non-equilibrium dynamical behavior, viz. magnetic
relaxation, aging effect, magnetic-memory effect, and temperature dependence of
heat capacity, along with density functional theory (DFT) calculations, suggest
that the ground state is magnetically frustrated spin-glass in nature, having
competing magnetic interactions of equivalent energies. DFT results further
reveal that the 3d/5d-conduction carriers are blocked in the system and act as
a barrier for the 4f-4f RKKY interactions, resulting in spin-frustration.
Presence of vacancy defects in the crystal are also conducive to the
spin-frustration. This is an unique mechanism of magnetic frustration, not
emphasized so far in any of the ternary R$_2$TX$_3$ (R=rare-earth, T=transition
elements and X=Si, Ge, In) type compounds. Due to the competing character of
the itinerant 3d and localized 4f moments, the compound exhibits anomalous
field dependence of magnetic coercivity.",2301.07140v1
2023-01-31,Signature of weakly coupled $f$ electrons and conduction electrons in magnetic Weyl semimetal candidates PrAlSi and SmAlSi,"Magnetic topological materials are a class of compounds with the underlying
interplay of nontrivial band topology and magnetic spin configuration.
Extensive interests have been aroused due to their application potential
involved with an array of exotic quantum states. With angle-resolved
photoemission spectroscopy and first-principles calculations, here we study the
electronic properties of two magnetic Weyl semimetal candidates PrAlSi and
SmAlSi. Though the two compounds harbor distinct magnetic ground states
(ferromagnetic and antiferromagnetic for PrAlSi and SmAlSi, respectively) and
4$f$ shell fillings, we find that they share quite analogous low-energy band
structure. By the measurements across the magnetic transitions, we further
reveal that there is no evident evolution of the band structure in both
compounds and the experimental spectra can be well reproduced by the
nonmagnetic calculations, together suggesting a negligible effect of the
magnetism on their electronic structures and a possibly weak coupling between
the localized 4$f$ electrons and the itinerant conduction electrons. Our
results offer essential insights into the interactions between magnetism,
electron correlations, and topological orders in the $R$Al$X$ ($R$ = light rare
earth and $X$ = Si or Ge) family.",2301.13768v1
2023-02-08,Stacked Cross-modal Feature Consolidation Attention Networks for Image Captioning,"Recently, the attention-enriched encoder-decoder framework has aroused great
interest in image captioning due to its overwhelming progress. Many visual
attention models directly leverage meaningful regions to generate image
descriptions. However, seeking a direct transition from visual space to text is
not enough to generate fine-grained captions. This paper exploits a
feature-compounding approach to bring together high-level semantic concepts and
visual information regarding the contextual environment fully end-to-end. Thus,
we propose a stacked cross-modal feature consolidation (SCFC) attention network
for image captioning in which we simultaneously consolidate cross-modal
features through a novel compounding function in a multi-step reasoning
fashion. Besides, we jointly employ spatial information and context-aware
attributes (CAA) as the principal components in our proposed compounding
function, where our CAA provides a concise context-sensitive semantic
representation. To make better use of consolidated features potential, we
further propose an SCFC-LSTM as the caption generator, which can leverage
discriminative semantic information through the caption generation process. The
experimental results indicate that our proposed SCFC can outperform various
state-of-the-art image captioning benchmarks in terms of popular metrics on the
MSCOCO and Flickr30K datasets.",2302.04676v1
2023-02-15,Super-Resolution of BVOC Maps by Adapting Deep Learning Methods,"Biogenic Volatile Organic Compounds (BVOCs) play a critical role in
biosphere-atmosphere interactions, being a key factor in the physical and
chemical properties of the atmosphere and climate. Acquiring large and
fine-grained BVOC emission maps is expensive and time-consuming, so most
available BVOC data are obtained on a loose and sparse sampling grid or on
small regions. However, high-resolution BVOC data are desirable in many
applications, such as air quality, atmospheric chemistry, and climate
monitoring. In this work, we investigate the possibility of enhancing BVOC
acquisitions, further explaining the relationships between the environment and
these compounds. We do so by comparing the performances of several
state-of-the-art neural networks proposed for image Super-Resolution (SR),
adapting them to overcome the challenges posed by the large dynamic range of
the emission and reduce the impact of outliers in the prediction. Moreover, we
also consider realistic scenarios, considering both temporal and geographical
constraints. Finally, we present possible future developments regarding SR
generalization, considering the scale-invariance property and super-resolving
emissions from unseen compounds.",2302.07570v4
2023-02-23,The influence of crystalline electric field on the magnetic properties of CeCd3X3 (X = P and As),"CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal
ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice
order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline
electric field (CEF) level scheme has been determined by fitting magnetic
susceptibility curves, magnetization isotherms, and Schottky anomalies in
specific heat. The calculated results, incorporating the CEF excitation, Zeeman
splitting, and molecular field, are in good agreement with the experimental
data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the
strong easy-plane magnetic anisotropy that has been observed in this family of
materials. A detailed examination of the CEF parameters suggests that the
fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF
induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a
small $c$-axis moment. The reliability of our CEF analysis is assessed by
comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For
both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$
magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is
achieved at the Weiss temperature $\theta_{p}$. Although the observed magnetic
entropy is reminiscent of delocalized 4$f$-electron magnetism with significant
Kondo screening, the electrical resistivity of these compounds follows a
typical metallic behavior. Measurements of thermoelectric power further
validate the absence of Kondo contribution in CeCd$_{3}X_{3}$.",2302.11714v1
2023-02-28,Combinatorial exploration of quantum spin liquid candidates in the herbertsmithite material family,"Geometric frustration of magnetic ions can lead to a quantum spin liquid
ground state where long range magnetic order is avoided despite strong exchange
interactions. The physical realization of quantum spin liquids comprises a
major unresolved area of contemporary materials science. One prominent
magnetically-frustrated structure is the kagome lattice. The naturally
occurring minerals herbertsmithite [ZnCu$_3$(OH)$_6$Cl$_2$] and Zn-substituted
barlowite [ZnCu$_3$(OH)$_6$BrF] both feature perfect kagome layers of
spin-$1/2$ copper ions and display experimental signatures consistent with a
quantum spin liquid state at low temperatures. To investigate other possible
candidates within this material family, we perform a systematic
first-principles combinatorial exploration of structurally related compounds
[$A$Cu$_3$(OH)$_6B_2$ and $A$Cu$_3$(OH)$_6BC$] by substituting non-magnetic
divalent cations ($A$) and halide anions ($B$, $C$). After optimizing such
structures using density functional theory, we compare various structural and
thermodynamic parameters to determine which compounds are most likely to favor
a quantum spin liquid state. Convex hull calculations using binary compounds
are performed to determine feasibility of synthesis. We also estimate the
likelihood of interlayer substitutional disorder and spontaneous distortions of
the kagome layers. After considering all of these factors as a whole, we select
several promising candidate materials that we believe deserve further
attention.",2303.00082v1
2023-03-02,Two-color soliton meta-atoms and molecules,"We present a detailed overview of the physics of two-color soliton molecules
in nonlinear waveguides, i.e. bound states of localized optical pulses which
are held together due to an incoherent interaction mechanism. The mutual
confinement, or trapping, of the subpulses, which leads to a stable propagation
of the pulse compound, is enabled by the nonlinear Kerr effect. Special
attention is paid to the description of the binding mechanism in terms of
attractive potential wells, induced by the refractive index changes of the
subpulses, exerted on one another through cross-phase modulation. Specifically,
we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting
of a strong trapping pulse and a weak trapped pulse, for which trapped states
of low intensity are determined by a Schr\""odinger-type eigenproblem. We
discuss the rich dynamical behavior of such meta-atoms, demonstrating that an
increase of the group-velocity mismatch of both subpulses leads to an
ionization-like trapping-to-escape transition. We further demonstrate that if
both constituent pulses are of similar amplitude, molecule-like bound-states
are formed. We show that z-periodic amplitude variations permit a coupling of
these pulse compound to dispersive waves, resulting in the resonant emission of
Kushi-comb-like multi-frequency radiation.",2303.01279v1
2023-04-06,Protection of Ising spin-orbit coupling in bulk misfit superconductors,"Low-dimensional materials have remarkable properties that are distinct from
their bulk counterparts. A paradigmatic example is Ising superconductivity that
occurs in monolayer materials such as NbSe2 which show a strong violation of
the Pauli limit. In monolayers, this occurs due to a combination of broken
inversion symmetry and spin-orbit coupling that locks the spins of the
electrons out-of-plane. Bulk NbSe2 is centrosymmetric and is therefore not an
Ising superconductor. We show that bulk misfit compound superconductors,
(LaSe)1.14(NbSe2) and (LaSe)1.14(NbSe2)2, comprised of monolayers and bilayers
of NbSe2, exhibit unexpected Ising protection with a Pauli-limit violation
comparable to monolayer NbSe2, despite formally having inversion symmetry. We
study these misfit compounds using complementary experimental methods in
combination with first-principles calculations. We propose theoretical
mechanisms of how the Ising protection can survive in bulk materials. We show
how some of these mechanisms operate in these bulk compounds due to a concerted
effect of charge-transfer, defects, reduction of interlayer hopping, and
stacking. This highlights how Ising superconductivity can, unexpectedly, arise
in bulk materials, and possibly enable the design of bulk superconductors that
are resilient to magnetic fields.",2304.03074v1
2023-04-09,Pressure-induced formation of cubic lutetium hydrides derived from trigonal LuH$_3$,"In recent years, there has been a fervent search for room-temperature
superconductivity within the binary hydrides. However, as the number of
untested compounds dwindled, it became natural to begin searching within the
ternary hydrides. This led to the controversial discovery of room-temperature
superconductivity at only 1GPa in nitrogen-doped lutetium hydride
[Dasenbrock-Gammon et al., Nature 615, 244 (2023)] and consequently provided
much impetus for the synthesis of nitrogen-based ternary hydrides. Here, we
report the synthesis of stable trigonal LuH$_3$ by hydrogenating pure lutetium
which was subsequently pressurised to $\sim$2GPa in a dilute-N$_2$/He-rich
pressure medium. Raman spectroscopy and x-ray diffraction were used to
characterise the structures throughout. After depressurising, energy-dispersive
and wavelength-dispersive X-ray spectroscopies characterised the final
compound. Though our compound under pressure exhibits similar structural
behaviour to the Dasenbrock-Gammon et al. sample, we do not observe any
nitrogen within the structure of the recovered sample at ambient pressure. We
observe two cubic structures under pressure that simultaneously explain the
X-ray diffraction and Raman spectra observed: the first corresponds well to
$Fm\overline{3}m$ LuH$_{2+x}$, whilst the latter is an $Ia\overline{3}$-type
structure.",2304.04310v3
2023-04-13,Enhancing Model Learning and Interpretation Using Multiple Molecular Graph Representations for Compound Property and Activity Prediction,"Graph neural networks (GNNs) demonstrate great performance in compound
property and activity prediction due to their capability to efficiently learn
complex molecular graph structures. However, two main limitations persist
including compound representation and model interpretability. While atom-level
molecular graph representations are commonly used because of their ability to
capture natural topology, they may not fully express important substructures or
functional groups which significantly influence molecular properties.
Consequently, recent research proposes alternative representations employing
reduction techniques to integrate higher-level information and leverages both
representations for model learning. However, there is still a lack of study
about different molecular graph representations on model learning and
interpretation. Interpretability is also crucial for drug discovery as it can
offer chemical insights and inspiration for optimization. Numerous studies
attempt to include model interpretation to explain the rationale behind
predictions, but most of them focus solely on individual prediction with little
analysis of the interpretation on different molecular graph representations.
This research introduces multiple molecular graph representations that
incorporate higher-level information and investigates their effects on model
learning and interpretation from diverse perspectives. The results indicate
that combining atom graph representation with reduced molecular graph
representation can yield promising model performance. Furthermore, the
interpretation results can provide significant features and potential
substructures consistently aligning with background knowledge. These multiple
molecular graph representations and interpretation analysis can bolster model
comprehension and facilitate relevant applications in drug discovery.",2304.06253v1
2023-04-29,Anomalous Hall effect and magnetic structure of the topological semimetal (Mn$_{0.78}$Fe$_{0.22}$)$_{3}$Ge,"Me$_{3+\delta}$Ge, being a Weyl semimetal, shows a large anomalous Hall
effect (AHE), which decreases slowly with an increase in $\delta$ from 0.1 to
0.4. However, AHE in this compound remains significantly large in the whole
range of $\delta$ because of the robust nature of the topology of bands. To
explore the possibility of tuning the anomalous transport effects in Weyl
semimetals, we have studied the single-crystal
hexagonal-(Mn$_{0.78}$Fe$_{0.22}$)$_3$Ge compound. Magnetization of this
compound shows two magnetic transitions at 242 K ($T_{\text{N1}}$) and 120 K
($T_{\text{N2}}$). We observed that the AHE persists between $T_{\text{N2}}$ -
$T_{\text{N1}}$ and vanishes below $T_{\text{N2}}$. Further, we performed
single-crystal neutron diffraction experiments (using spherical neutron
polarimetry and unpolarized neutron diffraction) to determine the magnetic
structures of (Mn$_{0.78}$Fe$_{0.22}$)$_3$Ge at different temperatures. Our
neutron diffraction results show that the sample possesses a collinear
antiferromagnetic structure below $T_{\text{N2}}$. However, the magnetic
structure of the sample remains noncollinear antiferromagnetic, the same as
Mn$_3$Ge, between $T_{\text{N1}}$ to $T_{\text{N2}}$. The presence of AHE, and
noncollinear magnetic structure in (Mn$_{0.78}$Fe$_{0.22}$)$_3$Ge, between
$T_{\text{N1}}$ and $T_{\text{N2}}$, suggest the existence of Weyl points in
this temperature regime. Below $T_{\text{N2}}$, AHE is absent, and the magnetic
structure also changes to a collinear antiferromagnetic structure. These
observations signify a strong link between the magnetic structure of the sample
and AHE.",2305.00251v1
2023-05-16,Atomic structure of the unique antiferromagnetic 2/1 quasicrystal approximant,"The atomic structure of the recently discovered antiferromagnetic
Ga50Pd35.5Tb14.5 2/1 approximant to quasicrystal with the space group of
Pa-3(No. 205), a = 23.1449(0) angstrom was determined by means of a single
crystal X-ray diffraction. The refined structure model revealed two main
building units, namely, a Tsai-type rhombic triacontahedron (RTH) cluster with
three concentric inner shells and an acute rhombohedron filling the gaps in
between the RTH clusters. One of the interesting findings was a very low number
of chemically mixed sites in the structure, which amount to only 7.40 % of the
all the atomic sites within an RTH cluster. In particular, a disorder-free
environment was noticed within a nearest neighbor of an isolated Tb3+ ion,
which is presumably one of the main contributors in enhancing antiferromagnetic
order in the present compound. The second significant finding was the
observance of an orientationally ordered trigonal pyramid-like unit with a
height of 4.2441(7) angstrom at the center of the RTH cluster, which has never
been observed in Tsai-type compounds before. Such unit is noticed to bring
structural distortion to outer shells, in particular, to the surrounding
dodecahedron cage being another possible contributor of the antiferromagnetic
order establishment in the present compound. The results, therefore, are
suggestive of a possible link between chemical/positional order and the
antiferromagnetic order establishment.",2305.09334v1
2023-05-18,Ab-initio overestimation of the topological region in Eu-based compounds,"An underestimation of the fundamental band gap values by the density
functional theory within the local density approximation and associated
approaches is a well-known challenge of ab-initio electronic structure
computations. Motivated by recent optical experiments [D. Santos-Cottin et al.,
arXiv:2301.08014], we have revisited first-principle results obtained earlier
for EuCd2As2 and extended the computational studies to the whole class of
systems EuCd2X2 (X = P, As, Sb, Bi), to EuIn2X2 (X = P, As, Sb), and to
nonmagnetic AEIn2As2 (AE= Ca, Sr, Ba) employing a hybrid functional method. We
find that our approach provides the magnitude of the energy gap for EuCd2As2 in
agreement with the experimental value. Actually, our results indicate that
EuSn2As2, BaIn2As2, EuCd2Bi2 and EuCd2SbBi are robust topological insulators,
while all other compounds are topologically trivial semiconductors. The trivial
band gaps of EuCd2P2, EuCd2As2 and EuCd2Sb2 are in the range of 1.38-1.48 eV,
0.72-0.79 eV and 0.46-0.49 eV, respectively. The topologically trivial Eu-based
systems are antiferromagnetic semiconductors with a strong red shift of the
energy gap in a magnetic field caused by the exchange coupling of the band
states to spins localized on the 4f-shell of Eu ions. Additionally, the EuIn2X2
(X = P, As) compounds show altermagnetic exchange-induced band spin-splitting,
particularly noticeable in the case of states derived from 5d-Eu orbitals.",2305.10804v2
2023-05-18,A Compound Gaussian Least Squares Algorithm and Unrolled Network for Linear Inverse Problems,"For solving linear inverse problems, particularly of the type that appears in
tomographic imaging and compressive sensing, this paper develops two new
approaches. The first approach is an iterative algorithm that minimizes a
regularized least squares objective function where the regularization is based
on a compound Gaussian prior distribution. The compound Gaussian prior subsumes
many of the commonly used priors in image reconstruction, including those of
sparsity-based approaches. The developed iterative algorithm gives rise to the
paper's second new approach, which is a deep neural network that corresponds to
an ""unrolling"" or ""unfolding"" of the iterative algorithm. Unrolled deep neural
networks have interpretable layers and outperform standard deep learning
methods. This paper includes a detailed computational theory that provides
insight into the construction and performance of both algorithms. The
conclusion is that both algorithms outperform other state-of-the-art approaches
to tomographic image formation and compressive sensing, especially in the
difficult regime of low training.",2305.11120v3
2023-05-20,Ba9RE2(SiO4)6 (RE=Ho-Yb): A New Family of Rare-earth based Honeycomb Lattice Magnets,"Rare-earth (RE) based honeycomb-lattice materials with strong spin-orbit
coupled Jeff=1/2 moments have attracted great interest as a platform to realize
Kitaev quantum spin liquid (QSL) state. Herein, we report the discovery of a
new family of RE based honeycomb-lattice magnets Ba9RE2(SiO4)6(RE=Ho-Yb), which
crystallize into the rhombohedral structure with space group R-3. In these
serial compounds, magnetic RE3+ ions are arranged on a perfect honeycomb
lattice within the ab-plane and stacked in the ABCABC-type fashion along the
c-axis. All Ba9RE2(SiO4)6(RE=Ho-Yb) polycrystals exhibit the dominant
antiferromagnetic interactions and absence of magnetic order down to 2 K. In
combination with the magnetization and electron spin resonance (ESR) results,
distinct anisotropic magnetic behaviors are proposed for compounds with
different RE ions. Moreover, the synthesized Ba9Yb2Si6O24 single crystals show
large magnetic frustration and no long-range magnetic ordering down to 0.15 K,
being a possible QSL candidate state. These serial compounds are attractive for
exploring the exotic magnetic phases of Kitaev materials with 4f electrons.",2305.12214v1
2023-06-07,XInsight: Revealing Model Insights for GNNs with Flow-based Explanations,"Progress in graph neural networks has grown rapidly in recent years, with
many new developments in drug discovery, medical diagnosis, and recommender
systems. While this progress is significant, many networks are `black boxes'
with little understanding of the `what' exactly the network is learning. Many
high-stakes applications, such as drug discovery, require human-intelligible
explanations from the models so that users can recognize errors and discover
new knowledge. Therefore, the development of explainable AI algorithms is
essential for us to reap the benefits of AI.
  We propose an explainability algorithm for GNNs called eXplainable Insight
(XInsight) that generates a distribution of model explanations using GFlowNets.
Since GFlowNets generate objects with probabilities proportional to a reward,
XInsight can generate a diverse set of explanations, compared to previous
methods that only learn the maximum reward sample. We demonstrate XInsight by
generating explanations for GNNs trained on two graph classification tasks:
classifying mutagenic compounds with the MUTAG dataset and classifying acyclic
graphs with a synthetic dataset that we have open-sourced. We show the utility
of XInsight's explanations by analyzing the generated compounds using QSAR
modeling, and we find that XInsight generates compounds that cluster by
lipophilicity, a known correlate of mutagenicity. Our results show that
XInsight generates a distribution of explanations that uncovers the underlying
relationships demonstrated by the model. They also highlight the importance of
generating a diverse set of explanations, as it enables us to discover hidden
relationships in the model and provides valuable guidance for further analysis.",2306.04791v1
2023-06-15,MCPI: Integrating Multimodal Data for Enhanced Prediction of Compound Protein Interactions,"The identification of compound-protein interactions (CPI) plays a critical
role in drug screening, drug repurposing, and combination therapy studies. The
effectiveness of CPI prediction relies heavily on the features extracted from
both compounds and target proteins. While various prediction methods employ
different feature combinations, both molecular-based and network-based models
encounter the common obstacle of incomplete feature representations. Thus, a
promising solution to this issue is to fully integrate all relevant CPI
features. This study proposed a novel model named MCPI, which is designed to
improve the prediction performance of CPI by integrating multiple sources of
information, including the PPI network, CCI network, and structural features of
CPI. The results of the study indicate that the MCPI model outperformed other
existing methods for predicting CPI on public datasets. Furthermore, the study
has practical implications for drug development, as the model was applied to
search for potential inhibitors among FDA-approved drugs in response to the
SARS-CoV-2 pandemic. The prediction results were then validated through the
literature, suggesting that the MCPI model could be a useful tool for
identifying potential drug candidates. Overall, this study has the potential to
advance our understanding of CPI and guide drug development efforts.",2306.08907v1
2023-06-19,The 3d and 5d electronic structures and orbital hybridization in Ba- and Ca-doped La2CoIrO6 double perovskite,"Here we present a detailed investigation of the Co and Ir local electronic
structures in La1.5A0.5CoIrO6 (A = Ba, Ca) compounds in order to unravel the
orbital hybridization mechanism in these CoIr-based double perovskites. Our
results of x-ray powder diffraction, ac and dc magnetization, Co and Ir
L2,3-edges and Co K-edge x-ray absorption spectroscopy and x-ray magnetic
circular dichroism suggest a competition between magnetic interactions. A
dominant antiferromagnetic coupling is found to be responsible for the
ferrimagnetic behavior observed for A = Ca below approximately 96 K, the
competing magnetic phases and the cationic disorder in this compound giving
rise to a spin-glass state at low temperatures. For the A = Ba, on the other
hand, there is no evidence of long range order down to its spin-glass
transition temperature. The remarkably different magnetic properties observed
between these two compounds is discussed in terms of the structural distortion
that alters the strength of the Co - Ir couplings, with a relevant role played
by the Co 3d eg - Ir 5d j = 1/2 hybridization.",2306.10883v1
2023-07-04,SRCD: Semantic Reasoning with Compound Domains for Single-Domain Generalized Object Detection,"This paper provides a novel framework for single-domain generalized object
detection (i.e., Single-DGOD), where we are interested in learning and
maintaining the semantic structures of self-augmented compound cross-domain
samples to enhance the model's generalization ability. Different from DGOD
trained on multiple source domains, Single-DGOD is far more challenging to
generalize well to multiple target domains with only one single source domain.
Existing methods mostly adopt a similar treatment from DGOD to learn
domain-invariant features by decoupling or compressing the semantic space.
However, there may have two potential limitations: 1) pseudo attribute-label
correlation, due to extremely scarce single-domain data; and 2) the semantic
structural information is usually ignored, i.e., we found the affinities of
instance-level semantic relations in samples are crucial to model
generalization. In this paper, we introduce Semantic Reasoning with Compound
Domains (SRCD) for Single-DGOD. Specifically, our SRCD contains two main
components, namely, the texture-based self-augmentation (TBSA) module, and the
local-global semantic reasoning (LGSR) module. TBSA aims to eliminate the
effects of irrelevant attributes associated with labels, such as light, shadow,
color, etc., at the image level by a light-yet-efficient self-augmentation.
Moreover, LGSR is used to further model the semantic relationships on instance
features to uncover and maintain the intrinsic semantic structures. Extensive
experiments on multiple benchmarks demonstrate the effectiveness of the
proposed SRCD.",2307.01750v2
2023-07-06,PUFFIN: A Path-Unifying Feed-Forward Interfaced Network for Vapor Pressure Prediction,"Accurately predicting vapor pressure is vital for various industrial and
environmental applications. However, obtaining accurate measurements for all
compounds of interest is not possible due to the resource and labor intensity
of experiments. The demand for resources and labor further multiplies when a
temperature-dependent relationship for predicting vapor pressure is desired. In
this paper, we propose PUFFIN (Path-Unifying Feed-Forward Interfaced Network),
a machine learning framework that combines transfer learning with a new
inductive bias node inspired by domain knowledge (the Antoine equation) to
improve vapor pressure prediction. By leveraging inductive bias and transfer
learning using graph embeddings, PUFFIN outperforms alternative strategies that
do not use inductive bias or that use generic descriptors of compounds. The
framework's incorporation of domain-specific knowledge to overcome the
limitation of poor data availability shows its potential for broader
applications in chemical compound analysis, including the prediction of other
physicochemical properties. Importantly, our proposed machine learning
framework is partially interpretable, because the inductive Antoine node yields
network-derived Antoine equation coefficients. It would then be possible to
directly incorporate the obtained analytical expression in process design
software for better prediction and control of processes occurring in industry
and the environment.",2307.02903v2
2023-07-07,An Improved Compound Gaussian Model for Bivariate Surface EMG Signals Related to Strength Training,"Recent literature suggests that the surface electromyography (sEMG) signals
have non-stationary statistical characteristics specifically due to random
nature of the covariance. Thus suitability of a statistical model for sEMG
signals is determined by the choice of an appropriate model for describing the
covariance. The purpose of this study is to propose a Compound-Gaussian (CG)
model for multivariate sEMG signals in which latent variable of covariance is
modeled as a random variable that follows an exponential model. The parameters
of the model are estimated using the iterative Expectation Maximization (EM)
algorithm. Further, a new dataset, electromyography analysis of human
activities database 2 (EMAHA-DB2) is developed. Based on the model fitting
analysis on the sEMG signals from EMAHA-DB2, it is found that the proposed CG
model fits more closely to the empirical pdf of sEMG signals than the existing
models. The proposed model is validated by visual inspection, further validated
by matching central moments and better quantitative metrics in comparison with
other models. The proposed compound model provides an improved fit to the
statistical behavior of sEMG signals. Further, the estimate of rate parameter
of the exponential model shows clear relation to the training weights. Finally,
the average signal power estimates of the channels shows distinctive dependency
on the training weights, the subject's training experience and the type of
activity.",2307.03403v1
2023-07-10,Analysis of CN emission as a marker of organic compounds in meteoroids using laboratory simulated meteors,"Fragments of small solar system bodies entering Earth's atmosphere have
possibly been important contributors of organic compounds to the early Earth.
The cyano radical (CN) emission from meteors is considered as potentially one
of the most suitable markers of organic compounds in meteoroids, however, its
detection in meteor spectra has been thus far unsuccessful. With the aim to
improve our abilities to identify CN emission in meteor observations and use
its spectral features to characterize the composition of incoming asteroidal
meteoroids, we present a detailed analysis of CN emission from high-resolution
spectra of 22 laboratory simulated meteors including ordinary, carbonaceous,
and enstatite chondrites, as well as a large diversity of achondrites (i.e.,
ureilite, aubrite, lunar, martian, howardite, eucrite, and diogenite),
mesosiderite, and iron meteorites. We describe the variations of CN emission
from different classes of asteroidal meteor analogues, its correlation and time
evolution relative to other major meteoroid components. We demonstrate that CN
can be used as a diagnostic spectral feature of carbonaceous and carbon-rich
meteoroids, while most ordinary chondrites show no signs of CN. Our results
point out strong correlation between CN and H emission and suggest both
volatile features are suitable to trace contents of organic matter and water
molecules present within meteoroids. For the application in lower resolution
meteor observations, we demonstrate that CN can be best recognized in the early
stages of ablation and for carbon-rich materials by measuring relative
intensity ratio of CN band peak to the nearby Fe I-4 lines.",2307.04428v1
2023-07-14,Interpretable machine learning to understand the performance of semi local density functionals for materials thermochemistry,"This study investigates the use of machine learning (ML) to correct the
enthalpy of formation (Hf) from two separate DFT functionals, PBE and SCAN, to
the experimental Hf across 1011 solid-state compounds. The ML model uses a set
of 25 properties that characterize the electronic structure as calculated using
PBE and SCAN. The ML model significantly decreases the error in PBE-calculated
Hf values from an mean absolute error (MAE) of 195 meV/atom to an MAE = 80
meV/atom when compared to the experiment. For PBE, the PDP+GAM analysis shows
compounds with a high ionicity (I), i.e., I>0.22, have errors in Hf that are
twice as large as compounds having I < 0.22 (246 meV/atom compared to 113
meV/atom). Conversely, no analogous trend is observed for SCAN-calculated Hfs,
which explains why the ML model for PBE can more easily correct the systematic
error in calculated Hfs for PBE but not for SCAN. Although the literature
suggests PBE is reliable for intermetallics but less so for oxides and halides,
our analysis reveals intermetallics pose a challenge for PBE only when the
charge transfer is significant (I >0.22). Meanwhile, oxides and halides may be
described accurately by PBE for systems in which charge transfer is relatively
low (I < 0.22).",2307.07609v1
2023-07-26,A Discontinuous Galerkin Finite Element Model for Compound Flood Simulations,"Recent tropical cyclones, e.g., Hurricane Harvey (2017), have lead to
significant rainfall and resulting runoff with accompanying flooding. When the
runoff interacts with storm surge, the resulting floods can be greatly
amplified and lead to effects that cannot be modeled by simple superposition of
its distinctive sources. In an effort to develop accurate numerical simulations
of runoff, surge, and compounding floods, we develop a local discontinuous
Galerkin method for modified shallow water equations. In this modification,
nonzero sources to the continuity equation are included to incorporate rainfall
into the model using parametric rainfall models from literature as well as
hindcast data. The discontinuous Galerkin spatial discretization is accompanied
with a strong stability preserving explicit Runge Kutta time integrator. Hence,
temporal stability is ensured through the CFL condition and we exploit the
embarrassingly parallel nature of the developed method using MPI
parallelization. We demonstrate the capabilities of the developed method though
a sequence of physically relevant numerical tests, including small scale test
cases based on laboratory measurements and large scale experiments with
Hurricane Harvey in the Gulf of Mexico. The results highlight the conservation
properties and robustness of the developed method and show the potential of
compound flood modeling using our approach.",2307.14302v3
2023-08-11,Transcending the MAX phases concept of nanolaminated early transition metal carbides/nitrides -- the ZIA phases,"A new potential class of nanolaminated and structurally complex materials,
herein conceived as the Zigzag IntermetAllic (ZIA) phases, is proposed. A study
of the constituent phases of a specific Nb--Si--Ni intermetallic alloy revealed
that its ternary H-phase, \textit{i.e.}, the Nb$_3$SiNi$_2$ intermetallic
compound (IMC), is a crystalline solid with the close-packed \textit{fcc}
Bravais lattice, the 312 MAX phase stoichiometry and a layered atomic
arrangement that may define an entire class of nanolaminated IMCs analogous to
the nanolaminated ceramic compounds known today as the MAX phases. The electron
microscopy investigation of the Nb$_{3}$SiNi$_{2}$ compound -- the first
candidate ZIA phase -- revealed a remarkable structural complexity, as its
ordered unit cell is made of 96 atoms. The ZIA phases extend the concept of
nanolaminated crystalline solids well beyond the MAX phases family of early
transition metal carbides/nitrides, most likely broadening the spectrum of
achievable material properties into domains typically not covered by the MAX
phases. Furthermore, this work uncovers that both families of nanolaminated
crystalline solids, \textit{i.e.}, the herein introduced \textit{fcc} ZIA
phases and all known variants of the \textit{hcp} MAX phases, obey the same
overarching stoichiometric rule $P_{x+y}A_xN_y$, where $x$ and $y$ are integers
ranging from 1 to 6.",2308.06408v1
2023-08-15,Phases and magnetism at the microscale in compounds containing nominal Pb10-xCux(PO4)6O,"Achieving superconductivity at room temperature could lead to substantial
advancements in industry and technology. Recently, a compound known as Cu-doped
lead-apatite, Pb10-xCux(PO4)6O (0.9 < x < 1.1), referred to as ""LK-99"", has
been reported to exhibit unusual electrical and magnetic behaviors that appear
to resemble a superconducting transition above room temperature. In this work
we collected multiphase samples containing the nominal Pb10-xCux(PO4)6O phase
(no superconductivity observed in our measured samples), synthesized by three
independent groups, and studied their chemical, magnetic, and electrical
properties at the microscale to overcome difficulties in bulk measurements.
Through the utilization of optical, scanning electron, atomic force, and
scanning diamond nitrogen-vacancy microscopy techniques, we are able to
establish a link between local magnetic properties and specific microscale
chemical phases. Our findings indicate that while the Pb10-xCux(PO4)6O phase
seems to have a mixed magnetism contribution, a significant fraction of the
diamagnetic response can be attributed to Cu-rich regions (e.g., Cu2S derived
from a reagent used in the synthesis). Additionally, our electrical
measurements reveal the phenomenon of current path switch and a change in
resistance states of Cu2S. This provides a potential explanation for the
electrical behavior observed in compounds related to Pb10-xCux(PO4)6O.",2308.07800v3
2023-08-17,"Linguistically-Informed Neural Architectures for Lexical, Syntactic and Semantic Tasks in Sanskrit","The primary focus of this thesis is to make Sanskrit manuscripts more
accessible to the end-users through natural language technologies. The
morphological richness, compounding, free word orderliness, and low-resource
nature of Sanskrit pose significant challenges for developing deep learning
solutions. We identify four fundamental tasks, which are crucial for developing
a robust NLP technology for Sanskrit: word segmentation, dependency parsing,
compound type identification, and poetry analysis. The first task, Sanskrit
Word Segmentation (SWS), is a fundamental text processing task for any other
downstream applications. However, it is challenging due to the sandhi
phenomenon that modifies characters at word boundaries. Similarly, the existing
dependency parsing approaches struggle with morphologically rich and
low-resource languages like Sanskrit. Compound type identification is also
challenging for Sanskrit due to the context-sensitive semantic relation between
components. All these challenges result in sub-optimal performance in NLP
applications like question answering and machine translation. Finally, Sanskrit
poetry has not been extensively studied in computational linguistics.
  While addressing these challenges, this thesis makes various contributions:
(1) The thesis proposes linguistically-informed neural architectures for these
tasks. (2) We showcase the interpretability and multilingual extension of the
proposed systems. (3) Our proposed systems report state-of-the-art performance.
(4) Finally, we present a neural toolkit named SanskritShala, a web-based
application that provides real-time analysis of input for various NLP tasks.
Overall, this thesis contributes to making Sanskrit manuscripts more accessible
by developing robust NLP technology and releasing various resources, datasets,
and web-based toolkit.",2308.08807v1
2023-08-21,Compound Poisson statistics for dynamical systems via spectral perturbation,"We consider random transformations
$T_\omega^n:=T_{\sigma^{n-1}\omega}\circ\cdots\circ T_{\sigma\omega}\circ
T_\omega,$ where each map $T_{\omega}$ acts on a complete metrizable space $M$.
The randomness comes from an invertible ergodic driving map
$\sigma:\Omega\to\Omega$ acting on a probability space
$(\Omega,\mathcal{F},m).$ For a family of random target sets $H_{\omega,
n}\subset M$ that shrink as $n\to\infty$, we consider quenched compound Poisson
statistics of returns of random orbits to these random targets. We develop a
spectral approach to such statistics: associated with the random map cocycle is
a transfer operator cocycle
$\mathcal{L}^{n}_{\omega,0}:=\mathcal{L}_{\sigma^{n-1}\omega,0}\circ\cdots\circ\mathcal{L}_{\sigma\omega,0}\circ\mathcal{L}_{\omega,0}$,
where $\mathcal{L}_{\omega,0}$ is the transfer operator for the map $T_\omega$.
We construct a perturbed cocycle with generator
$\mathcal{L}_{\omega,n,s}(\cdot):=\mathcal{L}_{\omega,0}(\cdot
e^{is\mathbb{1}_{H_{\omega,n}}})$ and an associated random variable
$S_{\omega,n,k}(x):=\sum_{j=0}^{k-1}\mathbb{1}_{H_{\sigma^j\omega,n}}(T_\omega^jx)$,
which counts the number of visits to random targets in an orbit of length $k$.
Under suitable assumptions, we show that in the $n\to\infty$ limit, the random
variables $S_{\omega,n,n}$ converge in distribution to a compound Poisson
distributed random variable. We provide several explicit examples for piecewise
monotone interval maps in both the deterministic and random settings.",2308.10798v2
2023-08-24,Reconciling Inconsistent Molecular Structures from Biochemical Databases,"Information on the structure of molecules, retrieved via biochemical
databases, plays a pivotal role in various disciplines, such as metabolomics,
systems biology, and drug discovery. However, no such database can be complete,
and the chemical structure for a given compound is not necessarily consistent
between databases. This paper presents StructRecon, a novel tool for resolving
unique and correct molecular structures from database identifiers. StructRecon
traverses the cross-links between database entries in different databases to
construct what we call an identifier graph, which offers a more complete view
of the total information available on a particular compound across all the
databases. In order to reconcile discrepancies between databases, we first
present an extensible model for chemical structure which supports multiple
independent levels of detail, allowing standardisation of the structure to be
applied iteratively. In some cases, our standardisation approach results in
multiple structures for a given compound, in which case a random walk-based
algorithm is used to select the most likely structure among incompatible
alternates. We applied StructRecon to the EColiCore2 model, resolving a unique
chemical structure for 85.11 % of identifiers. StructRecon is open-source and
modular, which enables the potential support for more databases in the future.",2308.12735v1
2023-08-25,Effective tight-binding Hamiltonian for the low-energy electronic structure of the Cu-doped lead apatite and the parent compound,"We examine the origin of the formation of narrow bands in LK-99
(Pb$_{9}$Cu(PO$_4$)$_6$O) and the parent compound without the Cu doping using
density functional theory calculations and model Hamiltonian studies. Explicit
analytical expressions are given for a nearest-neighbor tight-binding (TB)
Hamiltonian in the momentum space for both the parent and the LK-99 compound,
which can serve as an effective model to study various quantum phenomena
including superconductivity. The parent material is an insulator with the
buckle oxygen atom on the stacked triangular lattice forming the topmost bands,
well-separated from the remaining oxygen band manifold. The $C_3$
symmetry-driven two-band TB model describes these two bands quite well. These
bands survive in the Cu-doped, LK-99, though with drastically altered band
dispersion due to the Cu-O interaction. A similar two-band model involving the
Cu $xz$ and $yz$ orbitals broadly describes the top two valence bands of LK-99.
However, the band dispersions of both the Cu and O bands are much better
described by the four-band TB model incorporating the Cu-O interactions on the
buckled honeycomb lattice. We comment on the possible mechanisms of
superconductivity in LK-99. even though the actual T$_c$ may be much smaller
than reported, and suggest that interstitial Cu clusters leading to broad bands
might have a role to play",2308.13275v1
2023-08-30,"Evolution of highly anisotropic magnetism in the titanium-based kagome metals LnTi$_3$Bi$_4$ (Ln: La...Gd$^{3+}$, Eu$^{2+}$, Yb$^{2+}$)","Here we present the family of titanium-based kagome metals of the form
LnTi$_3$Bi$_4$ (Ln: La...Gd$^{3+}$, Eu$^{2+}$, Yb$^{2+}$). Single crystal
growth methods are presented alongside detailed magnetic and thermodynamic
measurements. The orthorhombic (Fmmm) LnTi$_3$Bi$_4$ family of compounds
exhibit slightly distorted titanium-based kagome nets interwoven with zig-zag
lanthanide-based (Ln) chains. Crystals are easily exfoliated parallel to the
kagome sheets and angular resolved photoemission (ARPES) measurements highlight
the intricacy of the electronic structure in these compounds, with Dirac points
existing at the Fermi level. The magnetic properties and the associated
anisotropy emerge from the quasi-1D zig-zag chains of Ln, and impart a wide
array of magnetic ground states ranging from anisotropic ferromagnetism to
complex antiferromagnetism with a cascade of metamagnetic transitions. Kagome
metals continue to provide a rich direction for the exploration of magnetic,
topologic, and highly correlated behavior. Our work here introduces the
LnTi$_3$Bi$_4$ compounds to augment the continuously expanding suite of complex
and interesting kagome materials.",2308.16138v2
2023-09-04,Study on Susceptibilities of Superconductors BaPtSb and BaPtAs with Honeycomb Structure,"The low-energy electronic properties of the new superconductors BaPtSb and
BaPtAs with an ordered honeycomb network are investigated in the normal phase,
where the former compound is a candidate for time-reversal symmetry-breaking
superconductors. By means of the first-principles calculation, we show that
there exist two-dimensional cylinder-like Fermi surfaces around the kz axis and
one outer spherelike Fermi surface around the K and K' points in both
compounds, which are mainly composed of Pt 5d and Sb 5p/As 4p electrons. We
construct low-energy effective models, which are well described by using three
bands consisting of two Pt 5d orbitals and one Sb 5p/As 4p orbital. By
evaluating susceptibilities using effective models, we find that dominant
contributions to those susceptibilities result from the outer spherelike Fermi
surface. Whereas out-of-plane fluctuations are enhanced in both compounds in
the higher-temperature region, in-plane fluctuations become dominant in the
very low-temperature region in BaPtSb owing to a better nesting condition in
the k_z=0 plane from the outer spherelike Fermi surface. These fluctuations
yield instabilities to ordered states, such as superconductivity, and might be
associated with the occurrence of the superconducting state with time-reversal
symmetry breaking in BaPtSb.",2309.01295v1
2023-09-15,"Emergence of partially disordered antiferromagnetism and isothermal magnetization plateau due to geometrical frustration in a metallic compound, Er2RhSi3","Partially disordered antiferro (PDA) magnetism (in which one of the three
magnetic ions in a triangular network remains magnetically disordered), has
been known commonly among geometrically frustrated insulating materials. The
one-third plateau in isothermal magnetization (M) of such materials has been of
great theoretical interest. Here, we report these properties in a
AlB2-structure derived metallic material, Er2RhSi3 in which Er sublattice has
triangular networks. The presence of a well-defined lamda anomaly in the
temperature (T) dependence of heat capacity and its magnetic-field (H)
dependence, and the loss of spin-disorder contribution in electrical
resistivity (rho) confirm antiferromagnetic order below (TN=) 5 K. On the other
hand, the separation of zero-field-cooled and field-cooled dc magnetic
susceptibility (chi) curves, decay of isothermal remnant magnetization and the
frequency dependence of real and imaginary components of ac chi suggest the
onset of spin-glass freezing concomitant with the antiferromagnetic order. In
addition, interestingly, we observe one-third plateau in M(H) below 20 kOe for
T less than TN. The change in rho as a function of H at a given temperature
well below TN is also revealing, with this compound exhibiting a plateau below
20 kOe, with complexities at higher fields. Therefore, this compound serves as
a prototype for theoretical understanding of transport behavior across
one-third plateau due to PDA magnetism in a metal without any interference from
the 4f delocalization phenomena.",2309.08176v1
2023-10-16,A Tri-Level Optimization Model for Interdependent Infrastructure Network Resilience Against Compound Hazard Events,"Resilient operation of interdependent infrastructures against compound hazard
events is essential for maintaining societal well-being. To address consequence
assessment challenges in this problem space, we propose a novel tri-level
optimization model applied to a proof-of-concept case study with fuel
distribution and transportation networks -- encompassing one realistic network;
one fictitious, yet realistic network; as well as networks drawn from three
synthetic distributions. Mathematically, our approach takes the form of a
defender-attacker-defender (DAD) model -- a multi-agent tri-level optimization,
comprised of a defender, attacker, and an operator acting in sequence. Here,
our notional operator may choose proxy actions to operate an interdependent
system comprised of fuel terminals and gas stations (functioning as supplies)
and a transportation network with traffic flow (functioning as demand) to
minimize unmet demand at gas stations. A notional attacker aims to
hypothetically disrupt normal operations by reducing supply at the supply
terminals, and the notional defender aims to identify best proxy defense policy
options which include hardening supply terminals or allowing alternative
distribution methods such as trucking reserve supplies. We solve our DAD
formulation at a metropolitan scale and present practical defense policy
insights against hypothetical compound hazards. We demonstrate the
generalizability of our framework by presenting results for a realistic
network; a fictitious, yet realistic network; as well as for three networks
drawn from synthetic distributions. Additionally, we demonstrate the
scalability of the framework by investigating runtime performance as a function
of the network size. Steps for future research are also discussed.",2310.10587v1
2023-11-03,Hydride Units Filled B--C Clathrate: A New Pathway for High-Temperature Superconductivity at Ambient Pressure,"The pursuit of room-temperature superconductors has recently advanced with
the discovery of high-temperature superconductivity in compressed hydrides,
although sustaining the superconductivity of hydrides at ambient pressure
remains challenging. In parallel, $sp^3$-bonded frameworks comprising
lightweight elements (\textit{e.g.}, boron and carbon) have emerged as another
avenue for developing ambient-pressure superconductors. However, despite their
stability at low pressures, the critical temperature ($T_\text{c}$) values
observed in these materials have not yet reached the impressive benchmarks set
by hydride-based superconductors. Here we propose a novel design strategy for
achieving high-temperature superconductivity at ambient pressure by integrating
hydride units into B-C clathrate structures. This approach exploits the
beneficial properties of hydrogen, the lightest element, to enhance the
superconductivity beyond that of the parent compounds. For instance, our
computational predictions indicate that doping SrB$_3$C$_3$ with ammonium
(NH$_4$) yields a SrNH$_4$B$_6$C$_6$ compound with an estimated $T_\text{c}$ of
73 K at ambient pressure -- more than double that of its precursor (31 K).
Extensive substitution across the periodic table results in a family of
MNHNH$_4$B$_6$C$_6$ superconductors that are predicted to be superconducting at
ambient pressure. These compounds can potentially be synthesized using
high-pressure techniques and then quenched to ambient conditions, with the
highest predicted ambient-pressure $T_\text{c}$ of 86 K in PbNH$_4$B$_6$C$_6$.
Our findings present a promising strategy for discovering high-$T_\text{c}$
superconductors at ambient pressure, potentially revolutionizing technologies
reliant on superconducting materials.",2311.01656v1
2023-11-28,Deep Regularized Compound Gaussian Network for Solving Linear Inverse Problems,"Incorporating prior information into inverse problems, e.g. via
maximum-a-posteriori estimation, is an important technique for facilitating
robust inverse problem solutions. In this paper, we devise two novel approaches
for linear inverse problems that permit problem-specific statistical prior
selections within the compound Gaussian (CG) class of distributions. The CG
class subsumes many commonly used priors in signal and image reconstruction
methods including those of sparsity-based approaches. The first method
developed is an iterative algorithm, called generalized compound Gaussian least
squares (G-CG-LS), that minimizes a regularized least squares objective
function where the regularization enforces a CG prior. G-CG-LS is then
unrolled, or unfolded, to furnish our second method, which is a novel deep
regularized (DR) neural network, called DR-CG-Net, that learns the prior
information. A detailed computational theory on convergence properties of
G-CG-LS and thorough numerical experiments for DR-CG-Net are provided. Due to
the comprehensive nature of the CG prior, these experiments show that DR-CG-Net
outperforms competitive prior art methods in tomographic imaging and
compressive sensing, especially in challenging low-training scenarios.",2311.17248v3
2023-11-29,The new heavy fermion compound Ce$_3$Bi$_4$Ni$_3$,"The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile
ground for the discovery of novel correlated metallic and insulating phases.
Here, we report the synthesis of a new heavy fermion compound,
Ce$_3$Bi$_4$Ni$_3$. It is an isoelectronic analog of the prototypical Kondo
insulator Ce$_3$Bi$_4$Pt$_3$ and of the recently discovered Weyl-Kondo
semimetal Ce$_3$Bi$_4$Pd$_3$. In contrast to the volume-preserving Pt-Pd
substitution, structural and chemical analyses reveal a positive chemical
pressure effect in Ce$_3$Bi$_4$Ni$_3$ relative to its heavier counterparts.
Based on the results of electrical resistivity, Hall effect, magnetic
susceptibility, and specific heat measurements, we identify an energy gap of
65-70 meV, about 8 times larger than that in Ce$_3$Bi$_4$Pt$_3$ and about 45
times larger than that of the Kondo-insulating background hosting the Weyl
nodes in Ce$_3$Bi$_4$Pd$_3$. We show that this gap as well as other physical
properties do not evolve monotonically with increasing atomic number, i.e., in
the sequence Ce$_3$Bi$_4$Ni$_3$-Ce$_3$Bi$_4$Pd$_3$-Ce$_3$Bi$_4$Pt$_3$, but
instead with increasing partial electronic density of states of the $d$
orbitals at the Fermi energy. To understand under which condition topological
states form in these materials is a topic for future studies.",2311.17903v1
2023-11-29,C3Net: Compound Conditioned ControlNet for Multimodal Content Generation,"We present Compound Conditioned ControlNet, C3Net, a novel generative neural
architecture taking conditions from multiple modalities and synthesizing
multimodal contents simultaneously (e.g., image, text, audio). C3Net adapts the
ControlNet architecture to jointly train and make inferences on a
production-ready diffusion model and its trainable copies. Specifically, C3Net
first aligns the conditions from multi-modalities to the same semantic latent
space using modality-specific encoders based on contrastive training. Then, it
generates multimodal outputs based on the aligned latent space, whose semantic
information is combined using a ControlNet-like architecture called Control
C3-UNet. Correspondingly, with this system design, our model offers an improved
solution for joint-modality generation through learning and explaining
multimodal conditions instead of simply taking linear interpolations on the
latent space. Meanwhile, as we align conditions to a unified latent space,
C3Net only requires one trainable Control C3-UNet to work on multimodal
semantic information. Furthermore, our model employs unimodal pretraining on
the condition alignment stage, outperforming the non-pretrained alignment even
on relatively scarce training data and thus demonstrating high-quality compound
condition generation. We contribute the first high-quality tri-modal validation
set to validate quantitatively that C3Net outperforms or is on par with first
and contemporary state-of-the-art multimodal generation. Our codes and
tri-modal dataset will be released.",2311.17951v1
2023-12-04,"A unified framework combining coherent compounding, harmonic imaging and angular coherence for simultaneous high-quality B-mode and tissue Doppler in ultrafast echocardiography","Various methods have been proposed to enhance image quality in ultrafast
ultrasound. Coherent compounding can improve image quality using multiple
steered diverging transmits when motion occurring between transmits is
corrected for. Harmonic imaging, a standard technique in conventional focused
echocardiography, has been adapted for ultrafast imaging, reducing clutter.
Coherence-based approaches have also been shown to increase contrast in
clinical settings by enhancing signals from coherent echoes and reducing
clutter. Herein, we introduce a simple, unified framework that combines
motion-correction, harmonic imaging, and angular-coherence, showing for the
first time that their benefits can be combined in real-time. Validation was
conducted through in vitro testing on a spinning disk model and in vivo on 4
volunteers. In vitro results confirmed the unified framework capability to
achieve high contrast in large-motion contexts up to 17 cm/s. In vivo testing
highlighted proficiency in generating images of high quality during low and
high tissue velocity phases of the cardiac cycle. Specifically, during
ventricular filling, the unified framework increased the gCNR from 0.47 to 0.87
when compared against coherent compounding.",2312.01628v1
2023-12-11,Compound Text-Guided Prompt Tuning via Image-Adaptive Cues,"Vision-Language Models (VLMs) such as CLIP have demonstrated remarkable
generalization capabilities to downstream tasks. However, existing prompt
tuning based frameworks need to parallelize learnable textual inputs for all
categories, suffering from massive GPU memory consumption when there is a large
number of categories in the target dataset. Moreover, previous works require to
include category names within prompts, exhibiting subpar performance when
dealing with ambiguous category names. To address these shortcomings, we
propose Compound Text-Guided Prompt Tuning (TGP-T) that significantly reduces
resource demand while achieving superior performance. We introduce text
supervision to the optimization of prompts, which enables two benefits: 1)
releasing the model reliance on the pre-defined category names during
inference, thereby enabling more flexible prompt generation; 2) reducing the
number of inputs to the text encoder, which decreases GPU memory consumption
significantly. Specifically, we found that compound text supervisions, i.e.,
category-wise and content-wise, is highly effective, since they provide
inter-class separability and capture intra-class variations, respectively.
Moreover, we condition the prompt generation on visual features through a
module called Bonder, which facilitates the alignment between prompts and
visual features. Extensive experiments on few-shot recognition and domain
generalization demonstrate that TGP-T achieves superior performance with
consistently lower training costs. It reduces GPU memory usage by 93% and
attains a 2.5% performance gain on 16-shot ImageNet. The code is available at
https://github.com/EricTan7/TGP-T.",2312.06401v1
2023-12-28,Solitons in binary compounds with stacked two-dimensional honeycomb lattices,"We model the electronic properties of thin films of binary compounds with
stacked layers where each layer is a two-dimensional honeycomb lattice with two
atoms per unit cell. The two atoms per cell are assigned different onsite
energies in order to consider six different stacking orders: ABC, ABA, AA,
ABC$^{\prime}$, ABA$^{\prime}$, and AA$^{\prime}$. Using a minimal
tight-binding model with nearest-neighbor hopping, we consider whether a fault
in the texture of onsite energies in the vertical, stacking direction supports
localized states, and we find localized states within the bulk band gap for
ABC, ABA, and AA$^{\prime}$ stacking. Depending on the stacking type, parameter
values, and whether the soliton is atomically sharp or a smooth texture, there
are a range of different band structures including soliton bands that are
either isolated or that hybridize with other states, such as surface states,
and soliton bands that are either dispersive or flat, the latter yielding
narrow features in the density of states. We discuss the relevance of our
results to specific materials including graphene, hexagonal boron nitride and
other binary compounds.",2312.16949v2
2023-12-29,Spin-orbit coupling tuned crossover of gaped and gapless topological phases in the chalcopyrite HgSnX 2 (X=N/P): An ab-initio investigation,"The coupling between electron orbital momentum and spin momentum, known as
spin-orbit coupling (SOC), is a fundamental origin of a multitude of
fascinating physical phenomena, especially it holds paramount significance in
the realm of topological materials. In our work, we have predicted the
topological phase in Hg-based chalcopyrite compounds using the first principles
density functional theory. The initial focus was on HgSnN 2 , revealing it to
be a nonmagnetic Weyl semimetal, while HgSnP 2 displayed characteristics of a
strong topological insulator. What makes our work truly unique is that despite
both compounds having the same SOC strength, arises from Hg, they exhibit
distinct topological phases due to the distinct hybridization effect of the
Hg-5d and X-p bands. This finding can address a significant factor, i.e., the
effect of the band hybridization in deriving distinct topological phases,
keeping the symmetry aspect intact. Our results indicate that due to the
presence of band hybridization between the dominant X-np orbitals n=2 and 3 for
X=N and P respectively and a minor contribution from Hg-5d, we can tune the
topological phase by manipulating SOC strength, which equivalently achievable
by chemical substitutions. This investigation stands as a remarkable
illustration of the unique roles that hybridization plays in sculpting the
topological properties of these compounds while simultaneously preserving their
underlying symmetries.",2312.17669v1
2024-01-24,"Comparative study of the high-pressure behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8","We report a study of the high-pressure structural behavior of ZnV2O6,
Zn2V2O7, and Zn3V2O8, which has been explored by means of synchrotron powder
x-ray diffraction. We found that ZnV2O6 and Zn3V2O8 remain in the
ambient-pressure structure up to 15 GPa. In contrast, in the same pressure
range, Zn2V2O7 undergoes three phase transitions at 0.7, 3.0, and 10.8 GPa,
respectively. Possible crystal structures for the first and second
high-pressure phases are proposed. Reasons for the distinctive behavior of
Zn2V2O7 are discussed. The compressibility of the different polymorphs has been
determined. The response to pressure is found to be anisotropic in all the
considered compounds and the room-temperature equations of state have been
determined. The bulk moduli of ZnV2O6 (129(2) GPa) and Zn3V2O8 (120(2) GPa) are
consistent with a structural framework composed of compressible ZnO6 octahedra
and uncompressible VO4 tetrahedra. In contrast, Zn2V2O7 is highly compressible
with a bulk modulus of 58(9) GPa, which is almost half of the bulk modulus of
the other two vanadates. The large compressibility of Zn2V2O7 and its sequence
of structural transitions are related to the fact that this material is less
dense than the other zinc vanadates and to the penta-coordination of Zn atoms
by oxygen atoms in Zn2V2O7. A comparison to the high-pressure behavior of
related compounds is presented.",2401.13440v1
2024-02-29,Thermal stabilities Landscape of A$_2$BB$^{\prime}$O$_6$ compounds,"Perovskite oxides have been extensively studied for their wide range of
compositions and structures, as well as their valuable properties for various
applications. Expanding from single perovskite ABO$_3$ to double perovskite
$A_2BB^{\prime}$O$_6$ significantly enhances the ability to tailor specific
physical and chemical properties. However, the vast number of potential
compositions of $A_2BB^{\prime}$O$_6$ makes it impractical to explore them all
experimentally. In this study, we conducted high-throughput calculations to
systematically investigate the structures and stabilities of 4,900
$A_2BB^{\prime}$O$_6$ compositions (with $A$ = Ca, Sr, Ba, and La; $B$ and
$B^{\prime}$ representing metal elements) through over 42,000 density
functional theory (DFT) calculations. Our analysis lead to the discovery of
more than 1,500 new synthesizable $A_2BB^{\prime}$O$_6$ compounds, with over
1,100 of them exhibiting double perovskite structures, predominantly in the
$P2_1/c$ space group. By leveraging the high-throughput dataset, we developed
machine learning models that achieved mean absolute errors of 0.0444 and 0.0330
eV/atom for formation energy and decomposition energy, respectively. Using
these models, we identified 803 stable or metastable compositions beyond the
chemical space covered in our initial calculations, with 612 of them having
DFT-validated decomposition energies below 0.1 eV/atom, resulting in a success
rate of 76.2 \%. This study delineates the stability landscape of
$A_2BB^{\prime}$O$_6$ compounds and offers new insights for the exploration of
these materials.",2402.19220v1
2024-03-04,Polar Nematic Phases with Enantiotropic Ferro- and Antiferroelectric Behavior,"The recent discovery of a new ferroelectric nematic (NF) liquid crystalline
phase became of utmost interest for the liquid crystal (LC) and the whole soft
and condensed matter fields. Contrary to the previously known ferroelectric LC
materials, whose ferroelectric characteristics were much weaker, new polar
nematics exhibit properties comparable to solid ferroelectrics. This discovery
brought about tremendous efforts to further explore compounds showing these
phases, and fascinating physical properties have been reported. Herein, we
present the first synthesized compounds with the enantiotropic ferro- (NF) and
antiferroelectric (NX) nematic phases. The enantiotropic nature and an
unprecedentedly broad temperature range of NF and NX phases are confirmed by
various experimental techniques: polarized-light optical microscopy (POM)
observations, different scanning calorimetry (DSC), dielectric spectroscopy,
second harmonic generation (SHG), and molecular modeling. The presented
achievements in designing achiral compounds that exhibit enantiotropic polar
nematic phases with ferro- and antiferroelectric properties significantly
contribute to the development of multicomponent mixtures with a broad
temperature range of NF and NX phases down to room temperature. Furthermore,
this accomplishment considerably enhances the general understanding of the
structural correlations that promote polar nematic liquid crystal phases with
high thermodynamic stability. Finally, this work may benefit various
applications in photonic devices.",2403.02068v1
2024-03-06,Weyl points and anomalous transport effects tuned by the Fe doping in Mn$_3$Ge Weyl semimetal,"The discovery of a significantly large anomalous Hall effect in the chiral
antiferromagnetic system - Mn$_3$Ge - indicates that the Weyl points are widely
separated in phase space and positioned near the Fermi surface. In order to
examine the effects of Fe substitution in Mn$_3$Ge on the presence and location
of the Weyl points, we synthesized (Mn$_{1-\alpha}$Fe$_{\alpha})$$_3$Ge
($\alpha=0-0.30$) compounds. The anomalous Hall effect was observed in
compounds up to $\alpha=0.22$, but only within the temperature range where the
magnetic structure remains the same as the Mn$_3$Ge. Additionally, positive
longitudinal magnetoconductance and planar Hall effect were detected within the
same temperature and doping range. These findings strongly suggest the
existence of Weyl points in (Mn$_{1-\alpha}$Fe$_{\alpha})$$_3$Ge
($\alpha=0-0.22$) compounds. Further, we observed that with an increase in Fe
doping fraction, there is a significant reduction in the magnitude of anomalous
Hall conductivity, planar Hall effect, and positive longitudinal
magnetoconductance, indicating that the Weyl points move further away from the
Fermi surface. Consequently, it can be concluded that suitable dopants in the
parent Weyl semimetals have the potential to tune the properties of Weyl points
and the resulting anomalous electrical transport effects.",2403.03626v1
2024-03-10,Transferable Reinforcement Learning via Generalized Occupancy Models,"Intelligent agents must be generalists - showing the ability to quickly adapt
and generalize to varying tasks. Within the framework of reinforcement learning
(RL), model-based RL algorithms learn a task-agnostic dynamics model of the
world, in principle allowing them to generalize to arbitrary rewards. However,
one-step models naturally suffer from compounding errors, making them
ineffective for problems with long horizons and large state spaces. In this
work, we propose a novel class of models - generalized occupancy models (GOMs)
- that retain the generality of model-based RL while avoiding compounding
error. The key idea behind GOMs is to model the distribution of all possible
long-term outcomes from a given state under the coverage of a stationary
dataset, along with a policy that realizes a particular outcome from the given
state. These models can then quickly be used to select the optimal action for
arbitrary new tasks, without having to redo policy optimization. By directly
modeling long-term outcomes, GOMs avoid compounding error while retaining
generality across arbitrary reward functions. We provide a practical
instantiation of GOMs using diffusion models and show its efficacy as a new
class of transferable models, both theoretically and empirically across a
variety of simulated robotics problems. Videos and code at
https://weirdlabuw.github.io/gom/.",2403.06328v1
2024-03-27,"$J_{eff}$ states in a quasi one dimensional antiferromagnetic spin chain hexagonal Iridates Sr$_3$MIrO$_6$ (M=Mg, Zn, Cd): an $ab-initio$ comparative perspective","We employ first-principles density-functional theory, to perform a
comparative investigation of the effect of the spin-orbit coupling (SOC) on the
electronic and magnetic properties of three experimentally synthesized and
characterized hexagonal perovskites Sr$_3$MIrO$_6$(M=Mg, Zn, Cd). The
electronic structure calculations show that in all the compounds, Ir is the
only magnetically active site in +4[5$d^5$] configuration, whereas M$^{+2}$
(M=Cd, Zn, Mg), remains in nonmagnetic states with Cd/Zn and Mg featuring
$d^{10}$ and $d^{0}$ electronic configurations, respectively. The insulating
gap could be opened by switching on the correlation parameter $U$ for
Sr$_3$CdrO$_6$ and Sr$_3$ZnIrO$_6$ which qualifies it to be a correlated Mott
insulator. However, in the case of Sr$_3$MgIrO$_6$ both $U$ and
antiferromagnetic ordering is not enough and the gap could only be opened by
including the SOC which classifies it to fall under the category of a typical
SOC Mott insulator. The $j_{eff}$ states are visualized from the orbital
projected band structure. The magnetism is studied from the point of view of
exchange interactions and magnetocrystalline anisotropy in the presence of the
SOC. We also present the comparative analysis of the renormalized impact of SOC
on the three compounds, which shows that all the three compounds fall under the
$intermediate$ coupling regime, where Sr$_3$MgIrO$_6$ is comparatively closer
to the atomic $j_{eff}=\frac{1}{2}$ picture from the others.",2403.18408v1
2024-04-02,Determining the chemical composition of diamagnetic mixed solids via measurements of the magnetic susceptibility,"Mixed solid compounds are employed in a vast array of applications so an
accurate determination of their chemical compositions is of crucial importance.
All current characterization methods require specially-treated samples so the
availability of a more practical method with similar accuracy should alleviate
the quantification process. In this work, we show how the doping concentration
$\delta$ (or isotope concentration) of a mixed solid compound in powdered form,
where both parent compounds are diamagnetic, can be obtained from the
measurement of the mass magnetization. We exploit the additive nature of the
molar magnetic susceptibility $\chi_{Mol}$ and molar mass to construct two
equations with the same two unknowns in the $\chi_{Mol}$ vs. $\delta$ space to
simultaneously solve $\chi_{Mol}$ and $\delta$ of a mixed solid. Eight examples
are provided to show the wide applicability of this method:
NH$_{4(1-\delta)}$D$_{4\delta}$Br (where D = $^2$H),
NH$_4$I$_{1-\delta}$Br$_\delta$,
(NH$_4$H$_2$)$_{1-\delta}$(ND$_4$D$_2$)$_\delta$PO$_4$,
C$_{48}$H$_{22+6\delta}$Br$_{6(1-\delta)}$O$_{32}$Zr$_6$,
[creatine]$_{1-\delta}$[$_D$-glucose]$_\delta$, [$_L$-glutamic
acid]$_{1-\delta}$[$_L$-leucine]$_\delta$, [terephthalic
acid]$_{1-\delta}$[trimesic acid]$_\delta$ and
[p-terphenyl]$_{1-\delta}$[triphenylphosphine]$_\delta$. Experimental errors of
~1.2% were obtained for $\delta$ from average sample masses of 16.6 mg in
powdered form rendering the presented approach an attractive choice for
characterizing the ratios of mixed solids.",2404.02012v1
2024-04-07,Entropy Engineered Middle-In Synthesis of Dual Single-Atom Compounds for Nitrate Reduction Reaction,"Despite the immense potential of Dual Single-Atom Compounds (DSACs), the
challenges in their synthesis process, including complexity, stability, purity,
and scalability, remain primary concerns in current research. Here, we present
a general strategy, termed ""Entropy-Engineered Middle-In Synthesis of Dual
Single-Atom Compounds"" (EEMIS-DSAC), which is meticulously crafted to produce a
diverse range of DSACs, effectively addressing the aforementioned issues. Our
strategy integrates the advantages of both bottom-up and top-down paradigms,
proposing a new insight to optimize the catalyst structure. The as-fabricated
DSACs exhibited excellent activity and stability in the nitrate reduction
reaction (NO3RR). In a significant advancement, our prototypical CuNi DSACs
demonstrated outstanding performance under conditions reminiscent of industrial
wastewater. Specifically, under a NO3- concentration of 2000 ppm, it yielded a
Faradaic efficiency (FE) for NH3 of 96.97 %, coupled with a mass productivity
of 131.47 mg h-1 mg-1 and an area productivity of 10.06 mg h-1 cm-2.
Impressively, even under a heightened NO3- concentration of 0.5 M, the FE for
NH3 peaked at 90.61 %, with mass productivity reaching 1024.50 mg h-1 mg-1 and
an area productivity of 78.41 mg h-1 cm-2. This work underpins the potential of
the EEMIS-DSAC approach, signaling a promising frontier for high-performing
DSACs.",2404.05075v1
2024-04-09,Quantifying the U $5f$ covalence and degree of localization in U intermetallics,"A procedure for quantifying the U $5f$ electrons' covalence and degree of
localization in U intermetallic compounds is presented. To this end, bulk
sensitive hard and soft x-ray photoelectron spectroscopy were utilized in
combination with density-functional theory (DFT) plus dynamical mean-field
theory (DMFT) calculations. The energy dependence of the photoionization
cross-sections allows the disentanglement of the U\,$5f$ contribution to the
valence band from the various other atomic subshells so that the computational
parameters in the DFT\,+\,DMFT can be reliably determined. Applying this method
to UGa$_2$ and UB$_2$ as model compounds from opposite ends of the
(de)localization range, we have achieved excellent simulations of the valence
band and core-level spectra. The width in the distribution of atomic U\,$5f$
configurations contributing to the ground state, as obtained from the
calculations, quantifies the correlated nature and degree of localization of
the U\,5$f$. The findings permit answering the longstanding question why
different spectroscopic techniques give seemingly different numbers for the U
5$f$ valence in intermetallic U compounds.",2404.06266v1
1993-01-07,Electronic Structure of Superconducting Ba6c60,"We report the results of first-principles electronic-structure calculations
for superconducting Ba6C60. Unlike the A3C60 superconductors, this new compound
shows strong Ba-C hybridization in the valence and conduction regions, mixed
covalent/ionic bonding character, partial charge transfer, and insulating
zero-gap band structure.",9301006v1
1993-02-12,Possible Realization of Odd Frequency Pairing in Heavy Fermion Compounds,"Using Majorana Fermions to represent spins we re-examine the Kondo Lattice
model for heavy fermions. The simplest decoupling procedure provides a
realization of odd frequency superconductivity, with resonant pairing and
surfaces of gap zeros. Spin and charge coherence factors vanish linearly with
the energy on the Fermi surface, predicting a linear specific heat, but a $T^3$
NMR relaxation rate. Possible application to heavy fermions is suggested.",9302018v1
1995-07-21,Comment on ``Quantitative Model for the Superconductivity Suppression in R$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_7$ with Different Rare Earths'',"We argue that an effective single-particle model to explain the destructive
role of Pr on superconductivity in PrBa$_2$Cu$_3$O$_7$, is inconsistent with
the experimental ac conductivity in that compound.",9507095v1
1995-08-13,Superconductivity of nearly 2-D systems,"Effect of geometry on the superconductivity is considered. It is shown that
the for nearly two dimensional BCS systems the critical temperature is rapidly
increased with decreasing the thickness of the layer. The result is expected to
be useful in the explanation of high-Tc conductivity of the ceramic compounds.",9508045v1
1995-11-01,Coherent versus Incoherent Transport in Layered Doped Mott Insulators,"There exist strong experimental evidences for the dimensional cross-over from
two to three dimensions as \lan compounds are overdoped. In this paper we
describe the dimensional cross-over of the layered correlated metal in the
gauge theory framework. In particular, we obtain the anomalous exponent 3/2 for
the temperature dependence of resistivity observed in overdoped \lan.",9510173v1
1996-07-30,Spontaneous vortex phase discovered?,"It is argued that a spontaneous vortex phase may exist in the recently
discovered compound $ErNi_2B_2C$ at temperature below 2.3K. The consequences of
this proposal are discussed. In particular the magnetic response of the system
are studied both above and below 2.3K and further experiments proposed.",9607214v1
1996-11-15,On the Imbalance of the Dielectric Constant of the PbLixNb3xZr0.51Ti0.49-4xO3 Compound,"In the present paper, the dielectric behaviour of the
PbLixNb3xZr0.51Ti0.49-4xO3 ( PLNZT) system is analyzed. It is shown that the
decrease in the dielectric constant with respect to an increase of the impurity
content may be due to an aggregation trend of the interacting off-centre
dipoles rather than due to cooperative phenomena which renormalizes the dipole
moment of the off-centre impurity.",9611119v1
1999-04-22,Orbital Dynamics: The Origin of Anomalous Magnon Softening in Ferromagnetic Manganites,"We study the renormalization of magnons by charge and coupled orbital-lattice
fluctuations in colossal magnetoresistance compounds. The model considered is
an orbitally degenerate double-exchange system coupled to Jahn-Teller active
phonons. The modulation of ferromagnetic bonds by low-energy orbital
fluctuations is identified as the main origin of the unusual softening of the
zone-boundary magnons observed experimentally in manganites.",9904316v2
1999-05-21,Broken-Symmetry Ground States of Halogen-Bridged Binuclear Metal Complexes,"Based on a symmetry argument, we study ground states of what we call
MMX-chain compounds, which are the new class of halogen-bridged metal
complexes. Commensurate density-wave solutions of a relevant multi-band
Peierls-Hubbard model are systematically revealed within the Hartree-Fock
approximation. We numerically draw ground-state phase diagrams, where various
novel density-wave states appear.",9905312v1
1999-06-17,Formation of the Heavy-Fermion State - an Explanation in a Model Traditionally Called Localized,"In contrary to widely spread view about the substantial delocalization of f
electrons in heavy- fermion (h-f) compounds it is argued that h-f phenomena can
be understood with localized f electrons. Then the role of crystal-field
interactions is essential and the heavy-fermion behaviour can occur for the
localized Kramers-doublet ground state.",9906287v1
1999-12-02,Subdominant interactions and Hc2 in UBe13,"We discuss a model based on a field-induced mixture of two odd-parity
irreducible representations to explain the unusual features of Hc2(T) in the
heavy fermion compound UBe13. We compare its predictions with recent pressure
measurements as well as with the most prominent theoretical models which have
been proposed up to now.",9912030v1
2000-08-28,"Reply to the comment of Tallon et al. Cond-Mat/0008295 about Phys. Rev. Lett. 83, 4381 (1999)","It is shown both from a qualitative and quantitative analysis that the
T-dependence of the pure susceptibility detected by Tallon et al. in overdoped
compounds cannot explain the T-dependence of the Li NMR shift. This confirms
that the electronic correlations are still present in the overdoped regime as
pointed out in Phys. Rev. Lett. 83, 4381 (1999).",0008396v1
2000-09-17,Jarzynski Relations for Quantum Systems and Some Applications,"We derive quantum analogues of Jarzynski's relations, and discuss two
applications, namely, a derivation of the law of entropy increase for general
compound systems, and a preliminary analysis of heat transfer between two
quantum systems at different temperatures. We believe that the derivation of
the law of entropy increase is new and of importance.",0009244v2
2000-11-21,Spin and Orbital Order in Itinerant Ferromagnets,"The long-standing problem of the effect of correlations on the ferromagnetism
of is apparently nearing solution. The ferromagnetism of transition metals
compounds, for instance doped manganites, poses a new question: is there some
kind of orbital order coexisting with itinerant ferromagnetism? The ideas and
techniques introduced by Gutzwiller should be of use again.",0011354v1
2001-01-21,Electron-Electron Relaxation Effect on Auger Recombination in Direct Band Semiconductors,"Influence of electron-electron relaxation processes on Auger recombination
rate in direct band semiconductors is investigated. Comparison between
carrier-carrier and carrier-phonon relaxation processes is provided. It is
shown that relaxation processes are essential if the free path length of
carriers doesn't exceed a certain critical value, which exponentially increases
with temperature. For illustration of obtained results a typical InGaAsP
compound is used.",0101328v1
2001-03-23,Ab initio Hartree-Fock with electronic correlation study of the electronic properties of MgB2,"We performed all-electron ab initio self-consistent field Hartree-Fock linear
combination of atomic orbital, in which electronic correlation using density
functional were included to perform electronic calculations in MgB2 new
superconductor. Superconductivity in this compound was correlated with
existence of Px,y band holes at Gamma point.",0103477v1
2001-03-26,Zone-boundary excitations in coupled Haldane spin chain compounds PbNi2V2O8 and SrNi2V2O8,"Magnetic excitations in the quasi-one-dimensional quantum antiferromagnets
PbNi2V2O8 and SrNi2V2O8 are measured all the way up to the zone boundary energy
using inelastic neutron scattering from powder samples. An estimate for
next-nearest-neighbor in-chain interactions is obtained. The role played by
these interactions in spin-vacancy induced magnetic ordering in PbNi2V2O8 is
discussed.",0103546v1
2001-05-15,Superconductivity in the Re-B system,"Superconductivity was found for a rhenium boride Re3B at Tc=4.7 K and for
ReB2 with Tc in the range from 4.5 to 6.3 K depending on the boron
concentrations. Both compounds have the structure different from that of the
simple layered diborides, in particular from MgB2.",0105293v1
2001-07-08,Synthesis of MgB2 from elements,"Superconducting at 40 K MgB2 -samples were obtained by direct reaction from
elements in molybdenum crucibles under argon pressure. Pressure allows to
provide annealing at temperature up to 1400oC, that resulting in rise of Tc and
compactness of the ceramics, suggesting that there is a homogeneity range of
composition for the compound.",0107164v1
2002-01-17,"Elementary Excitations in Quantum Antiferromagnetic Chains: Dyons, Spinons and Breathers","Considering experimental results obtained on three prototype compounds, TMMC,
CsCoCl3 (or CsCoBr3) and Cu Benzoate, we discuss the importance of non-linear
excitations in the physics of quantum (and classical) antiferromagnetic spin
chains.",0201298v1
2002-03-07,Segmented Band Mechanism for Itinerant Ferromagnetism,"We introduce a novel mechanism for itinerant ferromagnetism, which is based
on a simple two-band model, and using numerical and analytical methods, we show
that the Periodic Anderson Model (PAM) contains this mechanism. We propose that
the mechanism, which does not assume an intra-atomic Hund's coupling, is
present in both the iron group and some $f$ electron compounds.",0203172v1
2002-07-28,Sliding Density-Wave in Sr_{14}Cu_{24}O_{41} Ladder Compounds,"We used transport and Raman scattering measurements to identify the
insulating state of self-doped spin 1/2 two-leg ladders of Sr_{14}Cu_{24}O_{41}
as a weakly pinned, sliding density wave with non-linear conductivity and a
giant dielectric response that persists to remarkably high temperatures.",0207666v1
2002-10-30,Symmetry Considerations for the Detection of Second-Harmonic Generation in Cuprates in the Pseudogap phase,"A proposal to test the proposed time-reversal and inversion breaking phase in
the Pseudogap region of the Cuprate compounds through the variation of
Second-harmonic generation intensity with temperature and polarization and
angle of incidence is presented.",0210672v1
2002-12-10,Oscillating Solitons Pinned to a Nonmagnetic Impurity in Layered Antiferromagnets,"We argue that an oscillatory motion of impurity-pinned solitons may occur in
layered antiferromagnetic compounds. The characteristic frequencies of these
modes, that may be detected by resonance or inelastic neutron scattering, are
estimated analytically and depend on the soliton sizes and types .",0212214v1
2003-03-17,Spin vs charge excitations in heavy-fermion compounds*,"It is pointed out that the answer on the question about the role played by
spin and charge excitations will help to solve the physical origin of the
heavy- fermion phenomena. Our answer is that neutral spin-like excitations are
responsible for the heavy-fermion phenomena whereas the role of the charge
excitations is negligible.
  Keywords: heavy fermion, spin excitations, charge excitations
  PACS No: 75.20.H",0303321v1
2003-04-17,Half-metallic Zinc-blende Compounds,"We report first-principles calculations of zinc-blende half-metals,
identifying systems for epitaxial growth with semiconductors, and present
calculations for CrAs/GaAs multilayers. We find that half-metallicity is
conserved troughout the heterostructure, making this a good candidate for
spintronics applications.",0304403v1
2003-08-20,Exact Unitary Transformation of the One-Dimensional Periodic Anderson Model,"An effective hamiltonian is derived exactly for the one-dimensional periodic
Anderson model via a canonical transformation. The canonical transformation has
been calculated up to infinite order, thus an exact transformation was
performed in the strict mathematical sense. We also discuss briefly the impact
of the obtained result on understanding the magnetic properties of several
Kondo lattice compounds.",0308405v1
2003-11-27,Optical response for a discrete stripe,"The optical response of a charge stripe in the presence of pinning impurities
is investigated. We address the issue of a discrete description of the stripe,
and discuss its quantitative relevance with respect to a continuum one in the
light of recent optical-conductivity measurements in cuprate compounds.",0311626v1
2004-03-01,Water Absorption and High Electric Conductivity in betha-PbO2 and Ag5Pb2O6,"Water absorption in lead peroxide betha-PbO2 and Bystroem-Evers compound
Ag2[Ag3Pb2O6] has been investigated by infrared spectrometry and electric
conductance measurements. Hydrated Ag5Pb2O6 exhibits, between room temperature
and 690 K, electric conductivity, at least, order of magnitude higher than pure
silver.",0403027v1
2004-03-15,The relative influences of disorder and of frustration on the glassy dynamics in magnetic systems,"The magnetisation relaxations of three different types of geometrically
frustrated magnetic systems have been studied with the same experimental
procedures as previously used in spin glasses. The materials investigated are
Y$_2$Mo$_2$O$_7$ (pyrochlore system), SrCr$_{8.6}$Ga$_{3.4}$O$_{19}$ (piled
pairs of Kagom\'e layers) and (H$_3$O)Fe$_3$(SO$_4$)$_2$(OH)$_6$ (jarosite
compound). Despite a very small amount of disorder, all the samples exhibit
many characteristic features of spin glass dynamics below a freezing
temperature $T_g$, much smaller than their Curie-Weiss temperature $\theta$.
The ageing properties of their thermoremanent magnetization can be well
accounted for by the same scaling law as in spin glasses, and the values of the
scaling exponents are very close. The effects of temperature variations during
ageing have been specifically investigated. In the pyrochlore and the
bi-Kagom\'e compounds, a decrease of temperature after some waiting period at a
certain temperature $T_p$ re-initializes ageing and the evolution at the new
temperature is the same as if the system were just quenched from above $T_g$.
However, as the temperature is raised back to $T_p$, the sample recovers the
state it had previously reached at that temperature. These features are known
in spin glasses as rejuvenation and memory effects. They are clear signatures
of the spin glass dynamics. In the Kagom\'e compound, there is also some
rejuvenation and memory, but much larger temperature changes are needed to
observe the effects. In that sense, the behaviour of this compound is
quantitatively different from that of spin glasses.",0403356v1
2004-03-27,Broken symmetry and symmetry classification of magnetic ordering in doped crystals,"The problem of the spontaneous breaking of the symmetry in the crystals with
variable composition is discussed. The character of the variation of the
inhomogeneous superstructure depending on the substitutional atom concentration
has been considered. The genesis of the structure and magnetic ordering in the
perovskite type compounds is discussed.",0403666v1
2004-06-16,Superconductivity in ferromagnetic metals and in compounds without inversion centre,"The symmetry properties and the general overview of the superconductivity
theory in the itinerant ferromagnets and in materials without space parity are
presented. The basic notions of unconventional superconductivity are introduced
in broad context of multiband superconductivity which is inherent property of
ferromagnetic metals or metals without centre of inversion.",0406371v1
2004-06-24,Orbital ordering and magnetic structures in $\LMFO$ and $\LWFO$ double perovskites,"We analyzed the possible magnetic and orbital orderings of double
perovskites, using a simple extension of the double exchange model well suited
for these compounds. Orbital ordering is favored by the on site repulsion at
the Fe ions. We obtain a rich phase diagram, including ferri- and
antiferromagnetic phases, which can, in turn, be metallic or insulating,
depending on the existence of orbital order.",0406605v1
2004-07-08,Quasi-one-dimensional anisotropic Heisenberg model in a transverse magnetic field,"The phase diagram of weakly coupled $XXZ$ chains in a transverse magnetic
field is studied using the mean-field approximation for the interchain coupling
and known exact results for an effective one-dimensional model. Results are
applied to the quasi-one-dimensional antiferromagnet $Cs_{2}CoCl_{4}$ and the
value of interchain interaction in this compound is estimated.",0407203v1
2004-08-13,Effect of hydrostatic pressure on the ambient pressure superconductor CePt_3Si,"We studied the evolution of superconductivity (sc) and antiferromagnetism
(afm) in the heavy fermion compound CePt_3Si with hydrostatic pressure. We
present a pressure-temperature phase diagram established by electrical
transport measurements. Pressure shifts the superconducting transition
temperature, T_c, to lower temperatures. Antiferromagnetism is suppressed at a
critical pressure P_c=0.5 GPa.",0408313v1
2004-10-06,New Electron-Doped Superconducting Cuprate Li_x_Sr_2_CuO_2_Br_2_,"A new electron-doped superconductor Li_x_Sr_2_CuO_2_Br_2_ with x = 0.15 has
successfully been synthesized by an electrochemical Li-intercalation technique.
The magnetic susceptibility shows superconductivity of bulk with the
superconducting transition temperature Tc = 8 K. This compound is the first
electron-doped superconducting cuprate with the K_2_NiF_4_ structure.",0410141v1
2005-01-24,New class of T-prime-structure cuprate superconductors,"High-temperature superconductivity has been discovered in La2-xBaxCuO4 [1], a
compound that derives from the undoped La2CuO4 crystallizing in the perovskite
T-structure. In this structure oxygen octahedra surround the copper ions. It is
common knowledge that charge carriers induced by doping in such an undoped
antiferromagnetic Mott-insulator lead to high-temperature superconductivity [2-
4]. The undoped material La2CuO4 is also the basis of the electron-doped
cuprate superconductors [5] of the form La2-xCexCuO4+y [6,7] which however
crystallize in the so called T-prime-structure, i.e. without apical oxygen
above or below the copper ions of the CuO2-plane. It is well known that for
La2-xCexCuO4+y the undoped T-prime-structure parent compound cannot be prepared
due to the structural phase transition back into the T-structure occuring
around x ~ 0.05. Here, we report that if La is substituted by RE = Y, Lu, Sm,
Eu, Gd, or Tb, which have smaller ionic radii but have the same valence as La,
nominally undoped La2-xRExCuO4 can be synthesized by molecular beam epitaxy in
the T-prime-structure. The second important result is that all these new
T-prime-compounds are superconductors with fairly high critical temperatures up
to 21 K. For this new class of cuprates La2-xRExCuO4, which forms the
T-prime-parent compounds of the La-based electron doped cuprates, we have not
been able to obtain the Mott-insulating ground state for small x before the
structural phase transition into the T-structure takes place.",0501575v1
2005-11-11,Spin current as a response to external stress,"It is theoretically predicted that a traveling shear wave will create a spin
current in certain direct-gap (for example III-V compound) semiconductors with
contributions from both the valence bands and the conduction band (for
$n$-doped semiconductors). We show that this spin-current is a property of the
Fermi-Dirac sea, and is controlled by a geometric phase accumulated by the
strain-induced Rashba parameters in a cycle.",0511270v1
2005-11-17,Nucleophilicity/Electrophilicity Excess in Analyzing Molecular Electronics,"Intramolecular electron transfer capability of all metal aromatic and
anti-aromatic aluminum cluster compounds is studied in terms of density
functional theory based global and local reactivity descriptors. This study
will provide important inputs towards the fabrication of the material required
for molecular electronics.",0511441v1
2006-03-08,Electronic Structure of Nearly Ferromagnetic compound HfZn$_{2}$,"The electronic structure of HfZn$_{2}$ has been studied based on the density
functional theory within the local-density approximation. The calculation
indicates that HfZn$_{2}$ shows ferromagnetic instability. Large enhancement of
the static susceptibility over its non-interacting value is found due to a peak
in the density of states at the Fermi level.",0603203v1
2006-03-31,Half-metallic diluted antiferromagnetic semiconductors,"The possibility of half-metallic antiferromagnetism, a special case of
ferrimagnetism with a compensated magnetization, in the diluted magnetic
semiconductors is highlighted on the basis of the first principles electronic
structure calculation. As typical examples, the electrical and magnetic
properties of II-VI compound semiconductors doped with 3d transition metal ion
pairs--(V, Co) and (Fe, Cr)--are discussed.",0603846v1
2006-06-01,Advances in structure prediction of inorganic compounds,"There is a huge and confusing literature about inorganic crystal structure
prediction. The word ""prediction"" is used sometimes as meaning ""structure
determination"" since the process described needs the knowledge of the chemical
composition and of the cell parameters. Some clarifications are presented here
together with a new software (GRINSP) and some of its predictions.",0606025v1
2006-09-06,Spectral functions for strongly correlated 5f-electrons,"We calculate the spectral functions of model systems describing 5f-compounds
adopting Cluster Perturbation Theory. The method allows for an accurate
treatment of the short-range correlations. The calculated excitation spectra
exhibit coherent 5f bands coexisting with features associated with local
intra-atomic transitions. The findings provide a microscopic basis for partial
localization. Results are presented for linear chains.",0609123v1
2006-09-11,"Inhomogeneous superconductivity and the ""pseudogap state of novel superconductors","Novel superconducting compounds such as the high Tc oxides are intrinsically
inhomogeneous systems. An inhomogeneous structure is created by doping and the
statistical nature of the distribution of dopants. Consequently, the critical
temperature is spatially dependent: Tc = Tc (r).",0609260v1
2006-10-04,Hydrogen ordering influence on the proton spin-lattice relaxation time in metal-hydrogen compoun Hydrogen ordering influence on the proton spin-lattice relaxation time in metal-hydrogen compounds,"Results of the experimental study of ordering lanthanum hydrides of LaHX
system are presented. It is shown that obtained results can be interpreted as
an indirect confirmation of the existence of order-order transformations in
LaH2+c hydrides.",0610100v1
2006-11-23,Landau theory applied to phase transitions in calcium orthotungstate and isostructural compounds,"The pressure-driven tetragonal-to-monoclinic phase transition in CaWO4 and
related scheelite-structured orthotungstates is analysed in terms of
spontaneous strains. Based upon our previous high-pressure x-ray diffraction
results and the Landau theory, it is suggested that the
scheelite-to-fergusonite transition is of second order in nature.",0611605v1
2007-01-23,"High field level crossing studies on spin dimers in the low dimensional quantum spin system Na$_2$T$_2$(C$_2$O$_4$)$_3$(H$_2$O)$_2$ with T=Ni,Co,Fe,Mn","In this paper we demonstrate the application of high magnetic fields to study
the magnetic properties of low dimensional spin systems. We present a case
study on the series of 2-leg spin-ladder compounds
Na$_2$T$_2$(C$_2$O$_4$)$_3$(H$_2$O)$_2$ with T = Ni, Co, Fe and Mn. In all
compounds the transition metal is in the $T^{2+}$ high spin configuation. The
localized spin varies from S=1 to 3/2, 2 and 5/2 within this series. The
magnetic properties were examined experimentally by magnetic susceptibility,
pulsed high field magnetization and specific heat measurements. The data are
analysed using a spin hamiltonian description. Although the transition metal
ions form structurally a 2-leg ladder, an isolated dimer model consistently
describes the observations very well. This behaviour can be understood in terms
of the different coordination and superexchange angles of the oxalate ligands
along the rungs and legs of the 2-leg spin ladder. All compounds exhibit
magnetic field driven ground state changes which at very low temperatures lead
to a multistep behaviour in the magnetization curves. In the Co and Fe
compounds a strong axial anisotropy induced by the orbital magnetism leads to a
nearly degenerate ground state and a strongly reduced critical field. We find a
monotonous decrease of the intradimer magnetic exchange if the spin quantum
number is increased.",0701575v1
2007-02-22,Alloying induced degradation of the absorption edge of InAs_{x}Sb_{1-x},"InAs_{x}Sb_{1-x} alloys show a strong bowing in the energy gap, the energy
gap of the alloy can be less than the gap of the two parent compounds. We
demonstrate that a consequence of this alloying is a systematic degradation in
the sharpness of the absorption edge. The alloy disorder induced band-tail
(Urbach tail) characteristics are quantitatively studied for
InAs_{0.05}Sb_{0.95}.",0702518v1
1993-11-05,High Energy Asymptotics of Multi--Colour QCD and Exactly Solvable Lattice Models,"The quantum inverse scattering method is applied to the solution of equations
for wave functions of compound states of $n$ reggeized gluons in the
multicolour QCD in a generalized leading logarithmic approximation.",9311037v1
2006-09-02,Dynamics of a system of sticking particles of a finite size on the line,"The continuous limit of large systems of particles of finite size on the line
is described. The particles are assumed to move freely and stick under
collision, to form compound particles whose mass and size is the sum of the
masses and sizes of the particles before collision, and whose velocity is
determined by conservation of linear momentum.",0609006v1
2000-03-29,Test of the Quantum Chaoticity Criterion for Diamagnetic Kepler Problem,"The earlier suggested criterion of quantum chaoticity, borrowed from the
nuclear compound resonance theory, is used in the analysis of the quantum
diamagnetic Kepler problem (the spinless charged particle motion in the Coulomb
and homogenious magnetic fields).",0003063v1
2002-09-13,"Comment on ``Entry Distribution, Fission Barrier, and Formation Mechanism of 254No''","A recent paper has reported the observation of the rotational band of 254No
for spins up to I=20, showing that the compound nucleus was formed and survived
fission decay at angular momenta I >= 20. We show that this survival is
consistent with the leading effects of angular momentum on the barrier height.",0209010v1
1996-03-05,Average over energy effect of parity nonconservation in neutron scattering on heavy nuclei,"Using semiclassical approximation we consider parity nonconservation (PNC)
averaged over compound resonances. We demonstrate that the result of the
averaging crucially depends on the properties of residual strong
nucleon-nucleon interaction. Natural way to elucidate this problem is to
investigate experimentally PNC spin rotation with nonmonachromatic neutron
beam: $E \sim \Delta E \sim 1MeV$. Value of the effect can reach $\psi \sim
10^{-5}-10^{-4}$ per mean free path.",9603002v1
1999-11-02,Dinuclear concept - cluster model of fusion,"The synthesis of superheavy elements is analysed within the dinuclear system
concept of compound nucleus formation. The perspectives for using radioactive
beams in complete fusion reactions are discussed.",9911009v1
2004-03-22,Components of an algebraic solution of the multichannel problem of low-energy n-${}^{12}$C scattering plus sub-threshold (${}^{13}$C) states,"The effects of components in an assumed model interaction potential, as well
as of the order to which its deformation is taken, upon resonances in the
low-energy cross sections and upon sub-threshold bound states of the compound
nucleus (${}^{13}$C) are discussed.",0403061v1
1998-10-26,Two-Photon Spectroscopy of Transition-Metal Ions in Cubical Symmetry,"Symmetry adaptation techniques are applied to the determination of
intensities of intra-configurational two-photon transitions for
transition-metal ions in cubical symmetry. This leads to a simple model giving
the polarization dependence of intensities of two-photon (electric dipolar)
transitions between Stark levels of the configuration 3dN (N = even or odd).",9810047v1
2004-06-24,Kinoform refraction lens with diffraction calculation,"By direct numerical simulations of the kinoform refractive lens within the
quazioptical approach the effects of shape misalinement were investigated. The
quazioptical approach was based on numerical integration of parabolic equation
for complex wave amplitude by spep-by-step method with ""splitting"" procedure.
The effect of 2pi- shift compensation was calculated for different orders and
imperfections. The performance of kinoform lens was compared with the compound
refractive lens and thin lens approximation.",0406115v1
2006-10-04,Fugacity of condensed media,"Appearance of physical properties of objects is a basic for their detection
in a media. Fugacity is a physical property of objects. Definition of
estimations fugacity for different objects can be executed on model which
principle of construction is considered in this paper. The model developed by
us well-formed with classical definition fugacity and open up possibilities for
calculation of physical ""fugacity"" for elementary and compound substances.",0610024v1
1999-03-09,"Comment on ``Consistency, amplitudes and probabilities in quantum theory'' by A. Caticha","A carefully written paper by A. Caticha [Phys. Rev. A57, 1572 (1998)] applies
consistency arguments to derive the quantum mechanical rules for compounding
probability amplitudes in much the same way as earlier work by the present
author [J. Math. Phys. 29, 398 (1988) and Int. J. Theor. Phys. 27, 543 (1998)].
These works are examined together to find the minimal assumptions needed to
obtain the most general results.",9903031v1
2000-08-03,Operational resolutions and state transitions in a categorical setting,"We define a category with as objects operational resolutions and with as
morphisms - not necessarily deterministic - state transitions. We study
connections with closure spaces and join-complete lattices and sketch physical
applications related to evolution and compoundness. An appendix with
preliminaries on quantaloids is included.",0008020v1
2005-12-06,Syntactic and Semantic Distribution in Quantum Measurement,"The nondistributivity of compound quantum mechanical propositions leads to a
theorem that rules out the possibility of microscopic deterministic hidden
variables, the Logical No-Go Theorem. We observe that there appear in fact two
distinct nondistributivity relations in the derivation: one with a semantics
governed by an empirical conjunctive syntax, the other composed of conjunctive
primitives in the quantum mechanical probability calculus. We venture to
speculate how the two come to be confused in the derivation of the theorem.",0512053v1
2007-03-07,Quantic Superpositions and the Geometry of Complex Hilbert Spaces,"The concept of a superposition is a revolutionary novelty introduced by
Quantum Mechanics. If a system may be in any one of two pure states x and y, we
must consider that it may also be in any one of many superpositions of x and y.
An in-depth analysis of superpositions is proposed, in which states are
represented by one-dimensional subspaces, not by unit vectors as in Dirac's
notation. Superpositions must be considered when one cannot distinguish between
possible paths, i.e., histories, leading to the current state of the system. In
such a case the resulting state is some compound of the states that result from
each of the possible paths. States can be compounded, i.e., superposed in such
a way only if they are not orthogonal. Since different classical states are
orthogonal, the claim implies no non-trivial superpositions can be observed in
classical systems. The parameter that defines such compounds is a proportion
defining the mix of the different states entering the compound. Two quantities,
p and theta, both geometrical in nature, relate one-dimensional subspaces in
complex Hilbert spaces: the first one is a measure of proximity relating two
rays, the second one is an angle relating three rays. The properties of the
operation of superposition are very different from those that govern linear
combination of vectors.",0703056v2
2007-04-10,Electronic structure of the noncentrosymmetric superconductor Mg10Ir19B16,"Electronic structure of a novel superconducting noncentrosymmetric compound
Mg10Ir19B16 was calculated using the Korringa-Kohn-Rostoker method. Electronic
part of the electron-phonon coupling constant, McMillan-Hopfield parameters,
were calculated using the rigid-muffin-tin approximation (RMTA). The magnitude
of the electron-phonon coupling constant, analysing atomic contributions, is
discussed. Our results show, that superconductivity in Mg10Ir19B16 is
presumably mediated by electron-phonon interaction.",0704.1295v1
2007-11-16,"Correlation between Thermal Properties, Electrical Conductivity and Crystal Structure in the BaCe0.80Y0.20O2.9 Proton Conductor","In this paper we report an extensive neutron diffraction investigation at
high temperature on the BaCe0.80Y0.20O2.9 proton conducting material. Our
results precisely define the structural evolution of the compound as a function
of temperature which is from a monoclinic (room temperature) to a cubic (800C)
structure. Neutron data have been correlated to calorimetric measurements (TGA
and DSC) and conductivity properties of the material.",0711.2565v1
2008-01-18,Compound basis arising from the basic $A^{(1)}_{1}$-module,"A new basis for the polynomial ring of infinitely many variables is
constructed which consists of products of Schur functions and Q-functions. The
transition matrix from the natural Schur function basis is investigated.",0801.2818v1
2008-01-27,Plotting Calibration Curve Using Biosynthetic Specifically Labeled Compounds for Accurate Mass Isotopomer Analysis,"This paper has been withdrawn by the author(s), due to the requirement of the
journal it currently submitted to",0801.4122v3
2008-02-21,A survey of liquid crystalline oxadiazoles,"We propose a survey of those oxadiazole compounds, which are mesogenic. We
will see that they can have bend-shaped molecules, a biaxial nematic phase, or
other interesting peculiarities in the nematic and smectic phase. With large
electric dipoles and luminescent properties, these materials are also very
appealing for technological applications.",0802.3108v1
2008-03-02,Towards new schemes: A Lie-group approach of the CBKDV and its derived equations,"The aim of this paper is to propose methods that enable us to build new
numerical schemes, which preserve the Lie symmetries of the original
differential equations. To this purpose, the compound Burgers-Korteweg-de Vries
(\textit{CBKDV}) equation is considered. The particular case of the Burgers
equation is taken as a numerical example, and the resulting semi-invariant
scheme is exposed.",0803.0135v1
2008-11-13,(Sr_3Sc_2O_5)Fe_2As_2 as a possible parent compound for FeAs-based superconductors,"A new compound with the FeAs-layers, namely (Sr_3Sc_2O_5)Fe_2As_2
(abbreviated as FeAs-32522), was successfully fabricated. It has a layered
structure with the space group of I4/mmm, and with the lattice constants a =
4.069 $\AA$ and c = 26.876 $\AA$. The in-plane Fe ions construct a square
lattice which is close to that of other FeAs-based superconductors, such as
REFeAsO (RE = rare earth elements) and (Ba,Sr)Fe_2As_2. However the inter
FeAs-layer spacing in the new compound is greatly enlarged. The temperature
dependence of resistivity exhibits a weak upturn in the low temperature region,
but a metallic behavior was observed above about 60 K. The magnetic
susceptibility shows also a non-monotonic behavior. Interestingly, the
well-known resistivity anomaly which was discovered in all other parent
compounds, such as REFeAsO, (Ba,Sr)Fe_2As_2 and (Sr,Ca,Eu)FeAsF and associated
with the Spin-Density-Wave (SDW)/structural transition has not been found in
the new system either on the resistivity data or the magnetization data. This
could be induced by the large spacing distance between the FeAs-planes,
therefore the antiferromagnetic correlation between the moments of Fe ions in
neighboring FeAs-layers cannot be established. Alternatively it can also be
attributed to the self-doping effect between Fe and Sc ions. The Hall
coefficient R_H is negative but strongly temperature dependent in wide
temperature region, which indicates the dominance of electrical conduction by
electron-like charge carriers and probably a multi-band effect or a spin
related scattering effect. It is found that the magnetoresistance cannot be
described by the Kohler's rule, which gives further support to above arguments.",0811.2205v2
2009-01-08,A new approach to mutual information. II,"A new concept of mutual pressure is introduced for potential functions on
both continuous and discrete compound spaces via discrete micro-states of
permutations, and its relations with the usual pressure and the mutual
information are established. This paper is a continuation of the paper of Hiai
and Petz in Banach Center Publications, Vol. 78.",0901.1072v1
2009-03-01,Excitonic spin density wave state in iron pnictides,"We examine the appearance of a spin density wave in the FeAs parent compounds
due to an excitonic instability. Using a realistic four-band model, we show
that the magnetic state depends very sensitively upon the details of the band
structure. We demonstrate that an orthorhombic distortion of the crystal
enhances the stability of the antiferromagnetic order.",0903.0124v1
2009-04-20,Entanglement Transmission Capacity of Compound Channels,"We determine the optimal achievable rate at which entanglement can be
reliably transmitted when the memoryless channel used during transmission is
unknown both to sender and receiver. To be more precise, we assume that both of
them only know that the channel belongs to a given set of channels. Thus, they
have to use encoding and decoding schemes that work well for the whole set.",0904.3011v1
2009-05-28,Very special divisors on real algebraic curves,"We study special linear systems called ""very special"" whose dimension does
not satisfy a Clifford type inequality given by Huisman. We classify all these
very special linear systems when they are compounded of an involution. Examples
of very special linear systems that are simple are also given.",0905.4663v1
2009-06-17,Magnetostructural Effect in the Multiferroic BiFeO3-BiMnO3 Checkerboard from First Principles,"Using first principles calculations, we present a magnetostructural effect in
the BiFeO3-BiMnO3 nanocheckerboard that is not found in either bulk parent
compound or in BiFeO3-BiMnO3 superlattices. We also demonstrate that the
atomic-scale checkerboard has a multiferroic ground state with the desired
properties of each constitutent material: polar and ferrimagnetic due to BiFeO3
and BiMnO3 respectively.",0906.3201v1
2009-08-13,Quasifission and difference in formation of evaporation residues in the $^{16}$O+$^{184}$W and $^{19}$F+$^{181}$Ta reactions,"The excitation functions of capture, complete fusion, and evaporation residue
formation in the $^{16}$O+$^{184}$W and $^{19}$F+$^{181}$Ta reactions leading
to the same $^{200}$Pb compound nucleus has been studied theoretically to
explain the experimental data showing more intense yield of evaporation residue
in the former reaction in comparison with that in the latter reaction. The
observed difference is explained by large capture cross section in the former
and by increase of the quasifission contribution to the yield of fission-like
fragments in the $^{19}$F+$^{181}$Ta reaction at large excitation energies. The
probability of compound nucleus formation in the $^{16}$O+$^{184}$W reaction is
larger but compound nuclei formed in both reactions have similar angular
momentum ranges at the same excitation energy. The observed decrease of
evaporation residue cross section normalized to the fusion cross section in the
$^{19}$F+$^{181}$Ta reaction in comparison with the one in the
$^{16}$O+$^{184}$W reaction at high excitation energies is explained by the
increase of hindrance in the formation of compound nucleus connected with more
quick increase of the quasifission contribution in the $^{19}$F induced
reaction. The spin distributions of the evaporation residue cross sections for
the two reactions are also presented.",0908.1957v2
2009-09-18,Single Crystal 31P NMR Studies of the Frustrated Square Lattice Compound Pb2(VO)(PO4)2,"The static and dynamic properties of V^{4+} spins (S = 1/2) in the frustrated
square lattice compound Pb2(VO)(PO4)2 were investigated by means of magnetic
susceptibility chi and 31P nuclear magnetic resonance (NMR) shift (K) and 31P
nuclear spin-lattice relaxation rate 1/T1 measurements on a single crystal.
This compound exhibits long-range antiferromagnetic order below TN \simeq 3.65
K. NMR spectra above TN show two distinct lines corresponding to two
inequivalent P sites present in the crystal structure. The observed asymmetry
in hyperfine coupling constant for the in-plane (P1) P site directly points
towards a distortion in the square lattice at the microscopic level, consistent
with the monoclinic crystal structure. The nearest- and next-nearest-neighbor
exchange couplings were estimated to be J1/kB = (-5.4 \pm 0.5) K
(ferromagnetic) and J2/kB = (9.3 \pm 0.6) K (antiferromagnetic), respectively.
1/(T1 T chi) is almost T-independent at high temperatures due to random
fluctuation of spin moments. Below 20 K, the compound shows an enhancement of
1/(T1 T chi) which arises from a growth of antiferromagnetic spin correlations
above TN. Below TN and for the field applied along the c-axis, the NMR spectrum
for the P1 site splits into two satellites and the spacing between them
increases monotonically with decreasing T which is a direct evidence of a
columnar antiferromagnetic ordering with spins lying in the ab-plane. This type
of magnetic ordering is consistent with expectation from the J2/J1 \simeq -1.72
ratio. The critical exponent beta = 0.25 \pm 0.02 estimated from the
temperature dependence of sublattice magnetization as measured by 31P NMR at
11.13 MHz is close to the value (0.231) predicted for the two-dimensional XY
model.",0909.3536v2
2009-10-12,Polaronic effect and its impact on Tc for novel layered superconducting systems,"The crystal lattice of a complex compound may contain a subsystem of ions
with each one possessing two close equilibrium positions (double-well
structure). For example, the oxygen ions in the cuprates form such a subsystem.
In such a situation it is impossible to separate electronic and local
vibrational motions. This leads to a large increase in the effective strength
of the electron-lattice interaction, which is beneficial for pairing.",0910.2259v1
2010-03-01,Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50K superconductor,"We report an easy single step synthesis route of title compound
NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The
title compound is synthesized via solid-state reaction route by encapsulation
in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray
diffraction data shows that compound crystallized in tetragonal structure with
space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R=0)
at 48 K and a very high upper critical field (Hc2) of up to 345 Tesla. Magnetic
measurements exhibited bulk superconductivity in terms of diamagnetic onset
below 50 K. The lower critical field (Hc1) is around 1000 Oe at 5 K. In normal
state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and
thus ruling out the presence of any ordered FeOx impurity in the matrix. In
specific heat measurements a jump is observed in the vicinity of
superconducting transition (Tc) along with an upturn at below T=4 K due to the
AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is
negative down to Tc, thus indicating dominant carriers to be of n-type in
NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting
NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain
contributions have been individuated by looking at various amplitude and
frequencies of the applied AC drive magnetic field.",1003.0273v3
2010-03-17,A nonlinear transmission problem for a compound plate with thermoelastic part,"In this paper we study a nonlinear transmission problem for a plate which
consists of thermoelastic and isothermal parts. The problem generates a
dynamical system in a suitable Hilbert space. Main result is the proof of the
asymptotic smoothness of this dynamical system. Also we prove the existence of
a compact global attractor in particular cases when the nonlinearity is of
Berger type or scalar.",1003.3332v1
2010-05-25,Astrophysical Reaction Rates as a Challenge for Nuclear Reaction Theory,"The relevant energy ranges for stellar nuclear reactions are introduced.
Low-energy compound and direct reactions are discussed. Stellar modifications
of the cross sections are presented. Implications for experiments are outlined.",1005.4611v1
2010-09-13,Concave Renewal Functions Do Not Imply DFR Inter-Renewal Times,"Brown (1980, 1981) proved that the renewal function is concave if the
inter-renewal distribution is DFR (decreasing failure rate), and conjectured
the converse. This note settles Brown's conjecture with a class of
counter-examples. We also give a short proof of Shanthikumar's (1988) result
that the DFR property is closed under geometric compounding.",1009.2463v1
2010-12-09,Andreev reflection spectroscopy of the new Fe-based superconductor EuAsFeO0.85F0.15: evidence for the strong order parameter anisotropy,"Andreev reflection spectra have been measured in a new superconductor
EuAsFeO0.85F0.15 having an unexpectedly low superconducting transition
temperature Tc~11.3 K among related FeAs compounds on a base Sm and Gd
surrounding Eu in the series of lanthanides. The nearly fivefold lower Tc, as
against the expected value, is attributed to the divalent properties of Eu ions
when in the compound investigated along with the weakly magnetic Eu3+ ions may
be present and the strongly magnetic Eu2+ ones that is a strong destructive
factor for superconductivity. Most of the spectra measured showed features that
corresponds to two energy gaps whose values varied from contact to contact
within 2{\Delta}s/kTc=2.2{\pm}4.7 and 2{\Delta}1/kTc=5.1{\pm}11.7 for small and
large gap, respectively. The corresponding variations for single-gap spectra
are 2{\Delta}/kTc = 2.6{\pm}6.4. The relatively large size of crystallites (no
less than ~25 \mu{m}) and the large number of contacts measured (several tens)
suggest with a high degree of probability that the spectra obtained account
quite fully for the gap distribution practically in all crystallographic
directions. The data obtained and the absence of zero gaps in the measured
spectra evidence in favor of the anisotropic s- or s\pm-symmetry of the order
parameter in EuAsFeO0.85F0.15 that was revealed in other similar compounds with
higher Tc. Thus, the character of the gap function {\Delta}(k) in this compound
is inconsistent with the d-wave superconductivity observed in some low-Tc
pnictides.",1012.2010v2
2011-02-22,Quantum Criticality,"This is a review of the basic theoretical ideas of quantum criticality, and
of their connection to numerous experiments on correlated electron compounds. A
shortened, modified, and edited version appeared in Physics Today. This arxiv
version has additional citations to the literature.",1102.4628v2
2011-04-18,Negative thermal expansion in ZnF$_2$,"We have investigated temperature dependence of the lattice parameters and the
unit cell volume of ZnF$_2$ by neutron diffraction and have discovered negative
thermal expansion (NTE) at low temperature. To understand why this simple
compound exhibits NTE we performed first principle calculations. These
calculations reproduce qualitatively the experimental temperature dependence of
volume.",1104.3529v1
2011-05-09,Pressure dependence of the low- temperature crystal structure and phase transition behaviour of CaFeAsF and SrFeAsF: A synchrotron x-ray diffraction study,"We report systematic investigation of high pressure crystal structures and
structural phase transition upto 46 GPa in CaFeAsF and 40 GPa in SrFeAsF at 40
K using powder synchrotron x-ray diffraction experiments and Rietveld analysis
of the diffraction data. We find that CaFeAsF undergoes orthorhombic to
monoclinic phase transition at Pc = 13.7 GPa while increasing pressure. SrFeAsF
exhibits coexistence of orthorhombic and monoclinic phases over a large
pressure range from 9 to 39 GPa. The coexistence of the two phases indicates
that the transition is of first order in nature. Unlike in the 122 compounds
(BaFe2As2 & CaFe2As2) we do not find any collapse tetragonal transition. The
transition to a lower symmetry phase (orthorhombic to monoclinic) in 1111
compounds under pressure is in contrast with the transition to a high symmetry
phase (orthorhombic to tetragonal) in 122 type compounds. On heating from 40 K
at high pressure, CaFeAsF undergoes monoclinic to tetragonal phase transition
around 25 GPa and 200 K. Further, it does not show any post-tetragonal phase
transition and remains in the tetragonal phase upto 25 GPa at 300 K. The dPc/dT
is found to be positive for the CaFeAsF & CaFe2As2, however the same was not
found in case of BaFe2As2. We discuss observations of structural evolution in
the context of superconductivity in these and other Fe-based compounds. It
appears that the closeness of the Fe-As-Fe bond angle to its ideal tetrahedral
value of 109.470 might be associated with occurrence of superconductivity at
low temperature.",1105.1649v1
2011-05-25,On improved estimation in a conditionally Gaussian regression,"The paper considers the problem of estimating a $p\geq2$\ dimensional mean
vector of a multivariate conditionally normal distribution under quadratic
loss. The problem of this type arises when estimating the parameters in a
continuous time regression model with a non-Gaussian Ornstein--Uhlenbeck
process driven by the mixture of a Brownian motion and a compound Poisson
process.",1105.5036v1
2011-06-29,Statistical Distribution of Crystallographic Groups for Inorganic Crystal Structure Database,"We introduce a method that defines the species (representatives) of inorganic
compounds, and studied the statistical distribution of the defined species
among space groups (distribution of space groups), by using ICSD (Inorganic
Crystal Structure Database). Here we show that the number of formula units in a
unit cell gives a natural classification to understand the statistical
distribution of crystallographic groups.",1106.5833v1
2011-07-17,On Toeplitz localization operators,"We present a unified approach to study properties of Toeplitz localization
operators based on the Calder\'on and Gabor reproducing formula. We show that
these operators with functional symbols on a plane domain may be viewed as
certain pseudodifferential operators (with symbols on a line, or certain
compound symbols).",1107.3269v1
2011-10-12,Notes on risk theory,"The paper contains a basic course on classical Risk Theory for a compound
Poisson process. It is based on probabilistic proofs using the method of the
""Ballot Theorem"" introduced by Tackas. This provides elegant and direct proofs.
Also large deviation methods are used to study the distribution of the time to
ruin.",1110.2642v1
2011-12-29,Mott-Hagedorn Resonance Gas and Lattice QCD Results,"A compound effective model reproducing the equation of state of hadronic
matter as obtained in recent lattice QCD simulations is presented.",1112.6408v1
2012-01-13,Mott-Hubbard localization in model of electronic subsystem of doped fullerides,"Microscopical model of a doped fulleride electronic subsystem taking into
account the triple orbital degeneracy of energy states is considered within the
configurational-operator approach. Using the Green function method the energy
spectrum of the model at integer band filling $n=1$ is calculated, which case
corresponds to $AC_{60}$ compounds. Possible correlation-driven metal-insulator
transition in the model is discussed.",1201.2748v1
2012-03-26,Thermo-magneto coupling in a dipole plasma,"On a dipole plasma, we observe the generation of magnetic moment, as the
movement of the levitating magnet-plasma compound, in response to
electron-cyclotron heating and the increase of $\beta$ (magnetically-confined
thermal energy). We formulate a thermodynamic model with interpreting heating
as injection of microscopic magnetic moment; the corresponding chemical
potential is the ambient magnetic field.",1203.5680v1
2012-10-26,Synthesis and structure of SrCo2Si2 and CaRh2Si2 - isoelectronic variants of the parent superconductors AeFe2As2 and study of the influence of the valence electron count in CaFe2-xRhxSi2,"The finding of superconductivity in Ba0.6K0.4Fe2As2 put the attention on the
investigation of compounds that crystallize with ThCr2Si2 structure type such
as AT2X2 (A = alkali/ alkaline earth/ rare earth element; T = transition metal
and X = element of the 13-15th group) . In this context the silicides CaFe2Si2,
CaFe0.68(6)Rh1.32(6)Si2, CaRh2Si2 and SrCo2Si2 have been synthesized by melting
mixtures of the elements in an arc-furnace under an argon atmosphere. Single
crystals were obtained by special heat treatment in welded niobium ampoules.
The compounds were investigated by means of powder and single crystal X-ray
diffraction. All compounds crystallize in the ThCr2Si2-type structure with
space group I4/mmm (No. 139): a = 3.939(1) {\AA}, c = 10.185(1) {\AA}, R1 =
0.045, 85 F2 values, 8 variable parameters for CaFe2Si2 ; a = 4.0612(3) {\AA},
c = 9.9373(9) {\AA}, R1 = 0.030, 90 F2 values, 10 variable parameters for
CaFe0.68(6)Rh1.32(6)Si2; a = 4.0695(1) {\AA}, c = 9.9841(3) {\AA}, R1 = 0.031,
114 F2 values, 8 variable parameters for CaRh2Si2; a = 3.974(1) {\AA}, c =
10.395(1) {\AA}, R1 = 0.036, 95 F2 values, 8 variable parameters for SrCo2Si2.
The structure of SrCo2Si2 contains isolated [Co2Si2]2- 2D layers in the ab
plane whereas in CaFe2-xRhxSi2 the [T2Si2] layers (T = Fe, Rh) are
interconnected along the c axis via Si Si bonds resulting in a
three-dimentional (3D) [T2Si2]2- and therefore belong to the so-called
collapsed form of the ThCr2Si2-type structure. The SrCo2Si2 and CaRh2Si2 are
isoelectronic to the parent 122 iron-pnictide superconductors AeFe2As2, whereas
CaFe2Si2 is a full substituted variant (As/Si) of CaFe2As2. The crystal
chemistry and chemical bonding in the title compounds are discussed in terms of
LMTO band structure calculations and a topological analysis using the Electron
Localization Function (ELF).",1210.7152v2
2012-11-21,Electronic and magnetic properties of two-dimensional Li$_{3}$N,"Using first-principles plane-wave calculations study of electronic and
magnetic properties of hypothetical two-dimensional structure of Li$_{2}$N
compound have been conducted. Calculations show, that electronic properties of
this this structure can be inflenced by hydrogenation, which may change the
system from wide-gap semiconductor to metal. Also, non-zero magnetic moment,
equal to 1 $\mu_{B}$ can be generated by intruduction of H vacanies in
hydrogenated structure.",1211.5005v1
2013-01-15,Modified associate formalism without entropy paradox: Part II. Comparison with similar models,"The modified associate formalism is compared with similar models, such as the
classical associate model, the associate species model and the modified
quasichemical model. Advantages of the modified associate formalism are
demonstrated.",1301.3215v1
2013-03-07,The thermodynamic properties of the high-pressure superconducting state in the hydrogen-rich compounds,"The ab initio calculations suggest that the superconducting state in CaH6
under the pressure at 150 GPa has the highest critical temperature among the
examined hydrogen-rich compounds. For this reason, the relevant thermodynamic
parameters of the superconducting state in CaH6 have been determined; a wide
range of the Coulomb pseudopotential has been assumed:
$\mu^{\star}\in\left<0.1,0.3\right>$. It has been found that: (i) The critical
temperature (Tc) changes in the range from 243 K to 180 K. (ii) The values of
the ratio of the energy gap to the critical temperature ($R_{\Delta}\equiv
2\Delta\left(0\right)/k_{B}T_{C}$) can be found in the range from 5.42 to 5.02.
(iii) The ratio of the specific heat jump ($\Delta C\left(T_{C}\right)$) to the
value of the specific heat in the normal state ($C^{N}\left(T_{C}\right)$),
which has been represented by the symbol Rc, takes the values from 3.30 to
3.18. (iv) The ratio $R_{H}\equiv
T_{C}C^{N}\left(T_{C}\right)/H^{2}_{C}\left(0\right)$, where
$H_{C}\left(0\right)$ denotes the critical thermodynamic field, changes from
0.122 to 0.125.
  The study has brought out the expressions that correctly predict the values
of the thermodynamic parameters for the superconducting state in CaH6 and for
the compounds: SiH4(H2)2, Si2H6, B2H6, SiH4, GeH4, and PtH. Next, in the whole
family of the hydrogen-rich compounds, the possible ranges of the values have
been determined for Tc, $R_{\Delta}$, Rc, and $R_{H}$. It has been found that
the maximum value of the critical temperature can be equal to 764 K, which very
well correlates with Tc for metallic hydrogen (p=2 TPa). Other parameters
($R_{\Delta}$, Rc, and $R_{H}$) should not deviate from the predictions of the
BCS theory more than the analogous parameters for CaH6.",1303.1641v1
2013-05-06,The $k$-th derivatives of the immanant and the $χ$-symmetric power of an operator,"In recent papers, R. Bhatia, T. Jain and P. Grover obtained formulas for
directional derivatives, of all orders, of the determinant, the permanent, the
$m$-th compound map and the $m$-th induced power map. In this paper we
generalize these results for immanants and for other symmetric powers of a
matrix.",1305.1143v1
2013-06-11,Convergence of the Fourth Moment and Infinite Divisibility,"In this note we prove that, for infinitely divisible laws, convergence of the
fourth moment to 3 is sufficient to ensure convergence in law to the Gaussian
distribution. Our results include infinitely divisible measures with respect to
classical, free, Boolean and monotone convolution. A similar criterion is
proved for compound Poissons with jump distribution supported on a finite
number of atoms. In particular, this generalizes recent results of Nourdin and
Poly.",1306.2674v1
2013-06-27,Stabilization of the multiferroic spin cycloid in Ni$_3$V$_2$O$_8$ by light Co-doping,"We present macroscopic and neutron diffraction data on multiferroic lightly
Co-doped Ni$_3$V$_2$O$_8$. Doping Co into the parent compound suppresses the
sequence of four magnetic phase transitions and only two magnetically ordered
phases, the paraelectric high temperature incommensurate (HTI) and
ferroelectric low temperature incommensurate (LTI), can be observed.
Interestingly, the LTI multiferroic phase with a spiral (cycloidal) magnetic
structure is stabilized down to at least 1.8 K, which could be revealed by
measurements of the electric polarization and confirmed by neutron diffraction
on single crystal samples. The extracted magnetic moments of the LTI phase
contain besides the main exchange also fine components of the cycloid allowed
by symmetry which result in a small amplitude variation of the magnetic moments
along the cycloid propagation due to the site-dependent symmetry properties of
the mixed representations. In the HTI phase a finite imaginary part of the
spine magnetic moment could be deduced yielding a spin cycloid instead of a
purely sinusoidal structure with an opposite spin chirality for different spine
spin chains. The magnetic ordering of the cross-tie sites in both phases is
different in comparison to the respective ones in the pure Ni compound. A wider
temperature stability range of the HTI phase has been observed in comparison to
Ni$_3$V$_2$O$_8$ which can be explained by an additional single-ion easy-axis
anisotropy due to Co-doping. The larger incommensurability of the Co-doped
compounds yields a larger ratio between the competing next-nearest neighbour
and nearest neighbour interaction, which is $J_2/J_1$=0.43 (0.47) for a doping
level of 7% (10%) Co compared to 0.39 in the parent compound.",1306.6488v3
2013-07-04,Magnetotransport and thermal properties characterization of 55 K superconductor SmFeAsO0.85F0.15,"Correlation between structural/microstructural and magneto-thermal transport
properties of FeAs-based SmFeAsO and SmFeAsO0.85F0.15 has been studied in
detail. The Rietveld analysis of room temperature powder X-ray diffraction
(XRD) data reveals that both the samples are single phase, with very small
amount of rare earth impurity in the F doped compound. Electron microscopic
investigations show that compounds have layered morphology and structure, with
the individual grains being surrounded by amorphous layers. The average grain
boundary thickness is ~5 nm. The F free material is found to be magnetic and
shows the appearance of Fe spin density wave (SDW) like order at T = 150 K. The
F doped compound (SmFeAsO0.85F0.15) shows the occurrence of superconductivity
at Tc(R=0, H=0)- 55 K, which decreases to 42 K at magnetic field (H) of 13 kOe.
The superconducting transition was also confirmed by DC magnetization and AC
susceptibility measurements. The intra-grain critical current density (Jc)
calculated using the Bean critical state model is found to be around 5.26 x
10^4 A/cm2 at 5 K in zero field (H=0). The dependence of thermally activated
flux flow energy (U/KB) on the applied magnetic field has been observed. AC
susceptibility measurements at different amplitude of applied AC drive field
confirm the granular nature of the superconducting compound. is confirmed. Both
Fe (SDW) at 150K for SmFeAsO and 55K superconductivity in case of
SmFeAsO0.85F0.15 sample has confirmed by Specific heat [Cp(T)] measurement too.
Further Sm orders anti-ferro-magnetically at 4.5K for non-superconducting and
at 3.5K for superconducting samples, also the entropy change is reduced
significantly for the later than the former. Summarily complete physical
property characterization for both non-superconducting SmFeAsO and 55K
superconductor SmFeAsO0.85F0.15 samples is provided and discussed in the
current article.",1307.1259v2
2013-08-01,Intrinsic compound kernel estimates for the transition probability density of a Lévy type processes and their applications,"In this paper we construct the fundamental solution to some
integro-differential equation, as well as the intrinsic upper and lower
estimates for this solution. As an application of constructed estimates we
state a criterion when a given Borel measure belongs to the respective Kato and
Dynkin classes.",1308.0310v2
2013-10-26,Compound kernel estimates for the transition probability density of a Lévy process in $\rn$,"We construct in the small-time setting the upper and lower estimates for the
transition probability density of a L\'evy process in $\rn$. Our approach
relies on the complex analysis technique and the asymptotic analysis of the
inverse Fourier transform of the characteristic function of the respective
process.",1310.7081v1
2014-01-28,Electronic Evidence of an Insulator-Superconductor Transition in Single-Layer FeSe/SrTiO3 Films,"In high temperature cuprate superconductors, it is now generally agreed that
the parent compound is a Mott insulator and superconductivity is realized by
doping the antiferromagnetic Mott insulator. In the iron-based superconductors,
however, the parent compound is mostly antiferromagnetic metal, raising a
debate on whether an appropriate starting point should go with an itinerant
picture or a localized picture. It has been proposed theoretically that the
parent compound of the iron-based superconductors may be on the verge of a Mott
insulator, but so far no clear experimental evidence of doping-induced Mott
transition has been available. Here we report an electronic evidence of an
insulator-superconductor transition observed in the single-layer FeSe films
grown on the SrTiO3 substrate. By taking angle-resolved photoemission
measurements on the electronic structure and energy gap, we have identified a
clear evolution of an insulator to a superconductor with the increasing doping.
This observation represents the first example of an insulator-superconductor
transition via doping observed in the iron-based superconductors. It indicates
that the parent compound of the iron-based superconductors is in proximity of a
Mott insulator and strong electron correlation should be considered in
describing the iron-based superconductors.",1401.7115v1
2014-02-03,"Spin-density-wave-induced anomalies in the optical conductivity of AFe2As2, (A=Ca, Sr, Ba) single-crystalline iron pnictides","We report the complex dielectric function of high-quality
$A\textrm{Fe}_2\textrm{As}_2$, ($A$=Ca, Sr, Ba) single crystals with
$T_{\mathrm{N}}\approx150\ \textrm{K}$, $200\ \textrm{K}$, and $138\
\textrm{K}$, respectively, determined by broadband spectroscopic ellipsometry
at temperatures $10\leq T\leq300\ \textrm{K}$ and wavenumbers from $100\
\textrm{cm}^{-1}$ to $52000\ \textrm{cm}^{-1}$. In
$\textrm{CaFe}_2\textrm{As}_2$ we identify the optical spin-density--wave gap
$2\Delta_{\mathrm{SDW}}\approx1250\ \textrm{cm}^{-1}$. The
$2\Delta_{\mathrm{SDW}}/(k_{\mathrm{B}}T_{\mathrm{N}})$ ratio, characterizing
the strength of the electron-electron coupling in the spin-density--wave state,
amounts to $\approx12$ in $\textrm{CaFe}_2\textrm{As}_2$, significantly larger
than the corresponding values for the $\textrm{SrFe}_2\textrm{As}_2$ and
$\textrm{BaFe}_2\textrm{As}_2$ compounds: 8.7 and 5.3, respectively. We further
show that, similarly to the Ba-based compound, two characteristic SDW energy
gaps can be identified in the infrared-conductivity spectra of both
$\textrm{SrFe}_2\textrm{As}_2$ and $\textrm{CaFe}_2\textrm{As}_2$ and
investigate their detailed temperature dependence in all three materials. This
analysis reveals the existence of an anomaly in $\textrm{CaFe}_2\textrm{As}_2$
at a temperature $T^*\approx80\ \textrm{K}$, well below the N\'eel temperature
of this compound, which implies weak coupling between the two SDW subsystems.
The coupling between the two subsystems evolves to intermediate in the Sr-based
and strong in the Ba-based material. The temperature dependence of the infrared
phonons reveals clear anomalies at the corresponding N\'eel temperatures of the
investigated compounds. In $\textrm{CaFe}_2\textrm{As}_2$, the phonons exhibit
signatures of SDW fluctuations above $T_N$ and some evidence for anomalies at
$T^*$. (full abstract in PDF)",1402.0325v1
2014-03-26,Hybrid improper ferroelectricity in a Multiferroic and Magnetoelectric hybrid organic-inorganic perosvkite,"There is great interest in hybrid organic-inorganic materials such as
metal-organic frameworks (MOFs). The compounds
[C(NH$_{2}$)$_{3}$]M(HCOO)$_{3}$, where M=Cu$^{2+}$ or Cr$^{2+}$ are
Jahn-Teller (JT) active ions, are MOF with perovskite topology which
crystallizes in polar space group Pna2$_{1}$. In inorganic compounds,
octahedral tilting and Jahn-Teller structural distortions are usually non-polar
distortions. However, in this MOF cooperative interactions between the
antiferro-distortive distortions of the framework and the C(NH2)$_{3}$ organic
cation via hydrogen bonding breaks the inversion symmetry and induces a
ferroelectric polarization.[Angew. Chem. Int. Ed. 50, 5847, 2011] Our ab-initio
study supports the picture of an orbital-order-induced ferroelectricity, a rare
example of dipolar ordering caused by electronic degrees of freedom. The
switching of polarization direction implies the reversal of the weak
ferromagnetic component. The microscopic mechanism in this JT-based MOF with
ABX$_{3}$ perovskite structure displays a Hybrid Improper Ferroelectric (HIF)
state, arising from a trilinear coupling between different structural
deformations that comprise tilting, rotations and Jahn-Teller distortions of
both the BX$_{3}$ framework and the organic cation at the A sites. Since these
distortion modes in perovskite-inorganic compounds usually freeze-in at
elevated temperatures, the trilinear coupling in MOF compounds may provide an
interesting route towards high-temperature multiferroicity. These results offer
an important starting point for tailoring multiferroic properties in this
emerging class of materials for various technological applications. In
particular, the high tunability of the ferroelectric polarization by means of
the modification of the organic A cation has been recently shown[J. Am. Chem.
Soc. 135 18126 (2013)]",1403.6648v1
2014-03-27,Helical states and solitons in noncentrosymmetric superconductors,"We show how the two-band nature of superconductivity in noncentrosymmetric
compounds leads to a variety of novel nonuniform superconducting states induced
by a magnetic field. At low fields, a two-band helical state is realized, with
a distinctly non-BCS quasiparticle spectrum. At high fields, the
superconducting state becomes unstable towards the formation of a lattice of
topological phase solitons.",1403.7101v1
2014-05-30,Pressure induced ferroelastic phase transition in LuLiF4 compound,"The behavior of LuLiF4 sheelite (I41/a, Z = 4) under hydrostatic pressure was
investigated by means of the first principles calculations. The ferroelastic
phase transition from the tetragonal structure of LuLiF4 to fergusonite
structure (C12/c1, Z = 4) has been found at 10.5 GPa. It has been determined
that this is the second order phase transition.",1405.7852v1
2014-08-29,Anomalous change of the magnetic moment direction by hole doping in CeRu$_2$Al$_{10}$,"We present a detailed investigation of the hole (3\% Re) doping effect on the
polycrystalline CeRu$_{2}$Al$_{10}$ sample by magnetization, heat capacity,
resistivity, muon spin rotation ($\mu$SR), and neutron scattering (both elastic
and inelastic) measurements. CeRu$_2$Al$_{10}$ is an exceptional cerium
compound with an unusually high Neel temperature of 27 K. Here we study the
stability of the unusual magnetic order by means of controlled doping, and we
uncover further surprising attributes of this phase transition. The heat
capacity, resistivity and $\mu$SR measurements reveal an onset of magnetic
ordering below 23 K, while a broad peak at 31 K (i.e. above $T_N$), has been
observed in the temperature dependent susceptibility, indicating an opening of
a spin gap above $T_N$. Our important finding, from the neutron diffraction, is
that the compound orders antiferromagnetically with a propagation vector $\bf
k$ = (1 0 0) and the ordered state moment is 0.20(1)$\mu_B$ along the $b-$axis.
This is in sharp contrast to the undoped compound, which shows AFM ordering at
27 K with the ordered moment of 0.39(3)$\mu_B$ along the $c-$axis. Similar to
CeRu$_2$Al$_{10}$ our inelastic neutron scattering study on the Re doped shows
a sharp spin gap-type excitation near 8 meV at 5 K, but with slightly reduced
intensity compared to the undoped compound. Further the excitation broadens and
shifts to lower energy ($\le$ 4 meV) near 35 K. These results suggest that the
low temperature magnetic properties of the hole doped sample is governed by the
competition between the anisotropic hybridization effect and crystal field
anisotropy as observed in hole-doped CeOs$_2$Al$_{10}$.",1408.6989v1
2014-10-23,Do the short helices exist in the nematic TB phase?,"Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical
texture related to the formation of arrays of focal conic defects. Some of the
focal conics show submicron internal structure with 8 nm periodicity, which is
very close to that found in the crystalline phase of the material, suggesting
surface freezing.",1410.6369v1
2014-11-15,"Orbital-selective behavior in Y5Mo2O12 and (Cd,Zn)V2O4","We present two examples of the real materials, which show orbital-selective
behavior. In both compounds a part of the electrons is localized on the
molecular orbitals, which lead to a significant reduction of the magnetic
moment on the transition metal ion.",1411.4147v2
2014-11-30,Phase behaviors of binary mixtures composed of banana-shaped and calamitic mesogens,"In this work, five mixtures with different concentrations of banana-shaped
and calamitic compounds have been prepared and subsequently studied by
polarizing optical microscopy, differential scanning calorimetry, and X-ray
diffraction on non-oriented samples. The phase sequences and molecular
parameters of the binary systems are presented.",1412.0264v1
2014-12-07,Distribution of some functionals for a Lévy process with matrix-exponential jumps of the same sign,"This paper provides a framework for investigations in fluctuation theory for
L\'evy processes with matrix-exponential jumps. We present a matrix form of the
components of the infinitely divisible factorization. Using this representation
we establish generalizations of some results known for compound Poisson
processes with exponential jumps in one direction and generally distributed
jumps in the other direction.",1412.2353v1
2015-01-27,Superconductivity of magnesium diboride,"Over the past 14 years MgB2 has gone from a startling discovery to a
promising, applied superconductor. In this article we present a brief overview
of the synthesis and the basic superconducting properties of this remarkable
compound. In particular, the effects of pressure, substitutions and neutron
irradiation on superconducting properties are discussed.",1501.06948v1
2015-01-29,"Contrasting chemical pressure effect on the moment direction in the Kondo semiconductor CeT$_2$Al$_{10}$ (T = Ru,Os)","The opening of a spin gap in the orthorhombic compounds CeT$_2$Al$_{10}$ (T =
Ru and Os) is followed by antiferromagnetic ordering at $T_N$ = 27 K and 28.5
K, respectively, with a small ordered moment (0.29$-$0.34$\mu_B$) along the
$c-$axis, which is not an easy axis of the crystal field (CEF). In order to
investigate how the moment direction and the spin gap energy change with 10\%
La doping in Ce$_{1-x}$La$_x$T$_2$Al$_{10}$ (T = Ru and Os) and also to
understand the microscopic nature of the magnetic ground state, we here report
on magnetic, transport, and thermal properties, neutron diffraction (ND) and
inelastic neutron scattering (INS) investigations on these compounds. Our INS
study reveals the persistence of spin gaps of 7 meV and 10 meV in the 10\%
La-doped T = Ru and Os compounds, respectively. More interestingly our ND study
shows a very small ordered moment of 0.18 $\mu_B$ along the $b-$axis (moment
direction changed compared with the undoped compound), in
Ce$_{0.9}$La$_{0.1}$Ru$_2$Al$_{10}$, however a moment of 0.23 $\mu_B$ still
along the $c-$axis in Ce$_{0.9}$La$_{0.1}$Os$_2$Al$_{10}$. This contrasting
behavior can be explained by a different degree of hybridization in
CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$, being stronger in the latter than in
the former. Muon spin rotation ($\mu$SR) studies on
Ce$_{1-x}$La$_x$Ru$_2$Al$_{10}$ ($x$ = 0, 0.3, 0.5 and 0.7), reveal the
presence of coherent frequency oscillations indicating a long$-$range
magnetically ordered ground state for $x$ = 0 to 0.5, but an almost temperature
independent Kubo$-$Toyabe response between 45 mK and 4 K for $x$ = 0.7. We will
compare the results of the present investigations with those reported on the
electron and hole$-$doping in CeT$_2$Al$_{10}$.",1501.07497v1
2015-04-19,Characterizations and Infinite Divisibility of Extended COM-Poisson Distribution,"This article provides some characterizations of extended COM-Poisson
distribution: conditional distribution given the sum, functional operator
characterization (Stein identity). We also give some conditions such that the
extended COM-Poisson distribution is infinitely divisible, hence some subclass
of extended COM-Poisson distributions are discrete compound Poisson
distribution.",1504.05443v2
2015-05-07,Role of orbital degrees of freedom in investigating the magnetic properties of geometrically frustrated vanadium spinels,"The inconsistency about the degree of geometrical frustration has been a long
issue in AV$_{2}$O$_{4}$ (A $\equiv$ Zn, Cd and Mg) compounds, which arises
from the two experimental results: (i) frustration indices and (ii) magnetic
moments. In the present study, we try to understand such inconsistency by using
{\it ab initio} electronic structure calculations. The orbital degrees of
freedom are found to play an important role in understanding the geometrically
frustrated magnetic behaviour of these compounds. The inclusion of the orbital
and spin angular momenta for calculating the frustration indices improves the
understanding about the degree of geometrical frustration in these compounds.
The calculated values of the frustration indices ($f$$_{\it J}$) are largest
for MgV$_{2}$O$_{4}$ and smallest for CdV$_{2}$O$_{4}$ for 3.3$\leq$ $U
\leq$5.3 eV. In this range of $U$, the calculated values of
$\Delta$M$_{2}$=M$_{\rm total}$-M$_{\rm exp}$ are largest for MgV$_{2}$O$_{4}$
and smallest for CdV$_{2}$O$_{4}$. Hence, the consistency about the degree of
geometrical frustration is achieved. The absolute values of the nearest
neighbour exchange coupling constant ({\it J$_{nn}$}) between V spins are found
to be largest for MgV$_{2}$O$_{4}$ and smallest for CdV$_{2}$O$_{4}$, which
indicate that the calculated absolute values of the Curie-Weiss temperature
($\varTheta$$_{CW}$)$_{\it J}$ are highest for MgV$_{2}$O$_{4}$ and smallest
for CdV$_{2}$O$_{4}$ for 3.3$\leq$ $U \leq$5.3 eV. In this range of $U$, the
magnetic transition temperature ($T$$_{N}$)$_{\it J}$ is found to be $\sim$150
K, $\sim$60 K and $\sim$22 K for MgV$_{2}$O$_{4}$, ZnV$_{2}$O$_{4}$ and
CdV$_{2}$O$_{4}$, respectively, which shows that the order of ($T$$_{N}$)$_{\it
J}$ is similar to that of ($T$$_{N}$)$_{\rm exp}$ for these compounds.",1505.01601v2
2015-06-22,New class of compounds - variators - are reprogramming substrate specificity of H3K4me3 epigenetic marks reading PHD domain of BPTF protein,"In lymphoma, mutations in genes of histone modifying proteins are frequently
observed. Notably, somatic mutations in the activatory histone modification
writing protein MLL2 and the repressive modification writer EZH2 are the most
frequent. Gain of function mutations are typically detected in EZH2 whilst MLL2
mutations are usually observed as conferring a homozygous loss of function. The
gain-of-function mutations in EZH2 provide an obvious target for the
development of inhibitors with therapeutic potential. To counter the loss of
functional MLL2 protein, we computationally predicted compounds that are able
to modulate the reader of the corresponding modifications, BPTF, to recognize
other forms of the histone H3 lysine 4, instead of the tri-methylated form
normally produced by MLL2. By forming a synthetic triple-complex of a compound,
the histone H3 tail and BPTF we potentially circumvent the requirement for
functional MLL2 methyl-transferase through the modulation of BPTF activity.
Here we show a proof-of-principle that special compounds, named variators, can
reprogram selectivity of protein binding and thus create artificial regulatory
pathways which can have a potential therapeutic role. A therapeutic role of
BPTF variators may extend to other diseases that involve loss of MLL2 function,
such as Kabuki syndrome or the aberrant functioning of H3K4 modification as
observed in Huntington disease and in memory formation.",1506.06433v1
2015-06-30,Comments on the paper: Synthesis growth and characterization of copper mercury thiocyanate crystal [Indian J Pure & App Phys 49 (2011) 340-343],"The unit cell parameters, infrared and UV-Vis spectral data reported in the
paper by Vijayabhaskaran et al (Indian J Pure & App Phys 49 (2011) 340-343)
cannot belong to the colourless crystalline compound formulated as copper
mercury thiocyanate CuHg(SCN)4 as claimed by the authors.",1506.09087v1
2015-08-11,Modeling Intercalated Group-4-Metal Nitride Halide Superconductivity with Interlayer Coulomb Coupling,"Behavior consistent with Coulomb-mediated high-T$_C$ superconductivity is
shown to be present in the intercalated group-4-metal nitride halides
A$_x$(S)$_y$MNX, where the MNX host (M = Ti, Zr, Hf; X = Cl, Br) is partially
intercalated with cations A$_x$ and optionally molecular species (S)$_y$ in the
van der Waals gap between the halide X layers, expanding the basal-plane
spacing d. The optimal transition temperature is modeled by T$_{C0}$
${\propto}$ {\zeta}$^{-1}$({\sigma}/$A$)$^{1/2}$, where the participating
fractional charge per area per formula unit {\sigma}/$A$ and the distance
{\zeta}, given by the transverse A$_x$-X separation ({\zeta} < d), govern the
interlayer Coulomb coupling. From experiment results for {\beta}-form compounds
based on Zr and Hf, in which concentrations x of A$_x$ are varied, it is shown
that {\sigma} = {\gamma}[v(x$_{opt}$ $-$ x$_0$)], where x$_{opt}$ is the
optimal doping, x$_0$ is the onset of superconducting behavior, v is the A$_x$
charge state, and {\gamma} = 1/8 is a factor determined by the model.
Observations of T$_C$ < T$_{C0}$ in the comparatively more disordered
{\alpha}-A$_x$(S)$_y$TiNX compounds are modeled as pair-breaking by remote
Coulomb scattering from the A$_x$ cations, which attenuates exponentially with
increasing {\zeta}. The T$_{C0}$ values calculated for nine A$_x$(S)$_y$MNCl
compounds, shown to be optimal, agree with the measured T$_C$ to within
experimental error. The model for T$_{C0}$ is also found to be consistent with
the absence of high-T$_C$ characteristics for A$_x$MNX compounds in which a
spatially separated intercalation layer is not formed.",1508.02523v1
2015-10-26,"Machine Learning, Quantum Mechanics, and Chemical Compound Space","We review recent studies dealing with the generation of machine learning
models of molecular and solid properties. The models are trained and validated
using standard quantum chemistry results obtained for organic molecules and
materials selected from chemical space at random.",1510.07512v3
2016-01-13,On electrical conductivity of melts of boron and its compounds under pressure,"The electrical conductivity of melts of boron and its carbide (B4C), nitride
(BN), and phosphide (BP) has been studied at pressures to 7.7 GPa and
temperatures to 3500 K. It has been shown that these melts are good conductors
with specific electrical conductivity values comparable with that of iron melt
at ambient pressure.",1601.06828v1
2016-04-21,"Newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX phases: A first-principles study","The structural, elastic, and electronic properties of newly synthesized
Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates
have been studied using first-principles density functional theory (DFT)
calculations for the first time. Theoretical Vickers hardness has also been
estimated for these compounds. All the calculated results are compared with
experimental data and also with that of recently discovered Zr2AlC phase, where
available. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sn
containing MAX compounds. The calculated structural parameters are found to be
in good agreement with the experimental data. The single crystal elastic
constants Cij and other polycrystalline elastic coefficients have been
calculated and the mechanical stabilities of these compounds have been
theoretically confirmed. The bulk modulus increases and the shear modulus
decreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculated
elastic moduli show that these Bi/Sn/Sb containing MAX phases are more
anisotropic than Zr2AlC, and have a tendency towards ductility. The Vickers
hardness decreases in the Bi/Sn/Sb containing compounds. Further, the
electronic band structures and electronic density of states (EDOS) are
calculated and the effects of different elemental substitution on these
properties are investigated. The electronic band structures show metallic
characteristics with contribution predominantly coming from the Zr 4d orbitals.
Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level to
some extent. Possible implications of the theoretical results for these
recently discovered MAX nanolaminates have been discussed in detail in this
paper.",1604.06317v4
2016-05-13,"The role of ionic sizes in inducing the cubic to tetragonal distortion in AV$_{2}$O$_{4}$ and ACr$_{2}$O$_{4}$ (A=Zn, Mg and Cd) compounds","Cubic to tetragonal distortion in spinel compounds have been a contentious
issue for last two decades. Different groups have proposed different mechanisms
to understand such a distortion in these spinels, which are: (i) spin lattice
coupling mechanism known as the spin driven Jahn-Teller (JT) effect, (ii) the
strong relativistic spin-orbit coupling, a moderate JT distortion and weak V-V
interactions and (iii) the JT effect. Now, in order to know the possible cause
for such a distortion, we have avoided these complexities (various interactions
among spin, electronic, orbital and lattice degrees of freedom) by carrying out
spin unpolarized calculations. The calculated values of bulk moduli for
ZnV$_{2}$O$_{4}$ (ZnCr$_{2}$O$_{4}$), MgV$_{2}$O$_{4}$ (MgCr$_{2}$O$_{4}$) and
CdV$_{2}$O$_{4}$ (CdCr$_{2}$O$_{4}$) are found to be $\sim$289 ($\sim$254),
$\sim$244 ($\sim$243) and $\sim$230 ($\sim$233) GPa, respectively. For
vanadates and chromates, the order of calculated values of lattice parameter
$a$ are found to CdV$_{2}$O$_{4}$$>$MgV$_{2}$O$_{4}$$>$ZnV$_{2}$O$_{4}$ and
CdCr$_{2}$O$_{4}$$>$MgCr$_{2}$O$_{4}$$>$ZnCr$_{2}$O$_{4}$, respectively and are
consistent with the experimental results. The calculated values of cubic to
tetragonal distortion (c/a), with c/a$<$1 for ZnV$_{2}$O$_{4}$
(ZnCr$_{2}$O$_{4}$), MgV$_{2}$O$_{4}$ (MgCr$_{2}$O$_{4}$) and CdV$_{2}$O$_{4}$
(CdCr$_{2}$O$_{4}$) are $\sim$0.996 ($\sim$0.997), $\sim$0.995 ($\sim$0.994)
and $\sim$0.997 ($\sim$0.998), respectively. These values are in good agreement
with the experimental data for ZnV$_{2}$O$_{4}$, MgV$_{2}$O$_{4}$,
ZnCr$_{2}$O$_{4}$ and MgCr$_{2}$O$_{4}$ compounds. The present study clearly
shows the role of ionic sizes in inducing the cubic to tetragonal distortion in
these spinels. These mechanisms also appear to be responsible for deciding the
other physical properties of these compounds.",1605.04152v2
2016-05-17,Structural and magnetic study of PrMn$_{1-x}$Fe$_x$O$_3$ $(0 \leq x \leq 1)$ compounds,"The structural and magnetic study of PrMn1-xFexO3(0 <= x <= 1) substitutional
orthorhombical system, was performed on polycrystalline (x <= 0.5) as well as
on the single crystalline (0.5 <= x <= 1) samples.",1605.05128v2
2016-05-24,A note on Malliavin smoothness on the Lévy space,"We consider Malliavin calculus based on the It\^o chaos decomposition of
square integrable random variables on the L\'evy space. We show that when a
random variable satisfies a certain measurability condition, its
differentiability and fractional differentiability can be determined by
weighted Lebesgue spaces. The measurability condition is satisfied for all
random variables if the underlying L\'evy process is a compound Poisson process
on a finite time interval.",1605.07413v1
2016-07-25,"Constrained DFT+$U$ approach for understanding the magnetic behaviour of ACr$_{2}$O$_{4}$ (A=Zn, Mg, Cd and Hg) compounds","In this work, we try to understand the inconsistency reported by [Yaresko,
Phys. Rev. B. {\bf 77}, 115106 (2008)] in the theoretically estimated nature
and the variation of magnitude of nearest neighbour exchange coupling constant
($\arrowvert${\it J$_{1}$}$\arrowvert$) with increasing $U$ in ACr$_{2}$O$_{4}$
(A=Zn, Cd, Mg and Hg) compounds by using density functional theory. In
unconstrained calculations, the nature and variation of $\arrowvert${\it
J$_{1}$}$\arrowvert$ as a function of $U$ in the present study are not
consistent with the experimental data and not according to the relation, {\it
J$_{1}$}$\propto$$\frac{t^{2}}{U}$ especially for CdCr$_{2}$O$_{4}$ and
HgCr$_{2}$O$_{4}$ for $U >$3 eV and U=2-6 eV, respectively. Such an
inconsistent behavior of $\arrowvert${\it J$_{1}$}$\arrowvert$ is almost
similar to that of Yaresko for these two compounds for $U$=2-4 eV. For
ZnCr$_{2}$O$_{4}$ and MgCr$_{2}$O$_{4}$, the nature and the variation of
$\arrowvert${\it J$_{1}$}$\arrowvert$ in the present work are in accordance
with the experimental data and above mentioned relation for $U$=2-6 eV and are
similar to that of Yaresko for ZnCr$_{2}$O$_{4}$ for $U$=2-4 eV. However, in
constrained calculations the nature and variation of $\arrowvert${\it
J$_{1}$}$_{c}$$\arrowvert$ in the present work are according to experimental
data and above above mentioned relation for all four compounds. Hence, the
present study shows the importance of constrained calculations in understanding
the magnetic behaviour of these spinels. The values of magnitude of Curie-Weiss
temperature [$\arrowvert$($\varTheta$$_{CW}$)$_{c}$$\arrowvert$] for
ZnCr$_{2}$O$_{4}$$>$MgCr$_{2}$O$_{4}$$>$CdCr$_{2}$O$_{4}$$>$HgCr$_{2}$O$_{4}$
for $U$=2-5 eV, which are according to the order of experimentally observed
values for these spinels.",1607.07225v1
2016-11-08,Polaron model of pseudogap state in quasi-one-dimentional systems,"A brief overview of the basic concepts and problems of the physics of
quasi-one-dimensional compounds is done. Consistent theoretical description of
the so-called pseudogap state remains the main problem. A simplified model of
the pseudogap state, based on the picture of small polarons formation in the
framework of cluster perturbation theory is considered.",1611.02544v1
2017-08-18,Real-space investigation of short-range magnetic correlations in fluoride pyrochlores NaCaCo$_2$F$_7$ and NaSrCo$_2$F$_7$ with magnetic pair distribution function analysis,"We present time-of-flight neutron total scattering and polarized neutron
scattering measurements of the magnetically frustrated compounds
NaCaCo$_2$F$_7$ and NaSrCo$_2$F$_7$, which belong to a class of recently
discovered pyrochlore compounds based on transition metals and fluorine. The
magnetic pair distribution function (mPDF) technique is used to analyze and
model the total scattering data in real space. We find that a
previously-proposed model of short-range XY-like correlations with a length
scale of 10-15 \AA, combined with nearest-neighbor collinear antiferromagnetic
correlations, accurately describes the mPDF data at low temperature, confirming
the magnetic ground state in these materials. This model is further verified by
the polarized neutron scattering data. From an analysis of the temperature
dependence of the mPDF and polarized neutron scattering data, we find that
short-range correlations persist on the nearest-neighbor length scale up to 200
K, approximately two orders of magnitude higher than the spin freezing
temperatures of these compounds. These results highlight the opportunity
presented by these new pyrochlore compounds to study the effects of geometric
frustration at relatively high temperatures, while also advancing the mPDF
technique and providing a novel opportunity to investigate a genuinely
short-range-ordered magnetic ground state directly in real space.",1708.05527v3
2017-08-25,Exotic Bifurcations Inspired by Walking Droplet Dynamics,"We identify two rather novel types of (compound) dynamical bifurcations
generated primarily by interactions of an invariant attracting submanifold with
stable and unstable manifolds of hyperbolic fixed points. These bifurcation
types - inspired by recent investigations of mathematical models for walking
droplet (pilot-wave) phenomena - are introduced and illustrated. Some of the
one-parameter bifurcation types are analyzed in detail and extended from the
plane to higher-dimensional spaces. A few applications to walking droplet
dynamics are analyzed.",1708.07593v1
2017-08-29,On the time of first level crossing and inverse Gaussian distribution,"We propose a new approximation for the distribution of the time of the first
level $u$ crossing by the random process $\homV{s}-cs$, where $\homV{s}$,
$s>0$, is compound renewal process and $c>0$. It is competitive with respect to
existing approximations, particularly in the region around the critical point
$c=\cS$ which separates processes with positive and negative drifts. This
approximation is tightly related to inverse Gaussian distributions.",1708.08665v1
2017-08-29,Generalized inverse Gaussian distributions and the time of first level crossing,"We propose a new approximation for the distribution of the time of the first
crossing of a high level $u$ by random process $\homV{s}-cs$, where $\homV{s}$,
$s>0$, is compound renewal process and $c>0$. It significantly outperforms the
existing approximations, particularly in the region around the critical point
$c=\cS$ which separates processes with positive and negative drifts. This
approximation is tightly related to generalized inverse Gaussian distributions.",1708.08671v1
2017-09-04,Local dependencies in random fields via a Bonferroni-type inequality,"We provide an inequality which is a useful tool in studying both large
deviation results and limit theorems for sums of random fields with
""negligible"" small values. In particular, the inequality covers cases of stable
limits for random variables with heavy tails and compound Poisson limits of
$0-1$ random variables.",1709.01165v1
2017-11-17,Metal-insulator transition in copper oxides induced by apex displacements,"High temperature superconductivity has been found in many kinds of compounds
built from planes of Cu and O, separated by spacer layers. Understanding why
critical temperatures are so high has been the subject of numerous
investigations and extensive controversy. To realize high temperature
superconductivity, parent compounds are either hole-doped, such as
{La$_{2}$CuO$_4$} (LCO) with Sr (LSCO), or electron doped, such as
{Nd$_{2}$CuO$_4$} (NCO) with Ce (NCCO). In the electron doped cuprates, the
antiferromagnetic phase is much more robust than the superconducting phase.
However, it was recently found that the reduction of residual out-of-plane
apical oxygens dramatically affects the phase diagram, driving those compounds
to a superconducting phase. Here we use a recently developed first principles
method to explore how displacement of the apical oxygen (A-O) in LCO affects
the optical gap, spin and charge susceptibilities, and superconducting order
parameter. By combining quasiparticle self-consistent GW (QS\emph{GW}) and
dynamical mean field theory (DMFT), that LCO is a Mott insulator; but small
displacements of the apical oxygens drive the compound to a metallic state
through a localization/delocalization transition, with a concomitant maximum
$d$-wave order parameter at the transition. We address the question whether NCO
can be seen as the limit of LCO with large apical displacements, and elucidate
the deep physical reasons why the behaviour of NCO is so different than the
hole doped materials. We shed new light on the recent correlation observed
between T$_c$ and the charge transfer gap, while also providing a guide towards
the design of optimized high-Tc superconductors. Further our results suggest
that strong correlation, enough to induce Mott gap, may not be a prerequisite
for high-Tc superconductivity.",1711.06651v1
2018-03-01,Conductance relaxation in GeBiTe - slow thermalization in an open quantum system,"This work describes the microstructure and transport properties of GeBiTe
films with emphasis on their out-of-equilibrium behavior.
Persistent-photoconductivity (PPC), previously studied in the phase-change
compound GeSbTe is also quite prominent in this system. Much weaker PPC
response is observed in the pure GeTe compound and when alloying GeTe with
either In or Mn. Films made from these compounds share the same
crystallographic structure, the same p-type conductivity, a similar
compositional disorder extending over mesoscopic scales, and similar mosaic
morphology. The enhanced PPC response exhibited by the Sb and Bi alloys may
therefore be related to their common chemistry. PPC is observable in GeBiTe
films at the entire range of sheet resistances studied in this work. The excess
conductance produced by a brief exposure to infrared illumination decays with
time as a stretched-exponential (Kohlrausch law). Intrinsic electron-glass
effects on the other hand, are observable in thin films of GeBiTe only for
samples that are strongly-localized just like it was noted with the seven
electron-glasses previously studied. These include a memory-dip which is the
defining attribute of the phenomenon. The memory-dip in GeBiTe is the widest
among the germanium-telluride alloys studied to date consistent with the high
carrier-concentration of this compound. The thermalization process exhibited in
either, the PPC-state or in the electron-glass regime is sluggish but the
temporal law of the relaxation from the out-of-equilibrium state is distinctly
different. Coexistence of the two phenomena give rise to some non-trivial
effects, in particular, the visibility of the memory-dip is enhanced in the
PPC-state. The relation between this effect and the dependence of the
memory-effect magnitude on the ratio between the interparticle-interaction and
quench-disorder is discussed.",1803.00564v1
2018-03-20,"Uncovering the Origin of Divergence in the CsM(CrO$_4$)$_2$ (M = La, Pr, Nd, Sm, Eu; Am) Family through Examination of the Chemical Bonding in a Molecular Cluster and by Band Structure Analysis","A series of f-block chromates, CsM(CrO$_4$)$_2$ (M = La, Pr, Nd, Sm, Eu; Am),
were prepared revealing notable differences between the AmIII derivatives and
their lanthanide analogs. While all compounds form similar layered structures,
the americium compound exhibits polymorphism and adopts both a structure
isomorphous with the early lanthanides as well as one that possesses lower
symmetry. Both polymorphs are dark red and possess band gaps that are smaller
than the LnIII compounds. In order to probe the origin of these differences,
the electronic structure of $\alpha$-CsSm(CrO$_4$)$_2$,
$\alpha$-CsEu(CrO$_4$)$_2$ and $\alpha$-CsAm(CrO$_4$)$_2$ were studied using
both a molecular cluster approach featuring hybrid density functional theory
and QTAIM analysis, and by the periodic LDA+GA and LDA+DMFT methods. Notably,
the covalent contributions to bonding by the f orbitals was found to be more
than twice as large in the AmIII chromate than in the SmIII and EuIII
compounds, and even larger in magnitude than the Am-5f spin-orbit splitting in
this system. Our analysis indicates also that the Am-O covalency in
$\alpha$-CsAm(CrO$_4$)$_2$ is driven by the degeneracy of the 5f and 2p
orbitals, and not by orbital overlap.",1803.07370v1
2018-05-31,Recent progress on the characterization of the high-pressure behaviour of AVO4 orthovanadates,"AVO4 vanadates are materials of technological importance due to their variety
of functional properties. They have applications as scintillators,
thermophosphors, photocatalysts, cathodoluminescence, and laser-host materials.
Studies at HP-HT are helpful for understanding the physical properties of the
solid state, in special, the phase behavior of AVO4 materials. For instance,
they have contributed to understand the macroscopic properties of vanadates in
terms of microscopic mechanisms. A great progress has been made in the last
decade towards the study of the pressure-effects on the structural,
vibrational, and electronic properties of AVO4 compounds. Thanks to the
combination of experimental and theoretical studies, novel metastable phases
with interesting physical properties have been discovered and the HP structural
sequence followed by AVO4 oxides has been understood. Here, we will review HP
studies carried out on the phase behavior of different AVO4 compounds. The
studied materials include rare-earth vanadates and other compounds; for
example, BiVO4, FeVO4, CrVO4, and InVO4. In particular, we will focus on
discussing the results obtained by different research groups, who have
extensively studied vanadates up to pressures exceeding 50 GPa. We will make a
systematic presentation and discussion of the results reported in the
literature. In addition, with the aim of contributing to the improvement of the
actual understanding of the high-pressure properties of ternary oxides, the HP
behavior of vanadates will be compared with related compounds; including
phosphates, chromates, and arsenates. The behavior of nanomaterials under
compression will also be briefly described and compared with their bulk
counterpart. Finally, the implications of the reported studies on technological
developments and geophysics will be commented and possible directions for the
future studies will be proposed.",1805.12418v1
2018-05-31,Observation of Meisser effect in Kapton Tapes,"Composed of organic compounds, Kapton tape is regularly used as a
non-conducting and non-magnetic material in cryogenic experiments. Here we
report the discovery of Meisser effect at transition temperature (Tc) of ~ 3.8
K and ~ 8.0 K in Kapton tapes. New organic superconducting materials may be
further explored in the tapes.",1805.12458v1
2019-11-20,"Tunable large spin Hall and spin Nernst effects in Dirac semimetals ZrXY (X=Si, Ge; Y=S, Se, Te)","The ZrSiS-type compounds are Dirac semimetals and have been attracting
considerable interest in recent years due to their topological electronic
properties and possible applications. In particular, gapped Dirac nodes can
possess large spin Berry curvatures and thus give rise to large spin Hall
effect (SHE) and spin Nernst effect (SNE), which may be used to generate pure
spin current for spintronics and spin caloritronics without applied magnetic
field or magnetic material. In this paper we study both SHE and SNE in ZrXY (X
= Si, Ge; Y = S, Se, Te) based on \textit{ab initio} relativistic band
structure calculations. Our theoretical calculations reveal that some of these
compounds exhibit large intrinsic spin Hall conductivity (SHC) and spin Nernst
conductivity (SNC). The calculated SHC of ZrSiTe is as large as -755
($\hbar$/e)(S/cm). Since the electric conductivity of these Dirac semimetals
are much smaller than that of platinum which has the largest intrinsic SHC of
$\sim$2200 ($\hbar$/e)(S/cm), this indicates that they will have a larger spin
Hall angle than that of platinum. Remarkably, we find that both the magnitude
and sign of the SHE and SNE in these compounds can be significantly tuned by
changing either the electric field direction or spin current direction and may
also be optimized by slightly varying the Fermi level via chemical doping.
Analysis of the calculated band- and $k$-resolved spin Berry curvatures show
that the large SHE and SNE as well as their remarkable tunabilities originate
from the presence of many slightly spin-orbit coupling-gapped Dirac nodal lines
near the Fermi level in these Dirac semimetals. Our findings suggest that the
ZrSiS-type compounds are promising candidates for spintronic and spin
caloritronic devices, and will certainly stimulate further experiments on these
Dirac semimetals.",1911.08902v1
2019-12-29,The Algebraic Theory of Fractional Jumps,"In this paper we start by briefly surveying the theory of Fractional Jumps
and transitive projective maps. Then, we give an efficient construction of a
fractional jump of a projective map and we extend the compound generator
construction for the Inversive Congruential Generator to Fractional jump
sequences. In addition, we provide new results on the absolute jump index, on
projectively primitive polynomials, and on the explicit description of
fractional jump generators.",2001.00474v1
2017-04-23,"Moments of inverses of $(m,n,β)$-Laguerre matrices","Wishart matrices are one of the fundamental matrix models in multivariate
statistics. We consider the classical $(m,n,\beta)$-Laguerre ensemble and give
a necessary and sufficient condition for finite moments for the inverse of
$(m,n,\beta)$-Laguerre matrices to exist. We extend the result to inverse
compound Wishart matrices for the values of $\beta = 1$ and $2$. Our result
complements the result by Letac and Massam [6], Matsumoto [7] and Collins et
al. [1].",1704.06878v1
2017-05-03,Changes in charge density vs changes in formal oxidation states: The case of Sn halide perovskites and their ordered vacancy analogues,"Shifting the Fermi energy in solids by doping, defect formation or gating
generally results in changes in the charge density distribution, which reflect
the ability of the bonding pattern in solids to adjust to such external
perturbations. In the ionic limit, such changes are described by the formal
oxidation states (FOS) whereby a single atom type is presumed to absorb the
full burden of the perturbation (change in charge) of the whole compound. In
this picture, when the solar absorber CsSnI3 loses 50 % of its Sn atoms thereby
forming the ordered vacancy compound Cs2SnI6, the Sn is said to change from
Sn2+ to Sn4+. In reality, the charge redistribution is more complex. To
understand the electronic properties of these two groups and to gauge the
trends in s-electron charge on the nucleus, we studied the 113/216 compound
pairs CsSnCl3/Cs2SnCl6; CsSnBr3/Cs2SnBr6, and CsSnI3/Cs2SnI6. We have
calculated the electronic structure of these three compound pairs,
complementing them by CsSnF3/Cs2SnF6 in the hypothetical cubic structure for
completing the chemical trends. These materials were also synthesized by
chemical routes and characterized by X-ray diffraction, Mossbauer spectroscopy
and K-edge X-ray Absorption Spectroscopy. We find that in going from 113 to 216
there is a decrease in the s charge on Sn, in agreement with the FOS picture.
However, at the same time, we observe an increase of the p charge via downshift
of the otherwise unoccupied p level, an effect that tends to replenish much of
the lost s charge. This effect is theoretically explained as a self-regulating
response [H. Raebiger, S. Lany, and A. Zunger, Nature 453, 763 (2008)] whereby
the system re-hybridizes to minimize the effect of the charge perturbation
created by vacancy formation. Our work clarifies the relation between FOS and
charge transfer that can be applied to a wide variety of materials.",1705.01565v2
2019-07-15,"Compound TCP with Random Early Detection (RED): stability, bifurcation and performance analyses","The problem of increased queueing delays in the Internet motivates the study
of currently implemented transport protocols and active queue management (AQM)
policies. We study Compound TCP (default protocol in Windows) with Random Early
Detection (RED). RED uses an exponentially weighted moving average of the queue
size to make packet-dropping decisions, aiming to control the queue size. One
must study RED with current protocols in order to explore its viability in the
context of increased queueing delays.
  We derive a non-linear time-delayed model for Compound TCP-RED. We derive a
sufficient condition for local stability of this model, and examine the impact
of (i) round-trip time (RTT) of the TCP flows, (ii) queue averaging parameter
and (iii) packet-dropping thresholds. Further, we establish that the system
undergoes a Hopf bifurcation as any of the above parameters is varied. This
suggests the emergence of limit cycles in the queue size, which may lead to
synchronisation of TCP flows and loss of link utilisation. Next, we study a
regime where queue size averaging is not performed, and packet-dropping
decisions are based on instantaneous queue size. In this regime, we derive the
necessary and sufficient condition for local stability. A comparison of the
stability results for Compound TCP-RED in the two regimes--with and without
queue size averaging--reveals that averaging may not be beneficial to system
stability. Packet-level simulations show that the queue size indeed exhibits
limit cycle oscillations as system parameters are varied. We then outline a
simple threshold-based queue policy, that could ensure stable low-latency
operation. We show that the threshold policy outperforms RED in terms of
queueing delay, flow completion time and packet loss. We highlight that the
threshold-based policy could mitigate the issue of increased queueing delays in
the Internet.",1907.06302v1
2019-10-05,The impact of pressure on the critical miscibility of nitro compounds and n-alkanes mixtures,"The impact of pressure on the critical consolute temperature in nitrobenzene,
nitrotoluene, and nitropropane plus n-alkanes from pentane to eicosane is
discussed.",1910.02309v1
2014-06-11,An R Implementation of the Polya-Aeppli Distribution,"An efficient implementation of the Polya-Aeppli, or geometirc compound
Poisson, distribution in the statistical programming language R is presented.
The implementation is available as the package polyaAeppli and consists of
functions for the mass function, cumulative distribution function, quantile
function and random variate generation with those parameters conventionally
provided for standard univatiate probability distributions in the stats package
in R",1406.2780v1
2018-12-27,Identifiability of parametric random matrix models,"We investigate parameter identifiability of spectral distributions of random
matrices. In particular, we treat compound Wishart type and signal-plus-noise
type. We show that each model is identifiable up to some kind of rotation of
parameter space. Our method is based on free probability theory.",1812.10678v1
2019-01-31,Riconoscimento ortografico per apostrofo ed espressioni polirematiche,"The work presents two algorithms of manipulation and comparison between
strings whose purpose is the orthographic recognition of the apostrophe and of
the compound expressions. The theory supporting general reasoning refers to the
basic concept of EditDistance, the improvements that ensure the achievement of
the objective are achieved with the aid of tools borrowed from the use of
techniques for processing large amounts of data on distributed platforms.",1902.00555v1
2019-06-18,Origins Vs. fingerprints of the Jahn-Teller effect in d-electron ABX$_3$ perovskites,"The Jahn-Teller (JT) distortion that can remove electronic degeneracies in
partially occupied states and results in systematic atomic displacements is a
common underlying feature to many of the intriguing phenomena observed in 3d
perovskites, encompassing magnetism, superconductivity, orbital ordering and
colossal magnetoresistance. Although the seminal Jahn and Teller theorem has
been postulated almost a century ago, the origins of this effect in perovskite
materials are still debated, including propositions such as super exchange,
spin-phonon coupling, sterically induced lattice distortions, and strong
dynamical correlation effects. Here we analyze the driving forces behind the
Jahn-Teller motions and associated electronic fingerprints in a full range of
ABX3 compounds. We identify (i) compounds that are prone to an
electronically-driven instabilities (i.e. a pure JT effect) such as KCrF3,
KCuF3 or LaVO3 and proceed to relax the structures, finding quantitatively the
JTD in excellent agreement with experiment; (ii) compounds such as LaMnO3 or
LaTiO3 that do not show electronically driven JTD despite orbital degeneracies,
because their strongly hybridized B, d-X, p states supply but too weak JT
forces to overcome the needed atomic distortions; (iii) although LaVO3 exhibits
similar B, d-X, p hybridizations as LaTiO3, the former compound exhibits a
robust electronic instability while LaTiO3 has zero stabilization energy, the
reason being that LaVO3 has two electrons t2g2 relative to LaTiO3 with just one
t2g1. (iv) We explain the trends in ""orbital ordering"" whereby electrons occupy
orbitals that point to orthogonal directions between all nearest-neighbor 3d
atoms. We thereby provide a unified vision to explain octahedra deformations in
perovskites that, at odds with common wisdom, does not require the celebrated
Mott-Hubbard mechanism.",1906.07587v2
2019-06-25,On a limit theorem for a non-linear scaling,"In this note, we proved that weak limits, of sums of independent positive
identically distributed random variables which are re-normalized by a
non-linear shrinking transform $\max(0, x-r)$, are either degenerate or (some)
compound Poisson distributions.",1906.10522v4
2020-04-14,"Magnetism, quantum criticality, and metal-insulator transitions in $R\mathrm{B}_{12}$","The physical properties of rare-earth (RE) dodecaborides, characterized by a
cage-glass crystal structure with loosely bound RE ions, are reviewed. These
compounds are strongly correlated electron systems with simultaneously active
charge, spin, orbital, and lattice degrees of freedom, which explains the
complexity of all $R\mathrm{B}_{12}$ compounds including antiferromagnetic
(TbB$_{12}$-TmB$_{12}$) and nonmagnetic (LuB$_{12}$) metals, on one side, and
the so-called Kondo insulator compound YbB$_{12}$ and Yb-based
Yb$_{x}R_{1-x}$B$_{12}$ solid solutions, on the other. The development of the
cooperative dynamic Jahn-Teller instability of the covalent boron network
produces trigonal and tetragonal distortions of the rigid cage and results in
the symmetry lowering of the fcc lattice in the dodecaborides. The
ferrodistortive dynamics in the boron sub-lattice generates both the collective
modes and quasilocal vibrations (rattling modes) of the heavy RE ions, causing
a modulation in the charge-carrier density and the emergence of dynamic charge
stripes. We consider their manifestations both in the properties of the
nonmagnetic reference compound LuB$_{12}$ and in the phase diagrams of the
$R\mathrm{B}_{12}$ antiferromagnets that exhibit multiple magnetic phases with
anisotropic field-angular phase diagrams in the form of the Maltese cross. We
also discuss the metal-insulator transitions in YbB$_{12}$ and Yb-based
dodecaborides in terms of the instability of the Yb 4$f$-electron
configuration, which appears in addition to the Jahn-Teller instability of the
boron cage, providing one more mechanism of the charge and spin fluctuations.
The experimental results challenge the established Kondo-insulator scenario in
YbB$_{12}$, providing arguments in favor of the appearance of Yb-Yb
vibrationally coupled pairs which should be considered as the main factor
responsible for the charge- and spin-gap formation.",2004.06371v1
2020-04-22,Light nuclei in the hadron resonance gas,"The description of the production of light (anti-)(hyper-)nuclei in a hadron
resonance gas, or statistical-thermal model approach, has proven to be rather
successful, despite the fact that the binding energies of these compound
objects are small compared to the emitting fireball temperature. We summarise
some recent developments and findings in this approach.",2004.10544v1
2020-04-23,Effective point-charge analysis of crystal electric fields -- application to rare-earth pyrochlores and tripod kagome magnets R3Mg2Sb3O14,"An indispensable step to understand collective magnetic phenomena in
rare-earth compounds is the determination of spatially-anisotropic single-ion
properties resulting from spin-orbit coupling and crystal field (CF). The CF
Hamiltonian has a discrete energy spectrum -- accessible to spectroscopic
probes such as neutron scattering -- controlled by a number of independent
parameters reflecting the point-symmetry of the magnetic sites. Determining
these parameters in low-symmetry systems is often challenging. Here, we
describe a general method to analyze CF excitation spectra using adjustable
effective point-charges. We benchmark our method to existing neutron-scattering
measurements on pyrochlore rare-earth oxides and obtain a universal
point-charge model that describes a large family of related materials. We adapt
this model to the newly discovered tripod Kagome magnets
($R_{3}$Mg$_2$Sb$_{3}$O$_{14}$, $R$ = Tb, Ho, Er, Yb) for which we report
broadband inelastic neutron-scattering spectra. Analysis of these data using
adjustable point-charges yields the CF wave-functions for each compound. From
this, we calculate thermomagnetic properties that accurately reflect our
measurements on powder samples, and predict the effective gyromagnetic tensor
for pseudo-spin degrees of freedom -- a crucial step to understand the exotic
collective properties of these kagome magnets at low temperature. We present
further applications of our method to other tripod kagome materials and
triangular rare-earth compounds $R$MgGaO$_4$ ($R$ =Yb, Tm). Overall, this study
establishes a widely applicable methodology to predict CF and single-ion
properties of rare-earth compounds based on interpretable and adjustable models
of effective point-charges.",2004.10957v3
2020-08-04,"On the complexity of graphs (networks) by information content, and conditional (mutual) information given other graphs","This report concerns the information content of a graph, optionally
conditional on one or more background, ""common knowledge"" graphs. It describes
an algorithm to estimate this information content, and includes some examples
based on chemical compounds.",2008.04744v1
2021-03-31,A lockdown survey on cDV singularities,"This is an expository survey article on compound Du Val (cDV) singularities,
with emphasis on recent homological approaches, including: noncommutative
resolutions, tilting theory, contraction algebras, classification, derived
categories, autoequivalences, stability conditions, deformation theory, and
cluster tilting theory.",2103.16990v2
2022-03-06,The odderon discovery by the D0 and TOTEM collaborations,"We describe the discovery of the colorless $C$-odd gluonic compound, the
odderon, by the D0 and TOTEM Collaborations by comparing elastic differential
cross sections measured in $pp$ and $p \bar{p}$ interactions at high energies.",2203.02931v1
2022-03-30,Comparative studies on unconventional superconductivity in Cr$_3$Ru compounds with bcc and A15 structures,"Chromium (Cr) is a transition metal element with 3$d$ orbital electrons. In
most compounds containing Cr, due to the correlation effect, twofold features
of localization and itinerancy are expected. The localization gives rise to a
magnetic moment, while the latter exhibits as the effective coherent weight for
conductivity. Here we report the physical properties of Cr$_3$Ru compounds with
bcc or A15 phases by using multiple experimental tools. The resistivity
measurements show sharp superconducting transitions at $T_{\rm c}$ = 2.77 K and
$T_{\rm c}$ = 3.37 K for the bcc and A15 structures. A high residual
resistivity exists for both samples with the mean-free-path about 2 nm.
Magnetization measurements also show rather narrow transitions, with a clear
hump structure at high temperatures around 150 K, which may be ascribed to the
remaining antiferromagnetic spin fluctuations. The specific heat coefficient
reveals a clear jump at $T_{\rm c}$. We find that s-wave gaps can be adopted to
fit the low temperature specific heat data yielding ratios of about
$2\Delta/k_{\scriptscriptstyle B}T_{\rm c}$ $\approx$ 3.6, indicating a
moderate pairing strength. Interestingly, the Wilson ratios are 3.81 and 3.62
for the bcc and A15 phases, suggesting a moderate correlation effect of
conducting electron in the normal state. Besides, for samples with A15
structure, another specific heat anomaly occurs at about 0.85 K and is
sensitive to magnetic fields. By applying high pressures, both system exhibit
an enhancement of $T_{\rm c}$ with a rate of about 0.019 K/GPa and 0.013 K/GPa
for the bcc and A15 phases. We also conduct tunneling spectrum measurements and
found that the coherence peaks are strongly smeared out. The strong suppression
to the coherence peaks may be ascribed to the strong scattering. Our
combinatory results point to an unconventional superconductivity in these Cr
based compounds.",2203.16235v1
2016-03-18,Emotion Classification from Noisy Speech - A Deep Learning Approach,"This paper investigates the performance of Deep Learning for speech emotion
classification when the speech is compounded with noise. It reports on the
classification accuracy and concludes with the future directions for achieving
greater robustness for emotion recognition from noisy speech.",1603.05901v3
2016-12-21,Phase stability and large in-plane resistivity in the 112-type iron-based superconductor Ca$_{1-x}$La$_{x}$FeAs$_{2}$,"The recently discovered high-T$_c$ superconductor
Ca$_{1-x}$La$_{x}$FeAs$_{2}$ is a unique compound not only because of its low
symmetry crystal structure, but also because of its electronic structure which
hosts Dirac-like metallic bands resulting from (spacer) zig-zag As chains. We
present a comprehensive first principles theoretical study of the electronic
and crystal structures of Ca$_{1-x}$La$_{x}$FeAs$_{2}$. After discussing the
connection between the crystal structure of the 112 family, which
Ca$_{1-x}$La$_{x}$FeAs$_{2}$ is a member of, with the other known structures of
Fe pnictide superconductors, we check the thermodynamic phase stability of
CaFeAs$_{2}$, and similar hyphothetical compounds SrFeAs$_{2}$ and BaFeAs$_{2}$
which, we find, are slightly higher in energy. We calculate the optical
conductivity of Ca$_{1-x}$La$_{x}$FeAs$_{2}$ using the DFT + DMFT method, and
predict a large in-plane resistivity anisotropy in the normal phase, which does
not originate from electronic nematicity, but is enhanced by the electronic
correlations. In particular, we predict a 0.34 eV peak in the $yy$ component of
the optical conductivity of the 30\% La doped compound, which correponds to
coherent interband transitions within a fast-dispersing band arising from the
zig-zag As-chains which are unique to this compound. We also study the Landau
free energy for Ca$_{1-x}$La$_{x}$FeAs$_{2}$ including the order parameter
relevant for the nematic transition and find that the free energy does not have
any extra terms that could induce ferro-orbital order. This explains why the
presence of As chains does not broaden the nematic transition in
Ca$_{1-x}$La$_{x}$FeAs$_{2}$.",1612.06964v1
2016-12-28,Using TDHF to study quasifission dynamics,"We show that the microscopic TDHF approach provides an important tool to shed
some light on the nuclear dynamics leading to the formation of superheavy
elements. In particular, we discuss studying quasifission dynamics and
calculating ingredients for compound nucleus formation probability
calculations.",1612.08917v1
2018-04-04,An unlikely route to low lattice thermal conductivity: small atoms in a simple layered structure,"In the design of materials with low lattice thermal conductivity, compounds
with high density, low speed of sound, and complexity at either the atomic,
nano- or microstructural level are preferred. The layered compound Mg$_3$Sb$_2$
defies these prevailing paradigms, exhibiting lattice thermal conductivity
comparable to PbTe and Bi$_2$Te$_3$, despite its low density and simple
structure. The excellent thermoelectric performance ($zT$ $\sim$ 1.5) in
$n$-type Mg$_3$Sb$_2$ has thus far been attributed to its multi-valley
conduction band, while its anomalous thermal properties have been largely
overlooked. To explain the origin of the low lattice thermal conductivity of
Mg$_3$Sb$_2$, we have used both experimental methods and ab initio phonon
calculations to investigate trends in the elasticity, thermal expansion and
anharmonicity of $A$Mg$_2Pn_2$ Zintl compounds with $A$ = Mg, Ca, Yb, and $Pn$
= Sb and Bi. Phonon calculations within the quasi-harmonic approximation reveal
large mode Gr\""uneisen parameters in Mg$_3$Sb$_2$ compared with isostructural
compounds, in particular in transverse acoustic modes involving shearing of
adjacent anionic layers. Measurements of the elastic moduli and sound velocity
as a function of temperature using resonant ultrasound spectroscopy provide a
window into the softening of the acoustic branches at high temperature,
confirming their exceptionally high anharmonicity. We attribute the anomalous
thermal behavior of Mg$_3$Sb$_2$ to the diminutive size of Mg, which may be too
small for the octahedrally-coordinated site, leading to weak, unstable
interlayer Mg-Sb bonding. This suggests more broadly that soft shear modes
resulting from undersized cations provide a potential route to achieving low
lattice thermal conductivity low-density, earth-abundant materials.",1804.01517v1
2018-04-21,Some examples of non-smoothable Gorenstein Fano toric threefolds,"We present a combinatorial criterion on reflexive polytopes of dimension 3
which gives a local-to-global obstruction for the smoothability of the
corresponding Fano toric threefolds. As a result, we show examples of singular
Gorenstein Fano toric threefolds which have compound Du Val, hence smoothable,
singularities but are not smoothable.",1804.07960v2
2019-03-01,Topology in abundance,"The topological classification of all known non-magnetic crystalline
compounds is now complete, revealing thousands of new candidate topological
materials waiting to be explored in the lab.",1903.00564v2
2019-03-07,Strongly mixing smooth planar vector field without asymptotic directions,"We use a Voronoi-type tessellation based on a compound Poisson point process
to construct a polynomially mixing stationary random smooth planar vector field
with bounded nonnegative components such that, with probability one, none of
the associated integral curves possess an asymptotic direction.",1903.02733v3
2019-09-11,"The zero-field-cooled exchange bias effect in phase-segregated La$_{2-x}$A$_{x}$CoMnO$_{6-δ}$ (A = Ba, Ca, Sr; x = 0, 0.5)","In the zero-field-cooled exchange bias (ZEB) effect the unidirectional
magnetic anisotropy is set at low temperatures even when the system is cooled
in the absence of external magnetic field. La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$
stands out as presenting the largest ZEB reported so far, while for
La$_{1.5}$Ca$_{0.5}$CoMnO$_{6}$ the exchange bias field ($H_{EB}$) is one order
of magnitude smaller. Here we show that La$_{1.5}$Ba$_{0.5}$CoMnO$_{6}$ also
exhibits a pronounced shift of its magnetic hysteresis loop, with intermediate
$H_{EB}$ value in respect to Ca- and Sr-doped samples. In order to figure out
the microscopic mechanisms responsible for this phenomena, these compounds were
investigated by means of synchrotron X-ray powder diffraction, Raman
spectroscopy, muon spin rotation and relaxation, AC and DC magnetization, X-ray
absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The
parent compound La$_{2}$CoMnO$_{6}$ was also studied for comparison, as a
reference of a non-ZEB material. Our results show that the Ba-, Ca- and
Sr-doped samples present a small amount of phase segregation, and that the ZEB
effect is strongly correlated to the system's structure. We also observed that
mixed valence states Co$^{2+}$/Co$^{3+}$ and Mn$^{4+}$/Mn$^{3+}$ are already
present at the La$_{2}$CoMnO$_{6}$ parent compound, and that
Ba$^{2+}$/Ca$^{2+}$/Sr$^{2+}$ partial substitution at La$^{3+}$ site leads to a
large increase of Co average valence, with a subtle augmentation of Mn formal
valence. Estimates of the Co and Mn valences from the $L$-edge XAS indicate the
presence of oxygen vacancies in all samples (0.05$\leq \delta \leq$0.1). Our
XMCD results show a great decrease of Co moment for the doped compounds, and
indicate that the shift of the hysteresis curves for these samples is related
to uncompensated antiferromagnetic coupling between Co and Mn.",1909.05287v1
2019-12-29,Giant momentum-dependent spin splitting in centrosymmetric low Z antiferromagnets,"The energy vs. crystal momentum E(k) diagram for a solid (band structure)
constitutes the road map for navigating its optical, magnetic, and transport
properties. By selecting crystals with specific atom types, composition and
symmetries, one could design a target band structure and thus desired
properties. A particularly attractive outcome would be to design energy bands
that are split into spin components with a momentum-dependent splitting, as
envisioned by Pekar and Rashba [Zh. Eksperim. i Teor. Fiz. 47 (1964)], enabling
spintronic application. The current paper provides ""design principles"" for
wavevector dependent spin splitting (SS) of energy bands that parallels the
traditional Dresselhaus and Rashba spin-orbit coupling (SOC) - induce
splitting, but originates from a fundamentally different source --
antiferromagnetism. We identify a few generic AFM prototypes with distinct SS
patterns using magnetic symmetry design principles. These tools allow also the
identification of specific AFM compounds with SS belonging to different
prototypes. A specific compound -- centrosymmetric tetragonal MnF2 -- is used
via density functional band structure calculations to quantitatively illustrate
one type of AFM SS. Unlike the traditional SOC-induced effects restricted to
non-centrosymmetric crystals, we show that antiferromagnetic-induced spin
splitting broadens the playing field to include even centrosymmetric compounds,
and gives SS comparable in magnitude to the best known ('giant') SOC effects,
even without SOC, and consequently does not rely on the often-unstable high
atomic number elements required for high SOC. We envision that use of the
current design principles to identify an optimal antiferromagnet with
spin-split energy bands would be beneficial for efficient spin-charge
conversion and spin orbit torque applications without the burden of requiring
compounds containing heavy elements.",1912.12689v3
2020-01-31,Machine learning on DNA-encoded libraries: A new paradigm for hit-finding,"DNA-encoded small molecule libraries (DELs) have enabled discovery of novel
inhibitors for many distinct protein targets of therapeutic value through
screening of libraries with up to billions of unique small molecules. We
demonstrate a new approach applying machine learning to DEL selection data by
identifying active molecules from a large commercial collection and a virtual
library of easily synthesizable compounds. We train models using only DEL
selection data and apply automated or automatable filters with chemist review
restricted to the removal of molecules with potential for instability or
reactivity. We validate this approach with a large prospective study (nearly
2000 compounds tested) across three diverse protein targets: sEH (a hydrolase),
ER{\alpha} (a nuclear receptor), and c-KIT (a kinase). The approach is
effective, with an overall hit rate of {\sim}30% at 30 {\textmu}M and discovery
of potent compounds (IC50 <10 nM) for every target. The model makes useful
predictions even for molecules dissimilar to the original DEL and the compounds
identified are diverse, predominantly drug-like, and different from known
ligands. Collectively, the quality and quantity of DEL selection data; the
power of modern machine learning methods; and access to large, inexpensive,
commercially-available libraries creates a powerful new approach for hit
finding.",2002.02530v1
2020-02-25,Extreme Value Theory with Spectral Techniques: application to a simple attractor,"We give a brief account of application of extreme value theory in dynamical
systems by using perturbation techniques associated to the transfer operator.
We will apply it to the baker's map and we will get a precise formula for the
extremal index. We will also show that the statistics of the number of visits
in small sets is compound Poisson distributed.",2002.10863v1
2020-06-16,Perpetual Integral Functionals of Multidimensional Stochastic Processes,"The paper is devoted to the existence of integral functionals $\int_0^\infty
f(X(t))\,{\mathrm{d}t}$ for several classes of processes in $\mathbb{R}$ with
$d\ge 3$. Some examples such as Brownian motion, fractional Brownian motion,
compound Poisson process, Markov processes admitting densities of transitional
probabilities are considered.",2006.09140v1
2020-07-06,Attacking COVID-19 Progression using Multi-Drug Therapy for Synergetic Target Engagement,"COVID-19 is a devastating respiratory and inflammatory illness caused by a
new coronavirus that is rapidly spreading throughout the human population. Over
the past 6 months, severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2), the virus responsible for COVID-19, has already infected over
11.6 million (25% located in United States) and killed more than 540K people
around the world. As we face one of the most challenging times in our recent
history, there is an urgent need to identify drug candidates that can attack
SARS-CoV-2 on multiple fronts. We have therefore initiated a computational
dynamics drug pipeline using molecular modeling, structure simulation, docking
and machine learning models to predict the inhibitory activity of several
million compounds against two essential SARS-CoV-2 viral proteins and their
host protein interactors; S/Ace2, Tmprss2, Cathepsins L and K, and Mpro to
prevent binding, membrane fusion and replication of the virus, respectively.
All together we generated an ensemble of structural conformations that increase
high quality docking outcomes to screen over >6 million compounds including all
FDA-approved drugs, drugs under clinical trial (>3000) and an additional >30
million selected chemotypes from fragment libraries. Our results yielded an
initial set of 350 high value compounds from both new and FDA-approved
compounds that can now be tested experimentally in appropriate biological model
systems. We anticipate that our results will initiate screening campaigns and
accelerate the discovery of COVID-19 treatments.",2007.02557v1
2020-07-17,Mössbauer studies of spin- and charge-modulations in BaFe2(As1-xPx)2,"The BaFe2(As1-xPx)2 compounds with x = 0 (parent), x = 0.10 (under-doped), x
= 0.31, 0.33, 0.53 (superconductors with Tc = 27.3 K, 27.6 K, 13.9 K,
respectively) and x = 0.70, 0.77 (over-doped) have been investigated versus
temperature using 57Fe M\""ossbauer spectroscopy. Special attention was paid to
regions of the spin-density-wave (SDW) antiferromagnetic order, spin-nematic
phase, and superconducting transition. The BaFe2(As0.90P0.10)2 compound
exhibits a reduced amplitude of SDW as compared to the parent compound and
preserved universality class of two-dimensional magnetic planes with
one-dimensional spins. The spin-nematic phase region for x = 0.10 is
characterized by an incoherent magnetic order. BaFe2(As0.69P0.31)2 shows
coexistence of a weak magnetic order and superconductivity due to the vicinity
of the quantum critical point. The charge density modulations in the
BaFe2(As0.67P0.33)2 and BaFe2(As0.47P0.53)2 superconductors are perturbed near
Tc. Pronounced hump of the average quadrupole splitting across superconducting
transition is observed for the system with x = 0.33. The phosphorus
substitution increases the Debye temperature of the BaFe2(As1-xPx)2 compound.
Moreover, experimental electron charge densities at Fe nuclei in this material
conclusively show that it should be recognized as a hole-doped system. The
measured M\""ossbauer spectral shift and spectral area are not affected by
transition to the superconducting state. This indicates that neither the
average electron density at Fe nuclei nor the dynamical properties of the
Fe-sublattice in BaFe2(As1-xPx)2 are sensitive to the superconducting
transition. Theoretical calculations of hyperfine parameters determining the
patterns of M\""ossbauer spectra of BaFe2(As1-xPx)2 with x = 0, 0.31, 0.5, and
1.0 are performed within the framework of the density functional theory.",2007.08858v2
2020-07-22,"Origin of the metamagnetic transitions in Y1-xErxFe2(H,D)4.2 compounds","The structural and magnetic properties of Y1-xErxFe2 intermetallic compounds
and their hydrides and deuterides Y1-xErxFe2H(D)4.2 have been investigated
using X-ray diffraction and magnetic measurements under static and pulsed
magnetic field up to 60 T. The intermetallics crystallize in the C15 cubic
structure , whereas corresponding hydrides and deuterides crystallize in a
monoclinic structure. All compounds display a linear decrease of the unit cell
volume versus Er concentration; the hydrides have a 0.8% larger cell volume
compared to the deuterides with same Er content. They are ferrimagnetic at low
field and temperature with a compensation point at x = 0.33 for the
intermetallics and x = 0.57 for the hydrides and deuterides. A sharp first
order ferromagnetic-antiferromagnetic (FM-AFM) transition is observed upon
heating at TFM-AFM for both hydrides and deuterides. These compounds show two
different types of field induced transitions, which have different physical
origin. At low temperature (T < 50 K), a forced ferri-ferromagnetic
metamagnetic transition with Btrans1 = 8 T, related to the change of the Er
moments orientation from antiparallel to parallel Fe moment, is observed.
Btrans1 is not sensitive to Er concentration, temperature and isotope effect. A
second metamagnetic transition resulting from antiferromagnetic to
ferrimagnetic state is also observed. The transition field Btrans2 increases
linearly versus temperature and relates to the itinerant electron metamagnetic
behavior of the Fe sublattice. An onset temperature TM0 is obtained by
extrapolating TFM-AFM (B) at zero field. TM0 decreases linearly versus the Er
content and is 45(5) K higher for the hydrides compared to the corresponding
deuteride. The evolution of TM0 versus cell volume shows that it cannot be
attributed exclusively to a pure volume effect and that electronic effects
should also be considered.",2007.11672v1
2020-07-29,Equivalence theorems for compound design problems with application in mixed models,"In the present paper we consider design criteria which depend on several
designs simultaneously. We formulate equivalence theorems based on moment
matrices (if criteria depend on designs via moment matrices) or with respect to
the designs themselves (for finite design regions). We apply the obtained
optimality conditions to the multiple-group random coefficient regression
models and illustrate the results by simple examples.",2007.14971v1
2020-09-11,"Optical floating zone crystal growth of rare-earth disilicates, $R\mathbf{_{2}}$Si$\mathbf{_{2}}$O$\mathbf{_{7}}$ ($R=$ Er, Ho, and Tm)","The wealth of structural phases seen in the rare-earth disilicate compounds
promises an equally rich range of interesting magnetic properties. We report on
the crystal growth by the optical floating zone method of members of the
rare-earth disilicate family, $R_{2}$Si$_{2}$O$_{7}$ (with $R=$ Er, Ho, and
Tm). Through a systematic study, we have optimised the growth conditions for
Er$_{2}$Si$_{2}$O$_{7}$. We have grown, for the first time using the floating
zone method, crystal boules of Ho$_{2}$Si$_{2}$O$_{7}$ and
Tm$_{2}$Si$_{2}$O$_{7}$ compounds. We show that the difficulties encountered in
the synthesis of polycrystalline and single crystal samples are due to the
similar thermal stability ranges of different rare-earth silicate compounds in
the temperature-composition phase diagrams of the $R$-Si-O systems. The
addition of a small amount of SiO$_{2}$ excess allowed the amount of impurity
phases present in the powder samples to be minimised. The phase composition
analysis of the powder X-ray diffraction data collected on the as-grown boules
revealed that they were of single phase, except in the case of thulium
disilicate, which comprised of two phases. All growths resulted in multi-grain
boules, from which sizable single crystals could be isolated. The optimum
conditions used for the synthesis and crystal growth of polycrystalline and
single crystal $R_{2}$Si$_{2}$O$_{7}$ materials are reported. Specific heat
measurements of erbium and thulium disilicate compounds confirm an
antiferromagnetic phase transition below $T_{\mathrm{N}}=$ 1.8 K for D-type
Er$_{2}$Si$_{2}$O$_{7}$ and a Schottky anomaly centered around 3.5 K in C-type
Tm$_{2}$Si$_{2}$O$_{7}$, suggesting the onset of short-range magnetic
correlations. Magnetic susceptibility data of E-type Ho$_{2}$Si$_{2}$O$_{7}$
reveals an antiferromagnetic ordering of the Ho spins below $T_\mathrm{{N}}=$
2.3 K.",2009.05536v1
2020-10-05,"NaInX2 (X = S, Se) layered materials for energy harvesting applications: First-principles insights into optoelectronic and thermoelectric properties","In the present study, the structural, electronic, optical and thermoelectric
properties of two isostructural chalcogenide materials, NaInS2 and NaInSe2 with
hexagonal symmetry (R-3m) have been studied using the first principles method.
A very good agreement has been found between our results with the available
experimental and theoretical ones. The studied materials are semiconducting in
nature as confirmed from the electronic band structure and optical
properties.The strong hybridizations among s orbitals of Na, In and Se atoms
push the bottom of the conduction band downward resulting in a narrower band
gap of NaInSe2 compared to that of NaInS2 compound. Different optical
(dielectric function, photoconductivity, absorption coefficient, reflectivity,
refractive index and loss function) and thermoelectric (Seebeck coefficient,
electrical conductivity, power factor and thermal conductivity) properties of
NaInX2 (X = S, Se) have been studied in detail for the first time. It is found
that all these properties are significantly anisotropic due to the strongly
layered structure of NaInX2 (X = S, Se). Strong optical absorption with sharp
peaks is found in the far visible to mid ultraviolet (UV) regions while the
reflectivity is low in the UV region for both the compounds. Such features
indicate feasibility of applications in optoelectronic sector.The calculated
thermoelectric power factors at 1000 K for NaInS2 and NaInSe2 along a-axis are
found to be 151.5 micro Watt /cmK2 and 154 micro Watt/cmK2, respectively and
the corresponding ZT values are ~0.70. The obtained thermal conductivity along
a-axis for both compounds is high (~22 W/mK).This suggests that the reduction
of such high thermal conductivity is important to achieve higher ZT values of
the NaInX2(X = S, Se) compounds.",2010.01816v1
2020-10-09,Theoretical Modelling of High-Resolution X-Ray Absorption Spectra at Uranium M4 Edge,"We investigate the origin of satellite features that appear in the
high-resolution x-ray absorption spectra measured at the uranium M 4 edge in
compounds where the uranium atoms are in the U 6+ oxidation state. We employ a
material-specific Anderson impurity model derived from the electronic structure
obtained by the density-functional theory.",2010.04410v1
2020-10-13,The first passage time on the (reflected) Brownian motion with broken drift hitting a random boundary,"In this paper we consider a (reflected) Brownian motion with broken drift
hitting a random boundary. Some dedicated calculations allow us to obtain the
formula on the joint Laplace transform of the hitting time and hitting
position. These develop the research on first rendezvous times of (reflected)
Brownian motion and compound Poisson-type processes by Perry et al. (2004).",2010.06397v1
2020-10-26,"Database, Features, and Machine Learning Model to Identify Thermally Driven Metal-Insulator Transition Compounds","Metal-insulator transition (MIT) compounds are materials that may exhibit
insulating or metallic behavior, depending on the physical conditions, and are
of immense fundamental interest owing to their potential applications in
emerging microelectronics. There is a dearth of thermally-driven MIT materials,
however, which makes delineating these compounds from those that are
exclusively insulating or metallic challenging. Here we report a material
database comprising temperature-controlled MITs (and metals and insulators with
similar chemical composition and stoichiometries to the MIT compounds) from
high quality experimental literature, built through a combination of
materials-domain knowledge and natural language processing. We featurize the
dataset using compositional, structural, and energetic descriptors, including
two MIT relevant energy scales, an estimated Hubbard interaction and the charge
transfer energy, as well as the structure-bond-stress metric referred to as the
global-instability index (GII). We then perform supervised classification,
constructing three electronic-state classifiers: metal vs non-metal (M),
insulator vs non-insulator (I), and MIT vs non-MIT (T). We identify two
important descriptors that separate metals, insulators, and MIT materials in a
2D feature space: the average deviation of the covalent radius and the range of
the Mendeleev number. We further elaborate on other important features (GII and
Ewald energy), and examine how they affect classification of binary vanadium
and titanium oxides. We discuss the relationship of these atomic features to
the physical interactions underlying MITs in the rare-earth nickelate family.
Last, we implement an online version of the classifiers, enabling quick
probabilistic class predictions by uploading a crystallographic structure file.",2010.13306v2
2020-12-01,"Magnetic ground-state of the one-dimensional ferromagnetic chain compounds $M$(NCS)$_2$(thiourea)$_2$; $M$ = Ni, Co","The magnetic properties of the two isostructural molecule-based magnets,
Ni(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 1, [thiourea = SC(NH$_2$)$_2$] and
Co(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 3/2, are characterised using several
techniques in order to rationalise their relationship with structural
parameters and ascertain magnetic changes caused by substitution of the spin.
Zero-field heat capacity and muon-spin relaxation measurements reveal
low-temperature long-range ordering in both compounds, in addition to
Ising-like ($D < 0$) single-ion anisotropy ($D_{\rm{Co}} \sim$ -100 K,
$D_{\rm{Ni}} \sim$ -10 K). Crystal and electronic structure, combined with
DC-field magnetometry, affirm highly quasi-one-dimensional behaviour, with
ferromagnetic intrachain exchange interactions $J_{\rm{Co}}\approx+4$ K and
$J_{\rm{Ni}}\sim+100$ K and weak antiferromagnetic interchain exchange, on the
order of $J'$ $\sim-0.1$ K. Electron charge and spin-density mapping reveals
through-space exchange as a mechanism to explain the large discrepancy in
$J$-values despite, from a structural perspective, the highly similar exchange
pathways in both materials. Both species can be compared to the similar
compounds $M$Cl$_2$(thiourea)$_4$, $M$ = Ni(II) (DTN) and Co(II) (DTC), where
DTN is know to harbour two magnetic field-induced quantum critical points.
Direct comparison of DTN and DTC with the compounds studied here shows that
substituting the halide Cl$^-$ ion, for the NCS$^-$ ion, results in a dramatic
change in both the structural and magnetic properties.",2012.00455v2
2020-12-11,Antiferromagnetic Kitaev interaction in $J_\rm{eff}=1/2$ cobalt honeycomb materials Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$,"Finding new materials with antiferromagnetic (AFM) Kitaev interaction is an
urgent issue to broaden and enrich the quantum magnetism research
significantly. By carrying out inelastic neutron scattering experiments and
subsequent analysis, we conclude that Na$_3$Co$_2$SbO$_6$ and
Na$_2$Co$_2$TeO$_6$ are new honeycomb cobalt-based AFM Kitaev systems. The
spin-orbit excitons at 20-28~meV in both compounds strongly supports the idea
that Co$^{2+}$ ions of both compounds have a spin-orbital entangled
$J_\rm{eff}=1/2$ state. Furthermore, we found that a generalized
Kitaev-Heisenberg Hamiltonian can well describe the spin-wave excitations of
both compounds with additional 3rd nearest-neighbor interaction. Our best-fit
parameters show large AFM Kitaev terms and off-diagonal symmetric anisotropy
terms of a similar magnitude in both compounds. We should stress that our
parameters' optimized magnetic structures are consistent with the magnetic
structures reported from neutron diffraction studies. Moreover, there is also
the magnon-damping effect at the higher energy part of the spin waves, as
usually observed in other Kitaev magnets. We demonstrate that
Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$ are the first experimental
realization of AFM Kitaev magnets based on the systematic studies of the spin
waves and analysis.",2012.06167v3
2020-12-17,Machine Learning of Free Energies in Chemical Compound Space Using Ensemble Representations: Reaching Experimental Uncertainty for Solvation,"Free energies govern the behavior of soft and liquid matter, and improving
their predictions could have a large impact on the development of drugs,
electrolytes or homogeneous catalysts. Unfortunately, it is challenging to
devise an accurate description of effects governing solvation such as
hydrogen-bonding, van der Waals interactions, or conformational sampling. We
present a Free energy Machine Learning (FML) model applicable throughout
chemical compound space and based on a representation that employs Boltzmann
averages to account for an approximated sampling of configurational space.
Using the FreeSolv database, FML's out-of-sample prediction errors of
experimental hydration free energies decay systematically with training set
size, and experimental uncertainty (0.6 kcal/mol) is reached after training on
490 molecules (80\% of FreeSolv). Corresponding FML model errors are also on
par with state-of-the art physics based approaches. To generate the input
representation for a new query compound, FML requires approximate and short
molecular dynamics runs. We showcase its usefulness through analysis of FML
solvation free energies for 116k organic molecules (all force-field compatible
molecules in QM9 database) identifying the most and least solvated systems, and
rediscovering quasi-linear structure property relationships in terms of simple
descriptors such as hydrogen-bond donors, number of NH or OH groups, number of
oxygen atoms in hydrocarbons, and number of heavy atoms. FML's accuracy is
maximal when the temperature used for the molecular dynamics simulation to
generate averaged input representation samples in training is the same as for
the query compounds. The sampling time for the representation converges rapidly
with respect to the prediction error.",2012.09722v5
2021-01-19,The different shapes of spin textures as a journey through Brillouin zone chiral and polar symmetries,"Crystallographic space group symmetry (CPGS) such as polar and nonpolar
crystal classes have long been known to classify compounds that have
spin-orbit-induced spin splitting. While taking a journey through the Brillouin
Zone (BZ) from one k-point to another for a fixed CPGS, it is expected that the
wavevector point group symmetry (WPGS) can change, and consequently a
qualitative change in the texture of the spin polarization (the expectation
value of spin operator $\vec{S}^{nk_{0}}$ in Bloch state $u(n,k)$ and the
wavevector $k_0$). However, the nature of the spin texture (ST) change is
generally unsuspected. In this work, we determine a full classification of the
linear-in-$k$ spin texture patterns based on the polarity and chirality
reflected in the WPGS at $k_0$. The spin-polarization vector $\vec{S}^{nk_{0}}$
controlling the ST is bound to be parallel to the rotation axis and
perpendicular to the mirror planes and hence, symmetry operation types in WPGSs
impose symmetry restriction to the ST. For instance, the ST is always parallel
to the wavevector $k$ in non-polar chiral WPGSs since they contain only
rotational symmetries. Some consequences of the ST classification based on the
symmetry operations in the WPGS include the observation of ST patterns that are
unexpected according to the symmetry of the crystal. For example, it is usually
established that spin-momentum locking effect requires the crystal inversion
symmetry breaking by an asymmetric electric potential. However, we find that
polar WPGS can have this effect even in compounds without electric dipoles or
external electric fields. We use the determined relation between WPGS and ST as
a design principle to select compounds with multiple ST near band edges at
different $k$-valleys. Based on high-throughput calculations for 1481
compounds, we find 37 previously fabricated materials with different ST near
band edges.",2101.07477v3
2021-06-25,Convergence of the Discrete-Time Compound Hawkes Processwith Exponential or Erlang Kernel,"Due to its clustering and self-exciting properties, the Hawkes process has
been used extensively in numerous fields ranging from sismology to finance.
Since data is often aquired on regular time intervals, we propose a piece-wise
constant model based on a Discrete-Time Hawkes Process (DTHP). We prove that
this discrete-time model converges to the usual continuous-time Hawkes process
as the time-step tends to zero.",2106.13459v1
2021-06-28,Alloying driven transition between ferro- and antiferromagnetism in UTGe compounds: the UCo1-xIrxGe case,"The evolution of magnetic properties of isostructural and isoelectronic solid
solutions of the superconducting itinerant 5f-electron ferromagnet UCoGe with
antiferromagnet UIrGe was studied by magnetization, AC susceptibility, specific
heat, and electrical resistivity measurements of a series of UCo1-xIrxGe
compounds in polycrystalline and single crystalline form at various
temperatures and magnetic fields. Both the weak ferromagnetism and
superconductivity in UCoGe were found to have vanished already for very low Ir
substitution for Co x = 0.02. The antiferromagnetism of UIrGe is gradually
suppressed. This is documented by a rapid decrease in both Neel temperature and
the critical field of the metamagnetic transition with decreasing Ir
concentration, which both tend to vanish just above x = 0.8. The section of the
T-x phase diagram in the range x between 0.02 and 0.8 is dominated by a
correlated paramagnetic phase exhibiting very broad bumps in temperature
dependencies of b-axis magnetization and specific heat developing with
increasing x. For x = 0.24, wide peaks appear in the c-axis thermomagnetic
curves due to antiferromagnetic correlations which may eventually lead to
frozen incoherent spin configurations at low temperatures. The correlated
paramagnetic phase is also accompanied by specific electrical resistivity
anomalies. The T-x phase diagram determined for the UCo1-xIrxGe compounds
contrasts with the behavior of the related URh1-xIrxGe system, which was
reported to exhibit an extended concentration range of stable ferromagnetism in
Rh rich compounds and a discontinuous transformation between the ferromagnetic
and antiferromagnetic phases at a critical Rh-Ir concentration.",2106.14502v2
2021-11-14,Improving Compound Activity Classification via Deep Transfer and Representation Learning,"Recent advances in molecular machine learning, especially deep neural
networks such as Graph Neural Networks (GNNs) for predicting structure activity
relationships (SAR) have shown tremendous potential in computer-aided drug
discovery. However, the applicability of such deep neural networks are limited
by the requirement of large amounts of training data. In order to cope with
limited training data for a target task, transfer learning for SAR modeling has
been recently adopted to leverage information from data of related tasks. In
this work, in contrast to the popular parameter-based transfer learning such as
pretraining, we develop novel deep transfer learning methods TAc and TAc-fc to
leverage source domain data and transfer useful information to the target
domain. TAc learns to generate effective molecular features that can generalize
well from one domain to another, and increase the classification performance in
the target domain. Additionally, TAc-fc extends TAc by incorporating novel
components to selectively learn feature-wise and compound-wise transferability.
We used the bioassay screening data from PubChem, and identified 120 pairs of
bioassays such that the active compounds in each pair are more similar to each
other compared to its inactive compounds. Our experiments clearly demonstrate
that TAc achieves significant improvement over all baselines across a large
number of target tasks. Furthermore, although TAc-fc achieves slightly worse
ROC-AUC on average compared to TAc, TAc-fc still achieves the best performance
on more tasks in terms of PR-AUC and F1 compared to other methods. In summary,
TAc-fc is also found to be a strong model with competitive or even better
performance than TAc on a notable number of target tasks.",2111.07439v2
2021-11-24,Group-9 Transition Metal Suboxides Adopting the Filled-Ti$_2$Ni Structure: A Class of Superconductors Exhibiting Exceptionally High Upper Critical Fields,"The Ti$_2$Ni and the related $\eta$-carbide structure are known to exhibit
various intriguing physical properties. The Ti$_2$Ni structure with the cubic
space group $Fd\bar{3}m$ is surprisingly complex, consisting of a unit cell
with 96 metal atoms. The related $\eta$-carbide compounds correspond to a
filled version of the Ti$_2$Ni structure. Here, we report on the structure and
superconductivity in the $\eta$-carbide type suboxides Ti$_4$M$_2$O with M =
Co, Rh, Ir. We have successfully synthesized all three compounds in single
phase form. We find all three compounds to be type-II bulk superconductors with
transition temperatures of $T_{\rm c}$ = 2.7, 2.8, and 5.4 K, and with
normalized specific heat jumps of $\Delta C/\gamma T_{\rm c}$ = 1.65, 1.28, and
1.80 for Ti$_4$Co$_2$O, Ti$_4$Rh$_2$O, and Ti$_4$Ir$_2$O, respectively. We find
that all three superconductors, exhibit high upper-critical fields.
Particularly noteworthy is Ti$_4$Ir$_2$O with an upper critical field of $\mu_0
H_{\rm c2}{\rm (0)}$ =~16.06~T, which exceeds by far the weak-coupling Pauli
limit of 9.86~T. The role of the void filling light atom X has so far been
uncertain for the overall physical properties of these materials. Herein, we
have successfully grown single crystals of Ti$_2$Co. In contrast to the
metallic $\eta$-carbide type suboxides Ti$_4$M$_2$O, we find that Ti$_2$Co
displays a semimetallic behavior. Hence, the octahedral void-filling oxygen
plays a crucial role for the overall physical properties, even though its
effect on the crystal structure is small. Our results indicate that the design
of new superconductors by incorporation of electron-acceptor atoms may in the
Ti$_2$Ni-type structures and other materials with crystallographic void
position be a promising future approach. The remarkably high upper critical
fields, in this family of compounds, may furthermore spark significant future
interest.",2111.12452v1
2021-11-26,The Parameter Sensitivities of a Jump-diffusion Process in Basic Credit Risk Analysis,"We detect the parameter sensitivities of bond pricing which is driven by a
Brownian motion and a compound Poisson process as the discontinuous case in
credit risk research. The strict mathematical deductions are given
theoretically due to the explicit call price formula. Furthermore, we
illustrate Matlab simulation to verify these conclusions.",2111.13334v1
2021-11-29,Equiseparability on Terminal Wiener Index and Distances,"Teminal Wiener index is one of the commonly used topological index in
mathematical chemistry. If two or more chemical compounds have the same
terminal Wiener index then they will have similar physico-chemical properties.
In this work we propose a new method for constructing equiseparable trees w.r.t
terminal Wiener index. The existing method is based on the number of pendent
vertices but the proposed method is based on distance parameters.",2111.14716v1
2022-01-21,AlphaFold Accelerates Artificial Intelligence Powered Drug Discovery: Efficient Discovery of a Novel Cyclin-dependent Kinase 20 (CDK20) Small Molecule Inhibitor,"The AlphaFold computer program predicted protein structures for the whole
human genome, which has been considered as a remarkable breakthrough both in
artificial intelligence (AI) application and structural biology. Despite the
varying confidence level, these predicted structures still could significantly
contribute to structure-based drug design of novel targets, especially the ones
with no or limited structural information. In this work, we successfully
applied AlphaFold in our end-to-end AI-powered drug discovery engines
constituted of a biocomputational platform PandaOmics and a generative
chemistry platform Chemistry42, to identify a first-in-class hit molecule of a
novel target without an experimental structure starting from target selection
towards hit identification in a cost- and time-efficient manner. PandaOmics
provided the targets of interest and Chemistry42 generated the molecules based
on the AlphaFold predicted structure, and the selected molecules were
synthesized and tested in biological assays. Through this approach, we
identified a small molecule hit compound for CDK20 with a Kd value of 8.9 +/-
1.6 uM (n = 4) within 30 days from target selection and after only synthesizing
7 compounds. Based on the available data, the second round of AI-powered
compound generation was conducted and through which, a more potent hit
molecule, ISM042-2 048, was discovered with a Kd value of 210.0 +/- 42.4 nM (n
= 2), within 30 days and after synthesizing 6 compounds from the discovery of
the first hit ISM042-2-001. To the best of our knowledge, this is the first
reported small molecule targeting CDK20 and more importantly, this work is the
first demonstration of AlphaFold application in the hit identification process
in early drug discovery.",2201.09647v2
2022-01-24,Dynamic optimization of volatile fatty acids to enrich biohydrogen production using a deep learning neural network,"A new strategy was developed to investigate the effect of volatile fatty
acids (VFAs) on the efficiency of biogas production with a focus on improving
bio-H$_2$. The inoculum used, anaerobic granular sludge obtained from a UASB
reactor treating poultry slaughterhouse wastewater, was pretreated with five
different pretreatments. The relationship between VFAs and biogas compounds was
studied as time-dependent components. In time-dependent processes with small
sample size data, regression models may not be good enough at estimating
responses. Therefore, a deep learning neural network (DNN) model was developed
to estimate the biogas compounds based on the VFAs. The accuracy of this model
to predict the biogas compounds was higher than that of multivariate regression
models. Further, it could predict the effect of time changes on biogas
compounds. Analysis showed that all the pretreatments were able to increase the
ratio of butyric acid / acetic acid successfully, decrease propionic acid
drastically, and increase the efficiency of bio-H$_2$ production. As
discovered, butyric acid had the greatest effect on bio-H$_2$, and propionic
acid had the greatest effect on CH$_4$ production. The best amounts of the VFAs
were determined using an optimization method, integrated DNN and desirability
analysis, dynamically retrained based on digestion time. Accordingly, optimal
ranges of acetic, propionic, and butyric acids were 823.2 - 1534.3, 36.3 -
47.4, and 1522 - 1822 mg/L, respectively, determined for digestion time of
25.23 - 123.63 h. These values resulted in the production of bio-H$_2$, N$_2$,
CO$_2$, and CH$_4$ in ranges of 6.4 - 26.2, 12.2 - 43.2, 5 - 25.3, and 0 - 1.4
mmol/L, respectively. The optimum ranges of VFAs are relatively wide ranges and
practically can be used in biogas plants.",2201.09837v2
2022-04-03,Analyzing Voting Power in Decentralized Governance: Who controls DAOs?,"We empirically study the state of three prominent DAO governance systems on
the Ethereum blockchain: Compound, Uniswap and ENS. In particular, we examine
how the voting power is distributed in these systems. Using a comprehensive
dataset of all governance token holders, delegates, proposals and votes, we
analyze who holds the voting rights and how they are used to influence
governance decisions.",2204.01176v1
2022-05-04,Compound virtual screening by learning-to-rank with gradient boosting decision tree and enrichment-based cumulative gain,"Learning-to-rank, a machine learning technique widely used in information
retrieval, has recently been applied to the problem of ligand-based virtual
screening, to accelerate the early stages of new drug development. Ranking
prediction models learn based on ordinal relationships, making them suitable
for integrating assay data from various environments. Existing studies of rank
prediction in compound screening have generally used a learning-to-rank method
called RankSVM. However, they have not been compared with or validated against
the gradient boosting decision tree (GBDT)-based learning-to-rank methods that
have gained popularity recently. Furthermore, although the ranking metric
called Normalized Discounted Cumulative Gain (NDCG) is widely used in
information retrieval, it only determines whether the predictions are better
than those of other models. In other words, NDCG is incapable of recognizing
when a prediction model produces worse than random results. Nevertheless, NDCG
is still used in the performance evaluation of compound screening using
learning-to-rank. This study used the GBDT model with ranking loss functions,
called lambdarank and lambdaloss, for ligand-based virtual screening; results
were compared with existing RankSVM methods and GBDT models using regression.
We also proposed a new ranking metric, Normalized Enrichment Discounted
Cumulative Gain (NEDCG), which aims to properly evaluate the goodness of
ranking predictions. Results showed that the GBDT model with learning-to-rank
outperformed existing regression methods using GBDT and RankSVM on diverse
datasets. Moreover, NEDCG showed that predictions by regression were comparable
to random predictions in multi-assay, multi-family datasets, demonstrating its
usefulness for a more direct assessment of compound screening performance.",2205.02169v2
2022-05-27,Tight-Binding Superconducting Phases in the Unconventional Compounds Strontium-Substituted Lanthanum Cuprate and Strontium Ruthenate,"We use the idea of the Wigner probability distribution (WPD) in a reduced
scattering phase space (RPS) for the elastic scattering cross-section, with the
help of a Tight-Binding (TB) numerical procedure allowing us to consider the
anisotropic quantum effects, to phenomenologically predict several phases in
these two novel unconventional superconductors. Unlike our previous works with
pieces of evidence that these two compounds are in the unitary strong
scattering regime and that superconductivity is suppressed by the atoms of
strontium in both materials, several phases are built. In the case of the
strontium-substituted lanthanum cuprate, it was found three phases from one
family of Wigner probabilistic distributions, one corresponding to the
antiferromagnetic compound La2CuO4 another one which consists of a coalescing
metallic phase for very lightly doped La2-xSrxCuO4, and finally a strong
self-consistent dependent strange metal phase with optimal levels of doping. In
the case of a triplet superconductor strontium ruthenate, three phases can be
differentiated from two families of Wigner distribution probabilities, one
family of WDP with point nodes where Cooper pairs and dressed scattered normal
quasiparticles are mixed for the whole range of frequencies and which
correspond to an FS $\gamma$ flat-sheet in the ground metallic state, and two
phases from another WPD family, where, in one of then, the Miyake-Narikiyo
quasinodal tiny gap model allows the unique presence of Cooper pairs in a tiny
interval of frequencies near the superconducting transition TC, the other phase
corresponds to the mixed-phase with Cooper pairs and dressed by stoichiometric
strontium non-magnetic atoms, where strong self-consistent effects are
noticeable. This approach allows comparing experimental results for samples in
both compounds with numerical analysis studies.",2205.14242v1
2022-07-25,"Compound Poisson Processes: Potentials, Green Measures and Random Times","In this paper we study the existence of Green measures for Markov processes
with a nonlocal jump generator. The jump generator has no second moment and
satisfies a suitable condition on its Fourier transform. We also study the same
problem for certain classes of random time changes Markov processes with jump
generator.",2207.12223v1
2022-10-18,Variance Gamma (non-local) equations,"We provide some equations for the Variance Gamma process due to the fact that
we do not consider only the definition as a time-changed Brownian motion. This
brings us to a new non-local equation, even true in the drifted case, involving
generalized Weyl derivatives. Then we focus on the connection to special
functions and we study a space equation for our process. At the end, we
conclude by observing the convergence in distribution of a compound Poisson
process to the Variance Gamma process.",2210.09816v1
2022-10-23,Analysis of Ayscough's Telescope Adapted to Use at Sea,"An unambiguous accordance between an objective lens for Ayscough's telescope
'Adapted to Use at Sea' and another compound lens which was described by
William Eastland in well-known Quere during the trial in October of 1765 was
revealed. Preliminary analysis of small fragments of Quere from Eastland',
Stedman' and Champneys' testimonies was carried.",2210.12876v1
2022-10-26,A family of potential-density pairs for galactic bars,"We present a family of analytical potential-density pairs for barred discs,
which can be combined to describe galactic bars in a realistic way, including
boxy/peanut components. We illustrate this with two reasonable compound models.
Computer code for the evaluation of potential, forces, density, and projected
density is freely provided.",2210.14853v1
2022-11-01,"Evolution of the spin dynamics in the van der Waals system $M_{\text{2}}$P$_{\text{2}}$S$_{\text{6}}$ ($\boldsymbol{M}_{\text{2}}$ = Mn$_{\text{2}}$, MnNi, Ni$_{\text{2}}$) series probed by electron spin resonance spectroscopy","In this work we report a detailed ESR spectroscopic study of the
single-crystalline samples of the van der Waals compounds
$M_{\text{2}}$P$_{\text{2}}$S$_{\text{6}}$ ($M_{\text{2}}$ = Mn$_{\text{2}}$,
MnNi, Ni$_{\text{2}}$), performed at an excitation frequency of 9.56 GHz, in a
broad range of temperatures above the magnetic order, and at different
orientations of the magnetic field with respect to the sample. Analyzing
temperature and angular dependences of the resonance field and of the linewidth
of the Mn$_2$P$_2$S$_6$ compound we have observed a significant change of the
spin dynamics from the dominance of the 3D-like fluctuations close to the
magnetic order to a relative increase of the 2D-like spin fluctuations at
higher temperatures. Such a behavior, which is opposite to the development of
the low-D signatures in the previously studied
Cr$_{\text{2}}$Ge$_{\text{2}}$Te$_{\text{6}}$ compound, can be explained by the
difference in the type of magnetic order in Mn$_2$P$_2$S$_6$ and
Cr$_{\text{2}}$Ge$_{\text{2}}$Te$_{\text{6}}$. On the other hand,
MnNiP$_2$S$_6$ compound exhibits angular dependences of the linewidth typical
for the system with 3D-like spin correlations in the whole measurement
temperature range, however the 2D-like correlations can be seen in the
temperature dependences of the resonance field and the linewidth.
Ni$_2$P$_2$S$_6$, in turn, does not show any 2D signatures. This suggests that
varying the Ni content in (Mn$_{1-x}$Ni$_x$)$_2$P$_2$S$_6$ one can control the
exchange interaction, possibly also in the third dimension.",2211.00521v2
2023-01-19,Silvanite AuAgTe$_4$: a rare case of gold superconducting material,"Gold is one of the most inert metals, forming very few compounds, some with
rather interesting properties, and only two of them currently known to be
superconducting under certain conditions (AuTe$_2$ and SrAuSi$_3$). Compounds
of another noble element, Ag, are also relatively rare, and very few of them
are superconducting. Finding new superconducting materials containing gold (and
silver) is a challenge - especially having in mind that the best high-$T_c$
superconductors at normal conditions are based upon their rather close
''relative'', Cu. Here we report combined X-ray diffraction, Raman, and
resistivity measurements, as well as first-principles calculations, to explore
the effect of hydrostatic pressure on the properties of the sylvanite mineral,
AuAgTe$_4$. Our experimental results, supported by density functional theory,
reveal a structural phase transition at $\sim$5 GPa from a monoclinic $P2/c$ to
$P2/m$ phase, resulting in almost identical coordinations of Au and Ag ions,
with rather uniform interatomic distances. Further, resistivity measurements
show the onset of superconductivity at $\sim$1.5 GPa in the $P2/c$ phase,
followed by a linear increase of $T_c$ up to the phase transition, with a
maximum in the $P2/m$ phase, and a gradual decrease afterwards. Our
calculations indicate phonon-mediated superconductivity, with the
electron-phonon coupling coming predominantly from the low-energy phonon modes.
Thus, along with the discovery of a new superconducting compound of
gold/silver, our results advance understanding of the mechanism of the
superconductivity in Au-containing compounds, which may pave the way to the
discovery of novel ones.",2301.08033v2
2023-05-03,Universal sublinear resistivity in vanadium kagome materials hosting charge density waves,"The recent discovery of a charge density (CDW) state in ScV$_6$Sn$_6$ at
$T_{\textrm{CDW}}$ = 91 K offers new opportunities to understand the origins of
electronic instabilities in topological kagome systems. By comparing to the
isostructural non-CDW compound LuV$_6$Sn$_6$, we unravel interesting electrical
transport properties in ScV$_6$Sn$_6$, above and below the charge ordering
temperature. We observed that by applying a magnetic field along the $a$ axis,
the temperature behavior of the longitudinal resistivity in ScV$_6$Sn$_6$
changes from metal-like to insulator-like above the CDW transition. We show
that in the charge ordered state ScV$_6$Sn$_6$ follows the Fermi liquid
behavior while above that, it transforms into a non-Fermi liquid phase in which
the resistivity varies sublinearly over a broad temperature range. The
sublinear resistivity, which scales by $T^{3/5}$ is a common feature among
other vanadium-containing kagome compounds exhibiting CDW states such as
KV$_3$Sb$_5$, RbV$_3$Sb$_5$, and CsV$_3$Sb$_5$. By contrast, the non-Fermi
liquid behavior does not occur in LuV$_6$Sn$_6$. We explain the $T^{3/5}$
universal scaling behavior from the Coulomb scattering between Dirac electrons
and Van Hove singularities; common features in the electronic structure of
kagome materials. Finally, we show anomalous Hall-like behavior in
ScV$_6$Sn$_6$ below $T_{\textrm{CDW}}$, which is absent in the Lu compound.
Comparing the transport properties of ScV$_6$Sn$_6$ and LuV$_6$Sn$_6$ is
valuable to highlight the impacts of the unusual CDW in the Sc compound.",2305.02393v2
2023-05-13,mechanical properties of CaFe2As2 ab-initio study,"We report results on the ab-initio study of the mechanical, electronic and
structural properties of the iron Pnictide compound CaFe_2 As_2 at zero
pressure. Ground State energy computation was done within the Density
Functional Theory (DFT) using the Projector Augmented Wave (PAW) Pseudo
Potentials and the Plane Wave (PW) basis set. The Generalized Gradient
Approximation (GGA) facilitated the exchange-correlation.",2305.07949v1
2023-05-19,Emergent room-temperature ferroelectricity in spark-plasma sintered DyCrO$_3$ and LaCrO$_3$,"Identification of novel multiferroic materials with high-ordering
temperatures remains at the forefront of condensed matter physics research. In
this regard, the antiferromagnetic RCrO$_3$ compounds (like GdCrO$_3$)
constitute a promising class of multiferroic compounds, which, however, mostly
become ferroelectric concomitant with the antiferromagnetic ordering much below
room-temperature, arising from a subtle competition between the ferroelectric
off-centering mode and a non-polar antiferrodistortive rotation mode that
inhibits ferroelectricity. Recently, room-temperature ferroelectricity of
structural origin, arising from off-centering displacements of R and Cr ions,
has been identified in spark-plasma sintered GdCrO$_3$ [Suryakanta Mishra et
al., Phys. Rev. B 104, L180101 (2021)]. Interestingly, some of the
experimentally observed non-ferroelectric RCrO$_3$ compounds have been
theoretically predicted to host similar ferroelectric instabilities. Here, we
have identified two such non-ferroelectric RCrO3 compounds, one DyCrO$_3$
(which is reported as a quantum paraelectric) and another LaCrO$_3$ (which is
paraelectric), and using a modified synthesis protocol involving
spark-plasma-sintering (SPS), we have been successful in engineering an
intrinsic room-temperature ferroelectricity in the paramagnetic state, driven
by noncentrosymmetric structural phase in both SPS sintered DyCrO$_3$ and
LaCrO$_3$, in contrast to room-temperature paraelectricity in solid-state
synthesized DyCrO$_3$ and LaCrO$_3$. While the ferroelectricity in SPS-prepared
DyCrO$_3$ and LaCrO$_3$ is stable at room-temperature, it undergoes an
irreversible transition from a ferroelectric (Pna2$_1$) phase to a paraelectric
(Pbnm) phase at 440 K. Significantly, SPS-sintered LaCrO$_3$, which undergoes
antiferromagnetic ordering at 290 K, emerges as a promising near
room-temperature multiferroic material.",2305.11546v2
2023-06-25,Ultrafast Cardiac Imaging Using Deep Learning For Speckle-Tracking Echocardiography,"High-quality ultrafast ultrasound imaging is based on coherent compounding
from multiple transmissions of plane waves (PW) or diverging waves (DW).
However, compounding results in reduced frame rate, as well as destructive
interferences from high-velocity tissue motion if motion compensation (MoCo) is
not considered. While many studies have recently shown the interest of deep
learning for the reconstruction of high-quality static images from PW or DW,
its ability to achieve such performance while maintaining the capability of
tracking cardiac motion has yet to be assessed. In this paper, we addressed
such issue by deploying a complex-weighted convolutional neural network (CNN)
for image reconstruction and a state-of-the-art speckle tracking method. The
evaluation of this approach was first performed by designing an adapted
simulation framework, which provides specific reference data, i.e. high
quality, motion artifact-free cardiac images. The obtained results showed that,
while using only three DWs as input, the CNN-based approach yielded an image
quality and a motion accuracy equivalent to those obtained by compounding 31
DWs free of motion artifacts. The performance was then further evaluated on
non-simulated, experimental in vitro data, using a spinning disk phantom. This
experiment demonstrated that our approach yielded high-quality image
reconstruction and motion estimation, under a large range of velocities and
outperforms a state-of-the-art MoCo-based approach at high velocities. Our
method was finally assessed on in vivo datasets and showed consistent
improvement in image quality and motion estimation compared to standard
compounding. This demonstrates the feasibility and effectiveness of deep
learning reconstruction for ultrafast speckle-tracking echocardiography.",2306.14265v2
2023-08-01,The use of the invariant's properties in the primality test and prime search,"The purpose of this article is to delve into the properties of invariants.
The properties, explained in [2], reveal new ways to develop algorithms that
allow us to test the primality of a number. In this article, some of these are
shown, indicating the advantages and disadvantages of these new algorithms. The
information provided by these algorithms also gives additional information
regarding the factorization of a compound number.",2308.00417v1
2023-08-01,"Understanding the local structure, magnetism and optical properties in layered compounds with d9 ions: Insight into silver fluorides and K2CuF4","Using first-principles DFT calculations, we analyze the origin of the
different crystal structures, optical and magnetic properties of two basic
families of layered fluoride materials with formula A2MF4 (M = Ag, Cu, Ni, Mn;
A = K, Cs, Rb). On one hand, Cs2AgF4 and K2CuF4 compounds (both with d9 metal
cations) crystallize in an orthorhombic structure with Cmca space group and MA
- F - MB bridge angle of 180, and they exhibit a weak ferromagnetism (FM) in
the layer plane. On the other hand, K2NiF4 or K2MnF4 compounds (with d8 and d5
metal cations, respectively) have a tetragonal I4/mmm space group with 180
bridge angle and exhibit antiferromagnetism (AFM) in the layer plane. Firstly,
we show that, contrary to what is claimed in the literature, the Cmca structure
of Cs2AgF4 and K2CuF4 is not related to a cooperative Jahn-Teller effect among
elongated MF64- units. Instead, first-principles calculations carried out in
the I4/mmm parent phase of these two compounds show that MF64- units are
axially compressed because the electrostatic potential from the rest of lattice
ions force the hole to lie in the 3z2 - r2 molecular orbital (z being
perpendicular to the layer plane). This fact increases the metal-ligand
distance in the layer plane and makes that covalency in the bridging ligand has
a residual character (clearly smaller than in K2NiF4 or KNiF3) stabilizing for
only a few meV (7.9 meV for Cs2AgF4) an AFM order. However, this I4/mmm parent
phase of Cs2AgF4 is unstable thus evolving towards the experimental Cmca
structure with an energy gain of 140 meV, FM ordering and orthorhombic MF64-
units.",2308.00433v1
2023-07-25,Turning hazardous volatile matter compounds into fuel by catalytic steam reforming: An evolutionary machine learning approach,"Chemical and biomass processing systems release volatile matter compounds
into the environment daily. Catalytic reforming can convert these compounds
into valuable fuels, but developing stable and efficient catalysts is
challenging. Machine learning can handle complex relationships in big data and
optimize reaction conditions, making it an effective solution for addressing
the mentioned issues. This study is the first to develop a
machine-learning-based research framework for modeling, understanding, and
optimizing the catalytic steam reforming of volatile matter compounds. Toluene
catalytic steam reforming is used as a case study to show how chemical/textural
analyses (e.g., X-ray diffraction analysis) can be used to obtain input
features for machine learning models. Literature is used to compile a database
covering a variety of catalyst characteristics and reaction conditions. The
process is thoroughly analyzed, mechanistically discussed, modeled by six
machine learning models, and optimized using the particle swarm optimization
algorithm. Ensemble machine learning provides the best prediction performance
(R2 > 0.976) for toluene conversion and product distribution. The optimal tar
conversion (higher than 77.2%) is obtained at temperatures between 637.44 and
725.62 {\deg}C, with a steam-to-carbon molar ratio of 5.81-7.15 and a catalyst
BET surface area 476.03-638.55 m2/g. The feature importance analysis
satisfactorily reveals the effects of input descriptors on model prediction.
Operating conditions (50.9%) and catalyst properties (49.1%) are equally
important in modeling. The developed framework can expedite the search for
optimal catalyst characteristics and reaction conditions, not only for
catalytic chemical processing but also for related research areas.",2308.05750v1
2023-10-06,Algebraic Enumeration of Polypolyhedra,"Polypolyhedra are edge-transitive compounds of polyhedra. In this paper we
use group theory to determine the number of distinct polypolyhedra whose
symmetry group is any given finite irreducible Coxeter group. We apply this
result in order to enumerate the 3-dimensional polypolyhedra.",2310.04473v1
2023-10-19,Explosive Chrysopoeia,"Fulminating gold, the first high-explosive compound to be discovered,
disintegrates in a mysterious cloud of purple smoke, the nature of which has
been speculated upon since its discovery in 1585. In this work, we show that
the colour of the smoke is due to the presence of gold nanoparticles.",2310.15125v1
2024-02-09,BaMn$_2$P$_2$: Highest magnetic ordering temperature 122-pnictide compound,"We report the growth of high-quality single crystals of ThCr$_2$Si$_2$-type
tetragonal BaMn$_2$P$_2$ and investigation of its structural, electrical
transport, thermal and magnetic properties. Our results of basal plane
electrical resistivity and heat capacity measurements show that the compound
has an insulating ground state with a small band gap. Anisotropic
susceptibility $\chi_{ab,c}(T)$ data infer a collinear local-moment N\'eel-type
antiferromagnetic (AFM) ground state below the ordering temperature $T_{\rm N}
= 795(15)$~K, which is highest among all the ThCr$_2$Si$_2$- and
CaAl$_2$Si$_2$-type 122-pnictide compounds reported so far suggesting that the
strength of magnetic exchange interactions is strongest in this material. The
magnetic transition temperatures of BaMn$_2$$Pn_{2}$ ($Pn$ = P, As, Sb, Bi)
compounds exhibit a monotonic decrease with the increase of tetragonal unit
cell parameters $a$ and $c$, suggesting a strong dependence of the strength of
the decisive magnetic exchange interactions on the separation between the
localized spins residing on the Mn-ions. The observed monotonic increase of
both $\chi_{ab}$ and $\chi_{c}$ for $T > T_{\rm N}$ suggests that short-range
dynamic quasi-two dimensional AFM correlations persist above the $T_{\rm N}$ up
to the highest temperature of the measurements. The large $T_{\rm N}$ of
BaMn$_2$P$_2$ demands for systematic hole-doping studies on this material as
similar investigations on related BaMn$_2$As$_{2}$ with $T_{\rm N} = 618$~K
have led to the discovery of an outstanding ground state where AFM of localized
Mn-spins and itinerant half-metallic ferromagnetism with $T_{\rm c} \approx
100$~K originating from the doped holes coexist together.",2402.06432v1
2024-03-01,"La$_4$Co$_4$X (X = Pb, Bi, Sb): a demonstration of antagonistic pairs as a route to quasi-low dimensional ternary compounds","We outline how pairs of strongly immiscible elements, referred to here as
antagonistic pairs, can be used to synthesize ternary compounds with
quasi-reduced dimensional motifs. By identifying third elements that are
compatible with a given antagonistic pair, ternary compounds can be formed in
which the third element segregates the immiscible atoms into spatially
separated substructures. Quasi-low dimensional structural units are a natural
consequence of the immiscible atoms seeking to avoid contact in the
solid-state. As proof of principle, we present the discovery and physical
properties of La$_4$Co$_4$X (X = Pb, Bi, Sb), a new family of intermetallics
based on the antagonistic pairs Co-Pb and Co-Bi. La$_4$Co$_4$X adopts a new
orthorhombic crystal structure (space group Pbam) containing quasi-2D Co slabs
and La-X layers that stack along the a-axis. Consistent with our proposal, the
La atoms separate the Co and X substructures, ensuring there are no direct
contacts between immiscible atoms. Within the Co slabs, the atoms occupy the
vertices of corner sharing tetrahedra and triangles, and this motif produces
flat electronic bands near the Fermi level that favor magnetism. The Co is
moment bearing in La$_4$Co$_4$X, and we show that whereas La$_4$Co$_4$Pb
behaves as a three dimensional antiferromagnet with T$_N$ = 220 K,
La$_4$Co$_4$Bi and La$_4$Co$_4$Sb have behavior consistent with low dimensional
magnetic coupling and ordering, with T$_N$ = 153 K and 143 K respectively. In
addition to the Pb, Bi, and Sb based La$_4$Co$_4$X compounds, we were likely
able to produce an analogous La$_4$Co$_4$Sn in polycrystalline form, although
we were unable to isolate single crystals. We anticipate that using mutually
compatible third elements with an antagonistic pair represents a generalizable
design principle for discovering new materials and structure types containing
low-dimensional substructures.",2403.00204v1
2024-03-04,Shell Effects in Quasi-fission in Reactions Forming 226Th Compound Nucleus,"Quasi-fission (QF) reactions occur in fully damped heavy-ion collisions
without the formation of an equilibrated compound nucleus, leading to the
formation of fragments with similar properties as in fission reactions. Similar
shell effects are expected to affect fragment formation in both fission and QF.
Our purpose is to investigate QF dynamics in different reactions forming the
same compound nucleus and search for possible signatures of shell effects in
fragment formation. 50Ca+176Yb and 96Zr+130Sn QF reactions are simulated with
the time-dependent Hartree-Fock code Sky3D near the Coulomb barrier. Evolutions
of the quadrupole (Q20) and octupole (Q30) moments are interpreted in terms of
features of the potential energy surface (PES) of the 226Th compound nucleus.
Both reactions encounter QF. In 50Ca+176Yb, those only occur at finite angular
momenta. In the more symmetric 96Zr+130Sn reaction with stronger Coulomb
repulsion in the entrance channel, QF also occurs in central collisions. In
agreement with earlier predictions, 50Ca+176Yb encounters partial mass
equilibration that is stopped when the heavy fragment reaches Z~54 protons, as
in the asymmetric fission mode of 226Th. 96Zr+130Sn encounters an inverse QF
also leading to similar fragments as in asymmetric fission. In both systems, QF
trajectories in the Q20-Q30 plane follow the asymmetric fission valley of 226Th
PES. The observation of an inverse QF is a clear prediction that shell effects
have a strong influence in QF. The similarity between fragments formed in
asymmetric fission and QF supports the idea that the same shell effects are at
play in both mechanisms. Interpreting QF dynamics with PES used in fission is
naturally limited by the fact that these PES are usually computed with axial
symmetry, no angular momentum and no excitation energy, thus motivating future
developments of PES for QF.",2403.02541v1
2024-04-04,Empirical Bayes for the Reluctant Frequentist,"Empirical Bayes methods offer valuable tools for a large class of compound
decision problems. In this tutorial we describe some basic principles of the
empirical Bayes paradigm stressing their frequentist interpretation. Emphasis
is placed on recent developments of nonparametric maximum likelihood methods
for estimating mixture models. A more extensive introductory treatment will
eventually be available in \citet{kg24}. The methods are illustrated with an
extended application to models of heterogeneous income dynamics based on PSID
data.",2404.03422v1
1997-09-29,Dynamical Friction for Compound Bodies,"In the framework of the fluctuation-dissipation approach to dynamical
friction, we derive an expression giving the orbital energy exchange
experienced by a compound body as it moves interacting with a non homogeneous
discrete background. The body is assumed to be composed of particles endowed
with a velocity spectrum and with a non homogeneous spatial distribution. The
Chandrasekhar formula is recovered in the limit of a point-like satellite with
zero velocity dispersion and infinite temperature moving through an homogeneous
infinite medium. In this same limit, but dropping the zero satellite velocity
dispersion ($\sigma_S$) condition, the orbital energy loss is found to be
smaller than in the $\sigma_S=0$ case by a factor of up to an order of
magnitude in some situations.",9709290v2
2005-04-08,Extrasolar Carbon Planets,"We suggest that some extrasolar planets <~ 60 Earth masses will form
substantially from silicon carbide and other carbon compounds. Pulsar planets
and low-mass white dwarf planets are especially good candidate members of this
new class of planets, but these objects could also conceivably form around
stars like the Sun. This planet-formation pathway requires only a factor of two
local enhancement of the protoplanetary disk's C/O ratio above solar, a
condition that pileups of carbonaceous grains may create in ordinary
protoplanetary disks. Hot, Neptune-mass carbon planets should show a
significant paucity of water vapor in their spectra compared to hot planets
with solar abundances. Cooler, less massive carbon planets may show
hydrocarbon-rich spectra and tar-covered surfaces. The high sublimation
temperatures of diamond, SiC, and other carbon compounds could protect these
planets from carbon depletion at high temperatures.",0504214v2
1993-05-11,Electronic Structure and Bonding in Epitaxially Stabilized Cubic Iron Silicides,"We present an ab initio full-potential linearized augmented plane-wave
(FLAPW) study of the structural and electronic properties of the two bulk
unstable compounds FeSi (CsCl structure) and FeSi$_2$ (CaF$_2$ structure) which
have recently been grown by molecular beam epitaxy on Si(111). We obtain
equilibrium bulk lattice constants of 2.72 \AA\ and 5.32 \AA\ for FeSi and
FeSi$_2$, respectively. The density of states (DOS) of FeSi agrees well with
experiment, and shows metallic behavior. In agreement with a previous
calculation the DOS of FeSi$_2$ shows a large density of $d$-states at the
Fermi level, explaining the instability of the bulk phase. The electron charge
distributions reveal a small charge transfer from Si to Fe atomic spheres in
both compounds. While in FeSi the Fe-Si bond is indeed partially ionic, we show
that in FeSi$_2$ the electron distribution corresponds to a covalent charge
accumulation in the Fe-Si bond region. The reversed order of $d$-bands in FeSi
with respect to FeSi$_2$ is understood in terms of crystal field splitting and
Fe-Fe nearest neighbor $dd$-interactions in the CsCl structure, and a strong Si
$p$/Fe $d$ bonding in the fluorite structure, respectively.",9305007v1
1994-04-13,Spectra of Hamiltonians with Generalized Single-Site Dynamical Disorder,"Starting from the deformed commutation relations \ba a_q(t) \,a_q^{\dag}(s) \
- \ q\,a_q^{\dag}(s)\,a_q(t)
  \ = \ \Gam(t-s) {\bf 1} , \quad -1\ \le \ q\ \le\ 1\nn \ea with a covariance
$\Gam(t-s)$ and a parameter $q$ varying between $-1$ and $1$, a stochastic
process is constructed which continuously deforms the classical Gaussian and
classical compound Poisson process. The moments of these distinguished
stochastic processes are identified with the Hilbert space vacuum expectation
values of products of $\hat{\om}_q (t) = \gam\,\big(\, a_q(t) + a_q^{\dag} (t)
\,\big)\;+ \; \xi\, a_q^{\dag} (t) a_q(t)$ with fixed parameters $q$, $\gam$
and $\xi$. Thereby we can interpolate between dichotomic, random matrix and
classical
  Gaussian and compound Poisson processes.
  The spectra of Hamiltonians with single-site dynamical disorder are
calculated for an exponential covariance (coloured noise) by means of the time
convolution generalized master equation formalism (TC-GME) and the",9404037v1
1994-05-11,"Infrared Spectroscopic Study of Phase Transisions in A1c60 Compounds (a=K,Rb,Cs)","Optical measurements on doped C$_{60}$ films provide evidence for a
transition from a high temperature conducting phase to a low temperature
insulating phase in quenched Rb$_1$C$_{60}$ and K$_1$C$_{60}$ compounds, while
Cs$_1$C$_{60}$ did not exhibit this behavior. For slow cooled samples our study
confirms earlier results indicating phase separation of K$_1$C$_{60}$ to
K$_3$C$_{60}$ and C$_{60}$, and the formation of a new Rb$_1$C$_{60}$ phase at
low temperatures. Upon slow cooling Cs$_1$C$_{60}$ behaves similar to
Rb$_1$C$_{60}$.",9405033v1
1994-08-17,High-Pressure Low-Symmetry Phases of Cesium Halides from First Principle Techniques,"The relative stability of different high-pressure phases of various Cesium
Halides is studied from first principles and analyzed using the Landau theory
of phase transitions. We present results for CsI, CsBr, and CsCl up to
pressures of about 100 GPa. A cubic-to-orthorhombic transition, driven by the
softening of an acoustic phonon at the M point of the Brillouin zone, is
competing with the cubic-to-tetragonal martensitic transition typical of these
compounds. The phonon softening takes place only in CsI and CsBr at a residual
volume of 0.64, 0.52 respectively. A cubic-to-tetragonal instability is found
instead to occur at 0.54 for all the compounds considered here. The
orthorhombic phase is stable only in CsI, whereas it is taken over by the
tetragonal one in the case of CsBr. Our analysis reveals the essential role
played by the phonon-strain coupling in stabilizing the orthorhombic phase and
in making the corresponding transition first-order.",9408044v1
1994-12-16,Reference Force Field and CDW Amplitude of Mixed-Valence Halogen-Bridged Pt Complexes,"The spectroscopic effects of electron-phonon coupling in mixed-valence
chlorine-bridged Pt chains complexes are investigated through a parallel
infrared and Raman study of three compounds with decreasing Pt-Pt distance
along the chain. The e-ph interaction is analyzed in terms of the
Herzberg-Teller coupling scheme. We take into account the quadratic term and
define a precise reference state. The force field relevant to this state is
constructed, whereas the electronic structure is analyzed in terms of a simple
phenomenological model, singling out a trimeric unit along the chain. In this
way we are able to account for all the available optical data of the three
compounds, and to estimate the relevant microscopic parameters, such as the
e-ph coupling constants and the CDW amplitude.",9412082v2
1995-06-21,A Model for High Temperature Superconductors using the Extended Hubbard Model,"We derive a method to study the phase diagram for high temperature
superconductors (HTCS). Our starting point is the Hubbard Hamiltonian with a
weak attractive interaction to obtain the formation of bound pairs. We consider
this attractive potential at different positions for different compounds
accordingly to the experimental results of the coherence length. We then
construct a wave function of the BCS type by a variational method using the
Fourier transform of this extended Hubbard potential and then derive an energy
gap equation. This approach allows us to obtain the critical temperature as
function of the doping concentration which gives very good agreement with the
experimental phase diagrams of YBaCuO and La(Sr,Ba)CuO compounds.",9506096v1
1996-01-20,Transmission Electron Study of Heteroepitaxial Growth in the BiSrCaCuO System,"Films of Bi$\rm _2$Sr$\rm _2$CaCu$\rm _2$O$\rm _8$ and Bi$\rm _2$Sr$\rm
_2$CuO$\rm _6$ have been grown using Atomic-Layer-by-Layer Molecular Beam
Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been
combined with layers of closely-related metastable compounds like Bi$\rm
_2$Sr$\rm _2$Ca$\rm _7$Cu$\rm _8$O$\rm _{20}$ (2278) and rare-earth-doped
compounds like Bi$\rm _2$Sr$\rm _2$Dy$\rm _x$Ca$\rm _{1-x}$Cu$\rm _2$O$\rm _8$
(Dy:2212) to form heterostructures with unique superconducting properties,
including superconductor/insulator multilayers and tunnel junctions.
Transmission electron microscopy (TEM) has been used to study the morphology
and microstructure of these heterostructures. These TEM studies shed light on
the physical properties of the films, and give insight into the growth mode of
highly anisotropic solids like Bi$\rm _2$Sr$\rm _2$CaCu$\rm _2$O$\rm _8$.",9601090v1
1996-03-07,Electronic and Magnetic Structure of LaCuO$_{2.5}$,"The recently-discovered ``ladder'' compound LaCuO$_{2.5}$ has been found to
admit hole doping without altering its structure of coupled copper oxide
ladders. While susceptibility measurements on the parent compound suggest a
spin gap and a spin-liquid state, NMR results indicate magnetic order at low
temperatures. These seemingly contradictory results may be reconciled if in
fact the magnetic state is near the crossover from spin liquid to
antiferromagnet, and we investigate this possibility. From a tight-binding fit
to the valence LDA bandstructure, we deduce that the strength of the
interladder hopping term is approximately half that of intraladder hopping,
showing that the material is three-dimensional in character. A mean-field
treatment of the insulating magnetic state gives a spin-liquid phase whose spin
gap decreases with increasing interladder coupling, vanishing (signalling a
transition to the ordered phase) at a value somewhat below that obtained for
LaCuO$_{2.5}$. The introduction of an on-site repulsion term, $U$, to the band
scheme causes a transition to an antiferromagnetic insulator for rather small
but finite values of $U$, reflecting the predominance of (one-dimensional)
ladder behavior, and an absence of any special nesting features.",9603054v2
1996-04-30,Investigation of the Spin-Peierls transition in CuGeO_3 by Raman scattering,"Raman experiments on the spin-Peierls compound CuGeO$_3$ and the substituted
(Cu$_{1- x}$,Zn$_x$)GeO$_3$ and Cu(Ge$_{1-x}$,Ga$_x$)O$_3$ compounds were
performed in order to investigate the response of specific magnetic excitations
of the one-dimensional spin-1/2 chain to spin anisotropies and
substitution-induced disorder. In pure CuGeO$_3$, in addition to normal phonon
scattering which is not affected at all by the spin-Peierls transition, four
types of magnetic scattering features were observed. Below T$_{SP}$=14 K a
singlet-triplet excitation at 30 cm$^{-1}$, two-magnon scattering from 30 to
227 cm$^{-1}$ and folded phonon modes at 369 and 819 cm$^{-1}$ were identified.
They were assigned by their temperature dependence and lineshape. For
temperatures between the spin-Peierls transition T$_{SP}$ and approximately 100
K a broad intensity maximum centered at 300 cm$^{-1}$ is observed.",9604181v1
1996-05-07,Electronic Hamiltonian for Transition Metal Oxide Compounds,"An effective electronic Hamiltonian for transition metal oxide compounds is
presented. For Mn-oxides, the Hamiltonian contains spin-2 ``spins'' and
spin-3/2 ``holes'' as degrees of freedom. The model is constructed from the
Kondo-lattice Hamiltonian for mobile $e_g$ electrons and localized $t_{2g}$
spins, in the limit of a large Hund's coupling. The effective electron bond
hopping amplitude fluctuates in sign as the total spin of the bond changes. In
the large spin limit, the hopping amplitude for electrons aligned with the core
ions is complex and a Berry phase is accumulated when these electrons move in
loops. The new model is compared with the standard double exchange Hamiltonian.
Both have ferromagnetic ground states at finite hole density and low
temperatures, but their critical temperatures could be substantially different
due to the frustration effects induced by the Berry phase.",9605041v1
1996-07-09,Correlations within Eigenvectors and Transition Amplitudes in the Two-Body Random Interaction Model,"It is shown that the two-body character of the interaction in a many-body
system gives rise to specific correlations between the components of compound
states, even if this interaction is completely random. Surprisingly, these
correlations increase with the increase of the number of active (valence)
particles. Statistical theory of transition amplitudes between compound states,
which takes into account these correlation is developed and tested within the
framework of the Two-Body Random Interaction Model. It is demonstrated that a
feature, which can be called ``correlation resonance'', appears in the
distribution of the transition matrix amplitudes, since the correlations
strongly reduce the transition amplitudes at the tails and increase them near
the maximum of the distribution.",9607067v1
1996-11-04,The J_1-J_2 model revisited : Phenomenology of CuGeO_3,"We present a mean field solution of the antiferromagnetic Heisenberg chain
with nearest (J_1) and next to nearest neighbor (J_2) interactions. This
solution provides a way to estimate the effects of frustration. We calculate
the temperature-dependent spin-wave velocity, v_s(T) and discuss the
possibility to determine the magnitude of frustration J_2/J_1 present in quasi
1D compounds from measurements of v_s(T). We compute the thermodynamic
susceptibility at finite temperatures and compare it with the observed
susceptibility of the spin-Peierls compound CuGeO_3. We also use the method to
study the two-magnon Raman continuum observed in CuGeO_3 above the spin-Peierls
transition.",9611018v1
1996-11-07,Substitution effects on spin fluctuations in the spin-Peierls compound CuGeO_3,"Using Raman scattering we studied the effect of substitutions on 1D spin
fluctuations in CuGeO_3 observed as a spinon continuum in frustration induced
exchange scattering. For temperatures below the spin-Peierls transition
(T_{SP}=14K) the intensity of this continuum at 120-500 cm^{-1} is
exponentially suppressed and transferred into a 3D two-magnon density of
states. Besides a spin-Peierls gap-induced mode at 30 cm^{-1} and additional
modes at 105 and 370 cm^{-1} are observed. Substitution of Zn on the Cu-site
and Si on the Ge-site of CuGeO_3 quenches easily the spin-Peierls state.
Consequently a suppression of the spin-Peierls gap observable below T_{SP}=14K
as well as a change of the temperature dependence of the spinon continuum are
observed. These effects are discussed in the context of a dimensional crossover
of this compound below T_{SP} and strong spin-lattice interaction.",9611053v1
1996-12-11,Magnon-magnon interactions in the Spin-Peierls compound CuGeO_3,"In a magnetic substance the gap in the Raman spectrum, Delta_R, is
approximatively twice the value of the neutron scattering gap, Delta_S, if the
the magnetic excitations (magnons) are only weakly interacting.
  But for CuGeO_3 the experimentally observed ratio Delta_R/Delta_S is
approximatively 1.49-1.78, indicating attractive magnon-magnon interactions in
the quasi-1D Spin-Peierls compound CuGe_3.
  We present numerical estimates for Delta_R/Delta_S from exact diagonalization
studies for finite chains and find agreement with experiment for intermediate
values of the frustration parameter alpha.
  An analysis of the numerical Raman intensity leads us to postulate a
continuum of two-magnon bound states in the Spin-Peierls phase. We discuss in
detail the numerical method used, the dependence of the results on the model
parameters and a novel matrix-element effect due to the dimerization of the
Raman-operator in the Spin-Peierls phase.",9612101v1
1997-02-21,First-principles theory of structural phase transitions for perovskites: competing instabilities,"We extend our previous first-principles theory for perovskite ferroelectric
phase transitions to treat also antiferrodistortive phase transitions. Our
approach involves construction of a model Hamiltonian from a Taylor expansion,
first-principles calculations to determine expansion parameters, and Monte
Carlo simulations to study the resulting system. We apply this approach to
three cubic perovskite compounds, SrTiO3, CaTiO3, and NaNbO3, that are known to
undergo antiferrodistortive phase transitions. We calculate their transition
sequences and transition temperatures at the experimental lattice constants.
For SrTiO3, we find our results agree well with experiment. For more
complicated compounds like CaTiO3 and NaNbO3, which can have many different
structures with very similar energy, the agreement is somewhat less.",9702198v1
1997-03-10,The Crossover beteween Aslamazov-Larkin and Short Wavelength Fluctuations Regimes in HTS Conductivity Experiments,"We present paraconductivity (AL) measurements in three different high
temperature superconductors: a melt textured $YBa_2Cu_3O_7$ sample, a
$Bi_2Sr_2CaCu_2O_8$ epitaxial thin film and a highly textured
$Bi_2Sr_2Ca_2Cu_3O_{10}$ tape. The crossovers between different temperature
regimes in excess conductivity have been analysed. The Lawrence-Doniach (LD)
crossover, which separates the 2D and 3D regimes, shifts from lower to higher
temperatures as the compound anisotropy decreases. Once the LD crossover is
overcome, the fluctuation conductivity of the three compounds shows the same
universal behaviour: for $\epsilon =\ln T/T_c > 0.23$ all the curves bend down
according to the $1/\epsilon^3$ law. This asymptotic behaviour was
theoretically predicted previously for the high temperature region where the
short wavelength fluctuations (SWF) become important.",9703090v1
1997-04-02,Dynamical properties of the spin-Peierls compound α'--NaV2O5,"Dynamical properties of the novel inorganic spin-Peierls compound
\alpha'--NaV2O5 are investigated using a one-dimensional dimerized Heisenberg
model. By exact diagonalizations of chains with up to 28 sites, supplemented by
a finite-size scaling analysis, the dimerization parameter \delta is determined
by requiring that the model reproduces the experimentally observed spin gap
\Delta. The dynamical and static spin structure factors are calculated. As for
CuGeO3, the existence of a low energy magnon branch separated from the
continuum is predicted. The present calculations also suggest that a large
magnetic Raman scattering intensity should appear above an energy threshold of
1.9 \Delta. The predicted photoemission spectrum is qualitatively similar to
results for an undimerized chain due to the presence of sizable short-range
antiferromagnetic correlations.",9704015v3
1997-06-03,A model for the doped copper oxide compounds,"We present a relativistic spin-fermion model for the cuprates, in which both
the charge and spin degrees of freedom are treated dynamically. The spin-charge
coupling parameter is associated with the doping fraction. The model is able to
account for the various phases of the cuprates and their properties, not only
at low and intermediate doping but also for (highly) over-doped compounds. In
particular, we acquire a qualitative understanding of high-T_c
superconductivity through Bose-Einstein condensation of bound charge pairs. The
mechanism that binds these pairs does not require a Fermi sea.",9706022v2
1997-06-16,A single chain analysis of doped quasi one dimensional spin 1 compounds: paramagnetic versus spin 1/2 doping,"We present a numerical study of single chain models of doped spin 1
compounds. We use low energy effective one-dimensional models for both the
cases of paramagnetic and spin-1/2 doping. In the case of paramagnetic doping,
the effective model is equivalent to the bond disordered spin-1/2 chain model
recently analyzed by means of real space renormalization group by Hyman and
Yang. By means of exact diagonalizations in the XX limit, we confirm the
stability of the Haldane phase for weak disorder. Above a critical amount of
disorder, the effective model flows to the so called random singlet fixed
point. In the case of spin-1/2 doping, we argue that the Haldane phase should
be destabilized even for weak disorder. This picture is not in contradiction
with existing experimental data. We also discuss the possible occurrence of
(unobserved) antiferromagnetically ordered phases.",9706158v1
1997-06-17,Disappearance of the Spin Gap in a Zn doped 2-Leg Ladder Compound Sr(Cu1-xZnx)2O3,"An inelastic neutron scattering study was performed on a Zn-substituted
spin-1/2 Heisenberg 2-leg ladder compound Sr(Cu1-xZnx)2O3 (x < 0.04) to
investigate nonmagnetic impurity effects on the quantum spin system with a
large spin gap of about 400 K. The magnitude of the spin gap was found to be
independent of Zn concentration, 33 meV, while the integrated magnetic
scattering which corresponds to the singlet-triplet excitation decreased
monotonically with increasing x. On account of the total-sum rule, this result
supports the existence of a finite in-gap density of states at E = 0 which was
suggested from the T-linear magnetic specific heat.",9706170v1
1997-06-17,Generalized calculation of magnetic coupling constants for Mott-Hubbard insulators: Application to ferromagnetic Cr compounds,"Using a Rayleigh-Schr\""odinger perturbation expansion of multi-band Hubbard
models, we present analytic expressions for the super-exchange coupling
constants between magnetic transition metal ions of arbitrary separation in
Mott-Hubbard insulators. The only restrictions are i) all ligand ions are
closed shell anions and ii) all contributing interaction paths are of equal
length. For short paths, our results essentially confirm the
Goodenough-Kanamori-Anderson rules, yet in general there does not exist any
simple rule to predict the sign of the magnetic coupling constants. The most
favorable situation for ferromagnetic coupling is found for ions with less than
half filled d shells, the (relative) tendency to ferromagnetic coupling
increases with increasing path length. As an application, the magnetic
interactions of the Cr compounds Rb$_2$CrCl$_4$, CrCl$_3$, CrBr$_3$ and CrI$_3$
are investigated, all of which except CrCl$_3$ are ferromagnets.",9706175v1
1997-07-23,Multiband model of high Tc superconductors,"We propose an extension to other high T_{c } compounds of a model introduced
earlier for YBCO. In the ''self-doped'' compounds we assume that the doping
part (namely the BiO, HgO, TlO planes in BSCCO, HBCCO, TBCCO respectively) is
metallic, which leads to a multiband model. This assumption is supported by
band structure calculations. Taking a repulsive pairing interaction between
these doping bands and the CuO_{2} bands leads to opposite signs for the order
parameter on these bands and to nodes whenever the Fermi surfaces of these
bands cross. We show that in BSCCO the low temperature dependence of the
penetration depth is reasonably accounted for. In this case the nodes are not
located near the 45^{o} direction, which makes the experimental determination
of the node locations an important test for our model. The situation in HBCCO
and TBCCO is rather analogous to BSCCO. We consider the indications given by
NMR and find that they rather favor a metallic character for the doping bands.
Finally we discuss the cases of NCCO and LSCO which are not ''self-doped'' and
where our model does not give nodes.",9707241v1
1997-08-18,Experimental Verification of the Gapless Point in the $S$=1 Antiferromagnetic Bond Alternating Chain,"Susceptibility and high field magnetization measurements have been performed
on powder samples of an $S$=1 bond alternating chain compound
[\{Ni(333-tet)($\mu$-N$_3$)\}$_n$](ClO$_4$)$_n$ (333-tet=tetraamine
N,N'-bis(3-aminopropyl)-1,3-propanediamine). As the temperature is decreased,
the susceptibility exhibits a round maximum at around 120 K and decreases
gradually down to 10 K, and then falls down rapidly with a logarithmic
curvature which is behavior of the susceptibility of a gapless or a nearly
gapless antiferromagnetic chain. Magnetization up to 50 T at 1.4 K shows no or
a very small gap in this compound. We have carried out numerical calculations
for the $S$=1 antiferromagnetic bond alternating chain with various alternating
ratios $\alpha$ and obtained a very good agreement between experiments and
calculations for $\alpha$=0.6. We verify experimentally that the gapless point
exists around $\alpha$=0.6.",9708127v1
1998-03-02,Exchange Narrowing Effects in the EPR Linewidth of Gd Diluted in Ce Compounds,"Anomalous thermal behavior on the EPR linewidths of Gd impurities diluted in
Ce compounds has been observed. In metals, the local magnetic moment EPR
linewidth, \Delta H, is expected to increase linearly with the temperature. In
contrast, in Ce_{x}La_{1-x}Os_{2} the Gd EPR spectra show a nonlinear increase.
In this work, the mechanisms that are responsible for the thermal behavior of
the EPR lines in Ce_{x}La_{1-x}Os_{2} are examined. We show that the exchange
interaction between the local magnetic moments and the conduction electrons are
responsible for the narrowing of the spectra at low temperatures. At high
temperatures, the contribution to the linewidth of the exchange interaction
between the local magnetic moments and the $Ce$ ions has an exponential
dependence on the excitation energy of the intermediate valent ions. A complete
fitting of the EPR spectra for powdered samples is obtained.",9803030v1
1998-03-26,Excitonic Correlations in the Intermetallic Fe2VAl,"The intermetallic compound Fe2VAl looks non-metallic in transport and
strongly metallic in thermodynamic and photoemission data. It has in its band
structure a highly differentiated set of valence and conduction bands leading
to a semimetallic system with a very low density of carriers. The pseudogap
itself is due to interaction of Al states with the d orbitals of Fe and V, but
the resulting carriers have little Al character. The effects of generalized
gradient corrections to the local density band structure as well spin-orbit
coupling are shown to be significant, reducing the carrier density by a factor
of three. Doping of this nonmagnetic compound by 0.5 electrons per cell in a
virtual crystal fashion results in a moment of 0.5 bohr magnetons and destroys
the pseudogap. We assess the tendencies toward formation of an excitonic
condensate and toward an excitonic Wigner crystal, and find both to be
unlikely. We propose a model is which the observed properties result from
excitonic correlations arising from two interpenetrating lattices of
distinctive electrons (e_g on V) and holes (t_2g on Fe) of low density (one
carrier of each sign per 350 formula units).",9803327v1
1998-05-08,Thermal Conductivity of the Spin Peierls Compound CuGeO_3,"The thermal conductivity of the Spin-Peierls (SP) compound CuGeO_3 was
measured in magnetic fields up to 16 T. Above the SP transition, the heat
transport due to spin excitations causes a peak at around 22 K, while below the
transition the spin excitations rapidly diminish and the heat transport is
dominated by phonons; however, the main scattering process of the phonons is
with spin excitations, which demonstrates itself in an unusual peak in the
thermal conductivity at about 5.5 K. This low-temperature peak is strongly
suppressed with magnetic fields in excess of 12.5 T.",9805099v1
1998-06-12,Interplane magnetic coupling effects in the multilattice compound Y_2Ba_4Cu_7O_{15},"We investigate the interplane magnetic coupling of the multilattice compound
Y_2Ba_4Cu_7O_{15} by means of a bilayer Hubbard model with inequivalent planes.
  We evaluate the spin response, effective interaction and the intra- and
interplane spin-spin relaxation times within the fluctuation exchange
approximation. We show that strong in-plane antiferromagnetic fluctuations are
responsible for a magnetic coupling between the planes, which in turns leads to
a tendency of the fluctuation in the two planes to equalize.
  This equalization effect grows whit increasing in-plane antiferromagnetic
fluctuations, i. e., with decreasing temperature and decreasing doping, while
it is completely absent when the in-layer correlation length becomes of the
order of one lattice spacing. Our results provide a good qualitative
description of NMR and NQR experiments in Y_2Ba_4Cu_7O_{15}.",9806155v2
1998-06-26,Electron-spin-resonance in the doped spin-Peierls compound Cu(1-x)Ni(x)GeO3,"ESR-study of the Ni-doped spin-Peierls compound CuGeO3 has been performed in
the frequency range 9-75 GHz. At low temperatures the g-factor is smaller than
the value expected for Cu- and Ni-ions. This anomaly is explained by the
formation of magnetic clusters around the Ni-ions within a nonmagnetic
spin-Peierls matrix. The transition into the AFM-state detected earlier by
neutron scattering for doped samples was studied by means of ESR. For x=0.032 a
gap in the magnetic resonance spectrum is found below the Neel temperature and
the spectrum is well described by the theory of antiferromagnetic resonance
based on the molecular field approximation. For x=0.017 the spectrum below the
Neel point remained gapless. The gapless spectrum of the antiferromagnetic
state in weekly doped samples is attributed to the small value of the Neel
order parameter and to the magnetically disordered spin-Peierls background.",9806325v1
1998-07-24,Spin Fluctuation-Induced Superconductivity in Organic Compounds,"Spin fluctuation-induced superconductivity in two-dimensional organic
compounds such as \kappa-(ET)_2-X is investigated by using a simplified dimer
Hubbard model with right-angled isosceles triangular lattice (transfer matrices
-\tau, -\tau^\prime). The dynamical susceptiblity and the self-energy are
calculated self-consistently within the fluctuation exchange approximation and
the value for T_c as obtained by solving the linearized Eliashberg-type
equations is in good agreement with experiment. The pairing symmetry is of
d_{x^2-y^2} type. The calculated (U/\tau)-dependence of T_c compares
qualitatively well with the observed pressure dependence of T_c. Varying the
value for \tau^\prime/\tau from 0 to 1 we interpolate between the square
lattice and the regular triangular lattice and find firstly that values of T_c
for \kappa-(ET)_2-X and cuprates scale well and secondly that T_c tends to
decrease with increasing \tau^\prime/\tau and no superconductivity is found for
\tau^\prime/\tau=1, the regular triangular lattice.",9807322v2
1998-07-25,A Model for the Schottky Anomaly in Metallic $Nd_{2-y}Ce_{y}CuO_{4}$,"We present a simple model for the doped compound $Nd_{2-y}Ce_{y}CuO_{4}$, in
order to explain some recent experimental results on the latter. Within a
Hartree-Fock context, we start from an impurity Anderson-like model and
consider the magnetic splitting of the $Nd$-$4f$ ground state Kramers doublet
due to exchange interactions with the ordered $Cu$ moments. Our results are in
very good agreement with the experimental data, yielding a Schottky anomaly
peak for the specific heat that reduces its amplitude, broadens and shifts to
lower temperatures, upon $Ce$ doping. For overdoped compounds at low
temperatures, the specific heat behaves linearly and the magnetic
susceptibility is constant. A smooth transition from this Fermi liquid like
behavior ocurrs as temperature is increased and at high temperatures the
susceptibility exhibits a Curie-like behavior. Finally, we discuss some
improvements our model is amenable to incorporate.",9807337v2
1998-07-30,Low Temperature Superfluid Response of High-Tc Superconductors,"We have reviewed our theoretical and experimental results of the low
temperature superfluid response function of high temperature superconductors
(HTSC). In clean high-Tc materials the in-plane superfluid density rho_s^{ab}
varies linearly with temperature. The slope of this linear T term is found to
scale approximately with 1/Tc which, according to the weak coupling BCS theory
for a d-wave superconductor, implies that the gap amplitude scales
approximately with Tc. A T^5 behavior of the out-of-plane superfluid density
rho_s^c for clean tetragonal HTSC was predicted and observed experimentally in
the single layer Hg-compound HgBa_2CuO_{4+delta}. In other tetragonal high-Tc
compounds with relatively high anisotropy, such as Hg_2Ba_2Ca_2Cu_3O_{8+delta},
rho_s^c varies as T^2 due to disorder effects. In optimally doped
YBa_2Cu_3O_{7-delta}, rho_s^c varies linearly with temperature at low
temperatures, but in underdoped YBa_2Cu_3O_{7-delta}, rho_s^c varies as T^2 at
low temperatures; these results are consistent with our theoretical
calculations.",9807404v1
1998-08-12,Electrons in High-Tc Compounds: Ab-Initio Correlation Results,"Electronic correlations in the ground state of an idealized infinite-layer
high-Tc compound are computed using the ab-initio method of local ansatz.
Comparisons are made with the local-density approximation (LDA) results, and
the correlation functions are analyzed in detail. These correlation functions
are used to determine the effective atomic-interaction parameters for model
Hamiltonians. On the resulting model, doping dependencies of the relevant
correlations are investigated. Aside from the expected strong atomic
correlations, particular spin correlations arise. The dominating contribution
is a strong nearest neighbor correlation that is Stoner-enhanced due to the
closeness of the ground state to the magnetic phase. This feature depends
moderately on doping, and is absent in a single-band Hubbard model. Our
calculated spin correlation function is in good qualitative agreement with that
determined from the neutron scattering experiments for a metal.",9808127v1
1998-10-28,An ordered stack of spin valves in a layered magnetoresistive perovskite,"The layered compound La2-2xSr1+2xMn2O7 (x=0.3) consists of bilayers of
metallic MnO2 sheets separated by insulating material. The compound exhibits
markedly anisotropic magnetoresistance at temperatures well below the
three-dimensional magnetic ordering temperature TC=90 K in addition to colossal
magnetoresistance around TC. We present neutron diffraction data which show
that the magnetic structure of this material switches from antiferromagnetic
stacking of the (ferromagnetically ordered) sheets in zero field to
ferromagnetic stacking in a field of 1.5 Tesla. The data are the first to be
collected on any manganite as a function of applied field, exactly as the
magnetoresistance data themselves are collected. They provide a natural
explanation of the low-field magnetoresistance in the ordered phase in terms of
spin-polarised tunnelling between the magnetic layers and suggest that the
material is a bulk stack of spin-valve devices.",9810382v1
1998-11-27,Large Low Temperature Magnetoresistance and Magnetic Anomalies in Tb$_2$PdSi$_3$ and Dy$_2$PdSi$_3$,"The results of heat-capacity, magnetic susceptibility, electrical resistivity
and magnetoresistance $(\Delta \rho/\rho)$ measurements on the compounds
Tb$_2$PdSi$_3$ and Dy$_2$PdSi$_3$, are reported. The results establish that
these compounds undergo long-range magnetic ordering (presumably with a complex
magnetic structure) below (Tc=) 23 and 8 K respectively. The $\Delta \rho/\rho
$ is negative in the vicinity of Tc and the magnitude grows as Tc is approached
from higher temperature as in the case of well-known giant magnetoresistance
systems (La manganite based perovskites); this is attributed to the formation
of some kind of magnetic polarons. The magnitude of magnetoresistance at low
temperatures is quite large, for instance, about 30% in the presence of 60 kOe
field at 5 K in the Dy sample.",9811387v1
1998-12-04,Thermodynamics of the Double Exchange Systems,"This article gives a comprehensive review on the recent studies of the double
exchange systems using non-perturbative approaches; the dynamical mean-field
theory and the Monte Carlo method. Investigations beyond mean-field type
treatments are described. Taking into account strong spin fluctuations which
create large changes in conduction electron structure, finite temperature
properties as well as dynamics of the system are calculated. Comparisons with
experimental data for colossal magnetoresistance manganites are made. We show
that high Curie temperature (Tc) compounds, e.g. (La,Sr)MnO3, are canonical
double-exchange systems. Properties of other compounds with lower Tc are
discussed in relation to inhomogeneities of the system including the issue of
phase separation.",9812066v1
1998-12-22,Magnetic precursor effects in Gd alloys,"The behaviour of electrical resistivity ($\rho$) and magnetoresistance in the
vicinity of respective magnetic ordering temperatures in a number of Gd alloys
is reported. In some compounds, e.g., GdNi_2Sn_2 and GdPt_2Ge_2, there is an
enhancement of $\rho$ prior to long range magnetic order over a wide
temperature range which can be highlighted by the suppression of $\rho$ caused
by the application of a magnetic field. However, such features are absent in
many other Gd compounds, e.g., GdCu_2Ge_2, GdAg_2Si_2, GdAu_2Si_2, GdPd_2Ge_2
and GdCo_2Si_2. Attempts to relate such features to magnetic precursor effects
in heat capacity are made. On the basis of our studies, we suggest that better
understanding of magnetic precursor effects in Gd alloys will be helpful to
throw light on some of the current trends in magnetism. Various other
interesting findings in the magnetically ordered state in some of these alloys
are also brought out.",9812365v1
1998-12-22,NMR imaging of the soliton lattice profile in the spin-Peierls compound CuGeO_3,"In the spin-Peierls compound CuGeO$_{3}$, the commensurate-incommensurate
transition concerning the modulation of atomic position and the local
spin-polarization is fully monitored at T=0 by the application of an external
magnetic field ($H$) above a threshold value $H_{c}\simeq $ 13 Tesla. The
solitonic profile of the spin-polarization, as well as its absolute magnitude,
has been precisely imaged from $^{65}Cu$ NMR lineshapes obtained for
$h=(H-H_{c})/H_{c}$ varying from 0.0015 to 2. This offers a unique possibility
to test quantitatively the various numerical and analytical methods developed
to solve a generic Hamiltonian in 1-D physics, namely strongly interacting
fermions in presence of electron-phonon coupling at arbitrary band filling.",9812370v1
1999-01-11,Coexistence of ferromagnetism and superconductivity in the hybrid ruthenate-cuprate compound RuSr_2GdCu_2O_8 studied by muon spin rotation (μ SR) and DC-magnetization,"We have investigated the magnetic and the superconducting properties of the
hybrid ruthenate-cuprate compound RuSr_{2}GdCu_{2}O_{8} by means of zero-field
muon spin rotation- (ZF-$\mu $SR) and DC magnetization measurements. The
DC-magnetisation data establish that this material exhibits ferromagnetic order
of the Ru-moments ($\mu (Ru) \approx 1 \mu_{B}$) below T_{Curie} = 133 K and
becomes superconducting at a much lower temperature T_c = 16 K. The ZF-$\mu $SR
experiments indicate that the ferromagnetic phase is homogeneous on a
microscopic scale and accounts for most of the sample volume. They also suggest
that the magnetic order is not significantly modified at the onset of
superconductivity.",9901084v2
1999-02-23,Transition from Haldane Phase to Spin Liquid and Incommensurate Correlation in Spin-1/2 Heisenberg Chains,"The bulk properties and impurity effect in the one-dimensional S=1/2
Heisenberg model with dimerization and next-nearest-neighbor exchange are
studied by the density matrix renormalization group (DMRG) and exact
diagonalization methods. This model widely covers the S=1 Heisenberg model,
two-leg ladders, bond-alternating chains and the S=1/2 Heisenberg model. Almost
the whole parameter space belongs to the Haldane phase. In the non-dimerizing
limit a transition to a kind of spin liquid takes place, characterized by the
delocalized spin polarization. This transition causes the distinct impurity
effects between a spin-Peierls compound CuGeO_{3} and the Haldane systems.
Experimental aspects of a bond-alternating compound CuNb_{2}O_{6} are also
discussed. Furthermore, the incommensurate correlation arising in this model is
extensively studied, and a phase diagram is constructed.",9902311v1
1999-03-12,Observation of spin freezing and relaxation at microwave frequencies in the spin ladder compound $Sr_{14-x}Ca_{x}Cu_{24}O_{41}$,"We report the observation of a frequency ($\omega $) and temperature (T)
-dependent loss peak in $\chi''$ and accompanying dispersion in $\chi'$ from
microwave (2-18GHz) measurements of the complex susceptibility
$\tilde{\chi}(\omega, T)=\chi'+i\chi''$ of $Sr_{14-x}Ca_{x}Cu_{24}O_{41}$. We
associate this phenomenon with a rapid decrease of spin disorder and
corresponding spin relaxation rate, representing a ``spin freezing transition''
accompanying charge ordering which occurs at temperatures $\sim 250K$. Our
results enable direct quantitative measurements of the spin relaxation rate,
and yield information on spin dynamics in these materials and the related
compounds $SrCuO_{2}$ and $Sr_{2}CuO_{3}$.",9903198v1
1999-03-12,On the Coexistence in RuSr2GdCu2O8 of Superconductivity and Ferromagnetism,"We review the reasons that make superconductivity unlikely to arise in a
ferromagnet. Then, in light of the report by Tallon and collaborators that
RuSr2GdCu2O8 becomes superconducting at approximately 35 K which is well below
the Curie temperature of 132 K, we consider whether the objections really apply
to this compound. Our considerations are supported by local spin density
calculations for this compound, which indeed indicate a ferromagnetic RuO2
layer. The Ru moment resides in t_2g orbitals but is characteristic of
itinerant magnetism (and is sensitive to choice of exchange-correlation
potential and to the atomic positions). Based on the small exchange splitting
that is induced in the Cu-O layers, the system seems capable of supporting
singlet superconductivity an FFLO-type order parameter and possibly a pi-phase
alternation between layers. If instead the pairing is triplet in the RuO2
layers, it can be distinguished by a spin-polarized supercurrent. Either type
of superconductivity seems to imply a spontaneous vortex phase if the
magnetization is rotated out of the plane.",9903210v2
1999-03-25,Spin Fluctuation-Induced Superconductivity in κ-BEDT-TTF Compounds,"Spin fluctuation-induced superconductivity in quasi-two dimensional organic
compounds, \kappa-BEDT-TTF salts, is investigated within a fluctuation exchange
(FLEX) approximation using a half-filled Hubbard model with a right-angled
isosceles triangular lattice (transfer matrices -\tau, -\tau^\prime), extending
a previous work above T_c. An energy gap of A_2 or (x^2-y^2)-type develops with
decreasing temperature below T_c more rapidly than in the BCS model. The
calculated dynamical susceptibilities enough below T_c show sharp resonance
peaks like those in certain cuprates superconductors. The calculated nuclear
spin-lattice relaxation rate 1/T_1 shows a T^3 behavior below T_c in accordance
with experiment. Estimated values of 1/T_1 are roughly consistent with
experimental results. A prediction is made for the doping concentration
dependence of T_c and the antiferromagnetic and superconductive instability
points are calculated in the U/\tau vs. \tau^\prime/\tau plane.",9903374v1
1999-04-14,Magnetic clusters formation in Li_{1-x}Ni_{1+x}O_2 compounds : experiments and numerical simulations,"The magnetic properties of Li_{1-x}Ni_{1+x}O_2 compounds with x ranging
between 0.02 and 0.2 are investigated. Magnetization and ac susceptibility
measured at temperatures between 2 K and 300 K reveal a high sensitivity to x,
the excess Nickel concentration. We introduce a percolation model describing
the formation of Ni clusters and use an Ising model to simulate their magnetic
properties. Numerical results, obtained by a Monte-Carlo technique, are
compared to the experimental data. We show the existence of a critical
concentration, x_c = 0.136, locating the Ni percolation threshold. The system
is superparamagnetic for x<x_c, while it is ferrimagnetic for x>x_c. The 180
Ni-O-Ni inter-plane super-exchange coupling J_\perp \simeq -110K is confirmed
to be the predominant magnetic interaction. From the low temperature behavior,
we find a clear indication of a 90 Ni-O-Ni intra-plane antiferromagnetic
interaction $J_\parallel \simeq -1.5K$ which implies magnetic frustration.",9904194v1
1999-05-21,Far-Infrared Spectroscopy in Spin-Peierls Compound CuGeO_3 under High Magnetic Fields,"Polarized far-infrared (FIR) spectroscopic measurements and FIR
magneto-optical studies were performed on the inorganic spin-Peierls compound
CuGeO_3. An absorption line, which was found at 98 cm$^{-1}$ in the dimerized
phase (D phase), was assigned to a folded phonon mode of B$_{3u}$ symmetry. The
splitting of the folded mode into two components in the incommensurate phase
(IC phase) has been observed for the first time. A new broad absorption
centered at 63 cm$^{-1}$ was observed only in the ${\bf E}\parallel b$ axis
polarization, which was assigned to a magnetic excitation from singlet ground
state to a continuum state.",9905325v2
1999-05-28,Magnetic behaviour of Eu_2CuSi_3: Large negative magnetoresistance above Curie temperature,"We report here the results of magnetic susceptibility,
electrical-resistivity, magnetoresistance (MR), heat-capacity and ^{151}Eu
Mossbauer effect measurements on the compound, Eu_2CuSi_3, crystallizing in an
AlB_2-derived hexagonal structure. The results establish that Eu ions are
divalent, undergoing long-range ferromagnetic-ordering below (T_C=) 37 K. An
interesting observation is that the sign of MR is negative even at temperatures
close to 3T_C, with increasing magnitude with decreasing temperature exhibiting
a peak at T_C. This observation, being made for a Cu containing magnetic
rare-earth compound for the first time, is of relevance to the field of
collosal magnetoresistance.",9905416v1
1999-06-18,Antiferromagnetism in hydrated 123 compounds,"Copper nuclear quadrupole resonance (NQR) and zero field nuclear magnetic
resonance (ZFNMR) studies of YBa$_2$Cu$_3$O$_{6.5}$ show that a magnetic phase
appears in underdoped 123 superconductors treated in ambient wet air. The
studies give convincing evidence that the ``empty'' CuO chains play the role of
easy water insertion channels. The reaction occurs first in ordered regions of
the crystallites. The final product of the reaction is a non-superconducting
antiferromagnetic compound characterized by at least two types of magnetically
ordered copper ions with ZFNMR spectra respectively in the frequency ranges of
46-96 and 96-135 MHz respectively. Even for powder samples fixed in an epoxy
resin, the reaction is found to occur partly after a few years.",9906295v1
1999-06-25,Direct exchange in the edge-sharing spin-1/2 compound MgVO_3,"Bandstructure calculations with different spin arrangement for the spin-chain
compound MgVO_3 have been performed, and paramagnetic as well as magnetic
solutions with ferro- and antiferromagnetically ordered chains are found, the
magnetic solutions being by 0.22 eV per formula unit lower than the
paramagnetic one. The orbital analysis of the narrow band crossing the Fermi
level in the paramagnetic solution reveals that the band has almost pure
vanadium 3d character, the lobes of the relevant d-orbitals at the neighboring
in-chain sites being directed towards each other, which suggests direct
exchange. The tight-binding analysis of the band confirms the strong exchange
transfer between neighboring in-chain V-ions. Besides, some additional
superexchange transfer terms are found, which give rise both to in-plane
coupling between the chains and to frustration, the dominant frustration
occuring due to the interchain interaction.",9906385v1
1999-07-28,Freezing of anisotropic spin clusters in La1.98Sr0.02CuO4,"A spin-glass compound, La$_{1.98}$Sr$_{0.02}$CuO$_4$, shows
quasi-three-dimensional magnetic ordering below $\sim$40 K. A remarkable
feature is that the magnetic correlation length along the orthorhombic
$a\rm_{ortho}$ axis is much longer than that along the $b\rm_{ortho}$ axis,
suggesting that the spin structure is closely related to the diagonal stripe
structure. The spin-glass state can be expressed as a random freezing of
quasi-three-dimensional spin clusters with anisotropic spin correlations
($\xi'_a\sim160$ \AA, $\xi'_b\sim25$ \AA, and $\xi'_c\sim4.7$ \AA at 1.6 K).
The new magnetic state is important as an intermediate phase between the
three-dimensional antiferromagnetic ordered phase in La$_2$CuO$_4$ and the
incommensurate phase in La$_{1.95}$Sr$_{0.05}$CuO$_4$ in which the positions of
the incommensurate peaks are rotated by 45$^\circ$ in reciprocal space about
($\pi$,$\pi$) from those observed in the superconducting La$_2$CuO$_4$
compounds.",9907435v2
1999-08-20,ESR experiments in the Kondo insulator CeNiSn,"Below a characteristic temperature, due to hybridisation effects Kondo
insulators exhibit a gap in the electronic density of states and behave like
semiconductors. By using Gd3+ electron spin resonance (ESR), the compound
CeNiSn was investigated as a representative of this class. In addition, the
metal-to-insulator transition was studied as a function of doping for
CeNi(1-x)Co(x)Sn and CeNi(1-y)Pt(y)Sn. The linewidth of the Gd resonance yields
direct information about the density of states at the Fermi energy. So the size
of the gap can clearly be estimated for the pure compound, and the closing of
the gap by substitution of Ni by Co or Pt can be followed in detail. These
results are compared to measurements of NMR, specific heat and susceptibility.",9908293v1
1999-09-02,Origin of Superconductivity in 2D-Organic Compounds and High-T_c Cuprates,"A phase diagram is drawn in a parameter space of the nearly half-filled
single band two-dimensional Hubbard model with U/t, t'/t and n as the
parameters, U, t, t' and n being the on-site interaction, the nearest and
second nearest neighbor transfer matrices and the number of electrons per site,
respectively. The parameter space is chosen so as to include the models for the
high-T_c cuprates as well as 2D-organic superconductors. The superconducting
and antiferromagnetic instability surfaces are drawn from the results of
calculations by using the spin fluctuation theory within the fluctuation
exchange approximation. The metal-insulator transition surface is also
indicated in the diagram. From this phase diagram we discuss the possibility of
the spin fluctuation mechanism being the common origin of the superconductivity
in the high-T_c cuprates and 2D-organic compounds.",9909024v1
1999-11-01,Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2,"We have performed elastic neutron-scattering experiments on the
heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found
that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly
enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at
1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m
increases slightly at a rate ~ 1 K/GPa, roughly following the transition
temperature T_o determined from macroscopic anomalies. We have also observed a
sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of
antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced
lattice constant.",9910509v1
1999-11-01,Band structure and transport studies on PdAl2Cl8-intercalated graphite,"The 2D Fermi surface of 1st stage PdAl2Cl8 acceptor-type graphite
intercalation compounds (GICs) has been investigated using the Shubnikov-de
Haas (SdH) effect. One fundamental frequency is observed, the angular variation
of which confirms its strongly 2D nature, as previously found through
electrical conductivity measurements. The energy spectrum can be described by
the 2D band structure model proposed by Blinowski et al. We obtain the
following parameter values: intraplane C-C interaction energy gamma_0 = 2.7 eV,
Fermi energy E_F = -1.1 eV and carrier density n_SdH= 1.1x10^27 m^-3. Some
fewer details are presented on stage 2 and 3 materials.",9910516v2
1999-11-12,Superconducting fluctuations and anomalous diamagnetism in underdoped YBa2Cu3O6+x from magnetization and 63Cu NMR-NQR relaxation measurements,"Magnetization and 63Cu NMR-NQR relaxation measurements are used to study the
superconducting fluctuations in YBa2Cu3O6+x (YBCO) oriented powders. In
optimally doped YBCO the fluctuating negative magnetization M_{fl}(H,T) is
rather well described by an anisotropic Ginzburg-Landau (GL) functional and the
curves M_{fl}/sqrt{H} cross at Tc. In underdoped YBCO, instead, over a wide
temperature range an anomalous diamagnetism is observed, stronger than in the
optimally doped compound by about an order of magnitude. The field and
temperature dependences of M_{fl} cannot be described either by an anisotropic
GL functional or on the basis of scaling arguments. The anomalous diamagnetism
is more pronounced in samples with a defined order in the Cu(1)O chains. The
63Cu(2) relaxation rate shows little, if any, field dependence in the vicinity
of the transition temperature Tc(H=0). It is argued how the results in the
underdoped compounds can be accounted for by the presence of charge
inhomogeneities, favoured by chains ordering.",9911182v1
1999-12-21,Specific heat of an S=1/2 Heisenberg ladder compound Cu$_2$(C$_5$H$_{12}$N$_2$)$_2$Cl$_4$ under magnetic fields,"Specific heat measurements down to 0.5 K have been performed on a single
crystal sample of a spin-ladder like compound
Cu$_{2}$(C$_{5}$H$_{12}$N$_{2}$)$_{2}$Cl$_{4}$ under magnetic fields up to 12
T. The temperature dependence of the observed data in a magnetic field below 6
T is well reproduced by numerical results calculated for the S=1/2 two-leg
ladder with $J_{\rm{rung}}$/$J_{\rm{leg}}$=5. In the gapless region above 7 T
($H_{\rm{c1}}$), the agreement between experiment and calculation is good above
about 2 K and a sharp and a round peak were observed below 2 K in a magnetic
field around 10 T, but the numerical data show only a round peak, the magnitude
of which is smaller than that of the observed one. The origin of the sharp peak
and the difference between the experimental and numerical round peak are
discussed.",9912385v1
2000-01-21,Superconductivity in a Ferromagnetic Layered Compound,"We examine superconductivity in layered systems with large Fermi-surface
splitting due to coexisting ferromagnetic layers. In particular, the hybrid
ruthenate-cuprate compound RuSr_2GdCu_2O_8 is examined on the coexistence of
the superconductivity and the ferromagnetism, which has been observed recently.
We calculate critical fields of the superconductivity taking into account the
Fulde-Ferrell-Larkin-Ovchinnikov state in a model with Fermi-surfaces which
shapes are similar to those obtained by a band calculation. It is shown that
the critical field is enhanced remarkably due to a Fermi-surface effect, and
can be high enough to make the coexistence possible in a microscopic scale. We
also clarify the direction of the spatial oscillation of the order parameter,
which may be observed by scanning tunneling microscope experiments.",0001318v2
2000-03-07,Collective Singlet Excitations and Evolution of Raman Spectral Weights in the 2D Spin Dimer Compound SrCu2(BO3)2,"We present a Raman light scattering study of the two-dimensional quantum spin
system SrCu2(BO3)2 and show that the magnetic excitation spectrum has a rich
structure, including several well-defined bound state modes at low temperature,
and a scattering continuum and quasielastic light scattering contributions at
high temperature. The key to the understanding of the unique features of
SrCu2(BO3)2 is the presence of strong interactions between well-localized
triplet excitations in the network of orthogonal spin dimers realized in this
compound. Based on our analysis of the Heisenberg model relevant for this
material, we argue that the collective excitations involving two and
three-particle singlet bound states have large binding energies and are
observed as well-defined peaks in the Raman spectrum.",0003094v2
2000-03-15,Compositional Inversion Symmetry Breaking in Ferroelectric Perovskites,"Ternary cubic perovskite compounds of the form A_(1/3)A'_(1/3)A''_(1/3)BO_3
and AB_(1/3)B'_(1/3)B''_(1/3)O_3, in which the differentiated cations form an
alternating series of monolayers, are studied using first-principles methods.
Such compounds are representative of a possible new class of materials in which
ferroelectricity is perturbed by compositional breaking of inversion symmetry.
For isovalent substitution on either sublattice, the ferroelectric double-well
potential is found to persist, but becomes sufficiently asymmetric that
minority domains may no longer survive. The strength of the symmetry breaking
is enormously stronger for heterovalent substitution, so that the double-well
behavior is completely destroyed. Possible means of tuning between these
behaviors may allow for the optimization of resulting materials properties.",0003264v1
2000-04-03,Effective Charge and Spin Hamiltonian for the Quarter-Filled Ladder Compound $α'$-NaV$_2$O$_5$,"An effective intra- and inter-ladder charge-spin hamiltonian for the
quarter-filled ladder compound $\alpha'$-NaV$_2$O$_5$ has been derived by using
the standard canonical transformation method. In the derivation, it is clear
that a finite inter-site Coulomb repulsion is needed to get a meaningful result
otherwise the perturbation becomes ill-defined. Various limiting cases
depending on the values of the model parameters have been analyzed in detail
and the effective exchange couplings are estimated. We find that the effective
intra-ladder exchange may become ferromagnetic for the case of zig-zag charge
ordering in a purely electronic model.
  We estimate the magnitude of the effective inter-rung Coulomb repulsion in a
ladder and find it to be about one-order of magnitude too small in order to
stabilize charge-ordering.",0004025v1
2000-05-15,Valence electronic structure of Mn in undoped and doped lanthanum manganites from relative K x-ray intensity studies,"Relative $K$ x-ray intensities of $Mn$ in $Mn$, $MnO_{2}$, $LaMnO_{3}$ and
$La_{0.7}B_{0.3}MnO_{3}$ ($B$ = $Ca$, $Sr$, and $Ce$) systems have been
measured following excitation by 59.54 keV $\gamma$-rays from a 200 mCi
$^{241}$Am point-source. The measured results for the compounds deviate
significantly from the results of pure $Mn$. Comparison of the experimental
data with the multiconfiguration Dirac-Fock (MCDF) effective atomic model
calculations indicates reasonable agreement with the predictions of ionic model
for the doped {manganites except} that the electron doped
$La_{0.7}Ce_{0.3}MnO_{3}$ and hole doped $La_{0.7}Ca_{0.3}MnO_{3}$ compounds
show some small deviations. The results of $MnO_{2}$ and $LaMnO_{3}$ deviate
considerably from the predictions of the ionic model. Our measured
$K\beta/K\alpha$ ratio of $Mn$ in $La_{0.7}Ca_{0.3}MnO_{3}$ cannot be explained
as a linear superposition of $K\beta/K\alpha$ ratios of $Mn$ for the end
members which is in contrast to the recent proposal by Tyson et al. from their
$Mn$ $K\beta$ spectra.",0005245v2
2000-05-22,Quasi-one-dimensional spin chains in CuSiO3: an EPR study,"Temperature dependent EPR studies were performed on a single crystal of
CuSiO3.This recently discovered compound is isostructural with the spin-Peierls
compound CuGeO3. The EPR signals show different characteristics than those of
CuGeO3 and aredue to Cu2+ spins located along quasi one-dimensional chains. For
T > 8.2K the spin susceptibility closely follows the predictions of a S=1/2
one-dimensional Heisenberg antiferromagnet with J/kB = 21K. Below T = 8.2K the
spin susceptibility immediately drops to zero indicating long range magnetic
order.",0005346v1
2000-05-26,Finite-temperature ordering in two-dimensional magnets,"We study the two dimensional quantum Heisenberg antiferromagnet on the square
lattice with easy-axis exchange anisotropy. By the semiclassical method called
pure-quantum self-consistent harmonic approximation we analyse several
thermodynamic quantities and investigate the existence of a finite temperature
transition, possibly describing the low-temperature critical behaviour
experimentally observed in many layered real compounds.
  We find that an Ising-like transition characterizes the model even when the
anisotropy is of the order of $10^{-2}J$ ($J$ being the intra-layer exchange
integral), as in most experimental situations. On the other hand, typical
features of the isotropic Heisenberg model are observed for both values of
anisotropy considered, one in the {\it quasi}-isotropic limit and the other in
a more markedly easy-axis region.
  The good agreement found between our theoretical results and the experimental
data relative to the real compound Rb$_2$MnF$_4$ shows that the insertion of
the easy-axis exchange anisotropy, with quantum effects properly taken into
account, provides a quantitative description and explanation of the
experimental data, thus allowing to recognize in such anisotropy the main agent
for the observed onset of finite temperature long-range order.",0005464v1
2000-07-01,Nonadiabatic theory of the superconducting state,"Fermi energies in fullerene compounds and cuprates are extremely small as
consequence of the small number of charge carriers and are comparable to the
phonon frequency scale. In this situation the conventional Migdal-Eliashberg
theory does not hold anymore and nonadiabatic effects need to be taken into
account. In previous studies, a generalization of Eliashberg theory in the
nonadiabatic regime has been proposed to calculate normal state properties and
the onset temperature $T_c$ of the superconductive phase. Here we extend the
nonadiabatic theory below $T_c$ where the opening of the superconducting order
parameter affects the nonadiabatic correction. The superconducting gap $\Delta$
is calculated in a self-consistent way. We find that large values of the ratio
$2 \Delta/T_c$ are obtained in the nonadiabatic theory by smaller
electron-phonon coupling $\lambda$ than in Migdal-Eliashberg theory. This
agrees with the picture that strong-coupling phenomenology can be achieved in
nonadiabatic theory by ``reasonable'' values of $\lambda$. We apply our
analysis to the case of the fullerene compounds.",0007007v1
2000-07-04,Toward an anisotropic atom-atom model for the crystalline phases of the molecular S8 compound,"We analize two anisotropic atom-atom models used to describe the crystalline
alpha,beta and gamma phases of S8 crystals, the most stable compound of
elemental sulfur in solid phases, at ambient pressure and T<=400 K. The
calculations are performed via a series of classical molecular dynamics (MD)
simulations, with flexible molecular models and using a constant
pressure-constant temperature algorithm for the numerical simulations. All
intramolecular modes that mix with lattice modes, and are therefore relevant on
the onset of structural phase transitions, are taken into account. Comparisons
with experimental data and previous results obtained with an isotropic
atom-atom molecular model are also performed.",0007059v2
2000-08-17,Enhanced Valence Fluctuations Caused by f-c Coulomb Interaction in Ce-Based Heavy Electrons: Possible Origin of Pressure-Induced Enhancement of Superconducting Transition Temperature in \Ge and Related Compounds,"Properties of an extended periodic Anderson model with the f-c Coulomb
interaction $\Ufc$ is studied as a model for \Ge and related compounds which is
cosidered to exhibit a sharp valence change under pressure. The problem is
treated by extending the {\it slave-boson} and large-N expansion method to
treat the present system. It is shown that, as the f-level $\epsilon_{\rm f}$
is increased relative to the Fermi level, the sharp valence change is caused by
the effect of $\Ufc$ with moderate strength of the order of the bandwith of
conduction electrons. The superconducting transition temperature $T_\rc$ due to
the valence-fluctuation exchange is estimated on the slave-boson fluctuation
approximation. In the model with spherical Fermi surface, $T_\rc$ exhibits
sharp peak as a function of $\epsilon_{\rm f}$, simulating the effect of
pressure, for the d-wave pairing channel.",0008249v1
2000-11-01,Magnetic properties of a new molecular-based spin-ladder system: (5IAP)2CuBr4*2H2O,"We have synthesized and characterized a new spin-1/2 Heisenberg
antiferromagnetic ladder: bis 5-iodo-2-aminopyridinium tetrabromocuprate(II)
dihydrate. X-ray diffraction studies show the structure of the compound to
consist of well isolated stacked ladders and the interaction between the Cu(2+)
atoms to be due to direct Br...Br contacts. Magnetic susceptibility and
magnetization studies show the compound to be in the strong-coupling limit,
with the interaction along the rungs (J' ~ 13 K) much greater than the
interaction along the rails (J ~ 1 K). Magnetic critical fields are observed
near 8.3 T and 10.4 T, respectively, establishing the existence of the energy
gap.",0011016v2
2000-11-03,Spin-Glass State in $\rm CuGa_2O_4$,"Magnetic susceptibility, magnetization, specific heat and positive muon spin
relaxation (\musr) measurements have been used to characterize the magnetic
ground-state of the spinel compound $\rm CuGa_2O_4$. We observe a spin-glass
transition of the S=1/2 $\rm Cu^{2+}$ spins below $\rm T_f=2.5K$ characterized
by a cusp in the susceptibility curve which suppressed when a magnetic field is
applied. We show that the magnetization of $\rm CuGa_2O_4$ depends on the
magnetic histo Well below $\rm T_f$, the muon signal resembles the dynamical
Kubo-Toyabe expression reflecting that the spin freezing process in $\rm
CuGa_2O_4$ results Gaussian distribution of the magnetic moments. By means of
Monte-Carlo simulati we obtain the relevant exchange integrals between the $\rm
Cu^{2+}$ spins in this compound.",0011055v1
2000-11-10,Triplet superconductivity induced by screened phonon interactions in ferromagnetic compounds,"We propose that screened pairing interactions mediated by phonons could give
rise to a spin triplet superconductivity in ferromagnetic compounds such as
UGe_2. It is pointed out that the pairing interactions include anisotropic
components such as those of p, d, f-waves in addition to dominant s-wave
component due to the momentum dependence. Since the ferromagnetic long-range
order coexists, there is a large splitting of the Fermi surfaces of up and down
spin electrons, which suppresses singlet pairing. Therefore, triplet pairing
occurs at last due to the sub-dominant anisotropic interactions, even in the
absence of magnetic contribution to the pairing interactions.",0011188v3
2000-11-20,Theory of the Hall Coefficient and the Resistivity on the Layered Organic Superconductors κ-(BEDT-TTF),"In the organic superconducting \kappa-(BEDT-TTF) compounds, various transport
phenomena exhibit striking non-Fermi liquid behaviors, which should be the
important clues to understanding the electronic state of this system.
Especially, the Hall coefficient ($R_H$) shows Curie-Weiss type temperature
dependence, which is similar to that of high-Tc cuprates. In this paper, we
study a Hubbard model on an anisotropic triangular lattice at half filling,
which is an effective model of \kappa-(BEDT-TTF) compounds. Based on the
fluctuation-exchange (FLEX) approximation, we calculate the resistivity
($\rho$) and $R_H$ by taking account of the vertex corrections for the current,
which is necessary for satisfying the conservation laws. Our theoretical
results of $R_H$ and $cot(\theta_H)$ explain the experimental behaviors well,
which are unable to be reproduced by the conventional Boltzmann transport
approximation. Moreover, we extend the standard Eliashberg's transport theory
and derive the more precise formula for the conductivity, which becomes
important at higher temperatures.",0011324v2
2000-12-20,Structural Phase Transition in the 2D Spin Dimer Compound SrCu2(BO3)2,"A displacive, 2nd order structural phase transition at Ts=395 K from space
group I`4 2 m below Ts to I 4/m c m above Ts has been discovered in the
two-dimensional spin dimer compound SrCu2(BO3)2. The temperature evolution of
the structure in both phases has been studied by X-ray diffraction and Raman
scattering, supplemented by differential scanning calorimetry and SQUID
magnetometry. The implications of this transition and of the observed phonon
anomalies in Raman scattering for spin-phonon and interlayer coupling in this
quantum spin system will be discussed.",0012383v1
2000-12-22,The magnetic ordering in the mixed valence compound beta-Na0.33V2O5,"The low-temperature electron spin resonance (ESR) spectra and the static
magnetization data obtained for the stoichiometric single crystals of
$\beta$-Na$_{0.33}$V$_2$O$_5$ indicate that this quasi-one-dimensional mixed
valence (V4+/V5+) compound demonstrates at $T_N=22$ K the phase transition into
the canted antiferromagnetically ordered state. The spontaneous magnetization
of $3.4\times 10^{-3}$ $\mu_B$ per V$^{4+}$ ion was found to be oriented along
the two-fold $b$ axis of the monoclinic structure, the vector of
antiferromagnetism is aligned with the $a$ axis and the Dzyaloshinsky vector is
parallel to the $c$-axis. The experimental data were successfully described in
the frame of the macroscopic spin dynamics and the following values for the
macroscopic parameters of the spin system were obtained: the Dzyaloshinsky
field $H_D=6$ kOe, the energy gaps of two branches of the spin wave spectrum
$\Delta_1=48$ GHz and $\Delta_2=24$ GHz.",0012434v1
2001-01-08,Is CeNiSn the Kondo semiconductor?: break-junction data,"IVC characteristics as well as their derivatives were recorded for contacts
on the base of CeNiSn, known as Kondo semiconductor, in the metallic and the
tunnelling regime at temperatures between 0.1-8 K and in magnetic fields up to
8 T using mechanically controllable break junctions (MCBJ). It was found that
CeNiSn behaves like a compound with typical metallic properties instead of the
expected semiconducting behaviour. The main spectral feature is a pronounced
zero-bias conductance minimum of about 10 meV width both for metallic and
tunnel regime, which appears to be of magnetic nature. The experiments provide
no clear-cut evidence for an energy (pseudo)gap in this compound.",0101087v1
2001-01-11,"Unusual valence, negative charge-transfer gaps and self-doping in transition-metal compounds","In this paper I discuss the electronic structure and properties of a
specific, rather unconventional class of transition metal (TM) compounds, e.g.
TM oxides, which formally have unusually high values of the oxidation state, or
valence, of TM. In contrast to the typical situation, in this case the
charge-transfer gap (excitation energy for the transfer of electrons from the
ligands to the TM) is very small and may even become negative. As a result a
profound modification of an electronic structure and of all the properties may
take place: there appear holes in the oxygen p-bands (``self-doping''); the
material may become the metal of a specific type; there may occur
insulator--metal transitions of a specific type; magnetic properties may be
quite different from the ones expected normally; the character of elementary
excitations may change drastically. I give general discussion of such situation
and consider several examples of corresponding systems and their specific
properties.",0101164v1
2001-02-02,Ab-initio study of disorder effects on the electronic and magnetic structures of Sr$_2$FeMoO$_6$,"We have investigated the electronic structure of ordered and disordered
Sr$_2$FeMoO$_6$ using {\it ab-initio} band structure methods. The effect of
disorder was simulated within super-cell calculations to realize several
configurations with mis-site disorders. It is found that such disorder effects
destroy the half-metallic ferro-magnetic state of the ordered compound. It also
leads to a substantial reduction of the magnetic moments at the Fe sites in the
disordered configurations. Most interestingly, it is found for the disordered
configurations, that the magnetic coupling within the Fe sub-lattice as well as
that within the Mo sub-lattice always remain ferro-magnetic, while the two
sub-lattices couple anti-ferromagnetically, in close analogy to the magnetic
structure of the ordered compound, but in contrast to recent suggestions.",0102024v1
2001-02-12,A first order phase transition induced by magnetic field and temperature,"Taking the pseudobinary C15-Laves phase compound
Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$ as a paradigm for studying a ferromagnetic(FM)
to antiferromagnetic(AFM) phase transition, we present interesting
thermomagnetic history effects in magnetotransport measurements across this
FM-AFM transition. We argue that these distinctive hysteretic features can be
used to identify the exact nature -first order or second order - of this kind
of transition in magnetic systems where electrical transport is strongly
correlated with the underlying magnetic order. A comparison is made with the
similar FM-AFM transitions observed in Nd and Pr-based manganese compounds with
perovskite-type structure.",0102199v1
2001-02-20,Electronic and structural properties of superconducting diborides and calcium disilicide in the $\rm AlB_2$ structure,"We report a detailed study of the electronic and structural properties of the
39K superconductor \mgbtwo and of several related systems of the same family,
namely \mgalbtwo, \bebtwo, \casitwo and \cabesi. Our calculations, which
include zone-center phonon frequencies and transport properties, are performed
within the local density approximation to the density functional theory, using
the full-potential linearized augmented plane wave (FLAPW) and the
norm-conserving pseudopotential methods. Our results indicate essentially
three-dimensional properties for these compounds; however, strongly
two-dimensional $\sigma$-bonding bands contribute significantly at the Fermi
level. Similarities and differences between \mgbtwo and \bebtwo (whose
superconducting properties have not been yet investigated) %it is not yet know
if it is a superconductor) are analyzed in detail. Our calculations for
\mgalbtwo show that metal substitution cannot be fully described in a rigid
band model. \casitwo is studied as a function of pressure, and Be substitution
in the Si planes leads to a stable compound similar in many aspects to
diborides.",0102358v2
2001-02-21,"Coordination and chemical effects on the structural, electronic and magnetic properties in Mn pnictides","Simple structures of MnX binary compounds, namely hexagonal NiAs and
zincblende, are studied as a function of the anion (X = Sb, As, P) by means of
the all-electron FLAPW method within local spin density and generalized
gradient approximations. An accurate analysis of the structural, electronic and
magnetic properties reveals that the cubic structure greatly favours the
magnetic alignment in these compounds leading to high magnetic moments and
nearly half-metallic behaviour for MnSb and MnAs. The effect of the anion
chemical species is related to both its size and the possible hybridization
with the Mn $d$ states; both contributions are seen to hinder the magnitude of
the magnetic moment for small and light anions. Our results are in very good
agreement with experiment - where available - and show that the generalized
gradient approximation is essential to correctly recover both the equilibrium
volume and magnetic moment.",0102376v1
2001-02-27,Unique Spin Dynamics and Unconventional Superconductivity in the Layered Heavy Fermion Compound CeIrIn_5:NQR Evidence,"We report measurements of the ^{115}In nuclear spin-lattice relaxation rate
(1/T_1) between T=0.09 K and 100 K in the new heavy fermion (HF) compound
CeIrIn_5. At 0.4 K < T < 100 K, 1/T_1 is strongly T-dependent, which indicates
that CeIrIn_5 is much more itinerant than known Ce-based HFs. We find that
1/T_1T, subtracting that for LaIrIn_5, follows a 1/(T+\theta)^{3/4} variation
with \theta=8 K. We argue that this novel feature points to anisotropic, due to
a layered crystal structure, spin fluctuations near a magnetic ordering. The
bulk superconductivity sets in at 0.40 K below which the coherence peak is
absent and 1/T_1 follows a T^3 variation, which suggests unconventional
superconductivity with line-node gap.",0102487v3
2001-03-09,Structure and superconductivity of Mg(B1-xCx)2 compounds,"In this paper, we reported the structural properties and superconductivity of
Mg(B1-xCx)2 compounds. Powder x-ray diffraction results indicate that the
samples crystallize in a hexagonal AlB2-type structure. Due to the chemical
activity of Mg powders, a small amount of MgO impurity phase was detected by
x-ray diffraction. The lattice parameters decrease slightly with increasing
carbon content. Magnetization measurements indicate the non-stoichiometry of
MgB2 has no influence on the superconducting transition temperature and the
transition temperature width. The addition of carbon results in a decrease of
Tc and an increase in the superconducting transition width, implying the loss
of superconductivity.",0103203v1
2001-03-16,Photoemission study of the skutterudite compounds Co(Sb$_{1-x}$Te$_{x}$)$_3$ and RhSb$_3$,"We have studied the electronic structure of the skutterudite compounds
Co(Sb$_{1-x}$Te$_{x}$)$_3$ (x= 0, 0.02, 0.04) by photoemission spectroscopy.
Valence-band spectra revealed that Sb 5p states are dominant near the Fermi
level and are hybridized with Co 3d states just below it. The spectra of {\it
p}-type CoSb$_3$ are well reproduced by the band-structure calculation, which
suggests that the effect of electron correlations is not strong in CoSb$_3$.
When Te is substituted for Sb and n-type carriers are doped into CoSb$_3$, the
spectra are shifted to higher binding energies as predicted by the rigid-band
model. From this shift and the free-electron model for the conduction and
valence bands, we have estimated the band gap of CoSb$_3$ to be 0.03-0.04 eV,
which is consistent with the result of transport measurements. Photoemission
spectra of RhSb$_3$ have also been measured and revealed similarities to and
differences from those of CoSb$_3$.",0103342v2
2001-03-20,Heat transport by lattice and spin excitations in the spin chain compounds SrCuO_2 and Sr_2CuO_3,"We present the results of measurements of the thermal conductivity of the
quasi one-dimensional spin S=1/2 chain compound SrCuO_2 in the temperature
range between 0.4 and 300 K along the directions parallel and perpendicular to
the chains. An anomalously enhanced thermal conductivity is observed along the
chains. The analysis of the present data and a comparison with analogous recent
results for Sr_2CuO_3 and other similar materials demonstrates that this
behavior is generic for cuprates with copper-oxygen chains and strong
intrachain interactions. The observed anomalies are attributed to the
one-dimensional energy transport by spin excitations (spinons), limited by the
interaction between spin and lattice excitations. The energy transport along
the spin chains has a non-diffusive character, in agreement with theoretical
predictions for integrable models.",0103419v1
2001-05-26,Direct Observation of Coexistence of Ferromagnetism and Superconductivity in RuSr2(Gd0.7Ce0.3)2Cu2O10,"Recent reports of the detecting of ferromagnetism and superconductivity in
ruthenium-cuprates have aroused great interest. Unfortunately, whether the two
antagonistic phenomena coexist in the same space in the compounds remains
unresolved. By employing the magneto-optical-imaging technique, ferromagnetism
and superconductivity were indeed directly observed to coexist in the same
space in RuSr2(Gd0.7Ce0.3)2Cu2O10 within the experimental resolution of ~ 10
(mu)m. The observation sets a length scale limit for models proposed to account
for the competition between ferromagnetism and superconductivity, especially
d-wave superconductivity, in this interesting class of compounds.",0105510v1
2001-08-08,Magnetic anisotropy of the spin ice compound Dy2Ti2O7,"We report magnetization and ac susceptibility of single crystals of the spin
ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the charasteristic axes
[100] and [110] agree with the expected values for an effective ferromagnetic
nearest-neighbor Ising pyrochlore with local <111> anisotropy, where each
magnetic moment is constrained to obey the `ice-rule'. At high enough magnetic
fields along the [111] axis, the saturated moment exhibits a beaking of the
ice-rule; it agrees with the value expected for a three-in one-out spin
configuration. Assuming the realistic magnetic interaction between Dy ions
given by the dipolar spin ice model, we completely reproduce the results at 2 K
by Monte Carlo calculations. However, down to at least 60 mK, we have not found
any experimental evidence of the long-range magnetic ordering predicted by this
model to occur at around 180 mK. Instead, we confirm the spin freezing of the
system below 0.5 K.",0108129v1
2001-09-04,Evidences for Tsallis non-extensivity on CMR manganites,"We found, from the analysis of $M$ vs. $T$ curves of some manganese oxides
(manganites), that these systems do not follow the traditional
Maxwell-Boltzmann statistics, but the Tsallis statistics, within the
\QTR{em}{normalized} formalism. Curves were calculated within the mean field
approximation, for various ferromagnetic samples and the results were compared
to measurements of our own and to various other authors published data, chosen
at random from the literature. The agreement between the experimental data and
calculated $M_{q}$ vs. $T^{\ast}$ curve, where $T^{\ast}$ is an effective
temperature, is excellent for all the compounds. The entropic parameter, $q$,
correlates in a simple way with the experimental value of $T_{c}$, irrespect
the chemical composition of the compounds, heat treatment or other details on
sample preparation. Examples include $q<1$ (superextensivity), $q=1$
(extensivity) and $q>1$ (subextensivity) cases.",0109061v2
2001-09-04,Unusual kondo behavior in the indium-rich heavy fermion antiferromagnet Ce3Pt4In13,"We report the thermodynamic, magnetic, and electronic transport properties of
the new ternary intermetallic system (Ce,La)3Pt4In13. Ce3Pt4In13 orders
antiferromagnetically at 0.95 K while the non-magnetic compound La3Pt4In13 is a
conventional 3.3 K superconductor. Kondo lattice effects appear to limit the
entropy associated with the Neel transition to (1/4)Rln2 as an electronic
contribution to the specific heat of gamma = 1 J/mole-Ce K2 is observed at TN;
roughly 35% of this gamma survives the ordering transition. Hall effect,
thermoelectric power, and ambient-pressure resistivity measurements confirm
this interpretation. These results suggest that RKKY and Kondo interactions are
closely balanced in this compound (TN = TK). Contrary to expectations based on
the Doniach Kondo necklace model, applied hydrostatic pressure modestly
enhances the magnetic ordering temperature with dTN/dP = +23 mK/kbar. As such
Ce3Pt4In13 provides a counterexample to Kondo systems with similar Kondo and
RKKY energy scales wherein applied pressure enhances TK at the expense of the
ordered magnetic state.",0109063v1
2001-09-21,Phenomenological theory of phase transitions in highly piezoelectric perovskites,"Recently discovered fine structure of the morphotropic phase boundaries in
highly piezoelectric mixture compounds PZT, PMN-PT, and PZN-PT demonstrates the
importance of highly non-linear interactions in these systems. We show that an
adequate Landau-type description of the ferroelectric phase transitions in
these compounds is achieved by the use of a twelfth-order expansion of the
Landau potential in terms of the phenomenological order parameter.
Group-theoretical and catastrophe-theory methods are used in constructing the
appropriate Landau potential. A complete phase diagram is calculated in
phenomenological parameter space. The theory describes both PZT and PZN-PT
types of phase diagrams, including the newly found monoclinic and orthorhombic
phases. Anomalously large piezoelectric coefficients are predicted in the
vicinity of the phase transition lines.",0109396v3
2001-09-28,Intercalation and High Temperature Superconductivity of Fullerides,"Intercalation of polyatomic molecules into a superconductor can drastically
affect the properties of the compound. A mechanism leading to a large increase
in Tc for such systems is proposed. It explains the recent remarkable
observation of high Tc superconductivity in the hole-doped C60/CHX3 (X=Cl,Br)
compounds and the large shift in their Tc upon Cl->Br substitution. The
increase in Tc is due to contribution to the pairing arising from the
interaction of electrons with the vibrational manifold of the molecule. The
proposed mechanism opens up the possibility to observe a site-selective isotope
effect. We also suggest that intercalating CHI3 would further increase the
critical temperature to Tc=140K.",0109553v2
2001-10-02,Bond-disordered spin systems: Theory and application to doped high-Tc compounds,"We examine the stability of magnetic order in a classical Heisenberg model
with quenched random exchange couplings. This system represents the spin
degrees of freedom in high-$T_\textrm{c}$ compounds with immobile dopants.
Starting from a replica representation of the nonlinear $\sigma$-model, we
perform a renormalization-group analysis. The importance of cumulants of the
disorder distribution to arbitrarily high orders necessitates a functional
renormalization scheme. From the renormalization flow equations we determine
the magnetic correlation length numerically as a function of the impurity
concentration and of temperature. From our analysis follows that
two-dimensional layers can be magnetically ordered for arbitrarily strong but
sufficiently diluted defects. We further consider the dimensional crossover in
a stack of weakly coupled layers. The resulting phase diagram is compared with
experimental data for La$_{2-x}$Sr$_x$CuO$_4$.",0110061v1
2001-10-15,"Synthesis, Crystal Structure and Magnetic Properties of the Linear-Chain Cobalt Oxide Sr5Pb3CoO12","The novel spin-chain cobalt oxide Sr5Pb3CoO12 [P-62m, a = 10.1093(2) A and c
= 3.562 51(9) A at 295 K] is reported. Polycrystalline sample of the compound
was studied by neutron diffraction (at 6 and 295 K) and magnetic susceptibility
measurements (5 to 390 K). The cobalt oxide was found to be analogous to the
copper oxide Sr5Pb3CoO12, which is comprised of magnetic-linear chains at
inter-chain distance of 10 A. Although the cobalt oxide chains (mu_eff of 3.64
mu_B per Co) are substantially antiferromagnetic (theta_W = -38.8 K), neither
low-dimensional magnetism nor long-range ordering has been found; a
local-structure disorder in the chains might impact on the magnetism. This
compound is highly electrically insulating.",0110292v1
2001-10-20,Finite-temperature perturbation theory for quasi-one-dimensional spin-1/2 Heisenberg antiferromagnets,"We develop a finite-temperature perturbation theory for quasi-one-dimensional
quantum spin systems, in the manner suggested by H.J. Schulz (1996) and use
this formalism to study their dynamical response. The corrections to the
random-phase approximation formula for the dynamical magnetic susceptibility
obtained with this method involve multi-point correlation functions of the
one-dimensional theory on which the random-phase approximation expansion is
built. This ``anisotropic'' perturbation theory takes the form of a systematic
high-temperature expansion. This formalism is first applied to the estimation
of the N\'eel temperature of S=1/2 cubic lattice Heisenberg antiferromagnets.
It is then applied to the compound Cs$_2$CuCl$_4$, a frustrated S=1/2
antiferromagnet with a Dzyaloshinskii-Moriya anisotropy. Using the next leading
order to the random-phase approximation, we determine the improved values for
the critical temperature and incommensurability. Despite the non-universal
character of these quantities, the calculated values are different by less than
a few percent from the experimental values for both compounds.",0110429v1
2001-11-20,"Crystal and magnetic structure of the La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound $(x=0.8,0.85)$","We studied the crystal and magnetic structure of the
La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound for $x=0.8$ and $x=0.85$. At T=300 K both
samples are paramagnetic with crystallographic symmetry $Pnma$. At low
temperatures they undergo a monoclinic distortion from orthorhombic $Pnma$-type
structure with $a_p\sqrt{2}\times 2a_p\times a_p\sqrt{2}$ to a monoclinic
structure with ($a_p\sqrt{2}\times 2a_p\times a_p\sqrt{2}$,
$\beta=90+\epsilon\sim 91.4^{\rm o}$) and $P2_1/m$ space group below $T_N$. The
onset of the structural transformation coincides with the development of the
$C$-type long range antiferromagnetic order with propagation vector ${\bf
k}=({1/2},0,{1/2})$. The monoclinic unit cell allowed us to determine the
direction of the Mn magnetic moment with respect to the crystallographic axes:
it is perpendicular to the propagation vector, ${\bf m}\perp {\bf
k}=({1/2},0,{1/2})$. The amplitude of the ordered magnetic moment at $T=1.6$ K
is found to be $2.53(2)$ and $2.47(2)\mu_{B}$ for $x=0.8$ and 0.85,
respectively.",0111352v1
2001-11-30,New mechanism of first order magnetization process in many-sublattice rare-earth compounds,"First-order field-induced spin reorientation transitions in multisublattice
intermetallic compounds are considered within an anisotropic Heisenberg model.
Unlike previous works, only leading-order anisotropy constants of the
sublattices are included. The exchange interactions both between the rare-earth
(RE) and transition metal (TM) sublattices and within the RE sublattice play an
important role in the model. The latter interaction results in the occurrence
of metastable states. One of the minima corresponds to the non-collinear
magnetic structure where the RE subsystem is divided into two sublattices, and
their moments deviate in opposite directions from the TM moment direction. The
possible FOMP scenarios for R$_2$Fe$_{17}$, HoFe$_{11}$Ti, and TbMn$_6$Sn$_6$
systems are discussed.",0111576v2
2002-01-11,The Nature of Heavy Quasiparticles in Magnetically Ordered Heavy Fermions,"The optical conductivity of the heavy fermions UPd2Al3 and UPt3 has been
measured in the frequency range from 10 GHz to 1.2 THz (0.04 meV to 5 meV) at
temperatures 1 K < T < 300 K. In both compounds a well pronounced pseudogap of
less than a meV develops in the optical response at low temperatures; we relate
this to the antiferromagnetic ordering. From the energy dependence of the
effective electronic mass and scattering rate we derive the energies essential
for the heavy quasiparticle. We find that the enhancement of the mass mainly
occurs below the energy which is related to magnetic correlations between the
local magnetic moments and the itinerant electrons. This implies that the
magnetic order in these compounds is the pre-requisite to the formation of the
heavy quasiparticle and eventually of superconductivity.",0201167v1
2002-01-15,Magnetic Resonant Mode in the Single-Layer High Temperature Superconductor Tl$_2$Ba$_2$Cu$_{6+δ}$,"An unusual spin excitation mode observed by neutron scattering has inspired
numerous theoretical studies of the interplay between charged quasiparticles
and collective spin excitations in the copper oxide high temperature
superconductors. The mode has thus far only been observed in materials with
crystal structures consisting of copper oxide bilayers, and it is notably
absent in the single-layer compound La$_{2-x}$Sr$_{x}$CuO$_{4+\delta}$. Neutron
scattering data now show that the mode is present in
Tl$_2$Ba$_2$Cu$_{6+\delta}$, a single-layer compound with T$_c$ $\sim$ 90 K,
thus demonstrating that it is a generic feature of the copper oxide
superconductors, independent of the layer sequence. This restricts the
theoretical models for the origin of the resonant mode and its role in the
mechanism of high temperature superconductivity.",0201252v1
2002-01-15,Model for the hydration of non-polar compounds and polymers,"We introduce an exactly solvable statistical-mechanical model of the
hydration of non-polar compounds, based on grouping water molecules in clusters
where hydrogen bonds and isotropic interactions occur; interactions between
clusters are neglected. Analytical results show that an effective strengthening
of hydrogen bonds in the presence of the solute, together with a geometric
reorganization of water molecules, are enough to yield hydrophobic behavior. We
extend our model to describe a non-polar homopolymer in aqueous solution,
obtaining a clear evidence of both ``cold'' and ``warm'' swelling transitions.
This suggests that our model could be relevant to describe some features of
protein folding.",0201254v1
2002-01-25,Energy bandstructures of MgB2 and the related compounds,"Energy band structures are calculated for the new superconductor MgB$_2$ and
the related compounds by using the LDA and an FLAPW method. It is found that
the strong three dimensional network in low-lying $\pi$ bands brings about two
dimensional $\sigma$ holes in MgB$_2$, which should be responsible for the
superconductivity. The de Haas-van Alphen frequencies and the cyclotron masses
are obtained for the Fermi surfaces. The $\sigma$ hole is not found in LiBC due
to the less three dimensional network. MgB$_2$C$_2$ is found a semiconductor,
but the top of the valence bands are similar to the $\sigma$ bands in MgB$_2$.
The total energy calculations are also performed for Mg$_{1-x}$Al$_x$B$_2$ to
investigate the structural phase instability, experimentally observed around
$x=$10%.",0201452v1
2002-02-15,Non-volatile magnetoresistive memory in phase separated La$_{0.325}$Pr$_{0.300}$Ca$_{0.375}$MnO$_3$,"We have measured magnetic and transport response on the polycrystalline
La$_{5/8-y}$Pr$_y$Ca$_{3/8}$MnO$_3$ ($y=0.30$, average grain size 2 microns)
compound. In the temperature range where ferromagnetic metallic and insulating
regions coexist we observed a persistent memory of low magnetic fields ($<$ 1
T) which is determined by the actual amount of the ferromagnetic phase. The
possibility to manipulate this fraction with relatively small external
perturbations is related to the phase separated nature of these manganese oxide
based compounds. The colossal magnetoresistance figures obtained (about 80%)
are determined by the fraction enlargement mechanism. Self-shielding of the
memory to external fields is found under certain described circumstances. We
show that this non-volatile memory has multilevel capability associated with
different applied low magnetic field values.",0202261v1
2002-03-19,"Specific heat and magnetic measurements in Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 samples","We studied the magnetization as a function of temperature and magnetic field
in the compounds Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3. It allowed
us to identify the ferromagnetic, antiferromagnetic and charge ordering phases
in each case. The intrinsic magnetic moments of Nd3+ and Ho3+ ions experienced
a short range order at low temperatures. We also did specific heat measurements
with applied magnetic fields between 0 and 9 T and temperatures between 2 and
300 K in all three samples. Close to the charge ordering and ferromagnetic
transition temperatures the specific heat curves showed peaks superposed to the
characteristic response of the lattice oscillations. Below 10 K the specific
heat measurements evidenced a Schottky-like anomaly for all samples. However,
we could not successfully fit the curves to either a two level nor a
distribution of two-level Schottky anomaly. Our results indicated that the peak
temperature of the Schottky anomaly was higher in the compounds with narrower
conduction band.",0203382v1
2002-04-03,Josephson Plasma in RuSr2GdCu2O8,"Josephson plasma in RuSr$_{2}$GdCu$_{2}$O$_{8}$,
Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), and
RuSr$_{2}$Eu$_{2-x}$Ce$_{x}$Cu$_{2}$O$_{10}$ (x = 0.5) compounds is
investigated by the sphere resonance method. The Josephson plasma is observed
in a low-frequency region (around 8.5 cm$^{-1}$ at T $\ll$ $T_{c}$) for
ferromagnetic RuSr$_{2}$GdCu$_{2}$O$_{8}$, while it increases to 35 cm$^{-1}$
for non-ferromagnetic Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), which
represents a large reduction in the Josephson coupling at ferromagnetic
RuO$_{2}$ block layers. The temperature dependence of the plasma does not shift
to zero frequency ({\it i.e.} $j_{c}$ = 0) at low temperatures, indicating that
there is no transition from the 0-phase to the $\pi$-phase in these compounds.
The temperature dependence and the oscillator strength of the peak are
different from those of other non-magnetic cuprates, and the origins of these
anomalies are discussed.",0204070v1
2002-05-14,"Comparative Study of the Electronic Structure of Alkaline-earth Borides (MeB2; Me=Mg, Al, Zr, Nb, and Ta) and their Normal-State Conductivity","By means of density functional theory the electronic structure of the MgB2
superconductor was characterised and compared with that of the related
iso-structural systems: AlB2, ZrB2, NbB2, and TaB2. Using the full-potential
linearized augmented plane waves (FP-LAPW) method and the generalised gradient
approximation, the electronic density distribution, density of states, and band
structures were obtained for these compounds. The electrical conductivity,
which cannot be easily measured in the c-direction, was calculated, in the
relaxation time approximation using band structure results. It was found that
the two-dimensional (2D) crystal structure character of these metallic
diborides is also reflected in the electronic charge distribution. This 2D
pattern is not completely seen in the electrical conductivity as it is, for
instance, in the superconductor high Tc cuprates. Indeed, it was found that, by
the electrical conductivity calculations, all these compounds have a bulk, yet
anisotropic, conductivity.",0205291v1
2002-05-20,Phase diagram of the La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound for $0.5\leq x\leq 0.9$,"We have studied the phase diagram of La$_{1-x}$Ca$_{x}$MnO$_{3}$ for $0.5\leq
x\leq 0.9$ using neutron powder diffraction and magnetization measurements. At
300 K all samples are paramagnetic and single phase with crystallographic
symmetry $Pnma$. As the temperature is reduced a structural transition is
observed which is to a charge-ordered state only for certain x. On further
cooling the material passes to an antiferromagnetic ground state with Neel
temperature $T_N$ that depends on x. For $0.8\leq x\leq 0.9$ the structural
transformation occurs at the same temperature as the magnetic transition.
Overall, the neutron diffraction patterns were explained by considering four
phase boundaries for which La$_{1-x}$Ca$_x$MnO$_3$ forms a distinct phase: the
CE phase at $x=0.5-0.55$, the charge-ordered phase at x=2/3, the monoclinic and
C-type magnetic structure at $x=0.80-0.85$ and the G-type magnetic structure at
x=1. Between these phase boundaries the magnetic reflections suggest the
existence of mixed compounds containing both phases of the adjacent phase
boundaries in a ratio determined by the lever rule.",0205410v1
2002-05-22,Superconducting properties of RuSr2GdCu2O8 studied by SQUID magnetometry,"For polycrystalline RuSr2GdCu2O8 (Ru-1212), distinct peaks have been reported
in d.c. magnetization in the superconducting state of the sample. Sr2GdRuO6
(Sr-2116), the precursor for the preparation of Ru-1212, shows similar peaks in
the same temperature regime. Based on measurements performed on both bulk and
powdered samples of Ru-1212 and Sr-2116, we exclude the possibility, that the
observed behavior of the magnetization of Ru-1212 is due to Sr-2116 impurities.
The effect is related to the superconductivity of Ru-1212, but it is not an
intrinsic property of this compound. We provide evidence that the observation
of magnetization peaks in the superconducting state of Ru-1212 is due to flux
motion generated by the movement of the sample in an inhomogeneous field,
during the measurement in the SQUID magnetometer. We propose several tests,
that help to decide, whether the features observed in a SQUID magnetization
measurement of Ru-1212 represent a property of the compound or not.",0205463v1
2002-05-26,Absence of a Competition between Magnetism and Superconductivity in the Layered Nickel Borocarbides: Common Correlation Tc with Crystal Chemical Parameters for Magnetic and Nonmagnetic Compounds,"In the work the analysis of crystal chemical researches of nickel
borocarbides RNi2B2C (R = rare earth) is given. The reasons of representation
of dependence of Tc from crystal chemical parameters by two separate curves for
magnetic and nonmagnetic R are considered. Common for all R dependences of Tc
from crystal chemical parameters similar existing in layered
quasi-two-dimensional systems (HTSC cuprates and diborides) are established.
The absence of influence on borocarbides Tc of magnetic properties R is
determined. On the basis of the found correlations the radii of a number of
rare earths are precised and Tc of compounds at various substitutions R are
calculated.",0205533v1
2002-06-19,Magnetic structure of antiferromagnetic NdRhIn5,"The magnetic structure of antiferromagnetic NdRhIn5 has been determined using
neutron diffraction. It has a commensurate antiferromagnetic structure with a
magnetic wave vector (1/2,0,1/2) below T_N = 11K. The staggered Nd moment at
1.6K is 2.6mu_B aligned along the c-axis. We find the magnetic structure to be
closely related to that of its cubic parent compound NdIn3 below 4.6K. The
enhanced T_N and the absence of additional transitions below T_N for NdRhIn5
are interpreted in terms of an improved matching of the
crystalline-electric-field (CEF), magnetocrystalline, and exchange interaction
anisotropies. In comparison, the role of these competing anisotropies on the
magnetic properties of the structurally related compound CeRhIn5 is discussed.",0206381v1
2002-07-23,A new macroscopically degenerate ground state in the spin ice compound Dy2Ti2O7 under a magnetic field,"The low temperature magnetic properties of pyrochlore compound Dy2Ti2O7 in
magnetic fields applied along the [111] direction are reported. Below 1 K, a
clear plateau has been observed in the magnetization process in the field range
2~9 kOe, followed by a sharp moment jump at around 10 kOe that corresponds to a
breaking of the spin ice state. We found that the plateau state is disordered
with the residual entropy of nearly half the value of the zero-field state,
whose macroscopic degeneracy comes from a frustration of the spins on the
kagome layers perpendicular to the magnetic field.",0207543v1
2002-09-12,Field dependent effective masses in YbAl$_{3}$,"We show for the intermediate valence compound YbAl$_{3}$ that the high field
(40 $\lesssim B \lesssim$ 60T) effective masses measured by the de Haas-van
Alphen experiment for field along the $<111>$ direction are smaller by
approximately a factor of two than the low field masses. The field $B^{*} \sim$
40T for this reduction is much smaller than the Kondo field $B_{K} \sim
k_{B}T_{K}/\mu_{B}$ ($T_{K}\sim$ 670K) but is comparable to the field
$k_{B}T_{coh}/\mu_{B}$ where $T_{coh}\sim$ 40K is the temperature for the onset
of Fermi liquid coherence. This suggests that the field scale $B^{*}$ does not
arise from 4$f$ polarization but is connected with the removal of the anomalies
that are known to occur in the Fermi liquid state of this compound.",0209303v1
2002-09-17,Sr2V3O9 and Ba2V3O9: quasi one-dimensional spin-systems with an anomalous low temperature susceptibility,"The magnetic behaviour of the low-dimensional Vanadium-oxides Sr2V3O9 and
Ba2V3O9 was investigated by means of magnetic susceptibility and specific heat
measurements. In both compounds, the results can be very well described by an
S=1/2 Heisenberg antiferromagnetic chain with an intrachain exchange of J = 82
K and J = 94 K in Sr2V3O9 and Ba2V3O9, respectively. In Sr2V3O9,
antiferromagnetic ordering at T_N = 5.3 K indicate a weak interchain exchange
of the order of J_perp ~ 2 K. In contrast, no evidence for magnetic order was
found in Ba2V3O9 down to 0.5 K, pointing to an even smaller interchain
coupling. In both compounds, we observe a pronounced Curie-like increase of the
susceptibility below 30 K, which we tentatively attribute to a staggered field
effect induced by the applied magnetic field. Results of LDA calculations
support the quasi one-dimensional character and indicate that in Sr2V3O9, the
magnetic chain is perpendicular to the structural one with the magnetic
exchange being transferred through VO4 tetrahedra.",0209409v1
2002-09-18,Charge ordered ferromagnetic phase in La0.5Ca0.5MnO3,"Mixed valent manganites are noted for their unusual magnetic,electronic and
structural phase transitions. The La1-xCaxMnO3 phase diagram shows that below
transition temperatures in the range 100-260 K, compounds with 0.2 < x < 0.5
are ferromagnetic and metallic whereas those with 0.5 < x < 0.9 are
antiferromagnetic and charge ordered. In a narrow region around x = 0.5, these
totally dissimilar states are thought to coexist. Uehara et al. have shown that
charge order and charge disorder can coexist in the related compound
La0.25Pr0.375Ca0.375MnO3. Here, we present electron microscopy data for
La0.5Ca0.5MnO3 that sheds light on the distribution of coexisting phases and
uncovers a novel and unexpected phase. Using electron holography and Fresnel
imaging, we find micron sized ferromagnetic regions spanning several grains
coexisting with similar sized regions with no local magnetisation. Holography
shows that the ferromagnetic regions have a local magnetisation of 3.4 +- 0.2
mB/Mn (the spin aligned value is 3.5 mB/Mn). We use electron diffraction and
dark field imaging to show that charge order exists in regions with no net
magnetisation and, surprisingly, can also occur in ferromagnetic regions.",0209436v1
2002-09-23,Variational Wave Function for Generalized Wigner Lattices in One Dimension,"We study a system of electrons on a one-dimensional lattice, interacting
through the long range Coulomb forces, by means of a variational technique
which is the strong coupling analog of the Gutzwiller approach. The problem is
thus the quantum version of Hubbard's classical model of the generalized Wigner
crystal [J. Hubbard, Phys. Rev. B 17, 494 (1978)]. The magnetic exchange energy
arising from quantum fluctuations is calculated, and turns out to be smaller
than the energy scale governing charge degrees of freedom. This approach could
be relevant in insulating quasi-one-dimensional compounds where the long range
Coulomb interactions are not screened. In these compounds charge order often
appears at high temperatures and coexists with magnetic order at low
temperatures.",0209518v1
2002-10-10,Spin-Ice and Other Frustrated Magnets on the Pyrochlore Lattice,"The recent identification of the dysprosium titanate compound $Dy_2 Ti_2 O_7$
as a ``Spin-Ice'', i.e. the spin analog of regular entropic ice of Pauling, has
created considerable excitement. The ability to manipulate spins using magnetic
fields gives a unique advantage over regular ice in these systems, and has been
used to study the recovery of entropy. Predicted magnetization plateaus have
been observed, testing the underlying model consisting of a competition between
short ranged super exchange, and long ranged dipolar interactions between
spins. I discuss other compounds that are possibly spin ice like: $Ho_2 Ti_2
O_7$, and the two stannates $Ho_2 Sn_2 O_7$, $Dy_2 Sn_2 O_7$.",0210230v1
2002-10-28,Fermi surface of the heavy fermion superconductor PrOs$_{4}$Sb$_{12}$,"We have investigated the de Haas-van Alphen effect in the Pr-based heavy
fermion superconductor PrOs$_4$Sb$_{12}$.The topology of Fermi surface is close
to the reference compound LaOs$_4$Sb$_{12}$ and well explained by the band
structure calculation based on the FLAPW-LDA+U method, where the 4{\it f}
electrons are localized. We have confirmed a highly enhanced cyclotron
effective mass 2.4$\sim7.6m_{\rm 0}$ which is apparently large compared to the
usual Pr-based compounds.",0210601v2
2002-10-28,"Structure, electric and magnetic properties of the electron-doped manganese oxide: La{sub(1-x)}Te{sub(x)}MnO{sub(3)}(x=0.1, 0.15)","In this letter, the electrical and magnetic properties of
La{sub(1-x)}Te{sub(x)}MnO{sub(3)}(x=0.1, 0.15), which is a new material and
shows good colossal magnetoresistance (CMR) behavior, have been investigated.
These compounds have rhombohedral structure. In this materical, Te replaced a
part of La ions, which induced the lattice cell constriction and Mn-O-Mn bond
angle widening. X-ray photoemission spectroscopy (XPS) measurement revealed
that the Te ions were in the tetravalent state and the manganese ions could be
considered as in a mixture state of Mn{sup(2+)} and Mn{Sup(3+)}. Thus the
material could be viewed as an electron-doped compound. The Curie temperature
(Tc) was about 240 K and 255 K for x=0.1, 0.15, respectively. The maximum
magnetoresistance ratio MR=[r(0)-r(H)]/r(0) was about 51% at 200 K and in the
applied magnetic field of 40 kOe.",0210609v2
2002-10-31,Electron-phonon interaction in n-doped cuprates: an Inelastic X-ray Scattering study,"Inelastic x-ray scattering (IXS) with very high (meV) energy resolution has
become a valuable spectroscopic tool, complementing the well established
coherent inelastic neutron scattering (INS) technique for phonon dispersion
investigations. In the study of crystalline systems IXS is a viable alternative
to INS, especially in cases where only small samples are available. Using IXS,
we have measured the phonon dispersion of Nd_{1.86}Ce_{0.14}CuO_{4+\delta}
along the [x,0,0] and [x,x,0] in-plane directions. Compared to the undoped
parent compound, the two highest longitudinal optical (LO) phonon branches are
shifted to lower energies because of Coulomb-screening effects brought about by
the doped charge carriers. An additional anomalous softening of the highest
branch is observed around q=(0.2,0,0). This anomalous softening, akin to what
has been observed in other compounds, provides evidence for a strong
electron-phonon coupling in the electron-doped high-temperature
superconductors.",0210700v1
2002-11-08,Spin Glass and Ferromagnetism in Kondo lattices compounds,"The Kondo lattice model has been analyzed in the presence of a random
inter-site interaction among localized spins with non zero mean Jo and standard
deviation J. Following the same framework previously introduced by us, the
problem is formulated in the path integral formalism where the spin operators
are expressed as bilinear combinations of Grassmann fields. The static
approximation and the replica symmetry ansatz have allowed us to solve the
problem at a mean field level. The resulting phase diagram displays several
phase transitions among a ferromagnetically ordered region,a spin glass one, a
mixed phase and a Kondo state depending on Jo, J and its relation with the
Kondo interaction coupling Jk. These results could be used to address part of
the experimental data for the CeNi_{1-x}Cu_x compound, when x =< 0.8.",0211170v2
2002-11-26,Coexistence of Antiferromagnetism and Superconductivity near the Quantum Criticality in Heavy Fermion Compound CeRhIn$_5$,"We report a study on the interplay between antiferromagnetism (AFM) and
superconductivity (SC) in a heavy-fermion compound CeRhIn$_5$ under pressure
$P=1.75$ GPa. The onset of the magnetic order is evidenced from a clear split
of $^{115}$In-NQR spectrum due to the spontaneous internal field below the
N\'eel temperature $T_N=2.5$ K. Simultaneously, bulk SC below $T_c=2.0$ K is
demonstrated by the observation of the Meissner diamagnetism signal whose size
is the same as in the exclusively superconducting phase. These results indicate
that the AFM coexists homogeneously with the SC at a microscopic level.",0211576v1
2002-11-28,Magneto-superconductivity of 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10,"Studied 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10 (Ru-1222) compound
crystallized in a tetragonal I4/mmm space group crystal structure.
Thermo-gravemetric (TG) analysis of the compound showed the release of oxygen
and breaking to metallic constituents in two distinct steps at around 350 and
500 0C. The DC magnetization data (M vs. T) revealed magnetic transition at 100
K followed by superconducting transition at 40 K. Low field M vs. H hysteresis
loop showed a lower critical field (Hc1) value of around 25 Oe. Ferromagnetic
component is evidenced at 5, 10, 20 and 40 K. Near saturation field of above 5
Tesla is observed at 5 K. Zero-field returning moment (Mr) and zero-moment
coercive field (Hc) values at 5 K are 0.35mB and 250 Oe. The resistance vs.
temperature (R vs. T) behaviour of the sample confirmed superconductivity at
around 43 K. Superconductivity transition (Tc) is broadened under magnetic
field with strong granularity like steps.",0211644v1
2003-01-14,Thermal Conductivity in Magnetic Superconductors,"We present here an overview of thermal conductivity behavior in magnetic
superconductors: rare-earth nickel borocarbide intermetallic compounds,
RNi_{2}B_{2}C, and the 2122 rare-earth rutheno-cuprates. The borocarbide family
of intermetallics exhibits the large variety of phenomena - only
superconductivity (R = Y, Lu), coexistence of superconductivity and magnetic
order (R = Tm, Er, Ho, Lu), only magnetic order (R = Tb, Gd), and heavy fermion
behavior (R = Yb) - within the same crystal structure. The rutheno-cuprate
Eu_{1.5}Ce_{0.5}RuSr_2Cu_{2}O_{10-\delta} exhibits coexistence of weak
ferromagnetism and superconductivity at a surprisingly high temperature
(\approx 45 K) and onset of antiferromagnetic order near 200 K. We demonstrate
how coexistence of superconductivity and magnetic order in these compounds is
releaved by the thermal conductivity studies.",0301207v1
2003-01-14,"Localized Character of 4f Electrons in CeRh$_x$(x=2,3) and CeNi$_x$(x=2,5)","We have measured Ce 4f spectral weights of extremely $\alpha$-like
Ce-transition metal intermetallic compounds CeRh$_x$ (x=2,3) and CeNi$_x$
(x=2,5) by using the {\it bulk-sensitive} resonant photoemission technique at
the Ce $M_5$($3d_{5/2}\to4f$)-edge. Unprecedentedly high energy resolution and
longer escape depth of photoemitted electron at this photon energy enabled us
to distinguish the sharp Kondo resonance tails at the Fermi level, which can be
well described by the Gunnarsson-Sch\""onhammer(GS) calculation based on the
Anderson Impurity Hamiltonian. On the other hand, the itinerant 4f band
description shows big discrepancies, which implies that Ce 4f electrons retain
localized characters even in extremely $\alpha$-like compounds.",0301209v1
2003-01-21,Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares,"We investigated the magnetic properties of two isostructural Ni(II) metal
complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form
almost perfect regular squares. Magnetic coupling and anisotropy of single
crystals were examined by magnetization measurements and in particular by
high-field torque magnetometry at low temperatures. The data were analyzed in
terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both
compounds, we found a weak intramolecular ferromagnetic coupling of the four
Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The
coupling strengths are roughly identical for both compounds, whereas the
zero-field-splitting parameters are significantly different. Possible reasons
for this observation are discussed.",0301373v1
2003-02-03,Bonding in MgSi and AlMgSi Compounds Relevant to AlMgSi Alloys,"The bonding and stability of MgSi and AlMgSi compounds relevant to AlMgSi
alloys is investigated with the use of (L)APW+(lo) DFT calculations. We show
that the $\beta$ and $\beta''$ phases found in the precipitation sequence are
characterised by the presence of covalent bonds between Si-Si nearest neighbour
pairs and covalent/ionic bonds between Mg-Si nearest neighbour pairs. We then
investigate the stability of two recently discovered precipitate phases, U1 and
U2, both containing Al in addition to Mg and Si. We show that both phases are
characterised by tightly bound Al-Si networks, made possible by a transfer of
charge from the Mg atoms.",0302027v1
2003-02-03,Thermodynamic Properties and Pressure Effect on the Superconductivity in CaAlSi and SrAlSi,"Superconductivity in the C32 compounds CaAlSi and SrAlSi is investigated by
heat capacity (Cp) measurements as well as high-pressure ac-susceptibility
experiments. The heat capacity in the superconducting state is well explained
by the BCS theory in the weak-coupling limit. The jump of Cp at the
superconducting transition (compared to the normal state electronic heat
capacity) is 1.62 and 1.21 for CaAlSi and SrAlSi, respectively, and agrees well
with the BCS value of 1.43. The magnitudes of the superconducting gaps are
estimated as 2.7 meV (CaAlSi) and 1.4 meV (SrAlSi). The pressure effect on the
superconducting transition temperature, dlnTc/dp, is positive in CaAlSi (+0.026
GPa-1) but negative in SrAlSi (-0.024 GPa-1). The opposite sign of the pressure
coefficients of Tc indicates distinct differences in the electronic structure
and the density of states at the Fermi energy of the two compounds in agreement
with recent band structure calculations.",0302057v3
2003-02-07,Organic superconductors,"This article will give an overview on the normal- and superconducting-state
properties of organic superconductors. There are a number of review articles on
this subject - most of them focus on either the quasi-one-dimensional or
two-dimensional materials. The intention of the present review is therefore to
provide a discussion which covers aspects common to both families on the same
footing. Instead of reviewing the whole diversity of behaviors found among the
various compounds with all their structural and chemical modifications, we will
mainly focus on selected compounds of both families. These are the most
extensively studied and best characterized (TMTSF)_2X and (BEDT-TTF)_2X salts
whose properties are representative for a wide class of materials. Special
attention is paid to the more recent developments including the controversial
discussions of some aspects, in particular the discussion on the nature and
symmetry of the superconducting state.",0302157v1
2003-02-18,Electronic structure of half-metallic double perovskites,"We present the self-interaction corrected local spin density (SIC-LSD)
electronic structure and total energy calculations, leading also to valencies
of the ground state configurations, for the half-metallic double perovskites
such as Sr$_{2}$FeMoO$_{6}$, Ba$_{2}$FeMoO$_{6}$, Ca$_{2}$FeMoO$_{6}$, and
Ca$_{2}$FeReO$_{6}$. We conclude that the Fe and Mo (or Re) spin magnetic
moments are anti-parallel aligned, and the magnitude of the hybridization
induced moment on Mo does not vary much between the different compounds. The
hybridization spin magnetic moment on Re is of the order of -1.1 $\mu_{B}$,
while that on Mo is about -0.4 $\mu_{B}$, independently of the alkaline earth
element. Also the electronic structure of all the compounds studied is very
similar, with a well defined gap in the majority spin component and metallic
density of states for the minority spin component, with highly hybridized Fe,
Mo (or Re), and oxygen bands.",0302360v1
2003-02-24,Magnetization study of RuSr2Y1.5Ce 0.5Cu2O10 (Ru-1222),"We have studied the magnetic properties of the non-superconducting
RuSr2Ln1.5Ce0.5Cu2O10 (Ln=Y, Dy and Ho, Ru-1222) compounds synthesized under
high pressure (6 Gpa) at elevated temperature. The materials become
magnetically ordered at TM =152(2) K regardless of Ln. The wide
ferromagnetic-like hysteresis loops which open at 5 K, close themselves around
Tirr= 90-100 K and the remanent magnetizations (Mrem) and the coercive fields
(HC) become zero. Surprisingly, at Tirr<T< TM a reappearance of the Mrem and HC
(with a peak at 120-130 K) is observed for all three samples studied. For the
non-magnetic Ln=Y compound, the extracted saturation moment at 5 K and the
effective paramagnetic moment are is 0.75 and 2.05 mB /Ru, values which are
close to the expected 1 mB and 1.73 mB respectively, for the low-spin state of
Ru5+. We argue that the Ru-1222 system becomes (i) anti-ferromagnetically (AFM)
ordered at TM. In this range a metamagnetic transition is induced by the
applied field (ii). At Tirr < TM, weak-ferromagnetism (W-FM) is induced by the
canting of the Ru moments.",0302475v1
2003-02-26,Field-induced structural evolution in the spin-Peierls compound CuGeO$_3$: high-field ESR study,"The dimerized-incommensurate phase transition in the spin-Peierls compound
CuGeO$_3$ is probed using multifrequency high-resolution electron spin
resonance (ESR) technique, in magnetic fields up to 17 T. A field-induced
development of the soliton-like incommensurate superstructure is clearly
indicated as a pronounced increase of the ESR linewidth $\Delta B$ (magnon
excitations), with a $\Delta B_{max}$ at $B_{c}\sim$ 13.8 T. The anomaly is
explained in terms of the magnon-soliton scattering, and suggests that the
soliton-like phase exists close to the boundary of the dimerized-incommensurate
phase transition. In addition, magnetic excitation spectra in 0.8% Si-doped
CuGeO$_3$ are studied. Suppression of the $\Delta B$ anomaly observed in the
doped samples suggests a collapse of the long-range-ordered soliton states upon
doping, that is consistent with high-field neutron scattering experiments.",0302542v2
2003-03-19,A new heavy fermion superconductor: the filled skutterudite compound PrOs$_4$Sb$_{12}$,"The filled skutterudite compound \PrOsSb{} exhibits superconductivity below a
critical temperature $T_\mathrm{c} = 1.85$ K that develops out of a nonmagnetic
heavy Fermi liquid with an effective mass $m^{*} \approx 50 m_\mathrm{e}$,
where $m_\mathrm{e}$ is the free electron mass. Analysis of magnetic
susceptibility, specific heat, electrical resistivity and inelastic neutron
scattering measurements within the context of a cubic crystalline electric
field yields a Pr$^{3+}$ energy level scheme that consists of a $\Gamma_{3}$
nonmagnetic doublet ground state that carries an electric quadrupole moment, a
low lying $\Gamma_{5}$ triplet excited state at $\sim 10$ K, and $\Gamma_{4}$
triplet and $\Gamma_{1}$ singlet excited states at much higher temperatures.
The superconducting state appears to be unconventional and to consist of two
distinct superconducting phases. An ordered phase of magnetic or quadrupolar
origin occurs at high fields and low temperatures, suggesting that the
superconductivity may occur in the vicinity of a magnetic or electric
quadrupolar quantum critical point.",0303370v1
2003-03-19,Superconductivity and the high field ordered phase in the heavy fermion compound PrOs$_4$Sb$_{12}$,"Superconductivity is observed in the filled skutterudite compound \PrOsSb{}
below a critical temperature temperature $T_\mathrm{c} = 1.85$ K and appears to
develop out of a nonmagnetic heavy Fermi liquid with an effective mass $m^{*}
\approx 50 m_\mathrm{e}$, where $m_\mathrm{e}$ is the free electron mass.
Features associated with a cubic crystalline electric field are present in
magnetic susceptibility, specific heat, electrical resistivity, and inelastic
neutron scattering measurements, yielding a Pr$^{3+}$ energy level scheme
consisting of a $\Gamma_{3}$ nonmagnetic doublet ground state, a low lying
$\Gamma_{5}$ triplet excitied state at $\sim 10$ K, and much higher temperature
$\Gamma_{4}$ triplet and $\Gamma_{1}$ singlet excited states. Measurements also
indicate that the superconducting state is unconventional and consists of two
distinct superconducting phases. At high fields and low temperatures, an
ordered phase of magnetic or quadrupolar origin is observed, suggesting that
the superconductivity may occur in the vicinity of a magnetic or quadrupolar
quantum critical point.",0303373v1
2003-03-19,Universal behavior of transition temperatures Vs residual resistivity in Mn site doped La-Ca-Mn-O perovskites,"We discuss here a comparative study of the role of local structure and/or
nature of local magnetic coupling on the electrical transport properties of Mn
site substituted La-Ca-Mn-O perovskites. Particular emphasis is being paid to
explore the strong correlation between the insulator-metal transition (TIM) and
the residual resistivity (rhoo) upon substitution. There exists an inverse
relationship between ro and TIM in the compounds under present discussion. Best
fit for TIM Vs ro could be obtained for the compounds understudy to a first
order exponential decay with a functional form TIM = TIMO + Aexp (-rhoo/t) than
that to a power law. There is a previous report wherein the similar correlation
in the case of rare earth substituted manganites has been attributed to
Anderson-type electron localization. The ""universal behavior"" as has been
observed between ro and TIM irrespective of the electronic, magnetic and
chemical nature of the substituting elements in the Mn site substituted
La-Ca-Mn-O perovskites needs a rigorous theoretical investigation.",0303378v1
2003-04-10,"First Investiation of magnetic ground states in the rare-earth intermetallic compounds RAl$_{0.9}$Si$_{1.1}$ (R = Ce, Pr, Gd)","We report the magnetic properties strongly varying with the rare-earth
elements in the newly found ternary compounds $R$Al$_{0.9}$Si$_{1.1}$, which
crystallize in the tetragonal $\alpha$-ThSi$_2$-type structure. For $R$ = Ce
the alloy has a weak ferromagnetism below 11 K and for $R$ = Pr it orders
ferromagnetically at 17 K, while for $R$ = Gd it is antiferromagnetic with
$T_{\rm N}$ = 30.5 K. In addition, we find no field effect on $T_{\rm N}$ of
$R$ = Gd because of the large internal mean field, but significant changes in
the magnetic properties of $R$ = Ce and Pr.",0304235v1
2003-04-23,"Structure and electronic properties of new model dinitride systems: A density-functional study of CN2, SiN2, and GeN2","The dinitrides CN2, SiN2, and GeN2 in assumed pyrite-type structures are
studied by means of density functional theory using both ultrasoft
pseudopotentials and the augmented spherical wave (ASW) method. The former two
materials constitute the large-x limit of the broader class of CNx and SiNx
compounds, which are well known for their interesting mechanical and electronic
properties. For CN2 a large bulk modulus B_0 of 405 GPa was determined . While
SiN2 is found to be a wide band gap compound, the calculated gaps of CN2 and
GeN2 are considerably smaller. The trends in structural and electronic
properties as e.g. bond lengths, band gaps and covalency are well understood in
terms of the interplay of different types of bonding.",0304502v1
2003-05-22,Anisotropic Release of the Residual Zero-point Entropy in the Spin Ice Compound Dy2Ti2O7: Kagome-ice Behavior,"We report the specific heat and entropy of single crystals of the spin ice
compound Dy2Ti2O7 at temperatures down to 0.35 K. We apply magnetic fields
along the four characteristic directions: [100], [110], [111] and [112].
Because of Ising anisotropy, we observe anisotropic release of the residual
zero-point entropy, attributable to the difference in frustration
dimensionality. In the high magnetic field along these four directions, the
residual entropy is almost fully released and the activation entropy reaches
Rln2. However, in the intermediate field region, the entropy in fields along
the [111] direction is different from those for the other three field
directions. For the [111] direction the frustration structure changes from that
of three-dimensional(3D) pyrochlore to that of two-dimensional(2D) Kagome-like
lattice with constraint due to the ice rule, leading to different values of
zero-point entropy.",0305529v1
2003-05-23,Superconductivity of up to 80 K for Tb-123 - TbSr2Cu2.7Mo0.3O7,"The Tb-123 phase has been synthesized in single-phase form with the
composition
  TbSr2Cu2.7Mo0.3O7 by solid-state reaction route and its phase purity is
confirmed by neutron powder diffraction experiments. As-synthesized sample does
not show superconductivity down to 5 K. An unusually high antiferromagnetic
ordering temperature (TN) of around 7 K is seen for Tb. After 120-atm-O2
post-annealing, bulk superconductivity is achieved in the compound at around 30
K, without any significant effect on TN. To achieve higher oxygen content and
higher Tc, the as-synthesized sample is subjected to high-pressure oxygenation
(HPO) carried out in a closed cell at 5 GPa and 400 oC in the presence of AgO
as an excess-oxygen source. This sample exhibited superconductivity onset at
around 80 K with a Meissner fraction of larger than 10 % at 5 K. Our
observation of superconductivity at 80 K is the highest Tc to-date among the
Tb-123 compounds.",0305555v1
2003-06-09,Effects of pressure on the local atomic structure of CaWO4 and YLiF4: Mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions,"The pressure response of the scheelite phase of CaWO4 (YLiF4) and the
occurrence of the pressure induced scheelite-to-wolframite (M-fergusonite)
transition are reviewed and discussed. It is shown that the change of the axial
parameters under compression is related with the different pressure dependence
of the W-O (Li-F) and Ca-O (Y-F) interatomic bonds. Phase transition mechanisms
for both compounds are proposed. Furthermore, a systematic study of the phase
transition in 16 different scheelite ABX4 compounds indicates that the
transition pressure increases as the packing ratio of the anionic BX4 units
around the A cations increases.",0306193v3
2003-06-18,Transition and spin dynamics at very low temperature in the pyrochlores Yb2Ti2O7 and Gd2Sn2O7,"The very low temperature properties of two pyrochlore compounds, Yb2Ti2O7 and
Gd2Sn2O7, were investigated using an ensemble of microscopic and bulk
techniques. In both compounds, a first order transition is evidenced, as well
as spin dynamics persisting down to the 20mK range. The transition however has
a quite different character in the two materials: whereas that in Gd2Sn2O7$ (at
1K) is a magnetic transition towards long range order, that in Yb2Ti2O7 (at
0.24K) is reminiscent of the liquid-gas transition, in the sense that it
involves a 4 orders of magnitude drop of the spin fluctuation frequency;
furthermore, no long range order is observed. These unusual features we
attribute to frustration of the antiferromagnetic exchange interaction in the
pyrochlore lattice.",0306470v2
2003-07-16,EXAFS and XRD studies of an amorphous Co$_{57}$Ti$_{43}$ alloy produced by mechanical alloying,"We have investigated the local atomic structure of an amorphous
Co$_{57}$Ti$_{43}$ alloy produced by Mechanical Alloying by means of x-ray
diffraction and EXAFS analyses on Co and Ti K-edges. Coordination numbers and
interatomic distances where found and compared with those determined using an
additive hard sphere (AHS) model associated with a RDF$(r)$ deconvolution, and
also with data from bcc-Co$_2$Ti compound. The EXAFS results obtained indicated
a shortening in the Co-Ti and Ti-Ti distances when compared to those found by
the AHS-RDF method and an increase in the Co-Co and Ti-Ti distances and a large
shortening in the Co-Ti one when compared to the distances found in the
bcc-Co$_2$Ti compound. In spite of these differences, coordination numbers
obtained from EXAFS and AHS-RDF are similar to each other and also to those
found in bcc-Co$_2$Ti.",0307375v2
2003-07-16,Diffusive energy transport in the S=1 Haldane chain compound AgVP2S6,"We present the results of measurements of the thermal conductivity $\kappa$
of the spin S=1 chain compound AgVP_2S_6 in the temperature range between 2 and
300 K and with the heat flow directed either along or perpendicular to the
chain direction. The analysis of the anisotropy of the heat transport allowed
for the identification of a small but non-negligible magnon contribution
$\kappa_m$ along the chains, superimposed on the dominant phonon contribution
$\kappa_ph$. At temperatures above about 100 K the energy diffusion constant
D_E(T), calculated from the $\kappa_m(T)$ data, exhibits similar features as
the spin diffusion constant D_S(T), previously measured by NMR. In this regime,
the behaviour of both transport parameters is consistent with a diffusion
process that is caused by interactions inherent to one-dimensional S=1 spin
systems.",0307383v1
2003-07-17,Specific heat investigation of the magnetic ordering in two frustrated spin-chain oxides: Ca3Co2O6 and Ca3CoRhO6,"Specific heat measurements were carried out on the closely related spin-chain
oxides Ca3Co2O6 and Ca3CoRhO6. Both compounds consist of Ising magnetic chains
that are arranged on a triangular lattice. The spin coupling along and between
the chains are ferromagnetic and antiferromagnetic, respectively. Geometrical
frustration is expected from the combination of these magnetic features. The
present study reports that the specific heat data of these compounds exhibit
similarities in the spin-freezing process at low T, whereas striking
differences exist in the antiferromagnetic interchain ordering at higher T.
These results are discussed in connection with previous magnetization and
neutron diffraction data.",0307433v1
2003-08-02,Double metal-insulator transitions and MR in La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (x</=0.10): A qualitative understanding in light of possible magnetic phase separation,"This paper is in continuation of our previous work on the structural,
electrical and magnetic properties of Ru doped La(0.67)Ca(0.33)MnO(3) compounds
(Ref.: L.Seetha Lakshmi et.al, J. Magn. Magn. Mater. 257, 195 (2003)). Here we
report the results of magnetotransport measurements on
La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (0<x< 0.1) compounds in the light of proposed
magnetic phase separation.",0308030v1
2003-08-06,On the break in the single-particle energy dispersions and the `universal' nodal Fermi velocity in the high-temperature copper-oxide superconductors,"Recent data from angle-resolved photoemission experiments published by Zhou
et al. [Nature, Vol. 423, 398 (2003)] concerning a number of hole-doped
copper-oxide-based high-temperature superconductors reveal that in the nodal
directions of the underlying square Brillouin zones (i.e. the directions along
which the d-wave superconducting gap is vanishing) the Fermi velocities for
some finite range of k inside the Fermi sea and away from the nodal Fermi
wavevector k_F are to within an experimental uncertainty of approximately 20%
the same both in all the compounds investigated and over a wide range of doping
concentrations and that, in line with earlier experimental observations, at
some characteristic wavevector k_* away from k_F the Fermi velocities undergo a
sudden change, with this change (roughly speaking, a finite discontinuity)
being the greatest (smallest) in the case of underdoped (overdoped) compounds.
In this paper we present a rigorous analysis concerning the implications of
these observations. [Short abstract]",0308090v2
2003-08-07,Statistical linguistic study of DNA sequences,"A new family of compound Poisson distribution functions from statistical
linguistic is used to study the n-tuples and nucleotide composition features of
DNA sequences. The relative frequency distribution of the 6-tuples and 7-
tuples occurrence studies suggest that most of the DNA sequences follow the
general shape of the compound Poisson distribution. It is also noted that the
$\chi$-square test indicated that some of the sequences follow this
distribution with a reasonable level of goodness of fit. The compositional
segmentation study fits quite well using this new family of distribution
functions. Furthermore, the absolute values of the relative frequency come out
naturally from the linguistic model without ambiguity. It is suggesting that
DNA sequences are not random sequences and they could possibly have subsequence
structures.",0308128v1
2003-08-27,Staircase-like metamagnetic transitions in phase-separated manganites: influence of thermal and mechanical treatments,"Substitutions in the Mn-sublattice of antiferromagnetic, charge and orbitally
ordered manganites was recently found to produce intriguing metamagnetic
transitions, consisting of a succession of sharp magnetization steps separated
by plateaus. The compounds exhibiting such features can be divided in two
categories, depending on whether they are sensitive to thermal cycling effects
or not. One compound of each category has been considered in the present study.
The paper reports on the influence of two treatments: high-temperature
annealing and grinding. It is shown that both of these treatments can
drastically affect the phenomenon of magnetization steps. These results provide
us with new information about the origin of these jumps in magnetization.",0308578v1
2003-08-29,Bond valence calculation for several perovskites and the evidences for a valence charge transfer process in these compounds,"This paper presents the bond valence calculation for several perovskite
systems and describes the evidences for a valence charge transfer process in
these compounds. The reviewing of the crystal structures of La1-xPbxMnO3
(x=0.1-0.5), La0.6Sr0.4-xTixMnO3 (x=0.0-0.25) and La1-xSrxCoO3 (x=0.1-0.5) is
also presented. On the basis of testing samples, the distribution of valence
charge has been evaluated which showed the failure of elastic bonding mechanism
on all studied systems and revealed the general deficit of valence charge in
the unit cell. This deficit was not equally localized on all coordination
spheres but proved asymmetrically distributed between the spheres. As the
content of substitution increased, the charge deficit declined systematically
from balanced level, signifying the continuous transfer of valence charge from
the B-O6 to A-O12 spheres. The transfered charge varied from system to system,
depending on the valence deviation of spheres and was not small. The total
valence deviation reached near 2electron/unit cell in the studied systems. The
local deviation may be more larger than this average value. The possible impact
of the limitted accuracy of the available structural data on the bond valence
results has been considered.",0308610v1
2003-09-08,Absence of magnetic order in Yb3Ga5O12: relation between phase transition and entropy in geometrically frustrated materials,"From muon spin relaxation spectroscopy experiments, we show that the sharp
peak (lambda type anomaly) detected by specific heat measurements at 54 mK for
the ytterbium gallium garnet compound, Yb3Ga5O12, does not correspond to the
onset of a magnetic phase transition, but to a pronounced building up of
dynamical magnetic pair-correlations. Beside the lambda anomaly, a broad hump
is observed at higher temperature in the specific heat of this garnet and other
geometrically frustrated compounds. Comparing with other frustrated magnetic
systems we infer that a ground state with long-range order is reached only when
at least 1/4-1/3 of the magnetic entropy is released at the lambda transition.",0309185v1
2003-09-15,Magnetic Raman scattering of the ordered tetrahedral spin-1/2 clusters in Cu_2Te_2O_5(Br_(1-x)Cl_x)_2 compounds,"Raman light-scattering experiments in the antiferromagnetic phase of the
Cu_2Te_2O_5(Br_(1-x)Cl_x)_2 compounds are analyzed in terms of a dimerized spin
model for the tetrahedral Cu-clusters. It is shown that the longitudinal
magnetic excitation in the pure Br system hybridizes with a localized singlet
excitation due to the presence of a Dzyaloshinskii-Moriya anisotropy term. The
drastic change of the magnetic scattering intensities observed when a
proportion of Br is replaced by Cl ions, is proposed to be caused by a change
of the magnetic order parameter. Instead of being parallel/antiparallel with
each other, the spins in the two pairs of spin-1/2 order perpendicular to each
other, when the composition x is larger than about 0.25.",0309351v1
2003-09-29,Magnons in CMR pyrochlore Tl2Mn2O7,"Well defined spin waves were observed when the spin dynamics of Tl2Mn2O7, the
first pyrochlore compound found to exhibit colossal magnetoresistance, was
measured [J.W.Lynn et al., Phys.Rev.Lett. 80,4582(1998)], in stark contrast
with the experimental results on the larger family of magnetoresistive
manganites with perovskite structure. In this work, we present our calculation
for the spin waves in Tl2Mn2O7, which we described using the microscopic
generic model proposed recently for this compound [C.I.Ventura and M.A.Gusmao,
Phys.Rev.B 65, 14422(2002)]. We have employed a canonical transformation to
determine perturbatively the effective spin-wave Hamiltonian, obtaining
therefrom the renormalization of the ferromagnetic spin waves related to the
localized Mn$^{4+}$ spins, due to their coupling with the conduction electrons
present. We have calculated the magnon dispersion relations along different
paths in the first Brillouin zone, comparing them with those which are obtained
for an ideal isotropic ferromagnet. This comparison evidences an agreement
between the ferromagnetic magnons obtained from the generic model and the bare
spin waves, such as had been found in neutron scattering experiments.",0309684v1
2003-09-30,Orbital ordering in transition-metal compounds: I. The 120-degree model,"We study the classical version of the 120-degree model. This is an attractive
nearest-neighbor system in three dimensions with XY (rotor) spins and
interaction such that only a particular projection of the spins gets coupled in
each coordinate direction. Although the Hamiltonian has only discrete
symmetries, it turns out that every constant field is a ground state. Employing
a combination of spin-wave and contour arguments we establish the existence of
long-range order at low temperatures. This suggests a mechanism for a type of
ordering in certain models of transition-metal compounds where the very
existence of long-range order has heretofore been a matter of some controversy.",0309691v3
2003-09-30,Orbital order in classical models of transition-metal compounds,"We study the classical 120-degree and related orbital models. These are the
classical limits of quantum models which describe the interactions among
orbitals of transition-metal compounds. We demonstrate that at low temperatures
these models exhibit a long-range order which arises via an ""order by disorder""
mechanism. This strongly indicates that there is orbital ordering in the
quantum version of these models, notwithstanding recent rigorous results on the
absence of spin order in these systems.",0309692v2
2003-09-30,"Structural and magnetic anomalies among the spin-chain compounds, Ca3Co1+xIr1-xO6","The results of x-ray diffraction, and ac and dc magnetization as a function
of temperature are reported for a new class of spin-chain oxides,
Ca3Co1+xIr1-xO6. While the x= 0.0, 0.3, 0.5 and 1.0 are found to form in the
K4CdCl6-derived rhombhohedral (space group R-3c) structure, the x= 0.7
composition is found to undergo a monoclinic distortion in contrast to a
literature report. Apparently, the change in the crystal symmetry with x
manifests itself as a change in the sign of paramagnetic Curie temperature for
this composition as though magnetic coupling sensitively depends on such
crystallographic distortions. All the compositions exhibit spin-glass anomalies
with an unusually large frequency dependence of the peak temperature in ac
susceptibility in a temperature range below 50 K, interestingly obeying
Voger-Fulcher relationship even for the stoichiometric compounds.",0309700v1
2003-10-14,Spin resonance peak in Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O superconductors: A probe of the pairing symmetry,"Motivated by the recent discovery of superconductivity in layered
Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O compound, we investigate theoretically the
spin dynamics in the superconducting state with three possible $p_{x}+ip_{y}$-,
$d+id'$-, and $f$-wave pairing symmetries in two-dimensional triangular
lattices. We find that a spin resonance peak, which is elaborated to have a
close relevance to the relative phase of the gap function and the geometry of
the Fermi surface, appears in both in-plane and out-of-plane components of the
spin susceptibility $\chi$ for the spin-singlet $d+id'$-wave pairing, while
only in the out-of-plane(in-plane) component of $\chi$ for the spin-triplet
$p_{x}+ip_{y}$-wave ($f$-wave) pairing. Because the pairing symmetry in this
compound is still hotly debated at present, this distinct feature may be used
to probe or determine it unambiguously with future neutron scattering
experiments.",0310308v1
2003-11-07,"Magnetic and thermodynamic properties of RMnO$_3$ (R = Pr, Nd)","The ground state properties of the pure perovskite compounds PrMnO$_3$ and
NdMnO$_3$ were investigated by magnetization, magnetic AC susceptibility and
specific heat measurements. A strongly anisotropic behavior has been detected
for temperatures below the antiferromagnetic phase transition $T_N$~100K. The
susceptibility and the weak spontaneous ferromagnetic moment appear to be
different in both compounds due to different anisotropic rare earth
contributions. The specific heat shows strong Schottky type contributions at
low temperatures, which for NdMnO$_3$ strongly depend on the magnetic field. A
spin reorientation phase transition (spin-flop type) induced by a magnetic
field along b axis was observed in NdMnO$_3$ at H~110kOe and T=5K. All results
can consistently be explained by anisotropic contributions of the rare earth
ions: In PrMnO$_3$ the electronic ground state is determined by a low lying
quasidoublet split by the crystal field ~19 K. In NdMnO$_3$ the Kramers doublet
is split by an exchange Nd-Mn field (~20K).",0311170v1
2003-11-25,Upper Critical Field of a Novel 18-K Superconductive Phase in Metastable Yttrium Sesquicarbide Prepared Using High Pressure Technique,"The metastable phase of an yttrium sesquicarbide compound, which was vary
recently reported as a new superconductive phase with a Tc value of 18 K, was
prepared under high pressure from the nominal composition of Y2C3 and
Y2C2.9B0.1 in order to investigate this phase. We have succeeded in
reproduction, and in the transport measurement for this 18-K phase. It is
considered that the reason for the higher Tc value than the 11.5 K reported
previously is not the small amount of B as the impurity element from the BN
crucible. The Bc2 value at 0 K estimated from the resistivity data for the 18-K
phase seems to be over 30 T. It means that the Tc and Bc2 values of the 18-K
phase are as high as those of the general A15 compounds.",0311561v1
2003-12-19,Field-Induced Disorder Point in Non-Collinear Ising Spin Chains,"We perform a theoretical study of a non-collinear Ising ferrimagnetic spin
chain inspired by the compound Co(hfac)2NITPhOMe. The basic building block of
its structure contains one Cobalt ion and one organic radical each with a spin
1/2. The exchange interaction is strongly anisotropic and the corresponding
axes of anisotropy have a period three helical structure. We introduce and
solve a model Hamiltonian for this spin chain. We show that the present
compound is very close to a so-called disorder point at which there is a
massive ground state degeneracy. We predict the equilibrium magnetization
process and discuss the impact of the degeneracy on the dynamical properties by
using arguments based on the Glauber dynamics.",0312528v1
2004-01-01,Extended moment formation and magnetic ordering in the trigonal chain compound Ca3Co2O6,"The results of electronic structure calculations for the one-dimensional
magnetic chain compound Ca3Co2O6 are presented. The calculations are based on
density functional theory and the local density approximation and used the
augmented spherical wave (ASW) method. Our results allow for deeper
understanding of recent experimental findings. In particular, alternation of Co
3d low- and high-spin states along the characteristic chains is related to
differences in the oxygen coordination at the inequivalent cobalt sites. Strong
hybridization of the d states with the O 2p states lays ground for polarization
of the latter and the formation of extended localized magnetic moments centered
at the high-spin sites. In contrast, strong metal-metal overlap along the
chains gives rise to intrachain ferromagnetic exchange coupling of the extended
moments via the d_{3z^2-r^2} orbitals of the low-spin cobalt atoms.",0401004v1
2004-01-30,Superconductivity in Organic Compounds with Pseudo-Triangular Lattice,"We study spin fluctuation (SF) mediated superconductivity (SC) in a
half-filled square lattice Hubbard model with the transfer matrices -t between
nearest neighbor sites and -t' between a half of next nearest neighbor sites
neighboring along only one of the <1,1> directions, considering application of
this model to organic kappa-(BEDT-TTF)2X compounds. Varying the t'/t value from
0 to 1, one can interpolate between a square and an equilateral triangular
lattice, the latter giving frustration to antiferromagnetically (AF) coupled
spin systems. Within the fluctuation exchange (FLEX) approximation, we
calculate chi(q,omega), Tc and the SC order parameter for various model
parameter values and find that both AF and SC are suppressed as one approaches
the frustration geometry or |(t'/t)-1| \to 0. The SC phase, however, extends
beyond the AF phase boundary fairly close to t'/t=1 for realistic U/t values.
The order parameter is of x2-y2-type for t'/t<1 and of xy-type for t'/t>1.",0401623v1
2004-02-03,23Na NMR Evidence for Charge Order and Anomalous Magnetism in NaxCoO2,"We have compared by $^{23}$Na NMR and magnetic susceptibility the magnetic
properties of oriented powder samples of Na$_{x}$CoO$_{2}$ compounds. The NMR
spectra are found identical for various samples with nominal $0.50\leq x\leq
0.70,$ which establishes that the dominant phase has a single composition
$x\approx 0.70$. Three Na sites are identified from their single valued
quadrupole effects and magnetic shifts which implies a very definite order of
the Na$^{+}$ ions and of the Co charges in the CoO$_{2}$ planes. The local
susceptibility of the magnetic cobalt sites displays a large enhancement below
100 K with respect to the usually found high $T$ Curie-Weiss law. A very
distinct much weaker Pauli like magnetism is detected for $x\approx 0.35$, the
parent of the superconducting hydrated compound.",0402074v1
2004-03-04,The Electronic and Superconducting Properties of Oxygen-Ordered MgB2 compounds of the form Mg2B3Ox,"Possible candidates for the Mg2B3Ox nanostructures observed in bulk of
polycrystalline MgB2 (Ref.1) have been studied using a combination of
Z-contrast imaging, electron energy loss spectroscopy (EELS) and
first-principles calculations. The electronic structures, phonon modes, and
electron phonon coupling parameters are calculated for two oxygen-ordered MgB2
compounds of composition Mg2B3O and Mg2B3O2, and compared with those of MgB2.
We find that the density of states for both Mg2B3Ox structures show very good
agreement with EELS, indicating that they are excellent candidates to explain
the observed coherent oxygen precipitates. Incorporation of oxygen reduces the
transition temperature and gives calculated TC values of 18.3 K and 1.6 K for
Mg2B3O and Mg2B3O2, respectively.",0403136v1
2004-03-12,Decoupling of orbital and spin degrees of freedom in Li1-xNaxNiO2,"In the Li1-xNaxNiO2 solid solutions three different single phase regions
exist: for x > 0.9, forx = 0.7 and for x < 0.3. Although the intermediate
compound does not show the cooperative Jahn-Teller transition of NaNiO2, its
magnetic properties remain very similar with, in particular, the low
temperature 3D magnetic ordering. Therefore, the strong coupling between
orbital and spindegrees of freedom, characteristic of other oxides like
perovskites, and usually invoked to explainthe absence of both long-range
orbital and magnetic ordering in LiNiO2, seems not to take placein these
layered compounds with 90-degree bonds. We also discuss the relevance of the O
crystal fieldsplitting induced by the trigonal distortion, in generating AFM
Ni-Ni in-plane interactions.",0403329v2
2004-03-13,High Field behavior of the Spin Gap compound Sr$_2$Cu(BO$_3$)$_2$,"We report magnetization and heat capacity measurements of single crystal
samples of the spin gap compound Sr$_2$Cu(BO$_3$)$_2$. Low-field data show that
the material has a singlet ground state comprising dimers with intradimer
coupling J = 100 K. High field data reveal the role of weak interdimer
coupling. For fields that are large compared to the spin gap, triplet
excitations are observed for significantly smaller fields than predicted for
isolated dimers, indicating that weak inter-dimer coupling leads to triplet
delocalization. High field magnetization behavior at low temperatures suggests
additional cooperative effects.",0403334v3
2004-03-17,Domain orbital state in ferromagnetic insulating La$_{0.825}$Ca$_{0.175}$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$ compound,"Using M\""ossbauer and EPR spectroscopy we have studied the insulating
ferromagnetic La$_{1-x}$Ca$_x$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$ ($x=0.175$)
compound prepared in air and reduced atmosphere. The average hyperfine field
follows a mean field approximation solution in contrast with the ferromagnetic
metallic regime where it significantly deviates from the order parameter
deduced from neutron diffraction data or mean field approximation. Although the
magnetic measurements show remarkable differences between air prepared and
reduced R samples the corresponding M\""ossbauer spectra are almost identical.
The strong temperature dependance of the hyperfine field distribution at the
$^{57}$Fe nucleus is related with the supertransferred magnetic field between
ferric ion and the oxygen bridged six nearest-neighbor manganese ions. The
sudden increasing of the width of the hyperfine field distribution above
$T_B\approx 100$ K has been attributed to the orbital disordering occurring for
$T>T_B$.",0403446v1
2004-03-21,Phase diagram and magnetic properties of La$_{1-x}$Ca$_x$MnO$_3$ compound for $0\leq x \leq 0.23$,"In this article a detailed study of La$_{1-x}$Ca$_x$MnO$_3$ ($0\leq x \leq
0.23$) phase diagram using powder x-ray diffraction and magnetization
measurements is presented. Unfortunately, in the related literature no properly
characterized samples have been used, with consequence the smearing of the real
physics in this complicated system. As the present results reveal, there are
two families of samples. The first family concerns samples prepared in
atmosphere ($P({\rm O}_2)=0.2$ Atm) which are all ferromagnetic with Curie
temperature rising with $x$. The second family concerns samples, where a post
annealing in nearly zero oxygen partial pressure is applied. These samples show
a canted antiferromagnetic structure for $0\leq x \leq 0.1$ below $T_N$, while
for $0.125\leq x <0.23$ an unconventional ferromagnetic insulated phase is
present below $T_c$. The most important difference between nonstoichiometric
and stoichiometric samples concerning the magnetic behavior, is the anisotropy
in the exchange interactions, in the stoichiometric samples putting forward the
idea that a new orbital ordered phase is responsible for the ferromagnetic
insulating regime in the La$_{1-x}$Ca$_x$MnO$_3$ compound.",0403543v1
2004-03-30,"Finite-Size effects in ""Single Chain Magnets"": an experimental and theoretical study","The problem of finite size effects in s=1/2 Ising systems showing slow
dynamics of the magnetization is investigated introducing diamagnetic
impurities in a Co$^{2+}$-radical chain. The static magnetic properties have
been measured and analyzed considering the peculiarities induced by the
ferrimagnetic character of the compound. The dynamic susceptibility shows that
an Arrhenius law is observed with the same energy barrier for the pure and the
doped compounds while the prefactor decreases, as theoretically predicted.
Multiple spins reversal has also been investigated.",0403731v1
2004-04-03,"Optical properties, electron-phonon coupling, and Raman scattering of vanadium ladder compounds","The electronic structure of two V-based ladder compounds, the quarter-filled
NaV$_2$O$_5$ in the symmetric phase and the iso-structural half-filled
CaV$_2$O$_5$ is investigated by ab initio calculations. Based on the
bandstructure we determine the dielectric tensor $\epsilon(\omega)$ of these
systems in a wide energy range. The frequencies and eigenvectors of the fully
symmetric A$_{g}$ phonon modes and the corresponding electron-phonon and
spin-phonon coupling parameters are also calculated from first-principles. We
determine the Raman scattering intensities of the A$_g$ phonon modes as a
function of polarization and frequency of the exciting light.
  All results, i.e. shape and magnitude of the dielectric function, phonon
frequencies and Raman intensities show very good agreement with available
experimental data.",0404076v2
2004-05-12,A novel route to phase formation of cobalt oxyhydrates using KMnO4 as an oxidizing agent,"We have first succeefully synthesized the sodium cobalt oxyhydrate
superconductors using KMnO4 as a de-intercalating and oxidizing agent. It is a
novel route to form the superconductive phase of NaxCoO2.yH2O without resorting
to the commonly used Br2/CH3CN solution. The role of the KMnO4 is to
de-intercalate the Na+ from the parent compound Na0.7CoO2 and oxidize the Co
ion as a result. The higher molar ratio of KMnO4 relative to the sodium content
tends to remove more Na+ from the parent compound and results in a slight
expansion of the c-axis in the unit cell. The superconducting transition
temperature is 4.6-3.8 K for samples treated by the aqueous KMnO4 solution with
the molar ratio of KMnO4 relative to the sodium content in the range of 0.3 and
2.29.",0405244v1
2004-05-21,Critical current density and flux pinning in La2-xPrxCa2xBa2Cu4+2xOz (x = 0.1 - 0.5) superconductors,"Polycrystalline La2-xPrxCa2xBa2Cu4+2xOz (LPCaBCO) compounds with x = 0.1 -
0.5 were synthesized by solid-state reaction method and studied by room
temperature X-ray diffraction, dc resistivity, dc magnetization and iodometry.
The superconducting transition temperatures in these tetragonal triple
perovskite compounds increases from 32 to 62 K (Tconset values) with increasing
dopant concentration. The mixing of rare earth La3+ and Pr3+/4+ ions at rare
earth site (La3+) along with substitution of divalent Ca2+ results in the
shrinkage of unit cell volume. The contraction of unit cell volume due to
larger ion being substituted by smaller ions, gives rise to creation of pinning
centers in the unit cell leading to increase in critical current density and
flux pinning",0405506v1
2004-05-24,"Study of Magnetic Properties of A_2B^'NbO_6 (A=Ba,Sr, (BaSr): and B^'=Fe and Mn) double perovskites","We have studied the magnetic properties of Ba_2FeNbO_6 and Ba_2MnNbO_6. it is
seen that Ba_2FeNbO_6 is an antiferromagnet with a weak ferromagnetic behaviour
at 5K while Ba_2MnNbO_6 shows two magnetic transitions one at 45 K and the
other at 12K. Electron spin resonance (ESR) measurements at room temperature
show that the Mn compound does not show any Jahn-Teller distortion. It is also
seen that the Neel temperature of the A_2FeNbO_6 (A=Ba,Sr, BaSr) compounds do
not vary significantly. However variations in the average A-site ionic radius
influence the formation of short range correlations that persist above T_N.",0405557v1
2004-05-27,"Magnetic, electrical resistivity, heat-capacity and thermopower anomalies in CeCuAs2","The results of magnetic susceptibility, electrical resistivity ($\rho$),
heat-capacity (C) and thermopower (S) measurements on CeCuAs2, forming in
ZrCuSi2-type tetragonal structure, are reported. Our investigations reveal that
Ce is trivalent and there is no clear evidence for long range magnetic ordering
down to 45 mK. The $\rho$ behavior is notable in the sense that (i) the
temperature (T)-coefficient of $\rho$ is negative in the entire range of
measurement (45 mK to 300 K) with large values of $\rho$, while S behavior is
typical of metallic Kondo lattices, and (ii) $\rho$ is proportional to T-0.6 at
low temperatures, without any influence on the exponent by the application of a
magnetic field, which does not seem to classify this compound into
hither-to-known non-Fermi liquid (NFL) systems. In contrast to the logarithmic
increase known for NFL systems, C/T measured down to 0.5 K exhibits a fall
below 2 K. The observed properties of this compound are unusual among Ce
systems.",0405638v1
2004-05-31,Orbital order and ferrimagnetic properties of the new compound $Sr_8 Ca Re_3 Cu_4 O_{24}$,"By means of the LSDA+U method and the Green function method, we investigate
the electronic and magnetic properties of the new material of
Sr$_8$CaRe$_3$Cu$_4$O$_{24}$. Our LSDA+U calculation shows that this system is
an insulator with a net magnetic moment of 1.01 $\mu_{\rm B}$/f.u., which is in
good agreement with the experiment. Magnetic moments are mainly located at Cu
atoms, and the magnetic moments of neighboring Cu sites align anti-parallel. It
is the non-magnetic Re atoms that induce an orbital order of $d$ electrons of
Cu atoms, which is responsible for the strong exchange interaction and the high
magnetic transition temperature. Based on the LSDA+U results, we introduce an
effective model for the spin degrees of freedom, and investigate the
finite-temperature properties by the Green function method. The obtained
results are consistent with the experimental results, indicating that the
spin-alternating Heisenberg model is suitable for this compound.",0405684v1
2004-06-11,Reduction of Pauli paramagnetic pair-breaking effect in antiferromagnetic superconductors,"Antiferromagnetic superconductors in a magnetic field are studied. We examine
a mechanism which significantly reduces the Pauli paramagnetic pair-breaking
effect. The mechanism is realized even in the presence of the orbital
pair-breaking effect. We illustrate it using a three-dimensional model with an
intercalated magnetic subsystem. The upper critical field is calculated for
various parameters. It is shown that the upper critical field can reach several
times the pure Pauli paramagnetic limit. The possible relevance to the large
upper critical field observed in the heavy fermion antiferromagnetic
superconductor CePt_3Si discovered recently is briefly discussed. We try to
understand the large upper critical field in the compound CePt_3Si and
field-induced superconductivity in the compound CePb_3 within a unified
framework.",0406288v5
2004-06-23,"Chemical Bond Type, Atom Packing, and Superconductivity of YBa2Cu3O7 and NaxWO3","The YBa2Cu3O8-x and NaxWO3 superconductors are treated not as an ionic
compounds but rather as an arrays of atoms featuring both covalent and metallic
bonding. We accept as particle radii the positions of the principal maxima in
the radial distribution functions of the charge density, which are very close
to the known covalent and metallic radii of atoms while differing strongly from
the traditional ionic radii. The graphic pattern of atomic packing in the
lattices reveals a number of features inherent in nonstoichiometric compounds.
The network of atoms Y and Ba in medium Cu-O and of atoms Na in medium WO3 may
be considered not as a dopant but rather as the second component of the
nanocomposite. The scheme of the onset of the superconducting state and
possible methods of its verification are discussed.",0406564v2
2004-06-28,Relevance of multiband Jahn-Teller effects on the electron-phonon interaction in $A_3$C$_{60}$,"Assessing the effective relevance of multiband effects in the fullerides is
of fundamental importance to understand the complex superconducting and
transport properties of these compounds. In this paper we investigate in
particular the role of the multiband effects on the electron-phonon (el-ph)
properties of the $t_{1u}$ bands coupled with the Jahn-Teller intra-molecular
$H_g$ vibrational modes in the C$_{60}$ compounds. We show that, assuming
perfect degeneracy of the electronic bands, vertex diagrams arising from the
breakdown of the adiabatic hypothesis, are one order of magnitude smaller than
the non-crossing terms usually retained in the Migdal-Eliashberg (ME) theory.
These results permit to understand the robustness on ME theory found by
numerical calculations. The effects of the non degeneracy of the $t_{1u}$ in
realistic systems are also analyzed. Using a tight-binding model we show that
the el-ph interaction is mainly dominated by interband scattering within a
single electronic band. Our results question the reliability of a degenerate
band modeling and show the importance of these combined effects in the
$A_3$C$_{60}$ family.",0406685v1
2004-07-07,Fractionalization and Fermi surface volume in heavy fermion compounds: the case of YbRh$_2$ Si$_2$,"We establish an effective theory for heavy fermion compounds close to a zero
temperature Anti-Ferromagnetic (AF) transition. Coming from the heavy Fermi
liquid phase across to the AF phase, the heavy electron fractionalizes into a
light electron, a bosonic spinon and a {\it new} excitation: a spinless
fermionic field. Assuming this field acquires dynamics and dispersion when one
integrates out the high energy degrees of freedom, we give a scenario for the
volume of its Fermi surface through the phase diagram. We apply our theory to
the special case of YbRh$_2$(Si$_{1-x}$ Ge$_x$)$_2$ where we recover, within
experimental resolution, several low temperature exponents for transport and
thermodynamics.",0407155v1
2004-07-08,"Heat-capacity anomalies in the presence of high magnetic fields in the spin-chain compound, Ca3Co2O6","Heat-capacity behavior in the presence of externally applied magnetic field
(H) up to 140 kOe is investigated (2-35 K) for the quasi-1-dimensional
compound, Ca3Co2O6, believed to order magnetically with the so-called partially
disordered anti-ferromagnetic structure. The results reveal that there is a
shift of the magnetic transition occurring around 24 K to a marginally higher
temperature (by 0.5 K) as H is increased from 10 to 30 kOe, uncharacteristic of
anti-ferromagnets. No peak attributable to magnetic ordering could be observed
in the entire field range of investigation in the vicinity of the second
magnetic transition, occurring around 10 K. However, hysteresis studies of
H-dependence of C indicate a subtle change in the magnetic structure as the T
is lowered across 10 K.",0407189v1
2004-07-21,YbNiSi3: a new antiferromagnetic Kondo lattice with strong exchange interaction,"We report on the structural, thermodynamic and transport properties of
high-quality single crystals of YbNiSi3 grown by the flux method. This compound
crystallizes in the SmNiGe3 layered structure type of the Cmmm space group. The
general physical behavior is that of a Kondo lattice showing an
antiferromagnetic ground state below T_N = 5.1 K. This is among the highest
ordering temperatures for a Yb-based intermetallic, indicating strong exchange
interaction between the Yb ions, which are close to +3 valency based on the
effective moment of 4.45 mu_B/f.u. The compound has moderately heavy-electron
behavior with Sommerfeld coefficient 190 mJ/mol K^2. Resistivity is highly
anisotropic and exhibits the signature logarithmic increase below a local
minimum, followed by a sharp decrease in the coherent/magnetically ordered
state, resulting in residual resistivity of 1.5 micro Ohm cm and RRR = 40.
Fermi-liquid behavior consistent with a ground-state doublet is clearly
observed below 1 K.",0407543v1
2004-07-21,Spin Fluctuation and Crystal Field Excitation of a Heavy Fermion Compound YbAgGe studied by Inelastic Neutron Scattering,"Inelastic neutron scattering experiment has been performed on a new heavy
fermion compound YbAgGe for a polycrystalline sample at zero magnetic field. A
quasielastic scattering and a crystal field excitation at 12 meV was observed.
Both of them are broadened with an intrinsic width of 0.9 meV at 1.5 K which
increases to about 3 meV at 300 K. The temperature dependence follows
Gamma_0+AT^(1/2) typically observed in Kondo systems. Crystal field parameters
were also deduced. To explain the result that only one excitation isobserved at
12 meV, it is concluded that the B22 term should be the main component.",0407549v1
2004-07-23,First-order Raman spectra of double perovskites AB$'{1/2}B$''{1/2}O3,"First principles computations of Raman intensities were performed for
perovskite-family compound CaAl$_{1/2}$Nb$_{1/2}$O$_3$ (CAN). This compound
features 1:1 (NaCl-type) ordering of Al and Nb superimposed onto the $b^-b^-c+$
octahedral tilting. Raman tensor for CAN was computed using the package for
first-principles computations ABINIT (URL \underline {http://www.abinit.org}).
Computations performed for both untilted cubic ($Fm\bar{3}m$) and tilted
monoclinic ($P2_1/n$) CAN structures showed that the strongest Raman lines are
associated with the ordering of Al and Nb. The computed spectrum agreed
qualitatively with the experimental data measured on powder (CAN is available
in polycrystalline form only). The effect of cation disorder on the Raman
intensities was considered using phenomenological theory of light scattering in
the vicinity of a phase transition. We suggest that, for certain modes, the
corresponding Raman intensities depend primarily on the average long range
order while, for other modes, the intensities are determined by fluctuations of
the order parameter.",0407625v1
2004-07-29,Electronic features around Fermi level correlating to occurrence of magnetism or superconductivity in Laves-phase intermetallic compounds,"Based on density functional calculations, the relationship between magnetism
or superconductivity and electronic states around Fermi level were derived, and
the location of the Fermi level in nonmagnetic ""form"" of Laves-phase compounds
is very sensitive to determine the presence of nonmagnetism, or ferromagnetism,
or antiferromagnetism, or superconductivity. The Fermi level at the nonbonding
and antibonding regions corresponds for the nonmagnetism and magnetism,
respectively, whereas at bonding region with responsibility for
superconductivity. This rules will be very useful and convenient to search the
new magnetic and superconductive materials.",0407753v1
2004-08-10,The role of intra-atomic non-collinear magnetization density in weak ferromagnetism,"We investigate the mechanism behind the breakdown of the compensation of
large magnetic moments leading to weak ferromagnetism. For this we use
first-principles calculations within density functional theory and we focus on
the weak ferromagnetic compound Mn3Sn. Our new implementation allows for an
exact treatment of the spin-density matrix and non-collinearity. In order to
gain some insight, our results are compared to the ones obtained by using the
atomic moment approximation (AMA) and its role is discussed. We find that the
appearance of the weak ferromagnetic moment in this compound originates not so
much as an effect of spin-orbit coupling as suggested previously from AMA
calculations, as from the non-collinearity of the Sn atom magnetization
density. This is confirmed by non-collinear calculations in which the SOC
effects are neglected.",0408200v1
2004-08-14,Structural and Magnetic Studies on La2-xDyxCa2xBa2Cu4+2xOz Type Superconducting Oxides,"The La-2125 type La2-xDyxCa2xBa2Cu4+2xOz (0.1 < x < 0.5; LDBO) compounds have
been synthesized and studied for their structural and superconducting
properties by room temperature neutron diffraction, high field dc
magnetization, four-probe resistivity and iodometric double titration. The
Rietveld analysis of the neutron diffraction data reveals tetragonal structure
for all the samples, which crystallizes into La-123 type tetragonal structure
in P4/mmm space group. Iodometric double titrations were performed to determine
the oxygen content values and calculate mobile charge carrier (holes) density.
The superconducting transition temperatures (Tc) increases from ~ 20 K for x =
0.1 to a maximum of 75 K for x = 0.5. Flux pinning force (Fp) and critical
current density (Jc), calculated from the low temperature hysteresis loops,
also increases with increasing dopant concentration. The paper presents the
studies on structure and superconducting properties of all LDBO compounds in
light of the role of calcium in inducing superconductivity in the tetragonal
non-superconducting oxide.",0408334v1
2004-08-18,Charge-Density-Wave Ordering in the Metal-Insulator Transition Compound PrRu4P12,"X-ray and electron diffraction measurements on the metal-insulator (M-I)
transition compound PrRu$_4$P$_{12}$ have revealed the emergence of a periodic
ordering of charge density around the Pr atoms. It is found that the ordering
is associated with the onset of a low temperature insulator phase. These
conclusions are supported by the facts that the space group of the crystal
structure transforms from Im$\bar{3}$ to Pm$\bar{3}$ below the M-I transition
temperature and also that the temperature dependence of the superlattice peaks
in the insulator phase follows the squared BCS function. The M-I transition
could be originated from the perfect nesting of the Fermi surface and/or the
instability of the $f$ electrons.",0408390v2
2004-09-10,$μ$SR study of the quantum dynamics in the frustrated $S=3/2$ kagome bilayers,"We present $\mu$SR experiments in the $S=3/2$ kagome bilayer compound
Ba$_{2}$Sn$_{2}$ZnGa$_{10-7p}$Cr$_{7p}$O$_{22}$ (BSZCGO$(p)$) and compare it to
the isostructural SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$ (SCGO$(p)$), including for
the latter new results for $p\geq0.89$. Quantum-dynamical low energy magnetic
excitations are evidenced in this novel compound. We study the evolution of the
muon relaxation rate with $p$, $T$ and field. A phenomenological model for the
muon relaxation based on sporadic dynamics due to spin excitations in a singlet
sea proposed by Uemura \emph{et al.} [Phys. Rev. Lett. \textbf{73}, 3306
(1994)]. is extended to all fields and $T$-range. Its connexion to the RVB
picture is discussed, and we argue that such coherent states might mediate the
interactions between ""impurities"" which induce the spin glass freezing.",0409257v2
2004-09-13,Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds,"The ground state and thermodynamic properties of spin-1 and spin-3/2 chains
are investigated via exactly solved su(3) and su(4) models with physically
motivated chemical potential terms. The analysis involves the Thermodynamic
Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1
chain with large single-ion anisotropy, a gapped phase occurs which is
significantly different from the valence-bond-solid Haldane phase. The
theoretical curves for the magnetization, susceptibility and specific heat are
favourably compared with experimental data for a number of spin-1 chain
compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at
zero external magnetic field. A middle magnetization plateau can be triggered
by the single-ion anisotropy term. Overall, our results lend further weight to
the applicability of integrable models to the physics of low-dimensional
quantum spin systems. They also highlight the utility of the exact HTE method.",0409311v1
2004-09-14,Superconductivity in heavy fermion compounds,"We review the current state of experimental and theoretical investigations of
heavy fermion superconductors. We discuss most of the Ce-based compounds like
Ce122, Ce115, Ce218 and Ce131 classes and U-based superconductors like UBe_13
and UPd_2Al_3. In the former the emphasis is on the connection to quantum
critical phenomena and non-Fermi liquid behaviour. Recent neutron scattering
and hydrostatic pressure results on SDW/SC competition in the Ce122 system are
included. For the U-compounds we discuss the significance of dual models with
both localised and itinerant 5f electrons for mass enhancement and
superconducting pair formation. Itinerant spin fluctuation theories for
unconventional superconductivity are also reviewed.",0409363v1
2004-09-29,First-principles characterization of ferromagnetic Mn5Ge3 for spintronic applications,"In the active search for potentially promising candidates for spintronic
applications, we focus on the intermetallic ferromagnetic Mn5Ge3 compound and
perform accurate first-principles FLAPW calculations within density functional
theory. Through a careful investigation of the bulk electronic and magnetic
structure, our results for the total magnetization, atomic magnetic moments,
metallic conducting character and hyperfine fields are found to be in good
agreement with experiments, and are elucidated in terms of a hybridization
mechanism and exchange interaction. In order to assess the potential of this
compound for spin-injection purposes, we calculate Fermi velocities and degree
of spin-polarization; our results predict a rather high spin-injection
efficiency in the diffusive regime along the hexagonal c-axis. Magneto-optical
properties, such as L_2,3 X-ray magnetic circular dichroism, are also reported
and await comparison with experimental data.",0409734v1
2004-10-06,Transport Properties for and Intermediate Valence Model of Tl$_{2}$Mn$_{2}$O$_{7}$,"The appearance of colossal magneto resistance (CM) in Tl$_{2}$Mn$_{2}$O$_{7}$
has stimulated many recent studies of the pyrochlore family of compounds
A$_{2}$B$_{2}$O$_{7}$. The double exchange (DE) model of Zener does not
describe the CM in Tl$_{2}$Mn$_{2}$O$_{7}$, because its metallic conductivity
cannot be explained by doping. Here we employ Hubbard operators to reformulate
the intermediate valence model used by Ventura and Alascio to describe the
electronic structure and transport properties of this compound $(Phys.Rev. B56,
14533 (1997)). Following Foglio and Figueira (Phys.Rev. B62, 7882 (2000)) we
use approximate one-electron Green's Functions (GF) to calculate the
thermopower and the static and dynamic conductivity of Tl$_{2}$Mn$_{2}$O$_{7}$
for several magnetic fields. A qualitative agreement was obtained with the
experimental measurements of those properties. Although the agreement is far
from perfect, these quantities are fairly well described by the same set of
system parameters.",0410163v1
2004-10-08,Electronic structure of the $Sr_{0.4}Ca_{13.6}Cu_{24}O_{41}$ incommensurate compound,"We extracted, from strongly-correlated ab-initio calculations, a complete
model for the chain subsystem of the $Sr_{0.4}Ca_{13.6}Cu_{24}O_{41}$
incommensurate compound. A second neighbor $t-J+V$ model has been determined as
a function of the fourth crystallographic parameter $\tau$, for both low and
room temperature crystallographic structures. The analysis of the obtained
model shows the crucial importance of the structural modulations on the
electronic structure through the on-site energies and the magnetic
interactions. The structural distortions are characterized by their long range
effect on the cited parameters that hinder the reliability of analyses such as
BVS. One of the most striking results is the existence of antiferromagnetic
nearest-neighbor interactions for metal-ligand-metal angles of $90^\circ$. A
detailed analysis of the electron localization and spin arrangement is
presented as a function of the chain to ladder hole transfer and of the
temperature. The obtained spin arrangement is in agreement with
antiferromagnetic correlations in the chain direction at low temperature.",0410204v2
2004-10-14,High-resolution soft x-ray photoemission study of a Kondo semiconductor and related compounds,"We have performed the bulk-sensitive high-resolution soft x-ray photoemission
study of a Kondo semiconductor CeRhAs and related compounds CeNiSn and CePdSn.
The comparison of the spectra of polycrystalline CePdSn on the fractured and
scraped surfaces shows that the fracturing of the samples is much better than
the scraping in order to obtain intrinsic photoemission spectra. The Ce 4d
core-level spectra show clear differences in the electronic states among the
materials.",0410366v1
2004-10-28,Inelastic neutron scattering study of single crystal heavy fermion YbAgGe,"Single crystals of the heavy-fermion compound YbAgGe have been studied by
neutron scattering. The magnetic ordering occurring below T1=0.5 K is
characterized by a commensurate propagation vector k=(1/3,0,1/3) and the
moments in the basal plane of the hexagonal structure. The dynamic magnetic
susceptibility is dominated by quasielastic spin fluctuations with a
characteristic energy Gamma of the order of 1 meV. The spins fluctuate
predominantly in the basal plane. No spin-wave excitations are observed in the
magnetically ordered phase. Below the Kondo temperature, TK=20 K, Gamma shows a
strong q dependence for wave vectors along the c* direction, but is
q-independent in the basal plane. Gamma shows initially a rapid increase with
temperature T at the antiferromagnetic zone center, but follows a standard
sqrt(T) law for other q values and for T>TK in general. These observations
classify YbAgGe as a well-behaved heavy-fermion compound with a particular
q-dependence of the antiferromagnetic spin fluctuations, possibly related to
the geometrical frustration of the Yb3+ ions.",0410736v1
2004-10-28,"High-pressure synthesis, crystal structure determination, and a Ca substitution study of the metallic rhodium oxide NaRh2O4","The sodium rhodate NaRh2O4 was synthesized for the first time and
characterized by neutron and x-ray diffraction studies, measurements of
magnetic susceptibility, specific heat, electrical resistivity, and the Seebeck
coefficient. NaRh2O4 crystallizes in the CaFe2O4-type structure, which is
comprised of a characteristic RhO6 octahedra network. The compound is metallic
in nature, probably reflecting the 1 to 1 mixed valence character of Rh(III)
and Rh(IV) in the network. For further studies of the compound, the Rh valence
was varied significantly by means of an aliovalent substitution: the full range
solid solution between NaRh2O4 and CaRh2O4 was achieved and characterized as
well. The metallic state was dramatically altered, and a peculiar magnetism
developed in the low Na concentration range.",0410742v1
2004-11-05,Influence of the structural modulations and the Chain-ladder interaction in the $Sr\_{14-x}Ca\_{x}Cu\_{24}O\_{41}$ compounds,"We studied the effects of the incommensurate structural modulations on the
ladder subsystem of the $Sr\_{14-x}Ca\_{x}Cu\_{24}O\_{41}$ family of compounds
using ab-initio explicitly-correlated calculations. From these calculations we
derived $t-J$ model as a function of the fourth crystallographic coordinate
$\tau$ describing the incommensurate modulations. It was found that in the
highly calcium-doped system, the on-site orbital energies are strongly
modulated along the ladder legs. On the contrary the two sites of the ladder
rungs are iso-energetic and the holes are thus expected to be delocalized on
the rungs. Chain-ladder interactions were also evaluated and found to be very
negligible. The ladder superconductivity model for these systems is discussed
in the light of the present results.",0411135v4
2004-11-17,Metallic ground state and glassy transport in single crystalline URh$_2$Ge$_2$: Enhancement of disorder effects in a strongly correlated electron system,"We present a detailed study of the electronic transport properties on a
single crystalline specimen of the moderately disordered heavy fermion system
URh$_2$Ge$_2$. For this material, we find glassy electronic transport in a
single crystalline compound. We derive the temperature dependence of the
electrical conductivity and establish metallicity by means of optical
conductivity and Hall effect measurements. The overall behavior of the
electronic transport properties closely resembles that of metallic glasses,
with at low temperatures an additional minor spin disorder contribution. We
argue that this glassy electronic behavior in a crystalline compound reflects
the enhancement of disorder effects as consequence of strong electronic
correlations.",0411437v1
2004-11-24,"Large magnetoresistance in the magnetically ordered state as well as in the paramagnetic state near 300 K in an intermetallic compound,Gd7Rh3","We report the response of electrical resistivity $\rho$ to the application of
magnetic fields (H) up to 140 kOe in the temperature interval 1.8-300 K for the
compound, Gd7Rh3, ordering antiferromagnetically below 150 K. We find that
there is an unusually large decrease of $\rho$ for moderate values of H in the
close vicinity of room temperature uncharacteristic of paramagnets, with the
magnitude of the magnetoresistance increasing with decreasing temperature as
though the spin-order contribution to $\rho$ is temperature dependent. In
addition, this compound exhibits giant magnetoresistance behaviour at rather
high temperatures (above 77 K) in the magnetically ordered state due to a
metamagnetic transition.",0411608v1
2004-11-30,Helicoidal magnetic order in a clean copper oxide spin chain compound,"We report susceptibility, specific heat, and neutron diffraction measurements
on NaCu$_2$O$_2$, a spin-1/2 chain compound isostructural to LiCu$_2$O$_2$,
which has been extensively investigated. Below 13 K, we find a long-range
ordered, incommensurate magnetic helix state with a propagation vector similar
to that of LiCu$_2$O$_2$. In contrast to the Li analogue, substitutional
disorder is negligible in NaCu$_2$O$_2$. We can thus rule out that the helix is
induced by impurities, as was claimed on the basis of prior work on
LiCu$_2$O$_2$. A spin Hamiltonian with frustrated longer-range exchange
interactions provides a good description of both the ordered state and the
paramagnetic susceptibility.",0411753v2
2004-12-01,Correlation Effects and Structural Dynamics in the $β$-Pyrochlore Superconductor KOs$_{2}$O$_{6}$,"Electronic, magnetic, and dynamical properties of the new superconducting
$\beta$-pyrochlore KOs$_2$O$_6$ and related RbOs$_2$O$_6$ and CsOs$_2$O$_6$
compounds are calculated and compared with experiment and contrasted with
structurally related spinel pyrochlores. The calculated susceptibility Stoner
enhancement (110%) and thermal mass enhancement $\lambda$ = 2.5-3 reflect
moderate but perhaps important Coulomb correlations. The K$^{+}$ ion optic mode
is found to be unstable, allowing large excursions of 0.5-0.6 \AA from its
ideal site of the K ion along $<111>$ directions. This dynamical mode is much
less anharmonic in the isostructural Rb and Cs compounds (with larger cations),
perhaps accounting for their progressively lower values of T$_c$. Electron
scattering from this very anharmonic mode may be the cause of the anomalous
concave-downward resistivity that is seen only in KOs$_2$O$_6$.",0412031v1
2004-12-14,Novel Pressure Induced Structural Phase Transition in AgSbTe$_{2}$,"We report a novel high pressure structural sequence for the functionally
graded thermoelectric, narrow band gap semiconductor AgSbTe$_{2}$, using angle
dispersive x-ray diffraction in a diamond anvil cell with synchrotron radiation
at room temperature. The compound undergoes a B1 to B2 transition; the
transition proceeds through an intermediate amorphous phase found between 17-26
GPa that is quenchable down to ambient conditions. The pressure induced
structural transition observed in this compound is the first of its type
reported in this ternary cubic family, and it is new for the B1-B2 transition
pathway reported to date. Density Functional Theory (DFT) calculations
performed for the B1 and B2 phases are in good agreement with the experimental
results.",0412347v1
2004-12-17,Inhomogeneity of the intrinsic magnetic field in superconducting YBa2Cu3OX compounds as revealed by rare-earth EPR-probe,"X-band electron paramagnetic resonance on doped Er3+ and Yb3+ ions in
Y0.99(Yb,Er)0.01Ba2Cu3OX compounds with different oxygen contents in the wide
temperature range (4-120)K have been made. In the superconducting species, the
strong dependencies of the linewidth and resonance line position from the sweep
direction of the applied magnetic field are revealed at the temperatures
significantly below TC. The possible origins of the observed hysteresis are
analyzed. Applicability of the presented EPR approach to extract information
about the dynamics of the flux-line lattice and critical state parameters
(critical current density, magnetic penetration depth, and characteristic
spatial scale of the inhomogeneity) is discussed",0412477v2
2004-12-17,Magnetoresistive memory in phase separated La$_{0.5}$Ca$_{0.5}$MnO$_{3}$,"We have studied a non volatile memory effect in the mixed valent compound
La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ induced by magnetic field (H). In a previous work
[R.S. Freitas et al., Phys. Rev. B 65 (2002) 104403], it has been shown that
the response of this system upon application of H strongly depends on the
temperature range, related to three well differentiated regimes of phase
separation occurring below 220 K. In this work we compare memory capabilities
of the compound, determined following two different experimental procedures for
applying H, namely zero field cooling and field cooling the sample. These
results are analyzed and discussed within the scenario of phase separation.",0412499v1
2004-12-22,Enhancing the Superconducting Transition Temperature in the Absence of Spin Correlations in Heavy Fermion Compound CeIrIn$_5$,"We report on a pressure($P$)-induced evolution of superconductivity and spin
correlations in CeIrIn$_5$ via the $^{115}$In nuclear-spin-lattice-relaxation
rate measurements. We find that applying pressure suppresses dramatically the
antiferromagnetic fluctuations that are strong at ambient pressure. At $P$ =
2.1 GPa, $T_{\rm c}$ increases to $T_{\rm c}$ = 0.8 K that is twice $T_{\rm
c}$($P$ = 0 GPa), in the background of Fermi liquid state. This is in sharp
contrast with the previous case in which negative, chemical pressure (replacing
Ir with Rh) enhances magnetic interaction and increases $T_{\rm c}$. Our
results suggest that multiple mechanisms work to produce superconductivity in
the same compound CeIrIn$_5$.",0412614v1
2004-12-23,Electronic Properties of Transuranium Compounds with HoCoGa$_5$-Type Tetragonal Crystal Structure,"By using a relativistic linear augmented-plane-wave method with the
one-electron potential in the local-density approximation, we investigate
energy band structures and the Fermi surfaces of transuranium compounds
NpTGa$_5$, PuTGa$_5$, and AmCoGa$_5$ with transition metal atoms T. It is found
in common that the energy bands in the vicinity of the Fermi level are mainly
due to the large hybridization between $5f$ and Ga $4p$ electrons. For
PuTGa$_5$, we observe several cylindrical sheets of Fermi surfaces with large
volume for T=Co, Rh, and Ir. The de Haas-van Alphen (dHvA) frequencies are
theoretically estimated for PuCoGa$_5$. It is also found that the Fermi
surfaces of NpFeGa$_5$, NpCoGa$_5$, and NpNiGa$_5$ are similar to those of
UCoGa$_5$, UNiGa$_5$, and PuCoGa$_5$, respectively, except for small details.
For AmCoGa$_5$, the Fermi surfaces are found to consist of large cylindrical
electron sheets and small closed hole sheets, similar to PuCoGa$_5$. The
similarity is basically understood by the change of electron numbers inside the
Fermi surfaces on the basis of a rigid-band picture. We discuss our theoretical
Fermi surfaces with the dHvA experimental results on NpTGa$_5$.",0412647v1
2005-01-20,Metal-insulator transition in PrRu$_4$P$_{12}$ and SmRu$_4$P$_{12}$ investigated by optical spectroscopy,"Electronic structures of the filled-skutterudite compounds PrRu$_4$P$_{12}$
and SmRu$_4$P$_{12}$, which undergo a metal-insulator transition (MIT) at
$T_{\rm MI}$ = 60 K and 16 K, respectively, have been studied by means of
optical spectroscopy. Their optical conductivity spectra develop an energy gap
of $\sim$ 10 meV below $T_{\rm MI}$. The observed characteristics of the energy
gap are qualitatively different from those of the Kondo semiconductors. In
addition, optical phonon peaks in the spectra show anomalies upon the MIT,
including broadening and shifts at $T_{\rm MI}$ and an appearance of new peaks
below $T_{\rm MI}$. These results are discussed in terms of density waves or
orbital ordering previously predicted for these compounds.",0501487v1
2005-02-03,Leading interactions in the $β$-$Sr V_6 O_{15}$ compound,"The present study shows that the electronic structure of the
$\beta$-$AV\_6O\_{15}$ family of compounds ($A = Sr, Ca, Na ...$) is based on
weakly interacting two-leg ladders, in contrast with the zig-zag chain model
one could expect from their crystal structure. Spin dimer analysis, based on
extended H\""{u}ckel tight-binding calculations, was performed to determine the
structure of the dominant transfer and magnetic interactions in the room
temperature $\beta$-$SrV\_6O\_{15}$ phase. Two different two-legs ladders,
associated with different charge/spin orders are proposed to describe these
one-dimensional $\beta$-type systems. The antiferromagnetic ladders are packed
in an 'IPN' geometry and coupled to each other through weak antiferromagnetic
interactions. This arrangement of the dominant interactions explains the
otherwise surprising similarities of the optical conductivity and Raman spectra
for the one-dimensional $\beta$-type phases and the two-dimensional
$\alpha$-type ones such as the well-known $\alpha^\prime$-$NaV\_2O\_5$ system.",0502107v1
2005-02-22,Electronic structure of Li2Pd3B and Li2Pt3B,"Li2Pd3B is known to be superconducting, while the isotypical Li2Pt3B compound
is not. Electronic structures of Li2Pd3B and Li2Pt3B have been calculated in
order to obtain an insight into this surprising difference, through an analysis
of the differences in the band structures. The electronic structures of these
systems were obtained using the Full Potential Linear Augmented Plane Wave plus
local orbitals (FP-LAPW+lo) method and it was found that four bands cross the
Fermi level (EF). Out of these four bands, only two bands contribute
significantly to the density of states at the EF. One of these bands is a hole
band and the other an electron band. Thus at least a two-band model is required
for studying the electronic properties of the Pd and Pt compounds. These two
bands are rather narrow and hence the coulombic correlations effects can be
significant.",0502525v1
2005-03-01,Ordering in the pyrochlore antiferromagnet due to Dzyaloshinsky-Moriya interactions,"The Heisenberg nearest neighbour antiferromagnet on the pyrochlore (3D)
lattice is highly frustrated and does not order at low temperature where
spin-spin correlations remain short ranged. Dzyaloshinsky-Moriya interactions
(DMI) may be present in pyrochlore compounds as is shown, and the consequences
of such interactions on the magnetic properties are investigated through mean
field approximation and monte carlo simulations. It is found that DMI (if
present) tremendously change the low temperature behaviour of the system. At a
temperature of the order of the DMI a phase transition to a long range ordered
state takes place. The ordered magnetic structures are explicited for the
different possible DMI which are introduced on the basis of symmetry arguments.
The relevance of such a scenario for pyrochlore compounds in which an ordered
magnetic structure is observed experimentally is dicussed.",0503009v1
2005-03-08,Thermal entanglement properties of small spin clusters,"Exchange interactions in spin systems can give rise to quantum entanglement
in the ground and thermal states of the systems. In this paper, we consider a
spin tetramer, with spins of magnitude 1/2, in which the spins interact via
nearest-neighbour, diagonal and four-spin interactions of strength J1, J2 and K
respectively. The ground and thermal state entanglement properties of the
tetramer are calculated analytically in the various limiting cases. Signatures
of quantum phase transition (QPT) in terms of appropriate entanglement measures
are obtained. The magnetic properties of a S = 1/2 AFM polyoxovanadate
compound, V12, are well explained by spin tetramers with only nearest-neighbour
exchange interactions. Treating the magnetic susceptibility chi as an
entanglement witness (EW), an estimate of the lower bound of the critical
entanglement temperature, T_c, above which the multipartite entanglement
disappears in the experimental compound, is determined. A second EW based on
energy provides an estimate of the entanglement temperature T_E, below which
bipartite entanglement is certainly present in the system, is determined. The
cases of the symmetric trimer and the tetrahedron are also considered.",0503170v3
2005-03-15,Direct evidence of the orbital contribution to the magnetic moment in AA'FeReO6 double perovskites,"Spin and orbital magnetic moments of Re in AA'FeReO6 double perovskites (A,A'
= Ba, Sr, Ca) have been directly probed employing XMCD spectroscopy at the Re
L2,3-edges. A considerable orbital magnetic moment is observed in all the
studied compounds despite octahedral coordination. Relative orbital to spin
contribution per Re atom rises with lattice distortion from mL/mS = -0.28 to
-0.34 for AA'=Ba2FeReO6 and Ca2FeReO6, respectively. A preliminary XMCD
measurements at the Fe L2,3-edges reveals also a significant orbital moment of
iron in Ca2FeReO6. The relation of the results to the magnetic properties of
the compounds is discussed.",0503358v1
2005-04-21,Possible canted antiferromagnetism in UCu$_9$Sn$_4$,"We report on the new compound UCu${}_9$Sn${}_4$ which crystallizes in the
tetragonal structure \emph{I}4/\emph{mcm} with lattice parameters $a =
8.600{\rm\AA}$ and $c = 12.359{\rm\AA}$. This compound is isotyp to the
ferromagnetic systems RECu${}_9$Sn${}_4$ (RE = Ce, Pr, Nd) with Curie
temperatures $T{}\rm_C$ = 5.5 K, 10.5 K and 15 K, respectively.
UCu${}_9$Sn${}_4$ exhibits an uncommon magnetic behavior resulting in three
different electronic phase transitions. Below 105 K the sample undergoes a
valence transition accompanied by an entropy change of 0.5 Rln2. At 32 K a
small hump in the specific heat and a flattening out in the susceptibility
curve probably indicate the onset of helical spin order. To lower temperatures
a second transition to antiferromagnetic ordering occurs which develops a small
ferromagnetic contribution on lowering the temperature further. These results
are strongly hinting for canted antiferromagnetism in UCu${}_9$Sn${}_4$.",0504552v1
2005-04-22,Localized excitation in the hybridization gap in YbAl3,"The intermediate valence compound YbAl3 exhibits a broad magnetic excitation
with characteristic energy E1 ~ 50meV, of order of the Kondo energy (TK ~
600-700K). In the low temperature (T < Tcoh ~ 40K) Fermi liquid state, however,
a new magnetic excitation arises at E2 ~ 33meV, which lies in the hybridization
gap that exists in this compound. We show, using inelastic neutron scattering
on a single-crystal sample, that while the scattering at energies near E1 has
the momentum (Q-) dependence expected for interband scattering across the
indirect gap, the scattering near E2 is independent of Q. This suggests that it
arises from a spatially-localized excitation in the hybridization gap.",0504596v2
2005-04-25,Optical investigations on $Y_{2-x} Bi_x Ru_2 O_7$: Electronic structure evolutions related to the metal-insulator transition,"Optical conductivity spectra of cubic pyrochlore $Y_{2-x} Bi_x Ru_2 O_7$
(0.0$\leq ${\it x}$\leq $2.0) compounds are investigated. As a metal-insulator
transition (MIT) occurs around {\it x}$=$0.8, large spectral changes are
observed. With increase of {\it x}, the correlation-induced peak between the
lower and the upper Hubbard bands seems to be suppressed, and a strong
mid-infrared feature is observed. In addition, the $p-d$ charge transfer peak
shifts to the lower energies. The spectral changes cannot be explained by
electronic structural evolutions in the simple bandwidth-controlled MIT
picture, but are consistent with those in the filling-controlled MIT picture.
In addition, they are also similar to the spectral changes of
Y$_{2-x}$Ca$_{x}$Ru$_{2}$O$_{7}$ compounds, which is a typical
filling-controlled system. This work suggests that, near the MIT, the Ru bands
could be doped with the easily polarizable Bi cations.",0504619v1
2005-04-28,Half-metallic properties of atomic chains of carbon-transition metal compounds,"We found that magnetic ground state of one-dimensional atomic chains of
carbon-transition metal compounds exhibit half-metallic properties. They are
semiconductors for one spin-direction, but show metallic properties for the
opposite direction. The spins are fully polarized at the Fermi level and net
magnetic moment per unit cell is an integer multiple of Bohr magneton. The
spin-dependent electronic structure can be engineered by changing the number of
carbon and type of transition metal atoms. These chains, which are stable even
at high temperature and some of which keep their spin-dependent electronic
properties even under moderate axial strain, hold the promise of potential
applications in nanospintronics.",0504747v2
2005-05-10,Novel organic-inorganic layered oxide with spin ladder structure,"Structural analysis of a layered manganese tungstate diaminoalkane hybrid
series suggests that this compound forms a spin-5/2 spin-ladder structure. We
use X-ray diffraction, electron microscopy and x-ray absorption spectroscopy
results to infer the structure. DC magnetization of the manganese compound and
a possible copper analogue appear to show that the manganese system behaves
like 1-dimensional antiferromagnetic Heisenberg chains (i.e. $J_{\parallel} \gg
J_{\perp})$ while the copper system is fitted well by a $S = {1/2}$ spin ladder
model, giving the parameters $g = 1.920 \pm 0.008$, $J_{\parallel}/k_B = -0.3
\pm 1.4$K; $J_{\perp}/k_B = 213.6 \pm 1.1$K. The ability to tune adjacent
inorganic layers of the hybrid materials by altering the length of the organic
`spacer' molecules gives enormous promise for the use of these materials,
especially when doped, to provide a greater understanding of spin ladder
systems.",0505224v1
2005-05-10,Silicon and III-V compound nanotubes: structural and electronic properties,"Unusual physical properties of single-wall carbon nanotubes have started a
search for similar tubular structures of other elements. In this paper, we
present a theoretical analysis of single-wall nanotubes of silicon and group
III-V compounds. Starting from precursor graphene-like structures we
investigated the stability, energetics and electronic structure of zigzag and
armchair tubes using first-principles pseudopotential plane wave method and
finite temperature ab-initio molecular dynamics calculations. We showed that
(n,0) zigzag and (n,n) armchair nanotubes of silicon having n > 6 are stable
but those with n < 6 can be stabilized by internal or external adsorption of
transition metal elements. Some of these tubes have magnetic ground state
leading to spintronic properties. We also examined the stability of nanotubes
under radial and axial deformation. Owing to the weakness of radial restoring
force, stable Si nanotubes are radially soft. Undeformed zigzag nanotubes are
found to be metallic for 6 < n < 11 due to curvature effect; but a gap starts
to open for n > 12. Furthermore, we identified stable tubular structures formed
by stacking of Si polygons. We found AlP, GaAs, and GaN (8,0) single-wall
nanotubes stable and semiconducting. Our results are compared with those of
single-wall carbon nanotubes.",0505263v1
2005-06-05,On the unusual behavior of nitride compounds,"This report presents consistent insight into the mechanism behind the unusual
behavior of nitride compounds from the perspective of tetrahedron bond
formation and its consequence on valence density of states. An extension of the
recent bond-band-barrier (BBB) correlation mechanism for oxidation [Sun CQ,
Prog Mater Sci 2003;48:521-685] to the electronic process of nitridation has
led to the essentiality of sp-orbital hybridization for a nitrogen atom upon
interacting with atoms in solid phase of arbitrary less-electronegative
element. In the process of nitridation, a nitrogen atom forms a
quasi-tetrahedron with surrounding host atoms through bonding and nonbonding
interaction associated with production of electronic holes and antibonding
dipoles, which add corresponding density of states to the valence band of the
host. It is suggested that the valance alteration of the system takes the
responsibility for the blue shift in photoluminescence, lowered work function
for cold cathode field emission, corrosion and wear resistant, high elasticity,
and magnetic modulation as well.",0506109v1
2005-06-08,Unusual quasi-one-dimensional electron dispersions in the spin-1/2 quantum magnet TiOCl,"We have studied the electronic structure of the spin-1/2 quantum magnet TiOCl
by polarization-dependent momentum-resolved photoelectron spectroscopy. From
that, we confirm the quasi-one-dimensional nature of the electronic structure
along the crystallographic b-axis and find no evidence for sizable
phonon-induced orbital fluctuations as origin for the non-canonical
phenomenology of the spin-Peierls transition in this compound. A comparison of
the experimental data to our own LDA+U and Hubbard model calculations reveals a
striking lack of understanding regarding the quasi-one-dimensional electron
dispersions in the normal state of this compound.",0506203v2
2005-06-12,Effect of Ti doping on the electrical transport and magnetic properties of layered compound Na0.8CoO2,"Effect of Ti doping on the electrical transport and magnetic properties of
layered Na0.8Co1-xTixO2 compounds has been investigated. The lattice parameters
a and c increase with x. A minor amount of Ti doping results in a
metal-insulator transition at low temperatures. For samples with x > 0.03, the
variable-range hopping process dominates the transport behavior above a certain
temperature. The temperature dependence of magnetization of all the samples is
found to obey the Curie-Weiss law. The mechanism of the doping effect is
discussed.",0506268v1
2005-06-20,Hall Effect anomalies near Quantum Critical Point in CeCu6-xAux,"Precision measurements of the Hall effect have been carried out for both
archetypal heavy fermion compound - CeCu6 and exemplary solid solutions
CeCu6-xAux (x= 0.1 and 0.2) with quantum critical behavior. The experimental
results have been obtained by technique with a sample rotation in magnetic
field in the temperature range 1.8-300K. The experiment revealed a complex
activation type dependence of the Hall coefficient RH(T) in CeCu6 with
activation energies Ea1/kB = 110K and Ea2/kB = 1.5K in temperature ranges
50-300K and 3-10K, respectively. Microscopic parameters of charge carriers
transport (effective masses, relaxation time) and localization radii ap1,2* of
heavy fermions (ap1*(T>50K)= 1.7 A and ap2*(T<20K)= 14 A) were estimated for
CeCu6. The second angular harmonic contribution has been established in the
Hall voltage of CeCu5.9Au0.1 and CeCu6 at temperatures below T*=24K. A
hyperbolic type divergence of the second harmonic term in Hall effect RH2(T)=
C(1/T-1/T*) at low temperatures is found to be accompanied with a power-law
behavior RH(T)= T -0.4 of the main contribution in the Hall coefficient for
CeCu5.9Au0.1 compound with quantum critical behavior.",0506502v1
2005-07-20,Novel Phase Transition Near the Quantum Critical Point in the Filled-Skutterudite Compound CeOs4Sb12: an Sb-NQR Study,"We report on a novel phase transition at $T$ = 0.9 K in the Ce-based
filled-skutterudite compound CeOs$_{4}$Sb$_{12}$ via measurements of the
nuclear-spin lattice relaxation rate $1/T_{1}$ and nuclear quadrupole resonance
(NQR) spectrum of Sb nuclei. The temperature ($T$) dependence of $1/T_1$
behaves as if approaching closely an antiferromagnetic (AFM) quantum critical
point (QCP), following the relation $1/T_{1}\propto T/(T-T_{\rm N})^{1/2}$ with
$T_{\rm N} = 0.06$ K in the range of $T=1.3-25$ K. The onset of either the
spin-density-wave (SDW) or charge-density-wave (CDW) order at $T_{\rm 0} = 0.9$
K, that is, of the first order, is evidenced by a broadening of the NQR
spectrum and a marked reduction in $1/T_1$ just below $T_{\rm 0}$. The
$f$-electron-derived correlated band realized in CeOs$_{4}$Sb$_{12}$ is
demonstrated to give rise to the novel phase transition on the verge of AFM
QCP.",0507470v1
2005-07-28,Half-skyrmion picture of single hole doped CuO_2 plane,"Based on the Zhang-Rice singlet picture, it is argued that the half-skyrmion
is created by the doped hole in the single hole doped high-T_c cuprates with
N'eel ordering. The spin configuration around the Zhang-Rice singlet, which has
the form of superposition of the two different d-orbital hole spin states, is
studied within the non-linear \sigma model and the CP^1 model. The spin
configurations associated with each hole spin state are obtained, and we find
that the superposition of these spin configuration turns out to be the
half-skyrmion that is characterized by a half of the topological charge. The
excitation spectrum of the half-skyrmion is obtained by making use of Lorentz
invariance of the effective theory and is qualitatively in good agreement with
angle resolved photoemission spectroscopy on the parent compunds. Estimated
values of the parameters contained in the excitation spectrum are in good
agreement with experimentally obtained values. The half-skyrmion theory
suggests a picture for the difference between the hole doped compounds and the
electron doped compounds.",0507666v1
2005-08-09,Magnetic Coupling Between Non-Magnetic Ions: Eu3+ in EuN and EuP,"We consider the electronic structure of, and magnetic exchange (spin)
interactions between, nominally nonmagnetic Eu^3+ ions (4f^6, S=3, L=3, J=0)
within the context of the rocksalt structure compounds EuN and EuP. Both
compounds are ionic [Eu^3+; N^3- and P^3-] semimetals similar to isovalent GdN.
Treating the spin polarization within the 4f shell, and then averaging
consistent with the J=0 configuration, we estimate semimetallic band overlaps
(Eu 5d with pnictide 2p or 3p) of ~0.1 eV (EuN) and ~1.0 eV (EuP) that increase
(become more metallic) with pressure. The calculated bulk modulus is 130 (86)
GPa for EuN (EuP). Exchange (spin-spin) coupling calculated from correlated
band theory is small and ferromagnetic in sign for EuN, increasing in magnitude
with pressure. Conversely, the exchange coupling is antiferromagnetic in sign
for EuP and is larger in magnitude, but decreases with compression. Study of a
two-site model with S_1*S_2 coupling within the J=0,1 spaces of each ion
illustrates the dependence of the magnetic correlation functions on the model
parameters, and indicates that the spin coupling is sufficient to alter the Van
Vleck susceptibility. We outline a scenario of a spin-correlation transition in
a lattice of S=3, L=3, J=0 nonmagnetic ions.",0508241v1
2005-09-19,Effect of random disorder and spin frustration on the reentrant spin glass phase and ferromagnetic phase in stage-2 Cu_{0.93}Co_{0.07}Cl_{2} graphite intercalation compound near the multicritical point,"Stage-2 Cu$_{0.93}$Co$_{0.07}$Cl$_{2}$ graphite intercalation compound
magnetically behaves like a reentrant ferromagnet near the multicritical point
($c_{MCP} \approx 0.96$). It undergoes two magnetic phase transitions at
$T_{RSG}$ ($= 6.64 \pm 0.05$ K) and $T_{c}$ ($= 8.62 \pm 0.05$ K). The static
and dynamic nature of the ferromagnetic and reentrant spin glass phase has been
studied using DC and AC magnetic susceptibility. Characteristic memory
phenomena of the DC susceptibility are observed at $T_{RSG}$ and $T_{c}$. The
nonlinear AC susceptibility $\chi_{3}^{\prime}$ has a positive local maximum at
$T_{RSG}$, and a negative local minimum at $T_{c}$. The relaxation time $\tau$
between $T_{RSG}$ and $T_{c}$ shows a critical slowing down: $\tau$ with $x =
13.1 \pm 0.4$ and $\tau_{0}^{*} = (2.5 \pm 0.5) \times 10^{-13}$ sec. The
influence of the random disorder on the critical behavior above $T_{c}$ is
clearly observed: $\alpha = -0.66$, $\beta = 0.63$, and $\gamma = 1.40$. The
exponent of $\alpha$ is far from that of 3D Heisenberg model.",0509494v1
2005-09-19,Field-Induced Transition on Triangular Plane in the Spin Ice Compound Dy2Ti2O7,"The origin of the lowest-temperature anomaly reported several years ago using
a polycrystalline sample of the spin ice compound Dy2Ti2O7 had remained
unresolved. Here we finally clarify its origin by susceptibility measurements
down to 65 mK using single crystals under accurate control of the magnetic
fields in two independent directions. We demonstrate that the transition is
induced under a subtle field combination that precisely cancel the
nearest-neighbor spin interactions acting on the spins on the triangular
lattice within the pyrochlore structure. Contrary to the other two fieldinduced
transitions, this transition is driven only by the interactions beyond the
nearest neighbors. Our observation thus provides the first qualitative evidence
for the essential importance of the dipolar interaction beyond the nearest
neighbors in the spin ice.",0509497v1
2005-10-02,Orbital order and fluctuations in Mott insulators,"Basic mechanisms controlling orbital order and orbital fluctuations in
transition metal oxides are discussed. The lattice driven classical orbital
picture, e.g. like in manganites LaMnO$_3$, is contrasted to the quantum
behavior of orbitals in frustrated superexchange models as realised in
pseudocubic titanites ATiO$_3$ and vanadates AVO$_3$. In YVO$_3$, the lattice
and superexchange effects strongly compete -- this explains the extreme
sensitivity of magnetic states to temperature and doping. Lifting the $t_{2g}$
orbital degeneracy by a relativistic spin-orbital coupling is considered on
example of the layered cobaltates. We find that the spin-orbital mixing of
low-energy states leads to unusual magnetic correlations in a triangular
lattice of the CoO$_2$ parent compound. Finally, the magnetism of sodium-rich
compounds Na$_{1-x}$CoO$_2$ is discussed in terms of a spin/orbital polaronic
liquid.",0510025v2
2005-10-28,Signatures of electron-electron correlations in the optical spectra of $α$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ ($M$=NH$_4$ and Rb),"We interpret the optical spectra of $\alpha$-(BEDT-TTF)$_2M$Hg(SCN)$_4$
(M=NH$_4$ and Rb) in terms of a 1/4 filled metallic system close to charge
ordering and show that in the conductivity spectra of these compounds a
fraction of the spectral weight is shifted from the Drude-peak to higher
frequencies due to strong electronic correlations. Analyzing the temperature
dependence of the electronic parameters, we distinguish between different
aspects of the influence of electronic correlations on optical properties. We
conclude, that the correlation effects are slightly weaker in the NH$_4$
compound compared to the Rb one.",0510788v1
2005-11-01,Structural phase separation in La2/3Ba1/3MnO3: macroscopic and microscopic aspects,"The structural phase transformation in the La2/3Ba1/3MnO3 perovskite
manganite was studied by ultrasound, neutron diffraction and electron
microscopy techniques. Minima of the velocity and maxima of the decrement of
the ultrasound point out the structural transition temperature Ts=200 K. The
hysteretic temperature behavior and giant alteration of the ultrasound velocity
and decrement present an evidence of martensitic character of the phase
transition at a macroscopic level. The martensitic transformation in
La2/3Ba1/3MnO3 is tightly connected with electronic transitions in both
coexisting high symmetry R3c and low symmetry Imma crystal phases. Neutron
diffraction data show that the electronic structure of the compound exhibits
anomalous behavior in the vicinity of Ts: temperature dependences of the
Mn-O-Mn bond angles and Mn-O bond lengths have singularities. Parameters of the
coexisting crystalline phases studied have different character of temperature
correlation with parameters of the magnetic subsystem of the compound.",0511017v1
2005-11-04,Magnetic excitations and phonons in the spin-chain compound NaCu2O2,"We report an inelastic light scattering study of single-crystalline
NaCu$_2$O$_2$, a spin-chain compound known to exhibit a phase with helical
magnetic order at low temperatures. Phonon excitations were studied as a
function of temperature and light polarization, and the phonon frequencies are
compared to the results of ab-initio lattice dynamical calculations, which are
also reported here. The good agreement between the observed and calculated
modes allows an assignment of the phonon eigenvectors. Two distinct high-energy
two-magnon features as well as a sharp low-energy one-magnon peak were also
observed. These features are discussed in terms of the magnon modes expected in
a helically ordered state. Their polarization dependence provides evidence of
substantial exchange interactions between two closely spaced spin chains within
a unit cell. At high temperatures, the spectral features attributable to
magnetic excitations are replaced by a broad, quasielastic mode due to
overdamped spin excitations.",0511116v1
2005-11-04,Low Temperature Thermodynamic Properties of the Heavy Fermion Compound YbAgGe Close to the Field-Induced Quantum Critical Point,"We present temperature and field dependent heat capacity and magnetization
data taken at temperatures down to 50 mK and in an applied magnetic field up to
11.5 Tesla for YbAgGe, a heavy-fermion compound with a field induced quantum
critical point. These data clearly indicate that the same electronic degrees of
freedom are responsible for the features seen in both specific heat and
magnetization data. In addition, they further refine the different boundaries
suggested for the H - T phase diagram of YbAgGe through previous,
magneto-transport measurements, and allow for further understanding of
different phases on the H - T phase diagram, in particular, clearly
disconnecting the field-induced quantum critical point in YbAgGe from any sort
of saturation of the Yb moment in higher applied magnetic field.",0511125v1
2005-12-07,Non-Fermi-liquid behavior in Ce(Ru$_{1-x}$Fe$_x$)$_2$Ge$_2$: cause and effect,"We present inelastic neutron scattering measurements on the intermetallic
compounds Ce(Ru$_{1-x}$Fe$_x$)$_2$Ge$_2$ ($x$=0.65, 0.76 and 0.87). These
compounds represent samples in a magnetically ordered phase, at a quantum
critical point and in the heavy-fermion phase, respectively. We show that at
high temperatures the three compositions have the identical response of a local
moment system. However, at low temperatures the spin fluctuations in the
critical composition are given by non-Fermi-liquid dynamics, while the spin
fluctuations in the heavy fermion system show a simple exponential decay in
time. In both compositions, the lifetime of the fluctuations is determined
solely by the distance to the quantum critical point. We discuss the
implications of these observations regarding the possible origins of
non-Fermi-liquid behavior in this system.",0512133v1
2005-12-14,Multiple ordered phases in the filled skutterudite compound PrOs$_{4}$As$_{12}$,"Magnetization, specific heat, and electrical resistivity measurements were
made on single crystals of the filled skutterudite compound
PrOs$_{4}$As$_{12}$. Specific heat measurements indicate an electronic specific
heat coefficient $\gamma$ $\sim 50-200$ mJ/mol K$^{2}$ at temperatures 10 K
$\leq T \leq 18$ K, and $\sim 1$ J/mol K$^{2}$ for $T \leq 1.6$ K.
Magnetization, specific heat, and electrical resistivity measurements reveal
the presence of two, or possibly three, ordered phases at temperatures below
$\sim 2.3$ K and in fields below $\sim 3$ T. The low temperature phase displays
antiferromagnetic characteristics, while the nature of the ordering in the
other phase(s) has yet to be determined.",0512325v2
2005-12-21,Quasiquartet CEF ground state with possible quadrupolar ordering in the tetragonal compound YbRu$_{2}$Ge$_{2}$,"e have investigated the magnetic properties of YbRu$_{2}$Ge$_{2}$ by means of
magnetic susceptibility $\chi$(T), specific heat C(T) and electrical
resistivity $\rho$(T) measurements performed on flux grown single crystals. The
Curie-Weiss behavior of $\chi$(T) along the easy plane, the large magnetic
entropy at low temperatures and the weak Kondo like increase in $\rho$(T)
proves a stable trivalent Yb state. Anomalies in C(T), $\rho$(T) and $\chi$(T)
at T$_{0}$ = 10.2 K, T$_{1}$ = 6.5 K and T$_{2}$ = 5.7 K evidence complex
ordering phenomena, T$_{0}$ being larger than the highest Yb magnetic ordering
temperature found up to now. The magnetic entropy just above T$_{0}$ amounts to
almost Rln4, indicating that the crystal electric field (CEF) ground state is a
quasiquartet instead of the expected doublet. The behavior at T$_{0}$ is rather
unusual and suggest that this transition is related to quadrupolar ordering,
being a consequence of the CEF quasiquartet ground state. The combination of a
quasiquartet CEF ground state, a high ordering temperature, and the relevance
of quadrupolar interactions makes YbRu$_{2}$Ge$_{2}$ a rather unique system
among Yb based compounds.",0512527v1
2005-12-22,Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6,"Results of high resolution x-ray diffraction experiments are presented for
single crystals of the spin gap compound BaCuSi$_2$O$_6$ in the temperature
range from 16 to 300 K. The data show clear evidence of a transition from the
room temperature tetragonal phase into an incommensurately modulated
orthorhombic structure below $\sim$100 K. This lattice modulation is
characterized by a resolution limited wave vector {\bf
q}$_{IC}$=(0,$\sim$0.13,0) and its 2$^{nd}$ and 3$^{rd}$ harmonics. The phase
transition is first order and exhibits considerable hysteresis. This
observation implies that the spin Hamiltonian representing the system is more
complex than originally thought.",0512560v1
2006-01-12,"Electronic structure, magnetic and optical properties of intermetallic compounds R2Fe17 (R=Pr,Gd)","In this paper we report comprehensive experimental and theoretical
investigation of magnetic and electronic properties of the intermetallic
compounds Pr2Fe17 and Gd2Fe17. For the first time electronic structure of these
two systems was probed by optical measurements in the spectral range of 0.22-15
micrometers. On top of that charge carriers parameters (plasma frequency and
relaxation frequency) and optical conductivity s(w) were determined.
Self-consistent spin-resolved bandstructure calculations within the
conventional LSDA+U method were performed. Theoretical interpetation of the
experimental s(w) dispersions indicates transitions between 3d and 4p states of
Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical
optical conductivity coincides well with our experimental data. Calculated by
LSDA+U method magnetic moments per formula unit are found to be in good
agreement with observed experimental values of saturation magnetization.",0601247v1
2006-01-23,Elastic Properties and Magnetic Phase Diagrams of Dense Kondo Compound Ce0.75La0.25B6,"We have investigated the elastic properties of the cubic dense Kondo compound
Ce0.75La0.25B6 by means of ultrasonic measurements. We have obtained magnetic
fields vs temperatures (H-T) phase diagrams under magnetic fields along the
crystallographic [001], [110] and [111] axes. An ordered phase IV showing the
elastic softening of c44 locates in low temperature region between 1.6 and 1.1
K below 0.7 T in all field directions. The phase IV shows an isotropic nature
with regard to the field directions, while the antiferro-magnetic phase III
shows an anisotropic character. A remarkable softening of c44 and a spontaneous
trigonal distortion &#949;yz+&#949;zx+&#949;xy recently reported by Akatsu et
al. [J. Phys. Soc. Jpn. 72 (2003) 205] in the phase IV favor a ferro-quadrupole
(FQ) moment of Oyz+Ozx+Oxy induced by an octupole ordering.",0601502v1
2006-01-25,The effect of Zn substitution on the state of oxygen deficiency and hole concentration in Y1-xCaxBa2(Cu1-yZny)3O7-d,"We have investigated the effect of Zn substitution on the hole content, p,
and the oxygen deficiency, d, for a series of high-quality crystalline c-axis
oriented thin films and polycrystalline Y1-xCaxBa2(Cu1-yZny)3O7-delta compounds
over a wide range of composition (x, y, and delta). p was determined from the
room-temperature thermopower, S[290K]. When annealed at a given temperature and
oxygen partial pressure, a small but systematic variation in S[290K] was
observed with Zn, for all the samples. From the analysis of the temperature
derivative of resistivity, drho/dT, at 300K, which varies almost linearly with
p, irrespective of the composition of the sample, and the thermo-gravimetric
analysis (TGA), we have found that annealing under identical conditions makes
the Zn-substituted compounds somewhat more oxygen deficient compared to the
Zn-free ones.",0601564v1
2006-01-26,Collinear-to-Spiral Spin Transformation without Changing Modulation Wavelength upon Ferroelectric Transition in Tb1-xDyxMnO3,"Lattice modulation and magnetic structures in magnetoelectric compounds
Tb1-xDyxMnO3 have been studied around the ferroelectric (FE) Curie temperature
T_C by x-ray and neutron diffraction. Temperature-independent modulation
vectors through T_C are observed for the compounds with 0.50< x < 0.68. This
indicates that ferroelectricity with a polarization (P) along the c axis in the
RMnO3 series cannot be ascribed to such an incommensurate-commensurate
transition of an antiferromagnetic order as was previously anticipated. Neutron
diffraction study of a single crystal with x=0.59 shows that the FE transition
is accompanied by the transformation of the Mn-spin alignment from sinusoidal
(collinear) antiferromagnetism into a transverse spiral structure. The observed
spiral structure below T_C is expected to produce P along the c axis with the
`inverse' Dzialoshinski-Moriya interaction, which is consistent with the
observation.",0601613v1
2006-01-29,Unusual Length Dependence of Conductance of Some Oligomers,"Recent experiment found a quantum length dependence of oligothiophene
molecule conductance at low bias [Xu et al., nano Lett. \textbf{5}, 1491
(2005)], the long molecule has large conductance. By means of a
first-principles method we obtain both the quantum length dependence of
conductance at low bias and the classical length dependence of conductance at
high bias region for oligothiophene. In between there is an oscillated
conductance behavior. The transport behaviors are determined by the distinct
electronic structures of the molecular compounds. The various conductance
length dependence may appear for the organic compounds. Our further
investigation finds that the classical conductance length dependence in
polyphenanthrene dithiolates and another unusual conductance length dependence
in polyacene ditholates: the quantum length dependence of conductance is at the
high bias and the classical length dependence of conductance is at the low
bias.",0601649v1
2006-02-01,Domain-wall excitons and optical conductivity in one-dimensional Wigner lattices,"Motivated by the recent finding that doped edge-sharing Cu-O chain compounds
like Na$_3$Cu$_2$O$_4$ and Na$_8$Cu$_5$O$_{10}$ are realizations of
one-dimensional Wigner crystals, we study the optical spectra of such systems.
Charge excitations in 1D Wigner crystals are described in terms of domain wall
excitations with fractional charge. We investigate analytically and numerically
the domain-wall excitations that dominate the optical absorption, and analyse
the dispersion and the parameter range of exciton states characteristic for the
long-ranged Coulomb attraction between domain walls. Here we focus on the
Wigner lattice at quarter-filling relevant for Na$_3$Cu$_2$O$_4$ and analyze in
particular the role of second neighbor hopping $t_2$ which is important in
edge-sharing chain compounds. Large $t_2$ drives an instability of the Wigner
lattice via a soft domain-wall exciton towards a charge-density wave with a
modulation period distinct from that of the Wigner lattice. Furthermore we
calculate the temperature dependence of the DC-conductivity and show that it
can be described by activated behavior combined with a $T^{-\alpha}$ dependent
mobility.",0602015v1
2006-02-07,Field-Induced Ferromagnetic Order and Colossal Magnetoresistance in La_{1.2}Sr_{1.8}Mn_2O_7: a ^{139}La NMR study,"In order to gain insights into the origin of colossal magneto-resistance
(CMR) in manganese oxides, we performed a ^{139}La NMR study in the
double-layered compound La_{1.2}Sr_{1.8}Mn_2O_7. We find that above the Curie
temperature T_C=126 K, applying a magnetic field induces a long-range
ferromagnetic order that persists up to T=330 K. The critical field at which
the induced magnetic moment is saturated coincides with the field at which the
CMR effect reaches to a maximum. Our results therefore indicate that the CMR
observed above T_C in this compound is due to the field-induced ferromagnetism
that produces a metallic state via the double exchange interaction.",0602161v1
2006-02-16,Two geometrically frustrated magnets studied by neutron diffraction,"In the pyrochlore compounds, Tb$_2$Ti$_2$O$_7$ and Tb$_2$Sn$_2$O$_7$, only
the Tb$^{3+}$ ions are magnetic. They exhibit quite abnormal -- and, in view of
their chemical similarity, strikingly different -- magnetic behaviour, as
probed by neutron diffraction at ambient and applied pressure.
Tb$_2$Ti$_2$O$_7$ is a cooperative paramagnet (`spin liquid'), without long
range order at ambient pressure; however, it does become ordered under
pressure. By contrast, Tb$_2$Sn$_2$O$_7$ enters an ""ordered spin ice"" state
already at ambient pressure. We analyse a simple model which already clearly
exhibits some of the qualitative features observed experimentally. Overall,
comparing these two compounds emphasizes the power of small perturbations in
selecting low-temperature states in geometrically frustrated systems.",0602384v1
2006-03-09,Enhancing the Superconducting Transition Temperature due to Strong-Coupling Effect under Antiferromagnetic Spin Fluctuations in CeRh1-xIrxIn5 : 115In-NQR Study,"We report on systematic evolutions of antiferromagnetic (AFM) spin
fluctuations and unconventional superconductivity (SC) in heavy-fermion (HF)
compounds CeRh$_{1-x}$Ir$_{x}$In$_5$ via $^{115}$In
nuclear-quadrupole-resonance (NQR) experiment. The measurements of nuclear
spin-lattice relaxation rate $1/T_1$ have revealed the marked development of
AFM spin fluctuations as a consequence of approaching an AFM ordered state with
increasing Rh content. Concomitantly the superconducting transition temperature
$T_{\rm c}$ and the energy gap $\Delta_0$ increase drastically from $T_{\rm c}
= 0.4$ K and $2\Delta_0/k_{\rm B}T_{\rm c} = 5$ in CeIrIn$_5$ up to $T_{\rm c}
= 1.2$ K and $2\Delta_0/k_{\rm B}T_{\rm c} = 8.3$ in
CeRh$_{0.3}$Ir$_{0.7}$In$_5$, respectively. The present work suggests that the
AFM spin fluctuations in close proximity to the AFM quantum critical point are
indeed responsible for the onset of strong-coupling unconventional SC with the
line node in the gap function in HF compounds.",0603247v1
2006-03-09,Evidence for unconventional superconducting fluctuations in heavy-fermion compound CeNi2Ge2,"We present evidence for unconventional superconducting fluctuations in a
heavy-fermion compound CeNi$_2$Ge$_2$. The temperature dependence of the
$^{73}$Ge nuclear-spin-lattice-relaxation rate $1/T_1$ indicates the
development of magnetic correlations and the formation of a Fermi-liquid state
at temperatures lower than $T_{\rm FL}=0.4$ K, where $1/T_1T$ is constant. The
resistance and $1/T_1T$ measured on an as-grown sample decrease below $T_{\rm
c}^{\rm onset} = 0.2$ K and $T_{\rm c}^{\rm NQR} = 0.1$ K, respectively; these
are indicative of the onset of superconductivity. However, after annealing the
sample to improve its quality, these superconducting signatures disappear.
These results are consistent with the emergence of unconventional
superconducting fluctuations in close proximity to a quantum critical point
from the superconducting to the normal phase in CeNi$_2$Ge$_2$.",0603253v1
2006-03-10,Magnetic Structure and Spin Waves in the Kagomé Jarosite compound ${\bf KFe_3(SO_4)_2(OH)_6}$,"We present a detailed study of the magnetic structure and spin waves in the
Fe jarosite compound ${\rm KFe_3(SO_4)_2(OH)_6}$ for the most general
Hamiltonian involving one- and two-spin interactions which are allowed by
symmetry. We compare the calculated spin-wave spectrum with the recent neutron
scattering data of Matan {\it et al.} for various model Hamiltonians which
include, in addition to isotropic Heisenberg exchange interactions between
nearest ($J_1$) and next-nearest ($J_2$) neighbors, single ion anisotropy and
Dzyaloshinskii-Moriya (DM) interactions. We concluded that DM interactions are
the dominant anisotropic interaction, which not only fits all the splittings in
the spin-wave spectrum but also reproduces the small canting of the spins out
of the Kagom\'e plane. A brief discussion of how representation theory
restricts the allowed magnetic structure is also given.",0603280v1
2006-03-20,Effect of Pressure on Superconducting Ca-intercalated Graphite CaC$_6$,"The pressure effect on the superconducting transition temperature ($T_c$) of
the newly-discovered Ca-intercalated graphite compound CaC$_6$ has been
investigated up to $\sim$ 16 kbar. $T_c$ is found to increase under pressure
with a large relative ratio $\Delta$$T_c$/$T_c$ of $\approx$ +0.4 %/kbar. Using
first-principles calculations, we show that the large and positive effect of
pressure on $T_c$ can be explained in the scope of electron-phonon theory due
to the presence of a soft phonon branch associated to in-plane vibrations of Ca
atoms. Implications of the present findings on the current debate about the
superconducting mechanism in graphite intercalation compounds are discussed.",0603530v3
2006-03-27,Stretched exponential relaxation in three dimensional short-range spin glass Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound is
a three-dimensional short-range spin glass with a spin freezing temperature
$T_{SG}$ ($= 3.92 \pm 0.11$ K). The time evolution of the zero-field cooled
magnetization $M_{ZFC}(t)$ has been measured under various combinations of wait
time ($t_{w}$), temperature ($T$), temperature-shift ($\Delta T$), and magnetic
field ($H$). The relaxation rate $S_{ZFC}(t)$ [$=(1/H)$d$M_{ZFC}(t)$/d$\ln t$]
shows a peak at a peak time $t_{cr}$. The shape of $S_{ZFC}(t)$ in the vicinity
of $t_{cr}$ is well described by stretched exponential relaxation (SER). The
SER exponent $b$ and the SER relaxation time $\tau_{SER}$ are determined as a
function of $t_{w}$, $T$, $H$, and $\Delta T$. The value of $b$ at $T=T_{SG}$
is nearly equal to 0.3. There is a correlation between $\tau_{SER}$ and $1/b$,
irrespective of the values of $t_{w}$, $T$, $H$, and $\Delta T$. These features
can be well explained in terms of a simple relaxation model for glassy
dynamics.",0603725v2
2006-04-05,Josephson effect for superconductors lacking center of inversion,"Due to the absence of a center of inversion in some superconducting
compounds, a p-wave admixture to the dominant d-wave order parameter must
exist. If time-reversal is also violated, an allowed invariant is the product
of the d-wave, p-wave and an appropriately directed current. We show that this
leads to an anomalous Josephson current for tunneling along the direction
parallel to the axis of the p-wave component, where the current is the Meissner
current and the Josephson loop current along the surface of the tunnel barrier.
These ideas are applied to the superconducting state of the cuprates in the
pseudogap region of the phase diagram where in the normal phase some
experiments have detected a time-reversal and inversion symmetry broken phase.
  The effect is relevant also to heavy-fermion compounds which lack center of
inversion due to crystalline symmetry.",0604140v1
2006-04-06,Magnetic properties of collinear structures of compound La1-xCaxMnO3,"With use of homogeneous model for magnetic sub-lattice of compound La1-x
CaxMnO3 allowing for Heisenberg superexchange and double exchange between
nearest neighbors the temperature dependence of spontaneous magnetization on a
separate site is investigated in molecular field approximation. The difference
from the usual magnets with one type of magnetic ions is in the fact that
system of equations appears with two unknowns, being the mean spin values of
ions Mn3+ and Mn4+, correspondingly. Near ordering temperature this system can
be solved analytically and at the same time the expression for the ordering
temperature can be obtained. To find the temperature dependence of
magnetization in the whole temperature range we used the exact expression for
double exchange operator containing spin operators under the square root. The
numerical solutions were found in this case.",0604161v1
2006-04-13,Angle-dependence of the Hall effect in HgBa2CaCu2O6 thin films,"Superconducting compounds of the family Hg-Ba-Ca-Cu-O have been the subject
of intense study since the current record-holder for the highest critical
temperature of a superconductor belongs to this class of materials. Thin films
of the compound with two adjacent copper-oxide layers and a critical
temperature of about 120 K were prepared by a two-step process that consists of
the pulsed-laser deposition of precursor films and the subsequent annealing in
mercury-vapor atmosphere. Like some other high-temperature superconductors,
Hg-Ba-Ca-Cu-O exhibits a specific anomaly of the Hall effect, a double-sign
change of the Hall coefficient close to the superconducting transition. We have
investigated this phenomenon by measurements of the Hall effect at different
angles between the magnetic field direction and the crystallographic c-axis.
The results concerning the upper part of the transition, where the first sign
change occurs, are discussed in terms of the renormalized fluctuation model for
the Hall conductivity, adapted through the field rescaling procedure in order
to take into account the arbitrary orientation of the magnetic field.",0604352v1
2006-04-20,New Ferromagnetic Nitrides CaN and SrN and their synthesis process,"We introduce new type of ferromagnets, CaN and SrN, which were designed using
first-principles calculations. These are half-metallic ferromagnets and they
have magnetic moments of 1 $\mu_{\rm B}$ per chemical formula unit. Out of the
typical structures of binary compounds, the rock-salt structure is the most
stable form for both CaN and SrN. The majority of the magnetic moment of these
compound originates from the N sites since the $p$ states of N are
spin-polarized. Their formation energies were calculated and the results show
that it should be feasible to synthesize these materials. The structural
stability of CaN was confirmed by performing first-principles molecular
dynamics simulations. We propose a synthesis process for CaN basd on the
first-principles.",0604484v3
2006-04-26,Superconductivity in the Nb2SnC compound,"Nb2SnC is a member of the large family of lamellar materials that crystallize
in the hexagonal structure with space group P63/mmc which are isomorphs with
Cr2AlC, also named H-phase. In spite of the great number of compounds which
belong to this family, the superconductivity has been reported only for two
cases: Mo2GaC and Nb2SC. In this work we show that superconductivity can be
observed in Nb2SnC depending on the synthesis method used. The quality of the
superconductor is strongly dependent of the synthesis method and the optimal
results were reached for samples synthesized at 2.5 GPa and 523 +/- 50oC. This
sample showed a critical temperature close to 7.8K, revealed from magnetization
and transport measurement, the highest critical temperature reported up to now
for an H-phase.",0604605v1
2006-04-30,Observation of three-dimensional bulk Fermi surfaces for a strongly correlated material by soft x-ray $hν$-dependent (700-860 eV) ARPES,"Three-dimensional Fermi surfaces at a high temperature have been clarified
for a strongly correlated Ce compound, ferromagnet CeRu$_2$Ge$_2$ in the
paramagnetic phase, by virtue of a soft x-ray $h\nu$-dependent (700-860 eV)
ARPES. Although the observed Fermi surfaces as well as quasiparticle
dispersions are partly explained by a band-structure calculation based on a
localized $4f$ model, qualitative discrepancy in experiments, between our APRES
in the paramagnetic phase and de Haas-van Alphen measurement in the
ferromagnetic phase, is revealed. This suggests a fundamental change in the
$4f$ contribution to the Fermi surfaces across the magnetic phase transition
widely seen for Ce compounds.",0605021v1
2006-05-18,An ab-initio evaluation of the local effective interactions in the superconducting compound $\rm Na\_{0.35} Co O\_2-1.3H\_2O$,"We used ab-initio quantum chemical methods, treating explicitly the strong
correlation effects within the cobalt 3d shell, as well as the screening
effects on the effective integrals, for accurately determining on-site and
nearest-neighbor (NN) interactions in the $\rm Na\_{0.35} Co O\_2-1.3H\_2O$
superconducting compound. The effective ligand field splitting within the
$t\_{2g}$ orbitals was found to be $\delta \sim 300 \rm meV$, the $a\_{1g}$
orbital being destabilized compared to the $e\_g^\prime$ ones. The effective
Hund's exchange and Coulomb repulsion were evaluated to $J\_H\sim 280 \rm meV$
and $U\sim 4.1$--$4.8 \rm eV$. The NN hopping parameters were determined within
the three $t\_{2g}$ orbitals and found to be of the same order of magnitude as
the $t\_{2g}$ ligand field splitting, supporting the hypothesis of a three band
model for this system. Finally we evaluated the NN effective exchange integral
to be antiferromagnetic and $J=-66 \rm meV$.",0605454v2
2006-05-22,Ab initio studies of electronic structure of defects in PbTe,"Understanding the detailed electronic structure of deep defect states in
narrow band-gap semiconductors has been a challenging problem. Recently,
self-consistent ab initio calculations within density functional theory (DFT)
using supercell models have been successful in tackling this problem. In this
paper, we carry out such calculations in PbTe, a well-known narrow band-gap
semiconductor, for a large class of defects: cationic and anionic
substitutional impurities of different valence, and cationic and anionic
vacancies. For the cationic defects, we study a series of compounds
RPb2n-1Te2n, where R is vacancy or monovalent, divalent, or trivalent atom; for
the anionic defects, we study compounds MPb2nTe2n-1, where M is vacancy, S, Se
or I. We find that the density of states (DOS) near the top of the valence band
and the bottom of the conduction band get significantly modified for most of
these defects. This suggests that the transport properties of PbTe in the
presence of impurities can not be interpreted by simple carrier doping
concepts, confirming such ideas developed from qualitative and
semi-quantitative arguments.",0605538v1
2006-06-06,Quenching of the Haldane gap in LiVSi2O6 and related compounds,"We report results of susceptibility chi and 7Li NMR measurements on LiVSi2O6.
The temperature dependence of the magnetic susceptibility chi(T) exhibits a
broad maximum, typical for low-dimensional magnetic systems. Quantitatively it
is in agreement with the expectation for an S=1 spin chain, represented by the
structural arrangement of V ions. The NMR results indicate antiferromagnetic
ordering below T_N=24 K. The intra- and interchain coupling J and J_p for
LiVSi2O6, and also for its sister compounds LiVGe2O6, NaVSi2O6 and NaVGe2O6,
are obtained via a modified random phase approximation which takes into account
results of quantum Monte Carlo calculations. While J_p is almost constant
across the series, J varies by a factor of 5, decreasing with increasing
lattice constant along the chain direction. The comparison between experimental
and theoretical susceptibility data suggests the presence of an easy-axis
magnetic anisotropy, which explains the formation of an energy gap in the
magnetic excitation spectrum below T_N, indicated by the variation of the NMR
spin-lattice relaxation rate at T << T_N.",0606150v1
2006-06-09,Spontaneous superconductivity and optical properties of high-Tc cuprates,"We suggest that the high temperature superconductivity in cuprate compounds
may emerge due to interaction between copper-oxygen layers mediated by in-plane
plasmons. The strength of the interaction is determined by the c-axis geometry
and by the ab-plane optical properties. Without making reference to any
particular in-plane mechanism of superconductivity, we show that the interlayer
interaction favors spontaneous appearance of the superconductivity in the
layers. At a qualitative level the model describes correctly the dependence of
the transition temperature on the interlayer distance, and on the number of
adjacent layers in multilayered homologous compounds. Moreover, the model has a
potential to explain (i) a mismatch between the optimal doping levels for
critical temperature and superconducting density and (ii) a universal scaling
relation between the dc-conductivity, the superfluid density, and the
superconducting transition temperature.",0606227v2
2006-06-23,Dynamical spin chirality and spin anisotropy in gapped S=1/2 quantum systems,"We have studied the spin anisotropy in spin-singlet ground state compounds
and the magnetic chirality, as measured by inelastic polarized neutron
scattering techniques, in the chain-sublattice of Sr14Cu24O41. In-plane and out
of plane magnetic fluctuations are measured to be anisotropic and further
discussed in the light of the current hypothesis of spin-orbit coupling. We
show that under appropriate conditions of magnetic field and neutron
polarization, the \textit{trivial} magnetic chirality selects only one of the
Zeeman splitted triplet states for scattering and erases the other one that
posses opposite helicity. Our analysis pertains to previous studies on
dynamical magnetic chirality and chiral critical exponents, where the ground
state is chiral itself, the so-called \textit{non-trivial} dynamical magnetic
chirality. As it turns out, both \textit{trivial} and \textit{non-trivial}
dynamical magnetic chirality have identical selection rules for inelastic
polarized neutron scattering experiments and it is not at all evident that they
can be distinguished in a paramagnetic compound.",0606598v1
2006-07-03,"Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)","We investigated the electronic structures of the two-dimensional layered
perovskite Sr$_{2}$\textit{M}O$_{4}$ (\textit{M}=4\textit{d} Ru, 4\textit{d}
Rh, and 5\textit{d} Ir) using optical spectroscopy and polarization-dependent O
1\textit{s} x-ray absorption spectroscopy. While the ground states of the
series of compounds are rather different, their optical conductivity spectra
$\sigma(\omega)$ exhibit similar interband transitions, indicative of the
common electronic structures of the 4\textit{d} and 5\textit{d} layered oxides.
The energy splittings between the two $e_{g}$ orbitals, $i.e.$,
$d_{3z^{2}-r^{2}}$ and $d_{x^{2}-y^{2}}$, are about 2 eV, which is much larger
than those in the pseudocubic and 3\textit{d} layered perovskite oxides. The
electronic properties of the Sr$_{2}$\textit{M}O$_{4}$ compounds are discussed
in terms of the crystal structure and the extended character of the 4\textit{d}
and 5\textit{d} orbitals.",0607026v2
2006-07-25,"Discovery of Li2(Pd,Pt)3B superconductors","Critical temperature Tc of the Li2(Pd1-xPtx)3B was reported to be 7-8K for
x=0 and 2.2-2.8K for x=1. In this article we present our preliminary results on
behavior of magnetization-temperature curves with starting composition of Pd-B
precursor, y-Li concentration in LiyPd3B and post-annealing of the Pd-end
compound. Results suggest that to maximize Tc ratio Pd:B should be close to
3:1, while y-Li has to be optimum. The lowest Tc for LiyPd3B was 4.4-4.6K,
while post-annealings at 560 deg. C allowed enhancement of Tc up to 8.2-8.4K.
Compositions Li2Z3B with Z=Ni, Ru, Rh, Re, Ag are not superconducting down to
1.8K. Exception is composition with Re showing superconductivity due to Re3B
compound. All samples were prepared by arc melting.",0607626v1
2006-08-07,Non-collinear Magnetic states of Mn5Ge3 compound,"Mn5Ge3 thin films epitaxially grown on Ge(111) exhibit metallic conductivity
and strong ferromagnetism up to about 300 K. Recent experiments suggest a
non-collinear spin structure. In order to gain deep insights into the magnetic
structure of this compound, we have performed fully unconstrained ab-initio
pseudopotential calculations within density functional theory, investigating
the different magnetic states corresponding to Collinear (C) and Non-Collinear
(NC) spin configurations. We focus on their relative stability under pressure
and strain field. Under pressure, the C and NC configurations are degenerate,
suggesting the possible occurrence of accidental magnetic degeneracy also in
Mn5Ge3 real samples. We found a continuous transition from a ferromagnetic C
low-spin state at small volumes to a NC high-spin state at higher volumes.
Remarkably, the degeneracy is definitely removed under the effect of uniaxial
strain: in particular, NC spin configurations is favoured under tensile
uniaxial strain.",0608176v2
2006-08-11,"Influence of simultaneous doping of Sb & Pb on phase formation, superconducting and microstructural characteristics of HgBa2Ca2Cu3O8+δ","We report systematic studies of structural, microstructural and transport
properties of (Hg_0.80 Sb_0.2-x Pb_x)Ba_2 Ca_2 Cu_3O_8+\delta (where x = 0.0,
0.05, 0.1, 0.15, 0.2) compounds. Bulk polycrystalline samples have been
prepared by two-step solid-state reaction route at ambient pressure. It has
been observed that simultaneous substitution of Sb and Pb at Hg site in oxygen
deficient HgO_\delta layer of HgBa2Ca2Cu3O8+\delta cuprate high-Tc
superconductor leads to the formation of Hg-1223 as the dominant phase.
Microstructural investigations of the as grown samples employing scanning
electron microscopy reveal single crystal like large grains embodying spiral
like features. Superconducting properties particularly transport current
density (Jct) have been found to be sensitive to these microstructural
features. As for example (Hg0.80Sb0.05Pb0.15)Ba2Ca2Cu3O8+\delta compound which
exhibits single crystal like large grains (~ 50 micrometer) and appears to
result through spiral growth mechanism, shows highest Jct (~ 1.85 x 103 A/cm2)
at 77K. A possible mechanism for the generation of spiral like features and
correlation between microstructural features and superconducting properties
have been put forward.",0608276v1
2006-08-15,Low temperature behavior of the heavy Fermion Ce3Co4Sn13,"The compound Ce3Co4Sn13 is an extremely heavy cubic heavy fermion system with
a low temperature electronic specific heat of order ~4 J/mol-K2. If the
compound is nonmagnetic, it would be one of the heaviest nonmagnetic Ce-based
heavy fermions reported to date and therefore would be expected to lie
extremely close to a quantum critical point. However, a broad peak of unknown
origin is observed at 0.8 K in the specific heat and magnetic susceptibility,
suggesting the possibility of antiferromagnetic order. We present neutron
diffraction data from polycrystalline samples which do not show any sign of
magnetic scattering below 0.8 K. In addition, we present inelastic neutron
scattering data from a single crystal sample which is consistent with the 1.2 K
energy scale for Kondo spin fluctuations determined from specific heat
measurements.",0608329v1
2006-08-30,Cohesion of BaReH$_9$ and BaMnH$_9$: Density Functional Calculations and Prediction of (MnH$_9)^{2-}$ Salts,"Density functional calculations are used to calculate the structural and
electronic properties of BaReH$_9$ and to analyze the bonding in this compound.
The high coordination in BaReH$_9$ is due to bonding between Re 5$d$ states and
states of $d$-like symmetry formed from combinations of H $s$ orbitals in the
H$_9$ cage. This explains the structure of the material, its short bond lengths
and other physical properties, such as the high band gap. We compare with
results for hypothetical BaMnH$_9$, which we find to have similar bonding and
cohesion to the Re compound. This suggests that it may be possible to
synthesize (MnH$_9)^{2-}$ salts. Depending on the particular cation, such salts
may have exceptionally high hydrogen contents, in excess of 10 weight %",0608686v1
2006-08-31,Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs$_{4}$Sb$_{12}$: Sb-NQR Study,"We have carried out nuclear quadrupole resonance (NQR) measurements in the
filled skutterudite compounds Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ ($x=0.1, 0.2$),
in order to gain insights into the symmetry of the superconducting gap
function. Upon replacing Os with Ru, the spin-lattice relaxation rate $1/T_1$
becomes proportional to temperature ($T$) at low $T$ far below $T_c$, and the
magnitude of $(1/T_1T)_{low-T}$ increases with increasing Ru content. These
results indicate that a finite density of states is induced at the Fermi level
by the impurity, and thus suggest that there exist nodes in the gap function of
PrOs$_{4}$Sb$_{12}$.",0608698v1
2006-09-04,Effect of structural distortions on the magnetism of doped spin-Peierls CuGeO3,"The chemical selectivity and great sensitivity of the Extended X-ray
Absorption Spectroscopy technique allowed the determination, in the
paramagnetic phase, of the structural distortions induced by doping in the
spin-Peierls CuGeO$_3$ compound. The distorted environments were analyzed as a
function of concentration, magnetic nature of impurity and the substitution
site (Ni, Mn and Zn impurities on the Cu site, Si impurity on the Ge site).
This has led to estimate the variation of the angles and pair distances, and
hence to evaluate the magnetic coupling along the Cu chains in the vicinity of
the impurities. The antiferromagnetic interaction between Cu first neighbors in
the pure sample is found to be weakened around Ni, almost cancelled in the case
of Mn doping, and even to change sign, producing a ferromagnetic coupling for
Si doping. More generally, the structural distortions on a local scale are
shown to be key parameters for the understanding of the magnetic properties of
doped spin-Peierls compounds.",0609054v2
2006-09-18,Sr$_2$Cu(PO$_4$)$_2$: A real material realization of the 1D nearest neighbor Heisenberg chain,"We present evidence that crystalline Sr_2Cu(PO_4)_2 is a nearly perfect
one-dimensional (1D) spin-1/2 anti-ferromagnetic Heisenberg model (AHM) chain
compound with nearest neighbor only exchange. We undertake a broad theoretical
study of the magnetic properties of this compound using first principles (LDA,
LDA+U calculations), exact diagonalization and Bethe-ansatz methodologies to
decompose the individual magnetic contributions, quantify their effect, and fit
to experimental data. We calculate that the conditions of one-dimensionality
and short-ranged magnetic interactions are sufficiently fulfilled that Bethe's
analytical solution should be applicable, opening up the possibility to explore
effects beyond the infinite chain limit of the AHM Hamiltonian. We begin such
an exploration by examining some extrinsic effects such as impurities and
defects.",0609430v1
2006-09-18,The spin-Peierls transition beyond the adiabatic approximation,"We develop a theory of the spin-Peierls transition taking into account the
three dimensional character of the phonon field. Our approach does not rely on
the adiabatic or mean field treatment for the phonons. It is instead based in
the exact integration of the phonon field, the exact long wavelength solution
of the one chain spin problem, and then a mean field approximation for the
interchain interaction. We show that the spin gap and the critical temperature
are strongly reduced due to the finite frequency effects of the phonon coupling
transverse to the magnetic chains. We claim that our results should be
applicable to the inorganic spin-Peierls compound CuGeO$_3$. We show that the
long standing discussion on absence of a soft mode in this compound can be
naturally resolved within our theory.",0609433v1
2006-10-04,One-dimensional versus two-dimensional correlation effects in the oxyhalides TiOCl and TiOBr,"We have performed a comparative study of the electronic structures of the
spin-Peierls systems TiOCl and TiOBr by means of photoemission spectroscopy and
density functional calculations. While the overall electronic structure of
these isostructural compounds is qualitatively similar, the bromide appears to
be less one-dimensional. We present a quantitative analysis of the experimental
dispersions in terms of exchange constant J and hopping integral t as well as a
discussion of the qualitative spectral features. From that we conclude that
despite the one-dimensional physics triggering the ground state in both
compounds a proper description of the normal state electronic structure has to
take into account the anisotropic frustrated interchain interactions on the
underlying triangular lattice.",0610106v1
2006-10-04,Quantum phase transition in the heavy-fermion compound YbIr$_2$Si$_2$,"We investigate the pressure-temperature phase diagram of YbIr$_2$Si$_2$ by
measuring the electrical resistivity $\rho(T)$. In contrast to the widely
investigated YbRh$_2$Si$_2$, YbIr$_2$Si$_2$ is a paramagnetic metal below
$p_c\simeq 8$ GPa. Interestingly, a first-order, presumably ferromagnetic,
transition develops at $p_c$. Similar magnetic properties were also observed in
YbRh$_2$Si$_2$ and YbCu$_2$Si$_2$ at sufficiently high pressures, suggesting a
uniform picture for these Yb compounds. The ground state of YbIr$_2$Si$_2$
under pressure can be described by Landau Fermi-liquid (LFL) theory, in
agreement with the nearly ferromagnetic Fermi-liquid (NFFL) model. Moreover,
evidence of a weak valence transition, characterized by a jump of the
Kadowaki-Woods (KW) ratio as well as an enhancement of the residual resistivity
$\rho_0$ and of the quasiparticle-quasiparticle scattering cross section, is
observed around 6 GPa.",0610126v1
2006-10-17,The kagome staircase compounds Ni$_{3}$V$_{2}$O$_{8}$ and Co$_{3}$V$_{2}$O$_{8}$ studied with implanted muons,"We present the results of muon-spin relaxation ($\mu^{+}$SR) measurements on
the kagome staircase compounds Ni$_{3}$V$_{2}$O$_{8}$ and
Co$_{3}$V$_{2}$O$_{8}$. The magnetic behavior of these materials may be
described in terms of two inequivalent magnetic ion sites, known as spine sites
and cross-tie sites. Our $\mu^{+}$SR results allow us to probe each of these
sites individually, revealing the distribution of the local magnetic fields
near these positions. We are able not only to confirm the magnetic structures
of the various phases proposed on the basis of bulk measurements but also to
give an insight into the temperature evolution of the local field distribution
in each phase.",0610477v2
2006-10-28,"Multiplet effects in the electronic structure of $δ$-Pu, Am and their compounds","We propose a straightforward and efficient procedure to perform dynamical
mean-field (DMFT) calculations on the top of the static mean-field LDA+U
approximation. Starting from self-consistent LDA+U ground state we included
multiplet transitions using the Hubbard-I approximation, which yields a very
good agreement with experimental photoelectron spectra of $\delta$-Pu, Am, and
their selected compounds.",0610794v1
2006-11-10,Superconductivity in two-band systems with variable charge carrier density. The case of MgB2,"The theory of thermodynamic properties of two-band superconductor with
reduced density charge carriers is developed on the base of phonon
superconducting mechanism with strong electron-phonon interaction. This theory
is adapted to describe the behavior of critical temperature Tc, energy gaps
Delta1, Delta2, and the relative jump of electron specific heat (Cs - Cn)/Cn in
the point T = Tc along with the variation of charge carrier density in the
compound MgB2 when substitutional impurities with different valence are
introduced into the system. It is shown, that according to the filling
mechanism of energy bands which overlap on Fermi surface, the quantities Tc,
Delta1, Delta2 decrease when this compound is doped with electrons and remain
constant or weakly change when the system is doped with holes. The theory
qualitatively agrees with the experimental data. Also is shown that the
consideration of inter- and intraband scattering of electrons on impurity
potential improves this agreement.",0611275v1
2006-11-10,"Evolution of the crystal-field splittings in the compounds CeX (X=P, As, Sb, Bi), \\CeY (Y=S, Se, Te) and their alloys CeX$_{1-x}$Y$_{x}$}","The crystal-field splittings of the monopnictides and monochalcogenides of
Cerium (CeX and CeY) and their alloys (CeX$_{1-x}$Y$_x$) are calculated by
means of an \emph{ab initio} many-body combined technique. The hybridization
functions of the 4f states of Cerium with the conduction band for each material
are obtained from first principles within the local density approximation (LDA)
and are used as input for the Anderson impurity model, which is solved within a
multi-orbital Non-Crossing Approximation (NCA). This realistic theoretical
approach (LDA-NCA) is able to reproduce the experimental results for the
crystal-field splittings of the CeX and CeY series in agreement with previous
theoretical calculations. It is also able to describe the non-linear evolution
of the splittings in the CeX$_{1-x}$Y$_x$ alloys as a function of x. An
analysis of the values of the crystal-field splittings in all the compounds can
be done in depth in this contribution, due to a detailed knowledge of the band
structure and crystal environment in combination with many-body physics.",0611293v1
2006-11-23,Quantum dissipation theory of slow magnetic relaxation mediated by domain-wall motion in one-dimensional chain compound [Mn(hfac)_{2}BNO_{H}}],"Based on a quantum dissipation theory of open systems, we present a
theoretical study of slow dynamics of magnetization for the ordered state of
the new molecule-based magnetic complex [Mn(hfac)_{2}BNO_{H}] composed from
antiferromagnetically coupled ferrimagnetic (5/2,1) spin chains. Experimental
investigations of the magnetization process in pulsed fields have shown that
this compound exhibits a metamagnetic AF-FI transition at a critical field in
the order of the interchain coupling. A strong frequency dependence for the
ac-susceptibility has been revealed in the vicinity of the AF-FI transition and
was associated with an AF-FI interface kink motion. We model these processes by
a field-driven domain-wall motion along the field-unfavorable chains correlated
with a dissipation effect due to a magnetic system-bath coupling. The
calculated longitudinal magnetization has a two-step relaxation after the field
is switched off and are found in good agreement with the experiment. The
relaxation time determined from the imaginary part of the model
ac-susceptibility agrees qualitatively with that found from the remanent
magnetization data.",0611610v1
2006-11-30,"Role of the presence of transition-metal atoms at the antisites in CrAs, CrSe and VAs zinc-blende compounds","In a recent publication [Galanakis I et al 2006 \PR B \textbf{74} 140408(R)]
we have shown that in the case of CrAs and related transition-metal
chalcogenides and pnictides, crystallizing in the zinc-blende structure, the
excess of the transition-metal atoms leads to half-metallic ferrimagnetism. The
latter property is crucial for spintronic applications with respect to
ferromagnets due to the lower stray fields created by these materials. We
extend this study to cover the case where the transition-metal atoms sitting at
antisites are not identical to the ones in the perfect sites. In Cr-based
compounds, the creation of Mn antisites keeps the half-metallic ferrimagnetic
character produced also by the Cr antisites. In the case of VAs, Cr and Mn
antisites keep the half-metallic character of VAs (contrary to V antisites) due
to the larger exchange-splitting exhibited by these atoms.",0611777v1
2006-12-18,Fluctuation spectra of free and supported membrane pairs,"Fluctuation spectra of fluid compound membrane systems are calculated. The
systems addressed contain two (or more) almost parallel membranes that are
connected by harmonic tethers or by a continuous, harmonic confining potential.
Additionally, such a compound system can be attached to a supporting substrate.
We compare quasi-analytical results for tethers with analytical results for
corresponding continuous models and investigate under what circumstances the
discrete nature of the tethers actually influences the fluctuations. A
tethered, supported membrane pair with similar bending rigidities and stiff
tethers can possess a nonmonotonic fluctuation spectrum with a maximum. A
nonmonotonic spectrum with a maximum and a minimum can occur for an either free
or supported membrane pair of rather different bending rigidities and for stiff
tethers. Typical membrane displacements are calculated for supported membrane
pairs with discrete or continuous interacting potentials. Thereby an estimate
of how close the constituent two membranes and the substrate typically approach
each other is given. For a supported membrane pair with discrete or continuous
interactions, the typical displacements of each membrane are altered with
respect to a single supported membrane, where those of the membrane near the
substrate are diminished and those of the membrane further away are enhanced.",0612453v1
2007-01-15,"Magnetic anomalies in a spin-chain compound, Sr3CuRhO6: Griffiths-phase-like behavior of magnetic susceptibility","We report the results of ac and dc magnetic susceptibility (chi),
heat-capacity (C), isothermal magnetization and isothermal remanent
magnetization measurements on the compound, Sr3CuRhO6, crystallizing in a
K4CdCl6-derived monoclinic structure. The magnetization data reveal distinct
magnetic anomalies near 6 and 12 K with decreasing temperature (T). While the
transition below (To=) 6K appears to be of a spin-glass-type as inferred from
all the data, the one at 12 K is not typical of bulk ferromagnetism in contrast
to an earlier proposal. In the range 6 to 12 K, the dc chi obeys the
theoretically expected form for very low dc fields and the values of chi
decrease gradually with the application of higher magnetic fields, mimicking
the behavior Griffiths-phases.",0701336v1
2007-01-18,"Magnetoelastic coupling in RETiO3 (RE = La, Nd, Sm, Gd, Y)","A detailed analysis of the crystal structure in RETiO3 with RE = La, Nd, Sm,
Gd, and Y reveals an intrinsic coupling between orbital degrees of freedom and
the lattice which cannot be fully attributed to the structural deformation
arising from bond-length mismatch. The TiO6 octahedra in this series are all
irregular with the shape of the distortion depending on the RE ionic radius.
These octahedron distortions vary more strongly with temperature than the tilt
and rotation angles. Around the Ti magnetic ordering all compounds exhibit
strong anomalies in the thermal-expansion coefficients, these anomalies exhibit
opposite signs for the antiferromagnetic and ferromagnetic compounds.
Furthermore the strongest effects are observed in the materials close to the
magnetic cross-over from antiferromagnetic to ferromagnetic order.",0701452v1
2007-01-20,Hyperfine Interactions in USb2 Crystal,"The hyperfine interactions at the uranium site in the antiferromagnetic USb2
compound were calculated within the density functional theory (DFT) employing
the augmented plane wave plus local orbital (APW+lo) method. We investigated
the dependence of the nuclear quadruple interactions to the magnetic structure
in USb2 compound. The investigation were performed applying the so called band
correlated LDA+U theory self consistently. The self consistent LDA+U
calculations were gradually added to the performed generalized gradient
approximation (GGA) including scalar relativistic spin orbit interactions in a
second variation scheme. The result, which is in agreement with experiment,
shows that the 5f-electrons have the tendency to be hybridized with the
conduction electrons in the ferromagnetic uranium planes.",0701497v1
2007-01-23,Density functional approach to study structural properties and Electric Field Gradients in rare earth materials,"We investigated the effect of spin polarization on the structural properties
and gradient of electric field (EFG) on Sn, In, and Cd impurity in RSn$_3$
(R=Sm, Eu, Gd) and RIn$_3$ (R=Tm, Yb, Lu) compounds. The calculations were
performed self-consistently using the scalar-relativistic full potential
linearized augmented plane wave method. The local density approximations (LDA)
and generalized gradient approximation without spin polarization (GGA) and with
spin polarization (GGA+SP) to density functional theory were applied. In
addition to that we performed some calculations within open core treatment
(GGA+open core). It is clearly seen that GGA+SP is successful in predicting the
larger lattice parameter and the dramatic drop of EFG for R=(Eu, Yb) relative
to other rare earth compounds. This is an indication that spin splitting
generated by spin polarization without any modification, is capable of treating
properly the highly correlated f electrons in these systems.",0701557v2
2007-01-24,Energy gap formation in a valence fluctuating compound CeIrSb probed by Sb NMR and NQR,"Sb-NMR/NQR study has revealed a formation of a pseudogap at the Fermi level
in the density of states in a valence fluctuating compound CeIrSb. The nuclear
spin-lattice relaxation rate divided by temperature, 1/T_1T has a maximum
around 300 K and decreases significantly as 1/T_1T ~ T^2, followed by a 1/T_1T
= const. relation at low temperature. This temperature dependence of 1/T_1T is
well reproduced by assuming a V-shaped energy gap with a residual density of
states at the Fermi level. The size of energy gap for CeIrSb is estimated to be
about 350 K, which is by one order of magnitude larger than those for the
isostructural Kondo semiconductors CeRhSb and CeNiSn. Despite the large
difference in the size of energy gap, CeIrSb, CeRhSb and CeNiSn are indicated
to be classified into the same group revealing a V-shaped gap due to c-f
hybridization. The temperature dependence of the Knight shift measured in a
high magnetic field agrees with the formation of this pseudogap.",0701582v1
2007-01-29,Parameters of the Dzyaloshinsky-Moriya type weak ferromagnetism for some perovskite compounds,"Compounds with distorted perovskite structure of the 4-f and 3-d transition
metals with the common formula LnTO3 (where Ln is rare-earth element, T is an
element from the Fe group) are the most multifold binary oxides of these two
groups elements. Wide range of stability for this structure allows the
realization of combinations of the Lanthanides with all the transition metals
except the Nickel. Quite interesting physical phenomena take place in these
oxides like charge and orbital ordering; relatively independent magnetic
lattices of the both metals; particular magnetic structures; high optical
indicators; giant magneto-resistance; peculiar dielectric and ferroelectric
properties etc. We have investigated the magnetic properties of pure ferrites
and chromium-based materials as well as of some mixed type oxides like
HoxTb1-xO3, HoMnxFe1-xO3, HoMnxCr1-xO3 and DyFexCr1-xO3.",0701708v1
2007-01-29,Peculiarities in the properties of some rare-earth compounds with orthorhombic structures,"Rare-earth manganites are fascinating, because they display a wide variety of
fundamental properties from magnetism to ferroelectricity, from colossal
magnetoresistance to semi-metallicity, and because they can be used in a number
of important technological applications such as controlling a magnetic memory
by an electric field or vice versa, new types of attenuators or transducers
etc. In this paper, we present our investigation on monocrystal samples with an
orthorhombic structure, grown in two different space groups: D2h(16) for
La0.78Pb0.22MnO3 and Pr0.7Sr0.3MnO3 and D2h(9) for HoMn2O5 and TbMn2O5. The
doped perovskite manganites Ln1-x Ax MnO3 (where Ln is a rare-earth ion and A
is a divalent ion) from the group D2h(16), which crystallized in different
modifications of the perovskite structure, characterized by the parameter
deformation of the type c/&#8730;2<b<a. Many properties of these compounds
(especially the giant magnetoresistance GMR, being interesting for practical
applications) depend strongly on the carrier density, on the specific zone
structure, on the type and the quantity of dopants, on the defects of the
crystal and their magnetic structure, or on the applied magnetic fields.",0701709v1
2007-02-12,Wannier functions and exchange integrals: The example of LiCu$_{2}$O$_{2}$,"Starting from a single band Hubbard model in the Wannier function basis, we
revisit the problem of the ligand contribution to exchange and derive explicit
formulae for the exchange integrals in metal oxide compounds in terms of atomic
parameters that can be calculated with constrained LDA and LDA+U. The analysis
is applied to the investigation of the isotropic exchange interactions of
LiCu$_{2}$O$_{2}$, a compound where the Cu-O-Cu angle of the dominant exchange
path is close to 90$^{\circ}$. Our results show that the magnetic moments are
localized in Wannier orbitals which have strong contribution from oxygen atomic
orbitals, leading to exchange integrals that considerably differ from the
estimates based on kinetic exchange only. Using LSDA+U approach, we also
perform a direct {\it ab-initio} determination of the exchange integrals
LiCu$_{2}$O$_{2}$. The results agree well with those obtained from the Wannier
function approach, a clear indication that this modelization captures the
essential physics of exchange. A comparison with experimental results is also
included, with the conclusion that a very precise determination of the Wannier
function is crucial to reach quantitative estimates.",0702276v1
2007-02-13,Singlet ground state in the spin-1/2 dimer compound Sr3Cr2O8,"Magnetic susceptibility and specific heat versus temperature measurements on
polycrystalline samples of Sr3Cr2O8 and the isostructural, nonmagnetic compound
Sr3V2O8 are reported. A Curie-Wiess fit to the high-temperature susceptibility
data for Sr3Cr2O8 indicates that the Cr atoms are in the rare Cr^5+ (Spin S =
1/2) valence state as expected from the composition. The ground state was found
to be a spin singlet with an excitation gap Delta/k_ B = 61.9(1) K to the
magnetic triplet states, and a weak interdimer coupling of 6(2) K was inferred.
The specific heat and susceptibility measurements on Sr3V2O8 reveal a phase
transition at 110 K which is evidently a structural transition.",0702309v2
2007-03-08,Spectroscopic fingerprints of the frustrated magnetic order in Li2VOSiO4: a t-J model study,"We have analyzed theoretically the photoemission spectra of the insulating
compound Li2VOSiO4.Recently, this compound has been proposed as the first
experimental realization of the frustrated J1-J2 Heisenberg model. Although it
is well known that Li2VOSiO4 is magnetically ordered in a collinear arrangement
below TN=2.8 K, there is some controversy about the coexistence of two
collinear phases above TN. Using a generalized t-J model we have obtained a
complex spectral structure that can be traced back to the underlying collinear
magnetic structures. We discuss the possibility to use ARPES experiments as a
way to discern among the different scenarios proposed in the literature.",0703221v1
2007-03-08,Anomalous thermal expansion and strong damping of the thermal conductivity of NdMnO$_3$ and TbMnO$_3$ due to 4f crystal-field excitations,"We present measurements of the thermal conductivity $\kappa $ and the thermal
expansion $\alpha$ of NdMnO$_3$ and TbMnO$_3$. In both compounds a splitting of
the $4f$ multiplet of the $R^{3+}$ ion causes Schottky contributions to
$\alpha$. In TbMnO$_3$ this contribution arises from a crystal-field splitting,
while in NdMnO$_3$ it is due to the Nd-Mn exchange coupling. Another
consequence of this coupling is a strongly enhanced canting of the Mn moments.
The thermal conductivity is greatly suppressed in both compounds. The main
scattering process at low temperatures is resonant scattering of phonons
between different energy levels of the $4f$ multiplets, whereas the complex 3d
magnetism of the Mn ions is of minor importance.",0703222v1
2007-03-21,Ab initio study on the effects of transition metal doping of Mg2NiH4,"Mg2NiH4 is a promising hydrogen storage material with fast (de)hydrogenation
kinetics. Its hydrogen desorption enthalpy, however, is too large for practical
applications. In this paper we study the effects of transition metal doping by
first-principles density functional theory calculations. We show that the
hydrogen desorption enthalpy can be reduced by ~0.1 eV/H2 if one in eight Ni
atoms is replaced by Cu or Fe. Replacing Ni by Co atoms, however, increases the
hydrogen desorption enthalpy. We study the thermodynamic stability of the
dopants in the hydrogenated and dehydrogenated phases. Doping with Co or Cu
leads to marginally stable compounds, whereas doping with Fe leads to an
unstable compound. The optical response of Mg2NiH4 is also substantially
affected by doping. The optical gap in Mg2NiH4 is ~1.7 eV. Doping with Co, Fe
or Cu leads to impurity bands that reduce the optical gap by up to 0.5 eV.",0703550v1
2007-03-26,Molecular dynamics study on planar clustering of xenon in UO2,"Interatomic potentials of uranium dioxide are investigated on their
applicability to model structural stabilities beyond fluorite phase by
comparing with ab-initio results. A high pressure cotunnite phase and loosely
stacking virtual crystal are involved in order to get a primary confidence for
large-scale deformation modelings of UO2 under irradiation damages. The
behavior of Xe atoms in UO2 fuel is studied with molecular dynamics
simulations. Besides the ground state bubble geometry, we find that a planar
distribution is also (meta-) stable for xenon under thermodynamic
perturbations. The Xe atoms with a planar configuration are in a liquid state
at a typical reactor temperature of 1000 K, which presents a modulated
layer-structure near the interface with solid UO2. A planar defects loop
remains after these Xe atoms are released out.",0703657v1
2007-03-26,Proposed low energy model Hamiltonian for spin-gapped system CuTe2O5,"Using first-principles electronic structure calculations based on the Nth
order muffin tin orbital (NMTO)-downfolding technique, we derived the
low-energy spin model for CuTe2O5. Our study reveals that this compound is a 2D
coupled spin-dimer system with the strongest Cu-Cu interaction mediated by two
O-Te-O bridges. We checked the goodness of our model by computing the magnetic
susceptibility with the Quantum Monte Carlo technique and by comparing it with
available experimental data. We also present magnetization and specific heat
results which may be compared with future experimental investigations. Our
derived model is in disagreement with a recently proposed model for this
compound [J. Deisenhofer et al, Phys. Rev. B,74 (2006) 174421]. The situation
needs to be settled in terms of further experimental investigations.",0703675v3
2007-03-27,Magnetic structure of Cd-doped CeCoIn5,"The heavy fermion superconductor CeCoIn5 is believed to be close to a
magnetic instability, but no static magnetic order has been found. Cadmium
doping on the In-site shifts the balance between superconductivity and
antiferromagnetism to the latter with an extended concentration range where
both types of order coexist at low temperatures. We investigated the magnetic
structure of nominally 10% Cd-doped CeCoIn5, being antiferromagnetically
ordered below T_N=3 K and superconducting below T_c=1.3 K, by elastic neutron
scattering. Magnetic intensity was observed only at the ordering wave vector
Q_AF = (1/2,1/2,1/2) commensurate with the crystal lattice. Upon entering the
superconducting state the magnetic intensity seems to change only little. The
commensurate magnetic ordering in CeCo(In1-xCdx)5 is in contrast to the
incommensurate antiferromagnetic ordering observed in the closely related
compound CeRhIn5. Our results give new insights in the interplay between
superconductivity and magnetism in the family of CeTIn5 (T=Co, Rh, and Ir)
based compounds.",0703703v1
1999-07-06,Cross-Language Information Retrieval for Technical Documents,"This paper proposes a Japanese/English cross-language information retrieval
(CLIR) system targeting technical documents. Our system first translates a
given query containing technical terms into the target language, and then
retrieves documents relevant to the translated query. The translation of
technical terms is still problematic in that technical terms are often compound
words, and thus new terms can be progressively created simply by combining
existing base words. In addition, Japanese often represents loanwords based on
its phonogram. Consequently, existing dictionaries find it difficult to achieve
sufficient coverage. To counter the first problem, we use a compound word
translation method, which uses a bilingual dictionary for base words and
collocational statistics to resolve translation ambiguity. For the second
problem, we propose a transliteration method, which identifies phonetic
equivalents in the target language. We also show the effectiveness of our
system using a test collection for CLIR.",9907007v2
2005-03-02,High efficiency and low absorption Fresnel compound zone plates for hard X-ray focusing,"Circular and linear zone plates have been fabricated on the surface of
silicon crystals for the energy of 8 keV by electron beam lithography and deep
ion plasma etching methods. Various variants of compound zone plates with
first, second, third diffraction orders have been made. The zone relief height
is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The
experimental testing of the zone plates has been conducted on SPring-8 and ESRF
synchrotron radiation sources. A focused spot size and diffraction efficiency
measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first
order circular zone plate.",0503005v2
1997-10-09,A lattice field theoretical model for high-$T_c$ superconductivity,"We present a 2+1-dimensional lattice model for the copper oxide
superconductors and their parent compounds, in which both the charge and spin
degrees of freedom are treated dynamically. The spin-charge coupling parameter
is associated to the doping fraction in the cuprates. The model is able to
account for the various phases of the cuprates and their properties, not only
at low and intermediate doping but also for (highly) over-doped compounds. We
acquire a qualitative understanding of high-$T_c$ superconductivity as a
Bose-Einstein condensation of bound charge pairs.",9710035v1
1996-10-07,Small-x physics in perturbative QCD,"We review the parton model and the Regge approach to the QCD description of
the deep-inelastic $ep$ scattering at the small Bjorken variable $x$ and
demonstrate their relation with the DGLAP and BFKL evolution equations. It is
shown, that in the leading logarithmic approximation the gluon is reggeized and
the pomeron is a compound state of two reggeized gluons. The conformal
invariance of the BFKL pomeron in the impact parameter space is used to
investigate the scattering amplitudes at high energies and fixed momentum
transfers. The remarkable properties of the Schr\""odinger equation for compound
states of an arbitrary number of reggeized gluons in the multi-colour QCD are
reviewed. The gauge-invariant effective action describing the gluon-Reggeon
interactions is constructed. The known next-to-leading corrections to the QCD
pomeron are discussed.",9610276v1
1998-01-21,WKB quantization of reggeon compound states in high-energy QCD,"We study the spectrum of the reggeized gluon compound states in high-energy
QCD. The energy of the states depends on the total set of quantum numbers whose
values are constrained by the quantization conditions. To establish their
explicit form we apply the methods of nonlinear WKB analysis to the
Schr\""odinger equation for the $N$ reggeon state in the separated coordinates.
We solve the quantization conditions for the N=3 reggeon states in the leading
order of the WKB expansion and observe a good agreement of the obtained
spectrum of quantum numbers with available exact solutions.",9801377v1
2000-04-11,"Different Hagedorn temperatures for mesons and baryons from experimental mass spectra, compound hadrons, and combinatorial saturation","We analyze the light-flavor particle mass spectra and show that in the region
up to ~1.8GeV the Hagedorn temperature for baryons is about 30% smaller than
for mesons, reflecting the fact that the number of baryon states grows more
rapidly with the mass. We also show that the spectra are well reproduced in a
model where hadrons are compound objects of quanta, whose available number
increases with mass. The rapid growth of number of hadronic states is a
combinatorial effect. We also point out that an upper limit on the excitation
energy of these quanta results in a maximum number of hadron states that can be
formed. According to this combinatorial saturation, no more light-flavor hadron
resonances exist above a certain mass.",0004104v2
2003-06-25,Multi-reggeon compound states and resummed anomalous dimensions in QCD,"We perform the OPE analysis of the contribution of colour-singlet compound
states of reggeized gluons to a generic hard process in QCD and calculate the
spectrum of the corresponding higher twist anomalous dimensions in multi-colour
limit. These states govern high energy asymptotics of the structure functions
and their energies define the intercept of the Regge singularities both in the
Pomeron and the Odderon sectors. We argue that due to nontrivial analytical
properties of the energy spectrum, the twist expansion does not hold for the
gluonic states with the minimal energy generating the leading Regge
singularities. It is restored however after one takes into account the states
with larger energies whose contribution to the Regge asymptotics is subleading.",0306250v2
1996-09-16,Integrable structures and duality in high-energy QCD,"We study the properties of color-singlet Reggeon compound states in
multicolor high-energy QCD in four dimensions. Their spectrum is governed by
completely integrable (1+1)-dimensional effective QCD Hamiltonian whose
diagonalization within the Bethe Ansatz leads to the Baxter equation for the
Heisenberg spin magnet. We show that nonlinear WKB solution of the Baxter
equation gives rise to the same integrable structures as appeared in the
Seiberg-Witten solution for $N=2$ SUSY QCD and in the finite-gap solutions of
the soliton equations. We explain the origin of hyperelliptic Riemann surfaces
out of QCD in the Regge limit and discuss the meaning of the Whitham dynamics
on the moduli space of quantum numbers of the Reggeon compound states, QCD
Pomerons and Odderons.",9609123v1
2004-10-06,Strong memoryless times and rare events in Markov renewal point processes,"Let W be the number of points in (0,t] of a stationary finite-state Markov
renewal point process. We derive a bound for the total variation distance
between the distribution of W and a compound Poisson distribution. For any
nonnegative random variable \zeta, we construct a ``strong memoryless time''
\hat \zeta such that \zeta-t is exponentially distributed conditional on {\hat
\zeta\leq t, \zeta>t}, for each t. This is used to embed the Markov renewal
point process into another such process whose state space contains a frequently
observed state which represents loss of memory in the original process. We then
write W as the accumulated reward of an embedded renewal reward process, and
use a compound Poisson approximation error bound for this quantity by
Erhardsson. For a renewal process, the bound depends in a simple way on the
first two moments of the interrenewal time distribution, and on two constants
obtained from the Radon-Nikodym derivative of the interrenewal time
distribution with respect to an exponential distribution.
  For a Poisson process, the bound is 0.",0410166v1
2005-03-23,The disorder problem for compound Poisson processes with exponential jumps,"The problem of disorder seeks to determine a stopping time which is as close
as possible to the unknown time of ``disorder'' when the observed process
changes its probability characteristics. We give a partial answer to this
question for some special cases of Levy processes and present a complete
solution of the Bayesian and variational problem for a compound Poisson process
with exponential jumps. The method of proof is based on reducing the Bayesian
problem to an integro-differential free-boundary problem where, in some cases,
the smooth-fit principle breaks down and is replaced by the principle of
continuous fit.",0503481v1
2006-04-22,Moments of minors of Wishart matrices,"For a random matrix following a Wishart distribution, we derive formulas for
the expectation and the covariance matrix of compound matrices. The compound
matrix of order $m$ is populated by all $m\times m$-minors of the Wishart
matrix. Our results yield first and second moments of the minors of the sample
covariance matrix for multivariate normal observations. This work is motivated
by the fact that such minors arise in the expression of constraints on the
covariance matrix in many classical multivariate problems.",0604488v2
2007-02-01,On Stein's method and perturbations,"Stein's (1972) method is a very general tool for assessing the quality of
approximation of the distribution of a random element by another, often
simpler, distribution. In applications of Stein's method, one needs to
establish a Stein identity for the approximating distribution, solve the Stein
equation and estimate the behaviour of the solutions in terms of the metrics
under study. For some Stein equations, solutions with good properties are
known; for others, this is not the case. Barbour and Xia (1999) introduced a
perturbation method for Poisson approximation, in which Stein identities for a
large class of compound Poisson and translated Poisson distributions are viewed
as perturbations of a Poisson distribution. In this paper, it is shown that the
method can be extended to very general settings, including perturbations of
normal, Poisson, compound Poisson, binomial and Poisson process approximations
in terms of various metrics such as the Kolmogorov, Wasserstein and total
variation metrics. Examples are provided to illustrate how the general
perturbation method can be applied.",0702008v1
2000-08-28,Resonantly Forced Inhomogeneous Reaction-Diffusion Systems,"The dynamics of spatiotemporal patterns in oscillatory reaction-diffusion
systems subject to periodic forcing with a spatially random forcing amplitude
field are investigated. Quenched disorder is studied using the resonantly
forced complex Ginzburg-Landau equation in the 3:1 resonance regime. Front
roughening and spontaneous nucleation of target patterns are observed and
characterized. Time dependent spatially varying forcing fields are studied in
the 3:1 forced FitzHugh-Nagumo system. The periodic variation of the spatially
random forcing amplitude breaks the symmetry among the three quasi-homogeneous
states of the system, making the three types of fronts separating phases
inequivalent. The resulting inequality in the front velocities leads to the
formation of ``compound fronts'' with velocities lying between those of the
individual component fronts, and ``pulses'' which are analogous structures
arising from the combination of three fronts. Spiral wave dynamics is studied
in systems with compound fronts.",0008035v2
2001-08-03,Light charged particle evaporation from hot ${31}^$P nucleus at E$^*$ ~ 60 MeV,"The energy spectra of evaporated light charged particles (LCP) $\alpha$, p, d
and t have been measured in $7^$Li(47 MeV) + ${24}^$Mg and ${19}^$F(96 MeV)+
${12}^$C reactions. Both the systems populate the same compound nucleus
${31}^$F at excitation energy E$^*$ ~ 60 MeV. It has been observed that the
light particle spectra obtained in Li + Mg reaction follow standard statistical
model prediction, whereas a deformed configuration of the compound nucleus is
needed to explain the LCP spectra for F + C reaction, which has been attributed
to the effect of larger input angular momentum in the case of ${19}^$F(96 MeV)+
${12}^$C system.",0108004v2
2002-09-12,Liquid-vapor phase transition in nuclei or compound nucleus decay?,"Recent analyses of multifragmentation in terms of Fisher's model and the
related construction of a phase diagram brings forth the problem of the true
existence of the vapor phase and the meaning of its associated pressure. Our
analysis shows that a thermal emission picture is equivalent to a Fisher-like
equilibrium description which avoids the problem of the vapor and explains the
recently observed Boltzmann-like distribution of the emission times. In this
picture a simple Fermi gas thermometric relation is naturally justified. Low
energy compound nucleus emission of intermediate mass fragments is shown to
scale according to Fisher's formula and can be simultaneously fit with the much
higher energy ISiS multifragmentation data.",0209009v1
2004-12-20,Study of Deformation Effects in the Charged Particle Emission from 46Ti,"The 46Ti compound nucleus, as populated by the fusion-evaporation reaction
27Al + 19F at the bombarding energy of 144 MeV, has been investigated by
charged particle spectroscopy using the multidetector array ICARE at the
VIVITRON tandem facility of the IReS (Strasbourg). The light charged particles
have been measured in coincidence with evaporation residues. The CACARIZO code,
a Monte Carlo implementation of the statistical-model code CASCADE, has been
used to calculate the spectral shapes of evaporated alpha-particles which are
compared with the experimental spectra. This comparison indicates the possible
signature of large deformations of the compound nucleus.",0412042v1
2005-08-09,Probable Level Densities and Radiative Strength Functions of Dipole gamma-Transitions in 57Fe Compound Nucleus,"From the published results of experimental research of 56Fe(n,2gamma)
reaction carried out in Budapest, the values of the most probable densities of
cascade intermediate levels with 1/2, 3/2 spin and radiative strength functions
of cascade E1 and M1 transitions in 57Fe compound nucleus have been determined.
These results correspond to analogous data for other nuclei studied by us and
contradict to predictions of conventional models.",0508007v1
2005-11-08,Parameters of the 125Te compound state cascade gamma-decay,"Reliable information on level density and radiative strength functions for
the excitation energy region with density of excited states more than 100
levels per 1 MeV and higher can be obtained now only by its model-free
extraction from intensities of two-step cascades proceeding between compound
states and few low-lying levels. Full model-free determination of these
parameters in any method is possible only if one can extract from additional
experimental information about general trend in dependence of ratio of strength
functions of emitted reaction products of a given type on excitation energy of
the nucleus under study. Analysis of the available experimental data for 125Te
shows that the peculiarities observed earlier in other nuclei are also inherent
to this nucleus.",0511017v1
2006-03-03,Tracing the evolution of the symmetry energy of hot nuclear fragments from the compound nucleus towards multifragmentation,"The evolution of the symmetry energy coefficient of the binding energy of hot
fragments with increasing excitation is explored in multifragmentation
processes following heavy-ion collisions below the Fermi energy. In this work,
high-resolution mass spectrometric data on isotopic distributions of
projectile-like fragments from collisions of 25 MeV/nucleon 86Kr and 64Ni beams
on heavy neutron-rich targets are systematically compared to calculations
involving the Statistical Multifragmentation Model. The study reveals a gradual
decrease of the symmetry energy coefficient from 25 MeV at the compound nucleus
regime (E*/A < 2 MeV) towards 15 MeV in the bulk multifragmentation regime
(E*/A > 4 MeV). The ensuing isotopic distributions of the hot fragments are
found to be very wide and extend towards the neutron drip-line. These findings
may have important implications to the composition and evolution of hot
astrophysical environments, such as core-collapse supernova.",0603006v3
2006-08-04,Deformation Effects in Hot Rotating 46Ti Probed by the Charged Particle Emission and GDR gamma-Decay,"The 46Ti* compound nucleus, as populated by the fusion-evaporation reaction
27Al+19F at the bombarding energy of E_lab=144 MeV, has been investigated by
charged particle spectroscopy using the multidetector array ICARE at the
VIVITRON tandem facility of the IReS (Strasbourg). The light charged particles
and high-energy gamma-rays from the GDR decay have been measured in coincidence
with selected evaporation residues. The CACARIZO code, a Monte Carlo
implementation of the statistical-model code CASCADE, has been used to
calculate the spectral shapes of evaporated alpha-particles which are compared
with the experimental coincident spectra. This comparison indicates the
signature of large deformations (possibly superdeformed and hyperdeformed
shapes) present in the compound nucleus decay. The occurrence of the Jacobi
shape transition is also discussed in the framework of a newly developed
rotating liquid drop model.",0608011v1
1995-11-29,Limits of Time-Reversal Violating Interaction from Compound Nuclear Experiments,"Mean square matrix elements of the time reversal invariance violating (TRIV)
interaction between the compound nuclear states are calculated within the
statistical model, using the explicit form of the TRIV interaction via the
$\rho$-meson exchange. From the comparison of the calculated values with the
data known for $p+ ^{27}Al \Leftrightarrow ^{24}Mg + \alpha$ reaction, and for
$\gamma$-correlation measurements in $^{113}Cd(n,\gamma)^{114}Cd$ process, the
bounds on the TRIV constant are obtained ${\bar g}_{\rho} \alt 1.8 \times
10^{-2}$ and ${\bar g}_{\rho} \alt 1.1 \times 10^{-2}$. The sensitivity of the
recently proposed detailed balance test experiments on isolated resonances in
$^{32}S$ to the value of ${\bar g}_{\rho}$ is shown to be as high as to reach
values ${\bar g}_{\rho} \sim 10^{-4}$.",9511035v1
1996-07-29,Behavior of the giant-dipole resonance in $^{120}$Sn and $^{208}$Pb at high excitation energ,"The properties of the giant-dipole resonance (GDR) are calculated as a
function of excitation energy, angular momentum, and the compound nucleus
particle decay width in the nuclei $^{120}$Sn and $^{208}$Pb, and are compared
with recent experimental data. Differences observed in the behavior of the
full-width-at-half-maximum of the GDR for $^{120}$Sn and $^{208}$Pb are
attributed to the fact that shell corrections in $^{208}$Pb are stronger than
in $^{120}$Sn, and favor the spherical shape at low temperatures. The effects
shell corrections have on both the free energy and the moments of inertia are
discussed in detail. At high temperature, the FWHM in $^{120}$Sn exhibits
effects due to the evaporation width of the compound nucleus, while these
effects are predicted for $^{208}$Pb.",9607057v1
1997-04-24,A Simple Mode on a Highly Excited Background: Collective Strength and Damping in the Continuum,"Simple states, such as isobaric analog states or giant resonances, embedded
into continuum are typical for mesoscopic many-body quantum systems. Due to the
coupling to compound states in the same energy range, a simple mode acquires a
damping width (""internal"" dynamics). When studied experimentally with the aid
of various reactions, such states reveal enhanced cross sections in specific
channels at corresponding resonance energies (""external"" dynamics which include
direct decay of a simple mode and decays of intrinsic compound states through
their own channels). We consider the interplay between internal and external
dynamics using a general formalism of the effective nonhermitian hamiltonian
and looking at the situation both from ""inside"" (strength functions and
spreading widths) and from ""outside"" (S-matrix, cross sections and delay
times). The restoration of isospin purity and disappearance of the collective
strength of giant resonances at high excitation energy are discussed as
important particular manifestations of this complex interplay.",9704055v1
1997-07-07,Fission and cluster decay of $^{76}$Sr nucleus in the ground-state and formed in heavy-ion reactions,"Calculations for fission and cluster decay of $^{76}Sr$ are presented for
this nucleus to be in its ground-state or formed as an excited compound system
in heavy-ion reactions. The predicted mass distribution, for the dynamical
collective mass transfer process assumed for fission of $^{76}Sr$, is clearly
asymmetric, favouring $\alpha $-nuclei. Cluster decay is studied within a
preformed cluster model, both for ground-state to ground-state decays and from
excited compound system to the ground-state(s) or excited states(s) of the
fragments.",9707013v1
1998-10-23,Restoration of Isospin Symmetry in Highly Excited Nuclei,"Explicit relations between the isospin mixing probability, the spreading
width $\Gamma_{IAS}^{\downarrow}$ of the Isobaric Analog State (IAS) and the
statistical decay width $\Gamma_c$ of the compound nucleus at finite excitation
energy, are derived by using the Feshbach projection formalism. The temperature
dependence of the isospin mixing probability is discussed quantitatively for
the first time by using the values of $\Gamma_{IAS}^{\downarrow}$ and of
$\Gamma_c$ calculated by means of microscopic models. It is shown that the
mixing probability remains essentially constant up to a temperature of the
order of 1 MeV and then decreases to about 1/4 of its zero temperature value,
at higher temperature than $\approx$ 3 MeV, due to the short decay time of the
compound system.",9810062v1
1999-11-16,Statistical Theory of Parity Nonconservation in Compound Nuclei,"We present the first application of statistical spectroscopy to study the
root-mean-square value of the parity nonconserving (PNC) interaction matrix
element M determined experimentally by scattering longitudinally polarized
neutrons from compound nuclei. Our effective PNC interaction consists of a
standard two-body meson-exchange piece and a doorway term to account for
spin-flip excitations. Strength functions are calculated using realistic
single-particle energies and a residual strong interaction adjusted to fit the
experimental density of states for the targets, ^{238} U for A\sim 230 and
^{104,105,106,108} Pd for A\sim 100. Using the standard Desplanques, Donoghue,
and Holstein estimates of the weak PNC meson-nucleon coupling constants, we
find that M is about a factor of 3 smaller than the experimental value for
^{238} U and about a factor of 1.7 smaller for Pd. The significance of this
result for refining the empirical determination of the weak coupling constants
is discussed.",9911057v2
2001-04-10,Gamma-ray strength functions in thermally excited rotating nuclei,"A general discussion and illustration is given of strength functions for
rotational transitions in two-dimensional E(gamma_1) x E(gamma_2) spectra.
Especially, a narrow component should be proportional to the compound damping
width, related to the mixing of basis rotational bands into compound bands with
fragmented transition strength. Three E(gamma_1) x E(gamma_2) spectra are made
by setting gates on triple coincidences, selecting cascades which feed into
specific low-lying bands in the nucleus 168Hf. In each of the gated spectra, we
find a ridge, carrying about 100 decay paths. This ridge is ascribed to
rotational transitions in the excitation energy range of 1.0 to 1.5 MeV above
the yrast line. The FWHM of the ridges are around 40 keV, about a factor of two
smaller than calculated on the basis of mixed cranked mean field bands.",0104034v1
2001-05-04,Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission,"A theoretical model of one-body nuclear friction which was developed earlier,
namely the chaos-weighted wall formula, is applied to a dynamical description
of compound nuclear decay in the framework of the Langevin equation coupled
with statistical evaporation of light particles and photons. We have used both
the usual wall formula friction and its chaos-weighted version in the Langevin
equation to calculate the fission probability and prescission neutron
multiplicity for the compound nuclei $^{178}$W, $^{188}$Pt, $^{200}$Pb,
$^{213}$Fr, $^{224}$Th, and $^{251}$Es. We have also obtained the contributions
of the presaddle and postsaddle neutrons to the total prescission multiplicity.
A detailed analysis of our results leads us to conclude that the chaos-weighted
wall formula friction can adequately describe the fission dynamics in the
presaddle region. This friction, however, turns out to be too weak to describe
the postsaddle dynamics properly. This points to the need for a suitable
explanation for the enhanced neutron emission in the postsaddle stage of
nuclear fission.",0105010v2
2003-02-07,Dynamics of many-particle fragmentation in a Cellular Automaton model,"A 3D Cellular Automaton model developed by the authors to deal with the
dynamics of N-body interactions has been adapted to investigate the head-on
collision of two identical bound clusters of particles, and the ensuing process
of fragmentation. The range of impact energies is chosen low enough, to secure
that a compound bound cluster can be formed. The model is devised to simulate
the laboratory set-up of fragmentation experiments as monitored by 4pi
detectors. The particles interact via a Lennard-Jones potential. At low impact
energies the numerical experiments following the dynamics of the individual
particles indicate a phase of energy sharing among all the particles of the
compound cluster. Fragments of all sizes are then found to evaporate from the
latter cluster. The cluster sizes, measured in our set-up by simulated 4pi
detectors, conform to a power law of exponent around 2.6.",0302016v1
2004-02-12,Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei,"The study of five-fold (P even, T odd) correlation in the interaction of slow
polarized neutrons with aligned nuclei is a possible way of testing the time
reversal invariance due to the expected enhancement of T violating effects in
compound resonances. Possible nuclear targets are discussed which can be
aligned both dynamically as well as by the ""brute force"" method at low
temperature. A statistical estimation is performed of the five-fold correlation
for low lying p wave compound resonances of the $^{121}$Sb, $^{123}$Sb and
$^{127}$I nuclei. It is shown that a significant improvement can be achieved
for the bound on the intensity of the fundamental parity conserving time
violating (PCTV) interaction.",0402043v3
2001-12-20,A Study of Polycarbonyl Compounds in Magnegases,"In this paper we study the structure and thermochemical properties of some
new polycarbonyl compounds, with particular attention devoted to the study of
(CO)$_n$ complexes, which are expected to be present in magnegases^TM. The
latter are anomalous gases produced by Hadronic Reactors^TM of molecular type
[2] (Patented and International Patents Pending) which expose atoms to the
extremely intense electronmagnetic fields existing at atomic distances from
electric arcs in such a way to create a toroidal distribution of the orbitals
of individual atoms, whether isolated or part of a valence bond. Polarized
atoms, dimers and molecules then attract each other via opposing magnetic
polarities resulting into stable clusters which constitute a new chemical
species called Santilli's magnecules [2]. Some of the numerous open problems in
the study of this intriguing new chemical species are pointed out.",0112068v1
2002-09-09,Accuracy and efficiency of modern methods for electronic structure calculation on heavy- and superheavy-element compounds,"The methods which are actively used for electronic structure calculations of
low-lying states of heavy- and superheavy-element compounds are briefly
described. The advantages and disadvantages of calculations with the
Dirac-Coulomb-Breit Hamiltonian, Huzinaga-type pseudopotential,
shape-consistent Relativistic Effective Core Potential (RECP) and Generalized
RECP are discussed. The nonvariational technique of the electronic structure
restoration in atomic cores after the RECP calculation of a molecule is
presented. The features of some approaches accounting for electron correlation,
the configuration interaction and coupled cluster methods, are also described.
The results of calculations on E113, E114, U and other heavy-atom systems are
presented.",0209035v2
2003-10-02,Multilevel Clustering Fault Model for IC Manufacture,"A hierarchical approach to the construction of compound distributions for
process-induced faults in IC manufacture is proposed. Within this framework,
the negative binomial distribution is treated as level-1 models. The
hierarchical approach to fault distribution offers an integrated picture of how
fault density varies from region to region within a wafer, from wafer to wafer
within a batch, and so on. A theory of compound-distribution hierarchies is
developed by means of generating functions. A study of correlations, which
naturally appears in microelectronics due to the batch character of IC
manufacture, is proposed. Taking these correlations into account is of
significant importance for developing procedures for statistical quality
control in IC manufacture. With respect to applications, hierarchies of yield
means and yield probability-density functions are considered.",0310012v1
2005-05-25,Interrelation of work function and surface stability: the case of BaAl4,"The relationship between the work function (Phi) and the surface stability of
compounds is, to our knowledge, unknown, but very important for applications
such as organic light-emitting diodes. This relation is studied using
first-principles calculations on various surfaces of BaAl4. The most stable
surface [Ba terminated (001)] has the lowest Phi (1.95 eV), which is lower than
that of any elemental metal including Ba. Adding barium to this surface neither
increases its stability nor lowers its work function. BaAl4 is also strongly
bound. These results run counter to the common perception that stability and a
low Phi are incompatible. Furthermore, a large anisotropy and a stable
low-work-function surface are predicted for intermetallic compounds with polar
surfaces.",0505176v1
2005-07-14,Phase resonances in obliquely illuminated compound gratings,"The existence of phase resonances in obliquely illuminated, perfectly
conducting compound gratings is investigated. The diffraction problem of a
p-polarized plane wave impinging on the structure is solved using the modal
approach. The results show that even under oblique illumination, where no
symmetry is imposed by the incident field, there are resonant wavelengths that
are clearly associated with a certain degree of symmetry in the phase
distribution of the magnetic field inside the cavities. New configurations of
this phase distribution take place, that were not allowed under normal
incidence conditions. It was found that the interior field is intensified in
the resonances, and the specularly reflected efficiency is maximized. In
particular, this efficiency is optimized for Littrow mount.",0507113v1
1995-11-20,Localisation and Nonlocality in Compound Energy-Momentum Eigenstates,"A thought experiment considering conservation of energy and momentum for a
pair of free bodies together with their internal energy is used to show the
existence of states that have localised position while being eigenstates of
energy and momentum. These states are applicable to all varieties of physical
bodies, including planets and stars in free motion in the universe. The states
are compound entanglements of multiple free bodies in which the momenta of the
bodies are anticorrelated so that they always sum to zero, while their total
kinetic energy is anticorrelated with their internal energies, so the total is
a constant, E. The bodies are relatively localised while the total state has
well-defined energy and momentum. These states do not violate Heisenberg
uncertainty because the total centre of mass is not localised, hence the states
naturally describe whole universes rather than isolated systems within a
universe. A further property of these states, resulting from the form of the
entanglement, is that they display nonlocality in the full sense of signal
transmission rather than the more restricted Bell sense.",9511023v1
1999-07-26,New Treatment of Systems of Compounded Angular Momentum,"The approach to quantum mechanics which we have used to derive the matrix
treatment of spin from first principles is now employed to treat systems of
compounded angular momentum. A general treatment is first given, which is then
applied to the concrete cases of a spin-0 and a spin-1 system obtained by
adding the spins of two spin-1/2 systems. Thus the probability amplitudes for
measurements on the systems are derived, as well as the matrix vectors and
operators corresponding to the systems. The matrix operators and states
obtained are different from the standard forms and are much more generalized.
The new results are applied to the case of joint measurements on the subsystems
of such a system; this is a problem that has been made very topical by the high
level of interest in the foundations of quantum mechanics. As a consequence of
the insights arising from this treatment, we show that the Clebsch-Gordan
coefficients are amenable to generalization, and we give the generalized forms
for these cases.",9907082v3
2000-03-15,Derivation of Standard Treatment of Spin Addition From Probability Amplitudes,"In a recent paper, we introduced a new way of treating systems of compounded
angular momentum. We obtained the probability amplitudes for measurements on
the systems and used these to derive the matrix treatment of compounded spin.
However, the matrix forms are in 3- and 4- dimensional space and are therefore
entirely different from the standard forms. This raises the question of the
connection between these forms and the standard forms. In this paper, we answer
this question. We not only derive the standard matrix treatment of spin
addition - we discover a more generalized form of the theory. We apply the new
generalized theory to the singlet and triplet states arising from the addition
of the spins of two systems of spin 1/2 each. We obtain new generalized forms
of the vectors and operators for these cases, and show that they reduce to the
standard forms in the appropriate limit.",0003056v1
2002-05-26,The Linearity of Quantum Mechanics at Stake: The Description of Separated Quantum Entities,"We consider the situation of a physical entity that is the compound entity
consisting of two 'separated' quantum entities. In earlier work it has been
proven by one of the authors that such a physical entity cannot be described by
standard quantum mechanics. More precisely, it was shown that two of the axioms
of traditional quantum axiomatics are at the origin of the impossibility for
standard quantum mechanics to describe this type of compound entity. One of
these axioms is equivalent with the superposition principle, which means that
separated quantum entities put the linearity of quantum mechanics at stake. We
analyze the conceptual steps that are involved in this proof, and expose the
necessary material of quantum axiomatics to be able to understand the argument",0205162v1
2002-05-26,Linearity and Compound Physical Systems: The Case of Two Separated Spin 1/2 Entities,"We illustrate some problems that are related to the existence of an
underlying linear structure at the level of the property lattice associated
with a physical system, for the particular case of two explicitly separated
spin 1/2 objects that are considered, and mathematically described, as one
compound system. It is shown that the separated product of the property
lattices corresponding with the two spin 1/2 objects does not have an
underlying linear structure, although the property lattices associated with the
subobjects in isolation manifestly do. This is related at a fundamental level
to the fact that separated products do not behave well with respect to the
covering law (and orthomodularity) of elementary lattice theory. In addition,
we discuss the orthogonality relation associated with the separated product in
general and consider the related problem of the behavior of the corresponding
Sasaki projections as partial state space mappings",0205166v1
2006-06-12,Entangled spin clusters: some special features,"In this paper, we study three specific aspects of entanglement in small spin
clusters. We first study the effect of inhomogeneous exchange coupling strength
on the entanglement properties of the S=1/2 antiferromagnetic linear chain
tetramer compound NaCuAsO_{4}. The entanglement gap temperature, T_{E}, is
found to have a non-monotonic dependence on the value of $\alpha$, the exchange
coupling inhomogeneity parameter. We next determine the variation of T_{E} as a
function of S for a spin dimer, a trimer and a tetrahedron. The temperature
T_{E} is found to increase as a function of S, but the scaled entanglement gap
temperature t_{E} goes to zero as S becomes large. Lastly, we study a spin-1
dimer compound to illustrate the quantum complementarity relation. We show that
in the experimentally realizable parameter region, magnetization and
entanglement plateaus appear simultaneously at low temperatures as a function
of the magnetic field. Also, the sharp increase in one quantity as a function
of the magnetic field is accompanied by a sharp decrease in the other so that
the quantum complementarity relation is not violated.",0606095v1
2006-11-07,On the Physical Interpretation of Partial Traces: Two Nonstandard Viewpoints,"Mixed states are introduced in physics in order to express our ignorance
about the actual state of a physical system and are represented in standard
quantum mechanics (QM) by density operators. Such operators also appear if one
considers a (pure) entangled state of a compound system $\Omega$ and performs
partial traces on the projection operator representing it. Yet, they do not
represent mixed states (or proper mixtures) of the subsystems in this case, but
improper mixtures, since the coefficients in the convex sums expressing them
never bear the ignorance interpretation. Hence, one cannot attribute states to
the subsystems of a compound physical system in QM (subentity problem). We
discuss here two alternative proposals that can be worked out within the
Brussels and Lecce approaches. We firstly summarize the general framework
provided by the former, which suggests that improper mixtures could be
considered as new pure states. Then, we show that improper mixtures can be
considered as true (yet nonpure) states also according to the latter. The two
proposals seem to be compatible notwithstanding their different terminologies.",0611072v2
2007-04-17,CeRuPO: A rare example of a Ferromagnetic Kondo lattice,"We have determined the physical ground state properties of the compounds
CeRuPO and CeOsPO by means of magnetic susceptibility chi(T), specific heat
C(T), electrical resistivity rho(T), and thermopower S(T) measurements. chi(T)
reveals a trivalent 4f1 cerium state in both compounds. For CeRuPO a pronounced
decrease of rho(T) below 50K indicates the onset of coherent Kondo scattering
which is confirmed by enhanced S(T). The temperature and magnetic field
dependence of chi(T) and C(T) evidence ferromagnetic (FM) order at TC=15K.
Thus, CeRuPO seems to be one of the rare example of a FM Kondo lattice. In
contrast, CeOsPO shows antiferromagnetic order at TN=4.4K despite only minor
changes in lattice parameters and electronic configuration. Additional 31P NMR
results support these scenarios. LSDA+U calculations evidence a quasi two
dimensional electronic band structure, reflecting a strong covalent bonding
within the CeO and RuP layers and a weak ionic like bonding between the layers.",0704.2170v2
2007-05-01,Effect of a small disruption of the Ca site on the geometrically frustrated magnetic behavior of Ca3CoRhO6,"The compound, Ca3CoRhO6, containing magnetic Co-Rh chains intervened by Ca
ions, has been known to be one of the few exhibiting partially disordered
antiferromagnetic structure (PDA) due to geometrical frustration. Here, we
report the influence of partial replacement of Ca by Y on the magnetic
anomalies by investigating the solid solution, Ca(3-x)Y(x)CoRhO6 by bulk
measurements. There are profound changes in the magnetic behavior, the most
notable one being that the features attributable to spin-chain magnetism and
PDA structure get suppressed dramatically by a small replacement of Ca by Y (x=
0.15), despite the fact that the magnetic chain is not disrupted. This finding
suggests that this compound is on the verge of PDA-structural-instability.",0705.0137v1
2007-05-10,Uniform Mixing of Antiferromagnetism and High-Tc Superconductivity in Electron-doped Layers in Four-layered Ba2Ca3Cu4O8F2 : A New Phenomenon in an Electron Underdoped RegimePhenomenon in an Electron Underdoped Regime,"We report Cu- and F-NMR studies on a four-layered high-temperature
superconductor Ba2Ca3Cu4O8F2(0234F(2.0)) with apical fluorine (F-1), an undoped
55 K-superconductor with a nominal Cu2+ valence on average. We reveal that this
compound exhibits the antiferromagnetism (AFM) with a Neel temperature TN=100 K
despite being a Tc= 55 K-superconductor. Through a comparison with a related
tri-layered cuprate Ba2Ca2Cu3O6F2 (0223F(2.0)), it is demonstrated that
electrons are transferred from the inner plane (IP) to the outer plane (OP) in
0234F(2.0) and 0223F(2.0), confirming the self-doped high-temperature
superconductivity (HTSC) having electron and hole doping in a single compound.
Remarlably, uniform mixing of AFM and HTSC takes place in both the
electron-doped OPs and the hole-doped IPs in 0234F(2.0).",0705.1472v2
2007-05-22,Magnetocaloric effect in the frustrated square lattice J1-J2 model,"We investigate the magnetocaloric properties of the two-dimensional
frustrated J1-J2 model on a square lattice. This model describes well the
magnetic behavior of two classes of quasi-two-dimensional S = 1/2 vanadates,
namely the Li2VOXO4 (X = Si, Ge) and AA'VO(PO4)2 (A, A' = Pb, Zn, Sr, Ba)
compounds. The magnetocaloric effect (MCE) consists in the adiabatic
temperature change upon changing the external magnetic field. In frustrated
systems, the MCE can be enhanced close to the saturation field because of
massive degeneracies among low lying excitations. We discuss results for the
MCE in the two distinct antiferromagnetic regimes of the phase diagram.
Numerical finite temperature Lanczos as well as analytical methods based on the
spin wave expansion are employed and results are compared. We give explicit
values for the saturation fields of the vanadium compounds. We predict that at
subcritical fields there is first a (positive) maximum followed by sign change
of the MCE, characteristic of all magnetically ordered phases.",0705.3094v2
2007-06-09,"Superconducting behavior of the solid solution, Y2Pd(1-x)Pt(x)Ge3","The compound Y2PdGe3 was earlier reported by us to be one of the very few
ternary superconducting compounds (T_c= 3 K) belonging to the same structure as
that of MgB2. Here we report the results of electrical resistivity,
magnetization and heat capacity measurements at low temperatures on the solid
solution with a nominal starting composition, Y2Pd(1-x)Pt(x)Ge3, to understand
the influence of gradual replacement of Pd by Pt on T_c. The superconducting
properties of this solution is distinctly interesting in the sense that the Tc
varies monotonically with increasing x in sharp contrast to the non-monotonic
variation for other isostructural solid solutions reported recently.",0706.1309v2
2007-06-13,Electronic band structure and carrier effective mass in calcium aluminates,"First-principles electronic band structure investigations of five compounds
of the CaO-Al2O3 family, 3CaO.Al2O3, 12CaO.7Al2O3, CaO.Al2O3, CaO.2Al2O3 and
CaO.6Al2O3, as well as CaO and alpha-, theta- and kappa-Al2O3 are performed. We
find that the conduction band in the complex oxides is formed from the oxygen
antibonding p-states and, although the band gap in Al2O3 is almost twice larger
than in CaO, the s-states of both cations. Such a hybrid nature of the
conduction band leads to isotropic electron effective masses which are nearly
the same for all compounds investigated. This insensitivity of the effective
mass to variations in the composition and structure suggests that upon a proper
degenerate doping, both amorphous and crystalline phases of the materials will
possess mobile extra electrons.",0706.1986v1
2007-06-14,Thermal stability of n-dodecane : experiments and kinetic modelling,"The thermal decomposition of n-dodecane, a component of some jet fuels, has
been studied in a jet-stirred reactor at temperatures from 793 to 1093 K, for
residence times between 1 and 5 s and at atmospheric pressure. Thermal
decomposition of hydrocarbon fuel prior the entrance in the combustion chamber
is an envisaged way to cool the wall of hypersonic vehicles. The products of
the reaction are mainly hydrogen, methane, ethane, 1,3-butadiene and 1-alkenes
from ethylene to 1-undecene. For higher temperatures and residence times
acetylene, allene, propyne, cyclopentene, 1,3-cyclopentadiene and aromatic
compounds from benzene to pyrene through naphthalene have also been observed. A
previous detailed kinetic model of the thermal decomposition of n-dodecane
generated using EXGAS software has been improved and completed by a
sub-mechanism explaining the formation and the consumption of aromatic
compounds.",0706.2058v1
2007-07-10,Spin and orbital magnetic response in metals: susceptibility and NMR shifts,"A DFT-based method is presented which allows the computation of all-electron
NMR shifts of metallic compounds with periodic boundary conditions. NMR shifts
in metals measure two competing physical phenomena. Electrons interact with the
applied magnetic field (i) as magnetic dipoles (or spins), resulting in the
Knight shift, (ii) as moving electric charges, resulting in the chemical (or
orbital) shift. The latter is treated through an extension to metals of the
Gauge Invariant Projector Augment Wave(GIPAW) developed for insulators. The
former is modeled as the hyperfine interaction between the electronic spin
polarization and the nuclear dipoles. NMR shifts are obtained with respect to
the computed shieldings of reference compounds, yielding fully ab-initio
quantities which are directly comparable to experiment. The method is validated
by comparing the magnetic susceptibility of interacting and non-interacting
homogeneous gas with known analytical results, and by comparing the computed
NMR shifts of simple metals with experiment.",0707.1531v1
2007-07-17,Rare-Earth Tetraborides RB$_4$: Analysis of Trends in the Electronic Structure,"Both the basic electronic structure of tetraborides, and the changes across
the lanthanide series in $R$B$_4$ ($R$ = rare earth) compounds, are studied
using the correlated band theory LDA+U method in the all-electron Full
Potential Local Orbital (FPLO) code. A set of boron bonding bands can be
identified that are well separated from the antibonding bands. Separately, the
``dimer B'' $2p_z$ orbital is non-bonding ({\it viz.} graphite and MgB$_2$),
and mixes strongly with the metal 4d or $5d$ states that form the conduction
states. The bonding bands are not entirely filled even for the trivalent
compounds (thus the cation $d$ bands have some filling), which accounts for the
lack of stability of this structure when the cations are divalent (with more
bonding states unfilled). The trends in the mean $4f$ level for both majority
and minority, and occupied and unoccupied, states are presented and
interpreted.",0707.2415v1
2007-07-25,Theory of Ultrasonic Dispersion in Local Phonon Systems Coupled with Conduction Electrons,"The physical origin of frequency dependence in elastic constants, which are
often found in an ultrasound propagation in filled skutterudites and clathrate
compounds, is investigated theoretically. This dependence arises from a
coupling between the acoustic phonon and some optical phonons, which strongly
interact with electrons. Using a self-consistent ladder approximation together
with a pseudofermion mapping of the phonon to the single site Holstein Anderson
model, a soft mode of the optical phonon at zero frequency is shown to emerge.
The temperature dependence of the spectral weight of this soft mode shows an
activation-type behavior, which is characterized by the optical phonon
frequency. These features can generate the frequency dependence and the
shoulder in the elastic constants observed in some filled skutterudites and
clathrate compounds.",0707.3683v1
2007-08-15,Optical Birefringence and Domain Structure of the as-grown Rb2xTl2(1-x)Cd2(SO4)3 Solid Solutions at Phase Transitions,"It is shown that the as-grown solid solutions Tl2xRb2(1-x)Cd2(SO4)3 possess a
residual optical birefringence in the cubic phase at room temperature. The
existence of both the residual birefringence and the residual domain structure
in the compound with x=0.8 at the room temperature, along with the domain walls
orientation and the orientation of extinction positions of the neighbouring
domains, indicate that the above domain structure corresponds to ""forbidden""
ferroelastic domains of the phase P212121. On the basis of measurements for the
temperature variation of the birefringence and observations of the domain
structure transformations, one can conclude that the phases with the symmetries
P213 and P21 coexist above Tc1 in the compounds with x = 0.7 - 1.0. The phase
transition temperatures Tc1, Tc2, and Tc3 obtained from the temperature
birefringence variations agree well with those obtained previously, using the
studies of thermal expansion and ultrasonic wave velocities.",0708.2027v1
2007-08-17,Comparative study of electron and hole doped High-Tc compounds in pseudogap regime: LDA+DMFT+Sk approach,"Pseudogap regime for the prototype high-Tc compounds hole doped
Bi2Sr2CaCu2O8-x (Bi2212) and electron doped Nd2-xCexCuO4 (NCCO) is described by
means of novel generalized LDA+DMFT+Sk approach. Here conventional dynamical
mean-field theory (DMFT) equations are supplied with additional (momentum
dependent) self-energy Sk. In the present case Sk describes non-local dynamical
correlations induced by short-ranged collective Heisenberg-like
antiferromagnetic spin fluctuations. Material specific model parameters of two
neighboring CuO2 layers of Bi2212 and single CuO2 layer of NCCO were obtained
within local density approximation (LDA) and constrained LDA method. We show
that Fermi surface in presence of the pseudogap fluctuations have perfectly
visible ""hot-spots"" for NCCO while in Bi2212 there is just rather broad region
with strong antiferromagnetic scattering. Results obtained are in good
agreement with recent ARPES and optical experiments.",0708.2313v2
2007-08-21,Magnons in Ferromagnetic Metallic Manganites,"Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of
special interest not only because they are a testing ground of the classical
doubleexchange interaction mechanism for the colossal magnetoresistance, but
also because they exhibit an extraordinary arena of emergent phenomena. These
emergent phenomena are related to the complexity associated with strong
interplay between charge, spin, orbital, and lattice. In this review, we focus
on the use of inelastic neutron scattering to study the spin dynamics, mainly
the magnon excitations in this class of FM metallic materials. In particular,
we discussed the unusual magnon softening and damping near the Brillouin zone
boundary in relatively narrow band compounds with strong Jahn-Teller lattice
distortion and charge/orbital correlations. The anomalous behaviors of magnons
in these compounds indicate the likelihood of cooperative excitations involving
spin, lattice, as well as orbital degrees of freedom.",0708.2891v1
2007-08-21,Structure-Activity Relationship Investigation of Some New Tetracyclines by Electronic Index Methodology,"Tetracyclines are an old class of molecules that constitute a broad-spectrum
antibiotics. Since the first member of tetracycline family were isolated, the
clinical importance of these compounds as therapeutic and prophylactic agents
against a wide range of infections has stimulated efforts to define their mode
of action as inhibitors of bacterial reproduction. We used three SAR
methodologies for the analysis of biological activity of a set of 104
tetracycline compounds. Our calculation were carried out using the
semi-empirical Austin Method One (AM1) and Parametric Method 3 (PM3).
Electronic Indices Methodology (EIM), Principal Component Analysis (PCA) and
Artificial Neural Networks (ANN) were applied to the classification of 14 old
and 90 new proposed derivatives of tetracyclines. Our results make evident the
importance of EIM descriptors in pattern recognition and also show that the EIM
can be effectively used to predict the biological activity of Tetracyclines.",0708.2931v1
2007-09-10,Spin-gap behaviour in the 2-leg spin-ladder BiCu2PO6,"We present magnetic suscceptibility and heat capacity data on a new S=1/2
two-leg spin ladder compound BiCu2PO6. From our susceptibility analysis, we
find that the leg coupling J1/k_B is ~ 80 K and the ratio of the rung to leg
coupling J2/J1 ~ 0.9. We present the magnetic contribution to the heat capacity
of a two-leg ladder. The spin-gap Delta/k_B =3 4 K obtained from the heat
capacity agrees very well with that obtained from the magnetic susceptibility.
Significant inter-ladder coupling is suggested from the susceptibility
analysis. The hopping integrals determined using Nth order muffin tin orbital
(NMTO) based downfolding method lead to ratios of various exchange couplings in
agreement with our experimental data. Based on our band structure analysis, we
find the inter-ladder coupling in the bc-plane J2 to be about 0.75J1 placing
the compound presumably close to the quantum critical limit.",0709.1338v1
2007-09-23,Two-orbital Systems with Crystal Field Splitting and Interorbital Hopping,"The nondegenerate two-orbital Hubbard model is studied within the dynamic
mean-field theory to reveal the influence of two important factors, i.e.
crystal field splitting and interorbital hopping, on orbital selective Mott
transition (OSMT) and realistic compound Ca$_{2-x}$Sr$_{x}$RuO$_{4}$. A
distinctive feature of the optical conductivity of the two nondegenerate bands
is found in OSMT phase, where the metallic character of the wide band is
indicated by a nonzero Drude peak, while the insulating narrow band has its
Drude peak drop to zero in the mean time. We also find that the OSMT regime
expands profoundly with the increase of interorbital hopping integrals. On the
contrary, it is shown that large and negative level splitting of the two
orbitals diminishes the OSMT regime completely. Applying the present findings
to compound Ca$_{2-x}$Sr$_{x}$RuO$_{4}$, we demonstrate that in the doping
region from $x=0.2$ to 2.0, the negative level splitting is unfavorable to the
OSMT phase.",0709.3618v2
2007-09-26,Multi-symmetry and Multi-band Superconductivity in Filled-skutterudites PrOs$_4$Sb$_{12}$ and PrRu$_4$Sb$_{12}$,"Thermal conductivity measurements were performed on single crystal samples of
the superconducting filled skutterudite compounds PrOs$_4$Sb$_{12}$ and
PrRu$_4$Sb$_{12}$ both as a function of temperature and magnetic field applied
perpendicular to the heat current. In zero magnetic field, the low temperature
electronic thermal conductivity of PrRu$_4$Sb$_{12}$ is vanishingly small,
consistent with a fully-gapped Fermi surface. For PrOs$_4$Sb$_{12}$, however,
we find clear evidence for residual electronic conduction as the temperature
tends to zero Kelvin which is consistent with the presence of nodes in the
superconducting energy gap. The field dependence of the electronic conductivity
for both compounds shows a rapid rise immediately above H$_{c1}$ and
significant structure over the entire vortex state. In the fully gapped
superconductor PrRu$_4$Sb$_{12}$, this is interpreted in terms of multi-band
effects. In PrOs$_4$Sb$_{12}$, we consider the Doppler shift of nodal
quasiparticles at low fields and multiband effects at higher fields.",0709.4265v1
2007-09-27,"Variation of the bonding interactions and magnetism in GdAuX (X = Mg, Cd, and In)","Results of first-principles electronic structure calculations for the
isotypic compounds GdAuX (ZrNiAl type, X = Mg, Cd, and In) are presented. We
report on a systematic examination of the electronic structure and nature of
the bonding in these intermetallics. Our calculations indicate a metallic state
for all of the compounds. We find that the indium in GdAuIn and magnesium in
GdAuMg have significant bonding interactions with Au. We have also identified
In s lone pair in GdAuIn has more localized behaviour as compared with Mg s in
GdAuMg. The magnetic properties are well described within the local density
approximation.",0709.4445v1
2007-10-04,Elastic properties of cubic crystals: Every's versus Blackman's diagram,"Blackman's diagram of two dimensionless ratios of elastic constants is
frequently used to correlate elastic properties of cubic crystals with
interatomic bondings. Every's diagram of a different set of two dimensionless
variables was used by us for classification of various properties of such
crystals. We compare these two ways of characterization of elastic properties
of cubic materials and consider the description of various groups of materials,
e.g. simple metals, oxides, and alkali halides. With exception of intermediate
valent compounds, the correlation coefficients for Every's diagrams of various
groups of materials are greater than for Blackaman's diagrams, revealing the
existence of a linear relationship between two dimensionless Every's variables.
Alignment of elements and compounds along lines of constant Poisson's ratio
$\nu(<100>,\textbf{m})$, ($\textbf{m}$ arbitrary perpendicular to <100>) is
observed. Division of the stability region in Blackman's diagram into region of
complete auxetics, auxetics and non-auxetics is introduced. Correlations of a
scaling and an acoustic anisotropy parameter are considered.",0710.1057v1
2007-10-08,Superconductivity in the New Platinum Germanides MPt4Ge12 (M = Rare-earth and Alkaline-earth Metals) with Filled Skutterudite Structure,"New germanium-platinum compounds with the filled-skutterudite crystal
structure were synthesized. The structure and composition were investigated by
X-ray diffraction and microprobe analysis. Magnetic susceptibility, specific
heat, and electrical resistivity measurements evidence superconductivity in
LaPt4Ge12 and PrPt4Ge12 below 8.3K. The parameters of the normal and
superconducting states were established. Strong coupling and a crystal electric
field singlet groundstate is found for the Pr compound. Electronic structure
calculations show a large density of states at the Fermi level. Similar
behavior with lower T_c was observed for SrPt4Ge12 and BaPt4Ge12.",0710.1413v1
2007-10-09,Spin ladder compound Pb(0.55)Cd(0.45)V(2)O(5): synthesis and investigation,"The complex oxide Pb(0.55)Cd(0.45)V(2)O(5) was synthesized and investigated
by means of X-ray powder diffraction, electron diffraction, magnetic
susceptibility measurements and band structure calculations. Its structure is
similar to that of MV(2)O(5) compounds (M = Na, Ca) giving rise to a spin
system of coupled S=1/2 two-leg ladders. Magnetic susceptibility measurements
reveal a spin gap-like behavior with \Delta ~ 270 K and a spin singlet ground
state. Band structure calculations suggest Pb(0.55)Cd(0.45)V(2)O(5) to be a
system of weakly coupled dimers in perfect agreement with the experimental
data. Pb(0.55)Cd(0.45)V(2)O(5) provides an example of the modification of the
spin system in layered vanadium oxides by cation substitution. Simple
correlations between the cation size, geometrical parameters and exchange
integrals for the MV(2)O(5)-type oxides are established and discussed.",0710.1806v1
2007-10-10,"Commensurate magnetic structures ofRMn2O5 (R=Y, Ho, Bi) determined by Single-crystal Neutron Diffraction","Precise magnetic structures of RMn2O5, with R= Y, Ho, Bi in the
commensurate/ferroelectric regime, have been determined by single-crystal
neutron diffraction. For each system, the integrated intensities of a large
number of independent magnetic Bragg reflections have been measured, allowing
unconstrained least-squares refinement of the structures. The analysis confirms
the previously reported magnetic configuration in the ab-plane, in particular
the existence of zig-zag antiferromagnetic chains. For the Y and Ho compounds
additional weak magnetic components parallel to the c-axis were detected which
are modulated in phase quadrature with the a-b components. This component is
extremely small in the BiMn2O5 sample, therefore supporting symmetric exchange
as the principal mechanism inducing ferroelectricity. For HoMn2O5, a magnetic
ordering of the Ho moments was observed, which is consistent with a
super-exchange interaction through the oxygens. For all three compounds, the
point symmetry in the magnetically ordered state is m2m, allowing the polar
b-axis found experimentally.",0710.2065v1
2007-10-24,Chirality-Biased Point Defects Dynamics on a Disclination Line in a Nematic Liquid Crystal,"Chiral additives in the nematic liquid crystal can alter the dynamics of
point defects moving on a disclination line. They exert a constant force on
defects, leading to the bimodal distribution of distances between them at long
times. The evolution of the system of defects in the presence of chiral
additives provides a very direct proof of the existence of repulsive forces
between the defects at large distances. We find that addition of a sufficient
amount of chiral compound removes all point defects from the system. The
process is studied in the system of 8CB (4-n-octyl-4 '-cyanobiphenyl) doped
with the chiral compound S811 (from Merck Co.) and in the computer simulations.",0710.4390v1
2007-10-25,High pressure behavior of CsC8 graphite intercalation compound,"The high pressure phase diagram of CsC8 graphite intercalated compound has
been investigated at ambient temperature up to 32 GPa. Combining X-ray and
neutron diffraction, Raman and X- ray absorption spectroscopies, we report for
the first time that CsC8, when pressurized, undergoes phase transitions around
2.0, 4.8 and 8 GPa. Possible candidate lattice structures and the transition
mechanism involved are proposed. We show that the observed transitions involve
the structural re- arrangement in the Cs sub-network while the distance between
the graphitic layers is continuously reduced at least up to 8.9 GPa. Around 8
GPa, important modifications of signatures of the electronic structure measured
by Raman and X-ray absorption spectroscopies evidence the onset of a new
transition.",0710.4616v1
2007-10-25,q-Dependence of the giant bond-stretching phonon anomaly in the stripe compound La1.48Nd0.4Sr0.12CuO4 measured by IXS,"Inelastic x-ray scattering (IXS) was used to study the Cu-O bond-stretching
vibrations in the static stripe phase compound La1.48Nd0.4Sr0.12CuO4. It was
found that the intrinsic width in Q-space of the previously reported huge
anomalous phonon softening and broadening is approximately 0.08r.l.u HWHM. A
detailed comparison was also made to inelastic neutron scattering (INS)
studies, which indicate a two-peak lineshape (with superimposed broad and
narrow peaks) in the vicinity of the anomaly. The high resolution IXS data show
that the narrow peak is mostly an artifact of the poor transverse Q-resolution
of INS. Otherwise the agreement between the INS and IXS was excellent.",0710.4782v2
2007-11-01,Interaction effects in mixed-valent Kondo insulators,"We study theoretically the class of mixed-valent Kondo insulators, employing
a recently developed local moment approach to heavy Fermion systems using the
asymmetric periodic Anderson model (PAM). Novel features in spectra and
transport, observable experimentally but lying outside the scope of the
symmetric PAM or the Kondo lattice model, emerge naturally within the present
theory. We argue in particular that a shoulder-like feature in the optical
conductivity, that is distinct from the usual mid-infrared or direct gap peak
and has been observed experimentally in mixed-valent compounds such as
CeOs4Sb12 and YbAl3, is of intrinsic origin. Detailed comparison is made
between the resultant theory and transport/optical experiments on the
filled-skutterudite compound CeOs4Sb12, and good agreement is obtained.",0711.0121v1
2007-11-07,Optical characterization of platinum-halide ladder compounds,"New varieties of quasi-one-dimensional halogen (X)-bridged transition-metal
(M) complexes, (C_8_H_6_N_4_)[Pt(C_2_H_8_N_2_)X]_2_X(ClO_4_)_3_\cdotH_2_O
(X=Br,Cl) and (C_10_H_8_N_2_)[Pt(C_4_H_13_N_3_)Br]_2_Br_4_\cdot2H_2_O,
comprising two-leg ladders of mixed-valent platinum ions, are described in
terms of a multiband extended Peierls-Hubbard Hamiltonian. The polarized
optical conductivity spectra are theoretically reproduced and the ground-state
valence distributions are reasonably determined. The latter variety, whose
interchain valence arrangement is out of phase, is reminiscent of conventional
MX single-chain compounds, while the former variety, whose interchain valence
arrangement is in phase, reveals itself as a novel d-p-\pi-hybridized multiband
ladder material.",0711.1052v1
2007-11-09,Insulator-metal transition on the triangular lattice,"Mott insulators with a half-filled band of electrons on the triangular
lattice have been recently studied in a variety of organic compounds. All of
these compounds undergo transitions to metallic/superconducting states under
moderate hydrostatic pressure. We describe the Mott insulator using its
hypothetical proximity to a Z_2 spin liquid of bosonic spinons. This spin
liquid has quantum phase transitions to descendant confining states with Neel
or valence bond solid order, and the insulator can be on either side of one of
these transitions. We present a theory of fermionic charged excitations in
these states, and describe the route to metallic states with Fermi surfaces. We
argue that an excitonic condensate can form near this insulator-metal
transition, due to the formation of charge neutral pairs of charge +e and
charge -e fermions. This condensate breaks the lattice space group symmetry,
and we propose its onset as an explanation of a low temperature anomaly in
kappa-(ET)2Cu2(CN)3. We also describe the separate BCS instability of the
metallic states to the pairing of like-charge fermions and the onset of
superconductivity.",0711.1538v1
2007-11-12,"Characterization and performances of new indium loaded organic liquid scintillators, based on novel indium carboxilate compounds","A novel formulation to dope organic liquid scintillators (OLS) with indium at
concentrations up to 10% is presented: it is based on specific indium
carboxylate compounds adequately synthesized. The produced In-OLS has been
characterized: it has light yield 8500 ph/MeV at indium concentration 5.5% and
light attenuation length of 2,5 m at wavelength of 430 nm. The scintillator
properties were stable during all time of investigation (~ 1 years). The
produced In-OLS is compared to other In-OLS formulations and shows superior
performances. The developed methodic to metal dope OLS can be easily extended
to other metals as Gd, Nd, Cd.",0711.1833v1
2007-11-13,Decomposition of neuronal assembly activity via empirical de-Poissonization,"Consider a compound Poisson process with jump measure $\nu$ supported by
finitely many positive integers. We propose a method for estimating $\nu$ from
a single, equidistantly sampled trajectory and develop associated statistical
procedures. The problem is motivated by the question whether nerve cells in the
brain exhibit higher-order interactions in their firing patterns. According to
the neuronal assembly hypothesis (Hebb [13]), synchronization of action
potentials across neurons of different groups is considered a signature of
assembly activity, but it was found notoriously difficult to demonstrate it in
recordings of neuronal activity. Our approach based on a compound Poisson model
allows to detect the presence of joint spike events of any order using only
population spike count samples, thus bypassing both the ``curse of
dimensionality'' and the need to isolate single-neuron spike trains in
population signals.",0711.1965v1
2007-11-15,Magnetic Field versus Temperature Phase Diagram of the Spin-1/2 Alternating Chain Compound F5PNN,"We have measured the specific heat of the S = 1/2 alternating Heisenberg
antiferromagnetic chain compound pentafluorophenyl nitronyl nitroxide in
magnetic fields using a single crystal and powder. A sharp peak due to
field-induced magnetic ordering (FIMO) is observed in both samples. The H-T
phase boundary of the FIMO of the single crystal is symmetric with respect to
the central field of the gapless field region HC1 < H < HC2, whereas it is
distorted for the powder whose ordering temperatures are lower. An analysis
employing calculations based on the finite temperature density matrix
renormalization group indicates the possibility of novel incommensurate
ordering due to frustration in the powder around the central field.",0711.2336v1
2007-11-23,"High-pressure effects on the optical-absorption edge of CdIn2S4, MgIn2S4, and MnIn2S4 thiospinels","The effect of pressure on the optical-absorption edge of CdIn2S4, MgIn2S4,
and MnIn2S4 thiospinels at room temperature is investigated up to 20 GPa. The
pressure dependence of their band-gaps has been analyzed using the Urbach rule.
We have found that, within the pressure-range of stability of the low-pressure
spinel phase, the band-gap of CdIn2S4 and MgIn2S4 exhibits a linear blue-shift
with pressure, whereas the band-gap of MnIn2S4 exhibits a pronounced non-linear
shift. In addition, an abrupt decrease of the band-gap energies occurs in the
three compounds at pressures of 10 GPa, 8.5 GPa, and 7.2 GPa, respectively.
Beyond these pressures, the optical-absorption edge red-shifts upon compression
for the three studied thiospinels. All these results are discussed in terms of
the electronic structure of each compound and their reported structural
changes.",0711.3702v1
2007-11-29,The underscreened Kondo lattice model applied to heavy fermion uranium compounds,"We present theoretical results for the underscreened Kondo lattice model with
localized S=1 spins coupled to a conduction band through a Kondo coupling,
$J_K$, and interacting among them ferromagnetically. We use a fermionic
representation for the spin operators and expand the Hamiltonian in terms of
bosonic fields. For large values of $J_K$, we obtain a ferromagnetically
ordered solution and a Kondo regime with a Kondo temperature, $T_K$, larger
than the Curie temperature, $T_C$. This finding suggests a scenario for a
coexistence of Kondo effect and ferromagnetic order. In some uranium compounds,
like $UTe$ or $UCu_{0.9}Sb_{2}$, this kind of coexistence has been
experimentally observed: they order ferromagnetically with a Curie temperature
of order $T_C \sim 100K$ and exhibit a Kondo behavior for $T > T_C$. The
proposed underscreened Kondo lattice model accounts well for the coexistence
between magnetic order and Kondo behavior and yields to a new ``ferromagnetic
Doniach diagram''.",0711.4765v1
2007-12-07,High multipole transitions in NIXS: valence and hybridization in 4f systems,"Momentum-transfer (q) dependent non-resonant inelastic x-ray scattering
measurements were made at the N4,5 edges for several rare earth compounds. With
increasing q, giant dipole resonances diminish, to be replaced by strong
multiplet lines at lower energy transfer. These multiplets result from two
different orders of multipole scattering and are distinct for systems with
simple 4f^0 and 4f^1 initial states. A many-body theoretical treatment of the
multiplets agrees well with the experimental data on ionic La and Ce phosphate
reference compounds. Comparing measurements on CeO2 and CeRh3 to the theory and
the phosphates indicates sensitivity to hybridization as observed by a
broadening of 4f^0-related multiplet features. We expect such strong, nondipole
features to be generic for NIXS from f-electron systems.",0712.1242v1
2007-12-14,Optical conductivity and the correlation strength of high temperature copper-oxide superconductors,"High temperature copper-oxide-based superconductivity is obtained by adding
carriers to insulating ""parent compounds"". It is widely believed the parent
compounds are ""Mott"" insulators, in which the lack of conduction arises from
anomalously strong electron-electron repulsion, and that the unusual properties
of Mott insulators are responsible for high temperature superconductivity. This
paper presents a comparison of optical conductivity measurements and
theoretical calculations which challenges this belief. The analysis indicates
that the correlation strength in the cuprates is not as strong as previously
believed, that the materials are not properly regarded as Mott insulators, that
antiferromagnetism is essential to obtain the insulating state and, by
implication, that antiferromagnetism is essential to the properties of the
doped metallic and superconducting state as well.",0712.2392v1
2007-12-18,"Absorption-Fluctuation Theorem for Nuclear Reactions: Brink-Axel, Incomplete Fusion and All That","We discuss the connection between absorption, averages and fluctuations in
nuclear reactions. The fluctuations in the entrance channel result in the
compound nucleus, Hauser-Feshbach, cross section, the fluctuations in the
intermediate channels, result in modifications of multistep reaction cross
sections, while the fluctuations in the final channel result in hybrid cross
sections that can be used to describe incomplete fusion reactions. We discuss
the latter in details and comment on the validity of the assumptions used in
the develpoment of the Surrogate method. We also discuss the theory of
multistep reactions with regards to intermediate state fluctuations and the
energy dependence and non-locality of the intermediate channels optical
potentials.",0712.2922v2
2008-01-08,Relevance of ferromagnetic correlations for the Electron Spin Resonance in Kondo lattice systems,"Electron Spin Resonance (ESR) measurements of the ferromagnetic Kondo lattice
system CeRuPO show a well defined ESR signal which is related to the magnetic
properties of the Ce3+ moment. In contrast, no ESR signal could be observed in
the antiferromagnetic homologue CeOsPO. Additionally, we detect an ESR signal
in a further ferromagnetic Yb compound, YbRh, while it was absent in a number
of Ce or Yb intermetallic compounds with dominant antiferromagnetic exchange,
independently of the presence of a strong Kondo interaction or the proximity to
a (quantum) critical point. Thus, the observation of an ESR signal in a Kondo
lattice is neither specific to Yb nor to the proximity of a quantum critical
point, but seems to be connected to the presence of ferromagnetic fluctuations.
These conclusions not only provide a basic concept to understand the ESR in
Kondo lattice systems even well below the Kondo temperature as observed in the
heavy fermion metal YbRh2Si2 but point out ESR as a prime method to investigate
directly the spin dynamics of the Kondo ion.",0801.1191v1
2008-01-17,Exotic (anti)ferromagnetism in single crystals of Pr6Ni2Si3,"The ternary intermetallic compound Pr6Ni2Si3, is a member of a structure
series of compounds based on a triangular structure where the number of Pr
atoms in the prism cross section can be systematically varied. Pr6Ni2Si3
contains two distinct Pr lattice sites which result in complex interactions
between the magnetic ions. Extensive measurements of specific heat and
magnetization on single crystal samples indicate that Pr6Ni2Si3 orders with
both a ferromagnet and an antiferromagnet component, with ordering temperatures
of 39.6 K and ~ 32 K, respectively. The ferromagnetic component // c-axis is
accompanied by a large hysteresis, and the antiferromagnetic component,_|_
c-axis is accompanied by a spin-flop-type transition. More detailed
measurements, of the vector magnetization, indicate that the ferromagnetic and
the antiferromagnetic order appear independent of each other. These results not
only clarify the behavior of Pr6Ni2Si3 itself, but also of the other members of
the structure series, Pr5Ni2Si3 and Pr15Ni7Si10.",0801.2704v1
2008-01-24,"Spin-driven ferroelectricity and possible antiferroelectricity in triangular lattice antiferromagnets ACrO2 (A = Cu, Ag, Li, or Na)","Correlation between dielectric and magnetic properties was investigated on
the triangular lattice antiferromagnets ACrO2 (A= Cu, Ag, Li, or Na) showing
120-degree spiral spin structure with easy-axis anisotropy. For the A= Cu and
Ag compounds with delafossite structure, ferroelectric polarization emerges
upon the spiral spin order, implying the strong coupling between the
ferroelectricity and spiral spin structure. On the other hand, for the A = Li
and Na compounds with ordered rock salt structure, no polarization but only
clear anomalies in dielectric constant can be observed upon the spiral spin
order. The absence of polarization can be interpreted as the antiferroelectric
state induced by the alternate stacking of Cr3+ layer with opposite spin vector
chirality. These results imply that a vast range of trigonally stacked
triangular-lattice systems with 120-degree spin structure can be multiferroic,
irrespective of their magnetic anisotropy.",0801.3757v1
2008-01-31,Enhancement of ferromagnetism by Co and Ni substitution in the perovskite LaBiMn2O6+d,"The substitution of cobalt and nickel for manganese in the perovskite
manganate LaBiMn2O6+d; has been realized, leading to the perovskites
LaBiMn2-x(M)xO6+d, with M = Co, Ni and x =0-2/3. In contrast to the literature
those phases are found to be orthorhombic with Pnma symmetry. More importantly,
it is shown that ferromagnetism is enhanced, TC being increased from 80 K for
the parent compound (x = 0) to 97 K for Ni-phase, and to 130 K for the
Co-phase. Moreover, a strong competition between ferromagnetism and a
glassy-ferromagnetic state in the case of nickel or a spin-glass behaviour in
the case of cobalt is observed. These phenomena are interpreted in the frame of
a phase separation scenario, where the ferromagnetic Mn4+/Ni2+ and Mn4+/Co2+
interactions reinforce the Mn3+/Mn4+ interactions. These compounds are found to
be insulating with a relatively large positive value of thermoelectric power.",0801.4916v1
2008-02-08,Reentrant magnetic ordering and percolation in a spin-crossover system,"Spin-crossover compounds, which are characterized by magnetic ions showing
low-spin and high-spin states at thermally accessible energies, are ubiquitous
in nature. We here focus on the effect of an exchange interaction on the
collective properties for the case of non-magnetic low-spin ions, which applies
to Fe(II) compounds. Monte Carlo simulations are used to study a
three-dimensional spin-crossover model for the full parameter range from
essentially pure high spin to essentially pure low spin. We find that as the
low-spin state becomes more favorable, the Curie temperature drops, the
universality class deviates from the three-dimensional Heisenberg class, and
the transition eventually changes to first order. A heat-bath algorithm that
grows or shrinks low-spin and high-spin domains is developed to handle the
first-order transition. When the ground state has low spin, a reentrant
magnetic transition is found in a broad parameter range. We also observe a
percolation transition of the high spins, which branches off the first-order
magnetic transition.",0802.1169v1
2008-02-19,Effect of oxygen-doping on Bi-2223 vortex matter: Crossover from electromagnetic to Josephson interlayer coupling,"We study the effect of oxygen-doping on the critical temperature, Tc, the
vortex matter phase diagram and the nature of the coupling mechanism between
the Cu-O layers in the three-layer Bi2Sr2Ca2Cu3O10+delta (Bi-2223) compound.
Contrary to previous reports, in the overdoped (OD) regime we do find a
variation of Tc with increasing the oxygen partial-pressure of the
post-annealing treatment. This variation is less significant than in the
bi-layer parental compound Bi-2212 and does not follow the universal Tc
vs.delta relation. Magnetic measurements reveal that increasing delta enlarges
the field and temperature stability of the Bragg glass phase. These findings
imply that the interlayer coupling between Cu-O layers enhances with delta. The
anisotropy parameter estimated from directional first-penetration field
measurements monotonously decreases from 50 in the underdoped (UD) to 15 in the
OD regimes. However, the in-plane penetration depth presents a boomerang-like
behaviour with $\delta$, reaching its minimum value close to optimal doping.
These two facts lead to a crossover from a Josephson(OD) to
electromagnetic(UD)-dominated coupling of adjacent Cu-O layers in the vicinity
of optimal doping.",0802.2617v1
2008-02-19,Jahn-Teller Distortion in Bimetallic Oxalates,"A C$_3$-symmetric crystal-field potential in the Fe(II)Fe(III) bimetallic
oxalates splits the L=2 Fe(II) multiplet into two doublets and a singlet. In
compounds that exhibit magnetic compensation, one of the doublets was predicted
to lie lowest in energy and carry a non-quenched orbital angular momentum $\pm
\ld $, where $\ld $ exceeds a threshold value. In a range of $\ld $, a
Jahn-Teller (JT) distortion increases the energy splitting of the low-lying
doublet and breaks the C$_3$ symmetry of the bimetallic planes around the
ferrimagnetic transition temperature. At low temperatures, the JT distortion
disappears in compounds that display magnetic compensation due to the
competition with the spin-orbit coupling. A comparison with recent measurements
provides strong evidence for this re-entrant, low-temperature JT transition and
a prediction for the normal, high-temperature JT transition. The size of the JT
distortion is estimated using first-principles calculations, which suggest that
the long-range ordering of smaller, non-C$_3$-symmetric organic cations can
eliminate magnetic compensation.",0802.2678v1
2008-03-02,The magnetoelectric coupling in the multiferroic compound LiCu2O2,"We investigate the possible types of coupling between ferroelectricity and
magnetism for the zig-zag spin chain multiferroic LiCu2O2 compound. We
construct a multi-order parameter phenomenological model for the material based
on a group theoretical analysis. From our calculation we conclude that a
coupling involving the inter-chain magnetic structure and ferroelectricity is
necessary to understand the experimental results of Park et.al. Our proposed
model is able to account for the electric polarization flop in the presence of
an externally applied magnetic field. Furthermore, based on our theoretical
model we can make specific selection rule predictions about electromagnon
excitations present in the LiCu2O2 system. We also predict that the
electromagnon peaks measured in an ac-conductivity measurement are field
dependent.",0803.0095v2
2008-03-03,Anisotropic Electron-Phonon Coupling and Dynamical Nesting on the Graphene Sheets in CaC6,"Superconductivity in graphite intercalated compounds has been studied for
more than 40 years and it is still not fully understood, despite the recent
progress and the discovery of relatively high Tc superconductivity in CaC6 and
YbC6. Recent studies now suggest that the electron-phonon coupling is most
likely responsible for pairing and that the intercalant-derived electronic
states and vibrations play the dominant role. Here, we present the first
studies of electronic structure in CaC6, a superconductor with Tc=11.6 K. Using
angle-resolved photoemission spectroscopy, we find that, contrary to
theoretical models, the EPC on the graphene-derived Fermi sheets is
surprisingly strong, reflecting the interaction with high-frequency
graphene-derived vibrations. Thus, in addition to the amazing properties in the
charge-neutral state, graphene sheets also show surprises in the heavily doped
regime: they may support strong pairing interactions and lead to
superconductivity in compounds in which they are building blocks.",0803.0254v1
2008-03-05,Short-range magnetic ordering process for the triangular lattice compound NiGa2S4: a positive muon spin rotation and relaxation study,"We report a study of the triangular lattice Heisenberg magnet NiGa2S4 by the
positive muon spin rotation and relaxation technique. We unravel three
temperature regimes: (i) below T_c = 9.2(2) K a spontaneous static magnetic
field at the muon site is observed and the spin dynamics is appreciable: the
time scale of the modes we probe is ~ 7 ns; (ii) an unconventional stretched
exponential relaxation function is found for T_c < T < T_{cross} where
T_{cross} = 12.6 K, which is a signature of a multichannel relaxation for this
temperature range; (iii) above T_{cross}, the relaxation is exponential as
expected for a conventional compound. The transition at T_c is of the
continuous type. It occurs at a temperature slightly smaller than the
temperature at which the specific heat displays a maximum at low temperature.
This is reminiscent of the behavior expected for the
Berezinskii-Kosterlitz-Thouless transition. We argue that these results reflect
the presence of topological defects above T_c.",0803.0718v2
2008-03-12,First-principles investigation of the electron-phonon interaction in OsN$_2$: Theoretical prediction of superconductivity mediated by N-N covalent bonds,"A first-principles investigation of the electron-phonon interaction in the
recently synthesized osmium dinitride (OsN$_2$) compound predicts that the
material is a superconductor. Superconductivity in OsN$_2$ would originate from
the stretching of covalently bonded dinitrogen units embedded in the
transition-metal matrix, thus adding dinitrides to the class of superconductors
containing covalently bonded light elements. The dinitrogen vibrations are
strongly coupled to the electronic states at the Fermi level and generate
narrow peaks in the Eliashberg spectral function $\alpha^2F(\omega)$. The total
electron-phonon coupling of OsN$_2$ is $\lambda=0.37$ and the estimated
superconducting temperature T$_c \approx 1$ K. We suggest that the
superconducting temperature can be substantially increased by hole doping of
the pristine compound and show that T$_c$ increases to 4 K with a doping
concentration of 0.25 holes/OsN$_2$ unit.",0803.1822v1
2008-03-25,Magnetic properties of BaCdVO(PO_4)_2: a strongly frustrated spin-1/2 square lattice close to the quantum critical regime,"We report magnetization and specific heat measurements on polycrystalline
samples of BaCdVO(PO_4)_2 and show that this compound is a S=1/2 frustrated
square lattice with ferromagnetic nearest-neighbor (J_1) and antiferromagnetic
next-nearest-neighbor (J_2) interactions. The coupling constants J_1\simeq -3.6
K and J_2\simeq 3.2 K are determined from a fitting of the susceptibility data
and confirmed by an analysis of the saturation field (H_s=4.2 T), the specific
heat, and the magnetic entropy. BaCdVO(PO_4)_2 undergoes magnetic ordering at
about 1 K, likely towards a columnar antiferromagnetic state. We find that
BaCdVO(PO_4)_2 with the frustration ratio \alpha=J_2/J_1\simeq -0.9 is closer
to a critical (quantum spin liquid) region of the frustrated square lattice
than any of the previously reported compounds. Positive curvature of the
magnetization curve is observed in agreement with recent theoretical
predictions for high-field properties of the frustrated square lattice close to
the critical regime.",0803.3535v2
2008-03-26,Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8,"Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d^2, Mn^{5+} ions
arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads
to a singlet ground state in zero-field. Here we present the first results of
thermodynamic measurements for single crystals probing the high-field ordered
states of this material associated with closing the spin gap to the excited
triplet states. Specific heat, magnetocaloric effect, and torque magnetometry
measurements were performed in magnetic fields up to 32 T and temperatures down
to 20 mK. For fields above H_{c1} ~ 8.7 T, these measurements reveal a single
magnetic phase for H parallel to c, but two distinct phases (approximately
symmetric about the center of the phase diagram) for H perpendicular to c.
Analysis of the simplest possible spin Hamiltonian describing this system
yields candidates for these ordered states corresponding to a simple spiral
structure for H parallel to c, and to two distinct modulated phases for H
perpendicular to c. Both single-ion anisotropy and geometric frustration play
crucial roles in defining the phase diagram.",0803.3830v1
2008-03-29,Superconductivity at 52 K in iron-based F-doped layered quaternary compound Pr[O1-xFx]FeAs,"Since the discovery of copper oxide superconductor in 1986 [1], extensive
efforts have been devoted to the search of new high-Tc superconducting
materials, especially high-Tc systems other than cuprates. The recently
discovered quaternary superconductor La[O1-xFx]FeAs with the superconducting
critical transition Tc of 26 K [2], which has a much simple layered structure
compared with cuprates, has attracted quick enthusiasm and is going to become a
new high-Tc system [3-6]. Here we report the discovery of bulk
superconductivity in the praseodymium-arsenide oxides Pr[O1-xFx]FeAs with an
onset drop of resistivity as high as 52 K, and the unambiguous zero-resistivity
and Meissner transition at low temperature, which will place these quaternary
compounds to another high-Tc superconducting system explicitly.",0803.4283v1
2008-03-31,Time Parallel Scalable Multiphysics/Multiscale Framework,"We propose a new computational framework that combines the recently developed
time-parallel (TP) and the compound wavelet matrix (CWM) methods. The
framework, termed tpCWM, offers significant computational acceleration by
making multiscale/multiphysics simulations computationally scalable in time and
space domains. We demonstrate the accuracy and the scalability of the method on
a prototype problem with oscillatory trajectory. The method corrects the coarse
solution by iterative use of the CWM, which compounds the fine and the coarse
solutions for the processes. Computational savings, over the fine solution as
well as the TP method, in terms of the real time required to perform the
simulations, can reach several orders of magnitude. We believe that this method
is general enough to be applicable to a wide-class of computational physics
problems. Tendency towards large number of cores and processors in parallel
computers is compatible with the computational scalability of the algorithm.",0804.0017v2
2008-04-02,Anomalous magnetic and transport properties of La(0.8-x)Eu(x)Sr0.2MnO3 (0.04 l.e. x l.e. 0.36) compounds,"Anomalous magnetic and transport properties observed in the
La0.8-xEuxSr0.2MnO3 (0.04 l.e x l.e. 0.36) compounds are presented in this
paper. The Curie temperature (TC) decreases from 260 K for x = 0.04 to 188 K
for x = 0.16 and surprisingly thereafter increases for higher Eu concentrations
(x > 0.16) and becomes nearly constant ~230 K. Resistivity increases with Eu
concentration up to x = 0.16 but decreases for higher Eu concentration (x >
0.16). In the magnetoresistance data, in addition to a peak corresponding to
the insulator-metal transition at (TI-M1), a second peak is also observed at a
relatively lower temperature, (TI-M2). Both TI-M1 and TI-M2 follow the same
trend as TC. The unique variation of TC and magnetoresistance is explained on
the basis of structure and disorder correlated to microscopic electronic phase
segregation. The studies with the existing studies also point to the
universibility of this consideration.",0804.0325v1
2008-04-11,"Two-magnon Raman scattering from the Cu3O4 layers in (Sr,Ba)2Cu3O4Cl2","(Sr$_{2}$,Ba$_{2}$)Cu$_{3}$O$_{4}$Cl$_{2}$ are antiferromagnetic insulators
which are akin to the parent compounds of the cuprate superconductors but with
two distinct magnetic ordering temperatures related to two magnetic Cu$_{I}$
and Cu$_{II}$ spin sublattices. Here we present a study of these materials by
means of Raman spectroscopy. Following the temperature and polarization
dependence of the data we readily identify two distinct features at around 3000
cm$^{-1}$ and 300 cm$^{-1}$ that are related to two-magnon scattering from the
two sublattices. The estimated spin-exchange coupling constants for the
Cu$_{I}$ and Cu$_{II}$ sublattices are found to be J$_{I}\sim$139-143(132-136)
meV and J$_{II}\sim$14(11) meV for Sr(Ba) compounds. Moreover, we observe modes
at around 480 and 445 cm$^{-1}$ for the Sr and Ba containing samples
respectively, that disappears at the ordering temperature of the Cu$_{II}$. We
argue that this modes may also be of magnetic origin and possibly related to
interband transitions between the Cu$_{I}$-Cu$_{II}$ sublattices.",0804.1859v2
2008-04-11,Room temperature soft ferromagnetism in the nanocrystalline form of YCo2 - a well-known bulk Pauli paramagnet,"The Laves phase compound, YCo2, is a well-known exchange-enahnced Pauli
paramagnet. We report here that, in the nanocrystalline form, this compound
interestingly is an itinerant ferromagnet at room temperature with a low
coercive-field. The magnitude of the saturation moment (about 1 Bohr-magneton
per formula unit) is large enough to infer that the ferromagnetism is not a
surface phenomenon in these nanocrystallites. Since these ferromagnetic
nanocrystallines are easy to synthesize with a stable form in air, one can
explore applications, particularly where hysteresis is a disadvantage.",0804.1926v2
2008-04-13,Superconductivity at 55 K in iron-based F-doped layered quaternary compound Sm[O1-xFx]FeAs,"Here we report the superconductivity in the iron-based oxyarsenide
Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0 K and
Meissner transition at 54.6 K. This compound has the same crystal structure as
LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the
highest critical temperature among all materials besides copper oxides.",0804.2053v2
2008-04-14,Anomalous Effects in Air While Cooling Water,"Water is a unique compound with many anomalies and properties not fully
understood. Designing an experiment in the laboratory to study such anomalies,
we set up a series of experiments where a tube was placed inside a sealed
container with thermocouples attached to the outer surface of the tube and in
the air adjacent to the tube. Alternately, deionized water and other compounds
were added to the tube and cooled to freezing. Several of the thermocouples
suspended in the air and adjacent to the tube showed thermal oscillations as
the overall temperature of the container was decreasing. The temperature of the
thermocouples increased and decreased in a sinusoidal way during part of the
cool down to freezing. Thermal oscillations as large as 3 degrees Celsius were
recorded with typical frequencies of about 5 oscillations per minute.",0804.2274v1
2008-04-16,Spin-state transition and spin-polaron physics in cobalt oxide perovskites: ab initio approach based on quantum chemical methods,"A fully ab initio scheme based on quantum chemical wavefunction methods is
used to investigate the correlated multiorbital electronic structure of a
3d-metal compound, LaCoO3. The strong short-range electron correlations,
involving both Co and O orbitals, are treated by multireference techniques. The
use of effective parameters like the Hubbard U and interorbital U', J terms and
the problems associated with their explicit calculation are avoided with this
approach. We provide new insight into the spin-state transition at about 90 K
and the nature of charge carriers in the doped material. Our results indicate
the formation of a t4e2 high-spin state in LaCoO3 for T>90 K. Additionally, we
explain the paramagnetic phase in the low-temperature lightly doped compound
through the formation of Zhang-Rice-like O hole states and ferromagnetic
clusters.",0804.2626v1
2008-04-18,Metamagnetism and 1/3 Plateau in the Spin Chain Compound CoV2O6,"The pseudo-one dimensional brannerite type compound CoV2O6 has been studied
by magnetisation and heat capacity measurements in the temperature range 1.8 <
T < 300 K and in applied fields of up to 9 T. Our measurements show an unusual
balance of exchange interactions (CW= 2.8(2) K) and a single antiferromagnetic
transition at TN = 7 K. M(H) isotherms recorded below 5 K show a metamagnetic
transition and a 1/3 magnetisation plateau. From 5-7 K, only the metamagnetic
transition is observed. For T < TN < ~ 25 K, our heat capacity and
magnetisation measurements show evidence for strong low dimensional
ferromagnetic fluctuations. We propose a simple phase diagram, discuss the
principle features and emphasise the importance of Ising anisotropy.",0804.2966v1
2008-04-18,Dzyaloshinsky-Moriya Anisotropy in the Spin-1/2 Kagomé Compound ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$,"We report the determination of the Dzyaloshinsky-Moriya interaction, the
dominant magnetic anisotropy term in the \kagome spin-1/2 compound {\herbert}.
Based on the analysis of the high-temperature electron spin resonance (ESR)
spectra, we find its main component $|D_z|=15(1)$ K to be perpendicular to the
\kagome planes. Through the temperature dependent ESR line-width we observe a
building up of nearest-neighbor spin-spin correlations below $\sim$150 K.",0804.3107v2
2008-04-28,Complete inclusion of parity-dependent level densities in the statistical description of astrophysical reaction rates,"Microscopic calculations show a strong parity dependence of the nuclear level
density at low excitation energy of a nucleus. Previously, this dependence has
either been neglected or only implemented in the initial and final channels of
Hauser-Feshbach calculations. We present an indirect way to account for a full
parity dependence in all steps of a reaction, including the one of the compound
nucleus formed in a reaction. To illustrate the impact on astrophysical
reaction rates, we present rates for neutron captures in isotopic chains of Ni
and Sn. Comparing with the standard assumption of equipartition of both
parities, we find noticeable differences in the energy regime of astrophysical
interest caused by the parity dependence of the nuclear level density found in
the compound nucleus even at sizeable excitation energies.",0804.4402v1
2008-04-29,Multiband magnetism and superconductivity in Fe-based compounds,"Recent discovery of high T_c superconductivity in Fe-based compounds may have
opened a new pathway to the room temperature superconductivity. The new
materials feature FeAs layers instead of the signature CuO_2 planes of
much-studied cuprates. A model Hamiltonian describing FeAs layers is
introduced, highlighting the crucial role of puckering of As atoms in promoting
d-electron itinerancy and warding off large local-moment magnetism of Fe ions,
the main enemy of superconductivity. Quantum many-particle effects in charge,
spin and multiband channels are explored and a nesting-induced spin
density-wave order is found in the parent compund. We argue that this largely
itinerant antiferromagnetism and high T_c itself are essentially tied to the
multiband nature of the Fermi surface.",0804.4678v4
2008-04-30,Sum-Capacity of Ergodic Fading Interference and Compound Multiaccess Channels,"The problem of resource allocation is studied for two-sender two-receiver
fading Gaussian interference channels (IFCs) and compound multiaccess channels
(C-MACs). The senders in an IFC communicate with their own receiver (unicast)
while those in a C-MAC communicate with both receivers (multicast). The
instantaneous fading state between every transmit-receive pair in this network
is assumed to be known at all transmitters and receivers. Under an average
power constraint at each source, the sum-capacity of the C-MAC and the power
policy that achieves this capacity is developed. The conditions defining the
classes of strong and very strong ergodic IFCs are presented and the multicast
sum-capacity is shown to be tight for both classes.",0804.4866v1
2008-05-20,An ab-initio evaluation of the local effective interactions in the $\rm Na_{x} Co O_2$ familly,"We used quantum chemical ab initio methods to determine the effective
parameters of Hubbard and $t-J$ models for the $\rm Na_{x}CoO_2$ compounds (x=0
and 0.5). As for the superconducting compound we found the $a_{1g}$ cobalt
orbitals above the $e_g^\prime$ ones by a few hundreds of meV due to the
$e_g^\prime$--$e_g$ hybridization of the cobalt $3d$ orbitals. The correlation
strength was found to increase with the sodium content $x$ while the in-plane
AFM coupling decreases. The less correlated system was found to be the pure
$CoO_2$, however it is still strongly correlated and very close to the Mott
transition. Indeed we found $U/t\sim 15$, which is the critical value for the
Mott transition in a triangular lattice. Finally, one finds the magnetic
exchanges in the $\rm CoO_2$ layers, strongly dependant of the weak local
structural distortions.",0805.3121v2
2008-05-27,Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2,"The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type
structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to
LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is
a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase
transition at 140 K, accompanied by strong anomalies in the specific heat,
electrical resistance and magnetic susceptibility. In the course of this
transition, the space group symmetry changes from tetragonal (I4/mmm) to
orthorhombic (Fmmm). 57Fe Moessbauer spectroscopy experiments show a single
signal at room temperature and full hyperfine field splitting below the phase
transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can
serve as a new parent compound for oxygen-free iron arsenide superconductors.",0805.4021v2
2008-06-02,Thermodynamic stabilities of ternary metal borides: An ab initio guide for synthesizing layered superconductors,"Density functional theory calculations have been used to identify stable
layered Li-$M$-B crystal structure phases derived from a recently proposed
binary metal-sandwich (MS) lithium monoboride superconductor. We show that the
MS lithium monoboride gains in stability when alloyed with electron-rich metal
diborides; the resulting ordered Li$_{2(1-x)}M_x$B$_2$ ternary phases may form
under normal synthesis conditions in a wide concentration range of $x$ for a
number of group-III-V metals $M$. In an effort to pre-select compounds with the
strongest electron-phonon coupling we examine the softening of the in-plane
boron phonon mode at $\Gamma$ in a large class of metal borides. Our results
reveal interesting general trends for the frequency of the in-plane boron
phonon modes as a function of the boron-boron bond length and the valence of
the metal. One of the candidates with a promise to be an MgB$_2$-type
superconductor, Li$_2$AlB$_4$, has been examined in more detail: according to
our {\it ab initio} calculations of the phonon dispersion and the
electron-phonon coupling $\lambda$, the compound should have a critical
temperature of $\sim4$ K.",0806.0061v1
2008-06-05,Magnetic and structural transitions in layered FeAs systems: AFe2As2 versus RFeAsO compounds,"Resistivity, specific heat and magnetic susceptibility measurements performed
on SrFe2As2 samples evidence a behavior very similar to that observed in
LaFeAsO and BaFe2As2 with the difference that the formation of the SDW and the
lattice deformation occur in a pronounced first order transition at T_0=205K.
Comparing further data evidences that the Fe-magnetism is stronger in SrFe2As2
and in EuFe2As2 than in the other layered FeAs systems investigated up to now.
Full potential LDA band structure calculations confirm the large similarity
between the compounds, especially for the relevant low energy Fe 3d states. The
relation between structural details and magnetic order is analyzed.",0806.1043v1
2008-06-07,Suppression of the commensurate spin-Peierls state in Sc-doped TiOCl,"We have performed x-ray scattering measurements on single crystals of the
doped spin-Peierls compound Ti(1-x)Sc(x)OCl (x = 0, 0.01, 0.03). These
measurements reveal that the presence of non-magnetic dopants has a profound
effect on the unconventional spin-Peierls behavior of this system, even at
concentrations as low as 1%. Sc-doping suppresses commensurate fluctuations in
the pseudogap and incommensurate spin-Peierls phases of TiOCl, and prevents the
formation of a long-range ordered spin-Peierls state. Broad incommensurate
scattering develops in the doped compounds near Tc2 ~ 93 K, and persists down
to base temperature (~ 7 K) with no evidence of a lock-in transition. The width
of the incommensurate dimerization peaks indicates short correlation lengths on
the order of ~ 12 angstroms below Tc2. The intensity of the incommensurate
scattering is significantly reduced at higher Sc concentrations, indicating
that the size of the associated lattice displacement decreases rapidly as a
function of doping.",0806.1285v1
2008-06-07,Superconductivity up to 37 K in (A1-xSrx)Fe2As2 with A=K and Cs,"A new hight Tc Fe-based compound system, AFe2As2 with A = K, Cs, K/Sr and
Cs/Sr has been found. Through electron-doping, Tc of the A = K and Cs compounds
rises to ~37 K, and finally enter a spin-density-wave state (SDW) through
further electron doping with Sr. The observation demonstrates the crucial role
of the (FeAs)-layers in the superconductivity in the Fe-based layered system
and the special feature of elemental A-layers in this complex chemical system
may provide new avenues to superconductivity at a higher Tc.",0806.1301v3
2008-06-10,Superconductivity above 50 K in Tb$_{1-x}$Th$_{x}$FeAsO,"We have successfully synthesized one member of LnFeAsO (Ln stands for
lanthanides) with Ln=Tb. By partial substitution of Tb$^{3+}$ by Th$^{4+}$,
superconductivity with onset $T_{c}$ up to 52 K was observed. In the undoped
parent compound, the magnetic moments of Tb$^{3+}$ ions order
antiferromagnetically (AFM) at $T_N$ of 2.5 K, and there exists an anomaly in
the resistivity at $T^*$ of about 124 K which corresponds to the structural
phase transition and/or AFM ordering of magnetic moments of Fe$^{2+}$ ions.
This anomaly is severely suppressed by Th doping, similar to the cases of F
doped LnFeAsO series. Thermopower measurements show that the charge carrier is
electron-like for both undoped and Th doped compounds, and enhanced thermopower
in Th doped samples was observed.",0806.1675v3
2008-06-11,Thermalized Non-Equilibrated Matter: Compound Processes and Beyond,"A characteristic feature of thermalized non-equilibrated matter is that, in
spite of energy relaxation (thermalization), a phase memory of the way the
strongly interacting many-body system was excited remains. In this contribution
we analyze a low energy evaporating proton data in nucleon induced reactions at
$\simeq$62 MeV incident energy with $^{197}$Au, $^{208}$Pb, $^{209}$Bi and
$^{nat}$U. Our analysis demonstrates that the thermalized non-equilibrated
matter survives a cascade of several evaporating particles. Thus the
experiments show that the effect of the anomalously slow phase relaxation, with
upper limits of the phase relaxation widths in the range 1-10$^{-4}$ eV, is
stable with respect to the multi-step evaporating cascade from the thermalized
compound nuclei. We also briefly mention manifestations and implications of the
thermalized non-equilibrated matter for some other fields.",0806.1905v1
2008-06-13,Stability of geometrically frustrated magnetic state of Ca3CoRhO6 to applications of positive and negative pressure,"The influence of negative chemical pressure induced by gradual replacement of
Ca by Sr as well as of external pressure (up to 10 kbar) on the magnetism of
Ca3CoRhO6 has been investigated by magnetization studies. It is found that the
solid solution, Ca(3-x)Sr(x)CoRhO6, exists at least till about x= 1.0 without
any change in the crystal structure. Apart from insensitivity of the spin-chain
feature to volume expansion, the characteristic features of geometrical
frustration interestingly appear at the same temperatures for all compositions,
in sharp contrast to the response to Y substitution for Ca (reported
previously). Interestingly, huge frequency dependence of ac susceptibility
known for the parent compound persists for all compositions. We do not find a
change in the properties under external pressure. The stability of the magnetic
anomalies of this compound to the volume change (about 4%) is puzzling.",0806.2342v1
2008-06-27,Observation of Spin Fluctuations in a High-Tc Parent Compound Using Resonant Inelastic X-ray Scattering,"We report the first observation of soft-x-ray scattering from spin
fluctuations in a high-Tc parent compound. An antiferromagnetic charge transfer
insulator, CaCuO2, was irradiated by Cu M-edge soft x-rays. Ultra-high
resolution measurements of scattered intensity revealed magnon-magnon
excitations, due to spin exchange scattering, as low-energy loss features. The
process is analogous to optical Raman scattering. The spectra provide the first
measurement of the two-magnon excitation energy and the antiferromagnetic
exchange parameter in infinite-layer CaCuO2. The results reveal resonant
inelastic soft x-ray scattering as a novel probe of the spin dynamics in
cuprates.",0806.4432v1
2008-06-29,Structural and magnetic phase transitions in the ternary iron arsenides SrFe2As2 and EuFe2As2,"The structural and magnetic phase transitions of the ternary iron arsenides
SrFe2As2 and EuFe2As2 were studied by temperature-dependent x-ray powder
diffraction and 57-Fe Moessbauer spectroscopy. Both compounds crystallize in
the tetragonal ThCr2Si2-type structure at room temperature and exhibit
displacive structural transitions at 203 K (SrFe2As2) or 190 K (EuFe2As2) to
orthorhombic lattice symmetry in agreement with the group-subgroup relationship
between I4/mmm and Fmmm. 57-Fe Moessbauer spectroscopy experiments with SrFe2
As2 show full hyperfine field splitting below the phase transition temperature
(8.91(1) T at 4.2 K). Order parameters were extracted from detailed
measurements of the lattice parameters and fitted to a simple power law. We
find a relation between the critical exponents and the transition temperatures
for AFe2As2 compounds, which shows that the transition of BaFe2As2 is indeed
more continuous than the transition of SrFe2As2 but it remains second order
even in the latter case.",0806.4782v2
2008-06-30,LDA + Negative U Solves a Puzzle of too Large Calculated Magnetic Moment in Iron-based Superconductor LaFeAsO_{1-x}F_x,"A puzzle in the iron-based superconductor LaFeAsO_{1-x}F_x is that the
magnetic moment obtained by first-principle electronic structure calculations
is unexpectedly much larger than the experimentally observed one. For example,
the calculated value is ~ 2.0 \mu_B in the mother compound, while it is ~ 0.3
\mu_B in experiments. We find that the puzzle is solved within the framework
LDA + U by expanding the U value into a slightly negative range. We show U
dependence of the obtained magnetic moment in both the undoped x=0.0 and doped
x = 0.125. These results reveal that the magnetic moment is drastically reduced
when entering to the slightly negative range of U. Moreover, the negative U
well explains other measurement data, e.g., lattice constants and electronic
DOS at the Fermi level. We discuss possible origins of the negative U in these
compounds.",0806.4804v1
2008-07-05,"Growth and characterization of A_{1-x}K_xFe_2As_2 (A = Ba, Sr) single crystals with x=0 - 0.4","Single crystals of A$_{1-x}$K$_x$Fe$_2$As$_2$ (A=Ba, Sr) with high quality
have been grown successfully by FeAs self-flux method. The samples have sizes
up to 4 mm with flat and shiny surfaces. The X-ray diffraction patterns suggest
that they have high crystalline quality and c-axis orientation. The
non-superconducting crystals show a spin-density-wave (SDW) instability at
about 173 K and 135 K for Sr-based and Ba-based compound, respectively. After
doping K as the hole dopant into the BaFe$_2$As$_2$ system, the SDW transition
is smeared, and superconducting samples with the compound of
Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (0 $< x \leqslant$ 0.4) are obtained. The
superconductors characterized by AC susceptibility and resistivity measurements
exhibit very sharp superconducting transition at about 36 K, 32 K, 27 K and 23
K for x= 0.40,0.28,0.25 and 0.23, respectively.",0807.0759v3
2008-07-05,Organic Matter in Space - an Overview,"Organic compounds are ubiquitous in space: they are found in diffuse clouds,
in the envelopes of evolved stars, in dense star-forming regions, in
protoplanetary disks, in comets, on the surfaces of minor planets, and in
meteorites and interplanetary dust particles. This brief overview summarizes
the observational evidence for the types of organics found in these regions,
with emphasis on recent developments. The Stardust sample-return mission
provides the first opportunity to study primitive cometary material with
sophisticated equipment on Earth. Similarities and differences between the
types of compounds in different regions are discussed in the context of the
processes that can modify them. The importance of laboratory astrophysics is
emphasized.",0807.0857v1
2008-07-07,Spin and Lattice Structure of Single Crystal SrFe2As2,"We use neutron scattering to study the spin and lattice structure on single
crystals of SrFe2As2, the parent compound of the FeAs based superconductor
(Sr,K)Fe2As2. We find that SrFe2As2 exhibits an abrupt structural phase
transitions at 220K, where the structure changes from tetragonal with lattice
parameters c > a = b to orthorhombic with c > a > b. At almost the same
temperature, Fe spins in SrFe2As2 develop a collinear antiferromagnetic
structure along the orthorhombic a-axis with spin direction parallel to this
a-axis. These results are consistent with earlier work on the RFeAsO (R = rare
earth elements) families of materials and on BaFe2As2, and therefore suggest
that static antiferromagnetic order is ubiquitous for the parent compound of
these FeAs-based high-transition temperature superconductors.",0807.1077v1
2008-07-10,Neutron diffraction on antiferromagnetic ordering in single-crystal BaFe2As2,"Neutron diffraction experiments have been carried out on a Sn-flux grown
BaFe2As2 single crystal, the parent compound of the A-122 family of FeAs-based
high-Tc superconductors. A tetragonal to orthorhombic structural phase
transition and a three dimensional long-range antiferromagnetic ordering of the
iron moment, with a unique magnetic propagation wavevector k = (1, 0, 1), have
been found to take place at ~90 K. The magnetic moments of iron are aligned
along the long a axis in the low temperature orthorhombic phase (Fmmm with
b<a<c). Our results thus demonstrate that the magnetic structure of BaFe2As2
single crystal is the same as those in other A-122 iron pnictides compounds. We
argue that the tin incorporation in the lattice is responsible for a smaller
orthorhombic splitting and lower Neel temperature T_N observed in the
experiment.",0807.1743v3
2008-07-11,Magnetic interactions and high-field properties of Ag(2)VOP(2)O(7): frustrated alternating chain close to the dimer limit,"We report on high-field magnetic properties of the silver vanadium phosphate
Ag(2)VOP(2)O(7). This compound has a layered crystal structure, but the
specific topology of the V-P-O framework gives rise to a one-dimensional spin
system, a frustrated alternating chain. Low-field magnetization measurements
and band structure calculations show that Ag(2)VOP(2)O(7) is close to the dimer
limit with the largest nearest-neighbor interaction of about 30 K. High-field
magnetization data reveal the critical fields \mu_0H_{c1} of about 23 T
(closing of the spin gap) and \mu_0H_{c2} of about 30 T (saturation by full
alignment of the magnetic moments). From H_{c1} to H_{c2} the magnetization
increases sharply similar to the system of isolated dimers. Thus, the magnetic
frustration in Ag(2)VOP(2)O(7) bears little influence on the high-field
properties of this compound.",0807.1849v1
2008-07-11,Large temperature dependence of the Casimir force at the metal-insulator transition,"The dependence of the Casimir force on material properties is important for
both future applications and to gain further insight on its fundamental
aspects. Here we derive a general theory of the Casimir force for
low-conducting compounds, or poor metals. For distances in the micrometer
range, a large variety of such materials is described by universal equations
containing a few parameters: the effective plasma frequency, dissipation rate
of the free carriers, and electric permittivity in the infrared range. This
theory can also describe inhomogeneous composite materials containing small
regions with different conductivity. The Casimir force for mechanical systems
involving samples made with compounds that have a metal-insulator transition
shows an abrupt large temperature dependence of the Casimir force within the
transition region, where metallic and dielectric phases coexist.",0807.1859v1
2008-07-16,Influence of doping on the Hall coefficient in Sr_{14-x}Ca_xCu_24O_41,"We present Hall-effect measurements of two-leg ladder compounds
Sr_{14-x}Ca_xCu_24O_41 (0 <= x <= 11.5) with the aim to determine the number of
carriers participating in dc transport. Distribution of holes between the
ladder and chain subsystems is one of the crucial questions important for
understanding the physics of these compounds. Our Hall effect and resistivity
measurements show typical semiconducting behavior for x < 11.5. However, for
x=11.5, the results are completely different, and the Hall coefficient and
resistivity behavior is qualitatively similar to that of high temperature
copper-oxide superconductors. We have determined the effective number of
carriers at room temperature and compared it to the number of holes in the
ladders obtained by other experimental techniques. We propose that going from
x=0 to x=11.5 less than 1 hole per formula unit is added to the ladders and is
responsible for a pronounced change in resistivity with Ca doping.",0807.2561v2
2008-07-16,"High Field de Haas - van Alphen Studies of the Fermi Surfaces of LaMIn$_{5}$ (M = Co, Rh, Ir)","We report measurements of the de Haas - van Alphen effect on a series of
compounds, LaMIn$_{5}$ (M = Co, Rh, Ir). The results show that each of the Co
and Ir Fermi surfaces (FSs) exhibit some portions that are two dimensional and
some portions that are three dimensional. The most two dimensional character is
exhibited in LaCoIn$_{5}$, less two dimensional behavior is seen in
LaIrIn$_{5}$, no part of Fermi surface of LaRhIn$_{5}$ is found to have a two
dimensional character. Thus the two dimensionality of portions of the FSs is
largely determined by the d character of the energy bands while all of the
effective masses remain $\leq$ 1.2. This fact has implications for the causes
of the heavy fermion nature of superconductivity and magnetism in the Ce-based
compounds having the similar composition and structure. All of the measurements
were performed at the National High Magnetic Field Laboratory using either
cantilever magnetometry or field modulation methods.",0807.2590v1
2008-07-21,Superconductivity at 34.7 K in the iron arsenide Eu0.7Na0.3Fe2As2,"EuFe2As2 is a member of the ternary iron arsenide family. Similar to BaFe2As2
and SrFe2As2, EuFe2As2 exhibits a clear anomaly in resistivity near 200 K. It
suggests that EuFe2As2 is another promising parent compound in which
superconductivity may be realized by appropriate doping. Here we report the
discovery of superconductivity in Eu0.7Na0.3Fe2As2 by partial substitution of
the europium site with sodium. ThCr2Si2 tetragonal structure, as expected for
EuFe2As2, is formed as the main phase for the composition Eu0.7Na0.3Fe2As2.
Resistivity measurement reveals a transition temperature as high as 34.7 K in
this compound, which is higher than the Tc of Eu0.5K0.5Fe2As2.",0807.3293v3
2008-07-24,"Influence of defects on the electronic and magnetic properties of half-metallic CrAs, CrSe and CrSb zinc-blende compounds","We present an extended study of single impurity atoms and atomic swaps in
half-metallic CrAs, CrSb and CrSe zinc-blende compounds. Although the perfect
alloys present a rather large gap in the minority-spin band, all defects under
study, with the exception of void impurities at Cr and sp sites and Cr
impurities at sp sites (as long as no swap occurs), induce new states within
the gap. The Fermi level can be pinned within these new minority states
depending on the lattice constant used for the calculations and the
electronegativity of the sp atoms. Although these impurity states are localized
in space around the impurity atoms and very fast we regain the bulk behavior,
their interaction can lead to wide bands within the gap and thus loss of the
half-metallic character.",0807.3836v1
2008-07-25,"Spin, orbital ordering and magnetic dynamics of LaVO3: magnetization, heat capacity and neutron scattering studies","We report the results of magnetization, heat capacity and neutron scattering
studies of LaVO3 single crystals. From the neutron diffraction studies, it was
found that the compound is magnetically ordered with a C-type antiferromagnetic
spin structure at about 136 K. In the vicinity of the ordering temperature, we
also observed hysteresis in the neutron diffraction data measured on cooling
and heating which indicates the first order nature of the phase transition. In
the antiferromagnetically ordered phase, the inelastic neutron scattering
studies reveal the presence of a temperature independent c axis spin-wave gap
of about 6 meV which is similar to that previously reported for the sister
compound YVO3.",0807.4195v1
2008-07-28,Compound Multiple Access Channels with Partial Cooperation,"A two-user discrete memoryless compound multiple access channel with a common
message and conferencing decoders is considered. The capacity region is
characterized in the special cases of physically degraded channels and
unidirectional cooperation, and achievable rate regions are provided for the
general case. The results are then extended to the corresponding Gaussian
model. In the Gaussian setup, the provided achievable rates are shown to lie
within some constant number of bits from the boundary of the capacity region in
several special cases. An alternative model, in which the encoders are
connected by conferencing links rather than having a common message, is studied
as well, and the capacity region for this model is also determined for the
cases of physically degraded channels and unidirectional cooperation. Numerical
results are also provided to obtain insights about the potential gains of
conferencing at the decoders and encoders.",0807.4548v1
2008-08-08,Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors,"Layered d-metal pnictide oxides are a unique class of compounds which
consists of characteristic d-metal pnictide layers and metal oxide layers. More
than 100 of these layered compounds, including the recently discovered Fe-based
superconducting pnictide oxides, can be classified into 9 structure types.
These structure types and the chemical and physical properties of the
characteristic d-metal pnictide layers and metal oxide layers of the layered
d-metal pnictide oxides are reviewed and discussed. Furthermore, possible
approaches to design new superconductors based on these layered d-metal
pnictide oxides are proposed.",0808.1158v6
2008-08-08,The filled skutterudite CeOs$_{4}$As$_{12}$: a hybridization gap semiconductor,"X-ray diffraction, electrical resistivity, magnetization, specific heat, and
thermoelectric power measurements are presented for single crystals of the new
filled skutterudite compound {\CeOsAs}, which reveal phenomena that are
associated with f - electron - conduction electron hybridization. Valence
fluctuations or Kondo behavior dominates the physics down to $T$ $\sim$ 135 K.
The correlated electron behavior is manifested at low temperatures as a
hybridization gap insulating state. The small energy gap $\Delta$$_1$/k$_B$
$\sim$ 73 K, taken from fits to electrical resistivity data, correlates with
the evolution of a weakly magnetic or nonmagnetic ground state, which is
evident in the magnetization data below a coherence temperature $T$$_{coh}$
$\sim$ 45 K. Additionally, the low temperature electronic specific heat
coefficient is small, $\gamma$ $\sim$ 19 mJ/mol K$^2$. Some results for the
nonmagnetic analogue compound {\LaOsAs} are also presented for comparison
purposes.",0808.1278v2
2008-08-09,Electronic transport and specific heat of 1T- VSe2,"The results of low temperature thermoelectric power and the specific heat of
1T-VSe2 (Vanadium diselenide) have been reported along with the electrical
resistivity, and Hall coefficient of the compound. The Charge Density Wave
(CDW) transition is observed near 110K temperature in all these properties. The
Thermoelectric power has been measured from 15K to 300K spanning the
incommensurate and commensurate CDW regions. We observed a weak anomaly at the
CDW transition for the first time in the specific heat of VSe2. The linear
temperature dependence of resistivity and thermoelectric power at higher
temperatures suggests a normal metallic behavior and electron-phonon scattering
above the CDW transition. The positive thermoelectric power and negative Hall
coefficient along with strongly temperature dependent behavior in the CDW phase
suggest a mixed conduction related to the strongly hybridized s-p-d bands in
this compound.",0808.1332v2
2008-08-12,Graphite intercalation compound KC$_8$ revisited: a key to graphene,"Electrons in isolated graphene layers are a two-dimensional gas of massless
Dirac Fermions. In realistic devices, however, the electronic properties are
modified by elastic deformations, interlayer coupling and substrate
interaction. Here we unravel the electronic structure of doped graphene,
revisiting the stage one graphite intercalation compound KC$_8$ using
angle--resolved photoemission spectroscopy and ab--initio calculations. The
full experimental dispersion is in excellent agreement to calculations of doped
graphene once electron correlations are included on the $GW$ level. This
highlights that KC$_8$ has negligible interlayer coupling. Therefore Dirac
Fermion behaviour is preserved and we directly determine the full experimental
Dirac cone of doped graphene. In addition we prove that superconductivity in
KC$_8$ is mediated by electron--phonon coupling to an iTO phonon, yielding a
strong kink in the quasiparticle dispersion at 166 meV. These results are key
for understanding, both, the unique electronic properties of graphene and
superconductivity in KC$_8$.",0808.1613v3
2008-08-13,Isoscaling in statistical fragment emission in an extended compound nucleus model,"Based on an extended compound nucleus model, isospin effects in statistical
fragment emission from excited nuclear systems are investigated. An
experimentally observed scaling behavior of the ratio of isotope yields
$Y_i(N,Z)$ from two similar emitting sources with different neutron-to-proton
ratios is predicted theoretically, i.e., the relationship of $Y_2/Y_1 \propto
exp(\alpha N + \beta Z)$ is demonstrated. The symmetry energy coefficient
$C_{sym}$ extracted from the simulation results is $\sim$ 27 MeV which is
consistent with realistic theoretical estimates and recent experimental data.
The influence of the surface entropy on the isoscaling behavior is discussed in
detail. It is found that although the surface entropy increases the numercial
values of isoscaling parameters $\alpha$ and $\beta$, it does not affect the
isoscaling behavior qualitatively and has only a minor effect on the extracted
symmetry energy coefficient.",0808.1917v1
2008-08-18,d- and f-orbital correlations in the REFeAsO compounds,"We estimate theoretically the strength of the local Coulomb interaction for
the Fe 3d and Ce 4f shells in the REFeAsO compunds. In LaFeAsO and CeFeAsO we
obtain values of the local Coulomb interaction parameter U for both Fe and Ce
which are larger than those of elemental Fe and Ce metals. The Fe 3d bandwidth
of REFeAsO is found to increase slightly as one moves along the RE-series.
Using a combined local density approximation and dynamical mean-field theory
(LDA+DMFT) approach, we study the behaviour of the localized 4f states along
the rare-earth oxyarsenides REFeAsO series (RE=Ce,Pr,Nd). In CeFeAsO the
occupied Ce 4f band is located just below the Fe 3d band leading possibly to a
Kondo screening of the 4f local moment under applied pressure, while the
unscreened local moment behaviour is expected for the Pr and Nd compounds.",0808.2442v1
2008-08-21,Magnetic order in Pr2Pd3Ge5 and possible heavy fermion behavior in Pr2Rh3Ge5,"We report our results on two new ternary intermetallic compounds
Pr$_{2}$Pd$_{3}$Ge$_{5}$ and Pr$_{2}$Rh$_{3}$Ge$_{5}$ based on magnetic
susceptibility, magnetization, specific heat, resistivity and magnetoresistance
data. These compounds form in U$_{2}$Co$_{3}$Si$_{5}$-type orthorhombic
structure (space group \textit{Ibam}). Pr$_{2}$Pd$_{3}$Ge$_{5}$ exhibits two
magnetic transitions at T$_{N1}$ = 7.5 K and T$_{N2}$ = 8.3 K. In the
magnetically ordered state Pr$_{2}$Pd$_{3}$Ge$_{5}$ exhibits a field induced
metamagnetic transition and unusually large magnetoresistance.
Pr$_{2}$Rh$_{3}$Ge$_{5}$ does not show any phase transition down to 0.5 K. It
has a CEF singlet ground state, separated from the first excited state by about
10 K. The low lying crystal field excitations lead to exciton mediated
electronic mass enhancement as evidenced by large Sommerfeld coefficient
($\gamma$ $\sim$ 80 mJ/mol K$^2$) in Pr$_{2}$Rh$_{3}$Ge$_{5}$.",0808.2896v1
2008-08-21,Magnetic ordering in the static intermediate-valent cerium compound Ce2RuZn4,"The low-temperature behavior of Ce2RuZn4 has been investigated. Specific heat
and magnetic susceptibility data reveal an antiferromagnetic transition at a
Neel temperature of 2 K. Ce2RuZn4 is a static intermediate-valent compound with
two crystallographically independent cerium atoms. The magnetic data clearly
show that only one cerium site is magnetic (Ce^3+), while the second one
carries no magnetic moment. The experimental data are interpreted with the help
of first principles electronic structure calculations using density functional
theory and the augmented spherical wave method. The calculations reveal the
occurrence of two different cerium sites, which are characterized by strongly
localized magneticmoments and strong Ce-Ru bonding, respectively.",0808.2916v1
2008-09-01,Dzyaloshinskii-Moriya interactions in valence bond systems,"We investigate the effect of Dzyaloshinskii-Moriya interactions on the low
temperature magnetic susceptibility for a system whose low energy physics is
dominated by short-range valence bonds (singlets). Our general perturbative
approach is applied to specific models expected to be in this class, including
the Shastry-Sutherland model of the spin-dimer compound SrCu_2(BO_3)_2 and the
antiferromagnetic Heisenberg model of the recently discovered S=1/2 kagome
compound ZnCu_3(OH)_6Cl_2. The central result is that a short-ranged valence
bond phase, when perturbed with Dzyaloshinskii-Moriya interactions, will remain
time-reversal symmetric in the absence of a magnetic field but the
susceptibility will be nonzero in the T\to 0 limit. Applied to
ZnCu_3(OH)_6Cl_2, this model provides an avenue for reconciling experimental
results, such as the lack of magnetic order and lack of any sign of a spin gap,
with known theoretical facts about the kagome Heisenberg antiferromagnet.",0809.0031v3
2008-09-06,Local Structure and It's Effect on The Ferromagnetic Properties of La$_{0.5}$Sr$_{0.5}$CoO$_3$ thin films},"We have used high-resolution Extended X-ray Absorption Fine-Structure and
diffraction techniques to measure the local structure of strained
La$_{0.5}$Sr$_{0.5}$CoO$_3$ films under compression and tension. The lattice
mismatch strain in these compounds affects both the bond lengths and the bond
angles, though the larger effect on the bandwidth is due to the bond length
changes. The popular double exchange model for ferromagnetism in these
compounds provides a correct qualitative description of the changes in Curie
temperature $T_C$, but quantitatively underestimates the changes. A microscopic
model for ferromagnetism that provides a much stronger dependence on the
structural distortions is needed.",0809.1178v2
2008-09-11,"Pressure-induced shift of T$_c$ in K$_x$Sr$_{1-x}$Fe$_2$As$_2$ (x=0.2, 0.4, 0.7): Analogy to the high-T$_c$ cuprate superconductors","The systematic pressure shifts of T_c were investigated in the whole phase
diagram of the FeAs-based superconducting compound K_xSr_{1-x}Fe_2As_2.
Different regions, arising from corresponding responses of T$_c$ to pressure
(dT_c/dp>0, =0, or <0), can be clearly distinguished. This reveals an
interesting similarity of the FeAs superconductors and the high-T_c cuprates.
This behavior is a manifestation of the layered structure of the FeAs compounds
and the pressure-induced charge transfer between the (Fe_2As_2) and (K/Sr)
layers. The coexistence of superconductivity and spin-density wave behavior
were also observed, and the pressure effects on the latter is explored.",0809.2054v2
2008-09-15,Role of covalent Fe-As bonding in the magnetic moment formation and exchange mechanisms in iron-pnictide superconductors,"The electronic origin of the huge magnetostructural effect in layered Fe-As
compounds is elucidated using LiFeAs as a prototype. The crucial feature of
these materials is the strong covalent bonding between Fe and As, which tends
to suppress the exchange splitting. The bonding-antibonding splitting is very
sensitive to the distance between Fe and As nuclei. We argue that the fragile
interplay between bonding and magnetism is universal for this family of
compounds. The exchange interaction is analyzed in real space, along with its
correlation with covalency and doping. The range of interaction and itinerancy
increase as the Fe-As distance is decreased. Superexchange makes a large
antiferromagnetic contribution to the nearest-neighbor coupling, which develops
large anisotropy when the local moment is not too small. This anisotropy is
very sensitive to doping.",0809.2586v3
2008-09-22,"Determination of the Spin Polarization of RFe2 (R = Dy, Er, Y) by Point Contact Andreev Reflection","Epitaxially grown intermetallic RFe2 (R = Dy, Er, Y) thin films have been
studied by point contact Andreev reflection. Spin polarization values were
extracted by fitting normalized conductance curves for mechanical Nb/RFe2 point
contacts, using a modified Blonder-Tinkham-Klapwijk (BTK) model. Good agreement
is found between this model and the experimentally obtained data. Extracted
values of spin polarization, which are close to the spin polarization of Fe,
reveal no variation with the rare earth component for the measured
intermetallic compounds. This suggests that using this technique we probe the
Fe sub-lattice, and that this lattice drives spintronic effects in these
compounds.",0809.3723v2
2008-10-02,Magnetic Modulation in Mechanical Alloyed Cr1.4fe0.6o3 Oxide,"We have synthesized Cr1.4Fe0.6O3 compound through mechanical alloying of
Cr2O3 and Fe2O3 powders and subsequent thermal annealing. The XRD spectrum, SEM
picture and microanalysis of EDAX spectrum have been used to understand the
structural evolution in the alloyed compound. The alloyed samples are matching
to rhombohedral structure with R3C space group. The observation of a modulated
magnetic order confirmed a systematic diffusion of Fe atoms into the Cr sites
of lattice structure. A field induced magnetic behaviour is seen in the field
dependence of magnetization data of the annealed samples. The behaviour is
significantly different from the mechanical alloyed samples. The experimental
results provided the indications of considering the present material as a
potential candidate for opto-electronic applications.",0810.0439v1
2008-10-13,"Synthesis, crystal structure and spin-density-wave anomaly of the iron arsenide-fluoride SrFeAsF","The new quaternary iron arsenide-fluoride SrFeAsF with the tetragonal
ZrCuSiAs-type structure was synthesized and the crystal structure was
determined by X-ray powder diffraction (P4/nmm, a = 399.30(1), c = 895.46(1)
pm). SrFeAsF undergoes a structural and magnetic phase transition at 175 K,
accompanied by strong anomalies in the specific heat, electrical resistance and
magnetic susceptibility. In the course of this transition, the space group
symmetry changes from tetragonal (P4/nmm) to orthorhombic (Cmme). 57Fe
Moessbauer spectroscopy experiments show a single signal at room temperature at
an isomer shift of 0.30(1) mm/s and magnetic hyperfine-field splitting below
the phase transition temperature. Our results clearly show that SrFeAsF
exhibits a spin density wave (SDW) anomaly at 175 K very similar to LaFeAsO,
the parent compound of the iron arsenide-oxide superconductors and thus SrFeAsF
may serve as a further parent compound for oxygen-free iron arsenide
superconductors.",0810.2120v1
2008-10-14,Enhancement in superconducting transition temperature and upper critical field of LaO0.8F0.2FeAs with antimony doping,"We report the synthesis and characterization of antimony doped oxypnictide
superconductor, LaO0.8F0.2FeAs1-xSbx (x = 0.05 and 0.10). The parent compound
LaOFeAs with fluorine doping exhibits superconductivity at maximum transition
temperature ~ 28.5 K [11]. Here we partially substitute As by Sb
(LaO0.8F0.2FeAs1-xSbx) and observe enhancement of the transition temperature to
30.1 K. This is the only instance so far where Tc increases with doping in the
conducting layer (FeAs) and this leads to the highest transition temperature in
any La-based oxypnictide. XRD and EDAX measurements confirm phase purity of the
samples and the presence of Sb. The magneto-resistance measurements show that
the value of upper critical field Hc2(0) to be about 73 T corresponding to a
coherence length of 22 angstrom. The Seebeck coefficient measurements indicate
electron transport with strong contribution from electron-electron correlation.
These results provide interesting insight to the origin of superconductivity in
these novel series of compounds.",0810.2362v1
2008-10-14,Anomalous electron-phonon interaction in doped LaOFeAs: a First Principles calculation,"We present first principles calculations of the atomic and electronic
structure of electron-doped LaOFeAs. We find that whereas the undoped compound
has an antiferromagnetic arrangement of magnetic moments at the Fe atoms, the
doped system becomes non magnetic at a critical electron concentration. We have
studied the electron-phonon interaction in the doped paramagnetic phase. For
the $A_{1g}$ phonon, the separation between the As and Fe planes induces a
non-collinear arrangement of the Fe magnetic moments. This arrangement is anti
parallel for interactions mediated by As, and perpendicular for Fe-Fe direct
interactions, thus avoiding frustration. This coupling of magnetism with
vibrations induces anharmonicities and an electron-phonon interaction much
larger than in the pure paramagnetic case. We propose that such enhanced
interactions play an essential role in superconducting compounds close to an
atiferromagnetic phase transition.",0810.2474v1
2008-10-15,"Electronic Structure, Magnetism and Superconductivity of Layered Iron Compounds","The layered iron superconductors are discussed using electronic structure
calculations. The four families of compounds discovered so far, including
Fe(Se,Te) have closely related electronic structures. The Fermi surface
consists of disconnected hole and electron cylinders and additional hole
sections that depend on the specific material. This places the materials in
proximity to itinerant magnetism, both due to the high density of states and
due to nesting. Comparison of density functional results and experiment
provides strong evidence for itinerant spin fluctuations, which are discussed
in relation to superconductivity. It is proposed that the intermediate phase
between the structural transition and the SDW transition in the oxy-pnictides
is a nematic phase.",0810.2682v2
2008-10-21,Radiative capture of nucleons at astrophysical energies with single-particle states,"Radiative capture of nucleons at energies of astrophysical interest is one of
the most important processes for nucleosynthesis. The nucleon capture can occur
either by a compound nucleus reaction or by a direct process. The compound
reaction cross sections are usually very small, specially for light nuclei. The
direct capture proceeds either via the formation of a single-particle
resonance, or a non-resonant capture process. In this work we calculate
radiative capture cross sections and astrophysical S-factors for nuclei in the
mass region A<20 using single-particle states. We carefully discuss the
parameter fitting procedure adopted in the simplified two-body treatment of the
capture process. Then we produce a detailed list of cases for which the model
works well. Useful quantities, such as spectroscopic factors and asymptotic
normalization coefficients, are obtained and compared to published data.",0810.3867v3
2008-10-30,Degradation of organic compounds and production of activated species in Dielectric Barrier Discharges and Glidarc reactors,"Major sterilization mechanisms are related to atoms and radicals, charged
parti-cles, excited molecules, ozone, and UV radiation. The ROS (Reactive
Oxygen Species) are well known as evildoers. These species are easily created
in ambient air and water and they live long enough to reach the cell and attack
the organic matter. Test molecules conversion in dry and wet air is studied
using Dielectric Barrier Discharge (DBD) and Gliding Arc Reactors (GAR). The
effects of tem-perature and energy deposition into the media on the active
species production and then on the organic compounds degradation are presented
for two non thermal plasma reactors: DBD and GAR. Main production species
investigated are OH, O3, NOx, CO and CxHyOz by-products. It is shown from
experiment analysis that the reactive species production is quite different
from one reactor to another. GAR and pulsed DBD are two chemical processing
ways in which the temperature of heavy species in ionized gas is determinant.
By reviewing the species production obtained from both reactors, a discussion
is open about plasma decontamination.",0810.5433v1
2008-11-12,Bond analysis of cobalt and iron based skutterudites: elongated lanthanum bonds in LaFe4P12,"Motivated by the possibility of further improving the thermoelectric
properties of skutterudites we investigate charge transfer and bonding in this
class of materials using density functional calculations. Results for the CoP3,
CoSb3, LaFe4P12 and the hypothetical FeP3 compounds are presented using the
procrystal as the non-binding reference. Spherical integration and Bader
analysis are performed to illustrate charge transfer differences between these
compounds. The results are in good qualitative agreement with simple
electronegativity considerations. The calculations confirm that the transition
metal-pnictogen and the pnictogen-pnictogen bonds are covalent, while the
filler atom-pnictogen bond is of a more polar and complex nature. The success
of the ""rattling"" cage as phonon inhibitor is explained by a unique
semi-correlated bonding scheme between lanthanum and phosphorus. Elongated
bonds along the crystal axes surrounds the lanthanum ion and generate a
dodecahedra grid. Vibrations along the crystal axes are then closely connected
to and scatter from the phosphorus rings. In the other directions, a more
uncorrelated vibration is possible. This duality widens the phonon dampening
possibilities.",0811.1889v1
2008-11-16,"Flux jumps, Second Magnetization Peak anomaly and the Peak Effect phenomenon in single crystals of $YNi_2B_2C$ and $LuNi_2B_2C$","We present magnetization measurements in single crystals of the tetragonal
$YNi_2B_2C$ compound, which exhibit the phenomenon of peak effect as well as
the second magnetization peak anomaly for H $>$ 0.5T (H $||$ c). At the lower
field (50mT $<$ H $<$ 200mT), we have observed the presence of flux jumps,
which seem to relate to a structural change in the local symmetry of the flux
line lattice (a first order re-orientation transition across a local field in
some parts of the sample, in the range of 100mT to 150mT). These flux jumps are
also observed in a single crystal of $LuNi_2B_2C$ for H $||$ c in the field
region from 2 mT to 25 mT, which are compatible with the occurrence of a
re-orientation transition at a lower field in a cleaner crystal of this
compound, as compared to those of $YNi_2B_2C$. Vortex phase diagrams drawn for
H $||$ c in $LuNi_2B_2C$ and $YNi_2B_2C$ show that the ordered elastic glass
phase spans a larger part of (H, T) space in the former as compared to latter,
thereby, reaffirming the difference in the relative purity of the two samples.",0811.2604v1
2008-11-18,"Direct determination of the crystal field parameters of Dy, Er and Yb impurities in the skutterudite compound CeFe$_{4}$P$_{12}$ by Electron Spin Resonance","Despite extensive research on the skutterudites for the last decade, their
electric crystalline field ground state is still a matter of controversy. We
show that Electron Spin Resonance (ESR) measurements can determine the full set
of crystal field parameters (CFPs) for the Th cubic symmetry (Im3) of the
Ce$_{1-x}$R$_{x}$Fe$_{4}$P$_{12}$ (R = Dy, Er, Yb, $x\lesssim 0.003$)
skutterudite compounds. From the analysis of the ESR data the three CFPs, B4c,
B6c and B6t were determined for each of these rare-earths at the Ce$^{3+}$
site. The field and temperature dependence of the measured magnetization for
the doped crystals are in excellent agreement with the one predicted by the
CFPs Bnm derived from ESR.",0811.2972v1
2008-11-20,New S=1/2 Kagome Antiferromagnets A$_2$Cu$_3$SnF$_{12}$: A=Cs and Rb,"We synthesized single crystals of the new hexagonal compounds
A$_2$Cu$_3$SnF$_{12}$ with A=Cs and Rb, and investigated their magnetic
properties. These compounds are composed of Kagom\'{e} layers of corner-sharing
CuF$_6$-octahedra. Cs$_2$Cu$_3$SnF$_{12}$ has the proper Kagom\'{e} layer at
room temperature, and undergoes structural phase transition at
$T_\mathrm{t}\simeq 185$ K. The temperature dependence of the magnetic
susceptibility in Cs$_2$Cu$_3$SnF$_{12}$ agrees well with the result of the
numerical calculation for $S=1/2$ two-dimensional Heisenberg Kagom\'{e}
antiferromagnet down to $T_\mathrm{t}$ with the nearest exchange interaction
$J/k_\mathrm{B}\simeq 240$ K. Although the magnetic susceptibility deviates
from the calculated result below $T<T_\mathrm{t}$, the rounded maxima were
observed at approximately $T\simeq (1/6)J/k_\mathrm{B}$ as predicted by the
theory. Cs$_2$Cu$_3$SnF$_{12}$ undergoes three-dimensional magnetic ordering at
$T_\mathrm{N} = 20$ K.",0811.3291v1
2008-11-24,Rescaled Levy-Loewner hulls and random growth,"We consider radial Loewner evolution driven by unimodular L\'evy processes.
We rescale the hulls of the evolution by capacity, and prove that the weak
limit of the rescaled hulls exists. We then study a random growth model
obtained by driving the Loewner equation with a compound Poisson process. The
process involves two real parameters: the intensity of the underlying Poisson
process and a localization parameter of the Poisson kernel which determines the
jumps. A particular choice of parameters yields a growth process similar to the
Hastings-Levitov $\rm{HL}(0)$ model. We describe the asymptotic behavior of the
hulls with respect to the parameters, showing that growth tends to become
localized as the jump parameter increases. We obtain deterministic evolutions
in one limiting case, and Loewner evolution driven by a unimodular Cauchy
process in another. We show that the Hausdorff dimension of the limiting
rescaled hulls is equal to 1. Using a different type of compound Poisson
process, where the Poisson kernel is replaced by the heat kernel, as driving
function, we recover one case of the aforementioned model and
$\rm{SLE}(\kappa)$ as limits.",0811.3857v1
2008-11-24,Effect of impurity pinning on conduction and specific heat in the Luttinger liquid,"We study theoretically two effects related to impurity depinning that are
common for 1D Luttinger liquid (LL) and linear-chain CDW conductors. First, we
consider the electron transport through a single impurity in a 1D conducting
channel and study a new regime of conduction related to LL sliding at voltage
above a threshold one. The DC current in this regime is accompanied by
oscillations with frequency $f =I/e$. This resembles the CDW depinning in
linear-chain conductors, the Josephson effect, and the Coulomb blockade.
Second, we found that strong pinning of the LL by impurities leads to a
magnetic field dependence of the low-temperature specific heat similar to that
observed experimentally in CDW compounds. We interpret this in favor of
possibility of formation of the LL in linear-chain compounds.",0811.3884v1
2008-11-25,Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors,"We develop an understanding of the anomalous metal state of the parent
compounds of recently discovered iron based superconductors starting from a
strong coupling viewpoint, including orbital degrees of freedom. On the basis
of an intermediate-spin (S=1) state for the Fe^{2+} ions, we derive a
Kugel-Khomskii spin-orbital Hamiltonian for the active t_{2g} orbitals. It
turns out to be a highly complex model with frustrated spin and orbital
interactions. We compute its classical phase diagrams and provide an
understanding for the stability of the various phases by investigating its
spin-only and orbital-only limits. The experimentally observed spin-stripe
state is found to be stable over a wide regime of physical parameters and can
be accompanied by three different types of orbital orders. Of these the
orbital-ferro and orbital-stripe orders are particularly interesting since they
break the in-plane lattice symmetry -- a robust feature of the undoped
compounds. We compute the magnetic excitation spectra for the effective spin
Hamiltonian, observing a strong reduction of the ordered moment, and point out
that the proposed orbital ordering pattern can be measured in resonant X-ray
diffraction.",0811.4104v1
2008-11-26,A new triclinic modification of the pyrochlore-type KOs2O6 superconductor,"A new modification of KOs2O6, the representative of a new structural type
(Pearson symbol aP18, a=5.5668(1)A, b=6.4519(2)A, c=7.2356(2)A, space group
P-1, no.2) was synthesized employing high pressure technique. Its structure was
determined by single-crystal X-ray diffraction. The structure can be described
as two OsO6 octahedral chains relating to each other through inversion and
forming big voids with K atoms inside. Quantum chemical calculations were
performed on the novel compound and structurally related cubic compound.
High-pressure X-ray study showed that cubic KOs2O6 phase was stable up to
32.5(2) GPa at room temperature.",0811.4353v1
2008-11-27,Entanglement transmission and generation under channel uncertainty: Universal quantum channel coding,"We determine the optimal rates of universal quantum codes for entanglement
transmission and generation under channel uncertainty. In the simplest scenario
the sender and receiver are provided merely with the information that the
channel they use belongs to a given set of channels, so that they are forced to
use quantum codes that are reliable for the whole set of channels. This is
precisely the quantum analog of the compound channel coding problem. We
determine the entanglement transmission and entanglement-generating capacities
of compound quantum channels and show that they are equal. Moreover, we
investigate two variants of that basic scenario, namely the cases of informed
decoder or informed encoder, and derive corresponding capacity results.",0811.4588v3
2008-11-27,Two-dimensional magnetism in the pnictide superconductor parent material SrFeAsF probed by muon-spin relaxation,"We report muon-spin relaxation measurements on SrFeAsF, which is the parent
compound of a newly discovered iron-arsenic-fluoride based series of
superconducting materials. We find that this material has very similar magnetic
properties to LaFeAsO, such as separated magnetic and structural transitions
(TN = 120 K, Ts = 175 K), contrasting with SrFe2As2 where they are coincident.
The muon oscillation frequencies fall away very sharply at TN, which suggests
that the magnetic exchange between the layers is weaker than in comparable
oxypnictide compounds. This is consistent with our specific heat measurements,
which find that the entropy change S = 0.05 J/mol/K largely occurs at the
structural transition and there is no anomaly at TN.",0811.4598v1
2008-11-28,Theory of the field-induced BEC in the frustrated spin-1/2 dimer compound BaCuSi2O6,"Building on recent neutron and NMR experiments, we investigate the
field-induced exotic criticality observed in the frustrated spin-1/2 dimer
compound BaCuSi2O6 using a frustrated model with two types of bilayers. A
semiclassical treatment of the effective hard-core boson model shows that
perfect inter-layer frustration leads to a 2D-like critical exponent phi=1
without logarithmic corrections and to a 3D low temperature phase with
different but non vanishing triplet populations in both types of bilayers.
These results further suggest a simple phenomenology in terms of a
field-dependent transverse coupling in the context of which we reproduce the
entire field-temperature phase diagram with Quantum Monte Carlo simulations.",0811.4745v4
2008-12-02,Inelastic X-ray Scattering by Electronic Excitations in Solids at High Pressure,"Investigating electronic structure and excitations under extreme conditions
gives access to a rich variety of phenomena. High pressure typically induces
behavior such as magnetic collapse and the insulator-metal transition in 3d
transition metals compounds, valence fluctuations or Kondo-like characteristics
in $f$-electron systems, and coordination and bonding changes in molecular
solids and glasses. This article reviews research concerning electronic
excitations in materials under extreme conditions using inelastic x-ray
scattering (IXS). IXS is a spectroscopic probe of choice for this study because
of its chemical and orbital selectivity and the richness of information it
provides. Being an all-photon technique, IXS has a penetration depth compatible
with high pressure requirements. Electronic transitions under pressure in 3d
transition metals compounds and $f$-electron systems, most of them strongly
correlated, are reviewed. Implications for geophysics are mentioned. Since the
incident X-ray energy can easily be tuned to absorption edges, resonant IXS,
often employed, is discussed at length. Finally studies involving local
structure changes and electronic transitions under pressure in materials
containing light elements are briefly reviewed.",0812.0538v2
2008-12-05,High-T_c superconductivity induced by doping rare earth elements into CaFeAsF,"We have successfully synthesized the fluoride-arsenide compounds
Ca$_{1-x}$RE$_x$FeAsF (RE=Nd, Pr; x=0, 0.6). The x-ray powder diffraction
confirmed that the main phases of our samples are Ca$_{1-x}$RE$_x$FeAsF with
the ZrCuSiAs structure. By measuring resistivity, superconductivity was
observed at 57.4 K in Nd-doped and 52.8 K in Pr-doped samples with x=0.6. Bulk
superconductivity was also proved by the DC magnetization measurements in both
samples. Hall effect measurements revealed hole-like charge carriers in the
parent compound CaFeAsF with a clear resistivity anomaly below 118 K, while the
Hall coefficient $R_H$ in the normal state is negative for the superconducting
samples Ca$_{0.4}$Nd$_{0.6}$FeAsF and Ca$_{0.4}$Pr$_{0.6}$FeAsF. This indicates
that the rare earth element doping introduces electrons into CaFeAsF which
induces the high temperature superconductivity.",0812.1192v1
2008-12-15,Structural and magnetic properties of the (Bi2-xPrx)Ru2O7 pyrochlore solid solution (0 <= x <= 2),"We report a detailed study of structural and magnetic properties of the
pyrochlore-type (Bi2-xPrx)Ru2O7 series. Eleven compositions with 0 <= x <= 2
were prepared by solid state reaction at 1050 degrees C and found to form a
solid solution in the whole range of compositions. Structural refinements from
X-ray powder diffraction data by the Rietveld method show that the main
variation concerns the ruthenium site. Ru-O distances increase and the Ru-O-Ru
angle (bridging corner-sharing Ru-O octahedra) decreases with increasing
praseodymium content, in agreement with the metal-semiconductor transition
observed previously in this system. Magnetic measurements show that the
metallic Pauli paramagnetism of Ru in Bi2Ru2O7 evolves to a magnetism of
localized low spin moments coexisting with the magnetism of Pr3+ cations
moments. Strong magnetic correlations are present at high Pr content, as
illustrated by a N\'eel temperature of -224 K for Pr2Ru2O7. However no evidence
of a magnetic ordering was found, suggesting that the end compound Pr2Ru2O7 of
the series might stabilize a spin liquid phase.",0812.2759v1
2009-01-03,Energy gap opening in submonolayer lithium on graphene: Local density functional and tight-binding calculations,"The adsorption of an alkali-metal submonolayer on graphene occupying every
third hexagon of the honeycomb lattice in a commensurate
$(\sqrt{3}\times\sqrt{3})R30^\circ$ arrangement induces an energy gap in the
spectrum of graphene. To exemplify this type of band gap, we present \textit{ab
initio} density functional theory calculations of the electronic band structure
of C$_6$Li. An examination of the lattice geometry of the compound system shows
the possibility that the nearest-neighbor hopping amplitudes have alternating
values constructed in a Kekul\'e-type structure. The band structure of the
textured tight-binding model is calculated and shown to reproduce the expected
band gap as well as other characteristic degeneracy removals in the spectrum of
graphene induced by lithium adsorption. More generally we also deduce the
possibility of energy gap opening in periodic metal on graphene compounds
C$_x$M if $x$ is a multiple of 3.",0901.0310v2
2009-01-07,Fission Barriers of Compound Superheavy Nuclei,"The dependence of fission barriers on the excitation energy of the compound
nucleus impacts the survival probability of superheavy nuclei synthesized in
heavy-ion fusion reactions. In this work, we investigate the isentropic fission
barriers by means of the self-consistent nuclear density functional theory. The
relationship between isothermal and isentropic descriptions is demonstrated.
Calculations have been carried out for $^{264}$Fm, $^{272}$Ds, $^{278}$112,
$^{292}$114, and $^{312}$124. For nuclei around $^{278}$112 produced in ""cold
fusion"" reactions, we predict a more rapid decrease of fission barriers with
excitation energy as compared to the nuclei around $^{292}$114 synthesized in
""hot fusion"" experiments. This is explained in terms of the difference between
the ground-state and saddle-point temperatures. The effect of the particle gas
is found to be negligible in the range of temperatures studied.",0901.0901v2
2009-01-14,"Electronic structure, linear, nonlinear optical susceptibilities and birefringence of CuInX2 (X = S, Se, Te) chalcopyrite-structure compounds","The electronic structure, linear and nonlinear optical properties have been
calculated for CuInX2 (X=S, Se, Te) chalcopyrite-structure single crystals
using the state-of-the-art full potential linear augmented plane wave (FP-LAPW)
method. We present results for band structure, density of states, and imaginary
part of the frequency-dependent linear and nonlinear optical susceptibilities.
We find that these crystals are semiconductors with direct band gaps. We have
calculated the birefringence of these crystals. The birefringence is negative
for CuInS2 and CuInSe2 while it is positive for CuInTe2 in agreement with the
experimental data. Calculations are reported for the frequency-dependent
complex second-order non-linear optical susceptibilities . The intra-band and
inter-band contributions to the second harmonic generation increase when we
replace S by Se and decrease when we replace Se by Te. We find that smaller
energy band gap compounds have larger values of in agreement with the
experimental data and previous theoretical calculations.",0901.2017v1
2009-01-14,ATR-FTIR spectroscopy detects alterations induced by organotin(IV) carboxylates in MCF-7 cells at sub-cytotoxic/-genotoxic concentrations,"The environmental impact of metal complexes such as organotin(IV) compounds
is of increasing concern. Genotoxic effects of organotin(IV) compounds (0.01
microg/ml, 0.1 microg/ml or 1.0 microg/ml) were measured using the alkaline
single-cell gel electrophoresis (comet) assay to measure DNA single-strand
breaks (SSBs) and the cytokinesis-block micronucleus (CBMN) assay to determine
micronucleus formation. Biochemical-cell signatures were also ascertained using
attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy.
In the comet assay, organotin(IV) carboxylates induced significantly-elevated
levels of DNA SSBs. Elevated micronucleus-forming activities were also
observed. Following interrogation using ATR-FTIR spectroscopy, infrared spectra
in the biomolecular range (900 cm-1 - 1800 cm-1) derived from orga...",0901.2039v1
2009-01-16,Evidence of spin-density-wave order in RFeAsO from measurements of thermoelectric power,"Data on the magneto-thermopower and specific heat of three compounds
belonging to '1111' oxypnictides family are reported. One specimen
(SmAsFeO0.8F0.2) is a superconductor with Tc = 53 K, while two others (SmAsFeO
and NdAsFeO) are nonsuperconducting parent compounds. Our results confirm that
spin density wave (SDW) order is present in SmAsFeO and NdAsFeO. In these two
samples a strict connection between the thermoelectric power and electronic
specific heat is found in the vicinity of SDW transition, what indicates that
the chemical potential of charge carriers strongly depends on temperature in
this region. Low temperature data suggest presence of significant contribution
magnon-drag to the thermoelectric power.",0901.2472v2
2009-01-16,Superconducting and magnetic properties of a new EuAsFeO0.85F0.15 superconductor,"Polycrystalline samples of a new superconducting EuAsFeO0.85F0.15 compound
with critical temperature Tc=11K were prepared by solid state synthesis. Its
electric and magnetic properties have been investigated in magnetic fields from
0.1 to 140000 Oe. Critical magnetic fields Hc1, and Hc2 were measured and hence
the magnetic penetration depths and the coherence length have been estimated.
The temperature dependence Hc2 (T) exhibits clear hyperbolic - type behavior
starting with the lowest fields. The data derived were used to estimate
probable high Tc and Hc2 in compounds doped with rare-earths having small
atomic radii.",0901.2478v1
2009-01-20,Field dependent mass enhancement in Pr_{1-x}La_xOs_4Sb_12 from aspherical Coulomb scattering,"The scattering of conduction electrons by crystalline electric field (CEF)
excitations may enhance their effective quasiparticle mass similar to
scattering from phonons. A wellknown example is Pr metal where the isotropic
exchange scattering from inelastic singlet-singlet excitations causes the mass
enhancement. An analogous mechanism may be at work in the skutterudite
compounds Pr_{1-x}La_xOs_4Sb_12 where close to x=1 the compound develops heavy
quasiparticles with a large linear specific heat coefficient. There the low
lying CEF states are singlet ground state and a triplet at 8 K. Due to the
tetrahedral CEF the main scattering mechanism must be the aspherical Coulomb
scattering. We derive the expression for mass enhancement in this model
including also the case of dispersive excitations. We show that for small to
moderate dispersion there is a strongly field dependent mass enhancement due to
the field induced triplet splitting. It is suggested that this effect may be
seen in Pr_{1-x}La_xOs_4Sb_12 with suitably large x when the dispersion is
small.",0901.3061v2
2009-01-24,Antiferromagnetic phase transition in four-layered high-T_c superconductors Ba_2Ca_3Cu_4O_8(F_yO_{1-y})_2 with T_c=55-102 K: Cu- and F-NMR studies,"We report on magnetic characteristics in four-layered high-T_c
superconductors Ba_2Ca_3Cu_4O_8(F_yO_{1-y})_2 with apical fluorine through Cu-
and F-NMR measurements. The substitution of oxygen for fluorine at the apical
site increases the carrier density (N_h) and T_c from 55 K up to 102 K. The NMR
measurements reveal that antiferromagnetic order, which can uniformly coexist
with superconductivity, exists up to N_h = 0.15, which is somewhat smaller than
N_h = 0.17 being the quantum critical point (QCP) for five-layered compounds.
The fact that the QCP for the four-layered compounds moves to a region of lower
carrier density than for five-layered ones ensures that the decrease in the
number of CuO_2 layers makes an interlayer magnetic coupling weaker.",0901.3810v1
2009-02-01,"Enhancement of positive magnetoresistance following a magnetic-field-induced ferromagnetic transition in an intermetallic compound, Tb5Si3","We report the existence of a field-induced ferromagnetic transition in the
magnetically ordered state (<69 K) of an intermetallic compound, Tb5Si3, and
this transition is distinctly first-order at 1.8 K (near 60 kOe), whereas it
appears to become second order near 20 K. The finding we stress is that the
electrical resistivity becomes suddenly large in the high-field state after
this transition and this is observed in the entire temperature range in the
magnetically ordered state. Such an enhancement of 'positive' magnetoresistance
(below 100 kOe) at the metamagnetic transition field is unexpected on the basis
that the application of magnetic field should favor a low-resistive state due
to alignment of spins.",0902.0153v1
2009-02-02,Density Functional Study of the Over-Doped Iron Chalcogenide: TlFe$_{2}$Se$_{2}$ with ThCr$_{2}$Si$_{2}$ structure,"We report density functional calculations of electronic structure and
magnetic properties of ternary iron chalcogenide TlFe$_{2}$Se$_{2}$, which
occurs in the ThCr$_{2}$Si$_{2}$ structure and discuss the results in relation
to the iron-based superconductors. The ground state is antiferromagnetic with
checkerboard order and Fe moment $\sim$ 1.90 $\mu$B. There is strong
magnetoelastic coupling similar to the Fe-based superconductors, reflected in a
sensitivity of the Se position to magnetism. Tl is monovalent in this compound,
providing heavy electron-doping of 0.5 additional carriers per Fe relative to
the parent compounds of the Fe-based superconductors. Other than the change in
electron count, the electronic structure is rather similar to those materials.
In particular, the Fermi surface is closely related to those of the Fe-based
superconductors, except that the electron cylinders are larger, and the hole
sections are suppressed. This removes the tendency towards a spin density wave.",0902.0265v1
2009-02-04,High Pressure Studies on Fe-Pnictide Superconductors,"A review of high-pressure studies on Fe-pnictide superconductors is given.
The pressure effects on the magnetic and superconducting transitions are
discussed for different classes of doped and undoped FeAs-compounds, ROFeAs (R
= rare earth), AeFe2As2 (Ae = Ca, Sr, Ba), and AFeAs (A = Li, Na). Pressure
tends to decrease the magnetic transition temperature in the undoped or only
slightly doped compounds. The superconducting Tc increases with pressure for
underdoped FeAs-pnictides, remains approximately constant for optimal doping,
and decreases linearly in the overdoped range. The undoped LaOFeAs and AeFe2As2
become superconducting under pressure although nonhydrostatic pressure
conditions seem to play a role in CaFe2As2. The superconductivity in the
(undoped) AFeAs is explained as a chemical pressure effect due to the volume
contraction caused by the small ionic size of the A-elements. The binary FeSe
shows the largest pressure coefficient of Tc in the Se-deficient
superconducting phase.",0902.0809v1
2009-02-10,Application of Secondary Neutral Mass Spectrometry in the investigation of doped perovskites,"Electromagnetic properties of doped perovskites depend sensitively on the
doping level. Both the superconducting transition temperature of
Bi2Sr2Ca(Pr)Cu2O8+d compounds and the magnetic and electronic transport
properties of La(Sr)Co(Fe)O3 perovskites change dramatically with the doping
level. Apart from doping, oxygen deficiency is influenced by the details of
preparation processes such as calcination and sintering. Simultaneous
determination of constituents is of crucial importance from sample
characterization point of view. Quantitative analysis of perovskite oxides can
be performed by Secondary Neutral Mass Spectrometry (SNMS) which is a suitable
technique to measure the chemical composition of almost any sample because the
flux of atoms sputtered from the sample is representative of the stoichiometry
of the top-most layers. The composition and oxygen content of
Bi2Sr2Ca0.86Pr0.14Cu2O8.4 and La1-xSrxCo0.975Fe0.025O3-d, where 0<x<0.5, were
determined by SNMS. The results show that the method is equally applicable for
insulating and conducting compounds. The observed electromagnetic properties
reflect well the compositions obtained experimentally.",0902.1649v1
2009-03-09,"Phonon Softening and Pressure-Induced Phase Transitions in Quartz Structured Compound, FePO4","Nuclear resonant inelastic x-ray scattering on quartz structured 57FePO4 as a
function of pressure, up to 8 GPa reveals hardening of the low-energy phonons
under applied pressures up to 1.5 GPa, followed by a large softening at 1.8 GPa
upon approaching the phase transition pressure of ~2 GPa. The pressure-induced
phase transitions in quartz-structured compounds have been predicted to be
related to a soft phonon mode at the Brillouin-zone boundary (1/3, 1/3, 0) and
to the break-down of the Born-stability criteria. Our results provide the first
experimental evidence of this predicted phonon softening.",0903.1550v1
2009-03-10,Multiferroicity with high-Tc in ceramics of the YBaCuFeO5 ordered perovskite,"A dielectric anomaly has been found near the incommensurate to commensurate
antiferromagnetic phase transition (TN2=230 K) in YBaCuFeO5 ceramics, a
compound which crystallizes in an ordered perovskite structure. The existence
of electric polarization below TN2 suggests the magnetism induced charge
polarization effect that is also confirmed by its strong magnetic field
dependence below TN2. Accordingly, the peak near TN2 of the magnetodielectric
effect indicates a maximum of magnetodielectric susceptibility near the spin
reorientation transition. Considering the abundance of magnetic compounds which
structures derive from the perovskite, these results might open up the way
toward the control of electric polarization near room temperature.",0903.1790v2
2009-03-10,The electronic structure of {\em R}NiC$_2$ intermetallic compounds,"First-principles calculations of the electronic structure of members of the
$R$NiC$_2$ series are presented, and their Fermi surfaces investigated for
nesting propensities which might be linked to the charge-density waves
exhibited by certain members of the series ($R$ = Sm, Gd and Nd). Calculations
of the generalized susceptibility, $\chi_{0}({\bf q},\omega)$, show strong
peaks at the same ${\bf q}$-vector in both the real and imaginary parts for
these compounds. Moreover, this peak occurs at a wavevector which is very close
to that experimentally observed in SmNiC$_2$. In contrast, for LaNiC$_2$ (which
is a superconductor below 2.7K) as well as for ferromagnetic SmNiC$_2$, there
is no such sharp peak. This could explain the absence of a charge-density wave
transition in the former, and the destruction of the charge-density wave that
has been observed to accompany the onset of ferromagnetic order in the latter.",0903.1814v2
2009-03-22,Influence of EGR compounds on the oxidation of an HCCI-diesel surrogate,"This paper presents an experimental and numerical study of the impact of
various additives on the oxidation of a typical automotive surrogate fuel
blend, i.e. n-heptane and toluene. It examines the impact of engine re-cycled
exhaust has compounds on the control of an Homogeneous Charge
Compression-Ignition (HCCI) engine. Series of experiments were performed in a
hihly diluted Jet-Stirred Reactor (JDR) at pressures of 1 and 10 atm (1 atm =
101,325 Pa). The chosen thermo-chemical conditions were close to those
characteristices of the pre-ignition period in an HCCI engine. The influence of
various additives, namely nitric oxide (NO), ethylene (C2H4) and methanol
(CH3OH), on the oxidation of a n-heptane/toluene blend was studied over a wide
range of temperatures (550-1100 K), including the zone of the Negative
Temperature Coefficient (NTC).",0903.3707v1
2009-03-25,Three- to Two-Dimensional Transition of the Electronic Structure in CaFe2As2 - parent compound for an iron arsenic high temperature superconductor,"We use angle-resolved photoemission spectroscopy (ARPES) to study the
electronic properties of CaFe2As2 - parent compound of a pnictide
superconductor. We find that the structural and magnetic transition is
accompanied by a three- to two-dimensional (3D-2D) crossover in the electronic
structure. Above the transition temperature (Ts) Fermi surfaces around Gamma
and X points are cylindrical and quasi-2D. Below Ts the former becomes a 3D
ellipsoid, while the latter remains quasi-2D. This finding strongly suggests
that low dimensionality plays an important role in understanding the
superconducting mechanism in pnictides.",0903.4388v1
2009-03-28,Formation of aromatics in rich methane flames doped by unsaturated compounds,"In order to better understand the importance of the different channels
leading to the first aromatic ring, we have investigated, the structure of a
laminar rich premixed methane flame doped with several unsaturated
hydrocarbons: allene and propyne, as they are precursors of propargyl radicals,
which are well known as having an important role in forming benzene,
1,3-butadiene, to put in evidence a possible production of benzene due to
reactions of C4 compounds, and, finally, cyclopentene, which is a source of
cyclopentadienyl methylene radicals which are supposed to easily isomerizes to
give benzene. A ratio additive / CH4 of 16 % and an equivalence ratio of 1.79
have been used. These flames have been stabilized on a burner at a pressure of
6.7 kPa using argon as dilutant. A new mechanism for the oxidation of allene,
propyne, 1,3 butadiene and cyclopentene has been proposed including the
formation and decomposition of benzene and toluene. The main reaction pathways
of formation of aromatics have been derived from flow rate analyses and have
been compared for the three types of additives.",0903.4947v1
2009-03-30,Ternary complexes of albumin-Mn(II)-bilirubin and Electron Spin Resonance studies of gallstones,"The stability of albumin-bilirubin complex was investigated depending on pH
of solution. It was shown that the stability of complex increases in presence
of Mn(II) ions. It was also investigated the paramagnetic composition of
gallstones by the electron spin resonance (ESR) method. It turned out that all
investigated gallstones contain a free bilirubin radical-the stable product of
its radical oxidation. Accordingly the paramagnetic composition gallstones
could be divided on three main types: cholesterol, brown pigment and black
pigment stones. ESR spectra of cholesterol stones is singlet with g=2.003 and
splitting between components 1.0 mT. At the same time the brown gallstones,
besides aforementioned signal contain the ESR spectrum which is characteristics
for Mn(II) ion complexes with inorganic compounds and, finally, in the black
pigment stones it was found out Fe(III) and Cu(II) complexes with organic
compounds and a singlet of bilirubin free radical. It is supposed that
crystallization centers of gallstones could be the polymer network of bilirubin
radical polymerization in complex with different metal ions earlier discovered
in gallstones.",0903.5313v1
2009-04-04,Electronic Evidence of Unusual Magnetic Ordering in a Parent Compound of FeAs-Based Superconductors,"High resolution angle-resolved photoemission measurements have been carried
out on BaFe2As2, a parent compound of the FeAs-based superconductors. In the
magnetic ordering state, there is no gap opening observed on the Fermi surface.
Instead, dramatic band structure reorganization occurs across the magnetic
transition. The appearance of the singular Fermi spots near (pi,pi) is the most
prominent signature of magnetic ordering. These observations provide direct
evidence that the magnetic ordering state of BaFe2As2 is distinct from the
conventional spin-density-wave state. They reflect the electronic complexity in
this multiple-orbital system and necessity in involving the local magnetic
moment in describing the underlying electron structure.",0904.0677v2
2009-04-06,Multipole decomposition of LDA+$U$ energy and its application to actinides compounds,"A general reformulation of the exchange energy of $5f$-shell is applied in
the analysis of the magnetic structure of various actinides compounds in the
framework of LDA+U method. The calculations are performed in an efficient
scheme with essentially only one free parameter, the screening length. The
results are analysed in terms of different polarisation channels, due to
different multipoles. Generally it is found that the spin-orbital polarisation
is dominating. This can be viewed as a strong enhancement of the spin-orbit
coupling in these systems. This leads to a drastic decrease in spin
polarisation, in accordance with experiments. The calculations are able to
correctly differentiate magnetic and non-magnetic Pu system. Finally, in all
magnetic systems a new multipolar order is observed, whose polarisation energy
is often larger in magnitude than that of spin polarisation.",0904.0742v5
2009-04-06,"New Series of Nickel-Based Pnictide Oxide Superconductors (Ni2Pn2)(Sr4Sc2O6) (Pn = P, As)","We have discovered new nickel-based pnictide oxide superconductors,
(Ni2Pn2)(Sr4Sc2O6) (Pn = P, As). These compounds have a tetragonal unit cell
with a space group of P4/nmm and they consist of alternate stacking of
anti-fluorite Ni2Pn2 layers and K2NiF4-type Sr4Sc2O6 blocking layers. Lattice
parameters were a = 4.044 A and c = 15.23 A for (Ni2P2)(Sr4Sc2O6) and a = 4.078
A and c = 15.41 A for (Ni2As2)(Sr4Sc2O6), indicating their thicker blocking
layers than that of LaNiPO (c ~ 8.1 A). Both (Ni2P2)(Sr4Sc2O6) and
(Ni2As2)(Sr4Sc2O6) exhibited superconductivity with zero resistivity at 3.3 K
and 2.7 K, respectively. The perfect diamagnetism observed in both compounds
guaranteed their bulk superconductivity.",0904.0825v4
2009-04-06,Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2,"Superconductivity was achieved in Ti-doped iron-arsenide compound
Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction
measurement shows that this material has a layered structure with the space
group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c =
15.8376 A. Clear diamagnetic signals in ac susceptibility data and
zero-resistance in resistivity data were detected at about 6 K, confirming the
occurrence of bulk superconductivity. Meanwhile we observed a superconducting
transition in the resistive data with the onset transition temperature at 29.2
K, which may be induced by the nonuniform distribution of the Cr/Ti content in
the FeAs-42622 phase, or due to some other minority phase.",0904.0972v3
2009-04-09,Model uncertainty in claims reserving within Tweedie's compound Poisson models,"In this paper we examine the claims reserving problem using Tweedie's
compound Poisson model. We develop the maximum likelihood and Bayesian Markov
chain Monte Carlo simulation approaches to fit the model and then compare the
estimated models under different scenarios. The key point we demonstrate
relates to the comparison of reserving quantities with and without model
uncertainty incorporated into the prediction. We consider both the model
selection problem and the model averaging solutions for the predicted reserves.
As a part of this process we also consider the sub problem of variable
selection to obtain a parsimonious representation of the model being fitted.",0904.1483v1
2009-04-09,Large Low Temperature Specific Heat in Pyrochlore Bi$_2$Ti$_2$O$_7$,"Both amorphous and crystalline materials frequently exhibit low temperature
specific heats in excess of what is predicted using the Debye model. The
signature of this excess specific heat is a peak observed in $C/T^3$
\textit{versus} $T$. To understand the curious absence of long-range ordering
of local distortions in the crystal structure of pyrochlore Bi$_2$Ti$_2$O$_7$,
we have measured the specific heat of crystalline Bi$_2$Ti$_2$O$_7$ and related
compounds. We find that the peak in $C/T^3$ versus $T$ in Bi$_2$Ti$_2$O$_7$
falls at a substantially lower temperature than other similar compounds,
consistent with the presence of disorder. This thermodynamic evidence for
disorder in crystalline Bi$_2$Ti$_2$O$_7$ is consistent with quenched
configurational disorder among Bi lone pairs produced by geometrical
frustration, which could represent a possible realization of ""charge ice"".",0904.1582v1
2009-04-15,"Direct imaging of the structural domains in iron pnictides AFe2As2 (A = Ca, Sr, Ba)","The parent compounds of recently discovered iron-arsenide superconductors,
$A$Fe$_2$As$_2$ with alkaline earth $A$=Ca, Sr, Ba, undergo simultaneous
structural and magnetic phase transitions at a temperature $T_{SM}$. Using a
combination of polarized light microscopy and spatially resolved high-energy
synchrotron X-ray diffraction we show that the orthorhombic distortion leads to
the formation of 45$^o$-type structural domains in all parent compounds.
Domains penetrate through the sample thickness in the $c$- direction and are
not affected by crystal defects such as growth terraces. The domains form
regular stripe patterns in the plane with a characteristic dimension of 10 to
50 $\mu m$. The direction of the stripes is fixed with respect to the
tetragonal (100) and (010) directions but can change by 90$^o$ on thermal
cycling through the transition. This domain pattern may have profound
implications for intrinsic disorder and anisotropy of iron arsenides.",0904.2337v2
2009-04-15,Fermi surface of SrFe$_2$P$_2$ determined by de Haas-van Alphen effect,"We report measurements of the Fermi surface (FS) of the ternary phosphide
SrFe$_2$P$_2$ using the de Haas-van Alphen effect. The calculated FS of this
compound is very similar to SrFe$_2$As$_2$, the parent compound of the high
temperature superconductors. Our data show that the Fermi surface is composed
of two electron and two hole sheets in agreement with bandstructure
calculations. Several of the sheets show strong c-axis warping emphasizing the
importance of three-dimensionality in the non-magnetic state of the ternary
pnictides. We find that the electron and hole pockets have a different
topology, implying that this material does not satisfy a nesting condition.",0904.2405v2
2009-04-20,First Principle Simulations of Heavy Fermion Cerium Compounds Based on the Kondo Lattice,"We propose a new framework for first-principle calculations of heavy-fermion
materials. These are described in terms of the Kondo lattice Hamiltonian with
the parameters extracted from a realistic density functional based calculation
which is then solved using continuous-time quantum Monte Carlo method and
dynamical mean field theory. As an example, we show our results for the Neel
temperatures of Cerium-122 compounds (CeX2Si2 with X=Ru, Rh, Pd, Cu, Ag, and
Au) where the general trend around the magnetic quantum critical point is
successfully reproduced. Our results are organized on a universal Doniach phase
diagram in a semi-quantitative way.",0904.3126v3
2009-04-21,Single step synthesis of Sr4V2O6Fe2As2: The blocking layer based potential future superconductor,"We report synthesis, structural details and transport measurements on
Sr4V2O6Fe2As2. Namely the stoichiometric amounts of V2O5 + SrO2 + Sr + 2FeAs
are weighed mixed, ground thoroughly and palletized in rectangular form in a
glove box in high purity Ar atmosphere. The pellet is further sealed in an
evacuated (10-5 Torr) quartz tube and put for heat treatments at 750 and 1150
0C in a single step for 12 and 36 hours respectively. Finally the quartz
ampoule is allowed to cool naturally to room temperature. The as synthesized
sample is black in color. The compound crystallized in P4/nmm space group with
lattice parameters a = b = 3.925A and c = 15.870A. Also seen are some small
impurity lines. The compound did not exhibit superconductivity but instead a
spin density wave (SDW) like metallic step at around 175 K is seen in R(T)
measurements",0904.3214v2
2009-04-23,First Principles Studies of Multiferroic Materials,"Multiferroics, materials where spontaneous long-range magnetic and dipolar
orders coexist, represent an attractive class of compounds, which combine rich
and fascinating fundamental physics with a technologically appealing potential
for applications in the general area of spintronics. Ab-initio calculations
have significantly contributed to recent progress in this area, by elucidating
different mechanisms for multiferroicity and providing essential information on
various compounds where these effects are manifestly at play. In particular,
here we present examples of density-functional theory investigations for two
main classes of materials: a) proper multiferroics (where ferroelectricity is
driven by hybridization or purely structural effects), with BiFeO_3 as
prototype material, and b) improper multiferroics (where ferroelectricity is
driven by correlation effects and is strongly linked to electronic degrees of
freedom such as spin, charge, or orbital ordering), with rare-earth manganites
as prototypes.",0904.3736v1
2009-04-24,A Compound Josephson Junction Coupler for Flux Qubits With Minimal Crosstalk,"An improved tunable coupling element for building networks of coupled
rf-SQUID flux qubits has been experimentally demonstrated. This new form of
coupler, based upon the compound Josephson junction rf-SQUID, provides a sign
and magnitude tunable mutual inductance between qubits with minimal nonlinear
crosstalk from the coupler tuning parameter into the qubits. Quantitative
agreement is shown between an effective one-dimensional model of the coupler's
potential and measurements of the coupler persistent current and
susceptibility.",0904.3784v3
2009-04-28,"Possible magnetoelectric coupling in the half doped charge ordered manganite, Pr_0.5Ca_0.5MnO_3-d","Magnetization, magnetoresistance, and magnetodielectric measurements have
been carried out on the half doped charge ordered manganite, Pr_0.5Ca_0.5MnO_3.
The low temperature state is found to be strongly dependent on the oxygen
stoichiometry whereas the high temperature state remains almost unaltered. A
disorder driven phase separation in the low temperature state is noticed in the
magnetic, magnetoresistance, and dielectric measurements which is attributed to
the oxygen deficiency in the compound. A considerable magnetodielectric (MD)
effect is noticed close to room temperature at 280 K which is fascinating for
technological applications. The strongest MD effect observed in between 180 K
and 200 K is found to be uncorrelated with magnetoresistance but it is
suggested to be due to a number of intricate processes occuring in this
temperature range which includes paramagnetic to antiferromagnetic transition,
incommensurate to commensurate charge ordering and orbital ordering. The
strongest MD effect seems to emerge from the high sensitivity of the
incommensurate state to the external perturbation such as external magnetic
field. The results propose the possible magnetoelectric coupling in the charge
ordered compound.",0904.4309v1
2009-04-28,Ising versus XY anisotropy in frustrated R$_{2}$Ti$_{2}$O$_7$ compounds as seen by polarized neutrons,"We studied the field induced magnetic order in R$_{2}$Ti$_{2}$O$_7$
pyrochlore compounds with either uniaxial (R=Ho, Tb) or planar (R=Er, Yb)
anisotropy, by polarized neutron diffraction. The determination of the local
susceptibility tensor \{$\chi_\parallel,\chi_\perp$\} provides a universal
description of the field induced structures in the paramagnetic phase (2-270
K), whatever the field value (1-7 T) and direction. Comparison of the thermal
variations of $\chi_\parallel$ and $\chi_\perp$ with calculations using the
rare earth crystal field shows that exchange and dipolar interactions must be
taken into account. We determine the molecular field tensor in each case and
show that it can be strongly anisotropic.",0904.4440v1
2009-04-28,Low-temperature thermal conductivity of BaFe2As2: Parent compound of iron-arsenide superconductors,"We report low-temperature thermal conductivity down to 40 mK of the
antiferromagnet BaFe$_2$As$_{2}$, which is the parent compound of recently
discovered iron-based superconductors. In the investigated temperature range
below 4 K, the thermal conductivity $\kappa$ is well described by the
expression $\kappa$ = $aT$ + $bT^{2.22}$. We attribute the ``$aT$''-term to an
electronic contribution which is found to satisfy the Wiedemann-Franz law in
the $T$ $\to$ 0 K limit, and the remaining thermal conductivity, $\sim$
$T^{2.22}$, is attributed to phonon conductivity. A small influence on thermal
conductivity by magnetic fields up to 8 T is well accounted by the observed
magnetoresistance. The result is consistent with a fully gapped magnon
spectrum, inferred previously from inelastic neutron scattering measurements.",0904.4470v3
2009-05-04,Unusual Fermi surface nesting in parent compounds of iron arsenic high temperature superconductors revealed by Angle Resolved Photoemission Spectroscopy,"We use angle resolved photoemission spectroscopy (ARPES) to study the band
structure of BaFe2As2 and CaFe2As2, two of the parent compounds of the iron
arsenic high temperature superconductors. We find clear evidence for band back
folding and hybridization demonstrating that conduction electrons are strongly
affected by the emergence of magnetic order. Our high quality data revealed
that although the Fermi surface is strongly three-dimensional, it does indeed
have long parallel segments along the kz direction that can lead to the
emergence of magnetic order. More interestingly, we find very unusual
incommensurate nesting of the Fermi surface in the a-b plane that is present
only at low temperatures. We speculate that this is a signature of a failed
Charge Density Wave (CDW) state that was predicted by renormalization group
studies.",0905.0271v1
2009-05-04,Asymmetric quintuplet condensation in the frustrated S=1 spin dimer compound Ba3Mn2O8,"Ba3Mn2O8 is a spin-dimer compound based on pairs of S = 1, 3d2, Mn5+ ions
arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads
to a singlet ground state in zero-field, with excited triplet and quintuplet
states at higher energy. High field thermodynamic measurements are used to
establish the phase diagram, revealing a substantial asymmetry of the
quintuplet condensate. This striking effect, all but absent for the triplet
condensate, is due to a fundamental asymmetry in quantum fluctuations of the
paramagnetic phases near the various critical fields.",0905.0467v2
2009-05-08,High-pressure structural investigation of several zircon-type orthovanadates,"Room temperature angle-dispersive x-ray diffraction measurements on
zircon-type EuVO4, LuVO4, and ScVO4 were performed up to 27 GPa. In the three
compounds we found evidence of a pressure-induced structural phase
transformation from zircon to a scheelite-type structure. The onset of the
transition is near 8 GPa, but the transition is sluggish and the low- and
high-pressure phases coexist in a pressure range of about 10 GPa. In EuVO4 and
LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa.
The equations of state for the zircon and scheelite phases are also determined.
Among the three studied compounds, we found that ScVO4 is less compressible
than EuVO4 and LuVO4, being the most incompressible orthovanadate studied to
date. The sequence of structural transitions and compressibilities are
discussed in comparison with other zircon-type oxides.",0905.1206v1
2009-05-09,Low ordered magnetic moment by off-diagonal frustration in undoped parent compounds to iron-based high-Tc superconductors,"A Heisenberg model over the square lattice recently introduced by Si and
Abrahams to describe local-moment magnetism in the new class of Fe-As high-Tc
superconductors is analyzed in the classical limit and on a small cluster by
exact diagonalization. In the case of spin-1 iron atoms, large enough
Heisenberg exchange interactions between neighboring spin-1/2 moments on
different iron 3d orbitals that frustrate true magnetic order lead to hidden
magnetic order that violates Hund's rule. It accounts for the low ordered
magnetic moment observed by elastic neutron diffraction in an undoped parent
compound to Fe-As superconductors. We predict that low-energy spin-wave
excitations exist at wavenumbers corresponding to either hidden Neel or hidden
ferromagnetic order.",0905.1359v2
2009-05-13,Temperature-dependent striped antiferromagnetism of LaFeAsO in a Green's function approach,"We use a Green's function method to study the temperature-dependent average
moment and magnetic phase-transition temperature of the striped
antiferromagnetism of LaFeAsO, and other similar compounds, as the parents of
FeAs-based superconductors. We consider the nearest and the next-nearest
couplings in the FeAs layer, and the nearest coupling for inter-layer spin
interaction. The dependence of the transition temperature TN and the
zero-temperature average spin on the interaction constants is investigated. We
obtain an analytical expression for TN and determine our temperature-dependent
average spin from zero temperature to TN in terms of unified self-consistent
equations. For LaFeAsO, we obtain a reasonable estimation of the coupling
interactions with the experimental transition temperature TN = 138 K. Our
results also show that a non-zero antiferromagnetic (AFM) inter-layer coupling
is essential for the existence of a non-zero TN, and the many-body AFM
fluctuations reduce substantially the low-temperature magnetic moment per Fe
towards the experimental value. Our Green's function approach can be used for
other FeAs-based parent compounds and these results should be useful to
understand the physical properties of FeAs-based superconductors.",0905.2005v1
2009-05-15,Mixed pairing symmetry in κ-(BEDT-TTF)_2 X organic superconductors from ultrasonic velocity measurements,"Discontinuities in elastic constants are detected at the superconducting
transition of layered organic conductors \kappa-(BEDT-TTF)_{2}X by longitudinal
and transverse ultrasonic velocity measurements. Symmetry arguments show that
discontinuities in shear elastic constants can be explained in the orthorhombic
compound only if the superconducting order parameter has a mixed character that
can be of two types, either A_{1g}+B_{1g} or B_{2g}+B_{3g} in the
classification of irreducible representations of the orthorhombic point group
D_{2h}. Consistency with other measurements suggests that the A_{1g}+B_{1g}
(d_{xy}+d_{z(x+y)}) possibility is realized. Such clear symmetry-imposed
signatures of mixed order parameters have not been observed in other
superconducting compounds.",0905.2609v1
2009-05-18,Specific Heat-Coefficient of YbAl3 Studied by Combined Nearly Free Electron Conduction Band Hybridized with Localized f Electrons with Correlation Effect,"Based on the recently proposed band model, the electronic specific heat of
moderately heavy electron compound YbAl$_3$ are investigated. The band term of
the Hamiltonian consists of three parts; conduction electrons described by the
nearly free electron method, localized 4f electrons of Yb ions and the
hybridization term between these electrons. Extracting several bands near the
Fermi level, we reconstruct the low-energy effective Hamiltonian in order to
consider the correlation effect, which is studied by using the self-consistent
second order perturbation theory combined with local approximation. The
temperature dependence of the specific heat $c_{\rm v}(T)$ is calculated as a
function of temperature $T$ from the numerical derivative of the internal
energy. Sommerfeld coefficient $\gamma$ is also calculated from the direct
formula. The overall structure of $c_{\rm v}(T)/T$ is in quantitative agreement
with the experimental results, which have the characteristic two-peak
structures. They originate from the correlation effect and the structure of the
non-interacting density of states, respectively. We show that our effective
Hamiltonian yielding the realistic band structure may describe quantitatively
heavy electron compounds with conduction bands composed of s- or p- electrons.",0905.2848v1
2009-05-18,Ferro-Orbital Order and Strong Magnetic Anisotropy in the Parent Compounds of Iron-Pnictide Superconductors,"The puzzling nature of magnetic and lattice phase transitions of iron
pnictides is investigated via a first-principles Wannier function analysis of
representative parent compound LaOFeAs. A rare ferro-orbital ordering is found
to give rise to the recently observed highly anisotropic magnetic coupling, and
drive the phase transitions--without resorting to widely employed frustration
or nesting picture. The revealed necessity of the additional orbital physics
leads to a correlated electronic structure fundamentally distinct from that of
the cuprates. In particular, the strong coupling to the magnons advocates
active roles of light orbitons in spin dynamics and electron pairing in iron
pnictides.",0905.2957v2
2009-05-20,Heavy fermion behavior in PrRh2B2C: Excitonic mass enhancement,"We report magnetic and transport properties of a new quaternary borocarbide
PrRh$_{2}$B$_{2}$C, based on magnetisation, resistivity and specific heat
studies. This compound forms in LuNi$_{2}$B$_{2}$C-type tetragonal structure
(space group {\it I4/mmm}) and does not exhibit magnetic ordering or
superconductivity down to 0.5 K. The crystal field analysis of specific heat
data suggests a singlet ground state in this compound. The high value of the
Sommerfeld coefficient, $\gamma$ $\approx$ 250 mJ/mole K$^{2}$, together with a
singlet ground state suggests that the heavy fermion behaviour in
PrRh$_{2}$B$_{2}$C results from the interaction of the conduction electrons
with the low lying crystal field excitations. No signature of magnetic ordering
or superconductivity is observed in PrRh$_{2}$B$_{2}$C under the application of
pressure up to 23 kbar.",0905.3266v1
2009-05-26,Compensated magnetism by design in double perovskite oxides,"Taking into account Goodenough's superexchange rules, including both full
structural relaxation and spin-orbit coupling, and checking strong correlation
effects, we look for compensated half metals within the class of oxide double
perovskites materials. Identifying likely half metallic (or half semimetallic)
antiferromagnets, the full complications including orbital magnetism are
included in order to arrive at realistic predictions of designed magnetic
compounds with (near) vanishing net moment. After sorting through several
candidates that have not been considered previously, two materials,
K$_2$MnRhO$_6$ and La$_2$CrWO$_6$, remain as viable candidates. An important
factor is obtaining compounds either with very small induced orbital moment
(helped by closed subshells) or with an orbital moment that compensates the
spin-orbit driven degradation of half metallic character. While thermodynamic
stability of these materials cannot be ensured, the development of
layer-by-layer oxide deposition techniques does not require that materials be
thermodynamically stable to be synthesized.",0905.4199v1
2009-05-28,Large-J approach to strongly coupled spin-orbital systems,"We present a novel approach to study the ground state and elementary
excitations in compounds where spins and orbitals are entangled by on-site
relativistic spin-orbit interaction. The appropriate degrees of freedom are
localized states with an effective angular momentum J. We generalize J to
arbitrary large values while maintaining the delicate spin-orbital
entanglement. After projecting the inter-site exchange interaction to the
manifold of effective spins, a systematic 1/J expansion of the effective
Hamiltonian is realized using the Holstein-Primakoff transformation.
Applications to representative compounds Sr2IrO4 and particularly vanadium
spinels AV2O4 are discussed.",0905.4728v3
2009-06-01,WDX-Analysis of the New Superconductors RO(1-x)F(x)FeAs and Its Consequences on the Electronic Phase Diagram,"Polycrystalline samples of RO1-xFxFeAs (0 < x < 0.25) (R = La, Sm, Gd) were
investigated by wavelength-dispersive X-ray spectroscopy (WDX) in the electron
microscope to determine the composition of the samples, in particular the
fluorine content. It was found that the measured fluorine content can deviate
considerably from the initial weight. In the lanthanum compound LaO1-xFxFeAs,
we found good agreement mainly for x > 0.05, but for x < 0.05 the fluorine
hardly goes into the sample. For the samarium compound we measured less than
half the fluorine in the sample as initially weighed at all fluorine
concentrations. These measured values are taken into account when drawing the
electronic phase diagrams of LaO1-xFxFeAs and SmO1-xFxFeAs. This leads to a
more consistent picture of both of the diagrams in comparison to the plot of
the initial weight.",0906.0326v1
2009-06-04,First principles calculations of X-ray absorption in an ultrasoft pseudopotentials scheme: from $α$-quartz to high-T$_c$ compounds,"We develop a first-principles scheme based on the continued fraction approach
an d ultrasoft pseudopotentials to calculate K-edge X-ray absorption spectra in
solids. The method allows for calculations of K-edge X-ray absorption spectra
in transition metal and rare-earths compounds with substantially reduced
cutoffs respect to the norm-conserving case. We validate the method by
calculating Si and O K-edges in $\alpha$ quartz, Cu K-edge in Copper and in
La$_2$CuO$_4$. For the case of Si and O edges in $\alpha$ quartz and in Copper
we obtain a good agreement with experimental data. In the Cu K-edge spectra of
La$_2$CuO$_4$, a material considered a real challeng e for density functional
theory we attribute all the near-edge and far-edge peaks to single particle
excitations.",0906.0897v2
2009-06-08,"The observation of a positive magnetoresistance and close correlation among lattice, spin and charge around TC in antipervoskite SnCMn3","The temperature dependences of magnetization, electrical transport, and
thermal transport properties of antiperovskite compound SnCMn3 have been
investigated systematically. A positive magnetoresistance (~11%) is observed
around the ferrimagnetic-paramagnetic transition (TC ~ 280 K) in the field of
50 kOe, which can be attributed to the field-induced magnetic phase transition.
The abnormalities of resistivity, Seebeck coefficient, normal Hall effect and
thermal conductivity near TC are suggested to be associated with an abrupt
reconstruction of electronic structure. Further, our results indicate an
essential interaction among lattice, spin and charge degrees of freedom around
TC. Such an interaction among various degrees of freedom associated with sudden
phase transition is suggested to be characteristic of Mn-based antiperovskite
compounds.",0906.1511v1
2009-06-10,Three-dimensional electronic structure of superconducting iron pnictides observed by angle-resolved photoemission spectroscopy,"We have performed an angle-resolved photoemission spectroscopy (ARPES) study
of the undoped and electron-doped iron pnictides BaFe2\_{-x}CoxAs2 (Ba122)
(x=0, 0.14) and studied the Fermi surfaces (FSs) and band dispersions near the
Fermi level. The FS sheets we observed are consistent with the shrinkage of the
hole-like pockets around the Brillouin Zone (BZ) center and the expansion of
the electron pockets around the BZ corner in the electron-doped compound as
compared to the undoped parent compound. Band dispersions and FSs around the BZ
center strongly depend on the photon energy, indicating the three-dimensional
(3D) electronic structure. This observation suggests that the
antiferromagnetism and superconductivity in the pnictides may have to be
considered including the orbital-dependent 3D electronic structure, where FS
nesting is not necessarily strong.",0906.1846v1
2009-06-17,On the Compound MIMO Broadcast Channels with Confidential Messages,"We study the compound multi-input multi-output (MIMO) broadcast channel with
confidential messages (BCC), where one transmitter sends a common message to
two receivers and two confidential messages respectively to each receiver. The
channel state may take one of a finite set of states, and the transmitter knows
the state set but does not know the realization of the state. We study
achievable rates with perfect secrecy in the high SNR regime by characterizing
an achievable secrecy degree of freedom (s.d.o.f.) region for two models, the
Gaussian MIMO-BCC and the ergodic fading multi-input single-output (MISO)-BCC
without a common message. We show that by exploiting an additional temporal
dimension due to state variation in the ergodic fading model, the achievable
s.d.o.f. region can be significantly improved compared to the Gaussian model
with a constant state, although at the price of a larger delay.",0906.3200v1
2009-06-18,Zig-zag ladders with staggered magnetic chirality in S = 3/2 compound beta-CaCr2O4,"The crystal and magnetic structures of the S = 3/2 chain antiferromagnet
beta-CaCr2O4 have been investigated by means of specific heat, magnetization,
muon relaxation and neutron powder diffraction between 300K and 1.5K. Owing to
the original topology of the Cr3+ magnetic lattice, which can be described as a
network of triangular ladders, equivalent to chains with nearest and
next-nearest neighbors interactions, evolution of the magnetic scattering
intensity in this compound evidences two magnetic regimes : for 21K < T < 270K,
a low-dimensionality magnetic ordering of the Cr3+ spins is observed,
simultaneously with a strong contraction of the ladder legs, parallel to c.
Below TN = 21K, a complex antiferromagnetic ordering is evidenced, with an
incommensurate propagation vector k = (0, 0, q) (q ~ 0.477 at 1.5K), as
exchange interactions between ladders become significant. This complex magnetic
ordering can be described as a honeycomb-like arrangement of cycloids, running
along c, with staggered chiralities. The experimental observation of this
staggered chirality can be understood by taking into account antisymmetric
Dzyaloshinskii-Moriya exchange terms.",0906.3378v1
2009-06-19,Non-adiabatic phonons within the doped graphene layers of XC$_6$ compounds,"We report the first Raman scattering measurements of BaC$_6$, SrC$_6$, and
YbC$_6$, which along with new data on CaC$_6$, permits a systematic study of
the phonons and the electron-phonon interaction within the doped graphene
layers of these compounds. The out-of-plane carbon phonon softens as the
spacing of the graphene layers is reduced in the series BaC$_6$, SrC$_6$,
YbC$_6$, and CaC$_6$. This is due to increasing charge in the $\pi^*$
electronic band. Electron-phonon interaction effects between the in-plane
carbon modes at $\approx1500$\invcm and the $\pi^*$ electrons cause a strong
non-adiabatic renormalization. As charge is transferred into the $\pi^*$ band
these non-adiabatic effects are found to increase concurrent with a reduction
in the phonon lifetime.",0906.3609v3
2009-06-21,Magnetotransport properties in purple bronze Li$_{0.9}$Mo$_6$O$_{17}$ Single Crystal,"We have measured resistivity along the a, b and c axes of
Li$_{0.9}$Mo$_6$O$_{17}$ single crystal. The anisotropy $\rho$$_c$ / $\rho$$_a$
and $\rho$$_c$ / $\rho$$_b$ is given, confirming the quasi-one-dimensionality
of the compound. The sharp decrease in the anisotropy below a certain
temperature (T$_M$) indicates dimensional crossover. Superconductivity occurs
at 1.8 K well below $T_M$. Negative MRs are observed with magnetic field (H)
applied along b axis. This could be ascribed to suppression of energy gap
associated with CDW state. While large positive MR is observed with H
$\parallel$ c-axis. The MR data can be well fitted by a modified two-band model
which has been used in CDW compounds such as quasi-two-dimensional purple
bronzes A$_{0.9}$Mo$_6$O$_{17}$ (A = K, Na, Tl) and quasi-one-dimensional
conductor NbSe$_3$. The behavior of MR provides a strong evidence for the
existence of CDW instability in $Li_{0.9}Mo_6O_{17}$.",0906.3855v1
2009-06-25,Rattling-Induced Superconductiviy in the Beta-Pyrochlore Oxides AOs2O6,"The superconducting properties of two beta-pyrochlore oxides, CsOs2O6 and
RbOs2O6, are studied by thermodynamic and transport measurements using
high-quality single crystals. It is shown that the character of
superconductivity changes systematically from weak coupling for CsOs2O6 to
moderately strong coupling for RbOs2O6, and finally to extremely strong
coupling with BCS-type superconductivity for KOs2O6, with increasing Tc.
Strong-coupling correction analyses of the superconducting properties reveal
that a low-energy rattling mode of the alkali metal ions is responsible for the
mechanism of the superconductivity in each compound. The large enhancement of
Tc from Cs to K is attributed to the increase in the electron-rattler coupling
with decreasing characteristic energy of the rattling and with increasing
anharmonicity. The existence of weak anisotropy in the superconducting gap or
in the electron-rattler interactions is found for the Cs and Rb compounds.",0906.4656v1
2009-07-02,Exploring the spin-1/2 frustrated square lattice model with high-field magnetization measurements,"We report on high-field magnetization measurements for a number of layered
vanadium phosphates that were recently recognized as spin-1/2 frustrated square
lattice compounds with ferromagnetic nearest-neighbor couplings (J_1) and
antiferromagnetic next-nearest-neighbor couplings (J_2). The saturation fields
of the materials lie in the range from 4 to 24 T and show excellent agreement
with the previous estimates of the exchange couplings deduced from low-field
thermodynamic measurements. The consistency of the high-field data with the
regular frustrated square lattice model provides experimental evidence for a
weak impact of spatial anisotropy on the nearest-neighbor couplings in layered
vanadium phosphates. The variation of the J_2/J_1 ratio within the compound
family facilitates the experimental access to the evolution of the
magnetization curve upon the change of the frustration magnitude. Our results
support the recent theoretical prediction by Thalmeier et al. [Phys. Rev. B,
77, 104441 (2008)] and give evidence for the enhanced bending of the
magnetization curves due to the increasing frustration of the underlying spin
system.",0907.0391v1
2009-07-09,Importance of the atom-pair bond in metallic alloying,"Rajasekharan and Girgis reported that binary systems with intermetallic
compounds of a particular crystal structure form a straight line on a map using
Miedema parameters. In this paper, the universality of that observation is
examined. Observations from a study of 143 binary systems that crystallize in
six different crystal structures at AB3 composition are discussed. Prediction
of concomitant and mutually exclusive structure types in binary metallic phase
diagrams, and of phase transitions among different structure types, has been
demonstrated. This behavior is unexpected because Miedema parameters are
isotropic in nature and structural energies are generally assumed to be small.
We argue in this paper that each point on the map stands for the energy of an
unlike atom-pair (A-B) bond, with the bond energy remaining nearly the same at
all compositions in the phase diagram. This argument is confirmed by comparing
the nearest-neighbour (A-B) bond lengths for the compounds of the structure
types CaCu5 and CsCl, when concomitant with MgCu2 structure type. This fact
leads to an important conclusion that one can define a bond energy for the
metallic unlike-atom-pair bond as is usually done for a conventional chemical
bond.",0907.1589v1
2009-07-15,Obtaining correct orbital ground states in $f$ electron systems using a nonspherical self-interaction corrected LDA+$U$ method,"The electronic structure of lanthanide and actinide compounds is often
characterized by orbital ordering of localized $f$-electrons.
Density-functional theory (DFT) studies of such systems using the currently
available LDA+$U$ method are plagued by significant orbital-dependent
self-interaction, leading to erroneous orbital ground states. An alternative
scheme that modifies the exchange, not Hartree, energy is proposed as a remedy.
We show that our LDA+$U$ approach reproduces the expected degeneracy of $f^1$
and $f^2$ states in free ions and the correct ground states in solid PrO$_2$.
We expect our method to be useful in studying compounds of $f$- and heavy-$d$
elements.",0907.2700v2
2009-07-23,Structural phase transition in TmxFe1-xSe0.85 (Tm = Mn and Cu) and its relation to superconductivity,"In this letter, we report the results of detailed studies on Mn- and
Cu-substitution to Fe-site of beta-FeSe, namely MnxFe1-xSe0.85 and
CuxFe1-xSe0.85. The results show that with only 10 at% Cu-doping the compound
becomes a Mott insulator. Detailed temperature dependent structural analyses of
these Mn- and Cu-substituted compounds show that the structural transition,
which is associated with the changes in the building block FeSe4 tetrahedron,
is essential to the occurrence of superconductivity in beta-FeSe.",0907.4001v1
2009-07-23,Nature of the Magnetic Order in BaMn2As2,"Neutron diffraction measurements have been performed on a powder sample of
BaMn2As2 over the temperature T range from 10 K to 675 K. These measurements
demonstrate that this compound exhibits collinear antiferromagnetic ordering
below the Neel temperature T_N = 625(1) K. The ordered moment mu = 3.88(4)
mu_B/Mn at T = 10 K is oriented along the c axis and the magnetic structure is
G-type, with all nearest-neighbor Mn moments antiferromagnetically aligned. The
value of the ordered moment indicates that the oxidation state of Mn is Mn^{2+}
with a high spin S = 5/2. The T dependence of mu suggests that the magnetic
transition is second-order in nature. In contrast to the closely related
AFe2As2 (A = Ca, Sr, Ba, Eu) compounds, no structural distortion is observed in
the magnetically ordered state of BaMn2As2.",0907.4094v2
2009-07-23,Superconductivity in the Iron-Pnictide Parent Compound SrFe2As2,"The appearance of superconductivity at ambient pressures in the undoped iron
pnictide parent compound SrFe2As2 is studied experimentally using several
techniques and approaches to aid in understanding the nature of this phase. Low
temperature magnetization measurements of single crystals of SrFe2As2 reveal
diamagnetic screening due to the onset of superconductivity below 21 K, with
volume fraction estimates varying between 0 and 15 percent. The effects of heat
treatment and cold-working via severe mechanical deformation on the
superconducting phase found are studied, showing that superconductivity can be
suppressed via modest annealing and reinstated by cold-working.",0907.4141v1
2009-07-30,Synthesis and structural characterization of 2Dioxane.2H2O.CuCl2: metal-organic compound with Heisenberg antiferromagnetic S=1/2 chains,"A novel organometallic compound 2Dioxane.CuCl2.2H2O has been synthesized and
structurally characterized by X-ray crystallography. Magnetic susceptibility
and zero-field inelastic neutron scattering have also been used to study its
magnetic properties. It turns out that this material is a weakly coupled
one-dimensional S=1/2 Heisenberg antiferromagnetic chain system with chain
direction along the crystallographic c axis and the nearest-neighbor
intra-chain exchange constant J=0.85(4) meV. The next-nearest-neighbor
inter-chain exchange constant J' is also estimated to be 0.05 meV. The observed
magnetic excitation spectrum from inelastic neutron scattering is in excellent
agreement with numerical calculations based on the Muller ansatz.",0907.5428v2
2009-08-03,"Electronic and magnetic properties of the kagome systems YBaCo4O7 and YBaCo3MO7 (M=Al, Fe)","We present a combined experimental and theoretical x-ray absorption
spectroscopy (XAS) study of the new class of cobaltates YBaCo4O7 and YBaCo3MO7
(M= Al, Fe). The focus is on the local electronic and magnetic properties of
the transition metal ions in these geometrically frustrated kagome compounds.
For the mixed valence cobaltate YBaCo4O7, both the Co2+ and Co3+ are found to
be in the high spin state. The stability of these high spin states in
tetrahedral coordination is compared with those in the more studied case of
octahedral coordination. For the new compound YBaCo3FeO7, we find exclusively
Co2+ and Fe3+ as charge states.",0908.0226v1
2009-08-10,Possible anisotropic superconducting pairing in cubic ThPt4Ge12,"Transverse-field muon-spin-rotation measurements have been carried out for
polycrystalline ThPt4Ge12. The magnetic penetration depth $\lambda$ and the
superconducting coherence length $\xi$ in the vortex state of this compound
were found to be 112(5) nm and 32(2) nm, respectively. We have estimated the
effective mass of the quasiparticles $m^* \approx 4.6\times m_e$, the
superfluid carrier density $n_s \approx 1.02 \times 10^{28}$ carriers/m$^{3}$,
and the zero-temperature superconducting gap 0.67 meV, corresponding to the
ratio: 2$\Delta(0)/k_BT_c$ = 3.76. We found markable difference between the
temperature dependence of the vortex state muon-spin relaxation rate ZFC- and
FC-$\sigma_s(T)$ below the irreversibility temperature $T_{ir} \sim $ 2.5 K.
Linear field dependence of $\lambda(H)$, small ratio $T_{ir}/T_c$, and power
law behavior of the temperature dependencies of $\lambda(T)$ seem to be
consistent with anisotropic superconducting pairing in the compound studied.
The analysis of correlation between the superconducting transition temperature
and the effective Fermi temperature within the Uemura classification scheme
reveals that ThPt4Ge belongs to the same class of exotic superconductors.",0908.1304v1
2009-08-12,Nonparametric empirical Bayes and compound decision approaches to estimation of a high-dimensional vector of normal means,"We consider the classical problem of estimating a vector
$\bolds{\mu}=(\mu_1,...,\mu_n)$ based on independent observations $Y_i\sim
N(\mu_i,1)$, $i=1,...,n$. Suppose $\mu_i$, $i=1,...,n$ are independent
realizations from a completely unknown $G$. We suggest an easily computed
estimator $\hat{\bolds{\mu}}$, such that the ratio of its risk
$E(\hat{\bolds{\mu}}-\bolds{\mu})^2$ with that of the Bayes procedure
approaches 1. A related compound decision result is also obtained. Our
asymptotics is of a triangular array; that is, we allow the distribution $G$ to
depend on $n$. Thus, our theoretical asymptotic results are also meaningful in
situations where the vector $\bolds{\mu}$ is sparse and the proportion of zero
coordinates approaches 1. We demonstrate the performance of our estimator in
simulations, emphasizing sparse setups. In ``moderately-sparse'' situations,
our procedure performs very well compared to known procedures tailored for
sparse setups. It also adapts well to nonsparse situations.",0908.1712v1
2009-08-14,Critical properties of the unconventional spin-Peierls system TiOBr,"We have performed detailed x-ray scattering measurements on single crystals
of the spin-Peierls compound TiOBr in order to study the critical properties of
the transition between the incommensurate spin-Peierls state and the
paramagnetic state at Tc2 ~ 48 K. We have determined a value of the critical
exponent beta which is consistent with the conventional 3D universality
classes, in contrast with earlier results reported for TiOBr and TiOCl. Using a
simple power law fit function we demonstrate that the asymptotic critical
regime in TiOBr is quite narrow, and obtain a value of beta_{asy} = 0.32 +/-
0.03 in the asymptotic limit. A power law fit function which includes the first
order correction-to-scaling confluent singularity term can be used to account
for data outside the asymptotic regime, yielding a more robust value of
beta_{avg} = 0.39 +/- 0.05. We observe no evidence of commensurate fluctuations
above Tc1 in TiOBr, unlike its isostructural sister compound TiOCl. In
addition, we find that the incommensurate structure between Tc1 and Tc2 is
shifted in Q-space relative to the commensurate structure below Tc1.",0908.2103v1
2009-08-20,Pressure-phase diagram of UCoGe by ac-susceptibility and resistivity measurements,"UCoGe is one of the few compounds showing the coexistence of ferromagnetism
and superconductivity at ambient pressure. With T_Curie = 3 K and T_SC = 0.6 K
it is near a quantum phase transition; the pressure needed to suppress the
magnetism is slightly higher than 1 GPa. We report simultaneous resistivity and
ac-susceptibility measurements under pressure on a polycrystal with very large
single-crystalline domains and a resistivity ratio of about 6. Both methods
confirm the phase diagram established before by resistivity measurements on a
polycrystal. The ferromagnetic phase is suppressed for P approximately 1.2 GPa.
Astonishingly, the superconductivity persists at pressures up to at least 2.4
GPa. In other superconducting and ferromagnetic heavy fermion compounds like
UGe2 and URhGe, the superconducting state is situated only inside the larger
ferromagnetic region. Therefore, UCoGe seems to be the first example where
superconductivity extends from the ferromagnetic to the paramagnetic region.",0908.2945v1
2009-08-21,Magnetic structure of EuFe2As2 determined by single crystal neutron diffraction,"Among various parent compounds of iron pnictide superconductors, EuFe2As2
stands out due to the presence of both spin density wave of Fe and
antiferromagnetic ordering (AFM) of the localized Eu2+ moment. Single crystal
neutron diffraction studies have been carried out to determine the magnetic
structure of this compound and to investigate the coupling of two magnetic
sublattices. Long range AFM ordering of Fe and Eu spins was observed below 190
K and 19 K, respectively. The ordering of Fe2+ moments is associated with the
wave vector k = (1,0,1) and it takes place at the same temperature as the
tetragonal to orthorhombic structural phase transition, which indicates the
strong coupling between structural and magnetic components. The ordering of Eu
moment is associated with the wave vector k = (0,0,1). While both Fe and Eu
spins are aligned along the long a axis as experimentally determined, our
studies suggest a weak coupling between the Fe and Eu magnetism.",0908.3142v1
2009-08-24,The two-dimensional frustrated Heisenberg model on the orthorhombic lattice,"We discuss new high-field magnetization data recently obtained by Tsirlin et
al. for layered vanadium phosphates in the framework of the square-lattice
model. Our predictions for the saturation fields compare exceptionally well to
the experimental findings, and the strong bending of the curves below
saturation agrees very well with the experimental field dependence. Furthermore
we discuss the remarkably good agreement of the frustrated Heisenberg model on
the square lattice in spite of the fact that the compounds described with this
model actually have a lower crystallographic symmetry. We present results from
our calculations on the thermodynamics of the model on the orthorhombic (i.e.,
rectangular) lattice, in particular the temperature dependence of the magnetic
susceptibility. This analysis also sheds light on the discussion of magnetic
frustration and anisotropy of a class of iron pnictide parent compounds, where
several alternative suggestions for the magnetic exchange models were proposed.",0908.3442v1
2009-09-04,"Unconventional electronic reconstruction in undoped (Ba,Sr)Fe$_2$As$_2$ across the spin density wave transition","Through a systematic high resolution angle-resolved photoemission study of
the iron pnictide compounds (Ba,Sr)Fe$_2$As$_2$, we show that the electronic
structures of these compounds are significantly reconstructed across the spin
density wave ordering, which cannot be described by a simple folding scenario
of conventional density wave ordering. Moreover, we find that LDA calculations
with an incorporated suppressed magnetic moment of 0.5$\mu_{\tiny{\textrm{B}}}$
can match well the details in the reconstructed electronic structure,
suggesting that the nature of magnetism in the pnictides is more itinerant than
local, while the origin of suppressed magnetic moment remains an important
issue for future investigations.",0909.0831v1
2009-09-10,Electronic structure of the two-dimensional Heisenberg antiferromagnet VOCl: a multi-orbital Mott insulator,"We have studied the electronic structure of the two-dimensional Heisenberg
antiferromagnet VOCl using photoemission spectroscopy and density functional
theory including local Coulomb repulsion. From calculated exchange integrals
and the observed energy dispersions we argue that the degree of
one-dimensionality regarding both the magnetic and electronic properties is
noticeably reduced compared to the isostructural compounds TiOCl and TiOBr.
Also, our analysis provides conclusive justification to classify VOCl as a
multi-orbital Mott insulator. In contrast to the titanium based compounds
density functional theory here gives a better description of the electronic
structure. However, a quantitative account of the low-energy features and
detailed line shapes calls for further investigations including dynamical and
spatial correlations.",0909.2029v1
2009-09-12,Implementation of Rule Based Algorithm for Sandhi-Vicheda Of Compound Hindi Words,"Sandhi means to join two or more words to coin new word. Sandhi literally
means `putting together' or combining (of sounds), It denotes all combinatory
sound-changes effected (spontaneously) for ease of pronunciation.
Sandhi-vicheda describes [5] the process by which one letter (whether single or
cojoined) is broken to form two words. Part of the broken letter remains as the
last letter of the first word and part of the letter forms the first letter of
the next letter. Sandhi- Vicheda is an easy and interesting way that can give
entirely new dimension that add new way to traditional approach to Hindi
Teaching. In this paper using the Rule based algorithm we have reported an
accuracy of 60-80% depending upon the number of rules to be implemented.",0909.2379v1
2009-09-13,Blue photoluminescence from chemically derived graphene oxide,"Fluorescent organic compounds are of significant importance to the
development of low-cost opto-electronic devices. Blue fluorescence from
aromatic or olefinic molecules and their derivatives is particularly important
for display and lighting applications. Thin film deposition of
low-molecular-weight fluorescent organic compounds typically requires costly
vacuum evaporation systems. On the other hand, solution-processable polymeric
counterparts generally luminesce at longer wavelengths due to larger
delocalization in the chain. Blue light emission from solution-processed
materials is therefore of unique technological significance. Here we report
near-UV to blue photoluminescence (PL) from solution-processed graphene oxide
(GO). The characteristics of the PL and its dependence on the reduction of GO
indicates that it originates from the recombination of electron-hole (e-h)
pairs localized within small sp2 carbon clusters embedded within an sp3 matrix.
These results suggest that a sheet of graphene provides a parent structure on
which fluorescent components can be chemically engineered without losing the
macroscopic structural integrity. Our findings offer a unique route towards
solution-processable opto-electronics devices with graphene.",0909.2456v1
2009-09-16,"Novel phase transition and the pressure effect in YbFe2Al10-type CeT2Al10 (T=Fe, Ru, Os)","We have succeeded in growing single crystals of orthorhombic CeT2Al10 (T=Fe,
Ru, Os) by Al self-flux method for the first time, and measured the electrical
resistivity at pressures up to 8 GPa, the magnetic susceptibility and specific
heat at ambient pressure. These results indicate that CeT2Al10 belongs to the
heavy fermion compounds. CeRu2Al10 and CeOs2Al10 show a similar phase
transition at T0 = 27.3 and 28.7 K, respectively. The temperature dependences
in the ordered phases are well described by the thermally activated form,
suggesting that partial gap opens over the Fermi surfaces below T0. When
pressure is applied to CeRu2Al10, T0 disappears suddenly between 3 and 4 GPa,
and CeRu2Al10 turns into a Kondo insulator, followed by a metal. The similarity
of CeT2Al10 under respective pressures suggests a scaling relation by some
parameter controlling the unusual physics in these compounds.",0909.2911v1
2009-09-25,Effect of Fe substitution on magnetocaloric effect in La0.7Sr0.3Mn1-xFexO3 (x = 0 to 0.2),"We have studied the effect of Fe substitution on magnetic and magnetocaloric
properties in La0.7Sr0.3Mn1-xFexO3 (x = 0.05, 0.07, 0.10, 0.15, and 0.20) over
a wide temperature range (T = 10-400 K). It is shown that substitution by Fe
gradually decreases the ferromagnetic Curie temperature (Tc) and saturation
magnetization up to x = 0.15 but a dramatic change occurs for x = 0.2. The x =
0.2 sample can be considered as a phase separated compound in which both
short-range ordered ferromagnetic and antiferromagnetic phases coexist. The
magnetic entropy change (DSm) was estimated from isothermal magnetization
curves and it decreases with increase of Fe content from 4.4 J/KgK at 343 K (x
= 0.05) to 1.3 J/KgK at 105 K (x = 0.2), under H = 5 T. The
La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating
temperature over 60 K range around room temperature with refrigerant capacity
of 225 J/Kg, and magnetic entropy of 4 J/kgK which will be an interesting
compound for application in room temperature refrigeration.",0909.4619v1
2009-09-28,Exciton doublet in the Mott-Hubbard LiCuVO$_4$ insulator identified by spectral ellipsometry,"Spectroscopic ellipsometry was used to study the dielectric function of
LiCuVO$_{4}$, a compound comprised of chains of edge-sharing CuO$_4$
plaquettes, in the spectral range (0.75 - 6.5) eV at temperatures (7-300) K.
For photon polarization along the chains, the data reveal a weak but
well-resolved two-peak structure centered at 2.15 and 2.95 eV whose spectral
weight is strongly enhanced upon cooling near the magnetic ordering
temperature. We identify these features as an exciton doublet in the
Mott-Hubbard gap that emerges as a consequence of the Coulomb interaction
between electrons on nearest and next-nearest neighbor sites along the chains.
Our results and methodology can be used to address the role of the long-range
Coulomb repulsion for compounds with doped copper-oxide chains and planes.",0909.5157v1
2009-10-14,"Effects of substituting Se with Te in the FeSe compound: structural, magnetization and Moessbauer studies","Polycrystalline samples of FeSe1-xTex (x = 0.00, 0.25, 0.50, 0.75 and 1.00)
were synthesized by solid-state reaction to study the effects of substituting
Se with Te in the system. The magnetization properties of the resulting
compounds were investigated and the crystallographic structures of the samples
analyzed through X-ray diffraction. Moessbauer spectroscopy was used to
determine the ionic state of the Fe ions and the hyperfine fields. The magnetic
susceptibility curves of the samples with x = 0.25, 0.50 and 0.75 show
superconducting behavior. The lattice parameters and the cell volume increase
monotonically with increasing Te concentration and the Moessbauer spectra
reveal the absence of internal magnetic hyperfine fields.",0910.2504v1
2009-10-16,Heavy fermion material: Ce versus Yb case,"Heavy fermion compounds are complex systems but excellent materials to study
quantum criticality with the switch of different ground states. Here a special
attention is given on the interplay between magnetic and valence instabilities
which can be crossed or approached by tuning the system by pressure or magnetic
field. By contrast to conventional rare earth magnetism or classical s wave
superconductivity, strong couplings may occur with drastic changes in spin or
charge dynamics. Measurements on Ce materials give already a sound basis with
clear key factors; they have pointed out that close to a magnetic or a valence
criticality unexpected phenomena such as unconventional superconductivity, non
Fermi liquid behaviour and the possibility of re-entrance phenomena under
magnetic field. Recent progresses in the growth of Yb heavy fermion compounds
give the perspectives of clear interplays between valence and magnetic
fluctuations and also the possibility to enter in new situations such as
valence transitions inside a sole doublet crystal field ground state.",0910.3110v2
2009-10-27,Simultaneously optimizing the interdependent thermoelectric parameters in Ce(Ni$_{1-x}$Cu$_x$)$_2$Al$_3$,"Substitution of Cu for Ni in the Kondo lattice system CeNi$_2$Al$_3$ results
in a simultaneous optimization of the three interdependent thermoelectric
parameters: thermoelectric power, electrical and thermal conductivities, where
the electronic change in conduction band induced by the extra electron of Cu is
shown to be crucial. The obtained thermoelectric figure of merit $zT$ amounts
to 0.125 at around 100 K, comparable to the best values known for Kondo
compounds. The realization of ideal thermoelectric optimization in
Ce(Ni$_{1-x}$Cu$_x$)$_2$Al$_3$ indicates that proper electronic tuning of Kondo
compounds is a promising approach to efficient thermoelectric materials for
cryogenic application.",0910.5065v1
2009-11-02,Double-Exchange Ferromagnetism and Orbital-Fluctuation-Induced Superconductivity in Cubic Uranium Compounds,"A double-exchange mechanism for the emergence of ferromagnetism in cubic
uranium compounds is proposed on the basis of a $j$-$j$ coupling scheme. The
idea is {\it orbital-dependent duality} of $5f$ electrons concerning itinerant
$\Gamma_8^-$ and localized $\Gamma_7^-$ states in the cubic structure. Since
orbital degree of freedom is still active in the ferromagnetic phase,
orbital-related quantum critical phenomenon is expected to appear. In fact,
odd-parity p-wave pairing compatible with ferromagnetism is found in the
vicinity of an orbital ordered phase. Furthermore, even-parity d-wave pairing
with significant odd-frequency components is obtained. A possibility to observe
such exotic superconductivity in manganites is also discussed briefly.",0911.0250v1
2009-11-14,"Evidence of Magnetically Driven Structural Phase Transition in Parent Compounds RFeAsO (R = La, Sm, Gd, Tb): study of low-temperature X-ray diffraction","We report measurements of structural phase transition of four parent
compounds $R$FeAsO ($R$ = La, Sm, Gd, and Tb) by means of low-temperature X-ray
diffraction (XRD). Magnetic transition temperatures associated with Fe ions
($T_{N1}$) are also determined from the temperature dependence of resistivity.
As $R$ is changed from La, through Sm and Gd, to Tb, both the c-axis and a-axis
lattice constants decrease significantly. Meanwhile both the structural phase
transition temperature ($T_S$) and $T_{N1}$ decrease monotonously. It is also
found that the temperature gap between $T_S$ and $T_{N1}$ becomes smaller when
the distance between FeAs layer becomes shorter. This result is consistent with
magnetically driven structural phase transition and suggests that the
dimensionality have an important effect on the AFM ordering.",0911.2779v1
2009-11-22,"Optimal control of a large dam, taking into account the water costs [New Edition]","This paper studies large dam models where the difference between lower and
upper levels, $L$, is assumed to be large. Passage across the levels leads to
damage, and the damage costs of crossing the lower or upper level are
proportional to the large parameter $L$. Input stream of water is described by
compound Poisson process, and the water cost depends upon current level of
water in the dam. The aim of the paper is to choose the parameters of output
stream (specifically defined in the paper) minimizing the long-run expenses.
The particular problem, where input stream is ordinary Poisson and water costs
are not taken into account, has been studied in [Abramov, \emph{J. Appl.
Prob.}, 44 (2007), 249-258]. The present paper addresses the question
\textit{How does the structure of water costs affect the optimal solution?}
Under natural assumptions we prove an existence and uniqueness of a solution
and study the case of linear structure of the costs.",0911.4228v2
2009-11-27,BiOCuS: A new superconducting compound with oxypnictide - related structure,"The discovery of about 50 K superconductivity in the tetragonal Fe-based
pnictides has stimulated the search for superconductivity in a wide class of
materials with similar structure. Copper forms compounds isostructural to
LaOFeAs. Single phase BiOCuS can be prepared by a solid state reaction at
temperature lower than 500 C from a mixture of Bi2O3, Bi2S3 and Cu2S. The
samples have been characterized by means of EDX analysis, X-ray diffraction,
magnetic and electrical measurements. The cell parameters are a = 3.8708 A, c =
8.565 A. Charge carrier doping can be realized either by F substitutions for O,
or by Cu off-stoichiometry. The latter doping route leads to the occurrence of
superconductivity below Tc = 5.8 K.",0911.5305v3
2009-11-30,Frustrated local moment models for Fe-pnictide magnetism,"The low energy spin excitations of the Fe pnictide parent compounds have been
determined by inelastic neutron scattering and interpreted within the local
moment J_1a,b-J_2 Heisenberg model with orthorhombic symmetry. This has led to
alternative exchange models that strongly differ in the size of anisotropy.
Although the compounds are itinerant the localised spin model can explain basic
features of the excitations. The inherent frustration of this model leads to
quantum fluctuations and possible moment reduction. We investigate this
question in detail using spin wave approximation and partly exact
diagonalisation Lanczos calculations for finite clusters. We find that the
orthorhombic anisotropy stabilizes the columnar AF phase and its moment. For
the exchange models proposed from inelastic neutron scattering we can exclude a
strong influcence of frustration on the moment size. We also investigate
dependence of magnetisation and susceptibility on field and temperature.",0911.5664v2
2009-12-04,Superfluid density of Ba(Fe$_{1-x}M_x$)$_2$As$_2$ from optical experiments,"The temperature dependence of the $ab$-plane optical reflectivity of
Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$
single crystals is measured in a wide spectral range. Upon entering the
superconducting regime, the reflectivity in both compounds increases
considerably at low frequency, leading to a clear gap in the optical
conductivity below 100 cm$^{-1}$. From the analysis of the complex conductivity
spectra we obtain the penetration depth $\lambda(T)=(3500\pm 350)$ \AA for
Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and $(3000\pm 300)$ \AA for
Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$. The calculated superfluid density
$\rho_s$ of both compounds nicely fits the scaling relation $\rho_s=(125\pm
25)\sigma_{dc}T_c$.",0912.0849v1
2009-12-11,Mechanisms producing fissionlike binary fragments in heavy collisions,"The mixing of the quasifission component to the fissionlike cross section
causes ambiguity in the quantitative estimation of the complete fusion cross
section from the observed angular and mass distributions of the binary
products. We show that the partial cross section of quasifission component of
binary fragments covers the whole range of the angular momentum values leading
to capture. The calculated angular momentum distributions for the compound
nucleus and dinuclear system going to quasifission may overlap: competition
between complete fusion and quasifission takes place at all values of initial
orbital angular momentum. Quasifission components formed at large angular
momentum of the dinuclear system can show isotropic angular distribution and
their mass distribution can be in mass symmetric region similar to the
characteristics of fusion-fission components. As result the unintentional
inclusion of the quasifission contribution into the fusion-fission fragment
yields can lead to overestimation of the probability of the compound nucleus
formation.",0912.2220v1
2009-12-17,Universal Decomposition of the Low-Frequency Conductivity Spectra of Iron-Pnictides Uncovering Fermi-Liquid Behavior,"Infrared reflectivity measurements on 122 iron-pnictides reveal the existence
of two electronic subsystems. The one gapped due to the spin-density-wave
transition in the parent materials, such as EuFe$_2$As$_{2}$, is responsible
for superconductivity in the doped compounds, like
Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$.
Analyzing the dc resistivity and scattering rate of this contribution, a hidden
$T^2$ dependence is found, indicating that superconductivity evolves out of a
Fermi-liquid state. The second subsystem gives rise to incoherent background,
present in all 122 compounds, which is basically temperature independent, but
affected by the superconducting transition.",0912.3334v2
2009-12-22,Finite size effects and magnetic order in the spin-1/2 honeycomb lattice compound InCu{2/3}V{1/3}O{3},"High field electron spin resonance, nuclear magnetic resonance and
magnetization studies addressing the ground state of the quasi two-dimensional
spin-1/2 honeycomb lattice compound InCu{2/3}V{1/3}O{3} are reported.
Uncorrelated finite size structural domains occurring in the honeycomb planes
are expected to inhibit long range magnetic order. Surprisingly, ESR data
reveal the development of two collinear antiferromagnetic (AFM) sublattices
below ~ 20 K whereas NMR results show the presence of the staggered internal
field. Magnetization data evidence a spin reorientation transition at ~ 5.7 T.
Quantum Monte-Carlo calculations show that switching on the coupling between
the honeycomb spin planes in a finite size cluster yields a Neel-like AFM spin
structure with a substantial staggered magnetization at finite temperatures.
This may explain the occurrence of a robust AFM state in InCu{2/3}V{1/3}O{3}
despite an unfavorable effect of structural disorder.",0912.4514v2
2009-12-31,Dielectric properties and spin-phonon coupling in multiferroic double perovskite Bi$_2$CoMnO$_6$,"First-principles electronic structure calculations have been performed for
the double perovskite Bi$_2$CoMnO$_6$ in its non-centrosymmetric polar state
using generalized gradient approximation plus Hubbard U approach. We find that
while Co is in a high spin state, Mn is in an intermediate spin state. The
calculated dynamical charge tensors are anisotropic reflecting a low-symmetry
structure of the compound. Magnetic structure dependent phonon frequencies
indicate the presence of spin-phonon coupling. Using Berry phase method, we
obtain a spontaneous electronic polarization of 5.88 ${\mu}C/cm^2$ which is
close to the experimental value observed for a similar compound,
Bi$_2$NiMnO$_6$.",1001.0128v2
2010-01-08,Non-reciprocal second harmonic generation in ferroelectric photonic structures,"Second harmonic generation is a powerful tool directly connected to the
symmetry of materials. Phase transitions, lattice rotations or electromagnetic
coupling in multiferroic compounds can be revealed by using second harmonic
generation.[1-4] Here we show that the sense of the spontaneous electric
polarization Ps in trigonal ferroelectrics can lead to a pronounced spatial
dependence of the second harmonic generation. By using a two-dimensional
nonlinear photonic structure we demonstrate that counter-propagating beams
along the polar axis generate non-reciprocal second harmonic patterns. In
optics, with some exception,[5] non-reciprocal phenomena are generally related
to the breaking of time-reversal symmetry involving a magnetic field.[6,7]
Here, in contrast, the non-reciprocity is inherent to the quadratic nonlinear
tensor being related to the inversion symmetry breaking at the ferroelectric
phase. These findings provide novel routes to generate nonreciprocal
light-matter interaction processes in two-dimensional structures assembled onto
polar surfaces,[8,9] including metals for plasmonics or biological compounds.",1001.1301v1
2010-01-11,Direct observation of spin-polarized surface states in the parent compound of a topological insulator using high-resolution spin-resolved-ARPES spectroscopy in a Mott-polarimetry mode,"We report high-resolution spin-resolved photoemission spectroscopy
(Spin-ARPES) measurements on the parent compound Sb of the recently discovered
3D topological insulator Bi1-xSbx [D. Hsieh et al., Nature 452, 970 (2008)]. By
modulating the incident photon energy, we are able to map both the bulk and
(111) surface band structure, from which we directly demonstrate that the
surface bands are spin polarized by the spin-orbit interaction and connect the
bulk valence and conduction bands in a topologically non-trivial way. A unique
asymmetric Dirac surface state gives rise to a k-splitting of its spin
polarized electronic channels. These results complement our previously
published works on this materials class and re-confirm our discovery of
topological insulator states in the Bi-Sb series.",1001.1574v1
2010-01-19,Internal conversion of nuclear transition in the ${}^{235m}U@C_{60-n}X_n$ molecules and related compounds,"The internal conversion of nuclear transition in the ${}^{235}U$ atom is
considered. The low-energy $\gamma-$quanta ($E_{\gamma} \approx$ 76.8 $eV$) are
emitted during the $E3-$transition from the excited state ($I = (\frac12)^+$)
of the ${}^{235}U$ nucleus to its ground state ($I = (\frac72)^-$). The decay
rate of this ${}^{235m}U$ isomer ($E \approx 76.8$ $eV$) noticeably depends
upon the chemical composition and actual physical conditions (i.e. temperature
$T$ and pressure $p$). By varying such a composition and physical conditions
one can change the life-time of the ${}^{235m}U$ isomer to relatively
large/small values. A specific attention is given to the fullerene molecules
containing the central ${}^{235}U$ atom. It is shown that the decay rate
$\lambda$ of the ${}^{235m}U$ isomer in the ${}^{235m}U@C_{60-n}X_n$ molecules
and related compounds can differ significantly from the values obtained for
isolated ${}^{235}U$ atoms. Some applications of this effect are considered.",1001.3180v1
2010-01-19,"Gd3+ rattling triggered by a ""weak"" M-I transition at 140-160 K in the Ce1-xGdxFe4$P12 x ~ 0.001 skutterudite compounds: an ESR study","In this work we report electron spin resonance (ESR) measurements in the
semiconducting Ce1-xGdxFe4P12 (x ~ 0.001) filled skutterudite compounds.
Investigation of the temperature (T) dependence of the ESR spectra and
relaxation process suggests, that in the T-interval of 140-160 K, the onset of
a ""weak"" metal-insulator (M-I) transition takes place due to the increasing
density of thermally activated carriers across the semiconducting gap of ~ 1500
K. In addition, the observed low-T fine and hyperfine structures start to
collapse at ~ 140 K and is completely absent for > 160 K. We claim that the
increasing carrier density is able to trigger the rattling of the Gd3+ ions
which in turn is responsible, via a motional narrowing mechanism, for the
collapse of the ESR spectra.",1001.3329v1
2010-01-22,Observables for FRW model with cosmological constant in the framework of loop cosmology,"We consider a flat cosmological model with a free massless scalar field and
the cosmological constant $\Lambda$ in the framework of loop quantum cosmology.
The scalar field plays the role of an intrinsic time. We apply the reduced
phase space approach. The dynamics of the model is solved analytically. We
identify elementary observables and their algebra. The compound physical
observables like the volume and the energy density of matter field are
analysed. Both compound observables are bounded and oscillate in the
$\Lambda<0$ case. The energy density is bounded and oscillates in the
$\Lambda>0$ case. However, the volume is unbounded from above, but periodic.
The difference between standard and nonstandard loop quantum cosmology is
described.",1001.3999v3
2010-01-25,"High-pressure synthesis, crystal and electronic structures of a new scandium tungstate, Sc0.67WO4","Negative thermal expansion (NTE) materials possess a low-density, open
structure which can respond to high pressure conditions, leading to new
compounds and/or different physical properties. Here we report that one such
NTE material -- white, insulating, orthorhombic Sc2W3O12 -- transforms into a
black compound when treated at 4 GPa and 1400 oC. The high pressure phase,
Sc0.67WO4, crystallizes in a defect-rich wolframite-type structure, a dense,
monoclinic structure (space group P2/c) containing 1-D chains of edge-sharing
WO6 octahedra. The chemical bonding of Sc0.67WO4 vis-a-vis the ambient pressure
Sc2W3O12 phase can be understood on the basis of the Sc defect structure.
Magnetic susceptibility, resistivity, thermoelectric power and IR spectroscopic
measurements reveal that Sc0.67WO4 is a paramagnet whose conductivity is that
of a metal in the presence of weak localization and electron-electron
interactions. Oxygen vacancies are suggested as a potential mechanism for
generating the carriers in this defective wolframite material.",1001.4561v1
2010-01-28,Probing Electronic Correlations in Actinide Materials Using Multipolar Transitions,"We report nonresonant inelastic x-ray scattering from the semi-core 5d levels
of several actinide compounds. Dipole-forbidden, high-multipole features form a
rich bound-state spectrum dependent on valence electron configuration and
spin-orbit and Coulomb interactions. Cross-material comparisons, together with
the anomalously high Coulomb screening required for agreement between atomic
multiplet theory and experiment, demonstrate sensitivity to the neighboring
electronic environment, such as is needed to address long-standing questions of
electronic localization and bonding in 5f compounds.",1001.5219v1
2010-02-02,Structural and Magnetic Properties of Co1-xFexSr2YCu2O7 compounds,"Here we study the structural and magnetic properties of the CoFeSr2YCu2O7
compound with x = 0.0 to 1.0. X-ray diffraction patterns and simulated data
obtained from Rietveld refinement of the same indicate that the iron ion
replacement in CoFeSr2YCu2O7 induces a change in crystal structure. The
orthorhombic Ima2 space group structure of Co-1212 changes to tetragonal P4/mmm
with increasing Fe ion. The XPS studies reveal that both Co and Fe ions are in
mixed states for the former and in case of later.Although none of the studied
as synthesized samples in CoFeSr2YCu2O7 are superconducting, the interesting
structural changes in terms of their crystallisation space groups and the weak
magnetism highlights the rich solid state chemistry of this class of materials.",1002.0402v2
2010-02-03,Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process,"Manufacturing superconducting circuits out of ultrathin films is a
challenging task when it comes to patterning complex compounds, which are
likely to be deteriorated by the patterning process. With the purpose of
developing high-T$_c$ superconducting photon detectors, we designed a novel
route to pattern ultrathin YBCO films down to the nanometric scale. We believe
that our method, based on a specific use of a focused-ion beam, consists in
locally implanting Ga^{3+} ions and/or defects instead of etching the film.
This protocol could be of interest to engineer high-T$_c$ superconducting
devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to
treat other sensitive compounds.",1002.0808v1
2010-02-08,Muon-spin relaxation and heat capacity measurements on the magnetoelectric and multiferroic pyroxenes LiFeSi2O6 and NaFeSi2O6,"The results of muon-spin relaxation and heat capacity measurements on two
pyroxene compounds LiFeSi2O6 and NaFeSi2O6 demonstrate that despite their
underlying structural similarity the magnetic ordering is considerably
different. In LiFeSi2O6 a single muon precession frequency is observed below
TN, consistent with a single peak at TN in the heat capacity and a commensurate
magnetic structure. In applied magnetic fields the heat capacity peak splits in
two. In contrast, for natural NaFeSi2O6, where multiferroicity has been
observed in zero-magnetic-field, a rapid Gaussian depolarization is observed
showing that the magnetic structure is more complex. Synthetic NaFeSi2O6 shows
a single muon precession frequency but with a far larger damping rate than in
the lithium compound. Heat capacity measurements reproduce the phase diagrams
previously derived from other techniques and demonstrate that the magnetic
entropy is mostly associated with the build up of correlations in the
quasi-one-dimensional Fe3+ chains.",1002.1635v1
2010-02-12,The thermopower as a signature of quantum criticality in heavy fermions,"We present a series of arguments showing that the Seebeck coefficient can be
used as a decisive experiment to characterize the nature of the quantum
critical point (QCP) in heavy fermion compounds. Being reactive almost
exclusively to the presence of delocalized entropic carriers, the Seebeck
coefficient shows a drastic collapse at the Kondo breakdown QCP, as the
reconstruction of the Fermi surface takes place. In contrast, around a Spin
Density Wave (SDW) QCP, the Seebeck coefficient is broadly symmetric. We
discuss the possibility of a change of sign at the QCP, the characteristic
variation of $| S / T | $ with temperature and external parameter, as well as
the capacity of the Seebeck coefficient to distinguish between localized and
itinerant anti-ferromagnetism (AF). Suggestions of experiments are given in the
case of four non conventional compounds : YbRh$_2$Si$_2$, Ce(Mn)In$_5$,
CeCu$_{6-x}$Au$_x$ and URu$_2$Si$_2$.",1002.2612v1
2010-02-18,Why some Iron-based superconductors are nodal while others are nodeless,"The symmetry of the order parameter in iron-based superconductors, especially
the presence or absence of nodes, is still a question of debate. While
contradictory experiments can be explained by appropriately tuned theories of
nodeless superconductivity in the iron-arsenide compounds, for LaOFeP all
experiments clearly point to a nodal order parameter. We put forward a scenario
that naturally explains the difference between the order-parameter character in
these two sets of compounds, and use functional renormalization group (fRG)
techniques to analyze it in detail. Our results show that, due to the orbital
content of the electron and hole bands, nodal superconductivity on the electron
pockets (hole pocket gaps are always nodeless) can naturally appear when the
third hole pocket which lies at wavevector (pi,pi) in the unfolded Brillouin
zone is absent, as is the case in LaOFeP. When present, the third hole pocket
has overwhelming d_{xy} orbital character, and the intra-orbital interaction
with the d_{xy} dominated part of the electron Fermi surface is enough to drive
the superconductivity nodeless (of s^+- form). However, in its absence, pair
hopping, inter-orbital, and electron-electron intra-orbital interactions render
the gap on the electron pockets softly nodal.",1002.3599v1
2010-02-23,Crystal and magnetic structure of the oxypnictide superconductor LaO(1-x)FxFeAs: evidence for magnetoelastic coupling,"High-resolution and high-flux neutron as well as X-ray powder-diffraction
experiments were performed on the oxypnictide series LaO(1-x)FxFeAs with
0<x<0.15 in order to study the crystal and magnetic structure. The magnetic
symmetry of the undoped compound corresponds to those reported for ReOFeAs
(with Re a rare earth) and for AFe2As2 (A=Ba, Sr) materials. We find an ordered
magnetic moment of 0.63(1)muB at 2 K in LaOFeAs, which is significantly larger
than the values previously reported for this compound. A sizable ordered
magnetic moment is observed up to a F-doping of 4.5% whereas there is no
magnetic order for a sample with a F concentration of x=0.06. In the undoped
sample, several interatomic distances and FeAs4 tetrahedra angles exhibit
pronounced anomalies connected with the broad structural transition and with
the onset of magnetism supporting the idea of strong magneto-elastic coupling
in this material.",1002.4326v1
2010-03-01,Magnetic field effect on Fe-induced short-range magnetic correlation and electrical conductivity in Bi$_{1.75}$Pb$_{0.35}$Sr$_{1.90}$Cu$_{0.91}$Fe$_{0.09}$O$_{6+y}$,"We report electrical resistivity measurements and neutron diffraction studies
under magnetic fields of
Bi$_{1.75}$Pb$_{0.35}$Sr$_{1.90}$Cu$_{0.91}$Fe$_{0.09}$O$_{6+y}$, in which hole
carriers are overdoped. This compound shows short-range incommensurate magnetic
correlation with incommensurability $\delta=0.21$, whereas a Fe-free compound
shows no magnetic correlation. Resistivity shows an up turn at low temperature
in the form of $ln(1/T)$ and shows no superconductivity. We observe reduction
of resistivity by applying magnetic fields (i.e., a negative magnetoresistive
effect) at temperatures below the onset of short-range magnetic correlation.
Application of magnetic fields also suppresses the Fe induced incommensurate
magnetic correlation. We compare and contrast these observations with two
different models: 1) stripe order, and 2) dilute magnetic moments in a metallic
alloy, with associated Kondo behavior. The latter picture appears to be more
relevant to the present results.",1003.0262v2
2010-03-10,Tetragonal tungsten bronze compounds: relaxor vs mixed ferroelectric - dipole glass behavior,"We demonstrate that recent experimental data (E. Castel et al J.Phys. Cond.
Mat. {\bf 21} (2009), 452201) on tungsten bronze compound (TBC)
Ba$_2$Pr$_x$Nd$_{1-x}$FeNb$_4$O$_{15}$ can be well explained in our model
predicting a crossover from ferroelectric ($x=0$) to orientational (dipole)
glass ($x=1$), rather then relaxor, behavior. We show, that since a ""classical""
perovskite relaxor like Pb(Mn$_{1/3}$ Nb$_{2/3}$)O$_3$ is never a
ferroelectric, the presence of ferroelectric hysteresis loops in TBC shows that
this substance actually transits from ferroelectric to orientational glass
phase with $x$ growth. To describe the above crossover theoretically, we use
the simple replica-symmetric solution for disordered Ising model.",1003.2177v1
2010-03-11,Charge and Spin Ordering in the Mixed Valence Compound LuFe2O4,"Landau theory and symmetry considerations lead us to propose an explanation
for several seemingly paradoxical behaviors of charge ordering (CO) and spin
ordering (SO) in the mixed valence compound LuFe2O4. Both SO and CO are highly
frustrated. We analyze a lattice gas model of CO within mean field theory and
determine the magnitude of several of the phenomenological interactions. We
show that the assumption of a continuous phase transition at which CO or SO
develops implies that both CO and SO are incommensurate. To explain how
ferroelectric fluctuations in the charge disordered phase can be consistent
with an antiferroelectric ordered phase, we invoke an electron-phonon
interaction in which a low energy (20meV) zone-center transverse phonon plays a
key role. The energies of all the zone-center phonons are calculated from first
principles. We give a Landau analysis which explains SO and we discuss a model
of interactions which stabilizes the SO state, if it is assumed commensurate.
However, we suggest a high resolution experimental determination to see whether
this phase is really commensurate, as believed up to now. The applicability of
representation analysis is discussed. A tentative explanation for the
sensitivity of the CO state to an applied magnetic field in field-cooled
experiments is given.",1003.2400v1
2010-03-14,The dominant spin relaxation mechanism in compound organic semiconductors,"Despite the recent interest in ""organic spintronics"", the dominant spin
relaxation mechanism of electrons or holes in an organic compound semiconductor
has not been conclusively identified. There have been sporadic suggestions that
it might be hyperfine interaction caused by background nuclear spins, but no
confirmatory evidence to support this has ever been presented. Here, we report
the electric-field dependence of the spin diffusion length in an organic
spin-valve structure consisting of an Alq3 spacer layer, and argue that this
data, as well as available data on the temperature dependence of this length,
contradict the notion that hyperfine interactions relax spin. Instead, they
suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction,
is more likely the dominant spin relaxing mechanism.",1003.2814v1
2010-03-17,Emission of charged particles from excited compound nuclei,"The formation of excited compound nucleus (CN) and its statistical decay is
investigated within the dinuclear system (DNS) model.The initial DNS is formed
in the entrance channel when the projectile is captured by a target, and then
the evolution of DNS in mass asymmetry coordinate leads to formation of the hot
CN. The emission barriers for complex fragments were calculated within the DNS
model by using the double folding procedure for the interaction potential. It
is shown that cross sections for complex fragment emission become larger when
excited CN is more neutron deficient. This approach gives also an opportunity
to calculate the new neutron deficient isotopes production cross sections and
can be applied to describe the hot fission of heavy systems.The model was
tested by comparison of calculated results with experimental data",1003.3427v1
2010-03-26,Evolution of the optical spectrum with doping in iron pnictides Ba(Fe1-xCox)2As2,"We investigated the optical spectrum of Ba(Fe1-xCox)2As2 single crystals with
various doping levels. It is found that the low-energy optical conductivity
spectrum of this system can be decomposed into two components: a sharp Drude
term and a broad ""incoherent"" term. For the compounds showing magnetic order, a
gap appears predominantly in the ""incoherent"" component, while an s-wave like
superconducting gap opens in both components for highly doped compounds. The
Drude weight steadily increases as doping proceeds, consistent with electron
doping in this system. On the other hand, the ""incoherent"" spectral weight is
almost doping independent, but its spectral feature is intimately connected
with the magnetism. We demonstrate that the presence of two distinct components
in the optical spectrum well explains the doping and temperature dependences of
the dc resistivity.",1003.5038v1
2010-03-26,"First Principles Studies on 3-Dimentional Strong Topological Insulators: Bi2Te3, Bi2Se3 and Sb2Te3","Bi2Se3, Bi2Te3 and Sb2Te3 compounds are recently predicted to be
3-dimentional (3D) strong topological insulators. In this paper, based on
ab-initio calculations, we study in detail the topological nature and the
surface states of this family compounds. The penetration depth and the
spin-resolved Fermi surfaces of the surface states will be analyzed. We will
also present an procedure, from which highly accurate effective Hamiltonian can
be constructed, based on projected atomic Wannier functions (which keep the
symmetries of the systems). Such Hamiltonian can be used to study the
semi-infinite systems or slab type supercells efficiently. Finally, we discuss
the 3D topological phase transition in Sb2(Te1-xSex)3 alloy system.",1003.5082v1
2010-04-12,"Isoelectronic Ru substitution at Fe-site in Sm(Fe1-xRux)As(O0.85F0.15) compound and its effects on structural, superconducting and normal state properties","In this work we present a systematic experimental and theoretical study of
the structural, transport and superconducting properties of
Sm(Fe1-xRux)As(O0.85F0.15) polycrystalline samples as a function of Ru content
(x) ranging from 0 to 1. The choice of Ru as isoelectronic substitution at Fe
site of F-doped compounds allows to better clarify the role of structural
disorder in modifying the normal and superconducting properties of these newly
discovered multiband superconductors. Two different regions are identified: the
Fe-rich phase (x<0.5) where superconducting and normal state properties are
strongly affected by disorder induced by Ru substitution; the Ru-rich phase
(x>0.5) where the system is metallic and strongly compensated and the presence
of Ru frustrates the magnetic moment on Fe ions. Here the lack of magnetic
features and related spin fluctuations may be the cause for the suppression of
superconductivity.",1004.1978v1
2010-04-14,On the optimal stacking of noisy observations,"Observations where additive noise is present can for many models be grouped
into a compound observation matrix, adhering to the same type of model. There
are many ways the observations can be stacked, for instance vertically,
horizontally, or quadratically. An estimator for the spectrum of the underlying
model can be formulated for each stacking scenario in the case of Gaussian
noise. We compare these spectrum estimators for the different stacking
scenarios, and show that all kinds of stacking actually decreases the variance
when compared to just taking an average of the observations. We show that,
regardless of the number of observations, the variance of the estimator is
smallest when the compound observation matrix is made as square as possible.
When the number of observations grow, however, it is shown that the difference
between the estimators is marginal: Two stacking scenarios where the number of
columns and rows grow to infinity are shown to have the same variance
asymptotically, even if the asymptotic matrix aspect ratios differ. Only the
cases of vertical and horizontal stackings display different behaviour, giving
a higher variance asymptotically. Models where not all kinds of stackings are
possible are also discussed.",1004.2392v1
2010-04-26,Fermiology and transport properties of the half-metallic itinerant ferromagnet CoS$_2$: influence of spin orbit coupling,"Electronic structure calculations were performed on the compound CoS$_2$, an
itinerant ferromagnet whose magnetic properties can be understood in terms of
spin fluctuation theory. We have identified nesting features in the Fermi
surface of the compound, active for long wavelength spin fluctuations. The
electronic structure of the material is close to a half-metal. We show the
importance of introducing spin-orbit coupling (SOC) in the calculations, that
partially destroys the half-metallicity of the material. By means of transport
properties calculations, we have quantified the influence of SOC in the
conductivity at room temperature, with an important decrease comparing to the
GGA alone conductivity. SOC also helps to understand the negative 0 of the
material, whose conductivity varies by a few percent with the introduction of
small perturbations in the states around the Fermi level.",1004.4472v1
2010-04-27,Magnetic properties and electronic structures of intermediate valence systems CeRhSi2 and Ce2Rh3Si5,"The crystal structures and the physical (magnetic, electrical transport and
thermodynamic) properties of the ternary compounds CeRhSi2 and Ce2Rh3Si5
(orthorhombic CeNiSi2- and U2Co3Si5-type structures, respectively) were studied
in wide ranges of temperature and magnetic field strength. The results revealed
that both materials are valence fluctuating systems, in line with previous
literature reports. Direct evidence for valence fluctuations was obtained by
means of Ce LIII-edge x-ray absorption spectroscopy and Ce 3d core-level x-ray
photoelectron spectroscopy. The experimental data were confronted with the
results of ab initio calculations of the electronic band structures in both
compounds.",1004.4731v1
2010-04-27,Universal A Posteriori Metrics Game,"Over binary input channels, uniform distribution is a universal prior, in the
sense that it allows to maximize the worst case mutual information over all
binary input channels, ensuring at least 94.2% of the capacity. In this paper,
we address a similar question, but with respect to a universal generalized
linear decoder. We look for the best collection of finitely many a posteriori
metrics, to maximize the worst case mismatched mutual information achieved by
decoding with these metrics (instead of an optimal decoder such as the Maximum
Likelihood (ML) tuned to the true channel). It is shown that for binary input
and output channels, two metrics suffice to actually achieve the same
performance as an optimal decoder. In particular, this implies that there exist
a decoder which is generalized linear and achieves at least 94.2% of the
compound capacity on any compound set, without the knowledge of the underlying
set.",1004.4815v1
2010-05-07,On the superconducting phase fluctuations above Tc in cuprates,"In this brief report an attempt is made for a 'mise-a-point' of the subject
of the phase fluctuations of the superconducting order parameter above Tc in
cuprates, particularly as they appear in underdoped compounds. Measurements of
torque magnetometry, Nernst effect and isothermal diamagnetic magnetization
curves published in the last years are taken into consideration. Although by
different experimental approaches and in different magnetic field ranges it can
be stated that vortex-antivortex excitations and phase fluctuations among
islands of local non-zero order parameter lacking of long range coherence do
occur in a relevant temperature range above Tc, particularly in underdoped
compounds. The role of the diamagnetic magnetization curves on approaching Tc
from above in opening the field with clear signature is remarked, while
enlightening comparison with other approaches appear possible.",1005.1139v2
2010-05-10,Anisotropy of Magnetic Interactions in the Spin-Ladder Compound (C$_5$H$_{12}$N)$_2$CuBr$_4$,"Magnetic excitations in the spin-ladder material (C$_5$H$_{12}$N)$_2$CuBr$_4$
[BPCB] are probed by high-resolution multi-frequency electron spin resonance
(ESR) spectroscopy. Our experiments provide a direct evidence for a biaxial
anisotropy ($\sim 5\%$ of the dominant exchange interaction), that is in
contrast to a fully isotropic spin-ladder model employed for this system
previously. It is argued that this anisotropy in BPCB is caused by spin-orbit
coupling, which appears to be important for describing magnetic properties of
this compound. The zero-field zone-center gap in the excitation spectrum of
BPCB, $\Delta_0/k_{B}=16.5$ K, is detected directly. Furthermore, an ESR
signature of the inter-ladder exchange interactions is obtained. The detailed
characterization of the anisotropy in BPCB completes the determination of the
full spin hamiltonian of this exceptional spin-ladder material and shows ways
to study anisotropy effects in spin ladders.",1005.1474v1
2010-05-12,Striped-magnetic-order suppresses giant optical anisotropy and drives structural distortion in iron arsenide superconductors,"To examine the role of magnetism in superconductivity of iron-based
superconductors, we first present first-principles optical calculations on
three representative parent compounds: LaFeAsO, BaFe2As2 and LiFeAs. Both
nonmagnetic (NM) and spin-density wave (SDW) with striped antiferromagnetic
order are considered. Due to their layer structure, these compounds in NM
states show anomalously large optical anisotropy with a conductivity ratio
$\sigma_{zz}/\sigma{xx}$ as large as 313% in LaFeAsO and 530% in LiFeAs.
Interestingly the giant optical anisotropy is significantly suppressed by SDW.
On the other hand, the variable-cell-shape optimizations confirm that SDW does
drive an orthorhombic-distortion. The drive force is dependent on the local
magnetic moment on Fe sublattice, which is tuned by its bonding environment.
Based on these results, we discussed the delicate role of magnetism in
superconductivity.",1005.2121v2
2010-05-13,Neutron structural studies on the superconducting (Nd1-xCax)(Ba1.6La0.4)Cu3Oz system,"We have investigated the influence of Ca ions substitution on the structural
and superconducting properties of (Nd1-xCax)(Ba1.6La0.4)Cu3Oz system.
Magnetization, X-ray diffraction and neutron diffraction studies have been
carried out on a series of compounds with x = 0.0 to 0.6. The superconducting
transition temperature Tc, determined from magnetization measurements increases
with increasing Ca2+ substitution. Neutron diffraction studies reveal that
these compounds crystallize in a tetragonal structure (space group P4/mmm). A
detailed analysis of the neutron diffraction data reveals that Ca and La ions
are intermixed at the nominal Ba and Nd sites. While a major fraction of Ca
ions occupy the usual Nd site, a small fraction occupies the Ba site.
Consequently, the corresponding amount of La substitutes at the nominal Nd
site. The intermixing of Ca and La sites randomizes the chain site oxygens
leading to a tetragonal structure despite an oxygen content close to 7.0 for
all the Ca doped samples. Further increase of Ca content lead to change in its
co-ordination from six-fold to eight-fold at x >= 0.4.",1005.2304v1
2010-05-13,London penetration depth in the tight binding approximation: Orthorhombic distortion and oxygen isotope effects in cuprates,"We present a simple derivation of an expression for the superfluid density $
n_s \propto 1/\lambda^2 $ in superconductors with the tight binding energy
dispersion. The derived expression is discussed in detail because of its
distinction from the known expressions for ordinary superconductors with
parabolic energy dispersion. We apply this expression for the experimental data
analysis of the isotope effect in London penetration depth parameter $ \lambda
$ in the BiSrCuO and YBaCuO family compounds near optimal doping, taking into
account the orthorhombic distortion of crystal structure, and estimate the
isotopic change of hopping parameters from the experimental data. We point out
that $1/\lambda^2$ temperature behaviour is very sensitive to the ratio $
2\Delta_m(T=0)/ k_B T_c $ and estimate this quantity for a number of compounds.",1005.2324v1
2010-05-14,Kagome staircase compound Co3V2O8 in an applied magnetic field: single-crystal neutron-diffraction study,"The magnetic properties of Co3V2O8 have been studied by single-crystal
neutron-diffraction. In zero magnetic field, the observed broadening of the
magnetic Bragg peaks suggests the presence of disorder both in the
low-temperature ferromagnetic and in the higher-temperature antiferromagnetic
state. The field dependence of the intensity and position of the magnetic
reflections in Co3V2O8 reveals a complex sequence of phase transitions in this
Kagome staircase compound. For H//a, a commensurate-incommensurate-commensurate
transition is found in a field of 0.072 T in the antiferromagnetic phase at 7.5
K. For H//c at low-temperature, an applied field induces an unusual
transformation from a ferromagnetic to an antiferromagnetic state at about 1 T
accompanied by a sharp increase in magnetisation.",1005.2510v1
2010-05-16,Si-compatible candidates for high-K dielectrics with the Pbnm perovskite structure,"We analyze both experimentally (where possible) and theoretically from
first-principles the dielectric tensor components and crystal structure of five
classes of Pbnm perovskites. All of these materials are believed to be stable
on silicon and are therefore promising candidates for high-K dielectrics. We
also analyze the structure of these materials with various simple models,
decompose the lattice contribution to the dielectric tensor into force constant
matrix eigenmode contributions, explore a peculiar correlation between
structural and dielectric anisotropies in these compounds and give phonon
frequencies and infrared activities of those modes that are infrared-active. We
find that CaZrO_3, SrZrO_3, LaHoO_3, and LaYO_3 are among the most promising
candidates for high-K dielectrics among the compounds we considered.",1005.2767v2
2010-05-20,Metastable magnetization behavior in magnetocaloric R6Co1.67Si3 (R=Tb and Nd) compounds,"Magnetic field and time induced steps have been observed in the recently
discovered ternary silicide R6Co1.67Si3. Huge relaxation steps are observed
across different loops in the low temperature magnetization isotherms. Giant
relaxation present in this system indicates the existence of incubation time to
get the saturated moment at a certain field. Measurement protocol sensitive
magnetization behavior observed in this system may arise from the strong
magnetostructural coupling and/or magnetic frustration. Electrical resistivity
and magnetoresistance also reflect the magnetic state of the compound.
Magnetocaloric effect is found to be large at temperatures close to the
magnetic transition temperature.",1005.3671v1
2010-05-21,Magnetization jumps and relaxation effect in doped CeFe2,"For the first time, we find that the dynamic antiferromagnetic phase present
in CeFe2 gets stabilized with Ga and Si substitutions. We find that phenomena
such as strain-induced first order jumps in the magnetization curves, asymmetry
between the M-H curves during the increasing and decreasing field cycles, the
envelope curve being inside the virgin curve, occur in these compounds.
Temperature and time dependences of magnetization show that the compounds
possess glassy behavior at low temperatures. Multi-step magnetization behavior,
unusual relaxation effect, thermal and magnetic history dependence, which are
signatures of the martensitic scenario due to the strong magneto-structural
coupling, are found to be present in this system. We also show that one can
induce the magnetization steps with the help of appropriate measurement
protocol. Detailed magnetization relaxation studies have been carried out to
understand the dynamics of magnetic phase transition.",1005.3931v1
2010-05-25,"Magnetic, magnetocaloric and neutron diffraction studies on TbNi5-xMx (M = Co and Fe) compounds","The effect of substitution of Co and Fe for Ni in TbNi5 on the structural,
magnetic and magneto-thermal properties has been investigated. Considerable
enhancement of Curie temperature is observed with Fe substitution, whereas the
increase is nominal in the case of Co. Neutron diffraction measurements reveal
the redistribution of moments and site preference of substitutional ions in Ni
2c and 3g sites. In TbNi4Fe, both Ni and Fe as well as Tb are found to carry
moment while in the case of TbNi4Co, mainly Tb carries the moment.
Magnetocaloric behavior has been investigated from the magnetization and the
heat capacity measurements. The magnetic and magnetocaloric properties are
found to be strongly correlated in these compounds.",1005.4535v2
2010-05-28,Scattering of nucleons from nuclei with couplings to particle-unstable excited states,"The physics of radioactive ion beams implies the description of weakly-bound
nuclear systems. One key aspect concerns the coupling to low-lying
collective-type excited states, which for these systems might not be stable
levels, but particle emitting resonances. In this work we describe how the
scattering cross section and compound spectra change when the colliding
fragments have such collective excitations featuring particle emission. We
explore this question in the framework of a multi-channel algebraic scattering
method of determining nucleon-nucleus cross sections at low energies. For a
range of light-mass, particle-unstable nuclear targets, scattering cross
sections as well as the spectra of the compound nuclei formed have been
determined from calculations that do and do not consider particle emission
widths for nuclear states. Assuming a resonance character for target states
markedly varies evaluated cross sections from those obtained assuming the
target spectrum to have entirely discrete states.",1005.5351v1
2010-05-31,Magnetic and the magnetocaloric properties of Ce1-xRxFe2 and Ce(Fe1-xMx)2 compounds,"We have studied selected rare earth doped and transition metal doped CeFe2
compounds by examining their structural, magnetic and magneto-thermal
properties. With substitution of Ce by 5 and 10% Gd and 10% Ho, the Curie
temperature can be tuned to the range of 267-318 K. Localization of Ce 4f
electronic state with rare earth substitutions is attributed for the
enhancement of Curie temperature. On the other hand, with Ga and Al
substitution at the Fe site, system undergoes paramagnetic to ferromagnetic
transition and then to an antiferromagnetic phase on cooling. The
magnetocaloric effect across the transitions has been studied from both
magnetization isotherms and heat capacity data. It is shown that by choosing
the appropriate dopant and its concentration, the magnetocaloric effect around
room temperature can be tuned.",1005.5650v1
2010-05-31,New high magnetic field phase of the frustrated $S=1/2$ chain compound LiCuVO$_4$,"Magnetization of the frustrated $S=1/2$ chain compound LiCuVO$_4$, focusing
on high magnetic field phases, is reported. Besides a spin-flop transition and
the transition from a planar spiral to a spin modulated structure observed
recently, an additional transition was observed just below the saturation
field. This newly observed magnetic phase is considered as a spin nematic
phase, which was predicted theoretically but was not observed experimentally.
The critical fields of this phase and its dM/dH curve are in good agreement
with calculations performed in a microscopic model (M. E. Zhitomirsky and H.
Tsunetsugu, preprint, arXiv:1003.4096v2).",1005.5668v2
2010-06-01,Ideas by S.V. Vonsovsky and Modern Model Treatment of Magnetism,"A review of fundamental works by Shubin and Vonsovsky on the formulation of
the polar and s-d(f) exchange models is given. Their ideas are compared with
subsequent developments in the theory of magnetism in d- and f-metals and their
compounds. Modern approaches including different slave-boson and slave-fermion
representations, formation of exotic quasiparticles etc. are discussed.
Internal connections between various many-electron models (the Heisenberg,
Hubbard, t-J, Anderson Hamiltonians) are presented. Description of anomalous
rare-earth and actinide compounds (Kondo lattices, systems with heavy fermions
and non-Fermi-liquid behavior) within the framework of the s-d(f) exchange
model and related models is considered.",1006.0108v1
2010-06-02,Pseudogap phase of high-Tc compounds described within the LDA+DMFT+Sigma approach,"LDA+DMFT+Sigma_k approach was applied to describe pseudogap phase of several
prototype high-Tc compounds e.g. hole doped Bi2212 and LSCO systems and
electron doped NCCO and PCCO, demonstrating qualitative difference of the Fermi
surfaces (FS) for these systems. Namely for Bi2212 and LSCO the so called
""hot-spots"" (intersection of a bare FS and AFM Brillouin zone (BZ) boundary),
where scattering on pseudogap fluctuations is most intensive were not observed.
Instead here we have Fermi arcs with smeared FS close to the BZ boundary.
However for NCCO and PCCO ""hot-spots"" are clearly visible. This qualitative
difference is shown to have material specific origin. Good agreement with known
ARPES data was demon strated not only for FS maps but also for spectral
function maps (quasiparticle bands in cluding lifetime and interaction
broadening).",1006.0295v1
2010-06-25,Microwave conductivity of heavy fermions in UPd2Al3,"Heavy-fermion compounds are characterized by electronic correlation effects
at low energies which can directly be accessed with optical spectroscopy. Here
we present detailed measurements of the frequency- and temperature-dependent
conductivity of the heavy-fermion compound UPd2Al3 using broadband microwave
spectroscopy in the frequency range 45 MHz to 40 GHz at temperatures down to
1.7 K. We observe the full Drude response with a relaxation time up to 50 ps,
proving that the mass enhancement of the heavy charge carriers goes hand in
hand with an enhancement of the relaxation time. We show that the relaxation
rate as a function of temperature scales with the dc resistivity. We do not
find any signs of a frequency-dependent relaxation rate within the addressed
frequency range.",1006.4974v1
2010-07-06,Unified description of fission in fusion and spallation reactions,"We present a statistical-model description of fission, in the framework of
compound-nucleus decay, which is found to simultaneously reproduce data from
both heavy-ion-induced fusion reactions and proton-induced spallation reactions
at around 1 GeV. For the spallation reactions, the initial compound-nucleus
population is predicted by the Li\`{e}ge Intranuclear Cascade Model. We are
able to reproduce experimental fission probabilities and fission-fragment mass
distributions in both reactions types with the same parameter sets. However, no
unique parameter set was obtained for the fission probability. The introduction
of fission transients can be offset by an increase of the ratio of
level-density parameters for the saddle-point and ground-state configurations.
Changes to the finite-range fission barriers could be offset by a scaling of
the Bohr-Wheeler decay width as predicted by Kramers. The parameter sets
presented allow accurate prediction of fission probabilities for excitation
energies up to 300 MeV and spins up to 60 \hbar.",1007.0963v3
2010-07-08,Neutron and ARPES Constraints on the Couplings of the Multiorbital Hubbard Model for the Pnictides,"The results of neutron scattering and angle-resolved photoemission
experiments for the Fe-pnictide parent compounds, and their metallic nature,
are shown to impose severe constraints on the range of values that can be
considered ""realistic"" for the intraorbital Hubbard repulsion U and Hund
coupling J in multiorbital Hubbard models treated in the mean-field
approximation. Phase diagrams for three- and five-orbital models are here
provided, and the physically realistic regime of couplings is highlighted, to
guide future theoretical work into the proper region of parameters of Hubbard
models. In addition, using the random phase approximation, the pairing
tendencies in these realistic coupling regions are investigated. It is shown
that the dominant spin-singlet pairing channels in these coupling regimes
correspond to nodal superconductivity, with strong competition between several
states that belong to different irreducible representations. This is compatible
with experimental bulk measurements that have reported the existence of nodes
in several Fe-pnictide compounds.",1007.1436v3
2010-07-11,Spin Dynamics in $S=1/2$ Chains with Next-Nearest-Neighbor Exchange Interactions,"Low-energy magnetic excitations in the spin-1/2 chain compound
(C$_6$H$_9$N$_2$)CuCl$_3$ [known as (6MAP)CuCl$_3$] are probed by means of
tunable-frequency electron spin resonance. Two modes with asymmetric (with
respect to the $h\nu=g\mu_B B$ line) frequency-field dependences are resolved,
illuminating the striking incompatibility with a simple uniform $S=\frac{1}{2}$
Heisenberg chain model. The unusual ESR spectrum is explained in terms of the
recently developed theory for spin-1/2 chains, suggesting the important role of
next-nearest-neighbor interactions in this compound. Our conclusion is
supported by model calculations for the magnetic susceptibility of
(6MAP)CuCl$_3$, revealing a good qualitative agreement with experiment.",1007.2143v2
2010-08-03,Alcoholic beverages induce superconductivity in FeTe$_{1-x}$S$_x$,"We found that hot alcoholic beverages were effective in inducing
superconductivity in FeTe$_{0.8}$S0$_{.2}$. Heating FeTe$_{0.8}$S0$_{.2}$
compound in various alcoholic beverages enhances the superconducting properties
compared to pure water-ethanol mixture as a control. Heating with red wine for
24 hours leads to the largest shielding volume fraction of 62.4% and the
highest zero resistivity temperature of 7.8 K. Some components present in
alcoholic beverages, other than water and ethanol, have the ability to induce
superconductivity in FeTe$_{0.8}$S0$_{.2}$ compound.",1008.0666v2
2010-08-04,Itinerant-Electron Magnet of the Pyrochlore Lattice: Indium-Doped YMn2Zn20,"We report on a ternary intermetallic compound, ""YMn2Zn20"", comprising a
pyrochlore lattice made of Mn atoms. A series of In-doped single crystals
undergo no magnetic long-range order down to 0.4 K, in spite of the fact that
the Mn atom carries a local magnetic moment at high temperatures, showing
Curie-Weiss magnetism. However, In-rich crystals exhibit spin-glass transitions
at approximately 10 K due to a disorder arising from the substitution, while,
with decreasing In content, the spin-glass transition temperature is reduced to
1 K. Then, heat capacity divided by temperature approaches a large value of 280
mJ K-2 mol-1, suggesting a significantly large mass enhancement for conduction
electrons. This heavy-fermion-like behavior is not induced by the Kondo effect
as in ordinary f-electron compounds, but by an alternative mechanism related to
the geometrical frustration on the pyrochlore lattice, as in (Y,Sc)Mn2 and
LiV2O4, which may allow spin entropy to survive down to low temperatures and to
couple with conduction electrons.",1008.0835v2
2010-08-06,Charge transfer in FeOCl intercalation compounds and its pressure dependence: An x-ray spectroscopic study,"We present a study of charge transfer in Na-intercalated FeOCl and
polyaniline-intercalated FeOCl using high-resolution x-ray absorption
spectroscopy and resonant x-ray emission spectroscopy at the Fe-K edge. By
comparing the experimental data with ab-initio simulations, we are able to
unambiguously distinguish the spectral changes which appear due to
intercalation into those of electronic origin and those of structural origin.
For both systems, we find that about 25% of the Fe sites are reduced to Fe2+
via charge transfer between FeOCl and the intercalate. This is about twice as
large as the Fe2+ fraction reported in studies using Mossbauer spectroscopy.
This discrepancy is ascribed to the fact that the charge transfer occurs on the
same time scale as the Mossbauer effect itself. Our result suggests that every
intercalated atom or molecule is involved in the charge-transfer process, thus
making this process a prerequisite for intercalation. The Fe2+ fraction is
found to increase with pressure for polyaniline-FeOCl, hinting at an
enhancement of the conductivity in the FeOCl intercalation compounds under
pressure.",1008.1159v2
2010-08-11,Ferrimagnetism of the magnetoelectric compound Cu$_2$OSeO$_3$ probed by $^{77}$Se NMR,"We present a thorough $^{77}$Se NMR study of a single crystal of the
magnetoelectric compound Cu$_2$OSeO$_3$. The temperature dependence of the
local electronic moments extracted from the NMR data is fully consistent with a
magnetic phase transition from the high-T paramagnetic phase to a low-T
ferrimagnetic state with 3/4 of the Cu$^{2+}$ ions aligned parallel and 1/4
aligned antiparallel to the applied field of 14.09 T. The transition to this
3up-1down magnetic state is not accompanied by any splitting of the NMR lines
or any abrupt modification in their broadening, hence there is no observable
reduction of the crystalline symmetry from its high-T cubic \textit{P}2$_1$3
space group. These results are in agreement with high resolution x-ray
diffraction and magnetization data on powder samples reported previously by Bos
{\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean
field theory description of the problem based on a microscopic spin Hamiltonian
with one antiferromagnetic ($J_\text{afm}\simeq 68$ K) and one ferromagnetic
($J_\text{fm}\simeq -50$ K) nearest-neighbor exchange interaction.",1008.2010v1
2010-08-13,Unusual signatures of the ferromagnetic transition in the heavy Fermion compound UMn$_2$Al$_{20}$,"Magnetic susceptibility results for single crystals of the new cubic
compounds UT$_2$Al$_{20}$ (T=Mn, V, and Mo) are reported. Magnetization,
specific heat, resistivity, and neutron diffraction results for a single
crystal and neutron diffraction and inelastic spectra for a powder sample are
reported for UMn$_2$Al$_{20}$. For T = V and Mo, temperature independent Pauli
paramagnetism is observed. For UMn$_2$Al$_{20}$, a ferromagnetic transition is
observed in the magnetic susceptibility at $T_c$ = 20 K. The specific heat
anomaly at $T_c$ is very weak while no anomaly in the resistivity is seen at
$T_c$. We discuss two possible origins for this behavior of UMn$_2$Al$_{20}$:
moderately small moment itinerant ferromagnetism, or induced local moment
ferromagnetism.",1008.2235v1
2010-08-19,Nodeless two-gap superconductivity in stoichiometric iron pnictide LiFeAs,"The variations of in- and inter- plane London penetration depths,
$\Delta\lambda(T)$, were measured using a tunnel diode resonator in single
crystals of the intrinsic pnictide superconductor LiFeAs. This compound appears
to be in the clean limit with a residual resistivity of 4 ($T\to0$) to 8
($T_c$) $\mu \Omega\cdot$cm and $RRR$ of 65 to 35, respectively. The superfluid
density, $\rho_s(T)=\lambda^2(0)/\lambda^2(T)$, is well described by the
self-consistent two-gap $\gamma-$model. Together with the previous data, our
results support the universal evolution of the superconducting gap from
nodeless to nodal upon departure from optimal doping. We also conclude that
pairbreaking scattering plays an important role in the deviation of the
low-temperature behavior of $\lambda(T)$ from exponential in Fe-based
compounds.",1008.3251v3
2010-08-23,Meta-orbital Transition in Heavy-fermion Systems: Analysis by Dynamical Mean Field Theory and Self-consistent Renormalization Theory of Orbital Fluctuations,"We investigate a two-orbital Anderson lattice model with Ising orbital
intersite exchange interactions by means of dynamical mean field theory
combined with the static mean field approximation of the intersite orbital
interactions. Focusing on Ce-based heavy-fermion compounds, we examine the
orbital crossover between the two orbital states, when the total f-electron
number per site n_f is n_f ~ 1. We show that a ""meta-orbital"" transition, at
which the occupancy of the two orbitals changes steeply, occurs when the
hybridization between the ground-state f-electron orbital and conduction
electrons are smaller than that between the excited f-electron orbital and
conduction electrons. Near the meta-orbital critical end point, the orbital
fluctuations are enhanced, and couple with the charge fluctuations. A critical
theory of the meta-orbital fluctuations is also developed by applying the
self-consistent renormalization theory of itinerant electron magnetism to the
orbital fluctuations. The critical end point, first-order transition and
crossover are described within Gaussian approximations of orbital fluctuations.
We discuss the relevance of our results to CeAl2, CeCu2Si2, CeCu2Ge2 and the
related compounds, which all have low-lying crystalline-electric-field excited
states.",1008.3804v2
2010-08-27,"Magnetization, Maxwell's Relations and the Local Physics of the Dilute System Th_{1-x}U_{x}Ru_{2}Si_{2}","The dilute Kondo compound, Th_{1-x}U_{x}Ru_{2}Si_{2} (TURS), displays
non-Fermi liquid behavior but no zero-point entropy; it thus appears to elude
description by known single-ion models. It may also provide a clue to the
underlying local degrees of freedom in its dense counterpart, URu_{2}Si_{2}.
Here we use high-resolution magnetization studies to cross-check the
thermodynamic consistency of previous experiments. Measurements of the
field-dependence of the temperature-scale, T_F(H), associated with Fermi liquid
behavior probes the nature of the underlying impurity fixed point. We find that
T_F(H) grows linearly with applied field, in contrast to the quadratic form
expected for the two-channel Kondo model. We use a scaling argument to show
that the observed behavior of T_F(H) is consistent with the absence of
zero-point entropy, suggesting novel impurity behavior in this material. More
generally, we suggest the field-magnetization as a probe of single-ion physics
and make predictions for its behavior in other actinide compounds.",1008.4798v1
2010-09-16,Spiral ground state in the quasi-two-dimensional spin-1/2 system Cu2GeO4,"We apply density functional theory band structure calculations, the
coupled-cluster method, and exact diagonalization to investigate the
microscopic magnetic model of the spin-1/2 compound Cu2GeO4. The model is
quasi-two-dimensional, with uniform spin chains along one direction and
frustrated spin chains along the other direction. The coupling along the
uniform chains is antiferromagnetic, J 130 K. The couplings along the
frustrated chains are J1 -60 K and J2 80 K between nearest neighbors and
next-nearest neighbors, respectively. The ground state of the quantum model is
a spiral, with the reduced sublattice magnetization of 0.62 mu_B and the pitch
angle of 84 deg, both renormalized by quantum effects. The proposed spiral
ground state of Cu2GeO4 opens a way to magnetoelectric effects in this
compound.",1009.3287v2
2010-10-01,Nanocrystalline Zr3Al Made through Amorphization by Repeated Cold Rolling and Followed by Crystallization,"The intermetallic compound Zr3Al is severely deformed by the method of
repeated cold rolling. By X-ray diffraction it is shown that this leads to
amorphization. TEM investigations reveal that a homogeneously distributed
debris of very small nanocrystals is present in the amorphous matrix that is
not resolved by X-ray diffraction. After heating to 773 K, the crystallization
of the amorphous structure leads to a fully nanocrystalline structure of small
grains (10 - 20 nm in diameter) of the non-equilibrium Zr2Al phase. It is
concluded that the debris retained in the amorphous phase acts as nuclei. After
heating to 973 K the grains grow to about 100 nm in diameter and the compound
Zr3Al starts to form, that is corresponding to the alloy composition.",1010.0190v1
2010-10-07,A Spitzer/IRS spectral study of a sample of galactic carbon-rich proto-planetary nebulae,"Recent infrared spectroscopic observations have shown that proto-planetary
nebulae (PPNs) are sites of active synthesis of organic compounds in the late
stages of stellar evolution. This paper presents a study of Spitzer/IRS spectra
for a sample of carbon-rich PPNs, all except one of which show the unidentified
21 micron emission feature. The strengths of the aromatic infrared band (AIB),
21 micron, and 30 micron features are obtained by decomposition of the spectra.
The observed variations in the strengths and peak wavelengths of the features
support the model that the newly synthesized organic compounds gradually change
from aliphatic to aromatic characteristics as stars evolve from PPNs to
planetary nebulae.",1010.1327v2
2010-10-07,Model misspecification in peaks over threshold analysis,"Classical peaks over threshold analysis is widely used for statistical
modeling of sample extremes, and can be supplemented by a model for the sizes
of clusters of exceedances. Under mild conditions a compound Poisson process
model allows the estimation of the marginal distribution of threshold
exceedances and of the mean cluster size, but requires the choice of a
threshold and of a run parameter, $K$, that determines how exceedances are
declustered. We extend a class of estimators of the reciprocal mean cluster
size, known as the extremal index, establish consistency and asymptotic
normality, and use the compound Poisson process to derive misspecification
tests of model validity and of the choice of run parameter and threshold.
Simulated examples and real data on temperatures and rainfall illustrate the
ideas, both for estimating the extremal index in nonstandard situations and for
assessing the validity of extremal models.",1010.1357v1
2010-10-15,Synthesis and magnetic properties of Mn12-based single molecular magnets with benzene and pentafluorobenzene carboxylate ligands,"We report on the synthesis and magnetic properties of Mn12-based single
molecular magnets (SMMs) with benzene and pentafluorobenzene carboxylate
ligands. The changes in ligand structure are shown to have a decisive effect on
magnetic properties of produced complexes. The compound with benzene
demonstrates unusual magnetic behaviour, namely, temperature dependencies of
magnetization taken under the zero field cooled and field cooled conditions are
split below 10 K and furthermore remnant magnetization and coercive force
remain nonzero in this temperature range. In contrast, compound with
pentafluorobenzene displays the customary signatures of a blocking temperature
at 3K. The effect of ligand substitution was theoretically studied within local
density approximation taking into account on-site Coloumb repulsion.
Calculation results confirm that the electronic structure and the magnetic
exchange interactions between different Mn atoms strongly depend on the type of
ligands.",1010.3057v1
2010-10-25,Three-dimensional gap solitons in Bose-Einstein condensates supported by one-dimensional optical lattices,"We study fundamental and compound gap solitons (GSs) of matter waves in
one-dimensional (1D) optical lattices (OLs) in a three-dimensional (3D)
weak-radial-confinement regime, which corresponds to realistic experimental
conditions in Bose-Einstein condensates (BECs). In this regime GSs exhibit
nontrivial radial structures. Associated with each 3D linear spectral band
exists a family of fundamental gap solitons that share a similar transverse
structure with the Bloch waves of the corresponding linear band. GSs with
embedded vorticity $m$ may exist \emph{inside} bands corresponding to other
values of $m$. Stable GSs, both fundamental and compound ones (including vortex
solitons), are those which originate from the bands with lowest axial and
radial quantum numbers. These findings suggest a scenario for the experimental
generation of robust GSs in 3D settings.",1010.5271v2
2010-11-04,Low-energy spin dynamics in the [YPc2]0 S=1/2 antiferromagnetic chain,"1H nuclear magnetic resonance (NMR) measurements in [YPc2]0, an organic
compound formed by radicals stacking along chains, are presented. The
temperature dependence of the macroscopic susceptibility, of the NMR shift and
of the spin-lattice relaxation rate 1/T1 indicate that the unpaired electron
spins are not delocalized but rather form a S=1/2 antiferromagnetic chain. The
exchange couplings estimated from those measurements are all in quantitative
agreement. The low-energy spin dynamics can be described in terms of diffusive
processes and the temperature dependence of the corresponding diffusion
constant suggests that a spin-gap around 1 K might be present in this compound.",1011.1141v2
2010-11-08,Rapidly fluctuating orbital occupancy above the orbital ordering transition in spin-gap compounds,"Several spin systems with low dimensionality develop a spin-dimer phase
within a molecular orbital below TS, competing with long-range
antiferromagnetic order. Very often, preferential orbital occupancy and
ordering are the actual driving force for dimerization, as in the so-called
orbitally-driven spin-Peierls compounds (MgTi2O4, CuIr2S4, La4Ru2O10,
NaTiSi2O6, etc.). Through a microscopic analysis of the thermal conductivity k
(T) in La4Ru2O10, we show that the orbital occupancy fluctuates rapidly above
TS, resulting in an orbital-liquid state. The strong orbital-lattice coupling
introduces dynamic bond-length fluctuations that scatter the phonons to produce
a k (T) proportional to T (i.e. glass-like) above TS. This phonon-glass to
phonon-crystal transition is shown to occur in other spin-dimer systems, like
NaTiSi2O6, pointing to a general phenomenon.",1011.1860v1
2010-11-11,"Structure, Transport and Magnetic properties in La$_{2x}$Sr$_{2-2x}$Co$_{2x}$Ru$_{2-2x}$O$_{6}$","The perovskite solid solutions of the type
La$_{2x}$Sr$_{2-2x}$Co$_{2x}$Ru$_{2-2x}$O$_{6}$ with 0.25 $\leq$ x $ \leq $
0.75 have been investigated for their structural, magnetic and transport
properties. All the compounds crystallize in double perovskite structure. The
magnetization measurements indicate a complex magnetic ground state with strong
competition between ferromagnetic and antiferromagnetic interactions.
Resistivity of the compounds is in confirmation with hopping conduction
behaviour though differences are noted especially for $x$ = 0.4 and 0.6. Most
importantly, low field (50Oe) magnetization measurements display negative
magnetization during the zero field cooled cycle. X-ray photoelectron
spectroscopy measurements indicate presence of Co$^{2+}$/Co$^{3+}$ and
Ru$^{4+}$/Ru$^{5+}$ redox couples in all compositions except $x$ = 0.5.
Presence of magnetic ions like Ru$^{4+}$ and Co$^{3+}$ gives rise to additional
ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the
observed negative magnetization.",1011.2559v1
2010-11-12,Antiferromagnetic ordering in the absence of a structural distortion in Ba(Fe{1-x}Mn{x})2As2,"Neutron and x-ray diffraction studies of Ba(Fe{1-x}Mn{x})2As2 for low doping
concentrations (x <= 0.176) reveal that at a critical concentration, 0.102 < x
< 0.118, the tetragonal-to-orthorhombic transition abruptly disappears whereas
magnetic ordering with a propagation vector of (1/2 1/2 1) persists. Among all
of the iron arsenides this observation is unique to Mn-doping, and unexpected
because all models for ""stripe-like"" antiferromagnetic order anticipate an
attendant orthorhombic distortion due to magnetoelastic effects. We discuss
these observations and their consequences in terms of previous studies of
Ba(Fe{1-x}TM{x})2As2 compounds (TM = Transition Metal), and models for magnetic
ordering in the iron arsenide compounds.",1011.2816v1
2010-11-22,`17-15' Superconductivity - Rh17S15 and Pd17Se15,"The presence of strongly correlated superconductivity in Rh17S15 has been
recently established. In this work, we compare the normal and superconducting
parameters of a single crystal of Rh17S15 with those of a polycrystalline
sample of Pd17Se15 which is reported here for the first time to be a
superconductor below 2.2 K. Pd17Se15, which is iso-structural to Rh17S15 (space
group Pm3m), has very different properties and provides for an interesting
study in contrast with Rh17S15. We see that large unit volume of Pd17Se15 and
the large separation of Pd-Pd atoms in its structure as compared those in a
pure Pd metal lead to the absence of strong correlations in this compound.
Finally, we report band structure calculations on these two compounds and
compare the density of states with estimates from heat capacity data. Upper
critical field, Heat capacity (down to 500 mK), Hall effect and band structure
studies suggest that Rh17S15 is a multiband superconductor.",1011.4809v2
2010-11-23,Design of a low band gap oxide ferroelectric: Bi$_6$Ti$_4$O$_{17}$,"A strategy for obtaining low band gap oxide ferroelectrics based on charge
imbalance is described and illustrated by first principles studies of the
hypothetical compound Bi$_6$Ti$_4$O$_{17}$, which is an alternate stacking of
the ferroelectric Bi$_4$Ti$_3$O$_{12}$. We find that this compound is
ferroelectric, similar to Bi$_4$Ti$_3$O$_{12}$ although with a reduced
polarization. Importantly, calculations of the electronic structure with the
recently developed functional of Tran and Blaha yield a much reduced band gap
of 1.83 eV for this material compared to Bi$_4$Ti$_3$O$_{12}$. Therefore,
Bi$_6$Ti$_4$O$_{17}$ is predicted to be a low band gap ferroelectric material.",1011.5089v2
2010-11-26,CaCu2(SeO3)2Cl2: spin-1/2 Heisenberg chain compound with complex frustrated interchain couplings,"We report the crystal structure, magnetization measurements, and
band-structure calculations for the spin-1/2 quantum magnet CaCu2(SeO3)2Cl2.
The magnetic behavior of this compound is well reproduced by a uniform spin-1/2
chain model with the nearest-neighbor exchange of about 133 K. Due to the
peculiar crystal structure, spin chains run in the direction almost
perpendicular to the structural chains. We find an exotic regime of frustrated
interchain couplings owing to two inequivalent exchanges of 10 K each. Peculiar
superexchange paths grant an opportunity to investigate bond-randomness effects
under partial Cl-Br substitution.",1011.5827v2
2010-11-28,Physical properties of the non-centrosymmetric superconductor Nb0.18Re0.82,"We report the synthesis and measurements of magnetic, transport, and thermal
properties of polycrystalline Nb0.18Re0.82, which has a superconducting
transition at Tc ~ 8.8 K. The non-centrosymmetric alpha-Mn structure of the
compound is confirmed by X-ray diffraction. Using the measured values for the
lower critical field Hc1, upper critical field Hc2, and the specific heat C, we
estimate the thermodynamic critical field Hc(0), coherence length {\xi}(0),
penetration depth {\lambda}(0), and the Ginzburg-Landau parameter {\kappa}(0).
The specific heat jump at Tc, {\Delta}C/{\gamma}Tc = 1.86, suggests that
Nb0.18Re0.82 is moderately coupled superconductor. Below Tc the electronic
specific heat decays exponentially, suggesting that the gap is isotropic. Our
data suggests that the triplet admixture is weak in the polycrystalline form of
compound. However, the estimated value of the upper critical field Hc2(0) is
close to the calculated Pauli limit indicating the need for single crystal
measurements.",1011.6099v1
2010-11-30,Heat capacity of the site-diluted spin dimer system Ba3(Mn1-xVx)2O8,"Heat capacity and susceptibility measurements have been performed on the
diluted spin dimer compound Ba3(Mn1-xVx)2O8. The parent compound Ba3Mn2O8 is a
spin dimer system based on pairs of antiferromagnetically coupled S = 1, 3d2
Mn5+ ions such that the zero field groundstate is a product of singlets.
Substitution of non-magnetic S = 0, 3d0 V5+ ions leads to an interacting
network of unpaired Mn moments, the low temperature properties of which are
explored in the limit of small concentrations, 0<x<0.05. The zero-field heat
capacity of this diluted system reveals a progressive removal of magnetic
entropy over an extended range of temperatures, with no evidence for a phase
transition. The concentration dependence does not conform to expectations for a
spin glass state. Rather, the data suggest a low temperature random singlet
phase, reflecting the hierarchy of exchange energies found in this system.",1011.6423v3
2010-11-30,Magnetic ordering and structural distortion in Ru doped BaFe2As2 single crystals studied by Neutron and X-ray diffraction,"We present a systematic investigation of the antiferromagnetic ordering and
structural distortion for the series of Ba(Fe{1-x}Ru{x})2As2 compounds (0 <= x
<= 0.246). Neutron and x-ray diffraction measurements demonstrate that, unlike
for the electron-doped compounds, the structural and magnetic transitions
remain coincident in temperature. Both the magnetic and structural transitions
are gradually suppressed with increased Ru concentration and coexist with
superconductivity. For samples that are superconducting, we find strong
competition between superconductivity, the antiferromagnetic ordering, and the
structural distortion.",1011.6446v1
2010-11-30,"Electronic and Structural Properties of AAl2Se4(A = Ag, Cu, Cd, Zn) Chalcopyrite Semiconductors","We have studied the structural and electronic properties of defect
chalcopyrite semiconductors AAl2Se4 (A = Ag, Cu, Cd, Zn) using Density
Functional Theory (DFT) based first principle technique within Tight binding
Linear Muffin Tin orbital (TB-LMTO) method. Our calculated structural
parameters such as lattice constants, anion displacement parameter (u),
tetragonal distortion ({\eta} = c/2a), bond lengths and bulk modulus are in
good agreement with other work. Our band structure calculation suggests that
these compounds are direct band gap semiconductors having band gaps 2.40, 2.50,
2.46 and 2.82 eV for AAl2 Se4 (A = Ag, Cu, Cd, Zn) respectively. Calculated
band gaps are in good agreement with other experimental and theoretical works
within LDA limitation. We have made a quantitative estimation of the effect of
p-d hybridization and structural distortion on the electronic properties. The
reduction in band gap due to p-d hybridization are 19.47%, 21.29%, 0% and 0.7%
for AAl2 Se4 (A = Ag, Cu, Cd, Zn) respectively. Increment of the band gap due
to structural distortion is 11.62%, 2.45%, 2.92% and 9.30% in case of AgAl2
Se4, CuAl2 Se4, CdAl2 Se4 and ZnAl2 Se4 respectively . We have also discussed
the bond nature of all four compounds.",1011.6463v1
2010-11-30,Neutron diffraction studies and the magnetism of an ordered perovskite: Ba2CoTeO6,"The complex perovskite Ba2CoTeO6 (BCTO) has been synthesised, and the crystal
structure and magnetic properties have been investigated using a combination of
X-ray and neutron powder diffraction, electron microscopy and dielectric,
calorimetric and magnetic measurements. It was shown that at room temperature
this compound adopts the 6L-trigonal perovskite structure, space group P-3m (N
164) (a= 5.7996(1){\AA}, c=14.2658(3){\AA}). The structure comprises dimers of
face-sharing octahedra as well as octahedra which share only vertices with
their neighbours. A long-range antiferromagnetically ordered state has been
identified from neutron diffraction and magnetic studies. The magnetic
diffraction peaks were registered below the magnetic transition at about 15 K
and a possible model for the magnetic structure is proposed. The structural and
magnetic features of this compound are discussed and compared with those of
other Co-based quaternary oxides adopting the perovskite structure.",1011.6637v1
2010-11-30,Phonons and their Coupling to Magnons in n=2 Ruddlesden-Popper Compounds,"The number of absorption and Raman optical modes for each Wyckoff orbit in
the high-temperature tetragonal (I4/mmm) parent lattice of the
Ruddlesden-Popper compounds Ca$_3$X$_2$O$_7$, with X=Mn or X=Ti is given. We
analyze the effect of sequential perturbations which lower the symmetry to Cmcm
and Cmc2$_1$ and finally include magnetic ordering. We determine the power law
behavior (within mean field theory) for the cross section for photon absorption
and Raman scattering of modes which appear as the symmetry is successively
lowered. In the Cmc2$_1$ phase we give a symmetry analysis to discuss the
magnon-phonon coupling which in other systems gives rise to ""electromagnons.""
From our results we suggest several experiments to clarify the phase diagram
and other properties of these systems.",1011.6672v2
2010-12-03,Magnetic and electrical properties and carrier doping effects on the Fe-based host compound Sr4Sc2Fe2As2O6,"Additional charge carriers were introduced to the iron oxyarsenide
Sr4Sc2Fe2As2O6 under a high-pressure condition, followed by measurements of
electrical resistivity, Hall coefficient, and magnetic susceptibility. The host
compound Sr4Sc2Fe2As2O6 shows metallic conductivity down to ~200 K and turns to
show a semiconducting-like conductivity accompanied by a positive
magneto-resistance (22% at 70 kOe). Although the carrier density is comparable
at 300 K (5.9x1021 cm-3) with that of the other Fe-based superconductors, no
superconductivity appears down to 2 K. This is primarily because the net
carrier density decreases over 3 orders of magnitude on cooling and
additionally a possible magnetic order at ~120 K prevents carriers from
pairing. The properties were altered largely by introducing the additional
carriers.",1012.0616v1
2010-12-07,Homogeneous coexistence of SDW and SC states in CaFe(1-x)Co(x)AsF studied by nuclear magnetic resonance,"We investigated the homogeneous coexistence of spin-density-wave (SDW) and
superconducting (SC) states via 75As-nuclear magnetic resonance (NMR) in
CaFe(1-x)Co(x)AsF and found that the electronic and magnetic properties of this
compound are intermediate between those of LaFeAsO(1-x)F(x) and
Ba(Fe(1-x)Co(x))2As2. For 6% Co-doped samples, the paramagnetic spectral weight
completely disappears in the crossover regime between the SDW and SC phases
followed by the anomalous behavior of relaxation rate (1/T1), implying that the
two phases are not segregated. The 59Co-NMR spectra show that spin moments are
not commensurate but spatially modulated. These experimental results suggest
that incommensurate SDW (IC-SDW) and SC states are compatible in this compound.",1012.1432v2
2010-12-08,Rare Earth Monopnictides and Monochalcogenides from First Principles: Towards an Electronic Phase Diagram of Strongly Correlated Materials,"We present results of an ab-initio study of the electronic structure of 140
rare earth compounds. Specifically we predict an electronic phase diagram of
the entire range of rare earth monopnictides and monochalcogenides, composed of
metallic, semiconducting and heavy fermion-like regions, and exhibiting valency
transitions brought about by a complex interplay between ligand chemistry and
lanthanide contraction. The calculations exploit the combined effect of a
first-principles methodology, which can adequately describe the dual character
of electrons, itinerant vs. localized, and high throughput computing made
possible by the increasing available computational power. Our findings,
including the predicted ""intermediate valent"" compounds SmO and TmSe, are in
overall excellent agreement with the available experimental data. The accuracy
of the approach, proven e.g. through the lattice parameters calculated to
within 1.5% of the experimental values, and its ability to describe
localization phenomena in solids, makes it a competitive atomistic simulation
approach in the search for and design of new materials with specific physical
properties and possible technological applications.",1012.1823v1
2010-12-16,Synthesis and crystal growth of Cs0.8(FeSe0.98)2: a new iron-based superconductor with Tc=27K,"We report on the synthesis of large single crystals of a new FeSe-layer
superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron
powder-diffraction and magnetization measurements have been used to compare the
crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of
the recently discovered potassium intercalated system KxFe2Se2. The new
compound Cs0.8(FeSe0.98)2 shows a slightly lower superconducting transition
temperature (Tc=27.4 K) in comparison to 29.5 in K0.8(FeSe0.98)2). The volume
of the crystal unit cell increases by replacing K by Cs - the c-parameter grows
from 14.1353(13) {\AA} to 15.2846(11) {\AA}. For the so far known alkali metal
intercalated layered compounds (K0.8Fe2Se2 and Cs0.8(FeSe0.98)2) the Tc
dependence on the anion height (distance between Fe-layers and Se-layers) was
found to be analogous to those reported for As-containing Fe-superconductors
and Fe(Se1-xChx), where Ch=Te, S.",1012.3637v1
2010-12-21,Resistivity scaling in 1111 iron-pnictide superconductors,"We show that the zero field normal-state resistivity above Tc for various
levels of electron doping - both for LaO1-xFxFeAs (La-1111) and SmO1-xFxFeAs
(Sm-1111) members of the 1111-iron-pnictide superconductor family - can be
scaled in a broad temperature range from 20 to 300 K onto single curves for
underdoped La-1111 (x=0.05-0.075), for optimally and overdoped La-1111
(x=0.1-0.2) and for underdoped Sm-1111 (x=0.06-0.1) compounds. The scaling was
performed using the energy scale {\Delta}, the resistivity {\rho}_{\Delta} and
the residual resistivity {\rho}_0 as scaling parameters as well as by applying
a recently proposed model-independent scaling method (H. G. Luo, Y. H. Su, and
T. Xiang, Phys. Rev. B 77, 014529 (2008)). The scaling parameters have been
calculated and the compositional variation of {\Delta} has been determined. The
observed scaling behaviour for {\rho}(T) is interpreted as an indication of a
common mechanism which dominates the scattering of the charge carriers in
underdoped La-1111, in optimally and overdoped La-1111 and in underdoped
Sm-1111 compounds..",1012.4682v1
2011-01-04,Incoherent Bi off-centering in Bi2Ti2O7 and Bi2Ru2O7: Insulator versus metal,"The cubic, stoichiometric oxide compounds Bi2Ti2O6O' (also written Bi2Ti2O7)
and Bi2Ru2O6O' (also written Bi2Ru2O7) have in common lone-pair active Bi3+
cations on the pyrochlore A-site with a propensity to off-center. Unlike
Bi2Ti2O6O', Bi2Ru2O6O' is a metal, so it is of interest to ask whether
conduction electrons and/or involvement of Bi 6s states at the Fermi energy
influence Bi3+ displacements. The Bi3+ off-centering in Bi2Ti2O6O' is
incoherent as revealed in detail by reverse Monte Carlo analysis of total
neutron scattering. Similar analysis of Bi2Ru2O6O' reveals incoherent
off-centering as well, of smaller magnitude and with distinctly different
orientational preference. Analysis of total scattering presented here shows
that Bi in both compounds is entirely Bi3+. Disorder in Bi2Ti2O6O' has the
effect of stabilizing valence while simultaneously providing space for the
electronic lone pair. In Bi2Ru2O6O', off-centering is not required to satisfy
valence, but is driven by the lone pair which is partially screened by
conduction electrons.",1101.0791v2
2011-01-13,Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4,"We report on the crystal structure and magnetic behavior of the spin-1/2
compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and
electron spin resonance measurements identify AgVOAsO4 as a gapped quantum
magnet with a spin gap Delta ~ 13 K and a saturation field H_s ~ 48.5 T.
Extensive band structure calculations establish the microscopic magnetic model
of spin chains with alternating exchange couplings J ~ 40 K and J' ~ 26 K.
However, the precise evaluation of the spin gap emphasizes the role of
interchain couplings which are frustrated due to the peculiar crystal structure
of the compound. The unusual spin model and the low energy scale of the
exchange couplings make AgVOAsO4 a promising candidate for an experimental
investigation of Bose-Einstein condensation and other exotic ground states in
high magnetic fields.",1101.2546v2
2011-01-21,Theoretical investigation of half-metallicity in Co/Ni substituted AlN,"Results of Co and Ni substituted AlN in the zinc blende phase are presented.
For spin up states the hybridized N-2p and Co/Ni-3d states form the valance
bands with a bandgap around the Fermi level for both materials, while in the
case of the spin down states the hybridized states cross the Fermi level and
hence show metallic nature. It is found that, Al0.75Co0.25N and Al0.75Ni0.25N
are ferromagnetic materials with magnetic moments of 4 {\mu}B and 3 {\mu}B
respectively. The integer magnetic moments and the full spin polarization at
the Fermi level make these compounds half-metallic semiconductors. Furthermore
it is also found that the interaction with the N-2p state splits the 5-fold
degenerate Co/Ni-3d states into t2g and eg states. The t2g states are located
at higher energies than the eg states caused by the tetrahedral symmetry of
these compounds.",1101.4057v1
2011-01-24,"Theory for superconductivity in (Tl,K)Fe$_x$Se$_2$ as a doped Mott insulator","Possible superconductivity in recently discovered (Tl,K)Fe$_x$Se$_2$
compounds is studied from the viewpoint of doped Mott insulator. The Mott
insulating phase is examined to be preferred in the parent compound at $x=1.5$
due to the presence of Fe vacancies. Partial filling of vacancies at the
Fe-sites introduces electron carriers and leads to electron doped
superconductivity. By using a two-orbital Hubbard model in the strong coupling
limit, we find that the s-wave pairing is more favorable at small Hund's
coupling, and d$_{x^2-y^2}$ wave pairing is more favorable at large Hund's
coupling.",1101.4462v3
2011-01-28,"On scattering cross sections and durations near an isolated compound-resonance, distorted by the non-resonant background, in the center-of-mass and laboratory systems","During last 20 years there was revealed and published the phenomenon of the
appearing of the time advance instead of the time delay at the region of a
compound-nucleus resonance, distorted by the non-resonant background (in the
center-of-mass (C-) system). This phenomenon is usually accompanied by a
minimum in the cross section near the same energy. Here we analyze the cross
section and the time delay of the nucleon-nucleus scattering in the laboratory
(L-) system. In the L-system the delay-advance phenomenon does not appear. We
use and concretize the non-standard analytical transformations of the cross
section from the C-system to the L-system, obtained in our previous papers.
They are illustrated by the calculations of energy dependences of cross
sections in the L-system for several cases of nucleon elastic scattering by
nuclei 12C, 16O, 28Si, 52Cr, 56Fe and 64Ni at the range of distorted resonances
in comparison with the experimental data.",1101.5541v1
2011-02-04,Thermodynamic aspects of materials' hardness: prediction of novel superhard high-pressure phases,"In the present work we have proposed the method that allows one to easily
estimate hardness and bulk modulus of known or hypothetical solid phases from
the data on Gibbs energy of atomization of the elements and corresponding
covalent radii. It has been shown that hardness and bulk moduli of compounds
strongly correlate with their thermodynamic and structural properties. The
proposed method may be used for a large number of compounds with various types
of chemical bonding and structures; moreover, the temperature dependence of
hardness may be calculated, that has been performed for diamond and cubic boron
nitride. The correctness of this approach has been shown for the recently
synthesized superhard diamond-like BC5. It has been predicted that the
hypothetical forms of B2O3, diamond-like boron, BCx and COx, which could be
synthesized at high pressures and temperatures, should have extreme hardness.",1102.0869v1
2011-02-14,Possibility of narrow resonances in nucleon-nucleon channels,"Compound states manifest themselves as bound states, resonances, or
primitives, and their character is determined by their interaction with the
continuum. If the interaction experiences a perturbation, a compound state can
change its manifestation. Phase analysis of nucleon-nucleon scattering
indicates the existence of primitives in the 3S1, 1S0, and 3P0 channels.
Electromagnetic interaction can shift primitives from the unitary cut, turning
them into narrow resonances. We evaluate this effect on the 1S0 proton-proton
scattering channel within the framework of the Simonov-Dyson model. We show
that electromagnetic interaction turns a primitve with a mass of 2000 MeV into
a dibaryon resonance of approximately the same mass and a width of 260 keV.
Narrow resonances of a similar nature may occur in other nucleon-nucleon
channels. Experimental confirmation of the existence of narrow resonances would
have important implications for the theory of nucleon-nucleon interaction.",1102.2718v2
2011-02-15,Crystal and magnetic structure of the superconductor CeNi$_{0.8}$Bi$_2$,"We have performed powder neutron diffraction on the new superconductor,
CeNi$_{0.8}$Bi$_2$ with a superconducting transtion temperature $T_\textrm{c}
\sim$ 4.2 K. The structural parameters of this compound at room temperature are
determined by Rietveld analysis. Below about 5 K, the clear magnetic Bragg
peaks with propagation vector $q$=(0 0 0) are observed. The observed
intensities of magnetic Bragg peaks can be explained by the magnetic structure
that the two Ce moments in the unit cell are antiparallel along c axis. The
magnetic Bragg peaks are observed in the superconducting state, indicating the
coexistence of the antiferromagnetic ordering and the superconductivity in this
compound. The intensity of magnetic Bragg peak monotonously increases with
decreasing temperature below $T_\textrm{N}$ and does not exhibit apparent
anomaly at $T_\textrm{c}$, obviously different from cases of heavy fermion
superconductors in which the magnetic ordering and the superconductivity
coexist, for example, Cd-doped CeCoIn$_5$. These results suggest that the 4$f$
electron of the Ce atom is not coupled with the superconducting carrier, and
the magnetic ordering is almost independent of the superconductivity in
CeNi$_{0.8}$Bi$_2$.",1102.2972v2
2011-02-21,Nonlinearity and optical bistability caused by local field effects in the interaction between a two level atomic system and a metamaterial,"We present a theoretical analysis of the nonlinear response of a metamaterial
consisting of an array of split ring resonators coupled to a two level atomic
system (2LS) without inversion. We calculated the total complex susceptibility
and the linear, third and fifth-order nonlinear solution of the Maxwell Bloch
equations that describe the coupled system. We analyzed the impact of the
nonlinear effects on the dynamics of an active metamaterial/2LS compound in
dependence of the magnitude of the external electric field when the 2LS is
pumped by an external pump source and population inversion is achieved. We
observed that nonlinear damping in the active metamaterial/2LS compound
significantly reduces the effect of spiking. Finally, we investigated the
conditions under which the system can exhibit the phenomenon of optical
bistability. We observed that optical bistability can only be obtained when the
atomic volume density of the 2LS attains unphysically high values and thus is
not expected in the system under investigation.",1102.4262v1
2011-02-23,Comparative study of the phonons in non-superconducting BaC6 and superconducting CaC6 using inelastic x-ray scattering,"The low energy phonons of two different graphite intercalation compounds
(GICs) have been measured as a function of temperature using inelastic x-ray
scattering (IXS). In the case of the non-superconductor BaC6, the phonons
observed are significantly higher (up to 20 %) in energy than those predicted
by theory, in contrast to the reasonable agreement found in superconducting
CaC6. Additional IXS intensity is observed below 15 meV in both BaC6 and CaC6.
It has been previously suggested that this additional inelastic intensity may
arise from defect or vacancy modes in these compounds, unpredicted by theory
(d'Astuto et al, Phys. Rev. B 81 104519 (2010)). Here it is shown that this
additional intensity can arise directly from the large disorder of the
available samples. Our results show that future theoretical work is required to
understand the relationship between the crystal structure, the phonons and the
superconductivity in GICs.",1102.4767v2
2011-03-03,Effect of structural distortion and nature of bonding on the electronic properties of defect and Li doped CulnSe2Chalcopyrite Semiconductors,"We report the structural and electronic properties of chalcopyrite
semiconductors CuInSe2, CuIn2 Se4 and Cu0.5Li0.5InSe2. Our calculation is based
on Density functional Theory within tight binding linear muffin-tin orbital
(TB-LMTO) method. The calculated lattice constants, anion displacement (u),
tetragonal distortion ({\eta} = c/2a) and bond lengths agree well with
experimental values. Our result shows these compounds are direct band gap
semiconductors. Our calculated band gaps, 0.79eV and 1.08 eV of CuInSe2 and
Cu0.5Li0.5InSe2 respectively agree well with the experimental values within the
limitation of LDA. The band gap of CuIn2Se4 is found to be 1.50 eV. The band
gap reduces by 59.57%, 23.61% and 48.82% due to p-d hybridization and reduces
by 16.85%, 9.10% and 0.92% due to structural distortion for CuInSe2, CuIn2Se4
and Cu0.5Li0.5InSe2 respectively. We also discuss the effect of bond nature on
electronic properties of all three compounds.",1103.0614v1
2011-03-08,Fusion Hindrance in the Heavy Ion Reactions -- Border Between the Normal and Hindered Fusions,"The fusion hindrance in heavy ion collisions is studied in the framework of
the two-center liquid drop model. It appears that the neck and the radial
degrees of freedom might both be hampered by an inner potential barrier on
their path between the contact configuration to the compound nucleus. Heavy ion
reactions with and without the two kinds of fusion hindrance are classified
through systematic calculations. It is found that the number of reactions
without radial fusion hindrance is much smaller than that without neck fusion
hindrance, and for both kinds of fusion hindrance the number of reactions
without fusion hindrance at small mass-asymmetry parameter $\alpha$ is smaller
than that at large $\alpha$. In the formation of a given compound nucleus, if a
reaction with $\alpha_c$ is not hindered, then other reactions with $\alpha >
\alpha_c$ are also not hindered as it is well known experimentally.",1103.1449v2
2011-03-08,Spin exchange dominated by charge fluctuations of the Wigner lattice in the newly synthesized chain cuprate Na5Cu3O6,"Na5Cu3O6, a new member of one dimensional charge ordered chain cuprates, was
synthesized via the azide/nitrate route by reacting NaN3, NaNO3 and CuO.
According to single crystal X-ray analysis, one dimensional CuO2 chains built
up from planar, edge-sharing CuO4 squares are a dominant feature of the crystal
structure. From the analysis of the Cu-O bond lengths we find that the system
forms a Wigner lattice. The commensurate charge order allows to explicitly
assign the valence states of either +2 or +3 to each copper atom resulting in a
repetition according to Cu(2+)-Cu(3+)-Cu(2+)-Cu(2+)-Cu(3+)-Cu(2+). Following
the theoretical analysis of the previously synthesized compounds Na3Cu2O4 and
Na8Cu5O10, the magnetic susceptibility was expected to show a large dimer gap.
Surprisingly, this is not the case. To resolve this puzzle, we show that the
magnetic couplings in this compound are strongly affected by excitations across
the Wigner charge gap. By including these contributions, which are distinct
from conventional superexchange in Mott-insulators, we obtain a quantitative
satisfying theoretical description of the magnetic susceptibility data.",1103.1588v1
2011-03-11,Computationally-Driven Experimental Discovery of the CeIr$_4$In Compound,"We present a combined experimental and computational methodology for the
discovery of new materials. Density functional theory (DFT) formation energy
calculations allow us to predict the stability of various hypothetical
structures. We demonstrate this approach by computationally predicting the
Ce-Ir-In ternary phase diagram. We predict previously-unknown compounds
CeIr$_4$In and Ce$_2$Ir$_2$In to be stable. Subsequently, we successfully
synthesize CeIr$_4$In and characterize it by X-ray diffraction. Magnetization
and heat capacity measurements of CeIr$_4$In are reported. The correct
prediction and discovery of CeIr$_4$In validates this approach for discovering
new materials.",1103.2259v1
2011-03-12,Varying Eu$^{2+}$ magnetic order in EuFe$_2$As$_2$ by chemical pressure,"Among iron 122 pnictide superconductors, the EuFe$_2$As$_2$ series draws
particular interest because, in addition to superconductivity or the long-range
spin-density-wave order in the Fe subsystem, the localized Eu$^{2+}$ magnetic
moments order at low temperatures. Here we present a novel scheme of how the
spins align in the Eu compounds when pressure varies the coupling; we explain
magnetization measurements on EuFe$_2$(As$_{1-x}$P$_x$)$_2$ single crystals as
well as other observations of the Eu$^{2+}$ ordering previously reported in
literature. The magnetic moments of the Eu$^{2+}$ ions are slightly canted even
in the parent compound EuFe$_2$As$_2$, yielding a ferromagnetic contribution
along the $c$-direction that becomes stronger with pressure. Reducing the
interlayer distance even further, the antiferromagnetic coupling of the $ab$
planes finally turns ferromagnetic.",1103.2446v1
2011-03-15,"Structural, Superconducting and Magnetic Properties of La(3-x)R(x)Ni2B2N3 (R = Ce, Pr, Nd)","We report on structural and superconducting properties of La(3-x)R(x)Ni2B2N3
where La is substituted by the magnetic rare-earth elements Ce, Pr, Nd. The
compounds Pr3Ni2B2N3 and Nd3Ni2B2N3 are characterized for the first time.
Powder X-ray diffraction confirmed all samples R3Ni2B2N3 with R = La, Ce, Pr,
Nd and their solid solutions to crystallize in the body centered tetragonal
La3Ni2B2N3 structure type. Superconducting and magnetic properties of
La(3-x)R(x)Ni2B2N3 were studied by resistivity, specific heat and
susceptibility measurements. While La3Ni2B2N3 has a superconducting transition
temperature Tc ~ 14 K, substitution of La by Ce, Pr, and Nd leads to magnetic
pair breaking and, thus, to a gradual suppression of superconductivity.
Pr3Ni2B2N3 exibits no long range magnetic order down to 2 K, Nd3Ni2B2N3 shows
ferrimagnetic ordering below T_C = 17 K and a spin reorientation transition to
a nearly antiferromagnetic state at 10 K.",1103.2947v1
2011-03-18,Evidence for impurity-induced frustration in La2CuO4,"Zero-field muon spin rotation and magnetization measurements were performed
in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by
M=Mg2+ spinless impurity. It is shown that while the doping dependence of the
sublattice magnetization (M(x)) is nearly the same for both compounds, the
N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the
Zn-doped compound. This difference, not taken into account within a simple
dilution model, is associated with the frustration induced by the Zn2+ impurity
onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin
stiffness is derived and found to be reduced by Zn doping more significantly
than expected within a dilution model. The effect of the structural
modifications induced by doping on the exchange coupling is also discussed.",1103.3563v1
2011-03-21,"Busy period, time of the first loss of a customer and the number of customers in $ M^{\varkappa}|G^δ|1|B$","A two-sided exit problem is solved for a difference of a compound Poisson
process and a compound renewal process. More precisely, the Laplace transforms
of the joint distribution of the first exit time, the value of the overshoot
and the value of a linear component at this instant are found. Further, we
study the process reflected in its supremum. We determine the main two-boundary
characteristics of the process reflected in its supremum. These results are
then applied for studying the $ M^{\varkappa}|G^{\delta}|1|B$ system. We derive
the distribution of a busy period and the numbers of customers in the system in
transient and stationary regimes. The advantage is that these results are in a
closed form, in terms of resolvent sequences of the process.",1103.4064v1
2011-03-23,Pressure effects on the transport coefficients of Ba(Fe1-xCox)2As2,"We report the temperature dependence of the resistivity and thermoelectric
power under hydrostatic pressure of the itinerant antiferromagnet BaFe2As2 and
the electron-doped superconductor Ba(Fe0.9Co0.1)2As2. We observe a hole-like
contribution to the thermopower below the structural-magnetic transition in the
parent compound that is suppressed in magnitude and temperature with pressure.
Pressure increases the contribution of electrons to transport in both the doped
and undoped compound. In the 10% Co-doped sample, we used a two-band model for
thermopower to estimate the carrier concentrations and determine the effect of
pressure on the band structure.",1103.4501v3
2011-04-11,The effects of strong temperature anisotropy on the kinetic structure of collisionless slow shocks and reconnection exhausts. Part II: Theory,"Simulations of collisionless oblique propagating slow shocks have revealed
the existence of a transition associated with a critical temperature anisotropy
epsilon=1-mu_0(P_parallel-P_perpendicular)/ B^2 = 0.25 (Liu, Drake and Swisdak
(2011)). An explanation for this phenomenon is proposed here based on
anisotropic fluid theory, in particular the Anisotropic Derivative
Nonlinear-Schrodinger-Burgers equation, with an intuitive model of the energy
closure for the downstream counter-streaming ions. The anisotropy value of 0.25
is significant because it is closely related to the degeneracy point of the
slow and intermediate modes, and corresponds to the lower bound of the coplanar
to non-coplanar transition that occurs inside a compound slow shock
(SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of
compound SS/RD waves that bound the outflows in magnetic reconnection, instead
of a pair of switch-off slow shocks as in Petschek's model. This fact might
explain the rareness of in-situ observations of
Petschek-reconnection-associated switch-off slow shocks.",1104.2055v1
2011-04-13,Terahertz conductivity of the heavy-fermion compound UNi2Al3,"We have studied the optical properties of the heavy-fermion compound UNi2Al3
at frequencies between 100 GHz and 1 THz (3 cm^-1 and 35 cm^-1), temperatures
between 2 K and 300 K, and magnetic fields up to 7 T. From the measured
transmission and phaseshift of radiation passing through a thin film of
UNi2Al3, we have directly determined the frequency dependence of the real and
imaginary parts of the optical conductivity (or permittivity, respectively). At
low temperatures the anisotropy of the optical conductivity along the a- and
c-axes is about 1.5. The frequency dependence of the real part of the optical
conductivity shows a maximum at low temperatures, around 3 cm^-1 for the a-axis
and around 4.5 cm^-1 for the c-axis. This feature is visible already at 30 K,
much higher than the Neel temperature of 4.6 K, and it does not depend on
external magnetic fields as high as 7 T. We conclude that this feature is
independent of the antiferromagnetic order for UNi2Al3, and this might also be
the case for UPd2Al3 and UPt3, where a similar maximum in the optical
conductivity was observed previously.",1104.2561v1
2011-04-21,^{59}Co-Nuclear Quadrupole Resonance and Nuclear Magnetic Resonance studies on YCoGe --- Comparison between YCoGe and UCoGe ---,"We have performed ^{59}Co-nuclear quadrupole resonance (NQR) and nuclear
magnetic resonance (NMR) studies on YCoGe, which is a reference compound of
ferromagnetic superconductor UCoGe, in order to investigate the magnetic
properties at the Co site. Magnetic and superconducting transitions were not
observed down to 0.3 K, but a conventional metallic behavior was found in
YCoGe, although its crystal structure is similar to that of UCoGe. From the
comparison between experimental results of two compounds, the ferromagnetism
and superconductivity observed in UCoGe originate from the U-5f electrons.",1104.4246v1
2011-04-27,First-principles calculations on temperature- dependent elastic constants of rare-earth intermetallic compounds:YAg and YCu,"we present the temperature-dependent elastic constants of two ductile
rare-earth intermetallic compounds YAg and YCu with CsCl-type B2 structure by
using a first-principles approach. The elastic moduli as a function of
temperature are predicted from the combination of static volumedependent
elastic constants obtained by the first-principles total-energy method with
density functional theory and the thermal expansion obtained by the
first-principles phonon calculations with density-functional perturbation
theory. The comparison between our calculated results and the available
experimental data for Ag and Cu provides good agreements. In the calculated
temperature $0-1000K$, the elastic constants of YAg and YCu follow a normal
behavior with temperature that those decrease with increasing temperature, and
satisfy the stability conditions for B2 structures. The Cauchy pressure for YAg
and YCu as a function of temperature is also discussed, and our results mean
that YAg and YCu become more ductile while increasing temperature.",1104.5143v1
2011-04-29,Upper critical magnetic field in Ba_0.68K_0.32Fe_2As_2 and Ba(Fe_0.93Co_0.07)_2As_2,"We report measurements of the temperature dependence of the radio-frequency
magnetic penetration depth in Ba_0.68K_0.32Fe_2As_2 and
Ba(Fe_0.93Co_0.07)_2As_2 single crystals in pulsed magnetic fields up to 60 T.
From our data, we construct an H-T phase diagram for the inter-plane (H || c)
and in-plane (H || ab) directions for both compounds. For both field
orientations in Ba_0.68K_0.32Fe_2As_2, we find a concave curvature of the
Hc2(T) lines with decreasing anisotropy and saturation towards lower
temperature. Taking into account Pauli spin paramagnetism we can describe
Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair
breaking is not essential for Ba(Fe_0.93Co_0.07)_2As_2. For this electron-doped
compound, the data support a Hc2(T) dependence that can be described by the
Werthamer Helfand Hohenberg model for H || ab and a two-gap behavior for H ||
c.",1104.5619v1
2011-05-04,Polar distortions in hydrogen bonded organic ferroelectrics,"Although ferroelectric compounds containing hydrogen bonds were among the
first to be discovered, organic ferroelectrics are relatively rare. The
discovery of high polarization at room temperature in croconic acid [Nature
\textbf{463}, 789 (2010)] has led to a renewed interest in organic
ferroelectrics. We present an ab-initio study of two ferroelectric organic
molecular crystals, 1-cyclobutene-1,2-dicarboxylic acid (CBDC) and
2-phenylmalondialdehyde (PhMDA). By using a distortion-mode analysis we shed
light on the microscopic mechanisms contributing to the polarization, which we
find to be as large as 14.3 and 7.0\,$\mu$C/cm$^{2}$ for CBDC and PhMDA
respectively. These results suggest that it may be fruitful to search among
known but poorly characterized organic compounds for organic ferroelectrics
with enhanced polar properties suitable for device applications.",1105.0766v1
2011-05-09,"NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations","19F isotropic chemical shifts for alkali, alkaline earth and rare earth of
column 3 basic fluorides are measured and the corresponding isotropic chemical
shieldings are calculated using the GIPAW method. When using PBE exchange
correlation functional for the treatment of the cationic localized empty
orbitals of Ca2+, Sc3+ (3d) and La3+ (4f), a correction is needed to accurately
calculate 19F chemical shieldings. We show that the correlation between
experimental isotropic chemical shifts and calculated isotropic chemical
shieldings established for the studied compounds allows to predict 19F NMR
spectra of crystalline compounds with a relatively good accuracy. In addition,
we experimentally determine the quadrupolar parameters of 25Mg in MgF2 and
calculate the electric field gradient of 25Mg in MgF2 and 139La in LaF3 using
both PAW and LAPW methods. The orientation of the EFG components in the
crystallographic frame, provided by DFT calculations, is analysed in term of
electron densities. It is shown that consideration of the quadrupolar charge
deformation is essential for the analysis of slightly distorted environments or
highly irregular polyhedra.",1105.1645v2
2011-05-11,"Systematics of the temperature-dependent inter-plane resistivity in Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$ with T= Rh, Ni, and Pd","Temperature-dependent inter-plane resistivity, $\rho_c(T)$, was measured
systematically as a function of transition metal substitution in the
iron-arsenide superconductors Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$, $T$= Ni, Pd, Rh.
The data are compared with the behavior found in
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, revealing resistive signatures of pseudogap. In
all compounds we find resistivity crossover at a characteristic pseudogap
temperature $T^*$ from non-metallic to metallic temperature dependence on
cooling. Suppression of $T^*$ proceeds very similar in cases of Ni and Pd
doping and much faster than in similar cases of Co and Rh doping. In cases of
Co and Rh doping an additional minimum in the temperature-dependent $\rho_c$
emerges for high dopings, when superconductivity is completely suppressed.
These features are consistent with the existence of a charge gap covering part
of the Fermi surface. The part of the Fermi surface affected by this gap is
notably larger for Ni and Pd doped compositions than in Co and Rh doped
compounds.",1105.2277v1
2011-05-12,Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: the Cr based dimer system Sr3Cr2O8,"We report on an extended fluctuation regime in the spin dimer system Sr3Cr2O8
based on anomalies in Raman active phonons and magnetic scattering. The
compound has two characteristic temperatures, TS = 275 K, related to a
Jahn-Teller transition with structural distortions and orbital ordering and a
second, T*= 150 K, which is due to further changes in the orbital sector. Below
TS quasielastic scattering marks strong fluctuations and in addition phonon
anomalies are observed. For temperatures below T* we observe an exponential
decrease of one phonon linewidth and determine a gap of the orbital
excitations. At low temperatures the observation of two- and three-magnon
scattering allows the determination of the spin excitation gap.",1105.2369v1
2011-05-18,Interplay of Sm4f and Co3d spins in SmCoAsO,"We present detailed magnetization and magneto-transport studies on the title
compound SmCoAsO. In a recent paper we reported [1] the complex magnetism of
this compound. SmCoAsO undergoes successive paramagnetic (PM) - ferro-magnetic
(FM) - anti-ferro-magnetic (AFM) transitions with decrease in temperature. This
is mainly driven via the c-direction interaction of Sm4f (SmO layer) spins with
adjacent (CoAs layer) ordered Co3d spins. In this article we present an
evidence of kinetic arrest for FM-AFM transition. The isothermal magnetization
(MH) loops for SmCoAsO exhibited the meta-magnetic transitions at 6, 8 and 10K
at around 80, 60 and 50kOe fields respectively with characteristic hysteresis
shoulders along with the non-zero moment at origin, thus suggesting the
possibility of kinetic arrest. Suggested kinetic arrest is further evident in
zero field-cooled (ZFC) and field-cooled (FC) hysteresis under high fields of
up to 140kOe magnetization (MT) and the magneto-transport measurements R(T)H
during FM-AFM transition. The time dependent moment experiments exhibited very
small (~2-3%) increase of the same below 20kO and decrease for 30kOe at 15K.",1105.3546v1
2011-05-19,Antiferromagnetism and Superconductivity in Cerium based Heavy Fermion Compounds,"The study of competing ground states is a central issue in condensed matter
physic. In this article we will discuss the interplay of antiferromagnetic
order and unconventional superconductivity in Ce based heavy-fermion compounds.
In all discussed examples superconductivity appears at the border of magnetic
order. Special focus is given on the pressure-temperature-magnetic field phase
diagram of CeRhIn5 and CeCoIn5 which allows to discuss microscopic coexistence
of magnetic order and superconductivity in detail. A striking point is the
similarity of the phase diagram of different classes of strongly correlated
systems which is discussed briefly. The recently discovered non-centrosymmetric
superconductors will open a new access with the possible mixing of odd and even
parity pairing.",1105.3989v1
2011-05-21,"Structural, electronic, magnetic, and thermal properties of single-crystalline UNi0.5Sb2","We studied the properties of the antiferromagnetic (AFM) UNi0.5Sb2 (TN
\approx 161 K) compound in Sb-flux grown single crystals by means of
measurements of neutron diffraction, magnetic susceptibility ({\chi}), specific
heat (Cp), thermopower (S), thermal conductivity ({\kappa}), linear thermal
expansion ({\Delta}L/L), and electrical resistivity ({\rho}) under hydrostatic
pressures (P) up to 22 kbar. The neutron diffraction measurements revealed that
the compound crystallizes in the tetragonal P42/nmc structure, and the value of
the U-moments yielded by the histograms at 25 K is \approx 1.85 \pm 0.12
{\mu}B/U-ion. In addition to the features in the bulk properties observed at
TN, two other hysteretic features centered near 40 and 85 K were observed in
the measurements of {\chi}, S, {\rho}, and {\Delta}L/L. Hydrostatic pressure
was found to raise TN at the rate of \approx 0.76 K/kbar, while suppressing the
two low temperature features. These features are discussed in the context of
Fermi surface and hybridization effects.",1105.4277v2
2011-05-30,"Strain driven onset of non-trivial topological insulating states in Zintl Sr$_2X$ compounds ($X$=Pb, Sn)","We explore the topological behavior of the binary Zintl phase of the alkaline
earth metals based compounds Sr$_2$Pb and Sr$_2$Sn using both standard and
hybrid density functional theory. It is found that Sr$_2$Pb lies on the verge
of a topological instability which can be suitably tuned through the
application of a small uniaxial expansion strain ($>$ 3%). The resulting
non-trivial topologically insulating state display well-defined metallic states
in the Sr$_{2}$Pb(010) surface, whose evolution is studied as a function of the
film thickness.",1105.5841v1
2011-05-31,Preformed heavy-electrons at the Quantum Critical Point in heavy fermion compounds,"The existence of multiple energy scales is regarded as a signature of the
Kondo breakdown mechanism for explaining the quantum critical behavior of
certain heavy fermion compounds, like YbRh$_{2}$Si$_{2}$. The nature of the
intermediate state between the heavy Fermi liquid and the quantum critical
region, however, remains elusive. In this study we suggest an incoherent
heavy-fermion scenario, where inelastic scattering with novel soft modes of the
dynamical exponent $z = 3$ gives rise to non-Fermi liquid physics for
thermodynamics and transport despite the formation of the heavy-fermion band.
We discuss a crossover from $z = 3$ to $z = 1$ for quantum phase fluctuations.",1105.6161v2
2011-06-03,Single-ion versus two-ion anisotropy in magnetic compounds: A neutron scattering study,"Anisotropy effects can significantly control or modify the ground-state
properties of magnetic systems. Yet the origin and the relative importance of
the possible anisotropy terms is difficult to assess experimentally and often
ambiguous. Here we propose a technique which allows a very direct distinction
between single-ion and two-ion anisotropy effects. The method is based on
high-resolution neutron spectroscopic investigations of magnetic cluster
excitations. This is exemplified for manganese dimers and tetramers in the
mixed compounds CsMnxMg1-xBr3 (0.05\leqx\leq0.40). Our experiments provide
evidence for a pronounced anisotropy of the order of 3% of the dominant
bilinear exchange interaction, and the anisotropy is dominated by the
single-ion term. The detailed characterization of magnetic cluster excitations
offers a convenient way to unravel anisotropy effects in any magnetic material.",1106.0615v1
2011-06-08,"In-plane electronic anisotropy of underdoped ""122"" Fe-arsenide superconductors revealed by measurements of detwinned single crystals","The parent phases of the Fe-arsenide superconductors harbor an
antiferromagnetic ground state. Significantly, the N\'eel transition is either
preceded or accompanied by a structural transition that breaks the four fold
symmetry of the high-temperature lattice. Borrowing language from the field of
soft condensed matter physics, this broken discrete rotational symmetry is
widely referred to as an Ising nematic phase transition. Understanding the
origin of this effect is a key component of a complete theoretical description
of the occurrence of superconductivity in this family of compounds, motivating
both theoretical and experimental investigation of the nematic transition and
the associated in-plane anisotropy. Here we review recent experimental progress
in determining the intrinsic in-plane electronic anisotropy as revealed by
resistivity, reflectivity and ARPES measurements of detwinned single crystals
of underdoped Fe arsenide superconductors in the ""122"" family of compounds.",1106.1675v1
2011-06-09,Magnetic properties in the doped spin-1/2 honeycomb-lattice compound In$_3$Cu$_2$VO$_9$,"We report the magnetic properties in the Co- and Zn-doped spin-1/2
honeycomb-lattice compound In$_3$Cu$_2$VO$_9$. The magnetic susceptibility and
specific heat experiments show no long-range ordering down to 2 K in
In$_3$Cu$_2$VO$_9$. In the low temperature range, approximately
T$^{2}$-dependent magnetic specific heat and linearly T-dependent spin
susceptibility were observed, suggesting a spin liquid candidate with a S = 1/2
honeycomb lattice. When Cu$^{2+}$ ions are partially substituted by Co$^{2+}$
ions, both impurity potential scattering and magnetic impurity scattering
induced by magnetic Co$^{2+}$ ions break the homogenous spin-singlet spin
liquid state, and lead to an antiferromagnetic(AFM) long-range correlation.
While replacing Cu$^{2+}$ with nonmagnetic Zn$^{2+}$ ions, the frustration and
antiferromagnetic correlation between Cu$^{2+}$ ions is weakened, leading to
breakage of a spin liquid state and suppression of the low-dimensional AFM.",1106.1713v1
2011-06-15,Electronic structure of the $\rm Ca_3Co_4O_9$ compound from ab initio local interactions,"We used fully correlated ab initio calculations to determine the effective
parameters of Hubbard and t - J models for the thermoelectric misfit compound
$\rm Ca_3Co_4O_9$. As for the $\rm Na_xCoO_2$ family the Fermi level orbitals
are the $a_{1g}$ orbitals of the cobalt atoms ; the $e'_g$ being always lower
in energy by more than 240\,meV. The electron correlation is found very large
$U/t\sim 26$ as well as the parameters fluctuations as a function of the
structural modulation. The main consequences are a partial $a_{1g}$ electrons
localization and a fluctuation of the in-plane magnetic exchange from AFM to
FM. The behavior of the Seebeck coefficient as a function of temperature is
discussed in view of the ab initio results, as well as the 496\,K phase
transition.",1106.2893v2
2011-06-23,The magnetic structures of the anisotropic inter-metallic compounds Er$_2$CoGa$_8$ and Tm$_2$CoGa$_8$,"Two members of the iso-structural R$_2$CoGa$_8$ inter-metallic series,
Er$_2$CoGa$_8$ and Tm$_2$CoGa$_8$, have been studied by powder neutron
diffraction. Antiferromagnetic ordering of the rare-earth sublattices was
confirmed to occur at 3.0 K and 2.0 K, respectively. Furthermore, determination
of the critical exponent showed Er$_2$CoGa$_8$ to adopt a 3D universality
class. In spite of a common magnetic easy axis and similar structural
characteristics, the antiferromagnetic structures were found to be different
for the erbium and thulium based compounds. The corresponding magnetic space
groups were determined to be $P_{2a}mmm'$ and $P_Cmmm$. The difference in
magnetic structures is discussed based on crystal electric field effects that
are known to be prevalent in such materials.",1106.4742v1
2011-06-28,Mott-insulator to metal transition in filling-controlled SmMnAsO_{1-x},"Transport and magnetic properties have been systematically investigated for
SmMnAsO_{1-x} with controlled electron-doping. As the electron band-filling is
increased with the increase of oxygen deficiency (x), the resistivity
monotonically decreases and the transition from Mott-insulator to metal occurs
between x=0.17 and 0.2. Seebeck coefficient at room temperature abruptly
changes around the critical doping level from a large value (\sim -300 \mu V/K)
to a small one (\sim -50 \mu V/K) both with negative sign. In the metallic
compounds with x=0.2 and x=0.3, Mn spins order antiferromagnetically around 30
K, and the Hall coefficient with the negative sign shows a reduction in
magnitude upon the magnetic transition, indicating the change in the multiple
Fermi surfaces. Gigantic positive magnetoresistance effect is observed in a
wide range of temperature, reaching up to 60 % at 2 K for the x=0.3 compound.
The effect is attributed to the field-induced change of the complex Fermi
surfaces in this multi-orbital correlated electron system.",1106.5630v1
2011-07-01,High-pressure Raman spectroscopy and lattice-dynamics calculations on scintillating MgWO4: A comparison with isomorphic compounds,"Raman scattering measurements and lattice-dynamics calculations have been
performed on magnesium tungstate under high pressure up to 41 GPa. Experiments
have been carried out under a selection of different pressure-media. The
influence of non-hydrostaticity on the structural properties of MgWO4 and
isomorphic compounds is examined. Under quasi-hydrostatic conditions a phase
transition has been found at 26 GPa in MgWO4. The high-pressure phase has been
tentatively assigned to a triclinic structure similar to that of CuWO4. We also
report and discuss the Raman symmetries, frequencies, and pressure coefficients
in the low- and high-pressure phases. In addition, the Raman frequencies for
different wolframites are compared and the variation of the mode frequency with
the reduced mass across the family is investigated. Finally, the accuracy of
theoretical calculations is systematically discussed for MgWO4, MnWO4, FeWO4,
CoWO4, NiWO4, ZnWO4, and CdWO4.",1107.0160v1
2011-07-01,"Magnetic model for A2CuP2O7 (A = Na, Li) revisited: 1D versus 2D behavior","We report magnetization measurements, full-potential band structure
calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets
A2CuP2O7 (A = Na, Li). Based on a quantitative evaluation of the leading
exchange integrals and the subsequent quantum Monte-Carlo simulations, we
propose a quasi-one-dimensional magnetic model for both compounds, in contrast
to earlier studies that conjectured on the two-dimensional scenario. The
one-dimensional nature of A2CuP2O7 is unambiguously verified by magnetization
isotherms measured in fields up to 50 T. The saturation fields of about 40 T
for both Li and Na compounds are in excellent agreement with the intrachain
exchange J1 ~ 27 K extracted from the magnetic susceptibility data. The
proposed magnetic structure entails spin chains with the dominating
antiferromagnetic nearest-neighbor interaction J1 and two inequivalent,
nonfrustrated antiferromagnetic interchain couplings of about 0.01*J1 each. A
possible long-range magnetic ordering is discussed in comparison with the
available experimental information.",1107.0250v3
2011-07-01,Slow magnetic dynamics and hysteresis loops of a bulk ferromagnet,"Magnetic dynamics of a bulk ferromagnet, a new single crystalline compound
Co7(TeO3)4Br6, was studied by ac susceptibility and the related techniques.
Very large Arrhenius activation energy of 17.2 meV (201 K) and long attempt
time (2x10^(-4)s) span the full spectrum of magnetic dynamics inside a
convenient frequency window, offering a rare opportunity for general studies of
magnetic dynamics. Within the experimental window the ac susceptibility data
build almost ideally semicircular Cole-Cole plots. Comprehensive study of
experimental dynamic hysteresis loops of the compound is presented and
interpreted within a simple thermal-activation-assisted spin lattice relaxation
model for spin reversal. Quantitative agreement between the experimental
results and the model's prediction for dynamic coercive field is achieved by
assuming the central physical quantity, the Debye relaxation rate, to depend on
frequency, as well as on the applied field strength and sample temperature.
Cross-over between minor- to major hysteresis loops is carefully analyzed.
Low-frequency limitations of the model, relying on domain wall pinning effects,
are experimentally detected and appropriately discussed.",1107.0255v2
2011-07-05,Quantum Excitations in Quantum Spin Ice,"Recent work has highlighted remarkable effects of classical thermal
fluctuations in the dipolar spin ice compounds, such as ""artificial
magnetostatics"", manifesting as Coulombic power-law spin correlations and
particles behaving as diffusive ""magnetic monopoles"". In this paper, we address
quantum spin ice, giving a unifying framework for the study of magnetism of a
large class of magnetic compounds with the pyrochlore structure, and in
particular discuss Yb2Ti2O7 and extract its full set of Hamiltonian parameters
from high field inelastic neutron scattering experiments. We show that
fluctuations in Yb2Ti2O7 are strong, and that the Hamiltonian may support a
Coulombic ""Quantum Spin Liquid"" ground state in low field and host an unusual
quantum critical point at larger fields. This appears consistent with puzzling
features in prior experiments on Yb2Ti2O7. Thus Yb2Ti2O7 is the first quantum
spin liquid candidate in which the Hamiltonian is quantitatively known.",1107.0761v1
2011-07-06,Na-Au intermetallic compounds formed under high pressure at room temperature,"High-pressure powder x-ray diffraction experiments have revealed that sodium
and gold react at room temperature and form new Na-Au intermetallic compounds
under high pressure. We have identified four intermetallic phases up to 60 GPa.
The first phase (phase I) is the known Na2Au with the tetragonal CuAl2-type
structure. It changed to the second phase (phase II) at about 0.8 GPa, which
has the composition Na3Au with the trigonal Cu3As-type or hexagonal Cu3P-type
structure. Phase II further transformed to phase III at 3.6 GPa. Phase III has
the same composition Na3Au with the cubic BiF3-type structure. Finally, phase
III changed to phase IV at around 54 GPa. Phase IV gives broad diffraction
peaks, indicating large structural disorder.",1107.1193v1
2011-07-10,Theoretical Investigation of Two-Dimensional Superconductivity in Intercalated Graphene Layers,"First-principles calculations of the electronic structure and vibrational
modes, in a system of graphene bilayers and trilayers intercalated with
alkaline earth atoms, are resented. It is found that, in similarity to the case
of superconducting graphite intercalation compounds, the Fermi level is crossed
by an s-band derived from the intercalant states, as well as graphitic
pi-bands. The electron-phonon coupling parameter is found to be 0.60 and 0.80,
respectively, in calcium intercalated graphene bilayers and trilayers. In
superconducting CaC6 graphite intercalation compound, the calculated value for
the electron-phonon coupling parameter is 0.83. It is concluded that
two-dimensional superconductivity is possible in a system of a few graphene
layers intercalated with calcium.",1107.1845v1
2011-07-13,First-principles calculation of topological invariants Z2 within the FP-LAPW formalism,"In this paper, we report the implementation of first-principles calculations
of topological invariants Z2 within the full-potential linearized augmented
plane-wave (FP-LAPW) formalism. In systems with both time-reversal and spatial
inversion symmetry (centrosymmetric), one can use the parity analysis of Bloch
functions at time-reversal invariant momenta to determine the Z2 invariants. In
systems without spatial inversion symmetry (noncentrosymmetric), however, a
more complex and systematic method in terms of the Berry gauge potential and
the Berry curvature is required to identify the band topology. We show in
detail how both methods are implemented in FP-LAPW formalism and applied to
several classes of materials including centrosymmetric compounds Bi2Se3 and
Sb2Se3 and noncentrosymmetric compounds LuPtBi, AuTlS2 and CdSnAs2. Our work
provides an accurate and effective implementation of first-principles
calculations to speed up the search of new topological insulators.",1107.2679v1
2011-07-31,Atypical thermodynamic behavior of Ce compounds in the vicinity of zero temperature Critical Points,"A systematic analysis of thermodynamic properties performed on Ce-base
exemplary compounds allows to identify different types of behaviors as the
system approaches the quantum critical region. They are recognized in the
respective magnetic phase boundaries (T_{N,C}(x)) as a change from the
classical negative curvature to a linear composition ($x$) dependence, the
occurrence of a critical point or the evanescence at finite temperature under
pressure at finite temperature. In the first case, an anomalous reduction of
the entropy S_m respect to the S_m = RLn2 value (expected for the usual
Ce-magnetic doublet ground state) is observed around x_{cr}, and analyzed
taking profit of detailed studies performed on CeIn_{3-x}Sn_x alloys. As
expected from Maxwell relations, the volume variation V_0(x) at T=>0 also shows
a non-monotonous behavior around x_{cr}.
  Different regimes in the entropy variation of the ordered phase (S_{MO}) are
recognized. Only in the former case S_{MO}=> 0 continuously as T_{N,C}=>0,
whereas in the second S_{MO}(x,B) remains constant till a first order
transition occurs. In the third case, the degrees of freedom of the MO phase
are progressively transferred to the heavy fermion component as indicated by
the decreasing C_m(T_N) jump which vanishes at finite temperature.",1108.0197v1
2011-08-03,Role of exchange interaction in self-consistent calculations of endohedral fullerenes,"Results of the self-consistent calculation of electronic structure of
endohedral fullerene Ar@C$_{60}$ within the Hartree-Fock and the local density
approximations are presented. Hartree-Fock approximation is used for the
self-consistent description for the first time. It is shown that the accurate
account of the exchange interaction between all electrons of the compound leads
to the significant modification of the atomic valent shell which causes the
noticeable charge redistribution inside the endohedral compound.",1108.0918v1
2011-08-04,Origin of the high Neel temperature in SrTcO3,"We investigate the origin of the high Neel temperature recently found in Tc
perovskites. The electronic structure in the magnetic state of SrTcO3 and its
3d analogue SrMnO3 is calculated within a framework combining band-structure
and many-body methods. In agreement with experiment, the Neel temperature of
SrTcO3 is found to be four times larger than that of SrMnO3. We show that this
is because the Tc-compound lies on the verge of the itinerant-to-localized
transition, and also has a larger bandwidth, while the Mn-compound lies deeper
into the localized side. For SrTcO3 we predict that the Neel temperature
depends weakly on applied pressure, in clear violation of Bloch's rule,
signaling the complete breakdown of the localized picture.",1108.1168v3
2011-08-29,Optical conductivity of superconducting Rb2Fe4Se5,"We report the complex dielectric function of high-quality
nearly-stoichiometric Rb2Fe4Se5 (RFS) single crystals with Tc=32 K determined
by wide-band spectroscopic ellipsometry and time-domain transmission
spectroscopy in the spectral range 1 meV<=$\hbar$\omega<=6.5 eV at temperatures
4 K<=T<=300 K. This compound simultaneously displays a superconducting and a
semiconducting optical response. It reveals a direct band-gap of 0.45 eV
determined by a set of spin-controlled interband transitions. Below 100 K we
observe in the lowest THz spectral range a clear metallic response
characterized by the negative dielectric permittivity \epsilon 1 and bare
(unscreened) \omega pl=100 meV. At the superconducting transition this metallic
response exhibits a signature of a superconducting gap below 8 meV. Our
findings suggest a coexistence of superconductivity and magnetism in this
compound as two separate phases.",1108.5698v1
2011-08-30,"Linear magnetoresistivity in the ternary AM2B2 and A3Rh8B6 phases (A = Ca, Sr; M = Rh, Ir)","We studied the magnetoresistivity of the AM2B2 and A3Rh8B6 (A = Ca, Sr; M =
Rh, Ir) compounds within the ranges 1.8<=T<=300 K and 0<=H<=50 kOe. The
zero-field resistivity {\rho}0(T) is metallic and follows closely the
Bloch-Gr\""uneisen description. A positive, nonsaturating, and dominantly
linear-in-H magnetoresistivity was observed in all samples, including the ones
with a superconducting ground state. Such {\Delta}{\rho}T(H)/{\rho}T(0),
reaching 1200% in favorable cases, was found to be much stronger for the AM2B2
compounds and to decrease with temperature as well as when Ca is replaced by
Sr, or Rh is replaced by Ir. Finally, the general features of the observed
magnetoresistivity will be discussed in terms of the Abrikosov model for the
linear magnetoresistivity in inhomogeneous materials.",1108.5803v1
2011-09-03,Low-temperature heat transport of the layered spin-dimer compound Ba_3Mn_2O_8,"We report the study on the low-temperature heat transport of Ba_3Mn_2O_8
single crystal, a layered spin-dimer compound exhibiting the
magnetic-field-induced magnetic order or the magnon Bose-Einstein condensation.
The thermal conductivities (\kappa) along both the ab plane and the c axis show
nearly isotropic dependence on magnetic field, that is, \kappa is strongly
suppressed with increasing field, particularly at the critical fields of
magnetic phase transitions. These results indicate that the magnetic
excitations play a role of scattering phonons and the scattering effect is
enhanced when the magnetic field closes the gap in the spin spectrum. In
addition, the magnons in the BEC state of this materials do not show notable
ability of carrying heat.",1109.0587v1
2011-09-09,Direct observation of local Mn-Mn distances in the paramagnetic compound CsMnxMg1-xBr3,"We introduce a novel method for local structure determination with a spatial
resolution of the order of 0.01 Angstroem. It can be applied to materials
containing clusters of exchange-coupled magnetic atoms. We use neutron
spectroscopy to probe the energies of the cluster excitations which are
determined by the interatomic coupling strength J. Since for most materials J
is related to the interatomic distance R through a linear relation
dJ/dR={\alpha} (for dR/R<<1), we can directly derive the local distance R from
the observed excitation energies. This is exemplified for the mixed
one-dimensional paramagnetic compound CsMnxMg1 xBr3 (x=0.05, 0.10) containing
manganese dimers oriented along the hexagonal c-axis. Surprisingly, the
resulting Mn-Mn distances R do not vary continuously with increasing internal
pressure, but lock in at some discrete values.",1109.1965v1
2011-09-09,Physical and magnetic properties of Ba(Fe_(1-x)Mn_x)_2As_2 single crystals,"Single crystals of Ba(Fe_(1-x)Mn_x)_2As_2, 0<x<0.148, have been grown and
characterized by structural, magnetic, electrical transport and thermopower
measurements. Although growths of single crystals of Ba(Fe_(1-x)Mn_x)_2As_2 for
the full 0<=x<=1 range were made, we find evidence for phase separation
(associated with some form of immiscibility) starting for x>0.1-0.2. Our
measurements show that whereas the structural/magnetic phase transition found
in pure BaFe_2As_2 at 134 K is initially suppressed by Mn substitution,
superconductivity is not observed at any substitution level. Although the
effect of hydrostatic pressure up to 20 kbar in the parent BaFe_2As_2 compound
is to suppress the structural/magnetic transition at the approximate rate of
0.9 K/kbar, the effects of pressure and Mn substitution in the x=0.102 compound
are not cumulative. Phase diagrams of transition temperature versus
substitution concentration, x, based on electrical transport, magnetization and
thermopower measurements have been constructed and compared to those of the
Ba(Fe_(1-x)TM_x)_2As_2 (TM=Co and Cr) series.",1109.2159v1
2011-09-30,Study of Supersolidity and Shear Modulus Anomaly of 4He in a Triple Compound Oscillator,"The recently discovered shear modulus anomaly in solid 4He bears a strong
similarity to the phenomenon of supersolidity in solid 4He and can lead to the
period shift and dissipative signals in torsional oscillator experiments that
are nearly identical to the classic NCRI signals observed by Kim and Chan. In
the experiments described here, we attempt to isolate the effects of these two
phenomena on the resonance periods of torsion oscillators. We have constructed
a triple compound oscillator with distinct normal modes. We are able to
demonstrate that, for this oscillator, the period shifts observed below 200 mK
have their primary origin in the temperature dependence of the shear modulus of
the solid 4He sample rather than the formation of a supersolid state.",1109.6818v1
2011-09-30,Possible high-temperature superconductors predicted from electronic structure and data-filtering algorithms,"We report here the completion of the electronic structure of the majority of
the known stoichiometric inorganic compounds, as listed in the International
Crystal Structure Data-base (ICSD). We make a detailed comparison of the
electronic structure, crystal geometry and chemical bonding of cuprate high
temperature superconductors, with the calculated over sixty thousand electronic
structures. Based on compelling similarities of the electronic structures in
the normal state and a data-filtering technique, we propose that high
temperature superconductivity is possible for electron- or hole-doping in a
much larger group of materials than previously considered. The indentified
materials are composed of over one hundred layered compounds, most which
hitherto are untested with respect to their super conducting properties. Of
particular interest are the following materials; Ca$_2$(CuBr$_2$O$_2$),
K$_2$CoF$_4$, Sr$_2$(MoO$_4$) and Sr$_4$V$_3$O$_{10}$, which are discussed in
detail.",1109.6935v1
2011-10-04,Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7,"We investigate the spin-induced polarization in the multiferroic compound
Ba2CuGe2O7 using variarional and finite temperature mean field approaches. The
compound is described by a spin-3/2 Heisenberg model extended with easy plane
anisotropy and Dzyaloshinskii-Moriya (DM) interaction. Applying magnetic field
parallel to the [110] axis, three phases can be distinguished: (i) At high
magnetic field we find a partially magnetized phase with spins parallel to the
fields and uniform polarization; (ii) Below a critical field the ground state
is a twofold degenerate canted antiferromagnet, where the degeneracy can be
lifted by a finite DM interaction; (iii) At zero field a U(1) symmetry breaking
phase takes place, exhibiting a Goldstone-mode. To reproduce the magnetization
and polarization measurements reported in Murakawa et al. [Phys. Rev. Lett.
105, 137202 (2010)], we introduce an additional term in the Hamiltonian that
couples the polarizations on neighboring tetrahedra. This results in the
appearance of a canted ferrimagnetic phase for h < 1 T, characterized by a
finite staggered polarization, as well as by a finite magnetization along the
[-1,1,0] axis that leads to torque anomalies.",1110.0788v1
2011-10-10,"Synthesis, crystal structure, and properties of novel perovskite oxychalcogenides, Ca2CuFeO3Ch (Ch = S, Se)","Two new perovskite oxychalcogenides, Ca2CuFeO3S and Ca2CuFeO3Se, have been
synthesized in evacuated quartz tubes. They crystallize in P4/nmm space group
with lattice parameters a = 3.8271(1), c = 14.9485(2) {\AA} and a = 3.8605(1),
c = 15.3030(2) {\AA} for Ca2CuFeO3S and Ca2CuFeO3Se, respectively. They appear
to be the first layered chalcogenide perovskites involving calcium and are
structural analogs of the corresponding Sr and Ba compounds. The new compounds
exhibit semiconducting properties with energy gap decreasing from the
oxysulfide to the oxyselenide. Possibility of introducing Ca2+ into structures
of known layered oxychalcogenides and oxypnictides is discussed.",1110.2035v1
2011-10-10,Magnetic order and frustrated dynamics in Li(Ni0.8Co0.1Mn0.1)O2: a study by μ+SR and SQUID magnetometry,"Recently, the mixed transition metal oxides of the form Li(Ni1-y-zCoyMnz)O2,
have become the center of attention as promising candidates for novel battery
material. These materials have also revealed very interesting magnetic
properties due to the alternate stacking of planes of metal oxides on a 2D
triangular lattice and the Li-layers. The title compound,
Li(Ni0.8Co0.1Mn0.1)O2, has been investigated by both magnetometry and
measurements and {\mu}+SR. We find the evolution of localized magnetic moments
with decreasing temperature below 70 K. The magnetic ground state (T = 2 K) is,
however, shown to be a frustrated system in 3D, followed by a transition into a
possible 2D spinglass above 22 K. With further increasing temperature the
compound show the presence of remaining correlations with increasing effective
dimensionality all the way up to the ferrimagnetic transition at TC = 70 K.",1110.2071v1
2011-10-25,Majorana fermions in superconducting helical magnets,"In a variety of rare-earth based compounds singlet superconductivity coexists
with helical magnetism. Here we demonstrate that surfaces of these systems
should generically host a finite density of zero-energy Majorana modes. In the
limit of vanishing disorder, these modes lead to a divergent contribution to
zero-energy density of states and to zero-temperature entropy proportional to
the sample surface area. When confined to a wire geometry, a discrete number of
Majorana modes can be isolated. The relatively large characteristic energy
scales for superconductivity and magnetism, compared to other proposals, as
well as the lack of need for fine-tuning, make helical magnetic superconducting
compounds favorable for the observation and experimental investigation of
Majorana fermions.",1110.5637v2
2011-10-31,Temperature-dependent multi-k magnetic structure in multiferroic Co3TeO6,"A complex magnetic order of the multiferroic compound Co3TeO6 has been
revealed by neutron powder diffraction studies on ceramics and crushed single
crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied
temperature range 2 K - 300 K but exhibits successive antiferromagnetic
transitions at low temperature. Incommensurate antiferromagnetic order with the
propagation vector k1 = (0, 0.485, 0.055) sets in at 26 K. A transition to a
second antiferromagnetic structure with k2 = (0, 0, 0) takes place at 21.1 K.
Moreover, a transition to a commensurate antiferromagnetic structure with k3 =
(0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined
by neutron powder diffraction using group theory analysis as a preliminary
tool. Different coordinations of the Co2+ ions involved in the low-symmetry
C2/c structure of Co3TeO6 render the exchange-interaction network very complex
by itself. The observed magnetic phase transformations are interpreted as an
evidence of competing magnetic interactions. The temperature dependent changes
in the magnetic structure, derived from refinements of high-resolution neutron
data, are discussed and possible mechanisms connected with the spin
reorientations are described.",1110.6776v1
2011-11-03,Effect of tensile stress on the in-plane resistivity anisotropy in BaFe2As2,"The effect of uniaxial tensile stress and the resultant strain on the
structural/magnetic transition in the parent compound of the iron arsenide
superconductor, BaFe$_2$As$_2$, is characterized by temperature-dependent
electrical resistivity, x-ray diffraction and quantitative polarized light
imaging. We show that strain induces a measurable uniaxial structural
distortion above the first-order magnetic transition and significantly smears
the structural transition. This response is different from that found in
another parent compound, SrFe$_2$As$_2$, where the coupled structural and
magnetic transitions are strongly first order. This difference in the
structural responses explains the in-plain resistivity anisotropy above the
transition in BaFe$_2$As$_2$. This conclusion is supported by the
Ginzburg-Landau - type phenomenological model for the effect of the uniaxial
strain on the resistivity anisotropy.",1111.0997v1
2011-11-08,Molecular processes from the AGB to the PN stage,"Many complex organic molecules and inorganic solid-state compounds have been
observed in the circumstellar shell of stars (both C-rich and O-rich) in the
transition phase between Asymptotic Giant Branch (AGB) stars and Planetary
Nebulae (PNe). This short (~100-10.000 years) phase of stellar evolution
represents a wonderful laboratory for astrochemistry and provides severe
constraints on any model of gas-phase and solid-state chemistry. One of the
major challenges of present day astrophysics and astrochemistry is to
understand the formation pathways of these complex organic molecules and
inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons,
fullerenes, and graphene in the case of a C-rich chemistry and oxides and
crystalline silicates in O-rich environments) in space. In this review, I
present an observational review of the molecular processes in the late stages
of stellar evolution with a special emphasis on the first detections of
fullerenes and graphene in PNe.",1111.1890v1
2011-11-08,A Bayesian approach to magnetic moment determination using muSR,"A significant challenge in zero-field muSR experiments arises from the
uncertainty in the muon site. It is possible to calculate the dipole field (and
hence precession frequency nu) at any particular site given the magnetic moment
mu and magnetic structure. One can also evaluate f(nu), the probability
distribution function of nu assuming that the muon site can be anywhere within
the unit cell with equal probability, excluding physically forbidden sites.
Since nu is obtained from experiment, what we would like to know is g(mu|nu),
the probability density function of mu given the observed nu. This can be
obtained from our calculated f(nu/mu) using Bayes' theorem. We describe an
approach to this problem which we have used to extract information about real
systems including a low-moment osmate compound, a family of molecular magnets,
and an iron-arsenide compound.",1111.1980v1
2011-11-16,Magnetic hyperfine field at \textit{s-p} impurities on Laves phase compounds,"Recent experimental results for the magnetic hyperfine field B_{\rm hf} at
the nuclei of \textit{s-p} impurities such as ${}^{119}$Sn in intermetallic
Laves phases RM_2 (R = Gd, Tb, Dy, Ho, Er; M = Fe, Co) and ${}^{111}$Cd in
RCo_{2}, the impurity occupying a $R$ site indicate that the ratio B_{\rm
hf}/\mu_{3d} exhibits different behavior when one goes from RFe_2 to RCo_2. In
this work, we calculate these local moments and the magnetic hyperfine fields.
In our model, B_{\rm hf} has two contributions: one arising from the $R$ ions,
and the other arising from magnetic 3d-elements; these separate contributions
allow the identification of the origin of different behavior of the ratio
mentioned above. For {}^{111}Cd in RCo_2 we present also the contributions for
B_{\rm hf} in the light rare earth Pr, Nd, Pm, Sm compounds. For the sake of
comparison we apply also the model to {}^{111}Cd diluted in RNi_2. Our
self-consistent magnetic hyperfine field results are in good agreement with
those recent experimental data.",1111.3790v1
2011-11-28,"Magnetic behavior of bulk and fine particles of RCr2Si2C (R = La, Ce)compounds: possible magnetic ordering from Cr","The magnetic behavior of the quaternary compounds, RCr2Si2C (R = La, Ce), has
been investigated by magnetization (M) and heat-capacity (C) measurements
(1.8-300 K) in the bulk polycrystals and nano forms (<1 {\mu}m) obtained by
high-energy balling. Our finding is that Cr appears to exhibit magnetic
ordering of an itinerant type at low temperatures (<20 K) in the bulk form, as
inferred from a combined look at all the data. The magnetic ordering gets
gradually suppressed with increasing milling time. Evidence for a mixed-valence
state of Ce for the bulk form is obtained from the tendency of magnetic
susceptibility to exhibit a maximum above 300 K. However, this feature vanishes
in the nano form, which exhibits a Curie-Weiss behavior above 200 K as though
Ce tends towards trivalency in these fine particles; in addition, there is a
weak upturn in C/T below 10 K in the bulk, which becomes very prominent in the
milled Ce-based specimens at lower temperatures, as though heavy-fermion
behavior gets stronger in smaller particles.",1111.6367v1
2011-11-28,"Isothermal magnetic entropy behavior in Tb5Si3: Sign reversal and non-monotonic variation with temperature, and implications","The magnetic entropy change (\DeltaS), a measure of the magnetocaloric
effect, in Tb5Si3, a compound exhibiting unusual positive magnetoresistance
following a magnetic-field-induced transition below magnetic transition
temperature (~ 69 K), has been investigated. We found that \DeltaS is negative
in the paramagnetic state. At the magnetic transition temperature, \DeltaS
shows sign reversal from negative (in the paramagnetic state) to positive value
in the magnetically ordered state. The high-field state which is interestingly
the high resistive state is found to be associated with higher entropy i.e.
large positive \DeltaS, behaving like a paramagnet. On the basis of this
observation, we conclude that the magnetic field induces magnetic fluctuations
in the system resulting in positive magnetoresistance, thereby rendering
support to the idea of 'inverse metamagnetism' in this compound. In addition,
we note that Arrott plots present an interesting scenario.",1111.6369v1
2011-12-16,Global Trie for Subterms,"A critical component in the implementation of an efficient tabling system is
the design of the table space. The most popular and successful data structure
for representing tables is based on a two-level trie data structure, where one
trie level stores the tabled subgoal calls and the other stores the computed
answers. The Global Trie (GT) is an alternative table space organization
designed with the intent to reduce the tables's memory usage, namely by storing
terms in a global trie, thus preventing repeated representations of the same
term in different trie data structures. In this paper, we propose an extension
to the GT organization, named Global Trie for Subterms (GT-ST), where compound
subterms in term arguments are represented as unique entries in the GT.
Experiments results using the YapTab tabling system show that GT-ST support has
potential to achieve significant reductions on memory usage, for programs with
increasing compound subterms in term arguments, without compromising the
execution time for other programs.",1112.3780v1
2011-12-18,Structure and magnetism of S = 1/2 kagome antiferromagnets NiCu3(OH)6Cl2 and CoCu3(OH)6Cl2,"We have successfully synthesized S = 1/2 kagome antiferromagnets MCu3(OH)6Cl2
(M = Ni and Co) by hydrothermal method with rotating pressure vessel.
Structural characterization shows that both compounds have the similar crystal
structure as ZnCu3(OH)6Cl2 with R-3m symmetry. Similar to ZnCu3(OH)6Cl2, the
compounds show no obvious hysteresis at 2 K. A spin glass transition is found
in both NiCu3(OH)6Cl2 and CoCu3(OH)6Cl2 at low temperatures (6.0 and 3.5 K
respectively) by AC susceptibility measurements. It indicates no long-range
magnetic order and a strong spin frustration. The substitution of Zn2+ by
magnetic ions Ni2+ or Co2+, effectively enhances interlayer exchange coupling
and changes the ground state of the kagome spin system.",1112.4117v3
2011-12-22,Superconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga),"A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin
and coworkers 40 years ago, is revisited to investigate the low-energy, local
vibrations of the A atoms and their influence on the electronic and
superconducting properties of the compound. Polycrystalline samples with A =
Al, Ga, Y, and La are studied through resistivity and heat capacity
measurements. Weak-coupling BCS superconductivity is observed below Tc = 1.49,
1.66, and 0.69 K for Ax = Al0.3, Ga0.2, and Y, respectively, but not above 0.4
K for Ax = La. Low-energy modes are detected only for A = Al and Ga, which are
approximately described by the Einstein model with Einstein temperatures of 24
and 8 K, respectively. A weak but significant coupling between the low-energy
modes, which are almost identical to those called rattling in recent study, and
conduction electrons manifests itself as anomalous enhancement in resistivity
at around low temperatures corresponding to the Einstein temperatures.",1112.5229v1
2012-01-08,Non-Centrosymmetric Heavy-Fermion Superconductors,"In this chapter we discuss the physical properties of a particular family of
non-centrosymmetric superconductors belonging to the class heavy-fermion
compounds. This group includes the ferromagnet UIr and the antiferromagnets
CeRhSi3, CeIrSi3, CeCoGe3, CeIrGe3 and CePt3Si, of which all but CePt3Si become
superconducting only under pressure. Each of these superconductors has
intriguing and interesting properties. We first analyze CePt3Si, then review
CeRhSi3, CeIrSi3, CeCoGe3 and CeIrGe3, which are very similar to each other in
their magnetic and electrical properties, and finally discuss UIr. For each
material we discuss the crystal structure, magnetic order, occurrence of
superconductivity, phase diagram, characteristic parameters, superconducting
properties and pairing states. We present an overview of the similarities and
differences between all these six compounds at the end.",1201.1648v1
2012-01-13,Towards predictive modelling of near-edge structures in electron energy loss spectra of AlN based ternary alloys,"Although electron energy loss near edge structure analysis provides a tool
for experimentally probing unoccupied density of states, a detailed comparison
with simulations is necessary in order to understand the origin of individual
peaks. This paper presents a density functional theory based technique for
predicting the N K-edge for ternary (quasi-binary) nitrogen alloys by adopting
a core hole approach, a methodology that has been successful for binary nitride
compounds. It is demonstrated that using the spectra of binary compounds for
optimising the core hole charge ($0.35\,\mathrm{e}$ for cubic Ti$_{1-x}$Al$_x$N
and $0.45\,\mathrm{e}$ for wurtzite Al$_x$Ga$_{1-x}$N), the predicted spectra
evolutions of the ternary alloys agree well with the experiments. The spectral
features are subsequently discussed in terms of the electronic structure and
bonding of the alloys.",1201.2842v1
2012-01-25,Experimental and theoretical study of structural properties and phase transitions in YAsO4 and YCrO4,"We have performed experimental and theoretical studies of the structural
stability of YAsO4 and YCrO4 at high pressures. X-ray diffraction experiments
together with ab initio total-energy and lattice-dynamics calculations have
allowed us to completely characterize a pressure-induced structural phase
transition from the zircon to the scheelite structure in both compounds.
Furthermore, total-energy calculations have been performed to check the
relative stabilities of different candidate structures at different pressures
and allow us to propose for YAsO4 the zircon \rightarrow scheelite \rightarrow
SrUO4-type sequence of structures. In this sequence, sixfold arsenic
coordination is attained for the SrUO4-type structure above 32 GPa. The whole
sequence of transitions is discussed in comparison with YVO4, YPO4, YNbO4,
YMoO4, and YTaO4. Also a comparative discussion of lattice-dynamics properties
is presented. The band-gap for YAsO4 and YCrO4 and band structure for YAsO4 are
also reported. Finally, the room-temperature equation of state of different
compounds is also obtained.",1201.5249v1
2012-01-28,Spin-spectral-weight distribution and energy range of the parent compound La$_2$CuO$_4$,"The spectral-weight distribution in recent neutron scattering experiments on
the parent compound La$_2$CuO$_4$ (LCO), which are limited in energy range to
about 450\,meV, is studied in the framework of the Hubbard model on the square
lattice. We find that the higher-energy weight extends to about 566\,meV and is
located at and near the momentum $[\pi,\pi]$. Our results confirm that the
$U/t$ value suitable to LCO is in the range $U/t\in (6,8)$. The continuum
weight energy-integrated intensity vanishes or is extremely small at momentum
$[\pi,0]$. This behavior of the intensity is consistent with that of spin
waves, which are damped at $[\pi,0]$.",1201.5940v1
2012-02-01,Theory of High-Tc Superconductivity: Transition Temperature,"It is demonstrated that the transition temperature (Tc) of high-Tc
superconductors is determined by their layered crystal structure, bond lengths,
valency properties of the ions, and Coulomb coupling between electronic bands
in adjacent, spatially separated layers. Analysis of 31 high-Tc materials
(cuprates, ruthenates, rutheno-cuprates, iron pnictides, organics) yields the
universal relationship for optimal compounds, kBTc0 = {\beta}/\ell{\zeta},
where \ell is related to the mean spacing between interacting charges in the
layers, {\zeta} is the distance between interacting electronic layers, {\beta}
is a universal constant and Tc0 is the optimal transition temperature
(determined to within an uncertainty of +/- 1.4 K by this relationship).
Non-optimum compounds, in which sample degradation is evident, e.g. by
broadened superconducting transitions and diminished Meissner fractions,
typically exhibit reduced Tc < Tc0. It is shown that Tc0 may be obtained from
an average of Coulomb interaction forces between the two layers.",1202.0306v1
2012-02-09,Interlayer magnetic frustration driven quantum spin disorder in honeycomb compound In$_{3}$Cu$_{2}$VO$_{9}$,"We present electronic and magnetic properties of a honeycomb compound
In$_{3}$Cu$_{2}$VO$_{9}$ in this paper. We find that the parent phase is a
charge transfer insulator with an energy gap of about 1.5 eV. Singly occupied
d$_{3z^{2}-r^{2}}$ electrons of copper ions contribute an $S$ = 1/2 spin, while
vanadium ions show nonmagnetism. Oxygen 2$p$ orbitals hybridizing with a small
fraction of Cu 3$d$ orbitals dominate the density of states near $E_{F}$. The
planar nearest-neighbor, next-nearest-neighbor and interplane superexchange
couplings of Cu spins are $J_{1}$ $\approx$ 16.2 meV, $J_{2}$ $\approx$ 0.3 meV
and $J_{z}$ $\approx$ 1.2 meV, suggesting a low-dimensional antiferromagnet
\cite{Sondhi10}. We propose that the magnetic frustration along the c-axis
leads to a quantum spin disorder in In$_{3}$Cu$_{2}$VO$_{9}$, in accordance
with the recent experiments. {abstract}",1202.1861v3
2012-02-10,Suppression of magnetism in BiFeO$_3$ ultrathin epitaxial multilayers,"The present manuscript completes the study presented in two recent research
articles [K. Koumpouras and I. Galanakis, \textit{J. Magn. Magn. Mater.} 323,
2328 (2011); \textit{ibid}, \textit{J. Spintron. Magn. Nanomater.} 1, in
press]. Preliminary first-principles calculations using the QUANTUM-espresso
package [P. Giannozzi et al \textit{J. Phys.:Condens. Matter} 21, 395502
(2009)] on the magnetic behavior of ultra-thin epitaxial multilayers between
the BiFeO$_3$ magnetoelectric compound and various types of spacers are
presented. As spacer we have considered i) InP semiconductor, ii) Fe which is a
ferromagnet, and iii) metallic V. In all cases under study the growth axis of
the multilayer was the [001]. Our results indicate that the magnetic properties
are seriously downgraded for the ultrathin BiFeO$_3$ multilayers independent of
the nature of the spacer and in some cases under study magnetism even vanishes.
More extensive calculations are needed to establish a more clear view of the
physical properties of the interfaces involving the BiFeO$_3$ compound.",1202.2213v2
2012-02-12,"Structural Properties and Relative Stability of (Meta)Stable Ordered, Partially-ordered and Disordered Al-Li Alloy Phases","We resolve issues that have plagued reliable prediction of relative phase
stability for solid-solutions and compounds. Due to its commercially important
phase diagram, we showcase Al-Li system because historically density-functional
theory (DFT) results show large scatter and limited success in predicting the
structural properties and stability of solid-solutions relative to ordered
compounds. Using recent advances in an optimal basis-set representation of the
topology of electronic charge density (and, hence, atomic size), we present DFT
results that agree reasonably well with all known experimental data for the
structural properties and formation energies of ordered, off-stoichiometric
partially-ordered and disordered alloys, opening the way for reliable study in
complex alloys.",1202.2500v1
2012-02-13,"NMR Evidence for Antiferromagnetic Transition in the Single-Component Molecular System, [Cu(tmdt)$_{2}$]","The magnetic state of the single-component molecular compound,
[Cu(tmdt)$_{2}$], is investigated by means of $^{1}$H-NMR. An abrupt spectral
broadening below 13 K and a sharp peak in nuclear spin-lattice relaxation rate,
$T_{1}^{-1}$, at 13 K are observed as clear manifestations of a second-order
antiferromagnetic transition, which is consistent with the previously reported
magnetic susceptibility and EPR measurement. The ordered moment is estimated at
$0.22-0.45$ ${\mu}_{\rm B}$/molecule. The temperature-dependence of
$T_{1}^{-1}$ above the transition temperature indicates one-dimensional spin
dynamics and supports that the spins are on the central part of the molecule
differently from other isostructural compounds.",1202.2691v1
2012-02-13,Concept Relation Discovery and Innovation Enabling Technology (CORDIET),"Concept Relation Discovery and Innovation Enabling Technology (CORDIET), is a
toolbox for gaining new knowledge from unstructured text data. At the core of
CORDIET is the C-K theory which captures the essential elements of innovation.
The tool uses Formal Concept Analysis (FCA), Emergent Self Organizing Maps
(ESOM) and Hidden Markov Models (HMM) as main artifacts in the analysis
process. The user can define temporal, text mining and compound attributes. The
text mining attributes are used to analyze the unstructured text in documents,
the temporal attributes use these document's timestamps for analysis. The
compound attributes are XML rules based on text mining and temporal attributes.
The user can cluster objects with object-cluster rules and can chop the data in
pieces with segmentation rules. The artifacts are optimized for efficient data
analysis; object labels in the FCA lattice and ESOM map contain an URL on which
the user can click to open the selected document.",1202.2895v1
2012-02-20,Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides,"The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity $\rho_{a}$ across the long
orthorhombic axis $a_{O}$ - along which the spins couple antiferromagnetically
below the magnetic transition temperature - is smaller than the resistivity
$\rho_{b}$ of the short orthorhombic axis $b_{O}$, i. e. $\rho_{a}<\rho_{b}$.
Here we report that in the hole-doped compounds
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, as the doping level increases, the
resistivity anisotropy initially becomes vanishingly small, and eventually
changes sign for sufficiently large doping, i. e. $\rho_{b}<\rho_{a}$. This
observation is in agreement with a recent theoretical prediction that considers
the anisotropic scattering of electrons by spin-fluctuations in the
orthorhombic/nematic state.",1202.4430v2
2012-03-05,Growth diagram and magnetic properties of hexagonal LuFe$_2$O$_4$ thin films,"A growth diagram of Lu-Fe-O compounds on MgO (111) substrates using pulsed
laser deposition is constructed based on extensive growth experiments.
  The LuFe$_2$O$_4$ phase can only be grown in a small range of temperature and
O$_2$ pressure conditions.
  An understanding of the growth mechanism of Lu-Fe-O compound films is offered
in terms of the thermochemistry at the surface.
  Superparamagnetism is observed in LuFe$_2$O$_4$ film and is explained in
terms of the effect of the impurity h-LuFeO$_3$ phase and structural defects .",1203.0955v1
2012-03-07,Origin of magnetic interactions and their influence on the structural properties of Ni2MnGa and related compounds,"In this work, we perform first principles DFT calculations to investigate the
interplay between magnetic and structural properties in Ni2MnGa. We demonstrate
that the relative stability of austenite (cubic) and non-modulated martensite
(tetragonal) phases depends critically on the magnetic interactions between Mn
atoms. While standard approximate DFT functionals stabilize the latter phase, a
more accurate treatment of electronic localization and magnetism, obtained with
DFT+U, suppresses the non-modulated tetragonal structure for the stoichiometric
compound, in better agreement with the experiments. We show that the Anderson
impurity model, with Mn atoms treated as magnetic impurities, can explain this
observation and that the fine balance between super-exchange RKKY type
interactions mediated by Ni d and Ga p orbitals determines the equilibrium
structure of the crystal. The Anderson model is also demonstrated to capture
the effect of the number of valence electrons per unit cell on the structural
properties, often used as an empirical parameter to tune the behavior of
Ni2MnGa based alloys. Finally, we show that off-stoichiometric compositions
with excess Mn promote transitions to a non-modulated tetragonal structure, in
agreement with experiments.",1203.1553v1
2012-03-20,Hierarchical structure and biomineralization in cricket tooth,"Cricket is a truculent insect with stiff and sharp teeth as a fighting
weapon. The structure and possible biomineralization of the cricket teeth are
always interested. Synchrotron radiation X-ray fluorescence, X-ray diffraction
and small angle X-ray scattering techniques were used to probe the element
distribution, possible crystalline structures and size distribution of
scatterers in cricket teeth. Scanning electron microscope was used to observe
the nanoscaled structure. The results demonstrate that Zn is the main heavy
element in cricket teeth. The surface of the cricket teeth has a crystalline
compound like ZnFe2(AsO4)2(OH)2(H2O)4. While, the interior of the teeth has a
crystalline compound like ZnCl2, which is from the biomineralization. The
ZnCl2-like biomineral forms nanoscaled microfibrils and their axial direction
points at the top of tooth cusp. The microfibrils aggregate random into
intermediate filaments, forming a hierarchical structure. A sketch map of the
cricket tooth cusp was proposed and a detailed discussion was given in this
paper.",1203.4334v1
2012-03-23,Pressure effects on the heavy-fermion antiferromagnet CeAuSb2,"The f-electron compound CeAuSb2, which crystallizes in the ZrCuSi2-type
tetragonal structure, orders antiferromagnetically between 5 and 6.8 K, where
the antiferromagnetic transition temperature T_N depends on the occupancy of
the Au site. Here we report the electrical resistivity and heat capacity of a
high-quality crystal CeAuSb2 with T_N of 6.8 K, the highest for this compound.
The magnetic transition temperature is initially suppressed with pressure, but
is intercepted by a new magnetic state above 2.1 GPa. The new phase shows a
dome shape with pressure and coexists with another phase at pressures higher
than 4.7 GPa. The electrical resistivity shows a T^2 Fermi liquids behavior in
the complex magnetic state, and the residual resistivity and the T^2
resistivity coefficient increases with pressure, suggesting the possibility of
a magnetic quantum critical point at a higher pressure.",1203.5164v1
2012-03-29,Fermi level tuning and a large activation gap achieved in the topological insulator Bi_{2}Te_{2}Se by Sn doping,"We report the effect of Sn doping on the transport properties of the
topological insulator Bi_{2}Te_{2}Se studied in a series of
Bi_{2-x}Sn_{x}Te_{2}Se crystals with 0 \leq x \leq 0.02. The undoped
stoichiometric compound (x = 0) shows an n-type metallic behavior with its
Fermi level pinned to the conduction band. In the doped compound, it is found
that Sn acts as an acceptor and leads to a downshift of the Fermi level. For x
\geq 0.004, the Fermi level is lowered into the bulk forbidden gap and the
crystals present a resistivity considerably larger than 1 Ohmcm at low
temperatures. In those crystals, the high-temperature transport properties are
essentially governed by thermally-activated carriers whose activation energy is
95-125 meV, which probably signifies the formation of a Sn-related impurity
band. In addition, the surface conductance directly obtained from the
Shubnikov-de Haas oscillations indicates that a surface-dominated transport can
be achieved in samples with several um thickness.",1203.6411v1
2012-04-01,"Are there nodes in LaFePO, BaFe$_2$(AsP)$_2$, and KFe$_2$As$_2$ ?","We reexamined the experimental evidences for the possible existence of the
superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC
compounds: LaFePO, BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$, and KFe$_2$As$_2$. We
showed that while the $T$-linear temperature dependence of the penetration
depth $\lambda(T)$ of these three compounds indicate extremely clean nodal gap
superconductors, the thermal conductivity data $\lim_{T,H \rightarrow 0}
\kappa_S (H,T)/T$ unambiguously showed that LaFePO and
BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ are extremely dirty, while KFe$_2$As$_2$
can be clean. This apparently conflicting experimental data casts a serious
doubt on the nodal gap possibility on LaFePO and
BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$.",1204.0212v2
2012-04-04,Effect of magnetic field in heavy-fermion compound YbCo$_2$Zn$_{20}$,"Inelastic neutron scattering experiments on poly crystalline sample of
heavy-fermion compound YbCo$_2$Zn$_{20}$ were carried out in order to obtain
microscopic insights on the ground state and its magnetic field response. At
zero field at 300 mK, inelastic response consists of two features: quasielastic
scattering and a sharp peak at 0.6 meV. With increasing temperature, a broad
peak comes up around 2.1 meV, whereas quasielastic response gets broader and
the peak at 0.6 meV becomes unclear. By applying magnetic field, the
quasielastic response exhibits significant broadening above 1 T, and the peak
at 0.6 meV is obscure under fields. The peaks in inelastic spectra and its
temperature variation can be ascribed to the suggested crystal-field model of
${{\Gamma}_6}$ - ${{\Gamma}_8}$ - ${{\Gamma}_7}$ with the overall splitting of
less than 3 meV. The observed quasielastic response and its rapid broadening
with magnetic field indicates that the heavy-electron state arises from the
ground state doublets, and are strongly suppressed by external field in
YbCo$_2$Zn$_{20}$.",1204.0854v1
2012-04-04,Suppression of f-Electron Itinerancy in CeRu2Si2 by a Strong Magnetic Field,"The valence state of Ce in a canonical heavy fermion compound CeRu2Si2 has
been investigated by synchrotron X-ray absorption spectroscopy at 1.8 K in high
magnetic fields of up to 40 T. The valence was slightly larger than for the
pure trivalent state (Ce3+: f1), as expected in heavy fermion compounds, and it
decreased toward the trivalent state as the magnetic field was increased. The
field-induced valence reduction indicates that the itinerant character of the
4f electrons in CeRu2Si2 was suppressed by a strong magnetic field. The
suppression was gradual and showed characteristic magnetic field dependence,
which reflects the metamagnetism around Hm \sim 8 T. The itinerant character
persisted, even at 40 T (\sim 5Hm), suggesting that the Kondo bound state is
continuously broken by magnetic fields and that it should completely collapse
at fields exceeding 200 T.",1204.0968v2
2012-04-05,"Crystallographic Study of U-Th bearing minerals in Tranomaro, Anosy Region- Madagascar","As an alternative to conventional fossil fuel, there is a renewed interest in
the nuclear fuel to support increasing energy demand. New studies are then
undertaken to characterize Madagascar U-Th bearing minerals. This is the case
for the urano-thorianite bearing pyroxenites in the south East of Madagascar.
In this region, several quarries were abandoned, after being mined by the
French Atomic Energy Commission (C.E.A) in the fifties and sixties and are now
explored by new mining companies. For this purpose, seven U-Th bearing mineral
samples from old abandoned uranium quarries in Tranomaro, Amboasary Sud,
Madagascar (46{\deg} 28' 0""E, 24{\deg} 36' 0""S), have been collected. To
determine the mineral microstructure, they were investigated for qualitative
and quantitative identification of crystalline compounds using X-ray powder
diffraction analytical method (XRD). Results showed that the U and Th
compounds, as minor elements, are present in various crystalline structures.
This is important to understand their environmental behaviours, in terms of
crystallographic dispersion of U-Th minerals and their impacts on human health.",1204.1499v1
2012-04-08,Two successive field-induced spin-flop transitions in single-crystalline CaCo$_{2}$As$_{2}$,"CaCo$_{2}$As$_{2}$, a ThCr$_{2}$Si$_{2}$-structure compound, undergoes an
antiferromagnetic transition at \emph{T$_{N}$}=76K with the magnetic moments
being aligned parallel to the \emph{c} axis. Electronic transport measurement
reveals that the coupling between conducting carriers and magnetic order in
CaCo$_{2}$As$_{2}$ is much weaker comparing to the parent compounds of iron
pnictide. Applying magnetic field along \emph{c} axis induces two successive
spin-flop transitions in its magnetic state. The magnetization saturation
behaviors with \emph{\textbf{H}$\parallel$c} and \emph{\textbf{H}$\parallel$ab}
at 10K indicate that the antiferromagnetic coupling along \emph{c} direction is
very weak. The interlayer antiferromagntic coupling constant \emph{J$_{c}$} is
estimated to be about 2 meV.",1204.1736v1
2012-04-19,"Paramagnetic Phase of a Heavy-Fermion Compound, CeFePO, Probed by 57Fe Mössbauer Spectroscopy","57Fe M\""{o}ssbauer spectroscopy was applied to an iron-based layered compound
CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed
in the M\""ossbauer spectra of CeFePO indicating a paramagnetic phase of the Fe
magnetic sublattice. All the spectra were fitted with a small quadrupole
splitting, and the Debye temperature of CeFePO was found to be \sim448 K. The
isomer shift at room temperature, 0.32 mm/s, was almost equal to those of
LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts
and unit cell volumes, it was found that the Fe of CeFePO has a similar valence
state to other layered iron-based quaternary oxypnictides except LaFePO.",1204.4266v1
2012-04-19,Trends and patterns of scintillator nonproportionality,"Data on the photon nonproportional response of 33 inorganic scintillation
materials are systemized and analyzed. The main trends of nonproportionality
for different groups of inorganic scintillators, especially for oxides and
halides, are highlighted. The dependence of the shape and degree of photon
nonproportional response versus chemical composition, dopant type, refractive
index and other fundamental properties of the materials is studied. Better
proportionality appears to be correlated with higher refractive index of the
compound. Another related factor is the width of the valence band in halide
compounds. With larger valence band width from fluorides, to chlorides, to
bromides, and to iodides, a better proportionality is observed.",1204.4350v1
2012-04-19,High intergrain critical current density in fine-grain (Ba0.6K0.4)Fe2As2 wires and bulks,"The K- and Co-doped BaFe2As2 (Ba-122) superconducting compounds are
potentially useful for applications because they have upper critical fields
(Hc2) of well over 50 T, Hc2 anisotropy Gamma < 2, and thin film critical
current densities exceeding 1 MAcm-2 at 4.2 K. However, thin-film bicrystals of
Co-doped Ba-122 clearly exhibit weak link behavior for [001] tilt
misorientations of more than about 5 degrees, suggesting that textured
substrates would be needed for applications, as in the cuprates. Here we
present a contrary and very much more positive result in which untextured
polycrystalline (Ba0.6K0.4)Fe2As2 bulks and round wires with high grain
boundary density have transport critical current densities well over 0.1 MAcm-2
(SF, 4.2 K), more than 10 times higher than that of any other ferropnictide
wire. The enhanced grain connectivity is ascribed to their much improved phase
purity and to the enhanced vortex stiffness of this low-anisotropy compound
(Gamma ~ 1-2) compared to YBa2Cu3O7-x (Gamma ~ 5).",1204.4426v3
2012-05-13,High-Field Fermi Surface Properties in the Low Carrier Heavy Fermion Compound URu2Si2,"We performed the Shubnikov-de Haas (SdH) experiments of the low carrier heavy
fermion compound URu2Si2 at high fields up to 34T and at low temperatures down
to 30mK. All main SdH branches named alpha, beta and gamma were observed for
all the measured field-directions (H // [001] -> [100], [100] -> [110] and
[001] -> [110]), indicating that these are attributed to the closed Fermi
surfaces with nearly spherical shapes. Anomalous split of branch alpha was
detected for the field along the basal plane, and the split immediately
disappears by tilting the field to [001] direction, implying a fingerprint of
the hidden order state. High field experiments reveal the complicated
field-dependence of the SdH frequencies and the cyclotron masses due to the
Zeeman spin-splitting associated with the Fermi surface reconstruction in the
hidden order state with small carrier numbers. A new SdH branch named omega
with large cyclotron mass of 25m0 was detected at high fields above 23T close
to the hidden order instabilities.",1205.2869v1
2012-05-18,Experimental evaluation and thermodynamic assessment of the LiF-LuF3 phase diagram,"The phase diagram of the system LiF-LuF3 has been revised using thermal
analysis. Specific heat capacity and enthalpy of phase transition and fusion
were measured by differential scanning calorimetry for all compounds belonging
to the system. A thermodynamic optimization of the LiF-LuF3 phase diagram was
performed by fitting the Gibbs energy functions to experimental data that were
taken from the literature or measured in this work. Excess energy terms, which
describe the effect of interaction between the two fluoride compounds in the
liquid solution, were expressed by the Redlich-Kister polynomial function. The
theoretical phase diagram assessed was in suitable agreement with the
re-evaluated experimental data.",1205.4180v1
2012-05-21,Superconducting Mechanism through direct and redox layer doping in Pnictides,"The mechanism of superconductivity in pnictides is discussed through direct
doping in superconducting FeAs and also in charge reservoir REO layers. The
un-doped SmFeAsO is charge neutral SDW (Spin Density Wave) compound with
magnetic ordering below 150 K. The Superconducting FeAs layers are doped with
Co and Ni at Fe site, whereas REO layers are doped with F at O site. The
electron doping in SmFeAsO through Co results in superconductivity with
transition temperature (Tc) maximum up to 15 K, whereas F doping results in Tc
upto 47 K in SmFeAsO. All these REFe/Co/NiAsO/F compounds are iso-structural to
ZrCuSiAs structure. The samples are crystallized in a tetragonal structure with
space group P4/nmm. Variation of Tc with different doping routes shows the
versatility of the structure and mechanism of occurrence of superconductivity.
It seems doping in redox layer is more effective than direct doping in
superconducting FeAs layer.",1205.4557v2
2012-05-25,Thermal Conductivity and Specific Heat of the Spin-Ice Compound Dy$_2$Ti$_2$O$_7$: Experimental Evidence for Monopole Heat Transport,"Elementary excitations in the spin-ice compound Dy$_2$Ti$_2$O$_7$ can be
described as magnetic monopoles propagating independently within the pyrochlore
lattice formed by magnetic Dy ions. We studied the magnetic-field dependence of
the thermal conductivity {\kappa}(B) for B || [001] and observe clear evidence
for magnetic heat transport originating from the monopole excitations. The
magnetic contribution {\kappa}_{mag} is strongly field-dependent and correlates
with the magnetization M(B). The diffusion coefficient obtained from the ratio
of {\kappa}_{mag} and the magnetic specific heat is strongly enhanced below 1 K
indicating a high mobility of the monopole excitations in the spin-ice state.",1205.5700v1
2012-05-28,Magneto-elastic coupling and magnetocaloric effect in hexagonal Mn-Fe-P-Si compounds,"Structural, magnetic and magnetocaloric properties of Fe2P-based Mn-Fe-P-Si
compounds were investigated. The study reveals a large magneto-elastic coupling
that starts to develop in the paramagnetic state and grows when the
ferromagnetic transition temperature is approached. Based on the behavior of
the magneto-elastic coupling, we show the thermal evolution of the magnetic
moments. On cooling, magnetic moments on the tetrahedral site form and
gradually increase in the paramagnetic state. At the magnetic ordering
temperature the moments attain a much larger value in a discontinuous step. We
also find that the hysteresis and magnetic entropy change are correlated with
discontinuous changes in the lattice parameters at the transition temperature.
Small hysteresis can be obtained while maintaining giant magnetocaloric effect.",1205.6196v1
2012-05-30,Phase separation in ion-irradiated compound semiconductors: an alternate route to ordered nano-structures,"In recent years, observations of highly-ordered, hexagonal arrays of
self-organized nanostructures on binary or impurity-laced targets under
normal-incidence ion irradiation have excited interest in this phenomenon as a
potential route to high-throughput, low-cost manufacture of nanoscale devices
or nanostructured coatings. The currently-prominent explanation for these
structures is a morphological instability driven by ion erosion discovered by
Bradley and Shipman; however, recent parameter estimates via molecular dynamics
simulations suggest that this erosive instability may not be active for the
representative GaSb system in which hexagonal structures were first observed.
  Motivated by experimental and numerical evidence suggesting the possible
importance of phase separation in ion-irradiated compounds, we here generalize
the Bradley-Shipman theory to include the effect of ion-assisted phase
separation. The resulting system admits a chemically-driven finite-wavelength
instability that can explain the order of observed patterns even when the
erosive Bradley-Shipman instability, and in a relevant simplifying limit,
provides an intuitive instability criteria that agrees qualitatively with
experimental observations on pattern wavelengths. Finally, we identify a
characteristic experimental signature that distinguishes the chemical and
morphological instabilities, and highlights the need for specific additional
experimental data on the GaSb system.",1205.6834v2
2012-06-07,Optical study of archetypical valence-fluctuating Eu-systems,"We have investigated the optical conductivity of the prominent valence
fluctuating compounds EuIr2Si2 and EuNi2P2 in the infrared energy range to get
new insights into the electronic properties of valence fluctuating systems. For
both compounds we observe upon cooling the formation of a renormalized Drude
response, a partial suppression of the optical conductivity below 100 meV and
the appearance of a mid-infrared peak at 0.15 eV for EuIr2Si2 and at 0.13 eV
for EuNi2P2. Most remarkably, our results show a strong similarity with the
optical spectra reported for many Ce- or Yb-based heavy fermion metals and
intermediate valence systems, although the phase diagrams and the temperature
dependence of the valence differ strongly between Eu- and Ce-/Yb-systems. This
suggests that the hybridization between 4f- and conduction electrons, which is
responsible for the properties of Ce- and Yb-systems, plays an important role
in valence fluctuating Eu-systems.",1206.1516v1
2012-06-12,Density functional theory calculations and vibrational spectroscopy on iron spin-crossover compounds,"Iron complexes with a suitable ligand field undergo spin-crossover (SCO),
which can be induced reversibly by temperature, pressure or even light.
Therefore, these compounds are highly interesting candidates for optical
information storage, for display devices and pressure sensors. The SCO
phenomenon can be conveniently studied by spectroscopic techniques like Raman
and infrared spectroscopy as well as nuclear inelastic scattering, a technique
which makes use of the M\""ossbauer effect. This review covers new developments
which have evolved during the last years like, e.g. picosecond infrared
spectroscopy and thin film studies but also gives an overviewon newtechniques
for the theoretical calculation of spin transition phenomena and vibrational
spectroscopic data of SCO complexes.",1206.2469v1
2012-06-13,"The nature of 4f electron magnetism in the diluted ferromagnetic Kondo lattice, CeIr2B2","We report on the physical properties of the series Ce_(1-x)La_xIr_2B_2 (x D
0-0.9), obtained by means of magnetization, heat capacity and electrical
resistivity measurements as a function of temperature (down to 0.7 K for the
latter two measurements). The Curie temperature of CeIr2B2 (?5 K) is lowered
due to La substitution, as expected. However, no quantum critical point or
'non-Fermi liquid' behavior was observed even in the dilute limit of x D 0:9.
Interestingly, ferromagnetic ordering persists even for Ce0:1La0:9Ir2B2, below
0.8 K. Among the Ce systems, CeIr2B2 is one of the compounds in which direct
4f-4f interaction does not appear to play any role in the magnetism, which is
controlled by the indirect exchange interaction alone. In this compound, the
Kondo effect persists in the ferromagnetic ordered state, as inferred from the
entropy data.",1206.2737v1
2012-06-15,Model of the electron-phonon interaction and optical conductivity of Ba$_{1-x}$K$_x$BiO$_3$ superconductors,"We investigate the physical properties of the Ba$_{1-x}$K$_x$BiO$_3$
compounds with a focus on the optical properties. Results from the simple
Holstein model, describing a single band coupled to an oxygen breathing mode
with parameters derived from first principles calculations, are in excellent
agreement with a broad range of experimental information. It accounts for an
insulating parent compound at $x=0$ %, with a direct- (optical) and an
indirect-gap, and a metal insulator transition around $x = 0.38$. Strong
electron-phonon coupling leads to spectral weight redistribution over a
frequency scale much larger than the characteristic phonon frequency and to
strongly anharmonic phonons. We find that the metallic phase in the vicinity of
phase boundary is close to the polaronic regime.",1206.3514v1
2012-06-20,Evolution of band structure from optimally doped to heavily overdoped Co-substituted NaFeAs,"Using angle-resolved photoemission spectroscopy, we studied the electronic
structure of NaFe$_{1-x}$Co$_x$As from an optimally doped superconducting
compound ($x=0.028$) to a heavily overdoped non-superconducting one
($x=0.109$). Similar to the case of ""122"" type iron pnictides, our data suggest
that Co dopant in NaFe$_{1-x}$Co$_x$As supplies extra charge carriers and
shifts the Fermi level accordingly. In the $x=0.109$ compound, the hole-like
bands around the zone center $\Gamma$ move to deeper binding energies and an
electron pocket appears instead. The overall band renormalization remains
basically the same throughout the doping range we studied, suggesting that the
local magnetic/electronic correlations are not affected by carrier doping. We
speculate that a balance between itinerant properties of mobile carriers and
local interactions may play an important role for the superconductivity.",1206.4402v1
2012-06-20,Mössbauer study of the '11' iron-based superconductors parent compound Fe(1+x)Te,"57Fe Moessbauer spectroscopy was applied to investigate the superconductor
parent compound Fe(1+x)Te for x=0.06, 0.10, 0.14, 0.18 within the temperature
range 4.2 K - 300 K. A spin density wave (SDW) within the iron atoms occupying
regular tetrahedral sites was observed with the square root of the mean square
amplitude at 4.2 K varying between 9.7 T and 15.7 T with increasing x. Three
additional magnetic spectral components appeared due to the interstitial iron
distributed over available sites between the Fe-Te layers. The excess iron
showed hyperfine fields at approximately 16 T, 21 T and 49 T for three
respective components at 4.2 K. The component with a large field of 49 T
indicated the presence of isolated iron atoms with large localized magnetic
moment in interstitial positions. Magnetic ordering of the interstitial iron
disappeared in accordance with the fallout of the SDW with the increasing
temperature.",1206.4439v1
2012-06-27,BaFe2Se2O as an Iron-Based Mott Insulator with Antiferromagnetic Order,"A new compound with a quasi-two-dimensional array of FeSe3O tetrahedra and an
orthorombic structure, namely BaFe2Se2O, has been successfully fabricated.
Experimental results show that this compound is an insulator and has an
antiferromagnetic (AF) transition at 240 K. Band structure calculation reveals
the narrowing of Fe 3d bands near the Fermi energy, which leads to the
localization of magnetism and the Mott insulating behavior. The large distances
between the Fe atoms perhaps are responsible for the characters. Linear
response calculation further indicates a strong in-plane AF exchange $J$, this
can account for the enhanced magnetic susceptibility (which has a maximum at
about 450 K) above the Neel temperature.",1206.6154v3
2012-07-09,"Structural and physical properties of layered oxy-arsenides LnRuAsO (Ln = La, Nd, Sm, Gd)","Polycrystalline samples of LaRuAsO, NdRuAsO, SmRuAsO, and GdRuAsO have been
synthesized and studied using powder x-ray diffraction, electrical transport,
magnetization, and heat capacity measurements. Variations in structural
properties across the series reveal a trend toward more ideal tetrahedral
coordination around Ru as the size of the rare earth element is reduced. The
lattice parameters of these Ru compounds show a more anisotropic response to
variation in Ln than their Fe analogues, and significant anisotropy in thermal
expansion is also observed. Transport measurements show metallic behavior, and
carrier concentrations near 10^21 - 10^22 electrons per cm^3 are inferred from
simple analysis of Hall effect measurements. Anomalies in resistivity,
magnetization, and heat capacity indicate antiferromagnetic ordering of rare
earth moments at 5 K for GdRuAsO, 4.5 K for SmRuAsO, and <2 K for NdRuAsO.
Magnetization measurements on LaRuAsO show no evidence of a magnetic moment on
Ru. Observed behaviors are compared to those reported for similar Fe and Ru
compounds.",1207.2040v1
2012-07-10,Induced Optical Losses in Optoelectronic Devices due to Focused Ion Beam Damages,"A study of damages caused by gallium focused ion beam (FIB) into III-V
compounds is presented. Potential damages caused by local heating, ion
implantation, and selective sputtering are presented. Preliminary analysis
shows that local heating is negligible. Gallium implantation is shown to occur
over areas tens of nanometers thick. Gallium accumulation as well as selective
sputtering during III-V compounds milling is expected. Particularly, for GaAs,
this effect leads to gallium segregation and formation of metallic clusters.
Microdisk resonators were fabricated using FIB milling with different emission
currents to analyze these effects on a device. It is shown that for higher
emission current, thus higher implantation doses, the cavity quality factor
rapidly decreases due to optical scattering losses induced by implanted gallium
atoms.",1207.2359v1
2012-07-10,A theoretical study of the hydrogen-storage potential of (H_2)_4CH_4 in metal organic framework materials and carbon nanotubes,"The hydrogen-methane compound (H_2)_4CH_4---or for short H4M---is one of the
most promising hydrogen-storage materials. This van der Waals compound is
extremely rich in molecular hydrogen: 33.3 mass%, not including the hydrogen
bound in CH_4; including it, we reach even 50.2 mass%. Unfortunately, H4M is
not stable under ambient pressure and temperature, requiring either low
temperature or high pressure. In this paper, we investigate the properties and
structure of the molecular and crystalline forms of H4M, using ab initio
methods based on van der Waals DFT (vdW-DF). We further investigate the
possibility of creating the pressures required to stabilize H4M through
external agents such as metal organic framework (MOF) materials and carbon
nanotubes, with very encouraging results. In particular, we find that certain
MOFs can create considerable pressure for H4M in their cavities, but not enough
to stabilize it at room temperature, and moderate cooling is still necessary.
On the other hand, we find that all investigated carbon nanotubes can create
the high pressures required for H4M to be stable at room temperature, with
direct implications for new and exciting hydrogen-storage applications.",1207.2447v1
2012-07-16,Infrared Measurement of the Pseudogap in P-Doped and Co-Doped BaFe2As2 High-Temperature Superconductors,"We report on infrared studies of charge dynamics in a prototypical pnictide
system: the BaFe2As2 family. Our experiments have identified hallmarks of the
pseudogap state in the BaFe2As2 system that mirror the spectroscopic
manifestations of the pseudogap in the cuprates. The magnitude of the infrared
pseudogap is in accord with that of the spin-density-wave gap of the parent
compound. By monitoring the superconducting gap of both P- and Co-doped
compounds, we find that the infrared pseudogap is unrelated to
superconductivity. The appearance of the pseudogap is found to correlate with
the evolution of the antiferromagnetic fluctuations associated with the
spin-density-wave instability. The strong-coupling analysis of infrared data
further reveals the interdependence between the magnetism and the pseudogap in
the iron pnictides.",1207.3567v1
2012-07-25,Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding,"Within the broad class of multiferroics (compounds showing a coexistence of
magnetism and ferroelectricity), we focus on the subclass of ""improper
electronic ferroelectrics"", i.e. correlated materials where electronic degrees
of freedom (such as spin, charge or orbital) drive ferroelectricity. In
particular, in spin-induced ferroelectrics, there is not only a {\em
coexistence} of the two intriguing magnetic and dipolar orders; rather, there
is such an intimate link that one drives the other, suggesting a giant
magnetoelectric coupling. Via first-principles approaches based on density
functional theory, we review the microscopic mechanisms at the basis of
multiferroicity in several compounds, ranging from transition metal oxides to
organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic
frameworks, MOFs)",1207.5918v1
2012-07-26,High pressure transport studies of the LiFeAs analogues CuFeTe2 and Fe2As,"We have synthesized two iron-pnictide/chalcogenide materials, CuFeTe2 and
Fe2As, which share crystallographic features with known iron-based
superconductors, and carried out high-pressure electrical resistivity
measurements on these materials to pressures in excess of 30 GPa. Both
compounds crystallize in the Cu2Sb-type crystal structure that is
characteristic of LiFeAs (with CuFeTe2 exhibiting a disordered variant). At
ambient pressure, CuFeTe2 is a semiconductor and has been suggested to exhibit
a spin-density-wave transition, while Fe2As is a metallic antiferromagnet. The
electrical resistivity of CuFeTe2, measured at 4 K, decreases by almost two
orders of magnitude between ambient pressure and 2.4 GPa. At 34 GPa, the
electrical resistivity decreases upon cooling the sample below 150 K,
suggesting the proximity of the compound to a metal-insulator transition.
Neither CuFeTe2 nor Fe2As superconduct above 1.1 K throughout the measured
pressure range.",1207.6272v1
2012-07-30,Prediction of inorganic superconductors with quasi-one-dimensional crystal structure,"Models of superconductors having a quasi-one-dimensional crystal structure
based on the convoluted into a tube Ginzburg sandwich, which comprises a
layered dielectric-metal-dielectric structure, have been suggested. The
critical crystal chemistry parameters of the Ginzburg sandwich determining the
possibility of the emergence of superconductivity and the Tc value in layered
high-Tc cuprates, which could have the same functions in quasi-one-dimensional
fragments (sandwich-type tubes), have been examined. The crystal structures of
known low-temperature superconductors, in which one can mark out similar
quasi-one- dimensional fragments, have been analyzed. Five compounds with
quasi-one-dimensional structures, which can be considered as potential parents
of new superconductor families, possibly with high transition temperatures,
have been suggested. The methods of doping and modification of these compounds
are provided.",1207.7112v2
2012-08-01,Textured Superconductivity in the Presence of a Coexisting Order: Ce115s and Other Heavy-Fermion Compounds,"Superconductivity in strongly correlated electron systems frequently emerges
in proximity to another broken symmetry. In heavy-electron superconductors, the
nearby ordered state most commonly is magnetism, and the so-called Ce115
heavy-electron compounds have been particularly instructive for revealing new
relationships between magnetism and superconductivity. From measurements of the
resistive and bulk transitions to superconductivity in these materials, we find
that the resistive transition appears at a temperature considerably higher than
the bulk transition when superconductivity and magnetic order coexist, but this
temperature difference disappears in the absence of long-range magnetic order.
Further, in the pressure-temperature region of coexistence in CeRhIn5, a new
anisotropy in the resistive transition develops even though the tetragonal
crystal structure apparently remains unchanged, implying a form of textured
superconductivity. We suggest that this texture may be a generic response to
coexisting order in these and other heavy-fermion superconductors.",1208.0253v1
2012-08-07,Optimal Maintenance Policy for a Compound Poisson Shock Model,"Engineered and infrastructure systems deteriorate (e.g., loss capacity) as a
result of adverse environmental or external conditions. Modeling deterioration
is essential to define optimum design strategies and inspection and maintenance
(intervention) programs. In particular, the main purpose of maintenance is to
increase the system availability by extending the life of the system. Most
strategies for maintenance optimization focus on defining long term strategies
based on the system's condition at the decision time (e.g., $t=0$). However,
due to the large uncertainty in the system's performance through life, an
optimal maintenance policy requires both permanent monitoring and a
cost-efficient plan of interventions. This paper presents a model to define an
optimal maintenance policy of systems that deteriorate as a result of shocks.
Deterioration caused by shocks is modeled as a compound Poisson process and the
optimal maintenance strategy is based on an impulse control model. In the model
the optimal time and size of interventions are executed according the the
system state, which is obtained from permanent monitoring.",1208.1327v1
2012-08-08,Evidence for two-gap superconductivity in the non-centrosymmetric compound LaNiC$_2$,"We study the superconducting properties of the non-centrosymmetric compound
LaNiC$_2$ by measuring the London penetration depth $\Delta \lambda (T)$, the
specific heat $C(T,B)$ and the electrical resistivity $\rho (T,B)$. Both
$\Delta\lambda (T)$ and the electronic specific heat $C_e(T)$ exhibit
exponential behavior at low temperatures and can be described in terms of a
phenomenological two-gap BCS model. The residual Sommerfeld coefficient in the
superconducting state, $\gamma_0(B)$, shows a fast increase at low fields and
then an eventual saturation with increasing magnetic field. A pronounced upturn
curvature is observed in the upper critical field $B_{c2}(T)$ near $T_{c}$. All
the experimental observations support the existence of two-gap
superconductivity in LaNiC$_2$.",1208.1596v1
2012-08-10,Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics,"Uranium and plutonium's 5f electrons are tenuously poised between strongly
bonding with ligand spd-states and residing close to the nucleus. The unusual
properties of these elements and their compounds (eg. the six different
allotropes of elemental plutonium) are widely believed to depend on the related
attributes of f-orbital occupancy and delocalization, for which a quantitative
measure is lacking. By employing resonant x-ray emission spectroscopy (RXES)
and x-ray absorption near-edge structure (XANES) spectroscopy and making
comparisons to specific heat measurements, we demonstrate the presence of
multiconfigurational f-orbital states in the actinide elements U and Pu, and in
a wide range of uranium and plutonium intermetallic compounds. These results
provide a robust experimental basis for a new framework for understanding the
strongly-correlated behavior of actinide materials.",1208.2234v1
2012-08-17,Anisotropic resistivity of Na$_{1-δ}$Fe$_{1-x}$Co$_x$As,"Temperature-dependent resistivity is studied in single crystals of
iron-arsenide superconductor Na$_{1-\delta}$Fe$_{1-x}$Co$_x$As for electrical
current directions along, $\rho_a (T)$, and transverse, $\rho_c (T)$, to the
Fe-As layers. Doping with Co increases stability of this compound to reaction
with the environment and suppresses numerous features in both $\rho_a(T)$ and
$\rho_c(T)$ compared to the stoichiometric NaFeAs. Evolution of $\rho_a (T)$
with $x$ follows a universal trend observed in other pnictide superconductors,
exhibiting a $T$-linear temperature dependence close to the optimal doping and
development of $T^2$ dependence upon further doping. $\rho_c (T)$ in parent
compound shows a non - monotonic behavior with a crossover from non-metallic
resistivity increase on cooling from room temperature down to $\sim$ 80 K to a
metallic decrease below this temperature. Both $\rho_a (T)$ and $\rho_c (T)$
show several correlated crossover - like features at $T>$ 80 K. Despite a
general trend towards more metallic behavior of inter - plane resistivity in
Co-doped samples, the temperature of the crossover from insulating to metallic
behavior (80 K) does not change much with doping.",1208.3646v1
2012-08-17,Routes to heavy-fermion superconductivity,"Superconductivity in lanthanide- and actinide-based heavy-fermion metals can
have different microscopic origins. Among others, Cooper pair formation based
on fluctuations of the valence, of the quadrupole moment or of the spin of the
localized 4f/5f shell have been proposed. Spin-fluctuation mediated
superconductivity in CeCu2Si2 was demonstrated by inelastic neutron scattering
to exist in the vicinity of a spin-density-wave quantum critical point. The
isostructural HF compound YbRh2Si2 which is prototypical for a Kondo-breakdown
quantum critical point has so far not shown any sign of superconductivity down
to approximately 10mK. In contrast, results of de-Haas-van-Alphen experiments
by Shishido et al. (J. Phys. Soc. Jpn. 74, 1103 (2005)) suggest
superconductivity in CeRhIn5 close to an antiferromagnetic quantum critical
point beyond the spin-density-wave type, at which the Kondo effect breaks down.
For the related compound CeCoIn5 however, a field-induced quantum critical
point of spin-density-wave type is extrapolated to exist inside the
superconducting phase.",1208.3684v1
2012-08-27,Evidence for entanglement at high temperatures in an engineered molecular magnet,"The molecular compound
[Fe$_{2}$($\mu_{2}$-oxo)(C$_{3}$H$_{4}$N$_{2}$)$_{6}$(C$_{2}$O$_{4}$)$_{2}$]
was designed and synthesized for the first time and its structure was
determined using single-crystal X-ray diffraction. The magnetic susceptibility
of this compound was measured from 2 to 300 K. The analysis of the
susceptibility data using protocols developed for other spin singlet
ground-state systems indicates that the quantum entanglement would remain at
temperatures up to 732 K, significantly above the highest entanglement
temperature reported to date. The large gap between the ground state and the
first-excited state (282 K) suggests that the spin system may be somewhat
immune to decohering mechanisms. Our measurements strongly suggest that
molecular magnets are promising candidate platforms for quantum information
processing.",1208.5459v2
2012-08-30,Spectroscopic fingerprints of valence and spin states in manganese oxides and fluorides,"We performed a systematic study of soft X-ray absorption spectroscopy in
various manganese oxides and fluorides. Both Mn L-edges and ligand (O and F)
K-edges are presented and compared with each other. Despite the distinct
crystal structure and covalent/ionic nature in different systems, the Mn-L
spectra fingerprint the Mn valence and spin states through spectral lineshape
and energy position consistently and evidently. The clear O- and F- K pre-edge
features in our high resolution spectra enable a quantitative definition of the
molecular orbital diagram with different Mn valence. In addition, while the
binding energy difference of the O-1s core electrons leads to a small shift of
the O-K leading edges between trivalent and quadrivalent manganese oxides, a
significant edge shift, with an order of magnitude larger in energy, was found
between divalent and trivalent compounds, which is attributed to the spin
exchange stabilization of half- filled 3d system. This shift is much enhanced
in the ionic fluoride system. This work provides the spectroscopic foundation
for further studies of complicated Mn compounds.",1208.6319v2
2012-08-31,Doping-induced spin-manipulation in complex trimer system Ca$_{3}$Cu$_{3}$(PO$_{4}$)$_{4}$: A First Principles Study,"Spin-manipulated doping with magnetic (Ni) and non-magnetic (Mg) dopants
constitutes the experimental attempts to obtain a singlet ground state system
from the linear chain Heisenberg antiferromagnetic Cu-based $d^{9}$ spin-1/2
trimer compound Ca$_{3}$Cu$_{3}$(PO$_{4}$)$_{4}$ with doublet ground state. The
present study is a first-principles based investigation of the effects of such
doping on the spin-exchange mechanism and electronic structure of the parent
compound. Site-selective doping with zero-spin dopants like Mg is proved to be
more efficient than an integral spin dopant Ni in obtaining a spin-gap system
with singlet ground state, as also observed in the experimental studies. Doping
induced dimerized state is found to be the lowest in ground-state energy.
Calculated spin exchange values along various possible paths resemble nicely
with earlier experimental results.",1208.6459v2
2012-09-29,Fracture Strength of AlLiB14,"The orthorhombic boride crystal family XYB$_{14}$, where X and Y are metal
atoms, plays a critical role in a unique class of superhard compounds, yet
there have been no studies aimed at understanding the origin of the mechanical
strength of this compound. We present here the results from a comprehensive
investigation into the fracture strength of the archetypal AlLiB$_{14}$
crystal. First-principles, \textit{ab initio}, methods are used to determine
the ideal brittle cleavage strength for several high-symmetry orientations. The
elastic tensor and the orientation-dependent Young's modulus are calculated.
From these results the lower bound fracture strength of AlLiB$_{14}$ is
predicted to be between 29 and 31 GPa, which is near the measured hardness
reported in the literature. These results indicate that the intrinsic strength
of AlLiB$_{14}$ is limited by the interatomic B--B bonds that span between the
B layers.",1210.0130v1
2012-10-05,Electronic transport and quantum localization effects in organic semiconductors,"We explore the charge transport mechanism in organic semiconductors based on
a model that accounts for the thermal intermolecular disorder at work in pure
crystalline compounds, as well as extrinsic sources of disorder that are
present in current experimental devices. Starting from the Kubo formula, we
develop a theoretical framework that relates the time-dependent quantum
dynamics of electrons to the frequency-dependent conductivity. The electron
mobility is then calculated through a relaxation time approximation that
accounts for quantum localization corrections beyond Boltzmann theory, and
allows us to efficiently address the interplay between highly conducting states
in the band range and localized states induced by disorder in the band tails.
The emergence of a ""transient localization"" phenomenon is shown to be a general
feature of organic semiconductors, that is compatible with the bandlike
temperature dependence of the mobility observed in pure compounds. Carrier
trapping by extrinsic disorder causes a crossover to a thermally activated
behavior at low temperature, which is progressively suppressed upon increasing
the carrier concentration, as is commonly observed in organic field-effect
transistors. Our results establish a direct connection between the localization
of the electronic states and their conductive properties, formalizing
phenomenological considerations that are commonly used in the literature.",1210.1673v2
2012-10-09,The Formation and Characteristics of Acrylonitrile/Urea Inclusion Compound,"The formation process and composition of the acrylonitrile/urea inclusion
compounds (AN/UIC) with different aging times and AN/urea molar feed ratios are
studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD).
It is suggested that DSC could be one of the helpful methods to determine the
guest/host ratio and the heat of decomposition. Meanwhile, the guest/host ratio
and heat of deformation are obtained, which are 1.17 and 5361.53 J/mol,
respectively. It is suggested AN molecules included in urea canal lattice may
be packed flat against each other. It is found that the formation of AN/UIC
depends on the aging time. XRD results reveal that once AN molecules enter urea
lattice, AN/UIC are formed, which possess the final structure. When AN
molecules are sufficient, the length of AN molecular arrays in urea canals
increases as aging time prolonging until urea tunnels are saturated by AN.",1210.2517v3
2012-10-20,A review on carbon-rich molecules in space,"We present and discuss carbon-rich compounds of astrochemical interest such
as polyynes, acetylenic carbon chains and the related derivative known as
monocyanopolyynes and dicyanopolyynes. Fullerenes are now known to be abundant
in space, while fulleranes - the hydrogenated fullerenes - and other
carbon-rich compounds such as very large polycyclic aromatic hydrocarbons
(VLPAHs) and heavy petroleum fractions are suspected to be present in space. We
review the synthesis, the infrared spectra as well as the electronic absorption
spectra of these four classes of carbon-rich molecules. The existence or
possible existence in space of the latter molecules is reported and discussed.",1210.5593v1
2012-10-30,Donor and acceptor levels of organic photovoltaic compounds from first principles,"Accurate and efficient approaches to predict the optical properties of
organic semiconducting compounds could accelerate the search for efficient
organic photovoltaic materials. Nevertheless, predicting the optical properties
of organic semiconductors has been plagued by the inaccuracy or computational
cost of conventional first-principles calculations. In this work, we
demonstrate that orbital-dependent density-functional theory based upon
Koopmans' condition [Phys. Rev. B 82, 115121 (2010)] is apt at describing donor
and acceptor levels for a wide variety of organic molecules, clusters, and
oligomers within a few tenths of an electron-volt relative to experiment, which
is comparable to the predictive performance of many-body perturbation theory
methods at a fraction of the computational cost.",1210.7973v3
2012-11-02,A unified model of droplet epitaxy for compound semiconductor nanostructures: experiments and theory,"We present a unified model of compound semiconductor growth based on kinetic
Monte Carlo simulations in tandem with new experimental results that can
describe and predict the mechanisms for the formation of various types of
nanostructures observed during droplet epitaxy. The crucial features of the
model include the explicit and independent representation of atoms with
different species and the ability to treat solid and liquid phases
independently. Using this model, we examine nanostructural evolution in droplet
epitaxy. The model faithfully captures several of the experimentally observed
structures, including compact islands and nanorings. Moreover, simulations show
the presence of Ga/GaAs core-shell structures that we validate experimentally.
A fully analytical model of droplet epitaxy that explains the relationship
between growth conditions and the resulting nanostructures is presented,
yielding key insight into the mechanisms of droplet epitaxy.",1211.0486v4
2012-11-07,"Microscopic properties of the ""pinwheel"" kagome compound Rb_2Cu_3SnF_{12}","Using $^{63,65}$Cu nuclear magnetic resonance (NMR) in magnetic fields up to
30 T we study the microscopic properties of the 12-site valence-bond-solid
ground state in the ""pinwheel"" kagome compound Rb$_2$Cu$_3$SnF$_{12}$. We find
that the ground state is characterized by a strong transverse staggered spin
polarization whose temperature and field dependence points to a mixing of the
singlet and triplet states. This is further corroborated by the field
dependence of the gap $\Delta (H)$, which has a level anticrossing with a large
minimum gap value of $\approx \Delta (0)/2$, with no evidence of a phase
transition down to 1.5\,K. By the exact diagonalization of small clusters, we
show that the observed anticrossing is mainly due to staggered tilts of the
$g$-tensors defined by the crystal structure, and reveal symmetry properties of
the low-energy excitation spectrum compatible with the absence of level
crossing.",1211.1443v3
2012-11-18,Superconducting parameters of BaPt(4-x)Au(x)Ge12 filled skutterudite,"We report on a study of the superconducting properties for a series of
polycrystalline BaPt(4-x)Au(x)Ge12 filled skutterudite compounds for x = 0,
0.5, 0.75, and 1. Muon spin rotation (muSR) spectroscopy as well as
magnetization, specific heat, and electrical resistivity measurements were
performed. The magnetic penetration depth \lambda, the coherence length \xi,
and the Ginzburg-Landau parameter \kappa are evaluated. The temperature
dependence of the superfluid density is well described by an s-wave
superconducting gap and this classical scenario is supported by the
field-independent \lambda. The gap-to-Tc ratio \Delta/kTc increases with the Au
content from 1.70 for x = 0 to 2.1(1) for x = 1. By combining muSR,
magnetization, and specific heat data, we find that BaPt(4-x)Au(x)Ge12
compounds are in between the dirty and clean limits with mean free paths of the
carriers l ~ \xi. Interestingly, resistivity data for BaPt4Ge12 indicate a much
higher upper critical field, which is probably due to defects or impurities
close to the surface of the crystallites.",1211.4222v2
2012-11-20,Bond Randomness Induced Magnon Decoherence in a Spin-1/2 Ladder Compound,"We have used a combination of neutron resonant spin-echo and triple-axis
spectroscopies to determine the energy and linewidth of the magnon resonance in
IPA-Cu(Cl$_{0.95}$Br$_{0.05}$)$_3$, a model spin-1/2 ladder antiferromagnet
where Br substitution induces bond randomness. We find that the bond defects
induce a blueshift, $\delta \Delta$, and broadening, $\delta \Gamma$, of the
magnon gap excitation compared to the pure compound. At temperatures exceeding
the energy scale of the inter-ladder exchange interactions, $\delta \Delta$ and
$\delta \Gamma$ are temperature independent within the experimental error, in
agreement with Matthiessen's rule according to which magnon-defect scattering
yields a temperature independent contribution to the magnon mean free path.
Upon cooling, $\delta \Delta$ and $\delta \Gamma$ become temperature dependent
and saturate at values lower than those observed at higher temperature,
consistent with the crossover from one-dimensional to two-dimensional spin
correlations with decreasing temperature previously observed in pure
IPA-CuCl$_3$. These results indicate limitations in the applicability of
Matthiessen's rule for magnon scattering in low-dimensional magnets.",1211.4741v1
2012-11-23,Pairing Symmetry in Layered BiS$_2$ Compounds Driven by Electron-Electron Correlation,"We investigate the pairing symmetry of layered BiS$_2$ compounds by assuming
that electron-electron correlation is still important so that the pairing is
rather short range. We find that the extended s-wave pairing symmetry always
wins over d-wave when the pairing is confined between two short range sites up
to next nearest neighbors. The pairing strength is peaked around the doping
level x=0.5, which is consistent with experimental observation. The extended
s-wave pairing symmetry is very robust against spin-orbital coupling because it
is mainly determined by the structure of Fermi surfaces. Moreover, the extended
s-wave pairing can be distinguished from conventional s-wave pairing by
measuring and comparing superconducting gaps of different Fermi surfaces.",1211.5435v2
2012-12-05,About the tolerance factor for pyrochlores and related structures,"In this work a new empirical tolerance factor for compounds with pyrochlore
structure is proposed. This suggested tolerance factor is based on experimental
structural data and on the tolerance factors currently proposed. However, since
it does not depend on the structural data, this new tolerance factor permits
the prediction of some properties of these compounds directly. Also, a good
structure stability field for the pyrochlore formation is observed when this
tolerance factor is used.",1212.0908v3
2012-12-18,Magnetoelasticity in ACr2O4 spinel oxides,"Dynamical properties of the lattice structure was studied by optical
spectroscopy in ACr2O4 chromium spinel oxide magnetic semiconductors over a
broad temperature region of T=10-335K. The systematic change of the A-site ions
(A=Mn, Fe, Co, Ni and Cu) showed that the occupancy of 3d orbitals on the
A-site, has strong impact on the lattice dynamics. For compounds with orbital
degeneracy (FeCr2O4, NiCr2O4 and CuCr2O4), clear splitting of infrared-active
phonon modes and/or activation of silent vibrational modes have been observed
upon the Jahn-Teller transition and at the onset of the subsequent long-range
magnetic order. Although MnCr2O4 and CoCr2O4 show multiferroic and
magnetoelectric character, no considerable magnetoelasticity was found in
spinel compounds without orbital degeneracy as they closely preserve the
high-temperature cubic spinel structure even in their magnetic ground state.
Besides lattice vibrations, intra-atomic 3d-3d transitions of the A$^{2+}$ ions
were also investigated to determine the crystal field and Racah parameters and
the strength of the spin-orbit coupling.",1212.4301v1
2012-12-18,Direct observation of low energy nuclear spin excitations in HoCrO$_3$ by high resolution neutron spectroscopy,"We have investigated low energy nuclear spin excitations in strongly
correlated electron compound HoCrO$_3$. We observe clear inelastic peaks at $E
= 22.18 \pm 0.04$ $\mu eV$ in both energy loss and gain sides. The energy of
the inelastic peaks remains constant in the temperature range 1.5 - 40 K at
which they are observed. The intensity of the inelastic peak increases at first
with increasing temperature and then decreases at higher temperatures. The
temperature dependence of the energy and intensity of the inelastic peaks is
very unusual compared to that observed in other Nd, Co and V compounds. Huge
quasielastic scattering appears at higher temperatures presumably due to the
fluctuating electronic moments of the Ho ions that get increasingly disordered
at higher temperatures.",1212.4338v1
2012-12-19,Spontaneous atomic ordering and magnetism in epitaxially stabilized double perovskites,"We have studied the atomic ordering of B-site transition metals and magnetic
properties in the pulsed-laser deposited films of La2CrFeO6 (LCFO) and La2VMnO6
(LVMO), whose bulk materials are known to be single perovskites with random
distribution of the B-site cations. Despite similar ionic characters of
constituent transition metals in each compound, the maximum B-site order
attained was surprisingly high, ~90% for LCFO and ~80% for LVMO, suggesting a
significant role of epitaxial stabilization in the spontaneous ordering
process. Magnetization and valence state characterizations revealed that the
magnetic ground state of both compounds was coincidently ferrimagnetic with
saturation magnetization of ~2myuB per formula unit, unlike those predicted
theoretically. In addition, they were found to be insulating with optical band
gaps of 1.6 eV and 0.9 eV for LCFO and LVMO, respectively. Our results present
a wide opportunity to explore novel magnetic properties of binary
transition-metal perovskites upon epitaxial stabilization of the ordered phase.",1212.4622v1
2012-12-21,Exponentiated Weibull Power Series Distributions and its Applications,"In this paper we introduce the exponentiated Weibull power series (EWPS)
class of distributions which is obtained by compounding exponentiated Weibull
and power series distributions, where the compounding procedure follows same
way that was previously carried out by Roman et al. (2010) and Cancho et al.
(2011) in introducing the complementary exponential-geometric (CEG) and the
two-parameter Poisson-exponential (PE) lifetime distributions, respectively.
This distribution contains several lifetime models such as: exponentiated
weibull-geometric (EWG), exponentiated weibull-binomial (EWB), exponentiated
weibull-poisson (EWP), exponentiated weibull-logarithmic (EWL) distributions as
a special case.
  The hazard rate function of the EWPS distribution can be increasing,
decreasing, bathtub-shaped and unimodal failure rate among others. We obtain
several properties of the EWPS distribution such as its probability density
function, its reliability and failure rate functions, quantiles and moments.
The maximum likelihood estimation procedure via a EM-algorithm is presented in
this paper. Sub-models of the EWPS distribution are studied in details. In the
end, Applications to two real data sets are given to show the flexibility and
potentiality of the EWPS distribution.",1212.5613v1
2012-12-31,Low-energy magnetic excitations in the quasi-one-dimensional spin-1 chain compound SrNi2V2O8,"Multi-frequency electron spin resonance (ESR) transmission spectra have been
measured as function of temperature and magnetic field on single crystals of
the quasi-one-dimensional spin-1 chain compound SrNi2V2O8 in the GHz frequency
range. Magnetic resonance modes above 50 K have been observed with an effective
g-factor of 2.24 at 100 K. Below 30 K, intra-triplet excitations have been
observed in the ESR spectra, which reveal the presence of single-ion anisotropy
with D = -0.29 meV.",1212.6859v2
2013-01-15,Low temperature high magnetic field $^{57}Fe$ M$\ddot{o}$ssbauer study of kinetic arrest in $Hf_{0.77}Ta_{0.23}Fe_2$,"Low temperature high magnetic field $^{57}Fe$ M$\ddot{o}$ssbauer measurements
were carried out on inter-metallic $Hf_{0.77}Ta_{0.23}Fe_2$ compound by
following novel paths in H-T space. The ferromagnetic (FM) fraction at 5K and
zero magnetic field is shown to depend on cooling field i.e., higher the field
higher is the FM fraction. M$\ddot{o}$ssbauer spectra collected in the presence
of 4 Tesla magnetic field shows that the antiferromagnetic (AFM) spins cant
with respect to the applied magnetic field and hence, contribute to the total
bulk magnetization in this compound. The data also show induced magnetic moment
even at the 2a site of AFM phase. M$\ddot{o}$ssbauer spectra collected using
CHUF (cooling and heating in un-equal magnetic fields) protocol shows
re-entrant transition when sample is cooled in zero field and measured during
warming in 4 Tesla showing FM state as the equilibrium state. The present work
is the first microscopic experimental evidence for the de-vitrification of
kinetically arrested magnetic state.",1301.3313v1
2013-01-16,Point-contact spectroscopy in Co-doped CaFe2As2: nodal superconductivity and topological Fermi surface transition,"We performed point-contact Andreev reflection spectroscopy measurements in
Ca(Fe_{1-x}Co_x)2As2 single crystals with effective x=0.060 +- 0.005. The
spectra of ab-plane contacts show a zero-bias maximum and broad shoulders at
about 5-6 meV. Their fit with the three-dimensional Blonder-Tinkham-Klapwijk
model (making use of a analytical expression for the Fermi surface that mimics
the one calculated from first principles) shows that this compound presents a
large isotropic gap on the quasi-2D electronlike Fermi surface sheets and a
smaller anisotropic (possibly nodal) gap on the 3D holelike Fermi surface
pockets centered at the Z point in the Brillouin zone. These results nicely fit
into the theoretical picture for the appearance of nodal superconductivity in
122 compounds.",1301.3719v1
2013-01-22,Different roles of Zn$^{2+}$ and Li$^{+}$ impurities in the CuO$_2$ plane in undoped cuprate compounds,"A planar Mott insulator with easy plane N\'eel order can be mapped onto a
Gutzwiller-projected spin Hall state. The in-plane substitution of Zn$^{2+}$
and Li$^{+}$ for Cu$^{2+}$ brings zero modes around the spin vacancy. The
Gutzwiller projection precludes single particle excitations, however, preserves
the zero modes which have a local spin moment for Zn$^{2+}$ and a local charged
hole for Li$^{+}$, respectively. While the local spin moment for Zn$^{2+}$ is
screened by the long-range spin correlations, the active charge degree of
freedom for Li$^{+}$ impurity twists the spin background with long ranged
disturbances. This proposal explains the very different roles of the Zn$^{2+}$
and Li$^{+}$ impurities on the magnetic perturbations in the CuO$_2$ plane in
the undoped cuprate compounds.",1301.5208v1
2013-01-25,Change in the order of magnetic transition in HoRhGe as probed by magnetoresistance and magnetocaloric studies,"Magnetoresistance and magnetocaloric properties of polycrystalline HoRhGe
have been studied. This compound orders antiferromagnetically with a Neel
temperature (TN) of 5.5 K and undergoes a first order metamagnetic transition
at 2 K. It shows a large negative magnetoresistance of 25% at TN, for a field
of 50 kOe. However, at 2 K and in lower fields, the magnetoresistance is found
to be positive with a magnitude of about 12%, which is attributed to the first
order metamagnetic transition. The compound also shows large magnetocaloric
effect near its Neel temperature. Field dependence of magnetic entropy change
also reflects the change in the nature of magnetic transition as the field is
increased. The value of magnetic entropy change (-{\Delta}SM) is found to be
11.1 J/kg K for a field change of 50 kOe. Field dependence of magnetoresistance
and magnetocaloric effect clearly shows the change in the order of the
metamagnetic transition with increase in field.",1301.6034v1
2013-01-29,Combinatorial approaches to Hopf bifurcations in systems of interacting elements,"We describe combinatorial approaches to the question of whether families of
real matrices admit pairs of nonreal eigenvalues passing through the imaginary
axis. When the matrices arise as Jacobian matrices in the study of dynamical
systems, these conditions provide necessary conditions for Hopf bifurcations to
occur in parameterised families of such systems. The techniques depend on the
spectral properties of additive compound matrices: in particular, we associate
with a product of matrices a signed, labelled digraph termed a DSR^[2] graph,
which encodes information about the second additive compound of this product. A
condition on the cycle structure of this digraph is shown to rule out the
possibility of nonreal eigenvalues with positive real part. The techniques
developed are applied to systems of interacting elements termed ""interaction
networks"", of which networks of chemical reactions are a special case.",1301.7076v4
2013-01-30,Rational material design of mixed-valent high T$_c$ superconductors,"We design, from first principles calculations, a novel family of thallium
halide-based compounds as candidates for new high temperature superconductors,
whose superconductivity is mediated by the recently proposed mechanism of
non-local correlation-enhanced strong electron-phonon coupling. Two prototype
compounds namely CsTlF$_3$ and CsTlCl$_3$ are studied with various hole doping
levels and volumes. The critical superconducting temperature T$_c$ are
predicted to be about 30 K and 20 K with $\sim$0.35/f.u. hole doping and
require only modest pressures ($\sim$10 and $\sim$2 GPa), respectively. Our
procedure of designing this class of superconductors is quite general and can
be used to search for other ""other high temperature superconductors"".",1301.7477v1
2013-01-31,Bounds on variable-length compound jumps,"In Euclidean space there is a trivial upper bound on the maximum length of a
compound ""walk"" built up of variable-length jumps, and a considerably less
trivial lower bound on its minimum length. The existence of this non-trivial
lower bound is intimately connected to the triangle inequalities, and the more
general ""polygon inequalities"". Moving beyond Euclidean space, when a modified
version of these bounds is applied in ""rapidity space"" they provide upper and
lower bounds on the relativistic composition of velocities. Similarly, when
applied to ""transfer matrices"" these bounds place constraints either (in a
scattering context) on transmission and reflection coefficients, or (in a
parametric excitation context) on particle production. Physically these are
very different contexts, but mathematically there are intimate relations
between these superficially very distinct systems.",1301.7524v2
2013-02-11,Coherent Raman spectro-imaging with laser frequency combs,"Optical spectroscopy and imaging of microscopic samples have opened up a wide
range of applications throughout the physical, chemical, and biological
sciences. High chemical specificity may be achieved by directly interrogating
the fundamental or low-lying vibrational energy levels of the compound
molecules. Amongst the available prevailing label-free techniques, coherent
Raman scattering has the distinguishing features of high spatial resolution
down to 200 nm and three-dimensional sectioning. However, combining fast
imaging speed and identification of multiple - and possibly unexpected-
compounds remains challenging: existing high spectral resolution schemes
require long measurement times to achieve broad spectral spans. Here we
overcome this difficulty and introduce a novel concept of coherent anti-Stokes
Raman scattering (CARS) spectro-imaging with two laser frequency combs. We
illustrate the power of our technique with high resolution (4 cm-1) Raman
spectra spanning more than 1200 cm-1 recorded within less than 15 microseconds.
Furthermore, hyperspectral images combining high spectral (10 cm-1) and spatial
(2 micrometers) resolutions are acquired at a rate of 50 pixels per second.
Real-time multiplex accessing of hyperspectral images may dramatically expand
the range of applications of nonlinear microscopy.",1302.2414v1
2013-02-13,Magnetism and Verwey transition in magnetite nanoparticles in thin polymer film,"Magnetic and structural properties of magnetite nanoparticles stabilized in
polyvinyl-alcohol thin films are investigated by using X-ray diffraction (XRD),
transmission electron microscopy (TEM), electron paramagnetic resonance (EPR)
and static magnetometry techniques. The nanoparticles have well-defined
crystallinity, and are superparamagnetic at room temperature. Their size
distribution is characterized by the distinct log-normal law (with average
diameters near 5-7 nm) and slight maximum near 70-80 nm. The EPR spectra and
static magnetization data demonstrated pronounced anomalies in the interval
between 130 K (corresponding to Verwey transition) and 200 K. The experimental
data obtained can be understood on the basis of the half-metallic electronic
structure, complex temperature behavior of the magnetic anisotropy, along with
effects of ""weak magnetic-electron"" sublattice of magnetite.",1302.3090v1
2013-02-15,Spin-flop and antiferromagnetic phases of the ferromagnetic half-twist ladder compounds Ba3Cu3In4O12 and Ba3Cu3Sc4O12,"The title compounds have dominant ferromagnetic (FM) exchange interactions
within one-dimensional (1D) half-twist ladders of s =1/2 Cu2^{+} ions and
antiferromagnetic(AFM) interactions between ladders, leading to ordered 3D
phases at temperatures below 20K. Here we show that a microscopic 1D model of
the paramagnetic (PM) phase combined with a phenomenological model based on
sublattice magnetization describes the observed temperature and field dependent
magnetism. The model identifies AFM, spin-flop (SF) and PM phases whose
boundaries have sharp features in the experimental magnetization M(T,H) and
specific heat CP(T,H). Exact diagonalization (ED) of the 1D model, possible for
24 spins due to special structural features of half-twist ladders, yields the
magnetization and spin susceptibility of the PM phase. AFM interactions between
ladders are included at the mean-field level using the field, HAF, obtained
from modeling the ordered phases. Isotropic exchange J1 = -135K and g-tensor g
= 2.1 within ladders, plus exchange and anisotropy fields HAF and HA, describe
the ordered phases, and are almost quantitative for the PM phase.",1302.3701v1
2013-02-16,Coordination Control of Heterogeneous Compounded-Order Multi-Agent Systems with Communication Delays,"Since the complexity of the practical environment, many distributed networked
systems can not be illustrated with the integer-order dynamics and only be
described as the fractional-order dynamics. Suppose multi-agent systems will
show the individual diversity with difference agents, where the heterogeneous
(integer-order and fractional-order) dynamics are used to illustrate the agent
systems and compose integer-fractional compounded-order systems. Applying
Laplace transform and frequency domain theory of the fractional-order operator,
consensus of delayed multi-agent systems with directed weighted topologies is
studied. Since integer-order model is the special case of fractional-order
model, the results in this paper can be extend to the systems with
integer-order models. Finally, numerical examples are used to verify our
results.",1302.3969v1
2013-02-25,Anisotropic Monopole Heat Transport in the Spin-Ice Compound Dy$_2$Ti$_2$O$_7$,"We report a study of the thermal conductivity $\kappa$ of the spin-ice
material Dy$_2$Ti$_2$O$_7$. From the anisotropic magnetic-field dependence of
\kappa$ and by additional measurements on the phononic reference compounds
Y$_2$Ti$_2$O$_7$ and DyYTi$_2$O$_7$, we are able to separate the phononic and
the magnetic contributions to the total heat transport, i.e. $\kappa_{ph}$ and
$\kappa_{mag}$, respectively, which both depend on the magnetic field. The
field dependent $\kappa_{ph}$ arises from lattice distortions due to
magnetic-field induced torques on the non-collinear magnetic moments of the Dy
ions. For $\kappa_{mag}$, we observe a highly anisotropic magnetic-field
dependence, which correlates with the corresponding magnetization data
reflecting the different magnetic-field induced spin-ice ground states. The
magnitude of $\kappa_{mag}$ increases with the degree of the ground-state
degeneracy. This anisotropic field dependence as well as various hysteresis
effects suggest that $\kappa_{mag}$ is essentially determined by the mobility
of the magnetic monopole excitations in spin ice.",1302.6114v1
2013-02-26,An irreversible magnetic-field dependence of low-temperature heat transport of spin-ice compound Dy_2Ti_2O_7 in a [111] field,"We study the low-temperature thermal conductivity (\kappa) of Dy_2Ti_2O_7
along and perpendicular to the (111) plane and under the magnetic field along
the [111] direction. Besides the step-like decreases of \kappa at the
field-induced transitions from the spin-ice state to the kagom\'e-ice state and
then to the polarized state, an abnormal phenomenon is that the \kappa(H)
isotherms show a clear irreversibility at very low temperatures upon sweeping
magnetic field up and down. This phenomenon surprisingly has no correspondence
with the well-known magnetization hysteresis. Possible origins for this
irreversibility are discussed; in particular, a pinning effect of magnetic
monopoles in spin ice compound by the weak disorders is proposed.",1302.6353v1
2013-03-03,The superconducting state in the B2H6 compound at 360 GPa,"In the paper, the thermodynamic properties of the superconducting state in
the $\rm{B_{2}H_{6}}$ compound have been characterized. The pressure of 360 GPa
has been taken into account. The calculations have been carried out in the
framework of the Eliashberg formalism for the wide range of the Coulomb
pseudopotential: $\mu^{\star}\in<0.1,0.3>$. It has been found that the critical
temperature ($T_{C}$) varies in the range from 147 K to 87 K, depending on the
assumed value of the Coulomb pseudopotential. The ratio of the energy gap to
the critical temperature ($R_{\Delta}\equiv 2\Delta(0)/k_{B}T_{C}$)
significantly exceeds the value predicted by the BCS theory:
$R_{\Delta}\in<4.24,3.98>$. In the similar manner behaves the ratio of the
specific heat jump to the heat of the normal state ($R_{C}\equiv\Delta
C(T_{C})/C^{N}(T_{C})$), namely: $R_{C}\in<2.33,2.17>$. The parameter
$R_{H}\equiv T_{C}C^{N}(T_{C})/H^{2}_{C}(0)$, where $H_{C}(0)$ is the
thermodynamic critical field, ranges from 0.144 to 0.168.",1303.0500v1
2013-03-04,Temperature-dependent optical conductivity of layered LaSrFeO_4,"Compounds with intermediate-size transition metals such as Fe or Mn are close
to the transition between charge-transfer systems and Mott-Hubbard systems. We
study the optical conductivity \sigma(\omega) of insulating layered LaSrFeO_4
in the energy range 0.5 - 5.5 eV from 15 K to 250 K by the use of spectroscopic
ellipsometry in combination with transmittance measurements. A multipeak
structure is observed in both \sigma^a(\omega) and \sigma^c(\omega). The
layered structure gives rise to a pronounced anisotropy, thereby offering a
means to disentangle Mott-Hubbard and charge-transfer absorption bands. We find
strong evidence that the lowest dipole-allowed excitation in LaSrFeO_4 is of
Mott-Hubbard type. This rather unexpected result can be attributed to Fe 3d - O
2p hybridization and in particular to the layered structure with the associated
splitting of the e_g level. In general, Mott-Hubbard absorption bands may show
a strong dependence on temperature. This is not the case in LaSrFeO_4, in
agreement with the fact that spin-spin and orbital-orbital correlations between
nearest neighbors do not vary strongly below room temperature in this compound
with a high-spin 3d^5 configuration and a Neel temperature of T_N = 366 K.",1303.0709v1
2013-03-05,A spin ladder compound doubles its superconducting TC under a gentle uniaxial pressure,"Discovery of new high TC superconductors, with TC > 23 K, continues to be
challenging. We have doubled the existing TC of single crystal Sr3Ca11Cu24O41,
a spin ladder cuprate, from 12K to 24K, using a gentle uniaxial pressure ~ 0.06
GPa. In contrast, earlier works used a nearly 100 times larger hydrostatic
pressure 5 GPa, only to reach a maximum TC ~ 12K. Our work exposes large and
nearly equal, but opposing contributions to changes in TC, arising from
compressions along and perpendicular to ladder planes, in hydrostatic pressure
experiments. In our resistivity measurements, uniaxial pressure applied along
ladder planes increase TC, while that perpendicular to ladder planes decrease
TC. Our findings i) offers a new hope for further increase in TC in spin ladder
compounds and ii) calls for a large shift in phase boundaries of the currently
accepted pressure-temperature phase diagram.",1303.0921v1
2013-03-07,Complex Magnetic Phase Diagram of a Geometrically Frustrated Sm Lattice: SmPd2Al3 case,"Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry
and neutron diffraction. SmPd2Al3 represents a distinctive example of the Sm
magnetism exhibiting complex magnetic behavior at low temperatures with four
consecutive magnetic phase transitions at 3.4, 3.9, 4.3 and 12.5 K. The rich
magnetic phase diagram of this compound reflects the specific features of the
Sm3+ ion, namely the energy nearness of the ground-state multiplet J = 5/2 and
the first excited multiplet J = 7/2 in conjunction with strong crystal field
influence. Consequently, a significantly reduced Sm magnetic moment in
comparison with the theoretical Sm3+ free-ion value is observed. Despite the
strong neutron absorption by natural samarium and the small Sm magnetic moment
(~ 0.2 {\mu}B) we have successfully determined the magnetic k-vector (1/3, 1/3,
0) of the phase existing in the temperature interval 12.5 - 4.3 K. This
observation classifies the SmPd2Al3 compound as a magnetically frustrated
system. The complex magnetic behavior of this material is further illustrated
by kinetic effects of the magnetization inducing rather complicated magnetic
structure with various metastable states.",1303.1607v1
2013-03-07,Longitudinal magnetoresistance in Co-doped BaFe2As2 and LiFeAs single crystals: Interplay between spin fluctuations and charge transport in iron-pnictides,"The longitudinal in-plane magnetoresistance (LMR) has been measured in
different Ba(Fe_(1-x)Co_x)2As2 single crystals and in LiFeAs. For all these
compounds, we find a negative LMR in the paramagnetic phase whose magnitude
increases as H^2. We show that this negative LMR can be readily explained in
terms of suppression of the spin fluctuations by the magnetic field. In the
Co-doped samples, the absolute value of the LMR coefficient is found to
decrease with doping content in the paramagnetic phase. The analysis of its T
dependence in an itinerant nearly antiferromagnetic Fermi liquid model
evidences that the LMR displays a qualitative change of T variation with
increasing Co content. The latter occurs at optimal doping for which the
antiferromagnetic ground state is suppressed. The same type of analysis for the
negative LMR measured in LiFeAs suggests that this compound is on the verge of
magnetism.",1303.1677v2
2013-03-14,Comparing the distribution of the electronic gap of an organic molecule with its photoluminescence spectrum,"The electronic gap structure the organic molecule
N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine, or TPD,
has been studied by means of a Scanning Tunneling Microscope (STM) operated
under ambient conditions, and by Photoluminescence (PL) analysis. Thousands of
current-voltage characteristics have been measured at different spots of the
sample showing the typical behavior of a semiconductor. The analysis of the
curves allows us to construct a gap distribution histogram which reassembles
the PL spectrum of this compound. Our analysis shows that in the TPD films most
of the observed distribution of the gap comes mainly from an uncertainty in the
position of the LUMO levels of the molecular compound as would be expected from
theory. This analysis demonstrates that STM can give relevant information, not
only related to the expected value of a semiconductor gap, but also on its
distribution which affects its physical properties such as the case of the PL
and absorption distributions as here is reported.",1303.3640v1
2013-03-17,Two-dimensional magnetic interactions in LaFeAsO,"Inelastic neutron scattering measurements demonstrate that the magnetic
interactions in antiferromagnetic LaFeAsO are two-dimensional. Spin wave
velocities within the Fe layer and the magnitude of the spin gap are similar to
the \textit{A}Fe$_2$As$_2$ based materials. However, the ratio of interlayer
and intralayer exchange is found to be less than $\sim 10^{-4}$ in LaFeAsO,
very similar to the cuprates, and $\sim$ 100 times smaller than that found in
\textit{A}Fe$_2$As$_2$ compounds. The results suggest that the effective
dimensionality of the magnetic system is highly variable in the parent
compounds of the iron arsenides and weak 3-D interactions may limit the maximum
attainable superconducting $T_{c}$.",1303.4033v1
2013-03-19,Electronic structure of relativistic Mott insulator Li$_2$RhO$_3$,"Motivated by studies of coexisting electron correlation and spin-orbit
coupling effect in Na$_2$IrO$_3$ and a recent experiment of its 4d analogue
Li$_2$RhO$_3$, we performed first-principles calculations of the rhodium oxide
compound. The experimentally observed ground state of Li$_2$RhO$_3$ can be
recovered only if both spin-orbit coupling and on-site Coulomb interaction are
taken into consideration. Within the proper $U$ range for 4d-orbitals
($2\leqslant U\leqslant 4$ eV), the ground state of Li$_2$RhO$_3$ could be
either zigzag-AFM or stripy-AFM, both yielding energy gap close to experimental
observation. Furthermore, the total energy differences between the competing
magnetic phases are $\leqslant 3$ meV/Rh within $2\leqslant U\leqslant 4$ eV,
manifesting strong magnetic frustration in the compound. Finally, the phase
energy of Li$_2$RhO$_3$ cannot be fitted with the two-dimensional
Heisenberg-Kitaev model involving only the nearest neighbor interactions, and
we propose that inter-layer interactions may be responsible for the
discrepancy.",1303.4675v1
2013-03-20,Challenging the nature of low energy plasmon excitations in CaC$_6$ using electron energy-loss spectroscopy,"The nature of low energy plasmon excitations plays an important role in
understanding the low energy electronic properties and coupling mechanism of
different superconducting compounds such as CaC$_6$. Recent ab-initio studies
predict a charge carrier intraband plasmon in keeping with a low energy
acoustic plasmon. Here, we have studied the low-energy electronic excitations
of CaC$_6$ using high-resolution electron energy-loss spectroscopy in
transmission at low temperatures. The analysis of the core-level excitations
leads to the conclusion that hybridization between graphite and calcium states
plays an essential role in this graphite intercalated compound. Regarding the
low energy plasmon excitation, we observe the formation of an intraband (charge
carrier) plasmon with a negative dispersion at about 3.5 eV in sound agreement
with the theory. Finally, a weak excitation around 1.2 eV with an almost linear
dispersion relation can be observed as predicted for an acoustic plasmon that
may mediate the superconducting coupling in CaC$_6$. However its optical limit
at ~1 eV challenges the theoretical predictions and safely rules out an
electronic superconducting coupling mechanism in CaC$_6$.",1303.4889v1
2013-03-25,"Superconductivity induced by electron doping in the system La1-xMxOBiS2 (M = Ti, Zr, Hf, Th)","We report a strategy to induce superconductivity in the BiS$_2$-based
compound LaOBiS$_2$. Instead of substituting F for O, we increase the
charge-carrier density (electron dope) via substitution of tetravalent
Th$^{+4}$, Hf$^{+4}$, Zr$^{+4}$, and Ti$^{+4}$ for trivalent La$^{+3}$. It is
found that both the LaOBiS$_2$ and ThOBiS$_2$ parent compounds are bad metals
and that superconductivity is induced by electron doping with \emph{T$_c$}
values of up to 2.85 K. The superconducting and normal states were
characterized by electrical resistivity, magnetic susceptibility, and heat
capacity measurements. We also demonstrate that reducing the charge-carrier
density (hole doping) via substitution of divalent Sr$^{+2}$ for La$^{+3}$ does
not induce superconductivity.",1303.6216v1
2013-03-29,Electronic structures of III-V zinc-blende semiconductors from atomistic first principles,"For analyzing quantum transport in semiconductor devices, accurate electronic
structures are critical for quantitative predictions. Here we report
theoretical analysis of electronic structures of all III-V zinc-blende
semiconductor compounds. Our calculations are from density functional theory
with the semi-local exchange proposed recently [F. Tran and P. Blaha, Phys.
Rev. Lett. 102, 226401 (2009)], within the linear muffin tin orbital scheme.
The calculated band gaps and effective masses are compared to experimental data
and good quantitative agreement is obtained. Using the theoretical scheme
presented here, quantum transport in nanostructures of III-V compounds can be
confidently predicted.",1303.7419v1
2013-04-22,Low Hole Effective Mass p-type Transparent Conducting Oxides: Identification and Design Principles,"The development of high performance transparent conducting oxides (TCOs) is
critical to many technologies from transparent electronics to solar cells.
While n-type TCOs are present in many devices, current p-type TCOs are not
largely commercialized as they exhibit much lower carrier mobilities, due to
the large hole effective masses of most oxides. Here, we conduct a
high-throughput computational search on thousands of binary and ternary oxides
and identify several highly promising compounds displaying exceptionally low
hole effective masses (up to an order of magnitude lower than state of the art
p-type TCOs) as well as wide band gaps. In addition to the discovery of
specific compounds, the chemical rationalization of our findings opens new
directions, beyond current Cu-based chemistries, for the design and development
of future p-type TCOs.",1304.6054v1
2013-04-26,Strong magnon softening in tetragonal FeCo compounds,"Magnons play an important role in fast precessional magnetization reversal
processes serving as a heat bath for dissipation of the Zeeman energy and thus
being responsible for the relaxation of magnetization. Employing \emph{ab
initio} many-body perturbation theory we studied the magnon spectra of the
tetragonal FeCo compounds considering three different experimental $c/a$
ratios, $c/a=$1.13, 1.18, and 1.24 corresponding to FeCo grown on Pd, Ir, and
Rh, respectively. We find that for all three cases the short-wave-length
magnons are strongly damped and tetragonal distortion gives rise to a
significant magnon softening. The magnon stiffness constant $D$ decreases
almost by a factor of two from FeCo/Pd to FeCo/Rh. The combination of soft
magnons together with the giant magnetic anisotropy energy suggests FeCo/Rh to
be a promising material for perpendicular magnetic recording applications.",1304.7091v1
2013-05-08,Angle-Resolved Photoemission Spectroscopy Study of BaCo2As2,"We use angle-resolved photoemission spectroscopy and full-potential
linearized augmented-plane-wave (FP-LAPW) calculations to study the electronic
structure of BaCo2As2. The Fermi surface (FS) maps and the corresponding band
dispersion data (at 90 K and 200 K) reveal a small electron pocket at the
center and a large electron pocket at the corner of the Brillouin zone.
Therefore the nesting between electron and hole FS pockets is absent in this
compound, in contrast to the parent compounds of FeAs-based high-T_c
superconductors. The electronic structure at about 500 meV binding energy is
very similar to features at the chemical potential in BaFe2As2. This indicates
that complete substitution of Co for Fe causes a nearly rigid shift in the
Fermi energy by adding two electrons per formula unit without significant
changes in the band dispersions. The experimental FS topology as well as band
dispersion data are in reasonable agreement with the FP-LAPW calculations.",1305.1848v1
2013-05-15,Termination dependent topological surface states of the natural superlattice phase Bi$_4$Se$_3$,"We describe the topological surface states of Bi$_4$Se$_3$, a compound in the
infinitely adaptive Bi$_2$-Bi$_2$Se$_3$ natural superlattice phase series,
determined by a combination of experimental and theoretical methods. Two
observable cleavage surfaces, terminating at Bi or Se, are characterized by
angle resolved photoelectron spectroscopy and scanning tunneling microscopy,
and modeled by ab-initio density functional theory calculations. Topological
surface states are observed on both surfaces, but with markedly different
dispersions and Kramers point energies. Bi$_4$Se$_3$ therefore represents the
only known compound with different topological states on differently terminated
surfaces.",1305.3558v3
2013-05-16,An Upper Bound on the Capacity of Vector Dirty Paper with Unknown Spin and Stretch,"Dirty paper codes are a powerful tool for combating known interference.
However, there is a significant difference between knowing the transmitted
interference sequence and knowing the received interference sequence,
especially when the channel modifying the interference is uncertain. We present
an upper bound on the capacity of a compound vector dirty paper channel where
although an additive Gaussian sequence is known to the transmitter, the channel
matrix between the interferer and receiver is uncertain but known to lie within
a bounded set. Our bound is tighter than previous bounds in the low-SIR regime
for the scalar version of the compound dirty paper channel and employs a
construction that focuses on the relationship between the dimension of the
message-bearing signal and the dimension of the additive state sequence.
Additionally, a bound on the high-SNR behavior of the system is established.",1305.3934v1
2013-05-16,Vapor-liquid-solid growth of serrated GaN nanowires: Shape selection driven by kinetic frustration,"Compound semiconducting nanowires are promising building blocks for several
nanoelectronic devices yet the inability to reliably control their growth
morphology is a major challenge. Here, we report the Au-catalyzed
vapor-liquid-solid (VLS) growth of GaN nanowires with controlled growth
direction, surface polarity and surface roughness. We develop a theoretical
model that relates the growth form to the kinetic frustration induced by
variations in the V(N)/III(Ga) ratio across the growing nanowire front. The
model predictions are validated by the trends in the as-grown morphologies
induced by systematic variations in the catalyst particle size and processing
conditions. The principles of shape selection highlighted by our study pave the
way for morphological control of technologically relevant compound
semiconductor nanowires.",1305.3936v1
2013-05-17,"Comparative Study of Electronic structure of New Superconductors (Sr,Ca)Pd2As2 and related compound BaPd2As2","This paper presents the comparative study of LDA calculated electronic
structure of new isostructural to iron based systems superconductors
(Sr,Ca)Pd2As2 with Tc about 1K and similar but structurally different system
BaPd2As2. Despite chemical formula looks similar to iron superconductors and
even main structural motif is the same - layers of Fe square lattices,
electronic structure of (Sr,Ca)Pd2As2 and BaPd2As2 differs from Fe(As,Se)-HTSC
completely. All these systems have essentially three dimensional Fermi surfaces
in contrast to Fe(As,Se) materials. The Fermi level is crossed by low intensive
tails of Pd-4d and As-4p states. However (Sr,Ca)Pd2As2 and BaPd2As2 materials
have rather well developed peaks of Pd-4d(x2-y2) band. Thus by doping of about
2 holes per unit cell one can increase density of states at the Fermi level by
a factor about 2.5. Since experimentally these compounds were found to be
simple BCS superconductors the hole doping may considerably increase Tc. LDA
calculated total densities of states at the Fermi level for stoichiometric
systems perfectly agree with experimental estimates signifying rather small
role of electronic correlations.",1305.3979v1
2013-05-21,"Restoration of magnetization reversal under hydrostatic pressure in the lightly electron-doped manganite compound (Ca,Sr)Mn0.95Sb0.05O3","We report on the anomalous magnetization reversal under hydrostatic pressure
in the lightly electron-doped manganite compound
(Ca$_{1-x}$Sr$_{x}$)Mn$_{0.95}$Sb$_{0.05}$O$_{3}$ with its fixed carrier
content. In a weakly magnetic field cooled measurement, diamagnetic
magnetization is observed for $x\leq 15\%$, which changes to positive values
for $x>15\%$. However, on an application of pressure on the samples with
$x=16\%$ and 17$\%$, magnetization reverses sign and diamagnetism is restored.
We present a magnetic phase diagram as a function of Sr concentration, under
both ambient and hydrostatic pressures. To understand better the
thermodynamical properties of this system, we have measured the specific heat
as a function of temperature under a field cooling of 100 Oe. Our data show no
anomalies associated with the temperature dependent magnetization reversal,
indicating the absence of a long-rang magnetic ordering. The $ac$ magnetic
susceptibility measurement points to the existence of magnetic frustration for
the Sr substituted samples exhibiting diamagnetic behavior.",1305.4708v2
2013-05-29,Mechanochemical synthesis of pnictide compounds and superconducting Ba0.6K0.4Fe2As2 bulks with high critical current density,"BaFe2As2 (Ba-122) and (Ba0.6K0.4)Fe2As2 (K-doped Ba-122) powders were
successfully synthesized from the elements using a reaction method, which
incorporates a mechanochemical reaction using high-impact ball milling.
Mechanically-activated, self-sustaining reactions (MSR) were observed while
milling the elements together to form these compounds. After the MSR, the
Ba-122 phase had formed, the powder had an average grain size < 1 {\mu}m, and
the material was effectively mixed. X-ray diffraction confirmed Ba-122 was the
primary phase present after milling. Heat treatment of the K-doped MSR powder
at high temperature and pressure yielded dense samples with high phase purity
but only granular current flow could be visualized by magneto optical imaging.
In contrast, a short, low temperature, heat treatment at ambient pressure
resulted in global current flow throughout the bulk sample even though the
density was lower and impurity phases were more prevalent. An optimized heat
treatment involving a two-step, low temperature, heat treatment of the MSR
powder produced bulk material with very high critical current density above 0.1
MAcm-2 (4.2 K, 0 T).",1305.6820v1
2013-05-30,Machine Learning of Molecular Electronic Properties in Chemical Compound Space,"The combination of modern scientific computing with electronic structure
theory can lead to an unprecedented amount of data amenable to intelligent data
analysis for the identification of meaningful, novel, and predictive
structure-property relationships. Such relationships enable high-throughput
screening for relevant properties in an exponentially growing pool of virtual
compounds that are synthetically accessible. Here, we present a machine
learning (ML) model, trained on a data base of \textit{ab initio} calculation
results for thousands of organic molecules, that simultaneously predicts
multiple electronic ground- and excited-state properties. The properties
include atomization energy, polarizability, frontier orbital eigenvalues,
ionization potential, electron affinity, and excitation energies. The ML model
is based on a deep multi-task artificial neural network, exploiting underlying
correlations between various molecular properties. The input is identical to
\emph{ab initio} methods, \emph{i.e.} nuclear charges and Cartesian coordinates
of all atoms. For small organic molecules the accuracy of such a ""Quantum
Machine"" is similar, and sometimes superior, to modern quantum-chemical
methods---at negligible computational cost.",1305.7074v1
2013-05-31,Adapting the Interrelated Two-way Clustering method for Quantitative Structure-Activity Relationship (QSAR) Modeling of a Diverse Set of Chemical Compounds,"Interrelated Two-way Clustering (ITC) is an unsupervised clustering method
developed to divide samples into two groups in gene expression data obtained
through microarrays, selecting important genes simultaneously in the process.
This has been found to be a better approach than conventional clustering
methods like K-means or self-organizing map for the scenarios when number of
samples much smaller than number of variables (n<<p). In this paper we used the
ITC approach for classification of a diverse set of 508 chemicals regarding
mutagenicity. A large number of topological indices (TIs), 3-dimensional, and
quantum chemical descriptors, as well as atom pairs (APs) have been used as
explanatory variables. In this paper, ITC has been used only for predictor
selection, after which ridge regression is employed to build the final
predictive model. The proper leave-one-out (LOO) method of cross-validation in
this scenario is to take as holdout each of the 508 compounds before predictor
thinning and compare the predicted values with the experimental data. ITC based
results obtained here are comparable to those developed earlier.",1305.7285v1
2013-06-06,Electrodynamics of BaFe2As2 from infrared measurements under pressure,"We report on an infrared study on the undoped compound BaFe2As2 as a function
of both pressure (up to about 10 GPa) at three temperatures (300, 160, and 110
K). The evolution with pressure and temperature of the optical conductivity
shows that, by increasing pressure, the mid-infrared absorptions associated
with magnetic order are lowered while the Drude term increases, indicating the
evolution towards a conventional metallic state. We evaluate the spectral
weight dependence on pressure comparing it to that previously found upon
doping. The whole optical results indicate that lattice modifications can not
be recognized as the only parameter determining the low-energy electrodynamics
in these compounds.",1306.1352v2
2013-06-18,Towards a Graph-Based Approach for Web Services Composition,"Nowadays, Web services (WS) remain a main actor in the implementation of
distributed applications. They represent a new promising paradigm for the
development, deployment and integration of Internet applications. The aim of
Web services composition is to use the skills of several departments to resolve
any problem that cannot be solved individually. The result of this composition
is a compound of Web services that define how they will be used. In this paper,
we propose an approach for automatic web services composition based on the
concepts of directed graphs for the representation and description of Web
services, and the ordering of web services compound execution. In this context,
the user query, defined by a set of inputs and outputs, can be viewed as a
directed graph composed of Web services.",1306.4280v1
2013-06-21,Change of magnetic ground state by light electron-doping in CeOs2Al10,"The effect of Ir substitution for Os in CeOs2Al10, with an unusually high
Neel temperature of T~28.5K, has been studied by high-resolution neutron
diffraction and magnetization measurements. A small amount of Ir (~ 8%) results
in a pronounced change of the magnetic structure of the Ce-sublattice. The new
magnetic ground state is controlled by the single ion anisotropy and implies
antiferromagnetic arrangement of the Ce-moments along the a-axis, as expected
from the anisotropy of the paramagnetic susceptibility. The value of the
ordered moments, 0.92(1) mu_B, is substantially bigger than in the undoped
compound, whereas the transition temperature is reduced down to 21K. A
comparison of the observed phenomena with the recently studied CeRu1.9Rh0.1Al10
system, exhibiting similar behaviour [A. Kondo et al., J. Phys. Soc. Jpn. 82,
054709 (2013)], strongly suggests the electron doping as the main origin of the
ground state changes. This provides a new way of exploring the anomalous
magnetic properties of the Ce(Ru/Os)2Al10 compounds.",1306.5269v1
2013-06-24,Compound Wishart Matrices and Noisy Covariance Matrices: Risk Underestimation,"In this paper, we obtain a property of the expectation of the inverse of
compound Wishart matrices which results from their orthogonal invariance. Using
this property as well as results from random matrix theory (RMT), we derive the
asymptotic effect of the noise induced by estimating the covariance matrix on
computing the risk of the optimal portfolio. This in turn enables us to get an
asymptotically unbiased estimator of the risk of the optimal portfolio not only
for the case of independent observations but also in the case of correlated
observations. This improvement provides a new approach to estimate the risk of
a portfolio based on covariance matrices estimated from exponentially weighted
moving averages of stock returns.",1306.5510v1
2013-06-25,Crystal field and magnetism of Pr$^{3+}$ and Nd$^{3+}$ ions in orthorhombic perovskites,"Fifteen parameters characterizing the crystal field of rare-earth ions in the
RMO$_3$ perovskites (R = Pr, Nd, M = Ga, Co) are calculated by expanding the
local Hamiltonian expressed in the basis of Wannier functions into a series of
spherical tensor operators. The method contains a single adjustable parameter
that characterizes the hybridization of R($4f$) states with the states of
oxygen ligands. Subsequently the energy levels and magnetic moments of
trivalent R ion are determined by diagonalization of an effective Hamiltonian
which, besides the crystal field, contains the $4f$ electron-electron
repulsion, spin-orbit coupling and interaction with magnetic field. In the Ga
compounds the energy levels of the ground multiplet agree within few meV with
those determined experimentally by other authors. For all four compounds in
question the temperature dependence of magnetic susceptibility is measured on
polycrystalline samples and compared with the results of calculation. For
NdGaO$_3$ theory is also compared with the magnetic measurements on a single
crystal presented by Luis {\it et al.} Phys. Rev. B {\bf 58}, 798 (1998). A
good agreement between the experiment and theory is found.",1306.5948v1
2013-07-01,"Dirac Fermions and Superconductivity in Homologous Structures (AgxPb1-xSe)5(Bi2Se3)3m,m = 1,2","A newly discovered topological insulator (AgxPb1-xSe)5(Bi2Se3)3m, m=2, has a
band gap of 0.5 eV, the largest value ever reported in topological insulators
(TIs). We present a magnetoconductivity study of the Dirac electrons of this
compound in the quantum diffusion regime. Two dimensional weak antilocalization
was observed and identified as destructive interference caused by the Berry
phase of this topological state. We find that the phase coherence length of the
Dirac electrons is independent of doping and disorder levels. This provides
proof for the absence of backscattering arising from the protection of time
reversal invariance in TI (AgxPb1-xSe)5(Bi2Se3)3m, m=2. We further report that
the homologous compound (AgxPb1-xSe)5(Bi2Se3)3m, m=1 is a superconductor with a
transition temperature Tc = 1.7 K. The related structures of these two phases
allow lateral intergrowth of crystals to occur naturally, offering an
opportunity to observe the Majorana Fermion state at the boundary of two
intergrown crystals.",1307.0260v2
2013-07-07,Andreev Reflection Like Enhancement Above Bulk $T_c$ in Electron Underdoped Iron Arsenides,"We use point contact spectroscopy (PCS) to probe the superconducting
properties of electron doped $\rm{Ba(Fe_{1-x}Co_x)_2As_2}$ ($\rm{x = 0.05,
0.055, 0.07, 0.08}$) and hole doped $\rm{Ba_{0.8}K_{0.2}Fe_2As_2}$. PCS
directly probes the low energy density of states via Andreev reflection,
revealing two distinct superconducting gaps in both compound families. Apart
from the electron underdoped $\rm{Ba(Fe_{1-x}Co_{x})_2As_2}$, the excess
current due to Andreev reflection for the compounds follows the typical BCS
temperature dependence. For underdoped $\rm{Ba(Fe_{1-x}Co_{x})_2As_2}$, the
temperature dependence of the excess current deviates from that of BCS,
developing a tail at higher temperatures and surviving above bulk $T_c$.
Possible explanations for this anomalous behavior are explored.",1307.1908v1
2013-07-09,"Synthesis, Crystal Structure and Physical Properties of Sr2FeOsO6","In the exploration of new osmium based double perovskites, Sr2FeOsO6 is a new
insertion in the existing family. The polycrystalline compound has been
prepared by solid state synthesis from the respective binary oxides. PXRD
analysis shows the structure is pseudo-cubic at room temperature, whereas
low-temperature synchrotron data refinements reveal the structure to be
tetragonal, space group I4/m. Heat capacity and magnetic measurements of
Sr2FeOsO6 indicated the presence of two magnetic phase transitions at T1 = 140
K and T2 = 67 K. Band structure calculations showed the compound as a narrow
energy gap semiconductor, which supports the experimental results obtained from
the resistivity measurements. The present study documents significant
structural and electronic effects of substituting Fe3+ for Cr3+ ion in
Sr2CrOsO6.",1307.2586v1
2013-07-10,Field-concentration phase diagram of a quantum spin liquid with bond defects,"The magnetic susceptibility of the gapped quantum spin liquid compound
(C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$ and its chemically disordered derivatives
(C$_4$H$_{12}$N$_2$)Cu$_2$(Cl$_{1-x}$Br$_{x}$)$_6$ are systematically studied
in magnetic fields of up to 45 T, as a function of Br concentration. The
corresponding field-temperature and field-concentration phase diagrams are
determined. Measurements on the disorder-free parent compound are not fully
consistent with previously published results by other authors [PRL{\bf 96},
257203 (2006)]. The effect of Br/Cl substitution on the magnetic properties is
superficially similar to that of finite temperature. However, important
differences are identified and discussed with reference to the previously
studied magnetic excitation spectra.",1307.2750v1
2013-07-10,Impact of strong disorder on the static magnetic properties of the spin-chain compound BaCu2SiGeO7,"The disordered quasi-1D magnet BaCu2SiGeO7 is considered as one of the best
physical realizations of the random Heisenberg chain model, which features an
irregular distribution of the exchange parameters and whose ground state is
predicted to be the scarcely investigated random-singlet state (RSS). Based on
extensive 29Si NMR and magnetization studies of BaCu2SiGeO7, combined with
numerical Quantum Monte Carlo simulations, we obtain remarkable quantitative
agreement with theoretical predictions of the random Heisenberg chain model and
strong indications for the formation of a random-singlet state at low
temperatures in this compound. As a local probe, NMR is a well-adapted
technique for studying the magnetism of disordered systems. In this case it
also reveals an additional local transverse staggered field (LTSF), which
affects the low-temperature properties of the RSS. The proposed model
Hamiltonian satisfactorily accounts for the temperature dependence of the NMR
line shapes.",1307.2814v1
2013-07-16,Single crystal growth and physical properties of a new uranium compound URhIn$_5$,"We have grown the new uranium compound URhIn$_5$ with the tetragonal
HoCoGa$_5$-type by the In self flux method. In contrast to the nonmagnetic
ground state of the isoelectronic analogue URhGa$_5$, URhIn$_5$ is an
antiferromagnet with antiferromagnetic transition temperature $T_{\rm N}$ = 98
K. The moderately large electronic specific heat coefficient $\gamma$ = 50
mJ/K$^2$mol demonstrates the contribution of 5$f$ electrons to the conduction
band. On the other hand, magnetic susceptibility in the paramagnetic state
roughly follows a Curie-Weiss law with a paramagnetic effective moment
corresponding to a localized uranium ion. The crossover from localized to
itinerant character at low temperature may occur around the characteristic
temperature 150 K where the magnetic susceptibility and electrical resistivity
show a marked anomaly.",1307.4231v1
2013-07-23,Mechanism of uniaxial magnetocrystalline anisotropy in transition metal alloys,"Magnetocrystalline anisotropy in transition metal alloys (FePt, CoPt, FePd,
MnAl, MnGa, and FeCo) was studied using first-principles calculations to
elucidate its specific mechanism. The tight-binding linear muffin-tin orbital
method in the local spin-density approximation was employed to calculate the
electronic structure of each compound, and the anisotropy energy was evaluated
using the magnetic force theorem and the second-order perturbation theory in
terms of spin-orbit interactions. We systematically describe the mechanism of
uniaxial magnetocrystalline anisotropy in real materials and present the
conditions under which the anisotropy energy can be increased. The large
magnetocrystalline anisotropy energy in FePt and CoPt arises from the strong
spin-orbit interaction of Pt. In contrast, even though the spin-orbit
interaction in MnAl, MnGa, and FeCo is weak, the anisotropy energies of these
compounds are comparable to that of FePd. We found that MnAl, MnGa, and FeCo
have an electronic structure that is efficient in inducing the
magnetocrystalline anisotropy in terms of the selection rule of spin-orbit
interaction.",1307.5961v2
2013-08-06,NMR evidence for spin fluctuations in the bilayer nickelate La3Ni2O6,"We report nuclear magnetic resonance data in the bilayer nickelate La3Ni2O6.
This material belongs to a family of low valence nickel oxides with square
planar coordination of the Ni ions and is isoelectronic to the high temperature
superconducting cuprates. Although the three layer nickelate compound exhibits
a spin-state transition accompanied by antiferromagnetic order, the bilayer
material shows no phase transition. The NMR data in the bilayer La3Ni2O6 reveal
the presence of antiferromagnetic spin fluctuations down to 5K that are
surprisingly similar to those present in the magnetically ordered trilayer
La4Ni3O8, suggesting a similar electronic structure in the paramagnetic phase
of both compounds.",1308.1322v1
2013-08-10,A large energy-gap oxide topological insulator based on the superconductor BaBiO3,"Mixed-valent perovskite oxides based on BaBiO3 (BBO) are, like cuperates,
well-known high-Tc superconductors. Recent ab inito calculations have assigned
the high-Tc superconductivity to a correlation-enhanced electron--phonon
coupling mechanism, stimulating the prediction and synthesis of new
superconductor candidates among mixed-valent thallium perovskites. Existing
superconductivity has meant that research has mainly focused on hole-doped
compounds, leaving electron-doped compounds relatively unexplored. Here we
demonstrate through ab inito calculations that BBO emerges as a topological
insulator (TI) in the electron-doped region, where the spin-orbit coupling
(SOC) effect is significant. BBO exhibits the largest topological energy gap of
0.7 eV among currently known TI materials, inside which Dirac-type topological
surface states (TSSs) exit. As the first oxide TI, BBO is naturally stable
against surface oxidization and degrading, different from chalcoginide TIs. An
extra advantage of BBO lies in its ability to serve an interface between the
TSSs and the superconductor for the realization of Majorana Fermions.",1308.2303v1
2013-08-11,Shadow gap in the over-doped (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ compound,"The electron band around $M$ point in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ compound
-- completely lifted above the Fermi level for $x > 0.7$ and hence has no Fermi
Surface (FS) -- can still form an isotropic s-wave gap ($\Delta_e$) and it is
the main pairing resource generating an s-wave gap ($\Delta_h$) with an
opposite sign on the hole pocket around $\Gamma$ point. The electron band
developing the SC order parameter $\Delta_e$ but having no FS displays a {\it
shadow gap} feature which will be easily detected by various experimental
probes such as angle-resolved photoemission spectroscopy (ARPES) and scanning
tunneling microscope (STM). Finally, the formation of the nodal gap
$\Delta_{nodal}$ with $A_{1g}$ symmetry on the other hole pocket with a larger
FS is stabilized due to the balance of the interband pairing interactions from
the main hole band gap $\Delta_h=+\Delta$ and the hidden electron band gap
$\Delta_e = -\Delta$.",1308.2413v1
2013-08-12,Electron Spin Resonance in Quasi-One-Dimensional Quantum Antiferromagnets: Relevance of Weak Interchain Interactions,"We discuss universal features on the electron spin resonance (ESR) of a
temperature-induced Tomonaga-Luttinger liquid phase in a wide class of weakly
coupled $S=1/2$ antiferromagnetic spin chains such as spin ladders, spin tubes
and three-dimensionally coupled spin chains. We show that the ESR linewidth of
various coupled chains increases with lowering temperature while the linewidth
of a single spin chain is typically proportional to temperature. This
broadening with lowering temperature is attributed to anisotropic interchain
interactions and has been indeed observed in several kinds of three-dimensional
(3D) magnets of weakly coupled spin chains above the 3D ordering temperature.
We demonstrate that our theory can account for anomalous behaviors of the
linewidths in an $S=1/2$ four-leg spin tube compound Cu$_2$Cl$_4 \cdot
$H$_8$C$_4$SO$_2$ (abbreviated to Sul-Cu$_2$Cl$_4$) and a three-dimensionally
coupled $S=1/2$ spin chain compound CuCl$_2\cdot 2$NC$_5$H$_5$.",1308.2714v2
2013-08-13,Canonical magnetic insulators with isotropic magnetoelectric coupling,"We have performed an exhaustive representation-theory-based search for the
simplest structures allowing isotropic magnetoelectric coupling. We find 30
such structures, all sharing a common pattern of atomic displacements in the
direction of atomic magnetic moments. We focus on one of these 30 canonical
structures and find that it is generically realized in a class of fractionally
substituted pyrochlore compounds with an all-in-all-out magnetic order.
Furthermore, we find that these substituted pyrochlore compounds have a
substantial Chern-Simons orbital magnetoelectric component (\theta=0.1--0.2).
While this component is also formally present in strong Z_2 topological
insulators (\theta=\pi), its effects are observable there only if time-reversal
symmetry is broken at the surface.",1308.2977v2
2013-08-14,Interpretation of experimental results on Kondo systems with crystal field,"We present a simple approach to calculate the thermodynamic properties of
single Kondo impurities including orbital degeneracy and crystal field effects
(CFE) by extending a previous proposal by K. D. Schotte and U. Schotte [Physics
Lett. A 55, 38 (1975)]. Comparison with exact solutions for the specific heat
of a quartet ground state split into two doublets shows deviations below $10\%$
in absence of CFE and a quantitative agreement for moderate or large CFE. As an
application, we fit the measured specific heat of the compounds CeCu$_2$Ge$_2$,
CePd$_{3}$Si$_{0.3}$, CePdAl, CePt, Yb$_2$Pd$_2$Sn and YbCo$_2$Zn$_{20}$. The
agreement between theory and experiment is very good or excellent depending on
the compound, except at very low temperatures due to the presence of magnetic
correlations (not accounted in the model).",1308.3256v3
2013-08-22,Conventional superconductivity and charge-density-wave ordering in Ba1-xNaxTi2Sb2O,"We have investigated the low temperature physical properties of BaTi2Sb2O and
Ba1-xNaxTi2Sb2O (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) by means of muon spin
rotation (muSR) and SQUID magnetometry. Our measurements reveal the absence of
magnetic ordering below TDW = 58 K in the parent compound. Therefore the phase
transition at this temperature observed by magnetometry is most likely due to
the formation of a charge density wave (CDW). Upon substitution of barium by
sodium in Ba1-xNaxTi2Sb2O we find for x = 0.25 superconductivity with a maximum
T_{c} = 5.1 K in the magnetization and a bulk T_{c,bulk} = 4.5 K in the muSR
measurements. The temperature dependency of the London penetration depth
lambda^-2(T) of the optimally doped compound can be well explained within a
conventional weak-coupling scenario in the clean limit.",1308.4818v2
2013-08-26,AFLOW: An automatic framework for high-throughput materials discovery,"Recent advances in computational materials science present novel
opportunities for structure discovery and optimization, including uncovering of
unsuspected compounds and metastable structures, electronic structure, surface,
and nano-particle properties. The practical realization of these opportunities
requires systematic generation and classification of the relevant computational
data by high-throughput methods. In this paper we present Aflow (Automatic
Flow), a software framework for high-throughput calculation of crystal
structure properties of alloys, intermetallics and inorganic compounds. The
Aflow software is available for the scientific community on the website of the
materials research consortium, aflowlib.org. Its geometric and electronic
structure analysis and manipulation tools are additionally available for online
operation at the same website. The combination of automatic methods and user
online interfaces provide a powerful tool for efficient quantum computational
materials discovery and characterization.",1308.5715v1
2013-09-03,Quantum Phases of the Shastry-Sutherland Kondo Lattice: Implications for the Global Phase Diagram of Heavy Fermion Metals,"Considerable recent theoretical and experimental efforts have been devoted to
the study of quantum criticality and novel phases of antiferromagnetic
heavy-fermion metals. In particular, quantum phase transitions have been
discovered in the compound Yb$_2$Pt$_2$Pb. These developments have motivated us
to study the competition between the RKKY and Kondo interactions on the
Shastry-Sutherland lattice. We determine the zero-temperature phase diagram as
a function of magnetic frustration and Kondo coupling within a slave-fermion
approach. Pertinent phases include the Shastry-Sutherland valence bond solid
and heavy Fermi liquid. In the presence of antiferromagnetic order, our
zero-temperature phase diagram is remarkably similar to the global phase
diagram proposed earlier based on general grounds. We discuss the implications
of our results for the experiments on Yb$_2$Pt$_2$Pb and other geometrically
frustrated heavy fermion compounds.",1309.0581v3
2013-09-04,The candidacy of shuffle and shear during compound twinning in hexagonal close-packed structures,"This paper proposes a systematic generalized formulation for calculating both
atomic shuffling and shear candidates for a given compound twinning mode in
hexagonal closed-packed metals. Although shuffles play an important role in the
mobility of twinning dislocations in non-Bravais metallic lattices, their
analytical expressions have not been previously derived. The method is
illustrated for both flat planes and corrugated planes which are exemplified by
{11-22} and {10-12} twinning modes, respectively. The method distinguishes
between shuffle displacements and net shuffles. While shuffle displacements
correspond to movements between ideal atom positions in the parent and twin
lattices, net shuffles comprise contributions from shear on overlying planes
which can operate along opposite directions to those of shuffle displacements.
Thus, net shuffles in the twinning direction can vanish in a limiting case, as
is interestingly the case for those needed in the second plane by the b_4
dislocation candidate in {11-22} twinning. It is found that while shuffle
displacement vectors can be irrational when K_1 is corrugated, net shuffle
vectors are always rational.",1309.1133v1
2013-09-06,Thermodynamics of the spin-1/2 two-leg ladder compound $(C_{5}H_{12}N)_{2} CuBr_{4}$,"The thermodynamic behavior of the spin $S=1/2$ antiferromagnetic two-leg
ladder compound $(C_{5}H_{12}N)_{2} CuBr_{4}$ in a uniform magnetic field is
studied using numerical and analytical approaches. The entropy $S(H,T)$ and
specific heat $C(H,T)$ are calculated. The specific heat shows various
behaviors in different regions of the magnetic field. The field-dependence of
the specific heat is almost symmetric about the average of quantum critical
fields in complete agreement with experimental results. In addition, it is
found that during an adiabatic demagnetization process, temperature drops in
the vicinity of the field induced zero-temperature quantum phase transitions.",1309.1548v1
2013-09-10,Thin films of the spin ice compound Ho2Ti2O7,"The pyrochlore compounds Ho2Ti2O7 and Dy2Ti2O7 show an exotic form of
magnetism called the spin ice state, resulting from the interplay between
geometrical frustration and ferromagnetic coupling. A fascinating feature of
this state is the appearance of magnetic monopoles as emergent excitations
above the degenerate ground state. Over the past years, strong effort has been
devoted to the investigation of these monopoles and other properties of the
spin ice state in bulk crystals. A tantalising prospect is to incorporate spin
ice materials into devices for spintronics and devices that can manipulate the
magnetic monopoles. This would require the availability of spin ice thin films.
Here, we report the fabrication of Ho2Ti2O7 thin films using pulsed laser
deposition. These films not only show a high crystalline quality, but also
exhibit the hallmarks of a spin ice: a pronounced magnetic anisotropy and an
intermediate plateau in the magnetisation along the [111] crystal direction.",1309.2441v1
2013-09-17,Tuning the Curie temperature of FeCo compounds by tetragonal distortion,"Combining density-functional theory calculations with a classical Monte Carlo
method, we show that for B2-type FeCo compounds tetragonal distortion gives
rise to a strong reduction of the Curie temperature $T_{\mathrm{C}}$. The
$T_{\mathrm{C}}$ monotonically decreases from 1575 K (for $c/a=1$) to 940 K
(for $c/a=\sqrtwo$). We find that the nearest neighbor Fe-Co exchange
interaction is sufficient to explain the $c/a$ behavior of the
$T_{\mathrm{C}}$. Combination of high magnetocrystalline anisotropy energy with
a moderate $T_{\mathrm{C}}$ value suggests tetragonal FeCo grown on the Rh
substrate with $c/a=1.24$ to be a promising material for heat-assisted magnetic
recording applications.",1309.4232v1
2013-09-24,Interatomic potential for the compound-forming Li-Pb liquid alloy,"Atomistic simulations of liquid alloys face the challenge of correctly
modeling basic thermodynamic properties. In this work we present an interatomic
potential for the Li-Pb system, as well as a study of physical properties of
Li-Pb alloys. Despite the complexity due to Li-Pb being a compound forming
system where charge transfer is expected, we show here how the empirical EAM
formalism is able to satisfactorily describe several physical properties in a
wide range of Li concentration. Application of our potential to Li-Pb eutectic
allows us to correctly predict many physical properties observed experimentally
and calculated with ab initio techniques, providing in this way a potential
suitable for future studies in the context of tritium breeder blanket designs
in Fusion technology.",1309.6152v1
2013-09-25,"Prediction of stable hafnium carbides: their stoichiometries, mechanical properties, and electronic structure","Hafnium carbides are studied by a systematic search for possible stable
stoichiometric compounds in the Hf-C system at ambient pressure using
variable-composition ab initio evolutionary algorithm implemented in the USPEX
code. In addition to well-known HfC, we predicted two additional compounds
Hf3C2 and Hf6C5. The structure of Hf6C5 with space group C2/m contains 11 atoms
in the primitive cell and this prediction revives the earlier proposal by A. I.
Gusev. The stable structure of Hf3C2 also has space group C2/m, and is more
energetically favorable than the Immm, P-3m1, P2 and C2221 structures put
forward by A. I. Gusev. Dynamical and mechanical stability of the newly
predicted structures have been verified by calculations of their phonons and
elastic constants. The bulk and shear moduli of Hf3C2 are 195.8 GPa and 143.1
GPa, respectively, while for Hf6C5 they are 227.9 GPa and 187.2 GPa,
respectively. Their mechanical properties are inferior to those of HfC due to
the presence of structural vacancies. Chemical bonding, band structure, and
Bader charge are presented and discussed.",1309.6516v1
2013-09-26,Magnetic frustration in BaCuSi2O6 released,"Han Purple (BaCuSi2O6) is not only an ancient pigment, but also a valuable
model material for studying Bose-Einstein condensation (BEC) of magnons in high
magnetic fields. Using precise low-temperature structural data and extensive
density-functional calculations, we elucidate magnetic couplings in this
compound. The resulting magnetic model comprises two types of nonequivalent
spin dimers, in excellent agreement with the (63,65)Cu nuclear magnetic
resonance data. We further argue that leading interdimer couplings connect the
upper site of one dimer to the bottom site of the contiguous dimer, and not the
upper-to-upper and bottom-to-bottom sites, as assumed previously. This finding
is verified by inelastic neutron scattering data and implies the lack of
magnetic frustration in BaCuSi2O6, thus challenging existing theories of the
magnon BEC in this compound.",1309.6762v1
2013-09-29,Transition-Metal Pentatelluride ZrTe$_5$ and HfTe$_5$: a Paradigm for Large-gap Quantum Spin Hall Insulators,"Quantum spin Hall (QSH) insulators, a new class of quantum matters, can
support topologically protected helical edge modes inside bulk insulating gap,
which can lead to dissipationless transport. A major obstacle to reach wide
application of QSH is the lack of suitable QSH compounds, which should be
easily fabricated and has large size of bulk gap. Here we predict that single
layer ZrTe$_5$ and HfTe$_5$ are the most promising candidates to reach the
large gap QSH insulators with bulk direct (indirect) band gap as large as 0.4
eV (0.1 eV), and robust against external strains. The 3D crystals of these two
materials are good layered compounds with very weak inter-layer bonding and are
located near the phase boundary between weak and strong topological insulators,
which pave a new way to future experimental studies on both QSH effect and
topological phase transitions.",1309.7529v1
2013-10-04,The electronic structure of the high-symmetry perovskite iridate Ba2IrO4,"We report angle-resolved photoemission (ARPES) measurements, density
functional and model tight-binding calculations on Ba$_2$IrO$_4$ (Ba-214), an
antiferromagnetic ($T_N=230$ K) insulator. Ba-214 does not exhibit the
rotational distortion of the IrO$_6$ octahedra that is present in its sister
compound Sr$_2$IrO$_4$ (Sr-214), and is therefore an attractive reference
material to study the electronic structure of layered iridates. We find that
the band structures of Ba-214 and Sr-214 are qualitatively similar, hinting at
the predominant role of the spin-orbit interaction in these materials.
Temperature-dependent ARPES data show that the energy gap persists well above
$T_N$, and favour a Mott over a Slater scenario for this compound.",1310.1307v2
2013-10-06,Machine learning with systematic density-functional theory calculations: Application to melting temperatures of single and binary component solids,"A combination of systematic density functional theory (DFT) calculations and
machine learning techniques has a wide range of potential applications. This
study presents an application of the combination of systematic DFT calculations
and regression techniques to the prediction of the melting temperature for
single and binary compounds. Here we adopt the ordinary least-squares
regression (OLSR), partial least-squares regression (PLSR), support vector
regression (SVR) and Gaussian process regression (GPR). Among the four kinds of
regression techniques, the SVR provides the best prediction. In addition, the
inclusion of physical properties computed by the DFT calculation to a set of
predictor variables makes the prediction better. Finally, a simulation to find
the highest melting temperature toward the efficient materials design using
kriging is demonstrated. The kriging design finds the compound with the highest
melting temperature much faster than random designs. This result may stimulate
the application of kriging to efficient materials design for a broad range of
applications.",1310.1546v2
2013-10-07,Isotropic Γ_6 Ground State in Caged Compound NdRu2Zn20,"The magnetic susceptibility $\chi$, the magnetization $M$, and the specific
heat $C$ were measured for the caged cubic compound NdRu$_2$Zn$_{20}$ at
temperatures down to 0.5 K in the magnetic field $H$ along the three
crystallographic principal axes, [100], [110], and [111]. The ferromagnetic
phase transition was observed at the Curie temperature $T_{\rm C}=1.9$ K in
both the temperature dependence of $\chi(T)$ and $C(T)$. Below $T_{\rm C}$, the
magnetization curves $M(H)$ show very weak magnetic anisotropy, and the $C(T)$
curves in the fields along the three principal axes show no magnetic anisotropy
both below and above $T_{\rm C}$. The easy direction of magnetization at 0.5 K
changes from the [111] direction in 0 T to the [110] diretion in 7 T. We
analyzed these characteristic behaviors theoretically taking into account the
crystalline-electric-field energy, the magnetic exchange interaction, and the
Zeeman energy. It was found that these features are originated from the
isotropic $\Gamma_6$ ground state mixing with the magnetic $\Gamma_8^{(1)}$
excited state. The temperature and the magnetic field dependences of $M(T,H)$
and $C(T,H)$ are quantitatively well analyzed by this theoretical calculation.",1310.1664v1
2013-10-09,Multiferroicity in the geometrically frustrated FeTe2O5Cl,"The layered FeTe2O5Cl compound was studied by specific-heat, muon spin
relaxation, nuclear magnetic resonance, dielectric, as well as neutron and
synchrotron x-ray diffraction measurements, and the results were compared to
isostructural FeTe2O5Br. We find that the low-temperature ordered state,
similarly as in FeTe2O5Br, is multiferroic - the elliptical amplitude-modulated
magnetic cycloid and the electric polarization simultaneously develop below 11
K. However, compared to FeTe2O5Br, the magnetic elliptical envelop rotates by
75(4) deg and the orientation of the electric polarization is much more
sensitive to the applied electric field. We propose that the observed
differences between the two isostructural compounds arise from geometric
frustration, which enhances the effects of otherwise subtle Fe3+ (S = 5/2)
magnetic anisotropies. Finally, x-ray diffraction results imply that, on the
microscopic scale, the magnetoelectric coupling is driven by shifts of the O1
atoms, as a response to the polarization of the Te4+ lone-pair electrons
involved in the Fe-O-Te-O-Fe exchange bridges.",1310.2373v2
2013-10-25,Non-vanishing Berry Phase in Chiral Insulators,"The binary compounds FeSi, RuSi, and OsSi are chiral insulators crystallizing
in the space group P2_13 which is cubic. By means of ab initio calculations we
find for these compounds a non-vanishing electronic Berry phase, the sign of
which depends on the handedness of the crystal. There is thus the possibility
that the Berry phase signals the existence of a macroscopic electric
polarization due to the electrons. We show that this is indeed so if a small
external magnetic field is applied in the [111]-direction. The electric
polarization is oscillatory in the magnetic field and possesses a signature
that distinguishes the handedness of the crystal. Our findings add to the
discussion of topological classifications of insulators and are significant for
spintronics applications, and in particular, for a deeper understanding of
skyrmions in insulators.",1310.6879v1
2013-10-29,Unexpected stable stoichiometries of sodium chlorides,"Sodium chloride (NaCl), or rocksalt, is well characterized at ambient
pressure. Due to the large electronegativity difference between Na and Cl
atoms, it has highly ionic chemical bonding, with stoichiometry 1:1 dictated by
charge balance, and B1-type crystal structure. Here, by combining theoretical
predictions and diamond anvil cell experiments we show that new materials with
different stoichiometries emerge at pressure as low as 20 GPa. Compounds such
us Na3Cl, Na2Cl, Na3Cl2, NaCl3 and NaCl7 are theoretically stable and have
unusual bonding and electronic properties. To test this prediction, at 55-80
GPa we synthesized cubic and orthorhombic NaCl3 at 55-70 GPa and 2D-metallic
tetragonal Na3Cl. This proves that novel compounds, violating chemical
intuition, can be thermodynamically stable even in simplest systems at
non-ambient conditions.",1310.7674v1
2013-10-29,XPS on corrosion products of ZnCr coated steel: on the reliability of Ar+ ion depth profiling for multi component material analysis,"X-ray photoelectron spectroscopy combined with Ar+ ion etching is a powerful
concept to identify different chemical states of compounds in depth profiles,
important for obtaining information underneath surfaces or at layer interfaces.
The possibility of occurring sputter damage is known but insufficiently
investigated for corrosion products of Zn-based steel coatings like ZnCr.
Hence, in this work reference materials are studied according to stability
against ion sputtering. Indeed some investigated compounds reveal a very
unstable chemical nature. On the basis of these findings the reliability of
depth profiles of real samples can be rated to avoid misinterpretations of
observed chemical species.",1310.7725v2
2013-10-31,Exchange bias associated with phase separation in the Nd2/3Ca1/3MnO3 manganite,"The exchange bias (EB) phenomenon has been found in Nd2/3Ca1/3MnO3
perovskite. The phenomenon manifests itself as a negative horizontal shift of
magnetization hysteresis loops. The EB phenomenon is evident of an interface
exchange coupling between coexisting antiferromagnetic (AFM) and ferromagnetic
(FM) phases and confirms the phase separated state of the compound at low
temperatures. The EB effect is found to be strongly dependent on the cooling
magnetic field and the temperature, which is associated with the evolution of
spontaneous AFM - FM phase separated state of the compound. Analysis of
magnetic hysteresis loops has shown that ferromagnetic moment $M_{FM}$
originating from the FM clusters saturates in a relatively low magnetic field
about H ~ 0.4T. The obtained saturation value $M_{FM}$(1T) ~ 0.45$\mu_{B}$ is
in a good agreement with our previous neutron diffraction data.",1310.8590v1
2013-10-31,Single crystal growth and characterization of the large-unit-cell compound Cu13Ba,"Single crystals of Cu$_{13}$Ba were successfully grown out of Ba-Cu self
flux. Temperature dependent magnetization, $M(T)$, electrical resistivity,
$\rho(T)$, and specific heat, $C_p(T)$, data are reported. Isothermal
magnetization measurements, $M(H)$, show clear de Haas-van Alphen oscillations
at $T$ = 2 K for applied fields as low as $\mu_0H$ = 1T. An anomalous behavior
of the magnetic susceptibility is observed up to $T$ ~ 50K reflecting the
effect of de Haas-van Alphen oscillations at fairly high temperatures. The
field- and temperature-dependencies of the magnetization indicate the presence
of diluted magnetic impurities with a concentration of the order of 0.01at.%.
Accordingly, the minimum and lower temperature rise observed in the electrical
resistivity at and below $T$ = 15K is attributed to the Kondo impurity effect.",1311.0027v1
2013-11-03,Phase Transitions and Cosparse Tomographic Recovery of Compound Solid Bodies from Few Projections,"We study unique recovery of cosparse signals from limited-angle tomographic
measurements of two- and three-dimensional domains. Admissible signals belong
to the union of subspaces defined by all cosupports of maximal cardinality
$\ell$ with respect to the discrete gradient operator. We relate $\ell$ both to
the number of measurements and to a nullspace condition with respect to the
measurement matrix, so as to achieve unique recovery by linear programming.
These results are supported by comprehensive numerical experiments that show a
high correlation of performance in practice and theoretical predictions.
Despite poor properties of the measurement matrix from the viewpoint of
compressed sensing, the class of uniquely recoverable signals basically seems
large enough to cover practical applications, like contactless quality
inspection of compound solid bodies composed of few materials.",1311.0423v1
2013-11-05,Quantum criticality and Lifshitz transition in the Ising system CeRu2Si2: Comparison with YbRh2Si2,"New thermoelectric power (TEP) measurements on prototype heavy-fermion
compounds close to magnetic quantum criticality are presented. The highly
sensitive technique of TEP is an unique tool to reveal Fermi surface
instabilities, referred here as Lifshitz transitions. The first focus is on the
Ising CeRu2Si2 series. Doping CeRu2Si2 with Rh produces a decoupling between
the first order metamagnetic transition and the pseudo-metamagnetism observed
in the pure compound. Comparison is made with the case of YbRh2Si2 which is
often considered as the archetype of local quantum criticality by contrast to
CeRu2Si2, taken as an example of spin-density wave criticality. Up to now for
ferromagnetic materials showing ferromagnetic wings, no simple case appears
where the Fermi surface is preserved between the ferromagnetic and paramagnetic
phases. An open issue is the consequence of Lifshitz transitions on
superconductivity in these multiband systems.",1311.1239v1
2013-11-06,Superconductivity in Ca1-xLaxFeAs2: A Novel 112-Type Iron Pnictide with Arsenic Zigzag Bonds,"We report superconductivity in the novel 112-type iron-based compound
Ca1-xLaxFeAs2. Single-crystal X-ray diffraction analysis revealed that the
compound crystallizes in a monoclinic structure (space group P21), in which
Fe2As2 layers alternate with Ca2As2 spacer layers such that monovalent arsenic
forms zigzag chains. Superconductivity with a transition temperature (Tc) of 34
K was observed for the x = 0.1 sample, while the x = 0.21 sample exhibited
trace superconductivity at 45 K. First-principles band calculations
demonstrated the presence of almost cylindrical Fermi surfaces, favorable for
the high Tc in La-doped CaFeAs2.",1311.1303v1
2013-11-06,Superconductivity in rubidium substituted Ba1-xRbxTi2Sb2O,"We report on the synthesis and the physical properties of Ba1-xRbxTi2Sb2O (x
< 0.4) by x-ray diffraction, SQUID magnetometery, resistivity and specific heat
measurements. Upon hole doping by substituting Ba with Rb, we find
superconductivity with a maximum Tc = 5.4 K. Simultaneously, the
charge-density-wave (CDW) transition temperature is strongly reduced from T_CDW
55 K in the parent compound BaTi2Sb2O and seems to be suppressed for x > 0.2.
The bulk character of the superconducting state for the optimally doped sample
(x = 0.2) is confirmed by the occurrence of a well developed discontinuity in
the specific heat at Tc, with \DeltaC/Tc = 22 mJ/mol K2, as well as a large
Meissner-shielding fraction of approximately 40 %. The lower and the upper
critical fields of the optimally doped sample (x = 0.2) are estimated to
\mu0Hc1(0) = 3.8 mT and \mu0Hc2(0) = 2.3 T, respectively, indicating that these
compounds are strongly type-II superconductors.",1311.1493v1
2013-11-12,Unconventional sign-changing superconductivity near quantum criticality in YFe$_2$Ge$_2$,"I present the results of first principles calculations of the electronic
structure and magnetic interactions for the recently discovered superconductor
YFe$_2$Ge$_2$ and use them to identify the nature of superconductivity and
quantum criticality in this compound. I find that the Fe $3d$ derived states
near the Fermi level show a rich structure with the presence of both linearly
dispersive and heavy bands. The Fermi surface exhibits nesting between hole and
electron sheets that manifests as a peak in the susceptibility at $(1/2,1/2)$.
I propose that the superconductivity in this compound is mediated by
antiferromagnetic spin fluctuations associated with this peak resulting in a
$s_\pm$ state similar to the previously discovered iron-based superconductors.
I also find that various magnetic orderings are almost degenerate in energy,
which indicates that the proximity to quantum criticality is due to competing
magnetic interactions.",1311.2922v1
2013-11-16,Hardness of FeB4: Density functional theory investigation,"A recent experimental study reported the successful synthesis of an
orthorhombic FeB4 with a high hardness of 62 GPa, which has reignited extensive
interests on whether transition metal borides (TRBs) compounds will become
superhard materials. However, it is contradicted with some theoretical studies
suggesting transition metal boron compounds are unlikely to become superhard
materials. Here, we examined structural and electronic properties of FeB4 using
density functional theory. The electronic calculations show the good
metallicity and covalent FeB bonding. Meanwhile, we extensively investigated
stress strain relations of FeB4 under various tensile and shear loading
directions. The calculated weakest tensile and shear stresses are 40 GPa and 25
GPa, respectively. Further simulations (e.g. electron localized function and
bond length along the weakest loading direction) on FeB4 show the weak Fe-B
bonding is responsible for this low hardness. Moreover, these results are
consistent with the value of Vickers hardness (11.7 to 32.3 GPa) by employing
different empirical hardness models and below the superhardness threshold of 40
GPa. Our current results suggest FeB4 is a hard material and unlikely to become
superhard.",1311.4006v2
2013-11-17,"Octahedral tilting and ferroelectricity in RbANb2O7 (A = Bi, Nd) from first principles","The effects of octahedral tilting of RbANb2O7 (A = Bi, Nd) compounds was
studied using density-functional theory. In this compound, the structural phase
transition was correlated with two octahedral tilting modes (a-a-c0 tilting and
a0a0c+ tilting), and magnitude of the octahedral tilting mode was analyzed in
the optimized structure. The theoretical results correlated well with the
recent experimental results on the ferroelectricity of RbBiNb2O7. The hybrid
improper ferroelectricity resulting from the coupling of two octahedral tilting
modes and off center displacement mode was analyzed by group theory and
symmetry mode analysis. The detailed relationship of the tilting modes to the
structural phase transition and the detailed physical properties of
ferroelectricity are also presented.",1311.4140v1
2013-11-18,Prediction of superconductivity of $3d$ transition-metal based antiperovskites via magnetic phase diagram,"We theoretically studied the electronic structure, magnetic properties, and
lattice dynamics of a series of $3d$ transition-metal antiperovskite compounds
AXM$_{3}$ by density function theory. Based on the Stoner criterion, we drew
the magnetic phase diagram of carbon-based antiperovskites ACM$_{3}$. In the
phase diagram, compounds with non-magnetic ground state but locating near the
ferromagnetic boundary are suggested to yield sizeable electron-phonon coupling
and behave superconductivity. To approve this deduction, we systematically
calculated the phonon spectra and electron-phonon coupling of a series of
Cr-based antiperovskites ACCr$_{3}$ and ANCr$_{3}$. The results show that
AlCCr$_{3}$, GaCCr$_{3}$, and ZnNCr$_{3}$ could be moderate coupling BCS
superconductors. The influence of spin fluctuation on superconductivity are
discussed. Furthermore, other potential superconducting AXM$_{3}$ including
some new Co-base and Fe-based antiperovskite superconductors are predicted from
the magnetic phase diagram.",1311.4240v3
2013-11-18,Magnetic properties of single crystalline CeMg$_{12}$,"Single crystal of CeMg$_{12}$ is obtained by Bridgman method. CeMg$_{12}$
crystallizes in the tetragonal structure with space group $I4/mmm$ (#139). The
Laue pattern confirms the tetragonal crystal structure of CeMg$_{12}$. We have
studied the magnetic properties by measuring magnetic susceptibility,
magnetization, heat capacity and electrical transport. Specific heat
measurement shows that the compound orders at 1.2 K. We have measured the
magnetic susceptibility in the temperature range 1.8 to 300 K, and the
susceptibility data show that [100] crystallographic direction is the easy axis
of magnetization. At high temperature inverse susceptibility varies linearly
with temperature, and follows the Curie-Weiss behaviour. The effective moment
is close to the free ion value thus indicating Ce is in trivalent state in this
compound.",1311.4379v1
2013-11-27,Evolution of the Fermi surface topology in doped 122 iron pnictides,"Based on the minimum two-orbital model and the phase diagram recently
proposed by Tai et al.\ (Europhys. Lett. \textbf{103}, 67001(2013)) for both
electron- and hole-doped 122 iron-based superconducting compounds, we use the
Bogoliubov-de Gennes equations to perform a comprehensive investigation of the
evolution of the Fermi surface (FS) topology in the presence of the collinear
spin-density-wave (SDW) order as the doping is changed. In the parent compound,
the ground state is the SDW order, where the FS is not completely gapped, and
two types of Dirac cones, one electron-doped and the other hole-doped emerge in
the magnetic Brillouin zone. Our findings are qualitatively consistent with
recent angle-resolved photoemission spectroscopy and magneto-resistivity
measurements. We also examine the FS evolution of both electron- and hole-doped
cases and compare them with measurements, as well as with those obtained by
other model Hamiltonians.",1311.7047v1
2013-11-28,Dynamic Spin Fluctuations at $T\rightarrow 0$ in a Spin-1/2 Ferromagnetic Kagome Lattice,"We report magnetization, electron spin resonance (ESR), and muon spin
relaxation ($\mu $SR) measurements on single crystals of the $S=1/2$ (Cu$%
^{+2}$) kagom\'{e} compound Cu(1,3-benzendicarboxylate). The $\mu $SR is
carried to temperatures as low as 45 mK. The spin Hamiltonian parameters are
determined from the analysis of the magnetization and ESR data. We find that
this compound has anisotropic ferromagnetic interactions. Nevertheless, no spin
freezing is observed even at temperatures two orders of magnitude lower than
the coupling constants. In light of this finding, the relation between
persistent spin dynamics and spin liquid are reexamined.",1311.7411v1
2013-12-07,Strain induced superconductivity in the parent compound BaFe2As2,"The discovery of superconductivity (SC) with a transition temperature, Tc, up
to 65K in single-layer FeSe (bulk Tc =8K) films grown on SrTiO3 substrates has
attracted special attention to Fe-based thin films. The high Tc is a
consequence of the combined effect of electron transfer from the oxygen-vacant
substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate
the realization of SC in the parent compound BaFe2As2 (no bulk Tc) just by
tensile lattice strain without charge doping. We investigate the interplay
between strain and SC in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4
single crystalline substrates. The strong interfacial bonding between Fe and
the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit
which leads to a suppression of the antiferromagnetic spin density wave and
induces SC with bulk-Tc ?10K. These results highlight the role of structural
changes in controlling the phase diagram of Fe-based superconductors.",1312.2107v1
2013-12-10,Charge-orbital-lattice coupling effects in the dd-excitation profile of one dimensional cuprates,"We identify dd-excitations in the quasi-one dimensional compound
Ca$_2$Y$_2$Cu$_5$O$_{10}$ using resonant inelastic x-ray scattering. By tuning
across the Cu L$_3$-edge, we observe abrupt shifts in the dd-peak positions as
a function of incident photon energy. This observation demonstrates
orbital-specific coupling of the high-energy excited states of the system to
the low-energy degrees of freedom. A Franck-Condon treatment of
electron-lattice coupling, consistent with other measurements in this compound,
reproduces these shifts, explains the Gaussian lineshapes, and highlights
charge-orbital-lattice renormalization in the high energy d-manifold.",1312.2639v1
2013-12-11,Nanoemulsions obtained via bubble bursting at a compound interface,"The bursting of bubbles at an air/liquid interface is a familiar occurrence
important to foam stability, cell cultures in bioreactors and mass transfer
between the sea and atmosphere. Here we document the hitherto unreported
formation and dispersal into the water column of submicrometre oil droplets
following bubble bursting at a compound air/oil/water-with-surfactant
interface. We show that dispersal results from the detachment of an oil spray
from the bottom of the bubble towards water during bubble collapse. We provide
evidence that droplet size is selected by physicochemical interactions between
oil molecules and the surfactants rather than by hydrodynamic effects. We
illustrate the unrecognized role that this dispersal mechanism may play in the
fate of the sea surface micro-layer and of pollutant spills by dispersing
petroleum in the water column. Finally, our system provides an energy-efficient
route, with potential upscalability and wide applicability, for applications in
drug delivery, food production and material science, which we demonstrate by
producing polymeric nanoparticles.",1312.3369v1
2013-12-13,Superconducting and magneto-transport properties of BiS2 based superconductor PrO1-xFxBiS2 (x = 0 to 0.9),"We report superconducting properties of PrO1-xFxBiS2 compounds, synthesized
by the vacuum encapsulation technique. The synthesized PrO1-xFxBiS2 (x=0.1,
0.3, 0.5, 0.7 and 0.9) samples are crystallized in a tetragonal P4/nmm space
group. Both transport and DC magnetic susceptibility measurements showed bulk
superconductivity below 4 K. The maximum Tc is obtained for x = 0.7 sample.
Under applied magnetic field both Tc onset and Tc (R =0) decrease to lower
temperatures. We estimated highest upper critical field [Hc2(0)] for
PrO0.3F0.7BiS2 sample to be above 4 T (Tesla). The thermally activated flux
flow (TAFF) activation energy (U0) is estimated 54.63 meV in 0.05 Tesla field
for PrO0.3F0.7BiS2 sample. Hall measurement results showed that electron charge
carriers are the dominating ones in these compounds. Thermoelectric effects
(Thermal conductivity and Seebeck coefficient) data suggest strong
electron-electron correlations in this material.",1312.3707v2
2013-12-20,Band antiferromagnetism in a two-band model for iron pnictides,"In this work I investigate a two-band Hubbard model using the Gutzwiller
wavefunction. The tight-binding part of the model was constructed to have a
gapless spin-density wave state which leads to Dirac points in the
bandstructure, a common feature of many iron-pnictide compounds. For quarter,
half and three-quarter fillings I show that the Hund's rule coupling has a
large impact on the metal-insulator transition in the paramagnetic phase. For
the half-filled model in the antiferromagnetic phase, the magnetism evolves in
a Stoner-like behavior and the size of the ordered moment is mainly determined
by the Hubbard interaction. As the Hund's coupling plays a minor role in this
state, the model does not describe a Hund's metal which is in contrast to more
realistic models for iron-pnictide compounds.",1312.5902v2
2014-01-07,Anomalous magnetism of Pr in PrCoAsO,"Detailed magnetization and magneto-transport measurements studies are carried
out to unearth the anomalous magnetism of Pr in PrCoAsO compound. The studied
PrCoAsO sample is single phase and crystallized in the tetragonal structure
with space group P4/nmm in analogy of ZrCuSiAs type compounds. Detailed
magnetization measurements showed that Co moments in PrCoAsO exhibit weakly
itinerant ferromagnetic Co spins ordering at below 80 K with a small magnetic
moments of 0.12 muB/f.u. High temperatures Curie-Weiss fit, resulted in
effective paramagnetic moment mueff (exp) of 5.91 muB/f.u., which can be
theoretically assigned to 3d Co (3.88 muB) and 4f Pr (3.58 muB). Further, a
positive Curie- Weiss temperature of 136 K is seen, indicating predominant
ferromagnetic interactions in PrCoAsO. Detailed transport measurements showed
that PrCoAsO exhibit metallic behavior and negative magneto-resistance below
ferro-magnetically (FM) ordered state. Surprisingly, the situation of PrCoAsO
is similar to non magnetic La containing LaCoAsO and strikingly different than
that as reported for magnetic Nd, Sm and Gd i.e., (Nd/Sm/Gd)CoAsO. The magnetic
behavior of PrCoAsO being closed to LaCoAsO and strikingly different to that of
(Nd/Sm/Gd)CoAsO is unusual.",1401.1281v2
2014-01-14,Simultaneously Magnetic- and Electric-dipole Active Spin Excitations Govern the Static Magnetoelectric Effect in Multiferroic Materials,"We derive a sum rule to demonstrate that the static magnetoelectric (ME)
effect is governed by optical transitions that are simultaneously excited via
the electric and magnetic components of light. By a systematic analysis of
magnetic point groups, we show that the ME sum rule is applicable to a broad
variety of non-centrosymmetric magnets including ME multiferroic compounds. Due
to the dynamical ME effect, the optical excitations in these materials can
exhibit directional dichroism, i.e. the absorption coefficient can be different
for counter-propagating light beams. According to the ME sum rule, the
magnitude of the linear ME effect of a material is mainly determined by the
directional dichroism of its low-energy optical excitations. Application of the
sum rule to the multiferroic Ba$_2$CoGe$_2$O$_7$, Sr$_2$CoSi$_2$O$_7$ and
Ca$_2$CoSi$_2$O$_7$ shows that in these compounds the static ME effect is
mostly governed by the directional dichroism of the spin-wave excitations in
the GHz-THz spectral range. On this basis, we argue that the studies of
directional dichroism and the application of ME sum rule can promote the
synthesis of new materials with large static ME effect.",1401.3306v1
2014-01-22,Improved chemical vapor transport growth of transition metal dichalcogenides,"In the crystal growth of transition metal dichalcogenides by the Chemical
Vapor Transport method (CVT), the choice of the transport agent plays a key
role. We have investigated the effect of various chemical elements and
compounds on the growth of TiSe2, MoSe2, TaS2 and TaSe2 and found that pure I2
is the most suitable for growing TiSe2, whereas transition metal chlorides
perform best with Mo- and Ta- chalcogenides. The use of TaCl5 as a transport
agent in the CVT process allows to selectively growth either polymorph of TaS2
and TaSe2 and the optimum growth conditions are reported. Moreover, by using
TaCl5 and tuning the temperature and the halogen starting ratio, it was
possible to grow whiskers of the compounds TaS2, TaSe2, TaTe2, TaS3 and TaSe3.",1401.5621v1
2014-01-22,The Nature of the Controversy over Time-Symmetric Quantum Counterfactuals,"It is proposed that the recent controversy over ""time-symmetric quantum
counterfactuals"" (TSQCs), based on the Aharonov-Bergmann-Lebowitz Rule for
measurements of pre- and post-selected systems, can be clarified by taking
TSQCs to be counterfactuals with a specific type of compound antecedent. In
that case, inconsistency proofs such as that of Sharp and Shanks (1993) are not
applicable, and the main issue becomes not whether such statements are true,
but whether they are nontrivial. The latter question is addressed and answered
in the negative. Thus it is concluded that TSQCs, understood as counterfactuals
with a compound antecedent, are true but only trivially so, and provide no new
contingent information about specific quantum systems (except in special cases
already identified in the literature).",1401.5790v1
2014-01-23,Q-dependence of the spin fluctuations in the intermediate valence compound CePd3,"We report inelastic neutron scattering experiments on a single crystal of the
intermediate valence compound CePd3. At 300 K the magnetic scattering is
quasielastic, with halfwidth of 23 meV, and is independent of momentum transfer
Q. At low temperature, the Q-averaged magnetic spectrum is inelastic,
exhibiting a broad peak centered near Emax = 55 meV. These results, together
with the temperature dependence of the susceptibility, 4f occupation number,
and specific heat, can be fit by the Kondo/Anderson impurity model. The low
temperature scattering near Emax, however, shows significant variations with Q,
reflecting the coherence of the 4f lattice. The intensity is maximal at (1/2,
1/2,0), intermediate at (1/2,0,0) and (0,0,0), and weak at (1/2,1/2,1/2). We
discuss this Q-dependence in terms of current ideas about coherence in heavy
fermion systems.",1401.5835v1
2014-01-29,Electronic structure of the BaTi$_2$As$_2$O parent compound of the titanium based oxypnictide superconductor,"The electronic structure of BaTi2As2O, a parent compound of the newly
discovered titanium-based oxypnictide superconductors, is studied by
angle-resolved photoemission spectroscopy. The electronic structure shows
multi-orbital nature and possible three-dimensional character. An anomalous
temperature-dependent spectral weight redistribution and broad lineshape
indicate the incoherent nature of the spectral function. At the
density-wave-like transition temperature around 200 K, a partial gap opens at
the Fermi patches. These findings suggest that BaTi2As2O is likely a charge
density wave material in the strong interaction regime.",1401.7430v1
2014-02-06,Magnetic frustration in iridium spinel compound CuIr$_2$S$_4$,"We demonstrate via a muon spin rotation experiment that the electronic ground
state of the iridium spinel compound, CuIr$_2$S$_4$, is not the presumed
spin-singlet state but a novel paramagnetic state, showing a quasistatic spin
glass-like magnetism below ~100 K. Considering the earlier indication that
IrS$_6$ octahedra exhibit dimerization associated with the metal-to-insulator
transition below 230 K, the present result suggests that a strong spin-orbit
interaction may be playing an important role in determining the ground state
that accompanies magnetic frustration.",1402.1250v1
2014-02-11,Quantum Oscillations in EuFe2As2 single crystals,"Quantum oscillation measurements can provide important information about the
Fermi surface (FS) properties of strongly correlated metals. Here, we report a
Shubnikov-de Haas (SdH) effect study on the pnictide parent compounds
EuFe$_{2}$As$_{2}$ (Eu122) and BaFe$_{2}$As$_{2}$ (Ba122) grown by In-flux.
Although both members are isovalent compounds with approximately the same
density of states at the Fermi level, our results reveal subtle changes in
their fermiology. Eu122 displays a complex pattern in the Fourier spectrum,
with band splitting, magnetic breakdown orbits, and effective masses
sistematically larger when compared to Ba122, indicating that the former is a
more correlated metal. Moreover, the observed pockets in Eu122 are more
isotropic and 3D-like, suggesting an equal contribution from the Fe $3d$
orbitals to the FS. We speculate that these FS changes may be responsible for
the higher spin-density wave ordering temperature in Eu122.",1402.2412v1
2014-02-11,Topological and magnetic phases with strong spin-orbit coupling on the hyperhoneycomb lattice,"We study the general phase diagram of correlated electrons for iridium-based
(Ir) compounds on the hyperhoneycomb lattice---a crystal structure where the
Ir$^{4+}$ ions form a three-dimensional network with three-fold coordination
recently realized in the $\beta$-Li${}_{2}$IrO${}_{3}$ compound. Using a
combination of microscopic derivations, symmetry analysis, and density
functional calculations, we determine the general model for the electrons
occupying the $j_{\text{eff}}=1/2$ orbitals at the Ir$^{4+}$ sites. In the
non-interacting limit, we find that this model allows for both topological and
trivial electronic band insulators along with metallic states. The effect of
Hubbard-type electron-electron repulsion on the above electronic structure in
stabilizing $\mathbf{q}=\mathbf{0}$ magnetic order reveals a phase diagram with
continuous phase transition between a topological band insulator and a Neel
ordered magnetic insulator.",1402.2654v1
2014-02-13,New insights on the thermal decomposition of lanthanide(III) and actinide(III) oxalates: from neodymium and cerium to plutonium,"Lanthanides are often used as surrogates to study the properties of actinide
compounds. Their behaviour is considered to be quite similar as they both
possess f valence electrons and are close in size and chemical properties. This
study examines the potential of using two lanthanides (neodymium and cerium) as
surrogates for plutonium during the thermal decomposition of isomorphic oxalate
compounds, in the trivalent oxidation state, into oxides. Thus, the thermal
decomposition of neodymium, cerium and plutonium (III) oxalates are
investigated by several coupled thermal analyses (TG-DTA/DSC-MS/FT-IR) and
complementary characterisation techniques (XRD, UV-vis, FT-IR, SEM, carbon
analyser) under both oxidizing and inert atmosphere. The thermal decomposition
mechanisms determined in this study confirmed some previous results reported in
the literature, among diverging propositions, while also elucidating some
original mechanisms not previously considered. Calculated thermodynamic and
kinetic parameters for the studied systems under both atmospheres are reported
and compared with available literature data. Similarities and differences
between the thermal behaviour of plutonium(III) and lanthanide(III) oxalates
are outlined.",1402.3046v1
2014-02-17,"Synthesis by molten salt method of the AFeO3 system (A = La, Gd) and its structural, vibrational and internal hyperfine magnetic field characterization","Polycrystalline samples of LaFeO3 and GdFeO3 were synthesized by the molten
salt method. Some properties and the quality of the resulting compounds were
investigated. The crystal structure and purity of the samples was determined
through X-ray diffraction and Rietveld analysis. The vibrational properties
were characterized by Raman and IR spectroscopy. M\""ossbauer spectroscopy was
used to determine the ionic state of the Fe ions and the internal hyperfine
magnetic fields Considerable reduction of the heat treatment (temperature and
time) for the reaction to take place was achieved without detriment of the
quality of the compounds.",1402.4060v1
2014-03-03,Fragile antiferromagnetism in the heavy-fermion compound YbBiPt,"We report results from neutron scattering experiments on single crystals of
YbBiPt that demonstrate antiferromagnetic order characterized by a propagation
vector, $\tau_{\rm{AFM}}$ = ($\frac{1}{2} \frac{1}{2} \frac{1}{2}$), and
ordered moments that align along the [1 1 1] direction of the cubic unit cell.
We describe the scattering in terms of a two-Gaussian peak fit, which consists
of a narrower component that appears below $T_{\rm{N}}~\approx 0.4$ K and
corresponds to a magnetic correlation length of $\xi_{\rm{n}} \approx$ 80
$\rm{\AA}$, and a broad component that persists up to $T^*\approx$ 0.7 K and
corresponds to antiferromagnetic correlations extending over $\xi_{\rm{b}}
\approx$ 20 $\rm{\AA}$. Our results illustrate the fragile magnetic order
present in YbBiPt and provide a path forward for microscopic investigations of
the ground states and fluctuations associated with the purported quantum
critical point in this heavy-fermion compound.",1403.0526v1
2014-03-07,"Chaotic behavior of the Compound Nucleus, open Quantum Dots and other nanostructures","It is well established that physical systems exhibit both ordered and chaotic
behavior. The chaotic behavior of nanostructure such as open quantum dots has
been confirmed experimentally and discussed exhaustively theoretically. This is
manifested through random fluctuations in the electronic conductance. What
useful information can be extracted from this noise in the conductance? In this
contribution we shall address this question. In particular, we will show that
the average maxima density in the conductance is directly related to the
correlation function whose characteristic width is a measure of energy- or
applied magnetic field- correlation length. The idea behind the above has been
originally discovered in the context of the atomic nucleus, a mesoscopic
system. Our findings are directly applicable to graphene.",1403.1871v1
2014-03-07,Iron based high transition temperature superconductors,"In a superconductor electrons form pairs and electric transport becomes
dissipation-less at low temperatures. Recently discovered iron based
superconductors have the highest superconducting transition temperature next to
copper oxides. In this article, we review material aspects and physical
properties of iron based superconductors. We discuss the dependence of
transition temperature on the crystal structure, the interplay between
antiferromagnetism and superconductivity by examining neutron scattering
experiments, and the electronic properties of these compounds obtained by angle
resolved photoemission spectroscopy in link with some results from scanning
tunneling microscopy/spectroscopy measurements. Possible microscopic model for
this class of compounds is discussed from a strong coupling point of view.",1403.2612v1
2014-03-17,A reentrant phenomenon in magnetic and dielectric properties of Dy2BaNiO5 and an intriguing influence of external magnetic field,"We report that the spin-chain compound Dy2BaNiO5 recently proven to exhibit
magnetoelectric coupling below its Neel temperature (T_N) of 58 K, exhibits
strong frequency-dependent behavior in ac magnetic susceptibility and complex
dielectric properties at low temperatures (<10K), mimicking 'reentrant'
multiglass phenomenon. Such a behavior is not known among undoped compounds. A
new finding in the field of multiferroics is that the characteristic magnetic
feature at such low temperatures moves towards higher temperatures in the
presence of a magnetic-field (H), whereas the corresponding dielectric feature
shifts towards lower temperatures with H, unlike the situation near T_N. This
observation indicates that the alignment of spins by external magnetic fields
tends to inhibit glassy-like slow electric-dipole dynamics, at least in this
system, possibly arising from peculiarities in the magnetic structure.",1403.4166v1
2014-03-20,Suppression of the Charge-Density-Wave State in Sr$_{10}$Ca$_{4}$Cu$_{24}$O$_{41}$ by External Pressure,"The influence of external pressure on the charge-density-wave (CDW) ground
state of the quasi-one-dimensional two-leg ladder compound
Sr$_{10}$Ca$_{4}$Cu$_{24}$O$_{41}$ has been studied by optical reflectivity
measurements as a function of temperature (10 - 300~K) and pressure $P$ (0.3 -
4.3~GPa) over the spectral range 580 - 6000 cm$^1$. With increasing pressure
the CDW transition temperature $T_{CDW}$ decreases with the linear pressure
coefficient $\approx$-70~K/GPa, and above $\approx$3~GPa the CDW phase is
suppressed at all temperatures. This behavior is similar to that in compounds
Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ with increasing Ca content $x$ at ambient
pressure, with the simple scaling $x \approx 3\cdot P(GPa)$. The size of the
CDW gap decreases with increasing pressure, whereas the dimensionality of the
high-temperature insulating phase in Sr$_{10}$Ca$_{4}$Cu$_{24}$O$_{41}$ within
the ladder plane is hardly affected by external pressure.",1403.5063v1
2014-03-27,Ambient Pressure Superconductivity emerging in the Local Moment Antiferromagnetic Phase of Ce$_{3}$PdIn$_{11}$,"We report on magnetization, specific heat and resistivity experiments on
single crystals of the novel heavy Fermion compound Ce$_3$PdIn$_{11}$. At
ambient pressure the compound exhibits two successive transitions at T$_{1}$ =
1.63 K and T$_{\mathrm {N}}$ = 1.49 K into incommensurate and commensurate
local moment antiferromagnetic states, respectively, before becoming
superconducting below T$_{\mathrm {c}}$ = 0.42 K. The large values of
dB$_{\mathrm {c2}}$/dT and B$_{\mathrm {c2}}$ = 2.8 T imply that heavy
quasiparticles form the Cooper pairs. Thus, Ce$_{3}$PdIn$_{11}$ is the first
ambient pressure heavy Fermion superconductor where 4f electrons are
simultaneously responsible for magnetic order and superconductivity.",1403.7010v2
2014-03-31,CuSe-based layered compound Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$ as a quasi-two-dimensional metal,"We have investigated the physical properties of a new layered oxyselenide
Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$, which crystallizes in an unusual intergrowth
structure with Cu$_{2}$Se$_{2}$ and Bi$_{2}$YO$_{4}$ layers. Electric transport
measurement indicates that Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$ behaves metallic.
Thermal transport and Hall measurements show that the type of the carriers is
hole-like and it may be a potential thermoelectric material at high
temperatures. First principle calculations are in agreement with experimental
results and show that Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$ is a quasi-2D metal.
Further theoretical investigation suggests the ground states of the
Bi$_{2}$YO$_{4}$Cu$_{2}$Se$_{2}$-type can be tuned by designing the blocking
layers, which will enrich the physical properties of these compounds.",1403.7892v3
2014-04-03,Itinerant magnetism in URhGe revealed by angle resolved photoelectron spectroscopy,"The electronic structure of the ferromagnetic superconductor URhGe in the
paramagnetic phase has been studied by angle-resolved photoelectron
spectroscopy using soft x rays (hn=595-700 eV). Dispersive bands with large
contributions from U 5f states were observed in the ARPES spectra, and form
Fermi surfaces. The band structure in the paramagnetic phase is partly
explained by the band-structure calculation treating all U 5f electrons as
being itinerant, suggesting that an itinerant description of U 5f states is a
good starting point for this compound. On the other hand, there are qualitative
disagreements especially in the band structure near the Fermi level (E_B < 0.5
eV). The experimentally observed bands are less dispersive than the
calculation, and the shape of the Fermi surface is different from the
calculation. The changes in spectral functions due to the ferromagnetic
transition were observed in bands near the Fermi level, suggesting that the
ferromagnetism in this compound has an itinerant origin.",1404.1324v1
2014-05-05,"Incommensurate, helical spin ground states on the Hollandite lattice","We present a model of classical Heisenberg spins on a Hollandite lattice,
which has been developed to describe the magnetic properties of
$\alpha$-MnO$_2$ and similar compounds. The model has nearest neighbor
interacting spins, however the strength and the sign of spin-spin interactions
is anisotropic and depends on the nature of the bonds. Our analysis shows that
the Hollandite lattice supports four different incommensurate and helical
magnetic ground states depending on the relative strengths and signs of
spin-spin interactions. We show that the incommensurate helical ground states
appear due to the geometrical frustration present in the model. We demonstrate
that each of the four helical incommensurate magnetic phases are continuously
connected to four different collinear antiferromagnetic ground states as the
strength of spin-spin interaction along some bonds is increased. The present
results give support to the presence of helical states that have been
previously suggested experimentally for Hollandite compounds. We provide an
in-depth analysis of the magnetic form factors for each helical phase and
describe how it could be used to identify each of these phases in neutron
diffraction experiments.",1405.0830v1
2014-05-21,Spin Glass Behavior in the Dy3-xYxTaO7 System,"Several x-compositions of the polycrystalline Dy3-xYxTaO7 system,
crystallizing in the weberite-type structure, were synthesized and structurally
characterized using Rietveld refinements based on X-ray diffraction data. In
previous magnetic characterization of Dy3TaO7 (x = 0), with the same crystal
structure, an antiferromagnetic transition at T = 2.3 K has been assigned to
this compound. On the basis of DC and AC magnetic susceptibilities analyses, we
show in this work that all compounds in the x range of 0-1.0 exhibit a spin
glass behavior. The nature of the spin glass behavior in Dy3-xYxTaO7, can be
attributed to the highly frustrated antiferromagnetic interaction of the Dy3+
sublattice and to the Dy3+-Dy3+ distorted tetrahedra array in the weberite-type
structure of this system. By fitting AC susceptibility data, using dynamical
scaling theory equations, we conclude that a cluster spin glass is present in
Dy3-xYxTaO7 in the low temperature range. Depending on the x-composition, Tg ~
2.2 - 3.2 K. In the range 15-300 K the system obeys a Curie-Weiss magnetic
behavior.",1405.5269v1
2014-05-22,Electronic structure of iron-based superconductors: from pnictides to chalcogenides and other similar systems,"This review discusses and compares electronic spectra of new iron-based
high-temperature superconductors (HTSC), as well as a number of chemically
similar compounds. Particular attention is payed to iron chalcogenide
K_{1-x}Fe_{2-y}Se_2, which is isostructural to BaFe_2As_2 (122) pnictide. It is
shown, that Fermi surfaces of K_{1-x}Fe_{2-y}Se_2 are essentially different
from those for pnictides. Using LDA+DMFT and LDA'+DMFT calculations we show,
that electronic correlations in K_{1-x}Fe_{2-y}Se_2 influence the electronic
structure much more significantly, than in the most studied 122 system. We also
discuss the electronic structure of several multiple-band superconductors,
chemically similar to iron-based HTSC, with relatively small values of $T_c$,
such as SrPt_{2}As_{2}, APt_{3}P, (Sr,Ca)Pd_2As_2, and non superconducting
compound BaFe_2Se_3. It is shown, that electronic structure of these systems is
very different from previously studies iron pnictides and chalcogenides. The
value of T_c in these systems can be understood within the simple BCS model.",1405.5677v1
2014-05-24,Triclinic Ni0.6Co0.4TiO3 Ilmenite Oxide,"Forming a solid-solution of NiTiO3 and CoTiO3, two isostructural (ilmenite)
and isosymmetrical (space group R-3) compounds, result in a single-phase
compound with a remarkably low crystal symmetry. By neutron and X-ray
synchrotron powder diffraction techniques, the space group symmetry of the
Ni0.6Co0.4TiO3 sample was found to be triclinic P-1 at room temperature, far
above the magnetic transition temperature. Ni and Co ions were found to prefer
positions close to the octahedron center, whereas Ti ions took off-center
positions. This structural distortion is the first known case in ilmenites and
opens up ways to modify functional properties of magnetic oxides. Origin of the
symmetry lowering is discussed.",1405.6330v1
2014-05-30,"Density functional study of electronic structure, elastic and optical properties of MNH$_2$ (M=Li, Na, K, Rb)","We report systematic first principles density functional study on the
electronic structure, elastic and optical properties of nitrogen based solid
hydrogen storage materials LiNH$_2$, NaNH$_2$, KNH$_2$, and RbNH$_2$. The
ground state structural properties are calculated by using standard density
functional theory and also dispersion corrected density functional theory. We
find that van der Waals interactions are dominant in LiNH$_2$ whereas they are
relatively weak in other alkali metal amides. The calculated elastic constants
show that all the compounds are mechanically stable and LiNH$_2$ is found to be
stiffer material among the alkali metal amides. The melting temperatures are
calculated and which follows the order RbNH$_2$ $<$ KNH$_2$ $<$ NaNH$_2$ $<$
LiNH$_2$. The electronic band structure is calculated by using the Tran-Blaha
modified Becke-Johnson potential and found that all the compounds are
insulators with a considerable band gap. The [NH$_2$]$^-$ derived states are
completely dominating in the entire valence band region while the metal atom
states occupy the conduction band. The calculated band structure is used to
analyze the different interband optical transitions occur between valence and
conduction bands. Our calculations show that these materials have considerable
optical anisotropy.",1405.7783v1
2014-07-02,Short-range cluster spin glass near optimal superconductivity in BaFe$_{2-x}$Ni$_{x}$As$_{2}$,"High-temperature superconductivity in iron pnictides occurs when electrons
are doped into their antiferromagnetic (AF) parent compounds. In addition to
inducing superconductivity, electron-doping also changes the static
commensurate AF order in the undoped parent compounds into short-range
incommensurate AF order near optimal superconductivity. Here we use neutron
scattering to demonstrate that the incommensurate AF order in
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ is not a spin-density-wave arising from the
itinerant electrons in nested Fermi surfaces, but consistent with a cluster
spin glass in the matrix of the superconducting phase. Therefore, optimal
superconductivity in iron pnictides coexists and competes with a mesoscopically
separated cluster spin glass phase, much different from the homogeneous
coexisting AF and superconducting phases in the underdoped regime.",1407.0568v1
2014-07-07,Superconductivity at 4K in Pd deficient layered Ta_2Pd_xS_6,"Here in this short note, we report on the low dimensional 4d and 5d
transition metals-chalcogenide based compounds i.e., Ta2PdxS6, showing
semiconducting to superconducting transition around 4K with upper critical
field outside Pauli paramagnetic limit. It seems couple of different
superconducting phases do exist in these new set of compounds. Our short note
in this regards is thought provoking, asking to explore various unearthed
possible superconducting phases in (Nb/Ta)2Pdx(S/Se/Te)y systems.",1407.1581v3
2014-07-07,Higher-order nonclassical properties of atom-molecule Bose-Einstein Condensate,"The transient quantum statistical properties of the atoms and molecules in an
atom-molecule BEC system are investigated by obtaining a third-order
perturbative solution of the Heisenberg's equations of motion corresponding to
the Hamiltonian of an atom-molecule BEC system where two atoms can collide to
form a molecule. Time dependent quantities like two boson correlation,
entanglement, squeezing, antibunching, etc., are computed and their properties
are compared. It is established that atom-molecule BEC system is highly
nonclassical as lower-order and higher-order squeezing and antibunching in pure
(atomic and molecular) modes, squeezing and antibunching in compound mode and
lower-order and higher-order entanglement in compound mode can be observed in
the atom-molecule BEC system. Exact numerical results are also reported and
analytic results obtained using the perturbative technique are shown to
coincide with the exact numerical results.",1407.1780v1
2014-07-16,Density matrix approach to the orbital ordering in the spinel vanadates: A case study,"In this work we apply the density matrices approach to orbital ordering (OO)
in order to study the OO of the spinel vanadates AV$_{2}$O$_{4}$ (A $\equiv$
Zn, Cd and Mg), which is normally believed to be responsible for the structural
transition from cubic to tetragonal phase observed in these compounds. The
density matrices of vanadium atoms are obtained by using {\it state-of-the-art}
full-potential linearized augmented plane wave method based GGA+U calculations.
In the absence of spin-orbit coupling, the present study shows the existence of
anti-ferro OO in the global (local octahedral) coordinate system where $d_{xz}$
and $d_{yz}$ ($d_{xz}$+$d_{yz}$ and $d_{xz}$-$d_{yz}$) orbitals are mainly
occupied at the neighboring V sites for all the compounds.",1407.4217v2
2014-07-31,The electronic structure of CeNiGe3 and YNiGe3 superconductors by ab initio calculations,"Band structures of pressure-induced CeNiGe3 and exotic BCS-like YNiGe3
superconductors have been calculated employing the full-potential local-orbital
code. Both the local density approximation (LDA) and LDA+U treatment of the
exchange-correlation energy were used. The investigations were focused on
differences between electronic properties of both compounds. Our results
indicate that the Ce-based system exhibits higher density of states at the
Fermi level, dominated by the Ce 4f states, in contrast to its non f-electron
counterpart. The Fermi surface (FS) of each compound originates from three
bands and consists of both holelike and electronlike sheets. The specific FS
nesting properties of only CeNiGe3 enable an occurrence of spin fluctuations of
a helicoidal antiferromagnetic character that may lead to unconventional
pairing mechanism in this superconductor. In turn, the topology of the FS in
YNiGe3 reveals a possibility of multi-band superconductivity, which can explain
the observed anomalous jump at Tc in its specific heat.",1407.8435v1
2014-08-01,Charge-Stripe Order in a Parent Compound of Iron-based Superconductors,"Charge ordering is one of the most intriguing and extensively studied
phenomena in correlated electronic materials because of its strong impact on
electron transport properties including superconductivity. Despite its
ubiquitousness in correlated systems, the occurrence of charge ordering in
iron-based superconductors is still unresolved. Here we use scanning tunneling
microscopy to reveal a long-range charge-stripe order and a highly anisotropic
dispersion of electronic states in the ground state of stoichiometric FeTe, the
parent compound of the Fe(Te, Se, S) superconductor family. The formation of
charge order in a strongly correlated electron system with integer nominal
valence (here Fe$^{2+}$) is unexpected and suggests that the iron-based
superconductors may exhibit more complex charge dynamics than originally
expected. We show that the present observations can be attributed to the
surpassing of the role of local Coulomb interaction by the poorly screened
longer-range Coulomb interactions, facilitated by large Hund's rule coupling.",1408.0057v1
2014-08-04,Discovery and characterization of magnetism in sigma-phase intermetallic Fe-Re compounds,"Systematic experimental (vibrating sample magnetometry) and theoretical
(electronic structure calculations using charge and spin self-consistent
Korringa-Kohn-Rostoker Green function method) studies were performed on a
series of intermetallic sigma-phase Fe(100-x)Re(x) (x = 43-53) compounds. Clear
evidence was found that all investigated samples exhibit magnetism with an
ordering temperature ranging between 65 K for x = 43 and 23 K for x = 53. The
magnetism was revealed to be itinerant and identified as a spin-glass (SG)
possibly having a re-entrant character. The SG was found to be heterogeneous
viz. two regimes could be distinguished as far as irreversibility in
temperature dependence of magnetization is concerned: (1) of a weak
irreversibility and (2) of a strong one. According to the theoretical
calculations the main contribution to the magnetism comes from Fe atoms
occupying all five sub lattices. Re atoms have rather small moments. However,
the calculated average magnetic moments are highly (ferromagnetic ordering
model) or moderately (antiparallel ordering model) overestimated relative to
the experimental data.",1408.0775v1
2014-08-13,On the superconductivity of TiNCl and ZrNCl: A local bonding perspective,"We analyze the superconductors TiNCl and ZrNCl from a local bonding
perspective. Although TiNCl crystallizes in an orthorhombic structure and ZrNCl
crystallizes in a hexagonal structure, both compounds show significant
structural similarities, for example that both consist of layered
metal-Nitrogen networks. The local bonding in those two structures is very
similar, giving rise to a dispersive conduction band mostly consisting of
metal-d -states. Upon doping both compounds show structural changes, which lead
to short metal-metal distances, indicating a bonding interaction that might be
important for the appearance of superconductivity in these systems. We
furthermore draw analogies to other superconductors that are close to a charge
density wave instability around a d 1 -configuration and offer a different
perspective on this class of superconductors, which show non-BCS-like
superconductivity.",1408.3099v1
2014-08-15,Phase diagram of La_{5/8-y}Nd_{y}Ca_{3/8}MnO_3 manganites,"We report a detailed study of the electric transport and magnetic properties
of the LaNdCaMnO manganite system. Substitution of LaIII by smaller NdIII ions,
reduces the mean ionic radius of the A site ion. We have studied samples in the
entire range between rich La and rich Nd compounds. Results of DC magnetization
and resistivity show that doping destabilize the FM character of the pure La
compound and triggers the formation of a phase separated state at intermediate
doping. We have also found evidence of a dynamical behaviour within the phase
separated state. A phase diagram is constructed, summarizing the effect of
chemical substitution on the system.",1408.3593v1
2014-09-01,Electronic structure of non-centrosymmetric superconductor LaPdSi3 and its reference compound LaPdGe3,"Electronic structures of a superconductor without inversion symmetry,
LaPdSi3, and its non-superconducting counterpart, LaPdGe3, have been calculated
employing the full-potential local-orbital method within the density functional
theory. The investigations were focused on analyses of densities of states at
the Fermi level in comparison with previous experimental heat capacity data and
an influence of the antisymmetric spin-orbit coupling on the band structures
and Fermi surfaces (FSs) being very similar for both considered here compounds.
Their FSs sheets originate from four bands and have a holelike character, but
exhibiting pronounced nesting features only for superconducting LaPdSi3. It may
explain a relatively strong electron-phonon coupling in the latter system and
its lack in non-superconducting LaPdGe3.",1409.0443v1
2014-09-02,Anisotropic magnetodielectric coupling behavior of Ca3Co1.4Rh0.6O6 due to geometrically frustrated magnetism,"We have investigated the magnetic, dielectric and magnetodielectric (MDE)
behavior of a geometrically frustrated spin-chain system, Ca3Co1.4Rh0.6O6, in
the single crystalline form for different orientations. The results bring out
that the magnetic behavior of this compound is by itself interesting in the
sense that this compound exhibits an anisotropic glassy-like magnetic behavior
with a huge frequency dependence of ac susceptibility peak for an orientation
along the spin-chain in the range 30-60 K; this behavior is robust to
applications of large external magnetic fields (H) unlike in canonical
spin-glasses. The temperature dependence of dielectric constant also shows
strong frequency dependence with similar robustness to H. The isothermal
H-dependent dielectric results at low temperatures establishes anisotropic MDE
coupling. It is intriguing to note that there is a 'step' roughly at one-third
of saturation values as in the case of isothermal magnetization curves for same
temperatures (for orientation along spin-chain), a correlation hitherto
unrealized for geometrically frustrated systems.",1409.0783v1
2014-09-05,The electronic structure of rare-earth iron silicide R2Fe3Si5 superconductors,"The electronic structures of R2Fe3Si5 (where R = Lu, Tm, Er, Tb, Yb)
intermetallics have been calculated from first principles in local-spin density
(LSDA) and LSDA + U approaches. The majority of rare-earth iron silicides,
except for the heavy-fermion Yb-based compound, exhibit almost equal values of
density of states at the Fermi level (EF) as well as very similar Fermi surface
topology. The electronic structure around EF in the 235-type Fe-based compounds
is completely dominated by the Fe 3d states. Thus the different superconducting
properties of some members of the R2Fe3Si5 family are rather related to a
presence of local magnetic moments of R-atoms than to electronic-structure
features at EF.",1409.1861v1
2014-09-05,Electronic structure of superconducting Lu2Ni3Si5 and its reference compound Y2Ni3Si5 by ab initio calculations,"Electronic structures of orthorhombic ternary nickel silicides:
superconducting Lu2Ni3Si5 and its non-superconducting counterpart, Y2Ni3Si5,
have been calculated employing the fully-relativistic and full-potential
local-orbital method within the density functional theory. Our investigations
were focused particularly on the band structures and Fermi surfaces (FSs),
being very similar for both ternaries. It appears that their FSs exist in four
bands and contain electronlike and holelike three-dimensional sheets and small
pockets, which suggests a presence of two- or even multi-band superconductivity
(SC) in Lu2Ni3Si5. The main difference between both systems is that only in
Lu2Ni3Si5 small electron FS pockets occur around the Gamma point. It allows for
arising BCS-like SC in this compound, as was deduced from previous
heat-capacity measurements, while no sign of SC has been detected (at least
down to 2 K) in Y2Ni3Si5. In the latter system, a possible formation of a
ferromagnetic ground state, which usually tends to destroy SC, has been
excluded by our calculations.",1409.1866v1
2014-09-06,Crossover between Fermi liquid and non-Fermi liquid behavior in the non-centrosymmetric compound Yb$_2$Ni$_{12}$P$_7$,"A crossover from a non-Fermi liquid to a Fermi liquid phase in
Yb$_2$Ni$_{12}$P$_7$ is observed by analyzing electrical resistivity $\rho(T)$,
magnetic susceptibility $\chi(T)$, specific heat $C(T)$, and thermoelectric
power $S(T)$ measurements. The electronic contribution to specific heat,
$C_{e}(T)$, behaves as $C_{e}(T)/T \sim -\ln(T)$ for 5 K $< T <$ 15 K, which is
consistent with non-Fermi liquid behavior. Below $T \sim$ 4 K, the upturn in
$C_{e}(T)/T$ begins to saturate, suggesting that the system crosses over into a
Fermi-liquid ground state. This is consistent with robust $\rho(T) - \rho_0 =
AT^2$ behavior below $T \sim$ 4 K, with the power-law exponent becoming
sub-quadratic for $T >$ 4 K. A crossover between Fermi-liquid and non-Fermi
liquid behavior suggests that Yb$_2$Ni$_{12}$P$_7$ is in close proximity to a
quantum critical point, in agreement with results from recent measurements of
this compound under applied pressure.",1409.2066v1
2014-09-08,Eigenvalue statistics for random Schrodinger operators with non rank one perturbations,"We prove that certain natural random variables associated with the local
eigenvalue statistics for generalized lattice Anderson models constructed with
finite-rank perturbations are compound Poisson distributed. This distribution
is characterized by the fact that the Levy measure is supported on at most a
finite set determined by the rank. The proof relies on a Minami-type estimate
for finite-rank perturbations. For Anderson-type continuum models on $\R^d$, we
prove a similar result for certain natural random variables associated with the
local eigenvalue statistics. We prove that the compound Poisson distribution
associated with these random variables has a Levy measure whose support is at
most the set of positive integers.",1409.2328v1
2014-09-09,Electronic structure of the heavy-fermion superconductor Ce2Ni3Ge5 and its reference Ce2Ni3Si5 compound by ab initio calculations,"Band structures of the pressure-induced, heavy-fermion superconductor
Ce2Ni3Ge5 and its non-superconducting, mixed-valence isostructural (Ibam)
counterpart Ce2Ni3Si5 have been calculated employing the full-potential
local-orbital code. Both the local density approximation (LDA) and LDA+U
approaches were applied. These investigations were focused particularly on the
topology of the Fermi surfaces (FSs) of the compounds. The results show that
the FSs are quite similar in these systems and exist in four bands, containing
three-dimensional holelike and electronlike sheets. However, the specific FS
nesting properties has been revealed only in Ce2Ni3Ge5. They support a
previously postulated presence of antiferromagnetic spin fluctuations (SF) in
the heavy-fermion superconducting state of this germanide under pressure. Such
SF can be responsible for the pressure-induced unconventional superconductivity
in this system.",1409.2648v1
2014-09-11,Multiferroic CuCrO2 under High Pressure: In-Situ X-Ray Diffraction and Raman Spectroscopic Studies,"The compression behavior of delafossite compound CuCrO2 has been investigated
by in-situ x-ray diffraction and Raman spectroscopic measurements upto 23.2 and
34 GPa respectively. X-ray diffraction data shows the stability of ambient
rhombohedral structure upto ~ 23 GPa. Material shows large anisotropy in axial
compression with c-axis compressibility, c= 1.2610-3(1) GPa-1 and a-axis
compressibility, a= 8.9010-3(6) GPa-1. Our XRD data shows an irreversible
broadening of diffraction peaks. Pressure volume data when fitted to 3rd order
Birch-Murnaghan equation of state gives the value of bulk modulus, B0 =
156.7(2.8) GPa with its pressure derivative, B0' as 5.3(0.5). All the observed
vibrational modes in Raman measurements show hardening with pressure.
Appearance of a new mode at ~24 GPa indicates the structural phase transition
in the compound. Our XRD and Raman results indicate that CuCrO2 may be
transforming to an ordered rocksalt type structure under compression.",1409.3333v1
2014-09-30,Copula Relations in Compound Poisson Processes,"We investigate in multidimensional compound Poisson processes (CPP) the
relation between the dependence structure of the jump distribution and the
dependence structure of the respective components of the CPP itself. For this
purpose the asymptotic $\lambda t\to \infty$ is considered, where $\lambda$
denotes the intensity and $t$ the time point of the CPP. For modeling the
dependence structures we are using the concept of copulas. We prove that the
copula of a CPP converges under quite general assumptions to a specific
Gaussian copula, depending on the underlying jump distribution.
  Let $F$ be a $d$-dimensional jump distribution $(d\geq 2)$, $\lambda>0$ and
let $\Psi(\lambda,F)$ be the distribution of the corresponding CPP with
intensity $\lambda$ at the time point $1$. Further, denote the operator which
maps a $d$-dimensional distribution on its copula as $\mathcal{T}$. The
starting point of our investigation was the validity of the equation
\begin{equation} \label{marFreeEq}
\mathcal{T}(\Psi(\lambda,F))=\mathcal{T}(\Psi(\lambda,\mathcal{T}F)).
\end{equation} Our asymptotic theory implies that this equation is, in general,
not true.
  A simulation study that confirms our theoretical results is given in the last
section.",1409.8621v1
2014-10-03,Synthesis and properties of SmO0.5F0.5BiS2 and enhancement in Tc in La1-ySmyO0.5F0.5BiS2,"Crystal structure and properties of a new member of oxy-bismuth-sulfide
SmO1-xFxBiS2 are reported here. The compounds SmO1-xFxBiS2 (x = 0.0 and 0.5)
are found to be isostructural with LaOBiS2 and crystallize in the CeOBiS2 type
structure (P4/nmm). Sm substitution in LaO0.5F0.5BiS2, (La1-ySmyO0.5F0.5BiS2),
leads to a gradual decrease in a-lattice constant however the c-lattice
constant does not show such a gradual trend. Enhancement in Tc is achieved upon
partially substituting La by smaller Sm ion. Maximum Tc ~ 4.6 K was observed
for composition with y = 0.8. Disobeying this trend Tc disappears unexpectedly
in composition SmO0.5F0.5BiS2 (y = 1.0). Both the undoped and F-doped (x = 0.0
and 0.5) compounds are paramagnetic exhibiting semiconducting behavior down to
2 K.",1410.0751v2
2014-10-17,Possible spin frustration in Nd$_2$Ti$_2$O$_7$ probed by muon spin relaxation,"Muon spin relaxation on Nd$_2$Ti$_2$O$_7$ (NTO) and NdLaTi$_2$O$_7$ (NLTO)
compounds are presented. The time spectra for both compounds are as expected
for the paramagnetic state at high temperatures, but deviate from the
exponential function below about 100 K. The muon spin relaxation rate increases
with decreasing temperature firstly, and then levels off below about 10 K,
which is reminiscent of the frustrated systems. An enhancement of the
relaxation rate by a longitudinal field in the paramagnetic state is observed
for NTO, and eliminated by a magnetic dilution for the NLTO sample. This
suggests that the spectral density is modified by a magnetic dilution and thus
indicates that the spins behave cooperatively rather than individually.
Zero-field measurement at 0.3 K indicates that the magnetic ground state for
NTO is ferromagnetic.",1410.4855v1
2014-10-23,On the origin of the electronic anisotropy in iron pnicitde superconductors,"We use polarization-resolved Raman spectroscopy to study the anisotropy of
the electronic characteristics of the iron-pnictide parent compounds
$A$Fe$_{2}$As$_{2}$ ($A$~=~Eu, Sr). We demonstrate that above the structural
phase transition at Ts the dynamical anisotropic properties of the 122
compounds are governed by the emergence of $xy$-symmetry critical collective
mode foretelling a condensation into a state with spontaneously broken
four-fold symmetry at a temperature $T^{*}$. However, the mode's critical
slowing down is intervened by a structural transition at Ts, about 80~K above
$T^{*}$, resulting in an anisotropic density wave state.",1410.6452v1
2014-10-24,Structural and Magnetic Phase Transitions in MnTe-MnSe solid solutions,"Neutron diffraction studies as a function of temperature on solid solutions
of MnSe and MnTe in the Se rich region are presented. Interestingly as Te is
doped in MnSe, the structural transformation to NiAs phase diminishes, both in
terms of \% fraction of compound as well as in terms of transition temperature.
In MnTe$_{0.3}$Se$_{0.7}$, the NaCl to NiAs phase transformation occurs at
about 40K and although it is present at room temperature in
MnTe$_{0.5}$Se$_{0.5}$, its volume fraction is only about 10\% of the total
volume of sample. The magnetic ordering temperature of the cubic phase
decreases with increasing Te content while the hexagonal phase orders at the
same temperature as in MnSe. Anomalies in thermal evolution of lattice
parameters at magnetic ordering as well as structural transition temperatures
indicate presence of magnetostructural coupling in these compounds.",1410.6562v1
2014-10-24,Strong magnetic coupling in the hexagonal R5Pb3 compounds (R = Gd-Tm),"We have synthesized R5Pb3 (R = Gd-Tm) compounds in polycrystalline form and
performed structural analysis, magnetization, and neutron scattering
measurements. For all R5Pb3 reported here the Weiss temperatures {\theta}W are
several times smaller than the ordering temperatures TORD, while the latter are
remarkably high (TORD up to 275 K for R = Gd) compared to other known R-M
binaries (M = Si, Ge, Sn and Sb). The magnetic order changes from ferromagnetic
in R = Gd, Tb to antiferromagnetic in R = Dy-Tm. Below TORD, the magnetization
measurements together with neutron powder diffraction show complex magnetic
behavior and reveal the existence of up to three additional phase transitions.
We believe this to be a result of crystal electric field effects responsible
for high magnetocrystalline anisotropy. The R5Pb3 magnetic unit cells for R =
Tb-Tm can be described with incommensurate magnetic wave vectors with spin
modulation either along the c axis in R = Tb, Er and Tm or within the ab-plane
in R = Dy and Ho.",1410.6732v1
2014-10-29,Low-Energy Optical Phonon Modes in the Caged Compound LaRu2Zn20,"The caged compound LaRu2Zn20 exhibits a structural transition at TS =150 K,
whose driving mechanism remains elusive. We have investigated atomic dynamics
by the measurements of specific heat C and inelastic X-ray scattering (IXS).
The lattice part of the specific heat Clat divided by T3, Clat/T3, shows a
broad peak at around 15 K, which is reproduced by two Einstein modes with
characteristic temperatures of 35 K and 82 K, respectively. IXS measurements
along the [111] and [110] directions reveal optical phonon modes at 3 meV (35
K) and 7 meV (80 K), respectively, whose values agree with the values of
Einstein temperatures. The first principles calculation has assigned the phonon
modes at 3 meV as the optical modes of Zn atoms located at the middle of two La
atoms. The low-energy vibration of the Zn atom perpendicular to the there-fold
axis is thought to lead the structural instability of LaRu2Zn20.",1410.7916v3
2014-11-11,First-principles study of an organometallic S=1/2 kagome compound,"Cu(1,3-benzenedicarboxylate) [Cu(1,3-bdc)] contains structurally perfect
kagom\'{e} planes formed by Cu$^{2+}$ ions without the presence of diamagnetic
defects. This organometallic compound should have served as a precious platform
to explore quantum frustrated magnetism, yet the experimental results so far
are mysterious, leading to questions such as ""Is Cu(1,3-bdc) just a trivial
weak ferromagnet?"". Using the the density functional theory, we have
systematically studied the electronic and magnetic properties of Cu(1,3-bdc),
putting forth a theoretical basis to clarify this novel material. We present
numerical evidences of a dominating antiferromagnetic (AFM) exchange between
nearest-neighbor (NN) Cu$^{2+}$ as experimentally extracted from the
high-temperature susceptibility data. We further show that beyond the NN AFM
exchange, the additional interactions in Cu(1,3-bdc) have similar strength as
those in the well-studied kagom\'{e} antiferromagnet, Herbertsmithite, by
designing a comparative study. In the end, the origin of the phase transition
and FM signals observed under low temperature is discussed based on the DFT
results.",1411.3026v3
2014-11-14,Modelling Dynamical Fluorescent Micro Thermal Imaging of the Heat Diffusion in the La5Ca9Cu24O41 Spin Ladder Compound,"The dynamical fluorescent microthermal imaging (FMI) experiment has been used
to investigate the phonon-magnon interaction in the 1D Heisenberg
antiferromagnet La5Ca9Cu24O41. This material shows highly anisotropic heat
conductivity due to the efficient magnetic heat transport along the spin
ladders in the compound. To extract information on the phonon-magnon
interaction we modelled the dynamic heat transport experiment using a two
temperature model approach, taking both the crystal as well as the PMMA/EuTTA
fluorescent heat imaging layer into account. The simulations are carried out by
the finite element method using COMSOL Multiphysics Heat Transfer Module. The
results of the numerical calculations are expected to be used for the data
analysis of the experimental studies.",1411.3872v2
2014-11-17,"Dirac and Weyl Semimetal in XYBi (X=Ba, Eu; Y=Cu, Ag and Au)","Weyl and Dirac semimetals recently stimulate intense research activities due
to their novel properties. Combining first-principles calculations and
effective model analysis, we predict that nonmagnetic compounds BaYBi (Y=Au, Ag
and Cu) are Dirac semimetals. As for the magnetic compound EuYBi, although the
time reversal symmetry is broken, their long-range magnetic ordering cannot
split the Dirac point into pairs of Weyl points. However, we propose that
partially substitute Eu ions by Ba ions will realize the Weyl semimetal.",1411.4394v3
2014-11-21,"Structural transitions, magnetic properties, and electronic structures of Co(Fe)-doped MnNiSi compounds","The structural transitions, magnetic properties, and electronic structures of
Co(Fe)-doped MnNiSi compounds are investigated by x-ray powder diffraction
(XRD), differential scanning calorimetry (DSC), magnetic measurements, and
first-principles calculations. Results indicate that all samples undergo a
martensitic transition from the Ni2In-type parent phase to TiNiSi-type
orthorhombic phase at high temperatures. The substitution of Co(Fe) for Mn in
Mn1-xCoxNiSi (x = 0.2, 0.3, 0.4) and Mn1-yFeyNiSi (y = 0.26, 0.30, 0.36, 0.46,
0.55) samples decreases the structural transition temperature (Tt) and Curie
temperature of martensite (TCM). The martensite phases show a typical
ferromagnetic behavior with saturation field (HS) being basically unchanged
with increasing Co(Fe) content, while the saturation magnetization (MS) shows a
decreasing tendency. The theoretically calculated moments are in good agreement
with the experimentally measured results. The orbital hybridizations between
different 3d elements are analyzed from the distribution of density of states.",1411.5766v1
2014-11-23,Compound Rank-k Projections for Bilinear Analysis,"In many real-world applications, data are represented by matrices or
high-order tensors. Despite the promising performance, the existing
two-dimensional discriminant analysis algorithms employ a single projection
model to exploit the discriminant information for projection, making the model
less flexible. In this paper, we propose a novel Compound Rank-k Projection
(CRP) algorithm for bilinear analysis. CRP deals with matrices directly without
transforming them into vectors, and it therefore preserves the correlations
within the matrix and decreases the computation complexity. Different from the
existing two dimensional discriminant analysis algorithms, objective function
values of CRP increase monotonically.In addition, CRP utilizes multiple rank-k
projection models to enable a larger search space in which the optimal solution
can be found. In this way, the discriminant ability is enhanced.",1411.6231v3
2014-11-25,Robust flat bands in RCo5 (R=rare earth) compounds,"The mechanism to realize the peculiar flat bands generally existing in RCo5
(R=rare earth) compounds is clarified by analyzing the first-principles band
structures and the tight-binding model. These flat bands are constructed from
the localized eigenstates, the existence of which is guaranteed by the partial
cancelation between the intersite hopping amplitudes among the Co-3d states at
the Kagome sites and those between the Kagome and honeycomb sites. Their
relative positions to other bands can be controlled by varying the lattice
parameters keeping their dispersion almost flat, which suggests the possibility
of flat-band engineering.",1411.6715v2
2014-11-26,Hybridization and Slow Coherence Crossover in the Intermediate Valence Compound YbAl$_3$ via Quasiparticle Scattering Spectroscopy,"The intermediate valence compound YbAl$_3$ is known to undergo a
hybridization process between itinerant and localized electrons. The resulting
heavy Fermi liquid remains non-magnetic and non-superconducting. A microscopic
understanding of the hybridization process in YbAl$_3$ is still lacking
although some characteristic temperature and energy scales have been
identified. Here we report results from novel spectroscopic measurements based
on quasiparticle scattering. From the conductance spectra taken over a wide
temperature range, we deduce that the band renormalization and hybridization
process begins around 110 K, causing the conductance enhancement with a Fano
background. This temperature, a new scale found in this work, is much higher
than the coherence temperature (34 K). Our observation is in agreement with the
slow crossover scenario discussed recently in the literature. The indirect
hybridization gap appears to open concomitantly with the emergence of a
coherent Fermi liquid. Thus, we suggest its measurement as a more rigorous way
to define the coherence temperature than just taking the temperature for a
resistivity peak.",1411.7073v1
2014-11-28,Cross-Modal Learning via Pairwise Constraints,"In multimedia applications, the text and image components in a web document
form a pairwise constraint that potentially indicates the same semantic
concept. This paper studies cross-modal learning via the pairwise constraint,
and aims to find the common structure hidden in different modalities. We first
propose a compound regularization framework to deal with the pairwise
constraint, which can be used as a general platform for developing cross-modal
algorithms. For unsupervised learning, we propose a cross-modal subspace
clustering method to learn a common structure for different modalities. For
supervised learning, to reduce the semantic gap and the outliers in pairwise
constraints, we propose a cross-modal matching method based on compound ?21
regularization along with an iteratively reweighted algorithm to find the
global optimum. Extensive experiments demonstrate the benefits of joint text
and image modeling with semantically induced pairwise constraints, and show
that the proposed cross-modal methods can further reduce the semantic gap
between different modalities and improve the clustering/retrieval accuracy.",1411.7798v1
2014-12-18,Quantum phase transition between disordered and ordered states in the spin-1/2 kagome lattice antiferromagnet (Rb$_{1-x}$Cs$_{x}$)$_2$Cu$_3$SnF$_{12}$,"We have systematically investigated the variation of the exchange parameters
and the ground state in the $S = 1/2$ kagome-lattice antiferromagnet
(Rb$_{1-x}$Cs$_{x}$)$_2$Cu$_3$SnF$_{12}$, via magnetic measurements using
single crystals. One of the parent compounds, Rb$_2$Cu$_3$SnF$_{12}$, which has
a distorted kagome lattice accompanied by four sorts of nearest-neighbor
exchange interaction, has a disordered ground state described by a pinwheel
valence-bond-solid state. The other parent compound, Cs$_2$Cu$_3$SnF$_{12}$,
which has a uniform kagome lattice at room temperature, has an ordered ground
state with the $q$ = 0 spin structure. The analysis of magnetic
susceptibilities shows that with increasing cesium concentration $x$, the
exchange parameters increase with the tendency to be uniform. It was found that
the ground state is disordered for $x$ < 0.53 and ordered for $x$ > 0.53. The
pseudogap observed for $x$ < 0.53 and the N\'{e}el temperature for $x$ > 0.53
approach zero at $x_{\rm c}$ $\simeq$ 0.53. This is indicative of the
occurrence of a quantum phase transition at $x_{\rm c}$.",1412.5770v2
2014-12-19,[(Li0.8Fe0.2)OH]FeS and the ferromagnetic superconductors [(Li0.8Fe0.2)OH]Fe(S1-xSex) (0<x<1),"[(Li0.8Fe0.2)OH]FeS and the series [(Li0.8Fe0.2)OH]Fe(S1-xSex) (0<x<1) were
synthesized by hydrothermal methods and characterized by X-ray single crystal
and powder diffraction, EDX and chemical analysis. Selenium-rich compounds show
the coexistence of magnetic ordering with superconductivity known from the pure
selenium compound. Sulphur doping decreases the critical temperature through
chemical pressure until superconductivity is completely absent in
[(Li0.8Fe0.2)OH]FeS, while the ferromagnetism in the [(Li0.8Fe0.2)OH] layers
persists. The Li:Fe ratio in the hydroxide layer, and thus the charge transfer
of 0.2 electrons from the hydroxide to the iron chalcogenide layers remains
unchanged in [(Li0.8Fe0.2)OH]Fe(S1-xSex), which indicates that the chemical
pressure effect of the smaller sulphide ions impedes superconductivity in
[(Li0.8Fe0.2)OH]FeS",1412.6475v1
2014-12-22,Transport Theory of Metallic B20 Helimagnets,"B20 compounds are a class of cubic helimagnets harboring nontrivial spin
textures such as spin helices and skyrmions. It has been well understood that
the Dzyaloshinskii-Moriya (DM) interaction is the origin of these textures, and
the physics behind the DM interaction is the spin-orbital coupling (SOC).
However the SOC shows its effect not only on the spins, but also on the
electrons. In this paper, we will discuss effects of the SOC on the electron
and spin transports in B20 compounds. An effective Hamiltonian is presented
from symmetry analysis, and the spin-orbital coupling therein shows anomalous
behaviors in anisotropic magnetoresistance (AMR) and helical resistance. New
effects such as inverse spin-galvanic effect is proposed, and the origin of the
DM interaction is discussed.",1412.7177v1
2014-12-24,Nonparametric Bayesian inference for multidimensional compound Poisson processes,"Given a sample from a discretely observed multidimensional compound Poisson
process, we study the problem of nonparametric estimation of its jump size
density $r_0$ and intensity $\lambda_0$. We take a nonparametric Bayesian
approach to the problem and determine posterior contraction rates in this
context, which, under some assumptions, we argue to be optimal posterior
contraction rates. In particular, our results imply the existence of Bayesian
point estimates that converge to the true parameter pair $(r_0,\lambda_0)$ at
these rates. To the best of our knowledge, construction of nonparametric
density estimators for inference in the class of discretely observed
multidimensional L\'{e}vy processes, and the study of their rates of
convergence is a new contribution to the literature.",1412.7739v2
2015-01-08,Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6,"Exchange bias effect in the ferromagnetic double perovskite compound
Y$_2$CoMnO$_6$, which is also a multiferroic, is reported. The exchange bias,
observed below 8~K, is explained as arising due to the interface effect between
the ferromagnetic and antiferromagnetic clusters created by {\it antisite}
disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with
metamagnetic ""steps"" and significant coercive field, $H_c \approx$ 10~kOe are
observed in this compound which has a $T_c \approx$ 75~K. A model based on
growth of ferromagnetic domains overcoming the elastic energy of structurally
pinned magnetic interfaces, which closely resembles martensitic-like
transitions, is adapted to explain the observed effects. The role of {\it
antisite} disorder in creating the domain structure leading to exchange bias
effect is highlighted in the present work.",1501.01766v1
2015-01-09,Anisotropic magnetic properties of URhIn$_{5}$ compound,"We report on synthesis and anisotropic physical properties of URhIn$_{5}$.
High quality single crystals were grown in In-flux. The compound undergoes a
second order phase transition into an antiferromagnetic state at
T$_{\textrm{N}}$ = 98 K. The transition is field independent up to 9 T. An
increase of the resistivity $\rho$ with j along the [100], [110] and [001]
tetragonal axis indicates a spin-density-wave induced order with the gap
opening first along the [001] direction. The magnetic susceptibility $\chi$ =
M/H exhibits a strong anisotropy. Above T $=$ 200 K, $\chi$(T) follows
Curie-Weiss law with the effective moment of $\mu_{\textrm{eff}}$ = 3.71
$\mu_{\textrm{B}}/$U and the Weiss temperatures of $\theta_{\textrm{P}}^{[100]}
= -900$ K and $\theta_{\textrm{P}}^{[001]} = -500$ K for H $\parallel$ [100]
and H $\parallel$ [001] respectively. The characteristic Kondo-like temperature
for URhIn$_{5}$ yields T$_{\textrm{K}} =$ 125 K.",1501.02150v1
2015-01-13,Exploring the efficacy of molecular fragments of different complexity in computational SAR modeling,"An important first step in computational SAR modeling is to transform the
compounds into a representation that can be processed by predictive modeling
techniques. This is typically a feature vector where each feature indicates the
presence or absence of a molecular fragment. While the traditional approach to
SAR modeling employed size restricted fingerprints derived from path fragments,
much research in recent years focussed on mining more complex graph based
fragments. Today, there seems to be a growing consensus in the data mining
community that these more expressive fragments should be more useful. We
question this consensus and show experimentally that fragments of low
complexity, i.e. sequences, perform better than equally large sets of more
complex ones, an effect we explain by pairwise correlation among fragments and
the ability of a fragment set to encode compounds from different classes
distinctly. The size restriction on these sets is based on ordering the
fragments by class-correlation scores. In addition, we also evaluate the
effects of using a significance value instead of a length restriction for path
fragments and find a significant reduction in the number of features with
little loss in performance.",1501.03015v1
2015-01-15,Polar codes in quantum information theory,"Polar codes are the first capacity achieving and efficiently implementable
codes for classical communication. Recently they have also been generalized to
communication over classical-quantum and quantum channels. In this work we
present our recent results for polar coding in quantum information theory,
including applications to classical-quantum multiple access channels,
interference channels and compound communication settings, including the first
proof of channel coding achieving the Han-Kobayashi rate region of the
interference channel without the need of a simultaneous decoder. Moreover we
add to the existing framework by extending polar codes to achieve the
asymmetric capacity and improving the block error probability for
classical-quantum channels. In addition we use polar codes to prove a new
achievable rate region for the classical-quantum broadcast channel. We also
discuss polar codes for quantum communication over quantum channels and state
results towards codes for compound quantum channels in this setting. We
conclude by stating a list of interesting open questions to invite further
research on the topic.",1501.03737v1
2015-01-23,Giant gap in the magnon excitations of the quasi-1D chain compound Sr3NiIrO6,"Inelastic neutron scattering on the spin-chain compound Sr$_3$NiIrO$_6$
reveals gapped quasi-1D magnetic excitations. The observed one-magnon band
between 29.5 and 39 meV consists of two dispersive modes. The spin wave
spectrum could be well fitted with an antiferromagnetic anisotropic exchange
model and single ion anisotropy on the Ni site. The extracted dominant
anisotropic antiferromagnetic intra-chain exchange interaction between Ir and
Ni ions are $J_z=19.5$ meV and $J_{xy}=12.1$ meV. These values justify previous
electronic structure calculations, showing the importance of Ir spin orbit
coupling on the electron correlations. The magnetic excitations survive up to
200 K well above the magnetic ordering temperature of $T_N \sim 70$ K, also
indicating a quasi-1D nature of the magnetic interactions in Sr$_3$NiIrO$_6$.
Our results not only support the idea of the existence of a new temperature
scale well above $T_N$, but also emphasize the need to consider new exchange
paths complicated by the SOC, resulting in additional characteristic
temperatures in such spin-chain systems.",1501.05735v1
2015-01-30,Spectroscopic Evidence for Strong Quantum Spin Fluctuations with Itinerant Character in YFe2Ge2,"We report x-ray absorption and photoemission spectroscopy of the electronic
structure in the normal state of metallic YFe2Ge2. The data reveal evidence for
large fluctuating spin moments on the Fe sites, as indicated by exchange
multiplets appearing in the Fe 3s core level photoemission spectra, even though
the compound does not show magnetic order. The magnitude of the multiplet
splitting is comparable to that observed in the normal state of the Fe-pnictide
superconductors. This shows a connection between YFe2Ge2 and the Fe-based
superconductors even though it contains neither pnictogens nor chalcogens. The
implication is that the chemical range of compounds showing at least one of the
characteristic magnetic signatures of the Fe-based superconductors is broader
than previously thought.",1501.07868v1
2015-02-03,A permutational-splitting sample procedure to quantify expert opinion on clusters of chemical compounds using high-dimensional data,"Expert opinion plays an important role when selecting promising clusters of
chemical compounds in the drug discovery process. We propose a method to
quantify these qualitative assessments using hierarchical models. However, with
the most commonly available computing resources, the high dimensionality of the
vectors of fixed effects and correlated responses renders maximum likelihood
unfeasible in this scenario. We devise a reliable procedure to tackle this
problem and show, using theoretical arguments and simulations, that the new
methodology compares favorably with maximum likelihood, when the latter option
is available. The approach was motivated by a case study, which we present and
analyze.",1502.00754v1
2015-02-03,Magnetic Single Domain State of the Monochiral Helimagnet MnSi in Zero Field Limit: Magnetic Properties Study,"Attention is drawn to a possibility to obtain the monochiral helimagnet MnSi
in a magnetic single domain state (SDS) in zero magnetic field limit. It is
shown that this metastable zero field magnetic SDS can be achieved by gradual
decrease of the field down to zero after initial transformation of MnSi to a
spin-polarized state in high fields $H$. This can be achieved only for
$\bf{H}\parallel$ [111]. Investigations of MnSi in magnetic SDS give us a
possibility to determine the two components of low field magnetic
susceptibility of this compound, $\chi_{\perp}(T)$ and $\chi_{\parallel}(T)$
[$\chi_{\perp}$ and $\chi_{\parallel}$ correspond to $\bf{H}\perp$, and
$\bf{H}\parallel$ (111)-plane containing magnetic moments in helically ordered
state]. These results are compared with macroscopic magnetic susceptibility of
MnSi earlier determined for this compound only in magnetic multi domain state
(MDS). In addition our results are compared with the data reported for some
non-monochiral helimagnets. Characteristic features of monochiral helimagnets
are elucidated.",1502.00810v2
2015-02-05,Light-induced mass transport in amorphous chalcogenides: Towards surface plasmon-assisted nanolithography and near-field nanoimaging,"Two types of amorphous functional materials, based on lightsensitive
inorganic compounds like Se and As20Se80 chalcogenide glass (ChG) were
investigated with the aim to establish the influence of plasmonic fields,
excited by the band-gap light in nanocomposite layers made of these compounds
and gold nanoparticles on their photomechanical response. Both these basic
materials are characterized by pronounced photoplastic effect and used for
real-time optical recording of optoelectronic elements (based mainly on surface
relief gratings) due to high photofluidity and polarization-dependent
masstransport. We established that mass-transport processes in these ChG can be
enhanced in the presence of localized plasmonic fields generated by light if
the condition of surface plasmon resonance (SPR) is fulfilled. The subjects of
special interest are the mass-transport processes at the nano-scale stimulated
in the nano-copmosite layers of either by the uniform or periodically
distributed optical fields. It was found that irradiation by light with SPR
really enhance the efficiency of masstransport and produce surface
nanostructurizations. The variation in the topography follows closely and
permanently the underlying near field intensity pattern.",1502.01576v1
2015-02-19,Occurrence of flat bands in strongly correlated Fermi systems and high-$T_c$ superconductivity of electron-doped compounds,"We consider a class of strongly correlated Fermi systems that exhibit an
interaction-induced flat band pinned to the Fermi surface, and generalize the
Landau strategy to accommodate a flat band and apply the more comprehensive
theory to electron systems of solids. The non-Fermi-liquid behavior that
emerges is compared with relevant experimental data on heavy-fermion metals and
electron-doped high-$T_c$ compounds. We elucidate how heavy-fermion metals have
extremely low superconducting transition temperature $T_c$, its maximum reached
in the heavy-fermion metal CeCoIn$_5$ does not exceed 2.3 K, and explain the
enhancement of $T_c$ observed in high-$T_c$ superconductors. We show that the
coefficient $A_1$ of the $T$-linear resistivity scales with $T_c$, in agreement
with the experimental behavior uncovered in the electron-doped materials. We
have also constructed schematic temperature-doping phase diagram of the copper
oxide superconductor $\rm La_{2-x}Ce_xCuO_4$ and explained the doping
dependence of its resistivity.",1502.05659v2
2015-02-22,Hyperpolarized Nanodiamond with Long Spin Relaxation Times,"The use of hyperpolarized agents in magnetic resonance (MR), such as
13C-labeled compounds, enables powerful new imaging and detection modalities
that stem from a 10,000-fold boost in signal. A major challenge for the future
of the hyperpolarizaton technique is the inherently short spin relaxation
times, typically < 60 seconds for 13C liquid-state compounds, which limit the
time that the signal remains boosted. Here, we demonstrate that 1.1% natural
abundance 13C spins in synthetic nanodiamond (ND) can be hyperpolarized at
cryogenic and room temperature without the use of toxic free- radicals, and,
owing to their solid-state environment, exhibit relaxation times exceeding 1
hour. Combined with the already established applications of NDs in the
life-sciences as inexpensive fluorescent markers and non-cytotoxic substrates
for gene and drug delivery, these results extend the theranostic capabilities
of nanoscale diamonds into the domain of hyperpolarized MR.",1502.06214v1
2015-02-23,Potential of volatile organic compounds as markers of entrapped humans for use in urban search-and-rescue operations,"Volatile organic compounds emitted by a human body form a chemical signature
capable of providing invaluable information on the physiological status of an
individual and, thereby, could serve as signs-of-life for detecting victims
after natural or man-made disasters. In this review a database of potential
biomarkers of human presence was created on the basis of existing literature
reports on volatiles in human breath, skin emanation, blood, and urine.
Approximate fluxes of these species from the human body were estimated and used
to predict their concentrations in the vicinity of victims. The proposed
markers were classified into groups of different potential for victim
detection. The major classification discriminants were the capability of
detection by portable, real-time analytical instruments and background levels
in urban environment. The data summarized in this review are intended to assist
studies on the detection of humans via chemical analysis and accelerate
investigations in this area of knowledge.",1502.06485v1
2015-02-25,Superconductivity in the presence of disorder in skutterudite-related La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ compounds; electrical transport and magnetic studies,"La$_3$Co$_4$Sn$_{13}$ and La$_3$Ru$_4$Sn$_{13}$ were categorized as BCS
superconductors. In a plot of the critical field $H_{c2}$ vs $T$,
La$_3$Ru$_4$Sn$_{13}$ displays a second superconducting phase at the higher
critical temperature $T_c^{\star}$, characteristic of inhomogeneous
superconductors, while La$_3$Co$_4$Sn$_{13}$ shows bulk superconductivity below
$T_c$. We observe a decrease in critical temperatures with external pressure
and magnetic field for both compounds with $\frac{dT_c^{\star}}{dP} >
\frac{dT_c}{dP}$. The pressure dependences of $T_c$ are interpreted according
to the McMillan theory and understood to be a consequence of lattice
stiffening. The investigation of the superconducting state of
La$_3$Co$_x$Ru$_{4-x}$Sn$_{13}$ shows a $T_c^{\star}$ that is larger then $T_c$
for $x<4$. This unique and unexpected observation is discussed as a result of
the local disorder and/or the effect of chemical pressure when Ru atoms are
partially replaced by smaller Co atoms.",1502.07324v1
2015-02-26,Polarization effects in ionic solids and melts,"Ionic solids and melts are compounds in which the interactions are dominated
by electrostatic effects. However, the polarization of the ions also plays an
important role in many respects as has been clarified in recent years thanks to
the development of realistic polarizable interaction potentials. After
detailing these models, we illustrate the importance of polarization effects on
a series of examples concerning the structural properties, such as the
stabilization of particular crystal structures or the formation of
highly-coordinated multivalent ions in the melts, as well as the dynamic
properties such as the diffusion of ionic species. The effects on the structure
of molten salts interfaces (with vacuum and electrified metal) is also
described. Although most of the results described here concern inorganic
compounds (molten fluorides and chlorides, ionic oxides...), the particular
case of the room-temperature ionic liquids, a special class of molten salts in
which at least one species is organic, will also be briefly discussed to
indicate how the ideas gained from the study of ""simple"" molten salts are being
transferred to these more complex systems.",1502.07534v1
2015-03-04,Structural instabilities and sequence of phase transitions in SrBi$_2$Ta$_2$O$_9$ and SrBi$_2$Nb$_2$O$_9$ from first principles and Monte Carlo simulations,"Despite their structural similarities, SrBi$_2$Ta$_2$O$_9$ (SBT) and
SrBi$_2$Nb$_2$O$_9$ (SBN) undergo a different sequence of phase transitions.
The phase diagram of SBT as a function of the temperature includes an
intermediate phase between the high-temperature phase and the ferroelectric
ground state, while in the Niobium compound the intermediate phase is
suppressed and a single transition between the high- and low temperature
structures is observed. We present \emph{ab initio} calculations that reveal
the relevance of a trilinear coupling between three symmetry-adapted modes to
stabilize the ground sate in both compounds, being this coupling much stronger
in SBN. Within the framework of the phenomenological Landau theory, it is shown
that by solely increasing the strength of the trilinear coupling the topology
of the phase diagram of SBT can change up to suppress the intermediate phase.
Monte Carlo simulations on an idealized $\phi^4$ Hamiltonian confirm that the
trilinear coupling is the key parameter that determines the sequence of phase
transitions and that for higher dimensionality of the order parameters the
stability region of the intermediate phase is narrower.",1503.01356v1
2015-03-04,Toxicity Prediction using Deep Learning,"Everyday we are exposed to various chemicals via food additives, cleaning and
cosmetic products and medicines -- and some of them might be toxic. However
testing the toxicity of all existing compounds by biological experiments is
neither financially nor logistically feasible. Therefore the government
agencies NIH, EPA and FDA launched the Tox21 Data Challenge within the
""Toxicology in the 21st Century"" (Tox21) initiative. The goal of this challenge
was to assess the performance of computational methods in predicting the
toxicity of chemical compounds. State of the art toxicity prediction methods
build upon specifically-designed chemical descriptors developed over decades.
Though Deep Learning is new to the field and was never applied to toxicity
prediction before, it clearly outperformed all other participating methods. In
this application paper we show that deep nets automatically learn features
resembling well-established toxicophores. In total, our Deep Learning approach
won both of the panel-challenges (nuclear receptors and stress response) as
well as the overall Grand Challenge, and thereby sets a new standard in tox
prediction.",1503.01445v1
2015-03-06,Mechanical properties and electronic structure of the incompressible rhenium carbides and nitrides: A first-principles study,"By means of first-principles calculations, the structural stability,
mechanical properties and electronic structure of the newly synthesized
incompressible Re2C, Re2N, Re3N and an analogous compound Re3C have been
investigated. Our results agree well with the available experimental and
theoretical data. The proposed Re3C is shown to be energetically, mechanically
and dynamically stable and also incompressible. Furthermore, it is suggested
that the incompressibility of these compounds is originated from the strong
covalent bonding character with the hybridization of 5d orbital of Re and the
2p orbital of C or N, and a zigzag topology of interconnected bonds, e.g.,
Re-Re, Re-C or Re-N bonding.",1503.02048v1
2015-03-12,Anomalous phonon redshift in K-doped BaFe2As2 iron pnictides,"The effect of K, Co and P dopings on the lattice dynamics in the
BaFe$_2$As$_2$ system is studied by infrared spectroscopy. We focus on the
phonon at $\sim$ 253 cm$^{-1}$, the highest energy in-plane infrared-active
Fe-As mode in BaFe$_2$As$_2$. Our studies show that the Co and P dopings lead
to a blue shift of this phonon in frequency, which can be simply interpreted by
the change of lattice parameters induced by doping. In sharp contrast, an
unusual red shift of the same mode was observed in the K-doped compound, at
odds with the above explanation. This anomalous behavior in K-doped
BaFe$_2$As$_2$ is more likely associated with the coupling between lattice
vibrations and other channels, such as charge or spin. This coupling scenario
is also supported by the asymmetric line shape and intensity growth of the
phonon in the K-doped compound.",1503.03838v1
2015-03-14,Effect of composition on magnetocaloric properties of Mn$ _{3} $Ga$ _{(1-x)} $Sn$ _{x} $C,"A study investigating the effect of Sn substitution on the magnetocaloric
properties of Mn$ _{3} $Ga$ _{(1-x)} $Sn$ _{x} $C compounds reveals that nature
of the MCE has a strong dependence on the nature of the magnetic ordering. For
small amounts of Sn ($ x\leq0.2 $) the MCE is of the inverse type wherein an
increase in the applied field beyond 5T gives rise to a table like temperature
dependence of the entropy due to a coupling between the first order FM - AFM
transition and the field induced AFM - FM transition. Replacement of Ga by
larger concentrations of Sn ($ x\geq0.71 $) $(\Delta S_M)$ results in a change
of the MCE to a conventional type with very little variation in the position of
$(\Delta S_M)_{max}$ with increasing magnetic field. This has been explained to
be due to the local strain introduced by A site ions (Ga/Sn) which affect the
magnetostructural coupling in these compounds.",1503.04276v1
2015-03-19,A new class of chiral materials hosting magnetic skyrmions beyond room temperature,"Skyrmions, topologically protected vortex-like nanometric spin textures in
magnets, have been attracting increasing attention for emergent electromagnetic
responses and possible technological applications for spintronics. In
particular, metallic magnets with chiral and cubic/tetragonal crystal structure
may have high potential to host skyrmions that can be driven by low electrical
current excitation. However, experimental observations of skyrmions have so far
been limited to below room temperature for the metallic chiral magnets,
specifically for the MnSi-type B20 compounds. Toward technological
applications, it is crucial to transcend this limitation. Here we demonstrate
the formation of skyrmions with unique spin helicity both at and above room
temperature in a family of cubic chiral magnets: beta-Mn-type Co-Zn-Mn alloys
with a different chiral space group from that of B20 compounds. Lorentz
transmission electron microscopy (LTEM), magnetization, and small angle neutron
scattering (SANS) measurements unambiguously reveal the formation of a skyrmion
crystal under the application of magnetic field (H<~1 kOe) in both thin- plate
(thickness<150 nm) and bulk forms.",1503.05651v1
2015-03-20,Unbiased crystal structure prediction of NiSi under high pressure,"Based on the unbiased structure prediction, we showed that the stable form of
NiSi compound under the pressure of 100 and 200 GPa is the Pmmn-structure.
Furthermore, we discovered a new stable phase - the deformed tetragonal
CsCl-type structure with a = 2.174 {\AA} and c = 2.69 {\AA} at 400 GPa.
Specifically, the sequence of high-pressure phase transitions is the following:
the Pmmn-structure - below 213 GPa, the tetragonal CsCl-type - in the range
213-522 GPa, and cubic CsCl - higher than 522 GPa. As the CsCl-type structure
is considered as the model structure of FeSi compound at the conditions of the
Earth's core, this result implies restrictions on the Fe-Ni isomorphic
miscibility in FeSi.",1503.06079v1
2015-03-24,On the magnetism of sigma-Fe54Cr46 alloy: AC and DC susceptibility studies,"Sigma-phase intermetallic compound of Fe54Cr46 was investigated using DC and
AC magnetic susceptibility techniques. A clear-cut evidence was found that the
sample orders magnetically at Tc=23.5 K and its ground magnetic state is
constituted by a spin glass. The temperature at which the zero-field cooled
magnetization has its maximum decreases with an external magnetic field in line
with the Gabay-Toulouse prediction. The temperature at which the AC magnetic
susceptibility has its maximum does not depend on frequency which, in the light
of the mean-field theory, testifies to very long magnetic interactions.",1503.06991v1
2015-03-24,Magnetically-induced ferroelectricity in the (ND4)2[FeCl5(D2O)] molecular compound,"The number of magnetoelectric multiferroic materials reported to date is
scarce, as magnetic structures that break inversion symmetry and induce an
improper ferroelectric polarization typically arise through subtle competition
between different magnetic interactions. The (NH4)2[FeCl5(H2O)] compound is a
rare case where such improper ferroelectricity has been observed in a molecular
material. We have used single crystal and powder neutron diffraction to obtain
detailed solutions for the crystal and magnetic structures of
(NH4)2[FeCl5(H2O)], from which we determined the mechanism of multiferroicity.
From the crystal structure analysis, we observed an order-disorder phase
transition related to the ordering of the ammonium counterion. We have
determined the magnetic structure below TN, at 2K and zero magnetic field,
which corresponds to a cycloidal spin arrangement with magnetic moments
contained in the ac-plane, propagating parallel to the c-axis. The observed
ferroelectricity can be explained, from the obtained magnetic structure, via
the inverse Dzyaloshinskii-Moriya mechanism.",1503.07130v1
2015-03-31,Magnetic Phase Diagram of the Breathing Pyrochlore Antiferromagnet LiGa1-xInxCr4O8,"The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore
lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation.
We show here that the solid solutions LiGa1-xInxCr4O8 between these two
'breathing' pyrochlore compounds display (i) rapid suppression of magnetic and
structural transitions upon doping the end members, (ii) spin-glass-like
freezing above 2 K in the range 0.1 $\lesssim$ x $\lesssim$ 0.6, and (iii)
apparent spin-gap behavior for x $\gtrsim$ 0.7. Furthermore, no transitions are
observed above 2 K at x ~ 0.9, where magnetic susceptibility remains finite at
2 K and magnetic heat capacity shows a quadratic temperature dependence at 1-5
K. Our work shows that breathing pyrochlore compounds provide a unique
opportunity for studying both geometrical frustration and bond alternation.",1503.08902v1
2015-04-06,Dependence of superconductivity in CuxBi2Se3 on quenching conditions,"Topological superconductivity, implying gapless protected surface states, has
recently been proposed to exist in the compound CuxBi2Se3. Unfortunately, low
diamagnetic shielding fractions and considerable inhomogeneity have been
reported in this compound. In an attempt to understand and improve on the
finite superconducting volume fractions, we have investigated the effects of
various growth and post-annealing conditions. With a melt-growth (MG) method,
diamagnetic shielding fractions of up to 56% in Cu0.3Bi2Se3 have been obtained,
the highest value reported for this method. We investigate the efficacy of
various quenching and annealing conditions, finding that quenching from
temperatures above 560C is essential for superconductivity, whereas quenching
from lower temperatures or not quenching at all is detrimental. A modified
floating zone (FZ) method yielded large single crystals but little
superconductivity. Even after annealing and quenching, FZ-grown samples had
much less chance of being superconducting than MG-grown samples. From the low
shielding fractions in FZ-grown samples and the quenching dependence, we
suggest that a metastable secondary phase having a small volume fraction in
most of the samples may be responsible for the superconductivity.",1504.01360v1
2015-04-08,First-principle study on bulk and (1 1 1) surface of MP (M=K and Rb) in rocksalt structure,"The electronic and magnetic properties of bulk and (1 1 1) surfaces for MP
(M=K ans Rb) in rocksalt structure have been investigated by employing
first-principle calculations. The results reveal that the compounds are
half-metallic ferromagnets at the equilibrium lattice constants with large
half-metallic band gaps of 0.46 and 0.74 eV. The (111) surfaces of KP and RbP
keep their bulk half-metallic property. We study the stabilities of the bulk
compounds and their (1 1 1) surfaces as well.",1504.01793v1
2015-04-08,Optimizing thermoelectric performances of low-temperature SnSe compounds by electronic structure design,"Recently SnSe compound was reported to have a peak thermoelectric figure-5
of-merit (ZT) of 2.62 at 923 K, but the ZT values at temperatures below 750 K
are relatively low. In this work, the electronic structures of SnSe are
calculated using the density functional theory, and the electro- and
thermo-transport properties upon varying chemical potential (or carrier
density) are evaluated by the semi-classic Boltzmann transport theory, showing
that the calculated ZT values along the a10 and c-axes below 675 K are in
agreement with reported values, but that along the b-axis can be as high as
2.57 by optimizing the carrier concentration to ~3.6*1019 cm-3. It is revealed
that a mixed ionic-covalent bonding and heavy-light band overlapping near the
valence band are the reasons for the higher thermoelectric performance",1504.01853v1
2015-04-14,Topological semimetals and topological insulators in rare earth monopnictides,"We use first principles calculations to study the electronic properties of
rock salt rare earth monopnictides La$X$ ($X=$N, P, As, Sb, Bi). A new type of
topological band crossing termed `linked nodal rings' is found in LaN when the
small spin-orbital coupling (SOC) on nitrogen orbitals is neglected. Turning on
SOC gaps the nodal rings at all but two points, which remain gapless due to
$C_4$-symmetry and leads to a 3D Dirac semimetal. Interestingly, unlike LaN,
compounds with other elements in the pnictogen group are found to be
topological insulators (TIs), as a result of band reordering due to the
increased lattice constant as well as the enhanced SOC on the pnictogen atom.
These TI compounds exhibit multi-valley surface Dirac cones at three
$\bar{M}$-points on the $(111)$-surface.",1504.03492v1
2015-04-17,"Ab initio calculations of the structural, electronic and elastic properties of the MZN2 (M=Be, Mg; Z=C, Si) chalcopyrite semiconductors","Four ternary semiconductors with the chalcopyrite structure (BeCN2, BeSiN2,
MgCN2, and MgSiN2) were studied using the first principles methods. The
structural, electronic, optical and elastic properties were calculated. All
these materials were found to be the indirect band gap semiconductors, with the
calculated band gaps in the range from 3.46 eV to 3.88 eV. Comparison of the
degree of covalency/ionicity of the chemical bonds in these compounds was
performed. Anisotropy of the optical properties of these tetragonal crystals
was demonstrated by calculating the real and imaginary parts of the dielectric
function {\epsilon}. Anisotropy of the elastic properties of these materials
was analyzed by plotting the three-dimensional dependences of the Young moduli
and their two-dimensional cross-sections. It was also shown (at least,
qualitatively) that there exists a correlation between the optical and elastic
anisotropy: the most optically anisotropic MgSiN2 is also most elastically
anisotropic material in the considered group. High hardness (bulk moduli up to
300 GPa) together with large band gaps may lead to new potential applications
of these compounds.",1504.04440v1
2015-04-23,Artefacts in geometric phase analysis of compound materials,"The geometric phase analysis (GPA) algorithm is known as a robust and
straightforward technique that can be used to measure lattice strains in high
resolution transmission electron microscope (TEM) images. It is also attractive
for analysis of aberration-corrected scanning TEM (ac-STEM) images that resolve
every atom column, since it uses Fourier transforms and does not require
real-space peak detection and assignment to appropriate sublattices. Here it is
demonstrated that in ac-STEM images of compound materials (i.e. with more than
one atom per unit cell) an additional phase is present in the Fourier
transform. If the structure changes from one area to another in the image (e.g.
across an interface), the change in this additional phase will appear as a
strain in conventional GPA, even if there is no lattice strain. Strategies to
avoid this pitfall are outlined.",1504.06089v1
2015-04-24,Low-density silicon allotropes for photovoltaic applications,"Silicon materials play a key role in many technologically relevant fields,
ranging from the electronic to the photovoltaic industry. A systematic search
for silicon allotropes was performed by employing a modified ab initio minima
hopping crystal structure prediction method. The algorithm was optimized to
specifically investigate the hitherto barely explored low-density regime of the
silicon phase diagram by imitating the guest-host concept of clathrate
compounds. In total 44 metastable phases are presented, of which 11 exhibit
direct or quasi-direct band-gaps in the range of $\approx$1.0-1.8 eV, close to
the optimal Shockley-Queisser limit of $\approx$1.4 eV, with a stronger overlap
of the absorption spectra with the solar spectrum compared to conventional
diamond silicon. Due to the structural resemblance to known clathrate compounds
it is expected that the predicted phases can be synthesized.",1504.06372v2
2015-04-27,Optical properties of V2O3 in its whole phase diagram,"Vanadium sesquioxide V2O3 is considered a textbook example of Mott-Hubbard
physics. In this paper we present an extended optical study of its whole
temperature/doping phase diagram as obtained by doping the pure material with
M=Cr or Ti atoms (V1-xMx)2O3. We reveal that its thermodynamically stable
metallic and insulating phases, although macroscopically equivalent, show very
different low-energy electrodynamics. The Cr and Ti doping drastically change
both the antiferromagnetic gap and the paramagnetic metallic properties. A
slight chromium content induces a mesoscopic electronic phase separation, while
the pure compound is characterized by short-lived quasiparticles at high
temperature. This study thus provides a new comprehensive scenario of the
Mott-Hubbard physics in the prototype compound V2O3.",1504.07279v1
2015-05-04,Superconducting gap and vortex lattice of the heavy fermion compound CeCu_2Si_2,"The order parameter and pairing mechanism for superconductivity in heavy
fermion compounds are still poorly understood. Scanning tunneling microscopy
and spectroscopy at ultra-low temperatures can yield important information
about the superconducting order parameter and the gap structure. Here, we study
the first heavy fermion superconductor, CeCu_2Si_2. Our data show the
superconducting gap which is not fully formed and exhibits features that point
to a multi-gap order parameter. Spatial mapping of the zero bias conductance in
magnetic field reveals the vortex lattice, which allows us to unequivocally
link the observed conductance gap to superconductivity in CeCu_2Si_2. The
vortex lattice is found to be predominantly triangular with distortions at
fields close to \sim 0.7 H_{c2}.",1505.00804v2
2015-05-05,"Suppression of magnetism in Ba5AlIr2O11: interplay of Hund's coupling, molecular orbitals and spin-orbit interaction","The electronic and magnetic properties of Ba$_5$AlIr$_2$O$_{11}$ containing
Ir-Ir dimers are investigated using the GGA and GGA+SOC calculations. We found
that strong suppression of the magnetic moment in this compound recently found
in [J. Terzic {\it et al.}, Phys. Rev. B {\bf 91}, 235147 (2015)] is not due to
charge-ordering, but is related to the joint effect of the spin-orbit
interaction and strong covalency, resulting in the formation of metal-metal
bonds. They conspire and act against the intra-atomic Hund's rule exchange
interaction to reduce total magnetic moment of the dimer. We argue that the
same mechanism could be relevant for other $4d$ and $5d$ dimerized transition
metal compounds.",1505.00877v2
2015-05-05,Metal-insulator transition and topological properties of pyrochlore iridates,"Combining density functional theory (DFT) and embedded dynamical mean-field
theory (DMFT) methods, we study the metal-insulator transition in
$R_2$Ir$_2$O$_7$ ($R$=Y, Eu, Sm, Nd, Pr, and Bi) and the topological nature of
the insulating compounds. Accurate free energies evaluated using the charge
self-consistent DFT+DMFT method reveal that the metal-insulator transition
occurs for an A-cation radius between that of Nd and Pr, in agreement with
experiments. The all-in-all-out magnetic phase, which is stable in the Nd
compound but not the Pr one, gives rise to a small Ir$^{4+}$ magnetic moment of
$\approx 0.5\mu_B$ and opens a sizable correlated gap. We demonstrate that
within this state-of-the-art theoretical method, the insulating bulk pyrochlore
iridates are topologically trivial.",1505.01203v1
2015-05-13,Organometallic-like localization of 4d-derived spins in an inorganic conducting niobium suboxide,"Based on the refined crystal structure comprised of columns of 3*4 planar
blocks of NbO6 octahedra and first principles electronic structure methods, we
find that orthorhombic (o)-Nb$_{12}$O$_{29}$ introduces a new class of
transition metal oxide. The electronic system consists of a large Nb
dimer-based localized orbital comparable in size to those in organometallic
compounds, yet is tightly bound and weakly interacting with itinerant
electronic bands. These local moments, a rare occurrence for Nb, form
one-dimensional spin chains that criss-cross perpendicularly oriented
conducting nanowires. The local moment bandwidth is comparable to what is seen
in rare earth compounds with extremely localized orbitals. The microscopic
origin is traced to the local structure of the NbO6 octahedra and associated
orbital+spin ordering. The resulting 1D$_s$*1D$_c$ anisotropic two dimensional
Heisenberg-Kondo lattice model (s=spin, c=charge) provides a strongly
anisotropic spin-fermion lattice system for further study.",1505.03563v1
2015-05-20,Structural and magnetic phase transitions in EuTi1-xNbxO3,"We investigate the structural and magnetic phase transitions in EuTi1-xNbxO3
with synchrotron powder X-ray diffraction (XRD), resonant ultrasound
spectroscopy (RUS), and magnetization measurements. Upon Nb-doping, the Pm-3m
to I4/mcm structural transition shifts to higher temperatures and the room
temperature lattice parameter increases while the magnitude of the octahedral
tilting decreases. In addition, Nb substitution for Ti destabilizes the
antiferromagnetic ground state of the parent compound and long range
ferromagnetic order is observed in the samples containing more than 10% Nb. The
structural transition in pure and doped compounds is marked by a step-like
softening of the elastic moduli in a narrow temperature interval near TS, which
resembles that of SrTiO3 and can be adequately modeled using the Landau free
energy model employing the same coupling between strain and octahedral tilting
order parameter as previously used to model SrTiO3.",1505.05528v1
2015-05-26,Reduced Dimensionality and Magnetic Frustration in KCr$_3$As$_3$,"We study the electronic and magnetic structures of the newly-discovered
compound KCr$_3$As$_3$. The non-magnetic state has five Fermi surface sheets
involving respectively three quasi-one-dimensional and two three-dimensional
energy bands. However, the ground state is magnetic, exhibiting a novel
interlayer antiferromagnetic order where the basic block-spin state of a unit
Cr triangle retains a high spin magnitude. Moreover, its Fermi surface involves
three one-dimensional sheets only, providing evidence for local moments in this
compound due to the reduced dimensionality. By fitting a twisted spin tube
model the magnetic frustrations caused by local moments are found to be
relaxed, leading to gapless spin excitations. A frustration-induced transition
to the disordered low block-spin state is expected upon increasing the
intralayer exchange interaction.",1505.06801v1
2015-06-01,Imaging Time-Series to Improve Classification and Imputation,"Inspired by recent successes of deep learning in computer vision, we propose
a novel framework for encoding time series as different types of images,
namely, Gramian Angular Summation/Difference Fields (GASF/GADF) and Markov
Transition Fields (MTF). This enables the use of techniques from computer
vision for time series classification and imputation. We used Tiled
Convolutional Neural Networks (tiled CNNs) on 20 standard datasets to learn
high-level features from the individual and compound GASF-GADF-MTF images. Our
approaches achieve highly competitive results when compared to nine of the
current best time series classification approaches. Inspired by the bijection
property of GASF on 0/1 rescaled data, we train Denoised Auto-encoders (DA) on
the GASF images of four standard and one synthesized compound dataset. The
imputation MSE on test data is reduced by 12.18%-48.02% when compared to using
the raw data. An analysis of the features and weights learned via tiled CNNs
and DAs explains why the approaches work.",1506.00327v1
2015-06-02,Effects of frustration and cyclic exchange on the spin-1/2 Heisenberg antiferromagnet within the self-consistent spin-wave theory,"The relevance of the quasi-two-dimensional spin-1/2 frustrated quantum
antiferromagnet due to its possibility of modelling the high-temperature
superconducting parent compounds has resulted in numerous theoretical and
experimental studies. This paper presents a detailed research of the influence
of the varying exchange interactions on the model magnetic properties within
the framework of self-consistent spin-wave theory based on Dyson-Maleev
representation. Beside the nearest neighbour interaction within the plane, the
planar frustration up to the third nearest neighbours, cyclic interaction and
the interlayer coupling are taken into account. The detailed description of the
elementary spin excitations, staggered magnetization, spin-wave velocity
renormalization factor and ground-state energy is given. The results are
compared to the predictions of the linear spin-wave theory and when possible
also to the second-order perturbative spin-wave expansion results. Finally,
having at our disposal improved experimental results for the in-plane spin-wave
dispersion in high-$T_c$ copper oxide $\mbox{La}_2\mbox{CuO}_4$, the
self-consistent spin-wave theory is applied to that compound in order to
correct earlier obtained set of exchange parameters and high temperature
spin-wave dispersion.",1506.00773v1
2015-06-20,Crossover from Metal to Insulator in Dense Lithium-Rich Compound $\textrm{CLi}_{4}$,"Crystal structures of $\textrm{CLi}_4$ compounds are explored through
\emph{ab} \emph{initio} evolutionary methodology. Phase transition from metal
to semimetal and semiconductor, and eventually to insulator with increasing
pressure are revealed under pressure. Pressure-induced evolution of
anti-metallization has been described quantitatively by Fermi Surface Filling
Ratio and electron energy band gap using \emph{ab} \emph{initio} \emph{GW}
calculations. Anti-metallization is attributed to the hybrid valence electrons
and their repulsion by core electrons into the lattice interstices. Very weak
electron-phonon coupling interactions are found in the metallic phases,
resulting in very low superconducting temperature.",1506.06187v3
2015-06-21,Magnetic and magnetotransport behavior of RFe5Al7 (R= Gd and Dy): Observation of re-entrant inverse-magnetocaloric phenomenon and asymmetric magnetoresistance behavior,"We have compared and contrasted magnetic, magnetocaloric and magnetoresistive
properties of Gd and Dy members of the rare-earth (R) series RFe5Al7,
crystallizing in ThMn12 structure, known to order antiferromagnetically. Among
other observations, we would like to emphasize on the following novel findings:
(i) There are multiple sign-crossovers in the temperature (T) dependence of
isothermal entropy change (DeltaS) in the case of Dy compound; in addition to
nil DeltaS at the magnetic compensation point known for two-magnetic-sublattice
systems, there is an additional sign-crossover at low temperatures, as though
there is a re-entrant inverse magnetocaloric phenomenon. Corresponding sign
reversals could also be observed in the magnetoresistance data. (ii) The plots
of magnetoresistance versus magnetic field are found to be highly asymmetric
with the reversal of the direction of magnetic-field (H) well below TN for both
compounds, similar to that known for an antiferromagnetic tunnel junctions. We
attribute these to subtle changes in spin orientations of R and Fe moments
induced by T and H.",1506.06373v1
2015-06-29,Magneto-infrared spectroscopy of Landau levels and Zeeman splitting of three-dimensional massless Dirac Fermions in ZrTe$_5$,"We present a magneto-infrared spectroscopy study on a newly identified
three-dimensional (3D) Dirac semimetal ZrTe$_5$. We observe clear transitions
between Landau levels and their further splitting under magnetic field. Both
the sequence of transitions and their field dependence follow quantitatively
the relation expected for 3D \emph{massless} Dirac fermions. The measurement
also reveals an exceptionally low magnetic field needed to drive the compound
into its quantum limit, demonstrating that ZrTe$_5$ is an extremely clean
system and ideal platform for studying 3D Dirac fermions. The splitting of the
Landau levels provides a direct and bulk spectroscopic evidence that a
relatively weak magnetic field can produce a sizeable Zeeman effect on the 3D
Dirac fermions, which lifts the spin degeneracy of Landau levels. Our analysis
indicates that the compound evolves from a Dirac semimetal into a topological
line-node semimetal under current magnetic field configuration.",1506.08676v2
2015-06-30,Quantum oscillations in heavy fermion compound YbPtBi,"We present quantum oscillations observed in the heavy fermion compound YbPtBi
in magnetic fields far beyond its field-tuned, quantum critical point. Quantum
oscillations are observed in magnetic fields as low as 60 kOe at 60 mK and up
to temperatures as high as 3 K, which confirms the very high quality of the
samples as well as the small effective mass of conduction carriers far from the
quantum critical point. Although the electronic specific heat coefficient of
YbPtBi reaches ~ 7.4 J/mol K2 in zero field, which is one of the highest
effective mass value among heavy fermion systems, it is suppressed quickly by
applied magnetic field. The quantum oscillations were used to extract the
quasiparticle effective masses of the order of the bare electron mass, which is
consistent with the behavior observed in specific heat measurements. Such a
small effective masses at high fields can be understood by considering the
suppression of Kondo screening.",1507.00064v1
2015-07-01,Charting the known chemical space for non-aqueous Lithium-air battery electrolyte solvents,"The Li-Air battery is a very promising candidate for powering future
mobility, but finding a suitable electrolyte solvent for this technology turned
out to be a major problem. We present a systematic computational investigation
of the known chemical space for possible Li-Air electrolyte solvents. It is
shown that the problem of finding better Li-Air electrolyte solvents is not
only - as previously suggested - about maximizing Li+ and O2- solubilities, but
about finding the optimal balance of these solubilities with the viscosity of
the solvent. As our results also show that trial-and-error experiments on known
chemicals are unlikely to succeed, full chemical sub-spaces for the most
promising compound classes are investigated, and suggestions are made for
further experiments. The proposed screening approach is transferable and robust
and can readily be applied to optimize electrolytes for other electrochemical
devices. It goes beyond the current state-of-the-art both in width (considering
the number of compounds screened and the way they are selected), as well as
depth (considering the number and complexity of properties included).",1507.00305v2
2015-07-06,The energy gap of the compound FeSe0.5Te0.5 determined by specific heat and point contact spectroscopy,"The superconductor $FeSe_{0.5}Te_{0.5}$ was studied with Point Contact
spectroscopy and specific heat in polycrystalline samples. The transition
temperature determined by magnetic measurement was $T_C =14.5$ K. The size of
the energy gap measured by junctions is $\Delta = 1.9$ meV, whereas the gap
determined by the specific heat measurements was $\Delta = 2.3 $ meV. The gap
evolution with temperature follows BCS, the ratio 2$\Delta$/$K_BT_C$ has values
between 2.88 $\leq 2\Delta/K_BT_C \leq 3.04$. The compound was grown by solid
state synthesis in quartz ampoules under vacuum at 950 C. Crystal structure was
characterized by X-ray diffraction. The superconducting properties were
characterized by magnetization, resistivity and specific heat. This
superconductor shows an isotropic energy gap as observed with the fitting of
the specific heat at low temperature.",1507.01633v1
2015-07-10,New synthesis route and magnetic structure of Tm2Mn2O7 - pyrochlore,"In this work we present a new chemical route to synthesize Tm2Mn2O7
pyrochlore, a compound which is thermodynamically unstable at ambient pressure.
Differently from the reported in the past high pressure synthesis of the same
compound applying oxides as starting materials, we have obtained a pure phase
Tm2Mn2O7 by a converting TmMnO3 at 1100 C and 1300 bar oxygen pressure. The
studies of Tm2Mn2O7 performed by a high resolution neutron powder diffraction
have shown, that a pure pyrochlore cubic phase Tm2Mn2O7 (space group Fd-3m)
have been obtained. On cooling below 25K there is a transition to a
ferromagnetically (FM) ordered phase observed with an additional
antiferromagnetic (AFM) canting suggesting a lowering of the initial cubic
crystal symmetry. The magnetic transition is accompanied by small but well
visible magnetostrsiction effect. Using symmetry analysis we have found a
solution for the AFM structure in the maximal Shubnikov subgroup I41/am'd'.",1507.02830v1
2015-07-17,Cross-section Fluctuations in Open Microwave Billiards and Quantum Graphs: The Counting-of-Maxima Method Revisited,"The fluctuations exhibited by the cross-sections generated in a
compound-nucleus reaction or, more generally, in a quantum-chaotic scattering
process, when varying the excitation energy or another external parameter, are
characterized by the width Gamma_corr of the cross-section correlation
function. In 1963 Brink and Stephen [Phys. Lett. 5, 77 (1963)] proposed a
method for its determination by simply counting the number of maxima featured
by the cross sections as function of the parameter under consideration. They,
actually, stated that the product of the average number of maxima per unit
energy range and Gamma_corr is constant in the Ercison region of strongly
overlapping resonances. We use the analogy between the scattering formalism for
compound-nucleus reactions and for microwave resonators to test this method
experimentally with unprecedented accuracy using large data sets and propose an
analytical description for the regions of isolated and overlapping resonances.",1507.04966v2
2015-07-15,Molecular geometry of alkaloids present in seeds of mexican prickly poppy,"The work is a study of the geometry of the molecules via molecular mechanics
of the main alkaloids found in the seeds of Argemone Mexicana Linn, a prickly
poppy, which is considered one of the most important species of plants in
traditional Mexican and Indian medicine system. The seeds have toxic properties
as well as bactericide, hallucinogenic, fungicide, insecticide, in
isoquinolines and sanguinarine alkaloids such as berberine. A computational
study of the molecular geometry of the molecules through molecular mechanics of
the main alkaloids compounds present in plant seeds is described in a computer
simulation. The plant has active ingredients compounds: allocryptopine,
berberine, chelerythrine, copsitine, dihydrosanguinarine, protopine and
sanguinarine. The studied alkaloids form two groups having similar charge
distribution among themselves, which have dipole moments of these two times
higher than in the other group.",1507.05042v1
2015-07-21,Pressure-induced Superconductivity in the Iron-based Ladder Material BaFe2S3,"All the iron-based superconductors identified to date share a square lattice
composed of Fe atoms as a common feature, despite having different crystal
structures. In copper-based materials, the superconducting phase emerges not
only in square lattice structures but also in ladder structures. Yet iron-based
superconductors without a square lattice motif have not been found despite
being actively sought out. Here, we report the discovery of pressure-induced
superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott
insulator with striped-type magnetic ordering below ~120 K. On the application
of pressure this compound exhibits a metal-insulator transition at about 11
GPa, followed by the appearance of superconductivity below Tc = 14 K, right
after the onset of the metallic phase. Our findings indicate that iron-based
ladder compounds represent promising material platforms, in particular for
studying the fundamentals of iron-based superconductivity.",1507.05864v1
2015-08-01,Non-collinear vs collinear description of the Ir-based one-$t_{2g}$ -hole perovskite-related compounds: SrIrO$_3$ and Sr$_2$IrO$_4$,"We present an analysis of the electronic structure of perovskite-related
iridates, 5d electron compounds where a subtle interplay between spin-orbit
coupling, tetragonal distortions and electron correlations determines the
electronic structure properties. We suggest via electronic structure
calculations that a non-collinear calculation is required to obtain solutions
close to the usually quoted $j_{eff}$ = 1/2 state to describe the $t_{2g}$ hole
in the $Ir^{4+} :d^5$ cation, while a collinear calculation yields a different
solution, the hole is in a simpler xz/yz complex combination with a smaller
$L_z /S_z$ ratio. We describe what the implications of this are in terms of the
electronic structure; surprisingly, both solutions barely differ in terms of
their band structure, and are similar to the one obtained by a tight binding
model involving $t_{2g}$ orbitals with mean field interactions. We also analyze
how the electronic structure and magnetism evolve with strain, with the
spin-orbit coupling strength and with the on-site Coulomb repulsion, suggest
the way the band structure gets modified and draw some comparisons with
available experimental observations.",1508.00107v2
2015-08-04,One-dimensional quantum antiferromagnetism in the $p-$orbital CsO$_2$ compound revealed by electron paramagnetic resonance,"Recently it was proposed that the orbital ordering of $\pi_{x,y}^*$ molecular
orbitals in the superoxide CsO$_2$ compound leads to the formation of spin-1/2
chains below the structural phase transition occuring at $T_{\rm{s1}}=61$~K on
cooling. Here we report a detailed X-band electron paramagnetic resonance (EPR)
study of this phase in CsO$_2$ powder. The EPR signal appears as a broad line
below $T_{\rm{s1}}$, which is replaced by the antiferromagnetic resonance below
the N\'{e}el temperature $T_{\rm N}=8.3$~K. The temperature dependence of the
EPR linewidth between $T_{\rm{s1}}$ and $T_{\rm{N}}$ agrees with the
predictions for the one-dimensional Heisenberg antiferromagnetic chain of
$S=1/2$ spins in the presence of symmetric anisotropic exchange interaction.
Complementary analysis of the EPR lineshape, linewidth and the signal intensity
within the Tomonaga-Luttinger liquid (TLL) framework allows for a determination
of the TLL exponent $K=0.48$. Present EPR data thus fully comply with the
quantum antiferromagnetic state of spin-1/2 chains in the orbitally ordered
phase of CsO$_2$, which is, therefore, a unique $p-$orbital system where such a
state could be studied.",1508.00789v1
2015-08-04,Magnetically induced phonon splitting in ACr$_2$O$_4$ spinels from first principles,"We study the magnetically-induced phonon splitting in cubic ACr$_2$O$_4$
(A=Mg, Zn, Cd, Hg) spinels from first principles, and demonstrate that the sign
of the splitting, which is experimentally observed to be opposite in
CdCr$_2$O$_4$ compared to ZnCr$_2$O$_4$ and MgCr$_2$O$_4$, is determined solely
by the particular magnetic ordering pattern observed in these compounds. We
further show that this interaction between magnetism and phonon frequencies can
be fully described by the previously proposed spin-phonon coupling model that
includes only the nearest neighbor exchange. Finally, using this model with
materials specific parameters calculated from first principles, we provide
additional insights into the physics of spin-phonon coupling in this intriguing
family of compounds.",1508.00834v1
2015-08-05,Superconductivity in Hf$_5$Sb$_3$$_-$$_x$Ru$_x$: Are Ru and Sb a critical charge-transfer pair for superconductivity?,"We address the hypothesis that in intermetallic compounds, contrary to a
long-standing view that considers electron count and crystal structure type as
the only significant chemical criteria for the occurrence of superconductivity,
consideration of the actual elements present is a third equally important
factor. The importance of chemical identity may seem obvious, especially to
chemists, but it has not previously been explicitly tested for intermetallic
superconductors. Here we test the hypothesis by searching for and finding a new
superconductor in the tetragonal symmetry Hf5Sb3-xMx solid solution. This phase
is ideal for this study, because M can be many 3d, 4d and 5d transition metals
in an M-Sb chain and is a minor elemental constituent. We find
superconductivity for M = Ru only. This is the case even when the electron
count can be adjusted to the same value with a different transition element
within the same structure type. This leads us to propose that, like Cu-O
(cuprate superconductors) and Fe-As (iron-pnictide superconductors) in
different classes of compounds, Ru and Sb may be a critical element pair for
superconductivity in intermetallic phases.",1508.01233v1
2015-08-06,The many faces of quantum kagome materials: Interplay of further-neighbour exchange and Dzyaloshinskii-Moriya interaction,"The field of frustrated magnetism has been enriched significantly by the
discovery of various kagome lattice compounds. These materials exhibit a great
variety of macroscopic behaviours ranging from magnetic orders to quantum spin
liquids. Using large-scale exact diagonalization, we construct the phase
diagram of the $S=1/2$ $J_1$-$J_2$ kagome Heisenberg model with $z$-axis
Dzyaloshinskii-Moriya interaction $D_z$. We show that this model can
systematically account for many of the experimentally observed phases. Small
$J_2$ and $D_z$ can stabilize respectively a gapped and a gapless spin liquid.
When $J_2$ or $D_z$ is substantial, the ground state develops a $\mathbf{Q}=0$,
$120^\textrm{o}$ antiferromagnetic order. The critical strengths for inducing
magnetic transition are $D^c_z \sim 0.1\, J_1$ at $J_2=0$, and $J^c_2\sim 0.4\,
J_1$ at $D_z=0$. The previously reported values of $D_z$ and $J_2$ for
herbertsmithite [ZnCu$_3$(OH)$_6$Cl$_2$] place the compound in close proximity
to a quantum critical point.",1508.01523v1
2015-08-10,The role of dimensionality in the Kondo Ce$TX_{2}$ family: the case of CeCd$_{1-δ}$Sb$_{2}$,"Motivated by the presence of competing magnetic interactions in the heavy
fermion family Ce$TX_2$ ($T$ = transition metal, $X$ = pnictogen), here we
study the novel parent compound CeCd$_{1-\delta}$Sb$_{2}$ by combining
magnetization, electrical resistivity, and heat-capacity measurements. Contrary
to the antiferromagnetic (AFM) ground state observed in most members of this
family, the magnetic properties of our CeCd$_{1-\delta}$Sb$_{2}$ single
crystals revealed a ferromagnetic (FM) ordering at $T_{\rm c}$ = 3 K with an
unusual soft behavior. By using a mean field model including anisotropic
nearest-neighbors interactions and the tetragonal crystalline electric field
(CEF) Hamiltonian, a systematic analysis of our macroscopic data was obtained.
Our fits allowed us to extract a simple but very distinct CEF scheme, as
compared to the AFM counterparts. As in the previously studied ferromagnet
CeAgSb$_{2}$, a pure $|\pm 1/2 \rangle$ ground state is realized, hinting at a
general trend within the ferromagnetic members. We propose a general scenario
for the understanding of the magnetism in this family of compounds based on the
subtle changes of dimensionality in the crystal structure.",1508.02116v1
2015-08-10,Localized itinerant electrons and unique magnetic properties of SrRu2O6,"SrRu2O6 has unique magnetic properties. It is characterized by a very high
N\'eel temperature, despite its quasi-two-dimensional structure, and has a
magnetic moment more than twice reduced compared to the formal ionic count.
First principles calculations show that only an ideal Neel ordering in the Ru
plane is possible, with no other metastable magnetic solutions, and, highly
unusually, yield dielectric gaps for both antiferromagnetic and nonmagnetic
states. We demonstrate that this strange behavior is the result of the
formation of very specific electronic objects, recently suggested for a
geometrically similar Na2IrO3 compound, whereby each electron is well localized
on a particular Ru6 hexagon, and completely delocalized over the corresponding
six Ru sites, thus making the compound $both$ strongly localized and highly
itinerant.",1508.02370v2
2015-08-12,Anisotropic physical properties of PrRhAl$_4$Si$_2$ single crystal a non-magnetic singlet ground state compound,"We have grown the single crystal of PrRhAl$_4$Si$_2$, which crystallizes in
the tetragonal crystal structure. From the low temperature physical property
measurements like, magnetic susceptibility, magnetization, heat capacity and
electrical resistivity, we found that this compound does not show any magnetic
ordering down to 70~mK. Our crystal field calculations on the magnetic
susceptibility and specific heat measurements reveal that the 9-fold degenerate
$(2J+1)$ levels of Pr atom in PrRhAl$_4$Si$_2$, splits into 7 levels, with a
singlet ground state and a well separated excited doublet state at 123~K, with
a overall level splitting energy of 320~K.",1508.02822v1
2015-08-12,Kinetic Arrest of Field-Temperature Induced First Order Phase Transition in Quasi- One Dimensional Spin System Ca3Co2O6,"We have found that the geometrically frustrated spin chain compound Ca3Co2O6
belonging to Ising like universality class with uniaxial anisotropy shows
kinetic arrest of first order intermediate phase (IP) to ferrimagnetic (FIM)
transition. In this system, dc magnetization measurements followed by different
protocols suggest the coexistence of high temperature IP with equilibrium FIM
phase in low temperature. Formation of metastable state due to hindered first
order transition has also been probed through cooling and heating in unequal
field (CHUF) protocol. Kinetically arrested high temperature IP appears to
persist down to almost the spin freezing temperature in this system.",1508.02894v1
2015-08-21,Superconductivity in a new layered nickel-selenide CsNi2Se2,"The physical properties of CsNi$_{2}$Se$_{2}$ were characterized by
electrical resistivity, magnetization and specific heat measurements. We found
that the stoichiometric CsNi$_{2}$Se$_{2}$ compound is a superconductor with a
transition temperature \textit{T$_{c}$}=2.7K. A large Sommerfeld coefficient
$\gamma$$_{n}$ ($\sim$77.90 mJ/mol$\cdot$K$^{-2}$), was obtained from the
normal state electronic specific heat. However, the Kadowaki-Woods ratio of
CsNi$_{2}$Se$_{2}$ was estimated to be about 0.041$\times$10$^{-5}$
$\mu\Omega$$\cdot$cm(mol$\cdot$K/mJ)$^{2}$, indicating the absence of strong
electron-electron correlations in this compound. In the superconducting state,
we found that the zero-field electronic specific heat data, $C_{es}(T)$ (0.5K
$\leq$ T $<$ 2.6K), can be well fitted with a two-gap BCS model. The comparison
with the results of the density functional theory (DFT) calculations suggested
that the large $\gamma$$_{n}$ in the nickel-selenide superconductors may be
related to the large Density of States (DOS) at the fermi surface.",1508.05167v1
2015-08-25,Regularized and Fractional Taylor expansions of Holderian functions,"Holderian functions have strong non-linearities, which result in
singularities in the derivatives. This manuscript presents several
fractional-order Taylor expansions of H\""olderian functions around points of
non- differentiability. These expansions are derived using the concept of a
fractional velocity, which can be used to describe the singular behavior of
derivatives and non-differentiable functions. Fractional velocity is defined as
the limit of the difference quotient of the increment of a function and the
difference of its argument raised to a fractional power. Fractional velocity
can be used to regularize ordinary derivatives. To this end, it is possible to
define regularized Taylor series and compound differential rules. In particular
a compound differential rule for Holder 1/2 functions is demonstrated. The
expansion is presented using the auxiliary concept of fractional co-variation
of functions.",1508.06086v1
2015-08-26,Insurance Premium Prediction via Gradient Tree-Boosted Tweedie Compound Poisson Models,"The Tweedie GLM is a widely used method for predicting insurance premiums.
However, the structure of the logarithmic mean is restricted to a linear form
in the Tweedie GLM, which can be too rigid for many applications. As a better
alternative, we propose a gradient tree-boosting algorithm and apply it to
Tweedie compound Poisson models for pure premiums. We use a profile likelihood
approach to estimate the index and dispersion parameters. Our method is capable
of fitting a flexible nonlinear Tweedie model and capturing complex
interactions among predictors. A simulation study confirms the excellent
prediction performance of our method. As an application, we apply our method to
an auto insurance claim data and show that the new method is superior to the
existing methods in the sense that it generates more accurate premium
predictions, thus helping solve the adverse selection issue. We have
implemented our method in a user-friendly R package that also includes a nice
visualization tool for interpreting the fitted model.",1508.06378v3
2015-08-31,Tunable giant exchange bias in single-phase rare earth-transition metal intermetallics YMn12-xFex with highly homogenous inter-sublattice exchange coupling,"In this paper, we have found a family of intermetallic compounds YMn12-xFex
(x = 6.6-8.8) showing a bulk form of tunable giant exchange bias effect which
arises from global interactions among ferromagnetic (FM) and antiferromagnetic
(AFM) sublattices but not the interfacial exchange coupling or inhomogeneous
magnetic clusters. A giant exchange bias with a loop shift up to 6.1 kOe has
been observed in YMn4.4Fe7.6 compound with the strongest competing magnetic
interactions. In a narrow temperature range, the exchange bias field shows a
sudden switching off whereas the coercivity shows a sudden switching on with
increasing temperature. This unique feature indicates that the inter-sublattice
exchange coupling is highly homogenous, which can be perfectly interperated by
our theoretical calculations.",1508.07833v1
2015-09-01,Random-matrix approach to the statistical compound nuclear reaction at low energies using the Monte-Carlo technique,"Using a random-matrix approach and Monte-Carlo simulations, we generate
scattering matrices and cross sections for compound-nucleus reactions. In the
absence of direct reactions we compare the average cross sections with the
analytic solution given by the Gaussian Orthogonal Ensemble (GOE) triple
integral, and with predictions of statistical approaches such as the ones due
to Moldauer, to Hofmann, Richert, Tepel, and Weidenm\""{u}ller, and to Kawai,
Kerman, and McVoy. We find perfect agreement with the GOE triple integral and
display the limits of validity of the latter approaches. We establish a
criterion for the width of the energy-averaging interval such that the relative
difference between the ensemble-averaged and the energy-averaged scattering
matrices lies below a given bound. Direct reactions are simulated in terms of
an energy-independent background matrix. In that case, cross sections averaged
over the ensemble of Monte-Carlo simulations fully agree with results from the
Engelbrecht-Weidenm\""{u}ller transformation. The limits of other approximate
approaches are displayed.",1509.00510v1
2015-09-07,Giant exchange interaction in mixed lanthanides,"Combining strong magnetic anisotropy with strong exchange interaction is a
long standing goal in the design of quantum magnets. The lanthanide complexes,
while exhibiting a very strong ionic anisotropy, usually display a weak
exchange coupling, amounting to only a few wavenumbers. Recently, an
isostructural series of mixed Ln$^{3+}$-N$_2^{3-}$-Ln$^{3+}$ (Ln $=$ Gd, Tb,
Dy, Ho, Er) have been reported, in which the exchange splitting is estimated to
reach hundreds wavenumbers. The microscopic mechanism governing the unusual
exchange interaction in these compounds is revealed here by combining detailed
modeling with density-functional theory and {\it ab initio} calculations. We
find it to be basically kinetic and highly complex, involving non-negligible
contributions up to seventh power of total angular momentum of each lanthanide
site. The performed analysis also elucidates the origin of magnetization
blocking in these compounds. Contrary to general expectations the latter is not
always favored by strong exchange interaction.",1509.02206v4
2015-09-11,Two-magnon Raman scattering and pseudospin-lattice interactions in Sr2IrO4 and Sr3Ir2O7,"We have used Raman scattering to investigate the magnetic excitations and
lattice dynamics in the prototypical spin-orbit Mott insulators Sr2IrO4 and
Sr3Ir2O7. Both compounds exhibit pronounced two-magnon Raman scattering
features with different energies, lineshapes, and temperature dependencies,
which in part reflect the different influence of long-range frustrating
exchange interactions. Additionally, we find strong Fano asymmetries in the
lineshapes of low-energy phonon modes in both compounds, which disappear upon
cooling below the antiferromagnetic ordering temperatures. These unusual phonon
anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is
not sufficiently strong to quench the orbital dynamics in the paramagnetic
state.",1509.03396v1
2015-09-22,From Hunds insulator to Fermi liquid: Optical spectroscopy study of K doping in BaMn$_2$As$_2$,"We present optical transmission measurements that reveal a charge gap of 0.86
eV in the local moment antiferromagnetic insulator BaMn$_2$As$_2$, an order of
magnitude larger than previously reported. Density functional theory plus
dynamical mean field theory (DFT+DMFT) calculations correctly reproduce this
charge gap only when a strong Hund's coupling is considered. Thus,
BaMn$_2$As$_2$ is a member of a wider class of Mn pnictide compounds that are
Mott-Hund's insulators. We also present optical reflectance for metallic 2% K
doped BaMn$_2$As$_2$ that we use to extract the optical conductivity at
different temperatures. The optical conductivity $\sigma_1$($\omega$) exhibits
a metallic response that is well described by a simple Drude term. Both
$\sigma$($\omega$$\rightarrow$0, T) and $\rho$(T) exhibit Fermi liquid
temperature dependencies. From these measurements, we argue that a more
strongly correlated Hund's metal version of the parent compounds of the iron
pnictide superconductors has not yet been realized by doping this class of
Hund's insulators.",1509.06759v1
2015-09-25,Enabling Arbitrary Wavelength Optical Frequency Combs on Chip,"A necessary condition for generation of bright soliton Kerr frequency combs
in microresonators is to achieve anomalous group velocity dispersion (GVD) for
the resonator modes. This condition is hard to implement in visible as well as
ultraviolet since the majority of optical materials are characterized with
large normal GVD in these wavelength regions. We overcome this challenge by
borrowing ideas from strongly dispersive coupled systems in solid state physics
and optics. We show that photonic compound ring resonators can possess large
anomalous GVD at any desirable wavelength, even if each individual resonator is
characterized with normal GVD. Based on this concept we design a mode locked
frequency comb with thin-film silicon nitride compound ring resonators in the
vicinity of Rubidium D1 line (794.6nm) and propose to use this optical comb as
a flywheel for chip-scale optical clocks.",1509.07902v1
2015-09-26,Logical operation of one-dimensional photonic crystal based on series and parallel connection,"In this paper, we have proposed the compound structure of one-dimensional
photonic crystal (PC), which includes series connection and parallel connection
PC. We have studied the transmission characteristics of series connection and
parallel connection PC, and obtained some new results. In addition, we have
proved the series connection one-dimensional PC can realize the logical AND
operation, and the parallel connection one-dimensional PC can realize the
logical OR operation. The compound structure of one-dimensional PC can design
more new type structure optical devices, and will provide the basic for
designing quantum computer.",1509.07967v1
2015-10-02,Local structures and local exchange interactions in doped magnetic materials of different dimensionality,"Defects intentionally introduced into magnetic materials often have a
profound effect on the physical properties. Specifically tailored neutron
spectroscopic experiments can provide detailed information on both the local
exchange interactions and the local distances between the magnetic atoms around
the defects. This is demonstrated for manganese dimer excitations observed for
the magnetically diluted three-, two- and one-dimensional compounds
KMnxZn1-xF3, K2MnxZn1-xF4 and CsMnxMg1-xBr3, respectively, with x=0.10. The
resulting local exchange interactions deviate up to 10% from the average, and
the local Mn-Mn distances are found to vary stepwise with increasing internal
chemical pressure due to the Mn/Zn or Mn/Mg substitution. Our analysis
qualitatively supports the theoretically predicted decay of atomic
displacements according to 1/r**2, 1/r and constant (for three-, two- and
one-dimensional compounds, respectively) where r denotes the distance of the
displaced atoms from the defect.",1510.00570v1
2015-10-01,Some New Results on the Curling Number of Graphs,"Let $S=S_1S_2S_3\ldots S_n$ be a finite string. Write $S$ in the form
$XYY\ldots Y=XY^k$, consisting of a prefix $X$ (which may be empty), followed
by $k$ copies of a non-empty string $Y$. Then, the greatest value of this
integer $k$ is called the curling number of $S$ and is denoted by $cn(S)$. Let
the degree sequence of the graph $G$ be written as a string of identity curling
subsequences say, $X^{k_1}_1\circ X^{k_2}_2\circ X^{k_3}_3 \ldots \circ
X^{k_l}_l$. The compound curling number of $G$, denoted $cn^c(G)$ is defined to
be, $cn^n(G) = \prod\limits^{l}_{i=1}k_i$. In this paper, we discuss the
curling number and compound curling number of certain products of graphs.",1510.01271v2
2015-10-13,"Magnetism, Superconductivity and Quantum Criticality in the Multi-Site Cerium Heavy Fermion Compound Ce3PtIn11","The properties of the novel heavy fermion superconductor Ce$_3$PtIn$_{11}$
are investigated by thermodynamic and transport measurements at ambient and
under hydrostatic pressure. At ambient pressure the compound exhibits two
successive magnetic transitions at $T_1$ $\approx$ 2.2 K and $T_{\rm N}$
$\approx$ 2 K into antiferromagnetically ordered states and enters into a heavy
fermion superconducting phase below $T_{\rm c}$ $\approx$ 0.32 K. The
coexistence of long-range magnetic order and superconductivity is discussed in
the context of the existence of the two crystallographically inequivalent
Ce-sites in the unit cell of Ce$_3$PtIn$_{11}$. The experimental data allow us
to construct the pressure-temperature phase diagram.",1510.03607v1
2015-10-16,Nonparametric estimation of infinitely divisible distributions based on variational analysis on measures,"The paper develops new methods of non-parametric estimation a compound
Poisson distribution. Such a problem arise, in particular, in the inference of
a Levy process recorded at equidistant time intervals. Our key estimator is
based on series decomposition of functionals of a measure and relies on the
steepest descent technique recently developed in variational analysis of
measures. Simulation studies demonstrate applicability domain of our methods
and how they positively compare and complement the existing techniques. They
are particularly suited for discrete compounding distributions, not necessarily
concentrated on a grid nor on the positive or negative semi-axis. They also
give good results for continuous distributions provided an appropriate
smoothing is used for the obtained atomic measure.",1510.04968v1
2015-10-19,Role of local geometry in spin and orbital structure of transition metal compounds,"We analyze the role of local geometry in the spin and orbital interaction in
transition metal compounds with orbital degeneracy. We stress that the tendency
observed for the most studied case (transition metals in O$_6$ octahedra with
one common oxygen -- common corner of neighboring octahedra and with $\sim
180^{\circ}$ metal--oxygen--metal bonds), that ferro-orbital ordering renders
antiferro-spin coupling, and, {\it vice versa}, antiferro-orbitals give
ferro-spin ordering, is not valid in general case, in particular for octahedra
with common edge and with $\sim 90^{\circ}$ M--O--M bonds. Special attention is
paid to the ``third case'', neighboring octahedra with common face (three
common oxygens) -- the case practically not considered until now, although
there are many real systems with this geometry. Interestingly enough, the
spin--orbital exchange in this case turns out to be to be simpler and more
symmetric than in the first two cases. We also consider, which form the
effective exchange takes for different geometries in case of strong spin--orbit
coupling.",1510.05371v1
2015-10-19,Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi$_{3}$ (A=Sr and Ba),"Recently, Bi-based compounds have attracted attentions because of the strong
spin-orbit coupling (SOC). In this work, we figured out the role of SOC in
ABi$_{3}$ (A=Sr and Ba) by theoretical investigation of the band structures,
phonon properties, and electron-phonon coupling. Without SOC, strong Fermi
surface nesting leads to phonon instabilities in ABi$_{3}$. SOC suppresses the
nesting and stabilizes the structure. Moreover, without SOC the calculation
largely underestimates the superconducting transition temperatures ($T_{c}$),
while with SOC the calculated $T_{c}$ are very close to those determined by
measurements on single crystal samples. The SOC enhanced superconductivity in
ABi$_{3}$ is due to not only the SOC induced phonon softening, but also the SOC
related increase of electron-phonon coupling matrix elements. ABi$_{3}$ can be
potential platforms to construct heterostructure of superconductor/topological
insulator to realize topological superconductivity.",1510.05719v1
2015-10-22,Execution of Compound Multi-Kernel OpenCL Computations in Multi-CPU/Multi-GPU Environments,"Current computational systems are heterogeneous by nature, featuring a
combination of CPUs and GPUs. As the latter are becoming an established
platform for high-performance computing, the focus is shifting towards the
seamless programming of these hybrid systems as a whole. The distinct nature of
the architectural and execution models in place raises several challenges, as
the best hardware configuration is behaviour and workload dependent. In this
paper, we address the execution of compound, multi-kernel, OpenCL computations
in multi-CPU/multi-GPU environments. We address how these computations may be
efficiently scheduled onto the target hardware, and how the system may adapt
itself to changes in the workload to process and to fluctuations in the CPU's
load. An experimental evaluation attests the performance gains obtained by the
conjoined use of the CPU and GPU devices, when compared to GPU-only executions,
and also by the use of data-locality optimizations in CPU environments.",1510.06585v1
2015-11-02,Multi-rate time stepping schemes for hydro-geomechanical model for subsurface methane hydrate reservoirs,"We present an extrapolation-based semi-implicit multirate time stepping (MRT)
scheme and a compound-fast MRT scheme for a naturally partitioned,
multi-time-scale hydro-geomechanical hydrate reservoir model. We evaluate the
performance of the two MRT methods compared to an iteratively coupled solution
scheme and discuss their advantages and disadvantages. The performance of the
two MRT methods is evaluated in terms of speed-up and accuracy by comparison to
an iteratively coupled solution scheme. We observe that the extrapolation-based
semi-implicit method gives a higher speed-up but is strongly dependent on the
relative time scales of the latent (slow) and active (fast) components. On the
other hand, the compound-fast method is more robust and less sensitive to the
relative time scales, but gives lower speed up as compared to the semi-implicit
method, especially when the relative time scales of the active and latent
components are comparable.",1511.00466v2
2015-11-04,Optical characterization of gaps in directly bonded Si compound optics using infrared spectroscopy,"Silicon direct bonding offers flexibility in the design and development of Si
optics by allowing manufacturers to combine subcomponents with a potentially
lossless and mechanically stable interface. The bonding process presents
challenges in meeting the requirements for optical performance because air gaps
at the Si interface cause large Fresnel reflections. Even small (35 nm) gaps
reduce transmission through a direct bonded Si compound optic by 4% at $\lambda
= 1.25 \; \mu$m at normal incidence. We describe a bond inspection method that
makes use of precision slit spectroscopy to detect and measure gaps as small as
14 nm. Our method compares low finesse Fabry-P\'{e}rot models to high precision
measurements of transmission as a function of wavelength. We demonstrate the
validity of the approach by measuring bond gaps of known depths produced by
microlithography.",1511.01183v1
2015-11-08,Learning Linguistic Biomarkers for Predicting Mild Cognitive Impairment using Compound Skip-grams,"Predicting Mild Cognitive Impairment (MCI) is currently a challenge as
existing diagnostic criteria rely on neuropsychological examinations. Automated
Machine Learning (ML) models that are trained on verbal utterances of MCI
patients can aid diagnosis. Using a combination of skip-gram features, our
model learned several linguistic biomarkers to distinguish between 19 patients
with MCI and 19 healthy control individuals from the DementiaBank language
transcript clinical dataset. Results show that a model with compound of
skip-grams has better AUC and could help ML prediction on small MCI data
sample.",1511.02436v2
2015-11-19,Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission,"We show the three-dimensional electronic structure of the Kondo lattice CeIn3
using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic
state. For the first time, we have directly observed the three-dimensional
topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has
a complicated hole pocket centred at the {\Gamma}-Z line and an elliptical
electron pocket centred at the R point of the Brillouin zone. Polarization and
photon-energy dependent photoemission results both indicate the nearly
localized nature of the 4f electrons in CeIn3, consistent with the theoretical
prediction by means of the combination of density functional theory and
single-site dynamical meanfield theory. Those results illustrate that the f
electrons of CeIn3, which is the parent material of CeMIn5 compounds, are
closer to the localized description than the layered CeMIn5 compounds.",1511.06046v2
2015-12-04,Thermodynamic Properties of Superconducting and Non-Superconducting Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-δ}$ Compounds with Metallic Double Chains,"To examine the thermodynamic properties of
Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-\delta }$ compounds with metallic CuO double
chains, we measured the specific heats of superconducting and
non-superconducting polycrystalline samples at low temperatures (1.8-40 K)
under various magnetic fields (up to 9 T). In the as-sintered
non-superconducting sample, a $\lambda-$like enhancement in the specific heat
measurement appeared near the antiferromagnetic transition temperature
$T_{N}=17$ K. In contrast, the reduced superconducting sample with
$T_{c,on}=26.5$ K exhibited no obvious superconducting anomaly in its specific
data, but a Schottky-like broad maximum appeared at low temperatures. The
Schottky-like anomaly was attributed to low-lying quasi-triplet splitting of
Pr$^{3+}$ ions under the crystal field effect.",1512.01300v1
2015-12-04,Cross-plane heat conduction in thin films with ab-initio phonon dispersions and scattering rates,"We present a first-principles study of the cross-plane thermal conductivity
$\kappa_{\perp}$ in a wide variety of semiconductor thin films. We introduce a
simple suppression model that matches variance-reduced Monte Carlo simulations
with ab-initio phonon dispersions and scattering rates within $\leq 5\%$ even
for anisotropic compounds. This, in turn, enables accurate $\kappa_{\perp}$
reconstruction from tabulated cumulative conductivity curves
$\kappa_{\Sigma}(\Lambda_{\perp})$. We furthermore reveal, and explain, a
distinct quasiballistic regime characterised by a fractional thickness
dependence $\kappa_{\perp} \sim L^{2-\alpha}$ in alloys (where $\alpha$ is the
L\'evy exponent) and logarithmic dependence $\kappa_{\perp} \sim \ln(L)$ in
single crystals. These observations culminate in the formulation of two compact
parametric forms for $\kappa_{\perp}(L)$ that can fit the first-principles
curves across the entire ballistic-diffusive range within a few percent for all
investigated compounds.",1512.01354v3
2015-12-12,Complex dielectric and impedance behavior of magnetoelectric Fe2TiO5,"We have investigated the complex dielectric and impedance properties of
magnetoelectric compound Fe2TiO5 (FTO) as a function of temperature (T) and
frequency (f) to understand the grain (G) and grain boundary (Gb) contributions
to its dielectric response. The temperature and frequency dependent dielectric
permittivity data shows a sharp increase in permittivity above 200K accompanied
with a frequency dependent peak in loss. At T less than 175K, only G
contribution dominates even at lower frequency (nearly 100Hz), but for T
greater than 175K, the Gb contribution starts appearing at low frequency. The
value of critical frequency distinguishing these two contributions increases
with increasing temperature. The observed non-Debye dielectric relaxation
follows thermally activated process and is attributed to polaron hopping.
Further the frequency dependence of ac conductivity follows the Jonscher
power-law. The temperature dependency of critical exponent s shows that the
correlated barrier hopping model is appropriate to define the conductivity
mechanism of FTO in the studied temperature regime.",1512.03889v1
2015-12-16,A computational model revealing the effect of dopamine on action selection,"In order to reveal the effect of nigrostriatal dopamine system on action
selection, first a computational model of the cortex-basal ganglia-thalamus
loop is proposed and based on this model a simple compound model realizing the
Stroop effect is established. Even though Stroop task is mostly used to examine
selective attention, the main objective of this work is to investigate the
effect of action selection on Stroop task. The computational model of the
cortex-basal ganglia-thalamus loop is a non-linear dynamical system which is
not only capable of revealing the action selection property of basal ganglia
but also capable of modelling the effect of dopamine on action selection. While
the interpretation of action selection is based on the solutions of the
non-linear dynamical system, the effect of dopamine is modelled by a parameter
of the model. The inhibiting effect of dopamine on the habitual behaviour which
corresponds to word reading in Stroop task and letting the novel one occur
corresponding to colour naming is investigated using the compound computational
model established in this work.",1512.05340v1
2015-12-22,Recent developments in heavy-ion fusion reactions around the Coulomb barrier,"The nuclear fusion is a reaction to form a compound nucleus. It plays an
important role in several circumstances in nuclear physics as well as in
nuclear astrophysics, such as synthesis of superheavy elements and
nucleosynthesis in stars. Here we discuss two recent theoretical developments
in heavy-ion fusion reactions at energies around the Coulomb barrier. The first
topic is a generalization of the Wong formula for fusion cross sections in a
single-channel problem. By introducing an energy dependence to the barrier
parameters, we show that the generalized formula leads to results practically
indistinguishable from a full quantal calculation, even for light symmetric
systems such as $^{12}$C+$^{12}$C, for which fusion cross sections show an
oscillatory behavior. We then discuss a semi-microscopic modeling of heavy-ion
fusion reactions, which combine the coupled-channels approach to the
state-of-the-art nuclear structure calculations for low-lying collective
motions. We apply this method to subbarrier fusion reactions of
$^{58}$Ni+$^{58}$Ni and $^{40}$Ca+$^{58}$Ni systems, and discuss the role of
anharmonicity of the low-lying vibrational motions.",1512.06954v1
2015-12-22,Spin-Rotation Symmetry Breaking in the Superconducting State of CuxBi2Se3,"Spontaneous symmetry breaking is an important concept for understanding
physics ranging from the elementary particles to states of matter. For example,
the superconducting state breaks global gauge symmetry, and unconventional
superconductors can break additional symmetries. In particular, spin rotational
symmetry is expected to be broken in spin-triplet superconductors. However,
experimental evidence for such symmetry breaking has not been conclusively
obtained so far in any candidate compounds. Here, by 77Se nuclear magnetic
resonance measurements, we show that spin rotation symmetry is spontaneously
broken in the hexagonal plane of the electron-doped topological insulator
Cu0.3Bi2Se3 below the superconducting transition temperature Tc=3.4 K. Our
results not only establish spin-triplet superconductivity in this compound, but
may also serve to lay a foundation for the research of topological
superconductivity.",1512.07086v1
2015-12-22,Ferromagnetism and correlation strength in cubic barium ruthenate in comparison to strontium and calcium ruthenate: a dynamical mean field study,"We present density functional plus dynamical mean field studies of cubic
BaRuO$_3$ using interaction parameters previously found to be appropriate for
the related materials CaRuO$_3$ and SrRuO$_3$. The calculated variation in
transition temperature between the Ba and Sr compounds is consistent with
experiment, confirming the assignment of the compounds to the Hund's metal
family of materials, and also confirming the appropriateness of the values for
the interaction parameters previously estimated and the appropriateness of the
single-site dynamical mean field approximation for these materials. The results
provide insights into the origin of magnetism and the role of the van Hove
singularity in the physics of Hund's metals.",1512.07261v1
2015-12-23,Superconductivity of novel tin hydrides (Sn$_n$H$_m$) under pressure,"With the motivation of discovering high-temperature superconductors,
evolutionary algorithm is employed to search for all stable compounds in the
Sn-H system. In addition to the traditional SnH$_4$, new hydrides SnH$_8$,
SnH$_{12}$ and SnH$_{14}$ are found to be thermodynamically stable at high
pressure. Dynamical stability and superconductivity of tin-hydrides are
systematically investigated. I$\bar{4}$m2-SnH$_8$, C2/m-SnH$_{12}$ and
C2/m-SnH$_{14}$ exhibit higher superconducting transition temperatures of 81,
93 and 97 K compared to the traditional compound SnH$_4$ with T$_c$ of 52 K at
200 GPa. An interesting bent H$_3^-$ in I$\bar{4}$m2-SnH$_8$ and novel liner
H$_4^-$ in C2/m-SnH$_{12}$ are observed. All the new tin-hydrides remain
metallic over their predicted range of stability. The intermediate-frequency
wagging and bending vibrations have more contribution to electron-phonon
coupling parameter than high-frequency stretching vibrations of H$_2$ and
H$_3$.",1512.07604v1
2015-12-28,Efficient nonparametric inference for discretely observed compound Poisson processes,"A compound Poisson process whose parameters are all unknown is observed at
finitely many equispaced times. Nonparametric estimators of the jump and L\'evy
distributions are proposed and functional central limit theorems using the
uniform norm are proved for both under mild conditions. The limiting Gaussian
processes are identified and efficiency of the estimators is established.
Kernel estimators for the mass function, the intensity and the drift are also
proposed, their asymptotic properties including efficiency are analysed, and
joint asymptotic normality is shown. Inference tools such as confidence regions
and tests are briefly discussed.",1512.08472v3
2015-12-19,Thermo-magnetic properties of the magnetocaloric layered materials based upon FeMnAsP: a Green function-method approach,"The compounds FeMnAsxP1-x are very promising as far as commercial
applications of the magnetocaloric effect are concerned. However, the
theoretical literature on magnetocaloric materials still adopts simple
molecular-field models in the description of important properties like the
entropy variation that accompanies applied isothermal magnetic field cycling,
for instance. We apply a Green function theoretical treatment for such
analysis. The advantages of such approach are well-known since the details of
the crystal structure are incorporated in the model, as well as a precise
description of correlations between spins of the transition metal ions can be
obtained. For the sake of simplcity we adopt a simple one-exchange parameter
Heisenberg model, and the observed first-order phase transitions are reproduced
by the introduction of a biquadratic term in the hamiltonian. Good agreement
with experimental magnetocaloric data for FeMnAsxP1-x compounds is obtained, as
well as an agreement with the magnetic field dependence for these properties
predicted from the Landau theory of continuous phase transitions.",1512.08503v1
2015-12-29,Effect of Hydrostatic Pressure on BiS2-Based Layered Superconductors: A Review,"We report impact of hydrostatic pressure on the newly discovered BiS2 based
superconductors. In last couple of years the new BiS2 based superconductor
attracted great attention of the condensed matter physics community. These new
layered BiS2-based compounds are very sensitive to the concentration of
carriers doping and pressure that cause profound changes in their physical
properties with appearance of superconductivity in the vicinity of their
insulating/semiconducting state. The BiS2-based new compounds are expected to
provide us with the next stage of exploring new superconductors and to discuss
their exotic superconductivity mechanisms. In current review, we present most
of our findings related to impact of hydrostatic pressure on superconductivity
of new BiS2 based superconductors at one place.",1512.08595v1
2016-01-08,Magnetic structure of the magnetocaloric compound AlFe2B2,"The crystal and magnetic structures of AlFe2B2 have been studied with a
combination of X-ray and neutron diffraction and electronic structure
calculations. The magnetic and magnetocaloric properties have been investigated
by magnetisation measurements. The samples have been produced using high
temperature synthesis and subsequent heat treatments. The compound crystallises
in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285
K through a second order phase transition. At temperatures below the magnetic
transition the magnetic moments align along the crystallographic $a$-axis. The
magnetic entropy change from 0 to 800 kA/m was found to be -1.3 J/K kg at the
magnetic transition temperature.",1601.01953v1
2016-01-09,Correlation of exchange bias with magneto-structural effects across the compensation temperature of Co(Cr$_{1-x}$Fe$_{x}$)$_2$O$_4$ (x = 0.05 and 0.075),"A small amount of Fe (5% and 7.5%) substitution in the Cr-site of the
multiferroic compound CoCr2O4 leads to a magnetization reversal. In these
compounds, we report a sign change in the exchange bias across the compensation
temperature, accompanied by a non-monotonic change in the local moments across
the compensation temperature. Such non-monotonic change in the magnetic moments
is triggered by a similar change in the lattice structure. We relate here the
sign change of exchange bias with that of the crystalline energy of the lattice
and the Zeeman energy term arising from the anti-site disorder.",1601.02086v1
2016-01-11,Probing 5f electronic hybridization in Uranium compounds via x-ray magnetic circular dichroism,"We study the spin-dependent electronic structure of UTe and UT_{2}Si_{2}
(T=Cu and Mn) compounds with a combination of x-ray magnetic circular dichroism
measurements and first principle calculations. By exploiting the presence of
sizable quadrupolar and dipolar contributions to the U L_{2,3}-edge x-ray
absorption cross section we are able to provide unique information on the
extent of hybridization between 5f and 6d/3d electronic states, a key parameter
regulating the physical properties of all actinide materials. Since this
information is hardly accessible to other probes, the new methodology opens up
new venues for investigating this important class of materials.",1601.02443v1
2016-01-12,Magnetic phase diagram of the helimagnetic spinel compound ZnCr2Se4 revisited by small-angle neutron scattering,"We performed small-angle neutron scattering (SANS) measurements on the
helimagnetic spinel compound ZnCr2Se4. The ground state of this material is a
multi-domain spin-spiral phase, which undergoes domain selection in a magnetic
field and reportedly exhibits a transition to a proposed spin-nematic phase at
higher fields. We observed a continuous change in the magnetic structure as a
function of field and temperature, as well as a weak discontinuous jump in the
spiral pitch across the domain-selection transition upon increasing field. From
our SANS results we have established the absence of any long-range magnetic
order in the high-field (spin-nematic) phase. We also found that all the
observed phase transitions are surprisingly isotropic with respect to the field
direction.",1601.03005v1
2016-01-13,Type Soundness for Path Polymorphism,"Path polymorphism is the ability to define functions that can operate
uniformly over arbitrary recursively specified data structures. Its essence is
captured by patterns of the form $x\,y$ which decompose a compound data
structure into its parts. Typing these kinds of patterns is challenging since
the type of a compound should determine the type of its components. We propose
a static type system (i.e. no run-time analysis) for a pattern calculus that
captures this feature. Our solution combines type application, constants as
types, union types and recursive types. We address the fundamental properties
of Subject Reduction and Progress that guarantee a well-behaved dynamics. Both
these results rely crucially on a notion of pattern compatibility and also on a
coinductive characterisation of subtyping.",1601.03271v2
2016-01-18,Spin-orbit coupling and odd-parity superconductivity in the quasi-one-dimensional compound Li$_{0.9}$Mo$_6$O$_{17}$,"Previous theoretical studies [W. Cho, C. Platt, R. H. McKenzie, and S. Raghu,
Phys. Rev. B 92, 134514 (2015); N. Lera and J. V. Alvarez, Phys. Rev. B 92,
174523 (2015)] have suggested that Li$_{0.9}$Mo$_6$O$_{17}$, a quasi-one
dimensional ""purple bronze"" compound, exhibits spin-triplet superconductivity
and that the gap function changes sign across the two nearly degenerate Fermi
surface sheets. We investigate the role of spin-orbit coupling (SOC) in
determining the symmetry and orientation of the $d$-vector associated with the
superconducting order parameter. We propose that the lack of local inversion
symmetry within the four-atom unit cell leads to a staggered spin-orbit
coupling analogous to that proposed for graphene, MoS$_2$, or SrPtAs. In
addition, from a weak-coupling renormalization group treatment of an effective
model Hamiltonian, we find that SOC favors the odd parity $A_{1u}$ state with
$S_z = \pm 1$ over the $B$ states with $S_z=0$, where $z$ denotes the
least-conducting direction. We discuss possible definitive experimental
signatures of this superconducting state.",1601.04757v1
2016-01-21,Thermoelectric behavior of Ruddlesden-Popper series iridates,"The goal of this work is studying the evolution of thermoelectric transport
across the members of the Ruddlesden-Popper series iridates Srn+1IrnO3n+1,
where a metal-insulator transition driven by bandwidth change occurs, from the
strongly insulating Sr2IrO4 to the metallic non Fermi liquid behavior of
SrIrO3. Sr2IrO4 (n=1), Sr3Ir2O7 (n=2) and SrIrO3 (n=inf.) polycrystals are
synthesized at high pressure and characterized by structural, magnetic,
electric and thermoelectric transport analyses. We find a complex
thermoelectric phenomenology in the three compounds. Thermal diffusion of
charge carriers accounts for the Seebeck behavior of Sr2IrO4, whereas
additional drag mechanisms come into play in determining the Seebeck
temperature dependence of Sr3Ir2O7 and SrIrO3. These findings reveal close
relationship between magnetic, electronic and thermoelectric properties, strong
coupling of charge carriers with phonons and spin fluctuations as well as
relevance of multiband description in these compounds.",1601.05667v1
2016-02-03,Gallium substitution in PuCoGa5,"The substitution of gallium by aluminum, germanium, tin and indium in
PuCoGa5, the actinide-based superconductor with the highest critical
temperature, has been investigated. Only systems with 20% substitution by Al
and Ge (i.e. PuCoGa4Al and PuCoGa4Ge) have been successfully synthesized by
annealing arc-melted samples. X-ray powder diffraction refinements indicate an
enhanced c/a ratio in these two compounds but the magnetic susceptibility
measurements reveal a large reduction of the critical temperature Tc compared
to PuCoGa5. DFT+ED calculations indicate significant changes in the Fermi
surface, probably related to the decrease of Tc, in these compounds. In
addition, the isotopic effect of the atomic mass of gallium, using 69Ga and
71Ga isotopes, was also investigated without observable influence on the
critical temperature of PuCoGa5.",1602.01354v1
2016-02-04,Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers,"The demand for petroleum dependent chemicals and materials has been
increasing despite the dwindling of their fossil resources. As the dead-end of
petroleum based industry has started to appear, today's modern society has to
implement alternative energy and valuable chemical resources immediately. Owing
to the importance of lignocellulosic biomass being the most abundant and
bio-renewable biomass on earth, this critical review provides insights into the
potential of lignocellulosic biomass as an alternative platform to fossil
resources. In this context, over 200 value-added compounds, which can be
derived from lignocellulosic biomass by various treatment methods, are
presented with their references. Lignocellulosic biomass based polymers and
their commercial importance are also reported mainly in the frame of these
compounds. This review article aims to draw the map of lignocellulosic biomass
derived chemicals and their synthetic polymers, and to reveal the scope of this
map in today's modern chemical and polymer industry.",1602.01684v1
2016-02-09,Prediction of phonon-mediated superconductivity in borophene,"Superconductivity in two-dimensional compounds is widely concerned, not only
due to its application in constructing nano-superconducting devices, but also
for the general scientific interests. Very recently, borophene (two-dimensional
boron sheet) has been successfully grown on the Ag(111) surface, through direct
evaporation of a pure boron source. The experiment unveiled two types of
borophene structures, namely $\beta_{12}$ and $\chi_3$. Herein, we employed
density-functional first-principles calculations to investigate the
electron-phonon coupling and superconductivity in both structures of borophene.
The band structures of $\beta_{12}$ and $\chi_3$ borophenes exhibit inherent
metallicity. We found electron-phonon coupling constants in the two compounds
are larger than that in MgB$_2$. The superconducting transition temperatures
were determined to be 18.7 K and 24.7 K through McMillian-Allen-Dynes formula.
These temperatures are much higher than theoretically predicted 8.1 K and
experimentally observed 7.4 K superconductivity in graphene. Our findings will
enrich the nano-superconducting device applications and boron-related material
science.",1602.02930v3
2016-02-10,"Magnetic Structure of the $S\,{=}\,1/2$ Quasi-Two-Dimensional Square-Lattice Heisenberg Antiferromagnet Sr$_2$CuTeO$_6$","The magnetic structure of the double perovskite compound Sr$_2$CuTeO$_6$ was
determined from neutron powder diffraction data. This material is magnetically
described as an $S\,{=}\,1/2$ quasi-two-dimensional square-lattice Heisenberg
model with antiferromagnetic nearest-neighbor and next-nearest-neighbor
interactions. Sr$_2$CuTeO$_6$ undergoes a magnetic phase transition at $T_{\rm
N}\,{\simeq}\,29\,$ K. The spin structure below $T_{\rm N}$ is N\'{e}el
antiferromagnetic on the square lattice, which means that the nearest-neighbor
interaction ($J_1$) is stronger than the next-nearest-neighbor interaction
($J_2$), in contrast to other isostructural compounds such as Ba$_2$CuWO$_6$
and Sr$_2$CuWO$_6$, for which $|J_1|\,{<}\,|J_2|$ is realized.",1602.03281v1
2016-02-12,A regional compound Poisson process for hurricane and tropical storm damage,"In light of intense hurricane activity along the U.S. Atlantic coast,
attention has turned to understanding both the economic impact and behaviour of
these storms. The compound Poisson-lognormal process has been proposed as a
model for aggregate storm damage, but does not shed light on regional analysis
since storm path data are not used. In this paper, we propose a fully Bayesian
regional prediction model which uses conditional autoregressive (CAR) models to
account for both storm paths and spatial patterns for storm damage. When fitted
to historical data, the analysis from our model both confirms previous findings
and reveals new insights on regional storm tendencies. Posterior predictive
samples can also be used for pricing regional insurance premiums, which we
illustrate using three different risk measures.",1602.03940v1
2016-02-17,"Quantum oscillations from `open' Fermi surface in quasi-one-dimensional lattices: Application to YBa2Cu3O6 cuprates, organic salts, ladder compounds, and related systems","According to the celebrated Onsagar-Lifshitz paradigm, the observation of
Shubnikov de-Haas and de-Haas van Alphen (SdHvA) oscillations is an indication
of the presence of `closed' orbit Fermi surface in the bulk. We present a
real-space based calculation of SdHvA oscillations in generalized
quasi-one-dimensional lattices by relaxing the quasi-classical approximations
embedded in this decades old Onsagar-Lifshitz paradigm. We find that sizable
quantum oscillation can arise from `open' Fermi surfaces as long as cyclotron
orbits can form in real-space with finite, but not necessarily equal, electron
hopping along both x- and y-directions. Our results quantitatively explain the
puzzling emergence of SdHvA oscillation in various quasi-one-dimensional
materials, including the chain state of YBa2Cu3O6 cuprates, organic materials,
various ladder compounds, weakly coupled linear chains, or quantum wires, and
other related systems.",1602.05269v1
2016-02-17,Thermoelectric properties of new Bi-chalcogenide layered compounds,"The layered Bi-chalcogenide compounds have been drawing much attention as a
new layered superconductor family since 2012. Due to the rich variation of
crystal structure and constituent elements, the development of new physics and
chemistry of the layered Bi-chalcogenide family and its applications as
functional materials have been expected. Recently, it was revealed that the
layered Bi chalcogenides can show a relatively high thermoelectric performance
(ZT = 0.36 in LaOBiSSe at ~650 K). Here, we show the crystal structure
variation of the Bi-chalcogenide family and their thermoelectric properties.
Finally, the possible strategies for enhancing the thermoelectric performance
are discussed on the basis of the experimental and the theoretical facts
reviewed here.",1602.05320v1
2016-02-17,Ground state of the U2Mo compound: Physical properties of the Omega-phase,"Using ab initio calculations, unexpected structural instability was recently
found in the ground state of the U$_2$Mo compound. Instead of the unstable
$I4/mmm$ structure, in this work the $P6/mmm$ ($\# 191$) space group, usually
called $\Omega$-phase, is proposed as the fundamental state. Electronic and
elastic properties are studied in this work in order to characterize the
physical properties of the new ground state. The stability of the
$\Omega$-phase is studied by means of its elastic constants calculation and
phonon dispersion spectrum. Analysis of isotropic indices shows that the new
phase is a ductile material with a minimal degree of anisotropy, suggesting
that U$_2$Mo in the $P6/mmm$ structure is an elastic isotropic material.
Analysis of charge density, density of electronic states (DOS) and the
character of the bands revealed a high level of hybridization between
$d$-molybdenum electronic states and $d$- and $f$-uranium ones.",1602.05552v1
2016-02-19,Magnetic excitations in the S = 1/2 antiferromagnetic-ferromagnetic chain compound BaCu2V2O8 at zero and finite temperature,"Unlike most quantum systems which rapidly become incoherent as temperature is
raised, strong correlations persist at elevated temperatures in $S=1/2$ dimer
magnets, as revealed by the unusual asymmetric lineshape of their excitations
at finite temperatures. Here we quantitatively explore and parameterize the
strongly correlated magnetic excitations at finite temperatures using the high
resolution inelastic neutron scattering on the model compound
BaCu$_2$V$_2$O$_8$ which we show to be an alternating
antiferromagnetic-ferromagnetic spin$-1/2$ chain. Comparison to state of the
art computational techniques shows excellent agreement over a wide temperature
range. Our findings hence demonstrate the possibility to quantitatively predict
coherent behavior at elevated temperatures in quantum magnets.",1602.06184v3
2016-02-22,Field-Temperature Phase Diagram and Entropy Landscape of CeAuSb$_2$,"We report a field-temperature phase diagram and an entropy map for the heavy
fermion compound CeAuSb$_2$. CeAuSb$_2$ orders antiferromagnetically below
$T_N=6.6$~K, and has two metamagnetic transitions, at 2.8 and 5.6~T. The
locations of the critical endpoints of the metamagnetic transitions, which may
play a strong role in the putative quantum criticality of CeAuSb$_2$ and
related compounds, are identified. The entropy map reveals an apparent entropy
balance with Fermi liquid behavior, implying that above the N\'{e}el transition
the Ce moments are incorporated into the Fermi liquid. High-field data showing
that the magnetic behavior is remarkably anisotropic are also reported.",1602.06742v1
2016-02-27,Observation of magnetoelectric effects in a S=1/2 frustrated spin chain magnet SrCuTe2O6,"The magnetoelectric (ME) effects are investigated in a cubic compound
SrCuTe2O6, in which uniform Cu2+ (S=1/2) spin chains with considerable spin
frustration exhibit a concomitant antiferromagnetic transition and dielectric
constant peak at TN=5.5 K. Pyroelectric Jp(T) and magnetoelectric current
JME(H) measurements in the presence of a bias electric field are used to reveal
that SrCuTe2O6 shows clear variations of Jp(T) across TN at constant magnetic
fields. Furthermore, isothermal measurements of JME(H) also develop clear peaks
at finite magnetic fields, of which traces are consistent with the spin-flop
transitions observed in the magnetization studies. As a result, the anomalies
observed in Jp(T) and JME(H) curves well match with the field-temperature phase
diagram constructed from magnetization and dielectric constant measurements,
demonstrating that SrCuTe2O6 is a new magnetoelectric compound with S=1/2 spin
chains.",1602.08560v1
2016-02-27,Avalanche-like metamagnetic transition in (LaNd)CaMnO manganites,"We investigate the behavior of ultrasharp metamagnetic transitions in
La(5/8-y)Nd(y)Ca(3/8)MnO(3) manganites. These compounds change from a low
temperature ferromagnetic metallic state at low Nd doping to a charge-ordered
antiferromagnetic insulator for high Nd content. At an intermediate doping a
phase-separated state is established. At low temperatures (2 K), we observe an
avalanche-like field-induced metamagnetic transition, when the entire compound
changes abruptly from one phase to the other. We investigate the signatures of
this ultrasharp transition using magnetization and specific heat measurements.
We observe a first order transition in the specific heat associated with
discontinuous jumps in the magnetization. A strong increase of the sample
temperature is simultaneously observed. The results are interpret in terms of
latent heat release from the field induced enhancement of the ferromagnetic
fraction, triggering the avalanche process.",1602.08594v1
2016-02-27,Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites,"We investigate a series of manganese oxides, the
La0.225Pr0.4(Ca1-xSrx)0.375MnO3 system. The x = 0 sample is a prototype
compound for the study of phase separation in manganites, where ferromagnetic
and charge ordered antiferromagnetic phases coexist. Replacing Ca2+ by Sr2+
gradually turns the system into a homogeneous ferromagnet. Our results show
that the material structure plays a major role in the observed magnetic
properties. On cooling, at temperatures below 100 K, a strong contraction of
the lattice is followed by an increase in the magnetization. This is observed
both through thermal expansion and magnetostriction measurements, providing
distinct evidence of magneto-elastic coupling in these phase separated
compounds.",1602.08597v3
2016-04-03,Prediction of a new ground state of superhard compound B6O at ambient conditions,"Boron suboxide B6O, the hardest known oxide, has an R-3m crystal structure
({\alpha}-B6O) that can be described as an oxygen-intercalated structure of
{\alpha}-boron, or, equivalently, as a cubic close packing of B12 icosahedra
with two oxygen atoms occupying all octahedral voids in it. Here we show a new
ground state of this compound at ambient conditions, Cmcm-B6O (\b{eta}-B6O),
which in all quantum-mechanical treatments that we tested (GGA, LDA, and hybrid
functional HSE06) comes out to be slightly but consistently more stable.
Increasing pressure and temperature further stabilize it with respect to the
known {\alpha}-B6O structure. \b{eta}-B6O also has a slightly higher hardness
and may be synthesized using different experimental protocols. We suggest that
\b{eta}-B6O is present in mixture with {\alpha}-B6O, and its presence accounts
for previously unexplained bands in the experimental Raman spectrum.",1604.00586v1
2016-04-11,Superconducting phase diagrams of cuprates and pnictides as a key to the HTSC mechanism,"This paper reviews experimental phase diagrams of cuprates and pnictides to
demonstrate that specific features of the superconducting phase diagrams in
bothHTSC families can be understood within the framework of the proposed
approach,which assumes the formation, under heterovalent doping, of localized
trion complexes consisting of a doped carrier and charge transfer (CT)
excitons. The geometry of such cells containing CT excitons (CT plaquettes) in
the basal plane of the crystal is determined by its crystal structure and the
type of dopant, so that the dopant concentration range corresponding to the
existence of a percolation cluster of CT plaquettes can be readily determined
for each particular compound. These dopant concentration ranges coincide with
good accuracy with the experimental ranges of superconducting domes in the
phase diagrams of the HTSC compounds considered. The generation of free
carriers and the mechanism of superconducting pairing in this pattern is
related to biexciton complexes (Heitler-London centers) emerging in neighboring
CT plaquettes.",1604.03028v6
2016-04-11,"Single crystal growth of CeTAl$_3$ (T = Cu, Ag, Au, Pd and Pt)","We report single crystal growth of the series of CeTAl$_3$ compounds with T =
Cu, Ag, Au, Pd and Pt by means of optical float zoning. High crystalline
quality was confirmed in a thorough characterization process. With the
exception of CeAgAl$_3$, all compounds crystallize in the non-centrosymmetric
tetragonal BaNiSn$_{3}$ structure (space group: I4mm, No. 107), whereas
CeAgAl$_3$ adopts the related orthorhombic PbSbO$_2$Cl structure (Cmcm, No.
63). An attempt to grow CeNiAl$_3$ resulted in the composition CeNi$_2$Al$_5$.
Low temperature resistivity measurements down to $\sim$0.1K did not reveal
evidence suggestive of magnetic order in CePtAl$_3$ and CePdAl$_3$. In
contrast, CeAuAl$_3$, CeCuAl$_3$ and CeAgAl$_3$ display signatures of magnetic
transitions at 1.3K, 2.1K and 3.2K, respectively. This is consistent with
previous reports of antiferromagnetic order in CeAuAl$_3$, and CeCuAl$_3$ as
well as ferromagnetism in CeAgAl$_3$, respectively.",1604.03146v1
2016-04-12,Ab initio determination of spin Hamiltonians with anisotropic exchange interactions: the case of the pyrochlore ferromagnet Lu$_2$V$_2$O$_7$,"We present a general framework for deriving effective spin Hamiltonians of
correlated magnetic systems based on a combination of relativistic ab initio
density functional theory calculations (DFT), exact diagonalization of a
generalized Hubbard Hamiltonian on finite clusters and spin projections onto
the low-energy subspace. A key motivation is to determine anisotropic bilinear
exchange couplings in materials of interest. As an example, we apply this
method to the pyrochlore Lu$_2$V$_2$O$_7$ where the vanadium ions form a
lattice of corner-sharing spin-1/2 tetrahedra. In this compound, anisotropic
Dzyaloshinskii-Moriya interactions (DMI) play an essential role in inducing a
magnon Hall effect. We obtain quantitative estimates of the nearest-neighbor
Heisenberg exchange, the DMI, and the symmetric part of the anisotropic
exchange tensor. Finally, we compare our results with experimental ones on the
Lu$_2$V$_2$O$_7$ compound.",1604.03472v1
2016-04-13,Hierarchical Compound Poisson Factorization,"Non-negative matrix factorization models based on a hierarchical
Gamma-Poisson structure capture user and item behavior effectively in extremely
sparse data sets, making them the ideal choice for collaborative filtering
applications. Hierarchical Poisson factorization (HPF) in particular has proved
successful for scalable recommendation systems with extreme sparsity. HPF,
however, suffers from a tight coupling of sparsity model (absence of a rating)
and response model (the value of the rating), which limits the expressiveness
of the latter. Here, we introduce hierarchical compound Poisson factorization
(HCPF) that has the favorable Gamma-Poisson structure and scalability of HPF to
high-dimensional extremely sparse matrices. More importantly, HCPF decouples
the sparsity model from the response model, allowing us to choose the most
suitable distribution for the response. HCPF can capture binary, non-negative
discrete, non-negative continuous, and zero-inflated continuous responses. We
compare HCPF with HPF on nine discrete and three continuous data sets and
conclude that HCPF captures the relationship between sparsity and response
better than HPF.",1604.03853v2
2016-04-14,"Optical, transport and magnetic properties of new compound CeCd3P3","We have found that CeCd$_{3}$P$_{3}$ crystallizes into a hexagonal
ScAl$_{3}$C$_{3}$-type structure. The optical, transport and magnetic
properties of CeCd$_{3}$P$_{3}$ were investigated by measuring the diffuse
reflectance, electrical resistivity and magnetization. CeCd$_{3}$P$_{3}$ is a
semiconductor with the fundamental band gap of approximately 0.75 eV. The 4$f$
electrons of Ce$^{3+}$ ions are well localized but do not show long range order
down to 0.48 K, presumably due to the geometrical frustration of Ce atoms. The
magnetic ordering temperature is possibly lower than that of isostructural
CeZn$_{3}$P$_{3}$ (0.75 K). Because several $f$-electron compounds with the
ScAl$_{3}$C$_{3}$-type structure are quantum spin systems, CeCd$_{3}$P$_{3}$
may be a candidate of quantum spin liquid. On the other hand, the relatively
large band gap compared to approximately 0.4 eV in CeZn$_{3}$P$_{3}$, would not
be intimate with the observation of photoinduced Kondo effect, providing a
potentially new range of applications of devices based on the Kondo effect.",1604.04016v1
2016-04-19,Local stability and Hopf bifurcation analysis for Compound TCP,"We conduct a local stability and Hopf bifurcation analysis for Compound TCP,
with small Drop-tail buffers, in three topologies. The first topology consists
of two sets of TCP flows having different round trip times, and feeding into a
core router. The second topology corresponds to two queues in tandem, and
consists of two distinct sets of TCP flows, regulated by a single edge router
and feeding into a core router. The third topology comprises of two distinct
sets of TCP flows, regulated by two separate edge routers, and feeding into a
common core router. For each of these cases, we conduct a detailed local
stability analysis and obtain conditions on the network and protocol parameters
to ensure stability. If these conditions get marginally violated, our analysis
shows that the underlying systems would lose local stability via a Hopf
bifurcation. After exhibiting a Hopf, a key concern is to determine the
asymptotic orbital stability of the bifurcating limit cycles. We present a
detailed analytical framework to address the stability of the limit cycles, and
the type of the Hopf bifurcation by invoking Poincare normal forms and the
center manifold theory. We conduct packet-level simulations to highlight the
existence and stability of the limit cycles in the queue size dynamics.",1604.05549v1
2016-04-19,Hydrogen sulfide at high pressure: change in stoichiometry,"Hydrogen-sulfide (H2S) was studied by x-ray synchrotron diffraction (XRD) and
Raman spectroscopy up to 150 GPa at 180-295 K and by quantum-mechanical
variable-composition evolutionary simulations. The experiments show that H2S
becomes unstable with respect to formation of new compounds with different
structure and composition, including Cccm and a body-centered-cubic (bcc) like
(R3m or Im-3m) H3S, the latter one predicted previously to show a record-high
superconducting transition temperature, Tc of 203 K. These experiments provide
experimental ground for understanding of this record high Tc. The experimental
results are supported by theoretical structure searches that suggest the
stability of new H3S, H4S3, H5S8, H3S5, and HS2 compounds at elevated
pressures.",1604.05752v1
2016-04-27,Superconductivity at 7.8 K in the ternary LaRu2As2 compound,"Here we report the discovery of superconductivity in the ternary LaRu2As2
compound. The polycrystalline LaRu2As2 samples were synthesized by the
conventional solid state reaction method. Powder X-ray diffraction analysis
indicates that LaRu2As2 crystallizes in the ThCr2Si2-type crystal structure
with the space group I4/mmm (No. 139), and the refined lattice parameters are a
= 4.182(6) {\AA} and c = 10.590(3) {\AA}. The temperature dependent resistivity
measurement shows a clear superconducting transition with the onset Tc
(critical temperature) at 7.8 K, and zero resistivity happens at 6.8 K. The
upper critical field at zero temperature m0Hc2(0) was estimated to be 1.6 T
from the resistivity measurement. DC magnetic susceptibility measurement shows
a bulk superconducting Meissner transition at 7.0 K, and the isothermal
magnetization measurement indicates that LaRu2As2 is a type-II superconductor.",1604.07958v1
2016-04-29,Superconductivity and abnormal pressure effect in Sr0.5La0.5FBiSe2 superconductor,"Through the solid state reaction method, we synthesized a new BiSe2-based
superconductor Sr0:5La0:5FBiSe2 with superconducting transition temperature
Tc?3.8 K. A strong diamagnetic signal below Tc in susceptibility ?(T) is
observed indicating the bulk nature of superconductivity. Different to most
BiS2-based compounds where superconductivity develops from a
semiconducting-like normal state, the present compound exhibits a metallic
behavior down to Tc. Under weak magnetic field or pressure, however, a
remarkable crossover from metallic to insulating behaviors takes place around
Tmin where the resistivity picks up a local minimum. With increasing pressure,
Tc decreases monotonously and Tmin shifts to high temperatures, while the
absolute value of the normal state resistivity at low temperatures first
decreases and then increases with pressure up to 2.5 GPa. These results imply
that the electronic structure of Sr0:5La0:5FBiSe2 may be different to those in
the other BiS2-based systems.",1604.08686v1
2016-05-07,Importance of resonance widths in low-energy scattering of weakly-bound light-mass nuclei,"What effect do particle-emitting resonances have on the scattering cross
section? What physical considerations are necessary when modelling these
resonances? These questions are important when theoretically describing
scattering experiments with radioactive ion beams which investigate the
frontiers of the table of nuclides, far from stability. Herein, a novel method
is developed that describes resonant nuclear scattering from which centroids
and widths in the compound nucleus are obtained when one of the interacting
bodies has particle unstable resonances. The method gives cross sections
without unphysical behavior that is found if simple Lorentzian forms are used
to describe resonant target states. The resultant cross sections differ
significantly from those obtained when the states in the coupled channel
calculations are taken to have zero width, and compound-system resonances are
better matched to observed values.",1605.02183v1
2016-05-09,Magnetic phase diagram of TbMn$_{1-x}$Fe$_x$O$_3$ $(0 \leq x \leq 1)$ substitutional solid solution,"We present the magnetic phase diagram of TbMn1-xFexO3 substitutional solid
solution in the whole concentration range 0 <= x <= 1 as determined from
magnetization and specific heat measurements. We have found that the dominant
magnetic ion in the concentration range 0 <= x < 0.3 is manganese, while iron
ions do not create independent magnetic structure, but strongly affect magnetic
properties of the parent compound by reducing transition to magnetically
ordered state and transition into a cycloidal phase. The magnetism in the
concentration range 0.3 < x <= 1 is driven by the Fe sublattice. The manganese
ions again do not order in long range magnetic ordered state, but stabilize
four different magnetic structures of Fe sublattice above 2 K. The magnetic
ordering of Tb sublattice was observed only on parent compounds TbMnO3 and
TbFeO3 and for doping level below 0.1, or over 0.9.",1605.02503v2
2016-05-14,First-principle study on compensated half metallic double perovskite compound $Ba_2PrVO_6$,"The first-principle study on double perovskite compound Ba$_2$PrVO$_6$ has
been presented in this paper. By analysing band structures and integrated
density of states, it is found that Ba$_2$PrVO$_6$ is ferromagnetic metallic
within LSDA and compensated half metallic whithin LSDA+U. According to the
total and partial density of states, the anti-ferromagnetism of Ba$_2$PrVO$_6$
is originated from the spin down state Pr$^{4+}$ ($4f_{-2}$) and the spin up
hybridized state between the partially filled $t_{2g}$ state of V and the
partially filled triple-degeneration state $4f_{-1}$, $4f_{+1}$, $4f_{+3}$ of
Pr. We have investigated the magnetic evaluation of Ba$_2$PrVO$_6$ through
fixed spin moment calculations, and the results indicate that the compensated
half-metallic state is the ground state. The thermodynamic properties of
Ba$_2$PrVO$_6$ are also studied by employing the quasi-harmonic Debye model.",1605.04383v1
2016-05-16,Optical Evidence of Itinerant-Localized Crossover of $4f$ Electrons in Cerium Compounds,"Cerium (Ce)-based heavy-fermion materials have a characteristic double-peak
structure (mid-IR peak) in the optical conductivity [$\sigma(\omega)$] spectra
originating from the strong conduction ($c$)--$f$ electron hybridization. To
clarify the behavior of the mid-IR peak at a low $c$-$f$ hybridization
strength, we compared the $\sigma(\omega)$ spectra of the isostructural
antiferromagnetic and heavy-fermion Ce compounds with the calculated unoccupied
density of states and the spectra obtained from the impurity Anderson model.
With decreasing $c$-$f$ hybridization intensity, the mid-IR peak shifts to the
low-energy side owing to the renormalization of the unoccupied $4f$ state, but
suddenly shifts to the high-energy side owing to the $f$-$f$ on-site Coulomb
interaction at a slight localized side from the quantum critical point (QCP).
This finding gives us information on the change in the electronic structure
across QCP.",1605.04981v2
2016-05-23,Van der Waals pressure and its effect on trapped interlayer molecules,"Van der Waals assembly of two-dimensional (2D) crystals continue attract
intense interest due to the prospect of designing novel materials with
on-demand properties. One of the unique features of this technology is the
possibility of trapping molecules or compounds between 2D crystals. The trapped
molecules are predicted to experience pressures as high as 1 GPa. Here we
report measurements of this interfacial pressure by capturing
pressure-sensitive molecules and studying their structural and conformational
changes. Pressures of 1.2 +/- 0.3 GPa are found using Raman spectrometry for
molecular layers of one nanometer in thickness. We further show that this
pressure can induce chemical reactions and several trapped salts or compounds
are found to react with water at room temperature, leading to 2D crystals of
the corresponding oxides. This pressure and its effect should be taken into
account in studies of van der Waals heterostructures and can also be exploited
to modify materials confined at the atomic interfaces.",1605.07106v1
2016-05-24,Search for high-Tc conventional superconductivity at megabar pressures in the lithium-sulfur system,"Motivated by the recent report of superconductivity above 200 K in
ultra-dense hydrogen sulfide, we search for high-\tc\ conventional
superconductivity in the phase diagram of the binary Li-S system, using {\em
ab-initio} methods for crystal structure prediction and linear response
calculations for the electron-phonon coupling. We find that at pressures higher
than 20 GPa, several new compositions, besides the known Li$_2$S, are
stabilized; many exhibit electride-like {\em interstitial} charge localization
observed in other alkali metal compounds. Of all predicted phases, only Li$_3$S
at P > 640 GPa displays a sizable \tc, in contrast to what is observed in
sulfur and phosphorus hydrides, where several stoichiometries lead to high \tc.
We attribute this difference to 2$s$-2$p$ hybridization and avoided core
overlap, and predict similar behavior for other alkali metal compounds.",1605.07564v1
2016-06-06,Band gap tuning and orbital mediated electron phonon coupling in $HoFe_{1-x}Cr_xO_3$,"We report on the evidenced orbital mediated electron phonon coupling and band
gap tuning in HoFe1-xCrxO3 compounds. From the room temperature Raman
scattering, it is apparent that the electron-phonon coupling is sensitive to
the presence of both the Fe and Cr at the B-site. Essentially, an Ag like local
oxygen breathing mode is activated due to the charge transfer between Fe3+ -
Cr3+ at around 670 cm-1, this observation is explained on the basis of
Franck-Condon (FC) mechanism. Optical absorption studies infer that there
exists a direct band gap in the HoFe1-xCrxO3 compounds. Decrease in band gap
until x = 0.5 is ascribed to the broadening of the oxygen p orbitals as a
result of the induced spin disorder due to Fe3+ and Cr3+ at B site. In
contrast, the increase in band gap above x = 0.5 is explained on the basis of
the reduction in the available unoccupied d - orbitals of Fe3+ at the
conduction band. We believe that above results would be helpful for the
development of the optoelectronic devices based on the ortho-ferrites.",1606.01698v1
2016-06-08,Coupling of Magnetic Orders in La2CuO4+x,"High transverse magnetic field and zero field muon spin rotation and
relaxation measurements have been carried out in a lightly oxygen-doped high-Tc
parent compound La2CuO4 in a temperature range from 2 K to 300 K. As in the
stoichiometric compound, muon spin rotation spectra reveal, along with the
antiferromagnetic local field, the presence of an additional source of magnetic
field at the muon. The results indicate that this second magnetic order is
driven by the antiferromagnetism at low temperature but the two magnetic orders
decouple at higher temperature. The ability of muSR to detect this additional
magnetism deteriorates with doping, thus rendering the technique impotent to
reveal time-reversal symmetry breaking in superconductors.",1606.02561v1
2016-06-10,Effect of Gd/Nd doping on the magnetic properties of PrMnO3,"A study on temperature dependent magnetic properties of single phase
orthorhombic perovskites system associated with space group Pbnm compounds
Pr1-x(Gd/Nd)xMnO3 (x=0.3, 0.5, 0.7) was carried out. A magnetization reversal
is observed below the Neel temperature (TN), in DC magnetization measurements
(at 50 Oe) in the doped compounds. This may be due to the antiparallel coupling
between the two magnetic sublattices (|Pr+Gd/Nd | and Mn). With lowering of
temperature, the |Pr+ Gd/Nd|) ions begin to polarize under the negative
internal field due to canted moment of Mn moments. The hysteresis plot taken at
50K shows a ferrimagnetic characteristic and the presence of spin canting of
ions in the magnetic sublattices. Arrott plot indicates field induced second
order paramagnetic to ferrimagnetic (PM-FiM) phase transition in this system.",1606.03274v1
2016-06-10,High throughput thermal conductivity of high temperature solid phases: The case of oxide and fluoride perovskites,"Using finite-temperature phonon calculations and machine-learning methods, we
calculate the mechanical stability of about 400 semiconducting oxides and
fluorides with cubic perovskite structures at 0 K, 300 K and 1000 K. We find 92
mechanically stable compounds at high temperatures -- including 36 not
mentioned in the literature so far -- for which we calculate the thermal
conductivity. We demonstrate that the thermal conductivity is generally smaller
in fluorides than in oxides, largely due to a lower ionic charge, and describe
simple structural descriptors that are correlated with its magnitude.
Furthermore, we show that the thermal conductivities of most cubic perovskites
decrease more slowly than the usual $T^{-1}$ behavior. Within this set, we also
screen for materials exhibiting negative thermal expansion. Finally, we
describe a strategy to accelerate the discovery of mechanically stable
compounds at high temperatures.",1606.03279v1
2016-06-10,Pressure-driven 4$f$ localized-itinerant crossover in heavy fermion compound CeIn$_{3}$: A first-principles many-body perspective,"The localized-itinerant nature of Ce-4$f$ valence electrons in heavy fermion
compound CeIn$_{3}$ under pressure is studied thoroughly by means of the
combination of density functional theory and single-site dynamical mean-field
theory. The detailed evolutions of electronic structures of CeIn$_{3}$,
including total and partial density of states, momentum-resolved spectral
functions, and valence state histograms etc., are calculated in a wide pressure
range where the corresponding volume compression $V/V_0 \in [0.6,1.0]$ (here
$V_0$ is the experimental crystal volume) at $T \cong 116$ K. Upon increasing
pressure, two strong peaks associated with the Ce-$4f$ states emerge near the
Fermi level, and the $c$-$f$ hybridization and valence state fluctuation are
enhanced remarkably. Moreover, the kinetic and potential energies raise, while
the occupancy, total angular momentum, and low-energy scattering rate of the
Ce-$4f$ electrons decline with respect to pressure. All the physical
observables considered here exhibit prominent kinks or fluctuations in $V/V_0
\in [0.80,0.90]$, which are probably the desired fingerprints for the Ce-4$f$
localized-itinerant crossover.",1606.03367v2
2016-06-10,Modifed Becke-Johnson exchange potential: improved modelling of lead halides for solar cell applications,"We report first-principles calculations, within density functional theory, on
the lead halide compounds PbCl2, PbBr2, and CH3NH3PbBr3-xClx, taking into
account spin-orbit coupling. We show that, when the modified Becke-Johnson
exchange potential is used with a suitable choice of defining parameters,
excellent agreement between calculations and experiment is obtained. The
computational model is then used to study the effect of replacing the
methylammonium cation in CH3NH3PbI3 and CH3NH3PbBr3 with either N2H+5 or N2H+3,
which have slightly smaller ionic radii than methylammonium. We predict that a
considerable downshift in the values of the band gaps occurs with this
replacement. The resulting compounds would extend optical absorption down to
the near-infrared region, creating excellent light harvesters for solar cells.",1606.03425v1
2016-06-20,Effective realization of random magnetic fields in compounds with large single-ion anisotropy,"We show that spin $S=1$ system with large and random single--ion anisotropy
can be at low energies mapped to a $S=1/2$ system with random magnetic fields.
This is for example realized in
\mbox{Ni(Cl$_{1-x}$Br$_{x}$)$_2$-4SC(NH$_2$)$_2$} compound (DTNX) and therefore
it represents a long sought realization of random local (on-site) magnetic
fields in antiferromagnetic systems. We support the mapping by numerical study
of $S=1$ and effective $S=1/2$ anisotropic Heisenberg chains and find excellent
agreement for static quantities and also for the spin conductivity. Such
systems can therefore be used to study the effects of local random magnetic
fields on transport properties.",1606.06013v2
2016-06-21,Mobility induced unsaturated high linear magnetoresistance in transition-metal monopnictides Weyl semimetals,"Discovery of Weyl fermions in semimetallic tansition-metal monopnictides is a
major breakthrough in condensed matter physics. A Weyl semimetal is
characterized by the existence of robust Weyl points and unclosed topological
surface states in the form of Fermi arc. All the four compounds of the Weyl
semimetal transition monopnictide family i.e. NbP, TaP, NbAs and TaAs exhibit
extremely high mobility and unsaturated high magnetoresistance (MR). For
example, MR values are 8.5x10^5% at 1.85 K for NbP and 1.5x10^5% at 3 K in 9 T
for TaAs. NbP also achieves very low value of residual resistivity 0.63
micro-ohm cm at 2 K due to suppression of scattering resulting in ultra-high
mobility 5x10^6 cm^2/Vs, Interestingly, we find that the mobility of these
compounds play an important role for such a large MR.",1606.06649v1
2016-06-22,Thermodynamic stability of mixed Pb:Sn methyl-ammonium halide perovskites,"Using density functional theory, we investigate systematically mixed
MA(Pb:Sn)X3 perovskites, where MA is CH3NH3+, and X is Cl, Br, or I. Ab initio
calculations of the orthorhombic, tetragonal, and cubic perovskite phases show
that the substitution of lead by tin has a much weaker influence on both
structure and cohesive energies than the substitution of the halogen. The
thermodynamic stability of the MA(Pb:Sn)X3 mixtures at finite, non-zero
temperatures is studied within the Regular Solution Model. We predict that it
will be possible to create MA(Pb:Sn)I3 mixtures at any temperature. Our results
imply that mixing is unlikely for the low-temperature phase of bromide and
chloride compounds, where instead local clusters are more likely to form. We
further predict that in the high-temperature cubic phase, Pb and Sn compounds
will mix for both MA(Pb:Sn)Br3 and MA(Pb:Sn)Cl3 due to the entropy contribution
to the Helmholtz free energy.",1606.06944v2
2016-07-05,"Predicted thermoelectric properties of olivine-type Fe2GeCh4 (Ch = S, Se and Te)","We present here the thermoelectric properties of olivine-type Fe2GeCh4 (Ch =
S, Se and Te) using the linear augmented plane wave method based on first
principles density functional calculations. The calculated transport properties
using the semi-local Boltzmann transport equation reveal very high thermopower
for both S and Se-based compounds compared to their Te counterparts. The main
reason for this high thermopower is the quasi-flat nature of the bands at the
valence and conduction band edges. The calculated thermopower of Fe2GeCh4 is in
good agreement with the experimental reports at room temperature, with the
carrier concentration around 1018-1019cm-3. All the investigated systems show
an anisotropic nature in their electrical conductivity, resulting in a value
less than the order of 102 along the a-axis compared to the b- and c-axes.
Among the studied compounds, Fe2GeS4 and Fe2GeSe4 emerge as promising
candidates with good thermoelectric performance.",1607.01111v1
2016-07-06,Solubility and partitioning of impurities in Be alloys,"The most energetically favourable accommodation processes for common
impurities and alloying elements in Be metal and Be-Fe-Al intermetallics were
investigated using atomic scale simulations. Fe additions, combined with
suitable heat treatments, may scavange Al and Si through their incorporation
into the FeBe5 intermetallic. In the absence of Fe, Al and Si will not be
associated with Be metal. Li and Mg are also not soluble, but may react with
other impurities if present (such as Al or H). Mg may also form the MgBe13
intermetallic phase under certain conditions. He and H exhibit negligible
solubility in all phases investigated and whilst He will tend to form bubbles,
H can precipitate as BeH2. Similarly, C additions will form the stable compound
Be2C. Finally, oxygen exhibits a strong affinity to Be, exhibiting both some
degree of solubility in all phases considered here (though especially metallic
Be) and a highly favourable energy of formation for BeO.",1607.01502v1
2016-07-12,"Superconducting properties and hydrostatic pressure effect on ABi3 (A=Ba,Sr) single crystals","We report on the crystal growth and characterization of ABi3 (A=Ba,Sr)
superconductors. Single crystals of both compounds were grown by the self-flux
technique. BaBi3 crystallized in a tetragonal structure with space group P4/mmm
and SrBi3 in a cubic structure with space group Pm-3m. Superconductivity at Tc
= 6.0 K for BaBi3 and Tc = 5.6 K for SrBi3 have been confirmed through dc
magnetic susceptibility and electrical transport measurements. The dc magnetic
susceptibility under hydrostatic pressure shows a positive pressure coefficient
of dTc/dP = 1.22 K/GPa for BaBi3 and a negative pressure coefficient of dTc/dP
= -0.48 K/GPa for SrBi3. The normal state electrical resistivity shows that
both compounds are highly metallic in nature. The upper critical fields Hc2
evaluated by resistivity under magnetic fields $\rho(T,H)$ are 22 kOe for BaBi3
and 2.9 kOe for SrBi3. A specific heat jump of $\Delta Ce/\gamma Tc = 1.05$
suggests weak coupling superconductivity in BaBi3, whereas $\Delta Ce/\gamma Tc
= 2.08$ for SrBi3 is higher than the BCS theory value of 1.43, indicating a
strong coupling superconductor.",1607.03477v1
2016-07-14,Room temperature polarization in the ferrimagnetic Ga2-xFexO3 ceramics,"The effect of the Fe-Ga ratio on the magnetic and electric properties of the
multiferroic Ga2-xFexO3 compound has been studied in order to determine the
composition range exhibiting magnetic and electric orders coexistence and their
critical temperatures. A magnetoelectric phase diagram, showing the evolution
of both the Neel magnetic ordering temperature and the electric ordering
temperature, versus the iron content has been established for x values between
0.9 and 1.4. While the ferrimagnetic Neel temperature increases with the iron
content, the electric ordering temperature shows an opposite trend. The
electric polarization has been found to exist far above room temperature for
the x value of 1.1 composition which shows the highest observed electric
ordering temperature of approx. 580K. The compounds with x values of 1.3 and
1.4 are ferrimagnetic-electric relaxors with both properties coexisting at room
temperature.",1607.04312v1
2016-07-19,Electronic and magnetic properties of the 2H-NbS$_2$ intercalated by 3d transition metal atoms,"The electronic structure and magnetic properties of the 2H-NbS$_2$ compound
intercalated by Cr, Mn and Fe, have been investigated by means of the
Korringa-Kohn-Rostoker (KKR) method. The calculations demonstrate easy plane
magneto-crystalline anisotropy (MCA) of Cr$_{1/3}$NbS$_2$ monotonously
decreasing towards the Curie temperature in line with the experimental results.
The modification of the electronic structure results in a change of the easy
axis from in-plane to out-of-plane. It is shown, that for Cr$_{1/3}$NbS$_2$ and
Mn$_{1/3}$NbS$_2$ the in-plane MCA and Dzyaloshinskii-Moriya interactions
results in a helimagnetic structure along the hexagonal $c$ axis, following the
experimental observations. The negative exchange interactions in the
Fe$_{1/3}$NbS$_2$ compound results in a non-collinear frustrated magnetic
structure if the MCA is not taken into account. It is shown, however, that a
strong MCA along the hexagonal $c$ axis leads to a magnetic ordering referred
to as an ordering of the third kind, which was observed experimentally.",1607.05738v1
2016-07-20,Superconductivity on the verge of electronic topological transition in Fe based superconductors,"A comprehensive first principles study on the electronic topological
transition in a number of 122 family of Fe based superconductors is presented.
Doping as well as temperature driven Lifshitz transitions are found from first
principles simulations in a variety of Fe based superconductors that are
consistent with experimental findings. In all the studied compounds the
Lifshitz transitions are consistently found to occur at a doping concentration
where superconductivity is highest and magnetism disappears. Systematically,
the Lifshitz transition occurs in the electron Fermi surfaces for hole doping,
whereas in hole Fermi surfaces for electron doping as well as iso-electronic
doping. Temperature driven Lifshitz transition is found to occur in the
iso-electronic Ru-doped BaFe$_2$As$_2$ compounds. Fermi surface areas are found
to carry sensitivity of topological modifications more acutely than the band
structures and can be used as a better experimental probe to identify
electronic topological transition.",1607.05931v1
2016-07-27,Magneto-transport properties of CeRu$_2$Al$_{10}$: Similarities to URu$_2$Si$_2$,"We report on magneto-transport properties of the Kondo semiconducting
compound CeRu$_2$Al$_{10}$, focusing on its exotic phase below $T_0$ = 27 K. In
this phase, an excess thermal conductivity $\kappa$ emerges and is gradually
suppressed by magnetic field, strikingly resembling those observed in the
hidden-order phase of URu$_2$Si$_2$. Our analysis indicates that low-energy
magnetic excitation is the most likely origin, as was also proposed for
URu$_2$Si$_2$ recently, despite the largely reduced magnetic moments. Likewise,
other transport properties such as resistivity, thermopower and Nernst effect
exhibit distinct features characterizing the very different charge dynamics
above and below $T_0$, sharing similarities to URu$_2$Si$_2$, too. Given the
exotic nature of the ordered phases in both compounds, whether a unified
interpretation to all these observations exists appears to be extremely
interesting.",1607.07945v1
2016-07-28,The importance of temperature dependent energy gap in the understanding of high temperature thermoelectric properties,"In the present work, we show the importance of temperature dependent energy
band gap, E$_{g}$(T), in understanding the high temperature thermoelectric (TE)
properties of material by considering LaCoO$_{3}$ (LCO) and ZnV$_{2}$O$_{4}$
(ZVO) compounds as a case study. For the fix value of band gap, E$_{g}$,
deviation in the values of $\alpha$ has been observed above 360 K and 400 K for
LCO and ZVO compounds, respectively. These deviation can be overcomed by
consideration of temperature dependent band gap. The change in used value of
E$_{g}$ with respect to temperature is $\sim$4 times larger than that of InAs.
This large temperature dependence variation in E$_{g}$ can be attributed to
decrement in the effective on-site Coulomb interaction due to lattice
expansion. At 600 K, the value of \textit{ZT} for \textit{n} and
\textit{p-doped}, LCO is $\sim$0.35 which suggest that it can be a used as a
potential material for TE device. This work clearly suggest that one should
consider the temperature dependent band gap in predicting the high temperature
TE properties of insulating materials.",1607.08632v2
2016-08-03,Epitaxial growth and electronic properties of mixed valence YbAl3 thin films,"We report the growth of thin films of the mixed valence compound YbAl$_{3}$
on MgO using molecular-beam epitaxy. Employing an aluminum buffer layer,
epitaxial (001) films can be grown with sub-nm surface roughness. Using x-ray
diffraction, in situ low-energy electron diffraction and aberration-corrected
scanning transmission electron microscopy we establish that the films are
ordered in the bulk as well as at the surface. Our films show a coherence
temperature of 37 K, comparable to that reported for bulk single crystals.
Photoelectron spectroscopy reveals contributions from both $\textit{f}^{13}$
and $\textit{f}^{12}$ final states establishing that YbAl$_{3}$ is a mixed
valence compound and shows the presence of a Kondo Resonance peak near the
Fermi-level.",1608.01045v1
2016-08-04,Outage Behavior of Integer Forcing With Random Unitary Pre-Processing,"Integer forcing is an equalization scheme for the multiple-input
multiple-output communication channel that has been demonstrated to allow
operating close to capacity for ""most"" channels. In this work, the measure of
""bad"" channels is quantified by considering a compound channel setting where
the transmitter communicates over a fixed channel but knows only its mutual
information. The transmitter encodes the data into independent streams, all
taken from the same linear code. The coded streams are transmitted after
applying a unitary transformation. At the receiver side, integer-forcing
equalization is applied, followed by standard single-stream decoding.
Considering pre-processing matrices drawn from a random ensemble, outage
corresponds to the event that the target rate exceeds the achievable rate of
integer forcing for a given channel matrix. For the case of the circular
unitary ensemble, an explicit universal bound on the outage probability for a
given target rate is derived that holds for any channel in the compound class.
The derived bound depends only on the gap-to-capacity and the number of
transmit antennas. The results are also applied to obtain universal bounds on
the gap-to-capacity of multiple-antenna closed-loop multicast, achievable via
linear pre-processed integer forcing.",1608.01588v2
2016-08-08,Magnetic-Field-Induced Change of Magneto-Electric Coupling in the in Molecular Multiferroic (ND4)2[FeCl5(D2O)],"Our results describe an unprecedented example of change in the mechanism of
magnetically-induced electric polarization from spin current to spin-dependent
p-d hybridization model. We have followed the evolution of the magnetic
structures of (ND4)2[FeCl5 D2O] compound using single crystal neutron
diffraction under external magnetic field. The spin arrangements change from
incommensurate cycloidal to commensurate distorted-cycloidal and finally to
quasi-collinear. The determination of the magnetic structures allows us to
explain the observed electric polarization in the different ferroelectric
phases. Two different magneto-electric coupling mechanisms are at play: the
spin-current mechanism for external magnetic field below 5 T, and the spin
dependent p-d hybridization mechanism for magnetic field above this value,
being this compound the first example reported presenting this sequence of
magneto-electric coupling mechanisms.",1608.02369v1
2016-08-09,"NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7: novel single crystal pyrochlore antiferromagnets","The crystal structures and magnetic properties of three previously unreported
A2B2F7 pyrochlore materials, NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7 are presented.
In these compounds, either S=2 Fe2+ or S=5/2 Mn2+ is on the B site, while
nonmagnetic Na and Ca (Na and Sr) are disordered on the A site. The materials,
which were grown as crystals via the floating zone method, display high
effective magnetic moments and large Curie-Weiss thetas. Despite these
characteristics, freezing of the magnetic spins, characterized by peaks in the
susceptibility or specific heat, is not observed until low temperatures. The
empirical frustration index, f=- {\theta}cw/Tf, for the materials are 36
(NaSrMn2F7), 27 (NaSrFe2F7), and 19 (NaCaFe2F7). AC susceptibility, DC
susceptibility, and heat capacity measurements are used to characterize the
observed spin glass behavior. The results suggest that the compounds are
frustrated pyrochlore antiferromagnets with weak bond disorder. The magnetic
phenomena that these fluoride pyrochlores exhibit, in addition to their
availability as relatively large single crystals, make them promising
candidates for the study of geometric magnetic frustration.",1608.02907v1
2016-08-15,Two-channel Kondo physics due to As vacancies in the layered compound ZrAs1.58Se0.39,"We address the origin of the magnetic-field independent -|A| T^{1/2} term
observed in the low-temperature resistivity of several As-based metallic
systems of the PbFCl structure type. For the layered compound
ZrAs_{1.58}Se_{0.39}, we show that vacancies in the square nets of As give rise
to the low-temperature transport anomaly over a wide temperature regime of
almost two decades in temperature. This low-temperature behavior is in line
with the non-magnetic version of the two-channel Kondo effect, whose origin we
ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As
layer with a C_4 symmetry. The pair-breaking nature of the dynamical defects in
the square nets of As explains the low superconducting transition temperature
T_{\rm{c}}\approx 0.14 K of ZrAs_{1.58}Se_{0.39}, as compared to the
free-of-vacancies homologue ZrP_{1.54}S_{0.46} (T_{\rm{c}}\approx 3.7 K). Our
findings should be relevant to a wide class of metals with disordered pnictogen
layers.",1608.04263v1
2016-08-17,Dynamic Collaborative Filtering with Compound Poisson Factorization,"Model-based collaborative filtering analyzes user-item interactions to infer
latent factors that represent user preferences and item characteristics in
order to predict future interactions. Most collaborative filtering algorithms
assume that these latent factors are static, although it has been shown that
user preferences and item perceptions drift over time. In this paper, we
propose a conjugate and numerically stable dynamic matrix factorization (DCPF)
based on compound Poisson matrix factorization that models the smoothly
drifting latent factors using Gamma-Markov chains. We propose a numerically
stable Gamma chain construction, and then present a stochastic variational
inference approach to estimate the parameters of our model. We apply our model
to time-stamped ratings data sets: Netflix, Yelp, and Last.fm, where DCPF
achieves a higher predictive accuracy than state-of-the-art static and dynamic
factorization models.",1608.04839v3
2016-08-19,Long-range magnetic order and interchain interactions in the $S=2$ chain system MnCl$_3$(bpy),"A compound with very weakly interacting chains, MnCl$_3$(bpy), has attracted
a great deal of attention as a possible $S=2$ Haldane chain. However,
long-range magnetic order of the chains prevents the Haldane gap from
developing below 11.5~K. Based on a four-sublattice model, a description of the
antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5~THz and
magnetic fields up to 50~T indicates that the interchain coupling is indeed
quite small but that the Dzaloshinskii-Moriya interaction produced by broken
inversion symmetry is substantial (0.12~meV). In addition, the
antiferromagnetic, nearest-neighbor interaction within each chain (3.3~meV) is
significantly stronger than previously reported. The excitation spectrum of
this $S=2$ compound is well-described by a $1/S$ expansion about the classical
limit.",1608.05635v1
2016-08-25,Temperature-field phase diagram of geometrically frustrated CePdAl,"From the electrical resistivity and ac susceptibility measurements down to
$T$ = 40 mK, a rich temperature-field phase diagram has been constructed for
the geometrically frustrated heavy-fermion compound CePdAl. In the limit of
zero temperature, the field-induced suppression of the antiferromagnetism in
this compound results in a sequence of phase transitions/corssovers, rather
than a single critical point, in a critical region of field 3$-$5 T. In the
lowest temperature region, a power-law description of the temperature-dependent
resistivity yields $A$$\cdot$$T^n$ with $n$$>$2 for all applied fields.
However, a quadratic-in-temperature resistivity term can be extracted when
assuming an additional electron scattering channel from magnon-like
excitations, with $A$ diverging upon approaching the critical regime. Our
observations suggest CePdAl to be a new playground for exotic physics arising
from the competition between Kondo screening and geometrical frustration.",1608.07123v1
2016-09-01,"Heterogeneous nucleation and heat flux avalanches in La(Fe,Si)$_{13}$ magnetocaloric compounds near the critical point","The phase transformation kinetics of
LaFe$_{11.41}$Mn$_{0.30}$Si$_{1.29}$-H$_{1.65}$ magnetocaloric compound is
addressed by low rate calorimetry experiments. Scans at 1 mK/s show that its
first order phase transitions are made by multiple heat fllux avalanches.
Getting very close to the critical point, the step-like discontinuous behavior
associated with avalanches is smoothed out and thermal hysteresis disappears.
This result is confirmed by magneto-resistivity measurements and allows to
measure accurate values of the zero field hysteresis ($\Delta T_{hyst}$ = 0.37
K) and of the critical field (H$_c$ = 1.19 T). The number and magnitude of heat
flux avalanches change with magnetic field, showing the interplay between the
intrinsic energy barrier between phases and the microstructural disorder of the
sample.",1609.00332v1
2016-09-06,Fluorinated surfaces: towards a universal matrix-free substrates for Laser Desorption Ionization,"Matrix Assisted Laser Desorption Ionization (MALDI) is a soft ionization
method that finds widespread applications in high-throughput mass spectrometric
analysis. One of the main limit of this technique is that it requires the use
of matrices: these molecules enable the analytes desorption and ionization
(D/I) processes but also generate strong interfering signals in the low mass
spectral region, preventing a suitable detection of low molecular weight
compounds. The possibility to avoid their use will ease both sample preparation
and mass spectrum (MS) interpretation. In recent years nanostructured surfaces
have been proposed as a viable method to achieve such goal but the results are
limited to specific classes of chemical compounds and the approach lacks in
generality. Here we demonstrate that the fluorination of surfaces is the only
step needed to activate the target and to achieve matrix-free operation with
the same detection limit obtained using nanostructured chips. The results of
this work suggest that D/I is a purely interfacial effect, with negligible
contribution from chemical nature of the underlying substrate, provided that
the substrate is conductive and able to efficiently absorb the UV laser beam.",1609.01498v1
2016-09-15,"Charge-density-wave state induced by structural distortion in heavy-fermion compounds Ce$_3$M$_4$Sn$_{13}$ (M=Co, Ru, Rh)","In previous reports a structural transition from a cubic phase of
Yb$_3$Rh$_4$Sn$_{13}$ - type to the superlattice variant has been reported at
$\sim160$ K for a series of skutterudite-related Ce$_3$M$_4$Sn$_{13}$
compounds, where M=Co, Ru or Rh. We have simulated the low-temperature XRD
diffraction patterns of the distorted unit cell using written for that purpose
DISTorX program. The method proposed here for x-ray diffraction analysis
obtains the XRD patterns from the atomic positions and allows to investigate
crystal structure without imposed symmetry operations. We have indicated
crystallographic plane where distortion occurs and explained possible origin of
CDW in these materials. We have also shown that distortion caused by the charge
density wave leads to significantly changes of the intensity of diffraction
lines.",1609.05239v2
2016-09-11,Phonon-limited electrical transport properties of intermetallic compound YbAl3 from first-principles calculations,"We combine first-principles calculations and Boltzmann transport theory to
study the electrical transport properties of intermetallic compound YbAl3. To
accurately predict the electronic relaxation time, we use the density
functional perturbation theory and Wannier interpolation techniques which can
effectively treat the electron-phonon scattering. Our calculated transport
coefficients of YbAl3 are in reasonable agreement with the experimentally
measured results. Strikingly, we discover that in evaluating the Seebeck
coefficient of YbAl3, the scattering term has a larger contribution than the
band term and should be explicitly considered in the calculations, especially
for the case with localized bands near the Fermi level. Moreover, we
demonstrate that by reducing the sample size to less than ~30 nm, the
electronic thermal conductivity of YbAl3 can be sufficiently suppressed so that
the thermoelectric figure of merit can be further enhanced.",1609.05858v1
2016-09-21,Bose glass behavior in (Yb$_{1-x}$Lu$_x$)$_4$As$_3$ representing the randomly diluted quantum spin-1/2 chains,"The site-diluted compound (Yb$_{1-x}$Lu$_x$)$_4$As$_3$ is a scarce
realization of the linear Heisenberg antiferromagnet partitioned into
finite-size segments and is an ideal model compound for studying
field-dependent effects of quenched disorder in the one-dimensional
antiferromagnets. It differentiates from the systems studied so far in two
aspects - the type of randomness and the nature of the energy gap in the pure
sample. We have measured the specific heat of single-crystal
(Yb$_{1-x}$Lu$_x$)$_4$As$_3$ in magnetic fields up to 19.5 T. The contribution
$C_{\perp}$ arising from the magnetic subsystem in an applied magnetic field
perpendicular to the chains is determined. Compared to pure Yb$_4$As$_3$, for
which $C_{\perp}$ indicates a gap opening, for diluted systems a
non-exponential decay is found at low temperatures which is consistent with the
thermodynamic scaling of the specific heat established for a Bose-glass phase.",1609.06472v1
2016-09-22,Log-convexity and the cycle index polynomials with relation to compound Poisson distributions,"We extend the exponential formula by Bender and Canfield (1996), which
relates log-concavity and the cycle index polynomials. The extension clarifies
the log-convexity relation. The proof is by noticing the property of a compound
Poisson distribution together with its moment generating function. We also give
a combinatorial proof of extended ""log-convex part"" referring Bender and
Canfield's approach, where the formula by Bruijn and Erd\""os (1953) is
additionally exploited. The combinatorial approach yields richer structural
results more than log-convexity. Furthermore, we consider normal and binomial
convolutions of sequences which satisfy the exponential formula. The operations
generate interesting examples which are not included in well known laws about
log-concavity/convexity.",1609.06875v2
2016-09-27,First-principles studies of the Optical anisotropy of R3 space group chalcogenides crystal AX2MQ6,"In order to explain the reason that all the sythesised \ce{AX2MQ6}
chalcogenides compounds are phase-matching while isomorphic chalcogenides
compounds \ce{AX4M5Q12} are not phase-matched materials. The linear optical
property birefringence and non-linear optical property of $R3$ space group
crystals \ce{AX2MQ6} have been calculated to compare with \ce{AX4M5Q12}. Their
Electron Localization Function(ELF) was calculated to show that the acentricity
of the bonds on $sp^3$ hybridization \ce{Q^2-} ions is the main origin of
optical anisotropy. To quantificat the acentricity, a geometric parameter
dihedral angle between tetrahedral undersides and xy-planes was defined. We
find theoretically the birefringence depend on the defined geometric parameter
and ion radius. This relation between birefringence and structure resonalbly
explain the abnormal difference of birefringence of isostructural \ce{AX2MQ6}
and \ce{AX4M5Q12} and useful for exploring new phase-matching IR-NLO crystals.",1609.08243v3
2016-09-28,Study of the hyperfine fields in the BaFe$_2$As$_2$ family and its relation to the magnetic moment,"The hyperfine field $B_\text{hf}$ and the magnetic properties of the
BaFe$_2$As$_2$ family are studied using the fully relativistic Dirac formalism
for different types of substitution. The study covers electron doped
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$, hole doped
(Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ and also isovalently doped
Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ and BaFe$_2$(As$_{1-x}$P$_x$)$_2$ for a wide
range of the concentration $x$. For the substituted compounds the hyperfine
fields show a very strong dependence on the dopant type and its concentration
$x$. Relativistic contributions were found to have a significantly stronger
impact for the iron pnictides when compared to bulk Fe. As an important
finding, we demonstrate that it is not sensible to relate the hyperfine field
$B_\text{hf}$ to the average magnetic moment $\mu$ of the compound, as it was
done in earlier literature.",1609.08802v1
2016-10-04,Anisotropic type-I superconductivity and anomalous superfluid density in OsB 2,"We present a microscopic study of superconductivity in OsB2 , and discuss the
origin and characteristic length scales of the superconducting state. From
first-principles we show that OsB2 is characterized by three different Fermi
sheets, and we prove that this fermiology complies with recent
quantum-oscillation experiments. Using the found microscopic properties, and
experimental data from the literature, we employ Ginzburg-Landau relations to
reveal that OsB2 is a distinctly type-I superconductor with very low
Ginzburg-Landau parameter kappa - a rare property among compound materials. We
show that the found coherence length and penetration depth corroborate the
measured thermodynamic critical field. Moreover, our calculation of the
superconducting gap structure using anisotropic Eliashberg theory and ab initio
calculated electron-phonon interaction as input reveals a single but
anisotropic gap. The calculated gap spectrum is shown to give an excellent
account for the unconventional behavior of the superfluid density of OsB2
measured in experiments as a function of temperature. This reveals that gap
anisotropy can explain such behavior, observed in several compounds, which was
previously attributed solely to a two-gap nature of superconductivity.",1610.00929v1
2016-10-09,Direct Meissner Effect Observation of Superconductivity in Compressed H2S,"Recently, an extremely high superconducting temperature (Tc) of ~200 K has
been reported in the sulfur hydride system above 100 GPa. This result is
supported by theoretical predictions and verified experimentally. The crystal
structure of the superconducting phase was also identified experimentally,
confirming the theoretically predicted structure as well as a decomposition
mechanism from H2S to H3S+S. Even though nuclear resonant scattering has been
successfully used to provide magnetic evidence for a superconducting state, a
direct measurement of the important Meissner effect is still lacking. Here we
report in situ alternating-current magnetic susceptibility measurements on
compressed H2S under high pressures. It is shown that superconductivity
suddenly appears at 117 GPa and that Tc reaches 183 K at 149 GPa before
decreasing monotonically with a further increase in pressure. This evolution
agrees with both theoretical calculations and earlier experimental
measurements. The idea of conventional high temperature superconductivity in
hydrogen-dominant compounds has thus been realized in the sulfur hydride system
under hydrostatic pressure, opening further exciting perspectives for possibly
realizing room temperature superconductivity in hydrogen-based compounds.",1610.02630v1
2016-10-11,"Comment on: Quantitative study of the $f$ occupation in CeMIn5 and other cerium compounds with hard X-rays, [arXiv:1601.03270]","This comment clarifies the mixed definition of the cerium valence in the
article entitled: Quantitative study of the $f$ occupation in CeMIn5 and other
cerium compounds with hard X-rays, published in Journal of Electron
Spectroscopy and Related Phenomena
http://www.sciencedirect.com/science/article/pii/S0368204816300123 and
available on arXiv:1601.03270. Indeed, it is unclear wether electrons belonging
on hybridized f-states are part or not of the valence. When one tries to
simulate the system, an Anderson impurity model only includes valence bands
electrons and localized 4-f states. Therefore hybridized 4-f states are mixed
with the localized ones. From a heavy fermion perspective it however essential
to differentiate hybridized and localized states as only the second are
responsible for strong correlations, such as obtained by susceptibility or
direct comparisons to model systems.",1610.03220v1
2016-10-19,Gossamer bulk high-temperature superconductivity in FeSe,"The cuprates and iron-based high-temperature superconductors share many
common features: layered strongly anisotropic crystal structure, strong
electronic correlations, interplay between different types of electronic
ordering, the intrinsic spatial inhomogeneity due to doping. The understanding
of complex interplay between these factors is crucial for a directed search of
new high-temperature superconductors. Here we show the appearance of
inhomogeneous gossamer superconductivity in bulk FeSe compound at ambient
pressure and at temperature 5 times higher than its zero-resistance $T_c$. This
discovery helps to understand numerous remarkable superconducting properties of
FeSe. We also find and prove a general property: if inhomogeneous
superconductivity in a anisotropic conductor first appears in the form of
isolated superconducting islands, it reduces electric resistivity
anisotropically with maximal effect along the least conducting axis. This gives
a simple and very general tool to detect inhomogeneous superconductivity in
anisotropic compounds, which is critically important to study the onset of
high-temperature superconductivity.",1610.06117v1
2016-10-20,Stable Co-Catalyst-Free Photocatalytic H2 Evolution From Oxidized Titanium Nitride Nanopowders,"In the present work, a simple strategy is used to thermally oxidize TiN
nanopowder (ca. 20 nm) to an anatase phase of a TiO2:Ti3+:N compound. In
contrast to the rutile phase of such a compound this photocatalyst provides
photocatalytic activity for hydrogen evolution under AM1.5 conditions - this
without the use of any noble metal co-catalyst. Moreover the photocatalyst is
active and stable over extended periods of time (tested for 4 months).
Importantly, to achieve successful conversion to the active anatase polymorph,
sufficiently small starting particles of TiN are needed. The key factor for
catalysis is the stabilization of the co-catalytically active Ti3+ species
against oxidation by nitrogen present in the starting material.",1610.06335v1
2016-10-29,Revealing extremely low energy amplitude modes in the charge-density-wave compound LaAgSb$_2$,"The layered lanthanum silver antimonide LaAgSb$_2$ was known to experience
two charge density (CDW) phase transitions, which were proposed recently to be
closely related to the newly identified Dirac cone. We present optical
spectroscopy and ultrafast pump-probe measurement on the compound. The
development of energy gaps were clearly observed below the phase transition
temperatures in optical conductivity, which removes most part of the free
carrier spectral weight. Time resolved measurement demonstrated the emergence
of strong oscillations upon entering the CDW states, which were illuminated to
come from the amplitude mode of CDW collective excitations. The frequencies of
them are surprisingly low: only 0.12 THz for the CDW order with higher
transition temperature and 0.34 THz for the lower one, which shall be caused by
their small modulation wave vectors. Furthermore, the amplitude and relaxation
time of photoinduced reflectivity stayed unchanged across the two phase
transitions, which might be connected to the extremely low energy scales of
amplitude modes.",1610.09468v1
2016-11-20,Sodium catalytic effect in the NaxLi6-xC60 hydrogen storage process,"We report on the hydrogen sorption investigation of the mixed alkali cluster
intercalated fulleride series NaxLi6-xC60. These compounds are isostructural to
Na6C60 and Li6C60 while the cubic lattice parameter is linearly dependent on x.
The H2 absorption/desorption was studied by means of charge/discharge kinetic
and coupled calorimetric - manometric measurements. By varying the
stoichiometry, we found the best compromise between absorption rate,
temperature and amount of hydrogen in Na1Li5C60. This system is able to
reversibly absorb up to 4.3 wt% H2 at 280 {\deg}C, which is 70 {\deg}C lower in
temperature than its parent compound Li6C60. Furthermore, the kinetics is
improved of 67% with respect Li6C60 and the dehydrogenation enthalpy is 13
kJ/mol H2 lower.",1611.06512v1
2016-11-23,"Electron interactions, spin-orbit coupling, intersite correlations in pyrochlore iridates","We perform combined density functional and dynamical mean-field calculations
to study the pyrochlore iridates Lu$_2$Ir$_2$O$_7$, Y$_2$Ir$_2$O$_7$ and
Eu$_2$Ir$_2$O$_7$. Both single-site and cluster dynamical mean-field
calculations are performed and spin-orbit coupling is included. Paramagnetic
metallic phases, antiferromagnetic metallic phases with tilted Weyl cones and
antiferromagnetic insulating phases are found. The magnetic phases display
all-in/all-out magnetic ordering, consistent with previous studies. Unusually
for electronically three dimensional materials, the single-site dynamical
mean-field approximation fails to reproduce qualitative material trends,
predicting in particular that the paramagnetic phase properties of
Y$_2$Ir$_2$O$_7$ and Eu$_2$Ir$_2$O$_7$ are almost identical, although in
experiments the Y compound has a much higher resistance than the Eu compound.
This qualitative failure is attributed to the importance of intersite magnetic
correlations in the physics of these materials.",1611.07997v2
2016-11-25,"Comment on ""Quasi-One-Dimensional Metal-Insulator Transitions in Compound Semiconductor Surfaces""","In a recent Letter, Zhao et al. [1] reported the origin of
quasi-one-dimensional metal-insulator (MI) transitions in compound
semiconductor surfaces. Based on a density-functional theory (DFT) calculation
within the generalized gradient approximation (GGA), they claimed that
one-atom-wide metallic structures formed by a selective bonding of H or Li
atoms to GaN(10-10) and ZnO(10-10) undergo the Peierls-type MI transitions,
leading to a charge-density-wave (CDW) formation with periodic lattice
distortion. However, we here demonstrate that such a CDW phase is due to the
artifact of the GGA, while the antiferromagnetic (AFM) ground state is
predicted by the hybrid DFT calculation and the exact-exchange plus correlation
in the random-phase approximation (EX + cRPA).
  [1] J. Z. Zhao, W. Fan, M. J. Verstraete, Z. Zanolli, J. Fan, X. B. Yang, H.
Xu, and S. Y. Tong, Phys. Rev. Lett. 117, 116101 (2016).",1611.08406v2
2016-11-28,Magnetism of a sigma-phase Fe60V40 alloy: magnetic susceptibilities and magnetocaloric effect studies,"Magnetic properties of a sigma-phase Fe60V40 intermetallic compound were
studied by means of ac and dc magnetic susceptibility and magnetocaloric effect
measurements. The compound is a soft magnet yet it was found to behave like a
re-entrant spin-glass system. The magnetic ordering temperature was found to be
T_C ca.170 K, while the spin-freezing temperature was ca.164 K. Its relative
shift per decade of ac frequency was 0.002, a value smaller than that typical
of canonical spin-glasses. Magnetic entropy change, DeltaS, in the vicinity of
T_C was determined for magnetic field, H, ranging between 5 and 50 kOe.
Analysis of DeltaS in terms of the power law yielded the critical exponent, n,
vs. temperature with the minimum value of 0.75 at T_C, while from the analysis
of a relative shift of the maximum value of DeltaS with the field a critical
exponent Delta=1.7 was obtained. Based on scaling laws relationships values of
other two exponents viz. betha=0.6 and gamma=1 were determined.",1611.09186v1
2016-11-30,Scalable Similarity Search for Molecular Descriptors,"Similarity search over chemical compound databases is a fundamental task in
the discovery and design of novel drug-like molecules. Such databases often
encode molecules as non-negative integer vectors, called molecular descriptors,
which represent rich information on various molecular properties. While there
exist efficient indexing structures for searching databases of binary vectors,
solutions for more general integer vectors are in their infancy. In this paper
we present a time- and space- efficient index for the problem that we call the
succinct intervals-splitting tree algorithm for molecular descriptors (SITAd).
Our approach extends efficient methods for binary-vector databases, and uses
ideas from succinct data structures. Our experiments, on a large database of
over 40 million compounds, show SITAd significantly outperforms alternative
approaches in practice.",1611.10045v3
2016-11-30,Novel Kondo-like behavior near magnetic instability in SmB$_6$ : temperature and pressure dependences of Sm valence,"We report a systematic study of Sm valence in the prototypical intermediate
valence compound SmB$_6$. Sm mean valence, $v_{\rm Sm}$, was measured by X-ray
absorption spectroscopy as functions of pressure ($1<P<13$ GPa) and temperature
($3<T<300$ K). Pressure induced magnetic order (MO) was detected above $P_c =
10$ GPa by resistivity measurements. A shift toward localized $4f$ state with
increasing $P$ and/or $T$ is evident from an increase in $v_{\rm Sm}$. However
$v_{\rm Sm}$ at $P_c$ is anomalously far below 3, which differs from the
general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From
the $T$ dependence of $v_{\rm Sm}(P,T)$, we found that $v_{\rm Sm}(P,T)$
consists of two different characteristic components: one is associated with
low-energy electronic correlations involving Kondo like behavior, and the other
with high-energy valence fluctuations.",1611.10126v3
2017-01-09,Coupled Compound Poisson Factorization,"We present a general framework, the coupled compound Poisson factorization
(CCPF), to capture the missing-data mechanism in extremely sparse data sets by
coupling a hierarchical Poisson factorization with an arbitrary data-generating
model. We derive a stochastic variational inference algorithm for the resulting
model and, as examples of our framework, implement three different
data-generating models---a mixture model, linear regression, and factor
analysis---to robustly model non-random missing data in the context of
clustering, prediction, and matrix factorization. In all three cases, we test
our framework against models that ignore the missing-data mechanism on large
scale studies with non-random missing data, and we show that explicitly
modeling the missing-data mechanism substantially improves the quality of the
results, as measured using data log likelihood on a held-out test set.",1701.02058v1
2017-01-10,Orbital-driven two-dome superconducting phases in iron-based superconductors,"Recent several experiments revealed that novel bipartite
magnetic/superconducting phases widely exist in iron pnictides and
chalcogenides. Nevertheless, the origin of the two-dome superconducting phases
in iron-based compounds still remains unclear. Here we theoretically
investigated the electronic structures, magnetic and superconducting properties
of three representative iron-based systems, i.e. LaFeAsO1-xHx, LaFeAs1-xPxO and
KFe2As2. We found that in addition to the degenerate in-plane anisotropic xz/yz
orbitals, the quasi-degenerate in-plane isotropic orbitals drive these systems
entering into the second parent phase. Moreover, the second superconducting
phase is contributed by the isotropic orbitals rather than the anisotropic ones
in the first superconducting phase, indicating an orbital-selective pairing
state. These results imply an orbital-driven mechanism and shed light on the
understanding of the two-dome magnetic/superconducting phases in iron-based
compounds.",1701.02500v1
2017-01-12,Training-induced inversion of spontaneous exchange bias field on La1.5Ca0.5CoMnO6,"In this work we report the synthesis and structural, electronic and magnetic
properties of La1.5Ca0.5CoMnO6 double-perovskite. This is a re-entrant spin
cluster material which exhibits a non-negligible negative exchange bias effect
when it is cooled in zero magnetic field from an unmagnetized state down to low
temperature. X-ray powder diffraction, X-ray photoelectron spectroscopy and
magnetometry results indicate mixed valence state at Co site, leading to
competing magnetic phases and uncompensated spins at the magnetic interfaces.
We compare the results for this Ca-doped material with those reported for the
resemblant compound La1.5Sr0.5CoMnO6, and discuss the much smaller spontaneous
exchange bias effect observed for the former in terms of its structural and
magnetic particularities. For La1.5Ca0.5CoMnO6, when successive magnetization
loops are carried, the spontaneous exchange bias field inverts its sign from
negative to positive from the first to the second measurement. We discuss this
behavior based on the disorder at the magnetic interfaces, related to the
presence of a glassy phase. This compound also exhibits a large conventional
exchange bias, for which there is no sign inversion of the exchange bias field
for consecutive cycles.",1701.03496v1
2017-01-15,$^{57}$Fe Mössbauer study of stoichiometric iron based superconductor CaKFe$_4$As$_4$: a comparison to KFe$_2$As$_2$ and CaFe$_2$As$_2$,"$^{57}$Fe M\""ossbauer spectra at different temperatures between $\sim 5$ K
and $\sim 300$ K were measured on an oriented mosaic of single crystals of
CaKFe$_4$As$_4$ . The data indicate that CaKFe$_4$As$_4$ is a well formed
compound with narrow spectral lines, no traces of other, Fe - containing,
secondary phases in the spectra and no static magnetic order. There is no
discernible feature at the superconducting transition temperature in any of the
hyperfine parameters. The temperature dependence of the quadrupole splitting
approximately follows the empirical ""$T^{3/2}$ law"".
  The hyperfine parameters of CaKFe$_4$As$_4$ are compared with those for
KFe$_2$As$_2$ measured in this work, and the literature data for
CaFe$_2$As$_2$, and were found to be in between those for these two, ordered,
122 compounds, in agreement with the gross view of CaKFe$_4$As$_4$ as a
structural analog of KFe$_2$As$_2$ and CaFe$_2$As$_2$ that has alternating Ca -
and K - layers in the structure.",1701.04104v1
2017-01-19,Superconductivity and unexpected chemistry of germanium hydrides under pressure,"Following the idea that hydrogen-rich compounds might be high-T$_c$
superconductors at high pressures, and the very recent breakthrough in
predicting and synthesizing hydrogen sulfide with record-high T$_c$ = 203 K, ab
initio evolutionary algorithm for crystal structure prediction was employed to
find stable germanium hydrides. In addition to the earlier structure of germane
with space group Ama2, we propose a new C2/m structure, which is energetically
more favorable at pressures above 278 GPa (with inclusion of zero point
energy). Our calculations indicate metallicity of the new C2/m phase of germane
with T$_c$ = 67 K at 280 GPa. Germane is found to exhibit thermodynamic
instability to decomposition to hydrogen and the new compound Ge$_3$H$_{11}$ at
pressures above 300 GPa. Ge$_3$H$_{11}$ with space group I$\bar{4}$m2 is found
to become stable at above 285 GPa with T$_c$ = 43 K. We find that the
pressure-induced phase stability of germanium hydrides is distinct from its
analogous isoelectronic systems, e.g., Si-hydrides and Sn-hydrides.
Superconductivity stems from large electron-phonon coupling associated with the
wagging, bending and stretching intermediate-frequency modes derived mainly
from hydrogen.",1701.05600v1
2017-01-23,"Time-reversal symmetry breaking hidden order in Sr$_2$(Ir,Rh)O$_4$","Layered 5$d$ transition iridium oxides, Sr$_2$(Ir,Rh)O$_4$, are described as
unconventional Mott insulators with strong spin-orbit coupling. The undoped
compound, Sr$_2$IrO$_4$, is a nearly ideal two-dimensional pseudospin-$1/2$
Heisenberg antiferromagnet, similarly to the insulating parent compound of
high-temperature superconducting copper oxides. Using polarized neutron
diffraction, we here report a hidden magnetic order in pure and doped
Sr$_2$(Ir,Rh)O$_4$, distinct from the usual antiferromagnetic pseudo-spin
ordering. We find that time-reversal symmetry is broken while the lattice
translation invariance is preserved in the hidden order phase. The onset
temperature matches that of the odd-parity hidden order recently highlighted
using optical second harmonic generation experiments. The novel magnetic order
and broken symmetries can be explained by the loop-current model, previously
predicted for the copper oxide superconductors.",1701.06485v1
2017-01-23,In situ X-ray diffraction studies of graphite oxidation reaction indicating different exfoliation mechanism than ex site studies,"We offer a brief overview of the solvent-based graphene production and
summarize the current knowledge on the formation mechanism of graphite oxide
that proceeds via graphite intercalation compounds. In addition, the results of
our in situ X-ray diffraction investigation into this process are presented,
discussed and contrasted to the findings by other authors, who employed the
same oxidation protocol but examined the samples by ex situ X-ray diffraction.
Our results suggest that, contrary to the numerous reports by other authors, no
strong crystalline order, unique to graphite intercalation compounds as well as
graphite oxide, develops if they remain in concentrated acid. Furthermore, it
also appears that, depending on the concentration, sulfuric acid molecules
significantly weaken graphene-graphene interactions in graphite. Consequently,
concentrated sulfuric acid may be a good solvent for graphene dispersions, if
only there is sufficient energy input to separate the layers of graphene.",1701.06493v1
2017-01-26,Ab-initio study of mechanical and electronic properties of MoAlB,"Using first-principles calculations, the structural, elastic and electronic
properties of MoAlB have been investigated for the first time. The optimized
lattice constants exhibit fair agreement with the experimental values. The
computed elastic constants satisfy the mechanical stability conditions for the
MoAlB. The Mo-based boride MoAlB is elastically anisotropic and can be
classified as brittle material. This boride is expected to show reasonable
thermal conductivity due to its high Debye temperature of 693 K. The metallic
electrical conductivity of this compound is predicted from the electronic band
structure calculations. The chemical bonding in MoAlB is basically covalent in
nature which is supported by the calculated electronic density of states (DOS),
Mulliken population, and charge density distribution. The estimated hardness
value of 11.6 GPa for MoAlB suggests that it is softer compared to many other
borides. The Fermi surface is formed due to low dispersive Mo 4d-like bands,
which makes the compound a conductive one.",1701.07672v1
2017-01-28,Multilevel Code Construction for Compound Fading Channels,"We consider explicit constructions of multi-level lattice codes that
universally approach the capacity of the compound block-fading channel.
Specifically, building on algebraic partitions of lattices, we show how to
construct codes with negligible probability of error for any channel
realization and normalized log-density approaching the Poltyrev limit. Capacity
analyses and numerical results on the achievable rates for each partition level
are provided. The proposed codes have several enjoyable properties such as
constructiveness and good decoding complexity, as compared to random one-level
codes. Numerical results for finite-dimensional multi-level lattices based on
polar codes are exhibited.",1701.08314v3
2017-03-07,"Organic-inorganic Copper(II)-based Material: a Low-Toxic, Highly Stable Light Absorber beyond Organolead Perovskites","Lead halide perovskite solar cells have recently emerged as a very promising
photovoltaic technology due to their excellent power conversion efficiencies;
however, the toxicity of lead and the poor stability of perovskite materials
remain two main challenges that need to be addressed. Here, for the first time,
we report a lead-free, highly stable C6H4NH2CuBr2I compound. The C6H4NH2CuBr2I
films exhibit extraordinary hydrophobic behavior with a contact angle of
approximately 90 degree, and their X-ray diffraction patterns remain unchanged
even after four hours of water immersion. UV-Vis absorption spectrum shows that
C6H4NH2CuBr2I compound has an excellent optical absorption over the entire
visible spectrum. We applied this copper-based light absorber in printable
mesoscopic solar cell for the initial trial and achieved a power conversion
efficiency of 0.5%. Our study represents an alternative pathway to develop
low-toxic and highly stable organic-inorganic hybrid materials for photovoltaic
application.",1703.02401v2
2017-03-08,Raman scattering study of large magnetoresistance semimetals TaAs$_2$ and NbAs$_2$,"We have performed polarized and temperature-dependent Raman scattering
measurements on extremely large magnetoresitance compounds TaAs$_2$ and
NbAs$_2$. In both crystals, all the Raman active modes, including six A$_g$
modes and three B$_g$ modes, are clearly observed and well assigned with the
combination of symmetry analysis and first-principles calculations. The
well-resolved periodic intensity modulations of the observed modes with
rotating crystal orientations, verify the symmetry of each assigned mode and
are fitted to experimentally determine the elements of Raman tensor matrixes.
The broadening of two A$_g$ modes seen in both compounds allows us to estimate
electron-phonon coupling constant, which suggests a relatively small
electron-phonon coupling in the semimetals TaAs$_2$ and NbAs$_2$. The present
study provides the fundamental lattice dynamics information on TaAs$_2$ and
NbAs$_2$ and may shed light on the understanding of their extraordinary large
magnetoresistance.",1703.02708v1
2017-03-08,"Interplay of Dirac electrons and magnetism in AMnBi2 (A=Ca, Sr)","Dirac materials exhibit intriguing low-energy carrier dynamics that offer a
fertile ground for novel physics discovery. Of particular interest is the
interplay of Dirac carriers with other quantum phenomena, such as magnetism.
Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a
prototypical magnetic Dirac system comprising alternating Dirac-carrier and
magnetic layers. We present the first accurate determination of the exchange
energies in these compounds and, by comparison to the reference compound
BaMn2Bi2, we show that the Dirac-carrier layers in AMnBi2 significantly enhance
the exchange coupling between the magnetic layers, which in turn drives a
charge-gap opening along the Dirac locus. Our findings break new grounds in
unveiling the fundamental physics of magnetic Dirac materials, which offer a
novel platform for probing a distinct type of spin-Fermion interaction. The
outstanding properties of these materials allow a delicate manipulation of the
interaction between the Dirac carriers and magnetic moments, thus holding great
promise for applications in magnetic Dirac devices.",1703.02712v1
2017-03-11,Graphene-like quaternary compound SiBCN: a new wide direct band gap semiconductor predicted by a first-principles study,"Due to the lack of two-dimensional silicon-based semiconductors and the fact
that most of the components and devices are generated on single-crystal silicon
or silicon-based substrates in modern industry, designing two-dimensional
silicon-based semiconductors is highly desired. With the combination of a swarm
structure search method and density functional theory in this work, a
quaternary compound SiBCN with graphene-like structure is found and displays a
wide direct band gap as expected. The band gap is of ~2.63 eV which is just
between ~2.20 and ~3.39 eV of the highlighted semiconductors SiC and GaN.
Notably, the further calculation reveals that SiBCN possesses high carrier
mobility with ~5.14x10^3 and ~13.07x10^3 cm^2V^-1s^-1 for electron and hole,
respectively. Furthermore, the ab initio molecular dynamics simulations also
show that the graphene-like structure of SiBCN can be well kept even at an
extremely high temperature of 2000 K. The present work tells that designing
ulticomponent silicides may be a practicable way to search for new
silicon-based low-dimensional semiconductors which can match well with the
previous Si-based substrates.",1703.03893v1
2017-03-15,Homogeneity range of ternary 11-type chalcogenides Fe$_{1+y}$Te$_{1-x}$Se$_x$,"The 11-type Fe-chalcogenides belong to the family of Fe-based
superconductors. In these compounds, the interstitial Fe is known to strongly
influence the magnetic and superconducting properties. Here we present the
chemical homogeneity range of ternary compounds Fe$_{1+y}$Te$_{1-x}$Se$_x$
based on powder x-ray diffraction, energy dispersive x-ray analysis and
magnetization measurements. Our investigations show that the maximum amount of
excess Fe in homogeneous Fe$_{1+y}$Te$_{1-x}$Se$_x$ decreases with increase in
Se substitution for Te. Using our synthesis procedure, single-phase
Fe$_{1+y}$Te$_{1-x}$Se$_x$, with $~0.5 \leq x <~1$ could not be formed for any
amount of excess Fe. Further, the superconducting volume fraction in the
material is found to be strongly suppressed by excess Fe.",1703.05180v1
2017-03-17,Raman signatures of monoclinic distortion in (Ba$_{1-x}$Sr$_{x}$)$_{3}$CaNb$_{2}$O$_{9}$ complex perovskites,"Octahedral tilting is most common distortion process observed in
centrosymmetric perovskite compounds (ABO$_{3}$). Indeed, crucial physical
properties of this oxide stem from the tilts of BO$_{6}$ rigid octahedra. In
microwave ceramics with perovskite-type structure, there is a close relation
between the temperature coefficient of resonant frequency and tilt system of
the perovskite structure. However, in many cases, limited access facilities are
needed to assign correctly the space group, including neutron scattering and
transmission electron microscopy. Here, we combine the Raman scattering and
group-theory calculations to probe the structural distortion in the perovskite
(Ba$_{1-x}$Sr$_{x}$)$_{3}$CaNb$_{2}$O$_{9}$ solid solution, which exhibits a
structural phase transition at $x$ $\geq$ 0.7, from D$_{3d}^{3}$ trigonal to
C$_{2h}^{3}$ monoclinic cell. Both phases are related by an octahedral tilting
distortion ($a^{0}b^{-}b^{-}$ in Glazer notation). Low temperature Raman
spectra corroborate the group-theoretical predictions for
Sr$_{3}$CaNb$_{2}$O$_{9}$ compound, since 36 modes detected at 25 K agree well
with those 42 (25A$_{g}$ $\oplus$ 17B$_{g}$) predicted ones.",1703.05939v1
2017-03-20,Superconductivity above 120 kelvin in a chain link molecule,"The search for new superconducting compounds with higher critical
temperatures $T_{c}^{\prime}$s has long been the very heart of scientific
research on superconductivity. It took 75 years for scientists to push the
$T_{c}$ above liquid nitrogen boiling temperature since the discovery of
superconductivity. So far, the record high $T_{c}$ of about 130 K at atmosphere
pressure was reported in some multilayer Hg(Tl)-Ba-Ca-Cu-O compounds.
Meanwhile, sulfur hydride system holds the highest $T_{c}$ of around 200 K at
high pressure of about 150 GPa. While keeping these records for
superconductivity, either the toxicity of these superconductors or the
requirement of extreme pressure condition for superconductivity limits their
technology applications. Here we show that doping a chain link molecule $-$
$p$-terphenyl by potassium can bring about superconductivity at 123 K at
atmosphere pressure, which is comparable to the highest $T_{c}$ in cuprates.
The easy processability, light weight, durability of plastics, and
environmental friendliness of this kind of new superconductor have great
potential for the fine-tuning of electrical properties. This study opens a
window for exploring high temperature superconductivity in chain link organic
molecules.",1703.06641v1
2017-03-24,Evolution of magnetic and dielectric properties in Sr-substituted high temperature multiferroic YBaCuFeO5,"We report the evolution of structural, magnetic and dielectric properties due
to partial substitution of Ba by Sr in the high temperature multiferroic
YBaCuFeO5. This compound exhibits ferroelectric and antiferromagnetic
transitions around 200 K and these two phenomena are presumed to be coupled
with each other. Our studies on magnetic and dielectric properties of the
YBa1-xSrxCuFeO5 (x = 0.0, 0.25 and 0.5) show that substitution of Sr shifts
magnetic transition towards higher temperature whereas dielectric transition to
lower temperature. These results points to the fact that magnetic and
dielectric transitions get decoupled as a result of chemical pressure in form
of Sr substitution. The nature of magnetodielectric coupling changes across the
series with the presence of higher order coupling terms. Additionally in these
compounds glassy dynamics of electric dipoles is observed at low temperatures.",1703.08319v1
2017-03-25,$d^0$ half-metallic ferromagnetism in CaN and CaAs pnictides: An ab initio study,"Conventional magnetism occurs in systems which contain transition metals or
rare earth ions with partially filled $d$ or $f$ shells. It is theoretically
predicted that compounds of groups IA and IIA with IV and V, in some structural
phases, are ferromagnetic half-metals which made them new candidates for
spintronics applications. Employing density functional theory (DFT) we
investigate magnetism in binary compounds CaN and CaAs. Regarding the structure
of analogous magnetic materials and experimental results of CaAs synthesis, we
have considered two cubic structures: rocksalt (RS) and zincblende (ZB), and
four hexagonal structures: NiAs, wurtzite (WZ), anti-NiAs, and NaO. The
calculated results show that CaN in cubic, NiAs, and wurtzite structures, and
CaAs only in zincblende phase have ferromagnetic ground states with a magnetic
moment of $1\mu _B$. Electronic structure analysis of these materials indicates
that magnetism originates from anion $p$ states. Existence of flat $p$ bands
and consequently high density of states at the Fermi level of magnetic
structures gives rise to Stoner spin splitting and spontaneous ferromagnetism.",1703.08691v1
2017-07-02,Dense superconducting phases of copper-bismuth at high pressure,"Although copper and bismuth do not form any compounds at ambient conditions,
two intermetallics, CuBi and Cu$_{11}$Bi$_7$, were recently synthesized at high
pressures. Here we report on the discovery of additional copper-bismuth phases
at elevated pressures with high-densities from ab initio calculations. In
particular, a Cu$_2$Bi compound is found to be thermodynamically stable at
pressures above 59 GPa, crystallizing in the cubic Laves structure. In strong
contrast to Cu$_{11}$Bi$_7$ and CuBi, cubic Cu$_2$Bi does not exhibit any voids
or channels. Since the bismuth lone pairs in cubic Cu$_2$Bi are
stereochemically inactive, the constituent elements can be closely packed and a
high density of 10.52 g/cm$^{3}$ at 0 GPa is achieved. The moderate
electron-phonon coupling of $\lambda=0.68$ leads to a superconducting
temperature of 2 K, which exceeds the values observed both in
Cu$_{11}$Bi$_7$and CuBi, as well as in elemental Cu and Bi .",1707.00335v1
2017-07-03,"Ab initio study of Li, Mg and Al insertion into rutile VO2: Fast diffusion and enhanced voltages","Vanadium oxides are among the most promising materials that can be used as
electrodes in rechargeable metal-ion batteries. In this work, we systematically
investigate thermodynamic, electronic and kinetic properties associated with
the insertion of Li, Mg and Al atoms in rutile VO2. Using first-principles
calculations, we systematically study the structural evolution and voltage
curves of LixVO2, MgxVO2 and AlxVO2 (0<x<1) compounds. The calculated lithium
intercalation voltage starts at 3.50 V for single-atom insertion and decreases
to 2.23 V for full lithiation, to the LiVO2 compound, which agrees well with
experimental results. The Mg insertion features a plateau about 1.6 V up to
Mg0.5VO2 and then another plateau-like region at around 0.5 V up to Mg1VO2. The
predicted voltage curve for Al insertion starts at 1.98 V, followed by two
plateaus at 1.48 V and 1.17 V. The diffusion barrier of Li, Mg and Al in the
tunnel structure of VO2 is 0.06, 0.33 and 0.50 eV, respectively. The
demonstrated excellent Li, Mg and Al mobility, high structural stability and
high specific capacity suggest a promising potential of rutile VO2 electrodes
especially for multivalent batteries.",1707.00447v1
2017-07-10,Pressure-dependent mechanical and thermodynamic properties of newly discovered cubic Na2He,"Recently for the first time a stable compound of He and Na (Na2He) is
predicted at high pressure. We explore the pressure dependent elastic,
mechanical and thermodynamic properties of this newly discovered Na2He by using
ab initio technique. The calculation presents good accordance between the
theoretical and experimental lattice parameters. Though the most stable
structure of Na2He is found at 300 GPa, present study ensures the mechanical
stability of this compound up to 500 GPa. However, the Debye temperature,
melting temperature and minimum thermal conductivity of Na2He are also
calculated and discussed at different pressure.",1707.02704v2
2017-07-11,Novel high-pressure calcium carbonates,"Calcium and magnesium carbonates are believed to be the host compounds for
most of the oxidized carbon in the Earth's mantle. Here, using evolutionary
crystal structure prediction method USPEX, we systematically explore the
MgO-CO2 and CaO-CO2 systems at pressures ranging from 0 to 160 GPa to search
for thermodynamically stable magnesium and calcium carbonates. While MgCO3 is
the only stable magnesium carbonate, three calcium carbonates are stable under
pressure: well-known CaCO3, and newly predicted Ca3CO5 and CaC2O5. Ca3CO5
polymorphs are found to contain isolated orthocarbonate (CO4)4- tetrahedra, and
are stable at relatively low pressures (>11 GPa), whereas CaC2O5 is stable
above 33 GPa and its polymorphs feature polymeric motifs made of CO4
tetrahedra. Detailed analysis of chemical stability of CaCO3, Ca3CO5 and CaC2O5
in the environment typical of the Earth's lower mantle reveals that none of
these compounds can exist in the Earth's lower mantle. We conclude that MgCO3
is the main host of oxidized carbon throughout the lower mantle.",1707.03226v2
2017-07-17,An independent axiomatisation for free short-circuit logic,"Short-circuit evaluation denotes the semantics of propositional connectives
in which the second argument is evaluated only if the first argument does not
suffice to determine the value of the expression. Free short-circuit logic is
the equational logic in which compound statements are evaluated from left to
right, while atomic evaluations are not memorised throughout the evaluation,
i.e., evaluations of distinct occurrences of an atom in a compound statement
may yield different truth values. We provide a simple semantics for free SCL
and an independent axiomatisation. Finally, we discuss evaluation strategies,
some other SCLs, and side effects.",1707.05718v3
2017-07-24,Cell cycle time series gene expression data encoded as cyclic attractors in Hopfield systems,"Modern time series gene expression and other omics data sets have enabled
unprecedented resolution of the dynamics of cellular processes such as cell
cycle and response to pharmaceutical compounds. In anticipation of the
proliferation of time series data sets in the near future, we use the Hopfield
model, a recurrent neural network based on spin glasses, to model the dynamics
of cell cycle in HeLa (human cervical cancer) and S. cerevisiae cells. We study
some of the rich dynamical properties of these cyclic Hopfield systems,
including the ability of populations of simulated cells to recreate
experimental expression data and the effects of noise on the dynamics. Next, we
use a genetic algorithm to identify sets of genes which, when selectively
inhibited by local external fields representing gene silencing compounds such
as kinase inhibitors, disrupt the encoded cell cycle. We find, for example,
that inhibiting the set of four kinases BRD4, MAPK1, NEK7, and YES1 in HeLa
cells causes simulated cells to accumulate in the M phase. Finally, we suggest
possible improvements and extensions to our model.",1707.07707v1
2017-08-05,Crystal growth with oxygen partial pressure of the $BaCuSi_2O_6$ and $Ba_{1-x}Sr_xCuSi_2O_6$ spin dimer compounds,"$BaCuSi_2O_6$ is a quasi-two dimensional spin dimer system and a model
material for studying Bose-Einstein condensation (BEC) of magnons in high
magnetic fields. The new $Ba_{1-x}Sr_xCuSi_2O_6$ mixed system, which can be
grown with x < 0.3, and $BaCuSi_2O_6$, both grown by using a crystal growth
method with enhanced oxygen partial pressure, have the same tetragonal
structure ($I4_1/acd$) at room temperature. The mixed system shows no
structural phase transition, so that the tetragonal structure is stable down to
low temperatures. The oxygen partial pressure acts as control parameter for the
growth process. A detailed understanding of the crystal structure depending on
the oxygen content will enable the study of the spin dynamics of field-induced
order states in this model magnetic compound of high current interest with only
one type of dimer layers, which shows the same distance between the Cu atoms,
in the structure.",1708.01739v1
2017-08-17,Enhanced superconductivity and anisotropy of FeTe0.6Se0.4 single crystals with Li-NH3 intercalation,"We report a systematic study of anisotropy resistivity, magnetoresistance and
Hall effect of Li0.32(NH3)yFe2Te1.2Se0.8 single crystals. When compared to the
parent compound FeTe0.6Se0.4, the Li-NH3 intercalation not only increases the
superconducting transition temperature, but also enhances the electronic
anisotropy in both normal and superconducting states. Moreover, in contrast to
the parent compound, the Hall coefficient RH becomes negative at low
temperature, indicating electron-type carriers are dominant due to Li doping.
On the other hand, the sign reverse of RH at high temperature and the failure
of scaling behavior of magnetoresistance imply that hole pockets may be still
crossing or just below the Fermi energy level, leading to the multiband
behavior in Li0.32(NH3)yFe2Te1.2Se0.8.",1708.05310v2
2017-08-25,Nematic superconductivity in Cu$_{x}$Bi$_{2}$Se$_{3}$: The surface Andreev bound states,"We study theoretically the topological surface states (TSSs) and the possible
surface Andreev bound states (SABSs) of Cu$_{x}$Bi$_{2}$Se$_{3}$ which is known
to be a topological insulator at $x=0$. The superconductivity (SC) pairing of
this compound is assumed to have the broken spin-rotation symmetry, similar to
that of the A-phase of $^{3}$He as suggested by recent nuclear-magnetic
resonance experiments. For both spheroidal and corrugated cylindrical Fermi
surfaces with the hexagonal warping terms, we show that the bulk SC gap is
rather anisotropic; the minimum of the gap is negligibly small as comparing to
the maximum of the gap. This would make the fully-gapped pairing effectively
nodal. For a clean system, our results indicate the bulk of this compound to be
a topological superconductor with the SABSs appearing inside the bulk SC gap.
The zero-energy SABSs which are Majorana fermions, together with the TSSs not
gapped by the pairing, produce a zero-energy peak in the surface density of
states (SDOS). The SABSs are expected to be stable against short-range
nonmagnetic impurities, and the local SDOS is calculated around a nonmagnetic
impurity. The relevance of our results to experiments is discussed.",1708.07800v1
2017-08-29,Strong-Correlation Derived Spin-Fermion Model for Skyrmions in MnGe,"MnGe has been reported as a candidate of three-dimensional (3D) skyrmion
crystal in comparison to the two-dimensional (2D) skyrmion observed in most
other B20 compounds like MnSi. In addition, the small-sized skyrmions in MnGe
are desired properties for information storage. By performing the density
functional theory (DFT) calculations and model simulations based on the
DFT-informed tight-binding Hamiltonian, we explore the nature of the 3D
skyrmion in MnGe. By invoking a dual nature of d-electrons on Mn atoms, we
propose a strong-correlation derived spin-fermion model with an
antiferromagnetic coupling between the localized and itinerant moments. This
model could explain the drastic difference of magnetic moments between MnGe and
MnSi compounds. In addition, we find that the 3D or 2D nature of skyrmions are
dependent on the coupling strength.",1708.08955v2
2017-09-17,Magnetic properties of the spin-1 chain compound NiCl$_3$C$_6$H$_5$CH$_2$CH$_2$NH$_3$,"We report experimental results of the static magnetization, ESR and NMR
spectroscopic measurements of the Ni-hybrid compound
NiCl$_3$C$_6$H$_5$CH$_2$CH$_2$NH$_3$. In this material NiCl$_3$ octahedra are
structurally arranged in chains along the crystallographic $a$-axis. According
to the static susceptibility and ESR data Ni$^{2+}$ spins $S = 1$ are isotropic
and are coupled antiferromagnetically (AFM) along the chain with the exchange
constant $J = 25.5$ K. These are important prerequisites for the realization of
the so-called Haldane spin-1 chain with the spin-singlet ground state and a
quantum spin gap. However, experimental results evidence AFM order at $T_{\rm
N} \approx 10$ K presumably due to small interchain couplings. Interestingly,
frequency-, magnetic field-, and temperature-dependent ESR measurements, as
well as the NMR data, reveal signatures which could presumably indicate an
inhomogeneous ground state of co-existent mesoscopically spatially separated
AFM ordered and spin-singlet state regions similar to the situation observed
before in some spin-diluted Haldane magnets.",1709.05692v1
2017-09-14,Dynamic heterogeneity in an orientational glass,"Family of compounds CBr$_n$Cl$_{4-n}$ has been proven helpful in unraveling
microscopic mechanisms responsible of glassy behavior. Some of the family
members show translational ordered phases with minimal disorder which appears
to reveal glassy features, thus deserving special attention in the search for
universal glass anomalies. In this work, we studied CBrCl$_3$ dynamics by
performing extensive molecular dynamics simulations. Molecules of this compound
perform reorientational discrete jumps, where the atoms exchange equivalent
positions among each other revealing a cage-orientational jump motion fully
comparable to the cage-rototranslational jump motion in supercooled liquids.
Correlation times were calculated from rotational autocorrelation functions
showing good agreement with previous reported dielectric results. From mean
waiting and persistence times calculated directly from trajectory results, we
are able to explain which microscopic mechanisms lead to characteristic times
associated with $\alpha$ and $\beta$-relaxation times measured experimentally.
We found that two nonequivalent groups of molecules have a longer
characteristic time than the other two nonequivalent groups, both of them
belonging to the asymmetric unit of the monoclinic (C2/c) lattice.",1709.07733v2
2017-09-23,On the magnetism of the C14 Nb0.975Fe2.025 Laves phase compound: Determination of the H-T phase diagram,"A C14 Nb0.975Fe2.025 Laves phase compound was investigated aimed at
determining the H-T magnetic phase diagram. Magnetization, M, and AC magnetic
susceptibility measurements were performed. Concerning the former field-cooled
and zero-field-cooled M-curves were recorded in the temperature range of 2-200K
and in applied magnetic field, H, up to 1000 Oe, isothermal M(H) curves at 2 K,
5 K, 50 K, 80 K and 110 K as well as hysteresis loops at several temperatures
over the field range of -10 to +10kOe. Regarding the AC susceptibility, both
real and imaginary components were registered as a function of increasing
temperature in the interval of 2 K - 150 K at the frequencies of the
oscillating field, f, from 3 Hz up to 999 Hz. An influence of the external DC
magnetic field, H, on the temperature dependence of the AC susceptibility was
investigated, too. The measurements clearly demonstrated that the magnetism of
the studied sample is weak, itinerant and has a reentrant character. Based on
the obtained results a magnetic phase diagram has been constructed in the H-T
coordinates.",1709.08064v2
2017-09-24,"Ab-initio study of structural, elastic, electronic, optical and thermodynamic properties of MgV2O6","We have performed ab-initio calculations using plane-wave ultraviolet
pseudopotential technique based on the density-functional theory (DFT) to study
the structural, mechanical, electronic, optical and thermodynamic properties of
orthorhombic MgV2O6. The calculated lattice parameters are in good agreement
with the available experimental data. The second-order elastic constants and
the other relevant quantities such as the Youngs modulus, shear modulus,
Poissons ratio, compressibility, anisotropy factor, sound velocity, and Debye
temperature have been calculated. After analyzing the calculated elastic
constants, it is shown that the compound under study is mechanically stable.
The analysis of the electronic band structure shows that this compound reveals
semiconducting nature with band gap 2.195 eV and the contribution predominantly
comes from O-2s states.",1709.08208v1
2017-09-25,Magnetic structure of Ba(TiO)Cu$_4$(PO$_4$)$_4$ probed using spherical neutron polarimetry,"The antiferromagnetic compound Ba(TiO)Cu$_4$(PO$_4$)$_4$ contains square
cupola of corner-sharing CuO$_4$ plaquettes, which were proposed to form
effective quadrupolar order. To identify the magnetic structure, we have
performed spherical neutron polarimetry measurements. Based on symmetry
analysis and careful measurements we conclude that the orientation of the
Cu$^{2+}$ spins form a non-collinear in-out structure with spins approximately
perpendicular to the CuO$_4$ motif. Strong Dzyaloshinskii-Moriya interaction
naturally lends itself to explain this phenomenon. The identification of the
ground state magnetic structure should serve well for future theoretical and
experimental studies into this and closely related compounds.",1709.08566v1
2017-09-29,Thermodynamic properties of Ba$_2$CoSi$_2$O$_6$Cl$_2$ in strong magnetic field: Realization of flat-band physics in a highly frustrated quantum magnet,"The search for flat-band solid-state realizations is a crucial issue to
verify or to challenge theoretical predictions for quantum many-body flat-band
systems. For frustrated quantum magnets flat bands lead to various
unconventional properties related to the existence of localized many-magnon
states. The recently synthesized magnetic compound Ba$_2$CoSi$_2$O$_6$Cl$_2$
seems to be an almost perfect candidate to observe these features in
experiments. We develop a theory for Ba$_2$CoSi$_2$O$_6$Cl$_2$ by adapting the
localized-magnon concept to this compound. We first show that our theory
describes the known experimental facts and then we propose new experimental
studies to detect a field-driven phase transition related to a
Wigner-crystal-like ordering of localized magnons at low temperatures.",1709.10356v2
2017-11-01,Dynamic Symmetry Breaking and Spin Splitting in Metal Halide Perovskites,"Metal halide perovskites exhibit a materials physics that is distinct from
traditional inorganic and organic semiconductors. While materials such as
CH3NH3PbI3 are non-magnetic, the presence of heavy elements (Pb and I) in a
non-centrosymmetric crystal environment result in a significant spin-splitting
of the frontier electronic bands through the Rashba-Dresselhaus effect. We
show, from a combination of \textit{ab initio} molecular dynamics,
density-functional theory, and relativistic quasi-particle \textit{GW} theory,
that the nature (magnitude and orientation) of the band splitting depends on
the local asymmetry around the Pb and I sites in the perovskite structure. The
potential fluctuations vary in time as a result of thermal disorder and a
dynamic lone pair instability of the Pb(II) 6s$^{2}$6p$^{0}$ ion. We show that
the same physics emerges both for the organic-inorganic CH3NH3PbI3 and the
inorganic CsPbI3 compound. The results are relevant to the photophysics of
these compounds and are expected to be general to other lead iodide containing
perovskites.",1711.00533v1
2017-11-02,Anomalous connection between antiferromagnetic and superconducting phases in pressurized non-centrosymmetric heavy fermion compound CeRhGe3,"Unconventional superconductivity frequently emerges as the transition
temperature of a magnetic phase, typically antiferromagnetic, is suppressed
continuously toward zero temperature. Here, we report contrary behavior in
pressurized CeRhGe3, a non-centrosymmetric heavy fermion compound. We find that
its pressure-tuned antiferromagnetic transition temperature (TN) appears to
avoid a continuous decrease to zero temperature by terminating abruptly above a
dome of pressure-induced superconductivity. Near 21.5 GPa, evidence for TN
suddenly vanishes, the electrical resistance becomes linear in temperature and
the superconducting transition reaches a maximum. In light of X-ray absorption
spectroscopy measurements, these characteristics appear to be related to a
pressured-induced Ce valence instability, which reveals as a sharp increase in
the rate of change of Ce valence with applied pressure.",1711.00688v1
2017-11-02,Topological superconductor in quasi-one-dimensional Tl2-xMo6Se6,"We propose that the quasi-one-dimensional molybdenum selenide compound
Tl2-xMo6Se6 is a time-reversal-invariant topological superconductor induced by
inter-sublattice pairing, even in the absence of spin-orbit coupling (SOC). No
noticeable change in superconductivity is observed in Tl-deficient (0<=x<=0.1)
compounds. At weak SOC, the superconductor prefers the triplet d vector lying
perpendicular to the chain direction and two-dimensional E2u symmetry, which is
driven to a nematic order by spontaneous rotation symmetry breaking. The
locking energy of the d vector is estimated to be weak and hence the proof of
its direction would rely on tunnelling or phase-sensitive measurements.",1711.00815v1
2017-11-09,"Triply degenerate nodal points in RERh$_{6}$Ge$_{4}$ (RE=Y, La, Lu)","As a new type of fermions without counterpart in high energy physics, triply
degenerate fermions show exotic physical properties, which are represented by
triply degenerate nodal points in topological semimetals. Here, based on the
space group theory analysis, we propose a practical guidance for seeking a
topological semimetal with triply degenerate nodal points located at a
symmetric axis, which is applicable to both symmorphic and nonsymmorphic
crystals. By using this guidance in combination with the first-principles
electronic structure calculations, we predict a class of triply degenerate
topological semimetals RERh$_{6}$Ge$_{4}$ (RE=Y, La, Lu). In these compounds,
the triply degenerate nodal points are located at the $\Gamma$-A axis and not
far from the Fermi level. Especially, LaRh$_{6}$Ge$_{4}$ has a pair of triply
degenerate nodal points located very closely to the Fermi level. Considering
the fact that the single crystals of RERh$_{6}$Ge$_{4}$ have been synthesized
experimentally, the RERh$_{6}$Ge$_{4}$ class of compounds will be an
appropriate platform for studying exotic physical properties of triply
degenerate topological semimetals.",1711.03370v1
2017-11-13,Electronic and gap properties of Sb and Bi based halide perovskites: An ab-initio study,"Halide perovskites are currently under intense investigation due to their
potential applications in optoelectronics and solar cells. Among them several
crystallize in low symmetry lattice structures like trigonal, hexagonal,
orthorhombic and monoclinic. Employing \textit{ab-initio} electronic structure
calculations in conjunction with generalized gradient approximation and hybrid
functionals we study a series of perovskites with the formula A$_3$B$_2$X$_9$
which have been grown experimentally. A stands for a monovalent cation like Cs,
Rb, K or the organic methylammonium molecule (MA), B is Sb or Bi, and X is a
halogen. Moreover we include in our study both the effect of spin-orbit
coupling in the halide perovskites and the influence of the orientation
disorder of the MA cation on the energy band gaps of these compounds. Most
compounds under study exhibit absorption in or close to the optical regime and
thus can find application in various optoelectronic devices. Our results pave
the way for further investigation on the use of these materials in technology
relevant applications.",1711.04846v1
2017-11-15,Orbital-dependent electron dynamics in Fe-pnictide superconductors,"We report on orbital-dependent quasiparticle dynamics in EuFe$_2$As$_2$, a
parent compound of Fe-based superconductors and a novel way to experimentally
identify this behavior, using time- and angle-resolved photoelectron
spectroscopy across the spin density wave transition. We observe two different
relaxation time scales for photo-excited d$_x$$_z$/d$_y$$_z$ and d$_x$$_y$
electrons. While d$_x$$_z$/d$_y$$_z$ electrons relax faster through the
electron-electron scattering channel, showing an itinerant character, d$_x$$_y$
electrons form a quasi-equilibrium state with the lattice due to their
localized character, and the state decays slowly. Our findings suggest that
electron correlation in Fe-pnictides is an important property, which should be
taken into careful account when describing the electronic properties of both
parent and electron-doped compounds, and therefore establish a strong
connection with cuprates.",1711.05464v3
2017-11-19,Photocatalytic Behavior of Fluorinated Rutile TiO$_2$(110) Surface: Understanding from the Band Model,"Surface fluorination of TiO$_2$ (F-TiO$_2$) has complicate photocatalytic
behavior in degradation of organic compounds. This work attempts to establish
an elegant scenario based on the band model to understand this behavior.
Density functional theory (DFT) calculations show that fluorination of the
rutile TiO$_2$(110) surface (F-TiO$_2$${110}$) results in the falling of band
edges. The falling of valence band edge (VBE) facilitates production of free
$\cdot$OH radicals, whereas the falling of conduction band edge (CBE) lowers
the reducing power of photo-electrons and inhibits reductive reactions mediated
by them. As a result, the photo-electrons are built up in the conduction band
which depresses photo-holes in the valence band to produce $\cdot$OH radicals
due to the requirement of electrical neutrality and thus leads to a low
degradation rate of organic compounds. Even though, our model suggests a route
to improve the degradation efficiency, by introducing a scavenger of
photo-electrons to promote formation of $\cdot$OH radicals.",1711.06980v1
2017-11-20,On the Feasibility of Interference Alignment in Compounded MIMO Broadcast Channels with Antenna Correlation and Mixed User Classes,"This paper presents a generalized closed-form beamforming technique that can
achieve the maximum degrees of freedom in compounded multiple-input
multiple-output (MIMO) broadcast channels with mixed classes of
multiple-antenna users. The contribution is firstly described within the
context of a three-cell network and later extended to the general multi-cell
scenario where we also show how to determine the conditions required to align
the interference in a subspace that is orthogonal to the one reserved for the
desired signals. This is then followed by an analysis of the impact of antenna
correlation for different channel state information acquisition models. The
proposed scheme is examined under both conventional and Large-scale MIMO
systems. It will be shown that the proposed technique enables networks with any
combination of user classes to achieve superior performance even under
significant antenna correlation, particularly in the case of the Large-scale
MIMO systems.",1711.07175v1
2017-11-24,Smith-Purcell Radiation from Compound Blazed Gratings,"Free electrons travelling in vacuum carry evanescent electric field, which
can only be coupled to free space light via interaction with a surrounding or
nearby medium: as Cherenkov radiation when travelling faster than the local
velocity of light or as ""Smith-Purcell"" (SP) radiation when passing over the
surface of a grating. The SP emission characteristics of simple gratings such
as a regular array of wires or slits are a well-understood phenomenon. Here we
show that for a compound grating made up of several closely-spaced slits
repeated for each period, the characteristic angular dispersion of
Smith-Purcell radiation can be selectively attenuated or enhanced. We analyze,
in particular, the change in intensity as slit elements are added to the
structure for two slit sizes and how this affects emission enhancement.",1711.09018v1
2017-11-28,Uncertainties and understanding of experimental and theoretical results regarding reactions forming heavy and superheavy nuclei,"Experimental and theoretical results of the $P_{\mathrm{CN}}$ fusion
probability of reactants in the entrance channel and the $W_{\mathrm{sur}}$
survival probability against fission at deexcitation of the compound nucleus
formed in heavy-ion collisions are discussed. The theoretical results for a set
of nuclear reactions leading to formation of compound nuclei (CNs) with the
charge number $Z=102\text{--}122$ reveal a strong sensitivity of
$P_{\mathrm{CN}}$ to the characteristics of colliding nuclei in the entrance
channel, dynamics of the reaction mechanism, and excitation energy of the
system. We discuss the validity of assumptions and procedures for analysis of
experimental data, and also the limits of validity of theoretical results
obtained by the use of phenomenological models. The comparison of results
obtained in many investigated reactions reveals serious limits of validity of
the data analysis and calculation procedures.",1711.10603v1
2017-11-30,Domain imaging across the magneto-structural phase transition in Fe$_{1+y}$Te,"The investigation of the magnetic phase transitions in the parent compounds
of Fe-based superconductors is regarded essential for an understanding of the
pairing mechanism in the related superconducting compounds. Even though the
chemical and electronic properties of these materials are often strongly
inhomogeneous on a nanometer length scale, studies of the magnetic phase
transitions using spatially resolved experimental techniques are still scarce.
Here, we present a real space spin-resolved scanning tunneling microscopy
investigation of the surface of Fe$_{1+y}$Te single crystals with different
excess Fe content, $y$, which are continuously driven through the magnetic
phase transition. For Fe$_{1.08}$Te, the transition into the low-temperature
monoclinic commensurate antiferromagnetic phase is accompanied by the sudden
emergence of ordering into four rotational domains with different orientations
of the monoclinic lattice and of the antiferromagnetic order, showing how
structural and magnetic order are intertwined. In the low-temperature phase of
Fe$_{1.12}$Te one type of the domain boundaries disappears, and the transition
into the paramagnetic phase gets rather broad, which is assigned to the
formation of a mixture of orthorhombic and monoclinic phases.",1711.11387v1
2017-12-03,Evolution of Structure and Magnetic Properties of Cu2MnBO5 under Partial Mn3+->Fe3+ Substitution,"Single crystals of Fe-substituted Cu2Mn1-xFexBO5 ludwigites have been
synthesized using flux technique (x=0.2, 0.4, 0.5 - in the initial flux
system). Structural properties of the synthesized compounds were studied by the
single crystal and powder X-ray diffraction analysis. Obtained results were
analyzed in the relationship with parent compound Cu2MnBO5. It was revealed
that the type of monoclinic distortions of Fe-substituted ludwigites is
different from the structure of Cu2MnBO5. The real cation composition and local
structure of Cu2Mn1-xFexBO5 ludwigites were studied using XANES and EXAFS
techniques, respectively. Analysis of field and thermal dependencies of
magnetization showed a strong dependence of the magnetic properties of these
ludwigites on x with changing the type of magnetic ordering.",1712.00799v1
2017-12-05,Magneto-elastic coupling in Fe-based superconductors,"We used polarization-resolved Raman scattering to study the magneto-elastic
coupling in the parent compounds of several families of Fe-based
superconductors (BaFe2As2, EuFe2As2, NaFeAs, LiFeAs, FeSe and LaFeAsO). We
observe an emergent Ag-symmetry As phonon mode in the XY scattering geometry
whose intensity is significantly enhanced below the magneto-structural
transition only for compounds showing magnetic ordering. We conclude that the
small lattice anisotropy is insufficient to induce the in-plane electronic
polarizability anisotropy necessary for the observed phonon intensity
enhancement, and interpret this enhancement below the Neel temperature in terms
of the anisotropy of the magnetic moment and magneto-elastic coupling. We
evidence a Fano line- shape in the XY scattering geometry resulting from a
strong coupling between the Ag (As) phonon mode and the B2g symmetry-like
electronic continuum. Strong electron-phonon coupling may be relevant to
superconductivity.",1712.01896v1
2017-12-11,Pyrochlore Oxide Superconductor Cd2Re2O7 Revisited,"The superconducting pyrochlore oxide Cd2Re2O7 is revisited with a particular
emphasis on the sample-quality issue. The compound has drawn attention as the
only superconductor (Tc = 1.0 K) that has been found in the family of
{\alpha}-pyrochlore oxides since its discovery in 2001. Moreover, it exhibits
two characteristic structural transitions from the cubic pyrochlore structure,
with the inversion symmetry broken at the first one at 200 K. Recently, it has
attracted increasing attention as a candidate spin-orbit coupled metal (SOCM),
in which specific Fermi liquid instability is expected to lead to an odd-parity
order with spontaneous inversion-symmetry breaking [L. Fu, Phys. Rev. Lett.
115, 026401 (2015)] and parity-mixing superconductivity [V. Kozii and L. Fu:
Phys. Rev. Lett. 115 (2015) 207002; Y. Wang et al., Phys. Rev. B 93 (2016)
134512]. We review our previous experimental results in comparison with those
of other groups in the light of the theoretical prediction of the SOCM, which
we consider meaningful and helpful for future progress in understanding this
unique compound.",1712.03617v1
2017-12-12,Substitution- and Strain-induced Magnetic Phase Transition in Iron Carbide,"Cementite-type carbides are of interest for magnetocaloric applications owing
to their temperature- or pressure-induced magnetic phase transition. Here,
using first-principles calculations, we investigate the magnetism and the
magnetic phase transition in iron carbide (Fe3C) with the substitution of Cr
atoms at Fe sites with the strain effect. The presence of Cr atoms is found to
give rise to a second-order magnetic phase transition from a ferromagnetic
phase for Fe3C to a nonmagnetic phase in chromium carbide (Cr3C).While the
ternary Fe2CrC and Cr2FeC compounds prefer the ferrimagnetic ground state, the
magnitudes of both the Fe and Cr spin moments, which are antiparallel in
orientation, decrease as x increases in Fe3-xCrxC (x = 0, 1, 2, and 3).
Furthermore, the fixed spin-moment calculations indicate that the magnetization
of Fe3-xCrxC compounds can be delicately altered via the strain effect and that
the magnetic-nonmagnetic phase transition occurs at an early stage of Cr
substitution, x = 2.",1712.04128v1
2017-12-12,Visible Photocatalytic Degradation of Methylene Blue on Magnetic Semiconducting La modified M-type Strontium Hexaferrite,"Methylene blue (MB) is a representative of a class of dyestuffs resistant to
biodegradation. This paper presents a novel photocatalytic degradation of
methylene blue (MB) by La modified M-type strontium hexaferrite
(La0.2Sr0.7Fe12O19) compound, which is a traditional permanent magnet and
displays a large magnetic hysteresis (M-H) loop. The remnant magnetic moment
and coercive field are determined to be 52emu/g and 5876Oe, respectively.
UV-Visible optical spectroscopy reveals that La0.2Sr0.7Fe12O19 is
simultaneously a semiconductor, whose direct and indirect band gap energies are
determined to be 1.47 eV and 0.88 eV, respectively. The near infrared band gap
makes it a good candidate to harvest sunlight for photocatalytic reaction or
solar cell devices. This magnetic compound demonstrates excellent
photocatalytic activity on degradation of MB under visible illumination. The
colour of MB dispersion solution changes from deep blue to pale white and the
absorbance decreases rapidly from 1.8 down to zero when the illumination
duration extends to 6 hours. Five absorption bands did not make any blue shifts
along with the reaction time, suggesting a one-stepwise degradation process of
MB, which makes La0.2Sr0.7Fe12O19 a unique magnetic catalyst and differs from
TiO2 and other conventional catalysts.",1712.04278v1
2017-12-13,"Bulk electronic structure of non-centrosymmetric EuTGe3 (T= Co, Ni, Rh, Ir) studied by hard x-ray photoelectron spectroscopy","Non-centrosymmetric EuTGe3 (T=Co, Ni, Rh, and Ir) possesses magnetic Eu2+
ions and antiferromagnetic ordering appears at low temperatures. Transition
metal substitution leads to changes of the unit cell volume and of the magnetic
ordering. However, the magnetic ordering temperature does not scale with the
volume change and the Eu valence is expected to remain divalent. Here we study
the bulk electronic structure of non-centrosymmetric EuTGe3 (T=Co, Ni, Rh, and
Ir) by hard x-ray photoelectron spectroscopy. The Eu 3d core level spectrum
confirms the robust Eu2+ valence state against the transition metal
substitution with a small contribution from Eu3+. The estimated Eu mean-valence
is around 2.1 in these compounds as confirmed by multiplet calculations. In
contrast, the Ge 2p spectrum shifts to higher binding energy upon changing the
transition metal from 3d to 4d to 5d elements, hinting of a change in the Ge-T
bonding strength. The valence bands of the different compounds are found to be
well reproduced by ab initio band structure calculations.",1712.04822v1
2017-12-18,133Cs-NMR study on aligned powder of competing spin chain compound Cs2Cu2Mo3O12,"S = 1/2 competing spin chain compound Cs2Cu2Mo3O12 has two dominant exchange
interactions of the nearest neighbouring ferromagnetic J1= 93 K and the second
nearest neighbouring antiferromagnetic J2= +33 K, and is expected to show the
nematic Tomonaga-Luttinger liquid (TLL) state under high magnetic field region.
The recent theoretical study by Sato et al. has shown that in the nematic TLL
state, the spin fluctuations are expected to be highly anisotropic, that is,
its transverse component is suppressed. Our previous NMR study on the present
system showed that the dominant contribution to nuclear spin relaxation comes
from the longitudinal component. In order to conclude that the transverse
component of spin fluctuations is suppressed, the knowledge of hyperfine
coupling is indispensable. This article is solely devoted to investigate the
hyperfine coupling of 133Cs-NMR site to prove that the anisotropic part of
hyperfine coupling, which connects the nuclear spin relaxation with the
transverse spin fluctuations is considerably large to be A_an=+770 Oe/mu_B.",1712.06219v1
2017-12-19,"Synthesis, Crystal Structure, and Physical Properties of New Layered Oxychalcogenide La2O2Bi3AgS6","We have synthesized a new layered oxychalcogenide La2O2Bi3AgS6. From
synchrotron X-ray diffraction and Rietveld refinement, the crystal structure of
La2O2Bi3AgS6 was refined using a model of the P4/nmm space group with a =
4.0644(1) {\AA} and c = 19.412(1) {\AA}, which is similar to the related
compound LaOBiPbS3, while the interlayer bonds (M2-S1 bonds) are apparently
shorter in La2O2Bi3AgS6. The tunneling electron microscopy (TEM) image
confirmed the lattice constant derived from Rietveld refinement (c ~ 20 {\AA}).
The electrical resistivity and Seebeck coefficient suggested that the
electronic states of La2O2Bi3AgS6 are more metallic than those of LaOBiS2 and
LaOBiPbS3. The insertion of a rock-salt-type chalcogenide into the van der
Waals gap of BiS2-based layered compounds, such as LaOBiS2, will be a useful
strategy for designing new layered functional materials in the layered
chalcogenide family.",1712.06726v1
2017-12-22,Magnetoresistance in YBi and LuBi semimetals due to nearly perfect carrier compensation,"Monobismuthides of yttrium and lutetium are shown as new representatives of
materials which exhibit extreme magnetoresistance and magnetic-field-induced
resistivity plateau. At low temperatures and in magnetic field of 9T the
magnetoresistance attains the order of magnitude of 10,000% and 1,000%, on YBi
and LuBi, respectively. Our thorough examination of electron transport
properties of both compounds show that observed features are the consequence of
nearly perfect carrier compensation rather than of possible nontrivial topology
of electronic states. The field-induced plateau of electrical resistivity can
be explained with Kohler scaling. Anisotropic multi-band model of electronic
transport describes very well the magnetic field dependence of electrical
resistivity and Hall resistivity. Data obtained from the Shubnikov-de Haas
oscillations analysis also confirm that Fermi surface of each compound contains
almost equal amounts of holes and electrons. First-principle calculations of
electronic band structure are in a very good agreement with the experimental
data.",1712.08433v3
2017-12-24,Infection model for analyzing biological control of coffee rust using bacterial anti-fungal compounds,"Coffee rust is one of the main diseases that affect coffee plantations
worldwide. This causes an important economic impact in the coffee production
industry in countries where coffee is an important part of the economy. A
common method for combating this disease is using copper hydroxide as a
fungicide, which can have damaging effects both on the coffee tree and on human
health. A novel method for biological control of coffee rust using bacteria has
been proven to be an effective alternative to copper hydroxide fungicides as
anti-fungal compounds. In this paper, we develop and explore a spatial
stochastic model for this interaction in a coffee plantation. We analyze
equilibria for specific control strategies, as well as compute the basic
reproductive number, R0, of individual coffee trees, conditions for local and
global stability under specific conditions, parameter estimation of key
parameters, as well as sensitivity analysis, and numerical experiments under
local and global control strategies for key scenarios.",1712.08958v2
2017-12-26,Thermoelectric Power of the CeCoAl$_4$ Antiferromagnet - Predominance of the Crystal Electric Field,"We report on the thermoelectric power $S(T)$, electrical resistivity and
thermal conductivity measurements on the antiferromagnetic CeCoAl$_4$ compound.
The N\'eel temperature of CeCoAl$_4$ is $T_N$=13.5K and a metamagnetic-like
transition occurs in the magnetic field of about 7.5T. We show that the
magnetic contribution to the thermoelectric power, $S_f(T)$, exhibits a large
peak due to the crystal electric field (CEF) at about 240K and a small anomaly
around the ordering temperature. Surprisingly, the CEF related $S_f(T)$ peak is
close to the upper CEF excitation energy $\Delta_2$=202K, in contrast to the
usual case of the peak position being a fraction of the real CEF excitation.
The applicability of different theoretical and phenomenological models
describing the temperature dependence of the Seebeck effect $S_f(T)$ has been
tested and finally a calculation is proposed, which incorporates a full CEF
levels scheme. For the nonmagnetic reference compound, LaCoAl$_4$, the
thermoelectric power measurements provide an evidence of the phonon drag
contribution, which is not present or masked in the case of CeCoAl$_4$.",1712.09385v1
2017-12-28,VO$_2$ as a natural optical metamaterial,"VO$_2$ is a unique phase change material with strongly anisotropic electronic
properties. Recently, samples have been prepared that present a co-existence of
phases and thus form metal-insulator junctions of the same chemical compound.
Using first principles calculations, the optical properties of metallic and
semiconducting VO$_2$ are here discussed to design self-contained natural
optical metamaterials, avoiding coupling with other dielectric media. The
analysis of the optical properties complements the experiments in the
description of the vast change in reflectance and metallicity for both
disordered and planar compounds. The present results also predict the
possibility to realize ordered VO$_2$ junctions operating as efficient
hyperbolic metamaterials in the THz-visible range, by simply adjusting the
ratio between metallic and insulating VO$_2$ content. The possibility to excite
propagating {\em volume plasmom polariton} across the metamaterial is finally
discussed.",1712.09806v1
2017-12-30,Prediction of $\mathrm{TiRhAs}$ as a Dirac Nodal Line Semimetal via First-Principles Calculations,"Using first-principles calculations we predict that $\mathrm{TiRhAs}$, a
previously synthesized compound, is a Dirac nodal line (DNL) semimetal. The DNL
in this compound is found to be protected both by the combination of inversion
and time-reversal symmetry, and by a reflection symmetry, in the absence of
spin-orbit coupling (SOC). Our calculations show that band velocities
associated with the nodal line have a high degree of directional anisotropy,
with in-plane velocities $v_\perp$ perpendicular to the nodal line between
$1.2-2.8\times10^5$ m/s. The crossings along the DNL are further found to
exhibit a prominent and position-dependent tilt along directions perpendicular
to the nodal line. We calculate $\mathbb{Z}_2$ indices based on parity
eigenvalues at time-reversal invariant momenta and show that $\mathrm{TiRhAs}$
is topological. A tight-binding model fit from our first-principles
calculations demonstrates the existence of two-dimensional drumhead surface
states on the surface Brillouin zone. Based on the small gapping of the DNL
upon inclusion of SOC and the clean Fermi surface free from trivial bands,
$\mathrm{TiRhAs}$ is a promising candidate for further studies of the
properties of topological semimetals.",1801.00116v1
2018-01-04,Direct observation of heavy quasiparticles in the Kondo lattice CeIn3,"The electronic structure of the Kondo lattice CeIn3 has been studied by
on-resonant angle-resolved photoemission spectroscopy and scanning tunneling
microscopy/spectroscopy. A weakly dispersive quasiparticle band has been
observed directly with an energy dispersion of 4 meV by photoemission, implying
the existence of weak hybridization between the f electrons and conduction
electrons. The hybridization is further confirmed by the formation of the
hybridization gap revealed by temperature-dependent scanning tunneling
spectroscopy. Moreover, we find the hybridization strength in CeIn3 is much
weaker than that in the more two-dimensional compounds CeCoIn5 and CeIrIn5. Our
results may be essential for the complete microscopic understanding of this
important compound and the related heavy-fermion systems.",1801.01214v1
2018-01-09,Time Reversal Symmetry Breaking in noncentrosymmetric superconductor Re6Ti,"We have investigated the superconducting state of the noncentrosymmetric
superconductor Re6Ti (Tc = 6.0 K) using muon-spin rotation/relaxation (muSR)
technique. The zero-field muon experiment shows the presence of spontaneous
magnetic fields in the superconducting state, indicating time-reversal symmetry
breaking (TRSB). However, the low-temperature transverse field muon
measurements suggest nodeless s-wave superconductivity. The time reversal
symmetry breaking further confirmed in the stoichiometric composition Re24Ti5.
These results indicate that the pairing symmetry is not affected by
spin-orbital coupling Re6X family of compounds. Altogether these studies
suggest unconventional nature (TRSB) of superconductivity is intrinsic to Re6X
family of compounds and paves the way for further studies of this family of
materials.",1801.02841v1
2018-01-12,Extended phase diagram of RNiC2 family: Linear scaling of the Peierls temperature,"Physical properties for the late-lanthanide-based RNiC2 (R = Dy, Ho, Er, and
Tm) ternary compounds are reported. All the compounds show antiferromagnetic
ground state with the N\'eel temperature ranging from 3.4 K for HoNiC2 to 8.5 K
for ErNiC2. The results of the transport and galvanomagnetic properties confirm
a charge density wave state at and above room temperature with transition
temperatures TCDW = 284, 335, 366, and 394 K for DyNiC2, HoNiC2, ErNiC2, and
TmNiC2, respectively. The Peierls temperature TCDW scales linearly with the
unit cell volume. A similar linear dependence has been observed for the
temperature of the lock-in transition T1 as well. Beyond the intersection point
of the trend lines, the lock-in transition is no longer observed. In this Rapid
Communication we demonstrate an extended phase diagram for the RNiC2 family.",1801.04113v1
2018-01-19,Observation of Meissner effect in potassium-doped \emph{p}-quinquephenyl},"The chain-like organic compounds with conjugated structure have the potential
to become high temperature superconductors. We examine this idea by choosing
p-quinquephenyl with five phenyl rings connected in para position. The dc
magnetic susceptibility measurements provide solid evidence for the presence of
Meissner effect when the compound is doped by potassium. The real part of the
ac susceptibility shows exactly same transition temperature as that in dc
magnetization, and the imaginary part of nearly zero value after transition
implies the realization of zero-resistivity. All these features support the
existence of superconductivity with a critical temperature of 7.3 K in this
material. The occurrence of bipolarons revealed by Raman spectra guarantees
potassium metal intercalated into p-quinquephenyl and suggests the important
role of this elementary excitation played on superconductivity.",1801.06324v2
2018-01-21,"Ab initio Simulations of Superionic H2O, H2O2, and H9O4 Compounds","Using density functional molecular dynamics simulations, we study the
behavior of different hydrogen-oxygen compounds at megabar pressures and
several thousands of degrees Kelvin where water has been predicted to occur in
superionic form. When we study the close packed hcp and dhcp structures of
superionic water, we find that they have comparable Gibbs free energies to the
fcc structure that we predicted previously [Phys. Rev. Lett., 110 (2013)
151102]. Then we present a comprehensive comparison of different superionic
water candidate structures with P2_1, P2_1/c, P3_121, Pcca, C2/m, and Pa3
symmetry that are based on published ground-state structures. We find that the
P2_1 and P2_1/c structures transform into a different superionic structure with
P2_1/c symmetry, which at 4000 K has a lower Gibbs free energy than fcc for
pressures higher than 22.8 +- 0.5 Mbar. This novel structure may also be
obtained by distorting a hcp supercell. Finally we show that H2O2 and H9O4
structures will also assume a superionic state at elevated temperatures. Based
on Gibbs free energy calculations at 5000 K, we predict that superionic water
decompose into H2O2 and H9O4 at 68.7 +- 0.5 Mbar.",1801.06907v1
2018-01-22,Electronic properties of Cs-based halide perovskites: An ab-initio study,"Halide perovskites consist a class of materials under intense investigation
due to their potential technological applications like solar cells,
optoelectronic devices and catalysis. Recently we have studied using electronic
band structure calculations from first principles, the cubic MABX$_3$ compounds
[A. Koliogiorgos et al., Comput. Mater. Sci. \textbf{138}, 92 (2017)], where MA
stands for the methylammonium cation, B is a divalent cation and X a halogen.
We expand our study in the case where Cs stands in place of the MA cation. Our
results suggest that the Cs-based compounds exhibit also a variety of lattice
constants and energy band gaps. The calculated equilibrium lattice constants
differ substantially from the experimental ones. The calculated energy gaps
also show large deviations for these lattice constants. Moreover, the use of
more sophisticated functionals leads to conflicting changes in the energy gap
values and its effect is materials dependent. Our results suggest that contrary
to the MA halide perovskites, the Cs halide perovskites consist a more delicate
case and there is still a long way for \textit{ab-initio} calculations to
accurate describe their structural and electronic properties.",1801.06983v1
2018-01-25,Quantum sensing of motion in colloids via time-dependent Purcell effect,"Light-matter interaction dynamics is governed by the strength of local
coupling constants, tailored by surrounding electromagnetic structures.
Characteristic decay times in dipole-allowed fluorescent transitions are much
faster than mechanical conformational changes within an environment and, as the
result, the latter can be assumed static during the emission process. However,
slow-decaying compounds can break this commonly accepted approximation and
introduce new interaction regimes. Here, slow decaying phosphorescent compounds
are proposed to perform quantum sensing of nearby structure's motion via
observation of collective velocity-dependent lifetime distributions. In
particular, characteristic decay of an excited dye molecule, being comparable
with its passage time next to a resonant particle, is modified via
time-dependent Purcell enhancement, which leaves distinct signatures on
properties of emitted light. Velocity mapping of uniformly moving particles
within a fluid solution of phosphorescent dyes was demonstrated via analysis of
modified lifetime distributions. The proposed interaction regime enables
performing studies of a wide range of phenomena, where time-dependent
light-matter interaction constants can be utilized for extraction of additional
information about a process",1801.08591v1
2018-01-25,Traces of Charge Density Waves in NbS$_2$,"Among Transition Metal Dichalcogenides (TMD), NbS$_2$ is often considered as
the archetypal compound that does not have a Charge Density Wave (CDW) in any
of its polytypes. By comparison, close iso-electronic compounds such as
NbSe$_2$, TaS$_2$ and TaSe$_2$ all have CDW in at least one polytype. Here, we
report traces of CDW in the 2H polytype of NbS$_2$, using diffuse x-ray
scattering measurements at 77\,K and room temperature. We observe 12 extremely
weak satellite peaks located at $\pm$13$^\mathrm{o}$ 54' from $\vec{a}^*$ and
$\vec{b}^*$ around each Bragg peaks in the $(h,k,0)$ plane. These satellite
peaks are commensurate with the lattice via $3\vec{q}-\vec{q}\,'=\vec{a}^*$,
where $\vec{q}\,'$ is the 120$^{\circ}$ rotation of $\vec{q}$, and define two
chiral $\sqrt{13}\,a\times\sqrt{13}\,a$ superlattices in real space. These
commensurate wavevectors and tilt angle are identical to those of the CDW
observed in the 1T polytype of TaS$_2$ and TaSe$_2$. To understand this
similarity and the faintness of the peaks, we discuss possible sources of local
1T polytype environment in bulk 2H-NbS$_2$ crystals.",1801.08617v2
2018-01-30,Magnetic phase diagram of the quantum spin chain compound SrCo$_{2}$V$_{2}$O$_{8}$: a single-crystal neutron diffraction study in magnetic field,"We explore the spin states in the quantum spin chain compound
SrCo$_{2}$V$_{2}$O$_{8}$ up to 14.9 T and down to 50 mK, using single-crystal
neutron diffraction. Upon cooling in zero-field, antiferromagnetic (AFM) order
of N\'eel type develops at $T_\mathrm{{N}}$ $\simeq$ 5.0 K. Applying an
external magnetic field ($H$ $\parallel$ $c$-axis) destabilizes the N\'eel
order, leading to an order-disorder transition when applying a field between
$T_\mathrm{{N}}$ and $\sim$ 1.5 K. Below 1.5 K, we observe a N\'eel to
longitudinal spin density wave (LSDW) order transition at 3.9 T, and a LSDW to
emergent AFM order transition at 7.0 T. Our results also reveal several unique
signatures for the states of the spins that are not present in the
isostructural counterpart BaCo$_{2}$V$_{2}$O$_{8}$.",1801.10237v2
2018-03-01,Love wave gas sensor based on DWNTs sensitive material,"This work focuses on the application related to the detection of low moisture
and environmental pollutants. A novel gas sensor with inkjet printed Double
Walled Carbon Nano Tubes (DWNTs) on a Love wave sensor platform was developed
for Volatile Organic Compounds (VOCs) and humidity detection application. The
experiments were conducted in real-time at ambient conditions. Results
demonstrate the adsorption of vapor compounds on DWNTs sensitive material and
leads for example to frequency shifts of 1.97 kHz and 2.93 kHz with 120 ppm of
ethanol vapor and 6.22 % RH, respectively.",1803.00456v1
2018-03-05,The when and where of water in the history of the universe,"It is undeniable that life as we know it depends on liquid water. It is
difficult to imagine any biochemical machinery that does not require water. On
Earth, life adapts to the most diverse environments and, once established, it
is very resilient. Considering that water is a common compound in the Universe,
it seems possible (maybe even likely) that one day we will find life elsewhere
in the universe. In this study, we review the main aspects of water as an
essential compound for life: when it appeared since the Big Bang, and where it
spread throughout the diverse cosmic sites. Then, we describe the strong
relation between water and life, as we know it.",1803.01452v1
2018-03-07,Antiphase Fermi-surface modulations accompanying displacement excitation in a parent compound of iron-based superconductors,"We investigate the transient electronic structure of BaFe2As2, a parent
compound of iron-based superconductors, by time- and angle-resolved
photoemission spectroscopy. In order to probe the entire Brillouin zone, we
utilize extreme ultraviolet photons and observe photoemission intensity
oscillation with the frequency of the A1g phonon which is antiphase between the
zone-centered hole Fermi surfaces (FSs) and zone-cornered electron FSs. We
attribute the antiphase behavior to the warping in one of the zone-centered
hole FSs accompanying the displacement of the pnictogen height, and find that
this displacement is the same direction as that induced by substitution of P
for As, where superconductivity is induced by a structural modification without
carrier doping in this system.",1803.02599v1
2018-03-21,Novel single-layer vanadium sulphide phases,"VS2 is a challenging material to prepare stoichiometrically in the bulk, and
the single layer has not been successfully isolated before now. Here we report
the first realization of single-layer VS2, which we have prepared epitaxially
with high quality on Au(111) in the octahedral (1T) structure. We find that we
can deplete the VS2 lattice of S by annealing in vacuum so as to create an
entirely new two-dimensional compound that has no bulk analogue. The transition
is reversible upon annealing in an H2S gas atmosphere. We report the structural
properties of both the stoichiometric and S-depleted compounds on the basis of
low-energy electron diffraction, X-ray photoelectron spectroscopy and
diffraction, and scanning tunneling microscopy experiments.",1803.07999v1
2018-03-23,Nonparametric inference on Lévy measures of compound Poisson-driven Ornstein-Uhlenbeck processes under macroscopic discrete observations,"This study examines a nonparametric inference on a stationary L\'evy-driven
Ornstein-Uhlenbeck (OU) process $X = (X_{t})_{t \geq 0}$ with a compound
Poisson subordinator. We propose a new spectral estimator for the L\'evy
measure of the L\'evy-driven OU process $X$ under macroscopic observations. We
also derive, for the estimator, multivariate central limit theorems over a
finite number of design points, and high-dimensional central limit theorems in
the case wherein the number of design points increases with an increase in the
sample size. Built on these asymptotic results, we develop methods to construct
confidence bands for the L\'evy measure and propose a practical method for
bandwidth selection.",1803.08671v5
2018-03-25,High temperature antiferromagnetism in Yb based heavy fermion systems proximate to a Kondo insulator,"Given the parallelism between the physical properties of Ce and Yb based
magnets and heavy fermions due to the electron-hole symmetry, it has been
rather odd that the transition temperature of the Yb based compounds is
normally very small, as low as $\sim$ 1 K or even lower, whereas Ce
counterparts may often have the transition temperature well exceeding 10 K.
Here, we report our experimental discovery of the transition temperature
reaching 20 K for the first time in a Yb based compound at ambient pressure.
The Mn substitution at the Al site in an intermediate valence state of
$\alpha$-YbAlB$_{4}$ not only induces antiferromagnetic transition at a record
high temperature of 20 K but also transforms the heavy fermion liquid state in
$\alpha$-YbAlB$_{4}$ into a highly resistive metallic state proximate to a
Kondo insulator.",1803.09366v2
2018-03-27,Adaptive nonparametric estimation for compound Poisson processes robust to the discrete-observation scheme,"A compound Poisson process whose jump measure and intensity are unknown is
observed at finitely many equispaced times. We construct a purely data-driven
estimator of the L\'evy density $\nu$ through the spectral approach using
general Calderon--Zygmund integral operators, which include convolution and
projection kernels. Assuming minimal tail assumptions, it is shown to estimate
$\nu$ at the minimax rate of estimation over Besov balls under the losses
$L^p(\mathbb{R})$, $p\in[1,\infty]$, and robustly to the observation regime
(high- and low-frequency). To achieve adaptation in a minimax sense, we use
Lepski\u{i}'s method as it is particularly well-suited for our generality.
Thus, novel exponential-concentration inequalities are proved including one for
the uniform fluctuations of the empirical characteristic function. These are of
independent interest, as are the proof-strategies employed to deal with general
Calderon--Zygmund operators, to depart from the ubiquitous quadratic structure
and to show robustness without polynomial-tail conditions. Part of the
motivation for such generality is a new insight we include here too that,
furthermore, allows us to unify the main two approaches to construct estimators
used in related literature.",1803.09849v2
2018-03-30,"First-principles study of the structural, phonon, elastic, and thermodynamic properties of Al$_{3}$Ta compound under high pressure","We have investigated the phonon, elastic and thermodynamic properties of
L1$_{2}$ phase Al$_{3}$Ta by density functional theory approach combining with
quasi-harmonic approximation model. The results of phonon band structure shows
that L1$_{2}$ phase Al$_{3}$Ta possesses dynamical stability in the pressure
range from 0 to 80 GPa due to the absence of imaginary frequencies. The
pressure dependences of the elastic constants $C_{ij}$, bulk modulus $B$, shear
modulus $G$, Young's modulus $Y$, $B/G$ and Poisson's ratio $\nu$ have been
analysed. The elastic constants are satisfied with mechanical stability
criteria up to the external pressure of 80 GPa. The results of the elastic
properties studies show that Al$_{3}$Ta compound possesses a higher hardness,
improved ductility and plasticity under higher pressures. Further, we
systematically investigate the thermodynamic properties, such as the Debye
temperature $\Theta$, heat capacity $C_{p}$, and thermal expansion coefficient
$\alpha$, and provide the relationships between thermal parameters and
pressure.",1803.11412v1
2018-05-07,Influence of strong-coupling and retardation effects on superconducting state in ${\rm YB_{6}}$ compound,"In the framework of strong-coupling formalism, we have calculated the
thermodynamic parameters of superconducting state in the ${\rm YB_{6}}$
compound. The values of critical temperature ($T_{C}$) are $9.5$~K and $7.9$~K
for the Coulomb pseudopotential $\mu^{\star}=0.1$ and $0.2$, respectively. In
the paper, we have determined the low temperature values of order parameter
($\Delta(0)$), specific heat jump at the critical temperature ($\Delta
C(T_{C})$), and thermodynamic critical field ($H_C(0)$). The dimensionless
thermodynamic ratios: $R_{\Delta}=2\Delta\left(0\right)/{k_BT_C}$, $R_C=\Delta
C\left(T_C\right)/C^N\left(T_C\right)$, and
$R_H=T_CC^N\left(T_C\right)/H_C^2\left(0\right)$ are equal to:
$R_{\Delta}\left(\mu^{\star}\right)\in\lbrace 4.48,4.35\rbrace$,
$R_{C}\left(\mu^{\star}\right)\in\lbrace 2.62,2.55\rbrace$, and
$R_{H}\left(\mu^{\star}\right)\in\lbrace 0.146,0.157\rbrace$. Due to the
significant strong-coupling and retardation effects ($k_{B}T_{C} / \omega_{\rm
ln}\sim 0.1$) those values highly deviate from the predictions of BCS theory.",1805.02694v1
2018-05-08,"Magnetic properties, chemical and phase composition of thin manganese silicide films fabricated by pulsed laser deposition","Manganese silicide (MnxSiy) thin films with Mn content (CMn) varied from 24
at. % to 52 at. % were grown on i-GaAs (100) substrates. Chemical, phase
composition and room temperature magnetic properties of the films were
investigated. It was demonstrated that manganese silicide films revealing
ferromagnetic properties are multiphase systems. The phases, which are believed
to be non-magnetic at room temperature, are compounds with Mn concentration
exceeding the average Mn content of the film (higher manganese silicide, MnSi
and Mn5Si3). Magnetic properties revealed are attributed with the secondary
phases which are Mn doped silicon (Mn:Si) or Mn depleted compounds. For nearly
single phase films (with very small 2-nd phase ratio) no room temperature
ferromagnetism was observed.",1805.02904v2
2018-05-09,Nature of the Magnetic Interactions in Sr$_3$NiIrO$_6$,"Iridates abound with interesting magnetic behaviours because of their strong
spin-orbit coupling. Sr$_3$NiIrO$_6$ brings together the spin-orbital
entanglement of the Ir$^{4+}$ ion with a 3$d$ Ni cation and a one-dimensional
crystal structure. It has a ferrimagnetic ground state with a 55 T coercive
field. We perform a theoretical study of the magnetic interactions in this
compound, and elucidate the role of anisotropic symmetric exchange as the
source of its strong magnetic anisotropy. Our first-principles calculations
reproduce the magnon spectra of this compound and predict a signature in the
cross sections that can differentiate the anisotropic exchange from single-ion
anisotopy.",1805.03733v2
2018-05-11,N-doped graphitic carbon materials hybridized with transition metals (compounds) for hydrogen evolution reaction: Understanding the synergistic effect from atomistic level,"The hybrid nanostructures of nitrogen doped carbon materials and nonprecious
transition metals are among the most promising electrocatalysts to replace
noble metal catalysts for renewable energy applications. However, the
fundamental principles governing the catalytic activity of such hybrid
materials remain elusive. Herein, we systematically explore the
electrocatalytic properties of transition metals, transition metal oxides and
carbides substrates covered by nitrogen-doped graphitic sheets for hydrogen
evolution reaction (HER). Our first-principles calculations show that the
graphitic sheet is prominently activated by the nitrogen doping and the
coordinate bond with metal (compound) substrate through intralayer and
interlayer charge transfer. Such hybrid materials can provide optimal binding
capability for HER catalysis with Tafel barrier down to 1.0 eV. The HER
activity can be correlated to the C pz band center, which is in turn governed
by the electronic coupling strength between the graphitic sheet and metal
substrate, thus paving a way to rational design of graphitic carbon/transition
metal hybrid electrocatalysts of high performance.",1805.04231v1
2018-05-21,The Geometric Blueprint of Perovskites,"Perovskite minerals form an essential component of the Earth's mantle, and
synthetic crystals are ubiquitous in electronics, photonics, and energy
technology. The extraordinary chemical diversity of these crystals raises the
question on how many and which perovskites are yet to be discovered. Here we
show that the ""no-rattling"" principle postulated by Goldschmidt in 1926,
describing the geometric conditions under which a perovskite can form, is much
more effective than previously thought, and allows us to predict new
perovskites with a fidelity of 80%. By supplementing this principle with
inferential statistics and internet data mining we establish that currently
known perovskites are only the tip of the iceberg, and we enumerate ninety
thousand hitherto-unknown compounds awaiting to be studied. Our results suggest
that geometric blueprints may enable the systematic screening of millions of
compounds, and offer untapped opportunities in structure prediction and
materials design.",1805.08250v2
2018-05-22,Compressive sensing lattice dynamics. I. General formalism,"{\it Ab initio\} calculations have been successfully used for evaluating
lattice dynamical properties of solids within the (quasi-)harmonic
approximation (i.e., assuming non-interacting phonons with infinite lifetimes),
but it remains difficult to treat anharmonicity in all but the simplest
compounds. We detail a systematic information theory based approach to deriving
{\it ab initio\} anharmonic force constants: compressive sensing lattice
dynamics (CSLD). The non-negligible terms that are necessary to reproduce the
first-principles calculated interatomic forces are automatically selected by
minimizing the $\ell_1$ norm (sum of absolute values) of the scaled force
constants. By using efficient sampling of the configuration space using a
modest number of atomic configurations with quasi-random displacements, CSLD is
well suited for deriving accurate anharmonic potentials for complex
multicomponent compounds with large unit cells. We demonstrate the power and
generality of CSLD by calculating the phonon lifetimes and thermal transport
properties of Type-I Si clathrates.",1805.08904v3
2018-05-25,"Suppression of ferromagnetic order by Ag-doping: A neutron scattering investigation on Ce2(Pd1-xAgx)2In (x = 0.20, 0.50)","The ground state magnetic behaviour of Ce2(Pd0.8Ag0.2)2In and
Ce2(Pd0.5Ag0.5)2In, found in the ferromagnetic branch of Ce2Pd2In, has been
investigated by neutron powder diffraction at low temperature.
Ce2(Pd0.8Ag0.2)2In is characterized by a ferromagnetic structure with the Ce
moments aligned along the c-axis and values of 0.96(2) mB. The compound retains
the P4/mbm throughout the magnetic transition, although the magnetic ordering
is accompanied by a significant decrease of the lattice strain along [00l],
suggesting a magnetostructural contribution. The magnetic behaviour of
Ce2(Pd0.5Ag0.5)2In is very different; this compound exhibits an extremely
reduced magnetic scattering contribution in the diffraction pattern, that can
be ascribed to a different kind of ferromagnetic ordering, with extremely
reduced magnetic moments (~ 0.1 mB) aligned along [0l0]. These results point to
a competition between different types of magnetic correlations induced by
Ag-substitution, giving rise to a magnetically frustrated scenario in
Ce2(Pd0.5Ag0.5)2In.",1805.10023v1
2018-05-29,Incorporation of charge- and pair-density-wave states into the one-band model of d-wave superconductivity,"We study the coexistence of pair- (PDW) and charge-density-wave (CDW) states
within the single-band $t$-$J$-$U$ and Hubbard models of $d$-$wave$
superconductivity and discuss our results in the context of the experimental
observations for the copper-based compounds. In order to take into account the
correlation effects with a proper precision, we use the approach based on the
diagrammatic expansion of the Gutzwiller wave function (DE-GWF), that goes
beyond the renormalized mean field theory (RMFT) in a systematic manner.
According to our analysis of the $t$-$J$-$U$ model, the transition between the
pure $d$-$wave$ superconducting phase (SC) and the coexistent CDW+PDW phase
takes place at $\delta\approx 0.18$ (close to the optimal doping), with the
modulated phase located in the underdoped regime. The situation is slightly
different for the case of the Hubbard model, where a narrow stability regime of
a precursor nematic phase sets in preceding the formation of the modulated
CDW+PDW state, with the decreasing hole doping. The results complete our
discussion of the standard phase diagram for high-T$_C$ superconducting
compounds within the DE-GWF variational approach in the single narrow-band
case.",1805.11443v1
2018-05-06,Basic Insights into Tunable Graphene Hydrogenation,"The hydrogenation and deuteration of graphite with potassium intercalation
compounds (GICs) as starting materials was investigated. Characterization of
the reactions products (hydrogenated and deuterated graphene) was carried out
by thermogravimetric analysis coupled with mass spectrometry (TG-MS) and Raman
spectroscopy including statistical Raman spectroscopy (SRS) and -microscopy
(SRM). The results reveal that the choice of the hydrogen/deuterium source, the
nature of the graphite (used as starting material), the potassium concentration
in the intercalation compound as well as the choice of the solvent have a great
impact on the reaction outcome. Furthermore, it was possible to proof that both
mono and few-layer hydrogenated/deuterated graphene can be produced.",1805.11672v1
2018-06-01,Stability of wurtzite semi-polar surfaces: algorithms and practices,"A complete knowledge of absolute surface energies with any arbitrary crystal
orientation is important for the improvements of semiconductor devices because
it determines the equilibrium and nonequilibrium crystal shapes of thin films
and nanostructures. It is also crucial in the control of thin film crystal
growth and surface effect studies in broad research fields. However, obtaining
accurate absolute formation energies is still a huge challenge for the
semi-polar surfaces of compound semiconductors. It mainly results from the
asymmetry nature of crystal structures and the complicated step morphologies
and related reconstructions of these surface configurations. Here we propose a
general approach to calculate the absolute formation energies of wurtzite
semi-polar surfaces by first-principles calculations, taking GaN as an example.
We mainly focused on two commonly seen sets of semi-polar surfaces: a-family
(11-2X) and m-family (10-1X). For all the semi-polar surfaces that we have
calculated in this paper, the self-consistent accuracy is within 1.5
meV/{\AA}^2. Our work fills the last technical gap to fully investigate and
understand the shape and morphology of compound semiconductors.",1806.00268v1
2018-06-04,Antiferromagnetic order in CaK(Fe[1-x]Ni[x])4As4 and its interplay with superconductivity,"The magnetic order in CaK(Fe[1-x]Ni[x])4As4 (1144) single crystals (x = 0.051
and 0.033) has been studied by neutron diffraction. We observe magnetic Bragg
peaks associated to the same propagation vectors as found for the collinear
stripe antiferromagnetic (AFM) order in the related BaFe2As2 (122) compound.
The AFM state in 1144 preserves tetragonal symmetry and only a commensurate,
non-collinear structure with a hedgehog spin-vortex crystal (SVC) arrangement
in the Fe plane and simple AFM stacking along the c direction is consistent
with our observations. The SVC order is promoted by the reduced symmetry in the
FeAs layer in the 1144 structure. The long-range SVC order coexists with
superconductivity, however, similar to the doped 122 compounds, the ordered
magnetic moment is gradually suppressed with the developing superconducting
order parameter. This supports the notion that both collinear and non-collinear
magnetism and superconductivity are competing for the same electrons coupled by
Fermi surface nesting in iron arsenide superconductors.",1806.01328v1
2018-06-08,Magnetostriction Reveals Orthorhombic Distortion in Tetrahedral Gd-compounds,"We report detailed thermal expansion and magnetostriction experiments on
GdCoIn$_5$ and GdRhIn$_5$ single crystal samples that show a sudden change in
the dilation at a field B$^\ast$ for temperatures below the N\'eel transition
temperature TN. We present a first-principles model including crystal-field
effects, dipolar and exchange interactions, and the dependence of the exchange
couplings with lattice distortions in order to fully account for the
magnetostriction and magnetic susceptibility data. The mean-field solution of
the model shows that a transition between metastable states occurs at the field
B$^\ast$. It also indicates that two degenerate phases coexist in the sample at
temperatures below TN. This allows to explain the lack of observation, in high
resolution x-ray experiments, of an orthorhombic distortion at the N\'eeel
transition even though the magnetic structure breaks the tetragonal symmetry
and the magnetoelastic coupling is significant. These conclusions could be
extended to other tetragonal Gd-based compounds that present the same
phenomenology.",1806.03268v1
2018-06-12,Field-induced magnetic charge in a cubic Laves compound UAl2,"Magnetic diffraction of polarized neutrons by the cubic Laves compound UAl2
in a magnetic field has unveiled weak Bragg spots that are nominally forbidden.
On the one hand, they can be viewed as magnetic analogues of the
basis-forbidden (2, 2, 2) reflection in diamond-type structures that has been
painstakingly and frequently investigated over almost a century. Alternatively,
the pattern of weak intensities can be assigned to Dirac multipoles imbedded in
field-induced magnetic charge. To this end, a published diffraction pattern is
successfully confronted with intensities calculated from the appropriate
magnetic space-group that includes Dirac dipoles (anapoles) to describe the
basis-forbidden magnetic reflections, and conventional (axial) dipole and
octupole multipoles to describe basis-allowed magnetic reflections.",1806.04461v4
2018-06-22,Observation of a pressure-induced transition from interlayer ferromagnetism to intralayer antiferromagnetism in Sr4Ru3O10,"Sr4Ru3O10 is a Ruddlesden-Popper compound with triple Ru-O perovskite layers
separated by Sr-O alkali layers. This compound presents a rare coexistence of
interlayer (c-axis) ferromagnetism and intralayer (basal-plane) metamagnetism
at ambient pressure. Here we report the observation of pressure-induced,
intralayer itinerant antiferromagnetism arising from the interlayer
ferromagnetism. The application of modest hydrostatic pressure generates an
anisotropy that causes a flattening and a tilting of RuO6 octahedra. All
magnetic and transport results from this study indicate these lattice
distortions diminish the c-axis ferromagnetism and basal-plane metamagnetism,
and induce a basal-plane antiferromagnetic state. The unusually large
magnetoelastic coupling and pressure tunability of Sr4Ru3O10 makes it a unique
model system for studies of itinerant magnetism.",1806.08466v1
2018-09-03,Microscopic Observation of Heavy Quasiparticle Formation in the Intermediate Valence Compound EuNi$_2$P$_2$: $^{31}$P NMR Study,"We report $^{31}$P NMR measurements under various magnetic fields up to 7 T
for the intermediate valence compound EuNi$_2$P$_2$, which shows heavy
electronic states at low temperatures. In the high-temperature region above 40
K, the Knight shift followed the Curie--Weiss law reflecting localized $4f$
states. In addition, the behavior corresponding to the temperature variation of
the average valence of Eu was observed in the nuclear spin-lattice relaxation
rate $1/T_1$. With the occurrence of the Kondo effect, $1/T_1$ was clearly
reduced below 40 K, and the Knight shift becomes almost constant at low
temperatures. From these results, the formation of heavy quasiparticles by the
hybridization of Eu $4f$ electrons and conduction electrons was clarified from
microscopic viewpoints. Furthermore, a characteristic spin fluctuation was
observed at low temperatures, which would be associated with valence
fluctuations caused by the intermediate valence state of EuNi$_2$P$_2$.",1809.00660v1
2018-09-04,Properties and superconductivity in Ti-doped NiTe2 single crystals,"Transition metal dichalcogenides (TMDs) usually show simple structures,
however, with interesting properties. Recently some TMDs have been pointed out
as type-II Dirac semimetals. In the present work, we investigate the physical
properties of a new candidate for type-II Dirac semimetal and investigate the
effect of titanium doping on physical properties of Ti-doped single crystalline
samples of NiTe2. It was found that this compound shows a superconducting
properties with a critical temperature close to 4.0 K. Interestingly, applied
pressures up to 1.3 GPa have no effect upon the superconducting state. Density
Functional Theory (DFT) calculations demonstrate the presence of a Dirac cone
in the band structure of NiTe2 literature when Spin-Orbit Coupling (SOC) is
included, which is in agreement with a recent report for this compound. Also,
our calculations demonstrate that Ti suppresses the formation of these
non-trivial states.",1809.00753v1
2018-09-13,Anisotropic hybridization in a new Kondo lattice compound CeCoInGa$_3$,"We report a detailed and comparative study of the single crystal CeCoInGa$_3$
in both experiment and theory. Resistivity measurements reveal the typical
behavior of Kondo lattice with the onset temperature of coherence, $T^*\approx
50\,$K. The magnetic specific heat can be well fitted using a spin-fluctuation
model at low temperatures, yielding a large Sommerfeld coefficient,
$\gamma\approx172\,$mJ/mol K$^2$ at 6 K, suggesting that this is a
heavy-fermion compound with a pronounced coherence effect. The magnetic
susceptibility exhibits a broad field-independent peak at $T_{\chi}$ and shows
an obvious anisotropy within the $bc$ plane, reflecting the anisotropy of the
coherence effect at high temperatures. These are compared with strongly
correlated calculations combining first-principles band structure calculations
and dynamical mean-field theory. Our results confirm the onset of coherence at
about 50 K and reveal a similar anisotropy in the hybridization gap, pointing
to a close connection between the hybridization strength of the low-temperature
Fermi-liquid state and the high-temperature coherence effect.",1809.04735v1
2018-09-16,Effects of entrance channels on the deexcitation properties of the same compound nucleus formed by different pairs of collision partners,"The properties of deexcitation of the same $^{220}$Th compound nucleus (CN)
formed by different mass (charge) asymmetric reactions are investigated. It is
demonstrated that the effective fission barrier $<B_{\rm fis}>$ value being a
function of the excitation energy $E^*_{\rm CN}$ is strongly sensitive to the
various orbital angular momentum $L=\ell\hbar$ distributions of CN formed with
the same excitation energy $E^*_{CN}$ by the very different entrance channels
$^{16}$O+$^{204}$Pb, $^{40}$Ar+$^{180}$Hf, $^{82}$Se+$^{138}$Ba and
$^{96}$Zr+$^{124}$Sn. Consequently, the competition between the fission and
evaporation of light particles (neutron, proton, and $\alpha$-particle)
processes along the deexcitation cascade of CN depends on the orbital angular
momentum distribution of CN. Therefore, the ratio between the evaporation
residue cross sections obtained after emission of neutral and charged particles
and neutrons only for the same CN with a given excitation energy $E^*_{CN}$ is
sensitive to the mass (charge) asymmetry of reactants in the entrance channel.",1809.05927v1
2018-09-21,"Origin of diverse nematic orders in Fe-based superconductors: 45$^\circ$ rotated nematicity in AFe$_2$As$_2$ (A=Cs, Rb)","The origin of diverse nematicity and their order parameters in Fe-based
superconductors have been attracting increasing attention. Recently, a new type
of nematic order has been discovered in heavily hole-doped ($n_d=5.5$) compound
AFe$_2$As$_2$ (A=Cs, Rb). The discovered nematicity has $B_{2g}$ (=$d_{xy}$)
symmetry, rotated by $45^\circ$ from the $B_{1g}$ (=$d_{x^2-y^2}$) nematicity
in usual compounds with $n_d\approx6$. We predict that the ""nematic bond
order"", which is the symmetry-breaking of the correlated hopping, is
responsible for the $B_{2g}$ nematic order in AFe$_2$As$_2$. The Dirac pockets
in AFe$_2$As$_2$ is essential to stabilize the $B_{2g}$ bond order. Both
$B_{1g}$ and $B_{2g}$ nematicity in A$_{1-x}$Ba$_x$Fe$_2$As$_2$ are naturally
induced by the Aslamazov-Larkin many-body process, which describes the
spin-fluctuation-driven charge instability. The present study gives a great
hint to control the nature of charge nematicity by modifying the orbital
character and the topology of the Fermi surface.",1809.08017v2
2018-09-21,Old puzzle of incommensurate crystal structure of calaverite AuTe$_2$ and predicted stability of novel AuTe compound,"It is shown that the long-standing puzzle of incommensurate crystal structure
of AuTe$_2$ can be solved, if this material is considered as a negative
charge-transfer system. Using modern computational methods, we demonstrate that
charge redistribution associated with incommensurate modulations of crystal
structure occurs not so much on Au, but predominantly on Te sites. This
substantially reduces Coulomb energy costs for creating such a unique crystal
structure. The same mechanism also explains superconductivity of doped
AuTe$_2$. Exploring different Au-Te compositions, we also discovered a
previously unknown compound AuTe, which theoretically is very stable, and we
predict its crystal structure.",1809.08052v1
2018-09-21,A Density Functional Theory based study of Electron Transport Through Ferrocene Compounds with Different Anchor Groups in Different Adsorption Configurations of A STM-setup,"In our theoretical study where we combine a nonequilibrium Green's function
(NEGF) approach with density functional theory (DFT) we investigate compounds
containing a ferrocene moiety which is connected to i) thiol anchor groups on
both sides in a para-connection, ii) a pyridyl anchor group on one side in a
meta-connection and a thiol group on the other side in a para-connection, in
both cases with acetylenic spacers in between the Ferrocene and the anchors. We
predict possible single molecule junction geometries within a scanning
tunneling microscopy (STM) setup where we find that the conductance trend for
the set of conformations are intriguing in the sense that the conductance does
not decrease while the junction length increases which we analyze and explain
in terms of Fermi level alignment. We also find a pattern for the
current-voltage (IV) curves within the linear-response regime for both
molecules we study, where the conductance variation with the molecular
configurations is surprisingly small.",1809.08174v1
2018-09-25,A Berry-Esseen theorem for Pitman's $α$-diversity,"This paper is concerned with the study of the random variable $K_n$ denoting
the number of distinct elements in a random sample $(X_1, \dots, X_n)$ of
exchangeable random variables driven by the two parameter Poisson-Dirichlet
distribution, $PD(\alpha,\theta)$. For $\alpha\in(0,1)$, Theorem 3.8 in
\cite{Pit(06)} shows that
$\frac{K_n}{n^{\alpha}}\stackrel{\text{a.s.}}{\longrightarrow}
S_{\alpha,\theta}$ as $n\rightarrow+\infty$. Here, $S_{\alpha,\theta}$ is a
random variable distributed according to the so-called scaled Mittag-Leffler
distribution. Our main result states that $$ \sup_{x \geq 0} \Big|
\ppsf\Big[\frac{K_n}{n^{\alpha}} \leq x \Big] - \ppsf[S_{\alpha,\theta} \leq x]
\Big| \leq \frac{C(\alpha, \theta)}{n^{\alpha}} $$ holds with an explicit
constant $C(\alpha, \theta)$. The key ingredients of the proof are a novel
probabilistic representation of $K_n$ as compound distribution and new, refined
versions of certain quantitative bounds for the Poisson approximation and the
compound Poisson distribution.",1809.09276v2
2018-09-27,An investigation of the interrelationship between pressure and correlation in LaFeAsO under pressure,"Here, we investigated the interrelationship between pressure and correlation
in the LaFeAsO compound by the density functional theory method combined with
the dynamical mean field theory (DFT+DMFT) method. The spectral function and
the occupation number (ON) of Fe-3d orbitals at different pressures were
extracted from the calculations, and the importance of the role of correlation
in superconductivity in iron-based compounds was indicated. The measured ON of
Fe-3d orbitals demonstrated charge transfer between them and also the crucial
role of the Fe-3dxy (xy) orbital in superconductivity in these materials. A
switching behavior between high and low TC through decreasing the correlation
was observed in our calculations, originating from the orbital switching. This
shows the significant role of the orbital degrees of freedom in iron-based
superconductors.",1809.10661v1
2018-11-01,Spin-lattice coupling mediated giant magnetodielectricity across the spin reorientation in Ca2FeCoO5,"The structural, phonon, magnetic, dielectric, and magneto dielectric
responses of the pure bulk Brownmillerite compound Ca2FeCoO5 are reported. This
compound showed giant magneto dielectric response (10%-24%) induced by strong
spin-lattice coupling across its spin reorientation transition (150-250 K). The
role of two Debye temperatures pertaining to differently coordinated sites in
the dielectric relaxations is established. The positive giant
magneto-dielectricity is shown to be a direct consequence of the modulations in
the lattice degrees of freedom through applied external field across the spin
reorientation transition. Our study illustrates novel control of
magneto-dielectricity by tuning the spin reorientation transition in a material
that possess strong spin lattice coupling.",1811.00404v1
2018-11-02,Analysing Dropout and Compounding Errors in Neural Language Models,"This paper carries out an empirical analysis of various dropout techniques
for language modelling, such as Bernoulli dropout, Gaussian dropout, Curriculum
Dropout, Variational Dropout and Concrete Dropout. Moreover, we propose an
extension of variational dropout to concrete dropout and curriculum dropout
with varying schedules. We find these extensions to perform well when compared
to standard dropout approaches, particularly variational curriculum dropout
with a linear schedule. Largest performance increases are made when applying
dropout on the decoder layer. Lastly, we analyze where most of the errors occur
at test time as a post-analysis step to determine if the well-known problem of
compounding errors is apparent and to what end do the proposed methods mitigate
this issue for each dataset. We report results on a 2-hidden layer LSTM, GRU
and Highway network with embedding dropout, dropout on the gated hidden layers
and the output projection layer for each model. We report our results on
Penn-TreeBank and WikiText-2 word-level language modelling datasets, where the
former reduces the long-tail distribution through preprocessing and one which
preserves rare words in the training and test set.",1811.00998v1
2018-11-05,Prediction of Novel High Pressure H2O-NaCl and Carbon Oxide Compounds with Symmetry-Driven Structure Search Algorithm,"Crystal structure prediction with theoretical methods is particularly
challenging when unit cells with many atoms need to be considered. Here we
employ a symmetry-driven structure search (SYDSS) method and combine it with
density functional theory (DFT) to predict novel crystal structures at high
pressure. We sample randomly from all 1,506 Wyckoff positions of the 230 space
groups to generate a set of initial structures. During the subsequent
structural relaxation with DFT, existing symmetries are preserved, but the
symmetries and the space group may change as atoms move to more symmetric
positions. By construction, our algorithm generates symmetric structures with
high probability without excluding any configurations. This improves the search
efficiency, especially for large cells with 20 atoms or more. We apply our
SYDSS algorithm to identify stoichiometric (H2O)_n-(NaCl)_m and C_nO_m
compounds at high pressure. We predict a novel H2O-NaCl structure with Pnma
symmetry to form at 3.4 Mbar, which is within the range of diamond anvil
experiments. In addition, we predict a novel C2O structure at 19.8 Mbar and C4O
structure at 44.0 Mbar with Pbca and C2/m symmetry respectively.",1811.01462v1
2018-11-05,Redefining Ultrasound Compounding: Computational Sonography,"Freehand three-dimensional ultrasound (3D-US) has gained considerable
interest in research, but even today suffers from its high inter-operator
variability in clinical practice. The high variability mainly arises from
tracking inaccuracies as well as the directionality of the ultrasound data,
being neglected in most of today's reconstruction methods. By providing a novel
paradigm for the acquisition and reconstruction of tracked freehand 3D
ultrasound, this work presents the concept of Computational Sonography (CS) to
model the directionality of ultrasound information. CS preserves the
directionality of the acquired data, and allows for its exploitation by
computational algorithms. In this regard, we propose a set of mathematical
models to represent 3D-US data, inspired by the physics of ultrasound imaging.
We compare different models of Computational Sonography to classical scalar
compounding for freehand acquisitions, providing both an improved preservation
of US directionality as well as improved image quality in 3D. The novel concept
is evaluated for a set of phantom datasets, as well as for in-vivo acquisitions
of muscoloskeletal and vascular applications.",1811.01534v1
2018-11-06,Superconductivity at an antiferromagnetic quantum critical point: the role of energy fluctuations,"Motivated by recent experiments reporting superconductivity only at very low
temperature in a class of heavy fermion compounds, we study the impact of
energy fluctuations with small momentum transfer on the pairing instability
near an antiferromagnetic quantum critical point. While these fluctuations,
formed by composite spin fluctuations, were proposed to explain the
thermodynamic and transport properties near the quantum critical point of
compounds such as YbRh$_{2}$Si$_{2}$ and CeCu$_{6-x}$Au$_{x}$ at $x\approx0.1$,
here they are found to strongly suppress $T_{c}$ of the $d$-wave pairing of the
hot quasiparticles promoted by the spin fluctuations. Interestingly, if energy
fluctuations are strong enough, they can induce triplet pairing involving the
quasiparticles of the cold regions of the Fermi surface. Overall, the opposing
effects of energy and spin fluctuations lead to a suppression of $T_{c}$.",1811.02170v1
2018-11-16,Broken symmetry driven topological semi-metal to gaped phase transitions in SrAgAs,"We show the occurence of Dirac, Triple point, Weyl semimetal and topological
insulating phase in a single ternary compound using specific symmetry
preserving perturbations. Based on {\it first principle} calculations,
\textbf{\textit{k.p}} model and symmetry analysis, we show that alloying
induced precise symmetry breaking in SrAgAs (space group P6$_3/mmc$) leads to
tune various low energy excitonic phases transforming from Dirac to topological
insulating via intermediate triple point and Weyl semimetal phase. We also
consider the effect of external magnetic field, causing time reversal symmetry
(TRS) breaking, and analyze the effect of TRS towards the realization of Weyl
state. Importantly, in this material, the Fermi level lies extremely close to
the nodal point with no extra Fermi pockets which further, make this compound
as an ideal platform for topological study. The multi fold band degeneracies in
these topological phases are analyzed based on point group representation
theory. Topological insulating phase is further confirmed by calculating Z2
index. Furthermore, the topologically protected surface states and Fermi arcs
are investigated in some detail.",1811.06685v2
2018-11-16,"A new family of two-dimensional crystals: open-framework T$_{3}$X (T=C, Si, Ge, Sn; X=O, S, Se, Te) compounds with tetrahedral bonding","To accelerate development of innovative materials, their modelings and
predictions with useful functionalities are of vital importance. Here, based on
a recently developed crystal structure prediction method, we find a new family
of stable two-dimensional crystals with an open-channel tetrahedral bonding
network, rendering a potential for electronic and energy applications. The
proposed structural prototype with a space group of Cmme hosts at least
thirteen different freestanding T$_{3}$X compounds with group IV (T=C, Si, Ge,
Sn) and VI (X=O, S, Se, Te) elements. Moreover, the proposed materials display
diverse electronic properties ranging from direct band gap semiconductor to
topological insulator at their pristine forms, which are further tunable by
mechanical strain.",1811.06894v2
2018-11-26,Observation of optical states below light cone with compound lattices,"For optical systems, states inside the light cone could be detected by
far-field measurement, while those below the light cone are not detectable by
far-field measurement. A new method for far-field detection has been developed
for observing states below the light cone with compound lattices. The basic
mechanism involved is that periodic weak scattering leads to band folding,
making the states out of the light cone to occur inside. By using
polarization-resolved momentum-space imaging spectroscopy the band structures
and iso-frequency contours of plasmonic lattices with different dimensions and
symmetries are experimentally mapped out, in good agreement with the
simulation.",1811.10235v1
2018-11-26,Local order in binary Ge-Te glasses - an experimental study,"The structure of $\mathrm{Ge}_x\mathrm{Te}_{100-x}$ (x = 14.5, 18.7, 23.6)
glasses prepared by twin roller quenching technique was investigated by neutron
diffraction, X-ray diffraction and Ge-K-edge X-ray absorption spectroscopy
measurements. Large scale structural models were obtained for each composition
by fitting the experimental datasets in the framework of the reverse Monte
Carlo technique. It was found that the majority of Ge and Te atoms satisfy the
8-N rule. Simulation results indicate that Ge-Ge bonding is not significant for
x = 14.5 and 18.7. The shape and position of the first peak of the Ge-Ge
partial pair correlation function evidence the presence of corner sharing
tetrahedra already in compositions (x = 14.5 and 18.7) where 'sharing' of a Te
atom by two Ge atoms could be avoided due to the low concentration of Ge.",1811.10341v1
2018-11-26,New observational constraints on interacting dark energy using galaxy clusters virial equilibrium states,"As the dark sector remains unknown in composition and interaction between
dark energy and dark matter stand out as natural, observations of galaxy
clusters out of equilibrium abound, opening a promising window on these
questions. We continue here the exploration of dark sector interaction
detection via clusters virial equilibrium state for all clusters
configurations. The dynamics of clusters is evaluated with the Layzer-Irvine
equation, a simple model of an interacting dark sector and some simplifying
assumptions to obtain the time-dependent part of the virial dynamics. The
clusters' data are concentrated in optical weak lensing and X-ray observations
that evaluate, respectively, the clusters' mass profiles and temperatures. The
global inconsistency of available X-ray data led us to constitute `gold'
cluster samples. Through a Bayesian analysis, they are processed to obtain
consistent interaction detected up to 3$\sigma$, in compounded interaction
strength for 11 clusters at $-0.027 \pm 0.009$ that translate in compounded
universal equilibrium virial ratio of $-0.61^{+0.04}_{-0.03}$. The level of
detection and inconsistency of X-ray data call for caution, although future
instruments promise a clearer detection soon.",1811.10712v1
2018-11-27,Layer dependent antiferromagnetism in the Sr4Ru3O10 ruthenate at the metamagnetic-like transition,"We have investigated the metamagnetic-like transition in the triple layer
ruthenate Sr4Ru3O10 by means of neutron diffraction from single crystals. The
magnetic structure of the compound appears to be determined in a complex way by
the two substructures of inequivalent ruthenium ions. At Tc=105K the system has
a sharp transition into a ferromagnetic state along the c-axis which is driven
by the ruthenium atoms in the central octahedra of the triple layers whereas
the substructure of the outer ruthenium atoms tend to align in the ab plane
achieving an antiferromagnetic order at the metamagnetic transition T*~50K.
Below T* the strong anisotropy along c prevails, the outer ruthenium tend to
align along the c-axis and the in-plane antiferromagnetic order disappears.
This finding confirms the delicate balance between antiferro and ferromagnetic
couplings in the (Sr,Ca)n+1RunO3n+1 family of compounds, and proves the layer
dependence of the magnetic anisotropy in Sr4Ru3O10.",1811.11065v3
2018-11-24,Study of the magnetic properties of the compound M_n B_i using the Monte Carlo simulations,"The aim of this paper is to investigate the magnetic properties of the M_n
B_i magnetic systems by using the Monte Carlo simulation. Indeed, we analyzed
the effect of the number of layers on the magnetic properties of the compound
M_n B_i. The magnetization, the binder cumulant, the Curie temperature and the
hysteresis cycle are also calculated in this work. We used the free boundary
conditions to simulate the properties of the studied system, and we presented
the effect of multilayer numbers on the magnetic properties of M_n B_i films.
Meanwhile, there are clear indications that coercive field increases
drastically with the increases multilayer numbers is consistent with the
experimental facts.",1811.11290v2
2018-11-29,Lattice dynamics and coupled quadrupole-phonon excitations in CeAuAl$_3$,"We report first principles calculations of the structural parameters and
phonon dispersion of the tetragonal non-centrosymmetric heavy fermion compound
CeAuAl$_3$. Taking into account weak magnetoelastic interactions of the
rare-earth (RE) ions with the spectrum of phonons, we obtain an analytical
expression for the hybridization of quadrupole excitations and phonons from the
poles of the one-phonon Green-function. In the paramagnetic phase, we predict
the formation of mixed modes that may be observed by inelastic neutron
scattering. Our results show that magnetoelastic interactions, albeit being
moderate, play an important role in CeAuAl$_3$. This suggests that
magnetoelastic interactions may be equally important in a wide range of related
compounds.",1811.11994v1
2019-11-06,Surfing multiple conformation-property landscapes via machine learning: Designing magnetic anisotropy,"The advent of computational statistical disciplines, such as machine
learning, is leading to a paradigm shift in the way we conceive the design of
new compounds. Today computational science does not only provide a sound
understanding of experiments, but also can directly design the best compound
for specific applications. This approach, known as reverse engineering,
requires the construction of models able to efficiently predict continuous
structure-property maps. Here we show that reverse engineering can be used to
tune the magnetic properties of a single-ion molecular magnet in an automated
intelligent fashion. We design a machine learning model to predict both the
energy and magnetic properties as function of the chemical structure. Then, a
particle-swarm optimization algorithm is used to explore the conformational
landscapes in the search for new molecular structures leading to an enhanced
magnetic anisotropy. We find that a 5% change in one of the coordination angles
leads to a 50% increase in the anisotropy. Our approach paves the way for a
machine-learning-driven exploration of the chemical space of general classes of
magnetic materials. Most importantly, it can be applied to any
structure-property relation and offers an effective way to automatically
generate new materials with target properties starting from the knowledge of
previously synthesized ones.",1911.02263v1
2019-11-10,Pressure-driven switching of magnetism in layered CrCl3,"Layered transition-metal compounds with controllable magnetic behaviors
provide many fascinating opportunities for the fabrication of high-performance
magneto-electric and spintronic devices. The tuning of their electronic and
magnetic properties is usually limited to the change of layer thickness,
electrostatic doping, and the control of electric and magnetic fields. However,
pressure has been rarely exploited as a control parameter for tailoring their
magneto-electric properties. Here, we report a unique pressure-driven
isostructural phase transition in layered CrCl3 accompanied by a simultaneous
switching of magnetism from a ferromagnetic to an antiferromagnetic ordering.
Our experiments, in combination with ab initio calculations, demonstrate that
such a magnetic transformation hinders the band-gap collapse under pressure,
leading to an anomalous semiconductor-to-semiconductor transition. Our findings
not only reveal high potential of CrCl3 in electronic and spintronic
applications under ambient and extreme conditions but also establish the basis
for exploring unusual phase transitions in layered transition-metal compounds.",1911.03846v1
2019-11-11,Compound-tunable embedding potential method and its application to ytterbium fluoride crystals YbF$_2$ and YbF$_3$,"Compound-tunable embedding potential (CTEP) method developed in previous
works to describe electronic structure of fragments in materials is applied to
crystals containing periodically arranged lanthanide atoms, which can have open
$4f$ shell. We consider YbF$_2$ and YbF$_3$ as examples such that $4f$ shell is
excluded from both the crystal and cluster stages of generating the CTEP.
Instead, 10 and 11 valence-electron pseudopotentials for Yb, correspondingly,
are applied and the latter treats the $4f$-hole implicitly. At the next stage
of the two-component embedded cluster studies of the YbF$_{2,3}$ crystals we
apply the 42 valence-electron relativistic pseudopotential for Yb and, thus,
$4f$ shell is treated explicitly. A remarkable agreement of the electronic
density and interatomic distances within the fragment with those of the
original periodic crystal calculation is attained.",1911.04332v1
2019-11-14,Hybrid functional calculations of electronic structure and carrier densities in rare-earth monopnictides,"The structural parameters and electronic structure of rare-earth pnictides
are calculated using density functional theory (DFT) with the Heyd, Scuseria,
and Ernzerhof (HSE06) screened hybrid functional. We focus on RE-V compounds,
with RE=La, Gd, Er, and Lu, and V=As, Sb, and Bi, and analyze the effects of
spin-orbit coupling and treating the RE 4$f$ electrons as valence electrons in
the projector augmented wave approach. The results of HSE06 calculations are
compared with DFT within the generalized gradient approximation (DFT-GGA) and
other previous calculations. We find that all these RE-V compounds are
semimetals with electron pockets at the $X$ point and hole pockets at $\Gamma$.
Whereas in DFT-GGA the carrier density is significantly overestimated, the
computed carrier densities using HSE06 is in good agreement with the available
experimental data.",1911.06184v1
2019-11-15,f-electron charge densities probed using core level non-resonant inelastic x-ray scattering,"Strongly correlated materials are characterized by the presence of
electron-electron interactions in their electronic structure. They often have
remarkable properties and transitions between competing phases of very
different electronic and magnetic order. This thesis focuses on strongly
correlated $f$-electron compounds containing Ce, Sm, and U. These materials
exhibit a so-called heavy-fermion or Kondo-lattice behavior. They can become
insulating due to hybridization effects (Kondo-insulator) or develop multipolar
(hidden) order. Kondo insulators have recently been discussed in the context of
strongly correlated topological insulators. This new aspect caused an enormous
activity in the field of Kondo insulators, theoretically as well as
experimentally. Multipolar order as well as the formation of a Kondo insulating
state strongly depend on the symmetry of the $f$ states involved. Also the
character of the surface states in a topological insulator is determined by the
properties of the bulk states. Therefore the scope of this thesis has been to
unveil the underlying symmetries of the bulk $f$ states. Here the compounds
CeB$_6$, UO$_2$, and URu$_2$Si$_2$, which exhibit multipolar order, as well as
the Kondo insulators (semimetals) SmB$_6$ and CeRu$_4$Sn$_6$ have been studied.",1911.06901v1
2019-11-18,Anisotropic magnetic properties of trigonal ErAl$_2$Ge$_2$ single crystal,"We report the anisotropic magnetic properties of the ternary compound
ErAl$_2$Ge$_2$. Single crystals of this compound were grown by high temperature
solution growth technique,using Al:Ge eutectic composition as flux. From the
powder x-ray diffraction we confirmed that ErAl$_2$Ge$_2$ crystallizes in the
trigonal CaAl$_2$Si$_2$-type crystal structure. The anisotropic magnetic
properties of a single crystal were investigated by measuring the magnetic
susceptibility, magnetization, heat capacity and electrical resistivity. A bulk
magnetic ordering occurs around 4 K inferred from the magnetic susceptibility
and the heat capacity. The magnetization measured along the $ab$-plane
increases more rapidly than along the $c$-axis suggesting the basal $ab$-plane
as the easy plane of magnetization. The magnetic susceptibility, magnetization
and the $4f$-derived part of the heat capacity in the paramagnetic regime
analysed based on the point charge model of the crystalline electric field
(CEF) indicate a relatively low CEF energy level splitting.",1911.07589v1
2019-11-28,Integro-differential equations linked to compound birth processes with infinitely divisible addends,"Stochastic modelling of fatigue (and other material's deterioration), as well
as of cumulative damage in risk theory, are often based on compound sums of
independent random variables, where the number of addends is represented by an
independent counting process. We consider here a cumulative model where,
instead of a renewal process (as in the Poisson case), a linear birth (or Yule)
process is used. This corresponds to the assumption that the frequency of
\textquotedblleft damage"" increments accelerates according to the increasing
number of \textquotedblleft damages"". We start from the partial differential
equation satisfied by its transition density, in the case of exponentially
distributed addends, and then we generalize it by introducing a
space-derivative of convolution type (i.e. defined in terms of the Laplace
exponent of a subordinator). Then we are concerned with the solution of
integro-differential equations, which, in particular cases, reduce to
fractional ones. Correspondingly, we analyze the related cumulative jump
processes under a general infinitely divisible distribution of the (positive)
jumps. Some special cases (such as the stable, tempered stable, gamma and
Poisson) are presented.",1911.12790v1
2019-11-29,Dynamic decoupling of laser phase noise in compound atomic clocks,"The frequency stability achieved by an optical atomic clock ultimately
depends on the coherence of its local oscillator. Even the best ultrastable
lasers only allow interrogation times of a few seconds, at present. Here we
present a universal measurement protocol that overcomes this limitation.
Engineered dynamic decoupling of laser phase noise allows any optical atomic
clock with high signal-to-noise ratio in a single interrogation to reconstruct
the laser's phase well beyond its coherence limit. A compound clock is then
formed in combination with another optical clock of any type, allowing the
latter to achieve significantly higher frequency stability than on its own. We
demonstrate implementation of the protocol in a realistic proof-of-principle
experiment with a phase reconstruction fidelity of 99 %. The protocol enables
minute-long interrogation for the best ultrastable laser systems. Likewise, it
can improve clock performance where less stable local oscillators are used,
such as in transortable systems.",1911.13146v1
2020-01-03,"Mapping the Dirac fermions in intrinsic antiferromagnetic topological insulators (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ (n=0, 1)","Topological surface states with intrinsic magnetic ordering in the
MnBi$_2$Te$_4$(Bi$_2$Te$_3$)$_n$ compounds have been predicted to host rich
topological phenomena including quantized anomalous Hall effect and axion
insulator state. Here we use scanning tunneling microscopy to image the surface
Dirac fermions in MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$. We have determined the
energy dispersion and helical spin texture of the surface states through
quasiparticle interference patterns far above Dirac energy, which confirms its
topological nature. Approaching the Dirac point, the native defects in the
MnBi$_2$Te$_4$ septuple layer give rise to resonance states which extend
spatially and potentially hinder the detection of a mass gap in the spectra.
Our results demonstrate that regulating defects is essential to realize exotic
topological states at higher temperatures in these compounds.",2001.00866v1
2019-12-02,Diverse fundamental properties in stage-n graphite alkali-intercalation compounds: anode materials of Li+-based batteries,"The diversified essential properties of the stage-n graphite
alkali-intercalation compounds are thoroughly explored by the first-principles
calculations. According to their main features, the lithium and non-lithium
materials might be quite different from each other in stacking configurations,
the intercalated alkali-atom concentrations, the free conduction electron
densities, and the atom-dominated & (carbon, alkali)-co-dominated energy bands.
The close relations between the alkali-doped metallic behaviors and the
geometric symmetries will be clarified through the interlayer atomic
interactions, in which the significant alkali-carbon chemical bondings are
fully examined from the atom- and orbital-decomposed van Hove singularities.
The blue shift of the Fermi level, the n-type doping, is clearly identified
from the low-energy features of the density of states. This study is able to
provide the partial information about anode of Li+-based battery. There are
certain important differences between AC$_6$/AC$_8$ and Li$_8$Si$_4$O$_{12}$.",2001.02042v2
2020-01-09,Option pricing in time-changed Lévy models with compound Poisson jumps,"The problem of European-style option pricing in time-changed L\'{e}vy models
in the presence of compound Poisson jumps is considered. These jumps relate to
sudden large drops in stock prices induced by political or economical hits. As
the time-changed L\'{e}vy models, the variance-gamma and the normal-inverse
Gaussian models are discussed. Exact formulas are given for the price of
digital asset-or-nothing call option on extra asset in foreign currency. The
prices of simpler options can be derived as corollaries of our results and
examples are presented. Various types of dependencies between stock prices are
mentioned.",2001.03064v1
2020-01-13,Magnetic phase diagram of the antiferromagnet U2Rh2Pb,"A new U-based compound of the U2Rh2Pb, a new compound of the U2T2X series was
prepared in a single-crystal form. Its structure was determined as belonging to
the tetragonal Mo2FeB2 structure type with the shortest U-U spacing along the
c. U2Rh2Pb undergoes an antiferromagnetic transition at TN of 20 K and exhibits
an enhanced Sommerfeld coefficient 150 mJ/molK2. In contrast to the two rhodium
analogues U2Rh2In and U2Rh2Sn, the easy-magnetization direction is the c with
rather low value of the critical field 4.3 T of the metamagnetic transition of
a spin-flip type. The observed dependences of TN and Hc on temperature and
magnetic field have been used for constructing a magnetic phase diagram. The
experimental observations are mostly supported by first-principles
calculations.",2001.04196v1
2020-01-22,Bulk superconductivity induced by Se substitution in self-doped BiCh2-based compound CeOBiS2-xSex,"We report the Se substitution effects on the crystal structure,
superconducting properties, and valence states of self-doped BiCh2-based
compound CeOBiS2-xSex. Polycrystalline CeOBiS2-xSex samples with x = 0-1.0 were
synthesized. For x = 0.4 and 0.6, bulk superconducting transitions with a large
shielding volume fraction were observed in magnetic susceptibility
measurements; the highest transition temperature (Tc) was 3.0 K for x = 0.6. A
superconductivity phase diagram of CeOBiS2-xSex was established based on Tc
estimated from the electrical resistivity and magnetization measurements. The
emergence of superconductivity in CeOBiS2-xSex was explained with two essential
parameters of in-plane chemical pressure and carrier concentration, which
systematically changed with increasing Se concentration.",2001.07928v1
2020-01-22,Simulation of the growth kinetics in group IV compound semiconductors,"We present a stochastic simulation method designed to study at an atomic
resolution the growth kinetics of compounds characterized by the sp3-type
bonding symmetry. Formalization and implementation details are discussed for
the particular case of the 3C-SiC material. A key feature of our numerical tool
is the ability to simulate the evolution of both point-like and extended
defects, whereas atom kinetics depend critically on process-related parameters.
In particular, the simulations can describe the surface state of the crystal
and the generation/evolution of defects as a function of the initial substrate
condition and the calibration of the simulation parameters. We demonstrate that
quantitative predictions of the microstructural evolution of the studied
systems can be readily compared with the structural characterization of actual
processed samples.",2001.07980v1
2020-01-21,Nowhere to Hide: Cross-modal Identity Leakage between Biometrics and Devices,"Along with the benefits of Internet of Things (IoT) come potential privacy
risks, since billions of the connected devices are granted permission to track
information about their users and communicate it to other parties over the
Internet. Of particular interest to the adversary is the user identity which
constantly plays an important role in launching attacks. While the exposure of
a certain type of physical biometrics or device identity is extensively
studied, the compound effect of leakage from both sides remains unknown in
multi-modal sensing environments. In this work, we explore the feasibility of
the compound identity leakage across cyber-physical spaces and unveil that
co-located smart device IDs (e.g., smartphone MAC addresses) and physical
biometrics (e.g., facial/vocal samples) are side channels to each other. It is
demonstrated that our method is robust to various observation noise in the wild
and an attacker can comprehensively profile victims in multi-dimension with
nearly zero analysis effort. Two real-world experiments on different biometrics
and device IDs show that the presented approach can compromise more than 70\%
of device IDs and harvests multiple biometric clusters with ~94% purity at the
same time.",2001.08211v1
2020-01-23,Universal behavior of the thermal Hall conductivity,"We report theoretical and experimental analyses of the thermal Hall
conductivity in correlated systems. For both fermionic and bosonic excitations
with nontrivial topology, we show that at ""intermediate"" temperatures, the
thermal Hall conductivity exhibits an unexpected universal scaling with a
simple exponential form. At low temperatures, it behaves differently and
reflects the spectral properties of underlying excitations. Our predictions are
examined as examples in two prototype compounds, the quantum paraelectric
SrTiO$_3$ and the spin-liquid compound RuCl$_3$. The experimental data can be
largely covered by our proposed minimal phenomenological model independent of
microscopic details, revealing dominant bosonic contributions in SrTiO$_3$ and
gapped fermionic excitations in RuCl$_3$. Our work establishes a
phenomenological link between microscopic models and experimental data and
provides a unified basis for analyzing the thermal Hall conductivity in
correlated systems over a wide temperature region.",2001.08385v2
2020-01-27,Nanoscale degeneracy lifting in a geometrically frustrated antiferromagnet,"The local atomic and magnetic structures of the compounds $A$MnO$_2$ ($A$ =
Na, Cu), which realize a geometrically frustrated, spatially anisotropic
triangular lattice of Mn spins, have been investigated by atomic and magnetic
pair distribution function analysis of neutron total scattering data. Relief of
frustration in CuMnO$_2$ is accompanied by a conventional cooperative
symmetry-lowering lattice distortion driven by N\'eel order. In NaMnO$_2$,
however, the distortion has a short-range nature. A cooperative interaction
between the locally broken symmetry and short-range magnetic correlations lifts
the magnetic degeneracy on a nanometer length scale, enabling long-range
magnetic order in the Na-derivative. The degree of frustration, mediated by
residual disorder, contributes to the rather differing pathways to a single,
stable magnetic ground state in these two related compounds. This study
demonstrates how nanoscale structural distortions that cause local-scale
perturbations can lift the ground state degeneracy and trigger macroscopic
magnetic order.",2001.09917v1
2020-01-29,Modifications of Simon text model,"We discuss probability text models and their modifications. We construct
processes of different and unique words in a text. The models are to correspond
to the real text statistics. The infinite urn model (Karlin model) and the
Simon model are the most known models of texts, but they do not give the
ability to simulate the number of unique words correctly. The infinite urn
model give sometimes the incorrect limit of the relative number of unique and
different words. The Simon model states a linear growth of the numbers of
different and unique words. We propose three modifications of the Karlin and
Simon models. The first one is the offline variant, the Simon model starts
after the completion of the infinite urn scheme. We prove limit theorems for
this modification in embedded times only. The second modification involves the
compound Poisson process in the infinite urn model. We prove limit theorems for
it. The third modification is the online variant, the Simon redistribution
works at any toss of the Karlin model. In contrast to the compound Poisson
model, we have no analytics for this modification. We test all the
modifications by the simulation and have a good correspondence to the real
texts.",2001.10973v2
2021-07-06,Phase diagram of the Shastry-Sutherland Compound SrCu2(BO3)2 under extreme combined conditions of field and pressure,"Motivated by the intriguing properties of the Shastry-Sutherland compound
SrCu2(BO3)2 under pressure, with a still debated intermediate plaquette phase
appearing at around 20 kbar and a possible deconfined critical point at higher
pressure upon entering the antiferromagnetic phase, we have investigated its
high-field properties in this pressure range using tunnel diode oscillator
(TDO) measurements. The two main new phases revealed by these measurements are
fully consistent with those identified by infinite Projected Entangled Pair
states (iPEPS) calculations of the Shastry-Sutherland model, a 1/5 plateau and
a 10 x 2 supersolid. Remarkably, these phases are descendants of the
full-plaquette phase, the prominent candidate for the intermediate phase of
SrCu2(BO3)2. The emerging picture for SrCu2(BO3)2 is shown to be that of a
system dominated by a tendency to an orthorhombic distortion at intermediate
pressure, an important constraint on any realistic description of the
transition into the antiferromagnetic phase.",2107.02929v1
2021-07-08,The role of transverse anisotropic elastic waves and Ehrenfest relationships in the superconducting state of the compound Sr$_2$RuO$_4$,"In this short review, some bulk threshold phenomena of the unconventional
superconductivity in the strontium ruthenate compound (Sr2RuO4) are mentioned.
Particularly, in Sr2RuO4, the Ehrenfest relations, the velocity propagation of
the elastic field modes, and the ultrasound attenuation find a common point to
study elastic anisotropic lattice field effects at the transition temperature
(Tc) between the normal and the superconducting state. Ehrenfest relations are
suitable for establishing a phase diagram of the Tc point according to symmetry
consideration of the electrons pairs in unconventional superconductors. Further
studies in this direction could turn into a new role for the spin polarization
of the transverse phonon field and its interaction with the conduction
electrons in anisotropic crystals with several conducting/superconducting bands
such as Sr2RuO4.",2107.03703v1
2021-07-15,Piezoelectricity in hafnia,"Because of its compatibility with semiconductor-based technologies, hafnia
(HfO$_{2}$) is today's most promising ferroelectric material for applications
in electronics. Yet, knowledge on the ferroic and electromechanical response
properties of this all-important compound is still lacking. Interestingly,
HfO$_2$ has recently been predicted to display a negative longitudinal
piezoelectric effect, which sets it apart form classic ferroelectrics (e.g.,
perovskite oxides like PbTiO$_3$) and is reminiscent of the behavior of some
organic compounds. The present work corroborates this behavior, by
first-principles calculations and an experimental investigation of HfO$_2$ thin
films using piezoresponse force microscopy. Further,the simulations show how
the chemical coordination of the active oxygen atoms is responsible for the
negative longitudinal piezoelectric effect. Building on these insights, it is
predicted that, by controlling the environment of such active oxygens (e.g., by
means of an epitaxial strain), it is possible to change the sign of the
piezoelectric response of the material.",2107.07414v1
2021-07-16,Continuous control of classical-quantum crossover by external high pressure in the coupled chain compound CsCuCl$_3$,"In solid materials, the parameters relevant to quantum effects, such as the
spin quantum number, are basically determined and fixed at the chemical
synthesis, which makes it challenging to control the amount of quantum
correlations. We propose and demonstrate a method for active control of the
classical-quantum crossover in magnetic insulators by applying external
pressure. As a concrete example, we perform high-field, high-pressure
measurements on CsCuCl$_3$, which has the structure of weakly-coupled spin
chains. The magnetization process experiences a continuous evolution from the
semi-classical realm to the highly-quantum regime with increasing pressure.
Based on the idea of ""squashing"" the spin chains onto a plane, we characterize
the change in the quantum correlations by the change in the value of the local
spin quantum number of an effective two-dimensional model. This opens a way to
access the tunable classical-quantum crossover of two-dimensional spin systems
by using alternative systems of coupled-chain compounds.",2107.07718v1
2021-07-21,Nonmagnetic $J = 0$ State and Spin-Orbit Excitations in K$_{2}$RuCl$_{6}$,"Spin-orbit Mott insulators composed of $t_{2g}^4$ transition metal ions may
host excitonic magnetism due to the condensation of spin-orbital $J=1$
triplons. Prior experiments suggest that the $4d$ antiferromagnet
Ca$_{2}$RuO$_{4}$ embodies this notion, but a $J = 0$ nonmagnetic state as a
basis of the excitonic picture remains to be confirmed. We use Ru $L_3$-edge
resonant inelastic x-ray scattering to reveal archetypal $J$ multiplets with a
$J=0$ ground state in the cubic compound K$_{2}$RuCl$_{6}$, which are well
described within the $LS$-coupling scheme. This result highlights the critical
role of unquenched orbital moments in $4d$-electron compounds and calls for
investigations of quantum criticality and excitonic magnetism on various
crystal lattices.",2107.10046v1
2021-07-30,Financial intermediation and risk in decentralized lending protocols,"We provide an overview of decentralized protocols like Compound and Aave that
offer collateralized loans for cryptoasset investors. Compound and Aave are two
of the most important application in the decentralized finance (DeFi)
ecosystem. Using publicly available information on rates, supply and borrow
activity, and accounts we analyze different elements of the protocols. In
particular, we estimate ex-post margins that give a comprehensive account of
the cost of financial intermediation. We find that ex-post margins considering
all markets are 1% and lower for stablecoin markets. In addition, we estimate
quarterly indicators regarding solvency, asset quality, earnings and market
risk similar to the ones used in traditional banking. This provides a first
look at the use of these metrics and a comparison between the similarities and
challenges to our understanding of financial intermediation in these protocols
based on tools used for traditional banking.",2107.14678v1
2017-04-01,Electronic bandstructure and van der Waals coupling of ReSe2 revealed by high-resolution angle-resolved photoemission spectroscopy,"ReSe2 and ReS2 are unusual compounds amongst the layered transition metal
dichalcogenides as a result of their low symmetry, with a characteristic
in-plane anisotropy due to in-plane rhenium chains. They preserve inversion
symmetry independent of the number of layers and, in contrast to more
well-known transition metal dichalcogenides, bulk and few-monolayer Re-TMD
compounds have been proposed to behave as electronically and vibrational
decoupled layers. Here, we probe for the first time the electronic band
structure of bulk ReSe2 by direct nanoscale angle-resolved photoemission
spectroscopy. We find a highly anisotropic in- and out-of-plane electronic
structure, with the valence band maxima located away from any particular
high-symmetry direction. The effective mass doubles its value perpendicular to
the Re chains and the interlayer van der Waals coupling generates significant
electronic dispersion normal to the layers. Our density functional theory
calculations, including spin-orbit effects, are in excellent agreement with
these experimental findings.",1704.00175v1
2017-04-12,Prediction of new Group IV-V-VI monolayer semiconductors based on first principle calculation,"Two-dimension (2D) semiconductor materials have attracted much attention and
research interest for their novel properties suitable for electronic and
optoelectronic applications. In this paper, we have proposed an idea in new 2D
materials design by using adjacent group elements to substitute half of the
atoms in the primitive configurations to form isoelectronic compounds. We have
successfully taken this idea on group V monolayers and have obtained many
unexplored Group IV-V-VI monolayer compounds: P2SiS, As2SiS, As2GeSe, Sb2GeSe,
Sb2SnTe, and Bi2SnTe. Relative formation energy calculations, phonon spectrum
calculations, as well as finite-temperature molecular dynamics simulations
confirm their stability and DFT calculations indicate that they are all
semiconductors. This idea broadens the scope of group V semiconductors and we
believe it can be extended to other type of 2D materials to obtain new
semiconductors with better properties for optoelectronic and electronic
applications.",1704.03756v1
2017-04-21,DFT analysis and FDTD simulation of CH3NH3PbI3-xClx mixed halide perovskite solar cells: role of halide mixing and light trapping technique,"Since perovskite solar cells have attracted a lot of attentions over the past
years, the enhancement of their optical absorption and current density are
among the basic coming challenges. For this reason, first, we have studied
structural and optical properties of organic-inorganic hybrid halide perovskite
CH3NH3PbI3 and the compounds doped by chlorine halogen CH3NH3PbI3-xClx in the
cubic phase by using density functional theory (DFT). Then, we investigate the
light absorption efficiency and optical current density of the single-junction
perovskite solar cell CH3NH3PbI3-xClx for the values (x=0,1,2,3) by utilizing
optical constants (n,k) resulted from these calculations. The results suggest
that increasing the amount of chlorine in the CH3NH3PbI3-xClx compound leads an
increase in bandgap energy, as well as a decrease in lattice constants and
optical properties like refractive index and extinction coefficient of the
structure. Also, the results obtained by simulation express that by taking
advantage of light trapping techniques of SiO2, a remarkable increase of light
absorption will be achieved to the magnitude of 83.13%, which is noticeable.",1704.06702v1
2017-04-25,Molecular De Novo Design through Deep Reinforcement Learning,"This work introduces a method to tune a sequence-based generative model for
molecular de novo design that through augmented episodic likelihood can learn
to generate structures with certain specified desirable properties. We
demonstrate how this model can execute a range of tasks such as generating
analogues to a query structure and generating compounds predicted to be active
against a biological target. As a proof of principle, the model is first
trained to generate molecules that do not contain sulphur. As a second example,
the model is trained to generate analogues to the drug Celecoxib, a technique
that could be used for scaffold hopping or library expansion starting from a
single molecule. Finally, when tuning the model towards generating compounds
predicted to be active against the dopamine receptor type 2, the model
generates structures of which more than 95% are predicted to be active,
including experimentally confirmed actives that have not been included in
either the generative model nor the activity prediction model.",1704.07555v2
2017-04-29,Resonant inelastic x-ray scattering operators for $t_{2g}$ orbital systems,"We derive general expressions for resonant inelastic x-ray scattering (RIXS)
operators for $t_{2g}$ orbital systems, which exhibit a rich array of
unconventional magnetism arising from unquenched orbital moments. Within the
fast collision approximation, which is valid especially for 4$d$ and 5$d$
transition metal compounds with short core-hole lifetimes, the RIXS operators
are expressed in terms of total spin and orbital angular momenta of the
constituent ions. We then map these operators onto pseudospins that represent
spin-orbit entangled magnetic moments in systems with strong spin-orbit
coupling. Applications of our theory to such systems as iridates and ruthenates
are discussed, with a particular focus on compounds based on $d^4$ ions with
Van Vleck-type nonmagnetic ground state.",1705.00215v2
2017-05-01,Tomonaga-Luttinger spin liquid in the spin-1/2 inequilateral diamond-chain compound K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$,"K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ is a highly one-dimensional spin-1/2
inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet
dimer excitations are observed in the inelastic neutron scattering spectra,
which is in excellent agreement with a theoretical prediction: a dimer-monomer
composite structure, where the dimer is caused by strong antiferromagnetic
(AFM) coupling and the monomer forms an almost isolated quantum AFM chain
controlling low-energy excitations. Moreover, muon spin rotation/relaxation
spectroscopy shows no long-range ordering down to 90~mK, which is roughly three
orders of magnitude lower than the exchange interaction of the quantum AFM
chain. K$_3$Cu$_3$AlO$_2$(SO$_4$)$_4$ is, thus, regarded as a compound that
exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to
the ground state.",1705.01158v2
2017-05-04,Ab initio study of sodium cointercalation with diglyme molecule into graphite,"The cointercalation of sodium with the solvent organic molecule into graphite
can resolve difficulty of forming the stage-I Na-graphite intercalation
compound, which is a predominant anode of Na-ion battery. To clarify the
mechanism of such cointercalation, we investigate the atomistic structure,
energetics, electrochemical properties, ion and electron conductance, and
charge transferring upon de/intercalation of the solvated Na-diglyme ion into
graphite with {\it ab initio} calculations. It is found that the
Na(digl)$_2$C$_n$ compound has the negatively lowest intercalation energy at
$n\approx$21, the solvated Na(digl)$_2$ ion diffuses fast in the interlayer
space, and their electronic conductance can be enhanced compared to graphite.
The calculations reveal that the diglyme molecules as well as Na atom donates
electrons to the graphene layer, resulting in the formation of ionic bonding
between the graphene layer and the moiety of diglyme molecule. This work will
contribute to the development of innovative anode materials for alkali-ion
battery applications.",1705.01673v1
2017-05-13,Interference Effect Between Neutron Direct and Resonance Capture Reactions For Neutron-Rich Nuclei,"Interference effect of neutron capture cross section between the compound and
direct processes is investigated. The compound process is calculated by
resonance parameters and the direct process by the potential mode. The
interference effect is tested for neutron-rich $^{82}$Ge and $^{134}$Sn nuclei
relevant to $r$-process and light nucleus $^{13}$C which is neutron poison in
the $s$-process and produces long-lived radioactive nucleus $^{14}$C
($T_{1/2}=5700$ y). The interference effects in those nuclei are significant
around resonances, and low energy region if $s$-wave neutron direct capture is
possible. Maxwellian averaged cross sections at $kT=30$ and $300$ keV are also
calculated, and the interference effect changes the Maxwellian averaged capture
cross section largely depending on resonance position.",1705.04848v1
2017-05-17,"Two-step nuclear reactions: The Surrogate Method, the Trojan Horse Method and their common foundations","In this Letter I argue that the Surrogate Method, used to extract the fast
neutron capture cross section on actinide target nuclei, which has important
practical application for the next generation of breeder reactors, and the
Trojan Horse Method employed to extract reactions of importance to nuclear
astrophysics, have a common foundation, the Inclusive Non-Elastic Breakup
(INEB)Theory. Whereas the Surrogate Method relies on the premise that the
extracted neutron cross section in a (d,p) reaction is predominantly a compound
nucleus one, the Trojan Horse Method, assumes a predominantly direct process
for the secondary reaction induced by the surrogate fragment. In general, both
methods contain both direct and compound contributions, and I show how theses
seemingly distinct methods are in fact the same but at different energies and
different kinematic regions. The unifying theory is the rather well developed
INEB theory.",1705.06305v1
2017-05-19,Survival Mediated Heavy Element Capture Cross Sections,"Formally, the cross section for producing a heavy evaporation residue,
{\sigma}EVR, in a fusion reaction can be written as. \begin{equation}
\sigma_{\rm EVR}(E)=\frac{\pi h^2}{2\mu E}\sum\limits_{\ell=0}^\infty
(2\ell+1)T(E,\ell)P_{\rm CN}(E,\ell)W_{\rm sur}(E,\ell), \end{equation} where E
is the center of mass energy, and T is the probability of the colliding nuclei
to overcome the potential barrier in the entrance channel and reach the contact
point. PCN is the probability that the projectile-target system will evolve
from the contact point to the compound nucleus. Wsur is the probability that
the compound nucleus will decay to produce an evaporation residue rather than
fissioning. However, one must remember that the Wsur term effectively sets the
allowed values of the spin, which in turn, restricts the values of the capture
and fusion cross sections. We point out the implications of this fact for
capture cross sections for heavy element formation reactions.",1705.07223v1
2017-05-24,Strongly Ideal Robust Weyl Semimetals in Cubic Symmetry with Spatial-Inversion Breaking,"We show that compounds in a family that possess time-reversal symmetry and
share a non-centrosymmetric cubic structure with the space group F-43m (No.
216) host robust ideal Weyl semi-metal fermions with desirable topologically
protected features. The candidates in this family are compounds with different
chemical formulas AB2, ABC, ABC2, and ABCD and their Fermi levels are
predominantly populated by nontrivial Weyl fermions. Symmetry of the system
requires that the Weyl nodes with opposite chirality are well separated in
momentum space. Adjacent Weyl points have the same chirality, thus these Weyl
nodes would not annihilate each other with respect to lattice perturbations. As
Fermi arcs and surface states connect Weyl nodes with opposite chirality, the
large separation of the latter in momentum space guarantees the appearance of
very long arcs and surface states. This work demonstrates the use of system
symmetry by first-principles calculations as a powerful recipe for discovering
new Weyl semi-metals with attractive features whose protected fermions may be
candidates of many applications.",1705.08782v1
2017-05-24,Magnetic-field-induced ordered phase in the chloro-bridged copper(II) dimer system [Cu2(apyhist)2Cl2](ClO4)2,"Specific heat and magnetization measurements of the compound
[Cu2(apyhist)2Cl2](ClO4)2, where apyhist =
(4-imidazolyl)ethylene-2-amino-1-ethylpyridine), were used to identify a
magnetic-field-induced long-range antiferromagnetic ordered phase at low
temperatures (T < 0.36 K) and magnetic fields (1.6 T < H < 5.3 T). This system
consists of a Schiff base copper(II) complex, containing chloro-bridges between
adjacent copper ions in a dinuclear arrangement, with an antiferromagnetic
intradimer interaction |Jintra|/kB = 3.65 K linked by an antiferromagnetic
coupling |Jinter|z/kB = 2.7 K. The magnetic-field-induced ordering behavior was
analyzed using the mean field approximation and Monte Carlo simulation results.
The obtained physical properties of the system are consistent with the
description of the ordered phase as a Bose-Einstein Condensation (BEC) of
magnetic excitations. We present the phase diagram of this compound, which
shows one of the lowest critical magnetic field among all known members of the
family of BEC quantum magnets.",1705.08879v1
2017-05-30,"High-pressure structural, elastic, and thermodynamic properties of zircon-type HoPO4 and TmPO4","Zircon-type HoPO4 and TmPO4 have been studied by single-crystal x-ray
diffraction and ab initio calculations. We report information on the influence
of pressure on the crystal structure, and on the elastic and thermodynamic
properties. The equation of state for both compounds is accurately determined.
We have also obtained information on the polyhedral compressibility which is
used to explain the anisotropic axial compressibility and the bulk
compressibility. Both compounds are ductile and more resistive to volume
compression than to shear deformation at all pressures. Furthermore, the
elastic anisotropy is enhanced upon compression. Finally, the calculations
indicate that the possible causes that make unstable the zircon structure are
mechanical instabilities and the softening of a silent B1u mode.",1705.10721v1
2018-07-02,Coevolutionary search for optimal materials in the space of all possible compounds,"Over the past decade, evolutionary algorithms, data mining, and other methods
showed great success in solving the main problem of theoretical
crystallography: finding the stable structure for a given chemical composition.
Here we develop a method that addresses the central problem of computational
materials science: the prediction of material(s), among all possible
combinations of all elements, that possess the best combination of target
properties. This nonempirical method combines our new coevolutionary approach
with the carefully restructured ""Mendelevian"" chemical space, energy filtering,
and Pareto optimization to ensure that the predicted materials have optimal
properties and a high chance to be synthesizable. The first calculations,
presented here, illustrate the power of this approach. In particular, we find
that diamond (and its polytypes, including lonsdaleite) are the hardest
possible materials and that bcc-Fe has the highest zero-temperature
magnetization among all possible compounds.",1807.00854v2
2018-07-04,Spin Waves in Detwinned BaFe$_2$As$_2$,"Understanding magnetic interactions in the parent compounds of
high-temperature superconductors forms the basis for determining their role for
the mechanism of superconductivity. For parent compounds of iron pnictide
superconductors such as $A$Fe$_2$As$_2$ ($A=$ Ba, Ca, Sr), although spin
excitations have been mapped out throughout the entire Brillouin zone (BZ),
measurements were carried out on twinned samples and did not allow for a
conclusive determination of the spin dynamics. Here we use inelastic neutron
scattering to completely map out spin excitations of $\sim$100\% detwinned
BaFe$_2$As$_2$. By comparing observed spectra with theoretical calculations, we
conclude that the spin excitations can be well described by an itinerant model
with important contributions from electronic correlations.",1807.01471v1
2018-07-10,Physical properties of noncentrosymmetric tungsten and molybdenum aluminides,"A lack of spatial inversion symmetry gives rise to a variety of
unconventional physics, from noncollinear order and Skyrmion lattice phases in
magnetic materials to topologically-protected surface states in certain band
insulators, to mixed-parity pairing states in superconductors. The search for
exotic physics in such materials is largely limited by a lack of candidate
materials, and often by difficulty in obtaining crystals. Here, we report the
single crystal growth and physical properties of the noncentrosymmetric
tungsten aluminide cage compounds Al$_4$W and Al$_5$W, alongside related
molybdenum aluminides in which spin-orbit coupling should be significantly
weaker. All compounds are nonmagnetic metals. Their high conductivities suggest
the opportunity to find superconductivity at lower temperatures, while the
limits we can place on their transition temperatures suggest that any
superconductivity may be expected to exhibit significant parity mixing.",1807.03476v2
2018-07-10,Impact of $e-e$ interactions on the superfluid density of dirty superconductors,"Landau's theory of the Fermi liquid is adapted to analyze the impact of
electron-electron ($e-e$) interactions on the deficit of the superfluid density
$\rho_{s0}=\rho_s(T=0)$ in dirty superconducting electron systems in which the
damping $\gamma$ of single-particle excitations exceeds the zero temperature
BCS gap $\Delta_0$. In the dirty strong-coupling limit $\gamma/\Delta_0\gg
1,m^*/m_e\gg 1$, the formula derived for $\rho_{s0}$ is shown to coincide with
the well-known empirical Uemura relation provided pair-breaking contributions
are nonexistent. The roles of the crystal lattice and magnetic pair-breaking
effects in the observed decline of the zero-temperature superfluid density
$\rho_{s0}$ in overdoped LSCO compounds are also discussed. Our method is also
applied to elucidation of results from the pioneering experimental studies
performed recently by Bozovi\`c and collaborators in overdoped LSCO compounds.",1807.03866v3
2018-07-16,Information Theoretic Model Predictive Control on Jump Diffusion Processes,"In this paper we present an information theoretic approach to stochastic
optimal control problems for systems with compound Poisson noise. We generalize
previous work on information theoretic path integral control to discontinuous
dynamics with compound Poisson noise and develop an iterative model predictive
control (MPC) algorithm using importance sampling. The proposed algorithm is
parallelizable and when implemented on a Graphical Processing Unit (GPU) can
run in real time. We test the performance of the proposed algorithm in
simulation for two control tasks using a cartpole system and a quadrotor. Our
simulations demonstrate improved performance of the new scheme and indicate the
importance of incorporating the statistical characteristics of stochastic
disturbances in the computation of the stochastic optimal control policies.",1807.06108v3
2018-07-17,On the Reactivity of Hydrogen-Helium and Hydrogen-Nitrogen at High Pressures,"Through a series of Raman spectroscopy studies, we investigate the behaviour
of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across wide
ranging concentrations. We find that there is no evidence of chemical
association, miscibility, nor any demixing of hydrogen and helium in the solid
state up to pressures of 250 GPa at 300 K. In contrast, we observe the
formation of concentration-dependent N$_2$-H$_2$ van der Waals solids, which
react to form N-H bonded compounds above 50 GPa. Through this combined study,
we can demonstrate that the recently claimed chemical association of H$_2$-He
can be attributed to significant N$_2$ contamination and subsequent formation
of N$_2$-H$_2$ compounds.",1807.06227v1
2018-07-17,Chiral spin-order in some purported Kitaev spin-liquid compounds,"We examine recent magnetic torque measurements in two compounds,
$\gamma$-Li$_2$IrO$_3$ and RuCl$_3$, which have been discussed as possible
realizations of the Kitaev model. The analysis of the reported discontinuity in
torque, as an external magnetic field is rotated across the $c-$axis in both
crystals, suggests that they have a translationally-invariant chiral spin-order
of the from $<{\bf S}_i. ({\bf S}_j ~\times ~ {\bf S}_k)> \ne 0$ in the ground
state and persisting over a very wide range of magnetic field and temperature.
An extra-ordinary $|B|B^2$ dependence of the torque for small fields, beside
the usual $B^2$ part, is predicted due to the chiral spin-order, and found to
be consistent with experiments upon further analysis of the data. Other
experiments such as inelastic scattering and thermal Hall effect and several
questions raised by the discovery of chiral spin-order, including its
topological consequences are discussed.",1807.06637v2
2018-07-18,"The pyrochlore Ho2Ti2O7: Synthesis, crystal growth and stoichiometry","We have investigated the effect of synthesis and growth conditions on the
magnetic, structural, and compositional properties of pyrochlore oxide holmium
titanate and demonstrate a method for growing high quality stoichiometric
single crystals. A series of polycrystalline samples with various contents of
Ti (-0.08 \leqslant x \leqslant 0.08, and nominal compositions of Ho2Ti2+xO7)
were synthesized at different temperatures, and characterized using powder
X-ray diffraction. The results show that synthesizing powders at a higher
temperature of 1500 {\deg}C yield single phase compounds. Ti deficient powders
showed an increase of lattice constant due to stuffing (Ho into Ti positions),
while Ti rich powders showed a decrease in lattice constant due to
anti-stuffing (Ti into Ho positions). A post annealing in O2 was found to be
necessary to accomplish the anti-stuffing process. Use of the conventional
floating zone (FZ) technique introduced Ti deficiency, stuffing, and oxygen
vacancies in the grown crystal. Growth of high structural quality and
stoichiometric single crystals of Ho2Ti2O7 by the traveling solvent floating
zone (TSFZ) is reported. AC susceptibility measurements revealed that the
stoichiometric crystal shows a higher ice freezing temperature, indicating that
crystal quality and stoichiometry play a key role on low temperature spin ice
properties of this compound.",1807.06788v1
2018-07-21,Optimal Dividend of Compound Poisson Process under a Stochastic Interest Rate,"In this paper we assume the insurance wealth process is driven by the
compound Poisson process. The discounting factor is modelled as a geometric
Brownian motion at first and then as an exponential function of an integrated
Ornstein-Uhlenbeck process. The objective is to maximize the cumulated value of
expected discounted dividends up to the time of ruin. We give an explicit
expression of the value function and the optimal strategy in the case of
interest rate following a geometric Brownian motion. For the case of the
Vasicek model, we explore some properties of the value function. Since we can
not find an explicit expression for the value function in the second case, we
prove that the value function is the viscosity solution of the corresponding
HJB equation.",1807.08081v1
2018-07-22,Itinerant-localized crossover and orbital dependent correlations for 4$f$ electrons in cerium-based ternary 122 compounds,"The electronic structures of cerium-based ternary 122 compounds
Ce$M_{2}$Si$_{2}$, where $M =$ Ru, Rh, Pd, and Ag, are investigated
systematically by using the density functional theory in combination with the
single-site dynamical mean-field theory. The momentum-resolved spectral
functions, total and 4$f$ partial density of states, self-energy functions, and
valence state fluctuations are calculated. The obtained results are in good
accord with the available experimental data. It is suggested that, upon
increasing atomic number from Ru to Ag, the 4$f$ electrons should become
increasingly localized. An itinerant-localized crossover for 4$f$ electrons
driven by chemical pressure may emerge when $M$ changes from Pd to Ag.
Particularly, according to the low-frequency behaviors of 4$f$ self-energy
functions, we identify an orbital selective 4$f$ insulating state in
CeAg$_{2}$Si$_{2}$, which is totally unexpected.",1807.08327v1
2018-07-24,Growth and characterization of HgBa2CaCu2O6+d and HgBa2Ca2Cu3O8+d crystals,"We report the successful synthesis of single-crystalline cuprate
superconductors HgBa$_{2}$CaCu$_{2}$O$_{6+\delta}$ and
HgBa$_{2}$Ca$_{2}$Cu$_{3}$O$_{8+\delta}$. These compounds are well-known for
their high optimal superconducting critical temperatures of $T_\mathrm{c}$ =
128 K and 134 K at ambient pressure, respectively, and for their challenging
synthesis. Using a conventional quartz-tube encapsulation method and a
two-layer encapsulation method that utilizes custom-built high-pressure
furnaces, we are able to grow single crystals with linear dimensions up to
several millimeters parallel to the CuO$_2$ planes. Extended post-growth
anneals are shown to lead to sharp superconducting transitions, indicative of
high macroscopic homogeneity. X-ray diffraction and polarized Raman
spectroscopy are identified as viable methods to resolve the seemingly
unavoidable inter-growth of the two compounds. Our work helps to remove
obstacles toward the study of these model cuprate systems with experimental
probes that require sizable high-quality crystals.",1807.08954v1
2018-07-24,Spin excitations in a 4f-3d heterodimer on MgO,"We report on the magnetic properties of HoCo dimers as a model system for the
smallest intermetallic transition metal-lanthanide compound. The dimers are
adsorbed on ultrathin MgO(100) films grown on Ag(100). New for $4f$ elements,
we detect inelastic excitations with scanning tunneling microscopy and prove by
their behaviour in applied magnetic field that they are spin-excitations. In
combination with density functional theory and spin Hamiltonian analysis we
determine the magnetic level distribution, as well as sign and magnitude of the
exchange interaction between the two atoms. In contrast to typical $4f-3d$ bulk
compounds, we find ferromagnetic coupling in the dimer.",1807.09316v1
2018-07-25,Bond disordered spin liquid and the honeycomb iridate H$_3$LiIr$_2$O$_6$ $-$ abundant low energy density of states from random Majorana hopping,"The 5d-electron honeycomb compound H$_3$LiIr$_2$O$_3$ [K. Kitagawa $et$
$al.$, Nature 554, 341-345 (2018)] exhibits an apparent quantum spin liquid
(QSL) state. In this intercalated spin-orbital compound, a remarkable pile up
of low-energy states was experimentally observed in specific heat and nuclear
magnetic (NMR) spin relaxation. We show that a bond disordered Kitaev model can
naturally account for this phenomenon, suggesting that disorder plays an
essential role in its theoretical description. In the exactly soluble Kitaev
model, we obtain, via spin fractionalization, a random bipartite hopping
problem of Majorana fermions in a random flux background. This has a divergent
low-energy density of states (DOS) of the required power-law form $N(E)\propto
E^{-\nu}$ with a drifting exponent which takes on the value $\nu \approx 1/2$
for relatively strong bond disorder. Breaking time reversal symmetry (TRS)
removes the divergence of the DOS, as does applying a magnetic field in
experiment. We discuss the implication of our scenario for future experiments
and its broader implications.",1807.09670v2
2018-07-28,"Polarization discontinuity driven two dimensional electron gas at A$_2$Mo$_3$O$_8$/B$_2$Mo$_3$O$_8$ (A, B : Zn,Mg,Cd) interfaces","We prospose a novel heterostructure system consisting of compounds with
chemical formula A$_2$Mo$_3$O$_8$ (A, B : Zn,Mg,Cd) that can host a two
dimensional electron/hole gas (2DEG/2DHG). We study spontaneous polarization
and piezoelectric properties of these compounds using first principles methods
and Berry phase approach. We show that these kind of heterostructures are very
stable due to extreamly low interfacial strain. The formation of a 2DEG/2DHG
has been investigated in case of Zn$_2$Mo$_3$O$_8$/Mg$_2$Mo$_3$O$_8$ and
polarization discontinuity has been found to be driving mechanism. The sheet
carrier densities and charge localization in these kind of heterostrcutures
have been found to be of the same order of magnitude in other well known system
that hosts 2DEG through similar mechanism, such as AlN/Al(Ga)N or ZnO/Zn(Mg)O.
In addition to conventional applications of a 2DEG, these materials hold
promise to exciting pioneering technolgy such as piezo-phototronics using solar
radiation, as they are also capable of absorbing a significant fraction of it
due to low optical gap of $\sim$ 2 eV",1807.10896v1
2018-07-30,Bayesian Calibration using Different Prior Distributions: an Iterative Maximum A Posteriori Approach for Radio Interferometers,"In this paper, we aim to design robust estimation techniques based on the
compound-Gaussian (CG) process and adapted for calibration of radio
interferometers. The motivation beyond this is due to the presence of outliers
leading to an unrealistic traditional Gaussian noise assumption. Consequently,
to achieve robustness, we adopt a maximum a posteriori (MAP) approach which
exploits Bayesian statistics and follows a sequential updating procedure here.
The proposed algorithm is applied in a multi-frequency scenario in order to
enhance the estimation and correction of perturbation effects. Numerical
simulations assess the performance of the proposed algorithm for different
noise models, Student's t, K, Laplace, Cauchy and inverse-Gaussian
compound-Gaussian distributions w.r.t. the classical non-robust Gaussian noise
assumption.",1807.11382v1
2018-10-03,First-order phase transitions in the Kuramoto model with compact bimodal frequency distributions,"The Kuramoto model of a network of coupled phase oscillators exhibits a
first-order phase transition when the distribution of natural frequencies has a
finite flat region at its maximum. First-order phase transitions including
hysteresis and bistability are also present if the frequency distribution of a
single network is bimodal. In this study we are interested in the interplay of
these two configurations and analyze the Kuramoto model with compact bimodal
frequency distributions in the continuum limit. As of yet, a rigorous analytic
treatment has been elusive. By combining Kuramoto's self-consistency approach,
Crawford's symmetry considerations, and exploiting the Ott-Antonsen ansatz
applied to a family of rational distribution functions that converge towards
the compact distribution, we derive a full bifurcation diagram for the system's
order parameter dynamics. We show that the route to synchronization always
passes through a standing wave regime when the bimodal distribution is
compounded by two unimodal distributions with compact support. This is in
contrast to a possible transition across a region of bistability when the two
compounding unimodal distributions have infinite support.",1810.01673v1
2018-10-03,"Nuclear and Magnetic Structures of the Frustrated Quantum Antiferromagnet Barlowite, Cu$_{4}$(OH)$_{6}$FBr","Barlowite, Cu$_{4}$(OH)$_{6}$FBr, has attracted much attention as the parent
compound of a new series of quantum spin liquid candidates,
Zn$_{x}$Cu$_{4-x}$(OH)$_{6}$FBr. While it is known to undergo a magnetic phase
transition to a long-range ordered state at $T_{N} = 15$ K, there is still no
consensus over either its nuclear or magnetic structures. Here, we use
comprehensive powder neutron diffraction studies on deuterated samples of
barlowite to demonstrate that the only space group consistent with the observed
nuclear and magnetic diffraction at low-temperatures is the orthorhombic $Pnma$
space group. We furthermore conclude that the magnetic intensity at $T < T_{N}$
is correctly described by the $Pn^\prime m^\prime a$ magnetic space group,
which crucially allows the ferromagnetic component observed in previous
single-crystal and powder magnetisation measurements. As such, the magnetic
structure of barlowite resembles that of the related material clinoatacamite,
Cu$_{4}$(OH)$_{6}$Cl$_{2}$, the parent compound of the well-known quantum spin
liquid candidate hebertsmithite, ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$.",1810.01684v1
2018-10-05,Thermal analysis and crystal growth of doped Nb$_2$O$_5$,"The systems Nb$_2$O$_5$-Ta$_2$O$_5$ and Nb$_2$O$_5$-V$_2$O$_5$ were
investigated using thermal analysis, X-ray powder diffraction and thermodynamic
simulations. Solid solution formation is possible for both systems;
furthermore, both contain one intermediate compound, VNb$_9$O$_{25}$ or
Ta$_2$Nb$_4$O$_{15}$, respectively. Phase relationships for pure
niobium(V)-oxide and tantalum(V)-oxide were studied under ambient pressure. It
was found that both compounds can occur in two stable solid modifications. For
niobium(V)-oxide this are the monoclinic high-temperature modification
(H-Nb$_2$O$_5$) and an orthorhombic low-temperature modification
(T-Nb$_2$O$_5$) and for tantalum(V)-oxide a tetragonal high-temperature form
($\alpha$-Ta$_2$O$_5$) and an orthorhombic low-temperature form
($\beta$-Ta$_2$O$_5$). Based on these results, crystal growth experiments with
various compositions from both systems were carried out using the optical
floating zone (OFZ) technique.",1810.02598v2
2018-10-12,Ternary Nitride Semiconductors in the Rocksalt Crystal Structure,"Inorganic nitrides with wurtzite crystal structures are well-known
semiconductors used in optoelectronic devices. In contrast, rocksalt-based
nitrides are known for their metallic and refractory properties. Breaking this
dichotomy, here we report on ternary nitride semiconductors with rocksalt
crystal structures, remarkable optoelectronic properties, and the general
chemical formula Mg$_{x}$TM$_{1-x}$N (TM=Ti, Zr, Hf, Nb). These compounds form
over a broad metal composition range and our experiments show that Mg-rich
compositions are nondegenerate semiconductors with visible-range optical
absorption onsets (1.8-2.1 eV). Lattice parameters are compatible with growth
on a variety of substrates, and epitaxially grown MgZrN$_{2}$ exhibits
remarkable electron mobilities approaching 100 cm$^{2}$V$^{-1}$s$^{-1}$. Ab
initio calculations reveal that these compounds have disorder-tunable optical
properties, large dielectric constants and low carrier effective masses that
are insensitive to disorder. Overall, these experimental and theoretical
results highlight Mg$_{G-3}$TMN$_{G-2}$ rocksalts as a new class of
semiconductor materials with promising properties for optoelectronic
applications.",1810.05668v1
2018-10-17,Fermi volume evolution and crystal field excitations in heavy-fermion compounds probed by time-domain terahertz spectroscopy,"We measure the quasiparticle weight in the heavy-fermion compound
CeCu$_{6-x}$Au$_{x}$ ($x=0,\ 0.1$) by time-resolved THz spectroscopy for
temperatures from 2 up to 300\,K. This method distinguishes contributions from
the heavy Kondo band and from the crystal-electric-field satellite bands by
different THz response delay times. We find that the formation of heavy bands
is controlled by an exponentially enhanced, high-energy Kondo scale once the
crystal-electric-field states become thermally occupied. We corroborate these
observations by temperature-dependent dynamical mean-field calculations for the
multi-orbital Anderson lattice model and discuss consequences for quantum
critical scenarios.",1810.07412v2
2018-10-17,Phase separation and effect of strain on magnetic properties of Mn$_3$Ga$_{1-x}$Sn$_x$C,"While the unit cell volume of compounds belonging to the
Mn$_3$Ga$_{1-x}$Sn$_x$C, (0 $ \le x \le $ 1) series shows a conformity with
Vegard's law, their magnetic and magnetocaloric properties behave differently
from those of parent compounds Mn$_3$GaC and Mn$_3$SnC. A correlation between
the observed magnetic properties and underlying magnetic and local structure
suggests that replacing Ga atoms by larger atoms of Sn results in the formation
of Ga-rich and Sn-rich clusters. As a result, even though the long range
structure appears to be cubic, Mn atoms find themselves in two different local
environments. The packing of these two different local structures into a single
global structure induces tensile/compressive strains on the Mn$_{6}$C
functional unit and is responsible for the observed magnetic properties across
the entire solid solution range.",1810.07486v1
2018-10-20,Realization of anisotropic compass model on the diamond lattice of Cu$^{2+}$ in CuAl$_2$O$_4$,"Spin-orbit (SO) Mott insulators are regarded as a new paradigm of magnetic
materials, whose properties are largely influenced by SO coupling and featured
by highly anisotropic bond-dependent exchange interactions between the
spin-orbital entangled Kramers doublets, as typically manifested in $5d$
iridates. Here, we propose that a very similar situation can be realized in
cuprates when the Cu$^{2+}$ ions reside in a tetrahedral environment, like in
spinel compounds. Using first-principles electronic structure calculations, we
construct a realistic model for the diamond lattice of the Cu$^{2+}$ ions in
CuAl$_2$O$_4$ and show that the magnetic properties of this compound are
largely controlled by anisotropic compass-type exchange interactions that
dramatically modify the magnetic ground state by lifting the spiral spin-liquid
degeneracy and stabilizing a commensurate single-$\boldsymbol{q}$ spiral.",1810.08818v2
2018-10-25,One-Shot Hierarchical Imitation Learning of Compound Visuomotor Tasks,"We consider the problem of learning multi-stage vision-based tasks on a real
robot from a single video of a human performing the task, while leveraging
demonstration data of subtasks with other objects. This problem presents a
number of major challenges. Video demonstrations without teleoperation are easy
for humans to provide, but do not provide any direct supervision. Learning
policies from raw pixels enables full generality but calls for large function
approximators with many parameters to be learned. Finally, compound tasks can
require impractical amounts of demonstration data, when treated as a monolithic
skill. To address these challenges, we propose a method that learns both how to
learn primitive behaviors from video demonstrations and how to dynamically
compose these behaviors to perform multi-stage tasks by ""watching"" a human
demonstrator. Our results on a simulated Sawyer robot and real PR2 robot
illustrate our method for learning a variety of order fulfillment and kitchen
serving tasks with novel objects and raw pixel inputs.",1810.11043v1
2018-10-26,Mechanochemical Synthesis of the Lead-Free Double Perovskite Cs2[AgIn]Br6 and its Optical Properties,"Hitting hard on the binary halides yields in the formation of Cs2[AgIn]Br6.
The lead-free double perovskite marks, although not usable itself, a further
step forward in finding sustainable and durable perovskite materials for
photovoltaic applications. Cs2[AgIn]Br6 is one of the prominent examples of
double perovskites materials that have been suggested to circumvent the use of
lead compounds in perovskite solar cells. We herein report the successful
synthesis of the material using a mechanochemical approach. It crystallizes in
an elpasolite-type structure, an ordered perovskite superstructure, with a cell
parameter of a = 11.00 {\AA}. However, the compound exhibits a relatively large
optical bandgap of 2.36 eV and is unstable under illumination, which impedes
its use as solar absorber material at this early stage. Still, substitution of
lead and the potential of this synthesis method are promising as well as the
fruitful combination of theoretical considerations with experimental materials
discovery.",1810.11330v1
2018-10-31,Evidence of partial gap opening and Ce-site dilution effects in a heavy fermion compound CeNiGe2,"We report the results of magnetization, non-linear dc susceptibility,
electrical transport, and heat capacity measurements on Y-substituted heavy
fermion CeNiGe2. Investigations are carried out on the compounds CeNiGe2,
Ce0.9Y0.1NiGe2, Ce0.8Y0.2NiGe2 and Ce0.6Y0.4NiGe2. It is observed that with the
increase in Y-concentration, the magnetic ordering temperature decreases. For
CeNiGe2, below ordering temperature Arrott plots suggest the presence of spin
density wave (SDW). Third and fifth order dc susceptibility indicates magnetic
instability which possibly leads to partial gap opening resulting in the
observation of SDW. These observations are further investigated through
resistivity and heat capacity measurements which also point toward partial gap
opening in CeNiGe2. Interestingly, with the increase in Y-substitution, it is
noted that the gap opening is suppressed and also shifted towards lower
temperature. Moreover, our investigations reveal absence of non-Fermi liquid
behavior or zero field quantum critical point even after 40% dilution of
Ce-site.",1810.13131v1
2019-01-01,Spontaneous non-stoichiometry and ordering of metal vacancies in degenerate insulators,"We point to a class of materials representing an exception to the Daltonian
view that compounds maintain integer stoichiometry at low temperatures, because
forming stoichiometry-violating defects cost energy. We show that carriers in
the conduction band (CB) of degenerate insulators in Ca-Al-O, Ag-Al-O, or
Ba-Nb-O systems can cause a self-regulating instability, whereby cation
vacancies form exothermically because a fraction of the free carriers in the CB
decay into the hole states formed by such vacancies, and this negative
electron-hole recombination energy offsets the positive energy associated with
vacancy bond breaking. This Fermi level-induced spontaneous non-stoichiometry
can lead to the formation of crystallographically ordered vacancy compounds
(OVCs), explaining the previously peculiar occurrence of unusual atomic
sequences such as BalNbmOn with l:m:n ratios of 1:2:6, 3:5:15, or 9:10:30. This
work has general ramifications as the degenerate insulators have found growing
interests in many fields ranging from transparent conductors to electrides that
are electron donating promotors for catalyst.",1901.00183v1
2019-01-03,"The Chemical Space of B, N-substituted Polycyclic Aromatic Hydrocarbons: Combinatorial Enumeration and High-Throughput First-Principles Modeling","Combinatorial introduction of heteroatoms in the two-dimensional framework of
aromatic hydrocarbons opens up possibilities to design compound libraries
exhibiting desirable photovoltaic and photochemical properties. Exhaustive
enumeration and first-principles characterization of this chemical space
provide indispensable insights for rational compound design strategies. Here,
for the smallest seventy-seven Kekulean-benzenoid polycyclic systems, we reveal
combinatorial substitution of C atom pairs with the isosteric and isoelectronic
B, N pairs to result in 7,453,041,547,842 (7.4 tera) unique molecules. We
present comprehensive frequency distributions of this chemical space, analyze
trends and discuss a symmetry-controlled selectivity manifestable in synthesis
product-yield. Furthermore, by performing high-throughput ab initio density
functional theory calculations of over thirty-three thousand (33k)
representative molecules, we discuss quantitative trends in the structural
stability and inter-property relationships across heteroarenes. Our results
indicate a significant fraction of the 33k molecules to be electronically
active in the 1.5-2.5 eV region, encompassing the most intense region of the
solar spectrum, indicating their suitability as potential light-harvesting
molecular components in photo-catalyzed solar cells.",1901.00649v3
2019-01-04,Intermultiplet transitions and magnetic long-range order in Sm-based pyrochlores,"We present bulk and neutron scattering measurements performed on the
isotopically enriched $^{154}\mathrm{Sm_2Ti_2O_7}$ and
$^{154}\mathrm{Sm_2Sn_2O_7}$ samples. Both compounds display sharp heat
capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron
scattering measurements are employed to determine the crystalline electric
field (CEF) level scheme, which includes transitions between the ground-state
and first excited $J$ multiplets of the $\mathrm{Sm}^{3+}$ ion. To further
validate those results, the single-ion magnetic susceptibility of the compounds
is calculated and compared with the experimental DC-susceptibility measured in
low applied magnetic fields. It is demonstrated that the inclusion of
intermultiplet transitions in the CEF analysis is fundamental to the
understanding of the intermediate and, more importantly, low temperature
magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity
anomaly is shown to correspond to the onset of an all-in-all-out long-range
order in the stannate sample, while in the titanate a dipolar long-range order
can be only indirectly inferred.",1901.00980v1
2019-01-04,Structure-Property Relationship in Layered BaMn2Sb2 and Ba2Mn3Sb2O2,"Layered transition-metal compounds have received great attention owing to
their novel physical properties. Here, we present the structural, electronic,
thermal, and magnetic properties of BaMn2Sb2 and Ba2Mn3Sb2O2 single crystals,
both with the layered structure analogous to high-temperature superconductors.
While the Mn moment in the MnSb4 tetrahedral environment forms G-type
antiferromagnetic (AFM) ordering in both BaMn2Sb2 (TN1~443 K) and Ba2Mn3Sb2O2
(TN1~314 K), a short-range AFM order is found in the intercalated MnO2 layer at
a much lower temperature (TN2~60 K) in Ba2Mn3Sb2O2. The directions of the
ordered moments in these two magnetic sub-lattices of Ba2Mn3Sb2O2 are
perpendicular to each other, even though the system is electrically conductive.
This indicates that the large magnetic moments in these compounds are highly
localized, leading to negligible coupling between MnSb4 and MnO2 layers in
Ba2Mn3Sb2O2. These findings provide an insight into the
structure-magnetism-based design principle for new superconductors.",1901.01320v1
2019-01-10,"Internal conversion and intersystem crossing pathways in UV excited, isolated uracils and their implications in prebiotic chemistry","The photodynamic properties of molecules determine their ability to survive
in harsh radiation environments. As such, the photostability of heterocyclic
aromatic compounds to electromagnetic radiation is expected to have been one of
the selection pressures influencing the prebiotic chemistry on early Earth. In
the present study, the gas-phase photodynamics of uracil, 5-methyluracil
(thymine) and 2-thiouracil -- three heterocyclic compounds thought to be
present during this era -- are assessed in the context of their recently
proposed intersystem crossing pathways that compete with internal conversion to
the ground state. Specifically, time-resolved photoelectron spectroscopy
measurements evidence femtosecond to picosecond timescales for relaxation of
the singlet 1$\pi\pi$* and 1n$\pi$* states as well as for intersystem crossing
to the triplet manifold. Trapping in the excited triplet state and intersystem
crossing back to the ground state are investigated as potential factors
contributing to the susceptibility of these molecules to ultraviolet
photodamage.",1901.03234v1
2019-01-13,Superconductivity in sodalite-like yttrium hydride clathrates,"We report ab-initio calculations of the superconducting properties of two
high-Tc sodalite-like clathrate yttrium hydrides, YH6 and YH10, within the
fully anisotropic ME theory, including Coulomb corrections. For both compounds
we find almost isotropic superconducting gaps, resulting from a uniform
distribution of the electron-phonon coupling over phonon modes and electronic
states of mixed Y and H character. The Coulomb screening is rather weak,
resulting in a Morel-Anderson pseudopotential mu*= 0:11, at odds with claims of
unusually large Tc in lanthanum hydrides. The corresponding critical
temperatures at 300 GPa exceed room temperature (Tc = 290 K and 310 K for YH6
and YH10), in agreement with a previous isotropic-gap calculation. The
different response of these two compounds to external pressure, along with a
comparison to low-Tc superconducting YH3, may inspire strategies to improve the
superconducting properties of this class of hydrides.",1901.04001v1
2019-01-15,Continuum damping effects in nuclear collisions associated with twisted boundary conditions,"The time-dependent Skyrme Hartree-Fock calculations have been performed to
study $^{24}$Mg +$^{24}$Mg collisions. The twisted boundary conditions, which
can avoid finite box-size effects of the employed 3D coordinate space, have
been implemented. The prolate deformed $^{24}$Mg has been set to different
orientations to study vibrations and rotations of the compound nucleus
$^{48}$Cr. Our time evolution results show continuum damping effects associated
with the twist-averaged boundary condition play a persistent role after the
fusion stage. In particular, a rotational damping in continuum is presented in
calculations of both twist-averaged and absorbing boundary conditions, in which
damping widths can be clearly extracted. It is unusual that the rotating
compound nucleus in continuum evolves towards spherical but still has a
considerable angular momentum.",1901.04736v2
2019-01-20,On the magnetic phase diagram of a sigma-phase Fe47Re53 compound in the H-T plane,"Sigma-phase Fe47Re53 compound was investigated by means of in-field DC and AC
magnetization measurements. Field cooled, MFC, and zero-field cooled, MZFC, DC
magnetization curves were recorded in the magnetic field, H, up to 1000 Oe. AC
magnetization measurements were performed at the constant frequency of 1465 Hz
in the field up to H=500 Oe. Both types of measurements gave evidence in favor
of a re-entrant character of magnetism in the studied sample. Based on
characteristic temperatures determined from the measurements magnetic phase
diagrams have been outlined in the H-T plane. The diagrams are similar but not
identical. The main difference is that in the diagram constructed based on the
DC data there is an intermediate antiferromagnetic-like phase which is absent
in the AC diagram. Furthermore, the border lines (irreversibility, cross-over
and Curie temperature) follow the power law but with correspondingly different
exponents. The studied sample was also characterized by determining the effect
of H on the degree of irreversibility and that of frustration.",1901.06667v1
2019-01-21,Ferromagnetic Kondo lattice behavior in Ce11Pd4In9,"We report on the low-temperature physical properties of a novel compound
Ce$_{11}$Pd$_4$In$_9$ that crystallizes with the orthorhombic
Nd$_{11}$Pd$_4$In$_9$-type crystal structure (space group $Cmmm$). The compound
exhibits ferromagnetic ordering at $T_{\rm {C}}$ = 18.6 K and an order-order
transition at $T_{\rm {t}}$ $\sim$~1.6 K, as inferred from the low-temperature
magnetic susceptibility, heat capacity and electrical resistivity data. In the
paramagnetic region, the electrical transport in Ce$_{11}$Pd$_4$In$_9$ is
dominated by Kondo effect. Below $T_{\rm {C}}$, a distinct contribution due to
ferromagnetic spin waves dominates the electrical resistivity data, while at
the lowest temperatures, the electrical transport and thermodynamic properties
are governed by strong electron-electron correlations. The features observed
conjointly hint at strongly correlated ground state in Ce$_{11}$Pd$_4$In$_9$ .",1901.06888v1
2019-01-21,Chemical Names Standardization using Neural Sequence to Sequence Model,"Chemical information extraction is to convert chemical knowledge in text into
true chemical database, which is a text processing task heavily relying on
chemical compound name identification and standardization. Once a systematic
name for a chemical compound is given, it will naturally and much simply
convert the name into the eventually required molecular formula. However, for
many chemical substances, they have been shown in many other names besides
their systematic names which poses a great challenge for this task. In this
paper, we propose a framework to do the auto standardization from the
non-systematic names to the corresponding systematic names by using the
spelling error correction, byte pair encoding tokenization and neural sequence
to sequence model. Our framework is trained end to end and is fully
data-driven. Our standardization accuracy on the test dataset achieves 54.04%
which has a great improvement compared to previous state-of-the-art result.",1901.07003v1
2019-01-22,"Energy, phonon, and dynamic stability criteria of 2d materials","First-principles calculations have become a powerful tool to exclude the
Edisonian approach in search of novel 2d materials. However, no universal
first-principles criteria to examine the realizability of hypothetical 2d
materials have been established in the literature yet. Because of this, and
since the calculations are always performed in an artificial simulation
environment, one can unintentionally study compounds that do not exist in the
experiments. Although investigations of physics and chemistry of unrealizable
materials can provide some fundamental knowledge, the discussion of their
applications can mislead experimentalists for years and increase the gap
between experimental and theoretical research. By analyzing energy convex hull,
phonon spectra, and structure evolution during ab initio molecular dynamics
simulations for a range of synthesized and recently proposed 2d materials, we
construct energy, phonon, and dynamic stability filters which need to be
satisfied before proposing novel 2d compounds. We demonstrate the power of the
suggested filters for several selected 2d systems, revealing that some of them
cannot be ever realized experimentally.",1901.07202v2
2019-01-26,Efficient Toxicity Prediction via Simple Features Using Shallow Neural Networks and Decision Trees,"Toxicity prediction of chemical compounds is a grand challenge. Lately, it
achieved significant progress in accuracy but using a huge set of features,
implementing a complex blackbox technique such as a deep neural network, and
exploiting enormous computational resources. In this paper, we strongly argue
for the models and methods that are simple in machine learning characteristics,
efficient in computing resource usage, and powerful to achieve very high
accuracy levels. To demonstrate this, we develop a single task-based chemical
toxicity prediction framework using only 2D features that are less compute
intensive. We effectively use a decision tree to obtain an optimum number of
features from a collection of thousands of them. We use a shallow neural
network and jointly optimize it with decision tree taking both network
parameters and input features into account. Our model needs only a minute on a
single CPU for its training while existing methods using deep neural networks
need about 10 min on NVidia Tesla K40 GPU. However, we obtain similar or better
performance on several toxicity benchmark tasks. We also develop a cumulative
feature ranking method which enables us to identify features that can help
chemists perform prescreening of toxic compounds effectively.",1901.09240v1
2019-01-29,Local orbital degeneracy lifting as a precursor to an orbital-selective Peierls transition,"Fundamental electronic principles underlying all transition metal compounds
are the symmetry and filling of the $d$-electron orbitals and the influence of
this filling on structural configurations and responses. Here we use a
sensitive local structural technique, x-ray atomic pair distribution function
analysis, to reveal the presence of fluctuating local-structural distortions at
high temperature of one such compound, \cis . We show that this hitherto
overlooked fluctuating symmetry lowering is electronic in origin and will
significantly modify the energy-level spectrum and electronic and magnetic
properties. The explanation is a local, fluctuating, orbital-degeneracy-lifted
state. The natural extension of our result would be that this phenomenon is
likely to be widespread amongst diverse classes of partially filled nominally
degenerate d-electron systems, with potentially broad implications for our
understanding of their properties.",1901.10104v2
2019-04-05,Hydrocarbons under pressure: phase diagrams and surprising new compounds in the C-H system,"Understanding the high-pressure behavior of C-H system is of great importance
due to its key role in organic, bio-, petroleum and planetary chemistry. We
have performed a systematic investigation of the pressure-composition phase
diagram of the C-H system at pressures up to 400 GPa using evolutionary
structure prediction coupled with ab initio calculations and discovered that
only saturated hydrocarbons are thermodynamically stable. Several stable
methane-hydrogen co crystals are predicted: 2CH4 * H2, earlier obtained
experimentally, is predicted to have I4/m space group and 2-90 GPa stability
range at 0 K, and two new thermodynamically stable compounds 2CH4 * 7H2 (P-3m1
space group) and CH4 * 9H2 (Cm space group), as potential energy storage
materials. P21/c phase of methane is predicted to be stable at pressures < 8
GPa; bulk graphane (CH) was shown to be thermodynamically stable at 7-18 and
18-50 GPa and 0 K in the P-3m and Cmca phases, respectively; polyethylene is
shown to have a narrow field of stability. We report the p-T-x phase diagram of
the C-H system and p-T phase diagram of CH4.",1904.03135v2
2019-04-08,Magnetic phase diagram of sigma-phase Fe55Re45 compound in the H-T coordinates,"In-field DC and AC magnetization measurements were carried out on a
sigma-phase Fe55Re45 intermetallic compound aimed at determination of the
magnetic phase diagram in the H-T plane. Field cooled, M_FC, and zero-field
cooled, M_ZFC, DC magnetization curves were measured in the magnetic field, H,
up to 1200 Oe. AC magnetic susceptibility measurements were carried out at a
constant frequency of 1465 Hz under DC fields up to H=500 Oe. The obtained
results provide evidences for re-entrant magnetism in the investigated sample.
The magnetic phase diagrams in the H-T plane have been outlined based on
characteristic temperatures determined from the DC and AC measurements. The
phase diagrams are similar yet not identical. The main difference is that in
the DC diagram constructed there are two cross-over transitions within the
strong-irreversibility spin-glass state, whereas in the AC susceptibility based
diagram only one transition is observed. The border lines (irreversibility,
cross-over) can be described in terms of the power laws.",1904.04249v1
2019-04-12,One-dimensionalization by Geometrical Frustration in the Anisotropic Triangular Lattice of the 5d Quantum Antiferromagnet Ca3ReO5Cl2,"We report on the emergence of antiferromagnetic spin chains from
two-dimensionally aligned spins on the anisotropic triangular lattice (ATL) in
the insulating calcium rhenium oxychloride Ca3ReO5Cl2. The compound contains
Re6+ ions each with one unpaired electron in the dxy orbital, which are
arranged to form a spin-1/2 ATL with J'/J ~ 0.32 and J = 41 K, where J and J'
are magnetic interactions in and between the chains, respectively. In spite of
the apparent two dimensionality, we observe clear evidence of a gapless spin
liquid that is characteristic of the spin-1/2 Heisenberg chain. This
one-dimensionalization must be caused by geometrical frustration: growing
antiferromagnetic correlations in every chain effectively cancel out
inter-chain zigzag couplings at low temperature. Ca3ReO5Cl2 provides us with a
detailed insight into the interesting physics of the ATL antiferromagnet,
especially via comparison with the typical ATL compound Cs2CuCl4.",1904.06095v1
2019-04-12,Synthesis of anti-perovskite-type carbides and nitrides from metal oxides and melamine,"Four anti-perovskite-type compounds, ZnNNi3, ZnCNi3, SnNCo3, and SnCCo3, are
synthesised through reactions between ingredient metal oxides and organic
compound melamine (C3H6N6). ZnNNi3 and ZnCNi3 are selectively synthesised by
choosing different reaction temperatures and nominal oxide-to-melamine ratios.
SnNCo3 is synthesised for the first time by this melamine method. Resistivity,
magnetisation, and heat capacity measurements reveal that SnNCo3 is a
correlated metal with a high density of states at the Fermi level. Our results
demonstrate that this feasible synthetic route using melamine is useful in the
search for complex metal carbides and nitrides toward novel functional
materials.",1904.06103v1
2019-04-12,3D photo-responsive optical devices manufactured by advanced printing technologies,"Photonic components responsive to external optical stimuli are attracting
increasing interest, because their properties can be manipulated by light with
fast switching times, high spatial definition, and potentially remote control.
These aspects can be further enhanced by novel architectures, which have been
recently enabled by the availability of 3D printing and additive manufacturing
technologies. However, current methods are still limited to passive optical
materials, whereas photo-responsive materials would require the development of
3D printing techniques able to preserve the optical properties of photoactive
compounds and to achieve high spatial resolution to precisely control the
propagation of light. Also, optical losses in 3D printed materials are an issue
to be addressed. Here we report on advanced additive manufacturing
technologies, specifically designed to embed photo-responsive compounds in 3D
optical devices. The properties of 3D printed devices can be controlled by
external UV and visible light beams, with characteristic switching times in the
range 1-10 s.",1904.06255v1
2019-04-17,"Structural, electronic properties and the features of chemical bonding in layered 1111-oxyarsenides LaRhAsO and LaIrAsO: ab initio modeling","The comparative study of structural, electronic properties, topology of the
Fermi surface, and the features of chemical bonding in layered
1111-oxyarsenides LaRhAsO and LaIrAsO has been performed based on the results
of ab initio modeling of their electronic structure. It was established that
only weak sensitivity with respect both to electron and hole doping is expected
for LaIrAsO being non-magnetic metal, however, the Rh-containing compound
should be characterized with weak band magnetism, and the hole doping is
expected to be able to move its ground state away from the boundary of magnetic
instability. The mentioned feature allows to consider LaRhAsO oxyarsenide as a
possible ""electron analogue"" of LaFeAsO compound being the initial phase for
the layered FeAs-superconductors.",1904.08158v1
2019-04-18,Limiting entry times distribution for arbitrary null sets SETS,"We describe an approach that allows us to deduce the limiting return times
distribution for arbitrary sets to be compound Poisson distributed. We
establish a relation between the limiting return times distribution and the
probability of the cluster sizes, where clusters consist of the portion of
points that have finite return times in the limit where random return times go
to infinity. In the special case of periodic points we recover the known
P\'olya-Aeppli distribution which is associated with geometrically distributed
cluster sizes. We apply this method to several examples the most important of
which is synchronisation of coupled map lattices. For the invariant absolutely
continuous measure we establish that the returns to the diagonal is compound
Poisson distributed where the coefficients are given by certain integrals along
the diagonal.",1904.08733v1
2019-04-18,Genie: A Generator of Natural Language Semantic Parsers for Virtual Assistant Commands,"To understand diverse natural language commands, virtual assistants today are
trained with numerous labor-intensive, manually annotated sentences. This paper
presents a methodology and the Genie toolkit that can handle new compound
commands with significantly less manual effort. We advocate formalizing the
capability of virtual assistants with a Virtual Assistant Programming Language
(VAPL) and using a neural semantic parser to translate natural language into
VAPL code. Genie needs only a small realistic set of input sentences for
validating the neural model. Developers write templates to synthesize data;
Genie uses crowdsourced paraphrases and data augmentation, along with the
synthesized data, to train a semantic parser. We also propose design principles
that make VAPL languages amenable to natural language translation. We apply
these principles to revise ThingTalk, the language used by the Almond virtual
assistant. We use Genie to build the first semantic parser that can support
compound virtual assistants commands with unquoted free-form parameters. Genie
achieves a 62% accuracy on realistic user inputs. We demonstrate Genie's
generality by showing a 19% and 31% improvement over the previous state of the
art on a music skill, aggregate functions, and access control.",1904.09020v1
2019-04-21,Quantum Photonic Estimation of Refractive Index in 2-methyl-4-nitroaniline ElectroOptic Crystal,"In this paper, we will try to explain the method of theoretical estimation of
index of refraction of an assymetric organic Electro-Optic compound called MNA
or 2,methyl,4,nitro-aniline. It is transparent in a wide range between
500nm-2000nm wavelengths. We assume a Quantum Photonic Model which is based on
Bohmian Mechanics for Electron-Photon interactions. The photons interact with
pi-electrons of MNA molecules, when they pass in the atomic layers. During this
electron-photon interaction the photon is temporarily annihilated and all of
its energy will be delivered into electron in orbit as kinetic energy in every
layer. After a short while the photon will be recreated. With reasonable and
precise calculations of these delays we may estimate theoretically Ordinary and
Extraordinary refractive indices of MNA compound. Quarter wave thickness for
MNA crystal has also been estimated according to phase retardation simulations.
Attained results from this Quantum Photonic model - Montecarlo time domain
method, is estimated to be very close to experimental quantities with errors
always less than 6 percents.",1904.10842v1
2019-04-27,"Complex magnetism of B20-MnGe: from spin-spirals, hedgehogs to monopoles","B20 compounds are the playground for various non-trivial magnetic textures
such as skyrmions, which are topologically protected states. Recent
measurements on B20-MnGe indicate no clear consensus on its magnetic behavior,
which is characterized by the presence of either spin-spirals or 3-dimensional
objects interpreted to be a cubic lattice of hedgehogs and anti-hedgehogs.
Utilizing a massively parallel linear scaling all-electron density functional
algorithm, we find from full first-principles simulations on cells containing
thousands of atoms that upon increase of the compound volume, the state with
lowest energy switches across different magnetic phases: ferromagnetic,
spin-spiral, hedgehog and monopole.",1904.12176v2
2019-06-30,"Electronic properties of A2Zr2O7 (A= Gd, Nd) ceramic","The density functional theory with generalized gradient approximation has
been used to investigate the electronic structure of gadolinium pyrochlore
A2Zr2O7 (A=Gd, Nd) ceramic synthesized in polycrystalline form by solid state
reaction. Structural characterization of the compound was done through X-ray
diffraction (XRD) followed by Rietveld analysis of the XRD pattern. The Zr-K
edge X-ray absorption (XAFS) spectra of A2Zr2O7 (A=Gd, Nd) were analysed
together with those Zr-foil, which was used as reference compounds. X-ray
photoemission spectroscopy (XPS), X-ray absorption near edge structure (XANES)
and extended X-ray absorption fine structure (EXAFS) for A2Zr2O7 (A=Gd, Nd) has
been employed to obtain quantitative structural information on the Zr-local
environment. The band gap is estimated using UV-Vis spectroscopy. The crystal
structure is face centered cubic, space group being Fd-3m (No. 227). The total
energies in this work were calculated using the generalized gradient
approximation to DFT plus on-site repulsion (U) method.",1907.00414v2
2019-07-01,"Structural phase diagram and magnetic properties of Sc-substituted rare earth ferrites R1-xScxFeO3 (R=Lu, Yb, Er, and Ho)","We have studied the structural stability of Sc-substituted rare earth (R)
ferrites R1-xScxFeO3, and constructed a structural phase diagram for different
R and x. While RFeO3 and ScFeO3 adopt the orthorhombic and the bixbyite
structure respectively, the substituted compound R1-xScxFeO3 may be stable in a
different structure. Specifically, for R0.5Sc0.5FeO3, the hexagonal structure
can be stable for small R, such as Lu and Yb, while the garnet structure is
stable for larger R, such as Er and Ho. The formation of garnet structure of
the R0.5Sc0.5FeO3 compounds which requires that Sc occupies both the rare earth
and the Fe sites, is corroborated by their magnetic properties.",1907.01052v1
2019-07-02,Phenomenological approach of the thermodynamic properties of CDW (SDW) systems,"The microscopic description of the CDW phase transition is still debated and
remains controversial. The question is how to extend the Peierls picture to
real systems in higher dimensions. A general tendency is found in the
thermodynamic properties such as the specific heat jump DCp and the decrease of
the longitudinal elastic stiffness constant DC11/C11 at the CDW phase
transition in several materials, such as quasi-one dimensional (K0.3MoO3),
transition metal dichalcogenide compounds (2H-NbSe2), rare earth tritellurides
(TbTe3, ErTe3, HoTe3) and intermetallic compound (Lu5Ir4Si10). DCp and DC11/C11
increase as the temperature of the phase transition TCDW and TCDW2
respectively. The same tendency is found at the spin density phase transition
in chromium and CuGeO3.Thermodynamic properties of almost all CDW systems,
although it has been recognized to exhibit large fluctuations, follow the
classical mean field BCS type behavior.",1907.01206v1
2019-06-17,Analyses of Multi-collection Corpora via Compound Topic Modeling,"As electronically stored data grow in daily life, obtaining novel and
relevant information becomes challenging in text mining. Thus people have
sought statistical methods based on term frequency, matrix algebra, or topic
modeling for text mining. Popular topic models have centered on one single text
collection, which is deficient for comparative text analyses. We consider a
setting where one can partition the corpus into subcollections. Each
subcollection shares a common set of topics, but there exists relative
variation in topic proportions among collections. Including any prior knowledge
about the corpus (e.g. organization structure), we propose the compound latent
Dirichlet allocation (cLDA) model, improving on previous work, encouraging
generalizability, and depending less on user-input parameters. To identify the
parameters of interest in cLDA, we study Markov chain Monte Carlo (MCMC) and
variational inference approaches extensively, and suggest an efficient MCMC
method. We evaluate cLDA qualitatively and quantitatively using both synthetic
and real-world corpora. The usability study on some real-world corpora
illustrates the superiority of cLDA to explore the underlying topics
automatically but also model their connections and variations across multiple
collections.",1907.01636v1
2019-07-09,Brittle to quasibrittle transition in a compound fiber bundle,"The brittle to quasibrittle transition has been studied for a compound of two
different kinds of fibrous materials, having distinct difference in their
breaking strengths under the framework of the fiber bundle model.
  A random fiber bundle model has been devised with a bimodal distribution of
the breaking strengths of the individual fibers. The bimodal distribution is
assumed to be consisting of two symmetrically placed rectangular probability
distributions of strengths $p$ and $1 - p$, each of width $d$, and separated by
a gap $2s$. Different properties of the transition have been studied varying
these three parameters and using the well known equal load sharing dynamics.
Our study exhibits a brittle to quasibrittle transition at the critical width
$d_c(s,p) = p(1/2 - s)/(1 + p)$ confirmed by our numerical results.",1907.03982v1
2019-07-12,Retrieving CeB$_6$'s lost magnetic entropy,"The reported temperature variations of CeB6 s magnetic entropy are
inconsistent with the fourfold degeneracy of the crystal field ground state.
This old question is here addressed through new specific heat measurements and
an improved description, in the cage context, of both the phonons and crystal
field contributions to the specific heat. The antiferromagnetic transition is
characterized as first-order and its latent heat determined. From the phonons
dispersion for a cage compound, the lattice specific heat contribution is
derived from the LaB6 data. Once corrected for the first-order transition and
lattice contributions, the magnetic entropy displays the characteristic plateau
of the quadruplet crystal field ground state, but at temperatures in excess of
30 K. Below 30 K, as the ordering temperature is approached, the magnetic
entropy is substantially reduced. This anomalous temperature dependence is
consistent with a crystal field ground state split by the rare-earth movement,
a phenomenon specific to rare-earth cage compounds.",1907.05775v1
2019-07-15,Quasidistribution of phases in Raman process with weak and strong pumps,"Nonclassicality is studied through a quasidistribution of phases for the
Raman process under both weak and strong pump conditions. In the former case,
the solution is applicable to both resonant and off-resonant Raman processes,
while strong classical pump is assumed at resonance. Under weak pump conditions
(i.e., in a complete quantum treatment), the phase difference of phases
described by single nonclassical modes is required to be filtered to describe a
regular distribution function, which is not the case with strong pump. Compound
Stokes-phonon mode shows nonclassical features of phases in both weak and
strong pumping, which effect is similar to that for compound pump-phonon
(Stokes-anti-Stokes) mode with weak (strong) pump. While anti-Stokes-phonon
mode is observed to be classical and coherence conserving in strong pump case,
pump-Stokes mode shows similar behavior in a special case in quantum treatment.",1907.06467v1
2019-07-17,Epitaxial stabilization of thin films of the frustrated Ge-based spinels,"Frustrated magnets can host numerous exotic many-body quantum and topological
phenomena. GeNi$_2$O$_4$ is a three dimensional $S=1$ frustrated magnet with an
unusual two-stage transition to the two-dimensional antiferromagnetic ground
state, while GeCu$_2$O$_4$ is a high-pressure phase with a strongly
tetragonally elongated spinel structure and magnetic lattice formed by $S=1/2$
CuO$_2$ linear chains with frustrated exchange interactions and exotic magnetic
behavior. Here we report on the first thin-film epitaxial stabilization of
these two compounds. Developed growth mode, surface morphology, crystal
structure and copper valence state were characterized by in-situ reflection
high-energy electron diffraction, atomic force microscopy, X-ray reflectivity,
X-ray diffraction, X-ray photoelectron spectroscopy and resonant X-ray
absorption spectroscopy. Our results pave an alternative route to the
comprehensive investigation of the puzzling magnetic properties of these
compounds and exploration of novel emergent features driven by strain.",1907.07785v3
2019-07-19,Toxicity Prediction by Multimodal Deep Learning,"Prediction of toxicity levels of chemical compounds is an important issue in
Quantitative Structure-Activity Relationship (QSAR) modeling. Although toxicity
prediction has achieved significant progress in recent times through deep
learning, prediction accuracy levels obtained by even very recent methods are
not yet very high. We propose a multimodal deep learning method using multiple
heterogeneous neural network types and data representations. We represent
chemical compounds by strings, images, and numerical features. We train fully
connected, convolutional, and recurrent neural networks and their ensembles.
Each data representation or neural network type has its own strengths and
weaknesses. Our motivation is to obtain a collective performance that could go
beyond individual performance of each data representation or each neural
network type. On a standard toxicity benchmark, our proposed method obtains
significantly better accuracy levels than that by the state-of-the-art toxicity
prediction methods.",1907.08333v1
2019-07-22,Enhanced superconductivity by Na doping in SnAs-based layered compound Na$_{1+x}$Sn$_{2-x}$As$_2$,"Superconducting transition temperature (Tc) reported in SnAs-based layered
compound NaSn$_2$As$_2$ varies from 1.2 to 1.6 K, implying that its
superconductivity is critically sensitive to non-stoichiometry. Here, we
demonstrate that Na-doping on the Sn site (Na$_{1+x}$Sn$_{2-x}$As$_2$) is
effective in enhancing superconductivity, leading to Tc = 2.1 K for x = 0.4.
First-principles calculation indicates that such a doping, or Na$_{\rm Sn}$
antisite defects, is energetically favored over other cation vacancies. Our
results pave the way for increasing Tc of layered tin pnictide superconductors.",1907.09287v1
2019-07-23,CeAu$_{2}$Bi: a new nonsymmorphic antiferromagnetic compound,"Here we report the structural and electronic properties of CeAu$_{2}$Bi, a
new heavy-fermion compound crystallizing in a nonsymmorphic hexagonal structure
($P63/mmc$). The Ce$^{3+}$ ions form a triangular lattice which orders
antiferromagnetically below $T_{N} = 3.1$~K with a magnetic hard axis along the
c-axis. Under applied pressure, $T_{N}$ increases linearly at a rate of
$0.07$~K/kbar, indicating that the Ce $f$-electrons are fairly localized. In
fact, heat capacity measurements provide an estimate of 150(10) mJ/mol.K$^{2}$
for the Sommerfeld coefficient. The crystal-field scheme obtained from our
thermodynamic data points to a ground state with dominantly
$|j_{z}=\pm1/2\rangle$ character, which commonly occurs in systems with a hard
c-axis. Finally, electronic band structure calculations and symmetry analysis
in $k$-space reveal that CeAu$_{2}$Bi hosts symmetry-protected crossings at
$k_{z} = \pi$ in the paramagnetic state",1907.10084v1
2019-07-31,Anisotropic thermoelectric properties of EuCd$_{2}$As$_{2}$ : An Ab-initio study,"In search of better thermoelectric materials, we have systematically
investigated the thermoelectric properties of a 122 Zintl phase compound
EuCd$_{2}$As$_{2}$ using \textit{ab-initio} density functional theory and
semi-classical Boltzmann transport theory within constant relaxation time
approximation. Considering the ground state magnetic structure which is A-type
antiferromagnetic (A-AFM) and non-magnetic (NM) structure, we evaluated various
thermoelectric parameters such as Seebeck coefficient, electrical and thermal
conductivity, power factor and figure of merit (ZT) as function temperature as
well as chemical potential. Almost all thermoelectric parameters show
anisotropy between $xx$ and $zz$ directions which is stronger in case of A-AFM
than in NM. Both A-AFM and NM phase of the compound display better
thermoelectric performance when hole doped. We observed high Seebeck
coefficient and low electronic thermal conductivity in A-AFM phase along $zz$
direction. The remarkably high ZT of 1.79 at 500 K in A-AFM phase and ZT$\sim$1
in NM phase suggest that EuCd$_{2}$As$_{2}$ is a viable thermoelectric material
when p-doped.",1907.13446v1
2019-10-08,Far-field Compound Super-resolution Lens for direct laser writing of arbitrary nano patterns and beyond,"A low-cost compound super-resolution lens, consisting of a Plano-Convex lens
and a Microsphere lens (PCM), was proposed and demonstrated for subwavelength
direct laser scanning writing application. The PCM lens can achieve a far-field
super-resolution of ~{\lambda}/3.5 in air (~6 um away from lens) which
surpasses resolution limit of existing commercial objective lenses and is the
first of its kind. Arbitrary nano-patterns can now be directly fabricated on
various substrates in a simpleand low-cost manner using developed PCM lens. The
lens can also be used for other applications including nano-imaging and sensing
as well in a confocal configuration. This work may lead to the development of
next-generation low-cost direct laser nanofabrication machine and
superresolution imaging nanoscope.",1910.03454v1
2019-10-09,Frustrated magnetic interactions in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3),"Inelastic neutron scattering study has been performed in an S=3/2 bilayer
honeycomb lattice compound Bi3Mn4O12(NO3) at ambient and high magnetic fields.
Relatively broad and monotonically dispersive magnetic excitations were
observed at ambient field, where no long range magnetic order exists. In the
magnetic field-induced long-range ordered state at 10 T, the magnetic
dispersions become slightly more intense, albeit still broad as in the
disordered state, and two excitation gaps, probably originating from an
easy-plane magnetic anisotropy and intrabilayer interactions, develop.
Analyzing the magnetic dispersions using the linear spin-wave theory, we
estimated the intraplane and intrabilayer magnetic interactions, which are
almost consistent with those determined by ab initio density functional theory
calculations [M. Alaei et al., Phys. Rev. B 96, 140404(R) (2017)], except the
3rd and 4th neighbor intrabilayer interactions. Most importantly, as predicted
by the theory, there is no significant frustration in the honeycomb plane but
frustrating intrabilayer interactions probably give rise to the disordered
ground state.",1910.03816v1
2019-10-11,Osmates on the verge of a Hund's-Mott transition: The different fates of NaOsO$_3$ and LiOsO$_3$,"We clarify the origin of the strikingly different spectroscopic properties of
the chemically similar compounds NaOsO$_3$ and LiOsO$_3$. Our first-principle
many-body analysis demonstrates that the highly sensitive physics of these two
materials is controlled by their proximity to an adjacent Hund's-Mott
insulating phase. In mildly correlated $5d$ oxides, this physics is triggered
by the {\sl cooperative} action of intraorbital repulsion and Hund's exchange
in half-filled $t_{2g}$ outer-shells. Small material-specific details hence
result in an extremely sharp change of the electronic mobility, explaining the
surprisingly different properties of the paramagnetic high-temperature phases
of the two compounds.",1910.05151v3
2019-10-14,Magnetic field driven quantum criticality in antiferromagnetic CePtIn4,"Physics of quantum critical point is one of the most perplexing topics in
current condensed-matter physics. Its conclusive understanding is forestalled
by the scarcity of experimental systems displaying novel aspects of quantum
criticality. We present a comprehensive experimental evidence of a magnetic
field tuned tricritical point separating paramagnetic, antiferromagnetic and
metamagnetic phases in novel compound CePtIn$_4$. Analyzing field variations of
its magnetic susceptibility, magnetoresistance and specific heat at very low
temperatures, we trace modifications of antiferromagnetic structure of the
compound. Upon applying magnetic field of increasing strength, the system
undergoes metamagnetic transitions which persist down to the lowest temperature
investigated, exhibiting first-order-like boundaries separating magnetic
phases. This yields a unique phase diagram where the second-order phase
transition line terminates at a tricritical point followed by two first-order
lines reaching quantum critical end points as $T\to$~0. Our findings
demonstrate that CePtIn$_4$ provides innovative perspective for studies of
quantum criticality.",1910.05975v1
2019-10-20,A General Framework for Empirical Bayes Estimation in Discrete Linear Exponential Family,"We develop a Nonparametric Empirical Bayes (NEB) framework for compound
estimation in the discrete linear exponential family, which includes a wide
class of discrete distributions frequently arising from modern big data
applications. We propose to directly estimate the Bayes shrinkage factor in the
generalized Robbins' formula via solving a scalable convex program, which is
carefully developed based on a RKHS representation of the Stein's discrepancy
measure. The new NEB estimation framework is flexible for incorporating various
structural constraints into the data driven rule, and provides a unified
approach to compound estimation with both regular and scaled squared error
losses. We develop theory to show that the class of NEB estimators enjoys
strong asymptotic properties. Comprehensive simulation studies as well as
analyses of real data examples are carried out to demonstrate the superiority
of the NEB estimator over competing methods.",1910.08997v1
2019-10-24,Unconventional High Temperature Superconductivity in Cubic Zinc-blende Transition Metal Compounds,"We consider possible high temperature superconductivity (high-T$_c$) in
transition metal compounds with a cubic zinc-blende lattice structure. When the
electron filling configuration in the d-shell is close to d$^7$, all three
t$_{2g}$ orbitals are near half filling with strong nearest neighbor
antiferromagnetic (AFM) superexchange interactions. We argue that upon doping,
this electronic environment can be one of ""genes"" to host unconventional high
T$_c$ with a time reversal symmetry broken $d_{2z^2-x^2-y^2} \pm i d_{x^2-y^2}$
pairing symmetry. With gappless nodal points along the diagonal directions,
this state is a direct three dimensional analogue to the two dimensional
$B_{1g}$ d-wave state in cuprates. We suggest that such a case may be realized
in electron doped CoN, such as CoN$_{1-x}$O$_x$ and (H, Li)$_{1-x}$CoN.",1910.10904v2
2019-10-22,"Proton-induced reactions on Fe, Cu, & Ti from threshold to 55 MeV","Theoretical models often differ significantly from measured data in their
predictions of the magnitude of nuclear reactions that produce radionuclides
for medical, research, and national security applications. In this paper, we
compare a priori predictions from several state-of-the-art reaction modeling
packages (CoH, EMPIRE, TALYS, and ALICE) to cross sections measured using the
stacked-target activation method. The experiment was performed using the LBNL
88-Inch Cyclotron with beams of 25 and 55 MeV protons on a stack of iron,
copper, and titanium foils. 34 excitation functions were measured for 4 < Ep <
55 MeV, including the first measurement of the independent cross sections for
natFe(p,x) 49,51Cr, 51,52m,52g,56Mn, and 58m,58gCo. All of the models failed to
reproduce the isomer-to-ground state ratio for reaction channels at compound
and pre-compound energies, suggesting issues in modeling the deposition or
distribution of angular momentum in these residual nuclei.",1910.11135v1
2019-10-25,First-Principles Mapping of the Electronic Properties of Two-Dimensional Materials for Strain-Tunable Nanoelectronics,"Herein, we demonstrate that first-principles calculations can be used for
mapping electronic properties of two-dimensional (2d) materials with respect to
non-uniform strain. By investigating four representative single-layer 2d
compounds with different symmetries and bonding characters, namely
2d-${MoS_2}$, phosphorene, ${\alpha}$-Te, and ${\beta}$-Te, we reveal that such
a mapping can be an effective guidance for advanced strain engineering and
development of strain-tunable nanoelectronics devices, including transistors,
sensors, and photodetectors. Thus, we show that ${\alpha}$-Te and ${\beta}$-Te
are considerably more elastic compared to the 2d compounds with strong chemical
bonding. In case of ${\beta}$-Te, the mapping uncovers an existence of curious
regimes where non-uniform deformations allow to achieve unique localization of
band edges in momentum space that cannot be realized under either uniform or
uniaxial deformations. For all other systems, the strain mapping is shown to
provide deeper insight into the known trends of band gap modulation and
direct-indirect transitions under strain. Hence, we prove that the standard way
of analyzing selected strain directions is insufficient for some 2d systems,
and a more general mapping strategy should be employed instead.",1910.11964v1
2019-10-29,Ferromagnetic van der Waals compound MnSb$_{1.8}$Bi$_{0.2}$Te$_4$,"The intersection of topology and magnetism represents a new playground to
discover novel quantum phenomena and device concepts. In this work, we show
that a van der Waals compound MnSb$_{1.8}$Bi$_{0.2}$Te$_4$ exhibits a
ferromagnetic ground state with a Curie temperature of 26 K, in contrast to the
antiferromagnetic order previously found for other members of the Mn(Sb,
Bi)$_2$Te$_4$ family. We employ magneto-transport, bulk magnetization and
neutron scattering studies to illustrate the magnetic and electrical properties
of MnSb$_{1.8}$Bi$_{0.2}$Te$_4$ and report on the observation of an unusual
anomalous Hall effect. Our results are an important step in the synthesis and
understanding of ferromagnetic topological insulators.",1910.13057v1
2019-10-30,Superconductivity in a Scandium Borocarbide with a Layered Crystal Structure,"The discovery of nearly room-temperature superconductivity in superhydrides
has motivated further materials research for conventional superconductors. To
realize the moderately high critical temperature $(T_\mathrm{c})$ in materials
containing light elements, we explored new superconducting phases in a scandium
borocarbide system. Here, we report the observation of superconductivity in a
new ternary Sc-B-C compound. The crystal structure, which was determined
through a Rietveld analysis, belongs to tetragonal space group $P4/ncc$. By
complementarily using the density functional theory calculations, a chemical
formula of the compound was found to be expressed as
Sc$_{20}$C$_{8-x}$B$_x$C$_{20}$($x=1\:\mathrm{or}\:2$). Interestingly, a small
amount of B is essential to stabilize the present structure. Our experiments
revealed the typical type-II superconductivity at
$T_\mathrm{c}=7.7\:\mathrm{K}$. Additionally, we calculated the density of
states within a first-principles approach and found that the contribution of
the Sc-3d orbital was mainly responsible for the superconductivity.",1910.13711v1
2012-09-01,Correlated electronic structure and chemical bonding of Ce pnictides and gamma-Ce,"We present calculated spectral properties and lattice parameters for cerium
pnictides (CeN, CeP, CeAs, CeSb, CeBi) and gamma-Ce, within the LDA/GGA+DMFT
(local density approximation/generalized gradient approximation + dynamical
mean field theory) approach. The effective impurity model arising in the DMFT
is solved by using the spin-polarized T-matrix fluctuation-exchange (SPTF)
solver for CeN compound, and the Hubbard I (HI) solver for CeP, CeAs, CeSb, and
CeBi. For all the addressed compounds the calculated spectral properties are in
reasonable agreement with measured photoelectron spectra at high binding
energies. At low binding energies the HI approximation does not manage to
capture the Kondo-like peak observed for several of the Ce-pnictides.
Nevertheless, the calculated lattice constants are in a good agreement with
available experimental data, showing that the such a peak does not play a major
role on the bonding properties. Furthermore, the HI calculations are compared
to a simpler treatment of the Ce 4f electron as core-like in LDA/GGA for CeP,
CeAs, CeSb, and CeBi, and the two approaches are found to give similar results.",1209.0132v1
2012-09-03,Magnetism and its microscopic origin in iron-based high-temperature superconductors,"High-temperature superconductivity in the iron-based materials emerges from,
or sometimes coexists with, their metallic or insulating parent compound
states. This is surprising since these undoped states display dramatically
different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el
temperatures. Although there is general consensus that magnetic interactions
are important for superconductivity, much is still unknown concerning the
microscopic origin of the magnetic states. In this review, progress in this
area is summarized, focusing on recent experimental and theoretical results and
discussing their microscopic implications. It is concluded that the parent
compounds are in a state that is more complex than implied by a simple Fermi
surface nesting scenario, and a dual description including both itinerant and
localized degrees of freedom is needed to properly describe these fascinating
materials.",1209.0381v1
2012-09-06,Enhanced thermoelectric response of hole-doped La$_2$NiO$_{4+δ}$ by ab initio calculations,"Thermoelectric properties of the system La$_2$NiO$_{4+\delta}$ have been
studied ab initio. Large Seebeck coefficient values are predicted for the
parent compound, and to some extent remain in the hole-doped metallic phase,
accompanied of an increase in the conductivity. This system, due to its layered
structure would be a suitable candidate for an improvement of its
thermoelectric figure of merit by nanostructurization in thin films, that has
already been shown to increase the electrical conductivity ($\sigma$). Our
calculations show that in the region around La$_2$NiO$_{4.05}$ the system has a
large thermopower at high temperatures and also a substantially increased
$\sigma$. Films grown with this low-doping concentration will show an optimal
relationship between thermopower and $\sigma$. This result is obtained for
various exchange-correlation schemes (correlated, uncorrelated and
parameter-free) that we use to analyze the electronic structure of the
hole-doped compound.",1209.1245v1
2012-09-07,Quadrupole Susceptibility of Gd-Based Filled Skutterudite Compounds,"It is shown that quadrupole susceptibility can be detected in Gd compounds
contrary to our textbook knowledge that Gd$^{3+}$ ion induces pure spin moment
due to the Hund's rules in an $LS$ coupling scheme. The ground-state multiplet
of Gd$^{3+}$ is always characterized by $J$=7/2, where $J$ denotes total
angular momentum, but in a $j$-$j$ coupling scheme, one $f$ electron in $j$=7/2
octet carries quadrupole moment, while other six electrons fully occupy $j$=5/2
sextet, where $j$ denotes one-electron total angular momentum. For realistic
values of Coulomb interaction and spin-orbit coupling, the ground-state
wavefunction is found to contain significant amount of the $j$-$j$ coupling
component. From the evaluation of quadrupole susceptibility in a simple
mean-field approximation, we point out a possibility to detect the softening of
elastic constant in Gd-based filled skutterudites.",1209.1469v1
2012-09-12,Giant magnetocaloric effect in magnetically frustrated EuHo$_2$O$_4$ and EuDy$_2$O$_4$ compounds,"We have investigated the magnetic and magnetocaloric properties of
EuHo$_2$O$_4$ and EuDy$_2$O$_4$ by magnetization and heat capacity measurements
down to 2 K. These compounds undergo a field-induced antiferromagnetic to
ferromagnetic transition and exhibit a huge entropy change. For a field change
of 0-8 T, the maximum magnetic entropy and adiabatic temperature changes are 30
(25) J kg$^{-1}$ K$^{-1}$ and 12.7 (16) K, respectively and the corresponding
value of refrigerant capacity is 540 (415) J kg$^{-1}$ for EuHo$_2$O$_4$
(EuDy$_2$O$_4$). These magnetocaloric parameters also remain large down to
lowest temperature measured and are even larger than that for some of the
potential magnetic refrigerants reported in the same temperature range for a
moderate field change. Moreover, these materials are highly insulating and
exhibit no thermal and field hysteresis, fulfilling the necessary conditions
for a good magnetic refrigerant in the low-temperature region.",1209.2513v1
2012-09-20,Anisotropic spin-dynamics in the Kondo semiconductor CeRu2Al10,"Spin dynamics in the new Kondo insulator compound CeRu2Al10 has been studied
using unpolarized and polarized neutron scattering on single crystals. In the
unconventional ordered phase forming below T0 = 27.3 K, two excitation branches
are observed with significant intensities, the lower one of which has a gap of
4.8 +/- 0.3 meV and a pronounced dispersion up to about 8.5 meV. Comparison
with RPA magnon calculations assuming crystal-field and anisotropic exchange
couplings captures major aspects of the data, but leaves unexplained
discrepancies, pointing to a key role of direction-specific hybridization
between 4f and conduction band states in this compound.",1209.4613v1
2012-09-21,Dominant itinerant ferromagnetism in Eu0.5Sr0.5CoO3: evidences from both critical analysis and Rhodes-Wohlfarth's criterion,"The critical behaviors of ferromagnet Eu0.5Sr0.5CoO3 arround TC=140.5K have
been comprehensively investigated by analyzing a series of isothermal
magnetization M(H) curves. Both Modified Arrott plot and Kouvel-Fisher methods
give nearly the same critical exponents, which scale nicely the M(H) curves
into two different branches below and above TC. The exponents {\gamma}=1.044
and {\delta}=3.06 demonstrate the relevance of mean-field characters for this
material. The conclusion of mean-field behavior proves a dominant itinerant
ferromagnetism (FM) due to a long range exchange interaction in the system.
Meanwhile, by using Rhodes-Wohlfarth's criterion [P. Rhodes and E. P.
Wohlfarth, Proc. R. Soc. Lond. A 273, 247 (1963)], it is further confirmed that
the itinerant FM dominates in the system.",1209.4790v2
2012-09-24,Electron-phonon superconductivity in $A$Pt$_3$P compounds: from weak to strong coupling,"We study the newly discovered Pt phosphides $A$Pt$_3$P ($A$=Sr, Ca, La) [ T.
Takayama et al. Phys. Rev. Lett. 108, 237001 (2012)] using first-principles
calculations and Migdal-Eliashberg theory. Given the remarkable agreement with
the experiment, we exclude the charge-density wave scenario proposed by
previous first-principles calculations, and give conclusive answers concerning
the superconducting state in these materials. The pairing increases from La to
Ca and Sr due to changes in the electron-phonon matrix elements and
low-frequency phonons. Although we find that all three compounds are well
described by conventional s-wave superconductivity and spin-orbit coupling of
Pt plays a marginal role, we show that it could be possible to tune the
structure from centrosymmetric to noncentrosymmetric opening new perspectives
towards the understanding of unconventional superconductivity.",1209.5253v3
2014-05-31,Point contact spectroscopy in the superconducting and normal state of $\mathrm{NaFe_{1-\textit{x}}Co_\textit{x}As}$,"We use point contact spectroscopy to probe the superconducting and normal
state properties of the iron-based superconductor
$\rm{NaFe_{1-\textit{x}}Co_{\textit{x}}As}$ with $\rm{\textit{x} = 0, 0.02,
0.06}$. Andreev spectra corresponding to multiple superconducting gaps are
detected in the superconducting phase. For $\rm{\textit{x} = 0.02}$, a broad
conductance enhancement around zero bias voltage is detected in both the normal
and the superconducting phase. Such a feature is not present in the
$\rm{\textit{x} = 0.06}$ samples. We suspect that this enhancement is caused by
orbital fluctuations, as previously detected in underdoped
$\rm{Ba(Fe_{1-\textit{x}}Co_\textit{x})_2As_2}$ (Phys. Rev. B 85, 214515
(2012)). Occasionally, the superconducting phase shows a distinct asymmetric
conductance feature instead of Andreev reflection. We discuss the possible
origins of this feature. NaFeAs (the parent compound) grown by two different
techniques is probed. Melt-grown NaFeAs shows a normal state conductance
enhancement. On the other hand, at low temperatures, flux-grown NaFeAs shows a
sharp dip in the conductance at zero bias voltage. The compounds are very
reactive in air and the different spectra are likely a reflection of their
different oxidation and purity levels.",1406.0038v1
2014-06-03,Propagation of defects in doped magnetic materials of different dimensionality,"Defects intentionally introduced into magnetic materials often have a
profound effect on the physical properties. Specifically tailored neutron
spectroscopic experiments can provide detailed information on both the local
exchange interactions and the local distances between the magnetic atoms around
the defects. This is demonstrated for manganese dimer excitations observed for
the magnetically diluted three- and two-dimensional compounds KMn(x)Zn(1-x)F(3)
and K(2)Mn(x)Zn(1-x)F(4), respectively. The resulting local exchange
interactions deviate up to 10% from the average, and the local Mn-Mn distances
are found to vary stepwise with increasing internal pressure due to the Mn/Zn
substitution. Our analysis qualitatively supports the theoretically predicted
decay of atomic displacements according to 1/r**2, 1/r, and constant (for
three-, two-, and one-dimensional compounds, respectively) where r denotes the
distance of the displaced atoms from the defect.",1406.0602v1
2014-06-03,Crystal-field interaction and oxygen stoichiometry effects in strontium-doped rare-earth cobaltates,"Inelastic neutron scattering was employed to study the crystal-field
interaction in the strontium-doped rare-earth compounds R(x)Sr(1-x)CoO(3-z)
(R=Pr, Nd, Ho, and Er). Particular emphasis is laid on the effect of oxygen
deficiencies which naturally occur in the synthesis of these compounds. The
observed energy spectra are found to be the result of a superposition of
crystal fields with different nearest-neighbor oxygen coordination at the R
sites. The experimental data are interpreted in terms of crystal-field
parameters which behave in a consistent manner through the rare-earth series,
thereby allowing a reliable extrapolation for rare-earth ions not considered in
the present work.",1406.0605v1
2014-06-17,"Comparative studies of low temperature X-ray diffraction experiments on R2Ir2O7 (R = Nd, Eu, and Pr)","The cubic symmetry of pyrochlore iridium oxides R2Ir2O7 (R = Nd, Eu, and Pr)
has been investigated by high resolution X-ray diffraction experiments down to
4 K,in order to clarify the relationship between the metal-insulator transition
(MIT) and the small structural phase transition suggested by Raman scattering
experiments in these compounds. We have found that a small negative thermal
expansion of the order of 10^-3 angstroms appears only in Nd2Ir2O7 below the
MIT, T_MIT = 34 K, resulting in the magnetovolume effect of the long-range
order of Ir moments. However, any breaking of the cubic symmetry of three
iridates has not been observed as appearance of superlattice reflections nor
splittings of cubic reflections below T_MIT. These results imply that lowering
of the cubic symmetry plays a minor role for the change in the electronic state
of these compounds, while a formation of the special arrangement of Ir moments
plays a major role for the MIT.",1406.4210v3
2014-06-17,Exchange bias in phase-segregated Nd2/3Ca1/3MnO3 as a function of temperature and cooling magnetic fields,"Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal
magnetoresistance perovskite below the Curie temperature $T_{C}$ = 70 K and
attributed to an antiferromagnetic (AFM) - ferromagnetic (FM) spontaneous phase
segregated state of this compound. Field cooled magnetic hysteresis loops
exhibit shifts toward negative direction of the magnetic field axis. The values
of exchange field $H_{EB}$ and coercivity $H_{C}$ are found to be strongly
dependent of temperature and strength of the cooling magnetic field $H_{cool}$.
These effects are attributed to evolution of the FM phase content and a size of
FM clusters. A contribution to the total magnetization of the system due to the
FM phase has been evaluated. The exchange bias effect decreases with increasing
temperature up to $T_{C}$ and vanishes above this temperature with
disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of
the compound manifests itself through a training effect also observed while
studying EB in Nd2/3Ca1/3MnO3.",1406.4404v1
2014-06-19,Magnetic form factor analysis on detwinned single crystal of BaFe$_2$As$_2$,"We have performed neutron diffraction measurement on a single crystal of
parent compound of iron-based superconductor, BaFe$_2$As$_2$ at 12~K. In order
to investigate in-plane anisotropy of magnetic form factor in the
antiferromagnetic phase, the detwinned single crystal is used in the
measurement. The magnetic structure factor and magnetic form factor are well
explained by the spin densities consisting of $3d_{yz}$ electrons with a
fraction of about 40~\% and the electrons in the other four $3d$ orbitals with
each fraction of about 15~\%. Such anisotropic magnetic form factor is
qualitatively consistent with the anisotropic magnetic behaviors observed in
the antiferromagnetic phase of the parent compound of iron-based
superconductor.",1406.4935v1
2018-02-02,Handwritten Isolated Bangla Compound Character Recognition: a new benchmark using a novel deep learning approach,"In this work, a novel deep learning technique for the recognition of
handwritten Bangla isolated compound character is presented and a new benchmark
of recognition accuracy on the CMATERdb 3.1.3.3 dataset is reported. Greedy
layer wise training of Deep Neural Network has helped to make significant
strides in various pattern recognition problems. We employ layerwise training
to Deep Convolutional Neural Networks (DCNN) in a supervised fashion and
augment the training process with the RMSProp algorithm to achieve faster
convergence. We compare results with those obtained from standard shallow
learning methods with predefined features, as well as standard DCNNs.
Supervised layerwise trained DCNNs are found to outperform standard shallow
learning models such as Support Vector Machines as well as regular DCNNs of
similar architecture by achieving error rate of 9.67% thereby setting a new
benchmark on the CMATERdb 3.1.3.3 with recognition accuracy of 90.33%,
representing an improvement of nearly 10%.",1802.00671v1
2018-02-04,Pressure-tuned magnetic interactions in honeycomb Kitaev materials,"A range of honeycomb-lattice compounds has been proposed and investigated in
the search for a topological Kitaev spin liquid. However, sizable Heisenberg
interactions and additional symmetry-allowed exchange anisotropies in the
magnetic Hamiltonian of these potential Kitaev materials push them away from
the pure Kitaev spin-liquid state. Particularly the Kitaev-to-Heisenberg
coupling ratio is essential in this respect. With the help of advanced
quantum-chemistry methods, we explore how the magnetic coupling ratios depend
on pressure in several honeycomb compounds (Na$_2$IrO$_3$,
$\beta$-Li$_2$IrO$_3$, and $\alpha$-RuCl$_3$). We find that the Heisenberg and
Kitaev terms are affected differently by uniform pressure or strain: the Kitaev
component increases more rapidly than the Heisenberg counterpart. This provides
a scenario where applying pressure or strain can stabilize a spin liquid in
such materials.",1802.01051v1
2018-02-02,Spin-orbit coupling induced magnetic anisotropy and large spin wave gap in $\rm Na Os O_3$,"The role of spin-orbit coupling and Hund's rule coupling on magnetic
ordering, anisotropy, and excitations are investigated within a minimal
three-orbital model for the $5d^3$ compound $\rm Na Os O_3$. Asymmetry between
the magnetic moments for the $xy$ and $xz,yz$ orbitals, arising from the
hopping asymmetry generated by the $\rm Os O_6$ octahedral tilting and
rotation, together with the weak correlation effect, are shown to be crucial
for the large SOC induced magnetic anisotropy and spin wave gap observed in
this compound. Due to the intrinsic SOC-induced changes in the electronic
densities under rotation of the staggered field, their coupling with the
orbital energy offset is also found to contribute significantly to the magnetic
anisotropy energy.",1802.01449v2
2018-02-08,Visualizing Heavy Fermion Confinement and Pauli-Limited Superconductivity in Layered CeCoIn5,"Layered material structures play a key role in enhancing electron-electron
interactions to create correlated metallic phases that can transform into
unconventional superconducting states. The quasi-two-dimensional electronic
properties of such compounds are often inferred indirectly through examination
of their bulk properties. Here we use scanning tunneling microscopy and
spectroscopy to directly probe in cross section the quasi-two-dimensional
correlated electronic states of the heavy fermion superconductor CeCoIn5. Our
measurements reveal the strong confined nature of heavy quasi-particles,
anisotropy of tunneling characteristics, and layer-by-layer modulated behavior
of the precursor pseudogap gap phase in this compound. Examining the interlayer
coupled superconducting state at low temperatures, we find that the orientation
of line defects relative to the d-wave order parameter determines whether
in-gap states form due to scattering. Spectroscopic imaging of the anisotropic
magnetic vortex cores directly characterizes the short interlayer
superconducting coherence length and shows an electronic phase separation near
the upper critical in-plane magnetic field, consistent with a Pauli-limited
first-order phase transition into a pseudogap phase.",1802.02711v1
2018-02-09,Antiferromagnetic ground state in the MnGa$_4$ intermetallic compound,"Magnetism of the binary intermetallic compound MnGa$_4$ is re-investigated.
Band-structure calculations predict antiferromagnetic behavior in contrast to
Pauli paramagnetism reported previously. Magnetic susceptibility measurements
on single crystals indeed reveal an antiferromagnetic transition at $T_N=393$
K. Neutron powder diffraction and $^{69,71}$Ga nuclear quadrupole resonance
spectroscopy show collinear antiferromagnetic order with magnetic moments
alligned along the [111] direction of the cubic unit cell. The magnetic moment
of 0.80(3)$\mu_B$ at 1.5 K extracted from the neutron data is in good agreement
with the band-structure results.",1802.03256v2
2018-02-10,Tipping the magnetic instability in paramagnetic Sr$_3$Ru$_2$O$_7$ by Fe impurities,"We report the magnetic and electronic properties of the bilayer ruthenate
Sr$_3$Ru$_2$O$_7$ upon Fe substitution for Ru. We find that
Sr$_3$(Ru$_{1-x}$Fe$_x$)$_2$O$_7$ shows a spin-glass-like phase below 4 K for
$x$ = 0.01 and commensurate E-type antiferromagnetically ordered insulating
ground state characterized by the propagation vector $q_c$ = (0.25 0.25 0) for
$x$ $\geq$ 0.03, respectively, in contrast to the paramagnetic metallic state
in the parent compound with strong spin fluctuations occurring at wave vectors
$q$ = (0.09 0 0) and (0.25 0 0). The observed antiferromagnetic ordering is
quasi-two-dimensional with very short correlation length along the $c$ axis, a
feature similar to the Mn-doped Sr$_3$Ru$_2$O$_7$. Our results suggest that
this ordered ground state is associated with the intrinsic magnetic instability
in the pristine compound, which can be readily tipped by the local magnetic
coupling between the 3$d$ orbitals of the magnetic dopants and Ru 4$d$
orbitals.",1802.03633v1
2018-02-14,Kondo behavior and metamagnetic phase transition in a heavy fermion compound CeBi2,"Heavy fermions represent an archetypal example of strongly correlated
electron systems which, due to entanglement among different interactions, often
exhibit exotic and fascinating physics involving Kondo screening, magnetism and
unconventional superconductivity. Here we report a comprehensive study on the
transport and thermodynamic properties of a cerium-based heavy fermion compound
CeBi$_2$ which undergoes an anti-ferromagnetic transition at $T_N$ $\sim$ 3.3
K. Its high temperature paramagnetic state is characterized by an enhanced heat
capacity with Sommerfeld coefficient $\gamma$ over 200 mJ/molK$^2$. The
magnetization in the magnetically ordered state features a metamagnetic
transition. Remarkably, a large negative magnetoresistance associated with the
magnetism was observed in a wide temperature and field-angle range.
Collectively, CeBi$_2$ may serve as an intriguing system to study the interplay
between $f$ electrons and the itinerant Fermi sea.",1802.05060v1
2018-02-14,Engineering Dzyaloshinskii-Moriya interaction in B20 thin film chiral magnets,"Chiral magnetic Mn$_x$Fe$_{1-x}$Ge compounds have an antisymmetric exchange
interaction that is tunable with the manganese stoichiometric fraction, $x$.
Although millimeter-scale, polycrystalline bulk samples of this family of
compounds have been produced, thin-film versions of these materials will be
necessary for devices. In this study, we demonstrate the growth of epitaxial
Mn$_x$Fe$_{1-x}$Ge thin films on Si (111) substrates with a pure B20 crystal
structure in the stoichiometric fraction range x from 0 to 0.81. Following
systematic physical and magnetic characterization including microwave
absorption spectroscopy, we quantify the antisymmetric exchange interaction and
helical period as a function of $x$, which ranges from 200 nm to 8 nm. Our
results demonstrate an approach to engineering the size of magnetic skyrmions
in epitaxial films that are grown using scalable techniques.",1802.05107v1
2018-02-16,Algorithmic Complexity and Reprogrammability of Chemical Structure Networks,"Here we address the challenge of profiling causal properties and tracking the
transformation of chemical compounds from an algorithmic perspective. We
explore the potential of applying a computational interventional calculus based
on the principles of algorithmic probability to chemical structure networks. We
profile the sensitivity of the elements and covalent bonds in a chemical
structure network algorithmically, asking whether reprogrammability affords
information about thermodynamic and chemical processes involved in the
transformation of different compound classes. We arrive at numerical results
suggesting a correspondence between some physical, structural and functional
properties. Our methods are capable of separating chemical classes that reflect
functional and natural differences without considering any information about
atomic and molecular properties. We conclude that these methods, with their
links to chemoinformatics via algorithmic, probability hold promise for future
research.",1802.05856v3
2018-02-27,Low lying magnetic states of the mixed valence cobalt ludwigite,"There are two interpretations offered for the different structural and
magnetic properties of the mixed valence homo-metallic ludwigites, Co3O2BO3 and
Fe3O2BO3. One of them associates the physical behavior to charge ordering
processes among the cations, as is well known in simpler oxides. The other
attributes the effects to local pairwise magnetic interactions. Recently first
principles calculations in the iron ludwigite have shown that the structural
cation dimerization is due to the formation of strong magnetic dyads supporting
the second model. Here we confirm the dominance of magnetic interactions to
explain the absence of dimerization in the cobalt compound. Density functional
non-collinear spin calculations are carried out on Co3O2BO3 to determine its
low temperature magnetic order. Low spin is found on tri-valent cobalt sites,
thus preventing the formation of the ferromagnetic dyad, the mechanism which
favors dimerization in Fe3O2BO3. We conclude that the difference between high
spin Fe3+ and low spin Co3+ pairwise interactions is responsible for the
observed differences between the two compounds. The pairwise magnetic
interactions also explain the difference between the existence of low
temperature bulk AF state in the Fe ludwigite and its absence in the Co
material.",1802.10063v2
2018-02-28,Distinctive Picosecond Spin Polarization Dynamics in Bulk Half-Metals,"Femtosecond laser excitations in half-metal (HM) compounds are theoretically
predicted to induce an exotic picosecond spin dynamics. In particular,
conversely to what is observed in conventional metals and semiconductors, the
thermalization process in HMs leads to a long living partially thermalized
configuration characterized by three Fermi--Dirac distributions for the
minority, majority conduction and majority valence electrons respectively.
Remarkably, these distributions have the same temperature but different
chemical potentials. This unusual thermodynamics state causes a persistent
non-equilibrium spin polarization only well above the Fermi energy. Femtosecond
spin dynamics experiments performed on Fe$_3$O$_4$ by time-, spin-, and
angle-resolved photoelectron spectroscopy confirm our model. Furthermore, the
spin polarization response proves to be very robust and it can be adopted to
selectively test the bulk HM character in a wide range of compounds.",1802.10356v1
2018-02-27,DiGrad: Multi-Task Reinforcement Learning with Shared Actions,"Most reinforcement learning algorithms are inefficient for learning multiple
tasks in complex robotic systems, where different tasks share a set of actions.
In such environments a compound policy may be learnt with shared neural network
parameters, which performs multiple tasks concurrently. However such compound
policy may get biased towards a task or the gradients from different tasks
negate each other, making the learning unstable and sometimes less data
efficient. In this paper, we propose a new approach for simultaneous training
of multiple tasks sharing a set of common actions in continuous action spaces,
which we call as DiGrad (Differential Policy Gradient). The proposed framework
is based on differential policy gradients and can accommodate multi-task
learning in a single actor-critic network. We also propose a simple heuristic
in the differential policy gradient update to further improve the learning. The
proposed architecture was tested on 8 link planar manipulator and 27 degrees of
freedom(DoF) Humanoid for learning multi-goal reachability tasks for 3 and 2
end effectors respectively. We show that our approach supports efficient
multi-task learning in complex robotic systems, outperforming related methods
in continuous action spaces.",1802.10463v1
2018-08-15,Real time optical observation and control of atomically thin transition metal dichalcogenide synthesis,"Understanding the mechanisms involved in chemical vapour deposition (CVD)
synthesis of atomically thin transition metal dichalcogenides (TMDCs) requires
the precise control of numerous growth parameters. All the proposed mechanisms
and their relation to the growth conditions are inferred from characterising
intermediate formations obtained by stopping the growth blindly. To fully
understand the reaction routes that lead to the monolayer formation, real time
observation and control of the growth are needed. Here, we demonstrate how a
custom-made CVD chamber that allows real time optical monitoring can be
employed to study the reaction routes that are critical to the production of
the desired layered thin crystals in salt assisted TMDC synthesis. Our real
time observations reveal the reaction between the salt and the metallic
precursor to form intermediate compounds which lead to the layered crystal
formation. We identified that both the vapour-solid-solid and
vapour-liquid-solid growth routes are in an interplay. Furthermore, we
demonstrate the role H$_{2}$ plays in the salt-assisted WSe$_{2}$ synthesis.
Finally, we guided the crystal formation by directing the liquid intermediate
compound through pre-patterned channels. The methods presented in this article
can be extended to other materials that can be synthesized via CVD.",1808.05036v1
2018-08-16,Electronic properties of binary compounds with high fidelity and high throughput,"We present example applications of an approach to high-throughput
first-principles calculations of the electronic properties of materials
implemented within the Exabyte.io platform. We deploy computational techniques
based on the Density Functional Theory with both Generalized Gradient
Approximation (GGA) and Hybrid Screened Exchange (HSE) in order to extract the
electronic band gaps and band structures for a set of 775 binary compounds. We
find that for HSE, the average relative error fits within 22%, whereas for GGA
it is 49%. We find the average calculation time on an up-to-date server
centrally available from a public cloud provider to fit within 1.2 and 36 hours
for GGA and HSE, respectively. The results and the associated data, including
the materials and simulation workflows, are standardized and made available
online in an accessible, repeatable and extensible setting.",1808.05325v1
2018-08-23,Bismuth and Antimony Based Oxyhalides and Chalcohalides as Potential Optoelectronic Materials,"In the last decade the ns$^2$ cations (e.g., Pb$^{2+}$ and Sn$^{2+}$) based
halides have emerged as one of the most exciting new classes of optoelectronic
materials, as exemplified by for instance hybrid perovskite solar absorbers.
These materials not only exhibit unprecedented performance in some cases, but
they also appear to break new ground with their unexpected properties, such as
extreme tolerance to defects. However, because of the relatively recent
emergence of this class of materials, there remain many yet to be fully
explored compounds. Here we assess a series of bismuth/antimony oxyhalides and
chalcohalides using consistent first principles methods to ascertain their
properties and obtain trends. Based on these calculations, we identify a subset
consisting of three types of compounds that may be promising as solar
absorbers, transparent conductors, and radiation detectors. Their electronic
structure, connection to the crystal geometry, and impact on band-edge
dispersion and carrier effective mass are discussed.",1808.07618v1
2018-08-30,Coexisting spinons and magnons in frustrated zigzag spin-1/2 chain compound $β$-TeVO$_4$,"We investigate magnetic excitations in the frustrated zigzag spin-1/2 chain
compound $\beta$-TeVO$_4$ by inelastic neutron scattering. In the magnetically
ordered ground state, the excitation spectrum exhibits coexisting magnon
dispersion, characteristic of long-range magnetic order, and a spinon-like
continuum that prevails above 2 meV, indicating the dominance of intrachain
interactions. Combining linear-spin-wave-theory and pre-calculated
spinon-continuum results, we reproduce the experimental spectrum. Our analysis
offers a minimal exchange-network model which determines dominant intrachain
interactions, their anisotropies and weak interchain interactions. The obtained
parameters explain the magnetic ordering vector and spin excitations in the
magnetic ground state.",1808.10174v1
2018-08-30,Influence of spin glass-like magnetic relaxation on the zero-field-cooled exchange bias effect,"The zero-field-cooled exchange bias (ZEB) effect is a remarkable phenomenon
recently reported for some reentrant spin glass-like compounds. In this work,
the time-evolution of magnetization is thoroughly investigated for two ZEB
materials in order to figure out the role played by the spin glass-like phase
on such effect. La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ and
La$_{1.5}$Ca$_{0.5}$CoMnO$_{6}$ were chosen as representative samples of ZEB
systems, since the former compound presents the largest ZEB reported so far,
while the second has a much smaller effect, despite being
structurally/chemically similar. Comprehensive magnetic measurements were
carried on both samples, and the results are discussed in terms of the amount
and time-evolution of the spin glass-like phase under the influence of a
varying field. We also propose a phenomenological model, based on the pinning
of spin glass-like moments and on the dynamics of their magnetic relaxation, to
explain the asymmetry observed in the hysteresis loops. The good agreement
between the simulated and experimental results confirms our hypothesis that the
spin glass-like phase is key to the ZEB effect.",1808.10305v1
2018-11-30,Corresponding Projections for Orphan Screening,"We propose a novel transfer learning approach for orphan screening called
corresponding projections. In orphan screening the learning task is to predict
the binding affinities of compounds to an orphan protein, i.e., one for which
no training data is available. The identification of compounds with high
affinity is a central concern in medicine since it can be used for drug
discovery and design. Given a set of prediction models for proteins with
labelled training data and a similarity between the proteins, corresponding
projections constructs a model for the orphan protein from them such that the
similarity between models resembles the one between proteins. Under the
assumption that the similarity resemblance holds, we derive an efficient
algorithm for kernel methods. We empirically show that the approach outperforms
the state-of-the-art in orphan screening.",1812.00058v1
2018-12-14,Ptychographic characterization of polymer compound refractive lenses manufactured by additive technology,"The recent success in the development of high precision printing techniques
allows one to manufacture free-standing polymer structures of high quality.
Two-photon polymerization lithography is a mask-less technique with down to 100
{\mu}m resolution that provides full geometric freedom. It has recently been
applied to the nanofabrication of X-ray compound refractive lenses (CRLs). In
this article we report on the characterization of two sets of CRLs of different
design produced by two-photon polymerization induced lithography.",1812.05897v1
2018-12-16,Temperature dependence of resistivity at the transition to a charge density wave state in rare-earth tritellurides,"About a half of the Fermi surface in rare-earth tritellurides RT e3 becomes
gapped below the transition to a charge-density-wave (CDW) state, as revealed
by ARPES data. However, the observed jump in resistivity during the CDW
transition is less than 20%. Previously this phenomenon was explained by
hypothesizing a very slow evolution of CDW energy gap below transition
temperature in RTe3 compounds, which contradicts the X-ray measurements. Here
we show that this weak change in resistivity can be explained in the framework
of standard mean-field temperature dependence of the CDW energy gap in
agreement with X-ray data. The change of resistivity caused by CDW is weak
because the decrease in conducting electron density at the Fermi level is
almost compensated by the decrease in their scattering rate. We calculate
resistivity in RTe3 compounds using the Boltzmann transport equation and the
mean-field description of the CDW state, and obtain a good agreement with
experimental data.",1812.06497v1
2018-12-20,Superconductivity in Ru0.55Rh0.45P and Ru0.75Rh0.25As probed by muon spin relaxation and rotation measurements,"Superconductivity in the pseudo-binary pnictides Ru0.55Rh0.45P and
Ru0.75Rh0.25As is probed by muon spin relaxation and rotation (muSR)
measurements in conjuction with magnetic susceptibility, heat capacity and
electrical resistivity measurements. Powder x-ray diffraction confirmed the
MnP-type orthorhombic structure (space group Pnma) and showed a nearly single
phase nature with small impurity phase(s) of about 5% for both the samples. The
occurence of bulk superconductivity is confirmed with Tc = 3.7 K for
Ru0.55Rh0.45P and T = 1.6 K for Ru0.75Rh0.25As. The superconducting state
electronic heat capacity data reveal weak-coupling single-band isotropic s-wave
gap BCS superconductivity. Various normal and superconducting state parameters
are determined which reveal a weak-coupling electron-phonon driven type-II
dirty-limit superconductivity for both the compounds. The upper critical field
shows a linear temperature dependence down to the lowest measured temperatures
which is quite unusual for a single-band superconductor. The muSR data confirm
the conventional type-II behavior, and show evidence for a single-band s-wave
singlet pairing superconductivity with a preserved time reversal symmetry for
both the compounds.",1812.08666v1
2018-12-21,"Local magnetism, magnetic order and spin freezing in the 'nonmetallic metal' FeCrAs","We present the results of x-ray scattering and muon-spin relaxation
($\mu^{+}$SR) measurements on the iron-pnictide compound FeCrAs. Polarized
non-resonant magnetic x-ray scattering results reveal the 120$^\circ$
periodicity expected from the suggested three-fold symmetric, non-collinear
antiferromagnetic structure. $\mu^+$SR measurements indicate a magnetically
ordered phase throughout the bulk of the material below $T_\mathrm{N}$=105(5)
K. There are signs of fluctuating magnetism in a narrow range of temperatures
above $T_\mathrm{N}$ involving low-energy excitations, while at temperatures
well below $T_\mathrm{N}$ behaviour characteristic of freezing of dynamics is
observed, likely reflecting the effect of disorder in our polycrystalline
sample. Using density functional theory we propose a distinct muon stopping
site in this compound and assess the degree of distortion induced by the
implanted muon.",1812.09252v3
2018-12-23,UBe13 and U1-xThxBe13: Unconventional Superconductors,"UBe13 was the second discovered heavy fermion superconductor, and numerous
pieces of evidence exist that imply that it is an unconventional (non-BCS,
non-s wave pairing symmetry) superconductor. Exhibiting even more signs of
unconventional superconductivity, Th-doped UBe13 is perhaps the most puzzling
of any of the unconventional superconductors. This review considers both the
parent, undoped compound as well as the more interesting Th-doped UBe13. After
summarizing the rather thorough characterization, which because of the interest
in these compounds has continued from their discovery in 1983 and 1984 to date,
these properties are compared with a recent template for determining whether a
superconductor is unconventional. Finally, further experiments are suggested.",1812.09777v2
2018-12-24,Uncovering and tailoring hidden Rashba spin-orbit splitting in centrosymmetric crystals,"Hidden Rashba and Dresselhaus spin-splittings in centrosymmetric crystals
with subunits (sectors) having non-centrosymmetric symmetries (the R-2 and D-2
effects) have been predicted and observed experimentally, but the microscopic
mechanism remains unclear. Here we demonstrate that the spin-splitting in R-2
is enforced by specific symmetries (such as the non-symmorphic in the present
example) which ensures that the pertinent spin wavefunctions segregate
spatially on just one of the two inversion-partner sectors and thus avoid
compensation. This finding establishes a common fundamental source for the
conventional Rashba (R-1) effect and the R-2 effect, both originating from the
local sector symmetries, rather than from the global crystal asymmetry alone
for R-1 per se. We further show that the effective Hamiltonian for the R-1
effect is also applicable for the R-2 effect, but applying a symmetry-breaking
electric field to an R-2 compound produces different spin-splitting pattern
than applying a field to a trivial (non-R-2) centrosymmetric compound.",1812.09823v1
2018-12-21,Deep and persistent spectral holes in Tm-doped yttrium orthosilicate for imaging applications,"With their optical wavelength in the near infrared (790-800nm) and their
unique spectroscopic properties at cryogenic temperatures, thulium-doped
crystals are at the center of many architectures linked to classical signal
processing and quantum information. In this work, we focus on Tm-doped YSO, a
compound that was left aside in the mid-1990s due to its rather short optical
coherence lifetime. By means of time-resolved hole-burning spectroscopy, we
investigate the anisotropic enhanced nuclear Zeeman effect and demonstrate
deep, sub-MHz, persistent spectral hole burning under specific magnetic field
orientation and magnitude. By estimating the experimental parameters
corresponding to a real-scale ultrasound optical tomography setup using Tm:YSO
as a spectral filter, we validate Tm:YSO as a promising compound for medical
imaging in the human body.",1812.10369v2
2018-12-29,"Investigation of Thermodynamic Properties of Cu(NH3)4SO4.H2O, a Heisenberg Spin Chain Compound","Detailed experimental investigations of thermal and magnetic properties are
presented for Cu(NH3)4SO4.H2O, an ideal uniform Heisenberg spin half chain
compound. A comparison of these properties with relevant spin models is also
presented. The temperature dependent magnetic susceptibility and specific heat
data has been compared with the exact solution for uniform Heisenberg chain
model derived by means of Bethe ansatz technique. Field dependent isothermal
magnetization curves are simulated by Quantum Monte Carlo technique and
compared with the corresponding experimental ones. Specific heat as a function
of magnetic field (up to 7T) and temperature (down to 2K) is reported.
Subsequently, the data are compared with the corresponding theoretical curves
for the infinite Heisenberg spin half chain model with J=6K. Moreover, internal
energy and entropy are calculated by analyzing the experimental specific heat
data. Magnetic field and temperature dependent behavior of entropy and internal
energy are in good agreement with the theoretical predictions.",1812.11301v1
2019-02-04,Predictive Uncertainty Quantification with Compound Density Networks,"Despite the huge success of deep neural networks (NNs), finding good
mechanisms for quantifying their prediction uncertainty is still an open
problem. Bayesian neural networks are one of the most popular approaches to
uncertainty quantification. On the other hand, it was recently shown that
ensembles of NNs, which belong to the class of mixture models, can be used to
quantify prediction uncertainty. In this paper, we build upon these two
approaches. First, we increase the mixture model's flexibility by replacing the
fixed mixing weights by an adaptive, input-dependent distribution (specifying
the probability of each component) represented by NNs, and by considering
uncountably many mixture components. The resulting class of models can be seen
as the continuous counterpart to mixture density networks and is therefore
referred to as compound density networks (CDNs). We employ both maximum
likelihood and variational Bayesian inference to train CDNs, and empirically
show that they yield better uncertainty estimates on out-of-distribution data
and are more robust to adversarial examples than the previous approaches.",1902.01080v2
2019-02-05,Intersublattice magnetocrystalline anisotropy using a realistic tight-binding method based on maximally localized Wannier functions,"Using a realistic tight-binding Hamiltonian based on maximally localized
Wannier functions, we investigate the two-ion magnetocrystalline anisotropy
energy (MAE) in $L1_0$ transition metal compounds. MAE contributions from
throughout the Brillouin zone are obtained using magnetic force theorem
calculations with and without perturbation theory. The results from either
method agree with one another, and both reflect features of the Fermi surface.
The intra-sublattice and inter-sublattice contributions to MAE are evaluated
using a Green's function method. We find that the sign of the inter-sublattice
contribution varies among compounds, and that its amplitude may be significant,
suggesting MAE can not be resolved accurately in a single-ion manner. The
results are further validated by scaling spin-orbit-coupling strength in
density functional theory. Overall, this realistic tight-binding method provide
an effective approach to evaluate and analyze MAE while retaining the accuracy
of corresponding first-principles methods.",1902.01561v2
2019-02-05,Classifying superconductivity in compressed H3S,"The discovery of high-temperature superconductivity in compressed H3S by
Drozdov and co-workers (A. Drozdov, et. al., Nature 525, 73 (2015)) heralded a
new era in superconductivity. To date, the record transition temperature of Tc
= 260 K stands with another hydrogen-rich compound, LaH10 (M. Somayazulu, et.
al., arXiv:1808.07695) which becomes superconducting at pressure of P = 190
GPa. Despite very intensive first-principle theoretical studies of
hydrogen-rich compounds compressed to megabar level pressure, there is a very
limited experimental dataset available for such materials. In this paper, we
analyze the upper critical field, Bc2(T), data of highly compressed H3S
reported by Mozaffari and co-workers (S. Mozaffari, et. al., LA-UR-18-30460,
DOI: 10.2172/1481108) by utilizing four different models of Bc2(T). In result,
we find that the ratio of superconducting energy gap, {\Delta}(0), to the Fermi
energy, {\epsilon}F, in all considered scenarios is 0.03 <
{\Delta}(0)/{\epsilon}F < 0.07, with respective ratio of Tc to the Fermi
temperature, TF, 0.012 < Tc/TF < 0.039. These characterize H3S as
unconventional superconductor and places it on the same trend line in Tc versus
TF plot, where all unconventional superconductors located.",1902.01772v1
2019-02-05,Evaluation of Mg compounds as coating materials in Mg batteries,"Mg batteries utilizing a Mg metal anode with a high-voltage intercalation
cathode define a potential pathway toward energy storage with high energy
density. However, the realization of Mg batteries is plagued by the instability
of existing electrolytes against the Mg-metal anode and high-voltage cathode
materials. One viable solution to this problem is the identification of
protective coating materials that could effectively separate the distinct
chemistries of the metal-anode and the cathode materials from the electrolyte.
Using first-principles calculations we map the electrochemical stability
windows for non-redox-active Mg binary and ternary compounds in order to
identify potential coating materials for Mg batteries. Our results identify
Mg-halides and Mg(BH$_4$)$_2$ as promising anode coating materials based on
their significant reductive stability. On the cathode side, we single out
MgF$_2$, Mg(PO$_3$)$_2$ and MgP$_4$O$_11$ as effective passivating agents.",1902.01925v1
2019-02-06,"Neutron diffraction study of a metallic kagome lattice, Tb3Ru4Al12","We present the results of neutron diffraction studies on polycrystals of a
metallic kagome lattice, Tb3Ru4Al12, reported recently to undergo reentrant
magnetism, with the onset of long range antiferromagnetic order below (TN=) 22
K and spin-glass features below about 17 K. The present results reveal
long-range antiferromagnetic order of an incommensurate type with the moments
oriented along c-axis at all temperatures below TN. There are however notable
changes in the T dependence of propagation vector along b-axis across 17 K. An
observation of interest is that there is no decrease of intensity of magnetic
Bragg peaks on entrance into the glassy phase (that is, below 17 K). This
finding suggests that the magnetism of this compound is an exotic one and we
wonder whether this compound is an example for dynamical spin-glass freezing
phenomenon, as a consequence of geometrical frustration.",1902.02146v1
2019-02-20,Kitaev-like honeycomb magnets: Global phase behavior and emergent effective models,"Compounds of transition metal ions with strong spin-orbit coupling recently
attracted attention due to the possibility to host frustrated bond-dependent
anisotropic magnetic interactions. In general, such interactions lead to
complex phase diagrams that may include exotic phases, e.g. the Kitaev spin
liquid. Here we report on our comprehensive analysis of the global phase
diagram of the extended Kitaev-Heisenberg model relevant to honeycomb lattice
compounds Na2IrO3 and alpha-RuCl3. We have utilized recently developed method
based on spin coherent states that enabled us to resolve arbitrary spin
patterns in the cluster ground states obtained by exact diagonalization. Global
trends in the phase diagram are understood in combination with the analytical
mappings of the Hamiltonian that uncover peculiar links to known models -
Heisenberg, Ising, Kitaev, or compass models on the honeycomb lattice - or
reveal entire manifolds of exact fluctuation-free ground states. Finally, our
study can serve as a methodological example that can be applied to other spin
models with complex bond-dependent non-Heisenberg interactions.",1902.07451v1
2019-02-26,Topological Semimetal features in the Multiferroic Hexagonal Manganites,"Using first-principles calculations we examine the band structures of
ferromagnetic hexagonal manganites $\mathrm{YXO_3}$ (X=V, Cr, Mn, Fe and Co) in
the nonpolar nonsymmorphic $P6_3/mmc$ space group. For $\mathrm{YVO_3}$ and
$\mathrm{YCrO_3}$ we find a band inversion near the Fermi energy that generates
a nodal ring in the $k_z=0$ mirror plane. We perform a more detailed analysis
for these compounds and predict the existence of the topological ""drumhead""
surface states. Finally, we briefly discuss the low-symmetry polar phases
(space group $P6_3cm$) of these systems, and show they can undergo a $P6_3/mmc
\rightarrow P6_3cm$ transition by condensation of soft $K_3$ and $\Gamma_2^-$
phonons. Based on our findings, stabilizing these compounds in the hexagonal
phase could offer a promising platform for studying the interplay of topology
and multiferroicity, and the coexistence of real-space and reciprocal-space
topological protection in the same phase.",1902.10085v1
2019-02-27,Single-Phase High-Entropy Intermetallic Compounds (HEICs): Bridging High-Entropy Alloys and Ceramics,"High-entropy intermetallic compounds (HEICs) were fabricated by mechanical
alloying and spark plasma sintering to fill a knowledge gap between the
traditional high-entropy alloys (HEAs) and emerging high-entropy ceramics
(HECs). Notably, several four- or five-component equimolar aluminides, such as
the B2-phase (Fe1/5Co1/5Ni1/5Mn1/5Cu1/5)Al, have been made into single-phase
HEICs for the first time. Thermodynamic modeling and a reversible,
temperature-dependent, phase-stability experiment suggest that such B2-phase
HEICs are entropy-stabilized phases. The structure of these HEICs resembles
that of HECs with high-entropy mixing of four or five elements of nearly equal
fractions in one and only one sublattice, but with significant (~10%) anti-site
defects (differing from typical HECs). A new phase stability rule for forming
single B2-phase HEICs is proposed. Five additional HEICs of predominantly D022
phases have also been made. This study broadens the families of equimolar,
single-phase, high-entropy materials that have been successfully fabricated.",1902.10420v1
2019-06-03,Know More about Each Other: Evolving Dialogue Strategy via Compound Assessment,"In this paper, a novel Generation-Evaluation framework is developed for
multi-turn conversations with the objective of letting both participants know
more about each other. For the sake of rational knowledge utilization and
coherent conversation flow, a dialogue strategy which controls knowledge
selection is instantiated and continuously adapted via reinforcement learning.
Under the deployed strategy, knowledge grounded conversations are conducted
with two dialogue agents. The generated dialogues are comprehensively evaluated
on aspects like informativeness and coherence, which are aligned with our
objective and human instinct. These assessments are integrated as a compound
reward to guide the evolution of dialogue strategy via policy gradient.
Comprehensive experiments have been carried out on the publicly available
dataset, demonstrating that the proposed method outperforms the other
state-of-the-art approaches significantly.",1906.00549v1
2019-06-04,Observation of spin-orbit excitations and Hund's multiplets in Ca$_2$RuO$_4$,"We use Ru $L_3$-edge (2838.5 eV) resonant inelastic x-ray scattering (RIXS)
to quantify the electronic structure of Ca$_2$RuO$_4$, a layered $4d$-electron
compound that exhibits a correlation-driven metal-insulator transition and
unconventional antiferromagnetism. We observe a series of Ru intra-ionic
transitions whose energies and intensities are well described by model
calculations. In particular, we find a $\rm{J}=0\rightarrow 2$ spin-orbit
excitation at 320 meV, as well as Hund's-rule driven $\rm{S}=1\rightarrow 0$
spin-state transitions at 750 and 1000 meV. The energy of these three features
uniquely determines the spin-orbit coupling, tetragonal crystal-field energy,
and Hund's rule interaction. The parameters inferred from the RIXS spectra are
in excellent agreement with the picture of excitonic magnetism that has been
devised to explain the collective modes of the antiferromagnetic state.
$L_3$-edge RIXS of Ru compounds and other $4d$-electron materials thus enables
direct measurements of interactions parameters that are essential for realistic
model calculations.",1906.01221v1
2019-06-04,Theory of the giant thermal Hall effect in the high temperature superconductors,"Recent transport measurement finds giant negative thermal Hall signal in the
pseudo-gap phase of the high temperature superconductors\cite{Taillefer}. Such
a signal is found to increase in magnitude with decreasing doping and to reach
its maximum in the half-filled antiferromagnetic ordered parent compounds. It
is still elusive what is the implication of such a phenomena for the mechanism
of the pseudo-gap phase. The observation of such a signal may also challenge
our well established understanding of the parent compounds as perfect
Heisenberg antiferromagnets. Here we show that such a giant thermal Hall effect
can be naturally understood as the orbital magnetic response of a quantum
Heisenberg antiferromagnet with sizable multi-spin exchange coupling. We also
argue that the observation of the giant thermal Hall effect in the pseudo-gap
phase imply that the origin of the pseudo-gap in the high temperature
superconductors is closely related to the antiferromagnetic correlation between
local spins.",1906.01712v2
2019-05-30,Negative binomial-reciprocal inverse Gaussian distribution: Statistical properties with applications,"In this article, we propose a new three parameter distribution by compounding
negative binomial with reciprocal inverse Gaussian model called negative
binomial-reciprocal inverse Gaussian distribution. This model is tractable with
some important properties not only in actuarial science but in other fields as
well where overdispersion pattern is seen. Some basic properties including
recurrence relation of probabilities for computation of successive
probabilities have been discussed. In its compound version, when the claims are
absolutely continuous, an integral equation for the probability density
function is discussed. Brief discussion about extension of univariate version
have also been done to its respective multivariate version. parameters involved
in the model have been estimated by Maximum Likelihood Estimation technique.
Applications of the proposed distribution are carried out by taking two real
count data sets. The result shown that the negative binomial-reciprocal inverse
Gaussian distribution gives better fit when compared to the Poisson and
negative binomial distributions.",1906.03224v1
2019-06-14,"Graph convolutional neural networks as ""general-purpose"" property predictors: the universality and limits of applicability","Nowadays the development of new functional materials/chemical compounds using
machine learning (ML) techniques is a hot topic and includes several crucial
steps, one of which is the choice of chemical structure representation.
Classical approach of rigorous feature engineering in ML typically improves the
performance of the predictive model, but at the same time, it narrows down the
scope of applicability and decreases the physical interpretability of predicted
results. In this study, we present graph convolutional neural networks (GCNN)
as an architecture that allows to successfully predict the properties of
compounds from diverse domains of chemical space, using a minimal set of
meaningful descriptors. The applicability of GCNN models has been demonstrated
by a wide range of chemical domain-specific properties. Their performance is
comparable to state-of-the-art techniques; however, this architecture exempts
from the need to carry out precise feature engineering.",1906.06256v2
2019-06-17,Photorealistic modelling of metals from first principles,"The colours of metals have attracted the attention of humanity since ancient
times, and coloured metals, in particular gold compounds, have been employed
for tools and objects symbolizing the aesthetics of power. In this work we
develop a comprehensive framework to obtain the reflectivity and colour of
metals, and show that the trends in optical properties and the colours can be
predicted by straightforward first-principles techniques based on standard
approximations. We apply this to predict reflectivity and colour of several
elemental metals and of different types of metallic compounds (intermetallics,
solid solutions and heterogeneous alloys), considering mainly binary alloys
based on noble metals. We validate the numerical approach through an extensive
comparison with experimental data and the photorealistic rendering of known
coloured metals.",1906.06942v1
2019-06-18,Interplay between disorder driven Non-Fermi-liquid behavior and magnetism in Ce0.24La0.76Ge compound,"In this work, we investigate the magnetic, heat capacity and electrical
transport properties of Ce0.6La0.4Ge and Ce0.24La0.76Ge compounds. Our results
show that two antiferromagnetic transitions (~ at 4.7 and 2.7 K) exhibited by
Ce0.6La0.4Ge are suppressed below 1.8 K for Ce0.24La0.76Ge. Interestingly, for
Ce0.24La0.76Ge, susceptibility, heat capacity and electrical resistivity vary
with temperature as: T0.75, T0.5 and T1.6 respectively. The observation of such
anomalous temperature variation suggests to the Non-Fermi-liquid (NFL) behavior
due to the presence of disordered 4f spins due to Ce-site dilution. Under the
application of magnetic field, it is noted that a crossover from the NFL to a
magnetic state occurs around 2 Tesla, where, short-range correlations among the
spins is prevalent due to the dominance of coupling between the magnetic
moments via conduction electrons. Magnetoresistance scaling indicates that
behavior of disorder driven NFL state is described by the dynamical mean field
theory of the spin glass quantum critical point.",1906.07482v1
2019-06-18,Weak Ferroelectricity in n = 2 pseudo Ruddlesden-Popper-type niobate Li2SrNb2O7,"Li2SrNb2O7 (LSNO) crystallizes in a structure closely related to n = 2
Ruddlesden-Popper-type compounds, which is gen-erally formed by intergrowth of
2-dimensional perovskite-type blocks and rocksalt-type layers. The present
study demonstrates a coexistence of spontaneous polarization and
anti-ferroelectric-like nonlinear response in LSNO at 80 K, suggesting a weak
ferroelectricity below the phase transition temperature of 217 K. A combination
of first-principles cal-culations and single crystal x-ray diffractions
clarifies a polar P21cn structure for the ground state of LSNO, where an
in-plane anti-ferroelectric displacement and an out-of-plane polar shift
simultaneously take place. The present study offers a new perspective to design
ferroelectric and antiferroelectric materials with Ruddlesden-Popper-type
compounds.",1906.07501v1
2019-06-20,"Crystal structure and the magnetic properties of the 5d transition metal oxide AOsO4 (A = K, Rb, Cs)","We synthesized the 5d1-transition metal oxides AOsO4 (A = K, Rb, Cs) by
solid-state reaction, and performed structure determination and magnetic and
heat capacity measurements. It was found that they crystallize in a scheelite
(A = K and Rb) or a quasi-scheelite structure (A = Cs) comprising of distorted
diamond lattices of septivalent Os (d1) ions tetrahedrally coordinated by four
oxide ions without local inversion symmetry; hence an antisymmetric spin-orbit
coupling is expected in the crystals. The K and Rb compounds have Weiss
temperatures of theta = -66 and -18 K, effective magnetic moments of mu_eff =
1.44 and 1.45 mu_B/Os, and antiferromagnetic transition temperatures of T_N =
36.9 and 21.0 K, respectively. In contrast, the Cs compound has theta = 12 K
and mu_eff = 0.8 mu_B/Os without magnetic transition above 2 K, instead
exhibiting a first-order structural transition at T_s = 152.5 K. The decline of
the Os moment from 1.73 mu_B/Os for the simple d1 spin, particularly for Cs, is
likely to originate from the antiparallel orbital moment, although the
spin-orbit coupling is generally quenched in the low-lying e orbitals.",1906.08519v1
2019-06-21,Production and characterization of a PbMoO$_4$ cryogenic detector from archaeological Pb,"We operated a PbMoO$_4$ scintillating cryogenic detector of 570 g, produced
with archaeological lead. This compound features excellent low temperature
characteristics in terms of light yield, 12 keV/MeV for $\beta/\gamma$
interactions, and FWHM energy resolution, 11.7 keV at 2.6 MeV. Furthermore, the
detector allows for an effective particle identification by means of pulse
shape analysis on the heat read-out channel. The implementation of innovative
techniques and procedures for the purification of raw materials used for the
crystal growth, and the highly-pure archaeological Pb, allowed the production
of large volume high quality crystal. The overall characteristics of the
detector operated at cryogenic temperatures makes PbMoO$_4$ an excellent
compound for neutrino physics applications, especially neutrinoless double-beta
studies.",1906.09296v2
2019-06-22,Observation of two-level critical state in the superconducting FeTe thin films,"FeTe, a non-superconducting parent compound in the iron-chalcogenide family,
becomes superconducting after annealing in oxygen. Under the presence of
magnetism, spin-orbit coupling, inhomogeneity and lattice distortion, the
nature of its superconductivity is not well understood. Here, we combined
mutual inductance technique with magneto transport to study the magnetization
and superconductivity of FeTe thin films. We found that the films with the
highest Tc showed non-saturating superfluid density and a strong magnetic
hysteresis distinct from that in a homogeneous superconductor. Such hysteresis
can be well explained by a two-level critical state model and suggested the
importance of granularity to superconductivity in this compound.",1906.09418v1
2019-06-24,Compound Probabilistic Context-Free Grammars for Grammar Induction,"We study a formalization of the grammar induction problem that models
sentences as being generated by a compound probabilistic context-free grammar.
In contrast to traditional formulations which learn a single stochastic
grammar, our grammar's rule probabilities are modulated by a per-sentence
continuous latent variable, which induces marginal dependencies beyond the
traditional context-free assumptions. Inference in this grammar is performed by
collapsed variational inference, in which an amortized variational posterior is
placed on the continuous variable, and the latent trees are marginalized out
with dynamic programming. Experiments on English and Chinese show the
effectiveness of our approach compared to recent state-of-the-art methods when
evaluated on unsupervised parsing.",1906.10225v9
2019-06-28,Crossover from charge density wave stabilized antiferromagnetism to superconductivity in Nd$_{1-x}$La$_x$NiC$_2$ compounds,"The path from the charge density wave antiferromagnet NdNiC$_2$ to a
noncentrosymmetric superconductor LaNiC$_2$ has been studied by gradual
replacement of Nd by La ions. The evolution of physical properties has been
explored by structural, magnetic, transport, magnetoresistance and specific
heat measurements. With the substitution of La for Nd, the Peierls temperature
is gradually suppressed, which falls within the BCS mean-field relation for
chemical pressure with a critical concentration of $x_c$ = 0.38. As long as
charge density wave is maintained, the antiferromagnetic ground state remains
robust against doping and despite of a N\'eel temperature reduction shows a
rapid and sharp magnetic transition. Once the CDW is completely suppressed,
intermediate compounds of the Nd$_{1-x}$La$_x$NiC$_2$ series reveal symptoms of
a gradual softening of the features associated with AFM transition and increase
of the spin disorder. Immediately after the antiferromagnetic transition is
depressed to zero temperature, the further incorporation of La ions results in
the emergence of superconductivity. This crossover in the
Nd$_{1-x}$La$_x$NiC$_2$ is discussed in the terms of the possible quantum
critical point.",1906.12022v1
2020-04-01,Modulations in magnetostructural coupling in C and Sn deficient Mn$_3$SnC,"The structural and magnetic interactions in stoichiometric (Mn$_3$SnC),
carbon deficient (Mn$_3$SnC$_{0.8}$) and tin deficient (Mn$_3$Sn$_{0.85}$C)
antiperovskite compounds are studied using x-ray absorption fine structure
spectroscopy and neutron diffraction. The study confirms the presence of local
structural distortions only around Mn atoms in the antiperovskite compounds
irrespective of their stoichiometry. The distortions in the Mn$_6$C octahedra
are such that only Mn atoms are displaced from their crystallographic positions
resulting in long and short Mn-Mn bonds. These long and short Mn-Mn bonds are
responsible for presence of ferromagnetic and antiferromagnetic moments on Mn
atoms. The C deficiency at the center of the octahedra increases the strain on
the Mn$_6$C octahedra and results in a wide variation of Mn-Mn bond distances
as a function of temperature and large hysteresis in magnetic properties. On
the other hand, Sn deficiency tends to relax strain by giving more space for
the octahedra to distort leading to temperature independent Mn-Mn bond
distances.",2004.00247v1
2020-04-01,"Thermoelectric and lattice dynamics properties of layered MX (M = Sn, Pb; X = S, Te) compounds","Lead and tin chalcogenides have been studied widely due to their promising
thermoelectric (TE) properties. Further enhancement in their TE efficiency has
been reported upon the reduction of the dimension, which is an important
feature in modern device fabrications. Using density functional theory combined
with the Semi-classical Boltzmann transport theory, we studied the structural,
electronic and TE properties of two-dimensional (2D) MX (M = Sn, Pb; X = S, Te)
monolayers. Spin-orbit coupling was found to have significant effects on their
electronic structure, particularly for the heavy compounds. Structural
optimization followed by phonon transport studies prevailed that the
rectangular ({\gamma}-) phase is energetically the most favorable for SnS and
SnTe monolayers, whereas the square structure is found the most stable for PbS
and PbTe monolayers. Our results are in good agreement with previous studies.
These 2D materials exhibit high Seebeck coefficients and power factors along
with low lattice thermal conductivities, which are essential features of good
TE materials. The maximum figure of merits (ZT) of 1.04, 1.46, 1.51 and 1.94
are predicted for n-type SnS, SnTe, PBS and p-type PbTe monolayers respectively
at 700 K, which are higher than their bulk ZT values. Hence, these monolayers
are promising candidates for TE applications.",2004.00688v1
2020-04-03,Inverse Design of Ultralow Lattice Thermal Conductivity Materials Via Lone Pair Cation Coordination Environment,"The presence of lone pair (LP) electrons is strongly associated with the
disruption of lattice heat transport, which is a critical component of
strategies to achieve efficient thermoelectric energy conversion. By exploiting
an empirical relationship between lattice thermal conductivity $\kappa_L$ and
the bond angles of pnictogen group LP cation coordination environments, we
develop an inverse design strategy based on a materials database screening to
identify chalcogenide materials with ultralow $\kappa_L$ for thermoelectrics.
Screening the $\sim$ 635,000 real and hypothetical inorganic crystals of the
Open Quantum Materials Database based on the constituent elements, nominal
electron counting, LP cation coordination environment, and synthesizability, we
identify 189 compounds expected to exhibit ultralow $\kappa_L$. As a
validation, we explicitly compute the lattice dynamical properties of two of
the compounds (Cu$_2$AgBiPbS$_4$ and MnTl$_2$As$_2$S$_5$) using
first-principles calculations and successfully find both achieve ultralow
$\kappa_L$ values at room temperature of $\sim$ 0.3--0.4 W/(m$\cdot$K)
corresponding to the amorphous limit. Our data-driven approach provides
promising candidates for thermoelectric materials and opens new avenues for the
design of phononic properties of materials.",2004.01579v1
2020-04-03,Spin-Phonon Coupling and Thermodynamic Behaviour in YCrO3 and LaCrO3: Inelastic Neutron Scattering and Lattice Dynamics,"We report detailed temperature-dependent inelastic neutron scattering and
ab-initio lattice dynamics investigation of magnetic perovskites YCrO3 and
LaCrO3. The magnetic neutron scattering from the Cr ions exhibits significant
changes with temperature and dominates at low momentum transfer regime.
Ab-inito calculations performed including magnetic interactions show that the
effect of magnetic interaction is very signicant on the low- as well as
high-energy phonon modes. We have also shown that the inelastic neutron
spectrum of YCrO3 mimics the magnon spectrum from a G-type antiferromagnetic
system, which is consistent with previously reported magnetic structure in the
compound. The ab-initio lattice dynamics calculations in both the compounds
exhibit anisotropic thermal expansion behaviour in the orthorhombic structure
and predict negative thermal expansion along the crystallographic a-axis at low
temperatures. We identify the anharmonic phonon modes responsible for this
anamolous behaviour in LaCrO3 involving low-energy La vibrations and
distortions of the CrO6 octahedra.",2004.01731v1
2020-04-05,On the Inhibition of COVID-19 Protease by Indian Herbal Plants: An In Silico Investigation,"COVID-19 has quickly spread across the globe, becoming a pandemic. This
disease has a variable impact in different countries depending on their
cultural norms, mitigation efforts and health infrastructure. In India, a
majority of people rely upon traditional Indian medicine to treat human
maladies due to less-cost, easier availability and without any side-effect.
These medicines are made by herbal plants. This study aims to assess the Indian
herbal plants in the pursuit of potential COVID-19 inhibitors using in silico
approaches. We have considered 18 extracted compounds of 11 different species
of these plants. Our calculated lipophilicity, aqueous solubility and binding
affinity of the extracted compounds suggest that the inhibition potentials in
the order; harsingar > aloe vera > giloy > turmeric > neem > ashwagandha > red
onion > tulsi > cannabis > black pepper. On comparing the binding affinity with
hydroxychloroquine, we note that the inhibition potentials of the extracts of
harsingar, aloe vera and giloy are very promising. Therefore, we believe that
these findings will open further possibilities and accelerate the works towards
finding an antidote for this malady.",2004.03411v1
2020-04-11,Monte Carlo simulations and critical behavior of the Rare Earth Based Alloy GdN,"Using Monte Carlo Simulations (MCS), based the Metropolis algorithm, we
examine in this study, the magnetic properties of the rare earth based compound
GdN. In a first step, we discuss and study the ground state phase diagrams
explored in the different planes of physical parameter. The obtained stable
configurations are illustrated by comparing the energies modeled by the
Hamiltonian of Eq. (1). For non-null temperature values, we present and discuss
the behavior the total magnetizations and susceptibilities as a function of:
the temperature, the crystal field, the exchange coupling interactions and the
external magnetic field. The hysteresis loops are illustrated and analyzed when
varying the external magnetic field for specific values of the physical
parameters: the temperature, the crystal field and the exchange coupling
interactions. In order to complete this study, we present the obtained values
of the critical exponents corresponding to compound GdN. Such results have been
compared with those existing in the literature.",2004.05457v1
2020-04-13,Suppression of long-range ordering and multiferroicity in Sr-substituted Ba3-xSrxMnNb2O9 (x = 1 and 3),"Effects of Sr substitution at A-site in ordered perovskite Ba3-xSrxMnNb2O9 (x
= 1 and 3) have been investigated using X-ray diffraction, magnetization,
dielectric/magnetodielectric and neutron diffraction measurements. The parent
compound Ba3MnNb2O9 having a large spin (S=5/2) is known to exhibit type-II
multiferroic properties with quasi 2D triangular lattice antiferromagnetic
ground state. A slight perturbation in exchange interaction due to substitution
of smaller size isovalent ion at the A-site in Ba3-xSrxMnNb2O9 (x = 1 and 3)
has been found to alter the ground states drastically and hence the
multiferroicity. The crucial role of various fluctuations (quantum and/or
thermal), weak lattice distortion induced by Sr-substitution and slight
imbalance between different fluctuations in determining the ground states and
the multiferroicity is discussed and compared with the results of smaller spin
compounds (S = 1/2 or 1).",2004.06175v1
2020-04-16,Fast exact computation of the $k$ most abundant isotope peaks with layer-ordered heaps,"The theoretical computation of isotopic distribution of compounds is crucial
in many important applications of mass spectrometry, especially as machine
precision grows. A considerable amount of good tools have been created in the
last decade for doing so. In this paper we present a novel algorithm for
calculating the top $k$ peaks of a given compound. The algorithm takes
advantage of layer-ordered heaps used in an optimal method of selection on
$X+Y$ and is able to efficiently calculate the top $k$ peaks on very large
molecules. Among its peers, this algorithm shows a significant speedup on
molecules whose elements have many isotopes. The algorithm obtains a speedup of
more than 31x when compared to $\textsc{IsoSpec}$ on \ch{Au2Ca10Ga10Pd76} when
computing 47409787 peaks, which covers 0.999 of the total abundance.",2004.07444v1
2020-04-16,Optically addressable molecular spins for quantum information processing,"Spin-bearing molecules are promising building blocks for quantum technologies
as they can be chemically tuned, assembled into scalable arrays, and readily
incorporated into diverse device architectures. In molecular systems, optically
addressing ground-state spins would enable a wide range of applications in
quantum information science, as has been demonstrated for solid-state defects.
However, this important functionality has remained elusive for molecules. Here,
we demonstrate such optical addressability in a series of synthesized
organometallic, chromium(IV) molecules. These compounds display a ground-state
spin that can be initialized and read out using light, and coherently
manipulated with microwaves. In addition, through atomistic modification of the
molecular structure, we tune the spin and optical properties of these
compounds, paving the way for designer quantum systems synthesized from the
bottom-up.",2004.07998v1
2020-04-19,"Hispidin and Lepidine E: two Natural Compounds and Folic acid as Potential Inhibitors of 2019-novel coronavirus Main Protease (2019-nCoVMpro), molecular docking and SAR study","2019-nCoV is a novel coronavirus was isolated and identified in 2019 in
Wuhan, China. On 17th February and according to world health organization, a
number of 71 429 confirmed cases worldwide, among them 2162 new cases recorded
in the last 24 hours. There is no drug or vaccine for human and animal
coronavirus. The inhibition of 3CL hydrolase enzyme provides a promising
therapeutic principle for developing treatments against CoViD-19. The 3CLpro
(Mpro) known for involving in counteracting the host innate immune response.
This work presents the inhibitory effect of some natural compounds against 3CL
hydrolase enzyme, and explain the main interactions in inhibitor-enzyme
complex. Molecular docking study carried out using Autodock Vina. By screening
several molecules, we identified three candidate agents that inhibit the main
protease of coronavirus. Hispidin, lepidine E, and folic acid bound tightly in
the enzyme, strong hydrogen bonds have been formed (1.69-1.80&[Aring]) with the
active site residues. This study provides a possible therapeutic strategy for
CoViD-19.",2004.08920v1
2020-04-22,Study of Reactively Sputtered Nickel Nitride Thin Films,"Nickel nitride (Ni-N) thin film samples were deposited using reactive
magnetron sputtering process utilizing different partial flow of N2 (RN2). They
were characterized using x-ray reflectivity (XRR), x-ray diffraction (XRD) and
x-ray absorption near edge spectroscopy (XANES) taken at N K-edge and Ni
L-edges. From XRR measurements, we find that the deposition rate and the
density of Ni-N films decrease due to successively progression in RN2,
signifying that Ni-N alloys and compounds are forming both at Ni target surface
and also within the thin film samples. The crystal structure obtained from XRD
measurements suggest an evolution of different Ni-N compounds given by: Ni,
Ni(N), Ni4N, Ni3N, and Ni2N with a gradual rise in RN2. XANES measurements
further confirm these phases, in agreement with XRD results. Polarized neutron
reflectivity measurements were performed to probe the magnetization, and it was
found Ni-N thin films become non-magnetic even when N incorporation increases
beyond few at%. Overall growth behavior of Ni-N samples has been compared with
that of rather well-known Fe-N and Co-N systems, yielding similarities and
differences among them.",2004.10405v1
2020-04-30,Compound Secure Groupcast: Key Assignment for Selected Broadcasting,"The compound secure groupcast problem is considered, where the key variables
at $K$ receivers are designed so that a transmitter can securely groupcast a
message to any $N$ out of the $K$ receivers through a noiseless broadcast
channel. The metric is the information theoretic tradeoff between key storage
$\alpha$, i.e., the number of bits of the key variable per message bit, and
broadcast bandwidth $\beta$, i.e., the number of bits of the broadcast
information per message bit.
  We have three main results. First, when broadcast bandwidth is minimized,
i.e., when $\beta = 1$, we show that the minimum key storage is $\alpha = N$.
Second, when key storage is minimized, i.e., when $\alpha = 1$, we show that
broadcast bandwidth $\beta = \min(N, K-N+1)$ is achievable and is optimal
(minimum) if $N=2$ or $K-1$. Third, when $N=2$, the optimal key storage and
broadcast bandwidth tradeoff is characterized as $\alpha+\beta \geq 3, \alpha
\geq 1, \beta \geq 1$.",2004.14986v1
2020-05-03,Microrheology to Probe Smectic Clusters in Bent-core Nematic Liquid Crystals,"Many bent-core nematic liquid crystals exhibit unusual physical properties
due to the presence of smectic clusters, known as ""cybotactic"" clusters in the
nematic phase. Effect of these clusters on complex shear modulus
($G^*(\omega)$) of such liquid crystals hitherto unexplored. Here, we study
flow viscosities and complex shear modulus of two asymmetric bent-core liquid
crystals using microrheology technique. The results are corroborated with the
measurements of curvature elastic constants. Compound with shorter hydrocarbon
chain (8OCH$_\text{3}$) exhibit only nematic (N) phase whereas the compound
with longer chain (16OCH$_\text{3}$) exhibits both nematic (N) and smectic-A
(SmA) phases. Our results show that the directional shear modulus of
16OCH$_\text{3}$, just above the SmA to N transition temperature is strikingly
different than 8OCH$_\text{3}$, owing to these smectic clusters. Thus,
microrheology enables us to probe smectic clusters in bent-core nematic liquid
crystals.",2005.00991v1
2020-05-04,Factorize Factorization,"Factorization -- a simple form of standardization -- is concerned with
reduction strategies, i.e. how a result is computed. We present a new technique
for proving factorization theorems for compound rewriting systems in a modular
way, which is inspired by the Hindley-Rosen technique for confluence.
Specifically, our technique is well adapted to deal with extensions of the
call-by-name and call-by-value lambda-calculi. The technique is first developed
abstractly. We isolate a sufficient condition (called linear swap) for lifting
factorization from components to the compound system, and which is compatible
with beta-reduction. We then closely analyze some common factorization schemas
for the lambda-calculus. Concretely, we apply our technique to diverse
extensions of the lambda-calculus, among which de' Liguoro and Piperno's
non-deterministic lambda-calculus and -- for call-by-value -- Carraro and
Guerrieri's shuffling calculus. For both calculi the literature contains
factorization theorems. In both cases, we give a new proof which is neat,
simpler than the original, and strikingly shorter.",2005.01808v2
2020-05-05,Study of single crystalline SrAgSb and SrAuSb semimetals,"Given renewed interest in the electronic properties of semimetallic compounds
with varying degrees of spin orbit coupling we have grown single crystals of
SrAgSb and SrAuSb, measured their temperature and field dependent electrical
resistivity and magnetization and performed density functional theory (DFT)
band structure calculations. Magnetization measurements are consistent with a
diamagnetic host with a small amount of local moment bearing impurities.
Although the residual resistivity ratio (RRR) for all samples studied was
relatively low, ranging between 2.4 and 3.4, the compounds had non-saturating
magnetoresistance (MR), reaching values of $\sim$ 17% and $\sim$ 70% at 4 K and
9 T for SrAgSb and SrAuSb respectively. Band structure calculations, using the
experimentally determined Wyckoff positions for the Sr, Ag/Au, and Sb atoms,
show that whereas SrAgSb is a topologically trivial, but compensated,
semimetal; SrAuSb is a topologically non-trivial, Dirac semimetal.",2005.02323v1
2020-05-06,Understanding the Curious Magnetic State of Sr$_{3}$OsO$_{6}$,"Motivated by the recent report on high T$_c$ ferromagnetic insulating state
of single transition metal containing double perovskite compound, Sr$_3$OsO$_6$
(Wakabayashi et. al., Nature Commun {\bf 10} 535, 2019), we study this curious
behavior by employing first-principles calculations in conjunction with exact
diagonalization of full $t_{2g}$ multiplet problem of two Os sites. Our
analysis highlights the fact that stabilization of Sr$_3$OsO$_6$ in the cubic
phase in epitaxially grown thin film is the key to both ferromagnetic
correlation and high temperature scale associated to it. This also provides a
natural explanation for the sister compound, Ca$_3$OsO$_6$ to exhibit low T$_N$
antiferromagnetism in its monoclinic structure. Further the insulating property
is found to be driven by opening of Mott gap in the half filled spin-orbit
coupled $j=3/2$ manifold of $d^{2}$ Os. We point out that Sr$_2$CaOsO$_6$ which
naturally forms in the cubic phase would be worthwhile to explore as a future
candidate to exhibit high T$_c$ ferromagnetic insulating state in bulk form.",2005.02582v2
2020-05-10,A Compound Decision Approach to Covariance Matrix Estimation,"Covariance matrix estimation is a fundamental statistical task in many
applications, but the sample covariance matrix is sub-optimal when the sample
size is comparable to or less than the number of features. Such
high-dimensional settings are common in modern genomics, where covariance
matrix estimation is frequently employed as a method for inferring gene
networks. To achieve estimation accuracy in these settings, existing methods
typically either assume that the population covariance matrix has some
particular structure, for example sparsity, or apply shrinkage to better
estimate the population eigenvalues. In this paper, we study a new approach to
estimating high-dimensional covariance matrices. We first frame covariance
matrix estimation as a compound decision problem. This motivates defining a
class of decision rules and using a nonparametric empirical Bayes g-modeling
approach to estimate the optimal rule in the class. Simulation results and gene
network inference in an RNA-seq experiment in mouse show that our approach is
comparable to or can outperform a number of state-of-the-art proposals.",2005.04549v4
2020-05-10,Pressure induced Lifshitz transition in ThFeAsN,"In this paper, we present pressure dependent structural parameters and
electronic structure of ThFeAsN superconductor. There are no anomalies in the
structural parameters as well as elastic constants with hydrostatic pressure
which is consistent with the experiments. We study the electronic structure of
this compound at different external pressures in terms of density of states,
band structure and Fermi surface. Density of states at the Fermi level, coming
from Fe-d orbitals follows the same trend as that of the superconducting
transition temperature (T$_c$) as a function of hydrostatic pressure. We also
observe a pressure induced orbital selective Lifshitz transition in ThFeAsN
compound which is quite different from the Lifshitz transitions observed in the
other families of Fe-based superconductors. Fermi surfaces of ThFeAsN specially
hole like Fermi surfaces at $\Gamma$ point are altered significantly with
pressure. This modification of Fermi surface topology with pressure seems to
play the major role in the reduction of T$_c$ with pressure in ThFeAsN
superconductor. Spin-orbit coupling does not affect the Lifshitz transition but
it modifies the energy ordering of bands near $\Gamma$ point at higher
pressure.",2005.04576v1
2020-05-10,Linear nonsaturating magnetoresistance in the Nowotny chimney ladder compound Ru$_2$Sn$_3$,"We present magnetoresistivity measurements in high-quality single crystals of
the Nowotny chimney ladder compound Ru$_2$Sn$_3$. We find a linear and
nonsaturating magnetoresistance up to 20 T. The magnetoresistance changes with
the magnetic field orientation at small magnetic fields, from a positive to a
negative curvature. Above 5 T, the magnetoresistance shows no sign of
saturation up to 20 T for any measured angle. The shape of the anisotropy in
the magnetoresistance remains when increasing temperature and Kohler's rule is
obeyed. We associate the linear and nonsaturating magnetoresistance to a small
Fermi surface with hot spots, possibly formed as a consequence of the
structural transition. We discuss the relevance of electron-electron
interactions under magnetic fields and aspects of the topologically nontrivial
properties expected in Ru$_2$Sn$_3$.",2005.04632v1
2020-05-12,Do not let the history haunt you -- Mitigating Compounding Errors in Conversational Question Answering,"The Conversational Question Answering (CoQA) task involves answering a
sequence of inter-related conversational questions about a contextual
paragraph. Although existing approaches employ human-written ground-truth
answers for answering conversational questions at test time, in a realistic
scenario, the CoQA model will not have any access to ground-truth answers for
the previous questions, compelling the model to rely upon its own previously
predicted answers for answering the subsequent questions. In this paper, we
find that compounding errors occur when using previously predicted answers at
test time, significantly lowering the performance of CoQA systems. To solve
this problem, we propose a sampling strategy that dynamically selects between
target answers and model predictions during training, thereby closely
simulating the situation at test time. Further, we analyse the severity of this
phenomena as a function of the question type, conversation length and domain
type.",2005.05754v1
2020-05-19,Transferability of neural network potentials for varying stoichiometry: phonons and thermal conductivity of Mn$_x$Ge$_y$ compounds,"Germanium manganese compounds exhibit a variety of stable and metastable
phases with different stoichiometry. These materials entail interesting
electronic, magnetic and thermal properties both in their bulk form and as
heterostructures. Here we develop and validate a transferable machine learning
potential, based on the high-dimensional neural network formalism, to enable
the study of Mn$_x$Ge$_y$ materials over a wide range of compositions. We show
that a neural network potential fitted on a minimal training set reproduces
successfully the structural and vibrational properties and the thermal
conductivity of systems with different local chemical environments, and it can
be used to predict phononic effects in nanoscale heterostructures.",2005.09591v1
2020-05-22,Monolayer 2D semiconducting tellurides for high-mobility electronics,"Discovery and design of two-dimensional (2D) materials with suitable band
gaps and high carrier mobility is of vital importance for photonics,
optoelectronics, and high-speed electronics. In this work, based on first
principles calculations using density functional theory (DFT) with PBE and HSE
functionals, we introduce a family of monolayer isostructural semiconducting
tellurides M2N2Te8, with M = {Ti, Zr, Hf} and N= {Si, Ge}. These compounds have
been identified to possess direct band gaps from 1.0 eV to 1.31 eV, which are
well suited for photonics and optoelectronics applications. Additionally,
anisotropic in-plane transport behavior is observed and small electron and hole
(0.11 - 0.15 me) effective masses are identified along the dominant transport
direction. Ultra-high carrier mobility is predicted for this family of 2D
compounds which host great promise for potential applications in high-speed
electronic devices. Detailed analysis of electronic structures reveals the
origins of the promising properties of this unique class of 2D telluride
materials.",2005.11377v2
2020-05-18,Compounding Injustice: History and Prediction in Carceral Decision-Making,"Risk assessment algorithms in criminal justice put people's lives at the
discretion of a simple statistical tool. This thesis explores how algorithmic
decision-making in criminal policy can exhibit feedback effects, where
disadvantage accumulates among those deemed 'high risk' by the state. Evidence
from Philadelphia suggests that risk - and, by extension, criminality - is not
fundamental or in any way exogenous to political decision-making. A close look
at the geographical and demographic properties of risk calls into question the
current practice of prediction in criminal policy. Using court docket summaries
from Philadelphia, we find evidence of a criminogenic effect of incarceration,
even controlling for existing determinants of 'criminal risk'. With evidence
that criminal treatment can influence future criminal convictions, we explore
the theoretical implications of compounding effects in repeated carceral
decisions.",2005.13404v1
2020-05-28,Fantastic flat bands and where to find them: The CoSn-type compounds,"Quantum interference on the kagome lattice generates electronic bands with
narrow bandwidth, called flat bands. Crystal structures incorporating this
lattice can host strong electron correlations with non-standard ingredients,
but only if these bands lie at the Fermi level. In the six compounds with the
CoSn structure type (FeGe, FeSn, CoSn, NiIn, RhPb, and PtTl) the transition
metals form a kagome lattice. The two iron variants are robust antiferromagnets
so we focus on the latter four and investigate their thermodynamic and
transport properties. We consider these results and calculated band structures
to locate and characterize the flat bands in these materials. We propose that
CoSn and RhPb deserve the community's attention for exploring flat band
physics.",2005.14119v1
2020-08-02,High-throughput screening of quaternary compounds and new insight for excellent thermoelectric performance,"It is well known that the high electric conductivity, large Seebeck
coefficient, and low thermal conductivity are preferred for enhancing
thermoelectric performance, but unfortunately, these properties are strongly
inter-correlated with no rational scenario for their efficient decoupling. This
big dilemma for thermoelectric research appeals for alternative strategic
solutions, while the high-throughput screening is one of them. In this work, we
start from total 3136 real electronic structures of the huge X2YZM4 quaternary
compound family and perform the high-throughput searching in terms of enhanced
thermoelectric properties. The comprehensive data-mining allows an evaluation
of the electronic and phonon characteristics of those promising thermoelectric
materials. More importantly, a new insight that the enhanced thermoelectric
performance benefits substantially from the coexisting quasi-Dirac and heavy
fermions plus strong optical-acoustic phonon hybridization, is proposed. This
work provides a clear guidance to theoretical screening and experimental
realization and thus towards development of performance-excellent
thermoelectric materials.",2008.00383v3
2020-08-05,Multigap superconductivity in the Mo$_5$PB$_2$ boron-phosphorus compound,"The tetragonal Mo$_5$PB$_2$ compound was recently reported to show
superconductivity with a critical temperature up to 9.2 K. In search of
evidence for multiple superconducting gaps in Mo$_5$PB$_2$, comprehensive
measurements, including magnetic susceptibility, electrical resistivity, heat
capacity, and muon-spin rotation and relaxation ($\mu$SR) measurements were
carried out. Data from both low-temperature superfluid density and electronic
specific heat suggest a nodeless superconducting ground state in Mo$_5$PB$_2$.
Two superconducting energy gaps $\Delta_0$ = 1.02 meV (25%) and 1.49 meV (75%)
are required to describe the low-$T$ electronic specific-heat data. The
multigap features are clearly evidenced by the field dependence of the
electronic specific-heat coefficient and the Gaussian relaxation rate in the
superconducting state (i.e., superfluid density), as well as by the temperature
dependence of the upper critical field. By combining our extensive experimental
results with numerical band-structure calculations, we provide compelling
evidence of multigap superconductivity in Mo$_5$PB$_2$.",2008.01982v1
2020-08-25,First principles study on the thermoelectric performance of CaAl$_2$Si$_2$-type Zintl phase compounds,"We investigate the thermoelectric properties of CaAl$_2$Si$_2$-type Zintl
phase compounds $AB_2X_2$ ($A$ = Mg, Ca, Sr, Ba, $B$ = Mg, Zn, Cd, and $X$ = P,
As, Sb) using first principles band calculations within the Boltzmann transport
theory assuming the constant relaxation time approximation. We introduce the
effective degree of valley degeneracy $n_{TE}$ to focus on the relationship
between the thermoelectric properties and the multivalley character of the
electronic band structure around the Fermi level. We also introduce a quantity
$\gamma_{TE}$, which takes into account $n_{TE}$ and anisotropy of the valley
structure, and it is found that $\gamma_{TE}$ enables us to well understand the
overall trend of the material dependence of the power factor. We finally
suggest promising thermoelectric materials, e.g. BaMg$_2$P$_2$ for PF $\sim
20\mu$W/cmK$^2$ and $ZT > 0.2$ at 300K and SrZn$_2$As$_2$ for PF $\sim
35\mu$W/cmK$^2$ and $ZT > 0.35$ at 300K assuming a relaxation time of 10 fs and
a lattice thermal conductivity value of 2 W/mK.",2008.10917v1
2020-08-27,Hard Magnetic Topological Semimetals in XPt3: Harmony of Berry Curvature,"Topological magnetic semimetals, like Co3Sn2S2 and Co2MnGa, are known to
display exotic transport properties, such as large intrinsic anomalous (AHE)
due to uncompensated Berry curvature. The highly symmetric XPt3 compounds
display anti-crossing gapped nodal lines, which are a driving mechanism in the
intrinsic Berry curvature Hall effects. Uniquely, these compounds contain two
sets of gapped nodal lines that harmoniously dominate the Berry curvature in
this complex multiband system. We calculate a maximum AHE of 1965 S/cm in the
CrPt3 by a state-of-the-art first principle electronic structure. We have grown
high-quality thin films by magnetron sputtering and measured a robust AHE of
1750 S/cm for different sputtering growth conditions. Additionally, the cubic
films display a hard magnetic axis along [111] direction. The facile and
scalable fabrication of these materials is prime candidates for integration
into topological devices.",2008.11914v1
2020-08-28,First-principles prediction of Structural Stability and Thermoelectric Properties of SrGaSnH,"Thermoelectric materials based on earth-abundant and non-toxic elements are
very useful in cost-effective and eco-friendly waste heat management systems.
The constituents of SrGaSnH are earth-abundant and non-toxic, thus we have
chosen SrSnGaH to study its structural stability and thermoelectric properties
by using DFT, DFPT, and semi-classical Boltzmann transport theory. Our elastic
and phonons calculations show that the compound has good structural stability.
The electronic structure calculation discloses that it is an indirect bandgap
(0.63 eV by mBJ+SOC) semiconductor. Light band hole effective mass leads to
higher electrical conductivity along x-axis than that of along z-axis. On the
other side, the weak phonon scattering leads to high lattice thermal
conductivity ~10.5 W m-1K-1 at 300 K. Although the power factor (PF) is very
high along the x-axis (above 10 mW m-1K-2 at 300 K), such large kl dramatically
reduces ZT. The maximum values of in-plane and cross-plane ZT are ~1 (n-type),
0.8 (p-type) and 0.6 (n-type), (0.2 p-type) at 700 K, respectively. The present
study has revealed that this compound has strong potential in eco-friendly TE
applications.",2008.12583v1
2021-03-03,An Empirical Study of Compound PCFGs,"Compound probabilistic context-free grammars (C-PCFGs) have recently
established a new state of the art for unsupervised phrase-structure grammar
induction. However, due to the high space and time complexities of chart-based
representation and inference, it is difficult to investigate C-PCFGs
comprehensively. In this work, we rely on a fast implementation of C-PCFGs to
conduct an evaluation complementary to that of~\citet{kim-etal-2019-compound}.
We start by analyzing and ablating C-PCFGs on English treebanks. Our findings
suggest that (1) C-PCFGs are data-efficient and can generalize to unseen
sentence/constituent lengths; and (2) C-PCFGs make the best use of
sentence-level information in generating preterminal rule probabilities. We
further conduct a multilingual evaluation of C-PCFGs. The experimental results
show that the best configurations of C-PCFGs, which are tuned on English, do
not always generalize to morphology-rich languages.",2103.02298v2
2021-03-08,The fate of compound with AgF$_2$ plus AgO stoichiometry. A theoretical study,"Metal oxyfluorides constitute a broad group of chemical compounds with rich
spectrum of crystal structures and properties. Here we predict, based on
evolutionary algorithm approach, the crystal structure and selected properties
of Ag$_2$OF$_2$. This system may be considered as the 1 to 1 adduct of AgF$_2$
(i.e. an antiferromagnetic charge transfer positive U insulator) and AgO (i.e.
a disproportionated negative U insulator). We analyze oxidation states of
silver in each structure, possible magnetic interactions, as well as energetic
stability. Prospect is outlined for synthesis of polytypes of interest using
diverse synthetic approaches.",2103.04733v1
2021-03-10,Crystal Growth of a New 8H Perovskite Sr8Os6.3O24 Exhibiting High TC Ferromagnetism,"Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24
have been synthesized, and structural and magnetic properties have been
determined. The compound crystallizes in a hexagonal cell with lattice
parameters a = 9.6988(3) {\AA} and c = 18.1657(5) {\AA}. The structure is an
eight-layered hexagonal B-site deficient perovskite with the layer sequence
(ccch)2 and represents the first example of a hexagonal structure among 5d
oxides adopting a twin option. The sample shows spontaneous ferromagnetic
magnetization below 430 K with a small saturation moment of 0.11 {\mu}B/Os ion.
This is the highest Curie temperature (TC) reported for any bulk perovskite
containing only 5d ions at the B site.",2103.06305v1
2021-03-11,Fast and Accurate Model Scaling,"In this work we analyze strategies for convolutional neural network scaling;
that is, the process of scaling a base convolutional network to endow it with
greater computational complexity and consequently representational power.
Example scaling strategies may include increasing model width, depth,
resolution, etc. While various scaling strategies exist, their tradeoffs are
not fully understood. Existing analysis typically focuses on the interplay of
accuracy and flops (floating point operations). Yet, as we demonstrate, various
scaling strategies affect model parameters, activations, and consequently
actual runtime quite differently. In our experiments we show the surprising
result that numerous scaling strategies yield networks with similar accuracy
but with widely varying properties. This leads us to propose a simple fast
compound scaling strategy that encourages primarily scaling model width, while
scaling depth and resolution to a lesser extent. Unlike currently popular
scaling strategies, which result in about $O(s)$ increase in model activation
w.r.t. scaling flops by a factor of $s$, the proposed fast compound scaling
results in close to $O(\sqrt{s})$ increase in activations, while achieving
excellent accuracy. This leads to comparable speedups on modern memory-limited
hardware (e.g., GPU, TPU). More generally, we hope this work provides a
framework for analyzing and selecting scaling strategies under various
computational constraints.",2103.06877v1
2021-03-14,"Thickness dependence of work function, ionization energy, and electron affinity of Mo and W dichalcogenides from DFT and GW calculations","Transition-metal dichalcogenides (TMDs) are promising for two-dimensional
(2D) semiconducting devices and novel phenomena. For 2D applications, their
work function, ionization energy, and electron affinity are required as a
function of thickness, but research on this is yet to cover the full family of
compounds. Here, we present the work function, ionization energy, and electron
affinity of few-layer and bulk MX2 (M = Mo, W and X = S, Se, Te) in 2H phase
obtained accurately by the density functional theory and GW calculations. For
each compound, we consider one-, two-, three-, four-layer, and bulk geometry.
In GW calculations, accurate results are obtained by nonuniform q sampling for
two-dimensional geometry. From band energies including the GW self-energy
correction, we estimate the work function, band gap, ionization energy, and
electron affinity as functions of the number of layers. We compare our results
with available theoretical and experimental reports, and we discuss types of
band alignments in in-plane and out-of-plane junctions of these few-layer and
bulk TMDs.",2103.07858v1
2021-03-14,Electron-beam Floating-zone Refined UCoGe,"The interplay between unconventional superconductivity and quantum critical
ferromagnetism in the U-Ge compounds represents an open problem in strongly
correlated electron systems. Sample quality can have a strong influence on both
of these ordered states in the compound UCoGe, as is true for most
unconventional superconductors. We report results of a new approach at UCoGe
crystal growth using a floating-zone method with potential for improvements of
sample quality and size as compared with traditional means such as Czochralski
growth. Single crystals of the ferromagnetic superconductor UCoGe were produced
using an ultra-high vacuum electron-beam floating-zone refining technique.
Annealed single crystals show well-defined signatures of bulk ferromagnetism
and superconductivity at $T_c \sim$2.6 K and $T_s \sim$0.55 K, respectively, in
the resistivity and heat capacity. Scanning electron microscopy of samples with
different surface treatments shows evidence of an off-stoichiometric uranium
rich phase of UCoGe collected in cracks and voids that might be limiting sample
quality.",2103.08000v1
2021-03-17,Infrared study of the pressure-induced isostructural metallic transition in Mo$_{0:5}$W$_{0:5}$S$_{2}$,"Ternary compounds of Transition Metal Dichalcogenides are emerging as an
interesting class of crystals with tunable electronic properties, which make
them attractive for nano-electronic and optoelectronic applications. Among
them, Mo$_x$W$_{1-x}$S$_2$ is one of the most studied alloys, due to the
well-known, remarkable features of its binary constituents, MoS$_2$ and WS$_2$.
The band-gap of this compound can be modelled varying Mo and W percentages in
the sample, and its vibrational modes result from a combination of MoS$_2$ and
WS$_2$ phonons. In this work, we report transmission measurements on a
Mo$_{0:5}$W$_{0:5}$S$_2$ single crystal in the far-infrared range. Absorbance
spectra collected at ambient conditions enabled, for the first time, a
classification of the infrared-active phonons, complementary to Raman studies.
High-pressure measurements allowed to study the evolution of both the lattice
dynamics and the free carrier density up to 31 GPa, indicating the occurrence
of an isostructural semiconductor-to-metal transition above 18 GPa.",2103.09517v1
2021-03-18,A Large Starphene Comprising Pentacene Branches,"Starphenes are attractive compounds due to their characteristic
physicochemical properties that are inherited from acenes, making them
interesting compounds for organic electronics and optics. However, the
instability and low solubility of larger starphene homologs make their
synthesis extremely challenging. Herein, we present a new strategy leading to
pristine [16]starphene in preparative scale. Our approach is based on a
synthesis of a carbonyl-protected starphene precursor that is thermally
converted in a solid-state form to the neat [16]starphene, which is then
characterised with a variety of analytical methods, such as 13C CP-MAS NMR,
TGA, MS MALDI, UV-Vis and FTIR spectroscopy. Furthermore, high-resolution STM
experiments unambiguously confirm its expected structure and reveal a moderate
electronic delocalisation between the pentacene arms. Nucleus-independent
chemical shifts NICS(1) are also calculated to survey its aromatic character.",2103.10072v1
2021-03-21,A Deep Deterministic Policy Gradient-based Strategy for Stocks Portfolio Management,"With the improvement of computer performance and the development of
GPU-accelerated technology, trading with machine learning algorithms has
attracted the attention of many researchers and practitioners. In this
research, we propose a novel portfolio management strategy based on the
framework of Deep Deterministic Policy Gradient, a policy-based reinforcement
learning framework, and compare its performance to that of other trading
strategies. In our framework, two Long Short-Term Memory neural networks and
two fully connected neural networks are constructed. We also investigate the
performance of our strategy with and without transaction costs. Experimentally,
we choose eight US stocks consisting of four low-volatility stocks and four
high-volatility stocks. We compare the compound annual return rate of our
strategy against seven other strategies, e.g., Uniform Buy and Hold,
Exponential Gradient and Universal Portfolios. In our case, the compound annual
return rate is 14.12%, outperforming all other strategies. Furthermore, in
terms of Sharpe Ratio (0.5988), our strategy is nearly 33% higher than that of
the second-best performing strategy.",2103.11455v1
2021-03-22,Spin-dependent optical excitations in LiFeO2,"The three-dimensional ternary LiFeO2 compound presents various unusual
essential properties. The main features are thoroughly explored by the density
functional and many-body perturbation theory. The concise physical/chemical
picture, the critical spin-polarizations and orbital hybridizations in the Li-O
and Fe-O bonds, are clearly examined through geometric optimization,
quasi-particle energy spectra, spin-polarized density of states, the spatial
charge densities, the spin-density distributions, and the strong optical
responses. The unusual optical transitions cover various frequency-dependent
absorption structures, and the most prominent plasmon modes are identified by
the dielectric functions, energy loss functions, reflectance spectra, and
absorption coefficients. Optical excitations are anisotropic and strongly
affected by excitonic effects. The close combinations of electronic, magnetic
and optical properties allow us to identify the significant spin-polarizations
and orbital hybridizations for each available excitation channel. The lithium
ferrite compound can be used for spintronic and photo-catalysis applications.",2103.11838v3
2021-03-24,VLGrammar: Grounded Grammar Induction of Vision and Language,"Cognitive grammar suggests that the acquisition of language grammar is
grounded within visual structures. While grammar is an essential representation
of natural language, it also exists ubiquitously in vision to represent the
hierarchical part-whole structure. In this work, we study grounded grammar
induction of vision and language in a joint learning framework. Specifically,
we present VLGrammar, a method that uses compound probabilistic context-free
grammars (compound PCFGs) to induce the language grammar and the image grammar
simultaneously. We propose a novel contrastive learning framework to guide the
joint learning of both modules. To provide a benchmark for the grounded grammar
induction task, we collect a large-scale dataset, \textsc{PartIt}, which
contains human-written sentences that describe part-level semantics for 3D
objects. Experiments on the \textsc{PartIt} dataset show that VLGrammar
outperforms all baselines in image grammar induction and language grammar
induction. The learned VLGrammar naturally benefits related downstream tasks.
Specifically, it improves the image unsupervised clustering accuracy by 30\%,
and performs well in image retrieval and text retrieval. Notably, the induced
grammar shows superior generalizability by easily generalizing to unseen
categories.",2103.12975v1
2022-02-08,"Spin-Phonon Relaxation in Magnetic Molecules: Theory, Predictions and Insights","Magnetic molecules have played a central role in the development of magnetism
and coordination chemistry and their study keeps leading innovation in
cutting-edge scientific fields such as magnetic resonance, magnetism,
spintronics, and quantum technologies. Crucially, a long spin lifetime well
above cryogenic temperature is a stringent requirement for all these
applications. In this chapter we review the foundations of spin relaxation
theory and provide a detailed overview of first-principles strategies applied
to the problem of spin-phonon relaxation in magnetic molecules. Firstly, we
present a rigorous formalism of spin-phonon relaxation based on open quantum
systems theory. These results are then used to derive classical
phenomenological relations based on the Debye model. Finally, we provide a
prescription of how to map the relaxation formalism onto existing electronic
structure methods to obtain a quantitative picture of spin-phonon relaxation.
Examples from the literature, including both transition metals and lanthanides
compounds, will be discussed in order to illustrate how Direct, Orbach and
Raman relaxation mechanisms can affect spin dynamics for this class of
compounds.",2202.03776v1
2022-02-11,Screening promising CsV3Sb5-like kagome materials from systematic first-principles evaluation,"CsV3Sb5 kagome lattice holds the promise for manifesting electron
correlation, topology and superconducting. However, by far only three
CsV3Sb5-like kagome materials have been experimentally spotted. In this work,
we enlarge this family of materials to 1386 compounds via element species
substitution, and the further screening process suggests that 28 promising
candidates have superior thermodynamic stability, hence they are highly likely
to be synthesized. Moreover, these compounds possess several identical
electronic structures, and can be categorized into five non-magnetic and three
magnetic groups accordingly. It is our hope that this work can greatly expand
the viable phase space of the CsV3Sb5-like materials for investigating or
tuning the novel quantum phenomena in kagome lattice.",2202.05645v1
2022-02-15,"Theoretical Investigation of Structural, Electronic Properties and Half-Metallic Ferromagnetism in Ti doped CaS","In this research paper, we investigated the structural, electronic, and
magnetic features of titanium atom substituting calciumatom in rock salt
structure of CaS to explore the new dilute magnetic semiconductor compounds.
The calculations are carried out using the full potential linearized augmented
plane wave (FP-LAPW) method based on spin-polarized density functional theory,
implemented in WIEN2k code. The generalized gradient approximation and
Tran-Balaha modified Becke-Johnson exchange potential. The stability of Ti
doped CaS in ferromagnetic state is provided by the total energy released from
the optimized structures and defect formation energies. The classical model of
Heisenberg is employed to estimate Curie temperature of these compounds. It is
found that the room temperature ferromagnetism is achieved at low
concentrations. The studied materials exhibit half metallic ferromagnetic
demeanor. The half metallic gaps (GHM) are the extremely significant factors to
consider for spintronic applications. The insertion of impurity significantly
decreased the value of GHM due the broadening of 3d Ti states in the gap of the
minority spin. Furthermore, to evaluate the effects of the exchange splitting
process, the pd exchange splitting and the exchange constants are predicted.",2202.06947v1
2022-02-15,Unconventional dual 1D-2D quantum spin liquid revealed by $ab$ $initio$ studies on organic solids family,"Organic solids host various electronic phases. Especially, a milestone
compound of organic solid, $\beta'$-$X$[Pd(dmit)$_2$]$_2$ with $X$=EtMe$_3$Sb
shows quantum spin-liquid (QSL) properties suggesting a novel state of matter.
However, nature of the QSL has been largely unknown. Here, we computationally
study five compounds comprehensively with different $X$ using 2D $ab$ $initio$
Hamiltonians and correctly reproduce experimental phase diagram with
antiferromagnetic order for $X$=Me$_4$P, Me$_4$As, Me$_4$Sb, Et$_2$Me$_2$As and
a QSL for $X$=EtMe$_3$Sb without adjustable parameters. We find that the QSL
for $X$=EtMe$_3$Sb exhibits 1D nature characterized by algebraic decay of spin
correlation along one direction, while exponential decay in the other
direction, indicating dimensional reduction from 2D to 1D. The 1D nature indeed
accounts for the experimental specific heat, thermal conductivity and magnetic
susceptibility. The identified QSL, however, preserves 2D nature as well
consistently with spin fractionalization into spinon with Dirac-like gapless
excitations and reveals duality bridging the 1D and 2D QSLs.",2202.07182v2
2022-02-15,Semi-metallicity and electron-hole liquid in two-dimensional C and BN based compounds,"Insulating-metallic transition mediated by substitutional atoms is predicted
in a series of two-dimensional carbon-based structures. Introducing Si atoms in
selected sites of tetrahexcarbon [Carbon 137 (2018) 266] according to rational
chemical rules, metallicity by trivial band inversion without band gap opening
is induced. Additional substitution of remaining C atoms by BN dimers
introduces no changes in the metallic properties. A series of isomorphous
two-dimensional materials with isoelectronic structures derived by exchanging
group IV elements exhibiting various band gaps is obtained. Dynamical stability
is verified with phonon analysis and beyond the harmonic approximation with
molecular dynamics up to room temperature. The semi-metallic compounds have
well-nested pockets of carriers and are good candidates for the formation of an
excitonic insulator.",2202.07618v1
2022-02-15,Ultrasound detection of emergent photons in generic quantum spin ice,"Experimental identification of quantum spin ice (QSI), a U(1) quantum spin
liquid on the pyrochlore lattice hosting emergent photons, is a major challenge
in frustrated magnets. In this work, we propose ultrasound measurements as a
novel tool for probing the emergent photons of various QSI phases. Our analysis
includes QSI phases in non-Kramers doublet compounds such as $\rm{Pr}_2
\rm{Zr}_2 \rm{O}_7$ as well as dipolar-octupolar Kramers doublet compounds such
as $\rm{Ce}_2 \rm{Zr}_2 \rm{O}_7$. The latter may host emergent photons
associated with an octupolar component which renders them difficult to detect
with inelastic neutron scattering. We demonstrate theoretically how the speed
of the emergent photons can be obtained from the renormalization of the phonon
spectrum and show that ultrasound measurements provide a means of
distinguishing the dipolar from the octupolar QSI phase in dipolar-octupolar
materials.",2202.07670v2
2022-03-05,On the Atomic Structure of Two-Dimensional Materials with Janus Structures,"The discrepancy between the bright theoretical projections for
two-dimensional (2D) Janus structures and the lack of experimental realisation
of these structures motivated us to study the effect of structural disorder on
the stability of MoSSe, SnSSe, PtSSe, In2SSe and GaInSe2. The calculation
results demonstrate that the difference between metal-sulfur and metal-selenium
bonds makes Janus structures frustrated and less energetically favourable than
less ordered allotropes of the same compounds. This result explains the
difficulties encountered in experimental fabrication of these materials. In the
bulk, there is an additional contribution to the total energy from
dipole-dipole interactions between layers with a Janus structure that can
overcome the energetic cost of structural frustration in layers for compounds
with sufficiently large dipole moments. However, the entropic contribution to
the free energy decreases the favourability of the ordered Janus structure. The
calculation results are used to make recommendations to enable the discovery
and synthesis of 2D materials with Janus structures.",2203.02731v1
2022-03-10,"Chiral phonons in binary compounds $A$Bi ($A$ = K, Rb, Cs) with P2$_1$/c structure","Binary compounds $A$Bi ($A$ = K, Rb, Cs) crystallize in P2$_1$/c structure
containing both clockwise and anticlockwise chiral chains of Bi atoms.
Electronic band structure exhibits the insulating nature of these systems, with
the band gap about $0.25$ eV. The presented study of dynamical properties
confirm a stability of the system with P2$_1$/c symmetry. The crystal structure
contains the quasi-one-dimensional Bi chains, exhibiting four-fold-like
rotational ``local'' symmetry. Nevertheless, the system formally posses
two-fold rotational symmetry. Independently of the absence of the three-fold
(or higher) rotational symmetry axes for the whole crystal, the chiral modes
propagate along the Bi atom chains in these systems. We discuss basic
properties of these modes in monoatomic chiral chains. We show that the
two-fold rotational symmetry axis affects the main properties of the chiral
phonons, which are not realized at the high-symmetry points, but along some
paths between them in the reciprocal space. In addition, in the doped system,
the chiral phonons possess non-zero total angular momentum.",2203.05524v2
2022-03-11,Engineering magnetic topological insulators in Eu$_5M_2X_6$ Zintls,"Magnetic topological insulator provide a prominent material platform for
quantum anomalous Hall physics and axion electrodynamics. However, the lack of
material realizations with cleanly gapped surfaces hinders technological
utilization of these exotic quantum phenomena. Here, using the Zintl concept
and the properties of non-symmorphic space groups, we computationally engineer
magnetic topological insulators. Specifically, we explore Eu$_5M_2X_6$
($M$=metal, $X$=pnictide) Zintl compounds and find that Eu$_5$Ga$_2$Sb$_6$,
Eu$_5$Tl$_2$Sb$_6$ and Eu$_5$In$_2$Bi$_6$ form stable structures with
non-trivial $\mathbb{Z}_2$ indices. We also show that epitaxial and uniaxial
strain can be used to control the $\mathbb{Z}_2$ index and the bulk energy gap.
Finally, we discuss experimental progress towards the synthesis of the proposed
candidates and provide insights that can be used in the search for robust
magnetic topological insulators in Zintl compounds.",2203.06212v2
2022-03-13,"Strong Magneto-Elastic Coupling in Mn$_3$X (X = Ge, Sn)","We measure the full elastic tensors of Mn$_3$Ge and Mn$_3$Sn as a function of
temperature through their respective antiferromagnetic phase transitions. Large
discontinuities in the bulk moduli at the N\'eel transitions indicate strong
magnetoelastic coupling in both compounds. Strikingly, the discontinuities are
nearly a factor of 10 larger in Mn$_3$Ge than in Mn$_3$Sn. We use the
magnitudes of the discontinuities to calculate the pressure derivatives of the
N\'eel temperature, which are 39 K/GPa 14.3 K/GPa for Mn$_3$Ge and Mn$_3$Sn,
respectively. We measured in-plane shear modulus $c_{66}$, which couples
strongly to the magnetic order, in magnetic fields up to 18 T and found
quantitatively similar behavior in both compounds. Recent measurements have
demonstrated strong piezomagnetism in Mn$_3$Sn: our results suggest that
Mn$_3$Ge may be an even better candidate for this effect.",2203.06650v2
2022-03-18,Goal-conditioned dual-action imitation learning for dexterous dual-arm robot manipulation,"Long-horizon dexterous robot manipulation of deformable objects, such as
banana peeling, is a problematic task because of the difficulties in object
modeling and a lack of knowledge about stable and dexterous manipulation
skills. This paper presents a goal-conditioned dual-action (GC-DA) deep
imitation learning (DIL) approach that can learn dexterous manipulation skills
using human demonstration data. Previous DIL methods map the current sensory
input and reactive action, which often fails because of compounding errors in
imitation learning caused by the recurrent computation of actions. The method
predicts reactive action only when the precise manipulation of the target
object is required (local action) and generates the entire trajectory when
precise manipulation is not required (global action). This dual-action
formulation effectively prevents compounding error in the imitation learning
using the trajectory-based global action while responding to unexpected changes
in the target object during the reactive local action. The proposed method was
tested in a real dual-arm robot and successfully accomplished the
banana-peeling task.",2203.09749v2
2022-03-21,Pathways of organic micropollutants degradation in atmospheric pressure plasma processing,"Concern of toxic compounds and their, potentially more harmful degradation
products, present in aquatic environment alarmed scientific community and
research on the development of novel technologies for wastewater treatment had
become of great interest. Up to this date, many papers pointed out the
challenges and limitations of conventional wastewater treatment and of some
advanced oxidation processes. Advanced technologies based on the use of
non-equilibrium or non-thermal plasma had been recognized as a possible
solution for, not only degradation, but for complete removal of recalcitrant
organic micropollutants. While previous review papers have been focused on
plasma physics and chemistry of different types of discharges for few organic
micropollutants, this paper brings comprehensive review of current knowledge on
the chemistry and degradation pathways by using different non-thermal plasma
types for several micropollutants classes, such as pharmaceuticals,
perfluorinated compounds, pesticides, phenols and dyes and points out some
major research gaps.",2203.10849v1
2022-03-29,Orbital-selective Band Hybridisation at the Charge Density Wave Transition in Monolayer TiTe$_2$,"An anomalous $(2\times2)$ charge density wave (CDW) phase emerges in
monolayer 1T-TiTe$_2$ which is absent for the bulk compound, and whose origin
is still poorly understood. Here, we investigate the electronic band structure
evolution across the CDW transition using temperature-dependent angle-resolved
photoemission spectroscopy. Our study reveals an orbital-selective band
hybridisation between the backfolded conduction and valence bands occurring at
the CDW phase transition, which in turn leads to a significant electronic
energy gain, underpinning the CDW transition. For the bulk compound, we show
how this energy gain is almost completely suppressed due to the
three-dimensionality of the electronic band structure, including via a
$k_z$-dependent band inversion which switches the orbital character of the
valence states. Our study thus sheds new light on how control of the electronic
dimensionalilty can be used to trigger the emergence of new collective states
in 2D materials.",2203.15560v1
2022-03-30,Atomistic modeling of spin and electron dynamics in two-dimensional magnets switched by two-dimensional topological insulators,"To design fast memory devices, we need material combinations which can
facilitate fast read and write operation. We present a heterostructure
comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as
a viable option for designing fast memory devices. We theoretically model
spin-charge dynamics between the 2D magnets and 2D TIs. Using the adiabatic
approximation, we combine the non-equilibrium Green's function method for
spin-dependent electron transport, and time-quantified Monte-Carlo for
simulating magnetization dynamics. We show that it is possible to switch the
magnetic domain of a ferromagnet using spin-torque from spin-polarized edge
states of 2D TI. We further show that the switching between TIs and 2D magnets
is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an
optimal interface exchange depending on the exchange interaction within the
magnet is required for efficient switching. Finally, we compare the
experimentally grown Cr-compounds and show that Cr-compounds with higher
anisotropy (such as $\rm CrI_3$) results in lower switching speed but more
stable magnetic order.",2203.16008v1
2016-03-05,Momentum-Resolved Electronic Structure of the High-$T_{c}$ Superconductor Parent Compound BaBiO$_{3}$,"We investigate the band structure of BaBiO$_{3}$, an insulating parent
compound of doped high-$T_{c}$ superconductors, using \emph{in situ}
angle-resolved photoemission spectroscopy on thin films. The data compare
favorably overall with density functional theory calculations within the local
density approximation, demonstrating that electron correlations are weak. The
bands exhibit Brillouin zone folding consistent with known BiO$_{6}$ breathing
distortions. Though the distortions are often thought to coincide with
Bi$^{3+}$/Bi$^{5+}$ charge ordering, core level spectra show that bismuth is
monovalent. We further demonstrate that the bands closest to the Fermi level
are primarily oxygen derived, while the bismuth $6s$ states mostly contribute
to dispersive bands at deeper binding energy. The results support a model of
Bi-O charge transfer in which hole pairs are localized on combinations of the O
$2p$ orbitals.",1603.01745v2
2016-03-07,Importance of effective dimensionality in manganese pnictides,"In this paper we investigate the two manganese pnictides BaMn$_2$As$_2$ and
LaMnAsO, using fully charge self-consistent density functional plus dynamical
mean-field theory calculations. These systems have a nominally half-filled d
shell, and as a consequence, electronic correlations are strong, placing these
compounds at the verge of a metal-insulator transition. Although their crystal
structure is composed of similar building blocks, our analysis shows that the
two materials exhibit a very different effective dimensionality, LaMnAsO being
a quasi-two-dimensional material in contrast to the much more three-dimensional
BaMn$_2$As$_2$. We demonstrate that the experimentally observed differences in
the N\'eel temperature, the band gap, and the optical properties of the
manganese compounds under consideration can be traced back to exactly this
effective dimensionality. Our calculations show excellent agreement with
measured optical spectra.",1603.02115v2
2016-03-09,Novel chemistry of lithium oxides and superconducting low-pressure LiO4,"We study the stability of Li-O compounds as a function of pressure, with Li
ion battery applications and fundamental chemical interest in mind. Using the
ab initio evolutionary algorithm, we predict stability of novel compounds LiO4,
Li5O3 and Li6O under pressure. LiO4, formed at the pressure of just 6 GPa, can
be seen as {\epsilon}-O8 accepting two electrons from two Li atoms. This phase
is superconducting, with Tc up to 12.2 K at 10 GPa. This is remarkable, because
elemental oxygen becomes superconducting at much higher pressure (96 GPa) and
has much lower Tc (<0.6 K), and suggests that chemical alloying with other
elements has the potential of not only decreasing metallization pressure, but
also of increasing Tc. Since {\epsilon}-O8 is called red oxygen, LiO4 can be
identified ""lithium red-oxid"", and is distinct from superoxide. Additionally,
Li5O3 is stable at pressures above 70 GPa and can be represented as a hybrid
structure 4Li2O {\cdot} Li2O2, and electride suboxide Li6O is stable above 62
GPa.",1603.02880v1
2016-03-09,Superconductivity at 9K in Mo5PB2 with evidence for multiple gaps,"Superconductivity is observed with critical temperatures near 9K in the
tetragonal compound Mo5PB2. This material adopts the Cr5B3 structure type
common to supercondcuting Nb5Si3-xBx, Mo5SiB2, and W5SiB2, which have critical
temperatures of 5.8-7.8 K. We have synthesized polycrystalline samples of the
compound, made measurements of electrical resistivity, magnetic susceptibility,
and heat capacity, and performed first principles electronic structure
calculations. The highest Tc value (9.2 K) occurs in slightly phosphorus rich
samples, with composition near Mo5P1.1B1.9, and the upper critical field Hc2 at
T = 0 is estimated to be about 17 kOe. Together, the measurements and band
structure calculations indicate intermediate coupling (lambda = 1.0), phonon
mediated superconductivity. The temperature dependence of the heat capacity and
upper critical field Hc2 below Tc suggest multiple superconducting gaps may be
present.",1603.02892v1
2016-03-14,New MAX Phase Compound Mo2TiAlC2: First-principles Study,"A theoretical study of Mo2TiAlC2 compound belonging to the MAX phases has
been performed by using the firstprinciples pseudopotential plane-wave method
within the generalized gradient approximation. We have calculated the
structural, elastic, electronic and optical properties of Mo2TiAlC2. To confirm
mechanical stability, the elastic constants Cij are calculated. Other elastic
parameters such as bulk modulus, shear modulus, compressibility, Young modulus,
anisotropic factor, Pugh ratio, Poisson ratio are also calculated. The energy
band structure and density of states are calculated and analyzed. The results
show that the electrical conductivity is metallic with a high density of states
at the Fermi level in which Mo 4d states dominate. Furthermore, the optical
properties such as dielectric function, refractive index, photoconductivity,
absorption coefficients, loss function and reflectivity are also calculated.
Its reflectance spectrum shows that it has the potential to be used as a
promising shielding material to avoid solar heating.",1603.04215v1
2016-03-16,Electron dichotomy on the SrTiO$_3$ defect surface augmented by many-body effects,"In a common paradigm, the electronic structure of condensed matter is divided
into weakly and strongly correlated compounds. While conventional band theory
usually works well for the former class, many-body effects are essential for
the latter. Materials like the familiar SrTiO$_3$ compound that bridge or even
abandon this characterization scheme are highly interesting. Here it is shown
by means of combining density functional theory with dynamical-mean field
theory that oxygen vacancies on the STO (001) surface give rise to a dichotomy
of weakly-correlated $t_{2g}$ low-energy quasiparticles and localized 'in-gap'
states of dominant $e_g$ character with subtle correlation signature. We
furthermore touch base with recent experimental work and study the surface
instability towards magnetic order.",1603.04986v1
2016-03-23,Complex superconductivity in the noncentrosymmetric compound Re$_{6}$Zr,"We report the electronic structure, synthesis, and measurements of the
magnetic, transport, and thermal properties of the polycrystalline
noncentrosymmetric compound Re$_{6}$Zr. We observed a bulk superconducting
transition at temperature $T_{c}$ $\sim$ 6.7 K, and measured the resistivity,
heat capacity, thermal conductivity, and the London penetration depth below the
transition, as well as performed doping and pressure studies. From these
measurements we extracted the critical field, and the superconducting
parameters of Re$_{6}$Zr. Our measurements indicate a relatively weak to
moderate contribution from a triplet component to the order parameter, and
favor a full superconducting gap, although we cannot exclude the existence of
point nodes based on our data.",1603.07297v4
2016-03-23,Structural investigation of the bilayer iridate Sr3Ir2O7,"A complete structural solution of the bilayer iridate compound Sr3Ir2O7
presently remains outstanding. Previously reported structures for this compound
vary and all fail to explain weak structural violations observed in neutron
scattering measurements as well as the presence of a net ferromagnetic moment
in the basal plane. In this paper, we present single crystal neutron
diffraction and rotational anisotropy second harmonic generation measurements
unveiling a lower, monoclinic symmetry inherent to Sr3Ir2O7 . Combined with
density functional theory, our measurements identify the correct structural
space group as No. 15 (C2/c) and provide clarity regarding the local symmetry
of Ir 4+ cations within this spin-orbit Mott material.",1603.07390v1
2016-03-30,Universal Lattice Codes for MIMO Channels,"We propose a coding scheme that achieves the capacity of the compound MIMO
channel with algebraic lattices. Our lattice construction exploits the
multiplicative structure of number fields and their group of units to absorb
ill-conditioned channel realizations. To shape the constellation, a discrete
Gaussian distribution over the lattice points is applied. These techniques,
along with algebraic properties of the proposed lattices, are then used to
construct a sub-optimal de-coupled coding schemes that achieves a gap to
compound capacity by decoding in a lattice that does not depend of the channel
realization. The gap is characterized in terms of algebraic invariants of the
codes, and shown to be significantly smaller than previous schemes in the
literature. We also exhibit alternative algebraic constructions that achieve
the capacity of ergodic fading channels.",1603.09263v2
2016-03-31,"Pseudo-Spin, Real-Spin and Spin Polarization of Photo-emitted Electrons","In this work, we discuss the connections between pseudo spin, real spin of
electrons in material and spin polarization of photo-emitted electrons out of
material. By investigating these three spin textures for Bi$_2$Se$_3$ and
SmB$_6$ compounds, we find that the spin orientation of photo-electrons for
SmB$_6$ has different correspondence to pseudo spin and real spin compare to
Bi$_2$Se$_3$, due to the different symmetry properties of the photo-emission
matrix between initial and final states. We calculate the spin polarization and
circular dichroism spectra of photo-emitted electrons for both compounds, which
can be detected by spin-resolved and circular dichroism angle resolved
photo-emission spectroscopy experiment.",1603.09677v1
2016-12-01,"A ""hidden"" transition in heavy fermion compound CeB$_{6}$ at $T\sim$ 20 K?","The temperature-dependent electronic structures of heavy fermion compound
CeB$_{6}$ are investigated thoroughly by means of the combination of density
functional theory and single-site dynamical mean-field theory. The band
structure, density of states, and 4$f$ valence state fluctuation of CeB$_{6}$
are calculated in a broad temperature range of 10 $\sim$ 120 K. Overall, the
4$f$ electrons remain incoherent, approximately irrespective of the
temperature. However, we find that these observables exhibit some unusual
features near 20 K. In addition, the evolution of 4$f$ orbital occupancy, total
angular momentum, and total energy with respect to temperature shows apparent
singularity around 20 K. We believe that these tantalizing characteristics are
probably related to a ""hidden"" electronic transition.",1612.00317v1
2016-12-05,Superconductivity in Solid Benzene Molecular Crystal,"Light-element compounds hold great promise of high critical temperature
superconductivity judging from the theoretical perspective. Hydrogen-rich
material, benzene, is such a kind of candidate but also an organic compound. A
series of first-principles calculations are performed on the electronic
structures, dynamics properties, and electron-phonon interactions of solid
benzene at high pressures. Benzene is found to be dynamically stable in the
pressure range of 180 - 200 GPa and to exhibit superconductivity with a maximum
transition temperature of 20 K at 195 GPa. The phonon modes of carbon atoms are
identified to mainly contribute to the electron-phonon interactions driving
this superconductivity. The predicted superconductivity in this simplest
pristine hydrocarbon shows a common feature in aromatic hydrocarbons and also
makes it a bridge to organic and hydrogen-rich superconductors.",1612.01217v2
2016-12-08,"Full-gap superconductivity in non-centrosymmetric Re$_6$Zr, Re$_{27}$Zr$_{5}$ and Re$_{24}$Zr$_{5}$","Non-centrosymmetric superconductor Re$_6$Zr has attracted much interest, for
its possible unconventional superconducting state with time reversal symmetry
broken. Here we report the $^{185/187}$Re nuclear quadrupole resonance (NQR)
measurements on Re$_6$Zr ($T_c$ = 6.72 K) and the isostructural compounds
Re$_{27}$Zr$_{5}$ ($T_c$ = 6.53 K) and Re$_{24}$Zr$_{5}$ ($T_c$ = 5.00 K). The
nuclear spin-lattice relaxation rate $1/T_1$ shows a coherence peak below $T_c$
and decreases exponentially at low temperatures in all three samples. The
superconducting gap $\Delta$ derived from the $1/T_1$ data is $2\Delta =3.58 $
$k_BT_c$, 3.55 $k_BT_c$, and 3.51 $k_BT_c$ for Re$_6$Zr ,Re$_{27}$Zr$_{5}$, and
Re$_{24}$Zr$_{5}$, respectively, which is close to the value of 3.53 $k_BT_c$
expected for weak-coupling superconductivity. These data suggest conventional
$s$-wave superconductivity with a fully-opened gap in this series of compounds.",1612.02520v1
2016-12-11,Single crystal growth and physical property characterizations of mixed valent compound YbFe$_2$Al$_{10}$,"We report single crystal growth and physical properties characterization of
YbFe$_2$Al$_{10}$ compounds. The measurements of resistivity, magnetic
susceptibility, and specific heat show different behaviors from previous
studies on polycrystal samples. A mixed valent characteristic with moderate
mass enhancement is indicated. In particular, the optical spectroscopy
measurement reveals formation of multiple hybridization energy gaps which
become progressively pronounced at low temperature. The multiple hybridization
energy gaps are likely caused by the hybridizations between the flat band from
Yb 4$f$ electrons and different bands of conduction electrons.",1612.03421v2
2016-12-15,Unusual magneto-transport from Si-square nets in topological semimetal HfSiS,"The class of topological semimetals comprises a large pool of compounds.
Together they provide a wide platform to realize exotic quasiparticles for
example Dirac, nodal line Dirac and Weyl fermions. In this letter, we report
the Berry phase, Fermi surface topology and anisotropic magnetoresistance of
HfSiS which has recently been predicted to be a nodal line semimetal. This
compound contains large carrier density, higher than most of the known
semimetals. Massive amplitudes of de Haas-van Alphen and Shubnikov-de Haas
oscillations up to 20 K in 7 T assist us in witnessing nontrivial pi-Berry
phase which is a consequence of topological Dirac-type dispersion of bands
originating from the hybridization of px + py and dx2-y2 orbitals of square-net
plane of Si and Hf atoms, respectively. Furthermore, we establish the 3D
Fermi-surface which consists of very asymmetric water caltrop-like electron and
barley seed-like hole pockets which account for the anisotropic
magnetoresistance in HfSiS.",1612.05176v1
2016-12-16,Machine Reading with Background Knowledge,"Intelligent systems capable of automatically understanding natural language
text are important for many artificial intelligence applications including
mobile phone voice assistants, computer vision, and robotics. Understanding
language often constitutes fitting new information into a previously acquired
view of the world. However, many machine reading systems rely on the text alone
to infer its meaning. In this paper, we pursue a different approach; machine
reading methods that make use of background knowledge to facilitate language
understanding. To this end, we have developed two methods: The first method
addresses prepositional phrase attachment ambiguity. It uses background
knowledge within a semi-supervised machine learning algorithm that learns from
both labeled and unlabeled data. This approach yields state-of-the-art results
on two datasets against strong baselines; The second method extracts
relationships from compound nouns. Our knowledge-aware method for compound noun
analysis accurately extracts relationships and significantly outperforms a
baseline that does not make use of background knowledge.",1612.05348v1
2016-12-21,Investigating Anomalous Thermal Expansion of Copper Halides by Inelastic Neutron Scattering and Ab-inito Phonon Calculations,"We investigate detailed lattice dynamics of copper halides CuX (X=Cl, Br, I)
using neutron inelastic scattering measurements and ab-initio calculations
aimed at a comparative study of their thermal expansion behavior. We identify
the low energy phonons which soften with pressure and are responsible for
negative thermal expansion. The eigenvector analysis of these modes suggests
that softening of the transverse-acoustic modes would lead to NTE in these
compounds. The calculations are in very good agreement with our measurements of
phonon spectra and thermal expansion behavior as reported in the literature.
Our calculations at high pressure further reveal that large difference in
negative thermal expansion behavior in these compounds is associated with the
difference of the unit cell volume.",1612.07068v1
2016-12-21,"Computational insight on the structural, mechanical and thermal properties of Cu$_2$CdSnSe$_4$ and Cu$_2$HgSnSe$_4$ adamantine materials","Through first-principles calculation based on the density functional theory
(DFT) within the pseudo potential-plane wave (PP-PW) approach, we studied the
structural, mechanical and thermal properties of Cu$_2$CdSnSe$_4$ and
Cu$_2$HgSnSe$_4$ adamantine materials. The calculated lattice parameters are in
good agreement with experimental and theoretical reported data. The elastic
constants are calculated for both compounds using the static finite strain
scheme. The hydrostatic pressure action on the elastic constants predicts that
both materials are mechanically stable up to 10 GPa. The polycrystalline
mechanical parameters, i.e., the anisotropy factor ($A$), bulk modulus ($B$),
shear modulus ($G$), Young's modulus ($E$), Lame's coefficient ($\lambda$) and
Poisson's ratio ($\nu$) have been estimated from the calculated single crystal
elastic constants. The analysis of $B/G$ ratio shows that the two studied
compounds behave as ductile. Based on the calculated mechanical parameters, the
Debye temperature and the thermal conductivity have been probed. In the
framework of the quasi-harmonic approximation, the temperature dependence of
the lattice heat capacity of both crystals has been investigated.",1612.07176v1
2016-12-21,Hyperfine local probe study of alkaline-earth manganites SrMnO3 and BaMnO3,"We report perturbed angular correlation measurements with 111mCd/111Cd and
111In/111Cd probes, at the ISOLDE-CERN facility, in the manganite compounds
BaMnO3 , with the 6H and 15R polymorphs, and SrMnO3 , with the 4H polymorph.
The electric field gradient (EFG) is measured, and found approximately constant
in a large temperature range for all the compounds. The EFG is also calculated
from first principles with density functional theory, and compared with
experimental results by considering diluted substitutional Cd impurities. Based
on the results, we assign as sites for the probes the Ba (for BaMnO3-6H, 15R)
and Sr (for SrMnO3-4H) sites, apart from fractions of undetermined origin in
the case of BaMnO3-6H. We predict the hyperfine parameters in the recently
synthesized multiferroic manganite Sr0.5Ba0.5MnO3 , and its variation with the
structure and electric polarization, which is found to be very small.",1612.07301v1
2016-12-30,Nuclear magnetic resonance signature of the spin-nematic phase in LiCuVO$_{4}$ at high magnetic fields,"We report a 51V nuclear magnetic resonance investigation of the frustrated
spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and
focused on high-field phases up to 55 T. For the crystal orientations H // c
and H // b we find a narrow field region just below the magnetic saturation
where the local magnetization remains uniform and homogeneous, while its value
is field dependent. This behavior is the first microscopic signature of the
spin-nematic state, breaking spin-rotation symmetry without generating any
transverse dipolar order, and is consistent with theoretical predictions for
the LiCuVO4 compound.",1612.09483v3
2017-02-01,Plasmonics of Topological Insulators at Optical Frequencies,"The development of nanoplasmonic devices, such as plasmonic circuits and
metamaterial superlenses in the visible to ultraviolet frequency range, is
hampered by the lack of low-loss plasmonic media. Recently, strong plasmonic
response was reported in a certain class of topological insulators. Here, we
present a first-principles density functional theory analysis of the dielectric
functions of topologically insulating quaternary (Bi,Sb)2(Te,Se)3
trichalcogenide compounds. Bulk plasmonic properties, dominated by interband
transitions, are observed from 2-3 eV and extend to higher frequencies.
Moreover, trichalcogenide compounds are better plasmonic media than gold and
silver at blue and UV wavelengths. By analysing thin slabs, we also show that
these materials exhibit topologically protected surface states, which are
capable of supporting propagating plasmon polariton modes over an extremely
broad spectral range, from the visible to the mid-infrared and beyond, owing to
a combination of inter- and intra-surface band transitions.",1702.00302v1
2017-02-02,Universal scaling in the Knight shift anomaly of doped periodic Anderson model,"We report a Dynamical Cluster Approximation (DCA) investigation of the doped
periodic Anderson model (PAM) to explain the universal scaling in the Knight
shift anomaly predicted by the phenomenological two-fluid model and confirmed
in many heavy-fermion compounds. We calculate the quantitative evolution of the
orbital-dependent magnetic susceptibility and reproduce correctly the two-fluid
prediction in a large range of doping and hybridization. Our results confirm
the presence of a temperature/energy scale $T^{\ast}$ for the universal scaling
and show distinctive behavors of the Knight shift anomaly in response to other
""orders"" at low temperatures. However, comparison with the temperature
evolution of the calculated resistivity and quasiparticle spectral peak
indicates a different characteristic temperature from $T^*$, in contradiction
with the experimental observation in CeCoIn$_5$ and other compounds. This
reveals a missing piece in the current model calculations in explaining the
two-fluid phenomenology.",1702.00568v1
2017-02-03,Tropical compound matrix identities,"We prove identities on compound matrices in extended tropical semirings. Such
identities include analogues to properties of conjugate matrices, powers of
matrices and~$\adj(A)\det(A)^{ -1}$, all of which have implications on the
eigenvalues of the corresponding matrices. A tropical Sylvester-Franke identity
is provided as well.",1702.00980v2
2017-02-08,Investigation of the complex magnetism in the breathing pyrochlore LiIn(Cr$_{1-x}$Rh$_x$)$_4$O$_8$,"We have performed a detailed investigation of the new `breathing' pyrochlore
compound LiInCr$_4$O$_8$ through Rh substitution with measurements of magnetic
susceptibility, specific heat, and x-ray powder diffraction. The
antiferromagnetic phase of LiInCr$_4$O$_8$ is found to be slowly suppressed
with increasing Rh, up to the critical concentration of $x$ = 0.1 where the
antiferromagnetic phase is still observed with the peak in specific heat $T_p$
= 12.5 K, slightly lower than $T_p$ = 14.3 K for the $x$ = 0 compound. From the
measurements of magnetization we also uncover evidence that substitution
increases the amount of frustration. Comparisons are made with the
LiGa$_y$In$_{1-y}$Cr$_4$O$_8$ system as well as other frustrated
pyrochlore-related materials and find comparable amounts of frustration. The
results of this work shows that engineered breathing pyrochlores presents an
important method to further understand the complex magnetism in frustrated
systems.",1702.02538v1
2017-02-10,Electronic and gap properties of lead-free perfect and mixed hybrid halide perovskites: An \textit{ab-initio} study,"Hybrid halide perovskites are currently under intense investigation due to
their potential applications in optoelectronics and solar cells. Among them,
MAPbI$_3$ where MA stands for the methylammonium cation, exhibits ideal
properties for solar cells. In attempt to identify new lead-free halide
perovskites we have studied using \textit{ab-initio} electronic structure
calculations in conjunction with hybrid functionals a series of MABX$_3$
compounds where B is a divalent cation and X a halogen atom. Our results
suggest that the compounds under study exhibit a variety of lattice constants
and energy band gaps. Especially, MAZnCl$_3$, MACdBr$_3$, MAGeCl$_3$ and
MAGeBr$_3$ are susceptible to replace MAPbI$_3$ in devices since they show
comparable energy gaps. Further calculations on the mixed hybrid halide
perovskites show that we can tune the values of the energy gap although no
simplified pattern exists. Our results pave the way for further investigation
on the use of these materials in technology relevant applications.",1702.03233v2
2017-02-13,Raman spectra of crystalline secondary amides,"The study of single-crystal Raman spectra of a series of crystalline
secondary amides (acetanilide, methacetin, phenacetine, orthorhombic and
monoclinic polymorphs of paracetamol) as well as simple amides formanilide and
benzanilide in the temperature range 5-300 K was carried out. The series of
compounds with the same molecular fragment, i.e. acetamide group, can serve as
a model system to study the interrelation between the latter and the properties
of the intermolecular ""peptide-type"" NH...O=C hydrogen bonds. For all the
""acetamide family"" of compounds, similar changes in the Raman spectra were
observed on cooling the samples: an appearance of new Amide I(-) and Amide I(+)
bands that are red and blue shifted respectively from the conventional Amide I
band by around of 5-10 inverse centimeters. An appropriated changes in the same
temperature range were observed for the N-H out-of-plane bending (Amide V) and
N-H stretching vibrations of the N-H...O=C hydrogen bond. All the spectral
changes on cooling the samples can be supposed to result from delocalization of
the Amide I and N-H modes and appearance of dynamical splitting at low
temperature.",1702.03610v1
2017-02-13,"Coexistence of localized and itinerant magnetism in intercalated iron-selenide (Li,Fe)OHFeSe","The electronic structure and magnetism of a new magnetic intercalation
compound (Li0.8Fe0.2)OHFeSe are investigated theoretically. The electronic
structure calculations predict that the Fe in the (Li,Fe)OH intercalated layer
is in +2 valence state, i.e. there is electron doping to the FeSe layer,
resulting in the shrinking of the Fermi surface (FS) pocket around Gamma and a
strong suppression of dynamical spin susceptibility at M in comparison with the
bulk FeSe compound. The ground state of the FeSe layer is a striped
antiferromagnetic (SAFM) metal, while the (Li,Fe)OH layer displays a very weak
localized magnetism, with an interlayer ferromagnetic (FM) coupling between the
FeSe and intercalated (Li,Fe)OH layers. Moreover, the (Li,Fe)OH is more than a
block layer; it is responsible for enhancing the antiferromagnetic (AFM)
correlation in the FeSe layer through interlayer magnetic coupling. We propose
that the magnetic spacer layer introduces a tuning mechanism for spin
fluctuations associated with superconductivity in iron-based superconductors.",1702.03845v1
2017-02-14,Pentazole and Ammonium Pentazolate: Crystalline Hydro-Nitrogens at High Pressure,"Two new crystalline compounds, pentazole (N_{5}H) and ammonium pentazolate
(NH_{4})(N_{5}), both featuring cyclo-{\rm N_{5}^{-}} are discovered using
first principles evolutionary search of the nitrogen-rich portion of the
hydro-nitrogen binary phase diagram (N_{x}H_{y}, x\geqy) at high pressures.
Both crystals consist of the pentazolate N_{5}^{-} anion and ammonium
NH_{4}^{+} or hydrogen H^{+} cations. These two crystals are predicted to be
thermodynamically stable at pressures above 30 GPa for (NH_{4})(N_{5}) and 50
GPa for pentazole N_{5}H. The chemical transformation of ammonium azide
(NH_{4})(N_{3}) mixed with di-nitrogen (N_{2}) to ammonium pentazolate
(NH_{4})(N_{5}) is predicted to become energetically favorable above 12.5 GPa.
To assist in identification of newly synthesized compounds in future
experiments, the Raman spectra of both crystals are calculated and mode
assignments are made as a function of pressure up to 75 GPa.",1702.04326v1
2017-02-15,Ab-initio prediction of the high-pressure phase diagram of BaBiO3,"BaBiO3 is a well-known example of a 3D charge density wavecompound, in which
the CDW behavior is induced by charge disproportionation at the Bi site. At
ambient pressure, this compound is a charge-ordered insulator, but little is
known about its high-pressure behavior. In this work, we study from
first-principles the high-pressure phase diagram of BaBiO3 using phonon modes
analysis and evolutionary crystal structure prediction. We show that charge
disproportionation is very robust in this compound and persists up to 100 GPa.
This causes the system to remain insulating up to the highest pressure we
studied.",1702.04600v1
2017-02-16,Magnetism of the antiferromagnetic spin-$\frac{3}{2}$ dimer compound CrVMoO$_7$ having an antiferromagnetically ordered state,"We measured magnetization, specific heat, electron spin resonance, neutron
diffraction, and inelastic neutron scattering of CrVMoO$_7$ powder. An
antiferromagnetically ordered state appears below $T_{\rm N} = 26.5 \pm 0.8$ K.
We consider that the probable spin model for CrVMoO$_7$ is an interacting
antiferromagnetic spin-$\frac{3}{2}$ dimer model. We evaluated the intradimer
interaction $J$ to be $25 \pm 1$ K and the effective interdimer interaction
$J_{\rm eff}$ to be $8.8 \pm 1$ K. CrVMoO$_7$ is a rare spin dimer compound
that shows an antiferromagnetically ordered state at atmospheric pressure and
zero magnetic field. The magnitude of ordered moments is $0.73(2) \mu_{\rm B}$.
It is much smaller than a classical value $\sim 3 \mu_{\rm B}$.
Longitudinal-mode magnetic excitations may be observable in single crystalline
CrVMoO$_7$.",1702.04828v1
2017-02-25,BARCHAN: Blob Alignment for Robust CHromatographic ANalysis,"Comprehensive Two dimensional gas chromatography (GCxGC) plays a central role
into the elucidation of complex samples. The automation of the identification
of peak areas is of prime interest to obtain a fast and repeatable analysis of
chromatograms. To determine the concentration of compounds or pseudo-compounds,
templates of blobs are defined and superimposed on a reference chromatogram.
The templates then need to be modified when different chromatograms are
recorded. In this study, we present a chromatogram and template alignment
method based on peak registration called BARCHAN. Peaks are identified using a
robust mathematical morphology tool. The alignment is performed by a
probabilistic estimation of a rigid transformation along the first dimension,
and a non-rigid transformation in the second dimension, taking into account
noise, outliers and missing peaks in a fully automated way. Resulting aligned
chromatograms and masks are presented on two datasets. The proposed algorithm
proves to be fast and reliable. It significantly reduces the time to results
for GCxGC analysis.",1702.07942v1
2017-06-06,Possible high-$T_c$ superconductivity due to incipient narrow bands originating from hidden ladders in Ruddlesden-Popper compounds,"We introduce a concept of hidden ladders for the bilayer Ruddlesden-Popper
type compounds: While the crystal structure is bilayer, $d_{xz}$ ($d_{yz}$)
orbitals in the relevant $t_{2g}$ sector of the transition metal form a two-leg
ladder along $x$ ($y$), since the $d_{xz}$ ($d_{yz}$) electrons primarily hop
along the leg direction $x$ ($y$) on top of the rung $z$ direction. We predict
that Sr$_3$Mo$_2$O$_7$ and Sr$_3$Cr$_2$O$_7$ are candidates for the
hidden-ladder material with a right position of $E_F$, from a first-principles
band calculation. Based on the analysis of Eliashberg equation for these
systems, we propose a possible occurrence of high temperature superconductivity
in these materials arising from the interband pair scattering processes between
the wide and ""incipient"" narrow bands on the ladder.",1706.01711v2
2017-06-13,Efficient Rare-Event Simulation for Multiple Jump Events in Regularly Varying Random Walks and Compound Poisson Processes,"We propose a class of strongly efficient rare event simulation estimators for
random walks and compound Poisson processes with a regularly varying
increment/jump-size distribution in a general large deviations regime. Our
estimator is based on an importance sampling strategy that hinges on the
heavy-tailed sample path large deviations result recently established in Rhee,
Blanchet, and Zwart (2016). The new estimators are straightforward to implement
and can be used to systematically evaluate the probability of a wide range of
rare events with bounded relative error. They are ""universal"" in the sense that
a single importance sampling scheme applies to a very general class of rare
events that arise in heavy-tailed systems. In particular, our estimators can
deal with rare events that are caused by multiple big jumps (therefore, beyond
the usual principle of a single big jump) as well as multidimensional processes
such as the buffer content process of a queueing network. We illustrate the
versatility of our approach with several applications that arise in the context
of mathematical finance, actuarial science, and queueing theory.",1706.03981v1
2017-06-15,The low-temperature highly correlated quantum phase in the charge-density-wave 1T-TaS_2 compound,"A prototypical quasi-2D metallic compound, 1T-TaS_2 has been extensively
studied due to an intricate interplay between a Mott-insulating ground state
and a charge density-wave (CDW) order. In the low-temperature phase, 12 out of
13 Ta_{4+} 5\textit{d}-electrons form molecular orbitals in hexagonal
star-of-David patterns, leaving one 5\textit{d}-electron with \textit{S} = 1/2
spin free. This orphan quantum spin with a large spin-orbit interaction is
expected to form a highly correlated phase of its own. And it is most likely
that they will form some kind of a short-range order out of a strongly
spin-orbit coupled Hilbert space. In order to investigate the low-temperature
magnetic properties, we performed a series of measurements including neutron
scattering and muon experiments. The obtained data clearly indicate the
presence of the short-ranged phase and put the upper bound on ~ 0.4
\textit{\mu}_B for the size of the magnetic moment, consistent with the
orphan-spin scenario.",1706.04735v1
2017-06-21,Phase Diagram and Soliton Picture of an Ideal Spin-Peierls Compound D-F$_{5}$PNN,"We investigate magnetic properties of an $S$=1/2 quasi-one dimensional
organic antiferromagnet, D-F$_{5}$PNN using magnetization measurements taken at
temperatures as low as 0.5 K. Three distinct phases were observed consisting of
uniform, dimerized (D), and incommensurate (I) spin structures in the magnetic
field versus temperature plane, where a significant hysteresis appears between
D-I transitions in the field scan measurements. A combination of magnon ($S$=1)
and soliton ($S$=1/2) excitations have successfully reproduced the observed
magnetic susceptibility. In addition, such excitations provide a reasonable
interpretation of the temperature dependent electron spin resonance (ESR)
spectra. By comparison with the theoretical study, we conclude that
D-F$_{5}$PNN is an ideal compound for investigating the spin-Peierls
transition.",1706.06797v1
2017-06-24,The magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS$_3$,"The magnetic properties and magnetic structure are presented for CoPS$_3$, a
quasi-two-dimensional antiferromagnet on a honeycomb lattice with a N\'eel
temperature of $T_N \sim 120$ K. The compound is shown to have XY-like
anisotropy in its susceptibility, and the anisotropy is analysed to extract
crystal field parameters. For temperatures between 2 K and 300 K, no phase
transitions were observed in the field-dependent magnetization up to 10 Tesla.
Single-crystal neutron diffraction shows that the magnetic propagation vector
is {\bf{k}}= $\left[010\right]$ with the moments mostly along the $\mathbf{a}$
axis and with a small component along the $\mathbf{c}$ axis, which largely
verifies the previously-published magnetic structure for this compound. The
magnetic Bragg peak intensity decreases with increasing temperature as a power
law with exponent $2\beta = 0.60 \pm 0.01$ for $T > 0.9~T_N$.",1706.07989v1
2017-06-24,Magnetization process of the S = 1/2 two-leg organic spin-ladder compound BIP-BNO,"We have measured the magnetization of the organic compound BIP-BNO
(3,5'-bis(N-tert-butylaminoxyl)-3',5-dibromobiphenyl) up to 76 T where the
magnetization is saturated. The S = 1/2 antiferromagnetic Heisenberg two-leg
spin-ladder model accounts for the obtained experimental data regarding the
magnetization curve, which is clarified using the quantum Monte Carlo method.
The exchange constants on the rung and the side rail of the ladder are
estimated to be J(rung)/kB = 65.7 K and J(leg)/kB = 14.1 K, respectively,
deeply in the strong coupling region: J(rung)/J(leg) > 1.",1706.08008v1
2017-06-25,"New 3,3'-(ethane-1, 2-diylidene)bis(indolin-2-one) (EBI)-based small molecule semiconductors for organic solar cells","A series of donor-acceptor-donor (D-A-D) structured small-molecule compounds,
with 3,3'-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) as a novel electron
acceptor building block coupled with various electron donor end-capping
moieties (thiophene, bithiophene and benzofuran), were synthesized and
characterized. When the fused-ring benzofuran is combined to EBI (EBI-BF), the
molecules displayed a perfectly planar conformation and afforded the best
charge tranport properties among these EBI compounds with a hole mobility of up
to 0.021 cm2 V-1 s-1. All EBI-based small molecules were used as donor material
along with a PC61BM acceptor for the fabrication of solution-processed
bulk-heterojunction (BHJ) solar cells. The best performing photovoltaic devices
are based on the EBI derivative using the bithiophene end-capping moiety
(EBI-2T) with a maximum power conversion efficiency (PCE) of 1.92%, owing to
the broad absorption spectra of EBI-2T and the appropriate morphology of the
BHJ. With the aim of establishing a correlation between the molecular structure
and the thin film morphology, differential scanning calorimetry, atomic force
microscopy and X-ray diffraction analysis were performed on neat and blend
films of each material.",1706.08074v1
2017-06-27,"Structure, Thermodynamic and Electronic Properties of Carbon-Nitrogen Cubanes and Protonated Polynitrogen Cations","Energy generation and storage are at the center of modern civilization.
Energetic materials constitute quite a large class of compounds with a high
amount of stored chemical energy that can be released. We hereby use a
combination of quantum chemistry methods to investigate feasibility and
properties of carbon-nitrogen cubanes and multi-charged polynitrogen cations in
the context of their synthesis and application as unprecedented energetic
materials. We show that the stored energy increases gradually with the nitrogen
content increase. Nitrogen-poor cubanes retain their stabilities in vacuum,
even at elevated temperatures. Such molecules will be probably synthesized at
some point. In turn, polynitrogen cations are highly unstable, except N8H+,
despite they are isoelectronic to all-carbon cubane. Kinetic stability of the
cation decays drastically as its total charge increases. High-level
thermodynamic calculations revealed that large amounts of energy are liberated
upon decompositions of polynitrogen cations, which produce molecular nitrogen,
acetylene, and protons. The present results bring a substantial insights to the
design of novel high energy compounds.",1706.09035v1
2017-06-27,Benchmark Results and Theoretical Treatments for Valence-to-Core X-ray Emission Spectroscopy in Transition Metal Compounds,"We report measurement of the valence-to-core (VTC) region of the K-shell
x-ray emission spectra from several Zn and Fe inorganic compounds, and their
critical comparison with several existing theoretical treatments. We find
generally good agreement between the respective theories and experiment, and in
particular find an important admixture of dipole and quadrupole character for
Zn materials that is much weaker in Fe-based systems. These results on
materials whose simple crystal structures should not, a prior, pose deep
challenges to theory, will prove useful in guiding the further development of
DFT and time-dependent DFT methods for VTC-XES predictions and their comparison
to experiment.",1706.09054v1
2017-06-28,First-principles prediction of high-entropy-alloy stability,"High entropy alloys (HEAs) are multicomponent compounds whose high
configurational entropy allows them to solidify into a single phase, with a
simple crystal lattice structure. Some HEA's exhibit desirable properties, such
as high specific strength, ductility, and corrosion resistance, while
challenging the scientist to make confident predictions in the face of multiple
competing phases. We demonstrate phase stability in the multicomponent alloy
system of Cr-Mo-Nb-V, for which some of its binary subsystems are subject to
phase separation and complex intermetallic-phase formation. Our
first-principles calculation of free energy predicts that the configurational
entropy stabilizes a single body-centered cubic (BCC) phase from T = 1,700K up
to melting, while precipitation of a complex intermetallic is favored at lower
temperatures. We form the compound experimentally and confirm that it forms as
a single BCC phase from the melt, but that it transforms reversibly at lower
temperatures.",1706.09282v1
2017-10-10,Chemical Gating of a Weak Topological Insulator: Bi14Rh3I9,"The compound Bi14Rh3I9 has recently been suggested as a weak
three-dimensional topological insulator on the basis of angle-resolved
photoemission and scanning-tunneling experiments in combination with density
functional (DF) electronic structure calculations. These methods unanimously
support the topological character of the headline compound, but a compelling
confirmation could only be obtained by dedicated transport experiments. The
latter, however, are biased by an intrinsic n-doping of the materials surface
due to its polarity. Electronic reconstruction of the polar surface shifts the
topological gap below the Fermi energy, which would also prevent any future
device application. Here, we report the results of DF slab calculations for
chemically gated and counter-doped surfaces of Bi14Rh3I9. We demonstrate that
both methods can be used to compensate the surface polarity without closing the
electronic gap.",1710.03466v1
2017-10-22,A Binary Wyner-Ziv Code Design Based on Compound LDGM-LDPC Structures,"In this paper, a practical coding scheme is designed for the binary Wyner-Ziv
(WZ) problem by using nested low-density generator-matrix (LDGM) and
low-density parity-check (LDPC) codes. This scheme contains two steps in the
encoding procedure. The first step involves applying the binary quantization by
employing LDGM codes and the second one is using the syndrome-coding technique
by utilizing LDPC codes. The decoding algorithm of the proposed scheme is based
on the Sum-Product (SP) algorithm with the help of a side information available
at the decoder side. It is theoretically shown that the compound structure has
the capability of achieving the WZ bound. The proposed method approaches this
bound by utilizing the iterative message-passing algorithms in both encoding
and decoding, although theoretical results show that it is asymptotically
achievable.",1710.07985v1
2017-10-24,Critical role of electronic correlations in determining crystal structure of transition metal compounds,"The choice that a solid system ""makes"" when adopting a crystal structure
(stable or metastable) is ultimately governed by the interactions between
electrons forming chemical bonds. By analyzing 6 prototypical binary
transition-metal compounds we demonstrate here that the orbitally-selective
strong $d$-electron correlations influence dramatically the behavior of the
energy as a function of the spatial arrangements of the atoms. Remarkably, we
find that the main qualitative features of this complex behavior can be traced
back to simple electrostatics, i.e., to the fact that the strong $d$-electron
correlations influence substantially the charge transfer mechanism, which, in
turn, controls the electrostatic interactions. This result advances our
understanding of the influence of strong correlations on the crystal structure,
opens a new avenue for extending structure prediction methodologies to strongly
correlated materials, and paves the way for predicting and studying
metastability and polymorphism in these systems.",1710.08586v2
2017-10-24,Effective model for $A_{2g}$ Raman signal in URu$_2$Si$_2$,"We propose an effective model to describe the $A_{2g}$ signal in Raman
scattering experiments in the URu$_{2}$Si$_{2}$ compound. We follow the scheme
proposed earlier by Khveshchenko and Wiegmann [Phys. Rev. Lett. 73, 500 (1994)]
to calculate the $A_{2g}$ scattering vertex. We extract the imaginary part of a
two-point current-current correlation function and compare it directly with the
Raman response. We obtain an inelastic peak at $A_{2g}$ channel owing to the
interplay between a local staggered ordering and a possible quantum spin liquid
behavior. Our results offer an explanation for the electronic Raman scattering
experiments at the hidden order phase in URu$_{2}$Si$_{2}$ compound [Phys. Rev.
Lett. 113, 266405 (2014)].",1710.08942v5
2017-10-26,First-principles theory of doping in layered oxide electrode materials,"Doping lithium-ion battery electrode materials LiMO$_2$ (M = Co, Ni, Mn) with
impurities has been shown to be an effective way to optimize their
electrochemical properties. Here, we report a detailed first-principles study
of layered oxides LiCoO$_2$, LiNiO$_2$, and LiMnO$_2$ lightly doped with
transition-metal (Fe, Co, Ni, Mn) and non-transition-metal (Mg, Al) impurities
using hybrid-density-functional defect calculations. We find that the lattice
site preference is dependent on both the dopant's charge and spin states, which
are coupled strongly to the local lattice environment and can be affected by
the presence of co-dopant(s), and the relative abundance of the host compound's
constituting elements in the synthesis environment. On the basis of the
structure and energetics of the impurities and their complexes with intrinsic
point defects, we determine all possible low-energy impurity-related defect
complexes, thus providing defect models for further analyses of the materials.
From a materials modeling perspective, these lightly doped compounds also serve
as model systems for understanding the more complex, mixed-metal,
LiMO$_2$-based battery cathode materials.",1710.09895v1
2017-10-26,Novel Potassium Polynitrides at High Pressures,"Polynitrogen compounds have attracted great interest due to their potential
applications as high energy density materials. Most recently, a rich variety of
alkali polynitrogens (R_{x}N_{y}; R=Li, Na, and Cs) have been predicted to be
stable at high pressures and one of them, CsN_{5} has been recently
synthesized. In this work, various potassium polynitrides are investigated
using first-principles crystal structure search methods. Several novel
molecular crystals consisting of N_{4} chains, N_{5} rings, and N_{6} rings
stable at high pressures are discovered. In addition, an unusual nitrogen-rich
metallic crystal with stoichiometry K_{2}N_{16} consisting of a planar
two-dimensional extended network of nitrogen atoms arranged in fused eighteen
atom rings is found to be stable above 70 GPa. An appreciable electron transfer
from K to N atoms is responsible for the appearance of unexpected chemical
bonding in these crystals. The thermodynamic stability and high pressure phase
diagram is constructed. The electronic and vibrational properties of the
layered polynitrogen K_{2}N_{16} compound are investigated, and the
pressure-dependent IR-spectrum is obtained to assist in experimental discovery
of this new high-nitrogen content material.",1710.09914v1
2017-10-26,Comparison and Evaluation of Isotope-Ratio Calculation Schemes for Compound-Specific Chlorine Isotope Analysis Using GC-EI-MS,"A recent article reported a comparison study concerning compound-specific
chlorine isotope analysis (CSIA-Cl) of organochlorines using gas
chromatography- isotope ratio mass spectrometry (GC-IRMS) and gas
chromatography-quadrupole mass spectrometry (GC-qMS). Comparable precisions
between the two instruments were achieved and trueness of the analysis results
was confirmed. The CSIA-Cl method using GC-qMS was originally developed by
Sakaguchi-S\""oder et al.and further improved by several relevant studies,and
has been used to evaluate organic contaminant attenuation in the environment.
The essential principle of the method is to calculate the chlorine isotope
ratio (37Cl/35Cl) by using the first pair of neighboring chlorine isotopologues
(two-mass apart) of either the molecular ion or a fragmental ion of a target
analyte, or using all the first isotopologue pairs of all molecular and
fragmental ions. These isotope-ratio calculation schemes using chlorine
isotopologue pair(s) were based on the binomial theorem and the prerequisite
hypothesis that the measured abundances of chlorine isotopologues of individual
analytes were binomially distributed. However, it is not true with the
hypothesis.",1710.10170v1
2018-03-29,An Ice Structuring Mechanism for Zirconium Acetate,"The control of ice nucleation and growth is critical in many natural and
engineering situations. Yet, very few compounds are able to interact directly
with the surface of ice crystals. Ice-structuring proteins, found in certain
fishes, plants and insects, bind to the surface of ice, thereby controlling
their growth. We recently revealed the ice-structuring properties of zirconium
acetate which are similar to those of ice-structuring proteins. Being a salt,
and therefore different from the proteins having ice-structuring properties,
its ice-structuring mechanism remains unelucidated. Here we investigate this
ice-structuring mechanism through the role of the concentration of zirconium
acetate and of the ice crystal growth velocity. We then explore other compounds
presenting similar functional groups (acetate, hydroxyl, or carboxylic groups).
Based on these results, we propose that zirconium acetate adopts a
hydroxy-bridged polymer structure which can bind to the surface of the ice
crystals through hydrogen bonding, thereby slowing down ice crystal growth.",1804.00045v1
2018-04-02,Gapped ground state in the zigzag pseudospin-1/2 quantum antiferromagnetic chain compound PrTiNbO6,"We report a single-crystal study on the magnetism of the rare-earth compound
PrTiNbO$_6$ that experimentally realizes the zigzag pseudospin-$\frac{1}{2}$
quantum antiferromagnetic chain model. Random crystal electric field caused by
the site mixing between non-magnetic Ti$^{4+}$ and Nb$^{5+}$, results in the
non-Kramers ground state quasi-doublet of Pr$^{3+}$ with the effective
pseudospin-$\frac{1}{2}$ Ising moment. Despite the antiferromagnetic intersite
coupling of about 4 K, no magnetic freezing is detected down to 0.1 K, whilst
the system approaches its ground state with almost zero residual spin entropy.
At low temperatures, a sizable gap of about 1 K is observed in zero field. We
ascribe this gap to off-diagonal anisotropy terms in the pseudospin
Hamiltonian, and argue that rare-earth oxides open an interesting venue for
studying magnetism of quantum spin chains.",1804.00687v1
2018-04-05,Charge density wave behavior and order-disorder in the antiferromagnetic metallic series Eu(Ga_1-xAl_x)_4,"The solid solution Eu(Ga_1-xAl_x)_4 was grown in single crystal form to
reveal a rich variety of crystallographic, magnetic, and electronic properties
that differ from the isostructural end compounds EuGa_4 and EuAl_4, despite the
similar covalent radii and electronic configurations of Ga and Al. Here we
report the onset of magnetic spin reorientation and metamagnetic transitions
for x = 0 - 1 evidenced by magnetization and temperature-dependent specific
heat measurements. T_N changes non-monotonously with x, and it reaches a
maximum around 20 K for x = 0.50, where the a lattice parameter also shows an
extreme (minimum) value. Anomalies in the temperature-dependent resistivity
consistent with charge density wave behavior exist for x = 0.50 and 1 only.
Density functional theory calculations show increased polarization between the
Ga-Al covalent bonds in the x = 0.50 structure compared to the end compounds,
such that crystallographic order and chemical pressure are proposed as the
causes of the charge density wave behavior.",1804.02076v1
2018-04-06,"Emergence of Topological insulator and Nodal line semi-metal states in XX'Bi (X=Na, K, Rb, Cs; X'=Ca, Sr)","In this letter, we predict the emergence of non-trivial band topology in the
family of XX'Bi compounds having $P\overline{6}2m$ (\# 189) space group. Using
first principles calculations within hybrid functional framework, we
demonstrate that NaSrBi and NaCaBi are strong topological insulator under
controlled band engineering. Here, we propose three different ways to engineer
the band topology to get a non-trivial order: (i) hydrostatic pressure, (ii)
biaxial strain (due to epitaxial mismatch), and (iii) doping. Non-triviality is
confirmed by investigating bulk band inversion, topological Z$_2$ invariant,
surface dispersion and spin texture. Interestingly, some of these compounds
also show a three dimensional topological nodal line semi-metal (NLS) state in
the absence of spin orbit coupling (SOC). In these NLS phases, the closed loop
of band degeneracy in the Brillouin zone lie close to the Fermi level.
Moreover, a drumhead like flat surface state is observed on projecting the bulk
state on the [001] surface. The inclusion of SOC opens up a small band gap
making them behave like a topological insulator.",1804.02225v1
2018-04-12,Magnetic and structural quantum phase transitions in CeCu6-xAux are independent,"The heavy-fermion compound CeCu$_{6-x}$Au$_x$ has become a model system for
unconventional magnetic quantum criticality. For small Au concentrations $0
\leq x < 0.16$, the compound undergoes a structural transition from
orthorhombic to monoclinic crystal symmetry at a temperature $T_{s}$ with
$T_{s} \rightarrow 0$ for $x \approx 0.15$. Antiferromagnetic order sets in
close to $x \approx 0.1$. To shed light on the interplay between quantum
critical magnetic and structural fluctuations we performed neutron-scattering
and thermodynamic measurements on samples with $0 \leq x\leq 0.3$. The
resulting phase diagram shows that the antiferromagnetic and monoclinic phase
coexist in a tiny Au concentration range between $x\approx 0.1$ and $0.15$. The
application of hydrostatic and chemical pressure allows to clearly separate the
transitions from each other and to explore a possible effect of the structural
transition on the magnetic quantum critical behavior. Our measurements
demonstrate that at low temperatures the unconventional quantum criticality
exclusively arises from magnetic fluctuations and is not affected by the
monoclinic distortion.",1804.04513v1
2018-04-16,Fabrication of high-temperature quasi-two-dimensional superconductors at the interface of a ferroelectric Ba$_{0.8}$Sr$_{0.2}$TiO$_{3}$ film and an insulating parent compound of La$_{2}$CuO$_{4}$,"We report the first observation of superconductivity in heterostructure
consisting of an insulating ferroelectric film (Ba$_{0.8}$Sr$_{0.2}$TiO$_3$)
grown on an insulating parent compound of La$_2$CuO$_4$ with [001] orientation.
The heterostructure was prepared by magnetron sputtering on a
non-atomically-flat surface with inhomogeneities of the order of 1-2 nm. The
measured superconducting transition temperature T$_c$ is about 30K. We have
shown that superconductivity is confined near the interface region. Application
of a weak magnetic field perpendicular to the interface leads to the appearance
of the finite resistance. That confirms the quasi-two-dimensional nature of the
superconductive state. The proposed concept promises ferroelectrically
controlled interface superconductivity which offers the possibility of novel
design of electronic devices.",1804.05519v3
2018-04-16,Structural response to the magnetic pre ordering in LiFeSi2O6,"We investigate the temperature evolution of the structural parameters of
potential ferrotoroidic LiFeSi2O6 compound across structural and magnetic phase
transitions. The structural transition (TS)is around 220K and the paramagnetic
to antiferromagnetic transition (TN) is around 18K. The lattice parameters
exhibit unusual temperature dependence and based on its behaviour, the exper-
imental results can be divided into 3 regions.In region I (300K to 240K), the
cell parameters are mainly governed by mere thermal effect. As the compound
enters region II (below 240K to 50K), the lattice parameters show non linear
behaviour. In this region, the exchange pathways that lead to the magnetic
interactions within and between the Fe-Fe chains do not show significant
response.The region III (below 50K) is dominated by the magnetic contribution
where we observe setting up of intra and inter-chain magnetic interaction. This
behaviour is unlike other low dimensional com- pounds like Ca3Co2O6, Sr3NiRhO6,
MnTiO3 etc. thereby suggesting the magnetism in LiFeSi2O6 is of three
dimensional nature. The present results will be helpful in understanding the
evolution of the spin rings that give rise to net toroidal moment and hence its
multiferroic behaviour.",1804.05594v1
2018-04-16,"Negative Thermal Expansion Behaviour in MZrF6 (M=Ca, Mg, Sr): Ab-initio Lattice Dynamical Studies","The thermal expansion behavior of metal fluorides can be tuned by choosing
appropriate metal cation. We present ab-initio lattice dynamical studies on the
metal fluorides (CaZrF6, MgZrF6 and SrZrF6) and identify the anharmonic phonon
modes responsible for the negative thermal expansion in these materials. These
phonons involve ZrF6 polyhedral rotational motion, which leads to large
transverse amplitude of the vibrations of the fluorine atom in the Zr-F-Zr
bond. The compounds with larger anisotropy in the thermal amplitude of the
fluorine atoms show larger NTE behaviour. This has enabled to understand the
large variation in thermal expansion behaviour of these compounds at high
temperature. The calculations also predict decrease of the frequency of these
anharmonic phonons with increasing temperature.",1804.05623v1
2018-04-18,"$A$-cation control of magnetoelectric quadrupole order in $A$(TiO)Cu$_4$(PO$_4$)$_4$ ($A$ = Ba, Sr, and Pb)","Ferroic magnetic quadrupole order exhibiting macroscopic magnetoelectric
activity is discovered in the novel compound $A$(TiO)Cu$_4$(PO$_4$)$_4$ with
$A$ = Pb, which is in contrast with antiferroic quadrupole order observed in
the isostructural compounds with $A$ = Ba and Sr. Unlike the famous lone-pair
stereochemical activity which often triggers ferroelectricity as in PbTiO$_3$,
the Pb$^{2+}$ cation in Pb(TiO)Cu$_4$(PO$_4$)$_4$ is stereochemically inactive
but dramatically alters specific magnetic interactions and consequently
switches the quadrupole order from antiferroic to ferroic. Our first-principles
calculations uncover a positive correlation between the degree of $A$-O bond
covalency and a stability of the ferroic quadrupole order.",1804.06772v1
2018-04-20,"Density Functional Studies Reveal Anomalous Lattice Behavior in Metal Cyanide, AgC8N5","We have investigated anomalous lattice behavior of metal organic framework
compound AgC8N5on application of pressure and temperature using ab-initio
density functional theory calculations. The van der Waals dispersion
interactions are found to play an important role in structural optimization and
stabilization of this compound. Our ab-initio calculations show negative linear
compressibility (NLC) along the c-axis of the unit cell. The ab-initio lattice
dynamics as well as the molecular dynamics simulations show large negative
thermal expansion (NTE) along the c-axis. The mechanism of NLC and NTE along
the c-axis of the structure is governed by the dynamics of Ag atoms in the a-b
plane. The NLC along the c-axis drives the NTE along that direction.",1804.07551v1
2018-04-24,Automated Mouse Organ Segmentation: A Deep Learning Based Solution,"The analysis of animal cross section images, such as cross sections of
laboratory mice, is critical in assessing the effect of experimental drugs such
as the biodistribution of candidate compounds in preclinical drug development
stage. Tissue distribution of radiolabeled candidate therapeutic compounds can
be quantified using techniques like Quantitative Whole-Body Autoradiography
(QWBA).QWBA relies, among other aspects, on the accurate segmentation or
identification of key organs of interest in the animal cross section image such
as the brain, spine, heart, liver and others. We present a deep learning based
organ segmentation solution to this problem, using which we can achieve
automated organ segmentation with high precision (dice coefficient in the
0.83-0.95 range depending on organ) for the key organs of interest.",1804.09205v2
2018-04-25,Anomalously high value of Coulomb pseudopotential for the $\rm H_{5}S_{2}$ superconductor,"The ${\rm H_{5}S_{2}}$ and ${\rm H_{2}S}$ compounds are the two candidates
for the low-temperature phase of compressed sulfur-hydrogen system. We have
shown that the value of Coulomb pseudopotential ($\mu^{\star}$) for ${\rm
H_{5}S_{2}}$ ($\left[T_{C}\right]_{\rm exp}=36$~K and $p=112$~GPa) is
anomalously high. The numerical results give the limitation from below to
$\mu^{\star}$ that is equal to $0.402$ ($\mu^{\star}=0.589$, if we consider the
first order vertex corrections to the electron-phonon interaction). Presented
data mean that the properties of superconducting phase in the ${\rm
H_{5}S_{2}}$ compound can be understood within the classical framework of
Eliashberg formalism only at the phenomenological level ($\mu^{\star}$ is the
parameter of matching the theory to the experimental data). On the other hand,
in the case of ${\rm H_{2}S}$ it is not necessary to take high value of Coulomb
pseudopotential to reproduce the experimental critical temperature relatively
well ($\mu^{\star}=0.15$). In our opinion, ${\rm H_{2}S}$ is mainly responsible
for the observed superconductivity state in the sulfur-hydrogen system at low
temperature.",1804.09760v2
2018-04-26,Large Thermoelectric Power Factor in One-Dimensional Telluride Nb4SiTe4 and Substituted Compounds,"We found that whisker crystals of Mo-doped Nb4SiTe4 show high thermoelectric
performances at low temperatures, indicated by the largest power factor of 70
microW cm-1 K-2 at 230-300 K, much larger than those of Bi2Te3-based practical
materials. This power factor is smaller than the maximum value in the 5d
analogue Ta4SiTe4, but is comparable to that with a similar doping level. First
principles calculation results suggest that the difference in thermoelectric
performances between Nb and Ta compounds is caused by the much smaller band gap
in Nb4SiTe4 than that in Ta4SiTe4, due to the weaker spin-orbit coupling in the
former. We also demonstrated that the solid solution of Nb4SiTe4 and Ta4SiTe4
shows a large power factor, indicating that their combination is promising as a
practical thermoelectric material, as in the case of Bi2Te3 and Sb2Te3. These
results advance our understanding of the mechanism of high thermoelectric
performances in this one-dimensional telluride system, as well as indicating
the high potential of this system as a practical thermoelectric material for
low temperature applications.",1804.09867v1
2018-04-26,Optical and Electronic Properties of Molecular Systems Derived from Rhodanine,"Push-Pull functional compounds consisting of dicyanorhodanine derivatives
have attracted a lot of interest because their optical, electronic, and charge
transport properties make them useful as building blocks for organic
photovoltaic implementations. The analysis of the frontier molecular orbitals
shows that the vertical transitions of electronic absorption are characterized
as intramolecular charge transfer; furthermore, we show that the analyzed
compounds exhibit bathochromic displacements when comparing the presence (or
absence) of solvent as an interacting medium. In comparison with materials
defined by their energy of reorganization of electrons (holes) as electron
(hole) transporters, we find a transport hierarchy whereby the molecule
(Z)-2-((1,1-Dicyanomethylene)-5-(4-dimethylamino)benzylidene)-1,3-thiazol-4 is
better at transporting holes than molecule
(Z)-2-((1,1-Dicyanomethylene)-5-(tetrathiafulvalene-2-ylidene)-1,3-thiazol-4.",1804.10300v3
2019-02-28,Doping-type-dependent pairing symmetry in predicted Ni-based high-$T_c$ superconductor La$_2$Ni$_2$Se$_2$O$_3$,"We study the electronic instabilities of newly predicted Ni-based high-$T_c$
superconducting material La$_2$Ni$_2$Se$_2$O$_3$ based on the random phase
approximation. Our calculations on the susceptibility indicate that the
collinear antiferromagnetic state in the parental compound is induced by the
perfect Fermi surface nesting. Our further calculations reveal that the ground
states of the doped compound are the $s_{\pm}$- and $d_{xy}$-wave
superconducting states driven by the antiferromagnetic spin fluctuations
enhanced by the quasi-nestings. Interestingly, the $s$- and $d$-wave pairings
occur in the hole and electron doping cases, respectively. This doping-type
dependence of the pairing symmetry can be understood from the doping dependence
of the nested Fermi pockets.",1903.00098v1
2019-03-01,Electronic structure of the quadrupolar ordered heavy-fermion compound YbRu2Ge2 measured by angle-resolved photoemission,"We studied the electronic structure of the heavy fermion compound
Yb(Ru$_{1-x}$Rh$_{x}$)$_2$Ge$_2$ with $x=0$ and nominally $x=0.125$ using ARPES
and LDA calculations. We find a valence band structure of Yb corresponding to a
non-integer valence close to $3+$. The three observed crystal electric field
levels with a splitting of 32 and 75 meV confirm the suggested configuration
with a quasi-quartet ground state. The experimentally determined band structure
of the conduction electrons with predominantly Ru $4d$ character is well
reproduced by our calculations. YbRu$_2$Ge$_2$ undergoes a non-magnetic phase
transition into a ferroquadrupolar ordered state below 10.2\,K and then to an
antiferromagnetically ordered state below 6.5\,K. A small hole Fermi surface
shows nesting features in our calculated band structure and its size determined
by ARPES is close to the magnetic ordering wave vector found in neutron
scattering. The transitions are suppressed when YbRu$_2$Ge$_2$ is doped with
12.5% Rh. The electron doping leads to a shift of the band structure and
successive Lifshitz transitions.",1903.00151v1
2019-02-28,Topology of Triple-Point Metals,"We discuss and illustrate the appearance of topological fermions and bosons
in triple-point metals, where a band crossing of three electronic bands occurs
close to the Fermi level. Topological bosons appear in the phonon spectrum of
certain triple-point metals, depending on the mass of atoms that form the
binary triple-point metal. We first provide a classification of possible
triple-point electronic topological phases possible in crystalline compounds
and discuss the consequences of these topological phases, seen in Fermi arcs,
topological Lifshitz transitions and transport anomalies. Then we show how the
topological phase of phonon modes can be extracted and proven for relevant
compounds. Finally, we show how the interplay of electronic and phononic
topologies in triple-point metals puts these \textit{metallic} materials into
the list of the most efficient \textit{metallic} thermoelectrics known to date.",1903.01269v1
2019-03-11,"Magnetic excitations in the trimeric compounds A$_3$Cu$_3$(PO$_4$)$_4$ (A = Ca, Sr, Pb)","We study the magnetic excitations of the trimeric magnetic compounds
A$_3$Cu$_3$(PO$_4$)$_4$ (A = Ca, Sr, Pb). The spectra are analyzed in terms of
the Heisenberg model and a generic spin Hamiltonian that accounts for the
changes in valence electrons distribution along the bonds among magnetic ions.
The analytical results obtained in the framework of both Hamiltonians are
compared to each other and to the available experimental measurements. The
results based on our model show better agreement with the experimental data
than those obtained with the aid of the Heisenberg model. For all trimers, our
analysis reveals the existence of one thin energy band referring to the
flatness of observed excitation peaks.",1903.04967v1
2019-03-15,Phenotypic Profiling of High Throughput Imaging Screens with Generic Deep Convolutional Features,"While deep learning has seen many recent applications to drug discovery, most
have focused on predicting activity or toxicity directly from chemical
structure. Phenotypic changes exhibited in cellular images are also indications
of the mechanism of action (MoA) of chemical compounds. In this paper, we show
how pre-trained convolutional image features can be used to assist scientists
in discovering interesting chemical clusters for further investigation. Our
method reduces the dimensionality of raw fluorescent stained images from a high
throughput imaging (HTI) screen, producing an embedding space that groups
together images with similar cellular phenotypes. Running standard unsupervised
clustering on this embedding space yields a set of distinct phenotypic
clusters. This allows scientists to further select and focus on interesting
clusters for downstream analyses. We validate the consistency of our embedding
space qualitatively with t-sne visualizations, and quantitatively by measuring
embedding variance among images that are known to be similar. Results suggested
the usefulness of our proposed workflow using deep learning and clustering and
it can lead to robust HTI screening and compound triage.",1903.06516v1
2019-03-19,On the Sprague-Grundy function of compound games,"The classical game of {\sc Nim} can be naturally extended and played on an
arbitrary hypergraph $\cH \subseteq 2^V \setminus \{\emptyset\}$ whose vertices
$V = \{1, \ldots, n\}$ correspond to piles of stones. By one move a player
chooses an edge $H$ of $\cH$ and reduces arbitrarily all piles $i \in H$. In
1901 Bouton solved the classical {\sc Nim} for which $\cH = \{\{1\}, \ldots,
\{n\}\}$. In 1910 Moore introduced and solved a more general game $k$-{\sc
Nim}, for which $\cH = \{H \subseteq V \mid |H| \leq k\}$, where $1 \leq k <
n$. In 1980 Jenkyns and Mayberry obtained an explicit formula for the
Sprague-Grundy function of Moore's {\sc Nim} for the case $k+1 = n$. Recently
it was shown that the same formula works for a large class of hypergraphs. In
this paper we study combinatorial properties of these hypergraphs and obtain
explicit formulas for the Sprague-Grundy functions of the conjunctive and
selective compounds of the corresponding hypergraph {\sc Nim} games.",1903.08138v1
2019-03-21,Time reversal invariance violation in neutron-nucleus scattering,"Planning and interpretation of the experiments searching for the time
reversal (T) and parity (P) violation in neutron reactions require values of
the matrix elements of the T,P-violating nuclear forces between nuclear
compound states. We calculate the root mean square values and the ratio of the
matrix elements of the T,P-violating and P-violating interactions using
statistical theory based on the properties of chaotic compound states and
present the results in terms of the fundamental parameters in four different
forms: in terms of the constants of the contact nuclear interaction, meson
exchange constants, QCD theta-term and quark chromo-EDMs. Using current limits
on these parameters, we obtain the upper bounds on the ratio of the matrix
elements.",1903.08937v2
2019-03-25,Vibrational and dielectric properties of monolayer transition metal dichalcogenides,"First-principles studies of two-dimensional transition metal dichalcogenides
have contributed considerably to the understanding of their dielectric,
optical, elastic, and vibrational properties. The majority of works to date
focus on a single material or physical property. Here we use a single
first-principles methodology on the whole family of systems, to investigate in
depth the relationships between different physical properties, the underlying
symmetry and the composition of these materials, and observe trends. We compare
to bulk counterparts to show strong interlayer effects in triclinic compounds.
Previously unobserved relationships between these monolayer compounds become
apparent. These trends can then be exploited by the materials science,
nanoscience, and chemistry communities to better design devices and
heterostructures for specific functionalities.",1903.10179v1
2019-03-26,"Magnetic and magnetoelectric properties of $A$FeF$_5$ ($A$ = Ca, Sr) spin-chain compounds","Fluorides in general are characterized by big variety of crystal structures,
whereas those containing transition metals also often show sizable magnetic
properties. The tendency of fluorine to form linear chain structures in many
cases results in low-dimensional magnetism. Despite the plethora of magnetic
phenomena in fluorides, their magnetoelectric properties are less studied than
those of oxides. In the present work we theoretically study the magnetic and
magnetoelectric properties of spin-chain compounds CaFeF$_5$ and SrFeF$_5$. The
density functional theory is employed for determination of magnetic exchange
constants, which are then used in Monte Carlo calculations. The symmetry
analysis reveals that CaFeF$_5$ does not show magnetoelectric properties,
whereas SrFeF$_5$ is a multiferroic.",1903.10828v2
2019-03-26,"Axial GaAs/Ga(As,Bi) Nanowire Heterostructures","Bi-containing III-V semiconductors constitute an exciting class of metastable
compounds with wide-ranging potential optoelectronic and electronic
applications. However, the growth of III-V-Bi alloys requires group-III-rich
growth conditions, which pose severe challenges for planar growth. In this
work, we exploit the naturally-Ga-rich environment present inside the metallic
droplet of a self-catalyzed GaAs nanowire to synthesize metastable
GaAs/GaAs$_{1-\text{x}}$Bi$_{\text{x}}$ axial nanowire heterostructures with
high Bi contents. The axial GaAs$_{1-\text{x}}$Bi$_{\text{x}}$ segments are
realized with molecular beam epitaxy by first enriching only the
vapor-liquid-solid (VLS) Ga droplets with Bi, followed by exposing the
resulting Ga-Bi droplets to As$_2$ at temperatures ranging from 270 to
380$\,^{\circ}$C to precipitate GaAs$_{1-\text{x}}$Bi$_{\text{x}}$ only under
the nanowire droplets. Microstructural and elemental characterization reveals
the presence of single crystal zincblende GaAs$_{1-\text{x}}$Bi$_{\text{x}}$
axial nanowire segments with Bi contents up to (10$\pm$2)$\%$. This work
illustrates how the unique local growth environment present during the VLS
nanowire growth can be exploited to synthesize heterostructures with metastable
compounds.",1903.11039v2
2019-03-27,Effect of A-site ionic radius on metamagnetic transition in charge ordered $Sm_{0.5}(Ca_{0.5-y}Sr_{y})MnO_3$ compounds,"We investigate the ultra-sharp jump in the isothermal magnetization and the
resistivity in the polycrystalline $Sm_{0.5}(Ca_{0.5-y}Sr_{y})MnO_3$ $(y = 0,
0.1, 0.2, 0.25, 0.3, 0.5)$ compounds. The critical field $(H_{cr})$, required
for the ultra-sharp jump, decreases with increase of `Sr' concentration, i.e.
with increase of average A-site ionic radius $\langle r_A\rangle$. The
magnetotransport data indicate that the phase separation increases with the
increase of $\langle r_A\rangle$, i.e. with $y$. The dependency of $H_{cr}$
with magnetic field sweep rate reveals that the ultra-sharp jump from
antiferromagnetic (AFM) state to the ferromagnetic (FM) state is of martensitic
in nature. Our two-band double exchange model Hamiltonian calculations show
that the `Sr' doping induces the ferromagnetic clusters in the
antiferromagnetic insulating phase and in turn reduces the critical field. In
the end we present a phenomenological picture obtained from our combined
experimental and theoretical study.",1903.11348v1
2019-05-04,"A comparative theoretical study on physical properties of synthesized AVO3 (A = Ba, Sr, Ca, Pb) perovskites","In this paper, we employ CASTEP based on DFT (density functional theory)
calculations to investigate various physical properties of BaVO3, SrVO3, CaVO3
and PbVO3. The elastic constants, bulk modulus, Shear modulus, Young's modulus,
Pugh's ratio, Poisson's ratio, Vickers hardness, universal anisotropy index and
Peierls stress are calculated to rationalize the mechanical behavior of the
aforementioned compounds. The study of electronic band structure and density of
states (DOS) reveal the strong evidence of metallic behavior for all the
perovskites. The analysis of bonding properties exhibits the existence of
covalent, ionic and metallic bonds. The optical properties of AVO3 have been
carried out and are discussed in this paper as well. The analysis of phonon
property implies the dynamical stability of BaVO3 but not for SrVO3, CaVO3 and
PbVO3. The values of Debye temperature and minimum thermal conductivity imply
that only PbVO3 compound has potential to be used as TBC material.",1905.01437v1
2019-05-07,Mapping the structural diversity of C60 carbon clusters and their infrared spectra,"The current debate about the nature of the carbonaceous material carrying the
infrared (IR) emission spectra of planetary and proto-planetary nebulae,
including the broad plateaus, calls for further studies on the interplay
between structure and spectroscopy of carbon-based compounds of astrophysical
interest. The recent observation of C60 buckminsterfullerene in space suggests
that carbon clusters of similar size may also be relevant. In the present work,
broad statistical samples of C60 isomers were computationally determined
without any bias using a reactive force field, their IR spectra being
subsequently obtained following local optimization with the
density-functional-based tight-binding theory. Structural analysis reveals four
main structural families identified as cages, planar polycyclic aromatics,
pretzels, and branched. Comparison with available astronomical spectra
indicates that only the cage family could contribute to the plateau observed in
the 6-9 micron region. The present framework shows great promise to explore and
relate structural and spectroscopic features in more diverse and possibly
hydrogenated carbonaceous compounds, in relation with astronomical
observations.",1905.02550v1
2019-05-14,Revealing the complex nature of bonding in binary high-pressure compound FeO$_2$,"Extreme pressures and temperatures are known to drastically affect the
chemistry of iron oxides resulting in numerous compounds forming homologous
series $n$FeO$\cdot m$Fe$_2$O$_3$ and the appearance of FeO$_2$. Here, based on
the results of \emph{in situ} single-crystal X-ray diffraction, M\""ossbauer
spectroscopy, X-ray absorption spectroscopy, and DFT+dynamical mean-field
theory calculations we demonstrate that iron in high pressure cubic FeO$_2$ and
isostructural FeO$_2$H$_{0.5}$ is ferric (Fe$^{3+}$), and oxygen has a formal
valence less than two. Reduction of oxygen valence from 2, common for oxides,
down to 1.5 can be explained by a formation of a localized hole at oxygen
sites.",1905.05497v2
2019-05-16,Harvesting Information from Captions for Weakly Supervised Semantic Segmentation,"Since acquiring pixel-wise annotations for training convolutional neural
networks for semantic image segmentation is time-consuming, weakly supervised
approaches that only require class tags have been proposed. In this work, we
propose another form of supervision, namely image captions as they can be found
on the Internet. These captions have two advantages. They do not require
additional curation as it is the case for the clean class tags used by current
weakly supervised approaches and they provide textual context for the classes
present in an image. To leverage such textual context, we deploy a multi-modal
network that learns a joint embedding of the visual representation of the image
and the textual representation of the caption. The network estimates text
activation maps (TAMs) for class names as well as compound concepts, i.e.
combinations of nouns and their attributes. The TAMs of compound concepts
describing classes of interest substantially improve the quality of the
estimated class activation maps which are then used to train a network for
semantic segmentation. We evaluate our method on the COCO dataset where it
achieves state of the art results for weakly supervised image segmentation.",1905.06784v1
2018-12-16,Kinetic studies on using photocatalytic coatings for removal of indoor volatile organic compounds,"Titanium dioxide (TiO2) is a known photocatalyst with a capability of
decomposing organic substance. However, the photocatalysis of the pure TiO2 is
not effective for the indoor environment due to a lack of the ultraviolet
irradiation inside the building. Doping TiO2 with substance such as C, N or
metal can extend the threshold of the absorption spectrum to the visible
spectrum region. Thus, doped-TiO2 is able to decompose volatile organic
compounds (VOCs) under an indoor environment. To date, most experimental work
reported on photocatalytic kinetics were conducted inside small-scale devices.
The performance of air purification function under the actual indoor
application scenery need to be further clarified. For this purpose, it is
crucial to predict the performance of autogenous air quality improvements by
visible light driven photocatalyst for the actual applications. This work has
developed a model to evaluate the performance of functional coating with
photocatalyst in removing VOCs. Factors such as the effects of coating designs
and indoor ambient conditions on the air purification efficiency were studied.
This work demonstrates that doped-TiO2 photocatalytic coating is effective to
improve the indoor air quality.",1905.06936v1
2019-05-23,Electromigration Response of Microjoints in 3DIC Packaging Systems,"In multilevel 3D integrated packaging, three major microstructures are viable
due to the application of low volume of solders in different sizes, and/or
processing conditions. Thermodynamics and kinetics of binary compounds in
Cu/Sn/Cu low volume interconnection is taken into account. We show that current
crowding effects can induce a driving force to cause excess vacancies saturate
and ultimately cluster in the form of microvoids. A kinetic analysis is
performed for electromigration mediated intermetallic growth using
multi-phase-field approach. Faster growth of intermetallic compounds (IMCs) in
anode layer in the expense of shrinkage of cathode IMC layer in shown. This
work paves the road for computationally study the ductile failure due to
formation of microvoids in low volume solder interconnects in 3DICs.",1905.09901v1
2019-05-29,Topological Techniques in Model Selection,"The LASSO is an attractive regularisation method for linear regression that
combines variable selection with an efficient computation procedure. This paper
is concerned with enhancing the performance of LASSO for square-free
hierarchical polynomial models when combining validation error with a measure
of model complexity. The measure of the complexity is the sum of Betti numbers
of the model which is seen as a simplicial complex, and we describe the model
in terms of components and cycles, borrowing from recent developments in
computational topology. We study and propose an algorithm which combines
statistical and topological criteria. This compound criterion would allow us to
deal with model selection problems in polynomial regression models containing
higher-order interactions. Simulation results demonstrate that the compound
criteria produce sparser models with lower prediction errors than the
estimators of several other statistical methods for higher order interaction
models.",1905.12269v1
2019-05-20,Recommendation from Raw Data with Adaptive Compound Poisson Factorization,"Count data are often used in recommender systems: they are widespread (song
play counts, product purchases, clicks on web pages) and can reveal user
preference without any explicit rating from the user. Such data are known to be
sparse, over-dispersed and bursty, which makes their direct use in recommender
systems challenging, often leading to pre-processing steps such as
binarization. The aim of this paper is to build recommender systems from these
raw data, by means of the recently proposed compound Poisson Factorization
(cPF). The paper contributions are three-fold: we present a unified framework
for discrete data (dcPF), leading to an adaptive and scalable algorithm; we
show that our framework achieves a trade-off between Poisson Factorization (PF)
applied to raw and binarized data; we study four specific instances that are
relevant to recommendation and exhibit new links with combinatorics.
Experiments with three different datasets show that dcPF is able to effectively
adjust to over-dispersion, leading to better recommendation scores when
compared with PF on either raw or binarized data.",1905.13128v2
2019-08-02,Origin of magnetic anisotropy in the spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$,"The $S=1/2$ spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ (BPCB) is
studied by means of high-resolution inelastic neutron scattering. In agreement
with previous studies we find a band of triplet excitations with a spin gap of
$\sim0.8$~meV and a bandwidth of $\sim0.6$~meV. In addition, we observe a
distinct splitting of the triplet band of $50(1)$~$\mu$eV or $40(2)$~$\mu$eV at
the band minimum or maximum, respectively. By comparison to a strong coupling
expansion calculation of the triplet dispersion for a spin ladder with
anisotropic exchange, weakly anisotropic leg interactions are identified as the
dominant source of magnetic anisotropy in BPCB. Based on these results, we
discuss the nature of magnetic exchange anisotropy in BPCB and in related
transition-metal insulators.",1908.00724v2
2019-08-02,An accelerating approach of designing ferromagnetic materials via machine learning modeling of magnetic ground state and Curie temperature,"Magnetic materials have a plethora of applications ranging from informatics
to energy harvesting and conversion. However, such functionalities are limited
by the magnetic ordering temperature. In this work, we performed machine
learning on the magnetic ground state and the Curie temperature (TC), using
generic chemical and crystal structural descriptors. Based on a database of
2805 known intermetallic compounds, a random forest model is trained to
classify ferromagnetic and antiferromagnetic compounds and to do regression on
the TC for the ferromagnets. The resulting accuracy is about 86% for
classification and 92% for regression (with a mean absolute error of 58K).
Composition based features are sufficient for both classification and
regression, whereas structural descriptors improve the performance. Finally, we
predict the magnetic ordering and TC for all the intermetallic magnetic
materials in the Materials Project. Our work paves the way to accelerate the
development of magnetic materials for technological applications.",1908.00926v2
2019-08-02,Ergodic control of diffusions with compound Poisson jumps under a general structural hypothesis,"We study the ergodic control problem for a class of controlled jump
diffusions driven by a compound Poisson process. This extends the results of
[SIAM J. Control Optim. 57 (2019), no. 2, 1516-1540] to running costs that are
not near-monotone. This generality is needed in applications such as optimal
scheduling of large-scale parallel server networks.
  We provide a full characterization of optimality via the
Hamilton-Jacobi-Bellman (HJB) equation, for which we additionally exhibit
regularity of solutions under mild hypotheses. In addition, we show that
optimal stationary Markov controls are a.s. pathwise optimal. Lastly, we show
that one can fix a stable control outside a compact set and obtain near-optimal
solutions by solving the HJB on a sufficiently large bounded domain. This is
useful for constructing asymptotically optimal scheduling policies for
multiclass parallel server networks.",1908.01068v1
2019-08-05,Evidence of the impurity spin coupling with quantum paraelectric fluctuations in CaTi1-xRuxO3,"Quantum paraelectrics are materials in which a long-range
ferroelectric/antiferroelectric order is suppressed by quantum fluctuations,
i.e. zero-point motion of the lattice prevents condensation of the soft polar
phonon mode even at T = 0 K. The most prominent quantum paraelectric materials
are SrTiO3, KTaO3, and CaTiO3. Here we focus on peculiar properties of the
pseudo-cubic perovskite CaTi1-xRuxO3 system. Namely, as soon as any
concentration of either Ru or Ti is introduced into the pure compounds, a
concentration-independent ferromagnetic-like transition occurs at low
temperatures. We present the experimental evidence of the spin-polarized ground
state of CaTi1-xRuxO3 induced by coupling of magnetic moments of Ru impurities
with quantum paraelectric fluctuations in the host compound CaTiO3.",1908.01631v1
2019-08-06,Competing magnetic interactions in the antiferromagnetic topological insulator MnBi$_{2}$Te$_{4}$,"The antiferromagnetic (AF) compound MnBi$_{2}$Te$_{4}$ is suggested to be the
first realization of an antiferromagnetic (AF) topological insulator. Here we
report on inelastic neutron scattering studies of the magnetic interactions in
MnBi$_{2}$Te$_{4}$ that possess ferromagnetic (FM) triangular layers with AF
interlayer coupling. The spin waves display a large spin gap and pairwise
exchange interactions within the triangular layer are frustrated due to large
next-nearest neighbor AF exchange. The degree of frustration suggests proximity
to a variety of magnetic phases, potentially including skyrmion phases, that
could be accessed in chemically tuned compounds or upon the application of
symmetry-breaking fields.",1908.02332v1
2019-08-07,Momentum Dependence of the Nematic Order Parameter in Iron-Based Superconductors,"The momentum dependence of the nematic order parameter is an important
ingredient in the microscopic description of iron-based high-temperature
superconductors. While recent reports on FeSe indicate that the nematic order
parameter changes sign between electron and hole bands, detailed knowledge is
still missing for other compounds. Combining angle-resolved photoemission
spectroscopy (ARPES) with uniaxial strain tuning, we measure the nematic band
splitting in both FeSe and BaFe$_2$As$_2$ without interference from either
twinning or magnetic order. We find that the nematic order parameter exhibits
the same momentum dependence in both compounds with a sign change between the
Brillouin center and the corner. This suggests that the same microscopic
mechanism drives the nematic order in spite of the very different phase
diagrams.",1908.02790v1
2019-08-14,Magnetic ground state of distorted 6H perovskite Ba$_3$CdIr$_2$O$_9$,"Perovskite iridates of 6H hexagonal structure present a plethora of
possibilities in terms of the variety of ground states resulting from a
competition between spin-orbit coupling (SOC), hopping, noncubic crystal field
($\Delta_{CFE}^{NC}$) and superexchange energy scales within the Ir$_2$O$_9$
dimers. Here we have investigated one such compound Ba$_3$CdIr$_2$O$_9$ by
x-ray diffraction, dc magnetic susceptibility($\chi$), heat capacity($C_p$) and
also ${}^{113}$Cd nuclear magnetic resonance (NMR) spectroscopy. We have
established that the magnetic ground state has a small but finite magnetic
moment on Ir$^{5+}$ in this system, which likely arises from intradimer Ir-Ir
hopping and local crystal distortions. Our heat capacity, NMR, and dc magnetic
susceptibility measurements further rule out any kind of magnetic
long-/short-range ordering among the Ir moments down to at least 2K. In
addition, the magnetic heat capacity data shows linear temperature dependence
at low temperatures under applied high fields ($>$ 30 kOe), suggesting gapless
spin-density of states in the compound.",1908.05163v1
2019-08-19,Reverse chemistry of iron in the deep Earth,"In this work, we demonstrate a remarkable change of chemical trend of Iron
under high pressure that is of great importance for understanding the
distribution of elements in the Earth's mantle and core. Using first principles
crystal structure search method, we conduct a systematic study of the
propensity of p block elements to chemically bind with iron under high
pressures ranging from ambient conditions to that of Earth's core. We show that
under increasing pressure, iron tends to reverse its chemical nature, changing
from an electron donor (reductant) to an electron acceptor, and oxidizes
p-block elements in many compounds. Such reverse chemistry has a significant
impact on the stoichiometries, bond types and strengths, structures and
properties of iron compounds under deep planetary conditions.",1908.06569v1
2019-08-19,Stripe Antiferromagnetism and Disorder in the Mott Insulator NaFe$_{1-x}$Cu$_{x}$As ($x \lesssim 0.5$),"Neutron scattering measurements have demonstrated that the heavily Cu-doped
NaFe$_{1-x}$Cu$_{x}$As compound behaves like a Mott insulator exhibiting both
real space Fe-Cu stripes, as well as antiferromagnetism below a N\'eel
temperature for $x\lesssim 0.5$. We have investigated evolution of structural
and magnetic ordering using $^{23}$Na and $^{75}$As NMR for single crystals
($x$ = 0.39 and 0.48), confirming antiferromagnetism in the form of magnetic
stripes. We show that end-chain defects in these stripes are the principal
source of magnetic disorder and are responsible for cluster spin-glass
transitions in both compounds, in the latter case coexistent with
antiferromagnetism. Aided by our numerical simulation of the $^{75}$As spectra,
we show that a staggered magnetization at the Fe sites is induced by
non-magnetic Cu dopants.",1908.07035v3
2019-08-24,Magnetic order and anisotropic interactions induced by mixing between the $J=1/2$ and $3/2$ sectors in spin-orbit coupled honeycomb-lattice compounds,"Novel magnetic ordering on the honeycomb lattice due to emergent weak
anisotropic interactions generated by the mixing between the $J=1/2$ sector and
the magnetically inactive 3/2 sector is investigated in a three-orbital
interacting electron model in the absence of Hund's coupling. Self-consistent
determination of magnetic order yields anisotropic N\'{e}el and zigzag orders
for different parameter regimes, highlighting the effect of the emergent
single-ion anisotropy. Study of magnon excitations shows extremely small magnon
energy scale compared to the hopping energy scale, and enhancement of
anisotropy effects for smaller spin-orbit coupling. These results account for
several features of the honeycomb lattice compounds such as $\rm Na_2 Ir O_3$
and $\rm Ru Cl_3$, where the leading order anisotropic interactions within the
magnetically active $J=1/2$ sector are completely quenched due to the
edge-sharing octahedra.",1908.09130v1
2019-08-27,Crystal electric field splitting and f-electron hybridization in heavy fermion CePt2In7,"We use high-resolution angle-resolved photoemission spectroscopy to
investigate the electronic structure of the antiferromagnetic heavy fermion
compound CePt2In7, which is a member of the CeIn3-derived heavy fermion
material family. Weak hybridization among 4f electron states and conduction
bands was identified in CePt2In7 at low temperature much weaker than that in
the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum
shows fine structures near the Fermi energy, reflecting the crystal electric
field splitting of the 4f^1_5/2 and 4f^1_7/2 states. Also, we find that the
Fermi surface has a strongly three-dimensional topology, in agreement with
density-functional theory calculations.",1908.09975v1
2019-08-29,A look at multiparticle production via modified combinants,"As shown recently, one can obtain additional information from the measured
charged particle multiplicity distributions, $P(N)$, by investigating the
so-called modified combinants, $C_j$, extracted from them. This information is
encoded in the observed specific oscillatory behaviour of $C_j$, which
phenomenologically can be described only by some combinations of compound
distributions based on the Binomial Distribution. So far this idea has been
checked in $pp$ and $e^+e^-$ processes (where observed oscillations are
spectacularly strong). In this paper, we continue observation of multiparticle
production from the modified combinants perspective by investigating
dependencies of the observed oscillatory patterns on type of colliding
particles, their energies and the phase space where they are observed. We also
offer some tentative explanations based on different types of compound
distributions and stochastic branching processes.",1908.11062v3
2019-08-29,Deep Learning for Estimating Synaptic Health of Primary Neuronal Cell Culture,"Understanding the morphological changes of primary neuronal cells induced by
chemical compounds is essential for drug discovery. Using the data from a
single high-throughput imaging assay, a classification model for predicting the
biological activity of candidate compounds was introduced. The image
recognition model which is based on deep convolutional neural network (CNN)
architecture with residual connections achieved accuracy of 99.6$\%$ on a
binary classification task of distinguishing untreated and treated rodent
primary neuronal cells with Amyloid-$\beta_{(25-35)}$.",1908.11399v1
2019-08-30,Transport Spectroscopy of the Field Induced Cascade of Lifshitz Transitions in YbRh2Si2,"A series of strong anomalies in the thermoelectric power is observed in the
heavy fermion compound YbRh$_2$Si$_2$ under the effect of magnetic field
varying in the range from 9.5~T to 13~T. We identify these features with a
sequence of topological transformations of the sophisticated Fermi surface of
this compound, namely a cascade of Lifshitz topological transitions. In order
to undoubtedly attribute these anomalies to the specific topological changes of
the Fermi surface, we employ the renormalized band method. Basing on its
results we suggest a simplified model consisting of the large peripheral Fermi
surface sheet and the number of continuously appearing (disappearing) small
""voids"" or ""necks"". We account for the multiple electron scattering processes
between various components of the Fermi surface, calculate the corresponding
scattering times, and, finally, find the magnetic field dependence of the
Seebeck coefficient. The obtained analytical expression reproduces reasonably
the observed positions of the maxima and minima as well as the overall line
shapes and allows us to identify the character of corresponding topological
transformations.",1908.11700v1
2019-08-30,Magnetic states of iron-based two-leg ladder tellurides,"The recent discovery of superconductivity at high pressure in the two-leg
ladder compounds BaFe$_2X_3$ ($X$=S, Se) started the novel field of
quasi-one-dimensional iron-based superconductors. In this publication, we use
Density Functional Theory (DFT) to predict that the previously barely explored
ladder compound RbFe$_2$Te$_3$ should be magnetic with a CX-type arrangement
involving ferromagnetic rungs and antiferromagnetic legs, at the realistic
density of $n=5.5$ electrons per iron. The magnetic state similarity with
BaFe$_2$S$_3$ suggests that RbFe$_2$Te$_3$ could also become superconducting
under pressure. Moreover, at $n=6.0$ our DFT phase diagrams (with and without
lattice tetramerization) reveal that the stable magnetic states could be either
a 2$\times$2 magnetic Block-type, as for $X$=Se, or a previously never observed
before CY-type state, with ferromagnetic legs and antiferromagnetic rungs. In
the Te-based studies, electrons are more localized than in S, implying that the
degree of electronic correlation is enhanced for the Te case.",1908.11765v2
2019-09-03,Single-site magnetic anisotropy governed by inter-layer cation charge imbalance in triangular-lattice AYbX$_2$,"The behavior in magnetic field of a paramagnetic center is characterized by
its $g$ tensor. An anisotropic form of the latter implies different kind of
response along different crystallographic directions. Here we shed light on the
anisotropy of the $g$ tensor of Yb$^{3+}$ 4$f^{13}$ ions in NaYbS$_2$ and
NaYbO$_2$, layered triangular-lattice materials suggested to host spin-liquid
ground states. Using quantum chemical calculations we show that, even if the
ligand-cage trigonal distortions are significant in these compounds, the
crucial role in realizing strongly anisotropic, `noncubic' $g$ factors is
played by inter-layer cation charge imbalance effects. The latter refer to the
asymmetry experienced by a given Yb center due to having higher ionic charges
at adjacent metal sites within the magnetic $ab$ layer, i.e., 3+ nearest
neighbors within the ab plane versus 1+ species between the magnetic layers.
According to our results, this should be a rather general feature of 4$f^{13}$
layered compounds: less inter-layer positive charge is associated with stronger
in-plane magnetic response.",1909.01224v1
2019-09-09,Sublattice Melting in Binary Superionic Colloidal Crystals,"In superionic compounds one component pre-melts providing high ionic
conductivity to solid state electrolytes. Here, we find sublattice melting in
colloidal crystals of oppositely charged particles that are highly asymmetric
in size and charge in salt solutions. The small particles in ionic compounds
melt when the temperature increases forming a superionic phase. These
delocalized small particles in a crystal of large oppositely charged particles,
in contrast to superionic phases in atomic systems, form crystals with
non-electroneutral stoichiometric ratios. This generates structures with
multiple domains of ionic crystals in percolated superionic phases with
adjustable stoichiometries.",1909.04191v4
2019-09-12,Compound Sequential Change-point Detection in Parallel Data Streams,"We consider sequential change-point detection in parallel data streams, where
each stream has its own change point. Once a change is detected in a data
stream, this stream is deactivated permanently. The goal is to maximize the
normal operation of the pre-change streams, while controlling the proportion of
post-change streams among the active streams at all time points. Taking a
Bayesian formulation, we develop a compound decision framework for this
problem. A procedure is proposed that is uniformly optimal among all sequential
procedures which control the expected proportion of postchange streams at all
time points. We also investigate the asymptotic behavior of the proposed method
when the number of data streams grows large. Numerical examples are provided to
illustrate the use and performance of the proposed method.",1909.05903v2
2019-09-18,"NMR, magnetization, and heat capacity studies of the uniform spin-1/2 chain compound Bi6V3O16","We report the local (NMR) and bulk (magnetization and heat capacity)
properties of the vanadium-based S=1/2 uniform spin chain compound
Bi6V3O16(Bi4V2O10.66). In the low-temperature {\alpha} phase, the magnetic ions
(V4+) are arranged in one-dimensional chains. The magnetic susceptibility shows
a broad maximum around 50 K signifying a short-range magnetic order. Heat
capacity measurements also reveal low-dimensional magnetism. The 51V magic
angle spinning nuclear magnetic resonance measurements clearly show that the
magnetic V4+ and nonmagnetic V5+ species are located on different
crystallographic sites with no mixed occupation. The spin susceptibility
calculated from the shift of the 51V NMR spectra reproduces the behavior
observed in magnetic susceptibility and agrees well with the S=1/2 uniform spin
chain model with J=113(5) K.",1909.08594v1
2019-09-21,Neutralization of low energy Na$^{+}$ scattered from InAs(001),"The neutralization probability of low energy Na$^{+}$ ions scattered from In-
and As-rich InAs(001) surfaces is measured by time-of-flight spectroscopy. It
is found that the neutralization probability for projectiles scattered from As
sites is larger than from In sites for both types of surfaces. A modification
of the resonant charge transfer model is proposed in which a freezing contour
that follows the atomic structure is combined with molecular dynamics and
density functional theory. Together, these approaches show that the
neutralization of alkali projectiles scattered from a compound solid material
is determined by multiple factors, particularly the surface atomic and
electronic structures. This model is applicable to any system in which the
surface potential is inhomogeneous, such as compound materials and
adsorbate-covered surfaces.",1909.09751v2
2019-09-22,"Electronic structure studies on single crystalline Nd2PdSi3, an exotic Nd-based intermetallic: Evidence for Nd 4f hybridization","In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it
exhibits ferromagnetic order unlike other members in this family. The magnetic
ordering temperature is also unusually high compared to the expected value for
a Nd-based system, assuming 4f localization. Here, we have studied the
electronic structure of single crystalline Nd2PdSi3 employing high resolution
photoemission spectroscopy and ab initio band structure calculations.
Theoretical results obtained for the effective electron correlation strength of
6 eV corroborate well with the experimental valence band spectra. While there
is significant Pd 4d-Nd 4f hybridization, the states near the Fermi level are
found to be dominated by hybridized Nd 4f-Si 3p states. Nd 3d core level
spectrum exhibits multiple features manifesting strong final state effects due
to electron correlation, charge transfer and collective excitations. These
results serve as one of the rare demonstrations of hybridization of Nd 4$f$
states with the conduction electrons possibly responsible for the exoticity of
this compound.",1909.10011v1
2019-09-26,Self-doped Mott insulator for parent compounds of nickelate superconductors,"We propose the parent compound of the newly discovered superconducting
nickelate Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ as a self-doped Mott insulator, in which
the low-density Nd-$5d$ conduction electrons couple to localized Ni-3$%
d_{x^{2}-y^{2}}$ electrons to form Kondo spin singlets at low temperatures.
This proposal is motivated with our analyses of the reported resistivity and
Hall coefficient data in the normal state, showing logarithmic temperature
dependence at low temperatures. In the strong Kondo coupling limit, we derive a
generalized $t$-$J$ model with both Kondo singlets and nickel holons moving
through the lattice of otherwise nickel spin-1/2 background. The
antiferromagnetic long-range order is therefore suppressed as observed in
experiments. With Sr-doping, the number of holons on the nickel sites
increases, giving rise to the superconductivity and a strange metal phase
analogous to those in superconducting copper oxides.",1909.11845v1
2019-09-27,Semi-classical electronic transport properties of ternary compound AlGaAs$_2$: Role of different scattering mechanisms,"We present a comprehensive investigation of semi-classical transport
properties of n-type ternary compound AlGaAs2, using Rode's iterative method.
Four scattering mechanisms, have been included in our transport calculation,
namely, ionized impurity, piezoelectric, acoustic deformation and polar optical
phonon (POP). The scattering rates have been calculated in terms of ab-initio
parameters. We consider AlGaAs2 to have two distinct crystal geometries, one in
tetragonal phase (space group: ), while the other one having body centered
tetragonal crystal structure (space group:). We have observed higher electron
mobility in the body centered tetragonal phase, thereby making it more suitable
for high mobility device application, over the tetragonal phase. In order to
understand the differences in electron moblities for these two phases,
curvatures of the E-k graph of the conduction bands for these phases have been
compared. At room temperature, the dominant contribution in electron mobility
was found to be provided by inelastic POP scattering. We have also noted that
mobility is underestimated in relaxation time approximation as compared with
the Rode's iterative approach.",1909.12523v1
2019-11-30,Microwave dynamics of pure and doped anisotropic S=1 chain antiferromagnet NiCl2-4SC(NH2)2,"We studied electron spin resonance in a quantum magnet NiCl2-4SC(NH2)2,
demonstrating a field-induced quantum phase transition from a
quantum-disordered phase to an antiferromagnet. We observe two branches of the
antiferromagnetic resonance of the ordered phase, one of them has a gap and the
other is a Goldstone mode with zero frequency at a magnetic field along the
four-fold axis. This zero frequency mode acquires a gap at a small tilting of
the magnetic field with respect to this direction. The upper gap was found to
be reduced in the doped compound Ni(Cl(1-x)Br(x))2-4SC(NH2)2 with $x=0.21$.
This reduction is unexpected because of the previously reported rise of the
main exchange constant in a doped compound. Further, a nonresonant diamagnetic
susceptibility $\chi^{\prime}$ was found for the ordered phase in a wide
frequency range above the quasi-Goldstone mode. This dynamic diamagnetism is as
large as the dynamic susceptibility of the paramagnetic resonance. We speculate
that it originates from a two-magnon absorption band of low-frequency
dispersive magnon branch.",1912.00172v1
2019-11-29,Self-Calibration for Massive MIMO with Channel Reciprocity and Channel Estimation Errors,"In time-division-duplexing (TDD) massive multiple-input multiple-output
(MIMO) systems, channel reciprocity is exploited to overcome the overwhelming
pilot training and the feedback overhead. However, in practical scenarios, the
imperfections in channel reciprocity, mainly caused by radio-frequency
mismatches among the antennas at the base station side, can significantly
degrade the system performance and might become a performance limiting factor.
In order to compensate for these imperfections, we present and investigate two
new calibration schemes for TDD-based massive multi-user MIMO systems, namely,
relative calibration and inverse calibration. In particular, the design of the
proposed inverse calibration takes into account a compound effect of channel
reciprocity error and channel estimation error. We further derive closed-form
expressions for the ergodic sum rate, assuming maximum ratio transmissions with
the compound effect of both errors. We demonstrate that the inverse calibration
scheme outperforms the traditional relative calibration scheme. The proposed
analytical results are also verified by simulated illustrations.",1912.01503v1
2019-12-07,Design and Characteristics of a Population Inversion X-ray Laser Oscillator,"Oscillators are at the heart of optical lasers, providing stable transform
limited pulses. In contrast, X-ray free electron lasers use self-amplified
spontaneous emission (SASE), resulting in large stochastic intensity and
spectral fluctuations. Amplified spontaneous emission (ASE) of the $K\alpha_1$
line has been recently observed for Ne gas, Cu compounds and Mn solutions at
the LCLS and SACLA X-ray free electron lasers (XFELs), using an X-ray SASE
pulse as a pump to create population inversion. Here we describe the physics
and realization of an X-ray laser oscillator (XLO) based on periodically
pumping a Cu compound gain medium in a tunable Bragg cavity with a SASE pulse
train, generating intense ($\sim$ 5 x 10$^{10}$ ph/pulse), fully coherent,
transform limited 8 keV pulses with 48 meV spectral resolution. We also discuss
extending these results to other elements to operate XLO from about 5 to 12
keV, improving X-ray-based research beyond current capabilities.",1912.03554v3
2019-12-11,Electronic and magnetic properties of new binary uranium-boron compounds with 2D and 3D boron networks: A revisit of the U:B system,"Based on crystal chemistry rationale and calculations within the density
functional theory DFT, the U:B system is complemented with additional binary
compounds UB3, U2B6, and UB6 possessing two-dimensional 2D and 3D boron
substructures. Observations are supported quantitatively with the trends of
cohesive energies, charge transfers onto the boron sub-lattice and geometry
optimized structures. The results point out to a structure crossover from
hexagonal (layer B network) to 3D boron network at compositions above UB3 found
to be connected with a threshold amount of charge onto boron which is ~0.46.
From the energy-volume of states EOS considering spin degenerate and
spin-polarized configurations, hexagonal UB3, and cubic UB6 were found in a
stable ferromagnetic ground state with 1.47 and 2.40Bohr Magnetons spin-only
moments. The volume variations of magnetization show respectively a smooth and
abrupt evolution for UB3 and UB6.",1912.05224v1
2019-12-15,Dirac Nodal Line and Rashba Splitting Surface States in Nonsymmorphic ZrGeTe,"Dirac semimetals (DSMs) are three dimensional analogue to graphene with
symmety enforced bulk Dirac nodes. Among various DSMs, ZrSiS has been
attracting more interests recently, due to its three dimensional Dirac nodal
line protected by the nonsymmorphic symmetry. It actually belongs to a large
family of isostructural compounds with unique quantum phenomenon. Here we
present a comprehensive study of the first principle calculation,
angle-resolved photoemission spectroscopy (ARPES) measurements, and scanning
tunneling microscope (STM) experiments on ZrGeTe, a member of the ZrSiS family
with stronger spin-orbit coupling (SOC). Our band structure calculation shows
the existence of floating gapless surface states at $\bar{X}$ with Rashba
splitted helical spin texture, which are confirmed by our ARPES measurements.
We also perform quasiparticle scattering interference (QPI) imaging and find
several q-vectors, with two Umklapp scattering vectors not observed in other
family compounds. All the q-vectors can be identified with joint density of
states (JDOS) simulation. Our results demonstrate the interesting electronic
structure of ZrGeTe and might benefit the potential application by utilizing
its exotic quantum states in the future.",1912.07002v1
2019-12-27,Spatial risk estimation in Tweedie compound Poisson double generalized linear models,"Tweedie exponential dispersion family constitutes a fairly rich sub-class of
the celebrated exponential family. In particular, a member, compound Poisson
gamma (CP-g) model has seen extensive use over the past decade for modeling
mixed response featuring exact zeros with a continuous response from a gamma
distribution. This paper proposes a framework to perform residual analysis on
CP-g double generalized linear models for spatial uncertainty quantification.
Approximations are introduced to proposed framework making the procedure
scalable, without compromise in accuracy of estimation and model complexity;
accompanied by sensitivity analysis to model mis-specification. Proposed
framework is applied to modeling spatial uncertainty in insurance loss costs
arising from automobile collision coverage. Scalability is demonstrated by
choosing sizable spatial reference domains comprised of groups of states within
the United States of America.",1912.12356v2
2020-02-07,Observation of flat bands due to band hybridization in 3d-electron heavy-fermion compound CaCu3Ru4O12,"We report angle-resolved photoemission spectroscopy and first-principles
numerical calculations for the band structure evolution of the 3d heavy-fermion
compound CaCu3Ru4O12. Below 200 K, we observed an emergent hybridization gap
between the Cu 3d electron-like band and the Ru 4d hole-like band and the
resulting flat band features near the Fermi energy centered around the
Brillouin zone corner. Our results confirm the non-Kondo nature of CaCu3Ru4O12,
in which the Cu 3dxy electrons are less correlated and not in the Kondo limit.
Comparison between theory and experiment also suggests that other mechanism
such as nonlocal interactions or spin fluctuations beyond the local dynamical
mean-field theory may be needed in order to give a quantitative explanation of
the peculiar properties in this material.",2002.02588v1
2020-02-08,Multi-Objective Molecule Generation using Interpretable Substructures,"Drug discovery aims to find novel compounds with specified chemical property
profiles. In terms of generative modeling, the goal is to learn to sample
molecules in the intersection of multiple property constraints. This task
becomes increasingly challenging when there are many property constraints. We
propose to offset this complexity by composing molecules from a vocabulary of
substructures that we call molecular rationales. These rationales are
identified from molecules as substructures that are likely responsible for each
property of interest. We then learn to expand rationales into a full molecule
using graph generative models. Our final generative model composes molecules as
mixtures of multiple rationale completions, and this mixture is fine-tuned to
preserve the properties of interest. We evaluate our model on various drug
design tasks and demonstrate significant improvements over state-of-the-art
baselines in terms of accuracy, diversity, and novelty of generated compounds.",2002.03244v3
2020-02-10,Structural and magneto-transport studies of iron intercalated Bi2Se3 single crystals,"A detailed investigation on the structural and magneto-transport properties
of iron intercalated Bi2Se3 single crystals have been presented. The x-ray
diffraction and Raman studies confirm the intercalation of Fe in the van der
Waals gaps between the layers. The electrical resistivity of the compounds
decreases upon intercalation, and Hall resistivity shows the enhancement of the
charge carriers upon intercalation. The magnetoresistance shows the
non-saturating linear behavior at higher magnetic field and low temperature.
Intercalation of Fe increases the onset of the linear magnetoresistance
behavior, indicating the reduction in quantum effects. The Kohler scaling
employed on the magnetoresistance data indicates single scattering process for
all these compounds in the measured temperature range of 3- 300 K.",2002.03609v2
2020-02-10,Lattice dynamics in the spin-1/2 frustrated kagome compound herbertsmithite,"We investigate the lattice dynamics in the spin-1/2 frustrated kagome
compound herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$ by a combination of infrared
spectroscopy measurements and ab initio density functional theory calculations,
and provide an unambiguous assignment of infrared-active lattice vibrations
involving in-plane and out-of-plane atom displacements in the kagome layers.
Upon cooling, non-thermal red-shifts and broadening appear specifically for
modes that deform the kagome layer or affect the Cu-O-Cu bond angles, thus
creating pronounced modifications of the antiferromagnetic exchange coupling.
Our results indicate the presence of a strong magnetoelastic coupling to the
spin system. We discuss the effects of this coupling and its relation to recent
experiments reporting a global symmetry reduction of the kagome lattice
symmetry.",2002.04042v1
2020-02-11,The role of delocalized chemical bonding in square-net-based topological semimetals,"Principles that predict reactions or properties of materials define the
discipline of chemistry. In this work we derive chemical rules, based on atomic
distances and chemical bond character, which predict topological materials in
compounds that feature the structural motif of a square-net. Using these rules
we identify over 300 potential new topological materials. We show that simple
chemical heuristics can be a powerful tool to characterize topological matter.
In contrast to previous database-driven materials categorization our approach
allows us to identify candidates that are alloys, solid-solutions, or compounds
with statistical vacancies. While previous material searches relied on density
functional theory, our approach is not limited by this method and could also be
used to discover magnetic and statistically-disordered topological semimetals.",2002.04611v1
2020-02-12,Intrinsic anomalous Hall effect in Ni-substituted magnetic Weyl semimetal Co3Sn2S2,"Topological materials have recently attracted considerable attention among
materials scientists as their properties are predicted to be protected against
perturbations such as lattice distortion and chemical substitution. However,
any experimental proof of such robustness is still lacking. In this study, we
experimentally demonstrate that the topological properties of the ferromagnetic
kagome compound Co3Sn2S2 are preserved upon Ni substitution. We systematically
vary the Ni content in Co3Sn2S2 single crystals and study their magnetic and
anomalous transport properties. For the intermediate Ni substitution, we
observe a remarkable increase in the coercive field while still maintaining
significant anomalous Hall conductivity. The large anomalous Hall conductivity
of these compounds is intrinsic, consistent with first-principle calculations,
which proves its topological origin. Our results can guide further studies on
the chemical tuning of topological materials for better understanding.",2002.05062v1
2020-02-24,Origin of pressure-induced insulator-to-metal transition in the van der Waals compound FePS3 from first-principles calculations,"Pressure-induced insulator-to-metal transition (IMT) has been studied in the
van der Waals compound iron thiophosphate (FePS3) using first-principles
calculations within the periodic linear combination of atomic orbitals method
with hybrid Hartree-Fock-DFT B3LYP functional. Our calculations reproduce
correctly the IMT at ~15 GPa, which is accompanied by a reduction of the unit
cell volume and of the vdW gap. We found from the detailed analysis of the
projected density of states that the 3p states of phosphorus atoms contribute
significantly at the bottom of the conduction band. As a result, the collapse
of the band gap occurs due to changes in the electronic structure of FePS3
induced by relative displacements of phosphorus or sulfur atoms along the
c-axis direction under pressure.",2002.10419v1
2020-02-25,"Symmetry protection and giant Fermi arcs from multifold fermions in binary, ternary, and quaternary compounds","Higher-fold chiral fermions that go beyond two-fold Weyl fermions have
recently been reported in crystalline systems. Here, we focus on such
excitations in several binary, ternary and quaternary alloys/compounds with
CoGe, BiSbPt and KMgBO3 as the representative examples that belong to the
crystal space group (SG) 198. We found distinct three-fold, four-fold and
six-fold chiral fermions in the bulk via Density Functional computations. We
provide general symmetry arguments for the protection of these degeneracies
with special emphasis on the four-fold fermions. Our surface spectra
simulations show that the size of Fermi arcs resulting from these chiral
fermions are large, robust and untouched from the bulk states due to the near
absence of trivial bulk Fermi pockets. All these features make these systems --
especially CoGe and KMgBO3 -- promising topological semimetal candidates to
realize higher-fold fermions in future photo-emission and transport
experiments.",2002.11145v2
2020-02-25,Tetragonal mixed system $Cs_2CuCl_{4-x}Br_x$ complemented by the tetragonal phase realisation of $Cs_2CuCl_4$,"Realisation of the tetragonal phase of $Cs_2CuCl_4$ is possible using
specific crystal growth conditions at a temperature below $281K$. This work
deals with the comparison of the magnetic susceptibility and the magnetization
of this new tetragonal compound with the magnetic behaviour of tetragonal
$Cs_2CuCl_{2.9}Br_{1.1}$, $Cs_2CuCl_{2.5}Br_{1.5}$, $Cs_2CuCl_{2.2}Br_{1.8}$
and presents consistent results for such quasi $2-D$ antiferromagnets.
Structural investigation at low temperature for $Cs_2CuCl_{2.2}Br_{1.8}$ shows
no phase transition. The structure remains in the tetragonal symmetry $I4/mmm$.
Furthermore, several magnetic reflections corresponding to the propagation
vector $k = (0, 0, 0)$ are observed for this tetragonal compound through
neutron diffraction experiments below the magnetic phase transition at $T_N =
11.3K$ confirming its antiferromagnetic nature.",2002.11202v1
2020-02-26,Spin-orbit-phonon interaction as an origin of helical-symmetry breaking spin-triplet superconducting state,"The excess increase of the local field distribution width $\Delta
H\equiv\sigma/\gamma_{\mu}$ (with $\gamma_{\mu}=135.5\,$MHz/T being the
gyromagnetic ratio of $\mu^{+}$), and/or the spontaneous magnetic field $H_{\rm
spon}$, have been reported in the superconducting state of a series of
compounds more than 10 by $\mu$SR (muon spin rotation or relaxation)
experiment. Sizes of these quantities are of the order of 1G on the whole. We
propose that the increase of the local field distribution $\Delta H$ in those
compounds, including ions with strong spin-orbit interaction of 5d electrons,
such as La in LaNiGa$_2$ or Re in Re$_6$Zr, is possible through the cooperation
of the spin-orbit coupling between the quasiparticles and ionic vibrations
(phonons) and the conventional quasiparticles-phonon coupling, inducing the
spin-triplet p-wave pairing with helical symmetry breaking superconducting
state with chiral super spin current around stopped $\mu^{+}$ site. The size of
$\Delta H$ is estimated as of the order of 1G, in consistent with experimental
observations.",2002.11344v1
2020-02-28,Mixed system $Cs_3Cu_3Cl_{8-x}Br_xOH$ with weakly connected Cu-triangles,"To study the relationship between the properties of low-dimensional spin
systems with weakly coupled Cu-triangles and their crystal structure, single
crystals of $Cs_3Cu_3Cl_8OH$ (1) and the new $Cs_3Cu_3Cl_{7.6}Br_{0.4}OH$ (2)
were grown. Both compounds are isostructural and crystallize in a monoclinic
structure with space group $P2_1/c$. The magnetic susceptibility of (1) shows a
maximum at $2.23 K$ and of (2) at $2.70 K$, which are attributed to
antiferromagnetic phase transitions. Furthermore, the magnetization along the
$b$-axis at $1.9 K$ for both compounds shows a spin-flop transition into a new
antiferromagnetic phase. This transition occurs at $0.61 T$ for (1) and at $2.0
T$ for (2). The antiferromagnetic order can be suppressed by a magnetic field
$B_{C1}= 1.1 T$ for (1) and $B_{C2}= 1.2 T$ for (2). First single crystal
neutron diffraction measured on (1) at different temperatures reveals the
magnetic signal on the top of the nuclear reflection at (-1 0 0). Its magnetic
ordering temperature was found to be at $T_{N1}= 2.12(3) K$.",2002.12720v1
2020-03-01,Magnetic Properties of an Effective Spin-$\frac{1}{2}$ Triangular-Lattice Compound LiYbS$_2$,"Here, we report the synthesis and magnetic properties of a Yb-based
triangular-lattice compound LiYbS$_2$. At low temperatures, it features an
effective spin-$\frac{1}{2}$ state due to the combined effect of crystal
electric field and spin orbit coupling. Magnetic susceptibility measurements
and $^7$Li nuclear magnetic resonance experiments reveal the absence of
magnetic long range ordering down to 2~K, which suggests a possible quantum
spin liquid ground state. A dominant antiferromagnetic nearest neighbour
exchange interaction $J/k_{\rm B}\simeq$ 5.3~K could be extracted form the
magnetic susceptibility. The NMR linewidth analysis yields the coupling
constant between the Li nuclei and Yb$^{3+}$ ions which was found to be purely
dipolar in nature.",2003.00566v1
2020-03-02,Short range order and topology of Ge$_{x}$Ga$_{x}$Te$_{100-2x}$ glasses,"Chemical short range order and topology of Ge$_{x}$Ga$_{x}$Te$_{100-2x}$
glasses was investigated by neutron- and x-ray diffraction as well as Ge and Ga
K-edge extended x-ray absorption fine structure (EXAFS) measurements. Large
scale structural models were obtained by fitting experimental datasets
simultaneously with the reverse Monte Carlo simulation technique. Models,
relying only on experimental data and basic physical information without
constraining the average coordination numbers, give 3.9 - 4.1 for the number of
the atoms in the first coordination sphere of Ge atoms, while the average
number of first neighbors of Ga atoms scatters around 3.8. The average
coordination number of Te atoms is significantly higher than 2 for $x$ = 12.5
and 14.3. It is found that the vast majority of MTe$_4$ (M=Ge or Ga) tetrahedra
have at least one corner sharing MTe$_4$ neighbor.",2003.00772v2
2020-03-04,Magnetism in Rb$_{x}$Sr$_{1-x}$C novel alloy,"We report a study on the electronic and magnetic properties of a novel
Rb$_{x}$Sr$_{1-x}$C alloy. We find that the variation of the lattice parameter
as function of Rb composition exhibits a deviation from the Vegard's law of
about 0.4 {\AA}. The total energy results predict a ferromagnetic ordering for
Sr-rich alloy, and antiferromagnetic ordering for RbC-rich alloy with a total
magnetic moment ranging from 2 to 3$\mu_\text{B}$ per cation. As for the parent
compounds, RbC and SrC, the origin of magnetism arises from the polarization of
the carbon $p$-orbitals. From the spin-polarized calculations, we note that the
half-metallicity in the Rb$_{x}$Sr$_{1-x}$C alloy is confirmed for $x<0.875$.
On the other hand, a direct band gap is observed in the semiconducting spin
part, in contrast to the pure parent compounds.",2003.02047v1
2020-03-05,Lifshitz Transition in Triangular Lattice Kondo-Heisenberg Model,"Motivated by recent experimental progress on triangular lattice heavy-fermion
compounds, we investigate possible Lifshitz transitions and the scanning tunnel
microscope (STM) spectra of the Kondo-Heisenberg model on the triangular
lattice. In the heavy Fermi liquid state, the introduced Heisenberg
antiferromagnetic interaction ($J_H$) results in the twice Lifshitz transition
at the case of the nearest-neighbour electron hopping but with
next-nearest-neighbour hole hopping and the case of the nearest-neighbour hole
hopping but with next-nearest-neighbour electron hopping, respectively. Driven
by $J_H$, the Lifshitz transitions on triangular lattice are all continuous in
contrast to the case in square lattice. Furthermore, the STM spectra shows rich
line-shape which is influenced by the Kondo coupling $J_{K}$, $J_{H}$ and the
ratio of the tunneling amplitude $t_{f}$ versus $t_{c}$. Our work provides a
possible scenario to understand the Fermi surface topology and the quantum
critical point in heavy-fermion compounds.",2003.02403v1
2020-03-09,A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Exotic Molecules and Radicals,"Aiming at completing the sets of FCI-quality transition energies that we
recently developed (\textit{J.~Chem.~Theory Comput.} \textbf{14} (2018)
4360--4379, \textit{ibid.}~\textbf{15} (2019) 1939--1956, and
\textit{ibid.}~\textbf{16} (2020) 1711--1741), we provide, in the present
contribution, ultra-accurate vertical excitation energies for a series of
""exotic"" closed-shell molecules containing F, Cl, P, and Si atoms and small
radicals, such as CON and its variants, that were not considered to date in
such investigations. This represents a total of 81 high-quality transitions
obtained with a series of diffuse-containing basis sets of various sizes. For
the exotic compounds, these transitions are used to perform benchmarks with a
vast array of lower-level models, $\textit{i.e.}$ CIS(D), EOM-MP2,
(SOS/SCS)-CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, (SOS-)ADC(2), and ADC(3).
Additional comparisons are made with literature data. For the open-shell
compounds, we have compared the performances of both the unrestricted and
restricted open-shell CCSD and CC3 formalisms.",2003.04183v1
2020-03-06,Free Radical Scavenging and Cytotoxic Activities of Substituted Pyrimidines,"A library of substituted pyrimidines was synthesized and evaluated for free
radical scavenging, and in vitro cytotoxic activity in 3T3 cells. All compounds
showed good free radical scavenging activity with IC50 values in the range of
42.9 + 0.31 to 438.3 3.3 {\mu}M as compared to the standard butylated
hydroxytoluene having IC50 value of 128.83 2. 1 {\mu}M. The structure
activity-relationship was also established. Selected analogues 1, 2, 3, 5, 6,
7, 8, 9, 10, 12, 13, 15, 19, 20, 21, 24, 25, 26 and 28 were tested for
cytotoxicity in mouse fibroblast 3T3 cell line using MTT assay, and most of the
analogues showed cytotoxicity. This study has identified a number of cytotoxic
novel substituted pyrimidines having free radical scavenging activities that
can be used as inhibitory compounds for those cancer cells whose growth is
mediated by reactive oxygen species.",2003.04536v1
2020-03-15,Dynamics of tritrophic interaction with volatile compounds in plants,"In this paper we will consider a mathematical model that describes, the
tritrophic interaction between plants, herbivores and their natural enemies,
where volatiles organic compounds (VOCs) released by plants play an important
role. We show positivity and boundedness of the system solutions, existence of
positive equilibrium and its local stability, we analyse global stability of
positive equilibrium via the geometrical approach of Li and Muldowney. We pay
attention to parameters in order to discuss different types of bifurcations.
Finally, we present some numerical simulations to justify our analytical
results.",2003.07941v3
2020-03-20,Quantum Fluctuations in the Non-Fermi Liquid System CeCo$_{2}$Ga$_{8}$ Investigated Using $μ$SR,"Reduced dimensionality offers a crucial information in deciding the type of
the quantum ground state in heavy fermion materials. Here we have examined
stoichiometric CeCo$_{2}$Ga$_{8}$ compound, which crystallizes in a
quasi-one-dimensional crystal structure with Ga-Ce-Co chains along the
$c$-axis. The low-temperature behavior of magnetic susceptibility
($\chi\sim-\ln T$), heat capacity ($C_p/T\sim-\ln T$), and resistivity
($\rho\sim T^{n}$) firmly confirm the non-Fermi liquid ground state of
CeCo$_{2}$Ga$_{8}$. We studied the low-energy spin dynamics of
CeCo$_{2}$Ga$_{8}$ compound utilizing zero field (ZF-) and longitudinal field
(LF-) muon spin relaxation ($\mu$SR) measurements. ZF-$\mu$SR measurement
reveals the absence of long-range magnetic ordering down to 70 mK, and
interestingly below 1 K, the electronic relaxation rate sharply rises,
intimating the appearance of low energy quantum spin fluctuations in
CeCo$_{2}$Ga$_{8}$.",2003.09104v1
2020-03-20,Theoretical investigation of superconductivity in trilayer square-planar nickelates,"The discovery of superconductivity in Sr-doped NdNiO$_{2}$ is a crucial
breakthrough in the long pursuit for nickel oxide materials with electronic and
magnetic properties similar to those of the cuprates. NdNiO$_2$ is the
infinite-layer member of a family of square-planar nickelates with general
chemical formula R$_{n+1}$Ni$_n$O$_{2n+2}$ (R = La, Pr, Nd, $n= 2, 3, ...
\infty$). In this letter, we investigate superconductivity in the trilayer
member of this series (R$_4$Ni$_3$O$_8$) using a combination of
first-principles and $t-J$ model calculations. R$_4$Ni$_3$O$_8$ compounds
resemble cuprates more than RNiO$_2$ materials in that only
Ni-$d_{x^{2}-y^{2}}$ bands cross the Fermi level, they exhibit a largely
reduced charge transfer energy, and as a consequence superexchange interactions
are significantly enhanced. We find that the superconducting instability in
doped R$_4$Ni$_3$O$_8$ compounds is considerably stronger with a maximum gap
about four times larger than that in Sr$_{0.2}$Nd$_{0.8}$NiO$_2$.",2003.09132v1
2020-03-22,Theoretical Study of Ternary CoSP Semiconductor: a Candidate for Photovoltaic Applications,"The electronic structure of pyrite-type cobalt phosphosulfide (CoSP) has been
studied using density-functional theory. The calculated band structure reveals
the non-magnetic semiconducting character of the compound. The electronic
structure is described through the electronic band structure and the densities
of states. A band gap of 1.14 eV has been computed within standard GGA, a value
which is enhanced using hybrid functional. It separates the upper part of the
valence band dominated by Co-3d-t2g states from the lower part of the
conduction band made exclusively of Co-3d-eg , above of which lie S-3p and P-3p
ones. The obtained values are suitable for applications in solar cells,
according to Shockley-Queisser theory of light to electric conversion
efficiency. The origin of the larger CoSP band gap, with respect to the one of
the promising FeS2 compound, is explained and the chemical bonding properties
are addressed. A comparative picture is established where several similarities
have been found, suggesting that CoSP could be for a great practical interest
in photovoltaics.",2003.09864v1
2020-03-24,In Silico Investigations on the Potential Inhibitors for COVID-19 Protease,"A novel strain of coronavirus, namely, COVID-19 has been identified in Wuhan
city of China in December 2019. There are no specific therapies available and
investigations regarding the treatment of the COVID-19 are still lacking. This
prompted us to perform a preliminary in silico study on the COVID-19 protease
with anti-malarial compounds in the search of potential inhibitor. We have
calculated log P and log S values in addition to molecular docking and PASS
predictions. Among the seven studied compounds, mepacrine appears as the
potential inhibitor of the COVID-19 followed by chloroquine, hydroxychloroquine
and phomarin. Therefore, these anti-malarial drugs may be potential drug
candidate for the treatment of this novel coronavirus. A detailed analysis on
these inhibitors is currently in progress and clinical studies are invited to
investigate their potential medicinal use for the COVID-19.",2003.10642v2
2020-03-25,Dualism of the 4f electrons and high-temperature antiferromagnetism of the heavy-fermion compound YbCoC$_{2}$,"We report on the first study of the noncentrosymmetric ternary carbide
YbCoC$_{2}$. Our magnetization, specific heat, resistivity and neutron
diffraction measurements consistently show that the system behaves as a
heavy-fermion compound, displaying an amplitude-modulated magnetic structure
below the N\'eel temperature reaching $T_{N}$ = 33 K under pressure. Such a
large value, being the highest among the Yb-based systems, is explained in the
light of our ab initio calculations, which show that the 4f electronic states
of Yb have a dual nature -- i.e., due to their strong hybridization with the 3d
states of Co, 4f states expose both localized and itinerant properties.",2003.11601v1
2020-03-30,Tunable interlayer magnetism and band topology in van der Waals heterostructures of MnBi2Te4-family materials,"Manipulating the interlayer magnetic coupling in van der Waals magnetic
materials and heterostructures is the key to tailoring their magnetic and
electronic properties for various electronic applications and fundamental
studies in condensed matter physics. By utilizing the MnBi2Te4-family compounds
and their heterostructures as a model system, we systematically studied the
dependence of the sign and strength of interlayer magnetic coupling on
constituent elements by using first-principles calculations. It was found that
the coupling is a long-range superexchange interaction mediated by the chains
of p orbitals between the magnetic atoms of neighboring septuple-layers. The
interlayer exchange is always antiferromagnetic in the pure compounds, but can
be tuned to ferromagnetic in some combinations of heterostructures, dictated by
d orbital occupations. Strong interlayer magnetic coupling can be realized if
the medial p electrons are delocalized and the d bands of magnetic atoms are
near the Fermi level. The knowledge on the interlayer coupling mechanism
enables us to engineer magnetic and topological properties of MnBi2Te4-family
materials as well as many other insulating van der Waals magnetic materials and
heterostructures.",2003.13485v1
2020-05-31,Thousands of reactants and transition states for competing E2 and S$_\text{N}$2 reactions,"Reaction barriers are a crucial ingredient for first principles based
computational retro-synthesis efforts as well as for comprehensive reactivity
assessments throughout chemical compound space. While extensive databases of
experimental results exist, modern quantum machine learning applications
require atomistic details which can only be obtained from quantum chemistry
protocols. For competing E2 and S$_\text{N}$2 reaction channels we report 4'466
transition state and 143'200 reactant complex geometries and energies at
respective MP2/6-311G(d) and single point DF-LCCSD/cc-pVTZ level of theory
covering the chemical compound space spanned by the substituents NO$_2$, CN,
CH$_3$, and NH$_2$ and early halogens (F, Cl, Br) as nucleophiles and leaving
groups. Reactants are chosen such that the activation energy of the competing
E2 and S$_\text{N}$2 reactions are of comparable magnitude. The correct
concerted motion for each of the one-step reactions has been validated for all
transition states. We demonstrate how quantum machine learning models can
support data set extension, and discuss the distribution of key internal
coordinates of the transition states.",2006.00504v1
2020-06-02,"Spin-Coupling Topology in the Copper Hexamer Compounds A$_2$Cu$_3$O(SO$_4$)$_3$ (A=Na, K)","The compounds A$_2$Cu$_3$O(SO$_4$)$_3$ (A=Na, K) are characterized by copper
hexamers which are weakly coupled to realize antiferromagnetic order below TN=3
K. They constitute novel quantum spin systems with S=1 triplet ground-states.
We investigated the energy-level splittings of the copper hexamers by inelastic
neutron scattering experiments covering the entire range of the magnetic
excitation spectra. The observed transitions are governed by very unusual
selection rules which we ascribe to the underlying spin-coupling topology. This
is rationalized by model calculations which allow an unambiguous interpretation
of the magnetic excitations concerning both the peak assignments and the nature
of the spin-coupling parameters.",2006.01593v1
2020-06-12,A benchmark study on reliable molecular supervised learning via Bayesian learning,"Virtual screening aims to find desirable compounds from chemical library by
using computational methods. For this purpose with machine learning, model
outputs that can be interpreted as predictive probability will be beneficial,
in that a high prediction score corresponds to high probability of correctness.
In this work, we present a study on the prediction performance and reliability
of graph neural networks trained with the recently proposed Bayesian learning
algorithms. Our work shows that Bayesian learning algorithms allow
well-calibrated predictions for various GNN architectures and classification
tasks. Also, we show the implications of reliable predictions on virtual
screening, where Bayesian learning may lead to higher success in finding hit
compounds.",2006.07021v2
2020-06-14,Equilibrium of Blockchain Miners with Dynamic Asset Allocation,"We model and analyze blockchain miners who seek to maximize the compound
return of their mining businesses. The analysis of the optimal strategies finds
a new equilibrium point among the miners and the mining pools, which predicts
the market share of each miner or mining pool. The cost of mining determines
the share of each miner or mining pool at equilibrium. We conclude that neither
miners nor mining pools who seek to maximize their compound return will have a
financial incentive to occupy more than 50% of the hash rate if the cost of
mining is at the same level for all. However, if there is an outstandingly
cost-efficient miner, then the market share of this miner may exceed 50% in the
equilibrium, which can threaten the viability of the entire ecosystem.",2006.08016v2
2020-06-22,Essential electronic properties on stage-1 Li/Li+-graphite-intercalation compounds for different concentrations,"We use first-principles calculation within the density functional theory
(DFT) to explore the electronic properties on stage-1 Li- and
Li+-graphite-intercalation compounds (GIC) for different concentrations,
LiCx/Li+Cx with x= 6,12,18,24,32 and 36. The essential properties, e.g.
geometric structures, band structures and spatial charge distributions are
determined by the hybridization of orbitals, the main focus of our works. The
band structures/density of states/spatial charge distribution display that the
Li-GIC possesses blue shift of fermi energy and just like metals, but the
Li+-GIC still preserves as original graphite or so-call semimetal possessing
the same densities of free electrons and holes. According to these properties,
we find that there exists weak but significant van der Waals interactions
between interlayer of graphite, and 2s-2pz hybridization between Li and C.
There scarcely exists strong interactions between Li+-C. The dominant
interaction between the Li and C is 2s-2pz orbital-orbital couple; the
orbital-orbital couple is not significant in Li+ and C case but the
dipole-diploe couple.",2006.12055v2
2020-06-22,Magnetic structure and exchange interactions in the layered semiconductor CrPS4,"Compounds with two-dimensional (2D) layers of magnetic ions weakly connected
by van der Waals bonding offer routes to enhance quantum behavior, stimulating
both fundamental and applied interest. CrPS4 is one such magnetic van der Waals
material, however, it has undergone only limited investigation. Here we present
a comprehensive series of neutron scattering measurements to determine the
magnetic structure and exchange interactions. The observed magnetic excitations
allow a high degree of constraint on the model parameters not normally
associated with measurements on a powder sample. The results demonstrate the 2D
nature of the magnetic interactions, while also revealing the importance of
interactions along 1D chains within the layers. The subtle role of competing
interactions is observed, which manifest in a non-trivial magnetic transition
and a tunable magnetic structure in a small applied magnetic field through a
spin-flop transition. Our results on the bulk compound provide insights that
can be applied to an understanding of the behavior of reduced layer CrPS4.",2006.12539v1
2020-06-23,A superconducting praseodymium nickelate with infinite layer structure,"A variety of nickel oxide compounds have long been studied for their
manifestation of various correlated electron phenomena. Recently,
superconductivity was observed in nanoscale infinite layer nickelate thin films
of Nd$_{0.8}$Sr$_{0.2}$NiO$_2$, epitaxially stabilized on SrTiO$_3$ substrates
via topotactic reduction from the perovskite precursor phase. Here we present
the synthesis and properties of PrNiO$_2$ thin films on SrTiO$_3$. Upon doping
in Pr$_{0.8}$Sr$_{0.2}$NiO$_2$, we observe superconductivity with a transition
temperature of 7-12 K, and robust critical current density at 2 K of 334
kA/cm$^2$. These findings indicate that superconductivity in the infinite layer
nickelates is relatively insensitive to the details of the rare earth 4$f$
configuration. Furthermore, they motivate the exploration of a broader family
of compounds based on two-dimensional NiO$_2$ planes, which will enable
systematic investigation of the superconducting and normal state properties and
their underlying mechanisms.",2006.13369v1
2020-06-24,Localization of 5f-electrons and pressure effects on magnetism in U intermetallics in the light of spin-fluctuation theory,"UCoGa and URhGa, two isostructural compounds show opposite signs of the
initial response of Curie temperature to applied hydrostatic premenssure. To
determine the physical origin of this contradiction the magnetization data
measured with respect to temperature, magnetic field and hydrostatic pressure
were analyzed in the framework of the Takahashi's spin-fluctuation theory. The
parameters T0 and TA characterizing the distribution widths of the
spin-fluctuation spectrum in the energy and wave vector space, respectively,
and TC/T0, the degree of the 5f-electron localization have been determined.
Examination of available experimental data for the other UTX (T = a transition
metal, X = Al, Ga) ferromagnets having the ZrNiAl-type structure revealed some
correlations between the degree of the 5f-electron localization represented by
the spin-fluctuation parameters and the response of Curie-temperature on the
applied pressure. These observations may be applied more generally to describe
the localization and magnetic behaviors of the majority of the uranium
ferromagnetic compounds.",2006.13683v2
2020-06-11,Bi-Level Graph Neural Networks for Drug-Drug Interaction Prediction,"We introduce Bi-GNN for modeling biological link prediction tasks such as
drug-drug interaction (DDI) and protein-protein interaction (PPI). Taking
drug-drug interaction as an example, existing methods using machine learning
either only utilize the link structure between drugs without using the graph
representation of each drug molecule, or only leverage the individual drug
compound structures without using graph structure for the higher-level DDI
graph. The key idea of our method is to fundamentally view the data as a
bi-level graph, where the highest level graph represents the interaction
between biological entities (interaction graph), and each biological entity
itself is further expanded to its intrinsic graph representation
(representation graphs), where the graph is either flat like a drug compound or
hierarchical like a protein with amino acid level graph, secondary structure,
tertiary structure, etc. Our model not only allows the usage of information
from both the high-level interaction graph and the low-level representation
graphs, but also offers a baseline for future research opportunities to address
the bi-level nature of the data.",2006.14002v1
2020-06-30,Near-field cavity optomechanical coupling in a compound semiconductor nanowire,"A III-V compound semiconductor nanowire is an attractive material for a novel
hybrid quantum interface that interconnects photons, electrons, and phonons
through a wavelength-tunable quantum structure embedded in its free-standing
structure. In such a nanomechanical element, however, a challenge is how to
detect and manipulate a small number of phonons via its tiny mechanical motion.
A solution would be to couple an optical cavity to a nanowire by introducing
the ``cavity optomechanics'' framework, but the typical size difference between
them becomes a barrier to achieving this. Here, we demonstrate near-field
coupling of a silica microsphere cavity and an epitaxially grown InP/InAs
free-standing nanowire. The evanescent optomechanical coupling enables not only
fine probing of the mechanical motion by balanced homodyne interferometry but
also tuning of the resonance frequency, linewidth, Duffing nonlinearity, and
vibration axis in the nanowire. Combining this cavity optomechanics with
epitaxial nanowire engineering opens the way to novel quantum metrology and
information processing.",2006.16538v1
2020-07-01,Hydration free energies from kernel-based machine learning: Compound-database bias,"We consider the prediction of a basic thermodynamic property---hydration free
energies---across a large subset of the chemical space of small organic
molecules. Our in silico study is based on computer simulations at the
atomistic level with implicit solvent. We report on a kernel-based machine
learning approach that is inspired by recent work in learning electronic
properties, but differs in key aspects: The representation is averaged over
several conformers to account for the statistical ensemble. We also include an
atomic-decomposition ansatz, which we show offers significant added
transferability compared to molecular learning. Finally, we explore the
existence of severe biases from databases of experimental compounds. By
performing a combination of dimensionality reduction and cross-learning models,
we show that the rate of learning depends significantly on the breadth and
variety of the training dataset. Our study highlights the dangers of fitting
machine-learning models to databases of narrow chemical range.",2007.00407v1
2020-07-01,Colossal Seebeck coefficient in Aurivillius Phase-Perovskite Oxide Composite,"We propose an inexpensive scalable approach for achieving extremely high
values of Seebeck coefficient ($\alpha$) by exploiting the natural superlattice
structure in Aurivillius phase oxides. In particular, we report an $\alpha
\approx $ 319\,mV/K at 300\,K in a composite of Aurivillius phase compound
SrBi$_4$Ti$_4$O$_{15}$ (as a matrix) and a perovskite phase material (e.g.,
La$_{0.7}$Sr$_{0.3}$MnO$_3$ or, La$_{0.7}$Sr$_{0.3}$CoO$_3$ as filler). Such a
colossal value of $\alpha$ can be attributed to contributions from the enhanced
density of states due to the effective low dimensional character of Bi$_2$O$_2$
layer. The corresponding thermal conductivity ($\kappa$) and the electrical
conductivity ($\sigma$) lies in the range 0.7 - 1.25 W/m-K and 10 - 100
$\mu$S/m, respectively at 300\,K. Attributed to the high $\alpha$ values, such
oxide composites can be used as thermopile sensors and highly sensitive
bolometric applications. We anticipate that the demonstration of colossal
$\alpha$ in oxide composites using a simple synthesis strategy also sets the
stage for future material innovations for high temperature thermoelectric
applications.",2007.00632v2
2020-07-04,Putative quantum critical point in the itinerant magnet ZrFe$_4$Si$_2$ with a frustrated quasi-one-dimensional structure,"The Fe sublattice in the compound ZrFe$_4$Si$_2$ features geometrical
frustration and quasi-one-dimensionality. We therefore investigated the
magnetic behavior in ZrFe$_4$Si$_2$ and its evolution upon substituting Ge for
Si and under the application of hydrostatic pressure using structural,
magnetic, thermodynamic, and electrical-transport probes. Magnetic measurements
reveal that ZrFe$_4$Si$_2$ holds paramagnetic Fe moments with an effective
moment $\mu_{\rm eff}= 2.18~\mu_{B}$. At low temperatures the compound shows a
weak short-range magnetic order below 6 K. Our studies demonstrate that
substituting Ge for Si increases the unit-cell volume and stabilizes the
short-range order into a long-range spin-density wave type magnetic order. On
the other hand, hydrostatic pressure studies using electrical-resistivity
measurements on ZrFe$_4$(Si$_{0.88}$Ge$_{0.12}$)$_2$ indicate a continuous
suppression of the magnetic ordering upon increasing pressure. Therefore, our
combined chemical substitution and hydrostatic pressure studies suggest the
existence of a lattice-volume-controlled quantum critical point in
ZrFe$_4$Si$_2$.",2007.02129v2
2020-07-07,Investigation of in-plane anisotropy of c-axis magnetoresistance for BiCh2-based layered superconductor NdO0.7F0.3BiS2,"We have investigated the in-plane anisotropy of the c-axis magnetoresistance
(MR) in both superconducting and normal states of single crystals of
NdO0.7F0.3BiS2 under in-plane magnetic fields. In the superconducting states of
NdO0.7F0.3BiS2, four-fold-symmetric in-plane anisotropy of the c-axis MR was
observed below the superconducting transition temperature. Since the crystal
structure of NdO0.7F0.3BiS2 is tetragonal, the rotational symmetry in the
superconducting state is preserved in the present compound. This result is
clearly different from the previous report observed in LaO0.5F0.5BiSSe single
crystals, where the in-plane MR in the superconducting state shows two-fold
symmetry. On the other hand, in the normal states of NdO0.7F0.3BiS2, two-fold
symmetric MR with a small amplitude was observed. The possible origin of the
two-fold-symmetric behavior was discussed with the presence of local structural
disorder in the conducting plane of BiCh2-based compounds.",2007.03235v1
2020-07-06,"GPU-Accelerated Drug Discovery with Docking on the Summit Supercomputer: Porting, Optimization, and Application to COVID-19 Research","Protein-ligand docking is an in silico tool used to screen potential drug
compounds for their ability to bind to a given protein receptor within a
drug-discovery campaign. Experimental drug screening is expensive and time
consuming, and it is desirable to carry out large scale docking calculations in
a high-throughput manner to narrow the experimental search space. Few of the
existing computational docking tools were designed with high performance
computing in mind. Therefore, optimizations to maximize use of high-performance
computational resources available at leadership-class computing facilities
enables these facilities to be leveraged for drug discovery. Here we present
the porting, optimization, and validation of the AutoDock-GPU program for the
Summit supercomputer, and its application to initial compound screening efforts
to target proteins of the SARS-CoV-2 virus responsible for the current COVID-19
pandemic.",2007.03678v1
2020-07-08,Anisotropic properties of monolayer 2D materials: an overview from the C2DB database,"We analyze the occurrence of in-plane anisotropy in the electronic, magnetic,
elastic and transport properties of more than one thousand 2D materials from
the C2DB database. We identify hundreds of anisotropic materials and classify
them according to their point group symmetry and degree of anisotropy. A
statistical analysis reveals that a lower point group symmetry and a larger
amount of different elements in the structure favour all types of anisotropies,
which could be relevant for future materials design approaches. Besides, we
identify novel compounds, predicted to be easily exfoliable from a parent bulk
compound, with anisotropies that largely outscore those of already known 2D
materials. Our findings provide a comprehensive reference for future studies of
anisotropic response in atomically-thin crystals and point to new previously
unexplored materials for the next generation of anisotropic 2D devices.",2007.04152v2
2020-07-10,Versatile Physical Properties of a Novel Two-Dimensional Materials Composed of Group IV-V Elements,"Owing to the fascinating physical characteristics of two-dimensional (2D)
materials and their heterostructure, much effort has been devoted to exploring
their basic physical properties as well as discovering other novel 2D
materials. Herein, based on first-principles calculations, we propose novel 2D
material groups with the form A$_2$B$_2$, composed of group IV (A = C, Si, Ge,
or Sn) and V (B = N, P, As, Sb, or Bi) elements; the group forms two stable
phases with the $P\bar{6}m2$ ($\mathcal{M}$ phase) and $P\bar{3}m1$
($\mathcal{I}$ phase) crystal symmetries. We found that a total of 40 different
freestanding A$_2$B$_2$ compounds were dynamically stable and displayed
versatile physical properties, such as insulating, semiconducting, or metallic
properties, depending on their elemental compositions. Our calculation results
further revealed that the newly proposed 2D materials expressed high electrical
and thermal transport properties. Additionally, some of the compounds that
contained heavy elements exhibited non-trivial topological properties due to
strong spin-orbit interactions.",2007.05137v1
2020-07-14,In-plane p-wave coherence length in iron-based superconductors,"High-temperature superconductivity in iron-based layered compounds discovered
by Hosono group (Kamihara et al 2006 J. Am. Chem. Soc. 128 10012) is
fascinating physical phenomenon which still has many unanswered questions. One
of these questions is the superconducting gap symmetry in iron-based
superconductors (IBS), for which the most agreed concept is multiple-band
$s$-wave symmetry. Recently, an alternative concept of single-band $p$-wave
symmetry has been proposed. To disprove/reaffirm the latter concept, in this
paper we analyse temperature dependent in-plane coherence length in FeSe,
FeSe1-xTex, Ba(Fe1-x(Co,Ni)x)2As2 and Ca10(Pt4As8)((Fe,Pt)2As2)5 in order to
extract the gap-to-critical-temperature ratio, 2$\Delta$(0)/$k$$_B$$T$$_c$, and
the specific-heat-jump ratio, $\Delta$C/C,in these compounds. In the result, we
report that deduced ratios are in a good agreement with the concept of
single-band $p$-wave superconductivity in these materials.",2007.07110v1
2020-07-14,High pressure crystal structures of orthovanadates and their properties,"Pressure-induced phase transitions in orthovanadates have led to interesting
physical phenomena. The observed transitions usually involve large volume
collapses and drastic changes in the electronic and vibrational properties of
the materials. In some cases, the phase transitions implicate coordination
changes in vanadium, which has important consequences in the physical
properties of vanadates. In this Perspective, we explore the current knowledge
of the behavior of MVO4 vanadates under compression. In particular, we
summarize studies of the structural, vibrational, and electronic properties and
a few illustrative examples of high-pressure research in the compounds of
interest are discussed. A systematic understanding of the high-pressure
behavior of MVO4 compounds is presented, putting the emphasis on results that
could be relevant for practical applications. Recent advances and future
challenges in the study of orthovanadates under extreme pressure will be
reviewed, along with conclusions that could have consequences for the studies
of related oxides. Some ideas on topics that may lead to exciting breakthroughs
in the near future will be presented too.",2007.07146v1
2020-07-16,A characterization of equivalent martingale probability measures in a mixed renewal risk model with applications in Risk Theory,"If a given aggregate process $S$ is a compound mixed renewal process under a
probability measure $P$, we provide a characterization of all probability
measures $Q$ on the domain of $P$ such that $Q$ and $P$ are progressively
equivalent and $S$ is converted into a compound mixed Poisson process under
$Q$. This result extends earlier works of Delbaen & Haezendonck [2], Embrechts
& Meister [5], Lyberopoulos & Macheras [11], and of the authors [14].
Implications to the ruin problem and to the computation of premium calculation
principles in an insurance market possessing the property of no free lunch with
vanishing risk are also discussed.",2007.09051v1
2020-07-26,High-Tc state of Lanthanum hydrides,"The high critical temperature phase of lanthanum hydrides deserves special
attention because this phase displays the highest observed critical
temperature. We focus on the evaluation of the critical temperature, isotope
coefficient, and their pressure dependence of this phase (Fm3m phase of the
LaH10 compound). By combining the method of two coupling constants, describing
the interaction with the optical and acoustic modes, and two characteristic
frequencies with first-principle calculations we are able to analyze the role
of the light hydrogen in the amplitude of the critical temperature in this
unique compound. Specifically, the critical temperature of 254 K and the
isotope coefficient of 0.45 are evaluated at high pressure, and the results are
in good agreement with the experimental data. The peculiar decrease in the
value of the critical temperature upon further increase in pressure is
explained by the presence of a flat region on the Fermi surface and the
appearance of a two-gap structure, which should be experimentally observable by
tunneling spectroscopy.",2007.13043v1
2020-07-29,Antiviral Drug-Membrane Permeability: the Viral Envelope and Cellular Organelles,"To shorten the time required to find effective new drugs, like antivirals, a
key parameter to consider is membrane permeability, as a compound intended for
an intracellular target with poor permeability will have low efficacy. Here, we
present a computational model that considers both drug characteristics and
membrane properties for the rapid assessment of drugs permeability through the
coronavirus envelope and various cellular membranes. We analyze 79 drugs that
are considered as potential candidates for the treatment of SARS-CoV-2 and
determine their time of permeation in different organelle membranes grouped by
viral baits and mammalian processes. The computational results are correlated
with experimental data, present in the literature, on bioavailability of the
drugs, showing a negative correlation between fast permeation and most
promising drugs. This model represents an important tool capable of evaluating
how permeability affects the ability of compounds to reach both intended and
unintended intracellular targets in an accurate and rapid way. The method is
general and flexible and can be employed for a variety of molecules, from small
drugs to nanoparticles, as well to a variety of biological membranes.",2007.14965v1
2020-07-30,Three-site transition-metal clusters: going from localized electrons to molecular orbitals,"A recently synthesised series of isostructural compounds
Ba$_4$NbTM$_3$O$_{12}$ (TM = Mn, Rh and Ir) with transition-metal trimers in a
face-sharing geometry makes it possible to examine a tendency to the molecular
orbitals (MO) formation going from $3d$ to $5d$ transition metal ions. Our $ab$
$initio$ calculations of electronic and magnetic properties describe the
experimental findings and demonstrate gradual transition from the picture of
localized electrons for Mn to the MO picture for Rh and especially for Ir. We
also show that the often used criterion, according to which the metal-metal
distance in a compound shorter than in a respective metal always gives MO, may
break down in some cases.",2007.15230v1
2020-07-30,Endogenous and microbial volatile organic compounds in cutaneous health and disease,"Human skin is a region of high metabolic activity where a rich variety of
biomarkers are secreted from the stratum corneum. The skin is a constant source
of volatile organic compounds (VOCs) derived from skin glands and resident
microbiota. Skin VOCs contain the footprints of cellular activities and thus
offer unique insights into the intricate processes of cutaneous physiology.
This review examines the growing body of research on skin VOC markers as they
relate to skin physiology, whereby variations in skin-intrinsic and microbial
metabolic processes give rise to unique volatile profiles. Emerging evidence
for volatile biomarkers linked to skin perturbations and skin cancer are
examined. Microbial-derived VOCs are also investigated as prospective
diagnostic markers, and their potential to shape the composition of the local
skin microbiota, and consequently cutaneous health, is considered. Finally, a
brief outlook on emerging analytical challenges and opportunities for skin
VOC-based research and diagnostics is presented.",2007.15507v2
2020-09-04,Geometric and Electronic Properties of Li$_2$GeO$_3$,"The 3D ternary Li$_2$GeO$_3$ compound, which could serve as the electrolyte
material in Li+-based batteries, exhibits an unusual lattice symmetry
(orthorhombic crystal), band structure, charge density distribution and density
of states. The essential properties are fully explored through the
first-principles method. In the delicate calculations and analyses, the main
features of atom-dominated electronic energy spectrum, space-charge
distribution, and atom-/orbital-projected density of states are suffi$cient to
identify the critical multi-orbital hybridizations of the chemical bonds:
2s-(2p$_x, 2p$_y$, 2p$_z$) and (4s, 4p$_x$, 4p$_y$, 4p$_z$)-(2s, 2p$_x$,
2p$_y$, 2p$_z$), respectively, for Li-O and Ge-O. This system possesses a large
indirect gap of Eg = 3.77 eV. There exist a lot of significant covalent bonds,
with an obvious non-uniformity and anisotropy. In addition, spin-dependent
magnetic configurations are completely absent. The theoretical framework could
be developed to investigate the important features of anode and cathode
materials related to lithium oxide compounds.",2009.02154v1
2020-09-10,Exceptional compound plasmon-polariton waves,"Ordinarily, a trimaterial structure comprising a sufficiently thin metal film
interposed between two homogeneous dielectric materials guides compound
plasmon-polariton (CPP) waves, for which the fields on both sides of the metal
film decay exponentially with distance from the nearest metal/dielectric
interface. However, if one of the dielectric materials is anisotropic then the
trimaterial structure can guide an exceptional CPP wave for a particular
propagation direction. On the side of the metal film occupied by the
anisotropic dielectric material, the fields of the exceptional CPP wave decay
as the product of a linear function and an exponential function of the distance
from the nearest metal/dielectric interface. The canonical boundary-value
problem for CPP-wave propagation has been analyzed and solved numerically;
thereby, the spatial field profiles for exceptional CPP waves for a
uniaxial-dielectric/metal/isotropic-dielectric structure have been established.",2009.04717v1
2020-09-11,The K-theory of (compound) Du Val singularities,"This thesis gives a complete description of the Grothendieck group and
divisor class group for large families of two and three dimensional
singularities. The main results presented throughout, and summarised in Theorem
8.1.1, give an explicit description of the Grothendieck group and class group
of Kleinian singularities, their deformations, and compound Du Val (cDV)
singularities in a variety of settings. For such rings R, the main results
assert that there exists an isomorphism between $G_0(R)$ and $\mathbb{Z} \oplus
\mathrm{Cl}(R)$, and the class group is explicitly presented.
  More precisely, we establish these results for 2-dimensional deformations of
global type A Kleinian singularities, 3-dimensional isolated complete local cDV
singularities admitting a noncommutative crepant resolution, any 3-dimensional
type A complete local cDV singularity, polyhedral quotient singularities (which
are non-isolated), and any isolated cDV singularity admitting a minimal model
with only type cAn cDV singularities. We also study various complex reflection
groups in the setting of symplectic quotient singularities, for which this
isomorphism does not hold, and conjecture based on computer evidence that the
reduced Grothendieck group in the case of the symmetric group has size $n!$.",2009.05291v1
2020-09-16,Structure analysis of high-pressure phase for skyrmion-hosting multiferroic Cu2OSeO3,"Cu2OSeO3 is known as a unique example of insulating multiferroic compounds
with skyrmion spin texture, which is characterized by the chiral cubic crystal
structure at ambient pressure. Recently, it has been reported that this
compound shows pressure-induced structural transition with large enhancement of
magnetic ordering temperature Tc. In the present study, we have investigated
the detailed crystal structure in the high pressure phase, by combining the
synchrotron X-ray diffraction experiment with the diamond anvil cell and the
analysis based on the genetic algorithm. Our results suggest that the original
pyrochlore Cu network is sustained even after the structural transition, while
the orientation of SeO3 molecule as well as the position of oxygen in the
middle of Cu tetrahedra are significantly modified. The latter features may be
the key for the reported enhancement of Tc and associated stabilization of
skyrmion phase at room temperature.",2009.07577v1
2020-09-19,Characterization of Probability Distributions via Functional Equations of Power-Mixture Type,"We study power-mixture type functional equations in terms of
Laplace-Stieltjes transforms of probability distributions. These equations
arise when studying distributional equations of the type Z = X + TZ, where T is
a known random variable, while the variable Z is defined via X, and we want to
`find' X. We provide necessary and sufficient conditions for such functional
equations to have unique solutions. The uniqueness is equivalent to a
characterization property of a probability distribution. We present results
which are either new or extend and improve previous results about functional
equations of compound-exponential and compound-Poisson types. In particular, we
give another affirmative answer to a question posed by J. Pitman and M. Yor in
2003. We provide explicit illustrative examples and deal with related topics.",2009.09148v1
2020-09-21,Determining electronic properties from L-edge X-ray absorption spectra of transition metal compounds with artificial neural networks,"X-ray absorption spectroscopy at the L-edge probes transitions of
2p-electrons into unoccupied d-states. Applied to transition metal atoms, this
experimental technique can provide valuable information about the electronic
structure of d-states. However, multiplet effects, spin-orbit coupling, a large
number of possible transitions can cause a rather involved nature of 2p XAS
spectra, which can often complicate extracting of information directly from
them. Here, artificial neural networks trained on simulated spectra of a 2p XAS
model Hamiltonian are presented that can directly determine information about
atomic properties and the electronic configuration of d-states from L-edge
X-ray absorption spectra. Moreover, the adaptable nature of artificial neural
networks (ANNs) allows extending their capability to obtain information about
the electronic ground state and core hole lifetimes from 2p XAS spectra as well
as to incorporate external factors, such as temperature and experimental
convolution that can affect details in spectral features. The effects of noise
and background contributions in spectra on the accuracy of ANNs are discussed
and the method is validated on experimental spectra of transition metal
compounds, including metal-organic molecules and metal oxides.",2009.09684v1
2020-09-22,Ferromagnetic phase of spinel compound MgV$_2$O$_4$ and its spintronics properties,"Spinel compound, MgV$_2$O$_4$, known as a highly frustrated magnet has been
extensively studied both experimentally and theoretically for its exotic
quantum magnetic states. However, due to its intrinsic insulating nature in its
antiferromagnetic (AFM) ground state, its realistic applications in spintronics
are quite limited. Here, based on first-principles calculations, we examine the
ferromagnetic (FM) phase of MgV$_2$O$_4$, which was found to host
three-dimensional flat band (FB) right near the Fermi level, consequently
yielding a large anomalous Hall effect (AHE, $\sigma \approx
670\,\Omega^{-1}\cdot cm^{-1}$). Our calculations suggest that the
half-metallicity feature of MgV$_2$O$_4$ is preserved even after interfacing
with MgO due to the excellent lattice matching, which could be a promising spin
filtering material for spintronics applications. Lastly, we explore
experimental feasibility of stabilizing this FM phase through strain and doping
engineering. Our study suggests that experimentally accessible amount of hole
doping might induce a AFM-FM phase transition.",2009.10323v1
2020-09-22,Electronic and magnetic properties of transition-metal doped ScN for spintronics applications,"Motivated by the ongoing interest in nitrides as materials for spintronics
applications we have studied effects of doping with magnetic transition-metal
elements (T=Cr,Mn,Fe,Co and Ni) on the electronic properties of semiconducting
scandium nitride. Using density functional together with the generalized
gradient approximation (GGA) as well as PBE0r hybrid functional (with different
mixing of the exact exchange), two different doping amounts 25\% ($\rm
Sc_{0.75}T_{0.25}N$) and 10\% ($\rm Sc_{0.9}T_{0.1}N$) have been investigated.
This is done in comparison to the reference compound ScN with a strong focus on
identifying candidates for half-metallic or semiconducting ferromagnetic ground
states. Within GGA, only $\rm Sc_{0.75}Cr_{0.25}N$ and $\rm
Sc_{0.75}Mn_{0.25}N$ are found to be semiconducting and half-metallic,
respectively. The use of hybrid functional changes drastically these finding,
where $\rm Sc_{0.75}Fe(Co,Ni)_{0.25}N$ become half-metals and $\rm
Sc_{0.75}Cr(Mn)_{0.25}N$ are found both semiconductors. However, additional
calculations assuming antiferromagnetic ordering revealed that $\rm
Sc_{0.75}Cr_{0.25}N$ is the only compound of this series, which prefers an
antiferromagnetic (and semiconducting) ground state. For the lower
concentration, $\rm Sc_{0.9}T_{0.1}N$, similar results have been predicted, and
all the doped nitrides are found to prefer ferromagnetic ground state over an
antiferromagnetic one.",2009.10611v1
2020-09-24,Topological phases in $α$-Li$_{\rm 3}$N-type crystal structure of light-element compounds,"Materials with tunable topological features, simple crystal structure and
flexible synthesis, are in extraordinary demand towards technological
exploitation of unique properties of topological nodal points. The controlled
design of the lattice geometry of light elements is determined by utilizing
density functional theory and the effective Hamiltonian model together with the
symmetry analysis. This provides an intriguing venue for reasonably achieving
various distinct types of novel fermions. We, therefore, show that a nodal line
(type-I and II), Dirac fermion, and triple point (TP) fermionic excitation can
potentially appear as a direct result of a band inversion in group-I nitrides
with $\alpha$-Li$_{\rm 3}$N-type crystal structure. The imposed strain is
exclusively significant for these compounds, and it invariably leads to the
considerable modification of the nodal line type. Most importantly, a type-II
nodal loop can be realized in the system under strain. These unique
characteristics make $\alpha$-Li$_{\rm 3} $N-type crystal structure an ideal
playground to achieve various types of novel fermions well-suited for
technological applications.",2009.11941v1
2020-09-26,Superconductivity enhanced by $d$-band filling in La$Tr_2$Al$_{20}$ with $Tr$ = Mo and W,"Electrical resistivity, magnetic susceptibility, and specific heat
measurements on single crystals of La$Tr_2$Al$_{20}$ with $Tr$ = Mo and W
revealed that these compounds exhibit superconductivity with transition
temperatures $T_c$ = 3.22 and 1.81 K, respectively, achieving the highest
values in the reported La$Tr_2$Al$_{20}$ compounds. There appears a positive
correlation between $T_c$ and the electronic specific heat coefficient, which
increases with increasing the number of $4d$- and $5d$-electrons. This finding
indicates that filling of the upper $e_g$ orbitals in the $4d$ and $5d$ bands
plays an essential role for the significant enhancement of the superconducting
condensation energy. Possible roles played by the $d$ electrons in the strongly
correlated electron phenomena appearing in $RTr_{2}$Al$_{20}$ are discussed.",2009.13952v1
2020-10-02,Data Transfer Approaches to Improve Seq-to-Seq Retrosynthesis,"Retrosynthesis is a problem to infer reactant compounds to synthesize a given
product compound through chemical reactions. Recent studies on retrosynthesis
focus on proposing more sophisticated prediction models, but the dataset to
feed the models also plays an essential role in achieving the best generalizing
models. Generally, a dataset that is best suited for a specific task tends to
be small. In such a case, it is the standard solution to transfer knowledge
from a large or clean dataset in the same domain. In this paper, we conduct a
systematic and intensive examination of data transfer approaches on end-to-end
generative models, in application to retrosynthesis. Experimental results show
that typical data transfer methods can improve test prediction scores of an
off-the-shelf Transformer baseline model. Especially, the pre-training plus
fine-tuning approach boosts the accuracy scores of the baseline, achieving the
new state-of-the-art. In addition, we conduct a manual inspection for the
erroneous prediction results. The inspection shows that the pre-training plus
fine-tuning models can generate chemically appropriate or sensible proposals in
almost all cases.",2010.00792v1
2020-10-05,Layer shift factor in layered hybrid perovskites -- univocal quantitative descriptor of composition-structure-property relationships,"Asceding interest of the scientific community in layered hybrid halide
perovskites (LHHPs) as materials for innovative photovoltaic and optoelectronic
applications led to unprecedented expansion of this family of compounds,
reaching now several hundred refined structures. Despite the unique structural
diversity of LHHPs, traditional approaches of describing their structures, such
as dividing into Dion-Jacobson (DJ) or Ruddlesden-Popper (RP) phases for mostt
structures are ambiguous and unquantifiable. Here, we introduced a quantitative
layer shift factor (LSF) for a univocal classification and quantitative
comparison of the structures. We also developed an algorithm for automatic
calculation of the LSF for such structures. We demonstrate the application of
the proposed approach for an analysis of correlations between LSF and band gap
to reveal ""structure-property"" relationships. Our study gives a simple and
useful approach to classify of either the layered perovskite-like structures or
other layered compounds composed of layers of vertex-connected octahedra as a
structural unit.",2010.02309v2
2020-10-07,Evidence formagnetic phase separation in colossal magnetoresistance compound EuB5.99C0.01,"EuB5.99C0.01 is a low-carrier density ferromagnet that is believed to be
intrinsically inhomogeneous due to fluctuations of carbon content. In
accordance with our previous studies, electric trasport of EuB5.99C0.01 close
above temperature of the bulk ferromagnetic (FM) ordering is governed by
magnetic polarons. Carbon-rich regions are incompatible with FM phase and
therefore they act as spacers preventing magnetic polarons to link, to form FM
clusters, and eventually to percolate and establish a (homogoneous) bulk FM
state in this compound, what consequently causes additional (magneto)resistance
increase. Below the temperature of the bulk FM ordering, carbon-rich regions
give rise to helimagnetic domains, which are responsible for an additional
scattering term in the electrical resistivity. Unfortunately, there has not
been provided any direct evidence for magnetic phase separation in EuB5.99C0.01
yet. Here reported results of electrical, heat capacity, Hall resistivity and
small-angle neutron scattering studies bring evidence for formation of mixed
magnetic structure, and provide consistent support for the previously proposed
scenario of the magnetoresistance enhancement in EuB5.99C0.01.",2010.03377v1
2020-10-08,AFLOW-XtalFinder: a reliable choice to identify crystalline prototypes,"The accelerated growth rate of repository entries in crystallographic
databases makes it arduous to identify and classify their prototype structures.
The open-source AFLOW-XtalFinder package was developed to solve this problem.
It symbolically maps structures into standard designations following the AFLOW
Prototype Encyclopedia and calculates the internal degrees of freedom
consistent with the International Tables for Crystallography. To ensure
uniqueness, structures are analyzed and compared via symmetry, local atomic
geometries, and crystal mapping techniques, simultaneously grouping them by
similarity. The software i. distinguishes distinct crystal prototypes and atom
decorations, ii. determines equivalent spin configurations, iii. reveals
compounds with similar properties, and iv. guides the discovery of unexplored
materials. The operations are accessible through a Python module ready for
workflows, and through command line syntax. All the 4+ million compounds in the
AFLOW.org repositories are mapped to their ideal prototype, allowing users to
search database entries via symbolic structure-type. Furthermore, 15,000 unique
structures - sorted by prevalence - are extracted from the AFLOW-ICSD catalog
to serve as future prototypes in the Encyclopedia.",2010.04222v1
2020-10-10,Accessing Excited State Molecular Vibrations by Femtosecond Stimulated Raman Spectroscopy,"Excited-state vibrations are crucial for determining photophysical and
photochemical properties of molecular compounds. Stimulated Raman scattering
can coherently stimulate and probe molecular vibrations with optical pulses,
but it is generally restricted to ground state properties. Working in resonance
conditions, indeed, enables cross-section enhancement and selective excitation
to a targeted electronic level, but is hampered by an increased signal
complexity due to the presence of overlapping spectral contributions. Here, we
show how detailed information on ground and excited state vibrations can be
disentangled, by exploiting the relative time delay between Raman and probe
pulses to control the excited state population, combined with a diagrammatic
formalism to dissect the pathways concurring to the signal generation. The
proposed method is then exploited to elucidate the vibrational properties of
ground and excited electronic states in the paradigmatic case of Cresyl Violet.
We anticipate that the presented approach holds the potential for selective
mapping the reaction coordinates pertaining to transient electronic stages
implied in photo-active compounds.",2010.05029v1
2020-10-08,3DMolNet: A Generative Network for Molecular Structures,"With the recent advances in machine learning for quantum chemistry, it is now
possible to predict the chemical properties of compounds and to generate novel
molecules. Existing generative models mostly use a string- or graph-based
representation, but the precise three-dimensional coordinates of the atoms are
usually not encoded. First attempts in this direction have been proposed, where
autoregressive or GAN-based models generate atom coordinates. Those either lack
a latent space in the autoregressive setting, such that a smooth exploration of
the compound space is not possible, or cannot generalize to varying chemical
compositions. We propose a new approach to efficiently generate molecular
structures that are not restricted to a fixed size or composition. Our model is
based on the variational autoencoder which learns a translation-, rotation-,
and permutation-invariant low-dimensional representation of molecules. Our
experiments yield a mean reconstruction error below 0.05 Angstrom,
outperforming the current state-of-the-art methods by a factor of four, and
which is even lower than the spatial quantization error of most chemical
descriptors. The compositional and structural validity of newly generated
molecules has been confirmed by quantum chemical methods in a set of
experiments.",2010.06477v1
2020-10-14,Fission Dynamics of Compound Nuclei: Pairing versus Fluctuations,"Energy dependence of fission observables is a key issue for wide nuclear
applications. We studied real-time fission dynamics from low-energy to high
excitations in the compound nucleus $^{240}$Pu with the time-dependent
Hartree-Fock+BCS approach. It is shown that the evolution time of the later
phase of fission towards scission is considerably lengthened at finite
temperature. As the role of dynamical pairing is vanishing at high excitations,
the random transition between single-particle levels around the Fermi surface
to mimic thermal fluctuations is indispensable to drive fission. The obtained
fission yields and total kinetic energies with fluctuations can be divided into
two asymmetric scission channels, namely S1 and S2, which explain well
experimental results, and give microscopic support to the Brosa model. With
increasing fluctuations, S2 channel takes over S1 channel and the spreading
fission observables are obtained.",2010.06765v2
2020-10-16,Magnetic exchange interactions in the van der Waals layered antiferromagnet MnPSe3,"Two-dimensional van der Waals compounds with magnetic ions on a honeycomb
lattice are hosts to a variety of exotic behavior. The magnetic interactions in
one such compound, MnPSe$_3$, are investigated with elastic and inelastic
neutron scattering. Magnetic excitations are observed in the magnetically
ordered regime and persist to temperatures well above the ordering temperature,
$\rm T_N$ = 74 K, consistent with low dimensional magnetic interactions. The
inelastic neutron scattering results allow a model spin Hamiltonian to be
presented that includes dominant intralayer interactions of $J_{1ab}$=0.45 meV,
$J_{2ab}$=0.03 meV, $J_{3ab}$=0.19 meV, and appreciable interlayer interactions
of $J_c$=0.031(5) meV. No evidence for anisotropy in the form of a spin-gap is
observed in the data collected. The measurements on MnPSe$_3$ are contrasted
with those on MnPS$_3$ and reveal a large increase in the interlayer exchange
interactions in MnPSe$_3$, despite the quasi-2D magnetic behavior.",2010.08394v1
2020-10-21,Griffiths phase and spontaneous exchange bias in La$_{1.5}$Sr$_{0.5}$CoMn$_{0.5}$Fe$_{0.5}$O$_{6}$,"La$_{1.5}$Sr$_{0.5}$CoMn$_{0.5}$Fe$_{0.5}$O$_{6}$ (LSCMFO) compound was
prepared by solid state reaction and its structural, electronic and magnetic
properties were investigated. The material forms in rhombohedral $R\bar{3}c$
structure, and the presence of distinct magnetic interactions leads to the
formation of a Griffiths phase above its FM transition temperature (150 K),
possibly related to the nucleation of small short-ranged ferromagnetic
clusters. At low temperatures, a spin glass-like phase emerges and the system
exhibits both the conventional and the spontaneous exchange bias (EB) effects.
These results resemble those reported for La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ but
are discrepant to those found when Fe partially substitutes Co in
La$_{1.5}$Sr$_{0.5}$(Co$_{1-x}$Fe$_{x}$)MnO$_{6}$, for which the EB effect is
observed in a much broader temperature range. The unidirectional anisotropy
observed for LSCMFO is discussed and compared with those of resembling
double-perovskite compounds, being plausibly explained in terms of its
structural and electronic properties.",2010.11110v1
2020-10-22,Efficient Scale-Permuted Backbone with Learned Resource Distribution,"Recently, SpineNet has demonstrated promising results on object detection and
image classification over ResNet model. However, it is unclear if the
improvement adds up when combining scale-permuted backbone with advanced
efficient operations and compound scaling. Furthermore, SpineNet is built with
a uniform resource distribution over operations. While this strategy seems to
be prevalent for scale-decreased models, it may not be an optimal design for
scale-permuted models. In this work, we propose a simple technique to combine
efficient operations and compound scaling with a previously learned
scale-permuted architecture. We demonstrate the efficiency of scale-permuted
model can be further improved by learning a resource distribution over the
entire network. The resulting efficient scale-permuted models outperform
state-of-the-art EfficientNet-based models on object detection and achieve
competitive performance on image classification and semantic segmentation. Code
and models will be open-sourced soon.",2010.11426v1
2020-10-22,Excitonic Effects in the Optical Spectra of Lithium metasilicate (Li2SiO3),"The Li2SiO3 compound, a ternary electrolyte compound of Lithium-ion based
batteries, exhibits unique geometric and band structures, an atom-dominated
energy spectrum, charge densities distributions, atom and orbital-projected
density of states, and strong optical responses. The state-of-the-art analysis,
based on an ab-initio simulation, have successfully confirmed the concise
physical/chemical picture and the orbital bonding in Li-O and Si-O bonds.
Additionally, the unusual optical response behavior includes a large redshift
of the onset frequency due to the extremely strong excitonic effect, the
polarization of optical properties along three-directions, 22 optical
excitations structures and the most prominent plasmon mode in terms of the
dielectric functions, energy loss functions, absorption coefficients, and
reflectance spectra. The close connections of electronic and optical properties
can identify a specific orbital hybridization for each distinct excitation
channel. The developed theoretical framework will be very appropriate for fully
comprehending the diverse phenomena of cathode/electrolyte/anode materials in
ion-based batteries.",2010.11621v1
2020-10-23,On the Transformer Growth for Progressive BERT Training,"Due to the excessive cost of large-scale language model pre-training,
considerable efforts have been made to train BERT progressively -- start from
an inferior but low-cost model and gradually grow the model to increase the
computational complexity. Our objective is to advance the understanding of
Transformer growth and discover principles that guide progressive training.
First, we find that similar to network architecture search, Transformer growth
also favors compound scaling. Specifically, while existing methods only conduct
network growth in a single dimension, we observe that it is beneficial to use
compound growth operators and balance multiple dimensions (e.g., depth, width,
and input length of the model). Moreover, we explore alternative growth
operators in each dimension via controlled comparison to give operator
selection practical guidance. In light of our analyses, the proposed method
speeds up BERT pre-training by 73.6% and 82.2% for the base and large models
respectively, while achieving comparable performances",2010.12562v3
2020-11-01,Universal classical-quantum superposition coding and universal classical-quantum multiple access channel coding,"We derive universal classical-quantum superposition coding and universal
classical-quantum multiple access channel code by using generalized packing
lemmas for the type method. Using our classical-quantum universal superposition
code, we establish the capacity region of a classical-quantum compound
broadcast channel with degraded message sets. Our universal classical-quantum
multiple access channel codes have two types of codes. One is a code with joint
decoding and the other is a code with separate decoding. The former universally
achieves corner points of the capacity region and the latter universally
achieves general points of the capacity region. Combining the latter universal
code with the existing result by Quantum Inf Process. 18, 246 (2019), we
establish a single-letterized formula for the capacity region of a
classical-quantum compound multiple access channel.",2011.00410v3
2020-11-10,Low-symmetry two-dimensional BNP$_2$ and C$_2$SiS structures with high and anisotropic carrier mobilities,"We study the stability and electronic structure of previously unexplored
two-dimensional (2D) ternary compounds BNP$_2$ and C$_2$SiS. Using $ab$
$initio$ density functional theory, we have identified four stable allotropes
of each ternary compound and confirmed their stability by calculated phonon
spectra and molecular dynamics simulations. Whereas all BNP$_2$ allotropes are
semiconducting, we find C$_2$SiS, depending on the allotrope, to be
semiconducting or semimetallic. The fundamental band gaps of the semiconducting
allotropes we study range from $1.4$ eV to $2.2$ eV at the HSE06 level $0.5$ eV
to $1.4$ eV at the PBE level and display carrier mobilities as high as
$1.5{\times}10^5$ cm$^2$V$^{-1}$s$^{-1}$. Such high mobilities are quite
uncommon in semiconductors with so wide band gaps. Structural ridges in the
geometry of all allotropes cause a high anisotropy in their mechanical and
transport properties, promising a wide range of applications in electronics and
optoelectronics.",2011.04951v1
2020-11-12,Topological phonons in oxide perovskites controlled by light,"Perovskite oxides exhibit a rich variety of structural phases hosting
different physical phenomena that generate multiple technological applications.
We find that topological phonons, i.e., nodal rings, nodal lines, and Weyl
points, are ubiquitous in oxide perovskites in terms of structures (tetragonal,
orthorhombic, and rhombohedral), compounds (BaTiO3, PbTiO3, and SrTiO3), and
external conditions (photoexcitation, strain, and temperature). In particular,
in the tetragonal phase of these compounds, all types of topological phonons
can simultaneously emerge when stabilized by photoexcitation, whereas the
tetragonal phase stabilized by thermal fluctuations only hosts a more limited
set of topological phonon states. Additionally, we find that the photoexcited
carrier concentration can be used to tune the topological phonon states and
induce topological transitions even without associated structural phase
changes. Overall, we propose oxide perovskites as a versatile platform in which
to study topological phonons and their manipulation with light.",2011.06269v1
2020-11-18,A Compounded Probability Model for Decreasing Hazard and its Inferential Properties,"There are some real life issues that are exists in nature which has early
failure. This type of problems can be modelled either by a complex distribution
having more than one parameter or by finite mixture of some distribution. In
this article a single parameter continuous distribution is introduced to model
such type of problems. The base line distribution is exponential and it is
compounded by lindley distribution. Some important properties of the proposed
distribution such as distribution function, survival function, hazard function
and cumulative hazard function are derived. The maximum likelihood estimate of
the parameter is obtained which is not in closed form, thus iteration procedure
is used to obtain the estimate of parameter. The moments of the proposed
distribution does not exist thus median and mode is obtained. The distribution
is positively skewed and the hazard rate of this distribution is decreasing.
Some real data sets are used to see the performance of proposed distribution
with comparison of some other competent distributions of decreasing hazard
using Likelihood, AIC, AICc, BIC and KS statistics.",2011.09211v1
2020-11-18,"""Discrimination of virgin olive oils with different geographical origin: a rapid untargeted chromatographic approach based on volatile compounds""","Many studies have shown that the geographic origin is one of the most
influencing factors in the choice of olive oil. To avoid misleading, European
regulation has established specific rules to report the geographical origin of
extra virgin and virgin olive oils on the product label, but an official
analytical procedure to verify this information has not been yet defined. In
this work, a flash gas chromatography untargeted approach for determination of
volatile compounds, followed by a chemometric data elaboration, is proposed for
discrimination of EVOOs and VOOs according to their geographical origin (EU and
Extra-EU). A set of 210 samples was analyzed and two different classification
techniques were used, one linear and one non-linear. The two models were also
validated using an external data set. Satisfactory results were obtained for
both chemometric approaches: considering the PLS-DA, 89% and 81% of EU and
Extra-EU samples, respectively, were correctly classified; for ANN the
percentages were 93% and 89%, respectively. These results confirm the
reliability of the method as a rapid approach to discriminate EVOOs and VOOs
according to their geographical provenance.",2011.09273v1
2020-11-23,Superionic State Discovered in Ternary Hypervalent Silicon Hydrides via Sodium inside the Earth,"Superionic states are phases of matters that can simultaneously exhibit some
of the properties of a fluid and of a solid. Superionic states of ice,
H$_{3}$O, He-H$_{2}$O or He-NH$_{3}$ compounds have been reported in previous
works. Silicon, sodium, and hydrogen are abundant elements inside the earth.
Here, we use ab initio calculations to show that, at extreme conditions inside
the earth, Na, Si, and H can form many hypervalent compounds that some of them
can exist every close to ambient pressure, and surprisingly a previously
unknown type of superionic state of $P\overline3m1 - $Na$_{2}$SiH$_{6}$ can
form as well. Our work focused on new superionic state of Na$_{2}$SiH$_{6}$,
and the results also reveal several different hypervalent Si-H anions
discovered, which are different from individual SiH$_{5}^{\,-}$ and octahedral
SiH$_{6}^{\,2-}$ in previous research of ternary alkali hypervalent silicon
hydrides. Our work provides some advice on further investigations on potential
ternary hydrides inside the earth.",2011.11429v1
2020-11-25,Influence of the Fermi surface shape on magnetotransport: the MnAs case,"We analyze the influence of the Fermi surface (FS) shape on magnetotransport
properties, particularly on the Hall effect in the MnAs compound. It has been
observed in MnAs films evidence of opposite conduction polarities for different
crystal direction (goniopolarity) and a strong dependence of the carrier type
with applied magnetic field. In order to understand this behaviour, we
developed a model based on the semiclassical equations along with Boltzmann
transport theory that takes into account both, the applied magnetic field and
the FS shape. The FS of the MnAs compound is obtained by means of density
functional theory (DFT), showing a clear dominance of the hyperboloid shape.
Our study, corroborate that this specific topology of the FS gives rise to a
goniopolar behaviour in the Hall transport. This theoretical results are
supported by magnetotransport measurements on MnAs thin layers epitaxially
grown on GaAs(001) and GaAs(111), where both configurations allow us to explore
the transport characteristics for two different crystal directions of the MnAs.",2011.12782v3
2020-11-27,Entropic signatures of the skyrmion lattice phase in MnSi1-xAlx and Fe1-yCoySi,"The entropic signatures of magnetic phase transitions in the skyrmion lattice
host compounds MnSi0.962Al0.038 and Fe0.7Co0.3Si were investigated through low
field magnetization and ac susceptibility measurements. These data indicate
that the conical to skyrmion transition that occurs with the application of
magnetic field in MnSi0.962Al0.038 is characterized by clear discontinuity in
the magnetic entropy as expected for first order topological phase transition.
These same magnetoentropic features are negligibly small in isostructural
Fe0.7Co0.3Si due to the level of chemical substitution related disorder and
differences in the spin dynamics (range and timescales). Despite the obvious
similarities in the magnetic structures of these two compounds, the transitions
between these phases is substantially different indicating a surprising
non-universality to the magnetic phase transitions in this class of materials.",2011.14025v1
2020-12-03,State Masking Over a Two-State Compound Channel,"We consider fundamental limits for communicating over a compound channel when
the state of the channel needs to be masked. Our model is closely related to an
area of study known as covert communication that is a setting in which the
transmitter wishes to communicate to legitimate receiver(s) while ensuring that
the communication is not detected by an adversary. The main contribution in our
two-state masking setup is the establishment of bounds on the throughput-key
region when the constraint that quantifies how much the states are masked is
defined to be the total variation distance between the two channel-induced
distributions. For the scenario in which the key length is infinite, we provide
sufficient conditions for when the bounds to coincide for the throughput, which
follows the square-root law. Numerical examples, including that of a Gaussian
channel, are provided to illustrate our results.",2012.01706v1
2020-12-06,Compound plasmonic vortex generation based on spiral nanoslits,"In view of wide applications of structured light fields and plasmonic
vortices, we propose the concept of compound plasmonic vortex and design
several structured plasmonic vortex generators. This kind of structured
plasmonic vortex generators consists of multiple spiral nanoslits and they can
generate two or more concentric plasmonic vortices. Different from
Laguerre-Gaussian beam, the topological charge of the plasmonic vortex in
different region is different. Theoretical analysis lays the basis for the
design of radially structured plasmonic vortex generators and numerical
simulations for several examples confirm the effectiveness of the design
principle. The discussions about the interference of vortex fields definite the
generation condition for the structured vortex. This work provides a design
methodology for generating new vortices using spiral nanoslits and the advanced
radially structured plasmonic vortices is helpful for broadening the
applications of vortex fields.",2012.03271v1
2020-12-07,Core-Level Photoelectron Spectroscopy Study of UTe$_2$,"The valence state of UTe$_2$ was studied by core-level photoelectron
spectroscopy. The main peak position of the U $4f$ core-level spectrum of
UTe$_2$ coincides with that of UB$_2$, which is an itinerant compound with a
nearly $5f^3$ configuration. However, the main peak of UTe$_2$ is broader than
that of UB$_2$, and satellite structures are observed in the higher binding
energy side of the main peak, which are characteristics of mixed-valence
uranium compounds. These results suggest that the U 5$f$ state in UTe$_2$ is in
a mixed valence state with a dominant contribution from the itinerant $5f^3$
configuration.",2012.03526v1
2020-12-08,Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound,"The structural, electronic and magnetic properties of Fe7S8 material have
been studied within the framework of the ab-initio calculations, the mean field
approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two
forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin {\sigma}=5/2
are the most probable configurations. A mixed Ising model with ferromagnetic
spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and
with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has
been used to study the magnetic properties of this compound. We demonstrated
that the magnetic phase transition can be either of the first or of the second
order, depending on the value of the exchange interaction and crystal field.
The presence of vacancies in every second iron layer leads to incomplete
cancellation of magnetic moments, hence to the emergence of the ferrimagnetism.
Anomalies in the magnetization behavior have been found and compared with the
experimental results.",2012.04306v1
2020-12-14,Ab initio machine learning in chemical compound space,"Chemical compound space (CCS), the set of all theoretically conceivable
combinations of chemical elements and (meta-)stable geometries that make up
matter, is colossal. The first principles based virtual sampling of this space,
for example in search of novel molecules or materials which exhibit desirable
properties, is therefore prohibitive for all but the smallest sub-sets and
simplest properties. We review studies aimed at tackling this challenge using
modern machine learning techniques based on (i) synthetic data, typically
generated using quantum mechanics based methods, and (ii) model architectures
inspired by quantum mechanics. Such Quantum mechanics based Machine Learning
(QML) approaches combine the numerical efficiency of statistical surrogate
models with an {\em ab initio} view on matter. They rigorously reflect the
underlying physics in order to reach universality and transferability across
CCS. While state-of-the-art approximations to quantum problems impose severe
computational bottlenecks, recent QML based developments indicate the
possibility of substantial acceleration without sacrificing the predictive
power of quantum mechanics.",2012.07502v4
2020-12-16,Deep Learning of Cell Classification using Microscope Images of Intracellular Microtubule Networks,"Microtubule networks (MTs) are a component of a cell that may indicate the
presence of various chemical compounds and can be used to recognize properties
such as treatment resistance. Therefore, the classification of MT images is of
great relevance for cell diagnostics. Human experts find it particularly
difficult to recognize the levels of chemical compound exposure of a cell.
Improving the accuracy with automated techniques would have a significant
impact on cell therapy. In this paper we present the application of Deep
Learning to MT image classification and evaluate it on a large MT image dataset
of animal cells with three degrees of exposure to a chemical agent. The results
demonstrate that the learned deep network performs on par or better at the
corresponding cell classification task than human experts. Specifically, we
show that the task of recognizing different levels of chemical agent exposure
can be handled significantly better by the neural network than by human
experts.",2012.12125v1
2020-12-23,Invidious Comparisons: Ranking and Selection as Compound Decisions,"There is an innate human tendency, one might call it the ""league table
mentality,"" to construct rankings. Schools, hospitals, sports teams, movies,
and myriad other objects are ranked even though their inherent
multi-dimensionality would suggest that -- at best -- only partial orderings
were possible. We consider a large class of elementary ranking problems in
which we observe noisy, scalar measurements of merit for $n$ objects of
potentially heterogeneous precision and are asked to select a group of the
objects that are ""most meritorious."" The problem is naturally formulated in the
compound decision framework of Robbins's (1956) empirical Bayes theory, but it
also exhibits close connections to the recent literature on multiple testing.
The nonparametric maximum likelihood estimator for mixture models (Kiefer and
Wolfowitz (1956)) is employed to construct optimal ranking and selection rules.
Performance of the rules is evaluated in simulations and an application to
ranking U.S kidney dialysis centers.",2012.12550v3
2021-01-04,NbIr$_2$B$_2$ and TaIr$_2$B$_2$ -- new low symmetry noncentrosymmetric superconductors with strong spin orbit coupling,"Superconductivity was first observed more than a century ago, but the search
for new superconducting materials remains a challenge. The Cooper pairs in
superconductors are ideal embodiments of quantum entanglement. Thus, novel
superconductors can be critical for both learning about electronic systems in
condensed matter and for possible application in future quantum technologies.
Here two previously unreported materials, NbIr$_2$B$_2$ and TaIr$_2$B$_2$, are
presented with superconducting transitions at 7.2 and 5.2 K, respectively. They
display a unique noncentrosymmetric crystal structure, and for both compounds
the magnetic field that destroys the superconductivity at 0 K exceeds one of
the fundamental characteristics of conventional superconductors (the Pauli
limit), suggesting that the superconductivity may be unconventional. Supporting
this experimentally based deduction, first-principle calculations show a spin
split Fermi surface due to the presence of strong spin-orbit coupling. These
materials may thus provide an excellent platform for the study of non-BCS
superconductivity in intermetallic compounds.",2101.00862v1
2021-01-07,Quantum annealing simulation of out-of-equilibrium magnetization in a spin-chain compound,"Geometrically frustrated spin-chain compounds such as Ca3Co2O6 exhibit
extremely slow relaxation under a changing magnetic field. Consequently, both
low-temperature laboratory experiments and Monte Carlo simulations have shown
peculiar out-of-equilibrium magnetization curves, which arise from trapping in
metastable configurations. In this work we simulate this phenomenon in a
superconducting quantum annealing processor, allowing us to probe the impact of
quantum fluctuations on both equilibrium and dynamics of the system. Increasing
the quantum fluctuations with a transverse field reduces the impact of
metastable traps in out-of-equilibrium samples, and aids the development of
three-sublattice ferrimagnetic (up-up-down) long-range order. At equilibrium we
identify a finite-temperature shoulder in the 1/3-to-saturated phase
transition, promoted by quantum fluctuations but with entropic origin. This
work demonstrates the viability of dynamical as well as equilibrium studies of
frustrated magnetism using large-scale programmable quantum systems, and is
therefore an important step toward programmable simulation of dynamics in
materials using quantum hardware.",2101.02769v1
2021-01-08,Mössbauer Spectroscopic and XRD Studies of two eta-Fe2Al5 Intermetallics,"Two intermetallic FeAl compounds with Al content of 70.68 and 72.17 at.pct
were studied using M\""ossbauer spectroscopy (5 to 296 K) and X-ray diffraction
(15 to 300 K). The compounds were found to crystallize in the orthorhombic Cmcm
space group (eta-phase). The collected data revealed that dynamics of the Fe
atoms (harmonic in entire temperature range) is significantly different that Al
atoms. For the latter strong anharmonicity was evidenced. Moreover, it was
found that partial filling of the different Al sites leads to occurrence of low
and high symmetry coordination of Fe atoms, which was reflected in occurrence
of two distinct doublets in M\""ossbauer spectra. All spectral parameters of the
doublets as well as the Debye temperature, force constant, kinetic and
potential energies of vibrations were determined. Those results revealed
significant differences between both alloys, likely originating from
approaching the stability boundary of the eta-phase for Fe-Al 72.17 at.pct
alloy.",2101.03158v1
2021-01-16,Synthesis of Zn2NbN3 ternary nitride semiconductor with wurtzite-derived crystal structure,"Binary III-N nitride semiconductors with wurtzite crystal structure such as
GaN and AlN have been long used in many practical applications ranging from
optoelectronic to telecommunication. The structurally related ZnGeN2 or ZnSnN2
derived from the parent binary compounds by cation mutation (elemental
substitution) have recently attracted attention, but such ternary nitride
materials are mostly limited to II-IV-N2 compositions. This paper reports on
synthesis and characterization of zinc niobium nitride Zn2NbN3 - a previously
unreported II2-V-N3 ternary nitride semiconductor. The Zn2NbN3 thin films are
synthesized using a single-step adsorption-controlled growth, and a two-step
deposition/annealing method that prevents loss of Zn and N. Measurements
indicate that Zn2NbN3 crystalizes in wurtzite-derived structure, in contrast to
chemically related rocksalt-derived Mg2NbN3 compound synthesized here for
comparison using the two-step method. The estimated wurtzite lattice parameters
are a = 3.36A and c = 5.26A, (c/a = 1.55), and the optical absorption onset is
at 2.1 eV for this cation-disordered Zn2NbN3. For comparison, published
computational studies predict cation-ordered Zn2NbN3 to be a semiconductor with
effective wurtzite c/a = 1.62 and a band gap of 3.5 - 3.6 eV. Overall, this
work expands the wurtzite family of nitride semiconductors, and suggests that
other ternary nitrides should be possible to synthesize",2101.06449v1
2021-01-22,"Non-unitary triplet superconductivity tuned by field-controlled magnetization --URhGe, UCoGe and UTe$_2$--","We report on theoretical studies on ferromagnetic superconductors, URhGe, and
UCoGe and identifies the pairing state as a non-unitary spin-triplet one,
analogous to superfluid $^3$He-A phase. A recently found superconductor UTe$_2$
with almost ferromagnet is analyzed by the same manner. Through investigating
their peculiar upper critical field $H_{\rm c2}$ shapes, it is shown that the
pairing symmetry realized in all three compounds can be tuned by their
magnetization curves under applied fields. This leads to the reentrant $H_{\rm
c2}$ in URhGe, an S-shaped in UCoGe and an L-shaped $H_{\rm c2}$ in UTe$_2$
observed under the field direction parallel to the magnetic hard axis in
orthorhombic crystals in common. The identification with double chiral form:
${\bf d}(k)=(\hat{b}+i\hat{c})(k_b+ik_c)$ in UTe$_2$ naturally enables us to
understand (1) multiple phases with A$_1$, A$_2$, and A$_0$ phases observed
under pressure, (2) the enhanced reentrant $H_{\rm c2}$ for the off-axis
direction fields associated with first order meta-magnetic transition, and (3)
Weyl point nodes oriented along the $a$-axis. All three compounds are found to
be topologically rich solid-state materials worth further investigation.",2101.08963v1
2021-01-22,"Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-d (M = Fe, Co, Ni)","The discovery of superconductivity in copper oxide compounds has attracted
considerable attention over the past three decades. The high transition
temperature in these compounds, exhibiting proximity to an antiferromagnetic
order in their phase diagrams, remains one of the main areas of research. The
present study attempts to introduce Fe, Co and Ni magnetic impurities into the
superconducting Y-123 with the aim of exploring the transition temperature
behavior. The solid-state synthesis is exploited to prepare fully oxygenated
Y1-xMxBa2Cu3O7 (M = Co, Fe, Ni) samples with low levels of doping (0< x <
0.03). Systematic measurements are then employed to assess the synthesized
samples using AC magnetic susceptibility, electrical resistivity and X-ray
diffraction. The measurements revealed an increase in Tc as a result of
magnetic substitution for Y. However, the study of non-magnetic dopings on the
fully oxygenated Y1-xM'xBa2Cu3O7 (M' = Ca, Sr) samples showed a decrease in Tc.
Quantitative XRD analysis further suggested that the internal pressure could
have minor effects on the increase in Tc. The normal state resistivity vs
temperature showed a linear profile, confirming that the samples are at an
optimal doping of the carrier concentration.",2101.09292v1
2021-01-22,$k$-Neighbor Based Curriculum Sampling for Sequence Prediction,"Multi-step ahead prediction in language models is challenging due to the
discrepancy between training and test time processes. At test time, a sequence
predictor is required to make predictions given past predictions as the input,
instead of the past targets that are provided during training. This difference,
known as exposure bias, can lead to the compounding of errors along a generated
sequence at test time. To improve generalization in neural language models and
address compounding errors, we propose \textit{Nearest-Neighbor Replacement
Sampling} -- a curriculum learning-based method that gradually changes an
initially deterministic teacher policy to a stochastic policy. A token at a
given time-step is replaced with a sampled nearest neighbor of the past target
with a truncated probability proportional to the cosine similarity between the
original word and its top $k$ most similar words. This allows the learner to
explore alternatives when the current policy provided by the teacher is
sub-optimal or difficult to learn from. The proposed method is straightforward,
online and requires little additional memory requirements. We report our
findings on two language modelling benchmarks and find that the proposed method
further improves performance when used in conjunction with scheduled sampling.",2101.09313v1
2021-01-26,Magnetic-order-driven metal-insulator transitions in the quasi-one-dimensional spin-ladder compounds BaFe$_2$S$_3$ and BaFe$_2$Se$_3$,"The quasi-one-dimensional spin ladder compounds, BaFe$_2$S$_3$ and
BaFe$_2$Se$_3$, are investigated by infrared spectroscopy and density
functional theory (DFT) calculations. We observe strong anisotropic electronic
properties and an optical gap in the leg direction that is gradually filled
above the antiferromagnetic (afm) ordering temperature, turning the systems
into a metallic phase. Combining the optical data with the DFT calculations we
associate the optical gap feature with the $p$-$d$ transition that appears only
in the afm ordered state. Hence, the insulating ground state along the leg
direction is attributed to Slater physics rather than Mott-type correlations.",2101.10520v1
2021-01-28,High-pressure phase transition of AB3-type compounds: case of tellurium trioxide,"Tellurium trioxide, TeO3, is the only example of a trioxide adopting at
ambient conditions the VF3-type structure (a distorted variant of the cubic
ReO3 structure). Here we present a combined experimental (Raman scattering) and
theoretical (DFT modelling) study on the influence of high pressure (exceeding
100 GPa) on the phase stability of this compound. In experiment the
ambient-pressure VF3-type structure (R-3c symmetry) is preserved up to 110 GPa.
In contrast, calculations indicate that above 66 GPa the R-3c structure should
transform to a YF3-type polymorph (Pnma symmetry) with the coordination number
of Te6+ increasing from 6 to 8 upon the transition. The lack of this transition
in the room-temperature experiment is most probably connected with energetic
barriers, in analogy to what is found for compressed WO3. The YF3-type phase is
predicted to be stable up to 220 GPa when it should transform to a novel
structure of R-3 symmetry and Z = 18. We analyse the influence of pressure on
the band gap of TeO3, and discuss the present findings in the context of
structural transformations of trioxides and trifluorides adopting an extended
structure in the solid state",2101.11842v1
2021-01-30,"High-throughput search for magnetic topological materials using spin-orbit spillage, machine-learning and experiments","Magnetic topological insulators and semi-metals have a variety of properties
that make them attractive for applications including spintronics and quantum
computation, but very few high-quality candidate materials are known. In this
work, we use systematic high-throughput density functional theory calculations
to identify magnetic topological materials from 40000 three-dimensional
materials in the JARVIS-DFT database (https://jarvis.nist.gov/jarvisdft).
First, we screen materials with net magnetic moment > 0.5 {\mu}B and spin-orbit
spillage > 0.25, resulting in 25 insulating and 564 metallic candidates. The
spillage acts as a signature of spin-orbit induced band-inversion. Then, we
carry out calculations of Wannier charge centers, Chern numbers, anomalous Hall
conductivities, surface bandstructures, and Fermi-surfaces to determine
interesting topological characteristics of the screened compounds. We also
train machine learning models for predicting the spillage, bandgaps, and
magnetic moments of new compounds, to further accelerate the screening process.
We experimentally synthesize and characterize a few candidate materials to
support our theoretical predictions.",2102.00237v2
2021-02-04,Covalency driven modulation of paramagnetism and development of lone pair ferroelectricity in multiferroic Pb$_3$TeMn$_3$P$_2$O$_{14}$,"We have investigated the structural, magnetic and dielectric properties of
Pb-based langasite compound Pb$_3$TeMn$_3$P$_2$O$_{14}$ both experimentally and
theoretically in the light of metal-oxygen covalency, and the consequent
generation of multiferroicity. It is known that large covalency between Pb 6$p$
and O 2$p$ plays instrumental role behind stereochemical lone pair activity of
Pb. The same happens here but a subtle structural phase transition above room
temperature changes the degree of such lone pair activity and the system
becomes ferroelectric below 310 K. Interestingly, this structural change also
modulates the charge densities on different constituent atoms and consequently
the overall magnetic response of the system while maintaining global
paramagnetism behavior of the compound intact. This single origin of modulation
in polarity and paramagnetism inherently connects both the functionalities and
the system exhibits mutiferroicity at room temperature.",2102.02444v1
2021-02-04,Spin-orbit-entangled electronic phases in 4$d$ and 5$d$ transition-metal compounds,"Complex oxides with $4d$ and $5d$ transition-metal ions recently emerged as a
new paradigm in correlated electron physics, due to the interplay between
spin-orbit coupling and electron interactions. For $4d$ and $5d$ ions, the
spin-orbit coupling, $\zeta$, can be as large as 0.2-0.4 eV, which is
comparable with and often exceeds other relevant parameters such as Hund's
coupling $J_{\rm H}$, noncubic crystal field splitting $\Delta$, and the
electron hopping amplitude $t$. This gives rise to a variety of
spin-orbit-entangled degrees of freedom and, crucially, non-trivial
interactions between them that depend on the $d$-electron configuration, the
chemical bonding, and the lattice geometry. Exotic electronic phases often
emerge, including spin-orbit assisted Mott insulators, quantum spin liquids,
excitonic magnetism, multipolar orderings and correlated topological
semimetals. This paper provides a selective overview of some of the most
interesting spin-orbit-entangled phases that arise in $4d$ and $5d$
transition-metal compounds.",2102.02740v1
2021-02-06,"Structural and Electrical Properties of Bilayer SiX (X= N, P, As and Sb)","In this work, the structural, electrical, and optical properties of bilayer
SiX (X= N, P, As, and Sb) are studied using density functional theory (DFT).
Five different stacking orders are considered for every compound and their
structural properties are presented. The band structure of these materials
demonstrates that they are indirect semiconductors. The out-of-plane strain has
been applied to tune the bandgap and its electrical properties. The bandgap
increases with tensile strain, whereas, compressive strain leads to
semiconductor-to-metal transition. The sensitivity of the bandgap to the
pressure is investigated and bilayer SiSb demonstrates the highest bandgap
sensitivity to the pressure. These structures exhibit Mexican hat-like valence
band dispersion that can be approved by a singularity in the density of states.
The Mexican-hat coefficient can be tuned by out-of-plane strain. Optical
absorption of these compounds shows that the second and lower valence bands due
to the high density of states display a higher contribution to optical
transitions.",2102.03563v1
2021-02-16,Spin-glass behavior in Shastry-Sutherland lattice of Tm$_\textbf{2}$Cu$_\textbf{2}$In,"The spin-glass behavior in the ferromagnetic phase of $\mathrm{Tm_2Cu_2In}$
was investigated by dc-, ac-magnetization, and non-equilibrium dynamics
characterizations. Arc-melted polycrystalline compound of $\mathrm{Tm_2Cu_2In}$
crystallizes in $\mathrm{Mo_2FeB_2}$-type tetragonal structure (space group
$P_4/mbm$). The temperature variation dc-magnetization exhibits a ferromagnetic
behavior with Curie temperature $T_C$ = 32.5 K. The zero-field cooled (ZFC) and
field cooled (FC) magnetic curves show a thermomagnetic irreversible behavior
below $T_C$. The field dependence of irreversible temperature follows
Almeida-Thouless line. The frequency and ac-driven field-dependent anomalies in
ac-susceptibility results indicate the existence of spin-glass state in
$\mathrm{Tm_2Cu_2In}$. The time dependence of magnetization further supports
the spin-glass behavior observed in $\mathrm{Tm_2Cu_2In}$. The frequency
dependence of the freezing temperature in the real part of ac-susceptibility
has been analyzed on the basis power-law divergence and Vogel-Fulcher law. The
obtained results revealed that $\mathrm{Tm_2Cu_2In}$ belongs to a ferromagnetic
canonical spin-glass class of compounds.",2102.08230v2
2021-02-19,Observation of Kondo hybridization with an orbital-selective Mott phase in 4d Ca2-xSrxRuO4,"The heavy fermion state with Kondo-hybridization (KH), usually manifested in
f-electron systems with lanthanide or actinide elements, was recently
discovered in several 3d transition metal compounds without f-electrons.
However, KH has not yet been observed in 4d/5d transition metal compounds,
since more extended 4d/5d orbitals do not usually form flat bands that supply
localized electrons appropriate for Kondo pairing. Here, we report a doping-
and temperature-dependent angle-resolved photoemission study on 4d
Ca2-xSrxRuO4, which shows the signature of KH. We observed a spectral weight
transfer in the {\gamma}-band, reminiscent of an orbital-selective Mott phase
(OSMP). The Mott localized {\gamma}-band induces KH with the itinerant
\b{eta}-band, resulting in spectral weight suppression around the Fermi level.
Our work is the first to demonstrate the evolution of the OSMP with possible KH
among 4d electrons, and thereby expands the material boundary of Kondo physics
to 4d multi-orbital systems.",2102.09760v1
2021-02-24,Tunable ferroelectricity in hBN intercalated twisted double-layer graphene,"Van der Waals (vdW) assembly of two-dimensional materials has been long
recognized as a powerful tool to create unique systems with properties that
cannot be found in natural compounds. However, among the variety of vdW
heterostructures and their various properties, only a few have revealed
metallic and ferroelectric behaviour signatures. Here we show ferroelectric
semimetal made of double-gated double-layer graphene separated by an atomically
thin crystal of hexagonal boron nitride, which demonstrating high room
temperature mobility of the order of 10 m$^2$V$^{-1}$s$^{-1}$ and exhibits
robust ambipolar switching in response to the external electric field. The
observed hysteresis is tunable, reversible and persists above room temperature.
Our fabrication method expands the family of ferroelectric vdW compounds and
offers a route for developing novel phase-changing devices.",2102.12398v1
2021-02-25,s-d coupling enhanced phonon anharmonicity in copper-based compounds,"Materials with ultralow thermal conductivity are of great interest for
efficient energy conversion and thermal barrier coating. Copper-based
semiconductors such as copper chalcogenides and copper halides are known to
possess extreme low thermal conductivity, whereas the fundamental origin of the
low thermal conductivity observed in the copper-based materials remains
elusive. Here, we reveal that s-d coupling induced giant phonon anharmonicity
is the fundamental mechanism responsible for the ultralow thermal conductivity
of copper compounds. The symmetry controlled strong coupling of high-lying
occupied copper 3d orbital with the unoccupied 4s state under thermal vibration
remarkably lowers the lattice potential barrier, which enhances anharmonic
scattering between phonons. This understanding is confirmed by
temperature-dependent Raman spectra measurements. Our study offers an insight
at atomic level connecting electronic structures with phonon vibration modes,
and thus sheds light on materials properties that rely on electron-phonon
coupling, such as thermoelectricity and superconductivity.",2102.12619v1
2021-02-26,A complete description of thermodynamic stabilities of molecular crystals,"Predictions of relative stabilities of (competing) molecular crystals are of
great technological relevance, most notably for the pharmaceutical industry.
However, they present a long-standing challenge for modeling, as often
minuscule free energy differences are sensitively affected by the description
of electronic structure, the statistical mechanics of the nuclei and the cell,
and thermal expansion. The importance of these effects has been individually
established, but rigorous free energy calculations for general molecular
compounds, which simultaneously account for all effects,have hitherto not been
computationally viable. Here we present an efficient ""end to end"" frame-work
that seamlessly combines state-of-the art electronic structure calculations,
machine-learning potentials, and advanced free energy methods to calculate ab
initio Gibbs free energies for general organic molecular materials. The facile
generation of machine-learning potentials for a diverse set of polymorphic
compounds, benzene, glycine, and succinic acid, and predictions of
thermodynamic stabilities in qualitative and quantitative agreement with
experiments highlights that predictive thermodynamic studies of
industrially-relevant molecular materials are no longer a daunting task.",2102.13598v2
2021-04-02,Spin glass state in layered compound MnSb2Te4,"As a sister compound and isostructural of MnBi2Te4, the high quality MnSb2Te4
single crystals are grown via solid-state reaction where prolonged annealing
and narrow temperature window play critical roles on account of its thermal
metastability. X-ray diffraction analysis on MnSb2Te4 single crystals reveals
pronounced cation intermixing, 28.9(7)% Sb antisite defects on the Mn (3a) site
and 19.3(6)% Mn antisite defects on the Sb (6c) site, compared with MnBi2Te4.
Unlike antiferromagnetic (AFM) nature MnBi2Te4, MnSb2Te4 contains magnetic and
antiferromagnetic competition and exhibits a spin glass (SG) state below 24 K.
Its magnetic hysteresis, anisotropy, and relaxation process are investigated in
detail with DC and AC magnetization measurements. Moreover, anomalous Hall
effect as a p-type conductor is demonstrated through transport measurements.
This work grants MnSb2Te4 a possible access to the future exploration of exotic
quantum physics by removing the odd/even layer number restraint in intrinsic
AFM MnBi2Te4-family materials as a result of the crossover between its
magnetism and potential topology in the Sb-Te layer.",2104.00898v1
2021-04-02,Malliavin calculus for marked binomial processes: portfolio optimisation in the trinomial model and compound Poisson approximation,"In this paper we develop a stochastic analysis for marked binomial processes,
that can be viewed as the discrete analogues of marked Poisson processes. The
starting point is the statement of a chaotic expansion for square-integrable
(marked binomial) functionals, prior to the elaboration of a Markov-Malliavin
structure within this framework. We take advantage of the new formalism to deal
with two main applications. First, we revisit the Chen-Stein method for the
(compound) Poisson approximation which we perform in the paradigm of the built
Markov-Malliavin structure, before studying in the second one the problem of
portfolio optimisation in the trinomial model.",2104.00914v3
2021-04-02,High pressure study of low-Z superconductor Be$_{22}$Re,"With $T_c \sim 9.6~\mathrm{K}$, Be$_{22}$Re exhibits one of the highest
critical temperatures among Be-rich compounds. We have carried out a series of
high-pressure electrical resistivity measurements on this compound to 30 GPa.
The data show that the critical temperature $T_c$ is suppressed gradually at a
rate of $dT_c/dP = -0.05~\mathrm{K/GPa}$. Using density functional theory (DFT)
calculations of the electronic and phonon density of states (DOS) and the
measured critical temperature, we estimate that the rapid increase in lattice
stiffening in Be$_{22}$Re overwhelms a moderate increase in the electron-ion
interaction with pressure, resulting in the decrease in $T_c$. High pressure
x-ray diffraction measurements show that the ambient pressure crystal structure
of Be$_{22}$Re persists to at least 154 GPa. We discuss the relationship
between low-Z Be-rich superconductors and the high-$T_c$ superhydrides.",2104.01094v2
2021-04-06,"$x$-[Pd(dmit)$_2$]$_2$ as a quasi-1D, scalene Heisenberg model","From first principles, we calculate the Heisenberg interactions between
neighboring dimers in several compounds within the
Et$_{n}$Me$_{4-n}X$[Pd(dmit)$_2$]$_2$ (Et = ethyl, Me = methyl, dmit =
2-thioxo-1,3-dithiole-4,5-dithiolate) family using an atomistic approach; with
broken-symmetry density functional theory. In all materials, we find a scalene
triangular model where the strongest exchange coupling along one
crystallographic axis is up to three times larger than the others and that
frustration further enhances this quasi-one-dimensionality. We calculate the
N\'eel ordering temperature via the chain random phase approximation (CRPA). We
show that the difference in the frustrated interchain couplings is equivalent
to a single bipartite interchain coupling, favoring long-range magnetic order.
We find that the N\'eel ordering temperatures are in good agreement with the
experimentally measured values for most compounds.",2104.02277v1
2021-04-08,Unconventional Superconductivity arising from Multipolar Kondo Interactions,"The nature of unconventional superconductivity is intimately linked to the
microscopic nature of the pairing interactions. In this work, motivated by
cubic heavy fermion compounds with embedded multipolar moments, we
theoretically investigate superconducting instabilities instigated by
multipolar Kondo interactions. Employing multipolar fluctuations (mediated by
RKKY interaction) coupled to conduction electrons via two-channel Kondo and
novel multipolar Kondo interactions, we uncover a variety of superconducting
states characterized by higher-angular momentum Cooper pairs, $J=0,1,2,3$. We
demonstrate that both odd and even parity pairing functions are possible,
regardless of the total angular momentum of the Cooper pairs, which can be
traced back to the atypical nature of the multipolar Kondo interaction that
intertwines conduction electron spin and orbital degrees of freedom. We
determine that different (point-group) irrep classified pairing functions may
coexist with each other, with some of them characterized by gapped and point
node structures in their corresponding quasiparticle spectra. This work lays
the foundation for discovery and classification of superconducting states in
rare-earth metallic compounds with multipolar local moments.",2104.03971v1
2021-04-09,Video-aided Unsupervised Grammar Induction,"We investigate video-aided grammar induction, which learns a constituency
parser from both unlabeled text and its corresponding video. Existing methods
of multi-modal grammar induction focus on learning syntactic grammars from
text-image pairs, with promising results showing that the information from
static images is useful in induction. However, videos provide even richer
information, including not only static objects but also actions and state
changes useful for inducing verb phrases. In this paper, we explore rich
features (e.g. action, object, scene, audio, face, OCR and speech) from videos,
taking the recent Compound PCFG model as the baseline. We further propose a
Multi-Modal Compound PCFG model (MMC-PCFG) to effectively aggregate these rich
features from different modalities. Our proposed MMC-PCFG is trained end-to-end
and outperforms each individual modality and previous state-of-the-art systems
on three benchmarks, i.e. DiDeMo, YouCook2 and MSRVTT, confirming the
effectiveness of leveraging video information for unsupervised grammar
induction.",2104.04369v2
2021-04-10,Polymeric ruthenium precursor as a photoactivated antimicrobial agent,"In this work, the antibacterial activity of the polymeric precursor
dicarbonyldichlororuthenium has been studied against Escherichia coli and
Staphylococcus aureus. This Ru carbonyl precursor shows minimum inhibitory
concentration at nanogram per millilitre, which renders it a novel
antimicrobial polymer without any organic ligands. Besides,
dicarbonyldichlororuthenium antimicrobial activity is markedly boosted under
photoirradiation, which can be ascribed to the enhanced generation of reactive
oxygen species under UV irradiation. This compound has been able to inhibit
bacterial growth via the disruption of bacterial membranes and triggering
upregulation of stress responses as shown in microscopic measurements. The
activity of polymeric ruthenium as an antibacterial material is significant
even at very low concentrations while remaining biocompatible to the mammalian
cells at much higher concentrations. This study proves that this simple Ru
carbonyl precursor can be used as an antimicrobial compound with high activity
and a low toxicity profile in the context of need for new antimicrobial agents
to fight bacterial infections.",2104.04707v1
2021-04-10,A crossover of the solid substances solubility in supercritical fluids: what is it in fact?,"We investigate a well-known phenomenon of the appearance of the crossover
points, corresponding to the intersections of the solubility isotherms of the
solid compound in supercritical fluid. Opposed to the accepted understanding of
the existence of two fixed crossover points, which confine the region of the
inverse isobaric temperature dependence of the solubility, we have found that
these points tend to shift with the change of the temperature and in the limit
of the certain threshold value they converge to a single point. We demonstrate
this analyzing the solubility data of a set of poorly soluble drug compounds,
which have been computed in a wide area of the phase diagram via the approach,
based on the classical density functional theory. Thorough analysis of the
available in the literature experimental solubility data is found to be in an
agreement with our conclusions, as one can find that the wider temperature
region of the experimental study is, the more pronounced effect of the
crossover points drift can be observed.",2104.04776v1
2021-04-13,Spin dynamics of the director state in frustrated hyperkagome systems,"We present an experimental study of the magnetic structure and dynamics of
two frustrated hyperkagome compounds, Gd3Ga5O12 and Gd3Al5O12. It has
previously been shown that Gd3Ga5O12 exhibits long-range correlations of
multipolar directors, that are formed from antiferromagnetic spins on loops of
ten ions. Using neutron diffraction and Reverse Monte Carlo simulations we
prove the existence of similar magnetic correlations in Gd3Al5O12, showing the
ubiquity of these complex structures in frustrated hyperkagome materials.
  Using inelastic neutron scattering we shed further light on the director
state and the associated low lying magnetic excitations. In addition we have
measured quasielastic dynamics that show evidence of spin diffusion. Finally,
we present AC susceptibility measurements on both Gd3Ga5O12 and Gd3Al5O12,
revealing a large difference in the low frequency dynamics between the two
otherwise similar compounds.",2104.05987v2
2021-04-13,Multiple ferroelectric nematic phases of a highly polar liquid crystal compound,"Ferroelectric nematic liquid crystals represent not only interesting
fundamental science, but they also hold promise for storage capacitors with
high power density or new information display technology having sub-millisecond
switching. In this work we describe the synthesis and measurements of the
physical properties of a new highly polar ferroelectric nematic compound,
4-nitrophenyl 4-[(2,4-dimethoxylbenzoyl)oxy]-2-fluorobenzoate (RT11001). The
dipole moment of this material (along the long molecular axis) is calculated to
exceed 11.5 Debye. We employ a wide range of physical characterization methods
including differential scanning calorimetry (DSC), mass density measurement,
optical birefringence, polarizing optical microscopy (POM), electric current
analysis, and electro-optical switching, to show that RT11001 has three
distinct ferroelectric states, F1, F2 and F3. F1 is purely orientationally
ordered ferroelectric nematic phase (NF), F2 has a ferroelectric nematic with
possibly short-range hexagonal order normal to the director (NhF), and we
conjecture that F3 has a long-range hexagonal order normal to the director
(ColhF).",2104.06520v1
2021-04-15,Fitting Infinitely divisible distribution: Case of Gamma-Variance Model,"The paper examines the Fractional Fourier Transform (FRFT) based technique as
a tool for obtaining probability density function and its derivatives, and
mainly for fitting stochastic model with the fundamental probabilistic
relationships of infinite divisibility. The probability density functions are
computed and the distributional proprieties such as leptokurtosis, peakedness,
and asymmetry are reviewed for Variance-Gamma (VG) model and Compound Poisson
with Normal Compounding model. The first and second derivatives of probability
density function of the VG model are also computed in order to build the Fisher
information matrix for the Maximum likelihood method. The VG model has been
increasingly used as an alternative to the Classical Lognormal Model (CLM) in
modelling asset price. The VG model with fives parameters was estimated by the
FRFT. The data comes from the daily SPY ETF price data. The Kolmogorov-Smirnov
(KS) goodness-of-fit shows that the VG model fits better the empirical
cumulative distribution than the CLM. The best VG model comes from the FRFT
estimation.",2104.07580v2
2021-04-16,"Structural phase stability, electronic structure, magnetic properties and chemical bonding analysis of transition metal ammine borohydrides with amphoteric hydrogen for hydrogen storage","Usually the ions of a particular element in solids are in positive or
negative oxidation states, depending upon the chemical environment. It is
highly unusual for an atom having both positive as well as negative oxidation
states simultaneously within the same structural framework in a particular
compound. Our structural and chemical bonding analyses show that the hydrogen
ions in the transition metal ammine borohydrides (TMABHs) with the chemical
formula M(BH4)2(NH3)2 (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) have both
positive and negative oxidation states. Our detailed analyses confirm the
amphoteric behaviour of hydrogen where hydrogen closer to boron is in negative
oxidation state and that closer to nitrogen is in the positive oxidation state.
From the spin polarised van der Waals interaction included calculation, we
found that TMABHs has antiferromagnetic ordering as ground state. Our nudged
elastic band calculation show that the migration barrier for ammonia diffusion
in these materials are more than 1 eV and hence these compounds may be used for
energy storage applications since they have high weight percentage of hydrogen.
The presence of amphoteric behaviour of hydrogen in TMABHs has implication in
designing volume efficient hydrides for hydrogen storage applications.",2104.08140v1
2021-04-18,"Optical and Electronic Properties of SiTe_x(x=1,2) from First-Principles","The optical and electronic properties of the {\alpha}-SiTe, {\beta}-SiTe, and
RX-SiTe_2 are investigated. A detailed analysis of electronic properties is
done using standard density functional theory (DFT) and hybrid functional
(HSE06) methods. The optical dielectric properties are studied under three
different methods: standard DFT, many-body Green's functions (GW), and
Bethe-Salpeter equation (BSE). Our calculations show that the SiTe compounds
possess extremely high static dielectric constants in their bulk forms
({\epsilon}_0({\bot}) = 68.58, {\epsilon}_0({\parallel}) = 127.29 for
{\alpha}-SiTe, and {\epsilon}_0({\bot}) = 76.23, {\epsilon}_0({\parallel}) =
98.15 for {\beta}-SiTe). The frequency-dependent dielectric functions
Im({\epsilon}) have very large values (>100) in the optical regime, which are
among the highest of layered materials, suggesting them as excellent light
absorbents in the corresponding frequencies. {\alpha}-SiTe exhibits a high
degree of optical anisotropy as compared to the other two compounds, consistent
with their structural configurations. A strong interlayer excitonic effect is
observed in bulk RX-SiTe_2. In addition, an analysis of Raman intensity is also
performed.",2104.08909v1
2021-04-20,Superconductivity in ThMo2Si2C with Mo2C Square Net,"We report the superconductivity of a new quaternary compound ThMo$_2$Si$_2$C,
synthesized with the arc-melting technique. The compound crystallizes in a
tetragonal CeCr$_2$Si$_2$C-type structure with cell parameters of $a$ = 4.2296
\r{A}and $c$ = 5.3571 \r{A}. An interlayer Si-Si covalent bonding is suggested
by the atomic distance. The electrical resistivity and magnetic susceptibility
measurements indicate a Pauli-paramagnetic metal with dominant
electron-electron scattering in the normal-state. Bulk superconductivity at 2.2
K is demonstrated with a dimensionless specific-heat jump of
${\Delta}C/\gamma_{\rm n}T$ = 0.98. The superconducting parameters of the
critical magnetic fields, coherence length, penetration depth, and
superconducting energy gap are given.",2104.09822v1
2021-04-22,Hund's metal crossover and superconductivity in the 111 family of iron-based superconductors,"We study LiFeP, LiFeAs and NaFeAs in their paramagnetic metallic phase
including dynamical electronic correlations within a density functional theory
+ slave-spin mean-field framework. The three compounds are found to lie next to
the crossover between a normal and a Hund's metal, where a region of enhanced
electronic compressibility that may boost superconductivity is systematically
present in this type of systems. We find that LiFeP lies in the normal metallic
regime, LiFeAs at the crossover, and NaFeAs is in the Hund's metal regime,
which possibly explains the different experimental trends for the pressure- and
doping-dependence of superconductivity in these compounds. Our picture captures
the orbitally-resolved mass renormalizations measured in these materials, while
an analysis of the Sommerfeld specific-heat coefficient highlights some
limitations of currently used implementations of density-functional theory for
the correct prediction of the details of band structures in the iron-based
superconductors.",2104.11018v1
2021-04-24,Precarity: Modeling the Long Term Effects of Compounded Decisions on Individual Instability,"When it comes to studying the impacts of decision making, the research has
been largely focused on examining the fairness of the decisions, the long-term
effects of the decision pipelines, and utility-based perspectives considering
both the decision-maker and the individuals. However, there has hardly been any
focus on precarity which is the term that encapsulates the instability in
people's lives. That is, a negative outcome can overspread to other decisions
and measures of well-being. Studying precarity necessitates a shift in focus -
from the point of view of the decision-maker to the perspective of the decision
subject. This centering of the subject is an important direction that unlocks
the importance of parting with aggregate measures to examine the long-term
effects of decision making. To address this issue, in this paper, we propose a
modeling framework that simulates the effects of compounded decision-making on
precarity over time. Through our simulations, we are able to show the
heterogeneity of precarity by the non-uniform ruinous aftereffects of negative
decisions on different income classes of the underlying population and how
policy interventions can help mitigate such effects.",2104.12037v1
2021-05-05,"The crystal structure, chemical bonding and magnetic properties of the intercalation compounds Cr$_x$ZrTe$_2$ ($x$ = 0-0.3)","New intercalation compounds Cr$_x$ZrTe$_2$ were synthesized in the Cr
concentration range of x=0-0.3. A thorough study of the crystal and electronic
structure has been performed. It was found that there is competition in the
distribution of the Cr atoms over the octa- and tetrahedral sites in the van
der Waals gap, depending on the Cr content. The ordering of the Cr atoms was
found at x = 0.25; at the same time, the lattice symmetry decreases from
trigonal P-3m1 to monoclinic F2/m. This ordering stabilizes the octahedral
coordination of the Cr atoms by Te atoms. The analysis of the experimental data
on the electronic structure and DOS calculations showed that the Cr 3d states
are spin-split.",2105.02332v2
2021-05-09,Surface nanodroplet-based nanoextraction from sub-milliliter volumes of dense suspensions,"Cleaner analytic technique for quantifying compounds in dense suspension is
needed for wastewater and environment analysis, chemical or bio-conversion
process monitoring, biomedical diagnostics, food quality control among others.
In this work, we introduce a green, fast, one-step method called nanoextraction
for extraction and detection of target analytes from sub-milliliter dense
suspensions using surface nanodroplets without toxic solvents and pre-removal
of the solid contents. With nanoextraction, we achieve a limit of detection
(LOD) of 10^(-9) M for a fluorescent model analyte obtained from a particle
suspension sample. The LOD lower than that in water without particles 10^(-8)
M, potentially due to the interaction of particles and the analyte. The high
particle concentration in the suspension sample thus does not reduce the
extraction efficiency, although the extraction process was slowed down up to 5
min. As proof of principle, we demonstrate the nanoextraction for
quantification of model compounds in wastewater slurry containing 30 wt% sands
and oily components (i.e. heavy oils). The nanoextraction and detection
technology developed in this work may be used as fast analytic technologies for
complex slurry samples in environment industrial waste, or in biomedical
diagnostics.",2105.03929v1
2021-05-13,Unraveling exotic 5$f$ states and paramagnetic phase of PuSn$_3$,"Plutonium-based compounds establish an ideal platform for exploring the
interplay between long-standing itinerant-localized 5$f$ states and strongly
correlated electronic states. In this paper, we exhaustively investigate the
correlated 5$f$ electronic states of PuSn$_3$ dependence on temperature by
means of a combination of the density functional theory and the embedded
dynamical mean-field theory. It is found that the spectral weight of narrow
5$f$ band grows significantly and remarkable quasiparticle multiplets appear
around the Fermi level at low temperature. A striking $c-f$ hybridization and
prominent valence state fluctuations indicate the advent of coherence and
itinerancy of 5$f$ states. It is predicted that a 5$f$ localized to itinerant
crossover is induced by temperature accompanied by the change in Fermi surface
topology. Therefore itinerant 5$f$ states are inclined to take in active
chemical bonding, suppressing the formation of local magnetic moment of Pu
atoms, which partly elucidates the intrinsic feature of paramagnetic ground
state of PuSn$_3$. Furthermore, the 5$f$ electronic correlations are orbital
selective manifested themselves in differentiated band renormalizations and
electron effective masses. Consequently, the convincing results remain crucial
to our understanding of plutonium-based compounds and promote ongoing research.",2105.06154v1
2021-05-18,Spin Spiral and Topological Hall Effect in a Metamagnet Fe$_{3}$Ga$_{4}$,"A new mechanism for Topological Hall Effect (THE) was recently proposed for
the spiral magnet YMn$_{6}$Sn$_{6},$ which requires transverse conical spiral
(TCS) magnetism, induced by external magnetic field, combined with thermally
excite helical spiral magnons. In principle, this mechanism should be
applicable to other itinerant spiral magnets as well. In this paper, we show
that another metamagnetic compound, Fe$_{3}$Ga$_{4}$, where THE was observed
experimentally before, in one of its phases satisfies this condition, and the
proposed theory of thermal-fluctuation driven THE is quantitatively consistent
with the experiment. This finding suggests that this mechanism is indeed rather
universal, and the effect may have been observed in other compounds before, but
overlooked.",2105.08773v1
2021-05-26,Revealing the Heavy Quasiparticles in the Heavy-Fermion Superconductor CeCu2Si2,"The superconducting order parameter of the first heavy-fermion superconductor
CeCu2Si2 is currently under debate. A key ingredient to understand its
superconductivity and physical properties is the quasiparticle dispersion and
Fermi surface, which remains elusive experimentally. Here we present
measurements from angle-resolved photoemission spectroscopy. Our results
emphasize the key role played by the Ce 4f electrons for the low-temperature
Fermi surface, highlighting a band-dependent conduction-f electron
hybridization. In particular, we find a very heavy quasi-two-dimensional
electron band near the bulk X point and moderately heavy three-dimensional hole
pockets near the Z point. Comparison with theoretical calculations reveals the
strong local correlation in this compound, calling for further theoretical
studies. Our results provide the electronic basis to understand the heavy
fermion behavior and superconductivity; implications for the enigmatic
superconductivity of this compound are also discussed.",2105.12394v2
2021-05-28,Monte Carlo simulation of molecular dynamics for amino acid production from carboxylic acid via C-14 beta-decay,"To study the chemical origin of life, we investigated the amino acid
production probability from radiocarbon (C-14)-containing carboxylic acid via
beta-decay using a newly developed Monte Carlo simulator for molecular dynamics
calculation. Using the simulation, we calculated the dynamical trajectory of
N-14 recoiled via C-14 beta-decay in [3-C-14]propionic acid and evaluated the
staying probability of N-14 in the compound, which is the glycinium (a
protonated glycine) production probability from [3-C-14]propionic acid. The
glycinium production probability was calculated to be 78.7% assuming static
compound structures of [3-C-14]propionic acid and a glycinium C-N binding
potential energy of 3.93 eV. From calculations with various binding potential
parameters, a glycinium production probability of approximately 30% was
expected by simulation in case of a loose C-N binding potential energy of 2-eV.",2105.13622v1
2021-06-02,Anomalous diamagnetism of electride electrons in transition metal silicides,"Intermetallic silicide compounds, LaScSi and Y$_5$Si$_3$, known for being
hydrogen (H) storage materials, are drawing attention as candidates for
electrides in which anions are substituted by unbound electrons. It is inferred
from a muon spin rotation experiment that the local field at the muon site
(which is the same site as that for H) in these compounds exhibits a large
negative shift under an external magnetic field, which is mostly independent of
temperature. Such anomalous diamagnetism signals a unique property of electride
electrons associated with transition metals. Moreover, the diamagnetic shift
decreases with increasing H content, suggesting that the electride electrons
existing coherently in the hollow interstitial positions are adsorbed by H to
form hydride ions (H$^-$)",2106.00921v1
2021-06-07,Crystal field effects in the zig-zag chain compound SrTm$_2$O$_4$,"The single ion properties of the zig-zag chain compound SrTm$_2$O$_4$ have
been investigated using heat capacity, magnetic susceptibility, magnetization,
inelastic neutron scattering, and polarized muon spectroscopy. Two crystal
field models are employed to estimate the single ion properties; a Density
Function Theory based model and an effective charge model based on the
Hutchings point charge model. The latter describes our experimental results
well. This model estimates an easy-axis anisotropy for one of the Tm$^{3+}$
sites and an easy-plane anisotropy for the second site. It also predicts a
mixed ground state with dominating $J = 0$ characteristics for both sites.
Additionally, muon spin rotation/relaxation ($\mu^+$SR) spectra reveal
oscillations, typically a sign of long-range magnetic order. However, the
temperature dependence of the precession frequency and the relaxation rates
indicate that the system is in an extended critical regime and the observed
relaxation is actually dynamic.",2106.03704v3
2021-06-14,Phonon-mediated high-temperature superconductivity in ternary borohydride KB$_2$H$_8$ around 12 GPa,"Discovery of high-temperature superconductivity in hydrogen-rich compounds
has fuelled the enthusiasm for finding materials with more promising
superconducting properties among hydrides. However, the ultrahigh pressure
needed to synthesize and maintain high-temperature hydrogen-rich
superconductors hinders the experimental investigation of these materials. For
practical applications, it is also highly desired to find more hydrogen-rich
materials that superconduct at high temperatures but under relatively lower
pressures. Based on first-principles density functional theory, we calculate
the electronic and phonon band structures for a ternary borohydride formed by
intercalating BH$_4$ tetrahedrons into a face-centered-cubic potassium lattice,
KB$_2$H$_8$. Remarkably, we find that this material is dynamically stable and
one of its $sp^3$-hybridized $\sigma$-bonding bands is metallized (i.e.
partially filled) above a moderate high pressure. This metallized
$\sigma$-bonding band couples strongly with phonons, giving rise to a strong
superconducting pairing potential. By solving the anisotropic Eliashberg
equations, we predict that the superconducting transition temperature of this
compound is 134-146 K around 12 GPa.",2106.07322v1
2021-06-16,Correlated Non-Coherent Radar Detection for Gamma-Fluctuating Targets in Compound Clutter,"This work studies the problem of radar detection of correlated
gamma-fluctuating targets in the presence of clutter described by compound
models with correlated speckle. If the correlation is not accounted for in a
radar model, the required signal-to-interference ratio for a given probability
of detection will be incorrect, resulting in over-estimated performance.
Although more generally applicable, the is focus on airborne maritime radar
systems. Hence K-distributed sea clutter is used as the main example. Detection
via square-law non-coherent pulse integration is formulated in a way that
accommodates arbitrary partial correlation for both target radar cross-section
(RCS) and clutter speckle. The obstacle to including this degree of generality
in previous work was the fact that Swerling's original characterization of the
standard RCS fluctuation classes as gamma distributions for the power is not
sufficient for the inclusion of both correlation sources (i.e.target and
clutter speckle) for gamma-fluctuating targets. An extension of the model is
required at the quadrature component (i.e. voltage) level, as phase
relationships can no longer be neglected. This is addressed in the present
work, which not only postulates an extended model, but also demonstrates how to
efficiently compute it, with and without a number of simplifying approximation
schemes within the framework of the saddle-point technique.",2106.08593v1
2021-06-18,Magnetic transitions in the 1-D chain compounds NdPd5Ge3 and NdPt5Ge3,"We present the structural and initial magnetic characterization of the
previously unreported materials NdPd5Ge3 and NdPd5Ge3. These materials, with
1-dimensional Nd chains, crystallize in the orthorhombic YNi5Si3-type structure
in space group Pnma. Magnetic ordering is observed for both compounds at ~ 2.2
K for NdPd5Ge3 and ~ 3.0 K for NdPt5Ge3. A magnetic-field-induced transition is
clearly observed for NdPd5Ge3 below 2K, at an applied magnetic field of around
1.6 Tesla. The heat capacity data reveals that essentially all the available
magnetic entropy is released at the magnetic ordering transition for NdPd5Ge3
but that only 29% is seen for NdPt5Ge3 at temperatures down to 1.5 K, the data
implying that a second magnetic transition can be expected at lower
temperatures.",2106.10325v2
2021-06-24,Epitaxial growth of Ruddlesden-Popper neodymium nickelates Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ (${n}$ = 1-5),"A series of Ruddlesden-Popper nickelates, Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ (${n}$
= 1-5), have been stabilized in thin film form using reactive molecular-beam
epitaxy. High crystalline quality has been verified by X-ray diffraction and
scanning transmission electron microscopy. X-ray photoelectron spectroscopy
indicates the ${n}$-dependent valence states of nickel in these compounds.
Metal-insulator transitions show clear ${n}$ dependence for intermediate
members (${n}$ = 3-5), and the low-temperature resistivities of which show
logarithmic dependence, resembling the Kondo-scattering as observed in the
parent compounds of superconducting infinite-layer nickelates.",2106.12941v1
2021-06-30,Short-range magnetic correlation and magnetodielectric coupling in multiferroic Pb3TeMn3P2O14,"In this paper the structural, magnetic, and dielectric properties of
langasite compound Pb$_3$TeMn$_3$P$_2$O$_{14}$ have been investigated as a
candidate of short-range magnetic correlations driven development of dielectric
anomaly above N$\acute{e}$el temperature of ($T_N$=) 7 K. Presence of
dielectric anomaly, structural phase transition and a short range magnetic
correlation at the same temperature (at around 100 K) as well as magnetic field
dependent capacitance clearly indicate that this compound shows
magnetodielectric coupling at around 100 K. In addition, unusual behaviour is
observed in two polarization loop at room temperature and liquid nitrogen
temperature, where coercive field at liquid nitrogen temperature is larger than
room temperature. Further, $P$-$E$ loop at liquid nitrogen temperature with
different frequencies also affirm that the coercive field and remnant
polarization are firstly reduced (but very small value) but when frequency is
further increased to 15 Hz and 100 Hz, both of them are enhanced. Therefore, a
transition is observed at around 15 Hz in frequency dependent $P_r$ and $E_C$
curve, which may be usually attributed to the generalized pinning and depinning
of the dislocation arrays to polarization.",2106.15938v1
2021-08-01,A universal model for the formation energy prediction of inorganic compounds,"Harnessing the recent advance in data science and materials science, it is
feasible today to build predictive models for materials properties. In this
study, we employ the data of high-throughput quantum mechanics calculations
based on 170,714 inorganic crystalline compounds to train a machine learning
model for formation energy prediction. Different from the previous work, our
model reaches a fairly good predictive ability (R2=0.982 and MAE=0.07 eVatom-1,
DenseNet model) and meanwhile can be universally applied to the large phase
space of inorganic materials. The improvement comes from several effective
structure-dependent descriptors that are proposed to take the information of
electronegativity and structure into account. This model can provide a useful
tool to search for new materials in a vast phase space in a fast and
cost-effective manner.",2108.00349v1
2021-08-09,ChemiRise: a data-driven retrosynthesis engine,"We have developed an end-to-end, retrosynthesis system, named ChemiRise, that
can propose complete retrosynthesis routes for organic compounds rapidly and
reliably. The system was trained on a processed patent database of over 3
million organic reactions. Experimental reactions were atom-mapped, clustered,
and extracted into reaction templates. We then trained a graph convolutional
neural network-based one-step reaction proposer using template embeddings and
developed a guiding algorithm on the directed acyclic graph (DAG) of chemical
compounds to find the best candidate to explore. The atom-mapping algorithm and
the one-step reaction proposer were benchmarked against previous studies and
showed better results. The final product was demonstrated by retrosynthesis
routes reviewed and rated by human experts, showing satisfying functionality
and a potential productivity boost in real-life use cases.",2108.04682v1
2021-08-17,"Hexagonal-to-base-centered-orthorhombic $4Q$ charge density wave order in kagome metals KV$_3$Sb$_5$, RbV$_3$Sb$_5$, and CsV$_3$Sb$_5$","I search for the ground state structures of the kagome metals KV$_3$Sb$_5$,
RbV$_3$Sb$_5$, and CsV$_3$Sb$_5$ using first principles calculations.
Group-theoretical analysis shows that there are seventeen different distortions
that are possible due to the phonon instabilities at the $M$
$(\frac{1}{2},0,0)$ and $L$ $(\frac{1}{2},0,\frac{1}{2})$ points in the
Brilouin zone of the parent $P6/mmm$ phase of these materials. I generated
these structures for the three compounds and performed full structural
relaxations that minimize the atomic forces and lattice stresses. I find that
the $Fmmm$ phase with the order parameter $M_1^+$ $(a,0,0)$ $+$ $L_2^-$
$(0,b,b)$ has the lowest energy among these possibilities in all three
compounds. However, the $Fmmm$ exhibits a dynamical instability at its $Z$
$(0,0,1)$ point, which corresponds to the $A$ $(0,0,\frac{1}{2})$ point in the
parent $P6/mmm$ phase. Condensation of this instability leads to a
base-centered orthorhombic structure with the space group $Cmcm$ and $4Q$ order
parameter $M_1^+$ $(a,0,0)$ $+$ $L_2^-$ $(0,b,b)$ $+$ $A_6^+$
$(\frac{1}{2}c,\frac{-\sqrt{3}}{2}c)$.",2108.07784v1
2021-08-27,Identification of novel organic ferroelectrics: A study combining importance sampling with machine learning,"Recent advances in the synthesis of polar molecular materials have produced
practical alternatives to ferroelectric ceramics, opening up exciting new
avenues for their incorporation into modern electronic devices. However, in
order to realize the full potential of polar polymer and molecular crystals for
modern technological applications, it is paramount to assemble and evaluate all
the available data for such compounds, identifying descriptors that could be
associated with an emergence of ferroelectricity. In this work, we utilized
data-driven approaches to judiciously shortlist candidate materials from a wide
chemical space that could possess ferroelectric functionalities. An
importance-sampling based method was utilized to address the challenge of
having a limited amount of available data on already known organic
ferroelectrics. Sets of molecular- and crystal-level descriptors were combined
with a Random Forest Regression algorithm in order to predict spontaneous
polarization of the shortlisted compounds. First-principles simulations were
performed to further validate the predictions obtained from the machine
learning model.",2108.13206v3
2021-08-31,"Fermi surface nesting, vacancy ordering and the emergence of superconductivity in IrSb compounds","Fermi surface nesting, as a peculiar reciprocal space feature, is not only
closely correlated with the real space superstructure, but also directly
modulates the underlying electronic behavior. In this work, we elucidate the
Fermi surface nesting feature of the IrSb compound with
buckled-honeycomb-vacancy (BHV) ordering through Rh and Sn doping, and its
correlation with structure and electronic state evolution. The advantageous
substitution of atom sites (i.e., Rh on the Ir sites, Sn on the Sb sites,
respectively), rather than the direct occupation of vacancies, induces the
collapse of BHV order and the emergence of superconductivity. The distinct
superconducting behavior of Rh and Sn incorporated systems are ascribed to the
mismatch of Fermi surface nesting in the Sn case.",2108.13704v1
2021-09-09,Complex chiral columns made of achiral quinoxaline derivatives with semi-flexible cores,"Mesogenic materials, quinoxaline derivatives with semi-flexible cores, are
reported to form new type of 3D columnar structure with large crystallographic
unit cell and Fddd symmetry below columnar hexagonal phase. The 3D columnar
structure is a result of frustration imposed by arrangement of helical columns
of opposite chirality into triangular lattice. The studied materials exhibit
fluorescent properties that could be easily tuned by modification of molecular
structure, compounds with the extended {\pi} electron conjugated systems form
aggregates and fluorescence is quenched. For molecules with flexible structure
the fluorescence quantum yield reaches 25%. On the other hand, compounds with
more rigid mesogenic core, for which fluorescence is suppressed show strong
hole photocurrent. For some materials also bi-polar: hole and electron transfer
was observed.",2109.04263v1
2021-09-15,Definitive Detection of Orbital Angular Momentum States in Neutrons by Spin-polarized $^3$He,"A standard method to detect thermal neutrons is the nuclear interaction
$^3$He(n,p)$^3$H. The spin-dependence of this interaction is also the basis of
a neutron spin-polarization filter using nuclear polarized $^3$He. We consider
the corresponding interaction for neutrons placed in an intrinsic orbital
angular momentum (OAM) state. We derive the relative polarization-dependent
absorption cross-sections for neutrons in an $L=1$ OAM state. The absorption of
those neutrons results in compound states $J^\pi=0^-$, $1^-$, and $2^-$.
Varying the three available polarizations tests that an OAM neutron has been
absorbed and probes which decay states are physically possible. We describe the
energetically likely excited states of $^4$He after absorption, due to the fact
that the compound state has odd parity. This provides a definitive method for
detecting neutron OAM states and suggests that intrinsic OAM states offer the
possibility to observe new physics, including anomalous cross-sections and new
channels of radioactive decay.",2109.07454v1
2021-09-15,Exploring DFT$+U$ parameter space with a Bayesian calibration assisted by Markov chain Monte Carlo sampling,"Density-functional theory is widely used to predict the physical properties
of materials. However, it usually fails for strongly correlated materials. A
popular solution is to use the Hubbard corrections to treat strongly correlated
electronic states. Unfortunately, the exact values of the Hubbard $U$ and $J$
parameters are initially unknown, and they can vary from one material to
another. In this semi-empirical study, we explore the $U$ and $J$ parameter
space of a group of iron-based compounds to simultaneously improve the
prediction of physical properties (volume, magnetic moment, and bandgap). We
used a Bayesian calibration assisted by Markov chain Monte Carlo sampling for
three different exchange-correlation functionals (LDA, PBE, and PBEsol). We
found that LDA requires the largest $U$ correction. PBE has the smallest
standard deviation and its $U$ and $J$ parameters are the most transferable to
other iron-based compounds. Lastly, PBE predicts lattice parameters reasonably
well without the Hubbard correction.",2109.07617v1
2021-09-21,Improving the Silicon Interactions of GFN-xTB,"A general-purpose Density Functional Tight Binding method, the GFN-xTB model
is gaining increased popularity in accurate simulations that are out of scope
for conventional ab initio formalisms. We show that in its original GFN1-xTB
parametrization, organosilicon compounds are described poorly. This issue is
addressed by re-fitting the model's silicon parameters to a data set of ten
thousand reference compounds, geometry-optimized with the revPBE functional.
The resulting GFN1-xTB-Si parametrization shows improved accuracy in the
prediction of system energies, nuclear forces and geometries and should be
considered for all applications of the GFN-xTB Hamiltonian to systems that
contain silicon.",2109.10416v1
2021-10-05,Revealing a charge-density-wave gap in the predicted weak topological insulator HoSbTe,"HoSbTe was predicted to be a weak topological insulator, whose spin-orbit
coupling (SOC) gaps are reported to be as large as hundreds of meV. Utilizing
infrared spectroscopy, we find that the compound is of metallic nature from 350
K down to 10 K. Particularly, both of its itinerant carrier density and
scattering rate are demonstrated to decrease with temperature cooling, which is
responsible for the appearance of a broad hump feature in the temperature
dependent resistivity around 200 K. More importantly, we reveal the appearance
of a charge density wave (CDW) gap in addition to the SOC related gap. The
energy scale of the CDW gap is identified to be 364 meV at 10 K, which shift to
252 meV at 350 K. The coexistence of CDW and SOC gaps in the same compound
paves a new avenue to explore more intriguing physics.",2110.02184v1
2021-10-05,Experimental study of transport properties of Weyl semimetal LaAlGe thin films grown by molecular beam epitaxy,"Rare earth compounds display diverse electronic, magnetic, and
magneto-transport properties. Recently these compounds of the type RAlGe (R =
La, Ce, Pr) have been shown to exhibit Weyl semimetallic behavior. In this
work, we have investigated the crystal structure, electronic, and
magneto-transport properties of the Weyl semimetal LaAlGe thin films grown by
molecular beam epitaxy. The temperature dependence of longitudinal resistivity
at different magnetic fields is discussed. Observations of magnetoresistances
and Hall effect at different temperatures and their evolution with magnetic
field up to 6 T are also discussed with relevant mechanisms. We have observed
positive unsaturated magnetoresistances, with a small quadratic contribution at
low temperatures, which tends to saturate at higher fields. The Hall
measurements confirm the electron-dominated semimetallic conduction with an
average charge carrier density of ~ 9.68*10^21 cm^(-3) at room temperature.",2110.02322v1
2021-10-13,General Compound Hawkes Processes for Mid-Price Prediction,"High frequency financial data is burdened by a level of randomness that is
unavoidable and obfuscates the task of modelling. This idea is reflected in the
intraday evolution of limit orders book data for many financial assets and
suggests several justifications for the use of stochastic models. For instance,
the arbitrary distribution of inter arrival times and the subsequent dependence
structure between consecutive book events. This has lead to the development of
many stochastic models for the dynamics of limit order books. In this paper we
look to examine the adaptability of one family of such models, the General
Compound Hawkes Process (GCHP) models, to new data and new tasks. We further
focus on the prediction problem for the mid-price within a limit order book and
the practical applications of these stochastic models, which is the main
contribution of this paper. To this end we examine the use of the GCHP for
predicting the direction and volatility of futures and stock data and discuss
possible extensions of the model to help improve its predictive capabilities.",2110.07075v1
2021-10-20,"Type-II Nodal Line Fermions in New Z2 Topological Semimetals AV6Sb6 (A=K, Rb,and Cs) with Kagome Bilayer","The recently discovered layered kagome metals AV3Sb5 (A=K, Rb, and Cs)
attract intensive interest due to their intertwining with superconductivity,
charge-density-wave state, and nontrivial band topology. In this work, we show
by first-principles calculations and symmetry arguments that unconventional
type-II Dirac nodal line fermions close to the fermi level are present in
another latest class of experimentally synthesized kagome compounds AV6Sb6
(A=K, Rb, and Cs). These compounds possess a unique kagome (V3Sb)2 bilayer that
dominates their electronic and topological properties, instead of the kagome
V3Sb monolayer in AV3Sb5. Crystal symmetry guarantees that the type-II Dirac
nodal lines with quantized Berry phase lie in reflection-invariant planes of
the Brillouin zone. We further reveal that the type-II Dirac nodal lines remain
nearly intact in the presence of spin-orbital coupling and can be categorized
as a Z2 classification. The findings establish AV6Sb6 as a class of new
fascinating prototypes, which will extend the knowledge of interplay between
unconventionally topological fermions and exotic quantum ordered states in
kagome systems.",2110.10359v1
2021-10-21,Convex Joint Graph Matching and Clustering via Semidefinite Relaxations,"This paper proposes a new algorithm for simultaneous graph matching and
clustering. For the first time in the literature, these two problems are solved
jointly and synergetically without relying on any training data, which brings
advantages for identifying similar arbitrary objects in compound 3D scenes and
matching them. For joint reasoning, we first rephrase graph matching as a rigid
point set registration problem operating on spectral graph embeddings.
Consequently, we utilise efficient convex semidefinite program relaxations for
aligning points in Hilbert spaces and add coupling constraints to model the
mutual dependency and exploit synergies between both tasks. We outperform state
of the art in challenging cases with non-perfectly matching and noisy graphs,
and we show successful applications on real compound scenes with multiple 3D
elements. Our source code and data are publicly available.",2110.11335v1
2021-10-24,Oscillations in Modified Combinants of Hadronic Multiplicity Distributions,"Oscillations in modified combinants ($C_j$s) have been of interest to
multiparticle production mechanisms since the 1990s. Recently, there has been a
discussion on how these oscillations can be reproduced by compounding a
binomial distribution with a negative binomial distribution. In this work, we
explore a stochastic branching model based on a simple interaction term
$\lambda\overline{\psi}\phi\psi$ for partons and propose a hadronization scheme
to arrive at the final multiplicity distribution. We study the effects that
compounding our model with a binomial distribution has on $C_j$s and explore
its physical implications. We find that there is a significant difference in
the oscillations in $C_j$s between high energy $pp$ and $p\bar{p}$ scattering
that our model can reproduce.",2110.12409v1
2021-10-25,Anomalous thermoelectric effects and quantum oscillations in the kagome metal CsV$_3$Sb$_5$,"The kagome metal compounds $A$V$_3$Sb$_5$ ($A$ = K, Rb, and Cs) feature a
wealth of phenomena including nontrivial band topology, charge density wave
(CDW), and superconductivity. One intriguing property is the time-reversal
symmetry breaking in the CDW state without local moments, which leads to
anomalous transport responses. Here, we report the investigation of
magneto-thermoelectric effects on high-quality CsV$_3$Sb$_5$ single crystals. A
large anomalous Nernst effect is observed at temperatures below 30 K. Multiple
Fermi surfaces with small effective masses are revealed by quantum oscillations
in Nernst and Seebeck signals under high magnetic field. Furthermore, we find
an unknown frequency, and attribute it to the magnetic breakdown across two
smaller Fermi surfaces. A gap around 20 meV can be resolved from the breakdown
threshold field, which we propose to be introduced by the CDW. These results
shed new light on the CDW-related phenomena, particularly in $A$V$_3$Sb$_5$
compounds.",2110.13085v2
2021-10-26,Topological phase transitions in strongly correlated systems: application to Co$_3$Sn$_2$S$_2$,"The topological transition in the strongly correlated half-metallic
ferromagnetic compound Co$_3$Sn$_2$S$_2$ from Weyl semimetal (including chiral
massless fermions) to a non-magnetic state is treated. This transition goes
with a change in topological invariant, and is accompanied by a non-topological
transition from saturated ferromagnetic to paramagnetic state, the minority
Fermi surface being transformed from ghost (hidden) to real. A corresponding
description is given in terms of slave fermion representation for the effective
narrow-band Hubbard model. The system Co$_3$Sn$_2$S$_2$ provides a bright
example of coexistence of non-trivial topology and strong low-dimensional
ferromagnetism. A comparison is performed with other compounds where
frustrations result in formation of a correlated paramagnetic state.",2110.13709v1
2021-10-29,Droplet-superfluid compounds in binary bosonic mixtures,"While quantum fluctuations in binary mixtures of bosonic atoms with
short-range interactions can lead to the formation of a self-bound droplet, for
equal intra-component interactions but an unequal number of atoms in the two
components, there is an excess part that cannot bind to the droplet. Imposing
confinement, as here through periodic boundary conditions in a one-dimensional
setting, the droplet becomes amalgamated with a residual condensate. The
rotational properties of this compound system reveal simultaneous rigid-body
and superfluid behavior in the ground state and uncover that the residual
condensate can carry angular momentum even in the absence of vorticity. In
contradiction to the intuitive idea that the superfluid fraction of the system
would be entirely made up of the excess atoms not bound by the droplet, we find
evidence that this fraction is higher than what one would expect in such a
picture. Our findings are corroborated by an analysis of the elementary
excitations in the system, and shed new light on the coexistence of
localization and superfluidity.",2110.15675v1
2021-10-29,Granule Description based on Compound Concepts,"Concise granule descriptions for definable granules and approaching
descriptions for indefinable granules are challenging and important issues in
granular computing. The concept with only common attributes has been
intensively studied. To investigate the granules with some special needs, we
propose a novel type of compound concepts in this paper, i.e.,
common-and-necessary concept. Based on the definitions of concept-forming
operations, the logical formulas are derived for each of the following types of
concepts: formal concept, object-induced three-way concept, object oriented
concept and common-and-necessary concept. Furthermore, by utilizing the logical
relationship among various concepts, we have derived concise and unified
equivalent conditions for definable granules and approaching descriptions for
indefinable granules for all four kinds of concepts.",2111.00004v2
2021-11-01,Sr$_3$LiIrO$_6$: a potential quantum spin liquid candidate in the one dimensional $d^4$ iridate family,"Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary
magnetic and electronic properties in otherwise `ordinary pool' of heavy ion
oxides. Here we present a detailed study on an apparently isolated hexagonal
2$H$ spin-chain $d^4$ iridate Sr$_3$LiIrO$_6$ (SLIO) with geometric
frustration. Our structural studies clearly reveal perfect Li-Ir chemical order
in this compound. Our combined experimental and {\it ab-initio} electronic
structure investigations establish a magnetic ground state with finite
Ir$^{5+}$ magnetic moments in this compound, contrary to the anticipated
nonmagnetic $J$=0 state. Furthermore, the dc magnetic susceptibility ($\chi$),
heat capacity ($C_p$) and spin-polarized density functional theory (DFT)
studies unravel that despite having noticeable antiferromagnetic correlation
among the Ir$^{5+}$ local moments, this SLIO system evades any kind of magnetic
ordering down to at least 2 K due to geometrical frustration, arising from the
comparable interchain Ir-O-O-Ir superexchange interaction strengths, hence
promoting SLIO as a potential quantum spin liquid candidate.",2111.00925v1
2021-11-02,Floquet engineering of Kitaev quantum magnets,"In recent years, there has been an intense search for materials realizing the
Kitaev quantum spin liquid model. A number of edge-shared compounds with strong
spin-orbit coupling, such as RuCl$_3$ and iridates, have been proposed to
realize this model. Nevertheless, an effective spin Hamiltonian derived from
the microscopic model relevant to these compounds generally contains terms that
are antagonistic toward the quantum spin liquid. This is consistent with the
fact the zero magnetic field ground state of these materials is generally
magnetically ordered. It is a pressing issue to identify protocols to drive the
system to the limit of the Kitaev quantum spin model. In this work, we propose
Floquet engineering of these Kitaev quantum magnets by coupling materials to a
circularly polarized laser. We demonstrate that all the magnetic interactions
can be tuned in situ by the amplitude and frequency of the laser, hence
providing a route to stabilize the Kitaev quantum spin liquid phase.",2111.01316v1
2021-11-03,NaZnF3 as a low-pressure analogue of MgSiO3,"Solid-state systems whose properties at high pressure (exceeding 1 GPa) mimic
those of MgSiO3 are of large importance in the study of the interior of
planets. By means of Density Functional Theory (DFT) calculations we studied
the high pressure properties of a MgSiO3 analogue, NaZnF3. We reproduce the
phase-transition sequence previously reported for this compound (GdFeO3 ->
CaIrO3 -> La2S3), and predict that it should undergo a two-step dissociation:
decomposition into a equimolar mixture of Na2ZnF4 and NaZn2F5 at 25.4 GPa,
followed by a breakdown into ZnF2 and NaF at 66.8 GPa. These processes are
analogous to those predicted for compressed MgSiO3. Moreover, both Na2ZnF4 and
NaZn2F5 are isostructural with analogous phases from the Mg-Si-O system. We
also find that both these novel compounds are thermodynamically stable at
ambient conditions (Na2ZnF4) or at low pressure of 19 GPa (NaZn2F5). Our study
indicates that NaZnF3 could serve as a good low-pressure analogue of MgSiO3
exhibiting the same sequence of phase transitions, and pressure induced
decomposition, but at pressures an order of magnitude lower.",2111.02270v1
2021-11-06,A probabilistic formalization of contextual bias in forensic analysis: Evidence that examiner bias leads to systemic bias in the criminal justice system,"Although researchers have found evidence contextual bias in forensic science,
the discussion of contextual bias is currently qualitative. We formalize years
of empirical research and extend this research by showing quantitatively how
biases can be propagated throughout the legal system, all the way up to the
final determination of guilt in a criminal trial. We provide a probabilistic
framework for describing how information is updated in a forensic analysis
setting by using the ratio form of Bayes' rule. We analyze results from
empirical studies using our framework and use simulations to demonstrate how
bias can be compounded where experiments do not exist. We find that even minor
biases in the earlier stages of forensic analysis lead to large, compounded
biases in the final determination of guilt in a criminal trial.",2111.03762v1
2021-11-10,$μ$SR study of unconventional pairing symmetry in the quasi-1D Na$_2$Cr$_3$As$_3$ superconductor,"We report the finding of a novel pairing state in a newly discovered
superconductor Na$_2$Cr$_3$As$_3$. This material has a noncentrosymmetric
quasi-one-dimensional crystal structure and is superconducting at
$T_{\mathrm{C}}\sim$ 8.0 K. We find that the magnetic penetration depth data
suggests the presence of a nodal line $p_z$-wave pairing state with zero
magnetic moment using transverse-field muon-spin rotation (TF-$\mu$SR)
measurements. The nodal gap observed in Na$_2$Cr$_3$As$_3$ compound is
consistent with that observed in isostructural (K,Cs)$_2$Cr$_3$As$_3$ compounds
using TF-$\mu$SR measurements. The observed pairing state is consistent with a
three-band model spin-fluctuation calculation, which reveals the $S_z=0$
spin-triplet pairing state with the $\sin k_z$ pairing symmetry. The
long-sought search for chiral superconductivity with topological applications
could be aided by such a novel triplet $S_z=0$ $p$-wave pairing state.",2111.05492v1
2021-11-12,"Catastrophe, Compounding & Consistency in Choice","Conditional value-at-risk (CVaR) precisely characterizes the influence that
rare, catastrophic events can exert over decisions. Such characterizations are
important for both normal decision-making and for psychiatric conditions such
as anxiety disorders -- especially for sequences of decisions that might
ultimately lead to disaster. CVaR, like other well-founded risk measures,
compounds in complex ways over such sequences -- and we recently formalized
three structurally different forms in which risk either averages out or
multiplies. Unfortunately, existing cognitive tasks fail to discriminate these
approaches well; here, we provide examples that highlight their unique
characteristics, and make formal links to temporal discounting for the two of
the approaches that are time consistent. These examples can ground future
experiments with the broader aim of characterizing risk attitudes, especially
for longer horizon problems and in psychopathological populations.",2111.06804v1
2021-11-17,Shifted Brownian Fluctuation Game,"This article analyzes the behavior of a Brownian fluctuation process under a
mixed strategic game setup. A variant of a compound Brownian motion has been
newly proposed, which is called the Shifted Brownian Fluctuation Process to
predict the turning points of a stochastic process. This compound process
evolves until it reaches one step prior to the turning point. The Shifted
Brownian Fluctuation Game has been constructed based on this new process to
find the optimal moment of actions. Analytically tractable results are obtained
by using the fluctuation theory and the mixed strategy game theory. The joint
functional of the Shifted Brownian Fluctuation Process is targeted for
transformation of the first passage time and its index. These results enable us
to predict the moment of a turning point and the moment of actions to obtain
the optimal payoffs of a game. This research adapts the theoretical framework
to implement an autonomous trader for value assets including stocks and
cybercurrencies.",2111.09311v2
2021-11-18,Interplay between quadrupolar and magnetic interactions in 5$d^{1}$ double perovskite Ba$_2$MgReO$_6$ under pressure,"We measured the electrical resistivity, AC magnetic susceptibility, and
specific heat of the cubic double perovskite Ba$_2$MgReO$_6$ under pressure.
The application of pressure leads to a gradual increase in the transition
temperature to the canted antiferromagnetic order, while the quadrupolar order
is suppressed above 5 GPa, at which a collinear antiferromagnetic state
appears. The obtained unit cell volume-temperature phase diagram for the
compound as well as the related compounds suggests that Ba$_2$MgReO$_6$ exists
near the phase boundary between the noncollinear and the collinear
antiferromagnetic order with multipole decrees of freedom.",2111.09661v1
2021-11-22,Pressure induced phase transitions in Sm-doped BiFeO3 in the morphotropic phase boundary,"Sm-doped BiFeO3 compacted powders with composition across the morphotropic
phase boundary region were prepared by sol-gel method. Crystal structure,
morphology and magnetic state of the compounds were analyzed as a function of
dopant concentration, temperature and external pressure using synchrotron and
laboratory X-ray diffraction, electron microscopy, Raman and Mossbauer
spectroscopy. Application of external pressure shifts the phase transition from
the rhombohedral structure to the nonpolar orthorhombic structure towards lower
concentration of the dopant content, wherein the amount of the anti-polar
orthorhombic phase notably decreases. Raman and Mossbauer spectroscopy data
provides additional information about the structural distortion on local scale
level which testifies faster formation of nonpolar orthorhombic phase and
associated modification in the magnetic state in the compounds subjected to
high pressure. Temperature increase leads to the structural transition to the
nonpolar orthorhombic phase regardless the structural state at room
temperature; furthermore, application of external pressure decreases the phase
transition temperature.",2111.11167v1
2021-11-24,"Improvement of upper critical field by the compositionally-complex-alloy concept in A15 superconductor V3X (X: Al, Si, Ga, Ge, Sn)","Compositionally complex alloys (CCAs) are a new category of high-entropy
materials containing more than two high-entropy phases in an alloy sample. We
applied the concept of CCA to a A15-type compound superconductor V3X where X
site is occupied by Al, Si, Ga, Ge, and Sn. The V3X sample shows bulk
superconductivity with a transition temperature (Tc) of 6.4 K, which is close
to the Tc of V3Ge. The upper critical field (Bc2(0)) of V3X estimated from
magnetic susceptibility is 8.8 T, which is ~50% higher than that of V3Ge
(Bc2(0) = 5.8 T). The presence of at least five different A15 phases with high
configurational entropy of mixing were revealed. We consider that the examined
V3X sample is an example system of CCA-type superconducting intermetallic
compound.",2111.12391v1
2021-11-29,Andreev reflection spectroscopy on SnAs single crystals,"Binary compounds of SnT family(T= As, Sb, Te, S, Se, P) exhibit novel
properties like superconductivity, topologically protected states etc. Some of
these compounds crystallize in NaCl type structure or in layered structure,
both of which are considered potentially important for
high-temperature/unconventional superconductivity. It was previously shown that
K-doped BaBiO$_3$ with NaCl type structure exhibits superconducting state below
$\sim$ 30 K. SnAs has crystallographic configuration that is exactly similar to
K-doped BaBiO$_3$ and this warrants for the investigation of superconductivity
in this material. Previously it was reported that SnAs exhibits weakly coupled
type I superconductivity with an energy gap of 0.7 meV. Recently, the
electronic bandstructure calculations has hinted to the existence of possible
topologically protected states in SnAs. This has motivated us to investigate
the superconducting nature of SnAs using point contact Andreev reflection
spectroscopy. Our investigation revealed that superconductivity in SnAs can be
well explained within the BCS framework in the weak coupling limit.",2111.14425v1
2021-12-01,Giant topological Hall effect in centrosymmetric tetragonal Mn2-xZnxSb,"Topological magnetism typically appears in noncentrosymmetric compounds or
compounds with geometric frustration. Here we report the effective tuning of
magnetism in centrosymmetric tetragonal Mn2-xZnxSb by Zn substitution. The
magnetism is found to be closely coupled to the transport properties, giving
rise to to a very large topological hall effect is possibly associated with
topological magnetism. Our finding suggests Mn2-xZnxSb is a candidate material
for the centrosymmetric tetragonal topological magnetic system, offers
opportunities for studying and tuning spin textures and developing near room
temperature spin-based devices.",2112.00805v1
2021-12-02,Sample-Efficient Generation of Novel Photo-acid Generator Molecules using a Deep Generative Model,"Photo-acid generators (PAGs) are compounds that release acids ($H^+$ ions)
when exposed to light. These compounds are critical components of the
photolithography processes that are used in the manufacture of semiconductor
logic and memory chips. The exponential increase in the demand for
semiconductors has highlighted the need for discovering novel photo-acid
generators. While de novo molecule design using deep generative models has been
widely employed for drug discovery and material design, its application to the
creation of novel photo-acid generators poses several unique challenges, such
as lack of property labels. In this paper, we highlight these challenges and
propose a generative modeling approach that utilizes conditional generation
from a pre-trained deep autoencoder and expert-in-the-loop techniques. The
validity of the proposed approach was evaluated with the help of subject matter
experts, indicating the promise of such an approach for applications beyond the
creation of novel photo-acid generators.",2112.01625v1
2021-12-04,Stage Conscious Attention Network (SCAN) : A Demonstration-Conditioned Policy for Few-Shot Imitation,"In few-shot imitation learning (FSIL), using behavioral cloning (BC) to solve
unseen tasks with few expert demonstrations becomes a popular research
direction. The following capabilities are essential in robotics applications:
(1) Behaving in compound tasks that contain multiple stages. (2) Retrieving
knowledge from few length-variant and misalignment demonstrations. (3) Learning
from a different expert. No previous work can achieve these abilities at the
same time. In this work, we conduct FSIL problem under the union of above
settings and introduce a novel stage conscious attention network (SCAN) to
retrieve knowledge from few demonstrations simultaneously. SCAN uses an
attention module to identify each stage in length-variant demonstrations.
Moreover, it is designed under demonstration-conditioned policy that learns the
relationship between experts and agents. Experiment results show that SCAN can
learn from different experts without fine-tuning and outperform baselines in
complicated compound tasks with explainable visualization.",2112.02278v1
2021-12-06,Randomness and Frustration in a S = 1/2 Square-Lattice Heisenberg Antiferromagnet,"We explore the interplay between randomness and magnetic frustration in the
series of $S = 1/2$ Heisenberg square-lattice compounds
Sr$_2$CuTe$_{1-x}$W$_x$O$_6$. Substituting W for Te alters the magnetic
interactions dramatically, from strongly nearest-neighbor to
next-nearest-neighbor antiferromagnetic coupling. We perform neutron scattering
measurements to probe the magnetic ground state and excitations over a range of
$x$. We propose a bond-disorder model that reproduces ground states with only
short-ranged spin correlations in the mixed compounds. The calculated neutron
diffraction patterns and powder spectra agree well with the measured data and
allow detailed predictions for future measurements. We conclude that quenched
randomness plays the major role in defining the physics of
Sr$_2$CuTe$_{1-x}$W$_x$O$_6$ with frustration being less significant.",2112.03312v4
2021-12-07,"Crossover from nematic to magnetic low-temperature ground state in Fe(Se,Te) compounds","A comparative analysis of the properties of FeSe${}_{1-x}$Te${}_{x}$ crystals
in the range of x values of about 0.4 and pure FeSe crystals is presented. We
found that the anomaly in R (T) at the structural transition for the former
differs significantly from the corresponding anomaly for the latter. This
indicates a change in the type of the ground state in the studied compounds.
Within the framework of the crystal field model, this can be explained as a
consequence of a change in the distortion of the tetrahedral environment of
iron, which leads to a change in the positions of the energy levels within
$t_{2g}$ multiplet. Depending on the mutual position of the degenerate xz and
yz levels and the xy level, the type of transition can change from orbital
ordering to magnetic ordering.",2112.03956v1
2021-12-08,Field-Effect Transistor Based on MoSi$_2$N$_4$ and WSi$_2$N$_4$ Monolayers Under Biaxial Strain: A Computational Study of the Electronic Properties,"The electronic properties of a field-effect transistor with two different
structures of MoSi$_2$N$_4$ and WSi$_2$N$_4$ monolayers as the channel material
in the presence of biaxial strain are investigated. The band structures show
that these compounds are semiconductors with an indirect bandgap. Their band
gaps can be adjusted by applying in-plane biaxial strain. In the following, the
variation of the energies of the valleys and corresponding effective masses
with respect to the strain are explored. Finally, the strained MoSi$_2$N$_4$ or
WSi$_2$N$_4$ are used as the channel of a p-type FET and the corresponding
current-voltage characteristic is explored. The results show this FET has an
I$\mathrm{_{ON}}$/I$\mathrm{_{OFF}}$ ratio larger than $\mathrm{10^6}$ and
subthreshold swing in the range of 96-98 mV/dec. The
I$\mathrm{_{ON}}$/I$\mathrm{_{OFF}}$ ratio of these compounds with respect to
strain are compared.",2112.04171v1
2021-12-09,Sign-Free Determinant Quantum Monte Carlo Study of Excitonic Density Orders in a Two-Orbital Hubbard-Kanamori Model,"While excitonic instabilities in multiorbital systems recently have come
under scrutiny in a variety of transition-metal compounds, understanding
emergence of these instabilities from strong electronic interactions has
remained a challenge. Here, we present a sign-problem-free determinant quantum
Monte Carlo study of excitonic density orders in a half-filled two-orbital
Hubbard-Kanamori model with broken orbital degeneracy, which accounts for the
role of Hund's coupling in transition-metal compounds. For strong inverted
(negative) Hund's exchange, we find numerical evidence for the emergence of
excitonic density order, with competition between anti-ferro-orbital order and
$\mathbf{Q} = (\pi,\pi)$ excitonic density order as a function of orbital
splitting and Hund's coupling. While inverted Hund's coupling stabilizes a
spin-singlet excitonic density phase for weak orbital splitting, positive
Hund's coupling favors a spin-triplet excitonic density phase.",2112.04718v1
2021-12-20,Bad topological semimetals in layered honeycomb compounds,"The Mott transition in honeycomb compounds with significant spin-orbit
coupling is explored. At finite temperatures we identify a novel semimetallic
phase located between a topological insulator and a topological Mott insulator.
This semimetal is characterized by having no charge gap, no quasiparticles and
gapped spin excitations with non-trivial topological properties. While charge
conduction is incoherent involving mean-free paths violating the
Mott-Ioffe-Regel limit, spin excitations can be transported ballistically along
the edges giving rise to a quantized spin conductance. Such bad topological
semimetal could be searched for close to the Mott transition in certain twisted
bilayers of transition metal dicalchogenides.",2112.10455v2
2021-12-20,Ligand-metal covalency effects in resonance enhanced x-ray Bragg diffraction,"Chlorine covalently bonded to an open shell metal is present in many
materials with desirable or intriguing physical properties. Materials include
highly luminescent nontoxic alternatives to lead halide perovskites for
optoelectronic applications K2CuCl3 and Rb2CuCl3, enantiomorphic CsCuCl3 that
presents magneto-chiral dichroism at a low temperature, and cubic K2RuCl6 that
possesses a singlet ground state generated by antiparallel spin and orbital
angular momenta. Structural chirality of CsCuCl3 has been confirmed by resonant
x-ray Bragg diffraction. We explore likely benefits of the technique at the
chlorine K-edge using a symmetry inspired method of calculation applied to
chlorine multipoles. Already, a low energy feature in corresponding x-ray
absorption spectra of many compounds has been related to the chlorine-metal
bond. Bragg diffraction from chlorine in cubic K2RuCl6 is treated in detail.
Diffraction patterns for rhombohedral compounds that present space-group
forbidden Bragg spots are found to be relatively simple.",2112.10723v1
2021-12-28,Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound NiTe$_2$O$_5$,"A $^{125}$Te nuclear magnetic resonance (NMR) study was carried out in the
paramagnetic state of the recently discovered quasi-one-dimensional spin-1
chain compound NiTe$_2$O$_5$. We observed that the $^{125}$Te NMR spectrum
splits into two in a magnetic field applied along the $c$ axis. Based on the
strong temperature variation of the relative intensity ratio of the split
lines, we infer that the line splitting arises from the two sublattice
susceptibilities induced in opposite directions along the chains. In great
support of this interpretation, a quantitative analysis of the spin-lattice
relaxation rate $T_1^{-1}$ and the Knight shift data unravels dominant
transverse spin fluctuations. We conclude that Ising-like uniaxial spin
correlations persist up to surprisingly high temperatures compared to the
exchange energy scales. Spin-charge coupling mechanism via a self-doping effect
may be important.",2112.13950v1
2021-12-28,"Nested Nonparametric Instrumental Variable Regression: Long Term, Mediated, and Time Varying Treatment Effects","Several causal parameters in short panel data models are scalar summaries of
a function called a nested nonparametric instrumental variable regression
(nested NPIV). Examples include long term, mediated, and time varying treatment
effects identified using proxy variables. However, it appears that no prior
estimators or guarantees for nested NPIV exist, preventing flexible estimation
and inference for these causal parameters. A major challenge is compounding ill
posedness due to the nested inverse problems. We analyze adversarial estimators
of nested NPIV, and provide sufficient conditions for efficient inference on
the causal parameter. Our nonasymptotic analysis has three salient features:
(i) introducing techniques that limit how ill posedness compounds; (ii)
accommodating neural networks, random forests, and reproducing kernel Hilbert
spaces; and (iii) extending to causal functions, e.g. long term heterogeneous
treatment effects. We measure long term heterogeneous treatment effects of
Project STAR and mediated proximal treatment effects of the Job Corps.",2112.14249v3
2022-01-10,Contrasting Magnetic Structures in SrLaCuSbO$_{6}$ and SrLaCuNbO$_{6}$: Spin-1/2 Quasi-Square-Lattice $J_1 {-} J_2$ Heisenberg Antiferromagnets,"We report the magnetic properties of the double perovskites SrLaCuSbO$_6$
(SLCSO) and SrLaCuNbO$_6$ (SLCNO). The temperature dependence of the magnetic
susceptibilities of both compounds shows a broad maximum characteristic of an
$S\,=\,1/2$ square lattice Heisenberg antiferromagnet. Magnetic ordering occurs
at $T_{\rm N}\,{=}\,13.6$ and 15.7 K for SLCSO and SLCNO, respectively. Neutron
powder diffraction measurements reveal contrasting spin structures in both
compounds. The spin structures of SLCSO and SLCNO below $T_{\rm N}$ are
N\'{e}el antiferromagnetic and collinear antiferromagnetic, respectively. This
result demonstrates that the nearest-neighbor interaction is dominant in SLCSO,
whereas the next-nearest-neighbor interaction is dominant in SLCNO. The
magnitude of the ordered moment was evaluated at 3.5 K to be
$m\,{=}\,0.39(3)\,\mu_{\rm B}$ for SLCSO and $0.37(1)\,\mu_{\rm B}$ for SLCNO,
which are significantly smaller than those calculated using linear spin wave
theory. We infer that the small ordered moment is caused by the effect of
exchange bond randomness arising from the site disorder of Sr and La ions.",2201.03232v1
2022-01-19,First-Order Antiferromagnetic Transition and Novel Gapless Excitation in a 4f Zigzag Chain Compound YbCuS2,"We report on the 63/65Cu-nuclear magnetic resonance and nuclear quadrupole
resonance (NQR) studies of trivalent Yb zigzag chain compound YbCuS2. Sharp NQR
signals were observed in the paramagnetic (PM) state. Below TO = 0.95 K, the
multi peaks induced by the internal magnetic fields arising from the
antferromagnetic (AFM) ordered moments appear and coexist with the PM signal
down to 0.85 K, evidencing the first-order AFM phase transition at TO. In
addition, the nuclear spin-lattice relaxation rate 1/T1 abruptly decreases
below TO and shows the T-linear behavior below 0.5 K. The significant large
1/T1T value strongly suggests the presence of the novel gapless spin excitation
in low temperature region.",2201.07563v1
2022-01-19,Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2,"The 12442 compounds are a recently discovered family of iron-based
superconductors, that share several features with the cuprates due to their
strongly anisotropic structure, but are so far poorly understood. Here, we
report on the gap structure and anisotropy of RbCa2(Fe1-xNix)4As4F2 single
crystals, investigated by a combination of directional point-contact
Andreev-reflection spectroscopy and coplanar waveguide resonator measurements.
Two gaps were identified, with clear signatures of d-wave-like nodal structures
which persist upon Ni doping, well described by a two-band d-d state with
symmetry-imposed nodes. A large London penetration depth anisotropy was
revealed, weakly dependent on temperature and fully compatible with the d-d
model.",2201.07593v1
2022-01-20,Emergent flat-band physics in $d^{9-δ}$ multilayer nickelates,"Recent experiments have shown that the reduced multilayer rare-earth (RE)
nickel oxides of form RE$_{p+1}$Ni$_p$O$_{2p+2}$ may belong to the novel family
of superconducting lanthanide nickelates. Here, the correlated electronic
structure of Pr$_{4}$Ni$_3$O$_{8}$ and Nd$_{6}$Ni$_5$O$_{12}$ is studied by
means of an advanced realistic many-body framework. It is revealed that the
low-energy physics of both systems is dominated by an interplay of
Ni-$d_{x^2-y^2}$ and Ni-$d_{z^2}$ degrees of freedom. Whilst the
Ni-$d_{x^2-y^2}$ orbitals are always highly correlated near an
(orbital-selective) Mott-insulating regime, the Ni-$d_{z^2}$ orbitals give rise
to intriguing non-dispersive features. At low temperature, the Pr compound
still displays QP-like Ni-$d_{x^2-y^2}$-derived states at the Fermi level, but
the interacting fermiology of the Nd compound is outshined by an emergent
Ni-$d_{z^2}$-controlling flat band. These findings translate well to the
previous characterization of doped infinite-layer nickelates, and hence further
make the case for a mechanism of unconventional superconductivity which is
distinct from the one in high-$T_{\rm c}$ cuprates.",2201.08123v2
2022-01-25,Effective minimal model and unconventional spin-singlet pairing in Kagome superconductor CsV3Sb5,"Recently synthesized Kagome compounds AV$_3$Sb$_5$ attract great attention
due to the unusual coexistence of the topology, charge density wave and
superconductivity. In this {\it Letter}, based on the band structures for
CsV$_3$Sb$_5$ in pristine phase, we fit an effective 6-band model for the
low-energy processes; utilizing the random phase approximation (RPA) on the
effective minimal model, we obtain the momentum-resolved static spin
susceptibility attributing the spin-fluctuation pairing mechanism, we find that
the superconducting pairing strengths increase with the lift of the Coulomb
correlation, and the superconductive pairing symmetry is singlet, the gap
functions are antisymmetric with respect to the x-axis and the y-axis in the
intermediate to strong Coulomb correlated regime,indicating the unconventional
superconductivity in Kagome compounds AV$_3$Sb$_5$.",2201.10088v2
2022-01-25,Superconductivity and Antiferromagnetism in NdNiO$_2$ and CaCuO$_2$: A Cluster DMFT Study,"We perform a comparative $2 \times 2$ real space cluster DMFT study on
minimal models for NdNiO$_2$ and CaCuO$_2$ obtained from downfolding DFT
states, using a Nambu formalism that allows for both superconducting and
antiferromagnetic order. We produce a phase diagram in temperature and doping.
We find that for the nickelate, like the cuprate, the stoichiometric compound
is antiferromagnetic. We find superconductivity in a doping range bounded, with
a small coexistence region, by the onset of antiferromagnetism at low doping
and with transition temperature becoming immeasurably small at high doping.
Superconductivity emerges at around the same hole doping for both compounds,
but requires a larger deviation from half filling for the nickelate. Both
antiferromagnetic and superconducting order lead to a partial gapping of the
$d_{x^2-y^2}$ Fermi surface sheet. Our similar results for the cuprate and
nickelate suggest that nickelate superconductivity is cupratelike. We compare
our results to the experimental phase diagram.",2201.10481v1
2022-01-27,Ab-initio study of the electronic structure and magnetic properties of Ce$_2$Fe$_{17}$,"The Ce$_2$Fe$_{17}$ intermetallic compound has been studied intensely for
several decades; its low-temperature state is reported experimentally either as
ferromagnetic or antiferromagnetic by different authors, with a measured
ordering temperature ranging within a hundred Kelvin. The existing theoretical
investigations overestimate the experimental total magnetic moment of
Ce$_2$Fe$_{17}$ by 20-40 % and predict a ferromagnetic ground state. By means
of first-principle electronic structure calculations, we show that the total
magnetic moment of Ce$_2$Fe$_{17}$ can be reproduced within the Local Density
Approximation while functionals based on the Generalized Gradient Approximation
fail. Atomistic spin dynamics simulations are shown to capture the change in
the magnetic state of Ce$_2$Fe$_{17}$ with temperature, and closely replicate
the reported helical structure that appears in some of the experimental
investigations.",2201.11573v1
2022-04-05,Low-temperature thermal expansion of the topological material candidates $β$-PtBi$_2$ and $β$-Bi$_2$Pd,"We report on the low-temperature ($T <$ 120 K) thermal expansion of the
bismuth-based topological semimetal $\beta$-PtBi$_2$ and topological
superconductor $\beta$-Bi$_2$Pd candidates. The linear thermal-expansion
coefficient of tetragonal $\beta$-Bi$_2$Pd shows a pronounced anisotropy
between the $a$- and $c$-axis while the volume thermal-expansion coefficient
$\alpha_V$($\beta$-Bi$_2$Pd) is considerable larger than
$\alpha_V$($\beta$-PtBi$_2$). The coefficient $\alpha_V$($\beta$-PtBi$_2$)
nearly matches the experimental specific heat, from which a Debye temperature
$\theta_D =$ 199 K is obtained. On the other hand, $\alpha_V$($\beta$-Bi$_2$Pd)
reasonably fits the Debye model with $\theta_D =$ 138 K, extracted from the
low-temperature specific heat. An almost constant Gr\""uneisen parameter $\Gamma
\approx$ 2 is obtained for both compounds. No magnetostriction is observed in
any of both compounds up to $\mu_0 H =$ 16 T. We compare our results with other
Bi-based topological materials.",2204.02327v1
2022-04-07,"Imitating, Fast and Slow: Robust learning from demonstrations via decision-time planning","The goal of imitation learning is to mimic expert behavior from
demonstrations, without access to an explicit reward signal. A popular class of
approach infers the (unknown) reward function via inverse reinforcement
learning (IRL) followed by maximizing this reward function via reinforcement
learning (RL). The policies learned via these approaches are however very
brittle in practice and deteriorate quickly even with small test-time
perturbations due to compounding errors. We propose Imitation with Planning at
Test-time (IMPLANT), a new meta-algorithm for imitation learning that utilizes
decision-time planning to correct for compounding errors of any base imitation
policy. In contrast to existing approaches, we retain both the imitation policy
and the rewards model at decision-time, thereby benefiting from the learning
signal of the two components. Empirically, we demonstrate that IMPLANT
significantly outperforms benchmark imitation learning approaches on standard
control environments and excels at zero-shot generalization when subject to
challenging perturbations in test-time dynamics.",2204.03597v2
2022-04-11,Segmentation Network with Compound Loss Function for Hydatidiform Mole Hydrops Lesion Recognition,"Pathological morphology diagnosis is the standard diagnosis method of
hydatidiform mole. As a disease with malignant potential, the hydatidiform mole
section of hydrops lesions is an important basis for diagnosis. Due to
incomplete lesion development, early hydatidiform mole is difficult to
distinguish, resulting in a low accuracy of clinical diagnosis. As a remarkable
machine learning technology, image semantic segmentation networks have been
used in many medical image recognition tasks. We developed a hydatidiform mole
hydrops lesion segmentation model based on a novel loss function and training
method. The model consists of different networks that segment the section image
at the pixel and lesion levels. Our compound loss function assign weights to
the segmentation results of the two levels to calculate the loss. We then
propose a stagewise training method to combine the advantages of various loss
functions at different levels. We evaluate our method on a hydatidiform mole
hydrops dataset. Experiments show that the proposed model with our loss
function and training method has good recognition performance under different
segmentation metrics.",2204.04956v1
2022-04-12,"Dynamical stability and superconductivity of (Ce,La)H9 under high pressure","Recent experiments have shown that CeH9 and (Ce,La)H9 can be synthesized
under high pressure between 90-170GPa and become a superconductor with a high
value of superconducting critical temperature (Tc) between 100-200K. In this
work, we performed a theoretical study of a (Ce,La)H9 compound where the Ce:La
ratio is equal to 1. We used the density functional theory and the {\it ab
initio} molecular dynamics (AIMD) method. From the phonon dispersion, there
exist some unstable modes around the K-point phonons. Then, we performed AIMD
simulation at around 203K and found that the compound becomes stable. The
superconducting spectral function can be calculated. We found that $\lambda$ is
as high as 3.0 at 200GPa. By using Allen-Dynes-modified McMillan equation in
the strong coupling regime, we found that Tc = 87K at 200GPa.",2204.05708v1
2022-04-15,Full superconducting gap in the candidate topological superconductor In$_{1-x}$Pb$_x$Te for x = 0.2,"High-pressure synthesis techniques have allowed for the growth of samples on
the indium-rich side of (Pb,In)Te, which have increased superconducting
transition temperatures compared to lead-rich compounds. In this study we
present measurements of the temperature dependence of the London penetration
depth $\Delta \lambda(T)$ in the compound In$_{0.8}$Pb$_{0.2}$Te, which shows a
bulk $T_{c,onset}$ of $\sim4.75$ K. The results indicate fully gapped BCS-like
behavior, ruling out odd-parity, topologically nontrivial $A_{2u}$ pairing;
however, odd-parity $A_{1u}$ pairing is still possible. Critical field values
measured below 1 K and other superconducting parameters are also presented.",2204.07635v1
2022-04-19,Rapid screening of high-throughput ground state predictions,"High-through computational thermodynamic approaches are becoming an
increasingly popular tool to uncover novel compounds. However, traditional
methods tend to be limited to stability predictions of stoichiometric phases at
absolute zero. Such methods thus carry the risk of identifying an excess of
possible phases that do not survive to temperatures of practical relevance. We
demonstrate how the Calphad formalism, informed by simple first-principles
input can be simply used to overcome this problem at a low computational cost
and deliver quantitatively useful phase diagram predictions at all
temperatures. We illustrate the method by re-assessing prior compound formation
predictions and reconcile these findings with long-standing experimental
evidence to the contrary.",2204.08963v1
2022-04-21,Magnetic Couplings in Edge-Sharing High-Spin $d^7$ Compounds,"High-spin $d^7$ Co(II) compounds have recently been identified as possible
platforms for realising highly anisotropic and bond-dependent couplings
featured in quantum-compass models such as the celebrated Kitaev model. In
order to evaluate this potential, we consider all symmetry-allowed
contributions to the magnetic exchange for ideal edge-sharing bonds. Though a
combination of ab-initio and cluster many-body calculations we conclude that
bond-dependent couplings are generally suppressed in favor of Heisenberg
exchange for real materials. Consequences for several prominent materials
including Na$_2$Co$_2$TeO$_6$ and BaCo$_2$(AsO$_4$)$_2$ are discussed.",2204.09856v3
2022-04-23,Anisotropic terahertz optostriction in group-IV monochalcogenide compounds,"Terahertz (THz) technology is a cutting-edge scheme with various promising
applications, such as next generation telecommunication, non-destructive
evaluation, security check, and in-depth characterization, owing to their
sensitivity to material geometric change and good transparency. Even though
tremendous progresses have been made during the past decade, exploration the
mechanisms of THz-matter interaction microscopically is still in its infancy.
In this work, we use thermodynamic theory to show how THz illumination deforms
materials and use group-IV monochalcogenide compounds to illustrate it.
According to our first-principles density functional theory calculations, THz
light with intermediate intensity (~109 W/cm2) could yield elastic deformations
on the order of ~0.1%, depending on laser polarization direction. Large
anisotropic opto-mechanical responses are also revealed. Finally, we show that
such strain can be detected via measuring the layer-resolved shift current
under a probe light irradiation.",2204.11029v1
2022-04-26,Nematic fluctuations mediated superconductivity revealed by anisotropic strain in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"Anisotropic strain is an external field capable of selectively addressing the
role of nematic fluctuations in promoting superconductivity. We demonstrate
this using polarization-resolved elasto-Raman scattering to probe the evolution
of nematic fluctuations under strain in the normal and superconducting states
of the paradigmatic iron-based superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$.
In the non-superconducting parent compound BaFe$_2$As$_2$ we observe a
strain-induced suppression of the nematic susceptibility which follows the
expected behavior of an Ising order parameter under a symmetry breaking field.
For the superconducting compound, the suppression of the nematic susceptibility
correlates with the decrease of the superconducting critical temperature $T_c$.
Our results indicate a significant contribution of nematic fluctuations to
electron pairing and validate theoretical scenarios of enhanced $T_c$ near a
nematic quantum critical point.",2204.12213v2
2022-04-26,A class of count time series models uniting compound Poisson INAR and INGARCH models,"INAR (integer-valued autoregressive) and INGARCH (integer-valued GARCH)
models are among the most commonly employed approaches for count time series
modelling, but have been studied in largely distinct strands of literature. In
this paper, a new class of generalized integer-valued ARMA (GINARMA) models is
introduced which unifies a large number of compound Poisson INAR and INGARCH
processes. Its stochastic properties, including stationarity and geometric
ergodicity, are studied. Particular attention is given to a generalization of
the INAR($p$) model which parallels the extension of the INARCH(p) to the
INGARCH(p, q) model. For inference, we consider moment-based estimation and a
maximum likelihood inference scheme inspired by the forward algorithm. Models
from the proposed class have a natural interpretation as stochastic epidemic
processes, which throughout the article is used to illustrate our arguments. In
a case study, different instances of the class, including both established and
newly introduced models, are applied to weekly case numbers of measles and
mumps in Bavaria, Germany.",2204.12449v3
2022-04-25,Trainable Compound Activation Functions for Machine Learning,"Activation functions (AF) are necessary components of neural networks that
allow approximation of functions, but AFs in current use are usually simple
monotonically increasing functions. In this paper, we propose trainable
compound AF (TCA) composed of a sum of shifted and scaled simple AFs. TCAs
increase the effectiveness of networks with fewer parameters compared to added
layers. TCAs have a special interpretation in generative networks because they
effectively estimate the marginal distributions of each dimension of the data
using a mixture distribution, reducing modality and making linear dimension
reduction more effective. When used in restricted Boltzmann machines (RBMs),
they result in a novel type of RBM with mixture-based stochastic units.
Improved performance is demonstrated in experiments using RBMs, deep belief
networks (DBN), projected belief networks (PBN), and variational auto-encoders
(VAE).",2204.12920v1
2022-05-02,"Enhanced Seebeck coefficient through the magnetic fluctuations in Sr$_2$Ru$_{1-x}M_x$O$_4$ ($M = $ Co, Mn)","The layered perovskite Sr$_2$RuO$_4$ is a most intensively studied
superconductor, but its pairing mechanism, which is often coupled intimately
with magnetic fluctuations in correlated materials, is still an open question.
Here we present a systematic evolution of the Seebeck coefficient in Co- and
Mn-substituted Sr$_2$RuO$_4$ single crystals, in which ferromagnetic and
antiferromagnetic glassy states respectively emerge in proximity to the
superconducting phase of the parent compound. We find that the Seebeck
coefficient $S$ divided by temperature $T$, $S/T$, shows a maximum near
characteristic temperatures seen in the irreversible magnetization $M_{\rm ir}$
in both of the Co- and Mn-substituted crystals, demonstrating both of the
ferromagnetic and antiferromagnetic fluctuations to enhance the Seebeck
coefficient. Interestingly, $S/T$ increases with lowering temperature in the
parent compound, reminiscent of non-Fermi-liquid behavior, indicating an
essential role of coexisting ferromagnetic and antiferromagnetic fluctuations
for the itinerant electrons in Sr$_2$RuO$_4$.",2205.00599v2
2022-05-09,The Compound Information Bottleneck Outlook,"We formulate and analyze the compound information bottleneck programming. In
this problem, a Markov chain $ \mathsf{X} \rightarrow \mathsf{Y} \rightarrow
\mathsf{Z} $ is assumed with fixed marginal distributions
$\mathsf{P}_{\mathsf{X}}$ and $\mathsf{P}_{\mathsf{Y}}$, and the mutual
information between $ \mathsf{X} $ and $ \mathsf{Z} $ is sought to be maximized
over the choice of conditional probability of $\mathsf{Z}$ given $\mathsf{Y}$
from a given class, under the \textit{worst choice} of the joint probability of
the pair $(\mathsf{X},\mathsf{Y})$ from a different class. We consider several
classes based on extremes of: mutual information; minimal correlation; total
variation; and the relative entropy class. We provide values, bounds, and
various characterizations for specific instances of this problem: the binary
symmetric case, the scalar Gaussian case, the vector Gaussian case and the
symmetric modulo-additive case. Finally, for the general case, we propose a
Blahut-Arimoto type of alternating iterations algorithm to find a consistent
solution to this problem.",2205.04567v1
2022-05-10,The spontaneous exchange bias effect in La2-xCaxCoMnO6 series,"Structural, electronic and magnetic properties of polycrystalline
La2-xCaxCoMnO6 (0 $\leq$ x $\leq$ 0.75) compounds are investigated by x-ray
diffraction and magnetometry. All the samples have an orthorhombic structure
and show a slight decrease in the unit cell with Ca-doping.
Temperature-dependent magnetization measurements reveal a complex magnetic
behavior with two ferromagnetic transitions. These transitions are ascribed to
Co2+--Mn4+ and Co3+--Mn3+ couplings and suggest the presence of additional
antiferromagnetic couplings in these disordered compounds. Field-dependent
magnetization curves, measured after cooling the samples in a zero external
magnetic field, reveal the spontaneous exchange bias (SEB) effect for the
Ca-doped samples. The strengthening of the uncompensated magnetic coupling at
the interfaces, caused by the increased antiferromagnetic phase, explains the
increase of SEB with increasing the Ca-content.",2205.04772v1
2022-05-14,Modeling survival probabilities of superheavy nuclei at high excitations,"This work investigated the first-chance survival probabilities of highly
excited compound superheavy nuclei in the prospect of synthesizing new
superheavy elements. The main feature of our modelings is the adoption of
microscopic temperature dependent fission barriers in calculations of fission
rates. A simple derivation is demonstrated to elucidate the connection between
Bohr-Wheeler statistical model and imaginary free energy method, obtaining a
new formula for fission rates. The best modeling is chosen with respect to
reproducing the experimental fission probability of $^{210}$Po. Systematic
studies of fission and survival probabilities of No, Fl, Og, and $Z$=120
compound nuclei are performed. Results show large discrepancies by different
models for survival probabilities of superheavy nuclei although they are close
for $^{210}$Po. We see that the first-chance survival probabilities of $Z$=120
are comparable to that of Fl and Og.",2205.07080v1
2022-05-28,Pressure-induced mixed states caused by spin-elastic interactions during first-order spin phase transition in spin crossover compounds,"Recently, the possibility of exploiting the phenomenon of spin transition
(ST) has been intensively investigated, therefore, it is particularly important
to study the behavior of ST under various stimuli. Here, the shape and content
of the intermediate phase of ST in Hoffmann-like compounds [Fe(Fpz)2M(CN)4](M =
Pt, Pd) under external stimuli are studied. For this purpose, magnetic and
Raman spectroscopy measurements were carried out. In pressure-induced spin
transition (PIST), a mixture of high-spin and low-spin states appears, while in
temperature-induced spin transition (TIST), a homogeneous state occurs. The
first-order ST induced by pressure has a hysteresis, but is not abrupt.
Whereas, the temperature-induced spin transition at ambient pressure is
hysteretic and abrupt. To investigate this difference, we discuss using a
thermodynamic model that considers elastic interactions, showing that the slope
of the hysteresis loop is related to the appearance of internal pressure, which
is related to the difference in sample compressibility under high spin and low
spin states.",2205.14386v1
2022-05-31,Electronic band structure in pristine and Sulfur-doped Ta$_2$NiSe$_5$,"We present an angle-resolved photoemission study of the electronic band
structure of the excitonic insulator Ta$_2$NiSe$_5$, as well as its evolution
upon Sulfur doping. Our experimental data show that while the excitonic
insulating phase is still preserved at a Sulfur-doping level of 25$\%$, such
phase is heavily suppressed when there is a substantial amount, $\sim$ 50$\%$,
of S-doping at liquid nitrogen temperatures. Moreover, our photon
energy-dependent measurements reveal a clear three dimensionality of the
electronic structure, both in Ta$_2$NiSe$_5$ and Ta$_2$Ni(Se$_{1-x}$S$_x$)$_5$
($x=0.25, 0.50$) compounds. This suggests a reduction of electrical and thermal
conductivities, which might make these compounds less suitable for electronic
transport applications.",2205.15883v1
2022-06-01,Charge density wave and superconductivity in 6R-TaS2,"The layered transition metal dichalcogenide compounds 1T-TaS2 and 4H-TaS2 are
well known for their exotic properties, which include charge density wave,
superconductivity, Mott transition, etc., and lately quantum spin liquid. Here,
we report the magnetic, transport and transmission electron microscopy study of
the charge density wave and superconductivity in 6R-TaS2 which is a relatively
less studied polymorph of this dichalcogenide TaS2. Our high temperature
electron microscopy reveals multiple charge density wave transitions between
room temperature and 650K. Magnetization, and the electrical resistivity
measurements in the temperature range of 2-400 K reveal that 6R-TaS2 undergoes
a charge density wave transition around 305 K and is followed by a transition
to a superconducting state around 3.5 K. The low temperature specific heat
measurement exhibits anomaly associated with the superconducting transition
around 2.4 K. The estimated Ginzburg Landau parameter suggests that this
compound lies at the extreme limit of type-II superconductivity.",2206.00281v3
2022-06-03,Dust Formation in Astrophysical Environments: The Importance of Kinetics,"Astronomical observations and analysis of stardust isolated from meteorites
have revealed a highly diverse interstellar and circumstellar grain inventory,
including a wide range of amorphous materials and crystalline compounds
(silicates and carbon). This diversity reflects the wide range of stellar
sources injecting solids into the interstellar medium each with its own
physical characteristics such as density, temperature and elemental composition
and highlights the importance of kinetics rather than thermodynamics in the
formation of these compounds. Based upon the extensive literature on soot
formation in terrestrial settings, detailed kinetic pathways have been
identified for the formation of carbon dust in C-rich stellar ejecta. These
have been incorporated in astronomical models for these environments. In recent
years, the chemical routes in the nucleation of oxides and silicates have been
the focus of much astronomical research. These aspects of stardust formation
will be reviewed and lessons for dust formation in planetary atmospheres will
be drawn with the emphasis on the influence of kinetics on the characteristics
and structure of dust in these environments.",2206.01548v1
2022-06-08,A multiferroic two-dimensional electron gas,"Multiferroics are compounds in which at least two ferroic orders coexist -
typically (anti)ferromagnetism and ferroelectricity. While magnetic order can
arise in both insulating and conducting compounds, ferroelectricity is in
principle not allowed in metals although a few two-dimensional (semi)metals
were reported to behave as ferroelectrics. Yet, the combination with magnetic
order to realize multiferroic metals remains elusive. Here, by combining x-ray
spectroscopy and magnetotransport, we show the coexistence of ferroelectricity
and magnetism in an oxide-based two-dimensional electron gas (2DEG). The data
evidence a non-volatile switching of the polar displacements and of the
anomalous Hall effect by the polarization direction, demonstrating a
magnetoelectric coupling. Our findings provide new opportunities in quantum
matter stemming from the interplay between ferroelectricity, ferromagnetism and
Rashba spin-orbit coupling in a 2DEG.",2206.03843v1
2022-06-09,Identification of High-Dielectric Constant Compounds from Statistical Design,"The discovery of high-dielectric materials is crucial to increasing the
efficiency of electronic devices and batteries. Here, we report three
previously unexplored materials with very high dielectric constants (69 $<$
$\epsilon$ $<$ 101) and large band gaps (2.9$<$ $E_{\text{g}}$(eV) $<$ 5.5)
obtained by screening materials databases using statistical optimization
algorithms aided by artificial neural networks (ANN). Two of these new
dielectrics are mixed-anion compounds (Eu$_5$SiCl$_6$O$_4$ and HoClO), and are
shown to be thermodynamically stable against common semiconductors via
phase-diagram analysis. We also uncovered four other materials with relatively
large dielectric constants (20$<$$\epsilon$$<$40) and band gaps
(2.3$<$$E_{\text{g}}$(eV)$<$2.7). While the ANN training data is obtained from
Materials Project, the search-space consists of materials from Open Quantum
Materials Database (OQMD) - demonstrating a successful implementation of
cross-database materials design. Overall, we report dielectric properties of 17
materials calculated using ab-initio calculations, that were selected in our
design workflow. The dielectric materials with high dielectric properties
predicted in this work open up further experimental research opportunities.",2206.04750v1
2022-06-10,What Information is Necessary and Sufficient to Predict Materials Properties using Machine Learning?,"Conventional wisdom of materials modelling stipulates that both chemical
composition and crystal structure are integral in the prediction of physical
properties. However, recent developments challenge this by reporting accurate
property-prediction machine learning (ML) frameworks using composition alone
without knowledge of the local atomic environments or long-range order. To
probe this behavior, we conduct a systematic comparison of supervised ML models
built on composition only vs. composition plus structure features. Similar
performance for property prediction is found using both models for compounds
close to the thermodynamic convex hull. We hypothesize that composition embeds
structural information of ground-state structures in support of
composition-centric models for property prediction and inverse design of stable
compounds.",2206.04968v2
2022-06-13,Anisotropic Dzyaloshinskii-Moriya interaction protected by D2d crystal symmetry in two-dimensional ternary compounds,"Magnetic skyrmions, topologically protected chiral spin swirling
quasiparticles, have attracted great attention in fundamental physics and
applications. Recently, the discovery of two-dimensional (2D) van der Waals
(vdW) magnets has aroused great interest due to their appealing physical
properties. Moreover, both experimental and theoretical works have revealed
that isotropic Dzyaloshinskii Moriya interaction (DMI) can be achieved in 2D
magnets or ferromagnet-based heterostructures. However, 2D magnets with
anisotropic DMI haven't been reported yet. Here, via using first-principles
calculations, we unveil that anisotropic DMI protected by D2d crystal symmetry
can exist in 2D ternary compounds MCuX2. Interestingly, by using micromagnetic
simulations, we demonstrate that ferromagnetic (FM) antiskyrmions, FM bimerons,
antiferromagnetic (AFM) antiskyrmions and AFM bimerons can be realized in MCuX2
family. Our discovery opens up an avenue to creating antiskyrmions and bimerons
with anisotropic DMI protected by D2d crystal symmetry in 2D magnets.",2206.06050v1
2022-06-17,Na-intercalation compounds and Na-ion batteries,"The widely use of lithium-ion (Li-ion) batteries in various fields, from
portable products to large-scale energy storage systems, has revolutionized our
daily life. The 2019 Nobel Prize in Chemistry has been awarded to John B.
Goodenough, M. Stanley Whittingham, and Akira Yoshino for their contributions
in developing Li-ion batteries. Although Li-ion batteries are currently
on-growing research topics, lithium availability is still a problem for mass
production. In contrast to lithium, sodium resources are almost unlimited on
Earth, and sodium is one of the most abundant elements in the Earth's crust.
Hence, sodium-ion (Na-ion) batteries as a counterpart of Li-ion batteries have
the potential to serve as the next-generation batteries. In this work, a brief
history and recent development of Na-ion batteries are described. The
fundamental physical and electronic properties, such as geometric structures,
band structure, density of states, and spatial charge distributions, of
Na-intercalation compounds are discussed. The outlook of Na-ion batteries is
given at the last.",2206.08762v1
2022-06-27,Taylor's Law for some infinitely divisible probabbility distributions from population models,"In a family of random variables, Taylor's law or Taylor's power law
offluctuation scaling is a variance function that gives the variance
$\sigma^{2}>0$ of a random variable (rv) $X$ with expectation $\mu >0$ as a
powerof $\mu$: $\sigma ^{2}=A\mu ^{b}$ for finite real $A>0,\ b$ that are
thesame for all rvs in the family. Equivalently, TL holds when $\log
\sigma^{2}=a+b\log \mu ,\ a=\log A$, for all rvs in some set. Here we analyze
thepossible values of the TL exponent $b$ in five families of
infinitelydivisible two-parameter distributions and show how the values of $b$
dependon the parameters of these distributions. The five families
areTweedie-Bar-Lev-Enis, negative binomial, compound Poisson-geometric,compound
geometric-Poisson (or P\'{o}lya-Aeppli), and gamma distributions.These families
arise frequently in empirical data and population models, and they are limit
laws of Markov processes that we exhibit in each case.",2206.13283v1
2022-07-01,Reduce Indonesian Vocabularies with an Indonesian Sub-word Separator,"Indonesian is an agglutinative language since it has a compounding process of
word-formation. Therefore, the translation model of this language requires a
mechanism that is even lower than the word level, referred to as the sub-word
level. This compounding process leads to a rare word problem since the number
of vocabulary explodes. We propose a strategy to address the unique word
problem of the neural machine translation (NMT) system, which uses Indonesian
as a pair language. Our approach uses a rule-based method to transform a word
into its roots and accompanied affixes to retain its meaning and context. Using
a rule-based algorithm has more advantages: it does not require corpus data but
only applies the standard Indonesian rules. Our experiments confirm that this
method is practical. It reduces the number of vocabulary significantly up to
57\%, and on the English to Indonesian translation, this strategy provides an
improvement of up to 5 BLEU points over a similar NMT system that does not use
this technique.",2207.00552v1
2022-07-05,Topological magnetic phase transition in Eu-based A-type antiferromagnets,"Recently, a colossal magnetoresistance (CMR) was observed in EuCd$_2$P$_2$ --
a compound that does not fit the conventional mixed-valence paradigm. Instead,
experimental evidence points at a resistance driven by strong magnetic
fluctuations within the two-dimensional ($2d$) ferromagnetic (FM) planes of the
layered antiferromagnetic (AFM) structure. While the experimental results have
not yet been fully understood, a recent theory relates the CMR to a topological
vortex-antivortex unbinding, i.e., Berezinskii-Kosterlitz-Thouless (BKT), phase
transition. Motivated by these observations, in this work we explore the
magnetic phases hosted by a microscopic classical magnetic model for
EuCd$_2$P$_2$, which easily generalizes to other Eu A-type antiferromagnetic
compounds. Using Monte Carlo techniques to probe the specific heat and the
helicity modulus, we show that our model can exhibit a vortex-antivortex
unbinding phase transition. We find that this phase transition displays the
same sensitivity to in-plane magnetization, interlayer coupling, and easy-plane
anisotropy that is observed experimentally in the CMR signal, providing
qualitative numerical evidence that the effect is related to a magnetic BKT
transition.",2207.02361v1
2022-07-07,High-throughput screening of Half-antiperovskites with a stacked kagome lattice,"Half-antiperovskites (HAPs) are a class of materials consisting of stacked
kagome lattices and thus host exotic magnetic and electronic states. We perform
high-throughput calculations based on density functional theory (DFT) and
atomistic spin dynamics (ASD) simulations to predict stable magnetic HAPs
M$_3$X$_2$Z$_2$ (M = Cr, Mn, Fe, Co, and Ni; X is one of the elements from Li
to Bi except noble gases and 4$f$ rare-earth metals; Z = S, Se, and Te), with
both thermodynamical and mechanical stabilities evaluated. Additionally, the
magnetic ground states are obtained by utilizing DFT calculations combined with
the ASD simulations. The existing spin frustration in an AFM kagome lattice
manifests as competing behavior of the in-plane FM and AFM couplings. For a
total number of 930 HAP compositions considered, we have found 23 compounds
that are stabilized at non-collinear antiferromagnetic (AFM) state and 11
compounds that possess ferromagnetic (FM) order.",2207.03365v1
2022-07-14,Revisiting the magnetic and crystal structure of multiferroic KNiPO$_4$,"The magnetic, dielectric and structural properties of type-I multiferroic
KNiPO$_4$ have been investigated by neutron powder diffraction, magnetization,
dielectric and high temperature synchrotron-XRD measurements. Below the
N\'{e}el transition of $T_\mathrm{N}$ = 25 K, KNiPO$_4$ displays a weakly
non-collinear antiferromagnetic (AFM) structure with the orientation of the
Ni$^{2+}$ magnetic moments mainly along $a$ axis. The compound crystallizes in
the polar orthorhombic $Pna2_1$ space group at room temperature. A second-order
structural phase transition corresponding to the onset ferroelectricity is
observed at around $T_\mathrm{C}\sim$ 594(3)$^\circ$C, above which the crystal
structure of KNiPO$_4$ adopts the centrosymmetric $Pnma$ space group. The
compound also displays another structural phase transition at
$T_\mathrm{0}\sim$ 469 -- 488$^\circ$C, with a first-order character, which is
attributed to the rearrangement of oxygen ligands, resulting in a change in the
nickel ion co-ordination from four to five.",2207.06969v1
2022-07-27,Impact of tensor force on quantum shell effects in quasifission reactions,"Quantum shell effects drive many aspects of many-body quantal systems and
their interactions. Among these are the quasifission reactions that impede the
formation of a compound nucleus in superheavy element (SHE) searches. Fragment
production in quasifission is influenced by shell effects as a nontrivial
manifestation of microscopic dynamics hindering the full equilibration of the
composite system to form the compound nucleus. In this Letter, we use the
microscopic time-dependent Hartree-Fock (TDHF) theory to study 48Ca+249Bk
collisions to investigate the influence of the tensor component of the
effective nucleon-nucleon interaction. The results show that the inclusion of
the tensor force causes the spherical shell effect to become more prominent,
particularly for the neutron number yield whose peak is exactly at magic number
N = 126. This suggests that the tensor force plays a compelling role in the
evolution of dynamical shell effects in nuclear reactions, influencing the
competition between spherical and deformed shell gaps.",2207.13327v2
2022-08-02,Melting of spin ice state and development of fifth order susceptibility with magnetic field in pyrochlore Tb2Sn2O7,"Pyrochlores offer an ideal playground to investigate the magnetic ground
state of frustrated magnetic systems. In this class of materials, competition
between various magnetic interactions remains frustrated and prevents an
ordered magnetic state at low temperatures. Tb2Sn2O7 has recently attracted
significant attention due to its ordered spin-ice state. Additionally, in such
systems, application of external magnetic field might result in exotic magnetic
states. Our current investigation on Tb2Sn2O7 reveal the presence of a new
phase associated with fifth order susceptibility at low temperatures and high
magnetic fields. In this compound, at zero fields, for a stabilized spin-ice
state, the singlet-singlet state separated by {\delta} play an imperative role.
Under magnetic fields, {\delta} increases and the Zeeman energy associated with
the magnetic anisotropy is believed to get enhanced; which can be the key
ingredient for evolution of higher-order moments, above 10 kOe, in this
compound.",2208.01279v1
2022-08-02,Magnetic Toroidal Moment under Partial Magnetic Order in Hexagonal Zigzag-Chain Compound Ce$_3$TiBi$_5$,"We theoretically investigate an antiferromagnetic structure in a hexagonal
zigzag-chain compound Ce$_3$TiBi$_5$, which shows a linear magnetoelectric
effect in metals and an unfamiliar temperature dependence of magnetic
susceptibility. We find a partial magnetic order as a coexistence of a
nonmagnetic zigzag chain and staggered antiferromagnetic zigzag chains. The
latter accompany in-plane magnetic toroidal dipole moments which are
responsible for the observed behaviors. We show that magnetic frustration
arising from competing exchange interactions plays an important role to realize
such a partial magnetic order. Furthermore, we present the important spin-orbit
coupling parameters to induce the physical phenomena driven by the magnetic
toroidal dipole moment, such as the linear magnetoelectric effect and nonlinear
transport.",2208.01754v1
2022-08-08,Direct Hydrogen Quantification in High-pressure Metal Hydrides,"High-pressure metal-hydride (MH) research evolved into a thriving field
within condensed matter physics following the realisation of metallic compounds
showing phonon mediated near room-temperature superconductivity. However,
severe limitations in determining the chemical formula of the reaction
products, especially with regards to their hydrogen content, impedes a deep
understanding of the synthesized phases and can lead to significantly erroneous
conclusions. Here, we present a way to directly access the hydrogen content of
MH solids synthesised at high pressures in (laser-heated) diamond anvil cells
using nuclear magnetic resonance (NMR) spectroscopy. We show that this method
can be used to investigate MH compounds with a wide range of hydrogen content,
from MHx with x=0.15 (CuH0.15) to x < 6.4 (H 6+-0.4 S 5).",2208.03942v1
2022-08-08,"Magnetic, thermal, and magnetocaloric properties of the holmium trialuminide HoAl$_{3}$ with polytypic phases","We investigate the magnetic, thermal, and magnetocaloric properties of the
intermetallic HoAl$_{3}$ compounds with two different crystal structures. The
room-temperature equilibrium trigonal phase HoAl$_{3}$ undergoes an
antiferromagnetic (AFM) transition at the Neel temperature $T^{\rm tri}_{\rm N}
=$ 9.8 K. The AFM ordering of the compound is strong against the magnetic
field, so that inverse magnetocaloric effect (MCE) is found even under a
magnetic field change of 0-50 kOe. The high-pressure cubic phase HoAl3,
prepared by a rapid-solidification process, is antiferromagnetically ordered
below $T^{\rm cub}_{\rm N} =$ 15 K. Magnetic and specific heat measurements
reveal that this long-range AFM state becomes unstable as the temperature drops
and then it is replaced by a magnetic glassy state below a spin freezing
temperature $T_{\rm f} =$ 11 K. The successive changes in magnetic state result
in complicated temperature and field dependence of the MCE at low temperatures.",2208.04027v1
2022-08-09,Single crystal synthesis and low-lying electronic structure of V$_3$S$_4$,"We report successful growth of millimeter-sized high quality single crystals
of V$_3$S$_4$, a candidate topological semimetal belonging to a low-symmetry
space group and consisting of only low atomic number elements. Using density
functional theory calculations and angle-resolved photoemission spectroscopy,
we show that the nonmagnetic phase of monoclinic V$_3$S$_4$ hosts type-II
Dirac-like quasiparticles which opens a sizable gap due to spin orbit coupling,
as well as theoretical multiple nodal lines that are eliminated also by spin
orbit coupling. These results suggest that relativistic effects give rise to
profound modifications of the topological properties even in compounds with
low-weight elements.",2208.04586v2
2022-08-10,Optimal response surface designs in the presence of model contamination,"Complete reliance on the fitted model in response surface experiments is
risky and relaxing this assumption, whether out of necessity or intentionally,
requires an experimenter to account for multiple conflicting objectives. This
work provides a methodological framework of a compound optimality criterion
comprising elementary criteria responsible for: (i) the quality of the
confidence region-based inference to be done using the fitted model
(DP-/LP-optimality); (ii) improving the ability to test for the lack-of-fit
from specified potential model contamination in the form of extra polynomial
terms; and (iii) simultaneous minimisation of the variance and bias of the
fitted model parameters arising from this misspecification. The latter two
components have been newly developed in accordance with the model-independent
'pure error' approach to the error estimation. The compound criteria and design
construction were adapted to restricted randomisation frameworks: blocked and
multistratum experiments, where the stratum-by-stratum approach was adopted. A
point-exchange algorithm was employed for searching for nearly optimal designs.
The theoretical work is accompanied by one real and two illustrative examples
to explore the relationship patterns among the individual components and
characteristics of the optimal designs, demonstrating the attainable
compromises across the competing objectives and driving some general practical
recommendations.",2208.05366v2
2022-08-18,Investigation of role of antisite disorder in the pristine cage compound FeGa$_3$,"The role of controlled disorder in the strong correlated narrow gap
semiconductor candidate FeGa$_3$ has been investigated. Polycrystalline samples
were synthesized by the combination of arc-melting furnace and successive
annealing processes. Deviations of the occupation number of Fe and Ga sites
from those expected in the pristine compound were quantified with X-ray
analysis. Besides that, electrical transport and magnetization measurements
reveal that hierarchy in Fe and Ga site disorder tunes the ground state of
FeGa$_3$ from paramagnetic semiconducting to a magnetic metal. These findings
are discussed within the framework of Anderson metal-insulator transitions and
spin fluctuations.",2208.09064v2
2022-08-20,Unravelling the contributions to spin-lattice relaxation in Kramers single-molecule magnets,"The study of how spin interacts with lattice vibrations and relaxes to
equilibrium provides unique insights on its chemical environment and the
relation between electronic structure and molecular composition. Despite its
importance for several disciplines, ranging from magnetic resonance to quantum
technologies, a convincing interpretation of spin dynamics in crystals of
magnetic molecules is still lacking due to the challenging experimental
determination of the correct spin relaxation mechanism. We apply ab initio spin
dynamics to a series of twelve coordination complexes of Co(II) and Dy(III)
ions selected among $\sim$240 compounds that largely cover the literature on
single-molecule magnets and well represent different regimes of spin
relaxation. Simulations reveal that the Orbach spin relaxation rate of known
compounds mostly depends on the ions' zero-field splitting and little on the
details of molecular vibrations. Raman relaxation is instead found to be also
significantly affected by the features of low-energy phonons. These results
provide a complete understanding of the factors limiting spin lifetime in
single-molecule magnets and revisit years of experimental investigations by
making it possible to transparently distinguish Orbach and Raman relaxation
mechanisms.",2208.09674v1
2022-08-26,$Ab~initio$ study of Li-Mg-B superconductors,"LiB, a predicted layered compound analogous to the MgB$_2$ superconductor,
has been recently synthesized via cold compression and quenched to ambient
pressure, yet its superconducting properties have not been measured. According
to prior isotropic superconductivity calculations, the critical temperature
($T_{\rm{c}}$) was expected to be only 10$-$15 K. Using the anisotropic
Migdal-Eliashberg formalism, we show that the $T_{\rm{c}}$ may actually exceed
32 K. Our analysis of the contribution from different electronic states helps
explain the detrimental effect of pressure and doping on the compound's
superconducting properties. In the search for related superconductors, we
screened Li-Mg-B binary and ternary layered materials and found metastable
phases with $T_{\rm{c}}$ close to or even 10$-$20% above the record 39 K value
in MgB$_2$. Our reexamination of the Li-B binary phase stability reveals a
possible route to synthesize the LiB superconductor at lower pressures readily
achievable in multianvil cells.",2208.12855v1
2022-09-03,Machine learning based approach for solving atomic structures of nanomaterials combining pair distribution functions with density functional theory,"Determination of crystal structures of nanocrystalline or amorphous compounds
is a great challenge in solid states chemistry and physics. Pair distribution
function (PDF) analysis of X-Ray or neutron total scattering data has proven to
be a key element in tackling this challenge. However, in most cases a reliable
structural motif is needed as starting configuration for structure refinements.
Here, we present an algorithm that is able to determine the crystal structure
of an unknown compound by means of an on-the-fly trained machine learning model
that combines density functional theory (DFT) calculations with comparison of
calculated and measured PDFs for global optimization in an artificial
landscape. Due to the nature of this landscape, even metastable configurations
can be determined.",2209.01358v2
2022-09-08,Normal approximation of compound Hawkes functionals,"We derive quantitative bounds in the Wasserstein distance for the
approximation of stochastic integrals with respect to Hawkes processes by a
normally distributed random variable. In the case of deterministic and
non-negative integrands, our estimates involve only the third moment of
integrand in addition to a variance term using a square norm of the integrand.
As a consequence, we are able to observe a ""third moment phenomenon"" in which
the vanishing of the first cumulant can lead to faster convergence rates. Our
results are also applied to compound Hawkes processes, and improve on the
current literature where estimates may not converge to zero in large time, or
have been obtained only for specific kernels such as the exponential or Erlang
kernels.",2209.03621v1
2022-09-13,Ultrafast hybrid nanocomposite scintillators: a review,"In recent years, demand for scintillation detectors with high time resolution
(better than 100 ps) has emerged in high-energy physics and medical imaging
applications. In particular, time of flight positron emission tomography
(TOF-PET) can greatly benefit from increasing time resolution of scintillators,
which leads to the increase of signal-to-noise ratio, decrease of patient dose,
and achievement of the superior spatial resolution of PET images. Currently,
extensive research of various types of materials is carried out to achieve the
best time resolution. In this review, the recent progress of various approaches
is summarized and scintillation compounds with the best temporal
characteristics are first reviewed. The review presents the physical processes
causing fast luminescence in inorganic and organic materials. Special attention
is paid to nanocomposites which belong to a new perspective class of
scintillating materials, consisting of a plastic matrix, inorganic
nanocrystalline fillers, and organic or inorganic luminescence activators and
shifters. The main features and functions of all parts of existing and
prospective nanocomposite scintillators are also discussed. A number of
currently created and investigated nanocomposite materials with various
compounds and structures are reviewed.",2209.05780v1
2022-09-13,Local symmetry breaking and low-energy continuum in K$_2$ReCl$_6 $,"Using polarization selective spontaneous Raman scattering, we have
investigated the 5$d$ transition metal compound K$_2$ReCl$_6$ which displays a
series of structural phase transitions. We observe a violation of the Raman
selection rules in the cubic high temperature phase as well as a low-energy
scattering continuum persistent throughout the investigated temperature range
from 300 down to 5 K. The continuum couples to one of the phonon modes at
temperatures above the lowest structural phase transition at 76 K. We propose a
common origin of these observations caused by local fluctuations in the
orientation of the ReCl$_6$ octahedra which locally break the long-range cubic
symmetry. Consistent results from the related non-magnetic compound
K$_2$SnCl$_6$ support this interpretation.",2209.05866v2
2022-09-14,Short range order and topology of binary Ge-S glasses,"Short range order and topology of Ge$_x$S$_{100-x}$ glasses over a broad
composition range (20 $\le$ x $\le$ 42 in at%) was investigated by neutron
diffraction, X-ray diffraction, and Ge K-edge extended X-ray absorption fine
structure (EXAFS) measurements. The experimental data sets were fitted
simultaneously in the framework of the reverse Monte Carlo simulation method.
It was found that both constituents (Ge and S) satisfy the Mott-rule in all
investigated glasses: Ge and S atoms have 4 and 2 neighbours, respectively. The
structure of these glasses can be described with the chemically ordered network
model: Ge-S bonds are preferred, S-S bonds are present only in S-rich glasses.
Dedicated simulations showed that Ge-Ge bonds are necessary in Ge-rich glasses.
Connections between Ge atoms (such as edge-sharing GeS$_{4/2}$ tetrahedra) in
stoichiometric and S-rich glasses were analysed. The frequency of primitive
rings was also calculated.",2209.06540v2
2022-09-15,"Multivariate Hawkes-based Models in LOB: European, Spread and Basket Option Pricing","In this paper, we consider pricing of European options and spread options for
Hawkes-based model for the limit order book. We introduce multivariate Hawkes
process and the multivariable general compound Hawkes process. Exponential
multivariate general compound Hawkes processes and limit theorems for them,
namely, LLN and FCLT, are considered then. We also consider a special case of
one-dimensional EMGCHP and its limit theorems. Option pricing with $1D$ EGCHP
in LOB, hedging strategies, and numerical example are presented. We also
introduce greeks calculations for those models. Margrabe's spread options
valuations with Hawkes-based models for two assets and numerical example are
presented. Also, Margrabe's spread option pricing with two $2D$ EMGCHP and
numerical example are included. Basket options valuations with numerical
example are included. We finally discuss the implied volatility and implied
order flow. It reveals the relationship between stock volatility and the order
flow in the limit order book system. In this way, the Hawkes-based model can
provide more market forecast information than the classical Black-Scholes
model.",2209.07621v1
2022-09-16,Observation of thermodynamics originating from a mixed-spin ferromagnetic chain,"We present a model compound that forms a mixed-spin ferromagnetic chain. Our
material design, based on the organic radicals, affords a verdazyl-based
complex (p-Py-V)2[Mn(hfac)2]. The molecular orbital calculations of the
compound indicate the formation of a mixed spin-(1/2, 1/2, 5/2) ferromagnetic
chain. The temperature dependence of magnetic susceptibility reveals its
ferromagnetic behavior. The magnetic specific heat exhibits a double-peak
structure and indicates a phase transition at the low-temperature peak. The
observed characteristics are explained using the quantum Monte Carlo
calculations. Furthermore, the modified spin-wave theory verifies that the
double-peak structure of the specific heat significantly reflects the relative
ration of the acoustic excitation band and the optical excitation gap.",2209.07681v1
2022-09-20,Towards Task-Prioritized Policy Composition,"Combining learned policies in a prioritized, ordered manner is desirable
because it allows for modular design and facilitates data reuse through
knowledge transfer. In control theory, prioritized composition is realized by
null-space control, where low-priority control actions are projected into the
null-space of high-priority control actions. Such a method is currently
unavailable for Reinforcement Learning. We propose a novel, task-prioritized
composition framework for Reinforcement Learning, which involves a novel
concept: The indifferent-space of Reinforcement Learning policies. Our
framework has the potential to facilitate knowledge transfer and modular design
while greatly increasing data efficiency and data reuse for Reinforcement
Learning agents. Further, our approach can ensure high-priority constraint
satisfaction, which makes it promising for learning in safety-critical domains
like robotics. Unlike null-space control, our approach allows learning globally
optimal policies for the compound task by online learning in the
indifference-space of higher-level policies after initial compound policy
construction.",2209.09536v1
2022-09-23,One-Shot Reachability Analysis of Neural Network Dynamical Systems,"The arising application of neural networks (NN) in robotic systems has driven
the development of safety verification methods for neural network dynamical
systems (NNDS). Recursive techniques for reachability analysis of dynamical
systems in closed-loop with a NN controller, planner, or perception can
over-approximate the reachable sets of the NNDS by bounding the outputs of the
NN and propagating these NN output bounds forward. However, this recursive
reachability analysis may suffer from compounding errors, rapidly becoming
overly conservative over a longer horizon. In this work, we prove that an
alternative one-shot reachability analysis framework which directly verifies
the unrolled NNDS can significantly mitigate the compounding errors for a
general class of NN verification methods built on layerwise abstraction. Our
analysis is motivated by the fact that certain NN verification methods give
rise to looser bounds when applied in one shot than recursively. In our
analysis, we characterize the performance gap between the recursive and
one-shot frameworks for NNDS with general computational graphs. The
applicability of one-shot analysis is demonstrated through numerical examples
on a cart-pole system.",2209.11827v2
2022-09-24,Evidence of Lattice Strain as a Precursor to Superconductivity in BaPb$_{0.75}$Bi$_{0.25}$O$_3$,"In this work, we have investigated the precursor effects to superconductivity
in BaPb$_{0.75}$Bi$_{0.25}$O$_3$ using temperature dependent resistivity, x-ray
diffraction technique and photoemission spectroscopy. The present compound
exhibits superconductivity around 11 K ($T_C$). The synthesis procedure adopted
is much simpler as compared to the procedure available in the literature. In
the temperature range (10 K-25 K) i.e. above $T_C$, our results show an
increase in both the orthorhombic and tetragonal strain. The well screened
features observed in Bi and Pb 4$f_{7/2}$ core levels are indicative of the
metallic nature of the sample. The compound exhibits finite intensity at the
Fermi level at 300 K and this intensity decreases with decrease in temperature
and develops into a pseudogap; the energy dependence of the spectral density of
states suggests disordered metallic state. Furthermore, our band structure
calculations reveal that the structural transition upon Pb doping results in
the closing of the band gap at the Fermi level.",2209.11926v2
2022-09-30,A New Group of Two-Dimensional Non-van der Waals Materials with Ultra Low Exfoliation Energies,"The exfoliation energy - quantifying the energy required to extract a
two-dimensional (2D) sheet from the surface of a bulk material - is a key
parameter determining the synthesizability of 2D compounds. Here, using ab
initio calculations, we present a new group of non-van der Waals 2D materials
derived from non-layered crystals which exhibit ultra low exfoliation energies.
In particular for sulfides, surface relaxations are essential to correctly
describe the associated energy gain needed to obtain reliable results. Taking
into account long-range dispersive interactions has only a minor effect on the
energetics and ultimately proves that the exfoliation energies are close to the
ones of traditional van der Waals bound 2D compounds. The candidates with the
lowest energies, 2D SbTlO$_3$ and MnNaCl$_3$, exhibit appealing electronic,
potential topological, and magnetic features as evident from the calculated
band structures making these systems an attractive platform for fundamental and
applied nanoscience.",2209.15485v1
2022-10-04,On the distance spectrum and distance-based topological indices of central vertex-edge join of three graphs,"Topological indices are molecular descriptors that describe the properties of
chemical compounds. These topological indices correlate specific
physico-chemical properties like boiling point, enthalpy of vaporization,
strain energy, and stability of chemical compounds. This article introduces a
new graph operation based on central graph called central vertex-edge join and
provides its results related to graph invariants like eccentric-connectivity
index, connective eccentricity index, total-eccentricity index, average
eccentricity index, Zagreb eccentricity indices, eccentric geometric-arithmetic
index, eccentric atom-bond connectivity index, and Wiener index. Also, we
discuss the distance spectrum of the central vertex-edge join of three regular
graphs. Furthermore, we obtain new families of $D$-equienergetic graphs, which
are non $D$-cospectral.",2210.01497v1
2022-10-10,Optoelectronic and stability properties of quasi-2D alkylammonium based perovskites,"Electronic and stability properties of quasi-2D alkylammonium perovskites are
investigated using density functional theory (DFT) calculations and validated
experimentally on selected classes of compounds. Our analysis is focused on
perovskite structures of formula (A)$_2$(A$'$)$_{n-1}$Pb$_n$X$_{3n+1}$, with
large cations A = butyl-, pentyl-, hexylammonium (BA, PA, HXA), small cations
A$'$ = methylammonium, formamidinium, ethylammonium, guanidinium (MA,FA,EA,GA)
and halogens X = I, Br, Cl. The role of the halogen ions is outlined for the
band structure, stability and defect formation energies. Two opposing trends
are found for the absorption efficiency versus stability, the latter being
assessed with respect to possible degradation mechanisms. Experimental
validation is performed on quasi-2D perovskites based on pentylammonium
cations, namely: (PA)$_2$PbX$_4$ and (PA)$_2$(MA)Pb$_2$X$_7$, synthesized by
antisolvent-assisted vapor crystallization. Structural and optical analysis are
inline with the DFT based calculations. In addition, the thermogravimetric
analysis shows an enhanced stability of bromide and chloride based compounds,
in agreement with the theoretical predictions.",2210.04596v1
2022-10-12,Beyond Single Tetrahedron Physics of Breathing Pyrochlore Compound Ba3Yb2Zn5O11,"Recently a new class of quantum magnets, the so-called breathing pyrochlore
spin systems, have attracted much attention due to their potential to host
exotic emergent phenomena. Here, we present magnetometry, heat capacity,
thermal conductivity, Muon-spin relaxation, and polarized inelastic neutron
scattering measurements performed on high-quality single-crystal samples of
breathing pyrochlore compound Ba3Yb2Zn5O11. We interpret these results using a
simplified toy model and provide a new insight into the low-energy physics of
this system beyond the single-tetrahedron physics proposed previously.",2210.06534v1
2022-10-13,Categorizing Semantic Representations for Neural Machine Translation,"Modern neural machine translation (NMT) models have achieved competitive
performance in standard benchmarks. However, they have recently been shown to
suffer limitation in compositional generalization, failing to effectively learn
the translation of atoms (e.g., words) and their semantic composition (e.g.,
modification) from seen compounds (e.g., phrases), and thus suffering from
significantly weakened translation performance on unseen compounds during
inference. We address this issue by introducing categorization to the source
contextualized representations. The main idea is to enhance generalization by
reducing sparsity and overfitting, which is achieved by finding prototypes of
token representations over the training set and integrating their embeddings
into the source encoding. Experiments on a dedicated MT dataset (i.e.,
CoGnition) show that our method reduces compositional generalization error
rates by 24\% error reduction. In addition, our conceptually simple method
gives consistently better results than the Transformer baseline on a range of
general MT datasets.",2210.06709v1
2022-10-14,Magnetic interactions in intercalated transition metal dichalcogenides: a study based on ab initio model construction,"Transition metal dichalcogenides (TMDs) are known to have a wide variety of
magnetic structures by hosting other transition metal atoms in the van der
Waals gaps. To understand the chemical trend of the magnetic properties of the
intercalated TMDs, we perform a systematic first-principles study for 48
compounds with different hosts, guests, and composition ratios. Starting with
calculations based on spin density functional theory, we derive classical spin
models by applying the Liechtenstein method to the ab initio Wannier-based
tight-binding model. We show that the calculated exchange couplings are overall
consistent with the experiments. In particular, when the composition rate is
1/3, the chemical trend can be understood in terms of the occupation of the
3d-orbital in the intercalated transition metal. The present results give us a
useful guiding principle to predict the magnetic structure of compounds that
are yet to be synthesized.",2210.07740v1
2022-10-18,Systematicity in GPT-3's Interpretation of Novel English Noun Compounds,"Levin et al. (2019) show experimentally that the interpretations of novel
English noun compounds (e.g., stew skillet), while not fully compositional, are
highly predictable based on whether the modifier and head refer to artifacts or
natural kinds. Is the large language model GPT-3 governed by the same
interpretive principles? To address this question, we first compare Levin et
al.'s experimental data with GPT-3 generations, finding a high degree of
similarity. However, this evidence is consistent with GPT3 reasoning only about
specific lexical items rather than the more abstract conceptual categories of
Levin et al.'s theory. To probe more deeply, we construct prompts that require
the relevant kind of conceptual reasoning. Here, we fail to find convincing
evidence that GPT-3 is reasoning about more than just individual lexical items.
These results highlight the importance of controlling for low-level
distributional regularities when assessing whether a large language model
latently encodes a deeper theory.",2210.09492v1
2022-10-20,A setup for direct measurement of the adiabatic temperature change in magnetocaloric materials,"In order to find a highly efficient, environment-friendly magnetic
refrigerant, direct measurements of the adiabatic temperature change $\Delta
T_{adb}$ is required. Here, in this work, a simple setup for the $\Delta
T_{adb}$ measurement is presented. Using a permanent magnet Halbach array with
a maximum magnetic field of $1.8$ T and a rate of magnetic field change of $5$
T/s, accurate determination of $\Delta T_{adb}$ is possible in this system. The
operating temperature range of the system is from $100$ K to $400$ K, designed
for the characterization of materials with potential for room temperature
magnetic refrigeration applications. Using the setup, the $\Delta T_{adb}$ of a
first-order and a second-order compound have been studied. Results from the
direct measurement for the first-order compound have been compared with $\Delta
T_{adb}$ calculated from the temperature and magnetic field dependent specific
heat data. By comparing results from direct and indirect measurements, it is
concluded that for a reliable characterization of the magnetocaloric effect,
direct measurement of $\Delta T_{adb}$ should be adopted.",2210.11509v1
2022-10-27,Robust cryogenic matched low-pass coaxial filters for quantum computing applications,"Electromagnetic noise is one of the key external factors decreasing
superconducting qubits coherence. Matched coaxial filters can prevent microwave
and IR photons negative influence on superconducting quantum circuits. Here, we
report on design and fabrication route of matched low-pass coaxial filters for
noise-sensitive measurements at milliKelvin temperatures. A robust transmission
coefficient with designed linear absorption (-1dB/GHz) and ultralow reflection
losses less than -20 dB up to 20 GHz is achieved. We present a mathematical
model for evaluating and predicting filters transmission parameters depending
on their dimensions. It is experimentally approved on two filters prototypes
different lengths with compound of Cu powder and Stycast commercial resin
demonstrating excellent matching. The presented design and assembly route are
universal for various compounds and provide high repeatability of geometrical
and microwave characteristics. Finally, we demonstrate three filters with
almost equal reflection and transmission characteristics in the range from 0 to
20 GHz, which is quite useful to control multiple channel superconducting
quantum circuits.",2210.15301v1
2022-11-04,"Structural, electronic and topological properties of 3D TmBi compound","Using density functional theory based methods we report the structural,
electronic and topological properties of the FCC crystal compound TmBi. This
material is found to be dynamically stable and shows a non magnetic semimetalic
character. By tuning the spin-orbit coupling, we observe a significant change
in the band structure, and the occurrence of band inversion along $\Gamma -X$
direction. The parity product at time-reversal invariant momentum points and
the Wannier charge center calculations provide a topological index $Z_{2}=1$ on
the $k_{j}=0$ plane (with $j=1,2$ and $3$) revealing the non trivial
topological character of TmBi. The existence of topologically protected surface
states of TmBi through the observation of a Dirac cones at $\bar{X}$ point
confirm our finding. The present work could inspire platforms for exploring
novel topological states within the family of rare-earth monobismuthides.",2211.02456v1
2022-11-04,De novo PROTAC design using graph-based deep generative models,"PROteolysis TArgeting Chimeras (PROTACs) are an emerging therapeutic modality
for degrading a protein of interest (POI) by marking it for degradation by the
proteasome. Recent developments in artificial intelligence (AI) suggest that
deep generative models can assist with the de novo design of molecules with
desired properties, and their application to PROTAC design remains largely
unexplored. We show that a graph-based generative model can be used to propose
novel PROTAC-like structures from empty graphs. Our model can be guided towards
the generation of large molecules (30--140 heavy atoms) predicted to degrade a
POI through policy-gradient reinforcement learning (RL). Rewards during RL are
applied using a boosted tree surrogate model that predicts a molecule's
degradation potential for each POI. Using this approach, we steer the
generative model towards compounds with higher likelihoods of predicted
degradation activity. Despite being trained on sparse public data, the
generative model proposes molecules with substructures found in known
degraders. After fine-tuning, predicted activity against a challenging POI
increases from 50% to >80% with near-perfect chemical validity for sampled
compounds, suggesting this is a promising approach for the optimization of
large, PROTAC-like molecules for targeted protein degradation.",2211.02660v1
2022-11-09,CrRhAs: a member of a large family of metallic kagome antiferromagnets,"Kagome lattice materials are an important platform for highly frustrated
magnetism as well as for a plethora of phenomena resulting from flat bands,
Dirac cones and van Hove singularities in their electronic structures. We study
the little known metallic magnet CrRhAs, which belongs to a vast family of
materials that include $3d$, $4f$ and $5f$ magnetic elements, as well as
numerous nonmagnetic metals and insulators. Using noncollinear spin density
functional calculations (mostly spin spirals), we extract a model magnetic
Hamiltonian for CrRhAs. While it is dominated by an antiferromagnetic second
nearest neighbor coupling in the kagome plane, the metallic nature of the
compound leads to numerous nonzero longer range couplings and to important ring
exchange terms. We analyze this Hamiltonian and find unusual ground states
which are dominated by nearly isolated antiferromagnetic triangles that adopt
120$^\circ$ order either with positive or with negative vector chirality. We
discuss the connection to the few known experimental facts about CrRhAs.
Finally, we give a brief survey of other interesting magnetic members of this
family of kagome compounds.",2211.04646v1
2022-11-13,Compound Super-oscillation Lens for Reflective Confocal Imaging,"The super-oscillation lens (SOL) can achieve super-resolution focusing but
have to trade-off with weaker hotspots and higher sidebands. We propose a
single compound SOL to achieve reflective confocal imaging in principle without
additional lenses. The designed SOL consists of an outer lens and an inner lens
which play the role of focusing lens and collective lens respectively. As a
result, focusing and collecting functions can be simultaneously realized. The
improved system can achieve excellent imaging performance with an ultra-high
resolution (<0.34{\lambda}/NA, NA stands for numerical aperture), and almost
negligible side lobe ratio and no side bands, which proved superior to
conventional laser scanning confocal microscopy and single SOL. This technology
can be attractive for a variety of applications in super-resolution imaging and
biomedical sciences.",2211.06806v1
2022-11-15,Pressure-Induced Insulator-to-Metal Transition in van der Waals compound CoPS$_3$,"We have studied the insulator-to-metal transition and crystal structure
evolution under high pressure in the van der Waals compound CoPS$_3$ through
$\textit{in-situ}$ electrical resistance, Hall resistance, magnetoresistance,
X-ray diffraction, and Raman scattering measurements. CoPS$_3$ exhibits a
$C2/m$ $\rightarrow$ $P\overline{3}$ structural transformation at 7 GPa
accompanied by a 2.9$\%$ reduction in the volume per formula unit.
Concomitantly, the electrical resistance decreases significantly, and CoPS$_3$
becomes metallic. This metallic CoPS$_3$ is a hole-dominant conductor with
multiple conduction bands. The linear magnetoresistance and the small volume
collapse at the metallization suggest the incomplete high-spin $\rightarrow$
low-spin transition in the metallic phase. Thus, the metallic CoPS$_3$ possibly
possesses an inhomogeneous magnetic moment distribution and short-range
magnetic ordering. This report summarizes the comprehensive phase diagram of
$M$PS$_3$ ($M$ = V, Mn, Fe, Co, Ni, and Cd) that metalize under pressures.",2211.07925v4
2022-11-21,"Topological superconductivity and large spin Hall effect in the kagome family Ti6X4 (X = Bi, Sb, Pb, Tl, In)","Topological superconductors (TSC) become a focus of research due to the
accompanying Majorana fermions. However, the experimentally reported TSC are
extremely rare. The recent experiments reported the kagome TSC AV$_{3}$Sb$_{5}$
(A=K, Rb, Cs), which exhibit unique superconductivity, topological surface
states (TSS), and Majorana bound states. More recently, the first
titanium-based kagome superconductor CsTi$ _{3} $Bi$ _{5} $ with nontrivial
topology was successfully synthesized as a perspective TSC. Given that Cs
contributes little to the electronic structures of CsTi$ _{3} $Bi$ _{5} $ and
binary compounds may be easier to be synthesized, here, by density functional
theory calculations, we predict five stable non-magnetic kagome compounds Ti$
_{6} $X$ _{4} $ (X = Bi, Sb, Pb, Tl, In) which exhibit superconductivity with
critical temperature Tc = 3.8$ - $5.1 K, nontrivial $\mathbb{Z}$$_2$ band
topology, and TSS close to the Fermi level. In addition, the large intrinsic
spin Hall effect is obtained in Ti$ _{6} $X$ _{4} $, which is caused by gapped
Dirac nodes and nodal lines due to a strong spin-orbit coupling. This work
offers new platforms for TSC and spintronic devices.",2211.11372v1
2022-11-22,Semi-supervised generative approach to point-defect formation in chemically disordered compounds: application to uranium-plutonium mixed oxides,"Machine-learning methods are nowadays of common use in the field of material
science. For example, they can aid in optimizing the physicochemical properties
of new materials, or help in the characterization of highly complex chemical
compounds. An especially challenging problem arises in the modeling of
chemically disordered solid solutions, for which some properties depend on the
distribution of chemical species in the crystal lattice. This is the case of
defect properties of uranium-plutonium mixed oxides nuclear fuels. The number
of possible configurations is so high that the problem becomes intractable if
treated with direct sampling. We thus propose a machine learning approach,
based on generative modeling, to optimize the exploration of this large
configuration space. A probabilistic, semi-supervised approach using Mixture
Density Network is applied to estimate the concentration of thermal defects in
(U, Pu)O2. We show that this method, based on the prediction of the density of
states of formation energy of a defect, is computationally much more
cost-efficient compared to other approaches available in the literature.",2211.12086v2
2022-11-28,Muon-spin relaxation investigation of magnetic bistability in a crystalline organic radical compound,"We present the results of a muon-spin relaxation ($\mu^{+}$SR) investigation
of the crystalline organic radical compound
4-(2-benzimidazolyl)-1,2,3,5-dithiadiazolyl (HbimDTDA), in which we demonstrate
the hysteretic magnetic switching of the system that takes place at $T = 274
\pm 11\,\mathrm{K}$ caused by a structural phase transition. Muon-site analysis
using electronic structure calculations suggests a range of candidate muon
stopping sites. The sites are numerous and similar in energy but,
significantly, differ between the two structural phases of the material.
Despite the difference in the sites, the muon remains a faithful probe of the
transition, revealing a dynamically-fluctuating magnetically disordered state
in the low-temperature structural phase. In contrast, in the high temperature
phase the relaxation is caused by static nuclear moments, with rapid electronic
dynamics being motionally narrowed from the muon spectra.",2211.15560v1
2022-11-29,Composition based oxidation state prediction of materials using deep learning,"Oxidation states are the charges of atoms after their ionic approximation of
their bonds, which have been widely used in charge-neutrality verification,
crystal structure determination, and reaction estimation. Currently only
heuristic rules exist for guessing the oxidation states of a given compound
with many exceptions. Recent work has developed machine learning models based
on heuristic structural features for predicting the oxidation states of metal
ions. However, composition based oxidation state prediction still remains
elusive so far, which is more important in new material discovery for which the
structures are not even available. This work proposes a novel deep learning
based BERT transformer language model BERTOS for predicting the oxidation
states of all elements of inorganic compounds given only their chemical
composition. Our model achieves 96.82\% accuracy for all-element oxidation
states prediction benchmarked on the cleaned ICSD dataset and achieves 97.61\%
accuracy for oxide materials. We also demonstrate how it can be used to conduct
large-scale screening of hypothetical material compositions for materials
discovery.",2211.15895v1
2022-12-05,Discovery of a metallic oxide with ultralow thermal conductivity,"A compound with metallic electrical conductivity usually has a considerable
total thermal conductivity because both electrons and photons contribute to
thermal transport. Here, we show an exceptional example of iridium oxide,
Bi3Ir3O11, that concurrently displays metallic electrical conductivity and
ultralow thermal conductivity approaching 0.61 W m-1 K-1 at 300 K. The compound
crystallizes into a cubic structural framework with space group Pn-3. The edge-
and corner-sharing IrO6 octahedra with a mixed Ir4.33+ charge state favor
metallic electrical transport. Bi3Ir3O11 exhibits an extremely low lattice
thermal conductivity close to the minimum limit in theory owing to its
tunnel-like structure with filled heavy atoms Bi rattling inside. Theoretical
calculations reveal the underlying mechanisms for the extraordinary
compatibility between metallic electrical conductivity and ultralow thermal
conductivity. This study may establish a new avenue for designing and
developing unprecedented heat-insulation metals.",2212.02040v1
2022-12-05,A Comprehensively Improved Hybrid Algorithm for Learning Bayesian Networks: Multiple Compound Memory Erasing,"Using a Bayesian network to analyze the causal relationship between nodes is
a hot spot. The existing network learning algorithms are mainly
constraint-based and score-based network generation methods. The
constraint-based method is mainly the application of conditional independence
(CI) tests, but the inaccuracy of CI tests in the case of high dimensionality
and small samples has always been a problem for the constraint-based method.
The score-based method uses the scoring function and search strategy to find
the optimal candidate network structure, but the search space increases too
much with the increase of the number of nodes, and the learning efficiency is
very low. This paper presents a new hybrid algorithm, MCME (multiple compound
memory erasing). This method retains the advantages of the first two methods,
solves the shortcomings of the above CI tests, and makes innovations in the
scoring function in the direction discrimination stage. A large number of
experiments show that MCME has better or similar performance than some existing
algorithms.",2212.03103v1
2022-12-07,Fermi Level Instability as a Way to Tailor Properties of La3Te4,"Traditionally, the formation of off-stoichiometric compounds is believed to
be the growth effect rather than the intrinsic tendency of the system. However,
here, using the example of La3Te4, we demonstrate that in n-type gapped metals
having a large internal gap between principal band edges and the Fermi level
inside of the principal conduction band, Fermi-level instability can develop,
resulting in a reduction of formation energy for acceptor defects.
Specifically, La vacancies in La3Te4 form spontaneously to produce the acceptor
states and remove a fraction of free carriers from the principal conduction
band via electron-hole recombination. Such a unique self-doping mechanism
allows to stabilize a range of off-stoichiometric La3-xTe4 compounds, which
have different electronic properties. Moreover, we thus show how controlling
synthesis conditions can be used as a knob to reach the target functionality,
including controllable metal-to-insulator transition.",2212.03611v1
2022-12-19,NaRuO$_2$: Kitaev-Heisenberg exchange in triangular-lattice setting,"Kitaev exchange, a new paradigm in quantum magnetism research, occurs for
90$^{\circ}$ metal-ligand-metal links, $t_{2g}^5$ transition ions, and sizable
spin-orbit coupling. It is being studied in honeycomb compounds but also on
triangular lattices. While for the former it is known by now that the Kitaev
intersite couplings are ferromagnetic, for the latter the situation is unclear.
Here we pin down the exchange mechanisms and determine the effective coupling
constants in the $t_{2g}^5$ triangular-lattice material NaRuO$_2$, recently
found to host a quantum spin liquid ground state. We show that, compared to
honeycomb compounds, the characteristic triangular-lattice cation surroundings
dramatically affect exchange paths and effective coupling parameters, changing
the Kitaev interactions to antiferromagnetic. The quantum chemical analysis and
subsequent effective spin model computations provide perspective onto the
nature of the experimentally observed quantum spin liquid -- it seemingly
implies finite longer-range exchange, and the atypical proximity to
ferromagnetic order is related to sizable ferromagnetic Heisenberg
nearest-neighbor couplings.",2212.09365v2
2022-12-28,"Machine learning reveals memory of the parent phases in ferroelectric relaxors Ba(Ti$_{1-x}$,Zr$_x$)O$_3$","Machine learning has been establishing its potential in multiple areas of
condensed matter physics and materials science. Here we develop and use an
unsupervised machine learning workflow within a framework of
first-principles-based atomistic simulations to investigate phases, phase
transitions, and their structural origins in ferroelectric relaxors,
Ba(Ti$_{1-x}$,Zr$_x$)O$_3$. We first demonstrate the applicability of the
workflow to identify phases and phase transitions in the parent compound, a
prototypical ferroelectric BaTiO$_3$. We then apply the workflow on
Ba(Ti$_{1-x}$,Zr$_x$)O$_3$, with $x\leq0.25$ to reveal (i) that some of the
compounds bear a subtle memory of BaTiO$_3$, phases beyond the point of the
pinched phase transition, which could contribute to their enhanced
electromechanical response; (ii) the existence of peculiar phases with
delocalized precursors of nanodomains -- likely candidates for the
controversial polar nanoregions; and (iii) nanodomain phases for the largest
concentrations of $x$",2212.14087v1
2023-01-10,Non-collinear magnetism in the post-perovskite thiocyanate frameworks CsM(NCS)$_3$,"AMX$_3$ compounds are structurally diverse, a notable example being the
post-perovskite structure which adopts a two-dimensional framework with corner-
and edge-sharing octahedra. Few molecular post-perovskites are known and of
these, none have reported magnetic structures. Here we report the synthesis,
structure and magnetic properties of molecular post-perovskites: CsNi(NCS)$_3$,
a thiocyanate framework, and two new isostructural analogues CsCo(NCS)$_3$ and
CsMn(NCS)$_3$. Magnetisation measurements show that all three compounds undergo
magnetic order. CsNi(NCS)$_3$ (Curie temperature, $T_\mathrm{C} = 8.5(1)\;$K)
and CsCo(NCS)$_3$ ($T_\mathrm{C} = 6.7(1)\;$K) order as weak ferromagnets. On
the other hand, CsMn(NCS)$_3$ orders as an antiferromagnet (N\'eel temperature,
$T_\mathrm{N}=16.8(8)\;$K). Neutron diffraction data of CsNi(NCS)$_3$ and
CsMn(NCS)$_3$, show that both are non-collinear magnets. These results suggest
molecular frameworks are fruitful ground for realising the spin textures
required for the next generation of information technology.",2301.03880v2
2023-01-11,Superconductivity in Ce-based cage compounds,"Cerium-based ternary compounds CeNi$_2$Cd$_{20}$ and CePd$_2$Cd$_{20}$ do not
exhibit long-range order down to millikelvin temperature range. Given the large
separation between cerium ions which significantly reduces the superexchange
interactions and vanishingly small RKKY interaction, here we show that nodal
superconductivity mediated by the valence fluctuations must be a ground state
in these materials. We propose that the critical temperature for the
superconducting transition can be significantly increased by applying
hydrostatic pressure. We employ an extended periodic Anderson lattice model
which includes the long-range Coulomb interactions between the itinerant
electrons as well as the local Coulomb interaction between the predominantly
localized and itinerant electrons to compute a critical temperature of the
superconducting transition. Using the slave-boson approach we show that
fluctuations mediated by the repulsive electron-electron interactions lead to
the emergence of d-wave superconductivity.",2301.04580v1
2023-01-12,Fusion of two stable elastic structures resulting in an unstable system,"It is shown that a compound elastic structure, which displays a dynamic
instability, may be designed as the union (or 'fusion') of two structures which
are stable when separately analyzed. The compound elastic structure has two
degrees of freedom and is made up of a rigid rod connected with two springs to
a smooth support, which evidences a jump in the curvature at the equilibrium
configuration. Instability is proven in a linearized context and is related to
the application of a non-conservative load of the follower type, so that the
instability disappears under dead loads. In the fully nonlinear range, the
instability is also confirmed through numerical simulations. The obtained
results may be useful in the design of new mechanical sensors, or devices for
energy harvesting, or architected materials. In addition, our findings have
conceptual implications on piecewise-linear theories of mechanics such as for
instance plasticity or frictional contact.",2301.04957v2
2023-01-12,Detection of HCN and diverse redox chemistry in the plume of Enceladus,"The Cassini spacecraft observed that Saturn's moon Enceladus possesses a
series of jets erupting from its South Polar Terrain. Previous studies of in
situ data collected by Cassini's Ion and Neutral Mass Spectrometer (INMS) have
identified H$_2$O, CO$_2$, CH$_4$, NH$_3$, and H$_2$ within the plume of
ejected material. Identification of minor species in the plume remains an
ongoing challenge, owing to the large number of possible combinations that can
be used to fit the INMS data. Here, we present the detection of several new
compounds of strong importance to the habitability of Enceladus, including HCN,
C$_2$H$_2$, C$_3$H$_6$, and C$_2$H$_6$. Our analyses of the low velocity INMS
data, coupled with our detailed statistical framework, enable discrimination
between previously ambiguous species in the plume by alleviating the effects of
high dimensional model fitting. Together with plausible mineralogical catalysts
and redox gradients derived from surface radiolysis, these compounds could
potentially support extant microbial communities or drive complex organic
synthesis leading to the origin of life.",2301.05259v2
2023-01-16,Hybrid quantum-classical convolutional neural networks to improve molecular protein binding affinity predictions,"One of the main challenges in drug discovery is to find molecules that bind
specifically and strongly to their target protein while having minimal binding
to other proteins. By predicting binding affinity, it is possible to identify
the most promising candidates from a large pool of potential compounds,
reducing the number of compounds that need to be tested experimentally.
Recently, deep learning methods have shown superior performance than
traditional computational methods for making accurate predictions on large
datasets. However, the complexity and time-consuming nature of these methods
have limited their usage and development. Quantum machine learning is an
emerging technology that has the potential to improve many classical machine
learning algorithms. In this work we present a hybrid quantum-classical
convolutional neural network, which is able to reduce by 20% the complexity of
the classical network while maintaining optimal performance in the predictions.
Additionally, it results in a significant time savings of up to 40% in the
training process, which means a meaningful speed up of the drug discovery
process.",2301.06331v2
2023-01-25,Stochastic particle transport by deep-water irregular breaking waves,"Correct prediction of particle transport by surface waves is crucial in many
practical applications such as search and rescue or salvage operations and
pollution tracking and clean-up efforts. Recent results have indicated
transport by deep-water breaking waves is enhanced compared to non-breaking
waves. To model particle transport in irregular waves, some of which break, we
develop a stochastic differential equation describing both mean particle
transport and its uncertainty. The equation combines a Brownian motion, which
captures non-breaking drift-diffusion effects, and a compound Poisson process,
which captures jumps in particle positions due to breaking.We corroborate these
predictions with new experiments, in which we track large numbers of particles
in irregular breaking waves. For breaking and non-breaking wave fields, our
experiments confirm that the variance of the particle position grows linearly
with time, in accordance with Taylor's single-particle dispersion theory. For
wave fields that include breaking, the compound Poisson process increases the
linear growth rate of the mean and variance and introduces a finite skewness of
the particle position distribution.",2301.10603v1
2023-01-31,Enhancement in physical properties of Pb-Based Perovskite Oxides ($PbGeO_{3}$): Ab initio Calculation,"In the present paper, the electronic, structural, thermodynamic, and elastic
properties of cubic $PbGeO_{3}$ perovskite oxide are presented and computed
using the WIEN2K code. The structural properties have been evaluated and they
are in good agreement with the theoretical and experimental data. A phonon
dispersion is made and it reveals that the cubic $PbGeO_{3}$ perovskite is
dynamically stable. In addition, the electronic properties of $PbGeO_{3}$ shows
an opening gap energy, meaning a semiconductor behavior with an indirect band
gap equal to $1.67 eV$. Moreover, the obtained elastic constants of cubic
$PbGeO_{3}$ satisfy Born's mechanical stability criteria, and this indicates
that our compound behaves as a stable ductile material. The
temperature-pressure effects on thermodynamic parameters are investigated using
the Gibbs$2$ package. Finally, based on the obtained results about the cubic
$PbGeO_{3}$ perovskite properties, we assume that this compound will have
potential applications.",2301.13493v1
2023-02-01,Explaining the Entropy Forming Ability with the atomic size mismatch,"To quickly screen for single-phased multi-principal-element materials, a
so-called entropy forming ability (EFA) parameter is sometimes used as a
descriptor. The higher the EFA, the higher is the propensity to form a
single-phase structure, which is stabilized against separation up to a certain
threshold by the configurational entropy. We have investigated this EFA
descriptor with atomic relaxations in special-quasi-random structures and
discovered that the EFA correlates inversely with the lattice distortion. Large
atomic size differences lead to multi-phase compounds, and little size
differences to single-phase compounds. Instead of configurational entropy, we
therefore demonstrate the applicability of the Hume-Rothery rules to phase
stability of solid solutions even in compositionally complex ceramics.",2302.00460v2
2023-02-02,Curriculum Learning for ab initio Deep Learned Refractive Optics,"Deep optical optimization has recently emerged as a new paradigm for
designing computational imaging systems using only the output image as the
objective. However, it has been limited to either simple optical systems
consisting of a single element such as a diffractive optical element (DOE) or
metalens, or the fine-tuning of compound lenses from good initial designs. Here
we present a DeepLens design method based on curriculum learning, which is able
to learn optical designs of compound lenses ab initio from randomly initialized
surfaces without human intervention, therefore overcoming the need for a good
initial design. We demonstrate the effectiveness of our approach by fully
automatically designing both classical imaging lenses and a large field-of-view
extended depth-of-field computational lens in a cellphone-style form factor,
with highly aspheric surfaces and a short back focal length.",2302.01089v3
2023-02-07,Observation of Weak Kondo Effect and Angle Dependent Magnetoresistance in Layered Antiferromagnetic V$_5$S$_8$ Single Crystal,"The compound V$_5$S$_8$ can also be represented by V$_{1.25}$S$_2$, a
transition metal dichalcogenide (TMDC) with excess V. Very few TMDCs show
magnetism and/or Kondo effect. Among them, the sister compounds VSe$_2$ and
VTe$_2$ are recently proved to show ferromagnetism in addition to the
low-temperature resistivity upturn due to Kondo effect. In this study, we show
Kondo effect in V$_5$S$_8$ originated from the antiferromagnetic exchange
interactions among the intercalated V atoms below the N$\acute{e}$el ($T_N$)
temperature of 27 K. We find isotropic magnetic properties above $T_N$, while a
strong magnetic anisotropy is noticed below $T_N$. In addition, below $T_N$ we
find an out-of-plane ($H\parallel c$) spin-flop transition triggered at a
critical field of 3.5 T that is absent from the in-plane ($H\perp c$).
Angle-dependent magnetoresistance is found to be highly anisotropic in the
antiferromagnetic state.",2302.03301v1
2023-02-10,Thermodynamic stability of Li-B-C compounds from first principles,"Prediction of high-$T_{\rm{c}}$ superconductivity in hole-doped Li$_x$BC two
decades ago has brought about an extensive effort to synthesize new materials
with honeycomb B-C layers, but the thermodynamic stability of Li-B-C compounds
remains largely unexplored. In this study, we use density functional theory to
characterize well-established and recently reported Li-B-C phases. Our
calculation of the Li chemical potential in Li$_x$BC helps estimate the
($T$,$P$) conditions required for delithiation of the LiBC parent material,
while examination of B-C phases helps rationalize the observation of metastable
BC$_3$ polymorphs with honeycomb and diamond-like morphologies. At the same
time, we demonstrate that recently reported BC$_3$, LiBC$_3$, and Li$_2$B$_2$C
phases with new crystal structures are both dynamically and thermodynamically
unstable. With a combination of evolutionary optimization and rational design,
we identify considerably more natural and favorable Li$_2$B$_2$C configurations
that, nevertheless, remain above the thermodynamic stability threshold.",2302.05325v1
2023-02-13,Topological phase diagram of Pb1-xSnxSe1-yTey,"We reproduce the mirror Chern number phase diagram for the quaternary
compound Pb1-xSnxSe1-yTey combining accurate density functional theory and
tight-biding model. The tight binding models are extracted from ab-initio
results, adding constraints to reproduce the experimental results. By using the
virtual crystalline approximation, we calculated the mirror Chern number as a
function of the concentrations x and y. We report different hamiltonians
depending on whether we want to focus on the experimental band gap or on the
experimental topological transition. We calculate the transition line between
the trivial insulating phase and topological insulating phase that results in
good agreement with the experimental results. Finally, we add in the phase
diagram the Weyl phase predicted in the literature providing a complete
topological phase diagram for the Pb1-xSnxSe1-yTey quaternary compound.",2302.06217v1
2023-02-13,Magnetic and electronic properties of Eu$_5$In$_2$Sb$_6$,"The intermetallic compound Eu$_5$In$_2$Sb$_6$, an antiferromagnetic material
with nonsymmorphic crystalline structure, is investigated by magnetic,
electronic transport and specific heat measurements. Being a Zintl phase,
insulating behavior is expected. Our thermodynamic and magnetotransport
measurements along different crystallographic directions strongly indicate
polaron formation well above the magnetic ordering temperatures. Pronounced
anisotropies of the magnetic and transport properties even above the magnetic
ordering temperature are observed despite the Eu$^{2+}$ configuration which
testify to complex and competing magnetic interactions between these ions and
give rise to intricate phase diagrams discussed in detail. Our results provide
a comprehensive framework for further detailed study of this multifaceted
compound with possible nontrivial topology.",2302.06324v1
2023-02-15,Superconducting ground state study of valence skip compound AgSnSe$_2$,"The valence-skipped superconductors are natural candidates for unconventional
superconductivity, as they can exhibit a negative effective, attractive
interaction for electron-pairing. This work reports comprehensive XRD,
magnetization, specific heat and muon spin rotation and relaxation measurements
($\mu$SR) on a valence-skipped compound: AgSnSe$_2$. The temperature dependence
of the electronic specific heat ($C_{el}(T)$) and of the upper critical field
($H_{c2}(T)$) provide evidence of two-gap superconductivity, which is also
confirmed by our transverse-field $\mu$SR measurements. Our zero-field $\mu$SR
measurements suggest preserved time-reversal symmetry in the superconducting
ground state of AgSnSe$_2$.",2302.07790v1
2023-02-22,Mapping the space of photoswitchable ligands and photodruggable proteins with computational modeling,"Light-activated drugs are a promising way to localize biological activity and
minimize side effects. However, their development is complicated by the
numerous photophysical and biological properties that must be simultaneously
optimized. To accelerate the design of photoactive drugs, we describe a
procedure that combines ligand-protein docking with chemical property
prediction based on machine learning (ML). We apply this procedure to 58
proteins and 9,000 photo-drug candidates based on azobenzene cis-trans
isomerism. We find that most proteins display a preference for trans isomers
over cis, and that the binding affinities of nominally active/inactive pairs
are in fact highly correlated. These findings have significant value for
photopharmacology research, and reinforce the need for virtual screening to
identify compounds with rare desirable properties. Further, we combine our
procedure with quantum chemical validation to identify promising candidates for
the photoactive inhibition of PARP1, an enzyme that is over-expressed in cancer
cells. The top compounds are predicted to have long-lived active forms,
differential bioactivity, and absorption in the near-infrared therapeutic
window.",2302.11490v1
2023-02-27,Interface tool from Wannier90 to RESPACK: wan2respack,"We develop the interface tool $\verb|wan2respack|$, which connects
$\verb|RESPACK|$ (software that derives the low-energy effective Hamiltonians
of solids) with $\verb|Wannier90|$ (software that constructs Wannier
functions). $\verb|wan2respack|$ converts the Wannier functions obtained by
$\verb|Wannier90|$ into those used in $\verb|RESPACK|$, which is then used to
derive the low-energy effective Hamiltonians of solids. In this paper, we
explain the basic usage of $\verb|wan2respack|$ and show its application to
standard compounds of correlated materials, namely, the correlated metal
SrVO$_3$ and the high-$T_{c}$ superconductor La$_2$CuO$_4$. Furthermore, we
compare the low-energy effective Hamiltonians of these compounds using Wannier
functions obtained by $\verb|Wannier90|$ and those obtained by
$\verb|RESPACK|$. We confirm that both types of Wannier functions give the same
Hamiltonians. This benchmark comparison demonstrates that $\verb|wan2respack|$
correctly converts Wannier functions in the $\verb|Wannier90|$ format into
those in the $\verb|RESPACK|$ format.",2302.13531v2
2023-02-27,Mathematical modeling for the synchronization of two interacting active rotors,"We investigate the synchronization of active rotors. A rotor is composed of a
free-rotating arm with a particle that releases a surface-active chemical
compound. It exhibits self-rotation due to the surface tension gradient
originating from the concentration field of the surface-active compound
released from the rotor. In a system with two active rotors, they should
interact through the concentration field. Thus, the interaction between them
does not depend only on the instantaneous positions but also on the dynamics of
the concentration field. By numerical simulations, we show that in-phase and
anti-phase synchronizations occur depending on the distance between the two
rotors. The stability of the synchronization mode is analyzed based on phase
reduction theorem through the calculation of the concentration field in the
co-rotating frame with the active rotor. We also confirm that the numerical
results meet the prediction by theoretical analyses.",2302.13786v2
2023-03-03,How To Guide Your Learner: Imitation Learning with Active Adaptive Expert Involvement,"Imitation learning aims to mimic the behavior of experts without explicit
reward signals. Passive imitation learning methods which use static expert
datasets typically suffer from compounding error, low sample efficiency, and
high hyper-parameter sensitivity. In contrast, active imitation learning
methods solicit expert interventions to address the limitations. However,
recent active imitation learning methods are designed based on human intuitions
or empirical experience without theoretical guarantee. In this paper, we
propose a novel active imitation learning framework based on a teacher-student
interaction model, in which the teacher's goal is to identify the best teaching
behavior and actively affect the student's learning process. By solving the
optimization objective of this framework, we propose a practical
implementation, naming it AdapMen. Theoretical analysis shows that AdapMen can
improve the error bound and avoid compounding error under mild conditions.
Experiments on the MetaDrive benchmark and Atari 2600 games validate our
theoretical analysis and show that our method achieves near-expert performance
with much less expert involvement and total sampling steps than previous
methods. The code is available at https://github.com/liuxhym/AdapMen.",2303.02073v1
2023-03-05,Oblique helicoidal state of the twist-bend nematic doped by chiral azo-compound,"A novel light-sensitive chiral dopant ChD-3816 (an azo compound containing
4-hexanoyloxyphenyl and 2-isopropyl-5-methylcyclohexylbenzoate moieties) was
used for inducing helical twisting in Ntb-forming mixtures of CB7CB/CB6OCB with
5CB added to decrease the phase transition temperatures. The effects of
ChD-3816 upon phase transition temperatures, as well as effects of its
concentration on the measured values of helical twisting were determined. Most
of the measured parameters could be varied due to light-induced trans-cis
isomerization of ChD-3816. Under electric field, selective reflection spectra
in the visible range were obtained for the emerging ChOH structures, with the
wavelengths controllable both by electric field and appropriate UV irradiation.
Possible applications for dynamic formation of contrast images are discussed.",2303.02642v1
2023-03-09,P-even and -odd asymmetries on $^{117}$Sn at the vicinity of the p-resonance E$_\mathrm{p}$=1.33 eV,"A self consistent description of angular correlations in neutron induced
reactions is required for quantitative analysis of parity violating (PV) and
time reversal invariance violating (TRIV) effects in neutron nucleus
scattering. The 1.33 eV p-wave compound resonance in $^{117}$Sn is one of the
few p-wave resonances where enough measurements have been performed to allow a
nontrivial test of the internal consistency of the theory. We present the
results of a global analysis of the several different asymmetries and angular
distribution measurements in ($n, \gamma$) reactions on the 1.33 eV p-wave
resonance in $^{117}$Sn conducted over the last few decades. We show that the
compound resonance mixing theory can give an internally consistent description
of all observations made in this system to date within the experimental
measurement errors. We also confirm the conclusions of previous analyses that a
subthreshold resonance in $^{117}$Sn dominates correlations related to s-p
mixing, and discuss the implications of these results for future searches for
TRIV in this system.",2303.05425v1
2023-03-13,QuTIE: Quantum optimization for Target Identification by Enzymes,"Target Identification by Enzymes (TIE) problem aims to identify the set of
enzymes in a given metabolic network, such that their inhibition eliminates a
given set of target compounds associated with a disease while incurring minimum
damage to the rest of the compounds. This is an NP-complete problem, and thus
optimal solutions using classical computers fail to scale to large metabolic
networks. In this paper, we consider the TIE problem for identifying drug
targets in metabolic networks. We develop the first quantum optimization
solution, called QuTIE (Quantum optimization for Target Identification by
Enzymes), to this NP-complete problem. We do that by developing an equivalent
formulation of the TIE problem in Quadratic Unconstrained Binary Optimization
(QUBO) form, then mapping it to a logical graph, which is then embedded on a
hardware graph on a quantum computer. Our experimental results on 27 metabolic
networks from Escherichia coli, Homo sapiens, and Mus musculus show that QuTIE
yields solutions which are optimal or almost optimal. Our experiments also
demonstrate that QuTIE can successfully identify enzyme targets already
verified in wet-lab experiments for 14 major disease classes.",2303.07508v2
2023-03-15,Accurate GW frontier orbital energies of 134 kilo molecules,"The QM9 dataset [Scientific Data, Vol. 1, 140022 (2014)] became a standard
dataset to benchmark machine learning methods, especially on molecular graphs.
It contains geometries as well as multiple computed molecular properties of
133,885 compounds at B3LYP/6-31G(2df,p) level of theory, including frontier
orbitals (HOMO and LUMO) energies. However, the accuracy of HOMO/LUMO
predictions from density functional theory, including hybrid methods such as
B3LYP, is limited for many applications. In contrast, the GW method
significantly improves HOMO/LUMO prediction accuracy, with mean unsigned errors
in the GW100 benchmark dataset of 100 meV. In this work, we present a new
dataset of HOMO/LUMO energies for the QM9 compounds, computed using the GW
method. This database may serve as a benchmark of HOMO/LUMO prediction,
delta-learning, and transfer learning, particularly for larger molecules where
GW is the most accurate but still numerically feasible method. We expect this
dataset to enable the development of more accurate machine learning models for
predicting molecular properties",2303.08708v1
2023-03-16,Machine learning guided discovery of superconducting calcium borocarbides,"Pursuit of superconductivity in light-element systems at ambient pressure is
of great experimental and theoretical interest. In this work, we combine a
machine learning (ML) method with first-principles calculations to efficiently
search for the energetically favorable ternary Ca-B-C compounds. Three new
layered borocarbides (stable CaBC5 and metastable Ca2BC11 and CaB3C3) are
predicted to be phonon-mediated superconductors at ambient pressure. The
hexagonal CaB3C3 possesses the highest Tc of 26.05 K among the three compounds.
The {\sigma}-bonging bands around the Fermi level account for the large
electron-phonon coupling ({\lambda} = 0.980) of hexagonal CaB3C3. The ML-guided
approach opens up a way for greatly accelerating the discovery of new high-Tc
superconductors.",2303.09342v1
2023-03-20,"Magnetization, dielectric and thermal studies in the double perovskite polycrystalline compound Tm2CoMnO6","We report here a comprehensive study on structural, magnetic, caloric and
electronic properties of the monoclinic phase of double perovskite compound
Tm2CoMnO6 (TCMO) in its polycrysttaline format. Magnetic measurements confirm
the presence of thermal hysteresis in magnetization indicates towards a first
order magnetic transition at its critical point (Tc). Our study finds the
metamagnetic jump in isothermal M(H) at 2 K that signifies the rare earth spin
allignement in loop cycling above a certain critical field. This jump is only
present at very low T that dies out as the T raises. M(H) measurements at
different temperature stipulate that Co2+ and Mn4+ do not order completely
inspite of strong ferromagnetic correlation that is against the previous study
on TCMO. The concurrence of structral, magnetic and dielectric anomaly at Tc
suggest its possible magnetostructural copuling. We found a high dielectric
constant (2700) in TCMO and the Maxwell-Wagner electrial loss spectrum analysis
hints towards a long range hopping mechanism. Sizeable magnetocaloric effect in
terms of entropy change across the transition temperatures has been obtained
from heat capacity data that clearly corroborates its intrinsic behaviour.",2303.10907v2
2023-03-20,Electronic and magnetic properties of Lu and LuH$_2$,"Clarifying the electronic and magnetic properties of lutetium, lutetium
dihydride, and lutetium oxide is very helpful to understand the emergent
phenomena in lutetium-based compounds (such as room-temperature
superconductivity). However, this kind of study is still scarce at present.
Here, we report on the electronic and magnetic properties of lutetium metals,
lutetium dihydride powders, and lutetium oxide powders. Crystal structures and
chemical compositions of these samples were characterized by X-ray diffraction
and X-ray photoemission spectroscopy, respectively. Electrical transport
measurements show that the resistance of lutetium has a linear behavior
depending on temperature, whereas the resistance of lutetium dihydride powders
is independent of temperature. More interestingly,
paramagnetism-ferromagnetism-spin glass transitions were observed at near 240
and 200 K, respectively, in lutetium metals. Our work uncovered the complex
magnetic properties of Lu-based compounds.",2303.11063v2
2023-03-20,Magnetic and singlet phases in the three-dimensional periodic Anderson Model,"Heavy fermion materials are compounds in which localized $f$-orbitals
hybridize with delocalized $d$ ones, leading to quasiparticles with large
renormalized masses. The presence of strongly correlated $f$-electrons at the
Fermi level may also lead to long-range order, such as magnetism, or
unconventional superconductivity. From a theoretical point of view, the
``standard model'' for heavy fermion compounds is the Periodic Anderson Model
(PAM). Despite being extensively scrutinized, its thermodynamic properties in
three-dimensional lattices have not been carefully addressed by unbiased
methodologies. Here we investigate the 3D PAM employing state-of-the-art finite
temperature auxiliary field quantum Monte Carlo simulations. We present the
behavior of the kinetic energy, the entropy, the specific heat, and the double
occupancy as functions of the temperature and the hybridization strength. From
these quantities, and by the analysis of the spin-spin correlation functions,
we investigate the occurrence of magnetic phase transitions at finite
temperatures, and determine the phase diagram of the model, including the
behavior of the N\'eel temperature as a function of the external parameters.",2303.11500v1
2023-03-23,Parameterized Algorithms for Topological Indices in Chemistry,"We have developed efficient parameterized algorithms for the enumeration
problems of graphs arising in chemistry. In particular, we have focused on the
following problems: enumeration of Kekul\'e structures, computation of Hosoya
index, computation of Merrifield-Simmons index, and computation of graph
entropy based on matchings and independent sets. All these problems are known
to be $\# P$-complete. We have developed FPT algorithms for bounded treewidth
and bounded pathwidth for these problems with a better time complexity than the
known state-of-the-art in the literature. We have also conducted experiments on
the entire PubChem database of chemical compounds and tested our algorithms. We
also provide a comparison with naive baseline algorithms for these problems,
along with a distribution of treewidth for the chemical compounds available in
the PubChem database.",2303.13279v1
2023-03-27,Dramatically Accelerated Formation of Graphite Intercalation Compounds Catalyzed by Sodium,"Graphite intercalation compounds (GICs) have a variety of functions due to
their rich material variations, and thus,innovative methods for their synthesis
are desired for practical applications. We have discovered that Na has a
catalytic property that dramatically accelerates the formation of GICs. We
demonstrate that LiC6n (n = 1, 2), KC8, KC12n (n = 2, 3, 4), and NaCx are
synthesized simply by mixing alkali metals and graphite powder with Na at room
temperature (~25 {\deg}C), and AEC6 (AE = Ca, Sr, Ba) are synthesized by
heating Na-added reagents at 250 {\deg}C only for a few hours. The NaCx, formed
by the mixing of C and Na, is understood to act as a reaction intermediate for
a catalyst, thereby accelerating the formation of GICs by lowering the
activation energy of intercalation. The Na-catalyzed method, which enables the
rapid and mass synthesis of homogeneous GIC samples in a significantly simpler
manner than conventional methods, is anticipated to stimulate research and
development for GIC applications.",2303.14909v1
2023-04-06,Unraveling the Crystallization Kinetics of the Ge$_2$Sb$_2$Te$_5$ Phase Change Compound with a Machine-Learned Interatomic Potential,"The phase change compound Ge$_2$Sb$_2$Te$_5$ (GST225) is exploited in
advanced non-volatile electronic memories and in neuromorphic devices which
both rely on a fast and reversible transition between the crystalline and
amorphous phases induced by Joule heating. The crystallization kinetics of
GST225 is a key functional feature for the operation of these devices. We
report here on the development of a machine-learned interatomic potential for
GST225 that allowed us to perform large scale molecular dynamics simulations
(over 10000 atoms for over 100 ns) to uncover the details of the
crystallization kinetics in a wide range of temperatures of interest for the
programming of the devices. The potential is obtained by fitting with a deep
neural network (NN) scheme a large quantum-mechanical database generated within
Density Functional Theory. The availability of a highly efficient and yet
highly accurate NN potential opens the possibility to simulate phase change
materials at the length and time scales of the real devices.",2304.03109v2
2023-04-10,Faster Lead Optimization Mapper Algorithm for Large-Scale Relative Free Energy Perturbation,"In recent years, free energy perturbation (FEP) calculations have garnered
increasing attention as tools to support drug discovery. The lead optimization
mapper (Lomap) was proposed as an algorithm to calculate the relative free
energy between ligands efficiently. However, Lomap requires checking whether
each edge in the FEP graph is removable, which necessitates checking the
constraints for all edges. Consequently, conventional Lomap requires
significant computation time, at least several hours for cases involving
hundreds of compounds, and is impractical for cases with more than tens of
thousands of edges. In this study, we aimed to reduce the computational cost of
Lomap to enable the construction of FEP graphs for hundreds of compounds. We
can reduce the overall number of constraint checks required from an amount
dependent on the number of edges to one dependent on the number of nodes by
using the chunk check process to check the constraints for as many edges as
possible simultaneously. Moreover, the output graph is equivalent to that
obtained using conventional Lomap, enabling direct replacement of the original
Lomap with our method. With our improvement, the execution was tens to hundreds
of times faster than that of the original Lomap.
https://github.com/ohuelab/FastLomap",2304.04713v1
2023-04-10,NutriFD: Proving the medicinal value of food nutrition based on food-disease association and treatment networks,"There is rising evidence of the health benefit associated with specific
dietary interventions. Current food-disease databases focus on associations and
treatment relationships but haven't provided a reasonable assessment of the
strength of the relationship, and lack of attention on food nutrition. There is
an unmet need for a large database that can guide dietary therapy. We fill the
gap with NutriFD, a scoring network based on associations and therapeutic
relationships between foods and diseases. NutriFD integrates 9 databases
including foods, nutrients, diseases, genes, miRNAs, compounds, disease
ontology and their relationships. To our best knowledge, this database is the
only one that can score the associations and therapeutic relationships of
everyday foods and diseases by weighting inference scores of food compounds to
diseases. In addition, NutriFD demonstrates the predictive nature of nutrients
on the therapeutic relationships between foods and diseases through machine
learning models, laying the foundation for a mechanistic understanding of food
therapy.",2304.04775v2
2023-04-11,"Centrosymmetric-noncentrosymmetric Structural Phase Transition in Quasi one-dimensional compound, (TaSe$_4$)$_3$I","(TaSe$_4$)$_3$I, a compound belonging to the family of quasi-one-dimensional
transition-metal tetrachalcogenides, has drawn significant attention due to a
recent report on possible coexistence of two antagonistic phenomena,
superconductivity and magnetism below 2.5~K (Bera et. al, arXiv:2111.14525).
Here, we report a structural phase transition of the trimerized phase at
temperature, $T~\simeq$~145~K using Raman scattering, specific heat, and
electrical transport measurements. The temperature-dependent single-crystal
X-ray diffraction experiments establish the phase transition from a
high-temperature centrosymmetric to a low-temperature non-centrosymmetric
structure, belonging to the same tetragonal crystal family. The first-principle
calculation finds the aforementioned inversion symmetry-breaking structural
transition to be driven by the hybridization energy gain due to the off-centric
movement of the Ta atoms, which wins over the elastic energy loss.",2304.05113v1
2023-04-13,Aromatic molecules as sustainable lubricants explored by ab initio simulations,"In the pursuit of sustainable lubricant materials, the conversion of common
organic molecules into graphitic material has been recently shown to
effectively reduce friction of metallic interfaces. Aromatic molecules are
perfect candidates due to their inertness and possibility to form carbon-based
tribofilms. Among many promising possibilities, we selected a group of common
aromatic compounds and we investigated their capability to reduce the adhesion
of iron interface. Ab initio molecular dynamic simulations of the sliding
interface show that hypericin, a component of St. John's wort, effectively
separates the mating iron surfaces better than graphene. This phenomenon is due
to the size of the molecule, the reactivity of the moieties at its edges and
the possibility to stack several of these structures that can easily slide on
top of each other. The decomposition of the lateral groups of hypericin
observed in the dynamic simulations suggests that the clustering of several
molecules is possible, offering innovative paths to lubricate sliding contacts
with compounds not typically employed in tribology.",2304.06501v2
2023-04-17,ERTIM@MC2: Diversified Argumentative Tweets Retrieval,"In this paper, we present our participation to CLEF MC2 2018 edition for the
task 2 Mining opinion argumentation. It consists in detecting the most
argumentative and diverse Tweets about some festivals in English and French
from a massive multilingual collection. We measure argumentativity of a Tweet
computing the amount of argumentation compounds it contains. We consider
argumentation compounds as a combination between opinion expression and its
support with facts and a particular structuration. Regarding diversity, we
consider the amount of festival aspects covered by Tweets. An initial step
filters the original dataset to fit the language and topic requirements of the
task. Then, we compute and integrate linguistic descriptors to detect claims
and their respective justifications in Tweets. The final step extracts the most
diverse arguments by clustering Tweets according to their textual content and
selecting the most argumentative ones from each cluster. We conclude the paper
describing the different ways we combined the descriptors among the different
runs we submitted and discussing their results.",2304.08047v1
2023-04-17,Ultrafast Relaxation Dynamics of Spin-Density Wave Order in BaFe$_2$As$_2$ under High Pressures,"BaFe$_2$As$_2$ is the parent compound for a family of iron-based
high-temperature superconductors as well as a prototypical example of the
spin-density wave (SDW) system. In this study, we perform an optical pump-probe
study of this compound to systematically investigate the SDW order across the
pressure-temperature phase diagram. The suppression of the SDW order by
pressure manifests itself by the increase of relaxation time together with the
decrease of the pump-probe signal and the pump energy necessary for complete
vaporization of the SDW condensate. We have found that the pressure-driven
suppression of the SDW order at low temperature occurs gradually in contrast to
the thermally-induced SDW transition. Our results suggest that the
pressure-driven quantum phase transition in BaFe$_2$As$_2$ (and probably other
iron pnictides) is continuous and it is caused by the gradual worsening of the
Fermi-surface nesting conditions.",2304.08080v1
2023-04-20,Canting angle behavior of magnetic moments in Y- substituted Tb2BaNiO5 and its relevance for magnetoelectric coupling,"The Haldane-spin chain compound, Tb2BaNiO5, has been known to be an exotic
multiferroic system, exhibiting antiferromagnetic anomalies at T_N1= 63 K and
T_N2= 25 K, with ferroelectricity appearing below T_N2 only. Previous reports
in addition established that, interestingly, Tb ions play a direct and decisive
role to lead to multiferroic properties with a critical canting angle of
magnetic moments, unlike other well-known multiferroics. Here, we report the
results of temperature dependent neutron powder diffraction studies on Tb_2-x
Y_x BaNiO_5, to get an insight into the critical canting angle for multiferroic
behavior. While multiferroic transition temperature decreases linearly with Y
concentration, there is an abrupt drop of relative canting angle (of Tb and Ni
magnetic moments) with respect to that in parent compound for an initial
substitution ofx = 0.5 in the multiferroic region, without any notable change
thereafter. We therefore infer that this critical canting angle is made up of
two components - cooperative (long-range) and local (short-range)
contributions.",2304.10133v1
2023-04-21,SILVR: Guided Diffusion for Molecule Generation,"Computationally generating novel synthetically accessible compounds with high
affinity and low toxicity is a great challenge in drug design. Machine-learning
models beyond conventional pharmacophoric methods have shown promise in
generating novel small molecule compounds, but require significant tuning for a
specific protein target. Here, we introduce a method called selective iterative
latent variable refinement (SILVR) for conditioning an existing diffusion-based
equivariant generative model without retraining. The model allows the
generation of new molecules that fit into a binding site of a protein based on
fragment hits. We use the SARS-CoV-2 Main protease fragments from Diamond
X-Chem that form part of the COVID Moonshot project as a reference dataset for
conditioning the molecule generation. The SILVR rate controls the extent of
conditioning and we show that moderate SILVR rates make it possible to generate
new molecules of similar shape to the original fragments, meaning that the new
molecules fit the binding site without knowledge of the protein. We can also
merge up to 3 fragments into a new molecule without affecting the quality of
molecules generated by the underlying generative model. Our method is
generalizable to any protein target with known fragments and any
diffusion-based model for molecule generation.",2304.10905v1
2023-04-28,Ab-initio study of short-range ordering in vanadium-based disordered rocksalt structures,"Disordered rocksalt Li-excess (DRX) compounds are attractive new cathode
materials for Li-ion batteries as they contain resource-abundant metals and do
not require the use of cobalt or nickel. Understanding the delithiation process
and cation short-range ordering (SRO) in DRX compounds is essential to
improving these promising cathode materials. Herein, we use first-principles
calculations along with the cluster-expansion approach to model the disorder in
DRX Li2-xVO3, 0 < x < 1. We discuss the SRO of Li in tetrahedral and octahedral
sites, and the order in which Li delithiates and V oxidizes with respect to
local environments. We reveal that the number of nearest-neighbor V dictates
the order of delithiation from octahedral sites and that V are oxidized in a
manner that minimizes the electrostatic interactions among V. Our results
provide valuable insight for tailoring the performance of V-based DRX cathode
materials in general by controlling the SRO features that reduce energy
density.",2304.14645v1
2023-04-28,Experimental observation of metallic states with different dimensionality in a quasi-1D charge density wave compound,"TaTe$_4$ is a quasi-1D tetrachalcogenide that exhibits a CDW instability
caused by a periodic lattice distortion. Recently, pressure-induced
superconductivity has been achieved in this compound, revealing a competition
between these different ground states and making TaTe$_4$ very interesting for
fundamental studies. Although TaTe$_4$ exhibits CDW ordering below 475 K,
transport experiments have reported metallic behavior with a resistivity
plateau at temperatures lower than 10 K. In this paper, we study the electronic
structure of TaTe$_4$ using a combination of high-resolution angle-resolved
photoemission spectroscopy and density functional calculations. Our results
reveal the existence of the long-sought metallic states. These states exhibit
mixed dimensionality, while some of them might have potential topological
properties.",2305.00053v1
2023-04-30,Superconductivity in graphite intercalation compounds with sodium,"The discovery of superconductivity in CaC6 with a critical temperature (Tc)
of 11.5 K reignites much interest in exploring high-temperature
superconductivity in graphite intercalation compounds (GICs). Here we identify
a GIC NaC4, discovered by ab initio evolutionary structure search, as a
superconductor with a computed Tc of 41.2 K at 5 GPa. This value is eight times
higher than that of the synthesized GIC NaC2 and possesses the highest Tc among
available GICs. The remarkable superconductivity of GIC NaC4 mainly arises from
the coupling of {\pi} electrons in graphene with the low-frequency vibrations
involving both Na and C atoms. These findings suggest that Na-GICs may hold
great promise as high-Tc superconductors.",2305.00444v2
2023-05-04,A small-gain theorem for 2-contraction of nonlinear interconnected systems,"This paper introduces small-gain sufficient conditions for $2$-contraction of
feedback interconnected systems, on the basis of individual gains of suitable
subsystems arising from a modular decomposition of the second additive compound
equation. The condition applies even to cases when individual subsystems might
fail to be contractive (due to the extra margin of contraction afforded by the
second additive compound matrix). Examples of application are provided to
illustrate the theory and show its degree of conservatism and scope of
applicability.",2305.03211v4
2023-05-10,Vibronic effect on resonant inelastic x-ray scattering in cubic iridium hexahalides,"In resonant inelastic x-ray scattering (RIXS) spectra of K$_2$IrCl$_6$, the
peak for the $j=3/2$ multiplet states shows a splitting that resembles
non-cubic crystal-field effect although the compound is cubic down to 0.3 K.
Here we theoretically describe the RIXS spectra concomitantly treating the
spin-orbit and vibronic interactions. We found that the dynamic Jahn-Teller
effect in the $j=3/2$ multiplet states gives rise to the splitting of the RIXS
spectra and the broadening of the spectra in raising the temperature. The
validity of the interaction parameters for the simulations is supported by our
{\it ab initio} calculations. Our results suggest that, in cubic iridium
compounds, the dynamic Jahn-Teller effect induces the splitting of RIXS spectra
without lowering the symmetry.",2305.05853v4
2023-05-10,Double-layer Kagome Metals Pt3Tl2 and Pt3In2,"The connectivity and inherent frustration of the kagome lattice can produce
interesting electronic structures and behaviors in compounds containing this
structural motif. Here we report the properties of Pt3X2 (X = In and Tl) that
adopt a double-layer kagome net structure related to that of the topologically
nontrivial high temperature ferromagnet Fe3Sn2 and the density wave hosting
compound V3Sb2. We examined the structural and physical properties of single
crystal Pt3Tl2 and polycrystalline Pt3In2 using x-ray and neutron diffraction,
magnetic susceptibility, heat capacity, and electrical transport measurements,
along with density functional theory calculations of the electronic structure.
Our calculations show that Fermi levels lie in pseudogaps in the densities of
states with several bands contributing to transport, and this is consistent
with our Hall effect, magnetic susceptibility, and heat capacity measurements.
While electronic dispersions characteristic of simple kagome nets with
nearest-neighbor hopping are not clearly seen, likely due to the extended
nature of the Pt 5d states, we do observe moderately large and non-saturating
magnetoresistance values and quantum oscillations in the magnetoresistance and
magnetization associated with the kagome nets of Pt.",2305.06491v1
2023-05-11,Consequences and control of multi-scale (dis)order in chiral magnetic textures,"Transition metal-intercalated transition metal dichalcogenides (TMDs) are
promising platforms for next-generation spintronic devices based on their wide
range of electronic and magnetic phases, which can be tuned by varying the host
lattice or the identity of the intercalant, along with its stoichiometry and
spatial order. Some of these compounds host a chiral magnetic phase in which
the helical winding of magnetic moments propagates along a high-symmetry
crystalline axis. Previous studies have demonstrated that variation in
intercalant concentrations can have a dramatic impact on the formation of
chiral domains and ensemble magnetic properties. However, a systematic and
comprehensive study of how atomic-scale order and disorder impacts collective
magnetic behavior are so far lacking. Here, we leverage a combination of
imaging modes in the (scanning) transmission electron microscope (S/TEM) to
directly probe (dis)order across multiple length scales and show how subtle
changes in the atomic lattice can be leveraged to tune the mesoscale spin
textures and bulk magnetic response, with direct implications for the
fundamental understanding and technological implementation of such compounds.",2305.06656v1
2023-05-19,Phase diagrams and superconductivity of ternary Ca-Al-H compounds under high pressure,"The search for high-temperature superconductors in hydrides under high
pressure has always been a research hotspot. Hydrogen-based superconductors
offer an avenue to achieve the long-sought goal of superconductivity at room
temperature. We systematically explore the high-pressure phase diagram,
electronic properties, lattice dynamics and superconductivity of the ternary
Ca-Al-H system using ab initio methods. We found two stable ternary hydrides at
50 GPa: Cmcm-CaAlH5 and Pnnm-CaAl2H8, which both are semiconductors. At 200
GPa, a new phase of P21/m-CaAlH5, P4/mmm-CaAlH7 and a metastable compound
Immm-Ca2AlH12 were found. Furthermore, P4/mmm-CaAlH7 has obvious phonon
softening of high frequency vibrations along the Z-A direction, point A and
point X, which improves the strength of electron-phonon coupling. Therefore, a
superconducting transition temperature Tc of 71 K is generated at 50 GPa. In
addition, the thermodynamic metastable Immm-Ca2AlH12 exhibits a superconducting
transition temperature of 118 K at 250 GPa. These results are very useful for
the experimental searching of new high-Tc superconductors in ternary hydrides.",2305.11678v1
2023-05-20,"Novel correlated 5f electronic states in cubic AnSn3 (An=U, Np, Pu) intermetallics","The intricate interplay between itinerant-localized 5f states and strongly
correlated electronic states have been systematically investigated in
isostructural actinide compounds AnSn3 (An=U, Np, Pu) by using a combination of
the density functional theory and the embedded dynamical mean-field approach.
The obvious narrow flat 5f electronic band with remarkable spectral weight
emerges in the vicinity of Fermi level for three compounds. Subsequently the
significant hybridization between 5f states and conduction bands opens evident
gaps together with conspicuous valence state fluctuations jointly indicating
the partially itinerant 5f electrons. Especially, prominent quasiparticle
multiplets only appear in PuSn3 due to the sizable valence state fluctuations
and multiple competing atomic eigenstates. Therefore itinerant 5f states tend
to involve in active chemical bonding, restraining the formation of local
magnetic moment of actinide atoms, which partly elucidates the underlying
mechanism of paramagnetic USn3 and PuSn3, as well as itinerant-electron
antiferromagnetic NpSn3. Correspondingly, the 5f electronic correlation
strength expressed in band renormalization and electron effective masse
intertwines with itinerant-localized 5f states. Consequently, detail electronic
structure of 5f states dependence on actinide series shall gain deep insight
into our understanding of AnSn3 (An=U, Np, Pu) intermetallics and promote
ongoing research.",2305.12195v1
2023-05-24,Phonon-mediated superconductivity in the Sb-square-net compound LaCuSb$_2$,"We investigated the electronic structure and superconducting properties of
single-crystalline LaCuSb$_2$. The resistivity, magnetization, and specific
heat measurements showed that LaCuSb$_2$ is a bulk superconductor. The observed
Shubnikov-de Haas oscillation and magnetic field dependence of the Hall
resistivity can be reasonably understood assuming a slightly hole-doped Fermi
surface. Electron-phonon coupling calculation clarified the difference from the
isostructural compound LaAgSb$_2$ indicating that (i) low-frequency vibration
modes related to the interstitial layer sandwiched between the Sb-square nets
significantly contribute to the superconductivity and (ii) carriers with
sizable electron--phonon coupling distribute isotropically on the Fermi
surface. These are assumed to be the origin of higher superconducting
transition temperature compared with LaAgSb$_2$. We conclude that the
superconducting properties of LaCuSb$_2$ can be understood within the framework
of conventional phonon-mediated mechanism.",2305.15619v1
2023-06-04,Realization of two-sublattice exchange physics in the triangular lattice compound Ba3Er(BO3)3,"We have synthesized high-quality single crystal samples of the erbium-based
triangular lattice compound Ba3Er(BO3)3. Thermal and magnetic measurements
reveal large anisotropy and a possible phase transition at 100 mK. The
low-temperature magnetic heat capacity can be understood from the two Wyckoff
positions that the magnetic ions Er3+ occupy, which have distinct symmetry
properties and crystal field environments. A point charge calculation for the
crystal electric field levels is consistent with this understanding. Based on
symmetry analysis and classical simulation, we argue that Ba3Er(BO3)3 realizes
an interesting two-sublattice exchange physics, in which the honeycomb lattice
spins develop ferromagnetic correlations due to the additional spins at the
hexagon centers but eventually order antiferromagnetically. Additionally, our
results suggest that quantum fluctuations need to be considered in order to
fully explain the experimental observations.",2306.02463v1
2023-06-10,"Optoelectronic Study of (MA)$_2$NaBiX$_6$ (MA= methylammonium; X=Cl,Br, I) Hybrid Double Perovskites by Ab initio Simulation","High prospects for different optoelectronic applications have drawn much
effort towards hybrid double perovskites for the commercialization of
environmentally friendly Pb-free non-toxic perovskites. Herein, the
optoelectronic study of (MA)$_2$NaBiX$_6$ (MA= methylammonium; X=Cl,Br, I)
hybrid double perovskites by ab initio simulation was investigated.
(MA)$_2$NaBiBr$_6$ and (MA)$_2$NaBiCl$_6$ have indirect X-M bandgaps while
(MA)$_2$NaBiI$_6$ have indirect X-$\Gamma$ bandgap of 2.98 eV, 3.64 eV and 2.32
eV respectively. The results also show that the iodide-based compound,
(MA)$_2$NaBiI$_6$ exhibits superior optoelectronic properties compared to the
bromide and chloride-based compounds, (MA)$_2$NaBiBr$_6$ and
(MA)$_2$NaBiCl$_6$. These findings indicate that the (MA)$_2$NaBiI$_6$ hybrid
double perovskite is a potential material for optoelectronic applications owing
to its high absorption coefficient (on the order of 106cm-1), dielectric
constant ($\approx 3.34$), and refractive index (2.50) in addition to its high
formation energy, which shows its stability.",2306.06417v1
2023-06-10,"Investigation of (CsMA)NaBiX$_6$ (MA= methylammonium; X=Cl,Br, I) Organic-Inorganic Hybrid Double Perovskites for Optoelectronic Applications: A First Principles Study","Organic-inorganic hybrid double perovskites have attracted increasing
interest in the commercialization of lead-free and nontoxic perovskites due to
their unique optoelectronic properties compared with inorganic perovskites. In
this study, the structural, electronic, optical and properties of 3 Pb-free
compounds (CsMA)NaBiX$_6$ (MA= methylammonium; X= Cl, Br, I) were simulated
using first-principles density functional theory (DFT). Results show that the
investigated compounds are semiconductors with tunable bandgaps characteristics
that can be used in devices like light emitting diodes, and predict the
suitability of the (CsMA)NaBiI$_6$ organic-inorganic hybrid double perovskite
in this study for optoelectronic applications owing to its high absorption
coefficient (in the order of $10^6$cm$^{-1}$), dielectric constant ($\approx
3.24$), and refractive index (2.50) as well as its stability as revealed by its
high formation energy. Additionally, the high absorption coefficient, high
refractive indices and dielectric constants of the investigated materials
posits that they have a number of optoelectronic applications including
photovoltaic cells among others.",2306.07295v1
2023-06-14,Families of jets of arc type and higher (co)dimensional Du Val singularities,"Families of jets through singularities of algebraic varieties are here
studied in relation to the families of arcs originally studied by Nash. After
proving a general result relating them, we look at normal locally complete
intersection varieties with rational singularities and focus on a class of
singularities we call ""higher Du Val singularities"", a higher dimensional (and
codimensional) version of Du Val singularities that is closely related to
Arnold singularities. More generally, we introduce the notion of ""higher
compound Du Val singularities"", whose definition parallels that of compound Du
Val singularities. For such singularities, we prove that there exists a
one-to-one correspondence between families of arcs and families of jets of
sufficiently high order through the singularities. In dimension two, the result
partially recovers a theorem of Mourtada on the jet schemes of Du Val
singularities. As an application, we give a solution of the Nash problem for
higher Du Val singularities.",2306.08291v2
2023-06-26,"Comment on ""Light-induced melting of competing stripe orders without introducing superconductivity in La$_{1.875}$Ba$_{0.125}$CuO$_4$"" (arXiv:2306.07869v1)","In the manuscript arXiv:2306.07869v1, N. L. Wang and co-authors report the
results of a near-infrared pump / terahertz probe study in the stripe-ordered
cuprate La$_{1.875}$Ba$_{0.125}$CuO$_4$. They measured a change in optical
conductivity, but did not find signatures of transient superconductivity. From
this observation they extrapolate that in all cuprates in which striped states
have been excited with light, there must be no light-induced superconductivity.
They conclude that ""transient superconductivity cannot be induced by melting of
the competing stripe orders with pump pulses whose photon energy is much higher
than the superconducting gap of cuprates."" Here we show that this extrapolation
is unwarranted. First, the absence of light-induced superconductivity in this
particular compound was already reported in a previous paper, which instead
showed positive evidence for La$_{1.885}$Ba$_{0.115}$CuO$_4$. In addition, the
experiment discussed here used photo-excitation with too low fluence and at a
suboptimal wavelength. More broadly, a negative result in one compound is
rarely compelling indication of the absence of an effect in an entire class of
materials.",2306.14438v1
2023-06-26,Sliding ferroelectricity in a bulk misfit layer compound (PbS)$_{1.18}$VS$_2$,"Twisted heterostructures of two-dimensional crystals can create a moir\'{e}
landscape, which can change the properties of it's parent crystals. However,
the reproducibility of manual stacking is far from perfect. Here, the
alternated stacking of post-transition metal monochalcogenides and transition
metal dichalcogenides in misfit layer compound crystals is used as a moir\'{e}
generator. Using X-ray diffraction, the presence of twins with a well-defined
small twist angle between them is shown. Due to the twist, the surface
electrical potential from the induced ferroelectricity is observed using
scanning probe microscopy and electron microscopy.",2306.14446v1
2023-06-26,Origin of Charge Density Wave in Topological Semimetals SrAl4 and EuAl4,"Topological semimetals in BaAl4-type structure show many interesting
behaviors, such as charge density wave (CDW) in SrAl4 and EuAl4, but not the
isostructural and isovalent BaAl4, SrGa4 and BaGa4. Here using Wannier
functions based on density functional theory, we calculate the susceptibility
functions with millions of k-points to reach the small q-vector and study the
origin and driving force behind the CDW. Our comparative study reveals that the
origin of the CDW in SrAl4 and EuAl4 is the strong electron-phonon coupling
interaction for the transverse acoustic mode at small q-vector along the
\{Gamma}-Z direction besides the maximum of the real part of the susceptibility
function from the nested Fermi surfaces of the Dirac-like bands, which explains
well the absence of CDW in the other closely related compounds in a good
agreement with experiment. We also connect the different CDW behaviors in the
Al compounds to the macroscopic elastic properties.",2306.15068v2
2023-06-29,HYDRA: Hybrid Robot Actions for Imitation Learning,"Imitation Learning (IL) is a sample efficient paradigm for robot learning
using expert demonstrations. However, policies learned through IL suffer from
state distribution shift at test time, due to compounding errors in action
prediction which lead to previously unseen states. Choosing an action
representation for the policy that minimizes this distribution shift is
critical in imitation learning. Prior work propose using temporal action
abstractions to reduce compounding errors, but they often sacrifice policy
dexterity or require domain-specific knowledge. To address these trade-offs, we
introduce HYDRA, a method that leverages a hybrid action space with two levels
of action abstractions: sparse high-level waypoints and dense low-level
actions. HYDRA dynamically switches between action abstractions at test time to
enable both coarse and fine-grained control of a robot. In addition, HYDRA
employs action relabeling to increase the consistency of actions in the
dataset, further reducing distribution shift. HYDRA outperforms prior imitation
learning methods by 30-40% on seven challenging simulation and real world
environments, involving long-horizon tasks in the real world like making coffee
and toasting bread. Videos are found on our website:
https://tinyurl.com/3mc6793z",2306.17237v2
2023-07-19,Nonparametric estimation of the jump-size distribution for a stochastic storage system with periodic observations,"This work presents a non-parametric estimator for the cumulative distribution
function (CDF) of the jump-size distribution for a storage system with compound
Poisson input. The workload process is observed according to an independent
Poisson sampling process. The nonparametric estimator is constructed by first
estimating the characteristic function (CF) and then applying an inversion
formula. The convergence rate of the CF estimator at $s$ is shown to be of the
order of $s^2/n$, where $n$ is the sample size. This convergence rate is
leveraged to explore the bias-variance tradeoff of the inversion estimator. It
is demonstrated that within a certain class of continuous distributions, the
risk, in terms of MSE, is uniformly bounded by $C n^{-\frac{\eta}{1+\eta}}$,
where $C$ is a positive constant and the parameter $\eta>0$ depends on the
smoothness of the underlying class of distributions. A heuristic method is
further developed to address the case of an unknown rate of the compound
Poisson input process.",2307.10116v1
2023-07-26,Computational prediction of high thermoelectric performance in As$_{2}$Se$_{3}$ by engineering out-of-equilibrium defects,"We employed first-principles calculations to investigate the thermoelectric
transport properties of the compound As$_2$Se$_3$. Early experiments and
calculations have indicated that these properties are controlled by a kind of
native defect called antisites. Our calculations using the linearized Boltzmann
transport equation within the relaxation time approximation show good agreement
with the experiments for defect concentrations of the order of 10$^{19}$
cm$^{-3}$. Based on our total energy calculations, we estimated the equilibrium
concentration of antisite defects to be about 10$^{14}$ cm$^{-3}$. These
results suggest that the large concentration of defects in the experiments is
due to kinetic and/or off-stoichiometry effects and in principle it could be
lowered, yielding relaxation times similar to those found in other chalcogenide
compounds. In this case, for relaxation time higher than 10 fs, we obtained
high thermoelectric figures of merit of 3 for the p-type material and 2 for the
n-type one.",2307.14078v1
2023-07-26,Waypoint-Based Imitation Learning for Robotic Manipulation,"While imitation learning methods have seen a resurgent interest for robotic
manipulation, the well-known problem of compounding errors continues to afflict
behavioral cloning (BC). Waypoints can help address this problem by reducing
the horizon of the learning problem for BC, and thus, the errors compounded
over time. However, waypoint labeling is underspecified, and requires
additional human supervision. Can we generate waypoints automatically without
any additional human supervision? Our key insight is that if a trajectory
segment can be approximated by linear motion, the endpoints can be used as
waypoints. We propose Automatic Waypoint Extraction (AWE) for imitation
learning, a preprocessing module to decompose a demonstration into a minimal
set of waypoints which when interpolated linearly can approximate the
trajectory up to a specified error threshold. AWE can be combined with any BC
algorithm, and we find that AWE can increase the success rate of
state-of-the-art algorithms by up to 25% in simulation and by 4-28% on
real-world bimanual manipulation tasks, reducing the decision making horizon by
up to a factor of 10. Videos and code are available at
https://lucys0.github.io/awe/",2307.14326v1
2023-07-26,Laplacian eigenvalues of independence complexes via additive compound matrices,"The independence complex of a graph $G=(V,E)$ is the simplicial complex
$I(G)$ on vertex set $V$ whose simplices are the independent sets in $G$. We
present new lower bounds on the eigenvalues of the $k$-dimensional Laplacian
$L_k(I(G))$ in terms of the eigenvalues of the graph Laplacian $L(G)$. As a
consequence, we show that for all $k\geq 0$, the dimension of the $k$-th
reduced homology group (with real coefficients) of $I(G)$ is at most \[ \left|
\left\{ 1\leq i_1<\cdots<i_{k+1}\leq |V| : \,
\lambda_{i_1}+\lambda_{i_2}+\cdots+\lambda_{i_{k+1}} \geq |V|\right\}\right|,\]
where $\lambda_1\geq\lambda_2\geq \cdots\geq \lambda_{|V|}=0$ are the
eigenvalues of $L(G)$. In particular, if $k$ is the minimal number such that
the sum of the $k$ largest eigenvalues of $L(G)$ is at least $|V|$, then
$\tilde{H}_i(I(G);\mathbb{R})=0$ for all $i\leq k-2$. This extends previous
results by Aharoni, Berger and Meshulam. Our proof relies on a relation between
the $k$-dimensional Laplacian $L_k(I(G))$ and the $(k+1)$-th additive compound
matrix of $L_0(I(G))$, which is an $\binom{n}{k+1}\times\binom{n}{k+1}$ matrix
whose eigenvalues are all the possible sums of $k+1$ eigenvalues of the
$0$-dimensional Laplacian. Our results apply also in the more general setting
of vertex-weighted Laplacian matrices.",2307.14496v1
2023-07-28,Compound heat wave and PM2.5 pollution episodes in U.S. cities,"This study analyzes heat waves (HWs), air pollution (AP) episodes, and
compound HW and AP events (CE) in the urban environment and provides a
comparison between events in urban areas (UAs) and rural areas (RAs). A 1-km
gridded daily minimum temperature dataset and a 1-km gridded daily PM2.5
concentration dataset were used along with geospatial data to characterize
events by their frequency, intensity in heat, intensity in pollution, and
duration. The greatest differences between UAs and RAs in frequency, heat
intensity, pollution intensity, and duration for all events were seen in the
West and Southwest regions. For both UAs and RAs, it was found that HWs were
the most frequent, intense, and longest lasting in the West and Southwest
regions, AP episodes were the most frequent and longest lasting in the
Northeast, Ohio Valley, and Southeast regions, and AP episodes were the most
intense in the Northern Rockies and Plains and Upper Midwest regions. It was
concluded that HWs (AP episodes) had a greater impact on CEs than AP episodes
(HWs) in regions with more prominent HWs (AP episodes).",2307.15296v1
2023-07-29,Developing novel ligands with enhanced binding affinity for the sphingosine 1-phosphate receptor 1 using machine learning,"Multiple sclerosis (MS) is a debilitating neurological disease affecting
nearly one million people in the United States. Sphingosine-1-phosphate
receptor 1, or S1PR1, is a protein target for MS. Siponimod, a ligand of S1PR1,
was approved by the FDA in 2019 for MS treatment, but there is a demonstrated
need for better therapies. To this end, we finetuned an autoencoder machine
learning model that converts chemical formulas into mathematical vectors and
generated over 500 molecular variants based on siponimod, out of which 25
compounds had higher predicted binding affinity to S1PR1. The model was able to
generate these ligands in just under one hour. Filtering these compounds led to
the discovery of six promising candidates with good drug-like properties and
ease of synthesis. Furthermore, by analyzing the binding interactions for these
ligands, we uncovered several chemical properties that contribute to high
binding affinity to S1PR1. This study demonstrates that machine learning can
accelerate the drug discovery process and reveal new insights into protein-drug
interactions.",2307.16037v1
2023-07-31,Definition of the invariant and the relationship with the compounds numbers. Generalisation of the Euler theorem,"The purpose of this article is to introduce the concept of invariance and its
properties. These properties can be used to check the primality of a number.
Combining these properties with the Euler theorem, it is possible to generalize
this theorem for all the values of $a^{\varphi(m)}$ where $0 < a < m {\pmod
{m}}$ independently if a is co prime or not with m. As $a^{\varphi(m)+1} \equiv
a$ if $m = a \cdot b$ and $GCD(a, b) = 1$. As the following steps, a new
hypothesis is formulated regarding the substitution of the Totien function for
an equivalent function that explains the Carmichael numbers. Keywords: Prime
Numbers, Compound Numbers, Primality test, Euler theorem",2307.16616v2
2023-08-04,Kinetics of Li transport in vanadium-based disordered rocksalt structures,"Disordered rocksalt Li-excess (DRX) compounds have emerged as promising new
cathode materials for lithium-ion batteries, as they can consist solely of
resource-abundant metals and eliminate the need for cobalt or nickel. A deeper
understanding of the lithium-ion transport kinetics in DRX compounds is
essential for enhancing their rate performance. This study employs
first-principles calculations, cluster expansion techniques, and kinetic Monte
Carlo simulations to investigate the Li+ transport properties in DRX Li2-xVO3,
where 0 <= x <= 1. Our findings underscore (i) the necessity of accounting for
both tetrahedral and octahedral Li occupancy when predicting the transport
properties in DRX materials, (ii) the factors influencing the variation in the
diffusion coefficients with Li content in Li2-xVO3, and (iii) the impact of Li+
correlated motion on the kinetics of Li+ transport. We reveal that the relative
stability of tetrahedral and octahedral Li determines the number of active
sites within the percolation network, subsequently affecting the Li+ transport
properties. Furthermore, we demonstrate that the wide site-energy distribution
causes correlated motion in Li2-xVO3, which hinders Li+ transport. Although our
study focuses on Li2-xVO3 as a model system, the insights gained apply to all
DRX materials, given their inherently broader site-energy distributions.",2308.02725v1
2023-08-08,Investigating dissociation pathways of nitrobenzene via mega-electron-volt ultrafast electron diffraction,"As the simplest nitroaromatic compound, nitrobenzene is an interesting model
system to explore the rich photochemistry of nitroaromatic compounds. Previous
measurements of nitrobenzene's photochemical dynamics have probed structural
and electronic properties, which, at times, paint a convoluted and sometimes
contradictory description of the photochemical landscape. A sub-picosecond
structural probe can complement previous electronic measurements and aid in
determining the photochemical dynamics with less ambiguity. We investigate the
ultrafast dynamics of nitrobenzene triggered by photoexcitation at 267 nm
employing megaelectronvolt ultrafast electron diffraction with femtosecond time
resolution. We measure the first 5 ps of dynamics and, by comparing our
measured results to simulation, we unambiguously distinguish the lowest singlet
and triplet electronic states. We observe ground state recovery within 160 +/-
60 fs through internal conversions and without signal corresponding to
photofragmentation. Our lack of dissociation signal within the first 5 ps
indicates that previously observed photofragmenation reactions take place in
the vibrationally ""hot"" ground state on timescales considerably beyond 5 ps.",2308.03996v1
2023-08-08,"Structural, electronic, magnetic properties of Cu-doped lead-apatite Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O","The recent report of superconductivity in the Cu-doped PbPO compound
stimulates the extensive researches on its physical properties. Herein, the
detailed atomic and electronic structures of this compound are investigated,
which are the necessary information to explain the physical properties,
including possible superconductivity. By the first-principles electronic
structure calculations, we find that the partial replacement of Pb at $4f$ site
by Cu atom, instead of Pb at $6h$ site, plays a crucial role in dominating the
electronic state at Fermi energy. The $3d$ electronic orbitals of Cu atom
emerge near the Fermi energy and exhibit strong spin-polarization, resulting in
the local moment around the doped Cu atom. Particularly, the ground state of
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O (x = 1) is determined to be a semiconducting
phase, in good agreement with the experimental measurements.",2308.04344v1
2023-08-10,Evaluation of insulating behavior by Pb Substitution and Pressure-Induced Superconductivity in La2O2Bi3-xPb1+xS6,"We report synthesis, characterization, and physical properties of layered
bismuth-sulfide compounds La2O2Bi3-xPb1+xS6. We synthesized a new La2O2Bi3PbS6
compound, whose crystal structure is similar to those of the La2O2Bi3AgS6
superconductor or La2O2Bi2Pb2S6 (insulator) with a four-layer-type conducting
layer. The crystal structure of La2O2Bi3PbS6 is characterized in a tetragonal
P4/nmm space group, and the lattice parameters are a = 4.084(1) {\AA} and c =
19.71(2) {\AA}. The obtained La2O2Bi3PbS6 sample exhibits narrow gap
semiconductor (metallic-like) transport behavior with an anomaly near the 160
K. A metallic-like to insulator transition has been observed through Pb
substitution, with increasing x in La2O2Bi3-xPb1+xS6. Furthermore, we applied
external pressure for x = 0 and observed pressure-induced superconductivity.
The onset of superconductivity appeared at 0.93 GPa, and the highest transition
temperature was 3.1 K at 2.21 GPa.",2308.05300v1
2023-08-11,Empirical Bayes Estimation with Side Information: A Nonparametric Integrative Tweedie Approach,"We investigate the problem of compound estimation of normal means while
accounting for the presence of side information. Leveraging the empirical Bayes
framework, we develop a nonparametric integrative Tweedie (NIT) approach that
incorporates structural knowledge encoded in multivariate auxiliary data to
enhance the precision of compound estimation. Our approach employs convex
optimization tools to estimate the gradient of the log-density directly,
enabling the incorporation of structural constraints. We conduct theoretical
analyses of the asymptotic risk of NIT and establish the rate at which NIT
converges to the oracle estimator. As the dimension of the auxiliary data
increases, we accurately quantify the improvements in estimation risk and the
associated deterioration in convergence rate. The numerical performance of NIT
is illustrated through the analysis of both simulated and real data,
demonstrating its superiority over existing methods.",2308.05883v1
2023-08-15,Tilt-induced charge localisation in phosphide antiperovskite photovoltaics,"Antiperovskites are a rich family of compounds with applications in battery
cathodes, superconductors, solid-state lighting, and catalysis. Recently, a
novel series of antimonide phosphide antiperovskites (A$_3$SbP, where A = Ca,
Sr, Ba) were proposed as candidate photovoltaic absorbers due to their ideal
band gaps, small effective masses and strong optical absorption. In this work,
we explore this series of compounds in more detail using relativistic hybrid
density functional theory. We reveal that the proposed cubic structures are
dynamically unstable and instead identify a tilted orthorhombic Pnma phase as
the ground state. Tilting is shown to induce charge localisation that widens
the band gap and increases the effective masses. Despite this, we demonstrate
that the predicted maximum photovoltaic efficiencies remain high (24-31% for
200 nm thin films) by bringing the band gaps into the ideal range for a solar
absorber. Finally, we assess the band alignment of the series and suggest hole
and electron contact materials for efficient photovoltaic devices.",2308.07858v1
2023-08-20,Tetrahedral rotations in alkaline-earth metal orthovanadates,"The alkaline-earth orthovanadate Sr$_3$V$_2$O$_8$ with the palmierite
structure is reported to host a dielectric anomaly as well as a structural
phase transition above the room temperature. With V$^{5+}$ ions and tetrahedral
oxygen coordination, the crystal structure of this compound is not studied in
detail from first principles yet. In this work, we perform a detailed analysis
of the crystal structure and instabilities of M$_3$V$_2$O$_8$ ($\text{M} =
\text{Ca, Sr, Ba}$) orthovanadates with the palmierite structure using first
principles density functional theory. We find that as the M$^{2+}$ cation size
decreases, a significant structural distortion that changes the symmetry from
$R\bar{3}m$ to $C2/c$ emerges. This change is accompanied with a rotation of
the oxygen tetrahedra. Our calculations also indicate that the polar
instability in these compounds are suppressed by these tetrahedral rotations.",2308.10342v2
2023-08-22,"Tuning of Electrical, Magnetic, and Topological Properties of Magnetic Weyl Semimetal Mn$_{3+x}$Ge by Fe doping","We report on the tuning of electrical, magnetic, and topological properties
of the magnetic Weyl semimetal (Mn$_{3+x}$Ge) by Fe doping at the Mn site,
Mn$_{(3+x)-\delta}$Fe$_{\delta}$Ge ($\delta$=0, 0.30, and 0.62). Fe doping
significantly changes the electrical and magnetic properties of Mn$_{3+x}$Ge.
The resistivity of the parent compound displays metallic behavior, the system
with $\delta$=0.30 of Fe doping exhibits semiconducting or bad-metallic
behavior, and the system with $\delta$=0.62 of Fe doping demonstrates a
metal-insulator transition at around 100 K. Further, we observe that the Fe
doping increases in-plane ferromagnetism, magnetocrystalline anisotropy, and
induces a spin-glass state at low temperatures. Surprisingly, topological Hall
state has been noticed at a Fe doping of $\delta$=0.30 that is not found in the
parent compound or with $\delta$=0.62 of Fe doping. In addition, spontaneous
anomalous Hall effect observed in the parent system is significantly reduced
with increasing Fe doping concentration.",2308.11183v1
2023-08-25,Solar wind ion charge state distributions and compound cross sections for solar wind charge exchange X-ray emission,"Solar Wind Charge eXchange X-ray (SWCX) emission in the heliosphere and
Earth's exosphere is a hard to avoid signal in soft X-ray observations of
astrophysical targets. On the other hand, the X-ray imaging possibilities
offered by the SWCX process has led to an increasing number of future dedicated
space missions for investigating the solar wind-terrestrial interactions and
magnetospheric interfaces. In both cases, accurate modelling of the SWCX
emission is key to correctly interpret its signal, and remove it from
observations, when needed. In this paper, we compile solar wind abundance
measurements from ACE for different solar wind types, and atomic data from
literature, including charge exchange cross-sections and emission
probabilities, used for calculating the compound cross-section $\alpha$ for the
SWCX X-ray emission. We calculate $\alpha$ values for charge-exchange with H
and He, relevant to soft X-ray energy bands (0.1 - 2.0 keV) for various solar
wind types and solar cycle conditions.",2308.13647v1
2023-08-31,Electronic band reconstruction across the insulator-metal transition in colossal magnetoresistive EuCd2P2,"While colossal magnetoresistance (CMR) in Eu-based compounds is often
associated with strong spin-carrier interactions, the underlying reconstruction
of the electronic bands is much less understood from spectroscopic experiments.
Here using angle-resolved photoemission, we directly observe an electronic band
reconstruction across the insulator-metal (and magnetic) transition in the
recently discovered CMR compound EuCd2P2. This transition is manifested by a
large magnetic band splitting associated with the magnetic order, as well as
unusual energy shifts of the valence bands: both the large ordered moment of Eu
and carrier localization in the paramagnetic phase are crucial. Our results
provide spectroscopic evidence for an electronic structure reconstruction
underlying the enormous CMR observed in EuCd2P2, which could be important for
understanding Eu-based CMR materials, as well as designing CMR materials based
on large-moment rare-earth magnets.",2308.16844v1
2023-09-05,Enumeration of saturated and unsaturated substituted N-heterocycles,"Mathematical and computational approaches in chemistry and biochemistry fill
a gap in respect to the analysis of the physicochemical features of compounds
and their functionality and provide an overview of known as well as yet
unknown, but hypothetically possible structures. Nitrogen containing
heterocycles such as aziridine, azetidine and pyrrolidine bear a high potential
in pharmacology, biotechnology and synthetic biology. Here, we present a
mathematical enumeration procedure for all possible azaheterocycles with at
least one substituent depending on the number of atoms in the ring, in the
sense of saturated and unsaturated congeners. One subgroup belonging to that
substance class is constituted by ring-shaped amino acids with a secondary
amino group such as proline. A recursion formula is derived, which results in a
modified Lucas number series. Moreover, an explicit formula for determining the
number of such substances based on the Golden Ratio is given and a second one,
based on binomial coefficients, is newly derived. This enumeration is a helpful
tool for construction or complementation of virtual compound databases and for
computer-assisted chemical synthesis route planning.",2309.02343v1
2023-09-05,Phononic drumhead surface state in distorted kagome compound RhPb,"RhPb was initially recognized as one of a CoSn-like compounds with $P6/mmm$
symmetry, containing an ideal kagome lattice of $d$-block atoms. However,
theoretical calculations predict the realization of the phonon soft mode which
leads to the kagome lattice distortion and stabilization of the structure with
$P\bar{6}2m$ symmetry [A. Ptok et al., Phys. Rev. B 104, 054305 (2021)]. Here,
we present the single crystal x-ray diffraction results supporting this
prediction. Furthermore, we discuss the main dynamical properties of RhPb with
$P\bar{6}2m$ symmetry. The bulk phononic dispersion curves contain several
flattened bands, Dirac nodal lines, and triple degenerate Dirac points. As a
consequence, the phononic drumhead surface state is realized for the (100)
surface, terminated by the zigzag-like edge of Pb honeycomb sublattice.",2309.02419v1
2023-09-08,Re-entrance of resistivity due to the interplay of superconductivity and magnetism in $\ce{Eu_{0.73}Ca_{0.27}(Fe_{0.87}Co_{0.13})2As2}$,"By simultaneous Co and Ca-doping we were able to obtain an
$\ce{EuFe2As2}$-based compound with superconductivity appearing above the
antiferromagnetic order of $\ce{Eu^{2+}}$ magnetic moments. However, as soon as
the antiferromagnetic order appears a re-entrance behavior is observed
\textemdash{} instead of zero resistivity and diamagnetic signal down to the
temperature of \unit[2]{K}. By investigating magnetization, ac susceptibility
and electrical transport properties of
$\ce{Eu_{0.73}Ca_{0.27}(Fe_{0.87}Co_{0.13})2As2}$ and comparing them to
previously studied M\""ossbauer effect and neutron scattering measurements of
this and similar compounds an explanation of such behavior is proposed.",2309.04308v2
2023-09-14,Photo-induced reversible modification of the Curie-Weiss temperature in paramagnetic gadolinium compounds,"Gadolinium oxyhydride GdHO is a photochromic material that darkens under
illumination and bleaches back by thermal relaxation. As an inorganic
photochromic material that can be easily deposited by magnetron sputtering,
GdHO has very interesting potential applications as a functional material,
specially for smart glazing applications. However, the underlying reasons
behind the photochromic mechanism-which can be instrumental for the correct
optimisation of GdOH for different applications-are not completely understood.
In this paper, we rely on the well-stablished magnetic properties of Gd$^{3+}$
to shed light on this matter. GdOH thin films present paramagnetic behaviour
similar to other Gd$^{3+}$ compounds such as Gd$_2$O$_3$. Illumination of the
films result in a reversible increase of the Curie-Weiss temperature pointing
to RKKY interactions, which is consistent with the resistivity decrease
observed in the photo-darkened films.",2309.07978v1
2023-09-20,No need for an oracle: the nonparametric maximum likelihood decision in the compound decision problem is minimax,"We discuss the asymptotics of the nonparametric maximum likelihood estimator
(NPMLE) in the normal mixture model. We then prove the convergence rate of the
NPMLE decision in the empirical Bayes problem with normal observations. We
point to (and use) the connection between the NPMLE decision and Stein unbiased
risk estimator (SURE).
  Next, we prove that the same solution is optimal in the compound decision
problem where the unobserved parameters are not assumed to be random.
  Similar results are usually claimed using an oracle-based argument. However,
we contend that the standard oracle argument is not valid. It was only
partially proved that it can be fixed, and the existing proofs of these partial
results are tedious. Our approach, on the other hand, is straightforward and
short.",2309.11401v1
2023-09-28,Variations of GIT quotients and dimer combinatorics for toric compound Du Val singularities,"A dimer model is a bipartite graph described on the real two-torus, and it
gives the quiver as the dual graph. It is known that for any three-dimensional
Gorenstein toric singularity, there exists a dimer model such that a GIT
quotient parametrizing stable representations of the associated quiver is a
projective crepant resolution of this singularity for some stability parameter.
It is also known that the space of stability parameters has the
wall-and-chamber structure, and for any projective crepant resolution of a
three-dimensional Gorenstein toric singularity can be realized as the GIT
quotient associated to a stability parameter contained in some chamber. In this
paper, we consider dimer models giving rise to projective crepant resolutions
of a toric compound Du Val singularity. We show that sequences of zigzag paths,
which are special paths on a dimer model, determine the wall-and-chamber
structure of the space of stability parameters. Moreover, we can track the
variations of stable representations under wall-crossing using the sequences of
zigzag paths.",2309.16112v1
2023-09-28,Open Compound Domain Adaptation with Object Style Compensation for Semantic Segmentation,"Many methods of semantic image segmentation have borrowed the success of open
compound domain adaptation. They minimize the style gap between the images of
source and target domains, more easily predicting the accurate pseudo
annotations for target domain's images that train segmentation network. The
existing methods globally adapt the scene style of the images, whereas the
object styles of different categories or instances are adapted improperly. This
paper proposes the Object Style Compensation, where we construct the
Object-Level Discrepancy Memory with multiple sets of discrepancy features. The
discrepancy features in a set capture the style changes of the same category's
object instances adapted from target to source domains. We learn the
discrepancy features from the images of source and target domains, storing the
discrepancy features in memory. With this memory, we select appropriate
discrepancy features for compensating the style information of the object
instances of various categories, adapting the object styles to a unified style
of source domain. Our method enables a more accurate computation of the pseudo
annotations for target domain's images, thus yielding state-of-the-art results
on different datasets.",2309.16127v1
2023-10-11,Magnetic State Control of Non-van der Waals 2D Materials by Hydrogenation,"Controlling the magnetic state of two-dimensional (2D) materials is crucial
for spintronic applications. By employing data-mining and autonomous density
functional theory calculations, we demonstrate the switching of magnetic
properties of 2D non-van der Waals materials upon hydrogen passivation. The
magnetic configurations are tuned to states with flipped and enhanced moments.
For 2D CdTiO$_3$ - a nonmagnetic compound in the pristine case - we observe an
onset of ferromagnetism upon hydrogenation. Further investigation of the
magnetization density of the pristine and passivated systems provides a
detailed analysis of modified local spin symmetries and the emergence of
ferromagnetism. Our results indicate that selective surface passivation is a
powerful tool for tailoring magnetic properties of nanomaterials such as
non-vdW 2D compounds.",2310.07329v1
2023-10-19,CCIL: Continuity-based Data Augmentation for Corrective Imitation Learning,"We present a new technique to enhance the robustness of imitation learning
methods by generating corrective data to account for compounding errors and
disturbances. While existing methods rely on interactive expert labeling,
additional offline datasets, or domain-specific invariances, our approach
requires minimal additional assumptions beyond access to expert data. The key
insight is to leverage local continuity in the environment dynamics to generate
corrective labels. Our method first constructs a dynamics model from the expert
demonstration, encouraging local Lipschitz continuity in the learned model. In
locally continuous regions, this model allows us to generate corrective labels
within the neighborhood of the demonstrations but beyond the actual set of
states and actions in the dataset. Training on this augmented data enhances the
agent's ability to recover from perturbations and deal with compounding errors.
We demonstrate the effectiveness of our generated labels through experiments in
a variety of robotics domains in simulation that have distinct forms of
continuity and discontinuity, including classic control problems, drone flying,
navigation with high-dimensional sensor observations, legged locomotion, and
tabletop manipulation.",2310.12972v1
2023-10-21,Anionic Character of the Conduction Band of Sodium Chloride,"The alkali halides are ionic compounds. Each alkali atom donates an electron
to a halogen atom, leading to ions with full shells. The valence band is mainly
located on halogen atoms, while, in a traditional picture, the conduction band
is mainly located on alkali atoms. Scanning tunnelling microscopy of NaCl at 4
K actually shows that the conduction band is located on Cl$^-$ because the
strong Madelung potential reverses the order of the Na$^+$ 3s and Cl$^-$ 4s
levels. We verify this reversal is true for both atomically thin and bulk NaCl,
and discuss implications for II-VI and I-VII compounds.",2310.14070v1
2023-10-22,Critical behavior and magnetocaloric effect in Tsai-type 2/1 and 1/1 quasicrystal approximants,"Stable Tsai-type quinary 1/1 and 2/1 approximant crystals (ACs) with chemical
compositions Au56.25Al10Cu7In13Tb13.75 and Au55.5Al10Cu7In13Tb14.5,
respectively, exhibiting ferromagnetic (FM) long-range orders were successfully
synthesized and studied for their magnetic properties and magnetocaloric
effect. The 1/1 and 2/1 ACs primarily differ in their long-range atomic
arrangement and rare earth (RE) distribution, with the latter approaching
quasiperiodic order while still preserving periodicity. Analyses based on the
scaling principle and Kouvel-Fisher (KF) relations suggested mean-field-like
behavior near Curie temperatures in both compounds. From magnetization
measurements and the Maxwell equation, a magnetic entropy change of -4.3 and
-4.1 J/K mol Tb were derived under a magnetic field change of 7 T for the 1/1
and 2/1 ACs, respectively. The results indicated a prominent role of
intra-cluster magnetic interactions on critical behavior and magnetic entropy
of the Tsai-type compounds.",2310.14292v1
2023-10-23,A Theoretical Perspective on the Photochemistry of Boron-Nitrogen Lewis Adducts,"Boron-Nitrogen (B-N) Lewis adducts form a versatile family of compounds with
numerous applications in functional molecules. Despite the growing interest in
this family of compounds for optoelectronic applications, little is currently
known about their photophysics and photochemistry. Even the electronic
absorption spectrum of ammonia borane, the textbook example of a B-N Lewis
adduct, is unavailable. Given the versatility of the light-induced processes
exhibited by these molecules, we propose in this work a detailed theoretical
study of the photochemistry and photophysics of simple B-N Lewis adducts. We
used advanced techniques in computational photochemistry to identify and
characterize the possible photochemical pathways followed by ammonia borane,
and extended this knowledge to the substituted B-N Lewis adducts
pyridine-borane and pyridine-boric acid. The photochemistry observed for this
series of molecules allows us to extract qualitative rules to rationalize the
light-induced behavior of more complex B-N containing molecules.",2310.15268v1
2023-10-25,Critical-point anomalies in doped CeRhIn5,"The heavy-fermion compound CeRhIn$_5$ can be tuned through a quantum critical
point, when In is partially replaced by Sn. This way additional charge carriers
are introduced and the antiferromagnetic order is gradually suppressed to zero
temperature. Here we investigate the temperature-dependent optical properties
of CeRh(In$_{1-x}$Sn$_x$)$_5$ single crystals for $x = 4.4\%$, $6.9\%$ and
$9.8\%$. With increasing Sn concentration the infrared conductivity reveals a
clear enhancement of the $c$-$f$ hybridization strength. At low temperatures we
observed a non-Fermi-liquid behavior in the frequency dependence of the
scattering rate and effective mass in all three compounds. In addition, below a
characteristic temperature $T^* \approx 10$ K, the temperature dependent
resistivity $\rho(T)$ follows a $\log T$ behavior, typical for a non-Fermi
liquid. The temperature-dependent magnetization also exhibits anomalous
behavior below $T^*$. Our investigation reveal that below $T^*$ the system
shows a pronounced non-Fermi-liquid behavior and $T^*$ monotonically increases
as the quantum critical point is approached.",2310.16689v1
2023-10-29,Investigation of correlation effects in FeSe and FeTe by LDA + U method,"Correlation effects are observed strong in Iron chalcogenides superconductors
by experimental and theoretical investigations. We present a comparative study
of the influence of Coulomb interaction and Hund's coupling in the electronic
structure of FeSe and FeTe. The calculation is based on density functional
theory (DFT) with local density approximation(LDA+U) framework employed in
TB-LMTO ASA code. We found the correlation effects were orbital selective due
to the strength of interorbital hybridization among different Fe-3d orbitals
mediated via chalcogen (Se/Te-p) orbitals is different in both the compounds,
however Coulomb interaction is screened significantly by Te-p bands in FeTe.
Similarly the orbital section is different in both the compounds because of the
difference in the chalcogen height.",2310.18994v1
2023-10-30,Plasma treatment as an unconventional molecular magnet engineering method,"Molecular magnetism aims to design materials with unique properties at the
molecular level, focusing on the systematic synthesis of new chemical
compounds. In this paper, we propose an alternative route to engineer molecular
magnetic materials through plasma irradiation. Our research indicates that the
long-range magnetic order temperature in the three-dimensional
$\mathrm{\{[Mn^{II}(H_2O)_2]_2[Nb^{IV}(CN)_8]\cdot 4H_2O\}_n}$ molecular
ferrimagnet increases by 20 K after plasma treatment. The core structure of the
compound does not reveal significant changes after plasma processing, as
confirmed by the X-ray powder diffraction analysis. The observed results are
attributed to the release of crystallized water molecules. The described
procedure can serve as a viable approach to altering the magnetic properties of
the molecular systems.",2310.19467v1
2023-10-30,"Heptazine, Cyclazine, and Related Compounds: Chemically-Accurate Estimates of the Inverted Singlet-Triplet Gap","Molecules that violate Hund's rule and exhibit an inverted gap between the
lowest singlet $S_1$ and triplet $T_1$ excited states have attracted
considerable attention due to their potential applications in optoelectronics.
Amongst these molecules, the triangular-shaped heptazine, and its derivatives,
have been in the limelight. However, conflicting reports have arisen regarding
the relative energies of $S_1$ and $T_1$. Here, we employ highly accurate
levels of theory, such as CC3, to not only resolve the debate concerning the
sign but also quantify the magnitude of the $S_1$-$T_1$ gap. We also determine
the 0-0 energies to evaluate the significance of the vertical approximation. In
addition, we compute reference $S_1$-$T_1$ gaps for a series of 10 related
molecules. This enables us to benchmark lower-order methods for future
applications on larger systems within the same family of compounds. This
contribution can serve as a reliable foundation for the design of
triangular-shaped molecules with enhanced photophysical properties.",2310.19768v2
2023-11-05,"Computing Remoteness Functions of Moore, Wythoff, and Euclid's games","We study remoteness function $\mathcal R$ of impartial games introduced by
Smith in 1966. The player who moves from a position $x$ can win if and only if
$\mathcal R(x)$ is odd. The odd values of $\mathcal R(x)$ show how soon the
winner can win, while even values show how long the loser can resist, provided
both players play optimally. This function can be applied to the conjunctive
compounds of impartial games, in the same way as the Sprague-Grundy function is
applicable to their disjunctive compounds.
  We provide polynomial algorithms computing $\mathcal R(x)$ for games Euclid
and generalized Wythoff. For Moore's NIM we give a simple explicit formula for
$\mathcal R(x)$ if it is even and show that computing it becomes an NP-hard
problem for the odd values.",2311.02685v1
2023-11-06,Bonus-Malus scale premiums for tweedie's compound poisson models,"Based on the recent paper by Delong et al. (2021), two distributions for the
total claims amount (loss cost) are considered: Compound Poisson-gamma (CPG)
and Tweedie. Each is used as an underlying distribution in the Bonus-Malus
Scale (BMS) model described in the paper by Boucher (2023). The BMS model links
the premium of an insurance contract to a function of the insurance experience
of the related policy. In other words, the idea is to model the increase and
the decrease in premiums for insureds that do or do not file claims. Therefore,
our proposed models can be seen as a generalization of the paper of Delong et
al. (2021) and an extension of the work of Boucher (2023). We applied our
approach to a sample of data from a major insurance company in Canada. Data fit
and predictability were analyzed. We showed that the studied models are
exciting alternatives to consider from a practical point of view, and that
predictive ratemaking models can address some importantpractical
considerations.",2311.03222v1
2023-11-06,Repulsive Tomonaga-Luttinger Liquid in Quasi-one-dimensional Alternating Spin-$1/2$ Antiferromagnet NaVOPO$_4$,"We probe the magnetic field-induced Tomonaga-Luttinger liquid (TLL) state in
the bond-alternating spin-$1/2$ antiferromagnetic (AFM) chain compound
NaVOPO$_4$ using thermodynamic as well as local $\mu$SR and $^{31}$P NMR probes
down to milli-K temperatures in magnetic fields up to 14~T. The $\mu$SR and NMR
relaxation rates in the gapless TLL regime decay slowly following
characteristic power-law behaviour, enabling us to directly determine the
interaction parameter $K$ as a function of the magnetic field. These estimates
are cross-checked using magnetization and specific heat data. The
field-dependent $K$ lies in the range of $0.4 < K < 1$ and indicates repulsive
nature of interactions between the spinless fermions, in line with the
theoretical predictions. This renders NaVOPO$_4$ the first experimental
realization of TLL with repulsive fermionic interactions in hitherto studied
$S=1/2$ bond-alternating AFM-AFM chain compounds.",2311.03231v1
2023-11-10,AV$_3$Sb$_5$ Kagome Superconductors: Progress and Future Directions,"The recent discovery of the AV$_3$Sb$_5$ (A=K, Rb, Cs) kagome superconductors
launched a growing field of research investigating electronic instabilities in
kagome metals. Specifically, the AV$_3$Sb$_5$ family naturally exhibits a Fermi
level tuned to the Van Hove singularities associated with the saddle points
formed from the prototypical kagome band structure. The charge density wave and
superconducting states that form within the kagome networks of these compounds
exhibit a number of anomalous properties reminiscent of theoretical predictions
of exotic states in kagome metals tuned close to their Van Hove fillings. Here
we provide an overview of the key structural and electronic features of
AV$_3$Sb$_5$ compounds and review the status of investigations into their
unconventional electronic phase transitions.",2311.05946v1
2023-11-10,Unconventional superconductivity without doping: infinite-layer nickelates under pressure,"High-temperature unconventional superconductivity quite generically emerges
from doping a strongly correlated parent compound, often (close to) an
antiferromagnetic insulator. The recently developed dynamical vertex
approximation is a state-of-the-art technique that has quantitatively predicted
the superconducting dome of nickelates. Here, we apply it to study the effect
of pressure in the infinite-layer nickelate Sr$_x$Pr$_ {1-x}$NiO$_2$. We
reproduce the increase of the critical temperature ($T_c$) under pressure found
in experiment up to 12 GPa. According to our results, $T_c$ can be further
increased with higher pressures. Even without Sr-doping the parent compound,
PrNiO$_2$, will become a high-temperature superconductor thanks to a strongly
enhanced self-doping of the \nidxsqysq{} orbital under pressure. With a maximal
\Tc{} of 100\,K around 100\,GPa, nickelate superconductors can reach that of
the best cuprates.",2311.06195v1
2023-11-15,"Ba6RE2Ti4O17 (RE= Nd, Sm,Gd, Dy-Yb): A family of Rare-earth based layered triangular lattice magnets","Rare-earth-based triangular-lattice magnets provide the fertile ground to
explore the exotic quantum magnetic state. Herein, we report a new family of
RE-based triangular-lattice magnets Ba6RE2Ti4O17(RE= rare earth ions)
crystallized into the hexagonal structure with space group of P63 mmc, where
magnetic rare earth ions form an ideal triangular lattice within the ab-plane
and stack in an AA -type fashion along the c-axis. The low-temperature magnetic
susceptibility results reveal all the serial compounds have the dominant
antiferromagnetic interactions and an absence of magnetic ordering down to 1.8
K. The magnetization and electron spin resonance results indicate distinct
magnetic anisotropy for the compounds with different RE ions. Moreover,
Ba6Nd2Ti4O17 single crystal is successfully grown and it exhibits strong Ising
like anisotropy with magnetic easy-axis perpendicular to the triangle-lattice
plane, being a candidate to explore quantum spin liquid state with dominant
Ising-type interaction.",2311.08937v2
2023-11-26,"Quantum oscillations in kagome metals (Ti, Zr, Hf)V6Sn6 at van Hove filling","Kagome materials have recently drawn great attention due to the interplay
between nontrivial band topology, electron correlations and van Hove
singularities related many-body orders. Here we report three new vanadium-based
kagome metals, TiV6Sn6, ZrV6Sn6 and HfV6Sn6, and conduct a comprehensive
investigation on their structural, magnetic and electrical transport
properties. All three compounds exhibit large unsaturated magnetoresistances
and multiband Hall effects at low temperatures, indicating the existence of
multiple highly mobile carriers. Both the diagonal and off-diagonal resistivity
show quantum oscillations with nontrivial Berry phases and high quantum
mobilities. First-principles calculations together with quantum oscillation
analyses suggest the van Hove singularities at the M point for the three
compounds all locate in close vicinity of the Fermi level, and there also exist
multiple topological nontrivial band crossings including a nodal ring and a
massive Dirac cone. Our work extends the kagome R166 family and paves the way
for searching possible van Hove physics in the V kagome lattice.",2311.15239v1
2023-11-30,Generalized Lyapunov conditions for k-contraction: analysis and feedback design,"Recently, the concept of k-contraction has been introduced as a promising
generalization of contraction for dynamical systems. However, the study of
k-contraction properties has faced significant challenges due to the reliance
on complex mathematical objects called matrix compounds. As a result, related
control design methodologies have yet to appear in the literature. In this
paper, we overcome existing limitations and propose new sufficient conditions
for k-contraction which do not rely on matrix compounds. Our design-oriented
conditions stem from a strong geometrical interpretation and establish a
connection between kcontraction and p-dominance. Notably, these conditions are
also necessary in the linear time-invariant framework. Leveraging on these
findings, we propose a feedback design methodology for both the linear and the
nonlinear scenarios.",2311.18388v1
2023-12-06,Concatenated Backward Ray Mapping on the Compound Parabolic Concentrator,"Concatenated backward ray mapping is an alternative for ray tracing in 2D. It
is based on the phase-space description of an optical system. Phase space is
the set of position and direction coordinates of light rays intersecting a
surface. The original algorithm is limited to optical systems consisting of
only straight surfaces; we generalize it to accommodate curved surfaces. The
algorithm is applied to a standard optical system, the compound parabolic
concentrator. We compare the accuracy and speed of the generalized algorithm,
the original algorithm and Monte Carlo ray tracing. The results show that the
generalized algorithm outperforms both other methods.",2312.03366v1
2023-12-06,Fingerprints of the Jahn-Teller and superexchange physics in optical spectra of manganites,"Transition metal oxides incorporating Jahn-Teller (JT) ions Mn3+ (3d4) in
manganites and Cu2+ (3d9) in cuprates exhibit outstanding magnetic and
electronic properties, including colossal magnetoresistance (CMR) and
high-temperature superconductivity (HTSC). The physics of these compounds is
associated with the orbitally-degenerate electronic states of JT ions, leading
to the linear electron-lattice interaction, complemented by the entirely
electronic superexchange (SE) interaction. Here, we discuss the fingerprints of
the JT and SE physics in the temperature-dependent complex dielectric function
spectra and multi-order Raman scattering spectra measured in a detwinned LaMnO3
crystal, which is a famous compound exhibiting cooperative JT effect, being
also a progenitor of magnetic materials exhibiting CMR effect. In accordance
with the obtained experimental evidence, the associated effective parameters
characterizing the JT and SE physics in manganites are presented.",2312.03677v1
2023-12-12,CompdVision: Combining Near-Field 3D Visual and Tactile Sensing Using a Compact Compound-Eye Imaging System,"As automation technologies advance, the need for compact and multi-modal
sensors in robotic applications is growing. To address this demand, we
introduce CompdVision, a novel sensor that employs a compound-eye imaging
system to combine near-field 3D visual and tactile sensing within a compact
form factor. CompdVision utilizes two types of vision units to address diverse
sensing needs, eliminating the need for complex modality conversion. Stereo
units with far-focus lenses can see through the transparent elastomer for depth
estimation beyond the contact surface. Simultaneously, tactile units with
near-focus lenses track the movement of markers embedded in the elastomer to
obtain contact deformation. Experimental results validate the sensor's superior
performance in 3D visual and tactile sensing, proving its capability for
reliable external object depth estimation and precise measurement of tangential
and normal contact forces. The dual modalities and compact design make the
sensor a versatile tool for robotic manipulation.",2312.07146v2
2023-12-14,Quantifying the Uncertainty of Sensitivity Coefficients Computed from Uncertain Compound Admittance Matrix and Noisy Grid Measurements,"The power-flow sensitivity coefficients (PFSCs) are widely used in the power
system for expressing linearized dependencies between the controlled (i.e., the
nodal voltages, lines currents) and control variables (e.g., active and
reactive power injections, transformer tap positions, etc.). The PFSCs are
often computed by knowing the compound admittance matrix of a given network and
the grid states. However, when the branch parameters (or admittance matrix) are
inaccurate or known with limited accuracy, the computed PFSCs can not be relied
upon. Uncertain PFSCs, when used in control, can lead to infeasible control
set-points. In this context, this paper presents a method to quantify the
uncertainty of the PFSCs from uncertain branch parameters and noisy grid-state
measurements that can be used for formulating safe control schemes. We derive
an analytical expression using the error-propagation principle. The developed
tool is numerically validated using Monte Carlo simulations.",2312.09351v1
2023-12-15,Single PW takes a shortcut to compound PW in US imaging,"Reconstruction of ultrasound (US) images from radio-frequency data can be
conceptualized as a linear inverse problem. Traditional deep learning
approaches, which aim to improve the quality of US images by directly learning
priors, often encounter challenges in generalization. Recently, diffusion-based
generative models have received significant attention within the research
community due to their robust performance in image reconstruction tasks.
However, a limitation of these models is their inherent low speed in generating
image samples from pure Gaussian noise progressively. In this study, we exploit
the inherent similarity between the US images reconstructed from a single plane
wave (PW) and PW compounding PWC). We hypothesize that a single PW can take a
shortcut to reach the diffusion trajectory of PWC, removing the need to begin
with Gaussian noise. By employing an advanced diffusion model, we demonstrate
its effectiveness in US image reconstruction, achieving a substantial reduction
in sampling steps. In-vivo experimental results indicate that our approach can
reduce sampling steps by 60%, while preserving comparable performance metrics
with the conventional diffusion model.",2312.09514v1
2023-12-19,Informatics-based learning of oxygen vacancy ordering principles in oxygen-deficient perovskites,"Ordered oxygen vacancies (OOVs) in perovskites can exhibit long-range order
and may be used to direct materials properties through modifications in
electronic structures and broken symmetries. Based on the various vacancy
patterns observed in previously known compounds, we explore the ordering
principles of OOVs in oxygen-deficient perovskite oxides with
$AB\mathrm{O}_{2.5}$ stoichiometry to identify other OOV variants. We performed
first-principles calculations to assess the OOV stability on a dataset of 50
OOV structures generated from our bespoke algorithm. The algorithm employs
uniform planar vacancy patterns on (111) pseudocubic perovskite layers and the
approach proves effective for generating stable OOV patterns with minimal
computational loads. We find as expected that the major factors determining the
stability of OOV structures include coordination preferences of transition
metals and elastic penalties resulting from the assemblies of polyhedra.
Cooperative rotational modes of polyhedra within OOV structures reduce elastic
instabilities by optimizing the bond valence of $A$- and $B$-cations. This
finding explains the observed formation of vacancy channels along low-index
crystallographic directions in prototypical OOV phases. The identified ordering
principles enable us to devise other stable vacancy patterns with longer
periodicity for targeted property design in yet to be synthesized compounds.",2312.11886v1
2023-12-19,On-Surface Synthesis of Silole and Disilacyclooctaene Derivatives,"Sila-cyclic rings are a class of organosilicon cyclic compounds and have
abundant application in organic chemistry and materials science. However, it is
still challenging to synthesize compounds with sila-cyclic rings in solution
chemistry due to their low solubility and high reactivity. Recently, on-surface
synthesis was introduced into organosilicon chemistry as 1,4- disilabenzene
bridged nanostructures were obtained via coupling between bromo-substituted
molecules and silicon atoms on Au(111). Here, we extend this strategy for
syntheses of silole derivatives and graphene nanoribbons with eight-membered
sila-cyclic rings from 2,2',6,6'- tetrabromobiphenyl and
1,4,5,8-tetrabromonaphthalene on Au(111), respectively. Their structures and
electronic properties were investigated by a combination of scanning tunneling
microscopy/spectroscopy and density functional theory calculations. This work
demonstrates a generality of this synthesis strategy to fabricate various
silicon incorporated nanostructures.",2312.11959v1
2023-12-20,Robustly Improving Bandit Algorithms with Confounded and Selection Biased Offline Data: A Causal Approach,"This paper studies bandit problems where an agent has access to offline data
that might be utilized to potentially improve the estimation of each arm's
reward distribution. A major obstacle in this setting is the existence of
compound biases from the observational data. Ignoring these biases and blindly
fitting a model with the biased data could even negatively affect the online
learning phase. In this work, we formulate this problem from a causal
perspective. First, we categorize the biases into confounding bias and
selection bias based on the causal structure they imply. Next, we extract the
causal bound for each arm that is robust towards compound biases from biased
observational data. The derived bounds contain the ground truth mean reward and
can effectively guide the bandit agent to learn a nearly-optimal decision
policy. We also conduct regret analysis in both contextual and non-contextual
bandit settings and show that prior causal bounds could help consistently
reduce the asymptotic regret.",2312.12731v1
2023-12-21,Orbital-resolved DFT+U for molecules and solids,"We present an orbital-resolved extension of the Hubbard $U$ correction to
density-functional theory (DFT). Compared to the conventional shell-averaged
approach, the prediction of energetic, electronic and structural properties is
strongly improved, particularly for compounds characterized by both localized
and hybridized states in the Hubbard manifold. The numerical values of all
Hubbard parameters are readily obtained from linear-response calculations. The
relevance of this more refined approach is showcased by its application to bulk
solids pyrite (FeS$_2$) and pyrolusite ($\beta$-MnO$_2$), as well as to six
Fe(II) molecular complexes. Our findings indicate that a careful definition of
Hubbard manifolds is indispensable for extending the applicability of DFT+$U$
beyond its current boundaries. The present orbital-resolved scheme aims to
provide a computationally undemanding yet accurate tool for electronic
structure calculations of charge-transfer insulators, transition-metal (TM)
complexes and other compounds displaying significant orbital hybridization.",2312.13580v1
2023-11-22,Docking-based generative approaches in the search for new drug candidates,"Despite the great popularity of virtual screening of existing compound
libraries, the search for new potential drug candidates also takes advantage of
generative protocols, where new compound suggestions are enumerated using
various algorithms. To increase the activity potency of generative approaches,
they have recently been coupled with molecular docking, a leading methodology
of structure-based drug design. In this review, we summarize progress since
docking-based generative models emerged. We propose a new taxonomy for these
methods and discuss their importance for the field of computer-aided drug
design. In addition, we discuss the most promising directions for further
development of generative protocols coupled with docking.",2312.13944v1
2023-12-21,"Amine-Modified ZIF-8 for Enhanced CO$_2$ Capture: Synthesis, Characterization and Performance Evaluation","The urgent need for sustainable and innovative approaches to mitigate the
increasing levels of atmospheric CO$_2$ necessitates the development of
efficient methods for its removal. In this study, we focus on the synthesis and
functionalization of metal-organic framework (MOF) ZIF-8 at room temperature to
enhance its capacity for CO$_2$ capture. Specifically, we investigated the
impact of four amino-compounds, namely tetraethylenepentamine (TEPA),
hexadecylamine (HDA), ethanolamine (ELA), and cyclopropylamine (CPA), on the
chemical structure, size, surface area and porosity and CO$_2$ capturing of
ZIF-8 powder. By varying concentrations of the amino-compounds, we examined
their influence on the ZIF-8 properties. These results highlight the potential
of simple synthesis and functionalization techniques for MOFs in enhancing
their CO$_2$ capture capabilities. The findings from this study offer new
opportunities for the development of strategies to mitigate CO$_2$ emissions
using MOFs.",2312.14974v1
2023-12-29,Significance of the compound nucleus surface energy coefficients in the synthesis of the superheavy nuclei with $\textbf{Z=112-120}$,"This paper investigates the impacts of the different surface energy
coefficients on the compound nucleus decay modes during heavy ion fusion
reactions, with focus given to the superheavy nuclei (SHN) in the range of
$Z=112-118$. The evaporation-residue (ER) cross sections were calculated for
different surface asymmetric constants, $k_{s}$ and surface energy constants,
$\gamma_{0}$. In these calculations, the di-nuclear system model and proximity
potential, along with considering deformed nuclei, were employed. Comparing the
experimental data and this theoretical approach, the best values of $k_{s}$ and
$\gamma_{0}$ are $0.7546$ and $0.9180~\mathrm{MeV~fm^{-2}}$, respectively.
Furthermore, this new model was used to investigate the probability of
synthesis of experimentally unknown heavier systems with $Z=119$ and $120$.
There exist five promising combinations to synthesize SHN with $Z=119$: a)
${^{249}}\mathrm{Cf}({^{45}}\mathrm{Sc},3n){^{291}}119$, b)
${^{249}}\mathrm{Cf}({^{45}}\mathrm{Sc},4n){^{290}}119$, c) ${^{247}}\mathrm
{Bk}({^{50}}\mathrm{Ti},3n){^{294}}119$, d)
${^{254}}\mathrm{Es}({^{48}}\mathrm{Ca},3n){^{299}}119$, and e)
${^{254}}\mathrm{Es}({^{48}}\mathrm{Ca},4n){^{298}}119$. In addition, it is
found that the best combinations to synthesize SHN with $Z=120$ are
${^{249}}\mathrm{Cf}({^{50}}\mathrm{Ti},3n){^{296}}120$, and
${^{251}}\mathrm{Cf}({^{50}}\mathrm{Ti},3n){^{298}}120$.",2312.17567v1
2024-01-02,Excitonic Instability in Ta$_2$Pd$_3$Te$_5$,"By systematic theoretical calculations, we have revealed an excitonic
insulator (EI) in a van der Waals layered compound Ta$_2$Pd$_3$Te$_5$.
First-principles calculations show that the monolayer is a nearly zero-gap
semiconductor with the modified Becke-Johnson functional. Due to the like
symmetry of the band-edge states, the 2D polarization $\alpha_{2D}$ would be
finite as the band gap goes to zero, allowing for the EI state in the compound.
Using the first-principles many-body perturbation theory, the $GW$-BSE
calculation shows that the exciton binding energy $E_b$ is larger than the
single particle band gap $E_g$, indicating the excitonic instability.
Additionally, no structure instability is found in the phonon spectrum of this
material. Our findings suggest that the Ta$_2$Pd$_3$Te$_5$ monolayer is an
excitonic insulator without structure distortion.",2401.01222v2
2024-01-05,The Fate of Simple Organics on Titan's Surface: A Theoretical Perspective,"Atmospheric photochemistry on Titan continuously transforms methane and
nitrogen gases into various organic compounds. This study explores the fate of
these molecules when they land on Titan's surface. Our analytical exploration
reveals that most simple organics found in Titan's atmosphere, including all
nitriles, triple-bonded hydrocarbons, and benzene, land as solids. Only a few
compounds are in the liquid phase, while only ethylene remains gaseous. For the
simple organics that land as solids, we further examine their interactions with
Titan's lake liquids. Utilizing principles of buoyancy, we found that flotation
can be achieved via porosity-induced (25-60% porosity) or capillary
force-induced buoyancy for HCN ices on ethane-rich lakes. Otherwise, these ices
would sink and become lakebed sediments. By evaluating the timescale of
flotation, our findings suggest that porosity-induced flotation of
millimeter-sized and larger sediments is the only plausible mechanism for
floating solids to explain the transient ""magic islands"" phenomena on Titan's
lakes.",2401.02640v1
2024-01-15,Animal-associated marine Acidobacteria with a rich natural product repertoire,"Sponges have long been recognized as a rich source of bioactive natural
products. Various studies suggest that many of these compounds are produced by
symbiotic bacteria. However, substance supplies and functional insights about
the producers remain limited because cultivation remains unsuccessful. To
identify alternative, sustainable sources of sponge-derived polyketides, we
computationally analyzed 5289 characterized and orphan trans-acyltransferase
polyketide synthases, enzymes with widespread roles in polyketide biosynthesis
by bacterial symbionts. The analytical workflow predicted marine animal-derived
Acidobacteria of the family Acanthopleuribacteraceae with large sets of
biosynthetic gene clusters to be enriched in sponge-type chemistry. Targeted
compound isolation from a chiton-associated strain yielded new congeners of the
phorboxazoles and calyculins, potent and scarce cytotoxins exclusively known
from sponges. These first natural products of Acidobacteria and new coral
metagenomic data on a third family member suggest animal-associated
Acanthopleuribacteraceae as a rich source of sponge-type as well as novel
metabolites",2401.07730v2
2024-01-16,BanglaNet: Bangla Handwritten Character Recognition using Ensembling of Convolutional Neural Network,"Handwritten character recognition is a crucial task because of its abundant
applications. The recognition task of Bangla handwritten characters is
especially challenging because of the cursive nature of Bangla characters and
the presence of compound characters with more than one way of writing. In this
paper, a classification model based on the ensembling of several Convolutional
Neural Networks (CNN), namely, BanglaNet is proposed to classify Bangla basic
characters, compound characters, numerals, and modifiers. Three different
models based on the idea of state-of-the-art CNN models like Inception, ResNet,
and DenseNet have been trained with both augmented and non-augmented inputs.
Finally, all these models are averaged or ensembled to get the finishing model.
Rigorous experimentation on three benchmark Bangla handwritten characters
datasets, namely, CMATERdb, BanglaLekha-Isolated, and Ekush has exhibited
significant recognition accuracies compared to some recent CNN-based research.
The top-1 recognition accuracies obtained are 98.40%, 97.65%, and 97.32%, and
the top-3 accuracies are 99.79%, 99.74%, and 99.56% for CMATERdb,
BanglaLekha-Isolated, and Ekush datasets respectively.",2401.08035v2
2024-01-19,Leveraging Domain Adaptation for Accurate Machine Learning Predictions of New Halide Perovskites,"We combine graph neural networks (GNN) with an inexpensive and reliable
structure generation approach based on the bond-valence method (BVM) to train
accurate machine learning models for screening 222,960 halide perovskites using
statistical estimates of the DFT/PBE formation energy (Ef), and the PBE and HSE
band gaps (Eg). The GNNs were fined tuned using domain adaptation (DA) from a
source model, which yields a factor of 1.8 times improvement in Ef and 1.2 -
1.35 times improvement in HSE Eg compared to direct training (i.e., without
DA). Using these two ML models, 48 compounds were identified out of 222,960
candidates as both stable and that have an HSE Eg that is relevant for
photovoltaic applications. For this subset, only 8 have been reported to date,
indicating that 40 compounds remain unexplored to the best of our knowledge and
therefore offer opportunities for potential experimental examination.",2401.10998v1
2024-01-27,On the origin of metal-insulator transitions in the parent compounds of ruthenium-pnictide superconductors,"We study the interplay of the structural phase transition, flat electronic
band dispersion, and metal-to-insulator transition (MIT) in the parent
compounds of the Ru-pnictide superconductors by using first-principles
calculations. Our electron and phonon calculations reveal that Ru(P,As) undergo
MIT accompanied by orthorhombic to monoclinic distortion at low temperature,
but RuSb stays orthorhombic and metallic in agreement with the experimental
findings. We find that although small monoclinic distortion can remove the van
Hove singularity at the Fermi level, it does not immediately gap out the Fermi
surface and a large value of monoclinic distortion is necessary for a clear MIT
suggesting the possibility of an intermediate pseudogapped monoclinic metallic
phase. Furthermore, we predict a light-induced two-step insulator-to-metal and
structural transitions in the monoclinic phases of RuP and RuAs, which can be
tested in future ultrafast pump-probe experiments as an alternative ideal play
ground to VO$_2$.",2401.15302v1
2024-01-29,Using multiple Dirac delta points to describe inhomogeneous flux density over a cell boundary in a single-cell diffusion model,"Biological cells can release compounds into their direct environment,
generally inhomogeneously over their cell membrane, after which the compounds
spread by diffusion. In mathematical modelling and simulation of a collective
of such cells, it is theoretically and numerically advantageous to replace
spatial extended cells with point sources, in particular when cell numbers are
large, but still so small that a continuum density description cannot be
justified, or when cells are moving. We show that inhomogeneous flux density
over the cell boundary may be realized in a point source approach, thus
maintaining computational efficiency, by utilizing multiple, clustered point
sources (and sinks). In this report, we limit ourselves to a sinusoidal
function as flux density in the spatial exclusion model, and we show how to
determine the amplitudes of the Dirac delta points in the point source model,
such that the deviation between the point source model and the spatial
exclusion model is small.",2401.16261v1
2024-01-29,Copper alloys deterioration due to anthropogenic action,"Results are presented from several samples taken from leaves of the Pardon
Portico of Mosque-Cathedral of Cordoba, where an alteration on their surface
was detected. Metal samples analyzed using X-ray microanalysis and powder x-ray
diffraction were predominantly constituted by copper with some amounts of zinc
attributed to brass, whereas other samples were also constituted by copper, tin
and lead attributed to bronze. Surface samples were analyzed using the same
techniques. In addition Fourier transform infrared spectroscopy was also
used.The main compound identified in all the surface of the leaves is copper
chloride hydroxide (atacamite). Lead chlorides have also been found. These data
show that the sudden alteration that appears may be attributed to the use of
some cleaning product containing chloride. Other compounds detected in the
surface were gypsum, quartz and oxalates coming from environmental
contamination.",2401.16538v1
2024-01-30,Coexistence of low and high spin states in La$_{18}$Co$_{28}$Pb$_{3}$,"The electronic structure and magnetic properties of a newly predicted stable
ternary compound La$_{18}$Co$_{28}$Pb$_{3}$ are studied using electronic
structure analysis. The ground state of this compound is ferromagnetic, with
three positions of nonequivalent magnetic Co atoms. A strong dependence of
magnetic properties on volume shows that this system is situated near the point
of magnetic instability. A coexistence of high- and low-spin ferromagnetic
states as a function of volume near equilibrium was discovered. A corresponding
spin tunneling splitting was estimated. The stability of the theoretically
predicted magnetic ground state was tested by varying the Hubbard parameter.
The thermal spin fluctuations were added to estimate the paramagnetic moment
and a Curie temperature. The necessity of experimental verification of the
obtained results is emphasized.",2401.17091v1
2024-02-02,Magnetic properties of a spin-1/2 octagonal lattice,"We successfully synthesized a verdazyl-based complex,
($p$-Py-V-$p$-CN)$_2$[Cu(hfac)$_2$]. Molecular orbital calculations reveal that
three types of antiferromagnetic (AF) interactions are involved in the
formation of a spin-1/2 distorted octagonal lattice composed of the verdazyl
radical and Cu spins. The magnetic properties of the compound exhibited
contributions from AF correlations and a phase transition to an AF ordered
state at approximately $T_{\rm{N}}$ = 2.5 K. Below $T_{\rm{N}}$, we observed a
$T^2$ dependence of the specific heat, indicating dominant two-dimensional AF
correlations within the octagonal lattice. The magnetization curve in the
low-temperature region exhibited a low-field linear increase, subsequent
bending at 1/3 magnetization, and high-field nonlinear increase. We reproduced
the observed unique magnetic behavior through the numerical analysis based on
the octagonal lattice. These results demonstrate that the present compound
exhibits magnetic properties characteristic of octagonal lattice topology.",2402.01200v1
2024-02-02,Convergence rates for Backward SDEs driven by Lévy processes,"We consider L\'evy processes that are approximated by compound Poisson
processes and, correspondingly, BSDEs driven by L\'evy processes that are
approximated by BSDEs driven by their compound Poisson approximations. We are
interested in the rate of convergence of the approximate BSDEs to the ones
driven by the L\'evy processes. The rate of convergence of the L\'evy processes
depends on the Blumenthal--Getoor index of the process. We derive the rate of
convergence for the BSDEs in the $\mathbb L^2$-norm and in the Wasserstein
distance, and show that, in both cases, this equals the rate of convergence of
the corresponding L\'evy process, and thus is optimal.",2402.01337v1
2024-02-02,Magnetism of CuCr$_2$X$_4$ (X= S and Se) spinels studied with muon spin rotation and relaxation ($μ$SR),"We present muon spin rotation and relaxation ($\mu$SR) results for
chalcogenide spinels CuCr$_2$X$_4$ with X= S and Se. Both compounds are known
as ferromagnetic metals with high Curie temperatures. Our $\mu$SR and
magnetization data show clear signatures for additional magnetic transitions
far below the respective Curie temperatures. They can be related to changes in
the Cr valence system from the mixed valence between Cr$^{3+}$ and Cr$^{4+}$ at
high temperatures and collinear ferromagnetism to a charge-ordered state at low
temperatures with a conical or even more complex structure. Our results
demonstrate that the electronic systems and the related spin structures of both
compounds are more complex than assumed so far.",2402.01562v1
2024-02-05,Compound Poisson distributions for random dynamical systems using probabilistic approximations,"We obtain quenched hitting distributions to be compound Poissonian for a
certain class of random dynamical systems. The theory is general and designed
to accommodate non-uniformly expanding behavior and targets that do not overlap
much with the region where uniformity breaks. Based on annealed and quenched
polynomial decay of correlations, our quenched result adopts annealed Kac-type
time-normalization and finds limits to be noise-independent. The technique
involves a probabilistic blockapproximation where the quenched hit-counting
function up to annealed Kac-normalized time is split into equally sized blocks
which are mimicked by an independency of random variables distributed just like
each of them. The theory is made operational due to a result that allows
certain hitting quantities to be recovered from return quantities. Our
application is to a class of random piecewise expanding one-dimensional
systems, casting new light on the well-known deterministic dichotomy between
periodic and aperiodic points, their usual extremal index formula
EI=1-1/JT^p(x_0) , and recovering the PolyaAeppli case for general
Bernoulli-driven systems, but distinct behavior otherwise. Future and on-going
investigations aim to produce and accommodate examples of bonafide nonuniformly
expanding random systems and targets approaching their neutral points.",2402.02759v1
2024-02-11,Impact of oxygen ordering on titanium lattice parameters,"Variations with oxygen concentration of titanium lattice parameters are
obtained by means of ab initio calculations, considering the impact of oxygen
ordering. The quasiharmonic approximation is used to take into account the
thermal expansion at finite temperature. Results show that lattice parameters
depend mainly on oxygen concentration and, to a lesser extent, on the ordering
state. Knowing these theoretical variations, one can get insights into the
composition of ordered compounds existing in Ti-O binary alloys from their
lattice mismatch measured experimentally by x-ray diffraction. The approach is
used in a binary alloy containing 6000 ppm in weight of oxygen. It is concluded
that the ordered compounds, which are observed after a recrystallization heat
treatment, do not have the expected Ti6O stoichiometry but have a composition
close to the nominal concentration. Oxygen ordering proceeds, therefore, before
oxygen partitioning in titanium.",2402.07147v1
2024-02-15,"Exploring 2D Materials by High Pressure Synthesis: hBN, Mg-hBN, b-P, b-AsP, and GeAs","In materials science, selecting the right synthesis technique for specific
compounds is one of the most important steps. High-pressure conditions have a
significant effect on the crystal growth processes, leading to the creation of
unique structures and properties that usually are not possible under normal
conditions. The prime objective of this article is to illustrate the benefits
of using high-pressure, high-temperature (HPHT) technique when developing
two-dimensional (2D) materials. We could successfully grow bulk single crystals
of hexagonal boron nitride (hBN) and magnesium doped hexagonal boron nitride
(Mg-hBN) from Mg-B-N solvent. Further exploration of the Mg-B-N system could
lead to the crystallization of isotopically 10B and 11B enriched hBN crystals,
and other doped variants of it. Black phosphorus (b-P) and black phosphorus
doped with arsenic (b-AsP) were obtained by directly converting its elements
into melt and subsequently crystallizing them under HPHT. Germanium arsenide
(GeAs) bulk single crystals were also obtained from the melt at a pressure of 1
GPa. Upon crystallization, all these compounds exhibit the anticipated layered
structures, which makes them easy to exfoliate into 2D flakes, thus providing
opportunities to modify their electrical behavior and create new useful
devices.",2402.10019v1
2024-02-22,Non-relativistic spin splitting in compensated magnets that are not altermagnets,"The non-relativistic spin-splitting (NRSS) of electronic bands in
""altermagnets"" has sparked renewed interest in antiferromagnets (AFMs) that
have no net magnetization. However, altermagnets with collinear and compensated
magnetism are not the only type of NRSS AFMs. In this study, we identify the
symmetry conditions and characteristic signatures of a distinct group of NRSS
AFMs that go beyond the description of altermagnets. These compounds exhibit a
broken spin-degeneracy among the spin-polarized bands at the $\Gamma$ point in
the absence of spin-orbit coupling (SOC). We use density functional theory
calculations to validate these models in ternary magnetic nitrides,
specifically MnXN$_2$ (X = Si, Ge, Sn), and their cation ordered variants. By
removing the previous NRSS constraint on $\Gamma$, these compounds may
facilitate the generation of spin currents without cancellation arising from
the alternating spin polarizations. Our findings expand the scope of NRSS
eligible materials.",2402.14321v1
2024-02-23,Rotational phase transitions in antifluorite-type osmate and iridate compounds,"We present temperature-dependent single-crystal diffraction results on seven
antifluorite-type $A_2MeX_6$ compounds with $Me$=Os or Ir: K$_2$OsCl$_6$,
$A_2$OsBr$_6$ with $A$=K, Rb, Cs and NH$_4$, and K$_2$Ir$X_6$ with $X$=Cl and
Br. The structural transitions in this family arise from $MeX_6$ octahedron
rotations that generate a rich variety of symmetries depending on the rotation
axis and stacking schemes. In order to search for local distortions in the
high-symmetry phase we perform refinements of anharmonic atomic displacement
parameters with comprehensive data sets. Even at temperatures close to the
onset of structural distortions, these refinements only yield a small
improvement indicating only small anharmonic effects. The phase transitions in
these antifluorites are essentially of displacive character. However, some
harmonic displacement parameters are very large reflecting soft phonon modes
with the softening covering large parts of the Brillouin zone. The occurrence
of the rotational transitions in the antifluorite-type family can be remarkably
well analyzed in terms of a tolerance factor of ionic radii.",2402.15358v1
2024-02-27,"Novel Ternary AgIICoIIIF5 Fluoride: Synthesis, Structure and Magnetic Characteristics","We present a new compound in the silver cobalt fluoride system, featuring
paramagnetic silver (d9) and high-spin cobalt (d6), synthesized by solid state
method in an autoclave under F2 overpressure. Based on powder X ray
diffraction, we determined that AgIICoIIIF5 crystallizes in a monoclinic system
with space group C2/c. The calculated fundamental band gap falls in the visible
range of the electromagnetic spectrum, and the compound has the character of
charge-transfer insulator. AgCoF5 is a ferrimagnet with one predominant
superexchange magnetic interaction constant between mixed spin cations (Ag ...
Co) of minus 62 meV (SCAN result). Magnetometric measurements conducted on a
powdered sample allowed the identification of a transition at 128 K, which
could indicate magnetic ordering.",2402.17399v1
2024-03-01,Prospect of high-temperature superconductivity in layered metal borocarbides,"Delithiation of the known layered LiBC compound was predicted to induce
conventional superconductivity at liquid nitrogen temperatures but extensive
experimental work over the past two decades has detected no signs of the
expected superconducting transition. Using a combination of first-principles
stability analysis and anisotropic Migdal-Eliashberg formalism, we have
investigated possible Li$_x$BC morphologies and established what particular
transformations of the planar honeycomb BC layers are detrimental to the
material's superconductivity. We propose that Li$_x$BC reintercalation with
select alkali and alkaline earth metals could lead to synthesis of otherwise
inaccessible metastable Li$_x$M$_y$BC superconductors with critical
temperatures ($T_{c}$) up to 73 K. The large-scale exploration of metal
borocarbides has revealed that NaBC and Li$_{1/2}$Na$_y$BC layered phases are
likely true ground states at low temperatures. The findings indicate that this
compositional space may host overlooked synthesizable compounds with potential
to break the $T_{c}$ record for conventional superconductivity in
ambient-pressure materials.",2403.00738v1
2024-03-03,Location and migration of interstitial Li ions in CsPbI$_3$ crystals,"Halide perovskites are highly promising light-harvesting materials with
strong ionic character, enabling in principle the combination of a solar cell
and a Li-ion battery in one integrated photo-battery device. Here, we
investigate Li ions inside crystals of CsPbI$_3$, as a prototype compound, by
means of density-functional-theory calculations. Our findings demonstrate that
the interstitial location and migration of Li ions depend strongly on the
dynamic nature of the crystal structure of the perovskite compound. We consider
two limiting cases for Li in CsPbI$_{3}$,(i) the cubic-symmetry structure as a
model for the limit of fast ion motion and (ii) a distorted cubic structure as
a model for the limit of slow ion motion. For both limiting cases we obtain
moderate energy barriers for migrating Li ions, which highlight the potential
of halide perovskites like CsPbI$_3$ for applications in photo-battery devices.",2403.01557v1
2024-03-04,Designing Quaternary Hydrides with Potential High T$_c$ Superconductivity,"We propose three parent structures for designing quaternary hydrides of
increasing complexity to optimize parameters correlated with high T$_c$
superconductivity. The first is a simple Pm$\overline{3}$m cell inspired by the
FCC RH$_3$ structures (R = trivalent rare earths), which we show has moderately
promising potential for high T$_c$ compounds. The second is an
Fm$\overline{3}$m heterostructure inspired by our work on Lu$_8$H$_{23}$N that
consistently produces metallic hydrogen sublattices, whose quantum interference
with Lewis bases is designed to high DOS$_H$(E$_F$). Several examples are put
forward that first-principles calculations confirm have hydrogen-dominant metal
character, as well as strong network connectivity as measured with the Electron
Localization Function (ELF). The third quaternary model structure allows for a
more precise description of doping as well as symmetry breaking of octahedral
hydrogen which improves the hydrogen network connectivity. These model
structures/formulae predict compounds with high predicted T$_c$ and have enough
flexibility to optimize for both T$_c$ and stability at low pressures.",2403.01688v1
2024-03-04,Half-Metallic Ferromagnetic Weyl Fermions Related to Dynamic Correlations in the Zinc-blende Compound VAs,"The realization of 100\% polarized topological Weyl fermions in half-metallic
ferromagnets is of particular importance for fundamental research and
spintronic applications. Here, we theoretically investigate the electronic and
topological properties of the zinc-blende compound VAs, which was deemed as a
half-metallic ferromagnet related to dynamic correlations. Based on the
combination of density functional theory and dynamical mean field theory, we
uncover that the half-metallic ferromagnet VAs exhibit attractive Weyl
semimetallic behaviors with twelve pairs of Weyl points, which are very close
to the Fermi level. Meanwhile, we also investigate the magnetization-dependent
topological properties; the results show that the change of magnetization
directions only slightly affects the positions of Weyl points, which is
attributed to the weak spin-orbital coupling effects. The topological surface
states of VAs projected on semi-infinite (001) and (111) surfaces are
investigated. The Fermi arcs of all Weyl points are clearly visible on the
projected Fermi surfaces. Our findings suggest that VAs is a fully
spin-polarized Weyl semimetal with many-body correlated effects for spintronic
applications.",2403.02157v2
2024-03-04,"Highly unusual, doubly-strongly-correlated, altermagnetic, 3D analogue of parent compounds of high-Tc cuprates","Discovery of high-temperature superconductivity (HTSC) in strongly correlated
cuprates opened a new chapter in condensed matter physics, breaking existing
stereotypes of what is a material base for a good superconductor (""Matthias
rules""), at the same time emphasizing richness and challenge of strongly
correlated physics, personified by the most strongly correlated 3d ion, Cu2+. A
recently reported new compound, CuAg(SO4)2, combines in a fascinating way the
same ion with the most strongly correlated 4d one, Ag2+. In this Letter, we
present a detailed analysis of electronic and magnetic properties of this
material, and show that it is very different from the HTSC cuprates in several
different ways, and opens a door into further research of superconductivity and
magnetism, in particular altermagnetism, in strongly correlated materials.",2403.02201v1
2024-03-07,ALTO: An Efficient Network Orchestrator for Compound AI Systems,"We present ALTO, a network orchestrator for efficiently serving compound AI
systems such as pipelines of language models. ALTO achieves high throughput and
low latency by taking advantage of an optimization opportunity specific to
generative language models: streaming intermediate outputs. As language models
produce outputs token by token, ALTO exposes opportunities to stream
intermediate outputs between stages when possible. We highlight two new
challenges of correctness and load balancing which emerge when streaming
intermediate data across distributed pipeline stage instances. We also motivate
the need for an aggregation-aware routing interface and distributed
prompt-aware scheduling to address these challenges. We demonstrate the impact
of ALTO's partial output streaming on a complex chatbot verification pipeline,
increasing throughput by up to 3x for a fixed latency target of 4 seconds /
request while also reducing tail latency by 1.8x compared to a baseline serving
approach.",2403.04311v1
2024-03-18,Comparative Raman Scattering Study of Crystal Field Excitations in Co-based Quantum Magnets,"Co-based materials have recently been explored due to potential to realise
complex bond-dependent anisotropic magnetism. Prominent examples include
Na$_2$Co$_2$TeO$_6$, BaCo$_2$(AsO$_4$)$_2$, Na$_2$BaCo(PO$_4$)$_2$, and CoX$_2$
(X = Cl, Br, I). In order to provide insight into the magnetic interactions in
these compounds, we make a comparative analysis of their local crystal electric
field excitations spectra via Raman scattering measurements. Combining these
measurements with theoretical analysis confirms the validity of $j_{\rm eff} =
1/2$ single-ion ground states for all compounds, and provides accurate
experimental estimates of the local crystal distortions, which play a prominent
role in the magnetic couplings between spin-orbital coupled Co moments.",2403.11980v1
2024-03-20,Searching Materials Space for Hydride Superconductors at Ambient Pressure,"We employed a machine-learning assisted approach to search for
superconducting hydrides under ambient pressure within an extensive dataset
comprising over 150 000 compounds. Our investigation yielded around 50 systems
with transition temperatures surpassing 20 K, and some even reaching above 70
K. These compounds have very different crystal structures, with different
dimensionality, chemical composition, stoichiometry, and arrangement of the
hydrogens. Interestingly, most of these systems displayed slight thermodynamic
instability, implying that their synthesis would require conditions beyond
ambient equilibrium. Moreover, we found a consistent chemical composition in
the majority of these systems, which combines alkali or alkali-earth elements
with noble metals. This observation suggests a promising avenue for future
experimental investigations into high-temperature superconductivity within
hydrides at ambient pressure.",2403.13496v1
2024-03-21,Epitaxial growth and magnetic properties of Mn5(SixGe1-x)3 thin films,"Structural and magnetic properties of Mn5(SixGe1-x)3 thin films were
investigated. Ferromagnetic Mn5Ge3 and anti-ferromagnetic Mn5Si3 thin films
have been synthesized and characterized as these compounds exhibit interesting
features for the development of spintronics. Here, Mn5(SixGe1-x)3 thin films
were grown on Ge(111) substrates by co-deposition using molecular beam epitaxy.
Crystalline thin films can be produced with controlled Si concentrations
ranging from 0 to 1. The thin films were relaxed by dislocations at the
interface with the substrate. A lattice parameter variation was observed as the
Si content increased, which is comparable to previous works done in bulk.
Reflection highenergy electron diffraction diagrams and X-ray diffraction
profiles showed that lattice parameters a and c are shrinking and that the
surface roughness and crystallinity degrade as the Si amount increases.
Magnetometric measurements revealed a ferromagnetic behavior for all Si
concentrations. The measured average ferromagnetic moment per manganese atom
decreased from 2.33 to 0.05 {\mu}B/Mn atom. No ferro to anti-ferromagnetic
transition was observed contrary to the bulk Mn5(SixGe1-x)3 compound.",2403.14215v1
2024-03-22,"Linear magnetoelectricity in the Zintl phase pnictides (Ba, Ca, Sr)$\mathrm{Mn}_2\mathrm{(P, As, Sb)}_2$ from first principles calculations","We report a comprehensive set of density functional theory calculations on
the family of layered antiferromagnetic manganese pnictides (Ba, Ca,
Sr)$\mathrm{Mn}_2\mathrm{(P, As, Sb)}_2$. We characterize all components to the
linear magnetoelectric (ME) tensor $\alpha$ which are parsed into their
contributions from spin and orbital moments for both lattice-mediated and their
clamped-ion electronic analogs. Our main results show that the orbital
magnetization components cannot be neglected in these systems. The ME response
is dominated by electronic effects with total $\alpha$ values exceeding those
of the prototypical $\mathrm{Cr}_2\mathrm{O}_3$ (i.e. $\alpha \simeq$ 6.79 ps/m
in $\mathrm{BaMn}_2\mathrm{As}_2$). We also identify a strong correlation with
the computed ME susceptibility on pnictogen substitution in the trigonal
subfamily albeit with weaker amplitudes ($\alpha \simeq$ 0.2-1.7 ps/m).
Additionally, we provide the dependence of these predictions on the Hubbard +U
correction, at the level of the local density approximation, which show large
variations on the calculated ME coefficients in the tetragonal compounds
highlighting the role of strong correlation in these compounds.",2403.15222v1
2024-04-04,Computational Study Based Prediction of New Photocatalysts for water splitting by systematic manipulation of MXene surfaces,"The compositional and structural flexibility of functionalised
two-dimensional metal carbonitrides or MXenes has been exploited through a
combinatorial search for new materials that can act as catalysts for
photo-assisted water splitting by absorbing sunlight with energy in the
infra-red region. Detailed calculations on 49 Janus MXenes where two surfaces
are of asymmetric nature are carried out by first-principles Density Functional
Theory. A screening procedure is adopted to arrive at potential candidates. Our
calculations predict four new materials whose surfaces can activate both
hydrogen and oxygen evolution reactions upon splitting water, two out of which
are infra-red active, and the rest are visible light-active. We have performed
a detailed microscopic analysis to find out the interrelations of the
structural model of surface functionalisation, the chemistry of the surfaces,
the electronic structure, and the alignment of bands with respect to the
reaction potentials that explain our results. Apart from these four compounds,
we find thirteen other compounds that are suitable for either hydrogen
evolution or oxygen reduction reactions. This study lays out a guideline for
the systematic discovery of potential new catalysts for water splitting under
sunlight irradiation.",2404.03146v1
2024-04-04,Peculiar magnetism and magneto-transport properties in a non-centrosymmetric self-intercalated van der Waals ferromagnet Cr5Te8,"Trigonal Cr5Te8, a self-intercalated van der Waals ferromagnet with an out of
plane magnetic anisotropy, has long been known to crystallise in a
centrosymmetric structure. Through detailed structural analysis together with
second harmonic generation experiments, we show that the compound actually
adopts a non-centrosymmetric structure. A large anomalous Hall conductivity of
102 {\Omega}^(-1) cm^(-1) at low temperature stems from intrinsic origin, which
is larger than any previously reported values in bulk Cr-Te system. In
addition, we observe a hump-like feature in the field-dependent Hall
resistivity data, resembling a typical topological Hall signal. We demonstrate
that the feature is highly tunable and is not related to topological Hall
effect even though we observe N\'eel-type skyrmions by Lorentz transmission
electron microscopy which is consistent with the non-centrosymmetric structure
of the compound.",2404.03391v1
2024-04-12,Fully quantum arbitrarily varying channel coding for entanglement-assisted communication,"If a sender and a receiver lack precise knowledge about the communication
line that connects them, designing a scheme to reliably transmit information
becomes more challenging. This has been studied in classical and quantum
information theory in the context of compound channel models and arbitrarily
varying channel models. However, a fully quantum version of system uncertainty
allows for an even more challenging coding scenario with entangled channel
uses. This type of model has previously been investigated for classical and
quantum capacity. Here, we address the problem of entanglement-assisted
capacity in the presence of such system uncertainty. We find that, under the
assumption of a finite environment dimension, it is equal to a corresponding
compound capacity. Intriguingly, our results imply that in certain fully
quantum arbitrarily varying channel models, the entanglement-assisted capacity
can be positive while the classical capacity is equal to zero, a phenomenon
that does not occur in regular single-channel coding.",2404.08200v1
2024-03-13,QSPR Analysis with Curvilinear Regression Modeling and Temperature-based Topological Indices,"Establishing quantitative correlations between various molecular properties
and chemical structures is of great technological importance for environmental
and medical aspects. These approaches are referred to as Quantitative
Structure-Property Relationships (QSPR), which relate the physicochemical or
thermodynamic properties of compounds to their structures. The main goal of
QSPR studies is to find a mathematical relationship between the property of
interest and several molecular descriptors derived from the structure of the
molecule. Topological indices are the molecular descriptors that characterize
the formation of chemical compounds and predict certain physicochemical
properties. In this study, the QSPR models are designed using certain
temperature-based topological indices such as the sum connectivity temperature
index, product connectivity temperature index, F-temperature index, and
symmetric division temperature index to predict the thermodynamic properties,
such as enthalpies of formation ($\Delta H^{0}_{f}$ \hspace{1mm} liquid),
enthalpies of combustion ($\Delta H^{0}_{C}$ \hspace{1mm} liquid), and
enthalpies of vaporization ($\Delta H^{0}_{vap}$ \hspace{1mm} gas) of
monocarboxylic acids ($C_2H_{4}O_{2}$ - $C_{20}H_{40}O_{2}$). The relationship
analysis between thermodynamic properties and topological indices is done using
linear, quadratic, and cubic equations of a curvilinear regression model. These
regression models are then compared.",2404.08650v1
2024-04-14,Robust spin order and fragile charge order in Na0.5CoO2 as revealed by time-resolved terahertz spectroscopy,"Near-infrared (NIR) pump-terahertz (THz) probe spectroscopy is used to
investigate the charge and spin exciations in a strongly correlated electron
compound Na0.5CoO2. This compound exhibits a coexistence of various charge and
spin orders arising from intricate interactions among charge, spin, and orbital
degrees of freedom. NIR pulses create significantly diverse effects on the
charge and spin orders; while the charge order is easily melted,coherent magnon
excitations are present in all fluences examined. Furthermore, a novel {\pi}
phase shift of the coherent magnon oscillations is observed in the pump-induced
change of the terahertz electric field between regions of increasing and
decreasing field change. These results unequivocally illustrate that ultrashort
laser pulses enable the disentanglement of different interactions within
complex systems characterized by multiple orders, providing a fresh perspective
on the interplay between itinerant and localized electrons within the Co 3d t2g
multiplets.",2404.09185v1
2002-08-15,O and Ne K absorption edge structures and interstellar abundance towards Cyg X-2,"We have studied the O and Ne absorption features in the X-ray spectrum of Cyg
X-2 observed with the Chandra LETG. The O absorption edge is represented by the
sum of three absorption-edge components within the limit of the energy
resolution and the photon counting statistics. Two of them are due to the
atomic O; their energies correspond to two distinct spin states of
photo-ionized O atoms. The remaining edge component is considered to represent
compound forms of oxide dust grains. Since Cyg X-2 is about 1.4 kpc above the
galactic disk, the H column densities can be determined by radio (21 cm and CO
emission line) and H alpha observations with relatively small uncertainties.
Thus the O abundance relative to H can be determined from the absorption edges.
We found that the dust scattering can affect the apparent depth of the edge of
the compound forms. We determined the amplitude of the effect, which we
consider is the largest possible correction factor. The ratio of column
densities of O in atomic to compound forms and the O total abundance were
respectively determined to be in the range 1.7^{+3.0}_{-0.9} to
2.8^{+5.1}_{-1.5} (ratio), and 0.63 +/- 0.12 solar to 0.74 +/- 0.14 solar
(total), taking into account the uncertainties in the dust-scattering
correction and in the ionized H column density. We also determined the Ne
abundance from the absorption edge to be 0.75 +/- 0.20 solar. These abundance
values are smaller than the widely-used solar values but consistent with the
latest estimates of solar abundance.",0208290v1
2002-12-13,Gravitational Lensing by a Compound Population of Halos: Standard Models,"Based on observed rotation curves of galaxies and theoretical simulations of
dark matter halos, there are reasons for believing that at least three
different types of dark matter halos exist in the Universe classified by their
masses M and the inner slope of mass density -\alpha: Population A (galaxies):
10^{10} h^{-1} M_\odot < M < 2 \times 10^{13} h^{-1} M_\odot, \alpha = 2;
Population B (cluster halos): M > 2 \times 10^{13} h^{-1} M_\odot, \alpha =
1.3; and Population C (dwarf halos): M < 10^{10} h^{-1} M_\odot, \alpha = 1.3.
In this paper we calculate the lensing probability produced by such a compound
population of dark halos, for both image separation and time delay, assuming
that the mass function of halos is given by the Press-Schechter function and
the Universe is described by an LCDM, OCDM, or SCDM model. The LCDM model is
normalized to the WMAP observations, OCDM and SCDM models are normalized to the
abundance of rich clusters. We compare the predictions of the different
cosmological models with observational data and show that, both LCDM and OCDM
models are marginally consistent with the current available data, but the SCDM
model is ruled out. The fit of the compound model to the observed correlation
between splitting angle and time delay is excellent but the fit to the number
vs splitting angle relation is only adequate using the small number of sources
in the objective JVAS/CLASS survey. A larger survey of the same type would have
great power in discriminating among cosmological models. Furthermore,
population C in an LCDM model has a unique signature in the time domain, an
additional peak at ~3 seconds potentially observable in GRBs, which makes it
distinguishable from variants of CDM scenarios, such as warm dark matter,
repulsive dark matter, or collisional dark matter.",0212310v2
1997-07-24,Enhancement of Antiferromagnetic Correlations Induced by Nonmagnetic Impurities: Origin and Predictions for NMR Experiments,"Spin models that have been proposed to describe dimerized chains, ladders,
two dimensional antiferromagnets, and other compounds are here studied when
some spins are replaced by spinless vacancies, such as it occurs by $Zn$
doping. A small percentage of vacancies rapidly destroys the spin gap, and
their presence induces enhanced antiferromagnetic correlations near those
vacancies. The study is performed with computational techniques which includes
Lanczos, world-line Monte Carlo, and the Density Matrix Renormalization Group
methods. Since the phenomenon of enhanced antiferromagnetism is found to occur
in several models and cluster geometries, a common simple explanation for its
presence may exist. It is argued that the resonating-valence-bond character of
the spin correlations at short distances of a large variety of models is
responsible for the presence of robust staggered spin correlations near
vacancies and lattice edges. The phenomenon takes place regardless of the long
distance properties of the ground state, and it is caused by a ``pruning'' of
the available spin singlets in the vicinity of the vacancies. The effect
produces a broadening of the low temperature NMR signal for the compounds
analyzed here. This broadening should be experimentally observable in the
structurally dimerized chain systems
  $Cu(NO_3)_2\cdot2.5H_2O$, $CuWO_4$, $(VO)_2P_2O_7$, and
$Sr_{14}Cu_{24}O_{41}$, in ladder materials such as $Sr Cu_2 O_3$, in the
spin-Peierls systems $CuGeO_3$ and $NaV_2 O_5$, and in several others since it
is a universal effect common to a wide variety of models and compounds.",9707261v4
2002-01-28,"Fracton pairing mechanism for ""strange"" superconductors: Self-assembling organic polymers and copper-oxide compounds","Self-assembling organic polymers and copper-oxide compounds are two classes
of ""strange"" superconductors, whose challenging behavior does not comply with
the traditional picture of Bardeen, Cooper, and Schrieffer (BCS)
superconductivity in regular crystals. In this paper, we propose a theoretical
model that accounts for the strange superconducting properties of either class
of the materials. These properties are considered as interconnected
manifestations of the same phenomenon: We argue that superconductivity occurs
in the both cases because the charge carriers (i.e., electrons or holes)
exchange {\it fracton excitations}, quantum oscillations of fractal lattices
that mimic the complex microscopic organization of the strange superconductors.
For the copper oxides, the superconducting transition temperature $T_c$ as
predicted by the fracton mechanism is of the order of $\sim 150$ K. We suggest
that the marginal ingredient of the high-temperature superconducting phase is
provided by fracton coupled holes that condensate in the conducting
copper-oxygen planes owing to the intrinsic field-effect-transistor
configuration of the cuprate compounds. For the gate-induced superconducting
phase in the electron-doped polymers, we simultaneously find a rather modest
transition temperature of $\sim (2-3)$ K owing to the limitations imposed by
the electron tunneling processes on a fractal geometry. We speculate that
hole-type superconductivity observes larger onset temperatures when compared to
its electron-type counterpart. This promises an intriguing possibility of the
high-temperature superconducting states in hole-doped complex materials. A
specific prediction of the present study is universality of ac conduction for
$T\gtrsim T_c$.",0201504v3
2003-09-30,"Antiferromagnetic properties of a water vapor-inserted $YBa_2Cu_3O_{6.5}$ compound studied by NMR, NQR and $μ$ SR","We present a detailed NQR, NMR and $\mu $SR study of a magnetic phase
obtained during a topotactic chemical reaction of YBa$_{2}$Cu$_{3}$O$_{6.5}$
high- temperature superconductor with low-pressure water vapor. Our studies
give straightforward evidence that the ''empty'' Cu(1) chains play the role of
an easy water insertion channel. It is shown that the NQR spectrum of the
starting material transforms progressively under insertion of water, and
completely disappears when one H$_{2}$O molecule is inserted per unit cell.
Similarly, a Cu ZFNMR signal characteristic of this water inserted material
appears and grows with increasing water content, which indicates that the
products of the reaction are non-superconducting antiferromagnetic phases in
which the bilayers are ordered. These antiferromagnetic phases are felt by
proton NMR which reveals two sites with static internal fields of 150 and about
15 Gauss respectively. Two muon sites are also evidenced with similar local
fields which vanish at $T\approx 400$ K. This indicates that the magnetic
phases have similar N\'{e}el temperatures as the other bilayer undoped
compounds. An analysis of the internal fields on different sites of the
structure suggests that they can be all assigned to a single magnetic phase at
large water content in which the Cu(1) electron spins order with those of the
Cu(2). It appears that even samples packed in Stycast epoxy resin heated
moderately at a temperature (200$^{0}$C) undergo a reaction with epoxy
decomposition products which yield the formation of the same final compound. It
is then quite clear that such effects should be considered quite seriously and
avoided in experiments attempting to resolve tiny effects in such materials, as
those performed in some recent neutron scattering experiments.",0309698v2
2003-10-28,"Comparison of S=0 and S=1/2 Impurities in Haldane Chain Compound, $Y_{2}BaNiO_{5}$","We present the effect of Zn (S=0) and Cu (S=1/2) substitution at the Ni site
of S=1 Haldane chain compound $Y_{2}BaNiO_{5}$. $^{89}$Y NMR allows us to
measure the local magnetic susceptibility at different distances from the
defects. The $^{89}$Y NMR spectrum consists of one central peak and several
less intense satellite peaks. The shift of the central peak measures the
uniform susceptibility, which displays a Haldane gap $Delta$$equiv$100 K and it
corresponds to an AF coupling J$equiv$260 K between the near-neighbor Ni spins.
Zn or Cu substitution does not affect the Haldane gap. The satellites, which
are evenly distributed on the two sides of the central peak, probe the
antiferromagnetic staggered magnetization near the substituted site, which
decays exponentially. Its extension is found identical for both impurities and
corresponds accurately to the correlation length $xi$(T) determined by Monte
Carlo (QMC) simulations for the pure compound. In the case of non-magnetic Zn,
the temperature dependence of the induced magnetization is consistent with a
Curie law with an ""effective"" spin S=0.4 on each side of Zn, which is well
accounted by Quantum Monte Carlo computations of the spinless-defect-induced
magnetism. In the case of magnetic Cu, the similarity of the induced magnetism
to the Zn case implies a weak coupling of the Cu spin to the nearest- neighbor
Ni spins. The slight reductionin the induced polarization with respect to Zn is
reproduced by QMC computations by considering an antiferromagnetic coupling of
strength J'=0.1-0.2 J between the S=1/2 Cu-spin and nearest-neighbor Ni-spin.",0310645v1
2004-11-17,"Electronic structure and magnetic properties of RMnX (R= Mg, Ca, Sr, Ba, Y; X= Si, Ge) studied by KKR method","Electronic structure calculations, using the charge and spin self-consistent
Korringa- Kohn-Rostoker (KKR) method, have been performed for several $R$Mn$X$
compounds ($R$ = Mg, Ca, Sr, Ba, Y; $X$ = Si, Ge) of the CeFeSi-type structure.
The origin of their magnetic properties has been investigated emphasizing the
role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-$X$
interatomic distances on the Mn magnetic moment value is delineated from our
computations, supporting many neutron diffraction data. We show that the marked
change of $\mu_{Mn}$ with the Mn-Mn and Mn-$X$ distances resulted from a
redistribution between spin-up and spin-down $d$-Mn DOS rather than from
different fillings of the Mn 3$d$-shell. Bearing in mind that the neutron
diffraction data reported for the $R$Mn$X$ compounds are rather scattered, the
KKR computations of $\mu_{Mn}$ are in fair agreement with the experimental
values. Comparing density of states near $E_{F}$ obtained in different magnetic
orderings, one can notice that the entitled $R$Mn$X$ systems seem to 'adapt'
their magnetic structures to minimize the DOS in the vicinity of the Fermi
level. Noteworthy, the SrMnGe antiferromagnet exhibits a pseudo-gap behaviour
at $E_{F}$, suggesting anomalous electron transport properties. In addition,
the F-AF transition occurring in the disordered La$_{1-x}$Y$_{x}$MnSi alloy for
the $0.8<x<1$ range is well supported by the DOS features of
La$_{0.2}$Y$_{0.8}$MnSi. In contrast to the investigated $R$Mn$X$ compounds,
YFeSi was found to be non-magnetic, which is in excellent agreement with the
experimental data.",0411436v1
2005-03-16,Optical study of orbital excitations in transition-metal oxides,"The orbital excitations of a series of transition-metal compounds are studied
by means of optical spectroscopy. Our aim was to identify signatures of
collective orbital excitations by comparison with experimental and theoretical
results for predominantly local crystal-field excitations. To this end, we have
studied TiOCl, RTiO3 (R=La, Sm, Y), LaMnO3, Y2BaNiO5, CaCu2O3, and K4Cu4OCl10,
ranging from early to late transition-metal ions, from t_2g to e_g systems, and
including systems in which the exchange coupling is predominantly
three-dimensional, one-dimensional or zero-dimensional. With the exception of
LaMnO3, we find orbital excitations in all compounds. We discuss the
competition between orbital fluctuations (for dominant exchange coupling) and
crystal-field splitting (for dominant coupling to the lattice). Comparison of
our experimental results with configuration-interaction cluster calculations in
general yield good agreement, demonstrating that the coupling to the lattice is
important for a quantitative description of the orbital excitations in these
compounds. However, detailed theoretical predictions for the contribution of
collective orbital modes to the optical conductivity (e.g., the line shape or
the polarization dependence) are required to decide on a possible contribution
of orbital fluctuations at low energies, in particular in case of the orbital
excitations at about 0.25 eV in RTiO3. Further calculations are called for
which take into account the exchange interactions between the orbitals and the
coupling to the lattice on an equal footing.",0503405v2
2005-06-24,Paramagnetism of layered organic conductors (BEDO-TTF)_2ReO_4*H_2O and (BEDT-TTF)_xDy(NO_3)_z: analysis of phase transition at 200 K,"Layered organic conductors (BEDO-TTF)_2ReO_4*H_2O (metal) and
(BEDT-TTF)_xDy(NO_3)_z (paramagnetic insulator) are studied by CW-EPR and SQUID
methods. A correlation in resonance and transport properties of both compounds
is attributed to a similar mechanism of fine anion ordering (AO) at T_AO=200 K.
Due to the hydrogen bonds motif the small configuration changes in anion
sub-lattice bring a profound effect on electronic properties. It is shown that
the spin system of (BEDO-TTF)_2ReO_4*H_2O consists of a fraction of delocalized
pi-type holes (I_epr=n(e_F)), I_epr(300K)=1,62*10^(-4) emu/mol and
antiferromagnetically correlated local moments S=1/2, chi_p(300K)=1,86*10^(-3)
emu/mol. The phase transition Me-Me at T_AO=203 K is detected by paramagnetic
relaxation and resisitivity but it is not observed in spin susceptibility.
Fraction of delocalized holes gradually decreases by factor 2 at cooling down
to 100 K, whereas contribution from local moments reaches maximum at 50 K and
falls to zero at 14 K. However, at 2 K total spin susceptibility is fully
recovered approaching 6*10^(-2) emu/mol. In turn, (BEDT-TTF)_xDy(NO_3)_z does
not have solvent bridges (H_2O) between neighboring anions and the disorder in
anion layer converts this compound into paramagnetic insulator. Moreover, the
anion metal-complexes Dy(NO_3)_z^n(-) contain magnetic ions Dy^3(+).
Nonetheless, the phase transition of similar origin is also detected at T=197 K
by ESR and resistivity measurements. Two spin sub-systems co-exist in this
compound: hopping local moments S=1/2 (BEDT-TTF^(+)), I_epr(300K)=6,3*10^(-4)
emu/mol and strongly localized 4f^9-electrons, J=15/2 (Dy^3(+)),
chi_p(300K)=4*10^(-2) emu/mol.",0506634v1
2005-12-20,Integrable models and quantum spin ladders: comparison between theory and experiment for the strong coupling ladder compounds,"(abbreviated) This article considers recent advances in the investigation of
the thermal and magnetic properties of integrable spin ladder models and their
applicability to the physics of real compounds. The ground state properties of
the integrable two-leg spin-1/2 and the mixed spin-(1/2,1) ladder models at
zero temperature are analyzed by means of the Thermodynamic Bethe Ansatz.
Solving the TBA equations yields exact results for the critical fields and
critical behaviour. The thermal and magnetic properties of the models are
investigated in terms of the recently introduced High Temperature Expansion
method, which is discussed in detail. It is shown that in the strong coupling
limit the integrable spin-1/2 ladder model exhibits three quantum phases: (i) a
gapped phase in the regime $H<H_{c1}$, (ii) a fully polarised phase for
$H>H_{c2}$, and (iii) a Luttinger liquid magnetic phase in the regime
$H_{c1}<H<H_{c2}$. The critical behaviour in the vicinity of the critical
points is of the Pokrovsky-Talapov type. The temperature-dependent thermal and
magnetic properties are directly evaluated from the exact free energy
expression and compared to known experimental results for a range of strong
coupling ladder compounds. Similar analysis of the mixed spin-(1/2,1) ladder
model reveals a rich phase diagram, with a 1/3 and a full saturation
magnetisation plateau within the strong antiferromagnetic rung coupling regime.
For weak rung coupling, the fractional magnetisation plateau is diminished and
a new quantum phase transition occurs. The phase diagram can be directly
deduced from the magnetisation curve obtained from the exact result derived
from the HTE. The thermodynamics of the spin-orbital model with different
single-ion anisotropies is also investigated.",0512489v3
2007-03-20,Magnetothermopower in Nd1-xEuxNiO3 compounds,"We have measured magnetization M(T,H), electrical resistivity ro(T,H),
thermal conductivity k(T,H), and thermopower S(T,H) of polycrystalline samples
of Nd1-xEuxNiO3; 0 <= x <= 0.35; as a function of temperature and external
magnetic field. The data indicate a metal-insulator transition (MI) in a wide
range of temperature (200 < TMI < 325 K). The magnetic susceptibility X(T)
data, after the subtraction of the rare-earth contribution, exhibit a
Curie-Weiss like behavior at temperatures above TMI. Although a clear
antiferromagnetic AF transition of the Ni sub-lattice is observed at TN <= TMI,
X(T) still increases down to 5 K, suggesting a heterogeneous ground state. The
thermal conductivity of the NdNiO3 compound is not affected by an external
magnetic field of 90 kOe in a wide range of temperature, and its temperature
dependence below 15 K is approximately quadratic, strongly suggesting the
presence of disorder. S(T) is negative above TMI and varies linearly with
temperature. Below TMI, S(T) does not follow the expected behavior of
insulating compounds. There is a minimum close to 120 K, and S(T) changes its
sign at T ~ 30 K, indicating a competition between two types of charge
carriers. A pronounced peak in S(T) at TS ~ 20 K does not follow the expected
phonon-drag temperature dependence either above or below TS and the peak
remains unaltered under magnetic fields up to 90 kOe. However, its magnitude is
enhanced by ~ 25 % with applied magnetic field, exhibiting a clear
magnetothermopower effect. The combined results indicate a coexistence of
ordered and disordered phases below TN and that an applied magnetic field is
suitable for enhancing the thermoelectric properties close to TS.",0703512v1
2000-11-15,"Benchmark {\em ab initio} energy profiles for the gas-phase S$_N$2 reactions Y$^-$ + CH$_3$X $\to$ CH$_3$Y + X$^-$ (X,Y = F,Cl,Br). Validation of hybrid DFT methods","The energetics of the gas-phase S$_N$2 reactions Y$^-$ + CH$_3$X
$\longrightarrow$ CH$_3$Y + X$^-$ (where X,Y = F, Cl, Br), were studied using
(variants on) the recent W1 and W2 {\em ab initio} computational
thermochemistry methods. Our computed benchmark data (including cases for which
experimental data are unavailable altogether) are used to assess the quality of
a number of semiempirical compound thermochemistry schemes such as G2 theory,
G3 theory, and CBS-QB3, as well as a variety of density functional theory
methods. Upon applying some modifications to the level of theory used for the
reference geometry (adding diffuse functions, replacing B3LYP by the very
recently proposed mPW1K functional), the compound methods appear to perform
well. Only the 'half-and-half' functionals BH&HLYP and mPWH&HPW91, and the
empirical mPW1K functional, consistently find all required stationary points;
the other functionals fail to find a transition state in the F/Br case. BH&HLYP
and mPWH&HPW91 somewhat overcorrect for the tendency of B3LYP (and, to a lesser
extent, mPW1PW91) to underestimate barrier heights. The Becke97 and Becke97-1
functionals perform similarly to B3LYP for the problem under study, while the
HCTH and HCTH-120 functionals both appear to underestimate central barriers.
HCTH underestimates complexation energies; this problem is resolved in
HCTH-120. mPW1K appears to exhibit the best performance of the functionals
considered, although its energetics are still inferior to the compound
thermochemistry methods.",0011029v1
2008-10-22,Phonon Control of Magnetic Relaxation in the Pyrochlore Slab Compounds SCGO and BSZCGO,"We are interested in the phonon response in the frustrated magnets
SrCr$_{9x}$Ga$_{12-9x}$O$_{19}$ (SCGO) and
Ba$_{2}$Sn$_{2}$ZnCr$_{7x}$Ga$_{10-7x}$O$_{22}$ (BSZCGO). The motivation of the
study is the recently discovered, phonon-driven, magnetic relaxation in the
SCGO compound [Mutka et al. PRL {\bf 97} 047203 (2006)] pointing out the
importance of a low-energy ($\hbar\omega\sim$7 meV) phonon mode. In neutron
scattering experiments on these compounds the phonon signal is partly masked by
the magnetic signal from the Cr moments and we have therefore examined in
detail the non-magnetic isostructural counterparts SrGa$_{12}$O$_{19}$ (SGO)
and Ba$_{2}$Sn$_{2}$ZnGa$_{10}$O$_{22}$ (BSZGO). Our {\it ab-initio} lattice
dynamics calculations on SGO reveal a peak in the vibrational density of states
matching with the neutron observations on SGO and SCGO. A strong contribution
in the vibrational density of states comes from the partial contribution of the
Ga atoms on the 2b and 12k sites, involving modes at the M--point of the
hexagonal system. These modes comprise dynamics of the kagom\'e planes of the
pyrochlore slab magnetic sub-lattice, 12k sites, and therefore can drive
magnetic relaxation via spin-phonon coupling. Both BSZCGO and BSZGO show a
similar low-energy Raman peak but no corresponding peak in the neutron
determined density of states of BSZGO is seen. However, a strong non-Debye
enhancement of low-energy phonon response is observed. We attribute this
particular feature to the Zn/Ga disorder on the 2$d$ -site, already evoked
earlier to affect the magnetic properties of BSZCGO. We propose that this
disorder-induced phonon response explains the absence of a characteristic
energy scale and the much faster magnetic relaxation observed in BSZCGO.",0810.3941v2
2009-01-24,"Uniform mixing of antiferromagnetism and high-T_c superconductivity in multilayered copper oxides Ba_2Ca_{n-1}Cu_nO_{2n}F_2 with apical fluorines (n=2,3,4): Cu-NMR/NQR and F-NMR","We report Cu-NMR/NQR and F-NMR studies on the multilayered high-T_c copper
oxides Ba_2Ca_{n-1}Cu_nO_{2n}F_2 with n=2,3,4, where n is the number of CuO_2
planes. It is revealed that bi-layered Ba_2CaCu_2O_4F_2 is an underdoped
superconductor with hole carriers, which are introduced into CuO_2 planes by an
unexpected deviation from the nominal content of apical fluorines. In a
previous paper, we proposed a self-doping mechanism as the origin of carrier
doping in n=3 and n=4; in the mechanism, electrons are transferred from the
inner CuO_2 plane (IP) to the outer one (OP). However, since it has been found
that the bi-layered compound is hole doped, we have reexamined the
superconducting and magnetic properties in n=3 and n=4 by Cu-NMR/NQR and F-NMR.
The extensive NMR studies have confirmed that the apical-fluorine compounds are
not self-doped but hole-doped, and that antiferromagnetism (AFM) and
superconductivity (SC) coexist in a single CuO_2 plane. In n=4, the AFM
ordering occurs at T_N = 80 K, well above T_c=55 K, where the respective AFM
moments are M_AFM=0.11 mu_B and 0.18 mu_B at the OP and the IP. In n=3, on the
other hand, the underdoped single IP exhibits a spontaneous moment M_AFM=0.12
mu_B at low temperatures and a peak in the nuclear-spin-lattice relaxation rate
1/T_1 of F at T_N=23 K, much lower than T_c = 76 K. We note that the increase
in the number of IPs from one to two leads to an increase in T_N due to
strengthening the interlayer coupling, although the doping levels for both
compounds are almost comparable. The present results strongly suggest that the
uniform mixing of AFM and SC is a general property inherent to a single CuO_2
plane in the underdoped regime for hole-doping.",0901.3811v1
2009-01-28,Extension of the spin-1/2 frustrated square lattice model: the case of layered vanadium phosphates,"We study the influence of the spin lattice distortion on the properties of
frustrated magnetic systems and consider the applicability of the spin-1/2
frustrated square lattice model to materials lacking tetragonal symmetry. We
focus on the case of layered vanadium phosphates AA'VO(PO4)2 (AA' = Pb2, SrZn,
BaZn, and BaCd). To provide a proper microscopic description of these
compounds, we use extensive band structure calculations for real materials and
model structures and supplement this analysis with simulations of thermodynamic
properties, thus facilitating a direct comparison with the experimental data.
Due to the reduced symmetry, the realistic spin model of layered vanadium
phosphates AA'VO(PO4)2 includes four inequivalent exchange couplings: J1 and
J1' between nearest-neighbors and J2 and J2' between next-nearest-neighbors.
The estimates of individual exchange couplings suggest different regimes, from
J1'/J1 and J2'/J2 close to 1 in BaCdVO(PO4)2, a nearly regular frustrated
square lattice, to J1'/J1 ~ 0.7 and J2'/J2 ~ 0.4 in SrZnVO(PO4)2, a frustrated
square lattice with sizable distortion. The underlying structural differences
are analyzed, and the key factors causing the distortion of the spin lattice in
layered vanadium compounds are discussed. We propose possible routes for
finding new frustrated square lattice materials among complex vanadium oxides.
Full diagonalization simulations of thermodynamic properties indicate the
similarity of the extended model to the regular one with averaged couplings. In
case of moderate frustration and moderate distortion, valid for all the
AA'VO(PO4)2 compounds reported so far, the distorted spin lattice can be
considered as a regular square lattice with the couplings (J1+J1')/2 between
nearest-neighbors and (J2+J2')/2 between next-nearest-neighbors.",0901.4498v2
2009-02-03,High-field phase-diagram of Fe arsenide superconductors,"Here, we report an overview of the phase diagram of single layered and double
layered Fe arsenide superconductors at high magnetic fields. Our systematic
magnetotransport measurements of polycrystalline SmFeAsO$_{1-x}$F$_x$ at
different doping levels confirm the upward curvature of the upper critical
magnetic field $H_{c2}(T)$ as a function of temperature $T$ defining the phase
boundary between the superconducting and metallic states for crystallites with
the ab planes oriented nearly perpendicular to the magnetic field. We further
show from measurements on single crystals that this feature, which was
interpreted in terms of the existence of two superconducting gaps, is
ubiquitous among both series of single and double layered compounds. In all
compounds explored by us the zero temperature upper critical field $H_{c2}(0)$,
estimated either through the Ginzburg-Landau or the Werthamer-Helfand-Hohenberg
single gap theories, strongly surpasses the weak coupling Pauli paramagnetic
limiting field. This clearly indicates the strong coupling nature of the
superconducting state and the importance of magnetic correlations for these
materials. Our measurements indicate that the superconducting anisotropy, as
estimated through the ratio of the effective masses $\gamma =
(m_c/m_{ab})^{1/2}$ for carriers moving along the c-axis and the ab planes,
respectively, is relatively modest as compared to the high-$T_c$ cuprates, but
it is temperature, field and even doping dependent. Finally, our preliminary
estimations of the irreversibility field $H_m(T)$, separating the vortex-solid
from the vortex-liquid phase in the single layered compounds, indicates that it
is well described by the melting of a vortex lattice in a moderately
anisotropic uniaxial superconductor.",0902.0532v2
2010-03-23,A mathematical model for breath gas analysis of volatile organic compounds with special emphasis on acetone,"Recommended standardized procedures for determining exhaled lower respiratory
nitric oxide and nasal nitric oxide have been developed by task forces of the
European Respiratory Society and the American Thoracic Society. These
recommendations have paved the way for the measurement of nitric oxide to
become a diagnostic tool for specific clinical applications. It would be
desirable to develop similar guidelines for the sampling of other trace gases
in exhaled breath, especially volatile organic compounds (VOCs) which reflect
ongoing metabolism. The concentrations of water-soluble, blood-borne substances
in exhaled breath are influenced by: (i) breathing patterns affecting gas
exchange in the conducting airways; (ii) the concentrations in the
tracheo-bronchial lining fluid; (iii) the alveolar and systemic concentrations
of the compound. The classical Farhi equation takes only the alveolar
concentrations into account. Real-time measurements of acetone in end-tidal
breath under an ergometer challenge show characteristics which cannot be
explained within the Farhi setting. Here we develop a compartment model that
reliably captures these profiles and is capable of relating breath to the
systemic concentrations of acetone. By comparison with experimental data it is
inferred that the major part of variability in breath acetone concentrations
(e.g., in response to moderate exercise or altered breathing patterns) can be
attributed to airway gas exchange, with minimal changes of the underlying blood
and tissue concentrations. Moreover, it is deduced that measured end-tidal
breath concentrations of acetone determined during resting conditions and free
breathing will be rather poor indicators for endogenous levels. Particularly,
the current formulation includes the classical Farhi and the Scheid series
inhomogeneity model as special limiting cases.",1003.4475v3
2010-04-22,Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2,"Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction,
magnetic susceptibility, magnetization, electrical resistivity, and specific
heat measurements carried out in wide temperature and magnetic field ranges.
Moreover, the electronic structure of the compound was studied at room
temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The
physical properties were analyzed in terms of crystalline electric field and
compared with results of ab-initio band structure calculations performed within
the density functional theory approach. The compound was found to crystallize
in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma -- No.74,
Pearson symbol: oI24) with the lattice parameters: a = 7.1330(14) A, b =
9.7340(19) A, and c = 5.6040(11) A. Analysis of the magnetic and XPS data
revealed the presence of well localized magnetic moments of trivalent cerium
ions. All physical properties were found to be highly anisotropic over the
whole temperature range studied, and influenced by exceptionally strong
crystalline electric field with the overall splitting of the 4f1 ground
multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic
moments at TN = 4.70(1)K and their subsequent spin rearrangement at Tt =
4.48(1) K manifest themselves as distinct anomalies in the temperature
characteristics of all investigated physical properties and exhibit complex
evolution in an external magnetic field. A tentative magnetic B-T phase
diagram, constructed for B parallel to the b-axis being the easy magnetization
direction, shows very complex magnetic behavior of CeRh3Si2, similar to that
recently reported for an isostructural compound CeIr3Si2. The electronic band
structure calculations corroborated the antiferromagnetic ordering of the
cerium magnetic moments and well reproduced the experimental XPS valence band
spectrum.",1004.3858v1
2010-06-29,Induction of superconductivity by sulphur doping in FeTe system and post effect of low temperature oxygen annealing,"Here, we report the synthesis and characterization of sulphur-substituted
iron telluride i.e. FeTe1-xSx; (x = 0-30 %) system and study the impact of low
temperature oxygen (O2) annealing as well. Rietveld analysis of room
temperature x-ray diffraction (XRD) patterns shows that all the compounds are
crystallized in a tetragonal structure (space group P4/nmm) and no secondary
phases are observed. Lattice constants are decreased with increasing S
concentration. The parent compound of the system i.e. FeTe does not exhibit
superconductivity but shows an anomaly in the resistivity measurement at around
78 K, which corresponds to a structural phase transition. Heat capacity Cp(T)
measurement also confirms the structural phase transition of FeTe compound.
Superconductivity appears by S substitution; the onset of superconducting
transition temperature is about 8 K for FeTe0.75S0.25 sample. Thermoelectric
power measurements S(T) also shows the superconducting transition at around 7 K
for FeTe0.75S0.25 sample. The upper critical fields Hc2(10%), Hc2(50%) and
Hc2(90%) are estimated to be 400, 650 and 900 kOe respectively at 0 K by
applying Ginzburg Landau (GL) equation. Interestingly, superconducting volume
fraction is increased with low temperature (200 oC) O2 annealing at normal
pressure. Detailed investigations related to structural (XRD), transport [S(T),
R(T)H], magnetization (AC and DC susceptibility) and thermal [Cp(T)]
measurements for FeTe1-xS:O2 system are presented and discussed.",1006.5549v6
2010-09-29,Effects of Divalent Alkaline Earth Ions on the Magnetic and Transport Features of La0.65A0.35Mn0.95Fe0.05O3 Compounds,"We have studied the magnetic and transport behavior of doped La0.65 A0.35
Mn0.95Fe0.05 O3 (A= Ca, Sr, Pb, Ba) compounds. All the compositions show
ferromagnetic/metal to paramagnetic/insulator transition except the Pb doped
sample which is insulating and ferromagnetic in the entire temperature range.
The simultaneous occurrence of ferromagnetism and insulating behavior in Pb
doped compound is most likely due to the presence of FM clusters separated by
Fe and Mn ions that are coupled AFM and hence prevent the current from crossing
the inter-domain region. The magnetization and Tc are decreased by decreasing
the Cation size on La site. We observed that (for a fixed Fe content of 5%) the
transition temperature and magnetic moment at 77 K is a maximum for Sr doped
sample and is decreasing if we increase or decrease the cation size from Sr
size. The maximum value of Tc and magnetic moment for Sr based sample is most
likely due to the closer ionic sizes of La and Sr as compared to the other
dopants (Ca, Pb, Ba). The decrease in the transition temperature and magnetic
moment is due to the deviation of Mn-O-Mn angle from 1800 caused by the size
mismatch of the A site cations. This deviation leads to weakening of the FM
double exchange (DE). We observed a spin freezing type effect in the Pb doped
sample below 120 K in resistivity, AC susceptibility and in magnetization. This
suggests that the AFM interactions introduced by the Fe are most effective in
the Pb doped composition leading to increased competition between the FM and
AFM interactions. This FM and AFM interaction generates some degree of
frustration leading to the appearance of spin glass like phase whose typical
magnetic behavior is studied for small ion when the metallic like behavior is
lost.",1009.5903v1
2010-10-18,On the magnetism of Ln{2/3}Cu{3}Ti{4}O{12} (Ln = lanthanide),"The magnetic and thermodynamic properties of the complete
Ln$_{2/3}$Cu$_3$Ti$_4$O$_{12}$ series were investigated. Here $Ln$ stands for
the lanthanides La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. %Most
of the compounds were prepared as single phase polycrystalline powder %without
any traces of impurities. Marginal amounts of %impurities $(< 2%)$ were
detected $Ln=$ Gd, Er, and Tm. %Significant amounts of impurity phases were
found for $Ln=$ Ce and Yb. All the samples investigated crystallize in the
space group $Im\bar{3}$ with lattice constants that follow the lanthanide
contraction. The lattice constant of the Ce compound reveals the presence of
Ce$^{4+}$ leading to the composition Ce$_{1/2}$Cu$_3$Ti$_4$O$_{12}$. From
magnetic susceptibility and electron-spin resonance experiments it can be
concluded that the copper ions always carry a spin $S=1/2$ and order
antiferromagnetically close to 25\,K. The Curie-Weiss temperatures can
approximately be calculated assuming a two-sublattice model corresponding to
the copper and lanthanide ions, respectively. It seems that the magnetic
moments of the heavy rare earths are weakly coupled to the copper spins, while
for the light lanthanides no such coupling was found. The $4f$ moments remain
paramagnetic down to the lowest temperatures, with the exception of the Tm
compound, which indicates enhanced Van-Vleck magnetism due to a non-magnetic
singlet ground state of the crystal-field split $4f$ manifold. From
specific-heat measurements we accurately determined the antiferromagnetic
ordering temperature and obtained information on the crystal-field states of
the rare-earth ions. The heat-capacity results also revealed the presence of a
small fraction of Ce$^{3+}$ in a magnetic $4f^1$ state.",1010.3578v1
2010-11-10,5. Competing Interactions and Suppression of Ferromagnetism on La site Substitution in La0.65A0.35Mn0.95Fe0.05O3 Compounds,"We have studied the magnetic and transport behavior of doped La0.65 A0.35
Mn0.95Fe0.05 O3 (A= Ca, Sr, Pb, Ba) compounds. All the compositions show
ferromagnetic/metal to paramagnetic/insulator transition except the Pb doped
sample which is insulating and ferromagnetic in the entire temperature range.
The simultaneous occurrence of ferromagnetism and insulating behavior in Pb
doped compound is most likely due to the presence of FM clusters separated by
Fe and Mn ions that are coupled AFM and hence prevent the current from crossing
the inter-domain region. The magnetization and Tc are decreased by decreasing
the Cation size on La site. We observed that (for a fixed Fe content of 5%) the
transition temperature and magnetic moment at 77 K is a maximum for Sr doped
sample and is decreasing if we increase or decrease the cation size from Sr
size. The maximum value of Tc and magnetic moment for Sr based sample is most
likely due to the closer ionic sizes of La and Sr as compared to the other
dopants (Ca, Pb, Ba). The decrease in the transition temperature and magnetic
moment is due to the deviation of Mn-O-Mn angle from 1800 caused by the size
mismatch of the A site cations. This deviation leads to weakening of the FM
double exchange (DE). We observed a spin freezing type effect in the Pb doped
sample below 120 K in resistivity, AC susceptibility and in magnetization. This
suggests that the AFM interactions introduced by the Fe are most effective in
the Pb doped composition leading to increased competition between the FM and
AFM interactions. This FM and AFM interaction generates some degree of
frustration leading to the appearance of spin glass like phase whose typical
magnetic behavior is studied for small ion when the metallic like behavior is
lost.",1011.2286v1
2011-01-05,Magnetic Field and Pressure Phase Diagrams of Uranium Heavy-Fermion Compound U$_2$Zn$_{17}$,"We have performed magnetization measurements at high magnetic fields of up to
53 T on single crystals of a uranium heavy-fermion compound U$_2$Zn$_{17}$
grown by the Bridgman method. In the antiferromagnetic state below the N\'{e}el
temperature $T_{\rm N}$ = 9.7 K, a metamagnetic transition is found at $H_c$
$\simeq$ 32 T for the field along the [11$\bar{2}$0] direction ($a$-axis). The
magnetic phase diagram for the field along the [11$\bar{2}$0] direction is
given. The magnetization curve shows a nonlinear increase at $H_m$ $\simeq$ 35
T in the paramagnetic state above $T_{\rm N}$ up to a characteristic
temperature $T_{{\chi}{\rm max}}$ where the magnetic susceptibility or
electrical resistivity shows a maximum value. This metamagnetic behavior of the
magnetization at $H_m$ is discussed in comparison with the metamagnetic
magnetism of the heavy-fermion superconductors UPt$_3$, URu$_2$Si$_2$, and
UPd$_2$Al$_3$. We have also carried out high-pressure resistivity measurement
on U$_2$Zn$_{17}$ using a diamond anvil cell up to 8.7 GPa. Noble gas argon was
used as a pressure-transmitting medium to ensure a good hydrostatic
environment. The N\'{e}el temperature $T_{\rm N}$ is almost
pressure-independent up to 4.7 GPa and starts to increase in the
higher-pressure region. The pressure dependences of the coefficient of the
$T^2$ term in the electrical resistivity $A$, the antiferromagnetic gap
$\Delta$, and the characteristic temperature $T_{{\rho}{\rm max}}$ are
discussed. It is found that the effect of pressure on the electronic states in
U$_2$Zn$_{17}$ is weak compared with those in the other heavy fermion
compounds.",1101.0879v1
2011-07-04,"MEAM potentials for Al, Si, Mg, Cu, and Fe alloys","A set of Modified Embedded Atom Method (MEAM) potentials for the interactions
between Al, Si, Mg, Cu, and Fe was developed from a combination of each
element's MEAM potential in order to study metal alloying. Previously published
MEAM parameters of single elements have been improved for better agreement to
the generalized stacking fault energy (GSFE) curves when compared with
ab-initio generated GSFE curves. The MEAM parameters for element pairs were
constructed based on the structural and elastic properties of element pairs in
the NaCl reference structure garnered from ab-initio calculations, with
adjustment to reproduce the ab-initio heat of formation of the most stable
binary compounds. The new MEAM potentials were validated by comparing the
formation energies of defects, equilibrium volumes, elastic moduli, and heat of
formation for several binary compounds with ab-initio simulations and
experiments. Single elements in their ground state crystal structure were
subjected to heating to test the potentials at elevated temperatures. An Al
potential was modified to avoid formation of an unphysical solid structure at
high temperatures. The thermal expansion coefficient of a compound with the
composition of AA 6061 alloy was evaluated and compared with experimental
values. MEAM potential tests performed in this work, utilizing the universal
Atomistic Simulation Environment (ASE), are distributed to facilitate
reproducibility of the results.",1107.0544v6
2011-08-04,Ultrathin compound semiconductor on insulator layers for high performance nanoscale transistors,"Over the past several years, the inherent scaling limitations of electron
devices have fueled the exploration of high carrier mobility semiconductors as
a Si replacement to further enhance the device performance. In particular,
compound semiconductors heterogeneously integrated on Si substrates have been
actively studied, combining the high mobility of III-V semiconductors and the
well-established, low cost processing of Si technology. This integration,
however, presents significant challenges. Conventionally, heteroepitaxial
growth of complex multilayers on Si has been explored. Besides complexity, high
defect densities and junction leakage currents present limitations in the
approach. Motivated by this challenge, here we utilize an epitaxial transfer
method for the integration of ultrathin layers of single-crystalline InAs on
Si/SiO2 substrates. As a parallel to silicon-on-insulator (SOI) technology14,we
use the abbreviation ""XOI"" to represent our compound semiconductor-on-insulator
platform. Through experiments and simulation, the electrical properties of InAs
XOI transistors are explored, elucidating the critical role of quantum
confinement in the transport properties of ultrathin XOI layers. Importantly, a
high quality InAs/dielectric interface is obtained by the use of a novel
thermally grown interfacial InAsOx layer (~1 nm thick). The fabricated FETs
exhibit an impressive peak transconductance of ~1.6 mS/{\mu}m at VDS=0.5V with
ON/OFF current ratio of greater than 10,000 and a subthreshold swing of 107-150
mV/decade for a channel length of ~0.5 {\mu}m.",1108.1127v1
2011-12-22,Revised self-consistent continuum solvation in electronic-structure calculations,"The solvation model proposed by Fattebert and Gygi [Journal of Computational
Chemistry 23, 662 (2002)] and Scherlis et al. [Journal of Chemical Physics 124,
074103 (2006)] is reformulated, overcoming some of the numerical limitations
encountered and extending its range of applicability. We first recast the
problem in terms of induced polarization charges that act as a direct mapping
of the self-consistent continuum dielectric; this allows to define a functional
form for the dielectric that is well behaved both in the high-density region of
the nuclear charges and in the low-density region where the electronic
wavefunctions decay into the solvent. Second, we outline an iterative procedure
to solve the Poisson equation for the quantum fragment embedded in the solvent
that does not require multi-grid algorithms, is trivially parallel, and can be
applied to any Bravais crystallographic system. Last, we capture some of the
non-electrostatic or cavitation terms via a combined use of the quantum volume
and quantum surface [Physical Review Letters 94, 145501 (2005)] of the solute.
The resulting self-consistent continuum solvation (SCCS) model provides a very
effective and compact fit of computational and experimental data, whereby the
static dielectric constant of the solvent and one parameter allow to fit the
electrostatic energy provided by the PCM model with a mean absolute error of
0.3 kcal/mol on a set of 240 neutral solutes. Two parameters allow to fit
experimental solvation energies on the same set with a mean absolute error of
1.3 kcal/mol. A detailed analysis of these results, broken down along different
classes of chemical compounds, shows that several classes of organic compounds
display very high accuracy, with solvation energies in error of 0.3-0.4
kcal/mol, whereby larger discrepancies are mostly limited to self-dissociating
species and strong hydrogen-bond forming compounds.",1112.5332v1
2011-12-27,Comprehensive data-driven analysis of the impact of chemoinformatic structure on the genome-wide biological response profiles of cancer cells to 1159 drugs,"Detailed and systematic understanding of the biological effects of millions
of available compounds on living cells is a significant challenge. As most
compounds impact multiple targets and pathways, traditional methods for
analyzing structure-function relationships are not comprehensive enough.
Therefore more advanced integrative models are needed for predicting biological
effects elicited by specific chemical features. As a step towards creating such
computational links we developed a data-driven chemical systems biology
approach to comprehensively study the relationship of 76 structural
3D-descriptors (VolSurf, chemical space) of 1159 drugs with the gene expression
responses (biological space) they elicited in three cancer cell lines. The
analysis covering 11350 genes was based on data from the Connectivity Map. We
decomposed these biological response profiles into components, each linked to a
characteristic chemical descriptor profile. The integrated quantitative
analysis of the chemical and biological spaces was more informative about
protein-target based drug similarity than either dataset separately. We
identified ten major components that link distinct VolSurf features across
multiple compounds to specific biological activity types. For example,
component 2 (hydrophobic properties) strongly links to DNA damage response,
while component 3 (hydrogen bonding) connects to metabolic stress. Individual
structural and biological features were often linked to one cell line only,
such as leukemia cells (HL-60) specifically responding to cardiac glycosides.
In summary, our approach identified specific chemical structures shared across
multiple drugs causing distinct biological responses. The decoding of such
systematic chemical-biological relationships is necessary to build better
models of drug effects, including unidentified types of molecular properties
with strong biological effects.",1112.6015v1
2012-01-06,Antiferromagnetic order and domains in Sr3Ir2O7 probed by x-ray resonant scattering,"This article reports a detailed x-ray resonant scattering study of the
bilayer iridate compound, Sr3Ir2O7, at the Ir L2 and L3 edges. Resonant
scattering at the Ir L3 edge has been used to determine that Sr3Ir2O7 is a
long-range ordered antiferromagnet below TN 230K with an ordering wavevector,
q=(1/2,1/2,0). The energy resonance at the L3 edge was found to be a factor of
~30 times larger than that at the L2. This remarkable effect has been seen in
the single layer compound Sr2IrO4 and has been linked to the observation of a
Jeff=1/2 spin-orbit insulator. Our result shows that despite the modified
electronic structure of the bilayer compound, caused by the larger bandwidth,
the effect of strong spin-orbit coupling on the resonant magnetic scattering
persists. Using the programme SARAh, we have determined that the magnetic order
consists of two domains with propagation vectors k1=(1/2,1/2,0) and
k2=(1/2,-1/2,0), respectively. A raster measurement of a focussed x-ray beam
across the surface of the sample yielded images of domains of the order of 100
microns size, with odd and even L components, respectively. Fully relativistic,
monoelectronic calculations (FDMNES), using the Green's function technique for
a muffin-tin potential have been employed to calculate the relative intensities
of the L2,3 edge resonances, comparing the effects of including spin-orbit
coupling and the Hubbard, U, term. A large L3 to L2 edge intensity ratio (~5)
was found for calculations including spin-orbit coupling. Adding the Hubbard,
U, term resulted in changes to the intensity ratio <5%.",1201.1452v1
2012-04-18,Coherent excitations and electron phonon coupling in Ba/EuFe_2As_2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy,"We employed femtosecond time- and angle-resolved photoelectron spectroscopy
to analyze the response of the electronic structure of the 122 Fe-pnictide
parent compounds Ba/EuFe_2As_2 and optimally doped BaFe_{1.85}Co_{0.15}As_2
near the \Gamma point to femtosecond optical excitation. We identify pronounced
changes of the electron population within several 100 meV above and below the
Fermi level, which we explain as combination of (i) coherent lattice
vibrations, (ii) a hot electron and hole distribution, and (iii) transient
modifications of the chemical potential. The response of the three different
materials is very similar. In the Fourier transformation of the time-dependent
photoemission intensity we identify three modes at 5.6, 3.3, and 2.6 THz. While
the highest frequency mode is safely assigned to the A_{1g} mode, the other two
modes require a discussion in comparison to literature. The time-dependent
evolution of the hot electron distribution follows a simplified description of
a transient three temperature model which considers two heat baths of lattice
vibrations, which are more weakly and strongly coupled to transiently excited
electron population. Still the energy transfer from electrons to the strongly
coupled phonons results in a rather weak, momentum-averaged electron-phonon
coupling quantified by values for \lambda<\omega^2> between 30 and 70 meV^2.
The chemical potential is found to present a transient modulation induced by
the coherent phonons. This change in the chemical potential is particularly
strong in a two band system like in the 122 Fe-pnictide compounds investigated
here due to the pronounced variation of the electrons density of states close
to the equilibrium chemical potential.",1204.4069v1
2012-08-14,Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4,"Magnetic susceptibility and muon spin relaxation (muSR) experiments have been
carried out on the quasi-2D triangular-lattice spin S = 2 antiferromagnet
FeGa2S4. The muSR data indicate a sharp onset of a frozen or nearly-frozen spin
state at T* = 31(2) K, twice the spin-glass-like freezing temperature T_f =
16(1) K. The susceptibility becomes field dependent below T*, but no sharp
anomaly is observed in any bulk property. A similar transition is observed in
muSR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon
spin relaxation rate lambda_d(T) above T* agrees well with a calculation of
spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized
classical regime of a 2D frustrated quantum antiferromagnet. There is no firm
evidence for other mechanisms. At low temperatures lambda_d(T) becomes
temperature independent in both compounds, indicating persistence of spin
dynamics. Scaling of lambda_d(T) between the two compounds is observed from
~T_f to ~1.5T*. Although the muSR data by themselves cannot exclude a truly
static spin component below T*, together with the susceptibility data they are
consistent with a slowly-fluctuating ""spin gel"" regime between T_f and T*. Such
a regime and the absence of a divergence in lambda_d(T) at T* are features of
two unconventional mechanisms: (1) binding/unbinding of Z_2 vortex excitations,
and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence
of a sharp anomaly or history dependence at T* in the susceptibility of
FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest
transitions to low-temperature phases with unconventional dynamics.",1208.2914v1
2012-12-02,Tunable interplay between 3d and 4f electrons in Co-doped iron pnictides,"We study the interplay of 3d and 4f electrons in the iron pnictides
CeFe$_{1-x}$Co$_x$AsO and GdFe$_{1-y}$Co$_y$AsO, which correspond to two very
different cases of $4f$-magnetic moment. Both CeFeAsO and GdFeAsO undergo a
spin-density-wave (SDW) transition associated with Fe 3d electrons at high
temperatures, which is rapidly suppressed by Fe/Co substitution.
Superconductivity appears in a narrow doping range: $0.05 < x < 0.2$ for
CeFe$_{1-x}$Co$_x$AsO and $0.05 < y < 0.25$ for GdFe$_{1-y}$Co$_y$AsO, showing
a maximum transition temperature $T_\textup{sc}$ of about 13.5 K for Ce and 19
K for Gd. In both compounds, the $4f$-electrons form an antiferromagnetic (AFM)
order at low temperatures over the entire doping range and Co 3d electrons are
ferromagnetically ordered on the Co-rich side; the Curie temperature reaches
$T_\textup{C}^\textup{Co} \approx$ 75 K at $x = 1$ and $y = 1$. In the
Ce-compounds, the N\'{e}el temperature $T_\textup{N}^\textup{Ce}$ increases
upon suppressing the SDW transition of Fe and then remains nearly unchanged
with further increasing Co concentration up to $x \simeq 0.8$
($T_\textup{N}^\textup{Ce}\approx$ 4 K). Furthermore, evidence of Co-induced
polarization on Ce-moments is observed on the Co-rich side. In the
Gd-compounds, the two magnetic species of Gd and Co are coupled
antiferromagnetically to give rise to ferrimagnetic behavior in the magnetic
susceptibility on the Co-rich side. For $0.7 \leq y < 1.0$, the system
undergoes a possible magnetic reorientation below the N\'{e}el temperature of
Gd ($T_\textup{N}^\textup{Gd}$). Our results suggest that the effects of both
electron hybridizations and magnetic exchange coupling between the 3d-4f
electrons give rise to a rich phase diagram in the rare-earth iron pnictides.",1212.0221v2
2013-03-12,Valence Fluctuation in CeMo2Si2C,"We report on the valence fluctuation of Ce in CeMo$_{2}$Si$_{2}$C as studied
by means of magnetic susceptibility $\chi(T)$, specific heat $C(T)$, electrical
resistivity $\rho(T)$ and x-ray absorption spectroscopy. Powder x-ray
diffraction revealed that CeMo$_{2}$Si$_{2}$C crystallizes in
CeCr$_{2}$Si$_{2}$C-type layered tetragonal crystal structure (space group
\textit{P4/mmm}). The unit cell volume of CeMo$_{2}$Si$_{2}$C deviates from the
expected lanthanide contraction, indicating non-trivalent state of Ce ions in
this compound. The observed weak temperature dependence of the magnetic
susceptibility and its low value indicate that Ce ions are in valence
fluctuating state. The formal $L_{III}$ Ce valence in CeMo$_{2}$Si$_{2}$C
$<$$\widetilde{\nu}$$>$ = 3.11 as determined from x-ray absorption spectroscopy
measurement is well bellow the value $<$$\widetilde{\nu}$$> \simeq$ 3.4 in
tetravalent Ce compound CeO$_{2}$. The temperature dependence of specific heat
does not show any anomaly down to 1.8 K which rules out any magnetic ordering
in the system. The Sommerfeld coefficient obtained from the specific heat data
is $\gamma$ = 23.4 mJ/mol\,K$^{2}$. The electrical resistivity follows the
$T{^2}$ behavior in the low temperature range below 35 K confirming a Fermi
liquid behavior. Accordingly both the Kadowaki Wood ratio $A/\gamma^{2}$ and
the Sommerfeld Wilson ratio $\chi(0)/\gamma$ are in the range expected for
Fermi-liquid systems. In order to get some information on the electronic
states, we calculated the band structure within the density functional theory,
eventhough this approach is not able to treat 4f electrons accurately. The
non-$f$ electron states crossing the Fermi level have mostly Mo 4d character.
They provide the states with which the 4f sates are strongly hybridized,
leading to the intermediate valent state.",1303.2801v1
2013-04-19,Quorum sensing inhibitory compounds from extremophilic microorganisms isolated from a hypersaline cyanobacterial mat,"In this study extremely halophilic and moderately thermophilic microorganisms
from a hypersaline microbial mat were screened for their ability to produce
antibacterial, antidiatom, antialgal and quorum sensing (QS) inhibitory
compounds. Five bacterial strains belonging to the genera Marinobacter and
Halomonas and one archaeal strain belonging to the genus Haloterrigena were
isolated from a microbial mat. The strains were able to grow at a maximum
salinity of 22-25% and a maximum temperature of 45-60{\deg}C. Hexanes,
dichloromethane and butanol extracts from the strains inhibited the growth of
at least one out of nine human pathogens. Only butanol extracts of supernatants
of Halomonas sp. SK-1 inhibited growth of the microalga Dunaliella salina. Most
extracts from isolates inhibited QS of the acyl homoserine lactone producer and
reporter Chromobacterium violaceum CV017. Purification of QS inhibitory
dichloromethane extracts of Marinobacter sp. SK-3 resulted in isolation of four
related diketopiperazines (DKPs): cyclo(L-Pro-L-Phe), cyclo(L-Pro-L-Leu),
cyclo(L-Pro-L-isoLeu) and cyclo(L-Pro-D-Phe). QS inhibitory properties of these
DKPs were tested using C. violaceum CV017 and Escherichia coli-based QS
reporters (pSB401 and pSB1075) deficient in AHL production. Cyclo(L-Pro-L-Phe)
and cyclo(L-Pro-L-isoLeu) inhibited QS dependent production of violacein by C.
violaceum CV017. Cyclo(L-Pro-L-Phe), cyclo(L-Pro-L-Leu), and
cyclo(L-Pro-L-isoLeu) reduced QS dependent luminescence of the reporter E. coli
pSB401 induced by 3-oxo-C6-HSL. Our study demonstrated the ability of
halophilic and moderately thermophilic strains from a hypersaline microbial mat
produce biotechnologically-relevant compounds that could be used as antifouling
agents",1304.5324v1
2013-10-21,NMR study of the Superconducting gap variation near the Mott transition in Cs$_{3}$C$_{60}$,"Former extensive studies of superconductivity in the \textit{A}$_{3}$C$_{60}$
compounds, where \textit{A} is an alkali, have led to consider that Bardeen
Cooper Schrieffer (BCS) electron-phonon pairing prevails in those compounds,
though the incidence of electronic Coulomb repulsion has been highly debated.
The discovery of two isomeric fulleride compounds Cs$_{3}$C$_{60}$ which
exhibit a transition with pressure from a Mott insulator (MI) to a
superconducting (SC) state clearly re-opens that question. Using pressure ($p$)
as a single control parameter of the C$_{60}$ balls lattice spacing, one can
now study the progressive evolution of the SC properties when the electronic
correlations are increased towards the critical pressure $p_{c}$ of the Mott
transition. We have used $^{13}$C and $^{133}$Cs NMR measurements on the cubic
phase A15-Cs$_{3}$C$_{60}$ just above $p_{c}=5.0(3)$ kbar, where the SC
transition temperature $T_{c}$ displays a dome shape with decreasing cell
volume. From the $T$ dependence below $T_{c}$ of the nuclear spin lattice
relaxation rate $(T_{1})^{-1}$ we determine the electronic excitations in the
SC state, that is $2\Delta$, the SC gap value. We find that $2\Delta $
increases with decreasing $p$ towards $p_{c}$, where $T_{c}$ decreases on the
SC dome, so that $2\Delta /k_{B}T_{c}$ increases regularly upon approaching the
Mott transition. These results bring clear evidence that the increasing
correlations near the Mott transition are not significantly detrimental to SC.
They rather suggest that repulsive electron interactions might even reinforce
elecron-phonon SC, being then partly responsible for the large $T_{c}$ values,
as proposed by theoretical models taking the electronic correlations as a key
ingredient.",1310.5529v3
2014-03-05,Bond disorder and spinon heat transport in the $S=\tfrac{1}{2}$ Heisenberg spin chain compound Sr$_2$CuO$_3$: from clean to dirty limits,"We investigate the effect of disorder on the heat transport properties of the
$S=\tfrac{1}{2}$ Heisenberg chain compound Sr$_2$CuO$_3$ upon chemically
substituting Sr by increasing concentrations of Ca. As Ca occupies sites
outside but near the Cu-O-Cu spin chains, bond disorder, i.e. a spatial
variation of the exchange interaction $J$, is expected to be realized in these
chains. We observe that the magnetic heat conductivity
($\kappa_{\mathrm{mag}}$) due to spinons propagating in the chains is gradually
but strongly suppressed with increasing amount of Ca, where the doping
dependence can be understood in terms of increased scattering of spinons due to
Ca-induced disorder. This is also reflected in the spinon mean free path which
can be separated in a doping independent but temperature dependent scattering
length due to spinon-phonon scattering, and a temperature independent but
doping dependent spinon-defect scattering length. The latter spans from very
large ($>$ 1300 lattice spacings) to very short ($\sim$ 12 lattice spacings)
and scales with the average distance between two neighboring Ca atoms. Thus,
the Ca-induced disorder acts as an effective defect within the spin chain, and
the doping scheme allows to cover the whole doping regime between the clean and
the dirty limits. Interestingly, at maximum impurity level we observe, in
Ca-doped Sr$_2$CuO$_3$, an almost linear increase of $\kappa_{\mathrm{mag}}$ at
temperatures above 100 K which reflects the intrinsic low temperature behavior
of heat transport in a Heisenberg spin chain. These findings are quite
different from that observed for the Ca-doped double spin chain compound,
SrCuO$_2$, where the effect of Ca seems to saturate already at intermediate
doping levels.",1403.1145v2
2014-03-25,Impurity diffusion in highly-ordered intermetallic compounds studied by nuclear quadrupole interactions,"Diffusion of impurity atoms depends on the sublattices occupied, active
diffusion mechanisms, and jump frequencies to neighboring sites. The method of
perturbed angular correlation of gamma rays (PAC) has been applied over the
past decade to study impurity diffusion through measurement of nuclear
quadrupole interactions (NQI) at nuclei of 111In/Cd probe atoms. Extensive
measurements have been made on highly-ordered compounds having the L12 crystal
structure, including In3R, Sn3R, Ga3R, Al3R and Pd3R phases (R= rare-earth
element). Measurements in thermal equilibrium at high temperature served to
determine lattice locations of 111In parent probe-atoms, through characteristic
NQIs, and to measure diffusional jump-frequencies of 111Cd daughter
probe-atoms, through relaxation of the NQI. This paper summarizes results of
the jump-frequency measurements and relates them to the conventional
diffusivity. ... A change in diffusion mechanism was proposed in 2009 to
explain jump-frequency systematics for In3R phases. An alternative explanation
is proposed in the present paper based on site-preferences of 111Cd daughter
probes newly observed along the parallel Pd3R series. The diffusivity can be
expressed as the product of a jump-frequency such as measured in these studies
and a correlation factor for diffusion that depends on the diffusion mechanism.
The correlation factor can be modeled for the L12 structure and diffusion
sublattice of interest using a five-frequency model originally proposed for
metals. Although the correlation factor is an essential parameter for the
diffusion of impurities, it has never been measured. It is suggested that
values of the correlation factor can be determined feasibly by combining
results of jump-frequency measurements such as the present ones with
diffusivity measurements made for the same host-impurity systems.",1403.6515v1
2014-05-26,"On the oscillator realization of conformal U(2,2) quantum particles and their particle-hole coherent states","We revise the unireps. of $U(2,2)$ describing conformal particles with
continuous mass spectrum from a many-body perspective, which shows massive
conformal particles as compounds of two correlated massless particles. The
statistics of the compound (boson/fermion) depends on the helicity $h$ of the
massless components (integer/half-integer). Coherent states (CS) of
particle-hole pairs (""excitons"") are also explicitly constructed as the
exponential action of exciton (non-canonical) creation operators on the ground
state of unpaired particles. These CS are labeled by points $Z$ ($2\times 2$
complex matrices) on the Cartan-Bergman domain $\mathbb D_4=U(2,2)/U(2)^2$, and
constitute a generalized (matrix) version of Perelomov $U(1,1)$ coherent states
labeled by points $z$ on the unit disk $\mathbb D_1=U(1,1)/U(1)^2$. Firstly we
follow a geometric approach to the construction of CS, orthonormal basis,
$U(2,2)$ generators and their matrix elements and symbols in the reproducing
kernel Hilbert space $\mathcal H_\lambda(\mathbb D_4)$ of analytic
square-integrable holomorphic functions on $\mathbb D_4$, which carries a
unitary irreducible representation of $U(2,2)$ with index $\lambda\in\mathbb N$
(the conformal or scale dimension). Then we introduce a many-body
representation of the previous construction through an oscillator realization
of the $U(2,2)$ Lie algebra generators in terms of eight boson operators with
constraints. This particle picture allows us for a physical interpretation of
our abstract mathematical construction in the many-body jargon. In particular,
the index $\lambda$ is related to the number $2(\lambda-2)$ of unpaired quanta
and to the helicity $h=(\lambda-2)/2$ of each massless particle forming the
massive compound.",1405.6600v1
2014-11-23,Target Fishing: A Single-Label or Multi-Label Problem?,"According to Cobanoglu et al and Murphy, it is now widely acknowledged that
the single target paradigm (one protein or target, one disease, one drug) that
has been the dominant premise in drug development in the recent past is
untenable. More often than not, a drug-like compound (ligand) can be
promiscuous - that is, it can interact with more than one target protein. In
recent years, in in silico target prediction methods the promiscuity issue has
been approached computationally in different ways. In this study we confine
attention to the so-called ligand-based target prediction machine learning
approaches, commonly referred to as target-fishing. With a few exceptions, the
target-fishing approaches that are currently ubiquitous in cheminformatics
literature can be essentially viewed as single-label multi-classification
schemes; these approaches inherently bank on the single target paradigm
assumption that a ligand can home in on one specific target. In order to
address the ligand promiscuity issue, one might be able to cast target-fishing
as a multi-label multi-class classification problem. For illustrative and
comparison purposes, single-label and multi-label Naive Bayes classification
models (denoted here by SMM and MMM, respectively) for target-fishing were
implemented. The models were constructed and tested on 65,587 compounds and 308
targets retrieved from the ChEMBL17 database. SMM and MMM performed
differently: for 16,344 test compounds, the MMM model returned recall and
precision values of 0.8058 and 0.6622, respectively; the corresponding recall
and precision values yielded by the SMM model were 0.7805 and 0.7596,
respectively. However, at a significance level of 0.05 and one degree of
freedom McNemar test performed on the target prediction results returned by SMM
and MMM for the 16,344 test ligands gave a chi-squared value of 15.656, in
favour of the MMM approach.",1411.6285v1
2014-12-29,The importance of inversion disorder in the visible light induced persistent luminescence in Cr$^{3+}$ doped AB$_2$O$_4$ (A = Zn or Mg and B = Ga or Al),"Cr$^{3+}$ doped spinel compounds AB$_2$O$_4$ with A=Zn, Mg and B=Ga, Al
exhibit a long near infrared persistent luminescence when excited with UV or
X-rays. In addition, persistent luminescence of ZnGa$_2$O$_4$ and to a lesser
extent MgGa$_2$O$_4$, can also be induced by visible light excitation via
$^4$A$_2$ $ \rightarrow $ $^4$T$_2$ transition of Cr$^{3+}$, which makes these
compounds suitable as biomarkers for in vivo optical imaging of small animals.
We correlate this peculiar optical property with the presence of antisite
defects, which are present in ZnGa$_2$O$_4$ and MgGa$_2$O$_4$. By using X-ray
absorption fine structure (XAFS) spectroscopy, associated with electron
paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown
that an increase in antisite defects concentration results in a decrease in the
Cr-O bond length and the octahedral crystal field energy. A part of the defects
are in the close environment of Cr$^{3+}$ ions, as shown by the increasing
strain broadening of EPR and XAFS peaks observed upon increasing antisite
disorder. It appears that ZnAl$_2$O$_4$, which exhibits the largest crystal
field splitting of Cr$^{3+}$ and the smallest antisite disorder, does not show
considerable persistent luminescence upon visible light excitation as compared
to ZnGa$_2$O$_4$ and MgGa$_2$O$_4$. These results highlight the importance of
Cr$^{3+}$ ions with neighboring antisite defects in the mechanism of persistent
luminescence exhibited by Cr$^{3+}$ doped AB$_2$O$_4$ spinel compounds.",1412.8310v1
2014-12-31,Frustrated three-dimensional antiferromagnet Li$_{2}$CuW$_{2}$O$_{8}$: $^7$Li NMR and the effect of non-magnetic dilution,"We report a $^7$Li nuclear magnetic resonance (NMR) study of a frustrated
three-dimensional \mbox{spin-$\frac12$} antiferromagnet
Li$_{2}$CuW$_{2}$O$_{8}$ and also explore the effect of non-magnetic dilution.
The magnetic long-range ordering in the parent compound at $T_{\rm N}\simeq$
3.9~K was detected from the drastic line broadening and a peak in the
spin-lattice relaxation rate ($1/T_1$). The NMR spectrum above $T_{\rm N}$
broadens systematically, and its full width at half maximum (FWHM) tracks the
static spin susceptibility. From the analysis of FWHM vs. static
susceptibility, the coupling between the Li nuclei and Cu$^{2+}$ ions was found
to be purely dipolar in nature. The magnitude of the maximum exchange coupling
constant is $J_{\rm max}/k_{\rm B}\simeq 13$\,K. NMR spectra below $T_{\rm N}$
broaden abruptly and transform into a double-horn pattern reflecting the
commensurate nature of the spin structure in the ordered state. Below $T_{\rm
N}$, 1/$T_1$ follows a $T^5$ behavior. The frustrated nature of the compound is
confirmed by persistent magnetic correlations at high temperatures well above
$T_{\rm N}$. The dilution of the spin lattice with non-magnetic Zn atoms has
dramatic influence on $T_N$ that decreases exponentially similar to
quasi-one-dimensional antiferromagnets, even though Li$_2$CuW$_2$O$_8$ has only
a weak one-dimensional anisotropy. Heat capacity of doped samples follows power
law ($C_{\rm p} \propto T^{\alpha}$) below $T_{\rm N}$, and the exponent
($\alpha$) decreases from 3 in the parent compound to 1 in the 25\% doped
sample.",1501.00099v2
2015-05-05,Band-gap and Band-edge Engineering of Multicomponent Garnet Scintillators: A First-principles Study,"Complex doping schemes in RE$_3$Al$_5$O$_{12}$ (RE=rare earth element) garnet
compounds have recently led to pronounced improvements in scintillator
performance. Specifically, by admixing lutetium and yttrium aluminate garnets
with gallium and gadolinium, the band-gap was altered in a manner that
facilitated the removal of deleterious electron trapping associated with cation
antisite defects. Here, we expand upon this initial work to systematically
investigate the effect of substitutional admixing on the energy levels of band
edges. Density functional theory was used to survey potential admixing
candidates that modify either the conduction band minimum (CBM) or valence band
maximum (VBM). We considered two sets of compositions based on
Lu$_3$B$_5$O$_{12}$ where B = Al, Ga, In, As, and Sb; and RE$_3$Al$_5$O$_{12}$,
where RE = Lu, Gd, Dy, and Er. We found that admixing with various RE cations
does not appreciably effect the band gap or band edges. In contrast,
substituting Al with cations of dissimilar ionic radii has a profound impact on
the band structure. We further show that certain dopants can be used to
selectively modify only the CBM or the VBM. Specifically, Ga and In decrease
the band gap by lowering the CBM, while As and Sb decrease the band gap by
raising the VBM. These results demonstrate a powerful approach to quickly
screen the impact of dopants on the electronic structure of scintillator
compounds, identifying those dopants which alter the band edges in very
specific ways to eliminate both electron and hole traps responsible for
performance limitations. This approach should be broadly applicable for the
optimization of electronic and optical performance for a wide range of
compounds by tuning the VBM and CBM.",1505.01218v1
2015-09-23,Superconducting dome in doped quasi-2d organic Mott insulators: a paradigm for strongly-correlated superconductivity,"Layered organic superconductors of the BEDT family are model systems for the
interplay of the Mott transition with superconductivity, magnetic order and
frustration. Recent experimental studies on a hole-doped version of BEDT
compounds reveal an enhancement of superconductivity and a rapid crossover
between two different conducting phases above the superconducting dome. One of
these phases is a Fermi liquid, the other not. Using plaquette cellular
dynamical mean field theory with state of the art continuous-time quantum Monte
Carlo calculations, we study this problem with the two-dimensional Hubbard
model on the anisotropic triangular lattice. Phase diagrams as a function of
temperature $T$ and interaction strength $U/t$ are obtained for anisotropy
parameters $t'=0.4t$, $t'=0.8t$ and various fillings. As for cuprates, we find,
at finite doping, a first-order transition between two normal-state phases. For
$T$ above the critical point of the first-order transition, there is a Widom
line where crossovers occur. The results are in broad agreement with
experiment. This suggests that for compounds with intermediate to high
frustration, very light-doping should reveal the first-order transition and
associated crossovers. These crossovers could leave traces in the
superconducting phase. We also predict that destroying the superconducting
phase by a magnetic field should reveal the first-order transition. Finally, we
predict that electron-doping should also lead to an increased range of $U/t$
for superconductivity but with a reduced maximum $T_c$. This work also clearly
shows that the superconducting dome here is tied to the Mott transition and its
continuation as a transition separating pseudogap phase from correlated metal
in doped compounds, as in the cuprates. Contrary to heavy fermions for example,
the maximum $T_c$ is definitely not attached to an antiferromagnetic quantum
critical point.",1509.07086v1
2015-11-06,Unraveling the nature of carrier mediated ferromagnetism in diluted magnetic semiconductors,"After more than a decade of intensive research in the field of diluted
magnetic semiconductors (DMS), the nature and origin of ferromagnetism,
especially in III-V compounds is still controversial. Many questions and open
issues are under intensive debates. Why after so many years of investigations
Mn doped GaAs remains the candidate with the highest Curie temperature among
the broad family of III-V materials doped with transition metal (TM) impurities
? How can one understand that these temperatures are almost two orders of
magnitude larger than that of hole doped (Zn,Mn)Te or (Cd,Mn)Se? Is there any
intrinsic limitation or is there any hope to reach in the dilute regime room
temperature ferromagnetism? How can one explain the proximity of (Ga,Mn)As to
the metal-insulator transition and the change from
Ruderman-Kittel-Kasuya-Yosida (RKKY) couplings in II-VI compounds to double
exchange type in (Ga,Mn)N? In spite of the great success of density functional
theory based studies to provide accurately the critical temperatures in various
compounds, till very lately a theory that provides a coherent picture and
understanding of the underlying physics was still missing. Recently, within a
minimal model it has been possible to show that among the physical parameters,
the key one is the position of the TM acceptor level. By tuning the value of
that parameter, one is able to explain quantitatively both magnetic and
transport properties in a broad family of DMS. We will see that this minimal
model explains in particular the RKKY nature of the exchange in
(Zn,Mn)Te/(Cd,Mn)Te and the double exchange type in (Ga,Mn)N and simultaneously
the reason why (Ga,Mn)As exhibits the highest critical temperature among both
II-VI and III-V DMS.",1511.02127v1
2015-11-17,Pauli-limited superconductivity and antiferromagnetism in the heavy-fermion compound CeCo(In1-xZnx)5,"We report on the anisotropic properties of Pauli-limited superconductivity
(SC) and antiferromagnetism (AFM) in the solid solutions CeCo(In_{1-x}Zn_x)_5
(x<=0.07). In CeCo(In_{1-x}Zn_x)_5, the SC transition temperature T_c is
continuously reduced from 2.3 K (x=0) to ~1.4 K (x=0.07) by doping Zn, and then
the AFM order with the transition temperature of T_N~2.2 K develops for x
larger than ~0.05. The present thermal, transport and magnetic measurements
under magnetic field B reveal that the substitution of Zn for In yields little
change of low-temperature upper critical field \mu_0H_{c2} for both the
tetragonal a and c axes, while it monotonically reduces the SC transition
temperature T_c. In particular, the magnitudes of \mu_0H_{c2} at the nominal Zn
concentration of x = 0.05 (measured Zn amount of ~0.019) are 11.8 T for B||a
and 4.8 T for B||c, which are as large as those of pure compound though T_c is
reduced to 80% of that for x=0. We consider that this feature originates from a
combination of both an enhanced AFM correlation and a reduced SC condensation
energy in these alloys. It is also clarified that the AFM order differently
responds to the magnetic field, depending on the field directions. For B||c,
the clear anomaly due to the AFM transition is observed up to the AFM critical
field of ~5 T in the thermodynamic quantities, whereas it is rapidly damped
with increasing B for B||a. We discuss this anisotropic response on the basis
of a rich variety of the AFM modulations involved in the Ce115 compounds.",1511.05241v1
2016-01-13,Quantum-Critical Fluctuations in 2D Metals: Strange Metals and Superconductivity in Antiferromagnets and in Cuprates,"The anomalous transport and thermodynamic properties in the quantum-critical
region, in the cuprates, and in the quasi-two dimensional Fe-based
superconductors and heavy-fermion compounds, have the same temperature
dependences. This can occur only if, despite their vast microscopic
differences, a common statistical mechanical model describes their phase
transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as
the loop-current model for the cuprates, map to the dissipative XY model. The
solution of this model in 2+1 D reveals that the critical fluctuations are
determined by topological excitations, vortices and a variety of instantons,
and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type,
adapted by Moriya, Hertz and others for quantum-criticality. The absorptive
part of the fluctuations is a separable function of momentum ${\bf q}$,
measured from the ordering vector, and of the frequency $\omega$ and the
temperature $T$ which scale as $\tanh(\omega/2T)$ at criticality. Direct
measurements of the fluctuations by neutron scattering in the
quasi-two-dimensional heavy fermion and Fe-based compounds, near their
antiferromagnetic quantum critical point, are consistent with this form. Such
fluctuations, together with the vertex coupling them to fermions, lead to a
marginal fermi-liquid, with the imaginary part of the self-energy $\propto
max(\omega, T)$ for all momenta, a resistivity $\propto T$, a $T \ln T$
contribution to the specific heat, and other singular fermi-liquid properties
common to these diverse compounds, as well as to d-wave superconductivity. This
is explicitly verified, in the cuprates, by analysis of the pairing and the
normal self-energy directly extracted from the recent high resolution angle
resolved photoemission measurements.",1601.03403v2
2016-04-07,"Theoretical prediction of magnetic and noncentrosymmetric Weyl fermion semimetal states in the R-Al-X family of compounds (R=rare earth, Al=aluminium, X=Si, Ge)","Weyl semimetals are novel topological conductors that host Weyl fermions as
emergent quasiparticles. While the Weyl fermions in high-energy physics are
strictly defined as the massless solution of the Dirac equation and uniquely
fixed by Lorentz symmetry, there is no such constraint for a topological metal
in general. Specifically, the Weyl quasiparticles can arise by breaking either
the space-inversion ($\mathcal{I}$) or time-reversal ($\mathcal{T}$) symmetry.
They can either respect Lorentz symmetry (type-I) or strongly violate it
(type-II). To date, different types of Weyl fermions have been predicted to
occur only in different classes of materials. In this paper, we present a
significant materials breakthrough by identifying a large class of Weyl
materials in the RAlX (R=Rare earth, Al, X=Ge, Si) family that can realize all
different types of emergent Weyl fermions ($\mathcal{I}$-breaking,
$\mathcal{T}$-breaking, type-I or type-II), depending on a suitable choice of
the rare earth elements. Specifically, RAlX can be ferromagnetic, nonmagnetic
or antiferromagnetic and the electronic band topology and topological nature of
the Weyl fermions can be tuned. The unparalleled tunability and the large
number of compounds make the RAlX family of compounds a unique Weyl semimetal
class for exploring the wide-ranging topological phenomena associated with
different types of emergent Weyl fermions in transport, spectroscopic and
device-based experiments.",1604.02124v4
2016-04-20,Realistic multiband k.p approach from ab initio and spin-orbit coupling effects of InAs and InP in wurtzite phase,"Semiconductor nanowires based on non-nitride III-V compounds can be
synthesized under certain growth conditions to favor the appearance of wurtzite
crystal phase. Despite the reports in literature of ab initio band structures
for these wurtzite compounds, we still lack effective multiband models and
parameter sets that can be simply used to investigate physical properties of
such systems, for instance, under quantum confinement effects. In order to
address this deficiency, in this study we calculate the ab initio band
structure of bulk InAs and InP in wurtzite phase and develop an 8$\times$8 k.p
Hamiltonian to describe the energy bands around $\Gamma$ point. We show that
our k.p model is robust and can be fitted to describe the important features of
the ab initio band structure. The correct description of the spin splitting
effects that arise due to the lack of inversion symmetry in wurtzite crystals,
is obtained with the $k$-dependent spin-orbit term in the Hamiltonian, often
neglected in the literature. All the energy bands display a Rashba-like spin
texture for the in-plane spin expectation value. We also provide the density of
states and the carrier density as functions of the Fermi energy. Alternatively,
we show an analytical description of the conduction band, valid close to
$\Gamma$ point. The same fitting procedure is applied to the 6$\times$6 valence
band Hamiltonian. However, we find that the most reliable approach is the
8$\times$8 k.p Hamiltonian for both compounds. The k.p Hamiltonians and
parameter sets that we develop in this paper provide a reliable theoretical
framework that can be easily applied to investigate electronic, transport,
optical, and spin properties of InAs- and InP-based nanostructures.",1604.06014v2
2016-05-26,"Long-range and short-range magnetic correlations, and microscopic origin of net magnetization in the spin-1 trimer chain compound CaNi3P4O14","Spin-spin correlations and microscopic origin of net magnetization in the
spin-1 trimer chain compound CaNi3P4O14 have been investigated by powder
neutron diffraction. The present study reveals a 3D long-range magnetic
ordering below 16 K where the magnetic structure consists of ferromagnetic
trimers that are coupled ferromagnetically along the spin-chain. The moment
components along the a and c axes arrange antiferromagnetically. Our study
establishes that the uncompensated moment components along the b axis result in
a net magnetization per unit cell. The magnetic structure, determined in the
present study, is in agreement with the results of recent first principles
calculation; however, it is in contrast to a fascinating experimental
prediction of ferrimagnetic ordering based on the periodicity of the exchange
interactions in CaNi3P4O14. Our study also confirms the presence of broad
diffuse magnetic scattering, due to 1D short-range spin-spin correlations, over
a wide temperature range below ~50 K down to a temperature well below the Tc.
Total neutron scattering analysis by the RMC method reveals that the dominating
spin-spin correlation above Tc is ferromagnetic and along the b axis. The
nearest neighbour spin-spin correlations along the a and c axes are found to be
weakly antiferromagnetic. The nature of the trimer spin structure of the
short-range state is similar to that of the 3D long-range ordered state. The
present investigation of microscopic nature of the magnetic ground state also
explains the condition required for the 1/3 magnetization plateau to be
observed in the trimer spin-chains. In spite of the S=1 trimer chain system,
the present compound CaNi3P4O14 is found to be a good realization of 3D magnet
below the Tc=16 K with full ordered moment values of ~2 mu_B/Ni2+ (1.98 and
1.96 mu_B/Ni2+ for two Ni sites, respectively) at 1.5 K.",1605.08210v1
2016-06-09,Ternary borides Nb$_7$Fe$_3$B$_8$ and Ta$_7$Fe$_3$B$_8$ with Kagome-type iron framework,"Two new ternary borides $TM$$_7$Fe$_3$B$_8$ ($TM$ = Nb, Ta) were synthesized
by high-temperature thermal treatment of samples obtained by arc-melting. This
new type of structure with space group $P$6/$mmm$, comprises $TM$ slabs
containing isolated planar hexagonal [B$_6$] rings and iron centered $TM$
columns in a Kagome type of arrangement. Chemical bonding analysis in
Nb$_7$Fe$_3$B$_8$ by means of the electron localizability approach reveals
two-center interactions forming the Kagome net of Fe and embedded B, while
weaker multicenter bonding present between this net and Nb atoms. Magnetic
susceptibility measurements reveal antiferromagnetic order below $T_N$ = 240 K
for Nb$_7$Fe$_3$B$_8$ and $T_N$ =265 K for Ta$_7$Fe$_3$B$_8$. Small remnant
magnetization below 0.01 $\mu_B$/f.u. is observed in the antiferromagnetic
state. The bulk nature of the magnetic transitions was confirmed by the
hyperfine splitting of the M\""o{\ss}bauer spectra, the sizable anomalies in the
specific heat capacity, and the kinks in the resistivity curves. The high-field
paramagnetic susceptibilities fitted by the Curie-Weiss law show effective
paramagnetic moments $\mu_{eff}$ about 3.1 $\mu_B$/Fe in both compounds. The
temperature dependence of the electrical resistivity also reveals metallic
character of both compounds. Density functional calculations corroborate the
metallic behaviour of both compounds and demonstrate the formation of a sizable
local magnetic moment on the Fe-sites. They indicate the presence of both
antiferro- and ferromagnetic interactions.",1606.03123v1
2016-07-05,Two-dimensional superconductivity in a bulk single-crystal,"Both Nb$_3$Pd$_x$Se$_7$ and Ta$_4$Pd$_3$Te$_{16}$ crystallize in a monoclinic
point group while exhibiting superconducting transition temperatures as high as
$T_c\sim 3.5$ and $\sim 4.7 $ K, respectively. Disorder was claimed to lead to
the extremely large upper critical fields ($H_{c2}$) observed in related
compounds. Despite the presence of disorder and heavier elements, $H_{c2}$s in
Ta$_4$Pd$_3$Te$_{16}$ are found to be considerably smaller than those of
Nb$_3$Pd$_x$Se$_7$ while displaying an anomalous, non-saturating linear
dependence on temperature $T$ for fields along all three crystallographic axes.
In contrast, crystals of the latter compound displaying the highest $T_c$s
display $H_{c2}\propto (1-T/T_c)^{1/2}$, which in monolayers of transition
metal dichalcogenides is claimed to be evidence for an Ising paired
superconducting state resulting from strong spin-orbit coupling. This anomalous
$T$-dependence indicates that the superconducting state of Nb$_3$Pd$_x$Se$_7$
is quasi-two-dimensional in nature. This is further supported by a nearly
divergent anisotropy in upper-critical fields, i.e. $\gamma=
H_{c2}^{b}/H_{c2}^{a^{\prime}}$, upon approaching $T_c$. Hence, in
Nb$_3$Pd$_x$Se$_7$ the increase of $T_c$ correlates with a marked reduction in
electronic dimensionality as observed, for example, in intercalated FeSe. For
the Nb compound, Density functional theory (DFT) calculations indicate that an
increase in the external field produces an anisotropic orbital response, with
especially strong polarization at the Pd sites when the field is perpendicular
to their square planar environment. Therefore, DFT suggests the field-induced
pinning of the spin to the lattice as a possible mechanism for decoupling the
superconducting planes. Overall, our observations represent further evidence
for unconventional superconductivity in the Pd chalcogenides.",1607.01333v1
2016-07-22,"Inelastic neutron scattering investigations of an anisotropic hybridization gap in the Kondo insulators: CeT2Al10 (T=Fe, Ru and Os)","The recent discovery of topological Kondo insulating behaviour in strongly
correlated electron systems has generated considerable interest in Kondo
insulators both experimentally and theoretically. The Kondo semiconductors
CeT2Al10 (T=Fe, Ru and Os) possessing a c-f hybridization gap have received
considerable attention recently because of the unexpected high magnetic
ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the
Kondo insulating behaviour observed in the valence fluctuating compound
CeFe2Al10 with a paramagnetic ground state down to 50 mK. We are investigating
this family of compounds, both in polycrystalline and single crystal form,
using inelastic neutron scattering to understand the role of anisotropic c-f
hybridization on the spin gap formation as well as on their magnetic
properties. We have observed a clear sign of a spin gap in all three compounds
from our polycrystalline study as well as the existence of a spin gap above the
magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering
studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive
gapped spin wave excitations below TN. Analysis of the spin wave spectrum
reveals the presence of strong anisotropic exchange, along the c-axis (or
z-axis) stronger than in the ab-plane. These anisotropic exchange interactions
force the magnetic moment to align along the c-axis, competing with the single
ion crystal field anisotropy, which prefers moments along the a-axis. In the
paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also
observed dispersive gapped magnetic excitations which transform into
quasi-elastic scattering on heating to 100 K. We will discuss the origin of the
anisotropic hybridization gap in CeFe2Al10 based on theoretical models of
heavy-fermion semiconductors.",1607.06538v1
2016-07-29,Superconductivity and non-Fermi-liquid behavior in the heavy-fermion compound CeCo$_{1-x}$Ni$_x$In$_5$,"The effect of off-plane impurity on superconductivity and non-Fermi-liquid
(NFL) behavior in the layered heavy-fermion compound CeCo$_{1-x}$Ni$_x$In$_5$
is investigated by specific heat, magnetization, and electrical resistivity
measurements. These measurements reveal that the superconducting (SC)
transition temperature T$_c$ monotonically decreases from 2.3 K (x=0) to 0.8 K
(x=0.20) with increasing x, and then the SC order disappears above x=0.25. At
the same time, the Ni substitution yields the NFL behavior at zero field for
x=0.25, characterized by the -ln T divergence in specific heat divided by
temperature, C$_p$/T, and magnetic susceptibility, M/B. The NFL behavior in
magnetic fields for x=0.25 is quite similar to that seen at around the SC upper
critical field in pure CeCoIn$_5$, suggesting that both compounds are governed
by the same antiferromagnetic quantum criticality. The resemblance of the
doping effect on the SC order among Ni- , Sn-, and Pt-substituted CeCoIn5
supports the argument that the doped carriers are primarily responsible for the
breakdown of the SC order. The present investigation further reveals the
quantitative differences in the trends of the suppression of superconductivity
between Ce(Co,Ni)In$_5$ and the other alloys, such as the rates of decrease in
T$_c$, dT$_c$/dx, and specific heat jump at T$_c$, d($\Delta$C$_p$/T$_c$)/dx.
We suggest that the occupied positions of the doped ions play an important role
in the origin of these differences.",1607.08680v1
2016-10-05,An important role of temperature dependent scattering time in understanding the high temperature thermoelectric behavior of strongly correlated system: La$_{0.75}$Ba$_{0.25}$CoO$_{3}$,"In the present work, we have reported the temperature dependent thermopower
($\alpha$) behavior of La$_{0.75}$Ba$_{0.25}$CoO$_{3}$ compound in the
temperature range 300-600 K. Using the Heikes formula, the estimated value of
$\alpha$ corresponding to high-spin configuration of Co$^{3+}$ and Co$^{4+}$
ions is found to be $\sim$$16$ $\mu$V/K, which is close to the experimental
value, $\sim$13 $\mu$V/K, observed at $\sim$600 K. The temperature dependent TE
behavior of the compound is studied by combining the WIEN2K and BoltzTrap code.
The self consistency field calculations show that the compound have
ferromagnetic ground state structure. The electronic structure calculations
give half metallic characteristic with a small gap of $\sim$50 meV for down
spin channel. The large and positive value for down spin channel is obtained
due to the unique band structure shown by this spin channel. The temperature
dependent relaxation time for both the spin-channel charge carriers is
considered to study the thermopower data in temperature range 300-600 K. An
almost linear values of $\tau_{up}$ and a non-linear values of $\tau_{dn}$ are
taken into account for evaluation of $\alpha$. By taking the temperature
dependent values of relaxation time for both the spin channels, the calculated
values of $\alpha$ using two current model are found to be in good agreement
with experimental values in the temperature range 300-600 K. At 300 K, the
calculated value of electrical conductivity by using the same value of
relaxation time, i.e. 0.1 $\times $10$^{-14}$ seconds for spin-up and 0.66
$\times $10$^{-14}$ seconds for spin-dn channel, is found to be equal to the
experimentally reported value.",1610.01577v2
2016-10-26,"Structural and magnetic properties of two branches of the Tripod Kagome Lattice family A$_{2}$RE$_{3}$Sb$_{3}$O$_{14}$ (A = Mg, Zn; RE = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb)","We present a systematic study of the structural and magnetic properties of
two branches of the rare earth Tripod Kagome Lattice (TKL) family
A$_{2}$RE$_{3}$Sb$_{3}$O$_{14}$ (A = Mg, Zn; RE = Pr, Nd, Gd, Tb, Dy, Ho, Er,
Yb; here, we use abbreviation \textit{A-RE}, as in \textit{MgPr} for
Mg$_{2}$Pr$_{3}$Sb$_{3}$O$_{14}$), which complements our previously reported
work on \textit{MgDy}, \textit{MgGd}, and \textit{MgEr} \cite{TKL}. The present
susceptibility ($\chi_{dc}$, $\chi_{ac}$) and specific heat measurements reveal
various magnetic ground states, including the non-magnetic singlet state for
\textit{MgPr}, \textit{ZnPr}; long range orderings (LROs) for \textit{MgGd},
\textit{ZnGd}, \textit{MgNd}, \textit{ZnNd}, and \textit{MgYb}; a long range
magnetic charge ordered state for \textit{MgDy}, \textit{ZnDy}, and potentially
for \textit{MgHo}; possible spin glass states for \textit{ZnEr}, \textit{ZnHo};
the absence of spin ordering down to 80 mK for \textit{MgEr}, \textit{MgTb},
\textit{ZnTb}, and \textit{ZnYb} compounds. The ground states observed here
bear both similarities as well as striking differences from the states found in
the parent pyrochlore systems. In particular, while the TKLs display a greater
tendency towards LRO, the lack of LRO in \textit{MgHo}, \textit{MgTb} and
\textit{ZnTb} can be viewed from the standpoint of a balance among spin-spin
interactions, anisotropies and non-Kramers nature of single ion state. While
substituting Zn for Mg changes the chemical pressure, and subtly modifies the
interaction energies for compounds with larger RE ions, this substitution
introduces structural disorder and modifies the ground states for compounds
with smaller RE ions (Ho, Er, Yb).",1610.08396v2
2016-11-16,Cs$_2$InAgCl$_6$: A new lead-free halide double perovskite with direct band gap,"A$_2$BB$^\prime$X$_6$ halide double perovskites based on bismuth and silver
have recently been proposed as potential environmentally-friendly alternatives
to lead-based hybrid halide perovskites. In particular, Cs$_2$BiAgX$_6$ (X =
Cl, Br) have been synthesized and found to exhibit band gaps in the visible
range. However, the band gaps of these compounds are indirect, which is not
ideal for applications in thin film photovoltaics. Here, we propose a new class
of halide double perovskites, where the B$^{3+}$ and B$^{+}$ cations are
In$^{3+}$ and Ag$^{+}$, respectively. Our first-principles calculations
indicate that the hypothetical compounds Cs$_2$InAgX$_6$ (X = Cl, Br, I) should
exhibit direct band gaps between the visible (I) and the ultraviolet (Cl).
Based on these predictions, we attempt to synthesize Cs$_2$InAgCl$_6$ and
Cs$_2$InAgBr$_6$, and we succeed to form the hitherto unknown double perovskite
Cs$_2$InAgCl$_6$. X-ray diffraction yields a double perovskite structure with
space group $Fm\overline{3}m$. The measured band gap is 3.3 eV, and the
compound is found to be photosensitive and turns reversibly from white to
orange under ultraviolet illumination. We also perform an empirical analysis of
the stability of Cs$_2$InAgX$_6$ and their mixed halides based on Goldschmidt's
rules, and we find that it should also be possible to form
Cs$_2$InAg(Cl$_{1-x}$Br$_{x}$)$_6$ for $x<1$. The synthesis of mixed halides
will open the way to the development of lead-free double perovskites with
direct and tunable band gaps.",1611.05426v2
2017-03-09,High-$T_\textrm {C}$ superconductivity in Cs$_3$C$_{60}$ compounds governed by local Cs-C$_{60}$ Coulomb interactions,"Unique among alkali-doped $\textit {A}$$_3$C$_{60}$ fullerene compounds, the
A15 and fcc forms of Cs$_3$C$_{60}$ exhibit superconducting states varying
under hydrostatic pressure with highest transition temperatures at $T_\textrm
{C}$$^\textrm {meas}$ = 38.3 and 35.2 K, respectively. Herein it is argued that
these two compounds under pressure represent the optimal materials of the
$\textit {A}$$_3$C$_{60}$ family, and that the C$_{60}$-associated
superconductivity is mediated through Coulombic interactions with charges on
the alkalis. A derivation of the interlayer Coulombic pairing model of
high-$T_\textrm {C}$ superconductivity employing non-planar geometry is
introduced, generalizing the picture of two interacting layers to an
interaction between charge reservoirs located on the C$_{60}$ and alkali ions.
The optimal transition temperature follows the algebraic expression, $T_\textrm
{C0}$ = (12.474 nm$^2$ K)/$\ell$${\zeta}$, where $\ell$ relates to the mean
spacing between interacting surface charges on the C$_{60}$ and ${\zeta}$ is
the average radial distance between the C$_{60}$ surface and the neighboring Cs
ions. Values of $T_\textrm {C0}$ for the measured cation stoichiometries of
Cs$_{3-\textrm{x}}$C$_{60}$ with x $\approx$ 0 are found to be 38.19 and 36.88
K for the A15 and fcc forms, respectively, with the dichotomy in transition
temperature reflecting the larger ${\zeta}$ and structural disorder in the fcc
form. In the A15 form, modeled interacting charges and Coulomb potential
e$^2$/${\zeta}$ are shown to agree quantitatively with findings from
nuclear-spin relaxation and mid-infrared optical conductivity. In the fcc form,
suppression of $T_\textrm {C}$$^\textrm {meas}$ below $T_\textrm {C0}$ is
ascribed to native structural disorder. Phononic effects in conjunction with
Coulombic pairing are discussed.",1703.03350v2
2017-03-16,Entrance Channel Effects on the Quasifission Reaction Channel in Cr + W Systems,"Background: Formation of a fully equilibrated compound nucleus is a critical
step in the heavy-ion fusion reaction mechanism but can be hindered by orders
of magnitude by quasifission, a process in which the dinuclear system breaks
apart prior to full equilibration. To provide a complete description of
heavy-ion fusion it is important to characterize the quasifission process. In
particular, the impact of changing the neutron-richness of the quasifission
process is not well known. A previous study of Cr + W reactions at a constant
13 % above the Coulomb barrier concluded that an increase in neutron-richness
leads to a decrease in the prominence of the quasifission reaction channel.
Purpose: The interplay between the fusion-fission and quasifission reaction
channels, with varying neutron-richness, was explored at a constant excitation
energy, closer to the interaction barrier than the previous work, to see if the
correlation between neutron-richness and quasifission is valid at lower
energies. Methods: Mass distributions were determined for eight different
combinations of Cr + W reactions at the Australian National University at 52.0
MeV of excitation energy in the compound nucleus. Results: A curvature
parameter was determined for the fission-like fragment mass distributions and
compared to various reaction parameters known to influence quasifission.
Conclusions: The present work demonstrates that at energies near the
interaction barrier the deformation effects dominate over the neutron-richness
effects in the competition between quasifission and compound nucleus formation
in these Cr + W systems and is an important consideration for future with heavy
and superheavy element production reactions.",1703.05746v2
2017-03-31,Profunctor Optics: Modular Data Accessors,"CONTEXT: Data accessors allow one to read and write components of a data
structure, such as the fields of a record, the variants of a union, or the
elements of a container. These data accessors are collectively known as optics;
they are fundamental to programs that manipulate complex data. INQUIRY:
Individual data accessors for simple data structures are easy to write, for
example as pairs of ""getter"" and ""setter"" methods. However, it is not obvious
how to combine data accessors, in such a way that data accessors for a compound
data structure are composed out of smaller data accessors for the parts of that
structure. Generally, one has to write a sequence of statements or declarations
that navigate step by step through the data structure, accessing one level at a
time - which is to say, data accessors are traditionally not first-class
citizens, combinable in their own right. APPROACH: We present a framework for
modular data access, in which individual data accessors for simple data
structures may be freely combined to obtain more complex data accessors for
compound data structures. Data accessors become first-class citizens. The
framework is based around the notion of profunctors, a flexible generalization
of functions. KNOWLEDGE: The language features required are higher-order
functions (""lambdas"" or ""closures""), parametrized types (""generics"" or
""abstract types""), and some mechanism for separating interfaces from
implementations (""abstract classes"" or ""modules""). We use Haskell as a vehicle
in which to present our constructions, but languages such as Java, C#, or Scala
that provide the necessary features should work just as well. GROUNDING: We
provide implementations of all our constructions, in the form of a literate
program: the manuscript file for the paper is also the source code for the
program, and the extracted code is available separately for evaluation. We also
prove the essential properties demonstrating that our profunctor-based
representations are precisely equivalent to the more familiar concrete
representations. IMPORTANCE: Our results should pave the way to simpler ways of
writing programs that access the components of compound data structures.",1703.10857v1
2017-08-17,"Effect of Fe and Co substitution on martensitic stability, elastic, electronic and magnetic properties of Mn$_2$NiGa: insights from \textit{ab initio} calculations","We investigate the effects of Fe and Co substitutions on the phase stability
of the martensitic phase, mechanical, electronic and magnetic properties of
magnetic shape memory system Mn$_{2}$NiGa by first-principles Density
functional theory(DFT) calculations. The evolution of these aspects upon
substitution of Fe and Co at different crystallographic sites are investigated
by computing the electronic structure, mechanical properties and magnetic
exchange parameters. We find that the martensitic phase of Mn$_{2}$NiGa
gradually de-stabilises with increase in concentration of Fe/Co due to the
weakening of the minority spin hybridisation of Ni and Mn atoms occupying
crystallographically equivalent sites. The interplay between relative
structural stability and the compositional changes are understood from the
variations in the elastic modulii and electronic structures. We find that the
elastic shear modulus C$^{\prime}$ can be considered as a predictor of
composition dependence of martensitic transformation temperature in substituted
Mn$_{2}$NiGa. The magnetic properties of Mn$_{2}$NiGa are found to be greatly
improved by the substitutions due to stronger ferromagnetic interactions in the
compounds. The gradually weaker(stronger) Jahn-Teller distortion (covalent
bonding) in the minority spin densities of states due to substitutions lead to
a half-metallic like gap in these compounds resulting in materials with high
spin-polarisation when the substitutions are complete. The substitutions at the
Ga site result in two new compounds Mn$_{2}$NiFe and Mn$_{2}$NiCo with very
high magnetic moments and Curie temperatures. Thus, our work indicates that
although the substitutions de-stabilise the martensitic phase in Mn$_{2}$NiGa,
new magnetic materials with very good magnetic parameters and potentially
useful for novel magnetic applications can be obtained.",1708.05146v1
2017-09-12,Compound-Specific Chlorine Isotope Analysis of Organochlorines Using Gas Chromatography-Double Focus Magnetic-Sector High Resolution Mass Spectrometry,"Compound-specific chlorine isotope analysis (CSIA-Cl) is a practicable and
high-performance approach for quantification of transformation processes and
pollution source apportionment of chlorinated organic compounds. This study
developed a CSIA-Cl method for perchlorethylene (PCE) and trichloroethylene
(TCE) using gas chromatography-double focus magnetic-sector high resolution
mass spectrometry (GC-DFS-HRMS) with a bracketing injection mode. The achieved
highest precision for PCE was 0.021% (standard deviation of isotope ratios),
and that for TCE was 0.025%. When one standard was used as the external
isotopic standard for another of the same analyte, the lowest standard
deviations of relative isotope-ratio variations ({\delta}37Cl') between the two
corresponding standards were 0.064% and 0.080% for PCE and TCE, respectively.
As a result, the critical {\delta}37Cl' for differentiating two isotope ratios
are 0.26% and 0.32% for PCE and TCE, respectively, which are comparable with
those in some reported studies using GC-quadrupole MS (GC-qMS). The lower limit
of detection for CSIA-Cl of PCE was 0.1 ug/mL (0.1 ng on column), and that for
TCE was determined to be 1.0 ug/mL (1.0 ng on column). Two isotope ratio
calculation schemes, i.e., a scheme using complete molecular-ion isotopologues
and another one using a pair of neighboring isotopologues, were evaluated in
terms of precision and accuracy. The complete-isotopologue scheme showed
evidently higher precision and was deduced to be more competent to reflect
trueness in comparison with the isotopologue-pair scheme. The CSIA-Cl method
developed in this study will be conducive to future studies concerning
transformation processes and source apportionment of PCE and TCE, and light the
ways to method development of CSIA-Cl for more organochlorines.",1709.03718v1
2017-11-14,The Dominant Role of Critical Valence Fluctuations on High $T_{\rm c}$ Superconductivity in Heavy Fermions,"Despite almost 40 years of research, the origin of heavy-fermion
superconductivity is still strongly debated. Especially, the pressure-induced
enhancement of superconductivity in CeCu$_2$Si$_2$ away from the magnetic
breakdown is not sufficiently taken into consideration. As recently reported in
CeCu$_2$Si$_2$ and several related compounds, optimal superconductivity occurs
at the pressure of a valence crossover, which arises from a virtual critical
end point at negative temperature $T_{\rm cr}$. In this context, we did a
meticulous analysis of a vast set of top-quality high-pressure electrical
resistivity data of several Ce-based heavy fermion compounds. The key novelty
is the salient correlation between the superconducting transition temperature
$T_{\rm c}$ and the valence instability parameter $T_{\rm cr}$, which is in
line with theory of enhanced valence fluctuations. Moreover, it is found that,
in the pressure region of superconductivity, electrical resistivity is governed
by the valence crossover, which most often manifests in scaling behavior. We
develop the new idea that the optimum superconducting $T_{\rm c}$ of a given
sample is mainly controlled by the compound's $T_{\rm cr}$ and limited by
non-magnetic disorder. In this regard, the present study provides compelling
evidence for the crucial role of critical valence fluctuations in the formation
of Cooper pairs in Ce-based heavy fermion superconductors besides the
contribution of spin fluctuations near magnetic quantum critical points, and
corroborates a plausible superconducting mechanism in strongly correlated
electron systems in general.",1711.05145v2
2018-01-07,"Elastic, electronic, optical and thermoelectric properties of K2Cu2GeS4: a new chalcogenide material","We report the first principles study of structural, elastic, electronic,
optical and thermoelectric properties of newly synthesized K2Cu2GeS4. The
structural parameters are found to be in good agreement with experimental
results. The single crystal elastic constants (Cij) are calculated and
K2Cu2GeS4 is found to be mechanical stable. The analysis of polycrystalline
elastic constants reveals that the compound is expected to be soft in nature.
The values of Pugh and Poisson ratios suggested that the compound lies in the
border line of ductile/brittle behavior. The chemical bonding is primarily
ionic, the inter-atomic forces are central in nature and the compound is
mechanically anisotropic. The computed electronic band profile shows
semiconducting characteristics and the estimated band gap is strongly dependent
on the functional used representing the exchange correlations. The nature of
chemical bonding is explained using electronic charge density mapping.
Important optical constants such as dielectric constants, refractive index,
absorption coefficient, photoconductivity, reflectivity and loss function are
calculated and discussed in detail. Optical conductivity is found to be in good
qualitative agreement with the results of band structure calculations. The
Seebeck coefficients are positive for the entire temperature range used in this
study, suggesting the presence of p-type charge carriers. We have obtained
large Seebeck coefficent, 681 V/K at 100 K and 286 V/K at 300 K. At room
temperature, the electrical conductivity and electronic thermal conductivity
are 1.8 31018 ms)-1 and 0.5 1014 W/mK.s, respectively. The dimensionless figure
of merit of K2Cu2GeS4 is evaluated as ~1.0 at 300 K. This suggests that
K2Cu2GeS4 is a potential candidate for thermoelectric applications.",1801.02202v1
2018-01-18,Turning Copper Metal into Weyl Semimetal,"A search for new topological quantum systems is challenging due to the
requirement of non{trivial band connectivity that leads to protected surface
states of electrons. A progress in this field was primarily due to a
realization of band inversion mechanism between even and odd parity states that
was proven to be very useful in both predicting many of such systems and our
understanding their topological properties. Despite many proposed materials
assume the band inversion between s and p (or p/d, d/f) electrons, here, we
explore a different mechanism where the occupied d states subjected to a
tetrahedral crystal field produce an active t2g manifold behaving as a state
with an effective orbital momentum equal to negative one, and pushing jeff =
1=2 doublet at a higher energy. Via hybridization with nearest neighbor
orbitals realizable, e.g., in a zincblende structural environment, this allows
a formation of odd parity state whose subsequent band inversion with an
unoccupied s band becomes possible, prompting us to look for the compounds with
Cu+1 ionic state. Chemical valence arguments coupled to a search in materials
database lead us to systematically investigate electronic structures and
topological properties of CuY (Y=F, Cl, Br, I) and CuXO (X=Li, Na, K, Rb)
families of compounds. Our theoretical results show that CuF displays a
behavior characteristic of an ideal Weyl semimetal with 24 Weyl nodes at the
bulk Brillouin Zone. We also find that another compounds CuNaO and CuLiO are
the s-d inversion type topological insulators. Results for their electronic
structures and corresponding surfaces states are presented and discussed in the
context of their topological properties.",1801.06248v2
2018-01-26,Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy,"The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge
(1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption
fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target
from which the film was synthesized as well as a bulk {\alpha}-Zr reference.
Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at
the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound
target and ~22% O in the bulk {\alpha}-Zr reference after completed sputter
cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but
visible -111, 111, and 220 peaks from monoclinic ZrO2 together with peaks from
ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly
oriented target material. For the bulk {\alpha}-Zr reference no peaks from any
crystalline oxide were visible in the diffractogram recorded from the
0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples
demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in
the bulk ZrB2 attributed to the high atomic ordering within the columns of the
film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2,
but with a chemical shift towards higher energy of 4 eV in the film and 6 eV
for the bulk compared to {\alpha}-Zr (17.993 keV) from the charge-transfer from
Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen
content than in the epitaxial film, which is supported by XPS. In EXAFS, the
modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 {\AA},
c=3.520 {\AA}) in comparison to the bulk target material (a=3.175 {\AA},
c=3.540 {\AA}) while in hexagonal closest-packed metal ({\alpha}-phase, a=3.254
{\AA}, c=5.147 {\AA}).",1801.08663v1
2018-03-10,"Charge Transfer Effects in Naturally Occurring van der Waals Heterostructures (PbSe)1.16(TiSe2)m (m=1, 2)","Van der Waals heterostructures (VDWHs) exhibit rich properties and thus has
potential for applications, and charge transfer between different layers in a
heterostructure often dominates its properties and device performance. It is
thus critical to reveal and understand the charge transfer effects in VDWHs,
for which electronic structure measurements have proven to be effective. Using
angle-resolved photoemission spectroscopy, we studied the electronic structures
of (PbSe)1.16(TiSe2)m(m=1, 2), which are naturally occurring VDWHs, and
discovered several striking charge transfer effects. When the thickness of the
TiSe2 layers is halved from m=2 to m=1, the amount of charge transferred
increases unexpectedly by more than 250%. This is accompanied by a dramatic
drop in the electron-phonon interaction strength far beyond the prediction by
first-principles calculations and, consequently, superconductivity only exists
in the m=2 compound with strong electron-phonon interaction, albeit with lower
carrier density. Furthermore, we found that the amount of charge transferred in
both compounds is nearly halved when warmed from below 10 K to room
temperature, due to the different thermal expansion coefficients of the
constituent layers of these misfit compounds. These unprecedentedly large
charge transfer effects might widely exist in VDWHs composed of
metal-semiconductor contacts; thus, our results provide important insights for
further understanding and applications of VDWHs.",1803.03750v1
2018-03-22,Tuning magnetocrystalline anisotropy of Fe$_{3}$Sn by alloying,"The electronic structure, magnetic properties and phase formation of
hexagonal ferromagnetic Fe$_{3}$Sn-based alloys have been studied from first
principles and by experiment. The pristine Fe$_{3}$Sn compound is known to
fulfill all the requirements for a good permanent magnet, except for the
magnetocrystalline anisotropy energy (MAE). The latter is large, but planar,
i.e. the easy magnetization axis is not along the hexagonal c direction,
whereas a good permanent magnet requires the MAE to be uniaxial. Here we
consider Fe$_{3}$Sn$_{0.75}$M$_{0.25}$, where M= Si, P, Ga, Ge, As, Se, In, Sb,
Te and Bi, and show how different dopants on the Sn sublattice affect the MAE
and can alter it from planar to uniaxial. The stability of the doped Fe$_{3}$Sn
phases is elucidated theoretically via the calculations of their formation
enthalpies. A micromagnetic model is developed in order to estimate the energy
density product (BH)max and coercive field $\mu_{0}$H$_{c}$ of a potential
magnet made of Fe$_{3}$Sn$_{0.75}$Sb$_{0.25}$, the most promising candidate
from theoretical studies. The phase stability and magnetic properties of the
Fe$_{3}$Sn compound doped with Sb and Mn has been checked experimentally on the
samples synthesised using the reactive crucible melting technique as well as by
solid state reaction. The Fe$_{3}$Sn-Sb compound is found to be stable when
alloyed with Mn. It is shown that even small structural changes, such as a
change of the c/a ratio or volume, that can be induced by, e.g., alloying with
Mn, can influence anisotropy and reverse it from planar to uniaxial and back.",1803.08292v1
2018-05-15,Persistence of antiferromagnetic order upon La substitution in the $4d^4$ Mott insulator Ca$_2$RuO$_4$,"The chemical and magnetic structures of the series of compounds
Ca$_{2-x}$La$_x$RuO$_4$ [$x = 0$, $0.05(1)$, $0.07(1)$, $0.12(1)$] have been
investigated using neutron diffraction and resonant elastic x-ray scattering.
Upon La doping, the low temperature S-Pbca space group of the parent compound
is retained in all insulating samples [$x\leq0.07(1)$], but with significant
changes to the atomic positions within the unit cell. These changes can be
characterised in terms of the local RuO$_6$ octahedral coordination: with
increasing doping the structure, crudely speaking, evolves from an orthorhombic
unit cell with compressed octahedra to a quasi-tetragonal unit cell with
elongated ones. The magnetic structure on the other hand, is found to be
robust, with the basic $k=(0,0,0)$, $b$-axis antiferromagnetic order of the
parent compound preserved below the critical La doping concentration of
$x\approx0.11$. The only effects of La doping on the magnetic structure are to
suppress the A-centred mode, favouring the B mode instead, and to reduce the
N\'{e}el temperature somewhat. Our results are discussed with reference to
previous experimental reports on the effects of cation substitution on the
$d^4$ Mott insulator Ca$_2$RuO$_4$, as well as with regard to theoretical
studies on the evolution of its electronic and magnetic structure. In
particular, our results rule out the presence of a proposed ferromagnetic
phase, and suggest that the structural effects associated with La substitution
play an important role in the physics of the system.",1805.05796v2
2018-06-04,Predicting the thermodynamic stability of perovskite oxides using machine learning models,"Perovskite materials have become ubiquitous in many technologically relevant
applications, ranging from catalysts in solid oxide fuel cells to light
absorbing layers in solar photovoltaics. The thermodynamic phase stability is a
key parameter that broadly governs whether the material is expected to be
synthesizable, and whether it may degrade under certain operating conditions.
Phase stability can be calculated using Density Functional Theory (DFT), but
the significant computational cost makes such calculation potentially
prohibitive when screening large numbers of possible compounds. In this work,
we developed machine learning models to predict the thermodynamic phase
stability of perovskite oxides using a dataset of more than 1900 DFT-calculated
perovskite oxide energies. The phase stability was determined using convex hull
analysis, with the energy above the convex hull (Ehull) providing a direct
measure of the stability. We generated a set of 791 features based on elemental
property data to correlate with the Ehull value of each perovskite compound.
For classification, the extra trees algorithm achieved the best prediction
accuracy of 0.93 (+/- 0.02), with an F1 score of 0.88 (+/- 0.03). For
regression, leave-out 20% cross-validation tests with kernel ridge regression
achieved the minimal root mean square error (RMSE) of 28.5 (+/- 7.5) meV/atom
between cross-validation predicted Ehull values and DFT calculations, with the
mean absolute error (MAE) in cross-validation energies of 16.7 (+/- 2.3)
meV/atom. We further validated our model by predicting the stability of
compounds not present in the training set and demonstrated our machine learning
models are a fast and effective means of obtaining qualitatively useful
guidance for a wide-range of perovskite oxide stability, potentially impacting
materials design choices in a variety of technological applications.",1806.01038v1
2018-06-10,"New state of matter: heavy-fermion systems, quantum spin liquids, quasicrystals, cold gases, and high temperature superconductors","We report on a new state of matter manifested by strongly correlated Fermi
systems including various heavy-fermion (HF) metals, two-dimensional quantum
liquids such as $\rm ^3He$ films, certain quasicrystals, and systems behaving
as quantum spin liquids. Generically, these systems can be viewed as HF systems
or HF compounds, in that they exhibit typical behavior of HF metals. At zero
temperature, such systems can experience a so-called fermion-condensation
quantum phase transition (FCQPT). Combining analytical considerations with
arguments based entirely on experimental grounds we argue and demonstrate that
the class of HF systems is characterized by universal scaling behavior of their
thermodynamic, transport, and relaxation properties. That is, the quantum
physics of different HF compounds is found to be universal, emerging
irrespective of the individual details of their symmetries, interactions, and
microscopic structure. This observed universal behavior reveals the existence
of a new state of matter manifest in HF compounds. We propose a simple,
realistic model to study the appearance of flat bands in two-dimensional
ensembles of ultracold fermionic atoms, interacting with coherent resonant
light. It is shown that signatures of these flat bands may be found in
peculiarities in their thermodynamic and spectroscopic properties. We also show
that the FCQPT, in generating flat bands and altering Fermi surface topology,
is an essential progenitor of the exotic behavior of the overdoped
high-temperature superconductors represented by $\rm La_{2-x}Sr_xCuO_4$, whose
superconductivity differs from that predicted by the classical
Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good
agreement with recent experimental observations, closing the colossal gap
between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.",1806.03676v1
2018-11-18,Shannon meets von Neumann: A Minimax Theorem for Channel Coding in the Presence of a Jammer,"We study the setting of channel coding over a family of channels whose state
is controlled by an adversarial jammer by viewing it as a zero-sum game between
a finite blocklength encoder-decoder team, and the jammer. The encoder-decoder
team choose stochastic encoding and decoding strategies to minimize the average
probability of error in transmission, while the jammer chooses a distribution
on the state-space to maximize this probability. The min-max value of this game
is equivalent to channel coding for a compound channel -- we call this the
Shannon solution of the problem. The max-min value corresponds to finding a
mixed channel with the largest value of the minimum achievable probability of
error. When the min-max and max-min values are equal, the problem is said to
admit a saddle-point or von Neumann solution. While a Shannon solution always
exists, a von Neumann solution need not, owing to inherent nonconvexity in the
communicating team's problem. Despite this, we show that the min-max and
max-min values become equal asymptotically in the large blocklength limit, for
all but finitely many rates. We explicitly characterize this limiting value as
a function of the rate and obtain tight finite blocklength bounds on the
min-max and max-min value. As a corollary we get an explicit expression for the
$\epsilon$-capacity of a compound channel under stochastic codes -- the first
such result, to the best of our knowledge. Our results demonstrate a deeper
relation between the compound channel and mixed channel than was previously
known. They also show that the conventional information-theoretic viewpoint,
articulated via the Shannon solution, coincides asymptotically with the
game-theoretic one articulated via the von Neumann solution.",1811.07358v1
2021-07-05,Bulk NdNiO2 is thermodynamically unstable with respect to decomposition while hydrogenation reduces the instability and transforms it from metal to insulator,"Through CaH2 chemical reduction of a parent R3+Ni3+O3 perovskite form,
superconductivity was recently achieved in Sr-doped NdNiO2 on SrTiO3 substrate.
Using density functional theory (DFT) calculations, we find that stoichiometric
NdNiO2 is significantly unstable with respect to decomposition into 1/2[Nd2O3 +
NiO + Ni] with exothermic decomposition energy of +176 meV/atom, a considerably
higher instability than that for common ternary oxides. This poses the question
if the stoichiometric NdNiO2 nickelate compound used extensively to model the
electronic band structure of Ni-based oxide analog to cuprates and found to be
metallic is the right model for this purpose. To examine this, we study via DFT
the role of the common H impurity expected to be present in the process of
chemical reduction needed to obtain NdNiO2. We find that H can be incorporated
exothermically, i.e., spontaneously in NdNiO2, even from H2 gas. In the
concentrated limit, such impurities can result in the formation of a hydride
compound NdNiO2H, which has significantly reduced instability relative to
hydrogen-free NdNiO2. Interestingly, the hydrogenated form has a similar
lattice constant as the pure form (leading to comparable XRD patterns), but
unlike the metallic character of NdNiO2, the hydrogenated form is predicted to
be a wide gap insulator thus, requiring doping to create a metallic or
superconducting state, just like cuprates, but unlike unhydrogenated
nickelates. While it is possible that hydrogen would be eventually desorbed,
the calculation suggests that pristine NdNiO2 is hydrogen-stabilized. One must
exercise caution with theories predicting new physics in pristine
stoichiometric NdNiO2 as it might be an unrealizable compound. Experimental
examination of the composition of real NdNiO2 superconductors and the effect of
hydrogen on the superconductivity is called for.",2107.01790v1
2021-07-08,Metallization of colloidal crystals,"Colloidal crystals formed by size-asymmetric binary particles co-assemble
into a wide variety of colloidal compounds with lattices akin to ionic
crystals. Recently, a transition from a compound phase with a sublattice of
small particles to a metal-like phase in which the small particles are
delocalized has been predicted computationally and observed experimentally. In
this colloidal metallic phase, the small particles roam the crystal maintaining
the integrity of the lattice of large particles, as electrons do in metals. A
similar transition also occurs in superionic crystals, termed sublattice
melting. Here, we use energetic principles and a generalized molecular dynamics
model of a binary system of functionalized nanoparticles to analyze the
transition to sublattice delocalization in different co-assembled crystal
phases as a function of T, number of grafted chains on the small particles, and
number ratio between the small and large particles $n_s$:$n_l$. We find that
$n_s$:$n_l$ is the primary determinant of crystal type due to energetic
interactions and interstitial site filling, while the number of grafted chains
per small particle determines the stability of these crystals. We observe
first-order sublattice delocalization transitions as T increases, in which the
host lattice transforms from low- to high-symmetry crystal structures,
including A20 to BCT to BCC, Ad to BCT to BCC, and BCC to BCC/FCC to FCC
transitions and lattices. Analogous sublattice transitions driven primarily by
lattice vibrations have been seen in some atomic materials exhibiting an
insulator-metal transition also referred to as metallization. We also find
minima in the lattice vibrations and diffusion coefficient of small particles
as a function of $n_s$:$n_l$, indicating enhanced stability of certain crystal
structures for $n_s$:$n_l$ values that form compounds.",2107.03968v3
2021-07-21,Magnetic field tuning of the spin dynamics in the magnetic topological insulators (MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$,"We report a high frequency/high magnetic field electron spin resonance
(HF-ESR) spectroscopy study in the sub-THz frequency domain of the two
representatives of the family of magnetic topological insulators
(MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$ with $n = 0$ and 1. The HF-ESR
measurements in the magnetically ordered state at a low temperature of $T = 4$
K combined with the calculations of the resonance modes showed that the spin
dynamics in MnBi$_{\text{4}}$Te$_{\text{7}}$ is typical for an anisotropic
easy-axis type ferromagnet (FM) whereas MnBi$_{\text{2}}$Te$_{\text{4}}$
demonstrates excitations of an anisotropic easy-axis type antiferromagnet
(AFM). However, by applying the field stronger than a threshold value $\sim 6$
T we observed in MnBi$_{\text{2}}$Te$_{\text{4}}$ a crossover from the AFM
resonance modes to the FM modes which properties are very similar to the
ferromagnetic response of MnBi$_{\text{4}}$Te$_{\text{7}}$. We attribute this
remarkably unusual effect unexpected for a canonical easy-axis AFM, which,
additionally, can be accurately reproduced by numerical calculations of the
excitation modes, to the closeness of the strength of the AFM exchange and
magnetic anisotropy energies which appears to be a very specific feature of
this compound. Our experimental data evidences that the spin dynamics of the
magnetic building blocks of these compounds, the Mn-based septuple layers
(SLs), is inherently ferromagnetic featuring persisting short-range FM
correlations far above the magnetic ordering temperature as soon as the SLs get
decoupled either by introducing a nonmagnetic quintuple interlayer, as in
MnBi$_{\text{4}}$Te$_{\text{7}}$, or by applying a moderate magnetic field, as
in MnBi$_{\text{2}}$Te$_{\text{4}}$, which may have an effect on the surface
topological band structure of these compounds.",2107.09929v1
2017-04-19,Anisotropic magnetic interactions and spin dynamics in the spin-chain compound Cu(py)$_2$Br$_2$: An experimental and theoretical study,"We compare theoretical results for electron spin resonance (ESR) properties
of the Heisenberg-Ising Hamiltonian with ESR experiments on the
quasi-one-dimensional magnet Cu(py)$_2$Br$_2$ (CPB). Our measurements were
performed over a wide frequency and temperature range giving insight into spin
dynamics, spin structure, and magnetic anisotropy of this compound. By
analyzing the angular dependence of ESR parameters (resonance shift and
linewidth) at room temperature we show that the two weakly coupled inequivalent
spin chain types inside the compound are well described by Heisenberg-Ising
chains with their magnetic anisotropy axes perpendicular to the chain direction
and almost perpendicular to each other. We further determine the full
$g$-tensor from these data. In addition, the angular dependence of the
linewidth at high temperatures gives us access to the exponent of the algebraic
decay of a dynamical correlation function of the isotropic Heisenberg chain.
From the temperature dependence of static susceptibilities we extract the
strength of the exchange coupling ($J/k_B = 52.0\,\text{K}$) and the anisotropy
parameter ($\delta\approx -0.02$) of the model Hamiltonian. An independent
compatible value of $\delta$ is obtained by comparing the exact prediction for
the resonance shift at low temperatures with high-frequency ESR data recorded
at $4\,\text{K}$. The spin structure in the ordered state implied by the two
(almost) perpendicular anisotropy axes is in accordance with the propagation
vector determined from neutron scattering experiments. In addition to undoped
samples we study the impact of partial substitution of Br by Cl ions on spin
dynamics. From the dependence of the ESR linewidth on doping level we infer an
effective decoupling of the anisotropic component $J\delta$ from the isotropic
exchange $J$ in these systems.",1704.05705v2
2017-05-23,The chemical bond as an emergent phenomenon,"We first argue that the covalent bond and the various closed-shell
interactions can be thought of as symmetry broken versions of one and the same
interaction, viz., the multi-center bond. We use specially chosen molecular
units to show that the symmetry breaking is controlled by density and
electronegativity variation. We show that the bond order changes with bond
deformation but in a step-like fashion, regions of near constancy separated by
electronic localization transitions. These will often cause displacive
transitions as well so that the bond strength, order, and length are
established self-consistently. We further argue on the inherent relation of the
covalent, closed-shell, and multi-center interactions with ionic and metallic
bonding. All of these interactions can be viewed as distinct sectors on a phase
diagram with density and electronegativity variation as control variables; the
ionic and covalent/secondary sectors are associated with on-site and bond-order
charge density wave respectively, the metallic sectorwith an electronic fluid.
While displaying a contiguity at low densities, the metallic and ionic
interactions represent distinct phases separated by discontinuous transitions
at sufficiently high densities. Multi-center interactions emerge as a hybrid of
the metallic and ionic bond that results from spatial coexistence of
delocalized and localized electrons. In the present description, the issue of
the stability of a compound is that of mutual miscibility of electronic fluids
with distinct degrees of electron localization, supra-atomic ordering in
complex inorganic compounds comes about naturally. The notions of electronic
localization advanced hereby suggest a high throughput, automated procedure for
screening candidate compounds and structures with regard to stability, without
the need for computationally costly geometric optimization.",1705.08429v2
2018-07-05,A Mountaineering Strategy to Excited States: Highly-Accurate Reference Energies and Benchmarks,"Striving to define very accurate vertical transition energies, we perform
both high-level coupled cluster (CC) calculations (up to CCSDTQP) and selected
configuration interaction (sCI) calculations (up to several millions of
determinants) for 18 small compounds. By systematically increasing the order of
the CC expansion, the number of determinants in the CI expansion as well as the
size of the one-electron basis set, we have been able to reach near full CI
(FCI) quality transition energies. These calculations are carried out on
CC3/aug-cc-pVTZ geometries, using a series of increasingly large atomic basis
sets systematically including diffuse functions. In this way, we define a list
of 110 transition energies for states of various characters to be used as
references for further calculations. Benchmark transition energies are provided
at the aug-pVTZ level as well as with additional basis set corrections, in
order to obtain results close to the complete basis set limit. These reference
data are used to benchmark a series of twelve excited-state wave function
methods accounting for double and triple contributions, namely ADC(2), ADC(3),
CIS(D), CIS(D$_\infty$), CC2, STEOM-CCSD, CCSD, CCSDR(3), CCSDT-3, CC3, CCSDT
and CCSDTQ. It turns out that CCSDTQ yields a negligible difference with the
extrapolated CI values with a mean absolute error as small as $0.01$ eV,
whereas the coupled cluster approaches including iterative triples are also
very accurate (mean absolute error of $0.03$ eV). Consequently, CCSDT-3 and CC3
can be used to define reliable benchmarks. This observation does not hold for
ADC(3) that delivers quite large errors for this set of small compounds, with a
clear tendency to overcorrect its second-order version, ADC(2). Finally, we
discuss the possibility to use basis set extrapolation approaches so as to
tackle more easily larger compounds.",1807.02045v1
2019-01-10,Half-filled Stripes in a Hole-Doped Three-Orbital Spin-Fermion Model for Cuprates,"Using Monte Carlo techniques, we study a three-orbital CuO$_2$ spin-fermion
model for copper-based high critical temperature superconductors that captures
the charge-transfer properties of these compounds. Our studies reveal the
presence of spin order in the parent compound and, more importantly, stripe
spin and charge order under hole doping. Due to the $p$-$d$ orbital hybridizati
on, the added holes are approximately equally distributed among the two $p$
orbitals of the oxygen atoms and the $d$ orbital of the copper atoms in the
unit cell. In rectangular clusters of dimension $16\times 4$ %that break the
$\pi/2$ lattice rotational symmetry, {\it half-filled} stripes are observed
upon hole doping, namely when $N_h=2n$ holes are introduced in the system then
$n$ stripes of length 4 are formed along the short direction. The original
antiferromagnetic order observed in the parent compound develops a $\pi-$shift
across each stripe and the magnetic structure factor has a peak at wavevector
${\bf k}=(\pi-\delta,\pi)$ with $\delta=2\pi N_h/N=\pi N_h/2L$, where $L=16$.
The electronic charge is also modulated and the charge structure factor is
maximized at ${\bf k}=(2\delta,0)$. As electrons are removed from the system,
intracell orbital nematicity with $\langle n_{p_x}\rangle-\langle
n_{p_y}\rangle\ne 0$ dev elops in the oxygen sector, as well as intercell
magnetic nematicity with $\langle S^z_{{\bf i},d}(S^z_{{\bf i}+{\bf
x},d}-S^z_{{\bf i}+{\ bf y},d})\rangle\ne 0$ in the spin copper sector, in the
standard notation. This occurs not only in rectangular but also in square
8$\times$8 lattices. Overall, our results suggest that the essence of the
stripe spin and charge distribution experimentally observed in hole-doped
cuprates are captured by unbiased Monte Carlo studies of a simple hole-doped
charge-transfer insulator CuO$_2$ spin-fermion model.",1901.03320v1
2019-01-14,Magneto-structural and dynamic susceptibility studies on rare-earth rich intermetallic compound,"Complex magneto structural behaviour of rare rich intermetallic Tb$_3$Co is
reported in this study. Below the 84K (T$_N$), it undergoes a first order
magnetic transition 72K confirmed from specific heat and magnetization
measurements. Detailed study using magnetization, specific heat, neuron
diffraction and ac-susceptibility measurements suggests that the compound in
the question possesses canted magnetic structure. Neutron diffraction reveals
that Tb moments are aligned antiferromagnetically (AFM) in ab plane and
ferromagnetically (FM) along c direction. This study focusses on the
temperature evolution of magnetic order at low temperatures. Neutron
Diffraction clearly shows that magnetic structure remains more or less same up
to 70K although low field magnetization exhibits a transition like feature
around 30K. Field dependent neutron diffraction suggests that a strong
spin-lattice coupling is present at lower temperature region (below 20K)
compared to that for T above 40K. This is responsible for the observed drop in
ZFC magnetization around 30K and is not due to any change in magnetic
structure. Another important but surprising result that observed is the
signature of magnetic glass below 72K in frequency dependent ac susceptibility
measurements. Real part of ac-susceptibility data shows dispersion with
frequency which on detailed analysis provides evidence for spin glass behaviour
in the compound riding on top of non-collinear AFM order. Higher order
harmonics in ac non-linear) susceptibilities, which are expected to show a
well-defined behaviour for pure FM or AFM or spin glass or cluster glass
systems, were also measured. However, the non-linear susceptibilities do not
exhibit any well-known variation but show complex behaviour thus indicating
Tb$_3$Co is neither a pure AFM or FM or spin glass system but provides another
evidence for non-collinear magnetic structure.",1901.04191v1
2019-04-10,"An ab-initio study on physical properties of Pd2+ incorporated double perovskites CaPd3B4O12 (B = Ti, V)","Numerous physical properties of CaPd3Ti4O12 (CPTO) and CaPd3V4O12 (CPVO)
double perovskites have been explored based on density functional theory (DFT).
The calculated structural parameters fairly agree with the experimental data to
confirm their stability. The mechanical stability of these two compounds was
clearly observed by the Born stability criteria. To rationalize the mechanical
behavior, we investigate elastic constants, bulk, shear and Young's modulus,
Pugh's ratio, Poisson's ratio and elastic anisotropy index. The ductility index
confirms that both materials are ductile in nature. The electronic band
structure of CPTO and CPVO reveals the direct band gap semiconducting in nature
and metallic characteristics, respectively. The calculated partial density of
states indicates the strong hybridization between Pd 4d and O 2p orbital
electrons for CPTO and Pd 4d and V 3d O 2p for CPVO. The study of electronic
charge density map confirms the coexistence of covalent, ionic and metallic
bonding for both compounds. Fermi surface calculation of CPVO ensures both
electron and hole like surfaces indicating the multiple band nature. In the
midst of optical properties, photoconductivity and absorption coefficient of
both compounds reveal well qualitative compliance with consequences of band
structure computations. Among the thermodynamic properties, the Debye
temperature has been calculated to correlate its topical features including
thermoelectric behavior. The studied thermoelectric transport properties of
CPTO yielded the Seebeck coefficient (186 microVK-1), power factor (11.9
microWcm-1K-2) and figure of merit (ZT) value of about 0.8 at 800 K indicate
that this material could be a promising candidate for thermoelectric device
application.",1904.05099v1
2019-07-21,Simultaneous observation of concurrent two-dimensional carbon and chlorine/bromine isotope fractionations of halogenated organic compounds on gas chromatography,"It has been reported that isotope fractionation can occur on gas
chromatography (GC), yet little is known about concurrent dual-elements isotope
fractionations on GC. Revelation of concurrent two-dimensional carbon and
chlorine/bromine isotope fractionations of halogenated organic compounds (HOCs)
on GC may be of important significance for compound-specific isotope analysis
(CSIA). This study presents an in-depth investigation of the two-dimensional C
and Cl/Br isotope fractionations of HOCs on GC using GC-double focus
magnetic-sector high resolution mass spectrometry (GC-DFS-HRMS). The
two-dimensional C and Cl/Br isotope fractionations of four organochlorines and
four bromobenzenes on GC were simultaneously measured by GC-DFS-HRMS. The
isotope fractionations were evaluated with isotope ratios, relative variations
of isotope ratios and isotope fractionation extents. All the HOCs exhibited
significant inverse C and Cl/Br isotope fractionations. The isotope
fractionations were significant in both ends of chromatographic peaks, while
the isotope ratios in center retention-time segments were the closest to
comprehensive isotope ratios in the whole peaks. Significant correlations
between C isotope fractionation and Cl/Br isotope fractionation were observed,
indicating that the isotope fractionations might have strong relationships
and/or be dominated by similar factors. Relevant mechanisms for the
two-dimensional C and Cl/Br isotope fractionations were tentatively proposed on
basis of a modified two-film model and the theories related to zero point
energy. The results of this study gains new insights into concurrent
two-dimensional isotope fractionation behaviors of HOCs during physical
processes, and are conducive to CSIA studies involving C, Cl and Br for
obtaining high-quality data, particularly to dual-elements CSIA of C and Cl/Br.",1907.08900v1
2019-07-28,"Level scheme of $^{153}$Sm obtained from $^{152}$Sm($n_{th}$,$γ$) reaction using $γ-γ$ coincidence spectrometer","The level scheme of the compound $^{153}$Sm nucleus formed via the
$^{152}$Sm($n_{th}$,$\gamma$) reaction is studied by using the $\gamma-\gamma$
coincidence spectrometer at Dalat Nuclear Research Institute, Vietnam. All the
gamma cascades, which correspond to the decays from the compound state to 12
final levels of 0 ($\frac{3}{2}^+$), 7.535 ($\frac{5}{2}^+$), 35.844
($\frac{3}{2}^-$), 90.875 ($\frac{5}{2}^-$), 126.412 ($\frac{1}{2}^-$), 127.298
($\frac{3}{2}^-$), 182.902 ($\frac{5}{2}^-$), 321.113 ($\frac{3}{2}^+$),
404.129 ($\frac{1}{2}^-$), 405.470 ($\frac{3}{2}^-$), 414.924
($\frac{1}{2}^+$), and 481.088 ($\frac{3}{2}^+$) keV, have been measured. A
total number of 386 cascades corresponding to 576 gamma transitions has been
detected. Among these cascades, 103 primary gamma transitions together with
their corresponding intermediate levels and 299 secondary transitions have been
determined. In addition, 29 primary gamma transitions, 42 intermediate levels,
and 8 secondary transitions have been found to be the same as those extracted
from the ENSDF data. The remain 74 primary gamma transitions, 61 intermediate
levels, and 291 secondary transitions are therefore considered as the new data.
In particular, based on an assumption that most of the transitions are dipole,
we have tentatively assigned the unique spin value of $\frac{3}{2}\hbar$ for 53
observed intermediate levels corresponding to the cascades from the compound
state to the final ones of 7.535 ($\frac{5}{2}^+$), 90.875 ($\frac{5}{2}^-$),
and 182.902 ($\frac{5}{2}^-$) keV, whereas the remain levels are assigned with
the spin values in the range of $[\frac{1}{2},\frac{3}{2}]\hbar$...",1907.12068v1
2019-10-14,A-type Antiferromagnetic order in MnBi4Te7 and MnBi6Te10 single crystals,"MnBi$_4$Te$_{7}$ and MnBi$_6$Te$_{10}$ are two members with n=2 and 3 in the
family of MnBi$_{2n}$Te$_{3n+1}$ where the n=1 member, MnBi$_2$Te$_{4}$, has
been intensively investigated as the first intrinsic antiferromagnetic
topological insulator. Here we report the A-type antiferromagnetic order in
these two compounds by measuring magnetic properties, electrical and thermal
transport, specific heat, and single crystal neutron diffraction. Both
compounds order into an A-type antiferromagnetic structure as does
MnBi$_2$Te$_{4}$ with ferromagnetic planes coupled antiferromagnetically along
the crystallographic \textit{c} axis. While no evidence for any in-plane
ordered moment is found for MnBi$_2$Te$_{4}$ or MnBi$_6$Te$_{10}$, weak
reflections at half-L positions along the [0 0 L] direction are observed for
MnBi$_4$Te$_{7}$ suggesting an in-plane ordered moment around 0.15$\mu_{B}$/Mn.
The ordering temperature, T$_N$, is 13\,K for MnBi$_4$Te$_{7}$ and 11\,K for
MnBi$_6$Te$_{10}$. The magnetic order is also manifested in the anisotropic
magnetic properties. For both compounds, the interlayer coupling is weak and a
spin flip transition occurs when a magnetic field of around 1.6\,kOe is applied
along the \textit{c}-axis at 2\,K. As observed in MnBi$_2$Te$_4$, when cooling
across T$_N$, no anomaly was observed in the temperature dependence of
thermopower. On the other hand, critical scattering effects are observed in
thermal conductivity although the effect is less pronounced than that in
MnBi$_2$Te$_{4}$.",1910.06273v2
2019-10-17,"Tunable magnetic order in low-symmetry SeO$_3$ ligand linked $TM_3$(SeO$_3$)$_3$H$_2$O ($TM$ = Mn, Co and Ni) compounds","Generally, one has two strategies to achieve magnetic frustration: through
geometric means or interactions with different length scales. As the former
leads to much simpler theoretical treatments it is favored and so magnetic
sublattices with geometric frustration are sought after. One approach to
finding such lattices is to design them chemically by using non-magnetic linker
ligands. Here we report on the magnetic properties of one such family of
materials, the transition metal ($TM$) selenite hydrate compounds chemical
formula $TM_3$(SeO$_3$)$_3$H$_2$O . These materials link highly distorted
$TM$O$_6$ octahedra via non-magnetic [SeO$_3$]$^{2+}$ linkers. Using $TM$ = Mn,
Co and Ni we report on the structural effects of changing the $TM$ site and how
they may influence the magnetic structure. Using magnetic susceptibility and
neutron powder diffraction we identify low temperature magnetic transitions for
all three compounds characterized by the onset of long-range AFM order with
moderate frustration indexes. Consideration of the magnetic structures reveal
that the magnetic order is sensitive to the $TM$ site ion and is tunable as it
is changed - especially from Mn to Co - with changes in both the moment
direction and the ordering vector. Field dependent susceptibility and heat
capacity measurements reveal metamagnetic transitions in both
Mn$_3$(SeO$_3$)$_3$H$_2$O and Co$_3$(SeO$_3$)$_3$H$_2$O indicating nearby
magnetic ground states accessible under relatively small applied fields.
Density functional theory calculations broadly confirm these results, showing
both a sensitivity of the magnetic structure to the $TM$ and its local
environment. Although no spin liquid behavior is achieved, these results
suggest the fruitfulness of such synthesis philosophies and encourage future
work to engender higher frustration in these materials via doping, field,
pressure or larger linker ligands.",1910.08175v1
2019-10-22,Exploring the possibility of enhancing the figure-of-merit ( $>$ 2) of Na$_{0.74}$CoO$_{2}$: A combined experimental and theoretical study,"Search of new thermoelectric (TE) materials with high
\textit{figure-of-merit} (ZT) is always inspired the researcher in TE field.
Here, we present a combined experimental and theoretical study of TE properties
of Na$_{0.74}$CoO$_{2}$ compound in high-temperature region. The experimental
Seebeck coefficient (S) is found to vary from 64 to 118 $\mu$V/K in the
temperature range $300-620$ K. The positive values of S are indicating the
dominating p-type behaviour of the compound. The observed value of thermal
conductivity ($\kappa$) is $\sim$ 2.2 W/m-K at 300 K. In the temperature region
$300-430$ K, the value of $\kappa$ increases up to $\sim$ 2.6 W/m-K and then
decreases slowly till 620 K with the corresponding value of $\sim$ 2.4 W/m-K.
We have also carried out the theoretical calculations and the best matching
between experimental and calculated values of transport properties are observed
in spin-polarized calculation within DFT+\textit{U} by chosen \textit{U} = 4
eV. The maximum calculated value of ZT is found to be $\sim$ 0.67 at 1200 K for
p-type conduction. Our computational study suggests that the possibility of
n-type behaviour of the compound which can lead to a large value of ZT at
higher temperature region. Electron doping of $\sim$ 5.1$\times$10$^{20}$
cm$^{-3}$ is expected to give rise the high ZT value of $\sim$ 2.7 at 1200 K.
Using these temperature-dependent ZT values, we have calculated the maximum
possible values of efficiency ($\eta$) of thermoelectric generator (TEG) made
by p and n-type Na$_{0.74}$CoO$_{2}$. The present study suggests that one can
get the efficiency of a TE cell as high as $\sim$ 11$\%$ when the cold and hot
end temperature are fixed at 300 K and 1200 K, respectively. Such high values
of ZT and efficiency suggest that Na$_{0.74}$CoO$_{2}$ can be used as a
potential candidate for high-temperature TE applications.",1910.10191v2
2019-10-28,Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: temperature and trace species abundance profiles from 2004 to 2017,"The Cassini/Composite InfraRed Spectrometer (CIRS) instrument has been
observing the middle atmosphere of Titan over almost half a Saturnian year. We
used the CIRS dataset processed through the up-to-date calibration pipeline to
characterize seasonal changes of temperature and abundance profiles in the
middle atmosphere of Titan, from mid-northern winter to early northern summer
all around the satellite. We used limb spectra from 590 to 1500 cm$^{-1}$ at
0.5-cm$^{-1}$ spectral resolution, which allows us to probe different
altitudes. We averaged the limb spectra recorded during each flyby on a fixed
altitude grid to increase the signal-to-noise ratio. These thermal infrared
data were analyzed by means of a radiative transfer code coupled with an
inversion algorithm, in order to retrieve vertical temperature and abundance
profiles. These profiles cover an altitude range of approximately 100 to 600
km, at 10- or 40-km vertical resolution (depending on the observation). Strong
changes in temperature and composition occur in both polar regions where a
vortex is in place during the winter. At this season, we observe a global
enrichment in photochemical compounds in the mesosphere and stratosphere and a
hot stratopause located around 0.01 mbar, both linked to downwelling in a
pole-to-pole circulation cell. After the northern spring equinox, between
December 2009 and April 2010, a stronger enhancement of photochemical compounds
occurred at the north pole above the 0.01-mbar region, likely due to combined
photochemical and dynamical effects. During the southern autumn in 2015, above
the South pole, we also observed a strong enrichment in photochemical compounds
that contributed to the cooling of the stratosphere above 0.2 mbar. Close to
the northern spring equinox, in December 2009, the thermal profile at 74{\deg}N
exhibits an oscillation that we interpret in terms of an inertia-gravity wave.",1910.12677v1
2014-06-09,Competition between superconductivity and magnetic/nematic order as a source of anisotropic superconducting gap in underdoped Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$,"The in-plane London penetration depth, $\Delta\lambda(T)$, was measured using
a tunnel diode resonator technique in single crystals of
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ with doping levels $x$ ranging from heavily
underdoped, $x$=0.16 ($T_{c}$=7~K) to nearly optimally doped, $x$= 0.34
($T_{c}=$39 K). Exponential saturation of $\Delta\lambda(T)$ in the $T\to0$
limit is found in optimally doped samples, with the superfluid density
$\rho_{s}(T)\equiv(\lambda(0)/\lambda(T))^{2}$ quantitatively described by a
self-consistent $\gamma$-model with two nodeless isotropic superconducting
gaps. As the doping level is decreased towards the extreme end of the
superconducting dome at $x$=0.16, the low-temperature behavior of
$\Delta\lambda(T)$ becomes non-exponential and best described by the power-law
$\Delta\lambda(T)\propto T^{2}$, characteristic of strongly anisotropic gaps.
The change between the two regimes happens within the range of coexisting
magnetic/nematic order and superconductivity, $x<0.25$, and is accompanied by a
rapid rise in the absolute value of $\Delta\lambda(T)$ with underdoping. This
effect, characteristic of the competition between superconductivity and other
ordered states, is very similar to but of significantly smaller magnitude than
what is observed in the electron-doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$
compounds. Our study suggests that the competition between superconductivity
and magnetic/nematic order in hole-doped compounds is weaker than in
electron-doped compounds, and that the anisotropy of the superconducting state
in the underdoped iron pnictides is a consequence of the anisotropic changes in
the pairing interaction and in the gap function promoted by both magnetic and
nematic long-range order.",1406.2369v1
2018-02-02,Energetics of oxygen-octahedra rotations in perovskite oxides from first principles,"We use first-principles methods to study oxygen-octahedra rotations in ABO3
perovskite oxides. We focus on the short-period, perfectly antiphase or
in-phase, tilt patterns that characterize most compounds and control their
physical (e.g., conductive, magnetic) properties. Based on an analytical form
of the relevant potential energy surface, we discuss the conditions for the
stability of polymorphs presenting different tilt patterns, and obtain
numerical results for a collection of thirty-five representative materials. Our
results reveal the mechanisms responsible for the frequent occurrence of a
particular structure that combines antiphase and in-phase rotations, i.e., the
orthorhombic Pbnm phase displayed by about half of all perovskite oxides and by
many non-oxidic perovskites. The Pbnm phase benefits from the simultaneous
occurrence of antiphase and in-phase tilt patterns that compete with each
other, but not as strongly as to be mutually exclusive. We also find that
secondary antipolar modes, involving the A cations, contribute to weaken the
competition between different tilts and play a key role in their coexistence.
Our results thus confirm and better explain previous observations for
particular compounds. Interestingly, we also find that strain effects, which
are known to be a major factor governing phase competition in related (e.g.,
ferroelectric) perovskite oxides, play no essential role as regards the
relative stability of different rotational polymorphs. Further, we discuss why
the Pbnm structure stops being the ground state in two opposite limits, for
large and small A cations, showing that very different effects become relevant
in each case. Our work thus provides a comprehensive discussion on these
all-important and abundant materials, which will be useful to better understand
existing compounds as well as to identify new strategies for materials
engineering.",1802.00784v1
2018-02-14,Edge Attention-based Multi-Relational Graph Convolutional Networks,"Graph convolutional network (GCN) is generalization of convolutional neural
network (CNN) to work with arbitrarily structured graphs. A binary adjacency
matrix is commonly used in training a GCN. Recently, the attention mechanism
allows the network to learn a dynamic and adaptive aggregation of the
neighborhood. We propose a new GCN model on the graphs where edges are
characterized in multiple views or precisely in terms of multiple
relationships. For instance, in chemical graph theory, compound structures are
often represented by the hydrogen-depleted molecular graph where nodes
correspond to atoms and edges correspond to chemical bonds. Multiple attributes
can be important to characterize chemical bonds, such as atom pair (the types
of atoms that a bond connects), aromaticity, and whether a bond is in a ring.
The different attributes lead to different graph representations for the same
molecule. There is growing interests in both chemistry and machine learning
fields to directly learn molecular properties of compounds from the molecular
graph, instead of from fingerprints predefined by chemists. The proposed GCN
model, which we call edge attention-based multi-relational GCN (EAGCN), jointly
learns attention weights and node features in graph convolution. For each bond
attribute, a real-valued attention matrix is used to replace the binary
adjacency matrix. By designing a dictionary for the edge attention, and forming
the attention matrix of each molecule by looking up the dictionary, the EAGCN
exploits correspondence between bonds in different molecules. The prediction of
compound properties is based on the aggregated node features, which is
independent of the varying molecule (graph) size. We demonstrate the efficacy
of the EAGCN on multiple chemical datasets: Tox21, HIV, Freesolv, and
Lipophilicity, and interpret the resultant attention weights.",1802.04944v2
2018-02-28,"Vibrational anomalies in AFe$_\mathbf{2}$As$_\mathbf{2}$ (A$\,=\,$Ca, Sr, and Ba) single crystals","The detailed behavior of the in-plane infrared-active vibrational modes has
been determined in AFe$_2$As$_2$ (A$\,=\,$Ca, Sr, and Ba) above and below the
structural and magnetic transition at $T_N=$172, 195 and 138 K, respectively.
Above $T_N$, two infrared-active $E_u$ modes are observed. In all three
compounds, below $T_N$ the low-frequency $E_u$ mode is observed to split into
upper and lower branches; with the exception of the Ba material, the oscillator
strength across the transition is conserved. In the Ca and Sr materials, the
high-frequency $E_u$ mode splits into an upper and a lower branch; however, the
oscillator strengths are quite different. Surprisingly, in both the Sr and Ba
materials, below $T_N$ the upper branch appears be either very weak or totally
absent, while the lower branch displays an anomalous increase in strength. The
frequencies and atomic characters of the lattice modes at the center of the
Brillouin zone have been calculated for the high-temperature phase for each of
these materials. The high-frequency $E_u$ mode does not change in position or
character across this series of compounds. Below $T_N$, the $E_u$ modes are
predicted to split into features of roughly equal strength. We discuss the
possibility that the anomalous increase in the strength of the lower branch of
the high-frequency mode below $T_N$ in the Sr and Ba compounds, and the weak
(silent) upper branch, may be related to the orbital ordering and a change in
the bonding between the Fe and As atoms in the magnetically-ordered state.",1802.10505v1
2018-12-01,A theoretical study on the dynamics of a compound vesicle in linear shear flow,"The dynamics of a nucleate cell in shear flow is of great relevance in cancer
cells and circulatory tumor cells where they dominate the dynamics of blood.
Buoyed by the success of Giant Unilamellar vesicles in explaining the dynamics
of anucleate cells such as Red Blood cells, compound vesicles have been
suggested as a simple model for nucleate cells. In this work, a theoretical
model is presented to study the deformation and dynamics of a compound vesicle
in linear shear flow using small deformation theory and spherical harmonics
with higher order approximation to the membrane forces. The results indicate
that size of the inner vesicle does not affect the tank-treading dynamics of
the outer vesicle. The inner vesicle admits a greater inclination angle than
the outer vesicle. However, the transition to trembling-swinging and tumbling
is significantly affected. The inner and outer vesicle exhibit identical
dynamics in most of the modified viscosity-shear rate parameter space. At
moderate size of the inner vesicle, a swinging mode is observed for the inner
vesicle while the outer vesicle exhibits tumbling. The inner vesicle also
exhibits modification of the TU mode to IUS-Intermediate Tumbling Swinging
mode. Moreover, synchronization of the two vesicles at higher inner vesicle
size and a capillary number sensitive motion at small inner vesicle size is
observed in the tumbling regime. These results are in accordance with the few
experimental observations reported by Levant and Steinberg2014. A reduction in
the inclination angle is observed with an increase in size of the inner vesicle
when the inner vesicle is a solid inclusion. Additionally a very elaborate
phase diagram is presented in the modified viscosity-shear rate parameter
space, which could be tested in future experiments or numerical simulations",1812.00163v1
2019-06-21,"Accommodating three low-scale anomalies (g-2, Lamb shift, and Atomki) in the framed standard model","The framed standard model (FSM) predicts a $0^+$ boson with mass around 20
MeV in the ""hidden sector"", which mixes at tree level with the standard Higgs
$h_W$ and hence acquires small couplings to quarks and leptons which can be
calculated in the FSM apart from the mixing parameter $\rho_{Uh}$. The exchange
of this mixed state $U$ will contribute to $g - 2$ and to the Lamb shift. By
adjusting $\rho_{Uh}$ alone, it is found that the FSM can satisfy all present
experimental bounds on the $g - 2$ and Lamb shift anomalies for $\mu$ and $e$,
and for the latter for both hydrogen and deuterium.
  The FSM predicts also a $1^-$ boson in the ""hidden sector"" with a mass of 17
MeV, that is, right on top of the Atomki anomaly $X$. This mixes with the
photon at 1-loop level and couples thereby like a dark photon to quarks and
leptons. It is however a compound state and is thought likely to possess
additional compound couplings to hadrons. By adjusting the mixing parameter and
the $X$'s compound coupling to nucleons, the FSM can reproduce the production
rate of the $X$ in beryllium decay as well as satisfy all the bounds on $X$
listed so far in the literature.
  The above two results are consistent in that the $U$, being $0^+$, does not
contribute to the Atomki anomaly if parity and angular momentum are conserved,
while $X$, though contributing to $g - 2$ and Lamb shift, has smaller couplings
than $U$ and can, at first instance, be neglected there.
  Despite the tentative nature of the 3 anomalies in experiment and of the FSM
as theory, the accommodation of the former in the latter has strengthened the
credibility of both. If this FSM interpretation were correct, it would change
the whole aspect of the anomalies from just curiosities to windows into a vast
hitherto hidden sector comprising at least in part the dark matter which makes
up the bulk of our universe.",1906.09229v1
2019-06-26,Magnetic order in Nd$_2$PdSi$_3$ investigated using neutron scattering and muon spin relaxation,"The rare-earth based ternary intermetallic compounds $R_2TX_3$ ($R$ =
rare-earth, $T$ = transition-metal, $X$ = Si, Ge, Ga, In) have attracted
considerable interest due to a wide range of interesting low temperature
properties. Here we investigate the magnetic state of Nd$_{2}$PdSi$_{3}$ using
neutron diffraction, muon spin relaxation ($\mu$SR) and inelastic neutron
scattering (INS). This compound appears anomalous among the $R_{2}$PdSi$_{3}$
series, since it was proposed to order ferromagnetically, whereas others in
this series are antiferromagnets. Although some members of the $R_2TX_3$ series
have been reported to form ordered superstructures, our data are well described
by Nd$_{2}$PdSi$_{3}$ adopting the AlB$_2$-type structure with a single Nd
site, and we do not find evidence for superlattice peaks in neutron
diffraction. Our results confirm the onset of long range magnetic order below
$T_0=17$~K, where the whole sample enters the ordered state. Neutron
diffraction measurements establish the presence of a ferromagnetic component in
this compound, as well as an antiferromagnetic one which has a propagation
vector $\mathbf{k_2}=(1/2,1/2,1/4-\delta)$ with a temperature dependent
$\delta\approx0.02-0.04$, and moments orientated exclusively along the
$c$-axis. $\mu$SR measurements suggest that these components coexist on a
microscopic level, and therefore the magnetic structure of Nd$_{2}$PdSi$_{3}$
is predominantly ferromagnetic, with a sinusoidally modulated antiferromagnetic
contribution which reaches a maximum amplitude at 11~K, and becomes smaller
upon further decreasing the temperature. INS results show the presence of
crystalline-electric field (CEF) excitations above $T_0$, and from our analysis
we propose a CEF level scheme.",1906.11381v2
2020-04-27,Critical behavior and magnetocaloric effect across the magnetic transition in Mn$_{1+x}$Fe$_{4-x}$Si$_{3}$,"The nature of the magnetic transition, critical scaling of magnetization, and
magnetocaloric effect in Mn$_{1+x}$Fe$_{4-x}$Si$_{3}$ ($ x =$ 0 to 1) are
studied in detail. Our measurements show no thermal hysteresis across the
magnetic transition for the parent compound which is in contrast with the
previous report and corroborate the second order nature of the transition. The
magnetic transition could be tuned continuously with Mn substitution at the Fe
site. The Mn substitution leads to a linear increase in the unit cell volume
and a slight reduction in the effective moment. A detailed critical analysis of
the magnetization data for $x = 0.0$ and 0.2 is performed in the critical
regime using the modified Arrott plots, Kouvel-Fisher plot, universal curve
scaling, and scaling analysis of magnetocaloric effect. The magnetization
isotherms follow modified Arrott plots with critical exponent ($\beta \simeq
0.308$, $\gamma \simeq 1.448$, and $\delta \simeq 5.64$) for the parent
compound ($x=0.0$) and ($\beta \simeq 0.304$, $\gamma \simeq 1.445$, and
$\delta \simeq 5.64$) for $x = 0.2$. The Kouvel-Fisher and universal scaling
plots of the magnetization isotherms further confirm the reliability of our
critical analysis and values of the exponents. These values of the critical
exponents are found to be same for both the parent and doped samples which do
not fall under any of the standard universality classes. A reasonable
magnetocaloric effect $\Delta S_{\rm m}\simeq-6.67$~J/Kg-K and -5.84~J/Kg-K for
$x= 0.0$ and 0.2 compounds, respectively, with a huge relative cooling power
($RCP \sim 700$~J/Kg) for 9~T field change is observed. The universal scaling
of magnetocaloric effect further mimics the second order character of the
magnetic transition. The obtained critical exponents from the critical analysis
of magnetocaloric effect agree with the values deduced from the magnetic
isotherm analysis.",2004.12614v1
2022-01-28,Insights into performance evaluation of com-pound-protein interaction prediction methods,"Motivation: Machine learning based prediction of compound-protein
interactions (CPIs) is important for drug design, screening and repurposing
studies and can improve the efficiency and cost-effectiveness of wet lab
assays. Despite the publication of many research papers reporting CPI
predictors in the recent years, we have observed a number of fundamental issues
in experiment design that lead to over optimistic estimates of model
performance. Results: In this paper, we analyze the impact of several important
factors affecting generalization perfor-mance of CPI predictors that are
overlooked in existing work: 1. Similarity between training and test examples
in cross-validation 2. The strategy for generating negative examples, in the
absence of experimentally verified negative examples. 3. Choice of evaluation
protocols and performance metrics and their alignment with real-world use of
CPI predictors in screening large compound libraries. Using both an existing
state-of-the-art method (CPI-NN) and a proposed kernel based approach, we have
found that assessment of predictive performance of CPI predictors requires
careful con-trol over similarity between training and test examples. We also
show that random pairing for gen-erating synthetic negative examples for
training and performance evaluation results in models with better
generalization performance in comparison to more sophisticated strategies used
in existing studies. Furthermore, we have found that our kernel based approach,
despite its simple design, exceeds the prediction performance of CPI-NN. We
have used the proposed model for compound screening of several proteins
including SARS-CoV-2 Spike and Human ACE2 proteins and found strong evidence in
support of its top hits. Availability: Code and raw experimental results
available at https://github.com/adibayaseen/HKRCPI Contact:
Fayyaz.minhas@warwick.ac.uk",2202.00001v1
2022-03-31,The Bell-Touchard Counting process,"The Poisson process is one of the simplest stochastic processes defined in
continuous time, having interesting mathematical properties, leading, in many
situations, to applications mathematically treatable. One of the limitations of
the Poisson process is the rare events hypothesis; which is the hypothesis of
unitary jumps within an infinitesimal window of time. Although that restriction
may be avoided by the compound Poisson process, in most situations, we don't
have a closed expression for the probability distribution of the increments of
such processes, leaving us options such as working with probability generating
functions, numerical analysis and simulations. It is with this motivation in
mind, inspired by the recent developments of discrete distributions, that we
propose a new counting process based on the Bell-Touchard probability
distribution, naming it the Bell-Touchard process. We verify that the process
is a compound Poisson process, a multiple Poisson process and that it is closed
for convolution plus decomposition operations. Besides, we show that the
Bell-Touchard process arises naturally from the composition of two Poisson
processes. Moreover, we propose two generalizations; namely, the compound
Bell-Touchard process and the non-homogeneous Bell-Touchard process, showing
that the last one arises from the composition of a non-homogeneous Poisson
process along with a homogeneous Poisson process. We emphasize that since
previous works have been shown that the Bell-Touchard probability distribution
can be used quite effectively for modelling count data, the Bell-Touchard
process and its generalizations may contribute to the formulation of
mathematical treatable models where the rare events hypothesis is not suitable.",2203.16737v3
2016-03-01,"Structural, electronic and optical properties of well-known primary explosive: Mercury fulminate","Mercury Fulminate (MF) is one of the well-known primary explosives since 17th
century and it has rendered invaluable service over many years. However, the
correct molecular and crystal structures are determined recently after 300
years of its discovery. In the present study, we report pressure dependent
structural, elastic, electronic and optical properties of MF. Non-local
correction methods have been employed to capture the weak van der Waals
interactions in layered and molecular energetic MF. Among the non-local
correction methods tested, optB88-vdW method works well for the investigated
compound. The obtained equilibrium bulk modulus reveals that MF is softer than
the well known primary explosives Silver Fulminate (SF), silver azide and lead
azide. MF exhibits anisotropic compressibility (b>a>c) under pressure,
consequently the corresponding elastic moduli decrease in the following order:
C22>C11>C33. The structural and mechanical properties suggest that MF is more
sensitive to detonate along c-axis (similar to RDX) due to high compressibility
of Hg...O non-bonded interactions along that axis. Electronic structure and
optical properties were calculated including spin-orbit (SO) interactions using
full potential linearized augmented plane wave method within recently developed
Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The calculated TB-mBJ
electronic structures of SF and MF show that these compounds are indirect
bandgap insulators. Also, SO coupling is found to be more pronounced for 4d and
5d-states of Ag and Hg atoms of SF and MF, respectively. Partial density of
states and electron charge density maps were used to describe the nature of
chemical bonding. Ag-C bond is more directional than Hg-C bond which makes SF
to be more unstable than MF. The effect of SO coupling on optical properties
has also been studied and found to be significant for both of the compounds.",1603.00216v1
2016-03-11,"Magnetic structures of rare earth intermetallic compounds RCuAs$_2$ (R = Pr, Nd, Tb, Dy, Ho, and Yb)","Neutron scattering studies have been carried out on polycrystalline samples
of a series of rare earth intermetallic compounds RCuAs$_2$ (R = Pr, Nd, Dy,
Tb, Ho and Yb) as a function of temperature to determine the magnetic
structures and the order parameters. These compounds crystallize in the
ZrCuSi$_2$ type structure, which is similar to that of the RFeAsO (space group
P4/nmm) class of iron-based superconductors. PrCuAs$_2$ develops commensurate
magnetic order with K = (0, 0, 0.5) below T$_N$ = 6.4 (2) K, with the ordered
moments pointing along the c-axis. The irreducible representation analysis
shows either a ${\Gamma}$$^1_2$ or ${\Gamma}$$^1_3$ representation. NdCuAs$_2$
and DyCuAs$_2$ order below T$_N$ = 3.54(5) K and T$_N$ = 10.1(2) K,
respectively, with the same ordering wave vector but the moments lying in the
a-b plane (with a ${\Gamma}$$^2_9$ or ${\Gamma}$$^2_{10}$ representation).
TbCuAs$_2$ and HoCuAs$_2$ exhibit incommensurate magnetic structures below
T$_N$ = 9.44(7) and 4.41(2) K, respectively. For TbCuAs$_2$, two separate
magnetic ordering wave vectors are established as K$_{1(Tb)}$ =
(0.240,0.155,0.48) and K$_{2(Tb)}$ = (0.205, 0.115, 0.28), whereas HoCuAs$_2$
forms a single K$_{(Ho)}$ = (0.121, 0.041, 0.376) magnetic structure with
3$^{rd}$ order harmonic magnetic peaks. YbCuAs$_2$ does not exhibit any
magnetic Bragg peaks at 1.5 K, while susceptibility measurements indicate an
antiferromagnetic-like transition at 4 K, suggesting that either the ordering
is not long range in nature or the ordered moment is below the sensitivity
limit of $\approx$ 0.2 $\mu_B$.",1603.03704v2
2017-02-12,Geometrically frustrated Cairo pentagonal lattice stripe with Ising and Heisenberg exchange interactions,"Motivated by the recent discoveries of some compounds such as the
$\mathrm{Bi}_{2}\mathrm{Fe}_{4}\mathrm{O}_{9}$ which crystallizes in an
orthorhombic crystal structure with the $\mathrm{Fe}^{3+}$ ions, and iron-based
oxyfluoride ${\rm Bi}_{4}{\rm Fe}_{5}{\rm O}_{13}{\rm F}$ compounds following
the pattern of Cairo pentagonal structure, among some other compounds. We
propose a model for one stripe of the Cairo pentagonal Ising-Heisenberg
lattice, one of the edges of a pentagon is different, and this edge will be
associated with a Heisenberg exchange interaction, while the Ising exchange
interactions will associate the other edges. We study the phase transition at
zero temperature, illustrating five phases: a ferromagnetic phase (FM), a dimer
antiferromagnetic (DAF), a plaquette antiferromagnetic (PAF), a typical
antiferromagnetic (AFM) and a peculiar frustrated phase (FRU) where two types
of frustrated states with the same energy coexist. To obtain the partition
function of this model, we use the transfer matrix approach and following the
eight vertex model notation. Using this result we discuss the specific heat,
internal energy and entropy as a function of the temperature, and we can
observe some unexpected behavior in the low-temperature limit, such as
anomalous double peak in specific heat due to the existence of three phase
(FRU, PAF(AFM) and FM) transitions occurring in a close region to each other.
Consequently, the low-lying energy thermal excitation generates this double
anomalous peak, and we also discuss the internal energy at the low temperature
limit, where this double peak curve occurs. Some properties of our result were
compared with two dimensional Cairo pentagonal lattices, as well as orthogonal
dimer plaquette Ising-Heisenberg chain.",1702.03586v1
2017-06-28,Pr-magnetism in the quasi-skutterudite compound PrFe$_2$Al$_8$,"The intermetallic compound \PFA\ that possesses a three-dimensional network
structure of Al polyhedra centered at the transition metal element Fe and the
rare earth Pr is investigated through neutron powder diffraction and inelastic
neutron scattering in order to elucidate the magnetic ground state of Pr and Fe
and the crystal field effects of Pr. Our neutron diffraction study confirms
long-range magnetic order of Pr below $T_N $ = 4.5~K in this compound.
Subsequent magnetic structure estimation reveals a magnetic propagation vector
$k$ = ($\frac{1}{2}$~0~$\frac{1}{2}$) with a magnetic moment value of
2.5~$\mu_\mathrm{B}$/Pr along the orthorhombic $c$-axis and evidence the lack
of ordering in the Fe sublattice. The inelastic neutron scattering study
reveals one crystalline electric field excitation near 19~meV at 5~K in \PFA.
The energy-integrated intensity of the 19~meV excitation as a function of |$Q$|
$(A^{-1})$ follows the square of the magnetic form factor of Pr$^{3+}$ thereby
confirming that the inelastic excitation belongs to the Pr sublattice. The
second sum rule applied to the dynamic structure factor indicates only
1.6(2)~$\mu_\mathrm{B}$ evolving at the 19~meV peak compared to the
3.58~$\mu_\mathrm{B}$ for free Pr$^{3+}$, indicating that the crystal field
ground state is magnetic and the missing moment is associated with the
resolution limited quasi-elastic line. The magnetic order occurring in Pr in
\PFA\ is counter-intuitive to the symmetry-allowed crystal field level scheme,
hence, is suggestive of exchange-mediated mechanisms of ordering stemming from
the magnetic ground state of the crystal field levels.",1706.09081v1
2017-10-11,Fermi surface with Dirac fermions in CaFeAsF determined via quantum oscillation measurements,"Despite the fact that 1111-type iron arsenides hold the record transition
temperature of iron-based superconductors, their electronic structures have not
been studied much because of the lack of high-quality single crystals. In this
study, we completely determine the Fermi surface in the antiferromagnetic state
of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum
oscillation measurements and band-structure calculations. The determined Fermi
surface consists of a symmetry-related pair of Dirac electron cylinders and a
normal hole cylinder. From analyses of quantum-oscillation phases, we
demonstrate that the electron cylinders carry a nontrivial Berry phase $\pi$.
The carrier density is of the order of 10$^{-3}$ per Fe. This unusual metallic
state with the extremely small carrier density is a consequence of the
previously discussed topological feature of the band structure which prevents
the antiferromagnetic gap from being a full gap. We also report a nearly
linear-in-$B$ magnetoresistance and an anomalous resistivity increase above
about 30 T for $B \parallel c$, the latter of which is likely related to the
quantum limit of the electron orbit. Intriguingly, the electrical resistivity
exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal
phase ($T >$ 118 K), which may suggest an incoherent state. Our study provides
a detailed knowledge of the Fermi surface in the antiferromagnetic state of
1111 parent compounds and moreover opens up a new possibility to explore
Dirac-fermion physics in those compounds.",1710.03938v3
2019-03-29,Investigation of the magnetic ground state of PrRu$_2$Ga$_8$ compound,"We have investigated the ground state properties of the orthorhombic
structure compound PrRu$_2$Ga$_8$ through electronic and magnetic properties
studies. The compound crystallizes in the CaCo$_2$Al$_8$-type structure,
belonging to space group $Pbam$ (No. 55). The temperature dependence specific
heat shows a $\lambda$-type anomaly at $T_N$ = 3.3 K, indicating a bulk phase
transition probably of antiferromagnetic origin. At the N\'{e}el temperature
$T_N$, the entropy approaches the value of 4.66~J/mol.K which is about
0.8Rln(2), where R is the universal gas constant. The analysis of the low
temperature specific heat gives $\gamma$ = 46 mJ/mol.K$^2$. The temperature
dependence DC magnetic susceptibility $\chi(T)$ confirms the anomaly at 3.3 K
and follows the Curie-Weiss law for temperatures above 50~K, with the
calculated effective magnetic moment, $\mu_\mathrm{{eff}}$ = 3.47(2)~$\mu_B$/Pr
and Weiss temperature $\theta_p$ = --7.80(1)~K. This effective magnetic moment
value is in good agreement with the Hund$^\prime$s rule theoretical free-ion
value of 3.58~$\mu_B$ for Pr$^{3+}$. The electrical resistivity data also shows
an anomaly at $T_N$ and a broad curvature at intermediate temperatures probably
due to crystalline electric field (CEF) effects. The Pr$^{3+}$ in this
structure type has a site symmetry of $C_s$ which predicts a CEF splitting of
the $J$ = 4 multiplet into 9 singlets and thus rule out in principle the
occurrence of spontaneous magnetic order. In this article we discuss the
magnetic order in PrRu$_2$Ga$_8$ in line with an induced type of magnetism
resulting from the admixture of the lowest CEF level with the first excited
state.",1903.12405v1
2019-08-12,WWhittle Maximum Likelihood Estimate of spectral properties of Rayleigh-Taylor interfacial mixing using hot-wire anemometry experimental data,"Investigating the power density spectrum of fluctuations in Rayleigh-Taylor
(RT) interfacial mixing is a means of studying characteristic length- and
time-scales, anisotropies and anomalous processes. Guided by group theory,
analysing the invariance-based properties of the fluctuations, our work
examines raw time series from hot-wire anemometry measurements in the
experiment by Akula et al., JFM 816, 619-660 (2017). The results suggest that
the power density spectrum can be modelled as a compound function presented as
the product of a power law and an exponential. The data analysis is based on
Whittle's approximation of the power density spectrum for independent zero-mean
near-Gaussian signals to construct a Maximum likelihood Estimator (MLE) of the
parameters. Those that maximise the log-likelihood are computed numerically
through Newton-Raphson iteration. The Hessian of the log-likelihood is used to
evaluate the Fisher information matrix and provide an estimate of the
statistical error on the obtained parameters. The Kolmogorov-Smirnov test is
applied to analyse the goodness-of-fit, by verifying the hypothesis that the
ratio between the observed periodogram and the estimated power density spectrum
follows a chi-squared probability distribution. The dependence of the
parameters of the compound function is investigated on the range of mode
numbers over which the fit is performed. In the domain where the relative
errors of the power law exponent and the exponential decay rate are small and
the goodness-of-fit is excellent, the parameters of the compound function are
clearly defined, in agreement with the theory. The study of the power-law
spectra in RT mixing data suggests that rigorous physics-based statistical
methods can help researchers to see beyond visual inspection.",1908.03977v2
2019-08-16,"Evolution of electronic and magnetic properties in a series of iridate double perovskites Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1.0)","Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic
properties of 5$d$ iridates. In this paper we have experimentally investigated
the structural and physical properties of a series of Ir-based double
perovskite compounds Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1; hereafter
abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have
recently been proposed to undergo a transition from the spin-orbit-coupled Mott
insulating phase at $x$ = 0 to the elusive half-metallic antiferromagnetic
(HMAFM) state with Sr doping at $x$ = 1. However, our detailed magnetic and
electrical measurements refute any kind of HMAFM possibility in either of the
doped samples. In addition, we establish that within these
Pr$_{2-x}$Sr$_x$MgIrO$_6$ double perovskites, changes in Ir-oxidation states
(4+ for PMIO to 5+ for PSMIO via mixed 4+/5+ for PSMIO1505) lead to markedly
different magnetic behaviors. While SOC on Ir is at the root of the observed
insulating behaviors for all three samples, the correlated magnetic properties
of these three compounds develop entirely due to the contribution from local Ir
moments. Additionally, the magnetic Pr$^{3+}$ (4$f^2$) ions, instead of showing
any kind of ordering, only contribute to the total paramagnetic moment. It is
seen that the PrSrMgIrO$_6$ sample does not order down to 2 K despite
antiferromagnetic interactions. But, the $d^5$ iridate Pr$_2$MgIrO$_6$ shows a
sharp antiferromagnetic (AFM) transition at around 14 K, and in the mixed
valent Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ sample the AFM transition is shifted to a
much lower temperature ($\sim$ 6 K) due to weakening of the AFM exchange.",1908.05973v1
2019-12-09,The Schottky Conjecture and beyond,"The `Schottky Conjecture' deals with the electrostatic field enhancement at
the tip of compound structures such as a hemiellipsoid on top of a hemisphere.
For such a 2-primitive compound structure, the apex field enhancement factor
$\gamma_a^{(C)}$ is conjectured to be multiplicative ($\gamma_a^{(C)} =
\gamma_a^{(1)} \gamma_a^{(2)}$) provided the structure at the base (labelled 1,
e.g. the hemisphere) is much larger than the structure on top (referred to as
crown and labelled 2, e.g. the hemi-ellipsoid). We first demonstrate
numerically that for generic smooth structures, the conjecture holds in the
limiting sense when the apex radius of curvature of the primitive-base
$R_a^{(1)}$, is much larger than the height of the crown $h_2$ (i.e.
$h_2/R_a^{(1)} \rightarrow 0$). If the condition is somewhat relaxed, we show
that it is the electric field above the primitive-base (i.e. in the absence of
the crown), averaged over the height of the crown, that gets magnified instead
of the field at the apex of the primitive-base. This observation leads to the
Corrected Schottky Conjecture (CSC), which for 2-primitive structures reads as
$\gamma_a^{(C)}\simeq \langle \gamma_a^{(1)}\rangle\gamma_a^{(2)}$ where
$\langle . \rangle$ denotes the average value over the height of the crown. For
small protrusions ($h_2/h_1$ typically less than 0.2), $\langle
\gamma_a^{(1)}\rangle$ can be approximately determined using the Line Charge
Model so that $\gamma_a^{(C)} \simeq \gamma_a^{(1)}\gamma_a^{(2)}
(2R_a^{(1)}/h_2)\ln(1 + h_2/2R_a^{(1)})$. The error is found to be within $1\%$
for $h_2/R_a^{(1)} < 0.05$, increasing to about $3\%$ (or less) for
$h_2/R_a^{(1)} = 0.1$ and bounded below $5\%$ for $h_2/R_a^{(1)}$ as large as
0.5. The CSC is also found to give good results for 3-primitive compound
structures. The relevance of the Corrected Schottky Conjecture for field
emission is discussed.",1912.04074v3
2020-03-05,Quantum anomalous Hall effect in two-dimensional magnetic insulator heterojunctions,"Recent years have witnessed tremendous success in the discovery of
topological states of matter. Particularly, sophisticated theoretical methods
in time-reversal-invariant topological phases have been developed, leading to
the comprehensive search of crystal database and the prediction of thousands of
new topological materials. In contrast, the discovery of magnetic topological
phases that break time reversal is still limited to several exemplary materials
because the coexistence of magnetism and topological electronic band structure
is rare in a single compound. To overcome this challenge, we propose an
alternative approach to realize the quantum anomalous Hall (QAH) effect, a
typical example of magnetic topological phase, via engineering two-dimensional
(2D) magnetic van der Waals heterojunctions. Instead of a single magnetic
topological material, we search for the combinations of two 2D (typically
trivial) magnetic insulator compounds with specific band alignment so that they
can together form a type-III heterojunction with topologically non-trivial band
structure. By combining the data-driven materials search, first principles
calculations, and the symmetry-based analytical models, we identify 8 type-III
heterojunctions consisting of 2D ferromagnetic insulator materials from a
family of 2D monolayer MXY compounds (M = metal atoms, X = S, Se, Te, Y = F,
Cl, Br, I) as a set of candidates for the QAH effect. In particular, we
directly calculate the topological invariant (Chern number) and chiral edge
states in the MnNF/MnNCl heterojunction with ferromagnetic stacking. This work
illustrates how data-driven material science can be combined with
symmetry-based physical principles to guide the search for novel
heterojunction-based quantum materials hosting the QAH effect and other exotic
quantum states in general.",2003.02470v1
2020-03-09,CHO-bearing molecules in Comet 67P/Churyumov-Gerasimenko,"In 2004, the Rosetta spacecraft was sent to comet 67P/Churyumov-Gerasimenko
for the first ever long-term investigation of a comet. After its arrival in
2014, the spacecraft spent more than two years in immediate proximity to the
comet. During these two years, the ROSINA Double Focusing Mass Spectrometer
(DFMS) onboard Rosetta discovered a coma with an unexpectedly complex chemical
composition that included many oxygenated molecules. Determining the exact
cometary composition is an essential first step to understanding of the organic
rich chemistry in star forming regions and protoplanetary disks that are
ultimately conserved in cometary ices. In this study a joint approach of
laboratory calibration and space data analysis was used to perform a detailed
identification and quantification of CHO-compounds in the coma of
67P/Churyumov-Gerasimenko. The goal was to derive the CHO-compound abundances
relative to water for masses up to 100 u. For this study, the May 2015
post-equinox period represent the best bulk abundances of comet
67P/Churyumov-Gerasimenko. A wide variety of CHO-compounds were discovered and
their bulk abundances were derived. Finally, these results are compared to
abundances of CHO-bearing molecules in other comets, obtained mostly from
ground-based observations and modelling.",2003.03967v1
2020-03-20,Efficient Modelling of Ion Structure and Dynamics in Inorganic Metal Halide Perovskites,"Metal halide perovskites (MHPs) are nowadays one of the most studied
semiconductors due to their exceptional performance as active layers in solar
cells. Although MHPs are excellent solid-state semiconductors, they are also
ionic compounds, where ion migration plays a decisive role in their formation,
their photovoltaic performance and their long-term stability. Given the
above-mentioned complexity, molecular dynamics simulations based on classical
force fields are especially suited to study MHP properties, such as lattice
dynamics and ion migration. In particular, the possibility to model mixed
compositions is important since they are the most relevant to optimize the
optical band gap and the stability. With this intention, we employ DFT
calculations and a genetic algorithm to develop a fully transferable classical
force field valid for the benchmark inorganic perovskite compositional set
CsPb(Br_xI_(1-x))_3 (x = 0,1/3,2/3,1). The resulting force field reproduces
correctly, with a common set of parameters valid for all compositions, the
experimental lattice parameter as a function of bromide/iodide ratio, the
ion-ion distances and the XRD spectra of the pure and mixed structures. The
simulated thermal conductivities and ion migration activation energies of the
pure compounds are also in good agreement with experimental trends. Our
molecular dynamics simulations make it possible to predict the compositional
dependence of the ionic diffusion coefficient on bromide/iodide ratio and
vacancy concentration. For vacancy concentrations of around 9 10^21 cm^-3, we
obtained ionic diffusion coefficients at ambient temperature of 10^-11 and
10^-13 cm2/s for CsPbBr3 and CsPbI3, respectively. Interestingly, in comparison
with the pure compounds, we predict a significantly lower activation energy for
vacancy migration and faster diffusion for the mixed perovskites.",2003.09360v1
2020-07-01,"Structural and physical properties of trilayer nickelates $R_4$Ni$_3$O$_{10}$ ($R =$ La, Pr and Nd)","We investigate the low temperature structural and physical properties of the
trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity,
thermopower, thermal conductivity, specific heat, high-resolution synchrotron
powder X-ray diffraction and thermal expansion experiments. We show that all
three compounds crystallize with a monoclinic symmetry, and undergo a
metal-to-metal (MMT) transition at 135 K (La), 156 K (Pr) and 160 K (Nd). At
MMT, the lattice parameters show distinct anomalies; however, without any
lowering of the lattice symmetry. Unambiguous signatures of MMT are also seen
in magnetic and thermal measurements, which suggest a strong coupling between
the electronic, magnetic and structural degrees of freedom in these nickelates.
Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in
close agreement with experiments. We show that the 9-fold coordinated Pr ions
in the rocksalt (RS) layers have a crystal field (CF) split doublet ground
state with possible antiferromagnetic ordering at 5 K. The Pr ions located in
the perovskite block (PB) layers with 12-fold coordination, however, exhibit a
non-magnetic singlet ground state. The CF ground state of Nd in both RS and PB
layers is a Kramers doublet. Heat capacity of R = Nd shows a Schottky-like
anomaly near35 K, and an upturn below T = 10 K suggesting the presence of
short-range correlations between the Nd moments. However, no signs of
long-range ordering could be found down to 2 K despite a sizeable theta_p ~ -40
K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd
suggests the presence of strong magnetic frustration in these compounds. The
low-temperature resistivity shows a T^0.5 dependence. No evidence for the heavy
fermion behavior could be found in any of the three compounds.",2007.00498v3
2020-07-03,First-principles study of electronic transport and structural properties of Cu$_{12}$Sb$_4$S$_{13}$ in its high-temperature phase,"We present an ab initio study of the structural and electronic transport
properties of tetrahedrite, Cu$_{12}$Sb$_4$S$_{13}$, in its high-temperature
phase. We show how this complex compound can be seen as the outcome of an
ordered arrangement of S-vacancies in a semiconducting fematinite-like
structure (Cu3SbS4). Our calculations confirm that the S-vacancies are the
natural doping mechanism in this thermoelectric compound and reveal a similar
local chemical environment around crystallographically inequivalent Cu atoms,
shedding light on the debate on XPS measurements in this compound. To access
the electrical transport properties as a function of temperature we use the
Kubo-Greenwood formula applied to snapshots of first-principles molecular
dynamics simulations. This approach is essential to effectively account for the
interaction between electrons and lattice vibrations in such a complex crystal
structure where a strong anharmonicity plays a key role in stabilising the
high-temperature phase. Our results show that the Seebeck coeffcient is in good
agreement with experiments and the phonon-limited electrical resistivity
displays a temperature trend that compares well with a wide range of
experimental data. The predicted lower bound for the resistivity turns out to
be remarkably low for a pristine mineral in the Cu-Sb-S system but not too far
from the lowest experimental data reported in literature. The Lorenz number
turns out to be substantially lower than what expected from the free-electron
value in the Wiedemann-Franz law, thus providing an accurate way to estimate
the electronic and lattice contributions to the thermal conductivity in
experiments, of great significance in this very low thermal conductivity
crystalline material.",2007.01809v2
2020-07-06,"Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks","We report results of 0.05""-resolution observations toward the O-type
proto-binary system IRAS 16547-4247 with the Atacama Large
Millimeter/submillimeter Array (ALMA). We present dynamical and chemical
structures of the circumbinary disk, circumstellar disks, outflows and jets,
illustrated by multi-wavelength continuum and various molecular lines. In
particular, we detect sodium chloride, silicon compounds, and
vibrationally-excited water lines as probes of the individual protostellar
disks at a scale of 100 au. These are complementary to typical hot-core
molecules tracing the circumbinary structures on a 1000-au scale. The H2O line
tracing inner-disks has an upper-state energy of Eu/k>3000K, indicating a high
temperature of the disks. On the other hand, despite the detected transitions
of NaCl, SiO, and SiS not necessarily having high upper-state energies, they
are enhanced only in the vicinity of the protostars. We interpret that these
molecules are the products of dust destruction, which only happens in the inner
disks. This is the second detection of alkali metal halide in protostellar
systems after the case of the disk of Orion Source I, and also one of few
massive protostellar disks associated with high-energy transition water and
silicon compounds. These new results suggest these ""hot-disk"" lines may be
common in innermost disks around massive protostars, and have great potential
for future research of massive star formation. We also tentatively find that
the twin disks are counter-rotating, which might give a hint of the origin of
the massive proto-binary system IRAS 16547-4247.",2007.02962v4
2020-09-01,Computational screening of repurposed drugs and natural products against SARS-Cov-2 main protease (Mpro) as potential COVID-19 therapies,"There remains an urgent need to identify existing drugs that might be
suitable for treating patients suffering from COVID-19 infection. Drugs rarely
act at a single molecular target, with off target effects often being
responsible for undesirable side effects and sometimes, beneficial synergy
between targets for a specific illness. Off target activities have also led to
blockbuster drugs in some cases, e.g. Viagra for erectile dysfunction and
Minoxidil for male pattern hair loss. Drugs already in use or in clinical
trials plus approved natural products constitute a rich resource for discovery
of therapeutic agents that can be repurposed for existing and new conditions,
based on the rationale that they have already been assessed for safety in man.
A key question then is how to rapidly and efficiently screen such compounds for
activity against new pandemic pathogens such as COVID-19. Here we show how a
fast and robust computational process can be used to screen large libraries of
drugs and natural compounds to identify those that may inhibit the main
protease of SARS-Cov-2 (3CL pro, Mpro). We show how the resulting shortlist of
candidates with strongest binding affinities is highly enriched in compounds
that have been independently identified as potential antivirals against
COVID-19. The top candidates also include a substantial number of drugs and
natural products not previously identified as having potential COVID-19
activity, thereby providing additional targets for experimental validation.
This in silico screening pipeline may also be useful for repurposing of
existing drugs and discovery of new drug candidates against other medically
important pathogens and for use in future pandemics.",2009.00744v1
2020-10-15,Unconventional superparamagnetic behavior in the modified cubic spinel compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$,"Structural, electronic, and magnetic properties of modified cubic spinel
compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ are studied via x-ray diffraction,
resistivity, DC and AC magnetization, heat capacity, neutron diffraction,
$^7$Li nuclear magnetic resonance, magnetocaloric effect, magnetic relaxation,
and magnetic memory effect experiments. We stabilized this compound in a cubic
structure with space group $P4_{3}32$. It exhibits semiconducting character
with an electronic band gap of $\Delta/k_{\rm B} \simeq 0.4$ eV. The
interaction within each Mn$^{4+}$ and Ni$^{2+}$ sub-lattice and between
Mn$^{4+}$ and Ni$^{2+}$ sublattices is found to be ferromagnetic (FM) and
antiferromagnetic (AFM), respectively which leads to the onset of a
ferrimagnetic transition at $T_{\rm C} \simeq 125$~K. The reduced values of
frustration parameter ($f$) and ordered moments reflect magnetic frustration
due to competing FM and AFM interactions. From the $^7$Li NMR shift vs
susceptibility plot, the average hyperfine coupling between $^7$Li nuclei and
Ni$^{2+}$ and Mn$^{4+}$ spins is calculated to be $\sim 672.4$~Oe/$\mu_{\rm
B}$. A detailed critical behaviour study is done in the vicinity of $T_{\rm C}$
using modified-Arrott plot, Kouvel-Fisher plot, and universal scaling of
magnetization isotherms. The estimated critical exponents correspond to the 3D
XY universality class. A large magneto-caloric effect is observed with a
maximum isothermal change in entropy $\Delta S_m \simeq - 11.3$~J/Kg-K and a
maximum relative cooling power $RCP \simeq 604$~J/Kg for 9~T magnetic field
change. The imaginary part of the AC susceptibility depicts a strong frequency
dependent hump at $T=T_{\rm f2}$ well below the blocking temperature $T_{\rm
b}\simeq120$~K. The Arrhenius behaviour of frequency dependent $T_{\rm f2}$ and
the absence of ZFC memory confirm the existence of superparamagnetism in the
ferrimagnetically ordered state.",2010.07709v1
2020-11-22,"Quasi-two-dimensional heterostructures (K$M_{1-x}$Te)(LaTe$_{3}$) ($M$ = Mn, Zn) with charge density waves","Layered heterostructure materials with two different functional building
blocks can teach us about emergent physical properties and phenomena arising
from interactions between the layers. We report the intergrowth compounds
KLa$M$$_{1-x}$Te$_{4}$ ($M$ = Mn, Zn; $x\approx$ 0.35) featuring two chemically
distinct alternating layers [LaTe$_3$] and [K$M$$_{1-x}$Te]. Their crystal
structures are incommensurate, determined by single X-ray diffraction for the
Mn compound and transmission electron microscope (TEM) study for the Zn
compound. KLaMn$_{1-x}$Te$_{4}$ crystallizes in the orthorhombic superspace
group $Pmnm$(01/2${\gamma}$)$s$00 with lattice parameters $a$ = 4.4815(3)
{\AA}, $b$ = 21.6649(16) {\AA} and $c$ = 4.5220(3) {\AA}. It exhibits charge
density wave (CDW) order at room temperature with a modulation wave vector
$\mathbf{q}$ = 1/2$\mathbf{b}$* + 0.3478$\mathbf{c}$* originating from
electronic instability of Te-square nets in [LaTe$_{3}$] layers. The Mn analog
exhibits a cluster spin glass behavior with spin freezing temperature
$T_{\mathrm{f}}$ $\approx$ 5 K attributed to disordered Mn vacancies and
competing magnetic interactions in the [Mn$_{1-x}$Te] layers. The Zn analog
also has charge density wave order at room temperature with a similar
$\mathbf{q}$-vector having the $\mathbf{c}$* component ~ 0.346 confirmed by
selected-area electron diffraction (SAED). Electron transfer from
[K$M_{1-x}$Te] to [LaTe$_{3}$] layers exists in KLa$M_{1-x}$Te$_{4}$, leading
to an enhanced electronic specific heat coefficient. The resistivities of
KLa$M_{1-x}$Te$_{4}$ ($M$ = Mn, Zn) exhibit metallic behavior at high
temperatures and an upturn at low temperatures, suggesting partial localization
of carriers in the [LaTe$_{3}$] layers with some degree of disorder associated
with the $M$ atom vacancies in the [$M_{1-x}$Te] layers.",2011.11068v2
2020-12-03,Modeling transmission windows in Titan's lower troposphere: Implications for infrared spectrometers aboard future aerial and surface missions,"From orbit, the visibility of Titan's surface is limited to a handful of
narrow spectral windows in the near-infrared (near-IR), primarily from the
absorption of methane gas. This has limited the ability to identify specific
compounds on the surface -- to date Titan's bulk surface composition remains
unknown. Further, understanding of the surface composition would provide
insight into geologic processes, photochemical production and evolution, and
the biological potential of Titan's surface. One approach to obtain wider
spectral coverage with which to study Titan's surface is by decreasing the
integrated column of absorbers (primarily methane) and scatterers between the
observer and the surface. This is only possible if future missions operate at
lower altitudes in Titan's atmosphere. Herein, we use a radiative transfer
model to measure in detail the absorption through Titan's atmosphere from
different mission altitudes, and consider the impacts this would have for
interpreting reflectance measurements of Titan's surface. Over our modeled
spectral range of 0.4 - 10 micron, we find that increases in the width of the
transmission windows as large as 317% can be obtained for missions performing
remote observations at the surface. However, any appreciable widening of the
windows requires onboard illumination. Further, we make note of possible
surface compounds that are not currently observable from orbit, but could be
identified using the wider windows at low altitudes. These range from simple
nitriles such as cyanoacetylene, to building blocks of amino acids such as
urea. Finally, we discuss the implications that the identifications of these
compounds would have for Titan science.",2012.02247v1
2020-12-29,Geometric and electronic properties on stage-1 FeCl3-graphite intercalation compounds,"The calculated results of FeCl3 graphite intercalation compounds show the
detailed features. The stage-1 FeCl3-graphite intercalation compounds present
diversified electronic properties due to the intercalant. The first-principles
calculations on VASP are utilized to analyze the essential properties, such as
the geometric structures, spatial charge distributions, charge variations, band
structures and density of states. The density of states displays full
information for an explanation of the hybridizations with the special
structures van Hove singularities on it. The van Hove singularities in
graphite-related systems are very important and can provide full information
for examining the intercalation effects. The orbital-decomposed density of
states for C atoms shows that the {\pi} bondings are orthogonal to the sp2
bondings and the C-C bondings retain in the intralayer C atoms. The Fe atoms
and Cl atoms form the Fe-Cl bondings at some unique energy range, presenting
the multi-orbital hybridizations of [4s, 3dxy, 3dyz, 3dxz, 3dx2-y2, 3dz2]-[3px,
3py, 3pz]. For C-Cl and Cl-Cl bonds, the unique van Hove singularities exhibit
their coupling interactions, revealing the multi-orbital hybridizations of
[3px, 3py, 3pz]-[ 3px, 3py, 3pz] and [3s, 3px, 3py, 3pz]-[3s, 3px, 3py, 3pz],
respectively. The Fe-Cl bondings arise from multi-orbital hybridizations of
[4s, 3dxy, 3dyz, 3dxz, 3dx2-y2, 3dz2]-[ 3px, 3py, 3pz]. Due to the band
structures and density of states, the multi-orbital interactions between
intercalants and graphene layers dominate in the low-lying energy range. The
charge transfers per atom (electrons/atom) for C, Fe, Cl are -0.02 e/atom,
-0.28 e/atom and +0.46 e/atom, respectively. Thus, the C atoms in graphene
layers present as positive ones after intercalation, i.e., the graphite system
exhibit p-type doping features in agreement with previous study.",2012.14648v1
2021-01-22,Spin dynamics in NaFeAs and NaFe$_{0.53}$Cu$_{0.47}$As probed by resonant inelastic X-ray scattering,"The parent compounds of iron-based superconductors are magnetically-ordered
bad metals, with superconductivity appearing near a putative magnetic quantum
critical point. The presence of both Hubbard repulsion and Hund's coupling
leads to rich physics in these multiorbital systems, and motivated descriptions
of magnetism in terms of itinerant electrons or localized spins. The
NaFe$_{1-x}$Cu$_x$As series consists of magnetically-ordered bad metal ($x=0$),
superconducting ($x\approx0.02$) and magnetically-ordered
semiconducing/insulating ($x\approx0.5$) phases, providing a platform to
investigate the connection between superconductivity, magnetism and electronic
correlations. Here we use X-ray absorption spectroscopy and resonant inelastic
X-ray scattering to study the valence state of Fe and spin dynamics in two
NaFe$_{1-x}$Cu$_x$As compounds ($x=0$ and 0.47). We find that magnetism in both
compounds arises from Fe$^{2+}$ atoms, and exhibits underdamped dispersive spin
waves in their respective ordered states. The dispersion of spin excitations in
NaFe$_{0.53}$Cu$_{0.47}$As is consistent with being quasi-one-dimensional.
Compared to NaFeAs, the band top of spin waves in NaFe$_{0.53}$Cu$_{0.47}$As is
slightly softened with significantly more spectral weight of the spin
excitations. Our results indicate the spin dynamics in
NaFe$_{0.53}$Cu$_{0.47}$As arise from localized magnetic moments and suggest
the iron-based superconductors are proximate to a correlated insulating state
with localized iron moments.",2101.08948v1
2021-02-03,Charge ordering in Ir dimers in the ground state of Ba$_5$AlIr$_2$O$_{11}$,"It has been well established experimentally that the interplay of electronic
correlations and spin-orbit interactions in Ir$^{4+}$ and Ir$^{5+}$ oxides
results in insulating J$_{\rm eff}$=1/2 and J$_{\rm eff}$=0 ground states,
respectively. However, in compounds where the structural dimerization of iridum
ions is favourable, the direct Ir $d$--$d$ hybridisation can be significant and
takes a key role. Here, we investigate the effects of direct Ir $d$--$d$
hybridisation in comparison with electronic correlations and spin-orbit
coupling in Ba$_5$AlIr$_2$O$_{11}$, a compound with Ir dimers. Using a
combination of $ab$ $initio$ many-body wave function quantum chemistry
calculations and resonant inelastic X-ray scattering (RIXS) experiments, we
elucidate the electronic structure of Ba$_5$AlIr$_2$O$_{11}$. We find excellent
agreement between the calculated and the measured spin-orbit excitations.
Contrary to the expectations, the analysis of the many-body wave function shows
that the two Ir (Ir$^{4+}$ and Ir$^{5+}$) ions in the Ir$_2$O$_9$ dimer unit in
this compound preserve their local J$_{\rm eff}$ character close to 1/2 and 0,
respectively. The local point group symmetry at each of the Ir sites assumes an
important role, significantly limiting the direct $d$--$d$ hybridisation. Our
results emphasize that minute details in the local crystal field (CF)
environment can lead to dramatic differences in electronic states in iridates
and 5$d$ oxides in general.",2102.02178v1
2021-04-08,Mixed Formamidinium-Methylammonium Lead Iodide perovskite from first-principles: Hydrogen-bonding impact on the electronic properties,"Hybrid perovskites with mixed organic cations such as methylammonium and
formamidinium have attracted interest due to their improved stability and
capability to tune their properties varying the composition. In this work we
report on the local variation of the structural and electronic properties in
mixed A-site cation MA/FA lead iodide perovskites FAXMA1-XPBI3 evaluated from
static first-principles calculations in certain structures where the
orientations of organic cations result from examining the energy landscape of
some compositions. The cation replacement at the A-site to form the solid
solution causes an increase tilting of the inorganic PbI6 octahedra: in the
FA-rich compounds the replacement of FA by a smaller cation like MA is to
compensate the reduced space filling offered by the smaller cation, whereas in
the MA-rich compounds is to expand the space needed for the larger cation. In
fact, the effect of octahedron tiltings exceeds that of unit-cell size in
determining the band gap for these organic cation mixtures. Our calculations
indicate that the key role played by hydrogen bonds with iodine anions in pure
compounds is preserved in the cation mixed perovskites. It is found that MA-I
bonds remain stronger than FA-I bonds throughout the composition range
regardless of the unit-cell expansion as the FA content increases. Our
calculations reveal how the hydrogen bonds stabilize the no-bonding I-5p
orbitals, spatially perpendicular to the Pb-I-Pb bond axis, lowering their
energy when the H-I interaction occurs, which would explain the well-known role
of hydrogen bonding in the structural stabilization of hybrid perovskites.
These results contribute to the understanding on the role played by cation
mixing at A sites in the physics of lead halide perovskites.",2104.03697v1
2021-04-13,Vapor-solid-solid growth dynamics in GaAs nanowires,"Semiconductor nanowires are promising material systems for coming of age
nanotechnology. The usage of the vapor solid solid (VSS) route, where the
catalyst used for promoting axial growth of nanowire is a solid, offers certain
advantages compared to the common vapor liquid solid (VLS) route (using liquid
catalyst). The VSS growth of group-IV elemental nanowires have been
investigated by other groups in situ during growth in a transmission electron
microscope (TEM). Though it is known that compound nanowire growth has
different dynamics compared to monoatomic semiconductors, the dynamics of VSS
growth of compound nanowires has not been understood. Here we investigate VSS
growth of compound nanowires by in situ microscopy, using Au-seeded GaAs as a
model system. The growth kinetics and dynamics at the wire-catalyst interface
by ledge-flow is studied and compared for liquid and solid catalysts at similar
growth conditions. Here the temperature and thermal history of the system is
manipulated to control the catalyst phase. In the first experiment discussed
here we reduce the growth temperature in steps to solidify the initially liquid
catalyst, and compare the dynamics between VLS and VSS growth observed at
slightly different temperatures. In the second experiment we exploit thermal
hysteresis of the system to obtain both VLS and VSS at the same temperature.
The VSS growth rate is comparable or slightly slower than VLS growth. Unlike in
the VLS case, during VSS growth we see several occasions where a new layer
starts before the previous layer is completely grown, i.e. multilayer growth.
Understanding the VSS growth mode enables better control of nanowire properties
by widening the range of usable nanowire growth parameters.",2104.05875v1
2021-04-16,Charge-Density-Wave Order and Multiple Magnetic Transitions in Divalent Europium Compound EuAl$_4$,"Multiple transition phenomena in divalent Eu compound EuAl$_4$ with the
tetragonal structure were investigated via the single-crystal time-of-flight
neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition
temperature of $T_{\rm CDW}$ = 140 K, superlattice peaks emerge near nuclear
Bragg peaks described by an ordering vector $q_{\rm CDW}$=(0 0 ${\delta}_c$)
with ${\delta}_c{\sim}$0.19. In contrast, magnetic peaks appear at $q_2 =
({\delta}_2 {\delta}_2 0)$ with ${\delta}_2$ = 0.085 in a magnetic-ordered
phase at 13.5 K below $T_{\rm N1}$ = 15.4 K. By further cooling to below
$T_{\rm N3}$ = 12.2 K, the magnetic ordering vector changes into $q_1 =
({\delta}_1 0 0)$ with ${\delta}_1$ = 0.17 at 11.5 K and slightly shifts to
${\delta}_1$ = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak
was detected at $T_{\rm N2}$=13.2 K and $T_{\rm N4}$=10.0 K. The structural
modulation below $T_{\rm CDW}$ with $q_{\rm CDW}$ is characterized by the
absence of the superlattice peak in the (0 0 $l$) axis. As a similar CDW
transition was observed in SrAl$_4$, the structural modulation with $q_{\rm
CDW}$ could be mainly ascribed to the displacement of Al ions within the
tetragonal $ab$-plane. Complex magnetic transitions are in stark contrast to a
simple collinear magnetic structure in isovalent EuGa$_4$. This could stem from
different electronic structures with the CDW transition between two compounds.",2104.07935v1
2021-05-11,Retro Drug Design: From Target Properties to Molecular Structures,"To generate drug molecules of desired properties with computational methods
is the holy grail in pharmaceutical research. Here we describe an AI strategy,
retro drug design, or RDD, to generate novel small molecule drugs from scratch
to meet predefined requirements, including but not limited to biological
activity against a drug target, and optimal range of physicochemical and ADMET
properties. Traditional predictive models were first trained over experimental
data for the target properties, using an atom typing based molecular descriptor
system, ATP. Monte Carlo sampling algorithm was then utilized to find the
solutions in the ATP space defined by the target properties, and the deep
learning model of Seq2Seq was employed to decode molecular structures from the
solutions. To test feasibility of the algorithm, we challenged RDD to generate
novel drugs that can activate {\mu} opioid receptor (MOR) and penetrate blood
brain barrier (BBB). Starting from vectors of random numbers, RDD generated
180,000 chemical structures, of which 78% were chemically valid. About 42,000
(31%) of the valid structures fell into the property space defined by MOR
activity and BBB permeability. Out of the 42,000 structures, only 267 chemicals
were commercially available, indicating a high extent of novelty of the
AI-generated compounds. We purchased and assayed 96 compounds, and 25 of which
were found to be MOR agonists. These compounds also have excellent BBB scores.
The results presented in this paper illustrate that RDD has potential to
revolutionize the current drug discovery process and create novel structures
with multiple desired properties, including biological functions and ADMET
properties. Availability of an AI-enabled fast track in drug discovery is
essential to cope with emergent public health threat, such as pandemic of
COVID-19.",2105.05220v1
2021-05-18,Study of Fischer-Tropsch Type reactions on chondritic meteorites,"How simple organic matter appeared on Earth and the processes by which it
transformed into more evolved organic compounds, which ultimately led to the
emergence of life, is still an open topic. Different scenarios have been
proposed, the main one assumes that simple organic compounds were synthesized,
either in the gas phase or on the surfaces of dust grains, during the process
of star formation, and were incorporated into larger bodies in the
protoplanetary disk. Transformation of these simple organic compounds in more
complex forms is still a matter of debate. Recent discoveries point out to
catalytic properties of dust grains present in the early stellar envelope,
which can nowadays be found in the form of chondrites. The huge infall of
chondritic meteorites during the early periods of Earth suggests that the same
reactions could have taken place in certain environments of the Earth surface,
with conditions more favorable for organic synthesis. This work attempts the
synthesis of simple organic molecules, such as hydrocarbons and alcohols, via
Fischer-Tropsch Type reactions supported by different chondritic materials
under early-Earth conditions, to investigate if organic synthesis can likely
occur in this environment and which are the differences in selectivity when
using different types of chondrites. Fischer-Tropsch-type reactions are
investigated from mixtures of CO and H2 at 1 atm of pressure on the surfaces of
different chondritic samples. The different products obtained are analyzed in
situ by gas chromatography. Different Fischer-Tropsch reaction products are
obtained in quantitative amounts. The formation of alkanes and alkenes being
the main processes. Formation of alcohols also takes place in a smaller amount.
Other secondary products were obtained in a qualitative way.",2105.08498v1
2021-05-22,Correlation-driven topological and valley states in monolayer VSi$_{2}$P$_{4}$,"Electronic correlations could have significant impact on the material
properties. They are typically pronounced for localized orbitals and enhanced
in low-dimensional systems, so two-dimensional (2D) transition metal compounds
could be a good platform to study their effects. Recently, a new class of 2D
transition metal compounds, the MoSi$_2$N$_4$-family materials, have been
discovered, and some of them exhibit intrinsic magnetism. Here, taking
monolayer VSi$_{2}$P$_{4}$ as an example from the family, we investigate the
impact of correlation effects on its physical properties, based on the
first-principles calculations. We find that different correlation strength can
drive the system into a variety of interesting ground states, with rich
magnetic, topological and valley features. With increasing correlation
strength, while the system favors a ferromagnetic semiconductor state for most
cases, the magnetic anisotropy and the band gap type undergo multiple
transitions, and in the process, the band edges can form single, two or three
valleys for electrons or holes. Remarkably, there is a quantum anomalous Hall
(QAH) insulator phase, which has a unit Chern number. The boundary of the QAH
phase correspond to the half-valley semimetal state with fully valley polarized
bulk carriers. We further show that for phases with the out-of-plane magnetic
anisotropy, the interplay between spin-orbit coupling and orbital character of
valleys enable an intrinsic valley polarization for electrons but not for
holes. This electron valley polarization can be switched by reversing the
magnetization direction, providing a new route of magnetic control of
valleytronics. Our result sheds light on the possible role of correlation
effects in the 2D transition metal compounds, and it will open new perspectives
for spintronic, valleytronic and topological nanoelectronic applications based
on these materials.",2105.10705v2
2021-06-15,Quasi-uniaxial pressure induced superconductivity in stoichiometric compound UTe$_2$,"The recent discovery of superconductivity in heavy Fermion compound UTe2, a
candidate topological and triplet-paired superconductor, has aroused widespread
interest. However, to date, there is no consensus on whether the stoichiometric
sample of UTe2 is superconducting or not due to lack of reliable evidence to
distinguish the difference between the nominal and real compositions of
samples. Here, we are the first to clarify that the stoichiometric UT2 is
non-superconducting at ambient pressure and under hydrostatic pressure up to 6
GPa, however we find that it can be compressed into superconductivity by
application of quasi-uniaxial pressure. Measurements of resistivity,
magnetoresistance and susceptibility reveal that the quasi-uniaxial pressure
results in a suppression of the Kondo coherent state seen at ambient pressure,
and then leads to a superconductivity initially emerged on the ab-plane at 1.5
GPa. At 4.8 GPa, the superconductivity is developed in three crystallographic
directions. The superconducting state coexists with an exotic magnetic ordered
state that develops just below the onset temperature of the superconducting
transition. The discovery of the quasi-uniaxial-pressure-induced
superconductivity with exotic magnetic state in the stoichiometric UTe2 not
only provide new understandings on this compound, but also highlight the vital
role of Te deficiency in developing the superconductivity at ambient pressures.",2106.08002v3
2021-06-17,Defects and Phase Formation in Non-Stoichiometric LaFeO$_3$: a Combined Theoretical and Experimental Study,"The defect chemistry of perovskite compounds is directly related to the
stoichiometry and to the valence states of the transition-metal ions. Defect
engineering has become increasingly popular as it offers the possibility to
influence the catalytic properties of perovskites for applications in energy
storage and conversion devices such as solid-oxide fuel- and electrolyzer
cells. LaFeO$_3$ (LFO) can be regarded as a base compound of the family of
catalytically active perovskites La$_{1-x}$A$_x$Fe$_{1-y}$B$_y$O$_{3-\delta}$,
for which the defect chemistry as well as the electronic and ionic conductivity
can be tuned by substitution on cationic sites. Combining theoretical and
experimental approaches, we explore the suitability for A-site vacancy
engineering, namely the feasibility of actively manipulating the valence state
of Fe and the concentration of point defects by synthesizing La-deficient LFO.
Formation energies and concentrations of point defects were determined as a
function of processing conditions by first-principles DFT+U calculations. Based
on the results, significant compositional deviations from stoichiometric LFO
cannot be expected by providing rich or poor conditions of the oxidic precursor
compounds (Fe$_2$O$_3$ and La$_2$O$_3$) in a solid-state processing route. In
the experimental part, LFO was synthesized with a targeted La-site deficiency.
We analyze the resulting phases by X-ray diffraction and scanning electron
microscopy, (scanning) transmission electron microscopy in combination with
energy-dispersive X-ray spectroscopy, and electron energy-loss spectrometry.
Instead of a variation of the La/Fe ratio, a mixture of the two phases
Fe$_2$O$_3$ and LFO was observed, resulting in an invariant charge state of Fe,
in line with the theoretical results. We discuss our findings with respect to
partly differing assumptions made in previous studies on this material system.",2106.09571v2
2021-06-19,A-type antiferromagnetic order and magnetic phase diagram of the trigonal Eu spin-7/2 triangular-lattice compound EuSn2As2,"The trigonal compound EuSn2As2 was recently discovered to host Dirac surface
states within the bulk band gap and orders antiferromagnetically below the Neel
temperature TN = 24 K. Here the magnetic ground state of single-crystal
EuSn2As2 and the evolution of its properties versus temperature T and applied
magnetic field H are reported. Included are zero-field single-crystal
neutron-diffraction measurements versus T, magnetization M(H,T), magnetic
susceptibility chi(H,T) = M(T)/H, heat capacity Cp(H,T), and electrical
resistivity rho(H,T) measurements. The neutron-diffraction and chi(T)
measurements both indicate a collinear A-type antiferromagnetic (AFM) structure
below TN =23.5(2) K, where the Eu{2+} spins S = 7/2 in a triangular ab-plane
layer (hexagonal unit cell) are aligned ferromagnetically in the ab plane
whereas the spins in adjacent Eu planes along the c axis are aligned
antiferromagnetically. The chi(H{ab},T) and chi(H{c},T) data together indicate
a smooth crossover between the collinear AFM alignment and an unknown magnetic
structure at H ~ 0.15 T. Dynamic spin fluctuations up to 60 K are evident in
the chi(T), Cp(T) and rho(H,T) measurements, a temperature that is more than
twice TN. The rho(H,T) of the compound does not reflect a contribution of the
topological state, but rather is consistent with a low-carrier-density metal
with strong magnetic scattering. The magnetic phase diagrams for both H||c and
H||ab in the H-T plane are constructed from the TN(H), chi(H,T), Cp(H,T), and
rho(H,T) data.",2106.10519v1
2021-08-27,Machine learning on DNA-encoded library count data using an uncertainty-aware probabilistic loss function,"DNA-encoded library (DEL) screening and quantitative structure-activity
relationship (QSAR) modeling are two techniques used in drug discovery to find
small molecules that bind a protein target. Applying QSAR modeling to DEL data
can facilitate the selection of compounds for off-DNA synthesis and evaluation.
Such a combined approach has been shown recently by training binary classifiers
to learn DEL enrichments of aggregated ""disynthons"" to accommodate the sparse
and noisy nature of DEL data. However, a binary classifier cannot distinguish
between different levels of enrichment, and information is potentially lost
during disynthon aggregation. Here, we demonstrate a regression approach to
learning DEL enrichments of individual molecules using a custom negative
log-likelihood loss function that effectively denoises DEL data and introduces
opportunities for visualization of learned structure-activity relationships
(SAR). Our approach explicitly models the Poisson statistics of the sequencing
process used in the DEL experimental workflow under a frequentist view. We
illustrate this approach on a dataset of 108k compounds screened against CAIX,
and a dataset of 5.7M compounds screened against sEH and SIRT2. Due to the
treatment of uncertainty in the data through the negative log-likelihood loss
function, the models can ignore low-confidence outliers. While our approach
does not demonstrate a benefit for extrapolation to novel structures, we expect
our denoising and visualization pipeline to be useful in identifying SAR trends
and enriched pharmacophores in DEL data. Further, this approach to
uncertainty-aware regression is applicable to other sparse or noisy datasets
where the nature of stochasticity is known or can be modeled; in particular,
the Poisson enrichment ratio metric we use can apply to other settings that
compare sequencing count data between two experimental conditions.",2108.12471v2
2021-10-11,Computationally driven discovery of SARS-CoV-2 Mpro inhibitors: from design to experimental validation,"We report a fast-track computationally-driven discovery of new SARS-CoV2 Main
Protease (M$^{pro}$) inhibitors whose potency range from mM for initial
non-covalent ligands to sub-$\mu$M for the final covalent compound (IC50=830
+/- 50 nM). The project extensively relied on high-resolution all-atom
molecular dynamics simulations and absolute binding free energy calculations
performed using the polarizable AMOEBA force field. The study is complemented
by extensive adaptive sampling simulations that are used to rationalize the
different ligands binding poses through the explicit reconstruction of the
ligand-protein conformation spaces. Machine Learning predictions are also
performed to predict selected compound properties. While simulations
extensively use High Performance Computing to strongly reduce time-to-solution,
they were systematically coupled to Nuclear Magnetic Resonance experiments to
drive synthesis and to in vitro characterization of compounds. Such study
highlights the power of in silico strategies that rely on structure-based
approaches for drug design and allows to address the protein conformational
multiplicity problem. The proposed fluorinated tetrahydroquinolines open routes
for further optimization of M$^{pro}$ inhibitors towards low nM affinities.",2110.05427v4
2021-10-29,Nanoparticle Radiosensitization: from extended local effect modeling to a survival modificationframework of compound Poisson additive killing and its carbon dots validation,"Objective: To construct an analytical model instead of local effect modeling
for the prediction of the biological effectiveness of nanoparticle
radiosensitization. Approach: An extended local effects model is first proposed
with a more comprehensive description of the nanoparticles mediated local
killing enhancements, but meanwhile puts forward challenging issues that remain
difficult and need to be further studied. As a novel method instead of local
effect modeling, a survival modification framework of compound Poisson additive
killing is proposed, as the consequence of an independent additive killing by
the assumed equivalent uniform doses of individual nanoparticles per cell under
the LQ model. A compound Poisson killing (CPK)model based on the framework is
thus derived, giving a general expression of nanoparticle mediated LQ parameter
modification. For practical use, a simplified form of the model is also
derived, as a concentration dependent correction only to the {\alpha}
parameter, with the relative correction (alpha""/alpha)) dominated by the mean
number, and affected by the agglomeration of nanoparticles per cell. For
different agglomeration state, a monodispersion model of the dispersity factor
{\eta}=1, and an agglomeration model of 2/3<{\eta}<1,are provided for practical
prediction of (alpha""/alpha) value respectively. Main results: Initial
validation by the radiosensitization ofHepG2 cells by carbon dots showed a high
accuracy of the CPK model. In a safe range of concentration (0.003-0.03
{\mu}g/{\mu}L)of the carbon dots, the prediction errors of the monodispersion
and agglomeration models were both within 2%, relative to the clonogenic
survival data of the sensitized HepG2 cells.",2111.00037v2
2021-11-04,Compound Logics for Modification Problems,"We introduce a novel model-theoretic framework inspired from graph
modification and based on the interplay between model theory and algorithmic
graph minors. The core of our framework is a new compound logic operating with
two types of sentences, expressing graph modification: the modulator sentence,
defining some property of the modified part of the graph, and the target
sentence, defining some property of the resulting graph. In our framework,
modulator sentences are in counting monadic second-order logic (CMSOL) and have
models of bounded treewidth, while target sentences express first-order logic
(FOL) properties along with minor-exclusion. Our logic captures problems that
are not definable in first-order logic and, moreover, may have instances of
unbounded treewidth. Also, it permits the modeling of wide families of problems
involving vertex/edge removals, alternative modulator measures (such as
elimination distance or $\mathcal{G}$-treewidth), multistage modifications, and
various cut problems. Our main result is that, for this compound logic,
model-checking can be done in quadratic time. All derived algorithms are
constructive and this, as a byproduct, extends the constructibility horizon of
the algorithmic applications of the Graph Minors theorem of Robertson and
Seymour. The proposed logic can be seen as a general framework to capitalize on
the potential of the irrelevant vertex technique. It gives a way to deal with
problem instances of unbounded treewidth, for which Courcelle's theorem does
not apply. The proof of our meta-theorem combines novel combinatorial results
related to the Flat Wall theorem along with elements of the proof of
Courcelle's theorem and Gaifman's theorem. We finally prove extensions where
the target property is expressible in FOL+DP, i.e., the enhancement of FOL with
disjoint-paths predicates.",2111.02755v2
2021-12-27,ToxTree: descriptor-based machine learning models for both hERG and Nav1.5 cardiotoxicity liability predictions,"Drug-mediated blockade of the voltage-gated potassium channel(hERG) and the
voltage-gated sodium channel (Nav1.5) can lead to severe cardiovascular
complications. This rising concern has been reflected in the drug development
arena, as the frequent emergence of cardiotoxicity from many approved drugs led
to either discontinuing their use or, in some cases, their withdrawal from the
market. Predicting potential hERG and Nav1.5 blockers at the outset of the drug
discovery process can resolve this problem and can, therefore, decrease the
time and expensive cost of developing safe drugs. One fast and cost-effective
approach is to use in silico predictive methods to weed out potential hERG and
Nav1.5 blockers at the early stages of drug development. Here, we introduce two
robust 2D descriptor-based QSAR predictive models for both hERG and Nav1.5
liability predictions. The machine learning models were trained for both
regression, predicting the potency value of a drug, and multiclass
classification at three different potency cut-offs (i.e. 1$\mu$M, 10$\mu$M, and
30$\mu$M), where ToxTree-hERG Classifier, a pipeline of Random Forest models,
was trained on a large curated dataset of 8380 unique molecular compounds.
Whereas ToxTree-Nav1.5 Classifier, a pipeline of kernelized SVM models, was
trained on a large manually curated set of 1550 unique compounds retrieved from
both ChEMBL and PubChem publicly available bioactivity databases. The proposed
hERG inducer outperformed most metrics of the state-of-the-art published model
and other existing tools. Additionally, we are introducing the first Nav1.5
liability predictive model achieving a Q4 = 74.9% and a binary classification
of Q2 = 86.7% with MCC = 71.2% evaluated on an external test set of 173 unique
compounds. The curated datasets used in this project are made publicly
available to the research community.",2112.13467v1
2022-04-06,Sub-Task Decomposition Enables Learning in Sequence to Sequence Tasks,"The field of Natural Language Processing has experienced a dramatic leap in
capabilities with the recent introduction of huge Language Models. Despite this
success, natural language problems that involve several compounded steps are
still practically unlearnable, even by the largest LMs. This complies with
experimental failures for end-to-end learning of composite problems that were
demonstrated in a variety of domains. An effective mitigation is to introduce
intermediate supervision for solving sub-tasks of the compounded problem.
Recently, several works have demonstrated high gains by taking a
straightforward approach for incorporating intermediate supervision in
compounded natural language problems: the sequence-to-sequence LM is fed with
an augmented input, in which the decomposed tasks' labels are simply
concatenated to the original input. In this paper, we prove a positive learning
result that motivates these recent efforts. We show that when concatenating
intermediate supervision to the input and training a sequence-to-sequence model
on this modified input, unlearnable composite problems can become learnable. We
show that this is true for any family of tasks which on the one hand, are
unlearnable, and on the other hand, can be decomposed into a polynomial number
of simple sub-tasks, each of which depends only on O(1) previous sub-task
results. Beyond motivating contemporary empirical efforts for incorporating
intermediate supervision in sequence-to-sequence language models, our positive
theoretical result is the first of its kind in the landscape of results on the
benefits of intermediate supervision for neural-network learning: Until now,
all theoretical results on the subject are negative, i.e., show cases where
learning is impossible without intermediate supervision, while our result is
positive, showing that learning is facilitated in the presence of intermediate
supervision.",2204.02892v4
2022-04-26,"Electronic and structural properties of RbCeX$_2$ (X$_2$: O$_2$, S$_2$, SeS, Se$_2$, TeSe, Te$_2$)","Triangular lattice delafossite compounds built from magnetic lanthanide ions
are a topic of recent interest due to their frustrated magnetism and
realization of quantum disordered magnetic ground states. Here we report the
evolution of the structure and electronic ground states of RbCe$X_2$ compounds,
built from a triangular lattice of Ce$^{3+}$ ions, upon varying their anion
character ($X_2$= O$_2$, S$_2$, SeS, Se$_2$, TeSe, Te$_2$). This includes the
discovery of a new member of this series, RbCeO$_2$, that potentially realizes
a quantum disordered ground state analogous to NaYbO$_2$. Magnetization and
susceptibility measurements reveal that all compounds manifest mean-field
antiferromagnetic interactions and, with the exception of the oxide, possess
signatures of magnetic correlations onset below 1 K. The crystalline electric
field level scheme is explored via neutron scattering and \textit{ab initio}
calculations in order to model the intramultiplet splitting of the $J=5/2$
multiplet. In addition to the two excited doublets expected within the $J=5/2$
manifold, we observe one extra, local mode present across the sample series.
This added mode shifts downward in energy with increasing anion mass and
decreasing crystal field strength, suggesting a long-lived anomalous mode
endemic to anion motion about the Ce$^{3+}$ sites.",2204.12086v2
2022-05-19,An Effective Activation Method for Industrially Produced TiFeMn Powder for Hydrogen Storage,"This work proposes an effective thermal activation method with low technical
effort for industrially produced titanium-iron-manganese powders (TiFeMn) for
hydrogen storage. In this context, the influence of temperature and particle
size of TiFeMn on the activation process is systematically studied. The results
obtained from this investigation suggest that the activation of the TiFeMn
material at temperatures as low as 50 {\deg}C is already possible and that an
increase to 90 {\deg}C strongly reduces the incubation time for activation,
i.e. the incubation time of the 90 {\deg}C/90 {\deg}C sample is about 0.84 h
while ~ 277 h is required for the 50 {\deg}C/50 {\deg}C sample. Selecting
TiFeMn particles of larger size also leads to significant improvements in the
activation performance of the investigated material. The proposed activation
routine makes it possible to overcome the oxide layer existing on the compound
surface, which acts as a diffusion barrier for the hydrogen atoms. This
activation method induces further cracks and defects in the powder granules,
generating new surfaces for hydrogen absorption with greater frequency, and
thus leading to faster sorption kinetics in the subsequent
absorption-desorption cycles.",2205.09429v2
2022-05-31,"Complex interplay between 3d and 4f magnetic systems and magnetic chirality in multiferroic Dy$_{1-x}$Ho$_x$MnO$_3$ ($x = 0, 0.2$)","Structural, magnetic and multiferroic properties of single crystals of
Dy$_{1-x}$Ho$_x$MnO$_3$ ($x = 0, 0.2$) were investigated by the different
methods of polarized and classical neutron diffraction and macroscopic methods
in order to determine the effect of Ho doping on the magneto-electric behavior
of the title compounds. It is shown that substitution by Ho of 20% on the
position of Dy do not change overall crystal symmetry of compound. It remains
of Pnma type for both compositions down to the very low temperatures. Magnetic
ordering do not change the crystal structure. Precise magnetic order and it
detailed temperature and field evolution both in the pristine and substituted
compounds we determined using single crystal neutron diffraction and
magnetization measurements. The results show a complex interplay between
transition metal and rear earth magnetic sub lattices leading to so-called
""Mn-controlled"" and ""Dy-controlled"" magnetic states. Using polarized neutron
diffraction 3D character of rear earth magnetic order in
Dy$_{0.8}$Ho$_{0.2}$MnO$_3$ in contract to DyMnO$_3$ and occurrence of the
chiral type magnetic structure on Mn subsystem could be revealed. The influence
of the external electric field on the magnetic chirality could be directly
evidenced, proving strong magneto-electric coupling in multiferroic phase. The
study of the electric polarization under similar temperatures and fields on the
same samples provides the direct correlation between the results of the
microscopic and macroscopic investigations.",2205.15842v2
2022-07-21,Artificial intelligence enables mobile soil analysis for sustainable agriculture,"For optimizing production yield while limiting negative environmental impact,
sustainable agriculture benefits greatly from real-time, on-the-spot analysis
of soil at low cost. Colorimetric paper sensors are ideal candidates for cheap
and rapid chemical spot testing. However, their field application requires
previously unattained paper sensor reliability and automated readout and
analysis by means of integrated mobile communication, artificial intelligence,
and cloud computing technologies. Here, we report such a mobile chemical
analysis system based on colorimetric paper sensors that operates under
tropical field conditions. By mapping topsoil pH in a field with an area of 9
hectares, we have benchmarked the mobile system against precision agriculture
standards following a protocol with reference analysis of compound soil
samples. As compared with routine lab analysis, our mobile soil analysis system
has correctly classified soil pH in 97% of cases while reducing the analysis
turnaround time from days to minutes. Moreover, by performing on-the-spot
analyses of individual compound sub-samples in the field, we have achieved a
9-fold increase of spatial resolution that reveals pH-variations not detectable
in compound mapping mode. Our mobile system can be extended to perform
multi-parameter chemical tests of soil nutrients for applications in
environmental monitoring at marginal manufacturing cost.",2207.10537v1
2022-08-03,Hybrid Approach to Identify Druglikeness Leading Compounds against COVID-19 3CL Protease,"SARS-COV-2 is a positive single-strand RNA-based macromolecule that has
caused the death of more than 6.3 million people since June 2022. Moreover, by
disturbing global supply chains through lockdown, the virus has indirectly
caused devastating damage to the global economy. It is vital to design and
develop drugs for this virus and its various variants. In this paper, we
developed an in-silico study-based hybrid framework to repurpose existing
therapeutic agents in finding drug-like bioactive molecules that would cure
Covid-19. We employed the Lipinski rules on the retrieved molecules from the
ChEMBL database and found 133 drug-likeness bioactive molecules against SARS
coronavirus 3CL Protease. Based on standard IC50, the dataset was divided into
three classes active, inactive, and intermediate. Our comparative analysis
demonstrated that the proposed Extra Tree Regressor (ETR) based QSAR model has
improved prediction results related to the bioactivity of chemical compounds as
compared to Gradient Boosting, XGBoost, Support Vector, Decision Tree, and
Random Forest based regressor models. ADMET analysis is carried out to identify
thirteen bioactive molecules with ChEMBL IDs 187460, 190743, 222234, 222628,
222735, 222769, 222840, 222893, 225515, 358279, 363535, 365134 and 426898.
These molecules are highly suitable drug candidates for SARS-COV-2 3CL
Protease. In the next step, the efficacy of bioactive molecules is computed in
terms of binding affinity using molecular docking and then shortlisted six
bioactive molecules with ChEMBL IDs 187460, 222769, 225515, 358279, 363535, and
365134. These molecules can be suitable drug candidates for SARS-COV-2. It is
anticipated that the pharmacologist/drug manufacturer would further investigate
these six molecules to find suitable drug candidates for SARS-COV-2. They can
adopt these promising compounds for their downstream drug development stages.",2208.06362v3
2022-10-03,Interplay of broken symmetry and delocalized excitations in the insulating state of 1$T$-TaS$_2$,"Coexistence of localized and extended excitations is central to the
macroscopic properties of correlated materials. For 5d transition metal
compounds, electron correlations alone generally do not lead to a
metal-insulator (Mott) transition, with insulating behavior usually resulting
from their coupling with magnetic ordering and/or structural distortions.
1$T$-TaS$_2$ is a prototypical example of such correlated insulating behavior,
with a high-symmetry metallic phase transforming into a distorted, charge
density wave (CDW) insulating state at low temperatures. The relevance of the
localized electron physics at play in 3d compounds to these 5d transition metal
compounds remains an open question. We resolved this standing controversy in
1$T$-TaS$_2$ combining resonant inelastic X-ray spectroscopy and
first-principles calculations. We observed five electronic excitations arising
from the interband transitions of the Ta 5d orbitals and the S 3p ligand state,
with none of the excitations on the order of the Mott gap. These excitations
cannot be explained within the framework of standard multiplet calculations
that assume a localized wavefunction, but instead, are captured by a band
theory framework accounting for the low symmetry of the crystal field in the
CDW state. Our findings suggest that the electronic property of 1$T$-TaS$_2$ is
dominated by both plasmonic quasiparticles and inter-band transitions
associated with a Drude-type response, with no resonance associated with a
putative Mott transition. Our discovery provides new insights into the electron
localization and the onset of insulating behavior in 5d transition metal
materials.",2210.01181v2
2022-10-29,Coupling between colossal charge density wave ordering and magnetism in Ho2Ir3Si5,"Ho2Ir3Si5 belongs to the family of three-dimensional (3D) R2Ir3Si5 (R = Lu,
Er and Ho) compounds that exhibit a colossal first-order charge density wave
(CDW) transition where there is a strong orthorhombic-to-triclinic distortion
of the lattice accompanied by superlattice reflections. The analysis by
single-crystal X-ray diffraction (SXRD) has revealed that the Ir-Ir zigzag
chains along c are responsible for the CDW in all three compounds. The
replacement of the rare earth element from non-magnetic Lu to magnetic Er or Ho
lowers TCDW, where TCDWLu = 200 K, TCDWEr = 150 K and TCDWHo = 90 K. Out of the
three compounds, Ho2Ir3Si5 is the only system where second-order superlattice
reflections could be observed, indicative of an anharmonic shape of the
modulation wave. The CDW transition is observed as anomalies in the temperature
dependencies of the specific heat, electrical conductivity and magnetic
susceptibility, which includes a large hysteresis of 90 to 130 K for all
measured properties, thus corroborating the SXRD measurements. Similar to
previously reported Er2Ir3Si5, there appears to be a coupling between CDW and
magnetism such that the Ho3+ magnetic moments are influenced by the CDW
transition, even in the paramagnetic state. Moreover, earlier investigations on
polycrystalline material revealed antiferromagnetic (AFM) ordering at TN = 5.1
K, whereas AFM order is suppressed and only the CDW is present in our highly
ordered single-crystal. First-principles calculations predict Ho2Ir3Si5 to be a
metal with coexisting electron and hole pockets at the Fermi level. The Ho and
Ir atoms have spherically symmetric metallic-type charge density distributions
that are prone to CDW distortion. Phonon calculations affirm that the Ir atoms
are primarily responsible for the CDW distortion, which is in agreement with
the experiment.",2210.16445v1
2022-11-06,Stressing Dynamic Loss Models,"Stress testing, and in particular, reverse stress testing, is a prominent
exercise in risk management practice. Reverse stress testing, in contrast to
(forward) stress testing, aims to find an alternative but plausible model such
that under that alternative model, specific adverse stresses (i.e. constraints)
are satisfied. Here, we propose a reverse stress testing framework for dynamic
models. Specifically, we consider a compound Poisson process over a finite time
horizon and stresses composed of expected values of functions applied to the
process at the terminal time. We then define the stressed model as the
probability measure under which the process satisfies the constraints and which
minimizes the Kullback-Leibler divergence to the reference compound Poisson
model.
  We solve this optimization problem, prove existence and uniqueness of the
stressed probability measure, and provide a characterization of the
Radon-Nikodym derivative from the reference model to the stressed model. We
find that under the stressed measure, the intensity and the severity
distribution of the process depend on time and state. We illustrate the dynamic
stress testing by considering stresses on VaR and both VaR and CVaR jointly and
provide illustrations of how the stochastic process is altered under these
stresses. We generalize the framework to multivariate compound Poisson
processes and stresses at times other than the terminal time. We illustrate the
applicability of our framework by considering ``what if'' scenarios, where we
answer the question: What is the severity of a stress on a portfolio component
at an earlier time such that the aggregate portfolio exceeds a risk threshold
at the terminal time? Furthermore, for general constraints, we propose an
algorithm to simulate sample paths under the stressed measure, thus allowing to
compare the effects of stresses on the dynamics of the process.",2211.03221v3
2022-11-17,"Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry","Adiabatic scanning calorimetry (ASC) is capable of providing simultaneously
the specific enthalpy h(T) and the specific heat capacity cp(T), and is an
important tool to determine the order of transitions and to render
high-resolution information on pretransitional thermal behavior. Here we report
on ASC results on the compound DIO and on mixtures with RM734. Both compounds
exhibit a low-temperature ferroelectric nematic phase (NF) and a
high-temperature paraelectric nematic (N). In DIO these two phases are
separated by an intermediate phase (Nx). Detailed data of h(T) and cp(T),
indicated that the intermediate phase was present in all mixtures over the
complete composition range, albeit with strongly decreasing temperature width
with decreasing mole fraction of DIO (xDIO). The xDIO dependence of the two
transitions could be well described by a quadratic function and both
transitions were weakly first order. The true latent heat of the Nx-N
transition of DIO was as low as 0.0075 +/- 0.0005 J/g and 0.23 +/- 0.03 J/g for
the NF-Nx transition, about twice the previously reported value of 0.115 J/g
for the NF-N transition in RM734. In the mixtures both transition latent heats
decrease gradually with decreasing xDIO. At all the Nx-N transitions
pretransition fluctuation effects are absent and these transitions are purely
but very weakly first order. As in RM734 the transition from the NF to the
higher temperature phase exhibits substantial pretransitional behaviour. Power
law analysis of cp(T) resulted in an effective critical exponent of 0.88 +/-
0.10 for DIO and this value decreased in mixtures with decreasing xDIO towards
0.50 +/- 0.05 reported for RM734. Ideal mixture analysis of the phase diagram
was consistent with ideal mixture behavior for the total transition enthalpy
change",2211.09437v1
2022-11-24,Revised Magnetic Structure and Tricritical Behavior of the CMR Compound NaCr$_2$O$_4$ Investigated with High Resolution Neutron Diffraction and $μ^+$SR,"The mixed valence Cr compound NaCr$_2$O$_4$, synthesized using a
high-pressure technique, offers a unique playground for investigating
unconventional physical properties in condensed matter. In the present study,
muon spin rotation/relaxation ($\mu^+$SR) and high-resolution neutron powder
diffraction (NPD) measurements were carried out to clarify the true magnetic
ground state of this interesting compound. Our detailed study brings new
insight, allowing us to confirm the existence of a commensurate
antiferromagnetic order (C-AFM) and to extract its ordered Cr moment $\mu^{\rm
C}_{\rm Cr}=(4.30\pm0.01)\mu_B$. Such a value of the ordered moment is in fact
compatible with the existence of high-spin Cr sites. Further, the value of the
canting angle of the Cr spin axial vector is refined as $\theta_{\rm
c}=(8.8\pm0.5)^{\circ}$. Employing high-quality samples in combination with
time-of-flight NPD, a novel magnetic supercell was also revealed. Such
supercell display an incommensurate (IC)-AFM propagation vector
(0~0~${\textstyle \frac{1}{2}-}\delta$), having an ordered moment $\mu^{\rm
IC}_{\rm Cr}=(2.20\pm0.03)\mu_B$. It is suggested that the C-AFM and IC-AFM
modulations are due to itinerant and localized contributions to the magnetic
moment, respectively. Finally, the direct measurement of the magnetic order
parameter provided a value of the critical exponent $\beta = 0.245 \approx
\frac{1}{4}$, suggesting a non conventional critical behavior for the magnetic
phase transition in NaCr$_2$O$_4$.",2211.13405v1
2022-12-20,"Effect of antifluorite layer on the magnetic order in Eu-based 1111 compounds, EuTAsF (T = Zn, Mn, and Fe)","The 1111 compounds with an alternating sequence of fluorite and antifluorite
layers serve as structural hosts for the vast family of Fe-based
superconductors. Here, we use neutron powder diffraction and
density-functional-theory (DFT) band-structure calculations to study magnetic
order of Eu2+ in the [EuF]+ fluorite layers depending on the nature of the
[TAs]- antifluorite layer that can be non-magnetic semiconducting (T = Zn),
magnetic semiconducting (T = Mn), or magnetic metallic (T = Fe).
Antiferromagnetic transitions at TN ~ 2.4 - 3 K due to an ordering of the Eu2+
magnetic moments were confirmed in all three EuTAsF compounds. Whereas in
EuTAsF (T = Zn and Mn), the commensurate k1 = (1/2 1/2 0) stripe order pattern
with magnetic moments within the ab-plane is observed, the order in EuFeAsF is
incommensurate with k = (0 0.961(1) 1/2) and represents a cycloid of Eu2+
magnetic moments confined within the bc-plane. Additionally, the Mn2+
sublattice in EuMnAsF features a robust G-type antiferromagnetic order that
persists at least up to room temperature, with magnetic moments along the
c-direction. Although DFT calculations suggest stripe antiferromagnetic order
in the Fe-sublattice of EuFeAsF as the ground state, neutron diffraction
reveals no evidence of long-range magnetic order associated with Fe. We show
that the frustrating interplane interaction J3 between the adjacent [EuF]+
layers is comparable with in-plane J1-J2 interactions already in the case of
semiconducting fluorite layers [TAs]- (T = Zn and Mn) and becomes dominant in
the case of the metallic [FeAs]- ones. The latter, along with a slight
orthorhombic distortion, is proposed to be the origin of the incommensurate
magnetic structure observed in EuFeAsF.",2212.10312v1
2023-01-22,Stability of the In-Plane Room Temperature van der Waals Ferromagnet Chromium Ditelluride and Its Conversion to Chromium-Interleaved CrTe$_2$ Compounds,"Van der Waals magnetic materials are building blocks for novel kinds of
spintronic devices and playgrounds for exploring collective magnetic phenomena
down to the two-dimensional limit. Chromium-tellurium compounds are relevant in
this perspective. In particular, the 1$T$ phase of CrTe$_2$ has been argued to
have a Curie temperature above 300~K, a rare and desirable property in the
class of lamellar materials, making it a candidate for practical applications.
However, recent literature reveals a strong variability in the reported
properties, including magnetic ones. Using electron microscopy, diffraction and
spectroscopy techniques, together with local and macroscopic magnetometry
approaches, our work sheds new light on the structural, chemical and magnetic
properties of bulk 1$T$-CrTe$_2$ exfoliated in the form of flakes having a
thickness ranging from few to several tens of nanometers. We unambiguously
establish that 1$T$-CrTe$_2$ flakes are ferromagnetic above room temperature,
have an in-plane easy axis of magnetization, low coercivity, and we confirm
that their Raman spectroscopy signatures are two modes, $E_{2\text{g}}$
(103.5~cm$^{-1}$) and $A_{1\text{g}}$ (136.5~cm$^{-1}$). We also prove that
thermal annealing causes a phase transformation to monoclinic Cr$_5$Te$_8$ and,
to a lesser extent, to trigonal Cr$_5$Te$_8$. In sharp contrast with
1$T$-CrTe$_2$, none of these compounds have a Curie temperature above room
temperature, and they both have perpendicular magnetic anisotropy. Our findings
reconcile the apparently conflicting reports in the literature and open
opportunities for phase-engineered magnetic properties.",2301.09127v2
2023-01-25,Origin of ultra-low thermal conductivity in unconventional clathrates: Strong scattering from extremely low-frequency rattling modes,"Recent discoveries of materials with ultra-low thermal conductivity open a
pathway to significant developments in the field of thermoelectricity. Here, we
conduct a comparative study of three chemically similar antimonides to
establish the root causes of their extraordinarily low thermal conductivity
($0.4-0.6$ Wm$^{-1}$K$^{-1}$ at 525 K). The materials of interest are: the
unconventional type-XI clathrate K$_{58}$Zn$_{122}$Sb$_{207}$, the tunnel
compound K$_{6.9}$Zn$_{21}$Sb$_{16}$, and the type-I clathrate
K$_8$Zn$_{15.5}$Cu$_{2.5}$Sb$_{28}$ discovered herein. Calculations of the
phonon dispersions show that the type-XI compound exhibits localized (i.e.,
rattling) phonon modes with unusually low frequencies that span the entire
acoustic regime. In contrast, rattling in the type-I clathrate is observed only
at higher frequencies, and no rattling modes are present in the tunnel
structure. Modeling reveals that low-frequency rattling modes profoundly limit
the acoustic scattering time; the scattering time of the type-XI clathrate is
half that of the type-I clathrate and a quarter of the tunnel compound. For all
three materials, the thermal conductivities are additionally suppressed by soft
framework bonding that lowers the acoustic group velocities, and structural
complexity that leads to diffusonic character of the optical modes.
Understanding details of thermal transport in structurally complex materials
will be crucial for developing the next generation of thermoelectrics.",2301.10821v1
2023-03-06,Magnetic field induced valence change in Eu(Co$_{1-x}$Ni$_{x}$)$_{2}$P$_{2}$ up to 60 T,"The solid solution 122 compounds, Eu(Co$_{1-x}$Ni$_{x}$)$_{2}$P$_{2}$, show
valence transition between divalent state and intermediate valence states at
Eu, which is firmly correlated to multiple degrees of freedom in the solid such
as the isostructural transition between the collapsed tetragonal (cT) and
uncollapsed tetragonal (ucT) structures, $3d$ magnetism, and the formation of
P-P dimers. To gain insights into the correlated behavior, we investigate the
effect of high magnetic fields on the samples of $x = 0.4$ and $0.5$ using
magnetostriction and magnetization measurements up to 60 T. The samples are in
the Eu valence fluctuating regime, where the possible structural transition
from cT to ucT may be induced by the Eu valence change under the magnetic
fields. For both samples, magnetostriction smoothly increases with increasing
magnetic fields. The behavior is in good agreement with the calculated results
using the interconfigurational fluctuation (ICF) model that describes the
valence change. This indicates that $\Delta L$ represents the change of the Eu
valence state in these compounds. Magnetization curves for both compounds show
good agreement with the ICF model at high magnetic fields. In contrast, in the
low magnetic field region, magnetization curves do not agree with the ICF
model. These results indicate that the Eu valence changes manifest themselves
in the magnetization curves at high magnetic fields and that the magnetism of
the $3d$ electrons manifests itself in the magnetization at low magnetic
fields. Hence, we conclude that the valence change occurs within the Eu valence
fluctuation regime coupled with the cT structure. Thereby, we believe that the
transition to ucT structure which is firmly coupled with the divalent Eu state
does not occur within the magnetic field range of the present study.
(Continued)",2303.02910v3
2023-05-16,Synthesis of elements in compact stars in pycnonuclear reactions with Carbon isotopes: Quasibound states versus states of zero-points vibrations,"(1) Purpose: Conditions of formation of compound nuclear system needed for
synthesis of heavy nuclei in pycnonuclear reactions in compact stars are
studied on a quantum mechanical basis. (2) Methods: Method of multiple internal
reflections is generalized for pycnoreactions in compact stars with new
calculations of quasibound spectra and spectra of zero-point vibrations. (3)
Results: Peculiarities of the method are analyzed for reaction with isotopes of
Carbon. The developed method takes into account continuity and conservation of
quantum flux (describing pycnonuclear reaction) inside the full spacial region
of reaction including nuclear region. This gives appearance of new states
(called as quasibound states), in which compound nuclear systems of Magnesium
are formed with the largest probability. These states have not been studied yet
in synthesis of elements in stars. Energy spectra of zero-point vibrations and
spectra of quasibound states are estimated with high precision for reactions
with isotopes of Carbon. At the first time influence of plasma screening on
quasibound states and states of zero-point vibrations in pycnonuclear reactions
has been studied. (4) Conclusion: The probability of formation of compound
nuclear system in quasibound states in pycnonuclear reaction is essentially
larger than the probability of formation of this system in states of zero-point
vibrations studied by Zel'dovich and followers. So, synthesis of Magnesium from
isotopes of Carbon is more probable through the quasibound states than through
the states of zero-point vibrations in compact stars. Energy spectra of
zero-point vibrations are changed essentially after taking plasma screening
into account. Analysis shows that from all studied isotopes of Magnesium only
\isotope[24]{Mg} is stable after synthesis at energy of relative motion of
4.881~MeV of incident nuclei \isotope[12]{C}.",2305.09389v1
2023-05-22,"Structural, elastic, electronic, bonding, thermo-mechanical and optical properties of predicted NbAlB MAB phase in comparison to MoAlB: DFT based ab-initio insights","In this study, we have used density functional theory (DFT) based
first-principles investigation of the physical properties of prospective NbAlB
compound for the first time. From the analysis of the cohesive energy and
enthalpy of formation, it was found that NbAlB is chemically stable. The
physical properties of NbAlB have been compared and contrasted with those
obtained for MoAlB. Both these MAB phases are elastically anisotropic,
mechanically stable, machinable and brittle materials. Structural and elastic
features reflect the layered features. The estimated hardness of NbAlB is 19.0
GPa comparable to that of MoAlB (20.8 GPa) suggesting that predicted NbAlB is a
hard compound and is suitable for heavy duty industrial applications. NbAlB is
more machinable than MoAlB. Electronic band structure calculations reveal
conventional metallic behavior with the electronic density of states at the
Fermi level arising mainly due to the Nb 4d orbitals in NbAlB. The electronic
density of states at the Fermi level is significantly higher in NbAlB in
comparison to MoAlB, indicating that NbAlB is expected to exhibit higher level
of electrical conductivity. Electronic dispersion is highly anisotropic for
both MoAlB and NbAlB with substantially large electronic effective masses in
the out-of-plane directions. The bonding features have been elucidated via the
analysis of the band structure and charge density distribution. Both the
compounds have mixed covalent, ionic and metallic bonding characteristics. The
Fermi surfaces of MoAlB and NbAlB consists of electron and hole like sheets.
The Debye temperatures of MoAlB and NbAlB are comparable. The estimated melting
temperature of NbAlB is somewhat lower than that of MoAlB. NbAlB shows
excellent reflection characteristics suitable to be used as an efficient solar
reflector. NbAlB is also expected to absorb ultraviolet radiation very
effectively.",2305.12690v1
2023-07-05,Compound Attention and Neighbor Matching Network for Multi-contrast MRI Super-resolution,"Multi-contrast magnetic resonance imaging (MRI) reflects information about
human tissue from different perspectives and has many clinical applications. By
utilizing the complementary information among different modalities,
multi-contrast super-resolution (SR) of MRI can achieve better results than
single-image super-resolution. However, existing methods of multi-contrast MRI
SR have the following shortcomings that may limit their performance: First,
existing methods either simply concatenate the reference and degraded features
or exploit global feature-matching between them, which are unsuitable for
multi-contrast MRI SR. Second, although many recent methods employ transformers
to capture long-range dependencies in the spatial dimension, they neglect that
self-attention in the channel dimension is also important for low-level vision
tasks. To address these shortcomings, we proposed a novel network architecture
with compound-attention and neighbor matching (CANM-Net) for multi-contrast MRI
SR: The compound self-attention mechanism effectively captures the dependencies
in both spatial and channel dimension; the neighborhood-based feature-matching
modules are exploited to match degraded features and adjacent reference
features and then fuse them to obtain the high-quality images. We conduct
experiments of SR tasks on the IXI, fastMRI, and real-world scanning datasets.
The CANM-Net outperforms state-of-the-art approaches in both retrospective and
prospective experiments. Moreover, the robustness study in our work shows that
the CANM-Net still achieves good performance when the reference and degraded
images are imperfectly registered, proving good potential in clinical
applications.",2307.02148v3
2023-07-31,Semiconducting transport in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O sintered from Pb$_2$SO$_5$ and Cu$_3$P,"The very recent claim on the discovery of ambient-pressure room-temperature
superconductivity in modified lead-apatite has immediately excited sensational
attention in the entire society, which is fabricated by sintering lanarkite
(Pb2SO5) and copper(I) phosphide (Cu$_3$P). To verify this exciting claim, we
have successfully synthesized Pb$_2$SO$_5$, Cu$_3$P, and finally the modified
lead-apatite Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O. Detailed electrical transport and
magnetic properties of these compounds were systematically analyzed. It turns
out that Pb$_2$SO$_5$ is a highly insulating diamagnet with a room-temperature
resistivity of ~7.18x10$^9$ Ohm.cm and Cu$_3$P is a paramagnetic metal with a
room-temperature resistivity of ~5.22x10$^{-4}$ Ohm.cm. In contrast to the
claimed superconductivity, the resulting Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O
compound sintered from Pb$_2$SO$_5$ and Cu$_3$P exhibits semiconductor-like
transport behavior with a large room-temperature resistivity of ~1.94x10$^4$
Ohm.cm although our compound shows greatly consistent x-ray diffraction
spectrum with the previously reported structure data. In addition, when a
pressed Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O pellet is located on top of a commercial
Nd$_2$Fe$_{14}$B magnet at room temperature, no repulsion could be felt and no
magnetic levitation was observed either. These results imply that the claim of
a room-temperature superconductor in modified lead-apatite may need more
careful re-examination, especially for the electrical transport properties.",2307.16802v1
2023-08-26,"Ab initio Investigations on the Electronic Properties and Stability of Cu-Substituted Lead Apatite (LK-99) family with different doping concentrations (x=0, 1, 2)","The pursuit of room-temperature ambient-pressure superconductivity in novel
materials has sparked interest, with recent reports suggesting such properties
in Cu-substituted lead apatite, known as LK-99. However, these claims lack
comprehensive experimental and theoretical support. In this study, we address
this gap by conducting ab initio calculations to explore the impact of varying
doping concentrations (x = 0, 1, 2) on the stability and electronic properties
of five compounds in the LK-99 family. Our investigations confirm the isolated
flat bands that intersect the Fermi level in LK-99 (Pb9Cu(PO4)6O:Cu<Pb(1)>). In
contrast, the other four parent compounds exhibit insulating behavior with wide
band gaps. X-ray diffraction spectra based on the DFT simulations at 0K confirm
the presence of Cu substitution on Pb(1) sites in the originally synthesized
LK-99 sample, while an extra peak suggests potential alternative like
Pb8Cu2(PO4)6 phases due to compositional variations in the original LK-99
samples. Furthermore, the LK-99 structure undergoes substantial lattice
constriction, resulting in a significant 5.5% reduction in volume and 6.8% in
area of two mutually inverted triangles formed by Pb(2) atoms. Meanwhile,
energy calculations reveal a marginal energy preference for substituting Cu on
Pb(2) sites over Pb(1) sites, with a difference of approximately 0.010 eV per
atom (roughly 0.9645 k/mol). Intriguingly, at pressures exceeding 73 GPa,
stability shifts towards LK-99 containing Cu substitutions on Pb(1) sites.
Despite exhibiting higher electronic conductivity than parent compounds,
Pb9Cu(PO4)6O:Cu<Pb(1)> falls short of the conductivity levels observed in
metals or advanced oxide conductors with the simulation based on the Boltzmann
transport theory.",2308.13938v2
2023-09-14,"Discovery of a novel 1,3,4-oxadiazol-2-one-based NLRP3 inhibitor as a pharmacological agent to mitigate cardiac and metabolic complications in an experimental model of diet-induced metaflammation","Inspired by the recent advancements in understanding the binding mode of
sulfonylurea-based NLRP3 inhibitors to the NLRP3 sensor protein, we developed
new NLRP3 inhibitors by replacing the central sulfonylurea moiety with
different heterocycles. Computational studies evidenced that some of the
designed compounds were able to maintain important interaction within the NACHT
domain of the target protein similarly to the most active sulfonylurea-based
NLRP3 inhibitors. Among the studied compounds, the 1,3,4-oxadiazol-2-one
derivative 5 (INF200) showed the most promising results being able to prevent
NLRP3-dependent pyroptosis triggered by LPS/ATP and LPS/MSU by 66.3 +/- 6.6%
and 61.6 +/- 11.5% and to reduce IL-1\b{eta} release (35.5 +/- 8.8 % {\mu}M) at
10 {\mu}M in human macrophages. The selected compound INF200 (20 mg/kg/day) was
then tested in an in vivo rat model of high-fat diet (HFD)-induced
metaflammation to evaluate its beneficial cardiometabolic effects. INF200
significantly counteracted HFD-dependent ""anthropometric"" changes, improved
glucose and lipid profiles, and attenuated systemic inflammation and biomarkers
of cardiac dysfunction (particularly BNP). Hemodynamic evaluation on
Langendorff model indicate that INF200 limited myocardial damage-dependent
ischemia/reperfusion injury (IRI) by improving post-ischemic systolic recovery
and attenuating cardiac contracture, infarct size, and LDH release, thus
reversing the exacerbation of obesity-associated damage. Mechanistically, in
post-ischemic hearts, IFN200 reduced IRI-dependent NLRP3 activation,
inflammation, and oxidative stress. These results highlight the potential of
the novel NLRP3 inhibitor, INF200, and its ability to reverse the unfavorable
cardio-metabolic dysfunction associated with obesity.",2309.07939v1
2023-09-24,Nutritional composition and bioactive compounds of mini watermelon genotypes in Bangladesh,"Given the present rising trends in changing lifestyle and consumption
patterns, watermelon production has shifted from big to small-sized fruits
having desirable quality attributes. Hence, analyses of fruit quality traits of
mini watermelon are crucial to develop improved cultivars with enhanced
nutritional compositions, consumer-preferred traits and extended storage life.
In this context, fruit morphological and nutritional attributes of five mini
watermelon genotypes namely BARI watermelon 1 (W1), BARI watermelon 2 (W2),
L-32468 (W3), L-32236 (W4) and L-32394 (W5) were evaluated to appraise
promising genotypes with better fruit quality. The evaluated genotypes
expressed different levels of diversity for fruit physical qualitative traits
including differences in shape, rind and flesh color and texture. The study
also revealed significant variability among the genotypes regarding all
observed fruit morphological and nutritional aspects as well as bioactive
compounds. Among the studied genotypes, W1 stood out with the highest TSS as
well as rind vitamin C and total phenolic content accompanied by higher fruit
weight and thick rind. On the other hand, W3 genotype was featured with higher
amount of \b{eta} carotene, total phenolic and flavonoid content in its flesh
along with rind enriched with \b{eta} carotene and minerals. However,
comparatively higher amount of sugar and total flavonoid content was recorded
in the rind of W5 genotype. Therefore, W1 and W3 could be exploited for table
purpose and using in breeding program to develop mini watermelon cultivars with
more attractive fruits in terms of quality acceptance and nutritional value in
Bangladesh. Furthermore, rind of BARI watermelon 1 and L-32394 could be
considered as the potential cheap source of bioactive compounds to be used for
dietary and industrial purpose which would decrease the solid waste in the
environment.",2309.13565v1
2023-10-16,Electronic Transport and Fermi Surface Topology of Zintl phase Dirac Semimetal SrZn2Ge2,"We report a comprehensive study on the electronic transport properties of
SrZn$_2$Ge$_2$ single crystals. The in-plane electrical resistivity of the
compound exhibits linear temperature dependence for 80 K < T < 300 K, and T^2
dependence below 40 K, consistent with the Fermi liquid behavior. Both the
transverse and longitudinal magnetoresistance exhibit a crossover at critical
field B* from weak-field quadratic-like to high-field unsaturated linear field
dependence at low temperatures (T \leq 50 K). Possible sources of linear
magnetoresistance are discussed based on the Fermi surface topology, classical
and quantum transport models. The Hall resistivity data establish
SrZn$_2$Ge$_2$ as a multiband system with contributions from both the electrons
and holes. The Hall coefficient is observed to decrease with increasing
temperature and magnetic field, changing its sign from positive to negative.
The negative Hall coefficient observed at low temperatures in high fields and
at high temperatures over the entire field range suggests that the highly
mobile electron charge carriers dominate the electronic transport. Our
first-principles calculations show that nontrivial topological surface states
exist in SrZn$_2$Ge$_2$ within the bulk gap along the {\Gamma}-M path. Notably,
these surface states extend from the valence to conduction band with their
number varying based on the Sr and Ge termination plane. The Fermi surface of
the compound exhibits a distinct tetragonal petal-like structure, with one open
and several closed surfaces. Overall, these findings offer crucial insights
into the mechanisms underlying the electronic transport of the compound.",2310.10621v2
2023-10-26,"Bridgman-grown (Cd,Mn)Te and (Cd,Mn)(Te,Se): A comparison of suitability for X and gamma detectors","This study explores the suitability of semi-insulating compounds,
specifically (Cd,Mn)Te and (Cd,Mn)(Te,Se), as materials for room temperature
X-ray and gamma-ray detectors. These compounds were grown using the Bridgman
method, known for its efficient growth rate. The investigation aims to compare
their crystal structure, mechanical properties, optical characteristics, and
radiation detection capabilities. The addition of selenium to (Cd,Mn)Te
increased the compound's hardness. However, (Cd,Mn)(Te,Se) exhibited one order
of magnitude higher etch pit density compared to (Cd,Mn)Te. Photoluminescence
analysis at low temperatures revealed the presence of defect states in both
materials, characterized by shallow and deep donor-acceptor pair transitions
(DAP). Annealing in cadmium vapors effectively eliminated DAP luminescence in
(Cd,Mn)Te but not in (Cd,Mn)(Te,Se). Spectroscopic performance assessments
indicated that the (Cd,Mn)Te detector outperformed the (Cd,Mn)(Te,Se) detector
in responding to a Co-57 source. The reduced performance in the latter case may
be attributed to either the presence of a deep trap related to deep DAP
luminescence, minimally affected by annealing, or the dominant presence of
block-like structures in the samples, as indicated by X-ray diffraction
measurements. The block-like structures in (Cd,Mn)(Te,Se) showed ten times
larger misorientation angles compared to the (Cd,Mn)Te crystals. (Cd,Mn)Te
crystal revealed excellent single crystal properties, demonstrated by narrower
omega scan widths. The study also highlights the influence of grain boundaries
and twins on crystal structure quality. In our opinion, Bridgman-grown
(Cd,Mn)Te shows greater promise as a material for X-ray and gamma-ray detectors
compared to (Cd,Mn)(Te,Se).",2310.17231v1
2023-11-21,Laser-induced Demagnetization in van der Waals $XY$- and Ising-like Antiferromagnets NiPS$_3$ and FePS$_3$,"The critical behaviour of laser-induced changes in magnetic ordering is
studied experimentally in two-dimensional zigzag antiferromagnets $XY$-like
NiPS$_3$ and Ising-like FePS$_3$. To examine laser-induced dynamics in flakes
of these compounds, we employ time-resolved exchange linear dichroism effect
sensitive to zigzag magnetic ordering and independent of the orientation of the
antiferromagnetic vector. In both compounds laser excitation in the vicinity of
the absorption edge induces partial quenching of the antiferromagnetic ordering
manifested by exchange linear dichroism reduction. The amplitude of the effect
varies with temperature as the derivative of the antiferromagnetic vector and
exhibits a critical behaviour with the exponents corresponding to $XY$- and
Ising-models for NiPS$_3$ and FePS$_3$, respectively. Critical slowing down of
the demagnetization in the vicinity of N\'eel temperature is found, however,
only in FePS$_3$. In contrast, the increase of the demagnetization time near
the ordering temperature in NiPS$_3$ is minor. We show that the difference in
the demagnetization times correlates well with the spin specific heat in both
compounds. Beyond the range of slowing down, the demagnetization times in
NiPS$_3$ and FePS$_3$ are comparable, about 5 - 10 ps, and are longer than
those reported earlier for CoPS$_3$ and considerably shorter than for MnPS$_3$.
This points to the importance of the unquenched angular momentum of
transition-metal ions in laser-induced demagnetization process.",2311.12505v2
2024-01-20,"A family of rare-earth Quasi-One-Dimensional spin-chain compounds K2RENb5O15 (RE=Ce,Pr,Nd,Sm,Gd-Ho) with large interchain distance","One-dimensional spin chain systems have received special attention to
discover the novel magnetic ground states and emergent phenomena, while the
magnetic studies on rare-earth (RE)-based 1D spin chain materials are still
rare. Here, we report the synthesis, structure and magnetic behaviors on a
family of tetragonal tungsten-bronze structure K2RENb5O15 (RE = Ce, Pr, Nd, Sm,
Gd-Ho) compounds, which consist of 1D linear spin-chain structure built by RE3+
ions along the c-axis and well spatially separated by the nonmagnetic K/Nb-O
polyhedrons with large interchain distances of ~ 8.80-8.88 {\AA} in the
ab-plane. The low temperature magnetic measurements reveal the absence of
long-range magnetic order down to 1.8 K for all serial K2RENb5O15 compounds and
the dominant ferromagnetic interactions for RE=Ce,Dy and antiferromagnetic
interactions for other members. Among them, K2GdNb5O15 with spin only magnetic
moment S=7/2, exhibits a long-range magnetic order with TN~0.31 K and strong
spin fluctuations at low temperatures due to its low-dimension characteristics.
Moreover, a large magnetocaloric effect under low field change of 0-2 T is
realized at temperatures below 1 K for K2GdNb5O15, letting it as an ideal
candidate for adiabatic magnetic refrigeration applications at sub-kelvin
temperatures. The K2RENb5O15 become a rare family of insulting RE-based magnets
to explore the novel 1D spin chain physics beyond the 3d TM-based counterparts,
in terms of its combination of low dimension, strong spin-orbital coupling and
the rich diversity of RE ions.",2401.11091v1
2024-02-27,Magnetocaloric performance of RE$_{5}$Pd$_2$In$_4$ (RE = Tb-Tm) compounds,"Magnetocaloric performance of the RE$_{5}$Pd$_2$In$_4$ (RE = Tb-Tm) rare
earth compounds has been investigated using measurements of magnetization in
the function of temperature and applied magnetic field. The maximum magnetic
entropy change ($-\Delta S_{M}^{max}$) at magnetic flux density change ($\Delta
\mu_0 H$) of 0-9~T has been determined to be 3.3~J$\cdot$kg$^{-1}\cdot$K$^{-1}$
at 62~K for Tb$_{5}$Pd$_2$In$_4$, 7.0~J$\cdot$kg$^{-1}\cdot$K$^{-1}$ at 22~K
for Dy$_{5}$Pd$_2$In$_4$, 12.6~J$\cdot$kg$^{-1}\cdot$K$^{-1}$ at 22~K for
Ho$_{5}$Pd$_2$In$_4$, 12.1~J$\cdot$kg$^{-1}\cdot$K$^{-1}$ at 17~K for
Er$_{5}$Pd$_2$In$_4$ and 11.9~J$\cdot$kg$^{-1}\cdot$K$^{-1}$ at 9.0~K for
Tm$_{5}$Pd$_2$In$_4$. The temperature averaged entropy change (TEC) with 3~K
span equals 3.2, 7.0, 12.6, 12.2 and 11.8~J$\cdot$kg$^{-1}\cdot$K$^{-1}$ for RE
= Tb-Tm, respectively. The relative cooling power (RCP) and refrigerant
capacity (RC) are equal to respectively 258 and 215~J$\cdot$kg$^{-1}$ in
Tb$_{5}$Pd$_2$In$_4$, 498 and 325~J$\cdot$kg$^{-1}$ in Dy$_{5}$Pd$_2$In$_4$,
489 and 403~J$\cdot$kg$^{-1}$ in Ho$_{5}$Pd$_2$In$_4$, 403 and
314~J$\cdot$kg$^{-1}$ in Er$_{5}$Pd$_2$In$_4$ and 234 and 184~J$\cdot$kg$^{-1}$
in Tm$_{5}$Pd$_2$In$_4$. The magnetocaloric properties of RE$_{5}$Pd$_2$In$_4$
are comparable to those of other known magnetocaloric materials, which show
good magnetocaloric performance at low temperatures. Among
RE$_{5}$Pd$_2$In$_4$, the highest values of parameters characterizing the
magnetocaloric effect are found for RE = Ho and Er. Furthermore, for fixed RE
element, the RE$_{5}$Pd$_2$In$_4$ compound displays the highest RCP and RC
values when compared to those of its isostructural RE$_{5}$T$_2$In$_4$ (T = Ni,
Pt) analogues.",2402.17912v1
2024-03-04,Molecular intercalation in the van der Waals antiferromagnets FePS3 and NiPS3,"We have performed electrochemical treatment of the van der Waals
antiferromagnetic materials FePS$_3$ and NiPS$_3$ with the ionic liquid
EMIM-BF$_4$, achieving significant molecular intercalation. Mass analysis of
the intercalated compounds, EMIM$_x$-FePS$_3$ and EMIM$_x$-NiPS$_3$, indicated
respective intercalation levels, $x$, of approximately 27\% and 37\%, and X-ray
diffraction measurements demonstrated a massive (over 50\%) enhancement of the
$c$-axis lattice parameters. To investigate the consequences of these changes
for the magnetic properties, we performed magnetic susceptibility and $^{31}$P
nuclear magnetic resonance (NMR) studies of both systems. For
EMIM$_x$-FePS$_3$, intercalation reduces the magnetic ordering temperature from
$T_N = 120$~K to 78~K, and we find a spin gap in the antiferromagnetic phase
that drops from 45~K to 30~K. For EMIM$_x$-NiPS$_3$, the ordering temperature
is almost unaffected (changing from 148~K to 145~K), but a change towards
nearly isotropic spin fluctuations suggests an alteration of the magnetic
Hamiltonian. Such relatively modest changes, given that the huge extension of
the $c$ axes is expected to cause a very strong suppression any interlayer
interactions, point unequivocally to the conclusion that the magnetic
properties of both parent compounds are determined solely by two-dimensional
(2D), intralayer physics. The changes in transition temperatures and
low-temperature spin dynamics in both compounds therefore indicate that
intercalation also results in a significant modulation of the intralayer
magnetic interactions, which we propose is due to charge doping and
localization on the P sites. Our study offers chemical intercalation with ionic
liquids as an effective method to control not only the interlayer but also the
intralayer interactions in quasi-2D magnetic materials.",2403.01714v1
2024-03-13,"Room temperature charge density wave in a tetragonal polymorph of Gd2Os3Si5 and study of its origin in the R2T3X5 (R = Rare earth, T = transition metal, X = Si, Ge) series","Charge density wave (CDW) systems are proposed to exhibit application
potential for electronic and optoelectronic devices. Therefore, identifying new
materials that exhibit a CDW state at room temperature is crucial for the
development of CDW-based devices. Here, we present a non-layered tetragonal
polymorph of Gd2Os3Si5, which exhibits a CDW state at room temperature.
Gd2Os3Si5 crystallizes in the U2Mn3Si5-type tetragonal crystal structure with
the space group P4/mnc. Single-crystal x-ray diffraction (SXRD) analysis shows
that Gd2Os3Si5 possesses an incommensurately modulated structure with
modulation wave vector q = (0.53, 0, 0), while the modulation reduces the
symmetry to orthorhombic Cccm({\sigma}00)0s0. This differs in contrast to
isostructural Sm2Ru3Ge5, where the modulated phase has been reported to possess
the superspace symmetry Pm({\alpha} 0 {\gamma})0. However, reinvestigation of
Sm2Ru3Ge5 suggests that its modulated crystal structure can alternatively be
described by Cccm({\sigma}00)0s0, with modulations similar to Gd2Os3Si5. The
magnetic susceptibility, \c{hi}(T), exhibits a maximum at low temperatures that
indicates an antiferromagnetic transition at TN = 5.5 K. The \c{hi}(T)
furthermore shows an anomaly at around 345 K, suggesting a CDW transition at
TCDW = 345 K, that corroborates the result from high-temperature SXRD
measurements. Interestingly, R2T3X5 compounds are known to crystallize either
in the tetragonal Sc2Fe3Si5 type structure or in the orthorhombic U2Co3Si5
structure type. Not all of the compounds in the R2T3X5 series undergo CDW phase
transitions. We find that R2T3X5 compounds will exhibit a CDW transition, if
the condition : 0.526 < c/sqrt(ab) < 0.543 is satisfied. We suggest the wave
vector-dependent electron-phonon coupling to be the dominant mechanism of CDW
formation in the tetragonal polymorph of Gd2Os3Si5.",2403.08660v1
2024-03-21,Pressure-induced enhancement of superconductivity in a non-centrosymmetric compound LaPtGe,"We report a pressure-induced enhancement of the superconducting transition
temperature (Tc) in a non-centrosymmetric (NCS) compound, LaPtGe. With
pressure, till 3 GPa, we observed a modest enhancement of the Tc with a rate of
0.071 K/GPa. However, above this pressure, the rate showed a ~2.5 times
increase, 0.183 K/GPa. We observed a Tc of 3.94 K at 6 GPa, the highest
pressure value used in our transport study. Synchrotron high-pressure x-ray
powder diffraction (HP-XRPD) measurements do not reveal any structural phase
transition in this system in this pressure range. However, it showed an
apparent change of slope in the pressure dependence of lattice parameters above
and below 3 GPa. Pressure dependence of the unit-cell volume also followed a
distinct trend below and above 3 GPa, with the Birch-Murnaghan equation of
state fit providing a bulk modulus (B0) value of ~144 and ~162 GPa,
respectively, for two pressure regions. Further, the magnetotransport
measurement under pressure up to 2.45 GPa reveals the enhancement of the upper
critical field (Hc2(0)) from 0.7 T (0 GPa) to 0.92 T (2.45 GPa). In addition,
the upward curvature in Hc2(T) becomes stronger with increasing pressure,
suggesting a change of the underlying Fermi surface topology with pressure. The
signature for the inducible Hc2(T) with pressure, the distinct enhancement of
Tc around 3 GPa, and the noticeable change in lattice parameters around 3 GPa
suggests the possibility of multi-gap superconductivity in LaPtGe similar to
identical structure NCS compound, LaPtSi. The enhancement of Tc by pressure can
be correlated with the possible underlying lattice modulation by compression
and the change in the density of states at the Fermi level. Also, the bare
change in pressure-dependent activation energy U0 up to 2.45 GPa calculated
using the Arrhenius relation clearly shows that the shift in Tc does not arise
from grain boundaries.",2403.14568v1
2024-04-03,Unraveling the Mn $L_3$-edge RIXS spectrum of lightly manganese doped Sr$_{3}$Ru$_{2}$O$_{7}$,"Resonant inelastic x-ray scattering (RIXS) experiment was performed at the Mn
$L_3$ edge. A 10 $\%$ Mn-doped Sr$_{3}$Ru$_{2}$O$_{7}$ compound, where the
Mn$^{3+}$ ions are in the 3$d^4$ state, were probed for $dd$ excitations. The
dilute doping concentration allows one to treat the dopant Mn$^{3+}$ ions as
effectively free in the host ruthenium compound. The local nature of $dd$ RIXS
spectroscopy permits one to use a single-site model to simulate the
experimental spectra. The simulated spectra reproduces the in-plane [100]
experimental RIXS spectrum. We also predict the intensity for the in-plane
[110] direction and the out-of-plane spin orientation configuration [001].
Based on our single-ion model we were able to fit the experimental data to
obtain the crystal field parameters, the 10Dq value, and the intra-orbital
spin-flip energy 2$\mathcal{J}$(or $3J_{H}$, where $J_{H}$ is the Hund's
energy) of the Mn$^{3+}$ ion. Utilizing our computed RIXS quantum transition
amplitudes between the various $d$ orbitals of the Mn$^{3+}$ ion, the
expression for the Kramers-Heisenberg cross section, and a self-consistent
fitting procedure we also identify the energy boundaries of the non-spin-flip
and spin-flip $dd$ excitations present in the experimental data. From our
fitting procedure we obtain $2\mathcal{J} (3J_{H})=2.06$ eV, a value which is
in excellent agreement with that computed from the free ion Racah parameters.
We also identified the charge transfer boundary. In addition to predicting the
microscopic parameters, we find a quantum spin-flip transition in the non-cross
($\sigma_{in}-\sigma_{out}$, $\pi_{in}-\pi_{out}$) x-ray polarization channels
of the $dd$ RIXS spectra. A similar transition, was previously predicted to
occur in the $\pi-\pi$ channel of the magnon spectrum in the non-collinear
non-coplanar Kagome compound composed of Cu$^{2+}$ 3d$^{9}$ ion.",2404.02963v1
2002-01-31,Photochemical model of impact-produced lunar atmosphere,"The Lunar Prospector mission detected hydrogen-containing compounds in the
lunar polar regions. We have considered the comet hypothesis of the origin of
polar volatiles on the Moon. In the present paper we use our model of a comet
impact with photochemical processes to be included to estimate chemical
composition of volatiles which can be captured by the cold traps.",0201546v1
1994-06-07,Statistical Augmentation of a Chinese Machine-Readable Dictionary,"We describe a method of using statistically-collected Chinese character
groups from a corpus to augment a Chinese dictionary. The method is
particularly useful for extracting domain-specific and regional words not
readily available in machine-readable dictionaries. Output was evaluated both
using human evaluators and against a previously available dictionary. We also
evaluated performance improvement in automatic Chinese tokenization. Results
show that our method outputs legitimate words, acronymic constructions, idioms,
names and titles, as well as technical compounds, many of which were lacking
from the original dictionary.",9406015v1
1997-10-10,Use of Weighted Finite State Transducers in Part of Speech Tagging,"This paper addresses issues in part of speech disambiguation using
finite-state transducers and presents two main contributions to the field. One
of them is the use of finite-state machines for part of speech tagging.
Linguistic and statistical information is represented in terms of weights on
transitions in weighted finite-state transducers. Another contribution is the
successful combination of techniques -- linguistic and statistical -- for word
disambiguation, compounded with the notion of word classes.",9710001v1
1993-12-21,Magnetic Properties of the Spin-1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic Trimerized Heisenberg Chain:,"The magnetic properties of the ferromagnetic-ferromagnetic-antiferromagnetic
trimerized spin-1/2 Heisenberg chain are studied theoretically. The high
temperature susceptibilty and the ground state saturation magnetic field are
calculated and the exchange energies of the trimer compound 3CuCl${}_2\cdot$2dx
are determined. The magnetization curve is obtained by numerical
diagonalization of finite size systems. The result explains the low temperature
magnetization data for 3CuCl${}_2\cdot$2dx with the exchange energies obtained
as above. It is predicted that the magnetization curve has a plateau at 1/3 of
the saturation magnetization if the ferromagnetic exchange energy is comparable
to or smaller than the antiferromagnetic exchange energy.",9312084v1
1994-06-02,Inelastic Neutron Scattering from the Spin Ladder Compound (VO)2P2O7,"We present results from an inelastic neutron scattering experiment on the
candidate Heisenberg spin ladder vanadyl pyrophosphate, (VO)2P2O7. We find
evidence for a spin-wave excitation gap of $E_{gap} = 3.7\pm 0.2$ meV, at a
band minimum near $Q=0.8 A^{-1}$. This is consistent with expectations for
triplet spin waves in (VO)2P2O7 in the spin-ladder model, and is to our
knowledge the first confirmation in nature of a Heisenberg antiferromagnetic
spin ladder.",9406016v1
1994-06-10,Phase transitions in BaTiO$_3$ from first principles,"We develop a first-principles scheme to study ferroelectric phase transitions
for perovskite compounds. We obtain an effective Hamiltonian which is fully
specified by first-principles ultra-soft pseudopotential calculations. This
approach is applied to BaTiO$_3$, and the resulting Hamiltonian is studied
using Monte Carlo simulations. The calculated phase sequence, transition
temperatures, latent heats, and spontaneous polarizations are all in good
agreement with experiment. The order-disorder vs.\ displacive character of the
transitions and the roles played by different interactions are discussed.",9406049v1
1994-09-28,Magnetic properites of the Heavy Fermion Antiferromagnets YbNiAl and YbPtAl,"Measurements of electrical resistivity and Hall effect as a function of
magnetic field on the Heavy Fermion Systems YbNiAl and YbPtAl are presented.
Both compounds order antiferro magnetically and show metamagnetic behavior in a
magnetic field. Scaling behavior of the magnetoresistance above TN suggests
that the paramagnetic regime for YbNiAl can be described in terms of a single
ion Kondo effect.",9409115v1
1994-10-28,Interplane relaxation and the bilayer coupling in Y$_2$Ba$_4$Cu$_7$O$_{15}$,"The origin of the spin gap in the underdoped cuprate superconductors is still
mysterious. Experimental evidence from neutron scattering and NMR experiments
indicates that the spin gap might be present only in the bilayer compounds. A
naive calculation for a two plane Heisenberg model locates the order-disorder
transition only for very large exchange coupling between the bilayers. We
propose a interplane relaxation experiment which might quantitatively estimate
the strength of the bilayer coupling. We make detailed predictions for the size
and the temperature dependence of the interplane relaxation rate.",9410108v1
1994-01-04,Study of the magnetic susceptibility in the spin-Peierls system CuGeO$_3$,"We study numerically, using a one-dimensional Heisenberg model, the
spin-Peierls transition in the linear Cu$^{2+}$ spin-1/2 chains in the
inorganic compound CuGeO$_3$ which has been recently observed experimentally.
We suggest that the magnetic susceptibility, the temperature dependence of the
spin gap and the spin-Peierls transition temperature of this material can be
reasonably described by including nearest and next nearest neighbor
antiferromagnetic interactions along the chain. We estimate that the nearest
neighbor exchange parameter J is approximately $160\:\rm K$, and that the next
nearest neighbor exchange parameter is approximately $0.36\:\rm J$.",9412093v1
1995-01-25,Spectral weight function for the half-filled Hubbard model: a singular value decomposition approach,"The singular value decomposition technique is used to reconstruct the
electronic spectral weight function for a half-filled Hubbard model with
on-site repulsion $U=4t$ from Quantum Monte Carlo data. A two-band structure
for the single-particle excitation spectrum is found to persist as the lattice
size exceeds the spin-spin correlation length. The observed bands are flat in
the vicinity of the $(0,\pi),(\pi,0)$ points in the Brillouin zone, in
accordance with experimental data for high-temperature superconducting
compounds.",9501119v1
1995-05-11,ELECTRONIC STATES IN GRADED-GAP JUNCTIONS WITH BAND INVERSION,"We theoretically study electronic states in graded-gap junctions of IV-VI
compounds with band inversion. Using a two-band model within the ${\bf
k}\cdot{\bf p}$ approximation and assuming that the gap and the gap centre
present linear profiles, we demonstrate the existence of a set of localized
states along the growth direction with a discrete energy spectrum. The envelope
functions are found to be combination of harmonic oscillator eigenfunctions,
and the corresponding energy levels are proportional to the square root of the
quantum number. The level spacing can be directly controlled by varying the
structure thickness.",9505045v1
1995-07-24,Double Degeneracy and Jahn-Teller Effects in CMR Perovskites,"Jahn-Teller (JT) electron-phonon coupling effects in the colossal
magnetoresistance perovskite compounds $La_{1-x}A_xMnO_3$ are investigated.
Electron-electron correlations between two degenerate Mn $e_g$ orbitals are
studied in the Gutzwiller approximation. The static JT distortion and
antiadiabatic polaron effects are studied in a modified Lang-Firsov
approximation. We find that (i) the electron or hole character of the charge
carrier depends on the static JT distortion, and (ii) due to the two-component
nature of the JT coupling, fluctuations in the JT distortion direction
contribute to the charge transport in similar fashion as the local spins.",9507097v1
1995-08-16,Spin Dynamics of Hole Doped ${\rm Y_{2-x} Ca_x Ba Ni O_5}$,"We propose an electronic model for the recently discovered hole doped
compound ${\rm Y_{2-x} Ca_x Ba Ni O_5 }$. From a multiband Hamiltonian with
oxygen and nickel orbitals, a one band model is derived. Holes are described
using Zhang-Rice-like S=1/2 states at the nickels propagating on a S=1 spin
chain. Using numerical techniques to calculate the dynamical spin structure
factor ${\rm S(q,\omega)}$ in a realistic regime of couplings, spectral weight
in the Haldane gap is observed in agreement with neutron scattering data. Low
energy states with S=3/2 appear in the model. Several predictions are made to
test these ideas.",9508061v1
1995-08-21,Two--magnon scattering and the spin--phonon interaction beyond the adiabatic approximation,"We consider a model of Raman scattering for a two--dimensional $S=1/2$
Heisenberg Anti-Ferromagnet which includes a {\it dynamical} spin--phonon
interaction. We observe a broadening of the line shape due to increased
coupling with excited high--energy spin states. Our results are close to a
model of random static exchange interactions, first introduced in this context
by Haas {\it et al.} [J. Appl. Phys. {\bf 75}, 6340, (1994)], which, when
extended to large numbers of spins, explains experiments in the parent
insulating compounds of high-$T_c$ superconductors.",9508089v1
1995-09-15,Transition temperature and a spatial dependence of the superconducting gap for multilayer high-temperature superconductors,"We derive the expressions for the transition temperature $(T_{c})$, and the
spatial dependence of the superconducting gap for a multilayer high-$T_{c}$
superconductor composed of groups of tightly spaced planes separated by a
larger distance. The results are compared with experiment and provide a strong
support for an interlayer hopping as the driving force of the large $T_{c}$
enhancement in multilayered compounds. Our results are universal in the sense
that they are valid for an arbitrary pairing potential $V_{\bf k k'}$ in the
$\rm CuO_{2}$ planes, as well as for both Fermi and nonFermi liquids.",9509093v1
1995-10-06,Magnetic excitations and effects of magnetic fields on the spin-Peierls transition in CuGeO$_3$,"We analyze the magnetic excitations of a spin-1/2 antiferromagnetic
Heisenberg model with alternating nearest neighbor interactions and uniform
second neighbor interactions recently proposed to describe the spin-Peierls
transition in CuGeO$_3$. We show that there is good agreement between the
calculated excitation dispersion relation and the experimental one. We have
also shown that this model reproduces satisfactorily the experimental results
for the magnetization vs. magnetic field curve and its saturation value. The
model proposed also reproduces qualitatively some features of the magnetic
phase diagram of this compound and the overall behavior of the magnetic
specific heat in the presence of applied magnetic fields.",9509160v1
1995-11-07,Influence of frustration on a d=3 diluted antiferromagnet: $Fe_{x}Zn_{1-x}F_{2}$,"The influence of a frustrated bond on the magnetic properties of a d=3
uniaxial (Ising) b.c.c. diluted antiferromagnet, with emphasis in the compound
$Fe_{x}Zn_{1-x}F_{2}$, is investigated by a local mean-field numerical
simulation. In particular we find that the initial drop of the saturation
staggered magnetization ($M_{S}$) with concentration follows a percolation-like
phenomenon characterized by an exponent $\beta_{p}$. For the frustrated
samples, however, this regime is followed by a second one identified by a
``long tail"" effect such that $M_{S}$ is zero only at the percolation
threshold. Our numerical data also confirms a spin-glass phase near this
threshold.",9511036v1
1995-11-22,Static properties of a quasi one-dimensional antiferromagnet in magnetic field,"We calculate the effect of zero-point fluctuations on the magnetostatic
properties of a quasi one-dimensional antiferromagnetic helimagnet with and
without in-plane anisotropy. We find substantial reduction of the uniform
susceptibility and the sublattice magnetization from their classical values and
appreciable renormalization of the spin-flop field at $T=0$. The magnetization
curve varies nonlinearly at small fields and is described by a universal
formula at high fields. The results are compared with numerical simulations on
one-dimensional systems and measurements in the CsNiCl$_3$-type compounds.",9511106v1
1996-03-31,Linear and nonlinear optical characteristics of the Falicov-Kimball model,"We calculate the linear and nonlinear optical properties of the
Falicov-Kimball model for a mixed-valent system within the self-consistent
mean-field approximation. Second-harmonic generation can only occur if the
mixed-valent state has a built-in coherence between the itinerant d-electrons
and the localized f-holes. By contrast, second-harmonic generation cannot occur
for solutions of the model with f-site occupation as a good quantum number. As
an experimental test of coherence in mixed-valent compounds we propose a
measurement of the dynamic second-order susceptibility.",9603202v1
1996-04-23,Two-dimensional S=1/2 antiferromagnet on a plaquette lattice,"We consider a simplified model of the magnetic structure of the
two-dimensional compound $CaV_4O_9$ in terms of interacting square plaquettes
of spins with two distinct antiferromagnetic exchange constants. We analyze the
competition between two types of singlet ground states and the Neel ordered one
in terms of respectively, numerical cluster expansion and nonlinear spin wave
theory. The resulting phase diagram agrees well with known Quantum Monte Carlo
results and suggests a first order transition between ordered and singlet
ground states as a function of the exchange constants.",9604145v1
1996-05-01,Fluctuation Effects And Order Parameter Symmetry In The Cuprate Superconductors,"Effect of phase fluctuations on superconducting states with anisotropic order
parameters is studied in a BCS like lattice model of cuprate superconductors.
The degradation of the mean field transition temperature due to phase
fluctuations is estimated within a Kosterlitz-Thouless scenario. Values of the
interaction parameters for optimal doping, corresponding to a stable
superconducting state of $S_{xy}$ symmetry, which fit the nodal structure of
the superconducting order parameter in the Bi2212 compound, are obtained. The
angular position of the node is found to be insensitive to the dopant
concentration.",9604192v1
1996-06-12,Electronic and Magnetic States in the Giant Magneto-resistive Compounds,"The paramagnetic insulator to ferromagnetic metal transition in Lanthanum
manganites and the associated magnetoresistive phenomena is treated by
considering the localization due to random hopping induced by slowly
fluctuating spin configurations and electron-electron interactions. The
transition temperature and its variation with composition is derived. The
primary effect of the magnetic field on transport is to alter the localization
length, an effect which is enhanced as the magnetic susceptibility increases.
Expressions for the conductivity, its variation with magnetic field, and its
connection with magnetic susceptibility in the paramagnetic phase are given and
can be tested with further experiments.",9606086v1
1996-07-30,Non-magnetic impurities in two- and three- dimensional Heisenberg antiferromagnets,"In this paper we study in a large-S expansion effects of substituting spins
by non-magnetic impurities in two- and three- dimensional Heisenberg
antiferromagnets in a weak magnetic field. In particular, we demonstrate a
novel mechanism where magnetic moments are induced around non-magnetic
impurities when magnetic field is present. As a result, Curie-type behaviour in
magnetic susceptibility can be observed well below the Neel temperature, in
agreement with what is being observed in $La_2Cu_{1-x}Zn_{x}O_4$ and
$Sr(Cu_{1-x}Zn_x)_2O_3$ compounds.",9607213v1
1996-08-01,Quantum corrections to the conductivity of fermion - gauge field models: Application to half filled Landau level and high-$T_c$ superconductors,"We calculate the Altshuler-Aronov type quantum correction to the conductivity
of $2d$ charge carriers in a random potential (or random magnetic field)
coupled to a transverse gauge field. The gauge fields considered simulate the
effect of the Coulomb interaction for the fractional quantum Hall state at half
filling and for the $t-J$ model of high-$T_c$ superconducting compounds. We
find an unusually large quantum correction varying linearly or quadratically
with the logarithm of temperature, in different temperature regimes.",9608003v2
1996-08-08,Neutron Scattering Studies of Heavy Fermion Systems,"We review the results of recent studies of the elastic and inelastic neutron
scattering from a variety of heavy fermion compounds. This class of materials
exhibits a rich variety of ground states: antiferromagnetically ordered,
superconducting, semiconducting, and paramagnetic. Neutron scattering from
single crystals and powders has been a productive tool for probing the magnetic
order and fluctuations in all four cases. This review deals with work on UPt_3,
UPd_2Al_3, UNi_2Al_3, UNi_4B, CeNiSn, Y_{1-x}U_xPd_3, and UCu_{5-x}Pd_x.",9608046v1
1996-09-05,Temperature-dependent spin gap and singlet ground state in BaCuSi2O6,"Bulk magnetic measurements and inelastic neutron scattering were used to
investigate the spin-singlet ground state and magnetic gap excitations in
BaCuSi2O6, a quasi-2-dimensional antiferromagnet with a bilayer structure. The
results are well described by a model based on weakly interacting
antiferromagnetic dimers. A strongly temperature-dependent dispersion in the
gap modes was found. We suggest that the observed excitations are analogous to
magneto-excitons in light rare-earth compounds, but are an intrinsic property
of a simple Heisenberg Hamiltonian for the S=1/2 magnetic bilayer.",9609055v1
1996-09-27,Magnetoresistance in La(1-x)SrxCoO3 for 0.05 - x - 0.25,"The dc resistivity, magnetoresistance and magnetic susceptibility of
La(1-x)SrxCoO3 compounds have been investigated in the temperature range of 4K
to 300K for magnetic fields up to 7 T. In the doping range studied (0.05 - x -
0.25) the electronic properties of the material exhibit a crossover from
semiconducting to metallic behavior. The magnetoresistance is highest in the
semiconducting state. A correlation was found between the energy gap determined
from the dc conductivity and the energy scale identified from neutron
scattering data. The results are interpreted in terms of a double exchange
model.",9609274v1
1996-10-02,Non-magnetic impurities in S=1/2 spin-Peierls system and Heisenberg ladder systems,"In this paper we study the effect of non-magnetic impurities in spin-Peierls
system $CuGeO_3$ within the framework of non-linear sigma model plus
topological term. We show that local moments are induced in both the $Zn$-doped
and $Si$-doped $CuGeO_3$ compounds. Effective low energy theories for the
impurity-induced local moments are derived in both cases where interesting
differences between the two cases and between the $Zn$-doped Heisenberg
two-ladder system are pointed out. The low-energy physics of the $Zn$-doped
Heisenberg three-leg ladder system is also discussed.",9610016v1
1996-11-26,Phonon Anomalies Induced by Superconductivity,"We calculate the electronic polarizability in the superconducting state near
extremum vectors ${\vec Q}_0$ of the Fermi surface. A pole appears in the
polarizability at frequencies $\omega$ near the superconducting gap $2\Delta$
which leads to a sharp peak at $\omega$ just below $2 \Delta$ in the lattice
vibrations near ${\vec Q}_0$. A second order transition to a charge density
wave state below the superconducting transition is shown to be unlikely. The
results are compared with the recent inelastic neutron scattering measurements
in compounds, $ANi_2B_2C$, $A=Y$ or $Lu$.",9611212v2
1996-12-02,Spin dynamics of dimerized Heisenberg chains,"We study numerically the dimerized Heisenberg model with frustration
appropriate for the quasi-1D spin-Peierls compound CuGeO$_3$. We present
evidence for a bound state in the dynamical structure factor for any finite
dimerization $\delta$ and estimate the respective spectral weight. For the
homogeneous case ($\delta=0$) we show that the spin-wave velocity $v_s$ is
renormalized by the n.n.n. frustration term $\alpha$ as $v_s=\pi/2
J(1-b\alpha)$ with $b\approx1.12$",9612013v1
1997-01-09,Exact ground and excited states of frustrated antiferromagnets on the CaV_4O_9 lattice,"The experimental observation of a spin-gap in the antiferromagnetic spin-1/2
compound $CaV_4O_9$ has been attributed to the formation of a plaquette
resonating-valence-bond (PRVB) state in the underlying 1/5-depleted square
lattice. We construct a spin-1/2 model on the 1/5-depleted lattice for which
the PRVB state can be shown to be the exact ground state in a particular
parameter regime. In a subspace of this parameter regime, the first excited
state can be calculated exactly. In a different parameter regime, the dimer
state is shown to be the exact ground state.",9701058v2
1997-01-15,Spin dynamics of the spin-Peierls compound CuGeO_3 under magnetic field,"The magnetic field--driven transition in the spin-Peierls system CuGeO_3
associated with the closing of the spin gap is investigated numerically. The
field dependence of the spin dynamical structure factor (seen by inelastic
neutron scattering) and of the momentum dependent static susceptibility are
calculated. In the dimerized phase (H<H_c), we suggest that the strong field
dependence of the transverse susceptibility could be experimentally seen from
the low temperature spin-echo relaxation rate 1/T_{2G} or the second moment of
the NMR spectrum. Above H_c low energy spin excitations appear at
incommensurate wave vectors where the longitudinal susceptibility chi_{zz}(q)
peaks.",9701107v1
1997-02-12,Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors,"The flux-line lattice in the compound $ErNi_2B_2C$, which has a tendency to
ferromagnetic order in the a-b plane is studied with external magnetic field
direction close to the c-axis. We show the existence of an instability where
the direction of flux-lines spontaneously tilts away from that of the applied
field near the onset of ferromagnetic order. The enhanced fluctuations in the
flux lattice and the square flux lattice recently observed are explained and
further experiments suggested.",9702104v1
1997-02-13,Study of the Phase Diagram and the Tc Pressure Dependence for HgBaCuO Superconductors,"We apply a method recently derived based on the extended Hubbard Hamiltonian
and the BCS approach to obtain the superconducting critical temperature
dependence with carrier density for the HgBaCuO compounds. We show that this
procedure can be used to study pressure effect with the assumption that
pressure changes the supercondutor gap. The results reproduce well the
experimental data for the whole doping regime and the high and low pressure
dependence.",9702131v1
1997-02-24,Raman Scattering from Frustrated Quantum Spin Chains,"Magnetic Raman scattering from a frustrated spin-1/2 Heisenberg-chain is
considered with a focus on the uniform phase of the spin-Peierls compound
CuGeO_3. The Raman intensity is analyzed in terms of a Loudon-Fleury scattering
process using a spinless-fermion mean-field theory developed for the frustrated
spin-chain. A comparison to experimental data is presented and the frustration
and temperature dependence is studied. In good agreement with observed spectra
a broad inelastic four-spinon continuum is found at low temperatures above the
spin-Peierls transition. At high temperatures the intensity develops a
quasi-elastic line analogous to experiment.",9702210v1
1997-03-04,Magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9},"Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions,
we study the effect of iron disproportionation on the magnetic ordering, and
describe the first-order magnetic transition occurring in the perovskite
Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of
the exchange integrals for the antiferromagntic and ferromagnetic interactions,
in agreement with previous works on kindered compounds. Spin-wave theory yields
a magnon spectrum with a gapless antiferromagnetic mode together with two
gapped ferromagnetic ones.",9703044v1
1997-04-10,Magnetic Excitations in the S=1/2 Alternating Chain Compound (VO)_2P_2O_7,"Magnetic excitations in an array of (VO)_2P_2O_7 single crystals have been
measured using inelastic neutron scattering. Until now, (VO)_2P_2O_7 has been
thought of as a two-leg antiferromagnetic Heisenberg spin ladder with chains
running in the a-direction. The present results show unequivocally that
(VO)_2P_2O_7 is best described as an alternating spin-chain directed along the
crystallographic b-direction. In addition to the expected magnon with magnetic
zone-center energy gap \Delta = 3.1 meV, a second excitation is observed at an
energy just below 2\Delta. The higher mode may be a triplet two-magnon bound
state.",9704092v1
1997-05-12,Spontaneous polarization and piezoelectric constants of III-V nitrides,"The spontaneous polarization, dynamical Born charges, and piezoelectric
constants of the III-V nitrides AlN, GaN, and InN are studied ab initio using
the Berry phase approach to polarization in solids. The piezoelectric constants
are found to be up 10 times larger than in conventional III-V's and II-VI's,
and comparable to those of ZnO. Further properties at variance with those of
conventional III-V compounds are the sign of the piezoelectric constants
(positive as in II-VI's) and the very large spontaneous polarization.",9705105v2
1997-06-30,Anisotropy effects in a mixed quantum-classical Heisenberg model in two dimensions,"We analyse a specific two dimensional mixed spin Heisenberg model with
exchange anisotropy, by means of high temperature expansions and Monte Carlo
simulations. The goal is to describe the magnetic properties of the compound
(NBu_{4})_{2}Mn_{2}[Cu(opba)]_{3}\cdot 6DMSO\cdot H_{2}O which exhibits a
ferromagnetic transition at $T_{c}=15K$. Extrapolating our analysis on the
basis of renormalisation group arguments, we find that this transition may
result from a very weak anisotropy effect.",9706298v1
1997-07-17,Monte Carlo simulations of magnetovolume instabilities in anti-Invar systems,"We perform constant pressure Monte Carlo simulations of a spin-analogous
model which describes coupled spatial and magnetic degrees of freedom on an fcc
lattice. Our calculations qualitatively reproduce magnetovolume effects
observed in some rare earth manganese compounds, especially in the anti-Invar
material YMn2. These are a sudden collapse of the magnetic moment which is
connected with a huge volume change, and a largely enhanced thermal expansion
coefficient.",9707181v1
1997-07-25,Incommensurate spin fluctuations in the two-dimensional t-t'-U model,"Magnetic properties of the two-dimensional t-t'-U model are investigated by
studying the static spin magnetic susceptibility as a function of momentum for
various temperatures. The calculations are performed by means of the Composite
Operator Method in the static approximation. By increasing the value of the t'
parameter the magnetic scattering in the reciprocal space evolves to an
isotropic structure. It is shown that the results are in qualitative agreement
with the experimental situation observed in LSCO and YBCO compounds.",9707266v1
1997-09-09,Specific Heat of defects in the Haldane System Y_2BaNiO_5,"We calculate the specific heat of the antiferromagnetic spin-1 chain compound
Y_2BaNi_{1-x}Zn_xO_5 in the presence of a magnetic field. The low-energy
spectrum of a Heisenberg Hamiltonian, which includes realistic anisotropies,
has been solved using the density matrix renormalization group. The observed
Schottky anomaly is very well described by this theory. For large chains
($N>50$), contrary to previous interpretations of the specific heat data, we
find S=1/2 states. These results are thus also consistent with electron-
spin-resonance data for NENP.",9709111v1
1997-09-10,Observation of Spin Freezing in CaV4O9 and CaV2O5 by uSR,"We have performed muon spin relaxation and susceptibility measurements of
CaV_4O_9 and CaV_2O_5, systems in which spin gap-like behavior has been found.
We observe spin freezing in the two compounds below 12K and 50K, respectively.
Our results indicate the possibility that a substantial fraction of the of the
vanadium magnetic moment is not in a spin singlet sate at low temperatures in
either material.",9709123v1
1997-09-15,Dynamical properties of the compounds CuGeO_3 and α'--NaV_2O_5 at temperatures $T\neq 0$,"The dynamical structure factor of the frustrated spin 1/2 Heisenberg model
for a series of frustration parameters at finite temperatures is presented. A
sharp upper boundary of the spinon continuum is found. A simple method to
extract the nearest neighbour coupling J from the spectral width is suggested.
Signatures of frustration are discussed and a comparison with neutron inelastic
scattering data is given.",9709160v2
1997-09-18,Structural Stability of Vacancy-ordered Yb2.75C60,"The fcc-based structure of Yb2.75C60 is unique among metal-doped fullerene
compounds, exhibiting long-range-ordered vacancies, significantly off-centered
divalent Yb cations, and distorted, crystallographically inequivalent,
orientationally ordered C60 anions. A simple electrostatic-energy analysis,
which models the constituents using point charges, is shown to provide insight
into how each of these features stabilizes this unusual crystal structure. The
results have general implications for a variety of other intercalated metal
fullerides.",9709211v1
1997-10-07,Absence of spin gap in the superconducting ladder compound Sr_2Ca_{12}Cu_{24}O_{41},"Transport and 63^Cu-NMR, Knight shift and T_1, measurements performed on the
two-leg spin ladders of Sr_2Ca_{12}Cu_{24}O_{41} single crystals show a
collapse of the gap in ladder spin excitations when superconductivity is
stabilised under a pressure of 29 kbar. These results support the prediction
made with exact diagonalisation techniques in two-leg isotropic t-J ladders of
a transition between a low-doping spin gap phase and a gapless 1-D
Tomonaga-Luttinger regime.",9710063v1
1997-11-15,Phase Diagram of Doped Manganates,"The phase diagram of doped manganate compounds La_{1-x}A_xMnO_3 (with
divalent A) is studied. We analyze an extension of the double exchange model
using the Schwinger boson formalism. Earlier work by de Gennes on the existence
of a canted phase is reproduced, although this phase is shown to be unstable
towards phase separation in a broad regime of physical interest. We numerically
solve the model's mean field equations and plot its phase diagram.",9711145v1
1997-11-17,Suppressed Coherence due to Orbital Correlations in the Ferromagnetically Ordered Metallic Phase of Mn Compounds,"Small Drude weight $D$ together with small specific heat coefficient $\gamma$
observed in the ferromagnetic phase of R$_{1-x}$A$_x$MnO$_3$ (R=La, Pr, Nd, Sm;
A=Ca, Sr, Ba) are analyzed in terms of a proximity effect of the Mott
insulator. The scaling theory for the metal-insulator transition with the
critical enhancement of orbital correlations toward the staggered ordering of
two $e_g$ orbitals such as $3x^2-r^2$ and $3y^2-r^2$ symmetries may lead to the
critical exponents of $D \propto \delta^{u}$ and $\gamma \propto \delta^v$ with
$u=3/2$ and $v=0$. The result agrees with the experimental indications.",9711153v1
1997-12-15,Pressure Effects in Manganites with Layered Perovskite Structure,"Pressure effects on the charge and spin dynamics in the bilayer manganite
compounds $La_{2-2x}Sr_{1+2x}Mn_2O_7$ are studied theoretically by taking into
account the orbital degrees of freedom. The orbital degrees are active in the
layered crystal structure, and applied hydrostatic pressure stabilizes the
$3d_{x^2-y^2}$ orbital in comparison with $3d_{3z^2-r^2}$. The change of the
orbital states weakens the interlayer charge and spin couplings, and suppresses
the three dimensional ferromagnetic transition. Numerical results, based on an
effective Hamiltonian which includes the energy level difference of the
orbitals, show that the applied pressure controls the dimensionality of the
spin and charge dynamics through changes of the orbital states.",9712162v1
1997-12-18,Orbital polarization in LiVO_2 and NaTiO_2,"We present a band structure study of orbital polarization and ordering in the
two-dimensional triangular lattice transition metal compounds LiVO_2 and
NaTiO_2. It is found that while in NaTiO_2 the degeneracy of t_{2g} orbitals is
lifted due to the trigonal symmetry of the crystal and the strong on cite
Coulomb interaction, in LiVO_2 orbital degeneracy remains and orbital ordering
corresponding to the trimerization of the two-dimensional lattice develops.",9712230v1
1998-01-27,Electronic Structure of Ladder Cuprates,"We study the electronic structure of the ladder compounds (SrCa)CuO 14-24-41
and SrCuO 123. LDA calculations for both give similar Cu 3d-bands near the
Fermi energy. The hopping parameters estimated by fitting LDA energy bands show
a strong anisotropy between the t_perp t_par intra-ladder hopping and small
inter-ladder hopping. A downfolding method shows that this anisotropy arises
from the ladder structure.The conductivity perpendicular to the ladders is
computed assuming incoherent tunneling giving a value close to experiment.",9801280v1
1998-03-25,c-axis penetration depth of Hg-1201 single crystals,"We have magnetically imaged interlayer Josephson vortices emerging from an ac
face of single crystals of the single layer cuprate high-Tc superconductor
(Hg,Cu)Ba2CuO4+d. These images provide a direct measurement of the c-axis
penetration depth of about 10 microns. This length is a factor of 10 longer
than predicted by the interlayer tunneling model for the mechanism of
superconductivity in layered compounds, indicating that the condensation energy
available through this mechanism is 100 times smaller than is required for
superconductivity.",9803312v1
1998-04-15,Quantum Antiferromagnets in a Magnetic Field,"Motivated by recent experiments on low-dimensional quantum magnets in applied
magnetic fields, we present a theoretical analysis of their properties based on
the nonlinear sigma model. The spin stiffness and a 1/N expansion are used to
map the regimes of spin-gap behavior, predominantly linear magnetization, and
spin saturation. A two-parameter renormalization-group study gives the
characteristic properties over the entire parameter range. The model is
relevant to many systems exhibiting Haldane physics, and is applied here to the
two-chain spin ladder compound CuHpCl.",9804151v1
1998-05-05,Optical absorption edge in one-dimensional conductors,"The frequency-dependent conductivity is studied for both the one-dimensional
Hubbard model and a model of spinless fermions, using a selection rule, the
Bethe ansatz energy eigenstates, and conformal invariance. For densities where
the system is metallic the absorption spectrum has two contributions, a Drude
peak at \omega = 0 separated by a pseudo-gap from a broad absorption band whose
lower edge is characterized by a non-classical critical exponent. Our findings
are expected to shed new light on the ``far infrared puzzle'' of metallic
organic chain compounds.",9805043v1
1998-05-15,Frustrated Spin System in theta-(BEDT-TTF)_2RbZn(SCN)_4,"The origin of the spin gap behavior in the low-temperature dimerized phase of
theta-(BEDT-TTF)_2RbZn(SCN)_4 has been theoretically studied based on the
Hartree-Fock approximation for the on-site Coulomb interaction at absolute
zero. Calculations show that, in the parameter region considered to be relevant
to this compound, antiferromagnetic ordering is stabilized between dimers
consisting of pairs of molecules coupled with the largest transfer integral.
Based on this result an effective localized spin 1/2 model is constructed which
indicates the existence of the frustration among spins. This frustration may
result in the formation of spin gap.",9805184v1
1998-06-02,Lattice Dimerization in the Spin-Peierls Compound CuGeO$_3$,"The uniaxial pressure dependences of the exchange coupling and the structural
distortion in the dimerized phase of CuGeO$_3$ are analyzed. A minimum magnetic
dimerization of 3 % is obtained, incompatible with an adiabatic approach to the
spin-Peierls transition. Exploring the properties of an Heisenberg spin chain
with dynamical spin-phonon coupling, the dimerization dependence of the spin
excitation gap is found to be in qualitative agreement with experiment.",9806022v1
1998-06-03,Scalar-relativistic effects in solids in the framework of a Douglas-Kroll transformed Dirac-Coulomb Hamiltonian,"The Douglas-Kroll transformed Dirac-Coulomb Hamiltonian is used to describe
scalar-relativistic effects in solids. A Hartree-Fock approximation with
periodic boundary conditions makes it feasible to use methods originally
developed for atoms and molecules to solve the corresponding equations for
crystalline systems. The implementation is realized within the CRYSTAL program.
Scalar-relativistic effects in silver compounds of FCC structure such as AgF,
AgCl, AgBr and Ag are investigated for the molar formation energy, the lattice
parameter, the isothermal bulk modulus and the pressure derivative.",9806044v1
1998-07-08,Lattice Distortions and Charge Carriers in Cuprates,"A phenomenological model with itinerant bands and local states trapped by the
lattice on the Cu-sites, is discussed to describe global features of cuprates.
Relative energy positions of localized and itinerant states being tuned
(thermodynamically or by doping), the system must undergo 1st order Mott
metal-insulator transition. Decreasing the local level (from the metallic end
of a stoichiometric compound), charge separation instability occurs first
before the Mott transition. Crossing and hybridization between local (flat) and
itinerant bands introduce a structure in density of states which may account
for ``pseudogap'' features in cuprates. Model results in polaronic lattice
effects and is rich enough to serve as a phenomenology of cuprates.",9807118v1
1998-07-09,Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model,"We study the electronic states of the anisotropic triangular lattice Hubbard
model at half filling, which is a simple effective model for the organic
superconducting $\kappa$-BEDT-TTF compounds. We treat the effect of the Coulomb
interaction by the fluctuation exchange (FLEX) method, and obtain the phase
diagram of this model for various sets of parameters. It is shown that the
d-wave superconductivity is realized in the wide region of the phase diagram,
next to the antiferromagnetic states. The obtained phase diagram explains the
characters of the experimental results very well.",9807147v2
1998-07-10,Effects of dimerization and interchain one-particle hopping in a weakly coupled dimerized chain system at quarter filling,"Effects of the intrachain dimerization and the interchain one-particle
hopping, $t_{b}$, in a quasi-one-dimensional dimerized chain system at quarter
filling have been studied, based on the perturbative renormalization group
(PRG) approach. Based on the results, we discuss difference in the low-energy
properties between TMTTF and TMTSF compounds.",9807153v1
1998-07-30,Kondo Screening and Magnetic Ordering in Frustrated UNi4B,"UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.",9807408v1
1998-08-02,Infrared study of spin-Peierls compound alpha'-NaV2O5,"Infrared reflectance of alpha'-NaV2O5 single crystals in the frequency range
from 50 cm-1 to 10000 cm-1 was studied for a, b and c-polarisations. In
addition to phonon modes identification, for the a-polarised spectrum a broad
continuum absorption in the range of 1D magnetic excitation energies was found.
The strong near-IR absorption band at 0.8 eV shows a strong anisotropy with
vanishing intensity in c-polarisation. Activation of new phonons due to the
lattice dimerisation were detected below 35K as well as pretransitional
structural fluctuations up to 65K.",9808006v1
1998-08-03,Anderson localization in Hubbard ladders,"The effect of a weak random potential on two-leg Hubbard ladders is
investigated. The random potential is shown to induce Anderson localization
except for attractive enough interactions, supressing completely d-wave
superconductivity. These localization effects remain very strong even for many
ladders coupled by Josephson coupling. Both dc and ac conductivities and
localization lengths are obtained. Consequences for the superconducting ladder
compound Sr$_x$Ca$_{14-x}$Cu$_{24}$O$_{41+\delta}$ are discussed.",9808015v1
1998-08-17,Ultrasonic attenuation in clean d-wave superconductors,"We consider the attenuation of longitudinal ultrasonic waves in a clean
two-dimensional d-wave superconductor. We show that the attenuation coefficient
is linear in temperature at low temperatures for all in-plane directions of the
propagation of the ultrasound, and that the coefficient of the linear term can
be used to determine the parameters crucial for the low temperature transport
in these compounds.",9808178v2
1998-09-04,Critical properties of S=1/2 Heisenberg ladders in magnetic fields,"The critical properties of the $S=1/2$ Heisenberg two-leg ladders are
investigated in a magnetic field. Combining the exact diagonalization method
and the finite-size-scaling analysis based on conformal field theory, we
calculate the critical exponents of spin correlation functions numerically. For
a strong interchain coupling, magnetization dependence of the critical
exponents shows characteristic behavior depending on the sign of the interchain
coupling. We also calculate the critical exponents for the $S=1/2$ Heisenberg
two-leg ladder with a diagonal interaction, which is thought as a model
Hamiltonian of the organic spin ladder compound
${Cu}_2({1,4-diazacycloheptane})_2{Cl}_4$. Numerical results are compared with
experimental results of temperature dependence of the NMR relaxation rate
$1/T_1$.",9809088v1
1998-09-22,Magnetic Bound States in Dimerized Quantum Spin Systems,"Magnetic bound states are a general phenomenon in low dimensional
antiferromagnets with gapped singlet states. Using Raman scattering on three
compounds as dedicated examples we show how exchange topology, dimensionality,
defects and thermal fluctuations influence the properties and the spectral
weight of these states.",9809289v1
1998-09-24,Evidence for distinct polymer chain orientations in KC60 and RbC60,"The KC60 and RbC60 polymer phases exhibit contrasting electronic properties
while powder diffraction studies have revealed no definite structural
difference. We have performed single crystal X-ray diffraction and diffuse
scattering studies of these compounds. It is found that KC60 and RbC60 possess
different chain orientations about their axes, which are described by distinct
space groups Pmnn and I2/m, respectively. Such a structural difference will be
of great importance to a complete understanding of the physical properties.",9809325v1
1998-09-24,Polymer Chain Orientations in KC60 and RbC60 : Structural Analysis and Relation with Electronic Properties,"First single crystal X-ray diffraction studies of polymerized KC60 and RbC60
are presented. While powder diffraction studies showed no definite structural
differences, the single crystal diffraction data analysis reveals different
relative chain orientations in the two compounds. They are discussed in
relation with semi-empirical energy calculations. The structural difference
between KC60 and RbC60 may be a key feature for the understanding of their
contrasted conducting and magnetic properties.",9809327v1
1998-09-29,Liesegang patterns: Effect of dissociation of the invading electrolyte,"The effect of dissociation of the invading electrolyte on the formation of
Liesegang bands is investigated. We find, using organic compounds with known
dissociation constants, that the spacing coefficient, 1+p, that characterizes
the position of the n-th band as x_n ~ (1+p)^n, decreases with increasing
dissociation constant, K_d. Theoretical arguments are developed to explain
these experimental findings and to calculate explicitly the K_d dependence of
1+p.",9809385v1
1998-11-03,Polarized-neutron study of longitudinal Haldane-gap excitations in Nd$_2$BaNiO$_5$,"Polarized and unpolarized inelastic neutron scattering is used to study
Haldane-gap excitations in the mixed-spin linear-chain antiferromagnet
Nd2BaNiO5. The longitudinal mode, polarized along the direction of ordered
moments, is observed for the first time. The model of isolated Haldane chains
in a static staggered exchange field, that is known to work very well for
static properties and transverse spin excitations in R2BaNiO5 compounds, fails
to explain new results for the longitudinal spin gap.",9811040v1
1998-11-06,Bond-versus-site doping models for off-chain-doped Haldane-gap system Y$_2$ Ba Ni O$_5$,"Using the density matrix renormalization-group technique, we calculate the
impurity energy levels for two different effective models of off-chain doping
for quasi-one-dimensional Heisenberg chain compound Y$_2$ Ba Ni O$_5$:
ferromagnetic bond doping and antiferromagnetic site spin-1/2 doping.
Thresholds of the impurity strength for the appearance of localized states are
found for both models. However, the ground-state and low-energy excitations for
weak impurity strength are different for these two models and the difference
can be detected by experiments.",9811084v1
1998-11-23,Giant enhancement of anisotropy by electron-phonon interaction,"Anisotropic electron-phonon interaction is shown to lead to the anisotropic
polaron effect. The resulting anisotropy of the polaron band is an exponential
function of the electron-phonon coupling and might be as big as $10^3$. This
also makes anisotropy very sensitive to small changes of coupling and implies
wide variations of anisotropy among compounds of similar structure. The isotope
effect on mass anisotropy is predicted. Polaron masses are obtained by an exact
Quantum Monte Carlo method. Implications for high-temperature superconductors
are briefly discussed.",9811327v1
1998-12-04,Interlayer Coherence in the $ν=1$ and $ν=2$ Bilayer Quantum Hall States,"We have measured the Hall-plateau width and the activation energy of the
bilayer quantum Hall (BLQH) states at the Landau-level filling factor $\nu=1$
and 2 by tilting the sample and simultaneously changing the electron density in
each quantum well. The phase transition between the commensurate and
incommensurate states are confirmed at $\nu =1$ and discovered at $\nu =2$. In
particular, three different $\nu =2$ BLQH states are identified; the compound
state, the coherent commensurate state, and the coherent incommensurate state.",9812064v1
1999-01-08,"Orbital ordering, Jahn-Teller distortion, and anomalous X-Ray scattering in Manganates","We demonstrate with LSDA+U calculations that x-ray scattering at the K edge
of Mn is sensitive to orbital ordering in one energy range and Jahn-Teller
distortion in another. Contrary to what is suggested by atomic or cluster
models used to date we show that band structure effects rather than local
Coulomb interactions dominate the polarization dependence of the K edge
scattering and therefore it is sensitive to nearest neighbour bond length
distortions and next nearest neighbour orbital occupation. Based on this we
propose a new mechanism for K edge x-ray scattering in the manganates which we
suggest is also applicable to transition metal compounds in general.",9901058v1
1999-01-24,Half-Metallic Ferrimagnetism in Mn_2VAl,"We show that Mn_2VAl is a compound for which the generalized gradient
approximation (GGA) to the exchange-correlation functional in density
functional theory makes a qualitative change in predicted behavior compared to
the usual local density approximation (LDA). Application of GGA leads to
prediction of Mn_2VAl being a half-metallic ferrimagnet, with the minority
channel being the conducting one. The electronic and magnetic structure is
analyzed and contrasted with the isostructural enhanced semimetal Fe_2VAl.",9901253v2
1999-01-26,"Linear dependence of peak width in $χ(\bq, ω)$ vs T_c for YBCO superconductors","It is shown that the momentum space width of the peak in the spin
susceptibility, Im$\chi(q,\omega)$, is linearly proportional to the
superconducting $T_c$: $T_c = \hbar v^*\Delta q$ with $\hbar v^* \simeq 35
meV$\AA. This relation is similar to the linear relation between incommensurate
peak splitting and $T_c$ in LaSrCuO superconductors, as first proposed by
Yamada et al. (Phys. Rev. B 57, 6165, (1998)). The velocity $\hbar v^*$ is
smaller than Fermi velocity or the spin-wave velocity of the parent compound
and remains the same for a wide doping range. This result points towards strong
similarities in magnetic state of YBCO and LaSrCuO.",9901294v1
1999-02-17,Spin-ordering in S = 1 anisotropic Heisenberg models with nondiagonal spin exchange,"The properties of S = 1 anisotropic Heisenberg models with nondiagonal
exchange between axial and planar spin components are investigated using Monte
Carlo techniques. The quantum nature is taken into account in a semi-classical
approximation. The ordering of the spins when applying an external field with
axial and planar components is discussed. It is argued that the quantum nature
of the spins and the nondiagonal exchange may explain the peculiar shape of the
magnetic specific heat of FeBr2 as well as the weakly first-order phase
transition observed in the same compound when a tilted field is applied.",9902237v1
1999-02-18,BaCu_2Si_2O_7: a new quasi 1-dimensional S = 1/2 antiferromagnetic chain system,"The new antiferromagnetic (AF) compound BaCu_2Si_2O_7 is studied by magnetic
susceptibility and neutron scattering techniques. The observed behavior is
dominated by the presence of loosely coupled S=1/2 chains with the intrachain
AF exchange constant J = 24.1 meV. Long-range Neel ordering is observed below
Tn = 9.2 K. The results are discussed within the framework of the Mean
Field-RPA model for weakly interacting quantum spin chains.",9902251v1
1999-03-10,Large Thermopower in a Layered Oxide NaCo_2O_4,"A transition-metal oxide NaCo_2O_4 is a layered oxide in which CoO_2 and Na
alternately stack along the c axis. Recently we have found that this compound
shows unusually large thermopower with low resistivity, which is comparable to
those of Bi_2Te_3. The negative transverse magnetoresistance and the strongly
temperature-dependent Hall coefficient suggest that electron correlation
dominates the conduction mechanism in NaCo_2O_4.",9903162v1
1999-04-06,Extending the n=2 Ruddlesden-Popper Solid Solution La2-2xSr1+2xMn2O7 Beyond x=0.5: Synthesis of Mn4+-rich Compounds,"We report the synthesis and room temperature crystal structures of the
heretofore unknown, metastable manganites La2-2xSr1+2xMn2O7+delta (0.5 < x <
0.9) via high-temperature (T=1650 C) quenching followed by low-temperature
(T=400 C) annealing to fill oxygen vacancies; this approach enables access to
the electronic, magnetic, and structural properties of previously unexplored
compositions in this important CMR system.",9904078v1
1999-05-21,Theory of Unconventional Spin Density Wave: A Possible Mechanism of the Micromagnetism in U-based Heavy Fermion Compounds,"We propose a novel spin density wave (SDW) state as a possible mechanism of
the anomalous antiferromagnetism, so-called the micromagnetism, in URu_2Si_2
below 17.5[K]. In this new SDW, the electron-hole pair amplitude changes its
sign in the momentum space as in the case of the unconventional
superconductivity. It is shown that this state can be realized in an extended
Hubbard model within the mean field theory. We also examine some characteristic
properties of this SDW to compare with the experimental results. All these
properties well explain the unsolved problem of the micromagnetism.",9905316v1
1999-05-21,Magnetic Field Induced Ordering in Quasi-One-Dimensional Quantum Magnets,"Three-dimensional magnetic ordering transitions are studied theoretically in
strongly anisotropic quantum magnets. An external magnetic field can drive
quasi-one-dimensional subsystems with a spin gap into a gapless regime, thus
inducing long-range three-dimensional magnetic ordering due to weak residual
magnetic coupling between the subsystems. Compounds with higher spin degrees of
freedom, such as N-leg spin-1/2 ladders, are shown to have cascades of ordering
transitions. At high magnetic fields, zero-point fluctuations within the
quasi-1D subsystems are suppressed, causing quantum corrections to the ordering
temperature to be reduced.",9905331v1
1999-06-04,Optical Properties of MFe_4P_12 filled skutterudites,"Infrared reflectance spectroscopy measurements were made on four members of
the MFe_4P_12 family of filled skutterudites, with M=La, Th, Ce and U. In
progressing from M=La to U the system undergoes a metal-insulator transition.
It is shown that, although the filling atom induces such dramatic changes in
the transport properties of the system, it has only a small effect on lattice
dynamics. We discuss this property of the compounds in the context of their
possible thermoelectric applications.",9906056v1
1999-06-11,Theoretical study of the optical conductivity of $α'-NaV_2O_5$,"Using finite temperature diagonalization techniques it is shown that the
quarter-filled t-J-V model on a trellis lattice structure provides a
quantitative explanation of the highly anisotropic optical conductivity of the
$\alpha'-NaV_{2}O_{5}$ compound. The combined effects of the short-range
Coulomb interaction and valence fluctuations of V-ions determine the main
absorption and the fundamental gap. Inter-ladder hopping is necessary for the
explanation of the anomalous in-gap absorption and generation of spectral
weight at high energy. The role of valence fluctuations is explained in terms
of the domain wall excitations of an anisotropic 2D Ising model in a transverse
field close to criticality.",9906169v1
1999-06-29,Magnetic susceptibility of diluted pyrochlore and SCGO antiferromagnets,"We investigate the magnetic susceptibility of the classical Heisenberg
antiferromagnet with nearest-neighbour interactions on the geometrically
frustrated pyrochlore lattice, for a pure system and in the presence of
dilution with nonmagnetic ions. Using the fact that the correlation length in
this system for small dilution is always short, we obtain an approximate but
accurate expression for the magnetic susceptibility at all temperatures. We
extend this theory to the compound SrCr_{9-9x}Ga_{3+9x}O_{19} (SCGO) and
provide an explanation of the phenomenological model recently proposed by
Schiffer and Daruka [Phys. Rev. B56, 13712 (1997)].",9906421v1
1999-07-09,Relativistic effects in the electronic structure for the 3d paramagnetic ions,"It has been shown that relativistic spin-orbit effects have enormous
influence on the electronic structure of the correlated electron systems 3dn.
The s-o coupling produces the fine electronic structure with a large number of
low- energy, < 10 meV, localized states, These states affect enormously
electronic and magnetic properties of 3d-ion compounds at low- and
room-temperature regions. It is inferred that the relativistic s-o effects and
the multiplet structure on individual atoms are indispensable for the proper
evaluation of the electronic structure of paramagnetic 3d ions.",9907140v1
1999-07-31,Quantum phase transitions in antiferromagnets and superfluids,"We present a general introduction to the non-zero temperature dynamic and
transport properties of low-dimensional systems near a quantum phase
transition. Basic results are reviewed in the context of experiments on the
spin-ladder compounds, insulating two-dimensional antiferromagnets, and
double-layer quantum Hall systems. Recent large N computations on an extended
t-J model (cond-mat/9906104) motivate a global scenario of the quantum phases
and transitions in the high temperature superconductors, and connections are
made to numerous experiments.",9908008v1
1999-08-09,Realization of Bose-Einstein condensation of dilute magnons in TlCuCl$_3$,"The recent observation [Oosawa et al. J. Phys. : Condens. Matter {\bf 11},
265 (1999)] of the field-induced N\'{e}el ordering in a spin-gap magnetic
compound TlCuCl$_3$ is interpreted as a Bose-Einstein Condensation of magnons.
A mean-field calculation based on this picture is shown to describe well the
temperature dependence of the magnetization. The present system opens a new
area for studying Bose-Einstein condensation of thermodynamically large number
of particles in a grand-canonical ensemble.",9908118v1
1999-08-24,Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5),"We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.",9908347v1
1999-09-02,Orbital Polarization and Fluctuation in Manganese Oxides,"In a form which include the mother compound, we studied the extended
Hubbard-type model with the orbital degeneracy for any doping concentration.
Meanfield phase diagram and the spin wave excitation in RPA are calculated. It
turned out that a large orbital polarization is essential to reproduce the
magnetic phases depending on the doping concentration. Base on this result, we
discuss the spin canting, the spin wave dispersion, and spin wave stiffness
from the standing point of the large orbital polarization. We also discuss the
orbital fluctuation which turned out to be important in the ferromagnetic
metallic region where the CMR is observed. Spin wave softening near the zone
boundary is also discussed in this context.",9909023v1
1999-09-17,Calculation of Neel temperature for S=1/2 quasi-one-dimensional Heisenberg antiferromagnets,"Isotropic S=1/2 quasi-one-dimensional antiferromagnets are considered within
the bosonization method. The 1/zp-corrections to the interchain mean-field
theory (zp is the number of nearest neighbors in transverse to chain
directions) are obtained for the ground-state sublattice magnetization and Neel
temperature T_N. The corrections to T_N make up about 25% of mean-feld value,
while those to ground-state sublattice magnetization are small enough
(especially in the three-dimensional case). The fluctuation corrections
obtained improve considerably the agreement with the experimental data for
magnetic-chain compounds KCuF3, Sr2CuO3 and Ca2CuO3.",9909257v1
1999-09-29,Evidence for Anisotropic Kondo Behavior in Ce0.8La0.2Al3,"We have performed an inelastic neutron scattering study of the low energy
spin dynamics of the heavy fermion compound Ce0.8La0.2Al3 as a function of
temperature and external pressure up to 5 kbar. At temperatures below 3 K, the
magnetic response transforms from a quasi-elastic form, common to many heavy
fermion systems, to a single well-defined inelastic peak, which is extremely
sensitive to external pressure. The scaling of the spin dynamics and the
thermodynamic properties are in agreement with the predictions of the
anisotropic Kondo model.",9909438v1
1999-10-04,Numerical studies of the vibrational isocoordinate rule in chalcogenide glasses,"Many properties of alloyed chalcogenide glasses can be closely correlated
with the average coordination of these compounds. This is the case, for
example, of the ultrasonic constants, dilatometric softening temperature and
the vibrational densities of states. What is striking, however, is that these
properties are nevertheless almost independent of the composition at given
average coordination. Here, we report on some numerical verification of this
experimental rule as applied to vibrational density of states.",9910032v1
1999-10-07,Theory of anomalous magnon softening in ferromagnetic manganites,"In metallic manganites with low Curie temperatures, a peculiar softening of
the magnon spectrum close to the magnetic zone boundary has experimentally been
observed. Here we present a theory of the renormalization of the magnetic
excitation spectrum in colossal magnetoresistance compounds. The theory is
based on the modulation of magnetic exchange bonds by the orbital degree of
freedom of double-degenerate e_g electrons. The model considered is an
orbitally degenerate double-exchange system coupled to Jahn-Teller active
phonons which we treat in the limit of strong onsite repulsions. Charge and
coupled orbital-lattice fluctuations are identified as the main origin of the
unusual softening of the magnetic spectrum.",9910106v1
1999-10-25,Electron-phonon and spin-phonon coupling in NaV$_{2}$O$_{5}$: charge fluctuations effect,"We show that the asymmetric crystal environment of the V site in the ladder
compound NaV$_{2}$O$_{5}$ leads to a strong coupling of vanadium 3d electrons
to phonons. This coupling causes fluctuations of the charge on the V ions, and
favors a transition to a charge-ordered state at low temperatures. In the low
temperature phase the charge fluctuations modulate the spin-spin superexchange
interaction, resulting in a strong spin-phonon coupling.",9910403v1
1999-10-27,A Novel Longitudinal Mode in the Coupled Quantum Chain Compound KCuF3,"Inelastic neutron scattering measurements are reported that show a new
longitudinal mode in the antiferromagnetically ordered phase of the spin-1/2
quasi-one-dimensional antiferromagnet KCuF3. This mode signals the cross-over
from one-dimensional to three-dimensional behavior and indicates a reduction in
the ordered spin moment of a spin-1/2 antiferromagnet. The measurements are
compared with recent quantum field theory results and are found to be in
excellent agreement. A feature of the data not predicted by theory is a damping
of the mode by decay processes to the transverse spin-wave branches.",9910459v1
1999-11-09,The Mott transition in V_2 O_3 and Ni Se_x S_{2-x}: insights from dynamical mean field theory,"We discuss some aspects of the pressure (or interaction) driven Mott
transition, in three dimensional transition metal oxides by means of dynami cal
mean field theory. We isolate the universal properties of the transition from
the aspects which depend more on the detailed chemistry of the compounds. In
this light we can understand the main differences and the remarkable
similarities between these systems. Both theory and experiment converge on the
transfer of spectral weight from low energies to high energies as the universal
mechanism underlying the Mott transition, and we comment on the possible
relevance of these ideas to other metal to non metal transitions.",9911114v1
1999-11-09,Isotope effect in the presence of a pseudogap,"We investigate the question whether the unusual doping dependence of the
isotope exponent observed in underdoped high-Tc superconductors might be
related to another unusual phenomenon observed in these systems: the pseudogap
phenomenon. Within different approximations we study the influence of a
phenomenological pseudogap on the isotope exponent and find that it generally
strongly increases the isotope exponent, in qualitative agreement with
experiments on underdoped high-Tc compounds. This result is stable against
strong-coupling self-energy corrections and also holds for recently proposed
spinfluctuation exchange models, if a weak additional electron-phonon coupling
is considered.",9911123v1
1999-11-10,Magnetic field as a probe of gap energy scales in YBCO,"Among high T_c materials, the YBCO (YBa_2Cu_3O_{7-x}) compounds are special
since they have superconducting chains as well as planes. We show that a
discontinuity in the density of states as a function of magnetic field may
appear at a new energy scale, characteristic of the chain and distinct from
that set by the d wave gap. This is observable in experimental studies of the
thermodynamical properties of these systems, such as the specific heat.",9911145v1
1999-12-07,Hole dynamics and photoemission in a t-J model for SrCu_2(BO_3)_2,"The motion of a single hole in a t-J model for the two-dimensional spin-gap
compound SrCu_2(BO_3)_2 is investigated. The undoped Heisenberg model for this
system has an exact dimer eigenstate and shows a phase transition between a
dimerized and a Neel phase at a certain ratio of the magnetic couplings. We
calculate the photoemission spectrum in the disordered phase using a
generalized spin-polaron picture. By varying the inter-dimer hopping parameters
we find a cross-over between a narrow quasiparticle band regime known from
other strongly correlated systems and free-fermion behavior. The hole motion in
the Neel-ordered phase is also briefly considered.",9912099v1
1999-12-07,Breakdown of the Kondo Effect in Critical Antiferromagnets,"The breakdown of the Kondo effect may be the origin of the anomalous
properties of the heavy-fermion compounds at low temperatures. We study the
dynamics of one impurity embedded in an antiferromagnetic host at the quantum
critical point and show that the impurity is not screened and develops a power
law correlation function. This suggests that the breakdown of the Kondo effect
can simply be a consequence of the system's proximity to the quantum critical
point.",9912102v1
1999-12-14,Frustrated Hubbard ladders and superconductivity in $κ$-BEDT-TTF organic compounds,"Half-filled two-leg Hubbard ladders have spin-gapped short-range
antiferromagnetic correlations while three-leg ladders have power law
antoferromagnetic correlations, and both systems have d_{x^2-y^2}-power law
pairing correlations when they are doped. Thus these ladders exhibit some of
the phenomenology seen in the layered cuprates. Here we report results for
half-filled frustrated Hubbard ladders, based upon ladder segments taken from a
tight-binding model of kappa-BEDT-TTF. Although these ladders are half-filled,
varying the degree of frustration can drive them across an insulator-metal
transition. We suggest that the spin, charge and pairing correlations of these
frustrated ladders near the insulator-metal transition provide support for the
notion that kappa-BEDT-TTF is a strongly correlated superconductor.",9912236v1
1999-12-18,Nuclear spin relaxation in ordered bimetallic chain compounds,"A theoretical interpretation is given to recent proton spin relaxation-time
(T_1) measurements on NiCu(C_7H_6N_2O_6)(H_2O)_3$\cdot$2H_2O, which is an ideal
one-dimensional ferrimagnetic Heisenberg model system of alternating spins 1
and 1/2. The relaxation rate T_1^{-1} is formulated in temrs of the spin-wave
theory and is evaluated by the use of a quantum Monte Carlo method.
Calculations of the temperature and applied-field (H) dependences of T_1^{-1}
are in total agreement with the experimental findings. T_1 behaves as
$T_1^{-1}\propto H^{-1/2}$, which turns out an indirect observation of the
quadratic dispersion relations dominating the low-energy physics of quantum
ferrimagnets.",9912340v1
1999-12-21,Magnetotransport in the low carrier density ferromagnet EuB_6,"We present a magnetotransport study of the low--carrier density ferromagnet
EuB_6. This semimetallic compound, which undergoes two ferromagnetic
transitions at T_l = 15.3 K and T_c = 12.5 K, exhibits close to T_l a colossal
magnetoresistivity (CMR). We quantitatively compare our data to recent
theoretical work, which however fails to explain our observations. We attribute
this disagreement with theory to the unique type of magnetic polaron formation
in EuB_6.",9912390v1
2000-01-14,On the electronic structure of CaCuO2 and SrCuO2,"Recent electronic structure calculations for the prototypical lowdimensional
cuprate compounds CaCuO2 ans SrCuO2 performed by Wu et. al. (J. Phys.: Condens.
Matter v. 11 p.4637 (1999))are critically reconsidered, applying high precision
full-potential bandstructure methods. It is shown that the bandstructure
calculations presented by the authors contain several important
inconsistencies, which make their main conclusions highly questionable.",0001208v1
2000-01-17,Orbital Structure and Magnetic Ordering in Layered Manganites: Universal Correlation and Its Mechanism,"Correlation between orbital structure and magnetic ordering in bilayered
manganites is examined. A level separation between the $3d_{3z^2-r^2}$ and
$3d_{x^2-y^2}$ orbitals in a Mn ion is calculated in the ionic model for a
large number of the compounds. It is found that the relative stability of the
orbitals dominates the magnetic transition temperatures as well as the magnetic
structures. A mechanism of the correlation between orbital and magnetism is
investigated based on the theoretical model with the two $e_g$ orbitals under
strong electron correlation.",0001221v1
2000-01-19,Electron states in a one-dimensional random binary alloy,"We present a model for alloys of compound semiconductors by introducing a
one-dimensional binary random system where impurities are placed in one
sublattice while host atoms lie on the other sublattice. The source of disorder
is the stochastic fluctuation of the impurity energy from site to site.
Although the system is one-dimensional and random, we demonstrate analytical
and numerically the existence of extended states in the neighborhood of a given
resonant energy, which match that of the host atoms.",0001266v1
2000-02-04,Dielectric response of charge induced correlated state in the quasi-one-dimensional conductor (TMTTF)2PF6,"Conductivity and permittivity of the quasi-one-dimensionsional organic
transfer salt (TMTTF)2PF6 have been measured at low frequencies (10^3-10^7 Hz)
between room temperature down to below the temperature of transition into the
spin-Peierls state. We interpret the huge real part of the dielectric
permittivity (up to 10^6) in the localized state as the realization in this
compound of a charge ordered state of Wigner crystal type due to long range
Coulomb interaction.",0002068v1
2000-02-09,Vortex state in a doped Mott insulator,"We analyze the recent vortex core spectroscopy experiments in cuprate
superconductor and discuss what can be learned from them about the nature of
the ground state in these compounds. We argue that the data are inconsistent
with the assumption of a simple metallic ground state and exhibit
characteristics of a doped Mott insulator. A theory for a vortex core in such a
doped Mott insulator is developed based on the U(1) gauge field slave boson
model and is shown to exhibit properties qualitatively consistent with the
experimental data.",0002137v2
2000-02-22,A New Two-Pole Approximation in the Hubbard Model. Metal-Insulator Transition,"A new two-pole approximation, which allows to describe the transition from an
insulating state to a metallic one at increase of bandwidth, and also the
observable in some compounds transition from a metalic state to an insulating
one with increasing temperature, is presented. The case of a paramagnetic
narrow-band material at half-filling is considered. Single-particle Green
function and energy spectrum of electron system are calculated. The expressions
for energy gap width and the concentration of polar states (holes or doublons)
are obtained. The conditions for metallic and insulating states are found.",0002334v1
2000-03-10,Mesoscopic phase separation in La2CuO4.02 - a 139La NQR study,"In crystals of La2CuO4.02 oxygen diffusion can be limited to such small
length scales, that the resulting phase separation is invisible for neutrons.
Decomposition of the 139La NQR spectra shows the existence of three different
regions, of which one orders antiferromagnetically below 17K concomitantly with
the onset of a weak superconductivity in the crystal. These regions are
compared to the macroscopic phases seen previously in the title compound and
the cluster-glass and striped phases reported for the underdoped Sr-doped
cuprates.",0003165v4
2000-03-15,"Magnetic Double Structure for S=1, 1/2 Mixed-Spin Systems","We investigate the zero-temperature and the finite-temperature properties of
the two-dimensional antiferromagnetic quantum spin system composed of the s=1/2
and s=1 spins. The spin excitation spectrum as well as the thermodynamic
quantities are computed by means of the Schwinger-boson mean-field theory. We
discuss how the magnetic double structure with the gapful and the gapless
excitations is generated, and apply the results systematically to the Haldane
gap system in a staggered magnetic field and also to the weakly coupled
ferrimagnetic mixed-spin chains. It is confirmed that the results obtained are
consistent with the experiments for the quasi-one-dimensional Haldane compounds
$R_2 \rm BaNiO_5$.",0003252v1
2000-03-29,Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet : Sr_2FeMoO_6,"Ultrafast spin dynamics in ferromagnetic half-metallic compound Sr_2FeMoO_6
is investigated by pump-probe measurements of magneto-optical Kerr effect.
Half-metallic nature of this material gives rise to anomalous thermal
insulation between spins and electrons, and allows us to pursue the spin
dynamics from a few to several hundred picoseconds after the optical
excitation. The optically detected magnetization dynamics clearly shows the
crossover from microscopic photoinduced demagnetization to macroscopic critical
behavior with universal power law divergence of relaxation time for wide
dynamical critical region.",0003467v3
2000-04-11,Landau Model for Commensurate-Commensurate Phase Transitions in Uniaxial Improper Ferroelectric Crystals,"We propose the Landau model for lock-in phase transitions in uniaxially
modulated improper ferroelectric incommensurate-commensurate systems of class
I. It includes Umklapp terms of third and fourth order and secondary order
parameter representing the local polarization. The corresponding phase diagram
has the structure of harmless staircase, with the allowed wave numbers obeying
the Farey tree algorithm. Among the stable commensurate phases only those with
periods equal to odd number of lattice constants have finite macroscopic
polarizations. These results are in excellent agreement with experimental
findings in some A2BX4 compounds.",0004166v1
2000-04-27,First-principles study of lattice instabilities in Ba_xSr_(1-x)TiO_3,"Using first-principles calculations based on a variational density functional
perturbation theory, we investigate the lattice dynamics of solid solutions of
barium and strontium titanates. Averaging the information available for the
related pure compounds yields results equivalent to those obtained within the
virtual crystal approximation, providing frequencies which are a good
approximation to those computed for a (111) ordered supercell. Using the same
averaging technique we report the evolution of the ferroelectric and
antiferrodistortive instabilities with composition.",0004464v1
2000-05-05,Finite-frequency optical absorption in 1D conductors and Mott-Hubbard insulators,"The frequency-dependent conductivity is studied for the one-dimensional
Hubbard model, using a selection rule, the Bethe ansatz, and symmetries
associated with conservation laws. For densities where the system is metallic
the absorption spectrum has two contributions, a Drude peak at $\omega = 0$
separated by a pseudogap from a broad absorption band whose lower edge is
characterized by a non-classical critical exponent. Our findings shed new light
on the ``far infrared puzzle'' and other optical properties of metallic organic
chain compounds.",0005108v1
2000-05-09,Spin-Waves in itinerant ferromagnets,"We introduce a novel approach for the investigation of spin-wave excitations
in itinerant ferromagnets. Our theory is based on a variational treatment of
general multi-band Hubbard models which describe elements and compounds of
transition metals. The magnon dispersion is derived approximately as the energy
of a variational spin-wave state in the limit of large spatial dimensions. A
numerical evaluation of our results is feasible for general multi-band models.
As a first application we consider a model with two degenerate orbitals per
lattice site. From our results we can conclude that spin-wave excitations in
strong itinerant ferromagnets are very similar to those in ferromagnetic spin
systems.",0005154v1
2000-05-29,Orbital-ordering-induced anomalous softening of the ferromagnetic spin waves in perovskite manganites,"Spin wave excitations were measured in the ferromagnetic phase of
Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$ by neutron scattering. This compound is located
in proximity to the A-type antiferromagnetic state, and it shows a clear
anisotropy and anomalous softening of the spin wave excitations. The softening
in the ferromagnetic phase is induced by the orbital ordering.",0005497v2
2000-07-03,Charge Ordering and Spin Dynamics in NaV2O5,"We report high-resolution neutron inelastic scattering experiments on the
spin excitations of NaV2O5. Below Tc, two branches associated with distinct
energy gaps are identified. From the dispersion and intensity of the spin
excitation modes, we deduce the precise zig-zag charge distribution on the
ladder rungs and the corresponding charge order (about 0.6). We argue that the
spin gaps observed in the low-T phase of this compound are primarily due to the
charge transfer.",0007025v2
2000-07-05,"Competition of charge, orbital, and ferromagnetic correlations in layered manganites","The competition of charge, orbital, and ferromagnetic interactions in layered
manganites is investigated by magneto-Raman scattering spectroscopy. We find
that the colossal magnetoresistance effect in the layered compounds results
from the interplay of the orbital and ferromagnetic double-exchange
correlations. Inelastic scattering by charge-order fluctuations dominates the
quasiparticle dynamics in the ferromagnetic-metal state. The scattering is
suppressed at low frequencies, consistent with the opening of a charge-density
wave pseudogap.",0007082v1
2000-07-11,Band offsets and stability of BeTe/ZnSe (100) heterojunctions,"We present ab-initio studies of band offsets, formation energy, and stability
of (100) heterojunctions between (Zn,Be)(Se,Te) zincblende compounds, and in
particular of the lattice-matched BeTe/ZnSe interface. Equal band offsets are
found at Be/Se and Zn/Te abrupt interfaces, as well as at mixed interfaces, in
agreement with the established understanding of band offsets at isovalent
heterojunctions. Thermodynamical arguments suggest that islands of non-nominal
composition may form at the interface, causing offset variations over about 0.8
eV depending on growth conditions. Our findings reconcile recent experiments on
BeTe/ZnSe with the accepted theoretical description.",0007180v1
2000-07-25,Phenomenological model for magnetotransport in a multi-orbital system,"By means of the Boltzmann equation, we have calculated some magnetotransport
quantities for the layered multi-orbital compound Sr$_2$RuO$_4$. The Hall
coefficient, the magnetoresistance and the in-plane resistivity have been
determined taking into account the Fermi surface curvature and different time
collisions for the electrons in the $t_{2g}$ bands. A consistent explanation of
the experimental results has been obtained assuming different relaxation rates
for the in-plane transport with and without an applied magnetic field,
respectively.",0007391v1
2000-07-26,Specific heat of Ce_{0.8}La_{0.2}Al_{3} in magnetic fields: a test of the anisotropic Kondo picture,"The specific heat C of Ce_{0.8}La_{0.2}Al_{3} has been measured as a function
of temperature T in magnetic fields up to 14 T. A large peak in C at 2.3 K has
recently been ascribed to an anisotropic Kondo effect in this compound. A 14-T
field depresses the temperature of the peak by only 0.2 K, but strongly reduces
its height. The corresponding peak in C/T shifts from 2.1 K at zero field to
1.7 K at 14 T. The extrapolated specific heat coefficient C/T(T->0) increases
with field over the range studied. We show that these trends are inconsistent
with the anisotropic Kondo model.",0007428v1
2000-08-01,Introduction to the Bethe Ansatz III,"Having introduced the magnon in part I and the spinon in part II as the
relevant quasi-particles for the interpretation of the spectrum of low-lying
excitations in the one-dimensional (1D) s=1/2 Heisenberg ferromagnet and
antiferromagnet, respectively, we now study the low-lying excitations of the
Heisenberg antiferromagnet in a magnetic field and interpret these collective
states as composites of quasi-particles from a different species. We employ the
Bethe ansatz to calculate matrix elements and show how the results of such a
calculation can be used to predict lineshapes for neutron scattering
experiments on quasi-1D antiferromagnetic compounds. The paper is designed as a
tutorial for beginning graduate students. It includes 11 problems for further
study.",0008018v1
2000-08-03,Response: Spin-Singlet clusters in the ladder compound NaV2O5,"This response on a Comment on Reference 2 discusses the space group Fmm2
determination of the low temperature structure of NaV2O5. We show that while
conventional crystallography is consistent with 'zig-zag' charge ordering of
half of the ladders, recent spectroscopic measurements suggest that the
symmetry is lower than Fmm2. We suggest space group C2, consistent with full
'zig-zag' charge ordering of all the ladders.",0008054v1
2000-09-14,Field-induced 3- and 2-dimensional freezing in a quantum spin liquid,"Field-induced commensurate transverse magnetic ordering is observed in the
Haldane-gap compound \nd by means of neutron diffraction. Depending on the
direction of applied field, the high-field phase is shown to be either a
3-dimensional ordered N\'{e}el state or a short-range ordered state with
dominant 2-dimensional spin correlations. The structure of the high-field phase
is determined, and properties of the observed quantum phase transition are
discussed.",0009223v1
2000-10-05,Quantum Atomistic Solid-State Theory,"Postulates of the quantum atomistic solid-state theory (QUASST) have been
presented. QUASST is an extension of the crystal-field theory and is applicable
to compounds containing open-shell 3d, 4f and 5f atoms. QUASST points out the
existence in a solid of the atomic-like discrete electronic structure
determined by the crystal- field and spin-orbit interactions. This approach
unifies the description of 3d and 4f ions and allows to bridge the atomic
physics and the solid-state physics.",0010081v1
2000-10-25,Ca0.85Sm0.15MnO3: A mixed antiferromagnet with unusual properties,"We investigated electrical and magnetic properties of the electron-doped
manganites Ca1-xSmxMnO3 (0<x<0.2). Our results indicate the possibility of
phase separation in electron doped manganites. The compounds with x = 0.13-0.15
show unusual difference between zero-field cooled and field-cooled
resistivities which are not observed in lower compositions. Our results suggest
that electronic phase separation alone is insufficient to understand the origin
of the resistivity irreversibilities.",0010384v1
2000-10-31,Spin Driven Jahn-Teller Distortion in a Pyrochlore system,"The ground-state properties of the spin-1 antiferromagnetic Heisenberg model
on the corner-sharing tetrahedra, pyrochlore lattice, is investigated. By
breaking up each spin into a pair of 1/2-spins, the problem is reduced to the
equivalent one of the spin-1/2 tetrahedral network in analogy with the valence
bond solid state in one dimension. The twofold degeneracy of the spin-singlets
of a tetrahedron is lifted by a Jahn-Teller mechanism, leading to a cubic to
tetragonal structural transition. It is proposed that the present mechanism is
responsible for the phase transition observed in the spin-1 spinel compounds
ZnV$_2$O$_4$ and MgV$_2$O$_4$.",0010504v1
2000-11-08,Griffiths phase of the Kondo insulator fixed point,"Heavy fermion compounds have long been identified as systems which are
extremely sensitive to the presence of impurities and other imperfections. In
recent years, both experimental and theoretical work has demonstrated that such
disorder can lead to unusual, non-Fermi liquid behavior for most physical
quantities. In this paper, we show that this anomalous sensitivity to disorder,
as well as the resulting Griffiths phase behavior, directly follow from the
proximity of metallic heavy fermion systems to the Kondo insulator fixed point.",0011132v1
2000-11-15,Low-dimensional quantum spin systems,"Low-dimensional quantum spin systems are interacting many body systems for
which several rigorous results are known. Powerful techniques like the Bethe
Ansatz provide exact knowledge of the ground state energy and low-lying
excitation spectrum. A large number of compounds exists which can effectively
be described as low-dimensional spin systems. Thus many of the rigorous results
are also of experimental relevance. In this Lecture Note, an introduction is
given to quantum spin systems and the rigorous results known for such systems.
Some general theorems and exactly-solvable models are discussed. An elementary
introduction to the Bethe Ansatz technique is given.",0011262v1
2000-12-19,Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O,"In response to recent nuclear-magnetic-resonance measurements on a
ferrimagnetic chain compound NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O [Solid State
Commun. {\bf 113} (2000) 433], we calculate the nuclear spin-lattice relaxation
rate 1/T_1 in terms of a modified spin-wave theory. Emphasizing that the
dominant relaxation mechanism arises from the direct (single-magnon) process
rather than the Raman (two-magnon) one, we explain the observed temperature and
applied-field dependences of 1/T_1. Ferrimagnetic relaxation phenomena are
generally discussed and novel ferrimagnets with extremely slow dynamics are
predicted.",0012342v1
2000-12-19,Comment on ''the controlled charge ordering and evidence of the metallic state in Pr$_{0.65}$Ca$_{0.35}$MnO$_{3}$ films'',"In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12}
L133) Lee \QTR{it}{et al.} have studied the transport properties of
Pr$_{0.65}$Ca$_{0.35}$MnO$_{3}$ thin films. They claimed that they are able to
controlled the charge-ordered (CO) state by the lattice strains. We propose
herein another alternative since another indexation of the orientation of the
film can be found leading to almost no distortion of the cell, as compared to
the bulk compound.",0012345v1
2000-12-21,The calculation of parameters for Stevens Hamiltonian in a crystalline field generated by the electric charge uniformly extended in one direction,"Exact expressions for the parameters of Stevens Hamiltonian are derived
within the framework of a specific model that assumes uniform character of
charge density distribution in a certain direction over crystalline lattice.
The new model is developed to strengthen the possibilities for analysis of
experimental data obtained by inelastic neutron scattering. It is particularly
valuable for studying the charge distribution in the layered perovskite-like
compounds doped with the rare-earth ions being used as a local probe.",0012400v1
2000-12-21,A generalization of Clausius inequality for processes between nonequilibrium steady states in chemical reaction systems,"We investigate nonequilibrium chemical reaction systems from the view point
of steady state thermodynamics proposed by Oono and Paniconi [Prog. Theor.
Phys. Suppl. 130, 29 (1998)]. The concentrations of some compounds are operated
by an external system, so that a transition from a steady state to other steady
state takes place. We show that an analogue of Clausius inequality holds
macroscopically for the operation processes. This implies that the second law
of thermodynamics can be generalized, including nonequilibrium steady states.",0012404v1
2001-01-01,Characterization of halogen-bridged binuclear metal complexes as hybridized two-band materials,"We study the electronic structure of halogen-bridged binuclear metal (MMX)
complexes with a two-band Peierls-Hubbard model. Based on a symmetry argument,
various density-wave states are derived and characterized. The ground-state
phase diagram is drawn within the Hartree-Fock approximation, while the thermal
behavior is investigated using a quantum Monte Carlo method. All the
calculations conclude that a typical MMX compound Pt_2(CH_3CS_2)_4I should
indeed be regarded as a d-p-hybridized two-band material, where the oxidation
of the halogen ions must be observed even in the ground state, whereas another
MMX family (NH_4)_4[Pt_2(P_2O_5H_2)_4X] may be treated as single-band
materials.",0101007v1
2001-01-04,Strong anisotropy of superexchange in the copper-oxygen chains of La_{14-x}Ca_{x}Cu_{24}O_{41},"Electron spin resonance data of Cu^{2+} ions in La_{14-x}Ca_{x}Cu_{24}O_{41}
crystals (x=9,11,12) reveal a very large width of the resonance line in the
paramagnetic state. This signals an unusually strong anisotropy of ~10% of the
isotropic Heisenberg superexchange in the Cu-O chains of this compound. The
strong anisotropy can be explained by the specific geometry of two symmetrical
90 degree Cu-O-Cu bonds, which boosts the importance of orbital degrees of
freedom. Our data show the apparent limitations of the applicability of an
isotropic Heisenberg model to the low dimensional cuprates.",0101040v1
2001-02-02,Singlet Ground State and Magnetization Plateaus in Ba$_3$Mn$_2$O$_8$,"Magnetic susceptibility and the magnetization process have been measured in
\green polycrystal. In this compound, the magnetic manganese ion exists as
Mn$^{5+}$ in a tetrahedral environment, and thus the magnetic interaction can
be described by an S=1 Heisenberg model. The ground state was found to be a
spin singlet with an excitation gap $\Delta/k_{\rm B}=11.2$ K. Magnetization
plateaus were observed at zero and at half of the saturation magnetization.
These results indicate that the present system can be represented by a coupled
antiferromagnetic dimer model.",0102026v2
2001-02-08,Heavy-Fermion Formation at the Metal-to-Insulator Transition in Gd$_{1-x}$Sr$_x$TiO$_3$,"The perovskite-like transition-metal oxide Gd$_{1-x}$Sr$_x$TiO$_3$ is
investigated by measurements of resistivity, specific-heat, and electron
paramagnetic resonance (EPR). Approaching the metal-to-insulator transition
from the metallic regime ($x \geq 0.2$), the Sommerfeld coefficient $\gamma$ of
the specific heat becomes strongly enhanced and the resistivity increases
quadratically at low temperatures, which both are fingerprints of strong
electronic correlations. The temperature dependence of the dynamic
susceptibility, as determined from the Gd$^{3+}$-EPR linewidth, signals the
importance of strong spin fluctuations, as observed in heavy-fermion compounds.",0102161v1
2001-02-23,Pressure dependence of the spin dynamics around a quantum critical point : An inelastic neutron scattering study of Ce0.87La0.13Ru2Si2,"Inelastic neutron scattering experiments performed on a single crystal of the
antiferromagnetic compound Ce$_{0.87}$La$_{0.13}$Ru$_{2}$Si$_{2}$ under applied
pressures of up to 5 kbar are reported. A quantum critical point is reached at
around 2.6 kbar where long-range magnetic order disappears. The variation of
the characteristic energy scales with respect to temperature and pressure is
followed and found to saturate in the ordered phase.",0102427v1
2001-03-03,Effect of Li doping on structure and superconducting transition temperature of Mg1-xLixB2,"We report the preparation of Mg1-xLixB2 compounds. Nearly single phased
samples were obtained for x<0.3. The in-plane lattice parameter a decreases
with Li doping, while the lattice parameter c does not show obvious change. The
superconducting transition temperature of Mg1-xLixB2 decreases with Li doping
and loss of superconductivity occurs for x=0.5 sample. The results of our work
are consistent with the prediction of the hole superconductivity mechanism.",0103077v1
2001-03-07,Fluctuation Magnetoconductance in MgB2,"We report fluctuation magnetoconductance in a MgB2 superconductor prepared
under a high pressure of 3 GPa. This excess magnetoconductance,
$\Delta\sigma(H)$, follows the three-dimensional scaling function for the
critical fluctuations proposed by Ullah and Dorsey. This feature is inferred to
originate from the isotropic nature of the MgB2 compound.",0103161v1
2001-03-07,Optical measurements of the superconducting gap in MgB2,"Far-infrared reflectivity studies on the polycrystalline intermetallic
compound MgB_2 with a superconducting transition temperature T_c=39 K were
performed at temperatures 20 K to 300 K. We observe a significant raise of the
superconducting-to-normal state reflectivity ratio below 70 cm^{-1}, with a
maximum at about 25-30 cm^{-1}, which gives a lower estimate of the
superconducting gap of 2\Delta(0)\approx3-4 meV.",0103164v3
2001-03-12,Intralayer Carbon Substitution in the MgB2 Superconductor,"We report that the ternary MgB2-xCx compounds adopt an isostructural
AlB2-type hexagonal structure in a relatively small range of nominal carbon
concentration, x<0.1. The lattice parameter a decreases almost linearly with
increasing carbon content x, while the c parameter remains unchanged,
indicating that carbon is exclusively substituted in the boron honeycomb layer
without affecting the interlayer interactions. The superconducting transition
temperature Tc, determined by magnetometry experiments, also decreases
quasilinearly as a function of the carbon concentration. The structural and
electronic behavior of MgB2-xCx displays a remarkable similarity with the
isoelectronic Mg1-xAlxB2 despite the different substitution sites.",0103241v1
2001-03-14,First order phase transition from ferromagnetism to antiferromagnetism in Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$,"Taking the pseudobinary C15 Laves phase compound
Ce(Fe$_{0.96}$Al$_{0.04}$)$_2$ as a paradigm for studying a ferromagnetic to
antiferromagnetic phase transition, we present interesting thermomagnetic
history effects in magnetotransport as well as magnetisation measurements
across this phase transition. A comparison is made with history effects
observed across the ferromagnetic to antiferromagnetic transition in
R$_{0.5}$Sr$_{0.5}$MnO$_3$ crystals.",0103291v1
2001-03-23,Extremely Small Energy Gap in the Quasi-One-Dimensional Conducting Chain Compound SrNbO$_{3.41}$,"Resistivity, optical, and angle-resolved photoemission experiments reveal
unusual one-dimensional electronic properties of highly anisotropic
SrNbO$_{3.41}$. Along the conducting chain direction we find an extremely small
energy gap of only a few meV at the Fermi level. A discussion in terms of
typical 1D instabilities (Peierls, Mott-Hubbard) shows that neither seems to
provide a satisfactory explanation for the unique properties of SrNbO$_{3.41}$.",0103485v2
2001-03-27,Incipient superconductivity in TaB$_{2}$,"Magnetic properties of TaB$_{2}$ were studied by means of DC and AC
susceptibility measurements. It has been found that the compound becomes
superconducting at T$_{c}$ = 9.5 K. From upper critical field measurements the
superconducting parameters have been evaluated, which indicated that TaB$_{2}$
is a hard type-II superconductor. Possible reasons why superconductivity has
not been discovered in previous studies are briefly discussed.",0103571v2
2001-04-02,Quantum and Thermal Phase Transitions of Halogen-Bridged Binuclear Transition-Metal Complexes,"Aiming to settle the controversial observations for halogen-bridged binuclear
transition-metal (MMX) complexes, finite-temperature Hartree-Fock calculations
are performed for a relevant two-band Peierls-Hubbard model. Thermal, as well
as quantum, phase transitions are investigated with particular emphasis on the
competition between electron itinerancy, electron-phonon interaction and
electron-electron correlation. Recently observed distinct thermal behaviors of
two typical MMX compounds Pt_2(CH_3CS_2)_4I and
(NH_4)_4[Pt_2(P_2O_5H_2)_4I]2H_2O are supported and further tuning of their
electronic states is predicted.",0104014v1
2001-04-11,Anisotropic s-wave superconductivity in MgB_2,"It has recently been observed that MgB_2 is a superconductor with a high
transition temperature. Here we propose a model of anisotropic s-wave
superconductivity which consistently describes the observed properties of this
compound, including the thermodynamic and optical response in sintered MgB_2
wires. We also determine the shape of the quasiparticle density of states and
the anisotropy of the upper critical field and the superfluid density which
should be detectable once single-crystal samples become available.",0104207v1
2001-04-26,On metallic ferromagnetism of a generalized Hubbard model with correlated hopping,"In the paper a possibility of metallic ferromagnetic state realization in a
generalized Hubbard model with more complete accounting of electron-electron
interactions, in particular, the correlated hopping and exchange interaction
integrals is investigated. Recently obtained by means of mean-field
approximation single electron energy spectrum is used for the description of
finite temperature properties of the system. In the paper the expression for
the critical temperature of ferromagnet-paramagnet transition is found, the
behaviour of temperature dependencies of magnetization and paramagnetic
susceptibility is analyzed. Taking into account the correlated hopping allows
to explain some peculiarity of ferromagnetic behaviour of transition metals,
their alloys and compounds.",0104515v1
2001-04-26,Orbital effects in manganites,"In this paper I give a short review of some properties of the colossal
magnetoresistance manganites, connected with the orbital degrees of freedom.
Ions Mn{3+}, present in most of these compounds, have double orbital degeneracy
and are strong Jahn-Teller ions, causing structural distortions and orbital
ordering. Mechanisms leading to such ordering are shortly discussed, and the
role of orbital degrees of freedom in different parts of the phase diagram of
manganites is described. Special attention is paid to the properties of
low-doped systems (doping 0.1 - 0.25), to overdoped systems (x > 0.5), and to
the possibility of a novel type of orbital ordering in optimally doped
ferromagnetic metallic manganites.",0104517v1
2001-04-27,An Improved Method for Obtaining Single-Phase Sr2MoO4 under Controlled Ultra-low Oxygen Partial Pressure,"We investigated a method for obtaining a sintered bulk sample of single-phase
Sr2MoO4, which has recently increased in importance due to its similarities to
superconducting Sr2RuO4. We discovered that with the aid of Ti2O3 as a p(O2)
buffer, high-purity Sr2MoO4 is successfully synthesized in a sealed tube. We
confirmed the space group and determined the exact elemental composition of the
compound in order to establish its stoichiometry. The guideline for the
rational choice of a p(O2)-buffer material is discussed.",0104531v2
2001-05-11,Temperature dependence of the structural parameters of the non-oxide perovskite superconductor MgCNi3,"We report the structural parameters of superconducting MgCxNi3 (x=0.96,
TC=7.3 K) as a function of temperature, from 2 K to 295 K, determined by
neutron powder diffraction profile refinement. The compound has the perovskite
structure over the whole temperature range, with symmetry Pm3m and a=3.81221(5)
A at 295 K: no structural or long range magnetic ordering transitions were
observed. The lattice parameter a and the Debye-Waller factors for the
individual atoms decrease smoothly with decreasing temperature. There are no
unusual changes of the structural parameters near TC.",0105240v1
2001-05-17,"Electronic structure, magnetism and superconductivity of MgCNi$_{3}$","The electronic structure of the newly discovered superconducting perovskite
MgCNi$_3$ is calculated using the LMTO and KKR methods. The states near the
Fermi energy are found to be dominated by Ni-d. The Stoner factor is low while
the electron-phonon coupling constant is estimated to be about 0.7, which
suggests that the material is a conventional type of superconductor where T$_C$
is not affected by magnetic interactions. However, the proximity of the Fermi
energy to a large peak in the density of states in conjunction with the
reported non-stoichiometry of the compound, has consequences for the stability
of the results.",0105349v1
2001-05-18,Short-range Magnetic interactions in the Spin-Ice compound Ho$_{2}$Ti$_{2}$O$_{7}$,"Magnetization and susceptibility studies on single crystals of the pyrochlore
Ho$_{2}$Ti$_{2}$O$_{7}$ are reported for the first time. Magnetization
isotherms are shown to be qualitatively similar to that predicted by the
nearest neighbor spin-ice model. Below the lock-in temperature, $T^{\ast
}\simeq 1.97$ K, magnetization is consistent with the locking of spins along
[111] directions in a specific two-spins-in, two-spins-out arrangement. Below
$T^{\ast}$ the magnetization for $B||[111]$ displays a two step behavior
signalling the breaking of the ice rules.",0105362v1
2001-05-25,Half-metallic antiferromagnets in thiospinels,"We have theoretically designed the half-metallic (HM) antiferromagnets (AFMs)
in thiospinel systems, $\rm Mn(CrV)S_{4}$ and $\rm
Fe_{0.5}Cu_{0.5}(V_{0.5}Ti_{1.5})S_{4}$, based on the electronic structure
studies in the local-spin-density approximation (LSDA). We have also explored
electronic and magnetic properties of parent spinel compounds of the above
systems; $\rm CuV_{2}S_{4}$ and $\rm CuTi_{2}S_{4}$ are found to be HM
ferromagnets in their cubic spinel structures, while $\rm MnCr_{2}S_{4}$ is a
ferrimagnetic insulator. We have discussed the feasibility of material
synthesis of HM-AFM thiospinel systems.",0105492v1
2001-05-29,Nonadiabatic Channels in the Superconducting Pairing of Fullerides,"We show the intrinsic inconsistency of the conventional phonon mediated
theory of superconductivity in relation to the observed properties of
Rb$_3$C$_{60}$. The recent, highly accurate measurement of the carbon isotope
coefficient $\alpha_{\rm C}=0.21$, together with the high value of $T_c$ (30 K)
and the very small Fermi energy $E_{\rm F}$ (0.25 eV), unavoidably implies the
opening of nonadiabatic channels in the superconducting pairing. We estimate
these effects and show that they are actually the key elements for the high
value of $T_c$ in these materials compared to the very low values of graphite
intercalation compounds.",0105560v1
2001-06-10,Antiferro-quadrupole Ordering of CeB$_6$ Studied by Resonant X-ray Scattering,"Under zero magnetic field, a quadrupolar order parameter at q_Q=(1/2,1/2,1/2)
in a typical antiferro-quadrupole (AFQ) ordering compound CeB6 has been
observed for the first time by means of a resonant X-ray scattering (RXS) te\
chnique. The RXS is observed at the 2p->5d dipole transition energy of the Ce
L3-edge. Using this RXS technique to observe the pure order parameter of the
AFQ state, the magnetic phase diagram of Phase II is first determined.",0106183v1
2001-06-12,Driving current through single organic molecules,"We investigate electronic transport through two types of conjugated
molecules. Mechanically controlled break-junctions are used to couple thiol
endgroups of single molecules to two gold electrodes. Current-voltage
characteristics (IVs) of the metal-molecule-metal system are observed. These
IVs reproduce the spatial symmetry of the molecules with respect to the
direction of current flow. We hereby unambigously detect an intrinsic property
of the molecule, and are able to distinguish the influence of both the molecule
and the contact to the metal electrodes on the transport properties of the
compound system.",0106219v1
2001-06-14,Resonant Impurity States in the D-Density-Wave Phase,"We study the electronic structure near impurities in the d-density-wave (DDW)
state, a possible candidate phase for the pseudo-gap region of the
high-temperature superconductors. We show that the local DOS near a
non-magnetic impurity in the DDW state is {\it qualitatively} different from
that in a superconductor with $d_{x^2-y^2}$-symmetry. Since this result is a
robust feature of the DDW phase, it can help to identify the nature of the two
different phases recently observed by scanning tunneling microscopy experiments
in the superconducting state of underdoped Bi-2212 compounds.",0106285v1
2001-06-28,Superconductivity Near Ferromagnetism in MgCNi3,"An unusual quasi-two-dimensional heavy band mass van Hove singularity (vHs)
lies very near the Fermi energy in MgCNi3, recently reported to superconduct at
8.5 K. This compound is strongly exchange enhanced and is unstable to
ferromagnetism upon hole doping with 12% Mg --> Na or Li. The 1/4-depleted fcc
(frustrated) Ni sublattice and lack of Fermi surface nesting argues against
competing antiferromagnetic and charge density wave instabilities. We identify
an essentially infinite mass along the M-Gamma line, leading to
quasi-two-dimensionality of this vHs may promote unconventional p-wave pairing
that could coexist with superconductivity.",0106583v1
2001-07-01,Small-q phonon-mediated superconductivity in organic κ-BEDT-TTF compounds,"We propose a mew picture for superconductivity in $\kappa-(BEDT-TTF)_2X$
salts arguing that small-{\bf q} electron-phonon scattering dominates the
pairing. We reproduce the distinct X-shaped d-wave gap reported recently by
magnetooptic measurements and we argue that the softness of the momentum
structure of the gap and the near degeneracy of s- and d-wave gap states may be
at the origin of the experimental controversy about the gap symmetry. We show
that a magnetic field applied parallel to the planes may induce extended
gapless-regions on the FS accounting for the experimental signatures of a
Fulde-Ferrel-Larkin-Ovchinikov state and it may induce gap symmetry transitions
as well.",0107017v1
2001-07-13,Longitudinal spin-fluctuations and superconductivity in ferromagnetic ZrZn$_{2}$ from ab initio calculations,"The recent discovery of superconductivity coexisting with weak itinerant
ferromagnetism in the $d$-electron intermetallic compound ZrZn$_{2}$ strongly
suggests spin-fluctuation mediated superconductivity. {\it Ab initio}
electronic structure calculations of the Fermi surface and generalized
susceptibilities are performed to investigate the viability of longitudinal
spin-fluctuation-induced spin-triplet superconductivity in the ferromagnetic
state. The critical temperature is estimated to be of the order of 1 K.
Additionally, it is shown that in spite of a strong electron-phonon coupling
($\lambda_{ph}=0.7$), conventional s-wave superconductivity is inhibited by the
presence of strong spin-fluctuations.",0107304v1
2001-07-19,Field-domain spintronics in magnetic semiconductor multiple quantum wells,"We develop a theory of non-linear growth direction transport in magnetically
doped II-VI compound semiconductor multiple-quantum-well systems. We find that
the formation of electric field domains can be controlled by manipulating the
space dependence of the band electron spin-polarization, using its exchange
coupling to local moments. We emphasize the importance of band electron spin
relaxation in limiting the strength of these effects.",0107398v1
2001-08-01,Correlation between magnetic and transport properties of phase separated La$_{0.5}$Ca$_{0.5}$MnO$_{3}$,"The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.",0108026v2
2001-08-20,Response of the Heavy-Fermion Superconductor CeCoIn$_5$ to Pressure: Roles of Dimensionality and Proximity to a Quantum-Critical Point,"We report measurements of the pressure-dependent superconducting transition
temperature $T_c$ and electrical resistivity of the heavy-fermion compound
CeCoIn$_5$. Pressure moves CeCoIn$_5$ away from its proximity to a
quantum-critical point at atmospheric pressure. Experimental results are
qualitatively consistent with theoretical predictions for strong-coupled,
d-wave superconductivity in an anisotropic 3D superconductor.",0108319v2
2001-09-05,"Quantal phases, disorder effects and superconductivity in spin-Peierls systems","In view of recent developments in the investigation on cuprate high-T${}_{\rm
c}$ superconductors and the spin-Peierls compound CuGeO${}_{3}$, we study the
effect of dilute impurity doping on the spin-Peierls state in quasi-one
dimensional systems. We identify a common origin for the emergence of
antiferromagnetic order upon the introduction of static vacancies, and
superconductivity for mobile holes.",0109071v3
2001-09-06,MgB2 conductors for dc and ac applications,"The paper presents discussion on up to date results on MgB2 conductors from
the point of view of their future dc and ac applications. Basic physical
parameters of MgB2 compound relevant to conductors are introduced. Different
conductor preparation methods and conductor architectures are presented and
attainable critical current densities discussed. Some numerical results on
critical currents and ac losses of future multifilamentary MgB2 conductors with
magnetic cladding of their filaments are given. Recently observed anomalous
decrease of ac susceptibility at 50 K in copper clad Powder-in-tube, PIT, MgB2
wires is presented.",0109114v1
2001-09-13,Ferromagnetism of magnetic semiconductors--Zhang-Rice limit,"It is suggested that p-d hybridization contributes significantly to the hole
binding energy E_b of Mn acceptors in III-V compounds, leading in an extreme
case to the formation of Zhang-Rice-like small magnetic polarons. The model
explains both strong increase of E_b and evolution of Mn spin-resonance
spectrum with the magnitude of valence-band offsets. For such a structure of Mn
impurity in III-V materials, possible models accounting for the recently
determined Curie temperature of about 940 K in a compensated Ga(0.91)Mn(0.09)N
are discussed.",0109245v1
2001-09-27,Enhanced paramagnetism of the 4d itinerant electrons in the rhodium oxide perovskite SrRhO3,"Polycrystalline rhodium(IV) oxide perovskite SrRhO3 was obtained by
high-pressure synthesis techniques, followed by measurements of the magnetic
susceptibility, electrical resistivity, and specific heat. The title compound
has five 4d-electrons per perovskite unit and shows Fermi-liquid behavior in
its electrical resistivity. The magnetic susceptibility is large [chi(300K)
\~1.1*10^{-3} emu/mol-Rh] and proportional to 1/T^2 (< 380 K), while there is
no magnetic long-range order above 1.8 K. The specific heat measurements
indicate a probable magnetic contribution below ~ 15 K, which is not predicted
by the self-consistent renormalization theory of spin fluctuations for both
antiferro- and ferromagnetic 3D nearly-ordered metals.",0109522v2
2001-10-12,What High Pressure Studies Have Taught Us about High-Temperature Superconductivity,"Superconductivity is an important area of modern research which has benefited
enormously from experiments under high pressure conditions. The focus of this
paper will be on three classes of high-temperature superconductors: (1) the new
binary compound MgB2, (2) the alkali-doped fullerenes, and (3) the cuprate
oxides. We will discuss results from experiment and theory which illustrate the
kinds of vital information the high-pressure variable can give to help better
understand these fascinating materials.",0110267v1
2001-10-24,Robustness of the van Hove scenario for high-Tc superconductors,"The pinning of the Fermi level to the van Hove singularity and the formation
of flat bands in the two-dimensional t-t' Hubbard model is investigated by the
renormalization group technique. The ""van-Hove"" scenario of non-Fermi-liquid
behavior for high-Tc compounds can take place in a broad enough range of the
hole concentrations. The results are in qualitative agreement with the recent
ARPES data on La2CuO4.",0110516v2
2001-11-12,"The magnetic behavior of Li2MO3 (M=Mn, Ru and Ir) and Li2(Mn1-xRux)O3","The present study summerizes magnetic and Mossbauer measurements on ceramic
Li2MO3 M= Mn, Ru and Ir and the mixed Li2(Mn1-xRux)O3 materials, which show
many of the features reflecting to antiferromagnetic ordering or to existence
of paramagnetic states. Li2IrO3 and Li2RuO3 are paramagnetic down to 5 K.
Li2(Mn1-xRux)O3 compounds are antiferromagnetically ordered at TN = 48 K for
x=0. TN decreases as the Ru content increases and, for x=0.8, TN =34 K.",0111211v1
2001-11-30,Magnetic Correlations and the Anisotropic Kondo Effect in Ce1-xLaxAl3,"By combining the results of muon spin rotation and inelastic neutron
scattering in the heavy fermion compounds Ce1-xLaxAl3 (0.0 <= x <= 0.2), we
show that static magnetic correlations are suppressed above a characteristic
temperature, T*, by electronic dissipation rather than by thermal disorder.
Below T*, an energy gap opens in the single-ion magnetic response in agreement
with the predictions of the Anisotropic Kondo Model. Scaling arguments suggest
that similar behavior may underlie the ""hidden order"" in URu2Si2.",0112005v1
2001-12-13,Magnon softening and damping in the ferromagnetic manganites due to orbital correlations,"We present a theory for spin excitations in ferromagnetic metallic manganites
and demonstrate that orbital fluctuations have strong effects on the magnon
dynamics in the case these compounds are close to a transition to an orbital
ordered state. In particular we show that the scattering of the spin
excitations by low-lying orbital modes with cubic symmetry causes both the
magnon softening and damping observed experimentally.",0112252v2
2001-12-18,Elastic interaction and superstructures in manganites and other Jahn-Teller systems,"The role of elastic interactions between Jahn-Teller ions in formation of
various orbital- and charge-ordered structures in manganites and related
compounds is analyzed. It is shown that such interactions alone are often
sufficient to reproduce the structures observed in different regions of the
phase diagram. A special attention is focused on stripe structures at high
doping levels.",0112340v1
2001-12-20,Fluctuation induced hopping and spin polaron transport,"We study the motion of free magnetic polarons in a paramagnetic background of
fluctuating local moments. The polaron can tunnel only to nearby regions of
local moments when these fluctuate into alignment. We propose this fluctuation
induced hopping as a new transport mechanism for the spin polaron. We calculate
the diffusion constant for fluctuation induced hopping from the rate at which
local moments fluctuate into alignment. The electrical resistivity is then
obtained via the Einstein relation. We suggest that the proposed transport
mechanism is relevant in the high temperature phase of the Mn pyrochlore
colossal magneto resistance compounds and Europium hexaboride.",0112385v1
2001-12-26,Electrodynamics of metallic photonic crystals and problem of left-handed materials,"An exact analytical theory of the electromagnetic waves in metallic photonic
crystals with a small volume fraction of a metal is presented. It is shown that
there are waves with a very low cutoff frequency $\omega_0$ and that the
permittivity $\epsilon$ is negative below $\omega_0$. We show that if the
crystal is embedded into a medium with negative $\mu$, it has no propagating
modes at any frequency. Thus, such a compound system is not a left handed
material (LHM). The recent experimental results on the LHM are discussed.",0112461v3
2002-01-08,Quantum Critical Point in Electron-Doped Cuprates,"We analyze doping dependent spectral intensities and Fermi surface maps
obtained recently in Nd$_{2-x}$Ce$_x$CuO$_{4\pm\delta}$ (NCCO) via high
resolution ARPES measurements, and show that the behavior of this
electron-doped compound can be understood as the closing of a Mott (pseudo)
gap, leading to a quantum critical point just above optimal doping. The doping
dependence of the effective Hubbard $U$ adduced by comparing theoretical and
experimental spectra is in resonable accord with various estimates and a simple
screening calculation.",0201117v2
2002-01-10,Ordering of the Antiferromagnetic Heisenberg Model on a Pyrochlore Slab,"Ordering of the geometrically frustrated two-dimensional Heisenberg
antiferromagnet on a pyrochlore slab is studied by Monte Carlo simulations. The
model is expected to serve as a reference system of SrCrGaO compound studied
extensively. In sharp contrast to the kagom\'e Heisenberg antiferromagnet, the
model exhibits locally non-coplanar spin structures at low temperatures,
bearing nontrivial chiral degrees of freedom. We find that under certain
conditions the model exhibits a novel Kosterlitz-Thouless-type transition at a
finite temperature associated with these chiral degrees of freedom.
Implications to experiments are discussed.",0201144v1
2002-01-15,Quantum gas distributions prescribed by factorization hypothesis of probability,"Nonextensive quantum gas distributions are investigated on the basis of the
factorization hypothesis of compound probability required by thermodynamic
equilibrium. It is shown that the formalisms of Tsallis nonextensive
statistical mechanics with normalized average give distribution functions for
standard bosons and fermions obeying Pauli principle. The formalism with
unnormalized average leads to a intermediate quantum distribution comparable to
that of fractional exclusion statistics, with Fermi surface at T=0 depending on
the parameter $q$.",0201248v2
2002-01-16,Why ferromagnetic semiconductors?,"Rapid development of information technologies originates from the exponential
increase in the density of information that can be processed, stored, and
transfer by the unit area of relevant devices. There is, however, a growing
amount of evidences that the progress achieved in this way approaches its
limits. Various novel ideas put forward to circumvent barriers ahead are
described. Particular attention is paid to those concepts which propose to
exploit electron or nuclear spins as the information carriers. Here,
ferromagnetic semiconductors of III-V or II-VI compounds containing a sizable
concentration of transition metals appear as outstanding spintronic materials.",0201279v1
2002-01-18,Chiral fluctuations in MnSi above Tc,"Polarized neutrons are used to determine the antisymmetric part of the
magnetic susceptibility in non-centrosymmetric MnSi. The paramagnetic
fluctuations are found to be incommensurate with the chemical lattice and to
have a chiral character.
  We argue that antisymmetric interactions must be taken into account to
properly describe the critical dynamics in MnSi above T$_C$. The possibility of
directly measuring the polarization dependent part of the dynamical
susceptibility in a large class of compounds through polarised inelastic
neutron-scattering is outlined as it can yield direct evidence for
antisymmetric interactions like spin-orbit coupling in metals as well as in
insulators.",0201327v1
2002-01-22,Finite-temperature properties of the Hubbard chain with bond-charge interaction,"We investigate the one-dimensional Hubbard model with an additional
bond-charge interaction, recently considered in the description of compounds
that exhibit strong 1D features above the temperature of ordered phases. The
partition function of the model is exactly calculated for a value of the
bond-charge coupling; the behavior of the specific heat and spin susceptibility
as a function of temperature is derived at arbitrary filling, and particularly
discussed across the occurring metal-insulator transition. The results show
that the bond-charge terms weaken the spin excitations of the system.",0201391v2
2002-01-28,Anomalous Dispersion of Longitudinal Optical Phonons in $\mathrm{\mathbf{Nd_{1.86}Ce_{0.14}CuO_{4+\bmδ}}}$ Determined by Inelastic X-ray Scattering,"The phonon dispersions of $\mathrm{Nd_{1.86}Ce_{0.14}CuO_{4+\delta}}$ along
the $[\xi,0,0]$ direction have been determined by inelastic x-ray scattering.
Compared to the undoped parent compound, the two highest longitudinal phonon
branches, associated with the Cu-O bond-stretching and out-of-plane oxygen
vibration, are shifted to lower energies. Moreover, an anomalous softening of
the bond-stretching band is observed around $\mathbf{q}=(0.2,0,0)$. These
signatures provide evidence for strong electron-phonon coupling in this
electron-doped high-temperature superconductor.",0201501v1
2002-02-01,Impurity-Induced Antiferromagnetic Ordering in the Spin Gap System TlCuCl_3,"The magnetization measurements have been performed on the doped spin gap
system TlCu_{1-x}Mg_xCl_3 with x <= 0.025. The parent compound TlCuCl_3 is a
three-dimensional coupled spin dimer system with the excitation gap Delta/k_B =
7.7 K. The impurity-induced antiferromagnetic ordering was clearly observed.
The easy axis lies in the (0,1,0) plane. It was found that the transition
temperature increases with increasing Mg^{2+} concentration x, while the
spin-flop transition field is almost independent of x. The magnetization curve
suggests that the impurity-induced antiferromagnetic ordering coexists with the
spin gap for x <= 0.017.",0202004v2
2002-02-19,Nature of the spin-singlet ground state in CaCuGe2O6,"We investigate by means of ab initio electronic structure analysis and
Quantum Monte Carlo calculations the scenario where longer-ranged magnetic
interactions dominate over short-ranged interactions in the physical
description of compounds. This question is discussed, in particular, for the
case of CaCuGe$_2$O$_6$ which shows a spin-singlet behavior induced by third
nearest neighbor copper pairs.",0202310v2
2002-02-27,First-principles calculation of the piezoelectric tensor d of III-V nitrides,"We report direct first-principles density-functional calculations of the
piezoelectric tensor $\tensor{d}$ relating polarization to applied stress for
the binary compounds AlN, GaN, and InN. The values of $\tensor{d}$ are rather
sensitive to the choice of the exchange-correlation functional, and results are
presented for both the local-density and gradient approximations. A comparison
with experiment and with values predicted indirectly from the elastic and
e-piezoconstant tensors is also presented.",0202496v1
2002-03-01,Nonmagnetic Insulating States near the Mott Transitions on Lattices with Geometrical Frustration and Implications for $κ$-(ET)$_2$Cu$_2(CN)_3$,"We study phase diagrams of the Hubbard model on anisotropic triangular
lattices, which also represents a model for $\kappa$-type BEDT-TTF compounds.
In contrast with mean-field predictions, path-integral renormalization group
calculations show a universal presence of nonmagnetic insulator sandwitched by
antiferromagnetic insulator and paramagnetic metals. The nonmagnetic phase does
not show a simple translational symmetry breakings such as flux phases,
implying a genuine Mott insulator. We discuss possible relevance on the
nonmagnetic insulating phase found in $\kappa$-(ET)$_2$Cu$_2(CN)_3$.",0203020v1
2002-03-08,The second phase transition in the pyrochlore oxide Cd2Re2O7,"Evidence for another phase transition at 120 K in the metallic pyrochlore
oxide Cd2Re2O7, following the structural transition at 200 K and followed by
the superconducting transition at 1.0 K, is given through resistivity,
magnetoresistance, specific heat, and X-ray diffraction measurements. The
results indicate unique successive structural and electronic transitions
occurring in the pyrochlore compound, revealing an interesting interplay
between the crystal and electronic structures on the itinerant electron system
in the pyrochlore lattice.",0203178v1
2002-03-08,High-Energy Spin Dynamics in La$_{1.69}$Sr$_{0.31}$NiO$_4$,"We have mapped out the spin dynamics in a stripe-ordered nickelate,
La$_{2-x}$Sr$_{x}$NiO$_{4}$ with $x \simeq 0.31$, using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: $\hbar
c_s\sim 0.32$ eV \AA, very similar to the velocity in the undoped, insulating
parent compound, La$_{2}$NiO$_{4}$. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high-$T_c$ cuprates.",0203187v1
2002-03-15,High quality MgB2 thin films in-situ grown by dc magnetron sputtering,"Thin films of the recently discovered magnesium diboride (MgB2) intermetalic
superconducting compound have been grown using a magnetron sputtering
deposition technique followed by in-situ annealing at 830 C. High quality films
were obtained on both sapphire and MgO substrates. The best films showed
maximum Tc = 35 K (onset), a transition width of 0.5 K, a residual resistivity
ratio up to 1.6, a low temperature critical current density Jc > 1 MA/cm2 and
anisotropic critical field with gamma = 2.5 close to the values obtained for
single crystals. The preparation technique can be easily scaled to produce
large area in-situ films.",0203322v1
2002-04-08,Pressure Effect on the Superconducting and Magnetic Transitions of the Superconducting Ferromagnet RuSr2GdCu2O8,"The superconducting ferromagnet RuSr2GdCu2O8 was investigated at high
pressure. The intra-grain superconducting transition temperature, Tc, is
resolved in ac-susceptibility as well as resistivity measurements. It is shown
that the pressure shift of Tc is much smaller than that of other high-Tc
compounds in a similar doping state. In contrast, the ferromagnetic transition
temperature, Tm, increases with pressure at a relative rate that is about twice
as large as that of Tc. The high-pressure data indicate a possible competition
of the ferromagnetic and superconducting states in RuSr2GdCu2O8.",0204185v1
2002-04-12,Theory of the Shubnikov-de Haas effect in quasi-two-dimensional metals,"The Shubnikov - de Haas effect in quasi-two-dimensional normal metals is
studied. The interlayer conductivity is calculated using the Kubo formula. The
electron scattering on short-range is considered in the self-consistent Born
approximation. The result obtained differs from that derived from the Boltzmann
transport equation. This difference is shown to be a general feature of
conductivity in magnetic field. A detailed description of the two new
qualitative effects -- the field-dependent phase shift of beats and of the slow
oscillations of conductivity is provided. The results obtained are applicable
to strongly anisotropic organic metals and to other quasi-two-dimensional
compounds.",0204270v1
2002-04-14,Raman scattering through surfaces having biaxial symmetry,"Magnetic Raman scattering in two-leg spin ladder materials and the
relationship between the anisotropic exchange integrals are analyzed by P. J.
Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
dependence of the two-magnon scattering is shown to provide information for the
magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
point out that the experimental results of polarized Raman measurements at
arbitrary angles with respect to the crystal axes have to be corrected for the
light ellipticity induced inside the optically anisotropic crystals. We refer
quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
for spectroscopic studies in other materials with strong anisotropy.",0204312v1
2002-04-22,Instability of isolated triplet excitations on the Shastry-Sutherland lattice (SSL),"Configurations of singlets and triplets on the SSL have been proposed in the
literature as variational ground states of the Shastry-Sutherland model at
fixed magnetization M. We prove, that isolated triplet excitations on the SSL
are unstable if the coupling alpha falls below a critical value alpha_c=2.0
(approx.). The instability should be visible in the compound SrCu_2(BO_3)_2
where a coupling alpha^*=1.48 is realized.",0204465v1
2002-05-03,Interlayer Magnetic Frustration in Quasi-stoichiometric Li1-xNi1+xO2,"Susceptibility, high-field magnetization and submillimeter wave electron spin
resonance measurements of layered quasi-stoichiometric Li1-xNi1+xO2 are
reported and compared to isomorphic NaNiO2. A new mechanism of magnetic
frustration induced by the excess Ni ions always present in the Li layers is
proposed. We finally comment on the possible realization of an orbital liquid
state in this controversial compound.",0205059v1
2002-05-11,Continuum in the Excitation Spectrum of the S=1 Compound CsNiCl_3,"Recent neutron scattering experiments on CsNiCl_3 reveal some features which
are not well described by the nonlinear sigma model nor by numerical
simulations on isolated S=1 spin chains. In particular, in real systems the
intensity of the continuum of multiparticle excitations, at T=6K, is about 5
times greater than predicted. Also the gap is slightly higher and the
correlation length is smaller. We propose a theoretical scenario where the
interchain interaction is approximated by a staggered magnetic field, yielding
to a correct prediction of the observed quantities.",0205234v1
2002-06-07,Optical evidence for mass enhancement of quasiparticles in pyrochlore Cd$_2$Re$_2$O$_7$,"We report on the results of optical studies of the newly discovered
superconductor Cd$_2$Re$_2$O$_7$ in the normal state. We show that the compound
has an exotic metallic state at low temperature. The optical conductivity
spectrum exhibits two distinct features: a sharp renormalized resonance mode at
zero frequency and a broad mid-infrared excitation band. Detailed analysis
reveals a moderate enhancement of the effective mass at low temperature and low
frequency.",0206096v1
2002-06-10,Magnetic anisotropy of BaCu2Si2O7: theory and antiferromagnetic resonance,"Antiferromagnetic resonance (AFMR) of BaCu2Si2O7 and a microscopic theory of
the magnetic anisotropy of spin 1/2 chain compounds with folded CuO3 geometry
being in good agreement with the available data are presented. The AFMR studies
at 4.2 K show the existence of two gaps (40 and 76 GHz) at zero magnetic field
and of two spin re-orientation transitions for H||c. The microscopic origin of
the two gaps is shown to be Hund's rule coupling which leads to a ""residual
anisotropy"" beyond the compensation of the Dzyaloshinskii-Moriya term by the
symmetric anisotropy which would be valid without Hund's coupling.",0206151v1
2002-06-12,Magnetic polarization induced by nonmagnetic impurities in high Tc cuprates,"The magnetic polarization induced by nonmagnetic impurities such as Zn in
high Tc cuprate compounds is studied by the variational Monte Carlo simulation.
The variational wave function is constructed from the eigenstates obtained from
Bogoliubov de Gennes mean field Hamiltonian for the two-dimensional t-J model.
A Jastrow factor is introduced to account for the induced magnetic moment and
the repulsion between holes and the impurity. A substantial energy gain is
obtained by forming an antiferromagnetic polarization covering 4 or 5 lattice
sites around the impurity. We also found the doping dependence for the induced
magnetic moment consistent with experiments.",0206197v1
2002-06-21,Superconductivity in high-pressure synthesized pure and doped MgB2 compounds,"Dense pure and doped (Mg1-xAx)B2 samples with A = Na, Ca, Cu, Ag, Zn and Al
were synthesized at high pressure - high temperature in a multi anvils press
(3.5-6 GPa, 900-1000C) for x up to 0.20. They were studied by x-ray
diffraction, scanning electron microscopy and their superconducting properties
were investigated by a.c. susceptibility, magnetization and transport
measurements. Only Al is really substituted on the Mg site. The others elements
form secondary phases with B or Mg. No large effect is observed on the
superconducting properties Tc, jc critical current, Hirr and Hc2.",0206409v1
2002-06-28,Towards a Tetravalent Chemistry of Colloids,"We propose coating spherical particles or droplets with anisotropic
nano-sized objects to allow micron-scale colloids to link or functionalize with
a four-fold valence, similar to the sp3 hybridized chemical bonds associated
with, e.g., carbon, silicon and germanium. Candidates for such coatings include
triblock copolymers, gemini lipids, metallic or semiconducting nanorods and
conventional liquid crystal compounds. We estimate the size of the relevant
nematic Frank constants, discuss how to obtain other valences and analyze the
thermal distortions of ground state configurations of defects on the sphere.",0206552v2
2002-07-01,Upward curvature of the upper critical field in the Boson--Fermion model,"We report on a non-conventional temperature behavior of the upper critical
field ($H_{c2}(T)$) which is found for the Boson-Fermion (BF) model. We show
that the BF model properly reproduces two crucial features of the experimental
data obtained for high-$T_c$ superconductors: $H_{c2}(T)$ does not saturate at
low temperatures and has an upward curvature. Moreover, the calculated upper
critical field fits very well the experimental results. This agreement holds
also for overdoped compounds, where a purely bosonic approach is not
applicable.",0207031v1
2002-07-05,Synthesis and Stoichiometry of MgB2,"The system MgxB2 has been investigated to investigate possible
nonstoichiometry in MgB2. When synthesized at 850oC, MgB2 is a line compound
with a possible Mg vacancy content of about 1%. Small changes in lattice
constants as a function of starting composition result from grain interaction
stresses, whose character is different in the Mg-rich, near-stoichiometric, and
Mg-deficient regimes. A small linear decrease of the superconducting transition
temperature, Tc, in the Mg-rich regime results from accidental impurity doping.",0207161v1
2002-07-22,Approximate tight-binding sum rule for the superconductivity related change of c-axis kinetic energy in multilayer cuprate superconductors,"We present an extension of the c-axis tight-binding sum rule discussed by
Chakravarty, Kee, and Abrahams [Phys. Rev. Lett. 82, 2366 (1999)] that applies
to multilayer high-Tc cuprate superconductors (HTCS) and use it to
estimate--from available infrared data--the change below Tc of the c-axis
kinetic energy, Hc, in YBa2Cu3O(7-delta) (delta=0.45,0.25,0.07), Bi2Sr2CaCu2O8,
and Bi2Sr2Ca2Cu3O10. In all these compounds Hc decreases below Tc and except
for Bi2Sr2CaCu2O8 the change of Hc is of the same order of magnitude as the
condensation energy. This observation supports the hypothesis that in
multilayer HTCS superconductivity is considerably amplified by the interlayer
tunnelling mechanism.",0207511v1
2002-07-26,Molecular Bose-Einstein condensate as an amplifier of weak interactions,"Collisions and chemical reactions of molecules in Bose-Einstein condensates
(BECs) are extremely sensitive to weak fields. This sensitivity arises due to
the high density of compound resonances and a macroscopic number of molecules
with kinetic energy E=0 (perfect energy resolution). We suggest that chemical
reactions in molecular BECs could be used to enhance effects produced by small
external perturbations and search for a parity-violating energy difference in
chiral molecules.",0207627v1
2002-08-01,"Electron-phonon interaction in transition metal diborides TB_2 (T=Zr, Nb, Ta) studied by point-contact spectroscopy","The electron-phonon interaction (EPI) in transition metal diborides TB_2
(T=Zr, Nb, Ta) is investigated by point-contact (PC) spectroscopy. The PC EPI
functions were recovered and the EPI parameters lambda<0.1 were estimated for
all three compounds. Common and distinctive features between the EPI functions
for those diborides are discussed also in connection with the superconductivity
in MgB_2.",0208020v2
2002-08-02,Heat Conduction and Magnetic Phase Behavior in Electron-Doped Ca_{1-x} La_x MnO_3(0 <= x <= 0.2),"Measurements of thermal conductivity (kappa) vs temperature are reported for
a series of Ca_{1-x} La_x MnO_3(0 <= x <= 0.2) specimens. For the undoped
(x=0), G-type antiferromagnetic compound a large enhancement of kappa below the
Neel temperature (T_N ~ 125 K) indicates a strong coupling of heat-carrying
phonons to the spin system. This enhancement exhibits a nonmonotonic behavior
with increasing x and correlates remarkably well with the small ferromagnetic
component of the magnetization reported previously [Neumeier and Cohn, Phys.
Rev. B 61 14319 (2000).] Magnetoelastic polaron formation appears to underly
the behavior of kappa and the magnetization at x <= 0.02.",0208050v1
2002-08-08,"The unusual electronic structure of the ""pseudo-ladder"" compound CaCu2O3","Experimental and theoretical studies of the unoccupied electronic structure
of CaCu2O3 single crystals have been performed using polarization-dependent
x-ray absorption spectroscopy and band structure calculations. The measured
hole distribution shows an unusual large number of holes in orbitals parallel
to the interlayer direction which is in agreement with the theoretical
analysis. CaCu2O3 deviates significantly from the standard pd-sigma cuprate
picture. The corresponding strong interlayer exchange is responsible for the
missing spin gap generic for other two-leg ladder cuprates.",0208180v1
2002-08-13,Local lattice potentials and steady-state vacancies in ionic crystals,"Basing on peculiarities of local potentials, the two principal trends in
vacancy formation are revealed. The proximity to the threshold of local ionic
stability due to a giant potential contribution of electronic delocalization
accounts for thermal anion vacancies typical of intrinsic semiconductors of AB
type. On the other hand, the tendency towards equalizing the potential field
results in a high concentration of structural cation vacancies observed in Ni_3
Sb and relative compounds.",0208248v1
2002-08-25,Spin dynamics of a tetrahedral cluster magnet,"We study the magnetism of a lattice of coupled tetrahedral spin-1/2 clusters
which might be of relevance to the tellurate compounds Cu2Te2O5X2, with X=Cl,
Br. Using the flow equation method we perform a series expansion in terms of
the inter-tetrahedral exchange couplings starting from the quadrumer limit.
Results will be given for the magnetic instabilities of the quadrumer phase and
the dispersion of elementary triplet excitations. In limiting cases of our
model of one- or two dimensional character we show our results to be consistent
with findings on previously investigated decoupled tetrahedral chains and the
Heisenberg model on the 1/5-depleted square lattice.",0208472v1
2002-08-30,Electronic properties of the novel 4d metallic oxide SrRhO3,"The novel 4d perovskite compound SrRhO3 was investigated by isovalent doping
studies. The solubility limits of Ca and Ba onto Sr-site were below 80% and
20%, respectively. Although SrRhO3 was chemically compressed, approximately
5.7% by the Ca doping, no significant influence was observed on the magnetic
and electrical properties.",0208591v1
2002-09-04,High-pressure X-ray diffraction study on alpha-PbF2,"The high-pressure behaviour of alpha-PbF2 has been investigated by
angular-dispersive synchrotron X-ray powder diffraction up to 6.55(8) GPa. The
fit of a 3rd-order Birch-Murnaghan equation-of-state gave the volume at zero
pressure V0=194.14(4)\AA$^3 and the bulk modulus b_0=47.0(6)GPa with the
pressure derivative b'=7.9(4). The continuous-symmetry-measure approach has
been used for the quantification of the distortion of the coordination
polyhedron in alpha-PbF2 revealing an increasing distortion with pressure.
keywords here: high pressure, X-ray diffraction, inorganic compounds PACS:
61.10.N2, 62.50.+P, 64.20.+t, 07.35, 61.10.-i",0209082v1
2002-09-04,Magnetism and unconventional superconductivity in Ce$_n$M$_m$In$_{3n+2m}$ heavy-fermion crystals,"We review magnetic, superconducting and non-Fermi-liquid properties of the
structurally layered heavy-fermion compounds Ce$_n$M$_m$In$_{3n+2m}$ (M=Co, Rh,
Ir). These properties suggest d-wave superconductivity and proximity to an
antiferromagetic quantum-critical point.",0209115v1
2002-10-10,Electronic Properties of Mn-Compounds Under Strain,"We study the physical properties of MnAs under strain by using accurate
first-principles pseudopotential calculations. Our results provide new insight
on the physics of strained multilayer that are grown epitaxially on different
lattice mismatched substrates and which are presently of interest for
spintronic applications. We compute the strain dependence of the structural
parameters, electronic bands, density of states and magnetization. In the
region of strain/stress that is easily directly accessible to measurements, the
effects on these physical quantities are linear. We also address the case of
uniaxial stress inducing sizeable and strongly non linear effects on electronic
and magnetic properties.",0210235v1
2002-10-24,Violation of Ioffe-Regel condition but saturation of resistivity of the high Tc cuprates,"We demonstrate that the resistivity data of a number of high Tc cuprates, in
particular La(2-x)SrxCuO4, are consistent with resistivity saturation, although
the Ioffe-Regel condition is strongly violated. By using the f-sum rule
together with calculations of the kinetic energy in the t-J model, we show that
the saturation resistivity is unusually large. This is related to the strong
reduction of the kinetic energy due to strong correlation effects. The
fulfilment of the Ioffe-Regel condition for conventional transition metal
compounds is found to be somewhat accidental.",0210543v1
2002-11-04,Competition and coexistence of magnetic and quadrupolar ordering,"The large number of low-lying states of d- and f-shells supports a variety of
order parameters. The effective dimensionality of the local Hilbert space
depends on the strength, and kind, of intersite interactions. This gives rise
to complicated phase diagrams, and an enhanced role of frustration and
fluctuation effects. The general principles are illustrated on the example of
the effect of a magnetic field on quadrupolar phase transitions in some
Pr-based skutterudite compounds.",0211064v2
2002-11-07,Failure of the empirical OCT law in the Bi2Sr2CuO6+d compound,"We have studied the evolution of the thermoelectric power S(T) with oxygen
doping of single-layered Bi2Sr2CuO6+d thin films and ceramics in the overall
superconducting (Tc, S290K) phase diagram. While the universal relation between
the room-temperature thermopower S290K and the critical temperature is found to
hold in the strongly overdoped region (d>0.14), a strong violation is observed
in the underdoped part of the phase diagram. The observed behaviour is compared
with other cuprates and the different scenarios are discussed.",0211135v1
2002-11-12,Infrared properties of W-doped charge-density-wave material K$_{0.3}$MoO$_3$,"The optical conductivity spectra of quasi-one dimensional compounds
K$_{0.3}$Mo$_{1-x}$W$_x$O$_3$ (x=0, 0.03 and 0.15) have been studied over broad
frequencies. While the dc resistivity measurements indicate no sign of CDW
transition in heavily W-doped blue bronze, the optical conductivity spectra
still show a single particle gap at around 0.2 eV for \textbf{E} parallel to
the chain direction. Such impurity effect challenges our understanding about
the occurrence of the optical gap with the CDW transition.",0211225v1
2002-11-13,Test for Pairing Symmetry Based on Spin Fluctuations in Organic Superconductors $κ$-(BEDT-TTF)$_{2}$X,"We propose that the superconducting pairing symmetry of organic
superconductors $\kappa$-(BEDT-TTF)$_{2}$X can be determined by measuring the
position in momentum space of the incommensurate peaks of the spin
susceptibility. We show that the positions of these peaks are uniquely
determined by the symmetry of the superconducting state and the geometry of
Fermi surface. Based on the effective Hubbard model on an anisotropic
triangular lattice, we demonstrate the different incommensurate patters of spin
responses for $d_{x^{2}-y^{2}}$- and $d_{xy}$-like pairing states. In addition,
we predict the nonexistence of the spin resonance mode in this compound, which
is an important feature in high-$T_{c}$ superconductors.",0211256v1
2002-11-15,Observation of Superconductivity in Heavy-Fermion Compounds of Ce2CoIn8,"We succeeded in growing a single crystal of Ce2CoIn8 by the flux method. The
results of specific heat and electrical resistivity measurements indicate that
Ce2CoIn8 is a heavy-fermion superconductor below 0.4 K with an electronic
specific heat coefficient gamma as large as 500 mJ/K^2mol-Ce.",0211320v1
2002-11-20,Damping of Nodal Fermions Caused by a Dissipative Mode,"Using a $d_{x^2 - y^2}$ superconductor in 2+1 dimensions we show that the
Nambu Goldstone fluctuations are replaced by dissipative excitations. We find
that the nodal quasi-particles damping is caused by the strong dissipative
excitations near the nodal points. As a result we find that the scattering
rates are linear in frequency and not cubic as predicted in the literature for
the ``d'' wave superconductors. Our results explain the recent angle resolved
photoemission spectroscopy and optical conductivity in the BSCCO high $T_c$
compounds.",0211440v1
2002-11-28,Small polarons and c-axis transport in highly anisotropic metals,"Motivated by the anomalous c-axis transport properties of the quasi
two-dimensional metal, $\rm Sr_2 Ru O_4$, and related compounds, we have
studied the interlayer hopping of single electrons that are coupled strongly to
c-axis bosons. We find a c-axis resistivity that reflects the in-plane
electronic scattering in the low and very high temperature limits (relative to
the characteristic temperature of the boson $T_{\rm boson}$). For temperatures
near the $T_{\rm boson}$, a broad maximum in the resistivity can appear for
sufficiently strong electron-boson coupling. This feature may account for the
observed ``metallic to non-metallic crossover'' seen in these layered oxides,
where the boson may be a phonon.",0211675v1
2002-11-29,The dual nature of 5f electrons and origin of heavy fermions in U compounds,"We develop a theory for the electronic excitations in UPt$_3$ which is based
on the localization of two of the $5f$ electrons. The remaining $f$ electron is
delocalized and acquires a large effective mass by inducing intra-atomic
excitations of the localized ones. The measured deHaas-vanAlphen frequencies of
the heavy quasiparticles are explained as well as their anisotropic heavy mass.
A model calculation for a small cluster reveals why only the largest of the
different $5f$ hopping matrix elements is operative causing the electrons in
other orbitals to localize.",0211706v1
2002-12-02,Isospin model for suppression of charge order in hole- doped NaV_2O_5,"The layered perovskite compound NaV_2O_5 exhibits charge ordering (CO) and
spin gap formation which is driven by inter- site Coulomb forces and exchange
dimerisation. Experimentally it was found that the CO transition is rapidly
reduced by doping. Charge ordering in NaV_2O_5 has a quasi 1D character due to
inter- ladder frustration in the Trellis lattice. Based on an extended
pseudospin (T=1) approach for hole doped NaV_2O_5 ladders we construct an Ising
like model that explains qualitatively the destruction of the CO phase as
function of hole doping \delta and show how the CO parameter depends on \delta
and the ratio of Coulomb and hopping energies.",0212025v1
2002-12-10,"Kondo effect in ""bad metals""","We study the low-temperature properties of a Kondo lattice using the large-N
formalism. For a singular density of conduction states (DOS), we generalize the
single-impurity result of Withoff and Fradkin: the strong-coupling fixed point
becomes irrelevant if the DOS vanishes at the Fermi level E_F. However, for E_F
close enough to the singularity, and close to half-filling, the Kondo
temperature, $T_K$, can become much smaller than the characteristic Fermi
liquid scale. At T=0, a meta-magnetic transition occurs at the critical
magnetic field H_c ~ (k_B/mu_B) T_K. Our results provide a qualitative
explanation for the behavior of the YbInCu_4 compound below the valence-change
transition.",0212222v1
2002-12-19,Superconductivity in the Orbital Degenerate Model for Heavy Fermion Systems,"Magnetism and superconductivity of new heavy fermion compounds CeTIn$_5$
(T=Co, Rh and Ir) are investigated by applying fluctuation exchange
approximation to an orbital degenerate Hubbard model. The superconducting phase
with $d_{x^2-y^2}$-symmetry is found to appear next to the antiferromagnetic
phase with increasing the orbital splitting energy. The present theory suggests
that the orbital splitting energy plays a key role of controlling parameter for
the quantum phase transitions in the heavy fermion system.",0212467v1
2002-12-23,Intrinsic tunneling spectra of Bi_2(Sr_{2-x}La_x)CuO_6,"We have measured intrinsic-tunneling spectra of a single CuO-layer La-doped
Bi_2Sr_{2-x}La_xCuO_{6+\delta} (Bi2201-La_x). Despite a difference of a factor
of three in the optimal superconducting critical temperatures for
Bi2201-La_{0.4} and Bi2212 (32 and 95 K, respectively) and different spectral
energy scales, we find that the pseudogap vanishes at a similar characteristic
temperature T*\approx 230-300K for both compounds. We find also that in
Bi2201-La_x, PG humps are seen as sharp peaks and, in fact, even dominate the
intrinsic spectra.",0212562v1
2003-01-14,Ab-initio determination of the localized/delocalized f-manifold in UPd_2Al_3,"The electronic structure of UPd_2Al_3 is described using the self-interaction
corrected local-spin-density approximation to density functional theory. The
groundstate is found to be characterized by the coexistence of localized (f^2)
and delocalized U f electrons, in agreement with experimental evidence. We
observe significant difference in electronic structure between UPd_2Al_3 and
the previously studied UPt_3 compound. Even though a trend towards localization
exists in UPt_3, the total energies and the density of states at the Fermi
level favor a groundstate with localized f^1, rather than f^2 U ions.",0301215v1
2003-01-28,Longitudinal magnon in the tetrahedral spin system Cu2Te2O5Br2 near quantum criticality,"We present a comprehensive study of the coupled tetrahedra-compound
Cu2Te2O5Br2 by theory and experiments in external magnetic fields. We report
the observation of a longitudinal magnon in Raman scattering in the ordered
state close to quantum criticality. We show that the excited
tetrahedral-singlet sets the energy scale for the magnetic ordering temperature
T_N. This energy is determined experimentally. The ordering temperature T_N has
an inverse-log dependence on the coupling parameters near quantum criticality.",0301546v1
2003-02-07,Magnetization Plateaux in Bethe Ansatz Solvable Spin-S Ladders,"We examine the properties of the Bethe Ansatz solvable two- and three-leg
spin-$S$ ladders. These models include Heisenberg rung interactions of
arbitrary strength and thus capture the physics of the spin-$S$ Heisenberg
ladders for strong rung coupling. The discrete values derived for the
magnetization plateaux are seen to fit with the general prediction based on the
Lieb-Schultz- Mattis theorem. We examine the magnetic phase diagram of the
spin-1 ladder in detail and find an extended magnetization plateau at the
fractional value $<M > = {1/2}$ in agreement with the experimental observation
for the spin-1 ladder compound BIP-TENO.",0302135v1
2003-02-10,Correlated Doping in Semiconductors: The Role of Donors in III-V Diluted Magnetic Semiconductors,"We investigate the compositional dependence of the total energy of the mixed
crystals (Ga,Mn)As co-doped with As, Sn, and Zn. Using the ab initio LMTO-CPA
method we find a correlation between the incorporation of acceptors (Mn, Zn)
and donors (Sn, antisite As). In particular, the formation energy of As_Ga is
reduced by approx. 0.1 eV in the presence of Mn, and vice versa. This leads to
the self-compensating behavior of (Ga,Mn)As.",0302176v1
2003-02-12,Ab initio study of charge order in Fe3O4,"We present a self-interaction corrected local spin density (SIC-LSD) study of
the electronic structure and possible charge order of magnetite,
Fe$_{3}$O$_{4}$. The issue of charge order in magnetite is explored in both
cubic and orthorhombic structures, the latter being an approximation to the
true, low temperature, monoclinic structure. We find that the Verwey charge
ordered phase is not the groundstate solution for this compound neither in
cubic nor orthorhombic structure.",0302229v2
2003-02-17,Magnetic Susceptibility of an integrable anisotropic spin ladder system,"We investigate the thermodynamics of a spin ladder model which possesses a
free parameter besides the rung and leg couplings. The model is exactly solved
by the Bethe Ansatz and exhibits a phase transition between a gapped and a
gapless spin excitation spectrum. The magnetic susceptibility is obtained
numerically and its dependence on the anisotropy parameter is determined. A
connection with the compounds KCuCl3, Cu2(C5H12N2)2Cl4 and (C5H12N)2CuBr4 in
the strong coupling regime is made and our results for the magnetic
susceptibility fit the experimental data remarkably well.",0302336v1
2003-02-21,Quantum-Classical Reentrant Relaxation Crossover in Dy2Ti2O7 Spin-Ice,"We have studied spin relaxation in the spin ice compound Dy2Ti2O7 through
measurements of the a.c. magnetic susceptibility. While the characteristic spin
relaxation time is thermally activated at high temperatures, it becomes almost
temperature independent below Tcross ~ 13 K, suggesting that quantum tunneling
dominates the relaxation process below that temperature. As the low-entropy
spin ice state develops below Tice ~ 4 K, the spin relaxation time increases
sharply with decreasing temperature, suggesting the emergence of a collective
degree of freedom for which thermal relaxation processes again become important
as the spins become highly correlated.",0302453v1
2003-02-24,Study of low-energy magnetic excitations in single-crystalline CeIn3 by inelastic neutron scattering,"Inelastic neutron scattering experiments were performed on single crystals of
the heavy-fermion compound CeIn$_{3}$ for temperatures below and above the
N\'eel temperature, $T_N$. In the antiferromagnetically ordered phase,
well-defined spin-wave excitations with a bandwidth of 2 meV are observed. The
spin waves coexist with quasielastic (QE) Kondo-type spin-fluctuations and
broadened crystal-field (CF) excitations below $T_N$. Above $T_N$, only the QE
and CF excitations persist, with a weak temperature dependence.",0302487v1
2003-02-25,Superconductivity in Pr2Ba4Cu7O15-delta with metallic double chains,"We report superconductivity with $T_{c,onset}$=$\sim$10K in
Pr$_{2}$Ba$_{4}$Cu$_{7}$O$_{15-\delta}$ compound possessing metallic double
chains. A reduction treatment on as-sintered samples causes not only the
enhanced metallic conduction but also the appearance of superconductivity
accompanied by the c-axis elongation due to oxygen deficiency.",0302508v6
2003-03-27,Dynamical structure factor of the anisotropic Heisenberg chain in a transverse field,"We consider the anisotropic Heisenberg spin-1/2 chain in a transverse
magnetic field at zero temperature. We first determine all components of the
dynamical structure factor by combining exact results with a mean-field
approximation recently proposed by Dmitriev {\it et al}., JETP 95, 538 (2002).
We then turn to the small anisotropy limit, in which we use field theory
methods to obtain exact results. We discuss the relevance of our results to
Neutron scattering experiments on the 1D Heisenberg chain compound ${\rm
Cs_2CoCl_4}$.",0303587v1
2003-04-03,Orbital ordering and frustrations,"An orbital ordering occurs in many transition metal compounds with
Jahn-Teller ions and plays an important role in these materials. At the same
time, exchange interactions in orbitally degenerate systems are inherently
frustrated, even in materials with simple crystal lattices. We discuss the
origin of this frustration, considering in detail materials with a cubic and
triangular lattice of transition metal ions. We also discuss possible types of
ground states of such systems, e.g., disordered orbital liquids and ordering
due to the order-from-disorder mechanism.",0304089v1
2003-04-08,Ultrasonic evidence of an uncorrelated cluster formation temperature in manganites with first-order magnetic transition at T_C,"Ultrasonic attenuation and phase velocity measurements have been carried out
in the ferromagnetic perovskites La_{2/3}Ca_{1/3}MnO_3 and
La_{2/3}Sr_{1/3}MnO_3. Data show that the transition at the Curie temperature,
T_C, changes from first- to second-order as Sr replaces Ca in the perovskite.
The compound with first-order transition shows also another transition at a
temperature T* > T_C. We interpret the temperature window T_C < T < T* as a
region of coexistence of a phase separated regime of metallic and insulating
regions, in the line of recent theoretical proposals.",0304187v1
2003-04-17,Field-Induced Spin-Density-Wave Phases in Quasi-One-Dimensional Conductors: Theory versus Experiment,"We show that ""Quantizied Nesting"" model misses important features of the
magnetic field-induced spin-density-wave (FISDW) phase diagram. Among them are:
1) the FISDW wave vector is not strictly quantized; 2) in some compounds, the
FISDW diagram consists of two regions: a) at low temperatures, there are jumps
of the wave vector (i.e., the first order transitions between FISDW phases), b)
at high temperatures the jumps and the first order transitions disappear but
the wave vector is still a non-trivial function of a magnetic field. These are
in agreement with the experiments on (TMTSF)2PF6.",0304406v1
2003-04-22,Lattice and superexchange effects in doped CMR manganites,"We report on the influence of the lattice degrees of freedom on charge,
orbital and spin correlations in colossal magnetoresistance (CMR) manganites.
For the weakly doped compounds we demonstrate that the electron-phonon coupling
promotes the trapping of charge carriers, the disappearance of the orbital
polaron pattern and the breakdown of ferromagnetism at the CMR transition. The
role of different superexchange interactions is explored.",0304491v1
2003-04-23,Exciton spin relaxation in single semiconductor quantum dots,"We study the relaxation of the exciton spin (longitudinal relaxation time
$T_{1}$) in single asymmetrical quantum dots due to an interplay of the
short--range exchange interaction and acoustic phonon deformation. The
calculated relaxation rates are found to depend strongly on the dot size,
magnetic field and temperature. For typical quantum dots and temperatures below
100 K, the zero--magnetic field relaxation times are long compared to the
exciton lifetime, yet they are strongly reduced in high magnetic fields. We
discuss explicitly quantum dots based on (In,Ga)As and (Cd,Zn)Se semiconductor
compounds.",0304509v1
2003-04-28,High temperature thermal conductivity of 2-leg spin-1/2 ladders,"Based on numerical simulations, a study of the high temperature, finite
frequency, thermal conductivity $\kappa(\omega)$ of spin-1/2 ladders is
presented. The exact diagonalization and a novel Lanczos technique are
employed.The conductivity spectra, analyzed as a function of rung coupling,
point to a non-diverging $dc-$limit but to an unconventional low frequency
behavior. The results are discussed with perspective recent experiments
indicating a significant magnetic contribution to the energy transport in
quasi-one dimensional compounds.",0304629v1
2003-05-14,Magnetodielectric Effects from Spin Fluctuations in Isostructural Ferromagnetic and Antiferromagnetic Systems,"We report on the effects of spin fluctuations, magnetic ordering, and
external magnetic field on the dielectric constant of the ferromagnet SeCuO3,
and the antiferromagnet TeCuO3. A model based on the coupling between uniform
polarization and the q-dependent spin-spin correlation function is presented to
explain the different behaviors for these isostructural compounds. The large
magnetocapacitance near the transition temperature in the ferromagnet SeCuO3
suggests routes to enhancing the magnetodielectric response for practical
applications.",0305333v1
2003-05-19,Exploration of oxide-based diluted magnetic semiconductors toward transparent spintronics,"A review is given for the recent progress of research in the field of
oxide-based diluted magnetic semiconductor (DMS), which was triggered by
combinatorial discovery of transparent ferromagnet. The possible advantages of
oxide semiconductor as a host of DMS are described in comparison with
conventional compound semiconductors. Limits and problems for identifying novel
ferromagnetic DMS are described in view of recent reports in this field.
Several characterization techniques are proposed in order to eliminate
unidentified ferromagnetism of oxide-based DMS (UFO). Perspectives and possible
devices are also given.",0305435v1
2003-05-28,Growth of large single crystals of Rare Earth Hexaborides,"Single crystal growth of several rare earth hexaborides has been carried out
by the floating zone technique. A high power Xenon arc lamp image furnace was
used for the crystal growth. Large high quality crystals of LaB$_{6}$,
CeB$_{6}$, PrB$_{6}$ and NdB$_{6}$, about 1 cc in volume have been obtained.
Crystals of all these compounds have also been grown using enriched $^{11}$B
isotope for use in neutron scattering experiments.",0305656v1
2003-05-29,Magnetic Interactions in Transition-Metal Oxides,"This a review article, which presents a general framework for the analysis of
interatomic magnetic interactions in the spin-density-functional theory, which
is based on the magnetic force theorem, make a link with the models for
transition-metal oxides, and gives several examples of how this strategy can be
used for the analysis of magnetic properties of colossal-magnetoresistive
perovskite manganites, double perovskite and pyrochlore compounds.",0305668v1
2003-06-04,"Chiral Symmetry and Collective Excitations in p-wave, d-wave and f-wave Superconductors","We discuss the origin of charge density wave (CDW) and spin density wave
(SDW) in p-wave, d-wave and f-wave superconductors. To describe the low-energy
quasiparticle excitation of p-wave case, we introduce a two- (one for time and
one for space) dimensional massless Dirac model. After the non-Abelian
bosonization is performed, the charge and spin density waves emerge from the
model. By using this scheme, we try to explain the characteristic aspect of
phase diagrams of various compounds, oxides and organic superconductors. The
purpose of this paper is to make an argument that the dimensionality of the
nodal excitation in superconductors plays an important role in the
determination of the structure of the phase diagram.",0306095v1
2003-06-20,Magnetic properties of GaMnAs single layers and GaInMnAs superlattices investigated at low temperature and high magnetic field,"Magnetotransport properties of GaMnAs single layers and InGaMnAs/InGaAs
superlattice structures were investigated at temperatures from 4 K to 300 K and
magnetic fields up to 23 T to study the influence of carriers confinement
through different structures. Both single layers and superlattice structures
show paramagnetic-to-ferromagnetic phase transition. In GaMnAs/InGaAs
superlattice beside the Curie temperature (Tc ~ 40 K), a new phase transition
is observed close to 13 K.",0306534v1
2003-06-26,Variation of Superconducting Transition Temperature in Hole-Doped Copper-Oxides,"The experimentally observed difference of superconducting critical
temperature $T_{c}$ in hole-doped cuprates is studied by using an extended
interlayer coupling model for layered d-wave superconductors. We show that the
change of the maximum $T_{c}$ from series to series is determined by the next
nearest neighboring hopping $t^{\prime}$, while the difference of the maximum
$T_{c}$ among the compounds in a homogeneous series is controlled by the
interlayer pairing strength. Our results provide helpful guidelines in the
search for new high-$T_{c}$ superconductors.",0306680v1
2003-06-28,Low-Temperature Quantum Critical Behaviour of Systems with Transverse Ising-like Intrinsic Dynamics,"The low-temperature properties and crossover phenomena of $d$-dimensional
transverse Ising-like systems within the influence domain of the quantum
critical point are investigated solving the appropriate one-loop
renormalization group equations. The phase diagram is obtained near and at
$d=3$ and several sets of critical exponents are determined which describe
different responses of a system to quantum fluctuations according to the way of
approaching the quantum critical point. The results are in remarkable agreement
with experiments for a wide variety of compounds exhibiting a quantum phase
transition, as the ferroelectric oxides and other displacive systems.",0306713v1
2003-07-01,New Type of Degenerate Quantum Spin Phase,"Correlated electrons often crystalize to the Mott insulator usually with some
magnetic orders, whereas the ""quantum spin liquid"" has been a long-sought
issue. We report numerical evidences that a nonmagnetic insulating (NMI) phase
gets stabilized near the Mott transition with remarkable properties:
  The 2D Mott insulators on geometrically frustrated lattices contain a phase
with gapless spin excitations and degeneracy of the ground state in the whole
Brillouin zone of the total momentum. It has an interpretation for an
unexplored type of a quantum liquid. The present concept is useful in analyzing
a variety of experimental results in frustrated magnets including organic
BEDT-TTF compounds.",0307022v1
2003-07-17,"Specific heat and magnetization study on single crystals of a frustrated, quasi one-dimensional oxide: Ca3Co2O6","Specific heat and magnetization measurements have been carried out under a
range of magnetic fields on single crystals of Ca3Co2O6. This compound is
composed of Ising magnetic chains that are arranged on a triangular lattice.
The intrachain and interchain couplings are ferromagnetic and
antiferromagnetic, respectively. This situation gives rise to geometrical
frustration, that bears some similarity to the classical problem of a
two-dimensional Ising triangular antiferromagnet. This paper reports on the
ordering process at low-T and the possibility of one-dimensional features at
high-T.",0307429v1
2003-07-31,Carrier induced ferromagnetism in room temperature ferromagnetic semiconductor rutile TiO2 doped with Co,"A ferromagnetic semiconductor, rutile (Ti,Co)O2, exhibits anomalous Hall
effect at room temperature. Strong dependence of the anomalous Hall effect, as
well as the magneto-optic response, on the carrier concentration suggests
carrier induced ferromagnetism in this compound. Both ferromagnetic responses
are caused by the charge carriers at the band edge of host semiconductor,
indicating possibilities of spintronics devices operable at room temperature.",0307760v1
2003-08-10,The role of electronic correlations on the phonon modes of MnO and NiO,"The possibility of magnetic-order induced phonon anisotropy in single
crystals of MnO and NiO is investigated using inelastic neutron scattering.
Below Tn both compounds exhibit a splitting in their transverse optical phonon
spectra of approximately 10%. This behavior illustrates that, contrary to
general assumption, the dynamic properties of MnO and NiO are substantially
non-cubic.",0308188v1
2003-08-20,Pairing and condensation of Laughlin quasiparticles in fractional quantum Hall systems,"From the analysis of their interaction pseudopotentials, it is argued that
(at certain filling factors) Laughlin quasiparticles can form pairs. It is
further proposed that such pairs could have Laughlin correlations with one
another and form condensed states of a new type. The sequence of fractions
corresponding to these states includes all new fractions observed recently in
experiment (e.g., \nu=5/13, 3/8, or 4/11).",0308397v1
2003-08-23,"Presence of 3d Quadrupole Moment in LaTiO3 Studied by 47,49Ti NMR","Ti NMR spectra of LaTiO3 are reexamined and the orbital state of this
compound is discussed. The NMR spectra of LaTiO3 taken at 1.5 K under zero
external field indicate a large nuclear quadrupole splitting. This splitting is
ascribed to the presence of the rather large quadrupole moment of 3d electrons
at Ti sites, suggesting that the orbital liquid model proposed for LaTiO3 is
inappropriate. The NMR spectra are well explained by the orbital ordering model
expressed approximately as $1/\sqrt{3}(d_{xy}+d_{yz}+d_{zx})$ originating from
a crystal field effect. It is also shown that most of the orbital moment is
quenched.",0308462v1
2003-08-25,Magnetic Field Induced Non-Fermi-Liquid Behavior in YbAgGe Single Crystal,"Detailed anisotropic resistivity and heat capacity measurements down to ~0.4
K and up to 140 kOe are reported for a single crystalline YbAgGe. Based on
these data YbAgGe, a member of the hexagonal RAgGe series, can be classified as
new, stoichiometric heavy fermion compound with two magnetic ordering
temperatures below 1 K and field-induced non-Fermi-liquid behavior above 45-70
kOe and 80-110 kOe for $H || (ab) and H || c respectively.",0308517v1
2003-08-26,Magnetic Behavior of La7Ru3O18,"Rhombohedral La7Ru3O18 can be considered to be nearly geometrically
frustrated due to its close structural similarity to the strongly geometrically
frustrated compound La4.87Ru2O12. The magnetic ordering of La7Ru3O18 was
explored using a combination of dc and ac magnetic susceptibility measurements.
The magnetic phase diagram shows two different ordering regimes. A low field
magnetic phase occurs at applied fields of 0-3T and temperatures below 10K,
while a high field phase is found at fields of 3-5T and temperatures below 9K.",0308518v1
2003-09-08,Point-contact tunneling involving low-dimensional spin-triplet superconductors,"We modify and extend previous microscopic calculations of tunneling in
superconducting junctions based on a non-equilibrium Green function formalism
to include the case of spin-triplet pairing. We show that distinctive features
are present in the I-V characteristics of different kinds of junctions, in
particular when the effects of magnetic fields are taken into account, that
permit to identify the type of pairing. We discuss the relevance of these
results in the context of quasi one-dimensional organic superconductors like
(TMTSF)_2(PF_6) and layered compounds like Sr_2RuO_4.",0309195v2
2003-09-09,"Mott Insulators, No-Double-Occupancy, and Non-Abelian Superconductivity","SU(4) dynamical symmetry is shown to imply a no-double-occupancy constraint
on the minimal symmetry description of antiferromagnetism and d-wave
superconductivity. This implies a maximum doping fraction of 1/4 for cuprates
and provides a microscopic critique of the projected SO(5) model. We propose
that SU(4) superconductors are representative of a class of compounds that we
term non-abelian superconductors. We further suggest that non-abelian
superconductors may exist having SU(4) symmetry and therefore cuprate-like
dynamics, but without d-wave hybridization.",0309229v1
2003-09-16,Superconducting states in the tetrahedral compound PrOs4Sb12,"We find possible superconducting states for tetrahedral (Th) symmetry
crystals with strong spin-orbit coupling using Landau theory. Additional
symmetry breaking within the superconducting state is considered. We discuss
nodes of the gap functions for the different states, secondary superconducting
order parameters and coupling to the elastic strain. By comparing our results
to experiments, we find that superconductivity in PrOs4Sb12 is best described
by the three-dimensional representations of point group Th.",0309382v2
2003-10-01,Colossal Electric Conductivity in Ag-defect Ag5Pb2O6,"Bystroem-Evers compound Ag5 Pb2O6 has been annealed at 500-540 K under flow
of electric current which results in a textured structure and anisotropic
colossal electric conductivity (> 10^9 ohm-1cm-1) between 210-525 K. The
related physical properties are primarly governed by dissociation of Ag from
c-axis channels and lattice strains which in turn depend upon electric current.",0310011v2
2003-10-06,Helimagnetism in a disordered and geometrically frustrated quantum spin chain,"Neutron diffraction and bulk measurements are used to determine the nature of
the low-temperature ordered state in LiCu$_2$O$_2$, a $S=1/2$ spin-chain
compound with competing interactions. The magnetic structure is found to be
helimagnetic, with a propagation vector $(0.5,\zeta,0)$, $\zeta=0.174$. The
nearest-neighbor exchange constant and frustration ratio are estimated to be
$J=5.8$ meV and $J_2/J_1=0.29$, respectively. For idealized spin chains these
parameter values would signify a gapped spin-liquid ground state. Long-range
ordering is attributed to intrinsic non-stoichiometry.",0310126v1
2003-10-08,Magnetic Anisotropy of SrCu$_2$(BO$_3$)$_2$ System as Revealed by X-Band ESR,"X-band ESR measurements on a single crystal of the highly frustrated
SrCu$_2$(BO$_3$)$_2$ system are shown to provide an essential inspection of the
magnetic anisotropy present in this compound. The very broad absorption lines
seem to be consistent with the largest anisotropy term, namely, the
antisymmetric Dzyaloshinsky-Moriya (DM) interaction allowed by symmetry.
However, the previously well-accepted model of only interdimer interaction is
generalized with additional intradimer DM terms. Moreover, spin-phonon coupling
is recognized as the cause on the linewidth broadening with increasing
temperature.",0310178v1
2003-10-10,High Pressure phase transitions in BaWO4,"Using in-situ angle dispersive x-ray diffraction, we have shown that barium
tungstate, which exists in scheelite phase at ambient conditions, transforms to
a new phase about seven giga pascal. Analysis of our data based on Le bail
refinement suggests that this phase could be fergusonite and not mercuric
molybdate type, which was proposed earlier from the Raman investigations.
Beyond fourteen giga pascal this compound undergoes another phase
transformation to a significantly disordered structure. Both the phase
transitions are found to be reversible.",0310236v2
2003-10-12,Spin Fluctuation in Heavy Fermion CeRu_2Si_2,"Spin fluctuations of the archetypal heavy-fermion compound CeRu_2Si_2 have
been investigated by neutron scattering in an entire irreducible Brillouin
zone. The dynamical susceptibility is remarkably well described by the
self-consistent renormalization (SCR) theory of the spin fluctuation in a
phenomenological way, proving the effectiveness of the theory. The present
analysis using the SCR phenomenology has allowed us to determine fourteen
exchange constants, which show the long-range nature of the
Ruderman-Kittel-Kasuya-Yosida interaction.",0310270v3
2003-10-22,Why Tc of MgB2 is the highest in a number of diborides?,"It is shown, that the problem rising Tc diborides is a problem of
nonstoichiometry in a plane of boron in diborides of heavy metals being
compounds of variable composition.",0310511v1
2003-10-24,Lattice Distortion and Magnetic Ground State of YTiO$_3$ and LaTiO$_3$,"Effects of lattice distortion on the magnetic ground state of YTiO$_3$ and
LaiO$_3$ are investigated on the basis accurate tight-binding parametrization
of the $t_{2g}$ electronic structure extracted from the local-density
approximation. The complexity of these compounds is related with the fact that
the $t_{2g}$-level splitting, caused by lattice distortions, is comparable with
the energies of superexchange and spin-orbit interactions. Therefore, all these
interactions are equally important and should be treated on an equal footing.
The Hartree-Fock approximation fails to provide a coherent description
simultaneously for YTiO$_3$ and LaTiO$_3$, and it is essential to go beyond.",0310581v1
2003-10-24,Phonon spectrum and soft-mode behavior of MgCNi_3,"Temperature dependent inelastic neutron-scattering measurements of the
generalized phonon density-of-states for superconducting MgCNi_3, T_c=8 K, give
evidence for a soft-mode behavior of low-frequency Ni phonon modes. Results are
compared with ab initio density functional calculations which suggest an
incipient lattice instability of the stoichiometric compound with respect to Ni
vibrations orthogonal to the Ni-C bond direction.",0310592v1
2003-10-31,Magnetic excitations in La$_{1.5}$Sr$_{0.5}$CoO$_4$,"We report magnetization and neutron scattering measurements of the half-doped
compound La$_{1.5}$Sr$_{0.5}$CoO$_4$, which exhibits a checkerboard pattern of
charge ordering below ~800K. In the antiferromagnetically-ordered phase below
\~40K the spins are found to be canted in the ab plane. The spin excitation
spectrum includes spin-wave excitations with a maximum energy of 16 meV, and
diffuse magnetic modes at energies around 30 meV.",0310778v1
2003-11-06,Low work function of the (1000) Ca2N surface,"Polymer diodes require cathodes that do not corrode the polymer but do have
low work function to minimize the electron injection barrier. First-principles
calculations demonstrate that the work function of the (1000) surface of the
compound Ca2N is half an eV lower than that of the elemental metal Ca (2.35 vs.
2.87 eV). Moreover its reactivity is expected to be smaller. This makes Ca2N an
interesting candidate to replace calcium as cathode material for polymer light
emitting diode devices.",0311130v3
2003-11-13,Noncollinear magnetism in distorted perovskite compounds,"Using results of the band structure calculations in the local-spin-density
approximation we demonstrate how the crystal distortions affect the magnetic
structure of orthorhombically distorted perovskites leading to a non-collinear
spin arrangement. Our results suggest that the non-collinearity of the spin
magnetic moments, being generally small in La$M$O$_3$ series with $M$=Cr-Fe, is
large in SrRuO$_3$.",0311297v1
2003-11-13,Non-local Coulomb interactions and metal-insulator transition in Ti$_2$O$_3$: a cluster LDA+DMFT approach,"We present an ab initio quantum theory of the metal-insulator transition in
Ti$_2$O$_3$. The recently developed cluster LDA+DMFT scheme is applied to
describe the many-body features of this compound. The conventional single site
DMFT cannot reproduce a low temperature insulating phase for any reasonable
values of the Coulomb interaction. We show that the non-local Coulomb
interactions and the strong chemical bonding within Ti-Ti pair is the origin of
the small gap insulating ground state of Ti$_2$O$_3$.",0311319v1
2003-11-24,Effect of Hydrostatic Pressure on the Kondo Effect in the Heavy Fermion System Yb$_2$Fe$_3$Si$_5$,"We report the effect of hydrostatic pressure on the resistivity of the heavy
fermion Kondo lattice compound Yb$_2$Fe$_3$Si$_5$ in the temperature range
2-300 K and in pressures upto 10 Kbar. At ambient pressure the resistivity
shows a prominent Kondo effect. The Kondo minimum shifts from 22.5 K at ambient
pressure to 19.2 K at a pressure of 10 Kbar. The depth of the Kondo minimum
also progressively decreases with pressure. These results suggest a possible
weakening of the Kondo effect with the application of pressure.",0311548v1
2003-11-25,Remarks about the Zeeman splitting in quantum dots and single atom transistors,"An empirical formula is proposed to calculate the Kondo temperature in
quantum point contacts from the Zeeman splitting. A similar formula was used in
the point-contact spectroscopy (PCS) method to obtain from the Zeeman splitting
of the Kondo peak in the characteristics of the classical Kondo alloys AuFe and
CuMn [1]. Using this formula, it is possible to find the Kondo temperature
taking into account the temperature of the experiment and Lande factor of the
compounds.",0311578v1
2003-12-08,Superconductivity from doping boron icosahedra,"We propose a new route to achieve the superconducting state in Boron-rich
solids, the hole doping of B$_{12}$ icosahedra. For this purpose we consider a
prototype metallic phase of B$_{13}$C$_2$. We show that in this compound the
Boron icosahedral units are mainly responsible for the large phonon frequencies
logarithmic average, 65.8 meV, and the moderate electron-phonon coupling 0.8.
We suggest that this high critical temperature could be a general feature of
hole doped boron icosahedral solids.",0312200v2
2003-12-12,Realization of the anomalous scattering method in crystallography on the basis of the parametric X-ray radiation,"Spectra of parametric X-ray radiation (PXR) are considered in the range of
anomalous dispersion for one of the atoms in a crystal elementary cell. The PXR
spectra are calculated both for the ultra-relativistic and non-relativistic
electrons for the specific conditions corresponding to the organic compounds .
It is shown that analysis of the RXR angular distribution permits one to
realize the method of anomalous scattering for direct measurement of the phases
of structure amplitudes without additional isomorphic intrusion of a heavy
atom.",0312310v1
2003-12-16,Interplay between the magnetic fluctuations and superconductivity in the lanthanum cuprates,"We report the analysis of the magnetic fluctuations in the superconducing
La_{2-x}Sr_xCuO_4 and the related lanthanum cuprates having the different
symmetry of the low temperature structure. The NMR and ESR investigations
revealed the dynamical coexistence of the superconductivity and the
antiferromagnetic correlations in the large part of superconductivity region of
the phase diagram. We show that for all compounds, independent on their low
temperature symmetry and on their superconducting properties, the enhancement
of the spin stiffness near 1/8 doping takes place.",0312393v1
2003-12-22,The charge and spin sectors of the t-t' Hubbard model,"The charge and spin sectors, which are intimately coupled to the fermionic
one, of the t-t' Hubbard model have been computed self-consistently within the
two-pole approximation. The relevant unknown correlators appearing in the
causal bosonic propagators have been computed by enforcing the constraints
dictated by the hydrodynamics and the algebra of the composite operators coming
into play. The proposed scheme of approximation extends previous calculations
made for the fermionic sector of the t-t' Hubbard model and the bosonic sector
of the Hubbard model, which showed to be very effective to describe the
overdoped region of cuprates (the former) and the magnetic response of their
parent compounds (the latter).",0312578v1
2003-12-29,La0.95Sr0.05CoO3: An efficient room-temperature thermoelectric oxide,"We present measurements of electrical resistivity, thermal conductivity and
thermopower of polycrystalline Sr-doped LaCoO3 with composition
La0.95Sr0.05CoO3. Our data show that the investigated compound exhibits a very
respectable room temperature thermoelectric figure of merit value of 0.18. Our
results not only show that oxides are promising candidates for thermoelectric
cooling applications, but also point towards the need for careful theoretical
calculations that will serve as a guide in producing the next generation of
thermoelectric materials.",0312670v1
2004-01-09,Susceptibility and Dzyaloshinskii-Moriya interaction in the Haldane gap compound NENP,"The Haldane gap material NENP exhibits anomalies in its Knight shift, far
infrared absorption and field-dependent gaps, which have been explained using
the staggered $g$-tensor that occurs due to the low crystal symmetry. We point
out that the low-temperature susceptibility is also anomalous and that a
consistent interpretation of all data may require consideration of the
Dzyaloshinskii-Moriya interaction.",0401158v3
2004-01-11,Anomalous percolation and quantum criticality in diluted rare-earth nickelates,"A microscopic model for the diluted spin-mixed compounds
(R_xY_(1-x))_2BaNiO_5 (R=magnetic rare-earth) is studied using Quantum Monte
Carlo (QMC). The ordering temperature is shown to be a universal function of
the impurity concentration x and the intrinsic Ni-chain correlation length. An
effective model for the critical modes is derived. The possibility of a quantum
critical point driven by the rare earth-concentration and the existence of a
Griffiths phase in the high dilution limit is investigated. Several possible
experimental approaches to verify the results are put forward.",0401167v1
2004-01-19,Why magnesium diboride is not described by anisotropic Ginzburg-Landau theory,"It is well established that the superconductivity in the recently discovered
superconducting compound MgB$_{2}$ resides in the quasi-two-dimensional band
($\sigma$-band) and three-dimensional band ($\pi$-band). We demonstrate that,
due to such band structure, the anisotropic Ginzburg-Landau theory practically
does not have region of applicability, because gradient expansion in the $c$
direction breaks down. In the case of dirty $\pi$-band we derive the simplest
equations which describe properties of such superconductors near $T_{c}$ and
explore some consequences of these equations.",0401339v1
2004-01-30,Superconductivity Driven by Chain Coupling and Electronic Correlations,"We present an analysis of a system of weakly coupled Hubbard chains based on
combining an exact study of spectral functions of the uncoupled chain system
with a renormalization group method for the coupled chains. For low values of
the onsite repulsion $U$ and of the doping $\delta$, the leading instability is
towards a superconducting state. The process includes excited states above a
small correlation pseudogap. Similar features appear in extended Hubbard models
in the vicinity of commensurate fillings. Our theoretical predictions are
consistent with the phase diagram observed in the (TMTTF)$_2$X and (TMTSF)$_2$X
series of organic compounds.",0401642v2
2004-02-10,"Electron-lattice coupling, orbital stability and the phase diagram of Ca$_{2-x}$Sr$_x$RuO$_4$","Hartree-Fock calculations are presented of a theoretical model describing the
Sr/CaRuO$_4$ family of compounds. Both commensurate and incommensurate magnetic
states are considered, along with orbital ordering and the effect of lattice
distortions. For reasonable parameter values, interactions disfavor orbital
disproportionation. A coherent description of the observed phase diagram is
obtained.",0402267v2
2004-02-13,Intersite elastic coupling and invar effect,"The invar phenomenon (very small thermal expansion in some iron alloys or
compounds) is usually explained by the thermally-induced transitions between
different spin states of Fe, having different atomic volumes. We consider these
processes taking into account elastic interaction between Fe atoms in different
spin states. Inclusion of these interactions explains why thermal expansion may
be close to zero in a broad temperature interval and thus gives rise to the
invar effect.",0402374v1
2004-02-15,Systems analysis of the phase diagrams of complex structures,"In frameworks of the phenomenological approach we analyze of the phase
diagram of mixed compounds. We obtain space groups of symmetry of the real
structures as result of phase transition from close-packed degenerate
structure. The theory of a sequence of phase transitions with an incommensurate
phase is constructed, and influence of an electronic subsystem and distortions
on phase transitions is investigated. We investigate of dependence of the
temperature interval existence of an incommensurate phase on the electron
concentration and the component deformation tensor in doped semiconductors. The
comparison of theoretical results with optical, dielectric and structural data
is carried out and parameters of thermodynamic potential are determined.",0402394v1
2004-02-16,Uniform Magnetic Order in a Ferromagnetic-Antiferromagnetic Random Alternating Quantum Spin Chain,"An $S=1/2$ ferromagnetic (F) - antiferromagnetic (AF) random alternating
Heisenberg quantum spin chain model is investigated in connection to its
realization compound: (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$. The
exchange interaction bonds have alternating strong F-AF random bonds and weak
uniform AF bonds. Using the quantum Monte Carlo method we have found that the
excitation energy gap closes and the uniform AF order becomes critical in the
intermediate concentration region. This finding explains the experimental
observation of the magnetic transition by considering weak interchain
interactions. Present results suggest that the uniform AF order survives even
in the presence of randomly located ferromagnetic bonds. This may be a new
quantum effect.",0402402v1
2004-02-26,Proton incorporations and superconductivity in a cobalt oxyhydrate,"We report the evidence of proton incorporations in a newly-discovered cobalt
oxyhydrate superconductor. During the hydration process for
Na$_{0.32}$CoO$_{2}$ by the direct reaction with water liquid, it was shown
that substantial NaOH was gradually liberated, indicating that H$^{+}$ is
incorporated into the hydrated compound. Combined with the thermogravimetric
analysis, the chemical composition of the typical sample is
Na$_{0.22}$H$_{0.1}$CoO$_{2}\cdot 0.85$H$_{2}$O, which shows bulk
superconductivity at 4.4 K.",0402638v1
2004-02-29,Issues pertaining to D'yakonov-Perel' spin relaxation in quantum wire channels,"We elucidate the origin and nature of the D'yakonov-Perel' spin relaxation in
a quantum wire structure, showing (analytically) that there are three necessary
conditions for it to exist: (i) transport must be multi-channeled, (ii) there
must be a Rashba spin orbit interaction in the wire, and (iii) there must also
be a Dresselhaus spin orbit interaction. Therefore, the only effective way to
completely eliminate the D'yakonov-Perel' relaxation in compound semiconductor
channels with structural and bulk inversion asymmetry is to ensure strictly
single channeled transport. In view of that, recent proposals in the literature
that advocate using multi-channeled quantum wires for spin transistors appear
ill-advised.",0403021v1
2004-03-03,Detailed Measurements of Characteristic Profiles of Magnetic Diffuse Scattering in ErB$_2$C$_2$,"Detailed neutron diffraction measurements on a single crystalline
ErB$_2$C$_2$ were performed. We observed magnetic diffuse scattering which
consists of three components just above the transition temperatures, which is
also observed in characteristic antiferroquadrupolar ordering compounds
HoB$_2$C$_2$ and TbB$_2$C$_2$. The result of this experiments indicates that
the antiferroquadrupolar interaction is not dominantly important as a origin of
the magnetic diffuse scattering.",0403101v1
2004-03-10,The Spin-SAF transition in NaV2O5 induced by spin-pseudospin coupling,"We present microscopic estimates for the spin-spin and spin-speudospin
interactions of the quarter-filled ladder compound NaV2O5, obtained by exactly
diagonalizing appropriate clusters of the underlying generalized Hubbard
Hamiltonian. We present evidence for a substantial interladder spin-pseudospin
interaction term which would allow simultaneously for the
superantiferroelectric (SAF) charge (pseudospin) ordering and spin
dimerization. We discuss the values of the coupling constants appropriate for
NaV2O5 and deduce the absence of a soft antiferroelectric mode.",0403263v1
2004-03-24,New Pyrochlore Oxide Superconductor RbOs2O6,"We report the discovery of a new pyrochlore oxide superconductor RbOs2O6. The
compound crystallizes in the same beta-pyrochlore structure as the recently
discovered superconductor KOs2O6, where Os atoms form a corner-sharing
tetrahedral network called the pyrochlore lattice with Rb or K atoms in the
cage. Resistivity, magnetic susceptibility and specific heat measurements on
polycrystalline samples evidence a bulk superconductivity with Tc = 6.3 K.",0403601v2
2004-03-25,Evidence for multiband superconductivity in the heavy fermion compound UNi2Al3,"Epitaxial thin films of the heavy fermion superconductor UNi2Al3 with
Tc{max}=0.98K were investigated. The transition temperature Tc depends on the
current direction which can be related to superconducting gaps opening at
different temperatures. Also the influence of the magnetic ordering at TN=5K on
R(T) is strongly anisotropic indicating different coupling between the magnetic
moments and itinerant charge carriers on the multi-sheeted Fermi surface. The
upper critical field Hc2(T) suggests an unconventional spin-singlet
superconducting state.",0403634v2
2004-04-12,Magnetization measurements on Li2Pd3B superconductor,"Magnetization in DC magnetic fields and at different temperatures have been
measured on the Li2Pd3B compound. This material was recently found to show
superconductivity at 7-8K. Critical fields Hc1(0) and Hc2(0) have been
determined to be 135Oe and 4T, respectively. Critical current density, scaling
of the pinning force within the Kramer model and the irreversibility field data
are presented. Several superconductivity parameters were deduced: x(csi)=9.1
nm, l(lamda)=194nm and k=21. The material resembles other boride
superconductors from the investigated points of view.",0404257v1
2004-04-12,Phases and phase transitions in spin-triplet ferromagnetic superconductors,"Recent results for the coexistence of ferromagnetism and unconventional
superconductivity with spin-triplet Cooper pairing are reviewed on the basis of
the quasi-phenomenological Ginzburg-Landau theory. New results are reported.
The results are discussed in view of applications to metallic compounds as
UGe2, URhGe, ZrZn2.",0404261v1
2004-04-13,Electronic band structure and chemical bonding in the novel antiperovskite ZnCNi3 as compared with 8-K superconductor MgCNi3,"Energy band structure of the discovered ternary perovskite-like compound
ZnCNi3 reported by Park et al (2004) as a non-superconducting paramagnetic
metal was investigated using the FLMTO-GGA method. The electronic bands,
density of states, Fermi surface, charge density and electron localization
function distributions for ZnCNi3 are obtained and analyzed in comparison with
the isoelectronic and isostructural 8K superconductor MgCNi3. The effect of
external pressure on the electronic states of ZnCNi3 and MgCNi3 is studied.",0404283v1
2004-04-14,Investigation of the field-treated magnetic state in Gd5Ge4,"At low temperatures, the intermetallic compound Gd$_5$Ge$_4$ shows a sharp
field-induced transition into a ferromagnetic state around 25 kOe of applied
field. The material remains in the field treated ferromagnetic state even when
the magnetic field is removed. We have investigated the character of this
field-treated state by magnetization and heat capacity measurements. The nature
of the magnetization and the heat capacity are found to be different above and
below a charactersitic temperature Tirr = 25 K.",0404302v1
2004-04-21,Upper critical field $H_{c_2}$ in two-band superconductor,"It was obtained the equation for the definition of upper critical field $%
H_{c_2}$ in the system with two overlapping energetic bands on the Fermi
surface, which is valid for the whole temperature interval $0 \leq T < T_c$.
The analytic expressions for the value $H_{c_2}$ at $T \sim T_c$ and $T \ll
T_c$ cases were defined. The possibility of changing the curvature $H_{c_2}
(T)$ with changing of the electrons speed ratio $v_1 / v_2$ on different
cavities on the Fermi surface was revealed. It was obtained the qualitative
accordance with experimental data for the intermetallic compound $MgB_2$.",0404489v1
2004-04-21,The Crystal Field Potential of PrOs4Sb12: Consequences for Superconductivity,"The results of inelastic neutron scattering provide a solution for the
crystal field level scheme in PrOs4Sb12 in which the ground state in the cubic
crystal field potential of Th symmetry is a Gamma_1 singlet. The conduction
electron mass enhancement is consistent with inelastic exchange scattering, and
we propose that inelastic quadrupolar, or aspherical Coulomb, scattering is
responsible for enhancing the superconducting transition temperature. PrOs4Sb12
appears to be the first compound in which aspherical Coulomb scattering is
strong enough to overcome magnetic pair-breaking and increase Tc.",0404519v1
2004-04-22,Cyclotron resonance in the quasi-1D organic superconductor (TMTSF)2ClO4,"We report the observation of cyclotron resonance (CR) in a metal possessing
pure quasi-one-dimensional Fermiology - namely, the organic linear-chain
compound (TMTSF)2ClO4, whose Fermi surface consists of a pair of weakly warped
sheets. The CR phenomenon is related to weak inter-chain coupling, which allows
electrons constrained on open trajectories to acquire small transverse
velocities. Application of an appropriately oriented magnetic field induces
periodic motion transverse to the chain direction and, hence, to a resonance in
the AC conductivity. The field orientation dependence of the resonance is
related simply to the Fermi velocity and lattice periodicity.",0404545v2
2004-05-03,SO(5) Theory of Antiferromagnetism and Superconductivity,"Antiferromagnetism and superconductivity are both fundamental and common
states of matter. In many strongly correlated systems, including the high Tc
cuprates, the heavy fermion compounds and the organic superconductors, they
occur next to each other in the phase diagram and influence each other's
physical properties. The SO(5) theory unifies these two basic states of matter
by a symmetry principle and describes their rich phenomenology through a single
low energy effective model. In this paper, we review the framework of the SO(5)
theory, and its detailed comparison with numerical and experimental results.",0405038v1
2004-05-05,Panorama of Nodal Superconductors,"Since 1979, many new classes of superconductors have been discovered,
including heavy-fermion compounds, organic conductors, high-Tc cuprates, and
Sr2RuO4. Most of these superconductors are unconventional and/or nodal.
Therefore it is of central importance to determine the symmetry of the order
parameter in each of these superconductors. In particular, the
angular-controlled thermal conductivity in the vortex state provides a unique
means of investigating the nodal structure of the superconducting energy gap
when high-quality single crystals in the extremely clean limit are available.
Using this method, Izawa et al have recently succeeded in identifying the
energy gap symmetry of superconductivity in Sr2RuO4, CeCoIn5,
kappa-(ET)2Cu(NCS)2, YNi2B2C, and PrOs4Sb12.",0405099v1
2004-05-07,"Electrochemical De-intercalation, Oxygen Non-stoichiometry, and Crystal Growth of NaxCoO2-d","We report a detailed study of de-intercalation of Na from the compound
NaxCoO2-d using an electrochemical technique. We find evidence for stable
phases with Na contents near the fractions ~1/3, 1/2, 5/8, 2/3, and 3/4.
Details regarding the floating-zone crystal growth of Na0.75CoO2 single
crystals are discussed as well as results from magnetic susceptibility
measurements. We observe the presence of significant oxygen deficiencies in
powder samples of Na0.75CoO2-d prepared in air, but not in single crystal
samples prepared in an oxygen atmosphere. The oxygen deficiencies in a
Na0.75CoO2-d sample with d ~ 0.08 remain even after electrochemically
de-intercalating to Na0.3CoO2-d.",0405158v1
2004-05-22,"Oxygen stoichiometry, crystal structure, and magnetism in La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$","We have prepared a series of polycrystalline samples
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$} with $0 < \delta \le 0.21$ and
characterized their oxygen content, crystal structure, and magnetic properties.
While the fully oxygenated samples are good ferromagnets, samples with larger
$\delta$ values display increasingly broad magnetic transitions. The saturation
magnetization at 5 K falls rapidly as $\delta$ increases. First principles
electronic structure calculations provide insights into the magnetic behavior
of the fully oxygenated compound, and the manner in which ferromagnetic
ordering is affected by increasing oxygen non-stoichiometry.",0405535v2
2004-06-01,Elastic anomalies in HoNi2B2C single crystals,"We have measured temperature and magnetic field dependencies of the sound
velocities and the sound attenuation in HoNi2B2C single crystals. The main
result is a huge softening the velocity of C66 mode due to a cooperative
Jahn-Teller effect, resulting in a tetragonal-orthorhombic structural phase
transition. Anomalies in the behavior of the C66 mode through various magnetic
phase transitions permit us to revise the low temperature H-T phase diagrams of
this compound.",0406007v2
2004-06-02,Magnetoelectricity at room temperature in Bi0.9-xTbxLa0.1FeO3 system,"Magnetoelectric compounds with the general formula, Bi0.9-xRxLa0.1FeO3 (R
=Gd, Tb, Dy, etc.), have been synthesized. These show the coexistence of
ferroelectricity and magnetism, possess high dielectric constant and exhibit
magnetoelectric coupling at room temperature. Such materials may be of great
significance in basic as well as applied research.",0406044v1
2004-06-07,Spin switch and spin amplifier: magnetic bipolar transistor in the saturation regime,"It is shown that magnetic bipolar transistors (MBT) can amplify currents even
in the saturation regime, in which both the emitter-base and collector-base
junctions are forward biased. The collector current and the current gain can
change sign as they depend on the relative orientation of the equilibrium spin
in the base and on the nonequilibrium spin in the emitter and collector. The
predicted phenomena should be useful for electrical detection of nonequilibrium
spins in semiconductors, as well as for magnetic control of current
amplification and for current switching.",0406170v1
2004-06-14,"Compositional Dependence of Formation Energies of Substitutional and Interstitial Mn in Partially Compensated (Ga,Mn)As","We use the density-functional theory to calculate the total energy of mixed
crystals (Ga,Mn)As with a small concentration of various donors. We find that
the formation energy of Mn depends strongly on the partial concentrations of Mn
in the substitutional and interstitial positions, and on the concentration of
other dopants. The composition dependence of the formation energies represents
an effective feedback mechanism, resulting in the self-compensation property of
(Ga,Mn)As. We show that the partial concentrations of both substitutional and
interstitial Mn increase proportionally to the total concentration of Mn.",0406314v1
2004-06-16,Universal shapes of self-organized semiconductor quantum dots,"The model systems for self-organized quantum dots formed from elemental and
compound semiconductors, namely Ge grown on Si(001) and InAs on GaAs(001), are
comparatively studied by scanning tunneling microscopy. It is shown that in
both material combinations only two well-defined families of faceted and
defect-free nanocrystals exist (and coexist). These three-dimensional islands,
pyramids and domes, show common morphological characteristics, independently of
the specific material system. A universal behavior is further demonstrated in
the capping-passivation process that turns the nanocrystals in true quantum
dots.",0406380v1
2004-06-18,First-principles study of filled and unfilled skutterudite antimonies,"The electron localization tensor, Born effective charges, dielectric
constants and phonon dispersion relations of the skutterudite CoSb$_3$ and the
filled skutterudite TlFeCo$_3$Sb$_{12}$ have been studied using density
functional perturbation theory. The origin of the low energy peak in the phonon
density of states of TlFeCo$_3$Sb$_{12}$ observed recently by Neutron inelastic
scattering [R. P. Hermann {\it et al.}, Phys. Rev. Lett. {\bf 90}, 135505
(2003)] is attributed to the vibrations of Tl that show only weak coupling with
the normal modes of the host crystal. Moreover, the dielectric properties of
these materials show unsual features such as giant Born effective charges and a
strong increase of the optical and static dielectric tensor in the filled
compound.",0406418v1
2004-06-21,Large negative magnetoresistance in thiospinel CuCrZrS4,"We report on large negative magnetoresistance observed in ferromagnetic
thiospinel compound CuCrZrS$_{4}$. Electrical resistivity increased with
decreasing temperature according to the form proportional to
$\textrm{exp}(T_{0}/T)^{1/2} $, derived from variable range hopping with strong
electron-electron interaction. Resistivity under magnetic fields was expressed
by the same form with the characteristic temperature T0 decreasing with
increasing magnetic field. Magnetoresistance ratio $\rho (T,0)/\rho(T,H)$ is
1.5 at 100 K for H=90 kOe and increases divergently with decreasing temperature
reaching 80 at 16 K. Results of magnetization measurements are also presented.
Possible mechanism of the large magnetoresistance is discussed.",0406459v1
2004-06-21,Triplet superconductivity in the skutterudite PrOs_4Sb_12,"There is mounting evidence for triplet superconductivity in the recently
discovered skutterudite compound PrOs_4Sb_12. In this work, we propose nodal
order parameters for the A- and B-phases of this superconductor which are
consistent with angle dependent magnetothermal conductivity measurements and
with low-temperature thermal conductivity data in the range T > 150 mK. The
quasiparticle density of states and the thermal conductivity kappa_zz are
derived within the quasiclassical approximation.",0406492v1
2004-06-24,Exact diagonalization studies of doped Heisenberg spin rings,"Motivated by magnetization studies of the ""telephon number compound""
Sr_14Cu_24O_41 we investigate doped Heisenberg spin rings by means of complete
numerical diagonalization of a Heisenberg Hamiltonian that depends
parametrically on hole positions. A comparison with experimental magnetization
data reveals rather accurate information about the screened electrostatic
interaction between the charged holes on the ring which appears to be
astonishingly strong.",0406592v1
2004-07-07,Thermoelectricity of URu$_{2}$Si$_{2}$: giant Nernst effect in the hidden-order state,"We present a study of Nernst and Seebeck coefficients in the heavy-fermion
compound URu$_{2}$Si$_{2}$, which hosts a phase transition of unsettled origin.
A giant Nernst signal of unprecedented magnitude was found to emerge in the
ordered state. Moreover, our analysis of the Seebeck and Hall data indicates
that the ordering leads to a sudden increase in the entropy per itinerant
electron and to a drastic decrease in the scattering rate.",0407147v1
2004-07-15,Lattice Dynamics in a strongly dimerized low-dimensional model with orbital ordering,"We study the interplay of spin, orbital and lattice degrees of freedom in a
one-dimensional Kugel-Khomskii model coupled to phonons. In the vicinity of the
dimer point we analyze the excitation spectrum, mapping the spin and orbital
degrees of freedom to bond operators. In particular we study the
renormalization of the phonon propagator due to coupling to the orbital and
magnetic excitations. Considering both, ferro- and antiferro-orbital ordering
we will show that the appearance of orbiton shake-up processes in the phonon
spectrum is sensitive to the type of Jahn-Teller distortion. The relevance of
our results for optical spectroscopy on low dimensional transition metal
compounds will be discussed.",0407394v2
2004-07-23,"High Pressure Effects on Superconductivity in the beta-pyrochlore Oxides AOs2O6 (A=K, Rb, Cs)","Recently new pyrochlore oxides superconductors AOs2O6 (A=K,Rb,Cs) were found
and we measured the pressure dependence of magnetization up to 1.2 GPa in order
to deduce the pressure effect of Tc in the three beta-pyrochlore oxides. It is
found that the initial pressure dependence of Tc is positive for all the
compounds. Only KOs2O6 exhibits a saturation in Tc at 0.56 GPa and the downturn
at higher pressure",0407610v1
2004-07-27,On the Stacking Charge Order in NaV2O5,"We propose a mechanism for the observed stacking charge order in the
quarter-filled ladder compound NaV2O5. Via a standard mapping of the charge
degrees of freedom onto Ising spins we explain the stacking order as a result
of competition between couplings of the nearest and next-nearest planes with
the 4-fold degenerate super-antiferroelectric in-plane order.",0407700v1
2004-07-29,Field-induced spin density wave in (TMTSF)$_2$NO$_3$,"Interlayer magnetoresistance of the Bechgaard salt (TMTSF)$_2$NO$_3$ is
investigated up to 50 teslas under pressures of a few kilobars. This compound,
the Fermi surface of which is quasi two-dimensional at low temperature, is a
semi metal under pressure. Nevertheless, a field-induced spin density wave is
evidenced at 8.5 kbar above $\sim$ 20 T. This state is characterized by a
drastically different spectrum of the quantum oscillations compared to the low
pressure spin density wave state.",0407764v2
2004-08-09,Solid state Pomeranchuk effect,"Recently we have shown that $YbInCu_4$ and related compounds present a solid
state Pomeranchuk effect. These systems have a first order volume transition
where a local moment phase coexists with a renormalized Fermi liquid in analogy
with $^3He$ at its melting curve. We demonstrate here experimentally that the
solid state Pomeranchuk effect, controlled by a magnetic field, can be used to
produce cooling.",0408191v1
2004-08-17,Collective Spin-Density-Wave Response Perpendicular to the Chains of the Quasi One-Dimensional Conductor (TMTSF)2PF6,"Microwave experiments along all three directions of the spin-density-wave
model compound (TMTSF)$_2$PF$_6$ reveal that the pinned mode resonance is
present along the $a$ and $b^{\prime}$ axes. The collective transport is
considered to be the fingerprint of the condensate. In contrast to common quasi
one-dimensional models, the density wave also slides in the perpendicular
$b^{\prime}$ direction. The collective response is absent along the least
conducting $c^*$ direction.",0408382v1
2004-08-20,Observation of Hybrid Soliton Vortex-Ring Structures in Bose-Einstein Condensates,"We present the experimental discovery of compound structures comprising
solitons and vortex rings in Bose-Einstein condensates (BECs). We examine both
their creation via soliton-vortex collisions and their subsequent development,
which is largely governed by the dynamics of interacting vortex rings. A
theoretical model in three-dimensional (3D) cylindrical symmetry is also
presented.",0408464v1
2004-08-26,Spintronics and ferromagnetism in wide-band-gap semiconductors,"Recent progress in understanding and controlling spintronic properties of
(Ga,Mn)As and related compounds is contrasted to diverging experimental and
theoretical results concerning the origin of high temperature ferromagnetism
discovered in an ample class of magnetically doped wide-band-gap
semiconductors.",0408561v1
2004-08-30,Quantum Critical Point of the XY Model and Condensation of Field-Induced Quasiparticles in Dimer Compounds,"The quantum critical point of the three-dimensional XY model in a
symmetry-preserving field is investigated. The results of Monte Carlo
simulations with the directed-loop algorithm show that the quantum critical
behavior is characterized by the mean-field values of critical exponents. The
system-size dependence of various quantities is compared to a simple
field-theoretical argument that supports the mean-field scaling.",0408649v2
2004-09-17,Nanotubular Boron-Carbon Heterojunctions,"Linear nanotubular boron-carbon heterojunctions are systematically
constructed and studied with the help of ab initio total energy calculations.
The structural compatibility of the two classes of materials is shown, and a
simple recipe that determines all types of stable linear junctions is
illustrated in some detail. Our results also suggest the compatibility of
various technologically interesting types of nanotubular materials, leading to
novel types of nanotubular compound materials, and pointing out the possibility
of wiring nanotubular devices within heterogeneous nanotubular networks.",0409466v1
2004-09-24,Strong Coulomb effects in hole-doped Heisenberg chains,"Substances such as the ``telephone number compound''
  Sr14Cu24O41 are intrinsically hole-doped. The involved interplay of spin and
charge dynamics is a challenge for theory. In this article we propose to
describe hole-doped Heisenberg spin rings by means of complete numerical
diagonalization of a Heisenberg Hamiltonian that depends parametrically on hole
positions and includes the screened Coulomb interaction among the holes. It is
demonstrated that key observables like magnetic susceptibility, specific heat,
and inelastic neutron scattering cross section depend sensitively on the
dielectric constant of the screened Coulomb potential.",0409650v2
2004-10-01,Microscopic modelling of doped manganites,"Colossal magneto-resistance manganites are characterised by a complex
interplay of charge, spin, orbital and lattice degrees of freedom. Formulating
microscopic models for these compounds aims at meeting to conflicting
objectives: sufficient simplification without excessive restrictions on the
phase space. We give a detailed introduction to the electronic structure of
manganites and derive a microscopic model for their low energy physics.
Focussing on short range electron-lattice and spin-orbital correlations we
supplement the modelling with numerical simulations.",0410020v1
2004-10-06,Spin and Valence-Fluctuation Mediated Superconductivity in Pressurized Fe and CeCu2(Si/Ge)2,"We review the evidence supporting valence-fluctuation mediated
superconductivity in CeCu2Si2 and CeCu2Ge2, where Tc reaches 2.4 K at high
pressure. In these systems the valence and magnetic critical points, at p_V and
p_c respectively, are well separated. Characteristic signatures associated with
both phenomena are distinct. In contrast, the valence and spin fluctuation
regions appear much closer in most Ce based compounds. Concerning d-transition
metals, superconductivity in pure iron emerges in the pressure window 15-30 GPa
with the onset of Tc up to almost 3 K. All relevant observations point to
unconventional superconductivity, likely mediated by ferromagnetic spin
fluctuations.",0410143v1
2004-10-14,High Pressure Effects on Superconductivity,"The review is devoted to a discussion of the effects of high pressure imposed
on superconducting materials. Low-temperature superconductors, high-temperature
superconducting cuprates, and some unconventional superconducting compounds are
investigated. Experimental as well as theoretical results regarding the
pressure effects on Tc and other interesting properties are summarized.",0410367v1
2004-10-19,Haldane-gap chains in a magnetic field,"We consider quasi one dimensional spin-1 Heisenberg chains with crystal field
anisotropy in a uniform magnetic field. We determine the dynamical structure
factor in various limits and obtain a fairly complete qualitative picture of
how it changes with the applied field. In particular, we discuss how the width
of the higher energy single magnon modes depends on the field. We consider the
effects of a weak interchain coupling. We discuss the relevance of our results
for recent neutron scattering experiments on the quasi-1D Haldane-gap compound
NDMAP.",0410487v1
2004-10-20,Carbon isotope effect in superconducting MgCNi_3,"The effect of Carbon isotope substitution on T_c in the intermetallic
perovskite superconductor MgCNi_3 is reported. Four independent groups of
samples were synthesized and characterized. The average T_c for the Carbon-12
samples was found to be 7.12(2) K and the average T_c for the Carbon-13 samples
was found to be 6.82(2) K. The resulting carbon isotope effect coefficient is
alfa_C = 0.54(3). This indicates that carbon-based phonons play a critical role
in the presence of superconductivity in this compound.",0410504v1
2004-10-26,Renormalization Group Technique Applied to the Pairing Interaction of the Quasi-One-Dimensional Superconductivity,"A mechanism of the quasi-one-dimensional (q1d) superconductivity is
investigated by applying the renormalization group techniques to the pairing
interaction. With the obtained renormalized pairing interaction, the transition
temperature Tc and corresponding gap function are calculated by solving the
linearized gap equation. For reasonable sets of parameters, Tc of p-wave
triplet pairing is higher than that of d-wave singlet pairing due to the
one-dimensionality of interaction. These results can qualitatively explain the
superconducting properties of q1d organic conductor (TMTSF)2PF6 and the ladder
compound Sr2Ca12Cu24O41.",0410659v1
2004-10-28,Enhancement of rare-earth--transition-metal exchange interaction in Pr$_{2}$Fe$_{17}$ probed by inelastic neutron scattering,"The fundamental magnetic interactions of Pr$_{2}$Fe$_{17}$ are studied by
inelastic neutron scattering and anisotropy field measurements. Data analysis
confirms the presence of three magnetically inequivalent sites, and reveals an
exceptionally large value of the exchange field. The unexpected importance of
$J$-mixing effects in the description of the ground-state properties of
Pr$_{2}$Fe$_{17}$ is evidenced, and possible applications of related compounds
are envisaged.",0410731v1
2004-11-10,"Random Ising model in three dimensions: theory, experiment and simulation - a difficult coexistence","We discuss different approaches for studying the influence of disorder in the
three-dimensional Ising model. From the theoretical point of view,
renormalisation group calculations provide quite accurate results. Experiments
carried out on crystalline mixtures of compounds lead to measurements as
accurate as three digits on the values of critical exponents. Numerically,
extensive Monte Carlo simulations then pretend to be of comparable accuracy.
Life becomes complicated when details are compared between the three
approaches.",0411255v2
2004-11-24,Quantum Phase Transitions in Coupled Dimer Compounds,"We study the critical properties in cubic systems of antiferromagnetically
coupled spin dimers near magnetic-field induced quantum phase transitions. The
quantum critical points in the zero-temperature phase diagrams are determined
from quantum Monte Carlo simulations. Furthermore, scaling properties of the
uniform magnetization and the staggered transverse magnetization across the
quantum phase transition in magnetic fields are calculated. The critical
exponents are derived from Ginzburg-Landau theory. We find excellent agreement
between the quantum Monte Carlo simulations and the analytical results.",0411599v3
2004-11-25,A perturbative approach to J mixing in f-electron systems: Application to actinide dioxides,"We present a perturbative model for crystal-field calculations, which keeps
into account the possible mixing of states labelled by different quantum number
J. Analytical J-mixing results are obtained for a Hamiltonian of cubic symmetry
and used to interpret published experimental data for actinide dioxides. A
unified picture for all the considered compounds is proposed by taking into
account the scaling properties of the crystal-field potential.",0411649v1
2004-12-04,"Ferromagnetic Instability in AFe4Sb12 (A = Ca, Sr, and Ba)","Magnetic, transport and thermal properties of AFe4Sb12 (A = Ca, Sr, Ba) are
reported. All three compounds show a maximum in both the magnetic
susceptibility and thermopower at 50 K, and a large electronic specific heat
coefficient of 100 mJ/mol K2. These properties are the characteristics of a
nearly ferromagnetic metal. Furthermore, a remanent moment of the order of
10-3muB/Fe was observed below 54, 48, and 40 K for A = Ca, Sr, and Ba,
respectively. The volume fraction of the ferromagnetic component was estimated
to be 10-20% by zero-field muSR measurements.",0412094v1
2004-12-09,Modified Spin-Wave Theory for Nanomagnets : Application to the Keplerate Molecule Mo(72)Fe(30),"We adapt Takahashi's modified spin-wave theory to the context of
nano-magnets, and apply it to the molecular compound based on the giant
magnetic molecule Mo(72)Fe(30). This involves solving numerically the
mean-field equations and then forcing the sublattice magnetizations to zero by
means of local chemical potentials for the magnons. We have thus constructed a
quantum state with no local magnetization at all temperatures, appropriate to a
finite-size system, but with strong correlations. We compare theoretical
results to specific heat and ESR measurements.",0412244v1
2004-12-15,Photoinduced Absorption Spectra of Halogen-Bridged Binuclear Metal Complexes: Possible Contrast between R_4_[Pt_2_(P_2_O_5_H_2_)_4_X]nH_2_O and Pt_2_(CH_3_CS_2_)_4_I,"The optical conductivity of photogenerated solitons in quasi-one-dimensional
halogen-bridged binuclear metal (MMX) complexes is investigated with particular
emphasis on a comparison between the two family compounds
R_4_[Pt_2_(P_2_O_5_H_2_)_4_X]nH_2_O (X=Cl,Br,I;R=NH_4_,Na,K,...;
pop=diphosphonate=P_2_O_5_H_2_^2-^) and Pt_2_(dta)_4_I
(dta=dithioacetate=CH_3_CS_2_^-^). Soliton-induced absorption spectra for the
pop complexes should split into two bands, while those for the dta complex
should consist of a single band.",0412391v1
2005-01-06,First principles investigation of ferroelectricity in epitaxially strained Pb$_2$TiO$_4$,"The structure and polarization of the as-yet hypothetical Ruddlesden-Popper
compound Pb$_2$TiO$_4$ are investigated within density-functional theory. Zone
enter phonons of the high-symmetry K$_2$NiF$_4$-type reference structure, space
group $I4/mmm$, were calculated. At the theoretical ground-state lattice
constants, there is one unstable infrared-active phonon. This phonon freezes in
to give the $I2mm$ ferroelectric state. As a function of epitaxial strain, two
additional ferroelectric phases are found, with space groups $I4mm$ and $F2mm$
at compressive and tensile strains, respectively.",0501121v1
2005-01-11,The kinetic Monte Carlo Simulation scheme of the homoepicaxial growth of GaAs(001) for heterostructural growth on GaAs(001) substrate,"The simulation scheme for heterostructural growth of compound semiconductors
is presented based on the kinetic Monte Carlo method. The sheme is designed as
simple as possible in order to apply it for any heteroepitaxial growth on
GaAs(001) substrate. The parameters used in the simulation are determined with
the first-principles calculation to reproduce experimental RHEED intensity
curves for homoepitaxial growth of GaAs(001).",0501233v1
2005-01-11,Temperature-Dependent X-Ray Absorption Spectroscopy of Colossal Magnetoresistive Perovskites,"The temperature dependence of the O K-edge pre-edge structure in the x-ray
absorption spectra of the perovskites La(1-x)A(x)MnO(3), (A = Ca, Sr; x = 0.3,
0.4) reveals a correlation between the disappearance of the splitting in the
pre-edge region and the presence of Jahn-Teller distortions. The different
magnitudes of the distortions for different compounds is proposed to explain
some dissimilarity in the line shape of the spectra taken above the Curie
temperature.",0501273v1
2005-01-17,Fully Frustrated Cold Atoms,"Fully frustrated Josephson Junction arrays (FF-JJA's) exhibit a subtle
compound phase transition in which an Ising transition associated with discrete
broken translational symmetry and a Berezinskii-Kosterlitz-Thouless (BKT)
transition associated with quasi-long-range phase coherence occur nearly
simultaneously. In this Letter we discuss a cold atom realization of the FF-JJA
system. We demonstrate that both orders can be studied by standard
momentum-distribution-function measurements and present numerical results,
based on a successful self-consistent spin-wave approximation, that illustrate
the expected behavior of observables.",0501387v1
2005-01-24,Effects of Sr doping on the magnetic properties of Sr$_x$Ba$_{1-x}$CoO$_3$,"Magnetic properties of the Sr-doped BaCoO$_3$ are explained on the basis of
ab initio calculations and the analysis of experimental literature. Formation
of magnetic clusters bigger than in the parent compound and increase in the
blocking temperature are observed. Superparamagnetism remains at room
temperature. The possibility of tuning the size and properties of the magnetic
clusters with doping is explored.",0501556v1
2005-01-28,Ab-initio Phonon Calculations for the layered compound TiOCl,"We present first-principles frozen-phonon calculations for the three
Raman-active $A_g$ modes in the spin-1/2 layered TiOCl system within two
different well-known approaches: the local density approximation (LDA) and the
so-called LDA+U approximation. We observe that the inclusion of electron
correlation in a mean-field level as implemented in the LDA+U leads to a better
overall agreement with experimental results. We also discuss the implications
of the two approaches on the physics of TiOCl.",0501685v2
2005-01-28,Ce doping in T-La2CuO4 films: Broken electron-hole symmetry for high-Tc superconductivity,"We attempted Ce doping in La2CuO4 with the K2NiF4 (T) structure by molecular
beam epitaxy. At low growth temperature and with an appropriate substrate
choice, we found that Ce can be incorporated into the K2NiF4 lattice up to x ~
0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes
T-La2-xCexCuO4 more insulating, which is in sharp contrast to Ce doping in
La2CuO4 with the Nd2CuO4 structure, which makes the compounds superconducting.
The observed smooth increase in resistivity from hole-doped side
(T-La2-xSrxCuO4) to electron-doped side (T-La2-xCexCuO4) indicates that
electron-hole symmetry is broken in the T-phase materials.",0501703v1
2005-02-13,"Magnetic Field Dependence of CDW Phases in Per2M(mnt)2 (M=Pt, Au)","Recently the authors discovered that the suppression of the charge density
wave (CDW) ground states by high magnetic fields in the organic conductor
series Per2M(mnt)2 is followed by additional high field, CDW-like phases. The
purpose of this presentation is to review these compounds, to consider the
relevant parameters of the materials that describe the manner in which the CDW
ground state may undergo new field induced changes above the Pauli limit.",0502313v1
2005-02-17,LSDA+U approximation-based analysis of the electronic estructure of CeFeGe3,"We perform ab initio electronic structure calculations of the intermetallic
compound CeFeGe3 by means of the Tight Binding Linear Muffin-Tin
Orbitals-Atomic Sphere Approximation (TB-LMTO-ASA) within the Local Spin
Density Approximation containing the so-called Hubbard correction term
(LSDA+U^SIC), using the Sttutgart's TB (Tight Binding)-LMTO-ASA code in the
framework of the Density Funcional Theory (DFT).",0502410v1
2005-02-22,The Persistence and Memory of Polar Nano-Regions in a Ferroelectric Relaxor Under an Electric Field,"The response of polar nanoregions (PNR) in the relaxor compound
Pb[(Zn$_{1/3}$Nb$_{2/3}$)$_{0.92}$Ti$_{0.08}$]O$_3$ subject to a [111]-oriented
electric field has been studied by neutron diffuse scattering. Contrary to
classical expectations, the diffuse scattering associated with the PNR
persists, and is even partially enhanced by field cooling. The effect of the
external electric field is retained by the PNR after the field is removed. The
``memory'' of the applied field reappears even after heating the system above
$T_C$, and cooling in zero field.",0502540v1
2005-03-04,Orbital excitations in titanates,"Raman scattering is used to observe pronounced electronic excitations around
230 meV - well above the two-phonon range - in the Mott insulators LaTiO$_3$
and YTiO$_3$. Based on the temperature, polarization, and photon energy
dependence, the modes are identified as orbital excitations. The observed
profiles bear a striking resemblance to magnetic Raman modes in the insulating
parent compounds of the superconducting cuprates, indicating an unanticipated
universality of the electronic excitations in transition metal oxides.",0503106v1
2005-03-09,The two-fold superstructure of titanium(III)-oxybromide at T = 17.5 K,"The low-temperature (T = 17.5 K) structure of titanium(III)-oxybromide,
TiOBr, is reported as a two-fold superstructure of the crystal structure at
room temperature. Weak superlattice reflections could be measured with
synchrotron radiation x-rays, and they were analysed by structure refinements
employing superspace techniques. Both the low temperature and room temperature
tructures of TiOBr are isostructural to the corresponding structures of TiOCl.
The results indicate that at low temperatures TiOBr is in a spin-Peierls state
similar to TiOCl, but with the modulations and relevant interactions smaller
than in the latter compound.",0503214v2
2005-03-11,Ferromagnetic fluctuation and superconductivity in Na_0.35CoO_2*1.3H_2O: FLEX study of multi-orbital Hubbard model,"Spin and charge fluctuations and superconductivity in Na_0.35CoO_2*1.3H_2O
are studied based on a multi-orbital Hubbard model. By applying the fluctuation
exchange (FLEX) approximation, we show that the Hund's-rule coupling between
the Co t2g orbitals causes ferromagnetic spin fluctuation. Triplet pairing is
favored by this ferromagnetic fluctuation on the hole-pocket band. We propose
that, in Na_0.35CoO_2*1.3H_2O, Co t2g orbitals and inter-orbital Hund's-rule
coupling play important roles on the triplet pairing, and this compound can be
a first example of the triplet superconductor mediated by
inter-orbital-interaction-induced ferromagnetic fluctuation.",0503262v1
2005-03-14,Exchange coupling induced antiferromagnetic-ferromagnetic transition in $Pr_{0.5}Ca_{0.5}MnO_3/La_{0.5}Ca_{0.5}MnO_3$ superlattices,"Superlattices built from two antiferromagnetic (AFM) charge/orbital order
compounds, $Pr_{0.5}Ca_{0.5}MnO_3$ and $La_{0.5}Ca_{0.5}MnO_3$, have been
studied as the thickness of $La_{0.5}Ca_{0.5}MnO_3$ ($LCMO$) varied. High
structural quality thin films were obtained on $LaAlO_3$ substrates using the
pulsed laser deposition technique. An antiferromagnetic-to-ferromagnetic
transition, in addition to an enhancement of the coercivity, are observed as
the $LCMO$ layer thickness increases. The small shift in the origin of the
field-cooled hysteresis loop along the field axis indicates the presence of
ferromagnetic and antiferromagnetic phases in the superlattices. We attribute
these features to the AFM spin fluctuations at the
$Pr_{0.5}Ca_{0.5}MnO_3/La_{0.5}Ca_{0.5}MnO_3$ interfaces resulting from the
strain effects.",0503327v1
2005-03-15,Infrared signature of the charge-density-wave gap in $ZrTe_3$,"The chain-like $ZrTe_3$ compound undergoes a charge-density-wave (CDW)
transition at $T_{CDW}=63$ $K$, most strongly affecting the conductivity
perpendicular to the chains. We measure the temperature ($T$) dependence of the
optical reflectivity from the far infrared up to the ultraviolet with polarized
light. The CDW gap $\Delta(T)$ along the direction perpendicular to the chains
is compatible for $T<T_{CDW}$ with the behavior of an order parameter within
the mean-field Bardeen-Cooper-Schrieffer (BCS) theory. $\Delta(T)$ also
persists well above $T_{CDW}$, which emphasizes the role played by fluctuation
effects.",0503375v1
2005-03-18,High T_c superconductivity due to coexisting wide and narrow bands: A fluctuation exchange study on the Hubbard ladder as a test case,"We propose that when the Fermi level lies within a wide band and also lies
close to but not within a coexisting narrow band, high $T_c$ superconductivity
may take place due to the large number of interband pair scattering channels
and the small renormalization of the quasiparticles. We show using fluctuation
exchange method that this mechanism works for the Hubbard model on a ladder
lattice with diagonal hoppings. From this viewpoint, we give a possible
explanation for the low $T_c$ for the actual hole doped ladder compound, and
further predict a higher $T_c$ for the case of electron doping.",0503466v1
2005-03-24,Structural properties of the sesquicarbide superconductor La2C3 at high pressure,"The effect of pressure on the structural properties of lanthanum
sesquicarbide La2C3 (T_c = 13 K) has been investigated at room temperature by
angle-dispersive powder x-ray diffraction in a diamond anvil cell. The compound
remains in the cubic Pu2C3-type structure at pressures up to at least 30 GPa.
The corresponding equation of state parameters are reported and discussed in
terms of phase stability of La2C3. Pressure-volume data of the impurity phase
LaC2 are reported also for pressures up to 13 GPa.",0503597v1
2005-04-06,Intercalant-Driven Superconductivity in YbC$_{6}$ and CaC$_{6}$,"Recently deiscovered superconductivity in YbC$_6$ and CaC$_6$ at temperatures
substantially higher than previously known for intercalated graphites, raised
several new questions: (1) Is the mechanism considerably different from the
previously known intercalated graphites? (2) If superconductivity is
conventional, what are the relevant phonons? (3) Given extreme similarity
between YbC$_6$ and CaCa$_6$, why their critical temperatures are so different?
We address these questions on the basis of first-principles calculations and
conclude that coupling with intercalant phonons is likely to be the main force
for superconductivity in YbC$_6$ and CaC$_6$, but not in alkaline-intercalated
compounds, and explain the difference in $T_c$ by the ``isotope effect'' due to
the difference in Yb and Ca atomic masses.",0504127v1
2005-04-11,Lattice pinning of magnetic domains in the helimagnet Ba_2CuGe_2O_7,"The layered magnetic compound Ba_2CuGe_2O_7 exhibits spiral antiferromagnetic
order thanks to a Dzyaloshinskii-Moriya (DM) anisotropy that is allowed by
crystal symmetry. Here we theoretically examine some finer issues such as the
experimentally observed lattice pinning of the propagation vector of helical
magnetic domains. We find that DM anisotropy alone would lead to incorrect
pinning, but agreement with experiment is restored upon including an additional
exchange anisotropy that is also consistent with symmetry. The present results
shed light on the so-called bisection rule which has been abstracted from
experiment in presence of an in-plane magnetic field.",0504262v1
2005-04-12,Polaron Transport in the Paramagnetic Phase of Electron-Doped Manganites,"The electrical resistivity, Hall coefficient, and thermopower as functions of
temperature are reported for lightly electron-doped Ca(1-x)La(x)MnO(3)(0 <= x
<= 0.10). Unlike the case of hole-doped ferromagnetic manganites, the magnitude
and temperature dependence of the Hall mobility for these compounds is found to
be inconsistent with small-polaron theory. The transport data are better
described by the Feynman polaron theory and imply intermediate coupling (alpha
\~ 5.4) with a band effective mass, m*~4.3 m_0, and a polaron mass, m_p ~ 10
m_0.",0504303v1
2005-04-21,Field-induced suppression of the heavy-fermion state in YbRh_2Si_2,"We report DC magnetization measurements on YbRh_2Si_2 at temperatures down to
0.04K, magnetic fields B<11.5T and under hydrostatic pressure P<1.3GPa. At
ambient pressure a kink at B*=9.9T indicates a new type of field-induced
transition from an itinerant to a localized 4f-state. This transition is
different from the metamagnetic transition observed in other heavy fermion
compounds, as here ferromagnetic rather than antiferromagnetic correlations
dominate below B*. Hydrostatic pressure experiments reveal a clear
correspondence of B* to the characteristic spin fluctuation temperature
determined from specific heat.",0504563v2
2005-05-04,Simultaneous electric and magnetic field induced nonvolatile memory,"We investigate the electric field induced resistive switching effect and
magnetic field induced fraction enlargement on a polycrystalline sample of a
colossal magnetoresistive compound displaying intrinsic phase coexistence. Our
data show that the electric effect (presumably related to the presence of
inhomogeinities) is present in a broad temperature range(300 to 20 K), being
observable even in a mostly homogeneous ferromagnetic state. In the temperature
range in which low magnetic field determines the phase coexistence fraction,
both effects, though related to different mechanisms, are found to determine
multilevel nonvolatile memory capabilities simultaneously.",0505105v1
2005-05-05,The influence of electrostatic potentials on the apparent s-d exchange energy in III-V diluted magnetic semiconductors,"The muffin-tin model of an effective-mass electron interacting with magnetic
ions in semiconductors is extended to incorporate electrostatic potentials that
are present in the case of Mn-based III-V compounds (${Ga}_{1-x} {Mn}_x {N}$,
${Ga}_{1-x} {Mn}_x {As}$). Since the conduction band electron is repelled from
negatively charged magnetic ions and attracted by compensating donors, the
\emph{apparent} value of the s-d exchange coupling $N_0 \alpha$ is reduced. It
is shown that the magnitude of this effect increases when x diminishes. Our
model may explain an unusual behavior of electron spin splitting observed
recently in those two materials in the Mn concentration range x <= 0.2%.",0505126v1
2005-05-08,Orbital Disordering and metal-insulator transition with hole-doping in perovskite-type vanadium oxides,"Filling-control metal-insulator transitions (MITs) and related electronic
phase diagrams have been investigated for hole-doped vanadium oxides,
Pr_{1-x}Ca_xVO_3, Nd_{1-x}Sr_xVO_3 and Y_{1-x}Ca_xVO_3, with perovskite
structure. The increase of the doping level x causes the melting of the G-type
(and C-type) orbital order, prior to or concomitantly with the MIT, due partly
to the doped-hole motion and partly to the ramdom potential arising from the
quenched disorder. In particular, the G-type spin- and C-type orbital-ordered
phase present in Y_{1-x}Ca_xVO_3 disappears immediately upon hole doping,
around x=0.02. On the other hand, the critical doping level x for MIT is
governed by the electron-correlation strength of the undoped parent compound.",0505190v1
2005-05-23,Phonon modes of monoclinic BiB3O6,"We present a detailed study of the phonon modes of the monoclinic compound
BiB3O6 based on polarized reflectivity measurements on single crystals. The
spectra are analysed by means of a generalized Drude-Lorentz model, which
allows us to resolve the modes of A and B symmetry.",0505556v2
2005-05-24,The unusual temperature dependence of the Eu$^{2+}$ fluorescence lifetime in CaF$_2$ crystals,"Fluorescence lifetimes of Eu$^{2+}$ doped in CaF$_2$ are measured at various
temperatures between 4K and 450K. The lifetime increases with between 100K and
300K, in contrast to the usual lifetime-temperature dependence. At higher or
lower temperatures the lifetime decreases with increasing temperature. The
phenomenon is explained by simulation of the energy levels and lifetimes of
low-lying $4f^65d$ states involved in the fluorescence.",0505592v1
2005-06-03,Superconductivity in C6Ca,"Using density functional theory we demonstrate that superconductivity in C6Ca
is due to a phonon-mediated mechanism with electron-phonon coupling 0.83 and
phonon-frequency logarithmic-average 24.7 meV. The calculated isotope exponents
are 0.24 for Ca and 0.26 for C. Superconductivity is mostly due C vibrations
perpendicular and Ca vibrations parallel to the graphite layers. Since the
electron-phonon couplings of these modes are activated by the presence of an
intercalant Fermi surface, the occurrence of superconductivity in graphite
intercalated compounds requires a non complete ionization of the intercalant.",0506082v2
2005-06-06,"The Li intercalation potential of LiMPO4 and LiMSiO4 olivines with M = Fe, Mn, Co, Ni","The Li intercalation potential of LiMPO4 and LiMSiO4 compounds with M = Fe,
Mn, Co, and Ni is computed with the GGA+U method. It is found that this
approach is considerably more accurate than standard LDA or GGA methods. The
calculated potentials for LiFePO4, LiMnPO4 and LiCoOPO4 agree to within 0.1 V
with experimental results. The LiNiPO4 potential is predicted to be above 5 V.
The potentials of the silicate materials are all found to be rather high, but
LiFeSiO4 and LiCoSiO4 have negligible volume change upon Li extraction.",0506111v1
2005-06-06,Ionization by Impact Electrons in Solids: Electron Mean Free Path Fitted Over a Wide Energy Range,"We propose a simple formula for fitting the electron mean free paths in
solids both at high and at low electron energies. The free-electron-gas
approximation used for predicting electron mean free paths is no longer valid
at low energies (E < 50 eV), as the band structure effects become significant
at those energies. Therefore we include the results of the band structure
calculations in our fit. Finally, we apply the fit to 9 elements and 2
compounds.",0506136v1
2005-06-06,Pressure-Induced Anomalous Phase Transitions and Colossal Enhancement of Piezoelectricity in PbTiO$_3$,"We find an unexpected tetragonal-to-monoclinic-to-rhombohedral-to-cubic phase
transition sequence induced by pressure, and a morphotropic phase boundary in a
pure compound using first-principles calculations. Huge dielectric and
piezoelectric coupling constants occur in the transition regions, comparable to
those observed in the new complex single-crystal solid-solution piezoelectrics
such as Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$, which are expected to
revolutionize electromechanical applications. Our results show that
morphotropic phase boundaries and giant piezoelectric effects do not require
intrinsic disorder, and open the possibility of studying this effect in simple
systems.",0506149v1
2005-06-16,Bose-Einstein Condensation Picture of Superconductivity in YBa2 Cu3 O7 (91 K) and YBa2 Cu3Se7 (371 K). (Dilute metals),"A metal dilution degree in the compounds YBa2 Cu3 O7 and YBa2 Cu3Se7 is
defined as z=(rMe/rO2-;Se2-)3. A substitution of oxygen by selenium changes z
by 8 times and the Bose-Einstein condensation temperature equals TcSe = TcO*8
2/3 = 364 K. The ""active"" electron pairs density in YBa2 Cu3 O7 is about 1.7
1020 cm-3. The electron effective mass is about 5me and is proportional to the
dielectric constant.",0506399v1
2005-06-20,A phenomenological model of the Resonance peak in High Tc Superconductors,"A notable aspect of high-temperature superconductivity in the copper oxides
is the unconventional nature of the underlying paired-electron states. The
appearance of a resonance peak, observed in inelastic neutron spectroscopy in
the superconducting state of the High Tc cuprates, its apparent linear
correlation with the critical superconducting temperature of each of the
compounds and its disappearance in the normal state are rather intriguing. It
may well be that this peak is the signature of the singlet to triplet
excitation, and is an unique characteristic of a d-wave superconductor. We
develop a simple criterion for the resonance peak which is based on the concept
of twist sti ness and its disappearance at T=Tc.",0506490v1
2005-06-21,A critical assessment of the pairing symmetry in NaxCoO2.yH2O,"We examine each of the symmetry-allowed pairing states of NaxCoO2.yH2O and
compare their properties to what is experimentally and theoretically
established about the compound. In this way, we can eliminate the vast majority
of states that are technically allowed and narrow the field to two, both of
f-wave type states. We discuss the expected features of these states and
suggest experiments that can distinguish between them. We also discuss
odd-frequency gap pairing and how it relates to available experimental
evidence.",0506536v1
2005-06-23,Crystallography and Chemistry of Perovskites,"Despite the simplicity of the original perovskite crystal structure, this
family of compounds shows an enormous variety of structural modifications and
variants. In the following, we will describe several examples of perovskites,
their structural variants and discuss the implications of distortions and
non-stoichiometry on their electronic and magnetic properties.",0506606v1
2005-06-29,A Penetration Depth Study on Li2Pd3B and Li2Pt3B,"In this paper we present a penetration depth study on the newly discovered
superconductors Li$_2$Pd$_3$B and Li$_2$Pt$_3$B. Surprisingly, the
low-temperature penetration depth $f(T)$ demonstrates distinct behavior in
these two isostructural compounds. In Li$_2$Pd$_3$B, $f(T)$ follows an
exponential decay and can be nicely fitted by a two-gap BCS superconducting
model with a small gap $\delta_1=3.2$K and a large gap $\delta_2=11.5$K.
However, linear temperature dependence of $f(T)$ is observed in Li$_2$Pt$_3$B
below 0.3$T_c$, giving evidence of line nodes in the energy gap.",0506771v1
2005-07-06,Synthesis of Mg(B$_{1-x}$C$_x$)$_2$ Powders,"We have synthesized bulk Mg(B$_{1-x}$C$_x$)$_2$ from a mixture of elemental
Mg, B, and the binary compound B$_4$C. Carbon incorporation was dramatically
improved by a two step reaction process at an elevated temperature of 1200
$^o$C. This reaction process results in a solubility limit near x$\sim$0.07. We
found that impurities in the starting B cause an additive suppression of T$_c$.
We combine these data with T$_c$ and H$_{c2}$(T=0) data from CVD wires as well
as plasma spray synthesized powders and present a unifying H$_{c2}$ and T$_c$
versus x plot.",0507151v1
2005-07-13,Novel Magnetic and Thermodynamic Properties of Thiospinel Compound CuCrZrS$_{4}$,"We have carried out dc magnetic susceptibility, magnetization and specific
heat measurements on thiospinel CuCrZrS$_{4}$. Below $T_{\rm C}^{*} =$ 58 K, dc
magnetic susceptibility and magnetization data show ferromagnetic behavior with
a small spontaneous magnetization 0.27 $\mu_{\rm B}/$f. u..
  In dc magnetic susceptibility, large and weak irreversibilities are observed
below $T_{\rm f} =$ 6 K and in the range $T_{\rm f}< T < T_{\rm C}^{*}$
respectively.
  We found that there is no anomaly as a peak or step in the specific heat at
$T_{\rm C}^{*}$.",0507314v1
2005-07-15,The antiferromagnetic/paramagnetic transition in mixed-spin compounds R2BaNiO5,"We present an extensive Quantum Monte Carlo study of the magnetic properties
of the mixed-spin quantum systems R2BaNiO5 (R= magnetic rare earth) which show
coexistence of 3-dimensional magnetic long-range order with 1-dimensional
quantum gap excitations. We discuss the validity of the performed simulations
in the critical region and show the excellent agreement with experimental
results. We emphasize the importance of quantum fluctuations contained in our
study which is absent in previous mean-field-like treatments.",0507372v1
2005-07-29,Point Contact Study of the Superconducting Order Parameter in RuSr2GdCu2O8,"We have performed a detailed study of the conductance characteristics
obtained by point contact junctions realized between a normal Pt/Ir tip and
syntered RuSr2GdCu2O8 (Ru-1212) samples. Indeed, this compound is subject of
great interest due to the coexistence of both magnetic order and bulk
superconductivity. In our experiments, the low temperature tunneling spectra
reproducibly show a zero bias conductance peak that can be well reproduced by a
generalized BTK model in the case of d-wave symmetry of the superconducting
order parameter.",0508003v1
2005-07-30,"Multiferroic behavior in CdCr2X4 (X = S, Se)","The recently discovered multiferroic material CdCr2S4 shows a coexistence of
ferromagnetism and relaxor ferroelectricity together with a colossal
magnetocapacitive effect. The complex dielectric permittivity of this compound
and of the structurally related CdCr2Se4 was studied by means of broadband
dielectric spectroscopy using different electrode materials. The observed
magnetocapacitive coupling at the magnetic transition is driven by enormous
changes of the relaxation dynamics induced by the development of magnetic
order.",0508014v1
2005-07-30,Evidence for Magnetic Ordering Associated with Metal-Insulator Transition in SmRu4P12 Studied by Muon Spin Relaxation,"Muon spin relaxation measurements on the filled skutterudite compound
SmRu4P12 have been carried out in zero- and longitudinal-fields. Temperature
dependence of both initial asymmetry and muon-spin depolarization rate show the
appearance of a magnetically ordered state below the metal-insulator transition
temperature TMI. The present study indicates that the ordering below TMI is not
a non-magnetic antiferro-quadrupolar ordering but a magnetic one, which
supports a scenario that a magnetic octupolar ordering occurs below TMI in
SmRu4P12.",0508017v2
2005-08-02,Orbital polaron lattice formation in lightly doped La1-xSrxMnO3,"By resonant x-ray scattering at the Mn K-edge on La7/8Sr1/8MnO3, we show that
an orbital polaron lattice (OPL) develops at the metal-insulator transition of
this compound. This orbital reordering explains consistently the unexpected
coexistence of ferromagnetic and insulating properties at low temperatures, the
quadrupling of the lattice structure parallel to the MnO2-planes, and the
observed polarization and azimuthal dependencies. The OPL is a clear
manifestation of strong orbital-hole interactions, which play a crucial role
for the colossal magnetoresistance effect and the doped manganites in general.",0508064v2
2005-08-15,Electronic structure and anisotropic transport properties in hexagonal YPtIn and LuAgGe ternary compounds,"We present anisotropic, zero applied magnetic field, temperature dependent
resistivity measurements on hexagonal, non-magnetic, YPtIn and LuAgGe single
crystals. For these materials the in-plane resistivity, $\rho_{ab}$, is
significantly higher than the $c$ - axis one, $\rho_c$, with $\rho_{ab}/\rho_c
\approx 1.4$ for YPtIn and $\approx 4.2 - 4.7$ for LuAgGe. The connection
between the electronic structure and the anisotropic transport properties is
discussed using density functional calculations that link the observed
anisotropy with a specific shape of Fermi surface and anisotropy of the Fermi
velocities.",0508346v1
2005-08-19,Resonant Tunneling in Truly Axial Symmetry Mn12 Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling,"Magnetization measurements of a truly axial symmetry Mn12-tBuAc molecular
nanomagnet with a spin ground state of S = 10 show resonance tunneling. This
compound has the same magnetic anisotropy as Mn12-Ac but the molecules are
better isolated and the crystals have less disorder and a higher symmetry.
Hysteresis loop measurements at several temperatures reveal a well-resolved
step fine-structure which is due to level crossings of excited states. All step
positions can be modeled by a simple spin Hamiltonian. The crossover between
thermally assisted and pure quantum tunneling can be investigated with
unprecedented detail.",0508437v1
2005-08-25,Continuous Evolution of the Fermi Surface of CeRu2Si2 across the Metamagnetic Transition,"We present new, high resolution Hall effect and magnetoresistance
measurements across the metamagnetic transition in the heavy fermion compound
CeRu2Si2. The results force us to rethink the notion that the transition is
accompanied by an abrupt f-electron localisation. Instead, we explain our data
assuming a continuous change of the Fermi surface. We also point out
ambiguities in the interpretation of dHvA data and give a possible solution to
the problem of the ""missing mass"".",0508613v1
2005-08-30,Generation of tunable Terahertz radiation using Josephson vortices,"We propose how to control the THz radiation generated by fast moving
Josephson vortices in spatially modulated (either along the c-axis or the
ab-plane) samples of Bi-2212 and related superconducting compounds. We show
that the JVs moving in a subset of weaker junctions can generate
out-of-ab-plane and outside-the-cone Cherenkov radiation. The ab-plane
modulation of superconducting properties (achieved, for instance, by ion
irradiation lithography) can result in transition radiation within certain
frequency windows, i.e., allowing the design of tunable THz emitters and THz
photonic crystals.",0508722v1
2005-09-05,CeMnNi4: A soft ferromagnet with a high degree of transport spin polarization,"In this letter we introduce a new soft ferromagnetic compound, i.e. CeMnNi4,
which exhibits a large moment (~4.95mu_B/Mn) and high degree of spin
polarization. The system has a ferromagnetic transition temperature of 148K.
Isothermal magnetization measurements at 5K reveal that the material is a soft
ferromagnet with a magnetization saturating at about 500Oe and a coercive field
of < 5 Oe. We determine the transport spin polarization of this material from
Point Contact Andreev Reflection measurements to be 66% thereby making this
material potentially important for spintronic applications.",0509101v2
2005-09-13,Electronic Structure and Exchange Interactions of Na$_{2}$V$_{3}$O$_{7}$,"We have performed first-principle calculations of the electronic structure
and exchange couplings for the nanotube compound Na$_{2}$V$_{3}$O$_{7}$ using
the LDA+U approach. Our results show that while the intra-ring exchange
interactions are mainly antiferromagnetic, the inter-ring couplings are {\it
ferromagnetic}. We argue that this is a consequence of the strong hybridization
between filled and vacant 3d vanadium orbitals due to the low symmetry of
Na$_{2}$V$_{3}$O$_{7}$, which results into strong - and often dominant -
ferromagnetic contributions to the total exchange interaction between vanadium
atoms. A comparison with results of previous works is included.",0509315v1
2005-09-15,Reduction of the ordered magnetic moment in YMnO3 with hydrostatic pressure,"YMnO3 exhibits a ferroelectric transition at high temperature (~ 900 K) and
magnetic ordering at T_N ~ 70 K where the dielectric constant shows an anomaly
indicative of the magneto-dielectric effect. Here we report powder neutron
diffraction experiments in this compound that show that the magnetic moment at
saturation is reduced by application of hydrostatic pressure. Our results yield
further insight about the nature of the spin-lattice interaction in ferroic
materials.",0509413v1
2005-09-16,On electron-hole symmetry and phase separation in some electron doped cuprates,"We conclude from the analysis of the experimental NMR data for electron-doped
cuprates that the Coulomb effects caused by doping lead to dynamical spatial
phase separation that contributes to the nuclear spin relaxation. Remarkable,
the ""infinite-layer"" Sr0.9La0.1CuO2 reveals unexpected electron-hole symmetry.
Its 63^Cu nuclear spin relaxation rate is the sum of a constant and the
temperature dependent dissipation components, moreover, the latter turns out to
be identical to the 1/63^T_1(T)-behavior in the stoichiometric hole-type
compound YBa2Cu4O8. Connection to fluctuations of a magnetic sub-phase is
discussed.",0509445v1
2005-09-26,Mobility gap in intermediate valent TmSe,"The infrared optical conductivity of intermediate valence compound TmSe
reveals clear signatures for hybridization of light $d$- and heavy f-electronic
states with m* ~ 1.6 m_0 and m* ~ 16 m_0, respectively. At moderate and high
temperatures, the metal-like character of the heavy carriers dominate the
low-frequency response while at low temperatures (T_N < T < 100 K) a gap-like
feature is observed in the conductivity spectra below 10 meV which is assigned
to be a mobility gap due to localization of electrons on local Kondo singlets,
rather than a hybridization gap in the density of states.",0509652v1
2005-09-27,Electron-Hole Asymmetry in GdBaCo_{2}O_{5+x}: Evidence for Spin Blockade of Electron Transport in a Correlated Electron System,"In RBaCo_{2}O_{5+x} compounds (R is rare earth) variability of the oxygen
content allows precise doping of CoO_2 planes with both types of charge
carriers. We study transport properties of doped GdBaCo_{2}O_{5+x} single
crystals and find a remarkable asymmetry in the behavior of holes and electrons
doped into a parent insulator GdBaCo_{2}O_{5.5}. Doping dependences of
resistivity, Hall response, and thermoelectric power reveal that the doped
holes greatly improve the conductivity, while the electron-doped samples always
remain poorly conducting. This doping asymmetry provides strong evidence for a
spin blockade of the electron transport in RBaCo_{2}O_{5+x}.",0509673v1
2005-10-03,First principles study of the spin state transitions in GdBaCo$_2$O$_{5.5}$,"Electronic structure calculations were carried out on the compound
GdBaCo$_2$O$_{5.5}$. The electronic structure variation with a change in the
spin state of the Co$^{3+}$ ion in an octahedral environment has been studied.
All the insulating phases are described and possible scenarios for the metallic
ones are presented. Orbital ordering is shown to take place and the electronic
structure leading to it is determined. The Ising-like anisotropy shown
experimentally can be predicted. Also, big unquenched orbital angular momenta
are calculated and their origin is described.",0510046v2
2005-10-05,Orbital Polarization in Itinerant Magnets,"We propose a parameter-free scheme of calculation of the orbital polarization
(OP) in metals, which starts with the strong-coupling limit for the screened
Coulomb interactions in the random-phase approximation (RPA). For itinerant
magnets, RPA can be further improved by restoring the spin polarization of the
local-spin-density approximation (LSDA) through the local-field corrections.
The OP is then computed in the static GW approach, which systematically
improves the orbital magnetization and the magnetic anisotropy energies in
transition-metal and actinide compounds.",0510100v1
2005-10-18,Quantum Statistics of Interacting Dimer Spin Systems,"The compound TlCuCl3 represents a model system of dimerized quantum spins
with strong interdimer interactions. We investigate the triplet dispersion as a
function of temperature by inelastic neutron scattering experiments on single
crystals. By comparison with a number of theoretical approaches we demonstrate
that the description of Troyer, Tsunetsugu, and Wuertz [Phys. Rev. B 50, 13515
(1994)] provides an appropriate quantum statistical model for dimer spin
systems at finite temperatures, where many-body correlations become
particularly important.",0510487v1
2005-10-21,ESR study of the single-ion anisotropy in the pyrochlore antiferromagnet Gd2Sn2O7,"Single-ion anisotropy is of importance for the magnetic ordering of the
frustrated pyrochlore antiferromagnets Gd2Ti2O7 and Gd2Sn2O7. The anisotropy
parameters for the Gd2Sn2O7 were measured using the electron spin resonance
(ESR) technique. The anisotropy was found to be of the easy plane type, with
the main constant D=140mK. This value is 35% smaller than the value of the
corresponding anisotropy constant in the related compound Gd2Ti2O7.",0510575v1
2005-11-03,Unified phase diagram of models exhibiting neutral-ionic transition,"We have studied the neutral-ionic transition in organic mixed-stack
compounds. A unified model has been derived which, in limiting cases, is
equivalent to the models proposed earlier, the donor-acceptor model and the
ionic Hubbard model. Detailed numerical calculations have been performed on
this unified model with the help of the density-matrix renormalization-group
(DMRG) procedure calculating excitation gaps, ionicity, lattice site entropy,
two-site entropy, and the dimer order parameter on long chains and the unified
phase diagram has been determined.",0511082v1
2005-11-15,Magnetization plateaux induced by a coupling to the lattice,"We investigate a simple model of a frustrated spin-1/2 Heisenberg chain
coupled to adiabatic phonons under an external magnetic field. Using field
theoretic methods complemented by extensive Density Matrix Renormalisation
Group techniques generalized to include self-consistent lattice distortions, we
show that magnetization plateaux at non-trivial rational values of the
magnetization can be stabilized by the lattice coupling. We suggest that such a
scenario could be relevant for some low dimensional frustrated spin-Peierls
compounds.",0511368v1
2005-11-17,Nature of Chemisorption on Titanium Carbide and Nitride,"Extensive density-functional calculations are performed to understand atomic
chemisorption on the TiC(111) and TiN(111) surfaces, in particular the
calculated pyramid-shaped trends in the adsorption energies for second- and
third-period adatoms. Our previously proposed concerted-coupling model for
chemisorption on TiC(111) is tested against new results for adsorption on
TiN(111) and found to apply on this surface as well, thus reflecting both
similarities and differences in electronic structure between the two compounds.",0511440v1
2005-11-29,Magnetic field dependence of kinetic inductance in Bi2Sr2Ca2Cu3O10 superconducting strip and its feasible applications,"The kinetic inductance properties of a thin superconducting sample of
BSCCO-2223 compound is studied. A strong dependence of kinetic inductance with
the variation of applied magnetic field is found at low temperature in the
superconducting state. The kinetic inductance of a thin superconductor
increases linearly with increasing magnetic field. This behavior is used for
designing a superconducting modulator circuit. This behavior can be useful for
device applications and designing of superconducting electronic circuits like
superconducting power amplifier, superconducting transmitter and
superconducting ac current controller.",0511705v1
2005-12-02,Magnetic properties of Sr_2Fe_1+xMo_1-xO_6 with -1 <= x <= 0.25,"We have synthesized the solid solution, Sr_2Fe_1+xMo_1-xO_6 with -1 <= x <=
0.25, the composition x = 0 corresponding to the well-known double perovskite
system Sr2FeMoO6. We report structural and magnetic properties of the above
system, exhibiting systematic variations across the series. These results
restrict the range of models that can explain magnetism in this family of
compounds, providing an understanding of the magnetic structure.",0512059v1
2005-12-08,Physics of Complex Magnetic Materials: Quasiparticle Many-Body Dynamics,"A brief survey of the author's works on the quantum theory of magnetism.
Theoretical foundation and applications of the generalized spin-fermion (sp-d)
exchange lattice model to various magnetic systems, e.g., rare-earth metals and
compounds, and magnetic and diluted magnetic semiconductors are discussed
briefly. The main emphasis is put on the dynamic behavior of two interacting
subsystems, the localized spins and spin density of itinerant carriers. A
nonperturbative many-body approach was used to describe the quasiparticle
dynamics. The approach permits to investigate and clarify the role of various
interactions and disorder effects in combined quantum models of magnetism in
unified and coherent fashion.",0512183v1
2005-12-16,Studies of R2Ti2O7 (R=Gd and Yb); new results,"Specific heat and muon spin rotation and relaxation data are presented for
two geometrically frustrated systems: Gd2Ti2O7 which antiferromagnetically
orders and Yb2Ti2O7 which presents dynamical short range correlations at low
temperature. The muon data help to characterize the spin dynamics of these two
compounds.",0512389v1
2005-12-16,Spin dynamics in a compound semiconductor spintronic structure with a Schottky barrier,"We demonstrate theoretically that spin dynamics of electrons injected into a
GaAs semiconductor structure through a Schottky barrier possesses strong
non-equilibrium features. Electrons injected are redistributed quickly among
several valleys. Spin relaxation driven by the spin-orbital coupling in the
semiconductor is very rapid. At T = 4.2 K, injected spin polarization decays on
a distance of the order of 50 - 100 nm from the interface. This spin
penetration depth reduces approximately by half at room temperature. The spin
scattering length is different for different valleys.",0512414v1
2005-12-19,Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering,"Time-resolved inelastic neutron scattering measurements on an array of
single-crystals of the single-molecule magnet Mn12ac are presented. The data
facilitate a spectroscopic investigation of the slow relaxation of the
magnetization in this compound in the time domain.",0512453v1
2005-12-21,Derivation of the generalized Non Linear Sigma Model in the presence of the Dzyaloshinskii-Moriya interaction,"We derive the long-wavelength non-linear sigma model for a two-dimensional
Heisenberg system in the presence of the Dzyaloshinskii-Moriya and
pseudodipolar interactions. We show that the system is a non-conventional
easy-axis antiferromagnet, displaying an anomalous coupling between the
magnetic field and the staggered order parameter. Our results are in good
agreement with recent experimental data for undoped La2CuO4 compounds.",0512528v1
2005-12-24,Modified spin-wave theory of nuclear magnetic relaxation in one-dimensional quantum ferrimagnets: Three-magnon versus Raman processes,"Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
studied by means of a modified spin-wave theory. Calculating beyond the
first-order mechanism, where a nuclear spin directly interacts with spin waves
through the hyperfine coupling, we demonstrate that the
exchange-scattering-enhanced three-magnon nuclear relaxation may generally
predominate over the Raman one with increasing temperature and decreasing
field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest
that the major contribution to 1/T_1_ be made by the three-magnon scattering.",0512629v1
2005-12-24,Low-temperature thermodynamics of one-dimensional alternating-spin Heisenberg ferromagnets,"Motivated by a novel bimetallic chain compound in which alternating magnetic
centers are ferromagnetically coupled, we investigate thermodynamic properties
of one-dimensional spin-$(S,s)$ Heisenberg ferromagnets both numerically and
analytically. On the one hand, quantum Monte Carlo calculations illuminate the
overall thermal behavior. The specific heat may exhibit a double-peaked
structure at intermediate temperatures for $S\agt 3s$ in general. On the other
hand, a modified spin-wave theory precisely describes the low-temperature
properties. Expanding the specific heat and the magnetic susceptibility, we
reveal an analogy and a contrast between mixed-spin ferromagnets and
ferrimagnets.",0512630v1
2005-12-24,Nonlinear lattice relaxation of photoexcited diplatinum-halide chain compounds,"In order to reveal the relaxation mechanism of photogenerated charge-transfer
excitations in quasi-one-dimensional halogen-bridged diplatinum complexes, we
calculate the low-lying adiabatic potential energy surfaces of a
one-dimensional extended Peierls-Hubbard model. High-energy excitations above
the electron-hole continuum may relax into polarons, while excitons pumped
within the optical gap are self-localized and then either decay by luminescence
or divide into solitons. Neutral solitons, charged solitons, and polarons may
be simultaneously photogenerated in a diplatinum-halide chain, which has never
been observed in any conventional platinum-halide chain. Optical conductivity
is also simulated along the decay paths for experimental verification.",0512636v1
2006-01-25,Enhancement of Wigner crystallization in quasi low-dimensional solids,"The crystallization of electrons in quasi low-dimensional solids is studied
in a model which retains the full three-dimensional nature of the Coulomb
interactions. We show that restricting the electron motion to layers (or
chains) gives rise to a rich sequence of structural transitions upon varying
the particle density. In addition, the concurrence of low-dimensional electron
motion and isotropic Coulomb interactions leads to a sizeable stabilization of
the Wigner crystal, which could be one of the mechanisms at the origin of the
charge ordered phases frequently observed in such compounds.",0601578v1
2006-02-05,Half-metallic ferromagnetism induced by dynamic electron correlations in VAs,"The electronic structure of the VAs compound in the zinc-blende structure is
investigated using a combined density-functional and dynamical mean-field
theory approach. Contrary to predictions of a ferromagnetic semiconducting
ground state obtained by density-functional calculations, dynamical
correlations induce a closing of the gap and produce a half-metallic
ferromagnetic state. These results emphasize the importance of dynamic
correlations in materials suitable for spintronics.",0602112v2
2006-02-06,Magnetic ordering in Gd2Sn2O7: the archetypal Heisenberg pyrochlore antiferromagnet,"Low-temperature powder neutron diffraction measurements are performed in the
ordered magnetic state of the pyrochlore antiferromagnet Gd2Sn2O7. Symmetry
analysis of the diffraction data indicates that this compound has the ground
state predicted theoretically for a Heisenberg pyrochlore antiferromagnet with
dipolar interactions. The difference in magnetic structures of Gd2Sn2O7 and of
nominally analogous Gd2Ti2O7 is found to be determined by a specific type of
third-neighbor superexchange interaction on the pyrochlore lattice between
spins across empty hexagons.",0602138v1
2006-02-06,Role of oxygen in the electron-doped superconducting cuprates,"We report on resistivity and Hall measurements in thin films of the
electron-doped superconducting cuprate Pr$_{2-x}$Ce$_{x}$CuO$_{4\pm\delta}$.
Comparisons between x = 0.17 samples subjected to either ion-irradiation or
oxygenation demonstrate that changing the oxygen content has two separable
effects: 1) a doping effect similar to that of cerium, and 2) a disorder
effect. These results are consistent with prior speculations that apical oxygen
removal is necessary to achieve superconductivity in this compound.",0602142v1
2006-02-20,Spin liquid correlations in Nd-langasite anisotropic Kagomé antiferromagnet,"Dynamical magnetic correlations in the geometrically frustrated
Nd$\_3$Ga$\_5$SiO$\_{14}$ compound were probed by inelastic neutron scattering
on a single crystal. A scattering signal with a ring shape distribution in
reciprocal space and unprecedented dispersive features was discovered.
Comparison with calculated static magnetic scattering from models of correlated
spins suggests that the observed phase is a spin liquid inherent to an
antiferromagnetic kagom\'e-like lattice of anisotropic Nd moments.",0602457v2
2006-02-27,"Origin of the large thermoelectric power in oxygen-variable RBaCo_{2}O_{5+x} (R=Gd, Nd)","Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single
crystals have been studied upon continuous doping of CoO_2 planes with either
electrons or holes. The thermoelectric response and the resistivity behavior
reveal a hopping character of the transport in both compounds, providing the
basis for understanding the recently found remarkable divergence of the Seebeck
coefficient at x=0.5. The doping dependence of the thermoelectric power evinces
that the configurational entropy of charge carriers, enhanced by their spin and
orbital degeneracy, plays a key role in the origin of the large thermoelectric
response in these correlated oxides.",0602618v1
2006-03-01,"Structural Anomalies at the Magnetic and Ferroelectric Transitions in $RMn_2O_5$ (R=Tb, Dy, Ho)","Strong anomalies of the thermal expansion coefficients at the magnetic and
ferroelectric transitions have been detected in multiferroic $RMn_2O_5$. Their
correlation with anomalies of the specific heat and the dielectric constant is
discussed. The results provide evidence for the magnetic origin of the
ferroelectricity mediated by strong spin-lattice coupling in the compounds.
Neutron scattering data for $HoMn_2O_5$ indicate a spin reorientation at the
two low-temperature phase transitions.",0603032v1
2006-03-15,Charge transfer gap for T'-RE2CuO4 and T-La2CuO4 as estimated from Madelung potential calculations,"T'-RE2CuO4 (RE: rare-earth element), after appropriate ""reduction"", has
fairly high conductivity and also exhibits clear Fermi edge in photoemission
spectroscopy. To clarify the origin of conductivity in the T' mother compounds,
we evaluated the unscreened charge-transfer gap for T'-RE2CuO4 and T-La2CuO4.
The value of charge-transfer gap for T'-compounds almost linearly decreases
with increasing the ionic radius of RE from 12.24 eV for T'-Tm2CuO4 to 9.90 eV
for T'-La2CuO4. The results qualitatively explain metallic conductivity in
T'-RE2CuO4 for large RE.",0603403v1
2006-04-03,Electron-spectroscopic investigation of metal-insulator transition in Sr2Ru1-xTixO4 (x=0.0-0.6),"We investigate the nature and origin of the metal-insulator transition in
Sr2Ru1-xTixO4 as a function of increasing Ti content (x). Employing detailed
core, valence, and conduction band studies with x-ray and ultraviolet
photoelectron spectroscopies along with Bremsstrahlung isochromat spectroscopy,
it is shown that a hard gap opens up for Ti content greater than equal to 0.2,
while compositions with x<0.2 exhibit finite intensity at the Fermi energy.
This establishes that the metal-insulator transition in this homovalent
substituted series of compounds is driven by Coulomb interaction leading to the
formation of a Mott gap, in contrast to transitions driven by disorder effects
or band flling.",0604031v1
2006-04-06,Origin of ferromagnetism in Cs$_2$AgF$_4$: importance of Ag - F covalency,"The magnetic nature of Cs$_{2}$AgF$_{4}$, an isoelectronic and isostructural
analogue of La$_2$CuO$_4$, is analyzed using density functional calculations.
The ground state is found to be ferromagnetic and nearly half metallic. We find
strong hybridization of Ag-$d$ and F-$p$ states. Substantial moments reside on
the F atoms, which is unusual for the halides and reflects the chemistry of the
Ag(II) ions in this compound. This provides the mechanism for ferromagnetism,
which we find to be itinerant in character, a result of a Stoner instability
enhanced by Hund's coupling on the F.",0604167v1
2006-04-12,Electronic structure and transport in CsBi$_4$Te$_6$,"The band structure of the novel low-temperature thermoelectric material,
\CBT, is calculated and analyzed using the semi-classic transport equations. It
is shown that to obtain a quantitative agreement with measured transport
properties a band gap of 0.08 eV must be enforced. A gap in reasonable
agreement with experiment was obtained using the generalized gradient
functional of Engel and Vosko. We found that the experimental $p$-type sample
has a carrier concentration close to optimal. Furthermore the conduction bands
have a form equally well suited for thermoelectric properties and we predict
that an optimally doped $n$-type compound could have thermoelectric properties
exceeding those of the $p$-type.",0604303v1
2006-04-27,"""Artificial"" superconductors. Superconducting phases in the MgxWO3 nanocomposite (x = 0.037; 0.125 - Tcx = 140; 280 K)","Superconductivity of some compounds may be explained as resulting from
Bose-Einstein condensation (BEC) of atomic electron pairs of divalent atoms or
electron pairs of diatomic molecules made up of univalent atoms. ""Artificial""
superconductors of such types can be tailored using nonstoichiometric ompounds.
Synthesis of ""natural"" stoichiometric superconductors is a much more
complicated problem. In these cases, we have two methods of obtaining dilute
metals in a state intermediate between the metal and the insulator.",0604616v1
2006-05-06,Evidence for multimagnon-mediated nuclear spin relaxation in the intertwining double-cain ferrimagnet $Ca_3 Cu_3 (PO_4)_4$,"The nuclear spin-lattice relaxation time $T_1$ of $^{31}P$ nuclei in the
title compound is measured for the first time and interpreted in terms of a
modified spin-wave theory. We establish a novel scenario for one-dimensional
ferrimagnetic spin dynamics -- it is three-magnon processes enhanced by
exchange scattering, rather than Raman processes, that make the major
contribution to $1/T_1$.",0605157v2
2006-05-06,Competing ground states of metal-halide ladders,"Based on a symmetry argument, we investigate the ground-state properties of
newly synthesized metal-halide ladder compounds
(C_8_H_6_N_4_)[Pt(C_2_H_8_N_2_)X]_2_(ClO_4_)_4_ 2H_2_O (X=Cl, Br, I). Employing
a fully dressed two-band Peierls-Hubbard model, we systematically reveal
possible charge- or spin-ordered states. Numerical phase diagrams demonstrate a
variety of competing Peierls and Mott insulators with particular emphasis on
the transition between two types of mixed-valent state of Pt^II^ and Pt^IV^
driven by varying interchain hopping integrals and Coulomb interactions.",0605158v1
2006-05-10,Field-Induced Quantum Criticality of Systems with Ferromagnetically Coupled Structural Spin Units,"The field-induced quantum criticality of compounds with ferromagnetically
coupled structural spin units (as dimers and ladders) is explored by applying
Wilson's renormalization group framework to an appropriate effective action. We
determine the low-temperature phase boundary and the behavior of relevant
quantities decreasing the temperature with the applied magnetic field fixed at
its quantum critical point value. In this context, a plausible interpretation
of some recent experimental results is also suggested.",0605274v1
2006-05-12,Magnetic properties of spin-orbital polarons in lightly doped cobaltates,"We present a numerical treatment of a spin-orbital polaron model for
Na_xCoO_2 at small hole concentration (0.7 < x < 1). We demonstrate how the
polarons account for the peculiar magnetic properties of this layered compound:
They explain the large susceptibility; their internal degrees of freedom lead
both to a negative Curie-Weiss temperature and yet to a ferromagnetic
intra-layer interaction, thereby resolving a puzzling contradiction between
these observations. We make specific predictions on the momentum and energy
location of excitations resulting from the internal degrees of freedom of the
polaron, and discuss their impact on spin-wave damping.",0605334v1
2006-05-16,Issues on the transport of one dimensional systems,"In this paper, we will critically discuss recent theoretical and experimental
developments on the transport of one dimensional quantum systems. In
particular, we will focus on open issues and controversial results related to
the finite temperature dynamics of integrable quantum models. These singular
systems are commonly used in the description of quasi-one dimensional
materials. They have recently attracted a lot of interest in connection to the
interpretation of experiments, specially after the discovery of unusual thermal
conductivity in magnetic compounds.",0605405v1
2006-05-31,Checkerboard and stripe inhomogeneities in cuprates,"We systematically investigate charge-ordering phases by means of a restricted
and unrestricted Gutzwiller approximation to the single-band Hubbard model with
nearest ($t$) and next-nearest neighbor hopping ($t'$). When $|t'/t|$ is small,
as appropriate for ${\rm La_{2-x}Sr_xCuO_4}$, stripes are found, whereas in
compounds with larger $|t'/t|$ (such as ${\rm Ca_{2-x}Na_x CuO_2Cl_2}$ and
${\rm Bi_2Sr_2CaCu_2O_{8+\delta}}$) checkerboard structures are favored. In
contrast to the linear doping dependence found for stripes the charge
periodicity of checkerboard textures is locked to 4 unit cells over a wide
doping range. In addition we find that checkerboard structures are favored at
surfaces.",0606010v1
2006-06-02,First order phase transition in the frustrated triangular antiferromagnet CsNiCl3,"By means of high-resolution ultrasonic velocity measurements, as a function
of temperature and magnetic field, the nature of the different low temperatures
magnetic phase transitions observed for the quasi-one-dimensional compound
CsNiCl3 is established. Special attention has been devoted to the field-induced
120 degree phase transition above the multicritical point in the H-T phase
diagram where the elastic constant C44 reveals a step-like variation and
hysteresis effects. These results represent the first experimental evidence
that the 120 degree phase transition is weakly first order and contradict the
popular notion of new universality classes for chiral systems.",0606049v1
2006-06-07,Thermal expansion of the quasi two-dimensional magnetic layered compound BaNi$_{2}$V$_{2}$O$_{8}$ under magnetic fields along c-axis,"The quasi two-dimensional magnetic BaNi$_{2}$V$_{2}$O$_{8}$ is studied by
using high-resolution thermal expansion in magnetic fields up to 10 T applied
along the c-axis. A slight increase of about 1 % of the three-dimensional
antiferromagnetic ordering temperature $T_N$ is observed at 10 T. Positive and
negative pressure dependencies of $T_N$, respectively, are inferred from the
thermal expansion $\alpha(T)$ for pressures applied along the $a$- and
$c$-axes.",0606174v1
2006-06-09,Current spinon-holon description of the one-dimensional charge-transfer insulator SrCuO2: Angle-resolved photoemission measurements,"We have investigated the low-energy electronic structure of the strongly
correlated one-dimensional copper oxide chain compound SrCuO2 by angle resolved
photoemission as a function of excitation energy. In addition to the prominent
spinon-holon continuum we observe a peaklike and dispersive feature at the zone
boundary. By fine-tuning the experimental parameters we are able to monitor the
full holon branch and to directly measure the electronic hopping parameter with
unprecedented accuracy.",0606238v1
2006-06-12,Defects in CrAs and related compounds: a route to half-metallic ferrimagnetism,"Half-metallic ferrimagnetism is crucial for spintronic applications with
respect to ferromagnets due to the lower stray fields created by these
materials. Studying the effect of defects in CrAs and related transition-metal
chalcogenides and pnictides crystallizing in the zinc-blende structure, we
reveal that the excess of the transition-metal atoms leads to half-metallic
ferrimagnetism. The surplus of these atoms are antiferromagnetically coupled to
the transition-metal atoms sitting at the perfect lattice sites. The needed
condition to achieve half-metallic ferrimagnetism is to prevent the migration
of the $sp$ atoms to other sites and the atomic swaps.",0606286v1
2006-06-20,Effect of the pseudogap on the uniform magnetic susceptibility of Y1-xCaxBa2Cu3O7-d,"The effects of planar hole content, p, on the temperature-dependent uniform
(q = 0) magnetic susceptibility, c(T), of polycrystalline Y1-xCaxBa2Cu3O7-d
compounds with 0.0 </= x </= 0.20 were investigated over a wide range of oxygen
deficiency (d). Systematic variations in c(T) were found with changing p. The
characteristic pseudogap temperature scale, Eg(p)/kB, was extracted from the
analysis of the c(T,p) data. We have found clear evidence that the pseudogap in
the quasi-particle spectral weight appears abruptly at a planar hole content of
p ~ 0.19, and that it grows rapidly with decreasing p.",0606519v1
2006-06-23,Microwave losses of bulk CaC6,"We report a study of the temperature dependence of the surface resistance RS
in the graphite intercalated compound (GIC) CaC6, where superconductivity at
11.5 K was recently discovered. Experiments are carried out using a copper
dielectrically loaded cavity operating at 7 GHz in a ""hot finger""
configuration. Bulk CaC6 samples have been synthesized from highly oriented
pyrolytic graphite. Microwave data allows to extract unique information on the
quasiparticle density and on the nature of pairing in superconductors. The
analysis of RS(T) confirms our recent experimental findings that CaC6 behaves
as a weakly-coupled, fully gapped, superconductor.",0606616v1
2006-06-29,Relevance of quantum fluctuations in the Anderson-Kondo model,"We study a localized spin coupled to an Anderson impurity to model the
situation found in higher transition metal or rare earth compounds like e.g.\
LaMnO$_3$ or Gd monopnictides. We find that, even for large quantum numbers of
the localized spin, quantum fluctuations play an essential role for the case of
ferromagnetic coupling between the spin and the impurity levels. For
antiferromagnetic coupling, a description in terms of a classical spin is
appropriate.",0606762v1
2006-07-01,Amperean Pairing Instability in the U(1) Spin Liquid State with Fermi Surface and Application to $κ-(BEDT-TTF)_2 Cu_2 (CN)_3$,"Recent experiments on the organic compound $\kappa-(BEDT-TTF)_2 Cu_2 (CN)_3$
raise the possibility that the system may be described as a quantum spin
liquid. Here we propose a pairing state caused by the `Amperean' attractive
interaction between spinons on a Fermi surface mediated by the U(1) gauge
field. We show that this state can explain many of the observed low temperature
phenomena and discuss testable consequences.",0607015v1
2006-07-18,In-plane and transverse superconducting fluctuation diamagnetism in the presence of charge-density waves in 2H-NbSe2 single crystals,"The fluctuation-diamagnetism (FD) above the superconducting transition was
measured in 2H-NbSe2 single crystals. The moderate uniaxial anisotropy of this
compound, and some experimental improvements, allowed to measure the
superconducting fluctuation effects in the two main crystallographic
directions. These results reveal that the nonlocal electrodynamic effects on
the FD are highly anisotropic, and they also discard a possible contribution to
the FD coming from the charge-density waves (CDW) appearing below $Tcdw > Tc in
2H-NbSe2, in agreement with a phenomenological estimate.",0607451v2
2006-07-18,"Effects of mixed rare earth occupancy on the low temperature properties of (R, R',R''...)Ni2Ge2 single crystals","Temperature and applied magnetic field dependent magnetization measurements
on 34 single crystalline samples of (R, R',R''...)Ni2Ge2 compounds (R, R', R'',
etc. being primarily Gd-Lu, Y), were made. These measurements reveal that,
despite extremes in local moment anisotropy, the average de Gennes parameter is
a remarkably good predictor of the paramagnetic to antiferromagnetic ordering
temperature. In addition, the pronounced metamagnetic phase transitions seen in
the low temperature phase of TbNi2Ge2 are found to be remarkably robust to high
substitution levels of Gd and 25% substitutions of other heavy rare earths.",0607455v1
2006-07-21,Stabilization of charge ordering in La_(1/3)Sr_(2/3)FeO_(3-d) by magnetic exchange,"The magnetic exchange energies in charge ordered La_(1/3)Sr_(2/3)FeO_(3-d)
(LSFO) and its parent compound LaFeO_(3) (LFO) have been determined by
inelastic neutron scattering. In LSFO, the measured ratio of ferromagnetic
exchange between Fe3+ - Fe5+ pairs (J_F) and antiferromagnetic exchange between
Fe3+ - Fe3+ pairs (J_AF) fulfills the criterion for charge ordering driven by
magnetic interactions (|J_F/J_AF| > 1). The 30% reduction of J_AF as compared
to LFO indicates that doped holes are delocalized, and charge ordering occurs
without a dominant influence from Coulomb interactions.",0607570v1
2006-07-31,Kagomé ice state in the dipolar spin ice Dy_{2}Ti_{2}O_{7},"We have investigated the kagom\'{e} ice behavior of the dipolar spin-ice
compound Dy_{2}Ti_{2}O_{7} in magnetic field along a [111] direction using
neutron scattering and Monte Carlo simulations. The spin correlations show that
the kagom\'{e} ice behavior predicted for the nearest-neighbor (NN) interacting
model, where the field induces dimensional reduction and spins are frustrated
in each two-dimensional kagom\'{e} lattice, occurs in the dipole interacting
system. The spins freeze at low temperatures within the macroscopically
degenerate ground states of the NN model.",0607808v2
2006-08-01,Ferroelectricity in the Magnetic E-Phase of Orthorhombic Perovskites,"We show that the symmetry of the spin zigzag chain E phase of the
orthorhombic perovskite manganites and nickelates allows for the existence of a
finite ferroelectric polarization. The proposed microscopic mechanism is
independent of spin-orbit coupling. We predict that the polarization induced by
the E-type magnetic order can potentially be enhanced by up to two orders of
magnitude with respect to that in the spiral magnetic phases of TbMnO3 and
similar multiferroic compounds.",0608025v2
2006-08-08,Ferroelectricity in perovskite $HoMnO_3$ and $YMnO_3$,"Ferroelectricity is observed in orthorhombic $HoMnO_3$ and $YMnO_3$ at the
magnetic lock-in transitions into an E-type structure or an incommensurate
phase with a temperature independent wave vector, respectively. In $HoMnO_3$
the ferroelectric polarization strongly depends on the external magnetic field
indicating the involvement of the rare earth moment order in this compound. The
results are discussed within the framework of recent theoretical models, in
particular the double exchange driven polar displacements predicted for E-type
magnetic structures.",0608195v2
2006-08-09,Origin of the second coherent peak in the dynamical structure factor of an asymmetric spin-ladder,"Appearance of the second coherent peak in the dynamical structure factor of
an asymmetric spin ladder is suggested. The general arguments are confirmed by
the first order (with respect to the asymmetry) calculation for a spin ladder
with singlet-rung ground state. Basing on this result a new interpretation is
proposed for the inelastic neutron scattering data in the spin gap compound
CuHpCl.",0608231v2
2006-08-18,Direct Correlation between 1/f-magneto-noise and magnetoresistance in La0.7Sr0.3MnO3 and (La0.5Pr0.2)Ba0.3MnO3 manganites,"Temperature- and magnetic field-dependent electrical noise and electrical
resistivity measurements were carried out on epitaxial thin films of a large
bandwidth La0.7Sr0.3MnO3 and a disordered intermediate bandwidth
(La0.5Pr0.2)Ba0.3MnO3 manganite system. The power spectraldensity was dominated
by 1/f-noise. This 1/f-noise was observed to follow the overall temperature
dependence of the resistivity. Moreover, in these compounds the magneto-noise
effect was found to be of nearly the same magnitude as the magnetoresistance.
This direct correlation between magneto-noise and magnetoresistance suggests
that the enhanced 1/f-noise has its origin in intrinsic charge-carrier density
fluctuations.",0608419v1
2006-08-29,Quantum spin glass in anisotropic dipolar systems,"The spin-glass phase in the $\LHx$ compound is considered. At zero transverse
field this system is well described by the classical Ising model. At finite
transverse field deviations from the transverse field quantum Ising model are
significant, and one must take properly into account the hyperfine
interactions, the off-diagonal terms in the dipolar interactions, and details
of the full J=8 spin Hamiltonian to obtain the correct physical picture. In
particular, the system is not a spin glass at finite transverse fields and does
not show quantum criticality.",0608622v1
2006-09-08,Dynamics of photoexcited states in one-dimensional dimerized Mott insulators,"Dynamical properties of photoexcited states are theoretically studied in a
one-dimensional Mott insulator dimerized by the spin-Peierls instability.
Numerical calculations combined with a perturbative analysis have revealed that
the lowest photoexcited state without nearest-neighbor interaction corresponds
to an interdimer charge transfer excitation that belongs to dispersive
excitations. This excited state destabilizes the dimerized phase, leading to a
photoinduced inverse spin-Peierls transition. We discuss the purely electronic
origin of midgap states that are observed in a latest photoexcitation
experiment of an organic spin-Peierls compound, K-TCNQ
(potassium-tetracyanoquinodimethane).",0609186v1
2006-09-15,Two-dimensional frustrated spin systems in high magnetic fields,"We discuss our numerical results on the properties of the S = 1/2 frustrated
J1-J2 Heisenberg model on a square lattice as a function of temperature and
frustration angle phi = atan(J2/J1) in an applied magnetic field. We cover the
full phase diagram of the model in the range -pi <= phi <= pi. The discussion
includes the parameter dependence of the saturation field itself, and addresses
the instabilities associated with it. We also discuss the magnetocaloric effect
of the model and show how it can be used to uniquely determine the effective
interaction constants of the compounds which were investigated experimentally.",0609381v1
2006-09-30,Lattice dynamics of MC60 compounds in FCC phase,"Phonon dynamics of alkali metal atom, M doped in C60, forming MC60 solids in
fcc phase has been studied. The calculations take into account Van-der-Waals
and Coulomb interactions for M-C60 and C60-C60 and show fairly good agreement
with reported neutron scattering results for RbC60. The calculations have also
been done following Rigid Shell Model (RSM). We also perform calculations for
specific heat, Gruneisen parameter, thermal expansion and thermal expansion
coefficient.",0610008v1
2006-10-03,Magnetization of undoped 2-leg S = 1/2 spin ladders in La4Sr10Cu24O41,"Magnetization data of single crystalline La4Sr10Cu24O41 are presented. In
this compound, doped spin chains and undoped spin ladders are realized. The
magnetization, at low temperatures, is governed by the chain subsystem with a
finite interchain coupling which leads to short range antiferromagnetic spin
correlations. At higher temperatures, the response of the chains can be
estimated in terms of a Curie-Weiss law. For the ladders, we apply the
low-temperature approximation for a S=1/2 2-leg spin ladder by Troyer et al.",0610090v1
2006-10-06,Significant enhancement of room temperature ferromagnetism in surfactant coated polycrystalline Mn doped ZnO particles,"We report a surfactant assisted synthesis of Mn doped ZnO polycrystalline
samples showing robust room temperature ferromagnetism as characterized by
X-ray diffraction analysis, Transmission Electron Microscopy, Electron
Paramagnetic Resonance and DC magnetization mearurements. This surfactant
assisted synthesis method, developed by us, is found to be highly reproducible.
Further, it can also be extended to the synthesis of other transition metal
doped ZnO.",0610170v1
2006-10-22,Evidence for two fluids in the ground state of cuprates,"We report charge density measurements, using NMR, in the superconducting
compound (Ca_{x}La_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_{y}, which has two
independent variables x (family) and y (oxygen). For underdoped samples we find
the rate at which holes are introduced into the plane upon oxygenation to be
family-independent. In contrast, not all carriers contribute to either
antiferromagnetic or superconducting order parameters. This result is
consistent with a two fluid phenomenology or intrinsic mesoscopic
inhomogeneities in the bulk. We also discuss the impact of
weak-chemical-disorder on T_{c}.",0610595v1
2006-10-23,Magnetic properties and the electronic structure of LiCoO_2,"We have described properties of LiCoO_2 within the Quantum Atomistic Solid
State (QUASST) theory taking into account very strong electron correlations,
predominantly of the intra-atomic origin, spin-orbit coupling and the detailed
local crystallographic surroundings and its symmetry. Properties of LiCoO_2 are
consistently explained together with NaCoO_2 and LaCoO_3 - in all of these
compounds the Co^3+ ions occur in the low-spin state. This low-spin state is
the effect of the relatively strong crystal-field interactions (B_4^z = +320 K
<=> 10Dq = 3.3 eV) and is a manifestation of the very large orbital moment of
the Co^3+ ion.",0610611v1
2006-10-30,Magnetic state and electronic structure of plutonium from ``first principles'' calculations,"The goal to describe plutonium phases from ``first principles'' calculation
methods is complicated by the problem of 5f-electrons localization. While for
early actinides (Th, U,Np) standard DFT (Density Functional Theory) description
with itinerant 5f-electrons works well for late actinides (Am, Cm) DFT
calculations with completely localized (pseudocore) 5f-electrons give
satisfactory results. However plutonium presents a border case of partial
localization and both limits (itinerant and completely localized) are not
valid. We present a review of the methods used to solve this problem and
discuss what could be the reasons for their successes and failures.",0610829v1
2006-10-30,Kondo Breakdown as a Selective Mott Transition in the Anderson Lattice,"We show within the slave boson technique, that the Anderson lattice model
exhibits a Kondo breakdown quantum critical point (KB-QCP) where the
hybridization goes to zero at zero temper- ature. At this fixed point, the
f-electrons experience as well a selective Mott transition separating a
local-moment phase from a Kondo-screened phase. The presence of a multi-scale
QCP in the An- derson lattice in the absence of magnetism is discussed in the
context of heavy fermion compounds. This study is the first evidence for a
selective Mott transition in the Anderson lattice.",0610846v2
2006-11-01,Scaling of dynamic spin correlations in BaCu2SiGeO7,"The magnetic dynamic structure factor of the one-dimensional S = 1/2 chain
system BaCu2(Si0.5Ge0.5)2O7 is studied in a wide range of energy transfers and
temperatures. Contrary to previous erroneous reports [T. Masuda et al., Phys.
Rev. Lett. 93, 077206 (2004)], the scaling properties observed in the range
0.5-25 meV are found to be fully consistent with expectations for a Luttinger
spin liquid. At higher energies, a breakdown of scaling laws is observed and
attributed to lattice effects. The results are complementary to those found in
literature for other S = 1/2-chain compounds, such as KCuF3 and Cu-benzoate.",0611030v1
2006-11-08,Susceptibility of a spinon Fermi surface coupled to a U(1) gauge field,"We study the theory of a U(1) gauge field coupled to a spinon Fermi surface.
Recently this model has been proposed as a possible description of the organic
compound $\kappa-(BEDT-TTF)_2 Cu_2 (CN)_3$. We calculate the susceptibility of
this system and in particular examine the effect of pairing of the underlying
spin liquid. We show that this proposed theory is consistent with the observed
susceptibility measurements.",0611224v1
2006-11-20,Surface influence on stability and structure of III-V nanorods: First-principles studies,"We report ab initio investigations of hexagon-shaped, [111]/[0001] oriented
III-V semiconductor nanowires with varying crystal structure, surface
passivation, surface orientation, and diameter. Their stability is dominated by
the free surface energies of the corresponding facets which differ only weakly
from those of free surfaces. We observe a phase transition between local
zinc-blende and wurtzite geometry versus preparation conditions of the
surfaces, which is accompanied by a change in the facet orientation. The
influence of the actual III-V compound remains small. The atomic relaxation of
nanowires gives rise to smaller bond lengths in comparison to the bulk
zinc-blende structures resulting also in somewhat reduced bilayer thicknesses
parallel to the growth direction.",0611521v1
2006-11-30,Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-Tc,"Ab initio linear-response calculations are reported of the phonon spectra and
the electron-phonon interaction for several transition metal carbides and
nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and
superconducting properties are calculated in detail at various pressures and
the normal-pressure results are found to well agree with the experiment.
Factors accounting for the relatively low critical temperatures Tc in
transition metal compounds with light elements are considered and the possible
ways of increasing Tc are discussed.",0611782v1
2006-11-30,Heavy Fermions: electrons at the edge of magnetism,"An introduction to the physics of heavy fermion compounds is presented,
attempting to highlight the conceptual developments and emphasize the mysteries
and open questions that persist in this active field of research.",0612006v3
2006-12-03,R-matrices for integrable $SU(2)\times U(1)$-symmetric S=1/2 spin-orbital chains,"The Yang-Baxter equation for a $SU(2)\times U(1)$-symmetric $S=1/2$
spin-orbital chain was solved using the special computer algorithm developed by
the author. The 8 new $R$-matrices separated on 5 groups are presented. Among
the obtained integrable models there are special cases related to 1D
ferromagnet ${\rm TDAE-C}_{60}$, 1D superconductors ${\rm AC}_{60}$ (A=K, Cs,
Rb), the quarter filled ladder compound ${\rm NaV}_2{\rm O}_5$ and the model of
correlated electrons on a chain of Berry phase molecules.",0612067v2
2006-12-06,Hierarchical geometric frustration in La3Cu2VO9,"The crystallographic structure and magnetic properties of the La3Cu2VO9 were
investigated by powder neutron diffraction and magnetization measurements. The
compound materializes geometric frustration at two spatial scales, within
clusters and between clusters, and at different temperature scales. It is shown
by exactly solving the hamiltonian spectrum that collective spins are formed on
each clusters at low temperature before inter-clusters coupling operates.",0612142v1
2006-12-11,Theoretical study of doped-Tl$_{2}$Mn$_{2}$O$_{7}$ and Tl$_{2}$Mn$_{2}$O$_{7}$ under pressure,"Using first-principles density functional based calculations, we study the
effect of doping and pressure in manganese based pyrochlore
compound,Tl$_{2}$Mn$_{2}$O$_{7}$ that exhibits colossal magneto-resistive
behavior. The theoretical study is motivated by the counter-intuitive
experimental observation of suppression of ferromagnetic transition temperature
upon application of pressure and its enhancement upon substitution of Mn by
moderate amount of nonmagnetic Sb ion. We also attempt to resolve the issue
related to crystal structure changes that may occur upon application of
pressure.",0612245v2
2006-12-12,Magnetic field tuning of the low temperature state in YbNiSi3,"We present detailed, low temperature, magnetoresistance and specific heat
data of single crystal YbNiSi3 measured in magnetic field applied along the
easy magnetic axis, H || b. An initially antiferromagnetic ground state changes
into a field-induced metamagnetic phase at ~16 kOe (T -> 0). On further
increase of magnetic field, magnetic order is suppressed at ~85 kOe. The
functional behaviors of the resistivity and specific heat are discussed in
comparison with those of the few other stoichiometric, heavy fermion compounds
with established field-induced quantum critical point.",0612291v1
2006-12-13,Tuning alloy disorder in diluted magnetic semiconductors in high fields to 89 T,"Alloy disorder in II-VI diluted magnetic semiconductors (DMS) is typically
reduced when the local magnetic spins align in an applied magnetic field. An
important and untested expectation of current models of alloy disorder,
however, is that alloy fluctuations in many DMS compounds should increase again
in very large magnetic fields of order 100 tesla. Here we measure the disorder
potential in a Zn$_{.70}$Cd$_{.22}$Mn$_{.08}$Se quantum well via the low
temperature photoluminescence linewidth, using a new magnet system to 89 T.
Above 70 T, the linewidth is observed to increase again, in accord with a
simple model of alloy disorder.",0612332v1
2006-12-15,Theory of tunneling spectroscopy in UPd2Al3,"There is still significant debate about the symmetry of the order parameter
in the heavy-fermion superconductor UPd$_{2}$Al$_{3}$, with proposals for
cos(k3), cos(2k3), sin(k3),and exp(i\phi) sin(k3). Here we analyze the
tunneling spectroscopy of this compound and demonstrate that the experimental
results by Jourdan et al are inconsistent with the last two order parameters,
which are expected to show zero-bias conductance peaks. We propose a definitive
tunneling experiment to distinguish between the first two order parameters.",0612402v1
2006-12-20,Quantum cascade phenomenon in natural atomic superlattices formed in Bi2Sr2CaCu2O8 single crystals,"Natural atomic superlattices are formed in certain strongly anisotropic
layered compound. Here we study interlayer transport in single crystals of
Bi2Sr2CaCu2O8 cuprates, which represent stacks of atomic scale intrinsic
Josephson junctions. A series of resonant dips in conductance is observed at
condition when bremsstrahlung and recombination bands in non-equilibrium
spectrum of Josephson junctions overlap. The phenomenon is explained in terms
of self-detection of a new type of collective strongly non-equilibrium state in
stacked Josephson junctions, bearing certain resemblance with operation of a
Quantum Cascade Laser. Conclusions are supported by in-situ
generation-detection experiments, providing evidence for cascade amplification
of recombination radiation, and by numerical simulations.",0612535v1
2006-12-21,Subband filling and Mott transition in Ca_{2-x}Sr_xRuO_4,"A new concept is proposed for the paramagnetic metal insulator transition in
the layer perovskite Ca_{2-x}Sr_xRuO_4. Whereas the pure Sr compound is
metallic up to very large Coulomb energies due to strong orbital fluctuations,
structural changes induced by doping with Ca give rise to a interorbital charge
transfer which makes the material extremely sensitive to local correlations.
Using dynamical mean field theory based on finite temperature multi-band exact
diagonalization it is shown that the combination of crystal field splitting and
onsite Coulomb interactions leads to complete filling of the d_xy band and to a
Mott transition in the half-filled d_xz,yz bands.",0612539v1
2006-12-21,Effects of impurities on superconductivity in noncentrosymmetric compounds,"We microscopically derive the Ginzburg-Landau free energy functional for a
noncentrosymmetric superconductor with a large spin-orbit splitting of the
electron bands, in the presence of nonmagnetic impurities. The critical
temperature is found to be suppressed by disorder, both for conventional and
unconventional pairing, in the latter case according to the universal
Abrikosov-Gor'kov function. The impurity effect on the upper critical field
turns out to be nonuniversal, determined by the pairing symmetry and the band
structure. In a BCS-like model, Tc is not affected, while Hc2 increases with
disorder. For unconventional pairing, both Tc and Hc2 are suppressed by
disorder.",0612546v2
2007-01-16,Optical properties of the Ce and La di-telluride charge density wave compounds,"The La and Ce di-tellurides LaTe$_2$ and CeTe$_2$ are deep in the
charge-density-wave (CDW) ground state even at 300 K. We have collected their
electrodynamic response over a broad spectral range from the far infrared up to
the ultraviolet. We establish the energy scale of the single particle
excitation across the CDW gap. Moreover, we find that the CDW collective state
gaps a very large portion of the Fermi surface. Similarly to the related rare
earth tri-tellurides, we envisage that interactions and Umklapp processes play
a role in the onset of the CDW broken symmetry ground state.",0701386v1
2007-01-18,On the origin of unusual transport properties observed in densely packed polycrystalline CaAl_{2},"A possible origin of unusual temperature behavior of transport coefficients
observed in densely packed polycrystalline CaAl_{2} compound [M. Ausloos et
al., J. Appl. Phys. 96, 7338 (2004)] is discussed, including a power-like
dependence of resistivity with $\rho \propto T^{-3/4}$ and N-like form of the
thermopower. All these features are found to be in good agreement with the
Shklovskii-Efros localization scenario assuming polaron-mediated hopping
processes controlled by the Debye energy.",0701456v1
2007-01-22,Electronic structure and magnetism in the frustrated antiferromagnet LiCrO2,"LiCrO2 is a 2D triangular antiferromagnet, isostructural with the common
battery material LiCoO2 and a well-known Jahn-Teller antiferromagnet NaNiO2. As
opposed to the latter, LiCrO2 exibits antiferromagnetic exchange in Cr planes,
which has been ascribed to direct Cr-Cr d-d overlap. Using LDA and LDA+U first
principles calculations I confirm this conjecture and show that (a) direct d-d
overlap is indeed enhanced compared to isostructural Ni and Cr compounds, (b)
p-d charge transfer gap is also enhanced, thus suppressing the ferromagnetic
superexchange, (c) the calculated magnetic Hamiltonian maps well onto the
nearest neighbors Heisenberg exchange model and (d) interplanar inteaction is
antiferromagnetic.",0701520v1
2007-01-28,Nuclear spin diffusion in the semiconductor TlTaS3,"We report on a 203Tl and 205Tl nuclear magnetic resonance study of the chain
ternary semiconductor TlTaS3. We show that spin-lattice relaxation in this
compound is driven by two contributions, namely by interactions of nuclear
spins with thermally activated carriers and with localized electron spins. The
latter mechanism dominates at lower temperature; at that, our measurements
provide striking manifestation of the spin-diffusion-limited relaxation regime.
The experimental data obtained allow us to estimate the spin diffusion
coefficient.",0701688v1
2007-02-17,"Metal-insulator Transition in a Pyrochlore-type Ruthenium oxide, Hg2Ru2O7","A new pyrochlore ruthenium oxide, Hg2Ru2O7 was synthesized under a high
pressure of 6 GPa. In contrast to the extensively studied Ru4+ oxides, this
compound possesses a novel Ru5+ valence state, corresponding to a half-filled
t_2g_3 electron configuration. Hg2Ru2O7 exhibits a first order metal-insulator
transition at 107 K, accompanied by a structural transition from cubic to lower
symmetry. The behavior of the magnetic susceptibility suggests the possible
formation of a spin singlet in the insulating low temperature state.",0702411v1
2007-03-19,Efficient current-induced domain-wall displacement SrRuO3,"We demonstrate current-induced displacement of ferromagnetic domain walls in
sub-micrometer fabricated patterns of SrRuO3 films. The displacement, monitored
by measuring the extraordinary Hall effect, is induced at zero applied magnetic
field and its direction is reversed when the current is reversed. We find that
current density in the range of 10^9 - 10^10 A/m^2 is sufficient for
domain-wall displacement when the depinning field varies between 50 to 500 Oe.
These results indicate relatively high efficiency of the current in displacing
domain walls which we believe is related to the narrow width ~3 nm of domain
walls in this compound.",0703485v1
1998-09-23,"A Freely Available Morphological Analyzer, Disambiguator and Context Sensitive Lemmatizer for German","In this paper we present Morphy, an integrated tool for German morphology,
part-of-speech tagging and context-sensitive lemmatization. Its large lexicon
of more than 320,000 word forms plus its ability to process German compound
nouns guarantee a wide morphological coverage. Syntactic ambiguities can be
resolved with a standard statistical part-of-speech tagger. By using the output
of the tagger, the lemmatizer can determine the correct root even for ambiguous
word forms. The complete package is freely available and can be downloaded from
the World Wide Web.",9809050v1
2005-01-31,Context Related Derivation of Word Senses,"Real applications of natural language document processing are very often
confronted with domain specific lexical gaps during the analysis of documents
of a new domain. This paper describes an approach for the derivation of domain
specific concepts for the extension of an existing ontology. As resources we
need an initial ontology and a partially processed corpus of a domain. We
exploit the specific characteristic of the sublanguage in the corpus. Our
approach is based on syntactical structures (noun phrases) and compound
analyses to extract information required for the extension of GermaNet's
lexical resources.",0501095v1
1996-06-17,"Comment on ""Failure of standard conservation laws at a classical change of signature""","Hellaby & Dray (gr-qc/9404001) have recently claimed that matter conservation
fails under a change of signature, compounding earlier claims that the standard
junction conditions for signature change are unnecessary. In fact, if the field
equations are satisfied, then the junction conditions and the conservation
equations are satisfied. The failure is rather that the authors did not make
sense of the field equations and conservation equations, which are singular at
a change of signature.",9606045v1
2005-07-16,Quantum corrections to spin effects in general relativity,"Quantum power corrections to the gravitational spin-orbit and spin-spin
interactions, as well as to the Lense-Thirring effect, were found for particles
of spin 1/2. These corrections arise from diagrams of second order in Newton
gravitational constant G with two massless particles in the unitary cut in the
t-channel. The corrections obtained differ from the previous calculation of the
corrections to spin effects for rotating compound bodies with spinless
constituents.",0507070v1
1994-07-19,Clan Structure Analysis and Rapidity Gap Probability,"Clan structure analysis in rapidity intervals is generalized from negative
binomial multiplicity distribution to the wide class of compound Poisson
distributions. The link of generalized clan structure analysis with correlation
functions is also established. These theoretical results are then applied to
minimum bias events and evidentiate new interesting features, which can be
inspiring and useful in order to discuss data on rapidity gap probability at
TEVATRON and HERA.",9407325v1
1994-11-16,Multi-color QCD at High Energies and Exactly Solvable Lattice Theories,"We examine the generalized leading-logarithmic approximation (LLA) equations
for compound states of n-reggeized gluons. It is shown that in multi-color QCD,
when $N_c \rightarrow \infty$, these equations have a sufficient number of
conservation laws to be exactly solvable. Holomorphic factorization of the wave
functions is used to reduce the corresponding quantum mechanical problem to the
solution of the one-dimensional Heisenberg model with the spins being the
generators of the M$\ddot{o}$bius group of conformal transformations.",9411305v1
1998-07-23,Duality of Reggeon Interactions in QCD,"The duality symmetry of the hamiltonian and integrals of motion for reggeon
interactions in the multi-colour QCD is formulated as an integral equation for
the wave function of compound states of reggeized gluons, which together with
the property of holomorphic factorization allows one to reduce the Odderon
problem in QCD to the solution of the one-dimensional Schroedinger equation.",9807477v2
1998-12-11,Duality symmetry of Reggeon interactions in multicolour QCD,"The duality symmetry of the Hamiltonian and integrals of motion for Reggeon
interactions in multicolour QCD is formulated as an integral equation for the
wave function of compound states of $n$ reggeized gluons. In particular the
Odderon problem in QCD is reduced to the solution of the one-dimensional
Schr\""odinger equation. The Odderon Hamiltonian is written in a normal form,
which gives a possibility to express it as a function of its integrals of
motion.",9812336v3
1999-12-10,Electroweak characteristics of mesons in the relativistic quark model,"In this work the electromagnetic radius and the polarizability of the mesons
are obtained by use of the effective Lagrangians constructed on the one hand
with taking into account of general principles of the relativistic quantum
field theory and on the other hand with taking into account of the compound
relativistic model meson representation. Also using a relativistic constituent
quark model based on point form of Poincare-covariant quantum mechanics we
calculated electromagnetic radius and the decay constants of the mesons with
spinor quarks.",9912296v1
2001-01-22,Relativistic corrections to the electromagnetic polarizabilities of compound systems,"The low-energy amplitude of Compton scattering on the bound state of two
charged particles of arbitrary masses, charges and spins is calculated. A case
in which the bound state exists due to electromagnetic interaction (QED) is
considered. The term, proportional to $\omega^2$, is obtained taking into
account the first relativistic correction. It is shown that the complete result
for this correction differs essentially from the commonly used term
$\Delta\alpha$, proportional to the r.m.s. charge radius of the system. We
propose that the same situation can take place in the more complicated case of
hadrons.",0101240v1
2002-07-12,"On ""dual"" parametrizations of generalized parton distributions","We propose a parametrization for the generalized parton distributions (GPDs)
which is based on representation of parton distributions as an infinite series
of t-channel exchanges. The entire generalized parton distribution is given as
an infinite sum over contributions of generalized light-cone distribution
amplitudes in the t-channel. We also discuss the relations of the lowest Mellin
moments of GPDs to basic mechanical characteristics of the nucleon as a
compound system.",0207153v1
2004-12-20,Pion Photoproduction Amplitude Relations in the 1/N_c Expansion,"We derive expressions for pion photoproduction amplitudes in the 1/N_c
expansion of QCD, and obtain linear relations directly from this expansion that
relate electromagnetic multipole amplitudes at all energies. The leading-order
relations in 1/N_c compare favorably with available data, while the
next-to-leading order relations seem to provide only a small improvement.
However, when resonance parameters are compared directly, the agreement at
O(1/N_c) or O(1/N_c^2) is impressive.",0412294v1
1997-04-09,Solitons in high-energy QCD,"We study the asymptotic solutions of the Schr\""odinger equation for the
color-singlet reggeon compound states in multi-color QCD. We show that in the
leading order of asymptotic expansion, quasiclassical reggeon trajectories have
a form of the soliton waves propagating on the 2-dimensional plane of
transverse coordinates. Applying methods of the finite-gap theory we construct
their explicit form in terms of Riemann theta-functions and examine their
properties.",9704079v1
1999-01-27,Holographic Normal Ordering and Multi-particle States in the AdS/CFT Correspondence,"The general correlator of composite operators of N=4 supersymmetric gauge
field theory is divergent. We introduce a means for renormalizing these
correlators by adding a boundary theory on the AdS space correcting for the
divergences. Such renormalizations are not equivalent to the standard normal
ordering of current algebras in two dimensions. The correlators contain contact
terms that contribute to the OPE; we relate them diagrammatically to
correlation functions of compound composite operators dual to multi-particle
states.",9901144v3
2001-03-28,A Possible Candidate for Dark Matter,"On the basis of a new quantum field theory without divergence presented by us
we identify W-matter with dark matter and guess that the two new stars RXJ1865
and 3C58 and quasi-stellar objects are the compounds of a F-celestial body with
a W-celestial body with massive enough mass, and some earthquakes, some
tsunamis and some disasters in some areas like Bermuda are caused by W-objects.
Keywords: Dark matter; W-matter; Quasi-stellar objects.",0103234v2
1999-03-14,Free stochastic measures via noncrossing partitions,"We consider free multiple stochastic measures in the combinatorial framework
of the lattice of all diagonals of an n-dimensional space. In this free case,
one can restrict the analysis to only the noncrossing diagonals. We give
definitions of what free multiple stochastic measures are, and calculate them
for the free Poisson and free compound Poisson processes. We also derive
general combinatorial It\^{o}-type relationships between free stochastic
measures of different orders. These allow us to calculate, for example, free
Poisson-Charlier polynomials, which are the orthogonal polynomials with respect
to the free Poisson measure.",9903084v3
2003-11-20,Some Classes Of Distributions On The Non-Negative Lattice,"A method for constructing distributions on the non negative integers as
discrete analogue of continuous distributions on the non negative real is
presented. A justification of the definition of discrete self decomposable laws
is provided. Discrete analogue of distributions of the same type and the role
of Bernoulli law in this context is discussed. Generalizations of some discrete
laws and their properties are given. The geometric compounding problem for
discrete distributions is studied by introducing discrete semi Mittag Leffler
laws.",0311351v1
2007-02-13,Integral Equations in the Theory of Levy Processes,"In this article we consider the Levy processes and the corresponding
semigroup. We represent the generator of this semigroup in a convolution form.
Using the obtained convolution form and the theory of integral equations we
investigate the properties of a wide class of Levy processes (potential,
quasi-potential, the probability of the Levy process remaining within the given
domain, long time behavior, stable processes). We analyze in detail a number of
concrete examples of the Levy processes (stable processes, the variance damped
Levy processes, the variance gamma processes, the normal Gaussian process, the
Meixner process, the compound Poisson process).",0702378v1
2007-03-26,Poisson limit of an inhomogeneous nearly critical INAR(1) model,"An inhomogeneous first--order integer--valued autoregressive (INAR(1))
process is investigated, where the autoregressive type coefficient slowly
converges to one. It is shown that the process converges weakly to a Poisson or
a compound Poisson distribution.",0703754v1
2007-03-28,3-fold divisorial extremal neighborhoods over cE7 and cE6 Compound DuVal singularities,"Let X be the germ of a Gorenstein 3-fold singularity and C a smooth curve
through it such that the general hyperplane section S of X containing D is
DuVal of type E6 or E7. In this paper we obtain criteria for the existence of a
terminal divisorial extremal neighborhood f: Y-->X contracting an irreducible
divisor E onto C and classify all such neighborhoods.",0703855v2
2004-05-18,A characterization of the Aerts product of Hilbertian lattices,"Let H_1 and H_2 be complex Hilbert spaces, L_1=P(H_1) and L_2=P(H_2) the
lattices of closed subspaces, and let L be a complete atomistic lattice. We
prove under some weak assumptions relating L_i and L, that if L admits an
orthocomplementation, then L is isomorphic to the separated product of L_1 and
L_2 defined by Aerts. Our assumptions are minimal requirements for L to
describe the experimental propositions concerning a compound system consisting
of so called separated quantum systems. The proof does not require any
assumption on the orthocomplementation of L.",0405048v3
1995-03-14,Ab initio Molecular Dynamics in Adaptive Coordinates,"We present a new formulation of ab initio molecular dynamics which exploits
the efficiency of plane waves in adaptive curvilinear coordinates, and thus
provides an accurate treatment of first-row elements. The method is used to
perform a molecular dynamics simulation of the CO_2 molecule, and allows to
reproduce detailed features of its vibrational spectrum such as the splitting
of the Raman sigma+_g mode caused by Fermi resonance. This new approach opens
the way to highly accurate ab initio simulations of organic compounds.",9503004v2
1996-01-15,Semiconductor effective charges from tight-binding theory,"We calculate the transverse effective charges of zincblende compound
semiconductors using Harrison's tight-binding model to describe the electronic
structure. Our results, which are essentially exact within the model, are found
to be in much better agreement with experiment than previous
perturbation-theory estimates. Efforts to improve the results by using more
sophisticated variants of the tight-binding model were actually less
successful. The results underline the importance of including quantities that
are sensitive to the electronic wavefunctions, such as the effective charges,
in the fitting of tight-binding models.",9601002v1
2001-01-22,Stochastic Resonance in a Periodically Modulated Dissipative Nuclear Dynamics,"A fission decay of highly excited periodically driven compound nuclei is
considered in the framework of Langevin approach. We have used residual-time
distribution (RTD) as the tool for studying of dynamic features in a presence
of periodic perturbation. The structure of RTD essentially depends on the
relation between Kramers decay rate and the frequency of the periodic
perturbation. In particular, intensity of the first peak in RTD has a sharp
maximum at certain nuclear temperature depending on the frequency of the
periodic perturbation. This maximum should be considered as first-hand
manifestation of stochastic resonance in nuclear dynamics.",0101041v1
1996-07-09,Scaling Laws and Transient Times in 3He Induced Nuclear Fission,"Fission excitation functions of compound nuclei in a mass region where shell
effects are expected to be very strong are shown to scale exactly according to
the transition state prediction once these shell effects are accounted for. The
fact that no deviations from the transition state method have been observed
within the experimentally investigated excitation energy regime allows one to
assign an upper limit for the transient time of 10 zs.",9607005v1
1997-06-05,Astrophysical neutron capture rates in s- and r-process nucleosynthesis,"Astrophysical neutron capture rates of light and heavy nuclei have been
measured and calculated. For the measurements the activation technique was
applied at the 3.75 MV Karlsruhe Van de Graaff accelerator, and at the Geel
electron linear accelerator (GELINA) the time-of-flight (TOF) method was used.
The calculations were performed using direct and compound nuclear capture
models.",9706002v1
2001-10-18,Cascade Gamma-Decay of the 193Os Compound Nucleus and some Aspects of Dynamics of Change in Nuclear Properties below Bn,"Two-step cascades from the 192Os(n th,gamma)193Os reaction were studied in
gamma-gamma coincidence measurement. The decay scheme of 193Os was established
up to the excitation energy ~3 MeV. The excitation spectrum of intermediate
levels of most intense cascades was found to be practically harmonic.",0110011v1
2005-05-13,Entrance channel dependence in compound nuclear reactions with loosely bound nuclei,"The measurement of light charged particles evaporated from the reaction
6,7Li+6Li has been carried out at extreme backward angle in the energy range 14
- 20 MeV. Calculations from the code ALICE91 show that the symmetry of the
target-projectile combination and the choice of level density parameter play
important roles in explaining the evaporation spectra for these light particle
systems. In above barrier energy region the fusion cross-section is not
suppressed for these loosely bound nuclei.",0505015v1
1996-08-15,The Three-Body Continuum Coulomb Problem and the 3$α$ Structure of $^{12}$C,"We introduce an approach, based on the coordinate space Faddeev equations, to
solve the quantum mechanical three-body Coulomb problem in the continuum. We
apply the approach to compute measured properties of the first two $0^+$ levels
in $^{12}$C, including the width of the excited level, in a 3$\alpha$-particle
model. We use the two-body interaction which reproduces the low energy
$\alpha$-$\alpha$ scattering data and add a three-body force to account for the
compound state admixture.",9608028v2
1997-03-17,Fermionic Molecular Dynamics: Multifragmentation in heavy-ion collisions and in excited nuclei,"Within Fermionic Molecular Dynamics we investigate fragmentation of a
compound system which was created in a heavy-ion collision at a beam energy in
the Fermi energy domain and the decay of excited iron nuclei. We show that in
FMD many-body correlations play an important role in the formation of
fragments.",9703035v1
1997-06-23,"Decay of hot, rotating, compound nuclei","The fusion process and the competition between fission and n, p and
alpha-particle emission is studied. The calculations are performed for nuclei
at excitation energies from 80 MeV up to about 300 MeV. The nuclear fission is
described by a Langevin equation coupled to the Master equation for particle
evaporation. A significant influence of the initial spin distribution on the
prescission particles multiplicities is found.",9706055v1
1997-10-18,Fusion cross sections for superheavy nuclei in the dinuclear system concept,"Using the dinuclear system concept we present calculations of production
cross sections for the heaviest nuclei. The obtained results are in a good
agreement with the experimental data. The experimentally observed rapid
fall-off of the cross sections of the cold fusion with increasing charge number
$Z$ of the compound nucleus is explained. Optimal experimental conditions for
the synthesis of the superheavy nuclei are suggested.",9710042v1
1999-03-30,A program for coupled-channels calculations with all order couplings for heavy-ion fusion reactions,"A FORTRAN77 program is presented that calculates fusion cross sections and
mean angular momenta of the compound nucleus under the influence of couplings
between the relative motion and several nuclear collective motions. The
no-Coriolis approximation is employed to reduce the dimension of
coupled-channels equations. The program takes into account the effects of
non-linear couplings to all orders, which have been shown to play an important
role in heavy-ion fusion reactions at subbarrier energies.",9903074v1
1999-11-03,Melting or nucleon transfer in fusion of heavy nuclei?,"The time-dependent transition between a diabatic interaction potential in the
entrance channel and an adiabatic potential during the fusion process is
investigated within the two-center shell model. A large hindrance is obtained
for the motion to smaller elongations of near symmetric dinuclear systems. The
comparison of the calculated energy thresholds for the complete fusion in
different relevant collective variables shows that the dinuclear system prefers
to evolve in the mass asymmetry coordinate by nucleon transfer to the compound
nucleus.",9911011v1
1999-11-28,Isotopic dependence of fusion cross sections in reactions with heavy nuclei,"The dependence of fusion cross section on the isotopic composition of
colliding nuclei is analysed within the dinuclear system concept for compound
nucleus formation. Probabilities of fusion and surviving probabilities,
ingredients of the evaporation residue cross sections, depend decisively on the
neutron numbers of the dinuclear system. Evaporation residue cross sections for
the production of actinides and superheavy nuclei, listed in table form, are
discussed and compared with existing experimental data. Neutron-rich
radioactive projectiles are shown to lead to similar fusion cross sections as
stable projectiles.",9911078v1
2000-01-24,Dissipative dynamics of fission in the framework of asymptotic expansion of Fokker-Planck equation,"The dynamics of fission has been formulated by generalising the asymptotic
expansion of the Fokker-Planck equation in terms of the strength of the
fluctuations where the diffusion coefficients depend on the stochastic
variables explicitly. The prescission neutron multiplicities and the mean
kinetic energies of the evaporated neutrons have been calculated and compared
with the respective experimental data over a wide range of excitation energy
and compound nuclear mass. The mean and variance of the total kinetic energies
of the fission fragments have been calculated and compared with the
experimental values.",0001041v1
2000-11-10,Quantum Calculation of Dipole Excitation in Fusion Reaction,"The excitation of the giant dipole resonance by fusion is studied with N/Z
asymmetry in the entrance channel. the TDHF solution exhibits a strong dipole
vibration which can be associated with a giant vibration along the main axis of
a fluctuating prolate shape. The consequences on the gamma-ray emission from
hot compound nuclei are discussed.",0011042v2
2002-12-05,Two-Step Model of Fusion for Synthesis of Superheavy Elements,"A new model is proposed for fusion mechanisms of massive nuclear systems
where so-called fusion hindrance exists. The model describes two-body collision
processes in an approaching phase and shape evolutions of an amalgamated system
into the compound nucleus formation. It is applied to $^{48}$Ca-induced
reactions and is found to reproduce the experimental fusion cross sections
extremely well, without any free parameter. Combined with the statistical decay
theory, residue cross sections for the superheavy elements can be readily
calculated. Examples are given.",0212029v2
2003-05-10,Isomeric and hyperdeformed states at high spin for light nuclei,"We present a macroscopic model for the energy of rotation nuclei which has
several refinements relative to the rotating liquid drop model. The most
important features are the inclusion of the shell correction and using a new
family of triaxial compact and creviced shapes to describe transition of the
system from one sphere to a two separated spheres. With this model we calculate
the properties of point of equilibrium corresponding to nuclear ground states,
isomeric states and fission saddle-points. The model is applied to the nuclei
56Ni, 48Cr and 80Zr. The results obtained allowed to explain the light compound
nuclear system fission phenomena and predict the existence of hyperdeformed
states at very high spins.",0305026v1
2003-08-06,KEWPIE: a dynamical cascade code for decaying exited compound nuclei,"A new dynamical cascade code for decaying hot nuclei is proposed and
specially adapted to the synthesis of super-heavy nuclei. For such a case, the
interesting channel is the tiny fraction that will decay through particles
emission, thus the code avoids classical Monte-Carlo methods and proposes a new
numerical scheme. The time dependence is explicitely taken into account in
order to cope with the fact that fission decay rate might not be constant. The
code allows to evaluate both statistical and dynamical observables. Results are
successfully compared to experimental data.",0308020v1
2003-11-21,Theory of the radiative width of a highly excited nucleus,"A microscopic theory of the electromagnetic radiation emitted by a highly
excited nucleus is developed on the basis of the Landau theory of a Fermi
liquid. Closed formulae are obtained for the mean radiative width and its mean
square fluctuation from level to level. The temperatures of many nuclei are
found from the observed widths. The relaxation time is estimated from the
experimental data on the radiative-width fluctuations. The regions of
applicability of the various types of relations between the relaxation time and
the lifetime of the compound nucleus, as well as the relevant physical
consequences, are discussed.",0311077v1
2003-12-23,Inelastic interactions between nuclei at high energies,"A theory of nucleus-nucleus collisions has been developed for kinetic
energies substantially in excess of the binding energy. The very high pressure
produced in the compound system as a result of the fusion of the two colliding
nuclei is the reason for the subsequent hydrodynamic expansion of the nuclear
medium. The energy and angular distributions of the reaction products are
investigated. The charge distribution is also determined in the case where the
nucleon and ion components of the reaction products are predominant. A solution
is found for the expansion into vacuum of a sphere in which the initially
uniformly distributed material is initially at rest and at an ultrarelativistic
temperature.",0312102v1
2004-02-11,Adiabatic nucleus-nucleus potential at near-barrier energies from selfconsistent calculations,"Adiabatic fusion potentials, extended well into compound nucleus region, are
calculated for a number of reactions within the static Hartree-Fock method with
the Skyrme SkM* interaction. The calculated fusion barriers agree quite well
with the data, in spite of considerable errors in reaction Q values. This
suggests some error cancellation, possibly with the relative kinetic energy
term. Calculated berrier heights are consistent with the idea of fusion
hindrance in tip collisions. Adiabatic potentials differ considerably from the
results of the frozen density approximation. We briefly discuss relative
positions and heights of the fusion and fission potentials and speculate on
their possible connection with the fusion hindrance for large Zt Zp.",0402033v1
2004-06-07,Super-Radiance: From Nuclear Physics to Pentaquarks,"The phenomenon of super-radiance in quantum optics predicted by Dicke 50
years ago and observed experimentally has its counterparts in many-body systems
on the borderline between discrete spectrum and continuum. The interaction of
overlapping resonances through the continuum leads to the redistribution of
widths and creation of broad super-radiant states and long-lived compound
states. We explain the physics of super-radiance and discuss applications to
weakly bound nuclei, giant resonances and widths of exotic baryons.",0406019v1
2005-02-15,Quantum Statistical Effects on Fusion Dynamics of Heavy-Ions,"In order to describe the fusion of two very heavy nuclei at near barrier
energies, a generalized Langevin approach is proposed, which incorporates the
quantum statistical fluctuations in accordance with the fluctuation and
dissipation theorem. It is illustrated that the quantum statistical effects
introduce an enhancement of the formation of compound nucleus, though the
quantum enhancement is somewhat less pronounced as indicated in the previous
calculations.",0502043v1
2005-10-10,Low energy nuclear scattering and sub-threshold spectra from a multi-channel algebraic scattering theory,"A multi-channel algebraic scattering theory, to find solutions of
coupled-channel scattering problems with interactions determined by collective
models, has been structured to ensure that the Pauli principle is not violated.
Positive (scattering) and negative (sub-threshold) solutions can be found to
predict both the compound nucleus sub-threshold spectrum and all resonances due
to coupled channel effects that occur on a smooth energy varying background.",0510029v1
2005-10-27,Alpha-nucleus potential for alpha-decay and sub-barrier fusion,"The set of parameters for alpha-nucleus potential is derived by using the
data for both the alpha-decay half-lives and the fusion cross-sections around
the barrier for reactions alpha+40Ca, alpha+59Co, alpha+208Pb. The alpha-decay
half-lives are obtained in the framework of a cluster model using the WKB
approximation. The evaluated alpha-decay half-lives and the fusion
cross-sections agreed well with the data. Fusion reactions between
alpha-particle and heavy nuclei can be used for both the formation of very
heavy nuclei and spectroscopic studies of the formed compound nuclei.",0510082v1
2005-10-29,Low-energy neutron-12C analyzing powers: Results from a multichannel algebraic scattering theory,"Analyzing powers in low-energy neutron scattering from 12C are calculated in
an algebraic momentum-space coupled-channel formalism (MCAS). The results are
compared with recently obtained experimental data. The channel-coupling
potentials have been defined previously to reproduce the total cross section
and sub-threshold bound states of the compound system. Without further
adjustment, good agreement with data for the analyzing powers is obtained.",0510088v1
2005-11-23,The Resonance Theory of Proton and Alpha Decay from Hot Sources,"The consecutive microscopic solution is presented of the problem of tunneling
of a particle through a potential barrier. The method is applied to the alpha
and proton decay of compound systems formed in fusion reaction. Appearance of
the peaks in the spectrum of emitted particles is predicted. The peaks
correspond to quasistationary states inside the potential barrier.",0511063v1
2006-05-31,Quantum effects in the diffusion process to form a heavy nucleus in heavy-ion fusion reactions,"We discuss quantum effects in the diffusion process which is used to describe
the shape evolution from the touching configuration of fusing two nuclei to a
compound nucleus. Applying the theory with quantum effects to the case where
the potential field, the mass and friction parameters are adapted to realistic
values of heavy-ion collisions, we show that the quantum effects play
significant roles at low temperatures which are relevant to the synthesis of
superheavy elements.",0606001v1
2006-09-01,"Doorway states in nuclear reactions as a manifestation of the ""super-radiant"" mechanism","A mechanism is considered for generating doorway states and intermediate
structure in low-energy nuclear reactions as a result of collectivization of
widths of unstable intrinsic states coupled to common decay channels. At the
limit of strong continuum coupling, the segregation of broad
(''super-radiating"") and narrow (''trapped"") states occurs revealing the
separation of direct and compound processes. We discuss the conditions for the
appearance of intermediate structure in this process and doorways related to
certain decay channels.",0609004v1
2006-12-05,Cluster structure of a low-energy resonance in tetraneutron,"We theoretically investigate the possibility for a tetraneutron to exist as a
low-energy resonance state. We explore a microscopic model based on the
assumption that the tetraneutron can be treated as a compound system where
$^3$n+n and $^2$n+$^2$n coupled cluster configurations coexist. The influence
of the Pauli principle on the kinetic energy of the relative motion of the
neutron clusters is shown to result in their attraction. The strength of such
attraction is high enough to ensure the existence of a low-energy resonance in
the tetraneutron, provided that the oscillator length is large enough.",0612020v1
1997-05-31,Anomalous Weight Behavior in YBa2Cu3O7 Compounds at Low Temperature,"YBa2Cu3O7 high temperature superconductor samples were weighed on an
electronic balance during a warming cycle beginning at 77 degrees K. The
experiment was configured so that the YBa2Cu3O7 material was weighed along with
a magnet, a target mass, and liquid Nitrogen coolant. The weights were captured
during Nitrogen evaporation. Results indicated unexpected variations in the
system weight that appear as a function of temperature and possibly other
parameters.",9705043v1
1998-10-27,Symmetry Adaptation Techniques in n-Photon Absorption Spectroscopy,"We present some recent progress achieved in the application of symmetry
adaptation techniques to n-photon absorption spectroscopy of rare earth ions in
finite symmetry. More specifically, this work is concerned with the
determination of the intensity of n-photon transitions between Stark levels
(rather than J levels) of an ion in an environment with a given symmetry. The
role of symmetry is taken into account through the use of initial and final
state vectors characterized by irreducible representations of the (double)
group for the ion site symmetry. Two distinct situations are considered, viz.,
the case of parity-allowed and parity-forbidden n-photon transitions.",9810055v1
2000-10-06,Spontaneous formation and stability of small GaP fullerenes,"We report the spontaneous formation of a GaP fullerene cage in ab-initio
Molecular Dynamics simulations starting from a bulk fragment. A systematic
study of the geometric and electronic properties of neutral and ionized GaP
clusters suggests the stability of hetero-fullerenes formed by a compound with
zincblend bulk structure. We find that GaP fullerenes up to 28 atoms have high
symmetry, closed electronic shells, large HOMO-LUMO energy gaps and do not
dissociate when ionized. We compare our results for GaP with those obtained by
other groups for the corresponding BN clusters.",0010020v1
2001-01-29,A numerical ab initio study of harmonic generation from a ring-shaped model molecule in laser fields,"When a laser pulse impinges on a molecule which is invariant under certain
symmetry operations selection rules for harmonic generation (HG) arise. In
other words: symmetry controls which channels are open for the deposition and
emission of laser energy---with the possible application of filtering or
amplification. We review the derivation of HG selection rules and study
numerically the interaction of laser pulses with an effectively one-dimensional
ring-shaped model molecule. The harmonic yields obtained from that model and
their dependence on laser frequency and intensity are discussed. In a real
experiment obvious candidates for such molecules are benzene, other aromatic
compounds, or even nanotubes.",0101097v1
2001-02-09,Harmonic generation in ring-shaped molecules,"We study numerically the interaction between an intense circularly polarized
laser field and an electron moving in a potential which has a discrete
cylindrical symmetry with respect to the laser pulse propagation direction.
This setup serves as a simple model, e.g., for benzene and other aromatic
compounds. From general symmetry considerations, within a Floquet approach,
selection rules for the harmonic generation [O. Alon Phys. Rev. Lett. 80 3743
(1998)] have been derived recently. Instead, the results we present in this
paper have been obtained solving the time-dependent Schroedinger equation ab
initio for realistic pulse shapes. We find a rich structure which is not always
dominated by the laser harmonics.",0102023v2
2001-04-25,An Analysis of the Thermodynamics of Hydrophobic Solvation Based on Scaled Particle Theory,"A comprehensive, semi-quantitative model for the thermodynamics of
hydrophobic solvation is presented. The model is based on a very simple premise
suggested by the scaled particle theory and treats both solute and solvent
molecules as hard spheres. A connection between the peculiarly large
heat-capacity change for hydrophobic solvation and the large temperature
dependence of the thermal expansivity of water is found. Analysis reveals a
possible physical origin for the converging behavior of solvation entropies for
a series of homologous hydrophobic compounds. The model suggests that the low
solubility and the large heat-capacity change of hydrophobic solvation stem
from two distinct aspects of water molecules: the static geometry of the
molecule and the dynamic hydrogen bonding network, respectively.",0104085v1
2001-11-14,A Comparison of Two Approaches: Maximum Entropy on the Mean (MEM) and Bayesian Estimation (BAYES) for Inverse Problems,"To handle with inverse problems, two probabilistic approaches have been
proposed: the maximum entropy on the mean (MEM) and the Bayesian estimation
(BAYES). The main object of this presentation is to compare these two
approaches which are in fact two different inference procedures to define the
solution of an inverse problem as the optimizer of a compound criterion.
Keywords: Inverse problems, Maximum Entropy on the Mean, Bayesian inference,
Convex analysis.",0111122v1
2002-05-29,Numerical computation of critical properties and atomic basins from 3D grid electron densities,"InteGriTy is a software package that performs topological analysis following
AIM approach on electron densities given on 3D grids. Use of tricubic
interpolation is made to get the density, its gradient and hessian matrix at
any required position. Critical points and integrated atomic properties have
been derived from theoretical densities calculated for the compounds NaCl and
TTF-2,5Cl2BQ, thus covering the different kinds of chemical bonds: ionic,
covalent, hydrogen bonds and other intermolecular contacts.",0205082v2
2003-03-27,Electronic structure calculations for PrFe4P12 filled skutterudite using Extended Huckel tight-binding method,"To get insight into the electronic properties of PrFe4P12 skutterudite, band
electronic structure calculations, Total and Projected Density of States,
Crystal Orbital Overlap Population and Mulliken Population Analysis were
performed. The energy bands yield a semi metallic behavior with a direct gap
(at gamma) of 0.02 eV. Total and Projected Density of States provided
information of the contribution from each orbital of each atom to the total
Density of States. Moreover, the bonding strength between some atoms within the
unit cell was obtained. Mulliken Population analysis suggests ionic behavior
for this compound.",0303115v1
2003-05-02,On the Anomalous Structures of the Vector Leptonic Currents,"Each of the existing types of the electric charges come forwards in the
system as the source of a kind of the dipole moment. Therefore, to investigate
these regularities, we have established the compound structures of Dirac and
Pauli form factors. They state that the electron possesses as well as the
anomalous electric charge.",0305009v2
2003-06-12,The Flex-Pendulum -- Basis for an Improved Timepiece,"A compound pendulum of simple geometry was built from a lightweight rod to
which a pair of masses are clamped, one above and the other below the axis of
rotation. By making the position of the upper mass variable, it was found that
the characteristics of this pendulum can be altered dramatically. A theoretical
model of the instrument is presented, which is in reasonable agreement with
experimental observations. From the model it is shown that isochronism of the
flex-pendulum can be significantly greater than that of the simple pendulum",0306088v1
2003-12-03,An Unbinned Goodness-of-Fit Test Based on the Random Walk,"We describe a test statistic for unbinned goodness-of-fit of data in one
dimension. The statistic is based on the two-dimensional Random Walk. The
rejection power of this test is explored both for simple and compound
hypotheses and, for the examples explored, it is found to be comparable to that
for the chisquare test. We discuss briefly how it may be possible to extend
this test to multi-dimensional data.",0312014v2
2004-01-09,Neural Network Approach to Study of Langmuir Layers at the Water Surface,"The structure of the layers of a phthalocyanines is studied through a
measurement of surface pressure-area isotherms at various initial surface
concentrations of the spreaded compound. Layer characteristics are determined
from experimental data by replotting the isotherms in accordance with M. Volmer
s equation. Neural networks taught on approximations of the isoterms. The
method is compared with the traditional least square one. Another task for NN
is a forecast of main characteristics of the layers.",0401038v2
2004-12-07,"Relativistic quantum dynamics in strong fields: Photon emission from heavy, few-electron ions","Recent progress in the study of the photon emission from highly-charged heavy
ions is reviewed. These investigations show that high-$Z$ ions provide a unique
tool for improving the understanding of the electron-electron and
electron-photon interaction in the presence of strong fields. Apart from the
bound-state transitions, which are accurately described in the framework of
Quantum Electrodynamics, much information has been obtained also from the
radiative capture of (quasi-) free electrons by high-$Z$ ions. Many features in
the observed spectra hereby confirm the inherently relativistic behavior of
even the simplest compound quantum systems in Nature.",0412041v1
2005-10-03,The cubic period-distance relation for the Kater reversible pendulum,"We describe the correct cubic relation between the mass configuration of a
Kater reversible pendulum and its period of oscillation. From an analysis of
its solutions we conclude that there could be as many as three distinct mass
configurations for which the periods of small oscillations about the two pivots
of the pendulum have the same value. We also discuss a real compound Kater
pendulum that realizes this property.",0510010v1
2006-10-31,An approximate method for calculating transfer integrals based on the ZINDO Hamiltonian,"In this paper we discuss a method for calculating transfer integrals based on
the ZINDO Hamiltonian which requires only a single self consistent field on an
isolated molecule to be performed in order to determine the transfer integral
for a pair of molecules. This method is compared to results obtained by
projection of the pair of molecules' molecular orbitals onto the vector space
defined by the molecular orbitals of each isolated molecule. The two methods
are found to be in good agreement using three compounds as model systems:
pentacene, ethylene and hexabenzocoronene.",0610288v1
2007-03-09,A Conceptual DFT Approach Towards Developing New QSTR Models,"Quantitative-structure-toxicity-relationship (QSTR) models are developed for
predicting the toxicity (pIGC50) of 252 aliphatic compounds on Tetrahymena
pyriformis. The single parameter models with a simple molecular descriptor, the
number of atoms in the molecule, provide unbelievable results. Better QSTR
models with two parameters result when global electrophilicity is used as the
second descriptor. In order to tackle both charge- and frontier-controlled
reactions the importance of the local electro (nucleo) philicities and atomic
charges is also analyzed. Best possible three parameter QSTR models are
prescribed.",0703109v1
2005-10-12,The equilibrium theory of life evolution,"Apparent biodiversity on earth exists only if we compare different species
separated from their environments. Meanwhile coexisting species have to be
identical in terms of energetic interactions. Consider the biosphere as a
network of chemical reactions. This leads to the conclusion that forces which
drive life evolution may be found inside the process of the transformations of
molecules. From the thermodynamic point of view the system of reacting
particles reaches a steady state when the chemical potentials of reagents
become equal. Interactions between chemical compounds taking part in concurrent
reactions and the equilibration of their chemical potentials is the essence of
biological evolution and its only driving force.",0510023v1
1999-03-26,Quantum Entanglement and the Maximum Entropy States from the Jaynes Principle,"We show that the Jaynes principle is indeed a proper inference scheme when
applied to compound systems and will correctly produce the entangled maximum
entropy states compatible with appropriate data. This is accomplished by
including the dispersion of the entanglement along with its mean value as
constraints and an application of the uncertainty principle. We also construct
a ""thermodynamic-like"" description of the entanglement arising out of the
maximum entropy principle.",9903083v1
1999-06-09,Path Integral Solution to Non-central Potential,"We have studied the path integral solution of a system of particle moving in
certain class of non-central potential without using Kustannheimo-Stiefel
transformation. The Hamiltonian of the system has been converted to a separable
Hamiltonian of Liouville type in parabolic coordinates and has further reduced
to a Hamiltonian corresponding to two 2- dimensional simple harmonic
oscillators. The energy spectrum for this system is calculated analytically.
Hartmann ring-shaped potential and compound Coulomb plus Aharanov- Bohm
potential have also been studied as special cases.",9906028v1
2001-03-07,Virtual Quantum Subsystems,"The physical resources available to access and manipulate the degrees of
freedom of a quantum system define the set $\cal A$ of operationally relevant
observables. The algebraic structure of $\cal A$ selects a preferred tensor
product structure i.e., a partition into subsystems. The notion of compoundness
for quantum system is accordingly relativized. Universal control over virtual
subsystems can be achieved by using quantum noncommutative holonomies",0103030v2
2001-08-23,Time dependence of occupation numbers and thermalization time in closed chaotic many-body systems,"We study the time evolution of occupation numbers for interacting
Fermi-particles in the situation when exact compound states are ""chaotic"". This
situation is generic for highly excited many-particles states in heavy nuclei,
complex atoms, quantum dots, spin systems and quantum computer models.
Numerical data show perfect agreement with a simple theory for the onset of
thermalization in close systems of interacting particles.",0108109v1
2002-07-04,Entanglement and Concurrence in the BCS State,"An extension of the notion of concurrence introduced by Wooters is used to
quantify the entanglement of certain multipartite pure states, namely, the BCS
state of superconducting compounds. This leads to a definition of the
macrocanonical entanglement of pairing (MEP) for which we compute an analytical
formula in terms of two adimensional numbers, the cut-off and gap numbers,
which depend on measurable physical quantities. We find that strongly coupled
BCS elements like Pb and Nb have much larger MEP values than more conventional
BCS transition metal superconductors.",0207026v1
2002-11-13,"A Combinatory-Algebraic Perspective on Multipartiteness, Entanglement and Quantum Localization","We claim that both multipartiteness and localization of subsystems of
compound quantum systems are of an essentially relative nature crucially
depending on the set of operationalistically available states. In a more
general setting, to capture the relativity and variability of our structures
with respect to the observation means, sheaves of algebras may need be
introduced. We provide the general formalism based on algebras which exhibits
the relativity of multipartiteness and localization.",0211077v1
2002-11-20,Decoherence Versus the Idealization of Microsystems as Correlation Carriers Between Macrosystems,"It is argued that the appropriate framework to describe a microsystem as a
correlation carrier between a source and a detector is non-equilibrium
statistical mechanics for the compound source-detector system. An attempt is
given to elucidate how this idealized notion of microsystem might arise inside
a field theoretical description of isolated macrosystems: then decoherence
appears as the natural limit of this idealization.",0211130v1
2004-02-26,Detector Efficiency Limits on Quantum Improvement,"Although the National Institute of Standards and Technology has measured the
intrinsic quantum efficiency of Si and InGaAs APD materials to be above 98 % by
building an efficient compound detector, commercially available devices have
efficiencies ranging between 15 % and 75 %. This means bandwidth, dark current,
cost, and other factors are more important than quantum efficiency for existing
applications. This paper systematically examines the generic detection process,
lays out the considerations needed for designing detectors for non-classical
applications, and identifies the ultimate physical limits on quantum
efficiency.",0402201v1
2005-10-11,"Weak and strong coupling regimes, vacuum Rabi splitting and nonstandard resonances","For two discrete-level quantum systems in interaction, we follow the
displacement in the complex plane of the eigen-energies of the compound system
when the spectrum of one of the two systems becomes continuous. These new
points are usually called resonances. This allows us to define and to calculate
a critical value of the coupling constant which separates two well-known
coupling regimes. We also give an example of these resonances for the hydrogen
atom coupled to the continuum of the states of the transverse electromagnetic
field in the vacuum. We justify that some resonances be neglected.",0510075v1
2005-10-17,Theory of decoherence due to scattering events and Lévy processes,"A general connection between the characteristic function of a L\'evy process
and loss of coherence of the statistical operator describing the center of mass
degrees of freedom of a quantum system interacting through momentum transfer
events with an environment is established. The relationship with microphysical
models and recent experiments is considered, focusing on the recently observed
transition between a dynamics described by a compound Poisson process and a
Gaussian process.",0510127v1
2006-10-25,Dissipation Effects in Hybrid Systems,"The dissipation effect in a hybrid system is studied in this Letter. The
hybrid system is a compound of a classical magnetic particle and a quantum
single spin. Two cases are considered. In the first case, we investigate the
effect of the dissipative quantum subsystem on the motion of its classical
partner. Whereas in the second case we show how the dynamics of the quantum
single spin are affected by the dissipation of the classical particle.
Extension to general dissipative hybrid systems is discussed.",0610211v1
2007-02-10,Additivity of Entangled Channel Capacity for Quantum Input States,"An elementary introduction into algebraic approach to unified quantum
information theory and operational approach to quantum entanglement as
generalized encoding is given. After introducing compound quantum state and two
types of informational divergences, namely, Araki-Umegaki (a-type) and of
Belavkin-Staszewski (b-type) quantum relative entropic information, this paper
treats two types of quantum mutual information via entanglement and defines two
types of corresponding quantum channel capacities as the supremum via the
generalized encodings. It proves the additivity property of quantum channel
capacities via entanglement, which extends the earlier results of V. P.
Belavkin to products of arbitrary quantum channels for quantum relative entropy
of any type.",0702098v1
2007-02-19,Polynomial Solution of Non-Central Potentials,"We show that the exact energy eigenvalues and eigenfunctions of the
Schrodinger equation for charged particles moving in certain class of
non-central potentials can be easily calculated analytically in a simple and
elegant manner by using Nikiforov and Uvarov (NU) method. We discuss the
generalized Coulomb and harmonic oscillator systems. We study the Hartmann
Coulomb and the ring-shaped and compound Coulomb plus Aharanov-Bohm potentials
as special cases. The results are in exact agreement with other methods.",0702186v1
1995-01-19,Phonon Assisted Multimagnon Optical Absorption and Long Lived Two-Magnon States in Undoped Lamellar Copper Oxides,"We calculate the effective charge for multimagnon infrared (IR) absorption
assisted by phonons in the parent insulating compounds of cuprate
superconductors and the spectra for two-magnon absorption using interacting
spin-wave theory. Recent measured bands in the mid IR [Perkins et al. Phys.
Rev. Lett. {\bf 71} 1621 (1993)] are interpreted as involving one phonon plus a
two-magnon virtual bound state, and one phonon plus higher multimagnon
absorption processes. The virtual bound state consists of a narrow resonance
occurring when the magnon pair has total momentum close to $(\pi,0)$.",9501001v1
2007-04-03,Optical properties of the Holstein-t-J model from dynamical mean-field theory,"We employ dynamical mean-field theory to study the optical conductivity
$\sigma(\omega)$ of one hole in the Holstein-t-J model. We provide an exact
solution for $\sigma(\omega)$ in the limit of infinite connectivity. We apply
our analysis to Nd$_{2-x}$Ce$_x$CuO$_4$. We show that our model can explain
many features of the optical conductivity in this compounds in terms of
magnetic/lattice polaron formation.",0704.0333v1
2007-04-10,Y-formalism and $b$ ghost in the Non-minimal Pure Spinor Formalism of Superstrings,"We present the Y-formalism for the non-minimal pure spinor quantization of
superstrings. In the framework of this formalism we compute, at the quantum
level, the explicit form of the compound operators involved in the construction
of the $b$ ghost, their normal-ordering contributions and the relevant
relations among them. We use these results to construct the quantum-mechanical
$b$ ghost in the non-minimal pure spinor formalism. Moreover we show that this
non-minimal $b$ ghost is cohomologically equivalent to the non-covariant $b$
ghost.",0704.1219v1
2007-04-16,Classical nucleation theory in ordering alloys precipitating with L12 structure,"By means of low-temperature expansions (LTEs), the nucleation free energy and
the precipitate interface free energy are expressed as functions of the
solubility limit for alloys which lead to the precipitation of a stoichiometric
L12 compound such as Al-Sc or Al-Zr alloys. Classical nucleation theory is then
used to obtain a simple expression of the nucleation rate whose validity is
demonstrated by a comparison with atomic simulations. LTEs also explain why
simple mean-field approximation like the Bragg-Williams approximation fails to
predict correct nucleation rates in such an ordering alloy.",0704.1988v1
2007-04-23,Ferroelectricity driven by the non-centrosymmetric magnetic ordering in multiferroic TbMn_2O_5: a first-principles study,"The ground state structural, electronic and magnetic properties of
multiferroic TbMn$_2$O$_5$ are investigated via first-principles calculations.
We show that the ferroelectricity in TbMn$_2$O$_5$ is driven by the
non-centrosymmetric magnetic ordering, without invoking the spin-orbit coupling
and non-collinear spins. The {\it intrinsic} electric polarization in this
compound is calculated to be 1187 $nC\cdot$ cm$^{-2}$, an order of magnitude
larger than previously thought.",0704.2908v2
2007-04-29,Pinned Low Energy Electronic Excitation in Metal Exchanged Vanadium Oxide Nanoscrolls,"We measured the optical properties of mixed valent vanadium oxide nanoscrolls
and their metal exchanged derivatives in order to investigate the charge
dynamics in these compounds. In contrast to the prediction of a metallic state
for the metal exchanged derivatives within a rigid band model, we find that the
injected charges in Mn$^{2+}$ exchanged vanadium oxide nanoscrolls are pinned.
A low-energy electronic excitation associated with the pinned carriers appears
in the far infrared and persists at low temperature, suggesting that the
nanoscrolls are weak metals in their bulk form, dominated by inhomogeneous
charge disproportionation and Madelung energy effects.",0704.3861v1
2007-05-09,Ultracold Rydberg Atoms in a Ioffe-Pritchard Trap,"We discuss the properties of ultracold Rydberg atoms in a Ioffe-Pritchard
magnetic field configuration. The derived two-body Hamiltonian unveils how the
large size of Rydberg atoms affects their coupling to the inhomogeneous
magnetic field. The properties of the compound electronic and center of mass
quantum states are thoroughly analyzed. We find very tight confinement of the
center of mass motion in two dimensions to be achievable while barely changing
the electronic structure compared to the field free case. This paves the way
for generating a one-dimensional ultracold quantum Rydberg gas.",0705.1299v2
2007-05-14,Correlation between magnetostriction and polarization in orthorhombic manganites,"Recently we have reported the observation of colossal magnetostriction effect
in HoMn2O5 single crystals. Besides we have made the supposition for possible
correlation between the peculiarities, observed in the field depended
polarization measurements, and the colossal magnetostriction effect at a 4.2 K
temperature. In this article we present our results received by polarization
and magnetostriction measurements on HoMn2O5 and TbMn2O5 single crystals and
the strong correlation between magnetostriction and polarization phase
transition for these two compounds. The origin of this correlation is
discussed.",0705.2022v1
2007-05-14,Indirect magnetic interaction mediated by spin dimer in Cu$_2$Fe$_2$Ge$_4$O$_{13}$,"Cu$_2$Fe$_2$Ge$_4$O$_{13}$ is a bicomponent compound that consists of Cu
dimers and Fe chains with separate energy scale. By inelastic neutron
scattering technique with high-energy resolution we observed the indirect Fe -
Fe exchange coupling by way of the Cu dimers. The obtained parameters of the
effective indirect interaction and related superexchange interactions are
consistent with those estimated semi-statically. The consistency reveals that
the Cu dimers play the role of nonmagnetic media in the indirect magnetic
interaction.",0705.2052v1
2007-05-21,"On the Riemann zeta-function, Part III","An odd meromorphic function f(s) is constructed from the Riemann
zeta-function evaluated at one-half plus s. The partial fraction expansion,
p(s), of f(s) is obtained using the conjunction of the Riemann hypothesis and
hypotheses advanced by the author. That compound hypothesis and the expansion
p(s) are employed in Part IV to derive the two-sided Laplace transform
representation of f(s) on the open vertical strip of all s with real part
between zero and four.",0705.2995v1
2007-05-21,Lattice structures of Larkin-Ovchinnikov-Fulde - Ferrell (LOFF) state,"Starting from the Ginzburg-Landau free energy describing the normal state to
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state transition, we evaluate the free
energy of seven most common lattice structures such as stripe, square,
triangular,Simple Cubic (SC), Face centered Cubic (FCC),Body centered Cubic
(BCC) and Quasi-crystal (QC). We find that the stripe phase which is the
original LO state, is the most stable phase. This result maybe relevant to the
detection of LOFF state in some heavy fermion compounds and the pairing lattice
structure of fermions with unequal populations in the BCS side of Feshbach
resonance in ultra-cold atoms.",0705.3034v1
2007-05-31,Superconductivity due to co-operative Kondo effect in Pu 115's,"We outline key elements of a theory that accounts for anomalous properties of
the PuCoGa$_5$ and PuRhGa$_5$ compounds as a consequence of a two-body
interference between two Kondo screening channels. Virtual valence fluctuations
of the magnetic Pu configurations create two conduction channels of different
symmetry. Using the symplectic large-N approach, we are able to demonstrate our
pairing mechanism in an exactly solvable large-N limit. The critical
temperature reaches its maximum when the energy levels of excited valence
configurations are almost degenerate. The symmetry of the order parameter is
determined by the product of the Wannier form factors in the interfering
conduction channels.",0706.0016v1
2007-06-01,Power-law Conductivity inside the Mott gap: application to $κ-(BEDT-TTF)_2Cu_2(CN)_3$,"The charge dynamics of spin-liquid states described by U(1) gauge theory
coupling to fermionic spinons is discussed in this paper. We find that the
gapless spinons give rise to a power law optical conductivity inside the charge
gap. The theory is applied to explain the unusual optical conductivity observed
recently in the organic compound $\kappa-(BEDT-TTF)_2Cu_2(CN)_3$. We also
propose an optical experiment to search for the in-gap excitations in the
Kagome spin liquid insulator.",0706.0050v1
2007-06-01,The M-estimator in a multi-phase random nonlinear model,"This paper considers M-estimation of a nonlinear regression model with
multiple change-points occuring at unknown times. The multi-phase random design
regression model, discontinuous in each change-point, have an arbitrary error
$\epsilon$. In the case when the number of jumps is known, the M-estimator of
locations of breaks and of regression parameters are studied. These estimators
are consistent and the distribution of the regression parameter estimators is
Gaussian. The estimator of each change-point converges, with the rate $n^{-1}$,
to the smallest minimizer of the independent compound Poisson processes. The
results are valid for a large class of error distributions.",0706.0153v3
2007-06-05,Compounding Fields and Their Quantum Equations in the Curved Spaces,"Based on the concept of curved spacetime in Einsteinian General Relativity,
the field theories and their quantum theories in the curved octonion spaces etc
are discussed. The research results discover the close relationships of the
curved spacetimes with the field theories and quantum theories. In the field
theories of curved spacetimes, the curvatures have direct effect on field
strength and field source etc. While the curvatures have direct impact on wave
functions and quantum equations etc in the quantum theories of curved
spacetimes. The research results discover that some abnormal phenomena of field
source particles could be explained by the field theories or quantum theories
in the curved spacetimes.",0706.0573v2
2007-06-06,Up-conversion injection in Rubrene/Perylene-diimide-heterostructure electroluminescent diodes,"We implement and demonstrate a scheme that permits to drive
electroluminescence with an extremely low turn-on voltage. The device behaves
like compound semiconductors, in which the electroluminescence turn-on voltage
is about the same as the open circuit voltage for the photovoltaic effect.
However, the electroluminescence turn-on voltage is about half of the band gap
of the emitting material, that cannot be explained using current models of
charge injection in organic semiconductors. We hereby propose explanation
through an Auger-type two-step injection mechanism (Auger-fountain).",0706.0840v1
2007-06-07,Parity nonconservation in dielectronic recombination of multiply charged ions,"We discuss a parity nonconserving (PNC) asymmetry in the cross section of
dielectronic recombination of polarized electrons on multiply charged ions with
Z>40. This effect is strongly enhanced for close doubly-excited states of
opposite parity in the intermediate compound ion. Such states are known for
He-like ions. However, these levels have large energy and large radiative
widths which hampers observation of the PNC asymmetry. We argue that
accidentally degenerate states of the more complex ions may be more suitable
for the corresponding experiment.",0706.1027v1
2007-06-10,Magnon mode truncation in a rung-dimerized asymmetric spin ladder,"An exactly solvable effective model is suggested for an asymmetric spin
ladder with dimerized rungs. Magnon mode truncation originated from magnon
decay (recently observed in the 1D compound ${\rm IPA-CuCl}_3$) is naturally
described within this model. Using Bethe Ansatze we described a one-magnon
sector and obtained relations between interaction constants of the model and
experimentally observable quantities such as the gap and truncation energies,
spin velocity and the truncation wave vector. It is also shown that structure
factor turns to zero at the truncation point.",0706.1370v2
2007-06-11,Is Sr2RuO4 a triplet superconductor?,"The field dependence of the specific heat \gamma(H) at lower temperatures in
Sr2RuO4 is analyzed by solving microscopic Eilenberger equation numerically. We
find that systematic \gamma(H) behaviors from a concaved \sqrt H to a convex
H^{\alpha} (\alpha>1) under H orientation change are understood by taking
account of the Pauli paramagnetic effect. The magnetizations are shown to be
consistent with it. This implies either a singlet pairing or a triplet one with
d-vector locked in the basal plane, which allows us to explain other mysteries
of this compound in a consistent way.",0706.1426v1
2007-06-14,Use of detailed kinetic mechanisms for the prediction of autoignitions,"This paper describes how automatically generated detailed kinetic mechanisms
are obtained for the oxidation of alkanes and how these models could lead to a
better understanding of autoignition and cool flame risks at elevated
conditions. Examples of prediction of the occurrence of different autoignition
phenomena, such as cool flames or two-stage ignitions are presented depending
on the condition of pressure, temperature and mixture composition. Three
compounds are treated, a light alkane, propane, and two heavier ones, n-heptane
and n-decane.",0706.2067v1
2007-06-26,Isospin Effects on Astrophysical S-Factors,"We estimate the ratios of bare astrophysical S-factors at zero incident
energy for proton and deuteron induced reactions in a model which assumes a
compound nucleus formation probability plus a statistical decay. The obtained
ratios agree well with available experimental values, as far as the reactions
which have dominant s-wave entrance channel components are investigated. Due to
its simplicity the model could be used as a guidance for predictions on
reactions which have not been investigated yet.",0706.3864v2
2007-07-03,"Stability, Reactivity, and Aromaticity of Compounds of a Multivalent Superatom","In this communication we analyze the stability, reactivity and possible
aromatic behavior of two recently reported clusters (Reveles J. U.; Khanna S.
N.; Roach P. J.; Castleman A. W. jr. Proc. Natl. Acad. Sci, 2006, 103, 18405),
viz., Al7C- and Al7O- in the light of the principles of the maximum hardness
and minimum electrophilicity as well as the nucleus independent chemical shift
values.",0707.0337v1
2007-07-10,Neutron Scattering Study of the Localized Mode in the beta-Pyrochlore Superconductors AOs2O6,"Inelastic neutron scattering and neutron powder diffraction experiments were
carried out to investigate a localized mode, proposed from various bulk
measurements, in the beta-pyrochlore AOs2O6 (A=K, Rb, Cs). The localized mode
was identified in all the three compounds as well as another beta-pyrochlore
CsW2O6. The anharmonicity of the mode is weak in RbOs2O6 and CsOs2O6 but
substantial in KOs2O6.",0707.1366v2
2007-07-25,The charge and spin sectors of the $t$-$t'$ Hubbard model,"The charge and spin sectors, which are intimately coupled to the fermionic
one, of the $t$-$t'$ Hubbard model have been computed self-consistently within
the two-pole approximation. The relevant unknown correlators appearing in the
causal bosonic propagators have been computed by enforcing the constraints
dictated by the hydrodynamics and the algebra of the composite operators coming
into play. The proposed scheme of approximation extends previous calculations
made for the fermionic sector of the $t$-$t'$ Hubbard model and the bosonic
sector of the Hubbard model, which showed to be very effective to describe the
overdoped region of cuprates (the former) and the magnetic response of their
parent compounds (the latter).",0707.3836v1
2007-07-27,Spin-triplet pairing instability of the spinon Fermi surface in a U(1) spin liquid,"Recent experiments on the organic compound \kappa-(ET)_2Cu_2(CN)_3 have
provided a promising example of a two dimensional spin liquid state. This phase
is described by a two-dimensional spinon Fermi sea coupled to a U(1) gauge
field. We study Kohn-Luttinger-like pairing instabilities of the spinon Fermi
surface due to singular interaction processes with twice-the-Fermi-momentum
transfer. We find that under certain circumstances the pairing instability
occurs in odd-orbital-angular-momentum/spin-triplet channels. Implications to
experiments are discussed.",0707.4031v1
2007-07-27,Coupling Between An Optical Phonon and the Kondo Effect,"We explore the ultra-fast optical response of Yb_{14}MnSb_{11}, providing
further evidence that this Zintl compound is the first ferromagnetic,
under-screened Kondo lattice. These experiments also provide the first
demonstration of coupling between an optical phonon mode and the Kondo effect.",0707.4177v1
2007-08-10,Nano Calculators,"The whole circuit is obtained from the sun through a molecule called
""Rhodopsin and bacteriorhodopsin"". These molecules have the capability of
trapping and storing energy from the sun light. These molecules are placed on
the outer surface of the calculator to trap the energy and store it themselves
for latter usage. The thickness of the whole circuit measures less than
300nm.The top layer is made up of layer which will show the different keys and
a display unit. ""Molecules are not only meant for compounding But also for
computing"".",0708.1453v1
2007-08-16,Pressure-induced Superconductivity in CaLi2,"A search for superconductivity has been carried out on the hexagonal
polymorph of Laves-phase CaLi2, a compound for which Feng, Ashcroft, and
Hoffmann predict highly anomalous behavior under pressure. No superconductivity
is observed above 1.10 K at ambient pressure. However, high-pressure ac
susceptibility and electrical resistivity studies to 81 GPa reveal bulk
superconductivity in CaLi2 at temperatures as high as 13 K. The normal-state
resistivity shows a dramatic increase with pressure.",0708.2117v2
2007-08-28,About Goldbach strong conjecture,"In this work we use the number classification in families of the form 6n+1,
and 6n+5 with n integer (Such families contain all odd prime numbers greater
than 3 and other compound numbers related with primes). We will use this kind
of classification in order to attempt an approach to Goldbach strong
conjecture. By means of a geometric method of binary bands of numbers we
conceive a new form of study of the stated problem.",0708.3704v2
2007-08-30,Thermodynamic modeling of the Hf-Si-O system,"The Hf-O system has been modeled by combining existing experimental data and
first-principles calculations results through the CALPHAD approach. Special
quasirandom structures of $\alpha$ and $\beta$ hafnium were generated to
calculate the mixing behavior of oxygen and vacancies. For the total energy of
oxygen, vibrational, rotational and translational degrees of freedom were
considered. The Hf-O system was combined with previously modeled Hf-Si and Si-O
systems, and the ternary compound in the Hf-Si-O system, HfSiO$_4$ has been
introduced to calculate the stability diagrams pertinent to the thin film
processing.",0708.4239v1
2007-09-07,Possible co-existence of local itinerancy and global localization in a quasi-one-dimensional conductor,"In the chain compound PrBa$_2$Cu$_4$O$_8$ localization appears simultaneously
with a dimensional crossover in the electronic ground state when the scattering
rate in the chains exceeds the hopping rate between the chains. Here we report
the discovery of a large, transverse magnetoresistance in PrBa$_2$Cu$_4$O$_8$
in the localized regime. This result suggests a novel form of localization
whereby electrons retain their metallic (quasi-one-dimensional) character over
a microscopic length scale despite the fact that macroscopically, they exhibit
localized (one-dimensional) behavior.",0709.1115v1
2007-09-26,Single crystal growth and anisotropy of CeRuPO,"We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction.",0709.4144v2
2007-09-26,Signatures of non-monotonic d-wave gap in electron-doped cuprates,"We address the issue whether the data on optical conductivity and Raman
scattering in electron-doped cuprates below $T_c$ support the idea that the
$d-$wave gap in these materials is non-monotonic along the Fermi surface. We
calculate the conductivity and Raman intensity for elastic scattering, and find
that a non-monotonic gap gives rise to several specific features in optical and
Raman response functions. We argue that all these features are present in the
experimental data on Nd$_{2-x}$Ce$_{x}$CuO$_4$ and Pr$_{2-x}$Ce$_{x}$CuO$_4$
compounds.",0709.4146v1
2007-09-26,Giant magnetoresistance and extraordinary magnetoresistance in inhomogeneous semiconducting DyNiBi,"The semiconducting half-Heulser compound DyNiBi shows a negative giant
magnetoresistance (GMR) below 200 K. Except for a weak deviation, this
magnetoresistance scales roughly with the square of the magnetization in the
paramagnetic state, and is related to the metal-insulator transition. At low
temperature, a positive magnetoresistance is found, which can be suppressed by
high fields. The magnitude of the positive magnetoresistance changes slightly
with the amount of impurity phase.",0709.4182v2
2007-10-04,Pressure induced variation of the ground state of CeAl3,"Pressure-induced variations of $^{27}$Al NMR spectra of CeAl$_3$ indicate
significant changes in the ground-state characteristics of this prototypical
heavy-electron compound. Previously reported magnetic and electronic
inhomogeneities at ambient pressure and very low temperatures are removed with
external pressures exceeding 1.2 kbar. The spectra and results of corresponding
measurements of the NMR spin-lattice relaxation rates indicate a
pressure-induced emergence of a simple paramagnetic state involving electrons
with moderately enhanced masses and no magnetic order above 65 mK.",0710.1034v2
2007-10-05,The Debye-Waller factor of stabilized delta-Pu,"The Debye-Waller factor has been calculated for stabilized delta-phase
plutonium with 5% aluminum. A quasi-harmonic Born-von Karman force model with
temperature dependent phonon frequencies was used to calculate the mean-square
thermal atomic displacement from absolute zero to 800 K. Implementation of the
observed anomalous softening of the long wavelength phonons with increasing
temperature cannot account for the softening of the measured thermal parameter
at high temperatures nor for its rather high value at low temperatures. The
implications for diffraction measurements on delta-phase stabilized plutonium
alloys are discussed.",0710.1241v1
2007-11-02,Magnetic resonance as an orbital state probe,"Magnetic resonance in ordered state is shown to be the direct method for
distinguishing the orbital ground state. The example of perovskite titanates,
particularly, LaTiO3 and YTiO3, is considered. External magnetic field
resonance spectra of these crystals reveal glaring qualitative dependence on
assumed orbital state of the compounds: orbital liquid or static orbital
structure. Theoretical basis for using the method as an orbital state probe is
grounded.",0711.0333v2
2007-11-05,Decompounding under Gaussian noise,"Assuming that a stochastic process $X=(X_t)_{t\geq 0}$ is a sum of a compound
Poisson process $Y=(Y_t)_{t\geq 0}$ with known intensity $\lambda$ and unknown
jump size density $f,$ and an independent Brownian motion $Z=(Z_t)_{t\geq 0},$
we consider the problem of nonparametric estimation of $f$ from low frequency
observations from $X.$ The estimator of $f$ is constructed via Fourier
inversion and kernel smoothing. Our main result deals with asymptotic normality
of the proposed estimator at a fixed point.",0711.0719v1
2007-11-10,Structural and magnetic properties in the ruthenate Bi2.67Pr0.33Ru3O11,"An unreported praseodymium substituted phase of the Bi-Ru-O system with
formula Bi2.67Pr0.33Ru3O11was prepared. Its crystal structure and magnetic
properties were investigated. Pr substituted occurs only on one of the two Bi
sites. The magnetism of the compound is essentially dominated by a Pr3+
contribution. A non linear variation of the reciprocal magnetic susceptibility
is observed that appears to account for crystal electric field interactions on
the Pr3+ ions.",0711.1577v1
2007-11-22,Hadronic atoms in QCD + QED,"We review the theory of hadronic atoms in QCD + QED, based on a
non-relativistic effective Lagrangian framework. We first provide an
introduction to the theory, and then describe several applications:
meson-meson, meson-nucleon atoms and meson-deuteron compounds. Finally, we
compare the quantum field theory framework used here with the traditional
approach, which is based on quantum-mechanical potential scattering.",0711.3522v2
2007-11-23,Experimental Determination of Thermal Entanglement in Spin Clusters using Magnetic Susceptibility Measurements,"The present work reports an experimental observation of thermal entanglement
in a clusterized spin chain formed in the compound Na$_2$Cu$_5$Si$_4$O$_{14}$.
The presence of entanglement was investigated through two measured quantities,
an Entanglement Witness and the Entanglement of Formation, both derived from
the magnetic susceptibility. It was found that pairwise entanglement exists
below $ \sim 200$ K. Tripartite entanglement was also observed below $ \sim
240$ K. A theoretical study of entanglement evolution as a function of applied
field and temperature is also presented.",0711.3662v1
2007-12-06,High resolution quantization and entropy coding of jump processes,"We study the quantization problem for certain types of jump processes. The
probabilities for the number of jumps are assumed to be bounded by Poisson
weights. Otherwise, jump positions and increments can be rather generally
distributed and correlated. We show in particular that in many cases entropy
coding error and quantization error have distinct rates. Finally, we
investigate the quantization problem for the special case of
$\mathbb{R}^d$-valued compound Poisson processes.",0712.0964v1
2007-12-11,Superfluid density in gapless superconductor CeCoIn5,"Temperature dependence of the London penetration depth $\lambda$ measured in
single crystals of CeCoIn$_5$ is interpreted as caused by a strong
pair-breaking scattering that makes the superconductivity in this compound
gapless. For a gapless d-wave superconductor, we derive
$\lambda=\lambda_0/\sqrt{1-(T/T_c)^2}$ caused by combined effect of magnetic
and non-magnetic scattering in excellent agreement with the data in the full
temperature range and with the gapless s-wave case of Abrikosov and Gor'kov. We
also obtain the slope of the upper critical field at $T_c$ that compares well
with the measured slope.",0712.1632v1
2008-01-08,Magnetic excitations in SrCu2O3: a Raman scattering study,"We investigated temperature dependent Raman spectra of the one-dimensional
spin-ladder compound SrCu2O3. At low temperatures a two-magnon peak is
identified at 3160+/-10 cm^(-1) and its temperature dependence analyzed in
terms of a thermal expansion model. We find that the two-magnon peak position
must include a cyclic ring exchange of J_cycl/J_perp=0.09-0.25 with a coupling
constant along the rungs of J_perp approx. 1215 cm^(-1) (1750 K) in order to be
consistent with other experiments and theoretical results.",0801.1303v1
2008-01-11,Weak Ferromagnetism in Fe1-xCoxSb2,"Weak ferromagnetism in Fe1-xCoxSb2 is studied by magnetization and Mossbauer
measurements. A small spontaneous magnetic moment of the order of 10^-3 uB
appears along the b-axis for 0.2<= x <= 0.4. Based on the structural analysis,
we argue against extrinsic sources of weak ferromagnetism. We discuss our
results in the framework of the nearly magnetic electronic structure of the
parent compound FeSb2.",0801.1688v1
2008-01-11,Nucleosynthesis in Early Neutrino Driven Winds,"Nucleosynthesis in early neutrino winds is investigated. Presented is a brief
overview of two recent problems of supernova nucleosynthesis. In the first part
we investigate the effect of nuclear parameters on the synthesis of Mo92 and
Mo94. Based on recent experimental results, we find that the proton rich winds
of the model investigated here can not be the source of solar Mo92 and Mo94. In
the second part we investigate the nucleosynthesis from neutron rich bubbles
and show that they do not contribute to the overall nucleosynthesis.",0801.1828v1
2008-01-30,Polaronic signatures in the optical properties of Nd$_{2-x}$Ce$_x$CuO$_4$,"We investigate the temperature and doping dependence of the optical
conductivity $\sigma(\omega)$ of Nd$_{2-x}$Ce$_x$CuO$_4$ in terms of
magnetic/lattice polaron formation. We employ dynamical mean-field theory in
the context of the Holstein-t-J model where an exact analytical solution is
available in the limit of infinite connectivity. We show that the pseudogap
features in the optical conductivity of this compound can be associated to the
formation of lattice polarons assisted by the magnetic interaction.",0801.4691v1
2008-02-14,Absence of Hole Confinement in Transition Metal Oxides with Orbital Degeneracy,"We investigate the spectral properties of a hole moving in a two-dimensional
Hubbard model for strongly correlated t_2g electrons. Although superexchange
interactions are Ising-like, a quasi-one-dimensional coherent hole motion
arises due to effective three-site terms. This mechanism is fundamentally
different from the hole motion via quantum fluctuations in the conventional
spin model with SU(2) symmetry. The orbital model describes also propagation of
a hole in some e_g compounds, and we argue that orbital degeneracy alone does
not lead to hole self-localization.",0802.2012v1
2008-02-20,Empirical oscillating potentials for alloys from ab-initio fits,"By fitting to a database of ab-initio forces and energies, we can extract
pair potentials for alloys, with a simple six-parameter analytic form including
Friedel oscillations, which give a remarkably faithful account of many complex
intermetallic compounds. As examples we show results for (crystal or
quasicrystal) structure prediction and phonon spectrum for three systems:
Fe--B, Al--Mg--Zn, and Al--Cu--Fe.",0802.2926v2
2008-03-03,Condensation and growth of Kirkendall voids in intermetallic compounds,"A model for the simulation of Kirkendall voiding in metallic materials is
presented based on vacancy diffusion, elastic-plastic and rate-dependent
deformation of spherical voids. Starting with a phenomenological explanation of
the Kirkendall effect we briefly discuss the consequences on the reliability of
microelectronics. A constitutive model for void nucleation and growth is
presented, which can be used to predict the temporal development of voids in
solder joints during thermal cycling. We end with exemplary numerical studies
and discuss the potential of the results for the failure analysis of joining
connections.",0803.0196v1
2008-03-06,First-principles approach to lattice-mediated magnetoelectric effects,"We present a first-principles scheme for the computation of the
magnetoelectric response of magnetic insulators. The method focuses on the
lattice-mediated part of the magnetic response to an electric field, which we
argue can be expected to be the dominant contribution in materials displaying a
strong magnetoelectric coupling. We apply our method to Cr2O3, a relatively
simple and experimentally well studied magnetoelectric compound.",0803.0856v1
2008-03-12,Spin-lattice model of Magneto-electric Transitions in RbCoBr$_3$,"Extensive Monte Carlo simulations are performed to analyze a recent neutron
diffraction experiment on a distorted triangular lattice compound RbCoBr$_3$.
We consider a spin-lattice model, where both spin and lattice are Ising
variables. This model explains well successive magnetic and dielectric
transitions observed in the experiment. The exchange interaction parameters and
the spin-lattice coupling are estimated. It is found that the spin-lattice
coupling is important to explain the slow growth of a ferrimagnetic order. The
present simulations were made possible by developing a new Monte Carlo
algorithm, which accelerates slow Monte Carlo dynamics of quasi-one-dimensional
frustrated systems.",0803.1710v2
2008-04-03,Orbital Degeneracy and the Microscopic Model of the FeAs Plane in the Iron-Based Superconductors,"A microscopic model for the FeAs plane in the newly discovered Iron-based
superconductors is proposed with the emphasis on the role of the orbital
degeneracy between the Fe $3d_{xz}$ and $3d_{yz}$ orbital in the crystal field
environment. The model predicts commensurate antiferromagnetic ordered ground
state for the parent compounds and a d-wave superconducting ground state at
finite doping. Inter-orbital couplings plays an interesting role in enhancing
both orders. Correlated variational wave functions are proposed for both
ordered phases.",0804.0536v1
2008-04-10,Structural Ordering and Antisite Defect Formation in Double Perovskites,"We formulate an effective model for B-B' site ordering in double perovskite
materials A_2BB'O_6. Even within the simple framework of lattice-gas type
models, we are able to address several experimentally observed issues including
nonmonotonic dependence of the degree of order on annealing temperature, and
the rapid decrease of order upon overdoping with either B or B' species. We
also study ordering in the `ternary' compounds A_2BB'_{1-y}B''_yO_6 Although
our emphasis is on the double perovskites, our results are easily generalizable
to a wide variety of binary and ternary alloys.",0804.1681v1
2008-04-14,Conservation Properties in the Time-Dependent Hartree Fock Theory,"We discuss the conservation of angular momentum in nuclear time-dependent
Hartree-Fock calculations for a numerical representation of wave functions and
potentials on a three-dimensional cartesian grid. Free rotation of a deformed
nucleus performs extremely well even for relatively coarse spatial grids. Heavy
ion collisions produce a highly excited compound system associated with
substantial nucleon emission. These emitted nucleons reach the bounds of the
numerical box which leads to a decrease of angular momentum. We discuss
strategies to distinguish the physically justified loss from numerical
artifacts.",0804.2127v1
2008-04-16,On the solubility of Nd3+ in Y3Al5O12,"Neodymium doped yttrium aluminum garnet powders (Nd:YAG or
(Y{1-x}Nd{x})3Al5O12, x=0.15, 0.25, or 0.30, respectively) were prepared by a
sol-gel technique. By DTA measurements up to 2000 deg C eutectic and liquidus
temperatures could be determined. Exothermal peaks in the second and subsequent
DTA heating runs indicate that the crystallized DTA samples are not in
equilibrium. The section Y3Al5O12-Nd3Al5O12 of the concentration triangle
Al2O3-Nd2O3-Y2O3 is proposed on the basis of thermodynamic calculations that
allows to explain the experimental results by the balance of metastable phase
states in the previously crystallized DTA samples.",0804.2545v1
2008-04-25,"Atomic Structures of Graphene, Benzene and Methane with Bond Lengths as Sums of the Single, Double and Resonance Bond Radii of Carbon","Two dimensional layers of graphene are currently drawing a great attention in
fundamental and applied nanoscience. Graphene consists of interconnected
hexagons of carbon atoms as in graphite. This article presents for the first
time the structures of graphene at the atomic level and shows how it differs
from that of benzene, due to the difference in the double bond and resonance
bond based radii of carbon. The carbon atom of an aliphatic compound such as
methane has a longer covalent single bond radius as in diamond. All the atomic
structures presented here have been drawn to scale.",0804.4086v1
2008-05-08,"Electronic Structure, Phonons and Dielectric Anomaly in Ferromagnetic Insulating Double Perovskite La2NiMnO6","Using first-principles density functional calculations, we study the
electronic and magnetic properties of ferromagnetic insulating
double-perovskite compound La2NiMnO6, which has been reported to exhibit
interesting magnetic field sensitive dielectric anomaly as a function of
temperature. Our study reveals existence of very soft infra-red active phonons
that couple strongly with spins at the Ni and Mn sites through modification of
the super-exchange interaction. We suggest that these modes are the origin for
observed dielectric anomaly in La2NiMnO6.",0805.1112v1
2008-05-12,Negative differential resistance and pulsed current induced multi-level resistivity switching in charge ordered and disordered manganites,"We have investigated direct and pulsed current induced electroresistance in
two manganites with different electronic and magnetic ground states:
charge-orbital ordered 50 % Ca doped NdMnO3 and 50 % Mn doped LaNiO3. It has
been shown that negative differential resistance observed at high current
density in these compounds is related to Joule heating. However, bi-level and
multi-level resistivity switching induced by variations in pulse width and
pulse period at low current density can not be attributable to Joule heating
alone. We discuss possible origins.",0805.1643v1
2008-05-15,Growth of Oxide Compounds under Dynamic Atmosphere Composition,"Commercially available gases contain residual impurities leading to a
background oxygen partial pressure of typically several 10^{-6} bar,
independent of temperature. This oxygen partial pressure is inappropriate for
the growth of some single crystals where the desired oxidation state possesses
a narrow stability field. Equilibrium thermodynamic calculations allow the
determination of dynamic atmosphere compositions yielding such self adjusting
and temperature dependent oxygen partial pressures, that crystals like ZnO,
Ga2O3, or Fe{1-x}O can be grown from the melt.",0805.2217v1
2008-05-16,A toolkit for a generative lexicon,"In this paper we describe the conception of a software toolkit designed for
the construction, maintenance and collaborative use of a Generative Lexicon. In
order to ease its portability and spreading use, this tool was built with free
and open source products. We eventually tested the toolkit and showed it
filters the adequate form of anaphoric reference to the modifier in endocentric
compounds.",0805.2537v1
2008-05-20,The Exchange Parameters in Lanthanum Manganites,"The spin-wave spectrum in the metallic ferromagnetic lantha-num cubic
manganites was investigated. The interactions with four coordination spheres
(32 neighbors) were taken into ac-count. The Heisenberg superexchange between
all manganese ions as well as double exchange between the manganese ions with
different valence were under consideration. The obtained magnon spectrum
permits to investigate dispersion relations along an any crystallographic
directions. This possibility was used for the numerical evaluation of the
exchange parameters in the compounds La0.75Ca0.25MnO3 and La0.70Ca0.30MnO3 from
the inelastic neutron scattering data.",0805.3006v1
2008-06-05,Low temperature synthesis and pressure induced insulator-metal transition of the newly found NdFeAsO0.75,"As low as 900 oC, iron-based layered quaternary compound NdFeAsO0.75 was
synthesized through solid state reaction method. XRD measurements illustrate
almost pure phase of tetragonal phase NdFeAsO was formed. The synthesis
temperature in our experiment is the lowest among all the reported methods
without the help of any mineralizer. After further treatment under high
pressure of 6 GPa at temperature of 1300 oC for 2 hours, the electrical
transport property of NdFeAsO0.75 was transformed from insulator-like to metal-
like behavior.",0806.0976v1
2008-06-12,Surface-sensitive NMR in optically pumped semiconductors,"We present a scheme of surface-sensitive nuclear magnetic resonance in
optically pumped semiconductors, where an NMR signal from a part of the surface
of a bulk compound semiconductor is detected apart from the bulk signal. It
utilizes optically oriented nuclei with a long spin-lattice relaxation time as
a polarization reservoir for the second (target) nuclei to be detected. It
provides a basis for the nuclear spin polarizer [IEEE Trans. Appl. Supercond.
14, 1635 (2004)], which is a polarization reservoir at a surface of the
optically pumped semiconductor that polarizes nuclear spins in a target
material in contact through the nanostructured interfaces.",0806.1992v1
2008-06-17,Large Seebeck coefficients in Iron-oxypnictides : a new route towards n-type thermoelectric materials,"The iron-oxypnictide compounds, recently reported as a new class of
superconductors when appropriately doped, exhibit large Seebeck coefficients,
of the order of -100 microV/K, while keeping good electrical conductivity.
Their power factor shows a peak at low temperatures, suggesting possible
applications of these materials in thermoelectric cooling modules in the liquid
nitrogen temperature range.",0806.2751v1
2008-06-19,Magnetic Excitation in Artificially Designed Oxygen Molecule Magnet,"We performed inelastic neutron scattering experiment to study magnetic
excitation of O$_2$ molecules adsorbed in microporous compound. The
dispersionless excitation with characteristic intensity modulation is observed
at $\hbar \omega = 7.8$ meV at low temperature. The neutron cross section is
explained by spin dimer model with intradimer distance of 3.1 \AA . Anomalous
behaviour in the temperature dependence is discussed in the context of enhanced
magnetoelasticity in the soft framework of O$_2$ molecule.",0806.3117v1
2008-06-19,Anomalous Spin Response in Non-centrosymmetric Compounds,"We examine static spin susceptibilities $\chi_{\alpha\beta}({\bf q})$ of spin
components $S_{\alpha}$ and $S_{\beta}$ in the non-centrosymmetric tetragonal
system. These show anomalous momentum dependences like $\chi_{xx}({\bf
q})-\chi_{yy}({\bf q})\sim q_x^2-q_y^2$ and $\chi_{xy}({\bf q})+\chi_{yx}({\bf
q})\sim q_x q_y$, which vanish in centrosymmetric systems. The magnitudes of
the anomalous spin susceptibilities are enhanced by the on-site Coulomb
interaction, especially, around an ordering wave vector. The significant and
anomalous momentum dependences of these susceptibilities are explained by a
group theoretical analysis. As the direct probe of the anomalous spin
susceptibility, we propose a polarized neutron scattering experiment.",0806.3214v1
2008-06-20,Theory of magnetization plateaux in the Shastry-Sutherland model,"Using perturbative continuous unitary transformations, we determine the
long-range interactions between triplets in the Shastry-Sutherland model, and
we show that an unexpected structure develops at low magnetization with
plateaux progressively appearing at 2/9, 1/6, 1/9 and 2/15 upon increasing the
inter-dimer coupling. A critical comparison with previous approaches is
included. Implications for the compound SrCu$_2$(BO$_3$)$_2$ are also
discussed: we reproduce the magnetization profile around localized triplets
revealed by NMR, we predict the presence of a 1/6 plateau, and we suggest that
residual interactions beyond the Shastry-Sutherland model are responsible for
the other plateaux below 1/3.",0806.3406v1
2008-06-21,Atomic Structures of Riboflavin (Vitamin B2) and its Reduced Form with Bond Lengths Based on Additivity of Atomic Radii,"It has been shown recently that chemical bond lengths, in general, like those
in the components of nucleic acids, caffeine related compounds, all essential
amino acids, methane, benzene, graphene and fullerene are sums of the radii of
adjacent atoms constituting the bond. Earlier, the crystal ionic distances in
all alkali halides and lengths of many partially ionic bonds were also
accounted for by the additivity of ionic as well as covalent radii. Here, the
atomic structures of riboflavin and its reduced form are presented based on the
additivity of the same set of atomic radii as for other biological molecules.",0806.3462v1
2008-06-25,Anomalous Anisotropic Magnetoresistance in Heavy-Fermion PrFe4P12,"We have investigated the anisotropy of the magnetoresistance in the Pr-based
HF compound PrFe4P12. The large anisotropy of effective mass and its strong
field dependence have been confirmed by resistivity measurements. Particularly
for H||[111], where the effective mass is most strongly enhanced, the non-Fermi
liquid behavior has been observed. Also, we have found the angular dependence
of the magnetoresistance sharply enhanced at H||[111], which is evidently
correlated with both the non-Fermi liquid behavior and the high-field ordered
state (B-phase).",0806.4047v1
2008-06-30,The superconductivity at 18 K in LiFeAs system,"A new iron arsenide superconducting system LiFeAs was found that crystallizes
into a tetragonal structure with space group P4/nmm. The superconductivity with
Tc up to 18 K was observed in the compounds. This simple 111 type layered iron
arsenide superconductor can be viewed as an analogue of the infinite layer
structure of copper oxides.",0806.4688v3
2008-07-04,Field dependence of the thermopower of CeNiSn,"Previously measured thermopower data of CeNiSn exhibit a significant sample
dependence and non-monotonous behavior in magnetic fields. In this paper we
demonstrate that the measured thermopower S(T) may contain a contribution from
the huge Nernst coefficient of the compound, even in moderate fields of 2 T. A
correction for this effect allows to determine the intrinsic field dependence
of S(T). The observed thermopower behavior can be understood from Zeeman
splitting of a V-shaped pseudogap in magnetic fields.",0807.0737v1
2008-07-04,"Short note on magnetic impurities in SmFeAsO$_{1-x}$F$_x$ (x=0, 0.07) compounds revealed by zero-field $^{75}$As NMR","We have performed zero-field $^{75}$As nuclear magnetic resonance study of
SmFeAsO$_{1-x}$F$_x$ (x=0, 0.07) polycrystals in a wide frequency range at
various temperatures. $^{75}$As resonance line was found at around 265 MHz
revealing the formation of the intermetallic FeAs clusters in the new layered
superconductors. We have also demonstrated that NMR is a sensitive tool for
probing the quality of these materials.",0807.0769v2
2008-07-07,Effective Theory of Magnetization Plateaux in the Shastry-Sutherland Lattice,"We use the non-perturbative Contractor-Renormalization method (CORE) in order
to derive an effective model for triplet excitations on the Shastry-Sutherland
lattice. For strong enough magnetic fields, various magnetization plateaux are
observed, e.g. at 1/8, 1/4, 1/3 of the saturation, as found experimentally in a
related compound. Moreover, other stable plateaux are found at 1/9, 1/6 or 2/9.
We give a critical review of previous works and try to resolve some apparent
inconsistencies between various theoretical approaches.",0807.1071v2
2008-07-09,Electron-hole Asymmetry and Quantum Critical Point in Hole-doped BaFe$_2$As$_2$,"We show, from first-principles calculations, that the hole-doped side of
FeAs-based compounds is different from its electron-doped counterparts. The
electron side is characterized as Fermi surface nesting, and SDW-to-NM quantum
critical point (QCP) is realized by doping. For the hole-doped side, on the
other hand, orbital-selective partial orbital ordering develops together with
checkboard antiferromagnetic (AF) ordering without lattice distortion. A unique
SDW-to-AF QCP is achieved, and $J_2$=$J_1/2$ criteria (in the approximate
$J_1&J_2$ model) is satisfied. The observed superconductivity is located in the
vicinity of QCP for both sides.",0807.1401v1
2008-07-10,Dimensional crossover in a spin liquid to helimagnet quantum phase transition,"Neutron scattering is used to study magnetic field induced ordering in the
quasi-1D quantum spin-tube compound Sul--Cu$_2$Cl$_4$ that in zero field has a
non-magnetic spin-liquid ground state. The experiments reveal an incommensurate
chiral high-field phase stabilized by a geometric frustration of the magnetic
interactions. The measured critical exponents $\beta\approx0.235$ and
$\nu\approx0.34$ at $H_c\approx3.7$ T point to an unusual sub-critical scaling
regime and may reflect the chiral nature of the quantum critical point.",0807.1571v2
2008-07-14,Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers,"In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c
up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination,
magnetic susceptibility, electrical resistivity, and specific heat are
reported. The observation of bulk superconductivity in all thermodynamic
properties -- despite strong disorder in the Fe-As layer -- favors an itinerant
picture in contrast to the cuprates and renders a p- or d-wave scenario
unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3)
leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to
a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of
states.",0807.2223v1
2008-07-20,Orbital mixing and nesting in the bilayer manganites La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$,"A first principles study of La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ compounds for
doping levels $0.3\leq x\leq 0.5$ shows that the low energy electronic
structure of the majority spin carriers is determined by strong momentum
dependent interactions between the Mn $e_g$ $d_{x^2-y^2}$ and $d_{3z^2-r^2}$
orbitals, which in addition to an $x$ dependent Jahn-Teller distortion, differ
in the ferromagnetic and antiferromagnetic phases. The Fermi surface exhibits
nesting behavior that is reflected by peaks in the static susceptibility, whose
positions as a function of momentum have a non-trivial dependence on $x$.",0807.3162v2
2008-07-25,Finite-Temperature Phase Diagram of Quasi-One-Dimensional Molecular Conductors: Quantum Monte Carlo Study,"Finite-temperature phase transitions in quasi-one-dimensional quarter-filled
systems are investigated by the extended Hubbard model with electron-lattice
coupling. Using a quantum Monte Carlo method combined with the inter-chain
mean-field approximation, we clarify competing and coexisting behaviors among
charge ordering, dimer Mott, and spin-Peierls states. It is pointed out that an
anharmonicity of lattice distortions plays an important role in multi-critical
behaviors. The results are compared with experimental data for
quasi-one-dimensional molecular conductors such as DCNQI and TMTTF compounds.",0807.4004v2
2008-08-01,Magnetic correlations in La2-xSrxCoO4 studied by neutron scattering : possible evidence for stripe phases,"Spin correlations in LSCO have been studied by neutron scattering. The
commensurate antiferromagnetic order of the parent compound persists on a very
short range up to a Sr content of x=0.3, whereas small amounts of Sr suppress
commensurate antiferromagnetism in cuprates and in nickelates. For x>0.3 we
find incommensurate spin ordering with the modulation closely following the
amount of doping. These incommensurate phases strongly resemble the stripe
phases observed in cuprates and nickelates, but incommensurate magnetic
ordering appears only at larger Sr content in the cobaltates due to a reduced
charge mobility.",0808.0106v1
2008-08-04,Superconductivity in Co-doped SmFeAsO,"Here we report the synthesis and basic characterization of SmFe1-xCoxAsO
(x=0.10, 0.15). The parent compound SmFeAsO itself is not superconducting but
shows an antiferromagnetic order near 150 K, which must be suppressed by doping
before superconductivity emerges. With Co-doping in the FeAs planes,
antiferromagnetic order is destroyed and superconductivity occurs at 15 K.
Similar to LaFe1-xCoxAsO, the SmFe1-xCoxAsO system appears to tolerate
considerable disorder in the FeAs planes. This result is important, which
indicates difference between cuprare superconductors and the iron-based
arsenide ones.",0808.0197v2
2008-08-07,Correlated pressure effects on structure and superconductivity in LaFeAsO0.9F0.1,"We have studied the structural and superconductivity properties of the
compound LaFeAsO0.9F0.1 under pressures up to 32GPa using synchrotron radiation
and diamond anvil cells. We obtain an ambient pressure bulk modulus K_0 =
78(2)GPa, compressibility comparable to some cuprates. At high pressures, the
sample is in the overdoped region, with a linear decrease with pressure
variation of the superconducting transition temperature.",0808.1131v2
2008-08-09,Transport and Magnetic Properties of FexVse2 (x = 0 - 0.33),"We present our results of the effect of Fe intercalation on the structural,
transport and magnetic properties of 1T-VSe2. Intercalation of iron, suppresses
the 110K charge density wave (CDW) transition of the 1T-VSe2. For the higher
concentration of iron, formation of a new kind of first order transition at
160K takes place, which go on stronger for the 33% Fe intercalation.
Thermopower of the FexVSe2 compounds (x = 0 - 0.33), however do not show any
anomaly around the transition. The intercalation of Fe does not trigger any
magnetism in the weak paramagnetic 1T-VSe2, and Fe is the low spin state of
Fe3+.",0808.1333v1
2008-08-09,Optical excitations in Sr$_{2}$CuO$_{3}$,"We investigated excitation spectra of the one-dimensional chain compound
Sr$_{2}$CuO$_{3}$. The small peak at 2.3 eV in the loss function was turned to
correspond to the strong charge transfer transition at 1.8 eV in conductivity.
It has the excitonic character expected in one dimensional extended Hubbard
model of the transition from the lower Hubberd band to the Zhang-Rice singlet
state. The strongest peak at 2.7 eV in the loss function is attributed to the
continuum excitation of the excitonic charge transfer transition. The spectral
weight sum rule is satisfied within these transitions.",0808.1381v2
2008-08-12,Superconductivity in SrNi2As2 Single Crystals,"The electrical resistivity \rho(T) and heat capacity C(T) on single crystals
of SrNi2As2 and EuNi2As2 are reported. While there is no evidence for a
structural transition in either compound, SrNi2As2 is found to be a bulk
superconductor at T_c=0.62 K with a Sommerfeld coefficient of \gamma= 8.7
mJ/mol K^2 and a small upper critical field H_{c2} \sim 200 Oe. No
superconductivity was found in EuNi2As2 above 0.4 K, but anomalies in \rho and
C reveal that magnetic order associated with the Eu^{2+} magnetic moments
occurs at T_m = 14 K.",0808.1694v1
2008-08-20,Resistivity saturation in PrFeAsO$_{1-x}$F$_y$ superconductor: An evidence of strong electron-phonon coupling,"We have measured the resistivity of PrFeAsO$_{1-x}$F$_y$ samples over a wide
range of temperature in order to elucidate the role of electron-phonon
interaction on normal- and superconducting-state properties. The linear T
dependence of $\rho$ above 170 K followed by a saturationlike behavior at
higher temperature is a clear signature of strong electron-phonon coupling.
  From the analysis of T dependence of $\rho$, we have estimated several
normal-state parameters useful for understanding the origin of
superconductivity in this system. Our results suggest that Fe-based
oxypnictides are phonon mediated BCS superconductors like Chevrel phases and
A15 compounds.",0808.2695v1
2008-08-21,"GaMnAs: layers, wires and dots","Thin layers of GaMnAs ferromagnetic semiconductor grown by molecular beam
epitaxy on GaAs(001) substrates were studied. To improve their magnetic
properties the post-growth annealing procedures were applied, using the surface
passivation layers of amorphous arsenic. This post growth treatment effectively
increases the ferromagnetic-to-paramagnetic phase transition temperature in
GaMnAs, and provides surface-rich MnAs layer which can be used for formation of
low dimensional structures such as superlattices. If the surface rich MnAs
layer consists of MnAs dots, then it is possible to grow Mn-doped GaAs
nanowires",0808.2887v1
2008-09-01,Pressure induced superconductivity in the charge density wave compound TbTe3,"A series of high-pressure resistivity measurements on single crystals of
TbTe3 reveal a complex phase diagram involving the interplay of
superconducting, antiferromagnetic and charge density wave orders. The onset of
superconductivity reaches a maximum of ~ 3.5 K (onset) near 75 kbar.",0809.0092v3
2008-09-04,A Possible Phase Transition in beta-pyrochlore Compounds,"We investigate a lattice of interacting anharmonic oscillators by using a
mean field theory and exact diagonalization. We construct an effective
five-state hopping model with intersite repulsions as a model for
beta-pyrochlore AOs_2O_6(A=K, Rb or Cs). We obtain the first order phase
transition line from large to small oscillation amplitude phases as temperature
decreases. We also discuss the possibility of a phase with local electric
polarizations. Our theory can explain the origin of the mysterious first order
transition in KOs_2O_6.",0809.0732v1
2008-09-17,Phonon Density of States in Nd(O$_{1-x}$F$_{x}$)FeAs,"We report measurements of the phonon density-of-states in iron oxypnictide
superconductors by inelastic x-ray scattering. A good agreement with ab-initio
calculations that do not take into account strong electronic correlations is
found, and an unpredicted softening of phonon branches under F doping of these
compounds is observed. Raman scattering experiments lead us to conclude that
this softening is not related to zone center phonons, and consequently imply an
important softening of the relevant phonon branches at finite momentum transfer
Q.",0809.2898v1
2008-09-22,"High-Tc Superconductivity in some Heavy Rare-earth Iron-arsenide REFeAsO1-delta(RE = Ho, Y, Dy and Tb) Compounds","New iron-arsenide superconductors of REFeAsO1-delta (RE = Ho, Y, Dy and Tb)
were successfully synthesized by a high pressure synthesizing method with a
special rapid quenching process, with the onset superconducting critical
temperatures at 50.3 K, 46.5 K, 52.2K and 48.5 K for RE = Ho, Y, Dy and Tb
respectively.",0809.3582v1
2008-10-03,Synthesis and characterization of multiferroic BiMn$_7$O$_{12}$,"We report on the high pressure synthesis of BiMn$_7$O$_{12}$, a manganite
displaying a ""quadruple perovskite"" structure. Structural characterization of
single crystal samples shows a distorted and asymmetrical coordination around
the Bi atom, due to presence of the $6s^{2}$ lone pair, resulting in
non-centrosymmetric space group Im, leading to a permanent electrical dipole
moment and ferroelectric properties. On the other hand, magnetic
characterization reveals antiferromagnetic transitions, in agreement with the
isostructural compounds, thus evidencing two intrinsic properties that make
BiMn$_7$O$_{12}$ a promising multiferroic material.",0810.0667v1
2008-10-07,Possible large-N transitions for complex Wilson loop matrices,"It is shown that a very simple multiplicative random complex matrix model
generalizes the large-N phase structure found in the unitary case: A
perturbative regime is joined to a non-perturbative regime at a point where the
smoothness of some quantities breaks down. A generic complex Wilson loop matrix
in a field theory admitting a 't Hooft planar limit could display a phase
transition in that limit as nonlinear effects become dominating over linear
ones.",0810.1058v1
2008-10-07,Superconductivity under high pressure in LaFeAsO,"Electrical resistivity measurements under high pressures up to 29 GPa were
performed for oxypnictide compound LaFeAsO. We found a pressure-induced
superconductivity in LaFeAsO. The maximum value of Tc is 21 K at ~12 GPa. The
pressure dependence of the Tc is similar to those of LaFeAsO1-xFx series
reported previously.",0810.1153v1
2008-10-08,Pressure-induced superconductivity in Iron pnictide compound SrFe2As2,"Electrical resistivity under high pressure have been measured on nominally
pure SrFe2As2 up to 14 GPa. The resistivity drop appeared with increasing
pressure, and we clearly observed zero resistivity. The maximum of
superconducting transition temperature (Tc) is 38 K. The value is corresponding
to the one of optimally doping AFe2As2 (A=Sr, Ba) system with K+ ions at the
A2+ site.",0810.1377v1
2008-10-15,Electronic band structures and intra-atomic interactions in layered quaternary oxyarsenides LaZnAsO and YZnAsO,"First-principle FLAPW-GGA band structure calculations are employed to obtain
the structural, electronic properties and chemical bonding picture for two
related layered phases, namely, quaternary oxyarsenides LaZnAsO and YZnAsO.
These compounds are found to be direct-transition type semiconductors with the
GGA gaps of about 0.65-1.30 eV. The peculiarities of chemical bonding in these
phases are investigated and discussed in comparison with quaternary oxyarsenide
LaFeAsO - a basic phase for the newly discovered 26-52K superconductors.",0810.2606v1
2008-10-20,Family tree of perovskite-related superconductors,"A simple empirical relation has been found to exist between optimum Tc and
the formal mean cation charge <qc> of perovskite-related superconductors,
covering both conventional superconductors and superconducting cuprates. Tc is
shown to increase exponentially with decreasing <qc>. It is suggested that a
Ba-based cuprate with <qc> about 2 reach a Tc around 200 K. The strong
correlation may be thought of as an indication for a common mechanism of
superconductivity of the whole family of compounds. In addition, the structural
assignment for the 'cubic' high-Tc phase reported by Volkov (Tc = 117 K) to the
orthorhombic BaCuO2.5 prototype is proposed.",0810.3501v1
2008-10-22,The origin of the spontaneous electric polarization,"The phenomenon of the spontaneous electric polarization (ferro- and
antiferroelectricity) is one of the fundamental problems of the solid-state
physics. Although, there has been lot of experimental and theoretical progress,
still needs to be made to understand the origine of the spontaneous electric
polarization. A new microscopic theory that is based on the perfectly elastic
electron-atom and atom-atom collisions, crystal structure and the chemical
composition of the compounds is developed to calculate the critical
temperatures for materials with spontaneous electric polarization. The
reliability of this model was examined by comparing the experimental results
with calculated values.",0810.4088v1
2008-10-27,Macroscopic signature of protected spins in a dense frustrated magnet,"The inability of systems of interacting objects to satisfy all constraints
simultaneously leads to frustration. A particularly important consequence of
frustration is the ability to access certain protected parts of a system
without disturbing the others. For magnets such ""protectorates"" have been
inferred from theory and from neutron scattering, but their practical
consequences have been unclear. We show that a magnetic analogue of optical
hole-burning can address these protected spin clusters in a well-known,
geometrically frustrated Heisenberg system, gadolinium gallium garnet. Our
measurements additionally provide a resolution of a famous discrepancy between
the bulk magnetometry and neutron diffraction results for this magnetic
compound.",0810.4744v1
2008-11-01,Room Temperature Ferromagnetic Semiconductor Rutile Ti1-xCoxO2-δ Epitaxial Thin Films Grown by Sputtering Method,"Room temperature ferromagnetic semiconductor rutile Ti1-xCoxO2-\delta (101)
epitaxial thin films were grown on r-sapphire substrates by a dc sputtering
method. Ferromagnetic magnetization, magnetic circular dichroism, and anomalous
Hall effect were clearly observed at room temperature in sputter-grown films
for the first time. The magnetization value is nearly as large as 3\mu B/Co
that is consistent with the high spin state Co2+ in this compound recently
established by spectroscopic methods. Consequently, its originally large
magneto-optical response is further enhanced.",0811.0073v1
2008-11-04,A Hilbert Space Representation of Generalized Observables and Measurement Processes in the ESR Model,"The extended semantic realism (ESR) model recently worked out by one of the
authors embodies the mathematical formalism of standard (Hilbert space) quantum
mechanics in a noncontextual framework, reinterpreting quantum probabilities as
conditional instead of absolute. We provide here a Hilbert space representation
of the generalized observables introduced by the ESR model that satisfy a
simple physical condition, propose a generalization of the projection
postulate, and suggest a possible mathematical description of the measurement
process in terms of evolution of the compound system made up of the measured
system and the measuring apparatus.",0811.0531v2
2008-11-05,"High-pressure, transport, and thermodynamic properties of CeTe3","We have performed high-pressure, electrical resistivity, and specific heat
measurements on CeTe3 single crystals. Two magnetic phases with nonparallel
magnetic easy axes were detected in electrical resistivity and specific heat at
low temperatures. We also observed the emergence of an additional phase at high
pressures and low temperatures and a possible structural phase transition
detected at room temperature and at 45 kbar, which can possibly be related with
the lowering of the charge-density wave transition temperature known for this
compound.",0811.0792v2
2008-11-21,Fluorine effect in layered oxypnictide LaOFeAs,"Theoretical calculations under the scheme of WIEN2k computer package had been
performed on the pristine compound LaOFeAs, as well as on LaO1-xFxFeAs. One
factor crucial to the manifestation of superconductivity seems to be fluorine
doping; hence we search for its effect. Paying close attention to Fe d-orbitals
upon doping of F by O, at first, Fe d-orbitals have dz2 symmetry, changing
gradually to something akin to dx2-y2 which seems more prone to conductivity
than the former one. This issue agree with the accepted results happened in the
copper-based high-temperature superconductors.",0811.3473v1
2008-12-04,Generation of Total Angular Momentum Eigenstates in Remote Qubits,"We propose a scheme enabling the universal coupling of angular momentum of
$N$ remote noninteracting qubits using linear optical tools only. Our system
consists of $N$ single-photon emitters in a $\Lambda$-configuration that are
entangled among their long-lived ground-state qubits through suitably designed
measurements of the emitted photons. In this manner, we present an
experimentally feasible algorithm that is able to generate any of the $2^N$
symmetric and nonsymmetric total angular momentum eigenstates spanning the
Hilbert space of the $N$-qubit compound.",0812.0959v2
2008-12-11,Temperature-driven phase transitions in SrBi$_2$Ta$_2$O$_9$ from first-principles calculations,"The phase transition sequence of SrBi$_2$Ta$_2$O$_9$ is investigated using a
shell model with parameters fitted to first-principles calculations. We show
that the complex interplay between polar and nonpolar instabilities leads to
the presence of two phase transitions, corroborating the existence of an
intermediate orthorhombic paraelectric phase. This phase is characterized by
the rotation of the TaO$_6$ octahedra around the a-axis. We show that this
phase can be also detected from the dielectric response of the material. The
present approach constitutes a powerful tool for a theoretical prediction of
intermediate phases, not yet observed experimentally, in other Aurivillius
compounds.",0812.2175v1
2008-12-31,An effective 1-band model for the cuprate superconductors,"Starting from the copper-oxygen Hamiltonian of the CuO2 planes, we derive
analytically an extended 1-band Hubbard Hamiltonian for the electrons on copper
sites, through a canonical transformation which eliminates the oxygen sites.
The model sustains a variety of phases : checkerboard states, stripes,
antiferromagnetism, local pairs and mixtures thereof. This approach may be
helpful in understanding what is so special about the CuO2 planes, as opposed
to other compounds.",0901.0097v2
2009-01-11,A Possible Theoretical Model For Studying Superconductivity In Fe-based Systems,"A theoretical approach with a microscopic model is proposed for the observed
""high temperature superconductivity"" in the Iron-based compounds. The above
scheme takes into account two important aspects viz. (i) superconducting
transition close to magnetic ordering and (ii) the layered structure. From the
calculation of the superconducting transition temperature, it is shown that in
the Fe-based superconductors the magnetic mechanism for superconductivity,
operating through the effective attractive Coulomb interaction within the
framework of the Fermi Liquid theory, is highly plausible.",0901.1438v1
2009-01-12,"Spin-Peierls-like transition in AFe$_2$As$_2$(A=Ba, Sr)","From first-principles density functional theory calculations combined with
varying temperature Raman experiments, we show that AFe$_2$As$_2$ (A=Ba, Sr),
the parent compound of the FeAs based superconductors of the new structural
family, undergoes a spin-Peierls-like phase transition at low temperature. The
coupling between the phonons and frustrated spins is proved to be the main
cause of the structural transition from the tetragonal to orthorhombic phase.
These results well explain the magnetic and structural phase transitions in
AFe$_2$As$_2$(A=Ba, Sr) recently observed by neutron scattering.",0901.1525v1
2009-01-15,Persistent and Reversible Phase Control in GdMnO$_3$ near the Phase Boundary,"We have investigated temperature and magnetic-field dependence of dielectric
properties in the orthorhombic GdMnO$_3$ single crystal which is located near
the phase boundary between the ferroelectric/spiral-antiferromagnetic phase and
the paraelectric/$A$-type-antiferromagnetic one. In this compound, strong phase
competition between these two phases results in a unique phase diagram with
large temperature and magnetic-field hystereses. Based on the phase diagram, we
have successfully demonstrated the persistent and reversible phase switching
between them by application of magnetic fields.",0901.2181v1
2009-01-19,Glass-like Thermal-Transport in Symmetry-Broken Clathrates,"We present the quantitative interpretation for the glass-like behavior of
thermal conductivities $\kappa(T)$ for type-I clathrate compounds involving
off-centered guest ions. It is shown that the dipole-dipole interaction
generated in cage/guest-ion systems is crucial to reproduce the characteristics
of thermal conductivities for these symmetry-broken clathrates. The above
scenario also explains well the difference of $\kappa(T)$ between the $p$-type
and the $n$-type $\beta$-BGS found recently by K. Suekuni et al. [Phys. Rev. B,
77 (2008) 235119.]",0901.2957v2
2009-02-03,Double-stage continuous-discontinuous superconducting phase transition in the Pauli paramagnetic limit of a 3D superconductor: the URu$%_{2}$Si$_{2}$ case,"The sharp suppression of the de-Haas van-Alphen oscillations observed in the
mixed superconducting (SC) state of the heavy fermion compound URu$_{2}$Si$%
_{2}$ is shown to confirm a theoretical prediction of a narrow double-stage SC
phase transition, smeared by fluctuations, in a 3D paramagnetically-limitted
superconductor. The predicted scenario of a second order transition to a
nonuniform (FFLO) state followed by a first order transition to a uniform SC
state, obtained by using a non-perturbative approach, is also found to be
consistent with recent thermal conductivity measurements performed on this
material.",0902.0438v1
2009-02-06,Towards the Theory of Isotope Effect of the London Penetration Depth in Cuprates,"The expressions for the superfluid density have been discussed in both weak
and strong coupling approaches. The numerical calculations of temperature and
isotope composition dependencies have been performed for a number of High-Tc
compounds. The tight-binding parameters and corresponding Fermi surfaces are
taken in accord to the available photoemission data.",0902.1029v2
2009-02-06,Multiple phase transitions in single-crystalline Na$_{1-δ}$FeAs,"Specific heat, resistivity, susceptibility and Hall coefficient measurements
were performed on high-quality single crystalline Na$_{1-\delta}$FeAs. This
compound is found to undergo three successive phase transitions at around 52,
41, and 23 K, which correspond to structural, magnetic and superconducting
transitions, respectively. The Hall effect result indicates the development of
energy gap at low temperature due to the occurrence of spin-density-wave
instability. Our results provide direct experimental evidence of the magnetic
ordering in the nearly stoichiometric NaFeAs.",0902.1100v2
2009-02-15,Optimal Trade Execution in Illiquid Markets,"We study optimal trade execution strategies in financial markets with
discrete order flow. The agent has a finite liquidation horizon and must
minimize price impact given a random number of incoming trade counterparties.
Assuming that the order flow $N$ is given by a Poisson process, we give a full
analysis of the properties and computation of the optimal dynamic execution
strategy. Extensions, whereby (a) $N$ is a fully-observed regime-switching
Poisson process; and (b) $N$ is a Markov-modulated compound Poisson process
driven by a hidden Markov chain, are also considered.
  We derive and compare the properties of the three cases and illustrate our
results with computational examples.",0902.2516v1
2009-02-17,Simulation of the enhanced Curie temperature in Mn_5Ge_3C_x compounds,"Mn_5Ge_3C_x films with x>0.5 were experimentally shown to exhibit a strongly
enhanced Curie temperature T_C compared to Mn_5Ge_3. In this letter we present
the results of our first principles calculations within Green's function
approach, focusing on the effect of carbon doping on the electronic and
magnetic properties of the Mn_5Ge_3. The calculated exchange coupling constants
revealed an enhancement of the ferromagnetic Mn-Mn interactions mediated by
carbon. The essentially increased T_C in Mn_5Ge_3C is well reproduced in our
Monte Carlo simulations and together with the decrease of the total
magnetisation is found to be predominantly of an electronic nature.",0902.2913v1
2009-02-25,"Production of $^{93,94,95,96}$Tc through $^{7}$Li+$^{nat}$Zr and $^{9}$Be+$^{nat}$Y reactions: Measurement of excitation functions","For the first time two separate production routes of Tc radionuclides have
been studied bombarding $^{7}$Li on $^{nat}$Zr and $^{9}$Be on $^{89}$Y.
Excitation functions of the evaporation residues produced in those reactions
have been measured using stacked-foil technique followed by the
$\gamma$-spectrometric studies in the energy range 37-45 MeV and 30-48 MeV
respectively. Measured excitation functions have been compared with those
calculated using the nuclear reaction model codes PACE-II and ALICE91.
Experimental results show good agreement with the theoretical predictions.
Compound nuclear reaction is the key mechanism in producing evaporation
residues.",0902.4309v1
2009-03-05,Aromatic Borozene,"Based on our comprehensive theoretical investigation and known experimental
results for small boron clusters, we predict the existence of a novel aromatic
inorganic molecule, B12H6. This molecule, which we refer to as borozene, has
remarkably similar properties to the well-known benzene. Borozene is planar,
possesses a large first excitation energy, D3h symmetry, and more importantly
is aromatic. Furthermore, the calculated anisotropy of the magnetic
susceptibility of borozene is three times larger in absolute value than for
benzene. Finally, we can show that borozene molecules may be fused together to
give larger aromatic compounds with even larger anisotropic susceptibilities.",0903.1042v1
2009-03-09,d-Wave Spin Density Wave phase in the Attractive Hubbard Model with Spin Polarization,"We investigate the possibility of unconventional spin density wave (SDW) in
the attractive Hubbard model with finite spin polarization. We show that
pairing and density fluctuations induce the transverse d-wave SDW near the
half-filling. This novel SDW is related to the d-wave superfluidity induced by
antiferromagnetic spin fluctuations, in the sense that they are connected with
each other through Shiba's attraction-repulsion transformation. Our results
predict the d-wave SDW in real systems, such as cold Fermi atom gases with
population imbalance and compounds involving valence skipper elements.",0903.1491v1
2009-03-12,Mott transition in two-dimensional frustrated compounds,"The phase diagrams of isotropic and anisotropic triangular lattices with
local Coulomb interactions are evaluated within cluster dynamical mean field
theory. As a result of partial geometric frustration in the anisotropic
lattice, short range correlations are shown to give rise to reentrant behavior
which is absent in the fully frustrated isotropic limit. The qualitative
features of the phase diagrams including the critical temperatures are in good
agreement with experimental data for the layered organic charge transfer salts
kappa-(BEDT-TTF)_2Cu[N(CN)_2]Cl and kappa-(BEDT-TTF)_2Cu_2(CN)_3.",0903.2063v1
2009-03-18,State reconstruction of finite dimensional compound systems via local projective measurements and one-way classical communication,"For a finite dimensional discrete bipartite system, we find the relation
between local projections performed by Alice, and Bob post-selected state
dependence on the global state submatrices. With this result the joint state
reconstruction problem for a bipartite system can be solved with strict local
projections and one-way classical communication. The generalization to
multipartite systems is straightforward.",0903.3249v1
2009-03-23,"Vibrational spectra of copper polysilicate, CuSiO3","This is a representation of the first Raman and IR / FIR spectra for
orthorhombic copper polysilicate, CuSiO3, measured at room temperature on
polycrystalline samples and a comparison of the optical phonons with those
observed for the spin-Peierls compound CuGeO3. CuSiO3 represents a further
example of a quasi-one-dimensional spin = 1/2 antiferromagnetic Heisenberg
chain system. A mode assignment for the silicate is given. From the analysis of
the Davydov doublets a reduced intralayer- to-interlayer bond strength of the
silicate in comparison to the germanate is obtained allowing for different
magnetic response at low temperature.",0903.3901v1
2009-03-28,Magnetic structure and charge ordering in Fe3BO5 ludwigite,"The crystal and magnetic structures of the three-leg ladder compound Fe3BO5
have been investigated by single crystal x-ray diffraction and neutron powder
diffraction. Fe3BO5 contains two types of three-leg spin ladders. It shows a
charge ordering transition at 283 K, an antiferromagnetic transition at 112 K,
ferromagnetism below 70 K and a weak ferromagnetic behavior below 40K. The
x-ray data reveal a smooth charge ordering and an incomplete charge
localization down to 110K. Below the first magnetic transition, the first type
of ladders orders as ferromagnetically coupled antiferromagnetic chains, while
below 70K the second type of ladders orders as antiferromagnetically coupled
ferromagnetic chains.",0903.4945v1
2009-03-29,Detection of Striped Superconductors Using Magnetic Field Modulated Josephson Effect,"In a very interesting recent Letter\cite{berg}, the authors suggested that a
novel form of superconducting state is realized in La$_{2-x}$Ba$_x$CuO$_4$ with
$x$ close to 1/8. This suggestion was based on experiments\cite{li} on this
compound which found predominantly two-dimensional (2D) characters of the
superconducting state, with extremely weak interplane coupling. Later this
specific form of superconducting state was termed striped
superconductors\cite{berg08}. The purpose of this note is to point out that the
suggested form\cite{berg} of the superconducting order parameter can be
detected directly using magnetic field modulated Josephson effect.",0903.5052v2
2009-03-31,High-reflectivity broadband distributed Bragg reflector lattice matched to ZnTe,"We report on the realization of a high quality distributed Bragg reflector
with both high and low refractive index layers lattice matched to ZnTe. Our
structure is grown by molecular beam epitaxy and is based on binary compounds
only. The high refractive index layer is made of ZnTe, while the low index
material is made of a short period triple superlattice containing MgSe, MgTe,
and ZnTe. The high refractive index step of Delta_n=0.5 in the structure
results in a broad stopband and the reflectivity coefficient exceeding 99% for
only 15 Bragg pairs.",0903.5492v1
2009-04-02,Persistence and Success in the Attention Economy,"A hallmark of the attention economy is the competition for the attention of
others. Thus people persistently upload content to social media sites, hoping
for the highly unlikely outcome of topping the charts and reaching a wide
audience. And yet, an analysis of the production histories and success dynamics
of 10 million videos from \texttt{YouTube} revealed that the more frequently an
individual uploads content the less likely it is that it will reach a success
threshold. This paradoxical result is further compounded by the fact that the
average quality of submissions does increase with the number of uploads, with
the likelihood of success less than that of playing a lottery.",0904.0489v1
2009-04-04,Detergents and chaotropes for protein solubilization before two-dimensional electrophoresis,"Because of the outstanding ability of two-dimensional electrophoresis to
separate complex mixtures of intact proteins, it would be advantageous to apply
it to all types of proteins, including hydrophobic and membrane proteins.
Unfortunately, poor solubility hampers the analysis of these molecules. As
these problems arise mainly in the extraction and isoelectric focusing steps,
the solution is to improve protein solubility under the conditions prevailing
during isoelectric focusing. This chapter describes the use of chaotropes and
novel detergents to enhance protein solubility during sample extraction and
isoelectric focussing, and discusses the contribution of these compounds to
improving proteomic analysis of membrane proteins.",0904.0685v1
2009-04-09,On the Calculation of Puckering Free Energy Surfaces,"Cremer-Pople puckering coordinates appear to be the natural candidate
variables to explore the conformational space of cyclic compounds, and in
literature different parametrizations have been used to this end. However,
while every parametrization is equivalent in identifying conformations, it is
not obvious that they can also act as proper collective variables for the
exploration of the puckered conformations free energy surface. It is shown that
only the polar parametrization is fit to produce an unbiased estimate of the
free energy landscape. As an example, the case of a six-membered ring,
glucuronic acid, is presented, showing the artefacts that are generated when a
wrong parametrization is used.",0904.1473v1
2009-04-10,Properties of KCo$_2$As$_2$ and Alloys with Fe and Ru: Density Functional Calculations,"Electronic structure calculations are presented for KCo$_2$As$_2$ and alloys
with KFe$_2$As$_2$ and KRu$_2$As$_2$. These materials show electronic
structures characteristic of coherent alloys, with a similar Fermi surface
structure to that of the Fe-based superconductors, when the $d$ electron count
is near six per transition metal. However, they are less magnetic than the
corresponding Fe compounds. These results are discussed in relation to
superconductivity.",0904.1607v1
2009-04-10,First passage time law for some jump-diffusion processes : existence of a density,"Let (Xt, t >= 0) be a diffusion process with jumps, sum of a Brownian motion
with drift and a compound Poisson process. We consider T_x the first hitting
time of a fixed level x > 0 by (Xt, t >= 0). We prove that the law of T_x has a
density (defective when E(X1) < 0) with respect to the Lebesgue measure.",0904.1669v3
2009-04-29,Number of Measurements in Sparse Signal Recovery,"We analyze the asymptotic performance of sparse signal recovery from noisy
measurements. In particular, we generalize some of the existing results for the
Gaussian case to subgaussian and other ensembles. An achievable result is
presented for the linear sparsity regime. A converse on the number of required
measurements in the sub-linear regime is also presented, which cover many of
the widely used measurement ensembles. Our converse idea makes use of a
correspondence between compressed sensing ideas and compound channels in
information theory.",0904.4525v1
2009-05-05,"A new material for hydrogen storage, ScAl0.8Mg0.2","A novel aluminium rich alloy for hydrogen storage has been discovered,
ScAl0.8Mg0.2, which has superior properties regarding hydrogen storage
capacity, kinetics and stability towards air oxidation in comparison to
hydrogen absorption in state-of-the-art intermetallic compounds. Detailed
analysis of the hydrogen absorption in ScAl0.8Mg0.2 has been performed using in
situ synchrotron radiation powder X-ray diffraction, neutron powder diffraction
and quantum mechanical calculations. The results from calculations and
experiments are in good agreement with each other.",0905.0630v2
2009-05-07,Electronic Transport Properties of Carbon NanoBuds,"Fullerene functionalized carbon nanotubes -- NanoBuds -- form a novel class
of hybrid carbon materials, which possesses many advantageous properties as
compared to the pristine components. Here, we report a theoretical study of the
electronic transport properties of these compounds. We use both ab initio
techniques and tight-binding calculations to illustrate these materials'
transmission properties, and give physical arguments to interpret the numerical
results. Specifically, above the Fermi energy we find a strong reduction of
electron transmission due to localized states in certain regions of the
structure while below the Fermi energy all considered structures exhibit a
high-transmission energy band with a geometry dependent width.",0905.0969v1
2009-05-07,Consequences of lattice imperfections and interchain couplings for the critical properties of spin-1/2 chain compounds,"To allow for a comparison of theoretical predictions for spin chains with
experimental data, it is often important to take impurity effects as well as
interchain couplings into account. Here we present the field theory for finite
spin chains at finite temperature and calculate experimentally measurable
quantities like susceptibilities and nuclear magnetic resonance spectra. For
the interchain couplings we concentrate on geometries relevant for cuprate spin
chains like Sr$_2$CuO$_3$ and SrCuO$_2$. The field theoretical results are
compared to experimental as well as numerical data obtained by the density
matrix renormalization group.",0905.1075v1
2009-05-14,MgN: a new promising material for spintronic applications,"Density functional theory calculations demonstrate that rocksalt MgN is a
magnetic material at the verge of half-metallicity, with an electronic
structure robust against strong correlations and spin-orbit interaction.
Furthermore the calculated heat of formation describes the compound as
metastable and suggests that it can be fabricated by tuning the relative Mg and
N abundance during growth. Intriguingly the equilibrium lattice constant is
close to that of MgO, so that MgN is likely to form as an inclusion during the
fabrication of N-doped MgO. We then speculate that the MgO/MgN system may
represent a unique materials platform for magnetic tunnel junctions not
incorporating any transition metals.",0905.2387v1
2009-05-19,Magnetic and electrical properties of dhcp NpPd3 and U(1-x)Np(x)Pd3,"We have made an extensive study of the magnetic and electrical properties of
double-hexagonal closepacked NpPd3 and a range of U(1-x)Np(x)Pd3 compounds with
x=0.01, 0.02, 0.05, and 0.50 using magnetization, magnetic susceptibility,
electrical resistivity, and heat capacity measurements on polycrystalline
samples, performed in the temperature range 2-300 K and in magnetic fields up
to 9 T. Two transitions are observed in NpPd3 at T=10 and 30 K. Dilute Np
samples (x<0.05) exhibit quadrupolar transitions, with the transition
temperatures reduced from those of pure UPd3.",0905.3100v1
2009-05-22,Correlation effects in p-electron magnets: the case of RbO_2,"We present results of GGA+U calculations for the ""d^0 magnet"" RbO_2, where
magnetic properties are due to partially filled oxygen p orbitals. We show that
on-site interactions on the oxygen sites lead to a strong tendency towards the
formation of an orbitally polarized insulating state, in contrast to the
half-metallic behavior predicted for this class of compounds within pure
LDA/GGA. The obtained energy differences between different orbitally ordered
configurations are sizeable, indicating an orbital ordering temperature higher
than the antiferromagnetic Neel temperature of ~15 K. Our results demonstrate
the importance of correlation effects in p electron magnets such as RbO_2.",0905.3721v1
2009-05-29,"Spin-lattice coupling, frustration and magnetic order in multiferroic RMnO3","We have performed high resolution neutron diffraction and inelastic neutron
scattering experiments in the frustrated multiferroic hexagonal compounds RMnO3
(R=Ho, Yb, Sc, Y), which provide evidence of a strong magneto-elastic coupling
in the the whole family. We can correlate the atomic positions, the type of
magnetic structure and the nature of the spin waves whatever the R ion and
temperature. The key parameter is the position of the Mn ions in the unit cell
with respect to a critical threshold of 1/3, which determines the sign of the
coupling between Mn triangular planes.",0905.4824v1
2009-06-08,"Study of magnetic interactions in a spin liquid, Sr3NiPtO6 using density functional approach","We investigate the magnetic interactions in Sr3NiPtO6, characterized to be a
spin liquid using ab initio calculations. The results reveal a novel metal to
insulator transition due to finite exchange interaction strength; the magnetic
solutions (independent of magnetic ordering) are large band gap insulators,
while the non-magnetic solution is metallic. The Ni moment is found to be large
and the coupling among intra-chain Ni moments is antiferromagnetic unlike other
compounds in this family. These results, thus, reveal the importance of
intra-chain antiferromagnetic interaction in addition to geometrical
frustration to derive spin liquid phase.",0906.1404v1
2009-06-12,Identifying the pairing mechanism in Fe-As based superconductors: gaps and isotope effects,"The temperature dependencies of the coupled superconducting gaps, observed in
Fe-As based superconducting compounds is calculated and a universal temperature
scaling observed which is only present if the coupled order parameters both
have s-wave symmetry. Predictions for possible isotope effects on the
transition temperature are made if phonons are involved in the pairing or
polaronic effects are of importance. Comparison to experimental data is given
where these are available.",0906.2283v1
2009-06-12,Superconductivity in Fe and As based compounds: a bridge between MgB2 and cuprates,"By interpreting various experimental data for the new high temperature FeAs
type superconductors in terms of lattice mediated multi gap superconductivity,
it is shown that these systems strongly resemble MgB2, however, with the
distinction that local polaronic lattice effects exist. This fact establishes a
connection to cuprate high temperature superconductors where polaron formation
is essential for the pseudogap phase and the unconventional isotope effects
observed there. However, similar to MgB2 and in contrast to cuprates the two
superconducting gaps in the Fe-As based materials are isotropic s-wave gaps.",0906.2286v1
2009-06-12,Magnetic Anisotropy in Single Crystalline CeAu$_{2}$In$_{4}$,"We have grown the single crystals of LaAu$_{2}$In$_{4}$ and
CeAu$_{2}$In$_{4}$ by high temperature solution method and report on the
anisotropic magnetic behavior of CeAu$_{2}$In$_{4}$ . The compounds crystallize
in an orthorhombic structure with space group \textit {Pnma}.
LaAu$_{2}$In$_{4}$ shows a Pauli-paramagnetic behavior. CeAu$_{2}$In$_{4}$ do
not order down to 1.8 K. The easy axis of magnetization for CeAu$_{2}$In$_{4}$
is along [010] direction. The magnetization data is analyzed on the basis of
crystalline electric field (CEF) model.",0906.2299v2
2009-06-18,Possibility of Experimental Determination of Reliable Parameters of the Compound-State Gamma-Decay and Some Errors of Analysis: Mo-96 as an Example,"Comparison between potential possibilities and inevitable systematic errors
of one- and two-step reactions for obtaining of maximum reliable data on level
density and radiative strength functions after decay of excited levels of
complicated nuclei has been performed. It was shown that the use for this aim
of two-step reactions instead of one-step reactions provides for potential
possibility to decrease systematical errors of mentioned nuclear parameters, as
minimum, by several times.",0906.3333v1
2009-07-01,The Stoichiometry of FeSe,"Tetragonal iron selenide, FeSe, the layered parent compound of the recently
discovered superconducting arsenide family, has previously been shown to be non
magnetic and superconducting with a critical temperature near 8 K. There has,
however, been a lack of consensus as to whether selenium vacancies present due
to large deviations from ideal stoichiometry are required to give rise to the
superconductivity. Here we describe the results of experiments that demonstrate
simply that superconducting iron selenide can only be synthesized as a pure
material when near stoichiometric (i.e. FeSe). Significant selenium deficiency
or excess gives rise to secondary magnetic phases, and a suppression of the
superconductivity.",0907.0174v1
2009-07-08,Magnetic hysteresis in a molecular Ising ferrimagnet: Glauber dynamics approach,"Motivated by recent experimental results reporting giant coercive fields in
Co(II)-based molecular magnets we present a theory of hysteresis phenomena
based on the Glauber stochastic dynamics. Unusual form of hysteresis loops is
similar to those of found in Co-based quasi-one-dimensional ferrimagnet CoPhOMe
at low temperatures. Temperature dependence of the coercive field has a
characteristic form with an inflection that may serve as an indicator of the
Glauber dynamics in real compounds. A relevance of the model for other Co-based
molecular magnets is discussed.",0907.1348v1
2009-07-09,Exploring colourful holographic superconductors,"We explore a class of holographic superconductors built using non-abelian
condensates on probe branes in conformal and non-conformal backgrounds. These
are shown to exhibit behaviour of the specific heat which resembles that of
heavy fermion compounds in the superconducting phase. Instead of showing
BCS-like exponential behaviour, the specific heat is polynomial in the
temperature. It exhibits a jump at the critical temperature, in agreement with
real-world superconductors. We also analyse the behaviour of the energy gap and
the AC and DC conductivities, and find that the systems can be either
semi-conducting or metallic just above the critical temperature.",0907.1508v1
2009-07-14,Pattern Based Term Extraction Using ACABIT System,"In this paper, we propose a pattern-based term extraction approach for
Japanese, applying ACABIT system originally developed for French. The proposed
approach evaluates termhood using morphological patterns of basic terms and
term variants. After extracting term candidates, ACABIT system filters out
non-terms from the candidates based on log-likelihood. This approach is
suitable for Japanese term extraction because most of Japanese terms are
compound nouns or simple phrasal patterns.",0907.2452v1
2009-07-15,Decompounding on compact Lie groups,"Noncommutative harmonic analysis is used to solve a nonparametric estimation
problem stated in terms of compound Poisson processes on compact Lie groups.
This problem of decompounding is a generalization of a similar classical
problem. The proposed solution is based on a char- acteristic function method.
The treated problem is important to recent models of the physical inverse
problem of multiple scattering.",0907.2601v1
2009-07-30,Magnetoelectric response of multiferroic BiFeO3 and related materials,"We present a first-principles scheme for computing the magnetoelectric
response of multiferroics. We apply our method to BiFeO3 (BFO) and related
compounds in which Fe is substituted by other magnetic species. We show that
under certain relevant conditions -- i.e., in absence of incommensurate spin
modulation, as in BFO thin films and some BFO-based solid solutions -- these
materials display a large linear magnetoelectric response. Our calculations
reveal the atomistic origin of the coupling and allow us to identify the most
promising strategies to enhance it.",0907.5281v1
2009-08-10,Phase diagram of an anisotropic frustrated ferromagnetic spin-1/2 chain in a magnetic field: a density matrix renormalization group study,"We study the phase diagram of a frustrated spin-1/2 ferromagnetic chain with
anisotropic exchange interactions in an external magnetic field, using the
density matrix renormalization group method. We show that an easy-axis
anisotropy enhances the tendency towards multimagnon bound states, while an
easy-plane anisotropy favors chirally ordered phases. In particular, a moderate
easy-plane anisotropy gives rise to a quantum phase transition at intermediate
magnetization. We argue that this transition is related to the finite-field
phase transition experimentally observed in the spin-1/2 compound LiCuVO_4.",0908.1281v2
2009-08-28,"Structural and electronic properties of new ""122"" pnictogen-free superconductor SrPd2Ge2 as compared with SrNi2Ge2 and SrNi2As2: first principles calculations","Very recently the new low-temperature (TC ~ 3K) superconductor (SC) SrPd2Ge2
has been reported. This compound is isostructural with curently intensively
studied group of so-called ""122"" SC's (based on tetragonal AM2Pn2 phases, where
A are Sr, Ba; M are d metals and Pn are pnictogens: As or P), but it is
pnictogen-free. Here, by means of first-principle FLAPW-GGA calculations, we
have studied the electronic structure of new SC SrPd2Ge2. The band structure,
total and partial densities of states and Fermi surface topology for SrPd2Ge2
are evaluated and discussed in comparison with those of isostructural SrNi2Ge2
and SrNi2As2 phases.",0908.4135v1
2009-08-29,Spin-Phonon Coupling in Iron Pnictide Superconductors,"The magnetic moment in the parent phase of the iron-pnictide superconductors
varies with composition even when the nominal charge of iron is unchanged. We
propose the spin-lattice coupling due to the magneto-volume effect as the
primary origin of this effect, and formulate a Landau theory to describe the
dependence of the moment to the Fe-As layer separation. We then compare the
superconductive critical temperature of doped iron pnictides to the local
moment predicted by the theory, and suggest that the spin-phonon coupling may
play a role in the superconductivity of this compound.",0908.4361v1
2009-09-07,Pressure effects on FeSe family superconductors,"We investigated the pressure effects on the FeSe superconductor and the
related compounds. Pressure dependence of superconducting transition
temperature (Tc) for FeSe0.8S0.2 exhibits a dome-shaped behavior below 0.76
GPa. On the other hand, the Tc of FeSe0.25Te0.75 linearly increases up to 0.99
GPa. Here we discuss the relation between the physical pressure effects and the
chemical pressure effects on the FeSe system.",0909.1268v1
2009-09-09,Flexomagnetic effect in Mn-based antiperovskites,"We report appearance of the net magnetization in Mn-based antiperovskite
compounds as a result of the external strain gradient (flexomagnetic effect).
In particular, we describe the mechanism of the magnetization induction in the
Mn_{3}GaN at the atomic level in terms of the behavior of the local magnetic
moments (LMM) of the Mn atoms. We show that the flexomagnetic effect is linear
and results from the non-uniformity of the strain, i.e. it is absent not only
in the ground state but also when the applied external strain is uniform. We
estimate the flexomagnetic coefficient to be 1.95 mu_{B}*angstrom. We show that
at the moderate values of the strain gradient (~ 0.1%) the flexomagnetic
contribution is the only non-vanishing input to the induced magnetization.",0909.1813v1
2009-09-13,Spin dimers under staggered and random field in Cu$_2$Fe$_2$Ge$_4$O$_{13},"We study $S=1/2$ dimer excitation in a coupled chain and dimer compound
Cu$_2$Fe$_2$Ge$_4$O$_{13} by inelastic neutron scattering technique. The Zeeman
split of the dimer triplet by a staggered field is observed at low temperature.
With the increase of temperature the effect of random field is detected by a
drastic broadening of the triplet excitation. Basic dynamics of dimer in the
staggered and random fields are experimentally identified in
Cu$_2$Fe$_2$Ge$_4$O$_{13}.",0909.2402v2
2009-10-12,"Nucleus-nucleus potential, energy dissipation and mass dispersion in fusion and transfer reactions","The nucleus-nucleus potential and energy dissipation in fusion reactions are
obtained from microscopic mean-field dynamics. The deduced potentials nicely
reproduce the one extracted from experimental data. Energy dissipation shows a
universal behaviour between different reactions. Also, the dispersion of mass
distribution in transfer reaction is investigated in a stochastic mean-field
dynamics. By including initial fluctuations in collective space, the
description of the dispersion is much improved compared to that of mean field
only. The result is consistent with the macroscopic phenomenological analysis
of the experimental data.",0910.2194v1
2009-10-23,First-principles dynamical CPA to finite-temperature magnetism of transition metals,"We present here the first-principles dynamical CPA (coherent potential
approximation) combined with the tight-binding LMTO LDA+U method towards
quantitative calculations of the electronic structure and magnetism at finite
temperatures in transition metals and compounds. The theory takes into account
the single-site dynamical charge and spin fluctuations using the functional
integral technique as well as an effective medium. Numerical results for Fe,
Co, and Ni show that the theory explains quantitatively the high-temperature
properties such as the effective Bohr magneton numbers and the excitation
spectra in the paramagnetic state, and describes the Curie temperatures
semiquantitatively.",0910.4486v1
2009-10-26,Electron transport through symmetrical junctions of semimetal graphene ribbons,"Based on the nearest-neighbor tight-binding model, we present analytical
description of low-energy electron transport through a symmetrical junction of
two semimetal armchair ribbons. The results obtained demonstrate the
transmission suppression in the vicinity of the neutrality point except for the
junction of the ribbons consisting of 3p-1 and 3p+5 dimer lines, p/2 is odd.
Unlike other interconnections, these compounds are shown to be free of even
local levels arising at the junction interface and exhibit electron
backscattering to be inversely as the square of p+1.",0910.4848v1
2009-10-29,Genus expansion for real Wishart matrices,"We present an exact formula for moments and cumulants of several real
compound Wishart matrices in terms of an Euler characteristic expansion,
similar to the genus expansion for complex random matrices. We consider their
asymptotic values in the large matrix limit: as in a genus expansion, the terms
which survive in the large matrix limit are those with the greatest Euler
characteristic, that is, either spheres or collections of spheres. This
topological construction motivates an algebraic expression for the moments and
cumulants in terms of the symmetric group. We examine the combinatorial
properties distinguishing the leading order terms. By considering higher
cumulants, we give a central limit-type theorem for the asymptotic distribution
around the expected value.",0910.5541v1
2009-11-06,"Measurement and analysis of the Hall effect of A-Fe$_2$As$_2$ single crystals with A = Ba, Ca or Sr","We report measurements of the Hall coefficient $R_H$ for single crystals of
AFe$_2$As$_2$ with $A = Ba, Ca$ or $Sr$ which are the anti-ferromagnetic parent
compounds of some high temperature pnictide superconductors. We show that $R_H$
of Sr-122 is consistent with high field quantum oscillation data. Our $R_H(T)$
data can also be used to estimate values of the spin density wave gap, giving
$\Delta_{SDW}(0) = 710\pm 70$ K for Sr-122 and $435\pm 20$ K for Ba-122.",0911.1259v1
2009-11-11,Transport properties of the layered Rh oxide K_0.49RhO_2,"We report measurements and analyses of resistivity, thermopower and Hall
coefficient of single-crystalline samples of the layered Rh oxide K_0.49RhO_2.
The resistivity is proportional to the square of temperature up to 300 K, and
the thermopower is proportional to temperature up to 140 K. The Hall
coefficient increases linearly with temperature above 100 K, which is ascribed
to the triangular network of Rh in this compound. The different transport
properties between Na_xCoO_2 and K_0.49RhO_2 are discussed on the basis of the
different band width between Co and Rh evaluated from the magnetotransport.",0911.2156v1
2009-11-13,Calculating the optimum pressure and temperature for vacancy minimization from theory; Niobium is an example,"Self-resonance in the atomic vibration occurs when the average wavelength of
the phonon thermal vibration is equivalent or harmonic of the diameters of the
atoms. It is suggested that applying pressure at temperature corresponding to
the self-resonance should effectively reduce the number of vacancies. This
theoretical prediction is tested on Niobium by measuring the magnetic
susceptibility of the untreated and treated samples. The applied
pressure-temperature treatment increased the critical temperature of Niobium by
about 30 percent which was also accompanied with volume increase.",0911.2728v1
2009-11-14,Topological-Fermi-Liquid to Quantum-Hall-Liquid Transitions: $p$-Band and $d$-Band Fermions in a Magnetic Field,"We find that in a multi-orbital system with intraorbital and interorbital
hopping integrals, the Hall conductance exhibits various topological quantum
phase transitions (QPTs) induced by on-site orbital polarization: integer
quantum Hall (IQH) plateau transitions, and topological Fermi liquid to IQH
transitions. Such topological QPTs are demonstrated in two systems: a $p$-band
spinless fermionic system realizable with ultracold atoms in optical lattice,
and a $d$-band spinful fermionic system closely related to giant orbital Hall
effects in transition metals and their compounds.",0911.2758v2
2009-11-19,"Equivalence perspectives in communication, source-channel connections and universal source-channel separation","An operational perspective is used to understand the relationship between
source and channel coding. This is based on a direct reduction of one problem
to another that uses random coding (and hence common randomness) but unlike all
prior work, does not involve any functional computations, in particular, no
mutual-information computations. This result is then used to prove a universal
source-channel separation theorem in the rate-distortion context where
universality is in the sense of a compound ``general channel.''",0911.3872v1
2009-11-26,A versatile source of polarization-entangled photons,"We propose a method for the generation of a large variety of entangled
states, encoded in the polarization degrees of freedom of N photons, within the
same experimental setup. Starting with uncorrelated photons, emitted from N
arbitrary single photon sources, and using linear optical tools only, we
demonstrate the creation of all symmetric states, e.g., GHZ- and W-states, as
well as all symmetric and non-symmetric total angular momentum eigenstates of
the N qubit compound.",0911.5115v1
2009-11-27,High quality anti-relaxation coating material for alkali atom vapor cells,"We present an experimental investigation of alkali atom vapor cells coated
with a high quality anti-relaxation coating material based on alkenes. The
prepared cells with single compound alkene based coating showed the longest
spin relaxation times which have been measured up to now with room temperature
vapor cells. Suggestions are made that chemical binding of a cesium atom and an
alkene molecule by attack to the C=C bond plays a crucial role in such
improvement of anti-relaxation coating quality.",0911.5274v1
2009-12-25,First-principles investigation of uranium monochalcogenides,"We present first-principles investigation of the electronic structure and
magnetic properties of uranium monochalcogenides: US, USe, UTe. The
calculations were performed by using recently developed LDA+U+SO method in
which both Coulomb and spin-orbit interactions have been taken into account in
rotationally invariant form. We discuss the problem of choice of the Coulomb
interaction value. The calculated [111] easy axes agree with those
experimentally observed. The electronic configuration 5$f^3$ was found for all
uranium compounds under investigation.",0912.4969v1
2010-01-06,Quantum Kagome antiferromagnet ZnCu3(OH)6Cl2,"The frustration of antiferromagnetic interactions on the loosely connected
kagome lattice associated to the enhancement of quantum fluctuations for S=1/2
spins was acknowledged long ago as a keypoint to stabilize novel ground states
of magnetic matter. Only very recently, the model compound Herbersmithite,
ZnCu3(OH)6Cl2, a structurally perfect kagome antiferromagnet, could be
synthesized and enables a close comparison to theories. We review and classify
various experimental results obtained over the past years and underline some of
the pending issues.",1001.0801v1
2010-01-06,BCS-BEC model of high-Tc superconductivity in layered cuprates with unconventional pairing,"High-Tc superconductivity in layered cuprates is described in a BCS-BEC
formalism with linearly-dispersive s- and d-wave Cooper pairs moving in
quasi-2D finite-width layers about the CuO_2 planes. This yields a closed
formula for Tc determined by the layer width, the Debye frequency, the pairing
energy, and the in-plane penetration depth. The new formula reasonably
reproduces empirical values of superconducting Tc's for seven different
compounds among the LSCO, YBCO, BSCCO and TBCCO layered cuprates.",1001.0957v1
2010-02-04,Electromechanical Probing of Ionic Currents in Energy Storage Materials,"The electrochemical processes in energy storage materials are generally
linked with changes of molar volume of the host compound. Here, the frequency
dependent strain response of 1D electrochemically active systems to periodic
electric bias is analyzed. The sensitivity and resolution of these
electrochemical strain measurements are compared to the current-based
electrochemical impedance spectroscopy. The resolution and detection limits of
interferometric and atomic force microscopy based systems for probing
electrochemical reactions on the nanoscale are analyzed.",1002.0961v2
2010-02-04,The electron-phonon theory of superconductors: Tc map and vertex correction,"The strong coupling Eliashberg theory plus vertex correction is used to
calculate maps of transition temperature (Tc) in parameter-space characterizing
superconductivity. Based on these Tc maps, crossover behaviors are found when
electron-phonon interaction increases from weak-coupling region to strong
coupling region. Especially, the combined interaction of vertex correction and
Coulomb interaction can efficiently depress Tc from extremely high values in
standard strong-coupling theory to reasonable values found in experiments and
successfully explain the doing-dependent Tc of cuprate superconductors. The
strong non-adiabatic effect is the barrier for high-Tc in compounds with
compositions of light atoms and with high phonon frequencies.",1002.0998v2
2010-02-17,Evidence for an electron nematic phase transition in underdoped iron pnictide superconductors,"Electrical resistivity measurements of detwinned single crystals of the
representative iron arsenide Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ reveal a dramatic
in-plane anisotropy associated with the tetragonal-to-orthorhombic structural
transition that precedes the onset of long-range antiferromagnetic order. These
results indicate that the structural transition in this family of compounds is
fundamentally electronic in origin.",1002.3364v2
2010-02-26,"Comment on ""Nonmagnetic Impurity Resonances as a Signature of Sign-Reversal Pairing in Fe-As-Based Superconductors""","In a recent Letter [PRL 103, 186402 (2009)], the energy band structure of
Fe-As-based superconductors is fitted with a tight-binding model with two Fe
ions per unit cell and two degenerate xz and yz orbitals per Fe ion. The author
claims that the proposed model, which differs markedly from a model previously
used by other authors for the same two orbitals in the same compounds,
possesses the symmetry required to describe the Fe-As planes in iron-pnictide
superconductors. In this comment we argue that this is not the case.",1002.4939v1
2010-03-05,Theoretical evidence for strong correlations and incoherent metallic state in FeSe,"The role of electronic Coulomb correlations in iron-based superconductors is
an important open question. We provide theoretical evidence for strong
correlation effects in the FeSe compound, based on dynamical mean field
calculations. A lower Hubbard band is found in the spectral properties.
Moreover, together with significant orbital-dependent mass enhancements, we
find that the normal state is a bad metal over an extended temperature range,
implying a non-Fermi liquid. Predictions for angle-resolved photoemission
spectroscopy are made.",1003.1286v2
2010-03-12,Wave functions for quantum Monte Carlo calculations in solids: Orbitals from density functional theory with hybrid exchange-correlation functionals,"We investigate how the fixed-node diffusion Monte Carlo energy of solids
depends on single-particle orbitals used in Slater--Jastrow wave functions. We
demonstrate that the dependence can be significant, in particular in the case
of 3d transition-metal compounds, which we adopt as examples. We illustrate how
exchange-correlation functionals with variable exact-exchange component can be
exploited to reduce the fixed-node errors. On the basis of these results we
argue that the fixed-node quantum Monte Carlo provides a variational approach
for optimization of effective hamiltonians with parameters.",1003.2507v1
2010-03-16,Field-driven magnetisation steps in Ca3Co2O6: A single-crystal neutron-diffraction study,"We present single-crystal neutron-diffraction data for the spin-chain
compound Ca3Co2O6. The intensity and line shapes of the two families of Bragg
peaks characterising both the antiferromagnetic and the ferromagnetic
components of the magnetic order present in this material have been measured as
a function of temperature and applied magnetic fields of up to 5 T. We have
studied the microscopic nature of the magnetic order at each step seen in the
bulk magnetisation and investigated the evolution of the long and short-range
components of the magnetic order in Ca3Co2O6.",1003.3200v1
2010-03-26,Structurally driven metamagnetism in MnP and related Pnma compounds,"We investigate the structural conditions for metamagnetism in MnP and related
materials using Density Functional Theory. A magnetic stability plot is
constructed taking into account the two shortest Mn-Mn distances. We find that
a particular Mn-Mn separation plays the dominant role in determining the change
from antiferromagnetic to ferromagnetic order in such systems. We establish a
good correlation between our calculations and structural and magnetic data from
the literature. Based on our approach it should be possible to find new
Mn-containing alloys that possess field-induced metamagnetism and associated
magnetocaloric effects.",1003.5193v2
2010-04-01,Evidence for a Non-Fermi-Liquid Phase in Ge-Substituted YbRh2Si2,"The canonical view of heavy fermion quantum criticality assumes a single
quantum critical point separating the paramagnet from the antiferromagnet.
However, recent experiments on Yb-based heavy fermion compounds suggest the
presence of non-Fermi liquid behavior over a finite zero-temperature region.
Using detailed susceptibility and transport measurements we show that the
classic quantum critical system, Ge-substituted YbRh2Si2, also displays such
behavior. We advance arguments that this is not due to a disorder-smeared
quantum critical point, but represents a new class of metallic phase.",1004.0107v1
2010-04-07,Landau model for the phase diagrams of the orthorhombic rare-earth manganites RMnO3,"The present work aims to describe, within a single phenomenological approach,
the specific sequence of phase transitions observed in the rare-earth
manganites RMnO3 at zero magnetic field. It is shown that a single integrated
description of the temperature versus composition phase diagrams of these
compounds and related solid solutions can be obtained within the scope of
Landau theory by adopting the so called type-II description of the modulated
phases.",1004.1057v1
2010-04-15,Bonding distances as Exact Sums of the Radii of the Constituent Atoms in Nanomaterials - Boron Nitride and Coronene,"This paper presents for the first time the exact structures at the atomic
level of two important nanomaterials, boron nitride and coronene. Both these
compounds are hexagonal layer structures similar to graphene in two dimensions
and to graphite in three-dimensions. However, they have very different
properties: whereas graphene is a conductor, h-BN is an electrical insulator
and coronene is a polycyclic aromatic hydrocarbon of cosmological interest. The
atomic structures presented here for boron nitride, coronene and graphene have
been drawn to scale based on bond lengths as sums of the atomic radii.",1004.2667v2
2010-04-24,Alpha-cluster Condensations in Nuclei and Experimental Approaches for their Studies,"The formation of alpha-clusters in nuclei close to the decay thresholds is
discussed. These states can be considered to be boson-condensates, which are
formed in a second order phase transition in a mixture of nucleons and
alpha-particles. The de Broglie wavelength of the alpha-particles is larger
than the nuclear diameter, therefore the coherent properties of the
alpha-particles give particular effects for the study of such states. The
states are above the thresholds thus the enhanced emission of multiple-alphas
into the same direction is observed. The probability for the emission of
multiple-alphas is not described by Hauser-Feshbach theory for compound nucleus
decay.",1004.4247v1
2010-04-30,"Dimensional trend in CePt2In7, Ce-115 compounds, and CeIn3","We present realistic Kondo-lattice simulation results for the
recently-discovered heavy-fermion antiferromagnet CePt2In7 comparing with its
three-dimensional counterpart CeIn3 and the less two-dimensional ones,
Ce-115's. We find that the distance to the magnetic quantum critical point is
the largest for CeIn3 and the smallest for Ce-115's, and CePt2In7 falls in
between. We argue that the trend in quasi-two-dimensional materials stems from
the frequency dependence of the hybridization between Cerium 4f-electrons and
the conduction bands.",1004.5457v1
2010-05-06,"Comment on ""Isoelectronic Ru substitution at Fe-site in Sm(Fe$_{1-x}$Ru$_x$)AsO$_{0.85}$F$_{0.15}$ compound and its effects on structural, superconducting and normal state properties"" (arXiv:1004.1978)","Based on the five-orbital model, we derive the reduced impurity scattering
rate $g=z\gamma/2\pi T_{c0}$ in Sm(Fe$_{1-x}$Ru$_{x}$)AsO$_{0.85}$F$_{0.15}$
from the residual resistivity. At $x=0$, the transition temperature is
$T_{c0}=50$ K. For $0.05<x<0.36$ ($0.84>T_{c}/T_{c0}>0.3$) the obtained value
of $g$ ranges from 1.5 to 2.9, which suggests that the $s_\pm$-wave state
cannot survive. We point out that the magnetoresistance frequently gives an
underestimated value of $g$ in correlated electron systems.",1005.0942v1
2010-05-07,Spin Transport in Organic Semiconductors: A Brief Overview of the First Eight Years,"In this article we briefly review the current state of the experimental
research on spin polarized transport in organic semiconductors. These systems,
which include small molecular weight compounds and polymers, are central in the
rapidly maturing area of organic electronics. A great deal of effort has been
invested in the last eight years toward understanding spin injection and
transport in organics. These developments have opened up the possibility of
realizing a new family of organic spintronic devices which will blend the
chemical versatility of organic materials with spintronic functionalities.",1005.1118v1
2010-05-15,Thermodynamics of strongly frustrated magnet in a field: Ising antiferromagnet on triangular Husimi lattice,"Some strongly frustrated magnets such as the ""spin-ice"" compounds fail to
produce any magnetic order at finite temperatures even in the presence of
magnetic field. Still they have very unusual low-temperature thermodynamic
properties related to the field-induced ground state transitions. Here we show
that general qualitative picture of such peculiar thermodynamics can be
obtained in the antiferromagnetic Ising model on the triangular Husimi lattice.
The analytical results for this model show magnetic plateaus, entropy spikes,
crossing points and peculiarities in magnetic susceptibility and specific heat
behavior reflecting the existence of ground state transitions. These signatures
of strong frustration may help in search of new frustrated magnets and in the
interpretation of experimental data.",1005.2650v1
2010-05-21,Magnetostructural transition in Ce(Fe0.975Ga0.025)2 compound,"The magnetic and magnetostructural properties of the polycrystalline
Ce(Fe0.975Ga0.025)2 have been investigated as a function of temperature and
magnetic field. In Ce(Fe0.975Ga0.025)2 the magnetic transition from
antiferromagnetic (AFM) to ferromagnetic state (FM) is accompanied by a
structural transformation from rhombohedral to cubic structure. Phase
coexistence is present during both the temperature and field driven
transformations from the AFM to FM phase.",1005.3928v1
2010-05-28,Density functional theory calculations on magnetic properties of actinide compounds,"We have performed a detailed analysis of the magnetic (collinear and
noncollinear) order and atomic and the electron structures of UO2, PuO2 and UN
on the basis of density functional theory with the Hubbard electron correlation
correction (DFT+U). We have shown that the 3-k magnetic structure of UO2 is the
lowest in energy for the Hubbard parameter value of U=4.6 eV (and J=0.5 eV)
consistent with experiments when Dudarev's formalism is used. In contrast to
UO2, UN and PuO2 show no trend for a distortion towards rhombohedral structure
and, thus, no complex 3-k magnetic structure is to be anticipated in these
materials.",1005.5369v1
2010-06-07,Interaction strengths in cuprates from the inelastic neutron-scattering measurements,"The $t-U-V-J$ model is used to describe the positions of the experimental
peaks associated with commensurate and incommensurate structure of the magnetic
susceptibility probed by neutron scattering in cuprate compounds. Assuming that
the tight-binding form of the mean-field electron energy and the maximum gap
can be obtained by fitting the angle-resolved photoemission spectroscopy
(ARPES) data, we have determined the strengths of the on-site repulsive
interaction $U$, the spin-independent attractive interaction $V$ and the
spin-dependent antiferromagnetic interaction $J$ from the positions of the
commensurate and incommensurate peaks.",1006.1387v2
2010-06-07,Bethe-Salpeter equations for the collective modes of the $t-U-V-J$ model with d-wave pairing,"The Bethe-Salpeter equations for the collective modes of a $t$-$U$-$V$-$J$
model are used to analyze the resonance peak observed at $\bf{Q}=(\pi,\pi)$ in
neutron scattering experiments on the cuprates. We assume that the resonance
emerges due to the mixing between the spin channel and 19 other channels. We
have calculated the energy of the lowest mode of the extended Hubbard model
($J=0$) vs the on-site repulsive interaction $U$, as well as the $UJ$ lines in
the interaction parameter space which are consistent with the ARPES data and
reproduces the resonance peak at 40 meV in Bi2212 compound. We find that the
resonance is predominantly a spin exciton.",1006.1388v1
2010-06-10,Tunneling spectra of strongly coupled superconductors: Role of dimensionality,"We investigate numerically the signatures of collective modes in the
tunneling spectra of superconductors. The larger strength of the signatures
observed in the high-Tc superconductors, as compared to classical low-Tc
materials, is explained by the low dimensionality of these layered compounds.
We also show that the strong-coupling structures are dips (zeros in the d2I/dV2
spectrum) in d-wave superconductors, rather than the steps (peaks in d2I/dV2)
observed in classical s-wave superconductors. Finally we question the
usefulness of effective density of states models for the analysis of tunneling
data in d-wave superconductors.",1006.2105v2
2010-06-11,"First Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5] with Extremely Thick Blocking Layers","We have discovered first homologous series of iron pnictide oxide
superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5]. These compounds have
extremely thick blocking layers up to quintuple perovskite oxide layers
sandwiched by the Fe2As2 layers. These samples exhibited bulk superconductivity
with relatively high Tc up to 42 K. The relationship between Tc and the
iron-plane interlayer distance suggested that superconductivity due to the mono
Fe2As2 layer is substantially 40 K-class.",1006.2355v2
2010-06-28,On the Coupling Property of Lévy Processes,"We give necessary and sufficient conditions guaranteeing that the coupling
for L\'evy processes (with non-degenerate jump part) is successful. Our method
relies on explicit formulae for the transition semigroup of a compound Poisson
process and earlier results by Mineka and Lindvall-Rogers on couplings of
random walks. In particular, we obtain that a L\'{e}vy process admits a
successful coupling, if it is a strong Feller process or if the L\'evy (jump)
measure has an absolutely continuous component.",1006.5288v2
2010-07-01,A new lifetime model with decreasing failure rate,"In this paper we introduce a new lifetime distribution by compounding
exponential and Poisson-Lindley distributions, named exponential
Poisson-Lindley distribution. Several properties are derived, such as density,
failure rate, mean lifetime, moments, order statistics and R\'enyi entropy.
Furthermore, estimation by maximum likelihood and inference for large sample
are discussed. The paper is motivated by two applications to real data sets and
we hope that this model be able to attract wider applicability in survival and
reliability.",1007.0238v1
2010-07-02,Fermi arcs and the nature of carriers in cuprate HTSC,"Here we suggest a simple physical model of HTSC cuprates that provides
qualitative explanation of the main features of these compounds, including the
nature of Fermi arcs, pseudogap anomalies and the origin of free carriers.
According to this model, the unusual properties of HTSC cuprates result from
their unique electronic structure favourable for the formation of diatomic
negative-U centers (NUCs) and realization of an unusual mechanism of
electron-electron interaction.",1007.0320v2
2010-07-13,Hydrogen Compounds of Group-IV Nanosheets,"The structural and electronic properties of the hydrides of silicene and
germanene have been studied using ab initio calculations. The trend for the M-H
(M=C, Si, Ge) bond lengths, and corresponding bond energies, is consistent with
the atomic size trend, and comparable to those of MH_4 hydrides. Band
structures were also obtained for the buckled configuration, which is the
stable form for both silicene and germanene. Upon hydrogenation, both silicane
(indirect gap) and germanane (direct gap) are semiconducting.",1007.2110v1
2010-07-15,Stable antiferromagnetic graphone,"Density functional modeling of atomic structure and calculation of electronic
structure of one-side one-sublattice functionalized graphene (graphone) are
performed for hydrogen and fluorine adatoms. Shown that using of fluorine for
functionalization not on enhance stability of compound but also provide switch
of magnetic ground state from ferro- to antiferromagnetic. Half-metallic
ferromagnetic state in fluorine based graphone is also discussed.",1007.2455v1
2010-07-15,Anisotropic charge dynamics in detwinned Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"We investigate the optical conductivity as a function of temperature with
light polarized along the in-plane orthorhombic $a$- and $b$-axes of
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ for $x$=0 and 2.5$\%$ under uniaxial pressure.
The charge dynamics at low frequencies on these detwinned, single domain
compounds tracks the anisotropic $dc$ transport properties across their
structural and magnetic phase transitions. Our findings allow us to estimate
the dichroism, which extends to relatively high frequencies. These results are
consistent with a scenario in which orbital order plays a significant role in
the tetragonal-to-orthorhombic structural transition.",1007.2543v1
2010-07-20,Hydrogen kinetics in non-equilibrium plasma in the electrical discharge in Ar/CH3OH/H2O mixture,"Plasma kinetics of molecular hydrogen in the electrical discharge in
Ar/CH3OH/H2O mixture is theoretically investigated for the first time. It is
researched the dependence of [H2] on the breakdown field, the discharge power,
solution compound and the argon pumping rate through the interelectrode gap.
The highest hydrogen concentration is reached with the 20% methanol fraction in
the solution. It is shown that [H2] grows as the linear function of the
discharge power and decreases with the gas volume velocity increase.",1007.3449v1
2010-07-20,Model of d-wave electron pairing in hole doped cuprate superconductors: A possible explanation for the pseudogap regime,"The real-space localized hole pair is constructed in the Cu-O plane of the
hole-doped cuprate superconductors. We prove analytically and numerically that
two electrons, due to the nearest-neighbor Coulomb repulsive confinement
effect, can be in pairing inside a single plaquette with the d-wave symmetry.
The scenario supports the `no glue' pairing picture for the cuprates. Based on
the scenarios, the physical origin of the Fermi pocket (or Fermi arc) and the
two pseudogap behavior are provided. Our framework leads directly to a unified
linear relationship between the pseudogap temperature T* and the hole doping
level x in these compounds.",1007.3536v1
2010-07-22,"Size bias, sampling, the waiting time paradox, and infinite divisibility: when is the increment independent?","With $X^*$ denoting a random variable with the $X$-size bias distribution,
what are all distributions for $X$ such that it is possible to have $X^*=X+Y$,
$Y\geq 0$, with $X$ and $Y$ {\em independent}? We give the answer, due to
Steutel \cite{steutel}, and also discuss the relations of size biasing to the
waiting time paradox, renewal theory, sampling, tightness and uniform
integrability, compound Poisson distributions, infinite divisibility, and the
lognormal distributions.",1007.3910v1
2010-07-28,Observation of spontaneous magnetization jump and field-induced irreversibility in Nd5Ge3,"We report the observation of spontaneous and ultra-sharp jumps in the low
temperature magnetization isotherms of polycrystalline Nd5Ge3. Field-induced
and ultra-sharp jumps are also seen in resistivity and heat capacity data.
These jumps are accompanied by field-induced irreversibilities. The consistency
seen in these three data clearly shows that the spin, electronic and lattice
states are strongly coupled. Time-induced growth of the ferromagnetic phase is
observed at a constant field and temperature, implying the metastability of the
magnetic phase in the low field region. Various experimental findings point
towards a strong field-induced magneto-structural irreversibility in this
compound.",1007.4912v1
2010-07-30,Diamagnetic susceptibility of spin-triplet ferromagnetic superconductors,"We calculate the diamagnetic susceptibility in zero external magnetic field
above the phase transition from ferromagnetic phase to phase of coexistence of
ferromagnetic order and unconventional superconductivity. For this aim we use
generalized Ginzburg-Landau free energy of unconventional ferromagnetic
superconductor with spin-triplet electron pairing. A possible application of
the result to some intermetallic compounds is briefly discussed.",1007.5432v3
2010-08-06,Calculation of aggregate loss distributions,"Estimation of the operational risk capital under the Loss Distribution
Approach requires evaluation of aggregate (compound) loss distributions which
is one of the classic problems in risk theory. Closed-form solutions are not
available for the distributions typically used in operational risk. However
with modern computer processing power, these distributions can be calculated
virtually exactly using numerical methods. This paper reviews numerical
algorithms that can be successfully used to calculate the aggregate loss
distributions. In particular Monte Carlo, Panjer recursion and Fourier
transformation methods are presented and compared. Also, several closed-form
approximations based on moment matching and asymptotic result for heavy-tailed
distributions are reviewed.",1008.1108v1
2010-08-10,New Understandings of Quantum Mechanics Based on Interaction,"The interaction between two parts in a compound quantum system may be
reconsidered more completely than before and some new understandings and
conclusions different from current quantum mechanics are obtained, including
the conservation law in the evolution in an isolated quantum system, new
understandings of duality of particle and wave and the superposition principle
of states, three laws corresponding to Newton's laws, new understandings of
measurement and the uncertainty relation, arguments against the non-locality of
any entangled state and a simple criterion of coherence which is obtained for
the experimenter to examine the correctness of the non-locality. These may make
quantum mechanics be easily understood intuitively and some strange properties
will not appear.",1008.1691v2
2010-08-12,High-Frequency Electromagnon in GdMnO3,"We present the results of transmittance experiments on GdMnO3 multiferroic
manganite in the far infrared frequency range. The spectra allow to obtain the
positions and the intensity of the high frequency electromagnon (~ 75 cm-1) in
this compound. We present the comparative analysis of the high and low
frequency electromagnons across the phase diagram of GdMnO3. The traces of the
electromagnon excitation can be detected even at room temperature, i.e. deeply
in the paramagnetic state.",1008.2064v1
2010-08-17,Non-adiabatic effects of superconductor silane under high pressure,"Investigations of non-adiabatic effects by including vertex corrections in
the standard Eliashberg theory show that high phonon frequency is unfavorable
to superconductivity in regime of strong vertex correction. This means that it
is hard to find high-transition-temperature superconductors in the compounds
with light elements if the non-adiabatic effects are strong. The interplay
interaction between non-adiabatic effect and Coulomb interaction makes the
transition temperature of silane superconductor not so high as predicted by the
standard Eliashberg theory.",1008.2820v1
2010-08-18,Quadratic Involutions on Binary Forms,"There is a classical geometric construction which uses a binary quadratic
form to define an involution on the space of binary d-ics. We give a complete
characterization of a general class of such involutions which are definable
using compound transvectant formulae. We also study the associated varieties of
forms which are preserved by such involutions. Along the way we prove a
recoupling formula for transvectants, which is used to deduce a system of
equations satisfied by the coefficients in these involutions.",1008.3117v3
2010-08-23,Vortex states in hole-doped iron-pnictide superconductors,"Based on a phenomenological model with competing spin-density-wave (SDW) and
extended $s-$wave superconductivity, the vortex states in
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ are investigated by solving Bogoliubov-de
Gennes equations. Our result for the optimally doped compound without induced
SDW is in qualitative agreement with recent scanning tunneling microscopy
experiment. We also propose that the main effect of the SDW on the vortex
states is to reduce the intensity of the in-gap peak in the local density of
states and transfer the spectral weight to form additional peaks outside the
gap.",1008.3885v1
2010-08-24,A sharp lower bound for the Wiener index of a graph,"Given a simple connected undirected graph G, the Wiener index W(G) of G is
defined as half the sum of the distances over all pairs of vertices of G. In
practice, G corresponds to what is known as the molecular graph of an organic
compound. We obtain a sharp lower bound for W(G) of an arbitrary graph in terms
of the order, size and diameter of G.",1008.4039v1
2010-08-24,Convex Quantum Logic,"In this work we study the convex set of quantum states from a quantum logical
point of view. We consider an algebraic structure based on the convex subsets
of this set. The relationship of this algebraic structure with the lattice of
propositions of quantum logic is shown. This new structure is suitable for the
study of compound systems and shows new differences between quantum and
classical mechanics. This differences are linked to the nontrivial correlations
which appear when quantum systems interact. They are reflected in the new
propositional structure, and do not have a classical analogue. This approach is
also suitable for an algebraic characterization of entanglement.",1008.4168v1
2010-08-27,Electromagnons in the spin collinear state of a triangular lattice antiferromagnet,"Terahertz time-domain spectroscopy was performed to directly probe the
low-energy (1-5 meV) electrodynamics of triangular lattice antiferromagnets
CuFe1-xGaxO2 (x = 0.00, 0.01, and 0.035). We discovered an electromagnon
(electric-field-active magnon) excitation at 2.3 meV in the paraelectric
up-up-down-down collinear magnetic phase, while this electromagnon vanishes in
the ferroelectric helimagnetic phase. Anti-correlation with noncollinear
magnetism excludes the exchange-striction mechanism as the origin of dynamical
magnetoelectric coupling, and hence evidences the observation of spin-orbit
coupling mediated electromagnon in the present compound.",1008.4709v1
2010-08-28,Infra-red Spectroscopic Studies of GdBaCo2O5.5,"This paper reports infrared spectroscopic studies on GdBaCo$_{2}$O$_{5.5}$
layered perovskite which exhibits successive magnetic transitions from
paramagnetic to ferromagnetic to antiferromagnetic states as well as high
temperature metal to insulator transition and a change in charge transport
mechanism at low temperature. Infrared absorption spectra recorded at various
temperatures in the range 80 K to 350 K reveal changes in the positions of Co-O
stretching and bending frequencies which provide an explanation to the magnetic
and transport behaviour of this compound.",1008.4847v1
2010-08-31,Quantum chemistry studies of the O K-edge X-ray absorption in WO3 and AWO3,"In this work we present an interpretation of experimental O K-edge x-ray
absorption near edge structure (XANES) in perovskite-type WO3 and AWO3
compounds (A = H and Na) using three different first principles approaches: (i)
full-multiple-scattering (FMS) formalism (the real-space FEFF code), (ii)
hybrid density functional theory (DFT) method with partial incorporation of
exact Hartree-Fock exchange using formalism of the linear combination of atomic
orbitals (LCAO) as implemented in the CRYSTAL code; (iii) plane-wave DFT method
using formalism of the projector-augmented waves (PAW) as implemented in the
VASP code.",1008.5308v1
2010-09-08,Observation of tunable exchange bias in Sr$_2$YbRuO$_6$,"The double perovskite compound, Sr$_{2}$YbRuO$_{6}$, displays reversal in the
orientation of magnetic moments along with negative magnetization due to an
underlying magnetic compensation phenomenon. The exchange bias (EB) field below
the compensation temperature could be the usual negative or the positive
depending on the initial cooling field. This EB attribute has the potential of
getting tuned in a preselected manner, as the positive EB field is seen to
crossover from positive to negative value above $T_{\mathrm{comp}}$.",1009.1554v1
2010-09-14,High refractive index composite materials for THz waveguides: trade-off between index contrast and absorption loss,"Polymer compounds from titania-doped polyethylene are fabricated and their
linear optical properties characterized by THz-TDS. We show that high
concentration of dopants not only enhances the refractive index of the
composite material, but also can dramatically raise its absorption coefficient.
We demonstrate that the design of Bragg reflectors based on lossy composite
polymers depends on finding a compromise between index contrast and
corresponding losses. A small absorption value is also shown to be favorable,
compared to an ideal lossless reflector, as it enables to smooth the
transmission passbands. Transmission measurements of a fabricated hollowcore
Bragg fiber confirm simulation results.",1009.2667v1
2010-09-21,Electron Spin Resonance of the ferromagnetic Kondo lattice CeRuPO,"The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated
by Electron Spin Resonance (ESR) at microwave frequencies of 1, 9.4, and
34~GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+
resonance in a metallic Ce compound and can be followed below the ferromagnetic
transition temperature Tc=14 K. At T>Tc the interplay between the RKKY-exchange
interaction and the crystal electric field anisotropy determines the ESR
parameters. Near Tc the spin relaxation rate is influenced by the critical
fluctuations of the order parameter.",1009.4108v1
2010-09-21,Jastrow-Correlated Wavefunctions for Flat-Band Lattices,"The electronic band structure of many compounds, e.g., carbon-based
structures, can exhibit essentially no dispersion. Models of electrons in
flat-band lattices define non-perturbative strongly correlated problems by
default. We construct a set of Jastrow-correlated ansatz wavefunctions to
capture the low energy physics of interacting particles in flat bands. We test
the ansatz in a simple Coulomb model of spinless electrons in a honeycomb
ribbon. We find that the wavefunction accurately captures the ground state in a
transition from a crystal to a uniform quantum liquid.",1009.4194v2
2010-09-26,Spin dependent electron-phonon interaction in SmFeAsO by low-temperature Raman spectroscopy,"The interplay between spin dynamics and lattice vibration has been suggested
as an important part of the puzzle of high-temperature superconductivity. Here
we report the strong interaction between spin fluctuation and phonon in
SmFeAsO, a parent compound of the iron arsenide family of superconductors,
revealed by low-temperature Raman spectroscopy. Anomalous zone-boundary-phonon
Raman scattering from spin superstructure was observed at temperatures below
the antiferromagnetic ordering point, which offers compelling evidence on spin
dependent electron-phonon coupling in pnictides.",1009.5050v2
2010-10-21,Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field,"The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic
model, with a magnetic field applied in the easy plane, is studied using the
self-consistent harmonic approximation. We found a linear dependence of the
transition temperature as a function of the field for large values of the
field. Our results are in agreement with experimental data for the spin-1
honeycomb compound BaNi_2V_2O_3",1010.4539v1
2010-10-22,Non-linear effect of uniaxial pressure on superconductivity in CeCoIn5,"We study single-crystal CeCoIn5 with uniaxial pressure up to 3.97 kbar
applied along the c-axis. We find a non-linear dependence of the
superconducting transition temperature Tc on pressure, with a maximum close to
2 kbar. The transition also broadens significantly as pressure increases. We
discuss the temperature dependence in terms of the general trend that Tc
decreases in anisotropic heavy-fermion compounds as they move towards
three-dimensional behavior.",1010.4653v2
2010-10-25,Cluster-decay of $^{56}$Ni$^{\ast}$} compound system using different Fermi density parameters,"We have calculated the half-lives for $^{56}$Ni$^{\ast}$ within PCM and UFM
for clusters $\ge ^{16}$O. For PCM, the order of magnitude of cluster decay
constants for different density parameters is nearly same, except for SM
parameters. Similar trends are observed for UFM. The percentage variation in
the half-lives for the PCM lies within $\pm$5% excluding SM parameters, whereas
including SM parameters it lies within $\pm$13%. In the case of UFM, half-lives
lie within $\pm$1.5% for all density parameters except of SM. For SM parameters
these variations lie within $\pm$9%.",1010.5152v1
2010-10-26,Giant directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic oxide BaCo$_2$Ge$_2$O$_7$,"We propose that concurrently magnetic and ferroelectric, i.e. multiferroic,
compounds endowed with electrically-active magnetic excitations
(electromagnons) provide a key to produce large directional dichroism for long
wavelengths of light. By exploiting the control of ferroelectric polarization
and magnetization in a multiferroic oxide Ba$_2$CoGe$_2$O$_7$, we demonstrate
the realization of such a directional light-switch function at terahertz
frequecies in resonance with the electromagnon absorption. Our results imply
that this hidden potential is present in a broad variety of multiferroics.",1010.5420v1
2010-10-29,Tailoring strain in SrTiO3 compound by low energy He+ irradiation,"The ability to generate a change of the lattice parameter in a near-surface
layer of a controllable thickness by ion implantation of strontium titanate is
reported here using low energy He+ ions. The induced strain follows a
distribution within a typical near-surface layer of 200 nm as obtained from
structural analysis. Due to clamping effect from the underlying layer, only
perpendicular expansion is observed. Maximum distortions up to 5-7% are
obtained with no evidence of amorphisation at fluences of 1E16 He+ ions/cm2 and
ion energies in the range 10-30 keV.",1010.6152v1
2010-10-29,Vibrational properties of graphene fluoride and graphane,"The vibrational properties of graphene fluoride and graphane are studied
using ab initio calculations. We find that both sp3 bonded derivatives of
graphene have different phonon dispersion relations and phonon density of
states as expected from the different masses associated with the attached atoms
fluorine and hydrogen, respectively. These differences manifest themselves in
the predicted temperature behavior of the constant-volume specific heat of both
compounds.",1011.0018v1
2010-11-04,Investigation of structural and optoelectronic properties of BaThO3,"Structural and optoelectronic properties of BaThO3 cubic perovskite are
calculated using all electrons full potential linearized augmented plane wave
(FP-LAPW) method. Wide and direct band gap, 5.7 eV, of the compound predicts
that it can be effectively used in UV based optoelectronic devices. Different
characteristic peaks in the wide UV range emerges mainly due to the transition
of electrons between valance band state O-p and conduction band states Ba-d,
Ba-f, Th-f and Th-d.",1011.1042v1
2010-11-11,Effect of B-site Dopants on Magnetic and Transport Properties of LaSrCoRuO$_6$,"Effect of Co, Ru and Cu substitution at B and B' sites on the magnetic and
transport properties of LaSrCoRuO$_6$ have been investigated. All the doped
compositions crystallize in the monoclinic structure in the space group
$P2_1/n$ indicating a double perovskite structure. While the magnetization and
conductivity increase in Co and Ru doped compounds, antiferromagnetism is seen
to strengthen in the Cu doped samples. These results are explained on the basis
of a competition between linear Co-O-Ru-O-Co and perpendicular Co-O-O-Co
antiferromagnetic interactions and due to formation of Ru-O-Ru ferromagnetic
networks.",1011.2555v1
2010-11-12,"Comprehensive transport studies of anisotropy and ordering phenomena in quasi-one-dimensional (TMTTF)2X salts (X = PF6, AsF6, SbF6; BF4, ClO4, ReO4)","The temperature dependent dc resistivity of the quasi-one-dimensional organic
salts (TMTTF)2X ( X = PF6, AsF6, SbF6; BF4, ClO4, ReO4) has been measured in
all three crystal directions in order to investigate anisotropy, localization
effects, charge and anion ordering phenomena at low temperatures. For all
compounds and directions we extract the transport mechanisms in different
regimes. The data are thoroughly analyzed, related to structural properties,
and extensively discussed in view of previous studies and latest theories. It
becomes apparent that the anions have a severe influence on the physical
properties of the TMTTF salts.",1011.2856v1
2010-11-15,Electronic Correlation effects in superconducting picene from ab-initio calculations,"We show, by means of ab-initio calculations, that electron-electron
correlations play an important role in potassium-doped picene ($K_x$-picene),
recently characterized as a superconductor with $T_c = 18K$. The inclusion of
exchange interactions by means of hybrid functionals reproduces the correct gap
for the undoped compound and predicts an antiferromagnetic state for $x=3$,
where superconductivity has been observed. The latter finding is compatible
with a sizable value of the correlation strength, in agreement with simple
estimates. Our results highlight the similarity between potassium-doped picene
and alkali-doped fulleride superconductors.",1011.3308v2
2010-11-19,"Anisotropic spin fluctuations and superconductivity in ""115'' heavy fermion compounds: 59Co NMR study in PuCoGa5","We report results of $^{59}$Co nuclear magnetic resonance measurements on a
single crystal of superconducting PuCoGa5 in its normal state. The nuclear
spin-lattice relaxation rates and the Knight shifts as a function of
temperature reveal an anisotropy of spin fluctuations with finite wave vector
q. By comparison with the isostructural members, we conclude that
antiferromagnetic XY-type anisotropy of spin fluctuations plays an important
role in mediating superconductivity in these heavy fermion materials.",1011.4466v1
2010-11-23,"Fine structure of ""zero-mode"" Landau levels in HgTe/HgCdTe quantum wells","HgTe/HgCdTe quantum wells with the inverted band structure have been probed
using far infrared magneto-spectroscopy. Realistic calculations of Landau level
diagrams have been performed to identify the observed transitions.
Investigations have been greatly focused on the magnetic field dependence of
the peculiar pair of ""zero-mode"" Landau levels which characteristically split
from the upper conduction and bottom valence bands, and merge under the applied
magnetic field. The observed avoided crossing of these levels is tentatively
attributed to the bulk inversion asymmetry of zinc blend compounds.",1011.5233v1
2010-12-03,Magnetic vortex lattice in HgBa2CuO4+x observed by small-angle neutron scattering,"We report a direct observation of the magnetic vortex lattice in the model
high-temperature superconductor HgBa2CuO4+x. Using small-angle neutron
scattering on high-quality crystals, we observe two equal domains of
undistorted triangular vortex lattices well-aligned with the tetragonal
crystallographic axes. The signal decreases rapidly with increasing magnetic
field and vanishes above 0.4 Tesla, which we attribute to a crossover from a
three-dimensional to a two-dimensional vortex system, similar to previous
results for the more anisotropic compound Bi2.15Sr1.95CaCu2O8+x. Our result
indicates that a triangular vortex lattice at low magnetic fields is a generic
property to cuprates with critical temperatures above 80 K.",1012.0732v1
2010-12-03,Spontaneous toroidic effects in Ba2CoGe2O7,"The unusual magnetoelectric effects observed in the multiferroic phase
arising below TN=6.7K in Ba2CoGe2O7 (BCG) are related to the spontaneous
toroidal moment existing in this compound. The transition to the multiferroic
state, which involves spontaneous magnetization, polarization and toroidal
moment gives rise to spontaneous toroidic effects. These effects produce
specific contributions to the spontaneous polarization and magnetization under
applied magnetic or electric fields which provide indirect indications of the
existence and role of the toroidal moment in multiferroic materials. The
toroidic contribution to the electric polarization in BCG is shown to result
from single-ion effects.",1012.0785v1
2010-12-03,Disordered Ground State and Magnetic Field-Induced Long-Range Order in an S=3/2 Antiferromagnetic Honeycomb Lattice Compound Bi3Mn4O12(NO3),"Bi3Mn4O12(NO3), in which the Mn4+ ions carry S=3/2, is the first honeycomb
lattice system that shows no long-range magnetic order. Using neutron
scattering, we have determined that short-range antiferromagnetic correlations
develop at low temperatures. Applied magnetic fields induce a magnetic
transition, in which the short-range order abruptly expands into a long-range
order.",1012.0825v1
2010-12-08,Multiple spin-flop phase diagram of BaCu2Si2O7,"The quasi one-dimensional compound BaCu2Si2O7 demonstrates numerous
spin-reorientation transitions both for a magnetic field applied along the easy
axis of magnetization, and for a magnetic field applied perpendicular to it.
The magnetic phase diagram for all three principal orientations is obtained by
magnetization and specific heat measurements. Values of all critical fields and
low-temperature values of magnetization jumps are determined for all
transitions.",1012.1702v1
2010-12-09,Ferroelectromagnets. Fifty years after discovery,"Ferroelectromagnets - compounds with ferroelectric and magnetic orderings -
were discovered about fifty years ago. They are of great interest due to the
possibility of mutual control of electric (magnetic) properties by magnetic
(electric) field. At present such possibility of magnetoelectric control has
become reality which stimulated revival of scientific and practical interest in
ferroelectromagnets. The progress in experimental and theoretical
investigations of magnetoelectric phenomena in ferroelectromagnets for the last
years, especially the colossal magnetoelectric effects observed recently, are
considered. The problems and future prospects of enhancing magnetoelectric
effects in ferroelectromagnets are being discussed. The book is intended for
researchers in ferroelectricity and magnetism and for students of physical
specialities.",1012.2024v1
2010-12-13,Spin Triplet Pairing for Superconductivity,"A generalization of the Cooper pairing mechanism is proposed which allows for
a triplet state of lower energy. This is achieved by incorporating spin into
the canonical commutation relations and by modifying the $\delta$ potential
contact interaction. The gap equation contain as solutions both singlet and
triplet states. It is shown that the triplet state is lower in energy than the
singlet state which may explain the spin-triplet superconductivity observed in
heavy fermion compound UPt3 and in Sr$_2$RuO$_4$.",1012.2837v1
2010-12-14,Superconductivity in the iron selenide KxFe2Se2 (0 <= x <= 1),"We report the superconductivity at above 30 K in a new FeSe-layer compound
K0.8Fe2Se2 (nominal composition) achieved by metal K intercalating in between
FeSe layers. It is isostructural to BaFe2As2 and possesses the highest Tc for
FeSe-layer materials so far under ambient pressure. Hall effect indicates the
carriers are dominated by electron in this superconductor. We confirm that the
observed superconductivity at above 30 K is due to this new FeSe-based 122
phase. Our results demonstrate that FeSe-layer materials are really remarkable
superconductors via structure and carrier modulation.",1012.2924v1
2010-12-17,Ternary Tetradymite Compounds as Topological Insulators,"Ternary tetradymites Bi2Te2S, Bi2Te2Se and Bi2Se2Te are found to be stable,
bulk topological insulators via theory, showing band inversion between group V
and VI pz orbitals. We identify Bi2Se2Te as a good candidate to study massive
Dirac Fermions, with a (111) cleavage-surface-derived Dirac point (DP) isolated
in the bulk band gap at the Fermi energy Ef like Bi2Se3 but with a spin texture
alterable by layer chemistry. In contrast, Bi2Te2S and Bi2Te2Se (111) behave
like Bi2Te3, with a DP below Ef buried in bulk bands. Bi2Te2S offers large bulk
resistivity needed for devices.",1012.3974v3
2010-12-28,Weak ferromagnetism in cobalt oxalate crystals,"Microcrystals of diaquocobalt(II) oxalate have been synthesized by the
coprecipitation reaction of aqueous solutions of Cobalt (II) bromide and oxalic
acid. Chemical analysis and thermal experiments revealed that there is only one
phase present. X-ray powder diffraction studies show that this compound is
orthorhombic with space group Cccm. Molar susceptibility versus temperature
measurements show the existence of an antiferromagnetic ordering, however, the
hysteresis measured in magnetization measurements as a function of magnetic
field reveals a weak ferromagnetic behavior.",1012.5824v1
2011-01-15,Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review),"The basic known and hypothetic one- and two-element phases of the B-C-N-O
system (both superhard phases having diamond and boron structures and
precursors to synthesize them) are described. The attention has been given to
the structure, basic mechanical properties, and methods to identify and
characterize the materials. For some phases that have been recently described
in the literature the synthesis conditions at high pressures and temperatures
are indicated.",1101.2954v1
2011-01-17,Upper critical field of the 122-type iron pnictide superconductors,"The upper critical fields ($H_{c2}$) of the single crystals
$\rm(Sr,Na)Fe_2As_2$ and $\rm Ba_{0.55}K_{0.45}Fe_2As_2$ were determined by
means of measuring the electrical resistivity, $ \rho_{xx}(\mu_0H)$, using the
facilities of pulsed magnetic field at Los Alamos. In general, these compounds
possess a very large upper critical field ($H_{c2}(0)$) with a weak anisotropic
effect. The detailed curvature of $H_{c2}(T_c)$ may depend on the magnetic
field orientation and the sample compositions. We argue that such a difference
mainly results from the multi-band effect, which might be modified via doping.",1101.3150v1
2011-01-18,Temperature-dependent spin resonance energy in iron pnictides and multiband s\pm Eliashberg theory,"The phenomenology of iron-pnictides superconductors can be explained in the
framework of a three bands s\pm wave Eliashberg theory with only two free
parameters plus a feedback effect i.e. the effect of the condensate on the
antiferromagnetic spin fluctuactions responsible of the superconductivity in
these compounds. I have examined the experimental data of four materials:
LaFeAsO1-xFx, SmFeAsO1-xFx, Ba1-xKxFe2As2, and Ba(FexCo1-x)2As2 and I have
found that it is possible to reproduce the experimental critical temperature
and gap values in a moderate strong-coupling regime: ltot about 1.7-2.0.",1101.3473v2
2011-01-21,Cr doped III-V nitrides: potential candidates for spintronics,"Studies of Cr-doped III-V nitrides, dilute magnetic alloys, in the
zinc-blende crystal structure are presented. The objective of the work is to
investigate half-metallicity in Al(0.75)Cr(0.25)N, Ga(0.75)Cr(0.25)N and
In(0.75)Cr(0.25)N for their possible application in the spin based electronic
devices. The calculated spin polarized band structures, electronic properties
and magnetic properties of these compounds reveal that Al0.75Cr0.25N and
Ga0.75Cr0.25N are half-metallic dilute magnetic semiconductors while
In0.75Cr0.25N is metallic in nature. The present theoretical predictions
provide evidence that some Cr doped III-V nitrides can be used in spintronics
devices.",1101.4059v1
2011-01-21,White-Light Emission from Annealed ZnO:Si Nanocomposite Thin Films,"As grown ZnO:Si nanocomposites of different compositional ratios were
fabricated by thermal evaporation techniques. These films were subjected to
post deposition annealing under high vacuum at a temperature of $\rm 250C^o$
for 90min. The photoluminescence (PL) spectra of annealed samples have shown
marked improvements both in terms of intensity and broadening. For the first
time in ZnO:Si nanocomposite films we see huge UV, red and orange peaks at 310,
570 and 640nm. Structural and Raman analysis show formation of a Zn-Si-O shell
around ZnO nano clusters wherein on heating $\rm Zn_2SiO_4$ compound forms. The
new emissions are due to $\rm Zn_2SiO_4$ which completes white light spectrum.",1101.4119v1
2011-01-29,Cellular Ability to Sense Spatial Gradients in the Presence of Multiple Competitive Ligands,"Many eukaryotic and prokaryotic cells can exhibit remarkable sensing ability
under small gradient of chemical compound. In this study, we approach this
phenomenon by considering the contribution of multiple ligands to the chemical
kinetics within Michaelis-Menten model. This work was inspired by the recent
theoretical findings from Bo Hu et al. [Phys. Rev. Lett. 105, 048104 (2010)],
our treatment with practical binding energies and chemical potential provides
the results which are consistent with experimental observations.",1101.5681v3
2011-02-16,Dynamic response and electronic structure of potassium doped picene investigated by electron energy-loss spectroscopy,"We performed electron energy-loss spectroscopy studies in order to get a
deeper insight into the electronic properties of potassium intercalated picene,
a recently discovered superconductor. A comparison of the loss function of the
undoped and doped compound shows the appearance of a new peak in the optical
gap, which we attribute to the charge carrier plasmon. We find a dramatic
increase for the value of the background dielectric constant
$\epsilon_{\infty}$ upon doping. Our core level excitation data clearly signal
filling of the conduction bands with electrons upon potassium addition.",1102.3286v1
2011-02-17,Superconductivity on the verge of Mott localization in ternary iron sulfide,"We report the results of electrical and magnetic properties on two new
compounds, K0.8Fe1.7S2 and K0.8Fe1.7SeS, both having similar structures to
newly discovered superconducting K0.8Fe1.7Se2. K0.8Fe1.7S2 exhibits a
semiconductor-like electrical property and undergoes an anti-ferromagnetic
transition at about 260 K. Upon replacing half of S with Se, K0.8Fe1.7SSe
becomes a superconductor at 25 K, implying the superconductivity evolves from a
Mott AFM state in Fe-Se based superconductors.",1102.3505v1
2011-02-17,Quenching of superconductivity by Co doping in K0.8Fe2Se2,"We synthesized a series of K0.8Fe2-xCoxSe2 samples with nominal compositions
0\leq x\leq 0.035 and investigated their physical properties. The results show
that the superconductivity in K0.8Fe2-xCoxSe2 is quenched down to 5 K by 0.5
at. % Co doping, the fastest quenching rate ever-reported. The role played here
by Co is in contrast with the one in FeAs based superconductors where Co
usually induces superconductivity from parent compounds. Such a rapid quenching
favors a localized 3d model against the itinerant one for iron pnictide
superconductors.",1102.3506v1
2011-02-19,On the energy of vanishing flow for colliding nuclei leading to same compound nucleus,"Our present studies has shown that the mass dependence of EVF show mass
asymmetry independent behaviour. This is due the fact that with increase in
asymmetry, the number of nucleon-nucleon collisions and repulsive Coulomb
interactions decreases, therefore EVF increases. The increase in EVF with
asymmetry is more for lighter nuclei as compared to heavier nuclei due to the
further less magnitude of Coulomb repulsions in lighter nuclei as compared to
heavier ones.",1102.3963v1
2011-02-23,Influence of the initial condition in equilibrium last-passage percolation models,"In this paper we consider an equilibrium last-passage percolation model on an
environment given by a compound two-dimensional Poisson process. We prove an
$\LL^2$-formula relating the initial measure with the last-passage percolation
time. This formula turns out to be a useful tool to analyze the fluctuations of
the last-passage times along non-characteristic directions.",1102.4737v2
2011-02-24,Heavy Fermions and Quantum Phase Transitions,"Quantum phase transitions arise in many-body systems due to competing
interactions that promote rivaling ground states. Recent years have seen the
identification of continuous quantum phase transitions, or quantum critical
points, in a host of antiferromagnetic heavy-fermion compounds. Studies of the
interplay between the various effects have revealed new classes of quantum
critical points, and are uncovering a plethora of new quantum phases. At the
same time, quantum criticality has provided fresh insights into the electronic,
magnetic, and superconducting properties of the heavy-fermion metals. We review
these developments, discuss the open issues, and outline some directions for
future research.",1102.4896v1
2011-02-28,Effects of the sintering atmosphere on the superconductivity of SmFeAsO1-xFx compounds,"A series of SmFeAsO1-xFx samples were sintered in quartz tubes filled with
air of different pressures. The effects of the sintering atmosphere on the
superconductivity were systematically investigated. The SmFeAsO1-xFx system
maintains a transition temperature (Tc) near 50 K until the concentration of
oxygen in quartz tubes increases to a certain threshold, after which Tc
decreases dramatically. Fluorine losses, whether due to vaporization, reactions
with starting materials, and reactions with oxygen, proved to be detrimental to
the superconductivity of this material. The deleterious effects of the oxygen
in the sintering atmosphere were also discussed in detail.",1102.5571v1
2011-03-03,"Superconducting phase transition in YNiGe3, a non-f-electron reference to the unconventional superconductor CeNiGe3","A polycrystalline sample of YNiGe3, being a non-magnetic isostructural
counterpart to the unconventional pressure-induced superconductor CeNiGe3, was
studied by means of specific heat and electrical resistivity measurements at
temperatures down to 360 mK and in magnetic fields up to 500 Oe. The compound
was found to exhibit an ambient-pressure superconductivity below Tc = 0.46 K.
The superconducting state in YNiGe3 is destroyed by magnetic field of the order
of 500 Oe.",1103.0635v1
2011-03-10,From density functional theory to the functional renormalization group: superconductivity in the iron pnictide LiFeAs,"A combined density functional theory and functional renormalization group
method is introduced which takes into account orbital-dependent interaction
parameters to derive the effective low-energy theory of weakly to
intermediately correlated Fermi systems. As an application, the competing
fluctuations in LiFeAs are investigated, which is the main representative of
the 111 class of iron pnictides displaying no magnetic order, but
superconductivity, for the parent compound. The superconducting order parameter
is found to be of s+- type driven by collinear antiferromagnetic fluctuations.
They eventually exceed the ferromagnetic fluctuations stemming from the small
hole pocket at the Gamma point, as the system flows to low energies.",1103.2101v1
2011-03-11,Thermodynamic Properties of Kagome Lattice in ZnCu_3(OH)_6Cl_2 Herbertsmithite,"Strongly correlated Fermi systems are among the most intriguing and
fundamental systems in physics, whose realization in some compounds is still to
be discovered. We show that herbertsmithite ZnCu_3(OH)_6Cl_2 can be viewed as a
strongly correlated Fermi system whose low temperature thermodynamic in
magnetic fields is defined by a quantum critical spin liquid. Our calculations
of its thermodynamic properties are in good agreement with recent experimental
facts and allow us to reveal their scaling behavior which strongly resembles
that observed in HF metals and 2D 3He.",1103.2353v1
2011-03-13,Note on PI and Szeged indices,"In theoretical chemistry molecular structure descriptors are used for
modeling physico-chemical, pharmacological, toxicologic, biological and other
properties of chemical compounds. In this paper we study distance-based graph
invariants and present some improved and corrected sharp inequalities for PI,
vertex PI, Szeged and edge Szeged topological indices, involving the number of
vertices and edges, the diameter, the number of triangles and the Zagreb
indices. In addition, we give a complete characterization of the extremal
graphs.",1103.2513v1
2011-04-08,"Tb$_2$Ti$_2$O$_7$, a two singlet spin-liquid pyrochlore","The pyrochlore compound \tbti\ is known to remain in a spin-liquid state down
to the lowest attainable temperature (0.05\,K), whereas current theories
predict it should order into an antiferromagnetic structure. A number of models
have been developed in order to resolve this discrepancy, but they could not
obtain a spin-liquid ground state. We present here an explanation for the lack
of magnetic order in \tbti\ based on the presence of a Jahn-Teller-like
distortion from the local trigonal symmetry and on the physics of the
two-singlet system coupled by exchange.",1104.1584v1
2011-04-12,On the Coupling Property and the Liouville Theorem for Ornstein-Uhlenbeck Processes,"Using a coupling for the weighted sum of independent random variables and the
explicit expression of the transition semigroup of Ornstein-Uhlenbeck processes
driven by compound Poisson processes, we establish the existence of a
successful coupling and the Liouville theorem for general Ornstein-Uhlenbeck
processes. Then we present the explicit coupling property of Ornstein-Uhlenbeck
processes directly from the behaviour of the corresponding symbol or
characteristic exponent. This approach allows us to derive gradient estimates
for Ornstein-Uhlenbeck processes via the symbol.",1104.2166v2
2011-04-12,Quantm Magnetoresistance of the PrFeAsO oxypnictides,"We report the observation of an unusual $B$ dependence of transverse
magnetoresistance (MR) in the PrFeAsO, one of the parent compound of pnictide
superconductors. Below the spin density wave transition, MR is large, positive
and increases with decreasing temperature. At low temperatures, MR increases
linearly with $B$ up to 14 T. For $T$$\geq$40 K, MR vs $B$ curve develops a
weak curvature in the low-field region which indicates a crossover from $B$
linear to $B^2$ dependence as $B$$\rightarrow$0. The $B$ linear MR originates
from the Dirac cone states and has been explained by the quantum mechanical
model proposed by Abrikosov.",1104.2177v1
2011-04-12,Upper critical fields and superconducting anisotropy of K0.70Fe1.55Se1.01S0.99 and K0.76Fe1.61Se0.96S1.04 single crystals,"We have investigated temperature and angular dependence of resistivity of
K0.70(7)Fe1.55(7)Se1.01(2)S0.99(2) and K0.76(5)Fe1.61(5)Se0.96(4)S1.04(5)
single crystals. The upper critical fields Hc2(T) for both field directions
decrease with the increase in S content. On the other hand, the angle-dependent
magnetoresistivity for both compounds can be scaled onto one curve using the
anisotropic Ginzburg-Landau theory. The obtained anisotropy of Hc2(T) increases
with S content, implying that S doping might decrease the dimensionality of
certain Fermi surface parts, leading to stronger two dimensional character.",1104.2318v2
2011-04-19,Slow Magnetic Order-Order Transition in the Spin Chain Antiferromagnet Ca3Co2O6,"Using powder neutron diffraction we have discovered an unusual magnetic
order-order transition in the Ising spin chain compound Ca3Co2O6. On lowering
the temperature an antiferromagnetic phase with propagation vector
k=(0.5,-0.5,1) emerges from a higher temperature spin density wave structure
with k=(0, 0, 1.01). This transition occurs over an unprecedented time-scale of
several hours and is never complete.",1104.3880v2
2011-04-25,Aggregate claims when their sizes and arrival times are dependent and governed by a general point process,"We suggest a general method for analyzing aggregate insurance claims that
arrive according to a very general point process, known in the literature as
the order statistic point process, which includes as special cases the
classical compound Poisson and the Sparre Andersen models, among many others.
We also allow for the process to govern claim sizes via a general dependence
structure that relates claim sizes to claim and/or inter-claim times. The
obtained general results are supplemented with special closed-form illustrative
formulas, that also exemplify the potential for future research in the area.",1104.4742v1
2011-05-04,On the Feynman-alpha formula for fast neutrons,"In this contribution, a stochastic theory for a branching process in a
neutron population with two energy levels is investigated. In particular, a
variance to mean or Feynman-alpha formula is derived in this generalized
scenario using the Kolmogorov forward or master equation theory for the
probabilities in a system with a compound Poisson source.",1105.0750v1
2011-05-12,Double-$\it q$ Order in a Frustrated Random Spin System,"We use the three-dimensional Heisenberg model with site randomness as an
effective model of the compound Sr(Fe$_{1-x}$Mn$_x$)O$_2$. The model consists
of two types of ions that correspond to Fe and Mn ions. The nearest-neighbor
interactions in the ab-plane are antiferromagnetic. The nearest-neighbor
interactions along the c-axis between Fe ions are assumed to be
antiferromagnetic, whereas other interactions are assumed to be ferromagnetic.
From Monte Carlo simulations, we confirm the existence of the
double-$\boldsymbol{q}$ ordered phase characterized by two wave numbers,
$(\pi\pi\pi)$ and $(\pi\pi0)$. We also identify the spin ordering pattern in
the double-$\boldsymbol{q}$ ordered phase.",1105.2455v1
2011-05-17,Giant Magnetoelectric Effect in HoAl_3(BO_3)_4,"A giant magnetoelectric polarization is found in HoAl$_3$(BO$_3$)$_4$. The
polarization in transverse field geometry at 70 kOe reaches 3600 $\mu C/m^2$
which is significantly higher than reported values of linear magnetoelectric or
even multiferroic compounds. The magnetostrictive effect is also measured and
compared with the magnetoelectricity. The results show that spin-lattice
coupling in HoAl$_3$(BO$_3$)$_4$ is extremely strong and that the magnetic
field causes a large polar distortion of the ionic positions in the unit cell.",1105.3429v1
2011-05-24,Long-lived magnons throughout the Brillouin zone of the strong-leg spin ladder (C$_7$H$_{10}$N)$_2$CuBr$_4$,"Inelastic neutron scattering is used to measure spin excitations in fully
deuterated single crystal samples of the strong-leg antiferromagnetic S=1/2
spin ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_4$. Sharp resolution-limited
magnons are observed across the entire one-dimensional Brillouin zone. The
results validate the previously proposed {\it symmetric} spin ladder model and
provide a reliable estimate of the relevant exchange interactions.",1105.4832v1
2011-05-25,A simple mechanism for the generation of Earth's magnetic field,"Based on the ideal gas model, the dielectric polarization of mantle is
achieved, the physical-mathematical model is constructed and the estimate
calculation of a dipole of Earth's magnetic field with the considering of
rotation, parameters of density and temperature, potential of ionization and
static dielectric constant (relative dielectric permittivity), chemical
compound of substance in Earth's mantle is executed.",1105.5037v3
2011-05-27,Observation of Dirac Holes and Electrons in a Topological Insulator,"We show that in the new topological-insulator compound
Bi_{1.5}Sb_{0.5}Te_{1.7}Se_{1.3} one can achieve a surfaced-dominated transport
where the surface channel contributes up to 70% of the total conductance.
Furthermore, it was found that in this material the transport properties
sharply reflect the time dependence of the surface chemical potential,
presenting a sign change in the Hall coefficient with time. We demonstrate that
such an evolution makes us observe both Dirac holes and electrons on the
surface, which allows us to reconstruct the surface band dispersion across the
Dirac point.",1105.5483v1
2011-06-01,Ferromagnetic and antiferromagnetic dimer splittings in LaMn0.1Ga0.9O3,"Inelastic neutron scattering was employed to study the magnetic excitations
of Mn3+ dimers in LaMn0.1Ga0.9O3. The nearest-neighbor interaction of Mn3+ ions
is ferromagnetic in the basal (a,b)-plane, but antiferromagnetic along the
c-direction, thus two different types of dimer excitations are simultaneously
present in the experiments. From the observed energy spectra we derive
Heisenberg-type exchange interactions Jab=0.210(4) meV and Jc=-0.285(5) meV as
well as an axial anisotropy parameter D=0.036(6) meV. These parameters
considerably differ from those derived for the isostructural parent compound
LaMnO3 due to structural effects.",1106.0161v1
2011-06-03,Effective transition operators for resonant inelastic X-ray scattering,"Effective symmetry-based transition operators for resonant inelastic X-ray
scattering (RIXS) are derived that show how the scattering between different
states depends on the polarization of the incoming and outgoing X-rays. In
spherical symmetry, the effective operators can be rewritten in terms of spin
operators, although the expressions depend on the nature of the ground state.
For lower symmetries, the combined action of the crystal field and the
spin-orbit interaction breaks up the spin space and spin operators are no
longer appropiate operators. By taking iridium compounds as an example, it is
demonstrated that effective scattering operators can still be obtained. These
effective transition operators facilitate our understanding how RIXS couples to
elementary excitations.",1106.0640v1
2011-06-06,Statistical inference across time scales,"We investigate statistical inference across time scales. We take as toy model
the estimation of the intensity of a discretely observed compound Poisson
process with symmetric Bernoulli jumps. We have data at different time scales:
microscopic, intermediate and macroscopic. We quantify the smooth statistical
transition from a microscopic Poissonian regime to a macroscopic Gaussian
regime. The classical quadratic variation estimator is efficient in both
microscopic and macroscopic scales but surprisingly shows a substantial loss of
information in the intermediate scale that can be explicitly related to the
sampling rate. We discuss the implications of these findings beyond this
idealised framework.",1106.1031v1
2011-06-07,Direct observation of the influence of the As-Fe-As angle on the Tc of superconducting SmFeAsO$_{1-x}$F$_{x}$,"The electrical resistivity, crystalline structure and electronic properties
calculated from the experimentally measured atomic positions of the compound
SmFeAsO$_{0.81}$F$_{0.19}$ have been studied up to pressures ~20GPa. The
correlation between the pressure dependence of the superconducting transition
temperature (Tc) and crystallographic parameters on the same sample shows
clearly that a regular FeAs$_{4}$ tetrahedron maximizes Tc, through
optimization of carrier transfer to the FeAs planes as indicated by the
evolution of the electronic band structures.",1106.1361v1
2011-06-13,Mass Enhancement in an Intermediate-Valent Regime of Heavy-Fermion Systems,"We study the mechanism of the mass enhancement in an intermediate-valent
regime of heavy-fermion materials. We find that the crossovers between the
Kondo, intermediate valent, and almost empty f-electron regimes become sharp
with the Coulomb interaction between the conduction and f electrons. In the
intermediate-valent regime, we find a substantial mass enhancement, which is
not expected in previous theories. Our theory may be relevant to the observed
nonmonotonic variation in the effective mass under pressure in CeCu2Si2 and the
mass enhancement in the intermediate-valent compounds alpha-YbAlB4 and
beta-YbAlB4.",1106.2360v1
2011-06-15,Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$,"We report an infrared optical study of the pnictide high-temperature
superconductor BaFe$_{1.84}$Co$_{0.16}$As$_{2}$ and its parent compound
BaFe$_{2}$As$_{2}$. We demonstrate that electronic correlations are moderately
strong and do not change across the spin-density wave transition or with
doping. By examining the energy scale and direction of spectral weight
transfer, we argue that Hund's coupling \emph{J} is the primary mechanism that
gives rise to correlations.",1106.3114v1
2011-06-18,Orbital order and magnetism of FeNCN,"Based on density functional calculations, we report on the orbital order and
microscopic magnetic model of FeNCN, a prototype compound for orbital-only
models. Despite having a similar energy scale, the spin and orbital degrees of
freedom in FeNCN are only weakly coupled. The ground-state configuration
features the doubly occupied d_{3z^2-r^2} (a1g) orbital and four
singly-occupied d orbitals resulting in the spin S=2 on the Fe+2 atoms, whereas
alternative (Eg') configurations are about 75 meV/f.u. higher in energy.
Calculated exchange couplings and band gap are in good agreement with the
available experimental data. Experimental effects arising from possible orbital
excitations are discussed.",1106.3665v1
2011-06-24,Spin-orbit coupling induced Mott transition in Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ (0<x<0.2),"We propose a new mechanism for the paramagnetic metal-insulator transition in
the layered perovskite Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ (0<x<0.2). The LDA+U
approach including spin-orbit coupling is used to calculate the electronic
structures. In Ca$_{2}$RuO$_{4}$, we show that the spin-orbit effect is
strongly enhanced by the Coulomb repulsion, which leads to an insulating phase.
When Ca is substituted by Sr, the effective spin-orbit splitting is reduced due
to the increasing bandwidth of the degenerate $d_{xz}$ and $d_{yz}$ orbitals.
For x=0.2, the compound is found to be metallic. We show that these results are
in good agreement with the experimental phase diagram.",1106.5046v1
2011-07-13,An IDE to Build and Check Task Flow Models,"This paper presents the Eclipse plug-ins for the Task Flow model in the
Discovery Method. These plug-ins provide an IDE for the Task Algebra compiler
and the model-checking tools. The Task Algebra is the formal representation for
the Task Model and it is based on simple and compound tasks. The model-checking
techniques were developed to validate Task Models represented in the algebra.",1107.2683v1
2011-07-18,Molecular-spin dynamics study of electromagnons in multiferroic RMn$_2$O$_5$,"We investigate the electromagnon in magnetoferroelectrics RMn$_2$O$_5$ using
combined molecular-spin dynamics simulations. We identify the origin of the
electromagnon modes observed in the optical spectra and reproduce the most
salient features of the electromagnon in these compounds. We find that the
electromagnon frequencies are very sensitive to the magnetic wave vector along
the $a$ direction. We further investigate the electromagnon in magnetic field.
Although the modes frequencies change significant under magnetic field, the
static dielectric constant electromagnon does not change much in the magnetic
field.",1107.3349v1
2011-07-25,"Experimental study and critical review of structural, thermodynamic and mechanical properties of superhard refractory boron suboxide, B6O","In the present paper we performed the analysis of available data on
structural, thermodynamic and mechanical properties of B6O. Although the
compound is known for half a century and has been extensively studied, many
properties of this boron-rich solid remain unknown or doubtful. Semi-empirical
analysis of our experimental and literature data allowed us to choose the best
values of main thermodynamic and mechanical characteristics among previously
reported data, to predict the thermoelastic equation of state of B6O, and
dependence of its hardness on non-stoichiometry and temperature.",1107.4895v2
2011-07-25,Theoretical investigation of electronic specific heat of two-band superconductors,"We apply the generalized two-band model of superconductivity to calculate the
electronic contribution to the specific heat, superconducting gaps and
electron-boson coupling constants of the multi-band layered superconductors
MgB2 and Ba(Fe0.925Co0.075)2As2. For both compounds, the obtained
temperature-behavior of the specific heat well describes the experimental data.
We compare our findings with the ""two-band - model"" that is frequently used to
calculate the electronic specific heat, and that is applicable only for
superconductors with strong interband scattering (""dirty"" enough
superconductors).",1107.5024v1
2011-07-29,Review of Exotic Hadrons,"I review here the most recent results about the observation and the study of
hadronic bound states that do not fit well in the standard quarkonium picture.
Several new states have been observed in the last few years, at B-,
tau-Factories and hadron colliders. For most of them, quantum number
determinations are available and allow to develop the basis of a new
spectroscopy based on exotic compounds like tetraquarks or meson molecules.
Nonetheless, there is still a lot of work to do to complete the picture.",1107.5915v1
2011-07-29,Electron spin resonance shift in spin ladder compounds,"We analyze the effects of different coupling anisotropies in spin-1/2 ladder
on the Electron Spin Resonance (ESR) shift. Combining a perturbative expression
in the anisotropies with temperature dependent Density Matrix Renormalization
Group (T-DMRG) computation of the short range correlations, we provide the full
temperature and magnetic field evolution of the ESR paramagnetic shift. We show
that for well chosen parameters the ESR shift can be in principle used to
extract quantitatively the anisotropies and, as an example, discuss the
material $\mathrm{(C_5H_{12}N)_2CuBr_4}$ (BPCB).",1107.5965v2
2011-08-02,Single Molecule Magnets and the Lipkin-Meshkov-Glick model,"We discuss the description of quantum magnetization in the super paramagnetic
compound Fe$_8$ using a generalization of the Lipkin-Meshkov-Glick Hamiltonian.
We study the variation of the energy spectra and of the wave-functions as
functions of the intensity of an external magnetic field along the three
magnetic anisotropy axes.",1108.0706v1
2011-08-03,Pressure effects on Dirac fermions in α-(BEDT-TTF)2I3,"We investigate the pressure effect on the layered Dirac fermion system, which
is realized in quasi-two-dimensional organic compound {\alpha}-(BEDT-TTF)2I3.
The trajectory of the contact points is investigated using the tight-binding
model with the transfer integrals determined by X-ray diffraction experiments.
Vanishing of the Dirac fermion spectrum, opening of the gap, and pressure
dependence of inter-layer magnetoresistance are discussed.",1108.0791v1
2011-08-03,"The set-indexed Lévy process: Stationarity, Markov and sample paths properties","We present a satisfactory definition of the important class of L\'evy
processes indexed by a general collection of sets. We use a new definition for
increment stationarity of set-indexed processes to obtain different
characterizations of this class. As an example, the set-indexed compound
Poisson process is introduced. The set-indexed L\'evy process is characterized
by infinitely divisible laws and a L\'evy-Khintchine representation. Moreover,
the following concepts are discussed: projections on flows, Markov properties,
and pointwise continuity. Finally the study of sample paths leads to a
L\'evy-It\^o decomposition. As a corollary, the semimartingale property is
proved.",1108.0873v2
2011-08-18,"Non-Markovian Open Quantum Systems: Input-Output Fields, Memory, Monitoring","Principles of monitoring non-Markovian open quantum systems are analyzed. We
use the field representation of the environment (Gardiner and Collet, 1985) for
the separation of its memory and detector part, respectively. We claim the
system-plus-memory compound becomes Markovian, the detector part is tractable
by standard Markovian monitoring. Because of non-Markovianity, only the mixed
state of the system can be predicted, the pure state of the system can be
retrodicted. We present the corresponding non-Markovian stochastic
Schr\""odinger equation.",1108.3763v2
2011-08-24,Ferromagnetism and Superconductivity in Uranium Compounds,"Recent advances on ferromagnetic superconductors, UGe2, URhGe and UCoGe are
presented. The superconductivity (SC) peacefully coexists with the
ferromagnetism (FM), forming the spin-triplet state of Cooper pairs. The
striking new phenomena, such as SC reinforced by the magnetic field, are
associated with Ising-type ferromagnetic fluctuations. A variety of
ferromagnetic ordered moments between UGe2, URhGe and UCoGe affords to
understand the relation between FM, tricriticality and SC.",1108.4807v1
2011-08-31,Incommensurate magnetic excitations in superconducting LiFeAs,"Magnetic correlations in superconducting LiFeAs were studied by elastic and
by inelastic neutron scattering experiments. There is no indication for static
magnetic ordering but inelastic correlations appear at the incommensurate wave
vector (0:5+-d 0:-+d 0) with d=0.07 slightly shifted from the commensurate
ordering observed in other FeAs-based compounds. The incommensurate magnetic
excitations respond to the opening of the superconducting gap by a transfer of
spectral weight.",1108.6187v1
2011-09-06,Griffiths phase in solid-solution of ferromagnetic manganite and cobaltite,"We report the existence of Griffiths phase (GP) over a wide range of $x$ in
La$_{0.6}$Sr$_{0.4}$Mn$_{1-x}$Co$_x$O$_3$, the solid solution of ferromagnetic
(FM) La$_{0.6}$Sr$_{0.4}$MnO$_3$ and La$_{0.6}$Sr$_{0.4}$CoO$_3$, from
magnetization measurements. In this compound, GP arises due to the quenching of
randomly distributed Co-O-Mn antiferromagnetic bonds in the FM background. In
contrary to divalent doped manganites, GP in the present system can exist
entirely in the metallic state above $T_C$ (for $x$$<$0.10). Based on the
present study, a magnetoelectronic phase diagram is drawn.",1109.1090v1
2011-09-16,Magnetic properties of the antiferromagnetic spin-1/2 chain system $β$-TeVO$_{4}$,"The magnetic susceptibility and magnetization of high quality single crystal
beta-TeVO4 are reported. We show that this compound, made of weakly coupled
infinite chains of VO5 pyramids sharing corners, behaves as a S = 1/2
one-dimensional Heisenberg antiferromagnet. From magnetic experiments we deduce
the intrachain antiferromagnetic coupling constant J/kB = 21.4 $\pm$ 0.2 K.
Below 5 K a series of three phase transitions at 2.26, 3.28 and 4.65 K is
observed.",1109.3564v1
2011-09-29,Improved estimation in a non-Gaussian parametric regression,"The paper considers the problem of estimating the parameters in a continuous
time regression model with a non-Gaussian noise of pulse type. The noise is
specified by the Ornstein-Uhlenbeck process driven by the mixture of a Brownian
motion and a compound Poisson process. Improved estimates for the unknown
regression parameters, based on a special modification of the James-Stein
procedure with smaller quadratic risk than the usual least squares estimates,
are proposed. The developed estimation scheme is applied for the improved
parameter estimation in the discrete time regression with the autoregressive
noise depending on unknown nuisance parameters.",1109.6493v1
2011-09-30,Empirical oscillating potentials for alloys from ab-initio fits and the prediction of quasicrystal-related structures in the Al-Cu-Sc system,"By fitting to a database of ab-initio forces and energies, we can extract
pair potentials for alloys, with a simple six-parameter analytic form including
Friedel oscillations, which give a remarkably faithful account of many complex
intermetallic compounds. Furthermore, such potentials are combined with a
method of discovering complex zero-temperature structures with hundreds of
atoms per cell, given only the composition and the con- straint of known
lattice parameters, using molecular-dynamics quenches. We apply this approach
to structure prediction in the Al-Cu-Sc quasicrystal-related system.",1109.6931v1
2011-10-06,Thermoelectric transport across the metamagnetic transition of CeRu2Si2,"We have measured the thermopower across the metamagnetic transition of the
heavy fermion compound CeRu2Si2 at temperatures down to 0.1K and magnetic
fields up to 11.5T. We find a large negative enhancement of the thermopower on
crossing the metamagnetic field, as well as a sudden change in slope. We argue
that this is consistent with the Zeeman-driven deformation of the Fermi surface
through a topological transition. The field dependence of the thermopower
highlights the discrepancy between thermodynamic and transport properties
across the metamagnetic transition.",1110.1160v2
2011-10-06,Ferromagnetism in YbCu2Si2 at high pressure,"We demonstrate from detailed ac-susceptibility and calorimetry studies under
hydrostatic pressure that YbCu2Si2 probably orders ferromagnetically at high
pressure. The (p,H,T) phase diagram, shows that the transition temperature
increases with pressure, but also with an applied magnetic field. We suggest
that many ytterbium systems may show a trend towards ferromagnetism and we
discuss the possible reasons for this. We also examine the implications,
including the potential of YbCu2Si2 and other Yb compounds for further studies
of the rich physical properties that may occur near a ferromagnetic critical
point.",1110.1278v1
2011-10-13,Element gain drifts as an imaging dynamic range limitation in PAF-based interferometers,"Interferometry with phased-array feeds (PAFs) presents new calibration
challenges in comparison with single-pixel feeds. In particular, temporal
instability of the compound beam patterns due to element gain drifts (EGDs) can
produce calibration artefacts in interferometric images. To translate imaging
dynamic range requirements into PAF hardware and calibration requirements, we
must learn to relate EGD levels to imaging artefact levels. We present a
MeqTrees-based simulations framework that addresses this problem, and apply it
to the APERTIF prototype currently in development for the WSRT.",1110.2914v1
2011-10-16,Low temperature magnetic structure of geometrically frustrated SrHo2O4,"SrHo2O4 is a geometrically frustrated compound because the Ho^3+ ions are
arranged in a network of triangles and hexagons and coupled with
antiferromagnetic exchange interactions. Powder neutron diffraction
measurements show that long-range magnetic order is established at T_N = 0.68
K. The low temperature magnetic structure is made up of two distinct
components: a k = 0 long-range structure as well as a shorter-range
low-dimensional structure with scattering intensity around the (0 0 1/2)
position. The diffuse component of the magnetic scattering from SrHo2O4 remains
very intense at temperatures well above T_N.",1110.3521v1
2011-10-17,A Mössbauer study of the magneto-structural coupling effect in SrFe$_2$As$_2$ and SrFeAsF,"In the present paper, we report a comparison study of SrFe$_2$As$_2$ and
SrFeAsF using M\""ossbauer spectroscopy. The temperature dependence of the
magnetic hyperfine field is fitted with a modified Bean-Rodbell model. The
results give much smaller magnetic moment and magneto-structural coupling
effect for SrFeAsF, which may be understood as due to different inter-layer
properties of the two compounds.",1110.3550v1
2011-10-28,"Transport, magnetic, and thermal properties of non-centrosymmetric Yb2Co12P7","We report magnetization and specific heat measurements down to 2 K and
electrical resistivity down to millikelvin temperatures on polycrystalline
samples of the non-centrosymmetric compound Yb2Co12P7. In addition to the
previously reported ferromagnetic ordering of the cobalt sub-lattice at T_C =
136 K we find a magnetic transition below T_M = 5 K that is likely associated
with ordering of the Yb ions. The broad nature of the specific heat anomaly
suggests disordered magnetism and possible short range correlations well above
T_M.",1110.6423v1
2011-10-31,Shubnikov-de Haas measurements on LuRh2Si2,"We present Shubnikov-de Haas measurements on LuRh2Si2, the non-magnetic
reference compound to the prototypical heavy-fermion system YbRh2Si2. We find
an extensive set of orbits with clear angular dependences. Surprisingly, the
agreement with non-correlated band structure calculations is limited. This may
be related to an uncertainty in the calculations arising from a lack of
knowledge about the exact Si atom position in the unit cell. The data on
LuRh2Si2 provide an extensive basis for the interpretation of measurements on
YbRh2Si2 indicative of discrepancies between the high-field Fermi surface of
YbRh2Si2 and the ""small"" Fermi surface configuration.",1110.6763v1
2011-11-01,Electronic band structure of ferro-pnictide superconductors from ARPES experiment,"ARPES experiments on iron based superconductors show that the differences
between the measured and calculated electronic band structures look
insignificant but can be crucial for understanding of the mechanism of high
temperature superconductivity. Here we focus on those differences for 111 and
122 compounds and discuss the observed correlation of the experimental band
structure with the superconductivity.",1111.0288v1
2011-11-02,Stability and thermoelectric properties of transition metal silicides from first principles calculations,"We report an ab-initio study of the stability and electronic properties of
transition metal silicides in order to study their potential for high
temperature thermoelectric applications. We focus on the family M5Si3 (M = Ta,
W) which is stable up to about 2000 {\deg}C. We first investigate the
structural stability of the two compounds and then determine the thermopower of
the equilibrium structure using the electronic density of states and Mott's
law. We find that W5Si3 has a relatively large thermopower but probably not
sufficient enough for thermoelectric applications.",1111.0527v1
2011-11-04,Actinide Topological Insulator Materials with Strong Interaction,"Topological band insulators have recently been discovered in spin-orbit
coupled two and three dimensional systems. In this work, we theoretically
predict a class of topological Mott insulators where interaction effects play a
dominant role. In actinide elements, simple rocksalt compounds formed by Pu and
Am lie on the boundary of metal to insulator transition. We show that
interaction drives a quantum phase transition to a topological Mott insulator
phase with a single Dirac cone on the surface.",1111.1267v1
2011-11-10,Exponential suppression of interlayer conductivity in very anisotropic quasi-two-dimensional compounds in high magnetic field,"It is shown that in rather strong magnetic field the interlayer electron
conductivity is exponentially damped by the Coulomb barrier arising from the
formation of polaron around each localized electron state. The theoretical
model is developed to describe this effect, and the calculation of the
temperature and field dependence of interlayer magnetoresistance is performed.
The results obtained agree well with the experimental data in GaAs/AlGaAs
heterostructures and in strongly anisotropic organic metals. The proposed
theory allows to use the experiments on interlayer magnetoresistance to
investigate the electron states, localized by magnetic field and disorder.",1111.2432v1
2011-11-12,Control of Dams When the Input Is a Levy Type Process,"Zuckermann [10] considers the problem of optimal control of a finite dam
assuming that the input process is Wiener with positive drift term \mu \geq 0.
Lam and Lou [7] treat the case where the input is a Wiener process with a
reflecting boundary at its infimum, with a positive drift term, using the
long-run Average and total discounted cost criteria. Attia [3] obtains results
similar to those of Lam and Lou, through simpler and more direct methods. Bae
et al. [5] treat the long-run average cost case when the input process is a
compound Poisson process with a negative drift. In this paper we unify and
extend the results of these authors",1111.2923v1
2011-11-19,Empirical Quantile CLTs for Time Dependent Data,"We establish empirical quantile process CLTs based on $n$ independent copies
of a stochastic process $\{X_t: t \in E\}$ that are uniform in $t \in E$ and
quantile levels $\alpha \in I$, where $I$ is a closed sub-interval of $(0,1)$.
Typically $E=[0,T]$, or a finite product of such intervals. Also included are
CLT's for the empirical process based on $\{I_{X_t \le y} - \rm {Pr}(X_t \le
y): t \in E, y \in R \}$ that are uniform in $t \in E, y \in R$. The process
$\{X_t: t \in E\}$ may be chosen from a broad collection of Gaussian processes,
compound Poisson processes, stationary independent increment stable processes,
and martingales.",1111.4591v1
2011-12-08,Does deuteron-induced fission on actinide nuclei prevails over the breakup at low incident energies?,"An analysis of the $^{231}$Pa$(d,3n)$$^{230}$U reaction excitation function
at energies around the Coulomb barrier has taken into account the
pre-equilibrium and compound-nucleus cross sections corrected for the
deuteron-breakup decrease of the total reaction cross section, as well as the
inelastic breakup enhancement. The analysis reveals the dominance of the
deuteron breakup mechanism unlike a former assessment in this respect of the
deuteron-induced fission process.",1112.1832v1
2011-12-12,Second order corrections for the limits of normalized ruin times in the presence of heavy tails,"In this paper we consider a compound Poisson risk model with regularly
varying claim sizes. For this model in [1] an asymptotic formula for the finite
time ruin probability is provided when the time is scaled by the mean excess
function. In this paper we derive the rate of convergence for this finite time
ruin probability when the claims have a finite second moment.
  [1] S. Asmussen and C. Kl\""uppelberg. Large deviations results for
subexponential tails, with applications to insurance risk. Stochastic Process.
Appl., 64(1):103-125, 1996.",1112.2543v1
2011-12-12,The Uncertainty Relation for Quantum propositions,"Logical propositions with the fuzzy modality ""Probably"" are shown to obey an
uncertainty principle very similar to that of Quantum Optics. In the case of
such propositions, the partial truth values are in fact probabilities. The
corresponding assertions in the metalanguage, have complex assertion degrees
which can be interpreted as probability amplitudes. In the logical case, the
uncertainty relation is about the assertion degree, which plays the role of the
phase, and the total number of atomic propositions, which plays the role of the
number of modes. In analogy with coherent states in quantum physics, we define
""quantum coherent propositions"" those which minimize the above logical
uncertainty relation. Finally, we show that there is only one kind of compound
quantum-coherent propositions: the ""cat state"" propositions.",1112.2923v1
2011-12-16,Caged clusters in Al$_{11}$Ir$_4$: structural transition and insulating phase,"Using pair potentials fitted to an ab--initio database, combined with
replica--exchange simulated annealing, we show the complex,
quasicrystal-related Al$_{11}$Ir$_4$ compound contains a new version of the
""pseudo-Mackay"" icosahedral cluster, with non-icosahedral inner Al$_{10}$Ir
and/or Al$_9$Ir clusters that exist in various orientations and account for
partial occupancies in the reported structure. Two different compositions show
first-order transitions to orientationally ordered phases doubling the (cubic)
unit cell, which are respectively metallic and insulating.",1112.3804v2
2011-12-27,Quantum magnetic oscillations and angle-resolved photoemission from impurity bands in cuprate superconductors,"Present-day angle-resolved photoemission spectroscopy (ARPES) has offered a
tremendous advance in the understanding of electron energy spectra in cuprate
superconductors and some related compounds. However, in high magnetic field,
magnetic quantum oscillations at low temperatures indicate the existence of
small electron (hole) Fermi pockets seemingly missing in ARPES of hole
(electron) doped cuprates. Here ARPES and quantum oscillations are reconciled
in the framework of an impurity band in the charge-transfer Mott-Hubbard
insulator.",1112.6029v1
2011-12-28,"Comment on ""Phase fluctuation superconductivity in overdoped La2-xSrxCuO4""","By measuring the in-plane resistivity as a function of temperature and
magnetic field in overdoped La2-xSrxCuO4 (LSCO) superconductors, in a recent
Letter Rourke et al. [Nature Physics 7, 455 (2011)] have addressed the long
standing but still open issue of the interplay between pseudogap and
superconducting fluctuations in cuprates. Unfortunately, these authors have
analyzed their interesting measurements without taking into account the
unavoidable inhomogeneities of the zero-field critical temperature Tc0
associated with the random distribution of the Sr ions, in spite of the
different works on this issue in the same compounds. Here we will show that
such a shortcoming invalidates most of the conclusions of Rourke et al.",1112.6104v1
2011-12-31,Brief review on iron-based superconductors: are there clues for unconventional superconductivity?,"Study of superconductivity in layered iron-based materials was initiated in
2006 by Hosono's group, and boosted in 2008 by the superconducting transition
temperature, Tc, of 26 K in LaFeAsO1-xFx. Since then, enormous researches have
been done on the materials, with Tc reaching as high as 55 K. Here, we review
briefly experimental and theoretical results on atomic and electronic
structures and magnetic and superconducting properties of FeAs-based
superconductors and related compounds. We seek for clues for unconventional
superconductivity in the materials.",1201.0237v1
2012-01-05,Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure,"We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.",1201.1070v1
2012-01-08,Nodal gap structure in the noncentrosymmetric superconductor LaNiC2 from magnetic-penetration-depth measurements,"We report measurements of the temperature dependence of the magnetic
penetration depth in different quality polycrystalline samples of
noncentrosymmetric LaNiC2 down to 0.05 K. This compound has no magnetic phases
and breaks time-reversal symmetry. In our highest quality sample we observe a
T^2 dependence below 0.4Tc indicative of nodes in the energy gap. We argue that
previous results suggesting conventional s-wave behavior may have been affected
by magnetic impurities.",1201.1649v1
2012-01-17,Atom-photon interactions in a system of coupled cavities,"We give a theoretical treatment of single atom detection in an compound,
optical micro cavity. The cavity consists of a single mode semiconductor
waveguide with a gap to allow atoms to interact with the optical field in the
cavity. Optical losses, both in the semiconductor and induced by the gap are
considered and we give an estimate of the cavity finesse. We also compute the
cooperativity parameter and show how it depends on the gap width and cavity
length. Maximization of the cooperativity does not always correspond to
maximization of the coupling.",1201.3534v2
2012-01-30,Thermoelectric Properties of Ho-doped Bi1-xSbx,"The Seebeck coefficients, electrical resistivities, total thermal
conductivities, and magnetization are reported for temperatures between 5 and
350 K for n-type Bi0.88Sb0.12 nano-composite alloys made by Ho-doping at the 0,
1 and 3% atomic levels. The alloys were prepared using a dc hot-pressing
method, and are shown to be single phase for both Ho contents with grain sizes
on the average of 900 nm. We find the parent compound has a maximum of ZT =
0.28 at 231 K, while doping 1% Ho increases the maximum ZT to 0.31 at 221 K and
the 3% doped sample suppresses the maximum ZT = 0.24 at a temperature of 260 K.",1201.6304v1
2012-01-31,"Magnetoresistance, noise properties and the Koshino-Taylor effect in the quasi-1D oxide KRu_4O_8","The low temperature electronic and galvanomagnetic transport properties of
the low dimensional oxide KRu_4O_8 are experimentally considered. A quadratic
temperature variation of the resistivity is observed to be proportional to the
residual resistivity. It shows the role of inelastic electron scattering
against impurities, i.e. a large Koshino-Taylor effect, rather than a
consequence of strong electronic correlations. In the same temperature range,
the Kohler rule is not fulfilled. The resistance noise increases also sharply,
possibly due to a strong coupling of carriers with lattice fluctuations in this
low dimensional compound.",1201.6474v1
2012-02-06,"Magnetostructural study of the (Mn,Fe)3(P,Si) system","Using X-ray diffraction, DSC and magnetization measurements, a
magnoestructural map of the (Mn,Fe)3(Si,P) system was assembled and reported in
the current paper. Besides the already known cubic phase for Mn3-xFexSi system
and the tetragonal and orthorhombic phases for the Mn3-xFexP system, a novel
hexagonal phase has been observed for Mn3 xFexSi1-yPy, within the approximate
range of 0.2<x<2.0 and 0.2<y<0.9. Magnetization measurements both confirm and
further detail the already known properties of the Mn3-xFexSi and Mn3-xFexP
systems.",1202.1173v1
2012-02-06,Wasserstein decay of one dimensional jump-diffusions,"This work is devoted to the Lipschitz contraction and the long time behavior
of certain Markov processes. These processes diffuse and jump. They can
represent some natural phenomena like size of cell or data transmission over
the Internet. Using a Feynman-Kac semigroup, we prove a bound in Wasserstein
metric. This bound is explicit and optimal in the sense of Wasserstein
curvature. This notion of curvature is relatively close to the notion of
(coarse) Ricci curvature or spectral gap. Several consequences and examples are
developed, including an $L^2$ spectral for general Markov processes, explicit
formulas for the integrals of compound Poisson processes with respect to a
Brownian motion, quantitative bounds for Kolmogorov-Langevin processes and some
total variation bounds for piecewise deterministic Markov processes.",1202.1259v2
2012-02-07,Thermal Analysis and Phase Diagram of the LiF-BiF3 System,"Differential thermal analysis up to complete melting was performed for the
complete pseudobinary system LiF-BiF3. Melts with high bismuth fluoride
concentration show severe evaporation, nevertheless even pure BiF3 could be
molten at 655 deg. C. The system contains one intermediate compound BiLiF4
which melts by peritectic decomposition under the formation of LiF at 415 deg.
C. The eutectic between BiLiF4 and BiF3 melts at 415 deg. C. By thermodynamic
assessment the following parameters were found for BiLiF4: \Delta H=-1514900
J/mol, S=158.5 J/mol K, c_p=166.173 -0.01072 T (in J/mol K). The melt has
negative excess Gibbs free energy.",1202.1421v1
2012-02-17,Dual Features of Magnetic Susceptibility in Superconducting Cuprates: a comparison to inelastic neutron scattering,"Starting from the generalized t-J-G model Hamiltonian, we analyze the spin
response in the superconducting cuprates taking into account both local and
itinerant spin components which are coupled to each other self-consistently.
Derived expression reproduces the basic observations of neutron scattering data
in YBa2Cu3O6+y compounds near the optimal doping level.",1202.3904v1
2012-02-18,Quantum criticality in Ce2PdIn8: thermoelectric study,"We report the Nernst effect (v) and thermoelectric power (S) data for the
Ce2PdIn8 heavy-fermion compound. Both S and v behave anomalously at low
temperatures: the thermopower shows a Kondo-like maximum at T = 37 K, while the
Nernst coefficient becomes greatly enhanced and field dependent below T ~ 30 K.
In the zero-T limit S/T and v/T diverge logarithmically, what is related to
occurrence of the quantum critical point (QCP). Presented results suggest that
the antiferromagnetic spin-density-wave scenario may be applicable to QCP in
Ce2PdIn8.",1202.4079v1
2012-02-20,Observation of optical chemical shift by precision nuclear spin optical rotation measurements and calculations,"Nuclear spin optical rotation (NSOR) is a recently developed technique for
detection of nuclear magnetic resonance via rotation of light polarization,
instead of the usual long-range magnetic fields. NSOR signals depend on
hyperfine interactions with virtual optical excitations, giving new information
about the nuclear chemical environment. We use a multi-pass optical cell to
perform first precision measurements of NSOR signals for a range of organic
liquids and find clear distinction between proton signals for different
compounds, in agreement with our earlier predictions. Detailed first principles
quantum-mechanical NSOR calculations are found to be in good agreement with the
measurements.",1202.4241v1
2012-02-20,A parsimonious model for intraday European option pricing,"A stochastic model for pure-jump diffusion (the compound renewal process) can
be used as a zero-order approximation and as a phenomenological description of
tick-by-tick price fluctuations. This leads to an exact and explicit general
formula for the martingale price of a European call option. A complete
derivation of this result is presented by means of elementary probabilistic
tools.",1202.4332v1
2012-03-07,Structural distortion as prerequisite for superconductivity in LiFeAs,"The nonadiabatic Heisenberg model predicts a structural distortion in LiFeAs
below a temperature higher than (or at least equal to) the superconducting
transition temperature. Within this group-theoretical model, the reduction of
the symmetry caused by the distortion is a prerequisite for the superconducting
state in this compound and can be realized by a mere displacement of the iron
atoms from their positions in the space group P4/nmm.",1203.1543v1
2012-03-14,Combined analytical and numerical approach to magnetization plateaux in one-dimensional spin tube antiferromagnets,"In this paper, we investigate the properties of frustrated three-leg spin
tubes under a magnetic field. We concentrate on two kind of geometries for
these tubes, one of which is relevant for the compound
$\mathrm{[(CuCl_2tachH)_3Cl]Cl_2}$. We combine an analytical path integral
approach with a strong coupling approach, as well as large-scale Density Matrix
Renormalization Groups (DMRG) simulations, to identify the presence of plateaux
in the magnetization curve as a function of the value of spin $S$. We also
investigate the issue of gapless non-magnetic excitations on some plateaux,
dubbed chirality degrees of freedom for both tubes.",1203.3084v1
2012-03-23,Magnetic dispersion and anisotropy in multiferroic BiFeO3,"We have determined the full magnetic dispersion relations of multiferroic
BiFeO3. In particular, two excitation gaps originating from magnetic
anisotropies have been clearly observed. The direct observation of the gaps
enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction
and the single ion anisotropy. The DM interaction supports a strong
magneto-electric coupling in this compound.",1203.5294v3
2012-04-06,Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe2,"IrTe2, a layered compound with a triangular iridium lattice, exhibits a
structural phase transition at approximately 250 K. This transition is
characterized by the formation of Ir-Ir bonds along the b-axis. We found that
the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the
appearance of a structural critical point in the T = 0 limit at xc = 0.035.
Although both IrTe2 and PtTe2 are paramagnetic metals, superconductivity at Tc
= 3.1 K is induced by the bond breaking in a narrow range of x > xc in
Ir1-xPtxTe2. This result indicates that structural fluctuations can be involved
in the emergence of superconductivity.",1204.1421v1
2012-04-10,A possible chiral spin-liquid phase in non-centrosymmetric $R$BaCo$_4$O$_7$,"Based on a symmetry approach, we propose a possible explanation of the weak
ferromagnetic component recently observed in YBaCo$_3$FeO$_7$ (Valldor et al.
Phys Rev B, $\bf {84}$ 224426 (2011)) and other isostructural compounds in the
high-temperature spin-liquid phase. Due to the polar nature of their crystal
structure, a coupling between time-odd scalar spin chirality which we suggest
as the primary order parameter and macroscopic magnetization is possible as
follows from the general form of the appropriate free-energy invariant. The
deduced pseudoproper coupling between both physical quantities provides a
unique possibility to study the critical behaviour of the chiral order
parameter.",1204.2168v1
2012-04-19,A new two parameter lifetime distribution: model and properties,"In this paper a new lifetime distribution which is obtained by compounding
Lindley and geometric distributions, named Lindley-geometric (LG) distribution,
is introduced. Several properties of the new distribution such as density,
failure rate, mean lifetime, moments, and order statistics are derived.
Furthermore, estimation by maximum likelihood and inference for large sample
are discussed. The paper is motivated by two applications to real data sets and
we hope that this model be able to attract wider applicability in survival and
reliability.",1204.4248v1
2012-04-23,Heavy fermions in high magnetic field,"We give an overview on experimental studies performed in the last 25 years on
heavy-fermion systems in high magnetic field. The properties of field-induced
magnetic transitions in heavy-fermion materials close to a quantum
antiferromagnetic-to-paramagnetic instability are presented. Effects of a high
magnetic field to the Fermi surface, in particular the splitting of spin-up and
spin-down bands, are also considered. Finally, we review on recent advances on
the study of non-centrosymmetric compounds and ferromagnetic superconductors in
a high magnetic field.",1204.5128v2
2012-04-27,Organic conductors in high magnetic fields: model systems for quantum oscillations physics,"Even though organic conductors have complicated crystalline structure with
low symmetry and large unit cell, band structure calculations predict multiband
quasi-two dimensional electronic structure yielding very simple Fermi surface
in most cases. Although few puzzling experimental results are observed, data of
numerous compounds are in agreement with calculations which make them suitable
systems for studying magnetic quantum oscillations in networks of orbits
connected by magnetic breakdown. The state of the art of this problematics is
reviewed.",1204.6134v2
2012-04-28,Nearly itinerant ferromagnetism in CaNi2 and CaNi3,"Single crystals of CaNi2 and CaNi3 were successfully grown out of excess Ca.
Both compounds manifest a metallic ground state with enhanced, temperature
dependent magnetic susceptibility. The relatively high Stoner factors of Z =
0.79 and Z = 0.87 found for CaNi2 and CaNi3, respectively, reveal their close
vicinity to ferromagnetic instabilities. The pronounced field dependence of the
magnetic susceptibility of CaNi3 at low temperatures (T < 25 K) suggests strong
ferromagnetic fluctuations. A corresponding contribution to the specific heat
with a temperature dependence of T^3lnT was also observed.",1204.6355v2
2012-05-03,Towards a new metamodel for the Task Flow Model of the Discovery Method,"This paper presents our proposal for the evolution of the metamodel for the
Task Algebra in the Task Flow model for the Discovery Method. The original Task
Algebra is based on simple and compound tasks structured using operators such
as sequence, selection, and parallel composition. Recursion and encapsulation
were also considered. We propose additional characteristics to improve the
capabilities of the metamodel to represent accurately the Task Flow Model.",1205.0750v1
2012-05-04,Thermodynamic evidence for pressure-induced bulk superconductivity in the Fe-As pnictide superconductor CaFe2As2,"We report specific-heat and resistivity experiments performed in parallel in
a Bridgman-type of pressure cell in order to investigate the nature of
pressure-induced superconductivity in the iron pnictide compound CaFe2As2. The
presence of a pronounced specific-heat anomaly at Tc reveals a bulk nature of
the superconducting state. The thermodynamic transition temperature differs
dramatically from the onset of the resistive transition. Our data indicates
that superconductivity occurs in the vicinity of a crystallographic phase
transition. We discuss the discrepancy between the two methods as caused by
strain-induced superconducting precursors formed above the bulk thermodynamic
transition due to the vicinity of the structural instability.",1205.0874v1
2012-05-04,"Reply to Comment on ""Spin Ice: Magnetic Excitations without Monopole Signatures using Muon Spin Rotation""","We respond to the comment of Bramwell et al (arXiv:1111.4168v1) to our
original publication (S. R. Dunsiger et al, Phys. Rev. Lett. 107, 207207
(2011)), detailing muon spin rotation measurements of the Spin Ice compound
Dy2Ti2O7.",1205.0901v2
2012-05-04,Integration of invariant matrices and application to statistics,"We consider random matrices that have invariance properties under the action
of unitary groups (either a left-right invariance, or a conjugacy invariance),
and we give formulas for moments in terms of functions of eigenvalues. Our main
tool is the Weingarten calculus. As an application to statistics, we obtain new
formulas for the pseudo inverse of Gaussian matrices and for the inverse of
compound Wishart matrices.",1205.0956v1
2012-05-15,Neutron scattering study of role of partial disorder-type spin fluctuations in conductivity of frustrated conductor Mn$_3$Pt,"The spin-frustrated conductor Mn$_3$Pt exhibits a characteristic magnetic
structure called partial disorder in which some spin sites can form magnetic
order through the generation of non-ordered sites that locally relieve the
frustration. Here we report the results of a single-crystal inelastic neutron
scattering study of this compound. The measured momentum $\vec{Q}$ correlations
of diffusive magnetic scattering reveal that the paramagnetic phase exhibits
short-range spin fluctuations with the same type of partial disorder. Its
relation to conductivity is also discussed.",1205.3338v1
2012-05-15,The systematic study of the influence of neutron excess on the fusion cross sections using different proximity-type potentials,"Using different types of proximity potentials, we have examined the trend of
variations of barrier characteristics (barrier height and its position) as well
as fusion cross sections for 50 isotopic systems including various collisions
of C, O, Mg, Si, S, Ca, Ar, Ti and Ni nuclei with $1\leq N/Z < 1.6$ condition
for compound systems. The results of our studies reveal that the relationships
between increase of barrier positions and decrease of barrier heights are both
linear with increase of $N/Z$ ratio. Moreover, fusion cross sections also
enhance linearly with increase of this ratio.",1205.3418v1
2012-05-15,Magnetic softness in iron-based superconductors,"We examine the relevance of several major material-dependent parameters to
the magnetic softness in iron-base superconductors by first-principles
electronic structure analysis of their parent compounds. The results are
explained in the spin-fermion model where localized spins and orbitally
degenerate itinerant electrons coexist and are coupled by Hund's rule coupling.
We found that the difference in the strength of the Hund's rule coupling term
is the major material-dependent microscopic parameter for determining the
ground-state spin pattern. The magnetic softness in iron-based superconductors
is essentially driven by the competition between the double-exchange
ferromagnetism and the superexchange antiferromagnetism.",1205.3509v1
2012-05-27,"Beryllium Silicide Clusters, BenSin, Be2nSin (n = 1 - 4) and possible MgB2-like Superconductivity in some of them","The symmetry of the Periodic Table makes it possible to predict certain
properties of similar elements and compounds using one of them as a template.
Magnesium diboride, MgB2, presents a useful template in the search for similar
materials. Starting from electronegativity, valence electron and atomic number
equivalency, we identify many potential similar materials. One of them is the
beryllium silicide, Be2nSin cluster system. We establish that though not yet
produced in bulk, Be2Si exists. We show from symmetry principles that beryllium
silicide and some of its clusters will be MgB2-like superconductors with Tcs
close to or higher than 39K.",1205.5931v1
2012-06-04,Synchronization of coupled neural oscillators with heterogeneous delays,"We investigate the effects of heterogeneous delays in the coupling of two
excitable neural systems. Depending upon the coupling strengths and the time
delays in the mutual and self-coupling, the compound system exhibits different
types of synchronized oscillations of variable period. We analyze this
synchronization based on the interplay of the different time delays and support
the numerical results by analytical findings. In addition, we elaborate on
bursting-like dynamics with two competing timescales on the basis of the
autocorrelation function.",1206.0789v1
2012-06-07,Hybrid quantum-classical models as constrained quantum systems,"Constrained Hamiltonian description of the classical limit is utilized in
order to derive consistent dynamical equations for hybrid quantum-classical
systems. Starting with a compound quantum system in the Hamiltonian formulation
conditions for classical behavior are imposed on one of its subsystems and the
corresponding hybrid dynamical equations are derived. The presented formalism
suggests that the hybrid systems have properties that are not exhausted by
those of quantum and classical systems.",1206.1410v1
2012-06-13,Topological phase transition in Dirac fermionic heterostructures,"Materials with non-trivial topology in their electronic structures enforce
the existence of helical Dirac fermionic surface states. We discovered emergent
topological phases in the stacked structures of topological insulator and band
insulator layers where the surface Dirac fermions interact to each other with
particular helicity ordering. Using first-principles calculations and a model
Lagrangian, we explicitly demonstrated that such helicity ordering occurs in
real materials of ternary chalcogen compounds and determines their topological
insulating phase. Our results reveal the rich collective nature of interacting
surface Dirac fermions, and pave the way for utilizing topological phases for
technological devices such as non-volatile memories.",1206.2953v1
2012-06-14,Quasifission at extreme sub-barrier energies,"With the quantum diffusion approach the behavior of the capture cross-section
is investigated in the reactions $^{92,94}$Mo + $^{92,94}$Mo, $^{100}$Ru +
$^{100}$Ru, $^{104}$Pd + $^{104}$Pd, and $^{78}$Kr + $^{112}$Sn at deep
sub-barrier energies which are lower than the ground state energies of the
compound nuclei. Because the capture cross section is the sum of the complete
fusion and quasifission cross sections, and the complete fusion cross section
is zero at these sub-barrier energies, one can study experimentally the unique
quasifission process in these reactions after the capture.",1206.3040v1
2012-06-20,Fermi surface topology of LaFePO and LiFeP,"We perform charge self-consistent LDA+DMFT (density functional theory
combined with dynamical mean field theory) calculations to study correlation
effects on the Fermi surfaces of the iron pnictide superconductors LaFePO and
LiFeP. We find a distinctive change in the topology of the Fermi surface in
both compounds where a hole pocket with Fe dz^2 orbital character changes its
geometry from a closed shape in LDA to an open shape upon inclusion of
correlations.",1206.4551v3
2012-06-30,Anticollinear magnetic order induced by impurities in the frustrated Heisenberg model of pnictides,"We present Monte Carlo simulations for a classical antiferromagnetic
Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange
couplings on the square lattice in the presence of non-magnetic impurities. We
show that the order-by-disorder entropy selection, associated with the
Ising-like phase transition that appears for $J_2/J_1>1/2$ in the pure spin
model, is quenched at low temperature due to the presence of non-magnetic
impurities. Evidences that a new competing order is stabilized around the
impurities, and in turn induces a re-entrance phase transition are reported.
Implications for local magnetic measurement of the parent compound of iron
pnictides are briefly discussed.",1207.0095v1
2012-07-01,Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi$_2$Al$_{20}$,"The cubic compound PrTi$_2$Al$_{20}$ is a quadrupolar Kondo lattice system
that exhibits quadrupolar ordering due to the non-Kramers $\Gamma_3$ ground
doublet and has strong hybridization between $4f$ and conduction electrons. Our
study using high-purity single crystal reveals that PrTi$_2$Al$_{20}$ exhibits
type-II superconductivity at $T_{\rm c} = 200$ mK in the nonmagnetic
ferroquadrupolar state. The superconducting critical temperature and field
phase diagram suggests moderately enhanced effective mass of $m^*/m_0 \sim 16$.",1207.0215v2
2012-07-03,Anomalous Hall effect in heavy electron materials,"We propose a new empirical formula for the anomalous Hall effect in heavy
electron materials based on a phenomenological two-fluid description of the
f-electron states. The new formula incorporates two previous theories proposed
by Fert and Levy in 1987 and Kontani et al. in the early 1990s and takes into
account both incoherent and coherent skew scatterings from local and itinerant
f-electrons. We perform experimental analysis in several heavy electron
compounds and show that the new formula provides a consistent description of
the evolution of the Hall coefficient in the whole temperature range down to
only a few Kelvin.",1207.0646v2
2012-07-17,Magnetic properties of Mn-doped Ge46 and Ba8Ge46 clathrates,"We present a detailed study of the magnetic properties of unique cluster
assembled solids namely Mn doped Ge46 and Ba8Ge46 clathrates using density
functional theory. We find that ferromagnetic (FM) ground states may be
realized in both the compounds when doped with Mn. In Mn2Ge44, ferromagnetism
is driven by hybridization induced negative exchange splitting, a generic
mechanism operating in many diluted magnetic semiconductors. However, for
Mn-doped Ba8Ge46 clathrates incorporation of conduction electrons via Ba
encapsulation results in RKKY-like magnetic interactions between the Mn ions.
We show that our results are consistent with the major experimental
observations for this system.",1207.3996v1
2012-07-25,Lithium Subhydrides Under Pressure and their Superatom-Like Building Blocks,"Evolutionary structure searches are used to predict a new class of compounds
in the lithium--rich region of the lithium/hydrogen phase diagram under
pressure. First principles computations show that LimH, 4<m<9, are stabilized
with respect to LiH and Li between 50-100 GPa. The building block of all of the
lithium subhydrides is an Li8H cluster, which can be thought of as a
superalkali. The geometries and electronic structures of these phases is
analogous to that of the well-known alkali metal suboxides.",1207.6122v1
2012-08-01,Rational Design of High-Tc Superconductivity in the Z = 5.67 Family with Ne = 2.33,"The concepts of ""Rational Design of Superconductivity"" from Periodic Table
properties were proposed in an earlier paper (ArXiv: 1204.0233). We had shown
latter too that high-Tc superconductivity exists in the Z=7.333 family with
Ne=2.667, of which MgB2 is a member. Here we propose and show that compounds
with Z = 5.667 and Ne=2.333 will meet the conditions for high-Tc
superconductivity similar to the Z = 7.333 family. The predicted Tcs for the
ternary and quaternary systems of the Z =5.667 family would fall in the range
40K - 100K. We give material specific examples of some such possible rational
designs of high-Tc superconductivity.",1208.0071v1
2012-08-06,Probing the superconducting pairing symmetry from spin excitations in BiS$_2$ based superconductors,"Starting from a two-orbital model and based on the random phase
approximation, spin excitations in the superconducting state of the newly
discovered BiS$_2$ superconductors with three possible pairing symmetries are
studied theoretically. We show that spin response is uniquely determined by the
pairing symmetry. Possible spin resonance excitations might occur for the
d-wave symmetry at an incommensurate momentum about $(0.7\pi,0.7\pi)$. For the
p-wave symmetry the transverse spin excitation near $(0,0)$ is enhanced. For
the s-wave pairing symmetry there is no spin resonance signature. These
distinct features may be used for probing or determining the pairing symmetry
in this newly discovered compound.",1208.1101v1
2012-08-06,Low temperature ballistic spin transport in the S=1/2 antiferromagnetic Heisenberg chain compound SrCuO2,"We report zero and longitudinal magnetic field muon spin relaxation
measurements of the spin S=1/2 antiferromagnetic Heisenberg chain material
SrCuO2. We find that in a weak applied magnetic field B the spin-lattice
relaxation rate follows a power law B^n with n=-0.9(3). This result is
temperature independent for 5K < T < 300 K. Within conformal field theory and
using the M\""uller ansatz we conclude ballistic spin transport in SrCuO2.",1208.1162v1
2012-08-27,A BGO scintillating bolometer for gamma and alpha spectroscopy,"A 891 g BGO scintillating bolometer has been tested at 10 mK in the
underground Laboratori Nazionali del Gran Sasso (Italy). The discrimination
capability, the radio-purity of the compound and the main features of the
crystal have been studied in order to demonstrate the excellent performances
obtained by operating a scintillating bolometer in the field of gamma and alpha
spectroscopy. The sensitivity of this detector in the study of extremely low
surface contaminations has been investigated.",1208.5331v1
2012-10-01,Verification of the Wiedemann-Franz law in YbRh2Si2 at a quantum critical point,"The thermal conductivity measurements have been performed on the
heavy-fermion compound YbRh2Si2 down to 0.04 K and under magnetic fields
through a quantum critical point (QCP) at Bc = 0.66 T || c-axis. In the limit
as T -> 0, we find that the Wiedemann-Franz law is satisfied within
experimental error at the QCP despite the destruction of the standard signature
of Fermi liquid. Our results place strong constraints on models that attempt to
describe the nature of unconventional quantum criticality of YbRh2Si2.",1210.0350v1
2012-10-01,Heavy antiferromagnetic phases in Kondo lattices,"We propose a microscopic physical mechanism that stabilizes coexistence of
the Kondo effect and antiferromagnetism in heavy-fermion systems. We consider a
two-dimensional quantum Kondo-Heisenberg lattice model and show that long-range
electron hopping leads to a robust antiferromagnetic Kondo state. By using a
modified slave-boson mean-field approach we analyze the stability of the heavy
antiferromagnetic phase across a range or parameters, and discuss transitions
between different phases. We also address connection to experiments on heavy
fermion compounds.",1210.0573v2
2012-10-08,Decomposition results for stochastic storage processes and queues with alternating Lévy inputs,"In this paper we generalize known workload decomposition results for L\'{e}vy
queues with secondary jump inputs and queues with server vacations or service
interruptions. Special cases are polling systems with either compound Poisson
or more general L\'{e}vy inputs. Our main tools are new martingale results,
which have been derived in a companion paper.",1210.2213v1
2012-10-10,Raman scattering in iron-based superconductors,"Iron-based superconducting layered compounds have the second highest
transition temperature after cuprate superconductors. Their discovery is a
milestone in the history of high-temperature superconductivity and will have
profound implications for high-temperature superconducting mechanism as well as
industrial applications. Raman scattering has been extensively applied to
correlated electron systems including the new superconductors due to its unique
ability to probe multiple primary excitations and their coupling. In this
review, we will give a brief summary of the existing Raman experiments in the
iron-based materials and their implication for pairing mechanism in particular.
And we will also address some open issues from the experiments.",1210.2889v1
2012-10-15,Single-carrier impact ionization favored by a limited band dispersion,"A critical requirement for high gain and low noise avalanche photodiodes is
the single-carrier avalanche multiplication. We propose that the single-carrier
avalanche multiplication can be achieved in materials with a limited width of
the conduction or valence band resulting in a restriction of kinetic energy for
one of the charge carriers. This feature is not common to the majority of
technologically relevant semiconductors, but it is observed in chalcogenides,
such as Selenium and compound I2-II-IV-VI4 alloys.",1210.4119v1
2012-10-19,Superconductivity in defective pyrite-type iridium chalcogenides IrxCh2 (Ch = Se and Te),"We report superconductivity in defective pyrite-type iridium chalcogenides
IrxCh2. Maximum values of Tc of 6.4 K for Ir0.91Se2 and 4.7 K for Ir0.93Te2
were observed. It was found that Ir0.75Ch2 is close to the boundary between
metallic and insulating states and IrxCh2 systems undergo nonmetal to metal
transitions as x increases. On the basis of density functional theory
calculations and the observed large variation in the Ch-Ch distance with x, we
suggest that Ir0.75Ch2 is the parent compound for the present superconductors.",1210.5353v1
2012-10-23,Splitting of resonance excitations in nearly optimally doped Ba(Fe0.94Co0.06)2As2: an inelastic neutron scattering study with polarization analysis,"Magnetic excitations in Ba(Fe0.94Co0.06)2As2 are studied by polarized
inelastic neutron scattering (INS) above and below the superconducting
transition. In the superconducting state we find clear evidence for two
resonance-like excitations. At a higher energy of about 8 meV there is an
isotropic resonance mode with weak dispersion along the c-direction. In
addition we find a lower excitation at 4 meV that appears only in the
c-polarized channel and whose intensity strongly varies with the L-component of
the scattering vector. These resonance excitations behave remarkably similar to
the gap modes in the antiferromagnetic phase of the parent compound BaFe2As2.",1210.6386v1
2012-11-19,Variable Ultra-broadband and Narrowband Composite Polarization Retarders,"We propose and experimentally demonstrate novel types of composite sequences
of half-wave and quarter-wave polarization retarders, either permitting
operation at ultra-broad spectral bandwidth or narrow bandwidth. The retarders
are composed of stacked standard half-wave retarders and quarter-wave retarders
of equal thickness. To our knowledge, these home-built devices outperform all
commercially available compound retarders, made of several birefringent
materials.",1211.4358v1
2012-11-26,Correlated Topological Insulators with Mixed Valence,"We propose the local density approximation (LDA)+Gutzwiller method
incorporating Green's function scheme to study the topological physics of
correlated materials from the first-principles. Applying this method to typical
mixed valence materials SmB6, we found its non-trivial Z2 topology, indicating
that SmB6 is a strongly correlated topological insulator (TI). The unique
feature of this compound is that its surface states contain three Dirac cones
in contrast to most known TIs.",1211.5863v2
2012-12-03,Formation enthalpy of BaCe0.7Nd0.2In0.1O2.85,"In this paper for the first time we synthesized the compound
BaCe0.7Nd0.2In0.1O2.85 by solid-state reaction. The phase has orthorhombic
structure (space group Pmcn). We also measured the standard formation
enthalpies of BaCe0.7Nd0.2In0.1O2.85 by solution calorimetry in 1 M HCl with
0.1 M KI. We determined the stability of Nd(In)-doped barium cerate with
respect to mixtures of binary oxides. On the basis of these data we established
that above-mentioned mixed oxide is thermodynamically stable with respect to
their decomposition into binary oxides at room temperatures. We also
established that BaCe0.7Nd0.2In0.1O2.85 oxide is thermodynamically favoured
than BaCe0.8Nd0.2O2.9.",1212.0344v1
2012-12-04,Directed random walks on hierarchic trees with continuous branching: a renormalization group approach,"We investigate the directed random walk on hierarchic trees. Two cases are
investigated: random variables on deterministic trees with a continuous
branching, and random variables on the trees constructed trough the random
branching process. We derive renormalization group (partial differential)
equations for the branching models with binomial, Poisson and compound Poisson
distributions of random variables on the links of tree. These renormaliation
group equations are new class of reaction-diffusion equations in 1-dimension.",1212.0688v1
2012-12-04,A new class of fatigue life distributions,"In this paper, we introduce the Birnbaum-Saunders power series class of
distributions which is obtained by compounding Birnbaum-Saunders and power
series distributions. The new class of distributions has as a particular case
the two-parameter Birnbaum-Saunders distribution. The hazard rate function of
the proposed class can be increasing and upside-down bathtub shaped. We provide
important mathematical properties such as moments, order statistics, estimation
of the parameters and inference for large sample. Three special cases of the
new class are investigated with some details. We illustrate the usefulness of
the new distributions by means of two applications to real data sets.",1212.0707v2
2012-12-08,Radiative Strength Functions for Dipole Transitions in Zr-90,"Partial cross sections for the (p,gamma) reaction on the Y-89 nucleus that
were measured previously at proton energies between 2.17 and 5.00 MeV and which
were averaged over resonances were used to determine the absolute values and
the energy distribution of the strength of dipole transitions from
compound-nucleus states to low-lying levels of the Zr-90 nucleus. The data
obtained in this way were compared with the predictions of various models.",1212.1802v1
2012-12-18,First foot prints of chemistry on the shore of the Island of Superheavy Elements,"Chemistry has arrived on the shore of the Island of Stability with the first
chemical investigation of the superheavy elements Cn, 113, and 114. The results
of three experimental series leading to first measured thermodynamic data and
qualitatively evaluated chemical properties for these elements are described.
An interesting volatile compound class has been observed in the on-line
experiments for the elements Bi and Po. Hence, an exciting chemical study of
their heavier transactinide homologues, elements 115 and 116 is suggested.",1212.4292v1
2012-12-21,Low-temperature metastable states in a stacked triangular Ising antiferromagnet,"We study low-temperature magnetization processes in a stacked triangular
Ising antiferromagnet by Monte Carlo simulations. In increasing and decreasing
magnetic fields we observe multiple steps and hysteresis corresponding to
formation of different metastable states. Besides the equidistant threefold
splitting of the 1/3 ferrimagnetic plateau, we additionally confirm a fourth
plateau in the field-increasing branch and a sizable remanence when the field
is decreased to zero. The newly observed plateau only appears at sufficiently
low temperature and sufficiently large exchange interaction in the stacking
direction. These observations reasonably reproduce low-temperatures
measurements on the spin-chain compound $\rm{Ca}_3\rm{Co}_2\rm{O}_6$.",1212.5455v1
2012-12-31,Growth and band alignment of Bi2Se3 topological insulator on H-terminated Si(111) van der Waals surface,"The van der Waals epitaxy of single crystalline Bi2Se3 film was achieved on
hydrogen passivated Si(111) (H:Si) substrate by physical vapor deposition.
Valence band structures of Bi2Se3/H:Si heterojunction were investigated by
X-ray Photoemission Spectroscopy and Ultraviolet Photoemission Spectroscopy.
The measured Schottky barrier height at the Bi2Se3-H:Si interface was 0.31 eV.
The findings pave the way for economically preparing heterojunctions and
multilayers of layered compound families of topological insulators.",1212.6807v1
2013-01-04,Prediction of stable insulating intermetallic compounds,"We explore the stability of structure exhibiting hybridization gaps across a
broad range of binary and ternary intermetallic compositions by means of band
structure and total energy calculations. This search reveals previously unknown
metal-based insulators, some with large gaps exceeding 1 eV, such as Al2Fe and
Al4IrRe. We confirm large gaps using a hybrid density functional including
exact exchange, and predict a gap of 2.2 eV for AlMnSi in the Pearson type tP6
structure, which is a chemically ordered ternary variant of the prototype MoSi2
(Pearson type tI6) structure.",1301.0744v2
2013-01-08,Magnetic chirality as probed by neutron scattering,"We review the concept of chirality, at first briefly in a general context
then in the specific framework of the spin networks. We next discuss to what
extent neutron scattering appears as an unconvertible tool to probe magnetic
chirality in the static and dynamical regimes of the spins. The remarkable
chiral ground state and excitations of the Fe-langasite compound finally serves
to illustrate the use of neutron polarimetry in the experimental studies of the
magnetic chirality.",1301.1616v1
2013-01-12,Charge Density Wave and Superconducting Properties in Single Crystals of Lu5Ir4Si10,"We measured the electrical resistivity from 2K up to 900K on high quality
single crystals of Lu5Ir4Si10. A clear thermal hysteresis was found at the
onset of the Charge Density Wave (CDW), evidencing the first order nature of
the transition. When tantalum is included in the compound, the CDW is destroyed
and the superconducting critical temperature is enhanced. Finally, we present
specific heat and magnetic penetration depth in the Meissner state. We show
that the superconducting properties are very close to a weak coupling BCS
superconductor.",1301.2657v1
2013-01-15,Modified Associate Formalism without Entropy Paradox: Part I. Model Description,"A Modified Associate Formalism is proposed for thermodynamic modelling of
solution phases. The approach is free from the entropy paradox described by
L\""{u}ck et al. (Z. Metallkd. 80 (1989) pp. 270--275). The model is considered
in its general form for an arbitrary number of solution components and an
arbitrary size of associates. Asymptotic behaviour of chemical activities of
solution components in binary dilute solutions is also investigated.",1301.3213v1
2013-01-15,Quantum coherence in an all-solid-state dye-sentizied solar cell,"The reported new type of all-solid-state, inorganic solar cell will be
discussed by a semiclassical light-matter interaction method. The molecular
compound will be treated by a three times two-level coupled quantum system. The
equation of motion of the density matrix of this system will be analytical
solved, in linear approximation and due to the coherent superposition of
certain states, time-independent off-diagonal elements will be obtained. These
elements represent an important components for the overal optical performane of
this cell.",1301.3351v1
2013-01-19,On the Uniqueness of the Canonical Polyadic Decomposition of third-order tensors --- Part II: Uniqueness of the overall decomposition,"Canonical Polyadic (also known as Candecomp/Parafac) Decomposition (CPD) of a
higher-order tensor is decomposition in a minimal number of rank-1 tensors. In
Part I, we gave an overview of existing results concerning uniqueness and
presented new, relaxed, conditions that guarantee uniqueness of one factor
matrix. In Part II we use these results for establishing overall CPD uniqueness
in cases where none of the factor matrices has full column rank. We obtain
uniqueness conditions involving Khatri-Rao products of compound matrices and
Kruskal-type conditions.",1301.4603v1
2013-01-21,Ferrimagnetism of dilute Ising antiferromagnets,"It is shown that nearest-neighbor antiferromagnetic interactions of identical
Ising spins on imbalanced bipartite lattice and imbalanced bipartite
hierarchical fractal result in ferrimagnetic order instead of antiferromagnetic
one. On some crystal lattices dilute Ising antiferromagnets may also become
ferrimagnets due to the imbalanced nature of the magnetic percolation cluster
when it coexists with the percolation cluster of vacancies. As evidenced by the
existing experiments on $Fe_pZn_{1-p}F_2$, such ferrimagnetism is inherent
property of bcc lattice so thermodynamics of these compounds at low $p$ can be
similar to that of antiferromagnet on imbalanced hierarchical fractal.",1301.4754v3
2013-01-26,Electronic Structure and magnetism in Ir based double-perovskite Sr$_2$CeIrO$_6$,"The electronic structure and magnetism of Sr$_2$CeIrO$_6$, an Ir-based double
perovskite system has been investigated using first-principles calculations. We
found that a strong spin-orbit coupling dictate the electronic and magnetic
properties of this system. A small value of $U$ along with SOC could open up a
gap at the Fermi level, offering the possibility of novel J$_{eff}$ = 1/2 Mott
quantum state. Our calculations reveal that the magnetic ground state is
antiferromagnetic in agreement with the magnetization data and provide the
value of spin and orbital moment for this system which is in agreement with the
other isostructural Ir-based compound.",1301.6218v1
2013-01-30,Strong Enhancement of the Critical Current at the Antiferromagnetic Transition in ErNi2B2C Single Crystals,"We report on transport and magnetization measurements of the critical current
density Jc in ErNi2B2C single crystals that show strongly enhanced vortex
pinning at the Neel temperature TN and low applied fields. The height of the
observed Jc peak decreases with increasing magnetic field in clear contrast
with that of the peak effect found at the upper critical field. We also
performed the first angular transport measurements of Jc ever conducted on this
compound. They reveal the correlated nature of this pinning enhancement, which
we attribute to the formation of antiphase boundaries at TN.",1301.7146v1
2013-02-01,Unveiling the physics of the doped phase of the Kagome $t-J$ model,"We investigate the ground state properties of the Kagome lattice $t-J$ model
at low doping. We propose a new state of matter. Our results suggest an
interesting phase with a balance of spin-exchange and kinetic exchange through
the building blocks of stars and their internal hexagons, being linked by
triangles. The particles favor to hop in the hexagons, while the spin-exchange
is taking place mainly on the stars. The combined effect leads to the formation
of the ""Star of David"" valence bond crystal. We discuss our result in
connection with static impurities, and show the likely relevance to the diluted
Kagome lattice Heisenberg model, describing actual compounds.",1302.0155v1
2013-02-06,Self-passivation of vacancies in α-PbO,"We introduce a self-passivation of single lead (Pb) and oxygen (O) vacancies
in the \alpha-PbO compound through formation of a Pb-O vacancy pair. The
preferential mechanism for pair formation involves initial development of the
single Pb vacancy which, by weakening the covalent bonding, sets up the crystal
lattice for an appearance of the O vacancy. Binding of the Pb and O vacancies
occurs through the ionization interactions. Since no dangling bonds appear at
the Pb-O pair site, this defect has a minor effect on the electronic
properties. In such, vacancy self-passivation offers a practical way to improve
the transport properties in thermally grown PbO layers.",1302.1605v1
2013-02-08,Improper ferroelectricity and multiferroism in 2HBaMnO$_3$,"Using first-principles calculations, we study theoretically the stable 2H
hexagonal structure of BaMnO3. We show that from the stable high temperature
P63/mmc structure, the compound should exhibit an improper ferroelectric
structural phase transition to a P63cm ground state. Combined with its
antiferromagnetic properties, 2H-BaMnO3 is therefore expected to be
multiferroic at low temperature. The phase transition mechanism in BaMnO3
appears similar to what was reported in YMnO3 in spite of totally different
atomic arrangement, cation sizes and Mn valence state.",1302.2006v1
2013-02-19,Slater-Pauling behavior in half-metallic magnets,"We review the appearance of Slater-Pauling rules in half-metallic magnets.
These rules have been derived using ab-initio electronic structure calculations
and directly connect the electronic properties (existence of minority-spin
energy gap) to the magnetic properties (total spin magnetic moment) in these
compounds. Their exact formulation depends on the half-metallic family under
study and they can be easily derived if the hybridization of the orbitals at
various sites is taken into account.",1302.4699v1
2013-02-20,Is There a Role for Qualitative Risk Assessment?,"Classically, risk is characterized by a point value probability indicating
the likelihood of occurrence of an adverse effect. However, there are domains
where the attainability of objective numerical risk characterizations is
increasingly being questioned. This paper reviews the arguments in favour of
extending classical techniques of risk assessment to incorporate meaningful
qualitative and weak quantitative risk characterizations. A technique in which
linguistic uncertainty terms are defined in terms of patterns of argument is
then proposed. The technique is demonstrated using a prototype computer-based
system for predicting the carcinogenic risk due to novel chemical compounds.",1302.4970v1
2013-02-20,Fingerprints of Orbital Physics in Magnetic Resonant Inelastic X-ray Scattering,"Orbital degrees of freedom play a major role in the physics of many strongly
correlated transition metal compounds. However, they are still very difficult
to access experimentally, in particular by neutron scattering. We propose here
how to reveal orbital occupancies of the system ground state by magnetic
resonant inelastic x-ray scattering (RIXS). This is possible because, unlike in
neutron scattering, the intensity of the magnetic excitations in RIXS depends
essentially on the symmetry of the orbitals where the spins are in.",1302.5028v2
2013-02-22,Crystal structure and properties of barium thorate BaThO$_3$ from first principles,"The phonon spectrum of cubic BaThO$_3$ with the perovskite structure is
calculated from first principles within the density functional theory. The
analysis of unstable modes in the phonon spectrum enables to determine the
symmetry of all possible distorted phases, calculate their energies, and show
that the ground-state structure of barium thorate is $Pbnm$. For this
structure, the static and optical dielectric constants, elastic moduli, heat
capacity, Raman spectra, and the energy band gap in the LDA and $GW$
approximations are calculated. The possibility of the structural phase
transitions in BaThO$_3$ is also discussed.",1302.5614v1
2013-03-12,Fractional discrete processes: compound and mixed Poisson representations,"We consider two fractional versions of a family of nonnegative integer valued
processes. We prove that their probability mass functions solve fractional
Kolmogorov forward equations, and we show the overdispersion of these
processes. As particular examples in this family, we can define fractional
versions of some processes in the literature as the Polya-Aeppli, the Poisson
Inverse Gaussian and the Negative Binomial. We also define and study some more
general fractional versions with two fractional parameters.",1303.2861v1
2013-03-19,Asymptotics for sums of random variables with local subexponential behaviour,"We study distributions $F$ on $[0,\infty)$ such that for some $T\le\infty$,
$F^{*2}(x,x+T]\sim 2 F(x,x+T]$. The case $T=\infty$ corresponds to $F$ being
subexponential, and our analysis shows that the properties for $T<\infty$ are,
in fact, very similar to this classical case. A parallel theory is developed in
the presence of densities. Applications are given to random walks, the key
renewal theorem, compound Poisson process and Bellman-Harris branching
processes.",1303.4709v1
2013-03-22,"Magnetic and Magnetocaloric Exploration of Fe rich (Mn,Fe)2(P,Ge)","We explored the Fe rich side of the (Mn,Fe)2(P,Ge) magnetocaloric system. The
transition temperature of this system is extremely easy to tune with careful
manipulation of Fe and Ge content as well as stoichiometrical proportions,
which gives rise to the real possibility of lowering the price of this compound
and thus make it economically viable for practical magnetocaloric applications.
Novel and unexpected magnetic properties observed in this system suggest an
exciting potential for permanent magnet application in a limited concentration
range.",1303.5620v1
2013-03-22,Improving Li$_2$O$_2$ conductance via polaron preemption: an \textit{ab initio} study of Si doping,"We report on \textit{ab initio} electronic structure simulations of
Li$_2$O$_2$, where 1.6% of lithium atoms are substituted by silicon. It is
demonstrated that this leads to the formation of conducting impurity states in
the band gap of Li$_2$O$_2$. We show that these states originate from the
antibonding orbitals of the oxygen pairs and are remarkably stable against
possible polaron formation (upon electron injection). Through this polaron
preemption mechanism, the proposed compound is expected to show significantly
higher electronic mobility than stoichiometric Li$_2$O$_2$, which could have
significant applications in lithium-air batteries.",1303.5648v1
2013-03-25,Quantitative easing is an incomplete strategy that must be accompanied by the nullification of debt,"Compound interest as well as inflation grows exponentially with time, whereas
other means to repay debt grow polynomially. For this and other, mostly
political, reasons, debt without inflation is unsustainable. We suggest a
discontinuous way to eliminate debt by nullifying it. This scenario is
preferable to current central bank strategies of quantitative easing because it
allows the disposal of debt without hyperinflation or bloated balance sheets.",1303.6183v3
2013-03-28,Observation of giant magnetocaloric effect in HoCoSi,"We report the magnetic and magnetocaloric properties of HoCoSi, which shows
second order ferro-para magnetic transition at 14 K. It is found to exhibit a
large magnetic entropy change of 13 J/kg K for a field change of 20 kOe, which
increases to 20.5 J/kg K at 50 kOe. The refrigerant capacity is found to be 135
and 410 J/kg for 20 and 50 kOe, respectively. The large, low-field adiabatic
temperature change (~ 3 K) and a large refrigerant capacity make this compound
a suitable candidate for magnetic refrigeration applications at around 15 K.",1303.7188v2
2013-04-05,Emergent Heavy Fermion Behavior at the Wigner-Mott Transition,"We study charge ordering driven by Coulomb interactions on triangular
lattices relevant to the Wigner-Mott transition in two dimensions. Dynamical
mean-field theory reveals the pinball liquid phase, a charge ordered metallic
phase containing quasi-localized (pins) coexisting with itinerant (balls)
electrons. Based on an effective periodic Anderson model for this phase, we
find an antiferromagnetic Kondo coupling between pins and balls and strong
quasiparticle renormalization. Non-Fermi liquid behavior can occur in such
charge ordered systems due to spin-flip scattering of itinerant electrons off
the pins in analogy with heavy fermion compounds.",1304.1700v2
2013-04-18,Giant birefringence in layered compound LaOBiS2,"Birefringent crystals (BFC) have been extensively used in imaging
spectrometer, laser devices, and optical components. Seeking new BFC is of
important for both fundamental research and industrial application. Employed
first-principles density functional theory (DFT), we found that LaOBiS2 (space
group P4/nmm), the parent phase of recently discovered BiS2-superconductor,
exhibits superior birefringence with a maximum value of 2.94, which is 13.4
times larger than the extensively used YVO4 (0.22). Furthermore, LaOBiS2 is an
indirect semiconductor with a band-gap of 0.9 eV, which is suitable for optical
applications. The origin of giant inherent birefringence is discussed.",1304.5032v2
2013-04-22,Determining Local Transientness of Audio Signals,"We describe a new method for estimating the degree of ""transientness"" and
""tonality"" of a class of compound signals involving simultaneously transient
and harmonic features. The key assumption is that both transient and tonal
layers admit sparse expansions, respectively in wavelet and local cosine bases.
The estimation is performed using particular form of entropy (or theoretical
dimension) functions. We provide theoretical estimates on the behavior of the
proposed estimators, as well as numerical simulations. Audio signal coding
provides a natural field of application.",1304.5881v1
2013-04-23,Nonnormal small jump approximation of infinitely divisible distributions,"We consider a type of nonnormal approximation of infinitely divisible
distributions that incorporates compound Poisson, Gamma, and normal
distributions. The approximation relies on achieving higher orders of cumulant
matching, to obtain higher rates of approximation error decay. The parameters
of the approximation are easy to fix. The computational complexity of random
sampling of the approximating distribution in many cases is of the same order
as normal approximation. Error bounds in terms of total variance distance are
derived. Both the univariate and the multivariate cases of the approximation
are considered.",1304.6326v1
2013-04-25,Singularities with the highest Mather minimal log discrepancy,"This paper characterizes singularities with Mather minimal log discrepancies
in the highest unit interval, i.e., the interval between $d-1$ and $d$, where
$d$ is the dimension of the scheme. The class of these singularities coincides
with one of the classes of (1) compound Du Val singularities, (2) normal
crossing double singularities, (3) pinch points, and (4) pairs of non-singular
varieties and boundaries with multiplicities less than or equal to 1 at the
point. As a corollary, we also obtain one implication of an equivalence
conjectured by Shokurov for the usual minimal log discrepancies.",1304.7012v1
2013-05-02,Tuning the charge-transfer energy in hole-doped cuprates,"Chemical substitution, combined with strain, allows the charge-transfer
energy in hole-doped cuprates to be broadly tuned. We theoretically
characterize the structural and electronic properties of the family of
compounds $R_2$CuO$_2$S$_2$, constructed by sulfur replacement of the apical
oxygens and rare earth substitutions in the parent cuprate La$_2$CuO$_4$.
Additionally, the enthalpies of formation for possible synthesis pathways are
determined.",1305.0322v1
2013-05-11,Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet Edwardsite,"We prepared a powder sample of edwardsite Cd2Cu3(SO4)2(OH)6 4H2O, which is a
new candidate compound for the spin-1/2 kagome antiferromagnet, and studied its
magnetic properties by magnetic susceptibility and heat capacity measurements.
Edwardsite has a deformed kagome lattice with an average antiferromagnetic
interaction of 51 K between nearby spins and shows an antiferromagnetic order
accompanied by a small ferromagnetic moment below 4.3 K. The weak
ferromagnetism is likely due to spin canting caused by sizable
Dzyaloshinsky-Moriya interactions, which may stabilize the long-range magnetic
order instead of a spin-liquid state expected for the kagome antiferromagnet.",1305.2477v1
2013-05-15,Superconductivity Induced by Breaking Te2 Dimers of AuTe2,"Mineral calaverite AuTe2 is a layered compound with an incommensurately
modulated structure. The modulation is characterized by the formation of
molecular-like Te2 dimers. We have found that the breaking of Te2 dimers that
occurs in Au1-xPtxTe2 results in the emergence of superconductivity at Tc = 4.0
K.",1305.3335v1
2013-05-17,"Parity violation in nuclear magnetic resonance frequencies of chiral tetrahedral tungsten complexes NWXYZ (X, Y, Z = H, F, Cl, Br or I)","Density functional theory within the two-component quasi-relativistic
zeroth-order regular approximation (ZORA) is used to predict parity violation
shifts in 183W nuclear magnetic resonance shielding tensors of chiral,
tetrahedrally bonded tungsten complexes of the form NWXYZ (X, Y, Z = H, F, Cl,
Br or I). The calculations reveal that sub-mHz accuracy is required to detect
such tiny effects in this class of compounds, and that parity violation effects
are very sensitive to the choice of ligands.",1305.3963v1
2013-05-20,Antiferromagnetic Ising model saturation field entropies: ladders and kagome lattice,"Saturation field entropies of antiferromagnetic Ising models on quasi
one-dimensional lattices (ladders) and the kagome lattice are calculated. The
former is evaluated exactly by constructing the corresponding transfer
matrices, while the latter calculation uses Binder's algorithm for efficiently
and exactly computing the partition function of over 1300 spins to give, in
Boltzmann's units, S = 0.393589(6). We comment on the relation of the kagome
lattice to the experimental situation in the spin-ice compound dysprosium
titanium oxide.",1305.4606v2
2013-05-24,Design of Digital Response in Enzyme-Based Bioanalytical Systems for Information Processing Applications,"We investigate performance and optimization of the ""digital"" bioanalytical
response. Specifically, we consider the recently introduced approach of a
partial input conversion into inactive compounds, resulting in the ""branch
point effect"" similar to that encountered in biological systems. This
corresponds to an ""intensity filter,"" which can yield a binary-type
sigmoid-response output signal of interest in information and signal processing
and in biosensing applications. We define measures for optimizing the response
for information processing applications based on the kinetic modeling of the
enzymatic reactions involved, and apply the developed approach to the recently
published data for glucose detection.",1305.5803v1
2013-06-02,Efficient calculation of local dose distribution for response modelling in proton and ion beams,"We present an algorithm for fast and accurate computation of the local dose
distribution in MeV beams of protons, carbon ions or other heavy-charged
particles. It uses compound Poisson-process modelling of track interaction and
succesive convolutions for fast computation. It can handle mixed particle
fields over a wide range of fluences. Since the local dose distribution is the
essential part of several approaches to model detector efficiency or cellular
response it has potential use in ion-beam dosimetry and radiotherapy.",1306.0185v1
2013-06-18,Approximating dependent rare events,"In this paper we give a historical account of the development of Poisson
approximation using Stein's method and present some of the main results. We
give two recent applications, one on maximal arithmetic progressions and the
other on bootstrap percolation. We also discuss generalisations to compound
Poisson approximation, Poisson process approximation and multivariate Poisson
approximation, and state a few open problems.",1306.4158v3
2013-06-27,Layered compounds AFBiS2: superior birefringent crystals,"Stimulated by the discovery of the giant birefringence (GBF) in LaOBiS2 (H.
Wang, arxiv: 1304.5032), we check SrFBiS2 and find a superior birefringence up
to 1.28. Naturally, AF layer (i.e., SrF) is considered to be of important and
is demonstrated by the further study on AFBiS2 (A=Mg, Ca, Ba). Interestingly,
MgFBiS2 shows the largest birefringence of 1.65. Furthermore, the origin of GBF
is discussed in detail.",1306.6393v3
2013-06-29,$N$-representability in non-collinear spin-polarized density functional theory,"The $N$-representability problem for non-collinear spin-polarized densities
was left open in the pioneering work of von Barth and Hedin setting up the
Kohn-Sham density functional theory for magnetic compounds. In this letter, we
demonstrate that, contrarily to the non-polarized case, the sets of pure and
mixed state $N$-representable densities are different in general. We provide a
simple characterization of the latter by means of easily checkable necessary
and sufficient conditions on the components $\rho^{\alpha \beta} (\br)$ of the
spin-polarized density.",1307.0139v2
2013-07-10,Magnetocrystalline Anisotropy and the Magnetocaloric Effect in Fe2P,"Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric
polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a
moderate magnetic entropy change which spans over 70 K and the presence of
strong magnetization anisotropy proves this system is not fully itinerant but
displays a mix of itinerant and localized magnetism. The properties of pure
Fe2P are compared to those of giant magnetocaloric (Fe,Mn)2(P,A) compounds
helping understand the exceptional characteristics shown by the latter which
are so promising for heat pump and energy conversion applications.",1307.2784v1
2013-07-13,Nucleation of domain walls by $Z_2$ symmetry breaking transition in $p_x+ip_y$ superconductors,"We show that time reversal symmetry breaking $p_x+ip_y$ wave superconductors
undergo several phase transitions subjected to external magnetic field or
supercurrent. In such system the discrete $Z_2$ symmetry can recover before the
complete destruction of the order parameter. The topological defects associated
with $Z_2$ symmetry - domain walls can be created in a controllable way by
magnetic field or current sweep according to the Kibble-Zurek scenario. Such
domain wall generation can take place in exotic superconductors like
$Sr_2RuO_4$ and some heavy fermion compounds.",1307.3659v1
2013-07-15,Cobalt spin state above the valence and spin-state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3,"(Pr0.7Sm0.3)0.7Ca0.3CoO3 belongs to a class of cobalt oxides undergoing a
first-order transition (T* close to 90 K) associated to a coupled change in the
valence and spin-state degrees of freedom. The Curie-Weiss regime present
around room temperature (T >> T*) was analysed in detail to address the
controversial issue of the cobalt spin states above the transition. This
magnetic investigation indicates that the Co4+ are in an intermediate
spin-state, while the Co3+ are in a mixed state combining low-spin and
high-spin states. These results are discussed with respect to the literature on
related compounds and recent results of x-ray absorption spectroscopy.",1307.3966v1
2013-07-18,Spin correlated dielectric memory and rejuvenation in relaxor ferroelectric CuCrS2,"CuCrS2, a Heisenberg antiferromagnet with layered edge sharing triangular
lattice, exhibits a spiral magnetic order. Dielectric (E) and polarization
studies show magnetoelectric (ME) coupling at Neel temperature (T_N=38 K) where
simultaneous dielectric and magnetic long range order occur. The compound shows
a diffused ferroelectric (FE) transition and slow relaxation dynamics above
T_N, indicative of relaxor FE behavior. Interestingly, memory effect and
magnetic field induced rejuvenation are also observed in E, establishing
cooperative glassy dynamics and ME coupling even above T_N. We discuss the role
of geometrical frustration and metal ligand hybridization for these unusual
properties.",1307.4859v1
2013-07-18,Hydrostatic pressures dependence of superconductivity in PrO0.5F0.5BiS2 superconductor,"In this communication, we report the temperature dependence (3 to 300K) of
the electrical resistivity of BiS2 based layered PrO0.5F0.5BiS2 superconductor
at ambient and hydrostatic pressure of up to 3GPa. It is observed that Tc
increases with pressure at the rate of dTc/dP=0.45/GPa for PrO0.5F0.5BiS2
compound. It is envisaged that one may increase the Superconducting transition
temperature (Tc) of recently discovered PrO0.5F0.5BiS2 superconductor by
applying hydrostatic external or internal chemical pressure via suitable on
site substitutions.",1307.4877v1
2013-07-21,A Perfect Lens for Ballistic Electrons: A Kane's Model,"The analogy between electromagnetic waves and ballistic electrons within the
Kane's model is developed and subsequently applied to a theoretical description
of a quantum version of a metamaterial planar lens. Restrictions imposed on the
perfect lens and the poor man's lens by available semiconductor band structures
are discussed. A realistic implementation is proposed for the quantum poor
man's lens, which uses specific properties of the HgTe compound. The properties
of the lens are presented on the basis of a calculated transmission of oblique
electrons through the lens structure.",1307.5500v1
2013-07-22,Angle-resolved photoemission spectroscopy study on iron-based superconductors,"Angle-resolved photoemission spectroscopy (ARPES) has played an important
role in determining the band structure and the superconducting gap structure of
iron-based superconductors. Here from the ARPES perspective, we briefly review
the main results from our group in the recent years on the iron-based
superconductors and their parent compounds, and depict our current
understanding on the antiferromagnetism and superconductivity in these
materials.",1307.5754v3
2013-07-24,Non-uniform approximations for sums of discrete m-dependent random variables,"Non-uniform estimates are obtained for Poisson, compound Poisson, translated
Poisson, negative binomial and binomial approximations to sums of of
m-dependent integer-valued random variables. Estimates for Wasserstein metric
also follow easily from our results. The results are then exemplified by the
approximation of Poisson binomial distribution, 2-runs and $m$-dependent
$(k_1,k_2)$-events.",1307.6296v1
2013-08-08,Orbital order and Hund's rule frustration in Kondo lattices,"We analyze a microscopic origin of the Kondo effect-assisted orbital order in
heavy-fermion materials. By studying the periodic two-orbital Anderson model
with two local electrons, we show that frustration of Hund's rule coupling due
to the Kondo effect leads to an incommensurate spiral orbital and magnetic
order, which exists only inside the Kondo screened (heavy-electron) phase. This
spiral state can be observed in neutron and resonant X-ray scattering
measurements in ${\rm U}$- and ${\rm Pr}$-based heavy-fermion compounds, and
realized in cold atomic gases, e.g. fermionic ${}^{173}{\rm Yb}$.",1308.1741v2
2013-08-21,"Loop Current and Orbital Magnetism in Pyrite-Type $Ir_{3}Ch_{8}$ ($Ch=Se,Te$)","We study the parent compound of the pyrite-type $Ir_{x}Ch_{2}$ iridium
chalcogenide superconductors, $Ir_{0.75}Ch_{2}$ (or $Ir_{3}Ch_{8}$). While the
lattice structure of the material is rather complicated, we show that the
electron physics near the Fermi surface (FS) can be described by a three-band
tight-binding model. We find that the material possesses a loop current ground
state which is responsible for the highly anisotropic strong diamagnetism
observed in experiments. The fluctuations of this loop current state can be a
possible pairing mechanism for superconductivity.",1308.4476v3
2013-08-26,Ferromagnetic spin-orbital liquid of dipolar fermions in zigzag lattices,"Two-component dipolar fermions in zigzag optical lattices allow for the
engineering of spin-orbital models. We show that dipolar lattice fermions
permit the exploration of a regime typically unavailable in solid-state
compounds that is characterized by a novel spin-liquid phase with a finite
magnetization and spontaneously broken SU(2) symmetry. This peculiar spin
liquid may be understood as a Luttinger liquid of composite particles
consisting of bound states of spin waves and orbital domain walls moving in an
unsaturated ferromagnetic background. In addition, we show that the system
exhibits a boundary phase transitions involving non-local entanglement of edge
spins.",1308.5519v1
2013-08-26,Sulfur annealing effect for superconductivity in iron chalcogenide compounds,"We discovered a novel annealing method for Fe-chalcogenide superconductors.
It was found that sulfur annealing deintercalated excess Fe via formation of
FeS2. Due to its specifics, sulfur annealing is applicable when preparing
Fe-chalcogenide-based wires or cables.",1308.5642v1
2013-08-30,Thermodynamic assessment of probability distribution divergencies and Bayesian model comparison,"Within path sampling framework, we show that probability distribution
divergences, such as the Chernoff information, can be estimated via
thermodynamic integration. The Boltzmann-Gibbs distribution pertaining to
different Hamiltonians is implemented to derive tempered transitions along the
path, linking the distributions of interest at the endpoints. Under this
perspective, a geometric approach is feasible, which prompts intuition and
facilitates tuning the error sources. Additionally, there are direct
applications in Bayesian model evaluation. Existing marginal likelihood and
Bayes factor estimators are reviewed here along with their stepping-stone
sampling analogues. New estimators are presented and the use of compound paths
is introduced.",1308.6753v2
2013-09-15,CaMn$_{2}$Sb$_{2}:$ a fully frustrated classical magnetic system,"We show by means of density functional calculations that CaMn$_{2}$Sb$_{2}$
is very close to a mean-field critical point known for the classical Heisenberg
model on the honeycomb lattice. Three entirely different long range ordered
magnetic phases become degenerate at this point: the Neel phase and two
different spiral phases. We speculate that the unusual physical properties of
this compound, observed in recent experiments, in particular the enigmatic
intermediate temperature phase, are due to this proximity.",1309.3744v1
2013-09-21,Ground state of the competing spin chain Cs2Cu2Mo3O12,"The high-field ground state of the competing-spin-chain compound Cs2Cu2Mo3O12
with the ferromagnetic first-nearest-neighbor J1=-93 K and the
antiferromagnetic second-nearest-neighbor J2 = +33 K was investigated by
133Cs-NMR. A divergence of T1-1 and a peak-splitting in spectra were observed
at TN = 1.85 K, indicating the existence of a field-induced long range magnetic
order. In the paramagnetic region above 4 K, T1-1 showed a power-law
temperature dependence T2K-1. The exponent K was strongly field-dependent,
suggesting the possibility of the spin-nematic Tomonaga Luttinger Liquid state.",1309.5473v1
2013-10-07,"Low-temperature magnetisation process in the cubic pyrochlore quantum antiferromagnet, Er2Ti2O7","We report low-temperature susceptibility and magnetisation data for the cubic
pyrochlore Er2Ti2O7. By performing the measurements on single crystals we are
able to establish the degree of magnetic anisotropy present in this compound
and to determine the critical values for magnetic field induced transitions
below the magnetic ordering temperature of 1.2 K. We also present a magnetic
H-T phase diagram of this quantum XY antiferromagnet for different directions
of an applied field.",1310.1791v1
2013-10-19,Superconductivity and magnetism on flux grown single crystals of NiBi3,"We present resistivity, magnetization and specific heat measurements on flux
grown single crystals of NiBi3. We find typical behavior of a type-II
superconductor, with, however, a sizable magnetic signal in the superconducting
phase. There is a hysteretic magnetization characteristic of a ferromagnetic
compound. By following the magnetization as a function of temperature, we find
a drop at temperatures corresponding to the Curie temperature of ferromagnetic
amorphous Ni. Thus, we assign the magnetism in NiBi$_3$ crystals to amorphous
Ni impurities.",1310.5247v1
2013-10-23,Competition and cooperation between antiferrodistortive and ferroelectric instabilities in SrTiO$_3$,"We use density functional theory to explore the interplay between octahedral
rotations and ferroelectricity in the model compound SrTiO$_3$. We find that
over the experimentally relevant range octahedral rotations suppress
ferroelectricity as is generally assumed in the literature. Somewhat
surprisingly we observe that at larger angles the previously weakened
ferroelectric instability strengthens significantly. By analysing geometry
changes, energetics, force constants and charges, we explain the mechanisms
behind this transition from competition to cooperation with increasing
octahedral rotation angle.",1310.6213v1
2013-10-28,Radiative topological states in resonant photonic crystals,"We present a theory of topological edge states in one-dimensional resonant
photonic crystals with a compound unit cell. Contrary to the traditional
electronic topological states the states under consideration are radiative,
i.e., they decay in time due to the light escape through the structure
boundaries. We demonstrate that the states survive despite their radiative
decay and can be detected both in time- and frequency-dependent light
reflection.",1310.7432v1
2013-10-29,Pressure-induced quantum critical and multicritical points in a frustrated spin liquid,"The quantum spin liquid compound (C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$ (PHCC) is
studied by $\mu$SR under hydrostatic pressures up to 23.6 kbar. At low
temperatures, pressure-induced incommensurate magnetic order is detected beyond
a quantum critical point at $P_c\sim4.3$ kbar. An additional phase transition
to a different ordered phase is observed at $P_1\sim 13.4$ kbar. The data
indicate that the high-pressure phase may be a commensurate one. The
established $(P-T)$ phase diagram reveals the corresponding pressure-induced
multicritical point at $P_1$, $T_1=2.0$ K.",1310.7807v2
2013-10-30,Spontaneous breaking of isotropy observed in the electronic transport of rare-earth tritellurides,"We show that the isotropic conductivity in the normal state of rare-earth
tritelluride RTe_3 compounds is broken by the occurrence of the unidirectional
charge density wave (CDW) in the (a,c) plane below the Peierls transition
temperature. In contrast with quasi-one-dimensional systems, the resistivity
anomaly associated with the CDW transition is strong in the direction
perpendicular to the CDW wave vector Q (a-axis) and very weak in the CDW wave
vector Q direction (c-axis). We qualitatively explain this result by
calculating the electrical conductivity for the electron dispersion with
momentum-dependent CDW gap as determined by angle-resolved photoemission
spectroscopy (ARPES).",1310.8136v1
2013-11-01,Lattice dynamics and electronic structure of energetic solids LiN3 and NaN3: A first principles study,"We report density functional theory calculations on the crystal structure,
elastic, lattice dynamics and electronic properties of iso-structural layered
monoclinic alkali azides, LiN3 and NaN3. The effect of van der Waals
interactions on the ground- state structural properties is studied by using
various dispersion corrected density functionals. Based on the equilibrium
crystal structure, the elastic constants, phonon dispersion and phonon density
of states of the compounds are calculated. The accurate energy band gaps are
obtained by using the recently developed Tran Blaha-modified Becke Johnson
(TB-mBJ) functional and found that both the azides are direct band gap
insulators.",1311.0145v1
2013-11-16,Coexisting Itinerant and Localized Electrons in Iron-Based Superconductors,"The surprising discovery of high-$T_c$ superconductivity in iron-based
compounds has prompted an intensive investigation on the role of interaction
and magnetism in the these materials. Based on the general features of
multi-bands and intermediate coupling strengths, a phenomenological theory of
coexisting itinerant and localized electrons has been proposed to describe the
low-energy physics in iron-based superconductors. It provides a unified
framework to understand magnetic, superconducting, and normal phases, subject
to further microscopic justification and experimental verification.",1311.4094v2
2013-11-18,A note on the gaps in the support of discretely infinitely divisible laws,"In this note we discuss the nature of gaps in the support of a discretely
infinitely divisible distribution from the angle of compound Poisson
laws/processes. The discussion is extended to infinitely divisible
distributions on the non-negative real line.",1311.4536v2
2013-11-22,Can deeply underdoped superconducting cuprates be topological superconductors?,"The nodal $d_{x^2-y^2}$ superconducting gap is a hallmark of the cuprate high
T$_c$ superconductors. Surprisingly recent angle-resolved photoemission
spectroscopy of deeply underdoped cuprates revealed a nodeless energy gap which
is adhered to the Fermi surface. Importantly this phenomenon is observed for
compounds across several different cuprate families. In this letter we propose
an exciting possibility, namely the fully gapped state is a topological
superconductor.",1311.5892v1
2013-11-28,A local Gaussian filter and adaptive morphology as tools for completing partially discontinuous curves,"This paper presents a method for extraction and analysis of curve--type
structures which consist of disconnected components. Such structures are found
in electron--microscopy (EM) images of metal nanograins, which are widely used
in the field of nanosensor technology.
  The topography of metal nanograins in compound nanomaterials is crucial to
nanosensor characteristics. The method of completing such templates consists of
three steps. In the first step, a local Gaussian filter is used with different
weights for each neighborhood. In the second step, an adaptive morphology
operation is applied to detect the endpoints of curve segments and connect
them. In the last step, pruning is employed to extract a curve which optimally
fits the template.",1311.7430v1
2013-12-05,Magnetic properties of ferromagnetic Pu2Pt3Si5,"The structural, magnetic, and thermodynamic properties of a new plutonium
based compound, Pu2Pt3Si5, are reported. Single crystals produced by a Sn-flux
technique have been analyzed showing a ferromagnetic behavior at 58 K.
Pu2Pt3Si5 crystallizes in the U2Co3Si5-type orthorhombic Iabm structure (72)
with atomic parameters a = 9.9226(2) \AA, b = 11.4436(2) \AA and c = 6.0148(1)
\AA. The effective (\mu_eff ~0.74 \mu_B) and saturated (\mu_sat ~0.32 B/Pu)
moments as well as the Sommerfeld coefficient (\gamma_e ~2 mJ.mol-1.K-2/Pu)
could point towards 5f localization in this material.",1312.1576v1
2013-12-06,Strong spintronic magnetoelectric effect in layered magnetic metamaterial,"It is shown that external magnetic field or magnetization induces electric
polarization of microscopic isolated magnetic/non-magnetic hybrid structures
due to the spin-dependent electron redistribution and mutual capacity. The
magnetoelectric effect can be very strong, for instance the change of electric
polarization reaches $100$ $\mu C/m^{2}$ at a constant magnetic field of only
$1.5$ Tesla in the case of $100$ $\div$ $10$ nanometer structures which tightly
fill the space, composing a metamaterial. The effect does not require using
exotic compounds. Based on the obtained results we suggest a number of
recommendations for future experimental design.",1312.2023v1
2013-12-09,"Full susceptibility tensor for localized spin models with S=1, 3/2, 2, 5/2 and with rhombic anisotropy","A general discussion of the simulation procedure of the full susceptibility
tensor and isothermal magnetization pseudovector for compounds comprising
weakly-interacting magnetic centers is presented. A single-crystal-sample as
well as a powder-sample case are considered. The procedure is used to obtain
explicit expressions for the full susceptibility tensor for spins S=1, 3/2, 2,
and 5/2 for non-vanishing rhombic local anisotropy and any form of
spectroscopic tensor.",1312.2401v1
2013-12-17,High-temperature thermoelectric properties of novel layered bismuth-sulfide LaO1-xFxBiS2,"We have investigated the high-temperature thermoelectric properties of the
layered compound LaO1-xFxBiS2. The electrical resistivity of LaOBiS2 showed an
anomalous behavior; a metal-semiconductor transition was observed around 270 K.
It was found that the value of the electrical resistivity decreased with F
substitution. The Seebeck coefficient decreased with increasing F
concentration. The highest power factor of 1.9 W/cmK2 at 480 C was obtained for
LaOBiS2.",1312.4694v1
2013-12-17,Itinerant magnetism in doped semiconducting beta-FeSi2 and CrSi2,"Novel or unusual magnetism is a subject of considerable interest,
particularly in metals and degenerate semiconductors. In such materials the
interplay of magnetism, transport and other Fermi liquid properties can lead to
fascinating physical behavior. One example is in magnetic semiconductors, where
spin polarized currents may be controlled and used. We report density
functional calculations predicting magnetism in doped semiconducting beta-FeSi2
and CrSi2 at relatively low doping levels particularly for n-type. In this
case, there is a rapid cross-over to a half-metallic state as a function of
doping level. The results are discussed in relation to the electronic structure
and other properties of these compounds.",1312.4773v1
2013-12-17,Limit theory for the Gilbert graph,"For a given homogeneous Poisson point process in $\mathbb{R}^d$ two points
are connected by an edge if their distance is bounded by a prescribed distance
parameter. The behaviour of the resulting random graph, the Gilbert graph or
random geometric graph, is investigated as the intensity of the Poisson point
process is increased and the distance parameter goes to zero. The asymptotic
expectation and covariance structure of a class of length-power functionals are
computed. Distributional limit theorems are derived that have a Gaussian, a
stable or a compound Poisson limiting distribution. Finally, concentration
inequalities are provided using a concentration inequality for the convex
distance.",1312.4861v2
2014-01-01,Vibrational Spectroscopy of Methyl benzoate,"Methyl benzoate (MB) is studied as a model compound for the development of
new IR pulse schemes with possible applicability to biomolecules. Anharmonic
vibrational modes of MB are calculated on different level (MP2, SCS, CCSD(T)
with varying basis sets) ab-initio PESs using the vibrational self-consistent
field (VSCF) method and its correlation corrected extensions. Dual level
schemes, combining different quantum chemical methods for diagonal and coupling
potentials, are systematically studied and applied successfully to reduce the
computational cost. Isotopic substitution of {\beta}-hydrogen by deuterium is
studied to obtain a better understanding of the molecular vibrational coupling
topology.",1401.0333v1
2014-01-07,Inverse Quantum Chemistry: Concepts and Strategies for Rational Compound Design,"The rational design of molecules and materials is becoming more and more
important. With the advent of powerful computer systems and sophisticated
algorithms, quantum chemistry plays an important role in rational design. While
traditional quantum chemical approaches predict the properties of a predefined
molecular structure, the goal of inverse quantum chemistry is to find a
structure featuring one or more desired properties. Herein, we review inverse
quantum chemical approaches proposed so far and discuss their advantages as
well as their weaknesses.",1401.1512v2
2014-01-10,"A density functional theory study of FeAs comparing LDA+U, GGA+U and hybrid functionals","We use density functional theory within the local density approximation
(LDA), LDA+U, generalized gradient approximation (GGA), GGA+U, and
hybrid-functional methods to calculate the properties of iron monoarsenide.
FeAs, which forms in the MnP structure, is of current interest for potential
spintronic applications as well as being the parent compound for the
newly-identified pnictide superconductors. We compare the calculated
structural, magnetic and electronic properties obtained using the different
functionals to each other and to experiment, and investigate the origin of a
recently-reported magnetic spiral. Our results indicate the appropriateness or
otherwise of the various functionals for describing FeAs and the related
Fe-pnictide superconductors.",1401.2277v1
2014-01-13,Phase transitions in the domain structure of ferromagnetic superconductors,"Starting from the London - type model we study the domain structures in
ferromagnetic superconductors taking account of the nucleation of vortices and
antivortices coupled to the magnetic texture. We predict that the coupling
between domains and vortices results in the formation of two energetically
favorable domain configurations: (i) a Meissner - type vortex free
configuration with strong domain shrinking and (ii) a more rare domain
configuration with a dense vortex -- antivortex lattice. The switching between
these configurations is shown to result in the first order phase transitions
which could be observable in superconducting uranium based compounds.",1401.2806v1
2014-01-14,Half-Duplex Relaying for the Multiuser Channel,"This work focuses on studying the half-duplex (HD) relaying in the Multiple
Access Relay Channel (MARC) and the Compound Multiple Access Channel with a
Relay (cMACr). A generalized Quantize-and-Forward (GQF) has been proposed to
establish the achievable rate regions. Such scheme is developed based on the
variation of the Quantize-and-Forward (QF) scheme and single block with two
slots coding structure. The results in this paper can also be considered as a
significant extension of the achievable rate region of Half-Duplex Relay
Channel (HDRC). Furthermore, the rate regions based on GQF scheme is extended
to the Gaussian channel case. The scheme performance is shown through some
numerical examples.",1401.3250v1
2014-01-18,Spin injection via (110)-grown semiconductor barriers,"We study the tunneling of conduction electrons through a (110)-oriented
single-barrier heterostructure grown from III-V semiconductor compounds. It is
shown that, due to low spatial symmetry of such a barrier, the tunneling
current through the barrier leads to an electron spin polarization. The inverse
effect, generation of a direct tunneling current by spin polarized electrons,
is also predicted. We develop the microscopic theory of the effects and show
that the spin polarization emerges due to the combined action of the
Dresselhaus spin-orbit coupling within the barrier and the Rashba spin-orbit
coupling at the barrier interfaces.",1401.4526v1
2014-01-20,Superconducting properties of BiS2 based superconductor NdO1-xFxBiS2 (x=0 to 0.9),"We report the phase diagram of NdO1-xFxBiS2 (x=0.1, 0.3, 0.5, 0.7, 0.9)
compound. The samples synthesized by the vacuum encapsulation technique are
crystallized in a tetragonal P4/nmm space group. The superconductivity of all
samples is confirmed by DC magnetic susceptibility and electrical transport
measurements. The maximum Tc of 5.25K is seen for x = 0.7 sample. The upper
critical field is calculated from magneto transport measurements. The Thermal
activated flux flow - TAFF studies are also carried out. Hall measurements show
that electrons are the dominating charge carriers in these systems.",1401.4811v2
2014-01-24,"Dielectric, electromechanical and elastic properties of K$_{1-x}$(NH$_4$)$_x$H$_2$PO$_4$ compounds","We present the results of the thermodynamic theory of piezoelectric
ferroelectrics and of the phenomenological theory of thermodynamic
characteristics of the KH$_{2}$PO$_{4}$ type ferroelectrics. Available
experimental data for the dielectric, piezoelectric, and elastic
characteristics of the KH$_{2}$PO$_{4}$ type ferroelectrics and
NH$_4$H$_{2}$PO$_{4}$ type antiferroelectrics are described using the proposed
microscopic theory of these crystals. Using the results of the thermodynamic
theory and experimental data we calculate the dielectric, piezoelectric, and
elastic characteristics of the K$_{1-x}$(NH$_4$)$_x$H$_2$PO$_4$ type systems.",1401.6403v1
2014-01-26,Topological spin liquid phase in a low-dimensional organic molecular compound,"We report the discovery of a correlated insulator with a bulk gap at
two-thirds filling in a geometrically frustrated Hubbard model that describes
the low-energy physics of Mo$_3$S$_7$(dmit)$_3$. This is very different from
the Mott insulator expected at half-filling. We show that the insulating phase,
which persists even for very weak electron-electron interactions ($U$), is
adiabatically connected to the Haldane phase and is consistent with experiments
on Mo$_3$S$_7$(dmit)$_3$",1401.6605v3
2014-02-05,Fragility Distributions and their approximations,"Given a sequence of $n$ identically distributed random variables with common
distribution $F$, the \emph{fragility distribution of order $m$}, represented
by $\FD$, is the limit conditional distribution of the number of exceedances
given there are at least $m$ exceedances, as the threshold tends to the right
end point of $F$. In this paper we are concerned with the existence of $\FD$
and its asymptotic behaviour when $n$ becomes large. For a stationary sequence
with its exceedance process converging to a compound Poisson process, we derive
an explicit formula for calculating $\lim_{n \to \infty} \FD$. We also
establish Stein's method for estimating the errors involved in fragility
distribution approximations.",1402.0934v1
2014-02-05,Selective molecular capture mechanism in carbon nanotube networks,"Recent air pollution issues have raised significant attention to develop
efficient air filters, and one of the most promising candidates is that enabled
by nanofibers. We explore here selective molecular capture mechanism for
volatile organic compounds in carbon nanotube networks by performing atomistic
simulations. The results are discussed with respect to the two key parameters
that define the performance of nanofiltration, i.e. the capture efficiency and
flow resistance, which validate the advantage of carbon nanotube networks with
high surface-to-volume ratio and atomistically smooth surfaces. We also reveal
the important roles of interfacial adhesion and diffusion that govern selective
gas transport through the network.",1402.1011v1
2014-02-10,Handwritten Character Recognition In Malayalam Scripts- A Review,"Handwritten character recognition is one of the most challenging and ongoing
areas of research in the field of pattern recognition. HCR research is matured
for foreign languages like Chinese and Japanese but the problem is much more
complex for Indian languages. The problem becomes even more complicated for
South Indian languages due to its large character set and the presence of
vowels modifiers and compound characters. This paper provides an overview of
important contributions and advances in offline as well as online handwritten
character recognition of Malayalam scripts.",1402.2188v1
2014-02-15,Ferromagnetism and transport properties of the Kondo system Ce4Sb1.5Ge1.5,"Ferromagnetic ordering with a small magnetic moment is found below 14 K from
SQUID measurements for the compound Ce4Sb1.5Ge1.5. The transport
characteristics of a number of Ce4Sb3-xTx (T = Ge, Si, Sn, Pb, Al) systems were
measured at room temperature, Ce4Sb1.5Ge1.5 demonstrating the highest Seebeck
coefficient. Its transport properties (resistivity, thermal conductivity,
thermoelectric power) are experimentally investigated in detail up to low
temperatures. The Kondo-lattice behavior of resistivity and its anomaly at the
ordering point are found. A comparison with the Wiedemann-Franz law is
performed.",1402.3667v2
2014-02-19,Ultrafast Li Electrolytes Based on Abundant Elements: Li$_{10}$SnP$_2$S$_{12}$ and Li$_{11}$Si$_2$PS$_{12}$,"We report on the synthesis and characterization of two solid electrolytes,
Li$_{10}$SnP$_2$S$_{12}$ and Li$_{11}$Si$_2$PS$_{12}$, which are based
exclusively on abundant elements. Both compounds feature extremely high Li ion
diffusivities, with the Si-based material even surpassing the present record
holder, the related electrolyte Li$_{10}$GeP$_2$S$_{12}$. The structure and
dynamics were studied with multiple complementary techniques and the
macroscopic diffusion could be traced back to fast Li ion hopping in the
crystalline lattice.",1402.4586v1
2014-02-23,A continuous model of ant foraging with pheromones and trail formation,"We propose and numerically analyze a PDE model of ant foraging behavior. Ant
foraging is a prime example of individuals following simple behavioral rules
based on local information producing complex, organized and ``intelligent''
strategies at the population level. One of its main aspects is the widespread
use of pheromones, which are chemical compounds laid by the ants used to
attract other ants to a food source. In this work, we consider a continuous
description of a population of ants and simulate numerically the foraging
behavior using a system of PDEs of chemotaxis type. We show that, numerically,
this system accurately reproduces observed foraging behavior, such as trail
formation and efficient removal of food sources.",1402.5611v1
2014-02-24,The origin of the unusual anisotropic electrical conductivity of Ba3Al2As4,"Ba3Al2As4 exhibits an unusual anisotropic electrical conductivity, that is,
the electrical conductivity along the chain is smaller than those along other
two directions which conflicts previous conclusion. Earlier studies on Ca5M2Pn6
showed a high electrical conductivity along the chain. The band decomposed
charge density is used to explain such unusual behavior. The results indicate
that the existence of a conductive pathway near the Fermi level is responsible
for the electrons transport. Further, the Ba-As bonding of Ba3Al2As4 is some
degree covalency which is novel for the Zintl compounds.",1402.5714v2
2014-02-24,"Single crystal growth from light, volatile, and reactive materials using lithium and calcium flux","We present a method for the solution growth of single crystals from reactive
Li and Ca melts and its application to the synthesis of several, representative
compounds. Among these, single crystalline Li3N, Li2(Li{1-x}Tx)N with T = {Mn,
Fe, Co}, LiCaN, Li2C2, LiRh, and LiIr from Li-rich flux as well as Ca2N, CaNi2,
CaNi3, YbNi2, Y2Ni7, and LaNi5 from Ca-rich flux could be obtained. Special
emphasize is given on the growth of nitrides using commercially available Li3N
and Ca3N2 powders as the nitrogen source instead of N2 gas.",1402.6004v2
2014-02-27,Comment on Microscopic magnetic modeling for the S = 1/2 alternating chain compounds Na3Cu2SbO6 and Na2Cu2TeO6 (arXiv:1402.1091),"In a recent paper by Schmitt et al. (arXiv:1402.1091), signs of two exchange
interactions of one-dimensional alternating chains in distorted honeycomb
systems of Na3Cu2SbO6 and Na2Cu2TeO6 are argued by theoretical calculations.
Although the authors report that they have clarified that the interaction J1a
is ferromagnetic between the spins within a structural dimer, and J1b is
antiferromagnetic between these dimers, these results have been known for a
long time by our two papers, which are cited by Schmitt et al.",1402.6839v1
2014-02-27,Zero-temperature phase diagram of D$_2$ physisorbed on graphane,"We determined the zero-temperature phase diagram of D$_2$ physisorbed on
graphane using the diffusion Monte Carlo method. The substrate used was
C-graphane, an allotropic form of the compound that has been experimentally
obtained through hydrogenation of graphene. We found that the ground state is
the $\delta$ phase, a commensurate structure observed experimentally when D$_2$
is adsorbed on graphite, and not the registered $\sqrt 3 \times \sqrt 3$
structure characteristic of H$_2$ on the same substrate.",1402.6933v1
2014-03-04,Low-temperature magnetism in the honeycomb systems SrLn2O4,"Recent progress in the understanding of the complex magnetic properties of
the family of rare-earth strontium oxides, SrLn2O4, is reviewed. These
compounds consisting of hexagons and triangles are affected by geometrical
frustration and therefore exhibit its characteristic features, such as a
significant reduction of magnetic ordering temperatures and complex phase
diagrams in an applied field. Some of the observed features appear to be rather
remarkable even in the context of the unusual behavior associated with
geometrically frustrated magnetic systems. Of particular interest is the
coexistence at the lowest temperature of different magnetic structures
(exhibiting either long or short-range order) characterized by different
propagation vectors in materials without significant chemical or structural
disorder.",1403.0877v1
2014-03-04,Third-order chromatic dispersion stabilizes Kerr frequency combs,"Using numerical simulations of an extended Lugiato-Lefever equation, we
analyze the stability and nonlinear dynamics of Kerr frequency combs generated
in microresonators and fiber resonators taking into account third-order
dispersion effects. We show that cavity solitons underlying Kerr frequency
combs, normally sensitive to oscillatory and chaotic instabilities, are
stabilized in a wide range of parameter space by third-order dispersion.
Moreover, we demonstrate how the snaking structure organizing compound states
of multiple cavity solitons is qualitatively changed by third-order dispersion,
promoting an increased stability of Kerr combs underlined by a single cavity
soliton.",1403.0903v1
2014-03-05,Non Linear Susceptibility from High DC Field Torque Magnetometry,"Torque magnetometry is a convenient technique to measure the magnetic
properties of anisotropic materials. Advances in micromachining and the
availability of robust materials with which such magnetometers can be
fabricated has made them reliable even in adverse conditions such as very high
magnetic fields and both high and very low temperatures. In most applications
with such magnetometers the measured torque signals are used to arrive at the
linear magnetic susceptibilities only. In this short note we extend torque
magnetometry to measure nonlinear susceptibilities and illustrate our methods
with representative data on the heavy fermion compound UPt3",1403.1287v1
2014-03-11,Plasmaron excitations in p(2x2)-K/Graphite,"A new type of plasmarons formed by the compound of photoelectrons and
acoustic surface plasmon excitations is investigated in the system
p(2x2)-K/Graphite. The physics behind these types of plasmarons, e-plasmarons,
is different from the ones recently found in graphene where the loss feature is
argued to result from the photohole-plasmon interaction, h-plasmarons. Based on
first principles methods we calculate the dispersion of e-plasmaron excitation
rate which yields a broad feature below the parabolic quantum-well band with a
peak about 0.4 eV below the quantum well band in the Gamma-point.",1403.2500v2
2014-03-12,Determination of ground-state and low-energy structures of perovskite superlattices from first principles,"In the development of first-principles high-throughput searches for materials
with desirable functional properties, there is a clear need for an efficient
method to determine the ground state and low-energy alternative structures of
superlattices. A method based on a simple strategy -- to generate starting
structures based on low-energy structures of the constituent compounds, which
are then optimized via structural relaxation calculations -- is proposed. This
""stacking method"" is demonstrated on the 2:2 PbTiO$_3$/SrTiO$_3$ superlattice,
which has been the subject of recent experimental and theoretical interest.
Considerations relevant to wider use of the method are discussed.",1403.3032v1
2014-03-14,Structural studies on Multiferroic La1-xBixCrO3 Perovskites,"The synthesis and structural studies on the polycrystalline La1-xBixCrO3 (x
=0, 0.2, 0.25, 0.3, 0.35) have been done using XRD and TEM. The results of the
Reitveld refinement of XRD data shows that these compounds crystallize in an
orthorhombic structure with Pnma space group. With increasing Bi content, the
unit cell volume and lattice parameters undergo non monotonous changes within
the tolerance factor from 0.84092 to 0.84072. This has been attributed to the
anisotropy induced by lone pair of Bi3+, which may distorted the lattice.",1403.3526v1
2014-03-16,Two dimensional semiconductors with possible high room temperature mobility,"We calculated the longitudinal acoustic phonon limited electron mobility of
14 two dimensional semiconductors with composition of MX$_2$, where M (= Mo, W,
Sn, Hf, Zr and Pt) is the transition metal, and X is S, Se and Te. We treated
the scattering matrix by deformation potential approximation. We found that out
of the 14 compounds, MoTe$_2$, HfSe$_2$ and HfTe$_2$, are promising regarding
to the possible high mobility and finite band gap. The phonon limited mobility
can be above 2500 cm$^2$V$^{-1}$s$^{-1}$ at room temperature.",1403.3872v1
2014-03-19,Ab-inito study of low temperature magnetic properties of double perovskite Sr2FeOsO6,"Using density-functional theory calculations, we investigated the electronic
structure and magnetic exchange interactions of the ordered 3d-5d double
perovskite Sr2FeOsO6, which has recently drawn attention for interesting
antiferromagnetic transitions. Our study reveals the vital role played by
long-range magnetic exchange interactions in this compound. The competition
between the ferromagnetic nearest neighbor Os-O-Fe interaction and
antiferromagnetic next nearest neighbor Os-O-Fe-O-Os interaction induces strong
frustration in this system, which explains the lattice distortion and magnetic
phase transitions observed in experiments.",1403.4894v1
2014-03-21,Field induced large magnetocaloric effect and magnetoresistance in ErNiSi,"Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with
negligible hysteresis loss has been observed in ErNiSi compound, which
undergoes metamagnetic transition at low temperatures. Magnetization, heat
capacity and resistivity measurements confirm the metamagnetic transition. The
maximum value of isothermal entropy change and MR for a field change of 50 kOe
are found to be 19.1 J/kg K and -34 %. Large MCE with negligible magnetic
hysteresis loss could make this material promising for low temperature magnetic
refrigeration.",1403.5396v1
2014-03-24,Statistical Theory of Breakup Reactions,"We propose alternatives to coupled-channels calculations with loosely-bound
exotic nuclei (CDCC), based on the the random matrix (RMT) and the optical
background (OPM) models for the statistical theory of nuclear reactions. The
coupled channels equations are divided into two sets. The first set, described
by the CDCC, and the other set treated with RMT. The resulting theory is a
Statistical CDCC (CDCC$_S$), able in principle to take into account many pseudo
channels.",1403.5820v1
2014-04-03,Utility indifference pricing of derivatives written on industrial loss indexes,"We consider the problem of pricing derivatives written on some industrial
loss index via utility indifference pricing. The industrial loss index is
modelled by a compound Poisson process and the insurer can adjust her portfolio
by choosing the risk loading, which in turn determines the demand. We compute
the price of a CAT(spread) option written on that index using utility
indifference pricing.",1404.0879v1
2014-04-11,Transmit Pulse Shaping for Molecular Communications,"This paper presents a method for shaping the transmit pulse of a molecular
signal such that the diffusion channel's response is a sharp pulse. The impulse
response of a diffusion channel is typically characterised as having an
infinitely long transient response. This can cause severe
inter-symbol-interference, and reduce the achievable reliable bit rate. We
achieve the desired chemical channel response by poisoning the channel with a
secondary compound, such that it chemically cancels aspects of the primary
information signal. We use two independent methods to show that the chemical
concentration of the \emph{information signal} should be $\propto \delta(t)$
and that of the \emph{poison signal} should be $\propto t^{-3/2}$.",1404.3104v1
2014-04-13,Contact melting and the structure of binary eutectic near the eutectic point,"Computer simulations of contact melting and associated interfacial phenomena
in binary eutectic systems were performed on the basis of the standard
phase-field model with miscibility gap in solid state. It is shown that the
model predicts the existence of equilibrium three-phase (solid-liquid-solid)
states above the eutectic temperature, which suggest the explanation of the
phenomenon of phase separation in liquid eutectic observed in experiments. The
results of simulations provide the interpretation for the phenomena of contact
melting and formation of diffusion zone observed in the experiments with binary
metal-silicon systems.",1404.3379v2
2014-05-05,Perfluorooctanoic acid rigidifies a model lipid membrane,"We report a combined dynamic light scattering and neutron spin-echo (NSE)
study on vesicles composed of the phospholipid
1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine under the influence of varying
amounts of perfluorooctanoic acid. We study local lipid bilayer undulations
using NSE on time scales up to 200 ns. Similar to the effect evoked by
cholesterol, we attribute the observed lipid bilayer stiffening to a condensing
effect of the perfluorinated compound on the membrane.",1405.0845v1
2014-05-07,Correlation-driven electronic multiferroicity in (TMTTF)$_2$-$X$ organic crystals,"Using a combination of density functional theory and dynamical mean field
theory we show that electric polarization and magnetism are strongly
intertwined in (TMTTF)$_2$-$X$ (X$=$PF$_6$, As$F_6$, and SbF$_6$) organic
crystals and they originate from short-range Coulomb interactions. Electronic
correlations induce a charge-ordered state which, combined with the molecular
dimerization, gives rise to a finite electronic polarization and to a
ferroelectric state. We predict that the value of the electronic polarization
is enhanced by the onset of antiferromagnetism showing a sizable
magnetoelectric leading to a multiferroic behavior of (TMTTF)$_2$-$X$
compounds.",1405.1528v1
2014-05-07,Modeling of Lead Halide Perovskites for Photovoltaic Applications,"We report first-principles calculations, using the full potential linear
augmented plane wave method, on six lead halide semiconductors, namely,
CH3NH3PbI3, CH3NH3PbBr3, CsPbX3 (X=Cl, Br, I), and RbPbI3. Exchange is modeled
using the modified Becke-Johnson potential. With an appropriate choice of the
parameter that defines this potential, an excellent agreement is obtained
between calculated and experimental band gaps of the six compounds. We comment
on the possibility that the cubic phase of CsPbI3, under hydrostatic pressure,
could be a topological insulator.",1405.1706v2
2014-05-09,On asymptotic scales of independently stopped random sums,"We study randomly stopped sums via their asymptotic scales. First, finiteness
of moments is considered. To generalise this study, asymptotic scales
applicable to the class of all heavy-tailed random variables are used. The
stopping is assumed to be independent of the underlying process, which is a
random walk.
  The main result enables one to identify whether the asymptotic behaviour of a
stopped sum is dominated by the increment, or the stopping variable. As a
consequence of this result, new sufficient conditions for the moment
determinacy of compounded sums are obtained.",1405.2239v1
2014-07-02,On universal modular symbols,"We clarify the relationship between works of Lee-Szczarba and Ash-Rudolph on
the homology of the Steinberg module of a linear Tits building. This yields a
simple proof of the Solomon-Tits theorem in this special case. We also give a
(weak) relationship between this combinatorics and the one studied by van der
Kallen, Suslin and Nesterenko to compute the homology of the general linear
group with constant coefficients.",1407.0475v2
2014-07-17,Hidden spin-orbital hexagonal ordering induced by strong correlations in LiVS$_2$,"We present a first-principles many-body analysis of multi-orbital lattice
susceptibilities in the metallic phase of the quasi-twodimensional compound
LiVS$_2$. We base this on advanced correlated electronic structure methods for
the $t_{2g}$-shell to reveal a highly entangled spin-orbital hexagonal ordering
(SOHO) bringing about an inherently intersite order parameter for the
trimerization transition, which eventually leads to an intriguing insulating
phase at low temperature.",1407.4795v2
2014-07-25,Ferromagnetism in UGe2 : A microscopic model,"Anderson lattice model is used to rationalize the principal features of the
heavy fermion compound UGe2 by means of the generalized Gutzwiller approach
(the SGA method). This microscopic approach successfully reproduces magnetic
and electronic properties of this material, in a qualitative agreement with
experimental findings from the magnetization measurements, the neutron
scattering, and the de Haas-van Alphen oscillations. Most importantly, it
explains the appearance, sequence, character, and evolution in an applied
magnetic field of the observed in UGe2 ferro- and, para-magnetic phases as an
effect of a competition between the f-f electrons Coulomb interaction energy
and f-conduction electrons kinetic energy (hybridization)",1407.6911v1
2014-07-31,Electronic structure of non-centrosymmetric superconductors Re24(Nb;Ti)5 by ab initio calculations,"Electronic structures of superconducting Re24Nb5 and Re24Ti5 have been
calculated employing the full-potential local-orbital method within the density
functional theory. The investigations were focused on the influence of the
antisymmetric spin-orbit coupling on band structures and Fermi surfaces of
these non-centrosymmetric systems. The predicted here density of states at the
Fermi level for Re24Ti5 is abnormally low with respect to that deduced from
previous heat capacity measurements. This discrepancy suggests an intermediate
coupled superconducting state in Re24Ti5. The differences between electronic
properties of both compounds could explain more robust superconductivity in the
Nb-based material.",1407.8416v1
2014-08-30,Multiband Te $p$ Based Superconductivity of Ta$_4$Pd$_3$Te$_{16}$,"Ta$_4$Pd$_3$Te$_{16}$ is a recently discovered superconductor that has been
suggested to be an unconventional superconductor near magnetism. We report
electronic structure calculations showing that in spite of the layered crystal
structure the material is an anisotropic three dimensional metal. The Fermi
surface contains prominent one and two dimensional features, including nested
1D sheets, a 2D cylindrical section and a 3D sheet. The electronic states that
make up the Fermi surface are mostly derived from Te $p$ states, with small Ta
$d$ and Pd $d$ contributions. This places the compound far from magnetic
instabilities. The results are discussed in terms of multiband
superconductivity.",1409.0078v1
2014-09-30,Spin-phonon and magnetostriction phenomena in CaMn7O12 helimagnet probed by Raman spectroscopy,"In this letter we investigated the temperature-dependent Raman spectra of
CaMn7O12 helimagnet from room temperature down to 10 K. The temperature
dependence of the Raman mode parameters show remarkable anomalies for both
antiferromagnetic and incommensurate transitions that this compound undergoes
at low temperatures. The anomalies observed at the magnetic ordering transition
indicate a spin-phonon coupling at higher-temperature magnetic transition in
this material, while a magnetostrinction effect at the lower-temperature
magnetic transition.",1410.0073v1
2014-10-01,Breadth first search coding of multitype forests with application to Lamperti representation,"We obtain a bijection between some set of multidimensional sequences and this
of $d$-type plane forests which is based on the breadth first search algorithm.
This coding sequence is related to the sequence of population sizes indexed by
the generations, through a Lamperti type transformation. The same
transformation in then obtained in continuous time for multitype branching
processes with discrete values. We show that any such process can be obtained
from a $d^2$ dimensional compound Poisson process time changed by some integral
functional. Our proof bears on the discretisation of branching forests with
edge lengths.",1410.0250v1
2014-10-06,Analysis of point contact spectra of kfe2as2 in the thermal regime,"The point-contact spectra of the iron-based compound KFe2As2 were analyzed
according to the thermal regime theory. We have obtained the values of the
residual resistivity, the Lorentz number, and the electron mean free path in
the contacts. It was shown that the most point-contact spectra can be described
by this theory. The reasons for this behavior are discussed.",1410.1322v1
2014-10-12,Terahertz Electrodynamics of $180^\circ$ Domain Walls in Thin Ferroelectric Films,"We investigate oscillation dynamics of a periodic structure of the
$180^\circ$ domain walls in nanometricaly thin substrate-deposited
ferroelectric films and superlattices. We calculate dynamic permittivity of
such structures and reveal a collective resonance mode, which in the typical
ferroelectric compounds, PbTiO3/SrTiO3, lies in the sub- and low THz frequency
range of 0.3-3THz. We propose the reflection-absorbtion spectroscopy
experiments to observe this mode.",1410.3124v3
2014-10-15,Novel magneto-electric multiferroics from first-principles,"Interest in first-principles calculations within the multiferroic community
has been rapidly on the rise over the last decade. Initially considered as a
powerful support to explain experimentally observed behaviours, the trend has
evolved and, nowadays, density functional theory calculations has become also
an essential predicting tool for identifying original rules to achieve
multiferroism and design new magneto-electric compounds. This chapter aims to
highlight the key advances in the field of multiferroics for which
first-principles methods have contributed significantly. The essential
theoretical developments that made this search possible are also briefly
presented.",1410.4047v1
2014-10-17,Olfactory Signal Processing,"Olfaction, the sense of smell, has received scant attention from a signal
processing perspective in comparison to audition and vision. In this paper, we
develop a signal processing paradigm for olfactory signals based on new
scientific discoveries including the psychophysics concept of olfactory white.
We describe a framework for predicting the perception of odorant compounds from
their physicochemical features and use the prediction as a foundation for
several downstream processing tasks. We detail formulations for odor
cancellation and food steganography, and provide real-world empirical examples
for the two tasks. We also discuss adaptive filtering and other olfactory
signal processing tasks at a high level.",1410.4865v2
2014-10-23,Conductivity anisotropy helps to reveal the microscopic structure of a density wave at imperfect nesting,"Superconductivity or metallic state may coexist with density wave ordering at
imperfect nesting of the Fermi surface. In addition to the macroscopic spatial
phase separation, there are, at least, two possible microscopic structures of
such coexistence: (i) the soliton-wall phase and (ii) the ungapped
Fermi-surface pockets. We show that the conductivity anisotropy allows to
distinguish between these two microscopic density-wave structures. The results
obtained may help to analyze the experimental observations in layered organic
metals (TMTSF)$_{2}$PF$_{6}$, (TMTSF)$_{2}$ClO$_{4}$, $\alpha
$-(BEDT-TTF)$_{2}$KHg(SCN)$_{4}$ and in other compounds.",1410.6314v1
2014-10-24,Modeling-based determination of physiological parameters of systemic VOCs by breath gas analysis: a pilot study,"In this paper we develop a simple two compartment model which extends the
Farhi equation to the case when the inhaled concentration of a volatile organic
compound (VOC) is not zero. The model connects the exhaled breath concentration
of systemic VOCs with physiological parameters such as endogenous production
rates and metabolic rates. Its validity is tested with data obtained for
isoprene and inhaled deuterated isoprene-D5.",1410.6599v2
2014-10-28,"First principles studies of the structural, electronic and optical properties of LiInSe2 and LiInTe2 chalcopyrite crystals","Detailed first principles calculations of the structural, electronic and
optical properties of two representatives of the chalcopyrite group of
compounds (LiInSe2 and LiInTe2) are reported in the present paper. Both
materials are shown to be the direct band gap semiconductors. Analysis of the
electronic properties showed that the degree of covalency increases if Se is
substituted by Te. Calculations of the optical properties of both crystals
allowed getting reliable approximation of the refractive index as a function of
the wavelength. All calculated results were compared with the available
experimental data; good agreement was demonstrated.",1410.7489v1
2014-11-06,Phenomenological description of anisotropy effects in some ferromagnetic superconductors,"We study phenomenologically by using the previously derived Landau free
energy, the role of anisotropy in ferromagnetic superconductors UGe2, URhGe,
and UCoGe. The three compounds are separately discussed with the special stress
on UGe2. The main effect comes from the strong uniaxial anisotropy of
magnetization while the anisotropy of Cooper pairs and crystal anisotropy only
slightly change the phase diagram in the vicinity of Curie temperature. The
limitations of this approach are also discussed.",1411.1748v1
2014-11-14,Hellmann-Feynman Forces within the DFT+U in Wannier functions basis,"The most general way to describe localized atomic-like electronic states in
strongly correlated compounds is to utilize Wannier functions. In the present
paper we continue the development of widely-spread DFT+U method onto Wannier
function basis set and propose the technique to calculate the Hubbard
contribution to the forces. The technique was implemented as a part of
plane-waves pseudopotential code Quantum-ESPRESSO and successfully tested on a
charge transfer insulator NiO.",1411.3867v2
2014-11-15,Investigating the Role of Prior Disambiguation in Deep-learning Compositional Models of Meaning,"This paper aims to explore the effect of prior disambiguation on neural
network- based compositional models, with the hope that better semantic
representations for text compounds can be produced. We disambiguate the input
word vectors before they are fed into a compositional deep net. A series of
evaluations shows the positive effect of prior disambiguation for such deep
models.",1411.4116v1
2014-11-18,Active optomechanics through relaxation oscillations,"We propose an optomechanical laser based on III-V compounds which exhibits
self-pulsation in the presence of a dissipative optomechanical coupling. In
such a laser cavity, radiation pressure drives the mechanical degree of freedom
and its back-action is caused by the mechanical modulation of the cavity loss
rate. Our numerical analysis shows that even in a wideband gain material, such
dissipative coupling couples the mechanical oscillation with the laser
relaxation oscillations process. Laser self-pulsation is observed for
mechanical frequencies below the laser relaxation oscillation frequency under
sufficiently high optomechanical coupling factor.",1411.4710v1
2014-12-07,Ferroelectricity and Rashba effect in GeTe,"GeTe has been proposed as the father compound of a new class of functional
materials displaying bulk Rashba effects coupled to ferroelectricity:
ferroelectric Rashba semiconductors. In nice agreement with first principle
calculations, we show by angular resolved photoemission and piezo-force
microscopy that GeTe displays surface and bulk Rashba bands arising from the
intrinsic inversion symmetry breaking provided by the remanent ferroelectric
polarization. This work points to the possibility to control the spin chirality
of bands in GeTe by acting on its ferroelectric polarization.",1412.2386v1
2014-12-12,"Structure, magnetic order and excitations in the 245 family of Fe-based superconductors","Elastic neutron scattering simultaneously probes both the crystal structure
and magnetic order in a material. Inelastic neutron scattering measures phonons
and magnetic excitations. Here, we review the average composition, crystal
structure and magnetic order in the 245 family of Fe-based superconductors and
in related insulating compounds from neutron diffraction works. A
three-dimensional phase-diagram summarizes various structural, magnetic and
electronic properties as a function of the sample composition. A high pressure
phase diagram for the superconductor is also provided. Magnetic excitations and
the theoretic Heisenberg Hamiltonian are provided for the superconductor.
Issues for future works are discussed.",1412.3995v1
2014-12-12,Magnetism of sigma-phase Fe-Mo alloys: ac magnetic susceptibility study,"A series of four sigma-Fe(100-x)Mo(x) samples was investigated with ac
magnetic susceptibility measurements. An evidence was found that the ground
magnetic state of the samples is constituted by a spin glass (SG) with the spin
glass temperature ranging between ca. 34K for x=47 and ca. 16K for x=53. The SG
state is heterogeneous and it can be divided into a weak-irreversibility and a
strong-irreversibility domains. Its figures of merit are typical of metallic
(canonical) spin glasses.",1412.4078v1
2014-12-15,Pinball liquid phase from Hund's coupling in frustrated transition metal oxides,"The interplay of non-local Coulomb repulsion and Hund's coupling in the
d-orbital manifold in frustrated triangular lattices is analyzed by a mutliband
extended Hubbard model. We find a rich phase diagram with several competing
phases, including a robust pinball liquid phase, which is an unconventional
metal characterized by threefold charge order, bad metallic behavior and the
emergence of high spin local moments. Our results naturally explain the
anomalous charge-ordered metallic state observed in the triangular layered
compound AgNiO2. The potential relevance to other triangular transition metal
oxides is discussed.",1412.4696v2
2014-12-22,On the Spectroscopic Boundaries Between Normal and Peculiar Type~I Supernovae,"The spectrum of a supernova is a summation of numerous overlapping atomic
line signatures. Consequently, empirical measurements are limited in
application when compound features are assumed to be due to one or two spectral
lines. Here I address matters of spectroscopic boundaries between normal and
peculiar type I supernovae using multi-component empirical metrics. I discuss
some obstacles faced when using supernova spectra to pair model with data and I
demonstrate how spectrum synthesis can benefit from fairly complete
observational coverage in wavelength and time.",1412.7163v1
2014-12-25,"Highly Accurate Local Pseudopotentials of Li, Na, and Mg for Orbital Free Density Functional Theory","We present a method to make highly accurate pseudopotentials for use with
orbital-free density functional theory (OF-DFT) with given exchange-correlation
and kinetic energy functionals, which avoids the compounding of errors of
Kohn-Sham DFT and OF-DFT. The pseudopotentials are fitted to reference
(experimental or highly accurate quantum chemistry) values of interaction
energies, geometries, and mechanical properties, using a genetic algorithm.
This can enable routine large-scale ab initio simulations of many practically
relevant materials. Pseudopotentials for Li, Na, and Mg resulting in accurate
geometries and energies of different phases as well as of vacancy formation and
bulk moduli are presented as examples.",1412.7795v1
2015-01-20,Hydrogen Fluoride Capture by Imidazolium Acetate Ionic Liquid,"Extraction of hydrofluoric acid (HF) from oils is a drastically important
problem in petroleum industry, since HF causes quick corrosion of pipe lines
and brings severe health problems to humanity. Some ionic liquids (ILs)
constitute promising scavenger agents thanks to strong binding to polar
compounds and tunability. PM7-MD simulations and hybrid density functional
theory are employed here to consider HF capture ability of ILs. Discussing the
effects and impacts of the cation and the anion separately and together, I will
evaluate performance of imidazolium acetate and outline systematic search
guidelines for efficient adsorption and extraction of HF.",1501.05024v1
2015-01-26,Electric polarization of magnetic domain walls in magnetoelectrics,"Two prominent magnetoelectrics MnWO$_4$ and CuO possess low-temperature
commensurate paraelectric magnetically ordered phase. Here using Monte Carlo
simulations we show that the walls between the domains of this phase are
ferroelectric with the same electric polarization direction and value as that
in the magnetoelectric phases of these compounds. We also suggest that
experimental observation of electric polarization of domain walls in MnWO$_4$
should help to determine the macroscopic interactions responsible for its
magnetoelectric properties.",1501.06372v2
2015-01-31,Tuning Optical Properties of Transparent Conducting Barium Stannate by Dimensional Reduction,"We report calculations of the electronic structure and optical properties of
doped $n$-type perovskite BaSnO3 and layered perovskites. While doped BaSnO$_3$
retains its transparency for energies below the valence to conduction band
onset, the doped layered compounds exhibit below band edge optical conductivity
due to transitions from the lowest conduction band. This gives absorption in
the visible for Ba2SnO4. Thus it is important to minimize this phase in
transparent conducting oxide (TCO) films. Ba3Sn2O7 and Ba4Sn3O10 have strong
transitions only in the red and infrared, respectively. Thus there may be
opportunities for using these as wavelength filtering TCO.",1502.00171v1
2015-02-02,Electrical and magnetic properties of La$_{0.5}$Rh$_4$Sb$_{12}$ filled skutterudite synthesized at high pressure,"A filled skutterudite, La$_{0.5}$Rh$_4$Sb$_{12}$, with a lattice constant of
9.284(2) {\AA} was synthesized using a high-pressure technique. The electrical
resistivity showed semiconducting behavior and the energy gap was estimated to
be more than 0.08 eV. Magnetic susceptibility measurements indicated
temperature-independent diamagnetism, which originates from Larmor
diamagnetism. The electrical properties of this compound are more similar to
those of the La$_{0.5}$Rh$_4$As$_{12}$ semiconductor with an energy gap of 0.03
eV than to those of the La$_{0.6}$Rh$_4$P$_{12}$ superconductor.",1502.00337v2
2015-02-02,Bismuth-based perovskites as multiferroics,"This review devoted to multiferroic properties of Bismuth-based perovskites
falls into two parts. The first part focuses on BiFeO3 and summarizes the
recent progress made in the studies of its pressure-temperature phase diagram
and magnetoelectric coupling phenomena. The second part discusses in a more
general way the issue of polar - and multiferroic - phases in BiBO3 perovskites
and the competition between ferroelectricity and other structural
instabilities, from an inventory of recently synthetized compounds.",1502.00432v1
2015-02-04,Superconductivity with topological surface state in SrxBi2Se3,"By intercalation of alkaline-earth metal Sr in Bi2Se3, superconductivity with
large shielding volume fraction (~91.5% at 0.5 K) has been achieved in
Sr0.065Bi2Se3. The analysis of the Shubnikov-de Hass oscillations confirms the
1/2-shift expected from a Dirac spectrum, giving transport evidence of the
existence of surface states. Importantly, the SrxBi2Se3superconductor is stable
under air, making the SrxBi2Se3 compound an ideal material base for
investigating topological superconductivity.",1502.01105v2
2015-02-14,Gärtner-Ellis condition for squared asymptotically stationary Gaussian processes,"The G\""artner-Ellis condition for the square of an asymptotically stationary
Gaussian process is established. The same limit holds for the conditional
distri-bution given any fixed initial point, which entails weak multiplicative
ergodicity. The limit is shown to be the Laplace transform of a convolution of
Gamma distributions with Poisson compound of exponentials. A proof based on
Wiener-Hopf factorization induces a probabilistic interpretation of the limit
in terms of a regression problem.",1502.04218v1
2015-02-20,Renormalized Multicanonical Sampling,"For a homogeneous system divisible into identical, weakly interacting
subsystems, the muticanonical procedure can be accelerated if it is first
applied to determine of the density of states for a single subsystem. This
result is then employed to approximate the state density of a subsystem with
twice the size that forms the starting point of a new multicanonical iteration.
Since this compound subsystem interacts less on average with its environment,
iterating this sequence of steps rapidly generates the state density of the
full system.",1502.05846v1
2015-03-05,Photostrictive materials,"Light-matter interactions that lead to nonthermal changes in size of the
sample constitute a photostrictive effect in many compounds. The photostriction
phenomenon was observed in four main groups of materials, ferroelectrics,
polar, and non-polar semiconductors, as well as in organic-based materials that
are reviewed here. The key mechanisms of photostriction and its dependence on
several parameters and perturbations are assessed. The major literature of the
photostriction is surveyed, and the review ends with a summary of the proposed
technical applications.",1503.01642v1
2015-03-07,On the Range of Subordinators,"In this note we look into detail at the box-counting dimension of
subordinators. Given that $X$ is a non-decreasing Levy process, which is not a
compound Poisson process, we show that in the limit, the minimum number of
boxes of size $\delta$ that cover the range of $(X_s)_{s\leq t}$ is a.s. of
order $t/U(\delta)$, where $U$ is the potential function of $X$. This is a more
refined result than the lower and upper index of the box-counting dimension
computed in the literature which deals with the asymptotic number of boxes at
logarithmic scale.",1503.02149v1
2015-03-29,Geometric expansion of the log-partition function of the anisotropic Heisenberg model,"We study the asymptotic expansion of the log-partition function of the
anisotropic Heisenberg model in a bounded domain as this domain is dilated to
infinity. Using the Ginibre's representation of the anisotropic Heisenberg
model as a gas of interacting trajectories of a compound Poisson process we
find all the non-decreasing terms of this expansion. They are given explicitly
in terms of functional integrals. As the main technical tool we use the cluster
expansion method.",1503.08505v1
2015-03-30,Exponentiated Extended Weibull-Power Series Class of Distributions,"In this paper, we introduce a new class of distributions by compounding the
exponentiated extended Weibull family and power series family. This
distribution contains several lifetime models such as the complementary
extended Weibull-power series, generalized exponential-power series,
generalized linear failure rate-power series, exponentiated Weibull-power
series, generalized modified Weibull-power series, generalized Gompertz-power
series and exponentiated extended Weibull distributions as special cases. We
obtain several properties of this new class of distributions such as Shannon
entropy, mean residual life, hazard rate function, quantiles and moments. The
maximum likelihood estimation procedure via a EM-algorithm is presented.",1503.08653v1
2015-04-10,Electronic structure and the origin of the high ordering temperature in SrRu2O6,"SrRu2O6 is a layered honeycomb lattice material with an extraordinarily high
magnetic ordering temperature. We investigated this material using density
functional calculations. We find that the energy scales for moment formation
and ordering are similar and high. Additionally, we find that the magnetic
anisotropy is high and favors moments oriented along the $c$-axis. This
provides an explanation for the exceptionally high ordering temperature.
Finally, the compound is found to be semiconducting at the bare density
functional level, even without magnetic order. Experimental consequences of
this scenario for the high ordering temperature are discussed.",1504.02745v1
2015-04-22,Spin Polarization Inversion at Benzene-Absorbed Fe4N Surface,"We report a first-principle study on electronic structure and simulation of
the spin-polarized scanning tunneling microscopy graphic of a benzene/Fe4N
interface. Fe4N is a compound ferromagnet suitable for many spintronic
applications. We found that, depending on the particular termination schemes
and interface configurations, the spin polarization on the benzene surface
shows a rich variety of properties ranging from cosine-type oscillation to
polarization inversion. Spin-polarization inversion above benzene is resulting
from the hybridizations between C pz and the out-of-plane d orbitals of Fe
atom.",1504.05675v1
2015-04-22,Strongly Correlated Electrons in Solids,"Most emergent properties of the materials discovered since the 1980s are
related to the existence of electron-electron interactions which are large with
respect to the kinetic energies and could not be thoroughly studied before. The
occurrence of metal insulator transitions, of exotic magnetic and/or
superconducting properties in many new compounds have stimulated a large series
of ex- perimental and theoretical developments to grasp their physical
significance. We present here a simple introduction to the elementary aspects
of the physics of electron-electron interactions, which could be a starting
point for typical undergraduate students.",1504.05855v1
2015-04-30,MORPH: A Reference Architecture for Configuration and Behaviour Self-Adaptation,"An architectural approach to self-adaptive systems involves runtime change of
system configuration (i.e., the system's components, their bindings and
operational parameters) and behaviour update (i.e., component orchestration).
Thus, dynamic reconfiguration and discrete event control theory are at the
heart of architectural adaptation. Although controlling configuration and
behaviour at runtime has been discussed and applied to architectural
adaptation, architectures for self-adaptive systems often compound these two
aspects reducing the potential for adaptability. In this paper we propose a
reference architecture that allows for coordinated yet transparent and
independent adaptation of system configuration and behaviour.",1504.08339v1
2015-05-01,Entropy and diffuse scattering: comparison of NbTiVZr and CrMoNbV,"The chemical disorder intrinsic to high entropy alloys inevitably creates
diffuse scattering in their x-ray or neutron diffraction patterns. Through
first principles hybrid Monte Carlo/molecular dynamics simulations of two BCC
high entropy alloy forming compounds, CrMoNbV and NbTiVZr, we identify the
contributions of chemical disorder, atomic size and thermal fluctuations to the
diffuse scattering. As a side benefit, we evaluate the reduction in entropy due
to pair correlations within the framework of the cluster variation method.
Finally, we note that the preference of Ti and Zr for HCP structures at low
temperature leads to a mechanical instability reducing the local BCC character
of NbTiVZr, while preserving global BCC symmetry.",1505.00243v1
2015-05-12,Unified picture for the colossal thermopower compound FeSb$_2$,"We identify the driving mechanism of the gigantic Seebeck coefficient in
FeSb$_2$ as the phonon-drag effect associated with an in-gap density of states
that we demonstrate to derive from excess iron. We accurately model electronic
and thermoelectric transport coefficients and explain the so far ill-understood
correlation of maxima and inflection points in different response functions.
Our scenario has far-reaching consequences for attempts to harvest the
spectacular powerfactor of FeSb$_2$.",1505.02946v1
2015-05-20,Decorrelation estimates for random Schrödinger operators with non rank one perturbations,"We prove decorrelation estimates for generalized lattice Anderson models on
$Z^d$ constructed with finite-rank perturbations in the spirit of Klopp
\cite{klopp}. These are applied to prove that the local eigenvalue statistics
$\xi^\omega_{E}$ and $\xi^\omega_{E^\prime}$, associated with two energies $E$
and $E'$ satisfying $|E - E'| > 4d$, are independent. That is, if $I,J$ are two
bounded intervals, the random variables $\xi^\omega_{E}(I)$ and
$\xi^\omega_{E'}(J)$, are independent and distributed according to a compound
Poisson distribution whose L\'evy measure has finite support. We also prove
that the extended Minami estimate implies that the eigenvalues in the
localization region have multiplicity at most the rank of the perturbation.",1505.05218v1
2015-05-21,General Formalism for Magnetic Anisotropy Constants,"Direct expressions for the magnetic anisotropy constants are given at a
finite temperature from microscopic viewpoints. In the present derivation, it
is assumed that the Hamiltonian is a linear function with respect to the
magnetization direction. We discuss in detail the first-order constant $K_1$
and show that the results reproduce previous results. We also apply our method
to Nd$_2$Fe$_{14}$B compounds and demonstrate that the temperature dependencies
of the magnetocrystalline anisotropy constants $K_1$, $K_2$, and $K_3$ are
successfully computed.",1505.05686v1
2015-05-25,Halogenation of Imidazolium Ionic Liquids. Thermodynamics Perspective,"Imidazolium cations are promising for anion exchange membranes, and
electrochemical applications and gas capture. They can be chemically modified
in many ways including halogenation. Halogenation possibilities of the
imidazole ring constitute a particular interest. This work investigates
fluorination and chlorination reactions of all symmetrically non-equivalent
sites of the imidazolium cation. Halogenation of all carbon atoms is
thermodynamically permitted. Out of these, the most favorable site is the first
methylene group of the alkyl chain. In turn, the least favorable site is carbon
of the imidazole ring. Temperature dependence of enthalpy, entropy, and Gibbs
free energy at 1 bar is discussed. The reported results provide an important
guidance in functionalization of ionic liquids in search of task-specific
compounds.",1505.06526v1
2015-05-29,Pressure-Induced Superconductivity in BiS2-based EuFBiS2,"We measured the electrical resistivity of a BiS2-based compound EuFBiS2 under
high pressure. Polycrystalline EuFBiS2 shows insulator-metal transition and
pressure-induced superconductivity above 0.7 GPa. The superconducting
transition temperature increases with increasing applied pressure and shows the
maximum value around 8.6 K at 1.8 GPa.",1505.08002v2
2015-06-07,"Comment on: Synthesis, growth and characterization of a new metal organic Nlo material: Dibromo bis(L proline)Cd(II)","The title paper by Boopathi and Ramasamy reports a study on the crystal
growth and characterization of dibromobis (L-proline)Cd(II) (1). Many points of
criticism, concerning the crystal structure of (1) and the magnetic properties
of (1) dibromo bis(L-proline)Zn(II) (2) and diiodo bis(2-aminopyridine)Cd(II)
(3) are reported to show that compounds 1 to 3 are not soft magnets but instead
diamagnetic solids.",1506.02252v1
2015-05-03,Quantum Discord of $f$-Deformed Bipartite Entangled Oscillators,"Quantum correlations in compound systems are of great importance, and they
are fundamental resource for the development of quantum computation protocols
and quantum information. In this work we construct bipartite pure coherent
states using the $f$-deformed oscillator formalism and the Barut-Girardello
deformation function. Also we construct the extension of these systems to mixed
states using Werner like states. For the states constructed, we study the
dependence of the entanglement and quantum discord upon the deformation and
mixed parameters.",1506.05326v1
2015-06-24,Electrical and Thermal Transport of Layered Bismuth-chalcogenide EuBiS2F at temperatures between 300 and 623 K,"We demonstrate the electrical and thermal transport of layered bismuth-based
sulfide EuBiS2F from 300 to 623 K. Although significant hybridization between
Eu 4f and Bi 6p electrons was reported previously, the carrier transport of the
compound is similar to those of F-doped LaBiS2O, at least above 300 K. The
lattice thermal conductivity is lower than that of isostructural SrBiS2F, which
is attributed to heavier atomic mass of Eu ions.",1506.07340v3
2015-06-29,Intrinsic transparent conductors without doping,"Transparent conductors (TC's) combine the usually contraindicated properties
of electrical conductivity with optical transparency and are generally made by
starting with a transparent insulator and making it conductive via heavy
doping, an approach that generally faces severe 'doping bottlenecks'. We
propose a different idea for TC design-starting with a metallic conductor and
designing transparency by control of intrinsic interband transitions and
intraband plasmonic frequency. We identify the specific design principles for
three such prototypical intrinsic TC classes and then search computationally
for materials that satisfy them. Remarkably, one of the intrinsic TC,
Ag3Al22O34, is predicted also to be a prototype 3D compounds that manifest
natural 2D electron gas (2DEG) regions with very high electron density and
conductivity.",1506.08884v1
2015-07-05,How to estimate solid-electrolyte interphase features when screening electrolyte materials,"Computational screening of battery electrolyte components is an extremely
challenging task because very complex features like solidelectrolyte-interphase
(SEI) formation and graphite exfoliation need to be taken into account at least
at the final screening stage. We present estimators for both SEI formation and
graphite exfoliation based on a combinatorial approach with quantum chemistry
calculations on model system reactions, which can be applied automatically for
a large number of compounds and thus allows for a systematic first assessment
of the relevant properties within screening approaches. Thermodynamic effects
are assessed with quantum mechanical calculations, a more heuristic approach is
used to estimate kinetic effects.",1507.01271v1
2015-07-16,Structural Transition in Layered As$_{\sf\textbf{1-x}}$P$_{\sf\textbf{x}}$ Compounds: A Computational Study,"As a way to further improve the electronic properties of group V layered
semiconductors, we propose to form in-layer 2D heterostructures of black
phosphorus and grey arsenic. We use \textit{ab initio} density functional
theory to optimize the geometry, determine the electronic structure, and
identify the most stable allotropes as a function of composition. Since pure
black phosphorus and pure grey arsenic monolayers differ in their equilibrium
structure, we predict a structural transition and a change in frontier states,
including a change from a direct-gap to an indirect-gap semiconductor, with
changing composition.",1507.04448v1
2015-07-20,Some sharp inequalities for the Toader-Qi mean,"The Toader-Qi mean of positive numbers $a$ and $b$ defined by
\begin{equation*} TQ\left( a,b\right) =\frac{2}{\pi }\int_{0}^{\pi /2}a^{\cos
^{2}\theta }b^{\sin ^{2}\theta }d\theta \end{equation*} is related to the
modified Bessel function of the first kind. In this paper, we present several
properties of this mean, and establish some sharp inequalities for this mean in
terms of power and logarithmic means. From these a nice chain of inequalities
involving Gauss compound mean, Toader mean and Toader-Qi mean is presented.",1507.05430v1
2015-07-22,Theoretical Study of Coulomb Correlations and Spin-Orbit Coupling in SrIrO3,"Given that energy scales associated with crystal field splitting, spin orbit
coupling and coulomb correlations in iridates are comparable, hence leading to
exotic properties, we investigate the physical properties of orthorhombic
SrIrO3 using density functional theory. Our calculations, however, show that
SrIrO 3 is a bad metal with no long range magnetic ordering, unlike its sister
compounds Sr2IrO4 and Sr3Ir2O7. Moreover, despite having large band width, it
appears conclusive that the larger resistivity in SrIrO 3 is due to spin orbit
interactions. Besides, the effects of electron-electron correlations on its
electronic structure and magnetic properties are also discussed.",1507.06058v1
2015-08-02,On Bivariate Generalized Exponential-Power Series Class of Distributions,"In this paper, we introduce a new class of bivariate distributions by
compounding the bivariate generalized exponential and power-series
distributions.
  This new class contains some new sub-models such as the bivariate generalized
exponential distribution, the bivariate generalized exponential-poisson,
-logarithmic, -binomial and -negative binomial distributions. We derive
different properties of the new class of distributions. The EM algorithm is
used to determine the maximum likelihood estimates of the parameters. We
illustrate the usefulness of the new distributions by means of an application
to a real data set.",1508.00219v1
2015-08-06,Elastic and inelastic breakup of deuterons with energy below 100 MeV,"We present calculations of deuteron elastic and inelastic breakup cross
sections and angular distributions at deuteron energies below 100 MeV obtained
using the post-form DWBA approximation. The elastic breakup cross section was
extensively studied in the past. Very few calculations of inelastic breakup
have been performed, however. We also analyze the angular momentum - energy
distributions of the cross section for formation of the compound nucleus after
inelastic breakup.",1508.01466v1
2015-08-07,"Topotactic synthesis of a new BiS2-based superconductor Bi2(O,F)S2","A new BiS2-based superconductor Bi2(O,F)S2 was discovered. This is a layered
compound consisting of alternate stacking structure of rock-salt-type BiS2
superconducting layer and fluorite-type Bi(O,F) blocking layer. Bi2(O,F)S2 was
obtained as the main phase by topotactic fluorination of undoped Bi2OS2 using
XeF2, which is the first topotactic synthesis of an electron-doped
superconductor via reductive fluorination. With increasing F-content, a- and
c-axis length increased and decreased, respectively, and Tc increased up to 5.1
K.",1508.01654v1
2015-08-31,Comments on the papers recently published by Kalaivani et al,"We argue that the so-called l lysinium succinate (journal of crystal growth
426 (2015) 135), zinc chloride doped l lysinium succinate (journal of crystal
growth 428 (2015) 24), and l threonine phthalate (journal of crystal growth 427
(2015) 29) and sodium acetate doped l tyrosine (spectrochimica acta 136a (2015)
168) are all dubious crystals. Taking these compounds as examples we show that
that edax is an inappropriate method for characterization of new materials
based on elemental composition data.",1508.07843v2
2015-09-08,The influence of spin and charge fluctuations on the pressure dependence of the Neel temperature near a quantum phase transition in rare-earth intermetallic compounds,"In the one-loop approximation for the periodic Anderson model the
contributions of spin and charge fluctuations to the renormalization of the
antiferromagnetic order parameter are calculated. It is shown that taking into
account the fluctuation corrections allows to quantitatively describe the
pressure dependence of the Neel temperature observed in quasi-two-dimensional
intermetallic antiferromagnet with heavy fermions CeRhIn$_5$.",1509.02269v1
2015-09-09,On the Multidimensional Stable Marriage Problem,"We provide a problem definition of the stable marriage problem for a general
number of parties $p$ under a natural preference scheme in which each person
has simple lists for the other parties. We extend the notion of stability in a
natural way and present so called elemental and compound algorithms to generate
matchings for a problem instance. We demonstrate the stability of matchings
generated by both algorithms, as well as show that the former runs in $O(pn^2)$
time.",1509.02972v1
2015-09-11,Finite temperature magnetism of FeRh compounds,"The temperature dependent stability of the magnetic phases of FeRh were
investigated by means of total energy calculations with magnetic disorder
treated within the uncompensated disordered local moment (uDLM) approach. In
addition, Monte Carlo simulations based on the extended Heisenberg model have
been performed, using exchange coupling parameters obtained rom first
principles. The crucial role and interplay of two factors in the metamagnetic
transition in FeRh has been revealed, namely the dependence of the Fe-Fe
exchange coupling parameters on the temperature-governed degree of magnetic
disorder in the system and the stabilizing nature of the induced magnetic
moment on Rh-sites. An important observation is the temperature dependence of
these two competing factors.",1509.03581v1
2015-09-23,On the distribution of cumulative Parisian ruin,"We introduce the concept of cumulative Parisian ruin, which is based on the
time spent in the red by the underlying surplus process. Our main result is an
explicit representation for the distribution of the occupation time, over a
finite-time horizon, for a compound Poisson process with drift and exponential
claims. The Brownian ruin model is also studied in details. Finally, we analyze
for a general framework the relationships between cumulative Parisian ruin and
classical ruin, as well as with Parisian ruin based on exponential
implementation delays.",1509.06857v1
2015-09-30,Topological Phases in Two-Dimensional Materials: A Brief Review,"Topological phases with insulating bulk and gapless surface or edge modes
have attracted much attention because of their fundamental physics implications
and potential applications in dissipationless electronics and spintronics. In
this review, we mainly focus on the recent progress in the engineering of
topologically nontrivial phases (such as $\mathbb{Z}_2$ topological insulators,
quantum anomalous Hall effects, quantum valley Hall effects \textit{etc.}) in
two-dimensional material systems, including quantum wells, atomic crystal
layers of elements from group III to group VII, and the transition metal
compounds.",1509.09016v1
2015-10-01,Correlation-driven multigap d-wave superconductivity in Anderson lattice model,"We present the full Gutzwiller-wave-function solution of the Anderson lattice
model in two dimensions that leads to the correlation-driven multigap
superconducting (SC) ground state with the dominant $d_{x^2-y^2}$-wave
symmetry. The results are consistent with the principal properties of the
heavy-fermion superconductor CeCoIn$_5$. We regard the pairing mechanism as
universal and thus applicable to other Ce-based heavy-fermion compounds.
Additionally, a gain in kinetic energy in the SC state takes place, as is also
the case for high-temperature superconductors.",1510.00224v1
2015-10-01,Krypton oxides under pressure,"Under high pressure, krypton, one of the most inert elements is predicted to
become sufficiently reactive to form a new class of krypton compounds; krypton
oxides. Using modern ab-initio evolutionary algorithms in combination with
Density Functional Theory, we predict the existence of several
thermodynamically stable Kr/O species at elevated pressures. In particular, our
calculations indicate that at approx. 300 GPa the monoxide, KrO, should form
spontaneously and remain thermo- and dynamically stable with respect to
constituent elements and higher oxides. The monoxide is predicted to form
non-molecular crystals with short Kr-O contacts, typical for genuine chemical
bonds.",1510.00255v1
2015-10-07,"The structural, elastic, electronic and optical properties of MgCu under pressure: A first-principles study","The effect of pressure on the structural, elastic and electronic properties
of the intermetallic compound MgCu with a CsCl-type structure have been
investigated using ab-initio technique. The optical properties have been
studied under normal pressure. We have carried out the plane-wave
pseudopotential approach within the framework of the first-principle density
functional theory (DFT) implemented within the CASTEP code. The calculated
structural parameters show a good agreement with the experimental and other
theoretical results.",1510.02020v3
2015-10-11,Resonances and Reactions from Mean-Field Dynamics,"The time-dependent version of nuclear density functional theory, using
functionals derived from Skyrme interactions, is able to approximately describe
nuclear dynamics. We present time-dependent results of calculations of dipole
resonances, concentrating on excitations of valence neutrons against a proton
plus neutron core in the neutron-rich doubly-magic $^{132}$Sn nucleus, and
results of collision dynamics, highlighting potential routes to ternary fusion,
with the example of a collision of $^{48}$Ca+$^{48}$Ca+$^{208}$Pb resulting in
a compound nucleus of element 120 stable against immiedate fission",1510.03017v1
2015-10-09,Superconvergence to freely infinitely divisible distributions,"The phenomenon of superconvergence is proved for all freely infinitely
divisible distributions. Precisely, suppose that the partial sums of a sequence
of free identically distributed, infinitesimal random variables converge in
distribution to a nondegenerate freely infinitely divisible law. Then the
distribution of the sum becomes Lebesgue absolutely continuous with a
continuous density in finite time, and this density can be approximated by that
of the limit law uniformly, as well as in all $L^{p}$-norms for $p>1$, on the
real line except possibly in the neighborhood of one point. Applications
include the global superconvergence to freely stable laws and that to free
compound Poisson laws over the whole real line.",1510.03393v1
2015-10-13,A State-Dependent Dual Risk Model,"In a dual risk model, the premiums are considered as the costs and the claims
are regarded as the profits. The surplus can be interpreted as the wealth of a
venture capital, whose profits depend on research and development. In most of
the existing literature of dual risk models, the profits follow the compound
Poisson model and the cost is constant. In this paper, we develop a
state-dependent dual risk model, in which the arrival rate of the profits and
the costs depend on the current state of the wealth process. Ruin probabilities
are obtained in closed-forms. Further properties and results will also be
discussed.",1510.03920v2
2015-10-23,Uniform Asymptotics for Compound Poisson Processes with Regularly Varying Jumps and Vanishing Drift,"This paper addresses heavy-tailed large deviation estimates for the
distribution tail of functionals of a class of spectrally one-sided L\'evy
process. Our contribution is to show that these estimates remain valid in a
near-critical regime. This complements recent similar results that have been
obtained for the all-time supremum of such processes. Specifically, we consider
local asymptotics of the all-time supremum, the supremum of the process until
exiting $[0,\infty)$, the maximum jump until that time, and the time it takes
until exiting $[0,\infty)$. The proofs rely, among other things, on properties
of scale functions.",1510.06955v2
2015-10-24,"Normal Power Series Class of Distributions: Model, Properties and Applications","A new class of distributions, called as normal power series (NPS), which
contains the normal one as a particular case, is introduced in this paper. This
new class which is obtained by compounding the normal and power series
distributions, is presented as an alternative to the class of skew-normal and
Balakrishnan skew-normal distributions, among others. The density and
distribution functions of this new class of distributions, are given by a
closed expression which allows us to easily compute probabilities, moments and
related measurements. Estimation of the parameters of this new model by maximum
likelihood method via an EM- algorithm is given. Finally, some applications are
shown as examples.",1510.07180v1
2015-10-27,Evidence for a re-entrant character of magnetism of sigma-phase Fe-Mo alloys: non-linear susceptibilities,"Non-linear ac magnetic susceptibility terms viz. quadratic, chi2, and cubic,
chi3, were measured versus temperature and frequency for a series of the
sigma-phase Fe(100-x)Mo(x) (47<x<53) compounds. Clear evidence was found that
the ground magnetic state of the samples is mixed i.e. constituted by two
phases: a spin glass (SG) and a ferromagnet (FM), hence the magnetism of the
investigated samples can be regarded as re-entrant (RSG). Based on the present
data, previously reported magnetic phase diagram has been upgraded [J.
Przewoznik, S. M. Dubiel,J. Alloy. Comp., 630 (2015) 222].",1510.07811v1
2015-10-29,New intercalation superconductor Lix(C6H16N2)yFe2-zSe2 with a very large interlayer-spacing and Tc = 38 K,"A new iron-based superconductor, Lix(C6H16N2)yFe2-zSe2, with Tc = 38 K has
successfully been synthesized via the intercalation of lithium and
hexamethylenediamine into FeSe. The superconducting transition has been
confirmed not only by magnetic susceptibility measurements but also by
electrical resistivity ones. The interlayer spacing, namely, the dicstance
between neighboring Fe layers, d, is 16.225(5) $\mathring{\text{A}}$, which is
the largest among those of FeSe-based intercalation compounds. It has been
found that the dependence of Tc on d in FeSe-based intercalation
superconductors appears domic.",1510.08625v1
2015-11-05,Return times at periodic points in random dynamics,"We prove a quenched limiting law for random measures on subshifts at periodic
points. We consider a family of measures $\{\mu_\omega\}_{\omega\in\Omega}$,
where the `driving space' $\Omega$ is equipped with a probability measure which
is invariant under a transformation $\theta$. We assume that the fibred
measures $\mu_\omega$ satisfy a generalised invariance property and are
$\psi$-mixing. We then show that for almost every $\omega$ the return times to
cylinders $A_n$ at periodic points are in the limit compound Poisson
distributed for a parameter $\vartheta$ which is given by the escape rate at
the periodic point.",1511.01657v2
2015-11-05,Sodium Pentazolate: a Nitrogen Rich High Energy Density Material,"Sodium pentazolates NaN5 andNa2N5, new high energy density materials, are
discovered during first principles crystal structure search for the compounds
of varying amounts of elemental sodium and nitrogen. The pentazole anion N5- is
stabilized in the condensed phase by sodium Na+ cations at pressures exceeding
20 GPa, and becomes metastable upon release of pressure. The sodium azide
(NaN3) precursor is predicted to undergo a chemical transformation above 50 GPa
into sodium pentazolates NaN5 and Na2N5. The calculated Raman spectrum of NaN5
is in agreement with the experimental Raman spectrum of a previously
unidentified substance appearing upon compression and heating of NaN3.",1511.01879v1
2015-12-10,Class of Rashba ferroelectrics in hexagonal semiconductors,"We present a class of Rashba systems in hexagonal semiconducting compounds,
where an electrical control over spin-orbital texture is provided by their bulk
ferroelectricity. Our first-principles calculations reveal a number of such
materials with large Rashba coefficients. We, furthermore, show that strain can
drive a topological phase transition in such materials, resulting in a
ferroelectric topological insulating state. Our findings can open avenues for
interplay between Rashba effect, ferroelectricity and topological phenomena.",1512.03119v2
2015-12-31,New Approaches for ab initio Calculations of Molecules with Strong Electron Correlation,"Reliable quantum chemical methods for the description of molecules with
dense-lying frontier orbitals are needed in the context of many chemical
compounds and reactions. Here, we review developments that led to our
newcomputational toolbo x which implements the quantum chemical density matrix
renormalization group in a second-generation algorithm. We present an overview
of the different components of this toolbox.",1512.09267v2
2016-01-05,Long memory and multifractality: A joint test,"The properties of statistical tests for hypotheses concerning the parameters
of the multifractal model of asset returns (MMAR) are investigated, using Monte
Carlo techniques. We show that, in the presence of multifractality,
conventional tests of long memory tend to over-reject the null hypothesis of no
long memory. Our test addresses this issue by jointly estimating long memory
and multifractality. The estimation and test procedures are applied to exchange
rate data for 12 currencies. In 11 cases, the exchange rate returns are
accurately described by compounding a NIID series with a multifractal
time-deformation process. There is no evidence of long memory.",1601.00903v1
2016-01-07,Superconducting properties of FeSe0.5Te0.5 under high pressure,"This work reports studies performed in the superconducting compound
FeSe0:5Te0:5 under high pressure. Changes were observed in the transition
temperature, superconducting critical fields,anomalous variations in the
Meissner fraction, and in Ginzburg Landau parameters. The superconducting
properties were calculated and compared using the Werthamer-Helfand-Hohenber
approximation and Ginzburg-Landau theory. Hydrostatic pressure was produced
from atmospheric to 823 MPa, the increment in the critical temperature was from
14.45 to 20.5 K at a rate of change about 0.0069 K/MPa.",1601.01417v1
2016-01-26,Robust Optimal Risk Sharing and Risk Premia in Expanding Pools,"We consider the problem of optimal risk sharing in a pool of cooperative
agents. We analyze the asymptotic behavior of the certainty equivalents and
risk premia associated with the Pareto optimal risk sharing contract as the
pool expands. We first study this problem under expected utility preferences
with an objectively or subjectively given probabilistic model. Next, we develop
a robust approach by explicitly taking uncertainty about the probabilistic
model (ambiguity) into account. The resulting robust certainty equivalents and
risk premia compound risk and ambiguity aversion. We provide explicit results
on their limits and rates of convergence, induced by Pareto optimal risk
sharing in expanding pools.",1601.06979v1
2016-02-05,Magnetic order and spin excitations in the Kitaev--Heisenberg model on the honeycomb lattice,"We consider the quasi-two-dimensional pseudo-spin-1/2 Kitaev - Heisenberg
model proposed for A2IrO3 (A=Li, Na) compounds. The spin-wave excitation
spectrum, the sublattice magnetization, and the transition temperatures are
calculated in the random phase approximation (RPA) for four different ordered
phases, observed in the parameter space of the model: antiferomagnetic, stripe,
ferromagnetic, and zigzag phases. The N\'{e}el temperature and temperature
dependence of the sublattice magnetization are compared with the experimental
data on Na2IrO3.",1602.01961v1
2016-02-08,Extended formalism for simulating compound refractive lens-based x-ray microscopes,"We present a comprehensive formalism for the simulation and optimisation of
CRLs in both condensing and full-field imaging configurations. The approach
extends ray transfer matrix analysis to account for x-ray attenuation by the
lens material. Closed analytical expressions for critical imaging parameters
such as numerical aperture, vignetting, chromatic aberration and focal length
are provided for both thin- and thick-lens imaging geometries.",1602.02703v1
2016-02-16,N-Type Oxide Thermoelectrics Via Visual Search Strategies,"We discuss and present search strategies for finding new thermoelectric
compositions based on first principles electronic structure and transport
calculations. We illustrate them by application to a search for potential
n-type oxide thermoelectric materials. This includes a screen based on
visualization of electronic energy isosurfaces. We report compounds that show
potential as thermoelectric materials along with detailed properties, including
SrTiO3, which is a known thermoelectric, and appropriately doped KNbO3 and
rutile TiO2.",1602.05054v1
2016-02-18,Correlations induced orbital ordering and cooperative Jahn-Teller distortion in the paramagnetic insulator KCrF$_3$,"We investigate the origin of the orbital ordering in the paramagnetic phase
of KCrF$_3$. All previous studies described structural parameters of the
paramagnetic phase using a magnetic ordering in the compound. Our simulations
of real paramagnetic KCrF$_3$ were performed within an approach combining
density functional theory and dynamical mean field theory (DFT+DMFT). As a
result, it was found that the experimentally observed cooperative Jahn-Teller
effect is successfully described in a lattice relaxation calculation for
structure without any long-range magnetic ordering. It is established that the
existence of the orbital ordering even in undistorted perovskite structure
clearly confirms the electronic origin of the orbital ordering in KCrF$_3$.",1602.05802v1
2016-02-18,Metallic Nickel Silicides: Experiments and Theory for NiSi and First Principles Calculations for Other Phases,"We report detailed experimental investigation of the transport and magnetic
properties of orthorhombic NiSi along with first principles studies of this
phase and related nickel silicides. Neutron scattering shows no evidence for
magnetism, in agreement with first principles calculations. Comparison of first
principles results and experimental results from our measurements and
literature show a weak electron phonon coupling. We discuss transport and other
properties of NiSi and find behavior characteristic of a weak correlated metal
far from magnetism. Trends among the nickel silicides as a function of nickel
content are discussed.",1602.05840v1
2016-02-19,Learning to SMILE(S),"This paper shows how one can directly apply natural language processing (NLP)
methods to classification problems in cheminformatics. Connection between these
seemingly separate fields is shown by considering standard textual
representation of compound, SMILES. The problem of activity prediction against
a target protein is considered, which is a crucial part of computer aided drug
design process. Conducted experiments show that this way one can not only
outrank state of the art results of hand crafted representations but also gets
direct structural insights into the way decisions are made.",1602.06289v2
2016-02-25,Uniaxial pressure induced half-metallic ferromagnetic phase transition in LaMnO$_3$,"We use first-principles theory to predict that the application of uniaxial
compressive strain leads to a transition from an antiferromagnetic insulator to
a ferromagnetic half-metal phase in LaMnO$_3$. We identify the Q2 Jahn-Teller
mode as the primary mechanism that drives the transition, indicating that this
mode can be used to tune the lattice, charge, and spin coupling. Applying
$\simeq$ 6 GPa of uniaxial pressure along the [010] direction activates the
transition to a half-metallic $\textit{pseudo-cubic}$ state. The
half-metallicity opens the possibility of producing colossal magnetoresistance
in the stoichiometric LaMnO$_3$ compound at significantly lower pressure
compared to recently observed investigations using hydrostatic pressure.",1602.07984v1
2016-02-25,High-resolution magnetic penetration depth and inhomogeneities in locally noncentrosymmetric SrPtAs,"We present a magnetic-penetration-depth study on polycrystalline and granular
samples of SrPtAs, a pnictide superconductor with a hexagonal structure
containing PtAs layers that individually break inversion symmetry (local
noncentrosymmetry). Compact samples show a clear-cut s-wave-type BCS behavior,
which we consider to be the intrinsic penetration depth of SrPtAs. Granular
samples display a sample-dependent second diamagnetic drop, attributed to the
intergrain coupling. Our experimental results point to a nodeless isotropic
superconducting energy gap in SrPtAs, which puts strong constraints on the
driven mechanism for superconductivity and the order parameter symmetry of this
compound.",1602.08060v1
2016-02-29,On the boundedness of Pseudo-differential operators on Triebel-Lizorkin and Besov spaces,"In this work we show endpoint boundedness properties of pseudo-differential
operators of type $(\rho,\rho)$, $0<\rho<1$, on Triebel-Lizorkin and Besov
spaces. Our results are sharp and they also cover operators defined by compound
symbols.",1602.08811v5
2016-02-29,A medium-resolution monochromator for 73 keV x-rays - Nuclear resonant scattering of synchrotron radiation from 193-Ir,"We report on the development and characterization of a medium resolution
monochromator for synchrotron-based hyperfine spectroscopy at the 73 keV
nuclear resonance of 193-Ir. The device provides high throughput of 6*10^8 ph/s
in an energy bandwidth of 300(20) meV. We excited the nuclear resonance in
193-Ir at 73.04 keV and observed nuclear fluorescence of 193-Ir in Iridium
metal. The monochromator allows for Nuclear Forward Scattering spectroscopy on
Ir and its compounds.",1602.08874v1
2016-04-01,Occupation times of general Lévy processes,"For an arbitrary L\'evy process $X$ which is not a compound Poisson process,
we are interested in its occupation times. We use a quite novel and useful
approach to derive formulas for the Laplace transform of the joint distribution
of $X$ and its occupation times. Our formulas are compact, and more
importantly, the forms of the formulas clearly demonstrate the essential
quantities for the calculation of occupation times of $X$. It is believed that
our results are important not only for the study of stochastic processes, but
also for financial applications.",1604.00097v1
2016-04-11,First principles calculation of the valence band offsets for \b{eta}- polytype of A3B6 layered crystals,"The valence band offsets (VBO) for the \b{eta}-type A3B6 layered compounds
depending on the thickness of the crystals have been investigated from the
first principles, based on the density functional theory. To simulate the
structure of a given thickness the periodic slab model was used. Two adjacent
crystal slabs consisting of several layers were separated by a vacuum region of
two-layer width. It is shown that at the crystal thickness more than 12 layers,
photothreshold practically becomes independent on the thickness of the crystal.",1604.03069v1
2016-04-15,Exactly solvable time-dependent models of two interacting two-level systems,"Two coupled two-level systems placed under external time-dependent magnetic
fields are modeled by a general Hamiltonian endowed with a symmetry that
enables us to reduce the total dynamics into two independent two-dimensional
sub-dynamics. Each of the sub-dynamics is shown to be brought into an exactly
solvable form by appropriately engineering the magnetic fields and thus we
obtain an exact time evolution of the compound system. Several physically
relevant and interesting quantities are evaluated exactly to disclose
intriguing phenomena in such a system.",1604.04519v1
2016-04-16,The occurrence of a Mott-like gap in single-particle spectra of electron systems possessing flat bands,"An unconventional type of the Mott's insulators where the gap in the spectrum
of single-particle excitations is associated with repulsive effective
interactions between quasiparticles is shown to exist in strongly correlated
electron systems of solids that possess flat bands. The occurrence of this gap
is demonstrated to be the consequence of violation of particle-hole symmetry,
inherent in such systems. The results obtained are applied to elucidate the
Fermi arc structure observed at temperatures up to $100\,$ K in angle-resolved
photoemission spectra of the compound Sr$_2$IrO$_4$, not showing
superconductivity down to low $T$.",1604.04726v1
2016-04-22,Evidence for proximity of YFe$_2$Si$_2$ to a magnetic quantum critical point,"Calculations of the electronic and magnetic properties of the non-magnetic
metallic compound YFe$_2$Si$_2$ are reported. These show that at the density
functional level a magnetic state involving ordering along the $c$-axis. The
electronic structure is three dimensional, and is similar to that of the
unconventional superconductor YFe$_2$Ge$_2$ and as well as that of the high
pressure collapsed tetragonal phase of KFe$_2$As$_2$, which is also a
superconductor. Based on the results in relation to experiment, we infer that
properties of YFe$_2$Si$_2$ are strongly influenced by a nearby
antiferromagnetic quantum critical point.",1604.06768v1
2016-05-01,Further results on degree based topological indices of certain chemical networks,"There are various topological indices such as degree based topological
indices, distance based topological indices and counting related topological
indices etc. These topological indices correlate certain physicochemical
properties such as boiling point, stability of chemical compounds. In this
paper, we compute the sum-connectivity index and multiplicative Zagreb indices
for certain networks of chemical importance like silicate networks, hexagonal
networks, oxide networks, and honeycomb networks. Moreover, a comparative study
using computer-based graphs has been made to clarify their nature for these
families of networks.",1605.00253v2
2016-05-08,The tempered discrete Linnik distribution,"A tempered version of the discrete Linnik distribution is introduced in order
to obtain integer-valued distribution families connected to stable laws. The
proposal constitutes a generalization of the well-known Poisson-Tweedie law,
which is actually a tempered discrete stable law. The features of the new
tempered discrete Linnik distribution are explored by providing a series of
identities in law - which describe its genesis in terms of mixture and compound
Poisson law, as well as in terms of mixture discrete stable law. A manageable
expression of the corresponding probability function is also provided and
several special cases are analysed.",1605.02326v1
2016-05-18,"Comment on ""Solution of the $α$-Potential Mystery in the $γ$ Process and Its Impact on the Nd/Sm Ratio in Meteorites""","A competition of the low-energy Coulomb excitation (CE) with the compound
nucleus (CN) formation in $\alpha$-induced reactions below the Coulomb barrier
has been assumed by Rauscher [Phys. Rev. Lett. 111, 061104 (2013)] in order to
use the same optical model (OM) potential for description of the latter and the
alpha-particle emission as well. In this Comment we show that the corresponding
partial waves and integration radii provide evidence for the distinct account
of the CE cross section and OM total-reaction cross section.",1605.05455v2
2016-05-28,Lévy-driven GPS queues with heavy-tailed input,"In this paper we derive exact large-buffer asymptotics for a two-class
Generalized Processor Sharing (GPS) model, under the assumption that the input
traffic streams generated by both classes correspond to heavy-tailed L\'evy
processes. Four scenarios need to be distinguished, which differ in terms of
(i)~the level of heavy-tailedness of the driving L\'evy processes as well as
(ii)~the values of the corresponding mean rates relative to the GPS weights.
The derived results are illustrated by two important special cases, in which
the queues' inputs are modeled by heavy-tailed compound Poisson processes and
by $\alpha$-stable L\'evy motions.",1605.08862v1
2016-06-09,Exploring the properties of lead-free hybrid double perovskites using a combined computational-experimental approach,"Density functional theory screening of the hybrid double perovskites
(MA)2BIBiX6 (BI=K,Cu,Ag,Tl; X=Cl,Br,I) shows that systems with band gaps
similar to those of the MAPbX3 lead compounds can be expected for BI=Cu,Ag,Tl.
Motivated by these findings, (MA)2TlBiBr6, isoelectronic with MAPbBr3, was
synthesised and found to have a band gap of ~2.0eV.",1606.02916v1
2016-06-21,Magnetism of the antiferromagnetic spin-$\frac{1}{2}$ tetramer compound CuInVO$_5$,"We measured the temperature dependence of the magnetic susceptibility and
specific heat and the magnetic-field dependence of the magnetization of
CuInVO$_5$. An antiferromagnetically ordered state appears below $T_{\rm N} =
2.7$ K. We observed a $\frac{1}{2}$ quantum magnetization plateau above 30 T at
1.3 K. We show that the spin system consists of antiferromagnetic
spin-$\frac{1}{2}$ tetramers with $J_1 = 240 \pm 20$ and $J_2 = -142 \pm 10$ K
for the intratetramer interactions.",1606.06468v1
2016-06-22,Hyperpolarized Nanodiamond Surfaces,"The widespread use of nanodiamond as a biomedical platform for drug-delivery,
imaging, and sub-cellular tracking applications stems from their non-toxicity
and unique quantum mechanical properties. Here, we extend this functionality to
the domain of magnetic resonance, by demonstrating that the intrinsic electron
spins on the nanodiamond surface can be used to hyperpolarize adsorbed liquid
compounds at room temperature. By combining relaxation measurements with
hyperpolarization, spins on the surface of the nanodiamond can be distinguished
from those in the bulk liquid. These results are likely of use in signaling the
controlled release of pharmaceutical payloads.",1606.06822v1
2016-06-19,On some links between quantum physics and gravitation,"It is widely believed that quantum gravity effects are negligible in a
conventional laboratory experiment because quantum gravity should play its role
only at a distance of about Planck's length ($\sim10^{-33}$ cm). Sometimes that
is not the case as shown in this article. We discuss two new ideas about
quantum physics connections with gravity. First, the Hong-Ou-Mandel effect
relation to quantum gravity is examined. Second, it is shown that the very
existence of gravitons is a consequence of quantum statistics. Moreover, since
the Bose-Einstein statistics is a special case of Compound Poisson
Distribution, it predicts the existence of an infinite family of high-spin
massless particles.",1606.07744v2
2016-06-29,Molecular dynamics simulations of the lattice thermal conductivity of CuInTe2,"The lattice thermal conductivity of thermoelectric material CuInTe2 is
predicted using classical molecular dynamics simulations, where a simple but
effective Morse-type interatomic potential is constructed by fitting
first-principles total energy calculations. In a broad temperature range from
300 to 900 K, our simulated results agree well with those measured
experimentally, as well as those obtained from phonon Boltzmann transport
equation. By introducing the Cd impurity and Cu vacancy, the thermal
conductivity of CuInTe2 can be effectively reduced to further enhance the
thermoelectric performance of this chalcopyrite compound.",1606.08947v1
2016-07-01,Magnetic Properties of (La0.56Ce0.14)Sr0.30MnO3 Perovskite,"We investigate in this paper magnetic properties of the perovskite compound
(La0.56Ce0.14)Sr0.30MnO3. The method we use here is Monte Carlo simulation, in
which we take into account different kinds of interactions between nearest and
between next-nearest magnetic ions Mn 3+ (S = 2) , Mn 4+ (S = 3/2) and Ce 3+ (S
= 1/2). Using a classical spin model, we have calculated the internal energy,
the magnetization per ion type and their corresponding magnetic susceptibility,
as well as the Edwards-Anderson order parameter for each ion kind. We also
studied the applied-field effect on the system magnetization. Our results show
a good agreement with experiments.",1607.00221v1
2016-07-14,Cluster size distributions of extreme values for the Poisson-Voronoi tessellation,"We consider the Voronoi tessellation based on a homogeneous Poisson point
process in $\mathbf{R}^{d}$. For a geometric characteristic of the cells (e.g.
the inradius, the circumradius, the volume), we investigate the point process
of the nuclei of the cells with large values. Conditions are obtained for the
convergence in distribution of this point process of exceedances to a
homogeneous compound Poisson point process. We provide a characterization of
the asymptotic cluster size distribution which is based on the Palm version of
the point process of exceedances. This characterization allows us to compute
efficiently the values of the extremal index and the cluster size probabilities
by simulation for various geometric characteristics. The extension to the
Poisson-Delaunay tessellation is also discussed.",1607.04075v1
2016-07-13,Very low-energy nucleon + 16O coupled-channel scattering: results with a phenomenological vibrational model,"We employ a collective vibration coupled-channel model to describe the
nucleon-16O cluster systems, obtaining low-excitation spectra for 17O and 17F.
Bound and resonance states of the compound systems have been deduced, showing
good agreement with experimental spectra. Low energy scattering cross sections
of neutrons and protons from 16O also have been calculated and the results
compare well with available experimental data.",1607.04199v2
2016-07-15,Partial orders and immunity in reverse mathematics,"We identify computability-theoretic properties enabling us to separate
various statements about partial orders in reverse mathematics. We obtain
simpler proofs of existing separations, and deduce new compound ones. This work
is part of a larger program of unification of the separation proofs of various
Ramsey-type theorems in reverse mathematics in order to obtain a better
understanding of the combinatorics of Ramsey's theorem and its consequences. We
also answer a question of Murakami, Yamazaki and Yokoyama about pseudo Ramsey's
theorem for pairs.",1607.04506v2
2016-07-18,Imitation Learning with Recurrent Neural Networks,"We present a novel view that unifies two frameworks that aim to solve
sequential prediction problems: learning to search (L2S) and recurrent neural
networks (RNN). We point out equivalences between elements of the two
frameworks. By complementing what is missing from one framework comparing to
the other, we introduce a more advanced imitation learning framework that, on
one hand, augments L2S s notion of search space and, on the other hand,
enhances RNNs training procedure to be more robust to compounding errors
arising from training on highly correlated examples.",1607.05241v1
2016-07-25,Effects of entrance channel on fusion probability in hot fusion reactions,"Within the framework of the dinuclear system (DNS) model, the fusion
reactions leading to the compound nuclei 274Hs and 286Cn are investigated. The
fusion probability as a function of DNS excitation energy is studied. The
calculated results are in good agreement with the available experimental data.
The obtained results show that the fusion probabilities are obviously enhanced
for the reactions located at high place in potential energy surface, although
these reactions may have small values of mass asymmetry. It is found that the
enhancement is due to the large potential energy of the initial DNS.",1607.07148v1
2016-07-27,Alloy-like behaviour of the thermal conductivity of non-symmetric superlattices,"In this work, we show a phenomenological alloy-like fit of the thermal
conductivity of (A)d1:(B)d2 superlattices with d1 /= d2, i.e. non-symmetric
structure. The presented method is a generalization of the Norbury rule of the
summation of thermal resistivities in alloy compounds. Namely, we show that
this approach can be also extended to describe the thermal properties of
crystalline and ordered-system composed by two or more elements, and, has a
potentially much wider application range. Using this approximation we estimate
that the interface thermal resistance depends on the period and the ratio of
materials that form the superlattice structure",1607.08017v2
2016-08-09,Analytical solution to the Riemann problem of 1D elastodynamics with general constitutive laws,"Under the hypothesis of small deformations, the equations of 1D
elastodynamics write as a 2 x 2 hyperbolic system of conservation laws. Here,
we study the Riemann problem for convex and nonconvex constitutive laws. In the
convex case, the solution can include shock waves or rarefaction waves. In the
nonconvex case, compound waves must also be considered. In both convex and
nonconvex cases, a new existence criterion for the initial velocity jump is
obtained. Also, admissibility regions are determined. Lastly, analytical
solutions are completely detailed for various constitutive laws (hyperbola,
tanh and polynomial), and reference test cases are proposed.",1608.02721v1
2016-08-09,Search for the magnetocaloric effect in multiferroics oxides,"In this paper, we report on the magnetocaloric properties of some selected
multiferroic oxides, namely HoMn2O5 and La2(Ni,Co)MnO6 compounds which exhibit
transition points from 10K up to almost room temperature. In order to avoid
grain boundary effects and structural inhomogeneity observed frequently in
polycrystalline samples, only single crystals were considered for this study.",1608.02809v1
2016-08-14,Calculations for electron-impact ionization of beryllium in the method of interacting configurations in the complex number representation,"The beginning of the application of the method of interacting configurations
in the complex number representation to the compound atomic systems has been
presented. The spectroscopic characteristics of the Be atom in the problem of
the electron-impact ionization of this atom are investigated. The energies and
the widths of the lowest autoionizing states of Be atom are calculated.",1608.04078v1
2016-08-25,Two-dimensional Superconductors with Atomic-scale Thicknesses,"Recent progress in two-dimensional superconductors with atomic-scale
thicknesses is reviewed mainly from the experimental point of view. The
superconducting systems treated here involve a variety of materials and forms:
elemental-metal ultrathin films and atomic layers on semiconductor surfaces;
interfaces and superlattices of heterostructures made of cuprates, perovskite
oxides, and rare-earth metal heavy-fermion compounds; interfaces of
electric-double-layer transistors; graphene and atomic sheets of
transition-metal dichalcogenide; iron selenide and organic conductors on oxide
and metal surfaces, respectively. Unique phenomena arising from the ultimate
two-dimensionality of the system and the physics behind them are discussed.",1608.06997v1
2016-08-25,Thermodynamic Measurement of Angular Anisotropy at the Hidden Order Transition of URu$_2$Si$_2$,"The heavy fermion compound URu$_2$Si$_2$ continues to attract great interest
due to the unidentified hidden order it develops below 17.5K. The unique Ising
character of the spin fluctuations and low temperature quasiparticles is well
established. We present detailed measurements of the angular anisotropy of the
nonlinear magnetization that reveal a $\cos^4 \theta$ Ising anisotropy both at
and above the ordering transition. With Landau theory, we show this implies a
strongly Ising character of the itinerant hidden order parameter.",1608.07009v1
2016-08-25,"Multiband electronic transport in $α$-Yb$_{1-x}$Sr$_{x}$AlB$_{4}$ [x = 0, 0.19(3)] single crystals","We report on the evidence for the multiband electronic transport in
$\alpha$-YbAlB$_{4}$ and $\alpha$-Yb$_{0.81(2)}$Sr$_{0.19(3)}$AlB$_{4}$.
Multiband transport reveals itself below 10 K in both compounds via Hall effect
measurements, whereas anisotropic magnetic ground state sets in below 3 K in
$\alpha$-Yb$_{0.81(2)}$Sr$_{0.19(3)}$AlB$_{4}$. Our results show that Sr$^{2+}$
substitution enhances conductivity, but does not change the quasiparticle mass
of bands induced by heavy fermion hybridization.",1608.07277v1
2016-08-28,LC/ESI-MS analysis of underivatized amino acids and mass spectrum,"We report the method of LC/ESI-MS analysis of underivatized amino acids with
corresponding mass spectrum and fragmentation patterns. Diagnostic product ions
determined by mass spectrometry can support the qualitative identification and
quantitative estimation of individual amino acids. Therefore, the optimization
of chromatographic separation using the ion-pairing reagent (i.e.,
Nonafluoropentanoic acid, NFPA) is useful for the evaluation of target amino
acid and for further compound-specific nitrogen isotope studies of amino acids.",1608.07780v1
2016-09-12,A Meaning-oriented Approach to Semantic Data Modeling,"Semantic information is often represented as the entities and the
relationships among them with conventional semantic models. This approach is
straightforward but is not suitable for many posteriori requests in semantic
data modeling. In this paper, we propose a meaning-oriented approach to
modeling semantic data and establish a graph-based semantic data model. In this
approach we use the meanings, i.e., the subjective views of the entities and
relationships, to describe the semantic information, and use the semantic
graphs containing the meaning nodes and the meta-meaning relations to specify
the taxonomy and the compound construction of the semantic concepts. We
demonstrate how this meaning-oriented approach can address many important
semantic representation issues, including dynamic specialization and natural
join.",1609.03346v1
2016-10-04,Hidden Fermi-liquid charge transport in the antiferromagnetic phase of the electron-doped cuprates,"Systematic analysis of the planar resistivity, Hall effect and cotangent of
the Hall angle for the electron-doped cuprates reveals underlying Fermi-liquid
behavior even deep in the antiferromagnetic part of the phase diagram. The
transport scattering rate exhibits a quadratic temperature dependence, and is
nearly independent of doping, compound and carrier type (electrons vs. holes),
and hence universal. Our analysis moreover indicates that the material-specific
resistivity upturn at low temperatures and low doping has the same origin in
both electron- and hole-doped cuprates.",1610.01181v1
2016-10-25,Efficient technique for computational design of thermoelectric materials,"Efficient thermoelectric materials are highly desirable, and the quest for
finding them has intensified as they could be promising alternatives to fossil
energy sources. Here we present a general first-principles approach to predict,
in multicomponent systems, efficient thermoelectric compounds. The method
combines a robust evolutionary algorithm, a Pareto multiobjective optimization,
density functional theory and a Boltzmann semi-classical calculation of
thermoelectric efficiency. To test the performance and reliability of our
overall framework, we use the well-known system Bi$_2$Te$_3$-Sb$_2$Te$_3$.",1610.07824v2
2016-10-27,Phase transitions in large deviations of reset processes,"We study the large deviations of additive quantities, such as energy or
current, in stochastic processes with intermittent reset. Via a mapping from a
discrete-time reset process to the Poland-Scheraga model for DNA denaturation,
we derive conditions for observing first-order or continuous dynamical phase
transitions in the fluctuations of such quantities and confirm these conditions
on simple random walk examples. These results apply to reset Markov processes,
but also show more generally that subleading terms in generating functions can
lead to non-analyticities in large deviation functions of 'compound processes'
or 'random evolutions' switching stochastically between two or more
subprocesses.",1610.08842v2
2016-11-09,The quartet ground state in CeB$_6$: an inelastic x-ray scattering study,"We investigated the ground state symmetry of the cubic hidden order compound
CeB$_6$ by means of core level non-resonant inelastic x-ray scattering (NIXS).
The information is obtained from the directional dependence of the scattering
function that arises from higher than dipole transitions. Our new method
confirms that the ground state is well described using a localized
crystal-field model assuming a $\Gamma_8$ quartet ground state.",1611.02913v1
2016-11-16,A Way out of the Odyssey: Analyzing and Combining Recent Insights for LSTMs,"LSTMs have become a basic building block for many deep NLP models. In recent
years, many improvements and variations have been proposed for deep sequence
models in general, and LSTMs in particular. We propose and analyze a series of
augmentations and modifications to LSTM networks resulting in improved
performance for text classification datasets. We observe compounding
improvements on traditional LSTMs using Monte Carlo test-time model averaging,
average pooling, and residual connections, along with four other suggested
modifications. Our analysis provides a simple, reliable, and high quality
baseline model.",1611.05104v2
2016-11-17,Hund's metallicity and orbital-selective Mott localization of CrO$_{2}$ in the paramagnetic state,"We present electronic structure calculations of a CrO$_{2}$ compound in the
paramagnetic state within the computational scheme of density-functional theory
combined with dynamical mean-field theory. We find that CrO$_{2}$ in the
paramagnetic state is a strongly-correlated Hund's metal with mixed-valent Cr
ions. At high temperatures, CrO$_{2}$ shows an orbital-selective Mott phase, in
which the Cr $d_{xy}$ orbital is Mott-localized while the other Cr $t_{2g}$ $d$
orbitals remain itinerant. When the temperature is lowered, the
orbital-selective Mott state is found to evolve into a Kondo-like heavy-fermion
state with a small pseudo gap at the Fermi level if the system remains in the
paramagnetic state.",1611.05568v1
2016-11-22,Mapping chemical performance on molecular structures using locally interpretable explanations,"In this work, we present an application of Locally Interpretable
Machine-Agnostic Explanations to 2-D chemical structures. Using this framework
we are able to provide a structural interpretation for an existing black-box
model for classifying biologically produced fuel compounds with regard to
Research Octane Number. This method of ""painting"" locally interpretable
explanations onto 2-D chemical structures replicates the chemical intuition of
synthetic chemists, allowing researchers in the field to directly accept,
reject, inform and evaluate decisions underlying inscrutably complex
quantitative structure-activity relationship models.",1611.07443v1
2016-11-28,A new class of half-metallic ferromagnets from first principles,"Half-metallic ferromagnetism (HMFM) occurs rarely in materials and yet offers
great potential for spintronic devices. Recent experiments suggest a class of
compounds with the `ThCr$_{2}$Si$_{2}$' (122) structure -- isostructural and
containing elements common with Fe pnictide-based superconductors -- can
exhibit HMFM. Here we use $ab$ $initio$ density-functional theory calculations
to understand the onset of half-metallicity in this family of materials and
explain the appearance of ferromagnetism at a quantum critical point. We also
predict new candidate materials with HMFM and high Curie temperatures through
A-site alloying.",1611.09422v2
2016-11-30,The mixed-state Hall conductivity of single-crystal films $Nd_{2-x}Ce_xCuO_{4+δ}$ (x=0.14),"The magnetic-field dependencies of the longitudinal and Hall resistivity of
the electron-doped compounds $Nd_{2-x}Ce_xCuO_{4+\delta}$ in underdoped region
(x=0.14) were investigated. It was established experimentally a strong magnetic
field dependence of the Hall conductivity, $\sigma_{xy}(B)=C-b/B$, in the
region of magnetic fields corresponding to a transition from superconducting to
resistive state. The observed feature can be explained with the sum of
contributions of the quasiparticles and moving Abrikosov vortices into Hall
effect in a mixed state of type-II superconductor.",1611.10019v1
2017-01-01,Exit-Channel Suppression in Statistical Reaction Theory,"Statistical reaction theories such as Hauser-Feshbach assume that branching
ratios follow Bohr's compound nucleus hypothesis by factorizing into
independent probabilities for different channels. Corrections to the
factorization hypothesis are known in both nuclear theory and quantum transport
theory, particularly an enhanced memory of the entrance channel. We apply the
Gaussian orthogonal ensemble to study a complementary suppression of exit
channel branching ratios. The effect can be large enough to provide information
on the number of exit channels. The effect is demonstrated for the branching
ratios of neutron-induced reactions on a $^{235}$U target.",1701.00276v2
2017-01-08,Point contact spectroscopy of the high-temperature superconductor $La_{1.8}Sr_{0.2}CuO_{4}$,"The energy gap has been measured and the characteristic phonon energies
determined for the superconducting compound $La_{1.8}Sr_{02}CuO_4$ from the
current-voltage characteristics of point contacts with a copper
counterelectrode. The temperature dependence of the energy gap was determined.
pacs 73.40.Jn, 74.25.Kc, 74.45.+c, 73.40.-c, 74.20.Mn, 74.70.Ad, 74.72.-h, Dn",1701.01982v1
2017-03-09,Fractional compound Poisson processes with multiple internal states,"For the particles undergoing the anomalous diffusion with different waiting
time distributions for different internal states, we derive the Fokker-Planck
and Feymann-Kac equations, respectively, describing positions of the particles
and functional distributions of the trajectories of particles; in particular,
the equations governing the functional distribution of internal states are also
obtained. The dynamics of the stochastic processes are analyzed and the
applications, calculating the distribution of the first passage time and the
distribution of the fraction of the occupation time, of the equations are
given.",1703.03237v1
2017-03-14,An alternative representation of the negative binomial-Lindley distribution. New results and applications,"In this paper we present an alternative representation of the Negative
Binomial--Lindley distribution recently proposed by Zamani and Ismail (2010)
which shows some advantages over the latter model. This new formulation
provides a tractable model with attractive properties which makes it suitable
for application not only in insurance settings but also in other fields where
overdispersion is observed. Basic properties of the new distribution are
studied. A recurrence for the probabilities of the new distribution and an
integral equation for the probability density function of the compound version,
when the claim severities are absolutely continuous, are derived. Estimation
methods are discussed and a numerical application is given.",1703.04812v1
2017-07-03,Compositions of Poisson and Gamma processes,"In the paper we study the models of time-changed Poisson and Skellam-type
processes, where the role of time is played by compound Poisson-Gamma
subordinators and their inverse (or first passage time) processes. We obtain
explicitly the probability distributions of considered time-changed processes
and discuss their properties.",1707.00523v1
2017-07-08,Quasi-2D behavior of 112-type iron-based superconductors,"Fluctuation magnetoconductivity and magnetization above the superconducting
transition temperature (Tc) are measured on the recently discovered 112 family
of iron-based superconductors (IBS), Ca$_{1-x}$La$_x$Fe$_{1-y}$Ni$_y$As$_2$,
which presents an extra As-As chain spacer-layer. The analysis in terms of a
generalization of the Lawrence-Doniach (LD) approach to finite applied magnetic
fields indicates that these compounds are among the most anisotropic IBS
($\gamma$ up to ~30), and provides a compelling evidence of a
quasi-two-dimensional behavior for doping levels near the optimal one.",1707.02470v1
2017-07-13,Electric control of the bandgap in quantum wells with band-inverted junctions,"In IV-VI semiconductor heterojunctions with band-inversion, such as those
made of Pb$_{1-x}$Sn$_{x}$Te or Pb$_{1-x}$Sn$_{x}$Se, interface states are
properly described by a two-band model, predicting the appearance of a Dirac
cone in single junctions. However, in quantum wells the interface dispersion is
quadratic in momentum and the energy spectrum presents a gap. We show that the
interface gap shrinks under an electric field parallel to the growth direction.
Therefore, the interface gap can be dynamically tuned in experiments on
double-gated quantum wells based on band-inverted compounds.",1707.04154v2
2017-07-26,Superfluid neutron matter in the s-channel exchange nucleon-nucleon interaction models,"The superfluid pairing gap of neutron matter is calculated in the framework
of Quark Compound Bag model with nucleon-nucleon interactions generated by the
s-channel exchange of Jaffe-Low primitives (6-quark states).",1707.08424v1
2017-07-29,First-Principles Understanding of the Electronic Band Structure of Copper-Antimony Halide Perovskite: The Effect of Magnetic Ordering,"We report the understanding of the electronic band structure of
$Cs_4CuSb_2Cl_{12}$ perovskite through first-principles density-functional
theory calculations. We find that the most stable state has the
antiferromagnetic configuration where each $[CuCl_6]$ octahedral chain along
the [010] direction is antiferromagnetic. The reasonable band structure of the
compound can be obtained only if both the correct magnetic order and the
improved exchange interaction of the Cu $\it{d}$ electrons are taken into
account.",1707.09539v1
2017-08-03,Quenching Dependence on Superconductivity in the Synthesizing Process of Single Crystals of Rb$_x$Fe$_{2-y}$Se$_2$,"Superconducting single crystals of Rb-intercalated FeSe compounds
Rb$_x$Fe$_{2-y}$Se$_2$ were prepared by using a starting material of Rb$_2$Se
as a Rb source. The superconducting properties and the surface microstructures
were systematically controlled by varying the cooling rate in the quenching
process. The higher cooling rate in the sample provided a higher
superconducting transition temperature with highly connected superconducting
mesh-like surface structure. Extremely slow-cooling process led to the complete
isolation between the superconducting domains.",1708.01017v1
2017-08-29,On approximations for the distribution of first level crossing time,"We investigate performance of approximations put forth in
\citeNP{[Malinovskii 2017a]} and \citeNP{[Malinovskii 2017b]} for the
distribution of the time of first level $u$ crossing by the random process
$\homV{s}-cs$, $s>0$, where $\homV{s}$ is compound renewal process. In the case
of Exponential inter-renewal and jump size random variables, we compare the
approximations with exact and with simulation results. In a few other cases
including Erlang and Pareto inter-renewal and jump size random variables, where
exact results are absent, we compare the approximations with simulation
results.",1708.08678v1
2017-08-30,Time-Dependent Perpendicular Transport of Energetic Particles for Different Turbulence Configurations and Parallel Transport Models,"Recently a new theory for the transport of energetic particles across a mean
magnetic field was presented. Compared to other non-linear theories the new
approach has the advantage that it provides a full time-dependent description
of the transport. Furthermore, a diffusion approximation is no longer part of
that theory. It is the purpose of the current paper to combine this new
approach with a time-dependent model for parallel transport and different
turbulence configurations in order to explore the parameter regimes for which
we get ballistic transport, compound sub-diffusion, and normal Markovian
diffusion.",1708.09752v1
2017-09-04,Compositional nanodomain formation in hybrid formate perovskites,"We report the synthesis and structural characterisation of three mixed-metal
formate perovskite families [C(NH$_2$)$_3$]M$_{1-x}$Cu$_x$(HCOO)$_3$ (M = Mn,
Zn, Mg). Using a combination of infrared spectroscopy, non-negative matrix
factorization, and reverse Monte Carlo refinement, we show that the Mn- and
Zn-containing compounds support compositional nanodomains resembling the polar
nanoregions of conventional relaxor ferroelectrics. The M = Mg family exhibits
a miscibility gap that we suggest reflects the limiting behaviour of nanodomain
formation.",1709.00952v1
2017-09-10,Expectation thinning operators based on linear fractional probability generating functions,"We introduce a two-parameter expectation thinning operator based on a linear
fractional probability generating function. The operator is then used to define
a first-order integer-valued autoregressive \inar1 process. Distributional
properties of the \inar1 process are described. We revisit the
Bernoulli-geometric \inar1 process of Bourguignon and Wei{\ss} (2017) and we
introduce a new stationary \inar1 process with a compound negative binomial
distribution. Lastly, we show how a proper randomization of our operator leads
to a generalized notion of monotonicity for distributions on \bzp.",1709.03129v1
2017-09-20,ScPd2Al3 New Polymorphic Phase in Al-Pd-Sc System,"We have discovered a new compound of the composition ScPd2Al3 crystallizing
in unknown structure type. Moreover, ScPd2Al3 reveals polymorphism. We have
found an orthorhombic crystal structure at room temperature and a high
temperature cubic phase. The polymorphic phases are separated by a reversible
first order transition at 1053{\deg}C with a hysteresis of 19{\deg}C. ScPd2Al3
exists as a very stable intermetallic phase just in the vicinity of the
icosahedral quasicrystal Tsai-type i-phase Al54Pd30Sc16.",1709.06843v1
2017-09-28,An Extended Analytic Model for the Heating of Bondwires,"We present an extended analytic formula for the calculation of the
temperature profile along a bondwire embedded in a package. The resulting
closed formula is built by coupling the heat transfer equations of the bondwire
and the surrounding moulding compound by means of auxiliary variables that stem
from an \emph{ad-hoc} linearisation and mediate the wire-mould thermal
interaction. The model, which corrects typical simplifications in previously
introduced analytic models, is also optimised against carefully taken
experimental samples representing fusing events of bondwires within real
packages.",1709.10069v1
2017-11-01,Block-modified Wishart matrices: the easy case,"Associated to any complex Wishart matrix $W$ of parameters $(dn,dm)$ and any
linear map $\varphi:M_n(\mathbb C)\to M_n(\mathbb C)$ is the ""block-modified""
matrix $\tilde{W}=(id\otimes\varphi)W$. Following some previous work with
Nechita, we study here the asymptotic $*$-distribution of $\tilde{W}$, in the
$d\to\infty$ limit, in the case where the modification map $\varphi$ is ""easy"",
or more generally super-easy, in the quantum algebra/representation theory
sense. Under suitable assumptions on $\varphi$ we obtain in this way a compound
free Poisson law.",1711.00433v3
2017-11-25,Pt-Bi Antibonding Interaction: The Key Factor for Superconductivity in Monoclinic BaPt2Bi2,"In the search for superconductivity in BaAu2Sb2-type monoclinic structure, we
have successfully synthesized a new compound BaPt2Bi2, which crystallizes in
the space group P21/m (S.G. 11; Pearson symbol mP10) according to a combination
of powder and single crystal X-ray diffraction and scanning electron
microscopy. Sharp electrical resistivity drop and large diamagnetic
magnetization below 2.0 K indicates it owns the superconducting ground state.
This makes BaPt2Bi2 the first reported superconductor in mono-clinic
BaAu2Sb2-type structure, a previously unappreciated structure for
superconductivity. First-principles calculations considering the spin-orbit
coupling indicate that Pt-Bi anti-bonding interaction plays a critical role in
inducing superconductivity.",1711.09283v1
2017-12-06,Superconductivity in the ternary compound SrPt$_{10}$P$_4$ with complex new structure,"We report superconductivity at 1.4K in the ternary SrPt$_{10}$P$_4$ with a
complex new structure. SrPt$_{10}$P$_4$ crystallizes in a monoclinic
space-group C2/c (\#15) with lattice parameters a= 22.9151(9)$\AA$, b=
13.1664(5)$\AA$, c=13.4131(5)$\AA$, and $\beta$= 90.0270(5)${^\circ}$. Bulk
superconductivity in the samples has been demonstrated through resistivity, ac
susceptibility, and heat capacity measurements. High pressure measurements have
shown that the superconducting T$_C$ is systematically suppressed upon
application of pressure, with a dT$_C$/dP coefficient of -0.016 K/GPa.",1712.02010v1
2017-12-07,Microscopic mechanism for the unusual antiferromagnetic order and the pressure-induced transition to ferromagnetism in USb$_2$,"Uranium dipnictide USb$_2$ reflects enigmatic properties posing a substantial
challenge for a microscopic modeling. Among others, it develops a nonstandard
antiferromagnetic order of a $\uparrow\downarrow\downarrow\uparrow$-type along
[001] crystallographic direction, and under pressure it undergoes transition to
the ferromagnetic phase. Here we propose a minimal low-energy model of USb$_2$
which, as we demonstrate at the mean-field level, accommodates physical
mechanism for mentioned observations. Relying on the obtained results we also
comment on the features of magnetism observed in other U-based compounds:
UAs$_2$, UBi$_2$, UAsSe, URh$_x$Ir$_{1-x}$Ge and UGe$_2$.",1712.02534v1
2017-12-09,Powers of doubly-affine integer square matrices with one non-zero eigenvalue,"When doubly-affine matrices such as Latin and magic squares with a single
non-zero eigenvalue are powered up they become constant matrices after a few
steps. The process of compounding squares of orders m and n can then be used to
generate an infinite series of such squares of orders mn. The Cayley-Hamilton
theorem is used to understand this property, where their characteristic
polynomials have just two terms.",1712.03393v1
2017-12-10,Orthogonal polynomial expansions to evaluate stop-loss premiums,"A numerical method is proposed to evaluate the survival function of a
compound distribution and the stop-loss premiums associated with a
non-proportional global reinsurance treaty. The method relies on a
representation of the probability density function in terms of Laguerre
polynomials and the gamma density. We compare the method against a well
established Laplace transform inversion technique at the end of the paper.",1712.03468v2
2017-12-11,"Dimensionality, nematicity and Superconductivity in Fe-based systems","Study of Fe based compounds have drawn much attention due to the discovery of
superconductivity as well as many other exotic electronic properties. Here, we
review some of our works in these materials carried out employing density
functional theory and angle resolved photoemission spectroscopy. The results
presented here indicate that the dimensionality of the underlying electronic
structure plays important role in deriving their interesting electronic
properties. The nematicity found in most of these materials appears to be
related to the magnetic long range order. We argue that the exoticity in the
electronic properties are related to the subtlety in competing structural and
magnetic instabilities present in these materials.",1712.03710v1
2017-12-12,Dynamically Reconfigurable Sources for Arbitrary Gaussian States in Integrated Photonics Circuits,"We present a modular design for integrated programmable multimode sources of
arbitrary Gaussian states of light. The technique is based on current
technologies, in particular recent demonstrations of on-chip photon
manipulation and generation of highly squeezed vacuum states in semiconductors.
While the design is generic and independent of the choice of integrated
platform, we adopt recent experimental results on compound semiconductors as a
demonstrative example. Such a device would be valuable as a source for many
quantum protocols that range from imaging to communication and information
processing.",1712.04105v2
2017-12-15,"Modeling-based determination of physiological parameters of systemic VOCs by breath gas analysis, part 2","In a recent paper we presented a simple two compartment model which describes
the influence of inhaled concentrations on exhaled breath concentrations for
volatile organic compounds (VOCs) with small Henry constants. In this paper we
extend this investigation concerning the influence of inhaled concentrations on
exhaled breath concentrations for VOCs with higher Henry constants.
  To this end we extend our model with an additional compartment which takes
into account the influence of the upper airways on exhaled breath VOC
concentrations.",1712.05788v2
2017-12-18,word representation or word embedding in Persian text,"Text processing is one of the sub-branches of natural language processing.
Recently, the use of machine learning and neural networks methods has been
given greater consideration. For this reason, the representation of words has
become very important. This article is about word representation or converting
words into vectors in Persian text. In this research GloVe, CBOW and skip-gram
methods are updated to produce embedded vectors for Persian words. In order to
train a neural networks, Bijankhan corpus, Hamshahri corpus and UPEC corpus
have been compound and used. Finally, we have 342,362 words that obtained
vectors in all three models for this words. These vectors have many usage for
Persian natural language processing.",1712.06674v1
2017-12-23,Theory of type-II superconductivity in ferromagnetic metals with triplet pairing,"The superconducting state in uranium compounds UGe2, URhGe and UCoGe is
formed at temperatures far below the Curie temperature pointing on
nonconventional nature of superconductivity in these materials - namely the
superconductivity with triplet pairing. The emergence of superconductivity is
accompanied by the slight magnetization expulsion typical for the type-II
superconductors. Following classic Abrikosov paper I develop the theory of
type-II superconductivity in application to two-band ferromagnetic metal with
equal spin triplet pairing.",1712.08750v4
2017-12-31,Determination of the critical growth rate and growth temperature for group-III elements segregation using two exchanges Kinetic Model,"Segregation of group-III elements during the molecular-beam epitaxy growth of
III-V compounds leads to a non-abrupt interface. The composition asymmetry in
the structures such as quantum wells, quantum dots, and superlattices, in turn,
leads to the non-abrupt electronic band alignments that changes the
optoelectronic properties of those quantum structures. We have studied the
concentration profile of the group-III atoms for different growth parameters
using two exchanges Kinetic Model and have determined the critical growth
temperature and growth rate regions for the growth of structures with less than
10% segregation of group-III atoms.",1801.00275v1
2018-01-09,High-Throughput Identification of Electrides from all Known Inorganic Materials,"In this paper, we present the results of a large-scale, high-throughput
computational search for electrides among all known inorganic materials.
Analyzing a database of density functional theory results on more than 60,000
compounds, we identify 69 new electride candidates. We report on all these
candidates and discuss the structural and chemical factors leading to electride
formation. Among these candidates, our work identifies the first
partially-filled 3d transition metal containing electrides Ba3CrN3 and Sr3CrN3;
an unexpected finding that contravenes conventional chemistry.",1801.02948v1
2018-03-01,Incommensurate Magnetic Ordering from One-Dimensional Correlated Topological Bulk States,"A phenomenological model accounts for the calculation of incommensurate
ordering wave vectors (IC) in several Ce- and U-based f-electron itinerant
compounds (CePtSn, CePdSn, CeNiSn, CeRhIn$_5$, URu$_2$Si$_2$, CeNiAsO,
CeCu$_{(6-x)}$Au$_x$, UNi$_2$Al$_3$, CeCuSn) as well as in BSSCO,
Rb$_2$ZnBr$_4$, MnSi and prototypical IC system Chromium metal. This model is
justified by a many-body topological one-dimensional (1-D) Dirac Hamiltonian
after center of mass transformation on a chiral set of momenta defined by a
local expansion of crystallographic Bragg planes. Implications for the
emergence of long range bulk states driven by fluctuations with this model are
discussed.",1803.00270v3
2018-03-12,Machine Learning Harnesses Molecular Dynamics to Discover New $μ$ Opioid Chemotypes,"Computational chemists typically assay drug candidates by virtually screening
compounds against crystal structures of a protein despite the fact that some
targets, like the $\mu$ Opioid Receptor and other members of the GPCR family,
traverse many non-crystallographic states. We discover new conformational
states of $\mu OR$ with molecular dynamics simulation and then machine learn
ligand-structure relationships to predict opioid ligand function. These
artificial intelligence models identified a novel $\mu$ opioid chemotype.",1803.04479v1
2018-03-25,"Prospective phosphors for white LEDs based on double molybdates of the composition Ln2Zr3 (MoO4) 9 (Ln: Eu, Tb)","The results of the investigation of the spectral characteristics of new
luminescent substances based on rare-earth ions Eu3 + and Tb3 + in matrices of
double molybdates are presented in the article. The luminescence and excitation
spectra are considered, the decay times of the main transitions are determined,
and the color coordinates are determined. The results show the possible
suitability of using these compounds as white phosphor phosphor components.",1803.09214v1
2018-03-27,Superchiral Surface Waves for All-Optical Enantiomer Separation,"We introduce the use of superchiral surface waves for the all-optical
separation of chiral compounds. Using a combination of electrodynamics modeling
and analytical techniques, we show that the proposed approach provides chiral
optical forces two orders of magnitude larger than those obtained with
circularly polarized plane waves. Superchiral surface waves allow for
enantiomer separation on spatial, temporal and size scales than would not be
achievable with alternative techniques, thus representing a viable route
towards all-optical enantiomer separation.",1803.10010v1
2018-05-14,On Neighbourhood Zagreb index of product graphs,"There is powerful relation between the chemical behaviour of chemical
compounds and their molecular structures. Topological indices defined on these
chemical molecular structures are capable to predict physical properties,
chemical reactivity and biological activity. In this article, a new topological
index named as Neighbourhood Zagreb index $(M_N)$ is presented. Here the
chemical importance of this newly introduced index is studied and some explicit
results for this index of different product graphs such as Cartesian, Tensor
and Wreath product is derived. Some of these results are applied to obtain the
Neighbourhood Zagreb index of several chemically important graphs and
nano-structures.",1805.05273v1
2018-05-15,"Polaronic correlations and phonon renormalization in La1-xSrxMnO3 (x = 0.2, 0.3)","According to standard theory the magnetoresistance magnitude in ferromagnetic
manganites crucially depends on the electron-phonon coupling strength. We
showed that in La0.7Sr0.3MnO3 the phonon renormalization is strong, despite its
relatively small magnetoresistance. Here, we report results of a similar
inelastic neutron scattering investigation of a closely related compound,
La0.8Sr0.2MnO3, where the magnetoresistance is enhanced. We find similar phonon
renormalization and dynamic CE-type polaron correlations as in La0.7Sr0.3MnO3.
However, quantitative comparison of the results for the two samples shows that
only polaron lifetime is well correlated with the strength of the CMR.",1805.05596v1
2018-05-31,Mahler's work on the geometry of numbers,"Mahler has written many papers on the geometry of numbers. Arguably, his most
influential achievements in this area are his compactness theorem for lattices,
his work on star bodies and their critical lattices, and his estimates for the
successive minima of reciprocal convex bodies and compound convex bodies. We
give a, by far not complete, overview of Mahler's work on these topics and
their impact.",1806.00356v1
2018-06-12,Dynamical conductivity in topological nodal-line semimetal ZrSiS,"ZrSiS is one of the strong candidates for realistic nodal-line semimetal. We
theoretically investigate the dynamical conductivity in ZrSiS by using a
multi-orbital theoretical model based on the first-principles band calculation.
We find that the dynamical conductivity in the clean limit is actually not
frequency independent unlike the ideal Dirac model, while nearly flat
dependence is achieved by introducing the energy broadening possibly induced by
the disorder. The results can be applied to other compounds with the similar
crystal structure, such as ZrSiSe, ZrSiTe, and HfSiS.",1806.04283v1
2018-06-18,Superhalogen and Superacid,"A superhalogen $\rm{F@C_{20}(CN)_{20}}$ and a corresponding Br{\o}nsted
superacid were designed and investigated on DFT and DLPNO-CCSD(T) levels of
theory. Calculated compounds have outstanding electron affinity and
deprotonation energy, respectively. We consider superacid
$\rm{H[F@C_{20}(CN)_{20}]}$ to be able to protonate molecular nitrogen. The
stability of these structures is discussed, while some of the previous
predictions concerning Br{\o}nsted superacids of record strength are doubted.",1806.06969v5
2018-06-19,The local principle of large deviations for compound Poisson process with catastrophes,"The continuous time Markov process considered in this paper belongs to a
class of population models with linear growth and catastrophes. There, the
catastrophes happen at the arrival times of a Poisson process, and at each
catastrophe time, a randomly selected portion of the population is eliminated.
For this population process, we derive an asymptotic upper bound for the
maximum value and prove the local large deviation principle.",1806.07459v2
2018-06-21,Arbitrage-Free Interpolation in Models of Market Observable Interest Rates,"Models which postulate lognormal dynamics for interest rates which are
compounded according to market conventions, such as forward LIBOR or forward
swap rates, can be constructed initially in a discrete tenor framework.
Interpolating interest rates between maturities in the discrete tenor structure
is equivalent to extending the model to continuous tenor. The present paper
sets forth an alternative way of performing this extension; one which preserves
the Markovian properties of the discrete tenor models and guarantees the
positivity of all interpolated rates.",1806.08107v1
2018-06-24,The Internet of Things: Secure Distributed Inference,"The growth in the number of devices connected to the Internet of Things (IoT)
poses major challenges in security. The integrity and trustworthiness of data
and data analytics are increasingly important concerns in IoT applications.
These are compounded by the highly distributed nature of IoT devices, making it
infeasible to prevent attacks and intrusions on all data sources. Adversaries
may hijack devices and compromise their data. As a result, reactive
countermeasures, such as intrusion detection and resilient analytics, become
vital components of security. This paper overviews algorithms for secure
distributed inference in IoT.",1806.09199v1
2018-06-29,Multicasting Energy and Information Simultaneously,"Communication systems for multicasting information and energy simultaneously
to more than one user are investigated. In the system under study, a
transmitter sends the same message and signal to multiple receivers over
distinct and independent channels. The fundamental communication limit under a
received energy constraint, called the multicast capacity-energy function, is
studied and a single-letter expression is derived. This is based on coding
theorems for compound channels. The problem of receiver segmentation, where
receivers are divided into related groups, is also considered.",1806.11271v2
2018-09-06,High-temperature superconductors of the family (RE)Ba2Cu3O7-delta and their application (Review Article),"This review article is a commemoration of the 30th anniversary of the
discovery of YBa2Cu3O7-delta high-temperature superconductors (HTSCs). As a
result of this discovery a family of (RE)Ba2Cu3O7-delta (RE stands for ""rare
earth"") HTSCs has found great practical use. The review article consists of a
brief history of how YBa2Cu3O7-delta was conceived and five sections describing
the family of compounds: crystallography, phase diagrams, manufacturing
techniques, main superconducting properties, and fields of application.",1809.01988v1
2018-09-11,Al-Cu-Fe quasicrystals as anode of lithium ion battery,"In this paper, Al-Cu-Fe quasicrystal alloy was used as anode material of
lithium-ion batteries. The first specific discharge capacity of quasicrystal
was 204mAh/g. Cyclic voltammetry showed that oxidation peak of Al-Cu-Fe
quasicrystal was at about 1.4V. The reduction peak was at 0.3V. Al-Cu-Fe
quasicrystal have higher Li-ion diffusion impedance and Warburg in the first
cycle. X-ray diffraction analysis demonstrate that Li atom enter into
quasicrystal structure can not fully leave quasicrytal during first
charge/discharge cycle which induce the irreversible capacity.",1809.03667v1
2018-09-12,High Tc Hydrides: Interplay of Optical and Acoustic Modes and Comments Regarding the Upper Limit of Tc,"Phonon spectrum of many superconducting compounds and, especially, high Tc
hydrides, is broad and rather complicated ,because of presence of high
frequency optical modes. In order to analyze an interplay of optical and
acoustic phonon branches,it is convenient to introduce two coupling constants,
{\lambda}opt. and {\lambda}ac., along with to characteristic frequencies. The
correlation between the value of Tc with this interplay is demonstrated for the
family of tantal hydrides (TaH2/ TaH4/ TaH6). The problem of upper limit of Tc
is discussed. The phenomenon of room temperature superconductivity can be
provided by the electron-phonon interaction and described by the strong
coupling theory.",1809.04703v1
2018-09-23,Assessing the Utility of Structure in Amorphous Materials,"This paper presents a set of general strategies for the analysis of structure
in amorphous materials and a general approach to assessing the utility of a
selected structural description. Measures of structural diversity and utility
are defined and applied to two model glass forming binary atomic alloys. In
addition, a new measure of incipient crystal-like organization is introduced,
suitable for cases where the stable crystal is a compound structure.",1809.08589v2
2018-09-24,Non-trivial topology of the quasi-one-dimensional triplons in the quantum antiferromagnet ${\text{BiCu}}_{2}{\text{PO}}_{6}$,"Topological properties of physical systems are attracting tremendous
interest. Recently, magnetic solid state compounds with and without magnetic
order have become a focus. We show that ${\text{BiCu}}_{2}{\text{PO}}_{6}$ is
the first gapful quantum antiferromagnet with a finite Zak phase, which
characterises one-dimensional systems, and only the second with topological
non-trivial triplon excitations. Surprisingly, in spite of the bulk-boundary
correspondence no localised edge mode occurs. This unexpected behaviour is
explained by the distinction between direct and indirect gaps among the triplon
bands.",1809.09228v1
2018-09-11,"Knowledge extraction, modeling and formalization: EEG case study","Formal Concept Analysis (FCA) is a well-established method for data analysis
which finds many applications in data mining. Its extension on complex data
representation formats brought a wave of new applications to the problems such
as gene expression mining, prediction of toxicity of chemical compounds or
clustering of sequences in process event logs. Insipired from this work our
research inherits their model and designs an experiment for mining
electroencephalographic recordings for patterns of sleep spindles. The
contribution of this paper lies in the specification of desritizition procedure
and the architecture of FCA experiment. We also provide some reflection on the
related research papers.",1809.09955v1
2018-11-17,Intriguing properties of multiplicity distributions,"Multiplicity distributions exhibit, after closer inspection, peculiarly
enhanced void probability and oscillatory behavior of the modified combinants.
We discuss the possible sources of these oscillations and their impact on our
understanding of the multiparticle production mechanism. Theoretical
understanding of both phenomena within the class of compound distributions is
presented.",1811.07197v3
2019-11-06,Disclosing antiferromagnetism in tetragonal Cr2O3 by electrical measurements,"The tetragonal phase of chromium (III) oxide, although unstable in the bulk,
can be synthesized in epitaxial heterostructures. The theoretical investigation
by density functional theory predicts an antiferromagnetic ground state for
this compound. We demonstrate experimentally antiferromagnetism up to 40 K in
ultrathin films of t-Cr2O3 by electrical measurements exploiting interface
effect within a neighboring ultrathin Pt layer. We show that magnetotransport
in Pt is affected by both spin-Hall magnetoresistance and magnetic proximity
effect while we exclude any role of magnetism for the low-temperature
resistance anomaly observed in Pt.",1911.02596v1
2019-11-07,Magnetic monopoles and toroidal moments in LuFeO$_3$ and related compounds,"Magnetic monopoles and toroidal order are compelling features that have long
been theorized but remain elusive in real materials. Multiferroic hexagonal
ferrites are an interesting realization of frustrated triangular lattice, where
magnetic order is coupled to ferroelectricity and trimerization. Here we
propose a mechanism, through which magnetic monopolar and toroidal orders
emerge from the combination of 120$^\circ$ antiferromagnetism and
trimerization, present in hexagonal manganites and ferrites. The experimentally
observable signatures of magnetic monopolar and toroidal orders are identified
in the inelastic neutron scattering cross section, simulated from a microscopic
model of LuFeO3. The non-reciprocal magnon propagation is demonstrated.",1911.02704v1
2019-11-13,Haploid-Diploid Evolution: Nature's Memetic Algorithm,"This paper uses a recent explanation for the fundamental haploid-diploid
lifecycle of eukaryotic organisms to present a new memetic algorithm that
differs from all previous known work using diploid representations. A form of
the Baldwin effect has been identified as inherent to the evolutionary
mechanisms of eukaryotes and a simplified version is presented here which
maintains such behaviour. Using a well-known abstract tuneable model, it is
shown that varying fitness landscape ruggedness varies the benefit of
haploid-diploid algorithms. Moreover, the methodology is applied to optimise
the targeted delivery of a therapeutic compound utilizing nano-particles to
cancerous tumour cells with the multicellular simulator PhysiCell.",1911.07302v1
2020-01-07,Prediction of Drug Synergy by Ensemble Learning,"One of the promising methods for the treatment of complex diseases such as
cancer is combinational therapy. Due to the combinatorial complexity, machine
learning models can be useful in this field, where significant improvements
have recently been achieved in determination of synergistic combinations. In
this study, we investigate the effectiveness of different compound
representations in predicting the drug synergy. On a large drug combination
screen dataset, we first demonstrate the use of a promising representation that
has not been used for this problem before, then we propose an ensemble on
representation-model combinations that outperform each of the baseline models.",2001.01997v1
2019-12-04,Analyzing the Local Basis Set Superposition Error -- a case study of CO adsorption on rutile(110),"The aim of this letter is to introduce a new method to analyze the local
basis set superposition error (LBSSE) using local counterpoise corrections (CP)
in order to converge a basis set for a given compound. Using this approach, we
are able to define a basis set composition for a CO molecule adsorbed on
rutile(110), which can be regarded as complete. In addition to a new LBSSE
analysis, adsorption energies of CO on rutile(110) at the MP2 and CCSD level of
theory are presented.",2001.02495v1
2020-01-09,Wiener index of unicycle graphs with given number of even degree vertices,"The Wiener index of a connected graph is the sum of the distance of all pairs
of distinct vertices. It was introduced by Wiener in 1947 to analyze some
aspects of branching by fitting experimental data for several properties of
alkane compounds. Denote by $\mathcal{U}_{n,r}$ the set of unicyclic graphs
with $n$ vertices and $r$ vertices of even degree. In this paper we present a
structural result on the graphs in $\mathcal{U}_{n,r}$ with minimum Wiener
index and completely characterize such graphs when $ r\leq \frac{n+3}{2}$.",2001.02857v1
2020-01-13,Structural and magnetic characterization of the elusive Jahn-Teller active NaCrF3,"We report the structural and magnetic characterization of the elusive Jahn-
Teller active compound NaCrF3.",2001.04144v3
2020-01-20,Melting line and thermodynamic properties of a supeionic compound SrCl$_2$ by molecular dynamics simulation,"In the present paper we study the thermodynamic properties of superionic
conductor $SrCl_2$ at high temperatures by means of molecular dynamics method.
Firstly, we calculate the melting line. Then we compute the equations of state
and the response functions (heat capacity, thermal expansion coefficient, etc)
at the temperatures up to the melting. We show that the response functions show
maxima or minima at the temperatures well above the temperature of transition
into the conductive state, and therefore are not related to this transition.",2001.07112v1
2020-01-26,Matter-wave interference originates mass-angle correlation in fusion-fission,"Mass-angle correlation of fission fragments has been understood as
manifestation of quasifission. We show that this is not so: the effect can
originate from correlation between fusion-fission amplitudes with different
total spins signifying matter-wave interference in compound nucleus processes.
This resolves the well-known puzzle with the mass-angle correlation in the
complete fusion sub-barrier reaction $^{16}$O+$^{238}$U. Our finding is
important for more reliable predictions of production cross sections for
superheavy elements. Matter-wave interference also produces quantum-classical
transition to the time-orientation localization of the coherently rotating
dinucleus in quasifission.",2001.09511v1
2020-01-26,Pulse percolation conduction and multi-value memory,"We develop a theory of pulse conduction in percolation type of materials such
as noncrystalline semiconductors and nano-metal compounds. For short voltage
pulses, the corresponding electric currents are inversely proportional to the
pulse length and exhibit significant nonohmicity due to strong local fields in
resistive regions of the percolation bonds. These fields can trigger local
switching events incrementally changing bond resistances in response to pulse
trains. Our prediction opens a venue to a class of multi-value nonvolatile
memory implementable with a variety of materials.",2001.09512v3
2020-01-28,Magnetic multipoles and correlation shortage in pyrochlore cerium stannate,"Cerium electronic multipoles in trigonal symmetry viewed in magnetic neutron
diffraction are investigated. Analytic expressions for all the magnetic
multipoles, and radial integrals calculated with an established atomic code,
are used to scrutinize a recent claim to have observed an octupole-ice
configuration in a powder sample of pyrochlore Ce2Sn2O7. Three equally
plausible suites of multipoles belonging to uncorrelated cerium ions give
equally satisfactory accounts of the available diffraction pattern. Our
multipoles are suitable for future experiments using Bragg diffraction from a
compound that supports long-range magnetic order.",2001.10304v1
2021-07-15,Unexplained Spectral Phenomena in the Interstellar Medium: an introduction,"There exists a number of astronomical spectral phenomena that have remained
unidentified after decades of extensive observations. The diffuse interstellar
bands, the 220 nm feature, unidentified infrared emission bands, extended red
emissions, and 21 and 30 $\mu$m emission features are seen in a wide variety of
astrophysical environments. The strengths of these features suggest that they
originate from chemical compounds made of common elements, possibly organic in
nature. The quest to understand how such organic materials are synthesized and
distributed across the Galaxy represents a major challenge to our understanding
of the chemical content of the Universe.",2107.07571v1
2021-07-28,Number of visits in arbitrary sets for $φ$-mixing dynamics,"It is well-known that, for sufficiently mixing dynamical systems, the number
of visits to balls and cylinders of vanishing measure is approximately Poisson
compound distributed in the Kac scaling. Here we extend this kind of results
when the target set is an arbitrary set with vanishing measure in the case of
$\phi$-mixing systems. The error of approximation in total variation is derived
using Stein-Chen method. An important part of the paper is dedicated to
examples to illustrate the assumptions, as well as applications to temporal
synchronisation of $g$-measures",2107.13453v1
2021-07-29,Quantifying uncertainties in crystal electric field Hamiltonian fits to neutron data,"We systematically examine uncertainties from fitting rare earth single-ion
crystal electric field (CEF) Hamiltonians to inelastic neutron scattering data.
Using pyrochlore and delafossite structures as test cases, we find that
uncertainty in CEF parameters can be large despite visually excellent fits.
These results show Yb$^{3+}$ compounds have particularly large $g$-tensor
uncertainty because of the few available peaks. In such cases, additional
constraints are necessary for meaningful fits.",2107.14164v5
2017-04-01,Ubiquity of Unconventional Phenomena Associated with Critical Valence Fluctuations in Heavy Fermion Metals,"Ubiquity of unconventional phenomena observed in a series of heavy fermion
metals is discussed on the basis of an idea of critical valence fluctuations.
After surveying experimental aspects of these unconventional behaviors in
prototypical compounds, CeCu_2(Si,Ge)_2, under pressure, we propose that sharp
valence crossover phenomena are realized in CeCu_6, CeRhIn_5, and Ce(Ir,Rh)Si_3
by tuning the pressure and the magnetic field simultaneously, on the basis of
previous results for an extended Anderson lattice model with the Coulomb
repulsion U_fc between localized f-electron and itinerant conduction electrons.",1704.00114v1
2017-04-05,Extending means to several variables,"We begin the study of how to extend few variable means to several variable
ones and how to shrink means of several variables to less variables. With the
help of one of the techniques we show that it is enough to check an inequality
between two quasi-arithmetic means in 2-variables and that simply implies the
inequality in m-variables. The technique has some relation to Markov chains.
This method can be applied to symmetrization and compounding means as well.",1704.01643v2
2017-04-06,Thermoelectric power factor of Bi-Sb-Te and Bi-Te-Se alloys and doping strategy: First-principles study,"By performing first principles calculations combined with Boltzmann transport
equations, we calculate the thermoelectric power factor (PF) of Bi-Sb-Te and
Bi-Te-Se ternary alloys as a function of alloy composition ratio, carrier
concentration, and temperature. The point defect formation energy calculations
also perform to search potential n-type dopant candidates in ternaries.",1704.01723v1
2017-04-19,Time-Dependent Perpendicular Transport of Energetic Particles in Magnetic Turbulence with Transverse Complexity,"The motion of energetic particles in magnetic turbulence across a mean
magnetic field is explored analytically. The approach presented here allows for
a full time-dependent description of the transport, including compound
sub-diffusion. The first time it is shown systematically that as soon as there
is transverse structure of the turbulence, diffusion is restored even if no
Coulomb collisions are invoked. Criteria for sub-diffusion and normal Markovian
diffusion are found as well.",1704.05574v1
2017-04-19,On the possibility of revealing the transition of a baryon pair state to a six-quark confinement state,"Proton-proton collisions are considered to find favourable conditions for
searching for the transition of a baryon pair state to a hexa-quark confinement
state $(3q)+(3q)\rightarrow(6q)_\mathrm{cnf}$. It is admitted that central $pp$
collisions in a definite range of the initial energy can lead to creation of an
intermediate compound system where the hexa-quark dibaryon can be formed.
Criteria for selection of central collision events and for manifestation of the
quark-structure dibaryon production are proposed.",1704.06161v1
2017-04-20,Multiband Superconductivity in the time reversal symmetry broken superconductor Re6Zr,"We report point contact Andreev Reflection (PCAR) measurements on a
high-quality single crystal of the non-centrosymmetric superconductor Re6Zr. We
observe that the PCAR spectra can be fitted by taking two isotropic
superconducting gaps with Delta_1 ~ 0.79 meV and Delta_2 ~ 0.22 meV
respectively, suggesting that there are at least two bands which contribute to
superconductivity. Combined with the observation of time reversal symmetry
breaking at the superconducting transition from muon spin relaxation
measurements (Phys. Rev. Lett. 112, 107002 (2014)), our results imply an
unconventional superconducting order in this compound: A multiband singlet
state that breaks time reversal symmetry or a triplet state dominated by
interband pairing.",1704.06166v1
2017-05-04,Unconventional magnetic order in the conical state of MnSi,"In the temperature-magnetic field phase diagram, the binary metallic compound
MnSi exhibits three magnetic phases below Tc ~ 29 K. An unconventional
helicoidal phase is observed in zero field. At moderate field intensity a
conical phase sets in. Near Tc, in an intermediate field range, a skyrmion
lattice phase appears. Here we show the magnetic structure in the conical phase
to strongly depend on the field direction and to deviate substantially from a
conventional conical structure.",1705.01756v1
2017-05-05,Noncentral limit theorem for the generalized Rosenblatt process,"We use techniques of Malliavin calculus to study the convergence in law of a
family of generalized Rosenblatt processes $Z_\gamma$ with kernels defined by
parameters $\gamma$ taking values in a tetrahedral region $\Delta$ of $\RR^q$.
We prove that, as $\gamma$ converges to a face of $\Delta$, the process
$Z_\gamma$ converges to a compound Gaussian distribution with random variance
given by the square of a Rosenblatt process of one lower rank. The convergence
in law is shown to be stable. This work generalizes a previous result of Bai
and Taqqu, who proved the result in the case $q=2$ and without stability.",1705.02377v1
2017-05-20,On the geometry of carbon nanostructures formed at reaction of organic compounds at high pressure and temperature,"Based on the analysis of the data on the behavior of electric conductivity at
the detonation of condensed high explosives (HEs) with the composition CHNO and
the carbon mass fraction higher than 0.1, the conclusion was made of the
presence of long carbon nanostructures. These structures penetrate all the
space of reacting HE. The structures are formed already in the chemical peak
region, and they evolve along the detonation wave.",1705.07247v2
2017-05-20,Time-dependent mean-field investigations of the quasifission process,"We demonstrate that the microscopic Time-dependent Hartree-Fock (TDHF) theory
provides an important approach to shed light on the nuclear dynamics leading to
the formation of superheavy elements. In particular, we discuss studying
quasifission dynamics and calculating ingredients for compound nucleus
formation probability calculations. We also discuss possible extensions to TDHF
to address the distribution of observables.",1705.07324v1
2017-05-28,The finite-time ruin probability of the nonhomogeneous Poisson risk model with conditionally independent subexponential claims,"This paper obtains an asymptotic formula for the finite-time ruin probability
of the compound nonhomogeneous Poisson risk model with a constant interest
force, in which the claims are conditionally independent random variables with
a common subexponential distribution. The paper also obtains some asymptotic
relations of randomly weighted sums $\sum_{i=1}^n \theta_iX_i$, in which the
weights $\theta_i$ $i=1,2,\cdots, n$ are positive random variables which are
bounded above and the primary random variables $X_i$, $i=1,2,\cdots,n$ are
conditionally independent and follow subexponential distributions.",1705.09939v1
2018-07-03,Counterfactual Quantum Bit Commitment,"We propose a framework of bit commitment protocol using a comparison scheme
and present a compound comparison scheme based on counterfactual cryptography.
Finally, we propose a counterfactual quantum bit commitment protocol. In
security analysis, we give the proper security parameters for counterfactual
quantum bit commitment and prove that intercept attack and intercept/resend
attack are ineffective attack for our protocol. In addition, we explain that
counterfactual quantum bit commitment protocol cannot be attacked with no-go
theorem attack by current technology.",1807.01602v1
2018-07-05,Are fast radio bursts generated by cosmic string cusps?,"We revisit the idea that cosmic strings could source fast radio bursts by
taking into account Lorentz boosts and a weaker assumption about the scaling
law for the energy of particle decay. We show that the distance relation and
time scale, for a specific value of the scaling of energy, are still compatible
with observations. However, the event rate predicted by the model is too high
when compared to the data. We additionally show that a more realistic string,
with a finite thickness, further compounds the problem by prohibiting cusp
formation and point out how a superconducting wiggly string could circumvent
this issue.",1807.01976v1
2018-07-14,Evidence of spin-phonon coupling in CrSiTe$_3$,"We present the Raman scattering results on layered 2D semiconducting
ferromagnetic compound CrSiTe$_3$. Four Raman active modes, predicted by
symmetry, have been observed and assigned. The experimental results are
supported by DFT calculations. The self-energies of the $A_g^3$ and the $E_g^3$
symmetry modes exhibit unconventional temperature evolution around 180 K. In
addition, the doubly degenerate $E_g^3$ mode shows clear change of asymmetry in
the same temperature region. The observed behavior is consistent with the
presence of the previously reported short-range magnetic order and the strong
spin-phonon coupling.",1807.05447v1
2018-07-15,Improvement of Thermoelectric properties of Lanthanum cobaltate by Sr and Mn co-substitution,"We report thermoelectric (TE) properties of Sr and Mn co-substituted LaCoO3
system from room temperature to 700 K. Sr-substitutions at La and Mn at Co site
in LaCoO3 improves the electrical conductivity ({\sigma}). Thermal conductivity
(\k{appa}) of all the samples increases with the increase in temperature but
decreases with the substitution in LaCoO3. An estimation of the electronic
thermal conductivity (\k{appa}e) suggests a dominant phonon contribution to
thermal conductivity in this system. A maximum value of the figure of merit is
0.14 at 480 K for La0.95Sr0.05Co0.95Mn0.05O3",1807.05562v1
2018-07-20,Canonical threefold singularities with a torus action of complexity one and $k$-empty polytopes,"We classify the canonical threefold singularities that allow an effective
two-torus action. This extends classification results of Mori on terminal
threefold singularities and of Ishida and Iwashita on toric canonical threefold
singularities. Our classification relies on lattice point emptiness of certain
polytopal complexes with rational vertices. Scaling the polytopes by the least
common multiple $k$ of the respective denominators, we investigate
$k$-emptiness of polytopes with integer vertices. We show that two dimensional
$k$-empty polytopes either are sporadic or come in series given by Farey
sequences. We finally present the Cox ring iteration tree of the classified
singularities, where all roots, i.e. all spectra of factorial Cox rings, are
generalized compound du Val singularities.",1807.08022v1
2018-07-22,Transport properties of semimetallic transition metal dichalcogenides,"The Weyl semimetal requires the breaking of either the time-reversal symmetry
(TRS) or the lattice inversion symmetry. When the TRS and inversion symmetry
coexist, a pair of degenerate Weyl points may exist, leading to the related
Dirac semimetal phase. In other words, a Dirac semimetallic state can be
regarded as two copies of Weyl semimetal states. In this dissertation, we study
tellurium based compounds like the Weyl semimetal candidate MoTe2 and the Dirac
semimetal candidate PtTe2 within the transition metal dichalcogenides family.",1807.08227v1
2018-07-12,Data Infrastructure and Approaches for Ontology-Based Drug Repurposing,"We report development of a data infrastructure for drug repurposing that
takes advantage of two currently available chemical ontologies. The data
infrastructure includes a database of compound- target associations augmented
with molecular ontological labels. It also contains two computational tools for
prediction of new associations. We describe two drug-repurposing systems: one,
Nascent Ontological Information Retrieval for Drug Repurposing (NOIR-DR), based
on an information retrieval strategy, and another, based on non-negative matrix
factorization together with compound similarity, that was inspired by
recommender systems. We report the performance of both tools on a
drug-repurposing task.",1807.09754v1
2018-07-27,Loss-induced transparency in optomechanics,"We study optomechanically induced transparency (OMIT) in a compound system
consisting of coupled optical resonators and a mechanical mode, focusing on the
unconventional role of loss. We find that optical transparency can emerge at
the otherwise strongly absorptive regime in the OMIT spectrum, by using an
external nanotip to enhance the optical loss. In particular, loss-induced
revival of optical transparency and the associated slow-to-fast light switch
can be identified in the vicinity of an exceptional point. These results open
up a counterintuitive way to engineer micro-mechanical devices with tunable
losses for e.g., coherent optical switch and communications.",1807.10538v1
2018-10-04,Compound Binary Search Tree and Algorithms,"The Binary Search Tree (BST) is average in computer science which supports a
compact data structure in memory and oneself even conducts a row of quick
algorithms, by which people often apply it in dynamical circumstance. Besides
these edges, it is also with weakness on its own structure specially with poor
performance at worst case. In this paper, we will develop this data structure
into a synthesis to show a series of novel features residing in. Of that, there
are new methods invented for raising the performance and efficiency
nevertheless some existing ones in logarithm or linear time.",1810.02270v1
2018-10-05,"Structural and optoelectronic properties of the inorganic perovskites AGeX3 (A = Cs, Rb; X = I, Br, Cl) for solar cell application","We predict the structural, electronic and optic properties of the inorganic
Ge-based halide perovskites AGeX3 (A = Cs, Rb; X = I, Br, Cl) by using
first-principles method. In particular, absolute electronic energy band levels
are calculated using two different surface terminations of each compound,
reproducing the experimental band alignment.",1810.02543v1
2018-10-08,Tubeless Siphon Flow of Room Temperature Liquid Metal,"Tubeless siphon flow of liquid metal was made possible by way of sucking the
fluid via a syringe pump with a rubber tube. Through adjusting the flow rate
and tube diameter, the liquid column height and diameter can be changed
accordingly. A theoretical model was derived to predict the flow configuration
thus enabled. Adding micro copper particles evidently increased the extensional
viscosity of liquid metal. With the increase of particle concentration, the
enhancement of tubeless siphon becomes more remarkable. The intermetallic
compound CuGa2 produced by corrosion was considered as the reason for the
variation of rheological property of liquid metal.",1810.03354v1
2018-10-27,Calculations of Neutron Reflectivity in the eV Energy Range from Mirrors made of Heavy Nuclei with Neutron-Nucleus Resonances,"We evaluate the reflectivity of neutron mirrors composed of certain heavy
nuclei which possess strong neutron-nucleus resonances in the eV energy range.
We show that the reflectivity of such a mirror for some nuclei can in principle
be high enough near energies corresponding to compound neutron-nucleus
resonances to be of interest for certain scientific applications in
non-destructive evaluation of subsurface material composition and in the theory
of neutron optics beyond the kinematic limit.",1810.11590v1
2018-12-31,Poisson approximation,"We overview results on the topic of Poisson approximation that are missed in
existing surveys. The topic of Poisson approximation to the distribution of a
sum of integer-valued random variables is presented as well. We do not restrict
ourselves to a particular method, and overview the whole range of issues
including the general limit theorem, estimates of the accuracy of
approximation, asymptotic expansions, etc. Related results on the accuracy of
compound Poisson approximation are presented as well. We indicate a number of
open problems and discuss directions of further research.",1901.01847v2
2019-01-21,Nano-Mechanical Behaviour Of MnTiO3 Ceramics,"Here we investigate the mechanical behavior of the MnTiO3 ceramic.
Nanoindentation tests in a manganese titanate polycrystalline sample were
performed using a Berkovich indenter with a tip radius of 150 nm. On applying
the load, it shows the elastic and plastic behavior. The work done during the
elastic and plastic processes are 16757.78 {\mu}N.nm and 10045.72 {\mu}N.nm,
respectively. The estimated values of reduced modulus and hardness are 158GPa
and 10.5GPa, respectively. This suggests that this compound exhibits a
significant plastic character.",1901.06843v1
2019-01-31,"Anisotropic ferromagnetism and structure stability in $4f$-$3d$ intermetallics: ab initio structure optimization and magnetic anisotropy for RCo$_5$ (R=Ce, La, and Y)","Electronic mechanism in the interplay between ferromagnetism and structure
stability of $4f$-$3d$ intermetallics in the main phase of rare-earth permanent
magnets is investigated from first principles. We present a case study with an
archetypical materials family RCo$_5$ (R=Ce, La, Y), which was a part of the
earliest rare-earth permanent magnets and from which other representative
main-phase compounds can be regarded as a derived type. Comparison with the
champion magnet materials family R$_2$T$_{14}$B and recently revisited
materials family RT$_{12}$ (T=Co and Fe) points to a direction leading to a
mid-class magnet for the possible next generation materials.",1901.11498v1
2019-03-13,Backward non-unitary quantum evolution,"A non-linear backward equation with diffusive terms is postulated for the
probability density that depends on the Bohmian quantum potential. An
associated nonlinear Schr\""{o}dinger equation is also introduced and extension
of the analysis to several particle compounds is sketched along with the
implications following from this formalism regarding the non-conservation of
probability in the non-equilibrium regime. Some further conclusions are educed
with respect to the Onsager's relations and the generalized optical theorem.",1904.05150v2
2019-04-12,PubChemQC PM6: A dataset of 221 million molecules with optimized molecular geometries and electronic properties,"We report on the largest dataset of optimized molecular geometries and
electronic properties calculated by the PM6 method for 92.9% of the 91.2
million molecules cataloged in PubChem Compounds retrieved on Aug. 29, 2016. In
addition to neutral states, we also calculated those for cationic, anionic, and
spin flipped electronic states of 56.2%, 49.7%, and 41.3% of the molecules,
respectively. Thus, the grand total calculated is 221 million molecules. The
dataset is available at http://pubchemqc.riken.jp/pm6_dataset.html under the
Creative Commons Attribution 4.0 International license.",1904.06046v2
2019-04-18,Parity-Enhanced Quantum Optimal Measurements,"We find a large class of pure and mixed input states with which the phase
estimation precision saturates the Cramer-Rao bound under the compound
measurements of parity and particle number. We further propose a
quantum-phase-estimation protocol for arbitrary input states, through which the
precision achieved is always higher than or equal to that obtained via the
original input state. We also demonstrate the implementation of the proposed
scheme using a nonlinear interferometry and the realization of the
nondemolition parity measurement in atomic condensates.",1904.08738v2
2019-04-24,Exhaustive Search of Ligand Binding Pathways via Volume-based Metadynamics,"Determining the complete set of ligands' binding/unbinding pathways is
important for drug discovery and to rationally interpret mutation data. Here we
have developed a metadynamics-based technique that addressed this issue and
allows estimating affinities in the presence of multiple escape pathways. Our
approach is shown on a Lysozyme T4 variant in complex with the benzene
molecule. The calculated binding free energy is in agreement with experimental
data. Remarkably, not only we were able to find all the previously identified
ligand binding pathways, but also we uncovered 3 new ones. This results were
obtained at a small computational cost, making this approach valuable for
practical applications, such as screening of small compounds libraries.",1904.10726v1
2019-04-24,On Topological Properties of Third type of Hex Derived Networks,"In chemical graph theory, a topological index is a numerical representation
of a chemical network while a topological descriptor correlates certain
physico-chemical characteristics of underlying chemical compounds besides its
chemical representation. Graph plays an vital role in modeling and designing
any chemical network. F. Simonraj et al. derived new third type of Hex derived
networks [27]. In our work, we discuss the third type of hex derived networks
HDN3(r), THDN3(r) and RHDN3(r) and computed exact results for topological
indices which are based on degrees of end vertices.",1904.10827v1
2019-07-11,Real-world forward rate dynamics with affine realizations,"We investigate the existence of affine realizations for L\'{e}vy driven
interest rate term structure models under the real-world probability measure,
which so far has only been studied under an assumed risk-neutral probability
measure. For models driven by Wiener processes, all results obtained under the
risk-neutral approach concerning the existence of affine realizations are
transferred to the general case. A similar result holds true for models driven
by compound Poisson processes with finite jump size distributions. However, in
the presence of jumps with infinite activity we obtain severe restrictions on
the structure of the market price of risk; typically, it must even be constant.",1907.05072v1
2019-07-22,Applications of the perturbation formula for Poisson processes to elementary and geometric probability,"The binomial, the negative binomial, the Poisson, the compound Poisson and
the Erlang distribution do all admit integral representations with respect to
its (continuous) parameter. We use the Margulis-Russo type formulas for
Bernoulli and Poisson processes to derive these representations in a unified
way and to provide a probabilistic interpretation for the derivatives. By
similar variational methods, we obtain apparently new integro-differential
identities which the density of a strictly $\alpha$-stable multivariate density
satisfies. Then, we extend Crofton's derivative formula known in integral
geometry to the case of a Poisson process. Finally we use this extension to
give a new probabilistic proof of a version of this formula for binomial point
processes.",1907.09552v1
2019-05-26,Functionalization of Single-walled Carbon Nanotubes with Bis-astraphloxin,"This dissertation aims to demonstrate that photoluminescence spectroscopy
could be an efficient technique of functionalized carbon nanotube detection and
imaging. The advances in nanotechnology and the potential growth in carbon
nanotubes production, in which if control mechanisms not in place for safely
disposing off nanotubes, these nanotubes could pose as an environmental
pollutant, due to the severe, persistent and bio-accumulative nature of these
compounds. Therefore, the need for this scientific research is timely in case
of some technological disaster. Besides, the study on interaction of carbon
nanotubes with various organic materials provide a new knowledge and
opportunities for potential application of the nanotubes.",1907.10752v1
2019-10-06,First-principle Calculations of Electron-Phonon Interactions in $A^{II}B^{IV}C^{V}_2$ Crystals,"$Ab-initio$ probabilities of phonon-assisted intervalley scattering of
electrons in the conduction bands of ternary chalcopyrite compounds $ZnSiP_2$
and $ZnGeP_2$ between the central $\Gamma$ minima and the lowest lateral minima
(valleys) at $T$ and $N$ points have been calculated using the density
functional theory. The equilibrium parameters of crystal structures, spectra of
electrons and phonons are calculated self-consistently and are in fairly good
agreement with the experiment and available theoretical calculations. The
electron-phonon coupling constants with short-wave (inter-valley) phonons in
the chalcopyrite phosphides are close to their values in $Si$, $Ge$ and in
binary analog $GaP$.",1910.02347v1
2019-10-18,Electric-field control of spin transitions in molecular compounds,"We present a theoretical model of spin transitions in stacks of molecular
layers. Our model captures the already established physics of these systems
(thermal hysteretic transitions and crossovers) and suggests a way towards in
situ control of this physics by means of an external electric field. Our
results pave the way toward both temperature and voltage controllable organic
memory.",1910.08618v1
2019-10-20,Ab initio study of lattice dynamics of dodecaborides ZrB12 and LuB12,"We performed ab initio lattice-dynamics calculations of frame-cluster
dodecaborides ZrB12 and LuB12. As a whole, our calculated phonon frequencies
and atom-projected density of states are consistent with the results of
available first-principles calculations and experimental measurements. So we
conclude that the ab initio DFT approach is quite appropriate to study the
sufficiently subtle physics of these compounds. Our experiment-independent
calculations provide an explicit quantitative confirmation of mixing the
eigenvectors of boron and metal vibrations, which was previously observed in
experiments.",1910.09039v1
2019-10-27,A Novel Method to Construct NSSD Molecular Graphs,"A graph is said to be NSSD (= non-singular with a singular deck) if it has no
eigenvalue equal to zero, whereas all its vertex-deleted subgraphs have
eigenvalues equal to zero. NSSD graphs are of importance in the theory of
conductance of organic compounds. In this paper, a novel method is described
for constructing NSSD molecular graphs from the commuting graphs of the
$H_v$-group. An algorithm is presented to construct the NSSD graphs from these
commuting graphs.",1910.12218v1
2019-10-28,Charge Density Wave and Superconductivity in Transition Metal Dichalcogenides,"Competing orders in condensed matter give rise to the emergence of
fascinating, new phenomena. Here, we investigate the competition between
superconductivity and charge density wave in the context of layered-metallic
compounds, transition metal dichalcogenides, in which the superconducting state
is usually suppressed by the charge density wave. We show, using real-space
self-consistent Bogoliubov-de Gennes calculations and momentum-space
calculations involving density-functional theory and dynamical mean-field
theory, that there is a surprising reappearance of superconductivity in the
presence of non-magnetic disorder fluctuations, as observed in recent
experiments.",1910.12801v3
2019-10-31,Operator quantum machine learning: Navigating the chemical space of response properties,"The identification and use of structure property relationships lies at the
heart of the chemical sciences. Quantum mechanics forms the basis for the
unbiased virtual exploration of chemical compound space (CCS), imposing
substantial compute needs if chemical accuracy is to be reached. In order to
accelerate predictions of quantum properties without compromising accuracy, our
lab has been developing quantum machine learning (QML) based models which can
be applied throughout CCS. Here, we briefly explain, review, and discuss the
recently introduced operator formalism which substantially improves the data
efficiency for QML models of common response properties.",1910.14418v1
2012-09-08,Programming Languages for Scientific Computing,"Scientific computation is a discipline that combines numerical analysis,
physical understanding, algorithm development, and structured programming.
Several yottacycles per year on the world's largest computers are spent
simulating problems as diverse as weather prediction, the properties of
material composites, the behavior of biomolecules in solution, and the quantum
nature of chemical compounds. This article is intended to review specfic
languages features and their use in computational science. We will review the
strengths and weaknesses of different programming styles, with examples taken
from widely used scientific codes.",1209.1711v2
2012-09-14,Skyrmion Dynamics in Multiferroic Insulator,"Recent discovery of Skyrmion crystal phase in insulating multiferroic
compound Cu$_2$OSeO$_3$ calls for new ways and ideas to manipulate the
Skyrmions in the absence of spin transfer torque from the conduction electrons.
It is shown here that the position-dependent electric field, pointed along the
direction of the average induced dipole moment of the Skyrmion, can induce the
Hall motion of Skyrmion with its velocity orthogonal to the field gradient.
Finite Gilbert damping produces longitudinal motion. We find a rich variety of
resonance modes excited by a.c. electric field.",1209.3120v1
2014-06-13,Low thermal conductivity and triaxial phononic anisotropy of SnSe,"In this theoretical study, we investigate the origins of the very low thermal
conductivity of tin selenide (SnSe) using ab-initio calculations. We obtained
high-temperature lattice thermal conductivity values that are close to those of
amorphous compounds. We also found a strong anisotropy between the three
crystallographic axes: one of the in-plane directions conducts heat much more
easily than the other. Our results are compatible with most of the experimental
literature on SnSe, and differ markedly from the more isotropic values reported
by a recent study.",1406.3532v2
2014-06-15,Magnetotransport studies of FeSe under hydrostatic pressure,"The discoveries of iron-based superconductors with relatively high transition
temperature are under intense experimental and theoretical investigation. Here
we present magnetotransport measurements on FeSe superconductor under
hydrostatic pressure. We show that in Fe-deficient tetragonal FeSe binary
compound, the onset of superconducting transition is almost doubled under
1.98GPa pressure and the estimated upper critical field of 26.7Tesla is
increased to 47.5Tesla.",1406.3795v2
2014-06-16,Magnetic Order in the 2D Heavy-Fermion System CePt2In7 studied by muSR,"The low-temperature microscopic magnetic properties of the quasi-2D
heavyfermion compound, CePt2In7 are investigated by using a positive muon-spin
rotation and relaxation (?muSR) technique. Clear evidence for the formation of
a commensurate antiferromagnetic order below TN=5.40 K is presented. The
magnetic order parameter is shown to fit well to a modified BSC gap-energy
function in a strong-coupling scenario.",1406.3983v1
2014-06-19,Superconductivity in Uranium Compounds,"On the basis of microscopic theory it is demonstrated how the coupling
between the electrons by means of magnetization fluctuations in ferromagnetic
metal with orthorhombic symmetry gives rise equal spin pairing superconducting
state with general form of the order parameter dictated by symmetry. The strong
upturn of the upper critical field along $b$-direction above 5 Tesla in UCoGe
is explained by the increase of pairing interaction caused by the suppression
of the Curie temperature by magnetic field parallel to b-axis. It is proposed
that similar phenomenon at much higher field must take place also for the field
directed along the magnetically hardest a-direction.",1406.5030v3
2014-06-23,Spontaneous graphitization of ultrathin cubic structures: A computational study,"Results based on {\em ab initio} density functional calculations indicate a
general graphitization tendency in ultrathin slabs of cubic diamond, boron
nitride, and many other cubic structures including rocksalt. Whereas such
compounds often show an energy preference for cubic rather than layered atomic
arrangements in the bulk, the surface energy of layered systems is commonly
lower than that of their cubic counterparts. We determine the critical slab
thickness for a range of systems, below which a spontaneous conversion from a
cubic to a layered graphitic structure occurs, driven by surface energy
reduction in surface-dominated structures.",1406.5922v1
2014-06-25,On Stein operators for discrete approximations,"In this paper, a new method based on probability generating functions is used
to obtain multiple Stein operators for various random variables closely related
to Poisson, binomial and negative binomial distributions. Also, Stein operators
for certain compound distributions, where the random summand satisfies Panjer's
recurrence relation, are derived. A well-known perturbation approach for
Stein's method is used to obtain total variation bounds for the distributions
mentioned above. The importance of such approximations is illustrated, for
example, by the binomial convoluted with Poisson approximation to sums of
independent and dependent indicator random variables.",1406.6463v2
2014-06-25,First-principles study of superconducting Rare-earth doped CaFe2As2,"We report a systematic and ab-initio electronic structure calculation of
Ca0.75 M0.25 Fe2 As2 with M = Ca, Sr, Eu, La, Ce, Pr, Nd, Pm, Sm, Na, K, Rb.
The recently reported experimentally observed structural trends in rare
earths-doped CaFe2 As2 compounds are successfully predicted and a complete
theoretical description of the pressure induced orthorhombic to collapsed
tetragonal transition is given. We demonstrate that the transition pressure is
reduced by electron doping and rises linearly with the ionic size of the
dopants. We discuss the implications of our description for the realization of
a superconducting phase.",1406.6513v1
2018-02-06,Splitting models for multivariate count data,"Considering discrete models, the univariate framework has been studied in
depth compared to the multivariate one. This paper first proposes two criteria
to define a sensu stricto multivariate discrete distribution. It then
introduces the class of splitting distributions that encompasses all usual
multivariate discrete distributions (multinomial, negative multinomial,
multivariate hypergeometric, multivariate neg- ative hypergeometric, etc . . .
) and contains several new. Many advantages derive from the compound aspect of
split- ting distributions. It simplifies the study of their characteris- tics,
inferences, interpretations and extensions to regression models. Moreover,
splitting models can be estimated only by combining existing methods, as
illustrated on three datasets with reproducible studies.",1802.02074v1
2018-02-19,Rare events and Poisson point processes,"The aim of the present work is to show that the results obtained earlier on
the approximation of distributions of sums of independent terms by the
accompanying compound Poisson laws may be interpreted as rather sharp
quantitative estimates for the closeness between the sample containing
independent observations of rare events and the Poisson point process which is
obtained after a Poissonization of the initial sample.",1802.06638v1
2018-02-27,Fitting of the TB-SMA interatomic potentials for Pt/Cu(111) surface alloy,"In this paper we present new parameters of the TB-SMA interatomic potentials
for the Pt/Cu(111) surface alloy. The parameters are fitted using both the
experimental and {\it ab initio} data. The potentials reproduce not only the
bulk properties of copper and platinum, but also the energy characteristics of
the Pt/Cu(111) surface alloy. The potentials can be used for the simulations of
the growth of the Pt/Cu(111) surface alloy on the atomic scale.",1802.09965v1
2018-08-13,Mechanism for transitions between ferromagnetic and antiferromagnetic orders in $d$-electron metallic magnets,"We propose mechanism for pressure-induced transitions between ferromagnetic
and antiferromagnetic phases that relies on a competition between
characteristic energy scales ubiquitous among $d$-electron metallic magnetic
compounds. Principles behind the mechanism are demonstrated on the example of
the minimal two-orbital $p$-$d$ lattice model. We suggest that LaCrGe$_3$,
where pressure-induced ferromagnetic-to-antiferromagnetic phase transition has
been recently observed, is a promising candidate to realize discussed
mechanism.",1808.04109v3
2018-11-20,Application of resonant decay method for compound-systems at analysis inclusive spectra in high-energy nuclear reactions,"It is shown, that the exponential decrease of the energy spectra of the
fragments with growing its energy, which does not depend from the fragment
type, targets, projectiles and projectile energies, and which sometimes
accompanied slight oscillations, can be explained by the phenomenon of time
resonances. These time resonances correspond to decay of intermediate excited
nuclear composite system. For the first time, expressions for the decay rate
and the probability of survival of such system as a function of time are
obtained. Inclusive spectra for two real high-energy nuclear reactions are
calculated.",1812.00747v2
2018-12-18,Estimates for the closeness of convolutions of probability distributions on convex polyhedra,"The aim of the present work is to show that the results obtained earlier on
the approximation of distributions of sums of independent summands by the
accompanying compound Poisson laws and the estimates of the proximity of
sequential convolutions of multidimensional distributions may be transferred to
the estimation of the closeness of convolutions of probability distributions on
convex polyhedra.",1812.07473v1
2018-12-19,On strong stationary times and approximation of Markov chain hitting times by geometric sums,"Consider a discrete time, ergodic Markov chain with finite state space which
is started from stationarity. Fill and Lyzinski (2014) showed that, in some
cases, the hitting time for a given state may be represented as a sum of a
geometric number of IID random variables. We extend this result by giving
explicit bounds on the distance between any such hitting time and an
appropriately chosen geometric sum, along with other related approximations.
The compounding random variable in our approximating geometric sum is a strong
stationary time for the underlying Markov chain; we also discuss the
approximation and construction of this distribution.",1812.07896v1
2018-12-20,Giant Magnetoelastic-Coupling Driven Spin-Lattice Liquid State in Molybdate Pyrochlores,"We propose the idea of a spin-lattice liquid, in which spin and lattice
degrees of freedom are strongly coupled and remain disordered and fluctuating
down to low temperatures. We show that such a state arises naturally from a
microscopic analysis of a class of molybdate pyrochlore compounds, and is
driven by a giant magnetoelastic effect. Finally, we argue that this could
explain some of the experimental features of Y$_2$Mo$_2$O$_7$.",1812.08462v2
2018-12-21,Gamma strength functions and the Brink-Axel hypothesis,"Experimental tests of the Brink-Axel hypothesis relating gamma strength
functions (GSF) deduced from absorption and emission experiments are discussed.
High-resolution inelastic proton scattering at energies of a few hundred MeV
and at very forwrd angles including $0^\circ$ presents a new approach to test
the validity of the BA hypothesis in the energy region of the pygmy dipole
resonance. Such data not only provide the GSF but also the level density and
thus permit an independent test of their model-dependent decomposition in the
Oslo method.",1812.09072v1
2018-12-24,Role of fluctuations on the pairing properties of nuclei in the random spacing model,"The influence of thermal fluctuations on fermion pairing is investigated
using a semiclassical treatment of fluctuations. When the average pairing gaps
along with those differing by one standard deviation are used, the
characteristic discontinuity of the specific heat at the critical temperature
$T_c$ in the BCS formalism with its most probable gap becomes smooth. This
indicates the suppression of a second order phase transition as experimentally
observed in nano-particles and several nuclei. Illustrative calculations using
the constant spacing model and the recently introduced random spacing model are
presented.",1812.09988v1
2019-02-04,Restoration and extrapolation of structural transformation by dynamical general equilibrium feedbacks,"We model sectoral production by serially nesting (cascading) binary
compounding processes. The sequence of processes is discovered in a
self-similar hierarchical structure stylized in macroscopic input-output
transactions. The feedback system of unit cost functions, with recursively
estimated nest-wise CES parameters, is calibrated for sectoral productivities
to replicate two temporally distant cost share structures, observed in a set of
linked input--output tables. We model representative households by multifactor
CES, with parameters estimated by fixed effects regressions. By the integrated
dynamic general equilibrium model, we extrapolate potential structural
transformations, and measure the associated welfare changes, caused by
exogenous sectoral productivity shocks.",1902.01052v3
2019-02-10,Scattering Statistics of Generalized Spatial Poisson Point Processes,"We present a machine learning model for the analysis of randomly generated
discrete signals, modeled as the points of an inhomogeneous, compound Poisson
point process. Like the wavelet scattering transform introduced by Mallat, our
construction is naturally invariant to translations and reflections, but it
decouples the roles of scale and frequency, replacing wavelets with Gabor-type
measurements. We show that, with suitable nonlinearities, our measurements
distinguish Poisson point processes from common self-similar processes, and
separate different types of Poisson point processes.",1902.03537v2
2019-02-11,Magnon excitations in $Cs_2CuAl_4O_8$ - a bond alternating S=1/2 spin chain with next nearest neighbor coupling,"A recent density functional theory (DFT) based analysis, complemented with
Quantum Monte Carlo calculations revealed a highly spin-frustrating nature of
the one-dimensional spin-$\frac{1}{2}$ compound $Cs_2CuAl_4O_8$ that comprises
of unique bond alternations and relatively strong next nearest neighbor
interactions. This article gives a brief account on possible magnon excitations
that can appear in the ground state of such systems. We find that the spin
waves obtained on top of coplanar helical reference states show multiple magnon
modes (both acoustic and optical). However, those magnon modes turn out to be
stable only in the absence of bond alternations.",1902.04008v1
2019-02-18,Pressure-induced spin-state ordering in Sr$_2$CoO$_3$F,"We study theoretically low-temperature phases of a recently synthesized
compound Sr$_2$CoO$_3$F under pressure. The analysis combining LDA+DMFT and a
strong-coupling effective model points to the existence of not only normal
paramagnetic and antiferromagnetic regimes, but also a spin-state ordered phase
in a certain range of applied pressure and low temperature. This order is
characterized by a checkerboard arrangement of different spin states of cobalt
atoms in the lattice.",1902.06509v2
2019-02-18,Resonant interatomic Auger transition in chalcopyrite CuInSe2,"The interatomic Auger transitions in compounds containing atomic components
with core levels close in energy are studied theoretically and experimentally.
The Coulomb transitions of a hole between such levels lead to a resonant
enhancement of the Auger spectra (with respect to the energy difference between
the levels). Interatomic Auger transitions involving high lying levels are
formed by shaking up electrons due to the dynamic field of photo holes produced
during the transition. These effects were observed experimentally in XPS and
Auger spectra of CuInSe2 type materials.",1902.06524v1
2019-02-20,The cross sections for inelastic neutron scattering and radiative capture in the field of a light wave,"The mixing of the levels of a compound nucleus in the field of a
high-intensity light wave is considered. The cross sections for inelastic
neutron scattering and radiative capture are computed with allowance for this
effect. The effect of the electron shell on the effective charge for the dipole
interaction between the neutron + nucleus system and the external
electromagnetic field is taken into consideration.",1902.07610v1
2019-06-03,Unavoidable disorder and entropy in multi-component systems,"The need for improved functionalities is driving the search for more
complicated multi-component materials. Despite the factorially increasing
composition space, ordered compounds with 4 or more species are rare. Here, we
unveil the competition between the gain in enthalpy and entropy with increasing
number of species by statistical analysis of the AFLOW data repositories. A
threshold in the number of species is found where entropy gain exceeds enthalpy
gain. Beyond that, enthalpy can be neglected, and disorder - complete or
partial - is unavoidable.",1906.01085v1
2019-06-04,Controllable pulse patterns in fiber lasers,"An all-optical pulse power editing (PPE) technique is reported. Using the PPE
technique, pulses with different peak powers are output and directed to the
positive or reverse saturable absorption (SA) range of the saturable absorber.
Further, under the combined action of the PPE technique and SA, four pulse
patterns including dissipative soliton (DS), DS molecules, soliton compounds
composed of DS and noise-like pulse (NLP), and pure NLP are controllably
generated in fiber lasers. The results are conducive for developing advanced DS
lasers and can further clarify the onset of pulse dynamic patterns.",1906.01555v2
2019-06-18,Prediction properties of optimum response surface designs,"Prediction capability is considered an important issue in response surface
methodology. Following the line of argument that a design should have several
desirable properties we have extended an existing compound design criterion to
include prediction properties. Prediction of responses and of differences in
response are considered. Point and interval predictions are allowed for.
Extensions of existing graphical tools for inspecting prediction performances
of the designs in the whole region of experimentation are also introduced. The
methods are illustrated with two examples.",1906.07500v1
2019-06-27,A look at multiplicity distributions via modified combinants,"The experimentally measured multiplicity distributions exhibit, after closer
inspection, peculiarly enhanced void probability and oscillatory behavior of
the modified combinants. We show that both these features can be used as
additional sources of information, not yet fully explored, on the mechanism of
multiparticle production. We provide their theoretical understanding within the
class of compound distributions.",1906.11531v1
2020-04-13,Quantum critical dynamics and scaling in one-dimensional antiferromagnets,"For a number of quantum critical points in one dimension quantum field theory
has provided exact results for the scaling of spatial and temporal correlation
functions. Experimental realizations of these models can be found in certain
quasi one dimensional antiferromagnetc materials. Measuring the predicted
scaling laws experimentally presents formidable technical challenges. In many
cases it only became possible recently, thanks to qualitative progress in the
development of inelastic neutron scattering techniques and to the discovery of
new model compounds. Here we review some of the recent experimental studies of
this type.",2004.06012v2
2020-04-18,Is the anti-filarial drug diethylcarbamazine useful to treat COVID-19?,"The SARS-CoV-2 virus has resulted in a devastating pandemic of COVID-19.
Exploring compounds that could offer a breakthrough in treatment is the need of
the hour. Re-positioning cheap, freely available and safe drugs is a priority.
The paper proposes evidence for the potential use of diethylcarbamazine (DEC)
in the treatment of COVID-19. DEC has inhibitory effects on arachidonic acid
metabolism to prostaglandins, little known anti-viral effects on animal
retroviruses and demonstrated anti-inflammatory actions in animal models of
lung inflammation indicating the need to explore this hypothesis further. We
believe this is the first time DEC is being proposed to treat COVID-19.",2004.08491v1
2020-04-21,Anisotropic ferromagnet with two spins per site,"Green function diagrammatic technique is used to investigate a model
ferromagnet in the case, when the effective spin at a site is compounded of two
anisotropically interacting electron spins. The results are: the transverse
magnetic excitations and the longitudinal ones are obtained in the random phase
approximation, magnetization and critical temperature are calculated to the
first order in the reciprocal of the effective number z of ions interacting
with a given ion, and exchange interaction at the same site gives the contrary
effects in changes of the magnitudes mentioned above in dependence on the
exchange-isotropy parameter I and the exchange-anisotropy parameter D.",2004.09884v1
2020-04-22,The Origin of Mean-Field Behavior in an Elastic Ising Model,"Simple elastic models of spin-crossover compounds are known empirically to
exhibit classical critical behavior. We demonstrate how the long-ranged
interactions responsible for this behavior arise naturally upon integrating out
mechanical fluctuations of such a model. A mean field theory applied to the
resulting effective Hamiltonian quantitatively accounts for both thermodynamics
and kinetics observed in computer simulations, including a barrier to
magnetization reversal that grows extensively with system size. For
nanocrystals, which break translational symmetry, a straightforward extension
of mean field theory yields similarly accurate results.",2004.10373v1
2020-04-23,Predicting A Novel Phase of 2D SiTe$_2$,"Layered IV-VI$_2$ compounds often exist in the CdI$_2$ structure. Using the
evolution algorithm and first-principles calculations, we predict a novel
layered structure of silicon ditelluride (SiTe$_2$) that is more stable than
the CdI$_2$ phase. The structure has a triclinic unit cell in its bulk form and
exhibits the competition between the Si atoms' tendency to form tetrahedral
bonds and the Te atoms' tendency to form hexagonal close-packing. The
electronic and vibrational properties of the predicted phase are investigated.
The effective mass of electron is small among 2D semiconductors, which is
beneficial for applications such as field-effect transistors. The vibrational
Raman and IR spectra are calculated to facilitate future experimental
investigations",2004.11481v1
2020-04-24,Number of equidistant neighbors on honeycomb lattice,"A convenient scheme is presented for calculating potential energy of van der
Waals interacting bilayer graphene and other similar 2D compounds. It is based
on the notion of the existence of two types of local symmetry of carbon atoms
ordering, a 3- and 6-fold one. Potential energy of an atom is expressed as a
sum of contributions from rings of equidistant atoms on neighboring layer.
Methods are described to compute the radius of rings of equidistant atoms and
number of atoms they contain. Exact positions of atoms are found as well,
allowing to apply the introduced method in modelling of anisotropic potentials
and to be used when twisting between layers is present.",2004.11840v1
2020-04-28,Dual nature of 5$f$ electrons in the isostructural UM$_2$Si$_2$ family: from antiferro- to Pauli paramagnetism via hidden order,"Using inelastic x-ray scattering beyond the dipole limit and hard x-ray
photoelectron spectroscopy we establish the dual nature of the U $5f$ electrons
in UM$_2$Si$_2$ (M = Pd, Ni, Ru, Fe), regardless of their degree of
delocalization. We have observed that the compounds have in common a local
atomic-like state that is well described by the U $5f^2$ configuration with the
$\Gamma_1^{(1)}$ and $\Gamma_2$ quasi-doublet symmetry. The amount of the U
5$f^3$ configuration, however, varies considerably across the UM$_2$Si$_2$
series, indicating an increase of U5$f$ itineracy in going from M=Pd to Ni to
Ru, and to the Fe compound. The identified electronic states explain the
formation of the very large ordered magnetic moments in UPd$_2$Si$_2$ and
UNi$_2$Si$_2$, the availability of orbital degrees of freedom needed for the
hidden order in URu$_2$Si$_2$ to occur, as well as the appearance of Pauli
paramagnetism in UFe$_2$Si$_2$. A unified and systematic picture of the
U$M_2$Si$_2$ compounds may now be drawn, thereby providing suggestions for new
experiments to induce hidden order and/or superconductivity in U compounds with
the tetragonal body-centered ThCr$_2$Si$_2$ structure.",2004.13419v2
2020-05-11,Autonomous learning and chaining of motor primitives using the Free Energy Principle,"In this article, we apply the Free-Energy Principle to the question of motor
primitives learning. An echo-state network is used to generate motor
trajectories. We combine this network with a perception module and a controller
that can influence its dynamics. This new compound network permits the
autonomous learning of a repertoire of motor trajectories. To evaluate the
repertoires built with our method, we exploit them in a handwriting task where
primitives are chained to produce long-range sequences.",2005.05151v1
2020-05-11,The minor minimal intrinsically chiral graphs,"Molecular chirality is actively researched in a variety of areas of biology,
including biochemistry, physiology, pharmacology, etc., and today many chiral
compounds are widely known to exhibit biological properties. The molecular
structure is represented by a graph structure. Therefore, the study of the
mirror symmetry of a graph is important in the natural sciences. A graph $G$ is
said to be intrinsically chiral if no embedding of G is ambient isotopic to its
mirror image.
  In this paper, we find two minor minimal intrinsically chiral graphs
$\Gamma_7$ and $\Gamma_8$. Furthermore, we classify all intrinsically chiral
graphs with at most eleven edges.",2005.05161v1
2020-05-19,Magnetic order and instability in newly synthesized CoSeAs marcasite,"Marcasite class of compounds provide facile platform to explore novel
phenomena of fundamental and technological importance, such as unconventional
superconductivity or high performance electrocatalyst. We report the synthesis
and experimental investigation of a new marcasite CoSeAs in this letter.
Experimental investigation of the new material using neutron scattering
measurements reveal weak magnetic correlation of cobalt ions below $T$ = 36.2
K. The modest isotropic exchange interaction between cobalt moments, inferred
from random phase approximation analysis, hints of magnetically unstable
environment. It is a desirable characteristic to induce unconventional
superconductivity via chemical pressure application",2005.09732v1
2020-05-28,"Antiferromagnetism mediated by heavy electrons: singlet shielding vs ""high-order"" RKKY","Can the antiferromagnetic (AF) order be induced via the local moments'
hybridization with the heavy electrons instead of conduction electrons? We
address this intriguingly fundamental question via a prototypical model to
describe the interplay between local moments and heavy electrons. We discover
that the AF order can be mediated via the heavy electrons through the mechanism
of ""high-order"" Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Moreover, the
induced AF order can coexist with its metallicity in a finite regime of the
phase diagram, which competes with and ultimately destroys the AF order
concurrently with the breakdown of heavy electrons. The potential relevance to
the heavy fermion compound Ce$_3$(Pt/Pd)In$_{11}$ is discussed.",2005.14148v1
2020-08-03,Quantifying the stability of the anion ordering in SrVO$_2$H,"We investigate a text-book mixed-anion compound SrVO$_2$H using
first-principles calculation, to theoretically pin down the factors that
stabilize its anion ordering. We find that the $trans$ preference by the
characteristic crystal field in the VO$_4$H$_2$ octahedron in addition to a
coherent shrinkage along the V-H-V direction, taking place when such direction
is consistent among neighboring hydrogens, stabilize the anion ordering
observed in experiment. Our study gives an important clue for controlling the
anion ordering in transition metal oxyhydrides.",2008.00656v2
2020-08-21,Multipole Orders in a Chain Ferrate Na2FeSe,"Fundamental block and staggered orders of magnetic Fe multipoles in Na2FeSe2
are classified by their symmetry and magnetoelectric properties. Our structure
model incorporates ferromagnetic or antiferromagnetic coupling between chains.
The ferrate salt is valued in studies of highly correlated electrons as the
only iron selenide known to possess chain-like structural units hosting ferrous
cations. Axial and polar (Dirac) multipoles are compulsory in the electronic
structure since Fe ions exhibit enantiomorphic symmetry in the parent
K2ZnO2-type compound. Calculated Bragg diffraction patterns for neutrons and
x-rays reveal specific contributions from both multipole types.",2008.09374v1
2021-03-11,Growth induced instabilities in a circular hyperelastic plate,"In this work, we have explored growth-induced mechanical instability in an
isotropic circular hyperelastic plate. Consistent two-dimensional governing
equations for a plate under a general finite strain are derived using a
variational approach. The derived plate equations are solved using the compound
matrix method for two cases of axisymmetric growth conditions - purely radial,
and combined radial and circumferential growth. The effect of growth on the
buckling behaviour of the plate (in particular, the critical growth factor and
the associated buckling mode shapes) is investigated for different thickness
values. These results are applicable to model growth induced deformation in
planar soft tissues such as skin.",2103.06534v1
2021-03-20,Stability and superconductivity of K-Y-H hydrides under high pressure,"It has been a hot issue to search for hydrides at high pressure with high
superconducting transition temperature (Tc). In this work, ternary
hydrogen-rich compounds KYHn (n = 1-16) were studied and calculated using the
density function theory (DFT) method and he results showed that the KYH8
demonstrates good stability and superconductivity. And keep thermodynamically
stable in the pressure range of 50-300 GPa. The research found that the Tc of
KYH8-C2/m was predicted to be 111.3K, 122.0K, and 142.3K at 200, 250 and 300
GPa, respectively. Our current study provides a possibility for searching new
high-Tc superconductors in ternary hydrides.",2103.11121v1
2021-03-23,FoamFactor: Hydrogel-Foam Composite with Tunable Stiffness and Compressibility,"This paper presents FoamFactor, a novel material with tunable stiffness and
compressibility between hydration states, and a tailored pipeline to design and
fabricate artifacts consisting of it. This technique compounds hydrogel with
open-cell foams via additive manufacturing to produce a water-responsive
composite material. Enabled by the large volumetric changes of hydrogel
dispersions, the material is soft and compressible when dehydrated and becomes
stiffer and rather incompressible when hydrated. Leveraging this material
property transition, we explore its design space in various aspects pertaining
to the transition of hydration states, including multi-functional shoes,
amphibious cars, mechanical transmission systems, and self-deploying robotic
grippers.",2103.12645v1
2022-02-03,Software Complex for the Numerical Solution of the Isotropic Imaginary-Axis Eliashberg Equations,"At present, the task of searching for compounds with a high superconducting
transition temperature is a very relevant scientific direction. Usually, the
calculation of is carried out by numerically solving the system of Eliashberg
equations. In this paper, a set of programs for solving this system written in
various forms on the imaginary axis is presented. As an example of the
developed methods applications, calculations results of and thermodynamic
properties of the metallic hydrogen I41/AMD phase and some other substances
under high pressure are presented.",2202.01452v1
2022-02-04,The asymptotic expansion of the Humbert hyper-Bessel function,"We consider the asymptotic expansion of the Humbert hyper-Bessel function
expressed in terms of a ${}_0F_2$ hypergeometric function by
\[J_{m,n}(x)=\frac{(x/3)^{m+n}}{m! n!}\,{}_0F_2(-\!\!\!-;m+1, n+1; -(x/3)^3)\]
as $x\to+\infty$, where $m$, $n$ are not necessarily non-negative integers.
Particular attention is paid to the determination of the exponentially small
contribution. The main approach utilised is that described by the author (J.
Comput. Appl. Math. {\bf 234} (2010) 488-504); a leading-order estimate is also
obtained by application of the saddle-point method applied to an integral
representation containing a Bessel function. Numerical results are presented to
demonstrate the accuracy of the resulting compound expansion.",2202.02049v1
2022-01-23,"Axiomatizing consciousness, with applications","Consciousness will be introduced axiomatically, inspired by Buddhist insight
meditation and psychology, logic in computer science, and cognitive
neuroscience, as consisting of a stream of $configurations$ that is $compound$,
$discrete$, and (non-deterministically) $computable$. Within this context the
notions of self, concentration, mindfulness, and various forms of suffering can
be defined. As an application of this set up, it will be shown how a combined
development of concentration and mindfulness can attenuate and eventually
eradicate some of the forms of suffering.",2202.05700v1
2022-02-19,Superconductivity in Bi based Bi2PdPt,"We report synthesis and properties of superconducting Bi$_2$PdPt, a new
member of Bi-Pd based compounds known for their simultaneous existence of
topological surfaces states and superconductivity. It crystallizes in a
hexagonal structure having space group $P6_3/mmc$. A detailed investigation of
the properties via transport, magnetization, and specific heat measurements
confirm bulk superconductivity with transition temperature, \textit{T}$_{C}$ =
4.0(1) K in moderate coupling limit.",2202.09658v2
2022-02-21,Chiral superconductivity in cuprates mediated by spin-orbit coupling to spinon superfluidity,"We utilize the Hubbard model to demonstrate that doping of the
antiferromagnetic parent compounds of cuprate superconductors stabilizes a spin
liquid state. Superconductivity in such a state emerges due to the spin-orbit
coupling between charge current and superfluidity of spinon condensate,
resulting in a chiral relation between the order parameter phase gradient and
supercurrent. We propose simple experimental tests for the presented mechanism.",2202.09965v5
2022-02-25,Large deviations for stochastic fluid networks with Weibullian tails,"We consider a stochastic fluid network where the external input processes are
compound Poisson with heavy-tailed Weibullian jumps. Our results comprise of
large deviations estimates for the buffer content process in the vector-valued
Skorokhod space which is endowed with the product $J_1$ topology. To illustrate
our framework, we provide explicit results for a tandem queue. At the heart of
our proof is a recent sample-path large deviations result, and a novel
continuity result for the Skorokhod reflection map in the product $J_1$
topology.",2202.12770v2
2022-03-09,SparseChem: Fast and accurate machine learning model for small molecules,"SparseChem provides fast and accurate machine learning models for biochemical
applications. Especially, the package supports very high-dimensional sparse
inputs, e.g., millions of features and millions of compounds. It is possible to
train classification, regression and censored regression models, or combination
of them from command line. Additionally, the library can be accessed directly
from Python. Source code and documentation is freely available under MIT
License on GitHub.",2203.04676v1
2022-03-31,A readout-integrated time-bin qutrit analyzer for echo-based quantum memories,"We present a method to project time-bin qutrits stored in an echo-based
quantum memory using several successive partial readouts of the memory. We
demonstrate how this scheme can be used to implement projections onto a full
set of mutually unbiased bases and, therefore, enables the characterization of
arbitrary quantum states. Further, we study the integration of this protocol
for the case of atomic frequency comb spin-wave storage by simulating the full
storage process and performing a storage experiment with bright time-bin pulses
in $^{151}$Eu$^{3+}$:Y$_2$SiO$_5$. In this context, a compound pulse for
implementing partial readouts in quick succession is introduced and
characterized.",2203.16975v1
2016-03-04,373 K Superconductors,"Experimental evidence of superconductors with critical temperatures above
$373\:K$ is presented. In a family of different compounds we demonstrate the
superconductor state, the transition to normal state above $387\:K$, an
intermediate $242\:K$ superconductor, susceptibility up to $350\:K$, $I-V$
curves at $4.2\:K$ in magnetic field of $12\:T$ and current up to $60\:A$,
$300\:K$ Josephson Junctions and Shapiro steps with radiation of $5\:GHz$ to
$21\:THz$, $300\:K$ tapes tests with high currents up to $3000\:A$ and many
$THz$ images of coins and washers. Due to a pending patent, the exact chemical
characterization and technological processes for these materials are
temporarily withheld and will be presented elsewhere.",1603.01482v1
2016-03-08,"Joint law of the hitting time, overshoot and undershoot for a Lévy process","Let be $(X_t, t\geq 0)$ be a L\'evy process which is the sum of a Brownian
motion with drift and a compound Poisson process. We consider the first passage
time $\tau_x$ at a fixed level $x>0$ by $(X_t, t\geq 0)$ and $K_x:=
X_{\tau_x}-x$ the overshoot and $L_x:= x-X_{\tau_x^-}$ the undershoot. We first
study the regularity of the density of the first passage time. Secondly, we
calculate the joint law of $(\tau_x, K_x, L_x).$",1603.02506v1
2016-03-09,Predicting the optimized thermoelectric performance of MgAgSb,"Using first-principles method and Boltzmann theory, we provide an accurate
prediction of the electronic band structure and thermoelectric transport
properties of alpha-MgAgSb. Our calculations demonstrate that only when an
appropriate exchange-correlation functional is chosen can we correctly
reproduce the semiconducting nature of this compound. By fine tuning the
carrier concentration, the thermoelectric performance of alpha-MgAgSb can be
significantly optimized, which exhibits a strong temperature dependence and
gives a maximum ZT value of 1.7 at 550 K.",1603.02873v1
2016-03-20,Topological String Partition Function on Generalised Conifolds,"We show that the partition function on a generalised conifold $C_{m,n}$ with
${m+n \choose m}$ crepant resolutions can be equivalently computed on the
compound du Val singularity $A_{m+n-1}\times \mathbb C$ with a unique crepant
resolution.",1603.06168v2
2016-03-22,Optimal dividend payments for a two-dimensional insurance risk process,"We consider a two-dimensional optimal dividend problem in the context of two
branches of an insurance company with compound Poisson surplus processes
dividing claims and premia in some specified proportions. We solve the
stochastic control problem of maximizing expected cumulative discounted
dividend payments (among all admissible dividend strategies) until ruin of at
least one company. We prove that the value function is the smallest viscosity
supersolution of the respective Hamilton-Jacobi-Bellman equation and we
describe the optimal strategy. We analize some numerical examples.",1603.07019v3
2016-03-27,"On Arrangements of Six, Seven, and Eight Spheres: Maximal Bonding of Monatomic Ionic Compounds","Let $C(n)$ be the solution to the contact number problem, i.e., the maximum
number of touching pairs among any packing of $n$ congruent spheres in
$\mathbb{R}^3$. We prove the long conjectured values of $C(6)=12, C(7)=15$, and
$C(8)=18$. The proof strategy generalizes under an extensive case analysis to
$C(9)=21, C(10) = 25, C(11) = 29, C(12) = 33$, and $C(13) = 36$. These results
have great importance for condensed matter physics, materials science,
crystallography, organic and physical chemistry of interfaces.",1603.08201v1
2016-12-02,"Characterization of YbNi$_4$(P$_{1-{\it x}}$As$_{\it x}$)$_2$, $x = 0, 0.2$ single crystals grown by Czochralski method","We have investigated large single crystals of YbNi$_4$P$_2$ that were grown
from a levitating melt by the Czochralski method. The new samples facilitate
the determination of the absolute values of the electrical resistivity. Phase
pure polycrystalline samples of the non-magnetic reference LuNi$_4$P$_2$ were
prepared and the electrical resistivity was measured. Furthermore we have grown
a single crystal of the As substituted compound YbNi$_4$(P$_{1-{\it
x}}$As$_{\it x}$)$_2$, $x = 0.2$ and investigated the homogenity of the As
distribution.",1612.00753v1
2016-12-07,Knowledge Representation in Graphs using Convolutional Neural Networks,"Knowledge Graphs (KG) constitute a flexible representation of complex
relationships between entities particularly useful for biomedical data. These
KG, however, are very sparse with many missing edges (facts) and the
visualisation of the mesh of interactions nontrivial. Here we apply a
compositional model to embed nodes and relationships into a vectorised semantic
space to perform graph completion. A visualisation tool based on Convolutional
Neural Networks and Self-Organised Maps (SOM) is proposed to extract high-level
insights from the KG. We apply this technique to a subset of CTD, containing
interactions of compounds with human genes / proteins and show that the
performance is comparable to the one obtained by structural models.",1612.02255v1
2016-12-09,Multivariate compounds with equal number of summands,"The paper considers multivariate discrete random sums with equal number of
summands. Such distributions describe the total claim amount received by a
company in a fixed time point. In Queuing theory they characterize cumulative
waiting times of customers up to time t. In Theory of branching processes they
model the number of heirs at a fixed point in time.
  Here some general properties and formulae for numerical characteristics of
these distributions are derived and some particular cases are considered.",1612.02978v1
2016-12-13,Giant Nernst effect in the incommensurate charge density wave state of P4W12O44,"We report the study of Nernst effect in quasi-low dimensional tungsten bronze
P4W12O44 showing a sequence of Peierls instabilities. We demonstrate that both
condensation of the electronic carriers in the CDW state and the existence of
high-mobility electrons and holes originating from the small pockets remaining
in the incompletely nested Fermi surface give rise to a Nernst effect of a
magnitude similar to that observed in heavy fermion compounds.",1612.04045v1
2016-12-21,Unconventional superconductors: Iron-based diversity,"Nine years ago, superconductors based on the magnetic element iron were
discovered. A flurry of research activity has revealed an unprecedented
diversity of chemical structures and physical properties. Similarly to other
unconventional superconductors, stripe-type antiferromagnetism seems to play an
important role. Particularly interesting is its strong coupling to the crystal
lattice. The systematic comparison of different compounds may allow to identify
key elements in the mechanism of superconductivity and provide guidelines for
the search for new and better superconductors.",1612.07356v1
2016-12-22,Coulomb Correlations in 4d and 5d Oxides from First Principles - or How Spin-Orbit Materials choose their Effective Orbital Degeneracies,"The interplay of spin-orbit interactions and Coulomb correlations has become
a hot topic in condensed matter theory. Here, we review recent advances in
dynamical mean-field theory-based electronic structure calculations for
iridates and rhodates. We stress the notion of the effective degeneracy of the
compounds, which introduces an additional axis into the conventional picture of
a phase diagram based on filling and on the ratio of interactions to bandwidth.",1612.07546v1
2016-12-30,Ultrafast switching of composite order in A$_3$C$_{60}$,"We study the controlled manipulation of the Jahn-Teller metal state of
fulleride compounds using nonequilibrium dynamical mean field theory. This
anomalous metallic state is a spontaneous orbital-selective Mott phase, which
is characterized by one metallic and two insulating orbitals. Using protocols
based on transiently reduced hopping amplitudes or periodic electric fields, we
demonstrate the possibility to switch orbitals between Mott insulating and
metallic on a sub-picosecond timescale, and to rotate the order parameter
between three equivalent states that can be distinguished by their anisotropic
conductance. The Jahn-Teller metal phase of alkali-doped fullerides thus
provides a promising platform for ultrafast persistent memory devices.",1612.09584v1
2017-02-02,Derivation of the Hartree equation for compound Bose gases in the mean field limit,"We consider mixtures of Bose gases of different species. We prove that in the
mean field limit and under suitable conditions on the initial condition a
system composed of two Bose species can be effectively described by a system of
coupled Hartree equations. Moreover, we derive quantitative bounds on the rates
of convergence of the reduced density matrices in Sobolev trace norms. We treat
both the non-relativistic case in the presence of an external magnetic field
$A\in L^2_{\text{loc}}(\R^3;\R^3)$ and the semi-relativistic case.",1702.00827v2
2017-02-05,Prepositions in Context,"Prepositions are highly polysemous, and their variegated senses encode
significant semantic information. In this paper we match each preposition's
complement and attachment and their interplay crucially to the geometry of the
word vectors to the left and right of the preposition. Extracting such features
from the vast number of instances of each preposition and clustering them makes
for an efficient preposition sense disambigution (PSD) algorithm, which is
comparable to and better than state-of-the-art on two benchmark datasets. Our
reliance on no external linguistic resource allows us to scale the PSD
algorithm to a large WikiCorpus and learn sense-specific preposition
representations -- which we show to encode semantic relations and paraphrasing
of verb particle compounds, via simple vector operations.",1702.01466v1
2017-02-15,Quantum state of a frequency comb,"Uncertainties in the frequency parameters of a frequency comb laser, causes
it to represent a mixed quantum state. The formulation of such a quantum state
is compounded by the fact that it contains both particle-number degrees of
freedom and temporal degrees of freedom. Here we develop a formalism in terms
of which such a mixed quantum state can be expressed. For this purpose we also
need to compute the expression for the power spectral density of the frequency
comb laser. We do so by taking the uncertainties in the frequency parameters
into account.",1702.04514v2
2017-02-16,Gaussian and Sparse Processes Are Limits of Generalized Poisson Processes,"The theory of sparse stochastic processes offers a broad class of statistical
models to study signals. In this framework, signals are represented as
realizations of random processes that are solution of linear stochastic
differential equations driven by white L\'evy noises. Among these processes,
generalized Poisson processes based on compound-Poisson noises admit an
interpretation as random L-splines with random knots and weights. We
demonstrate that every generalized L\'evy process-from Gaussian to sparse-can
be understood as the limit in law of a sequence of generalized Poisson
processes. This enables a new conceptual understanding of sparse processes and
suggests simple algorithms for the numerical generation of such objects.",1702.05003v1
2017-02-24,Electronic properties and applications of MXenes: a theoretical review,"Recent chemical exfoliation of layered MAX phase compounds to novel
two-dimensional transition metal carbides and nitrides, so called MXenes, has
brought new opportunity to materials science and technology. This review
highlights the computational attempts that have been made to understand the
physics and chemistry of this very promising family of advanced two-dimensional
materials, and to exploit their novel and exceptional properties for electronic
and energy harvesting applications.",1702.07442v1
2017-06-01,Superconductivity in the Ferromagnet URhGe under uniaxial pressure,"Uniaxial pressure applied in the b crystallographic direction perpendicular
to spontaneous magnetization in heavy fermion ferromagnet URhGe strongly
stimulates superconductivity in this compound. The phenomenological approach
allows point out two mechanisms of superconducting temperature raising. They
originates from stimulation by the uniaxial stress both intraband and interband
amplitudes of triplet Cooper pairing. The phenomenon of reentrant
superconductivity under magnetic field along b-axis is also strongly sensitive
to the uniaxial stress in the same direction. The uniaxial stress accelerates
suppression the Curie temperature by the transversal magnetic field. The
emergence of the first order transition to the paramagnetic state occurs at
much lower field than in the absence of uniaxial stress.",1706.00354v1
2017-06-02,Magnetic structure of the MnGe helimagnet and representation analysis,"In the light of recent results obtained for the prototype helimagnet MnSi we
examine the possible magnetic structures of compounds of the same family,
consistent with the crystal symmetries when the magnetic propagation vector is
parallel to the [001] axis. The analysis of a published muon spin rotation
spectrum recorded in MnGe [Phys. Rev. B 93, 174405 (2016)] shows no deviation
from the canonical helimagnetic structure, unlike in MnSi. This qualitative
difference calls for further theoretical works on chiral magnets.",1706.00588v1
2017-06-08,Eigenvalue Statistics for higher rank Anderson model over Canopy tree,"This work is focused on the local eigenvalue statistics for the Anderson
tight binding model with non-rank-one perturbations over the canopy tree, at
large disorder. On the Hilbert space $\ell^2(\mathcal{C})$, where $ \mathcal{C}
$ is the canopy tree, the random operator we consider is
$\Delta_{\mathcal{C}}+\sum_{y\in J}\omega_y P_y$, where $\Delta_{\mathcal{C}}$
is the adjacency operator over the tree, $\{\omega_y\}_{y\in J}$ are i.i.d real
random variables following some absolutely continuous distribution having a
bounded density with compact support, and $P_y$ are projections on
$\ell^2(\{x\in\mathcal{C}: dist(y,x)< m_0 \& y\prec x\})$. For this operator,
we show that, the eigenvalue-counting point process converges to compound
Poisson process.",1706.02488v1
2017-06-18,Ferroelectricity and Antiferroelectricity in Elemental Group-V Monolayer Materials,"Ferroelectricity is usually found in compound materials composed by different
elements. Here, based on first-principles calculations, we reveal the first
example of spontaneous electrical polarization and ferroelectricity in stable
two-dimensional elemental materials: elemental Group-V (As, Sb, and Bi)
monolayers. The polarization is due to the spontaneous lattice distortion with
atomic layer buckling. Interestingly, for Bi monolayer, apart from the
ferroelectric phase, we find that it can also host an antiferroelectric phase.
The Curie temperatures of these elemental materials can be higher than room
temperature, making them promising for realizing ultrathin ferroelectric
devices of broad interest.",1706.05629v1
2017-06-21,The dynamic three-dimensional Anderson localization of optical fields in active percolating systems,"We study three-dimensional optical Anderson localization in medium with a
percolating disorder, where the percolating clusters are filled by the light
nanoemitters in the excited state. The peculiarity of situation is that in such
materials the field clusters join a fractal radiating system where the light is
both emitted and scattered by the inhomogeneity of clusters. Our numerical FDTD
simulations found that in this nonlinear compound the number of localized field
bunches drastically increases after the lasing starts. At longer times the
bunches leave nonlinear percolating structure and are radiated from the medium.
Monitoring the output of system allows to observe experimentally such dynamic
localized bunches in three-dimensional setup.",1706.06721v1
2017-06-19,Ir d-band Derived Superconductivity in the Lanthanum-Iridium System LaIr3,"The electronic properties of the heavy metal superconductor LaIr3 are
reported. The estimated superconducting parameters obtained from physical
properties measurements indicate that LaIr3 is a BCS-type superconductor.
Electronic band structure calculations show that Ir d- states dominate the
Fermi level. A comparison of electronic band structures of LaIr3 and LaRh3
shows that the Ir-compound has a strong spin-orbit-coupling effect, which
creates a complex Fermi surface.",1706.06885v2
2017-06-22,Self-organized compound pattern and pulsation of dissipative solitons in a passively mode-locked fiber laser,"We experimentally observe soliton self-organization and pulsation in a
passively mode-locked fiber laser. The optomechanical interaction in the
optical fiber is key to the formation of equidistant soliton bunches. These
solitons simultaneously undergo a pulsation process with a period corresponding
to tens of the cavity round trip time. Using the dispersive Fourier
transformation technique, we find that the Kelly sidebands in the shot-to-shot
spectra appear periodically, synchronizing with the pulsation.",1706.07172v1
2017-06-27,Orbital mismatch boosting nematic instability in iron-based superconductors,"We derive the effective action for the collective spin modes in iron-based
superconductors. We show that, due to the orbital-selective nature of spin
fluctuations, the magnetic and nematic instabilities are controlled by the
degrees of orbital nesting between electron and hole pockets. Within a
prototypical three-pockets model the hole-electron orbital mismatch is found to
boost spin-nematic order. This explains the enhancement of the nematic order in
FeSe as compared to 122 compounds, and its suppression under pressure, where
the emergence of the second hole pocket compensates the orbital mismatch of the
three-pockets configuration.",1706.08953v2
2017-10-02,Electrical resistivity across the tricriticality in itinerant ferromagnet,"We investigate the discontinuous ferromagnetic phase diagram near tricritical
point in UCo 1-x Ru x Al compounds by electrical resistivity measurements.
Separation of phases in UCo 0.995 Ru 0.005 Al at ambient pressure and in UCo
0.990 Ru 0.010 Al at pressure of 0.2 GPa and disappearance of ferromagnetism at
0.4 GPa is confirmed. The exponent of temperature dependence of electrical
resistivity implies change from Fermi liquid behavior to non-Fermi liquid at
0.2 GPa and reaches minimum at 0.4 GPa. Our results are compared to results
obtained on the pure UCoAl and explanation for different exponents is given.",1710.00860v1
2018-04-02,"Fluctuations in the $^{235}$U(n,f) cross section","We examine the autocorrelation function of the $^{235}$U(n,f) reaction with a
view to quantify the presence of intermediate structure in the cross section.
Fluctuations due to compound nucleus resonances on the eV energy scale are
clearly visible up to $\sim100$ keV neutron energies. Structure on the one-keV
energy scale is not present as a systematic feature of the correlation
function, although it is present in the data covering the region around 20 keV.",1804.00364v1
2018-04-06,Superconductivity in intercalated buckled two-dimensional materials: KGe$_2$,"Germanene has emerged as a novel two-dimensional material with various
interesting properties and applications. Here we report the possibility of
superconductivity in a stable potassium intercalated germanene compound,
KGe$_2$, with a transition temperature $T_c \sim 11$ K, and an electron-phonon
coupling of 1.9. Applying a 5\% tensile strain, which reduces the buckling
height by 4.5\%, leads to the reduction of the electron-phonon coupling by 11\%
and a slight increase in $T_c \sim 12$ K. That is, strong electron-phonon
coupling results from the buckled structure of the germanene layers. Despite
being an intercalated van der Waals material similar to intercalated graphite
superconductors, it does not possess an occupied interlayer state.",1804.02304v1
2018-04-19,Regular variation and free regular infinitely divisible laws,"In this article the relation between the tail behaviours of a free regular
infinitely divisible (positively supported) probability measure and its L\'evy
measure is studied. An important example of such a measure is the compound free
Poisson distribution, which often occurs as a limiting spectral distribution of
certain sequences of random matrices. We also describe a connection between an
analogous classical result of Embrechts et al. [1979] and our result using the
Bercovici-Pata bijection.",1804.07119v2
2018-04-25,Degree based Topological indices of Hanoi Graph,"There are various topological indices for example distance based topological
indices and degree based topological indices etc. In QSAR/QSPR study,
physiochemical properties and topological indices for example atom bond
connectivity index, fourth atom bond connectivity index, Randic connectivity
index, sum connectivity index, and so forth are used to characterize the
chemical compound. In this paper we computed the edge version of atom bond
connectivity index, fourth atom bond connectivity index, Randic connectivity
index, sum connectivity index, geometric-arithmetic index and fifth
geometric-arithmetic index of Double-wheel graph and Hanoi graph. The results
are analyzed and the general formulas are derived for the above mentioned
families of graphs.",1804.09431v1
2018-04-25,Diffusion-controlled growth of phases in metal-tin systems related to microelectronics packaging,"The electro–mechanical connection between under bump metallization (UBM) and
solder in flip–chip bonding is achieved by the formation of brittle
intermetallic compounds (IMCs) during the soldering process. These IMCs
continue to grow in the solid–state during storage at room temperature and
service at an elevated temperature leading to degradation of the contacts. In
this thesis, the diffusion–controlled growth mechanism of the phases and the
formation of the Kirkendall voids at the interface of UBM (Cu, Ni, Au, Pd, Pt)
and Sn (bulk/electroplated) are studied extensively.",1804.09595v1
2019-03-03,Database-driven high-throughput study for hybrid perovskite coating materials,"We developed a high-throughput screening scheme to acquire candidate coating
materials for hybrid perovskites. From more than 1.8 million entries of an
inorganic compound database, we collected 93 binary and ternary materials with
promising properties for protectively coating halide-perovskite photoabsorbers
in perovskite solar cells. These candidates fulfill a series of criteria,
including wide band gaps, abundant and non-toxic elements, water-insoluble, and
small lattice mismatch with surface models of halide perovskites.",1903.00898v1
2019-03-07,Calculation of the Anisotropic Coefficients of Thermal Expansion: A First-Principles Approach,"Predictions of the anisotropic coefficients of thermal expansion are needed
to not only compare to experimental measurement, but also as input for
macroscopic modeling of devices which operate over a large temperature range.
While most current methods are limited to isotropic systems within the
quasiharmonic approximation, our method uses first-principles calculations and
includes anharmonic effects to determine the temperature-dependent properties
of materials. These include the lattice parameters, anisotropic coefficients of
thermal expansion, isothermal bulk modulus, and specific heat at constant
pressure. Our method has been tested on two compounds (Cu and AlN) and predicts
thermal properties which compare favorably to experimental measurement over a
wide temperature range.",1903.02783v1
2019-03-20,Structural Instability and Magnetism of Superconducting KCr$_3$As$_3$,"We find a lattice instability in the superconductor KCr$_3$As$_3$,
corresponding to a distortion of the Cr metallic wires in the crystal
structure. This distortion couples strongly to both the electronic and magnetic
properties, in particular by making the electronic structure much more nearly
one-dimensional, and by shifting the compound away from magnetism. We discuss
the implications of these results in the context of the possibly unconventional
superconductivity of this phase.",1903.08457v1
2019-05-02,Method for real-time measurement of the nonlinear refractive index,"In this work, we propose a novel method for continuous real-time measurement
of the dynamics of the nonlinear refractive index n2. This is particularly
important for characterizing phenomena or materials (such as biological
tissues, gases and other compounds) whose nonlinear behavior or structure
varies rapidly with time. The proposed method ingeniously employs two powerful
tools: the spectral broadening induced by self-phase modulation and the
real-time spectral analysis using the dispersive Fourier transformation. The
feasibility of the technique is experimentally demonstrated, achieving
high-speed measurements at rates of several MHz.",1905.00942v1
2019-05-06,Computation of topological phase diagram of disordered Pb$_{1-x}$Sn$_{x}$Te using the kernel polynomial method,"We present an algorithm to determine topological invariants of inhomogeneous
systems, such as alloys, disordered crystals, or amorphous systems. Based on
the kernel polynomial method, our algorithm allows us to study samples with
more than $10^7$ degrees of freedom. Our method enables the study of large
complex compounds, where disorder is inherent to the system. We use it to
analyse Pb$_{1-x}$Sn$_{x}$Te and tighten the critical concentration for the
phase transition.",1905.02215v2
2019-05-08,Symmetry Enforced Dirac Points in Antiferromagnetic Semiconductors,"It is shown that the symmetry enforced Dirac points exist at some time
reversal symmetric momenta in antiferroemgnetic compound GdB$_4$. These Dirac
points may be controlled by the external magnetic field or by the deformation
of the crystal. Application of the external magnetic field leads to splitting
of these points into Weyl points or to opening of a gap depending on the field
direction. The application of the symmetry breaking deformation also opens a
gap in the spectrum. Suppression of the antiferromagnetic order leads to the
formation of the nodal line instead of the Dirac points. This indicates that
the symmetry enforced Dirac semimetals may be effectively used in different
spintronic devices.",1905.02943v1
2019-05-07,Neutron capture cross sections from surrogate reaction data and theory: connecting the pieces with a Markov-Chain Monte Carlo approach,"The neutron capture cross section for $^{90}Zr(n, \gamma)$ has recently been
determined using surrogate $^{92}Zr(p, d\gamma)$ data and nuclear reaction
theory. That work employed an approximate fitting method based on Bayesian
Monte Carlo sampling to determine parameters needed for calculating the
$^{90}Zr(n, \gamma)$ cross section. Here, we improve the approach by
introducing a more sophisticated Markov Chain Monte Carlo sampling method. We
present preliminary results.",1905.03055v2
2019-05-22,A Finite Horizon Optimal Switching Problem with Memory and Application to Controlled SDDEs,"We consider an optimal switching problem where the terminal reward depends on
the entire control trajectory. We show existence of an optimal control by
applying a probabilistic technique based on the concept of Snell envelopes. We
then apply this result to solve an impulse control problem for stochastic delay
differential equations driven by a Brownian motion and an independent compound
Poisson process. Furthermore, we show that the studied problem arises naturally
when maximizing the revenue from operation of a group of hydro-power plants
with hydrological coupling.",1905.09473v3
2019-09-05,Investigations of the superconducting ground state of Zr$_{3} $Ir: Introducing a new noncentrosymmetric superconductor,"Superconductivity in materials whose crystal structure lacks inversion
symmetry is a prime candidate for unconventional superconductivity. A new
noncentrosymmetric compound Zr$_{3}$Ir crystallizes in a tetragonal $ \alpha
$-V$_{3} $S structure. The magnetization, specific heat and muon spin rotation
confirm s-wave superconductivity, having a transition temperature T$_{c}$ = 2.3
K. Muon spin relaxation confirms the preservation of time reversal symmetry in
the superconducting ground state.",1909.02216v2
2019-12-16,Synthesis of Electron- and Hole-Doped Bulk BaFe2As2 Superconductors by Mechanical Alloying,"Here, we report the successful synthesis of electron- (Ni) and hole- (K)
doped bulk BaFe2As2 compounds by means of mechanical alloying (MA) process. The
MA technique allows one to obtain amorphous phase BaFe2As2 with a homogeneous
distribution of doping atoms at room temperature without continuous heating. We
found the optimum time for high-energy milling is in the range between 1-1.5
hours. Using pre-synthesised FeAs and NiAs precursors, we successfully obtained
BaFe2-xNixAs2 and Ba1-xKxFe2As2 superconducting bulk samples after short-range
heat treatment. This method can be easily scaled according to industrial needs
to provide high-quality bulk superconducting material for wires, trapped field
magnets and other applications.",1912.07264v1
2019-12-16,PDQ & TMK + PDQF -- A Test Drive of Facebook's Perceptual Hashing Algorithms,"Efficient and reliable automated detection of modified image and multimedia
files has long been a challenge for law enforcement, compounded by the harm
caused by repeated exposure to psychologically harmful materials. In August
2019 Facebook open-sourced their PDQ and TMK + PDQF algorithms for image and
video similarity measurement, respectively. In this report, we review the
algorithms' performance on detecting commonly encountered transformations on
real-world case data, sourced from contemporary investigations. We also provide
a reference implementation to demonstrate the potential application and
integration of such algorithms within existing law enforcement systems.",1912.07745v1
2019-12-17,Two-sided optimal stopping for Lévy processes,"Infinite horizon optimal stopping problems for a L\'evy processes with a
two-sided reward function are considered. A two-sided verification theorem is
presented in terms of the overall supremum and the overall infimum of the
process. A result to compute the angle of the value function at the optimal
thresholds of the stopping region is given. To illustrate the results, the
optimal stopping problem of a compound Poisson process with two-sided
exponential jumps and a two-sided payoff function is solved. In this example,
the smooth-pasting condition does not hold.",1912.08171v1
2020-02-20,Transverse asymmetry of $γ$ rays from neutron-induced compound states of ${}^{140}{\rm La}$,"A correlation term ${{ \sigma}_{n} }\cdot ({ k_{n}\times k_\gamma}) $ in the
${}^{139}{\rm La}(\vec{n},\gamma)$ reaction has been studied utilizing
epithermal polarized neutrons and germanium detectors. The transverse asymmetry
for single $\gamma$-ray transition was measured to be $0.60\pm0.19$ in the
$p$-wave resonance.",2002.08655v1
2020-02-26,Exceptional band touching for strongly correlated systems in equilibrium,"Quasi-particles described by Green's functions of equilibrium systems exhibit
non-Hermitian topological phenomena because of their finite lifetime. This
non-Hermitian perspective on equilibrium systems provides new insights into
correlated systems and attracts much interest because of its potential to solve
open questions in correlated compounds. In this paper, we provide a concise
review of the non-Hermitian topological band structures for quantum many-body
systems in equilibrium as well as their classification.",2002.11265v1
2020-03-03,Liquid crystal nose based on chiral photonic band gap materials: principles of selective response,"Novel liquid crystalline (LC) compositions are suggested and studied as
elements of LC-nose. This allows for optical detection of several volatile
organic compounds (VOCs). Ethanol, toluene, pyridine and acetic acid were
detected by means of colorimetric and spectroscopic techniques during their
diffusion inside chiral elements of LC-nose. Selectivity to different VOCs is
enhanced by means of components of liquid crystal matrix with different
viscosity, affinities to the solvents, and abilities to form hydrogen bonding.",2003.01832v1
2020-03-12,Pairing superbunching with compounded non-linearity in a resonant transition,"Through a quantitative analysis of an atomic transition driven strongly by
quantized electromagnetic fields of various quantum states, we explore the role
of quantum fluctuations on the behavior of the system. The emphasis is on
fields with super-Poissonian statistics manifested in photon bunching, with the
case of squeezed vacuum radiation serving as a prototype of superbuching. When
combined with non-linearly coupling of the resonant states, bunching and
superbunching lead to counter-intuitive behavior. The connection to recent
progress in squeezed vacuum sources and the opportunity for experimental
investigation, as well as challenging open theoretical problems are also
outlined.",2003.05717v1
2020-06-11,Loop currents in ladder cuprates: A dynamical mean field theory study,"We investigate the possibility of spontaneous loop currents in the two-leg
ladder cuprate Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ by applying cluster dynamical
mean field theory (CDMFT) to a seven-band Hubbard model for that compound, with
an exact diagonalization solver. We sample several values of the local
interaction $U_d$ and of the Cu-O energy difference $E_{pd}$, by applying an
external field that induces loop currents. We find no instance of spontaneous
loop currents once the external field is brought to zero.",2006.06128v1
2020-06-12,The structure of Zeckendorf expansions,"In this paper we classify the Zeckendorf expansions according to their digit
blocks. It turns out that if we consider these digit blocks as labels on the
Fibonacci tree, then the numbers ending with a given digit block in their
Zeckendorf expansion appear as compound Wythoff sequences in a natural way on
this tree. Here the digit blocks consisting of only $0$'s are an exception. We
also give a second description of these occurrence sequences as generalized
Beatty sequences. Finally, we characterize the numbers with a fixed digit block
occurring at an arbitrary fixed position in their Zeckendorf expansions, and
determine their densities.",2006.06970v1
2020-06-16,Random potentials for Markov processes,"The paper is devoted to the integral functionals $\int_0^\infty
f(X_t)\,{\mathrm{d}t}$ of Markov processes in $\X$ in the case $d\ge 3$. It is
established that such functionals can be presented as the integrals $\int_{\X}
f(y) \G(x, \mathrm{d}y, \omega)$ with vector valued random measure $\G(x,
\mathrm{d}y, \omega)$. Some examples such as compound Poisson processes,
Brownian motion and diffusions are considered.",2006.09047v1
2020-06-18,A unified framework for equivalences in social networks,"A key concern in network analysis is the study of social positions and roles
of actors in a network. The notion of ""position"" refers to an equivalence class
of nodes that have similar ties to other nodes, whereas a ""role"" is an
equivalence class of compound relations that connect the same pairs of nodes.
An open question in network science is whether it is possible to simultaneously
perform role and positional analysis. Motivated by the principle of
functoriality in category theory we propose a new method that allows to tie
role and positional analysis together. We illustrate our methods on two
well-studied data sets in network science.",2006.10733v1
2020-04-28,Thermal Stability of Superconductors,"A stability criterion is worked out for the superconducting phase. The
validity of a prerequisite, established previously for persistent currents, is
thereby confirmed. Temperature dependence is given for the specific heat and
concentration of superconducting electrons in the vicinity of the critical
temperature $T_c$. The isotope effect, mediated by electron-phonon interaction
and hyperfine coupling, is analyzed. Several experiments, intended at
validating this analysis, are presented, including one giving access to the
specific heat of high-$T_c$ compounds.",2006.13672v2
2020-07-01,On asymptotic properties of high moments of compound Poisson distribution,"We study asymptotic behavior of the moments $M_k(\lambda)$ of the sum
$X_1+\dots+X_{N_\lambda}$, where $N_\lambda$ follows the Poisson probability
distribution with mean value $\lambda$ and $\{X_j\}$ is a family of i.i.d.
random variables also independent from $N_\lambda$. We obtain an explicit
expression for the leading term of $M_k(\lambda)$ as $k\to\infty$ and study it
in dependence of the asymptotic behavior of $\lambda= \lambda_k$.",2007.00379v3
2020-07-04,Data-Mining Element Charges in Inorganic Materials,"Oxidation states are well-established in chemical science teaching and
research. We data-mine more than 168,000 crystallographic reports to find an
optimal allocation of oxidation states to each element. In doing so we uncover
discrepancies between text-book chemistry and reported charge states observed
in materials. We go on to show how the oxidation states we recommend can
significantly facilitate materials discovery and heuristic design of novel
inorganic compounds.",2007.02085v1
2020-07-08,Complex magnetic structure in Ba5Ru3O12 with isolated Ru3O12-trimer,"We report detailed magnetic, transport, heat-capacity, and neutron
diffraction measurements of Ba5Ru3O12, a compound consisting of isolated Ru3O12
trimers. We show that this system develops long-range antiferromagnetic
ordering at 60 K (TN) without structural distortion and metal-insulator-type
transition, which is in sharp contrast to other Barium Ruthenate trimer systems
such as 9R-BaRuO3 and Ba4Ru3O10. A complex magnetic structure is revealed which
is attributable to the magnetic frustration due to competing exchange
interactions between Ru ions on different crystallographic sites within the
Ru3O12 trimer.",2007.03854v2
2020-07-13,Einstein-aether theory in Weyl integrable geometry,"We study the Einstein-aether theory in Weyl integrable geometry. The scalar
field which defines the Weyl affine connection is introduced in the
gravitational field equation. We end up with an Einstein-aether scalar field
model where the interaction between the scalar field and the aether field has a
geometric origin. The scalar field plays a significant role in the evolution of
the gravitational field equations. We focus our study on the case of
homogeneous and isotropic background spacetimes and study their dynamical
evolution for various cosmological models.",2007.06435v1
2020-07-27,Optimal construction of a layer-ordered heap,"The layer-ordered heap (LOH) is a simple, recently proposed data structure
used in optimal selection on $X+Y$, thealgorithm with the best known runtime
for selection on $X_1+X_2+\cdots+X_m$, and the fastest method in practice for
computing the most abundant isotope peaks in a chemical compound. Here, we
introduce a few algorithms for constructing LOHs, analyze their complexity, and
demonstrate that one algorithm is optimal for building a LOH of any rank
$\alpha$. These results are shown to correspond with empirical experiments of
runtimes when applying the LOH construction algorithms to a common task in
machine learning.",2007.13356v2
2020-09-03,Exposing the hidden influence of selection rules on phonon-phonon scattering by pressure and temperature tuning,"Using ab initio calculations, we show that the hidden influence of selection
rules on three-phonon scattering can be exposed through anomalous signatures in
the pressure ($P$) and temperature ($T$) dependence of the thermal
conductivities, $\kappa$, of certain compounds. Boron phosphide reveals such
underlying behavior through an exceptionally sharp initial rise in $\kappa$
with increasing $P$, which may be the steepest of any material, and also a peak
and decrease in $\kappa$ at high $P$. These features are in stark contrast to
the measured behavior for many solids, and occur at experimentally accessible
conditions. Similar anomalous behavior is predicted for silicon carbide and
other related materials.",2009.01464v1
2020-09-04,Van der Waals Layered Ferroelectric CuInP2S6: Physical Properties and Device Applications,"Copper indium thiophosphate, CuInP2S6, has attracted much attention in recent
years due to its van der Waals layered structure and robust ferroelectricity at
room temperature. In this review, we aim to give an overview of the various
properties of CuInP2S6, covering structural, ferroelectric, dielectric,
piezoelectric and transport properties, as well as its potential applications.
We also highlight the remaining questions and possible research directions
related to this fascinating material and other compounds of the same family.",2009.02097v1
2020-09-07,Why Not Simply Translate? A First Swedish Evaluation Benchmark for Semantic Similarity,"This paper presents the first Swedish evaluation benchmark for textual
semantic similarity. The benchmark is compiled by simply running the English
STS-B dataset through the Google machine translation API. This paper discusses
potential problems with using such a simple approach to compile a Swedish
evaluation benchmark, including translation errors, vocabulary variation, and
productive compounding. Despite some obvious problems with the resulting
dataset, we use the benchmark to compare the majority of the currently existing
Swedish text representations, demonstrating that native models outperform
multilingual ones, and that simple bag of words performs remarkably well.",2009.03116v2
2020-09-08,Evidence for a soft-phonon-mode-driven Peierls-type distortion in Sc$_3$CoC$_4$,"We provide experimental and theoretical evidence for the realization of the
Peierls-type structurally distorted state in the quasi-one-dimensional
superconductor Sc$_3$CoC$_4$ by a phonon-softening mechanism. The transition
from the high- to the final low-temperature phase below 80K proceeds via an
extended intermediate temperature regime between 80K and 150K characterized by
phonon-driven atom displacements. In support of the low-dimensional character
of the title compound we find a highly anisotropic correlation-length of these
dynamic distortions.",2009.03833v1
2020-09-10,Super-resolution imaging with an achromatic multi-level diffractive microlens array,"Compound eyes found in insects provide intriguing sources of biological
inspiration for miniaturized imaging systems. Inspired by such insect eye
structures, we demonstrate an ultrathin arrayed camera enabled by a flat
multilevel diffractive microlens array for super-resolution visible imaging. We
experimentally demonstrated that the microlens array can achieve large fill
factor (hexagonal close packing with pitch=120um), thickness of 2.6um, and
diffraction-limited (strehl ratio = 0.88) achromatic performance in the visible
band (450nm to 650nm). We also demonstrate super-resolution imaging with
resolution improvement of 1.4 times by computationally merging 1600 images in
the array.",2009.05068v1
2020-09-17,Resistance of the cell wall to degradation is a critical parameter for isolation of high quality RNA from natural isolates of Bacillus subtilis,"Natural isolates of Bacillus subtilis are known for their ability to produce
a large panel of bioactive compounds. Unfortunately, their recalcitrance to
conventional molecular techniques limits their transcript studies. In this
work, diYculties to isolate RNA attributed to the cell wall were overcome,
Wnally authorising powerful RT-PCR's.",2009.08176v1
2020-09-17,"Folklore, the Borromean rings, the icosahedron, and three dimensions","There is a relationship between the Borromean rings, the icosahedron and
something called the Poincar\'e homology sphere. This relationship is explored
in a wandering path that introduces fundamental ideas from topology and a
geometric construction of an icosahedral compound of octahedra. This
exploration results in proofs that the orientation-preserving symmetry group of
an icosahedron is the alternating group of five symbols, the fact that the
Borromean rings are linked, and background related to the Poincar\'e
conjecture. This is an exposition of known results aimed at undergraduates.",2009.09836v1
2020-10-11,Autonomous Parking by Successive Convexification and Compound State Triggers,"In this paper, we propose an algorithm for optimal generation of nonholonomic
paths for planning parking maneuvers with a kinematic car model. We demonstrate
the use of Successive Convexification algorithms (SCvx), which guarantee path
feasibility and constraint satisfaction, for parking scenarios. In addition, we
formulate obstacle avoidance with state-triggered constraints which enables the
use of logical constraints in a continuous formulation of optimization
problems. This paper contributes to the optimal nonholonomic path planning
literature by demonstrating the use of SCvx and state-triggered constraints
which allows the formulation of the parking problem as a single optimisation
problem. The resulting algorithm can be used to plan constrained paths with
cusp points in narrow parking environments.",2010.05201v1
2020-10-20,Absence of high temperature superconductivity in hydrides under pressure,"The long-sought goal of room-temperature superconductivity has reportedly
recently been realized in a carbonaceous sulfur hydride compound under high
pressure, as reported by Snider et al. [1]. The evidence presented in that
paper is stronger than in other similar recent reports of high temperature
superconductivity in hydrides under high pressure [2-7], and has been received
with universal acclaim [8-10]. Here we point out that features of the
experimental data shown in Ref. [1] indicate that the phenomenon observed in
that material is not superconductivity. This observation calls into question
earlier similar claims of high temperature conventional superconductivity in
hydrides under high pressure based on similar or weaker evidence [2-7].",2010.10307v1
2020-11-05,Orientational decoherence within molecules and emergence of the molecular shape,"The question of classicality is addressed in relation with the shape of the
nuclear skeleton of molecular systems. As the most natural environment, the
electrons of the molecule are considered as continuously monitoring agents for
the nuclei. For this picture, an elementary formalism of decoherence theory is
developed and numerical results are presented for few-particle systems. The
numerical examples suggest that the electron-nucleus Coulomb interaction is
sufficient for inducing a blurred shape with strong quantum coherences in
compounds of the lightest elements, H$_2$, D$_2$, T$_2$, and HeH$^+$.",2011.02810v2
2020-11-09,Explaining Deep Graph Networks with Molecular Counterfactuals,"We present a novel approach to tackle explainability of deep graph networks
in the context of molecule property prediction tasks, named MEG (Molecular
Explanation Generator). We generate informative counterfactual explanations for
a specific prediction under the form of (valid) compounds with high structural
similarity and different predicted properties. We discuss preliminary results
showing how the model can convey non-ML experts with key insights into the
learning model focus in the neighborhood of a molecule.",2011.05134v1
2020-11-27,Low-temperature phase transitions in some quaternary solid solutions of IV-VI semiconductors,"Samples of PbS$_x$Se$_y$Te$_{1-x-y}$, Pb$_{1-x}$Sn$_x$Te$_{1-y}$Se$_y$, and
Pb$_{1-x}$Sn$_x$Te$_{1-y}$S$_y$ quaternary solid solutions were investigated in
the 4--200~K temperature range using electrical and X-ray methods. The regions
where low-temperature phase transitions occur were established. It was shown
that phase transitions in these solid solutions are associated with off-center
S and Sn ions. The dependence of the phase transition temperature on the
composition of solid solutions can be qualitatively described taking into
account the influence of substitutional disorder on the ordering and tunneling
of off-center ions.",2011.13992v1
2020-12-03,Dirac surface states in magnonic analogs of topological crystalline insulators,"We propose magnonic analogs of topological crystalline insulators which
possess Dirac surface states protected by the combined symmetry of
time-reversal and half translation. Constructing models of the topological
magnon systems, we demonstrate that the energy current flows through the
systems in response to an electric field, owing to the Dirac surface states
with the spin-momentum locking. We also propose a realization of the magnonic
analogs of topological crystalline insulators in a magnetic compound CrI$_{3}$
with a monoclinic structure.",2012.02034v2
2020-12-11,Ruin Probabilities for a Sparre Andersen Model with Investments,"We study a Sparre Andersen model in which the business activity of the
company is described by a compound renewal process with drift assuming that the
capital reserves are invested in a risky asset. The price of the latter is
assumed to evolve according to a geometric L\'evy process. We prove that the
asymptotic behavior of the ruin probability depends to a large extent only on
the properties of the price process.",2012.06673v1
2020-11-14,Towards room-temperature superconductivity,"By taking advantage of a stability criterion established recently, the
critical temperature $T_c$ is reckoned with help of the microscopic parameters,
characterising the normal and superconducting electrons, namely the
independent-electron band structure and a \textit{repulsive} two-electron
force. The emphasis is laid on the sharp $T_c$ dependence upon electron
concentration and inter-electron coupling, which might offer a practical route
toward higher $T_c$ values and help to understand why high-$T_c$ compounds
exhibit such remarkable properties.",2012.09611v2
2020-12-25,Material Optimization of Potential High-$T_{\text{c}}$ Superconducting Single-layer Cuprates,"We investigated the material parameters of several single-layer cuprates,
including those with fluorinated buffer layers, with the aim of identifying
possible high-temperature superconductors. To evaluate the material parameters,
we use the Wannierization techniques and the constrained random phase
approximation. The obtained single-band Hubbard models are studied using the
fluctuation-exchange approximation. Comparison among several cuprates reveals
unknown high-$T_{\text{c}}$ superconductors. In, Ga, Al, and Cd compounds in
particular show the potential to exhibit higher-$T_{\text{c}}$
superconductivity than Hg1201.",2012.13472v1
2021-01-12,From high-$T_c$ to low-$T_c$: Multi-orbital effects in transition metal oxides,"Despite the structural resemblance of certain cuprate and nickelate parent
compounds there is a striking spread of $T_c$ among such transition metal oxide
superconductors. We adopt a minimal two-orbital $e_g$ model which covers
cuprates and nickelate heterostructures in different parametric limits, and
analyse its superconducting instabilities. The joint consideration of
interactions, doping, Fermiology, and in particular the $e_g$ orbital splitting
allows us to explain the strongly differing pairing propensities in cuprate and
nickelate superconductors.",2101.04689v1
2021-01-14,The magnetic field induced ferromagnetism in EuPd$_2$Sn$_4$ novel compound,"We report on crystal structure, magnetic and thermal physical properties of
EuPd$_2$Sn$_4$ stannide. From the magnetic susceptibility measurements a
divalent state of Eu rare earth element was determined together with an
antiferromagnetic (AFM) order at 11 K. By applying magnetic field, the magnetic
behavior variation reveals a complex magnetic structure. Above a critical field
Bc a ferromagnetic (FM)-like character starts to prevail. AFM and FM regimes
are separated by a metamagnetic region. Heat capacity measurements confirm this
behavior.",2101.05854v1
2021-01-15,"Frustration, strain and phase co-existence in the mixed valent hexagonal iridate Ba$_{3}$NaIr$_{2}$O$_{9}$","Using detailed synchrotron diffraction, magnetization, thermodynamic and
transport measurements, we investigate the relationship between the mixed
valence of Ir, lattice strain and the resultant structural and magnetic ground
states in the geometrically frustrated triple perovskite iridate
Ba$_{3}$NaIr$_{2}$O$_{9}$. We observe a complex interplay between lattice
strain and structural phase co-existence, which is in sharp contrast to what is
typically observed in this family of compounds. The low temperature magnetic
ground state is characterized by the absence of long range order, and points
towards the condensation of a cluster glass state from an extended regime of
short range magnetic correlations.",2101.06075v1
2021-01-16,Modeling of fluid flow in a flexible vessel with elastic walls,"We exploit a two-dimensional model [7], [6] and [1] describing the elastic
behavior of the wall of a flexible blood vessel which takes interaction with
surrounding muscle tissue and the 3D fluid flow into account. We study time
periodic flows in a cylinder with such compound boundary conditions. The main
result is that solutions of this problem do not depend on the period and they
are nothing else but the time independent Poiseuille flow. Similar solutions of
the Stokes equations for the rigid wall (the no-slip boundary condition) depend
on the period and their profile depends on time.",2101.06533v1
2021-01-21,High-average-power femtosecond laser at 258 nm,"We present an ultrafast fiber laser system delivering 4.6 W average power at
258 nm based on two-stage fourth-harmonic generation in beta barium borate
(BBO). The beam quality is close to diffraction limited with an M2- value of
1.3 x 1.6. The pulse duration is 150 fs, which potentially is compressible down
to 40 fs. A plain BBO and a Sapphire-BBO compound are compared with respect to
the achievable beam quality in the conversion process. This laser is applicable
in scientific and industrial fields. Further scaling to higher average power is
discussed",2101.08500v1
2021-01-28,CP-Symmetry in Scattering of Neutrinos from Nuclei,"The elastic scattering of longitudinal and transversal neutrinos on a
spinless nucleus have been discussed taking into account the charge, magnetic,
anapole and electric dipole moments of fermions and their weak neutral
currents. Compound structure of the neutrino interaction cross section with
nuclei have been defined. Invariance of the considered process concerning the C
- and P-operations have been investigated in the polarization type dependence.",2101.11912v1
2021-02-09,Graph Energy-based Model for Substructure Preserving Molecular Design,"It is common practice for chemists to search chemical databases based on
substructures of compounds for finding molecules with desired properties. The
purpose of de novo molecular generation is to generate instead of search.
Existing machine learning based molecular design methods have no or limited
ability in generating novel molecules that preserves a target substructure. Our
Graph Energy-based Model, or GEM, can fix substructures and generate the rest.
The experimental results show that the GEMs trained from chemistry datasets
successfully generate novel molecules while preserving the target
substructures. This method would provide a new way of incorporating the domain
knowledge of chemists in molecular design.",2102.04600v1
2021-02-24,Several topological indices of random caterpillars,"In chemical graph theory, caterpillar trees have been an appealing model to
represent the molecular structures of benzenoid hydrocarbon. Meanwhile,
topological index has been thought of as a powerful tool for modeling
quantitative structure-property relationship and quantitative
structure-activity between molecules in chemical compounds. In this article, we
consider a class of caterpillar trees that are incorporated with randomness,
called random caterpillars, and investigate several popular topological indices
of this random class, including Zagreb index, Randi\'{c} index and Wiener
index, etc. Especially, a central limit theorem is developed for the asymptotic
distribution of the Zagreb index of random caterpillars.",2102.12535v1
2021-04-01,Thick lenses systems,"The optical matrix formalism is applied to find parameters such as focal
distance, back and front focal points, principal planes, and the equation
relating object and image distances for a thick spherical lens immerse in air.
Then, the formalism is applied to systems compound of two, three and N thick
lenses in cascade. It is found that a simple Gaussian equation is enough to
relate object and image distances no matter the number of lenses.",2104.00700v4
2021-04-05,Two-magnon Raman scattering in antiferromagnetic phases of frustrated spin models on the honeycomb lattice,"We calculate the two-magnon Raman scattering spectra in antiferromagnetic
phases of several frustrated spin models defined on the honeycomb lattice.
These include the N\'{e}el antiferromagnetic phase of a $J_1$-$J_2$-$J_3$ model
and the stripe phase of the Heisenberg-Kitaev model. We show that both the
magnetic frustration and the anisotropy of interactions may significantly
affect the Raman spectra. We further discuss the implications of our results to
the magnetic excitations of the iron-based compound BaFe$_2$Se$_2$O and show
how the magnetic interactions can be extracted from fit to the Raman spectrum.",2104.01903v1
2021-04-06,Merton Investment Problems in Finance and Insurance for the Hawkes-based Models,"We show how to solve Merton optimal investment stochastic control problem for
Hawkes-based models in finance and insurance, i.e., for a wealth portfolio X(t)
consisting of a bond and a stock price described by general compound Hawkes
process (GCHP), and for a capital R(t) of an insurance company with the amount
of claims described by the risk model based on GCHP. The novelty of the results
consists of the new Hawkes-based models and in the new optimal investment
results in finance and insurance for those models.",2104.02694v2
2021-04-08,Flux trapping in superconducting hydrides under high pressure,"High-temperature conventional superconductivity in hydrogen-rich materials
under high pressure has been reportedly found in twelve different compounds in
recent years. However, the experimental evidence on which these claims are
based has recently been called into question. Here we discuss the measurement
of trapped magnetic flux, that should establish definitively that these
materials are indeed high-temperature superconductors. Its absence should
confirm claims to the contrary.",2104.03925v3
2021-04-13,Development of Surrogate Methods for Energy Production Process Water Characterization,"Effluent streams of process water used in energy production are contaminated
with organic compounds which limits reusability of the water streams. Energy
producers develop expensive monitoring and treatment methods to limit impact of
the contamination on production. Standard methods for quantifying dissolved
organics is process-affected water is laborious and time-consuming. Results
from detailed characterization of process water with high concentration of
dissolved organics are presented. Methods applied to characterize effluent
stream include gravimetric analysis, elemental analysis, and LCMS. The results
are used to develop efficient surrogate methods that may be used in continuous
improvement in energy production operations.",2104.05876v1
2021-04-18,Worst of Both Worlds: Biases Compound in Pre-trained Vision-and-Language Models,"Numerous works have analyzed biases in vision and pre-trained language models
individually - however, less attention has been paid to how these biases
interact in multimodal settings. This work extends text-based bias analysis
methods to investigate multimodal language models, and analyzes intra- and
inter-modality associations and biases learned by these models. Specifically,
we demonstrate that VL-BERT (Su et al., 2020) exhibits gender biases, often
preferring to reinforce a stereotype over faithfully describing the visual
scene. We demonstrate these findings on a controlled case-study and extend them
for a larger set of stereotypically gendered entities.",2104.08666v2
2021-05-16,Adaptive Interference Coordination over Channels with Unknown State at the Encoder and the Decoder,"We generalize the problem of controlling the interference created to an
external observer while communicating over a discrete memoryless channel (DMC)
which was studied in \cite{serrano:2014}. In particular, we consider the
scenario where the transmission is established over a compound DMC channel with
unknown state at both the encoder and the decoder. Depending on the exact state
$s$ of the channel, we ask for a different level of average precision
$\Delta_s$ on the establishment of the interference coordination with the
external observer. For this set-up, we fully characterize the capacity region.",2105.07535v2
2021-05-21,Extraction of physically meaningful endmembers from STEM spectrum-images combining geometrical and statistical approaches,"This article addresses extraction of physically meaningful information from
STEM EELS and EDX spectrum-images using methods of Multivariate Statistical
Analysis. The problem is interpreted in terms of data distribution in a
multi-dimensional factor space, which allows for a straightforward and
intuitively clear comparison of various approaches. A new computationally
efficient and robust method for finding physically meaningful endmembers in
spectrum-image datasets is presented. The method combines the geometrical
approach of Vertex Component Analysis with the statistical approach of Bayesian
inference. The algorithm is described in detail at an example of EELS
spectrum-imaging of a multi-compound CMOS transistor.",2105.10416v1
2021-05-23,Impact of non-Hermitian Mode interaction on Inter-cavity Light transfer,"Understanding inter-site mutual mode interaction in coupled physical systems
is essential to comprehend large compound systems as this local interaction
determines the successive multiple inter-site energy transfer efficiency. We
demonstrate that only the non-Hermitian coupling can correctly account for the
light transfer between two coupled optical cavities. We also reveal that the
non-Hermitian coupling effect becomes much crucial as the system dimension gets
smaller. Our results provide an important insight to deal with general
coupled-devices in the quantum regime.",2105.10936v1
2021-05-29,Time-Spatial Mode Selective Quantum Frequency Converter,"We experimentally demonstrate a mode-selective quantum frequency converter
over a compound spatio-temporal Hilbert space. We show that our method can
achieve high-extinction for high-dimensional quantum state tomography by
selectively upconverting the signal modes with a modulated and delayed pump. By
preparing the pump in optimized modes through adaptive feedback control,
selective frequency conversion is demonstrated with up to 30 dB extinction. The
simultaneous operations over high-dimensional degrees of freedom in both
spatial and temporal domains can serve as a viable resource for
photon-efficient quantum communications and computation.",2105.14160v1
2021-05-31,On Compositional Generalization of Neural Machine Translation,"Modern neural machine translation (NMT) models have achieved competitive
performance in standard benchmarks such as WMT. However, there still exist
significant issues such as robustness, domain generalization, etc. In this
paper, we study NMT models from the perspective of compositional generalization
by building a benchmark dataset, CoGnition, consisting of 216k clean and
consistent sentence pairs. We quantitatively analyze effects of various factors
using compound translation error rate, then demonstrate that the NMT model
fails badly on compositional generalization, although it performs remarkably
well under traditional metrics.",2105.14802v1
2021-06-01,Transport properties of the parent LaNiO2,"Here we study the transport properties of a nickelate compound, namely LaNiO2
using density functional theory (DFT) in conjunction with dynamical mean field
theory (DMFT). An interacting multi-orbital spin-resolved scenario for LaNiO2
yields a metallic ground state with ferromagnetic correlations. The latter
contrasts an antiferromagnetic order reported earlier. The metallic behaviour
persists even at large values of the interaction energies. Further support of
the metallic state is provided by the angular resolved photoemission
spectroscopy (ARPES) data.",2106.00632v1
2021-06-15,Pixel-reassignment in Ultrasound Imaging,"We present an adaptation of the pixel-reassignment technique from confocal
fluorescent microscopy to coherent ultrasound imaging. The method, Ultrasound
Pixel-Reassignment (UPR), provides a resolution and signal to noise (SNR)
improvement in ultrasound imaging by computationally reassigning off-focus
signals acquired using traditional plane-wave compounding ultrasonography. We
theoretically analyze the analogy between the optical and ultrasound
implementations of pixel reassignment, and experimentally evaluate the imaging
quality on tissue-mimicking acoustic phantoms. We demonstrate that UPR provides
a $25\%$ resolution improvement and a $3dB$ SNR improvement in in-vitro scans,
without any change in hardware or acquisition scheme.",2106.07978v2
2021-06-16,Anomalous transport in Kane fermions,"Kane fermions are characterized by a linear Dirac cone intersecting with a
flat band, resembling a pseudo-spin-1 Dirac semimetal. Similar to relativistic
Dirac fermions, Kane fermions satisfy a linear energy-momentum relation and can
be classified as being pseudo-relativistic. Though not protected by symmetry or
by topology, Kane fermions can emerge by suitable band engineering, for
example, in mercury-telluride compounds. Here we study the Berry curvature of
Kane fermions that emerges in the presence of time-reversal symmetry breaking
weak Zeeman fields. We discuss the related anomalous transport coefficients and
discuss the anisotropy in these responses that can be probed in experiments.",2106.08588v1
2021-06-23,Quantum critical phenomena in a spin-1/2 frustrated square lattice with spatial anisotropy,"We present a model compound with a spin-1/2 spatially anisotropic frustrated
square lattice, in which three antiferromagnetic interactions and one
ferromagnetic interaction are competing. We observe an unconventional gradual
increase in the low-temperature magnetization curve reminiscent of the quantum
critical behavior between gapped and gapless phases. In addition, the specific
heat and electron spin resonance signals indicate one-dimensional
characteristics. These results demonstrate quantum critical behavior associated
with one dimensionalization caused by frustrated interactions in the spin-1/2
spatially anisotropic square lattice.",2106.12126v1
2021-06-30,Comparison of fission and quasi-fission modes,"Quantum shell effects are known to affect the formation of fragments in
nuclear fission. Shell effects also affect quasi-fission reactions occurring in
heavy-ion collisions. Systematic time-dependent Hartree-Fock simulations of
50Ca+176Yb collisions show that the mass equilibration between the fragments in
quasi-fission is stopped when they reach similar properties to those in the
asymmetric fission mode of the 226Th compound nucleus. Similar shell effects
are then expected to determine the final repartition of nucleons between the
nascent fragments in both mechanisms. Future experimental studies that could
test these observations are discussed.",2106.15959v2
2021-06-30,Stochastic applications of Caputo-type convolution operators with non-singular kernels,"We consider here convolution operators, in the Caputo sense, with
non-singular kernels. We prove that the solutions to some integro-differential
equations with such operators (acting on the space variable) coincide with the
transition densities of a particular class of L\'evy subordinators (i.e.
compound Poisson processes with non-negative jumps). We then extend these
results to the case where the kernels of the operators have random parameters,
with given distribution. This assumption allows greater flexibility in the
choice of the kernel's parameters and, consequently, of the jumps' density
function.",2106.15972v1
2021-08-02,Chiral symmetry breaking through spontaneous dimerization in kagomé metals,"Due to an uprise in the variety of candidate compounds, kagome metals have
recently gained significant attention. Among other features, kagome metals host
Dirac cones as a key band structure feature away from half filling, and
potentially yield an exceptionally large fine structure, beyond values found in
other 2D Dirac materials such as graphene. We investigate the possibility of
chiral symmetry breaking in kagome metals. Based on a heuristic lattice model,
we determine the critical coupling strength and the ordering pattern by means
of a Schwinger-Dyson mean-field analysis. As the leading instability we
identify a dimerization pattern which spontaneously opens an excitation gap at
the Dirac point and breaks the chiral symmetry.",2108.00961v1
2021-08-04,"Asymptotic analysis of Poisson shot noise processes, and applications","Poisson shot noise processes are natural generalizations of compound Poisson
processes that have been widely applied in insurance, neuroscience, seismology,
computer science and epidemiology. In this paper we study sharp deviations,
fluctuations and the stable probability approximation of Poisson shot noise
processes. Our achievements extend, improve and complement existing results in
the literature. We apply the theoretical results to Poisson cluster point
processes, including generalized linear Hawkes processes, and risk processes
with delayed claims. Many examples are discussed in detail.",2108.02048v2
2021-08-09,Deep2Lead: A distributed deep learning application for small molecule lead optimization,"Lead optimization is a key step in drug discovery to produce potent and
selective compounds. Historically, in silico screening and structure-based
small molecule designing facilitated the processes. Although the recent
application of deep learning to drug discovery piloted the possibility of their
in silico application lead optimization steps, the real-world application is
lacking due to the tool availability. Here, we developed a single user
interface application, called Deep2Lead. Our web-based application integrates
VAE and DeepPurpose DTI and allows a user to quickly perform a lead
optimization task with no prior programming experience.",2108.05183v1
2021-09-05,Spatial Domain Feature Extraction Methods for Unconstrained Handwritten Malayalam Character Recognition,"Handwritten character recognition is an active research challenge,especially
for Indian scripts. This paper deals with handwritten Malayalam, with a
complete set of basic characters, vowel and consonant signs and compound
characters that may be present in the script. Spatial domain features suitable
for recognition are chosen in this work. For classification, k-NN, SVM and ELM
are employed",2109.02153v1
2021-09-10,Scaffold-Induced Molecular Graph (SIMG): Effective Graph Sampling Methods for High-Throughput Computational Drug Discovery,"Scaffold based drug discovery (SBDD) is a technique for drug discovery which
pins chemical scaffolds as the framework of design. Scaffolds, or molecular
frameworks, organize the design of compounds into local neighborhoods. We
formalize scaffold based drug discovery into a network design. Utilizing
docking data from SARS-CoV-2 virtual screening studies and JAK2 kinase assay
data, we showcase how a scaffold based conception of chemical space is
intuitive for design. Lastly, we highlight the utility of scaffold based
networks for chemical space as a potential solution to the intractable
enumeration problem of chemical space by working inductively on local
neighborhoods.",2109.05012v1
2021-09-14,Deep Denerative Models for Drug Design and Response,"Designing new chemical compounds with desired pharmaceutical properties is a
challenging task and takes years of development and testing. Still, a majority
of new drugs fail to prove efficient. Recent success of deep generative
modeling holds promises of generation and optimization of new molecules. In
this review paper, we provide an overview of the current generative models, and
describe necessary biological and chemical terminology, including molecular
representations needed to understand the field of drug design and drug
response. We present commonly used chemical and biological databases, and tools
for generative modeling. Finally, we summarize the current state of generative
modeling for drug design and drug response prediction, highlighting the
state-of-art approaches and limitations the field is currently facing.",2109.06469v1
2021-09-15,Geographic Difference-in-Discontinuities,"A recent econometric literature has critiqued the use of regression
discontinuities where administrative borders serves as the 'cutoff'.
Identification in this context is difficult since multiple treatments can
change at the cutoff and individuals can easily sort on either side of the
border. This note extends the difference-in-discontinuities framework discussed
in Grembi et. al. (2016) to a geographic setting. The paper formalizes the
identifying assumptions in this context which will allow for the removal of
time-invariant sorting and compound-treatments similar to the
difference-in-differences methodology.",2109.07406v2
2021-09-24,Large extrinsic phonon thermal Hall effect from resonant scattering,"Recent experimental observations of unexpectedly large thermal Hall
conductivities, $\kappa_H$, in insulating materials, including the parent
compounds of the high temperature superconducting cuprates, likely reflect an
extrinsic contribution from a yet to be identified extrinsic source of skew
scattering of acoustic phonons. We show that resonant scattering of phonons
from a certain class of three-level systems produces strong skew scattering in
the presence of a modest magnetic field. We interpret this as a first step
towards understanding the experiments.",2109.12117v3
2021-09-28,Mean-field approach for skyrmion lattice in hexagonal frustrated antiferromagnets,"Simple mean-field approach for frustrated antiferromagnets on hexagonal
lattices, aimed to describe the high-temperature part of the
temperature-magnetic field phase diagram, is proposed. It is shown, that an
interplay between modulation vector symmetry, Zeeman energy and magneto-dipolar
interaction leads to stabilization of the triple-$Q$ skyrmion lattice in a
certain region of the phase diagram. Corresponding analytical expressions for
phase boundaries are derived. It is argued that the developed theory can be
applied for the description of the high-temperature part of the phase diagram
observed experimentally for Gd$_2$PdSi$_3$ compound.",2109.13682v1
2021-10-03,"Competition between $(γ,p)$ and $(γ,n)$ photo-disintegration yields","A comprehensive analysis of the competition between photo-proton and
photo-neutron disintegration yields is undertaken by constraining
photo-absorption data with physics principles -- namely, dipole sum rules,
decay properties to open channels, isospin selection rules and statistical
evaporation from compound nucleus formation. The trend and magnitude of
disintegration yields for self-conjugate nuclei are in agreement with the
evaporation model of Blatt and Weisskopf. A substantial improvement is found
between the exponential trend presented in this work and that determined by
Morinaga using a similar approach. This work allows for the evaluation of
frequently missing or inconsistent photo-proton contributions, which impacts
the photo-disintegration of light and neutron-deficient nuclei, where
photo-proton contributions are relevant.",2110.00979v1
2021-10-29,Comparing the influence of Floquet dynamics in various Kitaev-Heisenberg materials,"In this paper we examine the possibility of Floquet engineering in the three
candidate Kitaev materials $\mathrm{Na}_2\mathrm{IrO}_3$,
$\alpha$-$\mathrm{Li}_2\mathrm{IrO}_3$ and $\alpha$-$\mathrm{RuCl}_3$. We
derive an effective Floquet Hamiltonian and give an approximation for heating
processes arising from doublon holon propagation.This suggests that compounds
with stronger Hund's-rule coupling are less prone to heating. We then
investigate the impact of light frequency and amplitude on magnetic interaction
terms up to third-nearest-neighbor and find that third-neighbor Heisenberg
coupling $J_3$ is very susceptible to tuning by circularly polarized light.
Finally, we discuss uses of linear polarized light in selectively tuning single
bond directions.",2110.15673v1
2021-10-29,Realization of Quantum Dipoles in Triangular Lattice Crystal Ba3Yb(BO3)3,"We investigate the thermodynamic properties of the ytterbium-based triangular
lattice compound Ba3Yb(BO3)3. The results demonstrate the absence of any
long-range ordering down to 56 mK. Analysis of the magnetization,
susceptibility and specific heat measurements suggests that Ba3Yb(BO3)3 may
realize a S = 1/2 quantum dipole lattice, in which the dominant interaction is
the long range dipole-dipole coupling on the geometrically frustrated
triangular lattice, and exchange interactions are subdominant or negligible.",2111.00031v2
2021-11-02,The $k$-Compound of a Difference-Algebraic System,"The multiplicative and additive compounds of a matrix have important
applications in geometry, linear algebra, and the analysis of dynamical
systems. In particular, the $k$-compounds allow to build a $k$-compound
dynamical system that tracks the evolution of $k$-dimensional parallelotopes
along the original dynamics. This has recently found many applications in the
analysis of non-linear systems described by ODEs and difference equations.
Here, we introduce the $k$-compound system corresponding to a
differential-algebraic system, and describe several applications to the
analysis of discrete-time dynamical systems described by difference-algebraic
equations.",2111.01419v2
2021-11-04,Sequence of superconducting states in field cooled $FeCr_2S_4$,"In the present article we discuss theoretically the emergence of
superconductivity in field cooled $FeCr_2S_4$. The chromium electrons form a
triplet $t_{2g}$ states and due to antiferromagnetic exchange with the iron
spins have Zeeman splitting. Applied, during preparation, magnetic field along
the moment of iron ions, successively compensates the Zeeman splittings. The
chromium electrons with zero Zeeman energy form Cooper pairs induced by iron
magnons. In that way, we predict theoretically the existence of sequence of
superconducting states in field cooled $FeCr_2S_4$. Actually there are three
different superconductors prepared applying, during preparation, different
magnetic fields. In these compounds superconductivity coexist with the
saturated magnetism of iron ions.",2111.02765v1
2021-11-12,Observation of a new polyhalide phase in Ag-Cl$_2$ system at high pressure,"In this short contribution, we examine Raman spectroscopic data from
high-pressure and high-temperature experiments with Ag-Cl$_2$ system, and find
that they are in good agreement with previously observed and calculated spectra
of polychloride species. Our results imply the formation of a hitherto unknown
AgCl$_x$ compound, which warrants further study.",2111.06656v1
2021-11-23,Collective behavior of composite active particles,"We describe simulations of active Brownian particles carried out to explore
how dynamics and clustering are influenced by particle shape. Our particles are
composed of four disks, held together by springs, whose relative size can be
varied. These compound objects can be tuned smoothly from having a concave to a
convex surface. We show that even two of these composite particles can exhibit
collective motion modifying the effective Peclet number. We then investigate
how particle geometry can be used to explain the phase behaviour of many such
particles.",2111.13665v2
2021-12-09,Projection population analysis for molecules with heavy and superheavy atoms,"A new iterative version of population projection analysis is formulated and
applied to determine relativistic effective atomic configurations of superheavy
elements Cn and Fl and their lighter homologues (Hg and Pb) in the molecules of
their fluorides and oxides. The dependence of the computed populations on the
initial reference atomic spinors is completely avoided. The difference in
population of atomic spinors with the same orbital angular momentum and
different total angular momenta is demonstrated to be essential for
understanding the peculiarities of chemical bonding in superheavy element
compounds.",2112.05187v1
2021-12-13,Hill regions of charged three-body systems,"For charged three-body systems, we discuss the configurations and
orientations that are admissible for given values of the conserved total energy
and angular momentum. The admissible configurations and orientations are
discussed on a configuration space that is reduced by the translational,
rotational and dilation symmetries of charged three-body systems. We consider
the examples of the charged three-body systems given by the helium atom (two
electrons and a nucleus) and the compound of two electrons and one positron.
For comparison, the well known example of the Newtonian gravitational
three-body system is discussed for the scheme presented in this paper first.",2112.07032v1
2021-12-22,Intrinsically chiral ferronematic liquid crystals,"Strongly dipolar mesogenic compounds with a chiral center located in a
lateral alkyl chain were synthesized, and shown to form the ferroelectric
nematic phase. The presence of molecular chirality induced a helical structure
in both the N and NF phases, but with opposite helix sense in the two phases.
The relaxation frequency of the polar fluctuations was found to be lower for
the chiral NF phase than for its achiral, non-branched counterpart with the
same lateral chain length.",2112.11887v1
2022-01-06,Learning to be adversarially robust and differentially private,"We study the difficulties in learning that arise from robust and
differentially private optimization. We first study convergence of gradient
descent based adversarial training with differential privacy, taking a simple
binary classification task on linearly separable data as an illustrative
example. We compare the gap between adversarial and nominal risk in both
private and non-private settings, showing that the data dimensionality
dependent term introduced by private optimization compounds the difficulties of
learning a robust model. After this, we discuss what parts of adversarial
training and differential privacy hurt optimization, identifying that the size
of adversarial perturbation and clipping norm in differential privacy both
increase the curvature of the loss landscape, implying poorer generalization
performance.",2201.02265v1
2022-01-18,Emergent Spinon Dispersion and Symmetry Breaking in Two-Channel Kondo Lattices,"Two-channel Kondo lattice serves as a model for a growing family of
heavy-fermion compounds. We employ the dynamical large-N technique and go
beyond the independent bath approximation to study this model both numerically
and analytically using renormalization group ideas. We show that the Kondo
effect induces dynamic magnetic correlations that lead to an emergent spinon
dispersion. Furthermore, we develop a quantitative framework that interpolates
between infinite dimension where the channel-symmetry broken results of
mean-field theory are confirmed, and one-dimension where the channel symmetry
is restored and a critical fractionalized mode is found.",2201.06681v2
2022-03-31,Readout for Calorimetry at Future Colliders: A Snowmass 2021 White Paper,"Calorimeters will provide critical measurements at future collider detectors.
As the traditional challenge of high dynamic range, high precision, and high
readout rates for signal amplitudes is compounded by increasing granularity and
precision timing the readout systems will become increasingly complex. This
white paper reviews the challenges and opportunities in calorimeter readout at
future collider detectors.",2204.00098v1
2022-04-10,Maximal Inequalities and Some Applications,"A maximal inequality is an inequality which involves the (absolute) supremum
$\sup_{s\leq t}|X_{s}|$ or the running maximum $\sup_{s\leq t}X_{s}$ of a
stochastic process $(X_t)_{t\geq 0}$. We discuss maximal inequalities for
several classes of stochastic processes with values in an Euclidean space:
Martingales, L\'evy processes, L\'evy-type - including Feller processes,
(compound) pseudo Poisson processes, stable-like processes and solutions to
SDEs driven by a L\'evy process -, strong Markov processes and Gaussian
processes. Using the Burkholder-Davis-Gundy inequalities we als discuss some
relations between maximal estimates in probability and the Hardy-Littlewood
maximal functions from analysis.
  This paper has been accepted for publication in Probability Surveys",2204.04690v2
2022-04-16,On the analysis of the tin-inside-H3S Mössbauer experiment,"A simple analysis is presented of the particular experiment used to prove the
bulk nature of very-high-Tc superconductivity in H3S compound under ultra-high
pressure. In the experiment, an internal magnetic field was sensed by the
synchrotron M\""ossbauer spectroscopy in tin placed inside the H2S sample. The
experiment showed peculiar anisotropy with respect to the direction of the
applied field at first sight. By considering actual experimental geometries and
parameters of the experiment, we show that this particular observation is
consistent with the expectations for a regular type-II superconductor with
Meissner expulsion and pinning.",2204.07847v1
2022-05-06,Diverse Imitation Learning via Self-Organizing Generative Models,"Imitation learning is the task of replicating expert policy from
demonstrations, without access to a reward function. This task becomes
particularly challenging when the expert exhibits a mixture of behaviors. Prior
work has introduced latent variables to model variations of the expert policy.
However, our experiments show that the existing works do not exhibit
appropriate imitation of individual modes. To tackle this problem, we adopt an
encoder-free generative model for behavior cloning (BC) to accurately
distinguish and imitate different modes. Then, we integrate it with GAIL to
make the learning robust towards compounding errors at unseen states. We show
that our method significantly outperforms the state of the art across multiple
experiments.",2205.03484v1
2022-05-19,Orbital-slective behaviour in cubanite CuFe2S3,"Using {\it ab initio} band structure calculations we show that mineral
cubanite, CuFe$_2$S$_3$, demonstrates an orbital-selective behavior with some
of the electrons occupying molecular orbitals of $x^2-y^2$ symmetry and others
localized at atomic orbitals. This is a rare situation for $3d$ transition
metal compounds explains experimentally observed absence of charge
disproportionation, anomalous M\""ossbauer data, and ferromagnetic ordering in
between nearest neighbor Fe ions.",2205.09568v1
2022-06-01,Transition between long and short-range helical orders in mixed B20 cubic helimagnets,"A model of B20 helimagnet with strong (frustrating) defect bonds is
considered. Single defect provides dipolar field-like distortion of the helical
magnetic ordering. At finite defect bond concentrations, the spiral vector
acquires correction to its value in the pure system. Moreover, it is shown that
the strong defects of sufficient but small concentration are able to destroy
long-range order driving the system to the phase with short-range helical
ordering. It is argued that the developed approach allows describing main
experimental observations in Mn$_{1-x}$Fe$_x$Si and Mn$_{1-x}$Co$_x$Si
compounds.",2206.00292v1
2022-06-08,Optimal cash management using impulse control,"We consider the impulse control of Levy processes under the infinite horizon,
discounted cost criterion. Our motivating example is the cash management
problem in which a controller is charged a fixed plus proportional cost for
adding to or withdrawing from his/her reserve, plus an opportunity cost for
keeping any cash on hand. Our main result is to provide a verification theorem
for the optimality of control band policies in this scenario. We also analyze
the transient and steady-state behavior of the controlled process under control
band policies and explicitly solve for the optimal policy in the case in which
the Levy process to be controlled is the sum of a Brownian motion with drift
and a compound Poisson process with exponentially distributed jump sizes.",2206.04107v1
2022-06-19,Estimating the finite-time ruin probability of a surplus with a long memory via Malliavin calculus,"We consider a surplus process of drifted fractional Brownian motion with the
Hurst index $H>1/2$, which appears as a functional limit of drifted compound
Poisson risk models with correlated claims, and this is a kind of
representation of a surplus with a long memory. Our interest is to construct
confidence intervals of the ruin probability of the surplus when the volatility
parameter is unknown. We will obtain the derivative of the ruin probability
w.r.t. the volatility parameter via Malliavin calculus, and apply the delta
method to identify the asymptotic distribution of an estimated ruin
probability.",2206.09441v1
2022-06-22,First-principles method justifying the Dieke diagram and beyond,"We present a method to determine the model Hamiltonians to treat rare-earth
multiplets in solids from the results of the quasiparticle self-consistent
\textit{GW} (QSGW) method. We apply the method to trivalent Eu compounds
EuCl$_3$, EuN, and Eu-doped GaN after examining free rare-earth ions. We solve
the model Hamiltonian by the exact diagonalization. Our results justify
applying the Dieke diagram to ions in solid, while its limitation is clarified.
In particular, we show that the crystal fields cause sizable breaking of the
Russell-Saunders coupling.",2206.10862v2
2022-06-23,Metallic delafossite thin films for unique device applications,"Metallic delafossites (ABO2) are layered oxides with quasi-two dimensional
conduction layers. Metallic delafossites are among the most conducting
materials with the in-plane conductivity comparable with that of elemental
metals. In this perspective, we will discuss basic properties and future
research prospects of metallic delafossites, mainly focusing on thin films and
heterostructures. We exemplify the fascinating properties of these compounds
such as high conductivity and surface polarity and discuss how it can be
utilized in thin films and heterostructures.",2206.11482v1
2022-06-24,Comment on ''Traversable Wormholes in General Relativity'',"In the letter titled ''Traversable Wormholes in General Relativity'' [Phys.
Rev. Lett. 128, 091104 (2022)], R. A. Konoplya and A. Zhidenko have constructed
an asymmetric wormhole solution, which is not symmetric about the throat and is
compounded from smooth gravitational and charged Dirac fields. However, the
authors have claimed that a physically relevant condition on the throat is
imposed to lead to no gravitational force experienced by a stationary observer
at the throat. In this comment, we point out that the above condition is
unnecessary.",2206.12250v1
2022-07-04,Tunable cavity modes and light-pulse propagation in diarylethene-based photo-switchable polymeric microcavities,"Light responsive devices employing molecular photo-switches are interesting
for displays and dynamic light filtering. In this work, polymeric microcavities
embedding a layer of photochromic compound have been studied by means of the
transfer matrix method. Different polymers, such as poly vinyl carbazole, poly
styrene and cellulose acetate, have been used. A microcavity that includes
random one-dimensional photonic structures sandwiching the photochromic layer
has also been studied. Propagation of light pulses through the microcavities
has been analysed.",2207.01283v2
2022-07-07,Polychromatic Excitation of Delocalized Long-Lived Proton Spin States in Aliphatic Chains,"Long-lived states (LLS) involving pairs of magnetically inequivalent but
chemically equivalent proton spins in aliphatic (CH$_2$)$_n$ chains can be
excited by simultaneous application of weak selective radio-frequency (RF)
fields at n chemical shifts by polychromatic spin lock induced crossing
(poly-SLIC). The LLS are delocalized throughout the aliphatic chain by mixing
of intrapair singlet states and by excitation of LLS comprising products of
four or six spins. The measured lifetimes T$_{LLS}$ in a model compound are
about 5 times longer than T1, and are strongly affected by interactions with
macromolecules.",2207.03446v1
2022-07-20,Threshold estimation for jump-diffusions under small noise asymptotics,"We consider parameter estimation of stochastic differential equations driven
by a Wiener process and a compound Poisson process as small noises. The goal is
to give a threshold-type quasi-likelihood estimator and show its consistency
and asymptotic normality under new asymptotics. One of the novelties of the
paper is that we give a new localization argument, which enables us to avoid
truncation in the contrast function that has been used in earlier works and to
deal with a wider class of jumps in threshold estimation than ever before.",2207.09852v1
2022-08-09,Rapid suppression of charge density wave transition in LaSb2 under pressure,"LaSb2 is found to be an example of an exceptionally pressure sensitive and
tunable, two dimensional compound. In-plane electrical resistivity of LaSb2
under pressure up to 12.9 kbar was measured in zero and applied magnetic field.
The charge density wave transition (observed at ~ 350 K at ambient pressure) is
completely suppressed by 6-7 kbar with significant (in comparison with the
ambient pressure) increase in Fermi surface gapping and transition hysteresis
just above ambient pressure.",2208.04997v1
2022-08-17,Spin-Hall magnetoresistance in quasi-two-dimensional antiferromagnetic insulator/metal bilayer systems,"We study the temperature dependence of spin Hall magnetoresistance (SMR) in
antiferromagnetic insulator (AFI)/metal bilayer systems. We calculate the
amplitude of the SMR signal by using a quantum Monte Carlo simulation and
examine how the SMR depends on the amplitude of the spin, thickness of the AFI
layer, and randomness of the exchange interactions. Our results for simple
quantum spin models provide a useful starting point for understanding SMR
measurements on atomic layers of magnetic compounds.",2208.08096v2
2022-08-22,Computed multivalues of AGM reveal periodicities of inverse functions,"The article shows how two choices are possible whenever computing the
geometric mean, and the repetition of this process can in general yield
2-to-the power N different values when the choices are compounded in the first
N steps of evaluation of the arithmetic-geometric mean. This happens not only
in the simple AGM involved in the computation of the complete elliptic integral
of the first kind, but also in analogous methods for the computation of the
complete and incomplete elliptic integrals of the first and second kind.",2208.10614v2
2022-08-25,Single crystal synthesis and magnetic properties of a Shastry-Sutherland lattice compound BaNd2ZnS5,"Single crystals of a Shastry-Sutherland magnetic semiconductor, BaNd2ZnS5,
were synthesized through a high-temperature solution growth technique. Physical
properties were characterized by powder and single crystal x-ray diffraction,
temperature- and field-dependent magnetization, and temperature-dependent
specific heat measurements. BaNd2ZnS5 orders antiferromagnetically at 2.9 K,
with magnetic moments primarily aligned within the ab-plane. Magnetic
isothermal measurements show metamagnetic transitions at ~ 15 kOe for the [110]
direction and ~ 21 kOe for the [100] direction. Estimated magnetic entropy
suggests a double ground state for each Nd ion.",2208.12180v1
2022-08-26,PNO: A Promising Deep-UV Nonlinear Optical Material with Extremely High Second Harmonic Generation Effect,"In this work, the polar tetrahedron [PN$_2$O$_2$] was revealed as a new
deep-ultraviolet (deep-UV) nonlinear optically active unit. Accordingly, a
thermodynamically stable compound (PNO) consisting of the polar [PN$_2$O$_2$]
units was predicted and suggested as a promising candidate of deep-UV nonlinear
optical (NLO) material. Compared with other deep-UV materials known to date,
PNO possesses the strongest second harmonic generation (SHG) coefficient (about
6 times that of KH$_2$PO$_4$ (KDP)). Moreover, its three-dimensional
connectivity endows it with good mechanical and thermal properties. Therefore,
PNO should be a new option for non-$\pi$-conjugated deep-UV NLO materials.",2208.12475v1
2022-08-29,Measurement of minute volumes of chiral molecules using in-fiber polarimetry,"We report an opto-fluidic method that enables to efficiently measure the
enantiomeric excess of chiral molecules at low concentration. The approach is
to monitor the optical activity induced by a Kagome-lattice hollow-core
photonic crystal fiber filled with a sub-ul volume of chiral compound. The
technique also allows monitoring the enzymatic racemization of R mandelic acid.",2208.13457v1
2022-08-30,Fluctuation theory of continuous-time skip-free downward Markov chains with applications to branching processes with immigration,"We develop a new methodology for the fluctuation theory of continuous-time
skip-free Markov chains, extending the recent work of Choi and Patie [5] for
discrete-time skip-free Markov chains. As the main application we use it to
derive a full set of fluctuation identities regarding exiting a finite or
infinite interval for Markov branching processes with immigration, thereby
uncovering many new results for this classical family of continuous-time Markov
chains. The theory also allows us to recover in a simple manner fluctuation
identities for skip-free downward compound Poisson processes.",2208.14425v1
2022-09-09,S. Vonsovsky and the dawn of the theory of strongly correlated systems,"A survey of scientific and social activity of S. V. Vonsovsky is presented.
His fundamental works on the theory of electronic properties and magnetism of
transition and rare-earth metals and their compounds are reviewed. The
historical development of the many-electron polar (preceding the famous Hubbard
model) and $s-d(f)$ exchange (''Vonsovsky-Zener'', ''Kondo lattice'') models is
considered.",2209.04335v1
2022-09-13,Semiparametric Estimation of Optimal Dividend Barrier for Spectrally Negative Lévy Process,"We disucss a statistical estimation problem of an optimal dividend barrier
when the surplus process follows a L\'{e}vy insurance risk process. The optimal
dividend barrier is defined as the level of the barrier that maximizes the
expectation of the present value of all dividend payments until ruin. In this
paper, an estimatior of the expected present value of all dividend payments is
defined based on ``quasi-process'' in which sample paths are generated by
shuffling increments of a sample path of the L\'{e}vy insurance risk process.
The consistency of the optimal dividend barrier estimator is shown. Moreover,
our approach is examined numerically in the case of the compound Poisson risk
model perturbed by diffusion.",2209.05781v1
2022-10-17,Flat band induced room temperature ferromagnetism in two dimensional systems,"The remarkable and fascinating properties of two-dimensional materials have
raised them to the rank of most promising candidates for technological
applications. In particular, the possibility of long-range ferromagnetic order
in 2D materials is generating a growing excitement. Here, we demonstrate that
flat bands (FBs) may pave the way to room temperature ferromagnetism in 2D
compounds. Indeed, the magnetic exchanges between localized spins are largely
dominated by the FB-FB contribution. This contribution is ferromagnetic and
scales linearly with the local coupling, thus leading to cross-over
temperatures (ferromagnetic phase/ paramagnetic phase) higher by an order of
magnitude than those currently reported in experiments. Cross-over temperatures
as high as $600~ K$ could be reached in micrometer-sized FB systems.",2210.08896v1
2022-10-26,Nearly critical Galton--Watson processes,"We investigate Galton--Watson processes in varying environment, for which
$\bar f_n \uparrow 1$ and $\sum_{n=1}^\infty (1-\bar f_n) = \infty$, where
$\bar f_n$ stands for the offspring mean in generation $n$. Since the process
dies out almost surely, to obtain nontrivial limit we consider two scenarios:
conditioning on non-extinction, or adding immigration. In both cases we show
that the process converges in distribution without normalization to a
nondegenerate compound-Poisson limit law. The proofs rely on the shape function
technique, worked out by Kersting (2020).",2210.14694v1
2022-10-27,Change of measure in a Heston-Hawkes stochastic volatility model,"We consider the stochastic volatility model obtained by adding a compound
Hawkes process to the volatility of the well-known Heston model. A Hawkes
process is a self-exciting counting process with many applications in
mathematical finance, insurance, epidemiology, seismology and other fields. We
prove a general result on the existence of a family of equivalent (local)
martingale measures. We apply this result to a particular example where the
sizes of the jumps are exponentially distributed.",2210.15343v1
2022-11-01,Manipulation of individual judgments in the quantitative pairwise comparisons method,"Decision-making methods very often use the technique of comparing
alternatives in pairs. In this approach, experts are asked to compare different
options, and then a quantitative ranking is created from the results obtained.
It is commonly believed that experts (decision-makers) are honest in their
judgments. In our work, we consider a scenario in which experts are vulnerable
to bribery. For this purpose, we define a framework that allows us to determine
the intended manipulation and present three algorithms for achieving the
intended goal. Analyzing these algorithms may provide clues to help defend
against such attacks.",2211.01809v1
2022-11-27,A Scheme to fabricate magnetic graphene-like cobalt nitride CoN4monolayer proposed by first-principles calculations,"We propose a scheme to fabricate the cobalt nitride CoN4 monolayer, a
magnetic graphene-like two-dimensional material, in which all Co and N atoms
are in a plane. Under the pressure above 40 GPa, the bulk CoN4 is stabilized in
a triclinic phase. With the pressure decreasing, the triclinic phase of CoN4 is
transformed into an orthorhombic phase, and the latter is a layered compound
with large interlayer spacing. At ambient condition, the weak interlayer
couplings are so small that single CoN4 layer can be exfoliated by the
mechanical method.",2211.14765v1
2022-12-15,"Optical signature for distinguishing between Mott-Hubbard, intermediate and charge-transfer insulators","Determining the nature of band gaps in transition-metal compounds remains
challenging. We present a first-principles study on electronic and optical
properties of CoO using hybrid functional pseudopotentials. We show that
optical absorption spectrum can provide a clear fingerprint to distinguish
between Mott-Hubbard, intermediate and charge-transfer insulators. This
discrimination is reflected by the qualitative difference in peak satellites
due to unique interplay between $d$-$d$ and $p$-$d$ excitations, thus allowing
identification from experimental data alone, unlike the existing methods that
require additional theoretical interpretation. We conclude that the CoO is an
intermediate, rather than a Mott-Hubbard insulator as is initially believed.",2212.07660v1
2023-01-03,Crystal Chemistry at High Pressure,"An overview of the behavior of materials at high pressure is presented,
starting from the effects on single atoms driving electronic transitions and
changes in periodic trends. A range of high-pressure-induced phenomena in the
solid state are then discussed building on the atomic changes, including
bizarre electronic structures, electrides, compounds of noble gases, changes in
elemental miscibility, and strange structural and bonding configurations. In
the final section, the field of high pressure superconductivity is discussed,
as high pressure phases have generated immense study and excitement as some of
their critical superconducting temperatures approach room temperature.",2301.01139v1
2023-01-07,Option pricing under the normal SABR model with Gaussian quadratures,"The stochastic-alpha-beta-rho (SABR) model has been widely adopted in options
trading. In particular, the normal ($\beta=0$) SABR model is a popular model
choice for interest rates because it allows negative asset values. The option
price and delta under the SABR model are typically obtained via asymptotic
implied volatility approximation, but these are often inaccurate and
arbitrageable. Using a recently discovered price transition law, we propose a
Gaussian quadrature integration scheme for price options under the normal SABR
model. The compound Gaussian quadrature sum over only 49 points can calculate a
very accurate price and delta that are arbitrage-free.",2301.02797v1
2023-01-16,Towards an Automatic Consolidation of French Law,"We present preliminary results about Legistix, a tool we are developing to
automatically consolidate the French and European law. Legistix is based both
on regular expressions used in several compound grammars, similar to the
successive passes of a compiler, and on a new specialized language of
functional type, allowing to describe the changes applied to the texts. Instead
of creating manually a full consolidated version of a text at each modification
date, Legistix generates automatically programs from legal documents written in
natural language to automatically create the consolidated versions.",2301.06469v1
2023-01-28,Simple Realistic Model of Spin Reorientation in 4f-3d Compounds,"Spin reorientation is an important phenomenon of rare-earth perovskites,
orthoferrites and orthochromites. In this study, we consider a simple but
realistic microscopic theory of the spontaneous spin-reorientation transitions
induced by the 4f-3d interaction, more specifically, the interaction of the
main Kramers doublet or non-Kramers quasi-doublet of the 4f ion with an
effective magnetic field induced by the 3d sublattice. The obtained results
indicate that the cause of both the temperature and the character of the
spin-reorientation transition is a competition between the second and fourth
order spin anisotropy of the 3d sublattice, the crystal field for 4f ions, and
the 4f-3d interaction.",2301.12157v1
2023-01-31,Investigation of alumina formed by plasma electrolytic saturation,"The process of alumina coating on the steel surface plasma electrolytic
method is a method for increasing the corrosion resistance, in this process,
electrolytic aluminum containing compounds should be able to cover the surface.
The results show the size of a micron coating of cauliflower shape and distance
of an average of about 6 microns. The coating on steel sample acted as a
passive layer and corrosion resistance increases slightly. This is due to the
low corrosion resistance because of the lack of uniformity and surface finish
are not.",2301.13846v1
2023-02-15,Local subexponentiality and infinitely divisible distributions,"We completely characterize $\Delta$- and local subexponentialities of
positive-half compound Poisson distributions and extend the characterization on
two-sided distributions. Moreover, $\Delta$-subexponentiality of infinitely
divisible distributions is characterized with new conditions, and local
subexponentiality is newly characterized in the two-sided case. In the process
closedness properties of these subexponentialities are derived, particularly
for distributions on $\R$. Most results are obtained by exploiting
monotonic-type assumptions. We apply our results to distributions of supremum
of a random work and a randomly stopped iid sum.",2302.07487v2
2023-02-24,Retrospective Uncertainties for Deep Models using Vine Copulas,"Despite the major progress of deep models as learning machines, uncertainty
estimation remains a major challenge. Existing solutions rely on modified loss
functions or architectural changes. We propose to compensate for the lack of
built-in uncertainty estimates by supplementing any network, retrospectively,
with a subsequent vine copula model, in an overall compound we call Vine-Copula
Neural Network (VCNN). Through synthetic and real-data experiments, we show
that VCNNs could be task (regression/classification) and architecture
(recurrent, fully connected) agnostic while providing reliable and
better-calibrated uncertainty estimates, comparable to state-of-the-art
built-in uncertainty solutions.",2302.12606v1
2023-03-06,Empirical partially Bayes multiple testing and compound $χ^2$ decisions,"We study multiple testing in the normal means problem with estimated
variances that are shrunk through empirical Bayes methods. The situation is
asymmetric in that a prior is posited for the nuisance parameters (variances)
but not the primary parameters (means). If the prior were known, one could
proceed by computing p-values conditional on sample variances; a strategy
called partially Bayes inference by Sir David Cox. These conditional p-values
satisfy a Tweedie-type formula and are approximated at nearly-parametric rates
when the prior is estimated by nonparametric maximum likelihood. If the
variances are in fact fixed, the approach retains type-I error guarantees.",2303.02887v1
2023-03-09,Quasi-two-dimensional anisotropic superconductivity in Li intercalated 2H-TaS$_2$,"Two-dimensional (2D) superconductivity in artificial interfaces and
atomic-thin layers has gained attention for its exotic quantum phenomena and
practical applications. Although bulk van der Waals layered materials have been
explored for 2D superconductivity, most of these compounds do not exhibit
remarkable properties despite exhibiting 2D characteristics. Here we report a
comprehensive analysis of single crystals of Li intercalated 2H-TaS$_2$
superconductor, suggesting weakly coupled anisotropic superconductivity.
Angle-dependent magnetotransport and the Berezinskii-Kosterlitz-Thouless (BKT)
transition confirm quasi-2D superconductivity in 2H-Li$_x$TaS$_2$.",2303.05377v1
2023-03-14,Lévy Langevin Monte Carlo,"Analogue to the well-known Langevin Monte Carlo method, in this article we
provide a method to sample from a target distribution \(\pi\) by simulating a
solution of a stochastic differential equation. Hereby, the stochastic
differential equation is driven by a general L\'evy process which - other than
in the case of Langevin Monte Carlo - allows for non-smooth targets. Our method
will be fully explored in the particular setting of target distributions
supported on the half-line \((0,\infty)\) and a compound Poisson driving noise.
Several illustrative examples conclude the article.",2303.07743v1
2023-03-14,Magnetocaloric effect in the high-temperature antiferromagnet YbCoC2,"The magnetic $H$-$T$ phase diagram and magnetocaloric effect in the recently
discovered high-temperature heavy-fermion compound YbCoC$_2$ have been studied.
With the increase in the external magnetic field YbCoC$_2$ experiences the
metamagnetic transition and then transition to the ferromagnetic state. The
dependencies of magnetic entropy change -$\Delta S_m (T)$ have segments with
positive and negative magnetocaloric effects for $\Delta H \leq 6$~T. For
$\Delta H = 9$~T magnetocaloric effect becomes positive with a maximum value of
-$\Delta S_m (T)$ is 4.1 J / kg K and a refrigerant capacity is 56.6 J / kg.",2303.07802v1
2023-03-28,Open networks of infinite server queues with non-homogeneous multivariate batch Poisson arrivals,"In this paper, we consider the occupancy distribution for an open network of
infinite server queues with multivariate batch arrivals following a
non-homogeneous Poisson process, and general service time distributions. We
derive a probability generating function for the transient occupancy
distribution of the network, and prove that it is necessary and sufficient for
ergodicity that the expected occupancy time for each batch be finite. Further,
we recover recurrence relations for the transient probability mass function
formulated in terms of a distribution obtained by compounding the batch size
with a multinomial distribution.",2303.16120v1
2023-04-10,"Electron-phonon interactions in LuH$_2$, LuH$_3$, and LuN","This paper presents the calculation results of electron-phonon interactions
within the LuH$_2$, LuH$_3$, and LuN systems under 0 GPa and 10 GPa via density
functional theory at the GGA-PBE level. The purpose of this work is to provide
useful data that may be of the interests of the superconducting community as it
was reported that the Lu-H-N compound is likely to be a room-temperature
superconductor under 1 GPa [Nature, 615, 244 (2023)].",2304.06726v1
2023-04-25,Independent additive weighted bias distributions and associated goodness-of-fit tests,"We use a Stein identity to define a new class of parametric distributions
which we call ``independent additive weighted bias distributions.'' We
investigate related $L^2$-type discrepancy measures, empirical versions of
which not only encompass traditional ODE-based procedures but also offer novel
methods for conducting goodness-of-fit tests in composite hypothesis testing
problems. We determine critical values for these new procedures using a
parametric bootstrap approach and evaluate their power through Monte Carlo
simulations. As an illustration, we apply these procedures to examine the
compatibility of two real data sets with a compound Poisson Gamma distribution.",2304.13179v1
2023-05-14,Physics with intact protons at the LHC: from the odderon discovery to the sensitivity to beyond standard model physics,"We describe the discovery of the colorless $C$-odd gluonic compound, the
odderon, by the D0 and TOTEM Collaborations by comparing elastic differential
cross sections measured in $pp$ and $p \bar{p}$ interactions at high energies.
We also discuss the reach on quartic anomalous couplings and the sensitivity to
axion like particle production by using the LHC as a $\gamma \gamma$ collider
and detecting the intact protons at high luminosity.",2305.08160v1
2023-05-25,High-Speed Ultrasound Imaging of Laser-Induced Cavitation Bubbles,"While the ultrasound and cavitation based therapies have mushroomed over the
years, there is a lack of online monitoring the cavitation bubble dynamics in
biological tissue. {\color{black}Here we demonstrate that with ultrasonic plane
wave imaging the fast dynamics of single cavitation bubbles can be resolved
non-invasively in a tissue mimicking material}. Due to the high contrast of the
bubbles, plane wave compounding is not necessary and frame rates of up to 74
kHz can been achieved with a research grade ultrasound scanner. Comparison with
simultaneous high-speed imaging demonstrates excellent agreement of both
measurement modalities in water and in a tissue mimicking material.",2305.16071v1
2023-06-02,Superconductivity at 12 K in La$_2$IOs$_2$: a 5d metal with osmium honeycomb layer,"We discovered superconductivity at $T_c$ = 12 K in a layered compound
La$_2$IOs$_2$ with osmium honeycomb network. Despite heavy constituent elements
unfavorable for phonon mediated mechanism, $T_c$ is the highest among
lanthanoid iodides made of lighter elements such as La$_2$IRu$_2$ with $T_c$ =
4.8 K. Electronic anomalies are observed below 60 K similar to those observed
in La$_2$IRu$_2$ below 140 K. La$_2$IOs$_2$ is a layered 5d electron system
providing a platform to investigate the interplay between the electronic
anomaly, superconductivity, and strong magnetic field.",2306.01239v1
2023-06-16,Eu ions and copper selenide nanoparticles within silica sol-gel matrices,"The sol-gel technique was developed for preparation of silica glasses doped
with europium and copper chalcogenide nanoparticles. A synthesis of copper
compounds proceeded within the solid matrix at the different steps of the
process, and features of final products can be controlled by the precursor
composition and heat treatment conditions. Eu3+-ions within the silica matrix
serves as a luminescent probe sensitive to the environment and a tool for
studies of energy transfer between different absorption and emission centers
with efficient light absorption in nanoparticles and emission by Eu3+.",2306.10138v1
2023-07-10,Excited-state normal-modes analysis: the case of porphyrins,"Excited state normal modes analysis is systematically applied to investigate
and compare relaxation and internal conversion dynamics of a free-base
porphyrin with a novel functional porphyrin derivative. We discuss strenghts
and limitation of the method, and employ it to predict very different dynamical
behaviours in the two compounds and to clarify the role of high reorganization
energy modes in driving the system towards critical regions of the potential
energy landscape. For the functionalized porphyrin, we identify modes of
vibrations along which the energy gap between different excited state potential
energy surfaces within the Q band manifold may vanish, or be significantly
reduced, with respect to the one observed in the bare porphyrin.",2307.04511v1
2023-07-18,Batched Predictors Generalize within Distribution,"We study the generalization properties of batched predictors, i.e., models
tasked with predicting the mean label of a small set (or batch) of examples.
The batched prediction paradigm is particularly relevant for models deployed to
determine the quality of a group of compounds in preparation for offline
testing. By utilizing a suitable generalization of the Rademacher complexity,
we prove that batched predictors come with exponentially stronger
generalization guarantees as compared to the standard per-sample approach.
Surprisingly, the proposed bound holds independently of overparametrization.
Our theoretical insights are validated experimentally for various tasks,
architectures, and applications.",2307.09379v1
2023-06-28,Closed Shell States in Periodic Compounds,"Vanishing of the total angular momentum of the electrons occupying all
orbitals of a closed shell in an atom is a textbook fact. Understanding the
symmetry content of the atomic shell as irreducible representation of angular
momentum, enables straightforward transfer of the notion to (translational or
helically) periodic systems. More relevant generalizations naturally appear:
stratum shell is intermediate step to physically sound band representations,
including elementary and basic ones and connected components. We show that
nontrivial determinant representation indicates stable topology of band in
single colorless layer groups and obstructive limit in in single colorless line
groups.",2307.13652v1
2023-08-14,DiffHopp: A Graph Diffusion Model for Novel Drug Design via Scaffold Hopping,"Scaffold hopping is a drug discovery strategy to generate new chemical
entities by modifying the core structure, the \emph{scaffold}, of a known
active compound. This approach preserves the essential molecular features of
the original scaffold while introducing novel chemical elements or structural
features to enhance potency, selectivity, or bioavailability. However, there is
currently a lack of generative models specifically tailored for this task,
especially in the pocket-conditioned context. In this work, we present
DiffHopp, a conditional E(3)-equivariant graph diffusion model tailored for
scaffold hopping given a known protein-ligand complex.",2308.07416v1
2023-08-22,Time-reversal symmetry-breaking flux state in an organic Dirac fermion system,"We investigate symmetry breaking in the Dirac fermion phase of the organic
compound $\alpha$-(BEDT-TTF)$_2$I$_3$ under pressure, where BEDT-TTF denotes
bis(ethylenedithio)tetrathiafulvalene. The exchange interaction resulting from
inter-molecule Coulomb repulsion leads to broken time-reversal symmetry and
particle-hole symmetry while preserving translational symmetry. The system
breaks time-reversal symmetry by creating fluxes in the unit cell. This
symmetry-broken state exhibits a large Nernst signal as well as thermopower. We
compute the Nernst signal and thermopower, demonstrating their consistency with
experimental results.",2308.11141v2
2023-09-14,Quenched large deviations in renewal theory,"In this paper we introduce and study renewal-reward processes in random
environments where each renewal involves a reward taking values in a Banach
space. We derive quenched large deviation principles and identify the
associated rate functions in terms of variational formulas involving
correctors. We illustrate the theory with three examples: compound Poisson
processes in random environments, pinning of polymers at interfaces with
disorder, and returns of Markov chains in dynamic random environments.",2309.07502v1
2023-09-14,On geometric-type approximations with applications to risk and related processes,"We explore two aspects of geometric approximation via a coupling approach to
Stein's method. Firstly, we refine precision and increase scope for
applications by convoluting the approximating geometric distribution with a
simple translation selected based on the problem at hand. Secondly, we apply
our geometric and geometric-type approximations to risk processes and related
areas, including the approximation of Poisson processes with a random time
horizon and Markov chain hitting times. Particular attention is given to
geometric approximation of random sums, for which explicit bounds are
established. These are applied to give simple approximations, including error
bounds, for the infinite-horizon ruin probability in the compound binomial risk
process.",2309.07611v1
2023-09-15,"Subsystem symmetries, critical Bose surface and immobile excitations in an extended compass model","We propose an extended compass model that hosts subsystem symmetries and has
potential experimental relevance with 3d transition metal compounds. The
subsystem symmetries strongly constrain the mobility of spin excitations and
lead to profound consequences. At the quantum critical point we find the
presence of ""critical Bose surface"" along the entire $k_x$ and $k_y$ axis.
Across which we find a nodal-line spin liquid that undergoes nematic
instability at low temperatures. In the ferro-quadrupole phase, we find that
one excitation is immobile individually analogous to ""fractons"".",2309.08300v2
2023-08-22,Pb$_9$Cu(PO$_4$)$_6$O is a charge-transfer semiconductor,"By means of density functional theory and constrained random phase
approximation we analyze the bandstructure of Pb$_9$Cu(PO$_4$)$_6$O (named
LK-99). Our data show that the lead-phosphate apatite LK-99 in the proposed
Cu-doped structure is a semiconductor with predominant charge-transfer nature,
a result incompatible with a superconducting behaviour. In order to understand
the interesting electronic and magnetic properties of this compound, it will be
necessary to study the actual response to doping, the possibility of
alternative structural and stoichiometric (dis)orders and to clarify the
magnetic interactions as well as their impact on the electronic structure.",2310.00006v1
2023-10-06,Light one-electron quasi-molecular ions within the finite-basis-set method for the two-center Dirac equation,"The electronic spectra of light one-electron quasi-molecular compounds
H-H$^+$, He$^+$-He$^2+$ and He$^+$-H$^+$ are analyzed. To this end, the
two-center Dirac equation is solved by the dual-kinetically balanced
finite-basis-set method for axially symmetric systems termed as A-DKB. This
method allows a complete relativistic consideration of these systems at fixed
internuclear distances. A comparison of the obtained results with the
nonrelativistic and relativistic calculations presented in the literature is
performed. The advantages and disadvantages of the approach are discussed in
details.",2310.04057v1
2023-10-25,Solving and Applying Fractal Differential Equations: Exploring Fractal Calculus in Theory and Practice,"In this paper, we delve into the fascinating realm of fractal calculus
applied to fractal sets and fractal curves. Our study includes an exploration
of the method analogues of the separable method and the integrating factor
technique for solving $\alpha$-order differential equations. Notably, we extend
our analysis to solve Fractal Bernoulli differential equations. The
applications of our findings are then showcased through the solutions of
problems such as fractal compound interest, the escape velocity of the earth in
fractal space and time, and estimation of time of death incorporating fractal
time. Visual representations of our results are also provided to enhance
understanding.",2310.16515v1
2023-10-25,AFLOW for alloys,"Many different types of phases can form within alloys, from highly-ordered
intermetallic compounds, to structurally-ordered but chemically-disordered
solid solutions, and structurally-disordered (i.e. amorphous) metallic glasses.
The different types of phases display very different properties, so predicting
phase formation is important for understanding how materials will behave. Here,
we review how first-principles data from the AFLOW repository and the aflow++
software can be used to predict phase formation in alloys, and describe some
general trends that can be deduced from the data, particularly with respect to
the importance of disorder and entropy in multicomponent systems.",2310.16769v1
2023-10-27,Small antimicrobial resistance proteins (SARPs): Small proteins conferring antimicrobial resistance,"Small open reading frames are understudied as they have been historically
excluded from genome annotations. However, evidence for the functional
significance of small proteins in various cellular processes accumulates.
Proteins with less than 70 residues can also confer resistance to antimicrobial
compounds, including intracellularly-acting protein toxins, membrane-acting
antimicrobial peptides and various small-molecule antibiotics. Such herein
coined Small Antimicrobial Resistance Proteins (SARPs) have emerged on
evolutionary timescales or can be enriched from protein libraries using
laboratory evolution. Our review consolidates existing knowledge on SARPs and
highlights recent advancements in proteomics and genomics that reveal pervasive
translation of unannotated genetic regions into small proteins that show
features of known SARPs. The potential contribution of small proteins to
antimicrobial resistance is awaiting exploration.",2310.17905v1
2023-11-02,Superconducting Properties of Topological Semimetal 1$T$-RhSeTe,"Platinum-group transition-metal dichalcogenides have emerged as a subject of
considerable interest in condensed matter physics due to their remarkable
topological properties and unconventional superconducting behavior. In this
study, we report the synthesis and superconducting characteristics of a new
Dirac-type topological semimetallic compound 1$T$-RhSeTe. It shows type-II
superconductivity with a superconducting transition temperature of 4.72 K and a
high upper critical field. The coexistence of superconductivity and topological
properties makes it a prime candidate for hosting topological
superconductivity.",2311.01019v1
2023-11-09,Undulations of smectic A layers in achiral liquid crystals manifested as stripe textures,"Self-assembly of organic molecules represents a fascinating playground to
create various liquid crystalline (LC) nanostructures. In this work, we study
layer undulations on micrometer scale in smectic A phases for achiral
compounds, experimentally demonstrated as regular stripe patterns induced by
thermal treatment. Undulations including their anharmonic properties are
evaluated by means of polarimetric imaging and light diffraction experiments in
cells with various thicknesses. The key role in stripe formation is played by
high negative values of the thermal expansion coefficient.",2311.05365v1
2023-11-10,Revisiting the metal-to-metal transition in $2H$-AgNiO$_2$,"The layered delafossite compound AgNiO$_2$ with $2H$ stacking symmetry
undergoes a structural metal-to-metal transition at $T_{\rm S}\sim 365$ K. It
has been described in the past as a charge-ordering transition, where local
$S=1$ spins are formed on part of the Ni sites. By means of first-principles
many body calculations, we show that the transition is in fact a site-selective
Mott transition on the Ni sublattice with only minor charge differentiation.
Key to this finding is the uncovering of ligand-hole physics, rendering a
Ni$^{2+}$ instead of a formal Ni$^{3+}$ oxidation state, in conjunction with
strong local Coulomb repulsions.",2311.06053v1
2023-11-14,Broadening of In-Field Superconducting Transitions in Hydrides,"J. E. Hirsch and F. Marsiglio in their publication, Phys. Rev. B 103, 134505
(2021), assert that hydrogen-rich compounds do not exhibit superconductivity.
Their argument hinges on the absence of broadening of superconducting
transitions in applied magnetic fields. We argue, that this assertion is
incorrect, as it relies on a flawed analysis and a selective and inaccurate
report of published data, where data supporting the authors' perspective are
highlighted while data demonstrating clear broadening are disregarded.",2311.07865v3
2023-10-26,Study of electronic and optical properties of Si$_{1-x}$Ge$_x$O$_2$ with i phase structure to find high-k,"In this work, the electronic and optical properties of Si$_{1-x}$Ge$_x$O$_2$
at equilibrium and non-equilibrium condition were calculated using a full
potential linear augmented plane wave plus local orbital method. The effect of
Si and Ge on electronic and optical properties of Si$_{1-x}$Ge$_x$O$_2$ is
investigated. It was found that Si$_{1-x}$Ge$_x$O$_2$ compounds could be used
as a high-K in electronics devices",2311.12865v1
2023-12-27,"Structural stability, electronic band structure, and optoelectronic properties of quaternary chalcogenide CuZn2MS4 (M =In and Ga) compounds via first principles","Quaternary chalcogenide compositions have been broadly explored due to their
promising potential for various optoelectronic applications. The band
structure, density of states and optical properties of CuZn2InS4 and CuZn2GaS4
for kesterite and stannite structures were studied with full potential
augmented plane wave method (FP-LAPW) via Wien2k code. The total energy in
equilibrium was calculated for different possible crystal structures and their
phase stability, and transitions with p-d orbitals were analyzed. The
absorption coefficient, dielectric function, and refractive index of these
materials were also explored within a broad range of energy. We compared the
calculated band gap values with available experimental results.",2312.16390v1
2023-12-28,Fractional non-homogeneous counting process,"A new fractional non-homogeneous counting process has been introduced and
developed using the Kilbas and Saigo three-parameter generalization of the
Mittag-Leffler function. The probability distribution function of this process
reproduces for certain set of the fractality parameters the famous Poisson and
fractional Poisson probability distributions as well as the probability
distribution function of a counting process displaying stretched exponential
interarrival times distribution. Applications of the developed fractional
non-homogeneous counting process cover fractional compound process, the
generalization of combinatorial polynomials and numbers, statistics of the
fractional non-homogeneous counting process and a new representation of the
Kilbas and Saigo function.",2312.17389v1
2024-01-02,Noncentral moderate deviations for time-changed Lévy processes with inverse of stable subordinators,"In this paper we present some extensions of recent noncentral moderate
deviation results in the literature. In the first part we generalize the
results in \cite{BeghinMacciSPL2022} by considering a general L\'evy process
$\{S(t):t\geq 0\}$ instead of a compound Poisson process. In the second part we
assume that $\{S(t):t\geq 0\}$ has bounded variation and it is not a
subordinator; thus, in some sense, we have the difference of two independent
non-null subordinators. In this way we generalize the results in
\cite{LeeMacci} for Skellam processes.",2401.01396v1
2024-01-05,Zero-shot Microclimate Prediction with Deep Learning,"Weather station data is a valuable resource for climate prediction, however,
its reliability can be limited in remote locations. To compound the issue,
making local predictions often relies on sensor data that may not be accessible
for a new, previously unmonitored location. In response to these challenges, we
propose a novel zero-shot learning approach designed to forecast various
climate measurements at new and unmonitored locations. Our method surpasses
conventional weather forecasting techniques in predicting microclimate
variables by leveraging knowledge extracted from other geographic locations.",2401.02665v1
2024-01-15,Tree and Tripod Nim,"This paper introduces a variant of the impartial combinatorial game nim,
called tree nim, as well as a particular case of tree nim called tripod nim. A
certain existence-uniqueness result and a periodicity result are proven about
the distribution of $\mathcal{P}$-positions and Grundy values in tree nim.
Tripod nim is associated to a family of arrays similar to those which arise in
the study of sequential compound games. Using these arrays, a partial analysis
is given for tripod nim. Conjectures relating to the periods of the rows of
these arrays are put forward.",2401.07943v1
2023-09-20,Proof the Collatz Conjecture by a new view of natural numbers,"The two main strategies used in this study are the binary representation and
the decomposition of a natural number into many compound functions of odd
function and even function. The Collatz conjecture regarding odd even numbers
in number theory can be examined and discussed using them in this way: The
sequence created by the finite iterations of the Collatz function becomes the
ultimately periodic sequence if any natural number is the beginning value,
proving the conjecture that has been held for 85 years.",2402.00001v1
2024-02-20,The Behavior of the Intercalant AlCl_4 Anion during the Formation of Graphite Intercalation Compound: An X-ray Absorption Fine Structure Study,"This work aims to study the insertion of AlCl_4^- anion in the crystalline
structure of oriented pyrolytic graphite (PG) at the point of view of the anion
itself. The electronic and atomic structures of the anion at different
intercalation stages are studied. In particular double-edge (bicolor) X-ray
absorption spectroscopy at the Al and Cl K-edges is carried out, highlighting a
contraction of the anion bonding at the highest intercalation degree obtained
electrochemically (stage 3), while the electronic population changes for both
the edges upon cycle.",2402.12873v1
2024-02-28,Categorical absorption of a non-isolated singularity,"We study an example of a projective threefold with a non-isolated singularity
and its derived category. The singular locus can be locally described as a line
of surface nodes compounded with a threefold node at the origin. We construct a
semiorthogonal decomposition where one component absorbs the singularity in the
sense of Kuznetsov-Shinder, and the other components are equivalent to the
derived categories of smooth projective varieties. The absorbing category is
seen to be closely related to the absorbing category constructed for nodal
varieties by Kuznetsov-Shinder, reflecting the geometry of the singularity. We
further show that the semiorthogonal decomposition is induced by one on a
geometric resolution, and briefly consider the properties of the absorbing
category under smoothing.",2402.18513v1
2024-02-29,Discovery of magnetic phase transitions in heavy-fermion superconductor CeRh$_2$As$_2$,"We report on the specific heat studies performed on a new generation of
CeRh$_2$As$_2$ single crystals. Superior quality of the samples and dedicated
experimental protocol allowed us to observe an antiferromagnetic-like behavior
in the normal state and to detect the first-order phase transition of magnetic
origin within the superconducting state of the compound. Although in the
available literature the physical behavior of CeRh$_2$As$_2$ is most often
described with the use of quadrupole density wave scenario, we propose an
alternative explanation using analogies to antiferromagnetic heavy-fermion
superconductors CeRhIn$_5$ and Ce$_2$RhIn$_8$.",2402.18763v1
2024-03-03,Properties of the entropic risk measure EVaR in relation to selected distributions,"Entropic Value-at-Risk (EVaR) measure is a convenient coherent risk measure.
Due to certain difficulties in finding its analytical representation, it was
previously calculated explicitly only for the normal distribution. We succeeded
to overcome these difficulties and to calculate Entropic Value-at-Risk (EVaR)
measure for Poisson, compound Poisson, Gamma, Laplace, exponential,
chi-squared, inverse Gaussian distribution and normal inverse Gaussian
distribution with the help of Lambert function that is a special function,
generally speaking, with two branches.",2403.01468v1
2024-03-05,Superconductivity in Ca-intercalated bilayer silicene,"Within first-principles calculations, we explore superconductivity in
Ca-intercalated bilayer silicene compound, Si2CaSi2. This arises from the
coupling of interlayer flower-like \Gamma-centered Fermi surface formed by the
hybridization of Ca-3d and Si-3pz orbitals with low-energy out-of-plane
vibrations enabled by silicene's buckling. The consequent large electron-phonon
coupling, as evident from the Eliashberg spectral function leads to
superconductivity below 5.4 K in this two-dimensional covalent system. Our
results reveal the key control parameters to achieve superconductivity in
experimentally synthesizable silicon-based thin materials that can find diverse
applications.",2403.03036v1
2024-03-08,Two sided long-time optimization singular control problems for Lévy processes and Dynkin's games,"A relationship between two sided discounted singular control problems and
Dynkin games is established for real valued L\'evy processes. In addition, the
solution of a two-sided ergodic singular control problem is obtained as the
limit of the corresponding solution of the discounted one. With these results,
we conclude that the optimal controls within the class of cadlag strategies can
be in fact found in the class of reflecting barriers controls for both
problems, and solved through some deterministic equations. To illustrate the
results, three examples are given: compound Poisson processes with two-sided
exponential jumps with and without Gaussian component, and stable processes.",2403.05731v1
2024-03-13,RKKY Interactions and Multipole Order in Ab initio Wannier Model of CeCoSi,"We calculate the RKKY interactions derived from ab initio calculations for
the intermetallic compound CeCoSi exhibiting the hidden nonmagnetic order at
$T_0$ and examine the instability towards possible multipole orders within the
random phase approximation. All 36 multipole interactions up to rank 5 are
investigated, and the maximum susceptibility exhibits an antiferro order with
$\boldsymbol{q}=\boldsymbol{0}$ for nonmagnetic multipoles of monopole $I$ and
hexadecapole $H_{0}$, yielding a charge imbalance of $f$ electrons at two Ce
atoms in the unit cell. The obtained order can explain some experiments.",2403.08172v2
2024-03-26,Mean temperature and concentration profiles in turbulent internal flows,"We derive explicit formulas for the mean profiles of temperature or
concentration of a diffusing substance (modeled as passive scalars) in forced
turbulent convection, as a function of the Reynolds and Prandtl numbers. The
derivation leverages on the observed universality of the inner-layer thermal
eddy diffusivity with respect to Reynolds and Prandtl number variations and
across different flows, and on universality of the passive scalar defect in the
core flow. Matching of the inner- and outer-layer expression yields a smooth
compound passive scalar profile. We find excellent agreement of the analytical
profile with data from direct numerical simulations of pipe and channel flows
under various forcing conditions, and over a wide range of Reynolds and Prandtl
numbers.",2403.17689v1
2024-04-14,Interlayer Pairing Induced Partially Gapped Fermi Surface in Trilayer La$_4$Ni$_3$O$_{10}$ Superconductors,"We explore the superconducting pairing mechanisms in the trilayer
$\mathrm{La}_4\mathrm{Ni}_3\mathrm{O}_{10}$ material through self-consistent
mean-field calculations. Our findings demonstrate that intralayer pairings are
substantially weaker compared to interlayer ones. Remarkably, in the state
characterized by interlayer pairing, we detect the presence of partially gapped
Fermi surfaces, a fascinating occurrence attributable to the disparity between
the inner and outer conducting layers of
$\mathrm{La}_4\mathrm{Ni}_3\mathrm{O}_{10}$. Moreover, this study provides
valuable insights into the lower superconducting transition temperatures
observed in $\mathrm{La}_4\mathrm{Ni}_3\mathrm{O}_{10}$ compounds. This
contributes to a deeper understanding of its distinct superconducting
attributes.",2404.09162v1
1996-09-18,PKS 1830-211: A Possible Compound Gravitational Lens,"Measurements of the properties of gravitational lenses have the power to tell
us what sort of universe we live in. The brightest known radio Einstein
ring/gravitational lens PKS 1830-211 (Jauncey et al., 1991), whilst obscured by
our Galaxy at optical wavelengths, has recently been shown to contain
absorption at the millimetre waveband at a redshift of 0.89 (Wiklind and
Combes, 1996a). We report the detection of a new absorption feature, most
likely due to neutral hydrogen in a second redshift system at z = 0.19.
Follow-up VLBI observations have spatially resolved the absorption and reveal
it to cover the NE compact component and part of the lower surface brightness
ring. This new information, together with existing evidence of the unusual VLBI
radio structure and difficulties in modeling the lensing system, points to the
existence of a second lensing galaxy along our line of sight and implies that
PKS 1830-211 may be a compound gravitational lens.",9609117v1
1999-11-23,CFHT AO Imaging of the CLASS Gravitational Lens System B1359+154,"We present adaptive optics imaging of the CLASS gravitational lens system
B1359+154 obtained with the Canada-France-Hawaii Telescope (CFHT) in the
infrared K band. The observations show at least three brightness peaks within
the ring of lensed images, which we identify as emission from multiple lensing
galaxies. The results confirm the suspected compound nature of the lens, as
deduced from preliminary mass modeling. The detection of several additional
nearby galaxies suggests that B1359+154 is lensed by the compact core of a
small galaxy group. We attempted to produce an updated lens model based on the
CFHT observations and new 5-GHz radio data obtained with the MERLIN array, but
there are too few constraints to construct a realistic model at this time. The
uncertainties inherent with modeling compound lenses make B1359+154 a
challenging target for Hubble constant determination through the measurement of
differential time delays. However, time delays will offer additional
constraints to help pin down the mass model. This lens system therefore
presents a unique opportunity to directly measure the mass distribution of a
galaxy group at intermediate redshift.",9911420v2
2007-02-23,Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star,"Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to
high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in
earthlike atmospheres. We investigate to what extent this NOx may modify
biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as
related compounds such as water (H2O) (essential for life) and methane (CH4)
(which has both abiotic and biotic sources) . Our model results suggest that
such signals are robust, changing in the M-star world atmospheric column by up
to 20% due to the GCR NOx effects compared to an M-star run without GCR effects
and can therefore survive at least the effects of galactic cosmic rays. We have
not however investigated stellar cosmic rays here. CH4 levels are about 10
times higher than on the Earth related to a lowering in hydroxyl (OH) in
response to changes in UV. The increase is less than reported in previous
studies. This difference arose partly because we used different biogenic input.
For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike
on the Earth, relatively modest changes in these fluxes can lead to larger
changes in the concentrations of biomarker and related species on the M-star
world. We calculate a CH4 greenhouse heating effect of up to 4K. O3
photochemistry in terms of the smog mechanism and the catalytic loss cycles on
the M-star world differs considerably compared with the Earth.",0702622v1
1992-08-27,Electronic and structural properties of GaN by the full-potential LMTO method : the role of the $d$ electrons,"The structural and electronic properties of cubic GaN are studied within the
local density approximation by the full-potential linear muffin-tin orbitals
method. The Ga $3d$ electrons are treated as band states, and no shape
approximation is made to the potential and charge density. The influence of $d$
electrons on the band structure, charge density, and bonding properties is
analyzed. It is found that due to the energy resonance of the Ga 3$d$ states
with nitrogen 2$s$ states, the cation $d$ bands are not inert, and features
unusual for a III-V compound are found in the lower part of the valence band
and in the valence charge density and density of states. To clarify the
influence of the Ga $d$ states on the cohesive properties, additional full and
frozen--overlapped-core calculations were performed for GaN, cubic ZnS, GaAs,
and Si. The results show, in addition to the known importance of non-linear
core-valence exchange-correlation corrections, that an explicit description of
closed-shell repulsion effects is necessary to obtain accurate results for GaN
and similar systems. In summary, GaN appears to be somewhat exceptional among
the III-V compounds and reminiscent of II-VI materials, in that its band
structure and cohesive properties are sensitive to a proper treatment of the
cation $d$ bands, as a result of the presence of the latter in the valence band
range.",9208022v1
1995-03-02,Resonant two-magnon Raman scattering in parent compounds of high-T$_c$ superconductors.,"We propose a theory of two-magnon Raman scattering from the insulating parent
compounds of high-T$_c$ superconductors, which contains information not only on
magnetism, but also on the electronic properties in these materials. We use
spin density wave formalism for the Hubbard model, and study diagrammatically
the profile of the two-magnon scattering and its intensity dependence on the
incoming photon frequency $\omega_i$ both for $\omega_i \ll U$ and in the
resonant regime, in which the energy of the incident photon is close to the gap
between conduction and valence bands. In the nonresonant case, we identify the
diagrams which contribute to the conventional Loudon-Fleury Hamiltonian. In the
resonant regime, where most of the experiments have been done, we find that the
dominant contribution to Raman intensity comes from a different diagram, one
which allows for a simultaneous vanishing of all three of its denominators
(i.e., a triple resonance). We study this diagram in detail and show that the
triple resonance, combined with the spin-density-wave dispersion relation for
the carriers, explains the unusual features found in the two-magnon profile and
in the two-magnon peak intensity dependence on the incoming photon frequency.
In particular, our theory predicts a maximum of the two-magnon peak intensity
right at the upper edge of the features in the optical data, which has been one
of the key experimental puzzles.",9503010v1
1997-03-06,Effects of in-chain and off-chain substitutions on spin fluctuations in the spin-Peierls compound CuGeO_3,"The effect of in-chain and off-chain substitutions on 1D spin fluctuations in
the spin-Peierls compound CuGeO_3 has been studied using Raman scattering in
order to understand the interplay between defect induced states, enhanced
spin-spin correlations and the ground state of low dimensional systems.
In-chain and off-chain substitutions quench the spin-Peierls state and induce
3D antiferromagnetic order at T\leq 5 K. Consequently a suppression of a 1D
gap-induced mode as well as a constant intensity of a spinon continuum are
observed at low temperatures. A 3D two-magnon density of states now gradually
extends to higher temperatures T\leq 60K compared with pure CuGeO_3. This
effect is more pronounced in the case of off-chain substitutions (Si) for which
a N\'eel state occurs over a larger substitution range, starting at very low
concentrations. Besides, additional low energy excitations are induced. These
effects, i.e. the shift of a dimensional crossover to higher temperatures are
due to an enhancement of the spin-spin correlations induced by a small amount
of substitutions. The results are compared with recent Monte Carlo studies on
substituted spin ladders, pointing to a similar instability of coupled,
dimerized spin chains and spin ladders upon substitution.",9703060v1
1997-04-25,Electronic structure and magnetic properties of the linear chain cuprates Sr_2CuO_3 and Ca_2CuO_3,"Sr_2CuO_3 and Ca_2CuO_3 are considered to be model systems of strongly
anisotropic, spin-1/2 Heisenberg antiferromagnets. We report on the basis of a
band-structure analysis within the local density approximation and on the basis
of available experimental data a careful analysis of model parameters for
extended Hubbard and Heisenberg models. Both insulating compounds show
half-filled nearly one-dimensional antibonding bands within the LDA. That
indicates the importance of strong on-site correlation effects. The bonding
bands of Ca_2CuO_3 are shifted downwards by 0.7 eV compared with Sr_2CuO_3,
pointing to different Madelung fields and different on-site energies within the
standard pd-model. Both compounds differ also significantly in the magnitude of
the inter-chain dispersion along the crystallographical a-direction: \approx
100 meV and 250 meV, respectively. Using the band-structure and experimental
data we parameterize a one-band extended Hubbard model for both materials which
can be further mapped onto an anisotropic Heisenberg model. From the
inter-chain dispersion we estimate a corresponding inter-chain exchange
constant J_{\perp} \approx 0.8 and 3.6 meV for Sr_2CuO_3 and Ca_2CuO_3,
respectively. Comparing several approaches to anisotropic Heisenberg problems,
namely the random phase spin wave approximation and modern versions of coupled
quantum spin chains approaches, we observe the advantage of the latter in the
reproduction of reasonable values for the N\'eel temperature T_N and the
magnetization m_0 at zero temperature. Our estimate of $J_{\perp}$ gives the
right order of magnitude and the correct tendency going from Sr_2CuO_3 to
Ca_2CuO_3. In a comparative study we also include CuGeO_3.",9704210v1
1997-07-17,XAS Study of the High Pressure Behaviour of Quartzlike Compounds,"EXAFS spectroscopy experiments have been carried out on quartz-like GaAsO4
and AlAsO4 at high pressure and room temperature. It has been shown that these
materials exhibit two structural phase transitions; the first transition to a
high pressure crystalline form occurs at 9 GPa and is reversible upon
decompression, whereas the second transition occurs at higher pressures and is
irreversible. In GaAsO4, EXAFS measurements agree with the predicted transition
from four- to six-fold coordination of oxygen atoms around the cations, but the
two local coordination transformations are not dissociated; in fact, both As
and Ga atoms exhibit a coordination change at the onset of the first phase
transition, the rate of transformation being significantly higher for Ga atoms.
In both cases, the average bond length increases very rapidly with pressure
thus yielding the first compression stage after the transition. In the second
stage, the average bond lengths increase slowly, ultimately reaching six-fold
coordination above 28 GPa and 24 GPa for As and Ga respectively. The behaviour
of the As K-edge EXAFS is the same for both compounds, and enables us to link
the behaviour of Ga and Al atoms. The local transformations are well described
and a direct link with phosphate berlinites seems timely.",9707182v1
1997-12-30,Onset of magnetism in B2 transition metals aluminides,"Ab initio calculation results for the electronic structure of disordered bcc
Fe(x)Al(1-x) (0.4<x<0.75), Co(x)Al(1-x) and Ni(x)Al(1-x) (x=0.4; 0.5; 0.6)
alloys near the 1:1 stoichiometry, as well as of the ordered B2 (FeAl, CoAl,
NiAl) phases with point defects are presented. The calculations were performed
using the coherent potential approximation within the Korringa-Kohn-Rostoker
method (KKR-CPA) for the disordered case and the tight-binding linear
muffin-tin orbital (TB-LMTO) method for the intermetallic compounds. We studied
in particular the onset of magnetism in Fe-Al and Co-Al systems as a function
of the defect structure. We found the appearance of large local magnetic
moments associated with the transition metal (TM) antisite defect in FeAl and
CoAl compounds, in agreement with the experimental findings. Moreover, we found
that any vacancies on both sublattices enhance the magnetic moments via
reducing the charge transfer to a TM atom. Disordered Fe-Al alloys are
ferromagnetically ordered for the whole range of composition studied, whereas
Co-Al becomes magnetic only for Co concentration >0.5.",9712321v2
1998-09-02,Coexistence of charge density wave and spin-Peierls orders in quarter-filled quasi-one dimensional correlated electron systems,"Charge and spin-Peierls instabilities in quarter-filled (n=1/2) compounds
consisting of coupled ladders and/or zig-zag chains are investigated. Hubbard
and t-J models including local Holstein and/or Peierls couplings to the lattice
are studied by numerical techniques. Next nearest neighbor hopping and magnetic
exchange, and short-range Coulomb interactions are also considered. We show
that, generically, these systems undergo instabilities towards the formation of
Charge Density Waves, Bond Order Waves and (generalized) spin-Peierls modulated
structures. Moderate electron-electron and electron-lattice couplings can lead
to a coexistence of these three types of orders. In the ladder, a zig-zag
pattern is stabilized by the Holstein coupling and the nearest-neighbor Coulomb
repulsion. In the case of an isolated chain, bond-centered and site-centered
2k_F and 4k_F modulations are induced by the local Holstein coupling. In
addition, we show that, in contrast to the ladders, a small charge ordering in
the chains, strongly enhances the spin-Peierls instability. Our results are
applied to the NaV_2O_5 compound (trellis lattice) and various phases with
coexisting charge disproportionation and spin-Peierls order are proposed and
discussed in the context of recent experiments. The role of the long-range
Coulomb potential is also outlined.",9809028v1
1999-02-12,Competitions in layered ruthenates: ferro- vs. antiferromagnetism and triplet vs. singlet pairing,"Ru based perovskites demonstrate an amazing richness in their magnetic
properties, including 3D and quasi-2D ferromagnetism, antiferromagnetism, and
unconventional superconductivity. Tendency to ferromagnetism, stemming from the
unusually large involvement of O in magnetism in ruthenates, leads to
ferromagnetic spin fluctuations in Sr2RuO4 and eventually to p-wave
superconductivity. A related compound Ca2RuO4 was measured to be
antiferromagnetic, suggesting a possibility of antiferromagnetic fluctuations
in Sr2RuO4 as well. Here we report first principles calculations that
demonstrate that in both compounds the ferro- and antiferromagnetic
fluctuations coexist, leading to an actual instability in Ca2RuO4 and to a
close competition between p-wave and d-wave superconducting symmetries in
Sr2RuO4. The antiferromagnetism in this system appears to be mostly related
with the nesting, which is the strongest at Q=(2pi/3,2pi/3,0). Surprisingly,
for the Fermiology of Sr2RuO4 the p-wave state wins over the d-wave one
everywhere except in close vicinity of the antiferromagnetic instability. The
most stable state within the d-wave channel has vanishing order parameter at
one out of three Fermi surfaces in Sr2RuO4, while in the p channel its
amplitude is comparable at all three of them.",9902193v1
1999-05-29,Hall Effect and Resistivity in High-Tc Superconductors: The Conserving Approximation,"The Hall coefficient (R_H) of high-Tc cuprates in the normal state shows the
striking non-Fermi liquid behavior: R_H follows a Curie-Weiss type temperature
dependence, and |R_H|>>1/|ne| at low temperatures in the under-doped compounds.
Moreover, R_H is positive for hole-doped compounds and is negative for
electron-doped ones, although each of them has a similar hole-like Fermi
surface. In this paper, we give the explanation of this long-standing problem
from the standpoint of the nearly antiferromagnetic (AF) Fermi liquid. We
consider seriously the vertex corrections for the current which are
indispensable to satisfy the conservation laws, which are violated within the
conventional Boltzmann transport approximation. The obtained total current J_k
takes an enhanced value and is no more perpendicular to the Fermi surface due
to the strong AF fluctuations. By virtue of this mechanism, the anomalous
behavior of R_H in high-Tc cuprates is neutrally explained. We find that both
the temperature and the (electron, or hole) doping dependences of R_H in
high-T_c cuprates are reproduced well by numerical calculations based on the
fluctuation-exchange (FLEX) approximation, applied to the single-band Hubbard
model. We also discuss the temperature dependence of R_H in other nearly AF
metals, e.g., V_2O_3, kappa-BEDT-TTF organic superconductors, and heavy fermion
systems close to the AF phase boundary.",9905427v1
1999-08-17,Experiments on Ladders Reveal a Complex Interplay between a Spin-Gapped Normal State and Superconductivity,"In recent years, the study of ladder materials has developed into a
well-established area of research within the general context of Strongly
Correlated Electrons. This effort has been triggered by an unusual
cross-fertilization between theory and experiments. In this paper, the main
experimental results obtained in the context of ladders are reviewed from the
perspective of a theorist. Emphasis is given to the many similarities between
the two-dimensional high-$\rm T_c$ cuprates and the two-leg ladder compounds,
including Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (14-24-41) which has a
superconducting phase at high pressure and a small hole density. Examples of
these similarities include regimes of linear resistivity vs temperature in
metallic ladders and a normal state with spin-gap or pseudogap characteristics.
Some controversial results in this context are also discussed. It is remarked
that the ladder 14-24-41 is the first superconducting copper-oxide material
with a non-square-lattice layered arrangement, and certainly much can be
learned from a careful analysis of this compound. A short summary of the main
theoretical developments in this field is also included, as well as a brief
description of the properties of non-copper-oxide ladders. Suggestions by the
author on possible experiments are described in the text. Overall, it is
concluded that the enormous experimental effort carried out on ladders has
already unveiled quite challenging and interesting physics that adds to the
rich behavior of electrons in transition-metal-oxides, and in addition
contributes to the understanding of the two-dimensional cuprates. However,
still considerable work needs to be carried out to fully understand the
interplay between charge and spin degrees of freedom in these materials.",9908250v1
1999-09-23,The Pseudogap in La(2-x)Sr(x)CuO(4): A Raman Viewpoint,"We report the results of Raman scattering experiments on single crystals of
La(2-x)Sr(x)CuO(4) [La214] as a function of temperature and doping. In
underdoped compounds low-energy B1g spectral weight is depleted in association
with the opening of a pseudogap on regions of the Fermi surface located near
(pi, 0) and (0, pi). The magnitude of the depletion increases with decreasing
doping, and in the most underdoped samples, with decreasing temperature. The
spectral weight that is lost at low-energies (omega < 800 cm-1) is transferred
to the higher energy region normally occupied by multi-magnon scattering. From
the normal state B2g spectra we have determined the scattering rate
Gamma(omega, T) of qausiparticles located near the diagonal directions in
k-space, (pi/2, pi/2) regions. In underdoped compounds, Gamma(omega, T) is
suppressed at low temperatures for energies less than Eg(x) ~ 800 cm-1. The
observed doping dependence of the two-magnon scattering and the scattering rate
suppression thus suggest that the pseudogap is characterized by an energy scale
Eg ~ J, where J is the antiferromagnetic super-exchange energy. Comparison with
the results from other techniques provides a consistent picture of the
pseudogap in La214.",9909342v3
2000-04-04,Insulator-metal transition in high-T$_c$ superconductors as result of percolation over -U centers,"The mechanism of -U center formation in high-$T_{c}$ superconductors (HTS)
with doping is considered. It is shown that the transition of HTS from
insulator to metal passes through the particular dopant concentration range
where the local transfer of singlet electron pairs from oxygen ions to pairs of
neighboring cations (-U centers) are allowed while the single-electron
transitions are still forbidden. We believe it is this concentration range that
corresponds to the region of high-Tc superconductivity and the interelectron
attraction results from the interaction of electron pairs with -U centers.
Additional hole carriers are generated as the result of singlet electron pair
transitions from oxygen ions to -U-centers. The orbitals of the arising singlet
hole pairs are localized in the nearest vicinity of -U center. In such a system
the hole conductivity starts up at the dopant concentration exceeding the
classical 2D-percolation threshold for singlet hole pair orbitals. In the
framework of the proposed model the phase diagram Ln-214 HTS compounds is
constructed. The remarkable accord between calculated and experimental phase
diagrams may be considered as the confirmation of the supposed model. The main
features of hole carriers in HTS normal state are found to be the nondegenerate
distribution and the dominant contribution of electron-electron scattering to
the hole carrier relaxation processes. Various experimentally observed
anomalies of HTS properties are shown to be the consequences of the
above-mentioned features. The conclusion is made that HTS compounds are the
special class of solids where the unusual mechanism of superconductivity
different from BCS is realized.",0004036v1
2000-05-04,Optical Properties of the Spin-Ladder Compound Sr_{14}Cu_{24}O_{41},"We report the measurements of the pseudodielectric function, far-infrared
reflectivity and Raman scattering spectra in Sr_{14}Cu_{24}O_{41} single
crystal. We study the lattice and the spin dynamics of the Cu$_2$O$_3$ spin
ladders and CuO$_2$ chains of this compound. The ellipsometric and the optical
reflectivity measurements yield the gap values of 1.4 eV, 1.86 eV, 2.34 eV (2.5
eV) for the ladders (chains) along the {\bf c}-axis and 2.4 eV along the {\bf
a}-axis. The electronic structure of the Cu$_2$O$_3$ ladders is analyzed using
tight-binding approach for the correlated electron systems. The correlation gap
value of 1.4 eV is calculated with the transfer energy (hopping) parameters
$t=t_{0}$=0.26 eV, along and perpendicular to legs, $t_{xy}$=0.026 eV
(interladder hopping) and U=2.1 eV, as a Coulomb repulsion. The optical
parameters of the infrared active phonons and plasmons are obtained by
oscillator fitting procedure of the reflectivity spectra. Raman scattering
spectra are measured at different temperatures using different laser line
energies. The two-magnon peak is observed at about 2880 cm$^{-1}$. At
temperatures below 150 K the new infrared and Raman modes appear due to the
charge ordering.",0005096v1
2000-05-10,"Magnetic, thermal, and transport properties on single crystals of antiferromagnetic Kondo-lattice Ce2PdSi3","Magnetization, heat capacity, electrical resistivity, thermoelectric power,
and Hall effect have been investigated on single-crystalline Ce_2PdSi_3. This
compound is shown to order antiferromagnetically below N'eel temperature (T_N)
\~3 K. The Sommerfeld coefficient far below T_N is found to be about 110 mJ/K^2
mol Ce, which indicates the heavy-fermion character of this compound. The
transport and magnetic properties exhibit large anisotropy with an interplay
between crystalline-electric-field (CEF) and Kondo effects. The sign of
thermoelectric power is opposite for different directions at high temperatures
and the ordinary Hall coefficient is anisotropic with opposite sign for
different geometries, indicating the anisotropic Fermi surface. The CEF
analysis from the temperature dependence of magnetic susceptibility suggests
that the ground state is |+/-1/2>. The first and the second excited CEF doublet
levels are found to be located at about 30 and 130 K, respectively. The Kondo
temperature is estimated to be the same order as T_N, indicating the presence
of a delicate competition between the Kondo effect and magnetic order.",0005164v1
2000-10-18,Proposal of an extended t-J Hamiltonian for high-Tc cuprates from ab initio calculations on embedded clusters,"A series of accurate ab initio calculations on Cu_pO-q finite clusters,
properly embedded on the Madelung potential of the infinite lattice, have been
performed in order to determine the local effective interactions in the CuO_2
planes of La_{2-x}Sr_xCuO_4 compounds. The values of the first-neighbor
interactions, magnetic coupling (J_{NN}=125 meV) and hopping integral
(t_{NN}=-555 meV), have been confirmed. Important additional effects are
evidenced, concerning essentially the second-neighbor hopping integral
t_{NNN}=+110meV, the displacement of a singlet toward an adjacent colinear
hole, h_{SD}^{abc}=-80 meV, a non-negligible hole-hole repulsion
V_{NN}-V_{NNN}=0.8 eV and a strong anisotropic effect of the presence of an
adjacent hole on the values of the first-neighbor interactions. The dependence
of J_{NN} and t_{NN} on the position of neighbor hole(s) has been rationalized
from the two-band model and checked from a series of additional ab initio
calculations. An extended t-J model Hamiltonian has been proposed on the basis
of these results. It is argued that the here-proposed three-body effects may
play a role in the charge/spin separation observed in these compounds, that is,
in the formation and dynamic of stripes.",0010257v1
2001-01-19,"Optical studies of gap, hopping energies and the Anderson-Hubbard parameter in the zigzag-chain compound SrCuO2","We have investigated the electronic structure of the zigzag ladder (chain)
compound SrCuO2 combining polarized optical absorption, reflection,
photoreflectance and pseudo-dielectric function measurements with the model
calculations. These measurements yield an energy gap of 1.42 eV (1.77 eV) at
300 K along (perpendicular) to the Cu-O chains. We have found that the lowest
energy gap, the correlation gap, is temperature independent. The electronic
structure of this oxide is calculated using both the
local-spin-density-approximation with gradient correction method, and the
tight-binding theory for the correlated electrons. The calculated density of
electronic states for non-correlated and correlated electrons shows
quasi-one-dimensional character. The correlation gap values of 1.42 eV
(indirect transition) and 1.88 eV (direct transition) have been calculated with
the electron hopping parameters t = 0.30 eV (along a chain), t_yz = 0.12 eV
(between chains) and the Anderson-Hubbard repulsion on copper sites U= 2.0 eV.
We concluded that SrCuO_2 belongs to the correlated-gap insulators.",0101302v1
2001-04-13,"Magnetic Properties of RuSr2RECu2O8 (RE=Gd, Eu) and Ru1-xSr2GdCu2+xO8-y Superconductors","Synthesis in 1% oxygen at 930C leads to non-superconducting RuSr2GdCu2O8 in
which superconductivity subsequently can be induced with oxygen annealings
without observable stoichiometric changes. Detailed ac susceptibility and
zero-field muon spin rotation experiments reveal that the superconducting
compounds always exhibit a lower temperature of the magnetic transition and
larger values of the internal magnetic field in the ordered state of the Ru
sublattice. The same annealings in oxygen, however, lead to non-superconducting
RuSr2EuCu2O8. The magnetic properties of a newly discovered series of
Ru1-xSr2GdCu2+xO8-y superconductors (maximum Tc=72 K for x=0.4) are reported.
Low temperature behavior of the magnetization shows a significant contribution
of the paramagnetic system of Gd ions to the magnetic response below the
superconducting transition. Muon-spin rotation experiments reveal the presence
of bulk magnetic transitions at low temperature for compounds with x<=0.4.
XANES Cu-K absorption edge data show an increase in Cu valence with x.",0104248v1
2001-04-17,"The ""devil's staircase"" type phase transition in NaV2O5 under high pressure","The ""devil's staircase"" type phase transition in the quarter-filled
spin-ladder compound NaV2O5 has been discovered at low temperature and high
pressure by synchrotron radiation x-ray diffraction. A large number of
transitions are found to successively take place among higher-order
commensurate phases with 2a * 2b * zc type superstructures. The observed
temperature and pressure dependence of modulation wave number qc, defined by
1/z, is well reproduced by the Axial Next Nearest Neighbor Ising (ANNNI) model.
The qc is suggested to reflect atomic displacements coupled with charge
ordering in this system. The experimental fact implies that two competitive
inter-layer interactions between the Ising spins, i.e., the nearest neighbor
J1>0 (ferro) and the next nearest neighbor J2<0 (antiferro) along the c-axis,
are intrinsic in this compound. A microscopic origin of the inter-layer
interaction is not yet known; however, the nearest neighbor interaction J1>0
between the V2O5 layers is especially interesting. It is very surprising that
the phase transition of such a complicated charge-lattice-spin coupled system
NaV2O5 can be described by the simple ANNNI model.",0104286v1
2001-06-08,"Magnetic-field -induced structural changes in the electron doped manganites: CaxSm1-xMnO3 (x = 0.8, 0.85)","We studied the correlation between magnetic, electrical, structural, and
magnetostriction properties of the electron doped manganites
Ca$_x$Sm$_{1-x}$MnO$_3$ (x = 0.85, 0.8). The paramagnetic to antiferromagnetic
transition in both the compounds while cooling is accompanied by an abrupt
increase of the spontaneous volume thermal expansion ($\Delta $V/V = 0.07 % for
x = 0.85 and 0.25 % for x = 0.2). The x = 0.15 exhibits multiple phase
separation at 5 K: G-type, and C-type antiferromagnetic phases in orthorhombic
(\QTR{it}{Pnma}) and monoclinic (\QTR{it}{P2}$_1$\QTR{it}{/m}) structures
respectively. Magnetic study on x = 0.85 also suggest ferromagnetic regions
possibly in $Pnma$ structure coexist with the antiferromagnetic phases. The
magnetization (M = 1.2 $\mu_B$) of x = 0.85 does not reach the value expected
for the complete alignment of Mn spins even at 12 T and at 12 K. Metamagnetic
transitions (C-type to Ferromagnetic) in both compounds are accompanied by
contraction of volumes under high magnetic fields. We suggest that a high
magnetic field induces \QTR{it}{P2}$_1$\QTR{it}{/m} (high volume) to
\QTR{it}{Pnma} (low volume) structural transition. This is also supported by
the neutron diffraction study.",0106164v1
2001-07-13,Unconventional antiferromagnetic correlations of the doped Haldane gap system Y$_2$BaNi$_{1-x}$Zn$_x$O$_5$,"We make a new proposal to describe the very low temperature susceptibility of
the doped Haldane gap compound Y$_2$BaNi$_{1-x}$Zn$_x$O$_5$. We propose a new
mean field model relevant for this compound. The ground state of this mean
field model is unconventional because antiferromagnetism coexists with random
dimers. We present new susceptibility experiments at very low temperature. We
obtain a Curie-Weiss susceptibility $\chi(T) \sim C / (\Theta+T)$ as expected
for antiferromagnetic correlations but we do not obtain a direct signature of
antiferromagnetic long range order. We explain how to obtain the ``impurity''
susceptibility $\chi_{imp}(T)$ by subtracting the Haldane gap contribution to
the total susceptibility. In the temperature range [1 K, 300 K] the
experimental data are well fitted by $T \chi_{imp}(T) = C_{imp} (1 + T_{imp}/T
)^{-\gamma}$. In the temperature range [100 mK, 1 K] the experimental data are
well fitted by $T \chi_{imp}(T) = A \ln{(T/T_c)}$, where $T_c$ increases with
$x$. This fit suggests the existence of a finite N\'eel temperature which is
however too small to be probed directly in our experiments. We also obtain a
maximum in the temperature dependence of the ac-susceptibility $\chi'(T)$ which
suggests the existence of antiferromagnetic correlations at very low
temperature.",0107294v2
2001-07-21,Distinct origins of magnetic -field -induced resistivity irreversibility in two manganites with similar ground states : Pr$_{0.5}$Sr$_{0.41}$Ca$_{0.09}$MnO$_{3}$ and La$_{0.5}$Ca$_{0.5}$MnO$_{3}$,"Our investigation of the magnetotransport in two charge ordered manganites
with similar magnetic ground states reveals that the origin of
magnetoresistance can not be concluded from the isofield resistivity, $\rho
$(T, constant H), measurements alone. Both
Pr$_{0.5}$Sr$_{0.41}$Ca$_{0.09}$MnO$_{3}$ (PrSrCa) and
La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ (LaCa) show a ferromagnetic transition (T$_{C}$ =
260 K for PrSrCa, 230 K for LaCa) followed by an antiferromagnetic transition
(T$_{N}$ = 170 K for PrSrCa, 140 K for LaCa). These compounds show
qualitatively similar magnetotransport : Below the irreversibility temperature
T$_{IR}$, field cooled (FC) resistivity is lower than zero field cooled (ZFC)
and decreases continuously with T, whereas the ZFC $\rho $(T, H) resembles $\
$the behavior of $\rho $(T, H = 0 T). The value of $\rho $(ZFC)/$\rho $(FC) is
$\approx $ 10$^{4}$ at 5 K and $\mu_{0}$H = 7 T in both compounds. However,
isothermal magnetic measurements suggest distinct origins of magnetoresistance
: Field cooling enhances ferromagnetic phase fraction in LaCa whereas it drives
PrSrCa into a metastable state with high magnetization. The distinct origins of
magnetotransport is also reflected in other magnetic history dependent
properties.",0107448v1
2001-08-16,Review of superconducting properties of MgB2,"This review paper illustrates the main normal and superconducting state
properties of magnesium diboride, a material known since early 1950's, but
recently discovered to be superconductive at a remarkably high critical
temperature Tc=40K for a binary compound. What makes MgB2 so special? Its high
Tc, simple crystal structure, large coherence lengths, high critical current
densities and fields, transparency of grain boundaries to current promises that
MgB2 will be a good material for both large scale applications and electronic
devices. During the last seven month, MgB2 has been fabricated in various
forms, bulk, single crystals, thin films, tapes and wires. The largest critical
current densities >10MA/cm2 and critical fields 40T are achieved for thin
films. The anisotropy ratio inferred from upper critical field measurements is
still to be resolved, a wide range of values being reported, between 1.2 and 9.
Also there is no consensus about the existence of a single anisotropic or
double energy gap. One central issue is whether or not MgB2 represents a new
class of superconductors, being the tip of an iceberg who awaits to be
discovered. Up to date MgB2 holds the record of the highest Tc in its class.
However, the discovery of superconductivity in MgB2 revived the interest in
non-oxides and initiated a search for superconductivity in related materials,
several compounds being already announced to become superconductive: TaB2,
BeB2.75, C-S composites, and the elemental B under pressure.",0108265v2
2001-08-30,"Magnetization, Structural and Nuclear Quadrupole Resonance Study of RuSr2EuCeCu2O10+d","We present the results from a magnetization, structural, and nuclear
quadrupole resonance study of the ruthenate-cuprate, RuSr2R2-xCexCu2O10+d with
x=1 and R=Eu. This compound is a superconductor for Ce doping in the range
0.4<=x<=0.8 and displays ferromagnetic order for 0.4<=x<=1.0. We show that the
tilting and rotation of the RuO6 octahedra are essentially the same for x=1,
x=0.6 and the superconducting antiferromagnet, RuSr2GdCu2O8. However, the
moment per Ru in RuSr2EuCeCu2O10+d is comparable to that observed in
RuSr2EuCu2O8. These results indicate that it is unlikely that the different
magnetic order found in RuSr2R2-xCexCu2O10+d and RuSr2RCu2O8 (R=Y,Gd,Eu) is due
to changes in structurally induced distortions of the RuO6 octahedra as found
in the ruthenate compounds (e.g. Sr1-xCaxRuO3). We show that the Cu nuclear
quadrupole resonance (NQR) data are similar to those observed in the single
CuO2 layer superconductor, La1-xSrxCuO4, where the Cu spin-lattice relaxation
rate is dominated by hyperfine coupling within the CuO2 layers and any
additional hyperfine coupling from spin fluctuations in the RuO2 layers is
small.",0108521v2
2001-11-28,Exchange coupling in CaMnO$_3$ and LaMnO$_3$: configuration interaction and the coupling mechanism,"The equilibrium structure and exchange constants of CaMnO$_3$ and LaMnO$_3$
have been investigated using total energy unrestricted Hartree-Fock (UHF) and
localised orbital configuration interaction (CI) calculations on the bulk
compounds and Mn$_2$O$_{11}^{14-}$ and Mn$_2$O$_{11}^{16-}$ clusters. The
predicted structure and exchange constants for CaMnO$_3$ are in reasonable
agreement with estimates based on its N\'eel temperature. A series of
calculations on LaMnO$_3$ in the cubic perovskite structure shows that a
Hamiltonian with independent orbital ordering and exchange terms accounts for
the total energies of cubic LaMnO$_3$ with various spin and orbital orderings.
Computed exchange constants depend on orbital ordering. UHF calculations tend
to underestimate exchange constants in LaMnO$_3$, but have the correct sign
when compared with values obtained by neutron scattering; exchange constants
obtained from CI calculations are in good agreement with neutron scattering
data provided the Madelung potential of the cluster is appropriate. Cluster CI
calculations reveal a strong dependence of exchange constants on Mn d e$_g$
orbital populations in both compounds. CI wave functions are analysed in order
to determine which exchange processes are important in exchange coupling in
CaMnO$_3$ and LaMnO$_3$.",0111536v1
2001-12-21,Electronic Structure of B-2p State in AlB2 Single Crystal: Direct Observation ofpσand pπDensity of States,"X-ray emission (XES) and absorption (XAS) spectra near the B-$K$ edge were
measured on single-crystalline AlB$_2$ compound which is an isostructural
diboride of superconducting MgB$_2$. The partial density of states (PDOS) of
B-2$p\sigma$ and $p\pi$ orbitals were derived from the polarization dependence
of XES and XAS spectra. There are considerable amounts of PDOS near the Fermi
energy in AlB$_2$ similarly to that in MgB$_2$, but there are almost no PDOS in
$p\sigma$ orbitals of AlB$_2$ near the Fermi energy, i.e., a pseudo-gap in
$p\sigma$ state and a broad metallic state in $p\pi$ state are observed. The
present result indirectly supports scenarios that the $p\sigma$ holes play an
important role in the occurrence of superconductivity in MgB$_2$. The overall
features of PDOS were found to be in good agreement with the result of band
calculation of AlB$_2$, but a small discrepancy in the Fermi energy is
observed, which is attributed to the Al vacancy in the compounds, i.e., the
estimated concentration is Al$_{0.93}$B$_2$.",0112409v1
2002-02-13,"Comparison of the Crystal Structure of the Heavy-Fermion Materials CeCoIn5, CeRhIn5 and CeIrIn5","The crystal structure of the recently discovered heavy-fermion (HF)
superconductor CeCoIn5 (Tc = 2.3 K) has been determined by high-resolution
neutron powder diffraction. It is tetragonal (space group P4/mmm), with lattice
parameters a = 4.61292(9) A and c = 7.5513(2) A at ambient conditions. Whereas
CeCoIn5 is isostructural with the HF aniferromagnet CeRhIn5 and the HF
superconductor CeIrIn5, its cell constants and its only variable positional
parameter, zIn2, differ significantly from the corresponding ones of CeRhIn5
and CeIrIn5. As a result, the distortions of the cuboctahedron [CeIn3], which
is the key structural unit in all three materials, are different in CeCoIn5
from the ones in CeRhIn5 and CeIrIn5. The compounds CeCoIn5 and CeIrIn5, which
contain the most distorted (in one or another way) [CeIn3] cuboctahedra exhibit
superconductivity at ambient pressure below 2.3 K and 0.4 K respectively. On
the other hand, CeRhIn5, in which [CeIn3] cuboctahedra are the less distorted,
and the parent compound of the materials CeTIn5 i.e. the cubic HF CeIn3 are
antiferromagnets at ambient pressure with TN = 3.8 K and 10 K correspondingly.",0202211v1
2002-03-06,Concentration Dependence of Superconductivity and Order-Disorder Transition in the Hexagonal Rubidium Tungsten Bronze RbxWO3. Interfacial and bulk properties,"We revisited the problem of the stability of the superconducting state in
RbxWO3 and identified the main causes of the contradictory data previously
published. We have shown that the ordering of the Rb vacancies in the
nonstoichiometric compounds have a major detrimental effect on the
superconducting temperature Tc.The order-disorder transition is first order
only near x = 0.25, where it cannot be quenched effectively and Tc is reduced
below 1K. We found that the high Tc's which were sometimes deduced from
resistivity measurements, and attributed to compounds with .25 < x < .30, are
to be ascribed to interfacial superconductivity which generates spectacular
non-linear effects. We also clarified the effect of acid etching and set more
precisely the low-rubidium-content boundary of the hexagonal phase.This work
makes clear that Tc would increase continuously (from 2 K to 5.5 K) as we
approach this boundary (x = 0.20), if no ordering would take place - as its is
approximately the case in CsxWO3. This behaviour is reminiscent of the
tetragonal tungsten bronze NaxWO3 and asks the same question : what mechanism
is responsible for this large increase of Tc despite the considerable
associated reduction of the electron density of state ? By reviewing the other
available data on these bronzes we conclude that the theoretical models which
are able to answer this question are probably those where the instability of
the lattice plays a major role and, particularly, the model which call upon
local structural excitations (LSE), associated with the missing alkali atoms.",0203120v1
2002-04-25,Calorimetric and transport investigations of CePd_{2+x}Ge_{2-x} (x=0 and 0.02) up to 22 GPa,"The influence of pressure on the magnetically ordered CePd_{2.02}Ge_{1.98}
has been investigated by a combined measurement of electrical resistivity,
$\rho(T)$, and ac-calorimetry, C(T), for temperatures in the range 0.3 K<T<10 K
and pressures, p, up to 22 GPa. Simultaneously CePd_2Ge_2 has been examined by
$\rho(T)$ down to 40 mK. In CePd_{2.02}Ge_{1.98} and CePd_2Ge_2 the magnetic
order is suppressed at a critical pressure p_c=11.0 GPa and p_c=13.8 GPa,
respectively. In the case of CePd_{2.02}Ge_{1.98} not only the temperature
coefficient of $\rho(T)$, A, indicates the loss of magnetic order but also the
ac-signal $1/V_{ac}\propto C/T$ recorded at low temperature. The residual
resistivity is extremely pressure sensitive and passes through a maximum and
then a minimum in the vicinity of p_c. The (T,p) phase diagram and the
A(p)-dependence of both compounds can be qualitatively understood in terms of a
pressure-tuned competition between magnetic order and the Kondo effect
according to the Doniach picture. The temperature-volume (T,V) phase diagram of
CePd_2Ge_2 combined with that of CePd_2Si_2 shows that in stoichiometric
compounds mainly the change of interatomic distances influences the exchange
interaction. It will be argued that in contrast to this the much lower
p_c-value of CePd_{2.02}Ge_{1.98} is caused by an enhanced hybridization
between 4f and conduction electrons.",0204559v1
2002-05-08,Determination of the Fermi Velocity by Angle-dependent Periodic Orbit Resonance Measurements in the Organic Conductor alpha-(BEDT-TTF)2KHg(SCN)4,"We report detailed angle-dependent studies of the microwave (f=50 to 90 GHz)
interlayer magneto-electrodynamics of a single crystal sample of the organic
charge-density-wave (CDW) conductor alpha-(BEDT-TTF)2KHg(SCN)4. Recently
developed instrumentation enables both magnetic field (B) sweeps for a fixed
sample orientation and, for the first time, angle sweeps at fixed f/B. We
observe series' of resonant absorptions which we attribute to periodic orbit
resonances (POR) - a phenomenon closely related to cyclotron resonance. The
angle dependence of the POR indicate that they are associated with the low
temperature quasi-one-dimensional (Q1D) Fermi surface (FS) of the title
compound; indeed, all of the resonance peaks collapse beautifully onto a single
set of f/B versus angle curves, generated using a semiclassical
magneto-transport theory for a single Q1D FS. We show that Q1D POR measurements
provide one of the most direct methods for determining the Fermi velocity,
without any detailed assumptions concerning the bandstructure; our analysis
yields an average value of v_F=6.5x10^4 m/s. Quantitative analysis of the POR
harmonic content indicates that the Q1D FS is strongly corrugated. This is
consistent with the assumption that the low-temperature FS derives from a
reconstruction of the high temperature quasi-two-dimensional FS, caused by the
CDW instability. Detailed analysis of the angle dependence of the POR yields
parameters associated with the CDW superstructure which are consistent with
published results. Finally, we address the issue as to whether or not the
interlayer electrodynamics are coherent in the title compound.",0205159v1
2002-07-24,Divergence of the Heavy Quasiparticle Mass at the Antiferromagnetic Quantum Critical Point in YbRh_2Si_2,"We report low temperature specific heat, C, magnetization, M, susceptibility,
chi, and electrical resistivity, rho, measurements on high-quality single
crystals of the heavy-fermion system YbRh_2(Si_{1-x} Ge_x)_2 (x=0 and 0.05).
The undoped compound shows weak antiferromagnetic (AF) order at T_N=70 mK which
is suppressed to below 10 mK by a tiny volume expansion in the x=0.05 system.
In the latter pronounced deviations from Landau Fermi liquid (LFL) behavior
occur, e.g. Delta rho ~ T over three decades in T. Both thermodynamic and
magnetic properties show a crossover at about 0.3 K: At 0.3 K <= T <= 10 K we
observe C/T ~ log(T_0/T) and a ""non-Curie"" behavior chi^{-1} ~ T^alpha with
alpha<1 similar to what was found for the prototypical system CeCu_{5.9}
Au_{0.1}. Below 0.3 K, chi turns into a Curie-Weiss dependence chi^{-1} ~
(T-Theta) indicating large unscreened Yb^{3+} moments whereas in C(T)/T a
pronounced upturn occurs. In the undoped compound the AF order is suppressed
continuously by critical fields B_{c0} ~= 0.06 T and 0.7 T applied
perpendicular and parallel to the c-axis, respectively. For B>B_{c0} a LFL
state with Delta rho = A(B)T^2 and C(T)/T = gamma_0(B) is induced, that
fulfills the Kadowaki-Woods scaling A ~ gamma_0^2. Upon reducing the magnetic
field to B_{c0} a 1/(B-B_{c0}) dependence of A(B) and gamma_0^2(B) indicates
singular scattering at the whole Fermi surface and a divergence of the heavy
quasiparticle mass.",0207570v1
2002-08-09,Persistent magnetoresistive memory in phase separated manganites,"We have studied magnetic and transport properties on different manganese
oxide based compounds exhibiting phase separation: polycrystalline
La5/8-yPryCa3/8MnO3 (y=0.3) and La1/2Ca1/2Mn1-zFezO3 (z = 0.05), and single
crystals of La5/8-yPryCa3/8MnO3 (y=0.35). Time dependent effects indicate that
the fractions of the coexisting phases are dynamically changing in a definite
temperature range. We found that in this range the ferromagnetic fraction f can
be easily tuned by application of low magnetic fields (< 1 T). The effect is
persistent after the field is turned off, thus the field remains imprinted in
the actual value of f and can be recovered through transport measurements. This
effect is due both to the existence of a true phase separated equilibrium state
with definite equilibrium fraction f0, and to the slow growth dynamics. The
fact that the same global features were found on different compounds and in
polycrystalline and single crystalline samples, suggests that the effect is a
general feature of some phase separated media.",0208199v1
2002-12-02,On the effect of heterovalent substitutions in ruthenocuprates,"We discuss the properties of superconducting derivatives of the RuSr2GdCu2O8
(1212-type) ruthenocuprate, for which heterovalent doping has been achieved
through partial substitution of Cu ions into the RuO2 planes
(Ru1-xSr2GdCu2+xO8-d, 0<x<0.75, Tcmax=72 K for x=0.3-0.4) and Ce ions into the
Gd sites (RuSr2Gd1-yCeyCu2O8, 0<y<0.1). The measurements of XANES, thermopower,
and magnetization under external pressure reveal an underdoped character of all
compounds. Muon spin rotation experiments indicate the presence of magnetic
order at low temperatures (Tm=14-2 K for x=0.1-0.4). Properties of these two
series lead us to the qualitative phase diagram for differently doped 1212-type
ruthenocuprates. The difference in temperature of magnetic ordering found for
superconducting and non-superconducting RuSr2GdCu2O8 is discussed in the
context of the properties of substituted compounds. The high pressure oxygen
conditions required for synthesis of Ru1-xSr2RECu2+xO8-d, have been extended to
synthesis of a Ru1-xSr2Eu2-yCeyCu2+xO10-d series. The Cu->Ru doping achieved in
these phases is found to decrease the temperature for magnetic ordering as well
the volume fraction of the magnetic phase.",0212018v2
2002-12-26,"Study of the electron-phonon interaction in metal diborides MeB_2 (Me=Zr, Nb, Ta, Mg) by point-contact spectroscopy","We review investigations of the electron-phonon interaction (EPI) in metal
diborides MeB_2 (Me=Zr, Nb, Ta, Mg) by point-contact (PC) spectroscopy. For
transition metal compounds the PC EPI functions were recovered and EPI
parameter $\lambda\lesssim 0.1$ were estimated. The data are consistent with
the measured surface phonon dispersion curves. The low $\lambda$ value
questions some reports about superconductivity in these compounds. Contrary,
EPI in superconducting MgB_2 films manifests also in the PC spectra itself by
virtue of an elastic EPI contribution to the excess current determined by the
energy dependence of the superconducting order parameter. To analyse the phonon
features in the PC spectra of MgB$_2$ a two-band model is exploited and the
proximity effect in the {\bf k}-space is suggested.",0212599v1
2003-01-23,Pressure-tuning of the electron-phonon coupling: the insulator to metal transition in manganites,"A comprehensive understanding of the physical origin of the unique magnetic
and transport properties of A_(1-x)A'^xMnO_3 manganites (A = trivalent
rare-earth and A' = divalent alkali-earth metal) is still far from being
achieved. The complexity of these systems arises from the interplay among
several competing interactions of comparable strength. Recently the
electron-phonon coupling, triggered by a Jahn-Teller distortion of the MnO_6
octahedra, has been recognised to play an essential role in the insulator to
metal transition and in the closely related colossal magneto-resistance. The
pressure tuning of the octahedral distortion gives a unique possibility to
separate the basic interactions and, at least in principle, to follow the
progressive transformation of a manganite from an intermediate towards a weak
electron-phonon coupling regime. Using a diamond anvil cell, temperature and
pressure-dependent infrared absorption spectra of La_(0.75)Ca_(0.25)MnO_3 have
been collected and, from the spectral weight analysis, the pressure dependence
of the insulator to metal transition temperature T_IM has been determined for
the first time up to 11.2 GPa. The T_IM(P) curve we proposed to model the
present data revealed a universality character in accounting for the whole
class of intermediate coupling compounds. This property can be exploited to
distinguish the intermediate from the weak coupling compounds pointing out the
fundamental differences between the two coupling regimes.",0301452v1
2003-02-25,"Magnon Specific Heat of Single Crystal Borocarbides RNi2B2C (R=Tm, Er, Ho, Dy, Tb, Gd)","Zero-field specific heat of the single crystals RNi2B2C (R= Er, Ho, Dy, Tb,
Gd) was measured within the temperature range 0.1 K<T<25 K. Linearized spin
wave analysis was successfully applied to account for and to rationalize the
thermal evolution of the low--temperature magnetic specific heats of all the
studied compounds (as well as the one reported for TmNi2B2C) in terms of only
two parameters, namely an energy gap, delta, and a characteristic temperature,
theta. The evolution of the gap and theta across the studied compounds
correlates very well with the known magnetic properties. Theta, as a measure of
the effective RKKY exchange couplings, scales reasonably well with the de
Gennes factor. The gap, on the other hand, reflects predominately the
anisotropic properties: ~2 K for GdNi2B2C, ~6 K for ErNi2B2C, ~7 K for
TbNi2B2C, and ~8 K for each of HoNi2B2C and DyNi2B2C. The equality in the gap
of HoNi2B2C and DyNi2B2C, coupled with the similarity in their magnetic
configurations, indicates that a variation of x in the solid solution
HoxDy1-xNi2B2C (x<0.8 and Tc<Tn) would not lead to any softening of the gap.
This supports the hypothesis of Cho et al (PRL 77,163(1996)) concerning the
influence of the collective magnetic excitations on the superconducting state.
This work underlines the importance of spin-wave excitations for a valid
description of low-temperature thermodynamics of borocarbides.",0302526v1
2003-02-26,"Open Questions in CMR Manganites, Relevance of Clustered States, and Analogies with other Compounds","This is an informal paper that contains a list of ``things we know'' and
``things we do not know'' in manganites. It is adapted from the conclusions
chapter of a recent book by the author, {\it Nanoscale Phase Separation and
Colossal Magnetoresistance. The Physics of Manganites and Related Compounds},
Springer-Verlag, Berlin, November 2002. The main new result of recent manganite
investigations is the discovery of tendencies toward inhomogeneous states, both
in experiments and in simulations of models. The colossal magnetoresistance
effect appears to be closely linked to these mixed-phase tendencies, although
considerably more work is needed to fully confirm these ideas. The paper also
includes information on cuprates, diluted magnetic semiconductors, relaxor
ferroelectrics, cobaltites, and organic and heavy fermion superconductors.
These materials potentially share some common phenomenology with the
manganites, such as a temperature scale $T^*$ above the ordering temperature
where anomalous behavior starts. Many of these materials also present
low-temperature phase competition. The possibility of colossal-like effects in
compounds that do not involve ferromagnets is briefly discussed. Overall, it is
concluded that inhomogeneous ``clustered'' states should be considered a new
paradigm in condensed matter physics, since their presence appears to be far
more common than previously anticipated.",0302550v1
2003-03-04,A Reduced Moment Magnetic Ordering in a Kondo Lattice Compound: Ce8pd24ga,"The magnetic ground state of the antiferromagnet Kondo lattice compound
Ce8Pd24Ga has been investigated using neutron powder diffraction, inelastic
neutron scattering and zero-field muon spin relaxation measurements. The
neutron diffraction analysis, below TN (3.6(0.2)K), reveals a commensurate
type-C antiferromagnetic structure with the ordered state magnetic moment of
\~0.36 mB/Ce-atom along the cubic <111> direction. The analysis of the
inelastic neutron scattering (INS) data based on the crystal field (CF) model
reveals a doublet ground state with a ground state moment of 1.29 mB/Ce-atom.
The observed magnetic moment from neutron diffraction, which is small compared
to the expected value from CF-analysis, is attributed to screening of the local
Ce moment by the Kondo effect. This is supported by the observed Kondo-type
resistivity and a small change in the entropy of Ce8Pd24Ga at TN. The
zero-field muon spin relaxation rate exhibits a sharp increase below TN
indicating ordering of Ce moments, in agreement with the neutron diffraction
data. The present studies reveal that the physical properties of Ce8Pd24Ga are
governed by the onsite Kondo compensation, the moment stabilizing intersite
RKKY interaction and the crystal field effect.",0303066v1
2003-05-20,Variation of metal-insulator transition and formation of bipolarons by the Cd-doping in the thiospinel system of Cu$_{1-x}$Cd$_{x}$Ir$_{2}$S$_{4}$,"The pseudo-binary thiospinel system Cu$_{1-x}$Cd$_{x}$Ir$_{2}$S$_{4}$ was
investigated by the x-ray diffraction, electrical resistivity, magnetic
susceptibility and specific heat measurements. It was shown that the system
exhibits a miscibility-gap behavior for the Cd substitution, however, nearly
monophasic samples was obtained by quenching at 1373 K, except for $0.4< x
\leqslant 0.6$. With increasing the Cd concentration, the room-temperature
electrical conductivity and Pauli susceptibility decrease monotonically,
consistent with the hole-filling picture. The first-order metal-insulator
transition at about 230 K in the parent compound CuIr$_{2}$S$_{4}$ is changed
into a second-order transition around 185 K when $x\sim$ 0.25, whereafter the
second-order transition disappears at $x\sim 0.8$. No superconductivity was
observed down to 1.8 K. The end-member compound CdIr$_{2}$S$_{4}$ is shown as
an insulator with a band-gap of 0.3 eV. Analysis for the data of magnetic
susceptibility and electrical resistivity suggests the formation of bipolarons
below 185 K for $0.25 <x<$ 0.8, which accounts for the absence of
superconductivity in terms of the transition from the BCS Cooper pairs to small
bipolarons.",0305453v2
2003-08-11,Metal-insulator Crossover Behavior at the Surface of NiS_2,"We have performed a detailed high-resolution electron spectroscopic
investigation of NiS$_2$ and related Se-substituted compounds
NiS$_{2-x}$Se$_x$, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS$_2$ and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.",0308204v1
2003-08-25,Unconventional Superconductivity and Nearly Ferromagnetic Spin Fluctuations in Na$_x$CoO$_2$$\cdot y$H$_2$O,"Co NQR studies were performed in recently discovered superconductor
Na$_x$CoO$_2$$\cdot y$H$_2$O to investigate physical properties in the
superconducting (SC) and normal states. Two samples from the same Na$_x$CoO$_2$
were examined, SC bilayer-hydrate sample with $T_c \sim 4.7$ K and non-SC
monolayer-hydrate sample. From the measurement of nuclear-spin lattice
relaxation rate $1/T_1$ in the SC sample, it was found that the coherence peak
is absent just below $T_c$ and that $1/T_1$ is proportional to temperature far
below $T_c$. These results, which are in qualitatively agreement with the
previous result by Fujimoto {\it et al.}, suggest strongly that unconventional
superconductivity is realized in this compound. In the normal state, $1/T_1T$
of the SC sample shows gradual increase below 100K down to $T_c$, whereas
$1/T_1T$ of the non-SC sample shows the Korringa behavior in this temperature
range. From the comparison between $1/T_1T$ and $\chi_{\rm bulk}$ in the SC
sample, the increase of $1/T_1T$ is attributed to nearly ferromagnetic
fluctuations. These remarkable findings suggest that the SC sample possesses
nearly ferromagnetic fluctuations, which are possibly related with the
unconventional superconductivity in this compound. The implication of this
finding is discussed.",0308506v1
2003-09-10,First principles electronic structure of spinel LiCr2O4: A possible half-metal?,"We have employed first-principles electronic structure calculations to
examine the hypothetical (but plausible) oxide spinel, LiCr2O4 with the d^{2.5}
electronic configuration. The cell (cubic) and internal (oxygen position)
structural parameters have been obtained for this compound through structural
relaxation in the first-principles framework. Within the one-electron band
picture, we find that LiCr2O4 is magnetic, and a candidate half-metal. The
electronic structure is substantially different from the closely related and
well known rutile half-metal CrO2. In particular, we find a smaller conduction
band width in the spinel compound, perhaps as a result of the distinct topology
of the spinel crystal structure, and the reduced oxidation state. The magnetism
and half-metallicity of LiCr2O4 has been mapped in the parameter space of its
cubic crystal structure. Comparisons with superconducting LiTi2O4 (d^{0.5}),
heavy-fermion LiV2O4 (d^{1.5}) and charge-ordering LiMn2O4 (d^{3.5}) suggest
the effectiveness of a nearly-rigid band picture involving simple shifts of the
position of E_F in these very different materials. Comparisons are also made
with the electronic structure of ZnV2O4 (d^{2}), a correlated insulator that
undergoes a structural and antiferromagnetic phase transition.",0309246v2
2003-10-17,Yb-Yb correlations and crystal-field effects in the Kondo insulator YbB12 and its solid solutions,"We have studied the effect of Lu substitution on the spin dynamics of the
Kondo insulator YbB12 to clarify the origin of the spin-gap response previously
observed at low temperature in this material. Inelastic neutron spectra have
been measured in Yb1-xLuxB12 compounds for four Lu concentrations x = 0, 0.25,
0.90 and 1.0. The data indicate that the disruption of coherence on the Yb
sublattice primarily affects the narrow peak structure occurring near 15-20 meV
in pure YbB12, whereas the spin gap and the broad magnetic signal around 38 meV
remain almost unaffected. It is inferred that the latter features reflect
mainly local, single-site processes, and may be reminiscent of the inelastic
magnetic response reported for mixed-valence intermetallic compounds. On the
other hand, the lower component at 15 meV is most likely due to dynamic
short-range magnetic correlations. The crystal-field splitting in YbB12
estimated from the Er3+ transitions measured in a Yb0.9Er0.1B12 sample, has the
same order of magnitude as other relevant energy scales of the system and is
thus likely to play a role in the form of the magnetic spectral response.",0310417v2
2003-10-23,Ferroquadrupole ordering and Gamma_5 rattling motion in clathrate compound Ce_3Pd_20Ge_6,"Lattice effects in a cerium based clathrate compound Ce_3Pd_20Ge_6 with a
cubic Cr_23C_6-type structure have been investigated by ultrasonic and thermal
expansion measurements. Elastic softenings of (C_11-C_12)/2 and C_44
proportional to the reciprocal temperature 1/T above T_Q1 = 1.25 K are well
described in terms of the quadrupole susceptibility for the ground state
Gamma_8 quartet. A huge softening of 50 % in (C_11-C_12)/2 and a spontaneous
expansion DL/L = 1.9x10^-4 along the [001] direction in particular indicate the
ferroquadrupole ordering of O_2^0 below T_Q1. The elastic anomalies associated
with the antiferromagnetic ordering at T_N2 = 0.75 K and the incommensurate
antiferromagnetic ordering are also found. Notable frequency dependence of C_44
around 10 K is accounted for by the Debye-type dispersion indicating a Gamma_5
rattling motion of an off-center Ce ion along the [111] direction with eight
fractionally occupied positions around the 4a site in a cage. The thermally
activated Gamma_5 rattling motion obeying a relaxation time t = t_0exp(E/k_BT)
with an attempt time t_0 = 3.1x10^-11 sec and an activation energy E = 70 K
dies out with decreasing temperature, and then the off-center tunneling state
of Ce ion in the 4a-site cage will appear at low temperatures.",0310552v1
2003-10-30,Textural Analysis of a Mesophase with Banana Shaped Molecules,"Observed under the polarizing microscope, the B7bis phase in the banana
compound D14F3 [J.P. Bedel et al, Liq. Cryst., 27, 1411 (2000)] displays two
types of textures of defects, namely (a): helical ribbons, that nucleate in
large quantities when the samples are quenched from a sufficiently high
temperature in the isotropic phase (b)- shapes with no helicity having the
structure of developable domains much akin to those observed in columnar
phases, either resulting from the annealing of the helical ribbons or
nucleating under slow cooling processes. The existence of these two kinds of
defects points toward the complex nature of the structure of the B7 phase,
which is at the same time a columnar and a smectic phase. Our observations fit
the model [M. Kleman, J. de Phys., 46, 1193 (1985)] according to which the
geometry of a helical ribbon is that one of the central region of a screw
dislocation with a giant Burgers vector, split into two helical disclination
lines of strength k = 1/2 which bound the ribbon. Textures and defects, already
partly documented, and growth features and annealing processes, not yet
reported in the literature, are analyzed. We conclude that the helical ribbons
and the developable domains with no helicity are textures of two different B7
states, namely a metastable state and the ground state respectively.
Comparative textural analysis is performed for two other banana compounds
exhibiting B2 phases.",0310745v1
2003-11-12,"Superconductors with Superconducting Transition Temperatures Tc = 91K (1999), 120K (1994), 340K (2000), and 371K (1995): Experimental Errors or a Technological Puzzle? Two-Component Nonstoichiometric Compounds and the Insulator--Superconductor--Metal Transition","One of the reasons for the lack of understanding of both the mechanisms
underlying the HTSC phenomenon and of the instability of materials with Tc >
300 K may be the widely accepted but wrong ideas about the types of chemical
bonding in a substance and the radii of the atoms and ions. A revision of these
concepts started in the beginning of the XX century in connection with the
investigation of non-stoichiometric compounds (the berthollides) but did not
reach a critical level until recently. Most of the HTSC materials, however, are
actually non-stoichiometric nanocomposites, whose components ""dilute"" or
""stretch"" one another. Each component resides in an ""intermediate"" state, which
still remains poorly studied. For instance, in a system of particles having two
paired electrons each, the unbroken electron pairs may start tunneling at a
certain ""medium"" concentration with the system becoming a Bose superconductor
(the state between the insulator and the metal with BCS superconductivity). For
univalent atoms (Na,Ag), however, such possibility realizes neither in
intermediate nor in the final state. Univalent metals are not superconductors.
In the berthollides, however, a possible Jahn-Teller-Peierls-type instability
may give rise to formation of diatomic molecules (Na2, Ag2)with electron pairs,
and superconductivity can set in. It is possibly such systems that were
obtained by chance in experiments with univalent components and reported to
have Tc of up to 371 K. Structures of a number of HTSC materials are
considered.",0311265v2
2004-01-06,Ultrafast real-time spectroscopy of low dimensional charge density wave compounds,"We present a femtosecond time-resolved optical spectroscopy (TRS) as an
experimental tool to probe the changes in the low energy electronic density of
states as a result of short and long range charge density wave order. In these
experiments, a femtosecond laser pump pulse excites electron-hole pairs via an
interband transition in the material. These hot carriers rapidly release their
energy via electron-electron and electron-phonon collisions reaching states
near the Fermi energy within 10-100 fs. The presence of an energy gap in the
quasiparticle excitation spectrum inhibits the final relaxation step and
photoexcited carriers accumulate above the gap. The relaxation and
recombination processes of photoexcited quasiparticles are monitored by
measuring the time evolution of the resulting photoinduced absorption. This
way, the studies of carrier relaxation dynamics give direct information of the
temperature-dependent changes in the low energy density of states. Here we
present the application of the femtosecond time-resolved optical spectroscopy
for studying changes in the low energy electronic density of states in low
dimensional charge density wave systems associated with various charge density
wave (CDW) transitions and review some recent experiments on quasi 1D and 2D
CDW compounds.",0401059v1
2004-05-04,Carbon substitution in MgB2 single crystals: structural and superconducting properties,"Growth of carbon substituted magnesium diboride Mg(B1-xCx)2 single crystals
with 0<x<0.15 is reported and the structural, transport, and magnetization data
are presented. The superconducting transition temperature decreases
monotonically with increasing carbon content in the full investigated range of
substitution. By adjusting the nominal composition, Tc of substituted crystals
can be tuned in a wide temperature range between 10 and 39 K. Simultaneous
introduction of disorder by carbon substitution and significant increase of the
upper critical field Hc2 is observed. Comparing with the non-substituted
compound, Hc2 at 15K for x=0.05 is enhanced by more then a factor of 2 for H
oriented both perpendicular and parallel to the ab-plane. This enhancement is
accompanied by a reduction of the Hc2-anisotropy coefficient gamma from 4.5
(for non-substituted compound) to 3.4 and 2.8 for the crystals with x = 0.05
and 0.095, respectively. At temperatures below 10 K, the single crystal with
larger carbon content shows Hc2 (defined at zero resistance) higher than 7 and
24 T for H oriented perpendicular and parallel to the ab-plane, respectively.
Observed increase of Hc2 cannot be explained by the change in the coherence
length due to disorder-induced decrease of the mean free path only.",0405060v1
2004-06-18,Anisotropic Hall Effect in Single Crystal Heavy Fermion YbAgGe,"Temperature- and field-dependent Hall effect measurements are reported for
YbAgGe, a heavy fermion compound exhibiting a field-induced quantum phase
transition, and for two other closely related members of the RAgGe series: a
non-magnetic analogue, LuAgGe and a representative, ''good local moment'',
magnetic material, TmAgGe. Whereas the temperature dependent Hall coefficient
of YbAgGe shows behavior similar to what has been observed in a number of heavy
fermion compounds, the low temperature, field-dependent measurements reveal
well defined, sudden changes with applied field; in specific for $H \perp c$ a
clear local maximum that sharpens as temperature is reduced below 2 K and that
approaches a value of 45 kOe - a value that has been proposed as the $T = 0$
quantum critical point. Similar behavior was observed for $H \| c$ where a
clear minimum in the field-dependent Hall resistivity was observed at low
temperatures. Although at our base temperatures it is difficult to distinguish
between the field-dependent behavior predicted for (i) diffraction off a
critical spin density wave or (ii) breakdown in the composite nature of the
heavy electron, for both field directions there is a distinct temperature
dependence of a feature that can clearly be associated with a field-induced
quantum critical point at $T = 0$ persisting up to at least 2 K.",0406435v3
2004-07-31,Coexistence of antiferromagnetic order and unconventional superconductivity in heavy fermion compounds CeRh_{1-x}Ir_xIn_5: nuclear quadrupole resonance studies,"We present a systematic ^{115}In NQR study on the heavy fermion compounds
CeRh_{1-x}Ir_xIn_5 (x=0.25, 0.35, 0.45, 0.5, 0.55 and 0.75). The results
provide strong evidence for the microscopic coexistence of antiferromagnetic
(AF) order and superconductivity (SC) in the range of 0.35 \leq x \leq 0.55.
Specifically, for x=0.5, T_N is observed at 3 K with a subsequent onset of
superconductivity at T_c=0.9 K. T_c reaches a maximum (0.94 K) at x=0.45 where
T_N is found to be the highest (4.0 K). Detailed analysis of the measured
spectra indicate that the same electrons participate in both SC and AF order.
The nuclear spin-lattice relaxation rate 1/T_1 shows a broad peak at T_N and
follows a T^3 variation below T_c, the latter property indicating
unconventional SC as in CeIrIn_5 (T_c=0.4 K). We further find that, in the
coexistence region, the T^3 dependence of 1/T_1 is replaced by a T-linear
variation below T\sim 0.4 K, with the value \frac{(T_1)_{T_c}}{(T_1)_{low-T}}
increasing with decreasing x, likely due to low-lying magnetic excitations
associated with the coexisting magnetism.",0408006v1
2004-08-06,"Low temperature synthesis, magnetic and magnetotransport properties of (La1-xLux)0.67Ca0.33MnO3 (0 < x < 0.12) system","We have been able to synthesize Lu+3 substituted La0.67Ca0.33MnO3 (LCMO) by
an auto-combustion method. Synthesis of this compound is not successful by
conventional ceramic or other chemical methods. Magnetic and electrical
transport properties of the Lu substituted LCMO [(La1-xLux)0.67Ca0.33MnO3 (0 <
x < 0.12)] system have been investigated and compared with those of the Y+3,
Pr+3, Dy+3 and Tb+3 substituted LCMO systems. All the compounds show a
ferromagnetic metal to paramagnetic insulator transition at TC. The tolerance
factor reduces from 0.917 for x = 0 to 0.909 for x = 0.12 and for this range
all are ferromagnetic metals indicating the dominance of the coupling between
spins due to double exchange over the antiferromagnetic superexchange
interaction. The transition temperatures and magnetization decrease as the Lu
concentration increases. This is satisfactorily accounted for on the basis of
transition from ferromagnetic at x = 0 to canted spin order for x > 0. All the
samples show higher magnitude of MR compared to that in pure LCMO at 80 kOe
field in the temperature range of 5 to 320K. A fairly high value of low field
magnetoresistance (LFMR) of about 30% is obtained in all the samples at a field
less than 5 kOe.",0408129v1
2004-10-26,Aging dynamics across a dynamic Almeida-Thouless line in three dimensional short-range Issuing spin glass Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite intercalation compound is a
three-dimensional short-range Ising spin glass with a spin freezing temperature
$T_{c}$ ($= 3.92 \pm 0.11$ K). The stability of the spin glass phase in the
presence of a magnetic field $H$ is examined from (i) the spin freezing
temperature $T_{f}(\omega,H)$ at which the differential field-cooled (FC)
susceptibility $\partial M_{FC}(T,H)/\partial H$ coincides with the dispersion
$\chi^{\prime}(\omega,T,H=0)$ with the angular frequency $\omega$, and (ii) the
time dependence of zero-field cooled (ZFC) susceptibility $\chi_{ZFC}$ after a
ZFC aging protocol with a wait time $t_{W}$ ($= 1.0 \times 10^{4}$). The
relaxation rate $S(t)$ (= d$\chi_{ZFC}$/d$\ln t$) exhibits a local maximum at a
characteristic time $t_{cr}$, reflecting non-equilibrium aging dynamics. The
peak time $t_{cr}(T,H)$ decreases with increasing $H$ at the fixed temperature
$T$ (2.9 K $\leq T<T_{c}$). The spin freezing temperature $T_{f}(\omega,H)$
provides evidence for the instability of the spin glass phase in thermal
equilibrium in a finite magnetic field. Both $t_{cr}(T,H)$ and
$T_{f}(\omega,H)$ exhibit certain scaling behavior predicted from the droplet
picture, suggesting a dynamic crossover from SG dynamics to paramagnetic
behavior in the presence of $H$.",0410676v2
2004-11-18,Antiferromagnetism in Pr3In: Singlet/triplet physics with frustration,"We present neutron diffraction, magnetic susceptibility and specific heat
data for a single-crystal sample of the cubic (Cu3Au structure) compound Pr3In.
This compound is believed to have a singlet (Gamma1) groundstate and a
low-lying triplet (Gamma4) excited state. In addition, nearest-neighbor
antiferromagnetic interactions are frustrated in this structure.
Antiferromagnetic order occurs below T_N = 12K with propagation vector (0, 0,
0.5 +/-\delta) where \delta \approx 1/12. The neutron diffraction results can
be approximated with the following model: ferromagnetic sheets from each of the
three Pr sites alternate in sign along the propagation direction with a
twelve-unit-cell square-wave modulation. The three moments of the unit cell of
1 \mu_B magnitude are aligned so as to sum to zero as expected for
nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic
susceptibility indicates that in addition to the antiferromagnetic transition
at 12K, there is a transition near 70K below which there is a small (0.005
\mu_B) ferromagnetic moment. There is considerable field and sample dependence
to these transitions. The specific heat data show almost no anomaly at TN =
12K. This may be a consequence of the induced moment in the Gamma1 singlet, but
may also be a sample-dependent effect.",0411493v1
2004-11-23,Dilute Metals,"Superconductivity (Tc), like any other property of a condensate, depends
critically on the concentration of atoms. ""Physical"" dilution of metals exists
in nonstoichiometric compounds. In such stoichiometric compounds as oxides,
oxygen initiates ""chemical"" dilution of the metal, but its efficiency can be
estimated only if the real radius of the oxygen ion, r0 ~ 0.5 A, is used in the
calculation. The ground-state radii of metal atoms rm ~ (1.3--2.0 A) >> r0, so
that atoms of metals occupy in the lattice ~90% of the total volume. Therefore,
the lattice parameter and the electronic properties are determined by the
metal-atom ground states. (For TiO2, the parameter c = 2.95 A ~ 2rTi = 2.94 A;
for TiO, a*sqrt(2) = 5.99 A ~ 4rTi = 5.90 A; for BaTiO3, c = 4.05 A ~ 2rBa =
4.12 A; for Y-Ba-Cu-O, c = 11.68 A ~ (4rBa + 2rY) = 11.63 A, and so on.) Each
atomic quantum state can be identified with a specific physical property of the
condensate. As a result of superposition of the ground and ionic states of each
metal atom, the fraction of the ground states decreases at the expense of the
oxygen-excited ionic ones
  (thus reducing the effective concentration of atoms). The bands narrow down
(in the limit, to the electron localization length), with the metal becoming an
insulator, as is the case, for instance, with YBa2Cu3O8-x as x decreases from
xM to 0. Conceivably, reducing the lattice deficiency in oxygen by saturating
part of its valence bonds with H, Li, or B atoms could increase the Tc
(YBa2Cu3O7-x ~ YBa2Cu3O7-x(1 + x)H2O). ""Self-dilution"" of lattices of excited
atoms by ground-state atoms was observed to occur in Pd and inert gases.",0411574v1
2004-12-02,Dielectric resonances in disordered media,"Binary disordered systems are usually obtained by mixing two ingredients in
variable proportions: conductor and insulator, or conductor and
super-conductor. and are naturally modeled by regular bi-dimensional or
tri-dimensional lattices, on which sites or bonds are chosen randomly with
given probabilities. In this article, we calculate the impedance of the
composite by two independent methods: the so-called spectral method, which
diagonalises Kirchhoff's Laws via a Green function formalism, and the Exact
Numerical Renormalization method (ENR). These methods are applied to mixtures
of resistors and capacitors (R-C systems), simulating e.g. ionic
conductor-insulator systems, and to composites consituted of resistive
inductances and capacitors (LR-C systems), representing metal inclusions in a
dielectric bulk. The frequency dependent impedances of the latter composites
present very intricate structures in the vicinity of the percolation threshold.
We analyse the LR-C behavior of compounds formed by the inclusion of small
conducting clusters (``$n$-legged animals'') in a dielectric medium. We
investigate in particular their absorption spectra who present a pattern of
sharp lines at very specific frequencies of the incident electromagnetic field,
the goal being to identify the signature of each animal. This enables us to
make suggestions of how to build compounds with specific absorption or
transmission properties in a given frequency domain.",0412061v1
2005-01-11,Two dimensionality in quasi one-dimensional cobalt oxides,"By means of muon spin rotation and relaxation ($\mu^+$SR) techniques, we have
investigated the magnetism of quasi one-dimensional (1D) cobalt oxides
$AE_{n+2}$Co$_{n+1}$O$_{3n+3}$ ($AE$=Ca, Sr and Ba, $n$=1, 2, 3, 5 and
$\infty$), in which the 1D CoO$_3$ chain is surrounded by six equally spaced
chains forming a triangular lattice in the $ab$-plane, using polycrystalline
samples, from room temperature down to 1.8 K. For the compounds with $n$=1 - 5,
transverse field $\mu^+$SR experiments showed the existence of a magnetic
transition below $\sim$100 K. The onset temperature of the transition ($T_{\rm
c}^{\rm on}$) was found to decrease with $n$; from 100 K for $n$=1 to 60 K for
$n$=5. A damped muon spin oscillation was observed only in the sample with
$n$=1 (Ca$_3$Co$_2$O$_6$), whereas only a fast relaxation obtained even at 1.8
K in the other three samples. In combination with the results of susceptibility
measurements, this indicates that a two-dimensional short-range
antiferromagnetic (AF) order appears below $T_{\rm c}^{\rm on}$ for all
compounds with $n$=1 - 5; but quasi-static long-range AF order formed only in
Ca$_3$Co$_2$O$_6$, below 25 K. For BaCoO$_3$ ($n$=$\infty$), as $T$ decreased
from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF
transition occurred at 15 K.",0501232v1
2005-02-16,Combining GW calculations with exact-exchange density-functional theory: An analysis of valence-band photoemission for compound semiconductors,"We report quasiparticle-energy calculations of the electronic bandstructure
as measured by valence-band photoemission for selected II-VI compounds and
group-III-nitrides. By applying GW as perturbation to the ground state of the
fictitious, non-interacting Kohn-Sham electrons of density-functional theory
(DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO,
ZnS and CdS. Special emphasis is put on analysing the role played by the cation
semicore d-electrons that are explicitly included as valence electrons in our
pseudopotential approach. Unlike in the majority of previous GW studies, which
are almost exlusively based on ground state calculations in the local-density
approximation (LDA), we combine GW with exact-exchange DFT calculations in the
optimised-effective potential approach (OEPx). This is a much more elaborate
and computationally expensive approach. However, we show that applying the OEPx
approach leads to an improved description of the d-electron hybridisation
compared to the LDA. Moreover we find that it is essential to use OEPx
pseudopotentials in order to treat core-valence exchange consistently. Our OEPx
based quasiparticle valence bandstructures are in good agreement with available
photoemission data in contrast to the ones based on the LDA. We therefore
conclude that for these materials OEPx constitutes the better starting point
for subsequent GW calculations.",0502404v1
2005-02-18,Spin Dilution in Frustrated Two-Dimensional s=1/2 Antiferromagnets on a Square Lattice,"$^7$Li and $^{29}$Si NMR, $\mu$SR and magnetization measurements in
Li$_2$V$_{1-x}$OTi$_x$SiO$_4$, for $0 \leq x \leq 0.2$, are presented. The
$x=0$ compound is a prototype of frustrated two-dimensional Heisenberg
antiferromagnet on a square-lattice with competing nearest ($J_1$) and
next-nearest ($J_2$) neighbour exchange interactions. Ti$^{4+}$ (S=0) for
V$^{4+}$ (S=1/2) substitution yields the spin dilution of the antiferromagnetic
layers. The analysis of the magnetization and of the nuclear spin-lattice
relaxation rate shows that spin dilution not only reduces the spin-stiffness by
a factor $\simeq (1-x)^2$, but also causes the decrease of the effective ratio
$J_2(x)/J_1(x)$. Moreover, the sublattice magnetization curves derived from
zero-field $\mu$SR measurements in the collinear phase point out that, at
variance with non-frustrated two-dimensional Heisenberg antiferromagnets, spin
dilution affects the low-temperature staggered magnetization only to a minor
extent. This observation is supported also by the $x$ dependence of the
collinear ordering temperature. The results obtained for the Ti doped samples
are discussed in the light of the results previously obtained in the pure $x=0$
compound and in non-frustrated two-dimensional Heisenberg antiferromagnets with
spin-dilution.",0502452v1
2005-03-10,Crystal and magnetic structure of La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound $(0.11\leq x\leq 0.175,"We studied the crystal and magnetic structure of the
La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound for $(0.11\leq x\leq 0.175)$ using
stoichiometric samples. For $x<0.13$ the system's ground state is insulating
canted antiferromagnetic. For $0.13\le x \le 0.175$ e below the Jahn Teller
transition temperature ($T_{\rm JT}$) the crystal structure undergoes a
monoclinic distortion. The crystal structure can be described with $P 2_1/c$
space group which permits two Mn sites. The unit cell strain parameter
$s=2(a-c)/(a+c)$ increases for $T<T_{\rm JT}$, taking the maximum value at the
Curie point, and then decreases. Below $T_{\rm M^/M^{//}}\approx 60 $ K $s$
abruptly changes slope and finally approaches T=0 K with nearly zero slope. The
change of $s$ at $T_{\rm M^/M^{//}}$ is connected to a characteristic feature
in the magnetic measurements. As $x$ increases towards the ferromagnetic
metallic boundary, although $s$ is reduced appreciably, the monoclinic
structure is preserved. The monoclinic structure is discussed with relation to
the orbital ordering, which can produce the ferromagnetic insulating ground
state. We also studied samples that were prepared in air atmosphere. This
category of samples shows ferromagnetic insulating behavior without following
the particular variation of the $s$ parameter. The crystal structure of these
samples is related to the so-called O$^{*}$ ($c>a>b/\sqrt{2}$) structure.",0503253v2
2005-03-22,Raman Response of Magnetic Excitations in Cuprate Ladders and Planes,"An unified picture for the Raman response of magnetic excitations in cuprate
spin-ladder compounds is obtained by comparing calculated two-triplon Raman
line-shapes with those of the prototypical compounds SrCu2O3 (Sr123),
Sr14Cu24O41 (Sr14), and La6Ca8Cu24O41 (La6Ca8). The theoretical model for the
two-leg ladder contains Heisenberg exchange couplings J_parallel and J_perp
plus an additional four-spin interaction J_cyc. Within this model Sr123 and
Sr14 can be described by x:=J_parallel/J_perp=1.5, x_cyc:=J_cyc/J_perp=0.2,
J_perp^Sr123=1130 cm^-1 and J_perp^Sr14=1080 cm^-1. The couplings found for
La6Ca8 are x=1.2, x_cyc=0.2, and J_perp^La6Ca8=1130 cm^-1. The unexpected sharp
two-triplon peak in the ladder materials compared to the undoped
two-dimensional cuprates can be traced back to the anisotropy of the magnetic
exchange in rung and leg direction. With the results obtained for the isotropic
ladder we calculate the Raman line-shape of a two-dimensional square lattice
using a toy model consisting of a vertical and a horizontal ladder. A direct
comparison of these results with Raman experiments for the two-dimensional
cuprates R2CuO4 (R=La,Nd), Sr2CuO2Cl2, and YBa2Cu3O(6+delta) yields a good
agreement for the dominating two-triplon peak. We conclude that short range
quantum fluctuations are dominating the magnetic Raman response in both,
ladders and planes. We discuss possible scenarios responsible for the
high-energy spectral weight of the Raman line-shape, i.e. phonons, the
triple-resonance and multi-particle contributions.",0503558v2
2005-03-29,Band Calculation for Ce-compounds on the basis of Dynamical Mean Field Theory,"The band calculation scheme for $f$ electron compounds is developed on the
basis of the dynamical mean field theory (DMFT) and the LMTO method. The
auxiliary impurity problem is solved by a method named as NCA$f^{2}$v', which
includes the correct exchange process of the $f^{1} \to f^{2}$ virtual
excitation as the vertex correction to the non-crossing approximation (NCA) for
the $f^{1} \to f^{0}$ fluctuation. This method leads to the correct magnitude
of the Kondo temperature, $T_{\rm K}$, and makes it possible to carry out
quantitative DMFT calculation including the crystalline field (CF) and the
spin-orbit (SO) splitting of the self-energy. The magnetic excitation spectra
are also calculated to estimate $T_{\rm K}$. It is applied to Ce metal and CeSb
at T=300 K as the first step. In Ce metal, the hybridization intensity (HI)
just below the Fermi energy is reduced in the DMFT band. The photo-emission
spectra (PES) have a conspicuous SO side peak, similar to that of experiments.
$T_{\rm K}$ is estimated to be about 70 K in $\gamma$-Ce, while to be about
1700 K in $\alpha$-Ce. In CeSb, the double-peak-like structure of PES is
reproduced. In addition, $T_{\rm K}$ which is not so low is obtained because HI
is enhanced just at the Fermi energy in the DMFT band.",0503675v3
2005-03-31,"Local Electronic Structure of PbVO3, a New Member of PbTiO3 Family, studied by XANES/ELNES","Recently an interesting multi-ferroic system PbVO3 [Chem. Mater. 2004] was
successfully prepared using a high-pressure and high-temperature technique. The
crystallographic features were reported. In this note we concentrate on the
theoretical XANES spectra by considering the K-edge of Vanadium. The
tetragonality [c/a=1.229 at 300 K] of PbVO3 is the largest in the PbTiO3 family
of compounds. Thus one is led naturally to examine the effect of the change of
tetragonality and the axial oxygen position on the electronic structure [i.e.
XANES spectrum]. We study this effect in two ways. At a given temperature we
vary the tetragonality and the axial oxygen position and quantify it in terms
of XANES difference spectrum. Secondly, we compute the XANES spectra at three
different temperatures, 90 K, 300 K, and 530 K and quantify the change in terms
of the difference spectrum. We note that in this compound the tetragonality
increases almost monotonically with temperature from 12 K to 570 K without
transition to the cubic phase under ambient pressure. A key objective of the
current investigation is to gain an understanding of various absorption
features in the vicinity of K-edge of V, in terms of valence, local site
symmetry, local coordination geometry, local bond distances, charge transfer,
and local projected density of states. We consider both the polarized and the
unpolarized XANES spectra. In short we have performed a local electronic study,
which nicely complements the crystallographic features reported recently in
PbVO3.",0503737v1
2005-04-05,Thermodynamics of the vortex liquid in heavy ion-irradiated superconductors,"It is shown that the large effect of heavy ion-irradiation on the
thermodynamical properties of the anisotropic superconductor
YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ extends well into the superconducting
fluctuation regime. The presence of the induced amorphous columnar defects
shifts the specific heat maximum at the normal-to-superconducting transition.
This effect is similar to that recently put into evidence in cubic
K$_{x}$Ba$_{1-x}$BiO$_{3}$ ($x \simeq 0.35$). In both compounds, vortex pinning
manifests itself as a sharp angular dependence of the \em equilibrium \rm
torque. In YBa$_{2}$Cu$_{3}$O$_{7-\delta}$, pinning by the defects appears at
the temperature $T_{C_{p}}^{max}$ of the specific heat maximum, well above the
magnetic irreversibility line $T_{irr}(H)$. In isotropic
K$_{x}$Ba$_{1-x}$BiO$_{3}$, the onset of the pinning-related torque anomaly
tracks the onset of the specific heat anomaly and the irreversibility line. In
YBa$_{2}$Cu$_{3}$O$_{7-\delta}$, fluctuations of the amplitude of the order
parameter (and not vortex line wandering) are ultimately responsible for the
vanishing of pinning. In K$_{x}$Ba$_{1-x}$BiO$_{3}$, vortex pinning disappears
only at the superconducting-to-normal transition. The results indicate that in
both compounds, the pinning energy at the ``Bose glass'' transition is large
with respect to the total free energy gain in the superconducting state. By
implication, the mechanism of this latter transition should be reconsidered.",0504100v2
2005-04-21,Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in Ce$_{1-x}$La$_x$Ni$_9$Ge$_4$,"We report specific heat and magneto-resistance studies on the compound
Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$ for various concentrations over the entire
stoichiometric range. Our data reveal single-ion scaling with Ce-concentration
between $x = 0.1$ and 0.95. Furthermore, CeNi${}_9$Ge${}_4$ turns out to have
the largest ever recorded value of the electronic specific heat $\Delta c/T
\approx$ 5.5 J $\rm K^{-2}mol^{-1}$ at $T=0.08$ K which was found in Cerium
f-electron lattice systems. In the doped samples $\Delta c/T$ increases
logarithmically in the temperature range between 3 K and 50 mK typical for
non-Fermi liquid (nFl) behavior, while $\rho$ exhibits a Kondo-like minimum
around 30 K, followed by a single-ion local nFl behavior. In contrast to this,
CeNi${}_9$Ge${}_4$ flattens out in $\Delta c/T$ below 300 mK and displays a
pronounced maximum in the resistivity curve at 1.5 K indicating a coherent
heavy fermion groundstate. These properties render the compound
Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$ a unique system on the borderline between
Fermi liquid and nFl physics.",0504560v1
2005-05-23,"Hole redistribution in Sr\_(14-x)Ca\_xCu\_24O\_41 (x = 0, 12) spin ladder compounds: ^63Cu and ^17O NMR study under pressure","We report the results of a ^63Cu and ^17O NMR study of the nuclear quadrupole
interaction tensor, ^(17,63)nu\_{Q,alpha}, in the hole doped spin ladder system
Sr\_(14-x)Ca\_xCu\_24O\_41 (x = 0 and 12) performed under ambient and high
pressures. NMR data show that the hole density in the Cu\_2O\_3 ladder layer
grows with temperature, Ca content and an applied pressure. We have derived the
hole occupation of Cu 3d and O 2p orbitals at the different ion sites in the
Cu\_2O\_3 ladder as a function of the temperature, Ca substitution and
pressure. We also suggest that the most important role of high pressure for the
stabilization of a superconducting ground state in Ca-rich two-leg ladders is
an increase of the hole concentration in the conducting Cu\_2O\_3 planes. We
have obtained an estimate of 0.10 hole per Cu1 for the hole concentration at
low temperature in Ca12 under 32 kbar when this compound undergoes a
superconducting transition at 5K. Such a value fits fairly well with the doping
phase diagram of cuprate superconductors.",0505561v1
2005-06-09,Pressure-induced valence change in the rare earth metals:The case of Praseodymium,"The rare earth metal praseodymium (Pr) transforms from the d-fcc crystal
structure (Pr-III) to {$\alpha$}-U one (Pr-IV) at 20 GPa with a large volume
collapse (${\rm\Delta} V/V$ = 0.16), which is associated with the valence
change of the Pr ion. The two 4{\it f} electrons in the Pr ion is supposed to
be itinerant in the Pr-IV phase. In order to investigate the electronic state
of the phase IV, we performed the high pressure electrical resistance
measurement using the diamond anvil cell up to 32 GPa. In the Pr-IV phase, the
temperature dependence of the resistance shows an upward negative curvature,
which is similar to the itinerant 5{\it f} electron system in actinide metals
and compounds. This suggests the narrow quasiparticle band of the 4{\it f}
electrons near the Fermi energy. A new phase boundary is found at $T_{0}$ in
the Pr-IV phase. From the temperature and magnetic field dependences of the
resistance at 26 GPa, the ground state of the Pr-IV phase is suggested to be
magnetic. Several possibilities for the origin of $T_{0}$ are discussed.",0506222v1
2005-06-24,First-principle Wannier functions and effective lattice fermion models for narrow-band compounds,"We propose a systematic procedure for constructing effective lattice fermion
models for narrow-band compounds on the basis of first-principles electronic
structure calculations. The method is illustrated for the series of
transition-metal (TM) oxides: SrVO$_3$, YTiO$_3$, V$_2$O$_3$, and
Y$_2$Mo$_2$O$_7$. It consists of three parts, starting from LDA. (i)
construction of the kinetic energy Hamiltonian using downfolding method. (ii)
solution of an inverse problem and construction of the Wannier functions (WFs)
for the given kinetic energy Hamiltonian. (iii) calculation of screened Coulomb
interactions in the basis of \textit{auxiliary} WFs, for which the
kinetic-energy term is set to be zero. The last step is necessary in order to
avoid the double counting of the kinetic-energy term, which is included
explicitly into the model. The screened Coulomb interactions are calculated in
a hybrid scheme. First, we evaluate the screening caused by the change of
occupation numbers and the relaxation of the LMTO basis functions, using the
conventional constraint-LDA approach, where all matrix elements of
hybridization involving the TM $d$ orbitals are set to be zero. Then, we switch
on the hybridization and evaluate the screening associated with the change of
this hybridization in RPA. The second channel of screening is very important,
and results in a relatively small value of the effective Coulomb interaction
for isolated $t_{2g}$ bands. We discuss details of this screening and consider
its band-filling dependence, frequency dependence, influence of the lattice
distortion, proximity of other bands, and the dimensionality of the model
Hamiltonian.",0506632v1
2005-08-22,"Magnetoresistance, specific heat and magnetocaloric effect of equiatomic rare-earth transition-metal magnesium compounds","We present a study of the magnetoresistance, the specific heat and the
magnetocaloric effect of equiatomic $RET$Mg intermetallics with $RE = {\rm
La}$, Eu, Gd, Yb and $T = {\rm Ag}$, Au and of GdAuIn. Depending on the
composition these compounds are paramagnetic ($RE = {\rm La}$, Yb) or they
order either ferro- or antiferromagnetically with transition temperatures
ranging from about 13 to 81 K. All of them are metallic, but the resistivity
varies over 3 orders of magnitude. The magnetic order causes a strong decrease
of the resistivity and around the ordering temperature we find pronounced
magnetoresistance effects. The magnetic ordering also leads to well-defined
anomalies in the specific heat. An analysis of the entropy change leads to the
conclusions that generally the magnetic transition can be described by an
ordering of localized $S=7/2$ moments arising from the half-filled $4f^7$
shells of Eu$^{2+}$ or Gd$^{3+}$. However, for GdAgMg we find clear evidence
for two phase transitions indicating that the magnetic ordering sets in
partially below about 125 K and is completed via an almost first-order
transition at 39 K. The magnetocaloric effect is weak for the antiferromagnets
and rather pronounced for the ferromagnets for low magnetic fields around the
zero-field Curie temperature.",0508528v1
2005-08-27,Power Law Multi-Scaling of Material Strength,"Power law is one of the the simplest forms of the relationship between
different variables of a system. It leads naturally to the introduction of
compound parameters describing physical properties of the system. Often one of
the variables of interest is the object dimension, or time. The prevalence of a
simple power law over the entire range of dimensions or times can be helpfully
interpreted as size or time independence of the corresponding compound physical
parameter of the system. However, it is also often found that a simple power
law only persists for some extreme values, e.g. for very large and/or small
sizes, or very short or long times. Transitions between regimes of different
power law asymptotic behaviour are encountered frequently in the description of
a wide variety of physical systems. While asymptotic power law behaviour may
often be readily predicted, e.g. on dimensional grounds, the evaluation of the
relationship between system parameters in the transition range usually requires
laborious detailed solution. To obviate this difficulty we introduce, on rather
general basis, something we refer to as the merging, or 'knee' function. The
function possesses sufficient flexibility to describe transitions of various
sharpness. To demonstrate its usefuness, the merging function is applied to a
variety of well-known scaling laws in the mechanics and strength of materials
and structures.",0508653v1
2005-09-10,Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6,"Few examples of magnetic systems displaying a transition to pure dipolar
magnetic order are known to date, and single-molecule magnets can provide an
interesting example. The molecular cluster spins and thus their dipolar
interaction energy can be quite high, leading to reasonably accessible ordering
temperatures, provided the crystal field anisotropy is sufficiently small. This
condition can be met for molecular clusters of sufficiently high symmetry, as
for the Mn6 compound studied here. Magnetic specific heat and susceptibility
experiments show a transition to ferromagnetic dipolar order at T_{c} = 0.16 K.
Classical Monte-Carlo calculations indeed predict ferromagnetic ordering and
account for the correct value of T_{c}. In high magnetic fields we detected the
contribution of the ^{55}Mn nuclei to the specific heat, and the characteristic
timescale of nuclear relaxation. This was compared with results obtained
directly from pulse-NMR experiments. The data are in good mutual agreement and
can be well described by the theory for magnetic relaxation in highly polarized
paramagnetic crystals and for dynamic nuclear polarization, which we
extensively review. The experiments provide an interesting comparison with the
recently investigated nuclear spin dynamics in the anisotropic single molecule
magnet Mn12-ac.",0509261v2
2005-09-20,Magnetic structure and double exchange in hypothetical compound La1-xCaxMnO3,"Question about the appearance of different magnetic structures in the family
of compounds La1-xCaxMnO3,is investigated theoretically. It is supposed that
the whole series has GdFeO3 structure type. The problem is considered at
absolute zero temperature in the nearest neighbor approximation. Superexchange,
double exchange and anisotropy energy are taken into account-all together 10
interaction parameters. The spin operator of double exchange interaction in
crystal between ions with different valence Mn3+ and Mn4+ is the straight
generalization of two-spin operator in the known problem of Anderson and
Hasegawa molecule. Minimization of the ground state energy with respect to
direction angles of magnetic sub-lattices leads to a system of transcendental
equations whose solutions give 11 types of magnetic configurations: two
ferromagnetic, three collinear antiferromagnetic and six non-collinear. When
the concentration of Ca ions x changes one spin configuration replaces another
as the ground state. As a whole the sequence of configurations when x changes
from 0 till 1 can be brought in correspondence to those observed on the
experiment. The comparison with experiment was made by means of mixed
procedure: part of numerical values of interaction parameters and transition
concentrations x from one configuration to another were taken from experiment
while the missing values of these parameters were calculated with the help of
the corresponding theoretical relations representing the conditions of equality
of different phases energies at the concentration crossing.",0509507v1
2005-11-14,"On the dc Magnetization, Spontaneous Vortex State and Specific Heat in the superconducting state of the weakly ferromagnetic superconductor RuSr$_{2}$GdCu$_{2}$O$_{8}$","Magnetic-field changes $<$ 0.2 Oe over the scan length in magnetometers that
necessitate sample movement are enough to create artifacts in the dc
magnetization measurements of the weakly ferromagnetic superconductor
RuSr$_{2}$GdCu$_{2}$O$_{8}$ (Ru1212) below the superconducting transition
temperature $T_{c} \approx$ 30 K. The observed features depend on the specific
magnetic-field profile in the sample chamber and this explains the variety of
reported behaviors for this compound below $T_{c}$. An experimental procedure
that combines improvement of the magnetic-field homogeneity with very small
scan lengths and leads to artifact-free measurements similar to those on a
stationary sample has been developed. This procedure was used to measure the
mass magnetization of Ru1212 as a function of the applied magnetic field H (-20
Oe $\le$ H $\le$ 20 Oe) at $T < T_{c}$ and discuss, in conjunction with
resistance and ac susceptibility measurements, the possibility of a spontaneous
vortex state (SVS) for this compound. Although the existence of a SVS can not
be excluded, an alternative interpretation of the results based on the granular
nature of the investigated sample is also possible. Specific-heat measurements
of Sr$_{2}$GdRuO$_{6}$ (Sr2116), the precursor for the preparation of Ru1212
and thus a possible impurity phase, show that it is unlikely that Sr2116 is
responsible for the specific-heat features observed for Ru1212 at $T_{c}$.",0511323v1
2005-11-24,Magnetoresistance Anomalies in Ce-based Heavy Fermion Compounds,"The work presents experimental results of precision magnetoresistance dr(H,T)
measurements obtained for canonical heavy fermion compounds CeAl2, CeAl3, CeCu6
and substitutional solid solutions CeCu6-xAux (x=0.1 and 0.2) and
Ce(Al0.95M0.05)2 (M - Co, Ni). The research was performed in a wide range of
temperatures (1.8-30K) and magnetic fields (up to 80 kOe). The data analysis
indicates that the most consistent interpretation of magnetoresistance of both
paramagnetic and magnetically ordered Ce-based systems with strong electron
correlations can be obtained through the approach developed by K.Yosida
(Phys.Rev., 107, 396(1957)) that considers charge carrier scattering on
localized magnetic moments in metallic matrix. Within this approach local
magnetic susceptibility hiloc(H,T0)=(1/H d(dr/r)/dH)1/2 has been estimated
directly from the magnetoresistance data dr/r=f(H,T0). As a result, two
additional contributions to magnetoresistance in Ce-based magnetic
intermetallides have been established and classified. The procedure allowed to
determine the peculiarities of magnetic phase ht diagram as well as to reveal
the electron density of states renormalization effects in a wide vicinity of
quantum critical point in the archetypal Ce-based systems with strong electron
correlations.",0511600v1
2005-12-23,The role of strong electronic correlations in the metal-to-insulator transition in disordered LiAl_yTi_(2-y)O_4,"The compound LiAl_yTi_(2-y)O_4 undergoes a metal-to-insulator transition for
y_c ~0 .33. This system, in the absence of strong electronic correlations, is a
prototypical example of quantum site percolation. However, it is known that the
effects of disorder produced by such a percolating lattice are insufficient to
explain this transition: a quantum site percolation model predicts y_c ~ 0.8,
well above the experimental value. We have included an on-site Hubbard
interaction into a model of this compound, using a real-space Hartree-Fock
approach, and have found that for a Hubbard energy equal to 1.5 times the
non-interacting bandwidth one obtains y_c~0.35. Further, as a function of
increasing Hubbard energy, we find that an Altshuler-Aronov suppression of the
density of states, delta N(E) ~ sqrt(| E-E_F |), reduces the density of states
at the Fermi energy to zero at the critical Hubbard interaction. Using this
ratio of correlation to hopping energy one is led to a prediction for the value
of near-neighbour superexchange J/t~1/3 which is similar to that for the
cuprate superconductors.",0512619v3
2006-01-17,Fluxiod jumps coupled high critical current density of nano-Co3O4 doped MgB2,"Polycrystalline MgB2 samples with 0, 2, 4 and 6 percent added nano-Co3O4
being synthesized by vacuum (10-5 Torr) annealing at 750 0C for three hours
each are found to be nearly single phase with presence of only a small quantity
of Mg/MgO in pristine sample and in addition the Co2O3 in doped compounds. All
the samples exhibited clear and sharp diamagnetic transitions at around 38 K,
in Zero-field-cooled (ZFC) magnetic susceptibility measurements with sizeable
signal. The Field cooled (FC) measurements though having sharp transitions, but
showed a very small signal, indicating high level of pinning centers in these
samples. Further some of the doped samples exhibited
Paramagnetic-Meissner-Effect (PME) in applied field of 5 Oe. The critical
current density (Jc), being estimated by invoking Bean model for the pristine
compound increase by nearly an order of magnitude for 2 and 4 percent
nano-Co3O4 doping and later the same decreases sharply for 6 percent sample at
nearly all studied temperatures and applied fields. Further the increased Jc (~
10^8 A/cm2) is coupled with fluxiod jumps (T = 20 K and H = 1 T). Fluxiod Jumps
are not seen in relatively low Jc pristine or 6 percent sample. This means the
fluxiod-jumps are intrinsic only to the high Jc samples.",0601359v1
2006-03-15,"Anomalous Hall Effect in three ferromagnets: EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30","The Hall resistivity (Rho_xy), resistivity (Rho_xx), and magnetization of
three metallic ferromagnets are investigated as a function of magnetic field
and temperature. The three ferromagnets, EuFe4Sb12 (Tc = 84 K), Yb14MnSb11 (Tc
= 53 K), and Eu8Ga16Ge30 (Tc = 36 K) are Zintl compounds with carrier
concentrations between 1 x 10^21 cm^-3 and 3.5 x 10^21 cm^-3. The relative
decrease in Rho_xx below Tc [Rho_xx(Tc)/Rho_xx(2 K)] is 28, 6.5, and 1.3 for
EuFe4Sb12, Yb14MnSb11, and Eu8Ga16Ge30 respectively. The low carrier
concentrations coupled with low magnetic anisotropies allow a relatively clean
separation between the anomalous (Rho_'xy), and normal contributions to the
measured Hall resistivity. For each compound the anomalous contribution in the
zero field limit is fit to alpha Rho_xx + sigma_xy rho_xx^2 for temperatures T
< Tc. The anomalous Hall conductivity, sigma_xy, is -220 +- 5 (Ohm^-1 cm^-1),
-14.7 +- 1 (Ohm^-1 cm^-1), and 28 +- 3 (Ohm^-1 cm^-1) for EuFe4Sb12,
Yb14MnSb11, and Eu8Ga16Ge30 respectively and is independent of temperature for
T < Tc if the change in spontaneous magnetization (order parameter) with
temperature is taken into account. These data are consistent with recent
theories of the anomalous Hall effect that suggest that even for stochiometric
ferromagnetic crystals, such as those studied in this article, the intrinsic
Hall conductivity is finite at T = 0, and is a ground state property that can
be calculated from the electronic structure.",0603410v1
2006-03-24,Resonance reactions and enhancement of weak interactions in collisions of cold molecules,"With the creation of ultracold atoms and molecules, a new type of chemistry -
""resonance"" chemistry - emerges: chemical reactions can occur when the energy
of colliding atoms and molecules matches a bound state of the combined molecule
(Feshbach resonance). This chemistry is rather similar to reactions that take
place in nuclei at low energies. In this paper we suggest some problems for
future experimental and theoretical work related to the resonance chemistry of
ultracold molecules. Molecular Bose-Einstein condensates are particularly
interesting because in this system collisions and chemical reactions are
extremely sensitive to weak fields; also, a preferred reaction channel may be
enhanced due to a finite number of final states. The sensitivity to weak fields
arises due to the high density of narrow compound resonances and the
macroscopic number of molecules with kinetic energy E=0 (in the ground state of
a mean-field potential). The high sensitivity to the magnetic field may be used
to measure the distribution of energy intervals, widths, and magnetic moments
of compound resonances and study the onset of quantum chaos. A difference in
the production rate of right-handed and left-handed chiral molecules may be
produced by external electric and magnetic fields and the finite width of the
resonance. The same effect may be produced by the parity-violating energy
difference in chiral molecules.",0603639v2
2006-04-18,Excitation spectrum of a model antiferromagnetic spin-trimer,"We present an inelastic neutron scattering (INS) study of the excitation
spectrum of a model S = 1/2 equilateral Heisenberg trimer,
Cu_3(O_2C_16H_23)_6.1.2C_6H_12. Earlier measurements were interpreted on the
basis of a spin ground state consisting of a pair of degenerate S = 1/2
doublets, with an S = 3/2 quartet excited state. Given that the simplest model
of magnetism for this compound includes a degenerate ground state, using
thermodynamic probes to determine the excitation energy between the ground and
excited states is challenging. An estimate of the excitation energy between the
ground and excited states based on magnetic susceptibility measurements is
roughly ~28 meV. INS measurements of this compound are likewise challenging
since inter- and intramolecular vibrational modes associated with the organic
ligands are at frequencies similar to the magnetic excitations. However, by
measuring a non-magnetic analog, i.e. ligands only, as well as the temperature
dependence of the excitations in the magnetic system, we are able to determine
the excitation energy as being approximately 36.5 meV at T = 10 K, with a
gradual softening to 32 meV with increasing temperature. We emphasize the
consideration of ligand/lattice based excitations while interpreting magnetic
excitations of such nanomagnetic systems containing organic molecules while
underscoring the importance of INS in determining the magnetic excitation
spectrum in systems with degenerate ground states.",0604420v2
2006-04-20,Orbital ordering phenomena in $d$- and $f$-electron systems,"In recent decades, novel magnetism of $d$- and $f$-electron compounds has
been discussed very intensively both in experimental and theoretical research
fields of condensed matter physics. It has been recognized that those material
groups are in the same category of strongly correlated electron systems, while
the low-energy physics of $d$- and $f$-electron compounds has been separately
investigated rather in different manners. One of common features of both $d$-
and $f$-electron systems is certainly the existence of active orbital degree of
freedom, but in $f$-electron materials, due to the strong spin-orbit
interaction in rare-earth and actinide ions, the physics seems to be quite
different from that of $d$-electron systems. In general, when the number of
internal degrees of freedom and relevant interactions is increased, it is
possible to obtain rich phase diagram including large varieties of magnetic
phases by using several kinds of theoretical techniques. However, we should not
be simply satisfied with the reproduction of rich phase diagram. It is believed
that more essential point is to seek for a simple principle penetrating
complicated phenomena in common with $d$- and $f$-electron materials, which
opens the door to a new stage in orbital physics. In this sense, it is
considered to be an important task of this article to explain common features
of magnetism in $d$- and $f$-electron systems from a microscopic viewpoint,
using a key concept of orbital ordering, in addition to the review of the
complex phase diagram of each material group.",0604467v2
2006-07-05,Magnetic structure and critical behavior of GdRhIn$_{5}$: resonant x-ray diffraction and renormalization group analysis,"The magnetic structure and fluctuations of tetragonal GdRhIn5 were studied by
resonant x-ray diffraction at the Gd LII and LIII edges, followed by a
renormalization group analysis for this and other related Gd-based compounds,
namely Gd2IrIn8 and GdIn3. These compounds are spin-only analogs of the
isostructural Ce-based heavy-fermion superconductors. The ground state of
GdRhIn5 shows a commensurate antiferromagnetic spin structure with propagation
vector tau = (0,1/2, 1/2), corresponding to a parallel spin alignment along the
a-direction and antiparallel alignment along b and c. A comparison between this
magnetic structure and those of other members of the Rm(Co,Rh,Ir)n In3m+2n
family (R =rare earth, n = 0, 1; m = 1, 2) indicates that, in general, tau is
determined by a competition between first-(J1) and second-neighbor(J2)
antiferromagnetic (AFM) interactions. While a large J1 /J2 ratio favors an
antiparallel alignment along the three directions (the so-called G-AFM
structure), a smaller ratio favors the magnetic structure of GdRhIn5 (C-AFM).
In particular, it is inferred that the heavy-fermion superconductor CeRhIn5 is
in a frontier between these two ground states, which may explain its
non-collinear spiral magnetic structure. The critical behavior of GdRhIn5 close
to the paramagnetic transition at TN = 39 K was also studied in detail. A
typical second-order transition with the ordered magnetization critical
parameter beta = 0.35 was experimentally found, and theoretically investigated
by means of a renormalization group analysis.",0607140v1
2006-07-31,"Electronic properties of correlated metals in the vicinity of a charge order transition: optical spectroscopy of $α$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ ($M$ = NH$_4$, Rb, Tl)","The infrared spectra of the quasi-two-dimensional organic conductors
$\alpha$-(BEDT-TTF)$_2$$M$Hg(SCN)$_4$ ($M$ = NH$_4$, Rb, Tl) were measured in
the range from 50 to 7000 \cm down to low temperatures in order to explore the
influence of electronic correlations in quarter-filled metals. The
interpretation of electronic spectra was confirmed by measurements of pressure
dependant reflectance of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ at T=300 K. The
signatures of charge order fluctuations become more pronounced when going from
the NH$_4$ salt to Rb and further to Tl compounds. On reducing the temperature,
the metallic character of the optical response in the NH$_4$ and Rb salts
increases, and the effective mass diminishes. For the Tl compound, clear
signatures of charge order are found albeit the metallic properties still
dominate. From the temperature dependence of the electronic scattering rate the
crossover temperature is estimated below which the coherent charge-carriers
response sets in. The observations are in excellent agreement with recent
theoretical predictions for a quarter-filled metallic system close to charge
order.",0607816v2
2006-10-24,"Local distortion in LaCoO3 and PrCoO3: EXAFS, XRD and XANES studies","Room temperature Co K-edge extended x-ray absorption fine structure (EXAFS),
x-ray absorption near edge structure (XANES) including pre-edge and x-ray
diffraction (XRD) studies are carried out on LaCoO3 and PrCoO3. The Co-O,
Co-La/Pr and Co-Co bond lengths are obtained from EXAFS analysis and compared
with those obtained from XRD. The EXAFS analysis of data indicates that CoO6
octahedron is distorted in both LaCoO3 and PrCoO3. Such distortion is expected
in orthorhombic PrCoO3 but not in rhombohedral LaCoO3. This distortion in CoO6
octahedron is attributed to Jahn-Teller active Co3+ ion in intermediate spin
state in these compounds. Higher shell studies reveal that Debye-Waller (DW)
factors of Co-Pr and Co-Co bonds in PrCoO3 are more in comparison to Co-La and
Co-Co bonds in LaCoO3 indicating that these bonds are structurally more
disordered in PrCoO3. The comparison of Co-Co bond lengths and corresponding DW
factors indicates that the structural disorder plays an important role in
deciding the insulating properties of these compounds. XANES studies have shown
changes in the intensities and positions of different near edge features.",0610654v1
2006-11-27,Subtle competition between ferromagnetic and antiferromagnetic order in a Mn(II) - free radical ferrimagnetic chain,"The macroscopic magnetic characterization of the Mn(II) - nitronyl nitroxide
free radical chain (Mn(hfac)2(R)-3MLNN) evidenced its transition from a
1-dimensional behavior of ferrimagnetic chains to a 3-dimensional ferromagnetic
long range order below 3 K. Neutron diffraction experiments, performed on a
single crystal around the transition temperature, led to a different conclusion
: the magnetic Bragg reflections detected below 3 K correspond to a canted
antiferromagnet where the magnetic moments are mainly oriented along the chain
axis. Surprisingly in the context of other compounds in this family of magnets,
the interchain coupling is antiferromagnetic. This state is shown to be very
fragile since a ferromagnetic interchain arrangement is recovered in a weak
magnetic field. This peculiar behavior might be explained by the competition
between dipolar interaction, shown to be responsible for the antiferromagnetic
long range order below 3 K, and exchange interaction, the balance between these
interactions being driven by the strong intrachain spin correlations. More
generally, this study underlines the need, in this kind of molecular compounds,
to go beyond macroscopic magnetization measurements.",0611684v2
2006-12-10,"A study of transition metal K-edge x-ray absorption spectra of LaBO3 (B=Mn, Fe, Co, Ni), La2CuO4 and SrMnO3 using partial density of states","The transition metal K-edge x-ray absorption near edge structure (XANES)
studies have been carried on LaBO3 (B=Mn, Fe, Co, Ni), La2CuO4 and SrMnO3
compounds. The theoretical spectra have been calculated using transition metal
(TM) 4p density of states (DOS) obtained from full-potential LMTO density
functional theory. The exchange-correlation functional used in this calculation
is taken under local density approximation (LDA). The comparison of
experimental spectra with the calculated ones indicates that single-particle
transitions under LDA are sufficient to generate all the observed XANES
including those which have earlier been attributed to many-body shake-up
transitions and core-hole potentials. The present study reveals that all the
experimentally observed features are mainly due to distribution in TM 4p DOS
influenced by hybridization with other orbitals. Specifically, for LaMnO3, the
feature earlier attributed to shake-up process is seen to arise from
hybridization of Mn 4p with La 6p and O 2p orbitals; in La2CuO4 the features
attributed to core hole potential correspond to hybridization of Cu 4p with La
6p, La 5d and O 2p orbitals. To see the effect of inhomogeneous electronic
charge distribution and on-site Coulomb and exchange interaction (U) on the
XANES of these compounds generalized-gradient approximation and U corrections
are incorporated in the calculations. These corrections do not generate any new
features in the spectra but affect the detailed intensity and positions of some
of the features.",0612237v1
2007-02-02,Anomalous physical properties of underdoped weak-ferromagnetic superconductor RuSr$_2$EuCu$_{2}$O$_{8}$,"Similar to the optimal-doped, weak-ferromagnetic (WFM induced by canted
antiferromagnetism, T$_{Curie}$ = 131 K) and superconducting (T$_{c}$ = 56 K)
RuSr$_{2}$GdCu$_{2}$O$_{8}$, the underdoped RuSr$_{2}$EuCu$_{2}$O$_{8}$
(T$_{Curie}$ = 133 K, T$_{c}$ = 36 K) also exhibited a spontaneous vortex state
(SVS) between 16 K and 36 K. The low field ($\pm$20 G) superconducting
hysteresis loop indicates a weak and narrow Meissner state region of average
lower critical field B$_{c1}^{ave}$(T) = B$_{c1}^{ave}$(0)[1 -
(T/T$_{SVS}$)$^{2}$], with B$_{c1}^{ave}$(0) = 7 G and T$_{SVS}$ = 16 K. The
vortex melting transition (T$_{melting}$ = 21 K) below T$_{c}$ obtained from
the broad resistivity drop and the onset of diamagnetic signal indicates a
vortex liquid region due to the coexistence and interplay between
superconductivity and WFM order. No visible jump in specific heat was observed
near T$_{c}$ for Eu- and Gd-compound. This is not surprising, since the
electronic specific heat is easily overshadowed by the large phonon and
weak-ferromagnetic contributions. Furthermore, a broad resistivity transition
due to low vortex melting temperature would also lead to a correspondingly
reduced height of any specific heat jump. Finally, with the baseline from the
nonmagnetic Eu-compound, specific heat data analysis confirms the magnetic
entropy associated with antiferromagnetic ordering of Gd$^{3+}$ (J = S = 7/2)
at 2.5 K to be close to $\it{N_{A}k}$ ln8 as expected.",0702040v1
2004-12-20,Pricing of options on stocks driven by multi-dimensional operator stable Levy processes,"We model the price of a stock via a Lang\'{e}vin equation with
multi-dimensional fluctuations coupled in the price and in time. We generalize
previous models in that we assume that the fluctuations conditioned on the time
step are compound Poisson processes with operator stable jump intensities. We
derive exact relations for Fourier transforms of the jump intensity in case of
different scaling indices $\underline{\underline{E}}$ of the process. We
express the Fourier transform of the joint probability density of the process
to attain given values at several different times and to attain a given maximal
value in a given time period through Fourier transforms of the jump intensity.
Then we consider a portfolio composed of stocks and of options on stocks and we
derive the Fourier transform of a random variable $\mathfrak{D}_t$ (deviation
of the portfolio) that is defined as a small temporal change of the portfolio
diminished by the the compound interest earned. We show that if the price of
the option at time $t$ satisfies a certain functional equation specified in
text then the deviation of the portfolio has a zero mean $E[ \mathfrak{D}_t ] =
0$ and the option pricing problem may have a solution. We compare our approach
to other approaches that assumed the log-characteristic function of the
fluctuations that drive the stock price to be an analytic function.",0412071v3
2001-08-31,Deformation effects in $^{56}$Ni nuclei produced in $^{28}$Si+$^{28}$Si at 112 MeV,"Velocity and energy spectra of the light charged particles (protons and
$\alpha$-particles) emitted in the $^{28}$Si(E$_{lab}$ = 112 MeV) + $^{28}$Si
reaction have been measured at the Strasbourg VIVITRON Tandem facility. The
ICARE charged particle multidetector array was used to obtain exclusive spectra
of the light particles in the angular range 15 - 150 degree and to determine
the angular correlations of these particles with respect to the emission angles
of the evaporation residues. The experimental data are analysed in the
framework of the statistical model. The exclusive energy spectra of
$\alpha$-particles emitted from the $^{28}$Si + $^{28}$Si compound system are
generally well reproduced by Monte Carlo calculations using spin-dependent
level densities. This spin dependence approach suggests the onset of large
deformations at high spin. A re-analysis of previous $\alpha$-particle data
from the $^{30}$Si + $^{30}$Si compound system, using the same spin-dependent
parametrization, is also presented in the framework of a general discussion of
the occurrence of large deformation effects in the A$_{CN}$ ~ 60 mass region.",0108030v1
1994-04-05,Theory of parity violation in compound nuclear states; one particle aspects,"In this work we formulate the reaction theory of parity violation in compound
nuclear states using Feshbach's projection operator formalism. We derive in
this framework a complete set of terms that contribute to the longitudinal
asymmetry measured in experiments with polarized epithermal neutrons. We also
discuss the parity violating spreading width resulting from this formalism. We
then use the above formalism to derive expressions which hold in the case when
the doorway state approximation is introduced. In applying the theory we limit
ourselves in this work to the case when the parity violating potential and the
strong interaction are one-body. In this approximation, using as the doorway
the giant spin-dipole resonance and employing well known optical potentials and
a time-reversal even, parity odd one-body interaction we calculate or estimate
the terms we derived. In our calculations we explicitly orthogonalize the
continuum and bound wave functions. We find the effects of orthogonalization to
be very important. Our conclusion is that the present one-body theory cannot
explain the average longitudinal asymmetry found in the recent polarized
neutron experiments. We also confirm the discrepancy, first pointed out by
Auerbach and Bowman, that emerges, between the calculated average asymmetry and
the parity violating spreading width, when distant doorways are used in the
theory.",9404003v1
1995-07-29,Collisions of Deformed Nuclei: A Path to the Far Side of the Superheavy Island,"A detailed understanding of complete fusion cross sections in heavy-ion
collisions requires a consideration of the effects of the deformation of the
projectile and target. Our aim here is to show that deformation and orientation
of the colliding nuclei have a very significant effect on the fusion-barrier
height and on the compactness of the touching configuration. To facilitate
discussions of fusion configurations of deformed nuclei, we develop a
classification scheme and introduce a notation convention for these
configurations. We discuss particular deformations and orientations that lead
to compact touching configurations and to fusion-barrier heights that
correspond to fairly low excitation energies of the compound systems. Such
configurations should be the most favorable for producing superheavy elements.
We analyse a few projectile-target combinations whose deformations allow
favorable entrance-channel configurations and whose proton and neutron numbers
lead to compound systems in a part of the superheavy region where alpha
half-lives are calculated to be observable, that is, longer than 1 microsecond.",9507045v2
1995-08-23,Collisions of Deformed Nuclei and Superheavy-Element Production,"A detailed understanding of complete fusion cross sections in heavy-ion
collisions requires a consideration of the effects of the deformation of the
projectile and target. Our aim here is to show that deformation and orientation
of the colliding nuclei have a very significant effect on the fusion-barrier
height and on the compactness of the touching configuration. To facilitate
discussions of fusion configurations of deformed nuclei, we develop a
classification scheme and introduce a notation convention for these
configurations. We discuss particular deformations and orientations that lead
to compact touching configurations and to fusion-barrier heights that
correspond to fairly low excitation energies of the compound systems. Such
configurations should be the most favorable for producing superheavy elements.
We analyse a few projectile-target combinations whose deformations allow
favorable entrance-channel configurations and whose proton and neutron numbers
lead to compound systems in a part of the superheavy region where alpha
half-lives are calculated to be observable, that is, longer than 1 microsecond.",9508039v1
1997-11-21,Moscow-type NN-potentials and three-nucleon bound states,"A detailed description of Moscow-type (M-type) potential models for the NN
interaction is given. The microscopic foundation of these models, which appear
as a consequence of the composite quark structure of nucleons, is discussed.
M-type models are shown to arise naturally in a coupled channel approach when
compound or bag-like six-quark states, strongly coupled to the NN channel, are
eliminated from the complete multiquark wave function. The role of the
deep-lying bound states that appear in these models is elucidated. By
introducing additional conditions of orthogonality to these compound six-quark
states, a continuous series of almost on-shell equivalent nonlocal interaction
models, characterized by a strong reduction or full absence of a local
repulsive core (M-type models), is generated. The predictions of these
interaction models for 3N systems are analyzed in detail. It is shown that
M-type models give, under certain conditions, a stronger binding of the 3N
system than the original phase-equivalent model with nodeless wave functions.
An analysis of the 3N system with the new versions of the Moscow NN potential
describing also the higher even partial waves is presented. Large deviations
from conventional NN force models are found for the momentum distribution in
the high momentum region. In particular, the Coulomb displacement energy for
nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H
binding energy is extrapolated to the experimental value.",9711043v1
2002-11-08,The Role of Mass Asymmetry and Shell Structure in the Evaporation Residues Production,"The effects of the entrance channel and shell structure of reacting nuclei on
the experimental evaporation residues have been studied by analysing the
40Ar+176Hf, 86Kr+130,136Xe, 124Sn+92Zr and 48Ca+174Yb reactions leading to the
216Th* and 222Th* compound nuclei. The measured excitation function of
evaporation residues for the 124Sn+92Zr reaction was larger than that for the
86Kr+130Xe reaction. The experimental values of evaporation residues in the
86Kr+136Xe reaction were about 500 times larger than that in the 86Kr+130Xe
reaction. These results are explained by the initial angular momentum
dependence of the fusion excitation functions calculated in framework of the
dinuclear system concept and by the differences in survival probabilities
calculated in framework of advanced statistical model. The dependencies of the
fission barrier and the \Gamma_n / \Gamma_f ratio on the angular momentum of
the excited compound nucleus are taken into account.",0211024v1
2003-05-13,Cluster-decay of hot $^{56}$Ni$^*$ formed in $^{32}$S+$^{24}$Mg reaction,"The decay of $^{56}Ni^*$, formed in $^{32}S+^{24}Mg$ reaction at the incident
energies $E_{cm}$=51.6 and 60.5 MeV, is calculated as a cluster decay process
within the Preformed Cluster-decay Model (PCM) of Gupta et al. re-formulated
for hot compound systems. The observed deformed shapes of the exit channel
fragments are simulated by introducing the neck-length parameter at the
scission configuration, which nearly coincides the $^{56}Ni$ saddle
configuration. This is the only parameter of the model, which though is also
defined in terms of the binding energy of the hot compound system and the
ground-state binding energies of the various emitted fragments. The calculated
s-wave cross sections for nuclear shapes with outgoing fragments separated
within nuclear proximity limit (here $\sim$0.3 fm) can be compared with the
experimental data, and the TKEs are found to be in reasonably good agreement
with experiments for the angular momentum effects added in the sticking limit
for the moment of inertia. Also, some light particle production (other than the
statistical evaporation residue, not treated here) is predicted at these
energies and, interestingly, $^4He$, which belongs to evaporation residue, is
found missing as a dynamical cluster-decay fragment.",0305033v1
2004-09-18,Method of multiple internal reflections in description of nuclear alpha-decay,"A spatial-time method of description of alpha-decay of a nucleus is
presented. The method is based on the quantum mechanical model of the
alpha-decay of a compound nuclear system with the barrier. alpha-decay dynamics
is described on the basis of multiple internal reflections of wave packets from
boundaries of the decay barrier. The method allows to study this process in
details at any time moment or point of space. According to the method, some
time before the time moment of the nuclear decay the nucleus makes oscilations.
In the calculations of the time duration of the alpha-decay of the compound
nucleus we propose to take into account the time durations of these
oscillations. The method of the multiple internal reflections allows to
calculate the time of such oscillations before the alpha-decay and the total
alpha-decay time.",0409037v5
2006-09-18,Applications of Skyrme energy-density functional to fusion reactions for synthesis of superheavy nuclei,"The Skyrme energy-density functional approach has been extended to study the
massive heavy-ion fusion reactions. Based on the potential barrier obtained and
the parameterized barrier distribution the fusion (capture) excitation
functions of a lot of heavy-ion fusion reactions are studied systematically.
The average deviations of fusion cross sections at energies near and above the
barriers from experimental data are less than 0.05 for 92% of 76 fusion
reactions with $Z_1Z_2<1200$. For the massive fusion reactions, for example,
the $^{238}$U-induced reactions and $^{48}$Ca+$^{208}$Pb the capture excitation
functions have been reproduced remarkable well. The influence of structure
effects in the reaction partners on the capture cross sections are studied with
our parameterized barrier distribution. Through comparing the reactions induced
by double-magic nucleus $^{48}$Ca and by $^{32}$S and $^{35}$Cl, the
'threshold-like' behavior in the capture excitation function for $^{48}$Ca
induced reactions is explored and an optimal balance between the capture cross
section and the excitation energy of the compound nucleus is studied. Finally,
the fusion reactions with $^{36}$S, $^{37}$Cl, $^{48}$Ca and $^{50}$Ti
bombarding on $^{248}$Cm, $^{247,249}$Bk, $^{250,252,254}$Cf and
$^{252,254}$Es, and as well as the reactions lead to the same compound nucleus
with Z=120 and N=182 are studied further. The calculation results for these
reactions are useful for searching for the optimal fusion configuration and
suitable incident energy in the synthesis of superheavy nuclei.",0609045v1
1999-04-20,Towards standard methods for benchmark quality ab initio thermochemistry --- W1 and W2 theory,"Two new schemes for computing molecular total atomization energies (TAEs)
and/or heats of formation ($\Delta H^\circ_f$) of first-and second-row
compounds to very high accuracy are presented. The more affordable scheme, W1
(Weizmann-1) theory, yields a mean absolute error of 0.30 kcal/mol and includes
only a single, molecule-independent, empirical parameter. It requires CCSD
(coupled cluster with all single and double substitutions) calculations in
$spdf$ and $spdfg$ basis sets, while CCSD(T) [i.e. CCSD with a
quasiperturbative treatment of connected triple excitations] calculations are
only required in $spd$ and $spdf$ basis sets. On workstation computers and
using conventional coupled cluster algorithms, systems as large as benzene can
be treated, while larger systems are feasible using direct coupled cluster
methods. The more rigorous scheme, W2 (Weizmann-2) theory, contains no
empirical parameters at all and yields a mean absolute error of 0.23 kcal/mol,
which is lowered to 0.18 kcal/mol for molecules dominated by dynamical
correlation. It involves CCSD calculations in $spdfg$ and $spdfgh$ basis sets
and CCSD(T) calculations in $spdf$ and $spdfg$ basis sets. On workstation
computers, molecules with up to three heavy atoms can be treated using
conventional coupled cluster algorithms, while larger systems can still be
treated using a direct CCSD code. Both schemes include corrections for scalar
relativistic effects, which are found to be vital for accurate results on
second-row compounds.",9904038v2
2001-05-16,The Electrochemical Reduction of Hydrogen in the Presence of Bisulfate on Platinum(111),"A new model for the intermediate compound of the hydrogen evolution reaction
(HER) is proposed, for the electrochemical reduction of hydrogen in the
presence of bisulfate on platinum(111). The formation of this compound, a
regular 2 dimensional honeycomb ice lattice, occurs by a first order phase
transitions that involves the reorientation of water molecules. The model is
analyzed using new and simple effective cluster approach which highlights the
relevant transitions in system. This method is based on the cluster variation
method used successfully in our previous work on the UPD of Cu onto Au(111),
and permits us to explore a large region of parameter space, an essential
feature to study this complex system. The theory makes full use of the
properties of the diffuse layer: The water molecule is reoriented as the
potential is changed. For positive potentials it forms linear chains which are
responsible for the $\sqrt 3 \times \sqrt 7$ structure of the sulfate observed
by STM. At negative potentials water turns so that its dipole points towards
the Pt. Then it will form a regular honeycomb network of hydrogen bonded
molecules, with the sulfate at the center of the hexagons. Then the bisulfate
is desorbed, leaving the honeycomb HER structure behind. Our model thus
provides an explanation of the well known fact that only 2/3 of the Pt atoms
participate in the electroreduction of the hydrogen. The theory implies
geometrical constraints to the water potential.",0105051v2
2005-02-01,"Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems","Tungsten trioxide adopts a variety of structures which can be intercalated
with charged species to alter the electronic properties, thus forming `tungsten
bronzes'. Similar optical effects are observed upon removing oxygen from WO_3,
although the electronic properties are slightly different. Here we present a
computational study of cubic and hexagonal alkali bronzes and examine the
effects on cell size and band structure as the size of the intercalated ion is
increased. With the exception of hydrogen (which is predicted to be unstable as
an intercalate), the behaviour of the bronzes are relatively consistent. NaWO_3
is the most stable of the cubic systems, although in the hexagonal system the
larger ions are more stable. The band structures are identical, with the
intercalated atom donating its single electron to the tungsten 5d valence band.
Next, this was extended to a study of fractional doping in the Na_xWO_3 system
(0 < x < 1). A linear variation in cell parameter, and a systematic change in
the position of the Fermi level up into the valence band was observed with
increasing x. In the underdoped WO_3-x system however, the Fermi level
undergoes a sudden jump into the conduction band at around x = 0.2. Lastly,
three compounds of a layered WO_4&#215;a,wdiaminoalkane hybrid series were
studied and found to be insulating, with features in the band structure similar
to those of the parent WO_3 compound which relate well to experimental
UV-visible spectroscopy results.",0502002v1
2005-04-25,Valence Shell Charge Concentrations at Pentacoordinate d0 Transition Metal Centers: Non-VSEPR Structures of Me2NbCl3 and Me3NbCl2,"The molecular structures of the monomeric, pentacoordinated
ethylchloroniobium(V) compounds Me3NbCl2 and Me2NbCl3 have been determined by
gas electron diffraction (GED)and Density Functional Theory (DFT) calculations,
and, for Me3NbCl2, by single crystal X-ray diffraction. Each of the molecules
is found to have a heavy-atom skeleton in the form of a trigonal bipyramid
(TBP) with Cl atoms in the axial positions, in accord with their vibrational
spectra. The TBP is somewhat distorted in the case of Me2NbCl3 with the two
axial Nb-Cl bonds bent away from the equatorial, slightly shorter Nb-Cl bond.
In the case of Me3NbCl2, moreover, the X-ray model suggests structural
distortions away from the idealized C3h geometry, in line with the results of
quantum chemical calculations. The electronic structures of Me2NbCl3 and
Me3NbCl2 have been explored by rigorous analysis of both the wavefunction and
the topology of the electron density, employing DFT calculations. Hence the
structures of these compounds are shown to reflect repulsion between the Nb-C
and Nb-Cl bonding electron density and charge concentrations induced by the
methyl ligands in the valence shell of the Nb atom and arising mainly from use
of Nb(4d) functions in the Nb-C bonds.",0504180v1
2002-08-16,On Entangled Information and Quantum Capacity,"The pure quantum entanglement is generalized to the case of mixed compound
states on an operator algebra to include the classical and quantum encodings as
particular cases. The true quantum entanglements are characterized by quantum
couplings which are described as transpose-CP, but not Completely Positive
(CP), trace-normalized linear positive maps of the algebra.
  The entangled (total) information is defined in this paper as a relative
entropy of the conditional (the derivative of the compound state with respect
to the input) and the unconditional output states. Thus defined the total
information of the entangled states leads to two different types of the entropy
for a given quantum state: the von Neumann entropy, or c-entropy, which is
achieved as the supremum of the information over all c-entanglements and thus
is semi-classical, and the true quantum entropy, or q-entropy, which is
achieved at the standard entanglement.
  The q-capacity, defined as the supremum over all entanglements, coincides
with the topological entropy. In the case of the simple algebra it doubles the
c-capacity, coinciding with the rank-entropy. The conditional q-entropy based
on the q-entropy, is positive, unlike the von Neumann conditional entropy, and
the q-information of a quantum channel is proved to be additive.",0208115v1
2007-04-13,Low-density graph codes that are optimal for source/channel coding and binning,"We describe and analyze the joint source/channel coding properties of a class
of sparse graphical codes based on compounding a low-density generator matrix
(LDGM) code with a low-density parity check (LDPC) code. Our first pair of
theorems establish that there exist codes from this ensemble, with all degrees
remaining bounded independently of block length, that are simultaneously
optimal as both source and channel codes when encoding and decoding are
performed optimally. More precisely, in the context of lossy compression, we
prove that finite degree constructions can achieve any pair $(R, D)$ on the
rate-distortion curve of the binary symmetric source. In the context of channel
coding, we prove that finite degree codes can achieve any pair $(C, p)$ on the
capacity-noise curve of the binary symmetric channel. Next, we show that our
compound construction has a nested structure that can be exploited to achieve
the Wyner-Ziv bound for source coding with side information (SCSI), as well as
the Gelfand-Pinsker bound for channel coding with side information (CCSI).
Although the current results are based on optimal encoding and decoding, the
proposed graphical codes have sparse structure and high girth that renders them
well-suited to message-passing and other efficient decoding procedures.",0704.1818v1
2007-05-09,Inter comparison of the magneto transport of La2/3Ca1/3MnO3: Ag/In polycrystalline composites,"In this article, we report the synthesis, magneto transport features, and
magnetization of polycrystalline La2/3Ca1/3MnO3:Agx/Inx composites with x = 0,
0.1, 0.2, 0.3 and 0.4. In case of Ag the temperature coefficient of resistance
(TCR) near ferromagnetic (FM) transition enhances significantly with addition
of Ag. The FM transition temperature (TFM) is also increased slightly with Ag
doping. Magneto-transport measurements revealed that magneto-resistance (MR) is
found to be maximum near TFM. Very sharp TCR is seen near TFM with highest
value of up to 15 % for Ag (0.4) sample, which is an order of magnitude higher
than as for pristine sample and is the best value yet reported for any
polycrystalline LCMO compound. Increased TCR, TFM and significant above room
temperature MR of La2/3Ca1/3MnO3:Agx composites is explained on the basis of
improved grains size. Interestingly the La2/3Ca1/3MnO3:Inx composites behaved
exactly in opposite way resulting in decreased TFM, and TCR compared to
pristine LCMO compound. In fact the grains morphology of LCMO:Inx composites is
seen inferior to pristine LCMO which is opposite to the LCMO:Agx case.",0705.1212v1
2007-05-11,Itinerant to localized transition of f electrons in antiferromagnetic superconductor UPd2Al3,"Electrons in solids have been conventionally classified as either band-like
itinerant ones or atomic-like localized ones depending on their properties. For
heavy Fermion (HF) compounds, however, the f electrons show both itinerant and
localized behaviours depending on temperature. Above the characteristic
temperature T*, which is typically of the order of few K to few tens K, their
magnetic properties are well described by the ionic f-electron models,
suggesting that the f-electrons behave as 'localized' electrons. On the other
hand, well below T*, their Fermi surfaces (FS's) have been observed by
magneto-oscillatory techniques, and generally they can be explained well by the
'itinerant' f-electron model. These two models assume totally different natures
of felectrons, and how they transform between localized and itinerant state as
a function of temperatures has never been understood on the level of their
electronic structures. Here we have studied the band structure of the HF
antiferromagnetic superconductor UPd2Al3 well below and above T* by
angle-resolved photoelectron spectroscopy (ARPES), and revealed the temperature
dependence of the electronic structure. We have found that the f-bands, which
form the FS's at low temperatures are excluded from FS's at high temperatures.
The present results demonstrate how the same f-electrons show both itinerant
and localized behaviours on the level of electronic structure, and provide an
important information for the unified description of the localized and
itinerant nature of HF compounds.",0705.1734v1
2007-08-01,Multisource Bayesian sequential change detection,"Suppose that local characteristics of several independent compound Poisson
and Wiener processes change suddenly and simultaneously at some unobservable
disorder time. The problem is to detect the disorder time as quickly as
possible after it happens and minimize the rate of false alarms at the same
time. These problems arise, for example, from managing product quality in
manufacturing systems and preventing the spread of infectious diseases. The
promptness and accuracy of detection rules improve greatly if multiple
independent information sources are available. Earlier work on sequential
change detection in continuous time does not provide optimal rules for
situations in which several marked count data and continuously changing signals
are simultaneously observable. In this paper, optimal Bayesian sequential
detection rules are developed for such problems when the marked count data is
in the form of independent compound Poisson processes, and the continuously
changing signals form a multi-dimensional Wiener process. An auxiliary optimal
stopping problem for a jump-diffusion process is solved by transforming it
first into a sequence of optimal stopping problems for a pure diffusion by
means of a jump operator. This method is new and can be very useful in other
applications as well, because it allows the use of the powerful optimal
stopping theory for diffusions.",0708.0224v3
2007-08-27,Magnetic and thermal properties of the S = 1/2 zig-zag spin-chain compound In2VO5,"Static magnetic susceptibility \chi, ac susceptibility \chi_{ac} and specific
heat C versus temperature T measurements on polycrystalline samples of In2VO5
and \chi and C versus T measurements on the isostructural, nonmagnetic compound
In2TiO5 are reported. A Curie-Wiess fit to the \chi(T) data above 175 K for
In2VO5 indicates ferromagnetic exchange between V^{4+} (S = 1/2) moments. Below
150 K the \chi(T) data deviate from the Curie-Weiss behavior but there is no
signature of any long range magnetic order down to 1.8 K. There is a cusp at
2.8 K in the zero field cooled (ZFC) \chi(T) data measured in a magnetic field
of 100 Oe and the ZFC and field cooled (FC) data show a bifurcation below this
temperature. The frequency dependence of the \chi_{ac}(T) data indicate that
below 3 K the system is in a spin-glass state. The difference \Delta C between
the heat capacity of In2VO5 and In2TiO5 shows a broad anomaly peaked at 130 K.
The entropy upto 300 K is more than what is expected for S = 1/2 moments. The
anomaly in \Delta C and the extra entropy suggests that there may be a
structural change below 130 K in In2VO5.",0708.3651v2
2007-09-05,Resonant x-ray scattering study of NpRhGa_5 and NpCoGa_5,"We report a resonant x-ray scattering (RXS) study of antiferromagnetic
neptunium compounds NpCoGa_5 and NpRhGa_5 at the Np M_4 and Ga K-edges. Large
resonant signals of magnetic dipole character are observed below the Neel
temperatures at both edges. The signals at the Np edges confirm the behaviour
determined previously from neutron diffraction, i.e. the moments along [001] in
NpCoGa_{5} and in NpRhGa_5 a reorientation of the moments from the c-axis
direction to the ab plane. In the latter material, on application of magnetic
field of 9 Tesla along the [010] direction we observe a change in the
population of different [110]-type domains. We observe also a magnetic dipole
signal at the Ga K-edge, similarly to the reported UGa_3 case, that can be
interpreted within a semi-localized model as an orbital polarization of the Ga
4p states induced via strong hybridization with the Np 5f valence band.
Quantitative analysis of the signal shows that the Ga dipole on the two
different Ga sites follows closely the Np magnetic moment reorientation in
NpRhGa_5. The ratios of the signals on the two inequivalent Ga sites are not
the same for the different compounds.",0709.0696v1
2007-09-27,On the correctness of various approaches in the extraction of the nucleus parameters on example of analysis of the two-step gamma-cascades in 163Dy compound nucleus,"The model-free analysis of experimental data in the intensities of two-step
cascades into 163Dy shows, that the basically special features of the cascade
gamma-decay of its compound-state completely correspond to those observed in
other nuclei. Thus, the density of the levels in this nucleus with good
precision it is reproduced as sum of three, five, seven-quasiparticle
excitations with the tenfold, as the minimum, by an increase due to vibration
type excitations. The greatest changes in the sum of the radiation strength
functions of dipole primary gamma-transitions correlate with a change in the
number of excitable quasi-particles. Accordingly, model presentations about the
radiation strength functions of larger, than for those existing, accuracy must
consider as a quantity of excited quasi-particles, so the presence of the
vibration type excitations of all possible types. Moreover, the reliable
picture of the studied process can be obtained only from the approximation of
the distributions of the intensities of cascades in the function of energies of
their primary gamma-transitions.",0709.4304v1
2007-10-16,Optical phase diagram of perovskite-type colossal magnetoresistance manganites with near-half doping,"We present a systematic optical study for a bandwidth-controlled series of
nearly half doped colossal magnetoresistive manganites
RE$_{0.55}$AE$_{0.45}$MnO$_3$ (RE and AE being rare earth and alkaline earth
ions, respectively) under the presence of quenched disorder over a broad
temperature region $T=10-800$ K. The ground state of the compounds ranges from
the charge and orbital ordered insulator through the spin glass to the
ferromagnetic metal. The enhanced phase fluctuations, namely the short-range
charge and orbital correlations dominate the paramagnetic region of the phase
diagram above all the ground-state phases. This paramagnetic region is
characterized by a full-gap to pseudo-gap crossover towards elevated
temperatures where a broad low-energy electronic structure appears in the
conductivity spectra over a large variation of the bandwidth. This pseudo-gap
state with local correlations is robust against thermal fluctuations at least
up to T=800 K. For small bandwidth the onset of the long-range charge order is
accompanied by an instantaneous increase of the gap. The emergence of the
ferromagnetic state is manifested in the optical spectra as a first-order
insulator to metal transition for compounds with moderate bandwidth while it
becomes a second-order transition on the larger bandwidth side. Unusually large
scattering rate of the metallic carriers is observed in the ferromagnetic state
which is attributed to orbital correlation with probably rod-like
($3z^2-r^2$-like) character.",0710.3015v1
2007-10-29,Interplay of structure and spin-orbit strength in magnetism of metal-benzene sandwiches: from single molecules to infinite wires,"Based on first-principles density functional theory calculations we explore
electronic and magnetic properties of experimentally producible sandwiches and
infinite wires made of repeating benzene molecules and transition-metal atoms
of V, Nb, and Ta. We describe the bonding mechanism in the molecules and in
particular concentrate on the origin of magnetism in these structures. We find
that all the considered systems have sizable magnetic moments and ferromagnetic
spin-ordering, with the single exception of the V3-Bz4 molecule. By including
the spin-orbit coupling into our calculations we determine the easy and hard
axes of the magnetic moment, the strength of the uniaxial magnetic anisotropy
energy (MAE), relevant for the thermal stability of magnetic orientation, and
the change of the electronic structure with respect to the direction of the
magnetic moment, important for spin-transport properties. While for the V-based
compounds the values of the MAE are only of the order of 0.05-0.5 meV per metal
atom, increasing the spin-orbit strength by substituting V with heavier Nb and
Ta allows to achieve an increase in anisotropy values by one to two orders of
magnitude. The rigid stability of magnetism in these compounds together with
the strong ferromagnetic ordering makes them attractive candidates for
spin-polarized transport applications. For a Nb-benzene infinite wire the
occurrence of ballistic anisotropic magnetoresistance is demonstrated.",0710.5413v1
2007-12-10,"Long Range Antiferromagnetic Ordering in the S = 1/2 Ordered Rock Salt Oxide, Li5OsO6: Comparison with the Isoelectronicand Isostructural Spin Glass, Li4MgReO6","Li5OsO6 and Li5ReO6 polycrystalline samples were synthesized by conventional
solid state methods. Employing powder neutron diffraction data, the crystal
structure of Li5OsO6 was re-investigated. Li5OsO6 crystallizes in C2/m space
group in an ordered NaCl structure type where a = 5.0472(1) A, b = 8.7827(2) A,
c = 5.0079(1) A, Beta = 109.777(2) degree and V = 208.90(1).A^3 Magnetic
susceptibility and heat capacity data indicate an AFM long range order below
40K although there is evidence for low dimensional short range order above 80K.
As well, the frustration index, f = |theta|/TN ~1, in contrast to the
isostructural and isoelectronic compound, Li4MgReO6, which is a spin glass
below 12K and has f ~ 14. An attempt was made to rationalize these differences
using spin dimer analysis. The key results are that the spin exchange
interactions in the Re-based compound are stronger and are consistent with a
frustrated triangular lattice model while a low dimensional short range order
model is better for Li5OsO6. The main reason for this is a strong Jahn-Teller
distortion in the OsO6 octahedron material which constrains the unpaired
electron to occupy the dxy orbital.",0712.1580v1
2007-12-12,Magnetic anomalies in single crystalline ErPd2Si2,"Considering certain interesting features in the previously reported 166Er
Moessbauer effect and neutron diffraction data on the polycrystalline form of
ErPd2Si2 crystallizing in ThCr2Si2-type tetragonal structure, we have carried
out magnetic measurements (1.8 to 300 K) on the single crystalline form of this
compound. We observe significant anisotropy in the absolute values of
magnetization (indicating that the easy axis is c-axis) as well as in the
features due to magnetic ordering in the plot of magnetic susceptibility (chi)
versus temperature (T) at low temperatures. The chi(T) data reveal that there
is a pseudo-low dimensional magnetic order setting in at 4.8 K, with a
three-dimensional antiferromagnetic ordering setting in at a lower temperature
(3.8 K). A new finding in the chi(T) data is that, for H//<110>, but not for
H//<001>, there is a broad shoulder in the range 8-20 K, indicative of the
existence of magnetic correlations above 5 K as well, which could be related to
the previously reported slow-relaxation-dominated Moessbauer spectra.
Interestingly, the temperature coefficient of electrical resistivity is found
to be isotropic; no feature due to magnetic ordering could be detected in the
electrical resistivity data at low temperatures, which is attributed to
magnetic Brillioun-zone boundary gap effects. The results reveal complex nature
of the magnetism of this compound.",0712.2002v1
2007-12-18,"Manifestation of geometric frustration on magnetic and thermodynamic properties of pyrochlores $Sm_2X_2O_7$ (X=Ti, Zr)","We present here magnetization, specific heat and Raman studies on
single-crystalline specimens of the first pyrochlore member $Sm_2Ti_2O_7$ of
the rare-earth titanate series. Its analogous compound $Sm_2Zr_2O_7$ in the
rare-earth zirconate series is also investigated in the polycrystalline form.
The Sm spins in $Sm_2Ti_2O_7$ remain unordered down to at least T = 0.5 K. The
absence of magnetic ordering is attributed to very small values of exchange
($\theta_{cw} ~ -0.26 K$) and dipolar interaction ($\mu_{eff} ~ 0.15 \mu_B$)
between the $Sm^{3+}$ spins in this pyrochlore. In contrast, the pyrochlore
$Sm_2Zr_2O_7$ is characterized by a relatively large value of Sm-Sm spin
exchange ($\theta_{cw} ~ - 10 K$); however, long-range ordering of the
$Sm^{3+}$ spins is not established at least down to T = 0.67 K, due to
frustration of the $Sm^{3+}$ spins on the pyrochlore lattice. The ground state
of $Sm^{3+}$ ions in both pyrochlores is a well-isolated Kramer's doublet. The
higher-lying crystal field excitations are observed in the low-frequency region
of the Raman spectra of the two compounds recorded at T = 10 K. At higher
temperatures, the magnetic susceptibility of $Sm_2Ti_2O_7$ shows a broad
maximum at T = 140 K while that of $Sm_2Zr_2O_7$ changes monotonically. Whereas
$Sm_2Ti_2O_7$ is a promising candidate for investigating spin-fluctuations on a
frustrated lattice as indicated by our data, the properties of $Sm_2Zr_2O_7$
seem to conform to a conventional scenario where geometrical frustration of the
spin exclude their long-range ordering.",0712.3061v1
2007-12-19,Half Metallicity in Pr$_{0.75}$Sr$_{0.25}$MnO$_3$: A first Principle study,"In this communication we present a first principle study of
Pr$_{1-x}$Sr$_{x}$MnO$_3$ with $x = 0.25$. While the parent compounds of this
system are antiferromagnetic insulators with different structural and magnetic
ground states, the $x = 0.25$ is in the colossal magnetoresistance regime of
the Pr$_{1-x}$Sr$_{x}$MnO$_3$ phase diagram [C. Martin, A. Maignan, M. Hervieu,
B. Raveau, Phys. Rev. B 60 (1999) 12191]. Our band structure calculations for
the end-point compounds matches well with the existing theoretical and
experimental results [C. Martin, A. Maignan, M. Hervieu, B. Raveau, Phys. Rev.
B 60 (1999) 12191; Rune Sondena, P. Ravindran, Svein Stolen, Tor Grande,
Michael Hanfland, Phys. Rev. B 74 (2006) 144102]. Interestingly, our
calculations show that the Pr$_{0.75}$Sr$_{0.25}$MnO$_3$ has a half-metallic
character with a huge band gap of 2.8 eV in the minority band. We believe this
result would fuel further interest in some of these special compositions of
colossal magnetoresistive manganites as they could be potential candidates for
spintronic devices. We discuss the half-metallicity of the
Pr$_{0.75}$Sr$_{0.25}$MnO$_3$ in the light of changes in the orbital
hybridization as a result of Sr doping in PrMnO$_3$. Further, we highlight the
importance of half-metallicity for a consolidated understanding of colossal
magnetoresistance effect.",0712.3244v1
2008-02-01,Pressure effects on the structural and electronic properties of ABX4 scintillating crystals,"Studies at high pressures and temperatures are helpful for understanding the
physical properties of the solid state, including such classes of materials as,
metals, semiconductors, superconductors, or minerals. In particular, the phase
behaviour of ABX4 scintillating materials is a challenging problem with many
implications for other fields including technological applications and Earth
and planetary sciences. A great progress has been done in the last years in the
study of the pressure-effects on the structural and electronic properties of
these compounds. In particular, the high-pressure structural sequence followed
by these compounds seems now to be better understood thanks to recent
experimental and theoretical studies. Here, we will review studies on the phase
behaviour of different ABX4 scintillating materials. In particular, we will
focus on discussing the results obtained by different groups for the
scheelite-structured orthotungstates, which have been extensively studied up to
50 GPa. We will also describe different experimental techniques for obtaining
reliable data at simultaneously high pressure and high temperature. Drawbacks
and advantages of the different techniques are discussed along with recent
developments involving synchrotron x-ray diffraction, Raman scattering, and ab
initio calculations. Differences and similarities of the phase behaviour of
these materials will be discussed, on the light of the Fukunaga and Yamaoka and
the Bastide diagrams, aiming to improve the actual understanding of their
high-pressure behaviour. Possible technological and geophysical implications of
the reviewed results will be also commented.",0802.0160v1
2008-02-20,Intersite 4p-3d hybridization in cobalt oxides: a resonant x-ray emission spectroscopy study,"We report on strong dipole transitions to 3d orbitals of neighboring Co atoms
in the Co 1s x-ray absorption pre-edge. They are revealed by applying
high-resolution resonant x-ray emission spectroscopy (RXES) to compounds
containing CoO6 clusters. When contrasted to quadrupole local 1s3d excitations,
these non-local 1s3d transitions are identified by their energy dispersion and
angular dependence, their sensitivity to second-shell effects (i.e. the
connection mode of the CoO6 octahedra and the bond lengths), and an upwards
energy shift of 2.5 eV due to the poorer screening of the core hole. The
experiment reveals that the intensity of the non-local transitions gauges the
oxygen-mediated 4p-O-3d intersite hybridization. We propose a revised
interpretation of the pre-edges of transition metal compounds. Detailed
analysis of these new features in the pre-edge offers a unique insight in the
oxygen mediated metal-metal interactions in transition metal-based systems,
which is a crucial aspect in orbital ordering and related electronic and
magnetic properties. In addition, the exceptional resolving power of the
present 1s2p RXES experiment allows us to demonstrate the coherent second-order
nature of the underlying scattering process.",0802.2744v1
2008-03-07,Spin-spin correlations of the spin-ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ measured by magnetostriction and comparison to Quantum Monte Carlo results,"Magnetostriction and thermal expansion of the spin-ladder compound
piperidinium copper bromide (C$_5$H$_{12}$N)$_2$CuBr$_4$ are analyzed in
detail. We find perfect agreement between experiments and the theory of a
two-leg spin ladder Hamiltonian for more than a decade in temperature and in a
wide range of magnetic fields. Relating the magnetostriction along different
crystallographic directions to two static spin-spin correlation functions,
which we compute with Quantum Monte Carlo, allows us to reconstruct the
magnetoelastic couplings of (C$_5$H$_{12}$N)$_2$CuBr$_4$. We especially focus
on the quantum critical behavior near the two critical magnetic fields $H_{c1}$
and $H_{c2}$, which is characterized by strong singularities rooted in the low
dimensionality of the critical spin-system. Extending our discussion in Lorenz
et al [Phys. Rev. Lett., 100, 067208 (2008)], we show explicitly that the
thermal expansion near the upper critical field $H_{c2}$ is quantitatively
described by a parameter-free theory of one-dimensional, non-relativistic
Fermions. We also point out that there exists a singular quantum critical
correction to the elastic moduli. This correction is proportional to the
magnetic susceptibility $\chi$ which diverges as $\chi \sim 1/\sqrt{T}$ at the
critical fields and thus leads to a strong softening of the crystal.",0803.1072v1
2008-03-24,Effect of static and dynamic disorder on electronic transport of $RCo_2$ compounds: a study of $Ho(Al_xCo_{1-x})_2$ alloys,"We present experimental results on thermoelectric power ({\em S}) and
electrical resistivity ($\rho $) of pseudobinary alloys
Ho(Al$_x$Co$_{1-x}$)$_2$ ($0 \leq x \leq 0.1 $), in the temperature range 4.2 K
to 300 K. The work focuses on the effects of static (induced by alloying) and
dynamic (induced by temperature) disorder on the magnetic state and electronic
transport in a metallic system with itinerant metamagnetic instability. Spatial
fluctuations of the local magnetic susceptibility in the alloys lead to a
development of a partially ordered magnetic ground state of the itinerant 3d
electron system. This results in a strong increase of the residual resistivity
and a suppression of the temperature-dependent resistivity. Thermopower
exhibits a complex temperature variation in both the magnetically ordered and
in the paramagnetic state. This complex temperature variation is referred to
the electronic density of states features in vicinity of Fermi energy and to
the interplay of magnetic and impurity scattering. Our results indicate that
the magnetic enhancement of the Co 3d-band in RCo$_{\rm 2}$--based alloys upon
a substitution of Co by non-magnetic elements is mainly related to a
progressive localization of the Co -- 3d electrons caused by disorder. We show
that the magnitude of the resistivity jump at the Curie temperature for
RCo$_{\rm 2}$ compounds exhibiting a first order phase transition is a
non-monotonic function of the Curie temperature due to a saturation of the
3d--band spin fluctuation magnitude at high temperatures.",0803.3380v3
2008-03-25,"Structural and Magnetic Properties of Pyrochlore Solid Solutions (Y,Lu)2Ti2-x(Nb,Ta)xO7+/-y","The synthesis and characterization of the pyrochlore solid solutions,
Y2Ti2-xNbxO7-y, Lu2Ti2-xNbxO7-y, Y2Ti2-xTaxO7-y and Lu2TiTaO7-y (-0.4<y<0.5),
is described. Synthesis at 1600 C, and 10-5 Torr yields oxygen deficiency in
all systems. All compounds are found to be paramagnetic and semiconducting,
with the size of the local moments being less, in some cases substantially
less, than the expected value for the number of nominally unpaired electrons
present. Thermogravimetric analysis (TGA) shows that all compounds can be fully
oxidized while retaining the pyrochlore structure, yielding oxygen rich
pyrochlores as white powders. Powder neutron diffraction of Y2TiNbO7-based
samples was done. Refinement of the data for oxygen deficient Y2TiNbO6.76
indicates the presence of a distribution of oxygen over the 8b and 48f sites.
Refinement of the data for oxygen rich Y2TiNbO7.5 shows these sites to be
completely filled, with an additional half filling of the 8a site. The magnetic
and TGA data strongly suggest a preference for a Ti3+/(Nb,Ta)5+ combination, as
opposed to Ti4+/(Nb,Ta)4+, in this pyrochlore family. In addition, the evidence
clearly points to Ti3+ as the source of the localized moments, with no evidence
for localized Nb4+ moments.",0803.3568v1
2008-03-31,Superconductivity in iron-based F-doped layered quaternary compound Nd[O1-xFx]FeAs,"The recently discovered quaternary arsenide oxide superconductor
La[O1-xFx]FeAs with the superconducting critical transition temperature (Tc) of
26 K [1], has been quickly expanded to another high-Tc superconducting system
beyond copper oxides by the replacement of La with other rare earth elements,
such as Sm, Ce, and Pr etc. [2-4], and the Pr[O1-xFx]FeAs has become to be the
first non-cuprate superconductor that holding a Tc above 50 K. All these
arsenide (including phosphide) superconductors formed in a same tetragonal
layered structure with the space group P4/nmm which has an alternant stacked
Fe-As layer and RO (R = rare earth metals) layer. Here we report the discovery
of another superconductor in this system, the neodymium-arsenide Nd[O1-xFx]FeAs
with an resistivity onset Tc of 51.9 K, which is the second non-cuprate
compound that superconducts above 50 K.",0803.4234v2
2008-04-16,Properties of the hole and electron doped perovskites LnCoO3,"Two extreme members of the cobaltite series, LaCoO3 and DyCoO3, were
investigated by the electrical resistivity and thermopower measurements up to
800-1000 K. Special attention was given to effects of extra holes or electrons,
introduced by light doping of Co sites by Mg2+ or Ti4+ ions. The experiments on
the La based compounds were complemented with magnetic measurements. The study
shows that both kinds of charge carriers induce magnetic states on surrounding
CoIII sites and form thus thermally stable polarons of large total spin. Their
itinerancy is characterized by low temperature resistivity, which is of
Arrhenius type r~exp(EA/kT) for the hole (CoIV) doped samples, while an unusual
dependence r~1/Tn (n=8-10) is observed for the electron (CoII) doped samples.
At higher temperatures, additional hole carriers are massively populated in the
CoIII background, leading to a resistivity drop. This transition become evident
at ~300 K and 450 K and culminates at TI-M=540 and 780 K for the La and Dy
based samples, respectively.
  The electronic behaviours of the cobaltites are explained considering two
excitation processes in parent compounds. The first one is related to a local
excitation from the diamagnetic LS CoIII to close-lying paramagnetic HS CoIII
state. Secondarily, a metallic phase of the IS CoIII character is formed
through a charge transfer mechanism between LS/HS pairs. The magnetic polarons
associated with doped carriers are interpreted as droplets of such IS phase.",0804.2685v3
2008-04-29,Strong frustration due to competing ferromagnetic and antiferromagnetic interactions: magnetic properties of M(VO)2(PO4)2 (M = Ca and Sr),"We present a detailed investigation of the magnetic properties of complex
vanadium phosphates M(VO)2(PO4)2 (M = Ca, Sr) by means of magnetization,
specific heat, 31P NMR measurements, and band structure calculations.
Experimental data evidence the presence of ferro- and antiferromagnetic
interactions in M(VO)2(PO4)2 resulting in a nearly vanishing Curie-Weiss
temperature \theta_{CW} < 1 K that contrasts with the maximum of magnetic
susceptibility at 3 K. Specific heat and NMR measurements also reveal weak
exchange couplings with the thermodynamic energy scale J_c = 10-15 K.
Additionally, the reduced maximum of the magnetic specific heat indicates
strong frustration of the spin system. Band structure calculations show that
the spin systems of the M(VO)2(PO4)2 compounds are essentially
three-dimensional with the frustration caused by competing ferro- and
antiferromagnetic interactions. Both calcium and strontium compounds undergo
antiferromagnetic long-range ordering at T_N = 1.5 K and 1.9 K, respectively.
The spin model reveals an unusual example of controllable frustration in
three-dimensional magnetic systems.",0804.4667v2
2008-05-27,Fermi surface nesting in several transition metal dichalcogenides,"By means of high-resolution angle resolved photoelectron spectroscopy (ARPES)
we have studied the fermiology of 2H transition metal dichalcogenide polytypes
TaSe2, NbSe2, and Cu0.2NbS2. The tight-binding model of the electronic
structure, extracted from ARPES spectra for all three compounds, was used to
calculate the Lindhard function (bare spin susceptibility), which reflects the
propensity to charge density wave (CDW) instabilities observed in TaSe2 and
NbSe2. We show that though the Fermi surfaces of all three compounds possess an
incommensurate nesting vector in the close vicinity of the CDW wave vector, the
nesting and ordering wave vectors do not exactly coincide, and there is no
direct relationship between the magnitude of the susceptibility at the nesting
vector and the CDW transition temperature. The nesting vector persists across
the incommensurate CDW transition in TaSe2 as a function of temperature despite
the observable variations of the Fermi surface geometry in this temperature
range. In Cu0.2NbS2 the nesting vector is present despite different doping
level, which lets us expect a possible enhancement of the CDW instability with
Cu-intercalation in the CuxNbS2 family of materials.",0805.4105v1
2008-06-02,Spin-singlet superconductivity with multiple gaps in PrO0.89F0.11FeAs,"Since the discovery of high transition-temperature (Tc) superconductivity in
copper oxides two decades ago, continuous efforts have been devoted to
searching for similar phenomenon in other compounds. With the exception of MgB2
(Tc =39 K), however, Tc is generally far lower than desired. Recently,
breakthrough has been made in a new class of oxypnictide compounds. Following
the initial discovery of superconductivity in LaO1-x FxFeAs (Tc =26 K), Tc
onset has been raised to 55 K in ReO1-xFxFeAs (Re: Ce, Pr, Nd, Sm). Meanwhile,
unravelling the nature of the energy associated with the formation of
current-carrying pairs (Cooper pairs), referred to as the superconducting
energy gap, is the first and vital step towards understanding why the
superconductivity occurs at such high temperature and is also important for
finding superconductors with still higher Tc. Here we show that, on the basis
of the nuclear magnetic resonance (NMR) measurements in PrO0.89F0.11FeAs (Tc
=45 K), the Cooper pair is in the spin-singlet state (two spins are
anti-paralleled), with two energy gaps opening below Tc. The results strongly
suggest the existence of nodes (zeros) in the gap. None of superconductors
known to date has such unique gap features, although copper-oxides and MgB2
share part of them.",0806.0249v1
2008-06-11,"A New Unconventional Antiferromagnet, Yb$_3$Pt$_4$","We report the synthesis and basic properties of single crystals of a new
binary compound, Yb$_{3}$Pt$_{4}$. The Yb ions in this compound are fully
trivalent, and heat capacity measurements show that the crystal field scheme
involves a doublet ground state, well separated from the excited states, which
are fully occupied above $\sim$ 150 K. The heat capacity displays a large,
weakly first order anomaly at 2.4 K, where a cusp is observed in the magnetic
susceptibility signalling the onset of antiferromagnetic order. The entropy
associated with this order is the full Rln2 of the doublet ground state,
however the magnetic susceptibility in the ordered phase is dominated by a
large and temperature independent component below the Neel temperature. The
heat capacity in the ordered state originates with ferromagnetic spin waves,
giving evidence for the inherently local moment character of the ordered state.
The electrical resistivity is unusually large, and becomes quadratic in
temperature exactly at the Neel temperature. The absence of analogous Fermi
liquid behavior in the heat capacity and the magnetic susceptibility implies
that Yb$_{3}$Pt$_{4}$ is a low electron density system, where the Fermi surface
is further gapped by the onset of magnetic order.",0806.1943v1
2008-06-20,Role of multifragmentation in spallation reactions,"In nuclear reactions induced by hadrons and ions of high energies, nuclei can
disintegrate into many fragments during a short time (~100 fm/c). This
phenomenon known as nuclear multifragmentation was under intensive
investigation last 20 years. It was established that multifragmentation is an
universal process taking place in all reactions when the excitation energy
transferred to nuclei is high enough, more than 3 MeV per nucleon,
independently on the initial dynamical stage of the reactions. Very known
compound nucleus decay processes (sequential evaporation and fission), which
are usual for low energies, disappear and multifragmentation dominates at high
excitation energy. For this reason, calculation of multifragmentation must be
carried on in all cases when production of highly excited nuclei is expected,
including spallation reactions. From the other hand, one can consider
multifragmentation as manifestation of the liquid-gas phase transition in
finite nuclei. This gives way for studying nuclear matter at subnuclear
densities and for applications of properties of nuclear matter extracted from
multifragmentation reactions in astrophysics. In this contribution, the
Statistical Multifragmentation Model (SMM), which combines the compound nucleus
processes at low energies and multifragmentation at high energies, is
described. The most important ingredients of the model are discussed.",0806.3455v1
2008-06-29,Ab initio Derivation of Low-energy Model for Iron-Based Superconductors LaFeAsO and LaFePO,"Effective Hamiltonians for LaFeAsO and LaFePO are derived from the
downfolding scheme based on first-principles calculations and provide insights
for newly discovered superconductivity in the family of LnFeAsO$_{1-x}$F$_x$,
Ln = La, Ce, Pr, Nd, Sm, and Gd. Extended Hubbard Hamiltonians for five
maximally localized Wannier orbitals per Fe are constructed dominantly from
five-fold degenerate iron-3$d$ bands. They contain parameters for effective
Coulomb and exchange interactions screened by the polarization of other
electrons away from the Fermi level. The onsite Coulomb interaction estimated
as 2.2-3.3 eV is compared with the transfer integrals between the
nearest-neighbor Fe-3$d$ Wannier orbitals, 0.2-0.3 eV, indicating moderately
strong electron correlation. The Hund's rule coupling is found to be 0.3-0.6
eV. The derived model offers a firm basis for further studies on physics of
this family of materials. The effective models for As and P compounds turn out
to have very similar screened interactions with slightly narrower bandwidth for
the As compound.",0806.4750v2
2008-07-01,Light charged particle emission from hot $^{32}$S$^{*}$ formed in $^{20}$Ne + $^{12}$C reaction,"Inclusive energy distributions for light charged particles ($p, d, t$ and
$\alpha$) have been measured in the $^{20}$Ne (158, 170, 180, 200 MeV) +
$^{12}$C reactions in the angular range 10$^{o}$ -- 50$^{o}$. Exclusive light
charged particle energy distribution measurements were also done for the same
system at 158 MeV bombarding energy by in-plane light charged particle --
fragment coincidence. Pre-equilibrium components have been separated out from
proton energy spectra using moving source model considering two sources. The
data have been compared with the predictions of the statistical model code
CASCADE. It has been observed that significant deformation effects were needed
to be introduced in the compound nucleus in order to explain the shape of the
evaporated $d, t$ energy spectra. For protons, evaporated energy spectra were
rather insensitive to nuclear deformation, though angular distributions could
not be explained without deformation. Decay sequence of the hot $^{32}$S
nucleus has been investigated through exclusive light charged particle
measurements using the $^{20}$Ne (158 MeV) + $^{12}$C reaction. Information on
the sequential decay chain has been extracted through comparison of the
experimental data with the predictions of the statistical model. It is observed
from the present analysis that exclusive light charged particle data may be
used as a powerful tool to probe the decay sequence of hot light compound
systems.",0807.0118v2
2008-07-07,Local moment versus Kondo behavior of the 4f-electrons in rare-earth iron oxypnictides,"We consider the role played by the 4f states in the rare-earth oxyarsenides
REOFeAs (RE=Ce,Pr,Nd) and the oxyphosphate CeOFeP, using a first-principles
technique that combines the local density approximation and dynamical
mean-field theory (LDA+DMFT). In the Pr and Nd compounds, the 4f states are
located well below and above the Fermi level E_F, and essentially do not
interact with the iron 3d bands located near E_F, resulting in local moment
behavior. In the Ce compounds, our results reveal a qualitatively different
picture, with the 3d-4f hybridization being sufficiently strong to give rise to
an observable Kondo screening of the local 4f moment. Our LDA+DMFT electronic
structure calculations allow us to estimate the Kondo temperature T_K for both
CeOFeP and CeOFeAs. For the phosphate, the order of magnitude of our estimate
is consistent with the experimental observation of T_K around 10 K. At ambient
pressure, T_K is found to be negligibly small for CeOFeAs. Under applied
hydrostatic pressure, we predict an exponential increase of T_K which reaches
values comparable to the superconducting T_c around 40 K at pressures above 10
GPa. We conjecture that the competition between the Kondo effect and
superconductivity may be at the origin of the monotonous decrease of T_c
observed in CeOFeAs under pressure. We argue that the quantitative aspects of
this competition are inconsistent with a weak-coupling BCS description of the
superconductivity in the oxyarsenides.",0807.1037v2
2008-07-08,Dispersing bimagnons and doping induced bimagnon-charge modes in superconducting cuprates,"In the early days of high temperature superconductivity it was already
recognized that magnetic properties of these materials are intimately related
to the superconducting ones . When doped, the long-range ordered
antiferromagnetic background of pristine copper-oxide insulators melts away and
makes room for a spin liquid and superconductivity. By resonant inelastic x-ray
scattering (RIXS) in the soft regime we probe the hitherto inaccessible
dynamical multiple-spin correlations of the magnetic background in a series of
parent compounds and in high Tc materials [NCCO (Nd2-xCexCuO4) and LSCO
(La2-xSrxCuO4)]. High resolution measurements allows the clear observation of
dispersing bimagnon excitations. In the undoped compounds the theory, fits the
data on these coherent spin excitations without free parameters. In nearly
optimally doped LSCO we observe the appearance of a new collective excitation
at an energy of 250 +/- 60 meV having the signature of a coupled
bimagnon-charge mode. It has a strongly reduced dispersion and lies in a so far
unexplored region of momentum and energy space in the mid-infrared.",0807.1140v1
2008-07-08,Superconductivity induced by cobalt doping in iron-based oxyarsenides,"Chemical doping has recently become a very important strategy to induce
superconductivity especially in complex compounds. Distinguished examples
include Ba-doped La$_2$CuO$_4$ (the first high temperature superconductor),
K-doped BaBiO$_3$, K-doped C$_{60}$ and Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O. The
most recent example is F-doped LaFeAsO, which leads to a new class of high
temperature superconductors. One notes that all the above dopants are
non-magnetic, because magnetic atoms generally break superconducting Cooper
pairs. In addition, the doping site was out of the (super)conducting structural
unit (layer or framework). Here we report that superconductivity was realized
by doping magnetic element cobalt into the (super)conducting-active
Fe$_2$As$_2$ layers in LaFe$_{1-x}$Co$_{x}$AsO. At surprisingly small Co-doping
level of $x$=0.025, the antiferromagnetic spin-density-wave transition in the
parent compound is completely suppressed, and superconductivity with $T_c\sim $
10 K emerges. With increasing Co content, $T_c$ shows a maximum of 13 K at
$x\sim 0.075$, and then drops to below 2 K at $x$=0.15. This result suggests
essential differences between previous cuprate superconductor and the present
iron-based arsenide one.",0807.1304v2
2008-07-13,Electronic structure of the iron-based superconductor LaOFeP,"The recent discovery of superconductivity in the so-called iron-oxypnictide
family of compounds has generated intense interest. The layered crystal
structure with transition metal ions in planar square lattice form and the
discovery of spin-density-wave order near 130 K seem to hint at a strong
similarity with the copper oxide superconductors. A burning current issue is
the nature of the ground state of the parent compounds. Two distinct classes of
theories have been put forward depending on the underlying band structures:
local moment antiferromagnetic ground state for strong coupling approach and
itinerant ground state for weak coupling approach. The local moment magnetism
approach stresses on-site correlations and proximity to a Mott insulating state
and thus the resemblance to cuprates; while the latter approach emphasizes the
itinerant electron physics and the interplay between the competing
ferromagnetic and antiferromagnetic fluctuations. Such a controversy is partly
due to the lack of conclusive experimental information on the electronic
structures. Here we report the first angle-resolved photoemission spectroscopy
(ARPES) investigation of LaOFeP (Tc = 5.9 K), the first reported iron-based
superconductor. Our results favor the itinerant ground state, albeit with band
renormalization. In addition, our data reveal important differences between
these and copper based superconductors.",0807.2009v1
2008-07-23,Magnetic order and multipole interactions in CexPr1-xB6 solid solutions,"Magnetic ordering phenomena in CexPr1-xB6 solid solutions have been studied
using both powder and single-crystal neutron diffraction. A variety of magnetic
structures are observed depending on temperature and Ce concentration. Over a
broad composition range (x $\le$ 0.7), Pr-Pr interactions play a dominant role,
giving rise to incommensurate structures with wave vectors of the form
k{IC1}=(1/4-delta, 1/4, 1/2) or k{IC2}=(1/4-delta, 1/4-delta, 1/2). The
crossover to a CeB6-like regime takes place near x = 0.7-0.8. For the latter
composition, the antiferroquadrupolar phase transition observed in transport
measurements precedes the onset, at lower temperature, of a commensurate
magnetic order similar to that existing in CeB6. However, unlike in the pure
compound, an incommensurate magnetic order is formed at even higher temperature
and persists in the antiferroquadrupolar phase down to the lock-in transition.
These results are shown to reflect the interplay between various type of dipole
exchange and higher multipole interactions in this series of compounds.",0807.3689v2
2008-07-30,Coexistence of static magnetism and superconductivity in SmFeAsO1-xFx as revealed by muon spin rotation,"The recent observation of superconductivity with critical temperatures up to
55 K in the FeAs based pnictide compounds marks the first discovery of a non
copper-oxide based layered high-Tc superconductor (HTSC) [1-3]. It has raised
the suspicion that these new materials share a similar pairing mechanism to the
cuprates, since both exhibit superconductivity following charge doping of a
magnetic parent material. Here we present a muon spin rotation study on
SmFeAsO1-xFx (x=0-0.30), which shows that static magnetism persists well into
the superconducting regime. The analogy with the cuprates is quite surprising
since the parent compounds appear to have different magnetic ground states:
itinerant spin density wave for the pnictides contrasted with the Mott-Hubbard
insulator in the cuprates. Our findings suggest that proximity to magnetic
order and associated soft magnetic fluctuations, rather than the strong
electronic correlations in the vicinity of a Mott-Hubbard-metal-to-insulator
transition, may be the key ingredients of HTSC.",0807.4876v2
2008-08-03,Metamagnetic transition in EuFe$_2$As$_2$ single crystals,"We report the measurements of anisotropic magnetization and magnetoresistance
on single crystals of EuFe$_2$As$_2$, a parent compound of ferro-arsenide
high-temperature superconductor. Apart from the antiferromagnetic (AFM)
spin-density-wave transition at 186 K associated with Fe moments, the compound
undergoes another magnetic phase transition at 19 K due to AFM ordering of
Eu$^{2+}$ spins ($J=S=7/2$). The latter AFM state exhibits metamagnetic
transition under magnetic fields. Upon applying magnetic field with $H\parallel
c$ at 2 K, the magnetization increases linearly to 7.0 $\mu_{B}$/f.u. at
$\mu_{0}H$=1.7 T, then keeps at this value of saturated Eu$^{2+}$ moments under
higher fields. In the case of $H\parallel ab$, the magnetization increases
step-like to 6.6 $\mu_{B}$/f.u. with small magnetic hysteresis. A metamagnetic
phase was identified with the saturated moments of 4.4 $\mu_{B}$/f.u. The
metamagnetic transition accompanies with negative in-plane magnetoresistance,
reflecting the influence of Eu$^{2+}$ moments ordering on the electrical
conduction of FeAs layers. The results were explained in terms of
spin-reorientation and spin-reversal based on an $A$-type AFM structure for
Eu$^{2+}$ spins. The magnetic phase diagram has been established.",0808.0325v2
2008-08-22,Low-dimensional magnetism in the mixed Cr valence spin-chain compound Sr_4Cr_3O_9,"Sr_4Cr_3O_9 is the n = 2 member of a family of quasi-one-dimensional
compounds A_{n+2}T_{n+1}O_{3n+3} (A = Ca, Sr, or Ba, T = transition metal, and
n = 1 to \infty) having a crystal structure which consists of chains of n TO_6
octahedra alternated by one TO_6 trigonal prism running along the c-axis. The
chains are arranged on a triangular lattice in the ab-plane. We report the
synthesis, structure, magnetization M versus magnetic field H, magnetic
susceptibility \chi versus temperature T and specific heat C versus T
measurements on sintered and arc-melted polycrystalline samples of Sr_4Cr_3O_9.
The \chi data have a T dependence which is typical of low-dimensional magnetic
systems with dominant antiferromagnetic (AF) exchange interactions.
Specifically, \chi(T) shows a broad maximum at T_{max} \approx 200K for the
sintered pellet and T_{max}\approx 265K for the arc-melted sample, indicating
the onset of short-range magnetic order. Below T = 15K we observe 2 anomalies
in the \chi(T) data for both samples suggesting the onset of long-range
magnetic ordering. The corresponding anomalies in the C(T) data however are
weak indicating that only a small amount of the expected magnetic entropy is
recovered at the magnetic transitions and that strong short-range AF order
exists above these temperatures.",0808.3123v1
2008-09-04,Modeling the Unconventional Superconducting Properties of Expanded A$_3$C$_{60}$ Fullerides,"The trivalent alkali fullerides A$_3$C$_{60}$, where C$_{60}$ are a well
established family of molecular superconductors. The electron pairing has
s-wave symmetry and is due to standard electron-phonon coupling, in particular
by Jahn-Teller intramolecular C$_{60}$ vibrations.
  A source of renewed interest in these systems are indications of strong
electron-electron repulsion, which emerges especially in compounds where the
C$_{60}$-C$_{60}$ distance is expanded. In several compounds after an initial
increases T$_c$, further expansions leads to a decline of superconductivity and
its eventual disappearance in favor of a Mott insulating state
  We theoretically study a three-orbital Hubbard model including the
phonon-mediated interaction using Dynamical Mean-Field Theory, which is
particularly suitable due to the local nature of all the interactions. We
studied the system as a function of the ratio of intra-molecular repulsion $U$
over the electron bandwidth $W$, the increase of $U/W$ representing the main
effect of lattice expansion. The phase diagram is close to that of actual
materials, with a dome-shaped superconducting region preceding the Mott
transition. Unconventional properties predicted by this model include: (i) a
pseudogap in the normal phase; (ii) a gain of kinetic energy and of d.c.
conductivity at the onset of superconductivity; (iii) regular spin
susceptibility and specific heat despite strong correlations; (iv) the
emergence of more than one energy scale governing the renormalized single
particle dispersion. These predictions, if confirmed, would establish
fullerides, especially the expanded ones, as members of the wider family of
strongly correlated superconductors.",0809.0910v1
2008-09-30,"Evidence of spin density wave in LaFeAsO, the parent material of the new Fe-based oxypnictide superconductors","The Fe-based Oxypnicide superconductors have generated a huge amount of
interest; they are a high temperature superconductor, with a Tc of 55K, but do
not have the two dimensional copper oxygen layer that was thought essential for
superconductivity at these high temperatures. Initial studies have hinted
towards the possibility of a spin density wave (SDW) in these compounds and how
they could play an important role in the superconductivity. SDW's occur at low
temperatures in low-dimensional materials with strong electron correlations or
in metals with a high density of states at the Fermi surface. A transition to
the SDW state has many similarities to the superconducting transition, driven
by the condensation energy with an energy gap opening, and in many materials
the SDW state occurs adjacent in the phase diagram to the superconducting
state. In these materials it is believed that electron doping suppresses the
SDW instability allowing superconductivity to emerge. In this paper we report
on the first direct experimental evidence of a SDW in the LaFeAsO parent
compound as observed with inelastic neutron scattering. We show that these
excitation derive from a two-dimensional Fermi surface nesting with a nesting
vector of (\pi,\pi,0).",0809.5128v2
2008-10-19,Electronic Structure of New AFFeAs Prototype of Iron Arsenide Superconductors,"This work is provoked by recent discovery of new class prototype systems
AFFeAs (A=Sr,Ca) of novel layered ironpnictide High-Tc superconductors
(Tc=36K). Here we report ab initio LDA results for electronic structure of the
AFFeAs systems. We provide detailed comparison between electronic properties of
both new systems and reference LaOFeAs (La111) compound. In the vicinity of the
Fermi level all three systems have essentially the same band dispersions.
However for iron fluoride systems F(2p) states were found to be separated in
energy from As(4p) ones in contrast to La111, where O(2p) states strongly
overlaps with As(4p). Thus it should be more plausible to include only Fe(3d)
and As(4p) orbitals into a realistic noninteracting model than for La111.
Moreover Sr substitution with smaller ionic radius Ca in AFFeAs materials leads
to a lattice contruction and stronger Fe(3d)-As(4p) hybridization resulting in
smaller value of the density of states at the Fermi level in the case of Ca
compound. So to some extend Ca system reminds RE111 with later Rare Earths.
However Fermi surface of new fluorides is found to be nearly perfect
two-dimensional. Also we do not expect strong dependence of superconducting
properties with respect to different types of A substitutes.",0810.3377v1
2008-11-03,Fission decay of N = Z nuclei at high angular momentum: $^{60}$Zn,"Using a unique two-arm detector system for heavy ions (the BRS, binary
reaction spectrometer) coincident fission events have been measured from the
decay of $^{60}$Zn compound nuclei formed at 88MeV excitation energy in the
reactions with $^{36}$Ar beams on a $^{24}$Mg target at $E_{lab}(^{36}$Ar) =
195 MeV. The detectors consisted of two large area position sensitive (x,y) gas
telescopes with Bragg-ionization chambers. From the binary coincidences in the
two detectors inclusive and exclusive cross sections for fission channels with
differing losses of charge were obtained. Narrow out-of-plane correlations
corresponding to coplanar decay are observed for two fragments emitted in
binary events, and in the data for ternary decay with missing charges from 4 up
to 8. After subtraction of broad components these narrow correlations are
interpreted as a ternary fission process at high angular momentum through an
elongated shape. The lighter mass in the neck region consists dominantly of two
or three-particles. Differential cross sections for the different mass splits
for binary and ternary fission are presented. The relative yields of the binary
and ternary events are explained using the statistical model based on the
extended Hauser-Feshbach formalism for compound nucleus decay. The ternary
fission process can be described by the decay of hyper-deformed states with
angular momentum around 45-52 $hbar$.",0811.0018v1
2008-11-07,Effect of 3d Transition Metal Doping on the Superconductivity in Quaternary Fluoroarsenide CaFeAsF,"We examined doping effect of 3d transition metal elements (TM: Cr, Mn, Co,
Ni, and Cu) at the Fe site of a quaternary fluoroarsenide CaFeAsF, an analogue
of 1111-type parent compound LaFeAsO. The anomaly at ~120 K observed in
resistivity (rho) vs. temperature (T) plot for the parent compound is
suppressed by the doping of each TM element. Furthermore, Co- and Ni-doping
(CaFe1-xTMxAsF, TM = Co, Ni) induces superconductivity with a transition
temperature maximized at the nominal x = 0.10 for Co (22 K) and at x = 0.05 for
Ni (12 K). These optimal doping levels may be understood by considering that
Ni2+(3d8) adds double electrons to the FeAs layers compared with Co2+ (3d7).
Increased x for Co or Ni breaks the superconductivity while metallic nature
drho/dT > 0 is still kept. These observations indicate that Co and Ni work as
electron donors. In contrast, neither of Cr, Mn nor Cu-doping induce
superconductivity, yielding drho/dT < 0 in the below the rho-T anomaly
temperature, indicating that these transition metal ions act as scattering
centers. The two different behavior of TM replacing the Fe site is discussed in
relation to the changes in the lattice constants with the doping.",0811.1147v2
2008-12-05,Multiple temperature scales of the periodic Anderson model: the slave bosons approach,"The thermodynamic and transport properties of intermetallic compounds with
Ce, Eu, and Yb ions are discussed using the periodic Anderson model with an
infinite correlation between $f$ electrons. The slave boson solution of the
periodic model shows that the Fermi liquid scale T$_0$ and the Kondo scale
T$_K$ depend on the shape of the conduction electrons density of states ($c$
DOS) in the vicinity of the chemical potential, that the details of the band
structure determine the ratio T$_0$/T$_K$, and that the crossover between the
high- and low-temperature regimes in ordered compounds is system-dependent.
  A sharp peak in the $c$ DOS yields T$_0 \ll$T$_K$ and explains the 'slow
crossover' observed in YbAl$_3$ or YbMgCu$_4$. A minimum in the $c$ DOS yields
T$_0 \gg$T$_K$, which leads to the abrupt transition between the high- and
low-temperature regimes in YbInCu$_4$. In the case of CeCu$_2$Ge$_2$ and
CeCu$_2$Si$_2$, where T$_0 \simeq T_K$, the slave boson solution explains the
pressure experiments which reveal sharp peaks in the T$^2$ coefficient of the
electrical resistance, $A=\rho(T)/T^2$, and the residual resistance. These
peaks are due to the change in the degeneracy of the $f$ states induced by the
applied pressure.
  We show that the low-temperature response of the periodic Anderson model can
be enhanced (or reduced) with respect to the predictions based on the
single-impurity models that give the same high-temperature behavior.",0812.1137v1
2009-01-05,"Transport and magnetotransport properties of cold-pressed CrO$_2$ powder, prepared by hydrothermal synthesis","Submicron powder of CrO$_2$ was prepared by hydrothermal synthesis method
from chromium trioxide. Particles obtained were of rounded form with mean
diameter about 120 nm. The powder (stabilized with thin surface layer of
\beta-CrOOH) has been characterized by structural, X-ray and magnetic
measurements. The powder (with Curie temperature about 385 K) was cold-pressed
and its transport and magnetotransport properties have been measured in the
temperature range 4--450 K in magnetic field up to 1.6 T. The samples studied
is characterized by non-metallic temperature behavior of resistance and large
negative magnetoresistance (MR) in low temperature range. At T=5 K the MR
magnitude has been -17% at H=0.3 T and -20% at H=1.4 T. Its magnitude decreased
fast with increase in temperature reducing to 0.3% and less for T>200 K. It is
shown that this MR behavior is inherent for a system of magnetic grains with
spin-dependent intergrain tunnelling. Some peculiarities of MR behavior in
low-temperature range (below 40 K) can be associated with percolating character
of tunnelling conductivity of this granular system under conditions of
availability of only few conducting current paths through the sample.",0901.0491v1
2009-03-13,2D XY Behavior observed in quasi-2D quantum Heisenberg antiferromagnets,"The magnetic properties of a new family of molecular-based quasi-two
dimension $S=1/2$ Heisenberg antiferromagnets are reported. Three compounds,
($Cu(pz)_2(ClO_4)_2$, $Cu(pz)_2(BF_4)_2$, and $[Cu(pz)_2(NO_3)](PF_6)$) contain
similar planes of Cu$^{2+}$ ions linked into magnetically square lattices by
bridging pyrazine molecules (pz = $C_4H_4N_2$). The anions provide charge
balance as well as isolation between the layers. Single crystal measurements of
susceptibility and magnetization, as well as muon spin relaxation studies,
reveal low ratios of N\'{e}el temperatures to exchange strengths ($4.25 / 17.5
= 0.243$, $3.80/15.3=0.248$, and $3.05/10.8=0.282$, respectively) while the
ratio of the anisotropy fields $H_A$ (kOe) to the saturation field
$H_\mathrm{SAT}$ (kOe) are small ($2.6/490 = 5.3\times10^{-3}$,
$2.4/430=5.5\times10^{-3}$, and $0.07/300=2.3\times10^{-4}$, respectively),
demonstrating close approximations to a 2D Heisenberg model. The
susceptibilities of ClO$_4$ and BF$_4$ show evidence of an exchange anisotropy
crossover (Heisenberg to $XY$) at low temperatures; their ordering transitions
are primarily driven by the $XY$ behavior with the ultimate 3D transition
appearing parasitically. The PF$_6$ compound remains Heisenberg-like at all
temperatures, with its transition to the N\'{e}el state due to the interlayer
interactions. Effects of field-induced anisotropy have been observed.",0903.2470v1
2009-04-28,Exotic magnetism in the alkali sesquoxides Rb4O6 and Cs4O6,"Among the various alkali oxides the sesquioxides Rb4O6 and Cs4O6 are of
special interest. Electronic structure calculations using the local
spin-density approximation predicted that Rb4O6 should be a half-metallic
ferromagnet, which was later contradicted when an experimental investigation of
the temperature dependent magnetization of Rb4O6 showed a low-temperature
magnetic transition and differences between zero-field-cooled (ZFC) and
field-cooled (FC) measurements. Such behavior is known from spin glasses and
frustrated systems. Rb4O6 and Cs4O6 comprise two different types of dioxygen
anions, the hyperoxide and the peroxide anions. The nonmagnetic peroxide anions
do not contain unpaired electrons while the hyperoxide anions contain unpaired
electrons in antibonding pi*-orbitals. High electron localization (narrow
bands) suggests that electronic correlations are of major importance in these
open shell p-electron systems. Correlations and charge ordering due to the
mixed valency render p-electron-based anionogenic magnetic order possible in
the sesquioxides. In this work we present an experimental comparison of Rb4O6
and the related Cs4O6. The crystal structures are verified using powder x-ray
diffraction. The mixed valency of both compounds is confirmed using Raman
spectroscopy, and time-dependent magnetization experiments indicate that both
compounds show magnetic frustration, a feature only previously known from d-
and f-electron systems.",0904.4338v1
2009-04-28,Magnetic characterization of undoped and 15%F doped LaFeAsO and SmFeAsO compounds,"In this paper the magnetic behaviour of undoped and 15% F doped SmFeAsO
(Sm-1111) and LaFeAsO (La-1111) samples is presented and discussed.
Magnetization measurements are not a simple tool to use for the
characterisation of the new family of Fe-based superconductors because magnetic
impurities can be easily formed during the preparation procedure and may affect
the magnetic signal. In spite of this problem bulk magnetization measurements,
properly treated, may give very useful information. In the undoped samples we
gathered the main aspects of the physical behavior of the 1111 phase, i.e. the
onset of the Spin Density Wave (SDW), the antiferromagnetic ordering at the Sm
sublattice and the susceptibility increase with increasing temperature above
the SDW temperature, and, in addition, we were able to estimate the Pauli
contribution to susceptibility and therein the Wilson ratio both for LaFeAsO
and SmFeAsO compounds, and the amplitude of the jump at the SDW temperature. In
the doped samples, while the presence of magnetic signals due to impurities is
dominating in the normal state, the superconducting behavior may be clearly
observed and studied. In particular, in the Sm-1111 superconducting sample the
coexistence-competition between superconductivity and antiferromagnetic
ordering of the Sm ions was clearly observed.",0904.4348v1
2009-05-04,Vortex state in iron-based superconductors with collinear antiferromagnetic cores,"Magnetism in the FeAs stoichiometric compounds and its interplay with
superconductivity in vortex states are studied by self-consistently solving the
BdG equations based on a two-orbital model with including the on-site
interactions between electrons in the two orbitals. It is revealed that for the
parent compound, magnetism is caused by the strong Hund's coupling, and the
Fermi surface topology aids to select the spin-density-wave (SDW) pattern. The
superconducting (SC) order parameter with
$s_{\pm}=\Delta_{0}\cos(k_{x})\cos(k_{y})$ symmetry is found to be the most
favorable pairing for both the electron- and hole-doped cases, while the local
density-of-states (LDOS) exhibits the characteristic of nodal gap for the
former and full gap for the latter. In the vortex state, the emergence of the
field-induced SDW depends on the strength of the Hund's coupling and the
Coulomb repulsions. The field-induced SDW gaps the finite energy contours on
the electron and hole pocket sides, leading to the dual structures with one
reflecting the SC pairing and the other being related to the SDW order. These
features can be discernable in STM measurements for identifying the interplay
between the field-induced SDW order and the SC order around the core region.",0905.0382v3
2009-05-26,A Comparative Study of the Formation of Aromatics in Rich Methane Flames Doped by Unsaturated Compounds,"For a better modeling of the importance of the different channels leading to
the first aromatic ring, we have compared the structures of laminar rich
premixed methane flames doped with several unsaturated hydrocarbons: allene and
propyne, because they are precursors of propargyl radicals which are well known
as having an important role in forming benzene, 1,3-butadiene to put in
evidence a possible production of benzene due to reactions of C4 compounds,
and, finally, cyclopentene which is a source of cyclopentadienylmethylene
radicals which in turn are expected to easily isomerizes to give benzene. These
flames have been stabilized on a burner at a pressure of 6.7 kPa (50 Torr)
using argon as dilutant, for equivalence ratios (?) from 1.55 to 1.79. A unique
mechanism, including the formation and decomposition of benzene and toluene,
has been used to model the oxidation of allene, propyne, 1,3 butadiene and
cyclopentene. The main reaction pathways of aromatics formation have been
derived from reaction rate and sensitivity analyses and have been compared for
the three types of additives. These combined analyses and comparisons can only
been performed when a unique mechanism is available for all the studied
additives.",0905.4211v1
2009-05-28,Soft modes and thermal transport in guest-host crystalline structures,"We propose a simple phenomenological model describing vibrational dynamics in
a class of materials (like clathrates), which are crystalline compounds with
closed cavities in their structures. In the spirit of a minimalist approach,
our model includes only the minimum of ingredients necessary to capture the
generic features of this class of compounds as brought to light by experiments.
We consider only two kinds of particles: strongly coupled host atoms, which
form the structural cavities, and guest atoms confined in the cavities. In
spite of the confinement, for relatively small amplitude vibrations of the
guest atoms, their interaction with the host particles is assumed to be weaker
than between the host atoms. We calculate self-consistently the vibrational
mode (phonon) line broadenings for the empty and filled (by the guest atoms)
cavities. We show that the soft phonon dispersion sheet, which appears for
weakly bonded guest atoms, yields to large mode broadening via three waves
anharmonic mode coupling. In turn the Umklapp part of this broadening reduces
drastically the phonon thermoconductivity coefficient. We conclude that for a
system with a soft mode component in the vibrational spectrum phonon broadening
is always larger and thermal conductivity is always appreciably smaller than
for a system without this soft mode (provided all other characteristics are the
same). Although our model is minimal, in the sense of ignoring the complexity
of actual guest-host structures, when properly interpreted, it can yield quite
reasonable values for a variety of measurable quantities.",0905.4603v1
2009-06-15,Doping dependence of the chemical potential and surface electronic structure in YBa2Cu3O6+x and La2-xSrxCuO4 using hard x-ray photoemission spectroscopy,"The electronic structure of YBa2Cu3O6+x and La2-xSrxCuO4 for various values
of x has been investigated using hard x-ray photoemission spectroscopy. The
experimental results establish that the cleaving of YBa2Cu3O6+x compounds
occurs predominantly in the BaCuO3 complex leading to charged surfaces at
higher x and to uncharged surfaces at lower x values. The bulk component of the
core level spectra exhibits a shift in binding energy as a function of x, from
which a shift of the chemical potential as a function of hole concentration in
the CuO2 layers could be derived. The doping dependence of the chemical
potential across the transition from a Mott-Hubbard insulator to a
Fermi-liquid-like metal is very different in these two series of compounds. In
agreement with previous studies in the literature the chemical potential shift
in La2-xSrxCuO4 is close to zero for small hole concentrations. In YBa2Cu3O6+x,
similar to all other doped cuprates studied so far, a strong shift of the
chemical potential at low hole doping is detected. However, the results for the
inverse charge susceptibility at small x shows a large variation between
different doped cuprates. The results are discussed in view of various
theoretical models. None of these models turns out to be satisfactory.",0906.2674v1
2009-06-15,Unveiling the Atomic and Electronic Structure at the Surface of the Parent Pnictide SrFe2As2,"The parent compounds of the recently discovered iron-arsenic (pnictide) high
temperature superconductors transition into an intriguing spin density wave
(SDW) phase at low temperatures. Progress in understanding this SDW state has
been complicated by a complex band structure and by the fact that the spin,
electronic, and structural degrees of freedom are closely intertwined in these
compounds. Scanning tunneling microscopy (STM) measurements have added to this
complexity by revealing different topographies with no consensus on the surface
structure. In this paper, we use a combination of high-resolution STM imaging
and spectroscopy, and low energy electron diffraction (LEED) to determine the
atomic and electronic structure of the parent pnictide SrFe2As2. Our data
present a compelling picture of the existence of two coexisting homotopic
structures on the surface. Based on this, we construct a simple model for the
surface, which offers an explanation of the two classes of topographies seen by
STM. STM spectroscopy shows that while the high energy density of states (DOS)
profile is consistent with the Fe 3d and As 4p-electrons predicted by LDA it is
in better agreement with calculations that include electron correlations beyond
LDA. Importantly, we find a gap of ~15 meV in the low energy density of states
on both structures which may be linked with the SDW or the observed surface
reconstruction.",0906.2761v1
2009-06-29,A novel wear-resistant magnetic thin film material based on a $Ti_{1-x}Fe_xC_{1-y}$ nanocomposite alloy,"In this study we report on the film growth and characterization of thin
(approximately 50 nm thick) Ti-Fe-C films deposited on amorphous quartz. The
experimental studies have been complemented by first principles density
functional theory (DFT) calculations. Upon annealing of as-prepared films, the
composition of the metastable Ti-Fe-C film changes. An iron-rich phase is first
formed close to the film surface, but with increasing annealing time this phase
is gradually displaced toward the film-substrate interface where its position
stabilizes. Both the magnetic ordering temperature and the saturation
magnetization changes significantly upon annealing. The DFT calculations show
that the critical temperature and the magnetic moment both increase with
increasing Fe and C-vacancy concentration. The formation of the metastable
iron-rich Ti-Fe-C compound is reflected in the strong increase of the magnetic
ordering temperature. Eventually, after enough annealing time ($\geq 10$
minutes), nano-crystalline $\alpha$-Fe starts to precipitate and the amount and
size of these precipitates can be controlled by the annealing procedure; after
20 minutes of annealing, the experimental results indicate a nano-crystalline
iron-film embedded in a wear resistant TiC compound. This conclusion is further
supported by transmission electron microscopy studies on epitaxial Ti-Fe-C
films deposited on single crystalline MgO substrates where, upon annealing, an
iron film embedded in TiC is formed. Our results suggest that annealing of
metastable Ti-Fe-C films can be used as an efficient way of creating a
wear-resistant magnetic thin film material.",0906.5386v1
2009-07-03,Phase separation in lithium intercalated anatase: A theory,"Lithium intercalated anatase used in Li-ion batteries has some special
features: coexistence of Li-rich and Li-poor phases as well as two possible
positions for Li ions in the oxygen tetrahedron. A theoretical description of
the compound considering those peculiarities is presented. As shown by the
performed symmetry analysis, the intercalation induced lattice deformation can
be accompanied by the ordering of antiferroelectric type (internal
piezoeffect). In the following step, a qualitative illustration of the phase
separation in the lithiated anatase is given within the Landau expansion at the
proper choice of coefficients. A microscopic model for description of the
compound is also proposed which combines features of the Mitsui and
Blume-Emery-Griffits models and utilizes the symmetry analysis results. Various
ground state and temperature-dependent phase diagrams of the model are studied
to find a set of model parameters corresponding to the lithiated anatase. A
phase separation into the empty and half-filled phases in a wide temperature
range has been found closely resembling the phase coexistence in the
intercalated crystal. In the framework of the model, the two-position Li
subsystem could have the ordering of ferro- or antiferroelectric types which,
however, has not been yet observed by the experiment.",0907.0687v1
2009-07-16,Isoprene and acetone concentration profiles during exercise on an ergometer,"A real-time recording setup combining exhaled breath VOC measurements by
proton transfer reaction mass spectrometry (PTR-MS) with hemodynamic and
respiratory data is presented. Continuous automatic sampling of exhaled breath
is implemented on the basis of measured respiratory flow: a flow-controlled
shutter mechanism guarantees that only end-tidal exhalation segments are drawn
into the mass spectrometer for analysis.
  Exhaled breath concentration profiles of two prototypic compounds, isoprene
and acetone, during several exercise regimes were acquired, reaffirming and
complementing earlier experimental findings regarding the dynamic response of
these compounds reported by Senthilmohan et al. [1] and Karl et al. [2]. While
isoprene tends to react very sensitively to changes in pulmonary ventilation
and perfusion due to its lipophilic behavior and low Henry constant,
hydrophilic acetone shows a rather stable behavior. Characteristic (median)
values for breath isoprene concentration and molar flow, i.e., the amount of
isoprene exhaled per minute are 100 ppb and 29 nmol/min, respectively, with
some intra-individual day-to-day variation. At the onset of exercise breath
isoprene concentration increases drastically, usually by a factor of ~3-4
within about one minute. Due to a simultaneous increase in ventilation, the
associated rise in molar flow is even more pronounced, leading to a ratio
between peak molar flow and molar flow at rest of ~11.
  Our setup holds great potential in capturing continuous dynamics of
non-polar, low-soluble VOCs over a wide measurement range with simultaneous
appraisal of decisive physiological factors affecting exhalation kinetics.",0907.2943v1
2009-07-17,Pressure-induced lattice instabilities and superconductivity in YBa2Cu4O8 and optimally doped YBa2Cu3O7-δ,"Combined synchrotron angle-dispersive powder diffraction and micro-Raman
spectroscopy are used to investigate the pressure-induced lattice instabilities
that are accompanied by T$_{\rm c}$ anomalies in YBa$_{\rm 2}$Cu$_{\rm
4}$O$_{\rm 8}$, in comparison with the optimally doped YBa$_{\rm 2}$Cu$_{\rm
3}$O$_{\rm 7-\delta}$ and the non-superconducting PrBa$_{\rm 2}$Cu$_{\rm
3}$O$_{\rm 6.92}$. In the first two superconducting systems there is a clear
anomaly in the evolution of the lattice parameters and an increase of lattice
disorder with pressure, that starts at $\approx3.7 GPa$ as well as
irreversibility that induces a hysteresis. On the contrary, in the Pr-compound
the lattice parameters follow very well the expected equation of state (EOS) up
to 7 GPa. In complete agreement with the structural data, the micro-Raman data
of the superconducting compounds show that the energy and width of the A$_{\rm
g}$ phonons show anomalies at the same pressure range where the lattice
parameters deviate from the EOS and the average Cu2-O$_{pl}$ bond length
exhibits a strong contraction and correlate with the non-linear pressure
dependence of T$_{\rm c}$. This is not the case for the non superconducting Pr
sample, clearly indicating a connection with the charge carriers. It appears
that the cuprates close to optimal doping are at the edge of lattice
instability.",0907.3024v2
2009-07-28,Random effects compound Poisson model to represent data with extra zeros,"This paper describes a compound Poisson-based random effects structure for
modeling zero-inflated data. Data with large proportion of zeros are found in
many fields of applied statistics, for example in ecology when trying to model
and predict species counts (discrete data) or abundance distributions
(continuous data). Standard methods for modeling such data include mixture and
two-part conditional models. Conversely to these methods, the stochastic models
proposed here behave coherently with regards to a change of scale, since they
mimic the harvesting of a marked Poisson process in the modeling steps. Random
effects are used to account for inhomogeneity. In this paper, model design and
inference both rely on conditional thinking to understand the links between
various layers of quantities : parameters, latent variables including random
effects and zero-inflated observations. The potential of these parsimonious
hierarchical models for zero-inflated data is exemplified using two marine
macroinvertebrate abundance datasets from a large scale scientific bottom-trawl
survey. The EM algorithm with a Monte Carlo step based on importance sampling
is checked for this model structure on a simulated dataset : it proves to work
well for parameter estimation but parameter values matter when re-assessing the
actual coverage level of the confidence regions far from the asymptotic
conditions.",0907.4903v1
2009-08-09,Topological Surface States Protected From Backscattering by Chiral Spin Texture,"Topological insulators are a new class of insulators in which a bulk gap for
electronic excitations is generated by strong spin orbit coupling. These novel
materials are distinguished from ordinary insulators by the presence of gapless
metallic boundary states, akin to the chiral edge modes in quantum Hall
systems, but with unconventional spin textures. Recently, experiments and
theoretical efforts have provided strong evidence for both two- and
three-dimensional topological insulators and their novel edge and surface
states in semiconductor quantum well structures and several Bi-based compounds.
A key characteristic of these spin-textured boundary states is their
insensitivity to spin-independent scattering, which protects them from
backscattering and localization. These chiral states are potentially useful for
spin-based electronics, in which long spin coherence is critical, and also for
quantum computing applications, where topological protection can enable
fault-tolerant information processing. Here we use a scanning tunneling
microscope (STM) to visualize the gapless surface states of the
three-dimensional topological insulator BiSb and to examine their scattering
behavior from disorder caused by random alloying in this compound. Combining
STM and angle-resolved photoemission spectroscopy, we show that despite strong
atomic scale disorder, backscattering between states of opposite momentum and
opposite spin is absent. Our observation of spin-selective scattering
demonstrates that the chiral nature of these states protects the spin of the
carriers; they therefore have the potential to be used for coherent spin
transport in spintronic devices.",0908.1247v1
2009-09-23,Quantum Size Effects in Pb/Si(111) Thin Films from Density Functional Calculations,"The Pb/Si(111) thin films were simulated within the density functional theory
(DFT). The well-known Perdew-Burke-Ernzerhof (PBE) version of the generalized
gradient approximation (GGA) and its recent nonempirical successor Wu-Cohen
(WC) issue were used to estimate the exchange-correlation functional. Lattice
parameters were calculated for Bulk of the Pb and Si compounds to obtain more
reliable lattice mismatch at the interface to be consistent with our used
full-potential method of calculations. The WC-GGA result predicts the lattice
constants of the Pb and Si compounds better than the GGA when compared with
experiment. We have found that the spin-orbit coupling (SOC) does not
significantly influence the results. Our finding is in agreement with the
recent observation of the Rashba-type spin-orbit splitting of quantum well
states in ultrathin Pb/Si(111) films. Our result shows, in agreement with
experiment, that the top site (T1) is the most stable phase. A combination of
tight $\sigma$ and feeble $\pi$ bonds has been found at the interface, which
results in a covalent Pb-Si bond. Our calculated electric field gradient (EFG)
predicts quantum size effects (QSE) with respect to the number of deposited Pb
layers on the Si substrate. The QSE prediction shows that the EFG dramatically
drops on going from first to second layer. The EFG calculation shows that this
system is not an ideal paradigm to freestanding films.",0909.4171v1
2009-10-01,Theory of Magnetic Field-Induced Bose-Einstein Condensation of Triplons in Ba3Cr2O8,"Motivated by recent experiments on Ba$_{3}$Cr$_{2}$O$_8$, a new spin-dimer
compound with spin-1/2 moments of Cr$^{5+}$ ions, we theoretically investigate
the field-induced magnetic ordering in this material in view of the
Bose-Einstein condensation (BEC) of triplet excitations (triplons). We apply
the self-consistent Hartree-Fock-Popov (HFP) approach to a microscopic
Hamiltonian, using the realistic triplon dispersion measured in an inelastic
neutron scattering experiment. In particular, we ask to what extent the BEC of
dilute triplons near the critical field can explain the magnetic ordering in
this material. For example, we investigate the temperature range where the BEC
picture of triplons can be applied via the HFP approach. We also determine the
temperature regime where a quadratic approximation of the triplon dispersion
works. It is found that the strength of the effective repulsive interaction
between triplons is much weaker in Ba$_{3}$Cr$_{2}$O$_8$ than in the canonical
spin-dimer compound TlCuCl$_{3}$. Small effective repulsive interaction in
combination with the narrow band of triplons leads to higher density of
triplons $n_{cr}$ at the critical point. It turns out that the combined effect
points to a bigger HFP correction $U n_{cr}$ in Ba$_3$Cr$_2$O$_8$ than in
TlCuCl$_{3}$. Nonetheless, the HFP approach provides a reasonable explanation
of the transverse magnetization and the specific heat data of
Ba$_{3}$Cr$_{2}$O$_8$.",0910.0247v3
2009-10-01,Electronic structure of BiMeO3 multiferroics and related oxides,"We have performed a systematic study of the electronic structures of BiMeO3
(Me = Sc, Cr, Mn, Fe, Co, Ni) series by soft X-ray emission (XES) and
absorption (XAS) spectroscopy. The band gap values were estimated for all
compounds in the series. For BiFeO3 a band gap of ~0.9 eV was obtained from the
alignment of the O Ka XES and O 1s XAS. The O 1s XAS spectrum of BiNiO3
indicates that the formation of holes is due to a Ni2+ valency rather than a
Ni3+ valency. We have found that the O Ka XES and O 1s XAS of BiMeO3 probing
partially occupied and vacant O 2p states, respectively, are in agreement with
the O 2p densities of states obtained from spin-polarized band structure
calculations. The O Ka XES spectra show the same degree of Bi 6s--O 2p
hybridization for all compounds in the series. We argue herein that the
stereochemical activity of Bi 6s lone pairs must be supplemented with inversion
symmetry breaking to allow electric polarization. For BiMnO3 and BiFeO3, two
cases of multiferroic materials in this series, the former breaks the inversion
symmetry due to the antiferromagnetic order induced by particular orbital
ordering in the highly distorted perovskite structure and the latter has
rhombohedral crystal structure without inversion symmetry.",0910.0290v1
2009-10-17,Density functional study of the actinide nitrides,"The full potential all electron linearized augmented plane wave plus local
orbitals (FP-LAPW + lo) method, as implemented in the suite of software WIEN2K,
has been used to systematically investigate the structural, electronic, and
magnetic properties of the actinide compounds AnN (An = Ac, Th, Pa, U, Np, Pu,
Am). The theoretical formalism used is the generalized gradient approximation
to density functional theory (GGA-DFT) with the Perdew-Burke-Ernzerhof (PBE)
exchange-correlation functional. Each compound has been studied at six levels
of theory: non-magnetic (NM), non-magnetic with spin-orbit coupling (NM+SOC),
ferromagnetic (FM), ferromagnetic with spin-orbit coupling (FM+SOC),
anti-ferromagnetic (AFM), and anti-ferromagnetic with spin-orbit coupling
(AFM+SOC). The structural parameters, bulk moduli, densities of states, and
charge distributions have been computed and compared to available experimental
data and other theoretical calculations published in the literature. The total
energy calculations indicate that the lowest energy structures of AcN, ThN, and
PaN are degenerate at the NM+SOC, FM+SOC, and AFM+SOC levels of theory with
vanishing total magnetic moments in the FM+SOC and AFM+SOC cases, making the
ground states essentially non-magnetic with spin-orbit interaction. The ground
states of UN, NpN, PuN, and AmN are found to be FM+SOC at the level of theory
used in the present computations. The nature of the interactions between the
actinide metals and nitrogen atom, and the implications on 5f electron
delocalization and localization are discussed in detail.",0910.3337v1
2009-10-19,Hybrid functional study of proper and improper multiferroics,"We present a detailed study of the structural, electronic, magnetic and
ferroelectric properties of prototypical \textit{proper} and \textit{improper}
multiferroic (MF) systems such as BiFeO$_{3}$ and orthorhombic HoMnO$_{3}$,
respectively, within density functional theory (DFT) and using the
Heyd-Scuseria-Ernzerhof hybrid functional (HSE). By comparing our results with
available experimental data as well as with state-of-the-art GW calculations,
we show that the HSE formalism is able to account well for the relevant
properties of these compounds and it emerges as an accurate tool for predictive
first-principles investigations on multiferroic systems. We show that effects
beyond local and semilocal DFT approaches (as provided by HSE) are necessary
for a realistic description of MFs. For the electric polarization, a decrease
is found for MFs with magnetically-induced ferroelectricity, such as HoMnO$_3$,
where the calculated polarization changes from $\sim$ 6 $\mu C/cm^2$ using
Perdew-Burke-Ernzerhof (PBE) to $\sim$ 2 $\mu C/cm^2$ using HSE. However, for
\textit{proper} MFs, such as BiFeO$_{3}$, the polarization slightly increases
upon introduction of exact exchange. Our findings therefore suggest that a
general trend for the HSE correction to bare density functional cannot be
extracted; rather, a specific investigation has to be carried out on each
compound.",0910.3597v2
2009-12-01,"Electronic structure, magnetic and dielectric properties of the edge-sharing copper-oxide chain compound NaCu$_{2}$O$_{2}$","We report an experimental study of \nco, a Mott insulator containing chains
of edge-sharing CuO$_4$ plaquettes, by polarized x-ray absorption spectroscopy
(XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and
pyroelectric current measurements. The XAS data show that the valence holes
reside exclusively on the Cu$^{2+}$ sites within the copper-oxide spin chains
and populate a $d$-orbital polarized within the CuO$_4$ plaquettes. The RMXS
measurements confirm the presence of incommensurate magnetic order below a
N\'eel temperature of $T_N = 11.5$ K, which was previously inferred from
neutron powder diffraction and nuclear magnetic resonance data. In conjunction
with the magnetic susceptibility and XAS data, they also demonstrate a new
""orbital"" selection rule for RMXS that is of general relevance for magnetic
structure determinations by this technique. Dielectric property measurements
reveal the absence of significant ferroelectric polarization below $T_N$, which
is in striking contrast to corresponding observations on the isostructural
compound \lco. The results are discussed in the context of current theories of
multiferroicity.",0912.0168v1
2009-12-05,Synthesis and Structural details of BiOCu1-xS: Possible new entrant in series of exotic superconductors?,"We report an easy route single step synthesis of BiOCuS with and without Cu
deficiency. The title compound is synthesized via solid state reaction route by
encapsulation in an evacuated (10-3 Torr) quartz tube. Mixed components of the
ingredients in stoichiometric ratio (1/3Bi2O3 +0.34Bi +Cu1-x + S) are
pelletized, sealed in evacuated quartz tube and heat treated for 30 hours at
500 0C. Finally the sample is allowed to cool down to room temperature. The
resultant compound is black is color and could not hold in pellet form, but is
powdered. X-ray diffraction Reitveld analysis is carried out on all three
samples of series BiOCu1-xS with x = 0.0, 0.10 and 0.15. These samples
crystallize in single phase with space group P4/nmm and with cell parameters as
a = 3.868 A and c = 8.557 A for stoichiometric BiOCuS. The volume of the cell
slightly increases with an increase in Cu deficiency. The co-ordinate positions
are determined by fitting the observed XRD patterns of the studied samples.",0912.0991v4
2009-12-05,Synthesis and Physical Properties of FeSe1/2Te1/2 Superconductor,"One of the most important properties of very recently reported FeSe based
superconductors is the robustness of their superconductivity under applied
magnetic field. The synthesis and control of superconductivity in FeSe based
compounds is rather a difficult task. Synthesis and physical property
characterization for optimized superconductivity of FeSe1/2Te1/2 at 13 K is
reported here. The compound crystallized in a tetragonal structure with lattice
parameters a = 3.8008(10) and c = 6.0187 (15) A. Magnetization measurements
indicated bulk superconductivity with lower critical field (Hc1) of around 180
Oe. By applying Ginzburg Landau (GL) theory, the Hc2(0) value is estimated to
be = 1840 kOe for the 90% of resistive transition. A heat capacity measurement
revealed bulk superconductivity by a hump at Tc near 13 K, and an expected
decrease was observed under an applied magnetic field.",0912.0997v3
2010-01-04,Itinerant Nature of Magnetism in Iron Pnictides: A first principles study,"Within the framework of density functional theory we investigate the nature
of magnetism in various families of Fe-based superconductors. (i) We show that
magnetization of stripe-type antiferromagnetic order always becomes stronger
when As is substituted by Sb in LaOFeAs, BaFe$_2$As$_2$ and LiFeAs. By
calculating Pauli susceptibilities, we attribute the magnetization increase
obtained after replacing As by Sb to the enhancement of an instability at
$(\pi,\pi)$. This points to a strong connection between Fermi surface nesting
and magnetism, which supports the theory of the itinerant nature of magnetism
in various families of Fe-based superconductors. (ii) We find that within the
family LaOFe$Pn$ ($Pn$=P, As, Sb, Bi) the absence of an antiferromagnetic phase
in LaOFeP and its presence in LaOFeAs can be attributed to the competition of
instabilities in the Pauli susceptibility at $(\pi,\pi)$ and $(0,0)$, which
further strengthens the close relation between Fermi surface nesting and
experimentally observed magnetization. (iii) Finally, based on our relaxed
structures and Pauli susceptibility results, we predict that LaOFeSb upon
doping or application of pressure should be a candidate for a superconductor
with the highest transition temperature among the hypothetical compounds
LaOFeSb, LaOFeBi, ScOFeP and ScOFeAs while the parent compounds LaOFeSb and
LaOFeBi should show at ambient pressure a stripe-type antiferromagnetic
metallic state.",1001.0536v2
2010-01-20,Considerations on the Mechanisms and Transition Temperatures of Superconductors,"An overview of the momentum and frequency dependence of effective
electron-electron interactions which favor electronic instability to a
superconducting state in the angular-momentum channel $\ell$ and the properties
of the interactions which determine $T_c$ is provided. Both interactions
induced through exchange of phonons as well as purely electronic fluctuations
of spin density, charge density or current density are considered. Special
attention is paid to the role of quantum critical fluctuations including
pairing due to their virtual exchange as well as de-pairing due to inelastic
scattering. In light of the above, empirical data and theory specific to phonon
induced superconductivity, in cold atoms, superfluidity in liquid $He^3$,
superconductivity in some of the heavy fermion compounds, in Cuprates, in
pncitides and the valence skipping compound, is reviewed. The physical basis
for the following observation is provided: The universal ratio of s-wave $T_c$
to Fermi-energy for fermions at the unitarity limit with attractive
interactions is about 0.15, the ratio of the maximum $T_c$ to the typical
phonon frequency in phonon induced s-wave superconductivity is of the same
order; the ratio of p-wave $T_c$ to the renormalized Fermi-energy in liquid
$He^3$, a very strongly correlated Fermi-liquid near its melting pressure, is
only $O(10^{-3})$; in the Cuprates and the heavy-fermions where d-wave
superconductivity occurs in a region governed by a special class of
quantum-critical fluctuations, this ratio rises to $O(10^{-2})$. These
discussions also suggest factors important for obtaining higher $T_c$.",1001.3618v1
2010-01-25,Solution growth of Ce-Pd-In single crystals: characterization of the heavy-fermion superconductor Ce2PdIn8,"Solution growth of single crystals of the recently reported new compound
Ce2PdIn8 was investigated. When growing from a stoichiometry in a range 2:1:20
- 2:1:35, single crystals of CeIn3 covered by a thin (~50 um)
single-crystalline layer of Ce2PdIn8 were mostly obtained. Using palladium
richer compositions the thickness of the Ce2PdIn8 layers were increased, which
allowed mechanical extraction of single-phase slabs of the desired compound
suitable for a thorough study of magnetism and superconductivity. In some
solution growth products also CePd3In6 (LaNi3In6 - type of structure) and
traces of phases with the stoichiometry CePd2In7, Ce1.5Pd1.5In7 (determined
only by EDX) have been identified. Magnetic measurements of the Ce2PdIn8 single
crystals reveal paramagnetic behaviour of the Ce3+ ions with significant
magnetocrystalline anisotropy. Above 70 K the magnetic susceptibility follows
the Curie-Weiss law with considerably different values of the paramagnetic
Curie temperature, for the magnetic field applied along the a- (-90 K) and
c-(-50 K) axis. Below the reported critical temperature for superconductivity
Tc (0.69 K) the electrical resistivity drops to zero. Comparative measurements
of the electrical resistivity, heat capacity and AC susceptibility of several
crystals reveal that the superconducting transition is strongly
sample-dependent.",1001.4403v1
2010-01-25,Samarium Magnetism Studied on SmPd2Al3 Single Crystal,"In this paper, specific features of Sm magnetism in an intermetallic compound
have been studied. For this purpose, a high-quality single crystal of SmPd2Al3
was grown and subjected to detailed measurements of specific heat,
magnetization, ac susceptibility, and electrical resistivity with respect to
temperature and a magnetic field applied along the principal crystallographic
directions. SmPd2Al3 magnetism was found to be strongly anisotropic with the
easy-magnetization direction along the c axis where the main magnetic features
are concentrated. The a-axis response remains weak, paramagneticlike, even in
the magnetically ordered state. Ferromagnetism with TC=12.4 K has been
indicated by all the measured physical properties. At lower temperatures, three
successive order-order phase transitions have been observed on the temperature
dependence of the specific heat as three anomalies: at 3.4, 3.9, and 4.4 K,
respectively. The low-temperature magnetization data can be understood within a
scenario that considers the antiferromagnetic ground state as being gradually
destroyed through a series of four metamagnetic transitions at 0.03, 0.35, 0.5,
and 0.75 T, as detected in the 1.8 K magnetization data. The experimental data
are discussed together with the results of electronic-structure and
crystal-field calculations from first principles, which were performed as an
important part of the study for comprehension and explanation of the observed
behavior of the SmPd2Al3 compound.",1001.4409v1
2010-02-06,Anisotropic phase diagram of the frustrated spin dimer compound Ba3Mn2O8,"Heat capacity and magnetic torque measurements are used to probe the
anisotropic temperature-field phase diagram of the frustrated spin dimer
compound Ba3Mn2O8 in the field range from 0T to 18T. For fields oriented along
the c axis a single magnetically ordered phase is found in this field range,
whereas for fields oriented along the a axis two distinct phases are observed.
The present measurements reveal a surprising non-monotonic evolution of the
phase diagram as the magnetic field is rotated in the [001]-[100] plane. The
angle dependence of the critical field (Hc1) that marks the closing of the spin
gap can be quantitatively accounted for using a minimal spin Hamiltonian
comprising superexchange between nearest and next nearest Mn ions, the Zeeman
energy and single ion anisotropy. This Hamiltonian also predicts a
non-monotonic evolution of the transition between the two ordered states as the
field is rotated in the a-c plane. However, the observed effect is found to be
significantly larger in magnitude, implying that either this minimal spin
Hamiltonian is incomplete or that the magnetically ordered states have a
slightly different structure than previously proposed.",1002.1334v2
2010-03-29,"From (pi, 0) magnetic order to superconductivity with (pi, pi) magnetic resonance in Fe1.02(Te1-xSex)","The iron chalcogenide Fe1+y(Te1-xSex) is structurally the simplest of the
Fe-based superconductors. Although the Fermi surface is similar to iron
pnictides, the parent compound Fe1+yTe exhibits antiferromagnetic order with
in-plane magnetic wave-vector (pi, 0). This contrasts the pnictide parent
compounds where the magnetic order has an in-plane magnetic wave-vector (pi,
pi) that connects hole and electron parts of the Fermi surface. Despite these
differences, both the pnictide and chalcogenide Fe-superconductors exhibit
superconducting spin resonances around (pi, pi), suggesting a common symmetry
for their superconducting order parameter. A central question in this
burgeoning field is therefore how (pi, pi) superconductivity can emerge from a
(pi, 0) magnetic instability. Here, we report that the magnetic soft mode
evolving from the (pi, 0)-type magnetic long-range order is associated with
weak charge carrier localization. Bulk superconductivity occurs only as the
magnetic mode at (pi, pi) becomes dominant upon doping. Our results suggest a
common magnetic origin for superconductivity in iron chalcogenide and pnictide
superconductors.",1003.5647v1
2010-04-05,Magnetic-field-induced spin-crossover transition in [Mn$^{\textrm{III}}$(taa)] studied by X-ray absorption spectroscopy,"The X-ray absorption near-edge structure (XANES) of Mn in a spin-crossover
compound, [Mn$^{\textrm{III}}$(taa)], was studied in pulsed high magnetic
fields up to 37T. By applying magnetic fields to the low-temperature low-spin
(LS) state, significant changes in the spectra were observed, suggesting a
magnetic-field-induced spin-crossover to the high-spin (HS) state. At low
temperatures, the magnetic field dependence of the changes in the spectra
exhibited hysteresis. Furthermore, when the magnetic field was set to zero, a
considerable remanent component was observed. The energy barrier of the HS
$\to$ LS transition was evaluated from the temperature dependence of the decay
time of the remanent signal. The energy barrier of the transition was found to
be 134K, which is notably lower than that for other spin-crossover compounds
reported previously. Since the fraction of the field-induced HS state was at
most 30% and the thermodynamic macroscopic field-induced phase transition was
expected to occur in fields higher than 55T, the observed field-induced
transition at low temperatures down to 17K could be understood as a localized
microscopic transition at the single-molecular level.",1004.0551v1
2010-04-07,Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission,"Peripheral collisions with radioactive heavy-ion beams at relativistic
energies are discussed as an innovative approach for probing the transient
regime experienced by fissile systems evolving towards quasi-equilibrium. A
dedicated experiment using the advanced technical installations of GSI,
Darmstadt, permitted to realize ideal conditions for the investigation of
relaxation effects in the meta-stable well. Combined with a highly sensitive
experimental signature, it provides a measure of the transient effects with
respect to the flux over the fission barrier. Within a two-step reaction
process, 45 proton-rich unstable spherical isotopes produced by
projectile-fragmentation of a stable 238U beam have been used as secondary
projectiles. The fragmentation of the radioactive projectiles on lead results
in nearly spherical compound nuclei which span a wide range in excitation
energy and fissility. The decay of these excited systems by fission is studied
with a dedicated set-up which permits the detection of both fission products in
coincidence and the determination of their atomic numbers with high resolution.
The width of the fission-fragment nuclear charge distribution is shown to be
specifically sensitive to pre-saddle transient effects and is used to establish
a clock for the passage of the saddle point. The comparison of the experimental
results with model calculations points to a fission delay of (3.3+/-0.7).10-21s
for initially spherical compound nuclei, independent of excitation energy and
fissility. This value suggests a nuclear dissipation strength at small
deformation of (4.5+/-0.5).1021s-1. The very specific combination of the
physics and technical equipment exploited in this work sheds light on previous
controversial conclusions.",1004.1094v1
2010-04-28,"Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers","Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were
synthesized. Their temperature- and applied magnetic field-dependent
structural, transport, thermal, and magnetic properties were characterized by
means of x-ray and neutron diffraction, electrical resistivity rho, heat
capacity, magnetization and magnetic susceptibility measurements. These
compounds have a body-centered-tetragonal crystal structure (space group
I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the
CuO2 layers in high superconducting transition temperature Tc cuprate
superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the
FeAs layers in high-Tc pnictides. These two types of layers alternate along the
crystallographic c-axis and are separated by Sr atoms. The site occupancies of
Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron
powder diffraction data. The temperature dependences of rho suggest metallic
character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and
Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie
temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state
structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to
an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each
layer are ferromagnetically aligned, but are antiferromagnetically aligned
between layers.",1004.5038v1
2010-05-03,The Compound Multiple Access Channel with Partially Cooperating Encoders,"The goal of this paper is to provide a rigorous information-theoretic
analysis of subnetworks of interference networks. We prove two coding theorems
for the compound multiple-access channel with an arbitrary number of channel
states. The channel state information at the transmitters is such that each
transmitter has a finite partition of the set of states and knows which element
of the partition the actual state belongs to. The receiver may have arbitrary
channel state information. The first coding theorem is for the case that both
transmitters have a common message and that each has an additional common
message. The second coding theorem is for the case where rate-constrained, but
noiseless transmitter cooperation is possible. This cooperation may be used to
exchange information about channel state information as well as the messages to
be transmitted. The cooperation protocol used here generalizes Willems'
conferencing. We show how this models base station cooperation in modern
wireless cellular networks used for interference coordination and capacity
enhancement. In particular, the coding theorem for the cooperative case shows
how much cooperation is necessary in order to achieve maximal capacity in the
network considered.",1005.0291v3
2010-06-02,"A missing high-spin molecule in the family of cyano-bridged heptanuclear heterometal complexes, [(LCuII)6FeIII(CN)6]3+, and its CoIII and CrIII analogues, accompanied in the crystal by a novel octameric water cluster","Three isostructural cyano-bridged heptanuclear complexes,
[{CuII(saldmen)(H2O)}6{MIII(CN)6}](ClO4)3$\cdotp$8H2O (M = FeIII 2; CoIII, 3;
CrIII 4), have been obtained by reacting the binuclear copper(II) complex,
[Cu2(saldmen)2(mu-H2O)(H2O)2](ClO4)2$\cdotp$2H2O 1, with K3[Co(CN)6],
K4[Fe(CN)6], and, respectively, K3[Cr(CN)6] (Hsaldmen is the Schiff base
resulted from the condensation of salicylaldehyde with
N,N-dimethylethylenediamine). A unique octameric water cluster, with
bicyclo[2,2,2]octane-like structure, is sandwiched between the heptanuclear
cations in 2, 3 and 4. The cryomagnetic investigations of compounds 2 and 4
reveal ferromagnetic couplings of the central FeIII or CrIII ions with the CuII
ions (JCuFe = +0.87 cm-1, JCuCr = +30.4 cm-1). The intramolecular Cu-Cu
exchange interaction in 3, across the diamagnetic cobalt(III) ion, is -0.3
cm-1. The solid-state1H-NMR spectra of compounds 2 and 3 have been
investigated.",1006.0389v2
2010-06-18,"Polarons, free charge localisation and effective dielectric permittivity in oxides","This review will deal with several types of free charge localisation in
oxides and their consequences on the effective dielectric spectra of such
materials. The first one is the polaronic localisation at the unit cell scale
on residual impurities in ferroelectric networks. The second one is the
collective localisation of free charge at macroscopic interfaces like surfaces,
electrodes and grain boundaries in ceramics. Polarons have been observed in
many oxide perovskites mostly when cations having several stable electronic
configurations are present. In manganites, the density of such polarons is so
high as to drive a net lattice of interacting polarons. On the other hand, in
ferroelectric materials like BaTiO3 and LiNbO3, the density of polarons is
usually very small but they can influence strongly the macroscopic
conductivity. The contribution of such polarons to the dielectric spectra of
ferroelectric materials is described. Even residual impurities as for example
Iron can induce well defined anomalies at very low temperatures. This is mostly
resulting from the interaction between localised polarons and the highly
polarisable ferroelectric network in which they are embedded. The case of such
residual polarons in SrTiO3 will be described in more details, emphasizing the
quantum polaron state at liquid helium temperatures. Recently, several
non-ferroelectric oxides have been shown to display giant effective dielectric
permittivity. It is first shown that the frequency/temperature behaviour of
such parameters is very similar in very different compounds (donor doped
BaTiO3, CaCu3Ti4O12, LuFe2O4,Li doped NiO,...). This similarity calls for a
common origin of the giant dielectric permittivity in these compounds. A space
charge localisation at macroscopic interfaces can be the key for such extremely
high dielectric permittivity.",1006.3719v1
2010-06-19,Observation of Single Dirac Cone Topological Surface State in Compounds TlBiTe2 and TlBiSe2 from a New Topological Insulator Family,"Angle resolved photoemission spectroscopy (ARPES) studies were performed on
two compounds (TlBiTe$_2$ and TlBiSe$_2$) from a recently proposed three
dimensional topological insulator family in Thallium-based III-V-VI$_2$ ternary
chalcogenides. For both materials, we show that the electronic band structures
are in broad agreement with the $ab$ $initio$ calculations; by surveying over
the entire surface Brillouin zone (BZ), we demonstrate that there is a single
Dirac cone reside at the center of BZ, indicating its topological
non-triviality. For TlBiSe$_2$, the observed Dirac point resides at the top of
the bulk valance band, making it a large gap ($\geq$200$meV$) topological
insulator; while for TlBiTe$_2$, we found there exist a negative indirect gap
between the bulk conduction band at $M$ point and the bulk valance band near
$\Gamma$, making it a semi-metal at proper doping. Interestingly, the unique
band structures of TlBiTe$_2$ we observed further suggest TlBiTe$_2$ may be a
candidate for topological superconductors.",1006.3843v1
2010-06-29,Quantum computing by optical control of electron spins,"We review the progress and main challenges in implementing large-scale
quantum computing by optical control of electron spins in quantum dots (QDs).
Relevant systems include self-assembled QDs of III-V or II-VI compound
semiconductors (such as InGaAs and CdSe), monolayer fluctuation QDs in compound
semiconductor quantum wells, and impurity centers in solids such as P-donors in
silicon and nitrogen-vacancy centers in diamond. The decoherence of the
electron spin qubits is discussed and various schemes for countering the
decoherence problem are reviewed. We put forward designs of local nodes
consisting of a few qubits which can be individually addressed and controlled.
Remotely separated local nodes are connected by photonic structures
(microcavities and waveguides) to form a large-scale distributed quantum system
or a quantum network. The operation of the quantum network consists of optical
control of a single electron spin, coupling of two spins in a local nodes,
optically controlled quantum interfacing between stationary spin qubits in QDs
and flying photon qubits in waveguides, rapid initialization of spin qubits,
and qubit-specific single-shot non-demolition quantum measurement. The rapid
qubit initialization may be realized by selectively enhancing certain entropy
dumping channels via phonon or photon baths. The single-shot quantum
measurement may be in-situ implemented through the integrated photonic network.
The relevance of quantum non-demolition measurement to large-scale quantum
computation is discussed. To illustrate the feasibility and demand, the
resources are estimated for the benchmark problem of factorizing 15 with Shor's
algorithm.",1006.5544v1
2010-06-30,Recognition of Non-Compound Handwritten Devnagari Characters using a Combination of MLP and Minimum Edit Distance,"This paper deals with a new method for recognition of offline Handwritten
non-compound Devnagari Characters in two stages. It uses two well known and
established pattern recognition techniques: one using neural networks and the
other one using minimum edit distance. Each of these techniques is applied on
different sets of characters for recognition. In the first stage, two sets of
features are computed and two classifiers are applied to get higher recognition
accuracy. Two MLP's are used separately to recognize the characters. For one of
the MLP's the characters are represented with their shadow features and for the
other chain code histogram feature is used. The decision of both MLP's is
combined using weighted majority scheme. Top three results produced by combined
MLP's in the first stage are used to calculate the relative difference values.
In the second stage, based on these relative differences character set is
divided into two. First set consists of the characters with distinct shapes and
second set consists of confused characters, which appear very similar in
shapes. Characters of distinct shapes of first set are classified using MLP.
Confused characters in second set are classified using minimum edit distance
method. Method of minimum edit distance makes use of corner detected in a
character image using modified Harris corner detection technique. Experiment on
this method is carried out on a database of 7154 samples. The overall
recognition is found to be 90.74%.",1006.5908v1
2010-07-01,Antiferromagnetic I-Mn-V semiconductors,"After decades of research, the low Curie temperature of ferromagnetic
semiconductors remains the key problem in the development of magnetic
semiconductor spintronic technologies. Removing this roadblock might require a
change of the field's basic materials paradigm by looking beyond ferromagnets.
Recent studies of relativistic magnetic and magnetotransport anisotropy
effects, which in principle are equally well present in materials with
ferromagnetically and antiferromagnetically ordered spins, have inspired our
search for antiferromagnetic semiconductors suitable for high-temperature
spintronics. Since these are not found among the magnetic counterparts of
common III-V or II-VI semi- conductors, we turn the attention in this paper to
high N \'eel temperature I-II-V magnetic compounds whose electronic structure
has not been previously identified. Our combined experimental and theoretical
work on LiMnAs provides basic prerequisite for the systematic research of this
class of materials by demonstrating the feasibility to grow single crystals of
group-I alkali metal compounds by molecular beam epitaxy, by demonstrating the
semiconducting band structure of the I-Mn-V's, and by analyzing their
spin-orbit coupling characteristics favorable for spintronics.",1007.0177v1
2010-07-09,"Electronic Structure of CeFeAsO1-xFx (x=0, 0.11/x=0.12) compounds","We report an extensive study on the intrinsic bulk electronic structure of
the high-temperature superconductor CeFeAsO0.89F0.11 and its parent compound
CeFeAsO by soft and hard x-ray photoemission, x-ray absorption and soft-x-ray
emission spectroscopies. The complementary surface/bulk probing depth, and the
elemental and chemical sensitivity of these techniques allows resolving the
intrinsic electronic structure of each element and correlating it with the
local structure, which has been probed by extended-x-ray absorption fine
structure spectroscopy. The measurements indicate a predominant 4f1 (i.e. Ce3+)
initial state configuration for Cerium and an effective valence-band-to-4f
charge-transfer screening of the core hole. The spectra also reveal the
presence of a small Ce f0 initial state configuration, which we assign to the
occurrence of an intermediate valence state. The data reveal a reasonably good
agreement with the partial density of states as obtained in standard density
functional calculations over a large energy range. Implications for the
electronic structure of these materials are discussed.",1007.1594v1
2010-07-10,Magnetic Lattice Dynamics of the Oxygen-Free FeAs Pnictides: How Sensitive are Phonons to Magnetic Ordering?,"To shed light on the role of magnetism on the superconducting mechanism of
the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering
on phonon dynamics in the low-temperature orthorhombic parent compounds, which
present a spin-density wave. The study covers both the 122 (AFe2As2; A=Ca, Sr,
Ba) and 1111 (AFeAsF; A=Ca, Sr) phases. We extend our recent work on the Ca
(122 and 1111) and Ba (122) cases by treating computationally and
experimentally the 122 and 1111 Sr compounds. The effect of magnetic ordering
is investigated through detailed non-magnetic and magnetic lattice dynamical
calculations. The comparison of the experimental and calculated phonon spectra
shows that the magnetic interactions/ordering have to be included in order to
reproduce well the measured density of states. This highlights a
spin-correlated phonon behavior which is more pronounced than the apparently
weak electron-phonon coupling estimated in these materials. Furthermore, there
is no noticeable difference between phonon spectra of the 122 Ba and Sr,
whereas there are substantial differences when comparing these to CaFe2As2
originating from different aspects of structure and bonding.",1007.1711v1
2010-08-21,Crystal Structure Prediction via Particle Swarm Optimization,"We have developed a powerful method for crystal structure prediction from
""scratch"" through particle swarm optimization (PSO) algorithm within the
evolutionary scheme. PSO technique is dramatically different with the genetic
algorithm and has apparently avoided the use of evolution operators (e.g.,
crossover and mutation). The approach is based on a highly efficient global
minimization of free energy surfaces merging total-energy calculations via PSO
technique and requires only chemical compositions for a given compound to
predict stable or metastable structures at given external conditions (e.g.,
pressure). A particularly devised geometrical structure factor method which
allows the elimination of similar structures during structure evolution was
implemented to enhance the structure search efficiency. The application of
designed variable unit cell size technique has greatly reduced the
computational cost. Moreover, the symmetry constraint imposed in the structure
generation enables the realization of diverse structures, leads to
significantly reduced search space and optimization variables, and thus fastens
the global structural convergence. The PSO algorithm has been successfully
applied to the prediction of many known systems (e.g., elemental, binary and
ternary compounds) with various chemical bonding environments (e.g., metallic,
ionic, and covalent bonding). The remarkable success rate demonstrates the
reliability of this methodology and illustrates the great promise of PSO as a
major technique on crystal structure determination.",1008.3601v1
2010-08-29,Tunneling into clean Heavy Fermion Compounds: Origin of the Fano Lineshape,"Recently observed tunneling spectra on clean heavy fermion compounds show a
lattice periodic Fano lineshape similar to what is observed in the case of
tunneling to a Kondo ion adsorbed at the surface. We show that the translation
symmetry of a clean surface in the case of \emph{weakly correlated} metals
leads to a tunneling spectrum given by the superposition of the local weighted
density of states of all energy bands involved, which does not have a Fano
lineshape. In particular the spectrum will show any hybridization gap present
in the band structure. By contrast, in a \emph{strongly correlated} heavy
fermion metal the heavy quasiparticle states will be broadened by interaction
effects. The broadening grows as one moves away from the Fermi surface, up to a
value of the order of $T_K$, the Kondo scale. We show that the hybridization
gap is completely filled in this way, and an ideal Fano lineshape of width
$T_K$ results, similar to the impurity case. We also discuss the possible
influence of the tunneling tip on the surface, in (i) leading to additional
broadening of the Fano line, and (ii) enhancing the hybridization locally,
hence adding to the impurity type behavior. The latter effects depend on the
tip-surface distance.",1008.4923v1
2010-09-16,Magnetic structure and orbital ordering in KCrF3 perovskite,"KCrF3 represents another prototypical orbital-ordered perovskite, where Cr2+
possesses the same electronic configuration of 3d4 as that of strongly
Jahn-Teller distorted Mn3+ in many CMR manganites. The crystal and magnetic
structures of KCrF3 compound are investigated by using polarized and
unpolarized neutron powder diffraction methods. The results show that the KCrF3
compound crystallizes in tetragonal structure at room temperature and undergoes
a monoclinic distortion with the decrease in temperature. The distortion of the
crystal structure indicates the presence of cooperative Jahn-Teller distortion
which is driven by orbital ordering. With decreasing temperature, four magnetic
phase transitions are observed at 79.5, 45.8, 9.5, and 3.2 K, which suggests a
rich magnetic phase diagram. Below T_N = 79.5 K, the Cr2+ moment orders in an
incommensurate antiferromagnetic arrangement, which can be defined by the
magnetic propagation vector (1/2$\pm\,$$\delta\,$, 1/2$\pm\,$$\delta\,$, 0).
The incommensurate-commensurate magnetic transition occurs at 45.8 K and the
magnetic propagation vector locks into (1/2, 1/2, 0) with the Cr moment of
3.34(5) $\mu_B \,$ aligned ferromagnetically in (220) plane, but
antiferromagnetically along [110] direction. Below 9.5 K, the canted
antiferromagnetic ordering and weak ferromagnetism arise from the collinear
antiferromagnetic structure, while the Dzyaloshinskii-Moriya interaction and
tilted character of the single-ion anisotropy might give rise to the complex
magnetic behaviors below 9.5 K.",1009.3239v1
2010-09-20,Pressure induced Superconductivity in Topological Compound Bi2Te3,"Bi2Te3 compound has been theoretically predicted (1) to be a topological
insulator, and its topologically non-trivial surface state with a single Dirac
cone has been observed in photoemission experiments (2). Here we report that
superconductivity (Tc^~3K) can be induced in Bi2Te3 as-grown single crystal
(with hole-carriers) via pressure. The first-principles calculations show that
the electronic structure under pressure remains to be topologically nontrivial,
and the Dirac-type surface states can be well distinguished from bulk states at
corresponding Fermi level. The proximity effect between superconducting bulk
states and Dirac-type surface state could generate Majorana fermions on the
surface. We also discuss the possibility that the bulk state could be a
topological superconductor.",1009.3691v2
2010-10-07,The route to high temperature superconductivity in transition metal oxides,"The discovery of high temperature superconductivity in cuprates was possible
only through an intimate knowledge of perovskite oxides which have been
synthesized and characterized for decades at the IBM in the Z\""urich
laboratoty. Especially SrTiO3 and LaAlO3 have been in the focus at IBM as was
presented in Volume 1 of a series [1]. Probably for the first time detailed
microscopic investigations of the local properties of these compounds have been
obtained by studying by means of EPR the surroundings of transition metal
impurities in these materials. These experiments enabled the identification of
the order parameter of the structural instability observed in these oxides.
However, the idea to search for superconductivity came later motivated by
theoretical considerations that metallic hydrogen could become superconducting
at high temperatures. Since SrTiO3 is an insulator it was thought that the
implantation of hydrogen would render it metallic and eventually also
superconducting. This approach failed since the carrier density remained always
too small. In sequence it was then tried to achieve a metallic state in oxide
perovskites by varying their composition which was in so far promising as
reduced SrTiO3 exhibits superconductivity at 0.3K [2]. Furthermore it was
subsequently shown [3] that Tc can be enhanced to 1.2K by doping SrTiO3 with
Nb. In spite of the fact that Tc was far below values achieved in A15
compounds, a remarkable observation was connected with the Nb doped perovskite,
namely for the first time long before predicted two-gap superconductivity was
realized here.",1010.1377v1
2010-10-11,Physiological modeling of isoprene dynamics in exhaled breath,"Human breath contains a myriad of endogenous volatile organic compounds
(VOCs) which are reflective of ongoing metabolic or physiological processes.
While research into the diagnostic potential and general medical relevance of
these trace gases is conducted on a considerable scale, little focus has been
given so far to a sound analysis of the quantitative relationships between
breath levels and the underlying systemic concentrations. This paper is devoted
to a thorough modeling study of the end-tidal breath dynamics associated with
isoprene, which serves as a paradigmatic example for the class of low-soluble,
blood-borne VOCs.
  Real-time measurements of exhaled breath under an ergometer challenge reveal
characteristic changes of isoprene output in response to variations in
ventilation and perfusion. Here, a valid compartmental description of these
profiles is developed. By comparison with experimental data it is inferred that
the major part of breath isoprene variability during exercise conditions can be
attributed to an increased fractional perfusion of potential storage and
production sites, leading to higher levels of mixed venous blood concentrations
at the onset of physical activity. In this context, various lines of supportive
evidence for an extrahepatic tissue source of isoprene are presented.
  Our model is a first step towards new guidelines for the breath gas analysis
of isoprene and is expected to aid further investigations regarding the
exhalation, storage, transport and biotransformation processes associated with
this important compound.",1010.2145v1
2010-10-24,Jahn-Teller distortions and the magnetic order in the perovskite manganites,"We introduce an effective model for $e_g$ electrons to describe
three-dimensional perovskite (La$_{1-x}$Sr$_{x}$MnO$_3$ and
La$_{1-x}$Ca$_{x}$MnO$_3$) manganites and study the magnetic and orbital order
on $4\times 4\times 4$ cluster using correlated wave functions. The model
includes the kinetic energy, and on-site Coulomb interactions for $e_g$
electrons, antiferromagnetic superexchange interaction between $S=3/2$ core
spins, and the coupling between $e_g$ electrons and Jahn-Teller modes. The
model reproduces the experimentally observed magnetic order: ($i$) $A$-type
antiferromagnetic phase in the undoped insulator LaMnO$_3$, with alternating
$e_g$ orbitals and with small Jahn-Teller distortions, changing to a conducting
phase at 32 GPa pressure, and ($ii$) ferromagnetic order in one-eight doped
La$_{7/8}$Sr$_{1/8}$MnO$_3$ and in quarter doped La$_{3/4}$Sr$_{1/4}$MnO$_3$
compounds. For half-doped La$_{1/2}$Ca$_{1/2}$MnO$_3$ one finds a competition
between a ferromagnetic conductor and the CE insulating phase; the latter is
stabilized by the Jahn-Teller coupling being twice larger than for the
strontium-doped compound. Altogether, there is a subtle balance between all
Hamiltonian parameters and the phase diagram is quite sensitive to the precise
values they take.",1010.4982v1
2010-11-01,Trends in Heavy Fermion Matter,"A brief review on major advances in heavy fermion physics is presented
including the Ce metal phase diagram, the huge effective mass detected in
CeAl3, and the successive discoveries of unconventional superconductivity in
CeCu2Si2 and three U based compounds, UBe13, UPt3 and URu2Si2. In order to
track the origin of the huge effective mass, the case of intermediate valence
compounds is discussed with emphasis of the differences between Yb and Ce
materials. The formation of the effective mass is analyzed by two regular- and
singular-part contributions. Examples are given for both, antiferromagnetic
(CeRu2Si2 series) and ferromagnetic tricriticalities (UGe2). Pressure and
magnetic-field studies on the ferromagnetic superconductor URhGe illustrate the
role of the singular effective mass enhancement on the superconducting pairing.
The discovery of the Ce-115 material gives the opportunity to study deeply the
interplay of antiferromagnetism and superconductivity. This is clearly
demonstrated by field re-entrance AF inside the SC phase just below the
superconducting upper critical field (Hc2) for CeCoIn5 or on both side of Hc2
within a restricted pressure window for CeRhIn5. The present status of the
search for the hidden-order parameter of URu2Si2 is given and we emphasize that
it may correspond to a lattice unit-cell doubling which leads to a drastic
change in the band structure and spin dynamic, with the possibility of
competition between multipolar ordering and antiferromagnetism.",1011.0374v1
2010-11-30,Structural and magnetic properties of the ordered perovskite Pb2CoTeO6,"The complex perovskite Pb2CoTeO6 (PCTO) has been prepared as polycrystalline
powders by solid state reaction route, and the crystal structure and magnetic
properties have been investigated using a combination of X-ray and neutron
powder diffraction, electron microscopy, dielectric, calorimetric and magnetic
measurements. It was shown that at room temperature this compound adopts a
trigonal perovskite structure, space group R-3 (a= 5.6782(1){\AA}, c=
13.8552(3){\AA}). The compound undergoes a number of temperature-induced phase
transitions and adopts four different structures in the temperature range 5-500
K: monoclinic in P21/n(5<T<125K, tilt system (a+b-b-)), monoclinic in I2/m
(125<T<210 K, tilt system (a0b-b-)), rhombohedral in R-3 (210<T<370K, tilt
system (a-a-a-)), and finally cubic in Fm-3m (above 370K without any tilting).
These structural phase transitions are coupled to a change in the dielectric
constant and the heat capacity around 210 and 370K. A long-range
antiferromagnetically ordered state has been identified from neutron powder
diffraction and magnetic studies at different temperatures. Magnetic
diffraction peaks were registered below the transition at about 16 K and a
possible model for the magnetic structure is proposed. Possible coexistence of
long-range ordering of electrical dipoles and magnetic moments at low
temperatures making PCTO a multiferroic candidate is discussed and compared
with those of other Co-based quaternary oxides adopting the perovskite
structure.",1011.6638v1
2010-12-01,First-principles DFT+\emph{U} study of structural and electronic properties of PbCrO$_{3}$,"We have performed a systematic first-principles investigation to calculate
the structural, electronic, and magnetic properties of PbCrO$_{3}$, CrPbO$_{3}$
as well as their equiproportional combination. The local density approximation
(LDA)$+U$ and the generalized gradient approximation$+U$ theoretical formalisms
have been used to account for the strong on-site Coulomb repulsion among the
localized Cr 3d electrons. By choosing the Hubbard \emph{U} parameter around 4
eV, ferromagnetic, and/or antiferromagnetic ground states can be achieved and
our calculated lattice constants, bulk moduli, and equation of states are in
good agreement with recent experiments [W. Xiao \emph{et al.}, PNAS
\textbf{107}, 14026 (2010)]. The bonding nature of B$-$O bonds in these
ABO$_{3}$ compounds exhibit evident covalent character and our electron
transferring study indicates that the ionicity shows decreasing trend with
increasing fraction of CrO$_{6/2}$ octahedron within the
PbCrO$_{3}$-CrPbO$_{3}$ random compounds. The lengthes of B$-$O bonds determine
their lattice parameters, thus, clearly indicates that the abnormally large
volume and compressibility is due to the contain of CrPbO$_{3}$ in the
experimental sample and the transition of PbO$_{6/2}$ octahedron to CrO$_{6/2}$
upon compression.",1012.0143v2
2010-12-23,"Fe-based high temperature superconductivity with Tc=31K bordering an insulating antiferromagnet in (Tl,K)FexSe2 Crystals","Up to now, there have been two material families, the cuprates and the
iron-based compounds with high-temperature superconductivity (HTSC). An
essential open question is whether the two classes of materials share the same
essential physics. In both, superconductivity (SC) emerges when an
antiferromagnetical (AFM) ordered phase is suppressed. However, in cuprates,
the repulsive interaction among the electrons is so strong that the parent
compounds are ""Mott insulators."" By contrast, all iron-based parents are
metallic. One perspective is that the iron-based parents are weakly correlated
and that the AFM arises from a strong ""nesting"" of the Fermi surfaces. An
alternative view is that the electronic correlations in the parents are still
sufficiently strong to place the system close to the boundary between
itinerancy and electronic localization. A key strategy to differentiate theses
views is to explore whether the iron-based system can be tuned into a Mott
insulator. Here we identify an insulating AFM in (Tl,K)FexSe2 by introducing
Fe-vacancies and creating superconductivity in the Fe-planar. With the
increasing Fe-content, the AFM order is reduced. When the magnetism is
eliminated, a superconducting phase with Tc as high as 31K (and a Tc onset as
high as 40K) is induced. Our findings indicate that the correlation effect
plays a crucial role in the iron-based superconductors. (Tl,K)FexSe2,
therefore, represents the first Fe-based high temperature superconductor near
an insulating AFM.",1012.5236v1
2010-12-31,In-plane anisotropy of electrical resistivity in the strain-detwinned SrFe2As2,"Intrinsic, in-plane anisotropy of electrical resistivity was studied on
mechanically detwinned single crystals of SrFe$_2$As$_2$ above and below the
temperature of the coupled structural/magnetic transition, $T_{\textrm{TO}}$.
Resistivity is smaller for electrical current flow along the orthorhombic $a_o$
direction (direction of antiferromagnetically alternating magnetic moments) and
is larger for transport along the $b_o$ direction (direction of ferromagnetic
chains), which is similar to CaFe$_2$As$_2$ and BaFe$_2$As$_2$ compounds. A
strongly first order structural transition in SrFe$_2$As$_2$ was confirmed by
high-energy x-ray measurements, with the transition temperature, and character
unaffected by moderate strain. For small strain levels, which are just
sufficient to detwin the sample, we find a negligible effect on the resistivity
above $T_{\textrm{TO}}$. With the increase of strain, the resistivity
anisotropy starts to develop above $T_{\textrm{TO}}$, clearly showing the
relation of anisotropy to an anomalously strong response to strain. Our study
suggests that electronic nematicity cannot be observed in the FeAs based
compounds in which the structural transition is strongly first order.",1101.0274v1
2011-01-20,"Mean-field Study of Charge, Spin, and Orbital Orderings in Triangular-lattice Compounds ANiO2 (A=Na, Li, Ag)","We present our theoretical results on the ground states in layered
triangular-lattice compounds ANiO2 (A=Na, Li, Ag). To describe the interplay
between charge, spin, orbital, and lattice degrees of freedom in these
materials, we study a doubly-degenerate Hubbard model with electron-phonon
couplings by the Hartree-Fock approximation combined with the adiabatic
approximation. In a weakly-correlated region, we find a metallic state
accompanied by \sqroot3x\sqroot3 charge ordering. On the other hand, we obtain
an insulating phase with spin-ferro and orbital-ferro ordering in a wide range
from intermediate to strong correlation. These phases share many
characteristics with the low-temperature states of AgNiO2 and NaNiO2,
respectively. The charge-ordered metallic phase is stabilized by a compromise
between Coulomb repulsions and effective attractive interactions originating
from the breathing-type electronphonon coupling as well as the Hund's-rule
coupling. The spin-orbital-ordered insulating phase is stabilized by the
cooperative effect of electron correlations and the Jahn-Teller coupling, while
the Hund's-rule coupling also plays a role in the competition with other
orbital-ordered phases. The results suggest a unified way of understanding a
variety of low-temperature phases in ANiO2. We also discuss a keen competition
among different spin-orbital-ordered phases in relation to a puzzling behavior
observed in LiNiO2.",1101.3828v1
2011-01-20,"Equilibrium and pre-equilibrium processes in the 55Mn(6Li,xp) and 57Fe(a,xp) reactions","Spectra of outgoing neutrons and protons from the 6Li+55Mn reaction and
protons from the a+57Fe reaction have been measured with beams of 15 MeV 6Li
ions and 30 MeV alpha-particles. These reactions proceed through the same 61Ni
nucleus at the same excitation energy, thus allowing the difference in reaction
mechanism to be studied. It is shown that spectra from the first reaction
measured at backward angles are due to emission from a traditional compound
nucleus reaction, in which the intermediate nucleus has reached statistical
equilibrium; the spectra from the second reaction contain a significant
fraction of pre-equilibrium emission at all angles. Level density pa- rameters
of the residual nucleus 60Co have been obtained from the first reaction. Both
emission spectra and angular distributions have been measured for the second
reaction. It was found that the pre-equilibrium component exhibits a
forward-peaked angular distribution, as expected, but with a steeper slope than
predicted and with an unusual slight rise at angles above 120\deg. The
backward- angle rise is explained qualitatively by the dominance of the
multi-step compound mechanism at backward angles.",1101.3994v1
2011-02-11,Effects of $^3$He Impurity on Solid $^4$He Studied by Compound Torsional Oscillator,"Frequency shifts and dissipations of a compound torsional oscillator induced
by solid $^4$He samples containing $^3$He impurity concentrations ($x_3$ = 0.3,
3, 6, 12 and 25 in units of 10$^{-6}$) have been measured at two resonant mode
frequencies ($f_1$ = 493 and $f_2$ = 1164 Hz) at temperatures ($T$) between
0.02 and 1.1 K. The fractional frequency shifts of the $f_1$ mode were much
smaller than those of the $f_2$ mode. The observed frequency shifts continued
to decrease as $T$ was increased above 0.3 K, and the conventional
non-classical rotation inertia fraction was not well defined in all samples
with $x_3 \geq$ 3 ppm. Temperatures where peaks in dissipation of the $f_2$
mode occurred were higher than those of the $f_1$ mode in all samples. The peak
dissipation magnitudes of the $f_1$ mode was greater than those of the $f_2$
mode in all samples. The activation energy and the characteristic time
($\tau_0$) were extracted for each sample from an Arrhenius plot between mode
frequencies and inverse peak temperatures. The average activation energy among
all samples was 430 mK, and $\tau_0$ ranged from 2$\times 10^{-7}$ s to
5$\times 10^{-5}$ s in samples with $x_3$ = 0.3 to 25 ppm. The characteristic
time increased in proportion to $x_3^{2/3}$. Observed temperature dependence of
dissipation were consistent with those expected from a simple Debye relaxation
model \emph{if} the dissipation peak magnitude was separately adjusted for each
mode. Observed frequency shifts were greater than those expected from the
model. The discrepancies between the observed and the model frequency shifts
increased at the higher frequency mode.",1102.2371v1
2011-03-17,Planar CuO_2 hole density estimation in multilayered high-T_c cuprates,"We report that planar CuO_2 hole densities in high-T_c cuprates are
consistently determined by the Cu-NMR Knight shift. In single- and bi-layered
cuprates, it is demonstrated that the spin part of the Knight shift K_s(300 K)
at room temperature monotonically increases with the hole density $p$ from
underdoped to overdoped regions, suggesting that the relationship of K_s(300 K)
vs. p is a reliable measure to determine p. The validity of this K_s(300 K)-p
relationship is confirmed by the investigation of the p-dependencies of
hyperfine magnetic fields and of spin susceptibility for single- and bi-layered
cuprates with tetragonal symmetry. Moreover, the analyses are compared with the
NMR data on three-layered Ba_2Ca_2Cu_3O_6(F,O)_2, HgBa_2Ca_2Cu_3O_{8+delta},
and five-layered HgBa_2Ca_4Cu_5O_{12+delta}, which suggests the general
applicability of the K_s(300 K)-p relationship to multilayered compounds with
more than three CuO_2 planes. We remark that the measurement of K_s(300 K)
enables us to separately estimate p for each CuO_2 plane in multilayered
compounds, where doped hole carriers are inequivalent between outer CuO_2
planes and inner CuO_2 planes.",1103.3407v1
2011-03-17,Direct observation of spin-polarized surface states in the parent compound of topological insulator Bi-Sb using spin-resolved-ARPES in a 3D Mott-polarimetry spin mode,"We report high-resolution spin-resolved photoemission spectroscopy
(Spin-ARPES) measurements on the parent compound Sb of the first discovered 3D
topological insulator Bi{1-x}Sb{x} [D. Hsieh et al., Nature 452, 970 (2008)
Submitted 2007]. By modulating the incident photon energy, we are able to map
both the bulk and (111) surface band structure, from which we directly
demonstrate that the surface bands are spin polarized by the spin-orbit
interaction and connect the bulk valence and conduction bands in a
topologically non-trivial way. A unique asymmetric Dirac surface state gives
rise to a $k$-splitting of its spin polarized electronic channels. These
results complement our previously published works on this materials class and
re-confirm our discovery of first bulk (3D) topological insulator - topological
order in bulk solids. [Invited article for NJP-IOP Focus issue on ""Topological
Insulators""]",1103.3413v1
2011-03-23,Hall effect in the vicinity of quantum critical point in Tm1-xYbxB12,"The angular, temperature and magnetic field dependences of Hall resistance
roH for the rare-earth dodecaboride solid solutions Tm1-xYbxB12 have been
studied in a wide vicinity of the quantum critical point (QCP) xC~0.3. The
measurements performed in the temperature range 1.9-300 K on high quality
single crystals allowed to find out for the first time in these fcc compounds
both an appearance of the second harmonic contribution in ro2H at QCP and its
enhancement under the Tm to ytterbium substitution and/or with increase of
external magnetic field. When the Yb concentration x increases a negative
maximum of a significant amplitude was shown to appear on the temperature
dependences of Hall coefficient RH(T) for the Tm1-xYbxB12 compounds. Moreover,
a complicated activation type behavior of the Hall coefficient is observed at
intermediate temperatures for x>0.5 with activation energies Eg~200K and
Ea~55-75K in combination with the sign inversion of RH(T) at low temperatures
in the coherent regime. The density of states renormalization effects are
analyzed within the variation of Yb concentration and the features of the
charge transport in various regimes (charge gap formation, intra-gap manybody
resonance and coherent regime) are discussed in detail in Tm1-xYbxB12 solid
solutions.",1103.4517v1
2011-03-23,"On the origin of non-monotonic doping dependence of the in-plane resistivity anisotropy in Ba(Fe$_{1-x}T_x$)$_2$As$_2$, $T$ = Co, Ni and Cu","The in-plane resistivity anisotropy has been measured for detwinned single
crystals of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$.
The data reveal a non-monotonic doping dependence, similar to previous
observations for Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Magnetotransport measurements
of the parent compound reveal a non-linear Hall coefficient and a strong linear
term in the transverse magnetoresistance. Both effects are rapidly suppressed
with chemical substitution over a similar compositional range as the onset of
the large in-plane resistivity anisotropy. It is suggested that the relatively
small in-plane anisotropy of the parent compound in the spin density wave state
is due to the presence of an isotropic, high mobility pocket of reconstructed
Fermi surface. Progressive suppression of the contribution to the conductivity
arising from this isotropic pocket with chemical substitution eventually
reveals the underlying in-plane anisotropy associated with the remaining FS
pockets.",1103.4535v2
2011-03-25,Anisotropic intrinsic anomalous Hall effect in ordered 3dPt alloys,"By performing first principles calculations we investigate the intrinsic
anomalous Hall conductivity (AHC) and its anisotropy in ordered L1o FePt, CoPt
and NiPt ferromagnets, and their intermediate alloys. We demonstrate that the
AHC in this family of compounds depends strongly on the direction of the
magnetization in the crystal. We predict that such pronounced orientational
dependence in combination with the general decreasing trend of the AHC when
going from FePt to NiPt leads to a sign change of the AHC upon rotating the
magnetization direction in the crystal of CoPt alloy. We also suggest that for
a range of concentration x in Co(x)Ni(1-x)Pt alloy it is possible to achieve a
complete quenching of the anomalous Hall current for a certain direction of the
magnetization in the crystal. By analyzing the spin-resolved AHC in 3dPt alloys
we endeavor to relate the overall trend of the AHC in these compounds to the
changes in their densities of d-states around the Fermi energy upon varying the
atomic number. Moreover, we show the generality of the phenomenon of
anisotropic anomalous Hall effect by demonstrating its occurrence within the
three-band tight-binding model.",1103.4941v2
2011-04-22,Multiferroic properties and magnetic structure of Sm1-xYxMnO3,"We have successfully induced multiferroic behavior in the A-type
antiferromagnet SmMnO3 by the substitution of Y at the Sm site. A magnetic
transition develops at 24 K for Sm1-xYxMnO3 (x=0.4,0.5) which is not present in
the parent compound. This transition coincides with the onset of electric
order, with an electric polarization measured along the c axis. It is proposed
that the effect of Y doping is to bring about a subtle distortion of the MnO6
octahedra, causing a magnetic ordering of the Mn3+ moments similar to that
reported for the well studied multiferroic TbMnO3. Following on from our
previous study on polycrystalline samples, we present measurements of the
magnetic and electric properties of single crystal Sm0.6Y0.4MnO3 and
Sm0.5Y0.5MnO3. The data are summarized in a phase diagram for each of the
principal crystallographic axes for the x=0.5 compound. Powder neutron
diffraction experiments on SmMnO3 and Sm0.6Y0.4MnO3 show that the Y
substitution causes a change in the Mn-O-Mn bond angle towards the value found
for TbMnO3. The magnetic structure of Sm0.6Y0.4MnO3 has been shown to consist
of two phases: a sinusoidal ordering of the Mn3+ moments below 50 K and a
cycloidal ordering below 27 K. The cycloidal ordering occurs at the same
temperature as the previously observed ferroelectric polarization, suggesting a
similar multiferroic mechanism to that found in TbMnO3.",1104.4508v2
2011-05-06,"Effect of iron content and potassium substitution in A$_{0.8}$Fe$_{1.6}$Se$_2$ (A = K, Rb, Tl) superconductors: a Raman-scattering investigation","We have performed Raman-scattering measurements on high-quality single
crystals of the superconductors K$_{0.8}$Fe$_{1.6}$Se$_2$ ($T_c$ = 32 K),
Tl$_{0.5}$K$_{0.3}$Fe$_{1.6}$Se$_2$ ($T_c$ = 29 K), and
Tl$_{0.5}$Rb$_{0.3}$Fe$_{1.6}$Se$_2$ ($T_c$ = 31 K), as well as of the
insulating compound KFe$_{1.5}$Se$_2$. To interpret our results, we have made
first-principles calculations for the phonon modes in the ordered iron-vacancy
structure of K$_{0.8}$Fe$_{1.6}$Se$_2$. The modes we observe can be assigned
very well from our symmetry analysis and calculations, allowing us to compare
Raman-active phonons in the AFeSe compounds. We find a clear frequency
difference in most phonon modes between the superconducting and
non-superconducting potassium crystals, indicating the fundamental influence of
iron content. By contrast, substitution of K by Tl or Rb in
A$_{0.8}$Fe$_{1.6}$Se$_2$ causes no substantial frequency shift for any modes
above 60 cm$^{-1}$, demonstrating that the alkali-type metal has little effect
on the microstructure of the FeSe layer. Several additional modes appear below
60 cm$^{-1}$ in Tl- and Rb-substituted samples, which are vibrations of heavier
Tl and Rb ions. Finally, our calculations reveal the presence of ""chiral""
phonon modes, whose origin lies in the chiral nature of the
K$_{0.8}$Fe$_{1.6}$Se$_2$ structure.",1105.1198v2
2011-05-10,Magnetic-crystallographic phase diagram of superconducting parent compound Fe$_{1+x}$Te,"hrough neutron diffraction experiments, including spin-polarized
measurements, we find a collinear incommensurate spin-density wave with
propagation vector $ \mathbf k = $ ($0.4481(4) \, \,0 \, \, \frac1 2$) at base
temperature in the superconducting parent compound Fe$_{1+x}$Te. This critical
concentration of interstitial iron corresponds to $x \approx 12%$ and leads
crystallographic phase separation at base temperature. The spin-density wave is
short-range ordered with a correlation length of 22(3) \AA, and as the ordering
temperature is approached its propagation vector decreases linearly in the
H-direction and becomes long-range ordered. Upon further populating the
interstitial iron site, the spin-density wave gives way to an incommensurate
helical ordering with propagation vector $ \mathbf k =$ ($0.3855(2) \, \,0 \,
\, \frac1 2$) at base temperature. For a sample with $x \approx 9(1) %$, we
also find an incommensurate spin-density wave that competes with the
bicollinear commensurate ordering close to the N\'eel point. The shifting of
spectral weight between competing magnetic orderings observed in several
samples is supporting evidence for the phase separation being electronic in
nature, and hence leads to crystallographic phase separation around the
critical interstitial iron concentration of 12%. With results from both powder
and single crystal samples, we construct a magnetic-crystallographic phase
diagram of Fe$_{1+x}$Te for $ 5% < x <17%$",1105.1937v1
2011-05-20,Orbital-Selective Superconductivity and the Effect of Lattice Distortion in Iron-Based Superconductors,"The superconducting (SC) state of iron-based compounds in both tetragonal and
orthorhombic phases is studied on the basis of an effective Hamiltonian
composed of the kinetic energy including the five Fe 3d-orbitals, the
orthorhombic crystalline electric field (CEF) energy, and the two-orbital
Kugel'-Khomski\u{i}-type superexchange interaction. Our basic assumption is
that the antiferromagnetic (AF) state in the parent compounds can be described
by the $d_{xz}$ and $d_{yz}$ orbitals, and that the electrons in these orbitals
have relatively strong electron correlation in the vicinity of the AF state. In
order to study the physical origin of the structure-sensitive SC transition
temperature, the effect of orthorhombic distortion is taken into account as the
energy-splitting, $\Delta_{\textrm{ortho.}}$, between the $d_{xz}$ and $d_{yz}$
orbitals. We find that the eigenvalue of the linearized gap equation decreases
accompanied with the reduction of the partial density of states for the
$d_{xz}$ and $d_{yz}$ orbitals as $\Delta_{\textrm{ortho.}}$ increases, and
that the dominant pairing symmetry is an unconventional fully gapped
$s_{+-}$-wave pairing. We also find large anisotropy of the SC gap function in
the orthorhombic phase. We propose that the CEF energy plays an important role
in controlling $T_{\textrm{c}}$ and the SC gap function, and that
orbital-selective superconductivity is a key feature in iron-based
superconductors, which causes the structure-sensitive $T_{\textrm{c}}$.",1105.4028v1
2011-06-14,Optimal Dividend Payments for the Piecewise-Deterministic Poisson Risk Model,"This paper considers the optimal dividend payment problem in
piecewise-deterministic compound Poisson risk models. The objective is to
maximize the expected discounted dividend payout up to the time of ruin. We
provide a comparative study in this general framework of both restricted and
unrestricted payment schemes, which were only previously treated separately in
certain special cases of risk models in the literature. In the case of
restricted payment scheme, the value function is shown to be a classical
solution of the corresponding HJB equation, which in turn leads to an optimal
restricted payment policy known as the threshold strategy. In the case of
unrestricted payment scheme, by solving the associated integro-differential
quasi-variational inequality, we obtain the value function as well as an
optimal unrestricted dividend payment scheme known as the barrier strategy.
When claim sizes are exponentially distributed, we provide easily verifiable
conditions under which the threshold and barrier strategies are optimal
restricted and unrestricted dividend payment policies, respectively. The main
results are illustrated with several examples, including a new example
concerning regressive growth rates.",1106.2781v2
2011-06-15,Electronic identification of the actual parental phase of KxFe2-ySe2 superconductor and its intrinsic mesoscopic phase separation,"While the parent compounds of the cuprate high temperature superconductors
(high-Tc's) are Mott insulators, the iron-pnictide high-Tc's are in the
vicinity of a metallic spin density wave (SDW) state, which highlights the
difference between these two families. However, insulating parent compounds
were identified for the newly discovered KxFe2-ySe2. This raises an intriguing
question as to whether the iron-based high-Tc's could be viewed as doped Mott
insulators like the cuprates. Here we report angle-resolved photoemission
spectroscopy (ARPES) evidence of two insulating and one semiconducting phases
of KxFe2-ySe2, and the mesoscopic phase separation between the
superconducting/semiconducting phase and the insulating phases. The insulating
phases are characterized by the depletion of electronic states over a 0.5 eV
window below the chemical potential, giving a compelling evidence for the
presence of Mott-like physics. The charging effects and the absence of band
folding in the superconducting/semiconducting phase further prove that the
static magnetic and vacancy orders are not related to the superconductivity.
Instead, the electronic structure of the superconducting phase is much closer
to the semiconducting phase, indicating the superconductivity is likely
developed by doping the semiconducting phase rather than the insulating phases.",1106.3026v1
2011-07-04,Comparative studies of the scanning tunneling spectra in cuprate and iron-arsenide superconductors,"We report scanning tunneling spectroscopic studies of cuprate and
iron-arsenic superconductors, including YBa_2Cu_3O_{7-\delta} (Y-123, T_c = 93
K), Sr_{0.9}La_{0.1}CuO_2 (La-112, T_c = 43 K), and the ""122"" compounds
Ba(Fe_{1-x}Co_x)_2As_2 (Co-122 with x = 0.06, 0.08, 0.12 for T_c = 14, 24, 20
K). For H > 0, pseudogap (\Delta_{PG}) features are revealed inside the
vortices, with \Delta_{PG} = [(\Delta_{eff})^2+(\Delta_{SC})^2]^{1/2} >
\Delta_{SC} in Y-123 and \Delta_{PG} < \Delta_{SC} in La-112, suggesting that
the physical origin of \Delta_{PG} is a competing order coexisting with
superconductivity. Additionally, Fourier transformation (FT) of the Y-123
spectra exhibits two types of spectral peaks, one type is associated with
energy (\omega)-dependent quasiparticle interference (QPI) wave-vectors and the
other consists of \omega-independent wave-vectors due to competing orders and
(\pi,\pi) magnetic resonances. For the multi-band Co-122 compounds, two-gap
superconductivity is found for all doping levels. Magnetic resonant modes that
follow the temperature dependence of the superconducting gaps are also
identified. These findings, together with the \omega- and x-dependent QPI
spectra, are consistent with a sign-changing s-wave pairing symmetry in the
Co-122 iron arsenides. Our comparative studies suggest that the commonalities
among the cuprate and the ferrous superconductors include the proximity to
competing orders, antiferromagnetic (AFM) spin fluctuations and magnetic
resonances in the superconducting (SC) state, and the unconventional pairing
symmetries with sign-changing order parameters on different parts of the Fermi
surface.",1107.0697v1
2011-08-05,Anisotropic magnetic properties and superzone gap formation in CeGe single crystal,"Single crystals of CeGe and its non-magnetic analogue LaGe have been grown by
Czochralski method. CeGe compound crystallizes in the orthorhombic FeB-type
crystal structure with the space group \textit{Pnma} (#62). The anisotropic
magnetic properties have been investigated on well oriented single crystals by
measuring the magnetic susceptibility, electrical resistivity and heat
capacity. It has been found that CeGe orders antiferromagnetically at 10.5 K.
Both transport and magnetic studies have revealed large anisotropy reflecting
the orthorhombic crystal structure. The magnetization measurement measured at 2
K revealed metamagnetic transitions along the [010] direction at 4.8 and 6.4 T
and along [100] direction at a critical field of 10.7 T, while the
magnetiztaion along [001] direction was increasing linearly without any anomaly
up to a field of 16 T. From the magnetic susceptibility and the magnetization
measurements it has been found that [010] direction is the easy axis of
magnetization. The electrical resistivity along the three crystallographic
directions exhibited an upturn at $T_{\rm N}$ indicating the superzone gap
formation below $T_{\rm N}$ in this compound. We have performed the crystalline
electric field (CEF) analysis on the magnetic susceptibility and the heat
capacity data and found that the ground state is doublet and the splitting
energies from the ground state to the first and second excited doublet states
were estimated to be 39 and 111 K, respectively.",1108.1291v2
2011-08-06,"Interplay among superconductivity, pseudogap, and stripe correlations in different high-Tc cuprates","The effect of Zn substitution in the CuO2 plane on the superconducting
transition temperature, Tc, was studied for the La2-xSrxCu1-yZnyO4 and
YBa2(Cu1-yZny)3O7-d compounds over a wide range of hole concentration, p, and
Zn content (y). Zn induced rate of suppression of Tc, dTc(p)/dy, was found to
be strongly p-dependent and showed a monotonic variation with p, except in the
vicinity of p ~ 0.125, i.e., near the so-called 1/8th anomaly where the
charge/spin stripe correlations are at their strongest in hole doped cuprates.
The magnitude of dTc(p)/dy decreased significantly around this hole
concentration implying that Zn suddenly became less effective in degrading Tc
near the 1/8th anomaly for La2-xSrxCu1-yZnyO4. The same feature, somewhat at a
reduced scale, was also observed for YBa2(Cu1-yZny)3O7-d compounds. This is
counterintuitive since static stripe order itself degrades superconducting
order. We have discussed the possible scenarios that can give rise to such a
non-monotonic dTc(p)/dy near p ~ 0.125. We have also looked at the p-dependent
characteristic pseudogap energy scale, {\epsilon}g(p), which shows a nearly
linear decrease with increasing p without any noticeable feature at p ~ 0.125.
Moreover, there is no significant effect of Zn content on the value of
{\epsilon}g(p). All these observations are indicative of a complex and possibly
competing interplay among the superconducting, pseudogap, and stripe
correlations in the hole doped cuprates.",1108.1446v1
2011-08-08,"Spin-Orbital Locking, Emergent Pseudo-Spin, and Magnetic order in Honeycomb Lattice Iridates","The nature of the effective spin Hamiltonian and magnetic order in the
honeycomb iridates is explored by considering a trigonal crystal field effect
and spin-orbit coupling. Starting from a Hubbard model, an effective spin
Hamiltonian is derived in terms of an emergent pseudo-spin-1/2 moment in the
limit of large trigonal distortions and spin-orbit coupling. The present
pseudo-spins arise from a spin-orbital locking and are different from the jeff
= 1/2 moments that are obtained when the spin-orbit coupling dominates and
trigonal distortions are neglected. The resulting spin Hamiltonian is
anisotropic and frustrated by further neighbour interactions. Mean field theory
suggests a ground state with 4-sublattice zig-zag magnetic order in a parameter
regime that can be relevant to the honeycomb iridate compound Na2IrO3, where
similar magnetic ground state has recently been observed. Various properties of
the phase, the spin-wave spectrum and experimental consequences are discussed.
The present approach contrasts with the recent proposals to understand iridate
compounds starting from the strong spin-orbit coupling limit and neglecting
non-cubic lattice distortions.",1108.1806v3
2011-09-10,"Diffusion in binary and pseudo-binary L12 indides, stannides, gallides and aluminides of rare-earth elements as studied using perturbed angular correlation of 111In/Cd","Diffusional jumps can produce fluctuating electric field gradients at nuclei
of jumping atoms. Using perturbed angular correlation of gamma rays (PAC),
jumps of probe atoms cause nuclear quadrupole relaxation that can be fitted to
obtain the mean jump frequency. An overview is given of the application of this
approach to highly ordered intermetallic compounds having the L12 (Cu3Au)
crystal structure. New results are then presented for jump frequencies of
111In/Cd probe atoms in pseudo-binary L12 compounds of the forms In3(La1-xPrx)
and (In1-xSnx)3La. For the mixed rare-earth system, jump frequencies are found
to scale with composition between jump frequencies of the end-member phases
In3La and In3Pr. However, for the mixed sp-element system, a large decrease in
jump frequency is observed as Sn atoms substitute for In-atoms. This difference
in behavior appears to depend on whether atomic disorder is on the diffusion
sublattice (In-Sn substitution), as opposed to a neighboring sublattice (La-Pr
substitution), whether or not there is a difference in diffusion mechanism
between end-member phases, and/or whether or not there is a valence difference
between the mixing atoms. All three conditions apply for only (In1-xSnx)3La.",1109.2261v1
2011-09-19,Anisotropic optical response of the mixed-valent Mott-Hubbard insulator NaCu2O2,"We report the results of a comprehensive spectroscopic ellipsometry study of
NaCu2O2, a compound composed of chains of edge-sharing Cu2+O4 plaquettes and
planes of Cu1+ ions in a O-Cu1+-O dumbbell configuration, in the spectral range
0.75-6.5 eV at temperatures 7 -300 K. The spectra of the dielectric function
for light polarized parallel to the Cu1+ planes reveal a strong in-plane
anisotropy of the interband excitations. Strong and sharp absorption bands
peaked at 3.45 eV (3.7 eV) dominate the spectra for polarization along
(perpendicular) to the Cu2+O2 chains. They are superimposed on flat and
featureless plateaux above the absorption edges at 2.25 eV (2.5 eV). Based on
density-functional calculations, the anomalous absorption peaks can be assigned
to transitions between bands formed by Cu1+ 3dxz(dyz) and Cu2+ 3dxy orbitals,
strongly hybridized with O pstates. The major contribution to the background
response comes from transitions between Cu1+ 3dz2 and 4px(py) bands. This
assignment accounts for the measured in-plane anisotropy. The dielectric
response along the Cu2+O2 chains develops a weak two-peak structure centered at
2.1 and 2.65 eV upon cooling below 100 K, along with the appearance of spin
correlations along the Cu2+O2 chains. These features bear a striking
resemblance to those observed in the single-valent Cu2+O2 chain compound
LiCuVO4, which were identified as an exciton doublet associated with
transitions to the upper Hubbard band that emerges as a consequence of the
long-range Coulomb interaction between electrons on neighboring Cu2+ sites
along the chains. An analysis of the spectral weights of these features yields
the parameters characterizing the on-site and long-range Coulomb interactions.",1109.4120v1
2011-09-20,"Hybrid functional electronic structure of PbPdO$_2$, a small-gap semiconductor","PbPdO$_2$, a ternary compound containing the lone-pair active ion Pb$^{2+}$
and the square-planar d$^8$ Pd$^{2+}$ ion, has attracted recent interest
because of the suggestion that its electronic structure, calculated within
density functional theory using either the local density or the generalized
gradient approximations, displays zero-gap behavior. In light of the potential
ease of doping magnetic ions in this structure, it has been suggested that the
introduction of spin, in conjunction with zero band gap, can result in unusual
magnetic ground states and unusual magnetotransport. It is known that most
electronic structure calculations do not properly obtain a band gap even for
the simple oxide PdO, and instead obtain a metal or a zero-gap semiconductor.
Here we present density functional calculations employing a screened hybrid
functional (HSE) which correctly obtain a band gap for the electronic structure
of PdO. When employed to calculate the electronic ground state of PbPdO$_2$, a
band gap is again obtained, which is consistent both with the experimental data
on this compound, as well as a consideration of valence states and of
metal-oxygen connectivity in the crystal structure. We also present comparisons
of the absolute positions (relative to the vacuum level) of the conduction band
minima and the valence band maxima in {\alpha}-PbO, PdO and PbPdO$_2$, which
suggest ease of $p$-type doping in PbPdO$_2$ that has been observed even in
nominally pure materials.",1109.4446v2
2011-09-30,Identical effects of indirect and direct electron doping of superconducting BaFe2As2 thin films,"Electron doping of a 122-type iron pnictide BaFe2As2 by substituting the Ba
site with an aliovalent ion (indirect doping), which had been unsuccessful by
conventional solid-state synthesis methods, was achieved by a non-equilibrium
film growth process. The substitution with La was substantiated by a systematic
shrinkage of the c-axis lattice parameter due to the smaller ionic radius of
La3+ than that of Ba2+. A negative Hall coefficient indicated that the majority
carriers were electrons, as is consistent with this aliovalent ion doping. The
La substitution suppressed an antiferromagnetic transition and induced bulk
superconductivity at a maximum onset critical temperature (Tc) of 22.4 K. The
electronic phase diagram for (Ba1-xLax)Fe2As2 was built, which revealed that
the indirect electron doping at the Ba site with La [(Ba1-xLax)Fe2As2] exhibits
almost the same Tc - doping level relation as that of the direct
electron-doping at the Fe site with Co [Ba(Fe1-xCox)2As2]. This finding
clarified that Tc in 122-type compounds is not affected by a crystallographic
doping site, which is in sharp contrast to the 1111-type compounds, REFeAsO (RE
= rare earth). It is tentatively attributed to the differences in their
dimensionality of electronic structures and electron pairing symmetries.",1110.0045v2
2011-10-07,Evolution of magnetic properties in the normal spinel solid solution Mg(1-x)Cu(x)Cr2O4,"We examine the evolution of magnetic properties in the normal spinel oxides
Mg(1-x)Cu(x)Cr2O4 using magnetization and heat capacity measurements. The
end-member compounds of the solid solution series have been studied in some
detail because of their very interesting magnetic behavior. MgCr2O4 is a highly
frustrated system that undergoes a first order structural transition at its
antiferromagnetic ordering temperature. CuCr2O4 is tetragonal at room
temperature as a result of Jahn-Teller active tetrahedral Cu^2+ and undergoes a
magnetic transition at 135 K. Substitution of magnetic cations for diamagnetic
Mg^2+ on the tetrahedral A site in the compositional series Mg(1-x)Cu(x)Cr2O4
dramatically affects magnetic behavior. In the composition range 0 < x < 0.3,
the compounds are antiferromagnetic. A sharp peak observed at 12.5K in the heat
capacity of MgCr2O4 corresponding to a magnetically driven first order
structural transition is suppressed even for small x suggesting glassy
disorder. Uncompensated magnetism - with open magnetization loops - develops
for samples in the x range 0.43 < x < 1. Multiple magnetic ordering
temperatures and large coercive fields emerge in the intermediate composition
range 0.43 < x < 0.47. The Neel temperature increases with increasing x across
the series while the value of the Curie-Weiss Theta decreases. A magnetic
temperature-composition phase diagram of the solid solution series is
presented.",1110.1662v1
2011-10-11,Superposition of ferromagnetic and antiferromagnetic spin chains in the quantum magnet BaAg2Cu[VO4]2,"Based on density functional theory band structure calculations, quantum
Monte-Carlo simulations, and high-field magnetization measurements, we address
the microscopic magnetic model of BaAg2Cu[VO4]2 that was recently proposed as a
spin-1/2 anisotropic triangular lattice system. We show that the actual physics
of this compound is determined by a peculiar superposition of ferromagnetic and
antiferromagnetic uniform spin chains with nearest-neighbor exchange couplings
of Ja(1) ~ -19 K and Ja(2) ~ 9.5 K, respectively. The two chains featuring
different types of the magnetic exchange perfectly mimic the specific heat of a
triangular spin lattice, while leaving a clear imprint on the magnetization
curve that is incompatible with the triangular-lattice model. Both
ferromagnetic and antiferromagnetic spin chains run along the crystallographic
'a' direction, and slightly differ in the mutual arrangement of the magnetic
CuO4 plaquettes and non-magnetic VO4 tetrahedra. These subtle structural
details are, therefore, crucial for the ferromagnetic or antiferromagnetic
nature of the exchange couplings, and put forward the importance of
comprehensive microscopic modeling for a proper understanding of quantum spin
systems in transition-metal compounds.",1110.2329v2
2011-10-17,"Electronic and Thermoelectric Properties of RuIn_{3-x}A_{x} (A = Sn, Zn)","Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)]
transport measurements on the semiconducting intermetallic system RuIn3 and its
substitution derivatives RuIn_{3-x}A_{x} (A = Sn, Zn). Higher values of the
thermoelectric figure of merit (zT = 0.45) compared to the parent compound were
achieved by chemical substitution. Here, using density functional theory based
calculations, we report on the microscopic picture behind the measured
phenomenon. We show in detail that the electronic structure of the substitution
variants of the intermetallic system RuIn_{3-x}A_{x} (A = Sn, Zn) changes in a
rigid-band like fashion. This behavior makes possible the fine tuning of the
substitution concentration to take advantage of the sharp peak-like features in
the density of states of the semiconducting parent compound. Trends in the
transport properties calculated using the semi-classical Boltzmann transport
equations within the constant scattering time approximation are in good
agreement with the former experimental results for RuIn_{3-x}Sn_{x}. Based on
the calculated thermopower for the p-doped systems, we reinvestigated the
Zn-substituted derivative and obtained ZnO-free RuIn_{3-x}Zn_{x}. The new
experimental results are consistent with the calculated trend in thermopower
and yield large zT value of 0.8.",1110.3607v2
2011-10-17,Testing the sign-changing superconducting gap in iron-based superconductors with quasiparticle interference and neutron scattering,"We present a phenomenological calculation of the quasiparticle-interference
(QPI) pattern and inelastic Neutron scattering (INS) spectra in iron-pnictide
and layered iron-selenide compounds by using materials specific band-structure
and superconducting (SC) gap properties. As both the QPI and the INS spectra
arise due to scattering of the Bogolyubov quasiaprticles, they exibit an
one-to-one correspondence of the scattering vectors and the energy scales. We
show that these two spectroscopies complement each other in such a way that a
comparative study allows one to extract the quantitative and unambiguous
information about the underlying pairing structure and the phase of the SC gap.
Due to the nodeless and isotropic nature of the SC gaps, both the QPI and INS
maps are concentrated at only two energies in pnictide (two SC gaps) and one
energy in iron-selenide, while the associated scattering vectors q for
scattering of sign-changing and same-sign of the SC gaps change between these
spectroscopies. The results presented, particularly for newly iron-selenide
compounds, can be used to test the nodeless d-wave pairing in this class of
high temperature superconductors.",1110.3834v2
2011-11-23,Revisiting the Carrington Event: Updated modeling of atmospheric effects,"The terrestrial effects of major solar events such as the Carrington
white-light flare and subsequent geomagnetic storm of August-September 1859 are
of considerable interest, especially in light of recent predictions that such
extreme events will be more likely over the coming decades. Here we present
results of modeling the atmospheric effects, especially production of odd
nitrogen compounds and subsequent depletion of ozone, by solar protons
associated with the Carrington event. This study combines approaches from two
previous studies of the atmospheric effect of this event. We investigate
changes in NOy compounds as well as depletion of O3 using a two-dimensional
atmospheric chemistry and dynamics model. Atmospheric ionization is computed
using a range-energy relation with four different proxy proton spectra
associated with more recent well-known solar proton events. We find that
changes in atmospheric constituents are in reasonable agreement with previous
studies, but effects of the four proxy spectra used vary more widely than found
by one of those studies. In particular, we find greater impact for harder
proton spectra, given a constant total fluence. We report computed nitrate
deposition values and compare to measured values in ice cores. Finally, we
briefly investigate the impact of the modeled ozone depletion on surface-level
solar ultraviolet radiation.",1111.5590v1
2012-01-18,Statics and dynamics of weakly coupled antiferromagnetic spin-1/2 ladders in a magnetic field (PhD thesis),"We investigate weakly coupled spin-1/2 ladders in a magnetic field. The work
is motivated by recent experiments on the compound
$\mathrm{(C_5H_{12}N)_2CuBr_4}$ (BPCB). We use a combination of numerical and
analytical methods, in particular the density matrix renormalization group
(DMRG) technique, to explore the phase diagram and the excitation spectra of
such a system. We give detailed results on the temperature dependence of the
magnetization and the specific heat, and the magnetic field dependence of the
nuclear magnetic resonance (NMR) relaxation rate of single ladders. For coupled
ladders, treating the weak interladder coupling within a mean field approach,
we compute the transition temperature of triplet condensation and its
corresponding antiferromagnetic order parameter. Existing experimental
measurements are discussed and compared to our theoretical results. Furthermore
we compute, using time dependent DMRG, the dynamical correlations of a single
spin ladder. Our results allow to directly describe the inelastic neutron
scattering cross section up to high energies. We focus on the evolution of the
spectra with the magnetic field and compare their behavior for different
couplings. The characteristic features of the spectra are interpreted using
different analytical approaches such as the mapping onto a spin chain, a
Luttinger liquid (LL) or onto a t-J model. For values of parameters for which
such measurements exist, we compare our results to inelastic neutron scattering
experiments on the compound BPCB and find excellent agreement. We make
additional predictions for the high energy part of the spectrum that are
potentially testable in future experiments.",1201.5276v1
2012-02-08,Thermodynamic analysis of the Quantum Critical behavior of Ce-lattice compounds,"A systematic analysis of low temperature magnetic phase diagrams of Ce
compounds is performed in order to recognize the thermodynamic conditions to be
fulfilled by those systems to reach a quantum critical regime and,
alternatively, to identify other kinds of low temperature behaviors. Based on
specific heat ($C_m$) and entropy ($S_m$) results, three different types of
phase diagrams are recognized: i) with the entropy involved into the ordered
phase ($S_{MO}$) decreasing proportionally to the ordering temperature
($T_{MO}$), ii) those showing a transference of degrees of freedom from the
ordered phase to a non-magnetic component, with their $C_m(T_{MO})$ jump
($\Delta C_m$) vanishing at finite temperature, and iii) those ending in a
critical point at finite temperature because their $\Delta C_m$ do not decrease
with $T_{MO}$ producing an entropy accumulation at low temperature.
  Only those systems belonging to the first case, i.e. with $S_{MO}\to 0$ as
$T_{MO}\to 0$, can be regarded as candidates for quantum critical behavior.
Their magnetic phase boundaries deviate from the classical negative curvature
below $T\approx 2.5$\,K, denouncing frequent misleading extrapolations down to
T=0. Different characteristic concentrations are recognized and analyzed for
Ce-ligand alloyed systems. Particularly, a pre-critical region is identified,
where the nature of the magnetic transition undergoes significant
modifications, with its $\partial C_m/\partial T$ discontinuity strongly
affected by magnetic field and showing an increasing remnant entropy at $T\to
0$. Physical constraints arising from the third law at $T\to 0$ are discussed
and recognized from experimental results.",1202.1724v1
2012-04-04,Similar zone-center gaps in the low-energy spin-wave spectra of NaFeAs and BaFe2As2,"We report results of inelastic-neutron-scattering measurements of low-energy
spin-wave excitations in two structurally distinct families of iron-pnictide
parent compounds: Na(1-{\delta})FeAs and BaFe2As2. Despite their very different
values of the ordered magnetic moment and N\'eel temperatures, T_N, in the
antiferromagnetic state both compounds exhibit similar spin gaps of the order
of 10 meV at the magnetic Brillouin-zone center. The gap opens sharply below
T_N, with no signatures of a precursor gap at temperatures between the
orthorhombic and magnetic phase transitions in Na(1-{\delta})FeAs. We also find
a relatively weak dispersion of the spin-wave gap in BaFe2As2 along the
out-of-plane momentum component, q_z. At the magnetic zone boundary (q_z = 0),
spin excitations in the ordered state persist down to 20 meV, which implies a
much smaller value of the effective out-of-plane exchange interaction, J_c, as
compared to previous estimates based on fitting the high-energy spin-wave
dispersion to a Heisenberg-type model.",1204.0875v2
2012-04-21,"Ab-initio study of different structures of CaC: Magnetism, Bonding, and Lattice Dynamics","On the basis of ab-initio pseudopotential calculations, we study structural,
magnetic, dynamical, and mechanical properties of the hypothetical CaC ionic
compound in the rock-salt (RS), B2, zinc-blende (ZB), wurtzite (WZ), NiAs (NA),
anti-NiAs (NA*), and CrB (B33) structures. It is argued that the ZB, WZ, NA,
and RS structures are more ionic while the NA*, B2, and B33 structures are more
covalent systems. As a result of that, the nonmagnetic B33-CaC is the
energetically preferred system, while the more ionic structures prefer a
ferromagnetic ground state with high Fermi level spin polarization. The
observed ferromagnetism in the more ionic systems is attributed to the sharp
partially filled $p$ states of carbon atom in the system. In the framework of
density functional perturbation theory, the phonon spectra of these systems are
computed and the observed dynamical instabilities of the NA* and B2 structures
are explained in terms of the covalent bonds between carbon atoms. The
calculated Helmholtz and Enthalpy free energies indicate the highest stability
of the B33 structure in a wide range of temperatures and pressures. Among the
ferromagnetic structures, RS-CaC and ZB-CaC are reported, respectively, to be
the most and the least metastable systems in various thermodynamics conditions.
Several mechanical properties of the dynamically stable structures of CaC are
determined from their phonon spectra.",1204.4781v2
2012-04-21,A Diffusionless Transformation Path Relating Th3P4 and Spinel Structure: Opportunities to Synthesize Ceramic Materials at High Pressures,"This thesis investigates a transformation path between the Th3P4-type and the
spinel-type structures of hafnium (IV) and titanium (IV) nitride, M3N4 (M = Hf,
Ti) with computational methods. For both compounds, the Th3P4-type was
synthesized experimentally at high-pressure conditions and was quenched to
ambient conditions. Computations reveal that while at high pressure Th3P4-type
structures are favored by enthalpy, at low pressure the Th3P4-type is only
meta-stable. The spinel-type is energetically more favorable at zero pressure
than the Th3P4- type in both systems. However, even the spinel-type is
surpassed by another ground state modification for both Hf3N4 and Ti3N4. The
research presented in this thesis then addresses (i) thermal stability of the
Th3P4 polymorphs and (ii) the conditions necessary to synthesize spinel-type
structures of both compounds. The foundation for the study is a simple
structural relation between Th3P4-type and the spinel-type structures: while
the Th3P4-type is based on a body-centered cubic arrangement of anions with
cations in interstitial sites, the spinel-type is best described by a
face-centered cubic arrangement of anions with cations in interstitial sites.
With anions following the Bain path of the bcc-fcc transformation, and cations
undergoing a minor shuffle distortion, the Th3P4 to spinel transformation
parallels the martensitic transformation known in many metal systems -- only
with additional cations in the structure.",1204.4825v1
2012-05-22,Magnetic order tuned by Cu substitution in Fe1.1-zCuzTe,"We study the effects of Cu substitution in Fe1.1Te, the non-superconducting
parent compound of the iron-based superconductor, Fe1+yTe1-xSex, utilizing
neutron scattering techniques. It is found that the structural and magnetic
transitions, which occur at \sim 60 K without Cu, are monotonically depressed
with increasing Cu content. By 10% Cu for Fe, the structural transition is
hardly detectable, and the system becomes a spin glass below 22 K, with a
slightly incommensurate ordering wave vector of (0.5-d, 0, 0.5) with d being
the incommensurability of 0.02, and correlation length of 12 angstrom along the
a axis and 9 angstrom along the c axis. With 4% Cu, both transition
temperatures are at 41 K, though short-range incommensurate order at (0.42, 0,
0.5) is present at 60 K. With further cooling, the incommensurability decreases
linearly with temperature down to 37 K, below which there is a first order
transition to a long-range almost-commensurate antiferromagnetic structure. A
spin anisotropy gap of 4.5 meV is also observed in this compound. Our results
show that the weakly magnetic Cu has large effects on the magnetic
correlations; it is suggested that this is caused by the frustration of the
exchange interactions between the coupled Fe spins.",1205.5069v2
2012-06-11,Long-range transfer of electron-phonon coupling in oxide superlattices,"The electron-phonon interaction is of central importance for the electrical
and thermal properties of solids, and its influence on superconductivity,
colossal magnetoresistance, and other many-body phenomena in
correlated-electron materials is currently the subject of intense research.
However, the non-local nature of the interactions between valence electrons and
lattice ions, often compounded by a plethora of vibrational modes, present
formidable challenges for attempts to experimentally control and theoretically
describe the physical properties of complex materials. Here we report a Raman
scattering study of the lattice dynamics in superlattices of the
high-temperature superconductor $\bf YBa_2 Cu_3 O_7$ and the
colossal-magnetoresistance compound $\bf La_{2/3}Ca_{1/3}MnO_{3}$ that suggests
a new approach to this problem. We find that a rotational mode of the MnO$_6$
octahedra in $\bf La_{2/3}Ca_{1/3}MnO_{3}$ experiences pronounced
superconductivity-induced lineshape anomalies, which scale linearly with the
thickness of the $\bf YBa_2 Cu_3 O_7$ layers over a remarkably long range of
several tens of nanometers. The transfer of the electron-phonon coupling
between superlattice layers can be understood as a consequence of long-range
Coulomb forces in conjunction with an orbital reconstruction at the interface.
The superlattice geometry thus provides new opportunities for controlled
modification of the electron-phonon interaction in complex materials.",1206.2330v1
2012-06-11,Orthorhombic fulleride (CH3NH2)K3C60 close to Mott-Hubbard instability: Ab initio study,"We study the electronic structure and magnetic interactions in
methylamine-intercalated orthorhombic alkali-doped fullerene (CH3NH2)K3C60
within the density functional theory. As in the simpler ammonia intercalated
compound (NH3)K3C60, the orthorhombic crystal-field anisotropy \Delta lifts the
t1u triple degeneracy at the \Gamma point and drives the system deep into the
Mott-insulating phase. However, the computed \Delta and conduction electron
bandwidth W cannot alone account for the abnormally low experimental N\'eel
temperature, T_N = 11 K of the methylamine compound, compared to the much
higher value T_N = 40 K of the ammonia one. Significant interactions between
CH3NH2 and C60^{3-} are responsible for the stabilization of particular
pseudo-Jahn-Teller fullerene-cage distortions and the ensuing low-spin S = 1/2
state. These interactions also seem to affect the magnetic properties, as
interfullerene exchange interactions depend on the relative orientation of
pseudo-Jahn-Teller distortions of neighboring C60^{3-} molecules. For the
ferro-orientational order of CH3NH2-K^+ groups we find an apparent reduced
dimensionality in magnetic exchange interactions, which may explain the
suppressed N\'eel temperature. The disorder in exchange interactions caused by
orientational disorder of CH3NH2-K^+ groups could further contribute to this
suppression.",1206.2335v1
2012-06-14,Visualizing heavy fermions emerging in a quantum critical Kondo lattice,"In solids containing elements with f orbitals, the interaction between
f-electron spins and those of itinerant electrons leads to the development of
low-energy fermionic excitations with a heavy effective mass. These excitations
are fundamental to the appearance of unconventional superconductivity and
non-Fermi-liquid behaviour observed in actinide- and lanthanide-based
compounds. Here we use spectroscopic mapping with the scanning tunnelling
microscope to detect the emergence of heavy excitations with lowering of
temperature in a prototypical family of cerium-based heavy-fermion compounds.
We demonstrate the sensitivity of the tunnelling process to the composite
nature of these heavy quasiparticles, which arises from quantum entanglement of
itinerant conduction and f electrons. Scattering and interference of the
composite quasiparticles is used to resolve their energy-momentum structure and
to extract their mass enhancement, which develops with decreasing temperature.
The lifetime of the emergent heavy quasiparticles reveals signatures of
enhanced scattering and their spectral lineshape shows evidence of
energy-temperature scaling. These findings demonstrate that proximity to a
quantum critical point results in critical damping of the emergent heavy
excitation of our Kondo lattice system.",1206.3145v1
2012-08-15,Magnetic properties of the S=1/2 quasi square lattice antiferromagnet CuF2(H2O)2(pyz) (pyz=pyrazine) investigated by neutron scattering,"We have performed elastic and inelastic neutron experiments on single crystal
samples of the coordination polymer compound CuF2(H2O)2(pyz) (pyz=pyrazine) to
study the magnetic structure and excitations. The elastic neutron diffraction
measurements indicate a collinear antiferromagnetic structure with moments
oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60
+/- 0.03 muB/Cu. This value is significantly smaller than the single ion
magnetic moment, reflecting the presence of strong quantum fluctuations. The
spin wave dispersion from magnetic zone center to the zone boundary points (0.5
1.5 0) and (0.5 0 1.5) can be described by a two dimensional Heisenberg model
with a nearest neighbor magnetic exchange constant J2d = 0.934 +/-0.0025 meV.
The inter-layer interaction Jperp in this compound is less than 1.5% of J2d.
The spin excitation energy at the (0.5 0.5 0.5) zone boundary point is reduced
when compared to the (0.5 1 0.5) zone boundary point by ~10.3 +/- 1.4 %. This
zone boundary dispersion is consistent with quantum Monte Carlo and series
expansion calculations which include corrections for quantum fluctuations to
linear spin wave theory.",1208.3136v1
2012-08-28,"Mechanical, thermal and optical properties of perovskite borides RRh3B(R = Y, Zr, and Nb)","We report here ab initio density functional theory (DFT) calculations of
structural, elastic, Peierls stress, thermodynamic and optical properties of
RRh3B (R = Y, Zr and Nb) using the plane wave psedudopotential method. The
materials possess better ductile behavior in comparison with a selection of
layered MAX phases but the anisotropy is strong, particularly in NbRh3B. The
Peierls stress, approximately 3-4 times larger than in MAX phases, show that
dislocation movement may follow but with much reduced occurrences compared to
MAX phases. The temperature and pressure dependence of bulk modulus, specific
heats, thermal expansion coefficient, and Debye temperature are calculated for
the first time for two of the three compounds using the quasi-harmonic Debye
model with phononic effects for elevated temperature and pressure. The obtained
results are discussed in comparison to the behavior of other related compounds.
Further the features of optical functions obtained for the first time are
discussed. The study reveals that the reflectivity is high in the IR-UV regions
up to ~ 17.5 eV (YRh3B, ZrRh3B) and 20 eV (NbRh3B), thus showing promise as
good coating materials.
  Keywords: RRh3B; Quasi-harmonic Debye model; Thermodynamic properties;
Optical properties",1208.5567v1
2012-10-06,Antimony arsenide: Chemical ordering in the compound SbAs,"The semimetallic Group V elements display a wealth of correlated electron
phenomena due to a small indirect band overlap that leads to relatively small,
but equal, numbers of holes and electrons at the Fermi energy with high
mobility. Their electronic bonding characteristics produce a unique crystal
structure, the rhombohedral A7 structure, which accommodates lone pairs on each
site. Here we show that the A7 structure can display chemical ordering of Sb
and As, which were previously thought to mix randomly. Our structural
characterization of the compound SbAs is performed by single-crystal and
high-resolution synchrotron x-ray diffraction, and neutron and x-ray pair
distribution function analysis. All least-squares refinements indicate ordering
of Sb and As, resulting in a GeTe-type structure without inversion symmetry.
High-temperature diffraction studies reveal an ordering transition around 550
K. Transport and infrared reflectivity measurements, along with
first-principles calculations, confirm that SbAs is a semimetal, albeit with a
direct band separation larger than that of Sb or As. Because even subtle
substitutions in the semimetals, notably Bi_{1-x}Sb_x, can open semiconducting
energy gaps, a further investigation of the interplay between chemical ordering
and electronic structure on the A7 lattice is warranted.",1210.1986v1
2012-10-16,Performance Analysis Cluster and GPU Computing Environment on Molecular Dynamic Simulation of BRV-1 and REM2 with GROMACS,"One of application that needs high performance computing resources is
molecular d ynamic. There is some software available that perform molecular
dynamic, one of these is a well known GROMACS. Our previous experiment
simulating molecular dynamics of Indonesian grown herbal compounds show
sufficient speed up on 32 n odes Cluster computing environment. In order to
obtain a reliable simulation, one usually needs to run the experiment on the
scale of hundred nodes. But this is expensive to develop and maintain. Since
the invention of Graphical Processing Units that is also useful for general
programming, many applications have been developed to run on this. This paper
reports our experiments that evaluate the performance of GROMACS that runs on
two different environment, Cluster computing resources and GPU based PCs. We
run the experiment on BRV-1 and REM2 compounds. Four different GPUs are
installed on the same type of PCs of quad cores; they are Gefore GTS 250, GTX
465, GTX 470 and Quadro 4000. We build a cluster of 16 nodes based on these
four quad cores PCs. The preliminary experiment shows that those run on GTX 470
is the best among the other type of GPUs and as well as the cluster computing
resource. A speed up around 11 and 12 is gained, while the cost of computer
with GPU is only about 25 percent that of Cluster we built.",1210.4251v1
2012-10-22,"Synthesized inverse-perovskites Sc3InX (X = B, C, N): A theoretical investigation","We present first-principles density functional theory (DFT) investigations of
mechanical, thermodynamic and optical properties of synthesized
inverse-perovskites Sc3InX (X = B, C, N). The elastic constants at zero
pressure and temperature are calculated and the anisotropic behavior of the
compounds is illustrated. All the three materials are shown to be brittle in
nature. The computed Peierls stress, approximately 3 to 5 times larger than of
a selection of MAX phases, show that dislocation movement may follow but with
much reduced occurrences compared to these MAX phases. The Mulliken bonding
population and charge density maps show stronger covalency between Sc and X
atoms compared with Sc-Sc bond. The Vickers hardness values of Sc3InX are
predicted to be between 3.03 and 3.88 GPa. The Fermi surfaces of Sc3InX contain
both hole- and electron-like topology which changes as one replaces B with C or
N. The bulk modulus, specific heats, thermal expansion coefficient, and Debye
temperature are calculated as a function both temperature and pressure using
the quasi-harmonic Debye model with phononic effects. The results so obtained
are analysed in comparison to the characteristics of other related compounds.
Moreover optical functions are calculated and discussed for the first time. The
reflectivity is found to be high in the IR-UV regions up to ~ 10.7 eV (Sc3InB,
Sc3InC) and 12.3 eV (Sc3InN), thus showing promise as good coating materials.
  Keywords: Sc3InX, Mechanical properties; Fermi surface; Quasi-harmonic Debye
model; Thermodynamic properties; Optical properties",1210.5820v2
2012-10-23,Cooperating epidemics of foodborne diseases with diverse trade networks,"The frequent outbreak of severe foodborne diseases warns of a potential
threat that the global trade networks could spread fatal pathogens. The global
trade network is a typical overlay network, which compounds multiple standalone
trade networks representing the transmission of a single product and connecting
the same set of countries and territories through their own set of trade
interactions. Although the epidemic dynamic implications of overlay networks
have been debated in recent studies, some general answers for the overlay of
multiple and diverse standalone networks remain elusive, especially the
relationship between the heterogeneity and diversity of a set of standalone
networks and the behavior of the overlay network. In this paper, we establish a
general analysis framework for multiple overlay networks based on diversity
theory. The framework could reveal the critical epidemic mechanisms beyond
overlay processes. Applying the framework to global trade networks, we found
that, although the distribution of connectivity of standalone trade networks
was highly heterogeneous, epidemic behavior on overlay networks is more
dependent on cooperation among standalone trade networks rather than on a few
high-connectivity networks as the general property of complex systems with
heterogeneous distribution. Moreover, the analysis of overlay trade networks
related to 7 real pathogens also suggested that epidemic behavior is not
controlled by high-connectivity goods but that the actual compound mode of
overlay trade networks plays a critical role in spreading pathogens. Finally,
we study the influence of cooperation mechanisms on the stability of overlay
networks and on the control of global epidemics. The framework provides a
general tool to study different problems on overlay networks.",1210.6142v1
2012-10-24,Rattling and Superconducting Properties of the Cage Compound GaxV2Al20,"Low-energy rattling modes and their effects on superconductivity are studied
in the cage compound GaxV2Al20. A series of polycrystalline samples of 0 < x =<
0.6 are examined through resistivity, magnetic susceptibility, and heat
capacity measurements. A weak-coupling BCS superconductivity is observed below
Tc = 1.4-1.7 K for all the samples. For small Ga contents below 0.20,
approximately 30% of the cages are occupied by rattling Al atoms having an
Einstein temperature TE of 23 K, probably with most Ga atoms substituting for
the cage-forming Al atoms. For higher Ga contents, approximately 0.05 Ga and
0.25-0.35 Al atoms coexist statistically inside the cages and behave as
rattlers with TE ~ 8 and 23 K, respectively. A significant effect of Ga
rattling on the superconductivity is clearly evidenced by the observation of a
sharp rise in Tc by 8% at x = 0.20 when 0.05 Ga atoms are introduced into the
case. Probably, the electron-phonon interaction is significantly enhanced by an
additional contribution to the phonon density of states from the extremely low
energy rattling modes of Ga atoms. In addition, a large softening of the
acoustic modes is observed for x => 0.20, suggesting that the cage itself
becomes anomalously soft in the presence of low-energy Ga rattling modes.",1210.6461v1
2012-10-25,Universal superconducting fluctuations and the implications for the phase diagram of the cuprates,"Superconductivity in the cuprates emerges from an enigmatic metallic state.
There remain profound open questions regarding the universality of observed
phenomena and the character of precursor fluctuations above the superconducting
(SC) transition temperature (T_c). For single-CuO_2-layer La_{2-x}Sr_xCuO_4
(LSCO) and Bi_2(Sr,La)_2CuO_{6+\delta} (Bi2201), some experiments seem to
indicate an onset of SC fluctuations at very high temperatures (2-3 times
T_c^{max}, the T_c value at optimal hole concentration p), whereas other
measurements suggest that fluctuations are confined to the immediate vicinity
of T_c(p). Here we use torque magnetization to resolve this conundrum by
systematically studying LSCO, Bi2201 and HgBa_2CuO_{4+\delta} (Hg1201). The
latter is a more ideal single-layer compound, featuring high structural
symmetry, minimal disorder, and T_c^{max} = 97 K, a value more than twice those
of LSCO and Bi2201. We find in all three cases that SC diamagnetism vanishes in
an unusual exponential fashion above T_c, and at a rapid rate that is
universal. Furthermore, the high characteristic fluctuation temperatures of
LSCO and Bi2201 closely track T_c(p) of Hg1201. These observations suggest
that, rather than being indicative of SC diamagnetism, the fluctuations at high
temperatures in the low-T_c^{max} compounds are associated with a competing
order. This picture is further supported by an analysis of available results
for double-layer cuprates.",1210.6942v1
2012-11-02,Direct Observation of Giant Saturation Magnetization in Fe16N2,"Magnetic materials with giant saturation magnetization have been a holy grail
for magnetic researchers and condensed matter physicists for decades because of
its great scientific and technological impacts. As described by the famous
Slater-Pauling curve the material with highest Ms is the Fe65Co35 alloy. This
was challenged in 1972 by a report on the compound Fe16N2 with Ms much higher
than that of Fe65Co35. Following this claim, there have been enormous efforts
to reproduce this result and to understand the magnetism of this compound.
However, the reported Ms by different groups cover a broad range, mainly due to
the unavailability of directly assessing Ms in Fe16N2. In this article, we
report a direct observation of the giant saturation magnetization up to 2500
emu/cm3 using polarized neutron reflectometry (PNR) in epitaxial constrained
Fe16N2 thin films prepared using a low-energy and surface-plasma-free
sputtering process. The observed giant Ms is corroborated by a previously
proposed Cluster + Atom model, the characteristic feature of which, namely, the
directional charge transfer is evidenced by polarization-dependent x-ray
absorption near edge spectroscopy (XANES).",1211.0553v1
2012-12-03,Modeling non-stationarities in high-frequency financial time series,"We study tick-by-tick financial returns belonging to the FTSE MIB index of
the Italian Stock Exchange (Borsa Italiana). We can confirm previously detected
non-stationarities. However, scaling properties reported in the previous
literature for other high-frequency financial data are only approximately
valid. As a consequence of the empirical analyses, we propose a simple method
for describing non-stationary returns, based on a non-homogeneous normal
compound Poisson process. We test this model against the empirical findings and
it turns out that the model can approximately reproduce several stylized facts
of high-frequency financial time series. Moreover, using Monte Carlo
simulations, we analyze order selection for this model class using three
information criteria: Akaike's information criterion (AIC), the Bayesian
information criterion (BIC) and the Hannan-Quinn information criterion (HQ).
For comparison, we also perform a similar Monte Carlo experiment for the ACD
(autoregressive conditional duration) model. Our results show that the
information criteria work best for small parameter numbers for the compound
Poisson type models, whereas for the ACD model the model selection procedure
does not work well in certain cases.",1212.0479v4
2012-12-17,Selective Mottness as a key to iron superconductors,"The phase diagram of the high-Tc cuprates is dominated by the Mott insulating
phase of the parent compounds. As we approach it from large doping, a standard
Fermi-liquid gradually turns into a bad non-Fermi liquid metal, a process which
culminates in the pseudogap regime, in which the antinodal region in momentum
space acquires a gap before reaching a fully gapped Mott state.
  Here we show that experiments for electron- and hole-doped BaFe2As2 support
an analogous scenario. The doping evolution is dominated by the influence of a
Mott insulator that would be realized for half-filled conduction bands, while
the stoichiometric compound does not play a special role. Weakly and strongly
correlated conduction electrons coexist in much of the phase diagram, a
differentiation which increases with hole doping. We identify the reason for
this selective Mottness in a strong Hund's coupling, which decouples the
different orbitals. Each orbital then behaves as a single band Hubbard model,
where the correlation degree only depends on how doped is each orbital from
half-filling. Our scenario reconciles contrasting evidences on the electronic
correlation strength and establishes a deep connection with the cuprates.",1212.3966v2
2012-12-20,Measurement of Coherent Polarons in the Strongly Coupled Antiferromagnetically Ordered Iron-Chalcogenide Fe1.02Te using Angle-Resolved Photoemission Spectroscopy,"The nature of metallicity and the level of electronic correlations in the
antiferromagnetically ordered parent compounds are two important open issues
for the iron-based superconductivity. We perform a temperature-dependent
angle-resolved photoemission spectroscopy study of Fe1.02Te, the parent
compound for iron chalcogenide superconductors. Deep in the antiferromagnetic
state, the spectra exhibit a ""peak-dip-hump"" line shape associated with two
clearly separate branches of dispersion, characteristics of polarons seen in
manganites and lightly-doped cuprates. As temperature increases towards the
Neel temperature (T_N), we observe a decreasing renormalization of the peak
dispersion and a counterintuitive sharpening of the hump linewidth, suggestive
of an intimate connection between the weakening electron-phonon (e-ph) coupling
and antiferromagnetism. Our finding points to the highly-correlated nature of
Fe1.02Te ground state featured by strong interactions among the charge, spin
and lattice and a good metallicity plausibly contributed by the coherent
polaron motion.",1212.4946v1
2013-01-06,Effective Hamiltonian Crystal Field for Magnetic Interactions in Polynuclear Transition Metal Complexes. Sequential Derivation and Exemplary Numerical Estimates,"By this we extend our work of the year 1992 devoted to calculating the
intrashell excitations in the d-shells of coordination compounds of the first
transition metal row, which resulted in the Effective Hamiltonian Crystal Field
(EHCF) method, to their polinuclear analogs in order to assure the description
of several open d-shells and of magnetic interactions of the effective spins
residing in these shells. This is a challenging task since it requires
improving the precision of ca. 1000 cm$^{-1}$ (that of describing the
excitation energies of the single d-shells by the already well successful EHCF
method) to the that of ca. 10 $\div$ 100 cm$^{-1}$ characteristic for the
energies required to reorient the spins i.e. eventually by two orders of
magnitude. This is performed within the same paradigm as used for the EHCF
method: the concerted usage of the McWeeny's group-function approximation and
the L\""owdin partition technique. These are applied to develop the effective
description of the d-system of the polynuclear complexes, composed of several
d-shells, including the working formulae for the exchange parameters between
the d-shells belonging to different transition metal ions. These formulae are
implemented in the package kramers and tested against a series of binuclear
complexes of trivalent Cr and Fe cations featuring $\mu$-oxygen superexchange
paths in order to confirm the reproducibility of the trends in the series of
values of exchange parameters for the compounds differing by the chemical
substitutions and other details of composition and structure. The results of
calculations are in a reasonable agreement with available experimental data and
other theoretical methods.",1301.1036v2
2013-01-24,First-principles model potentials for lattice-dynamical studies: general methodology and example of application to ferroic perovskite oxides,"We present a scheme to construct model potentials, with parameters computed
from first principles, for large-scale lattice-dynamical simulations of
materials. Our method mimics the traditional solid-state approach to the
investigation of vibrational spectra, i.e., we start from a suitably chosen
reference configuration of the material and describe its energy as a function
of arbitrary atomic distortions by means of a Taylor series. Such a form of the
potential-energy surface is completely general, trivial to formulate for any
compound, and physically transparent. Further, the approximations involved in
our effective models are clear-cut, and the precision can be improved in a
systematic and well-defined fashion. Moreover, such a simple definition allows
for a straightforward determination of the parameters in the low-order terms of
the series, as they are the direct result of
density-functional-perturbation-theory calculations, which greatly simplifies
the model construction. Here we present such a scheme, discuss a practical and
versatile methodology for the calculation of the model parameters from first
principles, and describe our results for two challenging cases in which the
model potential is strongly anharmonic, namely, ferroic perovskite oxides
PbTiO3 and SrTiO3. The choice of test materials was partly motivated by
historical reasons, since our scheme can be viewed as a natural extension of
(and was initially inspired by) the so-called first-principles effective
Hamiltonian approach to the investigation of temperature-driven effects in
ferroelectric perovskite oxides. Thus, the study of these compounds allows us
to better describe the connections between the effective-Hamiltonian method and
ours.",1301.5731v1
2013-02-26,Inter-plane resistivity of isovalent doped BaFe$_2$(As$_{1-x}$P$_x$)$_2$,"Temperature-dependent inter-plane resistivity, $\rho_c(T)$, was measured for
the iron-based superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ over a broad
isoelectron phosphorus substitution range from $x$=0 to $x$=0.60, from
non-superconducting parent compound to heavily overdoped superconducting
composition with $T_c\approx 10 K$. The features due to structural and magnetic
transitions are clearly resolved in $\rho_c(T)$ of the underdoped crystals. A
characteristic maximum in $\rho_c(T)$, found in the parent BaFe$_2$As$_2$ at
around 200 K, moves rapidly with phosphorus substitution to high temperatures.
At the optimal doping, the inter-plane resistivity shows $T$-linear temperature
dependence without any cross-over anomalies, similar to the previously reported
in-plane resistivity. This observation is in stark contrast with dissimilar
temperature dependences found at optimal doping in electron-doped
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Our finding suggests that despite similar
values of the resistivity and its anisotropy, the temperature dependent
transport in the normal state is very different in electron and isoelectron
doped compounds. Similar temperature dependence of both in-plane and
inter-plane resistivities, in which the dominant contributions are coming from
different parts of the Fermi surface, suggests that scattering is the same on
the whole Fermi surface. Since magnetic fluctuations are expected to be much
stronger on the quasi-nested sheets, this observation may point to the
importance of the inter-orbital scattering between different sheets.",1302.6440v1
2013-02-28,Thermally activated magnetization reversal in bulk BiFe0.5Mn0.5O3,"We report on the synthesis and characterization of BiFe0.5Mn0.5O3, a
potential type-I multiferroic compound displaying temperature induced
magnetization reversal. Bulk samples were obtained by means of solid state
reaction carried out under the application of hydrostatic pressure at 6 GPa and
1100{\deg}C. The crystal structure is an highly distorted perovskite with no
cation order on the B site, where, besides a complex scheme of tilt and
rotations of the TM-O6 octahedra, large off-centering of the bismuth ions is
detected. Below T1 = 420 K the compound undergoes a first weak ferromagnetic
transition related to the ordering of iron rich clusters. At lower temperatures
(just below RT) two distinct thermally activated mechanisms are superimposed,
inducing at first an enhancement of the magnetization at T2 = 288 K, then a
spontaneous reversal process centered at T3 = 250 K, finally giving rise to a
negative response. The application of fields higher than 1500 Oe suppresses the
process, yielding a ferromagnetic like behaviour. The complementary use of
SQuID magnetometry and M\""ossbauer spectroscopy allowed the interpretation of
the overall magnetic behaviour in terms of an uncompensated weak competitive
coupling between non-equivalent clusters of interactions characterized by
different critical temperatures and resultant magnetizations. PACS numbers:
75.85.+t, 75.60.Jk, 76.80.+y, 75.30.Et, 75.30.Kz",1302.7231v2
2013-03-17,"Magnetism of CuX2 frustrated chains (X = F, Cl, Br): the role of covalency","Periodic and cluster density-functional theory (DFT) calculations, including
DFT+U and hybrid functionals, are applied to study magnetostructural
correlations in spin-1/2 frustrated chain compounds CuX2: CuCl2, CuBr2, and a
fictitious chain structure of CuF2. The nearest-neighbor and second-neighbor
exchange integrals, J1 and J2, are evaluated as a function of the Cu-X-Cu
bridging angle, theta, in the physically relevant range 80-110deg. In the ionic
CuF2, J1 is ferromagnetic for theta smaller 100deg. For larger angles, the
antiferromagnetic superexchange contribution becomes dominant, in accord with
the Goodenough-Kanamori-Anderson rules. However, both CuCl2 and CuBr2 feature
ferromagnetic J1 in the whole angular range studied. This surprising behavior
is ascribed to the increased covalency in the Cl and Br compounds, which
amplifies the contribution from Hund's exchange on the ligand atoms and renders
J1 ferromagnetic. At the same time, the larger spatial extent of X orbitals
enhances the antiferromagnetic J2, which is realized via the long-range
Cu-X-X-Cu paths. Both, periodic and cluster approaches supply a consistent
description of the magnetic behavior which is in good agreement with the
experimental data for CuCl2 and CuBr2. Thus, owing to their simplicity, cluster
calculations have excellent potential to study magnetic correlations in more
involved spin lattices and facilitate application of quantum-chemical methods.",1303.4063v1
2013-03-26,Superconductivity and Crystal Structure of the Palladium-Iron-Arsenides Ca10(Fe1-xPdxAs)10Pd3As8,"The palladium-iron-arsenides Ca10(Fe1-xPdxAs)10(Pd3As8) were synthesized by
solid state methods and characterized by X-ray powder and single crystal
diffraction. The triclinic crystal structure (space group P-1) is isotypic to
the homologue platinum 1038 type superconductors with alternating FeAs4/4- and
Pd3As8-layers, each separated by layers of calcium atoms. Iron is tetrahedral
and palladium is planar coordinated by four arsenic atoms. As2-dimers (dAs-As =
250 pm) are present in the Pd3As8-layer. Even though each layer itself has a
fourfold rotational symmetry, the shifted layer stacking causes the triclinic
space group. Resistivity measurements of La-doped samples show the onset of
superconductivity at 17 K and zero resistivity below 10 K. The magnetic
shielding fraction is about 20 % at 3.5 K. 57Fe-M\""ossbauer spectra exhibit one
absorption line and show no hint to magnetic ordering. The electronic structure
is very similar to the known iron-arsenides with cylinder-like Fermi surfaces
and partial nesting between hole- and electron-like sheets. Our results show
that superconductivity in the palladium-iron-compounds is present but
complicated by too high substitution of iron by palladium in the active
FeAs-layers. Since the electronic preconditions are satisfied, we expect higher
critical temperatures in Pd1038-compounds with lower or even without Pd-doping
in the FeAs-layer.",1303.6579v1
2013-04-01,Spin and Dipole Ordering in Ni_2InSbO_6 and Ni_2ScSbO_6 with corundum-related structure,"The complex metal oxides Ni2InSbO6 (NISO) and Ni2ScSbO6 (NSSO) have been
prepared in form of polycrystalline powders by a solid state reaction route.
The crystal structure and magnetic properties of the compounds were
investigated using a combination of X-ray and neutron powder diffraction,
electron microscopy, calorimetric and magnetic measurements. The compounds
adopt a trigonal structure, space group R3, of the corundum related Ni3TeO6
(NTO) type. Only one of the octahedral Ni positions (Ni(2)) of the NTO
structure was found to be occupied by In (Sc). NTO has non-centrosymmetric
structure and is ferroelectric below 1000 K, dielectric and second harmonic
measurements suggest that also NISO and NSSO are correspondingly ferroelectric.
Magnetization measurements signified antiferromagnetic ordering below TN=60 K
(NSSO) and 76 K (NISO). The magnetic structure is formed by two
antiferromagnetically coupled incommensurate helices with the spiral axis along
the b-axis and propagation vector k = [0, ky,0] with ky= 0.036(1) (NSSO) and
ky= 0.029(1) (NISO). The observed structural and magnetic properties of NISO
and NSSO are discussed and compared with those of NTO.",1304.0474v1
2013-04-10,R-matrix analysis of reactions in the 9B compound system,"Recent activity in solving the 'lithium problem' in big bang nucleosynthesis
has focused on the role that putative resonances may play in resonance-enhanced
destruction of 7Li. Particular attention has been paid to the reactions
involving the 9B compound nuclear system, d+7Be->9B. These reactions are
analyzed via the multichannel, two-body unitary R-matrix method using code
(EDA) developed by Hale and collaborators. We employ much of the known elastic
and reaction data, in a four-channel treatment. The data include elastic
3He+6Li differential cross sections from 0.7 to 2.0 MeV, integrated reaction
cross sections for energies from 0.7 to 5.0 MeV for 6Li(3He,p)8Be* and from 0.4
to 5.0 MeV for the 6Li(3He,d)7Be reaction. Capture data have been added to an
earlier analysis with integrated cross section measurements from 0.7 to 0.825
MeV for 6Li(3He,gamma)9B. The resulting resonance parameters are compared with
tabulated values, and previously unidentified resonances are noted. Our results
show that there are no near d+7Be threshold resonances with widths that are
10's of keV and reduce the likelihood that a resonance-enhanced mass-7
destruction mechanism, as suggested in recently published work, can explain the
7Li problem.",1304.3153v1
2013-04-17,Magnetism and electronic structure of La2ZnIrO6 and La2MgIrO6: candidate Jeff =1/2 Mott insulators,"We study experimentally and theoretically the electronic and magnetic
properties of two insulating double perovskites that show similar atomic and
electronic structure, but different magnetic properties. In magnetization
measurements, La2ZnIrO6 displays weak ferromagnetic behavior below 7.5 K
whereas La2MgIrO6 shows antiferromagnetic behavior (AFM) below TN = 12 K.
Electronic structure calculations find that the weak ferromagnetic behavior
observed in La2ZnIrO6 is in fact due to canted antiferromagnetism. The
calculations also predict canted antiferromagnetic behavior in La2MgIrO6, but
intriguingly this was not observed. Neutron diffraction measurements confirm
the essentially antiferromagnetic behavior of both systems, but lack the
sensitivity to resolve the small (0.22 {\mu}B/Ir) ferromagnetic component in
La2ZnIrO6. Overall, the results presented here indicate the crucial role of
spin-orbit coupling (SOC) and the on-site Coulomb repulsion on the magnetic,
transport, and thermodynamic properties of both compounds. The electronic
structure calculations show that both compounds, like Sr2IrO4, are Jeff = 1/2
Mott insulators. Our present findings suggest that La2ZnIrO6 and La2MgIrO6
provide a new playground to study the interplay between SOC and on-site Coulomb
repulsion in a 5d transition metal oxide.",1304.4769v1
2013-04-20,Electric-Field-Induced Resistive Switching in a Family of Mott Insulators : towards Non-Volatile Mott-RRAM Memories,"The fundamental building blocks of modern silicon-based microelectronics,
such as double gate transistors in non-volatile Flash memories, are based on
the control of electrical resistance by electrostatic charging. Flash memories
could soon reach their miniaturization limits mostly because reliably keeping
enough electrons in an always smaller cell size will become increasingly
difficult . The control of electrical resistance at the nanometer scale
therefore requires new concepts, and the ultimate resistance-change device is
believed to exploit a purely electronic phase change such as the Mott insulator
to insulator transition [2]. Here we show that application of short electric
pulses allows to switch back and forth between an initial high-resistance
insulating state (""0"" state) and a low-resistance ""metallic"" state (""1"" state)
in the whole class of Mott Insulator compounds AM4X8 (A = Ga, Ge; M= V, Nb, Ta;
X = S, Se). We found that electric fields as low as 2 kV/cm induce an
electronic phase change in these compounds from a Mott insulating state to a
metallic-like state. Our results suggest that this transition belongs to a new
class of resistive switching and might be explained by recent theoretical works
predicting that an insulator to metal transition can be achieved by a simple
electric field in a Mott Insulator. This new type of resistive switching has
potential to build up a new class of Resistive Random Access Memory (RRAM) with
fast writing/erasing times (50 ns to 10 {\mu}s) and resistance ratios \Delta
R/R of the order of 25% at room temperature.",1304.5607v1
2013-04-22,Effects of Zn substitution on the electronic structure of BaFe$_2$As$_2$ revealed by angle-resolved photoemission spectroscopy,"In Fe-based superconductors, electron doping is often realized by the
substitution of transition-metal atoms for Fe. In order to investigate how the
electronic structure of the parent compound is influenced by Zn substitution,
which supplies nominally four extra electrons per substituted atom but is
expected to induce the strongest impurity potential among the transition-metal
atoms, we have performed an angle-resolved photoemission spectroscopy
measurements on Ba(Fe_{1-x}Zn_x)_2As_2 (Zn-122). In Zn-122, the temperature
dependence of the resistivity shows a kink around T~135 K, indicating
antiferromagnetic order below the Neel temperature of T_N ~ 135 K. In fact,
folded Fermi surfaces (FSs) similar to those of the parent compound have been
observed below T_N. The hole and electron FS volumes are, therefore, different
from those expected from the rigid-band model. The results can be understood if
all the extra electrons occupy the Zn 3d state ~10 eV below the Fermi level and
do not participate in the formation of the FSs.",1304.5860v2
2013-04-24,"Anisotropic transport and magnetic properties, and magnetic-field tuned states of CeZn11 single crystals","We present detailed temperature and field dependent data obtained from
magnetization, resistivity, heat capacity, Hall resistivity and thermoelectric
power measurements performed on single crystals of CeZn11. The compounds orders
antiferromagnetically at $\sim$ 2 K. The zero-field resistivity and TEP data
show features characteristic of a Ce-based intermetallic with crystal electric
field splitting and possible correlated, Kondo lattice effects. We constructed
the T-H phase diagram for the magnetic field applied along the easy, [110],
direction which shows that the magnetic field required to suppress T_N below
0.4 K is in the range of 45-47.5 kOe. A linear behavior of the rho(T) data,
H||[110], was observed only for H=45 kOe for 0.46 K<T<1.96 K followed by the
Landau-Fermi-liquid regime for a limited range of fields, 47.5 kOe< H<60 kOe.
From the analysis of our data, it appears that CeZn11 is a weakly to moderately
correlated local moment compound with rather small Kondo temperature. The
thermoelectric and transport properties of CeZn11 are mostly governed by the
CEF effects. Given the very high quality of our single crystals, quantum
oscillations are found for both CeZn11 and its non-magnetic analogue, LaZn11.",1304.6752v1
2013-04-26,"Superconducting and Normal State Properties of APd2As2 (A = Ca, Sr, Ba) Single Crystals","The synthesis and crystallography, magnetic susceptibility chi, magnetization
M, specific heat Cp, in-plane electrical resistivity rho and in-plane magnetic
penetration depth measurements are reported for single crystals of APd2As2 (A =
Ca, Sr, Ba) versus temperature T and magnetic field H. The crystals were grown
using PdAs self-flux. CaPd2As2 and SrPd2As2 crystallize in a collapsed
body-centered tetragonal ThCr2Si2-type structure (I4/mmm), whereas BaPd2As2
crystallizes in the primitive tetragonal CeMg2Si2-type structure (P4/mmm), in
agreement with literature data. The rho(T) data exhibit metallic behavior for
all three compounds. Bulk superconductivity is reported for CaPd2As2 and
SrPd2As2 below Tc = 1.27 and 0.92 K, respectively, whereas only a trace of
superconductivity is found in BaPd2As2. No other phase transitions were
observed. The chi(T) and M(H) data reveal anisotropic diamagnetism in the
normal state, with chi_c > chi_ab for CaPd2As2 and BaPd2As2, and chi_c < chi_ab
for SrPd2As2. The normal and superconducting state data indicate that CaPd2As2
and SrPd2As2 are conventional type-II nodeless s-wave electron-phonon
superconductors. The electronic superconducting-state heat capacity data for
CaPd2As2, which has an extremely sharp heat capacity jump at Tc, are analyzed
using our recent elaboration of the alpha-model of the BCS theory of
superconductivity, which indicates that the s-wave gap in this compound is
anisotropic in momentum space.",1304.7148v2
2013-04-28,Octahedral tilting induced ferroelectricity in the ASnO${_3}$/BSnO${_3}$ superlattice,"The effect of the octahedral tilting of ASnO3 (A = Ca, Sr, Ba) parent
compound and bi-color ASnO3/BSnO3 superlattice (A, B = Ca, Sr, Ba) was
predicted from density-functional theory. In the ASnO3 parent compound, the
structural phase transition as a function of the A-site cation size was
correlated with the magnitude of the two octahedral tilting modes (a-a-c0
tilting and a0a0c+ tilting). The magnitude of the octahedral tilting modes in
the superlattices was analyzed quantitatively and found to be associated with
that of the constituent parent materials. The ASnO3/BSnO3 superlattices showed
hybrid improper ferroelectricity resulting from the coupling of two octahedral
tilting modes (a-a-c0 tilting and a0a0c+ tilting), which are also responsible
for the structural phase transition from a tetragonal to orthorhombic phase.
The ferroelectricity due to A-site mirror symmetry breaking is a secondary
order parameter for an orthorhombic phase transition in the bi-color
superlattice and is related to the {\Gamma}5- symmetry mode. The coupling
between the tilting modes and ferroelectric mode in the bi-color superlattice
of ASnO3/BSnO3 was analyzed by group theory and symmetry mode analysis.",1304.7419v2
2013-05-06,Effects of stoichiometric doping in superconducting Bi-O-S compounds,"Newly discovered Bi-O-S compounds remain an enigma in attempts to understand
their electronic properties. A recent study of Bi$_{4}$O$_{4}$S$_{3}$ has shown
it to be a mixture of two phases, Bi$_{2}$OS$_{2}$ and Bi$_{3}$O$_{2}$S$_{3}$,
the latter being superconducting [W. A. Phelan et al., J. Am. Chem. Soc. 135,
5372 (2013)]. Using density functional theory, we explore the electronic
structure of both the phases and the effect of the introduction of stacking
faults. Our results demonstrate that the S$_{2}$ layers dope the
bismuth-sulphur bands. The bands at the Fermi level are of clear
two-dimensional character. One band manifold is confined to the two adjacent,
square-lattice bismuth-sulphur planes, a second manifold is confined to the
square lattice of sulphur dimers. We show that the introduction of defects in
the stacking does not influence the electronic structure. Finally, we also show
that spin-orbit coupling does not have any significant effect on the states
close to the Fermi level at the energy scale considered.",1305.1201v4
2013-05-17,"Spins, Stripes, and Superconductivity in Hole-Doped Cuprates","One of the major themes in correlated electron physics over the last quarter
century has been the problem of high-temperature superconductivity in
hole-doped copper-oxide compounds. Fundamental to this problem is the
competition between antiferromagnetic spin correlations, a symptom of strong
Coulomb interactions, and the kinetic energy of the doped carriers, which
favors delocalization. After discussing some of the early challenges in the
field, I describe the experimental picture provided by a variety of
spectroscopic and transport techniques. Then I turn to the technique of neutron
scattering, and discuss how it is used to determine spin correlations,
especially in model systems of quantum magnetism. Neutron scattering and
complementary techniques have determined the extent to which antiferromagnetic
spin correlations survive in the cuprate superconductors. One experimental case
involves the ordering of spin and charge stripes. I first consider related
measurements on model compounds, such as La(2-x)Sr(x)NiO(4+d), and then discuss
the case of La(2-x)Ba(x)CuO(4). In the latter system, recent transport studies
have demonstrated that quasi-two-dimensional superconductivity coexists with
the stripe order, but with frustrated phase order between the layers. This has
led to new concepts for the coexistence of spin order and superconductivity.
While the relevance of stripe correlations to high-temperature
superconductivity remains a subject of controversy, there is no question that
stripes are an intriguing example of electron matter that results from strong
correlations.",1305.4118v1
2013-05-23,Observation of antiferromagnetic order collapse in the pressurized insulator LaMnPO,"The emergence of superconductivity in the iron pnictide and cuprate high
temperature superconductors usually accompanies the suppression of an
antiferromagnetically (AFM) ordered state in a corresponding parent compound
through the use of chemical doping or external pressure1-5. A great deal of
effort has been made to find superconductivity in Mn-based compounds6-14, which
are thought to bridge the gap between the two families of high temperature
superconductors7,15,16, but long-ranged AFM order was not successfully
suppressed via chemical doping in these investigations. Here we report the
first observation of the pressure-induced elimination of long-ranged AFM order
in LaMnPO single crystals that are iso-structural to the LaFeAsO
superconductor15,17. By combining in-situ high pressure resistance and ac
susceptibility measurements, we found that LaMnPO undergoes a crossover from an
AFM insulating to an AFM metallic state at a pressure ~20 GPa and that the
long-ranged AFM order collapses at a higher pressure ~32 GPa. Our findings are
of importance to explore potential superconductivity in Mn-based compounds and
to shed new light on the underlying mechanism of high temperature
superconductivity.",1305.5426v1
2013-05-28,Structures of cycloserine and 2-oxazolidinone probed by X-ray photoelectron spectroscopy,"The electronic structures and properties of 2-oxazolidinone and the related
compound cycloserine (CS) have been investigated using core and valence
photoelectron spectroscopy and theoretical calculations. Isomerization of the
central oxazolidine heterocycle and the addition of an amino group yields
cycloserine. Theory correctly predicts the C, N and O 1s core spectra, and
additionally we report theoretical natural bond orbital (NBO) charges. The
valence ionization energies are also in agreement with theory and previous
measurements. Although the lowest binding energy part of the spectra of the two
compounds show superficial similarities, analysis of the charge densities of
the frontier orbitals indicates substantial reorganization of the wave
functions as a result of isomerization. The Highest Occupied Molecular Orbital
of CS has leading carbonyl {\pi} character with contributions from other heavy
atoms in the molecule, while the Highest Occupied Molecular Orbital of
2-oxazolidinone has leading nitrogen, carbon and oxygen p{\pi} character. At
laboratory temperatures, CS is predicted to exist mainly as two low energy
conformers in the gas phase, separated in energy by 4.6 kJ mol-1, whereas
2-oxazolidinone is present as a single conformer in the gas phase. However the
experimental spectra do not provide proof of the presence of these
conformers.....",1305.6384v1
2013-06-14,Method of evaluating chemical shifts of X-ray emission lines in molecules and solids,"Method of evaluating chemical shifts of X-ray emission lines for sufficiently
heavy atoms (beginning from period 4 elements) in chemical compounds is
developed. This method is based on the pseudopotential model and one-center
restoration method (to reconstruct the proper electronic structure in
heavy-atom cores). The approximations of instantaneous transition and frozen
inner core spinors of the atom are used for derivation of an expression for
chemical shift as a difference between mean values of some effective operator.
The method allows one to avoid evaluating small values (chemical shifts ~$
0.01{-}1$ eV) as differences of very large values (transition energies ~
$1{-}100$ keV in various compounds). The results of our calculations of
chemical shifts for the $K\alpha_1$, $K\alpha_2$, and L transitions of the
group 14 metal cations with respect to neutral atoms are presented. The
calculations of chemical shift of $K\alpha_1$-line in the Pb-core transition
within PbO and PbF$_2$ with respect to the neutral Pb are also performed and
discussed. The accuracy of the used approximations is discussed and quality of
the performed calculations is analyzed.",1306.3424v5
2013-06-15,Wide temperature span of entropy change in first-order metamagnetic MnCo1-xFexSi,"The crystal structure and magnetic properties of MnCoxFe1-xSi (x=0-0.5)
compounds were investigated. With increasing Fe content, the unit cell changes
anisotropically and the magnetic property evolves gradually: Curie temperature
decreases continuously, the first-order metamagnetic transition from a
low-temperature helical antiferromagnetic state to a high-temperature
ferromagnetic state disappears gradually and then a spin-glass-like state and
another antiferromagnetic state emerge in the low temperature region. The Curie
transition leads to a moderate conventional entropy change. The metamagnetic
transition not only yields a larger negative magnetocaloric effect at lower
applied fields than in MnCoSi but also produces a very large temperature span
(103 K for H=5 T) of delta S(T), which results in a large refrigerant capacity.
These phenomena were explained in terms of crystal structure change and
magnetoelastic coupling mechanism. The low-cost MnCo1-xFexSi compounds are
promising candidates for near room temperature magnetic refrigeration
applications because of the large isothermal entropy change and the wide
working temperature span.",1306.3582v2
2013-06-21,Stripe Antiferromagnetic Spin Fluctuations in SrCo$_{2}$As$_{2}$,"Inelastic neutron scattering measurements of paramagnetic SrCo$_{2}$As$_{2}$
at T=5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a
wavevector of $\textbf{Q}_{\mathrm{AFM}}=(1/2,1/2,1)$ and possess a large
energy scale. These stripe spin fluctuations are similar to those found in
$A$Fe$_{2}$As$_{2}$ compounds, where spin-density wave AFM is driven by Fermi
surface nesting between electron and hole pockets separated by
$\textbf{Q}_{\mathrm{AFM}}$. SrCo$_{2}$As$_{2}$ has a more complex Fermi
surface and band structure calculations indicate a potential instability
towards either a ferromagnetic or stripe AFM ground state. The results suggest
that stripe AFM magnetism is a general feature of both iron and cobalt-based
arsenides and the search for spin fluctuation-induced unconventional
superconductivity should be expanded to include cobalt-based compounds.",1306.5174v3
2013-06-21,"Crystal, magnetic, and electronic structures, and properties of new BaMnPnF (Pn = As, Sb, Bi)","New fluoropnictides BaMnPnF with Pn = As, Sb, Bi, are synthesized by
stoichiometric reaction of elements with BaF\_2. The compounds crystallize in
the tetragonal P4/nmm (No. 129, Z = 2) space group, with the ZrCuSiAs-type
structure, as indicated by single crystal and powder X-ray diffraction results.
Electrical resistivity results indicate that Pn = As, Sb, and Bi are
semiconductors with band gaps of E\_g = 0.73 eV, E\_g = 0.48 eV and E\_g =
0.003 eV, respectively. Powder neutron diffraction reveals a G-type
antiferromagnetic order below T\_N = 338(1) K for Pn = As, and below T\_N =
272(1) K for Pn = Sb. Magnetic susceptibility increases with temperature above
100 K for all the materials. Density functional calculations also find
semiconducting antiferromagnetic compounds with strong in-plane and weaker
out-of-plane exchange coupling that may result in non-Curie Weiss behavior
above T\_N. There is strong covalency between Mn and pnictogen elements. The
ordered magnetic moments are 3.65(5) {\mu}B/Mn for Pn = As, and 3.66(3)
{\mu}B/Mn for Pn = Sb at 4 K, as refined from neutron diffraction experiments.",1306.5182v1
2013-06-28,Impact of sintering temperature on room temperature magneto-resistive and magneto-caloric properties of Pr2/3Sr1/3MnO3,"Magneto-resistive and magneto-caloric properties of polycrystalline
Pr2/3Sr1/3MnO3 have been studied as a function of sintering temperature (Ts)
between 1260-1450{\deg}C. Reitveld refinement of their X-ray diffraction (XRD)
patterns confirms their single phase crystalline structure with orthorhombic
Pbnm space group. The point of maximum value of temperature coefficient of
resistance (TCRmax) and Curie temperature (Tc) decreased slightly with Ts.
Magneto-resistance (MR) and magnetic entropy ({\Delta}SM) increased markedly
with sintering temperature. This could be attributed to the observed sharpness
of both the magnetic and resistive transitions due to better grain
connectivity. Optimum results are obtained for the sample with Ts =
1400{\deg}C. MR at Tc of the same is found to be as large as 32% at 1T and 58%
at 5T magnetic fields. The maximum entropy change ({\Delta}SMmax) near its Tc
is 2.3Jkg-1K-1 and 7.8 Jkg-1K-1 upon 1T and 5T fields change respectively.
These characteristics [MR (32% 1T, 58% 5T) and reasonable change in magnetic
entropy (7.8Jkg-1K-1, 5T)] generate possibility that the optimized compound can
be used as a potential magnetic refrigerant close to room temperature.",1306.6792v2
2013-07-03,Manifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds,"We present detailed multi frequency resonant Raman measurements of potassium
graphite intercalation compounds (GICs). From a well controlled and consecutive
in-situ intercalation and high temperature de-intercalation approach the
response of each stage up to stage VI is identified. The positions of the G and
2D lines as a function of staging depend on the charge transfer from K to the
graphite layers and on the lattice expansion. Ab-initio calculations of the
density and the electronic band-structure demonstrate that most (but not all)
of the transferred charge remains on the graphene sheets adjacent to the
intercalant layers. This leads to an electronic decoupling of these ""outer""
layers from the ones sandwiched between carbon layers and consequently to a
decoupling of the corresponding Raman spectra. Thus higher stage GICs offer the
possibility to measure the vibrations of single, double, and multi-layer
graphene under conditions of biaxial strain. This strain can additionally be
correlated to the in-plane lattice constants of GICs determined by x-ray
diffraction. The outcome of this study demonstrates that Raman spectroscopy is
a very powerful tool to identify local internal strain in pristine and weakly
charged single and few-layer graphene and their composites, yielding even
absolute lattice constants.",1307.1118v1
2013-07-08,Evolution of Magnetism in Single-Crystal Honeycomb Iridates,"We report the successful synthesis of single-crystals of the layered iridate,
(Na$_{1-x}$Li$_{x}$)$_2$IrO$_3$, $0\leq x \leq 0.9$, and a thorough study of
its structural, magnetic, thermal and transport properties. The new compound
allows a controlled interpolation between Na$_2$IrO$_3$ and Li$_2$IrO$_3$,
while maintaing the novel quantum magnetism of the honeycomb Ir$^{4+}$ planes.
The measured phase diagram demonstrates a dramatic suppression of the N\'eel
temperature, $T_N$, at intermediate $x$ suggesting that the magnetic order in
Na$_2$IrO$_3$ and Li$_2$IrO$_3$ are distinct, and that at $x\approx 0.7$, the
compound is close to a magnetically disordered phase that has been sought after
in Na$_2$IrO$_3$ and Li$_2$IrO$_3$. By analyzing our magnetic data with a
simple theoretical model we also show that the trigonal splitting, on the
Ir$^{4+}$ ions changes sign from Na$_2$IrO$_3$ and Li$_2$IrO$_3$, and the
honeycomb iridates are in the strong spin-orbit coupling regime, controlled by
$\jeff=1/2$ moments.",1307.2212v3
2013-07-09,Neutron diffraction evidence for kinetic arrest of first-order magneto-structural phase transitions in some functional magnetic materials,"Neutron diffraction measurements, performed in presence of an external
magnetic field, have been used to show structural evidence for the kinetic
arrest of the first-order phase transition from (i) the high temperature
austenite phase to the low temperature martensite phase in the magnetic shape
memory alloy Ni37Co11Mn42.5Sn9.5, (ii) the higher temperature ferromagnetic
phase to the lower temperature antiferromagnetic phase in the half-doped charge
ordered compound La0.5Ca0.5MnO3 and (iii) the formation of a glass-like
arrested state (GLAS). The CHUF (cooling and heating under unequal fields)
protocol has been used to establish phase coexistence of metastable and
equilibrium states of GLAS and also to demonstrate the devitrification of the
arrested metastable states in the neutron diffraction patterns. We also explore
the field-temperature (H,T) phase diagram for the two compounds, which depicts
the kinetic arrest line TK(H). TK is seen to increase as H increases.",1307.2486v3
2013-07-30,PAC study of the static and dynamic aspects of metal atom inside C60 cage,"30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on
preformed target of C60 with the thickness of 1 mg/cm2. Endofullerene
compounds, viz.,111mCd@C60 and 199mHg@C60 formed during implantation were
separated by filtration through micropore filter paper followed by solvent
extraction. Dried samples of the endofullerene compounds were counted for the
coincidence for the 151-245 keV cascade of 111mCd and 374-158 keV cascade for
199mHg for the TDPAC measurement on a six LaBr3 detector system coupled with
digital electronics. The results indicate a single site occupied by the Cd atom
in the fullerene cage with fast relaxation component which means that the Cd
atom does move inside the cage at room temperature. The quadrupole interaction
frequency and asymmetry parameter of the Cd atom occupying the site in C60 are
WQ=8.14(42) Mrad/s and eta= 0.42(9) respectively with a site population of 28%.
Fast relaxation constant is 0.003 ns-1 with a site contribution of 72%. On the
other hand, Hg atom has two static sites of quadrupole frequencies,
WQ1=281.60(16.9) Mrad/s and WQ2=202.30(22.7) Mrad/s. Respective asymmetry
parameters are eta1=0.1(1) and eta2=0.2(1). The static components have a
contribution of 40% with the rest 60% coming from the fast relaxing component.",1307.7818v1
2013-08-05,Ab initio investigation of the exchange interactions in Bi$_2$Fe$_4$O$_9$: The Cairo pentagonal lattice compound,"We present the \emph{ab initio} calculation of the electronic structure and
magnetic properties of Bi$_2$Fe$_4$O$_9$. This compound crystallizes in the
orthorhombic crystal structure with the Fe$^{3+}$ ions forming the Cairo
pentagonal lattice implying strong geometric frustration. The neutron
diffraction measurements reveal nearly orthogonal magnetic configuration, which
at first sight is rather unexpected since it does not minimize the total energy
of the pair of magnetic ions coupled by the Heisenberg exchange interaction.
Here we calculate the electronic structure and exchange integrals of Bi2Fe4O9
within the LSDA+U method. We obtain three different in-plane (J3=36 K, J4=73 K,
J5=23 K) and two interplane (J1=10 K, J2=12 K) exchange parameters. The derived
set of exchange integrals shows that the realistic description of Bi2Fe4O9
needs a more complicated model than the ideal Cairo pentagonal lattice with
only two exchange parameters in the plane. However, if one takes into account
only two largest exchange integrals, then according to the ratio x\equiv
J3/J4=0.49<\sqrt{2} (a critical parameter for the ideal Cairo pentagonal
lattice, see. Ref.~1) the ground state should be the orthogonal magnetic
configuration in agreement with experiment. The microscopic origin of different
exchange interactions is also discussed.",1308.0927v1
2013-08-24,Spin-chain magnetism and uniform Dzyaloshinsky-Moriya anisotropy in BaV$_3$O$_8$,"We report on the microscopic magnetic model of a spin-1/2 magnet
BaV$_3$O$_8$. In contrast to earlier phenomenological analysis, our
density-functional band-structure calculations combined with quantum
Monte-Carlo simulations establish a relatively simple and non-frustrated model
of weakly coupled spin chains with the intrachain coupling of $J\sim$ 38 K and
the Neel temperature of $T_N\sim$ 6 K, both in excellent agreement with the
experiment. The intrachain coupling between the spin-1/2 V$^{+4}$ ions takes
place via two contiguous V$^{+5}$O$_4$ tetrahedra forming an extended
superexchange pathway with the V$^{+4}$--V$^{+4}$ distance of 7.44 A.
Surprisingly, this pathway is preferred over shorter V$^{+4}$--V$^{+4}$
connections, owing to peculiarities in the interacting orbitals of the magnetic
V$^{+4}$ ions and V$^{+5}$ ions that are non-magnetic, but feature low-lying
$3d$ states contributing to the superexchange process. We also note that the
crystal structure of BaV$_3$O$_8$ supports the long-sought uniform arrangement
of Dzyaloshinsky-Moriya (DM) couplings on a spin-1/2 chain. While our
calculations yield only a weak DM anisotropy in BaV$_3$O$_8$, the crystal
structure of this compound provides a suitable framework for the search of spin
chains with the uniform DM anisotropy in other compounds of the vanadate
family.",1308.5305v2
2013-08-28,Strong electronic correlations in iron pnictides: Comparison of the optical spectra for BaFe2As2-related compounds,"We carried out combined transport and optical measurements for BaFe2As2 and
five isostructural transition-metal (TM) pnictides. The low-energy optical
conductivity spectra of these compounds are, to a good approximation,
decomposed into a narrow Drude (coherent) component and an incoherent
component. The iron arsenides, BaFe2As2 and KFe2As2, are distinct from other
pnictides in their highly incoherent charge dynamics or bad metallic behavior
with the coherent Drude component occupying a tiny fraction of the low-energy
spectral weight. The fraction of the coherent spectral weight or the degree of
coherence is shown to be well correlated with the TM-pnictogen bond angle and
the electron filling of TM 3d orbitals, which are measures of the strength of
electronic correlations. The iron arsenides are thus strongly correlated
systems, and the doping into BaFe2As2 controls the strength of electronic
correlations. This naturally explains a remarkable asymmetry in the charge
dynamics of electron- and hole-doped systems, and the unconventional
superconductivity appears to emerge when the correlations are fairly strong.",1308.6113v1
2013-10-04,The Gaussian Two-way Diamond Channel,"We consider two-way relaying in a Gaussian diamond channel, where two
terminal nodes wish to exchange information using two relays. A simple baseline
protocol is obtained by time-sharing between two one-way protocols. To improve
upon the baseline performance, we propose two compute-and-forward (CF)
protocols: Compute-and-forward Compound multiple access channel (CF-CMAC) and
Compute-and-forward-Broadcast (CF-BC). These protocols mix the two flows
through the two relays and achieve rates better than the simple time-sharing
protocol. We derive an outer bound to the capacity region that is satisfied by
any relaying protocol, and observe that the proposed protocols provide rates
close to the outer bound in certain channel conditions. Both the CF-CMAC and
CF-BC protocols use nested lattice codes in the compute phases. In the CF-CMAC
protocol, both relays simultaneously forward to the destinations over a
Compound Multiple Access Channel (CMAC). In the simpler CF-BC protocol's
forward phase, one relay is selected at a time for Broadcast Channel (BC)
transmission depending on the rate-pair to be achieved. We also consider the
diamond channel with direct source-destination link and the diamond channel
with interfering relays. Outer bounds and achievable rate regions are compared
for these two channels as well. Mixing of flows using the CF-CMAC protocol is
shown to be good for symmetric two-way rates.",1310.1153v1
2013-10-09,Theory of off-normal incidence ion sputtering of surfaces of type A_xB_{1-x} and a conformal map method for stochastic continuum models,"Bradley et. al. recently provided an explanation of nanodot and defect-free
ordered ripple production from binary compounds, for normal and oblique
incidence ion sputtering respectively, by the inclusion of the effect of the
preferential sputtering of one type of atom relative to the other type on the
surfaces of binary compounds. In this paper, we propose an extended anisotropic
model of such surfaces of type AxB1-x that addresses anisotropy in the
variations of the specie-composition as well. We show that this model gives the
anisotropic Cuerno-Barabasi model as x approaches unity, and analyze the
general properties of the model. Further, the complexity of the solutions of
non-linear higher-order differential equations in general has led to the
creation of great number of highly technical and computationally intensive
numerical schemes. We introduce a simple conformal map method which allows for
a fast and accurate simulation of the dynamical evolution of ion-sputtered
surfaces based on any stochastic continuum model. An optimization algorithm for
an efficient application of the scheme is also introduced. In this scheme the
noise term has a physical meaning which allows one to go beyond the usual white
noise approximation by actually being able to assign physical parameters to it.",1310.2445v3
2013-10-10,"Magnetization non-rational quasi-plateau and spatially modulated spin order in the model of the single-chain magnet, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN H_2O","Using the exact solution in terms of the generalized classical transfer
matrix method we presented a detailed analysis of the magnetic properties and
ground state structure of the simplified model of the single-chain magnet,
trimetallic coordination polymer compound, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN
H_2O is N,N'-propylenebis(3-methoxysalicylideneiminato). Due to appearance of
highly anisotropic Dy3+ ion this material is an unique example of the
one-dimensional magnets with Ising and Heisenberg bonds, allowing exact
statistical-mechanical treatment. We found two zero-temperature ground states
corresponding to different part of the magnetization curve of the material. The
zero-filed ground state is shown to be an antiferromagnetic configuration with
spatial modulation of the local Dy3+(which is proven to posses well defined
Ising like properties due two large anisotropy of g-factors) and composite
S=1/2 spin of the quantum spin trimer Cu-Mo-Cu in the form
""up""-""down""-""down""-""up"". Another important feature of this compound is the
appearance of the quasi-plateau at non rational value of magnetization due to
difference of the g-factors of the Cu- and Mo-ion in quantum spin trimers. The
quasi-plateau is an almost horizontal part of the magnetization curve where the
corresponding zero-temperature ground state of the chain demonstrate slow but
monotonous dependence of the magnetization on the external magnetic field,
while the $z$-projection of the total spin is constant.",1310.2811v2
2013-10-28,Electronic Structure Reconstruction across the Antiferromagnetic Transition in TaFe$_{1.23}$Te$_3$ Spin Ladder,"With angle-resolved photoemission spectroscopy, we studied the electronic
structure of TaFe$_{1.23}$Te$_3$, which is a two-leg spin ladder compound with
a novel antiferromagnetic ground state. Quasi-two-dimensional Fermi surface is
observed, indicating sizable inter-ladder hopping, which would facilitate the
in-plane ferromagnetic ordering through double exchange interactions. Moreover,
an energy gap is not observed at the Fermi surface in the antiferromagnetic
state. Instead, the shifts of various bands have been observed. Combining these
observations with density-functional-theory calculations, we propose that the
large scale reconstruction of the electronic structure, caused by the
interactions between the coexisting itinerant electrons and local moments, is
most likely the driving force behind the magnetic transition.
TaFe$_{1.23}$Te$_3$ thus provides a simpler system that contains similar
ingredients as the parent compounds of iron-based superconductors, which yet
could be readily modeled and understood.",1310.7348v1
2013-10-30,Matter-wave interference with particles selected from a molecular library with masses exceeding 10000 amu,"The quantum superposition principle, a key distinction between quantum
physics and classical mechanics, is often perceived as a philosophical
challenge to our concepts of reality, locality or space-time since it contrasts
our intuitive expectations with experimental observations on isolated quantum
systems. While we are used to associating the notion of localization with
massive bodies, quantum physics teaches us that every individual object is
associated with a wave function that may eventually delocalize by far more than
the body's own extension. Numerous experiments have verified this concept at
the microscopic scale but intuition wavers when it comes to delocalization
experiments with complex objects. While quantum science is the uncontested
ideal of a physics theory, one may ask if the superposition principle can
persist on all complexity scales. This motivates matter-wave diffraction and
interference studies with large compounds in a three-grating interferometer
configuration which also necessitates the preparation of high-mass nanoparticle
beams at low velocities. Here we demonstrate how synthetic chemistry allows us
to prepare libraries of fluorous porphyrins which can be tailored to exhibit
high mass, good thermal stability and relatively low polarizability, which
allows us to form slow thermal beams of these high-mass compounds, which can be
detected in electron ionization mass spectrometry. We present successful
superposition experiments with selected species from these molecular libraries
in a quantum interferometer, which utilizes the diffraction of matter waves at
an optical phase grating. We observe high-contrast quantum fringe patterns with
molecules exceeding a mass of 10 000 amu and 810 atoms in a single particle.",1310.8343v1
2013-11-04,Interplay of many-body and single-particle interactions in iridates and rhodates,"Motivated by recent experiments exploring the spin-orbit-coupled magnetism in
$4d$- and $5d$-band transition metal oxides, we study magnetic interactions in
Ir- and Rh-based compounds. In these systems, the comparable strength of
spin-orbit coupling (SOC), crystal field splitting (CF) and Coulomb and Hund's
coupling leads to a rich variety of magnetic exchange interactions, leading to
new types of ground states. Using a strong coupling approach, we derive
effective low-energy super-exchange Hamiltonians from the multi-orbital Hubbard
model by taking full account of the Coulomb and Hund's interactions in the
intermediate states. We find that in the presence of strong SOC and lattice
distortions the super-exchange Hamiltonian contains various kinds of magnetic
anisotropies.
  Here we are primarily interested in the magnetic properties of Sr$_2$IrO$_4$
and Sr$_2$Ir$_{1-x}$Rh$_x$O$_4$ compounds. We perform a systematic study of how
magnetic interactions in these systems depend on the microscopic parameters and
provide a thorough analysis of the resulting magnetic phase diagram. Comparison
of our results with experimental data shows good agreement. Finally, we discuss
the parameter space in which the spin-flop transition in Sr$_2$IrO$_4$,
experimentally observed under pressure, can be realized.",1311.0852v2
2013-11-06,Electronic topological transition in LaSn$_3$ under pressure,"The electronic structure, Fermi surface and elastic properties of the
iso-structural and iso-electronic LaSn$_3$ and YSn$_3$ intermetallic compounds
are studied under pressure within the framework of density functional theory
including spin-orbit coupling. The LaSn$_3$ Fermi surface consists of two
sheets, of which the second is very complex. Under pressure a third sheet
appears around compression $V/V_0=0.94$, while a small topology change in the
second sheet is seen at compression $V/V_0=0.90$. This may be in accordance
with the anomalous behaviour in the superconducting transition temperature
observed in LaSn$_3$, which has been suggested to reflect a Fermi surface
topological transition, along with a non-monotonic pressure dependence of the
density of states at the Fermi level. The same behavior is not observed in
YSn$_3$, the Fermi surface of which already includes three sheets at ambient
conditions, and the topology remains unchanged under pressure. The reason for
the difference in behaviour between LaSn$_3$ and YSn$_3$ is the role of
spin-orbit coupling and the hybridization of La - $4f$ states with the Sn - $p$
states in the vicinity of the Fermi level, which is well explained using the
band structure calculation. The elastic constants and related mechanical
properties are calculated at ambient as well as at elevated pressures. The
elastic constants increase with pressure for both compounds and satisfy the
conditions for mechanical stability under pressure.",1311.1361v1
2013-11-12,Crystal growth and characterization of Haldane chain compound Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$,"The bulk single crystals of $S = 1$ chain compound
Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$ are grown by using a slow evaporation
method at a constant temperature and a slow cooling method. It is found that
the optimum condition of growing large crystals is via slow evaporation at 25
$^\circ$C using 0.015 mol Ni(ClO$_4$)$_2$$\cdot$6H$_2$O, 0.015 mol NaNO$_2$,
and 0.03 mol 1,3-propanediamine liquid dissolved into 30 ml aqueous solvent.
High-quality crystals with size up to $18 \times 7.5 \times 5$ mm$^3$ are
obtained. The single crystals are characterized by measurements of x-ray
diffraction, magnetic susceptibility, specific heat and thermal conductivity.
The susceptibilities along three crystallographic axes are found to exhibit
broad peaks at $\sim 55$ K, and then decrease abruptly to zero at lower
temperatures, which is characteristic of a Haldane chain system. The specific
heat and the thermal conductivity along the $c$ axis can be attributed to the
simple phononic contribution and are analyzed using the Debye approximation.",1311.2682v1
2013-11-19,Compound cryopump for fusion reactors,"We reconsider an old idea: a three-stage compound cryopump for use in fusion
reactors such as DEMO. The helium ""ash"" is adsorbed on a 4.5 K charcoal-coated
surface, while deuterium and tritium are adsorbed at 15-22 K on a second
charcoal-coated surface. The helium is released by raising the first surface to
~30 K. In a separate regeneration step, deuterium and tritium are released at
~110 K. In this way, the helium can be pre-separated from other species. In the
simplest design, all three stages are in the same vessel, with a single valve
to close the pump off from the tokamak during regeneration. In an alternative
design, the three stages are in separate vessels, connected by valves, allowing
the stages to regenerate without interfering with each other. The inclusion of
the intermediate stage would not affect the overall pumping speed
significantly. The downstream exhaust processing system could be scaled down,
as much of the deuterium and tritium could be returned directly to the reactor.
This could reduce the required tritium reserve by almost 90%. We used a
well-established free Direct Simulation Monte Carlo (DSMC) code, DS2V. At very
high upstream densities (~1020 molecules/m3 and above) the flow into the pump
is choked. Enlarging the aperture is the only way to increase the pumping speed
at high densities. Ninety percent of the deuterium and tritium is successfully
trapped at 15 K (assuming that the sticking coefficient is 80-100% on the 15-22
K surface). On the other hand, the remaining 10% still exceeds the small amount
of helium in the gas input.",1311.4689v1
2013-11-25,Structural and Dielectric Characterization on Multiferroic xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 Particulate Composite,"We have carried out the powder x-ray diffraction and dielectric studies on
multiferroic particulate composite xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 with
x=0.15, 0.30, 0.45, 0.60, 0.75 and 0.90 to explore the structural and
ferroelectric properties. A conventional double sintering method was used to
prepare the xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 composites. The structure of
one of the component Ni0.9Zn0.1Fe2O4 is spinel cubic with space group Fd3m,
while the other component PbZr0.52Ti0.48O3 is selected around the morphotropic
phase boundary region in which the tetragonal and monoclinic phases with space
group P4mm and Cm coexist respectively. We have carried out Rietveld refinement
of the structure to check the formation of ideal composites with separate
ferroelectric and ferrite phases. Even though the structural characterization
does not reveal the formation of any new phase due to reaction between the two
components of the composite during sintering, the tetragonality of the
PbZr0.52Ti0.48O3 continuously decreases with increasing the ferrite fraction
while the lattice parameter of ferrite phase increases with increasing fraction
of the ferroelectric phase. Similarly, the dielectric study reveals clear shift
in the ferroelectric to paraelectric phase transition temperature of
PbZr0.52Ti0.48O3 during composite formation suggesting that part of Ni2+, Zn2+/
Fe3+ ions are diffusing at the B-site of PbZr0.52Ti0.48O3 replacing Ti4+, which
in turn decreases its transition temperature. Scanning electron micrograph of
sintered pellet surface confirms the presence of two types of particle
morphology in the particulate composite, corresponding to ferrite and
ferroelectric phases.",1311.6217v2
2013-12-11,Structure and thermodynamic properties of a weakly-coupled antiferromagnetic spin-1/2 chain compound (C5H12N)CuBr3,"Single crystals of a metal organic complex \ce{(C5H12N)CuBr3} (\ce{C5H12N} =
piperidinium, pipH for short) have been synthesized and the structure was
determined by single-crystal X-ray diffraction. \ce{(pipH)CuBr3} crystallizes
in the monoclinic group $C$2/$c$. Edging-sharing \ce{CuBr5} units link to form
zigzag chains along the $c$ axis and the neighboring Cu(II) ions with spin-1/2
are bridged by bi-bromide ions. Magnetic susceptibility data down to 1.8 K can
be well fitted by the Bonner-Fisher formula for antiferromagnetic spin-1/2
chain, giving the intrachain magnetic coupling constant $J$ $\sim$ 17 K. At
zero field, \ce{(pipH)CuBr3} shows three-dimensional (3D) order below $T_N$ =
1.68 K. Calculated by the mean-field theory, the interchain coupling constant
$J'$ = 0.65 K is obtained and the ordered magnetic moment $m_0$ is about 0.20
$\mu_B$. This value of $m_0$ makes \ce{(pipH)CuBr3} a rare compound suitable to
study the dimensional crossover problem in magnetism, since both 3D order and
one-dimensional (1D) quantum fluctuations are prominent. In addition, specific
heat measurements reveal two successive magnetic transitions with lowering
temperature when external field $H \geq$ 3 T is applied along the $a'$ axis.
The $H$ - $T$ phase diagram of \ce{(pipH)CuBr3} is roughly constructed. The
interplay between exchange interactions, dimensionality, Zeeman energy and
possible Dzyaloshinkii-Moriya interaction should be the driving force for the
multiple phase transitions.",1312.3209v1
2013-12-17,Longitudinal Excitations in Bipartite and Hexagonal Antiferromagnetic Spin Lattices,"Based on our recently proposed magnon-density-waves using the microscopic
many-body approach, we investigate the longitudinal excitations in quantum
antiferromagnets by including the second order corrections in the large-$s$
expansion. The longitudinal excitation spectra for a general spin quantum
number using the antiferromagnetic Heisenberg Hamiltonian are obtained for
various spin lattice models. For bipartite lattice models, we find that the
numerical results for the energy gaps for the longitudinal modes at $q\to0$ and
the magnetic ordering wavevector $\bf Q$ are reduced by about $40-50\%$ after
including the second order corrections. Thus, our estimate of the energy gaps
for the quasi-one-dimensional (quasi-1D) antiferromagnetic compound KCuF$_3$ is
in better agreement with the experimental result. For the quasi-1D
antiferromagnets on hexagonal lattices, the full excitation spectra of both the
transverse modes (i.e., magnons) and the longitudinal modes are obtained as
functions of the nearest-neighbor coupling and the anisotropy constants. We
find two longitudinal modes due to the non-collinear nature of the triangular
antiferromagnetic order, similar to that of the phenomenological field theory
approach by Affleck. We compare our results for the longitudinal energy gaps at
the magnetic wavevectors with the experimental results for several
antiferromagnetic compounds with both integer and non-integer spin quantum
numbers, and also find good agreement after the higher-order contributions are
included in our calculations.",1312.4929v1
2013-12-24,Phonon and magnetic dimer excitations in Fe-based S=2 spin ladder compound BaFe$_2$Se$_2$O,"Raman scattering spectra of new Fe-based S=2 spin ladder compound
BaFe$_2$Se$_2$O are measured in a temperature range between 15 K and 623 K. All
six A$_{1g}$ and two B$_{1g}$ Raman active modes of BaFe$_2$Se$_2$O, predicted
by the factor-group analysis, have been experimentally observed at energies
that are in a rather good agreement with the lattice dynamics calculation. The
antiferromagnetic long-range spin ordering in BaFe$_2$Se$_2$O below $T_N$=240 K
leaves a fingerprint both in the A$_{1g}$ and B$_{1g}$ phonon mode linewidth
and energy. In the energy range between 400 and 650 cm$^{-1}$ we have observed
magnetic excitation related structure in the form of magnon continuum, with the
peaks corresponding to the singularities in the one dimensional density of
magnon states. The onset value of magnetic continuum (2$\Delta_{S}$) is found
at about 437 cm$^{-1}$ at 15 K. The magnetic continuum disappears at about 623
K, which lead us to conclude that the short-range magnetic ordering in
BaFe$_2$Se$_2$O exists apparently up to 2.6$T_N$.",1312.6844v1
2013-12-30,UHg_{3} - A Heavy Fermion Antiferromagnet Similar to U_{2}Zn_{17} and UCd_{11},"Heavy Fermion physics deals with the ground state formation and interactions
in f-electron materials where the electron effective masses are extremely
large, more than 100 times the rest mass of an electron. The details of how the
f-electrons correlate at low temperature to become so massive lacks a coherent
theory, partially because so few materials display this heavy behavior and thus
global trends remain unclear. UHg_{3} is now found experimentally to be a heavy
Fermion antiferromagnet, just as are all the other U_{x}M_{y} compounds with
the metal M being in column II B (filled d electron shells) in the periodic
table (Zn/Cd/Hg) and the spacing between Uranium ions being greater than the
Hill limit of 3.5 Angstroms. This result that, independent of the structure of
these U_{x}M_{y}, M=Zn/Cd/Hg, compounds and independent of the value of their
Uranium Uranium spacings (ranging from 4.39 to 6.56 Angstroms), all exhibit
heavy Fermion antiferromagnetism, is a clear narrowing of the parameters
important for understanding the formation of this ground state. The sequence of
antiferromagnetic transition temperatures, T_{Neel}, of 9.7 K, 5.0 K, and 2.6 K
for U_{x}M_{y} as the metal M varies down column II B (Zn/Cd/Hg) indicates an
interesting regularity for the antiferromagnetic coupling strength.",1401.0043v1
2014-02-03,Hyperfine Interactions in MnAs studied by Perturbed Angular Correlations of $γ$-Rays using the probe $^{77}$Br$\rightarrow^{77}$Se and first principles calculations for MnAs and other Mn pnictides,"The MnAs compound shows a first-order transition at T$_C\approx42$ C, and a
second-order transition at T$_t\approx120$ C. The first-order transition, with
structural (hexagonal-orthorhombic), magnetic (FM-PM) and electrical
conductivity changes, is associated to magnetocaloric, magnetoelastic, and
magnetoresistance effects. We report a study in a large temperature range from
$-196$ up to $140$ C, using the $\gamma-\gamma$ perturbed angular correlations
method with the radioactive probe $^{77}$Br$\rightarrow^{77}$Se, produced at
the ISOLDE-CERN facility. The electric field gradients and magnetic hyperfine
fields are determined across the first- and second-order phase transitions
encompassing the pure and mixed phase regimes in cooling and heating cycles.
The temperature irreversibility of the 1st order phase transition is seen
locally, at the nanoscopic scale sensitivity of the hyperfine field, by its
hysteresis, detailing and complementing information obtained with macroscopic
measurements (magnetization and X-ray powder diffraction). To interpret the
results, hyperfine parameters were obtained with first-principles
spin-polarized density functional calculations using the generalized gradient
approximation with the full potential (L)APW+lo method (\textsc{Wien2k} code)
by considering the Se probe at both Mn and As sites. A clear assignment of the
probe location at the As site is made and complemented with the calculated
densities of states and local magnetic moments. We model electronic and
magnetic properties of the chemically similar MnSb and MnBi compounds,
complementing previous calculations.",1402.0352v1
2014-02-21,"The Compound Class of Linear Failure Rate-Power Series Distributions: Model, Properties and Applications","We introduce in this paper a new class of distributions which generalizes the
linear failure rate (LFR) distribution and is obtained by compounding the LFR
distribution and power series (PS) class of distributions. This new class of
distributions is called the linear failure rate-power series (LFRPS)
distributions and contains some new distributions such as linear failure rate
geometric (LFRG) distribution, linear failure rate Poisson (LFRP) distribution,
linear failure rate logarithmic (LFRL) distribution, linear failure rate
binomial (LFRB) distribution and Raylight-power series (RPS) class of
distributions. Some former works such as exponential-power series (EPS) class
of distributions, exponential geometric (EG) distribution, exponential Poisson
(EP) distribution and exponential logarithmic (EL) distribution are special
cases of the new proposed model.
  The ability of the LFRPS class of distributions is in covering five possible
hazard rate function i.e., increasing, decreasing, upside-down bathtub
(unimodal), bathtub and increasing-decreasing-increasing shaped. Several
properties of the LFRPS distributions such as moments, maximum likelihood
estimation procedure via an EM-algorithm and inference for a large sample, are
discussed in this paper. In order to show the flexibility and potentiality of
the new class of distributions, the fitted results of the new class of
distributions and some its submodels are compared using a real data set.",1402.5282v1
2014-02-24,Observation of strong-coupling pairing with weakened Fermi-surface nesting at optimal hole doping in Ca$_{0.33}$Na$_{0.67}$Fe$_2$As$_2$,"We report an angle-resolved photoemission investigation of optimally-doped
Ca$_{0.33}$Na$_{0.67}$Fe$_2$As$_2$. The Fermi surface topology of this compound
is similar to that of the well-studied Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$
material, except for larger hole pockets resulting from a higher hole
concentration per Fe atoms. We find that the quasi-nesting conditions are
weakened in this compound as compared to Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. As
with Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ though, we observe nearly isotropic
superconducting gaps with Fermi surface-dependent magnitudes. A small variation
in the gap size along the momentum direction perpendicular to the surface is
found for one of the Fermi surfaces. Our superconducting gap results on all
Fermi surface sheets fit simultaneously very well to a global gap function
derived from a strong coupling approach, which contains only 2 global
parameters.",1402.5875v1
2014-03-06,Spin-orbital Entangled Molecular $j_{\rm eff}$ States in Lacunar Spinel Compounds,"The entanglement of the spin and orbital degrees of freedom through the
spin-orbit coupling has been actively studied in condensed matter physics. In
several iridium-oxide systems, the spin-orbital entangled state, identified by
the effective angular momentum $j_{\rm eff}$, can host novel quantum phases
with the help of electron correlations. Here, we show that a series of lacunar
spinel compounds, Ga$M_4X_8$ ($M$ = Nb, Mo, Ta, and W and $X$ = S, Se, and Te),
gives rise to a $\textit{molecular}$ $j_{\rm eff}$ state as a new spin-orbital
composite on which the low energy effective Hamiltonian is based. A wide range
of electron correlations is accessible by tuning the bandwidth under external
and/or chemical pressure, enabling us to investigate the interesting
cooperation between spin-orbit coupling and electron correlations. As
illustrative examples, a two-dimensional topological insulating phase and an
anisotropic spin Hamiltonian are investigated in the weak and strong coupling
regimes, respectively. Our finding can provide an ideal platform for exploring
$j_{\rm eff}$ physics and the resulting emergent phenomena.",1403.1358v2
2014-03-24,Bipartite magnetic parent phases in the iron-oxypnictide superconductor,"High-temperature (high-$T_{\rm c}$) superconductivity appears as a
consequence of the carrier-doping of an undoped parent compound exhibiting
antiferromagnetic order; thereby, ground-state properties of the parent
compound are closely relevant to the superconducting state. On the basis of the
concept, a spin-fluctuation has been addressed as an origin of pairing of the
superconducting electrons in cuprates. Whereas, there is growing interest in
the pairing mechanism such as an unconventional spin-fluctuation or an advanced
orbital-fluctuation due to the characteristic multi-orbital system in
iron-pnictides. Here, we report the discovery of an antiferromagnetic order as
well as a unique structural transition in electron-overdoped
LaFeAsO$_{1-x}$H$_x$ ($x$ ~ 0.5), whereby another parent phase was uncovered,
albeit heavily doped. The unprecedented two-dome superconducting phases
observed in this material can be interpreted as a consequence of the
carrier-doping starting from the original at $x\sim0$ and advanced at
$x\sim0.5$ parent phases toward the intermediate region. The bipartite parent
phases with distinct physical properties in the second magnetic phase provide
us with an interesting example to illustrate the intimate interplay among the
magnetic interaction, structural change and orbital degree of freedom in
iron-pnictides.",1403.6021v1
2014-03-31,A Pre-Docking Filter Based on Image Recognition,"Molecular docking is a central method in the computer-based screening of
compound libraries as a part of the rational approach to drug design. Although
the method has proved its competence in predicting binding modes correctly, its
inherent complexity puts high demands on computational resources. Moreover the
chemical space to be screened is prohibitively large. Therefore the application
of filtering prior to docking is a promising concept. We implemented a
pre-docking filter based on the tangent distance algorithm originally conceived
for optical character recognition. The challenging transfer of the method from
two-dimensional to three-dimensional data was achieved by representing the
molecular structure by a set of density maps extracted from different views of
the compound. Additionally, our program applies a binary classification using
principal component analysis. Ligand and binding pocket are aligned according
to their centroidal axes, enabling a size-based filtering for the purpose of
enriching the dataset regarding ligands before docking. The evaluation of our
program via redocking produced RMSD values between 8{\AA} and 25{\AA},
indicating that the tangent distance approach is not suited for optimizing the
orientation of a ligand and binding pocket. Investigating probable explanations
lead to the conclusion that a likely cause for these results is the method's
known inability to approximate large transformations. A validation of the
principal component analysis alone performed better: Tests on a dataset of 170
ligands and 6,435 decoys yielded a sensitivity of 0.81, while keeping the
runtime within a reasonable timeframe (1 to 4 seconds). The dataset's
enrichment increased from 2.64% to 2.82%.",1403.8072v1
2014-04-01,Magnetic states of the five-orbital Hubbard model for one-dimensional iron-based superconductors,"The magnetic phase diagrams of models for quasi one-dimensional compounds
belonging to the iron-based superconductors family are presented. The
five-orbital Hubbard model and the real-space Hartree-Fock approximation are
employed, supplemented by density functional theory to obtain the hopping
amplitudes. Phase diagrams are constructed varying the Hubbard $U$ and Hund $J$
couplings and at zero temperature. The study is carried out at electronic
density (electrons per iron) $n = 5.0$, which is of relevance for the already
known material TlFeSe$_2$, and also at $n = 6.0$, where representative
compounds still need to be synthesized. At $n = 5.0$ there is a clear dominance
of staggered spin order along the chain direction. At $n = 6.0$ and the
realistic Hund coupling $J/U = 0.25$, the phase diagram is far richer including
a variety of ``block'' states involving ferromagnetic clusters that are
antiferromagnetically coupled, in qualitative agreement with recent Density
Matrix Renormalization Group calculations for the three-orbital Hubbard model
in a different context. These block states arise from the competition between
ferromagnetic order (induced by double exchange, and prevailing at large $J/U$)
and antiferromagnetic order (dominating at small $J/U$). The density of states
and orbital compositions of the many phases are also provided.",1404.0069v1
2014-04-15,Superconductivity at 25K under hydrostatic pressure for FeTe0.5Se0.5 superconductor,"We report the impact of hydrostatic pressure on the superconductivity and
normal state resistivity of FeTe0.5Se0.5 superconductor. At the ambient
pressure the FeTe0.5Se0.5 compound shows the superconducting transition
temperature Tconset at above 13K and TcR=0 at 11.5K. We measure pressure
dependent resistivity from 250K to 5K, which shows that the normal state
resistivity increases initially for the applied pressures of up to 0.55GPa and
then the same is decreased monotonically with increasing pressure of up to
1.97GPa. On the other hand the superconducting transition temperatures (Tconset
and TcR=0) increase monotonically with increasing pressure. Namely the Tconset
increases from 13K to 25K and TcR=0 from 11.5K to 20K for the pressures range
of 0-1.97GPa. Our results suggest that superconductivity in this class of
Fe-based compounds is very sensitive to pressure as the estimated pressure
coefficient dTc(onset)/dP is 5.8K/GPa. It may be suggested that FeTe0.5Se0.5
superconductor is a strong electron correlated system. The enhancement of Tc
with applying pressure is mainly attributed to an increase of charge carriers
at Fermi surface.",1404.3812v3
2014-04-25,An Information Theoretic Approach to Secret Sharing,"A novel information theoretic approach is proposed to solve the secret
sharing problem, in which a dealer distributes one or multiple secrets among a
set of participants that for each secret only qualified sets of users can
recover it by pooling their shares together while non-qualified sets of users
obtain no information about the secret even if they pool their shares together.
While existing secret sharing systems (implicitly) assume that communications
between the dealer and participants are noiseless, this paper takes a more
practical assumption that the dealer delivers shares to the participants via a
noisy broadcast channel. An information theoretic approach is proposed, which
exploits the channel as additional resources to achieve secret sharing
requirements. In this way, secret sharing problems can be reformulated as
equivalent secure communication problems via wiretap channels, and can be
solved by employing powerful information theoretic security techniques. This
approach is first developed for the classic secret sharing problem, in which
only one secret is to be shared. This classic problem is shown to be equivalent
to a communication problem over a compound wiretap channel. The lower and upper
bounds on the secrecy capacity of the compound channel provide the
corresponding bounds on the secret sharing rate. The power of the approach is
further demonstrated by a more general layered multi-secret sharing problem,
which is shown to be equivalent to the degraded broadcast multiple-input
multiple-output (MIMO) channel with layered decoding and secrecy constraints.
The secrecy capacity region for the degraded MIMO broadcast channel is
characterized, which provides the secret sharing capacity region. Furthermore,
these secure encoding schemes that achieve the secrecy capacity region provide
an information theoretic scheme for sharing the secrets.",1404.6474v1
2014-04-29,On infrared pseudogap in cuprate and pnictide high-temperature superconductors,"We investigate infrared manifestations of the pseudogap in the prototypical
cuprate and pnictide superconductors: YBa2Cu3Oy and BaFe2As2 (Ba122) systems.
We find remarkable similarities between the spectroscopic features attributable
to the pseudogap in these two classes of superconductors. The hallmarks of the
pseudogap state in both systems include a weak absorption feature at about 500
cm-1 followed by a featureless continuum between 500 and 1500 cm-1 in the
conductivity data and a significant suppression in the scattering rate below
700 - 900 cm-1. The latter result allows us to identify the energy scale
associated with the pseudogap $\Delta_{PG}$. We find that in the Ba122-based
materials the superconductivity-induced changes of the infrared spectra occur
in the frequency region below 100 - 200 cm-1, which is much lower than the
energy scale of the pseudogap. We performed theoretical analysis of the
scattering rate data of the two compounds using the same model which accounts
for the effects of the pseudogap and electron-boson coupling. We find that the
scattering rate suppression in Ba122-based compounds below $\Delta_{PG}$ is
solely due to the pseudogap formation whereas the impact of the electron-boson
coupling effects is limited to lower frequencies. The magnetic resonance modes
used as inputs in our modeling are found to evolve with the development of the
pseudogap, suggesting an intimate correlation between the pseudogap and
magnetism.",1404.7233v1
2014-05-05,Itinerant and local-moment magnetism in EuCr2As2 single crystals,"We report on the crystal structure, physical properties, and electronic
structure calculations for the ternary pnictide compound EuCr2As2. X-ray
diffraction studies confirmed that EuCr2As2 crystalizes in the ThCr2Si2-type
tetragonal structure (space group I4/mmm). The Eu ions are in a stable divalent
state in this compound. Eu moments in EuCr2As2 order magnetically below Tm = 21
K. A sharp increase in the magnetic susceptibility below Tm and the positive
value of the paramagnetic Curie temperature obtained from the Curie-Weiss fit
suggest dominant ferromagnetic interactions. The heat capacity exhibits a sharp
{\lambda}-shape anomaly at Tm, confirming the bulk nature of the magnetic
transition. The extracted magnetic entropy at the magnetic transition
temperature is consistent with the theoretical value Rln(2S+1) for S = 7/2 of
the Eu2+ ion. The temperature dependence of the electrical resistivity
\r{ho}(T) shows metallic behavior along with an anomaly at 21 K. In addition,
we observe a reasonably large negative magneto-resistance (~ -24%) at lower
temperature. Electronic structure calculations for EuCr2As2 reveal a moderately
high density of states of Cr-3d orbitals at the Fermi energy, indicating that
the nonmagnetic state of Cr is unstable against magnetic order. Our density
functional calculations for EuCr2As2 predict a G-type AFM order in the Cr
sublattice. The electronic structure calculations suggest a weak interlayer
coupling of the Eu moments.",1405.0996v1
2014-05-19,Infrared phonon spectrum of the tetragonal helimagnet Ba$_2$CuGe$_2$O$_7$,"The lattice dynamics of Ba$_2$CuGe$_2$O$_7$, a compound which develops
Dzyaloshinsky-Moriya (DM) helical magnetism below $T_N$ = 3.2 K, has been
studied by measuring the infrared reflectivity of a single crystal with the
radiation polarized both in the $ab$ plane and along the $c$ axis of its
tetragonal cell, from 7 K to 300 K. In this compound, where the unit cell has
no inversion symmetry, fourteen $E$ phonon modes of the $ab$ plane, out of the
eighteen predicted, and all the ten $B_2$ modes of the $c$ axis, have been
observed. They have been assigned to the atomic motions by a comparison with
shell-model calculations, which provided vibrational frequencies in good
agreement with the experiment, while most calculated intensities turned to be
much lower than the experimental values. This discrepancy has been tentatively
explained by assuming strong electron-phonon interactions, a hypothesis
supported by the failure of the $f$- sum rule if restricted to the phonon
region. Indeed, we observe a remarkable increase in the oscillator strengths at
$T$'s low but higher than $T_N$, which suggests that the dielectric constant of
Ba$_2$CuGe$_2$O$_7$ may increase at those temperatures.",1405.4610v1
2014-05-27,Concept of effective states of atoms in compounds to describe properties determined by the densities of valence electrons in atomic cores,"A new approach for describing the effective electronic states of ""atoms in
compounds"" to study the properties of molecules and condensed matter which are
circumscribed by the operators heavily concentrated in atomic cores is
proposed. Among the properties are hyperfine structure, space parity (P) and
time reversal invariance (T) nonconservation effects, chemical shifts of x-ray
emission lines (XES), M\""{o}ssbauer effect, etc. Advantage of the approach is
that a good quantitative agreement of predicted and experimental data can be
attained even for such difficult cases as XES chemical shifts providing correct
quantum-mechanical interpretation of the experimental data. From computational
point of view the method can be quite efficient being implemented in the
framework of the relativistic pseudopotential theory [Int.J. Quantum Chem. 71,
359 (1999)] and procedures of recovering the wave functions in heavy-atom cores
[Int.J. Quantum Chem. 104, 223 (2005)] after a molecular, cluster or periodic
structure calculation performed on the basis of pseudoorbitals smoothed near
the nuclei within the pseudopotential approximation. We report results of our
studies of a number of atomic and molecular systems to demonstrate the
capabilities of the approach.",1405.6892v4
2014-07-02,Monte Carlo Based Toy Model for Fission Process,"Fission yield has been calculated notoriously by two calculations approach,
macroscopic approach and microscopic approach. This work will proposes another
calculation approach which the nucleus is treated as a toy model. The toy model
of fission yield is a preliminary method that use random number as a backbone
of the calculation. Because of nucleus as a toy model hence the fission process
does not represent real fission process in nature completely. Fission event is
modeled by one random number. The number is assumed as width of distribution
probability of nucleon position in compound nuclei when fission process is
started. The toy model is formed by Gaussian distribution of random number that
randomizes distance like between particle and central point. The scission
process is started by smashing compound nucleus central point into two parts
that are left central and right central points. These three points have
different Gaussian distribution parameters such as mean ({\mu}CN, {\mu}L,
{\mu}R), and standard deviation ({\sigma}CN, {\sigma}L ,{\sigma}R). By
overlaying of three distributions, the number of particles ( NL, NR) that they
are trapped by central points is obtained. This process is iterated until ( NL,
NR) become constant numbers. The yield is determined from portion of nuclei
distribution which is proportional with portion of mass numbers. Smashing
process is repeated by changing {\sigma}L and {\sigma}R randomly",1407.0448v1
2014-07-06,Optical evidence of quantum rotor orbital excitations in orthorhombic manganites,"In magnetic compounds with Jahn-Teller (JT) ions (such as Mn3+ or Cu2+), the
ordering of the electron or hole orbitals is associated with cooperative
lattice distortions. There the role of JT effect, although widely recognised,
is still elusive in the ground state properties. We suggest that, in these
materials, there exist elementary excitations whose energy spectrum is
described in terms of the total angular momentum eigenstates and is quantised
as in quantum rotors found in JT centers. We observed features originating from
these excitations in the optical spectra of a model compound LaMnO3 using
ellipsometry technique. They appear clearly as narrow sidebands accompanying
the electron transition between the JT split orbitals on neighbouring Mn3+
ions, strongly influenced by anisotropic spin correlations. We present these
results together with new experimental data on photoluminescence and its
kinetics found in LaMnO3, which lend additional support to the ellipsometry
implying the existence of the quantum rotor orbital excitations. We note that
the discovered elementary excitations of quantum rotors may play an important
role in many unusual properties observed in these materials upon doping, such
as high-temperature superconductivity and colossal magnetoresistance.",1407.1475v1
2014-07-08,"Exploration of stable compounds, crystal structures, and superconductivity in the Be-H system","Using first-principles variable-composition evolutionary methodology, we
explored the high-pressure structures of beryllium hydrides between 0 and 400
GPa. We found that BeH$_2$ remains the only stable compound in this pressure
range. The pressure-induced transformations are predicted as $Ibam$
$\rightarrow $ $P\bar{3}m1$ $\rightarrow $ $R\bar{3}m$ $ \rightarrow $ $Cmcm$ $
\rightarrow $ $P4/nmm$, which occur at 24, 139, 204 and 349 GPa, respectively.
$P\bar{3}m1$ and $R\bar{3}m$ structures are layered polytypes based on close
packings of H atoms with Be atoms filling octahedral voids in alternating
layers. $Cmcm$ and $P4/nmm$ structures have 3D-networks of strong bonds, but
also feature rectanular and squre, respectively, layers of H atoms with short
H-H distances. $P\bar{3}m1$ and $R\bar{3}m$ are semiconductors while $Cmcm$ and
$P4/nmm$ are metallic. We have explored superconductivity of both metallic
phases, and found large electron-phonon coupling parameters of $ \lambda $=0.63
for $Cmcm$ (resulting in a $T_c$ of 32.1-44.1 K) at 250 GPa and $ \lambda
$=0.65 for $P4/nmm$ ($T_c$ = 46.1-62.4 K) at 400 GPa. The dependence of $T_c$
on pressure indicates that $T_c$ initially increases to a maximum of 45.1 K for
$Cmcm$ at 275 GPa and 97.0 K for $P4/nmm$ at 365 GPa, and then decreases with
increasing pressure for both phases.",1407.2000v2
2014-07-09,Contrasting electron and hole doping effects on the spin gap of the caged type Kondo semimetal CeOs$_2$Al$_{10}$: A muon spin relaxation and inelastic neutron scattering investigation,"The effects of electron (Ir) and hole (Re) doping on the hybridization gap
and antiferromagnetic order have been studied by magnetization, muon spin
relaxation ($\mu^+$SR), and inelastic neutron scattering on the polycrystalline
samples of Ce(Os$_{1-x}$Ir$_x$)$_2$Al$_{10}$ ($x$ = 0.08 and 0.15) and
CeOs$_{1.94}$Re$_{0.06}$Al$_{10}$. $\mu^+$SR spectra clearly reveals magnetic
ordering below 20 and 10 K for $x$ = 0.08 and 0.15 samples respectively with a
very weak signature of oscillations of the muon initial asymmetry at very short
time scale. Our important findings are that small amount of electron doping (i)
completely suppress the inelastic magnetic excitations near 11 meV down to 2K,
which were observed in the undoped compound, and the response transforms into a
broad quasielastic response and (ii) the internal field at the corresponding
muon site is remarkably enhanced by about ten times compared with the parent
compound. On the other hand with small amount of hole (3\% Re) doping the
intensity of the inelastic magnetic excitations near 11 meV is reduced
significantly. The main origin of the observed doping effect is an extra 5$d$
electrons being carried by Ir and a hole carried by Re compared with that the
Os atom. The obtained results demonstrate a great sensitivity of the carrier
doping and provides additional ways to study their anomalous magnetic
properties.",1407.2516v1
2014-08-27,Short-range magnetic correlations in the highly-correlated electron compound CeCu$_{4}Ga,"We present experimental results for the heavy-electron compound CeCu$_{4}$Ga
which show that it possesses short-range magnetic correlations down to a
temperature of $T = 0.1$ K. Our neutron scattering data show no evidence of
long-range magnetic order occurring despite a peak in the specific heat at
$T^{*} =1.2$ K. Rather, magnetic diffuse scattering occurs which corresponds to
short-range magnetic correlations occurring across two unit cells. The specific
heat remains large as $T\sim0$ K resulting in a Sommerfeld coefficient of
$\gamma_{0} = 1.44(2)$ J/mol-K$^{2}$, and, below $T^{*}$, the resistivity
follows $T^{2}$ behavior and the ac magnetic susceptibility becomes temperature
independent. A magnetic peak centered at an energy transfer of
$E_{\rm{c}}=0.24(1)$ meV is seen in inelastic neutron scattering data which
shifts to higher energies and broadens under a magnetic field. We discuss the
coexistence of large specific heat, magnetic fluctuations, and short-range
magnetic correlations at low temperatures and compare our results to those for
materials possessing spin-liquid behavior.",1408.6576v2
2014-09-01,Magnetic structures in the rich magnetic phase diagram of Ho$_2$RhIn$_8$,"The magnetic phase diagram of the tetragonal Ho$_2$RhIn$_8$ compound has
similar features to many related systems, revealing a zero magnetic field AF1
and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase
were not reported yet for any of the related compounds. In addition, only the
Ho$_2$RhIn$_8$ phase diagram contains a small region of the incommensurate
zero-field AF3 phase. We have performed a number of neutron diffraction
experiments on single crystals of Ho$_2$RhIn$_8$ using several diffractometers
including experiments in both horizontal and vertical magnetic fields up to 4
T. We present details of the magnetic structures in all magnetic phases of the
rich phase diagram of Ho$_2$RhIn$_8$. The Ho magnetic moments point along the
tetragonal $c$ axis in every phase. The ground-state AF1 phase is characterized
by propagation vector $\textbf{k}$ = (1/2, 0, 0). The more complex
ferrimagnetic AF2 phase is described by four propagation vectors
$\textbf{k}_{0}$ = (0, 0, 0), $\textbf{k}_{1}$ = (1/2, 0, 0), $\textbf{k}_{2}$
= (0, 1/2, 1/2), $\textbf{k}_{3}$ = (1/2, 1/2, 1/2). The magnetic structure in
the AF3 phase is incommensurate with $\textbf{k}_{AF3}$ = (0.5, $\delta$, 0).
Our results are consistent with theoretical calculations based on crystal field
theory.",1409.0433v2
2014-09-03,DC magnetization studies of nano- and micro-particles of bilayered manganite LaSr2Mn2O7,"Systematic studies of magnetic properties of LaSr2Mn2O7 as a function of
crystalline grain size provide information on how the crystalline grain size
affects the magnetic and charge ordering in this compound. The half-doped
bi-layered manganite LaSr2Mn2O7 (x=0.5) in its bulk form has CE-type
antiferromagnetic (CE-AFM) charge ordering phase transition. In this work, we
have prepared LaSr2Mn2O7 ceramic samples using Pechini sol-gel method to
produce different grain sizes and the effect of crystalline grain sizes between
150 200 to 1000 nm on magnetic properties results obtained by the SQUID
magnetometer have been investigated. The DC magnetization (DCM) measurements
for all samples indicate that the crystalline grain size has no considerable
effect on TCO. Just the temperature of charge ordering peak becomes sharper,
and susceptibility measurement in the zero field cooling (ZFC) and filed
cooling (FC) increases as the grain sizes becomes systematically smaller. The
results obtained from magnetic hysteresis curves confirm the anti-ferromagnetic
phase formation as a ground state and Arrott plots obtained manifest the
existence of first and second order magnetic phase transition in all samples.
In addition, in sample with a grain size of 150 200 nm, enhancement of the
magnetic properties, which is accompanied with the formation of FM phase on the
surface of grain or particle, is observed.",1409.0945v2
2014-09-05,Monoclinic (Mc) phase and electric field induced phase transformation in BaTiO3,"For decades it has been a well-known fact that among the few ferroelectric
compounds in the perovskite family namely BaTiO3, KNbO3, PbTiO3 Na1/2Bi1/2TiO3
the dielectric and piezoelectric properties of BaTiO3 is considerably higher
than the others in polycrystalline form at room temperature. Further, similar
to ferroelectric alloys exhibiting morphotropic phase boundary, single crystals
of BaTiO3 exhibits anomalously large piezoelectric response when poled away
from the direction of spontaneous polarization at room temperature. These
anomalous features in BaTiO3 remained unexplained so far from the structural
stand point. In this work we have used high resolution synchrotron X-ray powder
diffraction, atomic resolution aberration corrected transmission electron
microscopy, in conjunction with a novel powder poling technique, to reveal that
(i) the equilibrium state of BaTiO3 is characterized by coexistence of a subtle
monoclinic (Mc) phase and tetragonal phase, and (ii) strong electric field
induces an orthorhombic phase at 300 K. These results suggest that BaTiO3 at
room temperature is within an instability regime, and that this instability is
therefore the fundamental factor responsible for the anomalous dielectric and
piezoelectric properties of BaTiO3 as compared to the other homologous
ferroelectric perovskite compounds. The results demonstrate that pure BaTiO3 at
room temperature more akin to lead-based ferroelectric alloys close to the
morphotropic phase boundary where polarization rotation and field induced
ferroelectric-ferroelectric phase transformations play fundamental role in
influencing the piezoelectric behavior.",1409.1692v1
2014-09-18,Tuning of magnetic frustration in $S=1/2$ Kagomé lattices {[Cu$_{3}$(CO$_{3}$)$_{2}$$(bpe)_{3}$](ClO$_{4}$)$_2$}$_{n}$ and {[Cu$_{3}$(CO$_{3}$)$_{2}$$(bpy)_{3}$](ClO$_{4}$)$_2$}$_{n}$ through rigid and flexible ligands,"Single crystalline and polycrystalline samples of $S=1/2$ Kagom\'{e} lattices
{[Cu$_{3}$(CO$_{3}$)$_{2}$$(bpe)_{3}$](ClO$_{4}$)$_2$}$_{n}$ and
{[Cu$_{3}$(CO$_{3}$)$_{2}$$(bpy)_{3}$](ClO$_{4}$)$_2$}$_{n}$, respectively were
synthesized. Their structural and magnetic properties were characterized by
means of x-ray diffraction and magnetization measurements. Both compounds
crystalize in a hexagonal structure (space group $P-6$) consisting of CuO$_4$
Kagom\'{e} layers in the $ab$-plane but linked along $c$ direction through
either rigid $bpy$ or flexible $bpe$ ligands to form 3D frame works. Magnetic
measurements reveal that both the compounds undergo ferromagnetic ordering
($T_{\rm C}$) at low temperatures and the $T_{\rm C}$ and the extent of
frustration could be tuned by changing the nature of the pillar ligands.
{[Cu$_{3}$(CO$_{3}$)$_{2}$$(bpe)_{3}$](ClO$_{4}$)$_2$}$_{n}$ which is made up
of flexible $bpe$ ligands has a $T_{\rm C}$ of 5.7 K and a Curie-Weiss
temperature ($\theta_{\rm CW}$) of -39.7 K giving rise to a frustration
parameter of $\frac{|\theta_{\rm CW}|}{T_{\rm C}} \simeq$ 6.96. But the
replacement of $bpe$ by a more rigid and electronically delocalized $bpy$
ligand leads to an enhanced $T_{\rm C} \simeq$ 9.3 K and a reduced frustration
parameter of $\frac{|\theta_{\rm CW}|}{T_{\rm C}} \simeq$ 3.54.",1409.5323v1
2014-10-13,Probing Strongly Correlated 4f-Orbital Symmetry of the Ground State in Yb Compounds by Linear Dichroism in Core-Level Photoemission,"We show that the strongly correlated 4f-orbital symmetry of the ground state
is revealed by linear dichroism in core-level photoemission spectra as we have
discovered for YbRh2Si2 and YbCu2Si2. Theoretical analysis tells us that the
linear dichroism reflects the anisotropic charge distributions resulting from
crystalline electric field. We have successfully determined the ground-state 4f
symmetry for both compounds from the polarization-dependent angle-resolved
core-level spectra at a low temperature well below the first excitation energy.
The excited-state symmetry is also probed by temperature dependence of the
linear dichroism where the high measuring temperatures are of the order of the
crystal-field-splitting energies.",1410.3202v1
2014-10-17,Anisotropic strain in SmSe and SmTe: implications for electronic transport,"Mixed valence rare-earth samarium compounds SmX (X=Se,Te) have been recently
proposed as candidate materials for use in high-speed, low-power digital
switches driven by stress induced changes of resistivity. At room temperature
these materials exhibit a pressure driven insulator-to-metal transition with
resistivity decreasing by up to 7 orders of magnitude over a small pressure
range. Thus, the application of only a few GPa's to the piezoresistor (SmX)
allows the switching device to perform complex logic. Here we study from first
principles the electronic properties of these compounds under uniaxial strain
and discuss the consequences on carrier transport. The changes in the band
structure show that the piezoresistive response is mostly governed by the
reduction of band gap with strain. Furthermore, it becomes optimal when the
Fermi level is pinned near the localized valence band. The piezoresistive
effect under uniaxial strain which must be taken into account in thin films and
other systems with reduced dimensionality is also quantified. Under uniaxial
strain we find that the piezoresistive response can be substantially larger
than in the isotropic case. Analysis of complex band structure of SmSe yields a
tunneling length of the order of 1 nm. The results suggest that the conduction
mechanism governing the piezoresistive effect in bulk, i.e.~thermal promotion
of electrons, should still be dominant in few-nanometer-thick films.",1410.4740v1
2014-10-27,Scaling behavior of the thermopower of the archetypical heavy-fermion metal $\rm{YbRh_2Si_2}$,"We reveal and explain a scaling behavior of the thermopower $S/T$ exhibiting
by the archetypical heavy-fermion (HF) metal $\rm{YbRh_2Si_2}$ under the
application of magnetic field $B$ at temperatures $T$. We show that the same
scaling is demonstrated by such different HF compounds as $\beta$-${\rm
YbAlB_4}$ and the strongly correlated layered cobalt oxide $\rm
[BiBa_{0.66}K_{0.36}O_{2}]CoO_{2}$. Using $\rm{YbRh_2Si_2}$ as an example, we
demonstrate that the scaling behavior of $S/T$ is violated at the
antiferromagnetic phase transition, while both the residual resistivity
$\rho_0$ and the density of states $N$ experience jumps at the phase
transition, making the thermopower experience two jumps and change its sign.
Our elucidation is based on flattening of the single-particle spectrum that
profoundly affects $\rho_0$ and $N$. To depict the main features of the $S/T$
behavior, we construct the $T-B$ schematic phase diagram of $\rm{YbRh_2Si_2}$.
Our calculated $S/T$ for the HF compounds are in good agreement with
experimental facts and support our observations.",1410.7299v4
2014-10-31,"3D Dirac semimetals: current materials, design principles and predictions of new materials","Design principles and novel predictions of new 3D Dirac semimetals are
presented, along with the context of currently known materials. Current
materials include those based on a topological to trivial phase transition,
such as in TlBiSe$_{2-x}$S$_x$ and Hg$_{1-x}$Cd$_x$Te, Bi$_{1-x}$Sb$_x$,
Bi$_{2-x}$In$_x$Se$_3$, and Pb$_{1-x}$Sn$_x$Se. Some more recently revealed
materials, Na$_3$Bi and Cd$_3$As$_2$, are 3D Dirac semimetals in their native
composition. The different design principles presented each yield novel
predictions for new candidates. For Case I, 3D Dirac semimetals based on charge
balanced compounds, BaAgBi, SrAgBi, YbAuSb, PtBi$_2$ and SrSn$_2$As$_2$ are
identified as candidates. For Case II, 3D Dirac semi-metals in analogy to
graphene, BaGa$_2$ is identified as a candidate, and BaPt and Li$_2$Pt are
discussed. For Case III, 3D Dirac semi-metals based on glide planes and screw
axes, TlMo$_3$Te$_3$ and the AMo$_3$X$_3$ family in general (A=K, Na, In, Tl,
X=Se,Te) as well as the Group IVb trihalides such as HfI$_3$ are identified as
candidates. Finally we discuss conventional intermetallic compounds with Dirac
cones, and identify Cr$_2$B as a potentially interesting material.",1411.0005v1
2014-11-03,"Anisotropic putative ""up-up-down"" magnetic structure in EuTAl$_4$Si$_2$ (T = Rh and Ir)","We present detailed investigations in single crystals of two recently
reported quaternary intermetallic compounds EuRhAl$_4$Si$_2$ and
EuIrAl$_4$Si$_2$ employing magnetization, electrical resistivity in zero and
applied fields, heat capacity and $^{151}$Eu M\""{o}ssbauer spectroscopy
measurements. The two compounds order antiferromagnetically at $T_{\rm N1}$ =
11.7 and 14.7\,K, respectively, each undergoing two magnetic transitions: the
first from paramagnetic to incommensurate modulated antiferromagnetic, the
second at lower temperature to a commensurate antiferromagnetic phase as
confirmed by heat capacity and M\""{o}ssbauer spectra. The magnetic properties
in the ordered state present a large anisotropy despite Eu$^{2+}$ being an
$S$-state ion for which the single-ion anisotropy is expected to be weak. Two
features in the magnetization measured along the $c$-axis are prominent. At
1.8\,K, a ferromagnetic-like jump occurs at very low field to a value one third
of the saturation magnetization (1/3 M$_0$) followed by a wide plateau up to
2\,T for T = Rh and 4\,T for T = Ir. At this field value, a sharp hysteretic
spin-flop transition occurs to a fully saturated state (M$_0$). Surprisingly,
the magnetization does not return to origin when the field is reduced to zero
in the return cycle, as expected in an antiferromagnet. Instead, a remnant
magnetization 1/3 M$_0$ is observed and the magnetic loop around the origin
shows hysteresis. This suggests that the zero field magnetic structure has a
ferromagnetic component, and we present a model with up to third neighbor
exchange and dipolar interaction which reproduces the magnetization curves and
hints to an ""up-up-down"" magnetic structure in zero field.",1411.0379v1
2014-11-08,Pronounced photovoltaic response from multi-layered transition-metal dichalcogenides PN-junctions,"Transition metal dichalcogenides (TMDs) are layered semiconductors with
indirect band gaps comparable to Si. These compounds can be grown in large
area, while their gap(s) can be tuned by changing their chemical composition or
by applying a gate voltage. The experimental evidence collected so far, points
towards a strong interaction with light, which contrasts with the small
photovoltaic efficiencies $\eta \geq 1$ % extracted from bulk crystals or
exfoliated monolayers. Here, we evaluate the potential of these compounds by
studying the photovoltaic response of electrostatically generated PN-junctions
composed of approximately ten atomic-layers of MoSe$_2$ stacked onto the
dielectric $h$-BN. In addition to ideal diode-like response, we find that these
junctions can yield, under AM-1.5 illumination, photovoltaic efficiencies
$\eta$ exceeding 14 %, with fill-factors of ~ 70 %. Given the available
strategies for increasing $\eta$ such as gap tuning, improving the quality of
the electrical contacts, or the fabrication of tandem cells, our study suggests
a remarkable potential for photovoltaic applications based on TMDs.",1411.2086v3
2014-11-13,Quantum Critical Fluctuations in the Heavy fermion compound Ce(Ni$_{0.935}$Pd$_{0.065}$)$_2$Ge$_2$,"Electric resistivity, specific heat, magnetic susceptibility, and inelastic
neutron scattering experiments were performed on a single crystal of the heavy
fermion compound Ce(Ni$_{0.935}$Pd$_{0.065}$)$_2$Ge$_2$ in order to study the
spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP).
The resistivity and the specific heat coefficient for $T \leq$ 1 K exhibit the
power law behavior expected for a 3D itinerant AF QCP ($\rho(T) \sim T^{3/2}$
and $\gamma(T) \sim \gamma_0 - b T^{1/2}$). However, for 2 $\leq T \leq$ 10 K,
the susceptibility and specific heat vary as $log T$ and the resistivity varies
linearly with temperature. Furthermore, despite the fact that the resistivity
and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the
correlation length, correlation time, and staggered susceptibility of the spin
fluctuations remain finite at low temperature. We suggest that these deviations
from the divergent behavior expected for a QCP may result from alloy disorder.",1411.3689v1
2014-11-17,"Diverse Chemistry of Stable Hydronitrogens, and Implications for Planetary and Materials Sciences","Nitrogen hydrides, including ammonia (NH3), hydrazine (N2H4), hydrazoic acid
(HN3) and etc, are compounds of great fundamental and applied importance. Their
high-pressure behavior is important because of their abundance in giant planets
and because of the hopes of discoverying high-energy-density materials. Here,
we have performed a systematic investi- gation on the structural stability of
N-H system in a pressure range up to 800 GPa through evolutionary structure
prediction simulations. Surprisingly, we found that high pressure stabilizes a
series of previously unreported compounds with peculiar structural and
electronic properties, such as the N4H, N3H, N2H and NH phases composed of
nitrogen backbones, the N9H4 phase containing two dimensional metallic nitrogen
planes and novel N8H, NH2, N3H7, NH4 and NH5 molecular phases. Another surprise
is that NH3 becomes thermodynamically unstable above ~460 GPa. We found that
high-pressure chemistry is much more diverse that hydrocarbon chemistry at
normal conditions, leading to expectations that N-H-O and N-H-O-S systems under
pressure are likely to possess richer chemistry than the known organic
chemistry. This, in turn, opens a possibility of nitrogen-based life at high
pressure. The predicted phase diagram of the N-H system also provides a
reference for synthesis of high-energy-density materials.",1411.4513v3
2014-11-21,Non-virialised clusters for detection of Dark Energy-Dark Matter interaction,"The observation of galaxy and gas distributions, as well as cosmological
simulations in a $\Lambda$CDM Universe, suggests that clusters of galaxies are
still accreting mass and are not expected to be in equilibrium. In this work,
we investigate the possibility to evaluate the departure from virial
equilibrium in order to detect, in that balance, effects from a Dark
Matter--Dark Energy interaction. We continue, from previous works, using a
simple model of interacting dark sector, the Layzer--Irvine equation for
dynamical virial evolution, and employ optical observations in order to obtain
the mass profiles through weak lensing and X-ray observations giving the
intracluster gas temperatures. Through a Monte Carlo method, we generate, for a
set of clusters, measurements of observed virial ratios, interaction strength,
rest virial ratio and departure from equilibrium factors. We found a compounded
interaction strength of $-1.99^{+2.56}_{-16.00}$, compatible with no
interaction, but also a compounded rest virial ratio of $-0.79 \pm 0.13$, which
would entail a $2\sigma$ detection. We confirm quantitatively that clusters of
galaxies are out of equilibrium but further investigation is needed to
constrain a possible interaction in the dark sector.",1411.5863v3
2014-12-12,Magnetism of BaFe2Se3 studied by Mössbauer spectroscopy,"The compound BaFe2Se3 (Pnma) has been synthesized in the form of single
crystals with the average composition Ba0.992Fe1.998Se3. The Moessbauer
spectroscopy used for investigation of the valence states of Fe in this
compound at temperature ranging from 4.2 K till room temperature revealed the
occurrence of mixed-valence state for iron. The spectrum is characterized by
sharply defined electric quadrupole doublet above magnetic ordering at about
250 K. For the magnetically ordered state one sees four iron sites at least and
each of them is described by separate axially symmetric electric field gradient
tensor with the principal component making some angle with the hyperfine
magnetic field. They form two groups occurring in equal abundances. It is
likely that each group belongs to separate spin ladder with various tilts of
the FeSe4 tetrahedral units along the ladder. Two impurity phases are found,
i.e., superconducting FeSe and some other unidentified iron-bearing phase being
magnetically disordered above 80 K. Powder form of BaFe2Se3 is unstable in
contact with the air and decomposes slowly to this unidentified phase
exhibiting almost the same quadrupole doublet as BaFe2Se3 above magnetic
transition temperature.",1412.4024v2
2014-12-27,Spinodal nanodecomposition in magnetically doped semiconductors,"This review presents the recent progress in computational materials design,
experimental realization, and control methods of spinodal nanodecomposition
under three- and two-dimensional crystal-growth conditions in spintronic
materials, such as magnetically doped semiconductors. The computational
description of nanodecomposition, performed by combining first-principles
calculations with kinetic Monte Carlo simulations, is discussed together with
extensive electron microscopy, synchrotron radiation, scanning probe, and ion
beam methods that have been employed to visualize binodal and spinodal
nanodecomposition (chemical phase separation) as well as nanoprecipitation
(crystallographic phase separation) in a range of semiconductor compounds with
a concentration of transition metal (TM) impurities beyond the solubility
limit. The role of growth conditions, co-doping by shallow impurities, kinetic
barriers, and surface reactions in controlling the aggregation of magnetic
cations is highlighted. According to theoretical simulations and experimental
results the TM-rich regions appear either in the form of nanodots (the {\em
dairiseki} phase) or nanocolumns (the {\em konbu} phase) buried in the host
semiconductor. Particular attention is paid to Mn-doped group III arsenides and
antimonides, TM-doped group III nitrides, Mn- and Fe-doped Ge, and Cr-doped
group II chalcogenides, in which ferromagnetic features persisting up to above
room temperature correlate with the presence of nanodecomposition and account
for the application-relevant magneto-optical and magnetotransport properties of
these compounds. Finally, it is pointed out that spinodal nanodecomposition can
be viewed as a new class of bottom-up approach to nanofabrication.",1412.8062v3
2014-12-30,Non-BCS thermodynamic properties of H2S superconductor,"The present paper determines the thermodynamic properties of the
superconducting state in the ${\rm H_{2}S}$ compound. The values of the
pressure from $130$ GPa to $180$ GPa were taken into consideration. The
calculations were performed in the framework of the Eliashberg formalism. In
the first step, the experimental course of the dependence of the critical
temperature on the pressure was reproduced: $T_{C}\in\left<31,88\right>$ K,
whereas the Coulomb pseudopotential equal to $0.15$ was adopted. Next, the
following quantities were calculated: the order parameter at the temperature of
zero Kelvin ($\Delta\left(0\right)$), the specific heat jump at the critical
temperature ($\Delta C\left(T_{C}\right)\equiv
C^{S}\left(T_{C}\right)-C^{N}\left(T_{C}\right)$), and the thermodynamic
critical field ($H_{C}\left(0\right)$). It was found that the values of the
dimensionless ratios: $R_{\Delta}\equiv 2\Delta(0)/k_{B}T_{C}$,
$R_{C}\equiv{\Delta C\left(T_{C}\right)}/{C^{N}\left(T_{C}\right)}$, and
$R_{H}\equiv{T_{C}C^{N}\left(T_{C}\right)}/{H_{C}^{2}\left(0\right)}$ deviate
from the predictions of the BCS theory: $R_{\Delta}\in\left<3.64,4.16\right>$,
$R_{C}\in\left<1.59,2.24\right>$, and $R_{H}\in\left<0.144, 0.163\right>$.
Generalizing the results on the whole family of the ${\rm H_{n}S}$-type
compounds, it was shown that the maximum value of the critical temperature can
be equal to $\sim 290$ K, while $R_{\Delta}$, $R_{C}$ and $R_{H}$ adopt the
following values: $6.53$, $3.99$, and $0.093$, respectively.",1412.8640v3
2015-01-04,COSIMA-Rosetta calibration for in-situ characterization of 67P/Churyumov-Gerasimenko cometary inorganic compounds,"COSIMA (COmetary Secondary Ion Mass Analyser) is a time-of-flight secondary
ion mass spectrometer (TOF-SIMS) on board the Rosetta space mission. COSIMA has
been designed to measure the composition of cometary dust grains. It has a mass
resolution m/{\Delta}m of 1400 at mass 100 u, thus enabling the discrimination
of inorganic mass peaks from organic ones in the mass spectra. We have
evaluated the identification capabilities of the reference model of COSIMA for
inorganic compounds using a suite of terrestrial minerals that are relevant for
cometary science. Ground calibration demonstrated that the performances of the
flight model were similar to that of the reference model. The list of minerals
used in this study was chosen based on the mineralogy of meteorites,
interplanetary dust particles and Stardust samples. It contains anhydrous and
hydrous ferromagnesian silicates, refractory silicates and oxides (present in
meteoritic Ca-Al-rich inclusions), carbonates, and Fe-Ni sulfides. From the
analyses of these minerals, we have calculated relative sensitivity factors for
a suite of major and minor elements in order to provide a basis for element
quantification for the possible identification of major mineral classes present
in the cometary grains.",1501.00716v1
2015-01-05,Software Safety Demonstration and Idemnification,"Computers may control safety-critical operations in machines having embedded
software. This memoir proposes a regimen to verify such algorithms at
prescribed levels of statistical confidence. The United States Department of
Defense standard for system safety engineering (MIL-STD-882E) defines
development procedures for safety-critical systems. However, a problem exists:
the Standard fails to distinguish quantitative product assurance technique from
categorical process assurance method for software development. Resulting is
conflict in the technical definition of the term risk. The primary goal here is
to show that a quantitative risk-based product assurance method exists and is
consistent with hardware practice. Discussion appears in two major parts:
theory, which shows the relationship between automata and software; and
application, which covers demonstration and indemnification. Demonstration is a
technique for generating random tests; indemnification converts pass/fail test
results to compound Poisson parameters (severity and intensity). Together,
demonstration and indemnification yield statistical confidence that
safety-critical code meets design intent. Statistical confidence is the
keystone of quantitative product assurance. A secondary goal is resolving the
conflict over the term risk. The first meaning is an accident model known in
mathematics as the compound Poisson stochastic process, and so is called
statistical risk. Various of its versions underlie the theories of safety and
reliability. The second is called developmental risk. It considers software
autonomy, which considers time until manual recovery of control. Once these
meanings are separated, MIL-STD-882 can properly support either formal
quantitative safety assurance or empirical process robustness, which differ in
impact.",1501.00820v4
2015-01-06,Coexistence of Electron-Glass Phase and Persistent Photoconductivity in GeSbTe Compounds,"It is demonstrated that persistent-photoconductivity (PPC), well-studied in
lightly-doped semiconductors, is observable in GeSbTe compounds using infrared
excitation at cryogenic temperatures. The low level of energy-flux necessary to
induce an appreciable effect seems surprising given the high
carrier-concentration n of these ternary alloys. On the other hand, their high
density of carriers makes GeSbTe films favorable candidates for exhibiting
intrinsic electron-glass effects with long relaxation times. These are indeed
observed in GeSbTe thin-films that are Anderson-localized. In particular, a
memory-dip is observed in samples with sheet resistances larger than app. 100
kOhms at T=4K with similar characteristics as in other systems that exhibit
intrinsic electron-glass effects. Persistent-photoconductivity however is
observable in GeSbTe films even for sheet resistances of the order of 1 kOhm,
well below the range of disorder required for observing electron-glass effects.
These two non-equilibrium phenomena, PPC and electron-glass, are shown to be of
different nature in terms of other aspects as well. In particular, their
relaxation dynamics is qualitatively different; the excess conductance dG/G
associated with PPC decays with time as a stretched exponential whereas a
logarithmic relaxation law characterizes dG(t) of all electron-glasses studied
to date. Surprisingly, the magnitude of the memory-dip is enhanced when the
system is in the PPC state. This counter-intuitive result may be related to the
compositional disorder in these materials extending over mesoscopic scales.
Evidence in support of this scenario is presented and discussed.",1501.01163v2
2015-01-09,Superconductivity in quasi-one-dimensional Cs2Cr3As3 with large interchain distance,"Since the discovery of high-temperature superconductivity (SC) in
quasi-two-dimensional copper oxides, a few layered compounds, which bear
similarities to the cuprates, have also been found to host unconventional SC.
Our recent observation of SC at 6.1 K in correlated electron material K2Cr3As3
(J. K. Bao et al., arXiv: 1412.0067) represents an obviously different
paradigm, primarily because of its quasi-one-dimensional (Q1D) nature. The new
material is structurally featured by the (Cr3As3)2- double-walled subnano-tubes
composed of face-sharing Cr6/2 (As6/2) octahedron linear chains, which are well
separated by columns of K+ counterions. Later, an isostructural superconducting
Rb2Cr3As3 was synthesized, thus forming a new superconducting family. Here we
report the third member, Cs2Cr3As3, which possesses the largest interchain
distance. SC appears below 2.2 K. Similar to the former two sister compounds,
Cs2Cr3As3 exhibits a non-Fermi liquid behavior with a linear temperature
dependence of resistivity in the normal state, and a high upper critical field
beyond the Pauli limit as well, suggesting common unconventional SC in the Q1D
Cr-based material.",1501.02065v1
2015-01-15,"A comprehensive study of the magnetic, structural and transport properties of the III-V ferromagnetic semiconductor InMnP","The manganese induced magnetic, electrical and structural modification in
InMnP epilayers, prepared by Mn ion implantation and pulsed laser annealing,
are investigated in the following work. All samples exhibit clear hysteresis
loops and strong spin polarization at the Fermi level. The degree of
magnetization, the Curie temperature and the spin polarization depend on the Mn
concentration. The bright-field transmission electron micrographs show that InP
samples become almost amorphous after Mn implantation but recrystallize after
pulsed laser annealing. We did not observe an insulator-metal transition in
InMnP up to a Mn concentration of 5 at./%. Instead all InMnP samples show
insulating characteristics up to the lowest measured temperature.
Magneotresistance results obtained at low temperatures support the hopping
conduction mechanism in InMnP. We find that the Mn impurity band remains
detached from the valence band in InMnP up to 5 at./% Mn doping. Our findings
indicate that the local environment of Mn ions in InP is similar to GaMnAs,
GaMnP and InMnAs, however, the electrical properties of these Mn implanted
III-V compounds are different. This is one of the consequences of the different
Mn binding energy in these compounds.",1501.03597v1
2015-02-01,"Enhanced conduction band density of states in intermetallic EuTSi$_3$ (T=Rh, Ir)","We report on the physical properties of single crystalline EuRhSi$_3$ and
polycrystalline EuIrSi$_3$, inferred from magnetisation, electrical transport,
heat capacity and $^{151}$Eu M\""ossbauer spectroscopy. These previously known
compounds crystallise in the tetragonal BaNiSn$_3$-type structure. The single
crystal magnetisation in EuRhSi$_3$ has a strongly anisotropic behaviour at 2 K
with a spin-flop field of 13 T, and we present a model of these magnetic
properties which allows the exchange constants to be determined. In both
compounds, specific heat shows the presence of a cascade of two close
transitions near 50 K, and the $^{151}$Eu M\""ossbauer spectra demonstrate that
the intermediate phase has an incommensurate amplitude modulated structure. We
find anomalously large values, with respect to other members of the series, for
the RKKY N\'eel temperature, for the spin-flop field (13 T), for the spin-wave
gap ($\simeq$ 20-25 K) inferred from both resistivity and specific heat data,
for the spin-disorder resistivity in EuRhSi$_3$ ($\simeq 35$ $\mu$Ohm.cm) and
for the saturated hyperfine field (52 T). We show that all these quantities
depend on the electronic density of states at the Fermi level, implying that
the latter must be strongly enhanced in these two materials. EuIrSi$_3$
exhibits a giant magnetoresistance ratio, with values exceeding 600 % at 2 K in
a field of 14 T.",1502.00285v1
2015-02-03,Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd$_2$Si$_2$ single crystal,"Identifying the nature of magnetism, itinerant or localized, remains a major
challenge in condensed-matter science. Purely localized moments appear only in
magnetic insulators, whereas itinerant moments more or less co-exist with
localized moments in metallic compounds such as the doped-cuprate or the
iron-based superconductors, hampering a thorough understanding of the role of
magnetism in phenomena like superconductivity or magnetoresistance. Here we
distinguish two antiferromagnetic modulations with respective propagation wave
vectors of $Q_{\pm}$ = ($H \pm 0.557(1)$, 0, $L \pm 0.150(1)$) and $Q_\text{C}$
= ($H \pm 0.564(1)$, 0, $L$), where $\left(H, L\right)$ are allowed Miller
indices, in an ErPd$_2$Si$_2$ single crystal by neutron scattering and
establish their respective temperature- and field-dependent phase diagrams. The
modulations can co-exist but also compete depending on temperature or applied
field strength. They couple differently with the underlying lattice albeit with
associated moments in a common direction. The $Q_{\pm}$ modulation may be
attributed to localized 4\emph{f} moments while the $Q_\text{C}$ correlates
well with itinerant conduction bands, supported by our transport studies.
Hence, ErPd$_2$Si$_2$ represents a new model compound that displays
clearly-separated itinerant and localized moments, substantiating early
theoretical predictions and providing a unique platform allowing the study of
itinerant electron behavior in a localized antiferromagnetic matrix.",1502.00773v1
2015-02-06,Magnetic ground state of superconducting Eu(Fe0.88Ir0.12)2As2: A combined neutron diffraction and first-principles calculation study,"The magnetic order of the localized Eu$^{2+}$ spins in optimally-doped
Eu(Fe$_{1-x}$Ir$_{x}$)$_{2}$As$_{2}$ ($\mathit{x}$ = 0.12) with superconducting
transition temperature $\mathit{T_{SC}}$ = 22 K was investigated by
single-crystal neutron diffraction. The Eu$^{2+}$ moments were found to be
ferromagnetically aligned along the $\mathit{c}$-direction with an ordered
moment of 7.0(1) $\mu_{B}$ well below the magnetic phase transition temperature
$\mathit{T_{C}}$ = 17 K. No evidence of the tetragonal-to-orthorhombic
structural phase transition was found in this compound within the experimental
uncertainty, in which the spin-density-wave (SDW) order of the Fe sublattice is
supposed to be completely suppressed and the superconductivity gets fully
developed. The ferromagnetic groud state of the Eu$^{2+}$ spins in
Eu(Fe$_{0.88}$Ir$_{0.12}$)$_{2}$As$_{2}$ was supported by the first-principles
density functional calculation. In addition, comparison of the electronic
structure calculations between Eu(Fe$_{0.875}$Ir$_{0.125}$)$_{2}$As$_{2}$ and
the parent compound EuFe$_{2}$As$_{2}$ indicates stronger hybridization and
more expanded bandwith due to the Ir substitution, which together with the
introduction of electrons might work against the Fe-SDW in favor of the
superconductivity.",1502.01921v1
2015-02-10,Magnetic-field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compound Ce(1-x)La(x)B(6),"CeB(6) is a model compound exhibiting antiferroquadrupolar (AFQ) order, its
magnetic properties being typically interpreted within localized models. More
recently, the observation of strong and sharp magnetic exciton modes forming in
its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors
suggested a significant contribution of itinerant electrons to the spin
dynamics. Here we investigate the evolution of the AFQ excitation upon the
application of an external magnetic field and the substitution of Ce with
non-magnetic La, both parameters known to suppress the AFM phase. We find that
the exciton energy decreases proportionally to T_N upon doping. In field, its
intensity is suppressed, while its energy remains constant. Its disappearance
above the critical field of the AFM phase is preceded by the formation of two
modes, whose energies grow linearly with magnetic field upon entering the AFQ
phase. These findings suggest a crossover from itinerant to localized spin
dynamics between the two phases, the coupling to heavy-fermion quasiparticles
being crucial for a comprehensive description of the magnon spectrum.",1502.03139v2
2015-02-15,Helium ordered trapping in arsenolite under compression: Synthesis of He2As4O6,"The compression of arsenolite (cubic As2O3) has been studied from a joint
experimental and theoretical point of view. Experimental X-ray diffraction and
Raman scattering measurements of this molecular solid at high pressures with
different pressure-transmitting media have been interpreted with the help of ab
initio calculations. Our results confirm arsenolite as one of the softest
minerals in absence of hydrogen bonding and provide evidence for helium
trapping above 3 GPa between adamantane-type As4O6 cages, thus leading to a new
compound with stoichiometry He2As4O6. Helium trapping alters all properties of
arsenolite. In particular, pressure-induced amorphization, which occurs in pure
arsenolite above 15 GPa, is impeded when He is trapped between the As4O6 cages;
thus resulting in a mechanical stability of He2As4O6 beyond 30 GPa. Our work
paves the way for the modification of the properties of other molecular solids
by compression depending on their ability to trap relatively small atomic or
molecular species and form new compounds. Furthermore, our work suggests that
compression of molecular solids with noble gases as helium could result in
unexpected results compared to other pressure-transmitting media.",1502.04279v1
2015-02-26,A recommendation engine for suggesting unexpected thermoelectric chemistries,"The experimental search for new thermoelectric materials remains largely
confined to a limited set of successful chemical and structural families, such
as chalcogenides, skutterudites, and Zintl phases. In principle, computational
tools such as density functional theory (DFT) offer the possibility of
rationally guiding experimental synthesis efforts toward very different
chemistries. However, in practice, predicting thermoelectric properties from
first principles remains a challenging endeavor, and experimental researchers
generally do not directly use computation to drive their own synthesis efforts.
To bridge this practical gap between experimental needs and computational
tools, we report an open machine learning-based recommendation engine
(http://thermoelectrics.citrination.com) for materials researchers that
suggests promising new thermoelectric compositions, and evaluates the
feasibility of user-designed compounds. We show that this engine can identify
interesting chemistries very different from known thermoelectrics.
Specifically, we describe the experimental characterization of one example set
of compounds derived from our engine, RE12Co5Bi (RE = Gd, Er), which exhibits
surprising thermoelectric performance given its unprecedentedly high loading
with metallic d and f block elements, and warrants further investigation as a
new thermoelectric material platform.",1502.07635v3
2015-02-27,Effects of chemical pressure on the magnetic ground states of the osmate double perovskites SrCaCoOsO6 and Ca2CoOsO6,"The magnetic ground state in the double perovskite system Sr2-xCaxCoOsO6
changes from an antiferromagnet (x = 0), to a spin glass (x = 1), to a
ferrimagnet (x = 2) as the Ca content increases. This crossover is driven by
chemical pressure effects that control the relative strength of magnetic
exchange interactions. The synthesis, crystal structure, and magnetism of
SrCaCoOsO6 and Ca2CoOsO6 are investigated and compared with Sr2CoOsO6. Both
compounds adopt a monoclinic crystal structure with rock salt ordering of Co2+
and Os6+ and a-a-b+ octahedral tilting, but the average Co-O-Os bond angle
evolves from 158.0(3) degrees in SrCaCoOsO6 to 150.54(9) degrees in Ca2CoOsO6
as the smaller Ca2+ ion replaces Sr2+. While this change may seem minor it has
a profound effect on the magnetism, changing the magnetic ground state from
antiferromagnetic in Sr2CoOsO6 (TN1 = 108 K, TN2 = 70 K), to a spin glass in
SrCaCoOsO6 (Tf1 = 32 K, Tf2 = 13 K), to ferrimagnetic in Ca2CoOsO6 (TC = 145
K). In the first two compounds the observation of two transitions is consistent
with weak coupling between the Co and Os sublattices.",1503.00029v3
2015-03-03,"Theoretical study of ThF$^+$ in the search for T,P-violation effects: Effective state of a Th atom in ThF$^+$ and ThO compounds","We report the results of theoretical investigation of electronic structure of
ThF$^+$ cation which is one of the most interesting systems to search for the
electron electric dipole moment (eEDM) [H. Loh, K.C. Cossel, M.C. Grau, K.-K.
Ni, E.R. Meyer, J.L. Bohn, J. Ye, E.A. Cornell, Science {\bf 342}, 1220 (2013)]
and other effects of violation of time reversal (T) and spacial parity (P)
symmetries in fundamental interactions. For the working $^3\Delta_1$ state we
have found a quite high value of the effective electric field acting on
unpaired electrons (37.3 GV/cm). The field will be required to interpret the
experiment planed on ThF$^+$ in terms of eEDM. Within the concept of atoms in
compounds [A.V. Titov, Y.V. Lomachuk, and L.V. Skripnikov, Phys. Rev. A {\bf
90}, 052522 (2014)] we have compared the ThF$^+$ electronic structure with that
of ThO. Also we have calculated other parameters of T,P-odd interactions:
$W_{T,P}$, which is needed for interpretation of the experiment in terms of the
dimensionless constant $k_{T,P}$ characterizing the strength of the T,P-odd
pseudoscalar$-$scalar electron$-$nucleus neutral current interaction (50 kHz);
$W_M$, which is required to search for the Th nuclear magnetic quadrupole
moment in $^{229}$ThF$^+$ (0.88 $\frac{10^{33}\mathrm{Hz}}{e {\rm cm}^2}$). A
number of properties which can be measured are also calculated: hyperfine
structure constant, the molecule-frame dipole moment, and g-factor.",1503.01001v2
2015-03-10,In-plane electronic anisotropy in the antiferromagnetic-orthorhombic phase of isovalent-substituted Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$,"We have studied the anisotropy in the in-plane resistivity and the electronic
structure of isovalent Ru-substituted BaFe$_2$As$_2$ in the
antiferromagnetic-orthorhombic phase using well-annealed crystals. The
anisotropy in the residual resistivity component increases in proportional to
the Ru dopant concentration, as in the case of Co-doped compounds. On the other
hand, both the residual resistivity and the resistivity anisotropy induced by
isovalent Ru substitution is found to be one order of magnitude smaller than
those induced by heterovalent Co substitution. Combined with angle-resolved
photoemission spectroscopy results, which show almost the same anisotropic band
structure both for the parent and Ru-substituted compounds, we confirm the
scenario that the anisotropy in the residual resistivity arises from
anisotropic impurity scattering in the magneto-structurally ordered phase
rather than directly from the anisotropic band structure of that phase.",1503.02855v1
2015-03-11,Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5,"We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE)
behaviour of a Haldane spin-chain compound containing light rare-earth ion,
Nd2BaNiO5, in detail, as a function of temperature (T) and magnetic field (H)
down to 2 K. In addition to the well-known long range antiferromagnetic order
setting in at (T_N=) 48 K as indicated in dc magnetization (M), we have
observed another magnetic transition near 10 K; this transition appears to be
of a glassy-type which vanishes with a marginal application of external
magnetic field (even H= 100 Oe). There are corresponding anomalies in
dielectric constant as well with variation of T. The isothermal M(H) curves at
2 and 5 K reveal the existence of a magnetic-field induced transition around 90
kOe; the isothermal H-dependent dielectric constant also tracks such a
metamagnetic transition. These results illustrate the MDE coupling in this
compound. Additionally, we observe a strong frequency dependence of a step in
T-dependent dielectric constant with this feature appearing around 25-30 K for
the lowest frequency of 1 kHz, far below T_N. This is attributed to interplay
between crystal-field effect and exchange interaction between Nd and Ni, which
establishes the sensitivity of dielectric measurements to detect such effects.
Interestingly enough, the observed dispersions of the T-dependent dielectric
constant curves is essentially H-independent in the entire T-range of
measurement, despite the existence of MDE coupling, which is in sharp contrast
with other heavy rare-earth members in this series.",1503.03307v1
2015-03-24,Mixtures of g-priors in Generalized Linear Models,"Mixtures of Zellner's g-priors have been studied extensively in linear models
and have been shown to have numerous desirable properties for Bayesian variable
selection and model averaging. Several extensions of g-priors to Generalized
Linear Models (GLMs) have been proposed in the literature; however, the choice
of prior distribution of g and resulting properties for inference have received
considerably less attention. In this paper, we unify mixtures of g-priors in
GLMs by assigning the truncated Compound Confluent Hypergeometric (tCCH)
distribution to 1/(1 + g), which encompasses as special cases several mixtures
of g-priors in the literature, such as the hyper-g, Beta-prime, truncated
Gamma, incomplete inverse-Gamma, benchmark, robust, hyper-g/n, and intrinsic
priors. Through an integrated Laplace approximation, the posterior distribution
of 1/(1 + g) is in turn a tCCH distribution, and approximate marginal
likelihoods are thus available analytically, leading to ""Compound
Hypergeometric Information Criteria"" for model selection. We discuss the local
geometric properties of the g-prior in GLMs and show how the desiderata for
model selection proposed by Bayarri et al, such as asymptotic model selection
consistency, intrinsic consistency, and measurement invariance may be used to
justify the prior and specific choices of the hyper parameters. We illustrate
inference using these priors and contrast them to other approaches via
simulation and real data examples. The methodology is implemented in the R
package BAS and freely available on CRAN.",1503.06913v3
2015-03-26,Epsilon-Near-Zero Al-Doped ZnO for Ultrafast Switching at Telecom Wavelengths: Outpacing the Traditional Amplitude-Bandwidth Trade-Off,"Transparent conducting oxides have recently gained great attention as
CMOS-compatible materials for applications in nanophotonics due to their low
optical loss, metal-like behavior, versatile/tailorable optical properties, and
established fabrication procedures. In particular, aluminum doped zinc oxide
(AZO) is very attractive because its dielectric permittivity can be engineered
over a broad range in the near infrared and infrared. However, despite all
these beneficial features, the slow (> 100 ps) electron-hole recombination time
typical of these compounds still represents a fundamental limitation impeding
ultrafast optical modulation. Here we report the first epsilon-near-zero AZO
thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation
and recombination time below 1 ps) and an outstanding reflectance modulation up
to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength
of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the
result of a low temperature fabrication procedure promoting oxygen vacancies
and an ultra-high carrier concentration. As a proof-of-concept, an all-optical
AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and
operating at THz frequencies is numerically demonstrated. Our results overcome
the traditional ""modulation depth vs. speed"" trade-off by at least an order of
magnitude, placing AZO among the most promising compounds for
tunable/switchable nanophotonics.",1503.07832v1
2015-03-30,Implications of magnetic and magnetodielectric behavior of GdCrTiO5,"We have carried out dc magnetization (M), heat-capacity (C) and dielectric
studies down to 2K for the compound GdCrTiO5, crystallizing in orthorhombic
Pbam structure, in which well-known multiferroics RMn2O5 (R= Rare-earths) form.
The points of emphasis are: (i) The magnetic ordering temperature of Cr appears
to be suppressed compared to that in isostructural Nd counterpart, NdCrTiO5,
for which the Neel temperature is about 21 K. This finding on the Gd compound
suggests that Nd 4f orbital plays a role on the magnetism of Cr in contrast to
a proposal long ago. (ii) Dielectric constant does not exhibit any notable
feature below about 30 K in the absence of external magnetic field, but a peak
appears and gets stronger with the application of external magnetic fields,
supporting the existence of magnetodielectric coupling. (iii) The dielectric
anomalies appear even near 100 K, which can be attributed to short-range
magnetic-order. We also observe a gain in spectral weight below about 150 K in
Raman spectra in the frequency range 150 to 400 cm-1, which could be magnetic
in origin supporting short-range magnetic order. It is of interest to explore
whether geometrically frustration plays any role on the dielectric properties
of this family, as in the case of RMn2O5.",1503.08729v2
2015-04-29,Two distinct topological phases in the mixed valence compound YbB6 and its differences from SmB6,"We discuss the evolution of topological states and their orbital textures in
the mixed valence compounds SmB6 and YbB6 within the framework of the
generalized gradient approximation plus onsite Coulomb interaction (GGA+U)
scheme for a wide range of values of U. In SmB6, the topological Kondo
insulator (TKI) gap is found to be insensitive to the value of U, but in sharp
contrast, Kondo physics in isostructural YbB6 displays a surprising sensitivity
to U. In particular, as U is increased in YbB6, the correlated TKI state in the
weak-coupling regime transforms into a d-p-type topological insulator phase
with a band inversion between Yb-5d and B-2p orbitals in the intermediate
coupling range, without closing the insulating energy gap throughout this
process. Our theoretical predictions related to the TKI and non-TKI phases in
SmB6 and YbB6 are in substantial accord with recent angle-resolved
photoemission spectroscopy (ARPES) experiments.",1504.08038v2
2015-05-08,Electronic structures of ferromagnetic superconductors $\mathrm{UGe}_2$ and $\mathrm{UCoGe}$ studied by angle-resolved photoelectron spectroscopy,"The electronic structures of the ferromagnetic superconductors
$\mathrm{UGe}_2$ and $\mathrm{UCoGe}$ in the paramagnetic phase were studied by
angle-resolved photoelectron spectroscopy using soft X-rays ($h\nu =400-500$).
The quasi-particle bands with large contributions from $\mathrm{U}~5f$ states
were observed in the vicinity of $E_\mathrm{F}$, suggesting that the
$\mathrm{U}~5f$ electrons of these compounds have an itinerant character. Their
overall band structures were explained by the band-structure calculations
treating all the $\mathrm{U}~5f$ electrons as being itinerant. Meanwhile, the
states in the vicinity of $E_\mathrm{F}$ show considerable deviations from the
results of band-structure calculations, suggesting that the shapes of Fermi
surface of these compounds are qualitatively different from the calculations,
possibly caused by electron correlation effect in the complicated band
structures of the low-symmetry crystals. Strong hybridization between
$\mathrm{U}~5f$ and $\mathrm{Co}~3d$ states in $\mathrm{UCoGe}$ were found by
the $\mathrm{Co}~2p-3d$ resonant photoemission experiment, suggesting that
$\mathrm{Co}~3d$ states have finite contributions to the magnetic, transport,
and superconducting properties.",1505.01898v1
2015-05-15,Frequency Extension to THz Range in High Pressure ESR System and Its Application to Shastry-Sutherland Model Compound SrCu$_{2}$(BO$_{3}$)$_{2}$,"We have made a survey of ceramics for the inner parts of the
transmission-type pressure cell to achieve the high pressure and the high
transmission in THz range. By using the optimal combination of ZrO$_{2}$-based
ceramic and Al$_{2}$O$_{3}$ ceramic, we have succeeded in obtaining the
pressure up to 1.5 GPa and the frequency region up to 700 GHz simultaneously.
We show the high-pressure ESR results of Shastry-Sutherland compound
SrCu$_{2}$(BO$_{3}$)$_{2}$ as an application. We observed the direct ESR
transition modes between the singlet ground state and the triplet excited
states up to the pressure of 1.51 GPa successfully, and obtained the precise
pressure dependence of the gap energy. The gap energy is directly proved to be
suppressed by the pressure. Moreover, we found that the system approaches the
quantum critical point with pressure by comparing the obtained data with the
theory. This result also shows the usefulness of high-pressure ESR measurement
in THz region to study quantum spin systems.",1505.03995v1
2015-05-17,Analysis of a wet scrubber network in the air remediation of industrial workplaces: benefit for the city air quality,"Industrial activities carried out in confined spaces are characterized by a
very specific type of air pollution. The extended exposure to this kind of
pollution is often highly harmful, resulting in dramatic effects both on health
and safety aspects. The indoor industrial abatement systems, adopted to purify
the air, are typically applied to the emission points. The processed air is
subsequently emitted outside. In this study we present the experimental results
of three-stage wet scrubber systems installed in the industrial workplace of a
(i) fiberglass processing plant, where the highest exposure levels to volatile
compounds are nowadays today monitored,and of a (ii) waste-to-energy plant,
characterized by a very high particulate matter level. The adopted technology,
to be used as complementing strategy,does not require special disposal
procedures and the processed air is re-emitted in the same work environment for
the benefit of the work operators. The operation of the scrubbers network
during the working activities, in both the examined environments, has a)
reduced the level of volatile compounds by about 40% and b) maintained the
particulate matter concentration PM > 1 to a very low level. Industrial plants
are disseminated in mega-cities and represent dangerous diffuse pollution
emission sources. Remediation of highly polluted industrial plants inside our
towns, especially for the conventionally untreated emissions, is of extreme
benefit for the cities air quality.",1505.05085v1
2015-05-22,Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor,"In the family of iron-based superconductors, LaFeAsO-type materials possess
the simplest electronic structure due to their pronounced two-dimensionality.
And yet they host superconductivity with the highest transition temperature
Tc=55K. Early theoretical predictions of their electronic structure revealed
multiple large circular portions of the Fermi surface with a very good
geometrical overlap (nesting), believed to enhance the pairing interaction and
thus superconductivity. The prevalence of such large circular features in the
Fermi surface has since been associated with many other iron-based compounds
and has grown to be generally accepted in the field. In this work we show that
a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO, is at odds with
this description and possesses a distinctly different Fermi surface, which
consists of two singular constructs formed by the edges of several bands,
pulled to the Fermi level from the depths of the theoretically predicted band
structure by strong electronic interactions. Such singularities dramatically
affect the low-energy electronic properties of the material, including
superconductivity. We further argue that occurrence of these singularities
correlates with the maximum superconducting transition temperature attainable
in each material class over the entire family of iron-based superconductors.",1505.06152v1
2015-06-04,Magnetic neutron scattering studies on the Fe-based superconductor system Fe$_{1+y}$Te$_{1-x}$Se$_x$,"I present a brief overview on the interplay between magnetism and
superconductivity in one of the Fe-based superconductor systems, \fts, where
the research of our group has centered. The parent compound Fe$_{1+y}$Te is an
antiferromagnet; with Se doping, antiferromagnetic order is suppressed,
followed by the appearance of superconductivity; optimal superconductivity is
achieved when $x\sim50\%$, with a superconducting temperature \tc of
$\sim$15~K. The parent compound has an in-plane magnetic ordering wave vector
around (0.5,\,0) (using the tetragonal notation with two Fe atoms per cell).
When Se concentration increases, the spectral weight appears to be shifted to
the wave vector around (0.5,\,0.5), accompanying the optimization of
superconductivity. A neutron-spin resonance has been observed around
(0.5,\,0.5) below \tc, and is suppressed, along with superconductivity, by an
external magnetic field. Taking these evidences into account, it is concluded
that magnetism and superconductivity in this system couple to each other
closely---while the static magnetic order around (0.5,\,0) competes with
superconductivity, the spin excitations around (0.5,\,0.5) may be an important
ingredient for it. I will also discuss the nature of magnetism and substitution
effects of 3$d$ transition metals.",1506.01536v1
2015-06-16,"Strong enhancement of conventional superconductivity near a quantum critical point of (Ca,Sr)_3Ir_4Sn_13","Competing electronic states are found in the large majority of unconventional
superconductors, including high-Tc cuprates, iron based superconductors and
many heavy fermion systems. The complex interplay is reflected in phase
diagrams as a function of doping or other tuning parameters involving besides
superconducting other phases (often magnetic) and quantum critical points.
Superconductivity is also found in the vicinity of charge density wave (CDW)
order in phase diagrams reminiscent of superconductivity mediated by magnetic
fluctuations. There is however less knowledge about the interplay of
superconductivity and CDW compared to the magnetic analogon. Here we report
about microscopic studies by muon spin rotation as a function of pressure of
the Ca_3Ir_4Sn_13 and Sr_3Ir_4Sn_13 cubic compounds, which display
superconductivity and a structural phase transition associated with the
formation of a CDW. We find a strong enhancement of the superfluid density and
of the coupling strength above a pressure of about 1.6 GPa giving direct
evidence of the presence of a quantum critical point separating a
superconducting phase coexisting with CDW from a pure superconducting phase.
The superconducting order parameter in both phases are found to have the same
s-wave symmetry. In spite of the conventional phonon-mediated BCS character of
this compound, the dependence of the effective superfluid density on the
critical temperature puts this system in the ""Uemura"" plot close to
unconventional superconductors.",1506.04995v2
2015-06-18,Photoluminescence and Raman investigation of stability of InSe and GaSe thin films,"Layered III-chalcogenide compounds belong to a variety of layered crystals
that can be implemented in van der Waals heterostructures. Here we report an
optical study of the stability of two of these compounds: indium selenide
(InSe) and gallium selenide (GaSe). Micro-photoluminescence (PL) and Raman
spectroscopy are used to determine how the properties of thin films of these
materials change when they are exposed to air at room temperature. We find that
in GaSe films, PL signal decreases on average below 50% over 24 (72) hours of
exposure for films with thicknesses 10-25 (48-75) nm. In contrast, weak PL
decrease of less than 20% is observed for InSe nm films after exposure of 100
hours. Similar trends are observed in Raman spectroscopy: within a week, the
Raman signal decreases by a factor of 10 for a 24 nm thick GaSe, whereas no
decrease was found for a 16 nm InSe film. We estimate that when exposed to air,
the layers adjacent to the GaSe film surface degrade and become non-luminescent
with a rate of 0.14$\pm$0.05 nm/hour. We show that the life-time of the GaSe
films can be increased by up to two orders of magnitude (to several months) by
encapsulation in dielectric materials such as SiO$_2$ or Si$_x$N$_y$.",1506.05619v1
2015-06-28,"On magnitude, asymptotics and duration of drawdowns for Lévy models","This paper considers magnitude, asymptotics and duration of drawdowns for
some L\'{e}vy processes. First, we revisit some existing results on the
magnitude of drawdowns for spectrally negative L\'{e}vy processes using an
approximation approach. For any spectrally negative L\'{e}vy process whose
scale functions are well-behaved at $0+$, we then study the asymptotics of
drawdown quantities when the threshold of drawdown magnitude approaches zero.
We also show that such asymptotics is robust to perturbations of additional
positive compound Poisson jumps. Finally, thanks to the asymptotic results and
some recent works on the running maximum of L\'{e}vy processes, we derive the
law of duration of drawdowns for a large class of L\'{e}vy processes (with a
general spectrally negative part plus a positive compound Poisson structure).
The duration of drawdowns is also known as the ""Time to Recover"" (TTR) the
historical maximum, which is a widely used performance measure in the fund
management industry. We find that the law of duration of drawdowns
qualitatively depends on the path type of the spectrally negative component of
the underlying L\'{e}vy process.",1506.08408v2
2015-07-02,Discovery of a Weyl Semimetal in non-Centrosymmetric Compound TaAs,"Three-dimensional (3D) topological Weyl semimetals (TWSs) represent a novel
state of quantum matter with unusual electronic structures that resemble both a
""3D graphene"" and a topological insulator by possessing pairs of Weyl points
(through which the electronic bands disperse linearly along all three momentum
directions) connected by topological surface states, forming the unique
""Fermi-arc"" type Fermi-surface (FS). Each Weyl point is chiral and contains
half of the degrees of freedom of a Dirac point, and can be viewed as a
magnetic monopole in the momentum space. Here, by performing angle-resolved
photoemission spectroscopy on non-centrosymmetric compound TaAs, we observed
its complete band structures including the unique ""Fermi-arc"" FS and linear
bulk band dispersion across the Weyl points, in excellent agreement with the
theoretical calculations. This discovery not only confirms TaAs as the first 3D
TWS, but also provides an ideal platform for realizing exotic physical
phenomena (e.g. negative magnetoresistance, chiral magnetic effects and quantum
anomalous Hall effect) which may also lead to novel future applications.",1507.00521v2
2015-07-02,Convergence of Marked Point Processes of Excesses for Dynamical Systems,"We consider stochastic processes arising from dynamical systems simply by
evaluating an observable function along the orbits of the system and study
marked point processes associated to extremal observations of such time series
corresponding to exceedances of high thresholds. Each exceedance is marked by a
quantity intended to measure the severity of the exceedance. In particular, we
consider marked point processes measuring the aggregate damage by adding all
the excesses over the threshold that mark each exceedance (AOT) or simply by
adding the largest excesses in a cluster of exceedances (POT). We provide
conditions to prove the convergence of such marked point processes to a
compound Poisson process, for whose multiplicity distribution we give an
explicit formula. These conditions are shown to follow from a strong form of
decay of correlations of the system. Moreover, we prove that the convergence of
the marked point processes for a `nice' first return induced map can be carried
to the original system. The systems considered include non-uniformly expanding
maps (in one or higher dimensions), maps with intermittent fixed points or
non-recurrent critical points. For a general class of examples, the compound
Poisson limit process is computed explicitly and, in particular, in the POT
case we obtain a generalised Pareto multiplicity distribution.",1507.00599v2
2015-07-06,A metallic mosaic phase and the origin of Mott insulating state in 1T-TaS2,"Electron-electron and electron-phonon interactions are two major driving
forces that stabilize various charge-ordered phases of matter. The intricate
interplay between the two give rises to a peculiar charge density wave (CDW)
state, which is also known as a Mott insulator, as the ground state of layered
compound 1T-TaS2. The delicate balance also makes it possible to use external
perturbations to create and manipulate novel phases in this material. Here, we
study a mosaic CDW phase induced by voltage pulses from the tip of a scanning
tunneling microscope (STM), and find that the new phase exhibit electronic
structures that are entirely different from the Mott ground state of 1T-TaS2 at
low temperatures. The mosaic phase consists of nanometer-sized domains
characterized by well-defined phase shifts of the CDW order parameter in the
topmost layer, and by altered stacking relative to the layer underneath. We
discover that the nature of the new phases is dictated by the stacking order,
and our results shed fresh light on the origin of the Mott phase in this
layered compound.",1507.01312v1
2015-07-06,Unconventional superconductivity in the layered iron germanide YFe$_2$Ge$_2$,"Since the discovery of superconductivity in LaFePO in 2006, numerous
iron-based superconductors have been identified within diverse structure
families, all of which combine iron with a group-V (pnictogen) or group-VI
(chalco- gen) element. Unconventional superconductivity is extremely rare among
transition metal compounds outside these layered iron systems and the cuprates,
and it is almost universally associated with highly anisotropic electronic
properties and nearly 2D Fermi surface geometries. The iron-based intermetallic
YFe$_2$Ge$_2$ features a 3D Fermi surface and a strongly enhanced low
temperature heat capacity, which signals strong electronic correlations. We
present data from a new generation of high quality samples of YFe$_2$Ge$_2$,
which show superconducting transition anomalies below 1.8 K in thermodynamic as
well as transport measurements, establishing that superconductivity is
intrinsic in this layered iron compound outside the known superconducting iron
pnictide or chalcogenide families. The Fermi surface geometry of YFe$_2$Ge$_2$
resembles that of KFe$_2$As$_2$ in the high pressure collapsed tetragonal
phase, in which superconductivity at temperatures as high as 10 K has recently
been reported, suggesting an underlying connection between the two systems.",1507.01436v2
2015-07-06,Theory of Raman response in three-dimensional Kitaev spin liquids: application to $β-$ and $γ-$Li$_2$IrO$_3$ compounds,"We calculate the Raman response for the Kitaev spin model on the
$\mathcal{H}$-$0$, $\mathcal{H}$-$1$, and $\mathcal{H}$-$\infty$ harmonic
honeycomb lattices. We identify several quantitative features in the Raman
spectrum that are characteristic of the spin liquid phase. Unlike the dynamical
structure factor, which probes both the Majorana spinons and flux excitations
that emerge from spin fractionalization, the Raman spectrum in the Kitaev
models directly probes a density of states of pairs of fractional, dispersing
Majorana spinons. As a consequence, the Raman spectrum in all these models is
gapless for sufficiently isotropic couplings, with a low-energy power law that
results from the Fermi lines (or points) of the dispersing Majorana spinons. We
show that the polarization dependence of the Raman spectrum contains crucial
information about the symmetry of the ground state. We also discuss to what
extent the features of the Raman response that we find reflect generic
properties of the spin liquid phase, and comment on their possible relevance to
$\alpha-$, $\beta-$ and $\gamma-$Li$_2$IrO$_3$ compounds.",1507.01639v2
2015-07-22,Magnetic Orders Proximal to the Kitaev Limit in Frustrated Triangular Systems: Application to Ba$_3$IrTi$_2$O$_9$,"Frustrated transition metal compounds in which spin-orbit coupling (SOC) and
electron correlation work together have attracted much attention recently. In
the case of 5$d$ transition metals, where SOC is large, $j_\text{eff}=1/2$
bands near the Fermi level are thought to encompass the essential physics of
the material, potentially leading to a concrete realization of exotic magnetic
phases such as the Kitaev spin liquid. Here we derive a spin model on a
triangular lattice based on $j_\text{eff} = 1/2$ pseudospins that interact via
antiferromagnetic Heisenberg ($J$) and Kitaev ($K$) exchanges, and crucially,
an anisotropic $(\Gamma)$ exchange. Our classical analysis of the spin model
reveals that, in addition to small regions of 120$^\circ$, $\mathbb{Z}_2$ /
dual-$\mathbb{Z}_2$ vortex crystal and nematic phases, the stripy and
ferromagnetic phases dominate the $J$-$K$-$\Gamma$ phase diagram. We apply our
model to the 5$d$ transition metal compound, Ba$_3$IrTi$_2$O$_9$, in which the
Ir$^{4+}$ ions form layered two-dimensional triangular lattices. We compute the
band structure and nearest-neighbor hopping parameters using ab-initio
calculations. By combining our ab-initio and classical analyses, we predict
that Ba$_3$IrTi$_2$O$_9$ has a stripy ordered magnetic ground state.",1507.06307v1
2015-07-27,Room temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO$_{3}$ ceramics,"Room temperature dielectric and magnetic properties of BiFeO$_3$ samples,
co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe,
respectively, were reported. The nominal compositions of
Bi$_{0.9}$Gd$_{0.1}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.25) ceramics were
synthesized by conventional solid state reaction technique. X-ray diffraction
patterns revealed that the substitution of Fe by Ti induces a phase transition
from rhombohedral to orthorhombic at x $>$ 0.20. Morphological studies
demonstrated that the average grain size was reduced from $\sim {~}$1.5 $\mu m$
to $\sim {~}$200 $nm$ with the increase in Ti content. Due to Ti substitution,
the dielectric constant was stable over a wide range of high frequencies (30
kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric
properties of the compounds are associated with their improved morphologies and
reduced leakage current densities probably due to the lower concentration of
oxygen vacancies in the compositions. Magnetic properties of
Bi$_{0.9}$Gd$_{0.1}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.25) ceramics measured at
room temperature were enhanced with Ti substitution up to 20 $\%$ compared to
that of pure BiFeO$_3$ and Ti undoped Bi$_{0.9}$Gd$_{0.1}$FeO$_3$ samples. The
enhanced magnetic properties might be attributed to the substitution induced
suppression of spiral spin structure of BiFeO$_3$. An asymmetric shifts both in
the field and magnetization axes of magnetization versus magnetic field (M-H)
curves was observed. This indicates the presence of exchange bias effect in
these compounds notably at room temperature.",1507.07365v1
2015-07-28,Influence of substitutional disorder on the electrical transport and the superconducting properties of Fe$_{1+z}$Te$_{1-x-y}$Se$_{x}$S$_{y}$,"We have carried out an investigation of the structural, magnetic, transport
and superconducting properties of Fe$_{1+z}$Te$_{1-x-y}$Se$_x$S$_y$ ceramic
compounds, for $z=0$ and some specific Se (0$\leq$ x $\leq$ 0.5) and S (0
$\leq$ y $\leq$0.12) contents. The incorporation of Se and S to the FeTe
structure produces a progressive reduction of the crystallographic parameters
as well as different degrees of structural disorder associated with the
differences of the ionic radius of the substituting cations. In the present
study, we measure transport properties of this family of compounds and we show
the direct influence of disorder in the normal and superconductor states. We
notice that the structural disorder correlates with a variable range hopping
conducting regime observed at temperatures $T >$ 200 K. At lower temperatures,
all the samples except the one with the highest degree of disorder show a
crossover to a metallic-like regime, probably related to the transport of
resilient-quasi-particles associated with the proximity of a Fermi liquid state
at temperatures below the superconducting transition. Moreover, the
superconducting properties are depressed only for that particular sample, in
accordance to the condition that superconductivity is affected by disorder when
the electronic localization length $\xi_L$ becomes smaller than the coherence
length $\xi_{SC}$.",1507.07853v1
2015-08-03,"Probing the superconducting ground state of the rare-earth ternary boride superconductors $R$RuB$_2$ ($R$ = Lu,Y) using muon-spin rotation and relaxation","The superconductivity in the rare-earth transition metal ternary borides
$R$RuB$_2$ (where $R$ = Lu and Y) has been investigated using muon-spin
rotation and relaxation. Measurements made in zero-field suggest that
time-reversal symmetry is preserved upon entering the superconducting state in
both materials; a small difference in depolarization is observed above and
below the superconducting transition in both compounds, however this has been
attributed to quasistatic magnetic fluctuations. Transverse-field measurements
of the flux-line lattice indicate that the superconductivity in both materials
is fully gapped, with a conventional s-wave pairing symmetry and BCS-like
magnitudes for the zero-temperature gap energies. The electronic properties of
the charge carriers in the superconducting state have been calculated, with
effective masses $m^*/ m_\mathrm{e} = $ $9.8\pm0.1$ and $15.0\pm0.1$ in the Lu
and Y compounds, respectively, with superconducting carrier densities
$n_\mathrm{s} = $ ($2.73\pm0.04$) $\times 10^{28}$ m$^{-3}$ and ($2.17\pm0.02$)
$\times 10^{28}$ m$^{-3}$. The materials have been classified according to the
Uemura scheme for superconductivity, with values for
$T_\mathrm{c}/T_\mathrm{F}$ of $1/(414\pm6)$ and $1/(304\pm3)$, implying that
the superconductivity may not be entirely conventional in nature.",1508.00486v2
2015-08-05,Giant negative thermal expansion covering room temperature in nanocrystalline GaNxMn3,"Materials with negative thermal expansion (NTE), which contract upon heating,
are of great interest both technically and fundamentally. Here, we report giant
NTE covering room temperature in mechanically milled antiperovksite GaNxMn3
compounds. The micrograin GaNxMn3 exhibits a large volume contraction at the
antiferromagnetic (AFM) to paramagnetic (PM) (AFM-PM) transition within a
temperature window ({\Delta}T) of only a few kelvins. The grain size reduces to
~ 30 nm after slight milling, while {\Delta}T is broadened to 50K. The
corresponding coefficient of linear thermal expansion ({\alpha}) reaches ~ -70
ppm/K, which is almost two times larger than those obtained in chemically doped
antiperovskite compounds. Further reducing grain size to ~ 10 nm, {\Delta}T
exceeds 100 K and {\alpha} remains as large as -30 ppm/K (-21 ppm/K) for x =
1.0 (x = 0.9). Excess atomic displacements together with the reduced structural
coherence, revealed by high-energy X-ray pair distribution functions, are
suggested to delay the AFM-PM transition. By controlling the grain size via
mechanically alloying or grinding, giant NTE may also be achievable in other
materials with large lattice contraction due to electronic or magnetic phase
transitions.",1508.01063v1
2015-08-26,Spatial competition of the ground states in 1111 iron pnictides,"Using nuclear quadrupole resonance, the phase diagram of 1111
$R$FeAsO$_{1-x}$F$_x$ ($R$$=$La, Ce, Sm) iron pnictides is constructed as a
function of the local charge distribution in the paramagnetic state, which
features low-doping-like (LD-like) and high-doping-like (HD-like) regions.
Compounds based on magnetic rare earths (Ce, Sm) display a unified behavior,
and comparison with La-based compounds reveals the detrimental role of static
iron $3d$ magnetism on superconductivity, as well as a qualitatively different
evolution of the latter at high doping. It is found that the LD-like regions
fully account for the orthorhombicity of the system, and are thus the origin of
any static iron magnetism. Orthorhombicity and static magnetism are not
hindered by superconductivity but limited by dilution effects, in agreement
with 2D (respectively 3D) nearest-neighbor square lattice site percolation when
the rare earth is nonmagnetic (respectively magnetic). The LD-like regions are
not intrinsically supportive of superconductivity, on the contrary of the
HD-like regions, as evidenced by the well-defined Uemura relation between the
superconducting transition temperature and the superfluid density when
accounting for the proximity effect. This leads us to propose a complete
description of the interplay of ground states in 1111 pnictides, where
nanoscopic regions compete to establish the ground state through suppression of
superconductivity by static magnetism, and extension of superconductivity by
proximity effect.",1508.06532v1
2015-09-03,Prediction model of band-gap for AX binary compounds by combination of density functional theory calculations and machine learning techniques,"Machine learning techniques are applied to make prediction models of the G0W0
band-gaps for 156 AX binary compounds using Kohn-Sham band-gaps and other
fundamental information of constituent elements and crystal structure as
predictors. Ordinary least square regression (OLSR), least absolute shrinkage
and selection operator (LASSO) and non-linear support vector regression (SVR)
methods are applied with several levels of predictor sets. When the Kohn-Sham
band-gap by GGA (PBE) or modified Becke-Johnson (mBJ) is used as a single
predictor, OLSR model predicts the G0W0 band-gap of a randomly selected test
data with the root mean square error (RMSE) of 0.54 eV. When Kohn-Sham band gap
by PBE and mBJ methods are used together with a set of various forms of
predictors representing constituent elements and crystal structures, RMSE
decreases significantly. The best model by SVR yields the RMSE of 0.18 eV. A
large set of band-gaps estimated in this way should be useful as predictors for
materials exploration.",1509.00973v1
2015-09-15,Search for New Superconductors: An Electro-Magnetic Phase Transition in an Iron Meteorite Inclusion at 117 K,"The discovery of superconductivity in pnictides and iron chalcogenides
inspires the search for new iron based superconducting phases. Iron-rich
meteorites present a unique opportunity for this search, because they contain a
broad range of compounds produced under extreme growth conditions. We
investigated a natural iron sulfide based materials (Troilite) inclusion with
its associated minerals in the iron meteorite Tlacotepec. Tlacotepec formed in
an asteroidal core under high pressure and at high temperature over millions of
years, while insoluble sulfur rich materials segregated into inclusions during
cooling along with included minerals. The search for superconductivity in these
heterogeneous materials requires a technique capable of detecting minute
amounts of a superconducting phase embedded in a non-superconducting matrix. We
used Magnetic Field Modulated Microwave Spectroscopy (MFMMS), a very sensitive,
selective, and non-destructive technique, to search for superconductivity in
heterogeneous systems. Here, we report the observation of an electro-magnetic
phase transition at 117 K that causes a MFMMS-response typical of a
superconductor. A pronounced and reproducible peak together with isothermal
magnetic field sweeps prove the appearance of a new electromagnetic phase below
117 K. This is very similar to the characteristic response due to flux trapping
in a granular superconductor with a short coherence length. Although the
compound responsible for the peak in the MFMMS-spectra was not identified, it
is possibly an iron sulfide based phase, or another material heterogeneously
distributed over the inclusion.",1509.04452v2
2015-09-15,Crystal structure and magnetism in $α$-RuCl3: an ab-initio study,"$\alpha$-RuCl$_3$ has been proposed recently as an excellent playground for
exploring Kitaev physics on a two-dimensional (2D) honeycomb lattice. However,
structural clarification of the compound has not been completed, which is
crucial in understanding the physics of this system. Here, using {\it
ab-initio} electronic structure calculations, we study a full three dimensional
(3D) structure of $\alpha$-RuCl$_3$ including the effects of spin-orbit
coupling (SOC) and electronic correlations. Three major results are as follows;
i) SOC suppresses dimerization of Ru atoms, which exists in other Ru compounds
such as isostructural Li$_2$RuO$_3$, and making the honeycomb closer to an
ideal one. ii) The nearest-neighbor Kitaev exchange interaction between the
$j_{\rm eff}$=1/2 pseudospin depends strongly on the Ru-Ru distance and the Cl
position, originating from the nature of the edge-sharing geometry. iii) The
optimized 3D structure without electronic correlations has $P{\bar 3}1m$ space
group symmetry independent of SOC, but including electronic correlation changes
the optimized 3D structure to either $C2/m$ or $Cmc2_1$ within 0.1 meV per
formula unit (f.u.) energy difference. The reported $P3_112$ structure is also
close in energy. The interlayer spin exchange coupling is a few percent of
in-plane spin exchange terms, confirming $\alpha$-RuCl$_3$ is close to a 2D
system. We further suggest how to increase the Kitaev term via tensile strain,
which sheds new light in realizing Kitaev spin liquid phase in this system.",1509.04723v2
2015-09-21,Effects of Pb doping on structural and electronics properties of Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10}$,"Pb doping effect in the Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10}$ compound (Bi2223) on
the structural and electronic properties were investigated, using the Local
Density (LDA) and Virtual Crystal (VCA) approximations within the framework of
the Density Functional Theory (DFT), taking as reference the procedure
implemented by H.Lin {\it et al.} in the Bi2212 compound [{\it Phys. Rev.
Lett.} {\bf 96} (2006) 097001]. Results show that, the incorporation of
Pb-dopant in Bi2223 lead a rigid displacement of the Bi/Pb-O bands toward
higher energies, with a null contribution at the Fermi level, around the high
symmetry point $\overline{\text{M}}$ in the irreducible Brillouin zone, for Pb
doping concentration equal to or more than 26\%, avoiding the presence of the
so-called Bi-O {\it pockets} in the Fermi surface, in good agreement with
angle-resolved photoemission spectroscopy (ARPES) and nuclear magnetic
resonance (NMR) experiments, although a slight metallic character of the Bi-O
bonds is still observed which would disagree with some experimental reports.
The calculations show that the changes on the structural properties are
associated to the presence or absence of the Bi-O {\it pockets} in the Fermi
surface",1509.06388v1
2015-09-23,The Stan Math Library: Reverse-Mode Automatic Differentiation in C++,"As computational challenges in optimization and statistical inference grow
ever harder, algorithms that utilize derivatives are becoming increasingly more
important. The implementation of the derivatives that make these algorithms so
powerful, however, is a substantial user burden and the practicality of these
algorithms depends critically on tools like automatic differentiation that
remove the implementation burden entirely. The Stan Math Library is a C++,
reverse-mode automatic differentiation library designed to be usable, extensive
and extensible, efficient, scalable, stable, portable, and redistributable in
order to facilitate the construction and utilization of such algorithms.
  Usability is achieved through a simple direct interface and a cleanly
abstracted functional interface. The extensive built-in library includes
functions for matrix operations, linear algebra, differential equation solving,
and most common probability functions. Extensibility derives from a
straightforward object-oriented framework for expressions, allowing users to
easily create custom functions. Efficiency is achieved through a combination of
custom memory management, subexpression caching, traits-based metaprogramming,
and expression templates. Partial derivatives for compound functions are
evaluated lazily for improved scalability. Stability is achieved by taking care
with arithmetic precision in algebraic expressions and providing stable,
compound functions where possible. For portability, the library is
standards-compliant C++ (03) and has been tested for all major compilers for
Windows, Mac OS X, and Linux.",1509.07164v1
2015-10-16,Large anharmonic effect and thermal expansion anisotropy of metal chalcogenides: The case of antimony sulfide,"We derive a compact matrix expression for the linear thermal expansion
coefficients (TECs) for a general orthorhombic system which relates the elastic
properties and the integrated quantities based on deformation and mode
dependent Gruneisen parameters and mode dependent heat capacities. The density
of Gruneisen parameters $\Gamma(\nu)$ as a function of frequency $\nu$,
weighted by the number of phonon modes, is introduced and found to be
insightful in interpreting the TEC results. Using density-functional
perturbation theory and Gruneisen formalism for thermal expansion, we
illustrate the general usefulness of this method by calculating the linear and
volumetric TECs of a low-symmetry orthorhombic compound antimony sulfide
(Sb2S3), a compound belonging to a large class of technologically and
fundamentally important materials. Even though negative Gruneisen parameters
are found for deformations in all three crystal directions, the $\Gamma(\nu)$
data rule out the occurrences of negative TECs at all temperatures. Sb2S3
exhibits a large thermal expansion anisotropy where the TEC in the $b$
direction can reach as high as $13\times 10^{-6}$~(1/K) at high temperatures,
about two and seven times larger than the TECs in the $c$ and $a$ direction,
respectively. Our work suggests a general and practical first-principles
approach to calculate the thermal properties of other complicated low-symmetry
systems.",1510.04907v2
2015-10-19,"Sulvanite Compounds Cu3TMS4 (TM= V, Nb and Ta): Elastic, Electronic, Optical and Thermal Properties using First-principles Method","We present a systematic first-principles study of the structural, elastic,
electronic, optical and thermodynamics properties of the sulvanite compounds
Cu3TMS4 (TM = V, Nb and Ta). The structural, elastic and electronic properties
are in fact revisited using a different calculation code than that used by
other workers and the results are compared. The band gaps are found to be
1.041, 1.667 and 1.815 eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively which
are comparable to other available calculated results. The optical properties
such as dielectric function, refractive index, photoconductivity, absorption
coefficients, reflectivity and loss function have been calculated for the first
time. The calculated results are compared with the limited measured data on
energy dependent refractive index and reflectivity coefficient available only
for Cu3TaS4. All the materials are dielectric, transparent in the visible
range. The values of plasma frequencies are found to be 15.36, 15.58 and 15.64
eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively. Furthermore, following the
quasi-harmonic Debye model, the temperature effect on the bulk modulus, heat
capacity, and Debye temperature is calculated reflecting the anharmonic phonon
effects and these are compared with both experimental and other theoretical
data where available.",1510.05564v1
2015-10-21,Spin-Phonon Coupling and High Pressure Phase Transitions of RMnO3 (R= Ca and Pr): An Inelastic Neutron Scattering and First Principle Studies,"We report inelastic neutron scattering measurements over 7-1251 K in CaMnO3
covering various phase transitions, and over 6-150 K in PrMnO3 covering the
magnetic transition. The excitations around 20 meV in CaMnO3 and at 17 meV in
PrMnO3 are found to be associated with magnetic origin. In spite of similarity
of the structure of the two compounds, the neutron inelastic spectrum of PrMnO3
exhibits broad features at 150 K unlike well-defined peaks in the spectrum of
CaMnO3. This might result from the difference in nature of interactions in the
two compounds (magnetic and Jahn-Teller distortion). The interpretation and
analysis of the observed phonon spectra have been performed using ab-initio
phonon calculations. We also discuss the effect of pressure on the structural
distortions in the orthorhombic phase of CaMnO3 and PrMnO3. On application of
pressure, we found that the variations of Mn-O distances are isotropic for
CaMnO3 and highly anisotropic for PrMnO3. The calculated structure as a
function of pressure in PrMnO3 shows that suppression of Jahn-Teller distortion
and insulator to metal transition occurs simultaneously. Our calculations show
that this transition may not be associated with the occurrence of the
tetragonal phase above 20 GPa as reported in the literature, since the
tetragonal phase is found to be dynamically unstable although it is found to be
energetically favored over the orthorhombic phase above 20 GPa. CaMnO3 does not
show any phase transition up to 60 GPa.",1510.06210v1
2015-11-04,Level-resolved quantum statistical theory of electron capture into many-electron compound resonances in highly charged ions,"The strong mixing of many-electron basis states in excited atoms and ions
with open $f$ shells results in very large numbers of complex, chaotic
eigenstates that cannot be computed to any degree of accuracy. Describing the
processes which involve such states requires the use of a statistical theory.
Electron capture into these 'compound resonances' leads to electron-ion
recombination rates that are orders of magnitude greater than those of direct,
radiative recombination, and cannot be described by standard theories of
dielectronic recombination. Previous statistical theories considered this as a
two-electron capture process which populates a pair of single-particle
orbitals, followed by 'spreading' of the two-electron states into chaotically
mixed eigenstates. This method is similar to a configuration-average approach,
as it neglects potentially important effects of spectator electrons and
conservation of total angular momentum. In this work we develop a statistical
theory which considers electron capture into 'doorway' states with definite
angular momentum obtained by the configuration interaction method. We apply
this approach to electron recombination with W$^{20+}$, considering 2 million
doorway states. Despite strong effects from the spectator electrons, we find
that the results of the earlier theories largely hold. Finally, we extract the
fluorescence yield (the probability of photoemission and hence recombination)
by comparison with experiment.",1511.01221v1
2015-12-10,Electron-phonon coupling and thermal transport in the thermoelectric compound $\mathrm{Mo_3Sb_{7-x}Te_x}$,"Phonon properties of $\mathrm{Mo_3Sb_{7-x}Te_x}$ ($x=0,1.5, 1.7$), a
potential high-temperature thermoelectric material, have been studied with
inelastic neutron and x-ray scattering, and with first-principles simulations.
The substitution of Te for Sb leads to pronounced changes in the electronic
structure, local bonding, phonon density of states (DOS), dispersions, and
phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near
the top of the valence band, resulting in a strong suppression of
electron-phonon screening, and a large overall stiffening of interatomic
force-constants. The suppression in electron-phonon coupling concomitantly
increases group velocities and suppresses phonon scattering rates, surpassing
the effects of alloy-disorder scattering, and resulting in a surprising
increased lattice thermal conductivity in the alloy. We also identify that the
local bonding environment changes non-uniformly around different atoms, leading
to variable perturbation strengths for different optical phonon branches. The
respective roles of changes in phonon group velocities and phonon lifetimes on
the lattice thermal conductivity are quantified. Our results highlight the
importance of the electron-phonon coupling on phonon mean-free-paths in this
compound, and also estimates the contributions from boundary scattering,
umklapp scattering, and point-defect scattering.",1512.03120v1
2015-12-14,Polytypism in LaOBiS2-type compounds based on different three-dimensional stacking sequences of two-dimensional BiS2 layers,"LaOBiS2-type materials have drawn much attention recently because of various
interesting physical properties, such as low-temperature superconductivity,
hidden spin polarization, and electrically tunable Dirac cones. However, it was
generally assumed that each LaOBiS2-type compound has a unique and specific
crystallographic structure (with a space group P4/nmm) separated from other
phases. Using first-principles total energy and stability calculations we
confirm that the previous assignment of the centrosymetric P4/nmm structure to
LaOBiS2 is incorrect as a phonon instability renders this structure impossible.
Furthermore, we find that the unstable structure is replaced by a family of
energetically closely spaced modifications (polytypes) differing by the layer
sequences and orientations. We find that the local Bi-S distortion leads to
three polytypes of LaOBiS2 with different stacking patterns of the distorted
BiS2 layers. The energy difference between the polytypes of LaOBiS2 is merely
~1 meV/u.c., indicating the possible coexistence of all polytypes in the real
sample and that the particular distribution of polytypes may be growth-induced.
The in-plane distortion can be suppressed by pressure, leading to a phase
transition from polytypes to the high-symmetry P4/nmm structure with a pressure
larger than 2.5 GPa. In addition, different choices of the intermediate atoms
(replacing La) or active atoms (BiS2) could also manifest different ground
state structures. One can thus tune the distortion and the ground state by
pressure or substituting covalence atoms in LaOBiS2-family.",1512.04505v2
2015-12-14,Dilution effects in spin 7/2 systems. The case of the antiferromagnet GdRhIn$_5$,"We report the structural and magnetic characterization of La-substituted
Gd$_{1-x}$La$_x$RhIn$_5$ ($x\leq$ 0.50) antiferromagnetic (AFM) compounds. The
magnetic responses of pure GdRhIn$_5$ are well described by a $S=7/2$
Heisenberg model. When Gd$^{3+}$ ions are substituted by La$^{3+}$, the maximum
of the susceptibility and the inflection point of the magnetic specific heat
are systematically shifted to lower temperatures accompanied by a broadening of
the transition. The data is qualitatively explained by a phenomenological model
which incorporates a distribution of magnetic regions with different transition
temperatures ($T_N$). The universal behaviour of the low temperature specific
heat is found for La (vacancies) concentrations below $x=0.40$ which is
consistent with spin wave excitations. For $x=0.5$ this universal behaviour is
lost. The sharp second order transition of GdRhIn$_5$ is destroyed, as seen in
the specific heat data, contrary to what is expected for a Heisenberg model.
The results are discussed in the context of the magnetic behavior observed for
the La-substituted (Ce,Tb,Nd)RhIn$_5$ compounds.",1512.04571v1
2015-12-23,Magnetic Ordering and Crystal Field Effects in Quasi Caged Structure Compound PrFe$_2$Al$_8$,"The compound PrFe$_2$Al$_8$ possesses a three-dimensional network structure
resulting from the packing of Al polyhedra centered at the transition metal
element Fe and the rare earth Pr. Along the $c$-axis, Fe and Pr form {\em
chains} which are separated from each other by the Al-network. In this paper,
the magnetism and crystalline electric field effects in PrFe$_2$Al$_8$ are
investigated through the analysis of magnetization and specific heat data. A
magnetic phase transition in the Pr lattice is identified at
$T^{Pr}_{N}\approx$ 4~K in dc magnetization and ac susceptibility data. At 2~K,
the magnetization isotherm presents a ferromagnetic saturation, however,
failing to reach full spin-only ferromagnetic moment of Pr$^{3+}$. Metamagnetic
step-like low-field features are present in the magnetization curve at 2~K
which is shown to shift upon field-cooling the material. Arrott plots centered
around $T^{Pr}_{N}$ display ""S""-like features suggestive of an inhomogeneous
magnetic state. The magnetic entropy, $S_m$, estimated from specific heat
outputs a value of $R$ ln(2) at $T_{N2}$ suggesting a doublet state for
Pr$^{3+}$. The magnetic specific heat is modeled by using a 9-level Schottky
equation pertinent to the Pr$^{3+}$ ion with $J$ = 4. Given the crystalline
electric field situation of Pr$^{3+}$, the inference of a doublet state from
specific heat and consequent long-range magnetic order is an unexpected result.",1512.07488v1
2015-12-28,Comparing molecules and solids across structural and alchemical space,"Evaluating the (dis)similarity of crystalline, disordered and molecular
compounds is a critical step in the development of algorithms to navigate
automatically the configuration space of complex materials. For instance, a
structural similarity metric is crucial for classifying structures, searching
chemical space for better compounds and materials, and driving the next
generation of machine-learning techniques for predicting the stability and
properties of molecules and materials. In the last few years several strategies
have been designed to compare atomic coordination environments. In particular,
the Smooth Overlap of Atomic Positions (SOAP) has emerged as an elegant
framework to obtain translation, rotation and permutation-invariant descriptors
of groups of atoms, driven by the design of various classes of machine-learned
inter-atomic potentials. Here we discuss how one can combine such local
descriptors using a Regularized Entropy Match (REMatch) approach to describe
the similarity of both whole molecular and bulk periodic structures,
introducing powerful metrics that enable the navigation of alchemical and
structural complexity within a unified framework. Furthermore, using this
kernel and a ridge regression method we can predict atomization energies for a
database of small organic molecules with a mean absolute error below 1kcal/mol,
reaching an important milestone in the application of machine-learning
techniques to the evaluation of molecular properties.",1601.04077v2
2016-01-20,Band filling dependence of the Curie temperature in CrO2,"Rutile CrO$_2$ is an important half-metallic ferromagnetic material, which is
also widely used in magnetic recording. In an attempt to find the conditions,
which lead to the increase the Curie temperature ($T_{\rm C}$), we study
theoretically the band-filling dependence of interatomic exchange interactions
in the rutile compounds. For these purposes, we use the effective low-energy
model for the magnetic $t_{2g}$ bands, derived from the first-principles
electronic structure calculations in the Wannier basis, which is solved by
means of dynamical mean-field theory. After the solution, we calculate the
interatomic exchange interactions, by using the theory of infinitesimal spin
rotations, and evaluate $T_{\rm C}$. We argue that, as far as the Curie
temperature is concerned, the band filling realized in CrO$_2$ is far from
being the optimal one and much higher $T_{\rm C}$ can be obtained by decreasing
the number of $t_{2g}$ electrons ($n$) via the hole doping. We find that the
optimal $n$ is close to $1$, which should correspond to the case of VO$_2$,
provided that it is crystallized in the rutile structure. This finding was
confirmed by using the experimental rutile structure for both CrO$_2$ and
VO$_2$ and reflects the general tendency towards ferromagnetism for the
narrow-band compounds at the beginning of the band filling. In particular, our
results suggest that the strong ferromagnetism can be achieved in the thin
films of VO$_2$, whose crystal structure is controlled by the substrate.",1601.05171v1
2016-01-31,"Magnetic polarization of Ir in underdoped, non-superconducting Eu(Fe$_{0.94}$Ir$_{0.06}$)$_{2}$As$_{2}$","Using polarized neutron diffraction and x-ray resonant magnetic scattering
(XRMS) techniques, multiple phase transitions were revealed in an underdoped,
non-superconducting Eu(Fe$_{1-x}$Ir$_{x}$)$_{2}$As$_{2}$ ($\mathit{x}$ = 0.06)
single crystal. Compared with the parent compound EuFe$_{2}$As$_{2}$, the
tetragonal-to-orthorhombic structural phase transition and the
antiferromagnetic order of the Fe$^{2+}$ moments are significantly suppressed
to $\mathit{T_{S}}$ = 111 (2) K and $\mathit{T_{N,Fe}}$= 85 (2) K by 6% Ir
doping, respectively. In addition, the Eu$^{2+}$ spins order within the
$\mathit{ab}$ plane in the A-type antiferromagnetic structure similar to the
parent compound. However, the order temperature is evidently suppressed to
$\mathit{T_{N,Eu}}$= 16.0 (5) K by Ir doping. Most strikingly, the XRMS
measurements at the Ir $\mathit{L_{3}}$ edge demonstrates that the Ir
5$\mathit{d}$ states are also magnetically polarized, with the same propagation
vector as the magnetic order of Fe. With $\mathit{T_{N,Ir}}$ = 12.0 (5) K, they
feature a much lower onset temperature compared with $\mathit{T_{N,Fe}}$. Our
observation suggests that the magnetism of the Eu sublattice has a considerable
effect on the magnetic nature of the 5$\mathit{d}$ Ir dopant atoms and there
exists a possible interplay between the localized Eu$^{2+}$ moments and the
conduction $\mathit{d}$-electrons on the FeAs layers.",1602.00228v1
2016-02-13,Towards a Molecular Level Understanding of the Sulfanilamide-Soil Organic Matter-Interaction,"In-depth understanding of the sorption mechanisms of organic pollutants, like
the antibiotic sulfanilamide (SAA), in soil requires a combined experimental
and theoretical approach. Therefore, sorption experiments of SAA on
well-characterized samples of soil size-fractions were combined with the
modeling of SAA-soil-interaction via quantum chemical calculations. Freundlich
unit capacities were determined in batch experiments and it was found that they
increase with the soil organic matter (SOM) content according to the order fine
silt > medium silt > clay > whole soil > coarse silt > sand. The calculated
binding energies for mass-spectrometrically quantified sorption sites followed
the order ionic species > peptides > carbohydrates > phenols and lignin
monomers > lignin dimers > heterocyclic compounds > fatty acids > sterols >
aromatic compounds > lipids, alkanes, and alkenes. SAA forms H-bonds through
its different polar centers with polar SOM sorption sites. In contrast
dispersion and {\pi}-{\pi}-interactions predominate the interaction of the
sulfonamide aromatic ring with the non-polar moieties of SOM. Moreover, the
dipole moment, partial atomic charges, and molecular volume of the SOM sorption
sites are the main physical properties controlling the SAA-SOM-interaction. The
correlation between experimental and theoretical results was established by
reasonable estimates of the Freundlich unit capacities from the calculated
binding energies. Consequently, we suggest using this approach in forthcoming
studies to disclose the interactions of a wide range of organic pollutants with
SOM.",1602.04357v1
2016-02-17,Heart and diamond Fermi arcs in Pd and Pt oxide topological Dirac semimetals,"Topological Dirac semimetals (DSMs) exhibit nodal points through which energy
bands disperse linearly in three-dimensional (3D) momentum space, a 3D analogue
of graphene. The first experimentally confirmed DSMs with a pair of Dirac
points (DPs), Na$_{3}$Bi and Cd$_{3}$As$_{2}$, show topological surface Fermi
arc states and exotic magneto-transport properties, boosting the interest in
the search for stable and nontoxic DSM materials. Here, based on the {\it
ab-initio} band structure calculations we predict a family of palladium and
platinum oxides as robust 3D DSMs. The novel topological properties of these
compounds are distinct from all other previously reported DSMs, they are
rendered by the multiple number of DPs in the compounds. We show that along
three unit axes of the cubic lattice there exist three pairs of DPs, which are
linked by Fermi arcs on the surface. The Fermi arcs display a Lifshitz
transition from a heart- to a diamond-shape upon varying the chemical
potential. Corresponding oxides are already available as high-quality single
crystals, which is an excellent precondition for the verification of our
prediction by photoemission and magneto-transport experiments. Our findings not
only predict a number of much robust 3D DSM candidates but also extend DSMs to
transition metal oxides, a versatile family of materials, which opens the door
to investigate the interplay between DSMs and electronic correlations that is
not possible in the previously discovered DSM materials.",1602.05533v1
2016-02-19,Magnetic effects in sulfur-decorated graphene,"The interaction between two different materials can present novel phenomena
that are quite different from the physical properties observed when each
material stands alone. Strong electronic correlations, such as magnetism and
superconductivity, can be produced as the result of enhanced Coulomb
interactions between electrons. Two-dimensional materials are powerful
candidates to search for the novel phenomena because of the easiness of
arranging them and modifying their properties accordingly. In this work, we
report magnetic effects of graphene, a prototypical non-magnetic
two-dimensional semi-metal, in the proximity with sulfur, a diamagnetic
insulator. In contrast to the well-defined metallic behaviour of clean
graphene, an energy gap develops at the Fermi energy for the graphene/sulfur
compound with decreasing temperature. This is accompanied by a steep increase
of the resistance, a sign change of the slope in the magneto-resistance between
high and low fields, and magnetic hysteresis. A possible origin of the observed
electronic and magnetic responses is discussed in terms of the onset of
low-temperature magnetic ordering. These results provide intriguing insights on
the search for novel quantum phases in graphene-based compounds.",1602.06214v2
2016-02-19,A gapless micro-dielectric-barrier-discharge ion source for analytical applications,"Use of dielectric barrier discharge (DBD) as an ion source for sensitive
chemical analysis is uncommon because barrier discharges generate excess noise
due to spatial and temporal instability. This design uses contacted, crossed
glass-coated micro-wires to focus the field into a gradually vanishing gap,
suppressing spatial and temporal variability, reducing pressure, temperature,
and humidity effects, stabilizing discharge initiation and limiting chemical
fragmentation. Positive-ion-mode proton transfer, chemical fragmentation from a
micro-discharge, and NO+ adducts combine to allow broad chemical sensitivity.
We analyze noise properties of the ion source and report chemical responsivity
for a wide range of volatile organic compounds. Source noise spectral density
is compared for three systems: the contacted coated wires source, a gapped
dielectric barrier discharge source, and a 5 mCi Ni-63 radioactive source. The
crossed-wires source shows noise properties approaching those of the
white-noise Ni-63 source, while gapped discharge exhibits 1/f noise from
area-discharge random path and intensity variations. For chemical sensitivity
testing, dilute samples are delivered by vapor flow injection or by gas
chromatography, and then detected by differential ion mobility spectrometry
(DMS / FAIMS) and, in a few cases by mass spectrometry. The compounds tested in
positive ion mode include ketones and alcohols, simple aromatics (benzene,
toluene, xylenes, ethyl and propyl benzene), chlorinated and nitrated solvents
and aliphatics (hexanes and n-octane), with sensitivities from ppt to ppb
levels. The wires source for trace vapor detection is stable under a range of
environmental conditions from very low (ppb) humidity levels upward, has wider
chemical coverage than the radioactive nickel source with nearly equivalent
noise properties, and is adjustable to higher intensity.",1602.06242v1
2016-04-14,Quest for the Origin of Heavy Fermion Behavior in $d$-Electron Systems,"Spin fluctuation is presumed to be one of the key properties in understanding
the microscopic origin of heavy-fermion-like behavior in the class of
transition-metal compounds, including LiV$_2$O$_4$, Y(Sc)Mn$_2$, and
YMn$_2$Zn$_{20}$. In this review, we demonstrate by our recent study of muon
spin rotation/relaxation that the temperature ($T$) dependence of the
longitudinal spin relaxation rate ($\lambda\equiv 1/T_1$) in these compounds
exhibits a common trend of leveling off to a constant value ($\lambda\sim
const$.) below a characteristic temperature, $T^*$. This is in marked contrast
to the behavior predicted for normal metals from the Korringa relation,
$\lambda\propto T/\nu$, where the spin fluctuation rate ($\nu$) in the Pauli
paramagnetic state is given as a constant, $\nu\simeq 1/[h D(E_F)]$ [with
$D(E_F)$ being the density of states at the Fermi energy]. Thus, the observed
behavior of $\lambda$ implies that the spin fluctuation rate becomes linearly
dependent on temperature, $\nu\propto T$, suggesting that heavy quasiparticles
develop in a manner satisfying $D(E_F)\propto (m^*)^{\sigma}\propto 1/T$ at
lower temperatures ($\sigma$ determined by the electronic dispersion).
Considering that the theory of spin correlation for intersecting Hubbard chains
as a model of pyrochlore lattice predicts $\nu\propto T$, our finding strongly
indicates the crucial role of $t_{2g}$ bands which preserve the one-dimensional
character at low energies due to the geometrical frustration specific to the
undistorted pyrochlore lattice.",1604.04049v1
2016-04-23,"Giant magnetoresistance, three-dimensional Fermi surface and origin of resistivity plateau in YSb semimetal","Very strong magnetoresistance and a resistivity plateau impeding low
temperature divergence due to insulating bulk are hallmarks of topological
insulators and are also present in topological semimetals where the plateau is
induced by magnetic field, when time-reversal symmetry (protecting surface
states in topological insulators) is broken. Similar features were observed in
a simple rock-salt-structure LaSb, leading to a suggestion of the possible
non-trivial topology of 2D states in this compound. We show that its sister
compound YSb is also characterized by giant magnetoresistance exceeding one
thousand percent and low-temperature plateau of resistivity. We thus performed
in-depth analysis of YSb Fermi surface by band calculations, magnetoresistance,
and Shubnikov--de Haas effect measurements, which reveals only
three-dimensional Fermi sheets. Kohler scaling applied to magnetoresistance
data accounts very well for its low-temperature upturn behavior. The
field-angle-dependent magnetoresistance demonstrates a 3D-scaling yielding
effective mass anisotropy perfectly agreeing with electronic structure and
quantum oscillations analysis, thus providing further support for 3D-Fermi
surface scenario of magnetotransport, without necessity of invoking
topologically non-trivial 2D states. We discuss data implying that analogous
field-induced properties of LaSb can also be well understood in the framework
of 3D multiband model.",1604.06945v3
2016-04-27,"Crystal structure, stability and optoelectronic properties of the organic-inorganic wide bandgap perovskite CH3NH3BaI3: Candidate for transparent conductor applications","Structural stability, electronic structure and optical properties of
CH3NH3BaI3 hybrid perovskite is examined both from theory as well as
experiment. Solution-processed thin films of CH3NH3BaI3 exhibited a high band
gap of approximately 3.87 eV, which is in excellent agreement with the
theoretical estimate of 4 eV. Also, the XRD patterns of the thin films match
well with the l-peaks of the simulated pattern obtained from the relaxed unit
cell of CH3NH3BaI3, crystallizing in the I4/mcm space group, with lattice
parameters, a = 9.30 A, c = 13.94 A. Atom projected density of state and band
structure calculations reveal the conduction and valence band edges to be
comprised primarily of Barium d-orbitals and Iodine p-orbitals, respectively.
The larger band gap of CH3NH3BaI3 compared to CH3NH3PbI3 can be attributed to
the lower electro-negativity coupled with the lack of d-orbitals in the valence
band of Ba{2+}. A more detailed analysis reveals the excellent chemical and
mechanical stability of CH3NH3BaI3 against humidity, unlike its lead halide
counterpart, which degrades under such conditions. The dopability of the
CH3NH3BaI3 compound e.g. by doping La on the Ba site combined with its
structural and mechanical stability under the ambient conditions, suggests this
compound as a promising candidate for transparent conductor applications,
especially for all perovskite solar cells.",1604.08003v2
2016-05-02,An Enhanced Harmony Search Method for Bangla Handwritten Character Recognition Using Region Sampling,"Identification of minimum number of local regions of a handwritten character
image, containing well-defined discriminating features which are sufficient for
a minimal but complete description of the character is a challenging task. A
new region selection technique based on the idea of an enhanced Harmony Search
methodology has been proposed here. The powerful framework of Harmony Search
has been utilized to search the region space and detect only the most
informative regions for correctly recognizing the handwritten character. The
proposed method has been tested on handwritten samples of Bangla Basic,
Compound and mixed (Basic and Compound characters) characters separately with
SVM based classifier using a longest run based feature-set obtained from the
image subregions formed by a CG based quad-tree partitioning approach. Applying
this methodology on the above mentioned three types of datasets, respectively
43.75%, 12.5% and 37.5% gains have been achieved in terms of region reduction
and 2.3%, 0.6% and 1.2% gains have been achieved in terms of recognition
accuracy. The results show a sizeable reduction in the minimal number of
descriptive regions as well a significant increase in recognition accuracy for
all the datasets using the proposed technique. Thus the time and cost related
to feature extraction is decreased without dampening the corresponding
recognition accuracy.",1605.00420v1
2016-05-08,Exchange bias-like effect in TbFeAl intermetallic induced by atomic disorder,"Exchange bias-like effect observed in the intermetallic compound TbFeAl,
which displays a magnetic phase transition at $T^h_c \approx$ 198~K and a
second one at $T^l_c \approx$ 154~K, is reported. {\em Jump}-like features are
observed in the isothermal magnetization, $M (H)$, at 2~K which disappear above
8~K. The field-cooled magnetization isotherms below 10~K show loop-shifts that
are reminiscent of exchange bias, also supported by {\em training effect}.
Significant coercive field, $H_c \approx$ 1.5~T at 2~K is observed in TbFeAl
which, after an initial increase, shows subsequent decrease with temperature.
The exchange bias field, $H_{eb}$, shows a slight increase and subsequent
leveling off with temperature. It is argued that the inherent crystallographic
disorder among Fe and Al and the high magnetocrystalline anisotropy related to
Tb$^{3+}$ lead to the exchange bias effect. TbFeAl is recently reported to show
magnetocaloric effect and the present discovery of exchange bias makes this
compound a multifunctional one. The result obtained on TbFeAl generalizes the
observation of exchange bias in crystallographically disordered materials and
gives impetus for the search for materials with {\em exchange bias induced by
atomic disorder.}",1605.02381v1
2016-05-10,Development of HPLC-Orbitrap method for identification of N-bearing molecules in complex organic material relevant to planetary environments,"Although the Cassini Spacecraft and the Huygens lander provided numerous
information about Titan atmospheric chemistry and the formation of its
aerosols, the exact composition of these aerosols still remains unknown. A
fruitful proxy to investigate these aerosols is the use of laboratory
experiments that allow producing and studying analogs of Titan aerosol, the
so35 called tholins. Even when produced in the laboratory, unveiling the exact
composition of the aerosol remains problematic due to the high complexity of
the material. Numerous advances have been recently made using high-resolution
mass spectrometry (HRMS) (Pernot et al. 2010, Somogyi et al. 2012, Gautier et
al. 2014) that allowed the separation of isobaric compounds and a robust
identification of chemical species composing tholins regarding their molecular
formulae. Nevertheless isomeric species cannot be resolved by a simple mass
measurement. We propose here an analysis of tholins by high performance liquid
chromatography (HPLC) coupled to HRMS to unveil this isomeric ambiguity for
some of the major tholins compounds. By comparing chromatograms obtained when
analyzing tholins and chemical standards, we strictly identified seven
molecules in our tholins samples: melamine, cyanoguanidine,
6-methyl-1,3,5-triazine-2,4-diamine, 2,4,6-triaminopyrimidine, 3-amino-
1,2,4-triazole, 3,5-Dimethyl-1,2,4-triazole and 2,4-diamino-1,3,5-triazine.
Several molecules, including hexamethylenetriamine (HMT) were not present at
detectable levels in our sample. The use for the first time of a coupled
HPLC-HRMS technique applied to tholins study demonstrated the interest of such
a technique compared to single high-resolution mass spectrometry for the study
of tholins composition.",1605.03022v1
2016-05-13,Experimental elucidation of the origin of the `double spin resonances' in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"We report a combined study of the spin resonances and superconducting gaps
for underdoped ($T_c=19$ K), optimally doped ($T_c=25$ K), and overdoped
($T_c=19$ K) Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals with inelastic
neutron scattering and angle resolved photoemission spectroscopy. We find a
quasi two dimensional spin resonance whose energy scales with the
superconducting gap in all three compounds. In addition, anisotropic low energy
spin excitation enhancements in the superconducting state have been deduced and
characterized for the under and optimally doped compounds. Our data suggest
that the quasi two dimensional spin resonance is a spin exciton that
corresponds to the spin singlet-triplet excitations of the itinerant electrons.
However, the intensity enhancements of the anisotropic spin excitations are
dominated by the out-of-plane spin excitations of the ordered moments due to
the suppression of damping in the superconducting state. Hence we offer a new
interpretation of the double energy scales differing from previous
interpretations based on anisotropic superconducting energy gaps, and
systematically explain the doping-dependent trend across the phase diagram.",1605.04257v2
2016-05-15,Nearly massless Dirac fermions hosted by Sb square net in BaMnSb2,"Layered compounds AMnBi2 (A=Ca, Sr, Ba, or rare earth element) have been
established as Dirac materials. Dirac electrons generated by the
two-dimensional (2D) Bi square net in these materials are normally massive due
to the presence of a spin-orbital coupling (SOC) induced gap at Dirac nodes.
Here we report that the Sb square net in an isostructural compound BaMnSb2 can
host nearly massless Dirac fermions. We observed strong Shubnikov-de Haas (SdH)
oscillations in this material. From the analyses of the SdH oscillations, we
find key signatures of Dirac fermions, including light effective mass
(~0.052m0; m0, mass of free electron), high quantum mobility (1280 cm2V-1S-1)
and a Pi Berry phase accumulated along cyclotron orbit. Compared with AMnBi2,
BaMnSb2 also exhibits much more significant quasi two-dimensional (2D)
electronic structure, with the out-of-plane transport showing nonmetallic
conduction below 120K and the ratio of the out-of-plane and in-plane
resistivity reaching ~670. Additionally, BaMnSb2 also exhibits an
antiferromagnetic order with a weak ferromagnetic component. The combination of
nearly massless Dirac fermions on quasi-2D planes with a magnetic order makes
BaMnSb2 an intriguing platform for seeking novel exotic phenomena of massless
Dirac electrons.",1605.04613v2
2016-05-19,Giant Thermal Vibrations in the Framework Compounds Ba1-xSrxAl2O4,"Synchrotron X-ray diffraction (XRD) experiments were performed on the network
compounds Ba1-xSrxAl2O4 at temperatures between 15 and 800 K. The ferroelectric
phase of the parent BaAl2O4 is largely suppressed by the Sr-substitution and
disappears for $x\geq0.1$. Structural refinements reveal that the isotropic
atomic displacement parameter ($B_{\rm iso}$) in the bridging oxygen atom for
$x\geq0.05$ is largely independent of temperature and retains an anomalously
large value in the adjacent paraelectric phase even at the lowest temperature.
The $B_{\rm iso}$ systematically increases as $x$ increases, exhibiting an
especially large value for $x\geq0.5$. According to previous electron
diffraction experiments for Ba1-xSrxAl2O4 with $x\geq0.1$, strong thermal
diffuse scattering occurs at two reciprocal points relating to two distinct
soft modes at the M- and K-points over a wide range of temperatures below 800 K
[Y. Ishii et al., Sci. Rep. 6, 19154 (2016)]. Although the latter mode
disappears at approximately 200 K, the former does not condense, at least down
to 100 K. On the contrary, it still survives at low-temperature. The
anomalously large $B_{\rm iso}$ observed in this study is ascribed to these
soft modes existing in a wide temperature range.",1605.05880v1
2016-05-19,Characterization of aromaticity in analogues of titan's atmospheric aerosols with two-step laser desorption ionization mass spectrometry,"The role of polycyclic aromatic hydrocarbons (PAH) and Nitrogen containing
PAH (PANH) as intermediates of aerosol production in the atmosphere of Titan
has been a subject of controversy for a long time. An analysis of the
atmospheric emission band observed by the Visible and Infrared Mapping
Spectrometer (VIMS) at 3.28 micrometer suggests the presence of neutral
polycyclic aromatic species in the upper atmosphere of Titan. These molecules
are seen as the counter part of negative and positive aromatics ions suspected
by the Plasma Spectrometer onboard the Cassini spacecraft, but the low
resolution of the instrument hinders any molecular speciation.
  In this work we investigate the specific aromatic content of Titan's
atmospheric aerosols through laboratory simulations. We report here the
selective detection of aromatic compounds in tholins, Titan's aerosol
analogues, produced with a capacitively coupled plasma in a N2:CH4 95:5 gas
mixture. For this purpose, Two-Step Laser Desorption Ionization Time-of-Flight
Mass Spectrometry (L2DI-TOF-MS) technique is used to analyze the so produced
analogues. This analytical technique is based on the ionization of molecules by
Resonance Enhanced Multi-Photon Ionization (REMPI) using a {\lambda}=248 nm
wavelength laser which is selective for aromatic species. This allows for the
selective identification of compounds having at least one aromatic ring. Our
experiments show that tholins contain a trace amount of small PAHs with one to
three aromatic rings. Nitrogen containing PAHs (PANHs) are also detected as
constituents of tholins. Molecules relevant to astrobiology are detected as is
the case of the substituted DNA base adenine.",1605.06032v1
2016-05-26,Two-gap superconductivity in LaNiGa$_2$ with non-unitary triplet pairing and even parity gap symmetry,"The nature of the pairing states of superconducting LaNiC$_2$ and LaNiGa$_2$
has to date remained a puzzling question. Broken time reversal symmetry has
been observed in both compounds and a group theoretical analysis implies a
non-unitary triplet pairing state. However all the allowed non-unitary triplet
states have nodal gap functions but most thermodynamic and NMR measurements
indicate fully gapped superconductivity in LaNiC$_2$. Here we probe the gap
symmetry of LaNiGa$_2$ by measuring the London penetration depth, specific heat
and upper critical field. These measurements demonstrate two-gap nodeless
superconductivity in LaNiGa$_2$, suggesting that this is a common feature of
both compounds. These results allow us to propose a novel triplet
superconducting state, where the pairing occurs between electrons of the same
spin, but on different orbitals. In this case the superconducting wavefunction
has a triplet spin component but isotropic even parity gap symmetry, yet the
overall wavefunction remains antisymmetric under particle exchange. This model
leads to a nodeless two-gap superconducting state which breaks time reversal
symmetry, and therefore accounts well for the seemingly contradictory
experimental results.",1605.08356v1
2016-06-01,A systematic study of the superconducting critical temperature in two and three dimensional tight-binding models: a possible scenario for superconducting H$_3$S ?,"Ever since BCS theory was first formulated it was recognized that a large
electronic density of states at the Fermi level was beneficial to enhancing
$T_c$. The A15 compounds and the high temperature cuprate materials both have
had an enormous amount of effort devoted to studying the possibility that such
peaks play an important role in the high critical temperatures existing in
these compounds. Here we provide a systematic study of the effect of these
peaks on the superconducting transition temperature for a variety of
tight-binding models of simple structures, both in two and three dimensions. In
three dimensions large enhancements in $T_c$ can occur, due to van Hove
singularities that result in divergences in the density of states. Furthermore,
even in more realistic structures, where the van Hove singularity disappears,
large enhancements in $T_c$ continue due to the presence of `robust' peaks in
the densities of states. Such a peak, recently identified in the bcc structure
of H$_3$S, is likely the result of such a van Hove singularity. In certain
regimes, anomalies in the isotope coefficient are also expected.",1606.00430v3
2016-06-02,Fusion and quasifission dynamics in the reactions $^{48}$Ca+$^{249}$Bk and $^{50}$Ti+$^{249}$Bk using TDHF,"Background: Synthesis of superheavy elements (SHE) with fusion-evaporation
reactions is strongly hindered by the quasifission (QF) mechanism which
prevents the formation of an equilibrated compound nucleus and which depends on
the structure of the reactants. New SHE have been recently produced with
doubly-magic $^{48}$Ca beams. However, SHE synthesis experiments with
single-magic $^{50}$Ti beams have so far been unsuccessful. Purpose: In
connection with experimental searches for $Z=117,119$ superheavy elements, we
perform a theoretical study of fusion and quasifission mechanisms in
$^{48}$Ca,$^{50}$Ti+$^{249}$Bk reactions in order to investigate possible
differences in reaction mechanisms induced by these two projectiles. Methods:
The collision dynamics and the outcome of the reactions are studied using
unrestricted time-dependent Hartree-Fock (TDHF) calculations as well as the
density-constrained TDHF method to extract the nucleus-nucleus potentials and
the excitation energy in each fragment. Results: Nucleus-nucleus potentials,
nuclear contact times, masses and charges of the fragments, as well as their
kinetic and excitation energies strongly depend on the orientation of the
prolate $^{249}$Bk nucleus. Long contact times associated with fusion are
observed in collisions of both projectiles with the side of the $^{249}$Bk
nucleus, but not on collisions with its tip. The energy and impact parameter
dependences of the fragment properties, as well as their mass-angle and
mass-total kinetic energy correlations are investigated. Conclusions: Entrance
channel reaction dynamics are similar with both $^{48}$Ca and $^{50}$Ti
projectiles. Both are expected to lead to the formation of a compound nucleus
by fusion if they have enough energy to get in contact with the side of the
$^{249}$Bk target.",1606.00699v1
2016-06-07,"Quantum phase transition, universality and scaling behaviors in the spin-1/2 Heisenberg model with ferromagnetic and antiferromagnetic competing interactions on honeycomb lattice","The quantum phase transition, scaling behaviors, and thermodynamics in the
spin-1/2 quantum Heisenberg model with antiferromagnetic coupling $J>0$ in
armchair direction and ferromagnetic interaction $J'<0$ in zigzag direction on
a honeycomb lattice are systematically studied using the continuous-time
quantum Monte Carlo method. By calculating the Binder ratio $Q_{2}$ and spin
stiffness $\rho$ in two directions for various coupling ratio $\alpha=J'/J$
under different lattice sizes, we found that a quantum phase transition from
the dimerized phase to the stripe phase occurs at the quantum critical point
$\alpha_c=-0.93$. Through the finite-size scaling analysis on $Q_{2}$,
$\rho_{x}$ and $\rho_{y}$, we determined the critical exponent related to the
correlation length $\nu$ to be 0.7212(8), implying that this transition falls
into a classical Heisenberg O(3) universality. A zero magnetization plateau is
observed in the dimerized phase, whose width decreases with increasing
$\alpha$. A phase diagram in the coupling ratio $\alpha$-magnetic field $h$
plane is obtained, where four phases, including dimerized, stripe, canted
stripe and polarized phases are identified. It is also unveiled that the
temperature dependence of the specific heat $C(T)$ for different $\alpha$'s
intersects precisely at one point, similar to that of liquid $^{3}$He under
different pressures and several magnetic compounds under various magnetic
fields. The scaling behaviors of $Q_{2}$, $\rho$ and $C(T)$ are carefully
analyzed. The susceptibility is well compared with the experimental data to
give the magnetic parameters of both compounds.",1606.02069v1
2016-06-10,Evidence for interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator,"The discovery of high-temperature superconductivity in Fe-based compounds
[1,2] has triggered numerous investigations on the interplay between
superconductivity and magnetism [3] and, more recently, on the enhancement of
transition temperatures through interface effects [4]. It is widely believed
that the emergence of optimal superconductivity is intimately linked to the
suppression of long-range antiferromagnetic (AFM) order, although the exact
microscopic picture of this relationship remains elusive [1] due to the lack of
data with atomic spatial resolution [5-7]. Here, we present a spin-polarized
scanning tunneling spectroscopy (SP-STS) study of ultrathin FeTe$_{1-x}$Se$_x$
(x = 0, 0.5) films grown on prototypical Bi-based bulk topological insulators.
Surprisingly, we find an energy gap at the Fermi level indicating
superconducting correlations up to Tc ~ 6 K for one unit cell thin FeTe layers
grown on Bi2Te3 substrates, in contrast to the non-superconducting FeTe bulk
compound [8]. Moreover, SP-STS reveals that the energy gap spatially coexists
with bicollinear AFM order. This finding opens novel perspectives for
theoretical studies of competing orders in Fe-based superconductors as well as
for experimental investigations of exotic phases in heterostructures of
topological insulators and superconducting layers.",1606.03249v1
2016-06-21,Physical realization of a quantum spin liquid based on a novel frustration mechanism,"Unlike conventional magnets where the magnetic moments are partially or
completely static in the ground state, in a quantum spin liquid they remain in
collective motion down to the lowest temperatures. The importance of this state
is that it is coherent and highly entangled without breaking local symmetries.
Such phenomena is usually sought in simple lattices where antiferromagnetic
interactions and/or anisotropies that favor specific alignments of the magnetic
moments are ""frustrated"" by lattice geometries incompatible with such order
e.g. triangular structures. Despite an extensive search among such compounds,
experimental realizations remain very few. Here we describe the investigation
of a novel, unexplored magnetic system consisting of strong ferromagnetic and
weaker antiferromagnetic isotropic interactions as realized by the compound
Ca$_{10}$Cr$_7$O$_{28}$. Despite its exotic structure we show both
experimentally and theoretically that it displays all the features expected of
a quantum spin liquid including coherent spin dynamics in the ground state and
the complete absence of static magnetism.",1606.06463v1
2016-06-24,Type-II Topological Dirac Semimetals: Theory and Materials Prediction (VAl3 family),"The discoveries of Dirac and Weyl semimetal states in spin-orbit compounds
led to the realizations of elementary particle analogs in table-top
experiments. In this paper, we propose the concept of a three-dimensional
type-II Dirac fermion and identify a new topological semimetal state in the
large family of transition-metal icosagenides, MA3 (M=V, Nb, Ta; A=Al, Ga, In).
We show that the VAl3 family features a pair of strongly Lorentz-violating
type-II Dirac nodes and that each Dirac node consists of four type-II Weyl
nodes with chiral charge +/-1 via symmetry breaking. Furthermore, we predict
the Landau level spectrum arising from the type-II Dirac fermions in VAl3 that
is distinct from that of known Dirac semimetals. We also show a topological
phase transition from a type-II Dirac semimetal to a quadratic Weyl semimetal
or a topological crystalline insulator via crystalline distortions. The new
type-II Dirac fermions, their novel magneto-transport response, the topological
tunability and the large number of compounds make VAl3 an exciting platform to
explore the wide-ranging topological phenomena associated with
Lorentz-violating Dirac fermions in electrical and optical transport,
spectroscopic and device-based experiments.",1606.07555v1
2016-06-27,Novel Interplay between High-Tc Superconductivity and Antiferromagnetism in Tl-based Six-CuO2-Layered Cuprates : 205 Tl and 63 Cu-NMR Probes,"We report $^{63}$Cu- and $^{205}$Tl-NMR studies on six-layered ($n$=6)
high-$T_c$ superconducting (SC) cuprate TlBa$_2$Ca$_5$Cu$_6$O$_{14+\delta}$
(Tl1256) with $T_c\sim$100 K, which reveal that antiferromagnetic (AFM) order
takes place below $T_{\rm N}\sim$170 K. In this compound, four underdoped inner
CuO$_2$ planes ($n$(IP)=4) sandwiched by two outer planes (OPs) are responsible
for the onset of AFM order, whereas the nearly optimally-doped OPs responsible
for the onset of bulk SC. It is pointed out that an increase in the
out-of-plane magnetic interaction within an intra-unit-cell causes $T_{\rm
N}\sim$ 45 K for Tl1245 with $n$(IP)=3 to increase to $\sim$170 K for Tl1256
with $n$(IP)=4. It is remarkable that the marked increase in $T_{\rm N}$ and
the AFM moments for the IPs does not bring about any reduction in $T_c$, since
$T_c\sim 100$ K is maintained for both compounds with nearly optimally doped
OP. We highlight the fact that the SC order for $n\ge5$ is mostly dominated by
the long-range in-plane SC correlation even in the multilayered structure,
which is insensitive to the magnitude of $T_{\rm N}$ and the AFM moments at the
IPs or the AFM interaction among the IPs. These results demonstrate a novel
interplay between the SC and AFM orders when the charge imbalance between the
IPs and OP is significantly large.",1606.08147v1
2016-06-30,Metal-Insulator Transition and the Role of Electron Correlation in FeO2,"Iron oxide is a key compound to understand the state of the deep Earth. It
has been believed that previously known oxides such as FeO and Fe2O3 will be
dominant at the mantle conditions. However, recent observation of FeO2 shed
another light to the composition of the deep lower mantle (DLM) and thus
understanding of the physical properties of FeO2 will be critical to model DLM.
Here, we report the electronic structure and structural properties of FeO2 by
using density functional theory (DFT) and dynamic mean field theory (DMFT). The
crystal structure of FeO2 is composed of Fe2+ and O2 2- dimers, where the Fe
ions are surround by the octahedral O atoms. We found that the bond length of
O2 dimer, which is very sensitive to the change of the Coulomb interaction U of
Fe 3d orbital, plays an important role in determining the electronic
structures. The band structures of DFT+DMFT show that the metal-insulator
transition is driven by the change of U and pressure. We suggest that the
correlation effect should be considered to correctly describe the physical
properties of FeO2 compound.",1606.09582v2
2016-07-01,Solute-solute interactions in intermetallic compounds,"Two types of solute-solute interactions are investigated in this work.
Quadrupole interactions caused by nearby Ag-solute atoms were measured at
nuclei of 111In/Cd solute probe atoms in the binary compound GdAl2 using the
method of perturbed angular correlation of gamma rays (PAC). Locations of
In-probes and Ag-solutes on both Gd- and Al-sublattices were identified by
comparing site fractions in Gd-poor and Gd-rich GdAl2(Ag) samples. Interaction
enthalpies between solute-atom pairs were determined from temperature
dependences of observed site fractions. Repulsive interactions were observed
for close-neighbor complexes In/Gd/+Ag/Gd/ and In/Gd/+Ag/Al/ pairs, whereas a
slightly attractive interaction was observed for In/Al/+Ag/Al/. Interaction
enthalpies were all in the range +/- 0.15 eV. Temperature dependences of site
fractions of In-probes on locally defect-free Gd- and Al-sites yields a
transfer enthalpy that was found to be 0.343 eV in a previous study of undoped
GdAl2. The corresponding values in GdAl2(Ag) samples are much smaller. This is
attributed to competition of In- and Ag-solutes to occupy sites of the same
sublattice. While the difference in site-enthalpies of In-solutes on Gd- and
Al-sites is temperature independent, it is proposed that the transfer of
Ag-solutes from Gd- to Al-sites leads to a large temperature dependence of
degeneracies of levels available to In-solutes, resulting in an effective
transfer enthalpy that is much smaller than the difference in site-enthalpies.",1607.00155v1
2016-07-08,Magnetic structure of divalent europium compound EuGa$_4$ studied by single crystal time-of-flight neutron diffraction,"The magnetic structure of the intermetallic compound EuGa$_4$ was
investigated using single-crystal neutron diffraction with the time-of-flight
(TOF) Laue technique on the new diffractometer SENJU at MLF of J-PARC. In spite
of high neutron absorption of Eu, a vast number of diffraction spots were
observed without isotope enrichment. The magnetic reflections were appeared at
the positions with the diffraction indices of $h+k+l{\neq}2n$ below 16 K,
indicating that the ordering vector is ${\bf q}=(0~0~0)$. Continuous evolution
of magnetic reflection intensity below $T_{\rm N}$ follows a squared Brillouin
function for $S$=7/2. By adopting a wavelength-dependent absorption collection,
the magnetic structure of EuGa$_4$ was revealed that a nearly full magnetic
moment of 6.4$~{\mu}_{\rm B}$ of Eu lies within the basal plane of the lattice.
The present study reveals a well-localized divalent Eu magnetism in EuGa$_4$
and demonstrates a high ability of SENJU to investigate materials with high
neutron absorption.",1607.02239v1
2016-07-08,Nuclear Magnetic Resonance Reveals Disordered Level-Crossing Physics in the Bose-Glass Regime of the Br-doped Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$)$_2$ Compound at a High Magnetic Field,"By measuring the nuclear magnetic resonance (NMR) 1/T_1 relaxation rate in
the Br (bond) doped DTN compound, Ni(Cl(1-x)Br_x)2-4SC(NH2)2 (DTNX), we show
that the low-energy spin dynamics of its high magnetic field ""Bose-glass""
regime is dominated by a strong peak of spin fluctuations found at the nearly
doping-independent position H* = 13.6 T. From its temperature and field
dependence we conclude that this corresponds to a level crossing of the energy
levels related to the doping-induced impurity states. Observation of the local
NMR signal from the spin adjacent to the doped Br allowed us to fully
characterize this impurity state. We have thus quantified a microscopic
theoretical model that paves the way to better understanding of the Bose-glass
physics in DTNX, as revealed in the related theoretical study [M. Dupont, S.
Capponi, and N. Laflorencie, Phys. Rev. Lett. 118, 067204 (2017),
arXiv:1610.05136].",1607.02360v3
2016-07-10,Predicted electronic markers for polytypes of LaOBiS2 examined via angular resolved photoemission spectroscopy,"The natural periodic stacking of symmetry-inequivalent planes in layered
compounds can lead to the formation of natural superlattices; albeit close in
total energy, (thus in their thermodynamic stability), such polytype
superlattices can exhibit different structural symmetries, thus have markedly
different electronic properties which can in turn be used as ""structural
markers"". We illustrate this general principle on the layered LaOBiS2 compound
where density-functional theory (DFT) calculations on the (BiS2)/(LaO)/(BiS2)
polytype superlattices reveal both qualitatively and quantitatively distinct
electronic structure markers associated with the Rashba physics, yet the total
energies are only ~ 0.1 meV apart. This opens the exciting possibility of
identifying subtle structural features via electronic markers. We show that the
pattern of removal of band degeneracies in different polytypes by the different
forms of symmetry breaking leads to new Rashba ""mini gaps"" with characteristic
Rashba parameters that can be determined from spectroscopy, thereby narrowing
down the physically possible polytypes. By identifying these distinct
DFT-predicted fingerprints via ARPES measurements on LaBiOS2 we found the
dominant polytype with small amounts of mixtures of other polytypes. This
conclusion, consistent with neutron scattering results, establishes ARPES
detection of theoretically established electronic markers as a powerful tool to
delineate energetically quasidegenerate polytypes.",1607.02796v3